41 research outputs found
Memory effect in triglycine sulfate induced by a transverse electric field: specific heat measurement
The influence of a transverse electric field in the specific heat of
triglycine sulphate (TGS) has been studied. The specific heat of TGS has been
measured heating the sample from ferroelectric to paraelectric phase after
prolonged transverse electric field (i.e. perpendicular to the ferroelectric
axis). It is shown that the specific heat of TGS can remember the temperature
at which the transverse field was previously applied.Comment: ReVTeX4 Twocolumn 4 pages, 4 figure
Influence of the electric field on the latent heat of the ferroelectric phase transition in KDP
The specific heat, heat flux (DTA trace) and dielectric constant of KDP
ferroelectric crystal have been measured simultaneously for various electric
fields with a conduction calorimeter. The specific heat presents a strong
anomaly but these simultaneous measurements allow us to evaluate the latent
heat accurately. Latent heat decreases with field and the value of critical
electric field --that where latent heat disappears-- is estimated to be
(0.44\pm0.03) kV/cm. Incidentally, we have measured simultaneously the
dielectric permittivity which suggests that latent heat is developed as domains
are growing.Comment: 7 pages, 6 figures, ReVTeX, twocolumn format, to appear in J. Phys.
Cond. Matte
The order parameter-entropy relation in some universal classes: experimental evidence
The asymptotic behaviour near phase transitions can be suitably characterized
by the scaling of with , where is
the excess entropy and is the order parameter. As is obtained by
integration of the experimental excess specific heat of the transition , it displays little experimental noise so that the curve versus is better constrained than, say,
versus . The behaviour of for different
universality classes is presented and compared. In all cases, it clearly
deviates from being a constant. The determination of this function can then be
an effective method to distinguish asymptotic critical behaviour. For
comparison, experimental data for three very different systems, Rb2CoF4,
Rb2ZnCl4 and SrTiO3, are analysed under this approach. In SrTiO3, the function
does not deviate within experimental resolution from a straight
line so that, although Q can be fitted with a non mean-field exponent, the data
can be explained by a classical Landau mean-field behaviour. In contrast, the
behaviour of for the antiferromagnetic transition in Rb2CoF4 and
the normal-incommensurate phase transition in Rb2ZCl4 is fully consistent with
the asymptotic critical behaviour of the universality class corresponding to
each case. This analysis supports, therefore, the claim that incommensurate
phase transitions in general, and the ABX compounds in particular, in
contrast with most structural phase transitions, have critical regions large
enough to be observable.Comment: 13 pp. 9 ff. 2 tab. RevTeX. Submitted to J. Phys.: Cond. Matte
P9 23. Seudoaneurisma aórtico con infeción de prótesis en aorta ascendente. ¿Es necesario retirar siempre la prótesis? ¿Cuánto tiempo con tratamiento antibiótico?
IntroducciónEl seudoaneurisma aórtico con infección de prótesis en aorta ascendente (PIPAA) tras cirugía cardíaca es una entidad infrecuente (0,9-2%) pero grave (mortalidad intrahospitalaria > 40%). El tratamiento más extendido es la cirugía con recambio protésico y terapia antibiótica adecuada a antibiograma; pero el recambio protésico en ocasiones es técnicamente inviable e incluso puede aumentar la mortalidad perioperatoria. Existen casos en los que se ha preservado la prótesis infectada con éxito terapéutico, realizándose limpieza/reparación quirúrgica local apoyada con omentoplastia. No existe consenso en la duración de la terapia médica, y el tratamiento «supresor a largo plazo» en ocasiones se complica por efectos adversos de los antibióticos.ObjetivosAportar dos nuevos casos y evaluar el tratamiento realizado tras un seguimiento a largo plazo.MétodoAnálisis descriptivo de aspectos microbiológicos, farmacológicos y resultados de la terapia realizada, en dos casos de PIPAA de pacientes intervenidos por disección de aorta (prótesis de dacrón en posición supracoronariana) y por insuficiencia y anuloectasia aórtica (tubo valvulado). Se realiza tratamiento quirúrgico conservador de la prótesis aórtica (limpieza quirúrgica, reparación del seudoaneurisma y omentoplastia), asociándose terapia antibiótica prolongada ajustada a antibiograma.ConclusiónAmbos casos presentan, tras más de 1 año de seguimiento, según criterios clínicos, microbiológicos y pruebas de imagen, ausencia de signos de recidiva infecciosa, resultando la terapia adecuada. Aun sin poder establecer tiempo óptimo de tratamiento, serían razonables 6 semanas de tratamiento endovenoso seguidas de 24 semanas de terapia supresora, a ser posible oral, y valorar su retirada siempre que no existan signos de recidiva
Universal mechanism of discontinuity of commensurate-incommensurate transitions in three-dimensional solids: Strain dependence of soliton self-energy
We show that there exists a universal mechanism of long-range soliton
attraction in three-dimensional solids and, therefore, of discontinuity of any
commensurate-incommensurate (C-IC) phase transition. This mechanism is due to
the strain dependence of the soliton self-energy and specific features of the
solid-state elasticity. The role of this mechanism is studied in detail for a
class of C-IC transitions where the IC modulation is one-dimensional, the
anisotropy in the order parameter space is small, and the symmetry of the
systems allows the existence of the Lifshitz invariant. Two other mechanisms of
soliton attraction are operative here but the universal mechanism considered in
this paper is found to be the most important one in some cases. Comparison with
the most extensively studied C-IC transition in shows that the
experimentally observed thermal anomalies can be understood as a result of the
smearing of the theoretically predicted discontinuous transition.Comment: 8 pages (extended version, title changed
Controlling Groundwater Exploitation Through Economic Instruments: Current Practices, Challenges and Innovative Approaches
Groundwater can be considered as a common-pool resource, is often overexploited and, as a result, there are growing management pressures. This chapter starts with a broad presentation of the range of economic instruments that can be used for groundwater management, considering current practices and innovative approaches inspired from the literature on Common Pool Resources management. It then goes on with a detailed presentation of groundwater allocation policies implemented in France, the High Plains aquifer in the USA, and Chile. The chapter concludes with a discussion of social and political difficulties associated with implementing economic instruments for groundwater management
Mammalian Glutaminase Gls2 Gene Encodes Two Functional Alternative Transcripts by a Surrogate Promoter Usage Mechanism
Glutaminase is expressed in most mammalian tissues and cancer cells, but the regulation of its expression is poorly understood. An essential step to accomplish this goal is the characterization of its species- and cell-specific isoenzyme pattern of expression. Our aim was to identify and characterize transcript variants of the mammalian glutaminase Gls2 gene.We demonstrate for the first time simultaneous expression of two transcript variants from the Gls2 gene in human, rat and mouse. A combination of RT-PCR, primer-extension analysis, bioinformatics, real-time PCR, in vitro transcription and translation and immunoblot analysis was applied to investigate GLS2 transcripts in mammalian tissues. Short (LGA) and long (GAB) transcript forms were isolated in brain and liver tissue of human, rat and mouse. The short LGA transcript arises by a combination of two mechanisms of transcriptional modulation: alternative transcription initiation and alternative promoter. The LGA variant contains both the transcription start site (TSS) and the alternative promoter in the first intron of the Gls2 gene. The full human LGA transcript has two in-frame ATGs in the first exon, which are missing in orthologous rat and mouse transcripts. In vitro transcription and translation of human LGA yielded two polypeptides of the predicted size, but only the canonical full-length protein displayed catalytic activity. Relative abundance of GAB and LGA transcripts showed marked variations depending on species and tissues analyzed.This is the first report demonstrating expression of alternative transcripts of the mammalian Gls2 gene. Transcriptional mechanisms giving rise to GLS2 variants and isolation of novel GLS2 transcripts in human, rat and mouse are presented. Results were also confirmed at the protein level, where catalytic activity was demonstrated for the human LGA protein. Relative abundance of GAB and LGA transcripts was species- and tissue-specific providing evidence of a differential regulation of GLS2 transcripts in mammals
Genome-wide association analysis of dementia and its clinical endophenotypes reveal novel loci associated with Alzheimer's disease and three causality networks : The GR@ACE project
Introduction: Large variability among Alzheimer's disease (AD) cases might impact genetic discoveries and complicate dissection of underlying biological pathways. Methods: Genome Research at Fundacio ACE (GR@ACE) is a genome-wide study of dementia and its clinical endophenotypes, defined based on AD's clinical certainty and vascular burden. We assessed the impact of known AD loci across endophenotypes to generate loci categories. We incorporated gene coexpression data and conducted pathway analysis per category. Finally, to evaluate the effect of heterogeneity in genetic studies, GR@ACE series were meta-analyzed with additional genome-wide association study data sets. Results: We classified known AD loci into three categories, which might reflect the disease clinical heterogeneity. Vascular processes were only detected as a causal mechanism in probable AD. The meta-analysis strategy revealed the ANKRD31-rs4704171 and NDUFAF6-rs10098778 and confirmed SCIMP-rs7225151 and CD33-rs3865444. Discussion: The regulation of vasculature is a prominent causal component of probable AD. GR@ACE meta-analysis revealed novel AD genetic signals, strongly driven by the presence of clinical heterogeneity in the AD series
Social factors related to the clinical severity of influenza cases in Spain during the A(H1N1)2009 virus pandemic
Background During the 2009 influenza pandemic, a change in the type of patients most often affected by influenza was observed. The objective of this study was to assess the role of individual and social determinants in hospitalizations due to influenza A (H1N1) 2009 infection. Methods We studied hospitalized patients (cases) and outpatients (controls) with confirmed influenza A (H1N1) 2009 infection. A standardized questionnaire was used to collect data. Variables that might be related to the hospitalization of influenza cases were compared by estimation of the odds ratio (OR) and 95% confidence intervals (CI) and the variables entered into binomial logistic regression models. Results Hospitalization due to pandemic A (H1N1) 2009 influenza virus infections was associated with non-Caucasian ethnicity (OR: 2.18, 95% CI 1.17 − 4.08), overcrowding (OR: 2.84, 95% CI 1.20 − 6.72), comorbidity and the lack of previous preventive information (OR: 2.69, 95% CI: 1.50 − 4.83). Secondary or higher education was associated with a lower risk of hospitalization (OR 0.56, 95% CI: 0.36 − 0.87) Conclusions In addition to individual factors such as comorbidity, other factors such as educational level, ethnicity or overcrowding were associated with hospitalization due to A (H1N1) 2009 influenza virus infections