Privacy in resource allocation problems

Collaborative decision-making processes help parties optimize their operations, remain competitive in their markets, and improve their performances with environmental issues. However, those parties also want to keep their data private to meet their obligations regarding various regulations and not to disclose their strategic information to the competitors. In this thesis, we study collaborative capacity allocation among multiple parties and present that (near) optimal allocations can be realized while considering the parties' privacy concerns.We first attempt to solve the multi-party resource sharing problem by constructing a single model that is available to all parties. We propose an equivalent data-private model that meets the parties' data privacy requirements while ensuring optimal solutions for each party. We show that when the proposed model is solved, each party can only get its own optimal decisions and cannot observe others' solutions. We support our findings with a simulation study.The third and fourth chapters of this thesis focus on the problem from a different perspective in which we use a reformulation that can be used to distribute the problem among the involved parties. This decomposition lets us eliminate almost all the information-sharing requirements. In Chapter 3, together with the reformulated model, we benefit from a secure multi-party computation protocol that allows parties to disguise their shared information while attaining optimal allocation decisions. We conduct a simulation study on a planning problem and show our proposed algorithm in practice. We use the decomposition approach in Chapter 4 with a different privacy notion. We employ differential privacy as our privacy definition and design a differentially private algorithm for solving the multi-party resource sharing problem. Differential privacy brings in formal data privacy guarantees at the cost of deviating slightly from optimality. We provide bounds on this deviation and discuss the consequences of these theoretical results. We show the proposed algorithm on a planning problem and present insights about its efficiency.<br/

Masking primal and dual models for data privacy in network revenue management

We study a collaborative revenue management problem where multiple decentralized parties agree to share some of their capacities. This collaboration is performed by constructing a large mathematical programming model that is available to all parties. The parties then use the solution of this model in their own capacity control systems. In this setting, however, the major concern for the parties is the privacy of their input data, along with their individual optimal solutions. We first reformulate a general linear programming model that can be used for a wide range of network revenue management problems. Then we address the data privacy concern of the reformulated model and propose an approach based on solving an equivalent data-private model constructed with input masking via random transformations. Our main result shows that, after solving the data-private model, each party can safely access only its own optimal capacity allocation decisions. We also discuss the security of the transformed problem in the considered multi-party setting. Simulation experiments are conducted to support our results and evaluate the computational efficiency of the proposed data-private model. Our work provides an analytical approach and insights on how to manage shared resources in a network problem while ensuring data privacy. Constructing and solving a collaborative network problem requires information exchange between parties that may not be possible in practice. Including data privacy in decentralized collaborative network revenue management problems with capacity sharing is new to the literature and relevant to practice

Endocervical polyps in high risk human papillomavirus infections

Objectives: Human papillomavirus (HPV) positive patients with and without endocervical polyps is compared with respect to HPV genotypes and presence of pre-invasive diseases. To our knowledge, this is the first and largest report in the literature examining the endocervical polyps in HPV positive cases. Material and methods: Clinicopathological data for the first one million screening patients (n = 1 060 992) from around the entire country during 2015 and 2016 were targeted for this research. Colposcopy, colposcopic surgical diagnostic procedures and final pathology results of 3499 patients with high-risk (HR) HPV-positive were obtained from reference colposcopy centers. Patients with endocervical polyps (n = 243 [6.9 %]) were accepted as experimental arm while patients without any endocervical polyp (n = 3256 [93.1%]) were regarded as the control group. Age, HPV genotype, Pap smear abnormality, and final pathological results were compared between two groups using Student’s t-test and cross-tabulation chi-square test. Results: The incidence of endocervical polyp was found to be 6.9 % in HR HPV-positive women. The most common HPV genotypes observed in both groups were HPV 16 or 18. Abnormal cytology reports (≥ ASC-US) were not significantly different between both groups. However, with respect to final pathological diagnosis, patients with endocervical polyp had significantly lower numbers of pre-invasive diseases (31.3% vs 44.2%; p &lt; 0.10). Conclusions: Endocervical polyps may be more common in patients with HR HPV infections. HPV 18 is observed significantly more, in the HR HPV positive endocervical polyp group. Patients with endocervical polyps do not have increased risk for preinvasive cervical diseases

Yüksek performans yakın/kısa dalga boyu kızılötesi megapiksel InGaAs odak düzlem dizinlerinin fabrikasyonunun geliştirilmesi ve yeni dizayn önerileri

In0.53Ga0.47As is the most appropriate material system for Short Wavelength Infrared (SWIR) detection at ~1.7 μm cutoff wavelength with its relatively lower cost and high performance. Ultra-low dark current (~ nA/cm2) has been recently demonstrated in InGaAs photodetectors with planar type process by eliminating surface leakage current. Here, a fabrication procedure for planar InGaAs photodetectors with unique pixel isolation methods has been developed and ~10 nA/cm2 dark current density levels were obtained from 15 and 25 μm pitch megapixel and large format Focal Plane Arrays (FPA) where almost 100% internal quantum efficiency was measured. Mesa type InGaAs photodetectors were also fabricated to be able to make a comparison between two process types. Developed photodetectors were able to sense both Near Infrared (NIR) and visible region of electromagnetic spectrum by removing InP substrate and ~99.5% pixel operability was achieved in FPAs after flip-chip bonding and substrate removal. Furthermore, a novel all InGaAs nBn photodetector design was also proposed numerically in order to reduce surface leakage current particularly in mesa type photodetectors. Simulations were executed in Sentaurus TCAD numerical tool where InGaAs material properties were optimized with the data provided in literature, and also with the experimental results obtained in InGaAs photodetector fabrication. Shockley-Read-Hall (SRH), Auger, radiative and surface currents were modeled and more than 20 times improvement in dark current has been shown to be achievable by utilizing nBn photodetector compared to conventional p-n InP/InGaAs photodetectors without degrading responsivity.M.S. - Master of Scienc

Teslim süresi etkisi altında çok konumlu ürün çeşidi en iyilemesi

Cataloged from PDF version of article.Thesis (M.S.): Bilkent University, Department of Industrial Engineering, İhsan Doğramacı Bilkent University, 2018.Includes bibliographical references (leaves 61-69).We have investigated the assortment planning problem for an online retailer that has multiple ful llment centers to maximize its expected pro t. Each ful llment center is responsible for a customer segment which has its own customer pro le, and each customer segment's demand is governed by a multinomial logit model (MNL), resulting in a mixtures of MNL (MMNL) model. A demand is primarily met by the responsible ful llment center, if available. However, if a product is not available in the responsible ful llment center, the demand can be met by ful llment centers in other regions at an additional shipping cost paid by the rm. The shipping cost depends on the distance between regions, so it varies by origin and destination. We assume that each customer has access to the entire assortment in all ful llment centers. To solve this problem, di erent from the literature, we have formulated the problem using a conic quadratic mixed integer programming approach. Later, the conic formulation is strengthened with valid inequalities. We have provided a numerical study to test the performance of our formulation against other formulations. Results show that our conic formulation together with the valid inequalities delivers outstanding performance compared to others in the literature. We also validated our approach using data from a local chain that operates in Northwestern part of Turkey.by Utku Karaca.M.S

Hybrid Integration of Broadband Silicon Modulators and InGaAs Photodetectors

We present on-chip integration of silicon modulators and InGaAs photodetectors via flip-chip bonding. Modulators fabricated on silicon-on-insulator (SOI) and photodetectors grown on InP wafers were fabricated independently and the hybrid integration was achieved by the deposition of indium (In) bumps on both sides

Al/Sb Free InGaAs Unipolar Barrier Infrared Detectors

It is numerically shown that Al/Sb free InGaAs unipolar barrier detectors with superior performance compared to the conventional heterojunction detectors can be constructed. Compositionally graded layers provide the transition between the high bandgap InGaAs barrier and the lattice matched InGaAs absorber layers. In addition, the delta doped layers remove the valence band offset in order to block only majority carriers and allow unimpeded flow of minority carriers. More than one order of magnitude reduction in the dark current is observed while photocurrent remains nearly unchanged. Proposed barrier structure utilized in this study is not limited to short wave infrared (SWIR) and can be applied to a variety of materials operating in various infrared regions

All InGaAs Unipolar Barrier Infrared Detectors

Unipolar barrier detector design is a challenge for InGaAs material system since there is a lack of proper barrier material that blocks majority carriers and allows unimpeded flow of minority carriers. As a bandgap engineering solution, Al/Sb free all InGaAs unipolar barrier detectors have been numerically designed here by compositionally graded and delta-doped layers. Comparison with conventional heterojunction detectors results that there is at least one order of magnitude improvement in dark current without compromising any photoresponse performance. Detailed simulation characterization studies including sensitivity analysis with respect to the design parameters verify the robustness of the proposed structure

Band-to-Band Transition Based On-Chip Optical Modulator

Photonic crystal slab phase shifter based, area efficient and low operation voltage optical modulator design is presented. Required index difference between the Mach-Zehnder interferometer arms of the proposed modulator comes from the photonic band transition