134,454 research outputs found
Constructing IGA-suitable planar parameterization from complex CAD boundary by domain partition and global/local optimization
In this paper, we propose a general framework for constructing IGA-suitable
planar B-spline parameterizations from given complex CAD boundaries consisting
of a set of B-spline curves. Instead of forming the computational domain by a
simple boundary, planar domains with high genus and more complex boundary
curves are considered. Firstly, some pre-processing operations including
B\'ezier extraction and subdivision are performed on each boundary curve in
order to generate a high-quality planar parameterization; then a robust planar
domain partition framework is proposed to construct high-quality patch-meshing
results with few singularities from the discrete boundary formed by connecting
the end points of the resulting boundary segments. After the topology
information generation of quadrilateral decomposition, the optimal placement of
interior B\'ezier curves corresponding to the interior edges of the
quadrangulation is constructed by a global optimization method to achieve a
patch-partition with high quality. Finally, after the imposition of
C1=G1-continuity constraints on the interface of neighboring B\'ezier patches
with respect to each quad in the quadrangulation, the high-quality B\'ezier
patch parameterization is obtained by a C1-constrained local optimization
method to achieve uniform and orthogonal iso-parametric structures while
keeping the continuity conditions between patches. The efficiency and
robustness of the proposed method are demonstrated by several examples which
are compared to results obtained by the skeleton-based parameterization
approach
BCS-BEC Crossover in Symmetric Nuclear Matter at Finite Temperature: Pairing Fluctuation and Pseudogap
By adopting a -matrix based method within approximation for the
pair susceptibility, we studied the effects of pairing fluctuation on the
BCS-BEC crossover in symmetric nuclear matter. The pairing fluctuation induces
a pseudogap in the excitation spectrum of nucleon in both superfluid and normal
phases. The critical temperature of superfluid transition was calculated. It
differs from the BCS result remarkably when density is low. We also computed
the specific heat which shows a nearly ideal BEC type temperature dependence at
low density but a BCS type behavior at high density. This qualitative change of
the temperature dependence of specific heat may serve as a thermodynamic signal
for BCS-BEC crossover.Comment: 11 pages,11 figures,1 table, published version in Phys. Rev. C
A Graph-Based Approach to Address Trust and Reputation in Ubiquitous Networks
The increasing popularity of virtual computing environments such as Cloud and Grid computing is helping to drive the realization of ubiquitous and pervasive computing. However, as computing becomes more entrenched in everyday life, the concepts of trust and risk become increasingly important. In this paper, we propose a new graph-based theoretical approach to address trust and reputation in complex ubiquitous networks. We formulate trust as a function of quality of a task and time required to authenticate agent-to-agent relationship based on the Zero-Common Knowledge (ZCK) authentication scheme. This initial representation applies a graph theory concept, accompanied by a mathematical formulation of trust metrics. The approach we propose increases awareness and trustworthiness to agents based on the values estimated for each requested task, we conclude by stating our plans for future work in this area
Balancing the Tradeoff between Profit and Fairness in Rideshare Platforms During High-Demand Hours
Rideshare platforms, when assigning requests to drivers, tend to maximize profit for the system and/or minimize waiting time for riders. Such platforms can exacerbate biases that drivers may have over certain types of requests. We consider the case of peak hours when the demand for rides is more than the supply of drivers. Drivers are well aware of their advantage during the peak hours and can choose to be selective about which rides to accept. Moreover, if in such a scenario, the assignment of requests to drivers (by the platform) is made only to maximize profit and/or minimize wait time for riders, requests of a certain type (e.g. from a non-popular pickup location, or to a non-popular drop-off location) might never be assigned to a driver. Such a system can be highly unfair to riders. However, increasing fairness might come at a cost of the overall profit made by the rideshare platform. To balance these conflicting goals, we present a flexible, non-adaptive algorithm, \lpalg, that allows the platform designer to control the profit and fairness of the system via parameters and respectively. We model the matching problem as an online bipartite matching where the set of drivers is offline and requests arrive online. Upon the arrival of a request, we use \lpalg to assign it to a driver (the driver might then choose to accept or reject it) or reject the request. We formalize the measures of profit and fairness in our setting and show that by using \lpalg, the competitive ratios for profit and fairness measures would be no worse than and respectively. Extensive experimental results on both real-world and synthetic datasets confirm the validity of our theoretical lower bounds. Additionally, they show that \lpalg under some choice of can beat two natural heuristics, Greedy and Uniform, on \emph{both} fairness and profit
Superconducting properties of MgB2 thin films prepared on flexible plastic substrates
Superconducting MgB2 thin films were prepared on 50-micrometer-thick,
flexible polyamide Kapton-E foils by vacuum co-deposition of Mg and B
precursors with nominal thickness of about 100 nm and a special ex-situ rapid
annealing process in an Ar or vacuum atmosphere. In the optimal annealing
process, the Mg-B films were heated to approximately 600 C, but at the same
time, the backside of the structures was attached to a water-cooled radiator to
avoid overheating of the plastic substrate. The resulting MgB2 films were
amorphous with the onset of the superconducting transition at T_(c,on) about 33
K and the transition width of approximately 3 K. The critical current density
was > 7x10^5 A/cm^2 at 4.2 K, and its temperature dependence indicated a
granular film composition with a network of intergranular weak links. The films
could be deposited on large-area foils (up to 400 cm^2) and, after processing,
cut into any shapes (e.g., stripes) with scissors or bent multiple times,
without any observed degradation of their superconducting properties.Comment: 3 figure
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