Abstract:
La migración de mexicanos a Canadá, aunque es un fenómeno reciente, ha tenido uno de los incrementos más significativos entre los movimientos de personas de América Latina. Desde mediados de los noventa, el número de mexicanos en Canadá ha estado creciendo rápidamente como resultado del retorno de los descendientes de la población menonita que emigró a México y de las disposiciones del Tratado de Libre Comercio de América del Norte (tlcan), que facilita el ingreso de ciudadanos mexicanos. En este artículo se examina el número de mexicanos en Canadá, el tiempo de su ingreso y el número de migrantes temporales admitidos, y sugiere áreas de investigación para el futuro.

Abstract:
Thirty years ago the Hubbard model was introduced by Gutzwiller, Hubbard and Kanamori with the main purpose of mimicking the ferromagnetism of transition metals. Soon after, Nagaoka and Thouless pointed out a basic mechanism for ferromagnetism in strongly correlated electron systems by studying the motion of a single hole in a half--filled Hubbard model. This important work was hoped to shed light onto metallic ferromagnetism from the low doping regime. Unfortunately, this low doping route towards ferromagnetism has not been successful as far as rigorous results for finite doping concentrations are concerned. In the work presented here, we start from the opposite limit of low particle concentrations. In this limit we provide the first proof of a fully polarized metallic ground state for a Hubbard model. The proof proceeds by mapping Hubbard ``zigzag'' chains onto a continuum model with an additional degree of freedom and local first Hund's rule coupling. For this model the maximum total spin multiplet is shown to be the unique ground state for infinite Hubbard coupling. Our proof may open a low density route towards the understanding of the ferromagnetism of Hubbard models.

Abstract:
We study the effects of improvement on the locality of square-rooted staggered Dirac operators in lattice QCD simulations. We find the localisation lengths of the improved operators (FAT7TAD and ASQTAD) to be very similar to that of the one-link operator studied by Bunk et al., being at least the Compton wavelength of the lightest particle in the theory, even in the continuum limit. We conclude that improvement has no effect. We discuss the implications of this result for the locality of the nth-rooted fermion determinant used to reduce the number of sea quark flavours, and for possible staggered valence quark formulations.

Abstract:
It is well known that, starting with finite mass, the super-Brownian motion dies out in finite time. The goal of this article is to show that with some additional work, one can prove finite time die-out for two types of systems of stochastic differential equations on the lattice Z^d. Our first system involves the heat equation on the lattice Z^d, with a nonlinear noise term u(t,x)^gamma dB_x(t), with 1/2 <= gamma < 1. The B_x are independent Brownian motions. When gamma = 1/2, the measure which puts mass u(t,x) at x is a super-random walk and it is well-known that the process becomes extinct in finite time a.s. Finite-time extinction is known to be a.s. false if gamma = 1. For 1/2 < gamma < 1, we show finite-time die-out by breaking up the solution into pieces, and showing that each piece dies in finite time. Our second example involves the mutually catalytic branching system of stochastic differential equations on Z^d, which was first studied by Dawson and Perkins. Roughly speaking, this process consists of 2 superprocesses with the continuous time simple random walk as the underlying spatial motion. Furthermore, each process stimulates branching and dying in the other process. By using a somewhat different argument, we show that, depending on the initial conditions, finite time extinction of one type may occur with probability 0, or with probability arbitrarily close to 1.

Abstract:
We propose a set of lattice measurements which could test whether the deconfined, quark-gluon plasma, phase of QCD shows strong coupling aspects at temperatures a few times the critical temperature for deconfinement, in the region where the conformal anomaly becomes unimportant. The measurements refer to twist-two operators which are not protected by symmetries and which in a strong-coupling scenario would develop large, negative, anomalous dimensions, resulting in a strong suppression of the respective lattice expectation values in the continuum limit. Special emphasis is put on the respective operator with lowest spin (the spin-2 operator orthogonal to the energy-momentum tensor within the renormalization flow) and on the case of quenched QCD, where this operator is known for arbitrary values of the coupling: this is the quark energy-momentum tensor. The proposed lattice measurements could also test whether the plasma constituents are pointlike (as expected at weak coupling), or not.

Abstract:
At the Holifield Radioactive Ion Beam Facility (HRIBF) at Oak Ridge National Laboratory (ORNL), molecular ions extracted from a positive ion source and subsequently broken up in a charge exchange cell produce Radioactive Ion Beams (RIBs) with several hundred eV energy spread, preventing effective magnetic isobar separation. In order to perform magnetic isobar separation prior to charge exchange, a multi-harmonic buncher and a 12 MHz RFQ (Radio-Frequency Quadrupole) is proposed to supplement the present 300 kV injection system for the 25 MV tandem electrostatic accelerator. The RFQ will be mounted on a variable high voltage platform to accelerate ions with masses from 10 to 150 amu.

Abstract:
Ritt studied the functional decomposition of a univariate complex polynomial f into prime (indecomposable) polynomials, f = u_1 o u_2 o ... o u_r. His main achievement was a procedure for obtaining any decomposition of f from any other by repeatedly applying certain transformations. However, Ritt's results provide no control on the number of times one must apply the basic transformations, which makes his procedure unsuitable for many theoretical and algorithmic applications. We solve this problem by giving a new description of the collection of all decompositions of a polynomial. Our results have been used by Ghioca, Tucker and Zieve (arXiv:0807.3576) to describe the polynomials f,g having orbits with infinite intersection; they have also been used by Medvedev and Scanlon to describe the affine curves invariant under a coordinatewise polynomial action.

Abstract:
Planar functions over finite fields give rise to finite projective planes and other combinatorial objects. They exist only in odd characteristic, but recently Zhou introduced an even characteristic analogue which has similar applications. In this paper we determine all planar functions on F_q of the form c-->uc^t, where q is a power of 2, t is an integer with 0

Abstract:
This study compared ankle range of motion (AROM) including dorsiflexion, plantar flexion, inversion and eversion, and venous refill time (VRT) in leg skin inflamed by venous disorders, before and after a new cryotherapy ulcer prevention treatment. Fifty-seven individuals participated in the randomized clinical trial; 28 in the experimental group and 29 received usual care only. Results revealed no statistically significant differences between the experimental and usual care groups although AROM measures in the experimental group showed a consistent, non-clinically relevant decrease compared to the usual care group except for dorsiflexion. Within treatment group comparisons of VRT results showed a statistically significant increase in both dorsiflexion and plantar flexion for patients with severe VRT in the experimental group (6.9 ± 6.8; p = 0.002 and 5.8 ± 12.6; p = 0.02, respectively). Cryotherapy did not further restrict already compromised AROM, and in some cases, there were minor improvements.

Abstract:
We present 2D hydrodynamic simulations of the long-time accretion phase of a 15 solar mass star after core bounce and before the launch of a supernova explosion. Our simulations are performed with the Prometheus-Vertex code, employing multi-flavor, energy-dependent neutrino transport and an effective relativistic gravitational potential. Testing the influence of a stiff and a soft equation of state for hot neutron star matter, we find that the non-radial mass motions in the supernova core due to the standing accretion shock instability (SASI) and convection impose a time variability on the neutrino and gravitational-wave signals. These variations have larger amplitudes as well as higher frequencies in the case of a more compact nascent neutron star. After the prompt shock-breakout burst of electron neutrinos, a more compact accreting remnant radiates neutrinos with higher luminosities and larger mean energies. The observable neutrino emission in the direction of SASI shock oscillations exhibits a modulation of several 10% in the luminosities and ~1 MeV in the mean energies with most power at typical SASI frequencies of 20-100 Hz. At times later than 50-100 ms after bounce the gravitational-wave amplitude is dominated by the growing low-frequency (<200 Hz) signal associated with anisotropic neutrino emission. A high-frequency wave signal is caused by nonradial gas flows in the outer neutron star layers, which are stirred by anisotropic accretion from the SASI and convective regions. The gravitational-wave power then peaks at about 300-800 Hz with distinctively higher spectral frequencies originating from the more compact and more rapidly contracting neutron star. The detectability of the SASI effects in the neutrino and gravitational-wave signals is briefly discussed. (abridged)