Improvements in electrodeposited Cu2O as the wide bandgap cell for a tandem solar architecture

Paper presented to the 3rd Southern African Solar Energy Conference, South Africa, 11-13 May, 2015.Cuprous oxide is a well-known wide-bandgap material with Egap commonly reported around 2.0 eV, but with some reports ranging from 1.7eV to 2.5eV. With a bandgap around 2.0 eV it is a great candidate for the top cell of a stack tandem architecture paired with a bottom silicon cell. However the actual reported efficiencies of single junction devices are usually much lower than would be expected, probably rooted in possible defects, nonstoichiometry or microstructural flaws. We report on electrodeposited thin films and their growth modes under different conditions. Microstructural improvements have been made using seeding layers before electrodeposition; these are mainly focused on growing columnar shaped grains. Cu2O that has been electrodeposited has a flowering or dendritic microstructure. When the electrodeposition is seeded appropriately the dendrite arms from the flower no longer grow resulting in nicely faceted grains and a columnar shape. This well-crystallized columnar structure is meant to increase the hole collection length by avoiding recombination at grain boundary defects as a means of increasing the efficiency. Seeding the growth on the films has resulted in Cu2O films that are more controllable in the electrodeposition process, with a more consistent grain orientation. SEM and XRD analysis were performed to show these results.cf201

Migration efficiency of paired sperm in the tract of the peri-ovulatory female grey short-tailed opossum (Monodelphis domestica)

American marsupials are the only mammals known to ejaculate paired spermatozoa, which confer a motility advantage in vitro over single spermatozoa in viscous environments. In the only American marsupial examined, the Virginian opossum (Didelphidae), relatively low numbers of spermatozoa are ejaculated (106), but transport is extremely efficient with ~1 in 20 spermatozoa reaching the site of fertilization compared to ~1 in 10,000 in the rabbit. This study examined the post-copulatory distribution and state (paired or single) of spermatozoa at various times in the female reproductive tract of another didelphid, the polyovular grey short-tailed opossum (Monodelphis domestica). After a single mating, the reproductive tracts of 19 females were dissected at 0.5 (n=4), 6 (n=4), 12 (n=3), 18 (n=3) and 24h (n=5) post coitum (p.c.). Each tract was dissected into 8 major anatomical sections and spermatozoa were recovered by flushing. Mating occurred 5.4 ± 0.4d (mean ± SEM; n=19) after pairing, copulation lasted 4.4 ± 0.2 min (n=18) and ovulation occurred 18.0 - 24.1h p.c. (n=5). Shortly after mating (0.5h p.c.) the tract contained 1.2 ± 0.2g of seminal gel (n=2) and 2.0 ± 1.3 x106 spermatozoa (n=3; 38% of which were paired) found predominantly in the anterior vaginal culs de sac. A uterine sperm reservoir was never observed, but spermatozoa reached the isthmus and ampulla within 6 and 18h p.c. respectively. Paired spermatozoa localized almost exclusively in the isthmus from 6h p.c., and pairing decreased to only 4% of the total sperm population in the tract by the start of ovulation. In total ~1 in 300 ejaculated spermatozoa (~6.5 x103; n=9) reached the oviduct. In conclusion, sperm pairing appears to confer effective colonization of the isthmus in M. domestica and, like the Virginian opossum, transport of spermatozoa is relatively efficient

Questionnaire identifying management practices surrounding calving on spring-calving dairy farms and their associations with herd size and herd expansion

peer-reviewedHealthy calves are fundamental to any profitable dairy enterprise. Research to-date, has focused on year-round calving systems which experience many different challenges compared to spring-calving systems. The objective of the present study was to determine the on-farm dry cow, calving, and colostrum management practices of spring-calving dairy production systems, and quantify their associations with herd size and herd expansion status (i.e. expanding or not expanding). Information on these management practices was available from a survey of 262 Irish spring-calving dairy farmers, representative of the Irish national population. Herd expansion in the 2 years before, and the year that the survey was conducted was not associated with any of the management practices investigated. Fifty-three percent of respondents had an average calving season length of 10 to14 weeks with 35% of herds having a longer calving season. Previous research in cattle has documented that both colostrum source and feeding management are associated with the transmission of infectious disease from cow to calf. In the present study 60% of respondents fed calves colostrum from their own dam; however, 66% of those respondents allowed the calf to suckle the dam, 23% of survey respondents fed calves pooled colostrum. Larger herds were more likely (P<0.01) to use pooled colostrum supplies, while smaller herds were more likely (P<0.05) to allow the calf to suckle the dam. The majority (86%) of respondents had stored supplies of colostrum; average-sized herds had the greatest likelihood of storing colostrum (P<0.05), compared to other herd sizes; larger sized herds had a lesser likelihood (P<0.05) of storing colostrum in a freezer, compared to other herd sizes. Although freezing colostrum was the most common method used to store colostrum (54% of respondents), 17% of respondents stored colostrum at room temperature, 29% of which stored it at room temperature for greater than 4 days. The results from the present study indicate that a particular focus needs to be placed on calving and colostrum management because this study has highlighted a number of areas which are below international standards, and may have repercussions for calf health. Furthermore, management practices on larger farms could be improved and, as these represent the future of dairy farming, a focus needs to be placed on them. Expanding herds are not a particular concern as herd expansion, independent of herd size, does not seem to be associated with calving and colostrum management practices on Irish spring-calving dairy herds

The effect of colostrum storage conditions on dairy heifer calf serum immunoglobulin G concentration and preweaning health and growth rate

peer-reviewedThe objective of the present study was to compare serum IgG concentration, weight gain, and health characteristics in Irish spring-born dairy calves fed colostrum stored using a range of conditions. Immediately after birth, 75 dairy heifer calves were assigned to 1 of 5 experimental colostrum treatments: (1) fresh pasteurized colostrum, fed immediately after pasteurization; (2) fresh colostrum, fed immediately after collection but not pasteurized; (3) colostrum stored unpasteurized at 4°C in a temperature-controlled unit for 2d before being fed to calves; (4) colostrum stored unpasteurized at 13°C in a temperature-controlled unit for 2d before being fed to calves; and (5) colostrum stored unpasteurized at 22°C in a temperature-controlled unit for 2d before being fed to calves. All colostrum had IgG concentrations >50g/L and was fed to calves promptly after birth. Blood samples were obtained from calves via the jugular vein at 0h (before colostrum feeding) and at 24h of age to determine the rate of passive transfer of IgG; individual calf live-weights were recorded to monitor weight gain (kg/d) from birth to weaning. Colostrum stored in warmer conditions (i.e., 22°C) had >42 times more bacteria present and a pH that was 0.85 units lower and resulted in a serum IgG concentration that was almost 2 times lower compared with colostrum that was pasteurized, untreated, or stored at 4°C for 2d. Colostrum stored at 4°C for 2d had more bacteria present than pasteurized and fresh colostrum but did not result in reduced calf serum IgG concentrations. Average daily weight gain from birth to weaning did not differ among treatments. Even if colostrum has sufficient IgG (>50g/L) but cannot be fed to calves when freshly collected, storage at ≤4°C for 2d is advisable to ensure adequate passive transfer when it is consumed by the calf

Blue carbon as a natural climate solution

Blue carbon ecosystems (BCEs), including mangrove forests, seagrass meadows and tidal marshes, store carbon and provide co-benefits such as coastal protection and fisheries enhancement. Blue carbon sequestration has therefore been suggested as a natural climate solution. In this Review, we examine the potential for BCEs to act as carbon sinks and the opportunities to protect or restore ecosystems for this function. Globally, BCEs are calculated to store \u3e 30,000 Tg C across ~185 million ha, with their conservation potentially avoiding emissions of 304 (141–466) Tg carbon dioxide equivalent (CO2e) per year. Potential BCE restoration has been estimated in the range of 0.2–3.2 million ha for tidal marshes, 8.3–25.4 million ha for seagrasses and 9–13 million ha for mangroves, which could draw down an additional 841 (621–1,064) Tg CO2e per year by 2030, collectively amounting to ~3% of global emissions (based on 2019 and 2020 global annual fossil fuel emissions). Mangrove protection and/or restoration could provide the greatest carbon-related benefits, but better understanding of other BCEs is needed. BCE destruction is unlikely to stop fully, and not all losses can be restored. However, engineering and planning for coastal protection offer opportunities for protection and restoration, especially through valuing co-benefits. BCE prioritization is potentially a cost-effective and scalable natural climate solution, but there are still barriers to overcome before blue carbon project adoption will become widespread

The spectral gap for some spin chains with discrete symmetry breaking

We prove that for any finite set of generalized valence bond solid (GVBS) states of a quantum spin chain there exists a translation invariant finite-range Hamiltonian for which this set is the set of ground states. This result implies that there are GVBS models with arbitrary broken discrete symmetries that are described as combinations of lattice translations, lattice reflections, and local unitary or anti-unitary transformations. We also show that all GVBS models that satisfy some natural conditions have a spectral gap. The existence of a spectral gap is obtained by applying a simple and quite general strategy for proving lower bounds on the spectral gap of the generator of a classical or quantum spin dynamics. This general scheme is interesting in its own right and therefore, although the basic idea is not new, we present it in a system-independent setting. The results are illustrated with an number of examples.Comment: 48 pages, Plain TeX, BN26/Oct/9

Continuity theorems for the M/M/1/nM/M/1/n queueing system

In this paper continuity theorems are established for the number of losses during a busy period of the $M/M/1/n$ queue. We consider an $M/GI/1/n$ queueing system where the service time probability distribution, slightly different in a certain sense from the exponential distribution, is approximated by that exponential distribution. Continuity theorems are obtained in the form of one or two-sided stochastic inequalities. The paper shows how the bounds of these inequalities are changed if further assumptions, associated with specific properties of the service time distribution (precisely described in the paper), are made. Specifically, some parametric families of service time distributions are discussed, and the paper establishes uniform estimates (given for all possible values of the parameter) and local estimates (where the parameter is fixed and takes only the given value). The analysis of the paper is based on the level crossing approach and some characterization properties of the exponential distribution.Comment: Final revision; will be published as i

Variational and DMRG studies of the Frustrated Antiferromagnetic Heisenberg S=1 Quantum Spin Chain

We study a frustrated antiferromagnetic isotropic Heisenberg $S=1$ chain using a variational ansatz and the DMRG. At $\alpha_D=0.284(1)$, there is a disorder point of the second kind, marking the onset of incommensurate correlations in the chain. At $\alpha_L=0.3725(25)$ there is a Lifshitz point, at which the excitation spectrum develops a doubly degenerate structure. These points are the quantum remnants of the transition from antiferromagnetic to spiral order in the classical frustrated chain. At $\alpha_T=0.7444(6)$ there is a first order phase transition from an AKLT phase to a next-nearest neighbor generalization of the AKLT model. At the transition, the string order parameter shows a discontinuous jump of 0.085 to 0; the correlation length and the gap are both finite at the transition. The problem of edge states in open frustrated chains is discussed at length.Comment: 37 pages, 14 figures, submitted to Phys.Rev.

Heating and decoherence suppression using decoupling techniques

We study the application of decoupling techniques to the case of a damped vibrational mode of a chain of trapped ions, which can be used as a quantum bus in linear ion trap quantum computers. We show that vibrational heating could be efficiently suppressed using appropriate ``parity kicks''. We also show that vibrational decoherence can be suppressed by this decoupling procedure, even though this is generally more difficult because the rate at which the parity kicks have to applied increases with the effective bath temperature.Comment: 13 pages, 5 figures. Typos corrected, references adde