Multi-user cross-layer allocation design for LP-OFDM high-rate UWB

International audienceIn this paper, we investigate a cross-layer design for the packet scheduling and the resource allocation in UWB systems. This design considers the combination of queuing and channel state information (CSI) which provides QoS support for multimedia applications in UWB. For the physical layer, the use of a linear precoded orthogonal division multiplexing (LPOFDM) waveform is proposed because of its significant performance increase compared to the WiMedia proposal. For the medium access control layer, scheduling is performed in order to differentiate between the different users and to satisfy their quality of service constraints. This cross-layer approach optimizes the system spectral efficiency and solves the problem in the WiMedia solution of cohabitation of more than three users sharing the three sub-bands of the same channel. Simulation results show that the proposed scheme leads to a considerable improvement in resource allocation and can guarantee the required quality of service

Multicommodity hub-and-spoke network design -

Thesis. M.E.M. American University of Beirut. Engineering Management Program 2014. ET:6006Advisor : Dr. Joe Naoum-Sawaya, Assistant Professor, Enginering Management ; Committee members: Dr. Bacel Maddah, Associate Professor, Enginering Management, Dr. Walid Nasr, Assistant Professor, Suliman S. Olayan School of Business.Includes bibliographical references (leaves 48-52)Hub-and-spoke is a network architecture with several applications in a number of industries. This type of networks allows the flow of information, people, and products from origin to destination points through central nodes known as hubs. The consolidation of flow at central locations leads to significant reduction in cost due to the economies of scale. Although in practice, several types of commodities flow over such networks, the majority of models in the literature consider single commodity type networks. Dealing with a single commodity is a limitation for such networks, as it is impossible to model multiple types of flow and it does not allow modeling multiple source and destination pairs which is primordial in all sorts of fields. In this research, we present an optimization model for multicommodity hub-and-spoke network design. We present computational testing on a set of instances randomly generated with the Mulgen generator, in addition to a real case network inspired by the French rail network. The results show that small to medium-size networks can be solved within a reasonable computational time. Furthermore, since the major drawback of hub-and-spoke networks is congestion on hubs, we present an extension to the model that includes congestion costs, in order to mitigate the effect of congestion in the network. Since the resulting optimization problem is non-linear, we then present a cutting plane approach based on a piecewise linear approximation as a solution approach

Application of sieve methods to factorization and the discrete logarithm problem

Factoring large numbers and computing discrete logarithms are presumed to be hard problems. No polynomial time solution for those problem has yet been found. Those problems have many significant applications, particularly in cryptography. Several cryptosystems base their security on their supposed difficulty. In this thesis we present some of the algorithms to solve these two problems. We mainly explore sieving as a tool for that purpose. Among other material we describe the Quadratic Sieve and the Number Field Sieve as they apply to factoring. We finally sketch how the Number Field Sieve can be applied to compute discrete logarithms

Gasification of wood powder in a small-scale entrained flow gasifier

Gasification of wood powder milled from commercially available wood pellets have been performed in a small-scale entrained flow gasifier. The main aim of this study is to investigate operational and feedstock requirements (mainly particle size distribution, (PSD)) for this small-sized gasifier to perform with good carbon conversion ratio. The effects of several parameters were investigated, resulting in variable performance. The investigated parameters were equivalence ratio (lambda, λ), oxidant type (air or oxygen), thermal load, pressure, burner head configuration and PSD. The syngas quality, defined as cold gas efficiency (CGE) and/or carbon conversion efficiency (CC) was reported as function of the above parameters. The gasifier achieved a satisfactory conversion when using oxygen as oxidant and at elevated pressure (8.2 bar(a)).publishedVersio

Production and characterization of biocarbon from woody biomasses produced at 1000 °C

Controlled pyrolysis experiments have been performed on five different biomass types that include birch and spruce woodchips, wood pellets, steam exploded pellets and birch bark. Biocarbons have been produced at a temperature of 1000 °C at a slow heating rate of 10 °C/min. The focus of this work was to study and compare the characteristics of the produced biocarbons. The properties of the biocarbons were evaluated in terms of proximate and ultimate analyses, ash composition, SEM-EDX, Raman, XRD, density, and abrasion strength. In addition, the gas release and element distribution across the different pyrolytic products from pyrolysis of the studied biomasses are reported. The results showed that the yield and physio-chemical properties of the produced biocarbons differ across the tested materials. The bark biocarbon has the lowest fixed carbon and carbon content, in comparison to the other tested feedstocks. On the other hand, the bark biocarbon has a considerably higher ash content compared to the other biocarbons. The presence of ash-forming elements in the bark biocarbon was confirmed by SEM-EDS and XRD analysis, which are dominated by Ca and Si. SEM analysis also revealed that biocarbon produced from the birch and spruce wood have cellular and porous structure, whereas the biocarbon produced from the wood pellet and steam exploded pellets have much more dense and compact structure. Raman analysis results indicate that birch bark biocarbon has less ordered carbon structures. Abrasion test results showed that the birch bark biocarbon has poor mechanical properties and tends to fragment and break, forming particles and fines with small sizes. The biocarbon produced from the steam exploded pellets has superior mechanical strength with the least formation of fines compared to the other studied biocarbons.publishedVersio

Reducing Emissions from Current Clean-Burn Wood Stove Technology by Automating the Combustion Air Supply and Improving the End-User Interaction - Two Important Primary Measures

The current work concerns two of the most important primary measures to reduce emissions from small scale appliances for space heating; improvement and optimization of current technology and user behavior, where the latter is related to the effects of the ignition procedure, fuel quality and type, and amount of wood when loading and re-loading. Air-control both concerns user behavior and technology improvement. A recently developed in-house automatic air-control system was compared to manual operation. The ignition procedure is important and affects the quality of the combustion, not only for the ignition period itself but also for the subsequent burning periods. Two self-defined categories of primary measures were studied, primary measure A and B, as PMA (automated air flow) and PMB (manual operation varying the ignition procedure, wood specie, amount of fuel, log size and moisture content), respectively. Woodstove testing in our laboratory showed that for emissions related to primary measures, PMA, automating the combustion air reduced the particulate matter (PM) with 66% applying the Norwegian test method. Using the European test method, automation increased the efficiency with 8% and decreased PM, CO, and Organic gaseous compounds (OGC), with 12%, 34% and 55%, respectively. Comparing nominal and high fuel loads with birch, at low burn rates, automation reduced PM and CO with 4% and 61%, respectively, for a fuel load of 1.2 kg. For a 1.8 kg fuel load, automation resulted in even higher reductions in PM, CO and OGC of 68%, 52% and 82%, respectively. Automation also substantially decreased CO (70%) emissions when burning briquette presses. The effect of end-user operation as for the ignition from cold stove, and use of fuel with varying properties, as in PMB, showed significant variation in emissions over the ignition period. Good ignition, when firing according to the Norwegian standard, can be achieved repeatedly by assuring that the fuel catches fire before closing the door and/or reduce the primary/secondary air flows. Bad ignition due to over-/under firing and dense stacking, can produce at least twice as much PM and CO and 3-4 times the OGC, compared to correct ignition. No significant differences in emissions were found when comparing birch, spruce, and pine, for wood with equal moisture content. However, burning pine, showed higher emissions of total carbon particles, as elemental and organic carbon, on the same level as with poor ignitionpublishedVersio

Emission Levels and Emission Factors for Modern Wood Stoves

publishedVersio

Characteristics of polyps in Lebanese population

Background: The objective of this study is to describe characteristics of the polyps in Lebanese population and evaluate the dysplasia and its relation to the polyps’ locations. Methods: Retrospective descriptive study was conducted at the Department of National Institute of Pathology in Lebanon and comprised biopsy of colonic polyps or resected polyps from patients from 2007 to 2009. We collected demographic data and polyps’ characteristics. Then, we divided patients according to age sex, location, histology. Results: With 2298 polyps in 1470 patients, the mean age was 57.45 with 68% aged more than 50yo. 75.6% have one polyps and multiple polyps more commonly found in older patient (> 50 years). More than 20 % of polyps found in the recto-sigmoid area. In the right colon, people older than 50 years were more likely to have polyps (19%) compared to those < 30 years (8.3%) (p < 0.05). In the rectum, people < 30 years were more likely to have polyps compared to those > 50 years (p < 0.01). Concerning the histology, tubular adenoma is the most common type and more prevalent in left colon. Hyperplastic polyps mainly found in the recto-sigmoid area and mainly in age group 30-50 in contrast to adenomatous polyps found over 50yo. Adenocarcinomas and/or degenerative polyps were founded in 5.9% of our population. Conclusion: This study gives valuable information on colorectal polyp in Lebanese population about age, sex, dominant histology and anatomic location. We noted a male predominance and mainly above 50 years old. The majority had single polyps, >50% of polyps were localized in the recto sigmoid. Adenomatous polyps were the most common type

Numerical simulation of lignin gasification: The role of gasifying agents in entrained-flow reactors

Biomass gasification using an Entrained-Flow Reactor (EFR) is an effective strategy for sustainable energy production and climate change mitigation. However, optimizing gasification efficiency and syngas quality requires a thorough understanding of the influence of gasifying agents. This study investigates the effects of different gasifying agents—air, CO2, steam, and CO2-steam mixtures—on lignin gasification in an EFR. Utilizing a validated Eulerian-Lagrangian Computational Particle Fluid Dynamics (CPFD) model, we examine how these agents impact biomass conversion to syngas, focusing on key parameters like hydrogen to carbon monoxide ratio, and the lower heating value (LHV) of syngas. Our findings reveal that air, due to nitrogen dilution, results in suboptimal lignin-to-syngas conversion, yielding lower energy content and hydrogen production. In contrast, steam enhances conversion efficiency, significantly increasing hydrogen output and LHV. CO2 as a gasifying agent boosts carbon monoxide levels through interactions with solid carbon, leading to a higher energy content in the syngas. The CO2-steam mixture is particularly effective, producing syngas with a high hydrogen concentration, primarily due to the water–gas shift reaction and steam’s reaction with the lignin carbon. This research addresses the limitations of existing studies by providing detailed, quantitative insights into the impact of gasifying agents on lignin gasification in an EFR. By adjusting the CO2-to-steam ratio, operators can precisely control the composition of syngas for targeted applications such as Fischer-Tropsch synthesis, methanol production, and fermentation. The study highlights the potential of advanced simulation techniques to optimize biomass gasification processes, offering significant improvements in efficiency and energy yield over current methods.publishedVersio

Evaluation of CLC as a BECCS technology from tests on woody biomass in an auto-thermal 150-kW pilot unit

In this work, woody biomass is converted by chemical looping combustion (CLC) in the auto-thermally operated 150-kW pilot unit at SINTEF Energy Research in Norway, using ilmenite as an oxygen carrier. The pilot unit consists of two inter-connected circulating fluidized bed reactors, being the air and fuel reactor, respectively. The unit is simplified compared to many other lab and pilot units by not having a carbon stripper. The aim of the present study is to evaluate the main performance parameters when operating a relatively large CLC unit in auto-thermal mode, using a cheap natural mineral, ilmenite, as oxygen carrier. Another aspect with the tests is to verify if the omission of a carbon stripper can provide high enough capture efficiencies for solid fuels as biomass, with a large share of volatiles and a char remnant with high reactivity. As a comparison, tests with petcoke were performed, to assess the effect when using a fuel with a low share of volatiles and slow char conversion. The results imply that CO2 capture efficiencies can be well above 95 % in a larger industrial unit operating on biomass, even without a carbon stripper, but that a carbon stripper is definitely needed for fuels with less volatiles and low char reactivity.Evaluation of CLC as a BECCS technology from tests on woody biomass in an auto-thermal 150-kW pilot unitpublishedVersio