519 research outputs found
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
The Current Status of the Distribution Range of the Western Pine Beetle, Dendroctonus brevicomis (Curculionidae: Scolytinae) in Northern Mexico
Abstract The distribution range of the western pine beetle Dendroctonus brevicomis LeConte (Coleoptera: Curculionidae) is supported only by scattered records in the northern parts of Mexico, suggesting that its populations may be marginal and rare in this region. In this study, we review the geographical distribution of D. brevicomis in northern Mexico and perform a geometric morphometric analysis of seminal rod shape to evaluate its reliability for identifying this species with respect to other members of the Dendroctonus frontalis Zimmermann (Coleoptera: Curculionidae) complex. Our results provide 30 new records, with 26 distributed in the Sierra Madre Occidental and 4 in the Sierra Madre Oriental. These records extend the known distribution range of D. brevicomis to Durango and Tamaulipas states in northern Mexico. Furthermore, we find high geographic variation in size and shape of the seminal rod, with conspicous differences among individuals from different geographical regions, namely west and east of the Great Basin and between mountain systems in Mexico.
Key words: seminal rod shape, geometric morphometry, Dendroctonus frontalis comple
Global metabolic changes induced by plant-derived pyrrolizidine alkaloids following a human poisoning outbreak and in a mouse model
Several hundred cases of Hirmi Valley Liver Disease (HVLD), an often fatal liver injury, occurred from 2001 to 2011 in a cluster of rural villages in Tigray, Ethiopia. HVLD is principally caused by contamination of the food supply with plant derived pyrrolizidine alkaloids (PAs), with high exposure to the pesticide DDT among villagers increasing their susceptibility. In an untargeted global approach we aimed to identify metabolic changes induced by PA exposure through 1H NMR spectroscopic based metabolic profiling. We analysed spectra acquired from urine collected from HVLD cases and controls and a murine model of PA exposure and PA/DDT co-exposure, using multivariate partial least squares discriminant analysis. In the human models we identified changes in urinary concentrations of tyrosine, pyruvate, bile acids, N-acetylglycoproteins, N-methylnicotinamide and formate, hippurate, p-cresol sulphate, p-hydroxybenzoate and 3-(3-hydroxyphenyl) propionic acid. Tyrosine and p-cresol sulphate were associated with both exposure and disease. Similar changes to tyrosine, one-carbon intermediates and microbial associated metabolites were observed in the mouse model, with tyrosine correlated with the extent of liver damage. These results provide mechanistic insight and implicate the gut microflora in the human response to challenge with toxins. Pathways identified here may be useful in translational research and as âexposomeâ signals
A systematic review and meta-analysis on the effectiveness of xenograft to prevent periodontal defects after mandibular third molar extraction.
Background: To evaluate the use of guided bone regeneration with xenograft to prevent periodontal defect in the distal aspect of the second molar after the surgical removal of the mandibular third molar.Material and Methods: Three electronic databases (Pubmed, Cochrane Library and Scopus) were searched in April 2020. Randomized clinical trials in non-smokers and healthy patients, with at least six months follow-up, comparing periodontal probing depth, clinical attachment level, alveolar bone level and adverse events were selected by two independent investigators. The risk of bias assessment of the selected studies was evaluated by means of the Cochrane Collaboration's Tool. Finally, a meta-analysis of the outcomes of interest was performed.Results: Despite 795 articles were found in the initial search, only three randomized controlled clinical trials were included. Pooled results favoured the use of the xenograft plus collagen membrane over the spontaneous healing in terms of periodontal probing depth gain (MD=2.36; 95% CI 0.69 to 4.03; P=0.005) and clinical attachment level gain (MD=2.52; 95% CI 0.96 to 4.09; P=0.002). No other statistically significant differences were found. Conclusions: Within the limitations of the present review, the xenograft plus collagen membrane exhibited better periodontal results than spontaneous healing without increasing postoperative complications. However, future well-designed studies with larger samples are required to confirm our result
The X-ray binary 2S0114+650=LSI+65 010:A slow pulsar or tidally-induced pulsations?
The X-ray source 2S0114+650=LSI+65 010 is a binary system containing a B-type
primary and a low mass companion believed to be a neutron star. The system has
three reported periodicities: the orbital period, P{orb}~11.6 d, X-ray flaring
with P{flare}~2.7 hr, and a "superorbital" X-ray periodicity P{super}~30.7 d.
The objective of this paper is to show that the puzzling periodicities in the
system may be explained in the context of scenarios in which tidal interactions
drive oscillations in the B-supergiant star. We calculate the solution of the
equations of motion for one layer of small surface elements distributed along
the equator of the star, as they respond to the forces due to gas pressure,
centrifugal, coriolis, viscous forces, and the gravitational forces of both
stars. This calculation provides variability timescales that can be compared
with the observations. In addition, we use observational data obtained at the
Observatorio Astron\'omico Nacional en San Pedro M\'artir (OAN/SPM) between
1993-2004 to determine which of the periodicities may be present in the optical
region. We suggest that the tidal oscillations lead to a structured stellar
wind which, when fed to the neutron star, produces the X-ray modulations. The
connection between the stellar oscillations and the modulation of the mass
ejection may lie in the shear energy dissipation generated by the tangential
motions that are produced by the tidal interaction, particularly in the tidal
bulge region. The tidal oscillation scenario weakens the case for 2S0114+650
containing a magnetar descendent.Comment: 12 pages, 14 figure
Critical behavior of three-dimensional magnets with complicated ordering from three-loop renormalization-group expansions
The critical behavior of a model describing phase transitions in 3D
antiferromagnets with 2N-component real order parameters is studied within the
renormalization-group (RG) approach. The RG functions are calculated in the
three-loop order and resummed by the generalized Pade-Borel procedure
preserving the specific symmetry properties of the model. An anisotropic stable
fixed point is found to exist in the RG flow diagram for N > 1 and lies near
the Bose fixed point; corresponding critical exponents are close to those of
the XY model. The accuracy of the results obtained is discussed and estimated.Comment: 10 pages, LaTeX, revised version published in Phys. Rev.
Buckling Instabilities of a Confined Colloid Crystal Layer
A model predicting the structure of repulsive, spherically symmetric,
monodisperse particles confined between two walls is presented. We study the
buckling transition of a single flat layer as the double layer state develops.
Experimental realizations of this model are suspensions of stabilized colloidal
particles squeezed between glass plates. By expanding the thermodynamic
potential about a flat state of confined colloidal particles, we derive
a free energy as a functional of in-plane and out-of-plane displacements. The
wavevectors of these first buckling instabilities correspond to three different
ordered structures. Landau theory predicts that the symmetry of these phases
allows for second order phase transitions. This possibility exists even in the
presence of gravity or plate asymmetry. These transitions lead to critical
behavior and phases with the symmetry of the three-state and four-state Potts
models, the X-Y model with 6-fold anisotropy, and the Heisenberg model with
cubic interactions. Experimental detection of these structures is discussed.Comment: 24 pages, 8 figures on request. EF508
Skin gene therapy for acquired and inherited disorders
The rapid advances associated with the Human Genome Project combined with the development of proteomics technology set the bases to face the challenge of human gene therapy. Different strategies must be evaluated based on the genetic defect to be corrected. Therefore, the re-expression of the normal counterpart should be sufficient to reverse phenotype in single-gene inherited disorders. A growing number of candidate diseases are being evaluated since the ADA deficiency was selected for the first approved human gene therapy trial (Blaese et al., 1995). To cite some of them: sickle cell anemia, hemophilia, inherited immune deficiencies, hyper-cholesterolemia and cystic fibrosis. The approach does not seem to be so straightforward when a polygenic disorder is going to be treated. Many human traits like diabetes, hypertension, inflammatory diseases and cancer, appear to be due to the combined action of several genes and environment. For instance, several wizard gene therapy strategies have recently been proposed for cancer treatment, including the stimulation of the immune system of the patient (Xue et al., 2005), the targeting of particular signalling pathways to selectively kill cancer cells (Westphal and Melchner, 2002) and the modulation of the interactions with the stroma and the vasculature (Liotta, 2001; Liotta and Kohn, 2001).Our work is supported by grants SAF-2004-07717 from Ministerio de Ciencia y TecnologĂa (Spain) and LSHG-512073 from UE to M. Del Rio, LSHG-503447 from UE to J.L. Jorcano and LSHG-512102 from UE to F. Larcher. We express our gratitude to Dr. Y. Gache, Dr. F. Spirito and Dr. G. Meneguzzi for providing EM pictures to illustrate this work
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