32,230 research outputs found
Pushing NRQCD to the limit
Lattice NRQCD has proven successful in describing the physics of the upsilon
system and B-mesons, though some concerns arise when it is used in simulations
of charm quarks. It is certainly possible that the NRQCD expansion is not
converging fast enough at this scale. We present some preliminary results on
the low-mass breakdown of NRQCD, in particular the behaviour of heavy
quarkonium and heavy-light meson spectra as the bare heavy quark mass is
decreased well below 1, with the aim of understanding more about the
manifestation of this breakdown.Comment: Lattice 99 submission, 3 Pages, 3 eps figure
Macrophages come to mind as keys to cognitive decline
Cognitive impairment, an underappreciated consequence of hypertension, is linked to cerebral arteriolar disease through poorly defined mechanisms. A study by Faraco et al. in this issue of the JCI points to perturbations of neurovascular unit coupling caused by perivascular macrophages (PVMs) as a cause of hypertension-related cognitive impairment. Angiotensin II (Ang II) was shown to activate PVMs, causing them to produce superoxide and thereby alter the proper functioning of the adjacent arterioles. Faraco and colleagues also show that disruption of the blood-brain barrier occurs in hypertension, allowing circulating Ang II to access PVMs. This study provides important new insight into the role of inflammatory cells in the genesis of vascular dementia
Geometric phases in a scattering process
The study of geometric phase in quantum mechanics has so far be confined to
discrete (or continuous) spectra and trace preserving evolutions. Consider only
the transmission channel, a scattering process with internal degrees of freedom
is neither a discrete spectrum problem nor a trace preserving process. We
explore the geometric phase in a scattering process taking only the
transmission process into account. We find that the geometric phase can be
calculated by the some method as in an unitary evolution. The interference
visibility depends on the transmission amplitude. The dependence of the
geometric phase on the barrier strength and the spin-spin coupling constant is
also presented and discussed.Comment: 4 pages, 5 figure
Annealing-induced reduction in nanoscale heterogeneity of thermally evaporated amorphous As2S3 films
The morphology and structural order of thermally deposited and annealed amorphous As2S3 films
have been investigated using high resolution transmission electron microscopy. It was found that
both the as-deposited and annealed films contained sparsely distributed nanocrystallites of the
orpiment As2S3 crystalline phase. However, from selected area electron diffraction both films
appeared amorphous. Fluctuation electron microscopy revealed that the as-deposited film contained
greater nanoscale inhomogeneity. Low temperature annealing reduced the nanoscale inhomogeneity
and resulted in a more homogeneous and energetically favorable network. The reduction in
nanoscale inhomogeneity upon low temperature annealing was accompanied by the appearance of
a first sharp diffraction peak in the diffraction pattern. This first-sharp diffraction peak has been
attributed to chemical ordering of interstitial voids. Our measurements suggest that this chemical
short-range ordering is associated with the dissolution of the energetically unfavorable larger
correlated structures that contribute to the inhomogeneity of the as-deposited film
A simulated investigation on the machining instability and dynamic surface generation
In this paper, the authors propose the generic concept of machining instability based on the analysis of all kinds of machining instable behaviors and their features. The investigation covers all aspects of the machining process, including the machine tool structural response, cutting process variables, tooling geometry and workpiece material property in a full dynamic scenario. The paper presents a novel approach for coping with the sophisticated machining instability and enabling better understanding of its effect on the surface generation through a combination of the numerical method with the characteristic equations and using block diagrams/functions to represent implicit equations and nonlinear factors. It therefore avoids the lengthy algebraic manipulations in deriving the outcome and the solution scheme is thus simple, robust and intuitive. Several machining case studies and their simulation results demonstrate the proposed approach is feasible for shop floor CNC machining optimisation in particular. The results also indicate the proposed approach is useful to monitor the machining instability and surface topography and to be potentially applied in adaptive control of the instability in real time
Reconstructing CMEs with Coordinated Imaging and In Situ Observations: Global Structure, Kinematics, and Implications for Space Weather Forecasting
See the pdf for detailsComment: 45 pages, 16 figures, ApJ, in pres
Frustration Driven Stripe Domain Formation in Co/Pt Multilayer Films
We report microscopic mechanisms for an unusual magnetization reversal
behavior in Co/Pt multilayers where some of the first-order reversal curves
protrude outside of the major loop. Transmission x-ray microscopy reveals a
fragmented stripe domain topography when the magnetic field is reversed prior
to saturation, in contrast to an interconnected pattern when reversing from a
saturated state. The different domain nucleation and propagation behaviors are
due to unannihilated domains from the prior field sweep. These residual domains
contribute to random dipole fields that impede the subsequent domain growth and
prevent domains from growing as closely together as for the interconnected
pattern.Comment: 13 pages, 3 figures, to appear in AP
Supersonic propeller spindown of neutron stars in wind-fed mass-exchange close binaries
The supersonic propeller spindown of a neutron star moving in a strong
stellar wind of its massive companion is discussed. I show that the supersonic
propeller model presented by Davies & Pringle (1981}) is self-consistent if the
strength of the stellar wind of the normal companion is \dot{M}_{\rm c} \la 2.2
10^{18} (M_{\rm ns}/M_{\sun}) V_8 g/s. Under these conditions the model can be
used for the interpretation of the long-period pulsars in Be/X-ray transients.
The spin history of the neutron star in the long period Be/X-ray transient
A0535+26 is considered.Comment: 3 pages, published in A&A Letters 381, L61 (2002
The Uniqueness Problem of Sequence Product on Operator Effect Algebra
A quantum effect is an operator on a complex Hilbert space that satisfies
. We denote the set of all quantum effects by . In
this paper we prove, Theorem 4.3, on the theory of sequential product on which shows, in fact, that there are sequential products on which are not of the generalized L\"{u}ders form. This result answers a
Gudder's open problem negatively
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