Interband heating processes in a periodically driven optical lattice

We investigate multi-"photon" interband excitation processes in an optical lattice that is driven periodically in time by a modulation of the lattice depth. Assuming the system to be prepared in the lowest band, we compute the excitation spectrum numerically. Moreover, we estimate the effective coupling parameters for resonant interband excitation processes analytically, employing degenerate perturbation theory in Floquet space. We find that below a threshold driving strength, interband excitations are suppressed exponentially with respect to the inverse driving frequency. For sufficiently low frequencies, this leads to a rather sudden onset of interband heating, once the driving strength reaches the threshold. We argue that this behavior is rather generic and should also be found in lattice systems that are driven by other forms of periodic forcing. Our results are relevant for Floquet engineering, where a lattice system is driven periodically in time in order to endow it with novel properties like the emergence of a strong artificial magnetic field or a topological band structure. In this context, interband excitation processes correspond to detrimental heating.Comment: 11 pages, 4 figure

Orbital-driven melting of a bosonic Mott insulator in a shaken optical lattice

In order to study the interplay between localized and dispersive orbital states in a system of ultracold atoms in an optical lattice, we investigate the possibility to coherently couple the lowest two Bloch bands by means of resonant periodic forcing. Considering bosons in one dimension, it is shown that a strongly interacting Floquet system can be realized, where at every lattice site two (and only two) near-degenerate orbital states are relevant. By smoothly tuning both states into resonance we find that the system can undergo an orbital-driven Mott-insulator-to-superfluid transition. As an intriguing consequence of the kinetic frustration in the system, this transition can be either continuous or first-order, depending on parameters such as lattice depth and filling.Comment: 7 pages, 3 figure

Non-equilibrum dynamics in the strongly excited inhomogeneous Dicke model

Using the exact eigenstates of the inhomogeneous Dicke model obtained by numerically solving the Bethe equations, we study the decay of bosonic excitations due to the coupling of the mode to an ensemble of two-level (spin 1/2) systems. We compare the quantum time-evolution of the bosonic mode population with the mean field description which, for a few bosons agree up to a relatively long Ehrenfest time. We demonstrate that additional excitations lead to a dramatic shortening of the period of validity of the mean field analysis. However, even in the limit where the number of bosons equal the number of spins, the initial instability remains adequately described by the mean-field approach leading to a finite, albeit short, Ehrenfest time. Through finite size analysis, we also present indications that the mean field approach could still provide an adequate description for thermodynamically large systems even at long times. However, for mesoscopic systems one cannot expect it to capture the behavior beyond the initial decay stage in the limit of an extremely large number of excitations.Comment: 9 pages, 7 figures, Phys. Rev. B in pres

Crystal Structure of Thermotoga maritima α-Glucosidase AglA Defines a New Clan of NAD+-dependent Glycosidases

Glycoside hydrolase family 4 represents an unusual group of glucosidases with a requirement for NAD(+), divalent metal cations, and reducing conditions. The family is also unique in its inclusion of both alpha- and beta-specific enzymes. The alpha-glucosidase A, AglA, from Thermotoga maritima is a typical glycoside hydrolase family 4 enzyme, requiring NAD(+) and Mn2+ as well as strongly reducing conditions for activity. Here we present the crystal structure of the protein complexed with NAD(+) and maltose, refined at a resolution of 1.9 Angstrom. The NAD(+) is bound to a typical Rossman fold NAD(+)-binding site, and the nicotinamide moiety is localized close to the maltose substrate. Within the active site the conserved Cys-174 and surrounding histidines are positioned to play a role in the hydrolysis reaction. The electron density maps indicate that Cys-174 is oxidized to a sulfinic acid. Most likely, the strongly reducing conditions are necessary to reduce the oxidized cysteine side chain. Notably, the canonical set of catalytic acidic residues common to other glucosidases is not present in the active site. This, combined with a high structural homology to NAD-dependent dehydrogenases, suggests an unusual and possibly unique mechanism of action for a glycoside-hydrolyzing enzyme

Semi-synthetic zigzag optical lattice for ultracold bosons

We consider a one-dimensional "zigzag" lattice, pictured as a two-site wide single strip taken from a triangular lattice, affected by a tunable homogeneous magnetic flux piercing its triangular plaquettes. We focus on a semi-synthetic lattice produced by combining a one-dimensional spin-dependent lattice in the long direction with laser-induced transitions between atomic internal states that define the short synthetic dimension. In contrast to previous studies on semi-synthetic lattices, the atom-atom interactions are nonlocal in both lattice directions. We investigate the ground-state properties of the system for the case of strongly interacting bosons, and find that the interplay between the frustration induced by the magnetic field and the interactions gives rise to an exotic gapped phase at fractional filling factors corresponding to one particle per magnetic unit cell.Comment: 9 pages, 6 figures; v3: final version to appear in PR

ETHISCHE RATINGS FÜR UNTERNEHMEN AUS KONSUMENTENSICHT – MÖGLICHKEITEN, AUSWIRKUNGEN UND GRENZEN –

Bisherige wissenschaftliche Untersuchungen befassen sich vorwiegend mit einer ethischen Unternehmensbewertung aus der Anlegerperspektive. Im vorliegenden Beitrag soll jedoch die Perspektive des Konsumenten eingenommen werden und es sollen Möglichkeiten zur Gestaltung eines derartigen Ratings aus Verbrauchersicht erläutert werden. Hierzu werden zunächst die grundlegenden Begriffe Ethik und Rating definiert. Anschließend wird ein ethisches Rating entworfen, das anhand von konkreten Kriterien eine sozial-ökologische Unternehmensbewertung aus Verbrauchersicht ermöglicht. Zudem werden Wirkungen und Grenzen eines solchen Werkzeugs untersucht. Der Beitrag schließt mit einem Ausblick.Ethik, Rating, ethisches Rating

Frequency, symptoms and outcome of intestinal metastases of bronchopulmonary cancer. Case report and review of the literature

BACKGROUND: We report a new case of small bowel metastases from primary lung cancer. Such metastases are not exceptional, but their clinical manifestations are rare. CASE PRESENTATION: The case involved a 56-year-old man with a squamous cell carcinoma of the lung (stage IV) that had been treated with chemotherapy. He presented fourteen months after diagnosis with an acute abdominal pain. Abdominal CT-scan demonstrated a perforated jejunum and he underwent emergency surgery. Postoperative pathologic analysis confirmed the diagnosis of metastatic pulmonary carcinoma. The patient was discharged after ten days, but died 8 weeks after surgery at home on tumor progression. CONCLUSION: We were able to find 58 documented similar cases in the literature. Most cases presented with bowel perforation or obstruction. Squamous cell carcinoma was the most common histological cell type followed by large cell carcinoma. Other metastases are often present, and the prognosis is mostly fatal at short term

Gaudin models solver based on the Bethe ansatz/ordinary differential equations correspondence

We present a numerical approach which allows the solving of Bethe equations whose solutions define the eigenstates of Gaudin models. By focusing on a new set of variables, the canceling divergences which occur for certain values of the coupling strength no longer appear explicitly. The problem is thus reduced to a set of quadratic algebraic equations. The required inverse transformation can then be realized using only linear operations and a standard polynomial root finding algorithm. The method is applied to Richardson's fermionic pairing model, the central spin model and generalized Dicke model.Comment: 10 pages, 3 figures, published versio