Neutron Transversity at Jefferson Lab

Nucleon transversity and single transverse spin asymmetries have been the recent focus of large efforts by both theorists and experimentalists. On-going and planned experiments from HERMES, COMPASS and RHIC are mostly on the proton or the deuteron. Presented here is a planned measurement of the neutron transversity and single target spin asymmetries at Jefferson Lab in Hall A using a transversely polarized $^3$He target. Also presented are the results and plans of other neutron transverse spin experiments at Jefferson Lab. Finally, the factorization for semi-inclusive DIS studies at Jefferson Lab is discussed.Comment: 8 pages, 2 figures, proceedings of Como Transversity05 Worksho

General stationary charged black holes as charged particle accelerators

We study the possibility of getting infinite energy in the center of mass frame of colliding charged particles in a general stationary charged black hole. For black holes with two-fold degenerate horizon, it is found that arbitrary high center-of-mass energy can be attained, provided that one of the particle has critical angular momentum or critical charge, and the remained parameters of particles and black holes satisfy certain restriction. For black holes with multiple-fold degenerate event horizons, the restriction is released. For non-degenerate black holes, the ultra-high center-of-mass is possible to be reached by invoking the multiple scattering mechanism. We obtain a condition for the existence of innermost stable circular orbit with critical angular momentum or charge on any-fold degenerate horizons, which is essential to get ultra-high center-of-mass energy without fine-tuning problem. We also discuss the proper time spending by the particle to reach the horizon and the duality between frame dragging effect and electromagnetic interaction. Some of these general results are applied to braneworld small black holes.Comment: 23 pages, no figures, revised version accepted for publication in Phys. Rev.

Quantifying the Cloud Particle‐Size Feedback in an Earth System Model

Physical process‐based two‐moment cloud microphysical parameterizations, in which effective cloud particle size evolves prognostically with climate change, have recently been incorporated into global climate models. The impacts of cloud particle‐size change on the cloud feedback, however, have never been explicitly quantified. Here we develop a partial radiative perturbation‐based method to estimate the cloud feedback associated with particle‐size changes in the Community Earth System Model. We find an increase of cloud particle size in the upper troposphere in response to an instantaneous doubling of atmospheric CO2. The associated net, shortwave, and longwave cloud feedbacks are estimated to be 0.18, 0.33, and −0.15 Wm−2 K−1, respectively. The cloud particle‐size feedback is dominated by its shortwave component with a maximum greater than 1.0 Wm−2 K−1 in the tropics and the Southern Ocean. We suggest that the cloud particle‐size feedback is an underappreciated contributor to the spread of cloud feedback and climate sensitivity among current models.Plain Language SummaryEffects of clouds on Earth’s radiation budget vary with their spatial and temporal distribution and their physical properties, including water content and its partitioning between liquid and ice, and cloud particle size. Changes in cloud distribution and physical properties can amplify or damp anthropogenic global warming and is the largest source of uncertainty in predictions of future climate. The simulation of cloud physical properties in climate models is limited due to a lack of understanding from theory and observations about what controls these properties. Recent progress has been made in some models to predict cloud particle sizes based on physical processes. In this study, we find an increase of cloud particle size in response to anthropogenic warming and estimate the resulting cloud radiative effects. The larger particles increase scattering of solar radiation in the downward direction leading to an amplification of surface warming. We suggest cloud particle‐size changes play a role in the large spread of warming in model predictions of future climate.Key PointsCloud particle size increases with warming in an Earth system modelThe associated cloud particle‐size feedback is estimated to be 0.18, 0.33, and −0.15 Wm−2 K−1 for net, shortwave, and longwave componentsCloud particle‐size feedback is an underappreciated contributor to the spread of climate sensitivity in current modelsPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/151978/1/grl59600.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/151978/2/grl59600_am.pd

Uniqueness of Bessel models: the archimedean case

In the archimedean case, we prove uniqueness of Bessel models for general linear groups, unitary groups and orthogonal groups.Comment: 22 page

Interaction of a symmetrical α,α',δ,δ'-Tetramethyl-cucurbit[6]uril with Ln³⁺ : potential applications for isolation of lanthanides

The interaction of a symmetrical α,α′,δ,δ′-tetramethyl-cucurbit[6]uril (TMeQ[6]) with a series of lanthanide cations (Ln³⁺) was investigated in neutral water and in acidic solution. Analysis by single crystal X-ray diffraction revealed that different isomorphous families formed under different synthetic conditions. Such differences in the interaction between TMeQ[6] and Ln³⁺ could potentially be used for isolating heavier Ln³⁺ from their lighter counterparts in neutral solution, and lighter lanthanide cations from their heavier counterparts in acidic solution

Unanticipated proximity behavior in ferromagnet-superconductor heterostructures with controlled magnetic noncollinearity

Magnetization noncollinearity in ferromagnet-superconductor (F/S) heterostructures is expected to enhance the superconducting transition temperature (Tc) according to the domain-wall superconductivity theory, or to suppress Tc when spin-triplet Cooper pairs are explicitly considered. We study the proximity effect in F/S structures where the F layer is a Sm-Co/Py exchange-spring bilayer and the S layer is Nb. The exchange-spring contains a single, controllable and quantifiable domain wall in the Py layer. We observe an enhancement of superconductivity that is nonmonotonic as the Py domain wall is increasingly twisted via rotating a magnetic field, different from theoretical predictions. We have excluded magnetic fields and vortex motion as the source of the nonmonotonic behavior. This unanticipated proximity behavior suggests that new physics is yet to be captured in the theoretical treatments of F/S systems containing noncollinear magnetization.Comment: 17 pages, 4 figures. Physical Review Letters in pres

Therapeutic hypothermia reduces intestinal ischemia/reperfusion injury after cardiac arrest in rats

To investigate the effects of therapeutic hypothermia (TH) on the morphology and function of intestine after cardiac arrest and resuscitation, 45 male rats were randomly assigned into three groups: (1) normothermia group, animals underwent ventricular fibrillation (VF) and cardiopulmonary resuscitation (CPR) with the rectal temperature maintained at 36.8 ± 0.2°C until 4 h after return of spontaneous circulation (ROSC); (2) hypothermia group, TH was induced with the aid of ice packs and an electrical fan because VF occurred and was maintained at 33.5 ± 0.5°C for 4 h after ROSC; (3) sham-operated group, animals underwent identical anesthetic and surgical procedures without VF, CPR or defibrillation. Five animals in each group were sacrificed at 4, 24 and 72 h post resuscitation. Serum diamine oxidase (DAO) and apoptosis rate of intestinal epithelial cells were tested by ELISA and flow cytometry, respectively. The concentration of FITC-Dextran that leaked out of enteric cavity was used to analyze the permeability of intestine. Histological changes were graded and compared among the three groups. Serum DAO concentrations in normothermia group reached the peak at 4 h post resuscitation, and then decreased at 24 and 72 h. In comparison with normothermia group, serum DAO concentrations were lower at 4 h in hypothermia group (0.97 ± 0.16 vs. 1.24 ± 0.29, P < 0.05). The amount of FITC-Dextran that passed the wall of small intestine in hypothermia group was significantly lower than that in normothermia group at 24 h after ROSC (7.81 ± 1.11 vs. 13.07 ± 3.07, P < 0.05). The amount of FITC-Dextran had no difference between normothermia and hypothermia groups at 4 and 72 h post resuscitation. The detached intestinal epithelial cells in hypothermia group showed  significant lower frequency of apoptosis than those in normothermia group at 4 h (17.30 ± 2.56 vs. 25.63 ± 4.09, P < 0.05) and 24 h (9.38 ± 1.29 vs. 11.98 ± 1.78, P < 0.05). No obvious injury was observed in both normothermia and hypothermia groups at 4 h with grade of 0 to 1. The histopathological injury in normothermia group reached the peak at 24 h with grade of 2 to 3, which was significantly severe than that in hypothermia group with grade of 1 to 2. At 72 h post resuscitation, an almost complete restitution of the intestinal mucous could be observed both in hypothermia and normothermia groups. This study demonstrates that short term ischemia induced by cardiac arrest and resuscitation resulted in intestinal ischemia/reperfusion (IR) injury, which could be attenuated by therapeutic hypothermia.Key words: Rat, intestine, cardiac arrest, cardiopulmonary resuscitation, therapeutic hypothermia

Scaling in directed dynamical small-world networks with random responses

A dynamical model of small-world network, with directed links which describe various correlations in social and natural phenomena, is presented. Random responses of every site to the imput message are introduced to simulate real systems. The interplay of these ingredients results in collective dynamical evolution of a spin-like variable S(t) of the whole network. In the present model, global average spreading length \langel L >_s and average spreading time _s are found to scale as p^-\alpha ln N with different exponents. Meanwhile, S behaves in a duple scaling form for N>>N^*: S ~ f(p^-\beta q^\gamma t'_sc), where p and q are rewiring and external parameters, \alpha, \beta, \gamma and f(t'_sc) are scaling exponents and universal functions, respectively. Possible applications of the model are discussed.Comment: 4 pages, 6 Figure

Modification of the Two-equation Turbulence Model in NPARC to a Chien Low Reynolds Number K-epsilon Formulation

This report documents the changes that were made to the two-equation k-epsilon turbulence model in the NPARC (National-PARC) code. The previous model based on the low Reynolds number model of Speziale, was replaced with the low Reynolds number k-epsilon model of Chien. The most significant difference was in the turbulent Prandtl numbers appearing in the diffusion terms of the k and epsilon transport equations. A new inflow boundary condition and stability enhancements were also implemented into the turbulence model within NPARC. The report provides the rationale for making the change to the Chien model, code modifications required, and comparisons of the performances of the new model with the previous k-epsilon model and algebraic models used most often in PARC/NPARC. The comparisons show that the Chien k-epsilon model installed here improves the capability of NPARC to calculate turbulent flows