8,090 research outputs found
Differential expression of conserved germ line markers and delayed segregation of male and female primordial germ cells in a hermaphrodite, the leech helobdella.
In sexually reproducing animals, primordial germ cells (PGCs) are often set aside early in embryogenesis, a strategy that minimizes the risk of genomic damage associated with replication and mitosis during the cell cycle. Here, we have used germ line markers (piwi, vasa, and nanos) and microinjected cell lineage tracers to show that PGC specification in the leech genus Helobdella follows a different scenario: in this hermaphrodite, the male and female PGCs segregate from somatic lineages only after more than 20 rounds of zygotic mitosis; the male and female PGCs share the same (mesodermal) cell lineage for 19 rounds of zygotic mitosis. Moreover, while all three markers are expressed in both male and female reproductive tissues of the adult, they are expressed differentially between the male and female PGCs of the developing embryo: piwi and vasa are expressed preferentially in female PGCs at a time when nanos is expressed preferentially in male PGCs. A priori, the delayed segregation of male and female PGCs from somatic tissues and from one another increases the probability of mutations affecting both male and female PGCs of a given individual. We speculate that this suite of features, combined with a capacity for self-fertilization, may contribute to the dramatically rearranged genome of Helobdella robusta relative to other animals
The Entropy Function for the Black Holes of Nariai Class
Based on the fact that the near horizon geometry of the extremal
Schwarzschild-de Sitter black holes is Nariai geometry, we define the black
holes of Nariai class as the configuration whose near-horizon geometry is
factorized as two dimensional de Sitter space-time and some compact topology,
that is Nariai geometry. We extend the entropy function formalism to the case
of the black holes of Nariai class. The conventional entropy function (for the
extremal black holes) is defined as Legendre transformation of Lagrangian
density, thus the `Routhian density', over two dimensional anti-de Sitter. As
for the black holes of Nariai class, it is defined as {\em minus} `Routhian
density' over two dimensional de Sitter space-time. We found an exact agreement
of the result with Bekenstein-Hawking entropy. The higher order corrections are
nontrivial only when the space-time dimension is over four, that is, .
There is a subtlety as regards the temperature of the black holes of Nariai
class. We show that in order to be consistent with the near horizon geometry,
the temperature should be non-vanishing despite the extremality of the black
holes.Comment: references added, compatible with the published versio
Super Jackstraws and Super Waterwheels
We construct various new BPS states of D-branes preserving 8 supersymmetries.
These include super Jackstraws (a bunch of scattered D- or (p,q)-strings
preserving supersymmetries), and super waterwheels (a number of D2-branes
intersecting at generic angles on parallel lines while preserving
supersymmetries). Super D-Jackstraws are scattered in various dimensions but
are dynamical with all their intersections following a common null direction.
Meanwhile, super (p,q)-Jackstraws form a planar static configuration. We show
that the SO(2) subgroup of SL(2,R), the group of classical S-duality
transformations in IIB theory, can be used to generate this latter
configuration of variously charged (p,q)-strings intersecting at various
angles. The waterwheel configuration of D2-branes preserves 8 supersymmetries
as long as the `critical' Born-Infeld electric fields are along the common
direction.Comment: 23 pages, 10 figure
Oblique DLCQ M-theory and Multiple M2-branes
We propose an oblique DLCQ as a limit to realize a theory of multiple
M2-branes in M(atrix)-theory context. The limit is a combination of an infinite
boosting of a space-like circle and a tuned tilting of the circle direction. We
obtain a series of supergravity solutions describing various dual
configurations including multiple M2-branes. For an infinite boosting along a
circle wrapped obliquely around a rectangular torus, Seiberg's DLCQ limit
distorts the torus modulus. In the context of supergravity, we show explicitly
how this torus modulus of -theory is realized as the
vacuum modulus of dual IIB-theory.Comment: v3: 25pages, extended version, References adde
Plasmonic colloidal nanoparticles with open eccentric cavities via acid-induced chemical transformation
Surface-enhanced Raman spectroscopy (SERS) has been considered a promising technique for the detection of trace molecules in biomedicine and environmental monitoring. The ideal metal nanoparticles for SERS must not only fulfill important requirements such as high near-field enhancement and a tunable far-field response but also overcome the diffusion limitation at extremely lower concentrations of a target material. Here, we introduce a novel method to produce gold nanoparticles with open eccentric cavities by selectively adapting the structure of non-plasmonic nanoparticles via acid-mediated surface replacement. Copper oxide nanoparticles with open eccentric cavities are first prepared using a microwave-irradiation-assisted surfactant-free hydrothermal reaction and are then transformed into gold nanoparticles by an acidic gold precursor while maintaining their original structure. Because of the strong near-field enhancement occurring at the mouth of the open cavities and the very rough surfaces resulting from the uniformly covered hyperbranched sharp multi-tips and the free access of SERS molecules inside of the nanoparticles without diffusion limitation, adenine, one of the four bases in DNA, in an extremely diluted aqueous solution (1.0 pM) was successfully detected with excellent reproducibility upon laser excitation with a 785-nm wavelength. The gold nanoparticles with open eccentric cavities provide a powerful platform for the detection of ultra-trace analytes in an aqueous solution within near-infrared wavelengths, which is essential for highly sensitive, reliable and direct in vivo analysis.None1132sciescopu
Optimal deployments of defense mechanisms for the internet of things
Internet of Things (IoT) devices can be exploited by the attackers as entry points to break into the IoT networks without early detection. Little work has taken hybrid approaches that combine different defense mechanisms in an optimal way to increase the security of the IoT against sophisticated attacks. In this work, we propose a novel approach to generate the strategic deployment of adaptive deception technology and the patch management solution for the IoT under a budget constraint. We use a graphical security model along with three evaluation metrics to measure the effectiveness and efficiency of the proposed defense mechanisms. We apply the multi-objective genetic algorithm (GA) to compute the {\em Pareto optimal} deployments of defense mechanisms to maximize the security and minimize the deployment cost. We present a case study to show the feasibility of the proposed approach and to provide the defenders with various ways to choose optimal deployments of defense mechanisms for the IoT. We compare the GA with the exhaustive search algorithm (ESA) in terms of the runtime complexity and performance accuracy in optimality. Our results show that the GA is much more efficient in computing a good spread of the deployments than the ESA, in proportion to the increase of the IoT devices
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