10,333 research outputs found
Communication Satellite Output Devices
Solid state and vacuum tube output devices for communication satellite
Elemental surface analysis at ambient pressure by electron-induced x-ray fluorescence
The development of a portable surface elemental analysis tool, based on the excitation of characteristic x rays from samples at ambient pressure with a focused electron beam is described. This instrument relies on the use of a thin electron transmissive membrane to isolate the vacuum of the electron source from the ambient atmosphere. The major attributes of this instrument include rapid (several minutes) spectrum acquisition, nondestructive evaluation of elemental composition, no sample preparation, and high-to-medium (several hundreds µm) spatial resolution. The instrument proof-of-principle has been demonstrated in a laboratory setup by obtaining energy dispersive x-ray spectra from metal and mineral samples
Evolution of cracks in selvedge of the coal bed during its stationary working
Purpose. To study rupturing of the coal/rock seam selvedge by natural gas-filled cracks as phenomena that prepare and initiate sudden outbursts of coal, rock, and gas during the steady movement of the face.
Methods. The work is based on theoretical studies, including methods of thermodynamics, statistical physics, and asymptotic analysis.
Findings. A generalized Griffith’s criterion for the material rupture by a crack is applied to the selvedge part of a gas-saturated coal/rock seam during its stationary unloading.
Originality. The kinetic theory describing processes of gas-containing materials destruction is developed using the example of rupturing the selvedge part of a coal/rock seam by natural gas-filled cracks.
Practical implications. The criterion for changing the control parameters (reservoir gas pressure, crack dimensions, rock pressure, surface coal/rock energy, elastic modulus) is found at which spontaneous failure of the seam becomes possible. This allows to discuss the possibility of predicting sudden outbursts of coal, rock and gas.Цель. Исследование процессов разрыва краевой части угольного/породного пласта природными газонаполненными трещинами как явлений, подготавливающих и инициирующих внезапные выбросы угля, породы и газа при стационарном подвигании забоя.
Методика. Работа выполнена на основе теоретических исследований, включающих методы термодинамики, статистической физики, асимптотического анализа.
Результаты. Получен обобщенный критерий Гриффитса разрыва материала трещиной применительно к краевой части газонасыщенного угольного/породного пласта при его стационарной разгрузке.
Научная новизна. Развита кинетическая теория процессов разрушения газосодержащих материалов на примере разрыва краевой части угольного/породного пласта природными газонаполненными трещинами.
Практическая значимость. Найден критерий изменения управляющих параметров (пластового давления газа, размеров трещин, горного давления, поверхностной энергии угля/породы, модуля упругости), при котором спонтанное разрушение пласта становится возможным. Это позволяет обсуждать возможность прогноза внезапных выбросов угля, породы и газа.Мета. Дослідження процесів розриву крайової частини вугільного/породного пласта природними газонаповненими тріщинами як явищ, що підготовлюють та ініціюють раптові викиди вугілля, породи й газу при стаціонарному посуванні вибою.
Методика. Робота виконана на основі теоретичних досліджень, що включають методи термодинаміки, статистичної фізики, асимптотичного аналізу.
Результати. Отримано узагальнений критерій Гріффітса розриву матеріалу тріщиною стосовно крайової частини газонасиченого вугільного/породного пласта при його стаціонарному розвантаженні.
Наукова новизна. Розвинено кінетичну теорію процесів руйнування матеріалів, що містять газ, на прикладі розриву крайової частини вугільного/породного пласта природними газонаповненими тріщинами.
Практична значимість. Знайдено критерій зміни керуючих параметрів (пластового тиску газу, розмірів тріщин, гірського тиску, поверхневої енергії вугілля/породи, модуля пружності), при якому спонтанне руйнування пласта стає можливим. Це дозволяє обговорювати можливість прогнозу раптових викидів вугілля, породи і газу.Работа выполнена в рамках научно-исследовательс-кой темы НАН Украины “Массо-, теплоперенос и физика предвыбросных явлений в газонасыщенном трещиновато-пористом слоистом углепородном массиве”
LHC discovery potential for models with continuously distributed mass
We study the Large Hadron Collider (LHC) discovery potential for models
with continuously distributed mass for and 14 TeV
centre-of-mass energies. One of possible LHC signatures for such models is the
existence of broad resonance in Drell-Yan reaction .Comment: 14 pages, some references and formula adde
The Fourth Positive System of Carbon Monoxide in the Hubble Space Telescope Spectra of Comets
The rich structure of the Fourth Positive System (A-X) of carbon monoxide
accounts for many of the spectral features seen in long slit HST-STIS
observations of comets 153P/Ikeya-Zhang, C/2001 Q4 (NEAT), and C/2000 WM1
(LINEAR), as well as in the HST-GHRS spectrum of comet C/1996 B2 Hyakutake. A
detailed CO fluorescence model is developed to derive the CO abundances in
these comets by simultaneously fitting all of the observed A-X bands. The model
includes the latest values for the oscillator strengths and state parameters,
and accounts for optical depth effects due to line overlap and self-absorption.
The model fits yield radial profiles of CO column density that are consistent
with a predominantly native source for all the comets observed by STIS. The
derived CO abundances relative to water in these comets span a wide range, from
0.44% for C/2000 WM1 (LINEAR), 7.2% for 153P/Ikeya-Zhang, 8.8% for C/2001 Q4
(NEAT) to 20.9% for C/1996 B2 (Hyakutake). The subtraction of the CO spectral
features using this model leads to the first identification of a molecular
hydrogen line pumped by solar HI Lyman-beta longward of 1200A in the spectrum
of comet 153P/Ikeya-Zhang. (Abridged)Comment: 12 pages, 11 figures, ApJ accepte
Distinguishing Solar Flare Types by Differences in Reconnection Regions
Observations show that magnetic reconnection and its slow shocks occur in
solar flares. The basic magnetic structures are similar for long duration event
(LDE) flares and faster compact impulsive (CI) flares, but the former require
less non-thermal electrons than the latter. Slow shocks can produce the
required non-thermal electron spectrum for CI flares by Fermi acceleration if
electrons are injected with large enough energies to resonate with scattering
waves. The dissipation region may provide the injection electrons, so the
overall number of non-thermal electrons reaching the footpoints would depend on
the size of the dissipation region and its distance from the chromosphere. In
this picture, the LDE flares have converging inflows toward a dissipation
region that spans a smaller overall length fraction than for CI flares. Bright
loop-top X-ray spots in some CI flares can be attributed to particle trapping
at fast shocks in the downstream flow, the presence of which is determined by
the angle of the inflow field and velocity to the slow shocks.Comment: 15 pages TeX and 2 .eps figures, accepted to Ap.J.Let
Cervical masses in dogs and cats 1. Investigation and management
Abnormalities in the cervical region can be challenging to investigate and manage; however, the area is a common location for disease processes in dogs and cats. The anatomy of this region can make investigations and treatment difficult and a thorough understanding of this is essential before embarking on management and treatment of conditions in this location. Due to the various anatomical structures in the cervical area, there is often a long potential differential diagnoses list for mass lesions in this region. It is important to perform a thorough and logical investigative process in order to manage these masses appropriately. This article discusses investigation and management of cervical masses, while a second article, to be published in a subsequent issue of In Practice, will focus on differential diagnoses
Breakdown of anomalous channeling with ion energy for accurate strain determination in gan-based heterostructures
The influence of the beam energy on the determination of strain state with ion channeling in GaN-based heterostructures (HSs) is addressed. Experimental results show that anomalous channeling may hinder an accurate analysis due to the steering effects at the HS interface, which are more intense at lower ion energies. The experimental angular scans have been well reproduced by Monte Carlo simulations, correlating the steering effects with the close encounter probability at the interface. Consequently, limitations in the determination of the strain state by ion channeling can be overcome by selecting the adequate beam energy
Functional renormalization group approach to correlated fermion systems
Numerous correlated electron systems exhibit a strongly scale-dependent
behavior. Upon lowering the energy scale, collective phenomena, bound states,
and new effective degrees of freedom emerge. Typical examples include (i)
competing magnetic, charge, and pairing instabilities in two-dimensional
electron systems, (ii) the interplay of electronic excitations and order
parameter fluctuations near thermal and quantum phase transitions in metals,
(iii) correlation effects such as Luttinger liquid behavior and the Kondo
effect showing up in linear and non-equilibrium transport through quantum wires
and quantum dots. The functional renormalization group is a flexible and
unbiased tool for dealing with such scale-dependent behavior. Its starting
point is an exact functional flow equation, which yields the gradual evolution
from a microscopic model action to the final effective action as a function of
a continuously decreasing energy scale. Expanding in powers of the fields one
obtains an exact hierarchy of flow equations for vertex functions. Truncations
of this hierarchy have led to powerful new approximation schemes. This review
is a comprehensive introduction to the functional renormalization group method
for interacting Fermi systems. We present a self-contained derivation of the
exact flow equations and describe frequently used truncation schemes. Reviewing
selected applications we then show how approximations based on the functional
renormalization group can be fruitfully used to improve our understanding of
correlated fermion systems.Comment: Review article, final version, 59 pages, 28 figure
Constraints on Galaxy Bias, Matter Density, and Primordial Non--Gausianity from the PSCz Galaxy Redshift Survey
We compute the bispectrum for the \IRAS PSCz catalog and find that the galaxy
distribution displays the characteristic signature of gravity. Assuming
Gaussian initial conditions, we obtain galaxy biasing parameters
and , with no sign of
scale-dependent bias for h/Mpc. These results impose stringent
constraints on non-Gaussian initial conditions. For dimensional scaling models
with statistics, we find N>49, which implies a constraint on
primordial skewness .Comment: 4 pages, 3 embedded figures, uses revtex style file, minor changes to
reflect published versio
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