Cell loss dynamics and output process in a finite-buffer discrete-time queue with correlated arrivals

This paper analyzes the performance of an ATM switching node considering cell arrival correlation. An ATM switching node is modeled as a discrete-time finite-buffer queue. Cell arrivals are assumed to follow a semi-Markovian process, where the number of cell arrivals in a lot depends on the states of the underlying (M-state) Markov chain in the current and previous slots. This paper presents analyses for various characteristics of the cell loss, as well as the distribution function of the cell output process from an ATM switching node. Obtained results include the cell loss probability, the consecutive loss probability, the distribution of loss period lengths, the joint distribution of successive cell interdeparture times, and the distribution of busy and idle periods. Through the numerical results, it is shown that both the correlation and the variation of cell arrivals significantly affect the cell loss and the output process characteristics

Liking to be in America: Puerto Rico’s Quest for Difference in the United States

The interaction between wind turbines in simple wind farm layouts is investigated with the purpose of observing the influence of wake loss phenomenon on the energy production of downwind turbines. Following an intensive exploration stage about wind farm aerodynamics and wake modeling subjects, several tests cases are designed to represent various wind farm configurations, consisting of different number of wind turbines. These cases are simulated by using DNV GL WindFarmer software which provides the opportunity of performing simulations with two different wake modeling techniques, namely Modified PARK and Eddy Viscosity. Various terrain and ambient turbulence intensity conditions are considered during the test cases. Also three different turbine types having different hub heights, rotor diameters and power-thrust coefficients are used in order to observe the effect of turbine characteristics on wake formation. Besides WindFarmer, WAsP and MATLAB tools are used in some simulation stages in order to generate input data such as wind and terrain conditions or farm layout configurations; and to process the data obtained in the end of these test cases. Simulations which are executed in the presence of a predominant wind direction from a narrow direction bin indicate that, even though there exists no significant interaction between the turbines placed in abreast configurations, successive turbine rows affect each other strongly due to the existence of the wake region of upwind turbines. It is observed that downwind spacing between turbine rows required to recover wake deficit up to a certain level changes depending on terrain and ambient turbulence intensity conditions together with turbine characteristics. For instance increasing surface roughness length (or ambient turbulence intensity) of a given site by keeping all the other parameters constant can provide up to 20% (or 30%) decrease in the required downstream distance to reduce wake loss to 5% level in a simple tandem layout consisting of two wind turbines. Further test cases are executed with various numbers of wind turbines in different configurations to observe the effect of partial, full and multiple wake regions on total farm efficiency. The results obtained from these cases are used in order to have a comparison between several farm layouts and evaluate their advantages and drawbacks

Dimension reduction for linear separation with curvilinear distances

Any high dimensional data in its original raw form may contain obviously classifiable clusters which are difficult to identify given the high-dimension representation. In reducing the dimensions it may be possible to perform a simple classification technique to extract this cluster information whilst retaining the overall topology of the data set. The supervised method presented here takes a high dimension data set consisting of multiple clusters and employs curvilinear distance as a relation between points, projecting in a lower dimension according to this relationship. This representation allows for linear separation of the non-separable high dimensional cluster data and the classification to a cluster of any successive unseen data point extracted from the same higher dimension

Age-related efficiency loss of household refrigeration appliances: Development of an approach to measure the degradation of insulation properties

Despite the omnipresence of household refrigeration appliances, there is still a lack of knowledge about their age-related efficiency loss over time. Past studies provide basic evidence for increasing electricity consumption of cooling appliances with ageing but fail to investigate the associated technical wear. Concentrating on the degradation of the thermal insulation, we first determined the ageing process of sealed samples of polyurethane rigid foam by investigating changes in cell gas composition and thermal conductivity over time. Simultaneously, the main challenge was to develop an approach that investigates the age-related efficiency loss of the insulation without its destruction. This testing procedure is referred to as the Bonn method. The non-destructive Bonn method was applied to varying refrigerator models in a series of successive experiments to evaluate the insulation degradation over time. Subsequently, the physical relationship between the test value of the Bonn method and the heat transfer through the multi-layered compartment walls of domestic refrigeration appliances was established, ultimately characterising the degrading insulation in terms of increasing heat transfer. Our results give substantiated evidence that the efficiency loss of cooling appliances is greatly influenced by insulation degradation over time. The ageing of sealed samples of polyurethane rigid foam indicates a large initial increase of thermal conductivity by 15% within the first year, corresponding to a change in cell gas composition. These results are in line with those of the Bonn method, emphasising an increasing heat flow through the multi-layered compartment walls of domestic refrigerators with ageing. Therewith, the present study is of significance to a wide range of stakeholders and forms the basis for future research.BMWi, 03ET1544, ALGE: Alterungsmechanismen von Haushaltskältegeräte

Di-jet asymmetry and wave turbulence

We describe a new physical picture for the fragmentation of an energetic jet propagating through a dense QCD medium, which emerges from perturbative QCD and has the potential to explain the di-jet asymmetry observed in Pb-Pb collisions at the LHC. The central ingredient in this picture is the phenomenon of wave turbulence, which provides a very efficient mechanism for the transport of energy towards the medium, via many soft particles which propagate at large angles with respect to the jet axis.Comment: 6 pages, 3 figures. Invited plenary talk at the 6th International Conference on Hard and Electromagnetic Probes of High-Energy Nuclear Collisions (Hard Probes 2013), Stellenbosch, South Africa, Nov. 4-8, 201

Maximizing Energy Efficiency in Multiple Access Channels by Exploiting Packet Dropping and Transmitter Buffering

Quality of service (QoS) for a network is characterized in terms of various parameters specifying packet delay and loss tolerance requirements for the application. The unpredictable nature of the wireless channel demands for application of certain mechanisms to meet the QoS requirements. Traditionally, medium access control (MAC) and network layers perform these tasks. However, these mechanisms do not take (fading) channel conditions into account. In this paper, we investigate the problem using cross layer techniques where information flow and joint optimization of higher and physical layer is permitted. We propose a scheduling scheme to optimize the energy consumption of a multiuser multi-access system such that QoS constraints in terms of packet loss are fulfilled while the system is able to maximize the advantages emerging from multiuser diversity. Specifically, this work focuses on modeling and analyzing the effects of packet buffering capabilities of the transmitter on the system energy for a packet loss tolerant application. We discuss low complexity schemes which show comparable performance to the proposed scheme. The numerical evaluation reveals useful insights about the coupling effects of different QoS parameters on the system energy consumption and validates our analytical results.Comment: in IEEE trans. Wireless communications, 201