Episodes of particle ejection from the surface of the active asteroid (101955) Bennu.

Active asteroids are those that show evidence of ongoing mass loss. We report repeated instances of particle ejection from the surface of (101955) Bennu, demonstrating that it is an active asteroid. The ejection events were imaged by the OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer) spacecraft. For the three largest observed events, we estimated the ejected particle velocities and sizes, event times, source regions, and energies. We also determined the trajectories and photometric properties of several gravitationally bound particles that orbited temporarily in the Bennu environment. We consider multiple hypotheses for the mechanisms that lead to particle ejection for the largest events, including rotational disruption, electrostatic lofting, ice sublimation, phyllosilicate dehydration, meteoroid impacts, thermal stress fracturing, and secondary impacts.

Distinct Nucleation and Growth Kinetics of Amorphous SrTiO3 on (001) SrTiO3 and SiO2/Si: A Step toward New Architectures.

Integration of emerging complex-oxide compounds into sophisticated nanoscale single-crystal geometries faces significant challenges arising from the kinetics of vapor-phase thin-film epitaxial growth. A comparison of the crystallization of the model perovskite SrTiO3 (STO) on (001) STO and oxidized (001) Si substrates indicates that there is a viable alternative route that can yield three-dimensional epitaxial synthesis, an approach in which STO is crystallized from an amorphous thin film by postdeposition annealing. The crystallization of amorphous STO on single-crystal (001) STO substrates occurs via solid-phase epitaxy (SPE), without nucleation and with a temperature-dependent amorphous/crystalline interface velocity. In comparison, the crystallization of STO on SiO2/(001) Si substrates requires nucleation, resulting in a polycrystalline film with crystal sizes on the order of 10 nm. A comparison of the temperature dependence of the nucleation and growth processes for these two substrates indicates that it will be possible to create crystalline STO materials using low-temperature crystallization from a crystalline seed, even in the presence of interfaces with other materials. These processes provide a potential route for the formation of single crystals with intricate three-dimensional nanoscale geometries.

Electronic Transport Properties of Epitaxial Si/SiGe Heterostructures Grown on Single-Crystal SiGe Nanomembranes.

To assess possible improvements in the electronic performance of two-dimensional electron gases (2DEGs) in silicon, SiGe/Si/SiGe heterostructures are grown on fully elastically relaxed single-crystal SiGe nanomembranes produced through a strain engineering approach. This procedure eliminates the formation of dislocations in the heterostructure. Top-gated Hall bar devices are fabricated to enable magnetoresistivity and Hall effect measurements. Both Shubnikov-de Haas oscillations and the quantum Hall effect are observed at low temperatures, demonstrating the formation of high-quality 2DEGs. Values of charge carrier mobility as a function of carrier density extracted from these measurements are at least as high or higher than those obtained from companion measurements made on heterostructures grown on conventional strain graded substrates. In all samples, impurity scattering appears to limit the mobility.

The gravity field and interior structure of Enceladus.

The small and active Saturnian moon Enceladus is one of the primary targets of the Cassini mission. We determined the quadrupole gravity field of Enceladus and its hemispherical asymmetry using Doppler data from three spacecraft flybys. Our results indicate the presence of a negative mass anomaly in the south-polar region, largely compensated by a positive subsurface anomaly compatible with the presence of a regional subsurface sea at depths of 30 to 40 kilometers and extending up to south latitudes of about 50°. The estimated values for the largest quadrupole harmonic coefficients (10(6)J2 = 5435.2 ± 34.9, 10(6)C22 = 1549.8 ± 15.6, 1σ) and their ratio (J2/C22 = 3.51 ± 0.05) indicate that the body deviates mildly from hydrostatic equilibrium. The moment of inertia is around 0.335MR(2), where M is the mass and R is the radius, suggesting a differentiated body with a low-density core.

Tensilely strained germanium nanomembranes as infrared optical gain media.

The use of tensilely strained Ge nanomembranes as mid-infrared optical gain media is investigated. Biaxial tensile strain in Ge has the effect of lowering the direct energy bandgap relative to the fundamental indirect one, thereby increasing the internal quantum efficiency for light emission and allowing for the formation of population inversion, until at a strain of about 1.9% Ge is even converted into a direct-bandgap material. Gain calculations are presented showing that, already at strain levels of about 1.4% and above, Ge films can provide optical gain in the technologically important 2.1-2.5 µm spectral region, with transparency carrier densities that can be readily achieved under realistic pumping conditions. Mechanically stressed Ge nanomembranes capable of accommodating the required strain levels are developed and used to demonstrate strong strain-enhanced photoluminescence. A detailed analysis of the high-strain emission spectra also demonstrates that the nanomembranes can be pumped above transparency, and confirms the prediction that biaxial-strain levels in excess of only 1.4% are required to obtain significant population inversion.

Direct-bandgap light-emitting germanium in tensilely strained nanomembranes.

Silicon, germanium, and related alloys, which provide the leading materials platform of electronics, are extremely inefficient light emitters because of the indirect nature of their fundamental energy bandgap. This basic materials property has so far hindered the development of group-IV photonic active devices, including diode lasers, thereby significantly limiting our ability to integrate electronic and photonic functionalities at the chip level. Here we show that Ge nanomembranes (i.e., single-crystal sheets no more than a few tens of nanometers thick) can be used to overcome this materials limitation. Theoretical studies have predicted that tensile strain in Ge lowers the direct energy bandgap relative to the indirect one. We demonstrate that mechanically stressed nanomembranes allow for the introduction of sufficient biaxial tensile strain to transform Ge into a direct-bandgap material with strongly enhanced light-emission efficiency, capable of supporting population inversion as required for providing optical gain.

The role of HLA-DR-DQ haplotypes in variable antibody responses to anthrax vaccine adsorbed.

Host genetic variation, particularly within the human leukocyte antigen (HLA) loci, reportedly mediates heterogeneity in immune response to certain vaccines; however, no large study of genetic determinants of anthrax vaccine response has been described. We searched for associations between the immunoglobulin G antibody to protective antigen (AbPA) response to Anthrax Vaccine Adsorbed (AVA) in humans, and polymorphisms at HLA class I (HLA-A, -B, and -C) and class II (HLA-DRB1, -DQA1, -DQB1, -DPB1) loci. The study included 794 European-Americans and 200 African-Americans participating in a 43-month, double-blind and placebo-controlled clinical trial of AVA (clinicaltrials.gov identifier NCT00119067). Among European-Americans, genes from tightly linked HLA-DRB1, -DQA1, -DQB1 haplotypes displayed significant overall associations with longitudinal variation in AbPA levels at 4, 8, 26 and 30 weeks from baseline in response to vaccination with three or four doses of AVA (global P=6.53 × 10(-4)). In particular, carriage of the DRB1-DQA1-DQB1 haplotypes (*)1501-(*)0102-(*)0602 (P=1.17 × 10(-5)), (*)0101-(*)0101-(*)0501 (P=0.009) and (*)0102-(*)0101-(*)0501 (P=0.006) was associated with significantly lower AbPA levels. In carriers of two copies of these haplotypes, lower AbPA levels persisted following subsequent vaccinations. No significant associations were observed amongst African-Americans or for any HLA class I allele/haplotype. Further studies will be required to replicate these findings and to explore the role of host genetic variation outside of the HLA region.

An assessment of the association between childhood asthma and HLA DRB1*03 using extended haplotype analysis.

Ancestral haplotypes between human leukocyte antigen (HLA) class I and class II alleles are well-recognized in the literature. We previously published a positive association between the class II HLA allele DRB1*03 and the subsequent development of asthma in a retrospective cohort of 383 children. To refine this association, we investigated whether DRB1*03-specific haplotypes extending across the HLA are associated with asthma incidence. We found evidence of strong HLA DRB1*03-dependent linkage disequilibrium across the region, but no association between DRB1*03 ancestral haplotypes and childhood asthma. We did, however, observe a trend toward a positive association between HLA DRB1*03 and asthma by adding non-ancestral DRB1*03 positive haplotypes. Our results suggest that the role of the HLA DRB1*03 in asthma susceptibility is independent of ancestral-haplotype-mediated linkage disequilibrium.

Oxygen concentrators: a practical guide for clinicians and technicians in developing countries.

Hypoxaemia is a common problem causing child deaths in developing countries, but the cost-effective ways to address hypoxaemia are ignored by current global strategies. Improving oxygen supplies and the detection of hypoxaemia has been shown to reduce death rates from childhood pneumonia by up to 35%, and to be cheaper per life saved than other effective initiatives such as conjugate pneumococcal vaccines. Oxygen concentrators provide the cheapest and most consistent source of oxygen in health facilities where power supplies are reliable. To implement and sustain oxygen concentrators requires strengthening of health systems, with clinicians, teachers, administrators and technicians working together. Programmes built around the use of pulse oximetry and oxygen concentrators are an entry point for improving quality of care, and are a unique example of successful integration of appropriate technology into clinical care. This paper is a practical and up-to-date guide for all involved in purchasing, using and maintaining oxygen concentrators in developing countries.

Is there an association between spatial access to parks/green space and childhood overweight/obesity in Calgary, Canada?

BACKGROUND: The recent increase in childhood obesity is expected to add significantly to the prevalence of chronic diseases. We used multivariate multilevel analysis to examine associations between parks/green space and childhood overweight/obesity across communities in Calgary, Canada, a city characterized by intensified urban sprawl and high car use. METHODS: Body Mass Index was calculated from measured height and weight data obtained from 6,772 children (mean age = 4.95 years) attending public health clinics for pre-school vaccinations. Each child's home postal code was geocoded using ESRI ArcGIS 9.2. We examined four measures of spatial access to parks/green space (based on Geographic Information Systems): 1) the number of parks/green spaces per 10,000 residents, 2) the area of parks/green space as a proportion of the total area within a community, 3) average distance to a park/green space, and 4) the proportion of parks/green space service area as a proportion of the total area within a community. Analyses were adjusted for dissemination area median family income (as a proxy for an individual child's family income) community-level education, and community-level proportion of visible minorities. RESULTS: In general, parks/green space at the community level was not associated with overweight/obesity in Calgary, with the exception of a marginally significant effect whereby a moderate number of parks/green spaces per 10,000 residents was associated with lower odds of overweight/obesity. This effect was non-significant in adjusted analyses. CONCLUSION: Our null findings may reflect the popularity of car travel in Calgary, Canada and suggest that the role built environment characteristics play in explaining health outcomes may differ depending on the type of urban environment being studied.

Rotavirus vaccination.

Rotavirus is the leading cause of severe, dehydrating diarrhea worldwide and is responsible for more than 600 000 child deaths every year. In June 2009, the World Health Organization recommended inclusion of rotavirus vaccination in all national immunization programs. This universal endorsement of rotavirus vaccination should help the world's poorest countries to provide rotavirus vaccine to the poorest children, in order to achieve the Millennium Development Goal #4 of decreasing child mortality by two-thirds by 2015. This review will focus on the nature and epidemiology of the virus and on the history of rotavirus vaccine, its availability and current recommendations about its administration.

Timeliness of diagnosis of asthma in children and its predictors.

BACKGROUND: There is a paucity of literature using medical records to evaluate the timeliness of asthma diagnosis in children and the predictors associated with timeliness of asthma diagnosis. METHODS: Subjects were obtained from a convenience sample of 839 children, aged 5-13 years. We conducted comprehensive medical record reviews for these children to determine their asthma status by applying predetermined criteria for asthma. Predictors were evaluated for an association with timeliness of asthma diagnosis. RESULTS: Of 839 children, 276 children met the criteria for asthma before 18 years of age. Of these subjects, 97 had timely diagnosis of asthma while 179 did not have timely diagnosis of asthma with the median delay of 3.3 years. Children with definite asthma at the time of index date was three times more timely to be diagnosed with asthma [hazard ratios (HR) 3.3, 95% CI: 2.43-4.47, P < 0.001], compared to those with probable asthma. Children with a family history of asthma were more timely to be diagnosed with asthma (HR 1.36, 95% CI: 1.03-1.8, P = 0.031). Children with exercise-induced wheezing or bronchospasm were more timely to be diagnosed with asthma (HR 1.79, 95% CI: 0.95-3.36, P = 0.07), compared to those with spasmodic (or bronchospastic) cough. CONCLUSIONS: Many asthmatic children are not diagnosed with asthma in a timely manner, especially in those without the commonly recognized factors associated with asthma. Health care providers need to be reminded that asthma can still occur in those without commonly recognized risk factors. Asthma guidelines need to emphasize this aspect.

Associations between cytokine/cytokine receptor single nucleotide polymorphisms and humoral immunity to measles, mumps and rubella in a Somali population.

We genotyped a Somali population (n = 85; age < or =30 years) for 617 cytokine and cytokine receptor single nucleotide polymorphisms (SNPs) using Illumina GoldenGate genotyping to determine associations with measles, mumps and rubella immunity. Overall, 61 significant associations (P < or = 0.01) were found between SNPs belonging to cytokine receptor genes regulating T helper (Th)1 (IL12RB2, IL2RA and B) and Th2 (IL4R and IL10RB) immunity, and cytokine (IL1B, TNFA, IL6 and IFNB1) and cytokine receptor (IL1RA, IFNAR2, IL18R1, TNFRSF1A and B) genes regulating innate immunity and variations in antibody levels to measles, mumps and/or rubella. SNPs within two major inflammatory cytokine genes, TNFA and interleukin (IL) 6, showed associations with measles-specific antibodies. Specifically, the minor allele variant of rs1799964 (TNFA -1211 C>T) was associated with primarily seronegative values (median enzyme immunoassay index values < or =0.87; P = 0.002; q = 0.23) in response to measles disease and/or vaccination. A heterozygous variant CT for rs2069849 (IL6 +4272C>T; Phe201Phe) was also associated with seronegative values and a lower median level of antibody response to measles disease and/or vaccination (P = 0.004; q = 0.36) or measles vaccination alone (P = 0.008). Several SNPs within the coding and regulatory regions of cytokine and cytokine receptor genes showed associations with mumps and rubella antibody levels but were less informative as strong linkage disequilibrium patterns and lower frequencies for minor alleles were observed among these SNPs. Our study identifies specific SNPs in innate immune response genes that may play a role in modulating antibody responses to measles vaccination and/or infection in Somali subjects.

Development of a framework for international certification by the OIE of diagnostic tests validated as fit for purpose.

Historically, the OIE has focussed on test methods applicable to trade and the international movement of animals and animal products. With its expanding role as the World Organisation for Animal Health, the OIE has recognised the need to evaluate test methods relative to specific diagnostic applications other than trade. In collaboration with its international partners, the OIE solicited input from experts through consultants meetings on the development of guidelines for validation and certification of diagnostic assays for infectious animal diseases. Recommendations from the first meeting were formally adopted and have subsequently been acted upon by the OIE. A validation template has been developed that specifically requires a test to be fit or suited for its intended purpose (e.g. as a screening or a confirmatory test). This is a key criterion for validation. The template incorporates four distinct stages of validation, each of which has bearing on the evaluation of fitness for purpose. The OIE has just recently created a registry for diagnostic tests that fulfil these validation requirements. Assay developers are invited to submit validation dossiers to the OIE for evaluation by a panel of experts. Recognising that validation is an incremental process, tests methods achieving at least the first stages of validation may be provisionally accepted. To provide additional confidence in assay performance, the OIE, through its network of Reference Laboratories, has embarked on the development of evaluation panels. These panels would contain specially selected test samples that would assist in verifying fitness for purpose.

Heterogeneity in vaccine immune response: the role of immunogenetics and the emerging field of vaccinomics.

Recent advances in the fields of immunology, genetics, molecular biology, bioinformatics, and the Human Genome Project have allowed for the emergence of the field of vaccinomics. Vaccinomics encompasses the fields of immunogenetics and immunogenomics as applied to understanding the mechanisms of heterogeneity in immune responses to vaccines. In this study, we examine the role of HLA genes, cytokine genes, and cell surface receptor genes as examples of how genetic polymorphism leads to individual and population variations in immune responses to vaccines. In turn, this data, in concert with new high-throughput technology, inform the immune-response network theory to vaccine response. Such information can be used in the directed and rational development of new vaccines, and this new golden age of vaccinology has been termed "predictive vaccinology", which will predict the likelihood of a vaccine response or an adverse response to a vaccine, the number of doses needed and even whether a vaccine is likely to be of benefit (i.e., is the individual at risk for the outcome for which the vaccine is being administered?).

Oral mucosal immunity and HIV/SIV infection.

Human Immunodeficiency Virus (HIV) transmission through genital and rectal mucosa has led to intensive study of mucosal immune responses to HIV and to the development of a vaccine administered locally. However, HIV transmission through the oral mucosa is a rare event. The oral mucosa represents a physical barrier and contains immunological elements to prevent the invasion of pathogenic organisms. This particular defense differs between micro-compartments represented by the salivary glands, oral mucosa, and palatine tonsils. Secretory immunity of the salivary glands, unique features of cellular structure in the oral mucosa and palatine tonsils, the high rate of oral blood flow, and innate factors in saliva may all contribute to the resistance to HIV/Simian Immunodeficiency Virus (SIV) oral mucosal infection. In the early stage of HIV infection, humoral and cellular immunity and innate immune functions in oral mucosa are maintained. However, these particular immune responses may all be impaired as a result of chronic HIV infection. A better understanding of oral mucosal immune mechanisms should lead to improved prevention of viral and bacterial infections, particularly in immunocompromised persons with Acquired Immune Deficiency Syndrome (AIDS), and to the development of a novel strategy for a mucosal AIDS vaccine, as well as vaccines to combat other oral diseases, such as dental caries and periodontal diseases.

Childhood asthma and human leukocyte antigen type.

Little is known about the relationship between human leukocyte antigen (HLA) class II genes and family history of asthma or atopy in relation to the incidence of childhood asthma. The objective of the study was to determine whether specific HLA class II genes (e.g., DRB1*03) are associated with asthma and whether such association explains the influences of family history of asthma or atopy on asthma incidence. A stratified random sample of 340 children who had HLA data available from the Rochester Family Measles Study cohort (n= 876) and a convenience sample of healthy children aged 5-12 years were the participants. We conducted comprehensive medical record reviews to determine asthma status of these children. The associations between the presence of specific HLA alleles and development of asthma and the role of family history of asthma or atopy in the association were evaluated by fitting Cox models. The cumulative incidence of asthma by 12 years of age among children who carry HLA DRB1*03 was 33%, compared to 24.2% among those who did not carry this allele. Adjusting for family history of asthma or atopy, gender, low birth weight, season of birth, HLA DRB1*04, and HLA DQB1*0302, the hazards ratio for HLA DRB1*03 carriers was 1.8 (95% confidence interval: 1.1-2.9, P= 0.020). We concluded that the HLA DRB1*03 allele is associated with asthma. However, the HLA class II gene does not explain the influences of family history of asthma or atopy on development of asthma. The mechanism underlying the association between asthma and HLA genes needs to be elucidated.

Development of a framework for international certification by OIE of diagnostic tests validated as fit for purpose.

Historically, the OIE has focused on test methods applicable to trade and the international movement of animals and animal products. With its expanding role as the World Organisation for Animal Health, the OIE has recognised the need to evaluate test methods relative to specific diagnostic applications other than trade. In collaboration with its international partners, the OIE solicited input from experts through consultants' meetings on the development of guidelines for validation and certification of diagnostic assays for infectious animal diseases. Recommendations from the first meeting were formally adopted and have subsequently been acted upon by the OIE. A validation template has been developed that specifically requires a test to be fit or suited for its intended purpose (e.g. as a screening or a confirmatory test). This is a key criterion for validation. The template incorporates four distinct stages of validation, each of which has bearing on the evaluation of fitness for purpose. The OIE has just recently created a registry for diagnostic tests that fulfil these validation requirements. Assay developers are invited to submit validation dossiers to the OIE for evaluation by a panel of experts. Recognising that validation is an incremental process, tests methods achieving at least the first stages of validation may be provisionally accepted. To provide additional confidence in assay performance, the OIE, through its network of Reference Laboratories, has embarked on the development of evaluation panels. These panels would contain specially selected test samples that would assist in verifying fitness for purpose.

A familial syndrome of unilateral polymicrogyria affecting the right hemisphere.

A number of familial syndromes of bilateral polymicrogyria (PMG) have been described, but reported unilateral PMG cases have generally been sporadic. The authors identified four families in which unilateral right-sided PMG on MRI was present in more than one individual, with pathologic confirmation in one. Core clinical features included contralateral hemiparesis, developmental delay, and focal seizures. The authors' findings suggest that unilateral PMG exists in a familial syndrome of probable germline genetic origin.