6,120 research outputs found
"On the estimation of a large sparse Bayesian system: the Snaer program"
The Snaer program calculates the posterior mean and variance of variables on some of which we have data (with precisions), on some we have prior information (with precisions), and on some prior indicator ratios (with precisions) are available. The variables must satisfy anumber of exact restrictions. The system is both large and sparse. Two aspects of the sta-tistical and computational development are a practical procedure to solve a linear integer system, and a stable linearization routine for ratios. We test our numerical method to solve large sparse linear least-squares estimation problems, and find that it performs well, even when the n ~k design matrix is large(nk equivalent 2^27.5).
Crossover in the Efimov spectrum
A filtering method is introduced for solving the zero-range three-boson
problem. This scheme permits to solve the original Skorniakov Ter-Martirosian
integral equation for an arbitrary large Ultra-Violet cut-off and to avoid the
Thomas collapse of the three particles. The method is applied to a more general
zero-range model including a finite background two-body scattering length and
the effective range. A cross-over in the Efimov spectrum is found in such
systems and a specific regime emerges where Efimov states are long-lived
Differential Form of the Skornyakov--Ter-Martirosyan Equations
The Skornyakov--Ter-Martirosyan three-boson integral equations in momentum
space are transformed into differential equations. This allows us to take into
account quite directly the Danilov condition providing self-adjointness of the
underlying three-body Hamiltonian with zero-range pair interactions. For the
helium trimer the numerical solutions of the resulting differential equations
are compared with those of the Faddeev-type AGS equations.Comment: 4 pages, 2 figure
Deformations of Calabi-Yau hypersurfaces arising from deformations of toric varieties
There are easy "polynomial" deformations of Calabi-Yau hypersurfaces in toric
varieties performed by changing the coefficients of the defining polynomial of
the hypersurface. In this paper, we explicitly constructed the
``non-polynomial'' deformations of Calabi-Yau hypersurfaces, which arise from
deformations of the ambient toric variety
Effects of different levels of UV-B radiation on marine epilithic communities: a short-term microcosm study
Epilithic communities from brackish coastal water of the east coast of Sweden were studied in order to reveal their responses to different levels of UV-B radiation. The experiment was conducted for seven days in an indoor microcosm system. The epilithic communities were exposed daily to different doses of UV-B radiation: 1, 3, 5 and 7 hours, respectively. The intensity of the UV-B radiation used was similar to that in natural environments. After seven days clear shifts both in species composition and community structure were observed. All species of diatoms showed negative correlation with enhanced levels of UV-B. On the other hand, abundance of cyanobacteria was positively correlated with enhanced levels of UV-B (Calothrix aeruginea, R=0.49;Oscillatoria amphibia, R=0.93; Pseudanabaena mucicola, R=0.26). Communities dominated by diatoms and green algae at the initial stage of the experiment did show a drastic decrease in diatom abundance under UV-B stress and finally became dominated by cyanobacteria. Among green algae the abundance of Cladophora sericea correlated positively (R=0.33) with enhanced exposure to UV-B, while Monoraphidium-species exhibited negative correlation to UV-B. Otherwise, no significant correlation between other green algae species identified and UV-B stress could be detected. We conclude that UV-B radiation, even at lower levels, is capable to induce severe changes to marine epilithic communities. The trends revealed in the present study predict a shift from communities dominated by diatoms and green algae to those dominated by cyanobacteria.No disponibl
Some equivalences in linear estimation (in Russian)
Under normality, the Bayesian estimation problem, the best linear unbiased estimation problem, and the restricted least-squares problem are all equivalent. As a result we need not compute pseudo-inverses and other complicated functions, which will be impossible for large sparse systems. Instead, by reorganizing the inputs, we can rewrite the system as a new but equivalent system which can be solved by ordinary least-squares methods.Linear Bayes estimation, best linear unbiased, least squares, sparse problems, large-scale optimization
Preparation of Neutron-activated Xenon for Liquid Xenon Detector Calibration
We report the preparation of neutron-activated xenon for the calibration of
liquid xenon (LXe) detectors. Gamma rays from the decay of xenon metastable
states, produced by fast neutron activation, were detected and their activities
measured in a LXe scintillation detector. Following a five-day activation of
natural xenon gas with a Cf-252 (4 x 10^5 n/s) source, the activities of two
gamma ray lines at 164 keV and 236 keV, from Xe-131m and Xe-129m metastable
states, were measured at about 95 and 130 Bq/kg, respectively. We also observed
three additional lines at 35 keV, 100 keV and 275 keV, which decay away within
a few days. No long-lifetime activity was observed after the neutron
activation.Comment: to be published in NIM A, corrected typos in Table 1 and Fig.6 of the
previous versio
Near-Field Scanning Microwave Microscopy in the Single Photon Regime
The microwave properties of nano-scale structures are important in a wide
variety of applications in quantum technology. Here we describe a low-power
cryogenic near-field scanning microwave microscope (NSMM) which maintains
nano-scale dielectric contrast down to the single microwave photon regime, up
to times lower power than in typical NSMMs. We discuss the remaining
challenges towards developing nano-scale NSMM for quantum coherent interaction
with two-level systems as an enabling tool for the development of quantum
technologies in the microwave regime
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