1,224 research outputs found
Eigenvector sensitivity under general and structured perturbations of tridiagonal Toeplitz-type matrices
The sensitivity of eigenvalues of structured matrices under general or
structured perturbations of the matrix entries has been thoroughly studied in
the literature. Error bounds are available and the pseudospectrum can be
computed to gain insight. Few investigations have focused on analyzing the
sensitivity of eigenvectors under general or structured perturbations. The
present paper discusses this sensitivity for tridiagonal Toeplitz and
Toeplitz-type matrices.Comment: 21 pages, 4 figure
General Relativistic Effects in the Core Collapse Supernova Mechanism
We apply our recently developed code for spherically symmetric, fully general
relativistic (GR) Lagrangian hydrodynamics and multigroup flux-limited
diffusion neutrino transport to examine the effects of GR on the hydrodynamics
and transport during collapse, bounce, and the critical shock reheating phase
of core collapse supernovae. Comparisons of models computed with GR versus
Newtonian hydrodynamics show that collapse to bounce takes slightly less time
in the GR limit, and that the shock propagates slightly farther out in radius
before receding. After a secondary quasistatic rise in the shock radius, the
shock radius declines considerably more rapidly in the GR simulations than in
the corresponding Newtonian simulations. During the shock reheating phase, core
collapse computed with GR hydrodynamics results in a substantially more compact
structure from the center out to the stagnated shock. The inflow speed of
material behind the shock is also increased. Comparisons also show that the
luminosity and rms energy of any neutrino flavor during the shock reheating
phase increases when switching from Newtonian to GR hydrodynamics, and
decreases when switching from Newtonian to GR transport. This latter decrease
in neutrino luminosities and rms energies is less in magnitude than the
increase that arise when switching from Newtonian to GR hydrodynamics, with the
result that a fully GR simulation gives higher neutrino luminosities and harder
neutrino spectra than a fully Newtonian simulation of the same precollapse
model.Comment: 35 pages, 23 figure
Direct Reprogramming of Fibroblasts into Embryonic Sertoli-like Cells by Defined Factors
SummarySertoli cells are considered the âsupporting cellsâ of the testis that play an essential role in sex determination during embryogenesis and in spermatogenesis during adulthood. Their essential roles in male fertility along with their immunosuppressive and neurotrophic properties make them an attractive cell type for therapeutic applications. Here we demonstrate the generation of induced embryonic Sertoli-like cells (ieSCs) by ectopic expression of five transcription factors. We characterize the role of specific transcription factor combinations in the transition from fibroblasts to ieSCs and identify key steps in the process. Initially, transduced fibroblasts underwent a mesenchymal to epithelial transition and then acquired the ability to aggregate, formed tubular-like structures, and expressed embryonic Sertoli-specific markers. These Sertoli-like cells facilitated neuronal differentiation and self-renewal of neural progenitor cells (NPCs), supported the survival of germ cells in culture, and cooperated with endogenous embryonic Sertoli and primordial germ cells in the generation of testicular cords in the fetal gonad
Tet1 Is Dispensable for Maintaining Pluripotency and Its Loss Is Compatible with Embryonic and Postnatal Development
SummaryThe Tet family of enzymes (Tet1/2/3) converts 5-methylcytosine (5mC) to 5-hydroxymethylcytosine (5hmC). Mouse embryonic stem cells (mESCs) highly express Tet1 and have an elevated level of 5hmC. Tet1 has been implicated in ESC maintenance and lineage specification in vitro but its precise function in development is not well defined. To establish the role of Tet1 in pluripotency and development, we have generated Tet1 mutant mESCs and mice. Tet1â/â ESCs have reduced levels of 5hmC and subtle changes in global gene expression, and are pluripotent and support development of live-born mice in tetraploid complementation assay, but display skewed differentiation toward trophectoderm in vitro. Tet1 mutant mice are viable, fertile, and grossly normal, though some mutant mice have a slightly smaller body size at birth. Our data suggest that Tet1 loss leading to a partial reduction in 5hmC levels does not affect pluripotency in ESCs and is compatible with embryonic and postnatal development
Neutrino decoupling in the early Universe
A calculation of neutrino decoupling in the early Universe, including full
Fermi-Dirac statistics and electron mass dependence in the weak reaction rates,
is presented. We find that after decoupling, the electron neutrinos contribute
0.83\% more to the relativistic energy density than in the standard scenario,
where neutrinos are assumed not to share the heating from e annihilation.
The corresponding number for muon and tau neutrinos is 0.41\% . This has the
consequence of modifying the primordial He abundance by , and the cosmological mass limit on light neutrinos by
0.2--0.5 eV.Comment: 17 pages+4 figures, uuencoded, compressed postscript. Physical Review
D in pres
X-ray absorption studies of carbon-related materials
[[abstract]]X-ray absorption near-edge structure (XANES) measurements have been performed on nitrogen-doped diamond films with three different dopant concentrations and iron-layer-stabilized carbon nanotube (CNT) structures with various diameters at the C Kabsorption edge using the sample drain current mode. The C K-edge XANES spectra of these N-doped diamond films resemble that of the undoped diamond regardless of the dopant concentration, which suggest that the overall bonding configuration of the C atom is unaltered. N dopants are found to reduce the intensities of both the sp2 - and sp3 -bond-derived resonance features in the XANES spectra. On the other hand, the C K-edge XANES spectra of CNTs indicate that the intensities of the Ï* and Ï* bands and the interlayer-state features vary with the diameter of the CNT. This phenomenon may be caused by the Fe-layer-catalysed bending of the graphite sheet and the interaction between C and Fe atoms.[[notice]]èŁæŁćźçą[[journaltype]]ćć€[[booktype]]çŽæŹ[[booktype]]é»ćç[[countrycodes]]US
The effects of user characteristics on query performance in the presence of information request ambiguity
This paper investigates the effects of personality characteristics on individuals' abilities to compose queries from information requests containing various types of ambiguity. In particular, this research examines the effects of user personality characteristics on query performance in the presence of information requests that contained no extraneous, syntactic, or both extraneous and syntactic ambiguities. The results indicate that personality characteristics significantly affect users' abilities to compose accurate queries. Neuroticism, agreeableness, openness to experience, and conscientiousness significantly affected the number of errors made in the query formulations. Conscientiousness affected the length of time taken to compose the queries and neuroticism affected the confidence users had in the accuracy of their queries. Although several personality dimensions affected query performance, no significant interactions between personality dimensions and ambiguity were detected. Furthermore, both query complexity and information request ambiguity exhibited greater impacts on query performance than personality characteristics. Hence, organizations should attempt to train users to deal with query complexity and information request ambiguity before modifying their training programs for personality characteristics
Bound states of L-shaped or T-shaped quantum wires in inhomogeneous magnetic fields
The bound state energies of L-shaped or T-shaped quantum wires in inhomogeous
magnetic fields are found to depend strongly on the asymmetric parameter
, i.e. the ratio of the arm widths. Two effects of
magnetic field on bound state energies of the electron are obtained. One is the
depletion effect which purges the electron out of the OQD system. The other is
to create an effective potential due to quantized Landau levels of the magnetic
field. The bound state energies of the electron in L-shaped or T-shaped quantum
wires are found to depend quadratically (linearly) on the magnetic field in the
weak (strong) field region and are independent of the direction of the magnetic
field. A simple model is proposed to explain the behavior of the magnetic
dependence of the bound state energy both in weak and strong magnetic field
regions.Comment: 4 pages, 4 figure
Polymer Crystallization in 25 nm Spheres
Crystallization within the discrete spheres of a block copolymer mesophase
was studied by time-resolved x-ray scattering. The cubic packing of
microdomains, established by self-assembly in the melt, is preserved throughout
crystallization by strong interblock segregation even though the amorphous
matrix block is well above its glass transition temperature. Homogeneous
nucleation within each sphere yields isothermal crystallizations which follow
first-order kinetics, contrasting with the sigmoidal kinetics normally
exhibited in the quiescent crystallization of bulk polymers.Comment: accepted for publication in Physical Review Letters, 2/28/2000;
scheduled for 5/1/2000 issu
Results of Treatment for Patients With Multicentric or Bilaterally Predisposed Unilateral Wilms Tumor (AREN0534): A report from the Childrenâs Oncology Group
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/156248/2/cncr32958_am.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/156248/1/cncr32958.pd
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