Please note, due to essential maintenance online transactions will not be possible between 02:30 and 04:00 BST, on Tuesday 17th September 2019 (22:30-00:00 EDT, 17 Sep, 2019). We apologise for any inconvenience.
To send content items to your account,
please confirm that you agree to abide by our usage policies.
If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account.
Find out more about sending content to .
To send content items to your Kindle, first ensure email@example.com
is added to your Approved Personal Document E-mail List under your Personal Document Settings
on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part
of your Kindle email address below.
Find out more about sending to your Kindle.
Note you can select to send to either the @free.kindle.com or @kindle.com variations.
‘@free.kindle.com’ emails are free but can only be sent to your device when it is connected to wi-fi.
‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.
An updated compilation of published and new data of major-ion (Ca, Cl, K, Mg, Na, NO3, SO4) and methylsulfonate (MS) concentrations in snow from 520 Antarctic sites is provided by the national ITASE (International Trans-Antarctic Scientific Expedition) programmes of Australia, Brazil, China, Germany, Italy, Japan, Korea, New Zealand, Norway, the United Kingdom, the United States and the national Antarctic programme of Finland. The comparison shows that snow chemistry concentrations vary by up to four orders of magnitude across Antarctica and exhibit distinct geographical patterns. The Antarctic-wide comparison of glaciochemical records provides a unique opportunity to improve our understanding of the fundamental factors that ultimately control the chemistry of snow or ice samples. This paper aims to initiate data compilation and administration in order to provide a framework for facilitation of Antarctic-wide snow chemistry discussions across all ITASE nations and other contributing groups. The data are made available through the ITASE web page (http://www2.umaine.edu/itase/content/syngroups/snowchem.html) and will be updated with new data as they are provided. In addition, recommendations for future research efforts are summarized.
Ross River virus (RRV) is a mosquito-borne virus endemic to Australia. The disease, marked by arthritis, myalgia and rash, has a complex epidemiology involving several mosquito species and wildlife reservoirs. Outbreak years coincide with climatic conditions conducive to mosquito population growth. We developed regression models for human RRV notifications in the Mildura Local Government Area, Victoria, Australia with the objective of increasing understanding of the relationships in this complex system, providing trigger points for intervention and developing a forecast model. Surveillance, climatic, environmental and entomological data for the period July 2000–June 2011 were used for model training then forecasts were validated for July 2011–June 2015. Rainfall and vapour pressure were the key factors for forecasting RRV notifications. Validation of models showed they predicted RRV counts with an accuracy of 81%. Two major RRV mosquito vectors (Culex annulirostris and Aedes camptorhynchus) were important in the final estimation model at proximal lags. The findings of this analysis advance understanding of the drivers of RRV in temperate climatic zones and the models will inform public health agencies of periods of increased risk.
The focal article by Bergman and Jean (2016) raises an important issue by documenting the underrepresentation of nonprofessional and nonmanagerial workers in industrial and organizational (I-O) research. They defined workers as, “people who were not executive, professional or managerial employees; who were low- to medium-skill; and/or who were wage earners rather than salaried” (p. 89). This definition encompasses a wide range of employee samples: from individuals working in blue-collar skilled trades like electricians and plumbers to police officers, soldiers, and call center representatives to low-skill jobs such as fast food, tollbooth operators, and migrant day workers. Because there is considerable variability in the pay, benefits, skill level, autonomy, job security, schedule flexibility, and working conditions that define these workers’ experiences, a more fine-grained examination of who these workers are is necessary to understand the scope of the problem and the specific subpopulations of workers represented (or not) in existing I-O research.
The 2012 West Nile virus (WNV) epidemic was the largest since 2003 and the North Texas region was the most heavily impacted. We conducted a serosurvey of blood donors from four counties in the Dallas–Fort Worth area to characterize the epidemic. Blood donor specimens collected in November 2012 were tested for WNV-specific antibodies. Donors positive for WNV-specific IgG, IgM, and neutralizing antibodies were considered to have been infected in 2012. This number was adjusted using a multi-step process that accounted for timing of IgM seroreversion determined from previous longitudinal studies of WNV-infected donors. Of 4971 donations screened, 139 (2·8%) were confirmed WNV IgG positive, and 69 (1·4%) had IgM indicating infection in 2012. After adjusting for timing of sampling and potential seroreversion, we estimated that 1·8% [95% confidence interval (CI) 1·5–2·2] of the adult population in the Dallas–Fort Worth area were infected during 2012. The resulting overall estimate for the ratio of infections to reported WNV neuroinvasive disease (WNND) cases was 238:1 (95% CI 192–290), with significantly increased risk of WNND in older age groups. These findings were very similar to previous estimates of infections per WNND case, indicating no change in virulence as WNV evolved into an endemic infection in the United States.
Schizophrenia (SZ) and bipolar disorder (BD) have substantial negative impact on the quality of human life. Both, microRNA (miRNA) expression profiling in SZ and BD postmortem brains [and genome-wide association studies (GWAS)] have implicated miRNAs in disease etiology. Here, we aim to determine whether significant GWAS signals observed in the Psychiatric Genetic Consortium (PGC) are enriched for miRNAs.
A two-stage approach was used to determine whether association signals from PGC affect miRNAs: (i) statistical assessment of enrichment using a Simes test and sum of squares test (SST) and (ii) biological evidence that quantitative trait loci (eQTL) mapping to known miRNA genes affect their expression in an independent sample of 78 postmortem brains from the Stanley Medical Research Institute.
A total of 2567 independent single nucleotide polymorphisms (SNPs) (R2 > 0.8) were mapped locally, within 1 Mb, to all known miRNAs (miRBase v. 21). We show robust enrichment for SZ- and BD-related SNPs with miRNAs using Simes (SZ: p ≤ 0.0023, BD: p ≤ 0.038), which remained significant after adjusting for background inflation in SZ (empirical p = 0.018) and approached significance in BD (empirical p = 0.07). At a false discovery rate of 10%, we identified a total of 32 eQTLs to influence miRNA expression; 11 of these overlapped with BD.
Our approach of integrating PGC findings with eQTL results can be used to generate specific hypotheses regarding the role of miRNAs in SZ and BD.
Open science is a new concept for the practice of experimental laboratory-based research, such as drug discovery. The authors have recently gained experience in how to run such projects and here describe some straightforward steps others may wish to take towards more openness in their own research programmes. Existing and inexpensive online tools can solve many challenges, while some psychological barriers to the free sharing of all data and ideas are more substantial.
We carried out an extensive photometric and spectroscopic investigation of the SPB binary, HD 25558 (see Fig. 1 for the time and geographic distribution of the observations). The ~2000 spectra obtained at 13 observatories during 5 observing seasons, the ground-based multi-colour light curves and the photometric data from the MOST satellite revealed that this object is a double-lined spectroscopic binary with a very long orbital period of about 9 years. We determined the physical parameters of the components, and have found that both lie within the SPB instability strip. Accordingly, both components show line-profile variations consistent with stellar pulsations. Altogether, 11 independent frequencies and one harmonic frequency were identified in the data. The observational data do not allow the inference of a reliable orbital solution, thus, disentangling cannot be performed on the spectra. Since the lines of the two components are never completely separated, the analysis is very complicated. Nevertheless, pixel-by-pixel variability analysis of the cross-correlated line profiles was successful, and we were able to attribute all the frequencies to the primary or secondary component. Spectroscopic and photometric mode-identification was also performed for several of these frequencies of both binary components. The spectroscopic mode-identification results suggest that the inclination and rotation of the two components are rather different. While the primary is a slow rotator with ~6 d rotation period, seen at ~60° inclination, the secondary rotates fast with ~1.2 d rotation period, and is seen at ~20° inclination. Our spectropolarimetric measurements revealed that the secondary component has a magnetic field with at least a few hundred Gauss strength, while no magnetic field was detected in the primary.
The detailed analysis and results of this study will be published elsewhere.
In this work, we investigate the approach of a descending vortex pair to a horizontal ground plane. As in previous studies, the primary vortices exhibit a ‘rebound’, due to the separation of secondary opposite-sign vortices underneath each primary vortex. On each side of the flow, the weaker secondary vortex can become three-dimensionally unstable, as it advects around the stronger primary vortex. It has been suggested in several recent numerical simulations that elliptic instability is the origin of such waviness in the secondary vortices. In the present research, we employ a technique whereby the primary vortices are visualized separately from the secondary vortices; in fact, we are able to mark the secondary vortex separation, often leaving the primary vortices invisible. We find that the vortices are bent as a whole in a Crow-type ‘displacement’ mode, and, by keeping the primary vortices invisible, we are able to see both sides of the flow simultaneously, showing that the instability perturbations on the secondary vortices are antisymmetric. Triggered by previous research on four-vortex aircraft wake flows, we analyse one half of the flow as an unequal-strength counter-rotating pair, noting that it is essential to take into account the angular velocity of the weak vortex around the stronger primary vortex in the analysis. In contrast with previous results for the vortex–ground interaction, we find that the measured secondary vortex wavelength corresponds well with the displacement bending mode, similar to the Crow-type instability. We have analysed the elliptic instability modes, by employing the approximate dispersion relation of Le Dizés & Laporte (J. Fluid Mech., vol. 471, 2002, p. 169) in our problem, finding that the experimental wavelength is distinctly longer than predicted for the higher-order elliptic modes. Finally, we observe that the secondary vortices deform into a distinct waviness along their lengths, and this places two rows of highly stretched vertical segments of the vortices in between the horizontal primary vortices. The two rows of alternating-sign vortices translate towards each other and ultimately merge into a single vortex row. A simple point vortex row model is able to predict trajectories of such vortex rows, and the net result of the model’s ‘orbital’ or ‘passing’ modes is to bring like-sign vortices, from each secondary vortex row, close to each other, such that merging may ensue in the experiments.
The Velay granite pluton (Massif Central, France) is the youngest (304 ± 5 Ma) and largest (∼6,900 km2) of the major Massif Central monzogranites/granodiorites and was formed nearly 50 Ma after the cessation of Hercynian continental collision (Pin & Duthou 1990). It is a highly heterogeneous pluton consisting of I-type, high-Sr granites (Sr = 500-900 ppm) with low (+35 to +41) and high (-3 to -5), at its centre, grading into S-type and mixed I-S-type heterogeneous granites of more normal Sr content (100–420 ppm) and higher (+40 to +210) and lower (-3·8 to -7.3) at its margins.
The metasedimentary lower crust of the Massif Central was underplated/intruded by mafic mantle-derived magmas between 360 Ma and 300 Ma. From 300-280 Ma (Downes et al. 1991) underplating led to partial melting and granulite facies metamorphism of the underplated material (represented by felsic and mafic meta-igneous lower crustal xenoliths, = –11 to +112, = +2·2 to 8·2, Downes et al 1990). The partial melts assimilated mainly schist but also felsic gneiss and older granite country rock material ( = +100 to +300, = - 5 to -9) to produce the heterogeneous granites. Plagioclase and biotite were accumulated at the base of the intrusion which was intruded to high levels to form the high-Sr granites.
The structure of a-Si:H, deposited at rates in excess of 100Å/s by the hot wire chemical vapor deposition (HWCVD) technique, has been examined by x-ray diffraction (XRD), Raman spectroscopy, H evolution, and small-angle x-ray scattering (SAXS). As the film deposition rate (Rd) is increased, we find that the XRD, Raman and the H evolution peak curves are invariant with Rd, and exhibit structure consistent with state-of-the-art, compact a-Si:H films deposited at low Rd. The only exception is the SAXS signal, which increases by a factor of ∼100 over that for our best low Rd films. We relate changes in the film electronic structure (Urbach edge) to the increase in the SAXS signals. We also note the invariance of the saturated defect density versus Rd, and discuss possible reasons why the increase in the SAXS does not play a role in the Staebler-Wronski Effect for this type of material. Finally, device results are presented.
The heterogeneity of a-Si:H and a-Si:D films has been probed on the nano-scale by small-angle neutron scattering (SANS). Films were deposited by two techniques, plasma-enhanced chemical-vapor deposition (PECVD) and hot-wire chemical-vapor deposition (HWCVD) using conditions that yield high-quality films and devices. Four samples were examined in a light-soaked state (AM1.5, 300 h) and then re-examined after annealing (190°C, 1 h) in-situ to look for any change in SANS associated with the Staebler-Wronski effect. No changes were observed in the SANS intensity to a precision that could have readily detected the 25% change reported in 1985 (Chenevas-Paule et al). Significant differences are observed in hydrogenated and deuterated films, as well as in the PECVD versus the HWCVD materials.
We grow hydrogenated amorphous-silicon (a-Si:H) by the hot-wire chemical vapor deposition (HWCVD) technique. In our standard tube-reactor we use a single filament, centered 5 cm below the substrate and obtain deposition rates up to 20 Å/s. However, by adding a second filament, and decreasing the filament-to-substrate distance, we are able to grow a-Si:H at deposition rates exceeding 167 Å/s (1 µm/min). We find the deposition rate increases with increasing deposition pressure, silane flow rate, and filament current and decreasing filament-tosubstrate distance. There are significant interactions among these parameters that require optimization to grow films of optimal quality for a desired deposition rate. Using our best conditions, we are able to maintain an AM1.5 photoconductivity-to-dark-conductivity ratio of 105 at deposition rates up to 130 Å/s, beyond which the conductivity ratio decreases. Other electronic properties decrease more rapidly with increasing deposition rate, including the ambipolar diffusion length, Urbach energy, and the as-grown defect density. Measurements of void density by small-angle X-ray scattering (SAXS) reveal an increase by well over an order of magnitude when going from one to two filaments. However, both Raman and X-ray diffraction (XRD) measurements show no change in film structure with increasing deposition rates up to 144 Å/s, and atomic force microscopy (AFM) reveals little change in topology.
The advantage of using very high frequencies for preparation of a-Si:H materials at high rates (above 5 Å/s) for intrinsic layers (i-layer) of solar cells has been well documented. In an effort to identify film properties which may be related to this superior device performance, a study of the structural, optical and electrical properties of films made at various deposition rates between 1 and 15 Å/s using rf frequencies of 13.56 and 70 MHz has been made. The films were characterized using a number of techniques including small-angle x-ray scattering, infrared absorption spectroscopy, and scanning electron microscopy. For the films made using the 70 MHz frequency, the amount of nanovoids with sizes of < 100Å increases systematically as the deposition rates increases beyond 5 Å/s. Accompanying the increase in void fraction in the films are increases in the hydrogen content and the amount of 2070 cm-1 mode in the infrared absorption spectra. In addition to an increase in the amount of nanovoids in the films as the deposition rate exceeds 5 Å/s, the films made using the 13.56 MHz and high deposition rates have large amounts of SAXS related to scattering features with sizes > 200 Å. This scattering is associated with large bulk density fluctuations and/or enhanced surface roughness. None of the films in the study displayed signs of having columnar-like microstructures. The nanovoids are not related to changes in the solar cells with increasing i-layer deposition rate for both fabrication processes, perhaps due to the relatively small volume fractions of less than 0.2% and/or good void-surface passivation. However, the larger-scale structures detected in the films made using the 13.56 MHz technique could cause poorer performance in cells prepared at high growth rates.
The structure of thin film SiN, deposited by the hot wire chemical vapor deposition (HWCVD) technique using SiH4 and NH3 gas mixtures, has been examined as a function of the amount of H2 dilution of the gas mixture. For NH3/SiH4 gas ratios > 0.5/1, all films are a-SiN:H. While H2 dilution does not change the basic film structure, in that the films are amorphous with all dilutions, H2 dilution does increase the efficiency of NH3 dissociation in the gas phase, and causes a further reduction in the already small amount of N-H bonding in a-SiN:H films deposited by HWCVD. For NH3/SiH4 gas ratios typically <0.5/1 and with high H2 dilution, the first deposition of µc-SiN is demonstrated. X-ray diffraction (XRD) measurements demonstrate that the structure of these films consists of silicon crystallites embedded in an a-SiN:H matrix. An upper limit for N incorporation with the preservation of microcrystallinity was found, beyond which the films again became amorphous. The existence of this limit is explained in terms of structural disorder in the a-SiN:H tissue brought about by N incorporation.
A Gas Jet technique has been used to prepare microcrystalline silicon (μc-Si) thin films at deposition rates as high as 20 Å/s. The films have microcrystal sizes between 80 and 120 Å with a heterogeneous microstructure containing regions with columnar growth and other regions with a more randomly oriented microstructure. These materials have been used as i-layers for nip single-junction solar cells. The high deposition rates allow for fabrication of the required thicker μc-Si i-layers in a similar amount of time to those used for high quality a-SiGe:H i-layers (rates of 1-3 Å/s). Using a 610nm cutoff filter which only allows red light to strike the device, pre-light soaked short circuit currents of 8-10 mA/cm2 and 2.7% red-light efficiencies have been obtained while AM1.5 white light efficiencies are above 7%. These efficiencies are higher than those typically obtained for μc-Si cells prepared at the high i-layer growth rates using other deposition techniques. After 1000 h. of light soaking, the efficiencies on average degrade only by 2-5% (stabilized efficiencies of 2.6%) consistent with the expected high stability with the microcrystalline materials. The small amount of degradation compares with the 15-17% degradation in efficiencies for a-SiGe:H cells subjected to similar irradiation treatments (final light-soaked red light efficiencies of 3.2%). Improvements in the cell efficiencies may come through an understanding of the role that columnar microstructure and void structure plays in determining the device performance.
We have used small-angle X-ray scattering (SAXS) and Doppler-broadening measurements of positron-annihilation radiation to study changes in the microvoid distribution in PECVD a-Si:H films during annealing. From a comparison of data on deuterium diffusion with information obtained from SAXS we conclude that changes, during annealing, in the dispersive character of deuterium diffusion are likely to be caused by void formation through clustering of smaller structural defects.
We present the results of X-ray diffraction measurements on a series of device quality hot wire (HW) deposited a-Si:H films in which we vary only the substrate temperature of the growing film, which decreases the bonded film H content in a systematic fashion. By increasing the substrate temperature to ∼375°C, where we deposit our low H content (CH) HW films which exhibit a reduced Staebler-Wronski effect, the width of the first peak in the X-ray diffraction pattern narrows noticeably. We interpret this narrowing to be the first indication of improved medium range ordering in our low CH, device quality HW a-Si:H. We note in addition that measurements of the bond angle deviation, obtained from Raman measurements of the half width of the Si-Si TO phonon mode on the same samples, do not show this same evidence of improved ordering as the substrate temperature is increased. We discuss these differences in the context of sample annealing experiments designed to effuse H from the region of the sample probed by the surface sensitive Raman technique, while leaving the bulk of the material, which is sampled by the X-ray beam, largely unaffected.
The spectral transmittance, reflectance and emittance of silicon related materials and structures are measured simultaneously utilizing a spectral emissometer operating at near- and mid-IR spectral range and temperature range of 300 to 1500K. Several kinds of samples have been considered here: a) SiO2/Si with oxide in the thickness range of 653–5124A, b) SiO2/Si/ SiO2 with oxide thickness of 5000A on both front and back sides c)Multi-layers of SiO2/Si/ SiO2/poly-Si, with backside oxide of 1600A and 250A, respectively and d) separation by implantation of oxygen (SIMOX), with embedded oxide thickness of 4000A. An extensive analysis has been performed to interpret and compare the results obtained from these measurements.
Concerning the SiO2/Si, we find that the experimental results are in accord with the sinusoidal relation of emissivity as a function of the silicon oxide thickness and hence the Applied Materials model. Experimental results on SiO2/Si/SiO2 are also presented here. For the multi-layers of SiO2/Si/SiO2/poly-Si, it is interesting to note that for temperatures above 600°C, the emissivity is independent of temperature and wavelength for the backside oxide thickness of 1600 and 250A. SIMOX measurements are presented as well. The Fiory model has been utilized extensively to investigate the high temperature emissivity data. The applications and limitations of this model are discussed.