Management of Ascending Aorta Calcification in Coronary Artery Bypass Grafting

Neurological complications are one of the most common complications after coronary artery bypass grafting. With the development of off-pump coronary artery bypass grafting (OPCABG), the incidence of postoperative neurological complications caused by aortic intubation decreased significantly; however, the continuous suture of the great saphenous vein-aortic anastomosis in the coronary artery bypass grafting requires the operation of surgical clamp and perforation on the ascending aorta, which may lead to potential plaque detachment. Calcification of ascending aorta is an independent risk factor for cerebrovascular events after OPCABG. Therefore, it is crucial to explore and operate on the ascending aorta. There are three main methods of proximal anastomosis in OPCABG: (1) partial blocking of ascending aorta with side wall clamp for anastomosis; (2) application of proximal anastomosis auxiliary device (Enclose, Heartstring, etc.) for proximal anastomosis; and (3) original auxiliary device (urethra catheter-water sac) or no-clamp surgical techniques for proximal anastomosis

Sink Mobility Schemes in Wireless Sensor Networks for Network Lifetime Extension

Sensor nodes in Wireless Sensor Networks (WSNs) are normally battery-powered and remain stationary after deployment. When a sensor node runs out of energy it will no longer provide sensing and data processing. This can lead to a huge loss in the network due to the routing path re-allocation and failure of sensing and reporting events in the environment. Hence energy conservation has been receiving increased attention in WSN research works. The concept of mobile sink has been recently introduced for WSNs in order to improve the overall performance of WSNs as it shifts the burden of energy consumption from the sensor nodes to sink nodes, which are typically considered to have unconstrained energy supply and larger computational power. In this thesis we present two sink mobility schemes: Load Base sink Movement (LBM) and Residual Energy Aware Routing (REAR) to prolong network lifetime in a random event-driven scenario. LBM computes the optimal tentative sink node position considering both the geographical distance from sensors to sink and transmission load of sensors as well. REAR is a routing strategy that considers the residual energy of sensors when establishing routing paths. Experimental results confirm that the proposed schemes can significantly extend the network lifetime, compared to existing techniques

Extension rates across the northern Shanxi Grabens, China, from Quaternary geology, seismicity and geodesy

Discrepancies between geological, seismic and geodetic rates of strain can indicate that rates of crustal deformation, and hence seismic hazard, are varying through time. Previous studies in the northern Shanxi Grabens, at the northeastern corner of the Ordos Plateau in northern China, have found extension rates of anywhere between 0 and 6 mm a−1 at an azimuth of between 95° and 180°. In this paper we determine extension rates across the northern Shanxi Grabens from offset geomorphological features and a variety of Quaternary dating techniques (including new IRSL and Ar-Ar ages), a Kostrov summation using a 700 yr catalogue of historical earthquakes, and recent campaign GPS measurements. We observe good agreement between Quaternary, seismic and geodetic rates of strain, and we find that the northern Shanxi Grabens are extending at around 1–2 mm a−1 at an azimuth of ≈151°. The azimuth of extension is particularly well constrained and can be reliably inferred from catalogues of small earthquakes. We do not find evidence for any substantial variations in extension rate through time, though there is a notable seismic moment rate deficit since 1750. This deficit could indicate complex fault interactions across large regions, aseismic accommodation of deformation, or that we are quite late in the earthquake cycle with the potential for larger earthquakes in the relatively near future

Operations Management In The Presence Of Strategic Agents

My dissertation develops stylized models using analytical and numerical tools to understand innovative business models in the context of operations management. In the first chapter, using airlines as a backdrop, I study optimal overbooking policies with endogenous customer demand, when customers internalize their expected cost of being bumped. I first consider the traditional setting in which compensation for bumped passengers is fixed and booking limits are the airline\u27s only form of control. I provide sufficient conditions under which demand endogeneity leads to lower overbooking limits in this case. I then consider the broader problem of joint control of ticket price, bumping compensation, and booking limit. I show that price and bumping compensation can act as substitutes, which reduces the general problem to a more tractable one-dimensional search for optimal overbooking compensation and effectively allows the value of flying to be decoupled from the cost of being bumped. Finally, I extend our analysis to the case of auction-based compensation schemes and demonstrate that these generally outperform fixed compensation schemes. Numerical experiments that gauge magnitudes suggest that fixed-compensation policies that account for demand endogeneity can significantly outperform those that do not and that auction-based policies bring smaller but still significant additional gains. In the second chapter, I study the design of an emerging fundraising method for Blockchain-based startups, Initial Coin Offerings (ICOs), with a particular focus on capped ICOs. I propose a simple model of matching supply and demand with ICOs by companies involved in production of physical goods, aka inventory/asset ``tokenization\u27\u27. I examine how ICOs should be designed---including optimal token floating and pricing for both utility and equity tokens (aka, security token offerings, STOs)---in the presence of moral hazard, production risk and demand uncertainty, make predictions on ICO failure, and discuss the implications on firm operational decisions and profits. I show that in the current unregulated environment, ICOs lead to risk-shifting incentives (moral hazard), and hence to agency costs, underproduction, and loss of firm value. These inefficiencies, however, fade as product margin increases and market conditions improve, and are less severe under equity (rather than utility) token issuance. Importantly, the advantage of equity tokens stems from their inherent ability to better align incentives, and hence continues to hold even in unregulated environments. In the third chapter, I aim to understand how uncapped ICOs can fund service platforms under network effects. I propose an infinite horizon model that incorporates the interaction between the firm, speculators, service providers and customers. I find that both the platform\u27s service capacity and service providers\u27 profitability are enhanced by stronger network effect, larger customer base, and/or lower unit service cost. Moreover, I show that uncapped ICO is successful if and only if the cost of building the platform does not exceed the total service cost per period. I also extend the base model to account for firm\u27s moral hazard and show that under loose regulation, uncapped ICO can still be successful if the firm charges the right amount of service fee