11,688 research outputs found
Suspension flow: do particles act as mixers?
Recently, Roht et al. [J. Contam. Hydrol. 145, 10-16 (2013)] observed that
the presence of suspended non-Brownian macroscopic particles decreased the
dispersivity of a passive solute, for a pressure-driven flow in a narrow
parallel-plates channel at low Reynolds number. This result contradicts the
idea that the streamline distortion caused by the random diffusive motion of
the particles increases the dispersion and mixing of the solute. Therefore, to
estimate the influence of this motion on the dispersivity of the solute, and
investigate the origin of the reported decrease, we experimentally studied the
probability density functions (pdf) of the particle velocities, and
spatio-temporal correlations, in the same experimental configuration. We
observed that, as the mean suspension velocity exceeds a critical value, the
pdf of the streamwise velocities of the particles markedly changes from a
symmetric distribution to an asymmetric one strongly skewed to high velocities
and with a peak of most probable velocity close to the maximum velocity. The
latter observations and the analysis of suspension microstructure indicate that
the observed decrease in the dispersivity of the solute is due to particle
migration to the mid-plane of the channel, and consequent flattening of the
velocity profile. Moreover, we estimated the contribution of particle diffusive
motion to the solute dispersivity to be three orders of magnitude smaller than
the reported decrease, and thus negligible. Solute dispersion is then much more
affected by how particles modify the flow velocity profile across the channel,
than by their diffusive random motion
Method for analyzing radiation sensitivity of integrated circuits
A method for analyzing the radiation sensitivity of an integrated circuit is described to determine the components. The application of a narrow radiation beam to portions of the circuit is considered. The circuit is operated under normal bias conditions during the application of radiation in a dosage that is likely to cause malfunction of at least some transistors, while the circuit is monitored for failure of the irradiated transistor. When a radiation sensitive transistor is found, then the radiation beam is further narrowed and, using a fresh integrated circuit, a very narrow beam is applied to different parts of the transistor, such as its junctions, to locate the points of greatest sensitivity
Credit default swaps and financial stability: risks and regulatory issues.
The credit default swap (CDS) market has grown much faster than other derivatives markets since its inception. Even though it is dwarfed by the interest rate derivatives market, which is eight times larger, its growth has affected the stability of the financial system. CDS were originally designed as a risk transfer tool to allow investors to hedge their position in the debt of a reference entity, but much of the activity in this market is also speculative (Olléon-Assouan, 2004). Risk management in the CDS market has certainly improved significantly, reflected in the fact that gross notional volumes have fallen remarkably as a result of trade compression. Nevertheless there is still no accurate indication of how much risk has actually been transferred with these instruments, and this is a major concern for financial stability. Even a rough estimate of market size ranges from USD 29 trillion to USD 38 trillion at end-2008. Clarifying and harmonising information is vitally important, particularly since the uncertainty surrounding market participants’ risk exposure contains the seeds of systemic contagion. There is now a pressing need for better market supervision based on the active participation of regulators. The task has already been made easier by a number of public and private initiatives aimed at improving the functioning of the market and monitoring risks more effectively. The most tangible evidence of these combined efforts can be found in various plans for a clearinghouse that emerged in 2008 and 2009. Aside from its practical limitations, however, this solution cannot be extended to all CDS classes. And regulators still face the sizeable challenge of assessing overall counterparty risk on the CDS market and preventing concentration and formation of systemic exposures.
Velocity fluctuations and population distribution in clusters of settling particles at low Reynolds number
A study on the spatial organization and velocity fluctuations of non Brownian
spherical particles settling at low Reynolds number in a vertical Hele-Shaw
cell is reported. The particle volume fraction ranged from 0.005 to 0.05, while
the distance between cell plates ranged from 5 to 15 times the particle radius.
Particle tracking revealed that particles were not uniformly distributed in
space but assembled in transient settling clusters. The population distribution
of these clusters followed an exponential law. The measured velocity
fluctuations are in agreement with that predicted theoretically for spherical
clusters, from the balance between the apparent weight and the drag force. This
result suggests that particle clustering, more than a spatial distribution of
particles derived from random and independent events, is at the origin of the
velocity fluctuations.Comment: 13 pages, 8 figure
High-order optical nonlinearity at low light levels
We observe a nonlinear optical process in a gas of cold atoms that
simultaneously displays the largest reported fifth-order nonlinear
susceptibility \chi^(5) = 1.9x10^{-12} (m/V)^4 and high transparency. The
nonlinearity results from the simultaneous cooling and crystallization of the
gas, and gives rise to efficient Bragg scattering in the form of
six-wave-mixing at low-light-levels. For large atom-photon coupling strengths,
the back-action of the scattered fields influences the light-matter dynamics.
This system may have important applications in many-body physics, quantum
information processing, and multidimensional soliton formation.Comment: 5 pages, 3 figure
Total integrated dose testing of solid-state scientific CD4011, CD4013, and CD4060 devices by irradiation with CO-60 gamma rays
The total integrated dose response of three CMOS devices manufactured by Solid State Scientific has been measured using CO-60 gamma rays. Key parameter measurements were made and compared for each device type. The data show that the CD4011, CD4013, and CD4060 produced by this manufacturers should not be used in any environments where radiation levels might exceed 1,000 rad(Si)
Evidence for spin liquid ground state in SrDyO frustrated magnet probed by muSR
Muon spin relaxation (SR) measurements were carried out on
SrDyO, a frustrated magnet featuring short range magnetic correlations
at low temperatures. Zero-field muon spin depolarization measurements
demonstrate that fast magnetic fluctuations are present from K down to
20 mK. The coexistence of short range magnetic correlations and fluctuations at
mK indicates that SrDyO features a spin liquid ground state.
Large longitudinal fields affect weakly the muon spin depolarization, also
suggesting the presence of fast fluctuations. For a longitudinal field of
T, a non-relaxing asymmetry contribution appears below K,
indicating considerable slowing down of the magnetic fluctuations as
field-induced magnetically-ordered phases are approached.Comment: 6 pages, 4 figures, to be published as a proceeding of HFM2016 in
Journal of Physics: Conference Series (JPCS
All-Optical Switching with Transverse Optical Patterns
We demonstrate an all-optical switch that operates at ultra-low-light levels
and exhibits several features necessary for use in optical switching networks.
An input switching beam, wavelength , with an energy density of
photons per optical cross section [] changes
the orientation of a two-spot pattern generated via parametric instability in
warm rubidium vapor. The instability is induced with less than 1 mW of total
pump power and generates several Ws of output light. The switch is
cascadable: the device output is capable of driving multiple inputs, and
exhibits transistor-like signal-level restoration with both saturated and
intermediate response regimes. Additionally, the system requires an input power
proportional to the inverse of the response time, which suggests thermal
dissipation does not necessarily limit the practicality of optical logic
devices
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