44 research outputs found
Fluid Models of Many-server Queues with Abandonment
We study many-server queues with abandonment in which customers have general
service and patience time distributions. The dynamics of the system are modeled
using measure- valued processes, to keep track of the residual service and
patience times of each customer. Deterministic fluid models are established to
provide first-order approximation for this model. The fluid model solution,
which is proved to uniquely exists, serves as the fluid limit of the
many-server queue, as the number of servers becomes large. Based on the fluid
model solution, first-order approximations for various performance quantities
are proposed
Stable mode-locked pulses from mid-infrared semiconductor lasers
We report the unequivocal demonstration of mid-infrared mode-locked pulses
from a semiconductor laser. The train of short pulses was generated by actively
modulating the current and hence the optical gain in a small section of an
edge-emitting quantum cascade laser (QCL). Pulses with pulse duration at
full-width-at-half-maximum of about 3 ps and energy of 0.5 pJ were
characterized using a second-order interferometric autocorrelation technique
based on a nonlinear quantum well infrared photodetector. The mode-locking
dynamics in the QCLs was modelled and simulated based on Maxwell-Bloch
equations in an open two-level system. We anticipate our results to be a
significant step toward a compact, electrically-pumped source generating
ultrashort light pulses in the mid-infrared and terahertz spectral ranges.Comment: 26 pages, 4 figure
Towards a self-deploying and gliding robot
Strategies for hybrid locomotion such as jumping and gliding are used in nature by many different animals for traveling over rough terrain. This combination of locomotion modes also allows small robots to overcome relatively large obstacles at a minimal energetic cost compared to wheeled or flying robots. In this chapter we describe the development of a novel palm sized robot of 10\,g that is able to autonomously deploy itself from ground or walls, open its wings, recover in midair and subsequently perform goal- directed gliding. In particular, we focus on the subsystems that will in the future be integrated such as a 1.5\,g microglider that can perform phototaxis; a 4.5\,g, bat-inspired, wing folding mechanism that can unfold in only 50\,ms; and a locust-inspired, 7\,g robot that can jump more than 27 times its own height. We also review the relevance of jumping and gliding for living and robotic systems and we highlight future directions for the realization of a fully integrated robot
New principles in quantum mechanics. Their application to spade exploration and relativity.
(Exposition-University Book)OPLADEN-RUG0