21,471 research outputs found
ELASTOGRAPHY CAN EFFECTIVELY DECREASE THE NUMBER OF FINE-NEEDLE ASPIRATION BIOPSIES IN PATIENTS WITH CALCIFIED THYROID NODULES
When calcification, frequently found in both benign and malignant nodules, is present in thyroid nodules, non-invasive differentiation with ultrasound becomes challenging. The goal of this study was to evaluate the utility of elastography in differentiating calcified thyroid nodules. Consecutive patients (165 patients with 196 nodules) referred for fine-needle aspiration who had undergone both ultrasound elastography and B-mode examinations were analyzed retrospectively. Calcification was present in 45 benign and 20 malignant nodules. On 65 calcified nodules, elastography had 95% sensitivity, 51.1% specificity, 46.3% positive predictive value and 95.8% negative predictive value in detecting malignancy. Twenty-three of 45 benign calcified nodules were correctly diagnosed with elastography compared with 4 of 45 by B-mode ultrasound. Although it is difficult to differentiate benign and malignant calcified thyroid nodules solely with B-mode ultrasound, elastography has the potential to reduce the number of fine-needle aspiration biopsies performed on calcified nodules. (C) 2014 World Federation for Ultrasound in Medicine & Biology.1188Ysciescopu
Stability of central finite difference schemes for the Heston PDE
This paper deals with stability in the numerical solution of the prominent
Heston partial differential equation from mathematical finance. We study the
well-known central second-order finite difference discretization, which leads
to large semi-discrete systems with non-normal matrices A. By employing the
logarithmic spectral norm we prove practical, rigorous stability bounds. Our
theoretical stability results are illustrated by ample numerical experiments
Survey of LTE Downlink Schedulers Algorithms in Open Access Simulation Tools NS-3 and LTE-SIM
The LTE/LTE-A has become a catchphrase for research and lot of research are being conducted and carried out in LTE in various issues by various people. New tools are developed and introduced in the market to interpret the results of the new algorithms proposed by various people. Some tools are open access which are free to use but some tools are produced by the companies which are not open access. In this paper some of the open access simulation tools like LTE-Sim and NS-3 are analyzed and LTE downlink scheduler algorithms are simulated using those tools. In LTE systems, the downlink scheduler is an important component for radio resource management; hence in the context of LTE simulation, a study between the downlink scheduler models between the simulators are performed
Listen to genes : dealing with microarray data in the frequency domain
Background: We present a novel and systematic approach to analyze temporal microarray data. The approach includes
normalization, clustering and network analysis of genes.
Methodology: Genes are normalized using an error model based uniform normalization method aimed at identifying and
estimating the sources of variations. The model minimizes the correlation among error terms across replicates. The
normalized gene expressions are then clustered in terms of their power spectrum density. The method of complex Granger
causality is introduced to reveal interactions between sets of genes. Complex Granger causality along with partial Granger
causality is applied in both time and frequency domains to selected as well as all the genes to reveal the interesting
networks of interactions. The approach is successfully applied to Arabidopsis leaf microarray data generated from 31,000
genes observed over 22 time points over 22 days. Three circuits: a circadian gene circuit, an ethylene circuit and a new
global circuit showing a hierarchical structure to determine the initiators of leaf senescence are analyzed in detail.
Conclusions: We use a totally data-driven approach to form biological hypothesis. Clustering using the power-spectrum
analysis helps us identify genes of potential interest. Their dynamics can be captured accurately in the time and frequency
domain using the methods of complex and partial Granger causality. With the rise in availability of temporal microarray
data, such methods can be useful tools in uncovering the hidden biological interactions. We show our method in a step by
step manner with help of toy models as well as a real biological dataset. We also analyse three distinct gene circuits of
potential interest to Arabidopsis researchers
Fate of the Josephson effect in thin-film superconductors
The dc Josephson effect refers to the dissipationless electrical current --
the supercurrent -- that can be sustained across a weak link connecting two
bulk superconductors. This effect is a probe of the fundamental nature of the
superconducting state. Here, we analyze the case of two superconducting thin
films connected by a point contact. Remarkably, the Josephson effect is absent
at nonzero temperature, and the resistance across the contact is nonzero.
Moreover, the point contact resistance is found to vary with temperature in a
nearly activated fashion, with a UNIVERSAL energy barrier determined only by
the superfluid stiffness characterizing the films, an angle characterizing the
geometry, and whether or not the Coulomb interaction between Cooper pairs is
screened. This behavior reflects the subtle nature of the superconductivity in
two-dimensional thin films, and should be testable in detail by future
experiments.Comment: 16 + 8 pages. 1 figure, 1 tabl
Anomalies and the chiral magnetic effect in the Sakai-Sugimoto model
In the chiral magnetic effect an imbalance in the number of left- and
right-handed quarks gives rise to an electromagnetic current parallel to the
magnetic field produced in noncentral heavy-ion collisions. The chiral
imbalance may be induced by topologically nontrivial gluon configurations via
the QCD axial anomaly, while the resulting electromagnetic current itself is a
consequence of the QED anomaly. In the Sakai-Sugimoto model, which in a certain
limit is dual to large-N_c QCD, we discuss the proper implementation of the QED
axial anomaly, the (ambiguous) definition of chiral currents, and the
calculation of the chiral magnetic effect. We show that this model correctly
contains the so-called consistent anomaly, but requires the introduction of a
(holographic) finite counterterm to yield the correct covariant anomaly.
Introducing net chirality through an axial chemical potential, we find a
nonvanishing vector current only before including this counterterm. This seems
to imply the absence of the chiral magnetic effect in this model. On the other
hand, for a conventional quark chemical potential and large magnetic field,
which is of interest in the physics of compact stars, we obtain a nontrivial
result for the axial current that is in agreement with previous calculations
and known exact results for QCD.Comment: 35 pages, 4 figures, v2: added comments about frequency-dependent
conductivity at the end of section 4; references added; version to appear in
JHE
Efficient and exact sampling of simple graphs with given arbitrary degree sequence
Uniform sampling from graphical realizations of a given degree sequence is a
fundamental component in simulation-based measurements of network observables,
with applications ranging from epidemics, through social networks to Internet
modeling. Existing graph sampling methods are either link-swap based
(Markov-Chain Monte Carlo algorithms) or stub-matching based (the Configuration
Model). Both types are ill-controlled, with typically unknown mixing times for
link-swap methods and uncontrolled rejections for the Configuration Model. Here
we propose an efficient, polynomial time algorithm that generates statistically
independent graph samples with a given, arbitrary, degree sequence. The
algorithm provides a weight associated with each sample, allowing the
observable to be measured either uniformly over the graph ensemble, or,
alternatively, with a desired distribution. Unlike other algorithms, this
method always produces a sample, without back-tracking or rejections. Using a
central limit theorem-based reasoning, we argue, that for large N, and for
degree sequences admitting many realizations, the sample weights are expected
to have a lognormal distribution. As examples, we apply our algorithm to
generate networks with degree sequences drawn from power-law distributions and
from binomial distributions.Comment: 8 pages, 3 figure
Modular and predictable assembly of porous organic molecular crystals
Nanoporous molecular frameworks are important in applications such as separation, storage and catalysis. Empirical rules exist for their assembly but it is still challenging to place and segregate functionality in three-dimensional porous solids in a predictable way. Indeed, recent studies of mixed crystalline frameworks suggest a preference for the statistical distribution of functionalities throughout the pores rather than, for example, the functional group localization found in the reactive sites of enzymes. This is a potential limitation for 'one-pot' chemical syntheses of porous frameworks from simple starting materials. An alternative strategy is to prepare porous solids from synthetically preorganized molecular pores. In principle, functional organic pore modules could be covalently prefabricated and then assembled to produce materials with specific properties. However, this vision of mix-and-match assembly is far from being realized, not least because of the challenge in reliably predicting three-dimensional structures for molecular crystals, which lack the strong directional bonding found in networks. Here we show that highly porous crystalline solids can be produced by mixing different organic cage modules that self-assemble by means of chiral recognition. The structures of the resulting materials can be predicted computationally, allowing in silico materials design strategies. The constituent pore modules are synthesized in high yields on gram scales in a one-step reaction. Assembly of the porous co-crystals is as simple as combining the modules in solution and removing the solvent. In some cases, the chiral recognition between modules can be exploited to produce porous organic nanoparticles. We show that the method is valid for four different cage modules and can in principle be generalized in a computationally predictable manner based on a lock-and-key assembly between modules
Lung adenocarcinoma originates from retrovirus infection of proliferating type 2 pneumocytes during pulmonary post-natal development or tissue repair
Jaagsiekte sheep retrovirus (JSRV) is a unique oncogenic virus with distinctive biological properties. JSRV is the only virus causing a naturally occurring lung cancer (ovine pulmonary adenocarcinoma, OPA) and possessing a major structural protein that functions as a dominant oncoprotein. Lung cancer is the major cause of death among cancer patients. OPA can be an extremely useful animal model in order to identify the cells originating lung adenocarcinoma and to study the early events of pulmonary carcinogenesis. In this study, we demonstrated that lung adenocarcinoma in sheep originates from infection and transformation of proliferating type 2 pneumocytes (termed here lung alveolar proliferating cells, LAPCs). We excluded that OPA originates from a bronchioalveolar stem cell, or from mature post-mitotic type 2 pneumocytes or from either proliferating or non-proliferating Clara cells. We show that young animals possess abundant LAPCs and are highly susceptible to JSRV infection and transformation. On the contrary, healthy adult sheep, which are normally resistant to experimental OPA induction, exhibit a relatively low number of LAPCs and are resistant to JSRV infection of the respiratory epithelium. Importantly, induction of lung injury increased dramatically the number of LAPCs in adult sheep and rendered these animals fully susceptible to JSRV infection and transformation. Furthermore, we show that JSRV preferentially infects actively dividing cell in vitro. Overall, our study provides unique insights into pulmonary biology and carcinogenesis and suggests that JSRV and its host have reached an evolutionary equilibrium in which productive infection (and transformation) can occur only in cells that are scarce for most of the lifespan of the sheep. Our data also indicate that, at least in this model, inflammation can predispose to retroviral infection and cancer
Electrospun poly(vinyl alcohol) nanofibers: effects of degree of hydrolysis and enhanced water stability
ArticlePOLYMER JOURNAL. 42(3):273-276 (2010)journal articl
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