52,709 research outputs found
Chiral-Odd and Spin-Dependent Quark Fragmentation Functions and their Applications
We define a number of quark fragmentation functions for spin-0, -1/2 and -1
hadrons, and classify them according to their twist, spin and chirality. As an
example of their applications, we use them to analyze semi-inclusive
deep-inelastic scattering on a transversely polarized nucleon.Comment: 19 pages in Plain TeX, MIT CTP #221
Lorentz Symmetry and the Internal Structure of the Nucleon
To investigate the internal structure of the nucleon, it is useful to
introduce quantities that do not transform properly under Lorentz symmetry,
such as the four-momentum of the quarks in the nucleon, the amount of the
nucleon spin contributed by quark spin, etc. In this paper, we discuss to what
extent these quantities do provide Lorentz-invariant descriptions of the
nucleon structure.Comment: 6 pages, no figur
Quark Orbital-Angular-Momentum Distribution in the Nucleon
We introduce gauge-invariant quark and gluon angular momentum distributions
after making a generalization of the angular momentum density operators. From
the quark angular momentum distribution, we define the gauge-invariant and
leading-twist quark {\it orbital} angular momentum distribution . The
latter can be extracted from data on the polarized and unpolarized quark
distributions and the off-forward distribution in the forward limit. We
comment upon the evolution equations obeyed by this as well as other orbital
distributions considered in the literature.Comment: 8 pages, latex, no figures, minor corrections mad
Positivity Constraints for Spin-Dependent Parton Distributions
We derive new positivity constraints on the spin-dependent structure
functions of the nucleon. These model independent results reduce conside\-rably
their domain of allowed values, in particular for the chiral-odd parton
distribution .Comment: 8 pages,CPT-94/P.3059,LaTex,3 fig available on cpt.univ-mrs.fr
directory pub/preprints/94/fundamental-interactions/94-P.305
Simulation of an 1857-like Mw 7.9 San Andreas Fault Earthquake and the Response of Tall Steel Moment Frame Buildings in Southern California – A Prototype Study
In 1857, an earthquake of magnitude 7.9 occurred on the San Andreas fault, starting at Parkfield and rupturing
in a southeasterly direction for more than 360 km. Such a unilateral rupture produces significant directivity
toward the San Fernando and Los Angeles basins. The strong shaking in the basins due to this earthquake
would have had significant long-period content (2-8 s), and the objective of this study is to quantify the impact
of such an earthquake on two 18-story steel moment frame building models, hypothetically located at 636 sites
on a 3.5 km grid in southern California. End-to-end simulations include modeling the source and rupture of a
fault at one end, numerically propagating the seismic waves through the earth structure, simulating the damage
to engineered structures and estimating the economic impact at the other end using high-performance computing.
In this prototype study, we use an inferred finite source model of the magnitude 7.9, 2002 Denali fault
earthquake in Alaska, and map it onto the San Andreas fault with the rupture originating at Parkfield and
propagating southward over a distance of 290 km. Using the spectral element seismic wave propagation code,
SPECFEM3D, we simulate an 1857-like earthquake on the San Andreas fault and compute ground motions at
the 636 analysis sites. Using the nonlinear structural analysis program, FRAME3D, we subsequently analyze
3-D structural models of an existing tall steel building designed using the 1982 Uniform Building Code (UBC),
as well as one designed according to the 1997 UBC, subjected to the computed ground motion at each of these
sites. We summarize the performance of these structural models on contour maps of peak interstory drift.
We then perform an economic loss analysis for the two buildings at each site, using the Matlab Damage and
Loss Analysis (MDLA) toolbox developed to implement the PEER loss-estimation methodology. The toolbox
includes damage prediction and repair cost estimation for structural and non-structural components and allows
for the computation of the mean and variance of building repair costs conditional on engineering demand
parameters (i.e. inter-story drift ratios and peak floor accelerations). Here, we modify it to treat steel-frame
high-rises, including aspects such as mechanical, electrical and plumbing systems, traction elevators, and the
possibility of irreparable structural damage. We then generate contour plots of conditional mean losses for the
San Fernando and the Los Angeles basins for the pre-Northridge and modern code-designed buildings, allowing
for comparison of the economic effects of the updated code for the scenario event. In principle, by simulating
multiple seismic events, consistent with the probabilistic seismic hazard for a building site, the same basic
approach could be used to quantify the uncertain losses from future earthquakes
Appraising the Market Overt Exception
Under what circumstances can a sale of goods by a person, who is not the owner ofthe goods, nonetheless confer good title on the purchaser? The common law rule “nemo dat quodnon habet†embodies the principle that the transferee of goods cannot get better title than that of thetransferor. In other words, if goods are sold by a person who does not have title to the goods (forexample, because he had obtained the goods by theft), then he would be unable to pass title to asubsequent purchaser since he did not have title to begin with. The nemo dat rule thus protects thetrue or original owner of goods. One of the exceptions to this rule under the Hong Kong Sale ofGoods Ordinance is the market overt exception, which seeks to protect innocent purchasers. Thisarticle first considers the meanings of and rationales behind the nemo dat rule and the market overtexception respectively. Problems with the existing market overt exception will next be discussed. Asuggestion will then be made that the market overt exception be replaced with a rule that protectsinnocent buyers who deal as consumers and who have purchased goods from shops or markets inHong Kong
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