84,110 research outputs found
On Gorenstein Surfaces Dominated by P^2
In this paper we prove that a normal Gorenstein surface dominated by the
projective plane P^2 is isomorphic to a quotient P^2/G, where G is a finite
group of automorphisms of P^2 (except possibly for one surface V_8'). We can
completely classify all such quotients. Some natural conjectures when the
surface is not Gorenstein are also stated.Comment: Nagoya Mathematical Journal, to appea
The structural, mechanical, electronic, optical and thermodynamic properties of t-XAs (X Si, Ge and Sn) by first-principles calculations
The structural, mechanical, electronic, optical and thermodynamic properties
of the t-XAs (X Si, Ge and Sn) with
tetragonal structure have been investigated by first principles calculations.
Our calculated results show that these compounds are mechanically and
dynamically stable. By the study of elastic anisotropy, it is found that the
anisotropic of the t-SnAs is stronger than that
of t-SiAs and
t-GeAs. The band structures and density of states
show that the t-XAs (Si, Ge and Sn) are
semiconductors with narrow band gaps. Based on the analyses of electron density
difference, in t-XAs As atoms get electrons, X
atoms lose electrons. The calculated static dielectric constants,
, are 15.5, 20.0 and 15.1 eV for
t-XAs (X Si, Ge and Sn), respectively. The
Dulong-Petit limit of t-XAs is about 10 J
molK. The thermodynamic stability successively
decreases from t-SiAs to
t-GeAs to t-SnAs.Comment: 14 pages, 10 figures, 6 table
Algebraic varieties with automorphism groups of maximal rank
We confirm, to some extent, the belief that a projective variety X has the
largest number (relative to the dimension of X) of independent commuting
automorphisms of positive entropy only when X is birational to a complex torus
or a quotient of a torus. We also include an addendum to an early paper though
it is not used in the present paper.Comment: Mathematische Annalen (to appear
Gamma-Ray Bursts are Produced Predominately in the Early Universe
It is known that some observed gamma-ray bursts (GRBs) are produced at
cosmological distances and that the GRB production rate may follow the star
formation rate. We model the BATSE-detected intensity distribution of long GRBs
in order to determine their space density distribution and opening angle
distribution. Our main results are: the lower and upper distance limits to the
GRB production are z 0.24 and >10, respectively; the GRB opening angle follows
an exponential distribution and the mean opening angle is about 0.03 radians;
and the peak luminosity appears to be a better standard candle than the total
energy of a GRB.Comment: 12 pages, 2 figur
Giant electrocaloric effect in thin film Pb Zr_0.95 Ti_0.05 O_3
An applied electric field can reversibly change the temperature of an
electrocaloric material under adiabatic conditions, and the effect is strongest
near phase transitions. This phenomenon has been largely ignored because only
small effects (0.003 K V^-1) have been seen in bulk samples such as
Pb0.99Nb0.02(Zr0.75Sn0.20Ti0.05)0.98O3 and there is no consensus on macroscopic
models. Here we demonstrate a giant electrocaloric effect (0.48 K V^-1) in 300
nm sol-gel PbZr0.95Ti0.05O3 films near the ferroelectric Curie temperature of
222oC. We also discuss a solid state device concept for electrical
refrigeration that has the capacity to outperform Peltier or magnetocaloric
coolers. Our results resolve the controversy surrounding macroscopic models of
the electrocaloric effect and may inspire ab initio calculations of
electrocaloric parameters and thus a targeted search for new materials.Comment: 5 pages, 4 figure
A General Information Theoretical Proof for the Second Law of Thermodynamics
We show that the conservation and the non-additivity of the information,
together with the additivity of the entropy make the entropy increase in an
isolated system. The collapse of the entangled quantum state offers an example
of the information non-additivity. Nevertheless, the later is also true in
other fields, in which the interaction information is important. Examples are
classical statistical mechanics, social statistics and financial processes. The
second law of thermodynamics is thus proven in its most general form. It is
exactly true, not only in quantum and classical physics but also in other
processes, in which the information is conservative and non-additive.Comment: 4 page
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