405 research outputs found
Stochastic boundary conditions for molecular dynamics simulations
In this paper we develop a stochastic boundary conditions (SBC) for
event-driven molecular dynamics simulations of a finite volume embedded within
an infinite environment. In this method, we first collect the statistics of
injection/ejection events in periodic boundary conditions (PBC). Once
sufficient statistics are collected, we remove the PBC and turn on the SBC. In
the SBC simulations, we allow particles leaving the system to be truly ejected
from the simulation, and randomly inject particles at the boundaries by
resampling from the injection/ejection statistics collected from the current or
previous simulations. With the SBC, we can measure thermodynamic quantities
within the grand canonical ensemble, based on the particle number and energy
fluctuations. To demonstrate how useful the SBC algorithm is, we simulated a
hard disk gas and measured the pair distribution function, the compressibility
and the specific heat, comparing them against literature values.Comment: 24 pages, 16 figure
UNIMAS Outstanding Online Course Award, 2009
UNIMAS Outstanding Online Course Award, 2009 is coferred to Dr. Leaw Chui Pin in recognition of your outstanding use of Morpheus in supporting your teaching.
Organised by Centre for Applied Learning and Multimedia (CALM
The role of electron-electron interactions in two-dimensional Dirac fermions
The role of electron-electron interactions on two-dimensional Dirac fermions
remains enigmatic. Using a combination of nonperturbative numerical and
analytical techniques that incorporate both the contact and long-range parts of
the Coulomb interaction, we identify the two previously discussed regimes: a
Gross-Neveu transition to a strongly correlated Mott insulator, and a
semi-metallic state with a logarithmically diverging Fermi velocity accurately
described by the random phase approximation. Most interestingly, experimental
realizations of Dirac fermions span the crossover between these two regimes
providing the physical mechanism that masks this velocity divergence. We
explain several long-standing mysteries including why the observed Fermi
velocity in graphene is consistently about 20 percent larger than the best
values calculated using ab initio and why graphene on different substrates show
different behavior.Comment: 11 pages, 4 figure
Strategic Insights From Playing the Quantum Tic-Tac-Toe
In this paper, we perform a minimalistic quantization of the classical game
of tic-tac-toe, by allowing superpositions of classical moves. In order for the
quantum game to reduce properly to the classical game, we require legal quantum
moves to be orthogonal to all previous moves. We also admit interference
effects, by squaring the sum of amplitudes over all moves by a player to
compute his or her occupation level of a given site. A player wins when the
sums of occupations along any of the eight straight lines we can draw in the grid is greater than three. We play the quantum tic-tac-toe first
randomly, and then deterministically, to explore the impact different opening
moves, end games, and different combinations of offensive and defensive
strategies have on the outcome of the game. In contrast to the classical
tic-tac-toe, the deterministic quantum game does not always end in a draw. In
contrast also to most classical two-player games of no chance, it is possible
for Player 2 to win. More interestingly, we find that Player 1 enjoys an
overwhelming quantum advantage when he opens with a quantum move, but loses
this advantage when he opens with a classical move. We also find the quantum
blocking move, which consists of a weighted superposition of moves that the
opponent could use to win the game, to be very effective in denying the
opponent his or her victory. We then speculate what implications these results
might have on quantum information transfer and portfolio optimization.Comment: 20 pages, 3 figures, and 3 tables. LaTeX 2e using iopart class, and
braket, color, graphicx, multirow, subfig, url package
Synthesis of carbon self-doped titanium dioxide and its activity in the photocatalytic oxidation of styrene under visible light irradiation
Carbon self-doped titanium dioxide (C/TiO2) photocatalyst was synthesized by a simple sol-gel method using titanium isopropoxide as both the titanium precursor and carbon source. The effects of calcination temperatures in the range of 300 to 700 °C to the structure and physicochemical properties of the C/TiO2 were investigated by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) coupled with energy dispersive X-ray (EDX), Fourier transform infrared (FTIR) spectroscopy, UV-visible diffuse reflectance (UV-Vis DR) spectroscopy, photoluminescence spectroscopy, N2 adsorption-desorption and X-ray photoelectron spectroscopy (XPS). XPS results proved the presence of self-doped carbon at the interstitial and substitutional lattice of TiO2. The C/TiO2 calcined at 300 and 400 °C (C/TiO2-300 and C/TiO2-400, respectively) showed mesoporous characteristic and large surface area of about 100 m2 g-1. The C/TiO2 photocatalysts were then tested in the photo-oxidation of styrene under visible light irradiation with aqueous hydrogen peroxide as the oxidizing agent. The C/TiO2 photocatalysts were successfully activated under the irradiation of visible light, where C/TiO2-300 and C/TiO2-400 showed the highest total concentration of products (benzaldehyde and styrene oxide) at 1.1 mmol and 1.0 mmol, respectively
Release of curcumin incorporated in albumin loaded silica
In this work, we have prepared a new drug delivery system consisting of silica (SiO2) as the main carrier, while albumin acted as the co–carrier in order to control the release of drug. The system was prepared by simple wet chemical method. The efficiency of the designed system was tested in the delivery of a hydrophobic drug, curcumin through an in–vitro procedure. The results show that the release percentage of curcumin was increased with the presence of the co–carrier. The intermolecular interaction of curcumin with albumin and the competition between them to locate on the surface of silica affect the release system. Besides, the curcumin release amount was corresponded to the composition of the silica carrier in the systems. Consequently, the potential for silica/albumin use as a drug carrier was ascertained
Antiferromagnetism and chiral d-wave superconductivity from an effective model for twisted bilayer graphene
Starting from the strong-coupling limit of an extended Hubbard model, we
develop a spin-fermion theory to study the insulating phase and pairing
symmetry of the superconducting phase in twisted bilayer graphene. Assuming
that the insulating phase is an anti-ferromagnetic insulator, we show that
fluctuations of the anti-ferromagnetic order in the conducting phase can
mediate superconducting pairing. Using a self-consistent mean-field analysis,
we find that the pairing wave function has a chiral d-wave symmetry. Consistent
with this observation, we show explicitly the existence of chiral Majorana edge
modes by diagonalizing our proposed Hamiltonian on a finite-sized system. These
results establish twisted bilayer graphene as a promising platform to realize
topological superconductivity
Harmful Algal Blooms in Malaysian Waters
Harmful algal blooms (HABs) events have been increasingly reported in the country, not only of the frequency and severity
of the events, but also involved more species than previously known. In this paper, a decadal review of HABs events in
Malaysia is summarized. Bloom events caused by harmful dinoflagellate species including the shellfish poisoning events
were highlighted. Paralytic shellfish poisoning (PSP) is no longer restricted to Sabah coasts and Pyrodnium bahamense.
Bloom of Alexandrium minutum was reported for the first time in the Peninsula with six persons hospitalized including
one casualty after consuming the contaminated benthic clams. Algal blooms that are associated with incidence of massive
fish kills have been reported from both east and west coasts of the Peninsula in conjunction to finfish mariculture loses.
The culprits of these bloom events have been identified as the dinoflagellates, Cochlodinium polykrikoides, Neoceratium
furca, Prorocentrum minimum, Noctiluca scintillans and a raphidophyte, Chatonella ovata. In this paper, some of these
HABs species were characterized morphologically and genetically, including their toxicity. Therefore, with the increase of
coastal utilization and eutrophication, prevention, management and mitigation strategies, such as site selection, moving
pens, clay spraying should be adopted to minimize the impact of these natural events
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