1,398 research outputs found
Dynamics of Sound Waves in an Interacting Bose Gas
We consider a non-relativistic quantum gas of bosonic atoms confined to a
box of volume in physical space. The atoms interact with each other
through a pair potential whose strength is inversely proportional to the
density, , of the gas. We study the time evolution of
coherent excitations above the ground state of the gas in a regime of large
volume and small ratio . The initial state of
the gas is assumed to be close to a \textit{product state} of one-particle wave
functions that are approximately constant throughout the box. The initial
one-particle wave function of an excitation is assumed to have a compact
support independent of . We derive an effective non-linear equation
for the time evolution of the one-particle wave function of an excitation and
establish an explicit error bound tracking the accuracy of the effective
non-linear dynamics in terms of the ratio . We conclude
with a discussion of the dispersion law of low-energy excitations, recovering
Bogolyubov's well-known formula for the speed of sound in the gas, and a
dynamical instability for attractive two-body potentials.Comment: 42 page
Effective Dynamics of a Tracer Particle Interacting with an Ideal Bose Gas
We study a system consisting of a heavy quantum particle, called tracer
particle, coupled to an ideal gas of light Bose particles, the ratio of masses
of the tracer particle and a gas particle being proportional to the gas
density. All particles have non-relativistic kinematics. The tracer particle is
driven by an external potential and couples to the gas particles through a pair
potential. We compare the quantum dynamics of this system to an effective
dynamics given by a Newtonian equation of motion for the tracer particle
coupled to a classical wave equation for the Bose gas. We quantify the
closeness of these two dynamics as the mean-field limit is approached (gas
density ). Our estimates allow us to interchange the thermodynamic
with the mean-field limit.Comment: 27 pages, typos corrected, a few more explanations adde
Transmission electron microscopy characterization of microstructural features of Al-Li-Cu alloys
A transmission electron microscopy (TEM) examination of aluminum-lithium-copper alloys was conducted. The principal purpose is to characterize the nature, size, and distribution of stringer particles which result from the powder metallurgy (P/M) processing of these alloys. Microstructural features associated with the stringer particles are reported that help explain the stress corrosion susceptibility of the powder metallurgy-processed Al-Li-Cu alloys. In addition, matrix precipitation events are documented for a variety of heat treatments and process variations. Hot rolling is observed to significant alter the nature of matrix precipitation, and the observations are correlated with concomitant mechanical property variations
Stream dynamics between 1 AU and 2 AU: A detailed comparison of observations and theory
A radial alignment of three solar wind stream structures observed by IMP-7 and -8 (at 1.0 AU) and Voyager 1 and 2 (in the range 1.4 to 1.8 AU) in late 1977 is presented. It is demonstrated that several important aspects of the observed dynamical evolution can be both qualitatively and quantitatively described with a single-fluid 2-D MHD numerical model of quasi-steady corotating flow, including accurate prediction of: (1) the formation of a corotating shock pair at 1.75 AU in the case of a simple, quasi-steady stream; (2) the coalescence of the thermodynamic and magnetic structures associated with the compression regions of two neighboring, interacting, corotating streams; and (3) the dynamical destruction of a small (i.e., low velocity-amplitude, short spatial-scale) stream by its overtaking of a slower moving, high-density region associated with a preceding transient flow. The evolution of these flow systems is discussed in terms of the concepts of filtering and entrainment
Laterolateral teleradiography of the skull as a screening method for OSA/OSAS, in patients in orthodontic treatment
Aim: Obstructive sleep apnea syndrome (OSAS) is the most common
type of sleep apnea and it is caused by complete or partial obstruction of the
upper airway. Adenotonsillar hypertrophy, obesity, cranio-facial anomalies
and neuromuscular diseases are the main risk factors for the development of
OSAS in the pediatric age. Specially several studies identify the relationship
between respiratory disorders in sleep and obesity, and, in particular, between
OSAS and obesity, designing a prevalence of OSAS among obese subjects
between 14 and 78%. The diagnosis of OSAS in the child is of great importance
as it can lead to neurocognitive and behavioral complications, growth
retardation, systemic arterial hypertension, pulmonary hypertension, cardiovascular
disease and metabolism.
The WHO (World Health Organization) has established the new criteria
for the classification of Obesity on the basis of BMI and the risk of comorbidities,
identifying a moderate risk for underweight subjects, a very low risk for
normal weights and an increased risk from severe to severe for overweight
and obese individuals respectively.
According to that the aim of this study is to evaluate the correlation
between obstructive sleep apnea syndrome and cephalometric variables in
children considering age and BMI.
Materials and methods: Children aged 7â10 years and 11-14 years with
no genetic syndrome, previous otorhinolaryngologic or orthodontic therapy
treatments are being selected from our Departments of Paediatric Dentistry,
University of Palermo, and from the Department of Orthodontics, University
of Messina (Italy).
All patients so far recruited and visited for orthodontic problems were in
mixed or early permanent dentition phase, with the first upper molars fully
erupted and presented to the history of several symptoms of Osas, such
as recurring episodes of shallow or paused breathing during sleep, waking
up frequently to urinate, morning headaches, memory or learning problems
and not be able to concentrate or feeling irritable.
Dental records and lateral cephalometric radiographs were obtained for
all of the patients and than they have been subjected to paediatric, otolaryngology
and polysomnography visits.
Subject with a positive diagnosis of Osas were studied and they were
divided in group based on their BMI.
In all groups the inter-molar distance in dental records was measured, and the cephalometric traces have been calculated. As reported by the study by Galeotti et al. the cephalometric measurements analysed are S-PNS, ad1-PNS, and ad2-PNS for the nasopharynx; p-pp and pa for oropharynx; H-Hâ for the Hyoid bone; SNA for the maxilla; SNB;ANB and Go-Me for the mandible;
S-Go, N-Me and P-A for facial Height; SN for cranial base; SN-MP and PP-MP for the typology, and angle ArGoMe for Growth prevision.
At the time that children are still in the way of recruitment the results may not yet be defined; however it is necessary to emphasize the importance of the study, because in the child respiratory disturbances in the sleep, and in particular the OSAS, are often underestimated, despite representing the third place between the threats of health after the smoke and the excess of weight
Instantaneous flowrate measurements in high-pressure liquid flows
A new flowmeter suitable for high-pressure flows and with a prompt dynamic response is presented. It is constituted by two pressure transducers installed on the monitored high-pressure pipe at a fixed distance one from the other, together with a low-pressure flowmeter that provides a time-averaged flowrate. The measurement algorithm consists of an ordinary differential equation obtained by combining the mass conservation partial differential equation and the momentum balance one applied to the considered piece of pipe comprised between the two pressure transducers. Due to the absence of a master instrument that can be employed as reference to verify the consistency of the measured flowrate, the flowmeter accuracy has been demonstrated by means of numerical models of various hydraulic components, rigorously validated through pressure measurements. The flow ripple of gear pumps has been measured, as well as the flowrate entering a Common Rail injector. For all these cases, the measured flowrate and the one obtained by means of the numerical model are in very good agreement, leading to a robust validation of the presented measurement device
The Sunyaev-Zeldovich Effect at 1 and 2 mm towards ROSAT Clusters
An observing campaign was devoted to the search for the Sunyaev-Zeldovich
(S-Z) effect towards X-ray ROSAT Clusters in the millimetric spectral domain. A
double channel (1.2 and 2 {\it mm}) photometer was installed at the focus of
the 15m Swedish ESO Submillimeter Telescope (SEST) in Chile in september 1994
and 1995 and observations of the targets S1077, A2744, S295 and RXJ0658-5557
were gathered. Detections were found for A2744 at 1 {\it mm} and in both
channels (at 1.2 and 2 {\it mm}) towards RXJ0658-5557. For the first time there
is evidence for the S-Z enhancement and both the latter and the decrement were
detected on the same source. We discuss astrophysical and systematic effects
which could give origin to these signals.Comment: 6 pg Latex file (style file included) including 1 ps figure, XVIth
Moriond Astrophysics Meeting "The Anisotropies of the Cosmic Microwave
Background", Les Arcs, Savoie-France, March 16-23 199
Absence of Ground States for a Class of Translation Invariant Models of Non-relativistic QED
We consider a class of translation invariant models of non-relativistic QED
with net charge. Under certain natural assumptions we prove that ground states
do not exist in the Fock space
Ionization of Atoms by Intense Laser Pulses
The process of ionization of a hydrogen atom by a short infrared laser pulse
is studied in the regime of very large pulse intensity, in the dipole
approximation. Let denote the integral of the electric field of the pulse
over time at the location of the atomic nucleus. It is shown that, in the limit
where , the ionization probability approaches unity and the
electron is ejected into a cone opening in the direction of and of
arbitrarily small opening angle. Asymptotics of various physical quantities in
is studied carefully. Our results are in qualitative agreement with
experimental data reported in \cite{1,2}.Comment: 27 pages, 1 figure
Looking for the S-Z Effect towards Distant ROSAT Clusters of Galaxies
We report on observations of the Sunyaev-Zeldovich effect towards X-ray ROSAT
clusters taken with a double channel (1.2 and 2 mm) photometer installed at the
focus of the 15m SEST antenna in Chile. This paper describes the first results
obtained for the high-z clusters S1077, A2744 and S295. Marginal detections
were found for A2744 and at 1 mm for S1077. We discuss these data in terms of
contamination of sources along the line of sight and give a constraint on the
amplitude of the kinematic effect.Comment: 17 pg Latex file (using aasms4.sty) gzip'd tar'd uuencoded file
including 1 ps figure, ApJ Letter in pres
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