2,673 research outputs found
Dynamical Coulomb Blockade Observed in Nano-Sized Electrical Contacts
Electrical contacts between nano-engineered systems are expected to
constitute the basic building blocks of future nano-scale electronics. However,
the accurate characterization and understanding of electrical contacts at the
nano-scale is an experimentally challenging task. Here we employ
low-temperature scanning tunneling spectroscopy to investigate the conductance
of individual nano-contacts formed between flat Pb islands and their supporting
substrates. We observe a suppression of the differential tunnel conductance at
small bias voltages due to dynamical Coulomb blockade effects. The differential
conductance spectra allow us to determine the capacitances and resistances of
the electrical contacts which depend systematically on the island--substrate
contact area. Calculations based on the theory of environmentally assisted
tunneling agree well with the measurements.Comment: 5 pages, 3 figures, to appear in PR
Aerodynamic ground effect in fruitfly sized insect takeoff
Aerodynamic ground effect in flapping-wing insect flight is of importance to
comparative morphologies and of interest to the micro-air-vehicle (MAV)
community. Recent studies, however, show apparently contradictory results of
either some significant extra lift or power savings, or zero ground effect.
Here we present a numerical study of fruitfly sized insect takeoff with a
specific focus on the significance of leg thrust and wing kinematics.
Flapping-wing takeoff is studied using numerical modelling and high performance
computing. The aerodynamic forces are calculated using a three-dimensional
Navier--Stokes solver based on a pseudo-spectral method with volume
penalization. It is coupled with a flight dynamics solver that accounts for the
body weight, inertia and the leg thrust, while only having two degrees of
freedom: the vertical and the longitudinal horizontal displacement. The natural
voluntary takeoff of a fruitfly is considered as reference. The parameters of
the model are then varied to explore possible effects of interaction between
the flapping-wing model and the ground plane. These modified takeoffs include
cases with decreased leg thrust parameter, and/or with periodic wing
kinematics, constant body pitch angle. The results show that the ground effect
during natural voluntary takeoff is negligible. In the modified takeoffs, when
the rate of climb is slow, the difference in the aerodynamic forces due to the
interaction with the ground is up to 6%. Surprisingly, depending on the
kinematics, the difference is either positive or negative, in contrast to the
intuition based on the helicopter theory, which suggests positive excess lift.
This effect is attributed to unsteady wing-wake interactions. A similar effect
is found during hovering
OMA Browser—Exploring orthologous relations across 352 complete genomes
Motivation: Inference of the evolutionary relation between proteins, in particular the identification of orthologs, is a central problem in comparative genomics. Several large-scale efforts with various methodologies and scope tackle this problem, including OMA (the Orthologous MAtrix project). Results: Based on the results of the OMA project, we introduce here the OMA Browser, a web-based tool allowing the exploration of orthologous relations over 352 complete genomes. Orthologs can be viewed as groups across species, but also at the level of sequence pairs, allowing the distinction among one-to-one, one-to-many and many-to-many orthologs. Availability: http://omabrowser.org Contact: [email protected]
Dynamic Clustering in Object-Oriented Databases: An Advocacy for Simplicity
International audienceWe present in this paper three dynamic clustering techniques for Object-Oriented Databases (OODBs). The first two, Dynamic, Statistical & Tunable Clustering (DSTC) and StatClust, exploit both comprehensive usage statistics and the inter-object reference graph. They are quite elaborate. However, they are also complex to implement and induce a high overhead. The third clustering technique, called Detection & Reclustering of Objects (DRO), is based on the same principles, but is much simpler to implement. These three clustering algorithm have been implemented in the Texas persistent object store and compared in terms of clustering efficiency (i.e., overall performance increase) and overhead using the Object Clustering Benchmark (OCB). The results obtained showed that DRO induced a lighter overhead while still achieving better overall performance
OMA 2011: orthology inference among 1000 complete genomes
OMA (Orthologous MAtrix) is a database that identifies orthologs among publicly available, complete genomes. Initiated in 2004, the project is at its 11th release. It now includes 1000 genomes, making it one of the largest resources of its kind. Here, we describe recent developments in terms of species covered; the algorithmic pipeline—in particular regarding the treatment of alternative splicing, and new features of the web (OMA Browser) and programming interface (SOAP API). In the second part, we review the various representations provided by OMA and their typical applications. The database is publicly accessible at http://omabrowser.or
The Case of AB Aurigae's Disk in Polarized Light: Is There Truly a Gap?
Using the NICMOS coronagraph, we have obtained high-contrast 2.0 micron
imaging polarimetry and 1.1 micron imaging of the circumstellar disk around AB
Aurigae on angular scales of 0.3-3 arcsec (40-550 AU). Unlike previous
observations, these data resolve the disk in both total and polarized
intensity, allowing accurate measurement of the spatial variation of
polarization fraction across the disk. Using these observations we investigate
the apparent "gap" in the disk reported by Oppenheimer et al. 2008. In
polarized intensity, the NICMOS data closely reproduces the morphology seen by
Oppenheimer et al., yet in total intensity we find no evidence for a gap in
either our 1.1 or 2.0 micron images. We find instead that region has lower
polarization fraction, without a significant decrease in total scattered light,
consistent with expectations for back-scattered light on the far side of an
inclined disk. Radiative transfer models demonstrate this explanation fits the
observations. Geometrical scattering effects are entirely sufficient to explain
the observed morphology without any need to invoke a gap or protoplanet at that
location.Comment: Accepted to ApJ Letter
The Microbe browser for comparative genomics
The Microbe browser is a web server providing comparative microbial genomics data. It offers comprehensive, integrated data from GenBank, RefSeq, UniProt, InterPro, Gene Ontology and the Orthologs Matrix Project (OMA) database, displayed along with gene predictions from five software packages. The Microbe browser is daily updated from the source databases and includes all completely sequenced bacterial and archaeal genomes. The data are displayed in an easy-to-use, interactive website based on Ensembl software. The Microbe browser is available at http://microbe.vital-it.ch/. Programmatic access is available through the OMA application programming interface (API) at http://microbe.vital-it.ch/ap
Application to crankshaft manufacturing methodology, results and analysis
The gain of productivity in machining is generally sought through tools and/or cutting conditions optimization however an increase in productivity is achievable too through the workmaterial optimization. The metallurgical structure as well as the chemical composition of steels widely influence their ability to be machined. Mittal Steel Europe R & D develops new steel grades such as the Super High Strength Steels whose tensile stresses may reach 1000 or 1200 MPa. A cooperative research program between Mittal Steel Europe R&D and ENSAM tends to propose a methodology able to sort the steel grades in terms of ability to be manufactured (in forging and machining). This study focuses on such an industrial application : the heavy vehicles crankshaft manufacturing. The operation investigated consists in deep hole drilling and is concerned with the lubrication holes. This paper proposes some relevant criteria to compare the different steel grades and/or structures. Some experimental results are proposed
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