Showing papers by "ExxonMobil published in 1982"

Statistical ray optics.

Abstract: A statistical approach is taken toward the ray optics of optical media with complicated nonspherical and nonplanar surface shapes. As a general rule, the light in such a medium will tend to be randomized in direction and of 2n2(x) times greater intensity than the externally incident light, where n(x) is the local index of refraction. A specific method for doing optical calculations in statistical ray optics will be outlined. These optical enhancement effects can result in a new type of antireflection coating. In addition, these effects can improve the efficiency as well as reduce the cost of solar cells.

Random Walks with Infinite Spatial and Temporal Moments

Abstract: The continuous-time random walk of Montroll and Weiss has been modified by Scher and Lax to include a coupled spatial-temporal memory. We treat novel cases for the random walk and the corresponding generalized master equation when combinations of both spatial, and temporal moments of the memory are infinite. The asymptotic properties of the probability distribution for being at any lattice site as a function of time and its variance are calculated. The resulting behavior includes localized, diffusive, wavelike, and Levy's stable laws for the appropriate scaled variable. We show that an infinite mean waiting time can lead to long time diffusive behavior, while a finite mean waiting time is not sufficient to ensure the same.

Exact eigenfunctions for square-wave gratings: Application to diffraction and surface-plasmon calculations

Abstract: We show that for dielectric or metallic gratings with square-wave geometry the photon eigenfunctions in the grating region can be expressed in analytical form. The knowledge of these eigenfunctions makes the diffraction calculation not only simple and direct, but also devoid of the many limitations encountered in other solution techniques. In particular, diffraction from deep gratings and the calculation of surface-plasmon excitations present no difficulties. Numerical results on diffraction efficiency are in good agreement with our experimental data. The near-field electromagnetic properties of Ag gratings are examined in detail. These results are of particular importance in understanding the optical behavior of molecules near a rough metal surface (for example, in surface-enhanced Raman scattering). It is shown that coincident with the excitation of surface plasmon, there is an enhancement of the local- (surface-) field intensity by a factor of 100-500. For molecules on a grating surface, such increase in local fields can imply an amplification of ${10}^{4}$-3\ifmmode\times\else\texttimes\fi{}${10}^{5}$ for the Raman scattering signal.

Boundary-layer phase transition in nematic liquid crystals

Abstract: Phase-transition properties of nematic liquid crystals aligned by a short-range, arbitrary-strength-substrate potential are examined in the framework of Landau---de Gennes theory. It is shown that the substrate potential, which can arise from surface treatment of liquid-crystal display cells, not only induces a boundary layer in which the order-parameter values can be significantly different from that of the bulk, but also introduces a new "boundary-layer phase transition" which occurs at temperatures higher than the bulk-transition temperature. This novel transition is found to take place only in a limited range of substrate potential strength. For 4-pentyl-4'-cyanobiphenyl (PCB), the limiting values of this range are computed to be \ensuremath{\sim}0.075 and \ensuremath{\sim}0.15 erg/${\mathrm{cm}}^{2}$. Calculations are performed for both the semi-infinite-sample case and the finite-thickness-sample case. Various phase diagrams are presented to show the effects of sample thickness and substrate potential on the bulk as well as the boundary-layer phase-transition temperatures. The paper concludes with a discussion of experimental possibilities.

Ink jet method and apparatus

Abstract: An ink jet includes a variable volume chamber with an ink droplet ejecting orifice The volume of the chamber is varied by a transducer which expands and contracts in a direction having at least a component extending parallel with the axis ink droplet ejection from the orifice The transducer communicates with a moveable wall of the chamber which has a sufficiently small area such that the difference in the pressure pulse transit times from each point on the wall to the ink droplet ejection orifice is less than 1 microsecond

Realization of a thin film solar cell with a detached reflector

Abstract: The present invention is an optically enhanced solar cell having a detached reflector. The optically enhanced solar cell includes a semiconductor material bounded on each side by transparent electrical contacts and an optional antireflection coating with the surface of at least one of these layers being textured. Light is reflected in the cell by a reflector which is detached (i.e., spaced) from the enhanced cell using a layer of dielectric material.

H − T phase diagram for spin-glasses: An experimental study of Ag:Mn

Abstract: We present high-resolution SQUID (superconducting quantum interference device) measurements of the dc magnetization on two Ag:Mn samples containing 2.6 and 4.0 at.% Mn. We have measured in detail the temperature dependence of the magnetization on warming through the glass temperature, ${T}_{G}$, (i) after cooling to $Tl{T}_{G}$ in a near-zero field and then applying the measurement field, zero-field cooled, and (ii) after cooling to $Tl{T}_{G}$ in the measurement field. This has been done for fields $0.5\ensuremath{\le}H\ensuremath{\le}500$ Oe. The temperature derivative, $\frac{\mathrm{dM}(H,T)}{\mathrm{dT}}$, of the ZFC curve shows structure, allowing the identification of several characteristic temperatures associated with the paramagnetic to spin-glass transition in the presence of an external magnetic field. The temperature, ${T}_{B}$, where the crossover from a Curie-like to a nonlinear susceptibility occurs, behaves as $\ensuremath{\sim}{H}^{0.5\ifmmode\pm\else\textpm\fi{}0.1}$. Two further temperatures, $\overline{T}$ and ${T}_{P}$, where $\overline{T}l{T}_{P}l{T}_{G}^{0}(H\ensuremath{\rightarrow}0)$ are suggested as possible candidates for the theoretical-field-dependent transition temperature ${T}_{G}(H)$ given by ${1\ensuremath{-}[\frac{{T}_{G}(H)}{{T}_{G}^{0}}]}={\mathrm{Ah}}^{\frac{2}{3}}$ where $h=\frac{H}{J}=\frac{{g}_{{\ensuremath{\mu}}_{B}}H}{{k}_{B}{T}_{G}^{0}}$ and $A$ is of order unity. We find ${1\ensuremath{-}[\frac{\overline{T}(H)}{{T}_{G}^{0}}]}={\mathrm{Bh}}^{0.70\ifmmode\pm\else\textpm\fi{}0.05}$, but where $B$ is approximately ${(19)}^{2/3}$. However, the ${T}_{P}$ data are consistent with the theoretical prediction ($A\ensuremath{\simeq}1$) using no adjustable parameters, but the range of data is insufficient to enable an unambiguous verification of the theory. On the basis of recent theories, we suggest that the system entering the spin-glass phase at ${T}_{G}(H)$ should be marked experimentally by ${\ensuremath{\chi}}_{\mathrm{dc}}=\frac{M}{{H}_{\mathrm{static}}}g{\ensuremath{\chi}}_{\mathrm{ac}}(\ensuremath{ u},{H}_{\mathrm{osc}},{H}_{\mathrm{static}})$ where $M$ is the magnetization, ${H}_{\mathrm{static}}$ the magnitude of the dc field, ${H}_{\mathrm{osc}}$ the amplitude of the ac oscillating field, and $\ensuremath{ u}$ its frequency. This argument leads us to conclude that ${T}_{P}(H)$ should be taken as the experimental definition of ${T}_{G}(H)$.

Localization in One-Dimensional Lattices in the Presence of Incommensurate Potentials

Abstract: The density of states and the localized or extended nature of the eigenstates is investigated in one-dimensional crystals with a modulation potential incommensurate with that of the underlying lattice. Studies of the transmission coefficient $T$ and of the spatial dependence of the eigenstates show that even in one dimension it is possible to have a mobility edge. The implications of these results on experimentally measured quantities are also discussed.

Natural lithographic fabrication of microstructures over large areas

Abstract: Large area random and mosaic arrays of identical submicron microcolumnar structures can be produced on surfaces by directionally ion etching a monolayer film of spherical colloidal particles.

Fluorescent lifetimes of molecules on silver-island films.

Abstract: The fluorescence of molecules on silver-island films exhibits nonexponential decay and is several orders of magnitude more rapid than on a silica surface, while the total emission intensity is slightly increased. This behavior results from the electromagnetic coupling between the fluorescing molecules and the plasmon resonances of the silver islands. We obtain good agreement with a model that uses the same theory for the electromagnetic coupling as has been used to account for surface-enhanced Raman scattering.

Microbial Oxidation of Hydrocarbons: Properties of a Soluble Methane Monooxygenase from a Facultative Methane-Utilizing Organism, Methylobacterium sp. Strain CRL-26.

Abstract: Methylobacterium sp. strain CRL-26 grown in a fermentor contained methane monooxygenase activity in soluble fractions. Soluble methane monooxygenase catalyzed the epoxidation/hydroxylation of a variety of hydrocarbons, including terminal alkenes, internal alkenes, substituted alkenes, branched-chain alkenes, alkanes (C(1) to C(8)), substituted alkanes, branched-chain alkanes, carbon monoxide, ethers, and cyclic and aromatic compounds. The optimum pH and temperature for the epoxidation of propylene by soluble methane monooxygenase were found to be 7.0 and 40 degrees C, respectively. Among various compounds tested, only NADH(2) or NADPH(2) could act as an electron donor. Formate and NAD (in the presence of formate dehydrogenase contained in the soluble fraction) or 2-butanol in the presence of NAD and secondary alcohol dehydrogenase generated the NADH(2) required for the methane monooxygenase. Epoxidation of propylene catalyzed by methane monooxygenase was not inhibited by a range of potential inhibitors, including metal-chelating compounds and potassium cyanide. Sulfhydryl agents and acriflavin inhibited monooxygenase activity. Soluble methane monooxygenase was resolved into three components by ion-exchange chromatography. All three compounds are required for the epoxidation and hydroxylation reactions.

X-ray form factors and the electronic structure of graphite

Abstract: The bonding and spectroscopic properties of graphite are investigated by carrying out first-principles, self-consistent electronic structure calculations, and by comparing the results with high-resolution data from recent x-ray diffraction and angle-resolved photoemission measurements. The theoretical valence-charge density is in excellent agreement with values derived from experimental x-ray from factors. Unlike other group-IV covalent materials, the bonding charge exhibits a prominent double-humped structure due to the lack of $p$ core states. The energy band structure is also in good agreement with experimental measurements and previous calculations.

Excitation spectra of surface-enhanced Raman scattering on silver-island films

Abstract: Both the spectral dependence and the magnitude of the excitation spectra of surface-enhanced Raman scattering are found to be quantitatively related to the absorption spectra for silver-island films. This relationship is maintained even when the local electromagnetic enhancement at the islands is varied by coating the film with a layer of absorbing dye molecules. The results illustrate a simple experimental way to determine independently the role of the electronic plasma resonances in the enhancement process on these films and shed new insights into the details of the electromagnetic interactions responsible for surface-enhanced Raman scattering.

NMR of platinum catalysts. I. Line shapes

Abstract: The authors report spin-echo NMR studies of $^{195}\mathrm{Pt}$ in small particles of Pt supported on alumina. For the samples studied, the fraction of Pt atoms on the surface (called the dispersion) ranged from 4% to 58%. The studies were at fields ${H}_{0}$ of 80 to 85 kG, frequency ${\ensuremath{ u}}_{0}=74$ MHz, and at a temperature of 77 K. The lines are broad (3-5 kG), requiring special methods which permit substantial signal averaging (\ensuremath{\sim} 50 000 echoes). In the low-dispersion (large-particle) samples, there is a strong absorption at the position of the $^{195}\mathrm{Pt}$ NMR in bulk Pt metal ($\frac{{H}_{0}}{{\ensuremath{ u}}_{0}}=1.138$ kG/MHz) which becomes progressively weaker as the particle size decreases. A peak which is near the $^{195}\mathrm{Pt}$ resonance in typical diamagnetic compounds ($\frac{{H}_{0}}{{\ensuremath{ u}}_{0}}\ensuremath{\sim}1.09$ kG/MHz) is found in samples which are coated with adsorbed molecules. It disappears when the surface is cleaned. The authors show that this peak arises from the surface layer of Pt atoms, and that its position ($\frac{{H}_{0}}{{\ensuremath{ u}}_{0}}$) shows that coating the Pt atoms on the surface largely ties up the electron spins of the surface Pt atoms in bonds. The exact position of this peak depends on the chemical species which is adsorbed. The authors show that when Pt is cleaned, then exposed to air for long times, the surface peak reveals that the surface has reconstructed to form Pt${(\mathrm{OH})}_{6}$.

Structure of p ( 2 × 2 ) and c ( 2 × 2 ) Oxygen on Ni(100): A Surface Extended-X-Ray Absorption Fine-Structure Study

Abstract: In contrast to recent theoretical electronic structure calculations and analysis of electron energy-loss (ELS) spectra, surface extended-x-ray-absorption fine-structure measurements establish the local structural equivalence of $p(2\ifmmode\times\else\texttimes\fi{}2)$ and $c(2\ifmmode\times\else\texttimes\fi{}2)$ oxygen on Ni(100). In both cases the oxygen atoms chemisorb in the fourfold hollow site with an O-Ni bond length of 1.96 \ifmmode\pm\else\textpm\fi{} 0.03 \AA{} (i.e., ${d}_{\ensuremath{\perp}}=0.86\ifmmode\pm\else\textpm\fi{}0.07$ \AA{}). In the light of the present results the large ELS frequency shift (14 meV) between the $p(2\ifmmode\times\else\texttimes\fi{}2)$ and $c(2\ifmmode\times\else\texttimes\fi{}2)$ phases remains a puzzle.

Flow improver additive for distillate fuels, and concentrate thereof

Abstract: Polyoxyalkylene esters, ethers, ester/ethers or mixtures thereof containing two C 10 -C 30 linear saturated alkyl groups and a polyoxy (C 1 -C 4 alkylene glycol group of molecular weight 200 to 5,000 have been found to be effective distillate fuel flow improvers, especially for narrow boiling distillates hitherto difficult to treat, they may also be used in combination with conventional additives such as ethyleneiunsatu- rated ester copolymers and nitrogen compounds such as diamides or amide/amine saits, ester/amides of dicarboxylic acids.

Process for the selective removal of hydrogen sulfide from gaseous mixtures with severely sterically hindered secondary aminoether alcohols

Abstract: The selective removal of H 2 S gas from a normally gaseous mixture containing H 2 S and CO 2 is accomplished by contacting the gaseous mixture with an absorbent solution comprising a severely sterically hindered secondary aminoether alcohol having a cumulative - -E s value (Taft's steric hindrance constant) greater than about 1.75 whereby H 2 S is selectively absorbed from the mixture.

Electron Microscopic Analysis of Heterogeneous Precipitates in Hastelloy C-276

Abstract: Three distinct second phases were observed to form heterogeneously at grain and deformation twin boundaries when Hastelloy C-276 was aged in the temperature range of 923 to 1173 K. The most abundant was the faulted, molybdenum rich μ phase. The next most abundant phase was molybdenum rich M6C carbides, and the third phase, which was observed very infrequently, was tentatively identified as theP phase. The compositions of these phases were remarkably similar, and the need to employ several electron microscopy techniques is emphasized. The origin of the μ phase is discussed in the light of its chemistry.

Fundamentals and Use of Potassium/Polymer Drilling Fluids To Minimize Drilling and Completion Problems Associated With Hydratable Clays

Abstract: Water sensitive shales cause expensive problems and may defeat the purpose of drilling a well. Clay hydration can produce drilling problems such as wellbore instability, stuck pipe, bottomhole fill, torque, drag, and solids buildup in the drilling fluid. It also can produce completion problems such as formation damage in shaly sands, logging and coring failures, hole washout, and poor cement jobs. Proper application of an inhibitive drilling fluid will reduce drilling costs, rig time, formation damage, and completion costs. The potassium ion, when used at the proper concentration, is a powerful shale inhibitor. It interacts with clays, such as illite or montmorillonite, lowers the hydration energy, and reduces swelling. Relatively simple potassium/polymer drilling fluid systems, which provide excellent rheological and filtration properties, have been formulated at moderate costs. The systems, when properly used, are quite stable and easily maintained.

Recent advances in the chemical modification of unsaturated polymers

Abstract: The present discussion has the objective to update the most comprehensive reviews on the considered subject and to fill in the gaps of less complete, but more modern treatments. Only simple chemical functionalization or structural modification of unsaturated polymers are covered, and the literature of diene polymer modification since 1974 is emphasized. Attention is given to hydrogenation, halogenation and hydrohalogenation, cyclization, cis-trans isomerization, epoxidation, ene and other cycloaddition reactions, sulfonation, carboxylation, phosphonylation, sulfenyl chloride addition, carbene addition, metalation, and silylation. It is pointed out that modern synthetic reagents and catalysts have been advantageously employed to improve process and/or product quality. Synthetic techniques have been refined to allow the selective modification of specific polymer microstructures or blocks.