No description available.

Glutamate is the main excitatory neurotransmitter in the CNS and at the neuromuscular junctions (NMJs) of invertebrate. The characteristic similarities to CNS glutamatergic synapses in vertebrate and the anatomical simplicity of invertebrate NMJs favor the investigation of glutamatergic synaptic functions in this system. This dissertation mainly aimed to physiologically separate two functional vesicle groups, the reserve pool (RP) and readily releasable pool (RRP) within presynaptic nerve terminals of Procambarus Clarkii and Drosophila melanogaster. This was addressed in part by blocking the vesicular glutamate transporter (VGlut) with bafilomycin A1. Various frequencies of motor nerve stimulation, exposure time, and concentration of bafilomycin A1 were examined. The low-output tonic opener NMJs in crayfish exposed to 4μM bafilomycin A1 and 20Hz continuous stimulation decreased the EPSP amplitude to 50% in ∼30min with controls lasting 3h. After activity and bafilomycin A1-induced synaptic depression, the EPSPs were rapidly revitalized by serotonin (5-HT, 1μM) in the crayfish preparations. The 5-HT action can be blocked almost completely with a PLC inhibitor, but partially with a cAMP activator. The higher output synapses of the larval Drosophila NMJ when stimulated at 1Hz or 5Hz and exposed to 4μM of bafilomycin A1 showed a depression rate of 50% within ∼10min with controls lasting ∼40min. After low frequency depression and/or exposure to bafilomycin A1 a burst of higher frequency (10Hz) can recruit vesicles from the RP to the RRP. Physiological differences in low- (tonic like) and high-output (phasic like) synapses match many of the expected anatomical features of these terminals, part of this dissertation highlights physiological differences and differential modulation and/or extent of the vesicles in a RP for maintaining synaptic output during evoked depression of the RRP in crayfish abdomen extensor preparation. With the use of bafilomycin A1, the tonic terminal is fatigue resistant due to a large RRP, whereas the phasic depresses rapidly upon continuous stimulation. Upon depression of the tonic terminal, 5-HT has a large RP to act on to recruit vesicles to the RRP; whereas, the phasic terminal, 5-HT can recruit RP vesicles to the RRP prior to synaptic depression but not after depression.

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No description available.

No description available.

>Magister Scientiae - MSc / Fly ash is the most abundant of the waste materials generated from coal combustion in coal-fired power stations. South Africa uses more than 100 million tonnes of low grade bituminous coal annually to produce cheap electricity thereby generating huge amounts of fly ash each year. The disposal of fly ash has been a major concern to the world because of its potential environmental impact due to the possible leaching of the toxic elements contained in fly ash. This study centres on the chemical characterization and leaching behaviour of the fly ashes generated from SASOL Synfuels and ESKOM power station at Secunda and Tutuka in South Africa respectively. The aim is to understand the composition of the fly ashes and to determine the leachability of species from the ashes in order to predict the environmental effect of the different ash handling system of the coalfired stations (wet disposal system in Secunda and dry disposal system in Tutuka). Several leaching methods were employed in this study in order to develop a methodology for evaluating and modelling ash system and were able to discriminate between ash types and model ash handling system. Fly ashes from the two South African coal-fired stations were subjected to total acid-digestion and XRF analyses in order to determine the total amounts of major and minor species contained in the fly ashes. The total acid-digestion test and the XRF analysis revealed that the major species such as Al, Si, Ca, Na, Mg, K, Sr, Ba and S04, and minor species such as Fe, Ti, V, Mn, Cr, Ni and Cu were present in both fly ashes in fairly similar concentrations. The mineralogical characterization by XRD of Secunda and Tutuka fly ashes revealed mullite and quartz as the major mineral phases with minor peaks of CaO and calcite. Several leaching tests and different leaching conditions were employed in this study in order to develop a standardized replicable methodology for environmental impact assessment and for modelling the impact of different ash handling scenarios. The fly ashes were exposed to these different leaf leachant of different pHs on the leachability of species from the fly ashes. To achieve this, DIN-S4, TCLP and ANC tests were employed. The natural pH of the fly ash leachates were very high ranging between 12.56 and 13.08. The DIN-S4 leaching test revealed that the easily soluble species of the fly ashes include Ca, Mg, Na, K and S04 and various toxic elements. The leachates from the TCLP test recorded higher concentrations of Ca, Mg, Na, K and S04 which was attributed to the slight decrease in the pH due to the addition of a acidic leachant with a pH of 2.88. Comparison of the amount leached (DIN-S4) from the fly ashes with the total concentrations of each of the components of the fly ashes (determined by the total acid-digestion), the percentage of each of the readily soluble species ranged from 15-24.23% for Ca, 0.23-0.45% for K, 0.58-0.82% for Na, 0.0047-0.007% for Mg, 0.96-3.33% for Ba and 0.012-1.51 % for S04 per dry mass of each component in the fly ash. The ANC test revealed the effect of a leachant of specified pH on the release of species from the fly ashes with concentrations of the major and minor species leached out of the fly ashes found to be higher than the concentrations released into the leachates when DIN-S4 and TCLP test were considered at specific pH and showed the pH dependence of the solubility and release of species. These tests also showed the effect of the liquid to solid ratio upon leachability of species. In addition to the batch leaching tests mentioned above, dissolution kinetics and up-flow percolation tests were carried out on the fly ashes to determine the leaching behaviours of the fly ashes over time and the factors controlling the release of species from the fly ashes in the long term. The dissolution kinetics test was done for an extended period of 60 days with recycle of the leachant and the up-flow percolation test was carried out with constant leachant renewal until a liquid/solid ratio of 20 was attained (:::::;9d0ays). The geochemical computer code PHREEQC and MINTEQ database was used for geochemical modelling of the leachates at various reaction times and LIS ratios. The geochemical modelling results revealed that the release of the species from the fly ashes is controlled by the solubility of mineral phases in many case except for Na. The release of Ca, S04, Mg, Ba and Sr in the leachates of the fly ashes were predicted to be controlled by portlandite, gypsum, brucite, barite and celestite respectively while birnessite, magnetite, BaCr04, CaMo04 and Ba(As04h were predicted to be the mineral phases controlling the release of Mn, Fe, Cr, Mo and As respectively. The pH of the leachates plays a significant role in the leaching of both major and minor species from the fly ashes. The concentrations of species leached into solution at low pH (ANC and TCLP) were higher than the concentrations released at high pH (DIN-S4, dissolution kinetics and up-flow percolation tests). The amounts of the toxic elements such as As, Se, Cd, Cr and Pb that leached out of the fly ashes when in contact with demineralized water (DIN-S4) were very low and below the target water quality range (TWQR) of South African Department of Water Affairs and Forestry (DWAF), but the amounts of As and Se leached out by acidic leachant applied in the TCLP test and at lower pH ranging between 8 and 10 the case of the ANC test were slightly higher than the TWQR, which is an indication that the pH of the leaching solution and the contact time playa significant role on the leaching of species out of the fly ashes. This study revealed that the leaching of species from the fly ashes depends on various factors which include: physical and chemical characteristics and mineralogical composition of the fly ashes, the total concentrations of species in the ash, the rate of flow through the ash system and more importantly the pH of the leachant to which the ash system is exposed to. The results of different experiments and analysis carried out on the two South African fly ashes (Secunda and Tutuka fly ashes) showed that, despite the high concentrations of soluble species or leachable elements in the fly ashes, the leaching of major, minor and trace elements into the soils and the groundwater could be minimized if certain conditions such as avoiding acidic precipitation that could reduce the pH of the ash system are adhered to. The leaching trends of the species and the geochemical modelling data also showed that the formation of secondary mineral phases could reduce the release of toxic elements, the release of which would require aggressive low pH leachants, high flow rate, high recharge and long-term leaching for the dissolution of the formed mineral phases. In conclusion, the combination of the leaching tests employed in this study gives information on the leaching behaviour of the Secunda and Tutuka fly ashes and the factors controlling the leaching of the elements from the fly ashes. This study has been able to show that elements are leached out of the fly ashes at both alkaline and acidic pH. It is also revealed in the study that the disposal techniques employed by the coal-fired stations which were simulated by using the dissolution kinetics and up-flow percolation tests are adequate methods for modelling of the ash disposal scenario. These two methods show that the dry disposal system at Tutuka will encourage equilibration of the ash/water system thereby facilitating the precipitation of mineral phases that could control the release of both major and minor species from the fly ash, whereas the wet ashing system at Secunda may expose the ash to sufficient flow to rapidly leach species out into the environment.

Synaptic transmission alters the strength of the postsynaptic potential, through a process called short-term synaptic plasticity (STP). In this study, endplate potentials (EPPs) from the frog neuromuscular junction were used to resolve and quantify the presynaptic components involved in enhancement and depression of transmitter release during repetitive stimulation under normal quantal release conditions (2 mM Ca2+, 1mM Mg2+). During trains of stimulation given between 10 - 200 Hz, the amplitude of the EPPs first increased then decreased; a maximum increase of 77% was produced after 2-4 stimuli. EPP amplitudes began to increase at ~ 20 Hz, were maximal at ~ 55 Hz, and thereafter, decreased as the rate of stimulation increased. The integrated total release after 25 stimuli was little changed across frequencies between 10 - 100 Hz. EPPs ran down in two phases: a fast phase, attributed to the depletion of a readily releasable pool (RRP) of synaptic vesicles, followed by a slow phase, attributed to the depletion of vesicles from a depot pool (DP). Depletion of the readily releasable pool of synaptic vesicles (RRP) was determined by quantifying release under the fast and slow time rundowns and subtracting the number of vesicles associated with mobilization to the RRP from the total number of vesicles released during stimulation trains of 50 impulses. Impulses were delivered at 12 different rates ranging from 50 to 200 /s. Estimates of the number of vesicles released from the RRP increased with frequency of stimulation until maximal depletion levels of 5500 - 6000 vesicles were reached at stimulation rates between 90-130/s, assuming a control quantal content of 200 vesicles released per impulse. Depletion was less at lower frequencies when the number of stimuli delivered was identical. When the RRP maximally depleted, release was inversely related to stimulation rate, as would be expected if mobilization from the depot pool was the sole determinate of release during the slow phase. An equation constructed from four known components of enhancement and two components of depression - the depletion of vesicles from a readily releasable pool (RRP) and from the depot pool (DP) that refills the RRP, was used to fit and then simulate EPPs obtained during trains using different patterns of stimulation and varying amounts of extracellular Ca2+; the decay time constant parameters of enhancement, numerically derived from the observed data, were fixed at tau ~ 46, 220, 1600, and 20000 ms. The number of components of enhancement necessary to approximate the data decreased, from four in low (0.14 - 0.2mM) extracellular Ca2+, to one (tau ~ 46 ms) in 2.0 mM extracellular Ca2+, but four components of enhancement were necessary to fit the data when the amplitude of the EPP was not depressed below the control amplitude. This model was able to predict within ~ 3 % EPP amplitudes over a 10-fold range of frequency and Ca2+ concentration.

No description available.

Šiame darbe yra aprašomi lengvai biologiškai skaidomų organinių teršalų koncentracijos Palangos miesto nuotekose atskirais metų laikotarpiais bei Visagino miesto nuotekose tyrimai. Tyrimams nuotekos buvo imamos prieš biologinį valymą, o veiklusis dumblas – iš veikliojo dumblo reaktoriaus pabaigos. Tyrimai atlikti VGTU Vandentvarkos katedros ir UAB „Palangos vandenys“ laboratorijose. Siekiant įvertinti teršalų bei technologinių parametrų kitimą bei jų įtaką nuotekų išvalymo rodikliams, buvo surinkti ir statistiškai apdoroti Palangos ir Visagino nuotekų tyrimų rodikliai. Analizuota nuotekų parametrų priklausomybė, teršalų koncentracijų kaita, nuotekų valymo efektyvumas ir jų įtaka biologiniam fosforo šalinimui. Ištirtos lengvai biologiškai skaidomų organinių teršalų koncentracijos. Gauti rezultatai palyginti su anksčiau VGTU Vandentvarkos katedroje atliktų magistrantų nuotekų tyrimų rezultatais. / It is the investigations for determination of concentration of easily biodegradable organic matter in wastewater of Palanga and Visaginas towns. Wastewater for investigations have been taken before biological treatment, and active sludge - from the end of active sludge reactor. The investigations were carried out at Water Management Department of Vilnius Gediminas Technical University and UAB "Palangos vandenys" laboratories. The indicators of investigations of Palanga and Visaginas wastewater were collected and statistically processed in order to evaluate alteration of technological parameters and their influence to indicators of wastewater cleaning. It was analysed the relationship between various parameters in order to find out their influence for the efficiency of biological phosphorus removal. It was studied easily biodegradable organic pollutant concentrations too. The results are compared with previously results of investigations, made by postgraduates of Water Management Department of Vilnius Gediminas Technical University.

Die vorliegende Dissertation wurde mit dem Ziel entworfen, ein besseres Verständnis zu erlangen, was die Anforderungen sind, die den künftigen Arbeitsgruppenmitgliedern erlauben, Bedürfnissen von modernen Unternehmen zu genügen. Die Kooperationsbereitschaft von Gruppenmitgliedern scheint ein Schlüsselfaktor zu sein, der ihre Fähigkeit freisetzt, einer beliebigen Aufgabe entgegen zu handeln. Quantitative wie auch qualitative Daten wurden im Rahmen einer explorativen Studie erhoben. Ein Fragebogen (Intercultural Attitude Orientation) wurde mit der Absicht entwickelt, Einstellung von Individuen gegenüber Diversität quer durch Populationen abzufragen. An der explorativen Studie haben 1351 Individuen aus 97 Ländern teilgenommen. Bei einer Faktorenanalyse von 12 Items wurde die entgültige acht Items umfassende Skala gebildet. Eine experimentelle Gruppenstudie wurde entworfen, um Entscheidungsprozesse anzustoßen, die erkennen lassen, ob die Kooperationsbereitschaft der Gruppenmitglieder die Gruppenperformanz erhöht. An der experimetellen Studie haben 249 Individuen teilgenommen, die nach einem Zufallsverfahren in Arbeitsgruppen eingeteilt wurden. Die unabhängigen Variablen waren demografische Gruppenkomposition und Informationsdiversität. Die abhängigen Variablen waren Messungen der Gruppenperformanz. Es wurde festgestellt, dass trotz der demografischen Gruppenkomposition Arbeitsgruppen, die Pakete mit unterschiedlichen Informationen erhielten, besser abgeschnitten haben, als Gruppen, denen Pakete mit ähnlichen Informationen zur Verfügung gestellt wurden. Erfahrung der Gruppenmitglieder mit Diversität, ihre Einstellung gegenüber Diversität, Social Dominance Orientation, Zufriedenheit, Kooperation, Ähnlichkeit in Arbeitsstil und Anzahl der gesprochenen Sprachen wurden getrennt im Hinblick auf die Gruppenergebnisse analysiert. Es wurde herausgefunden, dass diese Messungen in einigen Fällen zueinander in Beziehung standen, was einen Einfluß auf Gruppenprozess hatte. / The current dissertation has been designed with the attempt to seek a better understanding of the requirements for prospective workgroup members to fit demands of today''s organizations. Members'' willingness to cooperate appears to be a key factor unlocking their ability to act upon any given task. Quantitative as well as qualitative data have been gathered in the context of an explorative study. A questionnaire (Intercultural Attitude Orientation) has been constructed with the intent to sense individuals'' attitude toward diversity across populations diverging in age, gender, nationality, and occupational status. The explorative study involved the participation of 1351 individuals from 97 different countries. Out of twelve explorative items, one factor solution was extracted, thus building the final 8-item scale. An experimental group study was designed to elicit decision-making procedures set to entangle whether or not members'' readiness to cooperate enhances group performance in the context of a short and cognitively demanding task. The experimental study involved the participation of 249 individuals randomly assigned into workgroups. The two independent variables were group demographical composition and information diversity. Demographical composition was defined either according to national or gender demographics. The outcome variables were measures of workgroup performance. It was found that despite workgroup demographical composition, groups which received diverse information, performed better than workgroups, which received similar information. Members'' quality and quantity of exposure to diversity, attitude toward diversity, social dominance orientation, satisfaction, cooperation, work-style similarity, and number of spoken languages were separately analyzed with regard to group outcomes. Findings revealed that these measures were in some cases linked to one another, thus affecting group process.