1,006 research outputs found
Maxwell stress in fluid mixtures
We examine the structure of Maxwell stress in binary fluid mixtures under an
external electric field and discuss its consequence. In particular, we show
that, in immiscible blends, it is intimately related to the statistics of
domain structure. This leads to a compact formula, which may be useful in the
investigation of electro-rheological effects in such systems. The stress tensor
calculated in a phase separated fluid under a steady electric field is in a
good agreement with recent experiments.Comment: 5 page
Nonlinear dynamics of the interface of dielectric liquids in a strong electric field: Reduced equations of motion
The evolution of the interface between two ideal dielectric liquids in a
strong vertical electric field is studied. It is found that a particular flow
regime, for which the velocity potential and the electric field potential are
linearly dependent functions, is possible if the ratio of the permittivities of
liquids is inversely proportional to the ratio of their densities. The
corresponding reduced equations for interface motion are derived. In the limit
of small density ratio, these equations coincide with the well-known equations
describing the Laplacian growth.Comment: 10 page
Advances in Non-Contact Thermal-Wave Imaging with Infrared Detection
We are making further advances in non-destructive and non-contact thermal imaging with infrared detection. We employ a chopped and scanned electron beam as heat source, a cooled HgCdTe infrared detector as temperature sensor, and digital processing of the measured temperature pattern for display and storage. The results give a convincing, high contrast image of subsurface structures
Nonlinear Stability of Static N\'eel Walls in Ferromagnetic Thin Films
In this paper, the nonlinear (orbital) stability of static 180^\circ N\'eel
walls in ferromagnetic films, under the reduced wave-type dynamics for the
in-plane magnetization proposed by Capella, Melcher and Otto [CMO07], is
established. It is proved that the spectrum of the linearized operator around
the static N\'eel wall lies in the stable complex half plane with non-positive
real part. This information is used to show that small perturbations of the
static N\'eel wall converge to a translated orbit belonging to the manifold
generated by the static wall.Comment: 45 page
DC-conductivity of a suspension of insulating particles with internal rotation
We analyse the consequences of Quincke rotation on the conductivity of a
suspension. Quincke rotation refers to the spontaneous rotation of insulating
particles dispersed in a slightly conducting liquid and subject to a high DC
electric field: above a critical field, each particle rotates continuously
around itself with an axis pointing in any direction perpendicular to the DC
field. When the suspension is subject to an electric field lower than the
threshold one, the presence of insulating particles in the host liquid
decreases the bulk conductivity since the particles form obstacles to ion
migration. But for electric fields higher than the critical one, the particles
rotate and facilitate ion migration: the effective conductivity of the
suspension is increased. We provide a theoretical analysis of the impact of
Quincke rotation on the apparent conductivity of a suspension and we present
experimental results obtained with a suspension of PMMA particles dispersed in
weakly conducting liquids
Photostimulated Luminescence and Thermoluminescence of LSO Scintillators
Photostimulated luminescence (PSL) and thermoluminescence (TL) from five Lu_(2(1-x/)Ce)_(2x)/(SiO_4)O (LSO) crystals with different light outputs is reported. Optical irradiation into the Ce^(3+) absorption bands causes the appearance of a broad absorption band near 280 nn which is ascribed to Ce^(4+). In addition, a tail is observed extending beyond 700 nm. Optical irradiation into this tail (PSL) or heating of the crystal (TL) results in Ce^(3+) emission. It is shown that both PSL and TL are due to the same traps: In addition, an anti-correlation is found between the light output under gamma-ray irradiation and the trap concentration in the crystal. The nature of the recombination centers responsible for the low light output in some crystals is not clear. Annealing experiments suggest that the traps and the recombination centers may be related to oxygen vacancies
Photostimulated Luminescence and Thermoluminescence of LSO Scintillators
Photostimulated luminescence (PSL) and thermoluminescence (TL) from five Lu_(2(1-x))Ce_(2x)(SiO_4)O (LSO) crystals with different light outputs is reported. Optical irradiation into the Ce^(3+) absorption bands causes the appearance of a broad absorption band near 280 nm which is ascribed to Ce^(4+). In addition, a tail is observed extending beyond 700 nm. Optical irradiation into this tail (PSL) or heating of the crystal (TL) results in Ce^(3+) emission. It is shown that both PSL and TL are due to the same traps: In addition, an anti-correlation is found between the light output under gamma-ray irradiation and the trap concentration in the crystal. The nature of the recombination centers responsible for the low light output in some crystals is not clear. Annealing experiments suggest that the traps and the recombination centers may be related to oxygen vacancies
Cold Helium Pressurization for Liquid Oxygen / Liquid Methane Propulsion Systems: Fully-Integrated Initial Hot-Fire Test Results
A prototype cold helium active pressurization system was incorporated into an existing liquid oxygen (LOX) / liquid methane (LCH4) prototype planetary lander and hot-fire tested to collect vehicle-level performance data. Results from this hot-fire test series were used to validate integrated models of the vehicle helium and propulsion systems and demonstrate system effectiveness for a throttling lander. Pressurization systems vary greatly in complexity and efficiency between vehicles, so a pressurization performance metric was also developed as a means to compare different active pressurization schemes. This implementation of an active repress system is an initial sizing draft. Refined implementations will be tested in the future, improving the general knowledge base for a cryogenic lander-based cold helium system
In-depth description of Electrohydrodynamic conduction pumping of dielectric liquids: physical model and regime analysis
In this work, we discuss the fundamental aspects of Electrohydrodynamic (EHD) conduction pumping of dielectric liquids. We build a mathematical model of conduction pumping that can be applied to all sizes, down to microsized pumps. In order to do this, we discuss the relevance of the Electrical Double Layer (EDL) that appears naturally on nonmetallic substrates. In the process, we identify a new dimensionless parameter related to the value of the zeta potential of the substrate-liquid pair, which quantifies the influence of these EDLs on the performance of the pump. This parameter also describes the transition from EHD conduction pumping to electro-osmosis. We also discuss in detail the two limiting working regimes in EHD conduction pumping: ohmic and saturation. We introduce a new dimensionless parameter, accounting for the electric field enhanced dissociation that, along with the conduction number, allows us to identify in which regime the pump operates.Ministerio de Ciencia, Innovación y Universidades PGC2018-099217-B-I0
Geometrical quadrupolar frustration in DyB
Physical properties of DyB have been studied by magnetization, specific
heat, and ultrasonic measurements. The magnetic entropy change and the
ultrasonic properties in the intermediate phase II indicate that the degeneracy
of internal degrees of freedom is not fully lifted in spite of the formation of
magnetic order. The ultrasonic attenuation and the huge softening of
in phase II suggests existence of electric-quadrupolar (orbital) fluctuations
of the 4-electron. These unusual properties originate from the geometrical
quadrupolar frustration.Comment: 4 pages, 4 figures, accepted for publication in Journal of the
Physical Society of Japa
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