The evolutionary development of high specific impulse electric thruster technology

Electric propulsion flight and technology demonstrations conducted primarily by Europe, Japan, China, the U.S., and the USSR are reviewed. Evolutionary mission applications for high specific impulse electric thruster systems are discussed, and the status of arcjet, ion, and magnetoplasmadynamic thrusters and associated power processor technologies are summarized

Nanomatemàtiques: modelització matemàtica a la nanoescala

En aquest article exposem tres problemes estudiats recentment al grup de Matemàtica Industrial del Centre de Recerca Matemàtica, en els quals l'aproximació del continu resulta vàlida per a descriure fenòmens a la nanoescala: 1. Transferència de calor en nanofluids: els resultats experimentals que confirmen l'increment de la capacitat de transferir calor dels nanofluids respecte dels fluids estàndard són sovint contradictoris. Mitjançant una anàlisi de capa límit mostrarem com el model matemàtic utilitzat en nombroses ocasions per justificar l'increment en la transferència de calor dels nanofluids preveu, de fet, una disminució d'aquesta propietat. 2. Fusió de nanopartícules: les nanopartícules mostren un increment abrupte de la velocitat de transició de fase a mesura que el seu radi decreix. Presentarem un model matemàtic que descriu aquest fenomen. El model preveu temps totals de transició sòlid-líquid que concorden amb les observacions experimentals. 3. Increment del flux d'un fluid en nanotubs de carboni (CNT): mostrarem que els resultats experimentals sobre l'increment de flux en nanotubs de carboni es poden explicar mitjançant les equacions estàndard de la dinàmica de fluids amb la incorporació d'una capa d'extinció (depletion layer) a la interfície entre el fluid i el sòlid.In this paper we discuss three problems recently studied within the Industrial Maths Research Group at the Centre de Recerca Matemàtica, where continuum theory may be applied to describe nanoscale phenomena: 1. Heat transfer with nanofluids: Experimental results concerning the remarkable heat transfer characteristics of nanofluids are at times contradictory. We apply a boundary layer analysis to show that a standard model which has been used by many authors to predict an improvement in heat transfer with increasing nanoparticle concentration in fact shows a decrease. 2. Nanoparticle melting: Nanoparticles often exhibit a sharp increase in melting rate as the size decreases. A mathematical model will be presented which predicts this phenomena and explains the experimentally observed abrupt melting of the smallest nanoparticles. 3. Enhanced flow in carbon nanotubes (CNTs): This model shows that the experimentally observed enhancement can be explained using standard flow equations but with a depletion layer between the liquid and solid interfaces. The results also provide one physical explanation for the Navierslip condition

Change Detection Using Synthetic Aperture Sonar: Preliminary Results from the Larvik Trial

International audienceIn April of 2011, FFI led a sea trial near Larvik, Norway on FFIs research vessel the H.U. Sverdrup II with participation by representatives from Canada, United States, and France. One objective of the sea trial was to acquire a data set suitable for examining incoherent and coherent change detection and automated target recognition (ATR) algorithms applied to Synthetic Aperture Sonar (SAS) imagery. The end goal is to produce an automated tool for detecting recently placed objects on the seafloor. To test these algorithms two areas were chosen, one with a comparatively benign seafloor and one with a boulder strewn complex seafloor. Each area was surveyed before and after deployment of objects. The survey time intervals varied from two days to eight days. In this paper we present the trial and show examples of SAS images and change detection of the images

Substitutions near the hemagglutinin receptor-binding site determine the antigenic evolution of influenza A H3N2 viruses in U.S. swine

Swine influenza A virus is an endemic and economically important pathogen in pigs, with the potential to infect other host species. The hemagglutinin (HA) protein is the primary target of protective immune responses and the major component in swine influenza A vaccines. However, as a result of antigenic drift, vaccine strains must be regularly updated to reflect currently circulating strains. Characterizing the cross-reactivity between strains in pigs and seasonal influenza virus strains in humans is also important in assessing the relative risk of interspecies transmission of viruses from one host population to the other. Hemagglutination inhibition (HI) assay data for swine and human H3N2 viruses were used with antigenic cartography to quantify the antigenic differences among H3N2 viruses isolated from pigs in the United States from 1998 to 2013 and the relative cross-reactivity between these viruses and current human seasonal influenza A virus strains. Two primary antigenic clusters were found circulating in the pig population, but with enough diversity within and between the clusters to suggest updates in vaccine strains are needed. We identified single amino acid substitutions that are likely responsible for antigenic differences between the two primary antigenic clusters and between each antigenic cluster and outliers. The antigenic distance between current seasonal influenza virus H3 strains in humans and those endemic in swine suggests that population immunity may not prevent the introduction of human viruses into pigs, and possibly vice versa, reinforcing the need to monitor and prepare for potential incursions

Modification of titania nanoparticles for photocatalytic antibacterial activity via a colloidal route with glycine and subsequent annealing

Changes in the colloid-chemical and photocatalytic properties of titania nanoparticles by attrition milling in the presence of glycine (Gly) and subsequent heat treatment were examined. By milling at 1500 rpm for 6 h, the average particle size was decreased from 123 to 85 nm, with simultaneous decrease in the specific surface area from 35.1 to 23.5 m2/g. Interfacial reactions between titania and Gly were confirmed by Fourier transform infrared spectroscopy, from the blue shift of the COO− related vibrational bands by 25 cm−1, relative to the same band from the pristine Gly. The bimodal N1s x-ray photoelectron spectroscopy peak similar to that from the reported titania—amino acid complex is another indication of the complex formation with the participation of nitrogen. When the dispersion was dried and calcined at 500 °C in air, the powder exhibited pale yellow color. Diffuse reflectance spectroscopy showed significant visible light absorption, suggesting nitrogen incorporation into titania. The fired product showed high photocatalytic antibacterial activity by irradiation of blue light centered at around 440 nm, using Escherichia coli as a specimen of bacterial species. Thus, the present Gly-modified titania nanoparticles could be used for eliminating indoor bacteria under soft blue illumination. The series of interfacial chemical processes involved are also discusse

NSTAR Ion Thruster Plume Impact Assessments

Tests were performed to establish 30-cm ion thruster plume impacts, including plume characterizations via near and farfield ion current measurements, contamination, and sputtering assessments. Current density measurements show that 95% of the beam was enclosed within a 22 deg half-angle and that the thrust vector shifted by less than 0.3 deg during throttling from 2.3 to 0.5 kW. The beam flatness parameter was found to be 0.47, and the ratio of doubly charged to singly charged ion current density decreased from 15% at 2.3 kW to 5% at 0.5 kW. Quartz sample erosion measurements showed that the samples eroded at a rate of between 11 and 13 pm/khr at 25 deg from the thruster axis, and that the rate dropped by a factor of four at 40 deg. Good agreement was obtained between extrapolated current densities and those calculated from tantalum target erosion measurements. Quartz crystal microbalance and witness plate measurements showed that ion beam sputtering of the tank resulted in a facility material backflux rate of -10 A/hr in a large space simulation chamber

Correlations between 21 cm Radiation and the CMB from Active Sources

Neutral hydrogen is ubiquitous, absorbing and emitting 21 cm radiation throughout much of the Universe's history. Active sources of perturbations, such as cosmic strings, would generate simultaneous perturbations in the distribution of neutral hydrogen and in the Cosmic Microwave Background (CMB) radiation from recombination. Moving strings would create wakes leading to 21 cm brightness fluctuations, while also perturbing CMB light via the Gott-Kaiser-Stebbins effect. This would lead to spatial correlations between the 21 cm and CMB anisotropies. Passive sources, like inflationary perturbations, predict no cross correlations prior to the onset of reionization. Thus, observation of any cross correlation between CMB and 21 cm radiation from dark ages would constitute evidence for new physics. We calculate the cosmic string induced correlations between CMB and 21 cm and evaluate their observability.Comment: 8 pages, 5 figure

Patient characteristics of the Accident and Emergency Department of Kenyatta National Hospital, Nairobi, Kenya: a cross-sectional, prospective analysis

Background Resource-limited settings are increasingly experiencing a ‘triple burden’ of disease, composed of trauma, non-communicable diseases (NCDs) and known communicable disease patterns. However, the epidemiology of acute and emergency care is not well characterised and this limits efforts to further develop emergency care capacity. Objective To define the burden of disease by describing the patient population presenting to the Accident and Emergency Department (A&E) at Kenyatta National Hospital (KNH) in Kenya. Methods We completed a prospective descriptive assessment of patients in KNH’s A&E obtained via systematic sampling over 3 months. Research assistants collected data directly from patients and their charts. Chief complaint and diagnosis codes were grouped for analysis. Patient demographic characteristics were described using the mean and SD for age and n and percentages for categorical variables. International Classification of Disease 10 codes were categorised by 2013 Global Burden of Disease Study methods. Results Data were collected prospectively on 402 patients with an average age of 36 years (SD 19), and of whom, 50% were female. Patients were most likely to arrive by taxi or bus (39%), walking (28%) or ambulance (17%). Thirty-five per cent of patients were diagnosed with NCDs, 24% with injuries and 16% with communicable diseases, maternal and neonatal conditions. Overall, head injury was the single most common final diagnosis and occurred in 32 (8%) patients. The most common patient-reported mechanism for head injury was road traffic accident (39%). Conclusion This study estimates the characteristics of the A&E population at a tertiary centre in Kenya and highlights the triple burden of disease. Our findings emphasise the need for further development of emergency care resources and training to better address patient needs in resource-limited settings, such as KNH

NSTAR Ion Thruster and Breadboard Power Processor Functional Integration Test Results

A 2.3 kW Breadboard Power Processing Unit (BBPPU) was developed as part of the NASA Solar Electric Propulsion Technology Application Readiness (NSTAR) Program. The NSTAR program will deliver an electric propulsion system based on a 30 cm xenon ion thruster to the New Millennium (NM) program for use as the primary propulsion system for the initial NM flight. The final development test for the BBPPU, the Functional Integration Test, was carried out to demonstrate all aspects of BBPPU operation with an Engineering Model Thruster. Test objectives included: (1) demonstration and validation of automated thruster start procedures, (2) demonstration of stable closed loop control of the thruster beam current, (3) successful response and recovery to thruster faults, and (4) successful safing of the system during simulated spacecraft faults. These objectives were met over the specified 80-120 VDC input voltage range and 0.5-2.3 output power capability of the BBPPU. Two minor anomalies were noted in discharge and neutralizer keeper current. These anomalies did not affect the stability of the system and were successfully corrected