1,714 research outputs found
Mass segregation in star clusters is not energy equipartition
Mass segregation in star clusters is often thought to indicate the onset of energy equipartition, where the most massive stars impart kinetic energy to the lower-mass stars and brown dwarfs/free floating planets. The predicted net result of this is that the centrally concentrated massive stars should have significantly lower velocities than fast-moving low-mass objects on the periphery of the cluster. We search for energy equipartition in initially spatially and kinematically substructured N-body simulations of star clusters with N = 1500 stars, evolved for 100 Myr. In clusters that show significant mass segregation we find no differences in the proper motions or radial velocities as a function of mass. The kinetic energies of all stars decrease as the clusters relax, but the kinetic energies of the most massive stars do not decrease faster than those of lower-mass stars. These results suggest that dynamical mass segregation -- which is observed in many star clusters -- is not a signature of energy equipartition from two-body relaxation
Changes in the electrical transport of ZnO under visible light
Complex impedance spectroscopy data in the frequency range 16Hz < f < 3 MHz
at room temperature were acquired on pure ZnO single crystal and thin film. The
measured impedance of the ZnO samples shows large changes with time after
exposure to or covering them from visible light. At fixed times
Cole-Cole-diagrams indicate the presence of a single relaxation process. A
simple analysis of the impedance data allows us to obtain two main relaxation
times. The behavior for both, ZnO crystal and thin film, is similar but the
thin film shows shorter relaxation times. The analysis indicates the existence
of two different photo-active defects with activation energies between ~0.8 eV
and ~1.1 eV.Comment: 11 pages, 9 figures. Solid state communications, in pres
Continuous-time quantum walk on integer lattices and homogeneous trees
This paper is concerned with the continuous-time quantum walk on Z, Z^d, and
infinite homogeneous trees. By using the generating function method, we compute
the limit of the average probability distribution for the general isotropic
walk on Z, and for nearest-neighbor walks on Z^d and infinite homogeneous
trees. In addition, we compute the asymptotic approximation for the probability
of the return to zero at time t in all these cases.Comment: The journal version (save for formatting); 19 page
Electronic Friction-Based Vibrational Lifetimes of Molecular Adsorbates: Beyond the Independent-Atom Approximation
Catalysis and Surface ChemistryTheoretical Chemistr
The Spectrum of the Dirac Operator in the Linear Sigma Model with Quarks
We derive the spectrum of the Dirac operator for the linear sigma-model with
quarks in the large N_c approximation using renormalization group flow
equations. For small eigenvalues, the Banks-Casher relation and the vanishing
linear term are recovered. We calculate the coefficient of the next to leading
term and investigate the spectrum beyond the low energy regime.Comment: 15 pages, 6 figures, to appear in Phys. Rev.
Comparative toxicity and effectiveness of trastuzumab-based chemotherapy regimens in older women with early-stage breast cancer
Purpose The combination of chemotherapy and trastuzumab is the standard of care for adjuvant treatment of human epidermal growth factor receptor 2-positive breast cancer. Two regimens have been widely adopted in the United States: doxorubicin, cyclophosphamide, paclitaxel, and trastuzumab (ACTH) and docetaxel, carboplatin, and trastuzumab (TCH). No head-to-head comparison of these regimens has been conducted in a clinical trial, and existing trial data have limited generalizability to older patients. Methods We used SEER-Medicare data from 2005 to 2013 to compare outcomes of ACTH versus TCH among patients age older than 65 years. Propensity score matching was used to balance cohort characteristics between treatment arms. Outcomes included toxicity-related hospitalization, survival, and trastuzumab completion. Data from 1,077 patients receiving ACTH or TCH were analyzed, and the propensity-matched subsample included 416 women. Results There was a significant shift toward TCH over time, with 88% of patients receiving ACTH in 2005 compared with 15% by 2011. Among propensity score-matched patients, we found no difference between regimens in health care use overall or for chemotherapy-related adverse events (ACTH, 34% v TCH, 36.5%; P = .46). Patients receiving TCH were significantly more likely to complete trastuzumab (89% v 77%; P = .001). There was no difference in 5-year breast cancer-specific survival (ACTH, 92% v TCH, 96%; hazard ratio, 2.08; 95% CI, 0.90 to 4.82) or overall survival. Conclusion Among a matched sample of older patients, ACTH compared with TCH was not associated with a higher rate of serious adverse events or hospitalizations, but it was associated with less completion of adjuvant trastuzumab.Wedid not detect a difference in 5-year survival outcomes for ACTH compared with TCH. In the context of limited evidence in older patients, selection between these two regimens on the basis of concerns about differential toxicity or efficacy may not be appropriate
Relation between the Polyakov loop and the chiral order parameter at strong coupling
We discuss the relation between the Polyakov loop and the chiral order
parameter at finite temperature by using the Gocksch-Ogilvie model with
fundamental or adjoint quarks. The model is based on the double expansion of
strong coupling and large dimensionality on the lattice. In an analytic way
with the mean field approximation employed, we show that the confined phase
must be accompanied by the spontaneous breaking of the chiral symmetry for both
fundamental and adjoint quarks. Then we proceed to numerical analysis to look
into the coupled dynamics of the Polyakov loop and the chiral order parameter.
In the case of fundamental quarks, the pseudo-critical temperature inferred
from the Polyakov loop behavior turns out to coincide with the pseudo-critical
temperature of the chiral phase transition. We discuss the physical implication
of the coincidence of the pseudo-critical temperatures in two extreme cases;
one is the deconfinement dominance and the other is the chiral dominance. As
for adjoint quarks, the deconfinement transition of first order persists and
the chiral phase transition occurs distinctly at higher temperature than the
deconfinement transition does. The present model study gives us a plausible
picture to understand the results from the lattice QCD and aQCD simulations.Comment: 19 pages, 9 figures, to appear in Phys.Rev.D. Appendix A is modified;
references are adde
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