Access Games: A Game Theoretic Framework For Fair Bandwidth Sharing In Distributed Systems

In this dissertation, the central objective is to achieve fairness in bandwidth sharing amongst selfish users in a distributed system. Because of the inherent contention-based nature of the distributed medium access and the selfishness of the users, the distributed medium access is modeled as a non-cooperative game; designated as the Access Game. A p-CSMA type medium access scenario is proposed for all the users. Therefore, in the Access Game, each user has two actions to choose from: transmit and wait . The outcome of the Access Game and payoffs to each user depends on the actions taken by all the users. Further, the utility function of each user is constructed as a function of both Quality of Service (QoS) and Battery Power (BP). Various scenarios involving the relative importance of QoS and BP are considered. It is observed that, in general the Nash Equilibrium of the Access Game does not result into fairness. Therefore, Constrained Nash Equilibrium is proposed as a solution. The advantage of Constrained Nash Equilibrium is that it can be predicated on the fairness conditions and the solution will be guaranteed to result in fair sharing of bandwidth. However, Constrained Nash Equilibrium is that it is not self-enforcing. Therefore, two mechanisms are proposed to design the Access Game in such a way that in each case the Nash Equilibrium of the Access Game satisfies fairness and maximizes throughput. Hence, with any of these mechanisms the solution of the Access Game becomes self-enforcing

Influence of phosphate on tungstate sorption on hematite: A macroscopic and spectroscopic evaluation of the mechanism

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Tungstate (VI) sorption on hematite: An in situ ATR-FTIR probe on the mechanism

Owing to the suspected toxicity and carcinogenicity of tungstate (VI) oxyanions [i.e. mono tungstate and several polytungstate, generally represented by W (VI)], the environmental fate of W (VI) has been widely studied. Sorption is regarded as a major mechanism by which W (VI) species are retained in the solid/water interface. Iron (hydr)oxides have been considered important environmental sinks for W (VI) species. Here we report sorption mechanisms of W (VI) on a common iron oxide mineral-hematite under environmentally relevant solution properties using in situ attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopic probes. Initial W (VI) loadings varied from 10 to 200 μM at fixed pH values ranged from 4.6 to 8.1. For pH envelop (pHs = 4.6, 5.0, 5.5, 6.0, 6.5, 7.5, and 8.1) experiments, fixed W (VI) concentrations (i.e. 10 & 200 μM) were used to understand the effects of pH. The results indicated that at acidic pH values (pH \u3c 6.0) the sorbed polytungstate surface species are prominent at 200 μM initial W (VI) conc. The pH envelop experiments revealed that sorbed polytungstates can be present even at lower initial W (VI) conc. (i.e. 10 μM) at pH values \u3c5.5. Overall, our in situ ATR-FTIR experiments indicated that W (VI) forms inner-sphere type bonds on hematite surface and the strength of the interaction increases with decreasing pH. In addition, initial W (VI) concentration affected the sorption mechanisms of W (VI) on hematite. Our study will aid the molecular level understanding of W (VI) retention on iron oxide surfaces

Nitrite Reduction by Siderite

Nitrate-dependent Fe(II) oxidation is an important process in the inhibition of soil Fe(III) reduction, yet the mechanisms are poorly understood. One proposed pathway includes chemical reoxidation of mineral forms of Fe(II) such as siderite [FeCO3(s)] by NO2 −. Accordingly, the objective of this study was to investigate the reactivity of FeCO3(s) with NO2 −. Stirred-batch reactions were performed in an anoxic chamber across a range of pH values (5.5, 6, 6.5, and 7.9), initial FeCO3(s) concentrations (5, 10, and 15 g L−1) and initial NO2 − concentrations (0.83–9.3 mmol L−1) for kinetic and stoichiometric determinations. Solid-phase products were characterized using x-ray diffraction (XRD). Siderite abiotically reduced NO2 − to N2O. During the process, FeCO3(s) was oxidized to lepidocrocite [γ-FeOOH(s)] based on the appearance of XRD peaks located at 0.624, 0.329, and 0.247 nm. The rate of NO2 − reduction was first order in total NO2 − concentration and FeCO3(s), with a second-order rate coefficient (k) of 0.55 ± 0.05 M−1 h−1 at pH 5.5 and 25°C. The reaction was proton assisted and k values increased threefold as pH decreased from 7.9 to 5.5. The influence of pH on NO2 − reduction was rationalized in terms of the availability of FeCO3(s) surface sites (\u3eFeHCO3 0, \u3eFeOH2 +, and \u3eCO3Fe+) and HNO2 concentration. These findings indicate that if FeCO3(s) is present in an Fe(III)-reducing soil where fertilizer NO3 − is applied, it can participate in secondary chemical reactions with NO2 − and lead to an inhibition in Fe(III) reduction. This process is relevant in soil environments where NO3 −– and Fe(III)-reducing zones overlap or across aerobic–anaerobic interfaces

Influence of Citrate and Phosphate on the Adsorption of Adenosine-5′-Monophosphate at the Hematite Water Interface

Nucleic acid derived organic phosphorus (Po) is an important source of plant available P when degraded to inorganic phosphate (P(V)i). It is known that when nucleic acids or components are adsorbed on mineral surfaces, the enzymatic degradation is hindered or delayed. Thus, understanding adsorption/desorption mechanisms of nucleic acids and their derivatives are key to assess the biogeochemical pathways of Po cycling. Here we report adsorption mechanisms of adenosine-5′-monophosphate (AMP) on hematite, a common iron oxide mineral, under various solution properties using macroscopic and in situ attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopic probes. The effects of citrate, mimicking organic acids from roots exudates, and the influence of P(V)i, representing inorganic fertilizer application, were also evaluated on the release of adsorbed AMP under various solution properties. The results suggested that AMP adsorbed with the hematite surface via the phosphate moiety, N7 atom and the π electron systems of the adenine moiety. The presence of citrate significantly decreased the AMP adsorption, which was also corroborated by the negative phosphate IR bands in the results of AMP and citrate competitive adsorption experiments monitored by in situ ATR-FTIR probe. Like citrate, P(V)i also reduced AMP adsorption on hematite. Our findings suggest a potential novel pathway of nucleic acid derived Po cycling in the soil environment

Liquid Swine Manure Nitrogen Utilization for Crop Production

Manure is an important resource for meeting the nutrient needs of corn and soybean grown in Iowa. Land application is the most widely accepted and best economic and agronomic use of manure. Concurrently, however, is the environmental concern when manure nitrogen (N) and phosphorus (P) is not adequately accounted for or utilized by crops. Use of manure as a crop nutrient source requires producer confidence in nutrient availability and maintenance of high crop yields. When that confidence is lacking, either because of unknown application rates or uncertain nutrient content and crop availability, then additional fertilizer or higher manure rates are applied to ensure adequate soil fertility levels. This leads to over-application of crop nutrients, reduced profits, and potential for off-site movement and water quality degradation

Antimony (V) Adsorption at the Hematite–Water Interface: A Macroscopic and In Situ ATR-FTIR Study

The environmental mobility of antimony (Sb) is largely unexplored in geochemical environments. Iron oxide minerals are considered major sinks for Sb. Among the different oxidation states of Sb, (+) V is found more commonly in a wide redox range. Despite many adsorption studies of Sb (V) with various iron oxide minerals, detailed research on the adsorption mechanism of Sb (V) on hematite using macroscopic, spectroscopic, and surface complexation modeling is rare. Thus, the main objective of our study is to evaluate the surface complexation mechanism of Sb (V) on hematite under a range of solution properties using macroscopic, in situ attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopic, and surface complexation modeling. The results indicate that the Sb (V) adsorption on hematite was highest at pH 4–6. After pH 6, the adsorption decreased sharply and became negligible above pH 9. The effect of ionic strength was negligible from pH 4 to 6. The spectroscopic results confirmed the presence of inner- and outer-sphere surface complexes at lower pH values, and only outer-sphere-type surface complex at pH 8. Surface complexation models successfully predicted the Sb (V) adsorption envelope. Our research will improve the understanding of Sb (V) mobility in iron-oxide-rich environments

Liquid swine manure as a nitrogen source for corn and soybean production

Liquid swine (Sus scrofa domesticus) manure is a large crop nutrient resource in Iowa, but one that should be managed appropriately to gain maximum effectiveness. A multi-year project was initiated on producers' fields to determine the impact of liquid swine manure-N on corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] production. Liquid swine manure was injected or broadcast applied (two sites) in field-length strips. The intended rates for corn-soybean were 0, 84, and 168 kg total manure-N ha−1, and for corn-corn and soybean-corn were 0, 112, and 224 kg total-N ha−1. Manure samples were collected during application, and in conjunction with applicator calibration, used to calculate total-N rates. Four fertilizer-N rates (0, 45, 90, and 135 kg N ha−1 for corn-soybean and 0, 67, 135, and 202 kg N ha−1 for corn-corn) were applied to small split-plots within each manure strip to measure response to additional N. Corn N status indicators and grain yield showed frequent and large increase to the low manure-N rate. Smaller additional yield increase was found with the high liquid swine manure-N rates at the most responsive sites. Corn typically produced highest yield increase to additional fertilizer-N when manure was not applied, frequent increase with the low manure rate (magnitude depending upon the site N responsiveness), and no response with the high manure rate. While it was not possible to determine the specific first-year availability of the liquid swine manure-N, we found no reason to estimate it is much different than fully crop available. Liquid swine manure application increased soybean grain yield at several sites, and did not reduce yield. When manure total-N was applied to soybean at rates < 225 kg total-N ha−1, post-harvest profile nitrate was similar to the control. This study has shown that liquid swine manure is an excellent source of N for corn production and application can improve soybean yield. Producers should consider that liquid swine manure-N is highly crop available. For it's best management, practices should focus on matching crop N needs through use of manure sampling, laboratory analyses, and application calibration.</p

Managing Qos For Wireless Cells Supporting Critical Load

In this paper we apply a novel algorithm to control and optimize the number of non-critical calls in a vide-intensive mobile environment supporting critical applications. The algorithm is based on graceful QoS reduction policy. We simulate a video-intensive scenario and determine the optimal bandwidth allocation required for maximizing the number of non-critical calls