Robust Rolling Research Articles

Robust Dual Sourcing Inventory Management: Optimality of Capped Dual Index Policies

(1) Problem Definition: How to dynamically replenish inventory from two supply sources or shipping modes with general lead times. The fast source is more expensive than the slow source. (2) Academic/Practical Relevance: Dual sourcing provides supply chain flexibility to mitigate demand and supply risk. Despite its relevance in practice, characterizing the optimal dual sourcing policy is extremely challenging, and the optimal stochastic policy for non-consecutive lead times has been unknown for over 50 years. (3) Methodology: We present and solve a robust rolling horizon model for periodically reviewed dual sourcing inventory systems that minimizes the total cost of purchasing, inventory holding and backlogging. (4) Results: We prove that the optimal robust policy is a dual index, dual base-stock policy that constrains or “caps” the slow order and provide closed-form expressions for the three control parameters. The optimality result is established for general lead times and can accommodate non-stationary demand. Our numerical study shows that as the lead time difference grows, the capped dual index policy increasingly smooths slow orders and, for stationary demand, converges to the tailored base surge policy, which places a constant slow order and has been shown to be asymptotically optimal. (5) Managerial Implications: Our capped dual index policy is easy to understand, explain and implement in practice. In an extensive simulation study, the capped dual index policy performs as well as, and can even outperform, the best heuristics presented in the stochastic inventory literature.

A historical perspective of the informational content of commodity futures

This article extends Chinn and Coibion (2014)'s work--Journal of Futures Markets 34-- on predictive content of commodity futures by considering a more comprehensive database and a longer time span, ranging from 25 to 65 years, and by presenting two extensions: multi-equation estimation of risk premiums and testing for the theory of storage.The empirical results show that futures-based forecasts for animal and agricultural products and industrial metals tend to be more efficient, in terms of mean absolute error, than random walk based-forecasts at a one-year horizon. On the other hand, based on robust rolling estimates, there is evidence of constant and time-varying risk premiums in agricultural and precious metals, but their statistical significance vary considerably along the sample period. In particular, gold and silver show evidence of a negative time-varying risk premium, as opposed to platinum.Multi-equation estimation brings efficiency gains in premium gauging, which leads to reject that the futures price is an unbiased estimate of the spot price for all commodity classes. On the other hand, the sampled commodities lend only partial support to the theory of storage, and for the specific case of industrial metals, inventories seem to matter more than interest rates to explain the basis. Altogether, this article finds mixed support for the premium-based model and for the theory of storage.

Does managerial myopia explain Bowman’s Paradox?

PurposeThe purpose of this paper is to investigate if Bowman’s Paradox (negative association between risk and return) is caused by managerial myopia. It also attempts to disentangle whether results are more consistent with one or more potential explanations.Design/methodology/approachThe paper uses univariate statistics and OLS regressions. Empirically examines the relationship between four risk and return proxies, across a wide ranging time period and utilizing a number of model specifications. Results hold after using three-way clustered errors and using a more robust rolling five year, fixed regression methodology measure.FindingsConfirms the existence of the Paradox. Also documents that the association between risk and return is positive in “winner” firms and negative in “loser” firms. Upon further analysis, the earlier negative risk-return relationship is found to entirely be due to the volatility of the (short term) income statement component of the performance terms. Results imply that executives of winner (loser) firms are less (more) likely to manage earnings or engage in other value destroying activities.Research limitations/implicationsThe study is confined by the typical archival study limitations; including potential endogeneity, selection biases and generalizability of the results.Practical implicationsAnecdotal evidence indicates that the business community makes extensive use of these performance measures. These performance measures are also pervasive in academic research. Given the importance of controlling for both managerial and firm performance, a good performance proxy is quintessential.Originality/valueAlthough over 30 years have passed since Bowman (1980) first observed the negative correlation, to date, no consensus explanation exists. Findings suggest that Bowman’s Paradox, is potentially a manifestation of managerial myopia. Thus, this result contributes to several existing research streams.

Railway Rolling Stock Planning: Robustness Against Large Disruptions

In this paper we describe a two-stage optimization model for determining robust rolling stock circulations for passenger trains. Here robustness means that the rolling stock circulations can better deal with large disruptions of the railway system. The two-stage optimization model is formulated as a large mixed-integer linear programming (MILP) model. We first use Benders decomposition to determine optimal solutions for the LP-relaxation of this model. Then we use the cuts that were generated by the Benders decomposition for computing heuristic robust solutions for the two-stage optimization model. We call our method Benders heuristic. We evaluate our approach on the real-life rolling stock-planning problem of Netherlands Railways, the main operator of passenger trains in the Netherlands. The computational results show that, thanks to Benders decomposition, the LP-relaxation of the two-stage optimization problem can be solved in a short time for a representative number of disruption scenarios. In addition, they demonstrate that the robust rolling stock circulation computed heuristically has total costs that are close to the LP lower bounds. Finally, we discuss the practical effectiveness of the robust rolling stock circulation: When a large number of disruption scenarios were applied to these robust circulations and to the nonrobust optimal circulations, the former appeared to be much more easily recoverable than the latter.

Engineered cell homing

AbstractOne of the greatest challenges in cell therapy is to minimally invasively deliver a large quantity of viable cells to a tissue of interest with high engraftment efficiency. Low and inefficient homing of systemically delivered mesenchymal stem cells (MSCs), for example, is thought to be a major limitation of existing MSC-based therapeutic approaches, caused predominantly by inadequate expression of cell surface adhesion receptors. Using a platform approach that preserves the MSC phenotype and does not require genetic manipulation, we modified the surface of MSCs with a nanometer-scale polymer construct containing sialyl Lewisx (sLex) that is found on the surface of leukocytes and mediates cell rolling within inflamed tissue. The sLex engineered MSCs exhibited a robust rolling response on inflamed endothelium in vivo and homed to inflamed tissue with higher efficiency compared with native MSCs. The modular approach described herein offers a simple method to potentially target any cell type to specific tissues via the circulation.

Abstract 296: Characterization of prostate cancer circulating tumor cells using E-selectin coated-microtubes

Abstract Background: Metastasis and invasion is facilitated by adhesion of circulating tumor cells (CTCs) to endothelial cells in the blood vessel. Initial recruitment of CTCs to the blood vessel endothelium is mediated through selectin proteins. We used microtube coated with selectin proteins to simulate CTC adhesion under flow, to elucidate the complex physicochemical dynamics that control CTC adhesion in the bloodstream. Methods: Sterilized microrenathane microtubes were functionalized by E-selectin +/- anti-PSMA (mAb J591) and anti-EpCAM antibodies. Functionalized microtubes were used to observe the rolling behavior of prostate cancer cell lines MDAPCa2b, LNCaP C4-2, and PC-3. MDAPCa2b cells alone or mixed with normal peripheral blood mononuclear cells (PBMCs) were incubated with fluorescently conjugated mAbJ591, and the mixture flowed through the microtube for identification and capture efficiency. PBMCs isolated from prostate cancer patient's blood were similarly processed. Results: MDAPCa2b cells showed robust rolling at 1 dyne/cm2 shear stress while LNCaP, C4-2, and PC-3 cells did not exhibit rolling behavior on E-selectin coated microtubes. 7.5 cells were observed rolling at 1 dyne/cm2 compared to 1.5 cells at 8 dyne/cm2 per 100 mm2 area. To determine if prostate cancer cells could be identified in a mixture of PBMCs, MDAPCa2b cells were spiked in PBMCs and labeled with fluorescently conjugated mAb J591. MDAPCa2b cells demonstrated selective fluorescence which did not alter their rolling behavior. A 50% capture efficiency of MDAPCa2b cells spiked in PBMCs was achieved when flowed through E-selectin and anti-PSMA coated microtube. After establishing rolling and selective fluorescence in prostate cancer cell line, we used prostate cancer patient's blood. CTCs in prostate cancer patient's blood showed rolling behavior on E-selectin coated microtube. Further, these CTCs were PSMA-positive after incubation with fluorescently conjugated mAbJ591 and easily identified during the flow through the microtube. Conclusion: Our data shows that CTCs in prostate cancer patients exhibit rolling behavior, which may facilitate invasion and metastasis. Further, selective ex vivo labeling of CTCs enables rapid identification for subsequent characterization of their adhesion and invasive phenotype. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 296. doi:10.1158/1538-7445.AM2011-296

Robust rolling stock in rapid transit networks

This paper focuses on the railway rolling stock circulation problem in rapid transit networks, in which frequencies are high and distances are relatively short. Although the distances are not very large, service times are high due to the large number of intermediate stops required to allow proper passenger flow. The main complicating issue is the fact that the available capacity at depot stations is very low, and both capacity and rolling stock are shared between different train lines. This forces the introduction of empty train movements and rotation maneuvers, to ensure sufficient station capacity and rolling stock availability.However, these shunting operations may sometimes be difficult to perform and can easily malfunction, causing localized incidents that could propagate throughout the entire network due to cascading effects. This type of operation will be penalized with the goal of selectively avoiding them and ameliorating their high malfunction probabilities. Critic trains, defined as train services that come through stations that have a large number of passengers arriving at the platform during rush hours, are also introduced.We illustrate our model using computational experiments drawn from RENFE (the main Spanish operator of suburban passenger trains) in Madrid, Spain. The results of the model, achieved in approximately 1min, have been received positively by RENFE planners.

Rolling Stability Control Utilizing Rollover Index for In-wheel Motor Electric Vehicle

In this paper, a novel integrated stability program (ISP) based on robust rolling stability control (RSC) for in-wheel electric vehicle (EV) is proposed. Since EVs are driven by electric motors, they have the following four remarkable advantages: (1) motor torque generation is quick and accurate, (2) motor torque can be estimated precisely, (3) a motor can be attached to each wheel, and (4) a motor can output negative torque as a brake actuator. These advantages enable a high-performance three-dimensional vehicle motion control with a distributed in-wheel-motor system. Rolling stability is important for all classes of light-vehicles, especially, for EVs that have narrow tread and high center of gravity. In this study, RSC is designed using two-degree-of-freedom control (2-DOF), which achieves tracking capability to reference value and disturbance suppression. However, as the drivability of the vehicle will be changed significantly if only RSC is applied, vehicle rolling motion should be controlled depending on the rolling state. Therefore, variable weight-ISP and variable reference-ISP are proposed using rolling state information. For detecting rolling state, rollover index (RI) is introduced. The validity of the proposed methods is shown by the simulation and the experimental results.

Rolling Stability Control Based on Electronic Stability Program for In-wheel-motor Electric Vehicle

In this paper, a novel robust rolling stability control (RSC) based on electronic stability program (ESP) for electric vehicle (EV) is proposed. Since EVs are driven by electric motors, they have the following four remarkable advantages: (1) motor torque generation is quick and accurate; (2) motor torque can be estimated precisely; (3) a motor can be attached to each wheel; and (4) motor can output negative torque as a brake actuator. These advantages enable high performance three dimensional vehicle motion control with a distributed in-wheel-motor system. RSC is designed using two-degree-of-freedom control (2-DOF), which achieves tracking capability to reference value and disturbance suppression. Generally, RSC and YSC are incompatible. Therefore, ESP, which is composed of estimation system(S1) and integrated vehicle motion control system(S2) is proposed. A distribution ratio of RSC and YSC is defined based on rollover index (RI) which is calculated in S1 from rolling state information. The effectiveness of proposed methods are shown by simulation and experimental results.

Chemical Engineering of Mesenchymal Stem Cells to Induce a Cell Rolling Response

Covalently conjugated sialyl Lewis X (SLeX) on the mesenchymal stem cell (MSC) surface through a biotin-streptavidin bridge imparts leukocyte-like rolling characteristics without altering the cell phenotype and the multilineage differentiation potential. We demonstrate that the conjugation of SLeX on the MSC surface is stable, versatile, and induces a robust rolling response on P-selectin coated substrates. These results indicate the potential to increase the targeting efficiency of any cell type to specific tissue.

Directional-rolling method for strained SiGe/Si films and its application to fabrication of hollow needles

A method enabling stress-driven directional rolling of patterned SiGe/Si films released from selectively etched Si substrates, is presented. Selective orientation-dependent etching of sacrificial single-crystal Si substrates is shown to permit: i) robust rolling of SiGe/Si films, released from substrates, in directions along which the lateral etch rate of the substrates is maximal; and ii) suppression of detrimental rolling of the films on pattern edges where vertical walls bounded by {111} stopping planes self-form during the etching. Efficiency of the method is demonstrated with the example of controlled directional rolling of SiGe/Si films, lithographically defined on (110) Si substrates as long narrow strips, in free-standing precise-diameter microtubes–needles. A technique making it possible to obtain chips with tubes protruding over substrate edges is introduced, which incorporates through-etching of (110) Si substrates in KOH : H 2O solution, followed by subsequent cleaving of the substrates with SiGe/Si rolled tubes along cleavage planes.

Sialyl Lewis X-Mediated, PSGL-1-Independent RollingAdhesion on P-selectin

Selectin-mediated cell adhesion is an essential component of the inflammatory response. In an attempt to unambiguously identify molecular features of ligands that are necessary to support rolling adhesion on P-selectin, we have used a reconstituted (“cell-free”) system in which ligand-coated beads are perfused over soluble P-selectin surfaces. We find that beads coated with the saccharides sialyl Lewis X (sLe X), sialyl Lewis a (sLe a), and sulfated Lewis X (HSO 3Le X) support rolling adhesion on P-selectin surfaces. Although it has been suggested that glycosylation and sulfation of P-selectin glycoprotein ligand-1 (PSGL-1) is required for high-affinity binding and rolling on P-selectin, our findings indicate that sulfation of N-terminal tyrosine residues is not required for binding or rolling. However, beads coated with a tyrosine-sulfated, sLe X-modified, PSGL-1-Fc chimera support slower rolling on P-selectin than beads coated with sLe X alone, suggesting that sulfation improves rolling adhesion by modulating binding to P-selectin. In addition, we find it is not necessary that P-selectin carbohydrate ligands be multivalent for robust rolling to occur. Our results demonstrate that beads coated with monovalent sLe X, exhibiting a more sparse distribution of carbohydrate than a similar amount of the multivalent form, are sufficient to yield rolling adhesion. The relative abilities of various ligands to support rolling on P-selectin are quantitatively examined among themselves and in comparison to human neutrophils. Using stop-time distributions, rolling dynamics at video frame rate resolution, and the average and variance of the rolling velocity, we find that P-selectin ligands display the following quantitative trend, in order of decreasing ability to support rolling adhesion on P-selectin: PSGL-1-Fc > sLe a ∼ sLe X > HSO 3Le X.