5,182 research outputs found
Transient Marangoni convection in hanging evaporating drops
Abstract. A combined experimental and numerical analysis has been carried out to study Marangoni effects during the evaporation of droplets. The experiments are performed with pendant drops of silicone oils (with different viscosities) and hydrocarbons. The temperature of the disk sustaining the drop is rapidly increased or decreased in order to study transient heating or cooling processes. The velocity field in the droplet is evaluated monitoring the motion of tracers in the meridian plane, using a laser sheet illumination system and a video camera. Surface temperature distributions of the drops are detected by infrared thermocamera. The numerical model is based on axisymmetric Navier-Stokes equations, taking into account the presence of Marangoni shear stresses and evaporative cooling at the liquid-air interface. Marangoni flows cause a larger, more uniform surface temperature, increasing heat transfer from disk to droplet, as well as evaporation rate. When Marangoni effects are negligible, larger surface temperature differences occur along the drop surface and heat transfer is relatively small. The role of Marangoni and buoyancy flows in silicone oils with different viscosities and hydrocarbons is discussed and correlations are presented between experimental and numerical results.
Keywords: Viscosity of liquids; diffusive momentum transport, Evaporation and condensation, Surface tension and related phenomena, Flows in ducts, channels, nozzles, and conduit
Improving Table Compression with Combinatorial Optimization
We study the problem of compressing massive tables within the
partition-training paradigm introduced by Buchsbaum et al. [SODA'00], in which
a table is partitioned by an off-line training procedure into disjoint
intervals of columns, each of which is compressed separately by a standard,
on-line compressor like gzip. We provide a new theory that unifies previous
experimental observations on partitioning and heuristic observations on column
permutation, all of which are used to improve compression rates. Based on the
theory, we devise the first on-line training algorithms for table compression,
which can be applied to individual files, not just continuously operating
sources; and also a new, off-line training algorithm, based on a link to the
asymmetric traveling salesman problem, which improves on prior work by
rearranging columns prior to partitioning. We demonstrate these results
experimentally. On various test files, the on-line algorithms provide 35-55%
improvement over gzip with negligible slowdown; the off-line reordering
provides up to 20% further improvement over partitioning alone. We also show
that a variation of the table compression problem is MAX-SNP hard.Comment: 22 pages, 2 figures, 5 tables, 23 references. Extended abstract
appears in Proc. 13th ACM-SIAM SODA, pp. 213-222, 200
Environment induced incoherent controllability
We prove that the environment induced entanglement between two non
interacting, two-dimensional quantum systems S and P can be used to control the
dynamics of S by means of the initial state of P. Using a simple, exactly
solvable model, we show that both accessibility and controllability of S can be
achieved under suitable conditions on the interaction of S and P with the
environment.Comment: revtex4, 5 page
Quantum and Superquantum Nonlocal Correlations
We present a simple hidden variable model for the singlet state of a pair of
qubits, characterized by two kinds, hierarchically ordered, of hidden
variables. We prove that, averaging over both types of variables, one
reproduces all the quantum mechanical correlations of the singlet state. On the
other hand, averaging only over the hidden variables of the lower level, one
obtains a general formal theoretical scheme exhibiting correlations stronger
than the quantum ones, but with faster-than-light communication forbidden. This
result is interesting by itself since it shows that a violation of the quantum
bound for nonlocal correlations can be implemented in a precise physical manner
and not only mathematically, and it suggests that resorting to two levels of
nonlocal hidden variables might led to a deeper understanding of the physical
principles at the basis of quantum nonlocality.Comment: 5 pages, 1 figure. Submitted for publicatio
A general hidden variable model for the two-qubits system
We generalize Bell's hidden variable model describing the singlet state of a
two-qubits system by extending it to arbitrary states and observables. As in
the original work, we assume a uniform, state-independent probability
distribution for the hidden variables which are identified with the unit
vectors of a 3-dimensional real space. By slightly modifying our model, we
provide also a minimal hidden variable description of the two-qubits system,
relying on a single hidden variable. We discuss the main features and the
implications of the model.Comment: 4 pages, submitted for publicatio
Decompositions of unitary evolutions and entanglement dynamics of bipartite quantum systems
We describe a decomposition of the Lie group of unitary evolutions for a
bipartite quantum system of arbitrary dimensions. The decomposition is based on
a recursive procedure which systematically uses the Cartan classification of
the symmetric spaces of the Lie group SO(n). The resulting factorization of
unitary evolutions clearly displays the local and entangling character of each
factor.Comment: 11 pages, revtex
Corporate amnesia in the micro business environment
Corporate amnesia is a phenomenon that has persistently threatened the livelihood of business organizations and their success in commercial activity. Several substantial studies on this observable fact have been undertaken with focus primarily aimed at the large corporations and the small to medium sized organizations. This vulnerability is however evermore present and significant within the smaller of businesses. In the micro enterprise, the impact of corporate amnesia is realized when even a single member of staff is absent for any lengthy period of time or vacates their post altogether. With more than 80% of the workforce in the US and separately in the UK directly engaged within a micro enterprise, the competitive benefits that can potentially be realized by addressing corporate amnesia is significant. This paper will identify the main causes of corporate amnesia within the micro business environment and propose a suitable framework for the enterprise to effectively facilitate the adoption of Knowledge Management and realize the associated competitive benefits
Buoyancy and surface tension-driven convection around a bubble
A combined experimental and numerical analysis has been carried out to study the behavior of a bubble under a horizontal heated surface. In this configuration, the interaction between buoyancy and surface tension driven convection produces complex fluid dynamic structures. An instability occurs in the form of an oscillatory three-dimensional fluctuation of the thermal and velocity field when a critical temperature difference is exceeded. The structure of this flow regime has been investigated with transient three-dimensional simulations carried out for normal gravity and zero gravity conditions. The velocity field around the bubble has been experimentally analyzed with a ``laser sheet'' technique for the flow visualization and a Wollaston prism interferometer has been utilized to capture the oscillatory temperature field. Good correlations are shown between experimental and numerical results.
Keywords: Thermal convection, Buoyancy-driven instabilities, Surface-tension-driven instability, Interaction
Gravitational Instantons and Fluxes from M/F-theory on Calabi-Yau fourfolds
We compactify four-dimensional N=1 gauged supergravity theories on a circle
including fluxes for shift-symmetric scalars. Four-dimensional Taub-NUT
gravitational instantons universally correct the three-dimensional
superpotential in the absence of fluxes. In the presence of fluxes these
Taub-NUT instanton contributions are no longer gauge-invariant. Invariance can
be restored by gauge instantons on top of Taub-NUT instantons. We establish the
embedding of this scenario into M-theory. Circle fluxes and gaugings arise from
a restricted class of M-theory four-form fluxes on a resolved Calabi-Yau
fourfold. The M5-brane on the base of the elliptic fourfold dualizes into the
universal Taub-NUT instanton. In the presence of fluxes this M5-brane is
anomalous. We argue that anomaly free contributions arise from involved
M5-brane geometries dual to gauge-instantons on top of Taub-NUT instantons.
Adding a four-dimensional superpotential to the gravitational instanton
corrections leads to three-dimensional Anti-de Sitter vacua at stabilized
compactification radius. We comment on the possibility to uplift these M-theory
vacua, and to tunnel to four-dimensional F-theory vacua.Comment: 47 pages, 2 figure
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