2,617 research outputs found
A Probe of New Physics in Top Quark Pair Production at Colliders
We describe how to probe new physics through examination of the form factors
describing the Ztt couplings via the scattering process e^-e^+->t+tbar. We
focus on experimental methods on how the top quark momentum can be determined
and show how this can be applied to select polarized samples of
pairs through the angular correlations in the final state leptons. We also
study the dependence on the energy and luminosity of an \ee\ collider to probe
a CP violating asymmetry at the level.}Comment: 24 pages in TeXsis (figures available upon request) (revised July
1993
Trends in Elasticity and Electronic Structure of Transition-Metal Nitrides and Carbides from First Principles
The elastic properties of the -structured transition-metal nitrides and
their carbide counterparts are studied using the {\it ab initio\} density
functional perturbation theory. The linear response results of elastic
constants are in excellent agreement with those obtained from numerical
derivative methods, and are also consistent with measured data. We find the
following trends: (1) Bulk moduli and tetragonal shear moduli
, increase and lattice constants decrease
rightward or downward on the Periodic Table for the metal component or if C is
replaced by N; (2) The inequality holds for
; (3) depends strongly on the number of valence electrons per
unit cell (). From the fitted curve of as a function of , we
can predict that MoN is unstable in structure, and transition-metal
carbonitrides ( ZrCN) and di-transition-metal carbides
( HfTaC) have maximum at .Comment: 4 pages, 2 figures, submitted to PRL. 2 typos in ref. 15 were
correcte
Gravitomagnetism in Quantum Mechanics
We give a systematic treatment of the quantum mechanics of a spin zero
particle in a combined electromagnetic field and a weak gravitational field,
which is produced by a slow moving matter source. The analysis is based on the
Klein-Gordon equation expressed in generally covariant form and coupled
minimally to the electromagnetic field. The Klein-Gordon equation is recast
into Schroedinger equation form (SEF), which we then analyze in the
non-relativistic limit. We include a discussion of some rather general
observable physical effects implied by the SEF, concentrating on
gravitomagnetism. Of particular interest is the interaction of the orbital
angular momentum of the particle with the gravitomagnetic field.Comment: 9 page
Tumor site immune markers associated with risk for subsequent basal cell carcinomas.
BackgroundBasal cell carcinoma (BCC) tumors are the most common skin cancer and are highly immunogenic.ObjectiveThe goal of this study was to assess how immune-cell related gene expression in an initial BCC tumor biopsy was related to the appearance of subsequent BCC tumors.Materials and methodsLevels of mRNA for CD3ε (a T-cell receptor marker), CD25 (the alpha chain of the interleukin (IL)-2 receptor expressed on activated T-cells and B-cells), CD68 (a marker for monocytes/macrophages), the cell surface glycoprotein intercellular adhesion molecule-1 (ICAM-1), the cytokine interferon-γ (IFN-γ) and the anti-inflammatory cytokine IL-10 were measured in BCC tumor biopsies from 138 patients using real-time PCR.ResultsThe median follow-up was 26.6 months, and 61% of subjects were free of new BCCs two years post-initial biopsy. Patients with low CD3ε CD25, CD68, and ICAM-1 mRNA levels had significantly shorter times before new tumors were detected (p = 0.03, p = 0.02, p = 0.003, and p = 0.08, respectively). Furthermore, older age diminished the association of mRNA levels with the appearance of subsequent tumors.ConclusionsOur results show that levels of CD3ε, CD25, CD68, and ICAM-1 mRNA in BCC biopsies may predict risk for new BCC tumors
The Generalized Uncertainty Principle and Black Hole Remnants
In the current standard viewpoint small black holes are believed to emit
radiation as black bodies at the Hawking temperature, at least until they reach
Planck size, after which their fate is open to conjecture. A cogent argument
against the existence of remnants is that, since no evident quantum number
prevents it, black holes should radiate completely away to photons and other
ordinary stable particles and vacuum, like any unstable quantum system. Here we
argue the contrary, that the generalized uncertainty principle may prevent
their total evaporation in exactly the same way that the uncertainty principle
prevents the hydrogen atom from total collapse: the collapse is prevented, not
by symmetry, but by dynamics, as a minimum size and mass are approached.Comment: 11 pages, 4 figures; Winner of 3rd Place in the 2001 Gravity Research
Foundation Essay Competitio
W-band extended interaction oscillations using post-accelerated pseudospark-sourced electron beams
This article presents the investigation of a millimetre-wave extended interaction oscillation using both pencil and sheet-shaped pseudospark (PS)-sourced electron beams. Two W-band (75-110 GHz) pencil and sheet beam extended interaction oscillators (EIO) were designed and constructed respectively. The PS-sourced pencil beam EIO structure was firstly driven by a four-gap PS discharge operating at 30.5 kV and the output power of 38 W was achieved. The same EIO structure was then driven by an improved PS-sourced beam produced by combining a single-gap PS structure with an integrated post-acceleration section which generated an output power of 200W. The preliminary PS-sourced sheet beam EIO structure will also be presented
Are Small Reimbursement Changes Enough to Change Cancer Care? Reimbursement Variation in Prostate Cancer Treatment
The Centers for Medicare and Medicaid Services recently initiated small reimbursement adjustments to improve the value of care delivered under fee-for-service. To estimate the degree to which reimbursement influences physician decision making, we examined utilization of gonadotropin-releasing hormone (GnRH) agonists among urologists as Part B drug reimbursement varied in a fee-for-service environment
Applications of Pseudospark produced electron beams in millimetre wave radiation sources
Pseudospark (PS) electron beams of outstanding performance have been studied recently with their application to a demanding field of millimeter-wave and terahertz radiation generation. To this end, the PS discharge process itself has been studied and millimeter wave sources which utilize a PS sourced electron beam in different beam-wave interaction structures have been designed and modelled using the particle-in-cell code MAGIC. The experimental demonstration of the PS-sourced electron beams of sub-millimeter diameter and the coherent millimeter wave radiation generated from PS sourced electron beams in different beam-wave interaction structures will be presented
Scaling and Formulary cross sections for ion-atom impact ionization
The values of ion-atom ionization cross sections are frequently needed for
many applications that utilize the propagation of fast ions through matter.
When experimental data and theoretical calculations are not available,
approximate formulas are frequently used. This paper briefly summarizes the
most important theoretical results and approaches to cross section calculations
in order to place the discussion in historical perspective and offer a concise
introduction to the topic. Based on experimental data and theoretical
predictions, a new fit for ionization cross sections is proposed. The range of
validity and accuracy of several frequently used approximations (classical
trajectory, the Born approximation, and so forth) are discussed using, as
examples, the ionization cross sections of hydrogen and helium atoms by various
fully stripped ions.Comment: 46 pages, 8 figure
Compact sub-terahertz radiation sources driven by pseudospark-produced electron beams
High quality intense electron beams play an important role in high power millimeter-wave and terahertz radiation generation. To this end, the pseudospark-sourced electron beam has been investigated with their applications in different beam-wave interaction structures. Different structures have been designed and modelled using the particle-in-cell codes MAGIC and CST Particle Studio. The experimental demonstration of the PS-sourced electron beams of submillimeter diameter and the coherent millimeter wave radiation generated from PS-sourced electron beams in different beam-wave interaction structures will be presented
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