Nonadiabatic quantum pumping in mesoscopic nanostructures

We consider a nonadiabatic quantum pumping phenomena in a ballistic narrow constriction. The pumping is induced by a potential that has both spatial and temporal periodicity characterized by $K$ and $\Omega$. In the zero frequency ($\Omega=0$) limit, the transmission through narrow constriction exhibits valley structures due to the opening up of energy gaps in the pumping region -- a consequence of the $K$ periodicity. These valley structures remain robust in the regime of finite $\Omega$, while their energies of occurrence are shifted by about $\hbar\Omega/2$. The direction of these energy shifts depend on the directions of both the phase-velocity of the pumping potential and the transmitting electrons. This frequency dependent feature of the valley structures gives rise to both the asymmetry in the transmission coefficients and the pumping current. An experimental setup is suggested for a possible observation of our nonadiabatic quantum pumping findings.Comment: 4 pages, 2 figure

Transport spectroscopy in a time-modulated open quantum dot

We have investigated the time-modulated coherent quantum transport phenomena in a ballistic open quantum dot. The conductance $G$ and the electron dwell time in the dots are calculated by a time-dependent mode-matching method. Under high-frequency modulation, the traversing electrons are found to exhibit three types of resonant scatterings. They are intersideband scatterings: into quasibound states in the dots, into true bound states in the dots, and into quasibound states just beneath the subband threshold in the leads. Dip structures or fano structures in $G$ are their signatures. Our results show structures due to 2$\hbar\omega$ intersideband processes. At the above scattering resonances, we have estimated, according to our dwell time calculation, the number of round-trip scatterings that the traversing electrons undertake between the two dot openings.Comment: 8 pages, 5 figure

Supply Chains Built for Speed and Customization

As emerging technologies like 3-D printing begin to bring personalized manufacturing to scale, a new supply chain model is following suit

Guiding the next generation of doctoral students in operations management

This paper presents ways for senior researchers to help future doctoral students in Operations Management (OM) to overcome multiple challenges in: (a) conducting relevant research while demonstrating greater rigor, and (b) exploring multi-disciplinary research projects while mastering a single research method. Recognizing that knowledge is generally created in four broad stages ((I) awareness, (II) framing, (III) modeling and (IV) validation), we first argue that different research approaches (analytical, behavioral, case study, or empirical) serve different roles in each of these stages: (1) case study approach for awareness, (2) empirical methods for framing, (3) analytical modeling for modeling and analysis, and (4) behavioral for validation in the real world. Then we discuss ways to enable doctoral students to overcome the aforementioned challenges

The OR/MS ecosystem: Strengths, weaknesses, opportunities, and threats

We believe that research, teaching, and practice are becoming increasingly disengaged from one another in the OR/MS ecosystem. This ecosystem comprises researchers, educators, and practitioners in its core along with end users, universities, and funding agencies. Continuing disengagement will result in OR/MS occupying only niche areas and disappearing as a distinct field even though its tools would live on. To understand the reasons for this disengagement better and to engender discussion among academics and practitioners on how to counter it, we present the ecosystem's strengths, weaknesses, opportunities, and threats. Incorporated in this paper are insights from a cluster of sessions at the 2006 INFORMS meeting in Pittsburgh (“Where Do We Want to Go in OR/MS?”) and from the literature

Coherent quantum transport in the presence of a finite-range transversely polarized time-dependent field

This work investigates the quantum transport in a narrow constriction acted upon by a finite-range transversely polarized time-dependent electric field. A generalized scattering-matrix method is developed that has incorporated a time-dependent mode-matching scheme. The transverse field induces coherent inelastic scatterings that include both intersubband and intersideband transitions. These scatterings give rise to the dc conductance $G$ a general suppressed feature that escalates with the chemical potential. In addition, particular suppressed features -- the dip structures -- are found in $G$. These features are recognized as the quasi-bound-state (QBS) features that arise from electrons making intersubband transitions to the vicinity of a subband bottom. For the case of larger field intensities, the QBS features that involve more photons are more evident. These QBS features are closely associated with the singular density of states at the subband bottoms. An experimental setup is proposed for the observation of these features.Comment: 8 pages, 4 figure

Differential conductance of a saddle-point constriction with a time-modulated gate-voltage

The effect of a time-modulated gate-voltage on the differential conductance $G$ of a saddle-point constriction is studied. The constriction is modeled by a symmetric saddle-point potential and the time-modulated gate-voltage is represented by a potential of the form $V_{0} \theta(a/2-|x-x_{c}|) \cos (\omega t)$. For $\hbar\omega$ less than half of the transverse subband energy level spacing, gate-voltage-assisted (suppressed) feature occurs when the chemical potential $\mu$ is less (greater) than but close to the threshold energy of a subband. As $\mu$ increases, $G$ is found to exhibit, alternatively, the assisted and the suppressed feature. For larger $\hbar\omega$, these two features may overlap with one another. Dip structures are found in the suppressed regime. Mini-steps are found in the assisted regime only when the gate-voltage covers region far enough away from the center of the constriction.Comment: 8 pages, 6 figure

POMS initiatives for promoting practice-driven research and research-influenced practice

The Production and Operations Management Society (POMS) and Production and Operations Management (POM) have developed new initiatives with these objectives: (1) to disseminate managerial insights of articles published in POM to practitioners, MBA students, and participants in executive development programs; (2) to solicit descriptions of current and emerging problems from practitioners and share them with academics; and (3) to recognize academic research based on direct work with practitioners

An Analysis of Partially-Guaranteed-Price Contracts between Farmers and Agri-Food Companies

Global agri-food companies such as Barilla and SABMiller are purchasing agricultural products directly from farmers using different types of contracts to ensure stable supply. We examine one such contract with partially-guaranteed prices (PGP). Under a PGP contract, around sowing time, the buying firm agrees to purchase the crop when harvested by the farmer, offering a guaranteed unit price for any fraction of the produce and offering the commodity market price prevailing at the time of delivery for the remainder. The farmer then chooses the fraction. By analyzing a Stackelberg game, we show (1) how the PGP contract creates mutual benefits when the firm’s purchase quantity is taken as being exogenous. We also analyze how the PGP contract is robust in creating value for both the firm and the farmer (2) when the firm’s purchase quantity is endogenously determined; (3) when the firm provides advisory services to the farmer; and (4) when the firm offers a price premium as an incentive for farmers to exert efforts to comply with ‘sustainable’ agricultural practices

An EOQ model for MRO customers under stochastic price to quantify bullwhip effect for the manufacturer

Motivated by a particular multinational cutting-tools manufacturer, we extend the traditional economic order quantity (EOQ) model for maintenance-repair-and-overhaul (MRO) customers under stochastic purchase price and use it to show how price variance leads to bullwhip effect for the MRO manufacturer despite constant consumption by the customer. Our extension of the EOQ model is based on two assumptions that are reasonable for MRO customers: (a) customer consumption rate of the product is constant; and (b) the customer places each order when the inventory level drops to a pre-specified level (say, zero). We determine the customer's optimal ordering quantity in closed form expressions, which enables us to examine the impact of sales price variance on the variance in the orders the customer places on the manufacturer, thus creating a pricing-induced bullwhip effect. We then extend our analysis to multiple products and multiple customer segments and discuss ways for the manufacturer to mitigate the variance in the customer's orders