Climatic Influences of Deglacial Drainage Changes in Southern Canada at 10 to 8 ka Suggested by Pollen Evidence

Enhanced meltwater discharge from proglacial lakes Agassiz and Barlow-Ojibway at about 9.6 to 8.3 ka BP. created cold localized climates over downstream water bodies, specifically Lake Minong and Mattawa phase lakes in the Great Lakes and Goldthwait Sea in the Gulf of St. Lawrence. The cooling effect of the meltwater drainage suppressed summer warming of the surface lake waters, reduced the growing season and thus altered the vegetation composition in the surrounding land areas. The vegetation responded in different ways as evidenced by five variants from the normal pollen succession.The pollen anomalies are most pronounced where the effect of increased meltwater discharge had a strong influence, such as within or along the margins of Lake Agassiz, Mattawa phase lakes, and the Goldthwait Sea, or in their lee areas, especially where these water bodies intersected ecotonal boundaries. Climatic effects were minimal or non-existent where the water surface areas were restricted such as the channelized drainage routes of the Ottawa and St. Lawrence rivers. Diversion of Lakes Agassiz and Barlow-Ojibway drainage to Hudson Bay after about 8.4 ka BP reinstated summer warming of the surface water in the Great Lakes-St. Lawrence system bringing the 9.6-8.3 ka cool period to a close.L'augmentation du débit de l'eau de fonte provenant des lacs glaciaires Agassiz et Barlow-Ojibway de 9,6 à 8 ka BP a engendré des micro-climats froids au-dessus des nappes d'eau en aval : le Lac Minong, les lacs de la phase de Mattawa, dans les Grands Lacs, et la Mer de Goidtwaith, dans le golfe du Saint-Laurent. L'effet refroidissant du drainage de l'eau de fonte a entravé le réchauffement estival de la surface des eaux lacustres, écourté la saison végétative et ainsi modifié la composition de la végétation des terres environnantes. La réponse de la végétation a été variable comme l'indiquent les cinq types de déviation (anomalies polliniques) par rapport à la succession pollinique normale. Les anomalies sont plus importantes là où l'effet de l'augmentation du débit de l'eau de fonte a été plus prononcé, notamment près des limites des nappes d'eau touchés ou de leurs zones, surtout près des écotones. L'influence climatique a été très limitée ou nulle là où les surfaces aquifères étaient réduites, comme celles des cours de l'Outaouais et du Saint-Laurent. Le détournement de l'écoulement des lacs Agassiz et Barlow-Ojibway vers la mer d'Hudson après 8,4 ka BP a rétabli le réchauffement estival des eaux de surface du réseau des Grands Lacs et du Saint-Laurent, mettant ainsi fin à la période froide qui a prévalu de 9,6 à 8 ka.Der EinfluQ des Wechsels der Schmelzwassermenge aufdas Klima im sûdlichen Kanada um 10 bis 8 ka anhand von Pollenbelegen. Verstàrktes Schmelz-wasserabflieBen von den proglazialen Seen Agassiz und Barlow-Ojibway um etwa 9.6 bis 8.3 ka v.u.Z. bewirkte ôrtlich beschrànktes kaltes Klima ùber den Wasser-flàchen stromabwàrts, und zwar Minong-See und Seen der Mattawa-Phase in den GroRen Seen, und das Goldtwaith-Meer im Golf des Sankt Lorenz. Die kùhlende Wirkung des abflieBenden Schmelzwassers verhinderte die sommerliche Erwàrmung des Oberflàchenwassers der Seen, reduzierte die Wachstumsperiode und verànderte so die Zusammensetzung der Vegetation in den umliegenden Landgebieten. Die Vegetation reagierte auf verschiedene Weisen, wie aus fùnf Varianten der normalen Pollenabfolge ersichtlich wird. Die Pollen-Abweichungen sind am deutlichsten, wo die Wirkung des verstàrkten Schmelzwasserabflusses am stârksten war, wie innerhalb oder entlang der Rander des Agassiz-Sees, der Seen der Mattawa-Phase und des Goldtwaith-Meeres, oder in ihren windgeschùtzten Gebieten, besonders wo dièse Wasserflàchen Ubergangszonengrenzen durchschneiden. Die Einwirkungen auf das Klima waren minimal oder inexistent, wo die Wasserflàchengebiete begrenzt waren, wie die kanalisierte Drânage-Route des Ottawa- und Sankt Lorenz-Stroms. Die Ableitung des Abflusses des Agassiz- und Barlow-Ojibway-Sees zur Hudson-Bay hin nach etwa 8.4 ka v.u.Z., stellte die sommerliche Erwàrmung der Ober-flàchenwasser im System der Grofîen Seen und des Sankt Lorenz wieder her und been-dete die von 9.6 bis 8.3 ka dauernde kalte Période

Operator-Based Truncation Scheme Based on the Many-Body Fermion Density Matrix

In [S. A. Cheong and C. L. Henley, cond-mat/0206196 (2002)], we found that the many-particle eigenvalues and eigenstates of the many-body density matrix $\rho_B$ of a block of $B$ sites cut out from an infinite chain of noninteracting spinless fermions can all be constructed out of the one-particle eigenvalues and one-particle eigenstates respectively. In this paper we developed a statistical-mechanical analogy between the density matrix eigenstates and the many-body states of a system of noninteracting fermions. Each density matrix eigenstate corresponds to a particular set of occupation of single-particle pseudo-energy levels, and the density matrix eigenstate with the largest weight, having the structure of a Fermi sea ground state, unambiguously defines a pseudo-Fermi level. We then outlined the main ideas behind an operator-based truncation of the density matrix eigenstates, where single-particle pseudo-energy levels far away from the pseudo-Fermi level are removed as degrees of freedom. We report numerical evidence for scaling behaviours in the single-particle pseudo-energy spectrum for different block sizes $B$ and different filling fractions \nbar. With the aid of these scaling relations, which tells us that the block size $B$ plays the role of an inverse temperature in the statistical-mechanical description of the density matrix eigenstates and eigenvalues, we looked into the performance of our operator-based truncation scheme in minimizing the discarded density matrix weight and the error in calculating the dispersion relation for elementary excitations. This performance was compared against that of the traditional density matrix-based truncation scheme, as well as against a operator-based plane wave truncation scheme, and found to be very satisfactory.Comment: 22 pages in RevTeX4 format, 22 figures. Uses amsmath, amssymb, graphicx and mathrsfs package

Gravity-induced Wannier-Stark ladder in an optical lattice

We discuss the dynamics of ultracold atoms in an optical potential accelerated by gravity. The positions and widths of the Wannier-Stark ladder of resonances are obtained as metastable states. The metastable Wannier-Bloch states oscillate in a single band with the Bloch period. The width of the resonance gives the rate transition to the continuum.Comment: 5 pages + 8 eps figures, submitted to Phys. Rev.

A new method for the estimation of variance matrix with prescribed zeros in nonlinear mixed effects models

We propose a new method for the Maximum Likelihood Estimator (MLE) of nonlinear mixed effects models when the variance matrix of Gaussian random effects has a prescribed pattern of zeros (PPZ). The method consists in coupling the recently developed Iterative Conditional Fitting (ICF) algorithm with the Expectation Maximization (EM) algorithm. It provides positive definite estimates for any sample size, and does not rely on any structural assumption on the PPZ. It can be easily adapted to many versions of EM.Comment: Accepted for publication in Statistics and Computin

Damped Bloch oscillations of cold atoms in optical lattices

The paper studies Bloch oscillations of cold neutral atoms in the optical lattice. The effect of spontaneous emission on the dynamics of the system is analyzed both analytically and numerically. The spontaneous emission is shown to cause (i) the decay of Bloch oscillations with the decrement given by the rate of spontaneous emission and (ii) the diffusive spreading of the atoms with a diffusion coefficient depending on {\em both} the rate of spontaneous emission and the Bloch frequency.Comment: 10 pages, 8 figure

Ladder approximation to spin velocities in quantum wires

The spin sector of charge-spin separated single mode quantum wires is studied, accounting for realistic microscopic electron-electron interactions. We utilize the ladder approximation (LA) to the interaction vertex and exploit thermodynamic relations to obtain spin velocities. Down to not too small carrier densities our results compare well with existing quantum Monte-Carlo (QMC) data. Analyzing second order diagrams we identify logarithmically divergent contributions as crucial which the LA includes but which are missed, for example, by the self-consistent Hartree-Fock approximation. Contrary to other approximations the LA yields a non-trivial spin conductance. Its considerably smaller computational effort compared to numerically exact methods, such as the QMC method, enables us to study overall dependences on interaction parameters. We identify the short distance part of the interaction to govern spin sector properties.Comment: 6 pages, 6 figures, to appear in Physical Review

Constraints on the pMSSM from LAT Observations of Dwarf Spheroidal Galaxies

We examine the ability for the Large Area Telescope (LAT) to constrain Minimal Supersymmetric Standard Model (MSSM) dark matter through a combined analysis of Milky Way dwarf spheroidal galaxies. We examine the Lightest Supersymmetric Particles (LSPs) for a set of ~71k experimentally valid supersymmetric models derived from the phenomenological-MSSM (pMSSM). We find that none of these models can be excluded at 95% confidence by the current analysis; nevertheless, many lie within the predicted reach of future LAT analyses. With two years of data, we find that the LAT is currently most sensitive to light LSPs (m_LSP < 50 GeV) annihilating into tau-pairs and heavier LSPs annihilating into b-bbar. Additionally, we find that future LAT analyses will be able to probe some LSPs that form a sub-dominant component of dark matter. We directly compare the LAT results to direct detection experiments and show the complementarity of these search methods.Comment: 24 pages, 9 figures, submitted to JCA

Probing the energy bands of a Bose-Einstein condensate in an optical lattice

We simulate three experimental methods which could be realized in the laboratory to probe the band excitation energies and the momentum distribution of a Bose-Einstein condensate inside an optical lattice. The values of the excitation energies obtained in these different methods agree within the accuracy of the simulation. The meaning of the results in terms of density and phase deformations is tested by studying the relaxation of a phase-modulated condensate towards the ground state.Comment: 5 pages, 5 figure

Theory of nonlinear Landau-Zener tunneling

A nonlinear Landau-Zener model was proposed recently to describe, among a number of applications, the nonadiabatic transition of a Bose-Einstein condensate between Bloch bands. Numerical analysis revealed a striking phenomenon that tunneling occurs even in the adiabatic limit as the nonlinear parameter $C$ is above a critical value equal to the gap $V$ of avoided crossing of the two levels. In this paper, we present analytical results that give quantitative account of the breakdown of adiabaticity by mapping this quantum nonlinear model into a classical Josephson Hamiltonian. In the critical region, we find a power-law scaling of the nonadiabatic transition probability as a function of $C/V-1$ and $\alpha$, the crossing rate of the energy levels. In the subcritical regime, the transition probability still follows an exponential law but with the exponent changed by the nonlinear effect. For $C/V>>1$, we find a near unit probability for the transition between the adiabatic levels for all values of the crossing rate.Comment: 9 figure