The pseudo-self-similar traffic model: application and validation

Since the early 1990¿s, a variety of studies has shown that network traffic, both for local- and wide-area networks, has self-similar properties. This led to new approaches in network traffic modelling because most traditional traffic approaches result in the underestimation of performance measures of interest. Instead of developing completely new traffic models, a number of researchers have proposed to adapt traditional traffic modelling approaches to incorporate aspects of self-similarity. The motivation for doing so is the hope to be able to reuse techniques and tools that have been developed in the past and with which experience has been gained. One such approach for a traffic model that incorporates aspects of self-similarity is the so-called pseudo self-similar traffic model. This model is appealing, as it is easy to understand and easily embedded in Markovian performance evaluation studies. In applying this model in a number of cases, we have perceived various problems which we initially thought were particular to these specific cases. However, we recently have been able to show that these problems are fundamental to the pseudo self-similar traffic model. In this paper we review the pseudo self-similar traffic model and discuss its fundamental shortcomings. As far as we know, this is the first paper that discusses these shortcomings formally. We also report on ongoing work to overcome some of these problems

INVESTIGATION OF SURFACE SPUTTERING AND IONIZATION PROCESSES UNDER NON-REACTIVE LIGHT ION IRRADIATION: TOWARDS 4D SIMS IMAGING

The progressive trend to miniaturize samples presents a challenge to materials characterization techniques in terms of both lateral resolution and chemical sensitivity. The latest generation of focused ion beam (FIB) platforms has allowed to advance in a variety of different fields, including nanotechnology, geology, soil, and life sciences. State-of-the-art ultra-high resolution electron microscopy (EM) devices coupled with secondary ion mass spectrometry (SIMS) systems have enabled to perform in-situ morphological and chemical imaging of micro- and even nanosized objects to better understand materials by studying their properties correlatively. However, SIMS images are prone to artefacts induced by the sample topography as the sputtering yield changes with respect to the primary ion beam incidence angle. Knowing the exact sample topography is crucial to understand SIMS images. Moreover, using non-reactive primary ions (Ne+) produced in a gas field ion source (GFIS) allows to image in SIMS with an excellent lateral resolution of < 20 nm, but it comes with a lower ionization probability compared to reactive sources (e.g., Cs+) and due to small probe sizes only a limited number of atoms are sputtered, resulting in low signal statistics. This thesis focused first on taking advantage of high-resolution in-situ EM-SIMS platforms for applications in specific research fields and to go beyond traditional correlative 2D imaging workflows by developing adapted methodologies for 3D surface reconstruction correlated with SIMS (3D + 1). Applying this method to soil microaggregates and sediments allowed not only to enhance their visualization but also to acquire a deeper understanding of materials’ intrinsic transformation processes, in particular the organic carbon sequestration in soil biogeochemistry. To gain knowledge of the influence of the topography on surface sputtering, using model samples the change of the sputtering yield under light ion bombardment (He+, Ne+) for different ranges of incidence angles of the primary ion beam was studied experimentally. This data was compared to Monte Carlo simulation results and fitted with existing sputtering model functions. We showed thus that these models developed and studied for heavier ions (Ar+, Cs+) are also applicable to light ions (He+, Ne+). Additionally, an algorithm used to correct SIMS images with respect to topographical artefacts resulting from local changes of the sputtering yield was presented. Finally, the contribution of oxygen on positive SI yields was studied for non-reactive primary ions (25 keV Ne+) under high primary ion current densities (up to 10^20 ions/(cm2 ∙ s)). It was shown that in order to maximize and maintain a high ionization probability oxygen needs to be provided continuously to the surface. Secondary ion signal enhancement of up to three orders of magnitude were achieved for silicon, opening the doors for SIMS imaging at both highest spatial resolution and high sensitivity

4D Surface Reconstruction of Micron-Sized Organic Calcite for the Characterization of Chemical Heterogeneity of Chalk Surfaces

Seawater injection into chalk reservoirs is a method for improved oil recovery (IOR) at the Norwegian Continental Shelf (NCS). During the injection of fluids for IOR, complex physicochemical interactions between the injected fluid and the reactive rock surface will take place, such as compaction and alterations of rock properties (e.g., porosity, permeability, wettability). The distribution of noncarbonate mineral phases in the reservoir and on the surface of the chalk will dictate wettability properties. Yet, the identification and quantification of nanometer-sized mineral phases on calcite surfaces have been challenging due to insufficient spatial resolution and sensitivity of the analytical methods used. On-shore chalk was used in this study. Helium ion microscopy (HIM) combined with in situ secondary ion mass spectrometry (SIMS) was used to produce secondary electron images for mapping surface morphology and topography correlated with chemical maps from SIMS. First, a 3D surface model was created from a series of secondary electron images acquired from different perspectives around the coccolith. A chemical image obtained by SIMS was developed on the same region of interest and projected onto the 3D surface model to create a 4D surface reconstruction (3D+1 concept). This includes surface chemistry information on sub-micron-sized noncarbonate phases on calcite grains. The surface distribution of noncarbonate phases added up to a minimum of 6.3%, where no 40Ca had been detected. Moreover, 39.8% of the entire area is characterized by 40Ca and 27Al plus 28Si. Compared with 5 wt % noncarbonate phases identified by whole-rock geochemistry, we identify at least 200–300% higher noncarbonate phase abundance than expected based on bulk geochemistry. This has a significant implication for the modeling of mineral surface charges, the major criteria for wettability calculations. Therefore, HIM-SIMS studies allow nanoscale mapping and mineral phase identification, which will enhance the knowledge of fluid–rock interactions for purposes related to IOR, carbon capture, and storage as well as for hydrogen storage.publishedVersio

High-Resolution Topographic and Chemical Surface Imaging of Chalk for Oil Recovery Improvement Applications

Chalk is a very fine-grained carbonate and can accommodate high porosity which is a key characteristic for high-quality hydrocarbon reservoirs. A standard procedure within Improved Oil Recovery (IOR) is seawater-injection which repressurizes the reservoir pore pressure. Long-term seawater-injection will influence mineralogical processes as dissolution and precipitation of secondary minerals. These secondary minerals (<1 micrometer) precipitate during flooding experiments mimicking reservoir conditions. Due to their small sizes, analysis from traditional scanning electron microscopy combined with energy dispersive X-ray spectroscopy is not conclusive because of insufficient spatial resolution and detection limit. Therefore, chalk was analyzed with high-resolution imaging by helium ion microscopy (HIM) combined with secondary ion mass spectrometry (SIMS) for the first time. Our aim was to identify mineral phases at sub-micrometer scale and identify locations of brine–rock interactions. In addition, we wanted to test if current understanding of these alteration processes can be improved with the combination of complementary imaging techniques and give new insights to IOR. The HIM-SIMS imaging revealed well-defined crystal boundaries and provided images of excellent lateral resolution, allowing for identification of specific mineral phases. Using this new methodology, we developed chemical identification of clay minerals and could define their exact location on micron-sized coccolith grains. This shows that it is essential to study mineralogical processes at nanometer scale in general, specifically in the research field of applied petroleum geology within IOR.publishedVersio

Effectiveness of Web-Delivered Acceptance and Commitment Therapy in Relation to Mental Health and Well-Being: A Systematic Review and Meta-Analysis

BACKGROUND: The need for effective interventions to improve mental health and emotional well-being at a population level are gaining prominence both in the United Kingdom and globally. Advances in technology and widespread adoption of Internet capable devices have facilitated rapid development of Web-delivered psychological therapies. Interventions designed to manage a range of affective disorders by applying diverse therapeutic approaches are widely available. OBJECTIVE: The main aim of this review was to evaluate the evidence base of acceptance and commitment therapy (ACT) in a Web-based delivery format. METHOD: A systematic review of the literature and meta-analysis was conducted. Two electronic databases were searched for Web-delivered interventions utilizing ACT for the management of affective disorders or well-being. Only Randomized Controlled Trials (RCTs) were included. RESULTS: The search strategy identified 59 articles. Of these, 10 articles met the inclusion criteria specified. The range of conditions and outcome measures that were identified limited the ability to draw firm conclusions about the efficacy of Web-delivered ACT-based intervention for anxiety or well-being. CONCLUSIONS: ACT in a Web-based delivery format was found to be effective in the management of depression. Rates of adherence to study protocols and completion were high overall suggesting that this therapeutic approach is highly acceptable for patients and the general public

Pathogenic Fungi Regulate Immunity by Inducing Neutrophilic Myeloid-Derived Suppressor Cells

Peer reviewedPublisher PD

Effects of image‐based and text‐based active learning exercises on student examination performance in a musculoskeletal anatomy course

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/138318/1/ase1684.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/138318/2/ase1684_am.pd

An ecological analysis of colorectal cancer incidence and mortality: Differences by sexual orientation

<p>Abstract</p> <p>Background</p> <p>Some have suggested gays and lesbians may carry a greater burden of colorectal cancer. To date, individual sexual orientation data are not available in cancer surveillance registries. This prevents an assessment of differences in colorectal cancer incidence and mortality by sexual orientation, using individual-level data.</p> <p>Methods</p> <p>We use an ecological approach to examine differences in colorectal cancer incidence and mortality by county-level sexual orientation data. From the Surveillance, Epidemiology and End Results (SEER) Program we obtain population-based surveillance data on colorectal cancer incidence and mortality from 1996 to 2004. We use Census 2000 data on same-sex partnered households, a proxy of sexual orientation, to derive county-level sexual orientation data. Using multiple regression models, we examined the county-level association of sexual minority density with colorectal cancer incidence and mortality.</p> <p>Results</p> <p>After controlling for race and SES, we identify a significant positive association between greater density of sexual minority men and women and colorectal cancer incidence. With respect to colorectal cancer mortality, we identify a positive association with density of sexual minority men, but not women.</p> <p>Conclusions</p> <p>In the absence of surveillance data on sexual minority individuals, ecological analyses provide estimates of associations at the aggregate level, thereby providing crucial information for follow-up studies.</p

Perioperative management of massive hemoptysis during flexible bronchoscopy : Case report

La broncoscopia flexible es un procedimiento diagnóstico o terapéutico con baja incidencia de complicaciones (0,08-6,8%). El sangrado por biopsia transbronquial es una complicación rara (0-2,8% de los casos), suele ser leve y resuelve con medidas locales. No existe una definición clara de hemoptisis masiva y, por su baja incidencia, no hay guías de práctica clínica para el tratamiento de esta complicación, que puede ser catastrófica. Presentamos un caso de hemoptisis masiva durante la realización de una broncoscopia flexible más biopsia transbronquial y revisamos la literatura acerca del manejo intraoperatorio.Q3Reporte de caso256-261Flexible bronchoscopy is a diagnostic or therapeutic procedure with a low incidence of complications (0.08–6.8%). Bleeding after transbronchial biopsy is a rare complication (0-2.8% of the cases), usually resulting in minor bleeding that resolves with local measures. There is no clear definition of massive hemoptysis and due to the low incidence of this condition, there are no practical guidelines for the treatment of this complication that may be catastrophic. This case discusses the occurrence of massive hemoptysis during a transbronchial biopsy under flexible bronchoscopy, including a literature review on perioperative management