1,718 research outputs found
The infinite Viterbi alignment and decay-convexity
The infinite Viterbi alignment is the limiting maximum a-posteriori estimate of the unobserved path in a hidden Markov model as the length of the time horizon grows. For models on state-space Rd satisfying a new âdecay-convexityâ condition, we develop an approach to existence of the infinite Viterbi alignment in an infinite dimensional Hilbert space. Quantitative bounds on the distance to the Viterbi process, which are the first of their kind, are derived and used to illustrate how approximate estimation via parallelization can be accurate and scaleable to high-dimensional problems because the rate of convergence to the infinite Viterbi alignment does not necessarily depend on d. The results are applied to approximate estimation via parallelization and a model of neural population activity
Mathematical and computational models of drug transport in tumours
The ability to predict how far a drug will penetrate into the tumour microenvironment within its pharmacokinetic (PK) lifespan would provide valuable information about therapeutic response. As the PK profile is directly related to the route and schedule of drug administration, an in silico tool that can predict the drug administration schedule that results in optimal drug delivery to tumours would streamline clinical trial design. This paper investigates the application of mathematical and computational modelling techniques to help improve our understanding of the fundamental mechanisms underlying drug delivery, and compares the performance of a simple model with more complex approaches. Three models of drug transport are developed, all based on the same drug binding model and parametrized by bespoke in vitro experiments. Their predictions, compared for a âtumour cordâ geometry, are qualitatively and quantitatively similar. We assess the effect of varying the PK profile of the supplied drug, and the binding affinity of the drug to tumour cells, on the concentration of drug reaching cells and the accumulated exposure of cells to drug at arbitrary distances from a supplying blood vessel. This is a contribution towards developing a useful drug transport modelling tool for informing strategies for the treatment of tumour cells which are âpharmacokinetically resistantâ to chemotherapeutic strategies
Elliptic flow at SPS and RHIC: from kinetic transport to hydrodynamics
Anisotropic transverse flow is studied in Pb+Pb and Au+Au collisions at SPS
and RHIC energies. The centrality and transverse momentum dependence at
midrapidity of the elliptic flow coefficient v_2 is calculated in the
hydrodynamic and low density limits. Hydrodynamics is found to agree well with
the RHIC data for semicentral collisions up to transverse momenta of 1-1.5
GeV/c, but it considerably overestimates the measured elliptic flow at SPS
energies. The low density limit LDL is inconsistent with the measured magnitude
of v_2 at RHIC energies and with the shape of its p_t-dependence at both RHIC
and SPS energies. The success of the hydrodynamic model points to very rapid
thermalization in Au+Au collisions at RHIC and provides a serious challenge for
kinetic approaches based on classical scattering of on-shell particles.Comment: 7 pages incl. 5 figures; submitted to Physics Letters B; Ref. 4 and a
few typos corrected; no changes in content
Formation of Small-Scale Condensations in the Molecular Clouds via Thermal Instability
A systematic study of the linear thermal instability of a self-gravitating
magnetic molecular cloud is carried out for the case when the unperturbed
background is subject to local expansion or contraction. We consider the
ambipolar diffusion, or ion-neutral friction on the perturbed states. In this
way, we obtain a non-dimensional characteristic equation that reduces to the
prior characteristic equation in the non-gravitating stationary background. By
parametric manipulation of this characteristic equation, we conclude that there
are, not only oblate condensation forming solutions, but also prolate solutions
according to local expansion or contraction of the background. We obtain the
conditions for existence of the Field lengths that thermal instability in the
molecular clouds can occur. If these conditions establish, small-scale
condensations in the form of spherical, oblate, or prolate may be produced via
thermal instability.Comment: 16 page, accepted by Ap&S
Cosmological parameter estimation using Very Small Array data out to â= 1500
We estimate cosmological parameters using data obtained by the Very Small Array (VSA) in its extended configuration, in conjunction with a variety of other cosmic microwave background (CMB) data and external priors. Within the flat Î cold dark matter (ÎCDM) model, we find that the inclusion of high-resolution data from the VSA modifies the limits on the cosmological parameters as compared to those suggested by the Wilkinson Microwave Anisotropy Probe (WMAP) alone, while still remaining compatible with their estimates. We find that Ωbh2= 0.0234+0.0012â0.0014, Ωdmh2= 0.111+0.014â0.016, h= 0.73+0.09â0.05, nS= 0.97+0.06â0.03, 1010AS= 23+7â3 and Ï= 0.14+0.14â0.07 for WMAP and VSA when no external prior is included. On extending the model to include a running spectral index of density fluctuations, we find that the inclusion of VSA data leads to a negative running at a level of more than 95 per cent confidence ( nrun=â0.069 ± 0.032 ), something that is not significantly changed by the inclusion of a stringent prior on the Hubble constant. Inclusion of prior information from the 2dF galaxy redshift survey reduces the significance of the result by constraining the value of Ωm. We discuss the veracity of this result in the context of various systematic effects and also a broken spectral index model. We also constrain the fraction of neutrinos and find that fÎœ < 0.087 at 95 per cent confidence, which corresponds to mÎœ < 0.32 eV when all neutrino masses are equal. Finally, we consider the global best fit within a general cosmological model with 12 parameters and find consistency with other analyses available in the literature. The evidence for nrun < 0 is only marginal within this model
Population redistribution in optically trapped polar molecules
We investigate the rovibrational population redistribution of polar molecules
in the electronic ground state induced by spontaneous emission and blackbody
radiation. As a model system we use optically trapped LiCs molecules formed by
photoassociation in an ultracold two-species gas. The population dynamics of
vibrational and rotational states is modeled using an ab-initio electric dipole
moment function and experimental potential energy curves. Comparison with the
evolution of the v"=3 electronic ground state yields good qualitative
agreement. The analysis provides important input to assess applications of
ultracold LiCs molecules in quantum simulation and ultracold chemistry.Comment: 6 pages, 5 figures, EPJD Topical issue on Cold Quantum Matter -
Achievements and Prospect
An epidemiologic study of linear enamel hypoplasia of deciduous anterior teeth in Guatemalan children
Although linear enamel hypoplasia is commonly seen in children of malnourished communities throughout the world, the aetiology is undetermined. This study attempted to explore the distribution of this enamel defect in 429 Guatemalan children (ages 6-83 months) from four rural villages. The prevalence ranged from 18 to 24 per cent in three villages to 62 per cent in the fourth. The prevalence did not increase with age, suggesting caries was not an aetiologic factor. Protein supplement made available to pregnant mothers and children did not appear to reduce the occurrence of the lesion in children. Relatively fewer children manifested the lesion when born in the latter part of the year. No sex differences were observed. Siblings of children with the lesion had a prevalence significantly greater than the total study population, suggesting that factors operating at the family level enhance the occurrence of the hypoplastic lesion in children.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/22245/1/0000681.pd
"Author! Author!" : Shakespeare and biography
Original article can be found at: http://www.informaworld.com/smpp/title~content=t714579626~db=all Copyright Informa / Taylor & Francis Group. DOI: 10.1080/17450910902764454Since 1996, not a year has passed without the publication of at least one Shakespeare biography. Yet for many years the place of the author in the practice of understanding literary works has been problematized, and even on occasions eliminated. Criticism reads the âworksâ, and may or may not refer to an author whose âlifeâ contributed to their meaning. Biography seeks the author in the works, the personality that precedes the works and gives them their characteristic shape and meaning. But the form of literary biography addresses the unusual kind of âlifeâ that puts itself into âworksâ, and this is particularly challenging where the âworksâ predominate massively over the salient facts of the âlifeâ. This essay surveys the current terrain of Shakespeare biography, and considers the key questions raised by the medium: can we know anything of Shakespeare's âpersonalityâ from the facts of his life and the survival of his works? What is the status of the kind of speculation that inevitably plays a part in biographical reconstruction? Are biographers in the end telling us as much about themselves as they tell us about Shakespeare?Peer reviewe
The ZEPLIN II dark matter detector: data acquisition system and data reduction
ZEPLIN-II is a two-phase (liquid/gas) xenon dark matter detector searching
for WIMP-nucleon interactions. In this paper we describe the data acquisition
system used to record the data from ZEPLIN-II and the reduction procedures
which parameterise the data for subsequent analysis.Comment: 11 pages, 10 figure
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