3,190 research outputs found
Reconstruction and Particle Identification for a DIRC System
We study the reconstruction and particle identification (PID) problem for
Ring Imaging devices providing a good knowledge of the direction of the
Cerenkov photons, as the DIRC system, on which we specialize. We advocate first
the use of the stereographic projection as a tool allowing a suitable
representation of the photon data, as it allows to represent the Cerenkov cone
always as a circle. We set up an algorithm able to perform reliably a fit of
circle arcs of small angular opening, by minimising a true Chi2 expression. The
system we develop for PID relies on this algorithm and on a procedure able to
remove background photons with a high efficiency. We thus show that, even when
the background is large, it is possible to perform an efficient PID by means of
a fit algorithm which finally provides all the circle parameters; these are
connected with the charged track direction and its Cerenkov angle. It is shown
that background effects can be dealt without spoiling significantly the
reconstruction probability distributions.Comment: 67 pages, 23 figure
Which group velocity of light in a dispersive medium?
The interaction between a light pulse, traveling in air, and a generic
linear, non-absorbing and dispersive structure is analyzed. It is shown that
energy conservation imposes a constraint between the group velocities of the
transmitted and reflected light pulses. It follows that the two fields
propagate with group velocities depending on the dispersive properties of the
environment (air) and on the transmission properties of the optical structure,
and are one faster and the other slower than the incident field. In other
words, the group velocity of a light pulse in a dispersive medium is
reminiscent of previous interactions. One example is discussed in detail.Comment: To be submitted on PR
f_B with lattice NRQCD including O(1/m_Q^2) corrections
We calculate the heavy-light meson decay constant using lattice NRQCD action
for the heavy quark and Wilson quark action for the light quark over a wide
range in the heavy quark mass. Simulations are carried out on a 16^3 x 32
lattice with 120 quenched gauge configurations generated with the plaquette
action at beta=5.8. For the heavy quark part of the calculation, two sets of
lattice NRQCD action and current operator are employed. The first set includes
terms up to O(1/m_Q) both in the action and the current operator, and the
second set up to O(1/m_Q^2), where m_Q is the bare mass of the heavy quark.
Tree-level values with tadpole improvement are employed for the coefficients in
the expansion. We compare the results obtained from the two sets in detail and
find that the truncation error of higher order relativistic corrections for the
decay constant are adequately small around the mass of the b quark. We also
calculate the 1S hyperfine splitting of B meson, M_{B_s} - M_B and f_{B_s}/f_B
with both sets and find that the 1/m_Q^2 corrections are negligible. Remaining
systematic errors and the limitation of NRQCD theory are discussed.Comment: 27 pages, 15 figures, RevTex, psfig.sty require
Investigating The Influence of Media on Preservice Teachers' Construction of Their Professional Identity
In this empirical paper, we investigate the influence that print media has on preservice teachers' construction of their teacher professional identity. Preservice teachers are a vulnerable group still undergoing training to shape their teacher identity; it is, therefore, essential to see how the stories told in the print media influence them. This paper is couched in the Social Learning Theory because it focuses on learning through interacting with social and environmental factors. This qualitative paper used focus group discussions with five purposefully sampled third-year education preservice teachers from a South African university. Data generated were thematically analysed. The findings revealed that media created multiple learning opportunities through reflection and engagement. In light of the findings, the study suggests using teacher education programs to deepen preservice teachers' sense of reflection and meaning-making beyond the information they might come across
Quantum statistics of overlapping modes in open resonators
We study the quantum dynamics of optical fields in weakly confining
resonators with overlapping modes. Employing a recently developed quantization
scheme involving a discrete set of resonator modes and continua of external
modes we derive Langevin equations and a master equation for the resonator
modes. Langevin dynamics and the master equation are proved to be equivalent in
the Markovian limit. Our open-resonator dynamics may be used as a starting
point for a quantum theory of random lasers.Comment: 6 pages, corrected typo
Convergence and divergence in the evolution of cat skulls: temporal and spatial patterns of morphological diversity
Background: Studies of biological shape evolution are greatly enhanced when framed in a phylogenetic perspective.
Inclusion of fossils amplifies the scope of macroevolutionary research, offers a deep-time perspective on tempo and mode
of radiations, and elucidates life-trait changes. We explore the evolution of skull shape in felids (cats) through morphometric
analyses of linear variables, phylogenetic comparative methods, and a new cladistic study of saber-toothed cats.
Methodology/Principal Findings: A new phylogenetic analysis supports the monophyly of saber-toothed cats
(Machairodontinae) exclusive of Felinae and some basal felids, but does not support the monophyly of various sabertoothed
tribes and genera. We quantified skull shape variation in 34 extant and 18 extinct species using size-adjusted linear
variables. These distinguish taxonomic group membership with high accuracy. Patterns of morphospace occupation are
consistent with previous analyses, for example, in showing a size gradient along the primary axis of shape variation and a
separation between large and small-medium cats. By combining the new phylogeny with a molecular tree of extant Felinae,
we built a chronophylomorphospace (a phylogeny superimposed onto a two-dimensional morphospace through time). The
evolutionary history of cats was characterized by two major episodes of morphological divergence, one marking the
separation between saber-toothed and modern cats, the other marking the split between large and small-medium cats.
Conclusions/Significance: Ancestors of large cats in the ‘Panthera’ lineage tend to occupy, at a much later stage,
morphospace regions previously occupied by saber-toothed cats. The latter radiated out into new morphospace regions
peripheral to those of extant large cats. The separation between large and small-medium cats was marked by considerable
morphologically divergent trajectories early in feline evolution. A chronophylomorphospace has wider applications in
reconstructing temporal transitions across two-dimensional trait spaces, can be used in ecophenotypical and functional
diversity studies, and may reveal novel patterns of morphospace occupation
Leptonic Decays of Heavy Quarks on the Lattice
The status of lattice calculations of heavy-light decay constants and of the
parameter is reviewed. After describing the lattice approach to heavy
quark systems, the main results are discussed, with special emphasis on the
systematic errors in present lattice calculations. A detailed analysis of the
continuum limit for decay constants is performed. The implications of lattice
results on studies of CP violation in the Standard Model are discussed.Comment: Invited review to be published in Int. J. Mod. Phys. A, 63 pages,
LaTeX, ijmpa1.sty (included), 8 postscript figure
Stability of the monoclinic phase in the ferroelectric perovskite PbZr(1-x)TixO3
Recent structural studies of ferroelectric PbZr(1-x)TixO3 (PZT) with x= 0.48,
have revealed a new monoclinic phase in the vicinity of the morphotropic phase
boundary (MPB), previously regarded as the the boundary separating the
rhombohedral and tetragonal regions of the PZT phase diagram. In the present
paper, the stability region of all three phases has been established from high
resolution synchrotron x-ray powder diffraction measurements on a series of
highly homogeneous samples with 0.42 <=x<= 0.52. At 20K the monoclinic phase is
stable in the range 0.46 <=x<= 0.51, and this range narrows as the temperature
is increased. A first-order phase transition from tetragonal to rhombohedral
symmetry is observed only for x= 0.45. The MPB, therefore, corresponds not to
the tetragonal-rhombohedral phase boundary, but instead to the boundary between
the tetragonal and monoclinic phases for 0.46 <=x<= 0.51. This result provides
important insight into the close relationship between the monoclinic phase and
the striking piezoelectric properties of PZT; in particular, investigations of
poled samples have shown that the monoclinic distortion is the origin of the
unusually high piezoelectric response of PZT.Comment: REVTeX file, 7 figures embedde
Quantum Communication with Correlated Nonclassical States
Nonclassical correlations between the quadrature-phase amplitudes of two
spatially separated optical beams are exploited to realize a two-channel
quantum communication experiment with a high degree of immunity to
interception. For this scheme, either channel alone can have an arbitrarily
small signal-to-noise ratio (SNR) for transmission of a coherent ``message''.
However, when the transmitted beams are combined properly upon authorized
detection, the encoded message can in principle be recovered with the original
SNR of the source. An experimental demonstration has achieved a 3.2 dB
improvement in SNR over that possible with correlated classical sources.
Extensions of the protocol to improve its security against eavesdropping are
discussed.Comment: 8 pages and 4 figures (Figure 1; Figures 2a, 2b; Figure 2
Foot pain and foot health in an educated population of adults: results from the Glasgow Caledonian University Alumni Foot Health Survey
Abstract Background Foot pain is common amongst the general population and impacts negatively on physical function and quality of life. Associations between personal health characteristics, lifestyle/behaviour factors and foot pain have been studied; however, the role of wider determinants of health on foot pain have received relatively little attention. Objectives of this study are i) to describe foot pain and foot health characteristics in an educated population of adults; ii) to explore associations between moderate-to-severe foot pain and a variety of factors including gender, age, medical conditions/co-morbidity/multi-morbidity, key indicators of general health, foot pathologies, and social determinants of health; and iii) to evaluate associations between moderate-to-severe foot pain and foot function, foot health and health-related quality-of-life. Methods Between February and March 2018, Glasgow Caledonian University Alumni with a working email address were invited to participate in the cross-sectional electronic survey (anonymously) by email via the Glasgow Caledonian University Alumni Office. The survey was constructed using the REDCap secure web online survey application and sought information on presence/absence of moderate-to-severe foot pain, patient characteristics (age, body mass index, socioeconomic status, occupation class, comorbidities, and foot pathologies). Prevalence data were expressed as absolute frequencies and percentages. Multivariate logistic and linear regressions were undertaken to identify associations 1) between independent variables and moderate-to-severe foot pain, and 2) between moderate-to-severe foot pain and foot function, foot health and health-related quality of life. Results Of 50,228 invitations distributed, there were 7707 unique views and 593 valid completions (median age [inter-quartile range] 42 [31–52], 67.3% female) of the survey (7.7% response rate). The sample was comprised predominantly of white Scottish/British (89.4%) working age adults (95%), the majority of whom were overweight or obese (57.9%), and in either full-time or part-time employment (82.5%) as professionals (72.5%). Over two-thirds (68.5%) of the sample were classified in the highest 6 deciles (most affluent) of social deprivation. Moderate-to-severe foot pain affected 236/593 respondents (39.8%). High body mass index, presence of bunions, back pain, rheumatoid arthritis, hip pain and lower occupation class were included in the final multivariate model and all were significantly and independently associated with moderate-to-severe foot pain (p < 0.05), except for rheumatoid arthritis (p = 0.057). Moderate-to-severe foot pain was significantly and independently associated lower foot function, foot health and health-related quality of life scores following adjustment for age, gender and body mass index (p < 0.05). Conclusions Moderate-to-severe foot pain was highly prevalent in a university-educated population and was independently associated with female gender, high body mass index, bunions, back pain, hip pain and lower occupational class. Presence of moderate-to-severe foot pain was associated with worse scores for foot function, foot health and health-related quality-of-life. Education attainment does not appear to be protective against moderate-to-severe foot pain
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