Tag Archiv: 上海水磨场2019

Inner Ear Hair Cells Overcome Friction

first_img The human ear has an extraordinarily large sensitivity range of a trillion to one, allowing us to hear a rocket launch or the footfalls of a cat on a carpet.  According to Werner Gitt, the ear is our highest-precision sense organ, capable of responding over twelve orders of magnitude without switching (The Wonder of Man, p.21).  Some of this sensitivity is amplified by the eardrum and middle ear ossicles, but the paper reported above shows even more fine-tuning inside the cochlea.  Gitt’s book is highly recommended for generating a profound feeling of awe over the design of our senses.  Proverbs said, “The seeing eye, and the hearing ear, the Lord has made them both” (Prov. 20:12).(Visited 48 times, 1 visits today)FacebookTwitterPinterestSave分享0 The cochlea, that spiral-shaped structure in the inner ear, is filled with fluid.  In this fluid, tiny hair cells called stereocilia are positioned in bundles along the length of the structure.  These bundles sense vibrations transmitted into the fluid from the bony levers of the inner ear.  The vibrations picked up by the hair cell bundles, each tuned to its own frequency, mechanically transduce the sound impulses by opening ion channels that set up electrical impulses in the auditory nerve, that travel to the brain.  But motion in fluid creates friction known as viscous drag.  How do the hair cell bundles overcome it?  Scientists have figured out that the hair cells in the bundles are not only finely tuned to reduce viscous drag, but actually to employ it for even higher sensitivity to sound. Publishing in Nature,1 scientists from Howard Hughes Medical Institute, with help from European academies, explained the problem of viscous drag, and two ways the ear deals with it: The detection of sound begins when energy derived from an acoustic stimulus deflects the hair bundles on top of hair cells.  As hair bundles move, the viscous friction between stereocilia and the surrounding liquid poses a fundamental physical challenge to the ear’s high sensitivity and sharp frequency selectivity. Part of the solution to this problem lies in the active process that uses energy for frequency-selective sound amplification.  Here we demonstrate that a complementary part of the solution involves the fluid-structure interaction between the liquid within the hair bundle and the stereocilia. What they found is that the positioning of the individual stereocilia causes them to move in concert, so that viscous drag within the bundle is dramatically reduced: “We find that the close apposition of stereocilia effectively immobilizes the liquid between them, which reduces the drag and suppresses the relative squeezing but not the sliding mode of stereociliary motion.”  They can thus slide as the bundle bends without stirring up the liquid.  Further, “The obliquely oriented tip links couple the mechanotransduction channels to this least dissipative coherent mode, whereas the elastic horizontal top connectors that stabilize the structure further reduce the drag.”  The relative motion is reduced to just a fraction of a billionth of a meter (nanometer). Their opening paragraph provides a picturesque view of the workings of this remarkable organ: A hair bundle is a microscopic array of quasi-rigid, cylindrical stereocilia separated by small gaps filled with viscous endolymph. Like an array of organ pipes, the stereocilia vary monotonically in length across the hair bundle…. The tip of each short stereocilium is attached to the side of the longest adjacent stereocilium by a tip link, the tension in which controls the opening and closing of transduction channels. Adjacent stereocilia are also interconnected along all three hexagonal axes by horizontal top connectors. At the tall edge of the bundle in many species stands a single kinocilium, the process to which mechanical stimuli are applied and that is ligated to the adjacent stereocilia by kinociliary links. Why are the stereocilia arranged in bundles?  “The small difference between the drag coefficients for a single stereocilium and for an entire hair bundle reveals the striking advantage that grouping stereocilia in a tightly packed array offers to the auditory system.”  Using models from a bullfrog inner ear magnified 12,000 times and various mathematical techniques, they were able to measure the viscous drag of the coherently-arranged stereocilia.  Their conclusion explains how the findings contribute to understanding the remarkable sensitivity of the ear: In conclusion, because all stereocilia and the liquid between them move in unison over the whole auditory spectrum, with the relative motions apparent only on a sub-nanometre scale, most stereocilia inside the hair bundle are shielded from the external liquid and experience little viscous drag. Although viscous forces might be thought to impair sensitivity and frequency selectivity, the hair bundle’s structure actually minimizes energy dissipation, making it easier for the active process to keep the ear tuned. The tight clustering of stereocilia even transforms liquid viscosity into an asset by using it as a simple means of activating numerous mechanosensitive ion channels in concert. The authors made no attempt to explain how this arrangement might have evolved.  1. Koslov, Baumgart et al., “Forces between clustered stereocilia minimize friction in the ear on a subnanometre scale,” Nature  474   (16 June 2011), pp. 376–379, doi:10.1038/nature10073.last_img read more

Gradient Maps and Blend Modes in After Effects

first_imgColor Dodge Blend Mode Gradient Maps in After EffectsTechnically, gradient map layers don’t exist in After Effects. However, you can mimic the effect with the tinting effects: Tint, Tritone, CC Toner, and Colorama. A gradient map recolors an image by using the gradient you set to replace the grayscale gradient in a black and white image. So, using a gradient like this:Results in this:Now that we can mimic the effect of a gradient map, put these effects on an adjustment layers and you get the ability to apply blend modes, just like in Photoshop!We’ll start out by using the gradient  above again and applying it to an adjustment layer. You can get a ton of different looks by changing the blend modes; some work better or more often with others depending on the colors you choose. This first gradient map has a lot of options that actually look pretty interesting:(Click images for larger view) Overlay w/ Adjustment at 50% Darken Blend ModeMultiply Blend Mode Here’s another gradient:This particular combination of colors really only had good results with two of the After Effects blend modes: Screen Blend Mode Add Blend ModeLighten Blend Modecenter_img Soft Light Blend Mode Overlay Blend Mode Combining gradient mapping and blend modes can be used to create fun, unique looks in After Effects.In this post, we share a quick way to give your footage unique color grades in Adobe After Effects.One of my favorite ways to add fun looks to photos in Photoshop is to combine gradient maps with blend modes:This particular gradient map combination is a favorite of mine that works well on a lot of images (especially outdoor):As you’ll see below, I added a gradient map to the image and changed the blend mode to “Screen”: Screen Blend ModeSoft Light Blend Mode Here’s another gradient combination:LightenAnd another:Soft LightNow here’s one that uses the tritone filter to add a third color to the mix:OverlayWith the CC Toner effect, you can fine tune your results even more, leaving the highlights and shadows alone to preserve good black and white points, but still adding a tint in those areas:Screen:Using a sepia color scheme gives some good results:Screen:Overlay:You can even recreate the popular “Blockbuster” look:Overlay:Soft Light:Gradients with Colorama in After EffectsFor ultimate control of the gradient, Colorama is the way to go. It’s a little unweildly to use since its gradient tool is radial instead of linear, but you can really fine tune the results or use multiple colors:Soft Light:Color dodge (with the base image adjusted for exposure to compensate):The color dodge effect made the shot too bright, so I dropped a levels filter on the original image to bring down the exposure:Experiment with exposure and contrast adjustments on the original image underneath the adjustment layer, as well as with different opacities on the adjustment layer to really get it looking the way you want it. After Effects does a great job of live-updating the look as you change your colors, so you can even pick a bland mode and fine-tune your colors live for the desired result!last_img read more

CPI(M) announces names for two seats in Bengal

first_imgFollowing a day-long meeting of the Left Front in Kolkata on Friday, the Communist Party of India (Marxist) unilaterally declared names of two candidates for two north Bengal Lok Sabha seats. The candidates are Md. Salim for Raiganj in Uttar Dinajpur and Badaruddoza Khan for Murshidabad in Murshidabad district. While the Left Front had won both seats in 2014, the Bengal Congress unit is reluctant to give up these seats in favour of the CPI(M) as part of a proposed ‘no contest’ deal. The parties are still engaged in discussions.last_img

Tree Authority defers Aarey cutting, seeks rehab details

first_imgThe Tree Authority (TA) on Wednesday deferred the proposal to remove 2,702 trees for the Metro car shed in Aarey Colony. The authority has asked for details related to the rehabilitation of tribals, as well as litigation on the issue. The Shiv Sena and Congress are still vociferously opposed to the proposal.Work on the Colaba-Bandra-Seepz Metro line is under way, but the proposal to build a car shed inside Aarey Colony — especially the removal of trees — has met with stiff resistance from the very beginning. The protesters have been supported by Shiv Sena leader Aaditya Thackeray and Mayor Vishwanath Mahadeshwar in the past.When the proposal was tabled before the Tree Authority earlier this month, members demanded a site visit, which took place on Tuesday. On both occasions, the Shiv Sena expressed its opposition to the car shed.Following the visit, the proposal was placed before the Tree Authority on Wednesday, but was sent back to the administration with queries. The administration will now have to table it with all the information demanded. Shiv Sena leader Yashwant Jadhav said, “There were alternatives of two other plots for the car shed. Why does Metro insist on Aarey Colony? We have received around 80,000 objections to the proposal. What are we going to do about those? Also, what about the rehabilitation of tribals in 27 hamlets? We want these answers.” The Shiv Sena has also demanded to know the status of two court cases in the matter.“In the 27 acres, trees have been cut on five acres without permission. The Brihanmumbai Municipal Corporation should file a first information report against Mumbai Metro Rail Corporation Limited,” said Ravi Raja, leader of the Opposition.Congress leader Milind Deora also tweeted, “The proposal from MMRCL to cut 2,703 trees at Aarey Colony for construction of Metro car shed was discussed in the BMC’s Tree Authority today. I informed Leader of Opposition @ravirajaINC that @INCIndia must oppose this proposal. Mumbai’s environment comes first!”last_img read more