507 research outputs found
Air cycle combined heating and cooling for the food industry
In the food industry there is often a need to both cook and cool food. Heating and cooling processes are rarely directly linked due to heat from refrigeration processes being insufficient to cook food. Therefore cooling and cooking is usually provided by separate pieces of equipment. This paper presents an air cycle system where the hot air was used for heating and the cold air used for fast freezing. The apparatus used a bootstrap unit developed for aircraft air conditioning which was unable to run at the low temperature required for food freezing, so a parallel compressor was added to enable the system to operate at the low temperature required for food freezing. This approach allowed temperatures as low as -140 °C and as high as 234 °C. The system cooked and froze beef burgers, and at the same time heated water up to 98 °C. © 2011 Elsevier Ltd and IIR. All rights reserved
Estimating Dissipation Rates Associated With Double Diffusion
Abstract: Double diffusion refers to a variety of turbulent processes in which potential energy is released into kinetic energy, made possible in the ocean by the difference in molecular diffusivities between salinity and temperature. Here, we present a new method for estimating the kinetic energy dissipation rates forced by doubleâdiffusive convection using temperature and salinity data alone. The method estimates the upâgradient diapycnal buoyancy flux associated with double diffusion, which is hypothesized to balance the dissipation rate. To calculate the temperature and salinity gradients on small scales we apply a canonical scaling for compensated thermohaline variance (or âspiceâ) on subâmeasurement scales with a fixed buoyancy gradient. Our predicted dissipation rates compare favorably with microstructure measurements collected in the Chukchi Sea. Fine et al. (2018), https://doi.org/10.1175/jpo-d-18-0028.1, showed that dissipation rates provide good estimates for heat fluxes in this region. Finally, we show the method maintains predictive skill when applied to a subâsampling of the Conductivity, Temperature, Depth (CTD) data
Prediction of the functional properties of ceramic materials from composition using artificial neural networks
We describe the development of artificial neural networks (ANN) for the prediction of the properties of ceramic materials. The ceramics studied here include polycrystalline, inorganic, non-metallic materials and are investigated on the basis of their dielectric and ionic properties. Dielectric materials are of interest in telecommunication applications, where they are used in tuning and filtering equipment. Ionic and mixed conductors are the subjects of a concerted effort in the search for new materials that can be incorporated into efficient, clean electrochemical devices of interest in energy production and greenhouse gas reduction applications. Multi-layer perceptron ANNs are trained using the back-propagation algorithm and utilise data obtained from the literature to learn compositionâproperty relationships between the inputs and outputs of the system. The trained networks use compositional information to predict the relative permittivity and oxygen diffusion properties of ceramic materials. The results show that ANNs are able to produce accurate predictions of the properties of these ceramic materials, which can be used to develop materials suitable for use in telecommunication and energy production applications
Cooper pairing near charged black holes
We show that a quartic contact interaction between charged fermions can lead
to Cooper pairing and a superconducting instability in the background of a
charged asymptotically Anti-de Sitter black hole. For a massless fermion we
obtain the zero mode analytically and compute the dependence of the critical
temperature T_c on the charge of the fermion. The instability we find occurs at
charges above a critical value, where the fermion dispersion relation near the
Fermi surface is linear. The critical temperature goes to zero as the marginal
Fermi liquid is approached, together with the density of states at the Fermi
surface. Besides the charge, the critical temperature is controlled by a four
point function of a fermionic operator in the dual strongly coupled field
theory.Comment: 1+33 pages, 4 figure
Reaction rates and transport in neutron stars
Understanding signals from neutron stars requires knowledge about the
transport inside the star. We review the transport properties and the
underlying reaction rates of dense hadronic and quark matter in the crust and
the core of neutron stars and point out open problems and future directions.Comment: 74 pages; commissioned for the book "Physics and Astrophysics of
Neutron Stars", NewCompStar COST Action MP1304; version 3: minor changes,
references updated, overview graphic added in the introduction, improvements
in Sec IV.A.
Pair-breaking quantum phase transition in superconducting nanowires
A quantum phase transition (QPT) between distinct ground states of matter is
a wide-spread phenomenon in nature, yet there are only a few experimentally
accessible systems where the microscopic mechanism of the transition can be
tested and understood. These cases are unique and form the experimentally
established foundation for our understanding of quantum critical phenomena.
Here we report the discovery that a magnetic-field-driven QPT in
superconducting nanowires - a prototypical 1d-system - can be fully explained
by the critical theory of pair-breaking transitions characterized by a
correlation length exponent and dynamic critical exponent . We find that in the quantum critical regime, the electrical
conductivity is in agreement with a theoretically predicted scaling function
and, moreover, that the theory quantitatively describes the dependence of
conductivity on the critical temperature, field magnitude and orientation,
nanowire cross sectional area, and microscopic parameters of the nanowire
material. At the critical field, the conductivity follows a
dependence predicted by phenomenological scaling theories and more recently
obtained within a holographic framework. Our work uncovers the microscopic
processes governing the transition: The pair-breaking effect of the magnetic
field on interacting Cooper pairs overdamped by their coupling to electronic
degrees of freedom. It also reveals the universal character of continuous
quantum phase transitions.Comment: 22 pages, 5 figure
Chiral Modulations in Curved Space I: Formalism
The goal of this paper is to present a formalism that allows to handle
four-fermion effective theories at finite temperature and density in curved
space. The formalism is based on the use of the effective action and zeta
function regularization, supports the inclusion of inhomogeneous and
anisotropic phases. One of the key points of the method is the use of a
non-perturbative ansatz for the heat-kernel that returns the effective action
in partially resummed form, providing a way to go beyond the approximations
based on the Ginzburg-Landau expansion for the partition function. The
effective action for the case of ultra-static Riemannian spacetimes with
compact spatial section is discussed in general and a series representation,
valid when the chemical potential satisfies a certain constraint, is derived.
To see the formalism at work, we consider the case of static Einstein spaces at
zero chemical potential. Although in this case we expect inhomogeneous phases
to occur only as meta-stable states, the problem is complex enough and allows
to illustrate how to implement numerical studies of inhomogeneous phases in
curved space. Finally, we extend the formalism to include arbitrary chemical
potentials and obtain the analytical continuation of the effective action in
curved space.Comment: 22 pages, 3 figures; version to appear in JHE
Gravitational waves from single neutron stars: an advanced detector era survey
With the doors beginning to swing open on the new gravitational wave
astronomy, this review provides an up-to-date survey of the most important
physical mechanisms that could lead to emission of potentially detectable
gravitational radiation from isolated and accreting neutron stars. In
particular we discuss the gravitational wave-driven instability and
asteroseismology formalism of the f- and r-modes, the different ways that a
neutron star could form and sustain a non-axisymmetric quadrupolar "mountain"
deformation, the excitation of oscillations during magnetar flares and the
possible gravitational wave signature of pulsar glitches. We focus on progress
made in the recent years in each topic, make a fresh assessment of the
gravitational wave detectability of each mechanism and, finally, highlight key
problems and desiderata for future work.Comment: 39 pages, 12 figures, 2 tables. Chapter of the book "Physics and
Astrophysics of Neutron Stars", NewCompStar COST Action 1304. Minor
corrections to match published versio
Shear Wave Splitting Analysis to Estimate Fracture Orientation and Frequency Dependent Anisotropy
Shear wave splitting is a well-known method for indication of orientation, radius, and length of fractures in subsurface layers. In this paper, a three component near offset VSP data acquired from a fractured sandstone reservoir in southern part of Iran was used to analyse shear wave splitting and frequency-dependent anisotropy assessment. Polarization angle obtained by performing rotation on radial and transverse components of VSP data was used to determine the direction of polarization of fast shear wave which corresponds to direction of fractures. It was shown that correct implementation of shear wave splitting analysis can be used for determination of fracture direction. During frequency- dependent anisotropy analysis, it was found that the time delays in shear- waves decrease as the frequency increases. It was clearly demonstrated throughout this study that anisotropy may have an inverse relationship with frequency. The analysis presented in this paper complements the studied conducted by other researchers in this field of research
Synchronous malignant vagal paraganglioma with contralateral carotid body paraganglioma treated by radiation therapy
Paragangliomas are rare tumors and very few cases of malignant vagal paraganglioma with synchronous carotid body paraganglioma have been reported. We report a case of a 20-year old male who presented with slow growing bilateral neck masses of eight years duration. He had symptoms of dysphagia to solids, occasional mouth breathing and hoarseness of voice. Fine needle aspiration cytology (FNAC) performed where he lived showed a sinus histiocytosis and he was administered anti-tubercular treatment for six months without any improvement in his symptoms. His physical examination revealed pulsatile, soft to firm, non-tender swellings over the anterolateral neck confined to the upper-mid jugulo-diagastric region on both sides. Direct laryngoscopy examination revealed a bulge on the posterior pharyngeal wall and another over the right lateral pharyngeal wall. Magnetic resonance imaging (MRI), 99mTc-labeled octreotide scan and angiography diagnosed the swellings as carotid body paraganglioma, stage III on the right side with left-sided vagal malignant paraganglioma. Surgery was ruled out as a high morbidity with additional risk to life was expected due to the highly vascular nature of the tumor. The patient was treated with radiation therapy by image guided radiation to a dose of 5040cGy in 28 fractions. At a follow-up at 16 months, the tumors have regressed bilaterally and the patient can take solids with ease
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