Добірка наукової літератури з теми "Nelson Diffusions"

The adsorption of methyl orange (MO) from aqueous solutions onto a KOH-activated polypyrrole-based adsorbent (PACK) was investigated using batch and fixed-bed column techniques. The structural, thermal, and morphological properties of the PACK, analyzed by various methods, support its applicability as an adsorbent. An adsorption kinetic study revealed a preferably pseudo-second-order (R2 = 0.9996) and rate-limiting step controlled by both film and intra-particle diffusions. The thermodynamic adsorption tests resulted in negative ΔG°, ΔH°, and ΔS° values, which decreased as the temperature and concentration increased, indicating the spontaneous and exothermic adsorption over 25–45 °C. The adsorption isotherms fit the experimental data in the order of Langmuir ≈ Freundlich > Temkin, with evidence of adsorption operating well via the monolayer physical adsorption process, and maximum monolayer adsorption ranging from 520.8 to 497.5 mg/g. The breakthrough curve of the fixed-bed column experiment was modeled using the Thomas, Yoon–Nelson, and Hill models, resulting in an equilibrium capacity of 57.21 mg/g. A 73% MO recovery was achieved, indicating the possibility of column regeneration. Compared to other adsorbents reported, PACK had comparable or even superior capacity toward MO. For cost-effectiveness, similar nitrogen-containing polymeric wastes could be exploited to obtain such excellent materials for various applications.

It is shown that uncertanity relations, as well as coherent and squeezed states, are structural properties of stochastic processes with Fokker–Planck dynamics. The quantum mechanical coherent and squeezed states are explicitly constructed via Nelson stochastic quantization. The method is applied to derive new minimum uncertainty states in time-dependent oscillator potentials.

Os trabalhos pioneiros de Nelson e Winter sugeriram uma nova forma de abordar a teoria microeconômica. O artigo de Silverberg, Dosi e Orsenigo, originalmente publicado em 1988 na revista The Economic Journal e agora reproduzida na RBI, parte dos elementos centrais da abordagem de Nelson e Winter e os desenvolve para dar sustentação a um modelo teórico que procura representar a dinâmica coevolutiva da inovação e da difusão de tecnologia.

The article is devoted to diffusion models. The authors discuss the theoretical and methodological foundations of diffusion models in financial mathematics. Like the economic system, the modern world is developing rapidly. It seems impossible to predict what will happen tomorrow, how the emergence of new technologies will affect the market, and how changes in random factors will affect the product and the market as a whole. Diffusion models are one of the main methods for studying economic objects and processes. This is why it is so important to develop a diffusion model. The authors propose extending the applicability of the models by passing from Itô type stochastic equations to equations with so-called derivatives in the mean. For this, following E. Nelson, the authors introduce the concept of derivatives in the mean on the right and on the left. The equation with the derivative in the mean does not involve the Wiener process, therefore, it is not assumed in advance that the solution is diffusional. The article describes some well-known diffusion models, in which the transition from equations like an Itô type stochastic differential equation to equations satisfying a system of equations with derivatives in the mean leads to an expansion of the set of possible solutions. The authors also consider a generalization of geometric Brownian motion that satisfies a system of stochastic equations with derivatives in the mean and can cover a wider class of problems.

We propose a generalization of quantum mechanical equations in the hydrodynamic form by introducing, into the Lagrangian density, terms taking into account the diffusion velocity at zero and finite temperatures and the diffusion pressure energy of the warm vacuum. Based on this, for the model of one-dimensional hydrodynamics, we construct a system of equations that are analogous to the Euler equations, but with the inclusion of quantum and thermal effects. They are a generalization of the equations of the Nelson stochastic mechanics. The numerical analysis of the system’s solutions’ behavior determined that this system can be used to describe the process of quantum-thermal fluctuation relaxation.

We develop a method for estimating equilibrium moisture content (EMC) and fuel moisture response time, using data collected for Eucalyptus twig litter. The method is based on the governing differential equation for the diffusion of water vapour from the fuel, and on a semi-physical formulation for EMC (Nelson 1984), based on the change in Gibbs free energy, which estimates the EMC as a function of fuel temperature and humidity. We then test the model on data collected in Western Australian mallee shrubland and in Tasmanian buttongrass moorland. This method is more generally applicable than those described by Viney and Catchpole (1991) and Viney (1992). The estimates of EMC and response time are in broad agreement with laboratory-based estimates for similar fuels (Anderson 1990a ; Nelson 1984). The model can be used to predict fuel moisture content by a book-keeping method. The predictions agree wellwith the observations for all three of our data sets.

The phenomenon of post-cold war fragmentation, above all the gradual disintegration of the Soviet Union and Yugoslavia and the re-emergence of a number of sub-national (ethnic-groups, tiny an small states etc.) and supranational actors, have taken scholars of international law and politics by surprise, thus baring in a flash the link between what we have come to regards as international politics and the exclusive, central position of the nation-state. The author analyses interpretative models of fragmentation within the contemporary theory of International Relations (including new theories of Russian and Eastern-European researchers) to see which of them best captures the essence and the dynamics of the fragmentation in the post-Cold War world. In fact, "orthodox" traditional theory is in difficulty in the face of new international developments, because it continues to a state-centered approach which is increasingly outdated. It is in this fact that the bugbear of a "return to the Middle Ages", of a "Neo-Medievalization", proves to be, despite itself, an important cognitive aspect. The contemporary fragmentation is more deep than the one which followed the First World War and does not bring the previous historical circumstances, but places it outside the modern model of the community of nations : it is not a regression, but a departure from it. This study offer an investigation of the break-up of states in Eastern Europe, as well as an explanation (theoretical and empirical) of the impact of this transformation on international relations and suggests some theoretical insights. The author took into account both domestic factors and those international aspects which influenced the course of disintegration of states. It is possible to establish the causal significance of various factors and thus lay the all-important groundwork for future, possible general theory of post- Cold War fragmentation. The close of an historical cycle of concentration of power has above all produced a profound collapse of territorial state, a crisis of statehood and of the constituents of the idea of state, particularly of borders and sovereignty. At present the former Yugoslav and soviet spaces are increasingly under the sway of uncontrollable forces of disintegration.

Despite significant efforts have been directed toward reducing waste generation and encouraging alternative waste management strategies, landfills still remain the main option for Municipal Solid Waste (MSW) disposal in many countries. Hence, landfills and related impacts on the surroundings are still current issues throughout the world. Actually, the major concerns are related to the potential emissions of leachate and landfill gas into the environment, that pose a threat to public health, surface and groundwater pollution, soil contamination and global warming effects. To ensure environmental protection and enhance landfill sustainability, modern sanitary landfills are equipped with several engineered systems with different functions. For instance, the installation of containment systems, such as bottom liner and multi-layers capping systems, is aimed at reducing leachate seepage and water infiltration into the landfill body as well as gas migration, while eventually mitigating methane emissions through the placement of active oxidation layers (biocovers). Leachate collection and removal systems are designed to minimize water head forming on the bottom section of the landfill and consequent seepages through the liner system. Finally, gas extraction and utilization systems, allow to recover energy from landfill gas while reducing explosion and fire risks associated with methane accumulation, even though much depends on gas collection efficiency achieved in the field (range: 60-90% Spokas et al., 2006; Huitric and Kong, 2006). Hence, impacts on the surrounding environment caused by the polluting substances released from the deposited waste through liquid and gas emissions can be potentially mitigated by a proper design of technical barriers and collection/extraction systems at the landfill site. Nevertheless, the long-term performance of containment systems to limit the landfill emissions is highly uncertain and is strongly dependent on site-specific conditions such as climate, vegetative covers, containment systems, leachate quality and applied stress. Furthermore, the design and operation of leachate collection and treatment systems, of landfill gas extraction and utilization projects, as well as the assessment of appropriate methane reduction strategies (biocovers), require reliable emission forecasts for the assessment of system feasibility and to ensure environmental compliance. To this end, landfill simulation models can represent an useful supporting tool for a better design of leachate/gas collection and treatment systems and can provide valuable information for the evaluation of best options for containment systems depending on their performances under the site-specific conditions. The capability in predicting future emissions levels at a landfill site can also be improved by combining simulation models with field observations at full-scale landfills and/or with experimental studies resembling landfill conditions. Indeed, this kind of data may allow to identify the main parameters and processes governing leachate and gas generation and can provide useful information for model refinement. In view of such need, the present research study was initially addressed to develop a new landfill screening model that, based on simplified mathematical and empirical equations, provides quantitative estimation of leachate and gas production over time, taking into account for site-specific conditions, waste properties and main landfill characteristics and processes. In order to evaluate the applicability of the developed model and the accuracy of emissions forecast, several simulations on four full-scale landfills, currently in operative management stage, were carried out. The results of these case studies showed a good correspondence of leachate estimations with monthly trend observed in the field and revealed that the reliability of model predictions is strongly influenced by the quality of input data. In particular, the initial waste moisture content and the waste compression index, which are usually data not available from a standard characterisation, were identified as the key unknown parameters affecting leachate production. Furthermore, the applicability of the model to closed landfills was evaluated by simulating different alternative capping systems and by comparing the results with those returned by the Hydrological Evaluation of Landfill Performance (HELP), which is the most worldwide used model for comparative analysis of composite liner systems. Despite the simplified approach of the developed model, simulated values of infiltration and leakage rates through the analysed cover systems were in line with those of HELP. However, it should be highlighted that the developed model provides an assessment of leachate and biogas production only from a quantitative point of view. The leachate and biogas composition was indeed not included in the forecast model, as strongly linked to the type of waste that makes the prediction in a screening phase poorly representative of what could be expected in the field. Hence, for a qualitative analysis of leachate and gas emissions over time, a laboratory methodology including different type of lab-scale tests was applied to a particular waste material. Specifically, the research was focused on mechanically biologically treated (MBT) wastes which, after the introduction of the European Landfill Directive 1999/31/EC (European Commission, 1999) that imposes member states to dispose of in landfills only wastes that have been preliminary subjected to treatment, are becoming the main flow waste landfilled in new Italian facilities. However, due to the relatively recent introduction of the MBT plants within the waste management system, very few data on leachate and gas emissions from MBT waste in landfills are available and, hence, the current knowledge mainly results from laboratory studies. Nevertheless, the assessment of the leaching characteristics of MBT materials and the evaluation of how the environmental conditions may affect the heavy metals mobility are still poorly investigated in literature. To gain deeper insight on the fundamental mechanisms governing the constituents release from MBT wastes, several leaching experiments were performed on MBT samples collected from an Italian MBT plant and the experimental results were modelled to obtain information on the long-term leachate emissions. Namely, a combination of experimental leaching tests were performed on fully-characterized MBT waste samples and the effect of different parameters, mainly pH and liquid to solid ratio (L/S,) on the compounds release was investigated by combining pH static-batch test, pH dependent tests and dynamic up-flow column percolation experiments. The obtained results showed that, even though MBT wastes were characterized by relatively high heavy metals content, only a limited amount was actually soluble and thus bioavailable. Furthermore, the information provided by the different tests highlighted the existence of a strong linear correlation between the release pattern of dissolved organic carbon (DOC) and several metals (Co, Cr, Cu, Ni, V, Zn), suggesting that complexation to DOC is the leaching controlling mechanism of these elements. Thus, combining the results of batch and up-flow column percolation tests, partition coefficients between DOC and metals concentration were derived. These data, coupled with a simplified screening model for DOC release, allowed to get a very good prediction of metal release during the experiments and may provide useful indications for the evaluation of long-term emissions from this type of waste in a landfill disposal scenario. In order to complete the study on the MBT waste environmental behaviour, gas emissions from MBT waste were examined by performing different anaerobic tests. The main purpose of this study was to evaluate the potential gas generation capacity of wastes and to assess possible implications on gas generation resulting from the different environmental conditions expected in the field. To this end, anaerobic batch tests were performed at a wide range of water contents (26-43 %w/w up to 75 %w/w on wet weight) and temperatures (from 20-25 °C up to 55 °C) in order to simulate different landfill management options (dry tomb or bioreactor landfills). In nearly all test conditions, a quite long lag-phase was observed (several months) due to the inhibition effects resulting from high concentrations of volatile fatty acids (VFAs) and ammonia that highlighted a poor stability degree of the analysed material. Furthermore, experimental results showed that the initial waste water content is the key factor limiting the anaerobic biological process. Indeed, when the waste moisture was lower than 32 %w/w the methanogenic microbial activity was completely inhibited. Overall, the obtained results indicated that the operative conditions drastically affect the gas generation from MBT waste, in terms of both gas yield and generation rate. This suggests that particular caution should be paid when using the results of lab-scale tests for the evaluation of long-term behaviour expected in the field, where the boundary conditions change continuously and vary significantly depending on the climate, the landfill operative management strategies in place (e.g. leachate recirculation, waste disposal methods), the hydraulic characteristics of buried waste, the presence and type of temporary and final cover systems.

L’indagine prende in esame l’uso e la funzione politica della figura del martire nello spazio pubblico contemporaneo. La ricerca, pur nel riferimento consapevole alla consolidata letteratura ormai classica sull'argomento, ha tra i propri riferimenti filosofici specificatamente la teoria del discorso di Michel Foucault, con la sua metodologia dell’analisi discorsiva, e segue un approccio transdiscipli¬nare fra scienze culturali e filosofia. Essa ha come punto di partenza, come caso di studio, la rappresentazione mediale del politico e statista democristiano Aldo Moro quale martire di stato durante e dopo il suo assassinio per opera delle Brigate Rosse nel 1978. La ricerca si sviluppa sulla scorta dell’ipotesi di una connessione fra procedure di legittimazione dell’autorità politica e delle strutture di potere e l’emergere della figura del martire di Stato. Le rappresentazioni martirologiche sono considerate pratiche discorsive performanti, attraverso le quali la morte di Moro viene ad assumere il significato di un martirio per lo Stato, la Repubblica Italiana e i valori democratici. L’ipotesi di lavoro è che, attraverso l’allocazione dello statuto di martire, la morte di Moro acquisisca il significato di un atto (volontario) di testimonianza della verità assoluta e trascendentale dei diritti umani, garantiti dalla costituzione (in particolare articolo 2 della Costituzione Italiana), così come della necessità dello Stato come garante di tali diritti. Attraverso questa significazione, la figura di Moro assurge inoltre a corpo simbolico dello Stato-nazione, legittimando lo stesso e fungendo da simbolo d’identificazione collettiva con la nazione. Si tratta qui di mettere in luce il rapporto intrinseco fra la figura del martire e una narrazione mitologica dello Stato, dove mito sta a indicare un «assolutismo del reale» (Absolutismus der Wirklichkeit). La ricerca vuole altresì mettere in luce la dimensione strumentale delle rappresentazioni martirologiche di Aldo Moro, le quali hanno mantenuto e tuttora mantengono un’efficacia performativa nonostante il chiaro ed evidente rifiuto, espresso da Moro stesso, di essere sacrificato «in nome di un astratto principio di legalità.» La ricerca si propone di dimostrare la valenza di tale ipotesi di lavoro attraverso l’analisi dell’apparizione e diffusione delle rappresentazioni martirologiche di Aldo Moro in forme mediali differenti nell’intervallo temporale di quattro decenni. Il corpus delle fonti preso in esame include: articoli di giornali e riviste, i documenti prodotti da Moro e della Brigate Rosse durante i 55 giorni di sequestro, trasmissioni televisive (documentari e reportage), opere letterarie e cinematografiche. La teoria discorsiva e l’analisi archeologico-genealogica sviluppate da Michel Foucault fungono da base teorico-metodologica del lavoro. Il taglio transdisciplinare dell’indagine rende necessaria la distinzione di due diversi piani di ricerca. In primo luogo, ci si pone come obiettivo di individuare e analizzare le diverse rappresentazioni come elementi di una formazione discorsiva il cui tema comune è la morte di Aldo Moro. Si tratta di operare una ricognizione, attraverso il lavoro empirico, dei modi di rappresentare l’uccisione di Aldo Moro e di individuare le regole che determinano ciò che può essere detto e mostrato a tale riguardo. In secondo luogo, a partire da qui, ci si propone di fare un’analisi critica dell’uso e della funzione del linguaggio e della simbologia di matrice religiosa all’interno della forma¬zione discorsiva presa in esame. L'obiettivo è di mettere così in luce non solo il dispositivo di legittimazione politica che presiede alla costruzione della figura del martire, ma anche la sua polivalenza.

A continuous random walk (CRW) turbulent diffusion model was developed for Lagrangian particles within flow fields simulated by hybrid RANS/LES methodologies. For RANS flow-fields, the conventional time-scale and length-scale constants were determined by the turbulence intensity and dissipation values computed by the single-phase solver with a k-ω (Menter SST) model and subsequent comparison with turbulent particle diffusion experimental results of Snyder & Lumley (1971). This allowed validation against data for four particle types ranging from hollow glass to copper shot in grid-generated turbulence. The stochastic diffusion model was then extended to utilize the Nichols-Nelson k-ω hybrid RANS-LES turbulence model in a more complex turbulent flow resulting from the unsteady, three dimensional wake of a cylinder at Mach number of 0.1 and Reynolds number (ReD) of 800. The gas flow was computed with a 5th-order upwind-biased scheme. Throughout the wake, the sub-grid random walk model yielded good predictions of particle diffusion as compared with DNS. Also, these results indicate that crossing trajectory effects and inertia-based drift corrections are critical to handling a variety of particle Stokes numbers as well as regions of non-homogeneous turbulence, even when most of the kinetic energy is captured with the resolved-scales of an LES approach.

Leak-Before-Break (LBB) has been applied in various industries for decades, and this paper explores using it for a new application. In the refining industry, various process units contain hydrogen at elevated temperatures where high temperature hydrogen attack (HTHA) can occur. This mechanism involves the reaction between hydrogen and carbides to form methane, but also the diffusion of hydrogen occurs in the steel. Under certain temperature and hydrogen partial pressures, the methane formation can cause grain boundary cavitation which leads to fissuring and eventually macroscopic cracking. Generally one designs to avoid such cracking from occurring following the so-called “Nelson Curves” contained in API RP 941; however, in recent years it has been found that non-stress relieved carbon steels are susceptible to HTHA below the original API 941 curve. As a result, the refining industry has experienced a number of leaks in piping and vessels. This paper presents some developmental efforts to apply LBB to non-stress relieved seamless carbon steel piping girth welds susceptible to (HTHA) cracking in refinery applications. Much of this approach builds on analyses, results, and experience from the commercial nuclear industry LBB efforts over the last 30 years. This paper will discuss the results of both mechanical testing as well as detailed modelling efforts to evaluate LBB technology to this new application for circumferential cracks, which to date implies that LBB may be applicable to seamless pipe girth welds. Cracks in tees or other components were not addressed in this work. Axial cracks in seam welds are not addressed in this work.

La necessità di reagire a situazioni nuove in ambito urbano, come quelle legate gli effetti dei cambiamenti climatici, sta favorendo lo sviluppo, in alcune città europee e americane, di azioni innovative da parte della cittadinanza. Se da un lato, infatti, sono ampiamente sperimentate politiche pubbliche urbane di mitigazione e adattamento ai cambiamenti climatici, dall'altro iniziano a fiorire esperienze 'dal basso' che si manifestano nello spazio quotidiano attraverso processi di cura e tutela del territorio promossi dagli abitanti. La traduzione fisica di queste pratiche sembra mostrare l'emergere di un nuovo tipo di spazio pubblico, dal forte carattere sociale, in cui si manifestano le volontà ecologiche della comunità. Queste esperienze, nate in America ma che hanno ormai una larga diffusione in altre parti del mondo, consistono in azioni più o meno organizzate, coordinate da amministrazioni e università, ma anche da associazioni studentesche, collettivi artistici e comunità di quartiere, e si attuano grazie alla presenza di una cittadinanza attiva e ricettiva. Il seguente intervento sostiene l'ipotesi che simili fenomeni rappresentino una risorsa importante per la conoscenza dei luoghi e lascino intravedere lo sviluppo di una rinnovata prospettiva di responsabilità condivisa e presa di coscienza sulle questioni ambientali. Si tenterà dunque di illustrare gli elementi che favoriscono un progetto condiviso di convivenza col rischio; delineare e definire quelli che sembrano essere i caratteri di un nuovo tipo di spazio pubblico; comprendere come la tecnologia 2.0 possa divenire dispositivo per lo scambio di risorse e di informazioni. Si tratta di una prima ricognizione che però lascia intravedere la ricchezza degli approcci e di possibili soluzioni.