High Temperature Conductance of the Single Electron Transistor

The linear conductance of the single electron transistor is determined in the high temperature limit. Electron tunneling is treated nonperturbatively by means of a path integral formulation and the conductance is obtained from Kubo's formula. The theoretical predictions are valid for arbitrary conductance and found to explain recent experimental data.Comment: 4 pages, 2 figure

Integrated crew scheduling in passenger transport industries under consideration of employee preferences

Due to the binary nature of the problem and the often large problem size, Crew Scheduling has always been a challenge in passenger transportation industries. Different strategies were developed to overcome the challenges; one of the most common approaches is separation of the problem into smaller problems. E.g. Airline Crew Scheduling traditionally has been separated into two planning steps: Crew Pairing, in which flights are combined into multiple-day-trips called "pairing", and Crew Assignment, in which the previously created pairings are assigned to crew members. A similar separation is used in some applications of crew scheduling for railways and other transportation industries. This separation ensures a solution in reasonable time but it sacrifices global optimality with regards to its objective cost as well as the chance to consider the employee preferences right from the start and not only in the second step - if at all. In times of staff shortage and high negotiation power of certain employee groups, consideration of employee's schedule preferences should increase employee satisfaction and thus limit employee turnover. We present an integrated crew scheduling model with the objective to minimize cost under consideration of employee preferences. Employee preferences for different schedule characteristics are estimated from a conjoint analysis and the tradeoff between employee satisfaction and cost is analyzed. Second, we provide an overview of current state of the art solution approaches specifically for integrated crew scheduling models, and suggest a column generation method to solve our problem . Third, we analyze and discuss the benefits from integration with regards to solution optimality, as well as the challenges with regard to solution times; furthermore, we provide an overview of suitable problem sizes and structures for using integration

Sustainable airline planning and scheduling

With sustainability becoming one of the core topics in politics, public discussion and, consequently, in various industries, the airline industry, as one of the major greenhouse gas emitters in the transport sector, has also come under scrutiny. Despite many advanced models for airline planning and scheduling, most models do not explicitly consider sustainability issues. Our paper extends existing research by including the five most strategic stages of the airline planning and scheduling process along with explicitly emphasizing sustainability considerations. We use the resulting mixed-integer quadratically constrained problem in a computational study to show that airlines in our setting can reduce the number of flights (and thereby the level of emissions) without the need to make a substantial sacrifice in profitability. Due to the complexity of the problem, the results also indicate the need for a solver specialized in efficiently solving mixed-integer convex problems

Direct Transmittance Estimation in Heterogeneous Participating Media Using Approximated Taylor Expansions

Evaluating the transmittance between two points along a ray is a key component in solving the light transport through heterogeneous participating media and entails computing an intractable exponential of the integrated medium's extinction coefficient. While algorithms for estimating this transmittance exist, there is a lack of theoretical knowledge about their behaviour, which also prevent new theoretically sound algorithms from being developed. For this purpose, we introduce a new class of unbiased transmittance estimators based on random sampling or truncation of a Taylor expansion of the exponential function. In contrast to classical tracking algorithms, these estimators are non-analogous to the physical light transport process and directly sample the underlying extinction function without performing incremental advancement. We present several versions of the new class of estimators, based on either importance sampling or Russian roulette to provide finite unbiased estimators of the infinite Taylor series expansion. We also show that the well known ratio tracking algorithm can be seen as a special case of the new class of estimators. Lastly, we conduct performance evaluations on both the central processing unit (CPU) and the graphics processing unit (GPU), and the results demonstrate that the new algorithms outperform traditional algorithms for heterogeneous mediums.Funding: Knut and Alice Wallenberg Foundation (KAW) [2013-0076]; SeRC (Swedish e-Science Research Center); Wallenberg AI, Autonomous Systems and Software Program (WASP); Swedish Foundation for Strategic Research (SSF) via the project ASSEMBLE [RIT15-0012]; ELLIIT environment for strategic research in Sweden</p

Optical See-Through Head Mounted Display : Direct Linear Transformation Calibration Robustness in the Presence of User Alignment Noise

The correct spatial registration between virtual and real objects in optical see-through augmented reality implies accurate estimates of the user’s eyepoint relative to the location and orientation of the display surface. A common approach is to estimate the display parameters through a calibration procedure involving a subjective alignment exercise. Human postural sway and targeting precision contribute to imprecise alignments, which in turn adversely affect the display parameter estimation resulting in registration errors between virtual and real objects. The technique commonly used has its origin incomputer vision, and calibrates stationary cameras using hundreds of correspondence points collected instantaneously in one video frame where precision is limited only by pixel quantization and image blur. Subsequently the input noise level is several order of magnitudes greater when a human operator manually collects correspondence points one by one. This paper investigates the effect of human alignment noise on view parameter estimation in an optical see-through head mounted display to determine how well astandard camera calibration method performs at greater noise levels than documented in computer vision literature. Through Monte-Carlo simulations we show that it is particularly difficult to estimate the user’s eyepoint in depth, but that a greater distribution of correspondence points in depth help mitigate the effects of human alignment noise