126,590 research outputs found
Improved laser ranging accuracy through dynamic threshold compensation
During a polar motion experiment (in which two laser ranging systems on a north-south line simultaneously tracked a satellite to determine motion of the pole), techniques for improving both the range noise and range bias were demonstrated. The corrections to the measured ranges (based on received signal levels relative to a fixed correction that would have been applied if pulse height information was not available) are given. It was shown that even existing long pulse systems (20 to 40 nsec duration) can be improved to the 20 to 30 cm level of precision without major or expensive changes to the system
What is a quantum simulator?
Quantum simulators are devices that actively use quantum effects to answer
questions about model systems and, through them, real systems. Here we expand
on this definition by answering several fundamental questions about the nature
and use of quantum simulators. Our answers address two important areas. First,
the difference between an operation termed simulation and another termed
computation. This distinction is related to the purpose of an operation, as
well as our confidence in and expectation of its accuracy. Second, the
threshold between quantum and classical simulations. Throughout, we provide a
perspective on the achievements and directions of the field of quantum
simulation.Comment: 13 pages, 2 figure
Update to the Mid-Term Evaluation for the CSFF for Objective 3, Report 321, Department for Work and Pensions
Acoustic model adaptation for ortolan bunting (Emberiza hortulana L.) song-type classification
Automatic systems for vocalization classification often require fairly large amounts of data on which to train models. However, animal vocalization data collection and transcription is a difficult and time-consuming task, so that it is expensive to create large data sets. One natural solution to this problem is the use of acoustic adaptation methods. Such methods, common in human speech recognition systems, create initial models trained on speaker independent data, then use small amounts of adaptation data to build individual-specific models. Since, as in human speech, individual vocal variability is a significant source of variation in bioacoustic data, acoustic model adaptation is naturally suited to classification in this domain as well. To demonstrate and evaluate the effectiveness of this approach, this paper presents the application of maximum likelihood linear regression adaptation to ortolan bunting (Emberiza hortulana L.) song-type classification. Classification accuracies for the adapted system are computed as a function of the amount of adaptation data and compared to caller-independent and caller-dependent systems. The experimental results indicate that given the same amount of data, supervised adaptation significantly outperforms both caller-independent and caller-dependent systems
Improvement of uncoupled Hartree-Fock expectation values for physical properties, II
Improvement of uncoupled Hartree-Fock expectation values for physical propertie
Diffusive Migration of Low-Mass Proto-planets in Turbulent Disks
Torque fluctuations due to magnetorotational turbulence in proto-planetary
disks may greatly influence the migration patterns and survival probabilities
of nascent planets. Provided that the turbulence is a stationary stochastic
process with finite amplitude and correlation time, the resulting diffusive
migration can be described with a Fokker-Planck equation, which we reduce to an
advection-diffusion equation. We calibrate the coefficients with existing
turbulent-disk simulations and mean-migration estimates, and solve the equation
both analytically and numerically. Diffusion tends to dominate over advection
for planets of low-mass and those in the outer regions of proto-planetary
disks, whether they are described by the Minimum Mass Solar Nebula (MMSN) or by
T-Tauri alpha disks. Diffusion systematically reduces the lifetime of most
planets, yet it allows a declining fraction of them to survive for extended
periods of time at large radii. Mean planet lifetimes can even be formally
infinite (e.g. in an infinite steady MMSN), though median lifetimes are always
finite. Surviving planets may linger near specific radii where the combined
effects of advection and diffusion are minimized, or at large radii, depending
on model specifics. The stochastic nature of migration in turbulent disks
challenges deterministic planet formation scenarios and suggests instead that a
wide variety of planetary outcomes are possible from similar initial
conditions. This would contribute to the diversity of (extrasolar) planetary
systems.Comment: 31 pages, 7 figures, accepted for publication in Ap
Theory of the evolutionary minority game
We present a theory which describes a recently introduced model of an
evolving, adaptive system in which agents compete to be in the minority. The
agents themselves are able to evolve their strategies over time in an attempt
to improve their performance. The present theory explicitly demonstrates the
self-interaction, or so-called market impact, that agents in such systems
experience
In vitro assessment of cytotoxicity of giomer on human gingival fibroblasts
Root coverage on restored root surfaces has been considered as a challenging issue. The evaluation of cytotoxic effects of restorative materials is a fundamental requirement for sustaining the cell attachment and the clinical success of root coverage. The aim of the present study was to compare the human gingival fibroblast cytotoxicity of the recently introduced giomer composite (GC) with resin ionomer (RI) restorative material. Discs (6x2 mm) of GC and RI restorative materials were prepared using sterile Teflon mold. Extracts from the materials were incubated to cell culture medium for 24, 48 and 72 h. Human gingival fibroblasts (HGF) were exposed to the extracts of the materials while the un-incubated media served as the control group. The cytotoxicity of the materials were evaluated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. In order to compare the mean values of the measured parameters a Kruskal-Walis test was carried out. MTT assay indicated that human gingival fibroblasts proliferated well in the presence of GC extract. The proliferation rate was higher in cells incubated with GC compared to RI extracts but the differences were not statistically significant (p= 0.09). This in vitro study indicated that GC is a non-toxic material for HGF. However, further studies are needed to assess the other biologic and clinical behavior of this material prior to it being considered as a potentially suitable restorative material to restore the carious root lesions candidated to root coverage procedures
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