4,050 research outputs found
Relativistic Particle Acceleration in a Folded Current Sheet
Two-dimensional particle simulations of a relativistic Harris current sheet
of pair plasmashave demonstrated that the system is unstable to the
relativistic drift kink instability (RDKI) and that a new kind of acceleration
process takes place in the deformed current sheet. This process contributes to
the generation of non-thermal particles and contributes to the fast magnetic
dissipation in the current sheet structure. The acceleration mechanism and a
brief comparison with relativistic magnetic reconnection are presented.Comment: 11 preprint pages, including 3 .eps figure
Phenotypic Plasticity of Mouse Spermatogonial Stem Cells
BACKGROUND:Spermatogonial stem cells (SSCs) continuously undergo self-renewal division to support spermatogenesis. SSCs are thought to have a fixed phenotype, and development of a germ cell transplantation technique facilitated their characterization and prospective isolation in a deterministic manner; however, our in vitro SSC culture experiments indicated heterogeneity of cultured cells and suggested that they might not follow deterministic fate commitment in vitro. METHODOLOGY AND PRINCIPAL FINDINGS:In this study, we report phenotypic plasticity of SSCs. Although c-kit tyrosine kinase receptor (Kit) is not expressed in SSCs in vivo, it was upregulated when SSCs were cultured on laminin in vitro. Both Kit(-) and Kit(+) cells in culture showed comparable levels of SSC activity after germ cell transplantation. Unlike differentiating spermatogonia that depend on Kit for survival and proliferation, Kit expressed on SSCs did not play any role in SSC self-renewal. Moreover, Kit expression on SSCs changed dynamically once proliferation began after germ cell transplantation in vivo. CONCLUSIONS/SIGNIFICANCE:These results indicate that SSCs can change their phenotype according to their microenvironment and stochastically express Kit. Our results also suggest that activated and non-activated SSCs show distinct phenotypes
Neuronal clearance of amyloid-β by endocytic receptor LRP1
Alzheimer\u27s disease (AD) is the most prevalent form of dementia in the elderly population. Accumulation, aggregation, and deposition of amyloid-β (Aβ) peptides generated through proteolytic cleavage of amyloid precursor protein (APP) are likely initiating events in the pathogenesis of AD. While Aβ production is accelerated in familial AD, increasing evidence indicates that impaired clearance of Aβ is responsible for late-onset AD. Because Aβ is mainly generated in neurons, these cells are predicted to have the highest risk of encountering Aβ among all cell types in the brain. However, it is still unclear whether they are also involved in Aβ clearance. Here we show that receptor-mediated endocytosis in neurons by the low-density lipoprotein receptor-related protein 1 (LRP1) plays a critical role in brain Aβ clearance. LRP1 is known to be an endocytic receptor for multiple ligands including Aβ. Conditional knock-out of Lrp1 in mouse forebrain neurons leads to increased brain Aβ levels and exacerbated amyloid plaque deposition selectively in the cortex of amyloid model APP/PS1 mice without affecting Aβ production. In vivo microdialysis studies demonstrated that Aβ clearance in brain interstitial fluid is impaired in neuronal Lrp1 knock-out mice. Because the neuronal LRP1-deletion did not affect the mRNA levels of major Aβ degrading enzymes, neprilysin and insulin-degrading enzyme, the disturbed Aβ clearance is likely due to the suppression of LRP1-mediated neuronal Aβ uptake and degradation. Together, our results demonstrate that LRP1 plays an important role in receptor-mediated clearance of Aβ and indicate that neurons not only produce but also clear Aβ
Particle Acceleration and Magnetic Dissipation in Relativistic Current Sheet of Pair Plasmas
We study linear and nonlinear development of relativistic and
ultrarelativistic current sheets of pair plasmas with antiparallel magnetic
fields. Two types of two-dimensional problems are investigated by
particle-in-cell simulations. First, we present the development of relativistic
magnetic reconnection, whose outflow speed is an order of the light speed c. It
is demonstrated that particles are strongly accelerated in and around the
reconnection region, and that most of magnetic energy is converted into
"nonthermal" part of plasma kinetic energy. Second, we present another
two-dimensional problem of a current sheet in a cross-field plane. In this
case, the relativistic drift kink instability (RDKI) occurs. Particle
acceleration also takes place, but the RDKI fast dissipates the magnetic energy
into plasma heat. We discuss the mechanism of particle acceleration and the
theory of the RDKI in detail. It is important that properties of these two
processes are similar in the relativistic regime of T > mc^2, as long as we
consider the kinetics. Comparison of the two processes indicates that magnetic
dissipation by the RDKI is more favorable process in the relativistic current
sheet. Therefore the striped pulsar wind scenario should be reconsidered by the
RDKI.Comment: To appear in ApJ vol. 670; 60 pages, 27 figures; References and typos
are fixe
Faster Family-wise Error Control for Neuroimaging with a Parametric Bootstrap
In neuroimaging, hundreds to hundreds of thousands of tests are performed
across a set of brain regions or all locations in an image. Recent studies have
shown that the most common family-wise error (FWE) controlling procedures in
imaging, which rely on classical mathematical inequalities or Gaussian random
field theory, yield FWE rates that are far from the nominal level. Depending on
the approach used, the FWER can be exceedingly small or grossly inflated. Given
the widespread use of neuroimaging as a tool for understanding neurological and
psychiatric disorders, it is imperative that reliable multiple testing
procedures are available. To our knowledge, only permutation joint testing
procedures have been shown to reliably control the FWER at the nominal level.
However, these procedures are computationally intensive due to the increasingly
available large sample sizes and dimensionality of the images, and analyses can
take days to complete. Here, we develop a parametric bootstrap joint testing
procedure. The parametric bootstrap procedure works directly with the test
statistics, which leads to much faster estimation of adjusted \emph{p}-values
than resampling-based procedures while reliably controlling the FWER in sample
sizes available in many neuroimaging studies. We demonstrate that the procedure
controls the FWER in finite samples using simulations, and present region- and
voxel-wise analyses to test for sex differences in developmental trajectories
of cerebral blood flow
Three Dimensional Polarimetric Neutron Tomography of Magnetic Fields
Through the use of Time-of-Flight Three Dimensional Polarimetric Neutron
Tomography (ToF 3DPNT) we have for the first time successfully demonstrated a
technique capable of measuring and reconstructing three dimensional magnetic
field strengths and directions unobtrusively and non-destructively with the
potential to probe the interior of bulk samples which is not amenable
otherwise.
Using a pioneering polarimetric set-up for ToF neutron instrumentation in
combination with a newly developed tailored reconstruction algorithm, the
magnetic field generated by a current carrying solenoid has been measured and
reconstructed, thereby providing the proof-of-principle of a technique able to
reveal hitherto unobtainable information on the magnetic fields in the bulk of
materials and devices, due to a high degree of penetration into many materials,
including metals, and the sensitivity of neutron polarisation to magnetic
fields. The technique puts the potential of the ToF time structure of pulsed
neutron sources to full use in order to optimise the recorded information
quality and reduce measurement time.Comment: 12 pages, 4 figure
Classifying the Arithmetical Complexity of Teaching Models
This paper classifies the complexity of various teaching models by their
position in the arithmetical hierarchy. In particular, we determine the
arithmetical complexity of the index sets of the following classes: (1) the
class of uniformly r.e. families with finite teaching dimension, and (2) the
class of uniformly r.e. families with finite positive recursive teaching
dimension witnessed by a uniformly r.e. teaching sequence. We also derive the
arithmetical complexity of several other decision problems in teaching, such as
the problem of deciding, given an effective coding of all uniformly r.e. families, any such that
, any and , whether or not the
teaching dimension of with respect to is upper bounded
by .Comment: 15 pages in International Conference on Algorithmic Learning Theory,
201
Abstractness of human speech sound representations
We argue, based on a study of brain responses to speech sound differences in Japanese, that memory encoding of functional speech sounds-phonemes-are highly abstract. As an example, we provide evidence for a theory where the consonants/p t k b d g/ are not only made up of symbolic features but are underspecified with respect to voicing or laryngeal features, and that languages differ with respect to which feature value is underspecified. In a previous study we showed that voiced stops are underspecified in English [Hestvik, A., & Durvasula, K. (2016). Neurobiological evidence for voicing underspecification in English. Brain and Language], as shown by asymmetries in Mismatch Negativity responses to /t/ and /d/. In the current study, we test the prediction that the opposite asymmetry should be observed in Japanese, if voiceless stops are underspecified in that language. Our results confirm this prediction. This matches a linguistic architecture where phonemes are highly abstract and do not encode actual physical characteristics of the corresponding speech sounds, but rather different subsets of abstract distinctive features
MUSCLE ACTIVITY IN THE SUBJECTS WITH FUNCTIONAL INSTABILITY OF THE ANKLE DURING A SINGLE-LEG DROP JUMP
Ankle sprain is one of the most common injuries experienced sporting participation, and Hertel J (2002) reported it’s recurrence rate is very high( 47-73 %). Presence of residual pain and functional problems (recurrent complaints of “giving way” or repeated sprain) following inversion ankle sprains are often reported. These symptoms of repeated complaints of “giving way” and/or recurrent sprains have been termed functional instability (FI) of the ankle joint with the report of Freeman, Dean and Hanham (1965). Including the report of Konradsen and Ravn (1991) and Hertsell and Spaulding (1999), There are many studies of muscle functions such as muscle strength, muscle activity, muscle response time of ankle joint evertor in the subjects with FI of the ankle joint. However, a few studies have researched muscle activity in the situation actually occurs ankle sprain such as jump landing on the subjects with FI of ankle joint. The purpose of this study was to identify differences in ankle joint muscle activity in subjects with FI of the ankle joint during a single-leg drop jump landing
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