15,128 research outputs found
Self-learning Kinetic Monte-Carlo method: application to Cu(111)
We present a novel way of performing kinetic Monte Carlo simulations which
does not require an {\it a priori} list of diffusion processes and their
associated energetics and reaction rates.
Rather, at any time during the simulation, energetics for all possible
(single or multi-atom) processes, within a specific interaction range, are
either computed accurately using a saddle point search procedure, or retrieved
from a database in which previously encountered processes are stored. This
self-learning procedure enhances the speed of the simulations along with a
substantial gain in reliability because of the inclusion of many-particle
processes.
Accompanying results from the application of the method to the case of
two-dimensional Cu adatom-cluster diffusion and coalescence on Cu(111) with
detailed statistics of involved atomistic processes and contributing diffusion
coefficients attest to the suitability of the method for the purpose.Comment: 18 pages, 9 figure
Monthly and Diurnal Variability of Rain Rate and Rain Attenuation during the Monsoon Period in Malaysia
Rain is the major source of attenuation for microwave propagation above 10 GHz. In tropical and equatorial regions where the rain intensity is higher, designing a terrestrial and earth-to-satellite microwave links is very critical and challenging at these frequencies. This paper presents the preliminary results of rain effects in a 23 GHz terrestrial point-to-point communication link 1.3km long. The experimental test bed had been set up at Skudai, Johor Bahru, Malaysia. In this area, a monsoon equatorial climate prevails and the rainfall rate can reach values well above 100mm/h with significant monthly and diurnal variability. Hence, it is necessary to implement a mitigation technique for maintaining an adequate radio link performance for the action of very heavy rain. Since we now know that the ULPC (Up Link Power Control) cannot guarantee the desired performance, a solution based on frequency band diversity is proposed in this paper. Here, a secondary radio link operating in a frequency not affected by rain (C band for instance) is placed parallel with the main link. Under no rain or light rain conditions, the secondary link carries without priority radio signals. When there is an outage of the main link due to rain, the secondary link assumes the priority traffic. The outcome of the research shows a solution for higher operating frequencies during rainy events
Structural, Vibrational and Thermodynamic Properties of AgnCu34-n Nanoparticles
We report results of a systematic study of structural, vibrational and
thermodynamical properties of 34-atom bimetallic nanoparticles from the
AgnCu34-n family using model interaction potentials as derived from the
embedded atom method and in the harmonic approximation of lattice dynamics.
Systematic trends in the bond length and dynamical properties can be explained
largely on arguments based on local coordination and elemental environment.
Thus increase in the number of silver atoms in a given neighborhood introduces
a monotonic increase in bond length while increase of the copper content does
the reverse. Moreover, based on bond lengths of the lowest coordinated (6 and
8) copper atoms with their nearest neighbors (Cu atoms), we find that the
nanoparticles divide into two groups with average bond length either close to
(~ 2.58 A) or smaller (~ 2.48 A) than that in bulk copper, accompanied by
characteristic features in their vibrational density of states. For the entire
set of nanoparticles, vibrational modes are found above the bulk bands of
copper/silver. Furthermore, a blue shift in the high frequency end with
increasing number of copper atoms in the nanoparticles is traced to a shrinkage
of bond lengths from bulk values. The vibrational densities of states at the
low frequency end of the spectrum scale linearly with frequency as for single
element nanoparticles, however, the effect is more pronounced for these
nanoalloys. The Debye temperature was found to be about one third of that of
the bulk for pure copper and silver nanoparticles with a non-linear increase
with increasing number of copper atoms in the nanoalloys.Comment: 37 pages, 12 figure
Pulse-induced acoustoelectric vibrations in surface-gated GaAs-based quantum devices
We present the results of a numerical investigation which show the excitation
of acoustoelectric modes of vibration in GaAs-based heterostructures due to
sharp nano-second electric-field pulses applied across surface gates. In
particular, we show that the pulses applied in quantum information processing
applications are capable of exciting acoustoelectric modes of vibration
including surface acoustic modes which propagate for distances greater than
conventional device dimensions. We show that the pulse-induced acoustoelectric
vibrations are capable of inducing significant undesired perturbations to the
evolution of quantum systems.Comment: To be published in Phys. Rev.
A tight-binding model for MoS monolayers
We propose an accurate tight-binding parametrization for the band structure
of MoS monolayers near the main energy gap. We introduce a generic and
straightforward derivation for the band energies equations that could be
employed for other monolayer dichalcogenides. A parametrization that includes
spin-orbit coupling is also provided. The proposed set of model parameters
reproduce both the correct orbital compositions and location of valence and
conductance band in comparison with ab initio calculations. The model gives a
suitable starting point for realistic large-scale atomistic electronic
transport calculations.Comment: 35 pages, 8 figure
Potential of proteins and their expression level in marine phytoplankton (Prymnesium parvum) as biomarker of N, P and Fe conditions in aquatic systems
Nitrogen (N), phosphorus (P) and Iron (Fe) are im-portant nutrients for phytoplankton, and are key limiting nutrients in many marine systems. In the present study, growth and protein expression of ma-rine phytoplankton Prymnesium parvum under dif-ferent nitrate, phosphate and iron conditions were investigated in order to evaluate whether proteins and their expression level can be used as biomarker of N, P, and Fe conditions in aquatic systems. The growth of P. parvum increased with the increase of nitrate, phosphate and iron concentrations in the culture medium. Protein expression levels also differed significantly (p < 0.001) for different nitrate, phosphate and iron conditions in the culture medium. The expression level of an 83 kDa protein at 0 and 5 µM nitrate treatments differed significantly (p < 0.001) from those at 20, 30, 50 and 100 µM nitrate treatments, indicating the expression levels of this protein as a biomarker of N status in the culture me-dium. A 121 kDa protein was up-regulated at phos-phate stress conditions ([P] = 1.0 µM), while this pro-tein was not expressed at phosphate replete conditions ([P] = 5 µM). Therefore, the expression of 121 kDa protein in P. parvum is indicative of phosphate replete condition in aquatic systems. The expression level of a 42 kDa was significantly higher (p < 0.01) at Fe-stress condition ([Fe] = 0.01 µM) than Fe-replete conditions ([Fe] = 0.1 µM). In addition, a new protein of 103 kDa was only expressed under Fe-deplete condition ([Fe] = 0.01 µM). Therefore, the 42 and 103 kDa proteins can be used as a biomarker of Fe-limitation condition of aquatic systems. However, further studies (two dimensional gel electrophoresis and mass spectrometry) are needed to identify and characterize these proteins in P. parvum
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