apostilb2016-12-11T12:01:24+00:00https://apostilb.github.ioThe psychology of perception tests an age-old fashion foible2016-09-10T00:00:00+00:00https://apostilb.github.io/2016/09/10/stripe-dress<p><em>Horizontal stripes on clothing are in fact slimming</em></p>
<p><a href="http://wp.me/p2UE9j-1da">The dress</a> sparked one of the hottest fashion debate of the 21st century, but another mystery has occupied scientists and fashionistas alike since the mid-19th century: do horizontal stripes make you look fat?
The answer may seem obvious, but experimental results and a well-documented illusion contradict many people’s intuition that horizontal stripes make the wearer look wider.</p>
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<p>As pioneering vision scientist Helmholtz <a href="http://poseidon.sunyopt.edu/helmholtz/OCRVolume3.pdf">noted back in 1867</a> (see page 206!), a person wearing horizontal stripes should, contrary to popular belief, appear <em>thinner</em> than someone with vertical stripes.
This observation is the basis for the <a href="http://www.bbc.co.uk/radio4/features/sywtbas/finalists/stripes/">Helmholtz illusion</a>, at least as it applies to shapes, not bodies.
A team of researchers from Japan tested whether the size of the body wearing stripes changes the strength of the effect.</p>
<p><a href="http://ipe.sagepub.com/content/2/1/69">In line with previous research</a>, they found that the common idea that horizontal stripes make one look fat is in fact wrong.
In the experiment, a group of students rated computer-generated figures wearing either a horizontally or vertically striped shirt.
The figures had different degrees of thin and fat body shapes to determine when the horizontal- and vertical-striped figures looked ‘equally fat’ for each observer.
This measurement is a baseline for each person’s perception, and all participants perceived a person with horizontal stripes to be thinner than a person with vertical stripes.
This agrees with the phenomenon of the Helmholtz illusion, that a horizontally striped square is perceived as ‘thinner’ than one with vertical stripes.</p>
<p><img src="https://apostilb.github.io/images/2016-09-10-stripe-dress.jpg" alt="Horizontal-striped dress" /></p>
<blockquote>
<p><em>Horizontal-striped dress. <a href="https://www.flickr.com/photos/gareth1953/9497924862">Image</a> by Gareth Williams / <a href="https://creativecommons.org/licenses/by/2.0/">CC BY 2.0</a></em></p>
</blockquote>
<p>With the experimental bodies, however, the effect was stronger for the thin figures than the fat ones.
Thus, as the title of this research paper states, “the Helmholtz illusion makes you look fit only when you are already fit”.
Whether the students were presented with the fat or thin figures first also made a difference: if fat figures were shown first, the Helmholtz effect was diminished, and for the fat figures the judgments actually bumped the baseline in the opposite direction.
In this condition, the horizontal stripes on fat figures really were perceived to make the figure fatter.</p>
<p>The main takeaway from this simple experiment is that context and timing can have a large effect on how something is perceived.
People’s perceptions are also far from uniform, as the researchers found that the students differed a lot in their ‘fatness’ judgments, even though they were all broadly in the same direction.
The researchers suggest that horizontally-striped maxi dresses may maximize the slimming effect of the Helmholtz illusion, but the clothes and bodies of surrounding people can conceivably alter the intended perception.</p>
<hr />
<p>Citation:</p>
<blockquote>
<p>Ashida, H., Kuraguchi, K., & Miyoshi, K. (2013). Helmholtz illusion makes you look fit only when you are already fit, but not for everyone. <em>i-Perception</em>, 4(5): 347-351. DOI: <a href="http://dx.doi.org/10.1068/i0595rep">10.1068/i0595rep</a></p>
</blockquote>
Low magnetic fields leave mouse DNA undamaged2016-08-27T00:00:00+00:00https://apostilb.github.io/2016/08/27/mouse-dna-magnetic-fields<p><em>Cells in brain, kidney and liver shown to withstand sustained exposure to magnetic fields</em></p>
<p>The 19th-century works of Hans Christian Ørsted, Michael Faraday, James Clerk Maxwell and others demonstrated that electricity and magnetism are in fact two sides of the same coin: a magnet moving near a coil of wires induces a current in the coil and circulating electric current generates magnetic fields.
We have since harnessed this unified electromagnetism to provide for the energy needs of billions around the globe.
However, it is thought that prolonged exposure to electromagnetic (EM) fields produced by everything from household appliances to the electrical lines that power them can affect certain cells in the body, causing a variety of cancers.
For this reason, several countries have adopted limits for EM exposure, with most European countries limiting ambient magnetic fields to 0.1 mT (<a href="https://en.wikipedia.org/wiki/Tesla_(unit)">milliteslas</a>).
It should be noted that medical devices such as <a href="https://en.wikipedia.org/wiki/Magnetic_resonance_imaging">MRI</a> machines generate fields of up to 3 T, but patients typically are in the vicinity of such high fields for brief durations only.</p>
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<p>To test the effects of EM fields on biological cells in a controlled environment, researchers exposed two groups of mice to fields of 0.1 mT and 1.0 mT respectively over eight weeks, while a third group of mice living in similar conditions but without the EM exposure served as a control.
The EM fields in the experiment were generated at a frequency of 50 Hz, which is the frequency in most countries of the transmission of electricity via power lines.
The same researchers previously found that an eight-week exposure to a higher field of 1.5 mT caused unrepaired DNA damage in mice.
In both these studies, the scientists used breaks in the DNA strands in the cell nuclei as a measure of DNA damage.
In the latest study, they also looked at whether DNA inside mitochondria was being produced regularly, a part of the normal DNA repair process in cells.</p>
<p>Previous research has suggested that extended exposure to EM fields damages cells that are involved in the transport, reabsorption or storage of iron.
The researchers therefore studied how cells involved in these activities in the brain, the kidney and the liver were affected by EM exposure.</p>
<p><img src="https://apostilb.github.io/images/2016-08-27-mouse-dna-magnetic-fields.jpg" alt="An artistic representation of DNA" /></p>
<blockquote>
<p><em>An artistic representation of DNA. <a href="https://commons.wikimedia.org/wiki/File:DNA_com_GGN.jpg">Image</a> by Nogas1974 / <a href="https://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA 4.0</a></em></p>
</blockquote>
<p>Three sets of mice were kept in otherwise identical conditions but were exposed to different EM fields: the first group to 0.1 mT, the second to 1.0 mT and the third group to no EM fields other than the Earth’s natural magnetic field.
After eight weeks, cells from mice randomly selected from each group were analysed for signs of DNA damage.</p>
<p>The researchers performed a so-called “blind” analysis, which means they didn’t know which mice the cells came from, so that they didn’t bias the results in any way with knowledge about the EM-exposure levels involved.
They looked for signs of DNA damage in the cells that could be tied to the EM-field levels each group of mice was exposed to.
The tests showed that exposure to EM fields of 0.1 mT and 1.0 mT did not result in unrepaired damage to DNA in the nuclei of cells.
Exposure to 1.0 mT, however, was linked to a reduction in synthesis of DNA in the mitochondria, the structures that make energy for the cell.
DNA synthesis is a part of the normal DNA repair process, so lower levels of synthesis may indicate some irregularity in DNA repair possibly linked to the EM exposure.</p>
<p>From these experiments, it doesn’t appear that continuous exposure to low-intensity magnetic fields causes more unrepaired damage to DNA than might occur from natural causes.
The small number of cell types analysed, however, doesn’t make this the final word on the effects of EM radiation on organisms and their DNA, though it does support the European safety limit of 0.1 mT.</p>
<hr />
<p>Citation:</p>
<blockquote>
<p>Korr, H., Angstman, N.B., Born, T.B., Bosse, K., Brauns, B., Demmler, M., Fueller, K., Kántor, O., Kever, B.M., Rahimyar, N., Salimi, S., Silny, J., & Schmitz, C. (2014). No evidence of persisting unrepaired nuclear DNA single strand breaks in distinct types of cells in the brain, kidney, and liver of adult mice after continuous eight-week 50 Hz magnetic field exposure with flux density of 0.1 mT or 1.0 mT. <em>PLOS One</em>, 9(10), e109774. DOI: <a href="http://dx.doi.org/10.1371/journal.pone.0109774">10.1371/journal.pone.0109774</a></p>
</blockquote>
Undersea volcano type could contribute to carbon-dioxide emissions2016-03-05T00:00:00+00:00https://apostilb.github.io/2016/03/05/co2-undersea-volcanoes<p><em>Previous estimates for volcanic CO<sub>2</sub> emissions had not accounted for “petit spot” volcanoes</em></p>
<p>Volcanoes eject more than just lava.
They also pump carbon dioxide (CO<sub>2</sub>) from within the Earth’s surface into the atmosphere.
Although <a href="http://volcanoes.usgs.gov/vhp/gas_climate.html">CO<sub>2</sub> emissions from volcanoes are less than one percent of the amount given out by human activity</a>, determining this natural phenomenon’s contribution to the planet’s carbon cycle is valuable for understanding the evolution of the Earth’s climate over geological time scales.
Previously, geologists accounted for the CO<sub>2</sub> output of three types of volcanic activity: <a href="https://en.wikipedia.org/wiki/Volcanic_arc">arc</a>, <a href="https://en.wikipedia.org/wiki/Mid-ocean_ridge">mid-ocean ridge</a> and <a href="https://en.wikipedia.org/wiki/Hotspot_%28geology%29">hotspot</a>.
In <a href="http://dx.doi.org/10.1130/G34620.1">a 2013 paper</a>, however, researchers began to wonder whether a new type of volcano discovered in 2006 — the <a href="http://news.nationalgeographic.com/news/2006/07/060727-new-volcano.html">petit spot</a> — might also contribute gases into the atmosphere.</p>
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<p>Petit-spot volcanism manifests deep in the ocean floor, in the cracks of tectonic plates.
Since petit-spot volcanoes were only identified a few years ago, they had not been part of the existing models of carbon-dioxide emissions from volcanoes.
To determine their CO<sub>2</sub> flux, the researchers examined <a href="https://en.wikipedia.org/wiki/Volcanic_glass">volcanic glass</a> formed around petit-spot volcanoes some six kilometres below sea level.
Specifically, they studied how much carbon dioxide and water was dissolved in the glass, using this to estimate the amount of carbon dioxide emitted by these volcanoes as a fraction of its magma output.</p>
<p><img src="https://apostilb.github.io/images/2016-03-05-co2-undersea-volcanoes.jpg" alt="The Stromboli stratovolcano off the coast of Sicily" /></p>
<blockquote>
<p><em>The Stromboli stratovolcano off the coast of Sicily. <a href="https://en.wikipedia.org/wiki/File:DenglerSW-Stromboli-20040928-1230x800.jpg">Image</a> by Steven W. Dengler / <a href="https://creativecommons.org/licenses/by-sa/3.0/">CC BY-SA 3.0</a></em></p>
</blockquote>
<p>But, estimating the CO<sub>2</sub> emission based on the amount dissolved in the glass is not straightfoward.
First, the researchers had to calculate the concentration of the carbon dioxide and water around bubbles that had formed in the volcanic glass.
Then, they had to take into account the temperature and pressure conditions when the glass formed; these conditions would influence how much of the emitted gas made its way into the glass.
Having performed these measurements, the researchers arrived an estimate of the amount of carbon dioxide given out by petit-spot volcanoes.</p>
<p>Since data on magma flow from petit-spot volcanoes is only available for two regions — the <a href="https://en.wikipedia.org/wiki/Japan_Trench">Japan Trench</a> and the <a href="https://en.wikipedia.org/wiki/Tonga_Trench">Tonga Trench</a> — the researchers took the average magma flow from the two as a first estimate in their calculations.
The geologists also concluded, based on their measurements, that CO<sub>2</sub> makes up between five and 10 percent of the magma by weight for petit-spot volcanoes.
They were thus able to compute that emissions from these volcanoes are not negligible: between 0.1% and 1.2% of the carbon-dioxide emissions from arc and mid-ocean-ridge volcanoes and between 0.3% and 14% of that from hotspot volcanoes.</p>
<p>The authors of the paper note however that, with only 35% of the Pacific-plate area having been surveyed, additional volcanoes might yet be found.
They also point out that their estimates for emissions may be on the lower side, because other types of volcanoes also emit carbon dioxide without erupting.
Nonetheless, the research sheds light on a potentially unaccounted-for contribution to the planet’s carbon cycle.</p>
<hr />
<p>Citation:</p>
<blockquote>
<p>Okumura, S., & Hirano, N. (2013). Carbon dioxide emission to Earth’s surface by deep-sea volcanism. <em>Geology</em>, 41(11), p.1167-1170. DOI: <a href="http://dx.doi.org/10.1130/G34620.1">10.1130/G34620.1</a></p>
</blockquote>
Copiers and printers puff out particulates2016-02-06T00:00:00+00:00https://apostilb.github.io/2016/02/06/office-air-printer<p><em>Office devices vent some unwelcome chemicals</em></p>
<p>Office air can contain many chemical compounds that come from sources like carpet cleaning, furniture, dry cleaned clothes, and computer peripherals.
These can cause allergic reactions, respiratory illness, headaches, and other symptoms collectively called <a href="https://en.wikipedia.org/wiki/Sick_building_syndrome">sick building syndrome</a>.
<a href="http://dx.doi.org/10.1007/s11356-014-3672-3">A recent study</a> specifically looked at the amounts and types of chemicals released by printers and copiers.</p>
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<p>When ink and toner are heated during the printing process, tiny amounts of their constituent chemicals are released into the surrounding air.
The amounts depend on the temperature and the frequency of use as well as the operation of the devices.
In addition, the circuit boards and plastic parts of devices can give off their own emissions.
Fine aerosol particles of paper can also contribute to the office air cocktail of volatile organic compounds (VOCs).
Volatile refers to the fact that a large number of molecules are released, not that these compounds are inherently dangerous or artificial, though one manufactured VOC is probably very familiar: <a href="https://en.wikipedia.org/wiki/New_car_smell">new car smell</a>.</p>
<p><img src="https://apostilb.github.io/images/2016-02-06-office-air-printer.jpg" alt="Exploded toner cartridges" /></p>
<blockquote>
<p><em>Exploded toner cartridges. <a href="https://www.flickr.com/photos/makenosound/2557526304/">Image</a> by Max Wheeler / <a href="https://creativecommons.org/licenses/by-nc-nd/2.0/">CC BY-NC-ND 2.0</a></em></p>
</blockquote>
<p>Researchers tested seven different inkjet and laser printers and copiers inside a Plexiglas chamber to capture any released substances.
The devices were all manufactured during the 1990s and 2000s, but their manufacturers and models were not identified.
Air inside the chambers was sampled for five hours a day over four days, with printing taking place for 30 minutes at a time followed by a 30-minute break.
To calculate how much each device was emitting, the researchers took into account the air flow inside the chamber, its volume, the sampling time and volumes they collected, the printing/copying time, and other factors.</p>
<p>Over 60 compounds were identified in the air samples, including toluene, benzene, xylenes, ethylbenzene and styrene, which according to the authors “pose [a] hazard to human health when present in air”.
Some of these came out of all devices during printing, while some were only sporadically released by certain devices that were tested.
Ethylbenzene had the highest emission level at 41 micrograms per cubic meter.
One device was measured as emitting 8400 micrograms of particulates per hour, on average.
The authors list two VOCs — tetrachloroethylene, otherwise known as “dry-cleaning fluid”, and trichloroethylene — as carcinogenic or possibly carcinogenic to humans.
An inkjet printer was the greatest source of VOCs; this was also the slowest-printing device.</p>
<p>A person’s exposure to any of these chemicals in an office environment will of course depend on proximity, office size, ventilation, the toner used, and how much printing and copying is done, but despite the low concentrations, long-term exposure may be a cause for concern.
However, because of the different devices and toners used in this study, not to mention their different ages and speeds, it’s hard to compare them or assess which is “safer”.
The authors of this research suggest office air quality should be monitored to protect human health.</p>
<hr />
<p>Citation:</p>
<blockquote>
<p>Kowalska, J., Szewczyńska, M., & Pośniak, M. (2015). Measurements of chlorinated volatile organic compounds emitted from office printers and photocopiers. <em>Environmental Science and Pollution Research</em>, 22(7), 5241-5252. DOI: <a href="http://dx.doi.org/10.1007/s11356-014-3672-3">10.1007/s11356-014-3672-3</a></p>
</blockquote>
LEDs could be cheaper and just as bright without a common component2016-01-30T00:00:00+00:00https://apostilb.github.io/2016/01/30/led-reflectors<p><em>Simulations show reflectors used in LEDs may be unnecessary</em></p>
<p>Low-cost and low-power light-emitting diodes (LEDs), especially white LEDs, have revolutionised lighting.
In fact, the inventors of blue LEDs — a crucial element for producing white light — <a href="http://www.nature.com/news/nobel-for-blue-led-that-revolutionized-lighting-1.16092">won the 2014 Nobel Prize in Physics</a>.
Now, <a href="http://dx.doi.org/10.1186/s40539-015-0031-z">researchers have demonstrated</a> that there may be even better ways to optimise how white LEDs are made, by eliminating one commonly used component.
Changing the manufacturing process based on this work can further reduce the costs of white LEDs by 5–10%.</p>
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<p>Unlike filament-based bulbs or fluorescent tubes, LEDs rely on <a href="https://en.wikipedia.org/wiki/Semiconductor">semiconductors</a>.
Layers of semiconducting materials are combined together, emitting photons when electricity is passed through them.
These layers and other components of a single LED must be assembled very precisely.
To secure the LED chip itself to the base of the final emitter package, a special adhesive or glue is used.
Conventionally used adhesives are made with silver and happen to absorb light that falls on them.
This reduces the final light output of the LED.
To counter this absorption, so-called backside reflectors are added between the LED chips and the adhesive layer, in order to allow higher light output.
When LED chips were tested before they were assembled into the final devices, backside reflectors boosted the light output by up to 50%, encouraging their continued use.</p>
<p>However, laboratory testing can vary from real-world performance.
In fact, it wasn’t clear if assembled LEDs would also have increased light output with reflectors, because this had not been tested.
Further, the materials used for backside reflectors in low-cost LEDs happen to reflect certain wavelengths much less, casting doubt on the overall effectiveness of the reflectors.
To add to this, using a newly developed, optically clear adhesive instead of the silver-based ones might even remove the need for including the reflectors in the first place, but this had not been verified before.</p>
<p><img src="https://apostilb.github.io/images/2016-01-30-led-reflectors.jpg" alt="White LEDs" /></p>
<blockquote>
<p><em>White LEDs. <a href="https://www.flickr.com/photos/oskay/2230059807/">Image</a> by Windell Oskay / <a href="https://creativecommons.org/licenses/by/2.0/">CC BY 2.0</a></em></p>
</blockquote>
<p>The researchers wanted to test how the reflector and clear glue affected light output; they experimented on the following combinations: (1) LED chips without backside reflectors, (2) the most-commonly used LED chips — ones with low-cost backside reflectors (which have low reflectance), and (3) LED chips with high-reflectance backside reflectors (which are more expensive and hence not used widely).
The data showed that reflector-free chips performed considerably better than chips that used low-cost reflectors, although chips with the expensive reflectors out-performed both.
This suggests that merely replacing the silver-based adhesives with the optically clear alternative can improve the light output and backside reflectors can be left out.</p>
<p>To test the real-world performance of the final LED devices, the researchers studied the effect of the packaging process on the devices’ light output
They did so using <a href="https://en.wikipedia.org/wiki/Monte_Carlo_method">Monte Carlo</a> software (<a href="https://optics.synopsys.com/lighttools/lighttools-feature-details.html"><em>LightTools</em></a>) to simulate models of packaged devices and naked LED chips, both of which used reflectors of varying reflectance.
Even though the light output of the naked chips benefited from the backside reflectors, the simulations showed that backside reflectors didn’t make the final LEDs brighter.
Experimental measurements also backed up the data from the simulations; this indicates the simulation method was valid.</p>
<p>These new results illustrate how expectations of how something <em>should</em> work are not always met and that testing in real-world situations as well as simulations are often needed.
The authors of the work show that by modifying the production techniques of LEDs, we can get better-performing devices at even lower costs.</p>
<hr />
<p>Citation:</p>
<blockquote>
<p>Kim, G., Shih, Y.-C., You, J.-P., & Shi, F. G. (2015). Optical role of die attach adhesive for white LED emitters: light output enhancement without chip-level reflectors. <em>Journal of Solid State Lighting</em>, 2:11. DOI: <a href="http://dx.doi.org/10.1186/s40539-015-0031-z">10.1186/s40539-015-0031-z</a></p>
</blockquote>
X-rays show hair treatments don't penetrate or fix hair2016-01-23T00:00:00+00:00https://apostilb.github.io/2016/01/23/hair-xray<p><em>But permanent waving does alter protein structure inside hair</em></p>
<p>Miracle products for fussy hair have probably been around longer than hair has even been studied.
Though hair structure has now been investigated in great detail, with tools like X-ray diffraction and electron microscopy, hair repair products proliferate, and their benefits can be dubious at best.
Beyond settling this cosmetic question, however, studying hair with imaging methods can be instructive for science — and health.
Abnormally curly or twisted hair can actually be indicative of an underlying disease state; <a href="http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3086309/">breast cancer</a>, for example, can be accurately predicted using hair samples.
Disease screening thus might benefit from hair imaging, but it’s only useful to study hair if the frequently used hair care products — shampoo, conditioner, and permanent waving treatments — don’t affect internal hair structure.</p>
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<p>In an <a href="https://doi.org/10.7717/peerj.619">earlier study on hair structure</a>, researchers sampled hair from a variety of individuals who used different amounts of shampoo and conditioner.
In their new study, they wanted to <a href="https://doi.org/10.7717/peerj.1296">study just one person’s hair</a>, to discount any effects of differential product use.</p>
<p>Shampoos and conditioners have a whole host of ingredients, many of them completely unnecessary for their primary functions: cleaning and smoothing.
Both products mainly interact with hair at the surface, or cuticle, level. Shampoo and conditioner will only reach the next layer, the cortex, if the cuticle is very damaged, in which case shampooing may contribute to even <em>more</em> hair damage.
Repeated shampooing extracts more hair surface lipids (oils) while conditioning retains ingredients on the hair surface.
Both products can affect the X-ray diffraction signal when the hair is imaged.
Perming, for its part, also induces major structural changes in hair, breaking and re-forming chemical bonds within hair and making the hair surface more likely to shed lipids during shampooing.</p>
<p><img src="https://apostilb.github.io/images/2016-01-23-hair-xray.jpg" alt="False-color scanning electron micrograph of a bleached and straightened strand of hair." /></p>
<blockquote>
<p><em>False-color scanning electron micrograph of a bleached and straightened strand of hair. <a href="https://www.flickr.com/photos/wellcomeimages/15854964238/">Image</a> by Wellcome Images / <a href="https://creativecommons.org/licenses/by-nc-nd/2.0/">CC BY-NC-ND 2.0</a></em></p>
</blockquote>
<p>One female participant volunteered her hair to be shampooed, conditioned, and permed for this study.
Roughly 400 strands of hair were divided between the eight different experimental treatments: with and without permanent waving, and with and without shampoo and conditioner (or both).
Using a common drugstore shampoo and conditioner, the hair strands were bathed in petri dishes.
Perming was done while the hair was still attached to the subject’s head.
Hair strands were then clamped onto some cardboard and loaded into an X-ray diffractometer, which bombards the samples with X-rays to reveal structural properties at atomic and molecular scales of one ten-billionth of a meter.</p>
<p>Shampoo or conditioner alone or in combination had virtually no effect on the X-ray images obtained.
This means it is likely that the hair’s internal lipid or keratin structure was not changed by shampooing or conditioning.
The X-ray signal intensity of the permed hair samples suggests changes to the keratin filaments and how they are packed within the hair.
Further, shampooing and conditioning had no “restorative” effect on the permed hair fibers.</p>
<p>This study is one more piece of evidence that shampoo and conditioner have only limited effects on the outermost hair layer, the cuticle, and do not alter the hair’s internal lipid or keratin structure.
This means that researchers can usefully employ X-ray profiling to study keratin within hair (for disease screening, for example) without worrying about whether participants’ use of shampoo or conditioner will fundamentally affect the result — as long as the hair is not permed.
Permed hair exhibited X-ray profiles consistent with broken bonds within the keratin microstructure.
These X-ray data also support the idea that perming changes hair structure at the intermediate filament level (a half-way zone between protein complexes and the macro hair strand).</p>
<hr />
<p>Citation:</p>
<blockquote>
<p>Zhang, Y., Alsop, R. J., Soomro, A., Yang, F. C., & Rheinstädter, M. C. (2015). Effect of shampoo, conditioner and permanent waving on the molecular structure of human hair. <em>PeerJ</em>, 3, e1296. DOI: <a href="https://dx.doi.org/10.7717/peerj.1296">10.7717/peerj.1296</a></p>
</blockquote>
Red shift, blue whale2016-01-16T00:00:00+00:00https://apostilb.github.io/2016/01/16/redshift-bluewhale<p><em>Variation of whale-song pitch not fully explained by Doppler shift</em></p>
<p><a href="https://en.wikipedia.org/wiki/Blue_whale#Vocalizations">Whale songs</a>, the deep, reverberating vocalisations made by the largest mammal, have been the subject of research for decades.
Recordings of the songs of the Antarctic blue whale show a pronounced drop in pitch between March and December before a “reset” over the following January and February.
In addition to this <em>intra-annual</em> variation, the recordings also show an overall drop in pitch over several years.
Several hypotheses have been proposed to explain both patterns.
Marine biologists recently <a href="http://dx.doi.org/10.1371/journal.pone.0107740">took to the oceans to test explanations for the intra-annual variation</a>, including the idea that the changes could be caused by Doppler shifts.</p>
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<p>The words “<a href="https://en.wikipedia.org/wiki/Doppler_effect">Doppler shift</a>” bring to mind the siren of an ambulance, seemingly getting higher in pitch as it approaches you and then lower as it rushes past.
This perceived change in sound is caused by the relative motion between the source of the sound and the listener: as the source and listener move closer to one another, the sound waves emitted get compressed, causing a rise in pitch, while relative motion away results in the emitted waves expanding and lowering the pitch.
The phenomenon can also be observed in electromagnetic waves: stars that move towards us have their light shifted to the blue end of the spectrum (blue shift) and light from those stars that move away from us is shifted to the red end of the spectrum (red shift).</p>
<p>Antarctic blue whales are believed to migrate northwards to warmer waters during southern-hemisphere winters.
Scientists have hypothesised that differences in whale-song pitch during a given year are caused by this movement of the mighty creatures.
According to this hypothesis, as the whales travel towards sound-recording stations, the pitch of their calls appears to increase, with a corresponding decrease in pitch detected when their movement is away from the recorders.</p>
<p><img src="https://apostilb.github.io/images/2016-01-16-redshift-bluewhale.jpg" alt="A blue whale" /></p>
<blockquote>
<p><em>A blue whale. <a href="https://www.flickr.com/photos/51647007@N08/5187320081">Image</a> courtesy of the NOAA Photo Library / Public domain (via <a href="https://commons.wikimedia.org/wiki/File:Anim1754_-_Flickr_-_NOAA_Photo_Library.jpg">Wikimedia Commons</a>)</em></p>
</blockquote>
<p>To test this hypothesis, members of the 2013 Antarctic Blue Whale Voyage of the Southern Ocean Research Partnership recorded the songs of blue whales using “sonobuoys” while also tracking their positions with special video cameras.
By carefully measuring (or accurately estimating, when measurements were unavailable) the relative motion of the recording buoys and the whales, the scientists were able to determine how well the intra-annual whale-song-pitch variations could be attributed to the Doppler shift.
However, although the variations followed the pattern predicted by the Doppler shift, they were also much greater than expected.</p>
<p>Environmental and biological explanations for the intra-annual variation were also considered.
Measurements of the whale-song pitch from dispersed, static recording stations ruled out environmental factors (such as temperature and salinity of water), since varied locations provided similar data.
Yet another possibility is that the changes in song pitch correspond to feeding patterns of the whales.
The minimum and maximum pitches seem to coincide with the arrival and departure of the whales to their feeding grounds.
Feeding habits would correspond to blubber thickness, and monthly measurements of this thickness correlated with the monthly change in pitch for whales less than 19 metres long but not for those more than 23 metres long.
Combined with these data on blubber thickness, the Doppler-shift explanation for changes in whale-song pitch is certainly promising, though it doesn’t it tell the whole story.</p>
<p>Null results, or in this case inconclusive ones, are crucial to science.
They help scientists refine their theories and discard unsatisfactory assumptions.
Also, future researchers are better equipped to take advantage of this work and correct for Doppler shifts when measuring the pitch of whale songs.</p>
<hr />
<p>Citation:</p>
<blockquote>
<p>Miller, H.S., Leaper, R., Calderan, S., & Gedamke, J. (2014).
Red shift, blue shift: investigating Doppler shifts, blubber thickness, and migration as explanations of seasonal variation in the tonality of Antarctic blue whale song.
<em>PLOS One</em>, 9(9), e107740.
DOI: <a href="http://dx.doi.org/10.1371/journal.pone.0107740"> 10.1371/journal.pone.0107740</a></p>
</blockquote>
Why does scratching an itch feel so good?2015-09-26T00:00:00+00:00https://apostilb.github.io/2015/09/26/itch-scratch<p><em>Broad network of brain areas mediates the satisfaction of scratching</em></p>
<p>The act of scratching not only relieves an itch but also evokes pleasant feelings.
These feelings of enjoyment can be traced to activation in regions of the brain involved in reward, or positive stimulation that reinforces certain behaviors.
While the pleasantness of scratching an itch has been documented before, <a href="http://dx.doi.org/10.1152/jn.00374.2013">a 2014 study</a> claims to be the first to identify the specific brain regions involved in this sensation.</p>
<!--break-->
<p>Researchers used functional magnetic resonance imaging (fMRI), which measures changes in blood flow in the brain, to see which areas “light up” in response to scratching.
The 16 participants in the study didn’t scratch themselves, though.
The researchers carefully controlled the duration (five seconds) and location of scratching, which was done with a tool consisting of two copper plates that apparently delivered the same sensation as using fingernails.
Itching was induced on participants’ wrists via electrical stimulation for four-and-a-half seconds.
In the “pleasant” condition, the wrist was then scratched by the experimenter; in a control condition, part of the forearm that was not itchy was scratched instead.
Participants also reported how pleasant the experience was 10 seconds after the scratching ended.
These conditions were done both with and without brain imaging; in the latter case, the participants also reported the duration of pleasantness by pressing a button.
An extra condition confirmed that there was no pleasant sensation derived from scratching without itch stimulation.</p>
<p><img src="https://apostilb.github.io/images/2015-09-26-bear-scratching.jpg" alt="A bear scratching its forehead" /></p>
<blockquote>
<p><em>A bear scratching its forehead. <a href="https://www.flickr.com/photos/tambako/4283191966/">Image</a> by Tambako The Jaguar / <a href="https://creativecommons.org/licenses/by-nd/2.0/">CC BY-ND 2.0</a></em></p>
</blockquote>
<p>Participants’ ratings showed that no pleasant feelings were evoked in the control condition.
In the other condition, the pleasant feeling from scratching lasted for five seconds on average, the same duration as the scratching itself.
Many brain regions were activated in both the pleasant and control conditions, as could be expected.
Significantly higher activation in the pleasant condition was found in areas including the supplementary motor area, inferior frontal gyrus, striatum, midbrain, premotor and somatosensory cortices, and the insular cortex.
The latter area is important for awareness of changes in the body and mind.
Many of the same regions were active in response to the itch stimulation itself or when participants rated the pleasantness of scratching.
It was not clear what the roles of inferior frontal gyrus or premotor cortex were in the feeling of pleasantness; activation in these areas had not been observed in previous studies.
Reduced activation was seen in both conditions in primary motor cortex, occipital cortex, medial orbitofrontal cortex and hippocampus.
This was similar to results of previous studies.</p>
<p>The numerous brain regions involved in the feeling of pleasure from scratching are also activated by other somatosensory stimuli such as touch or pain.
This led the researchers to surmise that the core of the pleasant scratching feeling is the somatic sensation itself; the fact that scratching the itch (i.e. relief) was preferable to the control condition likely also contributed to increased reward activity.
The activation seen in motor regions during the pleasant condition was also new, and was attributed to the desire to act (scratch) to alleviate the itch.
Activation of the motor regions may also explain how scratching-induced pleasantness reinforces the scratching behavior.
Midbrain and striatum dopaminergic neurons, part of the reward system activated during the pleasant sensation, may be responsible for recruiting the motor regions, as they <a href="https://en.wiktionary.org/wiki/innervate">innervate</a> these higher areas.</p>
<p>The pleasant feeling of scratching an itch thus comes from activation in reward areas of the brain, such as the striatum, midbrain and medial frontal regions.
The involvement of both motor and reward circuits is relevant to conditions like chronic itch and excessive non-pleasant scratching.</p>
<hr />
<p>Citation:</p>
<blockquote>
<p>Mochizuki, H., Tanaka, S., Morita, T., Wasaka, T., Sadato, N., & Kakigi, R. (2014). The cerebral representation of scratching-induced pleasantness. <em>Journal of Neurophysiology</em>, 111(3), 488-498. DOI: <a href="http://dx.doi.org/10.1152/jn.00374.2013">10.1152/jn.00374.2013</a></p>
</blockquote>
It's hot out there for a bear2015-07-25T00:00:00+00:00https://apostilb.github.io/2015/07/25/bear-foraging<p><em>Foraging for food takes precedence over staying cool</em></p>
<p>Grizzly bears have a dilemma.
They only have about seven months a year to eat 12 months’ worth of food, since they hibernate for the remaining five months.
This imperative to eat is at odds with high temperatures during the best feeding months.
Bears don’t have sweat glands, yet they must develop thick under-fur and a layer of fat for the winter.
Do the bears reduce their activity to beat the heat, or do they stick to their eating mission?</p>
<!--break-->
<p>Wildlife researchers followed small groups of grizzlies in British Columbia and recorded their activities.
Previous research found that other types of bears reduce their activity levels when temperatures reached 20 °C.
The researchers anticipated that grizzly bears would either be more active for longer periods during the summer while foraging for berries (the major high-energy food in the ecosystem they studied), or they would become more nocturnal and less active when it’s hot (since it is challenging for bears to dissipate their body heat).</p>
<p><img src="https://apostilb.github.io/images/2015-07-25-bear-foraging.jpg" alt="Grizzly bear in Denali, Alaska" /></p>
<blockquote>
<p><em>Grizzly bear in Denali, Alaska. <a href="https://www.flickr.com/photos/slobirdr/16630262729/">Image</a> by Gregory “Slobirdr” Smith / <a href="https://creativecommons.org/licenses/by-sa/2.0/">CC BY-SA 2.0</a></em></p>
</blockquote>
<p>Bears that had been fitted with GPS collars were tracked in a low-elevation area of the Coast Mountain Range that is steep and dry, with little shade but an abundance of berries.
While the bears were tracked across all seasons, the main period of interest was roughly from July to October (berry season).
The researchers also looked at day length, time of day, temperature, and duration of activity as they analyzed the bears’ behaviors.</p>
<p>When bears emerged from hibernation, their activity levels were initially low but then increased, remaining high from about July to September, then decreasing.
Female bears also appeared to be more active than males.
Different day lengths throughout the year didn’t influence activity levels, but active bouts for bears were longer in berry season.
As it turns out, bears were less active at night, but were active for 78% of the time between sunrise and sunset.
The bears also did not change their activity levels even when foraging in temperatures up to 40 °C.</p>
<p>The first hypothesis, that bears are more active for longer in summer, was thus supported, and bears did not reduce activity according to the heat dissipation limit theory.
This is somewhat surprising, given that other bears and large tropical mammals are known to decrease their activity when temperatures rise.
When sufficient food rewards are available, it seems, foraging takes precedence over heat.</p>
<p>These results may be specific to this ecosystem, where berries are the main source of energy for bears.
They also underscore the importance of daylight and vision for bear foraging.
It takes a long time to fill up on berries, so bears needs to stay active when berries are ripe and visible.
In other ecosystems, bears display activity patterns that do not differ across seasons like those of the British Columbia bears, probably due to different day lengths at other latitudes and the availability of different foods.
Because bears are successful across diverse climates, this shows they can change their habits to accommodate conditions.
Further study could have implications for conservation of these animals in the wake of climate change.</p>
<hr />
<p>Citation:</p>
<blockquote>
<p>McLellan, M. L., & McLellan, B. N. (2015). Effect of season and high ambient temperature on activity levels and patterns of grizzly bears (<em>Ursus arctos</em>). <em>PLOS One</em>, 10(2), e0117734. DOI: <a href="http://dx.doi.org/10.1371/journal.pone.0117734">10.1371/journal.pone.0117734</a></p>
</blockquote>
Mass muddles mental number line2015-06-20T00:00:00+00:00https://apostilb.github.io/2015/06/20/mental-number-line<p><em>Judgment of number influenced by other magnitudes and senses</em></p>
<p>People appear to have an inherent bias when it comes to number.
They tend to count from left to right and are quicker to react in psychological tests when smaller numbers are on the left and larger numbers are on the right; <a href="http://www.aaas.org/news/humans-chicks-count-left-right">chicks also display this same behavior</a>.
Studies have found this mental number line to be pervasive across tasks where people judge size, duration or emotional expression (preferring frownies on the left and smileys on the right, for example).
But is the mental number line just about number or is it part of a more general system that extends to any judgment of magnitude?</p>
<!--break-->
<p>Researchers sought to test this using a standard experiment with the addition of an irrelevant magnitude, a weight worn on the wrist.
Twenty-four participants had to quickly and accurately judge whether a number (0-9) on a screen is odd or even.
They gave their responses using a keyboard, and the experiment was balanced so that the ‘odd’ and ‘even’ responses were assigned to keys on the left (‘Q’) or right (‘P’) side of the keyboard, respectively, in half the trials, and reversed in the other half.
There were three conditions: participants wore a five-pound weight on the left wrist, the right wrist, or no weight (the baseline condition).</p>
<p><img src="https://apostilb.github.io/images/2015-06-20-rugani-chick.jpg" alt="Young chicks use a mental number line that reads left to right, just like humans" /></p>
<blockquote>
<p><em>Young chicks use a mental number line that reads left to right, just like humans. <a href="http://media.eurekalert.org/scipak/gallery/images/2015-01/rugani1HR.jpg">Image</a> by Rosa Rugani, University of Padova</em></p>
</blockquote>
<p>According to the SNARC <a href="https://en.wikipedia.org/wiki/Spatial-numerical_association_of_response_codes">(Spatial-Numerical Association of Response Codes)</a> effect usually seen in this experiment, people should react more quickly when stimuli conform to the mental number line.
That is, small numbers should elicit a faster left response and large numbers a faster right response.
The right-weighted condition should be similar to the baseline condition, because the increased weight on the right wrist agrees with the mental number line idea of greater magnitude being associated with a spatial location on the right.
The left-weighted condition is in conflict with the association of smaller numbers (or magnitudes) with the left side of space.
If the mental number line is specific to number, however, an external factor like weight shouldn’t affect performance.</p>
<p>First, the researchers removed any data with wrong answers or very slow responses.
On average, people responded equally fast in all three conditions.
In comparing the left and right responses, the authors found similar results for the baseline and right conditions: the number line effect was present, with left side responses faster for smaller numbers and right side responses faster for larger numbers.
The left condition, however, did not show this effect.
With left-weighted wrists, participants did not show any responses time differences in a left-right direction.
There weren’t any differences across conditions depending on which hand participants had used in their responses and, although most of the participants were right-handed, handedness also did not affect the results.</p>
<p>The conclusion is that the mental number line is about more than just number, it also organizes other magnitudes in the same spatial fashion.
The wrist weight was irrelevant to judging the parity of the on-screen number, yet it completely changed the response in the left-weighted condition, removing any trace of the mental number line effect.
The weight could have affected the perceived effort in the task, or its physical size could have influenced the participants.
The point is that the brain integrated asymmetries in space (the weight) with visual judgments of “size” (number).
Number, it seems, is not differentiated from other mental judgments of size.
Small and large numbers that are presented incongruously, as physically large and small, can also evoke slow responses.
This points to a dynamic organization of magnitudes across space, as well as a integration across the senses (in the case of this study, visual and haptic).</p>
<hr />
<p>Citation:</p>
<blockquote>
<p>Holmes, K. J., & Lourenco, S. F. (2013). When numbers get heavy: is the mental number line exclusively numerical. <em>PLOS One</em>, 8(3), e58381. DOI: <a href="http://dx.doi.org/10.1371/journal.pone.0058381">10.1371/journal.pone.0058381</a></p>
</blockquote>
Ultrahigh-energy cosmic neutrinos remain elusive2015-06-07T00:00:00+00:00https://apostilb.github.io/2015/06/07/cosmic-neutrinos<p><em>No signs of tell-tale particles despite years of data collection</em></p>
<p>We are all bathed in a constant stream of particles knows as cosmic rays<sup id="fnref:1"><a href="#fn:1" class="footnote">1</a></sup>, which are produced mostly outside the Solar System.
These high-energy particles were initially suspected to have Earthly origins, but <a href="http://timeline.web.cern.ch/events/victor-hess-discovers-cosmic-rays">Victor Hess demonstrated in 1912</a> that they arrive on our planet from non-terrestrial sources.
For decades, the enigmatic nature of cosmic rays has captivated scientists, who have sought explanations for their origins and the energies they possess.</p>
<!--break-->
<p>In 1966, Kenneth Greisen as well as Georgiy Zatsepin and Vadim Kuzmin proposed that the energy of cosmic rays originating from very distant sources wouldn’t exceed a certain value.
The <a href="https://en.wikipedia.org/wiki/Greisen%E2%80%93Zatsepin%E2%80%93Kuzmin_limit">Greisen–Zatsepin–Kuzmin (GZK) limit</a> comes from energy losses that ultrahigh-energy cosmic rays (UHECRs) experience when they interact with the photons from the cosmic microwave background radiation.
Indeed the flux of UHECRs tails off at energies above the GZK limit, as predicted.
However, there may be alternative explanations as to why this is the case, which can be tested by probing the composition, and therefore the sources, of the UHECRs.</p>
<p>One such probe involves searching for ultrahigh-energy cosmic neutrinos.
Neutrinos are particles that interact with matter extremely weakly, meaning that they can pass through lightyears of lead without interacting in any way with the dense metal.
Cosmic neutrinos can have two possible origins: they could be produced through the interactions of cosmic-ray particles such as protons with the cosmic microware background or they could be the result of the <a href="https://en.wikipedia.org/wiki/Particle_decay">decay</a> of ephemeral particles produced at the cosmic-ray source.
Observing and studying ultrahigh-energy neutrinos could shed light on the nature of UHECR that originate in very distant cosmic-ray sources.
It would also help validate or rule out theories that attempt to explain the UHECR energy spectrum.</p>
<p>The <a href="https://www.auger.org/">Pierre Auger Observatory</a> in Argentina is designed to detect ultrahigh-energy cosmic rays. It is operated by an international collaboration of more than 500 scientists and is the largest UHECR observatory with a detection area of around 3000 km<sup>2</sup> — the area of Rhode Island or around thrice the area of Hong Kong.
The Surface Detector (SD) array of the observatory can detect neutrinos that have energies of around and greater than 1 exaelectronvolt (10<sup>18</sup> eV).
These energies are over <a href="http://www.wolframalpha.com/input/?i=1+EeV+vs+6.5+TeV">150,000 times the energy we can produce in our most powerful particle accelerator, the Large Hadron Collider</a>.
The neutrinos are not observed directly but through cascading showers of particles (mostly electrons or their heavier cousins known as <a href="https://simple.wikipedia.org/wiki/Muon">muons</a>) produced when the neutrinos interact with the Earth’s atmosphere.</p>
<p><img src="https://apostilb.github.io/images/2015-06-07-cosmic-neutrinos.jpg" alt="Three of the stations of the Surface Detectors in the Pierre Auger Observatory" /></p>
<blockquote>
<p><em>Three of the stations of the Surface Detectors in the Pierre Auger Observatory in a row towards the Andes, at sunrise. <a href="https://commons.wikimedia.org/wiki/File:SD_tanks_and_Andes.JPG">Image</a> by Lorenzo Caccianiga / <a href="https://creativecommons.org/licenses/by-sa/3.0/">CC BY-SA 3.0</a></em></p>
</blockquote>
<p>The Auger team analysed data collected between January 2004 and June 2013, corresponding to around six and a half years of continuous operation.
During this period, they didn’t observe a single candidate for neutrino-induced showers.
In the absence of an observation, the null result has helped the Auger scientists establish their most stringent limit on the flux of ultrahigh-energy neutrinos in the energy range of <a href="http://www.wolframalpha.com/input/?i=1e17+eV">1e17 eV</a> to <a href="http://www.wolframalpha.com/input/?i=2.5e19+eV">2.5e19 eV</a>.
The limits thus set will allow theorists to further fine-tune their models and predictions on the nature and behaviour of ultrahigh-energy cosmic rays.</p>
<hr />
<p>Citation:</p>
<blockquote>
<p>Pierre Auger Collaboration (2015).
Improved limit to the diffuse flux of ultrahigh energy neutrinos from the Pierre Auger Observatory.
<em>Physical Review D</em>,
91(9).
DOI: <a href="http://dx.doi.org/10.1103/PhysRevD.91.092008">10.1103/PhysRevD.91.092008</a></p>
</blockquote>
<div class="footnotes">
<ol>
<li id="fn:1">
<p>An explanation of these particles can be found at <a href="https://www.auger.org/index.php/cosmic-rays/cosmic-ray-mystery">auger.org/index.php/cosmic-rays/cosmic-ray-mystery</a>. <a href="#fnref:1" class="reversefootnote">↩</a></p>
</li>
</ol>
</div>
Global warming may be key to finding E.T.2015-05-30T00:00:00+00:00https://apostilb.github.io/2015/05/30/hot-planet-astrobiology<p><em>Exoplanets that are too hot may be a sign of alien life</em></p>
<p>A new research paper suggests that scanning for waste heat radiating off of Earth-like planets may be important in the search for extraterrestrial intelligence.
Like the radio signals emitted by Earth, heat may serve as an interstellar smoke signal indicating energy production and consumption.
While this is not a new idea, the study argues that heat is a viable marker of alien civilization that should be considered in plans for building future telescopes.</p>
<!--break-->
<p>With nearly 2000 exoplanets discovered <a href="http://exoplanetarchive.ipac.caltech.edu/cgi-bin/TblView/nph-tblView?app=ExoTbls&config=planets">so far</a>, detailed study of them may yet reveal signs of alien civilization.
One signal that we have been listening for in the search for extraterrestrial intelligence is radio waves, which our rapidly industrialized Earth civilization has also been beaming into outer space for the past 100 years or so.
These artificial signals traveling at the speed of light were humanity’s first “hello” to the universe.
But even these signals are becoming silenced with the end of terrestrial broadcasting; if the same thing happened to E.T., what are some other large-scale signs that could indicate the presence of intelligent life?</p>
<p>The thermal radiation of a planet may be an unintentional calling card, a biomarker of extraterrestrial life.
In particular, the way heat is distributed as islands in space and time on a planet’s surface — think of the bright spots of illuminated cities on Earth at night — may be a signature of Earth-like civilizations.
Because the trend on this planet is towards ever greater energy consumption, civilizations as or more advanced than Earth’s may also be recognized by the heat (detected as infrared light) that accompanies energy production.</p>
<p><img src="https://apostilb.github.io/images/2015-05-30-Kepler_16b.jpg" alt="Kepler-16b, an exoplanet orbiting a pair of stars" /></p>
<blockquote>
<p><em>Kepler-16b, an exoplanet orbiting a pair of stars. Modified from original <a href="http://planetquest.jpl.nasa.gov/system/secondary_files/binaries/988/original/Kepler_16b_39x27.jpg">image</a> / Courtesy NASA/JPL-Caltech / Public Domain</em></p>
</blockquote>
<p>The researchers modeled heat signals that might be emitted by an exoplanet with Earth-like properties of reflectance, scattering, and geography, but a heat profile 50 times larger than Earth’s.
An advancing civilization will likely be accompanied by a warming planet; as the authors put it, “a civilization with growing power needs will eventually reach a point where they become uncomfortably warm”.
Even if the alien civilizations found a way to engineer their planet to reflect heat out of the atmosphere, this would still leave a detectable heat signature.</p>
<p>The more advanced a civilization is, the argument goes, the more energy it needs, and the more it will move towards harnessing all the available energy in its solar system, perhaps culminating in a <a href="http://en.wikipedia.org/wiki/Dyson_sphere">Dyson sphere</a>.
We can compare energy consumption with the theoretical maximum available (i.e. the amount of energy incident from the host star) to get a measure of how advanced (in terms of energy consumption and thus heat output) a civilization is.
For Earth, the researchers estimate we are now consuming 0.04% of the flux of the Sun; more advanced civilizations will tend towards 100%.</p>
<p>They gave the model planet certain energy inputs (solar and planetary heat sources) and outputs (from photosynthesis and other biological activity as well as technology) and found that the brightness of the planet changed predictably with its programmed rotation and planetary orbit period.
To discount parts of the observed brightness that are due to reflected radiation (e.g. from cloud cover), they removed the short-wavelength light.
In this way, they were able to show that the heat profile of a civilization is distinct from the heat profile attributable purely to planetary motion.</p>
<p>Looking at the visible and infrared light coming off a planet, it is thus in principle possible to ascertain thermal signatures compatible with alien civilization.
This method could be enhanced by coupling it with existing tools like spectroscopy, which looks at the reflected spectrum of electromagnetic radiation to determine the chemical composition of exoplanets and stars.
Still, the heat signature will be confounded by planets completely covered in clouds or water.</p>
<p>In order to find these hot planets, really big telescopes are needed, the authors argue.
The challenge is to achieve sufficient contrast sensitivity — being able to distinguish the planet’s faint thermal signatures from the heat generated by the star it orbits — and for that you need telescopes with <a href="http://en.wikipedia.org/wiki/Objective_%28optics%29#Telescope">large-diameter objectives</a>, plus other technology to block light from other stars and focus the light you <em>do</em> want to see.
A 70-meter telescope would be sufficient to study exoplanets in the habitable zones of stars in Earth’s near-neighorhood, within 20 parsecs.
The world’s largest planned telescopes, however, are all under 40 meters.
The authors therefore advocate for the 74-meter Colossus telescope that would have the contrast sensitivity required to detect the heat signatures of any advanced civilizations on near-Earth exoplanets.</p>
<p>Finally, the authors suggest, we can learn something important about the survival probability of advanced civilizations (very low) if no alien heat signatures are found with a survey of the habitable planets in the near-Earth neighborhood.</p>
<hr />
<p>Citation:</p>
<blockquote>
<p>Kuhn, J. R., & Berdyugina, S. V. (2015). Global warming as a detectable thermodynamic marker of Earth-like extrasolar civilizations: the case for a telescope like Colossus. <em>International Journal of Astrobiology</em>, 14(3), 401-410. DOI: <a href="http://dx.doi.org/10.1017/S1473550414000585">10.1017/S1473550414000585</a></p>
</blockquote>
Hearing with light, seeing with sound2015-05-23T00:00:00+00:00https://apostilb.github.io/2015/05/23/photoacoustic-penetration<p><em>Improvement to tissue-imaging technique based on photoacoustic spectroscopy shows promise for minimally invasive radiology</em></p>
<p>Photoacoustics (PA) involves shining light (<em>photo–</em>) on a material to produce sound (<em>acoustics</em>) and using the sound for spectroscopy<sup id="fnref:1"><a href="#fn:1" class="footnote">1</a></sup>. When energy from the incident light is absorbed by a material it expands slightly and when the light source is switched off the material contracts. Alternately shining and switching off the light source rapidly creates pressure differences that manifest as sound waves. Materials will vary in the sounds they produce depending on the wavelength of light shone on them. A light-vs-sound spectrum for a particular material can be prepared by “listening” to the pressure waves that various wavelengths of light make in it, allowing one to see with sound. The photoacoustic effect was discovered by Alexander Graham Bell in the late 19th century, but has found use in materials science and medicine relatively recently.</p>
<!--break-->
<p><img src="https://apostilb.github.io/images/2015-05-23-photoacoustic-penetration.png" alt="Schematic illustration of photoacoustic imaging" /></p>
<blockquote>
<p><em>Schematic illustration of photoacoustic imaging. <a href="https://commons.wikimedia.org/wiki/File:PASchematics_v2.png">Image</a> by Bme591wikiproject / <a href="https://creativecommons.org/licenses/by-sa/3.0/">CC BY-SA 3.0</a></em></p>
</blockquote>
<p>PA imaging provides a guiding mechanism for medical procedures without the risks of ionising radiation and the cost of expensive equipment. Light from lasers is shone on photoabsorbers, such as haemoglobin; the resulting sound waves are detected by transducers and translated into visual images of the targeted region. PA also provides high-contrast images of the surgical tools being used in the medical procedure.</p>
<p>This imaging technique has, however, come with a severe limitation so far: the deeper the light goes into tissue, the less photo-energy per unit area can be delivered, reducing the resolution and constraining PA imaging’s penetration depth. Since the energy of the laser cannot be arbitrarily increased to probe even deeper into tissue — these matters being regulated by bodies such as the American National Standards Institute — a new approach has recently been explored. In laboratory (non-clinical) conditions, researchers modified their surgical apparatus so that a fiber-optic light source could be inserted along with it into the material under observation, allowing the light to be shone not from the surface but from within the material (i.e. it is irradiated <em>interstitially</em>). The transducers, responsible for picking up the sound waves, continued to be located externally. Tests were carried out on a laboratory surrogate for tissue known as a <a href="http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3207386/">tissue-mimicking phantom</a> as well as prostate tissue from pigs and liver tissue from cows.</p>
<p>The researchers found that the use of an interstitial light source improved the penetration depth of the imaging technique well beyond previously established limits. Wires inserted into the tissue surrogate at depths of 7, 20, 37 and 47 mm were clearly visible using the novel method, whereas the conventional method only showed the wires at the two shallower depths. The tests on the prostate and liver tissue proved to be similarly successful. Shining light from within, the researchers demonstrated, was key to significantly expanding how deep within tissue PA imaging can be employed.</p>
<p>Despite the successes of the laboratory studies and the fact that the size of the fiber-optic cables needed is compatible with the surgical instruments currently used, the outlook remains conservative. For example, the researchers noted that the energy absorbed per unit area in the region immediately surrounding the interstitial fiber-optic laser may be a concern, but suggested that this could be mitigated by increasing the diameter of the fiber end-cap or by adding a diffuser around its tip.</p>
<hr />
<p>Citation:</p>
<blockquote>
<p>Mitcham, T., Dextraze, K., Taghavi, H. Melancon, M., & Bouchard, R. (2015). Photoacoustic imaging driven by an interstitial irradiation source. <em>Photoacoustics</em>, 3(2), 45-54. DOI: <a href="http://dx.doi.org/10.1016/j.pacs.2015.02.002">10.1016/j.pacs.2015.02.002</a></p>
</blockquote>
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<p>An overview of the phenomenon can be found at <a href="http://www.spectroscopyonline.com/photoacoustic-spectroscopy">spectroscopyonline.com/photoacoustic-spectroscopy</a>. <a href="#fnref:1" class="reversefootnote">↩</a></p>
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Prism break, cuttlefish style2015-05-16T00:00:00+00:00https://apostilb.github.io/2015/05/16/prism-break<p><em>A suggested biological color vision mechanism exploits optics</em></p>
<p>From humans to mantis shrimp, the key to seeing in color is to compare. With at least two different types of wavelength-sensitive cells in the eye, you can start to distinguish different parts of the spectrum, and thus different-colored objects in the environment. The more photoreceptor types you have, the more precisely you can interpret the incoming light, depending on how finely or evenly the <a href="https://arthropoda.files.wordpress.com/2010/03/human-vs-mantis.jpg">photoreceptor sensitivities are spaced on the spectrum</a>. Humans are trichromatic, with three kinds of cone cells well-tuned to the short, medium, and long wavelengths of our diurnal environment. The mantis shrimp has 16 photoreceptor types, suited to both its vibrant patchwork body coloring as well as its bright surroundings. The question then is, how many photoreceptors does the cuttlefish, <a href="https://www.youtube.com/watch?v=SfkhEm3LfvE">a squid-like underwater chameleon</a>, have?</p>
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<p>Alas, the cuttlefish has but one type of photoreceptor. The instantaneous color and texture changes exhibited by this mollusk allow it to blend in seamlessly with any background it encounters, but it is effectively color blind, at least if color vision depends on comparison between cell types. <a href="http://dx.doi.org/10.1101/017756">Some new research</a>, however, suggests that “color blind” cephalopods like the cuttlefish <em>can</em> sense chromatic information using an optical trick.</p>
<p><img src="https://apostilb.github.io/images/2015-05-16-prism-break.jpg" alt="Eye of Australian giant cuttlefish (Sepia apama)" /></p>
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<p><em>Eye of Australian giant cuttlefish (Sepia apama). <a href="https://www.flickr.com/photos/rling/5101121081/in/photostream/">Photo</a> by Richard Ling / <a href="https://creativecommons.org/licenses/by-nc-nd/2.0/">CC BY-NC-ND 2.0</a></em></p>
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<p>Cuttlefish eyes make use of some interesting properties of light. Specifically, their pupils are unusual W-shaped slits that amplify chromatic aberration, or the way light of different wavelengths bends slightly differently. Chromatic aberration explains purplish fringes sometimes seen in photographs: short wavelengths (blue light) get refracted or bent more than long wavelengths (red light)<sup id="fnref:1"><a href="#fn:1" class="footnote">1</a></sup>. Eliminating these “errors” is hard in any optical system, whether it’s eyes or cameras. For the cuttlefish, this aberration signal actually provides valuable color information that is undetectable with only a single photoreceptor type.</p>
<p>Unlike the round human pupil, the squiggly pupil of the cuttlefish lets in light peripherally, off of the optical axis. This means the chromatic effects – how differently the incoming wavelengths are focused – are enhanced. Through its normal accommodation (focusing), the cuttlefish can <em>infer</em> the colors of the environment, effectively using the distance it needs to focus as a clue to color.</p>
<p>For this system to work, the environment of the cuttlefish has to be full of cues to help it accommodate, like shadows and texture. Moreover, these features have be fairly sharply segregated spectrally (that is, neighboring objects need to be different and non-overlapping in hue), and fortunately for the cuttlefish they are. With its ersatz color vision mechanism the cuttlefish can’t distinguish a broad flat field of a single color, though.</p>
<p>Through computer simulations with different spectral inputs and pupil shapes, the researchers conclude that color information is in principle available to the cuttlefish. This may be the elusive mechanism to explain how cuttlefish make the spectral discriminations that are compatible with their vivid displays and camouflage abilities. New kinds of color vision tests, ones that don’t presuppose <a href="http://en.wikipedia.org/wiki/Opponent_process">opponency</a> or comparison mechanisms, are needed to experimentally determine the color sensitivity of cuttlefish vision; according to the simulations, the cuttlefish eye can distinguish colors unambiguously, as long as objects are at least 0.75 meters away. This kind of analysis also raises the question of how other species with annular pupils, such as certain dolphins, might make use of the cuttlefish’s optical trick for color discrimination.</p>
<p>Playing off sensitivity in one domain (color) against another (focal length) is a deft adaptation to compensate for apparent sensory deficits. Studying these adaptations, for example the <a href="http://jov.arvojournals.org/article.aspx?articleid=2142714">diversity of pupil shapes in nature</a>, demonstrates that the eye has evolved to be exquisitely tuned to its surroundings.</p>
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<p>Citation:</p>
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<p>Stubbs, A. L., & Stubbs, C. W. (2015). A Novel Mechanism for Color Vision: Pupil Shape and Chromatic Aberration Can Provide Spectral Discrimination for “Color Blind” Organisms. <em>bioRxiv</em>, 017756. DOI: <a href="http://dx.doi.org/10.1101/017756">10.1101/017756</a></p>
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<p>Light isn’t colored but we colloquially refer to long wavelengths of the visible spectrum as red and short wavelengths as blue. <a href="#fnref:1" class="reversefootnote">↩</a></p>
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