27,684 research outputs found
Neutron Activation Analysis of Traces of Palladium, Gold, and Iridium in Supernates from the Refining of Precious Metals
In the refining of precious metals it is desirable to be able
to determine amounts \u27of the elements remaining in solution after
various precipitations. Neutron-activation analysis can be used
advantageously in this field, and in the present report the application
of the method for the determination of traces of palladium,
gold and iridium is described. The nuclear reactor BEPO at
Harwell was used as the source of neutrons and each of the three
elements could be determined wHh high sensitivity in a 0.5-ml
aliquot of a sample solution. Results of analyses of microgram and
submicrogram quantities of palladium, gold and iridium in the
solutions under investigation showed good precision
Study of fuel systems for LH2-fueled subsonic transport aircraft, volume 1
Several engine concepts examined to determine a preferred design which most effectively exploits the characteristics of hydrogen fuel in aircraft tanks received major emphasis. Many candidate designs of tank structure and cryogenic insulation systems were evaluated. Designs of all major elements of the aircraft fuel system including pumps, lines, valves, regulators, and heat exchangers received attention. Selected designs of boost pumps to be mounted in the LH2 tanks, and of a high pressure pump to be mounted on the engine were defined. A final design of LH2-fueled transport aircraft was established which incorporates a preferred design of fuel system. That aircraft was then compared with a conventionally fueled counterpart designed to equivalent technology standards
Optimization of the derivative expansion in the nonperturbative renormalization group
We study the optimization of nonperturbative renormalization group equations
truncated both in fields and derivatives. On the example of the Ising model in
three dimensions, we show that the Principle of Minimal Sensitivity can be
unambiguously implemented at order of the derivative expansion.
This approach allows us to select optimized cut-off functions and to improve
the accuracy of the critical exponents and . The convergence of the
field expansion is also analyzed. We show in particular that its optimization
does not coincide with optimization of the accuracy of the critical exponents.Comment: 13 pages, 9 PS figures, published versio
Study of fuel systems for LH2-fueled subsonic transport aircraft, volume 2
For abstract, see N78-31085
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Rotational 3D Printing of Sensor Devices using Reactive Ink Chemistries
This paper charts progress in three key areas of a project supported by both UK
government and UK industry to manufacture novel sensor devices using rotary 3D printing
technology and innovative ink chemistries; (1) the development of an STL file slicing algorithm
that returns constant Z height 2D contour data at a resolution that matches the given print head
setup, allowing digital images to be generated of the correct size without the need for scaling;
(2) the development of image transformation algorithms which allow images to be printed at
higher resolutions using tilted print heads and; (3) the formulation of multi part reaction inks
which combine and react on the substrate to form solid material layers with a finite thickness. A
Direct Light Projection (DLP) technique demonstrated the robustness of the slice data by
constructing fine detailed three dimensional test pieces which were comparable to identical parts
built in an identical way from slice data obtained using commercial software. Material systems
currently under investigation include plaster, stiff polyamides and epoxy polymers and
conductive metallic’s. Early experimental results show conductivities of silver approaching
1.42x105 Siemens/m.Mechanical Engineerin
Casting Alloys: the Materials and "the Clinical Effects"
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/67282/2/10.1177_08959374920060011101.pd
Critical behavior of weakly interacting bosons: A functional renormalization group approach
We present a detailed investigation of the momentum-dependent self-energy
Sigma(k) at zero frequency of weakly interacting bosons at the critical
temperature T_c of Bose-Einstein condensation in dimensions 3<=D<4. Applying
the functional renormalization group, we calculate the universal scaling
function for the self-energy at zero frequency but at all wave vectors within
an approximation which truncates the flow equations of the irreducible vertices
at the four-point level. The self-energy interpolates between the critical
regime k > k_c, where k_c is the
crossover scale. In the critical regime, the self-energy correctly approaches
the asymptotic behavior Sigma(k) \propto k^{2 - eta}, and in the
short-wavelength regime the behavior is Sigma(k) \propto k^{2(D-3)} in D>3. In
D=3, we recover the logarithmic divergence Sigma(k) \propto ln(k/k_c)
encountered in perturbation theory. Our approach yields the crossover scale k_c
as well as a reasonable estimate for the critical exponent eta in D=3. From our
scaling function we find for the interaction-induced shift in T_c in three
dimensions, Delta T_c / T_c = 1.23 a n^{1/3}, where a is the s-wave scattering
length and n is the density, in excellent agreement with other approaches. We
also discuss the flow of marginal parameters in D=3 and extend our truncation
scheme of the renormalization group equations by including the six- and
eight-point vertex, which yields an improved estimate for the anomalous
dimension eta \approx 0.0513. We further calculate the constant lim_{k->0}
Sigma(k)/k^{2-eta} and find good agreement with recent Monte-Carlo data.Comment: 23 pages, 7 figure
Relaxation of strained silicon on Si0.5Ge0.5 virtual substrates
Strain relaxation has been studied in tensile strained silicon layers grown on Si0.5Ge0.5 virtual substrates, for layers many times the critical thickness, using high resolution x-ray diffraction. Layers up to 30 nm thick were found to relax less than 2% by the glide of preexisting 60° dislocations. Relaxation is limited because many of these dislocations dissociate into extended stacking faults that impede the dislocation glide. For thicker layers, nucleated microtwins were observed, which significantly increased relaxation to 14%. All these tensile strained layers are found to be much more stable than layers with comparable compressive strain
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