1,086 research outputs found
Electronic Phase Separation Transition as the Origin of the Superconductivity and the Pseudogap Phase of Cuprates
We propose a new phase of matter, an electronic phase separation transition
that starts near the upper pseudogap and segregates the holes into high and low
density domains. The Cahn-Hilliard approach is used to follow quantitatively
this second order transition. The resulting grain boundary potential confines
the charge in domains and favors the development of intragrain superconducting
amplitudes. The zero resistivity transition arises only when the intergrain
Josephson coupling is of the order of the thermal energy and phase
locking among the superconducting grains takes place. We show that this
approach explains the pseudogap and superconducting phases in a natural way and
reproduces some recent scanning tunneling microscopy dataComment: 4 pages and 5 eps fig
Resistivity study of the pseudogap phase for (Hg,Re) - 1223 superconductors
The pseudogap phase above the critical temperature of high
superconductors (HTSC) presents different energy scales and it is currently a
matter of intense study. The complexity of the HTSC normal state requires very
accurate measurements with the purpose of distinguishing different types of
phenomena. Here we have performed systematically studies through electrical
resistivity () measurements by several different current densities in
order to obtain an optimal current for each sample. This approach allows to
determine reliable values of the pseudogap temperature , the layer
coupling temperature between the superconductor layers , the
fluctuation temperature and the critical temperature as
function of the doping . The interpretation of these different temperature
scales allows to characterize possible scenarios for the (Hg,Re) - 1223 normal
state. This method, described in detail here, and used to derive the
(Hg,Re)-1223 phase diagram is general and can be applied to any HTSC.Comment: 31 pages, 12 figures, Latex; 25 pages, LaTeX; 11 figures; rewrited
section II and III; added 18 reference; rewrited title, added discussion
sectio
The mean energy, strength and width of triple giant dipole resonances
We investigate the mean energy, strength and width of the triple giant dipole
resonance using sum rules.Comment: 12 page
Peritoneal fluid modulates the sperm acrosomal exocytosis induced by N-acetylglucosaminyl neoglycoprotein
The effect of peritoneal fluid (PF) on the human sperm acrosome reaction (AR) was tested. Sperm was pre-incubated with PF and the AR was induced by calcium ionophore A23187 and a neoglycoprotein bearing N-acetylglycosamine residues (NGP). The AR induced by calcium ionophore was inhibited 40% by PF from controls (PFc) and 50% by PF from the endometriosis (PFe) group, but not by PF from infertile patients without endometriosis (PFi). No significant differences were found in the spontaneous AR. When the AR was induced by NGP, pre-incubation with PFc reduced (60%) the percentage of AR, while PFe and PFi caused no significant differences. The average rates of acrosome reactions obtained in control, NGP- and ionophore-treated sperm showed that NGP-induced exocytosis differed significantly between the PFc (11%) and PFe/PFi groups (17%), and the ionophore-induced AR was higher for PFi (33%) than PFc/PFe (25%). The incidence of the NGP-induced AR was reduced in the first hour of pre-incubation with PFc and remained nearly constant throughout 4 h of incubation. The present data indicate that PF possesses a protective factor which prevents premature AR.Hospital de Clínicas de Porto AlegreUniversidade Federal de São Paulo (UNIFESP)UNIFESPSciEL
Manejo e exploração sustentável de florestas naturais tropicais: opções, restrições e alternativas.
Introdução; Conceito e manejo florestal e sustentabilidade; Características das florestas naturais tropicais; Formas de manejo florestal; Manejo de produtos não-madeireiros; Manejo de uso múltiplo; Manejo florestal em área com população; Modelo geral para pequena propriedade; condições gerais para o manejo florestal; Condições imediatas para implantação do manejo florestal.bitstream/CNPF-2009-09/40472/1/doc110.pd
Crescimento inicial de porta enxertos cítricos em substratos alternativos.
A produção de mudas cítricas de qualidade, passa pela produção em ambiente protegido, que apesar de aumentar o preço das mudas, qualifica-as com padrão fitossanitário. Entretanto, o que limita a adoção desse sistema de forma irrestrita no país é o alto custo da estufa e do substrato comercial. Para tanto, estudos que visem à elaboração de substratos alternativos, de fácil e constante disponibilidade a um baixo custo, tornam-se essenciais para dar suporte à modernização na produção de mudas, principalmente pelos pequenos viveiristas da região Nordeste e especialmente do Estado da Paraíba
Herding model and 1/f noise
We provide evidence that for some values of the parameters a simple agent
based model, describing herding behavior, yields signals with 1/f power
spectral density. We derive a non-linear stochastic differential equation for
the ratio of number of agents and show, that it has the form proposed earlier
for modeling of 1/f^beta noise with different exponents beta. The non-linear
terms in the transition probabilities, quantifying the herding behavior, are
crucial to the appearance of 1/f noise. Thus, the herding dynamics can be seen
as a microscopic explanation of the proposed non-linear stochastic differential
equations generating signals with 1/f^beta spectrum. We also consider the
possible feedback of macroscopic state on microscopic transition probabilities
strengthening the non-linearity of equations and providing more opportunities
in the modeling of processes exhibiting power-law statistics
Aqueous biphasic systems composed of ionic liquids: one-step extraction/concentration techniques for water pollution tracers
Emergent micropollutants have become a serious global problem with a large impact in the environment and
human health, while their presence in aquatic systems has been registered as ranging from ng/L-1 to ug/L-1.
Pharmaceuticals are ubiquitous micropollutants since their continuous consumption and consequent release via
human excretions into aqueous systems are inevitable. Due to their usually low concentrations in aqueous
samples, the development of a pre-concentration technique in order to continuously quantify and to monitor these
components in aqueous streams is of major relevance.
Aqueous biphasic systems (ABS) composed of ionic liquids (ILs) can be seen as more sustainable separation
processes since they avoid the use of volatile and hazardous organic solvents (VOCs). As liquid-liquid
systems, ABS can be used as extraction, purification and concentration platforms. Due to the outstanding tunable
properties of ILs, IL-based ABS provide higher and more selective extraction efficiencies for a wide range of
compounds when compared to traditional polymer-based ABS. IL-based ABS were already employed and
adequately characterized for the extraction and concentration of endocrine disruptors, either from biological fluids
or aqueous matrices. The aim of this work is to demonstrate the applicability of IL-based ABS to completely
extract and concentrate, in one-step, two different and representative pharmaceutical pollution tracers, namely
caffeine (CAF) and carbamazepine (CBZ). The low concentration of these persistent pollutants (usually found in
ug/L-1 and ng/L-1 levels) does not allow a proper detection and quantification by conventional analytical
equipment without a previous concentration step. However, pre-concentration methods commonly applied are
costly, time-consuming, provide irregular recoveries and/or use VOCs. In this work, ABS composed of the IL
tetrabutylammonium chloride ([N4444]Cl) and the salt K3C6H5O7 was investigated, demonstrating to be able to
completely extract and concentrate CAF and CBZ in a single-step. Moreover, with this pre-treatment step it was
demonstrated to be possible to overcome the detection limits of a high performance liquid chromatography
coupled to an UV-Vis detector equipment. The results obtained demonstrate that IL-based ABS are
versatile pre-concentration techniques, and can be used for the extraction and concentration of a large plethora of
other micropollutants from environmental aqueous matrices.publishe
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