Hetero-/homogeneous combustion of hydrogen/air mixtures over platinum at pressures up to 10 bar

The hetero-/homogeneous combustion of fuel-lean hydrogen/air premixtures over platinum was investigated experimentally and numerically in the pressure range 1 bar  p  10 bar. Experiments were carried out in an optically accessible channel-flow catalytic reactor and included planar laser induced fluorescence (LIF) of the OH radical for the assessment of homogeneous (gas-phase) ignition, and 1-D Raman measurements of major gas-phase species concentrations for the evaluation of the heterogeneous (catalytic) processes. Simulations were performed with a full-elliptic 2-D model that included detailed heterogeneous and homogeneous chemical reaction schemes. The predictions reproduced the measured catalytic hydrogen consumption, the onset of homogeneous ignition at pressures of up to 3 bar and the diminishing gas-phase combustion at p  4 bar. The suppression of gaseous combustion at elevated pressures bears the combined effects of the intrinsic homogeneous hydrogen kinetics and of the hetero/homogeneous chemistry coupling via the catalytically produced water over the gaseous induction zone. Transport effects, associated with the large diffusivity of hydrogen, have a smaller impact on the limiting pressure above which gaseous combustion is suppressed. It is shown that for practical reactor geometrical confinements, homogeneous combustion is still largely suppressed at p  4 bar even for inlet and wall temperatures as high as 723 and 1250 K, respectively. The lack of appreciable gaseous combustion at elevated pressures is of concern for the reactor thermal management since homogeneous combustion moderates the superadiabatic surface temperatures attained during the heterogeneous combustion of hydrogen.     

Self assembled nanoparticle Pb1−xFexSe/single crystal Si heterojunctions

Nanoparticle Pb_1−xFe_xSe (0.00  x  0.16) thin films have been deposited on quartz, glass and silicon substrates by chemical bath deposition technique. Structural and optical properties of the films with iron concentration 0.00  x  0.16 indicate that the films grow as single-phase Pb_1−xFe_xSe ternary alloys with rocksalt structure and with direct optical band gaps (E_g) that increase with decrease in grain size and have values larger than 0.28 eV of the bulk PbSe. Average grain size in films grown at fixed bath temperature T_b of 85 °C is observed to decrease from 72 to 22 nm whereas lattice parameter is observed to increase from 6.12 to 6.14 Å with increase in Fe concentration from x = 0.00 to x = 0.16. The observed blue shift in film materials originates from quantum confinement in the nanograins. Nanoparticle Pb_1−xFe_xSe/single crystal Si heterojunctions show rectifying behavior. On illumination of heterojunctions with visible light current is observed to increase in forward and reverse bias. This increase in current in the presence of visible light is considered to be due to carrier multiplication by Auger electron emission.     

Morphological and electro-optical responses of dichroic polymer dispersed liquid crystal films

Dichroic polymer dispersed liquid crystal (DPDLC) films containing different concentration of dichroic dye have been prepared by polymerization induced phase separation technique using nematic liquid crystal material in UV curable polymer NOA 65 and anthraquinone dichroic dye. The effects of applied voltage and temperature on the LC droplet morphology and its optical characteristics were studied in detail. Liquid crystal droplets containing low concentration of dye (0.25%) in polymer matrix exhibit bipolar configuration at lower applied voltage (10 V) whereas at relatively higher voltage (15 V) maltese type liquid crystal droplets were seen. In addition, low concentration DPDLC film shows better optical transmission and higher contrast ratio.     

Modified Kolmogorov wave turbulence in QCD matched onto “Bottom-up” thermalization

We investigate modification of Kolmogorov wave turbulence in QCD calculating gluon spectra as functions of time in the presence of a low energy source which feeds in energy density in the infrared region at a time-dependent rate. Then considering the picture of saturation constraints as has been constructed in the “bottom-up” thermalization approach we revisit that picture for RHIC center-mass energy, W=130 GeV, and also extend it to LHC center-mass energy, W=5500 GeV, thus for two cases having an opportunity to calculate the equilibration time, τ_eq|therm, of the gluon system produced in a central heavy ion collision at mid-rapidity region. Thereby, at RHIC and LHC energies we can match the equilibration time, obtained from the late stage gluon spectrum of the modified Kolmogorov wave turbulence, onto that of the “bottom-up” thermalization and other evolutional approaches as well. In addition, from the revised “bottom-up” approach we find the gluon liberation coefficient to be on the average, ε0.81–1.06 at RHIC and ε0.50–0.56 at LHC. We also present other phenomenological estimates of τ_therm which, at QCD realistic couplings, yield 0.45–0.65 fmτ_therm0.97–2.72 fm at RHIC and 0.31–0.40 fmτ_therm0.86–2.04 fm at LHC. We show that the second upper-bounds of τ_therm in both cases are due to the late stage gluon spectrum of the original Kolmogorov wave turbulence in QCD, previously deduced with a low energy source which feeds in energy density at a constant rate. On the other hand, the lower-bounds and first upper-bounds of τ_therm are due to the late stage gluon spectrum of the modified QCD wave turbulence, deduced here at the specific time-dependent rate. In the latter case, at certain conditions, taking also into account both very small and realistic couplings we give estimates: 0.65 fmτ_therm1.29 fm at RHIC and 0.52 fmτ_therm1.16 fm at LHC, as well as at realistic couplings we find 0.53<τ_therm<0.7 fm at RHIC and 0.41<τ_therm<0.65 fm at LHC.     

Interband absorption and luminescence in small quantum dots under strong magnetic fields

Interband absorption and luminescence of quasi-two-dimensional, circularly symmetric, N_e-electron quantum dots are studied at high magnetic fields, 8B60 T, and low temperatures, T2 K. In the N_e=0 and 1 dots, the initial and final states of such processes are fixed, and thus the dependence on B of peak intensities is monotonic. For larger systems, ground state rearrangements with varying magnetic field lead to substantial modifications of the absorption and luminescence spectra. Collective effects are seen in the N_e=2 and 3 dots at “filling fractions” and .     

Effect of Ca doping on the superconducting properties of GdBaSrCu3O7−δ bulk samples

Gd_1−xCa_xBaSrCu₃O_7−δ samples (0  x  0.1) were prepared via solid-state reaction. Four-point probes method was used for resistance versus temperature measurements. Results show decrease in T_c by increasing x content. This variation is assumed to be irrelevant to the different phases or impurity effects since X-ray patterns show all samples are tetragonal single-phase. Ca doping decreases the oxygen content and lattice parameters of the samples. It is suggested that Ca prevents the dislocation of oxygen, and then disrupts the hole concentration of the system and antiferromagnetic correlation at CuO₂ planes. Subsequently, destroys the superconductivity of the samples.     

Laser induced fluorescence of formaldehyde and Raman measurements of major species during partial catalytic oxidation of methane with large H2O and CO2 dilution at pressures up to 10 bar

The catalytic partial oxidation (CPO) of CH₄/O₂ mixtures diluted with large amounts of H₂O and CO₂ (up to 43% and 21% vol., respectively) was investigated experimentally and numerically in the pressure range 4 bar  p  10 bar. Experiments were carried out in an optically accessible channel-flow catalytic reactor coated with Rh/ZrO₂, and included planar laser induced fluorescence (LIF) of formaldehyde for the assessment of homogeneous (gas-phase) ignition and one-dimensional spontaneous Raman measurements of all major gas-phase species for the evaluation of the heterogeneous (catalytic) processes. Simulations were performed with a full elliptic model that included detailed heterogeneous and homogeneous chemical reaction schemes. Over the reactor length with negligible gas-phase chemistry contribution, the employed heterogeneous reaction scheme provided good agreement to the measured methane consumption and synthesis gas yields, overpredicting mildly the partial over the total oxidation route. It was shown that the added water provided a source of O(s) and OH(s) surface radicals that enhanced the methane conversion and H₂ yields and reduced the CO yields. Moreover, the addition of CO₂ had a negligible chemical effect on the aforementioned parameters. An increase in pressure from 4 to 10 bar had a minor impact on the methane conversion and hydrogen selectivity. The employed gaseous scheme reproduced the LIF-measured onset of homogeneous ignition, although it underpredicted the extent of the formaldehyde zone ahead of the flame and the flame propagation characteristics at the highest investigated pressure (10 bar).     

Photoluminescence and structural properties of GaInNAs/GaAs quantum wells grown by molecular beam epitaxy under different arsenic pressures

GaInNAs/GaAs quantum wells grown by molecular beam epitaxy under different arsenic pressures have been studied using photoluminescence (PL), X-ray diffraction (XRD) and secondary-ion mass spectrometry (SIMS). The best optical properties are achieved with the V/III beam equivalent pressure ratio (V/III_BEP) of 10. The PL emission wavelength remains unchanged for 8V/III_BEP12, suggesting that within this range neither the alloy composition nor the nitrogen sticking coefficient is changed. For the lower and higher V/III_BEP ratios the PL wavelength is red-shifted or blue-shifted, respectively. The XRD results indicate that the nitrogen incorporation into the group-V sub-lattice is enhanced at low As pressures and reduced at high As pressures. The PL behaviour can thus be understood as a competition between As and N adatoms in occupying anion lattice sites.     

Antiferromagnetic Mn50Fe50 wire with large magnetostriction

This work presents a study on the relation between the fiber texture and the magnetostrictive performance in an antiferromagnetic Mn₅₀Fe₅₀ alloy wire, which was prepared through the combining process of hot rolling and cold drawing. The face-centered cubic (fcc) crystal structure can be retained during the plastic deformation process. Mixed fiber textures consisting of both 1 1 0 and 1 0 0 components were formed along the drawing direction (DD) in the wire. A large magnetostriction of 750 ppm was obtained along DD under 1.2 T, which can be ascribed to the single γ phase and the formation of preferred crystal orientation.     

Dielectric/piezoelectric properties and temperature dependence of domain structure evolution in lead free single crystal

(K_0.5Na_0.5)NbO₃ (KNN) single crystals were grown using a high temperature flux method. The dielectric permittivity was measured as a function of temperature for [001]-oriented KNN single crystals. The ferroelectric phase transition temperatures, including the rhombohedral–orthorhombic T_R−O, orthorhombic–tetragonal T_O−T and tetragonal–cubic T_C were found to be located at −149  C, 205 C and 393 C, respectively. The domain structure evolution with an increasing temperature in [001]-oriented KNN single crystal was observed using polarized light microscopy (PLM), where three distinguished changes of the domain structures were found to occur at −150  C, 213 C and 400 C, corresponding to the three phase transition temperatures.     

The extraction of total cross section from

We report on the first measurement of the differential cross section of -meson photoproduction for the d(γ,pK⁺K⁻)n exclusive reaction channel. The experiment was performed using a tagged-photon beam and the CEBAF Large Acceptance Spectrometer (CLAS) at Jefferson Lab. A combined analysis using data from the d(γ,pK⁺K⁻)n channel and those from a previous publication on coherent production on the deuteron has been carried out to extract the −N total cross section, σ_N. The extracted −N total cross section favors a value above 20 mb. This value is larger than the value extracted using vector-meson dominance models for photoproduction on the proton.     

Asymmetric di-jet production in polarized hadronic collisions

Using the collinear QCD factorization approach, we study the single-transverse-spin dependent cross section Δσ(S) for the hadronic production of two jets of momenta P₁=P+q/2 and P₂=−P+q/2. We consider the kinematic region where the transverse components of the momentum vectors satisfy PqΛ_QCD. For the case of initial-state gluon radiation, we show that at the leading power in q/P and at the lowest non-trivial perturbative order, the dependence of Δσ(S) on q decouples from that on P, so that the cross section can be factorized into a hard part that is a function only of the single scale P, and into perturbatively generated transverse-momentum dependent (TMD) parton distributions with transverse momenta .     

A high throughput approach to quantify protein adsorption on combinatorial metal/metal oxide surfaces using electron microprobe and spectroscopic ellipsometry

Although metallic biomaterials are widely used, systematic studies of protein adsorption onto such materials are generally lacking. Combinatorial binary films of Al_1−xTi_x and Al_1−xNb_x (0  x  1) and corresponding pure element films were produced on glass substrates using a unique magnetron sputtering technique. Fibrinogen and albumin adsorption amounts were measured by wavelength-dispersive spectroscopy (WDS) and spectroscopic ellipsometry (SE) equipment, both high throughput techniques with automated motion stage capabilities. X-ray diffraction revealed that the binary films have crystalline phases present near the ends of the compositional gradient with an amorphous region throughout the interior of the gradient. X-ray photoelectron spectroscopy provided the surface chemistry along the binary films and showed that Al₂O₃ preferentially formed at the surface. Protein adsorption onto these films was found to be closely correlated to the alumina surface fraction, with high alumina content at the surface leading to low amounts of adsorbed fibrinogen and albumin. Protein adsorption amounts obtained with WDS and SE were in excellent agreement for all films. This suggests that this combinatorial materials approach combined with these state-of-the-art, automated high throughput instruments provides a novel way to accurately monitor protein adsorption taking place at the surfaces of these metal/metal oxide materials.     

Heavy Majorana neutrinos in the effective Lagrangian description: Application to hadron colliders

We consider the effects of heavy Majorana neutrinos N with sub-TeV masses and argue that the mere observation of these particles would be a signal of physics beyond the minimal seesaw mechanism. We describe the N interactions using an effective Lagrangian and exhibit the complete set of effective operators of dimension 6 involving the N and Standard Model fields. We argue that these interactions can be relatively easy to track at high-energy colliders. For example, we find that new physics (beyond the N) at the TeV-scale can yield thousands of characteristic same-sign lepton number violating ℓ⁺ℓ⁺jj events (j = light jet) at the LHC if m_N600 GeV, which can also have a distinctive forward-backward asymmetry signal; even the Tevatron has good prospects for this signature if m_N300 GeV.     

A new simple tubular flow cell for use with variable angle spectroscopic ellipsometry: A high throughput in situ protein adsorption study

A simple and novel flow cell design is presented here for use with variable angle spectroscopic ellipsometry (VASE) to study the adsorption of liquid-borne species on reflective surfaces. The flow cell allows a sample as large as 6 mm × 75 mm to be probed point by point and at any common ellipsometric angle of incidence, unlike other designs. Using our flow cell system with VASE, combinatorial films of Al_1−xNb_x, Al_1−xTa_x, and Al_1−xTi_x (0  x  1) were tested in situ for fibrinogen affinity along their 75 mm long compositional gradients. Fibrinogen adsorption on the films was found to be closely correlated to the various surface oxide fractions, with high alumina content at the surface leading to low amounts of adsorbed fibrinogen for each binary library. Adsorbed amounts measured in situ were in agreement with previously obtained values found using ex situ techniques.     

Surface morphology and composition of c-, a- and m-sapphire surfaces in O2 and H2 environments

This paper reports that monitoring the composition of the c(0 0 0 1), a(11–20) and m(10–10) sapphire surfaces is essential for a proper interpretation of the surface morphologies obtained after annealing at 1253 and 1473 K in ArH₂ or ArO₂ atmospheres. Our experimental investigations, which have used Auger electron spectroscopy (AES) and atomic force microscopy (AFM) on the surfaces of 99.99% pure sapphire wafers, have led to the following original conclusions: (i) Calcium segregates at the c-surface of sapphire both under ArO₂ and ArH₂. (ii) Potassium adsorption enhances the kinetics of step-bunching on the c-surface under ArO₂. (iii) The step edges on the a-surface may develop a comb-like morphology made of parallel strips along the [10–10] direction. (iv) At 1253 K, clean m-surfaces may be stable. (v) Under ArH₂, alumina surface diffusion is much slower than under ArO₂ for all surface orientations, the surface concentration of impurities is low, and the Al–O ratio of the AES signals at the surface is significantly larger.     

Electric and magnetic losses and gains in determining the sign of refractive index

Within the framework of classic electromagnetic theories, we have studied the sign of refractive index of optical medias with the emphases on the roles of the electric and magnetic losses and gains. Starting from the Maxwell equations for an isotropic and homogeneous media, we have derived the general form of the complex refractive index and its relation with the complex electric permittivity and magnetic permeability, i.e. , in which the intrinsic electric and magnetic losses and gains are included as the imaginary parts of the complex permittivity and permeability, respectively, as  = _r + i_i and μ = μ_r + iμ_i. The electric and magnetic losses are present in all passive materials, which correspond, respectively, to the positive imaginary permittivity and permeability _i > 0 and μ_i > 0. The electric and magnetic gains are present in materials where external pumping sources enable the light to be amplified instead of attenuated, which correspond, respectively, to the negative imaginary permittivity and permeability _i < 0 and μ_i < 0. We have analyzed and determined uniquely the sign of the refractive index, for all possible combinations of the four parameters _r, μ_r, _i, and μ_i, in light of the relativistic causality. A causal solution requires that the wave impedance be positive Re{Z} > 0. We illustrate the results for all cases in tables of the sign of refractive index. One of the most important messages from the sign tables is that, apart from the well-known case where simultaneously  < 0 and μ < 0, there are other possibilities for the refractive index to be negative n < 0, for example, for _r < 0, μ_r > 0, _i > 0, and μ_i > 0, the refractive index is negative n < 0 provided μ_i/_i > μ_r/_r.     

1.3 μm range effectively cylindrical In0.53Ga0.47As/In0.52Al0.48As quantum wires grown on (2 2 1)A InP substrates by molecular beam epitaxy

Vertically coupled quantum wires (QWRs) have been made by alternately stacking nominally 3.6 nm thick In_0.53Ga_0.47As self-organized QWR layers and 1 nm thick In_0.52Al_0.48As barrier layers on (2 2 1)A-oriented InP substrates by molecular beam epitaxy. The surface of In_0.53Ga_0.47As QWR layers was corrugated at an amplitude of 1.1 nm and period of 27 nm, and lateral confinement potential is induced by their thickness modulation. The wavelength of photoluminescence (PL) from the stacked QWRs at 15 K becomes longer from 1220 to 1327 nm with increasing total number of stacked QWR layers, N_SL, from 1 to 9, while PL full-width at half-maximum is reduced from 22 to 8.6 meV. The PL intensity with the polarization parallel to the wire direction, I, is 1.30 times larger than that with the normal polarization, I, when N_SL=1. The PL intensity ratio, I/I, reaches as large as 4 when N_SL=9, indicating successful control of relative strength between vertical confinement and lateral confinement of carriers. The value of I/I obtained for the stacked QWRs with N_SL=9 is the same value as cylindrical QWRs have. The results indicate that effectively cylindrical QWRs with the best uniformity and 1.3 μm range emission were realized by stacking of self-organized QWR layers.     

Simulation of kinetically limited growth of electrodeposited polycrystalline Ni films

A kinetic Monte Carlo (KMC) technique was adopted to simulate the growth dynamics of electrodeposited polycrystalline Ni thin films under kinetically limited conditions with a two-dimensional triangle lattice mapping the cross-section of the film. Effects of surface diffusion and surface-energy anisotropy on the microstructures of the plated film such as shape and size of grains, density, surface roughness, and textures were examined. This work focuses on the microstructure evolutions for different deposition parameters (for example, deposition rate and electrolyte temperature). We obtained the growth exponent β=0.46, which characterizes the scaling behavior of this growth. Preferential orientation of 1 1 1 and 1 0 0 have been observed at elevated temperature and at elevated deposition rate, respectively. To simulate the evolution of texture, the influence of hydrogen absorption on the surface energy of six main surfaces of nickel was investigated.     

Microscopic description of superheavy nuclei

The results of extensive microscopic relativistic mean field (RMF) calculations for the nuclei appearing in the α-decay chains of recently discovered superheavy elements with 109  Z  118 are presented and discussed. The calculated ground-state properties like total binding energies, Q-values, deformations, radii, and densities closely agree with the corresponding experimental data, where available. The root mean square radii closely follow A^1/3 law (A being the mass number) with the constant r_o = 0.9639 ± 0.0005 fm. The double folding (tρρ) approximation is used to calculate the interaction potential between the daughter and the α, using RMF densities along with the density-dependent nucleon–nucleon interaction (M3Y). This in turn is employed within the WKB approximation to estimate the half-lives without any additional parameter for α-decay. The half-lives are highly sensitive to the Q-values used and qualitatively agree with the corresponding experimental values. The use of experimental Q-values in the WKB approximation improves the agreement with the experiment, indicating that the resulting interaction potential is reliable and can be used with confidence as the real part of the optical potential in other scattering and reaction processes.