9 research outputs found
Sojourn times in a processor sharing queue with multiple vacations
No full textWe study an M/G/1 processor sharing queue with multiple vacations. The server only takes a vacation when the system has become empty. If he finds the system still empty upon return, he takes another vacation, and so on. Successive vacations are identically distributed, with a general distribution. When the service requirements are exponentially distributed we determine the sojourn time distribution of an arbitrary customer. We also show how the same approach can be used to determine the sojourn time distribution in an M/M/1-PS queue of a polling model, under the following constraints: the service discipline at that queue is exhaustive service, the service discipline at each of the other queues satisfies a so-called branching property, and the arrival processes at the various queues are independent Poisson processes. For a general service requirement distribution we investigate both the vacation queue and the polling model, restricting ourselves to the mean sojourn time
Dramaturgy Like a Ghost? A Few Remarks on the Dramaturg and Words in Dance
No full textThe author begins with an observation by André Lepecki concerning the fear of working with a dramaturg. Recalling several concepts that define the role of the dramaturg in dance (Lepecki, Liesbeth Wildschut, Bojana Cvejić, Bojana Bauer, Maaike Bleeker), the author juxtaposes various interpretations of the scope and forms of collaboration with the dramaturg. She reaches the conclusion that although in a professional context, dramaturgy is most of the time associated with project-based work and the freelance economy, the fusion of various functions and the growing significance of the word in dance productions make the presence of the dramaturg increasingly desireable. At the same time, she notes that the viewer’s contribution can also be considered as belonging to dramaturgy, and that the understanding of dramaturgy goes beyond the dichotomy of word/text, and movement/stage interpretation
Stability of size-based scheduling disciplines in resource-sharing networks
No full textSize-based scheduling strategies such as Shortest Remaining Processing Time first (SRPT) and Least Attained Service first (LAS) provide popular mechanisms for improving the overall delay performance by favoring smaller service requests over larger ones. The performance gains from these disciplines have been thoroughly investigated for single-server systems, and have also been experimentally demonstrated in web servers for example. In the present paper we explore the fundamental stability properties of size-based scheduling strategies in multi-resource systems, such as bandwidth-sharing networks, where users require service from several shared resources simultaneously. In particular, we establish the exact stability conditions for the SRPT and LAS disciplines in various limiting regimes. The results indicate that size-based scheduling strategies may fail to use the available resources efficiently, and in fact cause instability effects, even at arbitrarily low traffic loads, and will therefore not yield optimal delay performance. The qualitative findings confirm the tendency for users with long routes and large service requirements to experience severe performance degradation
Monotonicity properties for multi-class queueing systems
No full textWe study multi-dimensional stochastic processes that arise in queueing models used in the performance evaluation of wired and wireless networks. The evolution of the stochastic process is determined by the scheduling policy used in the associated queueing network. For general arrival and service processes, we give sufficient conditions in order to compare sample-path wise the workload and the number of users under different policies. This allows us to evaluate the performance of the system under various policies in terms of stability, the mean overall delay and the mean holding cost. We apply the general framework to linear networks, where users of one class require service from several shared resources simultaneously. For the important family of weighted a-fair policies, stability results are derived and monotonicity of the mean holding cost with respect to the fairness parameter a and the relative weights is established. In order to broaden the comparison
results, we investigate a heavy-traffic regime and perform numerical experiments. In
addition, we study a single-server queue with two user classes, and show that under
Discriminatory Processor Sharing (DPS) or Generalized Processor Sharing (GPS) the mean overall sojourn time is monotone with respect to the ratio of the weights. Finally we extend the framework to obtain comparison results that cover the singleserver queue with an arbitrary number of classes as well
Delay optimization in bandwidth-sharing networks
No full textBandwidth-sharing networks as considered by Massoulie & Roberts provide a natural modeling framework for describing the dynamic flow-level interaction among elastic data transfers. Although valuable stability results have been obtained, crucial performance metrics such as flow-level delays and throughputs in these models have remained intractable in all but a few special cases. In particular, it is not well understood to what extent flow-level delays and throughputs achieved by standard bandwidth-sharing mechanisms such as alpha-fair strategies leave potential room for improvement. In order to gain a better understanding of the latter issue, we set out to determine the scheduling policies that minimize the mean delay in some simple linear bandwidth-sharing networks. We compare the performance of the optimal policy with that of various alpha-fair strategies so as to assess the efficacy of the latter and gauge the potential room for improvement. The results indicate that the optimal policy achieves only modest improvements, even when the value of a is simply fixed, provided it is not too small
Repercussion of megakaryocyte-specific Gata1 Loss on megakaryopoiesis and the hematopoietic precursor compartment
No full textDuring hematopoiesis, transcriptional programs are essential for the commitment and differentiation of progenitors into the different blood lineages. GATA1 is a transcription factor expressed in several hematopoietic lineages and essential for proper erythropoiesis and megakaryopoiesis. Megakaryocyte-specific genes, such as GP1BA, are known to be directly regulated by GATA1. Mutations in GATA1 can lead to dyserythropoietic anemia and pseudo gray-platelet syndrome. Selective loss of Gata1 expression in adult mice results in macrothrombocytopenia with platelet dysfunction, characterized by an excess of immature megakaryocytes. To specifically analyze the impact of Gata1 loss in mature committed megakaryocytes, we generated Gata1-Lox|Pf4-Cre mice (Gata1cKOMK). Consistent with previous findings, Gata1cKOMK mice are macrothrombocytopenic with platelet dysfunction. Supporting this notion we demonstrate that Gata1 regulates directly the transcription of Syk, a tyrosine kinase that functions downstream of Clec2 and GPVI receptors in megakaryocytes and platelets. Furthermore, we show that Gata1cKOMK mice display an additional aberrant megakaryocyte differentiation stage. Interestingly, these mice present a misbalance of the multipotent progenitor compartment and the erythroid lineage, which translates into compensatory stress erythropoiesis and splenomegaly. Despite the severe thrombocytopenia, Gata1cKOMK mice display a mild reduction of TPO plasma levels, and Gata1cK-OMK megakaryocytes show a mild increase in Pf4 mRNA levels; such a misbalance might be behind the general hematopoietic defects observed, affecting locally normal TPO and Pf4 levels at hematopoietic stem cell niches. © 2016 Meinders et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited
Management of gestational hypertension and mild pre-eclampsia at term
No full textZwangerschapshypertensie en preëclampsie compliceren 6-8% van alle zwangerschappen en vormen in Nederland de belangrijkste oorzaak van maternale morbiditeit en mortaliteit. Vaak is het ziektebeeld mild en treedt op in de aterme periode. Soms ontstaan ernstige complicaties, zoals eclampsie, abruptio placentae of het HELLP-syndroom. Wereldwijd was er tot nu toe geen overeenstemming over het beste beleid bij deze aandoeningen. Inleiding van de baring zou enerzijds maternale complicaties kunnen reduceren, maar anderzijds de kans op een sectio caesarea kunnen verhogen.
Het eerste deel van dit proefschrift beschrijft een multicentrisch gerandomiseerde klinische studie (HYPITAT trial (HYpertension and Pre-eclampsia Intervention Trial At Term)), uitgevoerd binnen het Verloskundige Consortium (www.studies-obsgyn.nl/hypitat). Wij onderzochten wat beter is voor vrouwen met een milde zwangerschapsgerelateerde aterme hypertensie: inleiden of afwachten, met het oog op klinische effectiviteit, maternale kwaliteit van leven en kosten. Deze studie werd uitgevoerd in 38 Nederlandse ziekenhuizen. In totaal werden 756 vrouwen gerandomiseerd voor inleiden (n=377) of afwachten (n=379). De resultaten wijzen uit dat inleiden de kans op maternale complicaties verkleint (31% versus 44%; RR 0.71; p<0.001), inleiden een tendens laat zien van minder sectio caesarea (14% versus 19%; RR0.75; p=0.085) en inleiden gemiddeld 831 euro per patiënt goedkoper is dan afwachten. De neonatale uitkomst en de maternale kwaliteit van leven is gelijk tussen beide strategieën. Daarom adviseren wij een inleiding van de baring bij vrouwen met een zwangerschapshypertensie of milde preëclampsie na 37 weken zwangerschap.
Het tweede gedeelte van dit proefschrift beschrijft welke factoren een slechte maternale uitkomst bij vrouwen met een aterme zwangerschapshypertensie of milde preëclampsie kunnen voorspellen. Voor deze studies hebben wij gebruik van de HYPITAT database.
Expanding the clinical spectrum of biglycan-related Meester-Loeys syndrome
No full textPathogenic loss-of-function variants in BGN, an X-linked gene encoding biglycan, are associated with Meester-Loeys syndrome (MRLS), a thoracic aortic aneurysm/dissection syndrome. Since the initial publication of five probands in 2017, we have considerably expanded our MRLS cohort to a total of 18 probands (16 males and 2 females). Segregation analyses identified 36 additional BGN variant-harboring family members (9 males and 27 females). The identified BGN variants were shown to lead to loss-of-function by cDNA and Western Blot analyses of skin fibroblasts or were strongly predicted to lead to loss-of-function based on the nature of the variant. No (likely) pathogenic missense variants without additional (predicted) splice effects were identified. Interestingly, a male proband with a deletion spanning the coding sequence of BGN and the 5' untranslated region of the downstream gene (ATP2B3) presented with a more severe skeletal phenotype. This may possibly be explained by expressional activation of the downstream ATPase ATP2B3 (normally repressed in skin fibroblasts) driven by the remnant BGN promotor. This study highlights that aneurysms and dissections in MRLS extend beyond the thoracic aorta, affecting the entire arterial tree, and cardiovascular symptoms may coincide with non-specific connective tissue features. Furthermore, the clinical presentation is more severe and penetrant in males compared to females. Extensive analysis at RNA, cDNA, and/or protein level is recommended to prove a loss-of-function effect before determining the pathogenicity of identified BGN missense and non-canonical splice variants. In conclusion, distinct mechanisms may underlie the wide phenotypic spectrum of MRLS patients carrying loss-of-function variants in BGN.</p
