1,721,048 research outputs found
Effect of Mg2+ and Ca2+ on the response to nickel toxicity in a serpentine endemic and nickel accumulating species
No full textThe effect of Ca2+, Mg3+ and Ni2+ on root elongation was studied in Alyssum bertolonii Desv., a nickel-accumulating and serpentine endemic species. The results confirm the detoxifying action of Ca2+ which reduces the toxic effect of Mg2+ and Ni2+ on root development. In addition, Ca2+ and Mg2+ interact positively in depressing Ni2+ uptake. The combined effect of these two ions is of relevance for the mechanism of nickel tolerance in A. bertolonii
Response to cadmium in higher plants
No full textThe paper summarizes present knowledge in the field of higher plant responses to cadmium, an important
environmental pollutant. The principal mechanisms reviewed here include phytochelatin-based sequestration and
compartmentalization processes, as well as additional defense mechanisms, based on cell wall immobilization, plasma
membrane exclusion, stress proteins, stress ethylene, peroxidases, metallothioneins, etc. An analysis of data taken
from the international literature has been carried out, in order to highlight possible ‘qualitative’ and ‘quantitative’
differences in the response of wild-type (non-tolerant) plants to chronic and acute cadmium stress. The dose-response
relationships indicate that plant response to low and high cadmium level exposures is a very complex phenomenon
indeed: cadmium evokes a number of parallel and:or consecutive events at molecular, physiological and morphological
levels. We propose that, above all in response to acute cadmium stress, various mechanisms might operate both
in an additive and in a potentiating way. Thus, a holistic and integrated approach seems to be necessary in the study
of the response of higher plants to cadmium. This multi-component model, which we would call ‘fan-shaped’
response, may accord with the Selyean ‘general adaptation syndrome’ hypothesis. While cadmium detoxification is a
complex phenomenon, probably under polygenic control, cadmium ‘real’ tolerance—found in mine plants or in plant
systems artificially grown under long-term selection pressure, exposed to high levels of cadmium—seems to be a
simpler phenomenon, possibly involving only monogenic:oligogenic control. We conclude that, following a ‘pyramidal’
model, (adaptive) tolerance is supported by (constitutive) detoxification mechanisms, which in turn rely on
(constitutive) homeostatic processes. The shift between homeostasis and ‘fan-shaped’ response can be rapid and
involve quick changes in (poly)gene expression. Differently, the slow shift from ‘fan-shaped’ response to ‘real’
cadmium tolerance is caused and affected by long-term selection pressure, which may increase the frequency (and
promote the expression) of one or a few tolerance gene(s)
Physiological role of root surface phosphatases in adaptation strategies of Alyssum bertolonii Desv. to serpentine edaphic conditions.
No full textRoot surface phosphatase activity and P nutrition in the presence of Ni2+ was studied in Alyssum bertolonii DESV., a Ni-accumulating species of Tuscan serpentine soils. Increasing external concentrations of inorganic phosphate reduced phosphatase activity. In the presence of an inhibiting concentration of inorganic phosphate, Ni2+ stimulated phosphatase activity of seedlings treated for seven days but did not affect root P content. Root surface phosphatase showed a higher activity towards phytate in comparison with other P organic substrates. Increased P levels were detected in the roots of Ni-treated seedlings supplied with phytate. We discuss the possible physiological role of root cell wall phosphatases, which in this study was shown to be tolerant to Ni2+
STUDIO DI UN SISTEMA DI CAPTAZIONE SOLARE A CONCENTRAZIONE CON TORRE ED ELIOSTATI IN TOSCANA
No full textNell’ambito delle attività di ricerca volte a valutare le effettive possibilità di diffusione delle fonti rinnovabili, e in particolare del solare a concentrazione (CSP), il presente lavoro descrive lo studio di un sistema di captazione solare a concentrazione basato su torre ed eliostati da installare nel territorio toscano. Il sistema è costituito da un campo di eliostati con inseguimento su due assi che concentrano tramite specchi la radiazione solare su un ricevitore posto alla sommità di una torre così da riscaldare un appropriato fluido termovettore. Lo studio, svolto avvalendosi di un strumento informatico appositamente sviluppato in ambiente Matlab, ha avuto come scopo ultimo la definizione della configurazione che massimizza l’efficienza di captazione.
A tale scopo, dopo aver caratterizzato il sito prescelto in termini di disponibilità solare e aver definito i movimenti orari di inseguimento biassale di ciascun eliostato così da garantire la concentrazione della radiazione solare diretta sul ricevitore posto sulla sommità della torre, è stata valutata l’influenza sulle prestazioni del sistema di captazione dei suoi parametri geometrici caratteristici, quali l’altezza della torre, il numero di eliostati, il posizionamento di ciascuno di essi all’interno del campo di captazione (layout). L’efficienza mostra un massimo rispetto all’altezza della torre ed è maggiore per un numero minore di eliostati. I campi specchi con le prestazioni migliori sono risultati quelli con rapporto tra la dimensione nord-sud e quella est-ovest prossimo all’unità.
E’ stato infine effettuato il dimensionamento di un sistema di captazione per il sito prescelto con un’efficienza superiore al 60% e con una quantità di energia termica fornita annualmente al fluido termovettore pari a circa 200 kWh per ogni metro quadrato di superficie occupata dal campo. Se fosse ubicato in Sicilia, tale sistema di captazione risulterebbe possedere prestazioni superiori di circa il 50%
Consignment stock theory with a fixed batch manufacturing process
No full textThis paper deals with stock control in a supply chain. The focus is on consignment stock (CS), an innovative
collaborative relationship, which can create a win–win situation between the vendor and the buyer. Recently
some analytical formulations have been proposed to optimise CS, and the present paper extends these models
by considering a new critical factor: a fixed batch production process at the vendor’s plant. This kind of
production is typical if there are batch processing machines that can hold and simultaneously process a finite
number of items, such as kilns for long heat treatment. Specifically, we consider a deterministic single-vendor
single-buyer system. The buyer consumes a single product at a constant rate and is replenished by the vendor
who produces in batches and incurs set-up costs. Each batch is dispatched to the buyer in a number of
shipments, some of which may take place while production is still running. To minimise total operating costs
(that is, manufacturing, replenishment and holding), two alternative production and shipment policies are
proposed and analytically formulated as integer optimisation models. A step by step heuristic procedure to
obtain the optimal solution is finally presented and demonstrated through numerical examples
Energy and economic performance assessment of the novel integration of an advanced configuration of liquid air energy storage plant with an existing large-scale natural gas combined cycle
No full textThis article proposes the novel integration of an advanced configuration of Liquid Air Energy Storage (LAES) plant and an additional gas turbine cycle with an existing large-scale Natural Gas Combined Cycle (NGCC). A novel mode of exploiting the electric energy stored within the LAES plant and additional gas turbine cycle in combination with the existing NGCC is aimed at increasing its revenues in the electricity market. The energy performance analysis of the integrated plant at off-design conditions is carried out in presence of simultaneous changes of the pressure in the liquid air storage site (p3) and of the pressure at the outlet of the cryogenic pump in the discharging circuit (p25). The maximum storage efficiency is 2.173. The uncertainty economic analysis is performed in three alternative economic scenarios - expected, pessimistic and optimistic - in order to assess the profitability of the installation and operability of the integrated plant compared with the stand-alone NGCC. In the expected scenario, the integrated plant leads to profitability in the whole range of each p3 and p25, with the exception of the minimum value of p25. With varying p3 and p25, the profitability is always absent in the pessimistic scenario, whereas it is always present in the optimistic one. The proposed approach can be extended to the integration of an LAES plant with a generic existing large-scale thermal power plant in order to increase its revenues in the electricity market
Potential for Cogeneration Through Solar Energy in the Tissue Industry: Technical and Economic Aspects
No full textThis paper investigates the feasibility of a solar cogeneration system, as a solution to reduce fossil fuel consumption and greenhouse gas emissions in a tissue mill, located in the industrial district of Lucca (North Italy). Although the paper sector has a high theoretical potential for the use of solar energy, the implementation of a solar thermal plant may not be economically sustainable, due to the expensive investment of such a system and to the uncertainty of future benefits. These issues are even more relevant in a moderate climate, where the high variability of the direct normal irradiance can prevent the technical feasibility of the plant. To demonstrate the possible use of solar energy in paper mills, a concentrating solar power plant with thermal storage, based on parabolic trough technology, has been chosen as a feasible solution for combined heat and power generation and its technical and economical performances have been evaluated through an extensive simulation analysis. The results obtained prove the feasibility of the proposed system and assure a good economic profitability. Results also show how the possibility of benefiting from economic incentives for renewable electric power generation is fundamental to reduce the payback period and to assure the profitability of the investment
A novel game theory based exit selection model in emergency conditions
No full textIn this paper, a new game theory based approach for the evacuees exit selection in emergency conditions is presented. It is founded on the theoretical concepts of multi-stage games with perfect information. In particular, an evacuee is a player and the available actions for a generic player are the accessible emergency exits. The developed mathematical model involves several psychological parameters, in order to make the emergency exit choice also affected by the individual character. Moreover, an evacuation simulation model incorporating this novel approach is shown. The model involves many other parameters and aspects attempting to obtain a satisfactory representation of the actual evacuation process and of the human behavior in emergency conditions. Finally, the effectiveness of the model is demonstrated with a simulative study
ANP/RPN: A Multi Criteria Evaluation of the Risk Priority Number
No full textThis paper presents an advanced version of the failure mode effects and criticality analysis (FMECA), whose capabilities are enhanced; in that the criticality assessment takes into account possible interactions among the principal causes of failure. This is obtained by integrating FMECA and Analytic Network Process, a multi-criteria decision making technique. Severity, Occurrence and Detectability are split into sub-criteria and arranged in a hybrid (hierarchy/network) decision-structure that, at the lowest level, contains the causes of failure. Starting from this decision-structure, the Risk Priority Number is computed making pairwise comparisons, so that qualitative judgements and reliable quantitative data can be easily included in the analysis, without using vague and unreliable linguistic conversion tables. Pairwise comparison also facilitates the effort of the design/maintenance team, since it is easier to place comparative rather than absolute judgments, to quantify the importance of the causes of failure. In order to clarify and to make evident the rational of the final results, a graphical tool, similar to the House of Quality, is also presented. At the end of the paper, a case study, which confirms the quality of the approach and shows its capability to perform robust and comprehensive criticality analyses, is reporte
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