[Show abstract][Hide abstract] ABSTRACT: We study the stationary distribution of a system of two parallel M/M/∞ queues managed by the Join the Shortest Queue load balancing policy; one motivation for characterizing the efficiency of that policy is its potential application to resource allocation issues in cloud computing. For the general system with distinct service rates, we first show that the tail of each marginal queue length distribution exhibits a much faster decay than that of a Poisson distribution. Second, the determination of the joint stationary distribution is shown to reduce to the resolution of a pair of linear integral equations. In the case when service rates are identical (“symmetric case”), that pair of integral equations simplifies to a single Fredholm integral equation of the first kind whose solution is explicitly given in terms of Legendre polynomials; this enables us to entirely determine the stationary distribution of the system. We provide, in particular, asymptotics for the second moment and the tail of the queue length distribution.
Full-text · Article · Aug 2015 · Stochastic Models
[Show abstract][Hide abstract] ABSTRACT: In this paper, we investigate the impact of mobility on user performance in the context of dense LTE-A networks. To this end, we propose simple analytical models that capture mobility through the distribution of the mobile users sojourn time, i.e., the time a mobile user is physically present in a given cell. We use these models to derive the throughput of users who remain spatially static during their whole data transmission and the amount of handovers generated by moving users. We analyze the impact on performance of some key parameters such as the size of the small cell, the speed and proportion of mobile users and the distribution of their sojourn time. Numerical evaluation and simulation results are provided to assess the accuracy of the latter model and gain insight into the global system performance.
[Show abstract][Hide abstract] ABSTRACT: La tomoscintigraphie par émission de positons (TEP) au 18-désoxy-fluoroglucose (18F-FDG) est une modalité d’imagerie de plus en plus utilisée dans le diagnostic d’infections en raison de sa capacité à détecter directement le foyer infectieux. Cependant, il existe aussi des signes indirects d’infection sur l’examen TEP. L’objectif de cette étude est d’identifier des signes indirects de sepsis en TEP chez des patients présentant un sepsis sévère d’origine inconnue et de déterminer leur valeur diagnostique.
No preview · Article · Mar 2015 · Medecine Nucleaire
[Show abstract][Hide abstract] ABSTRACT: In this paper, we evaluate the performance per-ceived by end-users with very high access rates, connected to a common backhaul link that aggregates the traffic of multiple access areas. We model, at flow level, the way a finite population of users with heterogeneous access rates and traffic demands shares the capacity of this common backhaul link. We then evaluate several practically interesting use cases, focusing particularly on the performance of users subscribing to recent FTTH offers in which the user access rates may be of the same order of magnitude as the backhaul link capacity. We show that, despite such high access rates, reasonable performance can be achieved as long as the total offered traffic is well below the backhaul link capacity. The obtained performance results are used to derive simple dimensioning guidelines for backhaul networks.
[Show abstract][Hide abstract] ABSTRACT: The performance of a cache with Random Replacement policy is addressed in the case of a population of objects having a Zipf popularity distribution with decay parameter s. The main purpose of the paper is to provide new theoretical results on this scheme, within the Independent Reference Model framework. When s > 1, we derive a closed-form expression for the miss probability which is exact when s is an even integer and provides good approximation for all real s. In the case s ≤ 1, we consider two different regimes where cache size C and document population N jointly grow to infinity. When C grows sublinearly with N, the miss probability tends to 1 and an asymptotic expression for the hit probability is provided for 1/2 < s < 1. When C is linear with N, the miss probability is proved to have a non-zero limit, whose analytic expression is given, if s < 1, and to be of order 1/log N if s = 1. Besides, some numerical experiments are reported which assess the validity and potential usefulness of the obtained analytical results.
[Show abstract][Hide abstract] ABSTRACT: Objectives : A French multicenter study was promoted by the national French cancer federation (Unicancer R&D) to assess the potential of [18F]FLT (positron emission tomography (PET) biomarker of proliferation)to manage breast cancer neoadjuvant chemotherapy (NAC). The main objective was to compare changes in tumor [18F]FLT uptake to histopathological changes induced by NAC, assuming an arrest of tumor growth related to the effectiveness of NAC.
Methods : 97 patients (age 48.6 +/- 10.2 y.) were included in 13 nuclear medicine centers. All patients were eligible to anthracycline-based NAC for a de novo unifocal breast cancer (ductal n = 84, lobular = 11, other type = 2; stage II n = 75, stage III n = 21 et stage IV n = 1). 90 patients underwent a baseline PET before the onset of NAC (PET1) and a final PET after the end of NAC and before surgery (PET3). PET acquisitions were performed 60±7min after FLT injection. SUVmax (maximum standardized uptake value), SUVpeak (1 cm3 ROI including pixel max) and SUV41 (isocontour 41% of pixel max) were computed. Changes in SUV on PET3 vs PET1 were analyzed in relation to histopathological findings at the end of NAC (Sataloff criteria).
Results : Tumor FLT uptake decreased markedly between TEP1 and TEP3 (SUVmax = 6.2±4.8 vs 1.3±1.2 respectively; SUVpeak = 4.6±3.2 vs 0.9±0.9; SUV41 = 3.6±2.8 vs 0.8±0.7). Total or near-total therapeutic effect (grade A) were obtained in 20 patients, more than 50% therapeutic effect but less than total or near-total effect (grade B) in 37 patients, less than 50% therapeutic effect but visible effect (grade C) in 22 patients, or no therapeutic effect (grade D) in 11 patients. SUVmax decreased dramatically (87.5%) to background levels in all patients with a complete response (grade A). Overall, changes in SUV differed depending on the type of histological response (p<0.01) i.e. SUVmax changes were more pronounced as pathological responses were good: 61% for grade D; 65.7% grade C and 69.8% grade B. The same results were obtained with the two other SUV types.
Conclusions : Pathologic response to NAC in breast cancer can be assessed accurately by FLT.
[Show abstract][Hide abstract] ABSTRACT: L’irradiation antalgique est une arme thérapeutique sûre et efficace. Les mécanismes d’action sont mal connus. La radiothérapie externe est le standard thérapeutique de prise en charge des métastases osseuses douloureuses non compliquées ou en prévention des complications. La radiothérapie en conditions stéréotaxiques peut être utile en cas de métastase rachidienne unique. La radiothérapie métabolique à titre antalgique est mal connue des cliniciens et donc sous-utilisée. Elle est également un traitement efficace et sûr pour les métastases osseuses douloureuses multiples non compliquées, seule ou en association avec la radiothérapie externe conformationnelle.
Radiotherapy for pain is a secure and effective treatment. Mechanism of action is hardly known. External beam radiation therapy is a standard treatment for painful uncomplicated bone metastases and/or prevention of morbidity. Stereotactic body radiation therapy can be useful for solitary or oligometastatic spinal bone metastases. Clinician is unfamiliar with radionuclide therapy which is so underused. It is also a secure and effective treatment (alone or associated with external beam radiation therapy) for painful multiple bone uncomplicated metastasis.
No preview · Article · Sep 2013 · Douleur et Analgésie
[Show abstract][Hide abstract] ABSTRACT: Paraneoplastics syndromes (PNS) represent a rare and heterogeneous group of entities whose clinical symptoms may sometimes precede the diagnosis of the tumor to which they are due. The identification of the underlying tumor becomes, in this context, very important for the patient's functional and maybe vital forecasts, by allowing an earliest treatment of the tumor. 18FDG PET/CT has become indispensable in the diagnosis and follow-up of numerous cancers but its role in etiological investigation of isolated paraneoplastics syndroms for the research of an occult tumor is not defined yet. Nevertheless, requests of PET/CT in this indication are frequent in nuclear medicine's departments, with an uncertain diagnostic yield. We have listed retrospectively 64 patients, sended in nuclear medicine's department of Nancy's university hospital between 2004 and 2010 for the research of an occult tumor because of a clinically suspected paraneoplastic's syndrom, in order to estimate its diagnostic's contribution in this indication. According to our results, 18FDG PET-CT would be interesting by its negative predictive value concerning the tumoral risk, in agreement with its known sensibility diagnostic's qualities; it may also present an interest for the diagnosis and the characterization of non-tumoral pathologies generating symptoms initially wrongly suspected to be paraneoplastics.
No preview · Article · Dec 2011 · Medecine Nucleaire