11,426 research outputs found
Discrete-Time Path Distributions on Hilbert Space
We construct a path distribution representing the kinetic part of the Feynman
path integral at discrete times similar to that defined by Thomas [1], but on a
Hilbert space of paths rather than a nuclear sequence space. We also consider
different boundary conditions and show that the discrete-time Feynman path
integral is well-defined for suitably smooth potentials
Three-dimensional Quantum Slit Diffraction and Diffraction in Time
We study the quantum slit diffraction problem in three dimensions. In the
treatment of diffraction of particles by a slit, it is usually assumed that the
motion perpendicular to the slit is classical. Here we take into account the
effect of the quantum nature of the motion perpendicular to the slit using the
Green function approach [18]. We treat the diffraction of a Gaussian wave
packet for general boundary conditions on the shutter. The difference between
the standard and our three-dimensional slit diffraction models is analogous to
the diffraction in time phenomenon introduced in [16]. We derive corrections to
the standard formula for the diffraction pattern, and we point out situations
in which this might be observable. In particular, we discuss the diffraction in
space and time in the presence of gravity
Do Malaria Vector control Measures Impact Disease-Related Behaviour and Knowledge? Evidence from a Large-scale Larviciding Intervention in Tanzania.
Recent efforts of accelerated malaria control towards the long-term goal of elimination had significant impacts in reducing malaria transmission. While these efforts need to be sustained over time, a scenario of low transmission could bring about changes in individual disease risk perception, hindering adherence to protective measures, and affecting disease-related knowledge. The goal of this study was to investigate the potential impact of a successful malaria vector control intervention on bed net usage and malaria-related knowledge. Dar es Salaam's Urban Malaria Control Program was launched in 2004 with the aim of developing a sustainable larviciding intervention. Larviciding was scaled-up using a stepped-wedge design. Cross-sectional and longitudinal data were collected using a randomized cluster sampling design (2004--2008). Prevalence ratios (PR) for the effect of the larviciding intervention on bed net usage (N = 64,537) and household heads' knowledge of malaria symptoms and transmission (N = 11,254) were obtained from random effects regression models.\ud
The probability that individuals targeted by larviciding had used a bed net was reduced by 5% as compared to those in non-intervention areas (PR = 0.95; 95% credible intervals (CrI): 0.94-0.97) and the magnitude of this effect increased with time. Larviciding also led to a decline in household heads' knowledge of malaria symptoms (PR = 0.88; 95% CrI: 0.83-0.92) but no evidence of effect on knowledge of malaria transmission was found. Successful control interventions could bring about further challenges to sustaining gains in reducing malaria transmission if not accompanied by strategies to avoid changes in individual knowledge and behaviour. This study points to two major research gaps. First, there is an urgent need to gather more evidence on the extent to which countries that have achieved significant decline in malaria transmission are also observing changes in individual behaviour and knowledge. Second, multidisciplinary assessments that combine quantitative and qualitative data, utilizing theories of health behaviour and theories of knowledge, are needed to optimize efforts of national malaria control programmes, and ultimately contribute to sustained reduction in malaria transmission
- Glueball Spectrum within a Constituent Picture
The quantum numbers and mass hierarchy of the glueballs observed in
-dimensional lattice QCD with gauge group SU() are shown to be in
agreement with a constituent picture. The agreement is maintained when going
from glueballs to gluelumps, and when the gauge group SO() is taken
instead of SU()
String deformations induced by retardation effects
The rotating string model is an effective model of mesons, in which the quark
and the antiquark are linked by a straight string. We previously developed a
new framework to include the retardation effects in the rotating string model,
but the string was still kept straight. We now go a step further and show that
the retardation effects cause a small deviation of the string from the straight
line. We first give general arguments constraining the string shape. Then, we
find analytical and numerical solutions for the string deformation induced by
retardation effects. We finally discuss the influence of the curved string on
the energy spectrum of the model.Comment: 3 figure
Recognizing well-parenthesized expressions in the streaming model
Motivated by a concrete problem and with the goal of understanding the sense
in which the complexity of streaming algorithms is related to the complexity of
formal languages, we investigate the problem Dyck(s) of checking matching
parentheses, with different types of parenthesis.
We present a one-pass randomized streaming algorithm for Dyck(2) with space
\Order(\sqrt{n}\log n), time per letter \polylog (n), and one-sided error.
We prove that this one-pass algorithm is optimal, up to a \polylog n factor,
even when two-sided error is allowed. For the lower bound, we prove a direct
sum result on hard instances by following the "information cost" approach, but
with a few twists. Indeed, we play a subtle game between public and private
coins. This mixture between public and private coins results from a balancing
act between the direct sum result and a combinatorial lower bound for the base
case.
Surprisingly, the space requirement shrinks drastically if we have access to
the input stream in reverse. We present a two-pass randomized streaming
algorithm for Dyck(2) with space \Order((\log n)^2), time \polylog (n) and
one-sided error, where the second pass is in the reverse direction. Both
algorithms can be extended to Dyck(s) since this problem is reducible to
Dyck(2) for a suitable notion of reduction in the streaming model.Comment: 20 pages, 5 figure
Bayesian Inference from Composite Likelihoods, with an Application to Spatial Extremes
Composite likelihoods are increasingly used in applications where the full
likelihood is analytically unknown or computationally prohibitive. Although the
maximum composite likelihood estimator has frequentist properties akin to those
of the usual maximum likelihood estimator, Bayesian inference based on
composite likelihoods has yet to be explored. In this paper we investigate the
use of the Metropolis--Hastings algorithm to compute a pseudo-posterior
distribution based on the composite likelihood. Two methodologies for adjusting
the algorithm are presented and their performance on approximating the true
posterior distribution is investigated using simulated data sets and real data
on spatial extremes of rainfall
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