Time decomposition of multi-period supply chain models

Many supply chain problems involve discrete decisions in a dynamic environment. The inventory routing problem is an example that combines the dynamic control of inventory at various facilities in a supply chain with the discrete routing decisions of a fleet of vehicles that moves product between the facilities. We study these problems modeled as mixed-integer programs and propose a time decomposition based on approximate inventory valuation. We generate the approximate value function with an algorithm that combines data fitting, discrete optimization and dynamic programming methodology. Our framework allows the user to specify a class of piecewise linear, concave functions from which the algorithm chooses the value function. The use of piecewise linear concave functions is motivated by intuition, theory and practice. Intuitively, concavity reflects the notion that inventory is marginally more valuable the closer one is to a stock-out. Theoretically, piecewise linear concave functions have certain structural properties that also hold for finite mixed-integer program value functions. (Whether the same properties hold in the infinite case is an open question, to our knowledge.) Practically, piecewise linear concave functions are easily embedded in the objective function of a maximization mixed-integer or linear program, with only a few additional auxiliary continuous variables. We evaluate the solutions generated by our value functions in a case study using maritime inventory routing instances inspired by the petrochemical industry. The thesis also includes two other contributions. First, we review various data fitting optimization models related to piecewise linear concave functions, and introduce new mixed-integer programming formulations for some cases. The formulations may be of independent interest, with applications in engineering, mixed-integer non-linear programming, and other areas. Second, we study a discounted, infinite-horizon version of the canonical single-item lot-sizing problem and characterize its value function, proving that it inherits all properties of interest from its finite counterpart. We then compare its optimal policies to our algorithm's solutions as a proof of concept.PhDCommittee Chair: George Nemhauser; Committee Member: Ahmet Keha; Committee Member: Martin Savelsbergh; Committee Member: Santanu Dey; Committee Member: Shabbir Ahme

Laboratory Studies of Structural Changes in Water-Poor and Water-Rich Ices: A Connection to Molecule Formation in Interstellar Ices

In this thesis I explore the results of ultra-high vacuum laboratory experiments performed at the Syracuse University Astrophysics and Surface Science Laboratory on structural changes of analogs of ice mantles that cover dust grains in dense clouds in the interstellar medium. We present the experimental and analytical techniques that we used and the motivations for the investigations in the context of molecular astrophysics. The primary contribution of this thesis is the meaningful insight into the long-standing question of how molecular diffusion and formation occur in or on ices in the interstellar medium under the conditions of low pressure and low temperature. Specifically, the focus is placed on an astrophysically relevant two layer ice geometry where the first layer is primarily composed of water molecules (water-rich), while the second layer’s dominant species is CO (water-poor). We consider each layer separately, first investigating the pore surface area of the water-rich layer and correspondingly its ability to store, trap, and facilitate the formation of complex organic molecules (COMs). We then consider the water poor layer where we report the discovery of a new phase transition in carbon monoxide ice at low temperature. We use CO2 as a probe within the CO ice matrix to demonstrate how this transition causes a diffusion and clustering of CO2 and consequentially suggests the potential mechanism for molecular formation in the ISM. This information is used to build a predictive model that is applied to an astrophysically relevant parameter space within which we are able to directly relate the time scale on which this transition occurs with that of stellar evolution

Depot differences in adipokine secretion from human omental and abdominal subcutaneous adipose tissues: potential role of adiporedoxin

Adiporedoxin (Adrx) is an adipose tissue specific protein discovered by the Pilch lab. It is a member of the peroxiredoxin family localized in the endoplasmic reticulum (ER). Previous studies showed that Adrx is involved in ER redox regulation and disulfide bond formation and secretion of adipokines. Further, Adrx mRNA expression and protein levels in human abdominal adipose tissue of young, healthy subjects, ranging in levels of obesity, correlated positively with adiponectin mRNA and protein, and negatively with adipose tissue inflammation (as indicated by phospho-Jun kinase). Since previous studies have shown depot differences in adipokine release, we wanted to determine the differences on adipose tissues depot in Adrx expression. However, there are no data on depot differences in Adrx expression and its association with changes in adipokine release in human adipose tissue. It is well known that omental adipose tissue is more inflamed, and reports on depot differences in adipokine release, especially adiponectin are inconsistent however leptin and IL-6 have being consistent. Adipokine release measured from adipose tissues reflects a more physiologic state and the characteristics of the subjects compared to cultured cells. Adiponectin is an insulin sensitizing protein, exclusively produced by mature adipocytes and highly secreted by adipose tissue. The native adiponectin exists as low molecular weight, middle-molecular weight and high molecular weight (HMW).The potency of adiponectin is linked to the HMW isoform. There are no previous reports on secretion of HMW adiponectin from human omental (Om) and abdominal subcutaneous (Abdsc) adipose tissues. In this study the goal is to determine the depot differences in Adrx expression and adipokine release in human Abdsc and Om adipose tissue in obese and morbidly obese subjects, mostly females and to determine the relationship between Adrx protein expression and adipokine release in Abdsc versus Om and circulating levels of adipokines, primarily total and HMW adiponectin. To clarify whether Adrx expression is implicated in the release and secretion of circulating adipokines. Adrx protein levels (assessed by Western blot) were ~1.4 fold higher in Abdsc than Om (p<0.05; paired t-test values). As expected, secretion per gram of tissue in 3hr incubation of total adiponectin (~ 25%) and leptin (~50%) was higher, and IL-6 secretion was lower (~30%) in Abdsc compared to Om. In western blot, total adiponectin is higher in Abdsc compared to Om. However, HMW adiponectin and % HMW are higher in Om. Adrx protein levels were positively correlated with total adiponectin and HMW release in Abdsc and only with HMW in Om. Adrx levels were negatively correlated with % HMW in Abdsc but not in Om. Adrx protein levels in Abdsc showed a negative trend with total adiponectin circulating levels (ng/ml measured by ELISA) and a positive trend in Om. However, total adiponectin by Western Blot showed a positive trend with Adrx levels in both Abdsc and Om. HMW adiponectin levels tended to be slightly positive with Adrx levels in Abdsc and Om. However, the percent of HMW adiponectin levels are not correlated with Adrx levels in either tissues. Since in Adrx KO mice found that presented lower total adiponectin in circulation, it was hypothesized that Adrx were positively correlated with circulating adiponectin, and wanted to study the correlation with serum adipokines. However, none of the correlations with Adrx and adipokines in serum were statistically significant. These data suggest that depot differences in Adrx expression may influence depot differences in adipokine secretion. The mechanism of higher HMW adiponectin secretion in Om with low Adrx levels needs further study

Comparison of the TaqMan and LightCycler systems in pharmacogenetic testing: evaluation of the CYP2C9*2/*3 polymorphisms.

Background: Pharmacogenetic testing for drugmetabolizing enzymes is not yet widely used in clinical practice. Methods: In an attempt to facilitate the application of this procedure, we have compared two real-time PCRbased methods, the TaqMan_ and the LightCycler_ for the pharmacogenetic evaluation of CYP2C9*2/*3 polymorphisms. Results and Conclusion: Both procedures are suitable for pharmacogenetic studies. The TaqMan procedure was less expensive in terms of cost per sample, but the TaqMan apparatus is more expensive than the LightCycler apparatus

The IID Prophet Inequality with Limited Flexibility

In online sales, sellers usually offer each potential buyer a posted price in a take-it-or-leave fashion. Buyers can sometimes see posted prices faced by other buyers, and changing the price frequently could be considered unfair. The literature on posted price mechanisms and prophet inequality problems has studied the two extremes of pricing policies, the fixed price policy and fully dynamic pricing. The former is suboptimal in revenue but is perceived as fairer than the latter. This work examines the middle situation, where there are at most $k$ distinct prices over the selling horizon. Using the framework of prophet inequalities with independent and identically distributed random variables, we propose a new prophet inequality for strategies that use at most $k$ thresholds. We present asymptotic results in $k$ and results for small values of $k$. For $k=2$ prices, we show an improvement of at least $11\%$ over the best fixed-price solution. Moreover, $k=5$ prices suffice to guarantee almost $99\%$ of the approximation factor obtained by a fully dynamic policy that uses an arbitrary number of prices. From a technical standpoint, we use an infinite-dimensional linear program in our analysis; this formulation could be of independent interest to other online selection problems