We report on a first principles theory for analyzing the parametric electron pump at a finite frequency. The pump is controlled by two pumping parameters with phase difference φ. In the zero frequency limit, our theory predicts the well known result that the pumped current is proportional to sin φ. For the more general situation of a finite frequency, our theory predicts a non-vanishing pumped current even when the two driving forces are in phase, in agreement with the recent experimental results. We present the physical mechanism behind the nonzero pumped current at φ = 0, which we found to be due to photon-assisted processes.73.23. Ad,73.40.Gk,72.10.Bg Parametric electron pump 1-7 is an interesting device which delivers a finite DC current to the outside world at zero bias potential, by cyclic variations of two device control parameters. Recently, an adiabatic quantum electron pump was reported in an open quantum dot where the pumping signal was produced in response to the cyclic deformation of the confining potential 2 . It was found that the pumping signal, V dot (φ), is sinusoidal in the phase difference φ between the two deforming potentials in the weak pumping regime, and it becomes non-sinusoidal in the strong pumping regime. The amplitude of the pumping signal increases linearly with the frequency of the deformation. Most notable, however, was the data 2 showing V dot (0) = 0 significantly at strong pumping, whereas V dot (π) ≈ 0 for all pumping strength. Even in the weaker pumping regime, small deviations from V dot (0) = 0 could already be seen 2 . The traditional and successful parametric pumping theory 3,4 , valid in the adiabatic regime and up to first order in frequency, requires two pumping parameters which traverse in a closed path in parameter space in each cyclic period and the pumping signal is proportional to the enclosed area by the path. Accordingly, if the two pumping parameters are in phase so that the enclosed area is zero, the pumping signal V dot (0) should vanish. It is extremely puzzling that the experimental data 2 consistently showed V dot (0) = 0, a fact which has not been understood so far, and, clearly, it calls for the development of a first principle theory going beyond the adiabatic regime and low frequencies.It is the purpose of this letter to present a theory for parametric pumping which is valid at finite frequency. Using this theory we investigate the frequency dependence of the pumping current I p (φ) = G dot V dot (φ) with G dot a constant, and it allows us to understand why it is possible to have a pumping signal even when the pumping forces are exactly in-phase. When frequency is low, our theory recovers the traditional results 3,4 . As the frequency increases, we predict a nonzero I p (0) which is a consequence of photon assisted processes, and our theory also predicts I p (π) ≈ 0. These results allows us to reach the conclusion that the experimental data 2 showing V dot (0) = 0 and V dot (π) ≈ 0, are generic nonlinear transport features of parametric pumps at fi...
A physically based energy-balance model with improved parameterization of solar radiation for a sloped ice surface has been developed to estimate the backwasting rate of an ice cliff in a debris-covered area. The model has been tested against observations between 5 August and 5 September 2008 on 38 ice cliffs in the debris-covered area of Koxkar glacier, Tuomuer mountain, China. We calculated that the energy-balance model gave a good estimate of the backwasting rates, with errors in the range ±1.96 cm d−1 and root-mean-square errors of 0.99 cm d−1. Errors arising from setting of surface albedo and turbulent flux parameterization were limited. We found that shortwave radiation is the most important heat source for ice-cliff ablation, contributing about 76% of the total heat available for ice melt, while the sensible heat flux provides nearly 24% of the total heat for ice-cliff wastage. The latent heat flux and net longwave radiation are comparatively small according to the model calculation. The mean backwasting rate of ice cliffs in the debris-covered area of Koxkar glacier is estimated at 7.64 m a−1 when the winter ablation is neglected. With this annual backwasting rate and given a mean slope angle of 46.4°, the backwasting of ice cliffs produces about 1.60 × 106 m3 of meltwater, accounting for about 7.3% of the total melt runoff from the debris-covered area.
In wheat (Triticum aestivum L), the leaves particularly flag leaves have been considered to be the key organs contributing to higher yields, whereas awns have been considered subsidiary organs. Compared with extensive investigations on the assimilation contribution of leaves, the photosynthetic characteristics of awns have not been well studied. In this study, we investigated the ultrastructure of chloroplasts, oxygen evolution, and phosphoenolpyruvate carboxylase [phosphoenolpyruvate carboxylase (PEPCase) EC 4.1.1.31)] activity in both flag leaves and awns during the ontogenesis of wheat. Transmission electron microscope observations showed initial increases in the sizes of grana and the degree of granum stacks from the florescenceemergence stage both in flag leaves and in awns, followed by the breakdown of membrane systems after the milk-development stage. The results of oxygen evolution assays revealed that in both organs, the rate of photosynthesis increased in the first few stages and then decreased, but the decrease occurred much earlier in flag leaves than in awns. A PEPCase activity assay demonstrated that the activity of PEPCase was much higher in awns than in flag leaves throughout ontogeny; the value was particularly high at the late stages of grain filling. Our results suggest that awns play a dominant role in contributing to large grains and a high grain yield in awned wheat cultivars, particularly during the grain-filling stages.
A late Middle Pleistocene mandible from Baishiya Karst Cave (BKC) on the Tibetan Plateau has been inferred to be from a Denisovan, an Asian hominin related to Neanderthals, on the basis of an amino acid substitution in its collagen. Here we describe the stratigraphy, chronology, and mitochondrial DNA extracted from the sediments in BKC. We recover Denisovan mitochondrial DNA from sediments deposited ~100 thousand and ~60 thousand years ago (ka) and possibly as recently as ~45 ka. The long-term occupation of BKC by Denisovans suggests that they may have adapted to life at high altitudes and may have contributed such adaptations to modern humans on the Tibetan Plateau.
The phylum Actinobacteria has been reported to be common or even abundant in deep marine sediments, however, knowledge about the diversity, distribution, and function of actinobacteria is limited. In this study, actinobacterial diversity in the deep sea along the Southwest Indian Ridge (SWIR) was investigated using both 16S rRNA gene pyrosequencing and culture-based methods. The samples were collected at depths of 1662–4000 m below water surface. Actinobacterial sequences represented 1.2–9.1% of all microbial 16S rRNA gene amplicon sequences in each sample. A total of 5 actinobacterial classes, 17 orders, 28 families, and 52 genera were detected by pyrosequencing, dominated by the classes Acidimicrobiia and Actinobacteria. Differences in actinobacterial community compositions were found among the samples. The community structure showed significant correlations to geochemical factors, notably pH, calcium, total organic carbon, total phosphorus, and total nitrogen, rather than to spatial distance at the scale of the investigation. In addition, 176 strains of the Actinobacteria class, belonging to 9 known orders, 18 families, and 29 genera, were isolated. Among these cultivated taxa, 8 orders, 13 families, and 15 genera were also recovered by pyrosequencing. At a 97% 16S rRNA gene sequence similarity, the pyrosequencing data encompassed 77.3% of the isolates but the isolates represented only 10.3% of the actinobacterial reads. Phylogenetic analysis of all the representative actinobacterial sequences and isolates indicated that at least four new orders within the phylum Actinobacteria were detected by pyrosequencing. More than half of the isolates spanning 23 genera and all samples demonstrated activity in the degradation of refractory organics, including polycyclic aromatic hydrocarbons and polysaccharides, suggesting their potential ecological functions and biotechnological applications for carbon recycling.
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