Differentially Private Linear Optimization for Multi-Party Resource Sharing

This study examines a resource-sharing problem involving multiple parties that agree to use a set of capacities together. We start with modeling the whole problem as a mathematical program, where all parties are required to exchange information to obtain the optimal objective function value. This information bears private data from each party in terms of coefficients used in the mathematical program. Moreover, the parties also consider the individual optimal solutions as private. In this setting, the concern for the parties is the privacy of their data and their optimal allocations. We propose a two-step approach to meet the privacy requirements of the parties. In the first step, we obtain a reformulated model that is amenable to a decomposition scheme. Although this scheme eliminates almost all data exchanges, it does not provide a formal privacy guarantee. In the second step, we provide this guarantee with a locally differentially private algorithm, which does not need a trusted aggregator, at the expense of deviating slightly from the optimality. We provide bounds on this deviation and discuss the consequences of these theoretical results. We also propose a novel modification to increase the efficiency of the algorithm in terms of reducing the theoretical optimality gap. The study ends with a numerical experiment on a planning problem that demonstrates an application of the proposed approach. As we work with a general linear optimization model, our analysis and discussion can be used in different application areas including production planning, logistics, and revenue management

The ‘radical combined approach’ in cerebral arteriovenous malformation treatment: Technical note

AVMs are vessel anomalies where a connection between arterial and venous systems is present and the capillary bed is absent between the two. AVMs tend to present with seizures, headaches, focal neurological deficits and hemorrhage. Hemorrhage is the most common form of presentation. AVM's have a 2–4% annual risk of hemorrhage. Certain studies report this rate as 1%. The greatest discussion in AVM treatment is whether to use interventional treatment or monitor with medical treatment. There are 3 modalities that can be used for interventional treatment; microsurgical resection, endovascular embolization and stereotactic radiosurgery. Combined techniques are also possible. We defined the ‘radical combined approach’ combines embolization and microsurgery. We will discuss this procedure in this article as we believe it has several advantages

The involvement of centralized and distributed processes in sub-second time interval adaptation: an ERP investigation of apparent motion

Accumulating evidence suggests that the timing of brief stationary sounds affects visual motion perception. Recent studies have shown that auditory time interval can alter apparent motion perception not only through concurrent stimulation but also through brief adaptation. The adaptation after-effects for auditory time intervals was found to be similar to those for visual time intervals, suggesting the involvement of a central timing mechanism. To understand the nature of cortical processes underlying such after-effects, we adapted observers to different time intervals using either brief sounds or visual flashes and examined the evoked activity to the subsequently presented visual apparent motion. Both auditory and visual time interval adaptation led to significant changes in the ERPs elicited by the apparent motion. However, the changes induced by each modality were in the opposite direction. Also, they mainly occurred in different time windows and clustered over distinct scalp sites. The effects of auditory time interval adaptation were centred over parietal and parieto-central electrodes while the visual adaptation effects were mostly over occipital and parieto-occipital regions. Moreover, the changes were much more salient when sounds were used during the adaptation phase. Taken together, our findings within the context of visual motion point to auditory dominance in the temporal domain and highlight the distinct nature of the sensory processes involved in auditory and visual time interval adaptation.Turkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) (113K547)Publisher's Versio

Stability and pricing of queueing models

textA queueing system can be described as a population of customers which from time to time utilize the resources of a service provider in order to obtain service. Since it is a difficult task to analyze a stochastic model, often macroscopic models are utilized to gain insight on high level properties of the real model. The contributions of this thesis can be summarized in three parts. In the first and second parts of the thesis, we investigate the stability of the fluid models and the relationship between the fluid and the stochastic models. In the third part, we use queueing theory to tackle a revenue management problem of a monopolistic firm. First, we investigate a fundamental property of fluid solutions in multiclass fluid networks. In [14] it is shown that if a fluid network has the finite decomposition property and is not weakly stable, then any queueing network associated with the fluid network is not rate stable. In particular, we show that the finite decomposition property holds for certain classes of two-pass fluid networks. Next, we try to characterize the intersection of stability regions of the static buffer priority service disciplines for a certain type of three station networks. The results expand the known stability region by utilizing fluid trajectories and a new methodology is proposed to identify if a service rate vector is in the aforementioned stability region or not. Finally, we investigate the pricing problem of a firm which dominates the market. In our model, there is a single server with exponential service times and arrivals follow a compound Poisson process where the number of customers in a group is a random variable. We let the firm to adjust the price as the length of the queue changes. A major difference between this research and the previous literature is that we allow group arrivals and the firm may only accept or reject customer groups as a whole. We identify the optimal acceptance policy that maximizes the revenue and show that this policy is also socially optimal.Operations Research and Industrial Engineerin

Treatment with ultrasound guided percutaneous cholecystostomy in acute cholecystitis: 10-year a single-center experience

Purpose: Evaluating the technical success, clinical outcomes and safety of ultrasound-guided percutaneous cholecystostomy (PC) in patients with acute cholecystitis. Material and Methods: Medical records of patients diagnosed as acute cholecystitis and treated with PC from year 2000 to 2011 were retrospectively examined. ASA scores, leukocyte counts, gall stone presence, bile cultures, additional interventions, interval surgery, procedure-related complications and mortality were reviewed. Results: PC catheters were placed in 127 patients (72 male, 55 female) aged from 31 to 100 years. Technical success of the procedure was 100%. Clinical success was obtained in 86% of the patients. No procedure related mortality or early major complications were observed. Minor complication rate was 7% (9/127) and late major complication rate was 3% (4/127). Thirty day in-hospital mortality rate was 8% (10/127). Six patients died after interval cholecystectomy and 4 patients died before the operation. PC served as a definitive treatment in 74% (17/23) of the patients with acalculous cholecystitis. Fifty-eight percent (31/53) of the patients with acute calculous cholecystitis were treated only with percutaneous cholecystostomy and only 10% (3/31) had recurrent cholecystitis in follow up. Conclusion: PC can be preferred over primary cholecystectomy in acute cholecystitis patients. The procedure has high technical success, high clinical response and low complication rates. It can also serve as a definitive treatment option in patients with high surgical risk