12,328 research outputs found
Heavy Quark Physics From Lattice QCD
We review the application of lattice QCD to the phenomenology of b- and
c-quarks. After a short discussion of the lattice techniques used to evaluate
hadronic matrix elements and the corresponding systematic uncertainties, we
summarise results for leptonic decay constants, B--Bbar mixing, semileptonic
and rare radiative decays. A discussion of the determination of heavy quark
effective theory parameters is followed by an explanation of the difficulty in
applying lattice methods to exclusive nonleptonic decays.Comment: 52 pages LaTeX with 10 eps files. Requires: hfsprocl.sty (included)
plus axodraw.sty, rotating.sty and array.sty. To appear in Heavy Flavours
(2nd edition) edited by A J Buras and M Lindner (World Scientific,
Singapore). Revised version corrects typo in axis labelling of Fig 1
Persistence and the Random Bond Ising Model in Two Dimensions
We study the zero-temperature persistence phenomenon in the random bond Ising model on a square lattice via extensive numerical simulations. We find
strong evidence for ` blocking\rq regardless of the amount disorder present in
the system. The fraction of spins which {\it never} flips displays interesting
non-monotonic, double-humped behaviour as the concentration of ferromagnetic
bonds is varied from zero to one. The peak is identified with the onset of
the zero-temperature spin glass transition in the model. The residual
persistence is found to decay algebraically and the persistence exponent
over the range . Our results are
completely consistent with the result of Gandolfi, Newman and Stein for
infinite systems that this model has ` mixed\rq behaviour, namely positive
fractions of spins that flip finitely and infinitely often, respectively.
[Gandolfi, Newman and Stein, Commun. Math. Phys. {\bf 214} 373, (2000).]Comment: 9 pages, 5 figure
Second order perturbation theory for spin-orbit resonances
We implement Lie transform perturbation theory to second order for the planar
spin-orbit problem. The perturbation parameter is the asphericity of the body,
with the orbital eccentricity entering as an additional parameter. We study
first and second order resonances for different values of these parameters. For
nearly spherical bodies like Mercury and the Moon first order perturbation
theory is adequate, whereas for highly aspherical bodies like Hyperion the spin
is mostly chaotic and perturbation theory is of limited use. However, in
between, we identify a parameter range where second order perturbation theory
is useful and where as yet unidentified objects may be in second order
resonances.Comment: To appear in A
Assessing the Effectiveness of Automated Emotion Recognition in Adults and Children for Clinical Investigation
Recent success stories in automated object or face recognition, partly fuelled by deep learning artificial neural network (ANN) architectures, has led to the advancement of biometric research platforms and, to some extent, the resurrection of Artificial Intelligence (AI). In line with this general trend, inter-disciplinary approaches have taken place to automate the recognition of emotions in adults or children for the benefit of various applications such as identification of children emotions prior to a clinical investigation. Within this context, it turns out that automating emotion recognition is far from being straight forward with several challenges arising for both science(e.g., methodology underpinned by psychology) and technology (e.g., iMotions biometric research platform). In this paper, we present a methodology, experiment and interesting findings, which raise the following research questions for the recognition of emotions and attention in humans: a) adequacy of well-established techniques such as the International Affective Picture System (IAPS), b) adequacy of state-of-the-art biometric research platforms, c) the extent to which emotional responses may be different among children or adults. Our findings and first attempts to answer some of these research questions, are all based on a mixed sample of adults and children, who took part in the experiment resulting into a statistical analysis of numerous variables. These are related with, both automatically and interactively, captured responses of participants to a sample of IAPS pictures
Hair radioactivity as a measure of exposure to radioisotopes
Since many radioisotopes accumulate in hair, this tropism was investigated by comparing the radioactivity of shaved with plucked hair collected from rats at various time intervals up to 24 hrs after intravenous injection of the ecologically important radioisotopes, iodine-131, manganese-54, strontium-85, and zinc-65. The plucked hair includes the hair follicles where biochemical transformations are taking place. The data indicate a slight surge of each radioisotpe into the hair immediately after injection, a variation of content of each radionuclide in the hair, and a greater accumulation of radioactivity in plucked than in shaved hair. These results have application not only to hair as a measure of exposure to radioisotopes, but also to tissue damage and repair at the hair follicle
Highly Ionized High-Velocity Clouds toward PKS 2155-304 and Markarian 509
To gain insight into four highly ionized high-velocity clouds (HVCs)
discovered by Sembach et al. (1999), we have analyzed data from the Hubble
Space Telescope (HST) and Far Ultraviolet Spectroscopic Explorer (FUSE) for the
PKS 2155-304 and Mrk 509 sight lines. We measure strong absorption in OVI and
column densities of multiple ionization stages of silicon (SiII/III/IV) and
carbon (CII/III/IV). We interpret this ionization pattern as a multiphase
medium that contains both collisionally ionized and photoionized gas. Toward
PKS 2155-304, for HVCs at -140 and -270 km/s, respectively, we measure
logN(OVI)=13.80+/-0.03 and log N(OVI)=13.56+/-0.06; from Lyman series
absorption, we find log N(HI)=16.37^(+0.22)_(-0.14) and 15.23^(+0.38)_(-0.22).
The presence of high-velocity OVI spread over a broad (100 km/s) profile,
together with large amounts of low-ionization species, is difficult to
reconcile with the low densities, n=5x10^(-6) cm^(-3), in the
collisional/photoionization models of Nicastro et al. (2002), although the HVCs
show a similar relation in N(SiIV)/N(CIV) versus N(CII)/N(CIV) as high-z
intergalactic clouds. Our results suggest that the high-velocity OVI in these
absorbers do not necessarily trace the WHIM, but instead may trace HVCs with
low total hydrogen column density. We propose that the broad high-velocity OVI
absorption arises from shock ionization, at bowshock interfaces produced from
infalling clumps of gas with velocity shear. The similar ratios of high ions
for HVC Complex C and these highly ionized HVCs suggest a common production
mechanism in the Galactic halo.Comment: 38 pages, including 10 figures. ApJ, 10 April, 2004. Replaced with
accepted versio
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An industrial profile of wood wool/cement slab manufacture
This profile describes a process developed at the Tropical Products Institute for the manufacture of wood wool/cement clabs. Unlike other commercially available processes this process involves the use of a cement slurry. The process is aimed at conditions in developing countries and significant features include minimum use of machinery, maximum use of labour, flexibility in production to suit market requirements and relatively low capital outlay. For a plant to produce 160 slabs per day, about £50,000 c.i.f. at September 1979 prices, excluding locally available items, is required. At least 28 employment opportunities are created. The profile includes a description of the process, a list of the machinery and equipment, components of capital cost, physical inputs and labour requirement
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