New Implementation (new + implementation)

Distribution by Scientific Domains


Selected Abstracts


New implementation of a SNOM suitable to study topographical features over wide areas

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 12 2005
A. Ustione
Abstract A new implementation of a SNOM is described, aiming at the topographical study of large areas and exploiting the advantages of the shear-force detection system. This technique finds very interesting application in the study of archeological or artistic samples, where it often occurs that an area to be examined at high resolution (optically, topographically or chemically) is enclosed in a wider one. The implemented system allows to obtain scans of wide areas by using dc-motors to move the sample under the probe tip, and thus it can face rough samples with height differences of several tens of micrometers. It allows the user to choose whether to use the SNOM to study the optical and topographical properties of a small part of the sample (up to tens of square micrometers), or to use the motor-driven scan technique, to study the topographical characteristic of a large area of the sample (up to some square millimeters) and even over rough surfaces. We show results detecting worn relieves over a coin. ( 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


A single qubit Landau-Zener gate

FORTSCHRITTE DER PHYSIK/PROGRESS OF PHYSICS, Issue 1 2003
V.G. Benza
We study the hamiltonian and dissipative dynamics of a system undergoing a sequence of level crossings. The resulting Landau-Zener effect makes a new implementation of a general single qubit gate possible. In the dissipative case, with a periodic bias, the level crossing counteracts the interlevel relaxation and drives the system toward a two dimensional attractor. This feature can in principle be used to implement quantum memory devices of new type. [source]


On the general dynamic model of oceanic island biogeography

JOURNAL OF BIOGEOGRAPHY, Issue 6 2009
Simone Fattorini
Abstract Aim, To investigate the biological meaning of equations used to apply the general dynamic model (GDM) of oceanic island biogeography proposed by R. J. Whittaker, K. A. Triantis and R. J. Ladle. Location, Analyses are presented for 17 animal groups living on the Aeolian Islands, a volcanic archipelago in the central Mediterranean, near Sicily. Methods, In addition to the mathematical implementation of the GDM proposed by Whittaker, Triantis and Ladle, and termed here logATT2 (, where S is species number or any other diversity metric, t is island age, A is island area, and a, b, c and d are fitted parameters), a new implementation based on the Arrhenius equation of the species,area relationship (SAR) is investigated. The new model (termed powerATT2) is: . For logATT2 and powerATT2 models, equations were developed to calculate (1) the expected number of species at equilibrium (i.e. when the island has reached maturity) per unit area (Seq), and (2) the time required to obtain this value (teq). Whereas the intercept in the Gleason model (S = C + z log A) or the coefficient of the Arrhenius power model (S = CAz) of the SAR can be considered measures of the expected number of species per unit area, this is not the case for the parameter a of the ATT2 models. However, values of Seq can be used for this purpose. The index of ,colonization ability' (CAB), calculated as the ratio , may provide a measure of the mean number of species added per unit area per unit time. Results, Both ATT2 models fitted most of the data well, but the powerATT2 model was in most cases superior. Equilibrial values of species richness (Seq) varied from c. 3 species km,2 (reptiles) to 100 species km,2 (mites). The fitted curves for the powerATT2 model showed large variations in d, from 0.03 to 3. However, most groups had values of d around 0.2,0.4, as commonly observed for the z -values of SARs modelled by a power function. Equilibration times ranged from about 170,000 years to 400,000 years. Mites and springtails had very high values of CAB, thus adding many more species per unit area per unit time than others. Reptiles and phytophagous scarabs showed very low values, being the groups that added fewest species per unit area per unit time. Main conclusions, Values of equilibrial species richness per unit area are influenced by species biology (e.g. body size and ecological specialization). Theoretical and empirical evidence suggests that higher immigration rates should increase the z -values of the Arrhenius model. Thus, in the same archipelago, groups with larger z -values should be characterized by higher dispersal ability. Results obtained here for the parameter d conform to this prediction. [source]


Modification to convolution CFS-PML for the ADI-FDTD method

MICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 2 2006
Linnian Wang
Abstract A new implementation of perfectly matched layer (PML) using the recursive-convolution technique is introduced for an alternating-direction implicit (ADI) finite-difference time-domain (FDTD) method. Based on a "complex frequency-shifted (CFS)" scaling function, this PML boundary condition is highly effective at absorbing low-frequency evanescent waves. The numerical results show that, compared with its previously suggested analogue, the new method improves the reflection error by 30 dB for large time-step sizes. 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 261,265, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21322 [source]


Design of electromagnetic crystal filters for rectangular waveguides

MICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 2 2001
Luis Mendioroz
Abstract In this paper, a new implementation of rectangular waveguide filters using dielectric periodic structures called electromagnetic crystals is presented. By tuning its forbidden band with the desired rejection band of the rectangular waveguide, the filtering behavior is obtained. The dependence of the filter features as a function of the periodic structure characteristics is shown. 2001 John Wiley & Sons, Inc. Microwave Opt Technol Lett 30: 81,84, 2001. [source]


The impact of radio feedback from active galactic nuclei in cosmological simulations: formation of disc galaxies

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2008
Takashi Okamoto
ABSTRACT In this paper, we present a new implementation of feedback due to active galactic nuclei (AGN) in cosmological simulations of galaxy formation. We assume that a fraction of jet energy, which is generated by an AGN, is transferred to the surrounding gas as thermal energy. Combining a theoretical model of mass accretion on to black holes with a multiphase description of star-forming gas, we self-consistently follow evolution of both galaxies and their central black holes. The novelty in our model is that we consider two distinct accretion modes: standard radiatively efficient thin accretion discs and radiatively inefficient accretion flows which we will generically refer to as RIAFs; motivated by theoretical models for jet production in accretion discs, we assume that only the RIAF is responsible for the AGN feedback. The focus of this paper is to investigate the interplay between galaxies and their central black holes during the formation of a disc galaxy. We find that, after an initial episode of bursting star formation, the accretion rate on to the central black hole drops so that the accretion disc switches to a RIAF structure. At this point, the feedback from the AGN becomes efficient and slightly suppresses star formation in the galactic disc and almost completely halts star formation in the bulge. This suppression of the star formation regulates mass accretion on to the black hole and associated AGN feedback. As a result, the nucleus becomes a stochastically fuelled low-luminosity AGN (Seyfert galaxy) with recurrent short-lived episodes of activity after the star bursts. During the ,on' events, the AGN produces reasonably powerful jets (radio-loud state) and is less luminous than the host galaxy, while in the ,off' phase, the nucleus is inactive and ,radio quiet'. Our model predicts several properties of the low-luminosity AGN including the bolometric luminosity, jet powers, the effect on kpc scale of the radio jet and the AGN lifetime, which are in broad agreement with observations of Seyfert galaxies and their radio activity. We also find that the ratios between the central black hole mass and the mass of the host spheroid at z= 0 are ,10,3 regardless of the strength of either supernova feedback or AGN feedback because the radiation drag model directly relates the star formation activity in the Galactic Centre and the mass accretion rate on to the central black hole. [source]


New implementation of a SNOM suitable to study topographical features over wide areas

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 12 2005
A. Ustione
Abstract A new implementation of a SNOM is described, aiming at the topographical study of large areas and exploiting the advantages of the shear-force detection system. This technique finds very interesting application in the study of archeological or artistic samples, where it often occurs that an area to be examined at high resolution (optically, topographically or chemically) is enclosed in a wider one. The implemented system allows to obtain scans of wide areas by using dc-motors to move the sample under the probe tip, and thus it can face rough samples with height differences of several tens of micrometers. It allows the user to choose whether to use the SNOM to study the optical and topographical properties of a small part of the sample (up to tens of square micrometers), or to use the motor-driven scan technique, to study the topographical characteristic of a large area of the sample (up to some square millimeters) and even over rough surfaces. We show results detecting worn relieves over a coin. ( 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Diagnosis and tuning of observational error in a quasi-operational data assimilation setting

THE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 615 2006
Bernard Chapnik
Abstract Desroziers and Ivanov proposed a method to tune error variances used for data assimilation. The implementation of this algorithm implies the computation of the trace of certain matrices which are not explicitly known. A method proposed by Girard, allowing an approximate estimation of the traces without explicit knowledge of the matrices, was then used. This paper proposes a new implementation of the Desroziers and Ivanov algorithm, including a new computation scheme for the required traces. This method is compared to Girard's in two aspects: its use in the implementation of the tuning algorithm, and the computation of a quantification of the observation impacts on the analysis known as Degrees of Freedom for Signal. Those results are illustrated by studies utilizing the French data assimilation/numerical weather-prediction system ARPEGE. The impact of a first quasi-operational tuning of variances on forecasts is shown and discussed. Copyright 2006 Royal Meteorological Society [source]