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 $\Lambda$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