Hybridization gap and anisotropic far-infrared optical conductivity of URu2Si2

We performed far-infrared optical spectroscopy measurements on the heavy fermion compound URu 2 Si 2 as a function of temperature. The light's electric-field was applied along the a-axis or the c-axis of the tetragonal structure. We show that in addition to a pronounced anisotropy, the optical conductivity exhibits for both axis a partial suppression of spectral weight around 12 meV and below 30 K. We attribute these observations to a change in the bandstructure below 30 K. However, since these changes have no noticeable impact on the entropy nor on the DC transport properties, we suggest that this is a crossover phenomenon rather than a thermodynamic phase transition.Comment: To be published in Physical Review

A Quantitative Measure of Interference

We introduce an interference measure which allows to quantify the amount of interference present in any physical process that maps an initial density matrix to a final density matrix. In particular, the interference measure enables one to monitor the amount of interference generated in each step of a quantum algorithm. We show that a Hadamard gate acting on a single qubit is a basic building block for interference generation and realizes one bit of interference, an ``i-bit''. We use the interference measure to quantify interference for various examples, including Grover's search algorithm and Shor's factorization algorithm. We distinguish between ``potentially available'' and ``actually used'' interference, and show that for both algorithms the potentially available interference is exponentially large. However, the amount of interference actually used in Grover's algorithm is only about 3 i-bits and asymptotically independent of the number of qubits, while Shor's algorithm indeed uses an exponential amount of interference.Comment: 13 pages of latex; research done at http://www.quantware.ups-tlse.fr

Theory of momentum resolved tunneling into a short quantum wire

Motivated by recent tunneling experiments in the parallel wire geometry, we calculate results for momentum resolved tunneling into a short one-dimensional wire, containing a small number of electrons. We derive some general theorems about the momentum dependence, and we carry out exact calculations for up to N=4 electrons in the final state, for a system with screened Coulomb interactions that models the situation of the experiments. We also investigate the limit of large $N$ using a Luttinger-liquid type analysis. We consider the low-density regime, where the system is close to the Wigner crystal limit, and where the energy scale for spin excitations can be much lower than for charge excitations, and we consider temperatures intermediate between the relevant spin energies and charge excitations, as well as temperatures below both energy scales.Comment: 19 pages, 13 figures, clarified text in a few points, added 1 figure, updated reference

Revealing the correlation between real-space structure and chiral magnetic order at the atomic scale

We image simultaneously the geometric, electronic and magnetic structure of a buckled iron bilayer film that exhibits chiral magnetic order. We achieve this by combining spin-polarized scanning tunneling microscopy and magnetic exchange force microscopy (SPEX), to independently characterize the geometric as well as the electronic and magnetic structure of non-flat surfaces. This new SPEX imaging technique reveals the geometric height corrugation of the reconstruction lines resulting from strong strain relaxation in the bilayer, enabling the decomposition of the real-space from the eletronic structure at the atomic level, and the correlation with the resultant spin spiral ground state. By additionally utilizing adatom manipulation, we reveal the chiral magnetic ground state of portions of the unit cell that were not previously imaged with SP-STM alone. Using density functional theory (DFT), we investigate the structural and electronic properties of the reconstructed bilayer and identify the favorable stoichiometry regime in agreement with our experimental result

Probably Safe or Live

This paper presents a formal characterisation of safety and liveness properties \`a la Alpern and Schneider for fully probabilistic systems. As for the classical setting, it is established that any (probabilistic tree) property is equivalent to a conjunction of a safety and liveness property. A simple algorithm is provided to obtain such property decomposition for flat probabilistic CTL (PCTL). A safe fragment of PCTL is identified that provides a sound and complete characterisation of safety properties. For liveness properties, we provide two PCTL fragments, a sound and a complete one. We show that safety properties only have finite counterexamples, whereas liveness properties have none. We compare our characterisation for qualitative properties with the one for branching time properties by Manolios and Trefler, and present sound and complete PCTL fragments for characterising the notions of strong safety and absolute liveness coined by Sistla

Actividad antioxidante de extractos de torta de aceite de semilla de Sclerocarya birrea

The antioxidant activity of methanolic extracts from Sclerocarya birrea kernel oil meal, extracted using two different methods was evaluated. The extraction was carried out using magnetic stirring of the material in methanol/water (80:20 v/v) overnight followed by two ultra-sonic treatments for 45 min. (Overnight extract, ONEXT) and three ultra-sonic treatments for 45 min. only (Ultra-sonic extract, USEXT), respectively. Three fractions were obtained from each extract and the contents of total phenolic compounds were determined in each fraction according to the Folin-Ciocalteau method as 34.6, 54.8, and 58.6 mg/g of dry product in ONEXT and 29.6, 84.8, 143.9 mg/g in USEXT, respectively. The antioxidant activity of the extracts was evaluated according to the β-carotene-linoleic acid assay, where the extracts and their fractions showed significant effect (pSe ha evaluado la actividad antioxidante de extractos metanólicos de torta de aceite de semilla de Sclerocarya birrea extraídos usando dos métodos diferentes. La extracción se llevó a cabo mediante agitación magnética del material en metanol/agua (80:20 v/v) durante toda la noche seguida de dos tratamientos con ultrasonidos durante 45 min. (extracto ONEXT) y solo tres tratamientos con ultrasonidos durante 45 min. (extracto USEXT), respectivamente. Se obtuvieron tres fracciones de cada extracto y el contenido total de compuestos fenólicos se determinó en cada fracción según el método de Folin-Ciocalteau como 34.6, 54.8 y 58.6 mg/g de producto seco en ONEXT y 29.6, 84.8 y 143.9 mg/g en USEXT, respectivamente. La actividad antioxidante de los extractos fue evaluada mediante el ensayo del β-carotenoácido linoleico donde los extractos y sus fracciones mostraron efectos significativos (