730 research outputs found
Method for rating power cables buried in surface troughs
An alternative method is detailed by which the ambient temperature parameter as applied to the calculation of ratings of cables buried in surface trough installations can be determined. Improvement in the accuracy of cable rating calculations will allow greater utilisation of the cable asset and assist for example in the planning of system outages for maintenance work. The proposed model calculates the temperature at the cable burial depth based on measurements of solar radiation, windspeed and air temperature. The model is based on physical laws rather than empirical approaches that have been shown to be generally conservative in application. Results based on weather data monitored over a two-year period show that the ambient temperature of the soil at cable depth can be accurately determined and the model provides a significant improvement on existing methods
Complete measurements of quantum observables
We define a complete measurement of a quantum observable (POVM) as a
measurement of the maximally refined version of the POVM. Complete measurements
give information from the multiplicities of the measurement outcomes and can be
viewed as state preparation procedures. We show that any POVM can be measured
completely by using sequential measurements or maximally refinable instruments.
Moreover, the ancillary space of a complete measurement can be chosen to be
minimal.Comment: Based on talk given in CEQIP 2012 conferenc
On the complementarity of the quadrature observables
In this paper we investigate the coupling properties of pairs of quadrature
observables, showing that, apart from the Weyl relation, they share the same
coupling properties as the position-momentum pair. In particular, they are
complementary. We determine the marginal observables of a covariant phase space
observable with respect to an arbitrary rotated reference frame, and observe
that these marginal observables are unsharp quadrature observables. The related
distributions constitute the Radon tranform of a phase space distribution of
the covariant phase space observable. Since the quadrature distributions are
the Radon transform of the Wigner function of a state, we also exhibit the
relation between the quadrature observables and the tomography observable, and
show how to construct the phase space observable from the quadrature
observables. Finally, we give a method to measure together with a single
measurement scheme any complementary pair of quadrature observables.Comment: Dedicated to Peter Mittelstaedt in honour of his eightieth birthda
Formulation and implementation of decohesion elements in an explicit finite element code
The Future Evolution of White Dwarf Stars Through Baryon Decay and Time Varying Gravitational Constant
Motivated by the possibility that the fundamental ``constants'' of nature
could vary with time, this paper considers the long term evolution of white
dwarf stars under the combined action of proton decay and variations in the
gravitational constant. White dwarfs are thus used as a theoretical laboratory
to study the effects of possible time variations, especially their implications
for the future history of the universe. More specifically, we consider the
gravitational constant to vary according to the parametric relation , where the time scale is the same order as
the proton lifetime. We then study the long term fate and evolution of white
dwarf stars. This treatment begins when proton decay dominates the stellar
luminosity, and ends when the star becomes optically thin to its internal
radiation.Comment: 12 pages, 10 figures, accepted to Astrophysics and Space Scienc
Tunneling times with covariant measurements
We consider the time delay of massive, non-relativistic, one-dimensional
particles due to a tunneling potential. In this setting the well-known Hartman
effect asserts that often the sub-ensemble of particles going through the
tunnel seems to cross the tunnel region instantaneously. An obstacle to the
utilization of this effect for getting faster signals is the exponential
damping by the tunnel, so there seems to be a trade-off between speedup and
intensity. In this paper we prove that this trade-off is never in favor of
faster signals: the probability for a signal to reach its destination before
some deadline is always reduced by the tunnel, for arbitrary incoming states,
arbitrary positive and compactly supported tunnel potentials, and arbitrary
detectors. More specifically, we show this for several different ways to define
``the same incoming state'' and ''the same detector'' when comparing the
settings with and without tunnel potential. The arrival time measurements are
expressed in the time-covariant approach, but we also allow the detection to be
a localization measurement at a later time.Comment: 12 pages, 2 figure
Sharp and fuzzy observables on effect algebras
Observables on effect algebras and their fuzzy versions obtained by means of
confidence measures (Markov kernels) are studied. It is shown that, on effect
algebras with the (E)-property, given an observable and a confidence measure,
there exists a fuzzy version of the observable. Ordering of observables
according to their fuzzy properties is introduced, and some minimality
conditions with respect to this ordering are found. Applications of some
results of classical theory of experiments are considered.Comment: 23 page
Quantum spin systems at positive temperature
We develop a novel approach to phase transitions in quantum spin models based
on a relation to their classical counterparts. Explicitly, we show that
whenever chessboard estimates can be used to prove a phase transition in the
classical model, the corresponding quantum model will have a similar phase
transition, provided the inverse temperature and the magnitude of the
quantum spins \CalS satisfy \beta\ll\sqrt\CalS. From the quantum system we
require that it is reflection positive and that it has a meaningful classical
limit; the core technical estimate may be described as an extension of the
Berezin-Lieb inequalities down to the level of matrix elements. The general
theory is applied to prove phase transitions in various quantum spin systems
with \CalS\gg1. The most notable examples are the quantum orbital-compass
model on and the quantum 120-degree model on which are shown to
exhibit symmetry breaking at low-temperatures despite the infinite degeneracy
of their (classical) ground state.Comment: 47 pages, version to appear in CMP (style files included
Mutations of the BRAF gene in human cancer
Cancers arise owing to the accumulation of mutations in critical genes that alter normal programmes of cell proliferation, differentiation and death. As the first stage of a systematic genome-wide screen for these genes, we have prioritized for analysis signalling pathways in which at least one gene is mutated in human cancer. The RAS RAF MEK ERK MAP kinase pathway mediates cellular responses to growth signals. RAS is mutated to an oncogenic form in about 15% of human cancer. The three RAF genes code for cytoplasmic serine/threonine kinases that are regulated by binding RAS. Here we report BRAF somatic missense mutations in 66% of malignant melanomas and at lower frequency in a wide range of human cancers. All mutations are within the kinase domain, with a single substitution (V599E) accounting for 80%. Mutated BRAF proteins have elevated kinase activity and are transforming in NIH3T3 cells. Furthermore, RAS function is not required for the growth of cancer cell lines with the V599E mutation. As BRAF is a serine/threonine kinase that is commonly activated by somatic point mutation in human cancer, it may provide new therapeutic opportunities in malignant melanoma
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