1,007 research outputs found
Unified derivation of Bohmian methods and the incorporation of interference effects
We present a unified derivation of Bohmian methods that serves as a common
starting point for the derivative propagation method (DPM), Bohmian mechanics
with complex action (BOMCA) and the zero-velocity complex action method
(ZEVCA). The unified derivation begins with the ansatz
where the action, , is taken to be complex and
the quantum force is obtained by writing a hierarchy of equations of motion for
the phase partial derivatives. We demonstrate how different choices of the
trajectory velocity field yield different formulations such as DPM, BOMCA and
ZEVCA. The new derivation is used for two purposes. First, it serves as a
common basis for comparing the role of the quantum force in the DPM and BOMCA
formulations. Second, we use the new derivation to show that superposing the
contributions of real, crossing trajectories yields a nodal pattern essentially
identical to that of the exact quantum wavefunction. The latter result suggests
a promising new approach to deal with the challenging problem of nodes in
Bohmian mechanics
Structural and electronic influences on phosphite basicity and its application to heterogeneous and homogeneous catalysis
NiL(,4) complexes of various monocyclic and bicyclic phosphite ligands have been shown to be effective catalysts for the isomerization and hydrocyanation of olefins. The catalytic activity of the NiL(,4) complex was found to be dependent upon the electronic and structural properties of the phosphite ligand. It was observed that in order for these complexes to function as catalysts, the presence of either a protic or a Lewis acid co-catalyst was required.;An x-ray structural investigation of a NiL(,4) complex containing a monocyclic phosphite showed that the complex is tetrahedrally coordinated. It is suggested that the marked difference in catalytic activity of these complexes is derived from the differences in the steric properties of the ligands contained in the complex.;Attempts were also made at heterogenizing these homogeneous NiL(,4) catalysts by means of ligand exchange with nonchelating diphosphorus ligands (P-P). Complexes of the following types were prepared and (UNFORMATTED TABLE FOLLOWS); L L L;-Ni-(P-P)-Ni-(P-P)-Ni-; L L L(TABLE ENDS);evaluated as catalysts for olefin isomerization under the same conditions used with the homogeneous NiL(,4) catalysts.;The structural and electronic properties of some selected monocyclic aminophosphite compounds were investigated in order to determine how their unique electronic and structural properties could influence the catalytic activities of the NiL(,4) compounds they formed.;A method for the quantitative analysis of alcohols using phosphorus-containing derivatizing reagents was developed. This method entailed the use of quantitative (\u2731)P NMR techniques
Trade policy reform and poverty alleviation
In this paper, developed as part of the World Bank's Poverty Reduction Strategy Sourcebook, the authors examine how to implement trade liberalization as part of a strategy for alleviating poverty in developing countries. They discuss trade policy instruments, institutions, complementary policies, sector issues, adjustment policies, and safety nets in an integrated approach to trade policy as a tool for poverty alleviation. The authors examine the patterns or models of trade policy that have been successful in alleviating poverty. They discuss the role of tariffs, nontariff barriers, contingent protection (such as safeguards and antidumping), special import regimes (such as duty drawback), export taxes, export subsidies, and trade-related institutions (such as standards, marketing, export finance, customs clearance, and regional trade arrangements). The authors also discuss policies that complement successful trade reform, including macroeconomic stability, a competitive exchange rate, flexible labor markets, competitive product markets, and policies that do not discriminate against foreigners in investment. They suggest approaches to policies and institutions in services and agriculture, key sectors in poverty reduction. They explain the roles of retraining and safety nets in dealing with the adjustment costs of trade liberalization. Finally, the authors elaborate guidelines for implementing trade reform and explain tools for assessing whether trade reform will help or harm the poor in particular sectors in the short run.Environmental Economics&Policies,Payment Systems&Infrastructure,Economic Theory&Research,Trade Policy,Labor Policies,TF054105-DONOR FUNDED OPERATION ADMINISTRATION FEE INCOME AND EXPENSE ACCOUNT,Environmental Economics&Policies,Economic Theory&Research,Trade Policy,Achieving Shared Growth
Complex trajectory method in time-dependent WKB
We present a significant improvement to a time-dependent WKB (TDWKB)
formulation developed by Boiron and Lombardi [JCP {\bf108}, 3431 (1998)] in
which the TDWKB equations are solved along classical trajectories that
propagate in the complex plane. Boiron and Lombardi showed that the method
gives very good agreement with the exact quantum mechanical result as long as
the wavefunction does not exhibit interference effects such as oscillations and
nodes. In this paper we show that this limitation can be overcome by
superposing the contributions of crossing trajectories. We also demonstrate
that the approximation improves when incorporating higher order terms in the
expansion. These improvements could make the TDWKB formulation a competitive
alternative to current time-dependent semiclassical methods
Optimal Design Of English Auctions With Discrete Bid Levels
This paper considers a form of ascending price English auction widely used in both live and online auctions. This discrete bid auction requires that the bidders submit bids at predetermined discrete bid levels, and thus, there exists a minimal increment by which the bid price may be raised. In contrast, the academic literature of optimal auction design deals almost solely with continuous bid auctions. As a result, there is little practical guidance as to how an auctioneer, seeking to maximize its revenue, should determine the number and value of these discrete bid levels, and it is this omission that is addressed here. To this end, a model of a discrete bid auction from the literature is considered, and an expression for the expected revenue of this auction is derived. This expression is used to determine both numerical and analytical solutions for the optimal bid levels, and uniform and exponential bidder’s valuation distributions are compared. Finally, the limiting case where the number of discrete bid levels is large is considered. An analytical expression for the distribution of the optimal discrete bid levels is derived, and an intuitive understanding of how this distribution maximizes the revenue of the auction is developed
Bragg Scattering as a Probe of Atomic Wavefunctions and Quantum Phase Transitions in Optical Lattices
We have observed Bragg scattering of photons from quantum degenerate
Rb atoms in a three-dimensional optical lattice. Bragg scattered light
directly probes the microscopic crystal structure and atomic wavefunction whose
position and momentum width is Heisenberg-limited. The spatial coherence of the
wavefunction leads to revivals in the Bragg scattered light due to the atomic
Talbot effect. The decay of revivals across the superfluid to Mott insulator
transition indicates the loss of superfluid coherence.Comment: 5 pages, 4 figure
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