528,027 research outputs found

### Explicit birational geometry of 3-folds of general type, I

Let $V$ be a complex nonsingular projective 3-fold of general type. We prove
$P_{12}(V):=\text{dim} H^0(V, 12K_V)>0$ and $P_{m_0}(V)>1$ for some positive
integer $m_0\leq 24$. A direct consequence is the birationality of the
pluricanonical map $\varphi_m$ for all $m\geq 126$. Besides, the canonical
volume $\text{Vol}(V)$ has a universal lower bound $\nu(3)\geq \frac{1}{63\cdot
126^2}$.Comment: 29 pages, Ann Sci Ecole Norm Sup (to appear

### Explicit birational geometry of threefolds of general type

Let $V$ be a complex nonsingular projective 3-fold of general type. We prove
$P_{12}(V)>0$ and $P_{24}(V)>1$ (which answers an open problem of J. Kollar and
S. Mori). We also prove that the canonical volume has an universal lower bound
$\text{Vol}(V) \geq 1/2660$ and that the pluri-canonical map $\Phi_m$ is
birational onto its image for all $m\geq 77$. As an application of our method,
we prove Fletcher's conjecture on weighted hyper-surface 3-folds with terminal
quotient singularities. Another featured result is the optimal lower bound
$\text{Vol}(V)\geq {1/420}$ among all those 3-folds $V$ with $\chi({\mathcal
O}_V)\leq 1$.Comment: (updated version on October 15, 2007) 55 pages, a couple of missing
P_2 terms in Section 5 added and slight rearrangements to the contex

### On the theory of the CO+OH reaction, including H and C kinetic isotope effects

The effect of pressure, temperature, H/D isotopes, and C isotopes on the kinetics of the OH+CO reaction are investigated using Rice-Ramsperger-Kassel-Marcus theory. Pressure effects are treated with a step-ladder plus steady-state model and tunneling effects are included. New features include a treatment of the C isotope effect and a proposed nonstatistical effect in the reaction. The latter was prompted by existing kinetic results and molecular-beam data of Simons and co-workers [J. Phys. Chem. A 102, 9559 (1998); J. Chem. Phys. 112, 4557 (2000); 113, 3173 (2000)] on incomplete intramolecular energy transfer to the highest vibrational frequency mode in HOCO*. In treating the many kinetic properties two small customary vertical adjustments of the barriers of the two transition states were made. The resulting calculations show reasonable agreement with the experimental data on (1) the pressure and temperature dependence of the H/D effect, (2) the pressure-dependent 12C/13C isotope effect, (3) the strong non-Arrhenius behavior observed at low temperatures, (4) the high-temperature data, and (5) the pressure dependence of rate constants in various bath gases. The kinetic carbon isotopic effect is usually less than 10 per mil. A striking consequence of the nonstatistical assumption is the removal of a major discrepancy in a plot of the kOH+CO/kOD+CO ratio versus pressure. A prediction is made for the temperature dependence of the OD+CO reaction in the low-pressure limit at low temperatures

### On a notion of maps between orbifolds, II. homotopy and CW-complex

This is the second of a series of papers which are devoted to a comprehensive
theory of maps between orbifolds. In this paper, we develop a basic machinery
for studying homotopy classes of such maps. It contains two parts: (1) the
construction of a set of algebraic invariants -- the homotopy groups, and (2)
an analog of CW-complex theory. As a corollary of this machinery, the classical
Whitehead theorem which asserts that a weak homotopy equivalence is a homotopy
equivalence is extended to the orbifold category.Comment: 51 pages, Communications in Contemporary Mathematics, to appea

### On the theory of the reaction rate of vibrationally excited CO molecules with OH radicals

The dependence of the rate of the reaction CO+OH-->H+CO2 on the CO-vibrational excitation is treated here theoretically. Both the Rice-Ramsperger-Kassel-Marcus (RRKM) rate constant kRRKM and a nonstatistical modification knon [W.-C. Chen and R. A. Marcus, J. Chem. Phys. 123, 094307 (2005).] are used in the analysis. The experimentally measured rate constant shows an apparent (large error bars) decrease with increasing CO-vibrational temperature Tv over the range of Tv's studied, 298–1800 K. Both kRRKM(Tv) and knon(Tv) show the same trend over the Tv-range studied, but the knon(Tv) vs Tv plot shows a larger effect. The various trends can be understood in simple terms. The calculated rate constant kv decreases with increasing CO vibrational quantum number v, on going from v=0 to v=1, by factors of 1.5 and 3 in the RRKM and nonstatistical calculations, respectively. It then increases when v is increased further. These results can be regarded as a prediction when v state-selected rate constants become available

### Isotopomer Fractionation in the UV Photolysis of N_2O: 3. 3D Ab Initio Surfaces and Anharmonic Effects

The wavelength-dependent isotopic fractionation of N_2O is calculated, extending our previous work, Parts 1 and 2, in several aspects: (1) the fully three-dimensional ab initio electronic potential and transition dipole moment surfaces of S. Nanbu and M. S. Johnson (J. Chem. Phys. A 2004, 108, 8905) are used to calculate the absorption cross sections, instead of a 2D surface and (2) the vibrational frequencies and wave functions with anharmonicity correction are used for the ground electronic state. The results for the absorption spectrum and for the isotopic fractionation of the different isotopomers are discussed. One difference between experiments measuring the absorption coefficient (von Hessberg et al. Atmos. Chem. Phys. 2004, 4, 1237) and the others that measure instead the photodissociation is also discussed. Experiments on the quantum yield for wavelengths longer than 200 nm (>50000 cm^(−1)) would be helpful in treating the observed difference

### Macroscale boundary conditions for a non-linear heat exchanger

Multiscale modelling methodologies build macroscale models of materials with
complicated fine microscale structure. We propose a methodology to derive
boundary conditions for the macroscale model of a prototypical non-linear heat
exchanger. The derived macroscale boundary conditions improve the accuracy of
macroscale model. We verify the new boundary conditions by numerical methods.
The techniques developed here can be adapted to a wide range of multiscale
reaction-diffusion-advection systems

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