The biology and evolution of polyspermy: insights from cellular and functional studies of sperm and centrosomal behavior in the fertilized egg

Recent studies of centrosome biogenesis, microtubule dynamics, and their management point to their role in mediating conditions such as aging and cancer. Centrosome dysfunction is also a hallmark of pathological polyspermy. Polyspermy occurs when the oocyte is penetrated by more than one sperm and can be pathological because an excess of centrosomes compromises development. However, in some taxa, multiple sperm enter the egg with no apparent adverse effect on zygote viability. Thus, some taxa can manage excess centrosomes and represent cases of non-pathological polyspermy. While these two forms of polyspermy have long been known, we argue that there is limited understanding of the proximate and ultimate processes that underlie this taxonomic variation in the outcome of polyspermy and that studying this variation could help uncover the control and role(s) of centrosomes during fertilization in particular, but also mitosis in general. To encourage such studies we: 1) describe taxonomic differences in the outcome of polyspermy, 2) discuss mechanistic aspects of reproductive biology that may contribute to the different consequences of polyspermy, and 3) outline the potential selective events that could lead to the evolution of variation in polyspermy outcomes. We suggest that novel insights into centrosome biology may occur by cooperative studies between reproductive and evolutionary biologists focusing on the mechanisms generating variation in the fitness consequences of polyspermy, and in the taxonomic distribution of all these events. The consequent discoveries of these studies may lead to informative insights into cancer and aging along with other centrosome-related diseases and syndromes.     

Evaluation of the effects of oxygen evolution on the capacity and cycle life of nickel hydroxide electrode materials

The effect of charge–discharge cycling on the capacity of surface-adhered nickel hydroxide (Ni(OH)₂) micro-particles is investigated in aqueous KOH by cyclic voltammetry, and compared with that for pasted nickel hydroxide electrodes. Cyclic voltammetry on adhered Ni(OH)₂ micro-particles enables rapid screening of four types of commercially available, battery-grade, nickel hydroxide samples and allows the separation of the oxidation process from the oxygen evolution reaction. With large pasted electrodes, due to their high uncompensated resistance (R_u), these processes are poorly resolved. Pasted β-nickel hydroxide electrodes with a specific capacity of between 190 and 210 mAh g⁻¹ are charged and discharged at constant currents greater than 15 C (18 mA cm⁻²). With no voltage limit in the charging profile, excess oxygen evolution occurs and capacity fading is observed within the first 50 cycles. Loss of capacity is attributed to the degradation of the electrode due to excess oxygen evolution at switching potentials greater than 0.55 V versus Hg/HgO (1 M KOH). X-ray diffraction (XRD) measurements confirm the formation of γ-NiOOH in these electrodes. Limiting the cell voltage to 1.5 V, and thereby minimizing oxygen evolution, results in no observed capacity loss within 100 cycles, and only β-Ni(OH)₂ can be detected by XRD phase analysis.     

Reconstruction and electronic properties of silicon nanosheets as a function of thickness

We have shown, using density functional theory calculations, that the properties of Si nanosheets change as a function of thickness. While Si(111) oriented nanosheets that are 0.56 nm thick (2-layers) display a novel reconstruction, classified as Si(111)-2 × 2 on both surface layers (T. Morishita, M. J. S. Spencer, S. P. Russo, I. K. Snook and M. Mikami, Chem. Phys. Lett., 2011, 506, 221), nanosheets that are up to a thickness of 1.42 nm show the Si(111)-2 × 1 surface reconstruction, that is seen on the bulk Si(111) surface, on both sides of the nanosheet. For these thicker nanosheets, the relative orientation of the π-chain structure on each surface of the nanosheet can either be the same or different, resulting in unique electronic properties. When the orientation is the same, there is a widening of the band gap, indicating that the interaction between the surface π-chains is not present when they are oriented in different directions. The electronic properties of the nanosheets approach those of the bulk by 1.42 nm thick. The variation in structural and electronic properties of Si nanosheets with different thicknesses, as shown in this study, highlights the novelty of these materials and their significance for applications in electronic device technologies.     

High-frequency ultrasound annular array imaging. Part II: digital beamformer design and imaging

This is the second part of a two-paper series reporting a recent effort in the development of a high-frequency annular array ultrasound imaging system. In this paper an imaging system composed of a six-element, 43 MHz annular array transducer, a six-channel analog front-end, a field programmable gate array (FPGA)-based beamformer, and a digital signal processor (DSP) microprocessor-based scan converter will be described. A computer is used as the interface for image display. The beamformer that applies delays to the echoes for each channel is implemented with the strategy of combining the coarse and fine delays. The coarse delays that are integer multiples of the clock periods are achieved by using a first-in-first-out (FIFO) structure, and the fine delays are obtained with a fractional delay (FD) filter. Using this principle, dynamic receiving focusing is achieved. The image from a wire phantom obtained with the imaging system was compared to that from a prototype ultrasonic backscatter microscope with a 45 MHz single-element transducer. The improved lateral resolution and depth of field from the wire phantom image were observed. Images from an excised rabbit eye sample also were obtained, and fine anatomical structures were discerned.