Total absolute deviation of job completion times on uniform and unrelated machines

Unlike other measures of variation of job completion times considered in scheduling literature, the measure of minimizing total absolute deviation of job completiontimes (TADC) was shown to have a polynomial time solution on a single machine. It was recently shown to remain polynomially solvable when position-dependent job processing times are assumed. In this paper we further extend these results, and show that minimizing TADC remains polynomial when position-dependent processing times are assumed (i) on uniform and unrelated machines and (ii) for a bicriteria objective consisting of a linear combination of total job completion times and TADC. These extensions are shown to be valid also for the measure of total absolute differences of job waiting times (TADW).     

Battery Powered Regenerative SCR Drive

In many applications where battery powered drives are used, high efficiency, low cost, and low weight are of prime importance. Such applications include electric vehicles, fork-lift trucks, submarines, etc.     

Outdoor measurements and temperature comparisons of seven monitoring stations: Preliminary studies in Curitiba,Brazil

Urbanization brings several changes to the natural environment. First, vegetation is supressed and natural scenery is modified, in order to accommodate manmade buildings and streets. Consequences bring a direct effect on fauna and flora and, due to a modified environment, with heat fluxes having a different pattern from that of the original site, on climatic features, such as on air temperature and humidity, radiative and convective heat exchanges. Thus, one of the factors that can contribute directly to the creation of urban climate is land use. The present study investigates how land use influences local temperatures in Curitiba, Brazil (25°31′S, 917 m elevation). For that purpose, seven different locations of the city were analyzed during a 1-month period by monitoring air temperature and humidity. Also, land use patterns around each location were quantified, according to five different categories established for that purpose: water area, built area, free area, paved area and green area. The monitoring of climatic data occurred in winter (June/July) of 2002. Comparisons were made regarding averages of the minimum, average and maximum temperatures for each location, qualitatively and quantitatively. As a final step of this study, formulas were developed expressing the local temperatures as a function of air temperatures, solar radiation and the wind speed of the meteorological station, which was used as reference station.     

Localized irradiation effects on tunnel diode transitions in multi-junction concentrator solar cells

Multi-junction concentrator solar cells incorporate tunnel diodes that undergo a transition from high-conductance tunneling to low-conductance thermal diffusion behavior, typically at threshold current densities of the order of 10²-10³ mA/mm². We present experimental evidence of a prominent heretofore unrecognized dependence of threshold current density on the degree of localized irradiation, in different solar cell architectures. We also show that solar cells with non-uniform metallization can exhibit an additional spatial dependence to the tunnel diode threshold current density. These previously undiscovered phenomena - which should be observable in all non-uniformly irradiated photovoltaic tunnel diodes - are interpreted as being derived from the lateral spreading of excess majority carriers (analogous to current spreading in light-emitting diodes (LEDs)). The consequences for concentrator photovoltaics are addressed.     

Scheduling on a proportionate flowshop to minimise total late work

We study a scheduling problem to minimise total late work, i.e. each job is penalised according to the duration of its parts scheduled after its due-date. The machine setting is an m-machine proportionate flow shop. Two versions of the problem are studied: (i) the case that total late work refers to the last operation of the job (i.e. the operation performed on the last machine of the flow shop); (ii) the case that total late work refers to all the operations (on all machines). Both versions are known to be NP-hard. We prove a crucial property of an optimal schedule, and consequently introduce efficient pseudo-polynomial dynamic programming algorithms for the two versions. The dynamic programming algorithms are tested numerically and proved to perform well on large size instances.     

Heuristics for scheduling problems with an unavailability constraint and position-dependent processing times

We study a single machine scheduling problem, where the machine is unavailable for processing for a pre-specified time period. We assume that job processing times are position-dependent. The objective functions considered are minimum makespan, minimum total completion time and minimum number of tardy jobs. All these problems are known to be NP-hard even without position-dependent processing times. For all three cases we introduce simple heuristics which are based on solving the classical assignment problem. Lower bounds, worst case analysis and asymptotic optimality are discussed. All heuristics are shown numerically to perform extremely well.     

Conjugates of Unsaturated Fatty Acids with Propylene Glycol as Potentially Less-Irritant Skin Penetration Enhancers

Fatty acids (FA) are well known as efficient enhancers for transdermal delivery of drugs; however, their frequent dermal toxicity limits their regular use. In order to utilize the fatty acid as a safe enhancer devoid of its irritant effect, we have synthesized and evaluated a series of fatty acids conjugated to propylene glycol (FA-PG). Each one of the conjugates was prepared as a mono- or di- acyl ester derivative. The effects of the synthetic enhancers on the porcine skin permeability were evaluated in a diffusion cell system using lidocaine as the model drug. In addition, in vivo examinations in rabbits were preformed for skin toxicological evaluation. The results indicate that among the FA-PG conjugates, oleic acid (C18:1_n–9)-PG, linoleic acid (C18:2_n–6)-PG and α-linolenic acid (C18:3_n–3)-PG, mono- or di-esters, enhance the penetration of lidocaine relatively to the vehicle (without enhancer). The conjugates of oleic acid (C18:1_n–9) and linoleic acid (C18:2_n–6) with PG have demonstrated a similar enhancing effect as the corresponding free fatty acids. Interestingly, although the mono- or the di- conjugates of α-linolenic acid (C18:3_n–3) with PG enhanced the lidocaine flux as the other two fatty acid conjugates, they resulted in a reduced permeability as compared to the action of their free acid. In addition, the mono-conjugates of α-linolenic acid (C18:3_n–3) with PG exhibited elevated skin irritation in rabbits (relative to the fatty acid alone) compared to the significantly reduced irritation of oleate-PG and linoeate-PG mono-conjugates. In conclusion, except saturated FA-PG and α-linolenic acid (C18:3_n–3)—PG mono-conjugates, unsaturated fatty acids (e.g., oleic and linoleic acids) after conjugation to PG may be safe and effective enhancers for delivering topical drugs.     

Robust random number generation for peer-to-peer systems

We consider the problem of designing an efficient and robust distributed random number generator for peer-to-peer systems that is easy to implement and works even if all communication channels are public. A robust random number generator is crucial for avoiding adversarial join–leave attacks on peer-to-peer overlay networks. We show that our new generator together with a light-weight rule recently proposed in [B. Awerbuch, C. Scheideler, Towards a scalable and robust DHT, in: Proc. of the 18th ACM Symp. on Parallel Algorithms and Architectures, SPAA, 2006. See also http://www14.in.tum.de/personen/scheideler] for keeping peers well distributed can keep various structured overlay networks in a robust state even under a constant fraction of adversarial peers.     

Traffic Engineering of Management Flows by Link Augmentations on Confluent Trees

Service providers rely on the management systems housed in their Network Operations Centers (NOCs) to remotely operate, monitor and provision their data networks. Lately there has been a tremendous increase in management traffic due to the growing complexity and size of the data networks and the services provisioned on them. Traffic engineering for management flows is essential for the smooth functioning of these networks to avoid congestion, which can result in loss of critical data such as billing records, network alarms, etc. As is the case with most intra-domain routing protocols, the management flows in many of these networks are routed on shortest paths connecting the NOC with the service provider’s POPs (points of presence). This collection of paths thus forms a “confluent” tree rooted at the gateway router connected to the NOC. The links close to the gateway router may form a bottleneck in this tree resulting in congestion. Typically this congestion is alleviated by adding layer two tunnels (virtual links) that offload the traffic from some links of this tree by routing it directly to the gateway router. The traffic engineering problem is then to minimize the number of virtual links needed for alleviating congestion. In this paper we formulate a traffic engineering problem motivated by the above mentioned applications. We show that the general versions of this problem are hard to solve. However, for some simpler cases in which the underlying network is a tree, we design efficient algorithms. In particular, we design fully polynomial-time approximate schemes (FPTAS) for different variants of this problem on trees. We use these algorithms as the basis for designing efficient heuristics for alleviating congestion in general (non-tree) service provider network topologies.     

Towards a Scalable and Robust DHT

The problem of scalable and robust distributed data storage has recently attracted a lot of attention. A common approach in the area of peer-to-peer systems has been to use a distributed hash table (or DHT). DHTs are based on the concept of virtual space. Peers and data items are mapped to points in that space, and local-control rules are used to decide, based on these virtual locations, how to interconnect the peers and how to map the data to the peers. DHTs are known to be highly scalable and easy to update as peers enter and leave the system. It is relatively easy to extend the DHT concept so that a constant fraction of faulty peers can be handled without any problems, but handling adversarial peers is very challenging. The biggest threats appear to be join-leave attacks (i.e., adaptive join-leave behavior by the adversarial peers) and attacks on the data management level (i.e., adaptive insert and lookup attacks by the adversarial peers) against which no provably robust mechanisms are known so far. Join-leave attacks, for example, may be used to isolate honest peers in the system, and attacks on the data management level may be used to create a high load-imbalance, seriously degrading the correctness and scalability of the system. We show, on a high level, that both of these threats can be handled in a scalable manner, even if a constant fraction of the peers in the system is adversarial, demonstrating that open systems for scalable distributed data storage that are robust against even massive adversarial behavior are feasible. Supported by NSF-ANIR 0240551, NSF-CCF 0515080, and NSF-CCR 0311795.