19,474 research outputs found
Servo-controlled intravital microscope system
A microscope system is described for viewing an area of a living body tissue that is rapidly moving, by maintaining the same area in the field-of-view and in focus. A focus sensing portion of the system includes two video cameras at which the viewed image is projected, one camera being slightly in front of the image plane and the other slightly behind it. A focus sensing circuit for each camera differentiates certain high frequency components of the video signal and then detects them and passes them through a low pass filter, to provide dc focus signal whose magnitudes represent the degree of focus. An error signal equal to the difference between the focus signals, drives a servo that moves the microscope objective so that an in-focus view is delivered to an image viewing/recording camera
Automatically-focusing microscope system for live tissue observation
System includes focus-sensing arrangement which controls servo to keep microscope constantly focused on target. Microscope objective is moved along optical axis. System includes two video cameras that are used as transducers for sensing focus. Incoming visual image is split by beam splitter so that one-half of information is fed to each camera
The School Improvement Partnership Programme: Using Collaboration and Enquiry to tackle Educational Inequity
No abstract available
A quantitative evaluation of metallic conduction in conjugated polymers
As the periodicity in crystalline materials creates the optimal condition for
electronic delocalization, one might expect that in partially crystalline
conjugated polymers delocalization is impeded by intergrain transport. However,
for the best conducting polymers this presumption fails. Delocalization is
obstructed by interchain rather than intergrain charge transfer and we propose
a model of weakly coupled disordered chains to describe the physics near the
metal-insulator transition. Our quantitative calculations match the outcome of
recent broad-band optical experiments and provide a consistent explanation of
metallic conduction in polymers.Comment: 4 pages incl. 3 figure
Ab Initio Spatial Phase Retrieval via Fluorescence Intensity Triple Correlations
A complete method for ab initio phase retrieval via spatial intensity triple correlations is described. Simulations demonstrate accurate phase retrieval for clusters of classical incoherent emitters
The vortex dynamics of a Ginzburg-Landau system under pinning effect
It is proved that the vortices are attracted by impurities or inhomogeities
in the superconducting materials. The strong H^1-convergence for the
corresponding Ginzburg-Landau system is also proved.Comment: 23page
Use of extended and prepared reference objects in experimental Fourier transform X-ray holography
The use of one or more gold nanoballs as reference objects for Fourier
Transform holography (FTH) is analysed using experimental soft X-ray
diffraction from objects consisting of separated clusters of these balls. The
holograms are deconvoluted against ball reference objects to invert to images,
in combination with a Wiener filter to control noise. A resolution of ~30nm,
smaller than one ball, is obtained even if a large cluster of balls is used as
the reference, giving the best resolution yet obtained by X-ray FTH. Methods of
dealing with missing data due to a beamstop are discussed. Practical prepared
objects which satisfy the FTH condition are suggested, and methods of forming
them described.Comment: 7 pages, 2 figures, submitted to Applied Physics Letter
Photoluminescence signature of skyrmions at \nu = 1
The photoluminescence spectrum of quantized Hall states near filling factor
\nu = 1 is investigated theoretically. For \nu >= 1 the spectrum consists of a
right-circularly polarized (RCP) line and a left-circularly polarized (LCP)
line, whose mean energy: (1) does not depend on the electron g factor for
spin-1/2 quasielectrons, (2) does depend on g for charged spin-texture
excitations (skyrmions). For \nu < 1 the spectrum consists of a LCP line
shifted down in energy from the LCP line at \nu >= 1. The g-factor dependence
of the red shift of the LCP line determines the nature of the negatively
charged excitations.Comment: 11 pages, 2 PostScript figures. Replaced with version to appear in
Physical Review B Rapid Communications. Minor changes, reference adde
Macroscopic control parameter for avalanche models for bursty transport
Similarity analysis is used to identify the control parameter RA for the subset of avalanching systems that can exhibit self-organized criticality (SOC). This parameter expresses the ratio of driving to dissipation. The transition to SOC, when the number of excited degrees of freedom is maximal, is found to occur when RA-->0. This is in the opposite sense to (Kolmogorov) turbulence, thus identifying a deep distinction between turbulence and SOC and suggesting an observable property that could distinguish them. A corollary of this similarity analysis is that SOC phenomenology, that is, power law scaling of avalanches, can persist for finite RA with the same RA-->0 exponent if the system supports a sufficiently large range of lengthscales, necessary for SOC to be a candidate for physical (RA finite) systems
SPEDEN: Reconstructing single particles from their diffraction patterns
Speden is a computer program that reconstructs the electron density of single
particles from their x-ray diffraction patterns, using a single-particle
adaptation of the Holographic Method in crystallography. (Szoke, A., Szoke, H.,
and Somoza, J.R., 1997. Acta Cryst. A53, 291-313.) The method, like its parent,
is unique that it does not rely on ``back'' transformation from the diffraction
pattern into real space and on interpolation within measured data. It is
designed to deal successfully with sparse, irregular, incomplete and noisy
data. It is also designed to use prior information for ensuring sensible
results and for reliable convergence. This article describes the theoretical
basis for the reconstruction algorithm, its implementation and quantitative
results of tests on synthetic and experimentally obtained data. The program
could be used for determining the structure of radiation tolerant samples and,
eventually, of large biological molecular structures without the need for
crystallization.Comment: 12 pages, 10 figure
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