22,993 research outputs found
Bounded Model Checking of State-Space Digital Systems: The Impact of Finite Word-Length Effects on the Implementation of Fixed-Point Digital Controllers Based on State-Space Modeling
The extensive use of digital controllers demands a growing effort to prevent
design errors that appear due to finite-word length (FWL) effects. However,
there is still a gap, regarding verification tools and methodologies to check
implementation aspects of control systems. Thus, the present paper describes an
approach, which employs bounded model checking (BMC) techniques, to verify
fixed-point digital controllers represented by state-space equations. The
experimental results demonstrate the sensitivity of such systems to FWL effects
and the effectiveness of the proposed approach to detect them. To the best of
my knowledge, this is the first contribution tackling formal verification
through BMC of fixed-point state-space digital controllers.Comment: International Symposium on the Foundations of Software Engineering
201
Power grids vulnerability: a complex network approach
Power grids exhibit patterns of reaction to outages similar to complex
networks. Blackout sequences follow power laws, as complex systems operating
near a critical point. Here, the tolerance of electric power grids to both
accidental and malicious outages is analyzed in the framework of complex
network theory. In particular, the quantity known as efficiency is modified by
introducing a new concept of distance between nodes. As a result, a new
parameter called net-ability is proposed to evaluate the performance of power
grids. A comparison between efficiency and net-ability is provided by
estimating the vulnerability of sample networks, in terms of both the metrics.Comment: 16 pages, 3 figures. Figure 2 and table II modified. Typos corrected.
Version accepted for publication in Chao
Non-Fermi liquid angle resolved photoemission lineshapes of Li0.9Mo6O17
A recent letter by Xue et al. (PRL v.83, 1235 ('99)) reports a Fermi-Liquid
(FL) angle resolved photoemission (ARPES) lineshape for quasi one-dimensional
Li0.9Mo6O17, contradicting our report (PRL v.82, 2540 ('99)) of a non-FL
lineshape in this material. Xue et al. attributed the difference to the
improved angle resolution. In this comment, we point out that this reasoning is
flawed. Rather, we find that their data have fundamental differences from other
ARPES results and also band theory.Comment: To be published as a PRL Commen
Maneuvering the Migration and Differentiation of Stem Cells with Electrospun Nanofibers
Electrospun nanofibers have been extensively explored as a class of scaffolding materials for tissue regeneration, because of their unique capability to mimic some features and functions of the extracellular matrix, including the fibrous morphology and mechanical properties, and to a certain extent the chemical/biological cues. This work reviews recent progress in applying electrospun nanofibers to direct the migration of stem cells and control their differentiation into specific phenotypes. First, the physicochemical properties that make electrospun nanofibers well-suited as a supporting material to expand stem cells by controlling their migration and differentiation are introduced. Then various systems are analyzed in conjunction with mesenchymal, neuronal, and embryonic stem cells, as well as induced pluripotent stem cells. Finally, some perspectives on the challenges and future opportunities in combining electrospun nanofibers with stem cells are offered to address clinical issues
On-Chip Matching Networks for Radio-Frequency Single-Electron-Transistors
In this letter, we describe operation of a radio-frequency superconducting
single electron transistor (RF-SSET) with an on-chip superconducting LC
matching network consisting of a spiral inductor L and its capacitance to
ground. The superconducting network has a lower parasitic capacitance and gives
a better matching for the RF-SSET than does a commercial chip inductor.
Moreover, the superconducting network has negligibly low dissipation, leading
to sensitive response to changes in the RF-SSET impedance. The charge
sensitivity 2.4*10^-6 e/(Hz)^1/2 in the sub-gap region and energy sensitivity
of 1.9 hbar indicate that the RF-SSET is operating in the vicinity of the shot
noise limit.Comment: 3 pages, 3 figures, REVTeX 4. To appear in Appl. Phys. Let
Reexamination of the galaxy formation-regulated gas evolution model in groups and clusters
As an alternative explanation of the entropy excess and the steepening of the
X-ray luminosity-temperature relation in groups and clusters, the galaxy
formation-regulated gas evolution (GG) model proposed recently by Bryan makes
an attempt to incorporate the formation of galaxies into the evolution of gas
without additional heating by nongravitational processes. This seems to provide
a unified scheme for our understanding of the structures and evolution of both
galaxies and gas in groups and clusters. In this paper, we present an extensive
comparison of the X-ray properties of groups and clusters predicted by the GG
model and those revealed by current X-ray observations, using various large
data sources in the literature and also taking the observational selection
effects into account. These include an independent check of the fundamental
working hypothesis of the GG model, i.e., galaxy formation was less efficient
in rich clusters than in groups, a new test of the radial gas distributions
revealed by both the gas mass fraction and the X-ray surface brightness
profiles, and an reexamination of the X-ray luminosity-temperature and
entropy-temperature relations. In particular, it shows that the overall X-ray
surface brightness profiles predicted by the GG model are very similar in
shape, insensitive to the X-ray temperature, and the shallower X-ray surface
brightness profiles seen at low-temperature systems may arise from the current
observational selection effect. This can be used as the simplest approach to
distinguishing between the GG model and the preheating scenario. The latter
yields an intrinsically shallower gas distribution in groups than in rich
clusters.Comment: 30 pages, 10 figures, accepted for publication in Ap
Liquid Crystal-Solid Interface Structure at the Antiferroelectric-Ferroelectric Phase Transition
Total Internal Reflection (TIR) is used to probe the molecular organization
at the surface of a tilted chiral smectic liquid crystal at temperatures in the
vicinity of the bulk antiferroelectric-ferroelectric phase transition. Data are
interpreted using an exact analytical solution of a real model for
ferroelectric order at the surface. In the mixture T3, ferroelectric surface
order is expelled with the bulk ferroelectric-antiferroelectric transition. The
conditions for ferroelectric order at the surface of an antiferroelectric bulk
are presented
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