659 research outputs found
Type inference for linear algebra with units of measurement
Refining types of numerical data with units of measurement has the potential
to increase safety of programming languages but is restricted to homogeneous
units when checked statically with parametric polymorphism. We lift units to
vectors and show how type inference of linear algebra expressions can statically
determine safety for data with heterogeneous units. The typing is based on
the dyadic product of units that is found in linear transformations and the
corresponding vector spaces. Since it is a refinement of Kennedy’s types for
units we automatically obtain a unification algorithm, which gives principal
types for linear algebra. The extension of unit-unification to numerical data with
heterogeneous units makes the safety of statically checked numerical expressions
available to a significantly larger set of use-cases
Analytic approximation and an improved method for computing the stress-energy of quantized scalar fields in Robertson-Walker spacetimes
An improved method is given for the computation of the stress-energy tensor
of a quantized scalar field using adiabatic regularization. The method works
for fields with arbitrary mass and curvature coupling in Robertson-Walker
spacetimes and is particularly useful for spacetimes with compact spatial
sections. For massless fields it yields an analytic approximation for the
stress-energy tensor that is similar in nature to those obtained previously for
massless fields in static spacetimes.Comment: RevTeX, 8 pages, no figure
Global Sourcing
Since the early 1990s international - or even global - outsourcing of intermediate
products from suppliers has been propagated as a key means to improve the performance of
firms. It is argued that becoming more lean and internationally focused is beneficial for
the buyer as well as for the supplier . Global sourcing is currently believed to be a
common phenomenon. Drawing upon a recent survey among a representative sample of 200 large
Dutch manufacturing firms this paper gives an answer to the question to what extent
internationalization of sourcing is indeed taking place and whether it affects a firm's
performance.
The analysis reveals that for this sample of firms global sourcing is the exception rather
than the rule. Although firms undertake considerable international outsourcing, this is
mostly limited to nearby ( European Union) countries. Statistical tests reveal that there is
no significant relation between international outsourcing and either market or financial
performance. International outsourcing can not be used to adequately explain firm
performance. Therefore, an alternative approach is discussed, in which the degree of
(international) outsourcing is contingent upon factors like the size and location of the
headquarters of the firm
Characterisation of the mode of action of Aurodox, a Type III secretion system inhibitor from Streptomyces goldiniensis
Recent work has demonstrated that the polyketide natural product Aurodox, from Streptomyces goldiniensis is able to block the pathogenesis of the murine pathogen Citrobacter rodentium. In this work we aimed to aimed gain a better understanding of the mechanism of action of the compound. We show that Aurodox downregulates the expression of the Type Three Secretion Systems of enteropathogenic and enterohaemorhagic Escherichia coli. Furthermore, we have used transcriptomic analysis to show that Aurodox inhibits the expression at the transcriptional level by repressing the master regulator, ler. Our data support a model in which Aurodox acts upstream of ler and not directly on the secretion system itself. Finally, we have shown that Aurodox, unlike some traditional antibiotics, does not induce expression of RecA, which is essential for the production of Shiga toxin. We propose that these properties nominate Aurodox as a promising anti-virulence therapy for the treatment of these infections
Myocardial extracellular volume quantification by cardiovascularagn magnetic resonance and computed tomography
Purpose of review This review article discusses the evolution of extracellular volume (ECV) quantification using both cardiovascular magnetic resonance (CMR) and computed tomography (CT).
Recent findings Visualizing diffuse myocardial fibrosis is challenging and until recently, was restricted to the domain of the
pathologist. CMR and CT both use extravascular, extracellular contrast agents, permitting ECV measurement. The evidence base
around ECV quantification by CMR is growing rapidly and just starting in CT. In conditions with high ECV (amyloid, oedema
and fibrosis), this technique is already being used clinically and as a surrogate endpoint. Non-invasive diffuse fibrosis quantification is also generating new biological insights into key cardiac diseases.
Summary CMR and CT can estimate ECV and in turn diffuse myocardial fibrosis, obviating the need for invasive
endomyocardial biopsy. CT is an attractive alternative to CMR particularly in those individuals with contraindications to the
latter. Further studies are needed, particularly in CT
Effects of fluticasone propionate on methacholine dose-response curves in nonsmoking atopic asthmatics
Methacholine is frequently used to determine bronchial hyperresponsiveness
(BHR) and to generate dose-response curves. These curves are characterized
by a threshold (provocative concentration of methacholine producing a 20%
fall in forced expiratory volume in one second (PC20) = sensitivity),
slope (reactivity) and maximal response (plateau). We investigated the
efficacy of 12 weeks of treatment with 1,000 microg fluticasone propionate
in a double-blind, placebo-controlled study in 33 atopic asthmatics. The
outcome measures used were the influence on BHR and the different indices
of the methacholine dose-response (MDR) curve. After 2 weeks run-in,
baseline lung function data were obtained and a MDR curve was measured
with doubling concentrations of the methacholine from 0.03 to 256 mg x
mL(-1). MDR curves were repeated after 6 and 12 weeks. A recently
developed, sigmoid cumulative Gaussian distribution function was fitted to
the data. Although sensitivity was obtained by linear interpolation of two
successive log2 concentrations, reactivity, plateau and the effective
concentration at 50% of the plateau value (EC50) were obtained as best fit
parameters. In the fluticasone group, significant changes occurred after 6
weeks with respect to means of PC20 (an increase of 3.4 doubling doses),
plateau value fall in forced expiratory volume in one second (FEV1) (from
58% at randomization to 41% at 6 weeks) and baseline FEV1 (from 3.46 to
3.75 L) in contrast to the placebo group. Stabilization occurred after 12
weeks. Changes for reactivity were less marked, whereas changes in log,
EC50 were not significantly different between the groups. We conclude that
fluticasone is very effective in decreasing the maximal airway narrowing
response and in increasing PC20. However, it is likely that part of this
increase is related to the decrease of the plateau of maximal response
Method to compute the stress-energy tensor for the massless spin 1/2 field in a general static spherically symmetric spacetime
A method for computing the stress-energy tensor for the quantized, massless,
spin 1/2 field in a general static spherically symmetric spacetime is
presented. The field can be in a zero temperature state or a non-zero
temperature thermal state. An expression for the full renormalized
stress-energy tensor is derived. It consists of a sum of two tensors both of
which are conserved. One tensor is written in terms of the modes of the
quantized field and has zero trace. In most cases it must be computed
numerically. The other tensor does not explicitly depend on the modes and has a
trace equal to the trace anomaly. It can be used as an analytic approximation
for the stress-energy tensor and is equivalent to other approximations that
have been made for the stress-energy tensor of the massless spin 1/2 field in
static spherically symmetric spacetimes.Comment: 34 pages, no figure
Magnetic trapping of ultracold neutrons
Three-dimensional magnetic confinement of neutrons is reported. Neutrons are
loaded into an Ioffe-type superconducting magnetic trap through inelastic
scattering of cold neutrons with 4He. Scattered neutrons with sufficiently low
energy and in the appropriate spin state are confined by the magnetic field
until they decay. The electron resulting from neutron decay produces
scintillations in the liquid helium bath that results in a pulse of extreme
ultraviolet light. This light is frequency downconverted to the visible and
detected. Results are presented in which 500 +/- 155 neutrons are magnetically
trapped in each loading cycle, consistent with theoretical predictions. The
lifetime of the observed signal, 660 s +290/-170 s, is consistent with the
neutron beta-decay lifetime.Comment: 17 pages, 18 figures, accepted for publication in Physical Review
Laser ablation loading of a radiofrequency ion trap
The production of ions via laser ablation for the loading of radiofrequency
(RF) ion traps is investigated using a nitrogen laser with a maximum pulse
energy of 0.17 mJ and a peak intensity of about 250 MW/cm^2. A time-of-flight
mass spectrometer is used to measure the ion yield and the distribution of the
charge states. Singly charged ions of elements that are presently considered
for the use in optical clocks or quantum logic applications could be produced
from metallic samples at a rate of the order of magnitude 10^5 ions per pulse.
A linear Paul trap was loaded with Th+ ions produced by laser ablation. An
overall ion production and trapping efficiency of 10^-7 to 10^-6 was attained.
For ions injected individually, a dependence of the capture probability on the
phase of the RF field has been predicted. In the experiment this was not
observed, presumably because of collective effects within the ablation plume.Comment: submitted to Appl. Phys. B., special issue on ion trappin
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