Network Interdiction under Uncertainty

We consider variants to one of the most common network interdiction formulations: the shortest path interdiction problem. This problem involves leader and a follower playing a zero-sum game over a directed network. The leader interdicts a set of arcs, and arc costs increase each time they are interdicted. The follower observes the leader\u27s actions and selects a shortest path in response. The leader\u27s optimal interdiction strategy maximizes the follower\u27s minimum-cost path. Our first variant allows the follower to improve the network after the interdiction by lowering the costs of some arcs, and the leader is uncertain regarding the follower\u27s cardinality budget restricting the arc improvements. We propose a multiobjective approach for this problem, with each objective corresponding to a different possible improvement budget value. To this end, we also present the modified augmented weighted Tchebychev norm, which can be used to generate a complete efficient set of solutions to a discrete multi-objective optimization problem, and which tends to scale better than competing methods as the number of objectives grows. In our second variant, the leader selects a policy of randomized interdiction actions, and the follower uses the probability of where interdictions are deployed on the network to select a path having the minimum expected cost. We show that this continuous non-convex problem becomes strongly NP-hard when the cost functions are convex or when they are concave. After formally describing each variant, we present various algorithms for solving them, and we examine the efficacy of all our algorithms on test beds of randomly generated instances

Probabilistic Estimation of Rare Random Collisions in 3-Space

A study of risk assessment for artillery fire randomly colliding with fixed wing aircraft is presented. The research lends itself to a general study of collision models. Current models of object collisions fall under one of three categories: the historical model, the gas particle model, and the satellite model. These three vary in data requirements and mathematical representation of the impact event. The gas particle model is selected for its flexibility and robust estimation. However, current mathematical development in the literature does not include certain spatial and dynamic components necessary for a general encounter (collision) model. These are derived in this work. For the specific application at hand Quadratic formulas estimate the ballistic arc of artillery shells to provide instantaneous relative velocities. An extended Poisson spatial process is applied over the relative volume within a collision radius during the conflict time window to provide a probability of collision. Implementation of the model for military use has been achieved via an Excel spreadsheet providing scenario study capability in real time. Results for several scenarios are presented which have been validated by experts. These results support current policy of strict deconfliction

Hydrogen bond network topology in liquid water and methanol: a graph theory approach

Networks are increasingly recognized as important building blocks of various systems in nature and society. Water is known to possess an extended hydrogen bond network, in which the individual bonds are broken in the sub-picosecond range and still the network structure remains intact. We investigated and compared the topological properties of liquid water and methanol at various temperatures using concepts derived within the framework of graph and network theory (neighbour number and cycle size distribution, the distribution of local cyclic and local bonding coefficients, Laplacian spectra of the network, inverse participation ratio distribution of the eigenvalues and average localization distribution of a node) and compared them to small world and Erdős–Rényi random networks. Various characteristic properties (e.g. the local cyclic and bonding coefficients) of the network in liquid water could be reproduced by small world and/or Erdős–Rényi networks, but the ring size distribution of water is unique and none of the studied graph models could describe it. Using the inverse participation ratio of the Laplacian eigenvectors we characterized the network inhomogeneities found in water and showed that similar phenomena can be observed in Erdős–Rényi and small world graphs. We demonstrated that the topological properties of the hydrogen bond network found in liquid water systematically change with the temperature and that increasing temperature leads to a broader ring size distribution. We applied the studied topological indices to the network of water molecules with four hydrogen bonds, and showed that at low temperature (250 K) these molecules form a percolated or nearly-percolated network, while at ambient or high temperatures only small clusters of four-hydrogen bonded water molecules exist

Evaluating Cu Printed Interconnects “Sinterconnects” versus Wire Bonds for Switching Converters

This paper demonstrates the feasibility of the printed copper (Cu) paste interconnects for applications in power semiconductor modules and switching converters. Copper sinter paste interconnects denoted as “Sinterconnects” have been recently introduced as an alternative to wire-bonding technology for power electronic device packaging. However, the electrical domain properties of these novel interconnects have not yet been investigated in detail. To address this research opportunity, this paper evaluates the performance of two different types of Sinterconnects applied to multi-chip, insulated gate bipolar transistor (IGBT) power modules. First, parasitic or stray inductances of these Sinterconnected systems are calculated analytically and by using three-dimensional finite element (FE) analysis. In addition to that, resistivity (ρ) of those has been analysed and compared with conventional wire bond technology. Finally, the performances of the Sinterconnects in power device assemblies are experimentally investigated. Two Sinterconnect structures (i.e., printed Cu paste and Cu clip attach) as well as a state-of-the-art wire-bonded IGBT module, have been integrated into a switching DC-DC converter and benchmarked. Experimental measurements show how converters with Sinterconnects enable efficient power conversion

Evaluating Cu Printed Interconnects “Sinterconnects” versus Wire Bonds for Switching Converters

This paper demonstrates the feasibility of the printed copper (Cu) paste interconnects for applications in power semiconductor modules and switching converters. Copper sinter paste interconnects denoted as “Sinterconnects” have been recently introduced as an alternative to wire-bonding technology for power electronic device packaging. However, the electrical domain properties of these novel interconnects have not yet been investigated in detail. To address this research opportunity, this paper evaluates the performance of two different types of Sinterconnects applied to multi-chip, insulated gate bipolar transistor (IGBT) power modules. First, parasitic or stray inductances of these Sinterconnected systems are calculated analytically and by using three-dimensional finite element (FE) analysis. In addition to that, resistivity (ρ) of those has been analysed and compared with conventional wire bond technology. Finally, the performances of the Sinterconnects in power device assemblies are experimentally investigated. Two Sinterconnect structures (i.e., printed Cu paste and Cu clip attach) as well as a state-of-the-art wire-bonded IGBT module, have been integrated into a switching DC-DC converter and benchmarked. Experimental measurements show how converters with Sinterconnects enable efficient power conversion

Sinterconnects: All-Copper Top-Side Interconnects Based on Copper Sinter Paste for Power Module Packaging

Copper sinter paste has been recently established as a robust die-attach material for high -power electronic packaging. This paper proposes and studies the implementation of copper sinter paste materials to create top-side interconnects, which can substitute wire bonds in power packages. Here, copper sinter paste was exploited as a fully printed interconnect and, additionally, as a copper clip-attach. The electrical and thermal performances of the copper-sinter paste interconnections (“sinterconnects”) were compared to a system with wire bonds. The results indicate comparable characteristics of the sinterconnect structures to the wire-bonded ones. Moreover, the performance of copper sinterconnects in a power module was further quantified at higher load currents via finite element analysis. It was identified that the full-area thermal and electrical contact facilitated by the planar sinterconnects can reduce ohmic losses and enhance the thermal management of the power packages

Preoperative estimates of glomerular filtration rate as predictors of outcome after surgery: a systematic review and meta-analysis

Kidney dysfunction is a strong determinant of prognosis in many settings.A systematic review and meta-analysis was undertaken to explore the relationship between estimated glomerular filtration rate (eGFR) and adverse outcomes after surgery. Cohort studies reporting the relationship between eGFR and major outcomes, including all-cause mortality, major adverse cardiovascular events, and acute kidney injury after cardiac or noncardiac surgery, were included.Forty-six studies were included, of which 44 focused exclusively on cardiac and vascular surgery. Within 30 days of surgery, eGFR less than 60 m l · min · 1.73 m(-2) was associated with a threefold increased risk of death (multivariable adjusted relative risk [RR] 2.98; 95% confidence interval [CI] 1.95-4.96) and acute kidney injury (adjusted RR 3.13; 95% CI 2.22-4.41). An eGFR less than 60 ml · min · 1.73(-2) m was associated with an increased risk of all-cause mortality (adjusted RR 1.61; 95% CI 1.38-1.87) and major adverse cardiovascular events (adjusted RR 1.49; 95% CI 1.32-1.67) during long-term follow-up. There was a nonlinear association between eGFR and the risk of early mortality such that, compared with patients having an eGFR more than 90 ml · min · 1.73m(-2) the pooled RR for death at 30 days in those with an eGFR between 30 and 60 ml · min · 1.73 m(-2) was 1.62 (95% CI 1.43-1.80), rising to 2.85 (95% CI 2.49-3.27) in patients with an eGFR less than 30 ml · min · 1.73 m(-2) and 3.75 (95% CI 3.44-4.08) in those with an eGFR less than 15 ml · min · 1.73 m(-2).: There is a powerful relationship between eGFR, and both short- and long-term prognosis after, predominantly cardiac and vascular, surgery