1,210 research outputs found
Why a simple herding model may generate the stylized facts of daily returns: Explanation and estimation
No full textThe paper proposes an elementary agent-based asset pricing model that, invoking the two trader types of fundamentalists and chartists, comprises four features: (i) price determination by excess demand; (ii) a herding mechanism that gives rise to a macroscopic adjustment equation for the market fractions of the two groups; (iii) a rush towards fundamentalism when the price misalignment becomes too large; and (iv) a stronger noise component in the demand per chartist trader than in the demand per fundamentalist trader, which implies a structural stochastic volatility in the returns. Combining analytical and numerical methods, the interaction between these elements is studied in the phase plane of the price and a majority index. In addition, the model is estimated by the method of simulated moments, where the choice of the moments reflects the basic stylized facts of the daily returns of a stock market index. A (parametric) bootstrap procedure serves to set up an econometric test to evaluate the model's goodness-of-fit, which proves to be highly satisfactory. The bootstrap also makes sure that the estimated structural parameters are well identified. --structural stochastic volatility,method of simulated moments,autocorrelation pattern,fat tails,bootstrapped p-values
Low Removal of As (V) and Cr (VI) by POU Devices Until Enabled with Selective Ion Exchange Media
No full textabstract: Consumers purchase point-of-use (POU) devices to further improve the quality of water provided by the tap. As awareness increases of harmful contaminants, an emerging market of advanced POU with claims of removing beyond what a typical activated carbon filter is capable of, such as heavy metals. This research compares four commercially available pitcher filters; two that claim to remove arsenic and hexavalent chromium and two without such claims. Arsenate (As (V)) and hexavalent chromium (Cr (VI)) co-occur in natural geologic formations and are known to have harmful effects on humans when ingested. Pitcher filters Epic Water Filter and Aquagear had claims of removing both As (V) and Cr (VI) up to 99% with a capacity of nearly 200 gallons. In contrast, pitcher filters Brita and Pur had no claims for removal of As(V) and Cr(VI) with a 40-gallon lifespan. A series of experiments were conducted to first determine the efficiency of each filter, then to add the ability or improve removal of As(V) and Cr(VI) in one filter for future design implementations. Experiment 1 was conducted by treating 100 gallons of spiked tap water (50 ppb for As (V) and 100 ppb for Cr (VI)) with each filter. All four pitcher filters showed low performance, resulting in Pur with the lowest removal percentage of 2% and Aquagear with the highest percentage 16% for As (V). For Cr (VI) Pur performed the worst with a removal of 5% and Brita had the best performance of 15%. The functionality of Brita was improved by embedding a selective ion exchange media, which when nanotized successfully removed Cr (VI) in previous studies. The optimal mass of resin to add to the pitcher was experimentally determined as 18.9 grams through Experiment 2. Finally, Experiment 3 compared an alternative placement of the resin material using the same 18.9 grams. The performance in Experiment 3 was significantly worse than Experiment 2. The final recommendation for future design implementation was to add 18.9 grams of SIR-700 resin below the filter media for optimum performance. Overall, the results demonstrate the limited removal of As(V) and Cr(VI) by the four commercial pitcher filters and show that by adding selective ion exchange media, the POUs can be nano-enabled to effectively remove As(V) and Cr(VI) from water
Control analysis of periodic phenomena in biological systems
No full textGeneral rights It is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), other than for strictly personal, individual use, unless the work is under an open content license (like Creative Commons). Disclaimer/Complaints regulations If you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: https://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible. Download date: 29 Jun 2019 Control Analysis of Periodic Phenomena in Biological Systems Boris N. Kholodenko,* , † Oleg V. Demin, ‡ and Hans V. Westerhoff §,| Department of Pathology, Anatomy and Cell Biology, Thomas Jefferson UniVersity, 1020 Locust Street, Philadelphia, PennsylVania 19107, A.N. Belozersky Institute of Physico-Chemical Biology, Moscow State UniVersity, 119899 Moscow, Russia, Department of Microbial Physiology, Free UniVersity, De Boelelaan 1087, NL-1081 HV Amsterdam, The Netherlands, and E. C. Slater Institute, Biocentrum, UniVersity of Amsterdam, Plantage Muidergracht 12, The Netherlands ReceiVed: July 31, 1996 In Final Form: January 7, 1997 X Principles of the control and regulation of steady-state metabolic systems have been identified in terms of the concepts and laws of metabolic control analysis (MCA). With respect to the control of periodic phenomena MCA has not been equally successful. This paper shows why in case of autonomous (self-sustained) oscillations for the concentrations and reaction rates, time-dependent control coefficients are not useful to characterize the system: they are neither constant nor periodic and diverge as time progresses. This is because a controlling parameter tends to change the frequency and causes a phase shift that continuously increases with time. This recognition is important in the extension of MCA for periodic phenomena. For oscillations that are enforced with an externally determined frequency, the time-dependent control coefficients over metabolite concentration and fluxes (reaction rates) are shown to have a complete meaning. Two such time-dependent control coefficients are defined for forced oscillations. One, the so-called periodic control coefficient, measures how the stationary periodic movement depends on the activities of one of the enzymes. The other, the socalled transient control coefficient, measures the control over the transition of the system between two stationary oscillations, as induced by a change in one of the enzyme activities. For forced oscillations, the two control coefficients become equal as time tends to infinity. Neither in the case of forced oscillations nor in the case of autonomous oscillations is the sum of the time-dependent control coefficients time-independent, not even in the limit of infinite time. The sums of either type of control coefficients with respect to time-independent characteristics of the oscillations, such as amplitudes and time averages, do fulfill simple laws. These summation laws differ between forced oscillations and autonomous oscillations. The difference in control aspects between autonomous and forced oscillations is illustrated by examples. Introduction Quantitative approaches have led to significant advances in the understanding of the control of metabolic and information pathways under stationary conditions. 1-9 In a biochemical/ biophysical reaction system such as a metabolic pathway in a living cell the control exerted by any enzyme on any steadystate flux (reaction rate) or concentration can be quantified in terms of the corresponding control coefficient defined by metabolic control analysis (MCA). The (stationary) control coefficient is the relative difference between the two steadystates in pathway flux or metabolite concentration, divided by the causative fractional change in the enzyme's activity, extrapolated to infinitesimally small change. Living cells also exhibit various important time-dependent phenomena however. In close vicinity of the (asymptotically) stable steady state the control over a relaxation process has been analyzed by Results A. Definitions of Time-Dependent Control Coefficients. A1. Forced Oscillations. Let us suppose that a system under study is exposed to periodic changes in the environment, resulting in periodic changes of some system parameters, e.g., kinetic constants and the concentration of "external" metabolites. Such a situation can also be described in terms of some periodic external force influencing the system. Here T is the period of the external force and e ) (e 1 , e 2 , ..., e n ) is the vector of the enzyme concentrations. Stationary periodic behavior caused by a periodic external force is called a forced oscillation. During the period of such an oscillation (T), the vector of metabolite concentrations (x) follows a closed trajectory. The system behavior described by eq 1, as well as the system behavior outside that closed trajectory is dictated by chemical processes developing in time according to the kinetic rate equations. Combination of these rates with the map of the chemical network leads to differential equations for all of the independent metabolic variables (x), the so-called chemical kinetics differential equations (eq A1 in Appendix A). The correspondence between the physical system and the mathematical equations allows one to use the work "solution" to refer to "system behavior". We shall assume that the eigenvalues of the Jacobian of this system of differential equations have negative real parts at all the points of the periodic trajectory. Under these conditions, the periodic solution, x i per (t), to eq A1 is unique and asymptotically stable. 17 So-called "conservative" systems (often considered in physics) lack the dissipation of free energy. Such systems usually have an infinitely large number (continuum) of periodic solutions determined by the initial conditions and will not be considered here. Here we consider isothermal, isobaric systems that continuously dissipate free energy, as found in chemical reaction systems Considering (fractional) changes in a steady-state periodic solution caused by a change in a particular enzyme concentration (e j ), one can define (steady-state) "periodic" control coefficients over metabolite concentrations and reaction rates (fluxes) as follows: Since the period T does not depend on system parameters, it follows from eq 1 that the control coefficients, C j x (t), are periodic functions of T. If the periodic solutions for the reaction rates can assume zero values at some time values, one should consider the non-normalized flux control coefficients 13 in eq 3. In eq 3 periodic control coefficients are defined as formal derivatives of the asymptotically stable periodic solution (eq 1) with respect to a parameter of choice (e.g., e j ) (cf. ref 43). This definition corresponds to the comparison of two steadystate periodic solutions (closed trajectories) that differ in e j by an infinitesimal change, ∆e j . Most importantly, these two solutions are synchronized by the periodic external force. In fact, a one-to-one correspondence exists between any point of either closed trajectory and a value of the periodic force. Hence, also between pairs of the points of the two different trajectories, a one-to-one correspondence exists. This synchronization makes it possible to assign an operational meaning to the (steady-state) periodic control coefficients in terms of (infinitesimal) perturbations (see below and Appendix A). Alternativley, let us consider the periodic solution x per -(t,e;t*,x*) and the other solution x tr (t,e+∆e;t*,x*) that occurs when a particular enzyme concentration (e j ) is perturbed by ∆e j at the moment t* (here and below the superscript "tr" specifies the transition process). The function x tr (t,e+∆e;t*,x*) is not periodic. It describes the transition process from the periodic solution corresponding to the value e j to the periodic solution corresponding to the value e j + ∆e j . Initially (t ) t*), the two Control Analysis of Periodic Phenomena J. Phys. Chem. B, Vol. 101, No. 11, 1997 2071 solutions coincide. At any time t > t*, the relative difference between x tr and x per divided by ∆e j /e j shows how the particular enzyme e j affects the metabolite concentration or flux during the transition. The resulting function, obtained in the limit of infinitesimally small ∆e j , is called a transient (time-dependent) control coefficient: Contrary to periodic control coefficients transient control coefficients do not depend on time periodically, although they do depend on time. Appendix A shows that in the case of forced oscillations the transient control coefficients (eq 4) tend to the corresponding periodic control coefficients (eq 3) as time tends to infinity: This clarifies the operational meaning of the formal periodic control coefficients defined by eq 3. They quantify the control when a system has already relaxed to a new oscillation pattern after a change in the activity of a particular enzyme. Appendix B shows that the periodic and the transient control coefficients satisfy the same variation equation. Periodic control coefficients are given by the unique periodic solution of the variation equation, whereas transient control coefficients are determined as a time-dependent solution, assuming the initial conditions equal to zero. To come to grips with this result, one may revisit the definitions given by eqs 3 and 4 and note that both the periodic and the transient solutions for metabolite concentrations and fluxes must satisfy the same kinetic equations (see Appendix A, eq A1). For explicit expressions for the periodic and transient control coefficients see Appendix B (cf. ref 38). It is instructive to compare these periodic and transient control coefficients, which describe the control of forced oscillations, to the corresponding control coefficients defined for perturbations near asymptotically stable steady states. 38,44 The periodic control coefficients (eq 3) defined by the formal differentiation of steady-state periodic solution correspond to the traditional steady-state control coefficients. Indeed, in standard MCA, eq 3 will define the usual control coefficients if the steady-state concentrations and fluxes are substituted in this equation for the periodic ones. The transient control coefficients of an oscillating system (eq 4) correspond to the time-dependent control coefficients, as introduced by Acerenza et al. A2. Autonomous Oscillations (Limit Cycles). The forced oscillations considered above arose from the influence of a periodic external force on a system that exhibited asymptotically stable steady states in the absence of that force. By contrast, autonomous oscillations occur at time-independent (internal and external) parameter values in systems in which the corresponding steady states are unstable. For autonomous oscillations one can define formally the control coefficients, C j x (t) and C j J (t), analogously to eq 3, i.e., as the log-log derivatives of a unique periodic solution with respect to the enzyme concentrations (or as the non-normalized derivatives if periodic reaction rates assume zero values at some time moments). However, in contrast to the case of forced oscillations these control coefficients do not depend on time strictly periodically. Moreover, they do not exist when time tends to infinity. To illustrate this, let us present a periodic solution (x k per ) by its Fourier series. We emphasize that both the Fourier coefficients and the frequency (ω) depend on systemic parameters, i.e., on enzyme concentrations (e): Here x k h (e) denotes hth Fourier coefficient and i is the imaginary unity. Differentiating the Fourier series (6) with respect to a particular enzyme concentration, e j (see eq 3), one obtains for the control coefficients, C j x k (t), Because of the second term on the right-hand side of this x i tr (t,e j +∆e j ;t*,x*) -x i per (t,e j ;t*,x*) J k tr (t,e j +∆e j ;t*,x*) -J k per (t,e j ;t*,x*) 2072 J. Phys. Chem. B, Vol. 101, No. 11, 1997 Kholodenko et al. equation, which is proportional to t, the control coefficients, C j x k (t), do not depend on time periodically. Since this term becomes unlimited with time, the coefficients C j x k (t) cannot be defined when time tends to infinity. The transient control coefficients, tr C j x k (t), are defined according to eq 4. Hence, they can be found by solving the variation equation (cf. ref 38 and Appendix B). mor the case of autonomous oscillations it has been proved 46 that no solution of the variation equation exists at time tending to infinity. Therefore, also the transient control coefficients with respect to metabolic concentrations or fluxes during the transition from the initial to a perturbed closed trajectory can only be defined for limited time intervals. In the limit of infinite time this control coefficient does not exist either. The question arises why both control coefficients, C j x (t) and tr C j x (t), fail to exist when the time of the observation of the periodic or transition process tends to infinity. For the control coefficients, C j x (t), this is explained by the phase difference between the original and perturbed oscillations, which continues to increase with time. For the control coefficients tr C j x (t), the time-dependent phase difference between the transition and the periodic movements is the culprit. Although the initial and the perturbed trajectories are very close in concentration space, due to the dependence of oscillation frequency on a perturbed parameter, e j , the phase difference does not vanish with vanishing of ∆e j when time tends to infinity; the infinitesimal difference in phase is amplified infinitely. From the reasoning above one may conclude that in the case of autonomous oscillations due to divergence of the initial and the perturbed movements, the control coefficients determined by either eq 3 or eq 4 cannot describe the control exerted by enzymes over periodic values of metabolic concentrations and reaction rates. However, the same reasoning shows that the control over those characteristics of self-sustained oscillations that do not depend on the phase of the movement can be defined (at any time of observation). The log-log derivatives of these time characteristics (Y) with respect to enzyme concentrations determine the coefficients, C j Y , that describe the control of (stationary) self-sustained oscillations. For instance, the control coefficients over the amplitude and period of oscillations and over various mean values do exist. B. Properties of Time-Dependent Control Coefficients in an Example of Forced Oscillations. We shall consider a simple example where a periodic solution (eq 1) and, hence, periodic control coefficients (eq 3) can be found analytically, as functions of time and parameters. This will make it possible to illustrate a number of the control properties, such as the variations of the control distribution with time, and to test whether the summation theorem that is true for steady-state control coefficients continues to apply in the case of forced oscillations. Scheme 1 shows a metabolic chain of two reactions, We shall suppose that the substrate concentration (S) changes periodically, and the product concentration (P) is kept zero: Here S 0 is the substrate concentration in the absence of (external) periodic force, ω 0 is the frequency of the periodic force, and a < 1 is the amplitude of the oscillation of the substrate concentration. Let us assume that the reaction rates, V 1 and V 2 , are linear functions of metabolite concentrations: Here k (i , i ) 1, 2, are the kinetic constants; e 1 , e 2 are the total enzyme concentrations; and x is the concentration of the intermediate. Thanks to the linearity of eq 9 with respect to x, its periodic solution (under the influence of the periodic force described by eq 8) can be found readily (see Appendix C): Substituting eq 10 into the rate equations (9), the periodic solution for the fluxes through the first (J 1 ) and the second (J 2 ) reactions are obtained: Here J 0 is the steady-state flux. A 1 and A 2 are the amplitudes of the oscillations of the reaction rates, and is the initial phase of oscillations of the J 1 (the explicit expressions for A 1 , A 2 , and are given in Appendix C). From eqs 11 it follows that the fluxes through the first and the second reactions differ at most times. Only their averages are equal. Consequently, in contrast to the case of systems at steady states, the control coefficients over the time-dependent fluxes through sequential reactions in oscillating systems will differ (see (10) S f X f P (scheme 1) Control Analysis of Periodic Phenomena J. Phys. Chem. B, Vol. 101, No. 11, 1997 2073 tude of the substrate oscillation increases further, even the direction of reaction rates changes during the period and such that they equal zero at some moments. In this case the control can become infinite. If the amplitude of the oscillation of the pathway substrate is small (a , S 0 ), the periodic control coefficients do not cross, but oscillate near the corresponding steady-state values (not shown). Using the explicit expressions for periodic control coefficients (see Appendix C), one can show readily that the summation theorem, which governs the steady-state control coefficients 4 and time-dependent control coefficients for the relaxation near steady states 38 (it requires the sum of these coefficients to be equal to 1), is not valid for periodic control coefficients: C. Summation Theorems. C1. Summations in the Case of a Forced Oscillation. Since the reactions rates depend linearly on the enzyme concentrations (activities), simultaneous transformation of these concentrations, of the time, and of the frequency of a periodic external force, leads to a new equation system that coincides with the initial system after eliminating the superscript (*). Therefore, if the initial conditions are the same, metabolite concentrations of the transformed system at the moment t/λ will coincide with concentrations of the initial system at the moment t, whereas the fluxes will increase by factor λ (proportional to the new enzyme activities): Applying to eq 14 Euler's theorem on homogeneous functions, one arrives at Although for forced oscillations the control coefficients with respect to the frequency of the external force (C ω 0 x , C ω 0 J ) can be defined formally as the derivative of the periodic solution with respect to ω 0 , they become unlimited as time tends to infinity. This is explained by the phase divergence of the initial periodic movement with the frequency ω 0 and the perturbed one with the frequency ω 0 + dω 0 , corresponding to the infinitesimal change in ω 0 . This phase difference does not remain infinitesimal at infinite times (cf. the case of autonomous oscillations above). Moreover, also the transient control coefficients defined by eq 4, in which the derivatives should be taken with respect to ω 0 (instead of e j ), become unlimited at infinitely large time. Hence, in a general case the summation theorems given by eqs 15 and 16 have no operational meaning as t tends to infinity. Note, however, that the sums given by the first terms in eqs 15 and 16 do exist at infinitely large times. For the above example of forced oscillations, eq 12 shows that the sum of flux control coefficients (the first term in eq 16) depends periodically on time. One may note that if the form (amplitude) of the oscillation in x were independent of the forcing frequency ω 0 , x could be written as In this case, the second and third term of eqs 16 disappear and the classical summation theorems, but now for periodic control coefficients, are retrieved. This condition holds in electrical networks without capacitances, and in linear chemical networks where the variable metabolites occur in such small volumes that the corresponding relaxation times are much smaller than the period of the applied oscillation. As illustrated by eq 10, Dependencies of periodic and steady-state enzyme control coefficients of the linear pathway of scheme 1 on time. Lines 1 and 3 refer to the periodic control coefficients over flux J1 with respect to the first (1) and the second (3) enzyme. Lines 2 and 4 refer to steadystate control coefficients over flux J1 with respect to the first (2) and the second (4) enzyme. The magnitudes of the parameters were k1 ) 35, k2 ) 30, k-1 ) 25, k-2 ) 1, S0 ) 20, e1 ) 0.1, e2 ) 0.05, a ) 0.1, and ω ) 1. Phys. Chem. B, Vol. 101, No. 11, 1997 Kholodenko et al. through the frequency dependence of the amplitude of the oscillation in x per , the form of oscillations in a metabolic network often depends on the frequency of the applied oscillations. The following summation theorems hold for the control coefficients of enzymes over the amplitude of stationary oscillations of metabolic concentrations (A x ) or fluxes (A J ) and their average values over the period (x j, J h) in the case of oscillations forced at a frequency ω 0 : In the example considered above (section B) the control coefficients over the amplitudes of metabolic concentrations and fluxes with respect to the frequency of the external force and of the enzyme concentrations can be calculated readily (see Appendix C). One can se
A model of yeast glycolysis based on a consistent kinetic characterisation of all its enzymes
No full textpeer reviewedWe present an experimental and computational pipeline for the generation of kinetic models of metabolism, and demonstrate its application to glycolysis in Saccharomyces cerevisiae. Starting from an approximate mathematical model, we employ a ‘‘cycle of knowledge’’ strategy, identifying the steps with most control over flux. Kinetic parameters of the individual isoenzymes within these steps are measured experimentally under a standardised set of conditions. Experimental strategies are applied to establish a set of in vivo concentrations for isoenzymes and metabolites. The data are integrated into a mathematical model that is used to predict a new set of metabolite concentrations and reevaluate the control properties of the system. This bottom-up modelling study reveals that control over the metabolic network most directly involved in yeast glycolysis is more widely distributed than previously thought.The Manchester Centre for Integrative Systems Biolog
Ultra-High Energy Cosmic Rays and Theirs Detection in Auger Project
No full textrigorozniprace. Michael Prouza: Kosmicke zdfeni extremne vysokych energii a jeho detekce v projektu A UGER Tato prace pfinasf pfehled principu pozorovam kosmickeho zafem s extremnevysokymi energiemi a popis designu a fungovam Observatore Pierra Augera (OPA). Specialni po- zornost je venovana fluorescencnfmu detektoru (FD) tohoto v soucasnosti nejvetsiho de- tektoru kosmickehosafem na svete, umi'steneho v argentinske pampe. Na zvlaste detailni urovni je diskutovano nekolik originalnich pffspevku autora teto prace: Zaprve, byl studovan vliv magnetickeho pole Galaxie na sifenf kosmickeho zafeni a byla provedena statisticka analyza prostoroveho rozlozeni ziskanych vysledku. 2adruhe, byl vyvinut specialni programovy kod, ktery umoznuje pozorovani s FD, kdyg je Mesic nad obzorem. Aplikace tohoto kodu vedla ke avyseni pozorovaciho casu FD o 20 %. Zatfeti, pozadova data z fluorescencniho detektoru byla vyuzita pro detailni analyzu pfesne ori- entace jednotlivych fluorescencnich teleskopu, coz je nezbytne pro pfesnou geometrickou rekonstrukci detekovanych sprsek kosmickeho zareni. 2actvrte, byl v Argentine v ramci OPA zkonstruovan roboticky fotometricky dalekohled FRAM. 2akladnfm ukolem FRAMu je sledovanf okamzite aerosolove extinkce, tento pnstroj se vsak venuje i pozorovani promennych hvezd a optickych..
Improving Activated Carbon Performance in Point Of Use and Municipal Processes
No full textabstract: Specific inorganic and organic pollutants in water (As(V), Cr(VI), THMs, and hardness) cause health concerns or aesthetic problems. The goal of this dissertation is to demonstrate novel approaches to improve the performance of point of use and municipal activated carbon processes to provide safe and reliable water to the public at distributed centralized locations.
Template Assisted Crystallization system would adjust saturation index (SI) value of TAC treated water to zero when SI value of influent water was in the range at 0.08~0.3. However, the reduction in SI when SI values were higher (e.g. 0.7~1.3) was similar to the reduction at lower SI values which could be due to limitations in kinetics or mass transfer with the template on TAC media.
Pre-chlorination prior to municipal-scale granular activated carbon (GAC) treatment was evaluated to control THM formation in distribution systems. Pre-chlorination decreased UVA, shift the dissolved organic carbon (DOC) molecular weight distribution and pre-formed trihalomethanes (THM). GAC treatment of pre-chlorinated water achieved lower THM formation in distribution systems.
To add functionality in POU systems to remove As(V) and Cr(VI), activated carbon was nano-tized to fabricate nano-enabled carbon block (CB) by (1) impregnating iron or titanium metal oxides chemically or (2) attaching titanium based P25 through electrostatic attraction force. Nanoparticle loadings of 5 to 10 wt % with respect to activated carbon enables reduction of As(V) or Cr(VI) from levels of common occurrence to below regulatory levels across carbon block designs. Minimal impacts on As(V) and Cr(VI) sorption were observed up to a nanoparticle pre-treatment temperature of 200 C, which is the temperature for CB production. Through controlling pH at 4.5 during mixing of nanoparticles with pH IEP=6 and activated carbon with pH IEP=3, electrostatic attachment of nanoparticles to activated carbon could be achieved prior to fabricating carbon block. A mini carbon block test device was designed, fabricated, and validated to mimic performances of full-scale carbon block using less volumes of test water. As(V) removal tests showed Fe impregnated CB achieved the highest As(V) removal while P25 attached CB had the lowest among three nanoparticles loaded CBs.Dissertation/ThesisDoctoral Dissertation Civil, Environmental and Sustainable Engineering 201
Cytochromes c550, c552 and c1 in the electron transport network of Paracoccus denitrificans: Reduntant or subtly different in function?
No full textParacoccus denitrificans strains with mutations in the genes encoding the cytochrome c550, c552, or c1 and in combinations of these genes were constructed, and their growth characteristics were determined. Each mutant was able to grow heterotrophically with succinate as the carbon and free-energy source, although their specific growth rates and maximum cell numbers fell variably behind those of the wild type. Maximum cell numbers and rates of growth were also reduced when these strains were grown with methylamine as the sole free-energy source, with the triple cytochrome c mutant failing to grow on this substrate. Under anaerobic conditions in the presence of nitrate, none of the mutant strains lacking the cytochrome bc1 complex reduced nitrite, which is cytotoxic and accumulated in the medium. The cytochrome c550-deficient mutant did denitrify provided copper was present. The cytochrome c552 mutation had no apparent effect on the denitrifying potential of the mutant cells. The studies show that the cytochromes c have multiple tasks in electron transfer. The cytochrome bc1 complex is the electron acceptor of the Q-pool and of amicyanin. It is also the electron donor to cytochromes c550 and c552 and to the cbb3-type oxidase. Cytochrome c552 is an electron acceptor both of the cytochrome bc1 complex and of amicyanin, as well as a dedicated electron donor to the aa3-type oxidase. Cytochrome c550 can accept electrons from the cytochrome bc1 complex and from amicyanin, whereas it is also the electron donor to both cytochrome c oxidases and to at least the nitrite reductase during denitrification. Deletion of the c-type cytochromes also affected the concentrations of remaining cytochromes c, suggesting that the organism is plastic in that it adjusts its infrastructure in response to signals derived from changed electron transfer routes
Estudos das potencialidades do reuso de água em uma indústria frigorífica
No full textDissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico. Programa de Pós-graduação em Engenharia de AlimentosA crescente preocupação com o uso racional da água no Brasil e no mundo impulsionou as empresas a aderirem a tecnologias e processos que procurem reduzir os rejeitos gerados, e a demanda de água sobre os mananciais. A redução do volume de efluentes, através da recirculação e reaproveitamento da água, constitui um dos desafios enfrentado pela indústria de alimentos. No processamento de carne bovina, que compreende as operações de recebimento, banho, atordoamento, sangria, esfola, evisceração até a operação final de divisão e lavagem das carcaças, é constatado um grande volume de água consumido e também de efluente gerado. Por este motivo, este trabalho teve por principal objetivo a caracterização das águas utilizadas nas várias etapas do processo e de seus respectivos efluentes e o estudo de possibilidades de reuso de água dentro do mesmo. Foram determinados os parâmetros: Temperatura, pH, alcalinidade total e parcial, série de sólidos (ST e SV) e demanda química de oxigênio (DQO) das correntes de processo de uma indústria frigorífica de grande porte do estado de Santa Catarina. Foi estabelecida uma estratégia para o reuso de água oriundo dos rejeitos da operação do processamento de lavagem de carcaças, o que representa 28,6% do total da vazão de água utilizada pela empresa. O impacto do reuso desta corrente na estação de tratamento de efluentes também foi verificado
Characterization of Carbonaceous Aerosol over the North Atlantic Ocean
No full textabstract: Atmospheric particulate matter has a substantial impact on global climate due to its ability to absorb/scatter solar radiation and act as cloud condensation nuclei (CCN). Yet, little is known about marine aerosol, in particular, the carbonaceous fraction. In the present work, particulate matter was collected, using High Volume (HiVol) samplers, onto quartz fiber substrates during a series of research cruises on the Atlantic Ocean. Samples were collected on board the R/V Endeavor on West–East (March–April, 2006) and East–West (June–July, 2006) transects in the North Atlantic, as well as on the R/V Polarstern during a North–South (October–November, 2005) transect along the western coast of Europe and Africa. The aerosol total carbon (TC) concentrations for the West–East (Narragansett, RI, USA to Nice, France) and East–West (Heraklion, Crete, Greece to Narragansett, RI, USA) transects were generally low over the open ocean (0.36±0.14 μg C/m3) and increased as the ship approached coastal areas (2.18±1.37 μg C/m3), due to increased terrestrial/anthropogenic aerosol inputs. The TC for the North–South transect samples decreased in the southern hemisphere with the exception of samples collected near the 15th parallel where calculations indicate the air mass back trajectories originated from the continent. Seasonal variation in organic carbon (OC) was seen in the northern hemisphere open ocean samples with average values of 0.45 μg/m3 and 0.26 μg/m3 for spring and summer, respectively. These low summer time values are consistent with SeaWiFS satellite images that show decreasing chlorophyll a concentration (a proxy for phytoplankton biomass) in the summer. There is also a statistically significant (p<0.05) decline in surface water fluorescence in the summer. Moreover, examination of water–soluble organic carbon (WSOC) shows that the summer aerosol samples appear to have a higher fraction of the lower molecular weight material, indicating that the samples may be more oxidized (aged). The seasonal variation in aerosol content seen during the two 2006 cruises is evidence that a primary biological marine source is a significant contributor to the carbonaceous particulate in the marine atmosphere and is consistent with previous studies of clean marine air masses.Dissertation/ThesisM.S. Chemistry 201
- …
