107 research outputs found
Causal Geometry of Einstein-Vacuum Spacetimes with Finite Curvature Flux
One of the central difficulties of settling the -bounded curvature
conjecture for the Einstein -Vacuum equations is to be able to control the
causal structure of spacetimes with such limited regularity.
In this paper we show how to circumvent this difficulty by showing that the
geometry of null hypersurfaces of Enstein-Vacuum spacetimes can be controlled
in terms of initial data and the total curvature flux through the hypersurface.Comment: The previous version has been corrected for minor errors and
expositio
Semi-classical limit and minimum decoherence in the Conditional Probability Interpretation of Quantum Mechanics
The Conditional Probability Interpretation of Quantum Mechanics replaces the
abstract notion of time used in standard Quantum Mechanics by the time that can
be read off from a physical clock. The use of physical clocks leads to apparent
non-unitary and decoherence. Here we show that a close approximation to
standard Quantum Mechanics can be recovered from conditional Quantum Mechanics
for semi-classical clocks, and we use these clocks to compute the minimum
decoherence predicted by the Conditional Probability Interpretation.Comment: 8 pages, references adde
Searching the Higgs with the Neurochip TOTEM
We show that neural network classifiers can be helpful in discriminating
Higgs production events from the huge background at LHC, assuming the case of a
mass value GeV. We use the high performance neurochip TOTEM,
trained by the Reactive Tabu Search algorithm (RTS), which could be used for
on-line purposes. Two different sets of input variables are compared.Comment: 4 pages,1 figure, requres espcrc2.sty and epsfig.sty. Work prsented
in The 5th Topical Seminar on ``The irresistible rise of the Standard
Model'', San Miniato, Tuscany, Italy, April 21-25 199
Errors in kinematic distances and our image of the Milky Way Galaxy
Errors in the kinematic distances, under the assumption of circular gas
orbits, were estimated by performing synthetic observations of a model disk
galaxy. It was found that the error is < 0.5 kpc for most of the disk when the
measured rotation curve was used, but larger if the real rotation curve is
applied. In both cases, the error is significantly larger at the positions of
the spiral arms. The error structure is such that, when kinematic distances are
used to develope a picture of the large scale density distribution, the most
significant features of the numerical model are significantly distorted or
absent, while spurious structure appears. By considering the full velocity
field in the calculation of the kinematic distances, most of the original
density structures can be recovered.Comment: Accepted for publication in A
Polycystic kidney disease in patients on the renal transplant waiting list: trends in hematocrit and survival
BACKGROUND: The patient characteristics and mortality associated with autosomal dominant polycystic kidney disease (PKD) have not been characterized for a national sample of end stage renal disease (ESRD) patients on the renal transplant waiting list. METHODS: 40,493 patients in the United States Renal Data System who were initiated on ESRD therapy between 1 April 1995 and 29 June 1999 and later enrolled on the renal transplant waiting list were analyzed in an historical cohort study of the relationship between hematocrit at the time of presentation to ESRD and survival (using Cox Regression) in patients with PKD as a cause of ESRD. RESULTS: Hematocrit levels at presentation to ESRD increased significantly over more recent years of the study. Hematocrit rose in parallel in patients with and without PKD, but patients with PKD had consistently higher hemoglobin. PKD was independently associated with higher hematocrit in multiple linear regression analysis (p < 0.0001). In logistic regression, higher hematocrit was independently associated with PKD. In Cox Regression analysis, PKD was associated with statistically significant improved survival both in comparison with diabetic (hazard ratio, 0.64, 95% CI 0.53â0.77, p < 0.001) and non-diabetic (HR 0.68, 95% CI 0.56â0.82, p = 0.001) ESRD patients, adjusted for all other factors. CONCLUSIONS: Hematocrit at presentation to ESRD was significantly higher in patients with PKD compared with patients with other causes of ESRD. The survival advantage of PKD in ESRD persisted even adjusted for differences in hematocrit and in comparison with patients on the renal transplant waiting list
Coherent quantum LQG control
Based on a recently developed notion of physical realizability for quantum
linear stochastic systems, we formulate a quantum LQG optimal control problem
for quantum linear stochastic systems where the controller itself may also be a
quantum system and the plant output signal can be fully quantum. Such a control
scheme is often referred to in the quantum control literature as "coherent
feedback control.'' It distinguishes the present work from previous works on
the quantum LQG problem where measurement is performed on the plant and the
measurement signals are used as input to a fully classical controller with no
quantum degrees of freedom. The difference in our formulation is the presence
of additional non-linear and linear constraints on the coefficients of the
sought after controller, rendering the problem as a type of constrained
controller design problem. Due to the presence of these constraints our problem
is inherently computationally hard and this also distinguishes it in an
important way from the standard LQG problem. We propose a numerical procedure
for solving this problem based on an alternating projections algorithm and, as
initial demonstration of the feasibility of this approach, we provide fully
quantum controller design examples in which numerical solutions to the problem
were successfully obtained. For comparison, we also consider the case of
classical linear controllers that use direct or indirect measurements, and show
that there exists a fully quantum linear controller which offers an improvement
in performance over the classical ones.Comment: 25 pages, 1 figure, revised and corrected version (mainly to Section
8). To be published in Automatica, Journal of IFAC, 200
Carcinogenic Effects in a Phenylketonuria Mouse Model
Phenylketonuria (PKU) is a metabolic disorder caused by impaired phenylalanine hydroxylase (PAH). This condition results in hyperphenylalaninemia and elevated levels of abnormal phenylalanine metabolites, among which is phenylacetic acid/phenylacetate (PA). In recent years, PA and its analogs were found to have anticancer activity against a variety of malignancies suggesting the possibility that PKU may offer protection against cancer through chronically elevated levels of PA. We tested this hypothesis in a genetic mouse model of PKU (PAHenu2) which has a biochemical profile that closely resembles that of human PKU. Plasma levels of phenylalanine in homozygous (HMZ) PAHenu2 mice were >12-fold those of heterozygous (HTZ) littermates while tyrosine levels were reduced. Phenylketones, including PA, were also markedly elevated to the range seen in the human disease. Mice were subjected to 7,12 dimethylbenz[a]anthracene (DMBA) carcinogenesis, a model which is sensitive to the anticancer effects of the PA derivative 4-chlorophenylacetate (4-CPA). Tumor induction by DMBA was not significantly different between the HTZ and HMZ mice, either in total tumor development or in the type of cancers that arose. HMZ mice were then treated with 4-CPA as positive controls for the anticancer effects of PA and to evaluate its possible effects on phenylalanine metabolism in PKU mice. 4-CPA had no effect on the plasma concentrations of phenylalanine, phenylketones, or tyrosine. Surprisingly, the HMZ mice treated with 4-CPA developed an unexplained neuromuscular syndrome which precluded its use in these animals as an anticancer agent. Together, these studies support the use of PAHenu2 mice as a model for studying human PKU. Chronically elevated levels of PA in the PAHenu2 mice were not protective against cancer
Gaussian quantum operator representation for bosons
We introduce a Gaussian quantum operator representation, using the most general possible multimode Gaussian operator basis. The representation unifies and substantially extends existing phase-space representations of density matrices for Bose systems and also includes generalized squeezed-state and thermal bases. It enables first-principles dynamical or equilibrium calculations in quantum many-body systems, with quantum uncertainties appearing as dynamical objects. Any quadratic Liouville equation for the density operator results in a purely deterministic time evolution. Any cubic or quartic master equation can be treated using stochastic methods
Problem images of children : Representations, preconceptions and strategies in BRIS children Ìs helpline during the period 1996- 98.
A number of countries including Sweden have developed childrenâs helplines as free and anonymous counseling services for children and youth. The aim of this study was to deepen knowledge about how the problems of children and youth are represented and constructed in Swedenâs BRIS (Childrenâs Rights in Society) Childrenâs Helpline, telephone support between the years 1996 and 1998. The work was social constructivistic, examining how helpline responders understand and interpret information received during support calls. The concept of âthe concernâ is highlighted as a point of study of problem constructions within micro-counselling. The empirical material consisted primarily of interviews with persons who worked at BRIS either as employed ombudspersons or as volunteer telephone responders. Eleven ombudspersons replied to questions about the Childrenâs Helpline and how support services are organized. Thirty eight interviews were carried out with helpline responders at two separate occasions during the study period. Fifteen of these interviews provided material for an in depth investigation of responders preconceptions of children and youthâs everyday life, as well as the themes of gender, problematic relationships and assault as well as the strategies that responders used in their supportive calls. Statistical information was collected from BRIS reports. Fifteen completed questionnaires from support calls were included in this study. Analytical processes resulted in the development of the two theoretical concepts of familiarity and micro-understanding. General representations of children and youth situations are put forth via descriptions of misery. The respondersâ concepts of childrenâs everyday life appear fragmentary because of the limited information available about the caller. Gender issues are constructed around questions of feminity and sexuality. The theme of assault contains calls from both girls and boys. Boysâ calls about assault are constructed around bullying and physical assault. Girlsâ call are also constructed around violence but also include sexual abuse and molestation. This study contributes to the growing field of knowledge about the problem images of children and youth that emanate from support calls made to telephone helplines
- âŠ