2,415 research outputs found
Surface losses and self-pumping effects in a long Josephson junction - a semi-analytical approach
The flux-flow dynamics in a long Josephson junction is studied both
analytically and numerically. A realistic model of the junction is considered
by taking into account a nonuniform current distribution, surface losses and
self-pumping effects. An approximate analytical solution of the modified
sine-Gordon equation is derived in the form of a unidirectional dense fluxon
train accompanied by two oppositely directed plasma waves. Next, some
macroscopic time-averaged quantities are calculated making possible to evaluate
the current-voltage characteristic of the junction. The results obtained by the
present method are compared with direct numerical simulations both for the
current-voltage characteristics and for the loss factor modulated spatially due
to the self-pumping. The comparison shows very good agreement for typical
junction parameters but indicates also some limitations of the method.Comment: 7 pages, 5 figure
Effect of Axial Agitator Configuration (Up-Pumping, Down-Pumping, Reverse Rotation) on Flow Patterns Generated in Stirred Vessels
Single phase turbulent flow in a tank stirred with two different axial impellers - a pitched blade turbine
(PBT) and a Mixel TT (MTT)- has been studied using Laser Doppler Velocimetry. The effect of the
agitator configuration, i.e. up-pumping, down-pumping and reverse rotation, on the turbulent flow field,
as well as power, circulation and pumping numbers has been investigated. An agitation index for each
configuration was also determined. In the down-pumping mode, the impellers induced one circulation
loop and the upper part of the tank was poorly mixed. When up-pumping, two circulation loops are
formed, the second in the upper vessel. The PBT pumping upwards was observed to have a lower flow
number and to consume more power than when down-pumping, however the agitation index and
circulation efficiencies were notably higher. The MTT has been shown to circulate liquid more efficiently
in the up-pumping configuration than in the other two modes. Only small effects of the MTT
configuration on the power number, flow number and pumping effectiveness have been observed
Phonon driven spin distribution due to the spin-Seebeck effect
Here we report on measurements of the spin-Seebeck effect of GaMnAs over an
extended temperature range alongside the thermal conductivity, specific heat,
magnetization, and thermoelectric power. The amplitude of the spin-Seebeck
effect in GaMnAs scales with the thermal conductivity of the GaAs substrate and
the phonon-drag contribution to the thermoelectric power of the GaMnAs,
demonstrating that phonons drive the spin redistribution. A phenomenological
model involving phonon-magnon drag explains the spatial and temperature
dependence of the measured spin distribution.Comment: 12 pages, 3 figure
HOLLYWOOD:The political economy and global citation of an emblematic language object
The HOLLYWOOD sign is arguably the world's most famous language object. Emblematic of prestige and cultural capital, the sign can be found not just in Los Angeles, but in citations all over the world. Beginning with the history of its valorization, HOLLYWOOD is shown to emanate symbolic value through a set of enregistered semiotic features. Drawing upon a set of globally sourced citations of HOLLYWOOD, the circulation and stratified bundling of size, emplacement, alignment, typeface, and color indicates how the citation of language objects is mediated by political economy. A process of diffuse citation is further observed, in which the quotation of language features is not overt, but the source of emanation is still tangible, revealing HOLLYWOOD as the source of a global linguistic-semiotic register. As this register circulates in citations overt and diffuse, language objects are revealed as key sites for the reproduction of commodity values. (The Hollywood sign, language object, citation, enregisterment, global emblems, recontexualization)
Thermoacoustic refrigerator driven by a combustion-powered thermoacoustic engine - Demonstrator of device for rural areas of developing countries
This paper presents the design, construction and experimental evaluation of a demonstrator thermoacoustic refrigerator driven by a combustion-powered thermoacoustic engine. The system was developed to be a low-cost device for users based in remote and rural areas of developing countries. It employs a thermoacoustic engine/refrigerator coupling based on a travelling wave looped-tube configuration because of its relatively good thermal performance and construction simplicity. In the present demonstrator, a propane gas burner is used to simulate the thermal input from biomass combustion which is envisaged to be the source of energy for driving the system. Atmospheric air is applied as working fluid, while the operating frequency of the loop is 58.6 Hz. The location of the refrigerator is optimized experimentally to achieve the maximum cooling performance. So far, the lowest temperature achieved at the cold end of the regenerator is -3.6°C, while the maximum COPR achieved is 1.42%
Spatio-temporal structure of cell distribution in cortical Bone Multicellular Units: a mathematical model
Bone remodelling maintains the functionality of skeletal tissue by locally
coordinating bone-resorbing cells (osteoclasts) and bone-forming cells
(osteoblasts) in the form of Bone Multicellular Units (BMUs). Understanding the
emergence of such structured units out of the complex network of biochemical
interactions between bone cells is essential to extend our fundamental
knowledge of normal bone physiology and its disorders. To this end, we propose
a spatio-temporal continuum model that integrates some of the most important
interaction pathways currently known to exist between cells of the osteoblastic
and osteoclastic lineage. This mathematical model allows us to test the
significance and completeness of these pathways based on their ability to
reproduce the spatio-temporal dynamics of individual BMUs. We show that under
suitable conditions, the experimentally-observed structured cell distribution
of cortical BMUs is retrieved. The proposed model admits travelling-wave-like
solutions for the cell densities with tightly organised profiles, corresponding
to the progression of a single remodelling BMU. The shapes of these spatial
profiles within the travelling structure can be linked to the intrinsic
parameters of the model such as differentiation and apoptosis rates for bone
cells. In addition to the cell distribution, the spatial distribution of
regulatory factors can also be calculated. This provides new insights on how
different regulatory factors exert their action on bone cells leading to
cellular spatial and temporal segregation, and functional coordination.Comment: 14 pages, 5 figures; v2: Completed model description after Eq. (16),
clarified discussion/description after Eq. (23), between Eqs. (29)-(31), and
in 2nd bullet point in conclusion
TRÓJWYMIAROWA WIZUALIZACJA STRUKTUR PRZEPŁYWÓW DWUFAZOWYCH PRZY UŻYCIU ELEKTRYCZNEJ TOMOGRAFII POJEMNOŚCIOWEJ – ALGORYTMY I OPROGRAMOWANIE
This paper presents the software for comprehensive processing and visualization of 2D and 3D electrical tomography data. The system name as TomoKIS Studio has been developed in the frame of DENIDIA international research project and has been improved in the frame of Polish Ministry of Science and Higher Education Project no 4664/B/T02/2010/38. This software is worldwide unique because it simultaneously integrates the process of tomographic data acquisition, numerical FEM modeling and tomographic images reconstruction. The software can be adapted to specific industrial applications, particularly to monitoring and diagnosis of two-phase flows. The software architecture is composed of independent modules. Their combination offers calibration, configuration and full-duplex communication with any tomographic acquisition system with known and open communication protocol. The other major features are: online data acquisition and processing, online and offline 2D/3D images linear and nonlinear reconstruction and visualization as well as raw data and tomograms processing. Another important ability is 2D/3D ECT sensor construction using FEM modeling. The presented software is supported with the multi-core GPU technology and parallel computing using Nvidia CUDA technology.W artykule autorzy przedstawiają środowisko komputerowe do kompleksowego przetwarzania i wizualizacji tomograficznych danych pomiarowych. Oprogramowanie TomoKIS Studio powstało w Instytucie Informatyki Stosowanej PŁ w ramach projektu DENIDIA i zostało rozwinięte w ramach projektu MNiSW nr 4664/B/T02/2010/38. Zbudowane oprogramowanie jest unikalne w skali światowej, gdyż integruje w sobie proces pozyskiwania danych pomiarowych, modelowanie numeryczne oraz proces konstruowania obrazów tomograficznych, z możliwością adaptacji dla różnych aplikacji przemysłowych, w szczególności dla potrzeb monitorowania i diagnostyki przepływów dwufazowych gaz-ciecz. Architektura aplikacji oparta jest na zestawie niezależnych modułów, które pozwalają na w pełni dwukierunkową komunikacją, konfigurację oraz kalibrację dowolnego urządzenia tomografii elektrycznej z otwartym protokołem pomiarowym, akwizycję i przetwarzanie danych pomiarowych on-line, liniową oraz nieliniową rekonstrukcję obrazów 2D i 3D w czasie rzeczywistym, a także wizualizację surowych danych pomiarowych i tomogramów. Istotnym elementem systemu jest moduł numerycznego modelowania czujników pojemnościowych wykorzystujący metodę elementów skończonych, oparty na autorskich algorytmach generowania siatek MES komputerowych modeli czujników pojemnościowych. Architektura prezentowanego systemu została zaprojektowana przy użyciu obliczeń równoległych na procesorach graficznych, z wykorzystaniem technologii Nvidia CUDA
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