2,323 research outputs found
Coherent States for Particle Beams in the Thermal Wave Model
In this paper, by using an analogy among {\it quantum mechanics}, {\it
electromagnetic beam optics in optical fibers}, and {\it charge particle beam
dynamics}, we introduce the concept of {\it coherent states} for charged
particle beams in the framework of the {\it Thermal Wave Model} (TWM). We give
a physical meaning of the Gaussian-like coherent structures of charged particle
distribution that are both naturally and artificially produced in an
accelerating machine in terms of the concept of coherent states widely used in
quantum mechanics and in quantum optics. According to TWM, this can be done by
using a Schr\"{o}dinger-like equation for a complex function, the so-called
{\it beam wave function} (BWF), whose squared modulus is proportional to the
transverse beam density profile, where Planck's constant and the time are
replaced by the transverse beam emittance and by the propagation coordinate,
respectively. The evolution of the particle beam, whose initial BWF is assumed
to be the simplest coherent state (ground-like state) associated with the beam,
in an infinite 1-D quadrupole-like device with small sextupole and octupole
aberrations, is analytically and numerically investigated.Comment: 21 pages, Late
Matrix Sigma-models for Multi D-brane Dynamics
We describe a dynamical worldsheet origin for the Lagrangian describing the
low-energy dynamics of a system of parallel D-branes. We show how matrix-valued
collective coordinate fields for the D-branes naturally arise as couplings of a
worldsheet sigma-model, and that the quantum dynamics require that these
couplings be mutually noncommutative. We show that the low-energy effective
action for the sigma-model couplings describes the propagation of an open
string in the background of the multiple D-brane configuration, in which all
string interactions between the constituent branes are integrated out and the
genus expansion is taken into account, with a matrix-valued coupling. The
effective field theory is governed by the non-abelian Born-Infeld target space
action which leads to the standard one for D-brane field theory.Comment: 14 pages LaTeX, 1 encapsulated postscript figure; uses epsf.te
Optical and infrared properties of V1647 Orionis during the 2003-2006 outburst. II. Temporal evolution of the eruptive source
The occurrence of new FU Orionis-like objects is fundamental to understand
the outburst mechanism in young stars and their role in star formation and disk
evolution. Our work is aimed at investigating the properties of the recent
outburst of V1647 Ori. Using optical and mid infrared long slit spectroscopy we
monitored V1647 Ori in outburst between February 2004 and January 2006. The
optical spectrum is characterized by Halpha and Hbeta in P-Cygni profile and by
many weak FeI and FeII emission lines. Short timescale variability was measured
in the continuum and line emission. On January 2006 we detected for the first
time forbidden emission lines ([OI], [SII] and [FeII]). These lines are likely
produced by an Herbig-Haro object driven by V1647 Ori. The mid infrared the
spectrum of V1647 Ori is flat and featureless at all epochs. The SED changed
drastically: the source was much redder in the early outburst than in the final
phase. The magnitude rise and the SED of V1647 Ori resembles that of a FUor
while the duration and recurrence of the outburst resemble that of a EXor. The
optical spectrum is clearly distinct from either the absorption line spectrum
of a FUor or the T Tauri-like spectrum of an EXor. Our data are consistent with
a disk instability event which led to an increase of the mass accretion rate.
The data also suggest the presence of a circumstellar envelope around the
star+disk system. The peculiar N band spectrum might be explained by dust
sublimation in the outer layers of the disk. The presence of the envelope and
the outburst statistics suggest that these instability events occur only in a
specific stage of a Class I source (e.g. in the transition phase to an
optically visible star surrounded by a protoplanetary disk). We discuss the
outburst mechanisms in term of the thermal instability model.Comment: 12 pages, 7 figures, accepted for publication in A&
Landau Damping and Coherent Structures in Narrow-Banded 1+1 Deep Water Gravity Waves
We study the nonlinear energy transfer around the peak of the spectrum of
surface gravity waves by taking into account nonhomogeneous effects. In the
narrow-banded approximation the kinetic equation resulting from a
nonhomogeneous wave field is a Vlasov-Poisson type equation which includes at
the same time the random version of the Benjamin-Feir instability and the
Landau damping phenomenon. We analytically derive the values of the Phillips'
constant and the enhancement factor for which the
narrow-banded approximation of the JONSWAP spectrum is unstable. By performing
numerical simulations of the nonlinear Schr\"{o}dinger equation we check the
validity of the prediction of the related kinetic equation. We find that the
effect of Landau damping is to suppress the formation of coherent structures.
The problem of predicting freak waves is briefly discussed.Comment: 4 pages, 3 figure
Probing the radial temperature structure of protoplanetary disks with Herschel/HIFI
Herschel/HIFI spectroscopic observations of CO J=10-9, CO J=16-15 and [CII]
towards HD 100546 are presented. The objective is to resolve the velocity
profile of the lines to address the emitting region of the transitions and
directly probe the distribution of warm gas in the disk. The spectra reveal
double-peaked CO line profiles centered on the systemic velocity, consistent
with a disk origin. The J=16-15 line profile is broader than that of the J=10-9
line, which in turn is broader than those of lower J transitions (6-5, 3-2,
observed with APEX), thus showing a clear temperature gradient of the gas with
radius. A power-law flat disk model is used to fit the CO line profiles and the
CO rotational ladder simultaneously, yielding a temperature of T_0=1100 \pm 350
K (at r_0 = 13 AU) and an index of q=0.85 \pm 0.1 for the temperature radial
gradient. This indicates that the gas has a steeper radial temperature gradient
than the dust (mean q_{dust} ~ 0.5), providing further proof of the thermal
decoupling of gas and dust at the disk heights where the CO lines form. The
[CII] line profile shows a strong single-peaked profile red-shifted by 0.5 km
s-1 compared to the systemic velocity. We conclude that the bulk of the [CII]
emission has a non-disk origin (e.g., remnant envelope or diffuse cloud).Comment: Accepted for publication in ApJ
Sistema di filologia computazionale per testi demotici
A project for a Demotic Inscriptions on Ostraka Database is being carried out in collaboration between ILC/CNR (Pisa), the Department of Electronic Engineering (Calabria University) and the Department of the Ancient World History (Egyptological section, Pisa University). The aim of the project is to analyse the digital colour images of demotic texts on ostraka (Medinet Madi, in Fayyum region) with the aid of computational tools. The module described in the paper is a neural component able to learn the graphical features of each demotic symbol, which has been previously segmented in the images thanks to a semiautomatic procedure. A specific neural network tries to recognize the text written in the images linking the symbols segmented within the ostraka images database to the correspondent symbols available on a virtual keyboard. The graphical interface is particularly useful for teaching and research activities on this type of archaeological documentation
The bubble heart'. an unusual natural history told by multimodality imaging- a case report
Background Intracardiac thrombosis is a relatively common pathological condition. Often, it is diagnosed at echocardiography during the subacute or chronic phase. In the very acute phase, tissue composition can make thrombus appearance very different from that usually seen. Fresh thrombosis has been previously found also in peripartum cardiomyopathy (PPC), but with imaging features different from our case.
Case summary A 27-year-old woman was referred to our hospital for PPC, with echocardiographic finding of intraventricular masses, resembling big bubbles. Cardiac magnetic resonance (CMR) allowed definitively diagnosing intracardiac 'very acute' thrombosis, which is rarely detected.
Discussion Our case provides a practical lesson about management of an unusual presentation of a common problem. When early echocardiography does not allow making a certain diagnosis, CMR can be helpful and decisive, due to its unique ability to provide characterization of intracardiac masses
Flavour anomalies and the muon g − 2 from feebly interacting particles
We perform a phenomenological analysis of simplified models of light, feebly interacting particles (FIPs) that can provide a combined explanation of the anomalies in b → sll transitions at LHCb and the anomalous magnetic moment of the muon. Different scenarios are categorised according to the explicit momentum dependence of the FIP coupling to the b−s and μ−μ vector currents and they are subject to several constraints from flavour and precision physics. We show that viable combined solutions to the muon g − 2 and flavour anomalies exist with the exchange of a vector FIP with mass larger than 4 GeV. Interestingly, the LHC has the potential to probe this region of the parameter space by increasing the precision of the Z → 4μ cross-section measurement. Conversely, we find that solutions based on the exchange of a lighter vector, in the mV < 1 GeV range, are essentially excluded by a combination of B → K+ invisible and W-decay precision bounds
Solitary wave interaction in a compact equation for deep-water gravity waves
In this study we compute numerical traveling wave solutions to a compact
version of the Zakharov equation for unidirectional deep-water waves recently
derived by Dyachenko & Zakharov (2011) Furthermore, by means of an accurate
Fourier-type spectral scheme we find that solitary waves appear to collide
elastically, suggesting the integrability of the Zakharov equation.Comment: 8 pages, 5 figures, 23 references. Other author's papers can be
downloaded at http://www.lama.univ-savoie.fr/~dutykh/ . arXiv admin note:
text overlap with arXiv:1204.288
Effects of angiotensin-converting enzyme inhibition on left ventricular geometric patterns in patients with essential hypertension
Although angiotensin-converting enzyme inhibitors have been shown to affect left ventricular (LV) remodeling favorably in several conditions, it remains unclear whether they can influence LV geometric pattern in hypertension. To address this issue, 122 patients (71 men and 51 women; mean age = 51 +/- 20 years) with mild to moderate hypertension were studied prospectively. All underwent clinical evaluation and Doppler echocardiography at entry and more than 2 years of quinapril therapy (10-40 mg/day). According to either LV mass (normal if <131 g/m(2) for men or <100 g/m(2) for women) or the ratio of LV posterior wall thickness to diastolic diameter (RWT; normal if <0.45) at baseline, 58 patients had normal mass and RWT, 18 patients had concentric remodeling (i.e., normal mass but increased RWT), 24 patients had eccentric hypertrophy (i.e., increased mass but normal RWT), and 22 patients had concentric hypertrophy (i.e., increase in both mass and RWT). After 6 months of quinapril therapy, all patients with normal left ventricles showed the maintenance of mass and RWT within normal limits. Patients with concentric remodeling showed no increase in mass but had a significant decrease in RWT. Patients with eccentric hypertrophy exhibited a significant reduction in mass with no substantial change in RWT. Patients with concentric hypertrophy had a significant reduction in both mass and RWT. Changes in LV mass and geometry were maintained during the 2-year period of treatment and were paralleled by improvements in Doppler in dices of LV diastolic function in each group. It is concluded that quinapril, with its well-known effects on LV hypertrophy, modifies the LV geometric pattern of hypertensive patients favorably, regardless of the presence of an abnormal LV mass or RWT
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