258 research outputs found
Thermal Logic Gates: Computation with phonons
Logic gates are basic digital elements for computers. We build up thermal
logic gates that can perform similar operations as their electronic
counterparts. The thermal logic gates are based on the nonlinear lattices,
which exhibit very intriguing phenomena due to their temperature dependent
power spectra. We demonstrate that phonons, the heat carriers, can be also used
to carry information and processed accordingly. The possibility of nanoscale
experiment is discussed.Comment: 5 pages, 5 figures. To appear in Phys. Rev. Let
Quantum Brayton cycle with coupled systems as working substance
We explore the quantum version of Brayton cycle with a composite system as
the working substance. The actual Brayton cycle consists of two adiabatic and
two isobaric processes. Two pressures can be defined in our isobaric process,
one corresponds to the external magnetic field (characterized by ) exerted
on the system, while the other corresponds to the coupling constant between the
subsystems (characterized by ). As a consequence, we can define two types
of quantum Brayton cycle for the composite system. We find that the subsystem
experiences a quantum Brayton cycle in one quantum Brayton cycle (characterized
by ), whereas the subsystem's cycle is of quantum Otto in another Brayton
cycle (characterized by ). The efficiency for the composite system equals
to that for the subsystem in both cases, but the work done by the total system
are usually larger than the sum of work done by the two subsystems. The other
interesting finding is that for the cycle characterized by , the subsystem
can be a refrigerator while the total system is a heat engine. The result in
the paper can be generalized to a quantum Brayton cycle with a general coupled
system as the working substance.Comment: 7 pages, 3 figures, accepted by Phys. Rev.
Systematically improvable optimized atomic basis sets for {\it ab inito} calculations
We propose a unique scheme to construct fully optimized atomic basis sets for
density-functional calculations. The shapes of the radial functions are
optimized by minimizing the {\it spillage} of the wave functions between the
atomic orbital calculations and the converged plane wave calculations for dimer
systems. The quality of the bases can be systematically improved by increasing
the size of the bases within the same framework. The scheme is easy to
implement and very flexible. We have done extensive tests of this scheme for
wide variety of systems. The results show that the obtained atomic basis sets
are very satisfactory for both accuracy and transferability
The dynamic electric polarizability of a particle bound by a double delta potential
In this paper we derive an expression for the dynamic electric polarizability
of a particle bound by a double delta potential for frequencies below and above
the absolute value of the particle's ground state energy. The derived
expression will be used to study some of the fundamental features of the system
and its representation of real systems. In addition we derive a general
expression of the dynamic electric polarizability for a potential of
multi-delta functions.Comment: 11 pages, 5 figure
Electronic structure and electric-field gradients analysis in
Electric field gradients (EFG's) were calculated for the compound at
both and sites. The calculations were performed within
the density functional theory (DFT) using the augmented plane waves plus local
orbital (APW+lo) method employing the so-called LDA+U scheme. The
compound were treated as nonmagnetic, ferromagnetic, and antiferromagnetic
cases. Our result shows that the calculated EFG's are dominated at the
site by the Ce-4f states. An approximately linear relation is
intuited between the main component of the EFG's and total density of states
(DOS) at Fermi level. The EFG's from our LDA+U calculations are in better
agreement with experiment than previous EFG results, where appropriate
correlations had not been taken into account among 4f-electrons. Our result
indicates that correlations among 4f-electrons play an important role in this
compound and must be taken into account
Complete d-Band Dispersion and the Mobile Fermion Scale in NaxCoO2
We utilize fine-tuned polarization selection coupled with excitation-energy
variation of photoelectron signal to image the \textit{complete d}-band
dispersion relation in sodium cobaltates. A hybridization gap anticrossing is
observed along the Brillouin zone corner and the full quasiparticle band is
found to emerge as a many-body entity lacking a pure orbital polarization. At
low dopings, the quasiparticle bandwidth (Fermion scale, many-body
\textit{E} 0.25 eV) is found to be smaller than most known oxide
metals. The low-lying density of states is found to be in agreement with
bulk-sensitive thermodynamic measurements for nonmagnetic dopings where the 2D
Luttinger theorem is also observed to be satisfied.Comment: 4+ pages, 5 Fig
Quantum Thermodynamic Cycles and quantum heat engines
In order to describe quantum heat engines, here we systematically study
isothermal and isochoric processes for quantum thermodynamic cycles. Based on
these results the quantum versions of both the Carnot heat engine and the Otto
heat engine are defined without ambiguities. We also study the properties of
quantum Carnot and Otto heat engines in comparison with their classical
counterparts. Relations and mappings between these two quantum heat engines are
also investigated by considering their respective quantum thermodynamic
processes. In addition, we discuss the role of Maxwell's demon in quantum
thermodynamic cycles. We find that there is no violation of the second law,
even in the existence of such a demon, when the demon is included correctly as
part of the working substance of the heat engine.Comment: 17 pages, 9 figures, 4 table
Electrochemical Generation of Superoxide in Room-Temperature Ionic Liquids
We have demonstrated that superoxide ion can be generated electrochemically in room-temperature ionic-liquid solvents. In the absence of impurities, cyclic voltammetry showed that the super oxide ion is stable in these solvents. Similar superoxide ion chemistry has previously been demonstrated in volatile and environmentally suspect aprotic solvents such as dimethyl formamide and acetonitrile. However, ionic liquids are nonvolatile and should minimize the problems of secondary solvent waste. It is proposed that the resultant superoxide ion can be used to perform low temperature oxidation of wastes. Low-temperature oxidation of waste solvents can provide a much needed alternative to high-temperature waste incinerators, whose use is greatly complicated by regulatory requirements and locating suitable sites
Quantum nucleation in ferromagnets with tetragonal and hexagonal symmetries
The phenomenon of quantum nucleation is studied in a ferromagnet in the
presence of a magnetic field at an arbitrary angle. We consider the
magnetocrystalline anisotropy with tetragonal symmetry and that with hexagonal
symmetry, respectively. By applying the instanton method in the
spin-coherent-state path-integral representation, we calculate the dependence
of the rate of quantum nucleation and the crossover temperature on the
orientation and strength of the field for a thin film and for a bulk solid. Our
results show that the rate of quantum nucleation and the crossover temperature
depend on the orientation of the external magnetic field distinctly, which
provides a possible experimental test for quantum nucleation in nanometer-scale
ferromagnets.Comment: 19 pages and 3 figures, Final version and accepted by Phys. Rev. B
(Feb. B1 2001
Low-energy electronic states of carbon nanocones in an electric field
«Non v’è salvezza al di fuori del mostruoso»; «la diserzione, intrinseca alla letteratura, diventa nel fantastico sfida blasfema, obiezione, tradimento»: in questi passi, lo scrittore italiano Giorgio Manganelli (1922-1990) riafferma la portata trasgressiva della sua opera, indicando nel superamento dei limiti razionali, del verosimile, dell’accettabile o, in altre parole, del narrabile la via per sottrarre la letteratura ad una funzione strumentale. Così, nel privilegiarla come atto di linguaggio e nel disimpegnarla da mansioni mimetico-realistiche, Manganelli la popola di esseri informi e metamorfici. Ad esempio, in opere quali Hilarotragoedia (1964) e Dall’inferno (1985) il mostruoso non si presenta come qualcosa di aberrante, ma piuttosto come il risultato di una sorta di teologia paradossale, in grado di sovvertire o burlare le grandi convenzioni umane. Partendo da tali questioni, l’articolo affronterà il tema del mostro quale infrazione e sovversione essenziali allo scardinamento di un orizzonte ermeneutico antropocentrico, come voleva, tra gli altri, Foucault. «There is no salvation beyond the monstrous»; «desertion, intrinsic to literature, becomes in the Fantastic a blasphemous challenge, objection and betrayal»: with these words, the Italian writer Giorgio Manganelli (1922-1990) reaffirms the transgression of his work. With the overcoming of rational limits, of the plausible, of the acceptable or, in other words, of the tellable, the writer illustrates the way to prevent the use of literature as an instrumental function. Therefore, by using literature as an act of speech and by disengaging it from its mimetic-realistic responsibilities, Manganelli populates it with shapeless and metamorphic beings. In works such as Hilarotragoedia (1964) and From Hell (1985), for example, the monstrous does not resemble something aberrant, but rather it represents a kind of paradoxical theology, capable of subverting or mocking the great human convictions. Starting from these questions, this paper will approach the subject of the monster as infringement and subversion essential for the disruption of a hermeneutic and anthropocentric horizon, as Foucault, among others, wished
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