192 research outputs found
Multireference calculations of the phosphorescence and photodissociation of chlorobenzene
Multireference complete active space self-consistent-field (CASSCF) and multireference CASSF second-order perturbation theory (MSCASPT2) calculations were performed on the ground state and a number of low-lying excited singlet and triplet states of chlorobenzene. The dual phosphorescence observed experimentally is clearly explained by the MSCASPT2 potential-energy curves. Experimental findings regarding the dissociation channels of chlorobenzene at 193, 248, and 266 nm are clarified from extensive theoretical information including all low-energy potential-energy curves
Incommensurability of a confined system under shear
We study a chain of harmonically interacting atoms confined between two sinusoidal substrate potentials, when the top substrate is driven through an attached spring with a constant velocity. This system is characterized by three inherent length scales and closely related to physical situations with confined lubricant films. We show that, contrary to the standard Frenkel-Kontorova model, the most favorable sliding regime is achieved by choosing chain-substrate incommensurabilities belonging to the class of cubic irrational numbers (e.g., the spiral mean). At large chain stiffness, the well known golden mean incommensurability reveals a very regular time-periodic dynamics with always higher kinetic friction values with respect to the spiral mean cas
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In-situ resonant band engineering of solution-processed semiconductors generates high performance n-type thermoelectric nano-inks.
Thermoelectric devices possess enormous potential to reshape the global energy landscape by converting waste heat into electricity, yet their commercial implementation has been limited by their high cost to output power ratio. No single "champion" thermoelectric material exists due to a broad range of material-dependent thermal and electrical property optimization challenges. While the advent of nanostructuring provided a general design paradigm for reducing material thermal conductivities, there exists no analogous strategy for homogeneous, precise doping of materials. Here, we demonstrate a nanoscale interface-engineering approach that harnesses the large chemically accessible surface areas of nanomaterials to yield massive, finely-controlled, and stable changes in the Seebeck coefficient, switching a poor nonconventional p-type thermoelectric material, tellurium, into a robust n-type material exhibiting stable properties over months of testing. These remodeled, n-type nanowires display extremely high power factors (~500 µW m-1K-2) that are orders of magnitude higher than their bulk p-type counterparts
Out-of-Equilibrium Admittance of Single Electron Box Under Strong Coulomb Blockade
We study admittance and energy dissipation in an out-of-equlibrium single
electron box. The system consists of a small metallic island coupled to a
massive reservoir via single tunneling junction. The potential of electrons in
the island is controlled by an additional gate electrode. The energy
dissipation is caused by an AC gate voltage. The case of a strong Coulomb
blockade is considered. We focus on the regime when electron coherence can be
neglected but quantum fluctuations of charge are strong due to Coulomb
interaction. We obtain the admittance under the specified conditions. It turns
out that the energy dissipation rate can be expressed via charge relaxation
resistance and renormalized gate capacitance even out of equilibrium. We
suggest the admittance as a tool for a measurement of the bosonic distribution
corresponding collective excitations in the system
Driven Dynamics: A Probable Photodriven Frenkel-Kontorova Model
In this study, we examine the dynamics of a one-dimensional Frenkel-Kontorova
chain consisting of nanosize clusters (the ''particles'') and photochromic
molecules (the ''bonds''), and being subjected to a periodic substrate
potential. Whether the whole chain should be running or be locked depends on
both the frequency and the wavelength of the light (keeping the other
parameters fixed), as observed through numerical simulation. In the locked
state, the particles are bound at the bottom of the external potential and
vibrate backwards and forwards at a constant amplitude. In the running state,
the initially fed energy is transformed into directed motion as a whole. It is
of interest to note that the driving energy is introduced to the system by the
irradiation of light, and the driven mechanism is based on the dynamical
competition between the inherent lengths of the moving object (the chain) and
the supporting carrier (the isotropic surface). However, the most important is
that the light-induced conformational changes of the chromophore lead to the
time-and-space dependence of the rest lengths of the bonds.Comment: 4 pages,5 figure
Dynamical phase diagram of the dc-driven underdamped Frenkel-Kontorova chain
Multistep dynamical phase transition from the locked to the running state of
atoms in response to a dc external force is studied by MD simulations of the
generalized Frenkel-Kontorova model in the underdamped limit. We show that the
hierarchy of transition recently reported [Braun et al, Phys. Rev. Lett. 78,
1295 (1997)] strongly depends on the value of the friction constant. A simple
phenomenological explanation for the friction dependence of the various
critical forces separating intermediate regimes is given.Comment: 12 Revtex Pages, 4 EPS figure
Весовые соотношения тимуса и надпочечников у антенатально погибших плодов
ТИМУСНАДПОЧЕЧНИКИтимомегалиядети первого года жизнидети раннего возрастаМЛАДЕНЕЦ, СМЕРТНОСТЬЭНДОКРИННОЙ СИСТЕМЫ БОЛЕЗНИСМЕРТНОСТЬ ДЕТСКАЯсиндром внезапной детской смерт
SiC Nanowires Synthesized by Rapidly Heating a Mixture of SiO and Arc-Discharge Plasma Pretreated Carbon Black
SiC nanowires have been synthesized at 1,600 °C by using a simple and low-cost method in a high-frequency induction furnace. The commercial SiO powder and the arc-discharge plasma pretreated carbon black were mixed and used as the source materials. The heating-up and reaction time is less than half an hour. It was found that most of the nanowires have core-shell SiC/SiO2nanostructures. The nucleation, precipitation, and growth processes were discussed in terms of the oxide-assisted cluster-solid mechanism
Arithmetical Chaos and Quantum Cosmology
In this note, we present the formalism to start a quantum analysis for the
recent billiard representation introduced by Damour, Henneaux and Nicolai in
the study of the cosmological singularity. In particular we use the theory of
Maass automorphic forms and recent mathematical results about arithmetical
dynamical systems. The predictions of the billiard model give precise
automorphic properties for the wave function (Maass-Hecke eigenform), the
asymptotic number of quantum states (Selberg asymptotics for PSL(2,Z)), the
distribution for the level spacing statistics (the Poissonian one) and the
absence of scarred states. The most interesting implication of this model is
perhaps that the discrete spectrum is fully embedded in the continuous one.Comment: 35 pages, 4 figures. to be published on Classical and Quantum Gravity
(scheduled for January 2009
Green function techniques in the treatment of quantum transport at the molecular scale
The theoretical investigation of charge (and spin) transport at nanometer
length scales requires the use of advanced and powerful techniques able to deal
with the dynamical properties of the relevant physical systems, to explicitly
include out-of-equilibrium situations typical for electrical/heat transport as
well as to take into account interaction effects in a systematic way.
Equilibrium Green function techniques and their extension to non-equilibrium
situations via the Keldysh formalism build one of the pillars of current
state-of-the-art approaches to quantum transport which have been implemented in
both model Hamiltonian formulations and first-principle methodologies. We offer
a tutorial overview of the applications of Green functions to deal with some
fundamental aspects of charge transport at the nanoscale, mainly focusing on
applications to model Hamiltonian formulations.Comment: Tutorial review, LaTeX, 129 pages, 41 figures, 300 references,
submitted to Springer series "Lecture Notes in Physics
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