The space microwave interferometer and the search for cosmic background gravitational wave radiation

Present and planned investigations which use interplanetary spacecraft for gravitational wave searches are severely limited in their detection capability. This limitation has to do both with the Earth-based tracking procedures used and with the configuration of the experiments themselves. It is suggested that a much improved experiment can now be made using a multiarm interferometer designed with current operating elements. An important source of gravitational wave radiation, the cosmic background, may well be within reach of detection with these procedures. It is proposed to make a number of experimental steps that can now be carried out using TDRSS spacecraft and would conclude in the establishment of an operating multiarm microwave interferometer. This interferometer is projected to have a sensitivity to cosmic background gravitational wave radiation with an energy of less than 10(exp -4) cosmic closure density and to periodic waves generating spatial strain approaching 10(exp -19) in the range 0.1 to 0.001 Hz

Atomic Force Microscopy-Based Investigation Of Plastic Deformation Mechanisms In Disordered Nanoparticle Packings

Understanding the plastic deformation mechanisms of disordered materials is a longstanding and complex problem in condensed matter physics and materials science. In particular, the elementary plastic rearrangement in a disordered material is believed to be the shear transformation zone, a localized cooperative motion of a handful of constituents. Although observed in mesoscale systems, the shear transformation zone has never been identified in an experiment at the nanoscale. In the present work, atomic force microscopy is used to probe the mechanical response of thin films of disordered nanoparticle packings that have been deposited by spin-coating and layer-by-layer deposition. Results demonstrate that these materials possess strong heterogeneity in their mechanical properties, which has also been observed in other materials including metallic glass. Topography imaging provides nanometer-level resolution, which allows rearrangements to be observed directly. These are the first rearrangements observed in a three-dimensional disordered material at the nanoscale. By changing the relative humidity in the atomic force microscope chamber, the size of the condensed capillary is controlled. It is found that increasing the humidity causes the nanoparticle film to transition from a strong, brittle state under ambient conditions to a more ductile state at relative humidity above 90%. At saturation, a nearly viscous state is observed. Disordered nanoparticle packings exhibit rearrangement events featuring avalanche scaling, which has previously been witnessed in numerous other materials including metallic glass and rocks. This is the first time that avalanche scaling has been observed in nanoscale granular materials. The number of rearrangement events is found to increase at high ambient humidity, but the shape of the distribution remains consistent regardless of the environmental conditions. This suggests that avalanche scaling is independent of the strength of particle interactions. The results presented in this work have implications how nanoparticle thin films might be toughened in commercial applications where they may be subjected to external stress. In addition, the close match in behavior between these nanoparticle packings and other disordered systems suggests that findings related to the present materials can also be applied to other disordered materials, including atomic glasses that cannot be probed at the constituent length scale

The sensitivity of the method of paired comparisons to the distribution function.

Thesis (M.A.)--Boston Universit

Dynamical clustering of counterions on flexible polyelectrolytes

Molecular dynamics simulations are used to study the local dynamics of counterion-charged polymer association at charge densities above and below the counterion condensation threshold. Surprisingly, the counterions form weakly-interacting clusters which exhibit short range orientational order, and which decay slowly due to migration of ions across the diffuse double layer. The cluster dynamics are insensitive to an applied electric field, and qualitatively agree with the available experimental data. The results are consistent with predictions of the classical theory only over much longer time scales

Testing Luminescence Dating Methods for Small Samples from Very Young Fluvial Deposits

The impetus behind this study is to understand the sedimentological dynamics of very young fluvial systems in the Amazon River catchment and relate these to land use change and modern analogue studies of tidal rhythmites in the geologic record. Initial quartz optically stimulated luminescence (OSL) dating feasibility studies have concentrated on spit and bar deposits in the Rio Tapajós. Many of these features have an appearance of freshly deposited pristine sand, and these observations and information from anecdotal evidence and LandSat imagery suggest an apparent decadal stability. The characteristics of OSL from small (~5 cm) sub-samples from ~65 cm by ~2 cm diameter vertical cores are quite remarkable. Signals from medium-sized aliquots (5 mm diameter) exhibit very high specific luminescence sensitivity, have excellent dose recovery and recycling, essentially independent of preheat, and show minimal heat transfer even at the highest preheats. These characteristics enable measurement of very small signals with reasonable precision and, using modified single-aliquot regenerative-dose (SAR) approaches, equivalent doses as low as ~4 mGy can be obtained. Significant recuperation is observed for samples from two of the study sites and, in these instances, either the acceptance threshold was increased or growth curves were forced through the origin; recuperation is considered most likely to be a measurement artefact given the very small size of natural signals. Dose rates calculated from combined inductively coupled plasma mass spectrometry/inductively coupled plasma optical emission spectrometry (ICP-MS/ICP-OES) and high-resolution gamma spectrometry range from ~0.3 to 0.5 mGya−1 , and OSL ages for features so far investigated range from 13 to 34 years to several 100 years. Sampled sands are rich in quartz and yields of 212–250 µm or 250–310 µm grains indicate high-resolution sampling at 1–2 cm intervals is possible. Despite the use of medium-sized aliquots to ensure the recovery of very dim natural OSL signals, these results demonstrate the potential of OSL for studying very young active fluvial processes in these settings

Molecular dynamics simulations of the evaporation of particle-laden droplets

We use molecular dynamics simulations to study the evaporation of particle-laden droplets on a heated surface. The droplets are composed of a Lennard-Jones fluid containing rigid particles which are spherical sections of an atomic lattice, and heating is controlled through the temperature of an atomistic substrate. We observe that sufficiently large (but still nano-sized) particle-laden drops exhibit contact line pinning, measure the outward fluid flow field which advects particle to the drop rim, and find that the structure of the resulting aggregate varies with inter-particle interactions. In addition, the profile of the evaporative fluid flux is measured with and without particles present, and is also found to be in qualitative agreement with earlier theory. The compatibility of simple nanoscale calculations and micron-scale experiments indicates that molecular simulation may be used to predict aggregate structure in evaporative growth processes

Shear flow pumping in open microfluidic systems

We propose to drive open microfluidic systems by shear in a covering fluid layer, e.g., oil covering water-filled chemical channels. The advantages as compared to other means of pumping are simpler forcing and prevention of evaporation of volatile components. We calculate the expected throughput for straight channels and show that devices can be built with off-the-shelf technology. Molecular dynamics simulations suggest that this concept is scalable down to the nanoscale.Comment: 4 pages, 4 figure, submitted to Phys. Rev. Let

Static Torsion Testing and Modeling of a Variable Thickness Hybrid Composite Bull Gear

Torsional strength of a variable thickness hybrid gear web was measured by performing static testing on the part in a large torsion test frame. The outer rim of the hybrid gear web was fixed to the bottom of the test frame and loading was applied to the web through a shaft. The test setup included the installation of digital image correlation (DIC) systems to obtain deformation and strain measurements from the surfaces of the hybrid gear web and the mechanical test equipment to ensure reliability of the test. The results indicated that the variable thickness hybrid gear web achieved approximately twice the torsional strength compared to that of previous hybrid gear designs. The DIC analysis showed significantly more straining of the loading shaft than the actual test article. Additionally, the results demonstrated the importance and affect that the metallic, lobed interlock features had on the principal strain and out-of-plane displacement fields. The analysis revealed that the fixed outer rim was in fact rotating and a rigid body motion compensation (RBMC) function was computed to determine the actual rotation of the hub and composite web relative to the outer rim. Modeling simulations were performed for the variable thickness hybrid gear web and correlated well with the RBMC rotational deformation seen in the DIC analysis. In addition to benchmarking the load capacity of the hybrid gear web, measuring its strength is useful information to define the parameters needed for dynamic, endurance, and other testing of the part