112,811 research outputs found
Does the Targeted Jobs Tax Credit Create Jobs at Subsidized Firms?
This paper uses the results of a survey of more than 3,500 private employers to determine whether use of the Targeted Jobs Tax Credit (TJTC) alters the level of a firm\u27s employment and/or whom the firm hires. We estimate that each subsidized hire generates between .13 and .3 new jobs at a participating firm. Use of the program also appears to induce employers to hire more young workers (age 25 and under). Our results suggest, however, that at least 70 percent of the tax credits granted employers are payments for workers who would have been hired even without the subsidy. Such payments represent mere transfers to employers
Asymptotic normality of extreme value estimators on
Consider i.i.d. random elements on . We show that, under an
appropriate strengthening of the domain of attraction condition, natural
estimators of the extreme-value index, which is now a continuous function, and
the normalizing functions have a Gaussian process as limiting distribution. A
key tool is the weak convergence of a weighted tail empirical process, which
makes it possible to obtain the results uniformly on . Detailed examples
are also presented.Comment: Published at http://dx.doi.org/10.1214/009053605000000831 in the
Annals of Statistics (http://www.imstat.org/aos/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Characterisation of porous solids using small-angle scattering and NMR cryoporometry
The characteristics of several porous systems have been studied by the use of small-angle neutron scattering [SANS] and nuclear magnetic resonance [NMR] techniques. The measurements reveal different characteristics for sol-gel silicas, activated carbons and ordered mesoporous silicas of the MCM and SBA type. Good agreement is obtained between gas adsorption measurements and the NMR and SANS results for pore sizes above 10 nm. Recent measurements of the water/ice phase transformation in SBA silicas by neutron diffraction are also presented and indicate a complex relationship that will require more detailed treatment in terms of the possible effects of microporosity in the silica substrate. The complementarity of the different methods is emphasised and there is brief discussion of issues related to possible future developments
About gauge invariance in compactified extra dimensions
Gauge theories formulated in a space-time manifold that includes compact
extra dimensions can show a nontrivial gauge structure. Depending on whether
the gauge parameters propagate or not in the extra dimensions, two different
Kaluza--Klein theories can arise when the extra dimensions are compactified. A
comparison between these two possibilities, in the context of a five
dimensional theory, is presented from both the theoretical and phenomenological
viewpoints. The phenomenological implications of these theories are contrasted
by discussing the one--loop decay of the Higgs boson into two photons. It is
shown that the amplitude for this decay differs substantially from one approach
to the other and that such a difference is intimately related to gauge
invariance.Comment: 5 pages, 1 figur
Breeding for improved nitrogen use efficiency in oilseed rape
Oilseed rape has a high requirement for nitrogen (N) fertiliser relative to its seed yield. This paper uses published and unpublished work to explore the extent to which the N use efficiency (seed yield Ć· N supply) of oilseed rape could be improved without reducing seed yield. It was estimated that if the concentration of N in the stem and pod wall at crop maturity could be reduced from 1.0 to 0.6%, the root length density increased to 1 cm/cm3 to 100 cm soil depth and the post flowering N uptake increased by 20 kg N/ha then the fertiliser requirement could be reduced from 191 to 142 kg N/ha and the N use efficiency could be increased from 15.2 to 22.4 kg of seed dry matter per kg N. Genetic variation was found for all of the traits that were estimated to be important for N use efficiency. This indicates that there is significant scope for plant breeders to reduce N use efficiency in oilseed rape
Electromagnetic Deflection of Spinning Particles
We show that it is possible to obtain self-consistent and physically
acceptable relativistic classical equations of motion for a point-like
spin-half particle possessing an electric charge and a magnetic dipole moment,
directly from a manifestly covariant Lagrangian, if the classical degrees of
freedom are appropriately chosen. It is shown that the equations obtained
encompass the well-tested Lorentz force and Thomas--Bargmann--Michel--Telegdi
spin equations, as well as providing a definite specification of the classical
_magnetic_dipole_ force_, whose exact form has been the subject of recent
debate. Radiation reaction---the force and torque on an accelerated particle
due to its self-interaction---is neglected at this stage.Comment: 18 pp. (latex, uses revtex 3), UM-P-92/9
Nuclear magnetic resonance cryoporometry
Nuclear Magnetic Resonance (NMR) cryoporometry is a technique for non-destructively determining pore size distributions in porous media through the observation of the depressed melting point of a confined liquid. It is suitable for measuring pore diameters in the range 2 nm-1 mu m, depending on the absorbate. Whilst NMR cryoporometry is a perturbative measurement, the results are independent of spin interactions at the pore surface and so can offer direct measurements of pore volume as a function of pore diameter. Pore size distributions obtained with NMR cryoporometry have been shown to compare favourably with those from other methods such as gas adsorption, DSC thermoporosimetry, and SANS. The applications of NMR cryoporometry include studies of silica gels, bones, cements, rocks and many other porous materials. It is also possible to adapt the basic experiment to provide structural resolution in spatially-dependent pore size distributions, or behavioural information about the confined liquid
The Foldy-Wouthuysen transformation
The Foldy-Wouthuysen transformation of the Dirac Hamiltonian is generally
taught as simply a mathematical trick that allows one to obtain a two-component
theory in the low-energy limit. It is not often emphasized that the transformed
representation is the only one in which one can take a meaningful *classical
limit*, in terms of particles and antiparticles. We briefly review the history
and physics of this transformation.Comment: Standard LaTeX, 6 page
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