874 research outputs found
Instabilities and Spatio-temporal Chaos of Long-wave Hexagon Patterns in Rotating Marangoni Convection
We consider surface-tension driven convection in a rotating fluid layer. For
nearly insulating boundary conditions we derive a long-wave equation for the
convection planform. Using a Galerkin method and direct numerical simulations
we study the stability of the steady hexagonal patterns with respect to general
side-band instabilities. In the presence of rotation steady and oscillatory
instabilities are identified. One of them leads to stable, homogeneously
oscillating hexagons. For sufficiently large rotation rates the stability
balloon closes, rendering all steady hexagons unstable and leading to
spatio-temporal chaos.Comment: 26 pages, 9 jpeg figures. Postscript file with all figures included
available at http://www.esam.northwestern.edu/~riecke/lit/lit.html Movies
available at
http://www.esam.northwestern.edu/~riecke/research/Marangoni/marangoni.htm
Surface pinning in amorphous ZrTiCuNiBe alloy
We have measured the amplitude and the phase of an electromagnetic (EM) field
radiated from superconductor (amorphous ZrTiCuNiBe alloy) in the mixed state
due to interaction of the flux lattice with an elastic wave. The results
undoubtedly point to an essential contribution of a surface pinning into the
flux lattice dynamics. We propose a model that describes radiation of EM field
from superconductors with non-uniform pinning. The model allows to reconstruct
the viscosity and the Labush parameters from the experimental data. The
behavior of the Labush parameter can be qualitatively explained in terms of the
collective pinning theory with the allowance of thermal fluctuations.Comment: 4 pages, 4 figure
Magnus force and acoustic Stewart-Tolman effect in type II superconductors
At zero magnetic field we have observed an electromagnetic radiation from
superconductors subjected by a transverse elastic wave. This radiation has an
inertial origin, and is a manifestation of the acoustic Stewart-Tolman effect.
The effect is used for implementing a method of measurement of an effective
Magnus force in type II superconductors. The method does not require the flux
flow regime and allows to investigate this force for almost the whole range of
the existence of the mixed state. We have studied behavior of the gyroscopic
force in nonmagnetic borocarbides and Nb. It is found that in borocarbides the
sign of the gyroscopic force in the mixed state is the same as in the normal
state, and its value (counted for one vortex of unit length) has only a weak
dependence on the magnetic field. In Nb the change of sign of the gyroscopic
force under the transition from the normal to the mixed state is observed.Comment: 4 pages, 5 figure
Low-temperature acoustic characteristics of the amorphous alloy Zr41.2Ti13.8Cu12.5Ni10Be22.5
The temperature dependences of the sound velocity v and attenuation alpha of high-frequency (50–160 MHz) sound in the bulk amorphous alloy Zr41.2Ti13.8Cu12.5Ni10Be22.5 are studied at helium temperatures in the normal and superconducting states. The alloy is characterized by a relatively small constant C determining the intensity of interaction between an elastic wave and two-level systems. The density of states of the latter systems is estimated. The peculiarities in the variation of v during the superconducting transition point to the possibility of a gapless superconductivity in a narrow temperature interval near Tc
Non-dissipative drag of superflow in a two-component Bose gas
A microscopic theory of a non-dissipative drag in a two-component superfluid
Bose gas is developed. The expression for the drag current in the system with
the components of different atomic masses, densities and scattering lengths is
derived. It is shown that the drag current is proportional to the square root
of the gas parameter. The temperature dependence of the drag current is studied
and it is shown that at temperature of order or smaller than the interaction
energy the temperature reduction of the drag current is rather small. A
possible way of measuring the drag factor is proposed. A toroidal system with
the drag component confined in two half-ring wells separated by two Josephson
barriers is considered. Under certain condition such a system can be treated as
a Bose-Einstein counterpart of the Josephson charge qubit in an external
magnetic field. It is shown that the measurement of the difference of number of
atoms in two wells under a controlled evolution of the state of the qubit
allows to determine the drag factor.Comment: 13 pages, 3 figures. This preprint is extended and substantially
revised variant of related preprint cond-mat/040456
Scaling up social businesses in developing markets
Most of the world's poor live in developing markets and face unmet needs in core areas such as education, health, energy, sanitation and financial services. This offers businesses a vast opportunity for growth as these economies emerge from low-income to middle-income status. Social businesses in particular address a social need while generating profits typically reinvested into the business itself, but there is limited understanding of the ways through which social businesses achieve scale. This paper investigates how social businesses can scale up. First, we define scaling up as “increasing the number of customers or members of a business as well as expanding its offer and maximising its revenues until it reaches millions of people.” Second, using three in-depth case studies of social businesses that successfully scaled up according to these definitions, BRAC, Aravind and Amul, we identify scaling up strategies for social businesses. We identified market penetration, market development, product development and diversification as key strategies at different stages of business maturity. We find that there are two ways of increasing income generated that are linked to these four strategies: increasing revenue per stream and diversifying revenue streams. Our findings give insight to companies aiming to pursue social businesses and adds to the sparse literature on scaling up social businesses. A fruitful future research avenue would be to investigate the best sequence for applying these scaling strategies across companies and sectors over time
Novel inferences of ionisation & recombination for particle/power balance during detached discharges using deuterium Balmer line spectroscopy
The physics of divertor detachment is determined by divertor power, particle
and momentum balance. This work provides a novel analysis technique of the
Balmer line series to obtain a full particle/power balance measurement of the
divertor. This supplies new information to understand what controls the
divertor target ion flux during detachment.
Atomic deuterium excitation emission is separated from recombination
quantitatively using Balmer series line ratios. This enables analysing those
two components individually, providing ionisation/recombination source/sinks
and hydrogenic power loss measurements. Probabilistic Monte Carlo techniques
were employed to obtain full error propagation - eventually resulting in
probability density functions for each output variable. Both local and overall
particle and power balance in the divertor are then obtained. These techniques
and their assumptions have been verified by comparing the analysed synthetic
diagnostic 'measurements' obtained from SOLPS simulation results for the same
discharge. Power/particle balance measurements have been obtained during
attached and detached conditions on the TCV tokamak.Comment: The analysis results of this paper were formerly in arXiv:1810.0496
Drag of superfluid current in bilayer Bose systems
An effect of nondissipative drag of a superfluid flow in a system of two Bose
gases confined in two parallel quasi two-dimensional traps is studied. Using an
approach based on introduction of density and phase operators we compute the
drag current at zero and finite temperatures for arbitrary ratio of densities
of the particles in the adjacent layers. We demonstrate that in a system of two
ring-shape traps the "drag force" influences on the drag trap in the same way
as an external magnetic flux influences on a superconducting ring. It allows to
use the drag effect to control persistent current states in superfluids and
opens a possibility for implementing a Bose analog of the superconducting
Josephson flux qubit.Comment: 12 pages, 2 figures, new section is added, refs are adde
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