Inverse problem for wave equation with sources and observations on disjoint sets

We consider an inverse problem for a hyperbolic partial differential equation on a compact Riemannian manifold. Assuming that $\Gamma_1$ and $\Gamma_2$ are two disjoint open subsets of the boundary of the manifold we define the restricted Dirichlet-to-Neumann operator $\Lambda_{\Gamma_1,\Gamma_2}$. This operator corresponds the boundary measurements when we have smooth sources supported on $\Gamma_1$ and the fields produced by these sources are observed on $\Gamma_2$. We show that when $\Gamma_1$ and $\Gamma_2$ are disjoint but their closures intersect at least at one point, then the restricted Dirichlet-to-Neumann operator $\Lambda_{\Gamma_1,\Gamma_2}$ determines the Riemannian manifold and the metric on it up to an isometry. In the Euclidian space, the result yields that an anisotropic wave speed inside a compact body is determined, up to a natural coordinate transformations, by measurements on the boundary of the body even when wave sources are kept away from receivers. Moreover, we show that if we have three arbitrary non-empty open subsets $\Gamma_1,\Gamma_2$, and $\Gamma_3$ of the boundary, then the restricted Dirichlet-to-Neumann operators $\Lambda_{\Gamma_j,\Gamma_k}$ for $1\leq j<k\leq 3$ determine the Riemannian manifold to an isometry. Similar result is proven also for the finite-time boundary measurements when the hyperbolic equation satisfies an exact controllability condition

Bonding mechanism from the impact of thermally sprayed solid particles

Power particles are mainly in solid state prior to impact on substrates from high velocity oxy-fuel (HVOF) thermal spraying. The bonding between particles and substrates is critical to ensure the quality of coating. Finite element analysis (FEA) models are developed to simulate the impingement process of solid particle impact on substrates. This numerical study examines the bonding mechanism between particles and substrates and establishes the critical particle impact parameters for bonding. Considering the morphology of particles, the shear-instability–based method is applied to all the particles, and the energy-based method is employed only for spherical particles. The particles are given the properties of widely used WC-Co powder for HVOF thermally sprayed coatings. The numerical results confirm that in the HVOF process, the kinetic energy of the particle prior to impact plays the most dominant role in particle stress localization and melting of the interfacial contact region. The critical impact parameters, such as particle velocity and temperature, are shown to be affected by the shape of particles, while higher impact velocity is required for highly nonspherical powder

Organics in comet 67P – a first comparative analysis of mass spectra from ROSINA–DFMS, COSAC and Ptolemy

The ESA Rosetta spacecraft followed comet 67P at a close distance for more than 2 yr. In addition, it deployed the lander Philae on to the surface of the comet. The (surface) composition of the comet is of great interest to understand the origin and evolution of comets. By combining measurements made on the comet itself and in the coma, we probe the nature of this surface material and compare it to remote sensing observations. We compare data from the double focusing mass spectrometer (DFMS) of the ROSINA experiment on ESA's Rosetta mission and previously published data from the two mass spectrometers COSAC (COmetary Sampling And Composition) and Ptolemy on the lander. The mass spectra of all three instruments show very similar patterns of mainly CHO-bearing molecules that sublimate at temperatures of 275 K. The DFMS data also show a great variety of CH-, CHN-, CHS-, CHO2- and CHNO-bearing saturated and unsaturated species. Methyl isocyanate, propanal and glycol aldehyde suggested by the earlier analysis of the measured COSAC spectrum could not be confirmed. The presence of polyoxymethylene in the Ptolemy spectrum was found to be unlikely. However, the signature of the aromatic compound toluene was identified in DFMS and Ptolemy data. Comparison with remote sensing instruments confirms the complex nature of the organics on the surface of 67P, which is much more diverse than anticipated

Tissue-specific inducible expression of antimicrobial peptide genes in Drosophila surface epithelia

The production of antimicrobial peptides is an important aspect of host defense in multicellular organisms. In Drosophila, seven antimicrobial peptides with different spectra of activities are synthesized by the fat body during the immune response and secreted into the hemolymph. Using GFP reporter transgenes, we show here that all seven Drosophila antimicrobial peptides can be induced in surface epithelia in a tissue-specific manner. The imd gene plays a critical role in the activation of this local response to infection. In particular, drosomycin expression, which is regulated by the Toll pathway during the systemic response, is regulated by imd in the respiratory tract, thus demonstrating the existence of distinct regulatory mechanisms for local and systemic induction of antimicrobial peptide genes in Drosophila

Evolution of water production of 67P/Churyumov-Gerasimenko: An empirical model and a multi-instrument study

We examine the evolution of the water production of comet 67P/Churyumov–Gerasimenko during the Rosetta mission (2014 June–2016 May) based on in situ and remote sensing measurements made by Rosetta instruments, Earth-based telescopes and through the development of an empirical coma model. The derivation of the empirical model is described and the model is then applied to detrend spacecraft position effects from the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) data. The inter-comparison of the instrument data sets shows a high level of consistency and provides insights into the water and dust production. We examine different phases of the orbit, including the early mission (beyond 3.5 au) where the ROSINA water production does not show the expected increase with decreasing heliocentric distance. A second important phase is the period around the inbound equinox, where the peak water production makes a dramatic transition from northern to southern latitudes. During this transition, the water distribution is complex, but is driven by rotation and active areas in the north and south. Finally, we consider the perihelion period, where there may be evidence of time dependence in the water production rate. The peak water production, as measured by ROSINA, occurs 18–22 d after perihelion at 3.5 ± 0.5 × 1028 water molecules s-1. We show that the water production is highly correlated with ground-based dust measurements, possibly indicating that several dust parameters are constant during the observed period. Using estimates of the dust/gas ratio, we use our measured water production rate to calculate a uniform surface loss of 2–4 m during the current perihelion passage

Molecular Analysis of Repeated Methicillin-Resistant Staphylococcus aureus Infections in Children

BACKGROUND: Methicillin-resistant Staphylococcus aureus (MRSA) is a major pathogen that causes severe morbidity and mortality in hospitalized patients. It is unclear whether repeated MRSA infections in pediatric patients are caused by relapse of previous infecting strains or by acquiring new strains from extrinsic sources. The study aimed to define the genetic relatedness of MRSA isolates from children with repeated infections. METHODOLOGY/PRINCIPAL FINDINGS: Children with multiple MRSA infections during 2004-2006 were identified in a teaching hospital. Repeated infections were confirmed by chart review and the responsible isolates were genotyped and screened for Panton-Valentine leukocidin (PVL) genes. Two consecutive episodes comprised an infection pair, and strain relatedness was defined for each pair as indistinguishable, highly related, or distinct if the isolates were of the same subtype, the same genotype, or different genotype, respectively. A total of 114 episodes comprising 66 infection pairs were identified in 48 children. The interval of infection pairs ranged from 15 days to 346 days, with a median duration of 57.5 days. Genotypings classified all isolates into 7 genotypes and 31 subtypes. Of 66 pairs, 46 (69.7%), 13 (19.7%) and 7 (10.6%) pairs were caused by indistinguishable, highly related and distinct strains, respectively. Subsequent infections caused by indistinguishable strains were more common for PVL-positive strains (17/18, 94.4%) than for PVL-negative strains (29/48, 60.4%, P = 0.007). The strain relatedness was not affected by the durations of interval between infections. CONCLUSIONS/SIGNIFICANCE: Most repeated MRSA infections in children are caused by indistinguishable strains even after a long period of interval, suggesting that persistent carriage and relapse of initial infecting strains were responsible for the majority of recurrent MRSA infections

The heterogeneous coma of comet 67P/Churyumov-Gerasimenko as seen by ROSINA: H <inf>2</inf> O, CO <inf>2</inf>, and CO from September 2014 to February 2016

Context. The ESA Rosetta mission has been investigating the environment of comet 67P/Churyumov-Gerasimenko (67P) since August 2014. Among the experiments on board the spacecraft, the ROSINA experiment (Rosetta Orbiter Spectrometer for Ion and Neutral Analysis) includes two mass spectrometers to analyse the composition of neutrals and ions and a COmet Pressure Sensor (COPS) to monitor the density and velocity of neutrals in the coma. Aims. We study heterogeneities in the coma during three periods starting in October 2014 (summer in the northern hemisphere) and ending in February 2016 (end of winter in the northern hemisphere). We provide a detailed description of the main volatiles dynamics (H2O, CO2, CO) and their abundance ratios. Methods. We analysed and compared the data of the Reflectron-Type Time-Of-Flight (RTOF) mass spectrometer with data from both the Double Focusing Mass Spectrometer (DFMS) and COPS during the comet escort phase. This comparison has demonstrated that the observations performed with each ROSINA sensor are indeed consistent. Furthermore, we used a Direct Simulation Monte Carlo (DSMC) model to compare modelled densitites with in situ detections. Results. Our analysis shows how the active regions of the main volatiles evolve with the seasons with a variability mostly driven by the illumination conditions; this is the case except for an unexpected dichotomy suggesting the presence of a dust layer containing water deposited in the northern hemisphere during previous perihelions hiding the presence of CO2. The influence of various parameters is investigated in detail: distance to the comet, heliocentric distance, longitude and latitude of sub-satellite point, local time, and phase angle

Electromechanical analysis of an adaptive piezoelectric energy harvester controlled by two segmented electrodes with shunt circuit networks

This paper presents an adaptive power harvester using a shunted piezoelectric control system with segmented electrodes. This technique has spurred new capability for widening the three simultaneous resonance frequency peaks using only a single piezoelectric laminated beam where normally previous works only provide a single peak for the resonance at the first mode. The benefit of the proposed techniques is that it provides effective and robust broadband power generation for application in self-powered wireless sensor devices. The smart structure beam with proof mass offset is considered to have simultaneous combination between vibration-based power harvesting and shunt circuit control-based electrode segments. As a result, the system spurs new development of the two mathematical methods using electromechanical closed-boundary value techniques and Ritz method-based weak-form analytical approach. The two methods have been used for comparison giving accurate results. For different electrode lengths using certain parametric tuning and harvesting circuit systems, the technique enables the prediction of the power harvesting that can be further proved to identify the performance of the system using the effect of varying circuit parameters so as to visualize the frequency and time waveform responses

Nanofluids Research: Key Issues

Nanofluids are a new class of fluids engineered by dispersing nanometer-size structures (particles, fibers, tubes, droplets) in base fluids. The very essence of nanofluids research and development is to enhance fluid macroscopic and megascale properties such as thermal conductivity through manipulating microscopic physics (structures, properties and activities). Therefore, the success of nanofluid technology depends very much on how well we can address issues like effective means of microscale manipulation, interplays among physics at different scales and optimization of microscale physics for the optimal megascale properties. In this work, we take heat-conduction nanofluids as examples to review methodologies available to effectively tackle these key but difficult problems and identify the future research needs as well. The reviewed techniques include nanofluids synthesis through liquid-phase chemical reactions in continuous-flow microfluidic microreactors, scaling-up by the volume averaging and constructal design with the constructal theory. The identified areas of future research contain microfluidic nanofluids, thermal waves and constructal nanofluids