497 research outputs found
Singularity Avoidance of Charged Black Holes in Loop Quantum Gravity
Based on spherically symmetric reduction of loop quantum gravity,
quantization of the portion interior to the horizon of a Reissner-Nordstr\"{o}m
black hole is studied. Classical phase space variables of all regions of such a
black hole are calculated for the physical case . This calculation
suggests a candidate for a classically unbounded function of which all
divergent components of the curvature scalar are composed. The corresponding
quantum operator is constructed and is shown explicitly to possess a bounded
operator. Comparison of the obtained result with the one for the Swcharzschild
case shows that the upper bound of the curvature operator of a charged black
hole reduces to that of Schwarzschild at the limit . This
local avoidance of singularity together with non-singular evolution equation
indicates the role quantum geometry can play in treating classical singularity
of such black holes.Comment: To be appeared in International Journal of Theoretical Physic
Optimization of detection of residual disease after neoadjuvant therapy in patients with esophageal cancer
Current treatments for locally advanced esophageal cancer consist of neoadjuvant chemotherapy (nCT) or chemoradiotherapy (nCRT) followed by surgery. Nearly one-third of patients obtain a pathologically complete response (pCR) after nCRT. Patients with a complete (clinical) response to nCRT might therefore be candidates for active surveillance, which entails postponement of surgery until recurrence of tumor is detected during clinical response evaluations (CREs). CREs should be performed with accurate diagnostic modalities to timely detect locoregional and distant disease after nCRT. The combination of endoscopy with bite-on-bite biopsies, endoscopic ultrasound with fine-needle aspiration (EUS-FNA) of suspected lymph nodes, and positron emission tomography/computed tomography (PET/CT) has shown 90% sensitivity for detecting substantial (i.e., >10%) residual disease. In this literature review, we address the current state of diagnostic modalities used in CREs and how accuracy for detection of residual tumor after nCRT could be improved. With regard to the currently adopted bite-on-bite biopsy technique, sufficient bite-on-bite biopsies should be taken over larger mucosal areas within the initial tumor site to reduce sampling errors. Detection of positive lymph nodes with EUS-FNA could be improved by sampling all visible lymph nodes. Developments in the field of PET/CT and magnetic resonance imaging (MRI) with simultaneous PET (PET/MRI) have potential to improve CREs by qualitative and quantitative assessment. Other promising techniques require further determination. With wide-area transepithelial sampling (WATS) larger mucosal areas could be sampled compared to regular biopsies, although data in patients treated with nCRT are to be awaited. The detection of positive lymph nodes might be improved by EUS elastography or contrast-enhanced harmonic EUS (CEH-EUS), but these techniques still require further investigation in a setting after nCRT. Finally, image analysis with radiomics, novel biomarkers derived from breath [volatile organic compounds (VOCs)] and liquid biopsies [circulating tumor DNA (ctDNA) as detected in blood samples] might be of complementary value to current diagnostics
Elevated Perioperative Transaminase Level Predicts Intrahepatic Recurrence in Hepatitis B-related Hepatocellular Carcinoma After Curative Hepatectomy
OBJECTIVEWe aimed to evaluate the role of elevated perioperative alanine aminotransferase (ALT) as a surrogate marker of hepatitis activity in determining the risk of recurrence and survival in hepatitis B-related hepatocellular carcinoma (HCC) after curative hepatectomy.METHODSA retrospective review of the hepatectomy database was performed and 142 patients were found who had hepatitis B-related HCC from January 2001 to March 2006. Their ALT levels preoperatively and 1 month, 3 months, and 6 months postoperatively were recorded. The risk factors for recurrence and prognostic factors of survival were analysed.RESULTSAn elevated perioperative ALT level (p = 0.021), multiple tumour nodules in the resected specimen (p < 0.001), and a tumour size greater than 5 cm (p = 0.001) were significant independent risk factors for tumour recurrence. The latter two factors were also independent prognostic factors for overall survival and disease-free survival. An elevated ALT level was an independent prognostic factor for disease-free survival (p = 0.025).CONCLUSIONAn elevated perioperative ALT level, which reflects increased hepatitis activity, is an independent risk factor for intrahepatic recurrence of hepatitis B-related HCC. It is also associated with a poorer disease-free survival rate
Hyperbolic billiards of pure D=4 supergravities
We compute the billiards that emerge in the Belinskii-Khalatnikov-Lifshitz
(BKL) limit for all pure supergravities in D=4 spacetime dimensions, as well as
for D=4, N=4 supergravities coupled to k (N=4) Maxwell supermultiplets. We find
that just as for the cases N=0 and N=8 investigated previously, these billiards
can be identified with the fundamental Weyl chambers of hyperbolic Kac-Moody
algebras. Hence, the dynamics is chaotic in the BKL limit. A new feature
arises, however, which is that the relevant Kac-Moody algebra can be the
Lorentzian extension of a twisted affine Kac-Moody algebra, while the N=0 and
N=8 cases are untwisted. This occurs for N=5, N=3 and N=2. An understanding of
this property is provided by showing that the data relevant for determining the
billiards are the restricted root system and the maximal split subalgebra of
the finite-dimensional real symmetry algebra characterizing the toroidal
reduction to D=3 spacetime dimensions. To summarize: split symmetry controls
chaos.Comment: 21 page
Tunneling and propagation of vacuum bubbles on dynamical backgrounds
In the context of bubble universes produced by a first-order phase transition
with large nucleation rates compared to the inverse dynamical time scale of the
parent bubble, we extend the usual analysis to non-vacuum backgrounds. In
particular, we provide semi-analytic and numerical results for the modified
nucleation rate in FLRW backgrounds, as well as a parameter study of bubble
walls propagating into inhomogeneous (LTB) or FLRW spacetimes, both in the
thin-wall approximation. We show that in our model, matter in the background
often prevents bubbles from successful expansion and forces them to collapse.
For cases where they do expand, we give arguments why the effects on the
interior spacetime are small for a wide range of reasonable parameters and
discuss the limitations of the employed approximations.Comment: 29 pages, 8 figures, typos corrected, matches published versio
The prevalence of different African horsesickness virus serotypes in the Onderstepoort area near Pretoria, during an outbreak of African horsesickness in South Africa in 1995/1996
During 1995/1996 parts of South Africa experienced exceptionally
high rainfall. Large numbers of Culicoides midges were seen and an
outbreak of African horse sickness (AHS) followed. In the Onderstepoort
area, near Pretoria in Gauteng, a number of horses died of suspected
AHS. Virus isolation and typing was done from blood and/or organ samples
of 21 suspected cases as well as from 5 zebra which were kept in the
area. Virus was isolated from 14 of the 21 suspected cases but not from
the zebra. The neutralizing antibody response of the zebra to the nine African
horsesickness virus (AHSV) serotypes was determined. Results indicated the highest prevalence of
serotypes 2 and 4 followed by serotypes 1, 6 and 9. Reverse
transcription polymerase chain reaction (RT-PCR) was performed on total
RNA extracted from blood samples of the zebra. AHSV RNA was detected in
three of five zebra by agarose gel electrophoresis analysis of amplicons and in
four of five zebra after Southern blot hybridization using a 32P-labelled
probe. RT-PCR can be used together with serological techniques in
studies of AHS to further clarify the epizootiology of the disease.The articles have been scanned in colour with a HP Scanjet 5590; 600dpi.
Adobe Acrobat v.9 was used to OCR the text and also for the merging and conversion to the final presentation PDF-format
Controls on luminescence signals in lake sediment cores:A study from Lake Suigetsu, Japan
The luminescence characteristics of sediments are driven by a range of environmental factors and can be used as indicators of both local and regional environmental shifts. Hence, rapid luminescence profiling techniques are increasingly employed during multiproxy analysis of sediment cores, overcoming the practical limitations of traditional (dating) methods. One emerging application of luminescence profiling is in the palaeoenvironmental investigation of lake cores. This study demonstrates the versatility of rapid core profiling using portable optically stimulated luminescence and laboratory profiling techniques for appraising the luminescence characteristics of the Lake Suigetsu (Japan) sediment cores. These techniques were employed across four key time periods, each selected for their unique environmental context and significance on either a local or global scale, in order to identify relationships between down-core luminescence and environmental change. We demonstrate that the luminescence characteristics of the cores are susceptible to a range of environmental perturbations and can therefore act as proxies of past change. Additionally, the quantification of these luminescence signals, alongside an assessment of dose rate variations down-core, supports the notion that future luminescence dating is feasible. The results of this analysis contribute to the wider understanding of the application of luminescence techniques – both profiling and dating – to lake sediment cores
The Centurion 18 telescope of the Wise Observatory
We describe the second telescope of the Wise Observatory, a 0.46-m Centurion
18 (C18) installed in 2005, which enhances significantly the observing
possibilities. The telescope operates from a small dome and is equipped with a
large-format CCD camera. In the last two years this telescope was intensively
used in a variety of monitoring projects.
The operation of the C18 is now automatic, requiring only start-up at the
beginning of a night and close-down at dawn. The observations are mostly
performed remotely from the Tel Aviv campus or even from the observer's home.
The entire facility was erected for a component cost of about 70k$ and a labor
investment of a total of one man-year.
We describe three types of projects undertaken with this new facility: the
measurement of asteroid light variability with the purpose of determining
physical parameters and binarity, the following-up of transiting extrasolar
planets, and the study of AGN variability. The successful implementation of the
C18 demonstrates the viability of small telescopes in an age of huge
light-collectors, provided the operation of such facilities is very efficient.Comment: 16 pages, 13 figures, some figures quality was degraded, accepted for
publication in Astrophysics and Space Scienc
Anomalous Heat Conduction and Anomalous Diffusion in Low Dimensional Nanoscale Systems
Thermal transport is an important energy transfer process in nature. Phonon
is the major energy carrier for heat in semiconductor and dielectric materials.
In analogy to Ohm's law for electrical conductivity, Fourier's law is a
fundamental rule of heat transfer in solids. It states that the thermal
conductivity is independent of sample scale and geometry. Although Fourier's
law has received great success in describing macroscopic thermal transport in
the past two hundreds years, its validity in low dimensional systems is still
an open question. Here we give a brief review of the recent developments in
experimental, theoretical and numerical studies of heat transport in low
dimensional systems, include lattice models, nanowires, nanotubes and
graphenes. We will demonstrate that the phonon transports in low dimensional
systems super-diffusively, which leads to a size dependent thermal
conductivity. In other words, Fourier's law is breakdown in low dimensional
structures
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