1,167 research outputs found
The Chemical and Dynamical Evolution of Isolated Dwarf Galaxies
Using a suite of simulations (Governato et al. 2010) which successfully
produce bulgeless (dwarf) disk galaxies, we provide an analysis of their
associated cold interstellar media (ISM) and stellar chemical abundance
patterns. A preliminary comparison with observations is undertaken, in order to
assess whether the properties of the cold gas and chemistry of the stellar
components are recovered successfully. To this end, we have extracted the
radial and vertical gas density profiles, neutral hydrogen velocity dispersion,
and the power spectrum of structure within the ISM. We complement this analysis
of the cold gas with a brief examination of the simulations' metallicity
distribution functions and the distribution of alpha-elements-to-iron.Comment: To appear in the proceedings of the JENAM 2010 Symposium "Dwarf
Galaxies: Keys to Galaxy Formation and Evolution" (Lisbon, 9-10 September
2010), P. Papaderos, S. Recchi, G. Hensler (eds.), Springer Verlag (2011), in
pres
Combinatorial Bounds and Characterizations of Splitting Authentication Codes
We present several generalizations of results for splitting authentication
codes by studying the aspect of multi-fold security. As the two primary
results, we prove a combinatorial lower bound on the number of encoding rules
and a combinatorial characterization of optimal splitting authentication codes
that are multi-fold secure against spoofing attacks. The characterization is
based on a new type of combinatorial designs, which we introduce and for which
basic necessary conditions are given regarding their existence.Comment: 13 pages; to appear in "Cryptography and Communications
Short One-Time Signatures
We present a new one-time signature scheme having short signatures. Our new scheme supports aggregation, batch verification, and admits efficient proofs of knowledge. It has a fast signing algorithm, requiring only modular additions, and its verification cost is comparable to ECDSA verification. These properties make our scheme suitable for applications on resource-constrained devices such as smart cards and sensor nodes. Along the way, we give a unified description of five previous one-time signature schemes and improve parameter selection for these schemes, and as a corollary we give a fail-stop signature scheme with short signatures
Secure and linear cryptosystems using error-correcting codes
A public-key cryptosystem, digital signature and authentication procedures
based on a Gallager-type parity-check error-correcting code are presented. The
complexity of the encryption and the decryption processes scale linearly with
the size of the plaintext Alice sends to Bob. The public-key is pre-corrupted
by Bob, whereas a private-noise added by Alice to a given fraction of the
ciphertext of each encrypted plaintext serves to increase the secure channel
and is the cornerstone for digital signatures and authentication. Various
scenarios are discussed including the possible actions of the opponent Oscar as
an eavesdropper or as a disruptor
Implementing Shor's algorithm on Josephson Charge Qubits
We investigate the physical implementation of Shor's factorization algorithm
on a Josephson charge qubit register. While we pursue a universal method to
factor a composite integer of any size, the scheme is demonstrated for the
number 21. We consider both the physical and algorithmic requirements for an
optimal implementation when only a small number of qubits is available. These
aspects of quantum computation are usually the topics of separate research
communities; we present a unifying discussion of both of these fundamental
features bridging Shor's algorithm to its physical realization using Josephson
junction qubits. In order to meet the stringent requirements set by a short
decoherence time, we accelerate the algorithm by decomposing the quantum
circuit into tailored two- and three-qubit gates and we find their physical
realizations through numerical optimization.Comment: 12 pages, submitted to Phys. Rev.
High precision spectra at large redshift for dynamical DE cosmologies
The next generation mass probes will investigate DE nature by measuring
non-linear power spectra at various z, and comparing them with high precision
simulations. Producing a complete set of them, taking into account baryon
physics and for any DE state equation w(z), would really be numerically
expensive. Regularities reducing such duty are essential. This paper presents
further n-body tests of a relation we found, linking models with DE state
parameter w(z) to const.-w models, and also tests the relation in hydro
simulations.Comment: PASCOS 2010, the 16th International Symposium on Particles, Strings
and Cosmology, Valencia (Spain), July 19th - 23rd, 201
Quantum Nondemolition Monitoring of Universal Quantum Computers
The halt scheme for quantum Turing machines, originally proposed by Deutsch,
is reformulated precisely and is proved to work without spoiling the
computation. The ``conflict'' pointed out recently by Myers in the definition
of a universal quantum computer is shown to be only apparent. In the context of
quantum nondemolition (QND) measurement, it is also shown that the output
observable, an observable representing the output of the computation, is a QND
observable and that the halt scheme is equivalent to the QND monitoring of the
output observable.Comment: 5 pages, RevTeX, no figures, revised, to appear in Phys. Rev. Let
Evolution of interfaces and expansion in width
Interfaces in a model with a single, real nonconserved order parameter and
purely dissipative evolution equation are considered. We show that a systematic
perturbative approach, called the expansion in width and developed for curved
domain walls, can be generalized to the interfaces. Procedure for calculating
curvature corrections is described. We also derive formulas for local velocity
and local surface tension of the interface. As an example, evolution of
spherical interfaces is discussed, including an estimate of critical size of
small droplets.Comment: Discussion of stability of the interface is added, and the numerical
estimates of width and velocity of the interface in the liquid crystal
example are corrected. 25 pages, Latex2
Cryptographic requirements for chaotic secure communications
In recent years, a great amount of secure communications systems based on
chaotic synchronization have been published. Most of the proposed schemes fail
to explain a number of features of fundamental importance to all cryptosystems,
such as key definition, characterization, and generation. As a consequence, the
proposed ciphers are difficult to realize in practice with a reasonable degree
of security. Likewise, they are seldom accompanied by a security analysis.
Thus, it is hard for the reader to have a hint about their security. In this
work we provide a set of guidelines that every new cryptosystems would benefit
from adhering to. The proposed guidelines address these two main gaps, i.e.,
correct key management and security analysis, to help new cryptosystems be
presented in a more rigorous cryptographic way. Also some recommendations are
offered regarding some practical aspects of communications, such as channel
noise, limited bandwith, and attenuation.Comment: 13 pages, 3 figure
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