Design of a Low Power 64 Point FFT Architecture for WLAN Applications

This paper presents a Radix-4(3) based FFT architecture suitable for OFDM based WLAN applications. The radix-4(3) parallel unrolled architecture presented here, uses a radix-4 butterfly unit which takes all four inputs in parallel and can selectively produce one out of the four outputs. A 64 point FFT processor based on the proposed architecture has been implemented in UMC 130nm 1P8M CMOS process with a maximum clock frequency of 100 MHz and area of 0.83mm(2). The proposed processor provides a throughput of four times the clock rate and can finish one 64 point FFT computation in 16 clock cycles. For IEEE 802.11a/g WLAN, the processor needs to be operated at a clock rate of 5 MHz with a power consumption of 2.27 mW which is 27% less than the previously reported low power implementations.

IS A DEEP ONE-CELL MERIDIONAL CIRCULATION ESSENTIAL FOR THE FLUX TRANSPORT SOLAR DYNAMO?

The solar activity cycle is successfully modeled by the flux transport dynamo, in which the meridional circulation of the Sun plays an important role. Most of the kinematic dynamo simulations assume a one-cell structure of the meridional circulation within the convection zone, with the equatorward return flow at its bottom. In view of the recent claims that the return flow occurs at a much shallower depth, we explore whether a meridional circulation with such a shallow return flow can still retain the attractive features of the flux transport dynamo (such as a proper butterfly diagram, the proper phase relation between the toroidal and poloidal fields). We consider additional cells of the meridional circulation below the shallow return flow-both the case of multiple cells radially stacked above one another and the case of more complicated cell patterns. As long as there is an equatorward flow in low latitudes at the bottom of the convection zone, we find that the solar behavior is approximately reproduced. However, if there is either no flow or a poleward flow at the bottom of the convection zone, then we cannot reproduce solar behavior. On making the turbulent diffusivity low, we still find periodic behavior, although the period of the cycle becomes unrealistically large. In addition, with a low diffusivity, we do not get the observed correlation between the polar field at the sunspot minimum and the strength of the next cycle, which is reproduced when diffusivity is high. On introducing radially downward pumping, we get a more reasonable period and more solar-like behavior even with low diffusivity.

Structure of an amidohydrolase, SACOL0085, from methicillin-resistant Staphylococcus aureus COL

Staphylococcus aureus is an opportunistic pathogen that rapidly acquires resistance to frontline antibiotics. The characterization of novel protein targets from this bacterium is thus an important step towards future therapeutic strategies. Here, the crystal structure of an amidohydrolase, SACOL0085, from S. aureus COL is described. SACOL0085 is a member of the M20D family of peptidases. Unlike other M20D peptidases, which are either monomers or dimers, SACOL0085 adopts a butterfly-shaped homotetrameric arrangement with extensive intersubunit interactions. Each subunit of SACOL0085 contains two Mn2+ ions at the active site. A conserved cysteine residue at the active site distinguishes M20D peptidases from other M20 family members. This cysteine, Cys103, serves as bidentate ligand coordinating both Mn2+ ions in SACOL0085.

Does size matter? Comparative population genetics of two butterflies with different wingspans

The dispersal ability of a species is central to its biology, affecting other processes like local adaptation, population and community dynamics, and genetic structure. Among the intrinsic, species-specific factors that affect dispersal ability in butterflies, wingspan was recently shown to explain a high amount of variance in dispersal ability. In this study, a comparative approach was adopted to test whether a difference in wingspan translates into a difference in population genetic structure. Two closely related butterfly species from subfamily Satyrinae, family Nymphalidae, which are similar with respect to all traits that affect dispersal ability except for wingspan, were studied. Melanitis leda (wingspan 60-80 mm) and Ypthima baldus (wingspan 30-40 mm) were collected from the same areas along the Western Ghats of southern India. Amplified fragment length polymorphisms were used to test whether the species with a higher wingspan (M. leda) exhibited a more homogenous population genetic structure, as compared to a species with a shorter wingspan (Y. baldus). In all analyses, Y. baldus exhibited greater degree of population genetic structuring. This study is one of the few adopting a comparative approach to establish the relationship between traits that affect dispersal ability and population genetic structure.

Genetic analysis of Indian tasar silkmoth (Antheraea mylitta) populations

Indian tasar silkmoth, Antheraea mylitta is an economically important wild silkmoth species distributed across India. A number of morphologically and ethologically well-defined ecotypes are known for this species that differ in their primary food plant specificity. Most of these ecotypes do not interbreed in nature, but are able to produce offspring under captive conditions. Microsatellite markers were developed for A. mylitta, and out of these, ten well-behaved microsatellite loci were used to analyze the population structure of different ecoraces. A total of 154 individual moths belonging to eight different ecoraces, were screened at each locus. Hierarchical analysis of population structure using Analysis of MOlecular VAriance (AMOVA) revealed significant structuring (F-ST = 0.154) and considerable inbreeding (F-IS = 0.505). A significant isolation by distance was also observed. The number of possible population clusters was investigated using distance method, Bayesian algorithm and self organization maps (SOM). The first two methods revealed two distinct clusters, whereas the SOM showed the different ecoraces not to be clearly differentiated. These results suggest that although there is a large degree of phenotypic variation among the different ecoraces of A. mylitta, genetically they are not very different, and the phenotypic differences may largely be a result of their respective ecology.