Dynamic bin packing of unit fractions items

LNCS v. 3580 entitled: Automata, Languages and Programming: 32nd International Colloquium, ICALP 2005, Lisbon, Portugal, July 11-15, 2005. ProceedingsThis paper studies the dynamic bin packing problem, in which items arrive and depart at arbitrary time. We want to pack a sequence of unit fractions items (i.e., items with sizes 1/ω for some integer w ≥ 1) into unit-size bins such that the maximum number of bins used over all time is minimized. Tight and almost-tight performance bounds are found for the family of any-fit algorithms, including first-fit, best-fit, and worst-fit. We show that the competitive ratio of best-fit and worst-fit is 3, which is tight, and the competitive ratio of first-fit lies between 2.45 and 2.4985. We also show that no on-line algorithm is better than 2.428-competitive. This result improves the lower bound of dynamic bin packing problem even for general items. © Springer-Verlag Berlin Heidelberg 2005.postprin

The impact of landscape sparsification on modelling and analysis of the invasion process

Climate change is a major threat to species, unless their populations are able to invade and colonise new landscapes of more suitable environment. In this paper, we propose a new model of the invasion process using a tool of landscape network sparsification to efficiently estimate a duration of the process. More specifically, we aim to simplify the structure of large landscapes using the concept of sparsification in order to substantially decrease the time required to compute a good estimate of the invasion time in these landscapes. For this purpose, two different simulation methods have been compared: full and R-local simulations, which are based on the concept of dense and sparse networks, respectively. These two methods are applied to real heterogeneous landscapes in the United Kingdom to compute the total estimated time to invade landscapes. We examine how the duration of the invasion process is affected by different factors, such as dispersal coefficient, landscape quality and landscape size. Extensive evaluations have been carried out, showing that the R-local method approximates the duration of the invasion process to high accuracy using a substantially reduced computation time

An efficient algorithm for optimizing whole genome alignment with noise

Motivation: This paper is concerned with algorithms for aligning two whole genomes so as to identify regions that possibly contain conserved genes. Motivated by existing heuristic-based software tools, we initiate the study of an optimization problem that attempts to uncover conserved genes with a global concern. Another interesting feature in our formulation is the tolerance of noise, which also complicates the optimization problem. A brute-force approach takes time exponential in the noise level. Results: We show how an insight into the optimization structure can lead to a drastic improvement in the time and space requirement [precisely, to O(k2n2) and O(k2n), respectively, where n is the size of the input and k is the noise level]. The reduced space requirement allows us to implement the new algorithm, called MaxMinCluster, on a PC. It is exciting to see that when tested with different real data sets, MaxMinCluster consistently uncovers a high percentage of conserved genes that have been published by GenBank. Its performance is indeed favorably compared to MUMmer (perhaps the most popular software tool for uncovering conserved genes in a whole-genome scale). © Oxford University Press 2004; all rights reserved.published_or_final_versio

Gestational Exposure to Antidepressants and Risk of Seizure in Offspring: A systematic review and meta-analysis

In spite of the preliminary evidence suggesting a link between gestational use of antidepressant and neurodevelopmental disorders in their offspring, the association between maternal use of antidepressants during pregnancy and the risk of neurologically-related adverse outcomes such as neonatal seizure is still unclear. This study summarises the available evidence on the association between gestational exposure to any antidepressants and the risk of seizure in neonates and children. We found that gestational antidepressant exposure is associated with a 2.3-fold higher incidence of seizure in offspring. Although a causal relationship cannot be confirmed in view of other potential confounders, our findings warrant future research on related clinical aspects, and possibly more careful monitoring of foetal neurodevelopment in pregnant women taking antidepressants during pregnancy. However, this does not suggest the abrupt withdrawal of antidepressants during pregnancy for all cases at risk of seizure in offspring as this must be balanced with the risk of negative consequences caused by untreated maternal depression, and decision-making should be individualised for each patient

Effect of Qigong on hypertension: a randomised controlled study

published_or_final_versio

Efficiency of data distribution in BitTorrent-like systems

BitTorrent (BT) in practice is a very efficient method to share data over a network of clients. In this paper we extend the recent work of Arthur and Panigrahy [1] on modelling the distribution of individual data blocks in BT systems, aiming at a better understanding of why BT can achieve a high degree of parallelism. In particular, we include in our study several new network features that BT systems are using, as well as different local heuristics for routing data blocks in each client. We conduct simulations to figure out to what extent the new network features and routing heuristics would affect the distribution efficiency. Our findings confirm that for the primitive network setting studied in [1], it does require Ω(blog n) phases for n clients to download 6 data blocks. More interestingly, our work suggests that for the more realistic network setting, the heuristics Random and Rarest Block First both allow n clients to download b blocks in b+O(log n) phases. We believe that the latter bound better reflects the high degree of parallelism of BT observed in reality. It is also worth-mentioning that b + log n is the smallest possible number of phases needed; it is interesting to see that some simple local routing heuristics have a performance so close to the optimal. © Springer-Verlag Berlin Heidelberg 2007.link_to_subscribed_fulltex

Dynamic bin packing of unit fractions items

This paper studies the dynamic bin packing problem, in which items arrive and depart at arbitrary times. We want to pack a sequence of unit fractions items (i.e., items with sizes 1 / w for some integer w ≥ 1) into unit-size bins, such that the maximum number of bins ever used over all time is minimized. Tight and almost-tight performance bounds are found for the family of any-fit algorithms, including first-fit, best-fit, and worst-fit. In particular, we show that the competitive ratio of best-fit and worst-fit is 3, which is tight, and the competitive ratio of first-fit lies between 2.45 and 2.4942. We also show that no on-line algorithm is better than 2.428-competitive. © 2008 Elsevier B.V. All rights reserved.link_to_subscribed_fulltex

Efficiency of data distribution in BitTorrent-like systems

BitTorrent (BT) in practice is a very efficient method to share data over a network of clients. In this paper we extend the recent work of Arthur and Panigrahy [1] on modelling the distribution of individual data blocks in BT systems, aiming at a better understanding of why BT can achieve a high degree of parallelism. In particular, we include in our study several new network features that BT systems are using, as well as different local heuristics for routing data blocks in each client. We conduct simulations to figure out to what extent the new network features and routing heuristics would affect the distribution efficiency. Our findings confirm that for the primitive network setting studied in [1], it does require Ω(blog n) phases for n clients to download 6 data blocks. More interestingly, our work suggests that for the more realistic network setting, the heuristics Random and Rarest Block First both allow n clients to download b blocks in b+O(log n) phases. We believe that the latter bound better reflects the high degree of parallelism of BT observed in reality. It is also worth-mentioning that b + log n is the smallest possible number of phases needed; it is interesting to see that some simple local routing heuristics have a performance so close to the optimal. © Springer-Verlag Berlin Heidelberg 2007.link_to_subscribed_fulltex