2,291 research outputs found
PASCO: Structural panel analysis and sizing code: Users manual - Revised
A computer code denoted PASCO is described for analyzing and sizing uniaxially stiffened composite panels. Buckling and vibration analyses are carried out with a linked plate analysis computer code denoted VIPASA, which is included in PASCO. Sizing is based on nonlinear mathematical programming techniques and employs a computer code denoted CONMIN, also included in PASCO. Design requirements considered are initial buckling, material strength, stiffness and vibration frequency. A user's manual for PASCO is presented
Resonant-Cavity-Induced Phase Locking and Voltage Steps in a Josephson Array
We describe a simple dynamical model for an underdamped Josephson junction
array coupled to a resonant cavity. From numerical solutions of the model in
one dimension, we find that (i) current-voltage characteristics of the array
have self-induced resonant steps (SIRS), (ii) at fixed disorder and coupling
strength, the array locks into a coherent, periodic state above a critical
number of active Josephson junctions, and (iii) when active junctions are
synchronized on an SIRS, the energy emitted into the resonant cavity is
quadratic with . All three features are in agreement with a recent
experiment [Barbara {\it et al}, Phys. Rev. Lett. {\bf 82}, 1963 (1999)]}.Comment: 4 pages, 3 eps figures included. Submitted to PRB Rapid Com
A spectral method for elliptic equations: the Dirichlet problem
An elliptic partial differential equation Lu=f with a zero Dirichlet boundary
condition is converted to an equivalent elliptic equation on the unit ball. A
spectral Galerkin method is applied to the reformulated problem, using
multivariate polynomials as the approximants. For a smooth boundary and smooth
problem parameter functions, the method is proven to converge faster than any
power of 1/n with n the degree of the approximate Galerkin solution. Examples
in two and three variables are given as numerical illustrations. Empirically,
the condition number of the associated linear system increases like O(N), with
N the order of the linear system.Comment: This is latex with the standard article style, produced using
Scientific Workplace in a portable format. The paper is 22 pages in length
with 8 figure
Dynamics of a Josephson Array in a Resonant Cavity
We derive dynamical equations for a Josephson array coupled to a resonant
cavity by applying the Heisenberg equations of motion to a model Hamiltonian
described by us earlier [Phys. Rev. B {\bf 63}, 144522 (2001); Phys. Rev. B
{\bf 64}, 179902 (E)]. By means of a canonical transformation, we also show
that, in the absence of an applied current and dissipation, our model reduces
to one described by Shnirman {\it et al} [Phys. Rev. Lett. {\bf 79}, 2371
(1997)] for coupled qubits, and that it corresponds to a capacitive coupling
between the array and the cavity mode. From extensive numerical solutions of
the model in one dimension, we find that the array locks into a coherent,
periodic state above a critical number of active junctions, that the
current-voltage characteristics of the array have self-induced resonant steps
(SIRS's), that when active junctions are synchronized on a SIRS, the
energy emitted into the resonant cavity is quadratic in , and that when a
fixed number of junctions is biased on a SIRS, the energy is linear in the
input power. All these results are in agreement with recent experiments. By
choosing the initial conditions carefully, we can drive the array into any of a
variety of different integer SIRS's. We tentatively identify terms in the
equations of motion which give rise to both the SIRS's and the coherence
threshold. We also find higher-order integer SIRS's and fractional SIRS's in
some simulations. We conclude that a resonant cavity can produce threshold
behavior and SIRS's even in a one-dimensional array with appropriate
experimental parameters, and that the experimental data, including the coherent
emission, can be understood from classical equations of motion.Comment: 15 pages, 10 eps figures, submitted to Phys. Rev.
A Spectral Method for Elliptic Equations: The Neumann Problem
Let be an open, simply connected, and bounded region in
, , and assume its boundary is smooth.
Consider solving an elliptic partial differential equation over with a Neumann boundary condition. The problem is converted
to an equivalent elliptic problem over the unit ball , and then a spectral
Galerkin method is used to create a convergent sequence of multivariate
polynomials of degree that is convergent to . The
transformation from to requires a special analytical calculation
for its implementation. With sufficiently smooth problem parameters, the method
is shown to be rapidly convergent. For
and assuming is a boundary, the convergence of
to zero is faster than any power of .
Numerical examples in and show experimentally
an exponential rate of convergence.Comment: 23 pages, 11 figure
The potential health impact of restricting less-healthy food and beverage advertising on UK television between 05.30 and 21.00 hours: A modelling study
BACKGROUND: Restrictions on the advertising of less-healthy foods and beverages is seen as one measure to tackle childhood obesity and is under active consideration by the UK government. Whilst evidence increasingly links this advertising to excess calorie intake, understanding of the potential impact of advertising restrictions on population health is limited. METHODS AND FINDINGS: We used a proportional multi-state life table model to estimate the health impact of prohibiting the advertising of food and beverages high in fat, sugar, and salt (HFSS) from 05.30 hours to 21.00 hours (5:30 AM to 9:00 PM) on television in the UK. We used the following data to parameterise the model: children's exposure to HFSS advertising from AC Nielsen and Broadcasters' Audience Research Board (2015); effect of less-healthy food advertising on acute caloric intake in children from a published meta-analysis; population numbers and all-cause mortality rates from the Human Mortality Database for the UK (2015); body mass index distribution from the Health Survey for England (2016); disability weights for estimating disability-adjusted life years (DALYs) from the Global Burden of Disease Study; and healthcare costs from NHS England programme budgeting data. The main outcome measures were change in the percentage of the children (aged 5-17 years) with obesity defined using the International Obesity Task Force cut-points, and change in health status (DALYs). Monte Carlo analyses was used to estimate 95% uncertainty intervals (UIs). We estimate that if all HFSS advertising between 05.30 hours and 21.00 hours was withdrawn, UK children (n = 13,729,000), would see on average 1.5 fewer HFSS adverts per day and decrease caloric intake by 9.1 kcal (95% UI 0.5-17.7 kcal), which would reduce the number of children (aged 5-17 years) with obesity by 4.6% (95% UI 1.4%-9.5%) and with overweight (including obesity) by 3.6% (95% UI 1.1%-7.4%) This is equivalent to 40,000 (95% UI 12,000-81,000) fewer UK children with obesity, and 120,000 (95% UI 34,000-240,000) fewer with overweight. For children alive in 2015 (n = 13,729,000), this would avert 240,000 (95% UI 65,000-530,000) DALYs across their lifetime (i.e., followed from 2015 through to death), and result in a health-related net monetary benefit of £7.4 billion (95% UI £2.0 billion-£16 billion) to society. Under a scenario where all HFSS advertising is displaced to after 21.00 hours, rather than withdrawn, we estimate that the benefits would be reduced by around two-thirds. This is a modelling study and subject to uncertainty; we cannot fully and accurately account for all of the factors that would affect the impact of this policy if implemented. Whilst randomised trials show that children exposed to less-healthy food advertising consume more calories, there is uncertainty about the nature of the dose-response relationship between HFSS advertising and calorie intake. CONCLUSIONS: Our results show that HFSS television advertising restrictions between 05.30 hours and 21.00 hours in the UK could make a meaningful contribution to reducing childhood obesity. We estimate that the impact on childhood obesity of this policy may be reduced by around two-thirds if adverts are displaced to after 21.00 hours rather than being withdrawn
How Reasoning Aims at Truth
Many hold that theoretical reasoning aims at truth. In this paper, I ask what it is for reasoning to be thus aim-directed. Standard answers to this question explain reasoning’s aim-directedness in terms of intentions, dispositions, or rule-following. I argue that, while these views contain important insights, they are not satisfactory. As an alternative, I introduce and defend a novel account: reasoning aims at truth in virtue of being the exercise of a distinctive kind of cognitive power, one that, unlike ordinary dispositions, is capable of fully explaining its own exercises. I argue that this account is able to avoid the difficulties plaguing standard accounts of the relevant sort of mental teleology
Theory of Two-Dimensional Josephson Arrays in a Resonant Cavity
We consider the dynamics of a two-dimensional array of underdamped Josephson
junctions placed in a single-mode resonant cavity. Starting from a well-defined
model Hamiltonian, which includes the effects of driving current and
dissipative coupling to a heat bath, we write down the Heisenberg equations of
motion for the variables of the Josephson junction and the cavity mode,
extending our previous one-dimensional model. In the limit of large numbers of
photons, these equations can be expressed as coupled differential equations and
can be solved numerically. The numerical results show many features similar to
experiment. These include (i) self-induced resonant steps (SIRS's) at voltages
V = (n hbar Omega)/(2e), where Omega is the cavity frequency, and n is
generally an integer; (ii) a threshold number N_c of active rows of junctions
above which the array is coherent; and (iii) a time-averaged cavity energy
which is quadratic in the number of active junctions, when the array is above
threshold. Some differences between the observed and calculated threshold
behavior are also observed in the simulations and discussed. In two dimensions,
we find a conspicuous polarization effect: if the cavity mode is polarized
perpendicular to the direction of current injection in a square array, it does
not couple to the array and there is no power radiated into the cavity. We
speculate that the perpendicular polarization would couple to the array, in the
presence of magnetic-field-induced frustration. Finally, when the array is
biased on a SIRS, then, for given junction parameters, the power radiated into
the array is found to vary as the square of the number of active junctions,
consistent with expectations for a coherent radiation.Comment: 11 pages, 8 eps figures, submitted to Phys. Rev
Spin-excitations of the quantum Hall ferromagnet of composite fermions
The spin-excitations of a fractional quantum Hall system are evaluated within
a bosonization approach. In a first step, we generalize Murthy and Shankar's
Hamiltonian theory of the fractional quantum Hall effect to the case of
composite fermions with an extra discrete degree of freedom. Here, we mainly
investigate the spin degrees of freedom, but the proposed formalism may be
useful also in the study of bilayer quantum-Hall systems, where the layer index
may formally be treated as an isospin. In a second step, we apply a
bosonization scheme, recently developed for the study of the two-dimensional
electron gas, to the interacting composite-fermion Hamiltonian. The dispersion
of the bosons, which represent quasiparticle-quasihole excitations, is
analytically evaluated for fractional quantum Hall systems at \nu = 1/3 and \nu
= 1/5. The finite width of the two-dimensional electron gas is also taken into
account explicitly. In addition, we consider the interacting bosonic model and
calculate the lowest-energy state for two bosons. Besides a continuum
describing scattering states, we find a bound-state of two bosons. This state
is interpreted as a pair excitation, which consists of a skyrmion of composite
fermions and an antiskyrmion of composite fermions. The dispersion relation of
the two-boson state is evaluated for \nu = 1/3 and \nu = 1/5. Finally, we show
that our theory provides the microscopic basis for a phenomenological
non-linear sigma-model for studying the skyrmion of composite fermions.Comment: Revised version, 14 pages, 4 figures, accepted to Phys. Rev.
The metallic state in disordered quasi-one-dimensional conductors
The unusual metallic state in conjugated polymers and single-walled carbon
nanotubes is studied by dielectric spectroscopy (8--600 GHz). We have found an
intriguing correlation between scattering time and plasma frequency. This
relation excludes percolation models of the metallic state. Instead, the
carrier dynamics can be understood in terms of the low density of delocalized
states around the Fermi level, which arises from the competion between
disorder-induced localization and interchain-interactions-induced
delocalization.Comment: 4 pages including 4 figure
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