31,110 research outputs found
Kinetic conversion of CO to CH4 in the Solar System
Some of the most interesting chemistry in the Solar System involves changes in the oxidation state of the simple carbon species. The chemical pathways for the conversion of CH4 to CO and CO2 are for the most part known. The reverse process, the reduction of CO to CH4, is, however, poorly understood. This is surprising in view of the importance of the reduction process in the chemistry of the Solar System. Recently we investigated the chemical kinetics of a hitherto unsuspected reaction. It is argued that the formation of the methoxy radical (CH3O) from H+H2CO may play an essential role in the reduction of CO to CH4. The rate coefficient for this reaction has been estimated using the approximate theory of J. Troe and transition state theory. We will discuss the implications of this reaction for the chemistry of CO on Jupiter, in the solar nebula, for interpreting the laboratory experiments of A. Bar-Nun and A. Shaviv and A. Bar-Nun and S. Chang, and for organic synthesis in the prebiotic terrestrial atmosphere. The possible relation of CO reduction in the solar nebula and polyoxymethylene observed in comet Halley will be discussed
Predicting FVIII Activity in Patients Who Use Recombinant FVIII Fc Fusion Protein for Prophylaxis and Treatment of Bleeding Episodes
ARPES and NMTO Wannier Orbital Theory of LiMoO - Implications for Unusually Robust Quasi-One Dimensional Behavior
We present the results of a combined study by band theory and angle resolved
photoemission spectroscopy (ARPES) of the purple bronze,
LiMoO. Structural and electronic origins of its unusually
robust quasi-one dimensional (quasi-1D) behavior are investigated in detail.
The band structure, in a large energy window around the Fermi energy, is
basically 2D and formed by three Mo -like extended Wannier orbitals,
each one giving rise to a 1D band running at a 120 angle to the two
others. A structural "dimerization" from to gaps
the and bands while leaving the bands metallic in the gap, but
resonantly coupled to the gap edges and, hence, to the other directions. The
resulting complex shape of the quasi-1D Fermi surface (FS), verified by our
ARPES, thus depends strongly on the Fermi energy position in the gap, implying
a great sensitivity to Li stoichiometry of properties dependent on the FS, such
as FS nesting or superconductivity. The strong resonances prevent either a
two-band tight-binding model or a related real-space ladder picture from giving
a valid description of the low-energy electronic structure. We use our extended
knowledge of the electronic structure to newly advocate for framing
LiMoO as a weak-coupling material and in that framework can
rationalize both the robustness of its quasi-1D behavior and the rather large
value of its Luttinger liquid (LL) exponent . Down to a temperature of
6K we find no evidence for a theoretically expected downward
renormalization of perpendicular single particle hopping due to LL fluctuations
in the quasi-1D chains.Comment: 53 pages, 17 Figures, 6 year
Matter-wave bistability in coupled atom-molecule quantum gases
We study the matter-wave bistability in coupled atom-molecule quantum gases,
in which heteronuclear molecules are created via an interspecies Feshbach
resonance involving either two-species Bose or two-species Fermi atoms at zero
temperature. We show that the resonant two-channel Bose model is equivalent to
the nondegenerate parametric down-conversion in quantum optics, while the
corresponding Fermi model can be mapped to a quantum optics model that
describes a single-mode laser field interacting with an ensemble of
inhomogeneously broadened two-level atoms. Using these analogy and the fact
that both models are subject to the Kerr nonlinearity due to the two-body
s-wave collisions, we show that under proper conditions, the population in the
molecular state in both models can be made to change with the Feshbach detuning
in a bistable fashion.Comment: 6 pages, 5 figure
Spatio-temporal vortex beams and angular momentum
We present a space-time generalization of the known spatial (monochromatic)
wave vortex beams carrying intrinsic orbital angular momentum (OAM) along the
propagation direction. Generic spatio-temporal vortex beams are polychromatic
and can carry intrinsic OAM at an arbitrary angle to the mean momentum.
Applying either (i) a transverse wave-vector shift or (ii) a Lorentz boost to a
monochromatic Bessel beam, we construct a family of either (i) time-diffracting
or (ii) non-diffracting spatio-temporal Bessel beams, which are exact solutions
of the Klein-Gordon wave equations. The proposed spatio-temporal OAM states are
able to describe either photon or electron vortex states (both relativistic and
nonrelativistic), and can find applications in particle collisions, optics of
moving media, quantum communications, and astrophysics.Comment: 9 pages, 6 figures, to appear in Phys. Rev.
Non-degenerate four-wave mixing in rubidium vapor: transient regime
We investigate the transient response of the generated light from Four-Wave
Mixing (FWM) in the diamond configuration using a step-down field excitation.
The transients show fast decay times and oscillations that depend on the
detunings and intensities of the fields. A simplified model taking into account
the thermal motion of the atoms, propagation, absorption and dispersion effects
shows qualitative agreement with the experimental observations with the energy
levels in rubidium (5S1/2, 5P1/2, 5P3/2 and 6S1/2). The atomic polarization
comes from all the contributions of different velocity classes of atoms in the
ensemble modifying dramatically the total transient behavior of the light from
FWM.Comment: 11 pages, 11 figures, to be published in Physical Review
Resistive destabilization of cycloidal electron flow and universality of (nearâ) Brillouin flow in a crossedâfield gap
It is shown that a small amount of dissipation, caused by current flow in a lossy external circuit, can produce a disruption of steadyâstate cycloidal electron flow in a crossedâfield gap, leading to the establishment of a turbulent steady state that is close to, but not exactly, Brillouin flow. This disruption, which has nothing to do with a diocotron or cyclotron instability, is fundamentally caused by the failure of a subset of the emitted electrons to return to the cathode surface as a result of resistive dissipation. This mechanism was revealed in particle simulations, and was confirmed by an analytic theory. These nearâBrillouin states differ in several interesting respects from classic Brillouin flow, the most important of which is the presence of a microsheath and a timeâvarying potential minimum very close to the cathode surface. They are essentially identical to that produced when (i) injected current exceeds a certain critical value [P. J. Christenson and Y. Y. Lau, Phys. Plasmas 1, 3725 (1994)] or (ii) a small rf electric field is applied to the gap [P. J. Christenson and Y. Y. Lau, Phys. Rev. Lett. 76, 3324 (1996)]. It is speculated that such nearâBrillouin states are generic in vacuum crossedâfield devices, due to the ease with which the cycloidal equilibrium can be disrupted. Another novel aspect of this paper is the introduction of transformations by which the nonlinear, coupled partial differential equations in the Eulerian description (equation of motion, continuity equation, Poisson equation, and the circuit equation) are reduced to an equivalent system of very simple linear ordinary differential equations. © 1996 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71350/2/PHPAEN-3-12-4455-1.pd
Investigation of the drivers of logistics outsourcing in the United Kingdom's pharmaceutical manufacturing industry
Logistics outsourcing is a practice commonly used by firms to allow them to access capabilities that they lack internally. Although the main drivers of outsourcing in general are fairly well known, the question of what explains logistics outsourcing decisions within the UK pharmaceutical manufacturing industry, in particular, remains under-researched. Therefore, this study aims to bridge the aforementioned gap in the literature. We surveyed 49 drug manufacturers located in the UK using a web-based questionnaire. The data collected were analysed using logistics regression, exploratory factor analysis, and t-tests. We found that UK drug manufacturers regard improving quality and reliability and reducing logistics costs as the most significant reasons for outsourcing logistics services. We also found a direct positive relationship between the service provider's techno-commercial offerings and delivery performance, and the likelihood of being selected to provide these services. We further explored materials transportation, product delivery, research and development, and clinical trials, which are among the most frequently outsourced logistics activities in the UK pharmaceutical manufacturing industry. The study contributes to the wider literature on logistics outsourcing, and more specifically to that on the UK pharmaceutical manufacturing industry. Findings from this research can also be used to guide outsourcing practitionersâ decisions about the selection of logistics service providers. In addition, the study can help to enhance the service providers' understanding of why firms buy logistics services and which services they are likely to buy
Advanced ceramic coating development for industrial/utility gas turbine applications
The effects of ceramic coatings on the lifetimes of metal turbine components and on the performance of a utility turbine, as well as of the turbine operational cycle on the ceramic coatings were determined. When operating the turbine under conditions of constant cooling flow, the first row blades run 55K cooler, and as a result, have 10 times the creep rupture life, 10 times the low cycle fatigue life and twice the corrosion life with only slight decreases in both specific power and efficiency. When operating the turbine at constant metal temperature and reduced cooling flow, both specific power and efficiency increases, with no change in component lifetime. The most severe thermal transient of the turbine causes the coating bond stresses to approach 60% of the bond strengths. Ceramic coating failures was studied. Analytic models based on fracture mechanics theories, combined with measured properties quantitatively assessed both single and multiple thermal cycle failures which allowed the prediction of coating lifetime. Qualitative models for corrosion failures are also presented
A conjecture on the origin of dark energy
The physical origin of holographic dark energy (HDE) is investigated. The
main existing explanations, namely the UV/IR connection argument of Cohen et
al, Thomas' bulk holography argument, and Ng's spacetime foam argument, are
shown to be not satisfactory. A new explanation of the HDE model is then
proposed based on the ideas of Thomas and Ng. It is suggested that the dark
energy might originate from the quantum fluctuations of spacetime limited by
the event horizon of the universe. Several potential problems of the
explanation are also discussed.Comment: 11 pages, no figure
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