806 research outputs found
Requirements for optimization of electrodes and electrolyte for the iron/chromium Redox flow cell
Improved catalyzation techniques that included a pretreatment of carbon substrate and provided normalized carbon surface for uniform gold deposition were developed. This permits efficient use of different batches of carbon felt materials which initially vary significantly in their physical and surface chemical properties, as well as their electrochemical behavior. Further modification of gold impregnation technique gave the best performing electrodes. In addition to the linear sweep voltammetry, cyclic voltammetry was used to determine the effects of different activation procedures on the Cr(3)/Cr(2) Redox and H2 evolution reactions. The roles of carbon, gold and lead in the overall Redox cycle are identified. The behavior of the electrodes at both normal battery operating potentials and more extreme potentials is discussed preparing efficient and stable electrodes for the energy storage battery is implicated
Resonant hyper-Raman scattering in spherical quantum dots
A theoretical model of resonant hyper-Raman scattering by an ensemble of
spherical semiconductor quantum dots has been developed. The electronic
intermediate states are described as Wannier-Mott excitons in the framework of
the envelope function approximation. The optical polar vibrational modes of the
nanocrystallites (vibrons) and their interaction with the electronic system are
analized with the help of a continuum model satisfying both the mechanical and
electrostatic matching conditions at the interface. An explicit expression for
the hyper-Raman scattering efficiency is derived, which is valid for incident
two-photon energy close to the exciton resonances. The dipole selection rules
for optical transitions and Fr\"ohlich-like exciton-lattice interaction are
derived: It is shown that only exciton states with total angular momentum
and vibrational modes with angular momentum contribute to the
hyper-Raman scattering process. The associated exciton energies, wavefunctions,
and vibron frequencies have been obtained for spherical CdSe zincblende-type
nanocrystals, and the corresponding hyper-Raman scattering spectrum and
resonance profile are calculated. Their dependence on the dot radius and the
influence of the size distribution on them are also discussed.Comment: 12 pages REVTeX (two columns), 2 tables, 8 figure
Experimental Quantification of the Effect of Nonlinearities on the EIS Spectra of the Cathodic Electrode of an Alkaline Electrolyzer
[EN] Electrochemical impedance spectroscopy (EIS) is a very powerful tool to study the behavior of electrochemical systems. According to Ohm¿s generalized law, the impedance concept is only valid if the linearity condition is met. In the case that the linearity condition is not achieved, the obtained impedance spectra will present distortions which may lead to biased or even erroneous results and conclusions. In this work, an experimental quantification of the effect of nonlinearities on EIS spectra was performed in order to determine
the order of magnitude of the effect of the nonlinearity of the system on the obtained spectra of the cathodic electrode of an alkaline electrolyzer.The authors are very grateful to the Generalitat Valenciana for its economic support in form of Vali+d grant (Ref: ACIF-2013-268).Giner-Sanz, J.; Ortega, E.; Pérez-Herranz, V. (2017). Experimental Quantification of the Effect of Nonlinearities on the EIS Spectra of the Cathodic Electrode of an Alkaline Electrolyzer. Fuel Cells. 17(3):391-401. https://doi.org/10.1002/fuce.201600137S39140117
Bose-Einstein condensation in an optical lattice: A perturbation approach
We derive closed analytical expressions for the order parameter
and for the chemical potential of a Bose-Einstein Condensate loaded into
a harmonically confined, one dimensional optical lattice, for sufficiently
weak, repulsive or attractive interaction, and not too strong laser
intensities. Our results are compared with exact numerical calculations in
order to map out the range of validity of the perturbative analytical approach.
We identify parameter values where the optical lattice compensates the
interaction-induced nonlinearity, such that the condensate ground state
coincides with a simple, single particle harmonic oscillator wave function
Formal analytical solutions for the Gross-Pitaevskii equation
Considering the Gross-Pitaevskii integral equation we are able to formally
obtain an analytical solution for the order parameter and for the
chemical potential as a function of a unique dimensionless non-linear
parameter . We report solutions for different range of values for the
repulsive and the attractive non-linear interactions in the condensate. Also,
we study a bright soliton-like variational solution for the order parameter for
positive and negative values of . Introducing an accumulated error
function we have performed a quantitative analysis with other well-established
methods as: the perturbation theory, the Thomas-Fermi approximation, and the
numerical solution. This study gives a very useful result establishing the
universal range of the -values where each solution can be easily
implemented. In particular we showed that for , the bright soliton
function reproduces the exact solution of GPE wave function.Comment: 8 figure
Heart Rate Variability Analysis Assessment for Asthma Control Stratification
Autonomic nervous system (ANS) has been suggested to play a major role in the pathogenesis of asthma. This hypothesis has motivated large research, revealing a reduced modulation of the heart rate in subjects with uncontrolled asthma, when compared to asthmatics with controlled symptomatology. In this work, we assessed ANS activity through heart rate variability analysis in a group of asthmatics classified attending to the control of their symptoms. This information was later used for training a logistic regression classifier aiming at differentiating between the levels of control in asthmatic patients. The accuracy of the classifier improved when including ANS information (71.77%, versus 64.73% when only clinical parameters were considered), suggesting that ANS assessment could contribute to better non-invasive asthma monitoring
VO2 indirect maximum and fitness age of sedentary and non-sedentary
El objetivo es: comparar la edad cronológica con la edad fitness obtenida
por medio del VO2 máximo indirecto, de un grupo de personas sedentarias y no
sedentarias. Método: 253 personas fueron evaluadas respecto a masa corporal,
estatura, perímetro de cintura, frecuencia cardiaca basal y un cuestionario del
modelo web "Fitness Calculator". Los resultados demostraron diferencias
significativas en las variables antropométricas y fisiológicas entre personas
sedentarias y no sedentarias (P<,001). Las personas no sedentarias tienen un
mayor VO2máx en comparación con las personas sedentarias. Las personas
sedentarias indican que presentan una edad fitness que se encuentra sobre 12
años cronológicos promedio de lo esperado. Conclusión: Las personas
sedentarias tienen una mayor edad fitness, esto permite establecer que su
cuerpo se deteriora más rápido que los no sedentarios. El bajo VO2 máx es un
potente predictor de la capacidad cardiorrespiratoria y se establece como un
predictor de enfermedades cardiovascularesThe purpose was to compare chronological age with fitness age obtained
through indirect VO2max in a group of sedentary and non-sedentary people.
Method: 253 people were evaluated for body mass, height, waist circumference,
basal heart rate and a web model questionnaire "Fitness Calculator". The
results: showed significant differences in anthropometric and physiological
variables between sedentary and non-sedentary people (P <.001). Non-
Sedentary people have a greater higher VO2máx group compared to sedentary
people. This indicates that sedentary people have a fitness age 12 years over
their expected chronological average age. Conclusion: Sedentary people have
a higher fitness age; therefore your body deteriorates faster than the nonsedentary
people. A low level of VO2máx is a powerful predictor of
cardiorespiratory capacity and of cardiovascular diseasesEl estudio fue financiado por la Escuela de Kinesiología de la Universidad Bernardo O`higgin
Spin-polarization in quantum wires: Influence of Dresselhaus spin-orbit interaction and cross-section effects
We examine the effects of the full Dresselhaus spin-orbit coupling on laterally confined quantum wire states. An analysis of the relative contributions due to linear, quadratic, and cubic Dresselhaus spin-orbit terms on the energy levels, spin splitting, and spin polarization has been carried out. The effects of wire cross-sectional geometry shapes on the electronic structure are explored. In particular we compared the results of semicylindrical and cylindrical confinements and have found important differences between the spin degeneracy of the ground-state level and the spin-polarization dependence on sign inversion of the free linear momentum quantum number along the wire axis. Different from other symmetries, in both cases here considered, the stronger spin-splitting effects come from the quadratic Dresselhaus term. We report ideal conditions for realization of spin-field filter devices based on symmetry properties of the spin splitting of the ground state in semicylindrical quantum wires
Generating Bounds for the Ground State Energy of the Infinite Quantum Lens Potential
Moment based methods have produced efficient multiscale quantization
algorithms for solving singular perturbation/strong coupling problems. One of
these, the Eigenvalue Moment Method (EMM), developed by Handy et al (Phys. Rev.
Lett.{\bf 55}, 931 (1985); ibid, {\bf 60}, 253 (1988b)), generates converging
lower and upper bounds to a specific discrete state energy, once the signature
property of the associated wavefunction is known. This method is particularly
effective for multidimensional, bosonic ground state problems, since the
corresponding wavefunction must be of uniform signature, and can be taken to be
positive. Despite this, the vast majority of problems studied have been on
unbounded domains. The important problem of an electron in an infinite quantum
lens potential defines a challenging extension of EMM to systems defined on a
compact domain. We investigate this here, and introduce novel modifications to
the conventional EMM formalism that facilitate its adaptability to the required
boundary conditions.Comment: Submitted to J. Phys.
- …