1,605 research outputs found
Compositional uniformity, domain patterning and the mechanism underlying nano-chessboard arrays
We propose that systems exhibiting compositional patterning at the nanoscale,
so far assumed to be due to some kind of ordered phase segregation, can be
understood instead in terms of coherent, single phase ordering of minority
motifs, caused by some constrained drive for uniformity. The essential features
of this type of arrangements can be reproduced using a superspace construction
typical of uniformity-driven orderings, which only requires the knowledge of
the modulation vectors observed in the diffraction patterns. The idea is
discussed in terms of a simple two dimensional lattice-gas model that simulates
a binary system in which the dilution of the minority component is favored.
This simple model already exhibits a hierarchy of arrangements similar to the
experimentally observed nano-chessboard and nano-diamond patterns, which are
described as occupational modulated structures with two independent modulation
wave vectors and simple step-like occupation modulation functions.Comment: Preprint. 11 pages, 11 figure
Magnetic superspace groups and symmetry constraints in incommensurate magnetic phases
Although superspace formalism has become the standard approach for the
analysis of structurally modulated crystals, it has remained during the last
thirty years almost unexplored as a practical tool to deal with magnetic
incommensurate structures. This situation has recently changed with the
development of new computer tools for magnetic phases based on this formalism.
In this context we show here that, as in the case of nonmagnetic incommensurate
systems, the concept of superspace symmetry provides a simple, efficient and
systematic way to characterize the symmetry and rationalize the structural and
physical properties of incommensurate magnetic materials. The method introduces
significant advantages over the most commonly employed method of representation
analysis for the description of the magnetic structure of a crystal. But, more
importantly, in contrast with that method, it consistently yields and
classifies all degrees of freedom of the system. The knowledge of the
superspace group of an incommensurate magnetic material allows to predict its
crystal tensor properties and to rationalize its phase diagram, previous to any
appeal to microscopic models or mechanisms. This is especially relevant when
the properties of incommensurate multiferroics are being studied. We present
first a summary of the superspace method under a very practical viewpoint
particularized to magnetic modulations. Its relation with the usual
representation analysis is then analyzed in detail, with the derivation of
important general rules for magnetic modulations with a single propagation
vector. The power and efficiency of the formalism is illustrated with various
selected examples, including some multiferroic materials
Characterizing and prognosticating chronic lymphocytic leukemia in the elderly: prospective evaluation on 455 patients treated in the United States.
BACKGROUND: Median age at diagnosis of patients with chronic lymphocytic leukemia (CLL) is \u3e 70 years. However, the majority of clinical trials do not reflect the demographics of CLL patients treated in the community. We examined treatment patterns, outcomes, and disease-related mortality in patients ≥ 75 years with CLL (E-CLL) in a real-world setting.
METHODS: The Connect® CLL registry is a multicenter, prospective observational cohort study, which enrolled 1494 adult patients between 2010-2014, at 199 US sites. Patients with CLL were enrolled within 2 months of initiating first line of therapy (LOT1) or a subsequent LOT (LOT ≥ 2). Kaplan-Meier methods were used to evaluate overall survival. CLL- and infection-related mortality were assessed using cumulative incidence functions (CIF) and cause-specific hazards. Logistic regression was used to develop a classification model.
RESULTS: A total of 455 E-CLL patients were enrolled; 259 were enrolled in LOT1 and 196 in LOT ≥ 2. E-CLL patients were more likely to receive rituximab monotherapy (19.3 vs. 8.6%; p \u3c 0.0001) and chemotherapy-alone regimens (p \u3c 0.0001) than younger patients. Overall and complete responses were lower in E-CLL patients than younger patients when given similar regimens. With a median follow-up of 3 years, CLL-related deaths were higher in E-CLL patients than younger patients in LOT1 (12.6 vs. 5.1% p = 0.0005) and LOT ≥ 2 (31.3 vs. 21.5%; p = 0.0277). Infection-related deaths were also higher in E-CLL patients than younger patients in LOT1 (7.4 vs. 2.7%; p = 0.0033) and in LOT ≥ 2 (16.2 vs. 11.2%; p = 0.0786). A prognostic score for E-CLL patients was developed: time from diagnosis to treatment \u3c 3 months, enrollment therapy other than bendamustine/rituximab, and anemia, identified patients at higher risk of inferior survival. Furthermore, higher-risk patients experienced an increased risk of CLL- or infection-related death (30.6 vs 10.3%; p = 0.0006).
CONCLUSION: CLL- and infection-related mortality are higher in CLL patients aged ≥ 75 years than younger patients, underscoring the urgent need for alternative treatment strategies for these understudied patients.
TRIAL REGISTRATION: The Connect CLL registry was registered at clinicaltrials.gov: NCT01081015 on March 4, 2010
Real-world clinical experience in the Connect® chronic lymphocytic leukaemia registry: a prospective cohort study of 1494 patients across 199 US centres.
The clinical course of chronic lymphocytic leukaemia (CLL) is heterogeneous, and treatment options vary considerably. The Connect® CLL registry is a multicentre, prospective observational cohort study that provides a real-world perspective on the management of, and outcomes for, patients with CLL. Between 2010 and 2014, 1494 patients with CLL and that initiated therapy, were enrolled from 199 centres throughout the USA (179 community-, 17 academic-, and 3 government-based centres). Patients were grouped by line of therapy at enrolment (LOT). We describe the clinical and demographic characteristics of, and practice patterns for, patients with CLL enrolled in this treatment registry, providing patient-level observational data that represent real-world experiences in the USA. Fluorescence in situ hybridization (FISH) analyses were performed on 49·3% of patients at enrolment. The most common genetic abnormalities detected by FISH were del(13q) and trisomy 12 (45·7% and 20·8%, respectively). Differences in disease characteristics and comorbidities were observed between patients enrolled in LOT1 and combined LOT2/≥3 cohorts. Important trends observed include the infrequent use of genetic prognostic testing, and differences in patient characteristics for patients receiving chemoimmunotherapy combinations. These data represent experiences of patients with CLL in the USA, which may inform treatment decisions in everyday practice
Localization and Absorption of Light in 2D Composite Metal-Dielectric Films at the Percolation Threshold
We study in this paper the localization of light and the dielectric
properties of thin metal-dielectric composites at the percolation threshold and
around a resonant frequency where the conductivities of the two components are
of the same order. In particular, the effect of the loss in metallic components
are examined. To this end, such systems are modelized as random networks,
and the local field distribution as well as the effective conductivity are
determined by using two different methods for comparison: an exact resolution
of Kirchoff equations, and a real space renormalization group method. The
latter method is found to give the general behavior of the effective
conductivity but fails to determine the local field distribution. It is also
found that the localization still persists for vanishing losses. This result
seems to be in agreement with the anomalous absorption observed experimentally
for such systems.Comment: 14 page latex, 3 ps figures. submitte
Finite strain Landau theory of high pressure phase transformations
The properties of materials near structural phase transitions are often
successfully described in the framework of Landau theory. While the focus is
usually on phase transitions, which are induced by temperature changes
approaching a critical temperature T-c, here we will discuss structural phase
transformations driven by high hydrostatic pressure, as they are of major
importance for understanding processes in the interior of the earth. Since at
very high pressures the deformations of a material are generally very large,
one needs to apply a fully nonlinear description taking physical as well as
geometrical nonlinearities (finite strains) into account. In particular it is
necessary to retune conventional Landau theory to describe such phase
transitions. In Troster et al (2002 Phys. Rev. Lett. 88 55503) we constructed a
Landau-type free energy based on an order parameter part, an order
parameter-(finite) strain coupling and a nonlinear elastic term. This model
provides an excellent and efficient framework for the systematic study of phase
transformations for a wide range of materials up to ultrahigh pressures
Creation of a functional S-nitrosylation site in vitro by single point mutation
Here we show that in extrahepatic methionine adenosyltransferase replacement of a single amino acid (glycine 120) by cysteine is sufficient to create a functional nitric oxide binding site without affecting the kinetic properties of the enzyme. When wild-type and mutant methionine adenosyltransferase were incubated with S-nitrosoglutathione the activity of the wild-type remained unchanged whereas the activity of the mutant enzyme decreased markedly. The mutant enzyme was found to be S-nitrosylated upon incubation with the nitric oxide donor. Treatment of the S-nitrosylated mutant enzyme with glutathione removed most of the S-nitrosothiol groups and restored the activity to control values. In conclusion, our results suggest that functional S-nitrosylation sites can develop from existing structures without drastic or large-scale amino acid replacement
Phonons from neutron powder diffraction
The spherically averaged structure function \soq obtained from pulsed
neutron powder diffraction contains both elastic and inelastic scattering via
an integral over energy. The Fourier transformation of \soq to real space, as
is done in the pair density function (PDF) analysis, regularizes the data, i.e.
it accentuates the diffuse scattering. We present a technique which enables the
extraction of off-center phonon information from powder diffraction experiments
by comparing the experimental PDF with theoretical calculations based on
standard interatomic potentials and the crystal symmetry. This procedure
(dynamics from powder diffraction(DPD)) has been successfully implemented for
two systems, a simple metal, fcc Ni, and an ionic crystal, CaF. Although
computationally intensive, this data analysis allows for a phonon based
modeling of the PDF, and additionally provides off-center phonon information
from powder neutron diffraction
S-Adenosylmethionine revisited: its essential role in the regulation of liver function
Dietary methionine is mainly metabolized in the liver where it is converted into S-adenosylmethionine (AdoMet), the main biologic methyl donor. This reaction is catalyzed by methionine adenosyltransferase I/III (MAT I/III), the product of MAT1A gene, which is exclusively expressed in this organ. It was first observed that serum methionine levels were elevated in experimental models of liver damage and in liver cirrhosis in human beings. Results of further studies showed that this pathological alteration was due to reduced MAT1A gene expression and MAT I/III enzyme inactivation associated with liver injury. Synthesis of AdoMet is essential to all cells in the organism, but it is in the liver where most of the methylation reactions take place. The central role played by AdoMet in cellular function, together with the observation that AdoMet administration reduces liver damage caused by different agents and improves survival of alcohol-dependent patients with cirrhosis, led us to propose that alterations in methionine metabolism could play a role in the onset of liver disease and not just be a consequence of it. In the present work, we review the recent findings that support this hypothesis and highlight the mechanisms behind the hepatoprotective role of AdoMet
Experimental evidence of stochastic resonance without tuning due to non Gaussian noises
In order to test theoretical predictions, we have studied the phenomenon of
stochastic resonance in an electronic experimental system driven by white non
Gaussian noise. In agreement with the theoretical predictions our main findings
are: an enhancement of the sensibility of the system together with a remarkable
widening of the response (robustness). This implies that even a single resonant
unit can reach a marked reduction in the need of noise tuning.Comment: 4 pages, 3 figure
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