2,306 research outputs found
Constellation Queries over Big Data
A geometrical pattern is a set of points with all pairwise distances (or,
more generally, relative distances) specified. Finding matches to such patterns
has applications to spatial data in seismic, astronomical, and transportation
contexts. For example, a particularly interesting geometric pattern in
astronomy is the Einstein cross, which is an astronomical phenomenon in which a
single quasar is observed as four distinct sky objects (due to gravitational
lensing) when captured by earth telescopes. Finding such crosses, as well as
other geometric patterns, is a challenging problem as the potential number of
sets of elements that compose shapes is exponentially large in the size of the
dataset and the pattern. In this paper, we denote geometric patterns as
constellation queries and propose algorithms to find them in large data
applications. Our methods combine quadtrees, matrix multiplication, and
unindexed join processing to discover sets of points that match a geometric
pattern within some additive factor on the pairwise distances. Our distributed
experiments show that the choice of composition algorithm (matrix
multiplication or nested loops) depends on the freedom introduced in the query
geometry through the distance additive factor. Three clearly identified blocks
of threshold values guide the choice of the best composition algorithm.
Finally, solving the problem for relative distances requires a novel
continuous-to-discrete transformation. To the best of our knowledge this paper
is the first to investigate constellation queries at scale
Dimensionality dependence of optical nonlinearity and relaxation dynamics in cuprates
Femtosecond pump-probe measurements find pronounced dimensionality dependence
of the optical nonlinearity in cuprates. Although the coherent two-photon
absorption (TPA) and linear absorption bands nearly overlap in both quasi-one
and two-dimensional (1D and 2D) cuprates, the TPA coefficient is one order of
magnitude smaller in 2D than in 1D. Furthermore, picosecond recovery of optical
transparency is observed in 1D cuprates, while the recovery in 2D involves
relaxation channels with a time scales of tens of picoseconds. The experimental
results are interpreted within the two-band extended Hubbard model.Comment: 10 pages, 4 figure
Comment on "Origin of Giant Optical Nonlinearity in Charge-Transfer--Mott Insulators: A New Paradigm for Nonlinear Optics"
Comment on Phys. Rev. Lett. 86, 2086 (2001)Comment: 1 page, 1 eps figur
Anomalous Hall Effect and Magnetic Monopoles in Momentum-Space
Efforts to find the magnetic monopole in real space have been made in cosmic
rays and in accelerators, but up to now there is no firm evidence for its
existence due to the very heavy mass GeV. However, we show that
the magnetic monopole can appear in the crystal-momentum space of solids in the
accessible low energy region (eV) in the context of the anomalous
Hall effect. We report experimental results together with first-principles
calculations on the ferromagnetic crystal SrRuO that provide evidence for
the magnetic monopole in the crystal-momentum space.Comment: 4 figures, the supporting-online-materails are include
Formation of superconducting yttrium barium copper oxide using sulphur-containing templates
The formation of yttrium barium copper oxide (YBCO) via biotemplated routes is often plagued by unwanted stable intermediates, some of which arise from the template itself. Here we describe a method which allows sulphur-containing templates, such as proteins, to form superconducting YBCO which would have hitherto resulted in non-superconducting sulphated phases
Pump Built-in Hamiltonian Method for Pump-Probe Spectroscopy
We propose a new method of calculating nonlinear optical responses of
interacting electronic systems. In this method, the total Hamiltonian (system +
system-pump interaction) is transformed into a different form that (apparently)
does not have a system-pump interaction. The transformed Hamiltonian, which we
call the pump built-in Hamiltonian, has parameters that depend on the strength
of the pump beam. Using the pump built-in Hamiltonian, we can calculate
nonlinear responses (responses to probe beams as a function of the pump beam)
by applying the {\em linear} response theory. We demonstrate the basic idea of
this new method by applying it to a one-dimensional, two-band model, in the
case the pump excitation is virtual (coherent excitation). We find that the
exponent of the Fermi edge singularity varies with the pump intensity.Comment: 6 page
Stress Promotes Drug Seeking Through Glucocorticoid-Dependent Endocannabinoid Mobilization in the Prelimbic Cortex
Background
Clinical reports suggest that rather than directly driving cocaine use, stress may create a biological context within which other triggers for drug use become more potent. We hypothesize that stress-induced increases in corticosterone “set the stage” for relapse by promoting endocannabinoid-induced attenuation of inhibitory transmission in the prelimbic cortex (PL).
Methods
We have established a rat model for these stage-setting effects of stress. In this model, neither a stressor (electric footshock) nor stress-level corticosterone treatment alone reinstates cocaine seeking following self-administration and extinction, but each treatment potentiates reinstatement in response to an otherwise subthreshold cocaine priming dose (2.5 mg/kg, intraperitoneal). The contributions of endocannabinoid signaling in the PL to the effects of stress-level corticosterone on PL neurotransmission and cocaine seeking were determined using intra-PL microinfusions. Endocannabinoid-dependent effects of corticosterone on inhibitory synaptic transmission in the rat PL were determined using whole-cell recordings in layer V pyramidal neurons.
Results
Corticosterone application attenuated inhibitory synaptic transmission in the PL via cannabinoid receptor type 1 (CB1R)– and 2-arachidonoylglycerol–dependent inhibition of gamma-aminobutyric acid release without altering postsynaptic responses. The ability of systemic stress-level corticosterone treatment to potentiate cocaine-primed reinstatement was recapitulated by intra-PL injection of corticosterone, the CB1R agonist WIN 55,212-2, or the monoacylglycerol lipase inhibitor URB602. Corticosterone effects on reinstatement were attenuated by intra-PL injections of either the CB1R antagonist, AM251, or the diacylglycerol lipase inhibitor, DO34.
Conclusions
These findings suggest that stress-induced increases in corticosterone promote cocaine seeking by mobilizing 2-arachidonoylglycerol in the PL, resulting in CB1R-mediated attenuation of inhibitory transmission in this brain region
Ultrafast photoinduced reflectivity transients in
The temperature dependence of ultrafast photoinduced reflectivity transients
is reported in NdSrMnO thin film. The photoinduced
reflectivity shows a complex response with very different temperature
dependences on different timescales. The response on the sub-ps timescale
appears to be only weakly sensitive to the 270K-metal-insulator phase
transition. Below K the sub-ps response displays a two component
behavior indicating inhomogeneity of the film resulting from the substrate
induced strain. On the other hand, the slower response on the 10-100 ps
timescale is sensitive only to the metal-insulator phase transition and is in
agreement with some previously published results. The difference in the
temperature dependences of the responses on nanosecond and s timescales
indicates that thermal equilibrium between the different degrees of fredom is
established relatively slowly - on a nanosecond timescale
- …