2,659 research outputs found
Casimir interactions in strained graphene systems
We theoretically study the strain effect on the Casimir interactions in
graphene based systems. We found that the interactions between two strained
graphene sheets are strongly dependent on the direction of stretching. The
influence of the strain on the dispersion interactions is still strong in the
presence of dielectric substrates but is relatively weak when the substrate is
metallic. Our studies would suggest new ways to design next generation devices.Comment: 5 pages, 4 figure
Adaptive Point-to-Multipoint Transmission for Multimedia Broadcast Multicast Services in LTE
This paper investigates point-to-multipoint (PTM) transmission supporting
adaptive modulation and coding (AMC) as well as retransmissions based on
incremental redundancy. In contrast to the classical PTM transmission which was
introduced by the Multimedia Broadcast Multicast Service (MBMS), the
adaptiveness requires user individual feedback channels that allow the
receivers to report their radio conditions and send positive or negative
acknowledgments (ACK/NACK) for a Layer 1 transport block to the eNodeB. In this
work, an adaptive PTM scheme based on feedback from multiple users is presented
and evaluated. Furthermore, a simple NACK-oriented feedback mechanism is
introduced to relieve the feedback channel that is used in the uplink. Finally,
the performance of different single-cell MBMS transmission modes is evaluated
by dynamic radio network simulations. It is shown that adaptive PTM
transmission outperforms the conventional MBMS configurations in terms of radio
resource consumption and user satisfaction rate.Comment: 6 pages, 7 figure
Theory of Activated Glassy Dynamics in Randomly Pinned Fluids
We generalize the force-level, microscopic, Nonlinear Langevin Equation (NLE)
theory and its elastically collective generalization (ECNLE theory) of
activated dynamics in bulk spherical particle liquids to address the influence
of random particle pinning on structural relaxation. The simplest neutral
confinement model is analyzed for hard spheres where there is no change of the
equilibrium pair structure upon particle pinning. As the pinned fraction grows,
cage scale dynamical constraints are intensified in a manner that increases
with density. This results in the mobile particles becoming more transiently
localized, with increases of the jump distance, cage scale barrier and NLE
theory mean hopping time; subtle changes of the dynamic shear modulus are
predicted. The results are contrasted with recent simulations. Similarities in
relaxation behavior are identified in the dynamic precursor regime, including a
roughly exponential, or weakly supra-exponential, growth of the alpha time with
pinning fraction and a reduction of dynamic fragility. However, the increase of
the alpha time with pinning predicted by the local NLE theory is too small, and
severely so at very high volume fractions. The strong deviations are argued to
be due to the longer range collective elasticity aspect of the problem which is
expected to be modified by random pinning in a complex manner. A qualitative
physical scenario is offered for how the three distinct aspects that quantify
the elastic barrier may change with pinning. ECNLE theory calculations of the
alpha time are then presented based on the simplest effective-medium-like
treatment for how random pinning modifies the elastic barrier. The results
appear to be consistent with most, but not all, trends seen in recent
simulations. Key open problems are discussed with regards to both theory and
simulation.Comment: 14 pages, 10 figures, under revie
The pH-dependent electrostatic interaction of a metal nanoparticle with the MS2 virus-like particles
The electrostatic interaction of metal nanoparticles with viruses is
attracting great interest due to their antiviral activity and their role in
enhancing the detection of viruses at ultra-low concentrations. We model the
MS2 virus devoid of its single strand RNA core using a core-shell model. The
dependence of the inner and outer surface charge density on the pH is taken
into account in our model of the interaction. Varying the pH causes a change in
the sign of the outer surface charge leading to the attractive-repulsive
transition in the electrostatic interaction between the MS2 virus and metal
nanoparticle at pH = 4.Comment: 6 pages, 4 figures, accepted for publication on Chemical Physics
Lette
Theory of the Spatial Transfer of Interface-Nucleated Changes of Dynamical Constraints and Its Consequences in Glass-Forming Films
We formulate a new theory for how caging constraints in glass-forming liquids
at a surface or interface are modified and then spatially transferred, in a
layer-by-layer bootstrapped manner, into the film interior in the context of
the dynamic free energy concept of the Nonlinear Langevin Equation theory
approach. The dynamic free energy at any mean location involves contributions
from two adjacent layers where confining forces are not the same. At the most
fundamental level of the theory, the caging component of the dynamic free
energy varies essentially exponentially with distance from the interface,
saturating deep enough into the film with a correlation length of modest size
and weak sensitivity to thermodynamic state. This imparts a roughly exponential
spatial variation of all the key features of the dynamic free energy required
to compute gradients of dynamical quantities including the localization length,
jump distance, cage barrier, collective elastic barrier and alpha relaxation
time. The spatial gradients are entire of dynamical, not structural nor
thermodynamic, origin. The theory is implemented for the hard sphere fluid and
diverse interfaces which can be a vapor, a rough pinned particle solid, a
vibrating pinned particle solid, or a smooth hard wall. Their basic description
at the level of the spatially-heterogeneous dynamic free energy is identical,
with the crucial difference arising from the first layer where dynamical
constraints can be weakened, softened, or hardly changed depending on the
specific interface. Numerical calculations establish the spatial dependence and
fluid volume fraction sensitivity of the key dynamical property gradients for
five different model interfaces. Comparison of the theoretical predictions for
the dynamic localization length and glassy modulus with simulations and
experiments for systems with a vapor interface reveals good agreement.Comment: 17 pages, 11 figures, Accepted on Journal of Chemical Physic
Elastically Collective Nonlinear Langevin Equation Theory of Dynamics in Glass-Forming Liquids: Transient Localization, Thermodynamic Mapping and Cooperativity
We analyze multiple new issues concerning activated relaxation in glassy hard
sphere fluids and molecular and polymer liquids based on the Elastically
Collective Nonlinear Langevin Equation (ECNLE) theory. By invoking a high
temperature reference state, a near universality of the apparent dynamic
localization length scale is predicted for liquids of widely varying fragility,
a result that is relevant to recent simulation studies and quasi-elastic
neutron scattering measurements. In contrast, in the same format strongly
non-universal behavior is found for the activation barrier that controls long
time relaxation. Two measures of cooperativity in ECNLE theory are analyzed. A
particle-level total displacement associated with the alpha relaxation event is
found to be only of order 1-2 particle diameters and weakly increases with
cooling. In contrast, an alternative cooperativity length is defined as the
spatial scale required to recover the full barrier and bulk alpha time. This
length scale grows strongly with cooling due to the emergence in the deeply
supercooled regime of collective long range elastic fluctuations required to
allow local hopping. It becomes very large as the laboratory Tg is approached,
though is relatively modest at degrees of supercooling accessible with
molecular dynamics simulation. The alpha time is found to be exponentially
related to this cooperativity length over an enormous number of decades of
relaxation time that span the lightly to deeply supercooled regimes. Moreover,
the effective barrier height increases almost linearly with the growing
cooperativity length scale. An alternative calculation of the collective
elastic barrier based on a literal continuum mechanics approach is shown to
result in very little change of the theoretical results for bulk properties,
but leads to a much smaller and less temperature-sensitive cooperativity length
scale.Comment: 12 pages, 10 figure
Modification of the Statistical Moment Method for the High-Pressure Melting Curve by the Inclusion of Thermal Vacancies
Melting behaviors of defective crystals under extreme conditions are
theoretically investigated using the statistical moment method. In our
theoretical model, heating processes cause missing atoms or vacancies in
crystal structures via dislocating them from their equilibrium positions. The
coordination number of some atoms is assumed to be removed by one unit and the
defect depends on temperature and external pressure. We formulate analytical
expressions to directly connect the equilibrium vacancy concentration, the
elastic modulus, and the melting temperature. Numerical calculations are
carried out for six transition metals including Cu, Ag, Au, Mo, Ta, and W up to
400 GPa. The obtained results show that vacancies strongly drive the melting
transition. Ignoring the vacancy formation leads to incorrect predictions of
the melting point. The good agreement between our numerical data and prior
experimental works validates the accuracy of our approach.Comment: 9 pages, 5 figures, accepted for publication on Vacuum 202
CANDECOMP/PARAFAC Decomposition of High-order Tensors Through Tensor Reshaping
In general, algorithms for order-3 CANDECOMP/-PARAFAC (CP), also coined
canonical polyadic decomposition (CPD), are easily to implement and can be
extended to higher order CPD. Unfortunately, the algorithms become
computationally demanding, and they are often not applicable to higher order
and relatively large scale tensors. In this paper, by exploiting the uniqueness
of CPD and the relation of a tensor in Kruskal form and its unfolded tensor, we
propose a fast approach to deal with this problem. Instead of directly
factorizing the high order data tensor, the method decomposes an unfolded
tensor with lower order, e.g., order-3 tensor. On basis of the order-3
estimated tensor, a structured Kruskal tensor of the same dimension as the data
tensor is then generated, and decomposed to find the final solution using fast
algorithms for the structured CPD. In addition, strategies to unfold tensors
are suggested and practically verified in the paper
Best Rank-One Tensor Approximation and Parallel Update Algorithm for CPD
A novel algorithm is proposed for CANDECOMP/PARAFAC tensor decomposition to
exploit best rank-1 tensor approximation. Different from the existing
algorithms, our algorithm updates rank-1 tensors simultaneously in parallel. In
order to achieve this, we develop new all-at-once algorithms for best rank-1
tensor approximation based on the Levenberg-Marquardt method and the rotational
update. We show that the LM algorithm has the same complexity of first-order
optimisation algorithms, while the rotational method leads to solving the best
rank-1 approximation of tensors of size . We
derive a closed-form expression of the best rank-1 tensor of tensors and present an ALS algorithm which updates 3 component at a time for
higher order tensors. The proposed algorithm is illustrated in decomposition of
difficult tensors which are associated with multiplication of two matrices.Comment: 33 page
Non-Orthogonal Tensor Diagonalization
Tensor diagonalization means transforming a given tensor to an exactly or
nearly diagonal form through multiplying the tensor by non-orthogonal
invertible matrices along selected dimensions of the tensor. It is
generalization of approximate joint diagonalization (AJD) of a set of matrices.
In particular, we derive (1) a new algorithm for symmetric AJD, which is called
two-sided symmetric diagonalization of order-three tensor, (2) a similar
algorithm for non-symmetric AJD, also called general two-sided diagonalization
of an order-3 tensor, and (3) an algorithm for three-sided diagonalization of
order-3 or order-4 tensors. The latter two algorithms may serve for canonical
polyadic (CP) tensor decomposition, and they can outperform other CP tensor
decomposition methods in terms of computational speed under the restriction
that the tensor rank does not exceed the tensor multilinear rank. Finally, we
propose (4) similar algorithms for tensor block diagonalization, which is
related to the tensor block-term decomposition.Comment: The manuscript was revised deeply, but the main idea is the same. The
algorithm has changed significantl
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