Heavy traffic limit for a processor sharing queue with soft deadlines

This paper considers a GI/GI/1 processor sharing queue in which jobs have soft deadlines. At each point in time, the collection of residual service times and deadlines is modeled using a random counting measure on the right half-plane. The limit of this measure valued process is obtained under diffusion scaling and heavy traffic conditions and is characterized as a deterministic function of the limiting queue length process. As special cases, one obtains diffusion approximations for the lead time profile and the profile of times in queue. One also obtains a snapshot principle for sojourn times.Comment: Published at http://dx.doi.org/10.1214/105051607000000014 in the Annals of Applied Probability (http://www.imstat.org/aap/) by the Institute of Mathematical Statistics (http://www.imstat.org

Diffusion limits for shortest remaining processing time queues

We present a heavy traffic analysis for a single server queue with renewal arrivals and generally distributed i.i.d. service times, in which the server employs the Shortest Remaining Processing Time (SRPT) policy. Under typical heavy traffic assumptions, we prove a diffusion limit theorem for a measure-valued state descriptor, from which we conclude a similar theorem for the queue length process. These results allow us to make some observations on the queue length optimality of SRPT. In particular, they provide the sharpest illustration of the well-known tension between queue length optimality and quality of service for this policy.Comment: 19 pages; revised, fixed typos. To appear in Stochastic System

On helium-dominated stellar evolution: the mysterious role of the O(He)-type stars

About a quarter of all post-asymptotic giant branch (AGB) stars are hydrogen-deficient. Stellar evolutionary models explain the carbon-dominated H-deficient stars by a (very) late thermal pulse scenario where the hydrogen-rich envelope is mixed with the helium-rich intershell layer. Depending on the particular time at which the final flash occurs, the entire hydrogen envelope may be burned. In contrast, helium-dominated post-AGB stars and their evolution are yet not understood. A small group of very hot, helium-dominated stars is formed by O(He)-type stars. We performed a detailed spectral analysis of ultraviolet and optical spectra of four O(He) stars by means of state-of-the-art non-LTE model-atmosphere techniques. We determined effective temperatures, surface gravities, and the abundances of H, He, C, N, O, F, Ne, Si, P, S, Ar, and Fe. By deriving upper limits for the mass-loss rates of the O(He) stars, we found that they do not exhibit enhanced mass-loss. The comparison with evolutionary models shows that the status of the O(He) stars remains uncertain. Their abundances match predictions of a double helium white dwarf merger scenario, suggesting that they might be the progeny of the compact and of the luminous helium-rich sdO-type stars. The existence of planetary nebulae that do not show helium enrichment around every other O(He) star, precludes a merger origin for these stars. These stars must have formed in a different way, for instance via enhanced mass-loss during their post-AGB evolution or a merger within a common-envelope (CE) of a CO-WD and a red giant or AGB star. A helium-dominated stellar evolutionary sequence exists, that may be fed by different types of mergers or CE scenarios. It appears likely, that all these pass through the O(He) phase just before they become white dwarfs.Comment: 29 pages, 27 figures, accepted for publication in A&

Respiratory response to walking training in overweight men

The aim of the study was to follow up changes in physiological responses to incremental exercise after 4 weeks of moderate-intensity training in overweight men. Prior to the training, all subjects underwent 2 identical control tests (C1 and C2). Each test included three treadmill running exercises, starting at the treadmill speed of 4 km/h, and increased by 1 km/h at the end of each 4 min stage. The same protocol was repeated after 4 weeks of training (T1). The subjects’ body mass index was not changed after the training. Heart rate, oxygen uptake and blood pressure were significantly reduced in C2 as compared with C1 test. After 4 weeks of training the respiratory frequency (Rf), was lower than that in the C2 but a significant difference was noted only at the running speeds of 4 and 6kmhr-1 (P<0.04). Tidal volume (TV) increased after training in comparison with C2. A significant difference was found at the running speeds of 5 and 6 km/h (P<0.03 and P<0.04, respectively). Minute ventilation (VE) was not significantly different between the tests. The present study showed that in obese subjects 4 weeks of moderate uncontrolled walking training is advantageous for changes in the respiratory pattern. However, it is too short for the cardiovascular adaptation and body weight loss. Familiarization of the subjects with the experimental procedure diminished activation of the sympathetic nervous system and has a important role for the results interpretation

The associations of selected lifestyle patterns and lung cancer risk: An evidence-based update

Diagnosis of lung cancer (LC) has been fraught with difficulty and by the time of definitive diagnosis, most patients are in later stages of the disease. Epidemiological studies have demonstrated that lifestyle behaviors play an etiological role in LC risk; however data in the literature on this topic often appears inconclusive or require further study. Understanding of the mechanisms operating between lifestyle patterns and their impact on LC is important for the disease’s prevention and treatment. The purpose of this study was to review the current evidence on the role of diet, body mass index (BMI), physical activity, smoking, alcohol consumption, and sex hormone use in LC development based on meta-analyses, systematic reviews and previously published epidemiologic studies. Regarded as the foremost cause of LC, evidence from studies have indicated that tobacco smoking causes LC. Additionally, exposure to outdoor air pollution and/or occupational-related exposures increase LC risk. Further, frequent consumption of red meat, processed meat increases adenocarcinoma and squamous cell carcinoma. Inverse associations between the disease risk and BMI ≥25 kg/m2 , higher level of physical activity, and fruit and vegetable consumption with a high frequency were reported. Future studies are warranted to validate the association between histologic subtypes of LC and lifestyle patterns

The rapid evolution of the exciting star of the Stingray Nebula

SAO244567, the exciting star of the Stingray nebula, is rapidly evolving. Previous analyses suggested that it has heated up from an effective temperature of about 21kK in 1971 to over 50kK in the 1990s. Canonical post-asymptotic giant branch evolution suggests a relatively high mass while previous analyses indicate a low-mass star. Fitting line profiles from static and expanding non-LTE model atmospheres to the observed UV and optical spectra, taken during 1988-2013, allowed us to study the temporal change of effective temperature, surface gravity, mass-loss rate, and terminal wind velocity. In addition, we determined the chemical composition of the atmosphere. We find that the central star has steadily increased its effective temperature from 38kK in 1988 to a peak value of 60kK in 2002. During the same time, the star was contracting, as concluded from an increase in surface gravity from log g = 4.8 to 6.0 and a drop in luminosity. Simultaneously, the mass-loss rate declined from log (dM/dt/Msun/yr)=-9.0 to -11.6 and the terminal wind velocity increased from 1800km/s to 2800km/s. Since around 2002, the star stopped heating and has cooled down again to 55kK by 2006. It has a largely solar surface composition with the exception of slightly subsolar carbon, phosphorus, and sulfur. By comparison with stellar-evolution calculations, we confirm that SAO244567 must be a low-mass star (M < 0.55 Msun). However, the slow evolution of the respective stellar evolutionary models is in strong contrast to the observed fast evolution and the young planetary nebula with a kinematical age of only about 1000 years. We speculate that the star could be a late He-shell flash object. Alternatively, it could be the outcome of close-binary evolution. Then SAO244567 would be a low-mass (0.354 Msun) helium prewhite dwarf after the common-envelope phase, during which the planetary nebula was ejected.Comment: 16 pages, 13 figures, accepted for publication in A&

Magnetic properties of iron cluster/chromium matrix nanocomposites

A custom-designed apparatus was used for the fine-tuned co-deposition of preformed Fe clusters into antiferromagnetic Cr matrices. Three series of samples with precisely defined cluster sizes, with accuracy to a few atoms, and controlled concentrations were fabricated, followed by a complete characterization of structure and magnetic performance. Relevant magnetic characteristics, reflecting the ferromagnetic/antiferromagnetic coupling between Fe clusters and the Cr matrix, i.e., blocking temperature, coercivity field, and exchange bias were measured and their dependence on cluster size and cluster concentration in the matrix was analyzed. It is evident that the blocking temperatures are clearly affected by both the cluster size and their concentration in the Cr matrix. In contrast the coercivity shows hardly any dependence on size or inter-cluster distance. The exchange bias was found to be strongly sensitive to the cluster size but not to the inter-cluster distances. Therefore, it was concluded to be an effect that is purely localized at the interfaces