4,518 research outputs found
Freezing of parallel hard cubes with rounded edges
The freezing transition in a classical three-dimensional system of parallel
hard cubes with rounded edges is studied by computer simulation and
fundamental-measure density functional theory. By switching the rounding
parameter s from zero to one, one can smoothly interpolate between cubes with
sharp edges and hard spheres. The equilibrium phase diagram of rounded parallel
hard cubes is computed as a function of their volume fraction and the rounding
parameter s. The second order freezing transition known for oriented cubes at s
= 0 is found to be persistent up to s = 0.65. The fluid freezes into a
simple-cubic crystal which exhibits a large vacancy concentration. Upon a
further increase of s, the continuous freezing is replaced by a first-order
transition into either a sheared simple cubic lattice or a deformed
face-centered cubic lattice with two possible unit cells: body-centered
orthorhombic or base-centered monoclinic. In principle, a system of parallel
cubes could be realized in experiments on colloids using advanced synthesis
techniques and a combination of external fields.Comment: Submitted to JC
Scaling Approach to the Phase Diagram of Quantum Hall Systems
We present a simple classification of the different liquid and solid phases
of quantum Hall systems in the limit where the Coulomb interaction between the
electrons is significant, i.e. away from integral filling factors. This
classification, and a criterion for the validity of the mean-field
approximation in the charge-density-wave phase, is based on scaling arguments
concerning the effective interaction potential of electrons restricted to an
arbitrary Landau level. Finite-temperature effects are investigated within the
same formalism, and a good agreement with recent experiments is obtained.Comment: 4 pages, 3 figures; to be published in Europhys. Lett.; new version
contains more detailed description of finite-temperature effect
A Clean-Slate Architecture for Reliable Data Delivery in Wireless Mesh Networks
In this paper, we introduce a clean-slate architecture for improving the delivery of data packets in IEEE 802.11 wireless mesh networks. Opposed to the rigid TCP/IP layer architecture which exhibits serious deficiencies in such networks, we propose a unitary layer approach that combines both routing and transport functionalities in a single layer. The new Mesh Transmission Layer (MTL) incorporates cross-interacting routing and transport modules for a reliable data delivery based on the loss probabilities of wireless links. Due to the significant drawbacks of standard TCP over IEEE 802.11, we particularly focus on the transport module, proposing a pure rate-based approach for transmitting data packets according to the current contention in the network. By considering the IEEE 802.11 spatial reuse constraint and employing a novel acknowledgment scheme, the new transport module improves both goodput and fairness in wireless mesh networks. In a comparative performance study, we show that MTL achieves up to 48% more goodput and up to 100% less packet drops than TCP/IP, while maintaining excellent fairness results
Effect of a thin AlO_x layer on transition-edge sensor properties
We have studied the physics of transition-edge sensor (TES) devices with an
insulating AlOx layer on top of the device to allow implementation of more
complex detector geometries. By comparing devices with and without the
insulating film, we have observed significant additional noise apparently
caused by the insulator layer. In addition, AlOx was found to be a relatively
good thermal conductor. This adds an unforeseen internal thermal feature to the
system.Comment: 6 pages, 5 figures, Low Temperature Detectors 14 conferenc
Extension of PRISM by Synthesis of Optimal Timeouts in Fixed-Delay CTMC
We present a practically appealing extension of the probabilistic model
checker PRISM rendering it to handle fixed-delay continuous-time Markov chains
(fdCTMCs) with rewards, the equivalent formalism to the deterministic and
stochastic Petri nets (DSPNs). fdCTMCs allow transitions with fixed-delays (or
timeouts) on top of the traditional transitions with exponential rates. Our
extension supports an evaluation of expected reward until reaching a given set
of target states. The main contribution is that, considering the fixed-delays
as parameters, we implemented a synthesis algorithm that computes the
epsilon-optimal values of the fixed-delays minimizing the expected reward. We
provide a performance evaluation of the synthesis on practical examples
Rapid and efficient stable gene transfer to mesenchymal stromal cells using a modified foamy virus vector
Mesenchymal stromal cells (MSCs) hold great promise for regenerative medicine. Stable ex vivo gene transfer to MSCs could improve the outcome and scope of MSC therapy, but current vectors require multiple rounds of transduction, involve genotoxic viral promoters and/or the addition of cytotoxic cationic polymers in order to achieve efficient transduction. We describe a self-inactivating foamy virus vector (FVV), incorporating the simian macaque foamy virus envelope and using physiological promoters, which efficiently transduces murine MSCs (mMSCs) in a single-round. High and sustained expression of the transgene, whether GFP or the lysosomal enzyme, arylsulphatase A (ARSA), was achieved. Defining MSC characteristics (surface marker expression and differentiation potential), as well as long-term engraftment and distribution in the murine brain following intracerebroventricular delivery, are unaffected by FVV transduction. Similarly, greater than 95% of human MSCs (hMSCs) were stably transduced using the same vector, facilitating human application. This work describes the best stable gene transfer vector available for mMSCs and hMSCs
- …