Precision mass measurements in solution reveal properties of single cells and bioparticles

Precise characterization of biological materials ranging from single cells (~1-20 microns) to extracellular vesicles (20-200 nm) is of fundamental interest because of their biological and translational value. Here we discuss the value of precision mass measurements in solution for informing various physical and biological parameters, such as mass accumulation rate, longitudinal cell growth or cell density. We introduce how the limits of the single-particle mass measurements can be pushed down to nano-scale dimensions enabling the resolution of extracellular vesicles and viruses in solution. We believe with future advancements on the precision and throughput of this approach, the capability of analyzing biologically relevant particles in solution will have broad biological and translational impact

Heliostat-array wind-tunnel study

CER78-79RLE-JAP-JEC31.Prepared for Martin Marietta Aerospace.Includes bibliographical references (page 24).January 1979

Wind-tunnel study of wind over an offshore platform helideck

CER78-79RE-JAP-JBC25.Prepared for Earl and Wright Consulting Engineers.Includes bibliographical references (page 16).December 1978

High-speed multiple-mode mass-sensing resolves dynamic nanoscale mass distributions

Simultaneously measuring multiple eigenmode frequencies of nanomechanical resonators can determine the position and mass of surface-adsorbed proteins, and could ultimately reveal the mass tomography of nanoscale analytes. However, existing measurement techniques are slow (<1 Hz bandwidth), limiting throughput and preventing use with resonators generating fast transient signals. Here we develop a general platform for independently and simultaneously oscillating multiple modes of mechanical resonators, enabling frequency measurements that can precisely track fast transient signals within a user-defined bandwidth that exceeds 500 Hz. We use this enhanced bandwidth to resolve signals from multiple nanoparticles flowing simultaneously through a suspended nanochannel resonator and show that four resonant modes are sufficient for determining their individual position and mass with an accuracy near 150 nm and 40 attograms throughout their 150-ms transit. We envision that our method can be readily extended to other systems to increase bandwidth, number of modes, or number of resonators.United States. Army Research Office (Grant W911NF-09-0001)Center for Integration of Medicine and Innovative Technology (Contract 09-440)National Science Foundation (U.S.) (Grant 1129359

Wind-tunnel model study of diffusion: Coalplex Project

July 1975.CER75-76RNM-JEC-JAG3.Includes bibliographical references.Prepared under contract to AE & CI Limited

Applications of physical modeling to the investigations of air pollution problems in urban areas

CER73-74JEC-DJL-RST36.March 1974.Sponsored by National Science Foundation.Includes bibliographical references.Wind tunnel modeling of atmospheric flow and diffusion in the boundary layer over an urban area are discussed. Measurements were made over a model of an urban area composed of a network of uniform city blocks and streets. Two line sources emitting a radioactive tracer gas represented automobile emissions in a one-block length of a city street. Pollutant concentrations were calculated from samples of the tracer gas collected on building faces, in street canyons, and in the flow field above the model. Non dimensionalized concentration patterns were constructed from the analysis of the samples. Three wind directions were considered. The effects of a simple modification of the uniform model were evaluated.Under grant GI-34813X

Magnetic excitations of the charge stripe electrons below half doping in La2−xSrxNiO4 (x = 0.45, 0.4)

The low energy magnetic excitation spectrum of charge stripe ordered La2−xSrxNiO4, x = 0.4 and x = 0.45 were studied by neutron scattering. Two excitation modes are observed in both materials, one from the ordered magnetic moments, and a second mode consistent with pseudo-onedimensional antiferromagnetic excitations of the charge stripe electrons (q-1D). The dispersion of the q-1D excitation follows the same relation as in x = 1/3 composition, with even spectral weight in the two counter-propagating branches of the x = 0.4, however in the x = 0.45 only one dispersion branch has any measurable spectral weight. The evolution of the q-1D excitations on doping to the checkerboard charge ordered phase is discussed

Water and Small-Molecule Permeation of Dormant Bacillus subtilis Spores

We use a suspended microchannel resonator to characterize the water and small-molecule permeability of Bacillus subtilis spores based on spores' buoyant mass in different solutions. Consistent with previous results, we found that the spore coat is not a significant barrier to small molecules, and the extent to which small molecules may enter the spore is size dependent. We have developed a method to directly observe the exchange kinetics of intraspore water with deuterium oxide, and we applied this method to wild-type spores and a panel of congenic mutants with deficiencies in the assembly or structure of the coat. Compared to wild-type spores, which exchange in approximately 1 s, several coat mutant spores were found to have relatively high water permeability with exchange times below the ∼200-ms temporal resolution of our assay. In addition, we found that the water permeability of the spore correlates with the ability of spores to germinate with dodecylamine and with the ability of TbCl₃ to inhibit germination with l-valine. These results suggest that the structure of the coat may be necessary for maintaining low water permeability.United States. Army Research Office (W911F-09-1-0286)United States. Army Research Office (W911NF-09-0001