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It is well known that X-ray luminosity (Lx) originating from high mass X-ray binaries (HMXBs) is tightly correlated with the host galaxy’s star formation rate (SFR). We explore this connection using a sample representative of the star-formation activity in the local Universe (Star-Formation Reference Survey; SFRS) along with a comprehensive set of star-formation (radio, FIR, 24μm, 8 μm, Hα, UV, SED fitting) and stellar mass (K-band, 3.6 μm, SED fitting) indicators, and Chandra observations. We investigate the Lx–SFR and Lx– stellar mass (M*) scaling relations down to sub-galactic scales of ∼lkpc2. This way we extend these relations to extremely low SFR (∼10−6M⊙.yr−1) and M* (∼104M⊙). We also quantify their scatter and their dependence on the age of the local stellar populations as inferred from the different age sensitive SFR indicators. These results are particularly important for setting the benchmark for the formation of X-ray binaries in vigorous, but low SFR objects such as galaxies in the early Universe.
This study focuses on the response of premixed flames to a transient hydrodynamic perturbation in an intermediate situation between laminar stretched flames and turbulent flames: an axisymmetric vortex interacting with a flame. The reasons motivating this choice are discussed in the framework of turbulent combustion models and flame response to the stretch rate. We experimentally quantify the dependence of the flame kinematic properties (displacement and consumption speeds) to geometrical scalars (stretch rate and curvature) in flames characterized by different effective Lewis numbers. Whilst the displacement speed can be readily measured using particle image velocimetry and tomographic diagnostics, providing a reliable estimate of the consumption speed from experiments remains particularly challenging. In the present work, a method based on a budget of fuel on a well chosen domain is proposed and validated both experimentally and numerically using two-dimensional direct numerical simulations of flame/vortex interactions. It is demonstrated that the Lewis number impact neither the geometrical nor the kinematic features of the flames, these quantities being much more influenced by the vortex intensity. While interacting with the vortex, the flame displacement (at an isotherm close to the leading edge) and consumption speeds are found to increase almost independently of the type of fuel. We show that the total stretch rate is not the only scalar quantity impacting the flame displacement and consumption speeds and that curvature has a significant influence. Experimental data are interpreted in the light of asymptotic theories revealing the existence of two distinct Markstein numbers, one characterizing the dependence of flame speed to curvature, the other to the total stretch rate. This theory appears to be well suited for representing the evolution of the displacement speed with respect to either the total stretch rate, curvature or strain rate. It also explains the limited dependence of the flame displacement speed to Lewis number and the strong correlation with curvature observed in the experiments. An explicit relationship between displacement and consumption speeds is also given, indicating that the fuel consumption rate is likely to be altered by both the total stretch rate and curvature.
This work presents the analysis of a transverse combustion instability in a reduced-scale rocket engine. The study is conducted on a time-resolved database of three-dimensional fields obtained via large-eddy simulation. The physical mechanisms involved in the response of the coaxial hydrogen/oxygen flames are discussed through the analysis of the Rayleigh term in the disturbance-energy equation. The interaction between acoustics and vorticity, also explicit in the disturbance-energy balance, is shown to be the main damping mechanism for this instability. The relative contributions of Rayleigh and damping terms, depending on the position of the flame with respect to the acoustic field, are discussed. The results give new insight into the phenomenology of transverse combustion instabilities. Finally, the applicability of spectral analysis on the nonlinear Rayleigh and dissipation terms is discussed.
Steady methane/air laminar premixed flames stabilised on a cylindrical bluff body subjected to a continuous rotation are analysed using joint direct numerical simulations (DNS) and experiments. DNS are carried out using a 19 species scheme for methane/air combustion and a lumped model to predict the cylinder temperature. Rotation of the cylinder induces a symmetry breaking of the flow, and leads to two distinct flame branches in the wake of the cylinder. DNS are validated against experiments in terms of flame topologies and velocity fields. DNS are then used to analyse flame structures and thermal effects. The location and structure of the two flames are differently modified by rotation and heat transfer: a superadiabatic flame branch stabilises close to the hot cylinder and burns preheated fresh gases while a subadiabatic branch is quenched over a large zone and anchors far downstream of the cylinder. Local flame structures are shown to be controlled to first order by the local enthalpy defect or excess due to heat transfer between the cylinder and the flow. An analysis of the local wall heat flux around the cylinder shows that, for low rotation speeds, the superadiabatic flame branch contributes to wall heat fluxes that considerably exceed typical values found for classical flame/wall interactions. However, for high rotation speeds, fluxes decrease because the cylinder is surrounded by a layer of burned gases that dilute incoming reactants and shield it from the flame.
Stable, electrically conductive, thin film materials are key components for high temperature sensors operating in harsh environments. In this work, nanocomposite Pt-Zr-B and Pt-Si thin film materials were grown to a nominal thickness of 200 nm on both r-cut sapphire (α-Al2O3) substrates using e-beam evaporation, and their structure, morphology, and chemical composition was characterized following thermal treatments in an air laboratory furnace up to 1300°C. In the Pt-Zr-B system, oxidation of a nanolaminate architecture consisting of ZrB2 and pure Pt layers leads to boron oxide evaporation and the formation of Pt grains decorated by tetragonal-ZrO2 nanocrystallites at high temperature. Electrical conductivity measurements with a 4-point probe show that this nanocomposite film structure can maintain a film conductivity > 1x106 S/m up to 1300°C, depending on the Pt/ZrB2 layer thickness ratio. In the Pt-Si system, film compositions were varied to yield either nanocrystalline Pt3Si, Pt2Si, or PtSi phases depending on the Pt-Si ratio, or an amorphous phase at high Si content. Above 1000°C in air, Pt-oxide and Si-oxide phases form and coexist with the Pt-Si phases, and some Pt-Si film conductivities remain as high as 1x106 S/m after annealing at 1000°C for 6 hours. It was found that a 100 nm thick amorphous alumina capping layer grown by atomic layer deposition (ALD) aids in limiting film oxidation, but film stress leads to regions of delamination.
The optical gaps of the low-bandgap PPVs (PM-20, PM-19, PM-18) are decreased down to 1.6-1.7 eV compared with that
of MDMO-PPV (2.2 eV). The best lateral hole mobility was determined to be 2.1 × 10-3 cm2/V s (PM-18) in
field effect transistors and exceeds that of MDMO-PPV (poly-[ 2-methoxy-5-(3'.7'-dimethyloctyloxy)-1.4-phenylenevinylene],
8.5 × 10-4 cm2/V s). This allows to reduce the PCBM ([6.6]-phenyl-C
-butanoic acid methyl
ester) content in solar cell devices down to 1:2 w/w giving a better
than for MDMO-PPV:-PCBM
cells (PM-19:-PCBM 2.32% on ITO-PET, 2.86% on ITO glass). The charge transfer to PCBM as acceptor occurs
quite normally and shows an effective charge separation using light-induced spin resonance spectroscopy (LESR). The
signals are shifted to lower field related to those of -PCBM
and overlap more with the polaron signal of PM-19. The LESR g-factor components of -PCBM
are reported for the first
time. The external quantum efficiency peak values achieve up to 42% at ~350–400 nm and 26% at ~640 nm
Researchers at the Pacific Northwest National Laboratory (PNNL) investigated the effects of gadolinium oxide concentration on the air oxidization of gadolinium oxide-doped uranium dioxide using thermogravimetry and differential scanning calorimetry to determine if such doping could improve uraniumdioxide's stability as a nuclear fuel during potential accident scenarios in a nuclear reactor or during long-term disposal. We undertook this study to determine whether the resistance of the uranium dioxide to oxidation to the orthorhombic U3O8 with its attendant crystal expansion could be prevented by addition of gadolinium oxide. Our studies found that gadolinium has little effect on the thermal initiation of the first step of the reported two-step air oxidation of UO2; however, increasing gadolinium oxide content does stabilize the initial tetragonal or cubic product allowing significant oxidation before the second expansive step to U3O8 begins.
Radiation damage experiments are being performed with pyrochlore and zirconolite in support of the disposition of surplus weapons-ready Pu. Pyrochlore becomes amorphous in approximately 1 year from the alpha recoil damage of ∼ 1018 alphas/g from the decay of 238Pu. The dissolution rate of 238Pu-bearing ceramics increases with increasing radiation damage as measured in a 3 d MCC-1 test at 90°C. Over the same period, zirconolite retains substantial crystallinity albeit with broadened diffraction peaks. The dissolution rate also increases with increasing radiation damage.
Biasing the substrate during deposition and the substrate's surface morphology may both have major effects on the structural properties of thin films. We present the results of structural investigations (Raman and FTIR spectroscopy, XRD, SAXS) of thin silicon films that were prepared at low temperatures by electron-cyclotron resonance (ECR) chemical-vapor deposition. The effect of substrate bias during the deposition was investigated for positive DC susceptor biases VB ranging from 0 to 45 V. For stainless steel substrates with an artificially enlarged surface roughness (smart substrates), an increase of the crystallinity could be observed with Raman spectroscopy. Films prepared under a susceptor bias of +15 V exhibited a texture inversion of preferential (220)- to (111)- oriented grains, which was accompanied by an increase in grain size from 18 to 42 nm. Small-angle X-ray scattering (SAXS) revealed the films as deposited on Al foil to exhibit significant free volume fractions (microvoids). The ability of tailoring the structure of thin Si films by applying a bias is discussed in terms of controlling the energy and intensity of ion flux to the surface of the growing film. This can efficiently be achieved in an ECR system, where the mean free path of gas particles exceeds the thickness of the plasma sheath.
The excretion of large amounts of P in effluent from intensive pig and poultry units is indicative of the poor availability of phytate-bound P in plant-derived feed ingredients. This environmental problem prompted the development and acceptance of microbial phytase feed enzymes for single-stomached animals. Their introduction led to an increasing recognition that phytate may have adverse effects on protein utilisation in addition to P. Consequently, the nutritional relevance of protein–phytate interactions for pigs and poultry is considered in the present review. Since the current understanding of the effects of protein–phytate interactions comes mainly from responses obtained to added phytase, literature on the influence of microbial phytases on amino acid digestibility and utilisation is summarised, followed by a discussion of possible mechanisms contributing to the negative effects of phytate. However, the rationale for the protein responses to added phytase remains largely speculative, and several modes of action are probably involved. It may be that the release of protein from protein–phytate complexes occurring naturally in feed ingredients, the prevention of formation of binary and ternary protein–phytate complexes within the gut, the alleviation of the negative impact of phytate on digestive enzymes and the reduction in endogenous amino acid losses are all contributing factors. A better understanding of the mechanisms of protein–phytate interactions and the modes of action of exogenous phytase enzymes is clearly desirable. Studies are also needed to identify and quantify the factors that contribute to the variable amino acid responses to added phytase. It appears that the relative solubilities of phytate salts and proteins from different feed ingredients and their effects on the extent of protein–phytate complex formation, coupled with variations in the effectiveness of phytase in different dietary contexts, may be the major factors responsible.
Electron cyclotron resonance chemical vapor deposition (ECR-CVD) is used to grow to prepare epitaxial films on Si(100), Si(111), and Si(311) at 325 °C with a growth rate of 10…12 nm/min. On Si(100) up to a layer thickness of more than 300 nm the films exhibit a well defined and smooth interface and a perfectly ordered lattice structure. Beyond a critical thickness of about 500 nm the formation of conically shaped, amorphous regions was observed. At a thickness of 1.6 µm only 10… 15 % of the surface consists of these amorphous cones. On Si(311), Si(111), and Si(011) the critical epitaxial thicknesses hepi depends on the crystallographic orientation of the substrate in the sequence hepi(311) > hepi(111) > hepi(011) with an abrupt change of the film structure from crystalline to amorphous
The gastrointestinal tract of the newly hatched chick is in a process of development and maturation. In the chicks of domestic fowl and turkeys considerable evidence suggests that, from hatching, the rate of development of the gastrointestinal tract exceeds the rate of body weight gain both physically (relative weight) and morphologically (villus height and perimeter, and villus volume). Rapid development is especially evident in the duodenum, jejunum and pancreas. Once hatched, the time at which maximum specific activities of digestive enzymes has been observed in the pancreas and intestinal brush border vary somewhat, but most often it occurs at or shortly after hatch. Subsequently, specific activities of these enzymes frequently decrease with age. Nevertheless, total digestive enzyme activity tends to increase during the early post-hatch period because of the rapid increase in the weight of the pancreas and intestines. In some instances the increases in total enzyme activity may be too small to keep up with increases in feed intake. For example, a lag in lipase secretion in relation to feed intake may contribute to the relatively poor utilization of some dietary lipids during the first 10 days or so after hatch. Although research findings on digestion and nutrient utilization have varied, there are numerous indications that, in addition to certain lipids, the utilization of some carbohydrates and protein is less efficient during the first week or two after hatch than in older chickens and turkeys. Overall, these observations suggest that additional research is warranted to obtain more definitive information on the development of gastrointestinal function in young poultry.
The junction properties of isotype and anisotype n+-ZnO/c-Si heterostructures have been studied by electrical and photoelectrical methods. We present evidence that the junction properties are strongly affected by a 10–30 nm thick ZnO layer closest to the heterointerface with distinctively different properties than those of the ZnO film bulk. This layer supports a dominant current flow via multistep tunnelling-recombination. When a 10 nm thin ZnS or ZnSe interlayer is inserted charge transport is controlled by thermionic emission. The interlayer acts as spacer and increases the band bending in the silicon absorber. However, there is still a too high trap density at the interlayer/c-Si interface, so that Voc does not exceed 0.25–0.32 V.
Pharmacological approaches to opiate addiction have for the most part been limited to a role in detoxification. A high percentage of patients who complete detoxification programmes relapse.
In the present study, we used a simple laboratory method to investigate suggestions from preclinical studies that 5-(hydroxytryptamine) HT3 receptor antagonists have a role in the treatment of addiction.
We showed that addicts stably maintained on methadone experienced significant craving, dysphoria, and withdrawal-like symptoms when exposed to a video containing drug-related cues. The craving was not lessened by treatment with the 5-HT3 receptor antagonist, ondansetron (4 mg orally).
Our current findings do not support a role for 5-HT3 receptor agonists in the reduction of craving in opiate addicts.
To assess the cost-effectiveness of human immunodeficiency virus (HIV) screening strategies of surgeons and dentists.
We constructed a model to project costs and HIV transmissions prevented over 15 years for four screening scenarios: 1) one-time voluntary screening, 2) one-time mandatory screening, 3) annual voluntary screening, and 4) annual mandatory screening. One-time screening occurs only in the first year of the program; annual screening occurs once each year. Under mandatory screening, all practitioners are tested and risks of practitioner-to-patient transmission are eliminated for all practitioners testing positive. Voluntary screening assumes 90% of HIV-positive and 50% of HIV-negative practitioners are tested, and risks of transmission in the clinical setting are eliminated for 90% of HIV-positive surgeons and dentists. All costs and benefits are discounted at 5% per annum over 15 years.
Using “best-case” scenario assumptions, we find for surgeons that a one-time voluntary screening program would be most cost-effective, at $899,336 for every HIV transmission prevented. For dentists, the one-time voluntary program also is the most cost-effective, at $139,571 per transmission prevented. Annual mandatory programs were least cost-effective for both surgeons and dentists, at $63.3 million and $2.2 million per transmission prevented, respectively.
HIV screening of surgeons and dentists ranks among the more expensive medical lifesaving programs, even using liberal assumptions about program effectiveness. Frequency of screening and whether testing is mandatory or voluntary dramatically affect cost per transmission prevented; these features should be considered carefully in designing specific HIV screening programs.
We have performed real time measurements of intrinsic stresses during growth by reactive dc magnetron sputtering of aluminum nitride (AlN) thin films on silicon substrates in an UHV growth chamber. An experimental setup based on laser beam reflection is constructed such that substrate curvature as well as film thickness can be continuously monitored as growth proceeds. On Si(111) substrates, stress measurements were carried out during growth of both polycrystalline and epitaxial A1N films as a function of deposition pressure. This is the first such comparative study to our knowledge for the AlN/Si system. Our room temperature measurements on polycrystalline films corroborates previous post-growth measurements. Our high temperature measurements provide evidence of large intrinsic stresses and negligible stress relaxation during epitaxial growth of AlN on Si(111). We further compared stress behavior during both room temperature and high temperature growth of AlN films on Si(111) and Si(001) substrates. Our observations indicate while intrinsic stresses during room temperature growth can be compressive or tensile depending on plasma conditions, it is tensile during late stage growth at high temperatures.
New x-ray diffraction measurements performed on bonm nitride films deposited by pulsed excimer laser deposition are presented. The x-ray data, taken with both a molybdenum rotating anode source and synchrotron radiation, indicate that the epitaxial cBN films are ≤ 200 Å thick. We also report the successful growth of oriented crystalline diamond on the (001) surface of cBN/Si substrates using the method of pulsed laser deposition. X-ray diffraction measurements indicate that the diamond layer is 200 Å thick with a lattice constant of 3.56 Å. The structures of metastable films (cBN and diamond) are very sensitive to growth conditions: we present evidence that an epitaxial-crystalline to incoherent phase transition occurs when the thickness of the films exceeds a critical value (∼ 200 Å for our present growth conditions).
We report the growth of boron nitride films on (001), (110), and (111) faces of silicon using the method of pulsed excimer laser ablation. The structure of the Alms grown on the (001) and (110) orientations of Si is cubic zincblende with a lattice constant of 3.619 Å. The films were found to be heteroepitaxial on silicon (001) with the cubic BN (100) axes parallel to Si (100), as characterized by x-ray diffraction and high-resolution transmission electron microscopy. In that system, we find evidence for an unusual 3:2 commensurate lattice matching. The films appear to cubic but randomly oriented on the Si (110), and no evidence for crystallinity is found for films grown on Si (111).
We report the successful growth of cubic boron nitride thin films on single crystal 100 silicon by using pulsed excimer laser ablation of a hexagonal boron nitride bulk target. Optical emission spectra were obtained during the film deposition giving insight into the deposition mechanism. The deposited films were characterized by transmission electron microscopy, scanning electron microscopy, optical microscopy, x-ray diffraction, and Auger electron microscopy. Regions of the films were found to exhibit epitaxy with the substrate.