581 research outputs found
Electric Field Effect in Ultrathin Films near the Superconductor-Insulator Transition
The effect of an electric field on the conductance of ultrathin films of
metals deposited on substrates coated with a thin layer of amorphous Ge was
investigated. A contribution to the conductance modulation symmetric with
respect to the polarity of the applied electric field was found in regimes in
which there was no sign of glassy behavior. For films with thicknesses that put
them on the insulating side of the superconductor-insulator transition, the
conductance increased with electric field, whereas for films that were becoming
superconducting it decreased. Application of magnetic fields to the latter,
which reduce the transition temperature and ultimately quench
superconductivity, changed the sign of the reponse of the conductance to
electric field back to that found for insulators. We propose that this
symmetric response to capacitive charging is a consequence of changes in the
conductance of the a-Ge layer, and is not a fundamental property of the physics
of the superconductor-insulator transition as previously suggested.Comment: 4 pages text, 4 figure
Zlato u prošlosti, sadašnjosti i budućnosti
This paper deals with gold, which is described as a chemical element. Special attention is paid to its physical-chemical properties and, furthermore, where or in what form it can be found in nature. We discuss the role it has played through history and we inform how gold has been developed to the level it has reached today’s value. Still more, when gold is broken into nanoparticles, this form could be highly useful for a wide range of processes, including general nanotechnology, electronics manufacturing and the synthesizing of different functional materials. It is important that we know that gold is also used in industry in many engineering applications (contacts in micro-electronics) and medicine (dental alloys, implants).Ovaj članak govori o zlatu kao kemijskom elementu. Posebna pažnja posvećena je njegovim fizikalno-kemijskim svojstvima i gdje i u kojem obliku se može pronaći u prirodi. Razmatra se uloga koju je zlato odigralo u povijesti i donosi se informacije o tome kako je doseglo razinu vrijednosti koju ima danas. Zlato razlomljeno na nanočestice upotrebljivo je u širem spektru procesuiranja, uključujući opću nanotehnologiju, elektroničku prizvodnju i spajanju materijala raznih funkcionalnosti. Važno je znati da se zlato koristi i u industriji, mnogim inženjerskim procesima (kontakti u mikro-elektronici) i medicini (dentalne slitine, implatanti)
Analysis of phyllometric parameters efficiency in discrimination of Croatian native V. vinifera cultivars
The aims of this study were to achieve correct cultivar classification of leaf samples by using phyllometric parameters to determine the performance of parameters applied as the discriminant criteria and to determine the minimal number of leaf parameters needed to accurately classify leaf samples within cultivars. Seventy-nine phyllometric parameters were measured/calculated on 360 leaf samples from eleven grapevine cultivars, gathered during several years, from different growing conditions and with some differences in the sampling methods applied. Stepwise discriminant analysis was used to rank the phyllometric parameters according to their efficiency in the discrimination of cultivars. A series of discriminant analyses was performed with successive introduction of new parameters as discriminatory elements until 100 % correct classification of leaf samples into the correct cultivar was achieved. This was achieved using only the seven highest ranking phyllometric parameters from the stepwise discriminant analysis. Additionally, canonical discriminant analysis was performed to evaluate the differences between cultivars in the same parameters. This study represents a model for analysis of the efficiency of different ampelometric parameters for discrimination of V. vinifera cultivars.
The Cosmological Constant and Advanced Gravitational Wave Detectors
Interferometric gravitational wave detectors could measure the frequency
sweep of a binary inspiral [characterized by its chirp mass] to high accuracy.
The observed chirp mass is the intrinsic chirp mass of the binary source
multiplied by , where is the redshift of the source. Assuming a
non-zero cosmological constant, we compute the expected redshift distribution
of observed events for an advanced LIGO detector. We find that the redshift
distribution has a robust and sizable dependence on the cosmological constant;
the data from advanced LIGO detectors could provide an independent measurement
of the cosmological constant.Comment: 13 pages plus 5 figure, LaTeX. Revised and final version, to appear
in Phys. Rev.
Attractor Metadynamics in Adapting Neural Networks
Slow adaption processes, like synaptic and intrinsic plasticity, abound in
the brain and shape the landscape for the neural dynamics occurring on
substantially faster timescales. At any given time the network is characterized
by a set of internal parameters, which are adapting continuously, albeit
slowly. This set of parameters defines the number and the location of the
respective adiabatic attractors. The slow evolution of network parameters hence
induces an evolving attractor landscape, a process which we term attractor
metadynamics. We study the nature of the metadynamics of the attractor
landscape for several continuous-time autonomous model networks. We find both
first- and second-order changes in the location of adiabatic attractors and
argue that the study of the continuously evolving attractor landscape
constitutes a powerful tool for understanding the overall development of the
neural dynamics
Estimation of parameters of gravitational waves from coalescing binaries
In this paper we deal with the measurement of the parameters of the
gravitational wave signal emitted by a coalescing binary signal.
We present the results of Monte Carlo simulations carried out for the case of
the initial LIGO, incorporating the first post-Newtonian corrections into the
waveform. Using the parameters so determined, we estimate the direction to the
source. We stress the use of the time-of-coalescence rather than the
time-of-arrival of the signal to determine the direction of the source. We show
that this can considerably reduce the errors in the determination of the
direction of the source.Comment: 5 pages, REVTEX, 2 figures (bundled via uufiles command along with
this paper) submitted to Praman
Collision Dynamics and Solvation of Water Molecules in a Liquid Methanol Film
Environmental molecular beam experiments are used to examine water
interactions with liquid methanol films at temperatures from 170 K to 190 K. We
find that water molecules with 0.32 eV incident kinetic energy are efficiently
trapped by the liquid methanol. The scattering process is characterized by an
efficient loss of energy to surface modes with a minor component of the
incident beam that is inelastically scattered. Thermal desorption of water
molecules has a well characterized Arrhenius form with an activation energy of
0.47{\pm}0.11 eV and pre-exponential factor of 4.6 {\times} 10^(15{\pm}3)
s^(-1). We also observe a temperature dependent incorporation of incident water
into the methanol layer. The implication for fundamental studies and
environmental applications is that even an alcohol as simple as methanol can
exhibit complex and temperature dependent surfactant behavior.Comment: 8 pages, 5 figure
Danube loess stratigraphy - Towards a pan-European loess stratigraphic model
The Danube River drainage basin is the second largest river catchment in Europe and contains a significant and extensive region of thick loess deposits that preserve a record of a wide variety of recent and past environments. Indeed, the Danube River and tributaries may themselves be responsible for the transportation of large volumes of silt that ultimately drive loess formation in the middle and lower reaches of this large catchment. However, this vast loess province lacks a unified stratigraphic scheme. European loess research started in the late 17th century in the Danube Basin with the work of Count Luigi Ferdinand Marsigli. Since that time numerous investigations provided the basis for the pioneering stratigraphic framework proposed initially by Kukla (1970, 1977) in his correlations of loess with deep-sea sediments. Loess-palaeosol sequences in the middle and lower reaches of the Danube River basin were a key part of this framework and contain some of the longest and most complete continental climate records in Europe, covering more than the last million years. However, the very size of the Danube loess belt and the large number of countries it covers presents a major limiting factor in developing a unified approach that enables continental scale analysis of the deposits. Local loess-palaeosol stratigraphic schemes have been defined separately in different countries and the difficulties in correlating such schemes, which often change significantly with advances in age-dating, have limited the number of basin-wide studies. A unified basin-wide stratigraphic model would greatly alleviate these difficulties and facilitate research into the wider significance of these loess records. Therefore we review the existing stratigraphic schemes and define a new Danube Basin wide loess stratigraphy based around a synthetic type section of the Mošorin and Stari Slankamen sites in Serbia. We present a detailed comparison with the sedimentological and palaeoclimatic records preserved in sediments of the Chinese Loess Plateau, with the oxygen isotope records from deep-sea sediments, and with classic European Pleistocene stratigraphic subdivisions. The hierarchy of Danubian stratigraphic units is determined by climatically controlled environmental shifts, in a similar way to the Chinese loess stratigraphic scheme. A new unified Danube loess stratigraphic model has a number of advantages, including preventing confusion resulting from the use of multiple national schemes, a more transparent basis, and the potential to set Pleistocene palaeoenvironmental changes recorded in the Danube catchment area into a global context. The use of a very simple labelling system based on the well-established Chinese loess scheme facilitates interpretation of palaeoenvironmental information reported from the Danube Basin loess sites in a wider more accessible context that can be readily correlated world-wide. This stratigraphic approach also provides, for the first time, an appropriate framework for the development of an integrated, pan-European and potentially pan-Eurasian loess stratigraphic scheme. © 2015 Elsevier B.V
Superfluid-insulator transition of the Josephson junction array model with commensurate frustration
We have studied the rationally frustrated Josephson-junction array model in
the square lattice through Monte Carlo simulations of D XY-model. For
frustration , the model at zero temperature shows a continuous
superfluid-insulator transition. From the measurement of the correlation
function and the superfluid stiffness, we obtain the dynamical critical
exponent and the correlation length critical exponent . While the dynamical critical exponent is the same as that for cases
, 1/2, and 1/3, the correlation length critical exponent is surprisingly
quite different. When , we have the nature of a first-order transition.Comment: RevTex 4, to appear in PR
Bayesian Bounds on Parameter Estimation Accuracy for Compact Coalescing Binary Gravitational Wave Signals
A global network of laser interferometric gravitational wave detectors is
projected to be in operation by around the turn of the century. Here, the noisy
output of a single instrument is examined. A gravitational wave is assumed to
have been detected in the data and we deal with the subsequent problem of
parameter estimation. Specifically, we investigate theoretical lower bounds on
the minimum mean-square errors associated with measuring the parameters of the
inspiral waveform generated by an orbiting system of neutron stars/black holes.
Three theoretical lower bounds on parameter estimation accuracy are considered:
the Cramer-Rao bound (CRB); the Weiss-Weinstein bound (WWB); and the Ziv-Zakai
bound (ZZB). We obtain the WWB and ZZB for the Newtonian-form of the coalescing
binary waveform, and compare them with published CRB and numerical Monte-Carlo
results. At large SNR, we find that the theoretical bounds are all identical
and are attained by the Monte-Carlo results. As SNR gradually drops below 10,
the WWB and ZZB are both found to provide increasingly tighter lower bounds
than the CRB. However, at these levels of moderate SNR, there is a significant
departure between all the bounds and the numerical Monte-Carlo results.Comment: 17 pages (LaTeX), 4 figures. Submitted to Physical Review
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