Faraday rotation of polarized emission from pulsars measured at radio frequencies provides a powerful tool to investigate the interstellar and interplanetary magnetic fields. However, besides being ...sensitive to the astrophysical media, pulsar observations in radio are affected by the highly time-variable ionosphere. In this article, the amount of ionospheric Faraday rotation has been computed by assuming a thin layer model. For this aim, ionospheric maps of the free electron density (based on Global Positioning System data) and semi-empirical geomagnetic models are needed. Through the data of five highly polarized pulsars observed with the individual German LOw-Frequency ARray stations, we investigate the performances of the ionospheric modelling. In addition, we estimate the parameters of the systematics and the correlated noise generated by the residual unmodelled ionospheric effects, and show the comparison of the different free-electron density maps. For the best ionospheric maps, we have found that the rotation measure corrections on 1 yr time-scales after subtraction of diurnal periodicity are accurate to similar to 0.06-0.07 rad m(-2).
Goat farming is a low-cost alternative to dairy production in developing countries. In Brazil, goat production has increased in recent years due in part to the implementation of programs encouraging ...this activity. Mycobacterium avium ssp. paratuberculosis (MAP) is the causative agent of paratuberculosis, a disease that causes chronic granulomatous enteritis in ruminants, but MAP transmission dynamics are still poorly understood in goats. In a previously published study of our research group, 10 dairy goat farms (467 animals) from Minas Gerais state were analyzed for MAP detection; 2 fecal cultures and 11 milk samples tested positive for MAP by conventional PCR and were confirmed by sequencing. Because no clinical signs were observed over 1 yr of monitoring, we hypothesized that these MAP-positive goats could be passive shedders. Thus, in the present study, 4 positive goats (4/13) from the previous study were purchased and feces and milk samples were collected for evaluation (twice, with an interval of 3 mo between tests) by culture of MAP, IS900 PCR, or both. All analyses were negative for MAP. At the last time point, blood samples were collected for ELISA, the animals were killed, and tissues collected for tissue culture and histopathology. At necropsy, no macroscopic lesions related to paratuberculosis were observed. Similarly, no histological changes were observed and MAP in samples stained by Ziehl–Neelsen was not detected. These animals were characterized as potential passive shedders with upward contamination of the teat canal by MAP. This is the first report of the passive shedding phenomenon in goats in Brazil and it highlights the importance of identifying these animals for control programs and to ensure the quality of dairy products.
Synthetic routes to the first boryl complexes of cadmium and mercury are reported via transmetallation from boryllithium; the syntheses of related group 14 systems highlight the additional factors ...associated with extension to more redox-active post-transition elements.
ABSTRACT
We report on the multifrequency timing observations of 21 pulsars discovered in the LOFAR Tied-Array All-Sky Survey (LOTAAS). The timing data were taken at central frequencies of 149 MHz ...(LOFAR) as well as 334 and 1532 MHz (Lovell Telescope). The sample of pulsars includes 20 isolated pulsars and the first binary pulsar discovered by the survey, PSR J1658+3630. We modelled the timing properties of the pulsars, which showed that they have, on average, larger characteristic ages. We present the pulse profiles of the pulsars across the three observing bands, where PSR J1643+1338 showed profile evolution that appears not to be well-described by the radius-to-frequency-mapping model. Furthermore, we modelled the spectra of the pulsars across the same observing bands, using a simple power law, and found an average spectral index of −1.9 ± 0.5. Amongst the pulsars studied here, PSR J1657+3304 showed large flux density variations of a factor of 10 over 300 d, as well as mode changing and nulling on time-scales of a few minutes. We modelled the rotational and orbital properties of PSR J1658+3630, which has a spin period of 33 ms in a binary orbit of 3.0 d with a companion of minimum mass of 0.87 M⊙, likely a carbon–oxygen or oxygen–neon–magnesium type white dwarf. PSR J1658+3630 has a dispersion measure of 3.0 pc cm−3, making it possibly one of the closest binary pulsars known.
The diagnosis of intramammary infections is mostly based on somatic cell count (SCC) and bacteriological analysis. As an alternative, differential cell counting (DCC) could be a useful method, ...because it identifies changes in the relative cell populations before the increase in total cell number occurs. The aim of the study was to identify cytological parameters that could be used in the field to classify mammary quarters as healthy or diseased, comparing cyto-bacteriological results with DCC. Overall, 48 cows were randomly selected from 3 herds in Lombardy region of Italy. Herd A was characterized by the absence of contagious microorganisms; in herds B and C, the prevalence of Staphylococcus aureus was 20 and 50%, respectively. Foremilk samples were aseptically collected from 188 quarters and submitted to bacteriological analysis, SCC, and DCC. For statistical analysis, the samples were clustered into 4 health groups, and DCC results were compared in each group. Ninety-six samples were classified as normal secretions (N), 30 as mastitis (M), 15 as latent mastitis (LM), and 47 as unspecific mastitis (UM) based on SCC and bacteriological results. Single percentages of lymphocytes, polymorphonuclear neutrophilic leukocytes (PMNL), or macrophages were first evaluated to established variables capable of identifying healthy and inflamed quarters. Then, combinations of cell populations were tested to increase the discrimination power of DCC: phagocytes, logarithmic PMNL:lymphocyte ratio, and logarithmic phagocyte:lymphocyte ratio. The mean percentage of lymphocytes was significantly higher in group N than in groups LM, UM, and M. The mean percentage of PMNL was significantly lower in group N than in groups UM and M, but not LM. Mean percentages of macrophages were not significantly influenced by the 4 groups. The mean value of phagocytes was significantly lower in group N than in the other groups. Both the logarithmic PMNL:lymphocyte and the logarithmic phagocyte:lymphocyte ratios were significantly lower in group N than in groups LM, UM, and M. Fisher (F-)values were calculated, and the highest F-value was that of log PMNL:lymphocytes ratio (48.23). The explanation for this could be that log PMNL:Lym is the only variable that involved both cell populations statistically influenced by health groups but excluded macrophages. Microscopic DCC has potential as a tool to identify cows affected by any inflammatory process of the mammary gland, with the best results being achieved using log PMNL:lymphocyte as variable.
Traditional palaeontological techniques of disease characterisation are limited to the analysis of osseous fossils, requiring several lines of evidence to support diagnoses. This study presents a ...novel stepwise concept for comprehensive diagnosis of pathologies in fossils by computed tomography imaging for morphological assessment combined with likelihood estimation based on systematic phylogenetic disease bracketing. This approach was applied to characterise pathologies of the left fibula and fused caudal vertebrae of the non-avian dinosaur Tyrannosaurus rex. Initial morphological assessment narrowed the differential diagnosis to neoplasia or infection. Subsequent data review from phylogenetically closely related species at the clade level revealed neoplasia rates as low as 3.1% and 1.8%, while infectious-disease rates were 32.0% and 53.9% in extant dinosaurs (birds) and non-avian reptiles, respectively. Furthermore, the survey of literature revealed that within the phylogenetic disease bracket the oldest case of bone infection (osteomyelitis) was identified in the mandible of a 275-million-year-old captorhinid eureptile Labidosaurus. These findings demonstrate low probability of a neoplastic aetiology of the examined pathologies in the Tyrannosaurus rex and in turn, suggest that they correspond to multiple foci of osteomyelitis.
Principles of atomic friction: from sticking atoms to superlubric sliding Hölscher, Hendrik; Schirmeisen, André; Schwarz, Udo D
Philosophical transactions of the Royal Society of London. Series A: Mathematical, physical, and engineering sciences,
04/2008, Letnik:
366, Številka:
1869
Journal Article
Recenzirano
Tribology-the science of friction, wear and lubrication-is of great importance for all technical applications where moving bodies are in contact. Nonetheless, little progress has been made in finding ...an exact atomistic description of friction since Amontons proposed his empirical macroscopic laws over three centuries ago. The advent of new experimental tools such as the friction force microscope, however, enabled the investigation of frictional forces occurring at well-defined contacts down to the atomic scale. This research field has been established as nanotribology. In the present article, we review our current understanding of the principles of atomic-scale friction based on recent experiments using friction force microscopy.
A small change with a big effect: Reaction of the titanium complex 1 with terminal alkynes gave the unusual acetylide–vinylhydrazide(1−) compounds 2 (R=4‐C6H4X (X=Me, CF3, OMe), C6F5, SiMe3) as ...hydrohydrazination intermediates. In contrast, a complex similar to 1 with bulkier trimethylsilyl substituents in place of the isopropyl groups is known to catalyze the 1,2‐diamination of alkynes with hydrazines.
A comprehensive analysis of contrast formation mechanisms in scanning tunneling microscopy (STM) experiments on a metal oxide surface is presented with the oxygen-induced (2√2×√2)R45° missing row ...reconstruction of the Cu(100) surface as a model system. Density functional theory and electronic transport calculations were combined to simulate the STM imaging behavior of pure and oxygen-contaminated metal tips with structurally and chemically different apexes while systematically varying bias voltage and tip–sample distance. The resulting multiparameter database of computed images was used to conduct an extensive comparison with experimental data. Excellent agreement was attained for a large number of cases, suggesting that the assumed model tips reproduce most of the commonly encountered contrast-determining effects. Specifically, we find that depending on the bias voltage polarity, copper-terminated tips allow selective imaging of two structurally distinct surface Cu sites, while oxygen-terminated tips show complex contrasts with pronounced asymmetry and tip–sample distance dependence. Considering the structural and chemical stability of the tips reveals that the copper-terminated apexes tend to react with surface oxygen at small tip–sample distances. In contrast, oxygen-terminated tips are considerably more stable, allowing exclusive surface oxygen imaging at small tip–sample distances. Our results provide a conclusive understanding of fundamental STM imaging mechanisms, thereby providing guidelines for experimentalists to achieve chemically selective imaging by properly selecting imaging parameters.
The preparation of sufficient amounts of high-quality samples is still the major bottleneck for the characterization of membrane proteins by in vitro approaches. The hydrophobic nature, the ...requirement for complicated transport and modification pathways, and the often observed negative effects on membrane properties are intrinsic features of membrane proteins that frequently cause significant problems in overexpression studies. Establishing efficient protocols for the production of functionally folded membrane proteins is therefore a challenging task, and numerous specific characteristics have to be considered. In addition, a variety of expression systems have been developed, and choice of appropriate techniques could strongly depend on the desired target membrane proteins as well as on their intended applications. The production of membrane proteins is a highly dynamic field and new or modified approaches are frequently emerging. The review will give an overview of currently established processes for the production of functionally folded membrane proteins.
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