493 research outputs found
A third order correction to the Helmholtz equation
In this work we derive a third order correction to the classical Helmholtz equation. Starting from nonâlinear Euler equations and using asymptotical analysis we get a decoupled system of linear, Helmholtz type equations, which are written in terms of the acoustical pressure functions. We present also a rather simple concept of the boundary conditions. Also numerical results and accompanying difficulties are discussed and presented.
Remiantis Oilerio lygtimis ir asimptotine analize gautas Helmholco lygties treÄiosios eiles patikslinimas. Akustiniam slegiui gauta Helmholco tipo lygtis bei jai iĆĄvestos salygos. Pateikti skaitinio modeliavimo rezultatai.
First Published Online: 14 Oct 201
Extracting Atoms on Demand with Lasers
We propose a scheme that allows to coherently extract cold atoms from a
reservoir in a deterministic way. The transfer is achieved by means of
radiation pulses coupling two atomic states which are object to different
trapping conditions. A particular realization is proposed, where one state has
zero magnetic moment and is confined by a dipole trap, whereas the other state
with non-vanishing magnetic moment is confined by a steep microtrap potential.
We show that in this setup a predetermined number of atoms can be transferred
from a reservoir, a Bose-Einstein condensate, into the collective quantum state
of the steep trap with high efficiency in the parameter regime of present
experiments.Comment: 11 pages, 8 figure
Higher-Order Termination: from Kruskal to Computability
Termination is a major question in both logic and computer science. In logic,
termination is at the heart of proof theory where it is usually called strong
normalization (of cut elimination). In computer science, termination has always
been an important issue for showing programs correct. In the early days of
logic, strong normalization was usually shown by assigning ordinals to
expressions in such a way that eliminating a cut would yield an expression with
a smaller ordinal. In the early days of verification, computer scientists used
similar ideas, interpreting the arguments of a program call by a natural
number, such as their size. Showing the size of the arguments to decrease for
each recursive call gives a termination proof of the program, which is however
rather weak since it can only yield quite small ordinals. In the sixties, Tait
invented a new method for showing cut elimination of natural deduction, based
on a predicate over the set of terms, such that the membership of an expression
to the predicate implied the strong normalization property for that expression.
The predicate being defined by induction on types, or even as a fixpoint, this
method could yield much larger ordinals. Later generalized by Girard under the
name of reducibility or computability candidates, it showed very effective in
proving the strong normalization property of typed lambda-calculi..
Strangeness Enhancement in and Interactions at SPS Energies
The systematics of strangeness enhancement is calculated using the HIJING and
VENUS models and compared to recent data on , and
collisions at CERN/SPS energies (). The HIJING model is used to
perform a {\em linear} extrapolation from to . VENUS is used to
estimate the effects of final state cascading and possible non-conventional
production mechanisms. This comparison shows that the large enhancement of
strangeness observed in collisions, interpreted previously as possible
evidence for quark-gluon plasma formation, has its origins in non-equilibrium
dynamics of few nucleon systems. % Strangeness enhancement %is therefore traced
back to the change in the production dynamics %from to minimum bias
and central collisions. A factor of two enhancement of at
mid-rapidity is indicated by recent data, where on the average {\em one}
projectile nucleon interacts with only {\em two} target nucleons. There appears
to be another factor of two enhancement in the light ion reaction relative
to , when on the average only two projectile nucleons interact with two
target ones.Comment: 29 pages, 8 figures in uuencoded postscript fil
New mechanism for the production of the extremely fast light particles in heavy-ion collisions in the Fermi energy domain
Employing a four-body classical model, various mechanisms responsible for the
production of fast light particles in heavy ion collisions at low and
intermediate energies have been studied. It has been shown that at energies
lower than 50 A MeV, light particles of velocities of more than two times
higher than the projectile velocities are produced due to the acceleration of
the target light-particles by the mean field of the incident nucleus. It has
also been shown that precision experimental reaction research in normal and
inverse kinematics is likely to provide vital information about which mechanism
is dominant in the production of fast light particles.Comment: 4 pages, 3 figures, LaTeX, to be published in Proceedings of VII
International School-Seminar on Heavy Ion Physics, May 27 - June 1, 2002,
Dubna, Russi
The play's the thing
For very understandable reasons phenomenological approaches predominate in the field of sensory urbanism. This paper does not seek to add to that particular discourse. Rather it takes Rortyâs postmodernized Pragmatism as its starting point and develops a position on the role of multi-modal design representation in the design process as a means of admitting many voices and managing multidisciplinary collaboration.
This paper will interrogate some of the concepts underpinning the Sensory Urbanism project to help define the scope of interest in multi-modal representations. It will then explore a range of techniques and approaches developed by artists and designers during the past fifty years or so and comment on how they might inform the question of multi-modal representation. In conclusion I will argue that we should develop a heterogeneous tool kit that adopts, adapts and re-invents existing methods because this will better serve our purposes during the exploratory phase(s) of any design project that deals with complexity
Percolation of color sources and critical temperature
We argue that clustering of color sources, leading to the percolation
transition, may be the way to achieve deconfinement in heavy ion collisions.
The critical density for percolation is related to the effective critical
temperature of the thermal bath asociated to the presence of strong color
fields inside the percolating cluster. We find that the temperature is
rapidity, centrality and energy dependent. We emphasize the similarities of
percolation of strings with color glass condensate.Comment: LaTeX, 9 page
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