5,062 research outputs found
Charge and momentum transfer in supercooled melts: Why should their relaxation times differ?
The steady state values of the viscosity and the intrinsic ionic-conductivity
of quenched melts are computed, in terms of independently measurable
quantities. The frequency dependence of the ac dielectric response is
estimated. The discrepancy between the corresponding characteristic relaxation
times is only apparent; it does not imply distinct mechanisms, but stems from
the intrinsic barrier distribution for -relaxation in supercooled
fluids and glasses. This type of intrinsic ``decoupling'' is argued not to
exceed four orders in magnitude, for known glassformers. We explain the origin
of the discrepancy between the stretching exponent , as extracted from
and the dielectric modulus data. The actual width of the
barrier distribution always grows with lowering the temperature. The contrary
is an artifact of the large contribution of the dc-conductivity component to
the modulus data. The methodology allows one to single out other contributions
to the conductivity, as in ``superionic'' liquids or when charge carriers are
delocalized, implying that in those systems, charge transfer does not require
structural reconfiguration.Comment: submitted to J Chem Phy
Electric and magnetic fields effects on the excitonic properties of elliptic core-multishell quantum wires
The effect of eccentricity distortions of core-multishell quantum wires on
their electron, hole and exciton states is theoretically investigated. Within
the effective mass approximation, the Schrodinger equation is numerically
solved for electrons and holes in systems with single and double radial
heterostructures, and the exciton binding energy is calculated by means of a
variational approach. We show that the energy spectrum of a core-multishell
heterostructure with eccentricity distortions, as well as its magnetic field
dependence, are very sensitive to the direction of an externally applied
electric field, an effect that can be used to identify the eccentricity of the
system. For a double heterostructure, the eccentricities of the inner and outer
shells play an important role on the excitonic binding energy, specially in the
presence of external magnetic fields, and lead to drastic modifications in the
oscillator strength.Comment: 17 pages, 10 figure
Isotretinoin and inflammatory bowel disease
[Excerpt] We read with great interest the recent
review published in your Journal by Reddy et al., which
suggests a possible association between isotretinoin use and
inflammatory bowel disease (IBD) (1). Although IBD is described as a possible adverse drug reaction in the product
information, little attention has been given in the literature to
this association.[...
Micropedologia de um Argissolo amarelo com horizontes antrópicos (Terra Preta de Índio) na Amazônia Central.
Estudos micropedológicos foram carreados em Terra Preta de Índio (TPI) com o objetivo de elucidar os processos envolvidos em sua gênese, bem como suas formas de utilização pré-colombiana. Blocos indeformados de solo foram coletados por horizonte e em suas respectivas transições em um perfil de Argissolo Amarelo A Antrópico (TPI) localizado no município de Iranduba, AM. As lâminas delgadas confeccionadas a partir dos blocos foram descritas por meio de microscopia óptica. Os resultados mostraram que os processos envolvidos na gênese desse solo envolveram: i) condições pedoambientais diferentes das atuais (pedorrelíquias - nódulos ferruginosos); ii) argiluviação, indicada por revestimentos de ferri-argilãs orientados na parede de poros entre agregados e canais; iii) migração de ferro impregnando o fundo matricial (cutãs de difusão); iv) bioturbação, atestada por preenchimento de poros por pelotas fecais e microagregação zoogenética e v) antropismo, que contribuiu com a queima de resíduos (partículas de carvões) e descarte de artefatos cerâmicos. A análise dos fragmentos cerâmicos corroborou a utilização de cauixi (Tubella reticulata e Parnula betesil) e cariapé (Bignoniacea) como antiplástico para o seu fabrico
Caracterização de dois perfis com horizonte antrópico (Terra Preta de Índio) no Lago do Limão - AM.
O trabalho teve por objetivo caracterizar dois perfis com horizonte antrópico no Lago do Limão, município de Iranduba
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