Mechanisms of chromium deposition and dissolution under direct and pulse reverse plating conditions

Baths containing sulphuric acid as catalyst and others with selected secondary catalysts (methane sulphonic acid - MSA, SeO2, a KBrO3/KIO3 mixture, indium, uranium and commercial high speed catalysts (HEEF-25 and HEEF-405)) were studied. The secondary catalysts influenced CCE, brightness and cracking. Chromium deposition mechanisms were studied in Part II using potentiostatic and potentiodynamic electroanalytical techniques under stationary and hydrodynamic conditions. Sulphuric acid as a primary catalyst and MSA, HEEF-25, HEEF-405 and sulphosalycilic acid as co-catalysts were explored for different rotation, speeds and scan rates. Maximum current was resolved into diffusion and kinetically limited components, and a contribution towards understanding the electrochemical mechanism is proposed. Reaction kinetics were further studied for H2SO4, MSA and methane disulphonic acid catalysed systems and their influence on reaction mechanisms elaborated. Charge transfer coefficient and electrochemical reaction rate orders for the first stage of the electrodeposition process were determined. A contribution was made toward understanding of H2SO4 and MSA influence on the evolution rate of hydrogen. Anodic dissolution of chromium in the chromic acid solution was studied with a number of techniques. An electrochemical dissolution mechanism is proposed, based on the results of rotating gold ring disc experiments and scanning electron microscopy. Finally, significant increases in chromium electrodeposition rates under non-stationary conditions (PRC mode) were studied and a deposition mechanisms is elaborated based on experimental data and theoretical considerations.

The role of cannabinoid receptors in modulation of GABAergic neurotransmission in the rat medial entorhinal cortex in vitro

Type 1 cannabinoid receptors (CB1R) have a well established role in modulating GABAergic signalling with the central nervous system, and are thought to be the only type present at GABAergic presynaptic terminals. In the medial entorhinal cortex (mEC), some cortical layers show high levels of ongoing GABAergic signalling (namely layer II) while others show relatively low levels (layer V). Using whole-cell patch clamp techniques, I have, for the first time, demonstrated the presence of functional CB1R in both deep and superficial layers of the mEC. Furthermore, using a range of highly specific ligands for both CB1R and CB2R, I present strong pharmacological evidence for CB2Rs being present in both deep and superficial layers of the mEC in the adult rat brain. In brain slices taken at earlier points in CNS development (P8-12), I have shown that while both CB1R and CB2R specific ligands do modulate GABAergic signalling at early developmental stages, antagonists/ inverse agonists and full agonists have similar effects, and serve only to reduce GABAergic signalling. These data suggest that the full cannabinoid signalling mechanisms at this early stage in synaptogenesis are not yet in place. During these whole-cell studies, I have developed and refined a novel recording technique, using an amantidine derivative (IEM1460) which allows inhibitory postsynaptic currents to be recorded under conditions in which glutamate receptors are not blocked and network activity remains high. Finally I have shown that bath applied CB1 and CB2 receptor antagonists/ inverse agonists are capable of modulating kainic acid induced persistent oscillatory activity in mEC. Inverse agonists suppressed oscillatory activity in the superficial layers of the mEC while it was enhanced in the deeper layers. It seems likely that cannabinoid receptors modulate the inhibitory neuronal activity that underlies network oscillations.

Typical case behaviour of spin systems in random graph and composite ensembles

This thesis includes analysis of disordered spin ensembles corresponding to Exact Cover, a multi-access channel problem, and composite models combining sparse and dense interactions. The satisfiability problem in Exact Cover is addressed using a statistical analysis of a simple branch and bound algorithm. The algorithm can be formulated in the large system limit as a branching process, for which critical properties can be analysed. Far from the critical point a set of differential equations may be used to model the process, and these are solved by numerical integration and exact bounding methods. The multi-access channel problem is formulated as an equilibrium statistical physics problem for the case of bit transmission on a channel with power control and synchronisation. A sparse code division multiple access method is considered and the optimal detection properties are examined in typical case by use of the replica method, and compared to detection performance achieved by interactive decoding methods. These codes are found to have phenomena closely resembling the well-understood dense codes. The composite model is introduced as an abstraction of canonical sparse and dense disordered spin models. The model includes couplings due to both dense and sparse topologies simultaneously. The new type of codes are shown to outperform sparse and dense codes in some regimes both in optimal performance, and in performance achieved by iterative detection methods in finite systems.

Approximate, Average, Dynamic Models of Uncontrolled Rectifiers for Aircraft Applications

To carry out stability and voltage regulation studies on more electric aircraft systems in which there is a preponderance of multi-pulse, rectifier-fed motor-drive equipment, average dynamic models of the rectifier converters are required. Existing methods are difficult to apply to anything other than single converters with a low pulse number. Therefore an efficient, compact method for deriving the approximate, linear, average model of 6- and 12-pulse rectifiers, based on the assumption of a small duration of the overlap angle is presented. The models are validated against detailed simulations and laboratory prototypes.

Persistence in a random bond ising model of socio-econo dynamics

We study the persistence phenomenon in a socio-econo dynamics model using computer simulations at a nite temperature on hypercubic lattices in dimensions up to ve. The model includes a \social" local eld which contains the magnetization at time t. The nearest neighbour quenched interactions are drawn from a binary distribution which is a function of the bond concentration, p. The decay of the persistence probability in the model depends on both the spatial dimension and p. We nd no evidence of \blocking" in this model. We also discuss the implications of our results for possible applications in the social and economic elds. It is suggested that the absence, or otherwise, of blocking could be used as a criterion to decide on the validity of a given model in dierent scenarios.

TDP-43-Immunoreactive pathology in frontotemporal lobar degeneration with TDP proteinopathy (FTLD-TDP) with and without associated motor neuron disease

A proportion of patients with motor neuron disease (MND) exhibit frontotemporal dementia (FTD) and some patients with FTD develop the clinical features of MND. Frontotemporal lobar degeneration (FTLD) is the pathological substrate of FTD and some forms of this disease (referred to as FTLD-U) share with MND the common feature of ubiquitin-immunoreactive, tau-negative cellular inclusions in the cerebral cortex and hippocampus. Recently, the transactive response (TAR) DNA-binding protein of 43 kDa (TDP-43) has been found to be a major protein of the inclusions of FTLD-U with or without MND and these cases are referred to as FTLD with TDP-43 proteinopathy (FTLD-TDP). To clarify the relationship between MND and FTLD-TDP, TDP-43 pathology was studied in nine cases of FTLD-MND and compared with cases of familial and sporadic FTLD–TDP without associated MND. A principal components analysis (PCA) of the nine FTLD-MND cases suggested that variations in the density of surviving neurons in the frontal cortex and neuronal cytoplasmic inclusions (NCI) in the dentate gyrus (DG) were the major histological differences between cases. The density of surviving neurons in FTLD-MND was significantly less than in FTLD-TDP cases without MND, and there were greater densities of NCI but fewer neuronal intranuclear inclusions (NII) in some brain regions in FTLD-MND. A PCA of all FTLD-TDP cases, based on TDP-43 pathology alone, suggested that neuropathological heterogeneity was essentially continuously distributed. The FTLD-MND cases exhibited consistently high loadings on PC2 and overlapped with subtypes 2 and 3 of FTLD-TDP. The data suggest: (1) FTLD-MND cases have a consistent pathology, variations in the density of NCI in the DG being the major TDP-43-immunoreactive difference between cases, (2) there are considerable similarities in the neuropathology of FTLD-TDP with and without MND, but with greater neuronal loss in FTLD-MND, and (3) FTLD-MND cases are part of the FTLD-TDP ‘continuum’ overlapping with FTLD-TDP disease subtypes 2 and 3.

Modulation of SERCA in the chronic phase of adjuvant arthritis as a possible adaptation mechanism of redox imbalance

Adjuvant arthritis (AA) is a condition that involves systemic oxidative stress. Unexpectedly, it was found that sarcoplasmic reticulum Ca2 +-ATPase (SERCA) activity was elevated in muscles of rats with AA compared to controls, suggesting possible conformational changes in the enzyme. There was no alteration in the nucleotide binding site but rather in the transmembrane domain according to the tryptophan polar/non-polar fluorescence ratio. Higher relative expression of SERCA, higher content of nitrotyrosine but no increase in phospholipid oxidation in AA SR was found. In vitro treatments of SR with HOCl showed that in AA animals SERCA activity was more susceptible to oxidative stress, but SR phospholipids were more resistant and SERCA could also be activated by phosphatidic acid. It was concluded that increased SERCA activity in AA was due to increased levels of SERCA protein and structural changes to the protein, probably induced by direct and specific oxidation involving reactive nitrogen species.

Mechanism of serca modulation from rats with adjuvant arthritis

We studied the structural and functional alterations of SERCA in rats suffering from adjuvant arthritis (AA). AA was induced by intradermal administration of Mycobacterium butyricum (MB) to the base of the tail of Lewis rats. Injury of SERCA from skeletal muscles of AA rats was analyzed on days 7, 14, 21 and 28 after MB injection. Neither fragmentation, aggregation of SERCA protein, alterations in SH groups, nor oxidation of phosphatidylcholines and phosphatidylethanolamines in SR vesicles were observed in animals with AA. The only ROS/RNS modification was increased formation of nitrotyrosine. The activity of SERCA from AA animals decreased on day 21 after MB injection and was associated with a significant increase of protein carbonyls in sarcoplasmic reticulum (SR). In contrast, on day 28 an increase of SERCA activity was observed and protein carbonyl level reversed to control level. Concerning kinetic parameters, maximum reaction velocity (Vmax) decrease and increase was observed with respect to both substrates (Ca, ATP) on days 21 and 28, respectively, suggesting possible conformational changes of the enzyme. These changes were not associated with alterations in nucleotide binding site situated in cytosol, but rather with tryptophan fluorescence intensity ratio (cytosol/membrane) related to the transmembrane domain of SERCA. Elevated SERCA activity on day 28 was caused by its higher expression. Acidic phospholipids (PA), probably present in SR of AA rats, may contribute to the elevation of Ca-ATPase activity, as PA administration in vitro increased this activity.

Modulation of sarcoplasmic/endoplasmic reticulum Ca(2+)-ATPase activity and oxidative modification during the development of adjuvant arthritis

Adjuvant arthritis (AA) was induced by intradermal administration of Mycobacterium butyricum to the tail of Lewis rats. In sarcoplasmic reticulum (SR) of skeletal muscles, we investigated the development of AA. SR Ca(2+)-ATPase (SERCA) activity decreased on day 21, suggesting possible conformational changes in the transmembrane part of the enzyme, especially at the site of the calcium binding transmembrane part. These events were associated with an increased level of protein carbonyls, a decrease in cysteine SH groups, and alterations in SR membrane fluidity. There was no alteration in the nucleotide binding site at any time point of AA, as detected by a FITC fluorescence marker. Some changes observed on day 21 appeared to be reversible, as indicated by SERCA activity, cysteine SH groups, SR membrane fluidity, protein carbonyl content and fluorescence of an NCD-4 marker specific for the calcium binding site. The reversibility may represent adaptive mechanisms of AA, induced by higher relative expression of SERCA, oxidation of cysteine, nitration of tyrosine and presence of acidic phospholipids such as phosphatidic acid. Nitric oxide may regulate cytoplasmic Ca(2+) level through conformational alterations of SERCA, and decreasing levels of calsequestrin in SR may also play regulatory role in SERCA activity and expression.

Mechanistic differences between GSH transport by multidrug resistance protein 1 (MRP1/ABCC1) and GSH modulation of MRP1-mediated transport

Multidrug resistance protein 1 (MRP1/ABCC1) is an ATP-dependent polytopic membrane protein that transports many anticancer drugs and organic anions. Its transport mechanism is multifaceted, especially with respect to the participation of GSH. For example, vincristine is cotransported with GSH, estrone sulfate transport is stimulated by GSH, or MRP1 can transport GSH alone, and this can be stimulated by compounds such as verapamil or apigenin. Thus, the interactions between GSH and MRP1 are mechanistically complex. To examine the similarities and differences among the various GSH-associated mechanisms of MRP1 transport, we have measured first the effect of GSH and several GSH-associated substrates/modulators on the binding and hydrolysis of ATP by MRP1 using 8-azidoadenosine-5'-[(32)P]-triphosphate ([(32)P]azidoATP) analogs, and second the initial binding of GSH and GSH-associated substrates/modulators to MRP1. We observed that GSH or its nonreducing derivative S-methylGSH (S-mGSH), but none of the GSH-associated substrate/modulators, caused a significant increase in [gamma-(32)P]azidoATP labeling of MRP1. Moreover, GSH and S-mGSH decreased levels of orthovanadate-induced trapping of [alpha-(32)P]azidoADP. [alpha-(32)P]azidoADP.Vi trapping was also decreased by estone sulfate, whereas vincristine, verapamil, and apigenin had no apparent effects on nucleotide interactions with MRP1. Furthermore, estrone sulfate and S-mGSH enhanced the effect of each other 15- and 10-fold, respectively. Second, although GSH binding increased the apparent affinity of MRP1 for all GSH-associated substrates/modulators tested, only estrone sulfate had a reciprocal effect on the apparent affinity of MRP1 for GSH. Overall, these results indicate significant mechanistic differences between MRP1-mediated transport of GSH and the ability of GSH to modulate MRP1 transport.

Modulation of network oscillatory activity and GABAergic synaptic transmission by CB1 cannabinoid receptors in the rat medial entorhinal cortex

Cannabinoids modulate inhibitory GABAergic neurotransmission in many brain regions. Within the temporal lobe, cannabinoid receptors are highly expressed, and are located presynaptically at inhibitory terminals. Here, we have explored the role of type-1 cannabinoid receptors (CB1Rs) at the level of inhibitory synaptic currents and field-recorded network oscillations. We report that arachidonylcyclopropylamide, an agonist at CB1R, inhibits GABAergic synaptic transmission onto both superficial and deep medial entorhinal (mEC) neurones, but this has little effect on network oscillations in beta/gamma frequency bands. By contrast, the CB1R antagonist/inverse agonist LY320135 (500?nM), increased GABAergic synaptic activity and beta/gamma oscillatory activity in superficial mEC, was suppressed, whilst that in deep mEC was enhanced. These data indicate that cannabinoid-mediated effects on inhibitory synaptic activity may be constitutively active in vitro, and that modulation of CB1R activation using inverse agonists unmasks complex effects of CBR function on network activity.

Prior action execution has no effect on corticospinal facilitation during action observation

Transcranial magnetic stimulation (TMS) has been used widely in research investigating corticospinal (CS) excitability during action observation. Generally, this work has shown that observation of an action performed by others, in the absence of overt movement, modulates the excitability of the CS pathway in humans. Despite the extent of the literature exploring action observation effects, however, there has been little research to date that has compared observation with the combination of observation and execution directly. Here, we report a single-pulse TMS study that investigated whether CS excitability during action observation was modulated by actions performed by the observers prior to viewing a ball pinching action. The results showed that CS excitability during action observation increased when compared to observation of a static hand, but that there was no additional motor facilitation when participants performed the same action prior to observing it. Our findings highlight the importance of action observation and its consequences on the CS system, whilst also illustrating the limited effect of prior action execution on the CS pathway for a simple action task.

Nonlinear pulse shaping in fibres for pulse generation and optical processing

The development of new all-optical technologies for data processing and signal manipulation is a field of growing importance with a strong potential for numerous applications in diverse areas of modern science. Nonlinear phenomena occurring in optical fibres have many attractive features and great, but not yet fully explored, potential in signal processing. Here, we review recent progress on the use of fibre nonlinearities for the generation and shaping of optical pulses and on the applications of advanced pulse shapes in all-optical signal processing. Amongst other topics, we will discuss ultrahigh repetition rate pulse sources, the generation of parabolic shaped pulses in active and passive fibres, the generation of pulses with triangular temporal profiles, and coherent supercontinuum sources. The signal processing applications will span optical regeneration, linear distortion compensation, optical decision at the receiver in optical communication systems, spectral and temporal signal doubling, and frequency conversion. © Copyright 2012 Sonia Boscolo and Christophe Finot.

Pulse shaping in mode-locked ring-cavity fibre lasers

By means of extensive numerical modelling we have demonstrated the possibility of nonlinear pulse shaping in a mode-locked fibre laser using control of the intra-cavity propagation dynamics by adjustment of the normal net dispersion and integrated gain. Beside self-similar mode-locking, the existence of a novel type of pulse shaping regime that produces pulses with a triangular temporal intensity profile and a linear frequency chirp has been observed.

Nonlinearly generated advanced pulse waveforms for optical signal processing

Nonlinear phenomena occurring in optical fibres have many attractive features and great, but not yet fully explored potential in signal processing. Here, we review recent progress on the use of fibre nonlinearities for the generation and shaping of optical pulses, and on the applications of advanced pulse waveforms in all-optical signal processing. Among other topics, we will discuss ultrahigh repetition-rate pulse sources, the generation of parabolic-shaped pulses in active and passive fibres, the generation of pulses with triangular temporal profiles, and coherent supercontinuum sources. The signal processing applications will span optical regeneration, linear distortion compensation, optical decision at the receiver in optical communication systems, spectral and temporal signal doubling, and frequency conversion. © 2012 IEEE.