2,741 research outputs found
Recommended from our members
Absorption of spherical bubbles in a square microchannel
This paper was presented at the 4th Micro and Nano Flows Conference (MNF2014), which was held at University College, London, UK. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute, ASME Press, LCN London Centre for Nanotechnology, UCL University College London, UCL Engineering, the International NanoScience Community, www.nanopaprika.eu.Microfluidics is a fast growing field in which the manipulation of bubbles in liquid phase is of
utmost importance. In this paper, the absorption of spherical bubbles in a square microchannel is investigated
for a bubbly flow. Numerical simulations of the gas-liquid two-phase flow and the mass transfer around
spherical bubbles in a square microchannel are carried out. Correlations are established for the bubble
velocity and the mass transfer rate. A model for the dissolution of spherical bubbles along a square
microchannel is proposed in the case of the bubbly flow regime and validated using existing experimental
data. This model can be used, for instance, for designing microabsorbers for lab-on-a-chip applications
Reconstruction of Rb-Rb inter-atomic potential from ultracold Bose-gas collision
Scattering phase shifts obtained from 87Rb Bose-gas collision experiments are
used to reconstruct effective potentials resulting, self-consistently, in the
same scattering events observed in the experiments at a particular energy. We
have found that the interaction strength close to the origin suddenly changes
from repulsion to attraction when the collision energy crosses, from below, the
l=2 shape resonance position at E = 275 mikroK. This observation may be
utilized in outlining future Bose-gas collision experiments.Comment: 4 pages, 4 figure
A combined FEG-SEM and TEM study of silicon nanodot assembly
Nanodots forming dense assembly on a substrate are difficult to characterize in terms of size, density, morphology and cristallinity. The present study shows how valuable information can be obtained by a combination of electron microscopy techniques. A silicon nanodots deposit has been studied by Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) to estimate essentially the dot size and density, quantities emphasized because of their high interest for application. High resolution SEM indicates a density of 1.6 × 1012 dots/cm2 for a 5 nm to 10 nm dot size. TEM imaging using a phase retrieval treatment of a focus series gives a higher dot density (2 × 1012 dots/cm2) for a 5 nm dot size. High Resolution Transmission Electron Microscopy (HRTEM) indicates that the dots are crystalline which is confirmed by electron diffraction. According to HRTEM and electron diffraction, the dot size is about 3 nm which is significantly smaller than the SEM and TEM results. These differences are not contradictory but attributed to the fact that each technique is probing a different phenomenon. A core-shell structure for the dot is proposed which reconcile all the results. All along the study, Fourier transforms have been widely used under many aspects
The valuation of European financial firms
We extend the recent literature concerning accounting based valuation models to investigate financial firms from six European countries with substantial financial sectors: France, Germany, Italy, Netherlands, Switzerland and the UK. Not only are these crucial industries worthy of study in their own right, but unusual accounting practices, and inter-country differences in those accounting practices, provide valuable insights into the accounting-value relationship. Our sample consists of 7,714 financial firm/years observations from 1,140 companies drawn from 1989-2000. Sub-samples include 1,309 firm/years for banks, 650 for insurance companies, 1,705 for real estate firms, and 3,239 for investment companies. In most countries we find that the valuation models work as well or better in explaining cross-sectional variations in the market-to-book ratio for financial firms as they do for industrial and commercial firms in the same countries, although Switzerland is an exception to this generalization. As expected, the results are sensitive to industrial differences, accounting regulation and accounting practices. In particular, marking assets to market value reduces the relevance of earnings figures and increases that of equity
Flexible structure control laboratory development and technology demonstration
An experimental structure is described which was constructed to demonstrate and validate recent emerging technologies in the active control and identification of large flexible space structures. The configuration consists of a large, 20 foot diameter antenna-like flexible structure in the horizontal plane with a gimballed central hub, a flexible feed-boom assembly hanging from the hub, and 12 flexible ribs radiating outward. Fourteen electrodynamic force actuators mounted to the hub and to the individual ribs provide the means to excite the structure and exert control forces. Thirty permanently mounted sensors, including optical encoders and analog induction devices provide measurements of structural response at widely distributed points. An experimental remote optical sensor provides sixteen additional sensing channels. A computer samples the sensors, computes the control updates and sends commands to the actuators in real time, while simultaneously displaying selected outputs on a graphics terminal and saving them in memory. Several control experiments were conducted thus far and are documented. These include implementation of distributed parameter system control, model reference adaptive control, and static shape control. These experiments have demonstrated the successful implementation of state-of-the-art control approaches using actual hardware
Emission of charged particles from excited compound nuclei
The formation of excited compound nucleus (CN) and its statistical decay is
investigated within the dinuclear system (DNS) model.The initial DNS is formed
in the entrance channel when the projectile is captured by a target, and then
the evolution of DNS in mass asymmetry coordinate leads to formation of the hot
CN. The emission barriers for complex fragments were calculated within the DNS
model by using the double folding procedure for the interaction potential. It
is shown that cross sections for complex fragment emission become larger when
excited CN is more neutron deficient. This approach gives also an opportunity
to calculate the new neutron deficient isotopes production cross sections and
can be applied to describe the hot fission of heavy systems.The model was
tested by comparison of calculated results with experimental dat
Magnetic-field dependence of transport in normal and Andreev billiards: a classical interpretation to the averaged quantum behavior
We perform a comparative study of the quantum and classical transport
probabilities of low-energy quasiparticles ballistically traversing normal and
Andreev two-dimensional open cavities with a Sinai-billiard shape. We focus on
the dependence of the transport on the strength of an applied magnetic field
. With increasing field strength the classical dynamics changes from mixed
to regular phase space. Averaging out the quantum fluctuations, we find an
excellent agreement between the quantum and classical transport coefficients in
the complete range of field strengths. This allows an overall description of
the non-monotonic behavior of the average magnetoconductance in terms of the
corresponding classical trajectories, thus, establishing a basic tool useful in
the design and analysis of experiments.Comment: 11 pages, 12 figures; minor revisions including updated inset of Fig.
4(b) and references; version as accepted for publication to Phys. Rev.
Extracting current-induced spins: spin boundary conditions at narrow Hall contacts
We consider the possibility to extract spins that are generated by an
electric current in a two-dimensional electron gas with Rashba-Dresselhaus
spin-orbit interaction (R2DEG) in the Hall geometry. To this end, we discuss
boundary conditions for the spin accumulations between a spin-orbit coupled
region and contact without spin-orbit coupling, i.e. a normal two-dimensional
electron gas (2DEG). We demonstrate that in contrast to contacts that extend
along the whole sample, a spin accumulation can diffuse into the normal region
through finite contacts and detected by e.g. ferromagnets. For an
impedance-matched narrow contact the spin accumulation in the 2DEG is equal to
the current induced spin accumulation in the bulk of R2DEG up to a
geometry-dependent numerical factor.Comment: 18 pages, 7 figures, submitted to NJP focus issue on Spintronic
- …