9,567 research outputs found
Fabrication of the 23-ft Collimating Mirror for the JPL 25-ft Space Simulator
Optical, structural, and thermal design criteria and fabrication techniques for collimating mirror in space simulato
Reentrant stability of BEC standing wave patterns
We describe standing wave patterns induced by an attractive finite-ranged
external potential inside a large Bose-Einstein Condensate (BEC). As the
potential depth increases, the time independent Gross-Pitaevskii equation
develops pairs of solutions that have nodes in their wavefunction. We elucidate
the nature of these states and study their dynamical stability. Although we
study the problem in a two-dimensional BEC subject to a cylindrically symmetric
square-well potential of a radius that is comparable to the coherence length of
the BEC, our analysis reveals general trends, valid in two and three
dimensions, independent of the symmetry of the localized potential well, and
suggestive of the behavior in general, short- and large-range potentials. One
set of nodal BEC wavefunctions resembles the single particle n node bound state
wavefunction of the potential well, the other wavefunctions resemble the n-1
node bound-state wavefunction with a kink state pinned by the potential. The
second state, though corresponding to the lower free energy value of the pair
of n node BEC states, is always unstable, whereas the first can be dynamically
stable in intervals of the potential well depth, implying that the standing
wave BEC can evolve from a dynamically unstable to stable, and back to unstable
status as the potential well is adiabatically deepened, a phenomenon that we
refer to as "reentrant dynamical stability".Comment: 13 pages, 9 figures; revised discussion in Sec.
Pembelajaran Enkripsi Metode Word Auto Key Encryption
Kriptografi Metode WAKE merupakan salah satu metode yang telah digunakan secara komersial. WAKE merupakan singkatan dari Word Auto Key Encryption. Metode ini ditemukan oleh David Wheeler pada tahun 1993 dan merupakan salah satu algoritma stream cipher yang cepat dalam implementasinya dalam perangkat lunak. Metode ini menggunakan kunci 128 bit, plaintext 32 bit dan sebuah tabel 256 x 32 bit. Dalam algoritmanya, metoda ini menggunakan operasi XOR, AND, OR dan Shift Right. Inti dari metode WAKE terletak pada proses pembentukan tabel S-Box dan proses pembentukan kunci. Tabel S-Box dari metode WAKE bersifat fleksibel dan berbeda-beda untuk setiap putaran. Perancangan perangkat lunak menggunakan metode perancangan RAD (Rapid Application Development), adapun langkah-langkah yang dilakukan yaitu : Bussiness Modeling, Data modelling, Process Modeling, GenerationApplicatio
Cosmological Simulations on a Grid of Computers
The work presented in this paper aims at restricting the input parameter
values of the semi-analytical model used in GALICS and MOMAF, so as to derive
which parameters influence the most the results, e.g., star formation, feedback
and halo recycling efficiencies, etc. Our approach is to proceed empirically:
we run lots of simulations and derive the correct ranges of values. The
computation time needed is so large, that we need to run on a grid of
computers. Hence, we model GALICS and MOMAF execution time and output files
size, and run the simulation using a grid middleware: DIET. All the complexity
of accessing resources, scheduling simulations and managing data is harnessed
by DIET and hidden behind a web portal accessible to the users.Comment: Accepted and Published in AIP Conference Proceedings 1241, 2010,
pages 816-82
Cosmic bulk viscosity through backreaction
We consider an effective viscous pressure as the result of a backreaction of
inhomogeneities within Buchert's formalism. The use of an effective metric with
a time-dependent curvature radius allows us to calculate the luminosity
distance of the backreaction model. This quantity is different from its
counterpart for a "conventional" spatially flat bulk viscous fluid universe.
Both expressions are tested against the SNIa data of the Union2.1 sample with
only marginally different results for the distance-redshift relation and in
accordance with the CDM model. Future observations are expected to be
able to discriminate among these models on the basis of indirect measurements
of the curvature evolution.Comment: 18 pages, 6 figures, comments and references added, accepted for
publication in GR
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