Search results for "BARD"

Time-resolved Observation and Control of Superexchange Interactions with Ultracold Atoms in Optical Lattices

2007

Quantum mechanical superexchange interactions form the basis of quantum magnetism in strongly correlated electronic media. We report on the direct measurement of superexchange interactions with ultracold atoms in optical lattices. After preparing a spin-mixture of ultracold atoms in an antiferromagnetically ordered state, we measure a coherent superexchange-mediated spin dynamics with coupling energies from 5 Hz up to 1 kHz. By dynamically modifying the potential bias between neighboring lattice sites, the magnitude and sign of the superexchange interaction can be controlled, thus allowing the system to be switched between antiferromagnetic or ferromagnetic spin interactions. We compare our…

Formation of spatial shell structures in the superfluid to Mott insulator transition

2006

International audience; We report on the direct observation of the transition from a compressible superfluid to an incompressible Mott insulator by recording the in-trap density distribution of a Bosonic quantum gas in an optical lattice. Using spatially selective microwave transitions and spin changing collisions, we are able to locally modify the spin state of the trapped quantum gas and record the spatial distribution of lattice sites with different filling factors. As the system evolves from a superfluid to a Mott insulator, we observe the formation of a distinct shell structure, in good agreement with theory.

Electronic momentum distribution in the one-dimensional extended Hubbard model: determinantal Monte Carlo study

2002

Abstract The effect of electron–electron (e–e) interaction on trans -polyacetylene ( t -PA) properties is investigated within the framework of an extended Hubbard model in one dimension. For numerical calculation, we use the determinantal version of quantum Monte Carlo approach, which provides a breakthrough to simulate statistical fluctuations in the systems with many degrees of freedom, in order to obtain mean values for observables of physical interest. This allows one to analyze the discrete system of fermions without encountering the numerical instabilities that generally occur from the original problem involving anticommuting fermion operators. We calculate the electronic momentum dis…

Testaments et pratique testamentaire dans le royaume franc (vie-viiie siècle)

2005

Les testaments merovingiens ont de longue date attire l'attention des diplomaties, des historiens du droit et de la societe. U. Nonn a montre la continuite entre testaments romains et merovingiens, mais on s'interroge toujours sur la diffusion de ces actes dans la societe et sur les conditions de leur disparition au IX e siecle. Un reexamen de la question (avec listes du materiel disponible) donne a penser que differents types d'actes a cause de mort etaient utilises dans la societe merovingienne et que les testaments aristocratiques - les seuls connus-, conserves de maniere preferentielle par les heritiers ecclesiastiques qu'ils instituaient, ne sont pas representatifs d'une pratique sans …

Quantum Phases in a Resonantly Interacting Boson-Fermion Mixture

2005

We consider a resonantly-interacting Bose-Fermi mixture of $^{40}$K and $^{87}$Rb atoms in an optical lattice. We show that by using a red-detuned optical lattice the mixture can be accurately described by a generalized Hubbard model for $^{40}$K and $^{87}$Rb atoms, and $^{40}$K-$^{87}$Rb molecules. The microscopic parameters of this model are fully determined by the details of the optical lattice and the interspecies Feshbach resonance in the absence of the lattice. We predict a quantum phase transition to occur in this system already at low atomic filling fraction, and present the phase diagram as a function of the temperature and the applied magnetic field.

Fast atom bombardment and field desorption mass spectrometry: Comparative aspects of analytical development and bioanalytical application

1983

Potere, consenso e dissenso nell’Ystoriola Langobardorum Beneventum degentium di Erchemperto

2021

Diversamente da quella narrata da Paolo Diacono nella «Historia Langobardorum», la storia dei Longobardi di Benevento fra l’VIII e il IX secolo, raccontata da Erchemperto nell’«Ystoriola Langobardorum Beneventum degentium», è una storia nella quale si alternano continuamente il bene e il male, Dio e Satana, il coraggio, la virtù, l’abnegazione da un lato e, dall’altro, la viltà, il tradimento, la perfidia. Personaggi positivi e personaggi negativi – insieme alle vicende delle quali, di volta in volta, essi sono protagonisti – si susseguono nell’«Ystoriola» a ritmo incalzante, e lo storico beneventano, talora in modo palese e scoperto, più spesso in maniera ellittica e sottintesa, manifesta …

Germline loss-of-function variants in the BARD1 gene are associated with early-onset familial breast cancer but not ovarian cancer

2019

Background The role of the BARD1 gene in breast cancer (BC) and ovarian cancer (OC) predisposition remains elusive, as published case-control investigations have revealed controversial results. We aimed to assess the role of deleterious BARD1 germline variants in BC/OC predisposition in a sample of 4920 BRCA1/2-negative female BC/OC index patients of the German Consortium for Hereditary Breast and Ovarian Cancer (GC-HBOC). Methods A total of 4469 female index patients with BC, 451 index patients with OC, and 2767 geographically matched female control individuals were screened for loss-of-function (LoF) mutations and potentially damaging rare missense variants in BARD1. All patients met the …

Trans-equatorial migration routes, staging sites and wintering areas of a High-Arctic avian predator: the Long-tailed Skua (Stercorarius longicaudus).

2013

The Long-tailed Skua, a small (,300 g) Arctic-breeding predator and seabird, is a functionally very important component of the Arctic vertebrate communities in summer, but little is known about its migration and winter distribution. We used lightlevel geolocators to track the annual movements of eight adult birds breeding in north-east Greenland (n = 3) and Svalbard (n = 5). All birds wintered in the Southern Hemisphere (mean arrival-departure dates on wintering grounds: 24 October-21 March): five along the south-west coast of Africa (0–40uS, 0–15uE), in the productive Benguela upwelling, and three further south (30–40uS, 0–50uE), in an area extending into the south-west Indian Ocean. Diffe…

Quantum Monte Carlo study of insulating state in NaV2O5

2003

Abstract Quantum Monte Carlo (QMC) methods are being increasingly used as complements to Hartree–Fock (HF) methods for computing the electronic structure of molecules and materials. We investigate the nature of the insulating state driven by electronic correlations in the ladder compound NaV 2 O 5 ; considered as a quarter-filled system. We use an extended Hubbard model (EHM) to study the role of on-site and inter-site Coulomb interaction. It is found that the insulating state in the charge-disordered phase of this compound take origin from the transfer of spectral density and dynamical fluctuations. Our calculation allows us also, to understand the origin of the insulating states above T C…