415 research outputs found
An innovative concept of use of redox-active electrolyte in asymmetric capacitor based on MWCNTs/MnO(2) and Fe(2)O(3) thin films
In present investigation, we have prepared a nanocomposites of highly porous MnO2 spongy balls and multi-walled carbon nanotubes (MWCNTs) in thin film form and tested in novel redox-active electrolyte (K3[Fe(CN)6] doped aqueous Na2SO4) for supercapacitor application. Briefly, MWCNTs were deposited on stainless steel substrate by "dip and dry" method followed by electrodeposition of MnO2 spongy balls. Further, the supercapacitive properties of these hybrid thin films were evaluated in hybrid electrolyte ((K3[Fe(CN)6 doped aqueous Na2SO4). Thus, this is the first proof-of-design where redox-active electrolyte is applied to MWCNTs/MnO2 hybrid thin films. Impressively, the MWCNTs/MnO2 hybrid film showed a significant improvement in electrochemical performance with maximum specific capacitance of 1012 Fg-1 at 2 mA cm-2 current density in redox-active electrolyte, which is 1.5-fold higher than that of conventional electrolyte (Na2SO4). Further, asymmetric capacitor based on MWCNTs/MnO2 hybrid film as positive and Fe2O3 thin film as negative electrode was fabricated and tested in redox-active electrolytes. Strikingly, MWCNTs/MnO2//Fe2O3 asymmetric cell showed an excellent supercapacitive performance with maximum specific capacitance of 226 Fg-1 and specific energy of 54.39 Wh kg-1 at specific power of 667 Wkg-1. Strikingly, actual practical demonstration shows lightning of 567 red LEDs suggesting "ready-to sell" product for industries.Nilesh R. Chodankar, Deepak P. Dubal, Abhishek C. Lokhande, Amar M. Patil, Jin H. Kim, Chandrakant D. Lokhand
Apparent horizons in simplicial Brill wave initial data
We construct initial data for a particular class of Brill wave metrics using
Regge calculus, and compare the results to a corresponding continuum solution,
finding excellent agreement. We then search for trapped surfaces in both sets
of initial data, and provide an independent verification of the existence of an
apparent horizon once a critical gravitational wave amplitude is passed. Our
estimate of this critical value, using both the Regge and continuum solutions,
supports other recent findings.Comment: 7 pages, 6 EPS figures, LaTeX 2e. Submitted to Class. Quant. Gra
La gestión del ingreso y la permanencia en la universidad como fortalecimiento del respeto a los derechos humanos y a las libertades fundamentales.
El artículo 26 de la Declaración Universal de los Derechos Humanos, establece que toda persona tiene derecho a la educación ¿cómo se transforma esa declaración en realidad en el nivel universitario? Democratizar el acceso y la permanencia en los estudios superiores, involucra un compromiso que aúna la política educativa institucional con la concepción de un proyecto pedagógico que genera condiciones para garantizar que las puertas abiertas de la universidad no se vuelvan giratorias . En tal sentido, implica reconocer las complejas situaciones que se presentan año a año en relación con las competencias académicas de los estudiantes, el imaginario docente sobre lo que deberían saber , lo que traen de la secundaria y las dificultades reales de los estudiantes -no circunscriptas solo a lo académico- si bien es el principal espacio donde se evidencia. Conocer quiénes son, qué piensan sobre sus fortalezas y sus debilidades para insertarse como alumno universitario, qué esperan de una tutoría, cuáles son sus hábitos de estudio, etc. son algunas de las cuestiones que, entre otro conjunto de iniciativas, el equipo del Programa de Tutorías para los ingresantes a la Carrera de Ingeniería en Alimentos intentó responder y en esta oportunidad, compartirlo con los colegas de América Latina
Geodesic Deviation in Regge Calculus
Geodesic deviation is the most basic manifestation of the influence of
gravitational fields on matter. We investigate geodesic deviation within the
framework of Regge calculus, and compare the results with the continuous
formulation of general relativity on two different levels. We show that the
continuum and simplicial descriptions coincide when the cumulative effect of
the Regge contributions over an infinitesimal element of area is considered.
This comparison provides a quantitative relation between the curvature of the
continuous description and the deficit angles of Regge calculus. The results
presented might also be of help in developing generic ways of including matter
terms in the Regge equations.Comment: 9 pages. Latex 2e with 5 EPS figures. Submitted to CQ
Cauchy-characteristic Evolution of Einstein-Klein-Gordon Systems
A Cauchy-characteristic initial value problem for the Einstein-Klein-Gordon
system with spherical symmetry is presented. Initial data are specified on the
union of a space-like and null hypersurface. The development of the data is
obtained with the combination of a constrained Cauchy evolution in the interior
domain and a characteristic evolution in the exterior, asymptotically flat
region. The matching interface between the space-like and characteristic
foliations is constructed by imposing continuity conditions on metric,
extrinsic curvature and scalar field variables, ensuring smoothness across the
matching surface. The accuracy of the method is established for all ranges of
, most notably, with a detailed comparison of invariant observables
against reference solutions obtained with a calibrated, global, null algorithm.Comment: Submitted to Phys. Rev. D, 16 pages, revtex, 7 figures available at
http://nr.astro.psu.edu:8080/preprints.htm
Molybdenum nitride nanocrystals anchored on phosphorus-incorporated carbon fabric as a negative electrode for high-performance asymmetric pseudocapacitor
Pseudocapacitors hold great promise to provide high energy-storing capacity; however, their capacitances are still far below their theoretical values and they deliver much lower power than the traditional electric double-layer capacitors due to poor ionic accessibility. Here, we have engineered MoN nanoparticles as pseudocapacitive material on phosphorus-incorporated carbon fabric with enhanced ionic affinity and thermodynamic stability. This nanocomposite boosts surface redox kinetics, leading to pseudocapacitance of 400 mF/cm² (2-fold higher than that of molybdenum nitride-based electrodes) with rapid charge-discharge rates. Density functional theory simulations are used to explain the origin of the good performance of MoN@P-CF in proton-based aqueous electrolytes. Finally, an all-pseudocapacitive solid-state asymmetric cell was assembled using MoN@P-CF and RuO₂ (RuO₂@CF) as negative and positive electrodes, respectively, which delivered good energy density with low relaxation time constant (τ₀) of 13 ms (significantly lower than that of carbon-based supercapacitors).Deepak P. Dubal, Safwat Abdel-Azeim, Nilesh R. Chodankar, and Young-Kyu Ha
Synthetic approach from polypyrrole nanotubes to nitrogen doped pyrolyzed carbon nanotubes for asymmetric supercapacitors
Pseudocapacitive materials are highly capable to achieve high energy density integrated with high power electrostatic capacitive materials. However, finding a suitable electrostatic capacitive material to integrate with pseudocapacitive material in order to achieve high energy density with good rate capability is still a challenge. Herein, we are providing a novel synthetic approach starting from the synthesis of polypyrrole nanotubes (PPy-NTs) and ending up at the carbonization of PPy-NTs to obtain N-doped carbon nanotubes (N-CNTs). With highly porous nature of PPy-NTs and great graphitic texture with copious heteroatom functionalities, N-CNTs significantly promoted the faradic pseudo-capacitors, demonstrating high single-electrode capacitance over 332 F/g and 228 F/g in 1 M HSO aqueous solution. Further, a novel asymmetric supercapacitor with PPy-NTs as positive and N-CNTs as negative electrode has been fabricated. This PPy-NTs//N-CNTs cell effectively provides high operation voltage (1.4 V) and hence high energy density over 28.95 W h/kg (0.41 mW h/cm) with a high power density of 7.75 kW/kg (113 mW/cm) and cyclic stability of 89.98% after 2000 cycles
Reaction mechanism and characteristics of T_{20} in d + ^3He backward elastic scattering at intermediate energies
For backward elastic scattering of deuterons by ^3He, cross sections \sigma
and tensor analyzing power T_{20} are measured at E_d=140-270 MeV. The data are
analyzed by the PWIA and by the general formula which includes virtual
excitations of other channels, with the assumption of the proton transfer from
^3He to the deuteron. Using ^3He wave functions calculated by the Faddeev
equation, the PWIA describes global features of the experimental data, while
the virtual excitation effects are important for quantitative fits to the
T_{20} data. Theoretical predictions on T_{20}, K_y^y (polarization transfer
coefficient) and C_{yy} (spin correlation coefficient) are provided up to GeV
energies.Comment: REVTEX+epsfig, 17 pages including 6 eps figs, to be published in
Phys. Rev.
Proton--induced deuteron breakup at GeV energies with forward emission of a fast proton pair
A study of the deuteron breakup reaction with forward emission
of a fast proton pair with small excitation energy 3 MeV has been
performed at the ANKE spectrometer at COSY--J\"ulich. An exclusive measurement
was carried out at six proton--beam energies ~0.6,~0.7,~0.8,~0.95,~1.35,
and 1.9 GeV by reconstructing the momenta of the two protons. The differential
cross section of the breakup reaction, averaged up to over the cm
polar angle of the total momentum of the pairs, has been obtained. Since
the kinematics of this process is quite similar to that of backward elastic scattering, the results are compared to calculations based on a
theoretical model previously applied to the process.Comment: 17 pages including 6 figures and 1 table v2: minor changes; v3: minor
change of author list; v4: changes in accordance with referee remark
Relativistic hydrodynamics on spacelike and null surfaces: Formalism and computations of spherically symmetric spacetimes
We introduce a formulation of Eulerian general relativistic hydrodynamics
which is applicable for (perfect) fluid data prescribed on either spacelike or
null hypersurfaces. Simple explicit expressions for the characteristic speeds
and fields are derived in the general case. A complete implementation of the
formalism is developed in the case of spherical symmetry. The algorithm is
tested in a number of different situations, predisposing for a range of
possible applications. We consider the Riemann problem for a polytropic gas,
with initial data given on a retarded/advanced time slice of Minkowski
spacetime. We compute perfect fluid accretion onto a Schwarzschild black hole
spacetime using ingoing null Eddington-Finkelstein coordinates. Tests of fluid
evolution on dynamic background include constant density and TOV stars sliced
along the radial null cones. Finally, we consider the accretion of
self-gravitating matter onto a central black hole and the ensuing increase in
the mass of the black hole horizon.Comment: 23 pages, 13 figures, submitted to Phys. Rev.
- …