2,068 research outputs found
Effective Field Theory of the Zero-Temperature Triangular-Lattice Antiferromagnet: A Monte Carlo Study
Using a Monte Carlo coarse-graining technique introduced by Binder et al., we
have explicitly constructed the continuum field theory for the zero-temperature
triangular Ising antiferromagnet. We verify the conjecture that this is a
gaussian theory of the height variable in the interface representation of the
spin model. We also measure the height-height correlation function and deduce
the stiffness constant. In addition, we investigate the nature of defect-defect
interactions at finite temperatures, and find that the two-dimensional Coulomb
gas scenario applies at low temperatures.Comment: 26 pages, 9 figure
First Observation of 15Be
The neutron-unbound nucleus 15Be was observed for the ïŹrst time. It was populated using neutron transfer from a deuterated polyethylene target with a 59 MeV/u 14Be beam. Neutrons were measured in coincidence with outgoing 14Be particles and the reconstructed decay energy spectrum exhibits a resonance at 1.8(1) MeV. This corresponds to 15Be being unbound by 0.45 MeV more then 16Be thus signiïŹcantly hindering the sequential two-neutron decay of 16Be to 14Be through this state
Population of 13Be in a Nucleon Exchange Reaction
The neutron-unbound nucleus 13Be was populated with a nucleon-exchange
reaction from a 71 MeV/u secondary 13B beam. The decay energy spectrum was
reconstructed using invariant mass spectroscopy based on 12Be fragments in
coincidence with neutrons. The data could be described with an s-wave resonance
at E = 0.73(9) MeV with a width of Gamma = 1.98(34) MeV and a d-wave resonance
at E = 2.56(13) MeV with a width of Gamma = 2.29(73) MeV. The observed spectral
shape is consistent with previous one-proton removal reaction measurements from
14B.Comment: Published in Phys. Rev.
Neutron-Unbound Excited States of 23N
Neutron unbound states in 23N were populated via proton knockout from an 83.4 MeV/nucleon 24O beam on a liquid deuterium target. The two-body decay energy displays two peaks at E1âŒ100keV and E2âŒ1MeV with respect to the neutron separation energy. The data are consistent with shell model calculations predicting resonances at excitation energies of âŒ3.6MeV and âŒ4.5MeV. The selectivity of the reaction implies that these states correspond to the first and second 3/2â states. The energy of the first state is about 1.3 MeV lower than the first excited 2+ in 24O. This decrease is largely due to coupling with the Ïpâ13/2 hole along with a small reduction of the N=16 shell gap in 23N
Further Insights into the Reaction Be14(CH2,X)10He
A previously published measurement of the reaction of a 59 MeV/nucleon 14Be beam on a deuterated polyethylene target was further analyzed to search for 12He as well as initial state effects in the population of the 10He ground state. No evidence for either was found. A lower limit of about 1 MeV was determined for a possible resonance in 12He. In addition, the three-body decay energy spectrum of 10He could not be described by a reaction mechanism calculation based on the halo structure of the initial 14Be assuming a direct α-particle removal reaction
Structure and Decay Correlations of Two-Neutron Systems Beyond the Dripline
The two-neutron unbound systems of 16Be, 13Li, 10He, and 26O have been measured using the Modular Neutron Array (MoNA) and 4 Tm Sweeper magnet setup. The correlations of the 3-body decay for the 16Be and 13Li were extracted and demonstrated a strong correlated enhancement between the two neutrons. The measurement of the 10He ground state resonance from a 14Be(â2p2n) reaction provided insight into previous predictions that wavefunction of the entrance channel, projectile, can influence the observed decay energy spectrum for the unbound system. Lastly, the decay-in-target (DiT) technique was utilized to extract the lifetime of the 26O ground state. The measured lifetime of 4.5+1.1 â1.5 (stat.)±3(sys.) ps provides the first indication of two-neutron radioactivity
Two-Neutron Sequential Decay of O
A two-neutron unbound excited state of O was populated through a
(d,d') reaction at 83.4 MeV/nucleon. A state at (stat) (sys) keV with a width of MeV was observed above the
two-neutron separation energy placing it at 7.65 0.2 MeV with respect to
the ground state. Three-body correlations for the decay of O
O + show clear evidence for a sequential decay
through an intermediate state in O. Neither a di-neutron nor phase-space
model for the three-body breakup were able to describe these correlations
Translational derepression of Elavl4 isoforms at their alternative 5âČ UTRs determines neuronal development
Neurodevelopment requires precise regulation of gene expression, including post-transcriptional regulatory events such as alternative splicing and mRNA translation. However, translational regulation of specific isoforms during neurodevelopment and the mechanisms behind it remain unknown. Using RNA-seq analysis of mouse neocortical polysomes, here we report translationally repressed and derepressed mRNA isoforms during neocortical neurogenesis whose orthologs include risk genes for neurodevelopmental disorders. We demonstrate that the translation of distinct mRNA isoforms of the RNA binding protein (RBP), Elavl4, in radial glia progenitors and early neurons depends on its alternative 5' UTRs. Furthermore, 5' UTR-driven Elavl4 isoform-specific translation depends on upstream control by another RBP, Celf1. Celf1 regulation of Elavl4 translation dictates development of glutamatergic neurons. Our findings reveal a dynamic interplay between distinct RBPs and alternative 5' UTRs in neuronal development and underscore the risk of post-transcriptional dysregulation in co-occurring neurodevelopmental disorders
Takagi-Taupin Description of X-ray Dynamical Diffraction from Diffractive Optics with Large Numerical Aperture
We present a formalism of x-ray dynamical diffraction from volume diffractive
optics with large numerical aperture and high aspect ratio, in an analogy to
the Takagi-Taupin equations for strained single crystals. We derive a set of
basic equations for dynamical diffraction from volume diffractive optics, which
enable us to study the focusing property of these optics with various grating
profiles. We study volume diffractive optics that satisfy the Bragg condition
to various degrees, namely flat, tilted and wedged geometries, and derive the
curved geometries required for ultimate focusing. We show that the curved
geometries satisfy the Bragg condition everywhere and phase requirement for
point focusing, and effectively focus hard x-rays to a scale close to the
wavelength.Comment: 18 pages, 12 figure
Field-induced Ordering in Critical Antiferromagnets
Transfer-matrix scaling methods have been used to study critical properties
of field-induced phase transitions of two distinct two-dimensional
antiferromagnets with discrete-symmetry order parameters: triangular-lattice
Ising systems (TIAF) and the square-lattice three-state Potts model (SPAF-3).
Our main findings are summarised as follows. For TIAF, we have shown that the
critical line leaves the zero-temperature, zero -field fixed point at a finite
angle. Our best estimate of the slope at the origin is . For SPAF-3 we provided evidence that the zero-field correlation
length diverges as , with , through analysis of the critical curve at plus crossover
arguments. For SPAF-3 we have also ascertained that the conformal anomaly and
decay-of-correlations exponent behave as: (a) H=0: ; (b) .Comment: RevTex, 7 pages, 4 eps figures, to be published in Phys. Rev.
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