Qualification and Issues with Space Flight Laser Systems and Components

The art of flight quality solid-state laser development is still relatively young, and much is still unknown regarding the best procedures, components, and packaging required for achieving the maximum possible lifetime and reliability when deployed in the harsh space environment. One of the most important issues is the limited and unstable supply of quality, high power diode arrays with significant technological heritage and market lifetime. Since Spectra Diode Labs Inc. ended their involvement in the pulsed array business in the late 199O's, there has been a flurry of activity from other manufacturers, but little effort focused on flight quality production. This forces NASA, inevitably, to examine the use of commercial parts to enable space flight laser designs. System-level issues such as power cycling, operational derating, duty cycle, and contamination risks to other laser components are some of the more significant unknown, if unquantifiable, parameters that directly effect transmitter reliability. Designs and processes can be formulated for the system and the components (including thorough modeling) to mitigate risk based on the known failures modes as well as lessons learned that GSFC has collected over the past ten years of space flight operation of lasers. In addition, knowledge of the potential failure modes related to the system and the components themselves can allow the qualification testing to be done in an efficient yet, effective manner. Careful test plan development coupled with physics of failure knowledge will enable cost effect qualification of commercial technology. Presented here will be lessons learned from space flight experience, brief synopsis of known potential failure modes, mitigation techniques, and options for testing from the system level to the component level

Protocol for a randomized, double blind, placebo controlled, crossover trial of Melatonin for treatment of Nocturia in adults with Multiple Sclerosis (MeNiMS)

Background: Nocturia (the symptom of needing to wake up to pass urine) is common in progressive Multiple Sclerosis (MS) patients. Moderate-to-severe nocturia affects quality of life, can exacerbate fatigue and may affect capacity to carry out daily activities. Melatonin is a natural hormone regulating circadian cycles, released by the pineal gland at night-time, and secretion is impaired in MS. Melatonin levels can be supplemented by administration in tablet form at bedtime. The aim of this study is to evaluate the effect of melatonin on mean number of nocturia episodes per night in MS patients. Secondary outcome measures will assess impact upon quality of life, urinated volumes, lower urinary tract symptoms (LUTS), cognition, sleep quality and sleep disturbance of partners. Methods: A randomized, double blind, placebo controlled, crossover trial consisting of two, six week treatment phases (active drug melatonin 2 mg or placebo), with a 1 month wash-out period in between. The primary outcome (change in nocturia episodes per night) in this two arm, two treatment, two period crossover design, will be objectively measured using frequency volume charts (FVC) at baseline and following both treatment phases. Questionnaires will be used to assess quality of life, sleep quality, safety and urinary tract symptoms. Qualitative interviews of participants and partners will explore issues including quality of life, mechanisms of sleep disturbance and impact of nocturia on partners. Discussion: This study will evaluate whether melatonin reduces the frequency of nocturia episodes in MS patients, and therefore whether 'Circadin' has the potential to reduce LUTS and fatigue, and improve cognition and overall quality of life. Trial registration: (EudraCT reference) 2012-00418321 registered: 25/01/13. ISRCTN Registry: ISRCTN38687869</p

The one-loop elastic coefficients for the Helfrich membrane in higher dimensions

Using a covariant geometric approach we obtain the effective bending couplings for a 2-dimensional rigid membrane embedded into a $(2+D)$-dimensional Euclidean space. The Hamiltonian for the membrane has three terms: The first one is quadratic in its mean extrinsic curvature. The second one is proportional to its Gaussian curvature, and the last one is proportional to its area. The results we obtain are in agreement with those finding that thermal fluctuations soften the 2-dimensional membrane embedded into a 3-dimensional Euclidean space.Comment: 9 page

Self-Dual Bending Theory for Vesicles

We present a self-dual bending theory that may enable a better understanding of highly nonlinear global behavior observed in biological vesicles. Adopting this topological approach for spherical vesicles of revolution allows us to describe them as frustrated sine-Gordon kinks. Finally, to illustrate an application of our results, we consider a spherical vesicle globally distorted by two polar latex beads.Comment: 10 pages, 3 figures, LaTeX2e+IOPar

Hard Spheres in Vesicles: Curvature-Induced Forces and Particle-Induced Curvature

We explore the interplay of membrane curvature and nonspecific binding due to excluded-volume effects among colloidal particles inside lipid bilayer vesicles. We trapped submicron spheres of two different sizes inside a pear-shaped, multilamellar vesicle and found the larger spheres to be pinned to the vesicle's surface and pushed in the direction of increasing curvature. A simple model predicts that hard spheres can induce shape changes in flexible vesicles. The results demonstrate an important relationship between the shape of a vesicle or pore and the arrangement of particles within it.Comment: LaTeX with epsfig; ps available at http://dept.physics.upenn.edu/~nelson/index.shtml Phys Rev Lett in press (1997

On the use of the group SO(4,2) in atomic and molecular physics

In this paper the dynamical noninvariance group SO(4,2) for a hydrogen-like atom is derived through two different approaches. The first one is by an established traditional ascent process starting from the symmetry group SO(3). This approach is presented in a mathematically oriented original way with a special emphasis on maximally superintegrable systems, N-dimensional extension and little groups. The second approach is by a new symmetry descent process starting from the noninvariance dynamical group Sp(8,R) for a four-dimensional harmonic oscillator. It is based on the little known concept of a Lie algebra under constraints and corresponds in some sense to a symmetry breaking mechanism. This paper ends with a brief discussion of the interest of SO(4,2) for a new group-theoretical approach to the periodic table of chemical elements. In this connection, a general ongoing programme based on the use of a complete set of commuting operators is briefly described. It is believed that the present paper could be useful not only to the atomic and molecular community but also to people working in theoretical and mathematical physics.Comment: 31 page

Monte-Carlo simulations of the recombination dynamics in porous silicon

A simple lattice model describing the recombination dynamics in visible light emitting porous Silicon is presented. In the model, each occupied lattice site represents a Si crystal of nanometer size. The disordered structure of porous Silicon is modeled by modified random percolation networks in two and three dimensions. Both correlated (excitons) and uncorrelated electron-hole pairs have been studied. Radiative and non-radiative processes as well as hopping between nearest neighbor occupied sites are taken into account. By means of extensive Monte-Carlo simulations, we show that the recombination dynamics in porous Silicon is due to a dispersive diffusion of excitons in a disordered arrangement of interconnected Si quantum dots. The simulated luminescence decay for the excitons shows a stretched exponential lineshape while for uncorrelated electron-hole pairs a power law decay is suggested. Our results successfully account for the recombination dynamics recently observed in the experiments. The present model is a prototype for a larger class of models describing diffusion of particles in a complex disordered system.Comment: 33 pages, RevTeX, 19 figures available on request to [email protected]

Fluid-membrane tethers: minimal surfaces and elastic boundary layers

Thin cylindrical tethers are common lipid bilayer membrane structures, arising in situations ranging from micromanipulation experiments on artificial vesicles to the dynamic structure of the Golgi apparatus. We study the shape and formation of a tether in terms of the classical soap-film problem, which is applied to the case of a membrane disk under tension subject to a point force. A tether forms from the elastic boundary layer near the point of application of the force, for sufficiently large displacement. Analytic results for various aspects of the membrane shape are given.Comment: 12 page

Variational Methods for Biomolecular Modeling

Structure, function and dynamics of many biomolecular systems can be characterized by the energetic variational principle and the corresponding systems of partial differential equations (PDEs). This principle allows us to focus on the identification of essential energetic components, the optimal parametrization of energies, and the efficient computational implementation of energy variation or minimization. Given the fact that complex biomolecular systems are structurally non-uniform and their interactions occur through contact interfaces, their free energies are associated with various interfaces as well, such as solute-solvent interface, molecular binding interface, lipid domain interface, and membrane surfaces. This fact motivates the inclusion of interface geometry, particular its curvatures, to the parametrization of free energies. Applications of such interface geometry based energetic variational principles are illustrated through three concrete topics: the multiscale modeling of biomolecular electrostatics and solvation that includes the curvature energy of the molecular surface, the formation of microdomains on lipid membrane due to the geometric and molecular mechanics at the lipid interface, and the mean curvature driven protein localization on membrane surfaces. By further implicitly representing the interface using a phase field function over the entire domain, one can simulate the dynamics of the interface and the corresponding energy variation by evolving the phase field function, achieving significant reduction of the number of degrees of freedom and computational complexity. Strategies for improving the efficiency of computational implementations and for extending applications to coarse-graining or multiscale molecular simulations are outlined.Comment: 36 page

Dynamic Fluctuation Phenomena in Double Membrane Films

Dynamics of double membrane films is investigated in the long-wavelength limit including the overdamped squeezing mode. We demonstrate that thermal fluctuations essentially modify the character of the mode due to its nonlinear coupling to the transversal shear hydrodynamic mode. The corresponding Green function acquires as a function of the frequency a cut along the imaginary semi-axis. Fluctuations lead to increasing the attenuation of the squeezing mode it becomes larger than the `bare' value.Comment: 7 pages, Revte