4,275 research outputs found
Layer thickness dependence of the current induced effective field vector in Ta|CoFeB|MgO
The role of current induced effective magnetic field in ultrathin magnetic
heterostructures is increasingly gaining interest since it can provide
efficient ways of manipulating magnetization electrically. Two effects, known
as the Rashba spin orbit field and the spin Hall spin torque, have been
reported to be responsible for the generation of the effective field. However,
quantitative understanding of the effective field, including its direction with
respect to the current flow, is lacking. Here we show vector measurements of
the current induced effective field in Ta|CoFeB|MgO heterostructrures. The
effective field shows significant dependence on the Ta and CoFeB layers'
thickness. In particular, 1 nm thickness variation of the Ta layer can result
in nearly two orders of magnitude difference in the effective field. Moreover,
its sign changes when the Ta layer thickness is reduced, indicating that there
are two competing effects that contribute to the effective field. The relative
size of the effective field vector components, directed transverse and parallel
to the current flow, varies as the Ta thickness is changed. Our results
illustrate the profound characteristics of just a few atomic layer thick metals
and their influence on magnetization dynamics
Subaru FOCAS Spectroscopic Observations of High-Redshift Supernovae
We present spectra of high-redshift supernovae (SNe) that were taken with the
Subaru low resolution optical spectrograph, FOCAS. These SNe were found in SN
surveys with Suprime-Cam on Subaru, the CFH12k camera on the
Canada-France-Hawaii Telescope (CFHT), and the Advanced Camera for Surveys
(ACS) on the Hubble Space Telescope (HST). These SN surveys specifically
targeted z>1 Type Ia supernovae (SNe Ia). From the spectra of 39 candidates, we
obtain redshifts for 32 candidates and spectroscopically identify 7 active
candidates as probable SNe Ia, including one at z=1.35, which is the most
distant SN Ia to be spectroscopically confirmed with a ground-based telescope.
An additional 4 candidates are identified as likely SNe Ia from the
spectrophotometric properties of their host galaxies. Seven candidates are not
SNe Ia, either being SNe of another type or active galactic nuclei. When SNe Ia
are observed within a week of maximum light, we find that we can
spectroscopically identify most of them up to z=1.1. Beyond this redshift, very
few candidates were spectroscopically identified as SNe Ia. The current
generation of super red-sensitive, fringe-free CCDs will push this redshift
limit higher.Comment: 19 pages, 26 figures. PASJ in press. see
http://www.supernova.lbl.gov/2009ClusterSurvey/ for additional information
pertaining to the HST Cluster SN Surve
Dynamic Expression of Cadherins Regulates Vocal Development in a Songbird
BACKGROUND: Since, similarly to humans, songbirds learn their vocalization through imitation during their juvenile stage, they have often been used as model animals to study the mechanisms of human verbal learning. Numerous anatomical and physiological studies have suggested that songbirds have a neural network called 'song system' specialized for vocal learning and production in their brain. However, it still remains unknown what molecular mechanisms regulate their vocal development. It has been suggested that type-II cadherins are involved in synapse formation and function. Previously, we found that type-II cadherin expressions are switched in the robust nucleus of arcopallium from cadherin-7-positive to cadherin-6B-positive during the phase from sensory to sensorimotor learning stage in a songbird, the Bengalese finch. Furthermore, in vitro analysis using cultured rat hippocampal neurons revealed that cadherin-6B enhanced and cadherin-7 suppressed the frequency of miniature excitatory postsynaptic currents via regulating dendritic spine morphology. METHODOLOGY/PRINCIPAL FINDINGS: To explore the role of cadherins in vocal development, we performed an in vivo behavioral analysis of cadherin function with lentiviral vectors. Overexpression of cadherin-7 in the juvenile and the adult stages resulted in severe defects in vocal production. In both cases, harmonic sounds typically seen in the adult Bengalese finch songs were particularly affected. CONCLUSIONS/SIGNIFICANCE: Our results suggest that cadherins control vocal production, particularly harmonic sounds, probably by modulating neuronal morphology of the RA nucleus. It appears that the switching of cadherin expressions from sensory to sensorimotor learning stage enhances vocal production ability to make various types of vocalization that is essential for sensorimotor learning in a trial and error manner
Acute WNT signalling activation perturbs differentiation within the adult stomach and rapidly leads to tumour formation
A role for WNT signalling in gastric carcinogenesis has been suggested due to two major observations. First, patients with germline mutations in adenomatous polyposis coli (APC) are susceptible to stomach polyps and second, in gastric cancer, WNT activation confers a poor prognosis. However, the functional significance of deregulated WNT signalling in gastric homoeostasis and cancer is still unclear. In this study we have addressed this by investigating the immediate effects of WNT signalling activation within the stomach epithelium. We have specifically activated the WNT signalling pathway within the mouse adult gastric epithelium via deletion of either glycogen synthase kinase 3 (GSK3) or APC or via expression of a constitutively active β-catenin protein. WNT pathway deregulation dramatically affects stomach homoeostasis at very short latencies. In the corpus, there is rapid loss of parietal cells with fundic gland polyp (FGP) formation and adenomatous change, which are similar to those observed in familial adenomatous polyposis. In the antrum, adenomas occur from 4 days post-WNT activation. Taken together, these data show a pivotal role for WNT signalling in gastric homoeostasis, FGP formation and adenomagenesis. Loss of the parietal cell population and corresponding FGP formation, an early event in gastric carcinogenesis, as well as antral adenoma formation are immediate effects of nuclear β-catenin translocation and WNT target gene expression. Furthermore, our inducible murine model will permit a better understanding of the molecular changes required to drive tumourigenesis in the stomach
Presynaptic partner selection during retinal circuit reassembly varies with timing of neuronal regeneration in vivo
Whether neurons can restore their original connectivity patterns during circuit repair is unclear. Taking advantage of the regenerative capacity of zebrafish retina, we show here the remarkable specificity by which surviving neurons reassemble their connectivity upon regeneration of their major input. H3 horizontal cells (HCs) normally avoid red and green cones, and prefer ultraviolet over blue cones. Upon ablation of the major (ultraviolet) input, H3 HCs do not immediately increase connectivity with other cone types. Instead, H3 dendrites retract and re-extend to contact new ultraviolet cones. But, if regeneration is delayed or absent, blue-cone synaptogenesis increases and ectopic synapses are made with red and green cones. Thus, cues directing synapse specificity can be maintained following input loss, but only within a limited time period. Further, we postulate that signals from the major input that shape the H3 HC's wiring pattern during development persist to restrict miswiring after damage
The grinch who stole wisdom
Dr. Seuss is wise. How the Grinch Stole Christmas (Seuss, 1957) could serve as a parable for our time. It can also be seen as a roadmap for the development of contemplative wisdom. The abiding popularity of How the Grinch Stole Christmas additionally suggests that contemplative wisdom is more readily available to ordinary people, even children, than is normally thought. This matters because from the point of view of contemplatives in any of the world's philosophies or religions, people are confused about wisdom. The content of the nascent field of wisdom studies, they might say, is largely not wisdom at all but rather what it's like to live in a particular kind of prison cell, a well appointed cell perhaps, but not a place that makes possible either personal satisfaction or deep problem solving. I believe that what the contemplative traditions have to say is important; they offer a different orientation to what personal wisdom is, how to develop it, and how to use it in the world than is presently contained in either our popular culture or our sciences. In order to illustrate this I will examine, in some detail, one contemplative path within Buddhism. Buddhism is particularly useful in this respect because its practices are nontheistic and thus avoid many of the cultural landmines associated with the contemplative aspects of Western religions
Suv4-20h Histone Methyltransferases Promote Neuroectodermal Differentiation by Silencing the Pluripotency-Associated Oct-25 Gene
Post-translational modifications (PTMs) of histones exert fundamental roles in regulating gene expression. During development, groups of PTMs are constrained by unknown mechanisms into combinatorial patterns, which facilitate transitions from uncommitted embryonic cells into differentiated somatic cell lineages. Repressive histone modifications such as H3K9me3 or H3K27me3 have been investigated in detail, but the role of H4K20me3 in development is currently unknown. Here we show that Xenopus laevis Suv4-20h1 and h2 histone methyltransferases (HMTases) are essential for induction and differentiation of the neuroectoderm. Morpholino-mediated knockdown of the two HMTases leads to a selective and specific downregulation of genes controlling neural induction, thereby effectively blocking differentiation of the neuroectoderm. Global transcriptome analysis supports the notion that these effects arise from the transcriptional deregulation of specific genes rather than widespread, pleiotropic effects. Interestingly, morphant embryos fail to repress the Oct4-related Xenopus gene Oct-25. We validate Oct-25 as a direct target of xSu4-20h enzyme mediated gene repression, showing by chromatin immunoprecipitaton that it is decorated with the H4K20me3 mark downstream of the promoter in normal, but not in double-morphant, embryos. Since knockdown of Oct-25 protein significantly rescues the neural differentiation defect in xSuv4-20h double-morphant embryos, we conclude that the epistatic relationship between Suv4-20h enzymes and Oct-25 controls the transit from pluripotent to differentiation-competent neural cells. Consistent with these results in Xenopus, murine Suv4-20h1/h2 double-knockout embryonic stem (DKO ES) cells exhibit increased Oct4 protein levels before and during EB formation, and reveal a compromised and biased capacity for in vitro differentiation, when compared to normal ES cells. Together, these results suggest a regulatory mechanism, conserved between amphibians and mammals, in which H4K20me3-dependent restriction of specific POU-V genes directs cell fate decisions, when embryonic cells exit the pluripotent state
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