21,242 research outputs found
A Tandem Fluid Network with L\'evy Input in Heavy Traffic
In this paper we study the stationary workload distribution of a fluid tandem
queue in heavy traffic. We consider different types of L\'evy input, covering
compound Poisson, -stable L\'evy motion (with ), and
Brownian motion. In our analysis we separately deal with L\'evy input processes
with increments that have finite and infinite variance. A distinguishing
feature of this paper is that we do not only consider the usual heavy-traffic
regime, in which the load at one of the nodes goes to unity, but also a regime
in which we simultaneously let the load of both servers tend to one, which, as
it turns out, leads to entirely different heavy-traffic asymptotics. Numerical
experiments indicate that under specific conditions the resulting simultaneous
heavy-traffic approximation significantly outperforms the usual heavy-traffic
approximation
Time-resolved magnetic field effect on triplet formation in photosynthetic reaction centers of rhodopseudomonas sphaeroides R-26
Recombination dynamics in bacterial photosynthetic reaction centers
The time dependence of magnetic field effects on light absorption by triplet-state and radical ions in quinone-depleted reaction centers of Rhodopseudomonas sphaeroides strain R-26 has been investigated. Measurements on the time scale of the hyperfine interaction in the radical pair [(BChl)2+. ...BPh-.)] provided kinetic data characterizing the recombination process. The results have been interpreted in terms of a recently proposed model that assumes an intermediate electron acceptor (close site) between the bacteriochlorophyll "special pair" (BChl)2 and the bacteriopheophytin BPh (distant site). Recombination is assumed to proceed through this intermediate acceptor. The experiments led to effective recombination rates for the singlet and triplet channel: k(Seff) = 3.9 . 107 s-1 and k(Teff) = 7.4 . 10(8) s-1. These correspond to recombination rates ks = 1 . 10(1) s-1 and kT = 7.1 . 10(11) s-1 in the close configuration. The upper bound of the effective spin dephasing rate k2eff approximately equal to 1 . 10(9) s-1 is identical with the rate of the electron hopping between the distant site of zero spin exchange interaction and the close site of large interaction. Interpretation of data for the case of direct recombination yields the recombination rates, spin dephasing rate, and exchange interaction in a straightforward way
Theory of rigid-plane phonon modes in layered crystals
The lattice dynamics of low-frequency rigid-plane modes in metallic (graphene
multilayers, GML) and in insulating (hexagonal boron-nitride multilayers, BNML)
layered crystals is investigated. The frequencies of shearing and compression
(stretching) modes depend on the layer number {\EuScript N} and are presented
in the form of fan diagrams. The results for GML and BNML are very similar. In
both cases only the interactions (van der Waals and Coulomb) between
nearest-neighbor planes are effective, while the interactions between more
distant planes are screened. A comparison with recent Raman scattering results
on low-frequency shear modes in GML [Tan {\it et al.}, arXiv:1106.1146v1
(2011)] is made. Relations with the low-lying rigid-plane phonon dispersions in
the bulk materials are established. Master curves which connect the fan diagram
frequencies for any given {\EuScript N} are derived. Static and dynamic
thermal correlation functions for rigid-layer shear and compression modes are
calculated. The results might be of use for the interpretation of friction
force experiments on multilayer crystals
CCD Photometry of Delta Scuti stars 7 Aql and 8 Aql
As a continuation of the study of the Delta Scuti stars 7 Aql and 8 Aql; new
CCD photometric data were acquired in 2007. We present a period analysis on
these data that confirm the dominant modes detected in each star in the
framework of the STEPHI XII campaign in 2003.Comment: 9 pages, 7 figures, 2 tables; Accepted for publication in
Communications in Asteroseismology, Vol 153, 200
Improving the accuracy of 1D SNMR surveys using the multi-central-loop configuration
Temeljna svrha i cilj ovoga rada bilo je ispitati koliko su potrošači skloni dijeljenju svojih turističkih iskustva s drugima te putem kojih medija. Osim navedenog, drugi cilj provedenog istraživanja bilo je utvrditi koliko su potrošačima važna iskustva i komentari drugih posjetitelja u procesu donošenja odluke o kupnji. Istraživanje je provedeno metodom ispitivanja, a kao instrument korišten je anketni upitnik sastavljen od 22 pitanja. Utvrđivanjem problema istraživanja, postavljene su tri hipoteze. Od tri hipoteze, u potpunosti je dokazana samo prva koja pretpostavlja da su potrošačima tuđa iskustva i komentari od velike važnosti kod planiranja i odabira putovanja. Druga hipoteza je djelomično potvrđena, tj. potvrđeno je da su potrošači skloni dijeliti svoja iskustva s drugima u situaciji kada su jako zadovoljni dok s druge strane nije potvrđeno kako su potrošači skloni dijeliti svoja iskustva u situaciji kada su nezadovoljni uslugom ili proizvodom. Na kraju, potvrđena je i treća hipoteza koja pretpostavlja kako su potrošači skloni dijeljenju vlastitog turističkog iskustva putem više društvenih medija, iako je utvrđeno kako najveći broj ispitanika ne dijeli svoja turistička iskustva. Istraživano je i mišljenje ispitanika o turističkoj destinaciji iz snova, a iznenađujuće, najveći broj ispitanika je navelo hrvatske destinacije kao svoje destinacije iz snova kao i one koje su im dosada pružile najnezaboravnije turističko iskustvo. Potrebno je provesti detaljnija istraživanja kako bi se detaljnije istražilo novije društvene medije koji su dostupni potrošačima za dijeljenje svog iskustva
Improving the accuracy of 1D SNMR surveys using the multi-central-loop configuration
A multi-central loop configuration has been studied through forward and inverse modelling of synthetics and real data. This set-up takes advantage of the multichannel features of the NMR device and consists of using several (2 to 3) additional receiver loops displayed concentrically with the main transmitter/receiver loop, which all record the NMR signal simultaneously within a single acquisition. If the loop diameters are chosen appropriately, the kernel sensitivity distributions for each receiver loop can show complementary features. Inverting simultaneously the data sets obtained through each different receiver loop can then enhance the accuracy of the final model. To do so, a 1D QT inversion scheme in the frequency domain dedicated to the inversion of multiple data sets is being used. One challenging feature is to adapt the regularization of the inverse process so as to handle correctly the noise originating from different data sets. The efficiency of this multi-central loop acquisition set-up and procedure is being assessed through the forward and inverse modelling of several scenarios implying varying aquifer characteristics. Finally a field case is being presented that was conducted on a low noise level site located in Germany, where conditions were favourable to the implementation and testing of circular multi-central loop configurations.We also introduce a new method for determining NMR parameters, named the prediction-focused-approach (PFA), that is based on statistical analysis of a large number of simple models. We observe, using synthetic examples, that the effciency of the method benefits from the use of the multi-central-loop configurations
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