4,184 research outputs found
Organization and operation of advisory councils for vocational agriculture
Advisory councils have been used In and for vocational agriculture in an advisory capacity since its beginning. The Use of advisory councils in agricultural education preceded the passage of the Smith-Hughes Act for Vocational Agriculture. As early as 1911¹ it was mandatory in Massachusetts to have advisory councils for local departments of agriculture.
Hamlin² stated that there were 117 advisory councils and committees in eighty schools having advisory groups in 1949. In New York³ it is the duty of the board of education to appoint an advisory board. In Tennessee, advisory council organization is being encouraged by the State Department of Vocational Education and the Department of Agricultural Education. Teacher trainers in thirty-three states who responded to Dr. Wilson’s letter&sup4; initiating the study said that they had one or more advisory councils in their state
A ray-trace analysis of X-ray multilayer Laue lenses for nanometer focusing
Thick diffractive optical elements offer a promising way to achieve focusing
or imaging at a resolution approaching 1 nm for X-ray wavelengths shorter than
about 0.1 nm. Efficient focusing requires that these are fabricated with
structures that vary in period and orientation so that rays obey Bragg's law
over the entire lens aperture and give rise to constructive interference at the
focus. Here the analysis method of ray-tracing of thick diffractive optical
elements is applied to such lenses to optimise their designs and to investigate
their operating and manufacturing tolerances. Expressions are provided of the
fourth-order series expansions of the wavefront aberrations and transmissions
of both axi-symmetric lenses and pairs of crossed lenses that each focuses in
only one dimension like a cylindrical lens. We find that aplanatic zone-plate
designs, whereby aberrations are corrected over a large field of view, can be
achieved by axi-symmetric lenses but not the crossed lenses. We investigate the
performance of 1 nm-resolution lenses with focal lengths of about 1 mm and show
their fields of view are mainly limited by the acceptance angle of Bragg
diffraction, and that aberrations can limit the performance of lenses with
longer focal lengths. We apply the ray-tracing formalism for a tolerancing
analysis of imperfect lenses and examine some strategies for the correction of
their aberrations.Comment: 44 pages, 15 figure
Phase Retrieval with Application to Optical Imaging
This review article provides a contemporary overview of phase retrieval in
optical imaging, linking the relevant optical physics to the information
processing methods and algorithms. Its purpose is to describe the current state
of the art in this area, identify challenges, and suggest vision and areas
where signal processing methods can have a large impact on optical imaging and
on the world of imaging at large, with applications in a variety of fields
ranging from biology and chemistry to physics and engineering
Photon statistics and signal to noise ratio for incoherent diffraction imaging
Intensity interferometry is a well known method in astronomy. Recently, a
related method called incoherent diffractive imaging (IDI) was proposed to
apply intensity correlations of x-ray fluorescence radiation to determine the
3D arrangement of the emitting atoms in a sample. Here we discuss inherent
sources of noise affecting IDI and derive a model to estimate the dependence of
the signal to noise ratio (SNR) on the photon counts per pixel, the temporal
coherence (or number of modes), and the shape of the imaged object. Simulations
in two- and three-dimensions have been performed to validate the predictions of
the model. We find that contrary to coherent imaging methods, higher
intensities and higher detected counts do not always correspond to a larger
SNR. Also, larger and more complex objects generally yield a poorer SNR despite
the higher measured counts. The framework developed here should be a valuable
guide to future experimental design
DriftRec: Adapting diffusion models to blind JPEG restoration
In this work, we utilize the high-fidelity generation abilities of diffusion
models to solve blind JPEG restoration at high compression levels. We propose
an elegant modification of the forward stochastic differential equation of
diffusion models to adapt them to this restoration task and name our method
DriftRec. Comparing DriftRec against an regression baseline with the same
network architecture and two state-of-the-art techniques for JPEG restoration,
we show that our approach can escape the tendency of other methods to generate
blurry images, and recovers the distribution of clean images significantly more
faithfully. For this, only a dataset of clean/corrupted image pairs and no
knowledge about the corruption operation is required, enabling wider
applicability to other restoration tasks. In contrast to other conditional and
unconditional diffusion models, we utilize the idea that the distributions of
clean and corrupted images are much closer to each other than each is to the
usual Gaussian prior of the reverse process in diffusion models. Our approach
therefore requires only low levels of added noise, and needs comparatively few
sampling steps even without further optimizations. We show that DriftRec
naturally generalizes to realistic and difficult scenarios such as unaligned
double JPEG compression and blind restoration of JPEGs found online, without
having encountered such examples during training.Comment: This work has been submitted to the IEEE for possible publication.
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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
New 5 Kilowatt Free-piston Stirling Space Convertor Developments
The NASA Vision for Exploration of the moon may someday require a nuclear reactor coupled with a free-piston Stirling convertor at a power level of 30-40 kW. In the 1990s, Mechanical Technology Inc. s Stirling Engine Systems Division (some of whose Stirling personnel are now at Foster-Miller, Inc.) developed a 25 kW free piston Stirling Space Power Demonstrator Engine under the SP-100 program. This system consisted of two 12.5 kW engines connected at their hot ends and mounted in tandem to cancel vibration. Recently, NASA and DoE have been developing dual 55 W and 80 W Stirling convertor systems for potential use with radioisotope heat sources. Total test times of all convertors in this effort exceed 120,000 hours. Recently, NASA began a new project with Auburn University to develop a 5 kW, single convertor for potential use in a lunar surface reactor power system. Goals of this development program include a specific power in excess of 140 W/kg at the convertor level, lifetime in excess of five years and a control system that will safely manage the convertors in case of an emergency. Auburn University awarded a subcontract to Foster-Miller, Inc. to undertake development of the 5 kW Stirling Convertor Assembly. The characteristics of the design along with progress in developing the system will be described
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