17,645 research outputs found

### Signal processing of anthropometric data

The Anthropometric Measurements Laboratory has accumulated a large body of data from a number of previous experiments. The data is very noisy, therefore it requires the application of some signal processing schemes. Moreover, it was not regarded as time series measurements but as positional information; hence, the data is stored as coordinate points as defined by the motion of the human body. The accumulated data defines two groups or classes. Some of the data was collected from an experiment designed to measure the flexibility of the limbs, referred to as radial movement. The remaining data was collected from experiments designed to determine the surface of the reach envelope. An interactive signal processing package was designed and implemented. Since the data does not include time this package does not include a time series element. Presently the results is restricted to processing data obtained from those experiments designed to measure flexibility

### On undecidability results of real programming languages

Original article can be found at : http://www.vmars.tuwien.ac.at/ Copyright Institut fur Technische InformatikOften, it is argued that some problems in data-flow analysis such as e.g. worst case execution time analysis are undecidable (because the halting problem is) and therefore only a conservative approximation of the desired information is possible. In this paper, we show that the semantics for some important real programming languages â€“ in particular those used for programming embedded devices â€“ can be modeled as finite state systems or pushdown machines. This implies that the halting problem becomes decidable and therefore invalidates popular arguments for using conservative analysis

### Hochschild homology invariants of K\"ulshammer type of derived categories

For a perfect field $k$ of characteristic $p>0$ and for a finite dimensional
symmetric $k$-algebra $A$ K\"ulshammer studied a sequence of ideals of the
centre of $A$ using the $p$-power map on degree 0 Hochschild homology. In joint
work with Bessenrodt and Holm we removed the condition to be symmetric by
passing through the trivial extension algebra. If $A$ is symmetric then the
dual to the K\"ulshammer ideal structure was generalised to higher Hochschild
homology in earlier work. In the present paper we follow this program and
propose an analogue of the dual to the K\"ulshammer ideal structure on the
degree $m$ Hochschild homology theory also to not necessarily symmetric
algebras

### Stripe-hexagon competition in forced pattern forming systems with broken up-down symmetry

We investigate the response of two-dimensional pattern forming systems with a
broken up-down symmetry, such as chemical reactions, to spatially resonant
forcing and propose related experiments. The nonlinear behavior immediately
above threshold is analyzed in terms of amplitude equations suggested for a
$1:2$ and $1:1$ ratio between the wavelength of the spatial periodic forcing
and the wavelength of the pattern of the respective system. Both sets of
coupled amplitude equations are derived by a perturbative method from the
Lengyel-Epstein model describing a chemical reaction showing Turing patterns,
which gives us the opportunity to relate the generic response scenarios to a
specific pattern forming system. The nonlinear competition between stripe
patterns and distorted hexagons is explored and their range of existence,
stability and coexistence is determined. Whereas without modulations hexagonal
patterns are always preferred near onset of pattern formation, single mode
solutions (stripes) are favored close to threshold for modulation amplitudes
beyond some critical value. Hence distorted hexagons only occur in a finite
range of the control parameter and their interval of existence shrinks to zero
with increasing values of the modulation amplitude. Furthermore depending on
the modulation amplitude the transition between stripes and distorted hexagons
is either sub- or supercritical.Comment: 10 pages, 12 figures, submitted to Physical Review

### Radiofrequency spectroscopy of $^6$Li p-wave molecules: towards photoemission spectroscopy of a p-wave superfluid

Understanding superfluidity with higher order partial waves is crucial for
the understanding of high-$T_c$ superconductivity. For the realization of a
superfluid with anisotropic order parameter, spin-polarized fermionic lithium
atoms with strong p-wave interaction are the most promising candidates to date.
We apply rf-spectroscopy techniques that do not suffer from severe final-state
effects \cite{Perali08} with the goal to perform photoemission spectroscopy on
a strongly interacting p-wave Fermi gas similar to that recently applied for
s-wave interactions \cite{Stewart08}. Radiofrequency spectra of both quasibound
p-wave molecules and free atoms in the vicinity of the p-wave Feshbach
resonance located at 159.15\,G \cite{Schunck05} are presented. The observed
relative tunings of the molecular and atomic signals in the spectra with
magnetic field confirm earlier measurements realized with direct rf-association
\cite{Fuchs08}. Furthermore, evidence of bound molecule production using
adiabatic ramps is shown. A scheme to observe anisotropic superfluid gaps, the
most direct proof of p-wave superfluidity, with 1d-optical lattices is
proposed.Comment: 5 pages, 3 figure

### Finite elements for contact problems in two-dimensional elastodynamics

A finite element approach for contact problems in two dimensional elastodynamics was proposed. Sticking, sliding, and frictional contact were taken into account. The method consisted of a modification of the shape functions, in the contact region, in order to involve the nodes of the contacting body. The formulation was symmetric (both bodies were contactors and targets), in order to avoid interpenetration. Compatibility over the interfaces was satisfied. The method was applied to the impact of a block on a rigid target. It is shown that the formulation can be applied to fluid structure interaction, and to problems involving material nonlinearity

### The Frequency Dependence of Critical-velocity Behavior in Oscillatory Flow of Superfluid Helium-4 Through a 2-micrometer by 2-micrometer Aperture in a Thin Foil

The critical-velocity behavior of oscillatory superfluid Helium-4 flow
through a 2-micrometer by 2-micrometer aperture in a 0.1-micrometer-thick foil
has been studied from 0.36 K to 2.10 K at frequencies from less than 50 Hz up
to above 1880 Hz. The pressure remained less than 0.5 bar. In early runs during
which the frequency remained below 400 Hz, the critical velocity was a
nearly-linearly decreasing function of increasing temperature throughout the
region of temperature studied. In runs at the lowest frequencies, isolated 2 Pi
phase slips could be observed at the onset of dissipation. In runs with
frequencies higher than 400 Hz, downward curvature was observed in the decrease
of critical velocity with increasing temperature. In addition, above 500 Hz an
alteration in supercritical behavior was seen at the lower temperatures,
involving the appearance of large energy-loss events. These irregular events
typically lasted a few tens of half-cycles of oscillation and could involve
hundreds of times more energy loss than would have occurred in a single
complete 2 Pi phase slip at maximum flow. The temperatures at which this
altered behavior was observed rose with frequency, from ~ 0.6 K and below, at
500 Hz, to ~ 1.0 K and below, at 1880 Hz.Comment: 35 pages, 13 figures, prequel to cond-mat/050203

### Operator product expansions as a consequence of phase space properties

The paper presents a model-independent, nonperturbative proof of operator
product expansions in quantum field theory. As an input, a recently proposed
phase space condition is used that allows a precise description of point field
structures. Based on the product expansions, we also define and analyze normal
products (in the sense of Zimmermann).Comment: v3: minor wording changes, as to appear in J. Math. Phys.; 12 page

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