6,216 research outputs found
On the spring and mass of the Dirac oscillator
The Dirac oscillator is a relativistic generalization of the quantum harmonic oscillator. In particular, the square of the Hamiltonian for the Dirac oscillator yields the Klein-Gordon equation with a potential of the form: (ar(sub 2) + b(L x S)), where a and b are constants. To obtain the Dirac oscillator, a 'minimal substitution' is made in the Dirac equation, where the ordinary derivative is replaced with a covariant derivative. However, an unusual feature of the covariant derivative in this case is that the potential is a non-trivial element of the Clifford algebra. A theory which naturally gives rise to gage potentials which are non-trivial elements of the Clifford algebra is that based on local automorphism invariance. An exact solution of the automorphism gage field equations which reproduces both the potential term and the mass term of the Dirac oscillator is presented
The Impact of Agricultural Technology in Sub-Saharan Africa: A Synthesis of Symposium Findings
The Symposium on the Impact of Technology on Agricultural Transformation in Sub-Saharan Africa funded by AID/AFR/ARTS and AID/RD/EID under the Michigan State University Food Security Cooperative Agreements, was held in Washington, D.C., Oct. 14-16, 1992. A primary purpose of the symposium was to present evidence which would either confirm or contradict the perception that the accomplishments of TDT were insufficient to justify continued funding. A secondary objective was to consider the adequacy of available analytical tools for impact assessment. The rate of return (ROR) is the most commonly used valuative measure of investments in technology development and transfer. Examined as a group, the estimated RORs support the proposition that African agricultural research has had people-level impacts, and that these impacts are large enough to justify the level of investment that led to the impacts. An important part of the impact assessment story is the analysis of factors that had a positive or negative effect on the impact of TDT. Five major factors emerged from the studies presented and comments by symposium participants: agroclimatic conditions, civil unrest, research system performance, policy, and markets. Progress has been made in moving forward with the process of TDT, in spite of adverse conditions. This progress includes enhancing the capabilities of national, regional and international institutions to generate new techniques, pushing forward the technology frontier, transferring technology, and increasing productivity both in farm production and post-harvest activities. Activities such as structural adjustment, improvements in agricultural and macroeconomic policy, greater reliance on democracy and capitalism, investments in infrastructure, and a greater willingness to work with the private sector have increased the potential for TDT to have significant impact. Given the importance of raising productivity in agriculture as a step towards agricultural transformation, continued investment in agricultural TDT is merited. The evidence of impact achieved from previous investments shows that those investments have paid off. Coupled with the evidence of beneficial changes in the macroeconomic policy environment in many countries, this provides the basis for expecting that future investments will pay off. What is perhaps unique about the symposium is the movement towards a commodity sector perspective as the next logical step toward including more demand-side considerations in the TDT agenda.International Development, Research and Development/Tech Change/Emerging Technologies, Downloads July 2008 - June 2009: 18,
ANALYSIS OF PROJECTS WITH PRICE EFFECTS, AND APPLICATION TO INNOVATION AND TECHNICAL CHANGE
Replaced with revised version of paper 04/21/06.Research and Development/Tech Change/Emerging Technologies,
Payoffs to Investments in Agricultural Technology in Sub-Saharan Africa
Research and Development/Tech Change/Emerging Technologies, Downloads July 2008-June 2009: 7,
In-Danger Animals
An Army Ranger reflects on his experiences with wild animals during his military career, especially an encounter with a tiger in the DMZ.
Articles, stories, and other compositions in this archive were written by participants in the Mighty Pen Project. The program, developed by author David L. Robbins, and in partnership with Virginia Commonwealth University and the Virginia War Memorial in Richmond, Virginia, offers veterans and their family members a customized twelve-week writing class, free of charge. The program encourages, supports, and assists participants in sharing their stories and experiences of military experience so both writer and audience may benefit
International Law and the Problem of Change: A Tale of Two Conventions
Extensive efforts have been made in the modern period to suppress the possession and use of both chemical and nuclear weapons. However, progress towards the abolition of these two types of weapons presents a rather sharp contrast, as this case study shows. In this article the conventional prohibitions on the possession and use of these weapons are outlined, including the recent Treaty on the Prohibition of Nuclear Weapons of 2017. This Treaty prohibits the possession and use of nuclear weapons but it has not been (and likely will not be) ratified by any of the States that possess nuclear weapons. There is a further, and consequent, contrast between the two kinds of weapons in terms of whether a customary prohibition on the possession and use of chemical and/or nuclear weapons exists; this is also examined. Ultimately, there are lessons to be learned in terms of whether international law can change unless those most concerned, in this case the States that possess chemical or nuclear weapons, want it to change. 
Effect of polar and non-polar solvents on the rotatory power and dispersion of L. benzoin, L. benzoin methyl ether, and methyl L-mandelate
The optical behaviour of L.-benzoin, L-benzoin
methyl ether and methyl L-mandelate, with change of
solvent, concentrat ion, and temperature has been examined
for a range of wavelengths over the visible region of
the spectrum. The results may be summarised as
follows.(a) On the whole the negative rotation of
L-benzoin varies with the polarity of the solvent in
such a manner that solvents of high polarity depress
the negative rotatory power. This depression is
attributed to the greater degree of association existing
between the active, solute and solvents of higher
polarity.(b) In agreement with (a), an increase in
the concentration of L-benzoin in a non-polar solvent
also lowers the negative rotation, owing to a rise in
the degree of association of the solute molecules with
one another.(c) Among non-polar solvents the solutions
with cyclohexane, mesitylene, toluene and benzene gave
abnormally low negative rotations as compared with their
non-polar character. These displacements were assumed
to be due to the association of L-benzoin in such media,
and this view is supported by molecular weight measurements .(d) On rise of temperature the T-R curves for
L-benzoin in bromobenzene and. nitrobenzene respectively
(typical of weakly and strongly polar solvents) tend to
converge. This is in agreement with the dipole theory.(e) For L-benzoin methyl ether, molecular
weight determinations now show that very little association
at low concentrations occurs even in non-polar solvents.
In agreement with this difference, the rotatory powers
of the ether are in much closer agreement with the
polarity of the solvents than was found for L-benzoin.
Cyclohexane, mesitylene, and other non-polar solvents
fall into position at one end of the series to give
dextro-rotatory solutions. Strongly polar solvents
On the other hand yield laevo-rotatory solutions.The typical effect of polar and non-polar
solvents corresponds to the remarkable variation in
rotatory power of L-benzoin methyl ether with
change of concentration in benzene solution. With
increase in concentration, the dextro-rotation changes
into a laevo-rotation.With rise of temperature the T-R curves for
mesitylene, bromobenzene and nitrobenzene converge
strongly. These solvents were selected as being
typical of non-polar, weakly polar and strongly polar
media respectively.(f) Methyl L-mandelate, as was expected,
resembles L-benzoin in many of its optical properties.
The laevo-rotation tends to fall with increase in the
dipole moment of the solvent, although certain non-
polar media yield abnormally low values. The latter
may be explained by the fact that the ester exists in
these solvents in the associated state. The changes
with rise of concentration and temperature are also in
agreement with the predictions of the theory of dipoles.(g) The dispersions of L-benzoin and methyl
L-mandelate are in every case normal and complex. When is plotted against λ² , the deviation of the
graph from the line joining the extreme points is in
the same direction.This statement also holds for L-benzoin
methyl ether in non-polar and strongly polar solvents
respectively. In solvents of medium polarity, or in
the homogeneous state the deviation of the graph may be
in the opposite direction to the above, or anomalous
dispersion may be exhibited
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