Determination of step rate thresholds corresponding to physical activity intensity classifications in adults

Current recommendations call for adults to be physically active at moderate and/or vigorous intensities. Given the popularity of walking and running, the use of step rates may provide a practical and inexpensive means to evaluate ambulatory intensity. Thus, the purpose of this study was to identify step rate thresholds that correspond to various intensity classifications. Methods: Oxygen consumption was measured at rest and during 10 minute treadmill walking and running trials at 6 standardized speeds (54, 80, 107, 134, 161, and 188 m∙min-1) in 9 men and 10 women (28.8 ± 6.8 yrs). Two observers counted the participants’ steps at each treadmill speed. Linear and nonlinear regression analyses were used to develop prediction equations to ascertain step rate thresholds at various intensities. Results: Nonlinear regression analysis of the metabolic cost versus step rates across all treadmill speeds yielded the highest R2 values for men (R2 = .91) and women (R2 = .79). For men, the nonlinear analysis yielded 94 and 125 step∙min-1 for moderate and vigorous intensities, respectively. For women, 99 and 135 step∙min-1 corresponded with moderate and vigorous intensities, respectively. Conclusions: Promoting a step rate of 100 step∙min-1 may serve as a practical public health recommendation to exercise at moderate intensity

Electron Capture Dissociation Mass Spectrometry of Metallo-Supramolecular Complexes

The electron capture dissociation (ECD) of metallo-supramolecular dinuclear triple-stranded helicate Fe2L3 4 ions was determined by Fourier transform ion cyclotron resonance mass spectrometry. Initial electron capture by the di-iron(II) triple helicate ions produces dinuclear double-stranded complexes analogous to those seen in solution with the monocationic metal centers CuI or AgI. The gas-phase fragmentation behavior [ECD, collision-induced dissociation (CID), and infrared multiphoton dissociation (IRMPD)] of the di-iron double-stranded complexes, (i.e., MS3 of the ECD product) was compared with the ECD, CID, and IRMPD of the CuI and AgI complexes generated from solution. The results suggest that iron-bound dimers may be of the formFeI 2L2 2 and that ECD by metallo-complexes allows access, in the gas phase,to oxidation states and coordination chemistry that cannot be accessed in solution

AlGaAs top solar cell for mechanical attachment in a multi-junction tandem concentrator solar cell stack

The AstroPower self-supporting, transparent AlGaAs top solar cell can be stacked upon any well-developed bottom solar cell for improved system performance. This is an approach to improve the performance and scale of space photovoltaic power systems. Mechanically stacked tandem solar cell concentrator systems based on the AlGaAs top concentrator solar cell can provide near term efficiencies of 36 percent (AMO, 100x). Possible tandem stack efficiencies greater than 38 percent (100x, AMO) are feasible with a careful selection of materials. In a three solar cell stack, system efficiencies exceed 41 percent (100x, AMO). These device results demonstrate a practical solution for a state-of-the-art top solar cell for attachment to an existing, well-developed solar cell

Suppression of prion protein in livestock by RNA interference

Given the difficulty of applying gene knockout technology to species other than mice, we decided to explore the utility of RNA interference (RNAi) in silencing the expression of genes in livestock. Short hairpin RNAs (shRNAs) were designed and screened for their ability to suppress the expression of caprine and bovine prion protein (PrP). Lentiviral vectors were used to deliver a transgene expressing GFP and an shRNA targeting PrP into goat fibroblasts. These cells were then used for nuclear transplantation to produce a cloned goat fetus, which was surgically recovered at 81 days of gestation and compared with an age-matched control derived by natural mating. All tissues examined in the cloned fetus expressed GFP, and PCR analysis confirmed the presence of the transgene encoding the PrP shRNA. Most relevant, Western blot analysis performed on brain tissues comparing the transgenic fetus with control demonstrated a significant (>90%) decrease in PrP expression levels. To confirm that similar methodologies could be applied to the bovine, recombinant virus was injected into the perivitelline space of bovine ova. After in vitro fertilization and culture, 76% of the blastocysts exhibited GFP expression, indicative that they expressed shRNAs targeting PrP. Our results provide strong evidence that the approach described here will be useful in producing transgenic livestock conferring potential disease resistance and provide an effective strategy for suppressing gene expression in a variety of large-animal models

An epigenetic role for maternally inherited piRNAs in transposon silencing

In plants and mammals, small RNAs indirectly mediate epigenetic inheritance by specifying cytosine methylation. We found that small RNAs themselves serve as vectors for epigenetic information. Crosses between Drosophila strains that differ in the presence of a particular transposon can produce sterile progeny, a phenomenon called hybrid dysgenesis. This phenotype manifests itself only if the transposon is paternally inherited, suggesting maternal transmission of a factor that maintains fertility. In both P- and I-element-mediated hybrid dysgenesis models, daughters show a markedly different content of Piwi-interacting RNAs (piRNAs) targeting each element, depending on their parents of origin. Such differences persist from fertilization through adulthood. This indicates that maternally deposited piRNAs are important for mounting an effective silencing response and that a lack of maternal piRNA inheritance underlies hybrid dysgenesis

A genome-wide RNAi screen identifies factors required for distinct stages of C-elegans piRNA biogenesis

In animals, piRNAs and their associated Piwi proteins guard germ cell genomes against mobile genetic elements via an RNAi-like mechanism. In Caenorhabditis elegans, 21U-RNAs comprise the piRNA class, and these collaborate with 22G RNAs via unclear mechanisms to discriminate self from nonself and selectively and heritably silence the latter. Recent work indicates that 21U-RNAs are post-transcriptional processing products of individual transcription units that produce similar to 26-nucleotide capped precursors. However, nothing is known of how the expression of precursors is controlled or how primary transcripts give rise to mature small RNAs. We conducted a genome-wide RNAi screen to identify components of the 21U biogenesis machinery. Screening by direct, quantitative PCR (qPCR)-based measurements of mature 21U-RNA levels, we identified 22 genes important for 21U-RNA production, termed TOFUs (Twenty-One-u Fouled Ups). We also identified seven genes that normally repress 21U production. By measuring mature 21U-RNA and precursor levels for the seven strongest hits from the screen, we assigned factors to discrete stages of 21U-RNA production. Our work identifies for the first time factors separately required for the transcription of 21U precursors and the processing of these precursors into mature 21U-RNAs, thereby providing a resource for studying the biogenesis of this important small RNA class

Molecular Dynamics Simulation of Compressible Fluid Flow in Two-Dimensional Channels

We study compressible fluid flow in narrow two-dimensional channels using a novel molecular dynamics simulation method. In the simulation area, an upstream source is maintained at constant density and temperature while a downstream reservoir is kept at vacuum. The channel is sufficiently long in the direction of the flow that the finite length has little effect on the properties of the fluid in the central region. The simulated system is represented by an efficient data structure, whose internal elements are created and manipulated dynamically in a layered fashion. Consequently the code is highly efficient and manifests completely linear performance in simulations of large systems. We obtain the steady-state velocity, temperature, and density distributions in the system. The velocity distribution across the channel is very nearly a quadratic function of the distance from the center of the channel and reveals velocity slip at the boundaries; the temperature distribution is only approximately a quartic function of this distance from the center to the channel. The density distribution across the channel is non-uniform. We attribute this non-uniformity to the relatively high Mach number, approximately 0.5, in the fluid flow. An equation for the density distribution based on simple compressibility arguments is proposed; its predictions agree well with the simulation results. Validity of the concept of local dynamic temperature and the variation of the temperature along the channel are discussed.Comment: 16 pages (in latex) + 8 figures (in a single ps file). Submitted to the Physical Review

Chemistry and structure by design: ordered CuNi(CN)4 sheets with copper(II) in a square-planar environment

Layered copper–nickel cyanide, CuNi(CN)4, a 2-D negative thermal expansion material, is one of a series of copper(II)-containing cyanides derived from Ni(CN)2. In CuNi(CN)4, unlike in Ni(CN)2, the cyanide groups are ordered generating square-planar Ni(CN)4 and Cu(NC)4 units. The adoption of square-planar geometry by Cu(II) in an extended solid is very unusual