Penis-rejection in a mangrove littorinid snail: why do females reject males?

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Temporal genetic variation in populations of the limpet Cellana grata from Hong Kong shores

Variations in the relative contributions of gene flow and spatial and temporal variation in recruitment are considered the major determinants of population genetic structure in marine organisms. Such variation can be assessed through repeated measures of the genetic structure of a species over time. To test the relative importance of these two phenomena, temporal variation in genetic composition was measured in the limpet Cellana grata, among four annual cohorts over 10 years at four rocky shores in Hong Kong. A total of 408 limpets, comprising individuals from 1998, 1999, 2006 and 2007 cohorts were screened for genetic variation using five microsatellite loci. Minor but significant genetic differentiation was detected among samples from the 1998/1999 collection (FST = 0.0023), but there was no significant differentiation among the 2006/2007 collection (FST = 0.0008). Partitioning of genetic variation among shores was also significant in 1998/1999 but not in the 2006/2007 collection, although there was no correlation between genetic and geographic distances. There was no significant difference between collections made in 1998/1999 and 2006/2007. This lack of clear structure implies a high level of gene flow, but differentiation with time may be the result of stochastic recruitment variation among shores. Estimates of effective population size were not high (599, 95% C. L. 352-11397), suggesting the potential susceptibility of the populations to genetic drift, although a significant bottleneck effect was not detected. These findings indicate that genetic structuring between populations of C. grata in space and time may result from spatio-temporal variation in recruitment, but the potential development of biologically significant differentiation is suppressed by a lack of consistency in recruitment variability and high connectivity among shores. © Springer-Verlag 2009.postprin

Aerothermodynamic Analysis of a Reentry Brazilian Satellite

This work deals with a computational investigation on the small ballistic reentry Brazilian vehicle SARA (acronyms for SAt\'elite de Reentrada Atmosf\'erica). Hypersonic flows over the vehicle SARA at zero-degree angle of attack in a chemical equilibrium and thermal non-equilibrium are modeled by the Direct Simulation Monte Carlo (DSMC) method, which has become the main technique for studying complex multidimensional rarefied flows, and that properly accounts for the non-equilibrium aspects of the flows. The emphasis of this paper is to examine the behavior of the primary properties during the high altitude portion of SARA reentry. In this way, velocity, density, pressure and temperature field are investigated for altitudes of 100, 95, 90, 85 and 80 km. In addition, comparisons based on geometry are made between axisymmetric and planar two-dimensional configurations. Some significant differences between these configurations were noted on the flowfield structure in the reentry trajectory. The analysis showed that the flow disturbances have different influence on velocity, density, pressure and temperature along the stagnation streamline ahead of the capsule nose. It was found that the stagnation region is a thermally stressed zone. It was also found that the stagnation region is a zone of strong compression, high wall pressure. Wall pressure distributions are compared with those of available experimental data and good agreement is found along the spherical nose for the altitude range investigated.Comment: The paper will be published in Vol. 42 of the Brazilian Journal of Physic

Nonideality-aware training for accurate and robust low-power memristive neural networks

Recent years have seen a rapid rise of artificial neural networks being employed in a number of cognitive tasks. The ever-increasing computing requirements of these structures have contributed to a desire for novel technologies and paradigms, including memristor-based hardware accelerators. Solutions based on memristive crossbars and analog data processing promise to improve the overall energy efficiency. However, memristor nonidealities can lead to the degradation of neural network accuracy, while the attempts to mitigate these negative effects often introduce design trade-offs, such as those between power and reliability. In this work, we design nonideality-aware training of memristor-based neural networks capable of dealing with the most common device nonidealities. We demonstrate the feasibility of using high-resistance devices that exhibit high $I$-$V$ nonlinearity -- by analyzing experimental data and employing nonideality-aware training, we estimate that the energy efficiency of memristive vector-matrix multipliers is improved by three orders of magnitude ($0.715\ \mathrm{TOPs}^{-1}\mathrm{W}^{-1}$ to $381\ \mathrm{TOPs}^{-1}\mathrm{W}^{-1}$) while maintaining similar accuracy. We show that associating the parameters of neural networks with individual memristors allows to bias these devices towards less conductive states through regularization of the corresponding optimization problem, while modifying the validation procedure leads to more reliable estimates of performance. We demonstrate the universality and robustness of our approach when dealing with a wide range of nonidealities

Research on human immunodeficiency virus (HIV) in Malawi: the Johns Hopkins University- Ministry of Health (JHU-MOH) project

No Abstrac

Optimally combining dynamical decoupling and quantum error correction

We show how dynamical decoupling (DD) and quantum error correction (QEC) can be optimally combined in the setting of fault tolerant quantum computing. To this end we identify the optimal generator set of DD sequences designed to protect quantum information encoded into stabilizer subspace or subsystem codes. This generator set, comprising the stabilizers and logical operators of the code, minimizes a natural cost function associated with the length of DD sequences. We prove that with the optimal generator set the restrictive local-bath assumption used in earlier work on hybrid DD-QEC schemes, can be significantly relaxed, thus bringing hybrid DD-QEC schemes, and their potentially considerable advantages, closer to realization.Comment: 6 pages, 1 figur

Membrane-containing virus particles exhibit the mechanics of a composite material for genome protection

The protection of the viral genome during extracellular transport is an absolute requirement for virus survival and replication. In addition to the almost universal proteinaceous capsids, certain viruses add a membrane layer that encloses their double-stranded (ds) DNA genome within the protein shell. Using the membrane-containing enterobacterial virus PRD1 as a prototype, and a combination of nanoindentation assays by atomic force microscopy and finite element modelling, we show that PRD1 provides a greater stability against mechanical stress than that achieved by the majority of dsDNA icosahedral viruses that lack a membrane. We propose that the combination of a stiff and brittle proteinaceous shell coupled with a soft and compliant membrane vesicle yields a tough composite nanomaterial well-suited to protect the viral DNA during extracellular transport

A comprehensive literature review of marine biodiversity in Hong Kong

Oral PresentationBiodiversity and Mammal ConservationWith the implementation of the Convention on Biodiversity (CBD), local and regional species inventories are becoming increasingly important for biodiversity assessments, marine resource monitoring and management, yet such inventories are often incomplete or compromised by not being updated by experts. The South China Sea, for example, is among the world's most species-rich marine areas but it is also one of the areas where species information is poorly categorized. Hong Kong's marine biota is relatively well explored and documented among the South China Sea region, and this study integrates most available species information to construct a species inventory. The coastline of Hong Kong is characterized by a range of diverse habitats such as ...postprin

Axisymmetric Waves in Layered Anisotropic Fibers and Composites

The complicated morphology of the new generation of advanced fibrous composites gave further impetus to the study of the interaction of ultrasonic waves with multilayered concentric cylindrical systems. Typically, the fiber consists of a cylindrical core embedded in a cladding region followed by a distinct interface zone separating the fiber system from the host (matrix) region. In addition, the cladding region itself often consists of subregions which can be identified as distinct layers. Each individual layer can posses certain degree of microscopic anisotropy adding to the macroscopic anisotropy produced by the presence of layering and imperfect interfaces. Relatively few efforts have been spent upon the study of free and immersed homogeneous anisotropic rods [1–5]. These works are insufficient to model real situations encountered in materials characterization of advanced fibrous composites. In order to better model advanced fibrous composites at least three major effects need to be accounted for. These are the inhomogeneous nature of the structure as reflected in its multilayering, the inherent microscopic anisotropy of some of the constituents and finally the quality of the interfaces. In this paper we briefly describe a unified analytical treatment of wave propagation along the fiber direction of multilayered coaxial fibrous systems embedded in a host material. A more detailed discussion of this general treatment will be presented elsewhere [6]. Figure 1 shows typical geometric situations including (a) a single multilayered fiber, (b) a single multilayered fiber either immersed in an infinite fluid or embedded in an infinite solid, and an infinite composite material with periodically distributed multilayered fiber