9,792 research outputs found
On the security of a new image encryption scheme based on chaotic map lattices
This paper reports a detailed cryptanalysis of a recently proposed encryption
scheme based on the logistic map. Some problems are emphasized concerning the
key space definition and the implementation of the cryptosystem using
floating-point operations. It is also shown how it is possible to reduce
considerably the key space through a ciphertext-only attack. Moreover, a timing
attack allows the estimation of part of the key due to the existent
relationship between this part of the key and the encryption/decryption time.
As a result, the main features of the cryptosystem do not satisfy the demands
of secure communications. Some hints are offered to improve the cryptosystem
under study according to those requirements.Comment: 8 pages, 8 Figure
Non-critical superstrings: a comparison between continuum and discrete approaches
We review the relation between the matrix model and Liouville approaches to
two-dimensional gravity as elaborated by Moore, Seiberg and Staudacher. Then,
based on the supersymmetric Liouville formulation and the discrete eigenvalue
model proposed by Alvarez-Gaum\'e, Itoyama, Ma\~nes and Zadra, we extend the
previous relation to the supersymmetric case. The minisuperspace approximation
for the supersymmetric case is formulated, and the corresponding wave equation
is found.Comment: 25 pages, plain tex, prep CERN-TH-7161/9
The \u3cem\u3elet-7\u3c/em\u3e MicroRNA Family Members \u3cem\u3emir\u3c/em\u3e-48, \u3cem\u3emir\u3c/em\u3e-84, and mir-241 Function Together to Regulate Developmental Timing in \u3cem\u3eCaenorhabditis elegans\u3c/em\u3e
The microRNA let-7 is a critical regulator of developmental timing events at the larval-to-adult transition in C. elegans. Recently, microRNAs with sequence similarity to let-7 have been identified. We find that doubly mutant animals lacking the let-7 family microRNA genes mir-48 and mir-84 exhibit retarded molting behavior and retarded adult gene expression in the hypodermis. Triply mutant animals lacking mir-48, mir-84, and mir-241 exhibit repetition of L2-stage events in addition to retarded adult-stage events. mir-48, mir-84, and mir-241 function together to control the L2-to-L3 transition, likely by base pairing to complementary sites in the hbl-1 3′ UTR and downregulating hbl-1 activity. Genetic analysis indicates that mir-48, mir-84, and mir-241 specify the timing of the L2-to-L3 transition in parallel to the heterochronic genes lin-28 and lin-46. These results indicate that let-7 family microRNAs function in combination to affect both early and late developmental timing decisions
Laser beam properties and microfluidic confinement control thermocavitation
Thermocavitation, the creation of a vapor bubble by heating a liquid with a
continuous-wave laser, has been studied for a wide range of applications.
Examples include the development of an actuator for needle-free jet injectors,
as the pumping mechanism in microfluidic channels and crystallization or
nanoparticle synthesis. Optimal use in these applications require control over
the dynamics of the laser-generated bubble through the laser power and beam
radius. In contrast to pulsed lasers, for continuous-wave lasers the influence
of the laser beam radius on the bubble characteristics is not fully understood.
Here, we present a novel way to control the size of the beam from an optical
fiber by changing the distance from the glass-liquid interface. We show that
the increase in beam size results in a longer nucleation time. Numerical
simulations of the experiment show that the maximum temperature at the moment
of nucleation is 2375{\deg}C and independent of laser parameters. Due to
delayed nucleation for larger beam sizes, more energy is absorbed by the liquid
at the nucleation instant. Consequently, a larger beam size results in a faster
growing bubble, producing the same effect as reducing the laser power. We
conclude that the total bubble energy only depends on the amount of absorbed
optical energy and it is independent of the beam radius and laser power for any
amount of absorbed energy. This effect contrasts with pulsed lasers, where an
increase in beam radius results in a reduction of bubble energy. Our results
are of relevance for the use of continuous-wave laser-actuated cavitation in
needle-free jet injectors as well as other applications of thermocavitation in
microfluidic confinement
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