2,929 research outputs found
Basal-plane Incommensurate Phases in HCP Structures
An Ising model with competing interaction is used to study the appearance of
incommensurate phases in the basal plane of an hexagonal closed-packed
structure. The calculated mean-field phase diagram reveals various
1q-incommensurate and lock-in phases. The results are applied to explain the
basal-plane incommensurate phase in some compounds of the A'A"BX_4 family, like
K_2MoO_4, K_2WO_4, Rb_2WO4 and to describe the sequence of high-temperature
phase transitions in other compounds of this family.Comment: 8 pages, RevTeX + 4 ps figure
Observation of the Kohn anomaly near the K point of bilayer graphene
The dispersion of electrons and phonons near the K point of bilayer graphene
was investigated in a resonant Raman study using different laser excitation
energies in the near infrared and visible range. The electronic structure was
analyzed within the tight-binding approximation, and the
Slonczewski-Weiss-McClure (SWM) parameters were obtained from the analysis of
the dispersive behavior of the Raman features. A softening of the phonon
branches was observed near the K point, and results evidence the Kohn anomaly
and the importance of considering electron-phonon and electron-electron
interactions to correctly describe the phonon dispersion in graphene systems.Comment: 4 pages, 4 figure
Interações entre ácido indol butírico, uniconazol e dois tipos de substrato, no enraizamento de estacas caulinares de Sapium glandulatum (Vell Pax (resultados preliminares)).
Organizado por Patrícia Póvoa de Mattos, Celso Garcia Auer, Paulo César Botosso e Rejane Stumpf Sberze
Nature of the constant factor in the relation between radial breathing mode frequency and tube diameter for single-wall carbon nanotubes
Resonance Raman scattering is used to determine the radial breathing mode (RBM) frequency (ωRBM) dependence on tube diameter (dt) for single-wall carbon nanotubes (SWNTs). We establish experimentally the ωRBM=227.0/dt as the fundamental relation for pristine SWNTs. All the other RBM values found in the literature can be explained by an upshift in frequency due mostly to van der Waals interaction between SWNTs and environment
Avaliação da absorção de água e viabilidade de três genótipos de sementes de Jatropha curcas L.
Edição dos resumos do 18º Congresso Brasileiro de Sementes, 2013, Florianópolis. CD-ROM
Caracterização das potencialidades germinativas de três genótipos de sementes de Jatropha curcas L.
Edição dos resumos do 18º Congresso Brasileiro de Sementes, 2013, Florianópolis. CD-ROM
The Yang-Baxter equation for PT invariant nineteen vertex models
We study the solutions of the Yang-Baxter equation associated to nineteen
vertex models invariant by the parity-time symmetry from the perspective of
algebraic geometry. We determine the form of the algebraic curves constraining
the respective Boltzmann weights and found that they possess a universal
structure. This allows us to classify the integrable manifolds in four
different families reproducing three known models besides uncovering a novel
nineteen vertex model in a unified way. The introduction of the spectral
parameter on the weights is made via the parameterization of the fundamental
algebraic curve which is a conic. The diagonalization of the transfer matrix of
the new vertex model and its thermodynamic limit properties are discussed. We
point out a connection between the form of the main curve and the nature of the
excitations of the corresponding spin-1 chains.Comment: 43 pages, 6 figures and 5 table
Characterization of resistant hypertension: Association between resistant hypertension, aldosterone, and persistent intravascular volume expansion
Background: Resistant hypertension is a common clinical problem and greatly increases the risk of target organ damage. Methods: We evaluated the characteristics of 279 consecutive patients with resistant hypertension (uncontrolled despite the use of 3 antihypertensive agents) and 53 control subjects (with normotension or hypertension controlled by using ≤2 antihypertensive medications). Participants were prospectively examined for plasma aldosterone concentration, plasma renin activity, aldosterone to renin ratio, brain-type natriuretic peptide, atrial natriuretic peptide, and 24-hour urinary aldosterone (UAldo), cortisol, sodium, and potassium values while adhering to a routine diet. Results: Plasma aldosterone (P < .001), aldosterone to renin ratio (P < .001), 24-hour UAldo (P = .02), brain-type natriuretic peptide (P = .007), and atrial natriuretic peptide (P = .001) values were higher and plasma renin activity (P = .02) and serum potassium (P < .001) values were lower in patients with resistant hypertension vs controls. Of patients with resistant hypertension, men had significantly higher plasma aldosterone (P = .003), aldosterone to renin ratio (P = .02), 24-hour UAldo (P < .001), and urinary cortisol (P < .001) values than women. In univariate linear regression analysis, body mass index (P = .01), serum potassium (P < .001), urinary cortisol (P < .001), urinary sodium (P = .02), and urinary potassium (P < .001) values were correlated with 24-hour UAldo levels. Serum potassium (P = .001), urinary potassium (P < .001), and urinary sodium (P = .03) levels were predictors of 24-hour UAldo levels in multivariate modeling. Conclusions: Aldosterone levels are higher and there is evidence of intravascular volume expansion (higher brain-type and atrial natriuretic peptide levels) in patients with resistant hypertension vs controls. These differences are most pronounced in men. A significant correlation between 24-hour urinary aldosterone levels and cortisol excretion suggests that a common stimulus, such as corticotropin, may underlie the aldosterone excess in patients with resistant hypertension
Microfluidic converging/diverging channels optimised for homogeneous extensional deformation
In this work we optimise microfluidic converging/diverging geometries in order to produce constant strain-rates along the centreline of the flow, for performing studies under homogeneous extension. The design is examined for both two-dimensional and three-dimensional flows where the effects of aspect ratio and dimensionless contraction length are investigated. Initially, pressure driven flows of Newtonian fluids under creeping flow conditions are considered, which is a reasonable approximation in microfluidics, and the limits of the applicability of the design in terms of Reynolds numbers are investigated. The optimised geometry is then used for studying the flow of viscoelastic fluids and the practical limitations in terms of Weissenberg number are reported. Furthermore, the optimisation strategy is also applied for electro-osmotic driven flows, where the development of a plug-like velocity profile allows for a wider region of homogeneous extensional deformation in the flow field
- …