955 research outputs found
Modeling contact formation between atomic-sized gold tips via molecular dynamics
The formation and rupture of atomic-sized contacts is modelled by means of
molecular dynamics simulations. Such nano-contacts are realized in scanning
tunnelling microscope and mechanically controlled break junction experiments.
These instruments routinely measure the conductance across the nano-sized
electrodes as they are brought into contact and separated, permitting
conductance traces to be recorded that are plots of conductance versus the
distance between the electrodes. One interesting feature of the conductance
traces is that for some metals and geometric configurations a jump in the value
of the conductance is observed right before contact between the electrodes, a
phenomenon known as jump-to-contact. This paper considers, from a computational
point of view, the dynamics of contact between two gold nano-electrodes.
Repeated indentation of the two surfaces on each other is performed in two
crystallographic orientations of face-centred cubic gold, namely (001) and
(111). Ultimately, the intention is to identify the structures at the atomic
level at the moment of first contact between the surfaces, since the value of
the conductance is related to the minimum cross-section in the contact region.
Conductance values obtained in this way are determined using first principles
electronic transport calculations, with atomic configurations taken from the
molecular dynamics simulations serving as input structures.Comment: 6 pages, 4 figures, conference submissio
Determinación de curvas para la estimación del contenido de humedad de diez maderas de frondosas mediante medidas de resistencia eléctrica
Accuracy in moisture content measurement is of great importance in the assurance of wood product quality and isnecessary to meet administrative and normative requirements. Improving the accuracy of resistance-type moisture meters,and meeting the normative demands of their annual calibration, requires the use of optimised curves relating electricalresistance to moisture content for the most commercially important wood types. The Samuelsson model, adjusted bylinear regression techniques, was used to describe the relationship between the electrical resistance and moisture contentof seven boreal and three tropical hardwoods available on the Spanish market. The curves produced can be used to predictthe moisture contents of these hardwoods via the measurement of their electrical resistance with an error of just ± 1.0%.These curves should also prove of great use in the calibration of wood resistance-type moisture meters.La precisión en la medida del contenido de humedad juega un papel fundamental no solo en el aseguramiento de lacalidad de los productos de la madera sino, también, en el cumplimiento de las exigencias normativas y administrativasque gravitan sobre los productos. Para ser capaces de mejorar la precisión de la medida tomada por los xilohigrómetrosde resistencia y cumplir con las exigencias normativas de calibración anual de los equipos, es necesario obtener curvasoptimizadas que relacionen la resistencia eléctrica con la humedad en las maderas de mayor importancia comercial.El modelo de Samuelsson, Log[Log(R) + 1] = a.h + b, ajustado mediante técnicas de regresión lineal, fue usado paradescribir la relación existente entre la resistencia eléctrica de la madera (R) y el contenido de humedad (h) de sietemaderas de frondosas boreales y tres de frondosas tropicales comercialmente disponibles en el mercado español. Lascurvas obtenidas pueden ser usadas para la predicción del contenido de humedad de dichas maderas, con un errormáximo de ± 1.0%, mediante la medición de su resistencia eléctrica. Estas curvas serían también de interés para lacalibración de medidores de humedad de madera por resistencia eléctrica
Benchmarking and viability assessment of optical packet switching for metro networks
Optical packet switching (OPS) has been proposed as a strong candidate for future metro networks. This paper assesses the viability of an OPS-based ring architecture as proposed within the research project DAVID (Data And Voice Integration on DWDM), funded by the European Commission through the Information Society Technologies (IST) framework. Its feasibility is discussed from a physical-layer point of view, and its limitations in size are explored. Through dimensioning studies, we show that the proposed OPS architecture is competitive with respect to alternative metropolitan area network (MAN) approaches, including synchronous digital hierarchy, resilient packet rings (RPR), and star-based Ethernet. Finally, the proposed OPS architectures are discussed from a logical performance point of view, and a high-quality scheduling algorithm to control the packet-switching operations in the rings is explained
Study of the dynamics of estuarine and coastal waters using remote sensing: the Tinto-Odiel estuary, SW Spain
Benchmarking and viability assessment of optical packet switching for metro networks
Optical packet switching (OPS) has been proposed as a strong candidate for future metro networks. This paper assesses the viability of an OPS-based ring architecture as proposed within the research project DAVID (Data And Voice Integration on DWDM), funded by the European Commission through the Information Society Technologies (IST) framework. Its feasibility is discussed from a physical-layer point of view, and its limitations in size are explored. Through dimensioning studies, we show that the proposed OPS architecture is competitive with respect to alternative metropolitan area network (MAN) approaches, including synchronous digital hierarchy, resilient packet rings (RPR), and star-based Ethernet. Finally, the proposed OPS architectures are discussed from a logical performance point of view, and a high-quality scheduling algorithm to control the packet-switching operations in the rings is explained
Comparison of users of an HIV/syphilis screening community-based mobile van and traditional voluntary counselling and testing sites in Guatemala
Determination of the b quark mass at the M_Z scale with the DELPHI detector at LEP
An experimental study of the normalized three-jet rate of b quark events with
respect to light quarks events (light= \ell \equiv u,d,s) has been performed
using the CAMBRIDGE and DURHAM jet algorithms. The data used were collected by
the DELPHI experiment at LEP on the Z peak from 1994 to 2000. The results are
found to agree with theoretical predictions treating mass corrections at
next-to-leading order. Measurements of the b quark mass have also been
performed for both the b pole mass: M_b and the b running mass: m_b(M_Z). Data
are found to be better described when using the running mass. The measurement
yields: m_b(M_Z) = 2.85 +/- 0.18 (stat) +/- 0.13 (exp) +/- 0.19 (had) +/- 0.12
(theo) GeV/c^2 for the CAMBRIDGE algorithm. This result is the most precise
measurement of the b mass derived from a high energy process. When compared to
other b mass determinations by experiments at lower energy scales, this value
agrees with the prediction of Quantum Chromodynamics for the energy evolution
of the running mass. The mass measurement is equivalent to a test of the
flavour independence of the strong coupling constant with an accuracy of 7
permil.Comment: 24 pages, 10 figures, Accepted by Eur. Phys. J.
Study of Leading Hadrons in Gluon and Quark Fragmentation
The study of quark jets in e+e- reactions at LEP has demonstrated that the
hadronisation process is reproduced well by the Lund string model. However, our
understanding of gluon fragmentation is less complete. In this study enriched
quark and gluon jet samples of different purities are selected in three-jet
events from hadronic decays of the Z collected by the DELPHI experiment in the
LEP runs during 1994 and 1995. The leading systems of the two kinds of jets are
defined by requiring a rapidity gap and their sum of charges is studied. An
excess of leading systems with total charge zero is found for gluon jets in all
cases, when compared to Monte Carlo Simulations with JETSET (with and without
Bose-Einstein correlations included) and ARIADNE. The corresponding leading
systems of quark jets do not exhibit such an excess. The influence of the gap
size and of the gluon purity on the effect is studied and a concentration of
the excess of neutral leading systems at low invariant masses (<~ 2 GeV/c^2) is
observed, indicating that gluon jets might have an additional hitherto
undetected fragmentation mode via a two-gluon system. This could be an
indication of a possible production of gluonic states as predicted by QCD.Comment: 19 pages, 6 figures, Accepted by Phys. Lett.
- …