32,237 research outputs found
Method for the preparation of thin-skinned asymmetric reverse osmosis membranes and products thereof
A method for preparing water insoluble asymmetric membranes from water soluble polymers is discussed. The process involves casting a film of the polymer, partially drying it, and then contacting it with a concentrated solution of a transition metal salt. The transition metal ions render the polymer insoluable and are believed to form a complex with it. Optionally, the polymer is crosslinked with heat or radiation. The most preferred polymer is poly(vinyl alcohol). The most preferred complexing salt is copper sulfate. The process and the metal ion linked membranes are discussed. The membranes are reverse osmosis membranes
A Conformal Truncation Framework for Infinite-Volume Dynamics
We present a new framework for studying conformal field theories deformed by
one or more relevant operators. The original CFT is described in infinite
volume using a basis of states with definite momentum, , and conformal
Casimir, . The relevant deformation is then considered using
lightcone quantization, with the resulting Hamiltonian expressed in terms of
this CFT basis. Truncating to states with , one can numerically find the resulting spectrum, as well
as other dynamical quantities, such as spectral densities of operators. This
method requires the introduction of an appropriate regulator, which can be
chosen to preserve the conformal structure of the basis. We check this
framework in three dimensions for various perturbative deformations of a free
scalar CFT, and for the case of a free CFT deformed by a mass term and a
non-perturbative quartic interaction at large-. In all cases, the truncation
scheme correctly reproduces known analytic results. We also discuss a general
procedure for generating a basis of Casimir eigenstates for a free CFT in any
number of dimensions.Comment: 48+37 pages, 17 figures; v2: references added, small clarification
Nonperturbative Matching Between Equal-Time and Lightcone Quantization
We investigate the nonperturbative relation between lightcone (LC) and
standard equal-time (ET) quantization in the context of theory
in . We discuss the perturbative matching between bare parameters and the
failure of its naive nonperturbative extension. We argue that they are
nevertheless the same theory nonperturbatively, and that furthermore the
nonperturbative map between bare parameters can be extracted from ET
perturbation theory via Borel resummation of the mass gap. We test this map by
using it to compare physical quantities computed using numerical Hamiltonian
truncation methods in ET and LC.Comment: 22+8 pages, 10 figure
Boydbolt, a positive-latch, simple-release fastener
Fastener /Boydbolt/ has recently been designed to furnish positive lock and release characteristics that positively prevent accidental adverse functions of lock or release
Inter-Industry Wage Differences and Theories of Wage Determination
Numerous studies have shown large differences in wages for apparently similar workers across industries. These findings pose a challenge to standard model s of labor market behavior. A problem with past studies of industry wage differences is that they have failed to distinguish between union and nonunion workers. Many economists may expect union workers wages to be set in a noncompetitive fashion but would be surprised if nonunion wages were. We examine the differences in wages across industries for both union and nonunion workers. We find that even after controlling for a wide range of personal characteristics and geographic location large wage differences persist for both union and nonunion workers. Furthermore the premiums of union and nonunion workers are highly correlated. We review past studies which demonstrate that industry wage premiums are also highly correlated across countries and have been very similar over many decades. We present new evidence that the wages of different occupations are highly correlated across industries -- that is if any occupation in an industry is highly paid all occupations are. We also review the evidence which suggests that people who move from low to high paying industries receive a large fraction of the industry wage premium and that those who move from high to low paying industries lose the premium. Finally, we review the evidence on the correlates of industry wage differences. Quit rates, human capital variables, capital labor ratios and market power measures are all positively correlated with industry wage differences individually though the data are not adequate to determine their independent contributions in multiple regression. On the basis of all the evidence we conclude that standard labor market clearing models can not easily explain all the facts. Several alternative models are discussed including efficiency wage and collective action threat mode1 s. These are found to be more consistent with the facts though some troubling problems remain.
The status of pentaquark spectroscopy on the lattice
The present work is a summary of the status of lattice pentaquark
calculations. After a pedagogic introduction to the basics of lattice hadron
spectroscopy we give a critical comparison of results presently available in
the literature. Special emphasis is put on presenting some of the possible
pitfalls of these calculations. In particular we discuss at length the choice
of the hadronic operators and the separation of genuine five-quark states from
meson-baryon scattering states.Comment: 13 pages LaTeX, 1 eps figur
Pentaquark hadrons from lattice QCD
We study spin 1/2 isoscalar and isovector candidates in both parity channels
for the recently discovered \Theta^+(1540) pentaquark particle in quenched
lattice QCD. Our analysis takes into account all possible uncertainties, such
as statistical, finite size and quenching errors when performing the chiral and
continuum extrapolations and we have indications that our signal is separated
from scattering states. The lowest mass that we find in the I^P=0^- channel is
in complete agreement with the experimental value of the \Theta^+ mass. On the
other hand, the lowest mass state in the opposite parity I^P=0^+ channel is
much higher. Our findings suggests that the parity of the \Theta^+ is negative.Comment: 13 pages, 5 figures. Final version, appeared in JHE
Perfect Scalars on the Lattice
We perform renormalization group transformations to construct optimally local
perfect lattice actions for free scalar fields of any mass. Their couplings
decay exponentially. The spectrum is identical to the continuum spectrum, while
thermodynamic quantities have tiny lattice artifacts. To make such actions
applicable in simulations, we truncate the couplings to a unit hypercube and
observe that spectrum and thermodynamics are still drastically improved
compared to the standard lattice action. We show how preconditioning techniques
can be applied successfully to this type of action. We also consider a number
of variants of the perfect lattice action, such as the use of an anisotropic or
triangular lattice, and modifications of the renormalization group
transformations motivated by wavelets. Along the way we illuminate the
consistent treatment of gauge fields, and we find a new fermionic fixed point
action with attractive properties.Comment: 26 pages, 11 figure
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