Towards Autonomic Service Provisioning Systems

This paper discusses our experience in building SPIRE, an autonomic system for service provision. The architecture consists of a set of hosted Web Services subject to QoS constraints, and a certain number of servers used to run session-based traffic. Customers pay for having their jobs run, but require in turn certain quality guarantees: there are different SLAs specifying charges for running jobs and penalties for failing to meet promised performance metrics. The system is driven by an utility function, aiming at optimizing the average earned revenue per unit time. Demand and performance statistics are collected, while traffic parameters are estimated in order to make dynamic decisions concerning server allocation and admission control. Different utility functions are introduced and a number of experiments aiming at testing their performance are discussed. Results show that revenues can be dramatically improved by imposing suitable conditions for accepting incoming traffic; the proposed system performs well under different traffic settings, and it successfully adapts to changes in the operating environment.Comment: 11 pages, 9 Figures, http://www.wipo.int/pctdb/en/wo.jsp?WO=201002636

Fire Spalling Prevention via Polypropylene Fibres: A Meso-and Macroscale Approach

A deep understanding of concrete at the mesoscale level is essential for a better comprehension of several concrete phenomena, such as creep, damage, and spalling. The latter one specifically corresponds to the separation of pieces of concrete from the surface of a structural element when it is exposed to high and rapidly rising temperatures; for this phenomenon a mesoscopic approach is fundamental since aggregates performance and their thermal properties play a crucial role. To reduce the risk of spalling of a concrete material under fire condition, the inclusion of a low dosage of polypropylene fibres in the mix design of concrete is largely recognized. PP fibres in fact evaporate above certain temperatures, thus increasing the porosity and reducing the internal pressure in the material by an increase of the voids connectivity in the cement paste. In this work, the contribution of polypropylene fibres on concrete behaviour, if subjected to elevated thermal ranges, has been numerically investigated thanks to a coupled hygrothermomechanical finite element formulation. Numerical analyses at the macro- and mesoscale levels have been performed

Wege der Mikroevolution und Artbildung bei Bienen (Apoidea, Hymenoptera): Populationsgenetische und empirische Aspekte

Bees are haplodiploid organisms: haploid males develop from unfertilized eggs, diploid females from fertilized eggs. Under haplodiploidy, deleterious mutations are effectively purged by purifying selection on haploid males. Therefore, genetic load and inbreeding depression are low in bees, which allow them to exist in very small populations, and facilitate the colonization of new areas and habitats by single fertilized females. Exceptions caused by distinct modes of genetic sex-determination are discussed. Owing to the purifying selection and the higher rate of genetic drift in small populations, the genetic variation of bees is only one third of the variation of diploid insects. As a consequence, bees have less genetic adaptability to environmental change, for which they compensate by exhibiting higher learning ability and greater behavioural plasticity than many other insect taxa. Most bee species need specific microclimatic conditions to perform the proper flight behaviour to provision their nests with larval food. Energy flow and metabolic rates in flight muscles of bees are among the highest ever measured in animal tissue. The temperature dependence of the enzymes which drive the flight muscle metabolism is therefore of critical importance for the functioning of the system. Mutations which change the thermal tolerance range of one of those enzymes might lead to changing habitat requirements, and parapatric or allochronous population divergence. The fact that bees choose their nesting site very carefully already hints at the critical role, temperature and humidity ranges play for bee development. Experiments show a remarkable dependence of learning ability and behaviour on developmental temperatures. Evolutionary and ecological aspects of social behaviour, social and cleptoparasitism, and flower choice in bees are discussed. Possible paths of population divergence and speciation are pointed out. The reproduction rate of bees is closer to the rates of primates than to that of other insects. Compared to other insects, bees evolve only slowly

Observational study on risk factors determining residual dizziness after successful benign paroxysmal positional vertigo treatment: The role of subclinical BPPV

After successful treatment for benign paroxysmal positional vertigo, many patients may complain of residual dizziness. Possible explanations may be the persistence of otolith into canal insufficient to provoke noticeable nystagmus, utricular dysfunction and undiagnosed coexisting vestibular disorder. We conducted a prospective observational case-control study, focusing on the role of risk factors in determining residual dizziness after BPPV treatment. In the present study, 148 patients were recruited and residual dizziness was documented in the 57.5% of the cohort. Among patients with residual dizziness 36 had subclinical BPPV and after retreatment, although nystagmus was not clinically evident, there was resolution of dizziness. We conclude that residual otoliths may play a role in determining post-maneuver residual dizziness that is often linked to subclinical BPPV; this conclusion is also supported by the high prevalence of BPPV recurrence in patients with residual dizziness, as confirmed by our analysis. The main cause appears to be linked with dispersed otolith in semicircular canals

Revenue maximization problems in commercial data centers

PhD ThesisAs IT systems are becoming more important everyday, one of the main concerns is that users may face major problems and eventually incur major costs if computing systems do not meet the expected performance requirements: customers expect reliability and performance guarantees, while underperforming systems loose revenues. Even with the adoption of data centers as the hub of IT organizations and provider of business efficiencies the problems are not over because it is extremely difficult for service providers to meet the promised performance guarantees in the face of unpredictable demand. One possible approach is the adoption of Service Level Agreements (SLAs), contracts that specify a level of performance that must be met and compensations in case of failure. In this thesis I will address some of the performance problems arising when IT companies sell the service of running ‘jobs’ subject to Quality of Service (QoS) constraints. In particular, the aim is to improve the efficiency of service provisioning systems by allowing them to adapt to changing demand conditions. First, I will define the problem in terms of an utility function to maximize. Two different models are analyzed, one for single jobs and the other useful to deal with session-based traffic. Then, I will introduce an autonomic model for service provision. The architecture consists of a set of hosted applications that share a certain number of servers. The system collects demand and performance statistics and estimates traffic parameters. These estimates are used by management policies which implement dynamic resource allocation and admission algorithms. Results from a number of experiments show that the performance of these heuristics is close to optimal.QoSP (Quality of Service Provisioning)British Teleco