32,983 research outputs found
Isochronal synchronization of delay-coupled systems
We consider small network models for mutually delay-coupled systems which
typically do not exhibit stable isochronally synchronized solutions. We show
that for certain coupling architectures which involve delayed self feedback to
the nodes, the oscillators become isochronally synchronized. Applications are
shown for both incoherent pump coupled lasers and spatio-temporal coupled fiber
ring lasers.Comment: 5 pages, accepted for publication in Physical Review
Unethical aspects of homeopathic dentistry
In the last year there has been a great deal of public debate about homeopathy, the system of alternative medicine whose main principles are that like cures like and that potency increases relative to dilution. The House of Commons Select Committee on Science and Technology concluded in November 2009 that there is no evidence base for homeopathy, and agreed with some academic commentators that homeopathy should not be funded by the NHS. While homeopathic doctors and hospitals are quite commonplace, some might be surprised to learn that there are also many homeopathic dentists practising in the UK. This paper examines the statements made by several organisations on behalf of homeopathic dentistry and suggests that they are not entirely ethical and may be in breach of various professional guidelines
Antioxidant requirements of rats exposed to 100 % oxygen. Part 2 - Effects of dietary ascorbic acid
Dietary ascorbic acid effects as antioxidants in rats exposed to 100 percent oxyge
Ethnic parity in labour market outcomes for benefit claimants
A significant gap exists in the UK between the employment rate for Ethnic Minorities and that for
Whites. From a policy perspective, it is important to know whether this gap is due to differences in
the characteristics of White and Ethnic Minority groups (which reduce the employability of Ethnic
Minority groups relative to Whites) or whether it results from some form of discriminatory behaviour
in the labour market. In this paper, we use administrative data to estimate ethnic differences in
employment and benefit receipt amongst individuals who began claiming a Jobcentre Plus benefit
in 2003. In contrast to much of the previous UK literature, we use a number of different quantitative
techniques to estimate this gap, and show that in a lot of cases the estimates obtained are very
sensitive to the techniques used. We argue that for the questions we are interested in and the data
we have, propensity score matching methods are the most robust approach to estimating ethnic
parity. We compare this preferred approach with estimates derived using alternative approaches
commonly used in the literature (generally regression-based techniques) to determine the extent to
which more straightforward methods are able to replicate those produced by matching. In many
cases, it turns out not to be possible to calculate satisfactory quantitative estimates even with
matching techniques: the characteristics of Whites and Ethnic Minorities are simply too different
before the Jobcentre Plus intervention to reliably estimate the parameters of interest. Moreover, for
a number of the groups, results seem to be very sensitive to the methodology used. This calls into
question previous results based on simple regression techniques, which are likely to hide the fact
that observationally different ethnic groups are de facto being compared on the basis of parametric
extrapolations. Two groups for which it was possible to calculate reasonably reliable results are
incapacity benefit (IB) and income support (IS). For these groups we find that large and significant
raw penalties almost always disappear once we appropriately control for pre-inflow background
and labour market characteristics. There is also a good degree of consistency across
methodologies
Screening of the transcriptional regulatory regions of vascular endothelial growth factor receptor 2 (VEGFR2) in amyotrophic lateral sclerosis
Background
Vascular endothelial growth factor (VEGF) has neurotrophic activity which is mediated by its main agonist receptor, VEGFR2. Dysregulation of VEGF causes motor neurone degeneration in a mouse model of amyotrophic lateral sclerosis (ALS), and expression of VEGFR2 is reduced in motor neurones and spinal cord of patients with ALS.
Methods
We have screened the promoter region and 4 exonic regions of functional significance of the VEGFR2 gene in a UK population of patients with ALS, for mutations and polymorphisms that may affect expression or function of this VEGF receptor.
Results
No mutations were identified in the VEGFR2 gene. We found no association between polymorphisms in the regulatory regions of the VEGFR2 gene and ALS.
Conclusion
Mechanisms other than genetic variation may downregulate expression or function of the VEGFR2 receptor in patients with ALS
The glitch activity of neutron stars
We present a statistical study of the glitch population and the behaviour of
the glitch activity across the known population of neutron stars. An unbiased
glitch database was put together based on systematic searches of radio timing
data of 898 rotation-powered pulsars obtained with the Jodrell Bank and Parkes
observatories. Glitches identified in similar searches of 5 magnetars were also
included. The database contains 384 glitches found in the rotation of 141 of
these neutron stars. We confirm that the glitch size distribution is at least
bimodal, with one sharp peak at approximately , which we
call large glitches, and a broader distribution of smaller glitches. We also
explored how the glitch activity , defined as the mean
frequency increment per unit of time due to glitches, correlates with the spin
frequency , spin-down rate , and various combinations of
these, such as energy loss rate, magnetic field, and spin-down age. It is found
that the activity is insensitive to the magnetic field and that it correlates
strongly with the energy loss rate, though magnetars deviate from the trend
defined by the rotation-powered pulsars. However, we find that a constant ratio
is consistent with the behaviour
of all rotation-powered pulsars and magnetars. This relation is dominated by
large glitches, which occur at a rate directly proportional to .
The only exception are the rotation-powered pulsars with the highest values of
, such as the Crab pulsar and PSR B054069, which exhibit a much
smaller glitch activity, intrinsically different from each other and from the
rest of the population. The activity due to small glitches also shows an
increasing trend with , but this relation is biased by selection
effects.Comment: Accepted for publication in A&
Laser Interferometer Gravitational-Wave Observatory beam tube component and module leak testing
Laser Interferometer Gravitational-Wave Observatory (LIGO) is a joint project of the California Institute of Technology and the Massachusetts Institute of Technology funded by the National Science Foundation. The project is designed to detect gravitational waves from astrophysical sources such as supernova and black holes. The LIGO project constructed observatories at two sites in the U.S. Each site includes two beam tubes (each 4 km long) joined to form an "L" shape. The beam tube is a 1.25 m diam 304 L stainless steel, ultrahigh vacuum tube that will operate at 1×10^–9 Torr or better. The beam tube was manufactured using a custom spiral weld tube mill from material processed to reduce the outgassing rate in order to minimize pumping costs. The integrity of the beam tube was assured by helium mass spectrometer leak testing each component of the beam tube system prior to installation. Each 2 km long, isolatable beam tube module was then leak tested after completion
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