122 research outputs found
Factor ordering in standard quantum cosmology
The Wheeler-DeWitt equation of Friedmann models with a massless quantum field
is formulated with arbitrary factor ordering of the Hamiltonian constraint
operator. A scalar product of wave functions is constructed, giving rise to a
probability interpretation and making comparison with the classical solution
possible. In general the bahaviour of the wave function of the model depends on
a critical energy of the matter field, which, in turn, depends on the chosen
factor ordering. By certain choices of the ordering the critical energy can be
pushed down to zero.Comment: 15 pages, 3 figure
On plane gravitational waves in real connection variables
We investigate using plane fronted gravitational wave space-times as model
systems to study loop quantization techniques and dispersion relations. In this
classical analysis, we start with planar symmetric space-times in the real
connection formulation. We reduce via Dirac constraint analysis to a final form
with one canonical pair and one constraint, equivalent to the metric and
Einstein equations of plane-fronted with parallel rays waves. Due to the
symmetries and use of special coordinates general covariance is broken.
However, this allows us to simply express the constraints of the consistent
system. A recursive construction of Dirac brackets results in non-local
brackets, analogous to those of self-dual fields, for the triad variables
chosen in this approach.Comment: v2: Matches published version, up to minor stylistic change
Isotropic Loop Quantum Cosmology with Matter
A free massless scalar field is coupled to homogeneous and isotropic loop
quantum cosmology. The coupled model is investigated in the vicinity of the
classical singularity, where discreteness is essential and where the quantum
model is non-singular, as well as in the regime of large volumes, where it
displays the expected semiclassical features. The particular matter content
(massless, free scalar) is chosen to illustrate how the discrete structure
regulates pathological behavior caused by kinetic terms of matter Hamiltonians
(which in standard quantum cosmology lead to wave functions with an infinite
number of oscillations near the classical singularity). Due to this
modification of the small volume behavior the dynamical initial conditions of
loop quantum cosmology are seen to provide a meaningful generalization of
DeWitt's initial condition.Comment: 18 pages, 4 figure
Towards Loop Quantization of Plane Gravitational Waves
The polarized Gowdy model in terms of Ashtekar-Barbero variables is further
reduced by including the Killing equations for plane-fronted parallel
gravitational waves with parallel rays. The resulting constraint algebra,
including one constraint derived from the Killing equations in addition to the
standard ones of General Relativity, are shown to form a set of first-class
constraints. Using earlier work by Banerjee and Date the constraints are
expressed in terms of classical quantities that have an operator equivalent in
Loop Quantum Gravity, making space-times with pp-waves accessible to loop
quantization techniques.Comment: 14 page
NUT Carcinoma—An Underdiagnosed Malignancy
NUT carcinoma (NC) is a rare and highly aggressive malignancy with a dismal prognosis and a median survival of 6–9 months only. Although very few cases of NC are reported each year, the true prevalence is estimated to be much higher, with NC potentially widely underdiagnosed due to the lack of awareness. NC primarily occurs in midline structures including thorax, head, and neck; however, other sites such as pancreas and kidney are also affected, albeit at lower frequencies. NC is characterized by a single translocation involving the NUTM1 (NUT midline carcinoma family member 1) gene and different partner genes. The resulting fusion proteins initiate tumorigenesis through a mechanism involving BET (bromo-domain and extra-terminal motif) proteins such as Bromodomain-containing protein 4 (BRD4) and inordinate acetylation of chromatin, leading to the dysregulation of growth and differentiation genes. While no clinical characteristics are specific for NC, some histologic features can be indicative; therefore, patients with these tumor characteristics should be routinely tested for NUTM1. The diagnosis of NC using immunohistochemistry with a highly specific antibody is straightforward. There are currently no standard-of-care treatment options for patients with NC. However, novel therapies specifically addressing the unique tumorigenic mechanism are under investigation, including BET inhibitors. This review aims to raise awareness of this underdiagnosed cancer entity and provide all patients the opportunity to be properly diagnosed and referred to a clinical study
Combining data of different GPR systems of surveys of the roman fort Qreiye-cAyyash, Syria
Introduction The Roman fort of Qreiye-cAyyash was founded in the late 2nd or early 3rd century AD and was abandoned in the mid-third of the 3rd century AD. It is situated immediately north of the modern village of cAyyash, 12 km upstream from Deir ez-Zor in Syria, on the edge of a plateau overlooking the valley of the river Euphrates. The Roman fort comprises 220 x 220Â m and was discovered in 1929 by A. Poidebard in the course of an aerial photographic reconnaissance (Poidebard, 1934, 87-88, ..
Wavelength-selected Neutron Pulses Formed by a Spatial Magnetic Neutron Spin Resonator
AbstractWe present a novel type of spatial magnetic neutron spin resonator whose time and wavelength resolution can be de- coupled from each other by means of a travelling wave mode of operation. Combined with a pair of highly efficient polarisers such a device could act simultaneously as monochromator and chopper, able to produce short neutron pulses, whose wavelength, spectral width and duration could be varied almost instantaneously by purely electronic means with- out any mechanical modification of the experimental setup. To demonstrate the practical feasibility of this technique we have designed and built a first prototype resonator consisting of ten individually switchable modules which allows to produce neutron pulses in the microsecond regime. It was installed at a polarised 2.6Ă… neutron beamline at the 250kW TRIGA research reactor of the Vienna University of Technology where it could deliver pulses of 55ÎĽs duration, which is about three times less than the passage time of the neutrons through the resonator itself. In order to further improve the achievable wavelength resolution to about 3% a second prototype resonator, consisting of 48 individual modules with optimised field homogeneity and enlarged beam cross-section of 6 Ă— 6cm2 was developed. We present the results of first measurements which demonstrate the successful operation of this device
Combining data of different GPR systems of surveys of the roman fort Qreiye-cAyyash, Syria
Introduction The Roman fort of Qreiye-cAyyash was founded in the late 2nd or early 3rd century AD and was abandoned in the mid-third of the 3rd century AD. It is situated immediately north of the modern village of cAyyash, 12 km upstream from Deir ez-Zor in Syria, on the edge of a plateau overlooking the valley of the river Euphrates. The Roman fort comprises 220 x 220Â m and was discovered in 1929 by A. Poidebard in the course of an aerial photographic reconnaissance (Poidebard, 1934, 87-88, ..
Big Crunch Avoidance in k = 1 Semi-Classical Loop Quantum Cosmology
It is well known that a closed universe with a minimally coupled massive
scalar field always collapses to a singularity unless the initial conditions
are extremely fine tuned. We show that the corrections to the equations of
motion for the massive scalar field, given by loop quantum gravity in high
curvature regime, always lead to a bounce independently of the initial
conditions. In contrast to the previous works in loop quantum cosmology, we
note that the singularity can be avoided even at the semi-classical level of
effective dynamical equations with non-perturbative quantum gravity
modifications, without using a discrete quantum evolution.Comment: Minor changes, To appear in Physical Review
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