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Minimizing Multi-zone Orders in the Correlated Storage Assignment ProblemGarfinkel, Maurice 14 January 2005 (has links)
A fundamental issue in warehouse operations is the storage location of the products it contains. Placing products intelligently within the system can allow for great reductions in order pick costs. This is essential because order picking is a major cost of warehouse operations. For example, a study by Drury conducted in the UK found that 63% of warehouse operating costs are due to order picking. When orders contain a single item, the COI rule of Heskett is an optimal storage policy. This is not true when orders contain multiple line items because no information is used about what products are ordered together. In this situation, products that are frequently ordered together should be stored together. This is the basis of the correlated storage assignment problem.
Several previous researchers have considered how to form such clusters of products with an ultimate objective of minimizing travel time. In this dissertation, we focus on the alternate objective of minimizing multi-zone orders. We present a mathematical model and discuss properties of the problem. A Lagrangian relaxation solution approach is discussed. In addition, we both develop and adapt several heuristics from the literature to give upper bounds for the model.
A cyclic exchange improvement method is also developed. This exponential size neighborhood can be efficiently searched in polynomial time. Even for poor initial solutions, this method finds solutions which outperform the best approaches from the literature.
Different product sizes, stock splitting, and rewarehousing are problem features that our model can handle. The cyclic exchange algorithm is also modified to allow these operating modes. In particular, stock splitting is a difficult issue which most previous research in correlated storage ignores. All of our algorithms are implemented and tested on data from a functioning warehouse. For all data sets, the cyclic exchange algorithm outperforms COI, the standard industry approach, by an average of 15%.
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Implementing Fluorescence Lifetime Imaging on a Confocal MicroscopeChiu, Yi-Chun 06 July 2005 (has links)
In this thesis, the development and implementation of fluorescence lifetime imaging microscopy that integrates time correlated single photon counting (TCSPC) and a confocal microscope will be described. The TCSPC method has high detection efficiency, with a time resolution limited only by the transit time spread of the detector, and directly delivers the decay functions in the time domain. TCSPC can also be used to obtain images that indicate the fluorescence resonance energy transfer (FRET) effect between critical fluorophores, an important method distinguish the difference between binding and co-localization. Estimation of distances between RET fluorophore pairs can also be established. Additionally, the effects of ion concentration, oxygen concentration, pH value, ..etc. can also be revealed.
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Timing effects of carbon mitigation and solar radiation management policiesQu, Jingwen 06 April 2012 (has links)
We study timing effects of carbon mitigation and solar radiation management (SRM) policies for correlated pollutants, CO₂ and SO₂. We show that national levels of carbon and sulfur emissions quotas and SRM implementation are positively correlated with each other. First-mover advantages exist when deciding both carbon quotas and SRM levels. Moreover, we use an example to illustrate that if international equity is considered, governments would be willing to choose SRM levels before carbon quotas since it yields higher payoffs and less acid rain and droughts damages. This timing was neglected by all previous theoretical economic models on geoengineering.
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The construction and role of non-covalent benchmarks in computational chemistryMarshall, Michael S. 02 July 2012 (has links)
This thesis focuses on the construction and role of benchmark quality computations in the area of
non-covalent interactions. We have provided a detailed error analysis of focal-point schemes
commonly used in benchmark quality computations, as well as provide error and speedup analysis of
commonly used approximations to these methods. An analysis of basis set effects on
higher-order corrections to MP2/CBS has been carried out, providing the community error bounds on future benchmarks. We demonstrate how these high-level computations can elucidate a better
understanding of non-bonded interactions in chemistry as well as provide high-quality reference data to refit existing methods against to increase the overall accuracy of the method.
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The role of inter-plane interaction in the electronic structure of high Tc cupratesKim, Timur K. 10 April 2004 (has links) (PDF)
This thesis represents a systematic study of electronic structure of the modulation-free Pb-doped Bi2212 superconducting cuprates with respect to interlayer coupling done by using the angle-resolved photoemission spectroscopy (ARPES), which is a leading technique in the experimental investigation of the single particle excitations in solids. The results presented in this work indicate a very different origin for the observed complex spectra lineshape. Specifically, the peak-dip-hump lineshape can be easily understood in terms of the superposition of spectral features due to bilayer band splitting, namely the splitting of the CuO2 plane derived electronic structure in bonding and antibonding bands due to the interlayer coupling of CuO2 bilayer blocks within the unit cell of Bi2212. By performing experiments at synchrotron beamlines where the energy of the incoming photons can be tuned over a very broad range, the detailed matrix elements energy dependence for both bonding and antibonding bands was determined. This gave the opportunity to study the electronic properties these two bands separately. For the first time, it was proved that the superconducting gap has the same value and symmetry for both bands. Furthermore, having recognized and sorted out the bilayer splitting effects, it became possible to identify more subtle effects hidden in the details of the ARPES lineshapes. On underdoped samples an "intrinsic" peak-dip-hump structure due to the interaction between electrons and a bosonic mode was observed. Studying the doping, temperature, and momentum dependence of the photoemission spectra it was established that: the mode has a characteristic energy of 38-40 meV and causes strong renormalization of the electronic structure only in the superconducting state; the electron-mode coupling is maximal around the (?à,0) point in momentum space and is strongly doping dependent (being greatly enhanced in the underdoped regime). From the above, it was concluded that the bosonic mode must correspond to the sharp magnetic resonance mode observed in inelastic neutron scattering experiments, and that this coupling is relevant to superconductivity and the pairing mechanism in the cuprates.
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Asymptotic Expansions for Second-Order Moments of Integral Functionals of Weakly Correlated Random FunctionsScheidt, Jrgen vom, Starkloff, Hans-Jrg, Wunderlich, Ralf 30 October 1998 (has links) (PDF)
In the paper asymptotic expansions for
second-order moments of integral functionals
of a class of random functions are considered.
The random functions are assumed to be
$\epsilon$-correlated, i.e. the values are not
correlated excluding a $\epsilon$-neighbourhood
of each point. The asymptotic expansions are
derived for $\epsilon \to 0$. With the help of
a special weak assumption there are found
easier expansions as in the case of general
weakly correlated functions.
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On the analytic representation of the correlation function of linear random vibration systemsGruner, J., Scheidt, J. vom, Wunderlich, R. 30 October 1998 (has links) (PDF)
This paper is devoted to the computation of statistical characteristics of
the response of discrete vibration systems with a random external excitation.
The excitation can act at multiple points and is modeled by a time-shifted
random process and its derivatives up to the second order. Statistical characteristics
of the response are given by expansions as to the correlation length
of a weakly correlated random process which is used in the excitation model.
As the main result analytic expressions of some integrals involved in the expansion terms are derived.
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Moving-Average approximations of random epsilon-correlated processesKandler, Anne, Richter, Matthias, vom Scheidt, Jürgen, Starkloff, Hans-Jörg, Wunderlich, Ralf 31 August 2004 (has links) (PDF)
The paper considers approximations of time-continuous epsilon-correlated random
processes by interpolation of time-discrete Moving-Average processes. These approximations
are helpful for Monte-Carlo simulations of the response of systems
containing random parameters described by
epsilon-correlated processes. The paper focuses
on the approximation of stationary
epsilon-correlated processes with a prescribed
correlation function. Numerical results are presented.
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Price models with weakly correlated processesRichter, Matthias, Starkloff, Hans-Jörg, Wunderlich, Ralf 31 August 2004 (has links) (PDF)
Empirical autocorrelation functions of returns of stochastic price processes show
phenomena of correlation on small intervals of time, which decay to zero after a
short time. The paper deals with the concept of weakly correlated random processes to describe a mathematical model which takes into account this behaviour of
statistical data. Weakly correlated functions have been applied to model numerous
problems of physics and engineering. The main idea is, that the values of the functions at two points are uncorrelated if the distance between the points exceeds a
certain quantity epsilon > 0. In contrast to the white noise model, for distances smaller
than epsilon a correlation between the values is permitted.
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Self-assembled quantum dots in advanced structuresCreasey, Megan Elizabeth 09 July 2013 (has links)
Advances in nanofabrication have bolstered the development of new optical devices with potential uses ranging from conventional optoelectronics, such as lasers and solar cells, to novel devices, like single photon or entangled photon sources. Quantum encryption of optical communications, in particular, requires devices that couple efficiently to an optical fiber and emit, on demand, indistinguishable photons. With these goals in mind, ultrafast spectroscopy is used to study the electron dynamics in epitaxially grown InAs/GaAs quantum dots (QDs). Quantifying the behavior of these systems is critical to the development of more efficient devices. Studies of two newly developed InGaAs QD structures, quantum dot clusters (QDCs) and QDs embedded in photonic wires, are presented herein.
GaAs photonic wires with diameters in the range of 200 to 250 nm support only the fundamental HE11 guided mode. To fully quantify these new systems, the emission dynamics of QDs contained within wires in a large range of diameters are studied. Time correlated single photon counting measurements of the ground state exciton lifetimes are in very good agreement with predicted theoretical values for the spontaneous emission rates. For diameters smaller than 200 nm, QD emission into the HE11 mode is strongly inhibited and non-radiative processes dominate the decay rate. The best small diameter wires exhibit inhibition factors as high as 16, on par with the current state of the art for photonic crystals.
The QDCs are the product of a hybrid growth technique that combines droplet heteroepitaxy with standard Stranski-Krastanov growth to create many different geometries of QDs. The work presented in this dissertation concentrates specifically on hexa-QDCs consisting of six InAs QDs around a GaAs nanomound. The first ever spectral and temporal properties of QDs within individual hexa-QDCs are presented. The QDs exhibit narrow exciton resonances with good temperature stability, indicating that excitons are well confined within individual QDs. A distinct biexponential decay is observed even at the single QD level. This behavior suggests that non-radiative decay mechanisms and exciton occupation of dark states play a significant role in the recombination dynamics in the QDCs. / text
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