96 research outputs found
Quantum Gowdy model: A unitary description
The quantization of the family of linearly polarized Gowdy spacetimes
is discussed in detail, starting with a canonical analysis in which the true
degrees of freedom are described by a scalar field that satisfies a
Klein-Gordon type equation in a fiducial time dependent background. A time
dependent canonical transformation, which amounts to a change of the basic
(scalar) field of the model, brings the system to a description in terms of a
Klein-Gordon equation on a background that is now static, although subject to a
time dependent potential. The system is quantized by means of a natural choice
of annihilation and creation operators. The quantum time evolution is
considered and shown to be unitary, allowing both the Schr\"odinger and
Heisenberg pictures to be consistently constructed. This has to be contrasted
with previous treatments for which time evolution failed to be implementable as
a unitary transformation. Possible implications for both canonical quantum
gravity and quantum field theory in curved spacetime are commented
Functional Evolution of Free Quantum Fields
We consider the problem of evolving a quantum field between any two (in
general, curved) Cauchy surfaces. Classically, this dynamical evolution is
represented by a canonical transformation on the phase space for the field
theory. We show that this canonical transformation cannot, in general, be
unitarily implemented on the Fock space for free quantum fields on flat
spacetimes of dimension greater than 2. We do this by considering time
evolution of a free Klein-Gordon field on a flat spacetime (with toroidal
Cauchy surfaces) starting from a flat initial surface and ending on a generic
final surface. The associated Bogolubov transformation is computed; it does not
correspond to a unitary transformation on the Fock space. This means that
functional evolution of the quantum state as originally envisioned by Tomonaga,
Schwinger, and Dirac is not a viable concept. Nevertheless, we demonstrate that
functional evolution of the quantum state can be satisfactorily described using
the formalism of algebraic quantum field theory. We discuss possible
implications of our results for canonical quantum gravity.Comment: 21 pages, RevTeX, minor improvements in exposition, to appear in
Classical and Quantum Gravit
Applications of Canonical Transformations
Canonical transformations are defined and discussed along with the
exponential, the coherent and the ultracoherent vectors. It is shown that the
single-mode and the -mode squeezing operators are elements of the group of
canonical transformations. An application of canonical transformations is made,
in the context of open quantum systems, by studying the effect of squeezing of
the bath on the decoherence properties of the system. Two cases are analyzed.
In the first case the bath consists of a massless bosonic field with the bath
reference states being the squeezed vacuum states and squeezed thermal states
while in the second case a system consisting of a harmonic oscillator
interacting with a bath of harmonic oscillators is analyzed with the bath being
initially in a squeezed thermal state.Comment: 14 page
Coherent States of the q--Canonical Commutation Relations
For the -deformed canonical commutation relations for in some Hilbert
space we consider representations generated from a vector
satisfying , where .
We show that such a representation exists if and only if .
Moreover, for these representations are unitarily equivalent
to the Fock representation (obtained for ). On the other hand
representations obtained for different unit vectors are disjoint. We
show that the universal C*-algebra for the relations has a largest proper,
closed, two-sided ideal. The quotient by this ideal is a natural -analogue
of the Cuntz algebra (obtained for ). We discuss the Conjecture that, for
, this analogue should, in fact, be equal to the Cuntz algebra
itself. In the limiting cases we determine all irreducible
representations of the relations, and characterize those which can be obtained
via coherent states.Comment: 19 pages, Plain Te
A new mathematical problem related to quantization of fields
This paper is a survey of author's mathematical and logical study of the
problem of quantization of fields.Comment: 11 pages, to appear in Russian Journal of Math. Phys. arXiv admin
note: text overlap with arXiv:hep-th/0601080, arXiv:1110.000
Quantization of Midisuperspace Models
We give a comprehensive review of the quantization of midisuperspace models.
Though the main focus of the paper is on quantum aspects, we also provide an
introduction to several classical points related to the definition of these
models. We cover some important issues, in particular, the use of the principle
of symmetric criticality as a very useful tool to obtain the required
Hamiltonian formulations. Two main types of reductions are discussed: those
involving metrics with two Killing vector fields and spherically symmetric
models. We also review the more general models obtained by coupling matter
fields to these systems. Throughout the paper we give separate discussions for
standard quantizations using geometrodynamical variables and those relying on
loop quantum gravity inspired methods.Comment: To appear in Living Review in Relativit
Introduction to representations of the canonical commutation and anticommutation relations
Lecture notes of a minicourse given at the Summer School on Large Coulomb
Systems - QED in Nordfjordeid, 2003, devoted to representations of the CCR and
CAR. Quasifree states, the Araki-Woods and Araki-Wyss representations, and the
lattice of von Neumenn algebras in a bosonic/fermionic Fock space are discussed
in detail
Phase IIa trial in Duchenne muscular dystrophy shows vamorolone is a first-in-class dissociative steroidal anti-inflammatory drug
\ua9 2018 The Authors We report a first-in-patient study of vamorolone, a first-in-class dissociative steroidal anti-inflammatory drug, in Duchenne muscular dystrophy. This 2-week, open-label Phase IIa multiple ascending dose study (0.25, 0.75, 2.0, and 6.0 mg/kg/day) enrolled 48 boys with Duchenne muscular dystrophy (4 to <7 years), with outcomes including clinical safety, pharmacokinetics and pharmacodynamic biomarkers. The study design included pharmacodynamic biomarkers in three contexts of use: 1. Secondary outcomes for pharmacodynamic safety (insulin resistance, adrenal suppression, bone turnover); 2. Exploratory outcomes for drug mechanism of action; 3. Exploratory outcomes for expanded pharmacodynamic safety. Vamorolone was safe and well-tolerated through the highest dose tested (6.0 mg/kg/day) and pharmacokinetics of vamorolone were similar to prednisolone. Using pharmacodynamic biomarkers, the study demonstrated improved safety of vamorolone versus glucocorticoids as shown by reduction of insulin resistance, beneficial changes in bone turnover (loss of increased bone resorption and decreased bone formation only at the highest dose level), and a reduction in adrenal suppression. Exploratory biomarkers of pharmacodynamic efficacy showed an anti-inflammatory mechanism of action and a beneficial effect on plasma membrane stability, as demonstrated by a dose-responsive decrease in serum creatine kinase activity. With an array of pre-selected biomarkers in multiple contexts of use, we demonstrate the development of the first dissociative steroid that preserves anti-inflammatory efficacy and decreases steroid-associated safety concerns. Ongoing extension studies offer the potential to bridge exploratory efficacy biomarkers to clinical outcomes
Pan-cancer whole-genome analyses of metastatic solid tumours
Contains fulltext :
215492.pdf (publisher's version ) (Open Access)Metastatic cancer is a major cause of death and is associated with poor treatment efficacy. A better understanding of the characteristics of late-stage cancer is required to help adapt personalized treatments, reduce overtreatment and improve outcomes. Here we describe the largest, to our knowledge, pan-cancer study of metastatic solid tumour genomes, including whole-genome sequencing data for 2,520 pairs of tumour and normal tissue, analysed at median depths of 106x and 38x, respectively, and surveying more than 70 million somatic variants. The characteristic mutations of metastatic lesions varied widely, with mutations that reflect those of the primary tumour types, and with high rates of whole-genome duplication events (56%). Individual metastatic lesions were relatively homogeneous, with the vast majority (96%) of driver mutations being clonal and up to 80% of tumour-suppressor genes being inactivated bi-allelically by different mutational mechanisms. Although metastatic tumour genomes showed similar mutational landscape and driver genes to primary tumours, we find characteristics that could contribute to responsiveness to therapy or resistance in individual patients. We implement an approach for the review of clinically relevant associations and their potential for actionability. For 62% of patients, we identify genetic variants that may be used to stratify patients towards therapies that either have been approved or are in clinical trials. This demonstrates the importance of comprehensive genomic tumour profiling for precision medicine in cancer
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