Solar Effects of Low-Earth Orbit objects in ORDEM 3.0

Variances in atmospheric density are directly related to the variances in solar flux intensity between 11- year solar cycles. The Orbital Debris Engineering Model (ORDEM 3.0) uses a solar flux table as input for calculating orbital lifetime of intact and debris objects in Low-Earth Orbit. Long term projections in solar flux activity developed by the NASA Orbital Debris Program Office (ODPO) extend the National Oceanic and Atmospheric Administration Space Environment Center (NOAA/SEC) daily historical flux values with a 5-year projection. For purposes of programmatic scheduling, the Q2 2009 solar flux table was chosen for ORDEM 3.0. Current solar flux activity shows that the current solar cycle has entered a period of lower solar flux intensity than previously forecasted in 2009. This results in a deviation of the true orbital debris environment propagation in ORDEM 3.0. In this paper, we present updated orbital debris populations in LEO using the latest solar flux values. We discuss the effects on recent breakup events such as the FY-1C anti-satellite test and the Iridium 33 / Cosmos 2251 accidental collision. Justifications for chosen solar flux tables are discussed

Spin density wave induced disordering of the vortex lattice in superconducting La2−x_{2-x}Srx_xCuO4_4

We use small angle neutron scattering to study the superconducting vortex lattice in La$_{2-x}$Sr$_x$CuO$_4$ as a function of doping and magnetic field. We show that near optimally doping the vortex lattice coordination and the superconducting coherence length $\xi$ are controlled by a van-Hove singularity crossing the Fermi level near the Brillouin zone boundary. The vortex lattice properties change dramatically as a spin-density-wave instability is approached upon underdoping. The Bragg glass paradigm provides a good description of this regime and suggests that SDW order acts as a novel source of disorder on the vortex lattice.Comment: Accepted in Phys. Rev.

SANS and dynamic light scattering to investigate the viscosity of toluene under high pressure up to 1800 bar

We present a joint experimental study of small angle neutron scattering (SANS) and dynamic light scattering (DLS) under high pressures up to 1800 bar on a colloidal suspension, which consists of a core-shell system made of sterically stabilized silica particles grafted with octadecyl chains in toluene. From the analysis of SANS contrast variation under pressure, we could estimate the amount of compression in both core and shell under the action of pressure. The DLS measurements under pressure yield a diffusion coefficient which enabled us together with the SANS result to evaluate the pressure-dependent viscosity of the dilute suspension which is to a good approximation the solvent viscosity on the basis of the Stokes-Einstein relation. The excellent comparison of the so-calculated pressure-dependent viscosities of toluene with literature values demonstrates the value of our method to measure viscosities under pressure

Structure and phase diagram of an adhesive colloidal dispersion under high pressure: A small angle neutron scattering, diffusing wave spectroscopy, and light scatttering study

We have applied small angle neutron scattering (SANS), diffusing wave spectroscopy (DWS), and dynamic light scattering (DLS) to investigate the phase diagram of a sterically stabilized colloidal system consisting of octadecyl grafted silica particles dispersed in toluene. This system is known to exhibit gas-liquid phase separation and percolation, depending on temperature T, pressure P, and concentration phi. We have determined by DLS the pressure dependence of the coexistence temperature and the spinodal temperature to be dP/dT=77 bar/K. The gel line or percolation limit was measured by DWS under high pressure using the condition that the system became nonergodic when crossing it and we determined the coexistence line at higher volume fractions from the DWS limit of turbid samples. From SANS measurements we determined the stickiness parameter tau(B)(P,T,phi) of the Baxter model, characterizing a polydisperse adhesive hard sphere, using a global fit routine on all curves in the homogenous regime at various temperatures, pressures, and concentrations. The phase coexistence and percolation line as predicted from tau(B)(P,T,phi) correspond with the determinations by DWS and were used to construct an experimental phase diagram for a polydisperse sticky hard sphere model system. A comparison with theory shows good agreement especially concerning the predictions for the percolation threshold. From the analysis of the forward scattering we find a critical scaling law for the susceptibility corresponding to mean field behavior. This finding is also supported by the critical scaling properties of the collective diffusion

A high pressure cell for small angle neutron scattering up to 500 MPa in combination with light scattering to investigate liquid samples

We report on a high pressure cell to use with small angle neutron scattering (SANS) in a pressure range up to 500 MPa. The cell offers the new possibility to investigate liquid samples by a specially designed sample chamber, which allows changing of samples relatively easily. Since the cell construction uses sapphire as window material, also light scattering investigations can be performed simultaneously to the SANS measurements. In this article we describe the construction of a high pressure cell and we demonstrate the applicability of the construction for SANS in combination with dynamic light scattering showing data on the biological molecule lysozyme

SANS and dynamic light scattering to investigate the viscosity of toluene under high pressure up to 1800 bar

We present a joint experimental study of small angle neutron scattering (SANS) and dynamic light scattering (DLS) under high pressures up to 1800 bar on a colloidal suspension, which consists of a core-shell system made of sterically stabilized silica particles grafted with octadecyl chains in toluene. From the analysis of SANS contrast variation under pressure, we could estimate the amount of compression in both core and shell under the action of pressure. The DLS measurements under pressure yield a diffusion coefficient which enabled us together with the SANS result to evaluate the pressure-dependent viscosity of the dilute suspension which is to a good approximation the solvent viscosity on the basis of the Stokes-Einstein relation. The excellent comparison of the so-calculated pressure-dependent viscosities of toluene with literature values demonstrates the value of our method to measure viscosities under pressure. © 2008 IOP Publishing Ltd.status: publishe