5,465 research outputs found
On the automorphisms of moduli spaces of curves
In the last years the biregular automorphisms of the Deligne-Mumford's and
Hassett's compactifications of the moduli space of n-pointed genus g smooth
curves have been extensively studied by A. Bruno and the authors. In this paper
we give a survey of these recent results and extend our techniques to some
moduli spaces appearing as intermediate steps of the Kapranov's and Keel's
realizations of , and to the degenerations of Hassett's spaces
obtained by allowing zero weights.Comment: 15 pages. The material of version 1 has been reorganized and expanded
in this paper and in arXiv:1307.6828 on automorphisms of Hassett's moduli
space
Finite difference approximations for a size-structured population model with distributed states in the recruitment
In this paper we consider a size-structured population model where
individuals may be recruited into the population at different sizes. First and
second order finite difference schemes are developed to approximate the
solution of the mathematical model. The convergence of the approximations to a
unique weak solution with bounded total variation is proved. We then show that
as the distribution of the new recruits become concentrated at the smallest
size, the weak solution of the distributed states-at-birth model converges to
the weak solution of the classical Gurtin-McCamy-type size-structured model in
the weak topology. Numerical simulations are provided to demonstrate the
achievement of the desired accuracy of the two methods for smooth solutions as
well as the superior performance of the second-order method in resolving
solution-discontinuities. Finally we provide an example where supercritical
Hopf-bifurcation occurs in the limiting single state-at-birth model and we
apply the second-order numerical scheme to show that such bifurcation occurs in
the distributed model as well
Reseña de la “Guía de los Fundamentos para la Dirección de Proyectos (Guía PMBOK)”
Review of the Project Management Body of Knowledge (PMBOK), 6th edition, which includes good practices for project management under the responsibility of the Project Management Institute.
Revisión de la 6ta edición del libro Project Management Body of Knowledge (PMBOK), el cual recoge las buenas prácticas para la gestión de proyectos bajo la autoría del Project Management Institute
Heat storage in alloy transformations
The feasibility of using metal alloys as thermal energy storage media was determined. The following major elements were studied: (1) identification of congruently transforming alloys and thermochemical property measurements; (2) development of a precise and convenient method for measuring volume change during phase transformation and thermal expansion coefficients; (3) development of a numerical modeling routine for calculating heat flow in cylindrical heat exchangers containing phase change materials; and (4) identification of materials that could be used to contain the metal alloys. Several eutectic alloys and ternary intermetallic phases were determined. A method employing X-ray absorption techniques was developed to determine the coefficients of thermal expansion of both the solid and liquid phases and the volume change during phase transformation from data obtained during one continuous experimental test. The method and apparatus are discussed and the experimental results are presented. The development of the numerical modeling method is presented and results are discussed for both salt and metal alloy phase change media
Construction of equilibrium networks with an energy function
We construct equilibrium networks by introducing an energy function depending
on the degree of each node as well as the product of neighboring degrees. With
this topological energy function, networks constitute a canonical ensemble,
which follows the Boltzmann distribution for given temperature. It is observed
that the system undergoes a topological phase transition from a random network
to a star or a fully-connected network as the temperature is lowered. Both
mean-field analysis and numerical simulations reveal strong first-order phase
transitions at temperatures which decrease logarithmically with the system
size. Quantitative discrepancies of the simulation results from the mean-field
prediction are discussed in view of the strong first-order nature.Comment: To appear in J. Phys.
Unanticipated differences between α- and γ-diaminobutyric acid-linked hairpin polyamide-alkylator conjugates
Hairpin polyamide–chlorambucil conjugates containing an {alpha}-diaminobutyric acid ({alpha}-DABA) turn moiety are compared to their constitutional isomers containing the well-characterized {gamma}-DABA turn. Although the DNA-binding properties of unconjugated polyamides are similar, the {alpha}-DABA conjugates display increased alkylation specificity and decreased rate of reaction. Treatment of a human colon carcinoma cell line with {alpha}-DABA versus {gamma}-DABA hairpin conjugates shows only slight differences in toxicities while producing similar effects on cell morphology and G2/M stage cell cycle arrest. However, striking differences in animal toxicity between the two classes are observed. Although mice treated with an {alpha}-DABA hairpin polyamide do not differ significantly from control mice, the analogous {gamma}-DABA hairpin is lethal. This dramatic difference from a subtle structural change would not have been predicted
An extremal effective survey about extremal effective cycles in moduli spaces of curves
We survey recent developments and open problems about extremal effective
divisors and higher codimension cycles in moduli spaces of curves.Comment: Submitted to the Proceedings of the Abel Symposium 2017. Comments are
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Ratiometric spectral imaging for fast tumor detection and chemotherapy monitoring in vivo
We report a novel in vivo spectral imaging approach to cancer detection and chemotherapy assessment. We describe and characterize a ratiometric spectral imaging and analysis method and evaluate its performance for tumor detection and delineation by quantitatively monitoring the specific accumulation of targeted gallium corrole (HerGa) into HER2-positive (HER2 +) breast tumors. HerGa temporal accumulation in nude mice bearing HER2 + breast tumors was monitored comparatively by a. this new ratiometric imaging and analysis method; b. established (reflectance and fluorescence) spectral imaging; c. more commonly used fluorescence intensity imaging. We also tested the feasibility of HerGa imaging in vivo using the ratiometric spectral imaging method for tumor detection and delineation. Our results show that the new method not only provides better quantitative information than typical spectral imaging, but also better specificity than standard fluorescence intensity imaging, thus allowing enhanced in vivo outlining of tumors and dynamic, quantitative monitoring of targeted chemotherapy agent accumulation into them
A Compact Microchip-Based Atomic Clock Based on Ultracold Trapped Rb Atoms
We propose a compact atomic clock based on ultracold Rb atoms that are
magnetically trapped near the surface of an atom microchip. An interrogation
scheme that combines electromagnetically-induced transparency (EIT) with
Ramsey's method of separated oscillatory fields can achieve atomic shot-noise
level performance of 10^{-13}/sqrt(tau) for 10^6 atoms. The EIT signal can be
detected with a heterodyne technique that provides noiseless gain; with this
technique the optical phase shift of a 100 pW probe beam can be detected at the
photon shot-noise level. Numerical calculations of the density matrix equations
are used to identify realistic operating parameters at which AC Stark shifts
are eliminated. By considering fluctuations in these parameters, we estimate
that AC Stark shifts can be canceled to a level better than 2*10^{-14}. An
overview of the apparatus is presented with estimates of duty cycle and power
consumption.Comment: 15 pages, 11 figures, 5 table
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