31,299 research outputs found
Thon rings from amorphous ice and implications of beam-induced Brownian motion in single particle electron cryo-microscopy
We have recorded dose-fractionated electron cryo-microscope images of thin
films of pure flash-frozen amorphous ice and pre-irradiated amorphous carbon on
a Falcon~II direct electron detector using 300 keV electrons. We observe Thon
rings \cite{Thon1966} in both the power spectrum of the summed frames and the
sum of power spectra from the individual frames. The Thon rings from amorphous
carbon images are always more visible in the power spectrum of the summed
frames whereas those of amorphous ice are more visible in the sum of power
spectra from the individual frames. This difference indicates that while
pre-irradiated carbon behaves like a solid during the exposure, amorphous ice
behaves like a fluid with the individual water molecules undergoing
beam-induced motion. Using the measured variation in the power spectra
amplitude with number of electrons per image we deduce that water molecules are
randomly displaced by mean squared distance of 1.1 \AA for every
incident 300 keV e/\AA. The induced motion leads to an optimal
exposure with 300 keV electrons of 4.0 e/\AA per image with which to
see Thon rings centred around the strong 3.7{\AA} scattering peak from
amorphous ice. The beam-induced movement of the water molecules generates
pseudo-Brownian motion of embedded macromolecules. The resulting blurring of
single particle images contributes an additional term, on top of that from
radiation damage, to the minimum achievable B-factor for macromolecular
structure determination.Comment: 11 pages, 6 figures, Supplementary information 6 pages with 5 figure
Development of a superconductor magnetic suspension and balance prototype facility for studying the feasibility of applying this technique to large scale aerodynamic testing
The basic research and development work towards proving the feasibility of operating an all-superconductor magnetic suspension and balance device for aerodynamic testing is presented. The feasibility of applying a quasi-six-degree-of freedom free support technique to dynamic stability research was studied along with the design concepts and parameters for applying magnetic suspension techniques to large-scale aerodynamic facilities. A prototype aerodynamic test facility was implemented. Relevant aspects of the development of the prototype facility are described in three sections: (1) design characteristics; (2) operational characteristics; and (3) scaling to larger facilities
Novel Method of Measuring Electron Positron Colliding Beam Parameters
Through the simultaneous measurement of the transverse size as a function of
longitudinal position, and the longitudinal distribution of luminosity, we are
able to measure the (vertical envelope function at the collision
point), vertical emittance, and bunch length of colliding beams at the Cornell
Electron-positron Storage Ring (CESR). This measurement is possible due to the
significant ``hourglass'' effect at CESR and the excellent tracking resolution
of the CLEO detector.Comment: 11 pages, 4 figures, submitted to NIM
CosmoDM and its application to Pan-STARRS data
The Cosmology Data Management system (CosmoDM) is an automated and flexible
data management system for the processing and calibration of data from optical
photometric surveys. It is designed to run on supercomputers and to minimize
disk I/O to enable scaling to very high throughput during periods of
reprocessing. It serves as an early prototype for one element of the
ground-based processing required by the Euclid mission and will also be
employed in the preparation of ground based data needed in the eROSITA X-ray
all sky survey mission. CosmoDM consists of two main pipelines. The first is
the single-epoch or detrending pipeline, which is used to carry out the
photometric and astrometric calibration of raw exposures. The second is the co-
addition pipeline, which combines the data from individual exposures into
deeper coadd images and science ready catalogs. A novel feature of CosmoDM is
that it uses a modified stack of As- tromatic software which can read and write
tile compressed images. Since 2011, CosmoDM has been used to process data from
the DECam, the CFHT MegaCam and the Pan-STARRS cameras. In this paper we shall
describe how processed Pan-STARRS data from CosmoDM has been used to optically
confirm and measure photometric redshifts of Planck-based Sunyaev-Zeldovich
effect selected cluster candidates.Comment: 11 pages, 4 figures. Proceedings of Precision Astronomy with Fully
Depleted CCDs Workshop (2014). Accepted for publication in JINS
Yang-Mills Theory on a Cylinder Coupled to Point Particles
We study a model of quantum Yang-Mills theory with a finite number of gauge
invariant degrees of freedom. The gauge field has only a finite number of
degrees of freedom since we assume that space-time is a two dimensional
cylinder. We couple the gauge field to matter, modeled by either one or two
nonrelativistic point particles. These problems can be solved {\it without any
gauge fixing}, by generalizing the canonical quantization methods of
Ref.\[rajeev] to the case including matter. For this, we make use of the
geometry of the space of connections, which has the structure of a Principal
Fiber Bundle with an infinite dimensional fiber. We are able to reduce both
problems to finite dimensional, exactly solvable, quantum mechanics problems.
In the case of one particle, we find that the ground state energy will diverge
in the limit of infinite radius of space, consistent with confinement. In the
case of two particles, this does not happen if they can form a color singlet
bound state (`meson').Comment: 37 pages, UR-1327 ER-40685-77
Morphological Thermodynamics of Fluids: Shape Dependence of Free Energies
We examine the dependence of a thermodynamic potential of a fluid on the
geometry of its container. If motion invariance, continuity, and additivity of
the potential are fulfilled, only four morphometric measures are needed to
describe fully the influence of an arbitrarily shaped container on the fluid.
These three constraints can be understood as a more precise definition for the
conventional term "extensive" and have as a consequence that the surface
tension and other thermodynamic quantities contain, beside a constant term,
only contributions linear in the mean and Gaussian curvature of the container
and not an infinite number of curvatures as generally assumed before. We verify
this numerically in the entropic system of hard spheres bounded by a curved
wall.Comment: 4 pages, 3 figures, accepted for publication in PR
Preliminary sonic boom correlation of predicted and measured levels for STS-1 entry
A preliminary analysis correlating peaks from sonic boom pressure signatures recorded during the descent trajectory of the Orbiter Columbia, which landed in the dry lake bed at Edwards Air Force Base (EAFB), California, with measured wind tunnel signatures extrapolated from flight altitudes to the ground has been made for Mach numbers ranging from 1.3 to 6. The flight pressure signatures were recorded by microphones positioned at ground level near the groundtrack, whereas the wind tunnel signatures were measured during a test of a 0.0041-scale model Orbiter. The agreement between overpressure estimates based on wind tunnel data using preliminary flight trajectory data and oscillograph traces from ground measurements appears reasonable at this time for the range of Mach numbers considered. More detailed studies using final flight trajectory data and digitized ground measured data will be performed
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