492 research outputs found
Hypothetical Reasoning via Provenance Abstraction
Data analytics often involves hypothetical reasoning: repeatedly modifying
the data and observing the induced effect on the computation result of a
data-centric application. Previous work has shown that fine-grained data
provenance can help make such an analysis more efficient: instead of a costly
re-execution of the underlying application, hypothetical scenarios are applied
to a pre-computed provenance expression. However, storing provenance for
complex queries and large-scale data leads to a significant overhead, which is
often a barrier to the incorporation of provenance-based solutions.
To this end, we present a framework that allows to reduce provenance size.
Our approach is based on reducing the provenance granularity using user defined
abstraction trees over the provenance variables; the granularity is based on
the anticipated hypothetical scenarios. We formalize the tradeoff between
provenance size and supported granularity of the hypothetical reasoning, and
study the complexity of the resulting optimization problem, provide efficient
algorithms for tractable cases and heuristics for others. We experimentally
study the performance of our solution for various queries and abstraction
trees. Our study shows that the algorithms generally lead to substantial
speedup of hypothetical reasoning, with a reasonable loss of accuracy
Hawking Radiation on an Ion Ring in the Quantum Regime
This paper discusses a recent proposal for the simulation of acoustic black
holes with ions. The ions are rotating on a ring with an inhomogeneous, but
stationary velocity profile. Phonons cannot leave a region, in which the ion
velocity exceeds the group velocity of the phonons, as light cannot escape from
a black hole. The system is described by a discrete field theory with a
nonlinear dispersion relation. Hawking radiation is emitted by this acoustic
black hole, generating entanglement between the inside and the outside of the
black hole. We study schemes to detect the Hawking effect in this setup.Comment: 42 pages (one column), 17 figures, published revised versio
On Multipartite Pure-State Entanglement
We show that pure states of multipartite quantum systems are multiseparable
(i.e. give separable density matrices on tracing any party) if and only if they
have a generalized Schmidt decomposition. Implications of this result for the
quantification of multipartite pure-state entanglement are discussed. Further,
as an application of the techniques used here, we show that any purification of
a bipartite PPT bound entangled state is tri-inseparable, i.e. has none of its
three bipartite partial traces separable.Comment: 8 Pages ReVTeX, 4 figures (eps); v2: Revised terminology, added two
references and other minor changes; v3: Minor changes, added two references,
added author's middle initial; v4: One footnote remove
Astrometric Control of the Inertiality of the Hipparcos Catalog
Based on the most complete list of the results of an individual comparison of
the proper motions for stars of various programs common to the Hipparcos
catalog, each of which is an independent realization of the inertial reference
frame with regard to stellar proper motions, we redetermined the vector
of residual rotation of the ICRS system relative to the extragalactic
reference frame. The equatorial components of this vector were found to be the
following: mas yr,
mas yr, and mas yr.Comment: 8 pages, 1 figur
NMR Simulation of an Eight-State Quantum System
The propagation of excitation along a one-dimensional chain of atoms is
simulated by means of NMR. The physical system used as an analog quantum
computer is a nucleus of 133-Cs (spin 7/2) in a liquid crystalline matrix. The
Hamiltonian of migration is simulated by using a special 7-frequency pulse, and
the dynamics is monitored by following the transfer of population from one of
the 8 spin energy levels to the other.Comment: 10 pages, 3 figure
Xenohormone transactivities are inversely associated to serum POPs in Inuit
This is an Open Access article distributed under the terms of the Creative Commons Attribution Licens
AhR transcriptional activity in serum of Inuits across Greenlandic districts
<p>Abstract</p> <p>Background</p> <p>Human exposure to lipophilic persistent organic pollutants (POPs) including polychlorinated dibenzo-<it>p</it>-dioxins/furans (PCDDs/PCDFs), polychlorinated biphenyls (PCBs) and organochlorine pesticide is ubiquitous. The individual is exposed to a complex mixture of POPs being life-long beginning during critical developmental windows. Exposure to POPs elicits a number of species- and tissue-specific toxic responses, many of which involve the aryl hydrocarbon receptor (AhR). The aim of this study was to compare the actual level of integrated AhR transcriptional activity in the lipophilic serum fraction containing the actual POP mixture among Inuits from different districts in Greenland, and to evaluate whether the AhR transactivity is correlated to the bio-accumulated POPs and/or lifestyle factors.</p> <p>Methods</p> <p>The study included 357 serum samples from the Greenlandic districts: Nuuk and Sisimiut (South West Coast), Qaanaaq (North Coast) and Tasiilaq (East Coast). The bio-accumulated serum POPs were extracted by ethanol: hexane and clean-up on Florisil columns. Effects of the serum extract on the AhR transactivity was determined using the Hepa 1.12cR mouse hepatoma cell line carrying an AhR-luciferase reporter gene, and the data was evaluated for possible association to the serum levels of 14 PCB congeners, 10 organochlorine pesticide residues and/or lifestyle factors.</p> <p>Results</p> <p>In total 85% of the Inuit samples elicited agonistic AhR transactivity in a district dependent pattern. The median level of the AhR-TCDD equivalent (AhR-TEQ) of the separate genders was similar in the different districts. For the combined data the order of the median AhR-TEQ was Tasiilaq > Nuuk ≥ Sisimiut > Qaanaaq possibly being related to the different composition of POPs. In overall, the AhR transactivity was inversely correlated to the levels of sum POPs, age and/or intake of marine food.</p> <p>Conclusion</p> <p>i) We observed that the proportion of dioxin like (DL) compounds in the POP mixture was the dominating factor affecting the level of serum AhR transcriptional activity even at very high level of non DL-PCBs; ii) The inverse association between the integrated serum AhR transactivity and sum of POPs might be explained by the higher level of compounds antagonizing the AhR function probably due to selective POP bioaccumulation in the food chain.</p
Microscopic Derivation of Non-Markovian Thermalization of a Brownian Particle
In this paper, the first microscopic approach to the Brownian motion is
developed in the case where the mass density of the suspending bath is of the
same order of magnitude as that of the Brownian (B) particle. Starting from an
extended Boltzmann equation, which describes correctly the interaction with the
fluid, we derive systematicaly via the multiple time-scale analysis a reduced
equation controlling the thermalization of the B particle, i.e. the relaxation
towards the Maxwell distribution in velocity space. In contradistinction to the
Fokker-Planck equation, the derived new evolution equation is non-local both in
time and in velocity space, owing to correlated recollision events between the
fluid and particle B. In the long-time limit, it describes a non-markovian
generalized Ornstein-Uhlenbeck process. However, in spite of this complex
dynamical behaviour, the Stokes-Einstein law relating the friction and
diffusion coefficients is shown to remain valid. A microscopic expression for
the friction coefficient is derived, which acquires the form of the Stokes law
in the limit where the mean-free in the gas is small compared to the radius of
particle B.Comment: 28 pages, no figure, submitted to Journal of Statistical Physic
Sub-femtosecond determination of transmission delay times for a dielectric mirror (photonic bandgap) as a function of angle of incidence
Using a two-photon interference technique, we measure the delay for
single-photon wavepackets to be transmitted through a multilayer dielectric
mirror, which functions as a ``photonic bandgap'' medium. By varying the angle
of incidence, we are able to confirm the behavior predicted by the group delay
(stationary phase approximation), including a variation of the delay time from
superluminal to subluminal as the band edge is tuned towards to the wavelength
of our photons. The agreement with theory is better than 0.5 femtoseconds (less
than one quarter of an optical period) except at large angles of incidence. The
source of the remaining discrepancy is not yet fully understood.Comment: 5 pages and 5 figure
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