{"id":3397,"date":"2011-04-01T00:31:00","date_gmt":"2011-03-31T22:31:00","guid":{"rendered":"http:\/\/localhost\/azgad\/wordpress\/?p=3397"},"modified":"2011-04-01T00:32:40","modified_gmt":"2011-03-31T22:32:40","slug":"%d7%90%d7%99%d7%9b%d7%95%d7%aa-%d7%a1%d7%91%d7%99%d7%91%d7%94-%d7%97%d7%a7%d7%a8-%d7%94%d7%9e%d7%95%d7%97-%d7%95%d7%a9%d7%a2%d7%95%d7%a0%d7%99%d7%9d-%d7%91%d7%99%d7%95%d7%9c%d7%95%d7%92%d7%99%d7%99-2","status":"publish","type":"post","link":"https:\/\/azgad.com\/?p=3397","title":{"rendered":"\u05d0\u05d9\u05db\u05d5\u05ea \u05e1\u05d1\u05d9\u05d1\u05d4, \u05d7\u05e7\u05e8 \u05d4\u05de\u05d5\u05d7 \u05d5\u05e9\u05e2\u05d5\u05e0\u05d9\u05dd \u05d1\u05d9\u05d5\u05dc\u05d5\u05d2\u05d9\u05d9\u05dd \u2013 \u05d7\u05d3\u05e9\u05d5\u05ea \u05de\u05d3\u05e2 \u05de\u05d9\u05e4\u05df \u05d4\u05de\u05d5\u05db\u05d4"},"content":{"rendered":"

.
\nSolar-powered \u2018nanoalloys\u2019<\/strong>
\n.
\ncan convert polluting nitrates into ammonia fertilizer without releasing
\ncarbon dioxide
\n.
\nNourishing crops with synthetic ammonia (NH3) fertilizers has increasingly pushed agricultural
\nyields higher, but such productivity comes at a price. Over-application of this chemical can build
\nup nitrate ion (NO3\u2013) concentrations in the soil\u2014a potential groundwater poison and food source
\nfor harmful algal blooms. Furthermore, industrial manufacturing of ammonia is an energy-intensive
\nprocess that contributes significantly to atmospheric greenhouse gases.
\nA research team led by Miho Yamauchi and Masaki Takata from the RIKEN SPring-8 Center in
\nHarima has now discovered an almost ideal way to detoxify the effects of ammonia fertilizers1.
\nBy synthesizing photoactive bimetallic nanocatalysts that generate hydrogen gas from water
\nusing solar energy, the team can catalytically convert NO3\u2013 back into NH3 through an efficient
\nroute free from carbon dioxide emissions.
\nReplacing the oxygen atoms of NO3\u2013 with hydrogen is a difficult chemical trick, but chemists
\ncan achieve this feat by using nanoparticles of copper\u2013palladium (CuPd) alloys to immobilize
\nnitrates at their surfaces and catalyzing a reduction reaction with dissolved hydrogen atoms.
\nHowever, the atomic distribution at the \u2018nanoalloy\u2019 surface affects the outcome of this procedure:
\nregions with large domains of Pd atoms tend to create nitrogen gas, while well-mixed alloys
\npreferentially produce ammonia.
\nAccording to Yamauchi, the challenge in synthesizing homogenously mixed CuPd alloys is getting
\n.
\n.
\n\"\"<\/a><\/p>\n

.
\n.
\nthe timing right\u2014the two metal ions transform into atomic states at different rates, causing phase
\nseparation. Yamauchi and her team used the powerful x-rays of the SPring-8 Center\u2019s synchrotron
\nto characterize the atomic structure of CuPd synthesized with harsh or mild reagents. Their
\nexperiments revealed that a relatively strong reducing reagent called sodium borohydride gave
\nalloys with near-perfect mixing down to nanoscale dimensions.
\n.
\nMost ammonia syntheses use hydrogen gas produced from fossil fuels, but the use of solar energy
\nby the researchers avoids this. They found that depositing the nanoalloy onto photosensitive
\ntitanium dioxide (TiO2) yielded a material able to convert ultraviolet radiation into energetic
\nelectrons; in turn, these electrons stimulated hydrogen gas generation from a simple
\nwater\/methanol solution . When they added nitrate ions to this mixture, the CuPd\/TiO2
\ncatalyst converted nearly 80% into ammonia\u2014a remarkable chemical selectivity that the
\nresearchers attribute to high concentrations of reactive hydrogen photocatalytically produced
\nnear the CuPd surface.
\n.
\nYamauchi is confident that this approach can help reduce the ecological impact of many
\nclassical chemical hydrogenation reactions. \u201cConsidering the environmental problems we face,
\nwe have to switch from chemical synthesis using fossil-based hydrogen to other clean processes,\u201d
\nshe says.
\n.
\n.
\n.
\nEncoding unchartered territory<\/strong>
\n.
\nEnsembles of neurons in the brain\u2019s hippocampus inform about future as well
\nas past experiences
\n.
\nWhen a mammal explores an unfamiliar environment, ensembles of \u2018place\u2019 cells in
\nthe hippocampus fire individually, recording specific locations in a cognitive map that
\naid future spatial navigation of the area. Once the relationship between place cell
\nactivity and location has been established, the activity of the cells can be used to
\npredict the animal\u2019s location within its environment. Activity patterns in the ensembles
\nare later \u2018replayed\u2019 during rest and sleep, and neuroscientists believe this is important
\nfor consolidating the spatial memories of the new environment.
\n.
\nNeuroscientists also contend that the sequence of place cell firing corresponding
\nto the new environment is established during the first exploration of that environment.
\nNow George Dragoi and Susumu Tonegawa from the RIKEN-MIT Center for Neural
\nCircuit Genetics at the Massachusetts Institute of Technology in Cambridge,
\nMassachusetts, report that the activity of place cell circuits is also preconfigured to
\nencode novel environments1.
\n.
\nDragoi and Tonegawa recorded the activity patterns of place cells in the CA1
\nregion of the hippocampus while mice navigated a familiar environment. They
\nalso recorded from the same cells afterwards, while the mice rested or slept. As
\nexpected, some of the place cell activity patterns they observed corresponded to
\nthe familiar environment that the animals had explored, but they also recorded
\nnew patterns from place cells that were previously silent.
\n.
\nThe researchers found that the novel activity patterns corresponded strongly to
\nthe sequences of place cell firing that were recorded when the mice subsequently
\nexplored an unfamiliar part of the environment. This suggests that the
\nactivity patterns represent \u2018preplay\u2019 of the unexplored locations rather than replay
\nof the familiar part of the environment. Thus, the activity of hippocampal place cells
\nappears not only to consolidate spatial memories of newly experienced environments,
\nbut also to predict how novel, unexplored environments can be encoded when they
\nare navigated in the future. The researchers also suggest that hippocampal preplay
\nmay accelerate spatial memory formation once the novel environment is eventually
\nexplored.
\n.\u201c
\nEncoding of new information makes use of the pre-existing organization of the
\nhippocampal network, and will stabilize faster compared to a case when the neuronal
\nnetwork has to re-organize to a new state that does not resemble the pre-existing one,\u201d
\nsays Dragoi. \u201cIn an immediate follow-up to this study, we will address the role of the
\nintact hippocampal circuitry in the mechanisms and dynamics of the preplay phenomenon,\u201d
\nhe adds.
\n.
\n.
\n.
\nKeeping to time counter-intuitively<\/strong>
\n.
\n.Experimental work proves the theory that a circadian body clock requires a delay
\nto function properly
\n.
\nFor more than 20 years, theoretical mathematical models have predicted that a delay built into
\na negative feedback system is at the heart of the molecular mechanism that governs circadian
\nclocks in mammalian cells. Now, the first experimental proof of this theory has been provided
\nby an international research team led by molecular biologists and information scientists from
\nthe RIKEN Center for Developmental Biology in Kobe1. The demonstration of the feedback
\ndelay should lead to a better understanding of how cellular clocks function, and therefore how
\nmammals adjust to the regular daily and seasonal changes in their environment. The work
\ncould also open the way to the development of treatments for circadian disorders, such as
\nseasonal affective disorder, jet lag and even bipolar disorder.
\n.
\nMammals not only show daily rhythms of waking and sleeping, but also body temperature,
\nhormone secretion, and many other biological activities. The master cellular clocks that act
\nas timers for these patterns are found in the suprachiasmatic nucleus of the brain. The molecular
\nwhich code for proteins that repress their own activation by binding with the products of two other
\ngenes Bmal1 and Clock. The whole clock system is orchestrated by the interaction of these
\nproteins with a complex array of promoters and enhancers, genetic sequences that regulate
\ngene activity.
\n.
\nWithin these clock-gene regulators are short sequences often known as clock-controlled
\nelements. Different clock-controlled elements bind with the different proteins likely to be
\nprevalent at different times of the day or night. The researchers carefully modified these
\nsequences, and observed the impact on circadian rhythms of cells. They focused their
\nstudies in particular on the gene Cry1, and observed how the rhythm of its activity was
\naffected by the modifications of clock-controlled elements within promoters and enhancers.
\nIn addition to revealing a previously unknown clock-controlled element in the Cry1 promoter,
\nthe researchers also found that different combinations of clock-controlled elements led to
\ndifferent lengths of delay in the activation of Cry1. They demonstrated that this delay of Cry1
\nwas required for the circadian clock to function.
\n.
\nBased on these findings, they proposed a simple model of the mammalian circadian clock
\nand now want to construct it using artificial components. \u201cWe think further experimental and
\ntheoretical analyses of this minimal circuit will lead to a deeper understanding of the mammalian
\ncircadian clock,\u201d say team members Rikuhiro Yamada and Maki Ukai-Tadenuma.<\/p>\n

.<\/p>\n","protected":false},"excerpt":{"rendered":"

. Solar-powered \u2018nanoalloys\u2019 . can convert polluting nitrates into ammonia fertilizer without releasing carbon dioxide . Nourishing crops with synthetic ammonia (NH3) fertilizers has increasingly pushed agricultural yields higher, but such productivity comes at a price. Over-application of this chemical can build up nitrate ion (NO3\u2013) concentrations in the soil\u2014a potential groundwater poison and food … <\/p>\n

\u05d4\u05de\u05e9\u05d9\u05db\u05d5 \u05d1\u05e7\u05e8\u05d9\u05d0\u05d4<\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_monsterinsights_skip_tracking":false,"_monsterinsights_sitenote_active":false,"_monsterinsights_sitenote_note":"","_monsterinsights_sitenote_category":0,"footnotes":""},"categories":[10],"tags":[261,513],"class_list":["post-3397","post","type-post","status-publish","format-standard","hentry","category-10","tag-261","tag-513","nodate","item-wrap"],"_links":{"self":[{"href":"https:\/\/azgad.com\/index.php?rest_route=\/wp\/v2\/posts\/3397","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/azgad.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/azgad.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/azgad.com\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/azgad.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=3397"}],"version-history":[{"count":3,"href":"https:\/\/azgad.com\/index.php?rest_route=\/wp\/v2\/posts\/3397\/revisions"}],"predecessor-version":[{"id":3401,"href":"https:\/\/azgad.com\/index.php?rest_route=\/wp\/v2\/posts\/3397\/revisions\/3401"}],"wp:attachment":[{"href":"https:\/\/azgad.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=3397"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/azgad.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=3397"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/azgad.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=3397"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}