AMPEROMETRIC FLOW-INJECTION ANALYSIS OF HYDRAZINE BY ELECTROCATALYTIC OXIDATION AT COBALT TETRAPHENYLPORPHYRIN MODIFIED ELECTRODE WITH HEAT-TREATMENT

Chemically modified electrodes prepared by treating the cobalt tetraphenylporphyrin modified glassy-carbon electrode at 750-degrees (HCME) are shown to catalyze the electrooxidation of hydrazine. The oxidation occurred at +0.63 V vs. Ag/AgCl (saturated potassium chloride) in pH 2.5 media. The catalytic response is evaluated with respect to solution pH, potential scan-rate, concentration dependence and flow-rate. The catalytic stability of the HCME is compared with that of the cobalt tetraphenylporphyrin adsorbed glassy-carbon electrode. The stability of the HCME was excellent in acidic solution and even in solutions containing organic solvent (50% CH3OH). When used as the sensing electrode in amperometric detection in flow-injection analysis, the HCME permitted sensitive detection of hydrazine at 0.5 V. The limit of detection was 0.1 ng. The linear range was from 50 ng to 2.4-mu-g. The method is very sensitive and selective.

A NEW KIND OF FLOW-THROUGH ELECTROCHEMICAL DETECTOR USING CARBON-FIBER ELECTRODE FOR LIQUID-CHROMATOGRAPHY

An electrochemical detector which was constracted by using a carbon fibre electrode in a flow-through cell was connected with a liquid chromatographic column. Thus a sensitive,

Fast Pose Estimation with Parameter Sensitive Hashing

Example-based methods are effective for parameter estimation problems when the underlying system is simple or the dimensionality of the input is low. For complex and high-dimensional problems such as pose estimation, the number of required examples and the computational complexity rapidly becme prohibitively high. We introduce a new algorithm that learns a set of hashing functions that efficiently index examples relevant to a particular estimation task. Our algorithm extends a recently developed method for locality-sensitive hashing, which finds approximate neighbors in time sublinear in the number of examples. This method depends critically on the choice of hash functions; we show how to find the set of hash functions that are optimally relevant to a particular estimation problem. Experiments demonstrate that the resulting algorithm, which we call Parameter-Sensitive Hashing, can rapidly and accurately estimate the articulated pose of human figures from a large database of example images.

Electrochemical biosensor based on microfabricated electrode arrays for life sciences applications

In developing a biosensor, the utmost important aspects that need to be emphasized are the specificity and selectivity of the transducer. These two vital prerequisites are of paramount in ensuring a robust and reliable biosensor. Improvements in electrochemical sensors can be achieved by using microelectrodes and to modify the electrode surface (using chemical or biological recognition layers to improve the sensitivity and selectivity). The fabrication and characterisations of silicon-based and glass-based gold microelectrode arrays with various geometries (band and disc) and dimension (ranging from 10 μm-100 nm) were reported. It was found that silicon-based transducers of 10 μm gold microelectrode array exhibited the most stable and reproducible electrochemical measurements hence this dimension was selected for further study. Chemical electrodeposition on both 10 μm microband and microdisc were found viable by electro-assisted self-assembled sol-gel silica film and nanoporous-gold electrodeposition respectively. The fabrication and characterisations of on-chip electrochemical cell was also reported with a fixed diameter/width dimension and interspacing variation. With this regard, the 10 μm microelectrode array with interspacing distance of 100 μm exhibited the best electrochemical response. Surface functionalisations on single chip of planar gold macroelectrodes were also studied for the immobilisation of histidine-tagged protein and antibody. Imaging techniques such as atomic force microscopy, fluorescent microscopy or scanning electron microscope were employed to complement the electrochemical characterisations. The long-chain thiol of self-assembled monolayer with NTA-metal ligand coordination was selected for the histidine-tagged protein while silanisation technique was selected for the antibody immobilisation. The final part of the thesis described the development of a T-2 labelless immunosensor using impedimetric approach. Good antibody calibration curve was obtained for both 10 μm microband and 10 μm microdisc array. For the establishment of the T-2/HT-2 toxin calibration curve, it was found that larger microdisc array dimension was required to produce better calibration curve. The calibration curves established in buffer solution show that the microelectrode arrays were sensitive and able to detect levels of T-2/HT-2 toxin as low as 25 ppb (25 μg kg-1) with a limit of quantitation of 4.89 ppb for a 10 μm microband array and 1.53 ppb for the 40 μm microdisc array.

Ca2+- and volume-sensitive chloride currents are differentially regulated by agonists and store-operated Ca2+ entry.

Using patch-clamp and calcium imaging techniques, we characterized the effects of ATP and histamine on human keratinocytes. In the HaCaT cell line, both receptor agonists induced a transient elevation of [Ca2+]i in a Ca2+-free medium followed by a secondary [Ca2+]i rise upon Ca2+ readmission due to store-operated calcium entry (SOCE). In voltage-clamped cells, agonists activated two kinetically distinct currents, which showed differing voltage dependences and were identified as Ca2+-activated (ICl(Ca)) and volume-regulated (ICl, swell) chloride currents. NPPB and DIDS more efficiently inhibited ICl(Ca) and ICl, swell, respectively. Cell swelling caused by hypotonic solution invariably activated ICl, swell while regulatory volume decrease occurred in intact cells, as was found in flow cytometry experiments. The PLC inhibitor U-73122 blocked both agonist- and cell swelling–induced ICl, swell, while its inactive analogue U-73343 had no effect. ICl(Ca) could be activated by cytoplasmic calcium increase due to thapsigargin (TG)-induced SOCE as well as by buffering [Ca2+]i in the pipette solution at 500 nM. In contrast, ICl, swell could be directly activated by 1-oleoyl-2-acetyl-sn-glycerol (OAG), a cell-permeable DAG analogue, but neither by InsP3 infusion nor by the cytoplasmic calcium increase. PKC also had no role in its regulation. Agonists, OAG, and cell swelling induced ICl, swell in a nonadditive manner, suggesting their convergence on a common pathway. ICl, swell and ICl(Ca) showed only a limited overlap (i.e., simultaneous activation), although various maneuvers were able to induce these currents sequentially in the same cell. TG-induced SOCE strongly potentiated ICl(Ca), but abolished ICl, swell, thereby providing a clue for this paradox. Thus, we have established for the first time using a keratinocyte model that ICl, swell can be physiologically activated under isotonic conditions by receptors coupled to the phosphoinositide pathway. These results also suggest a novel function for SOCE, which can operate as a "selection" switch between closely localized channels.

Fully differential cross sections for transfer ionization - a sensitive probe of high level correlation effects in atoms

The transfer ionization process offers a unique opportunity to study radial and angular electron correlations in the helium atom. We report calculations for the multiple differential cross sections of the transfer ionization process p + He --> H + He++ + e(-). The results of these calculations demonstrate the strong sensitivity of the fully differential cross sections to fine details of electron correlation in the target atom. Specifically, angular electron correlation in the ground state of helium results in a broad peak in the electron emission spectra in the backward direction, relative to the incoming beam. Our model explains some of the key effects observed in measurements of multiple differential cross sections using the COLTRIMS technique.

Transfer ionization process p+He -> H-0+He2++e(-) with the ejected electron detected in the plane perpendicular to the incident beam direction

A joint experimental and theoretical study of the transfer ionization process p+He→ H-0+He2++e(-) is presented for 630-keV proton impact energy, where the electron is detected in a plane perpendicular to the proton beam direction. With this choice of kinematics we find the triple-differential cross section to be particularly sensitive to angular correlation in the helium target. There is a good agreement between the experimental data and theoretical calculations.

Error sensitive historical GIS: Identifying areal interpolation errors in time series data

Historical GIS has the potential to re-invigorate our use of statistics from historical censuses and related sources. In particular, areal interpolation can be used to create long-run time-series of spatially detailed data that will enable us to enhance significantly our understanding of geographical change over periods of a century or more. The difficulty with areal interpolation, however, is that the data that it generates are estimates which will inevitably contain some error. This paper describes a technique that allows the automated identification of possible errors at the level of the individual data values.

The basis for the formation of stable metal clusters on an electrode surface

Metal nanoclusters can be produced cheaply and precisely in an electrochemical environment. Experimentally this method works in some systems, but not in others, and the unusual stability of the clusters has remained a mystery. We have simulated the deposition of the clusters using classical molecular dynamics and studied their stability by grand-canonical Monte Carlo simulations. We find that electrochemically stable clusters occur only in those cases where the two metals involved form stable alloys.

In vitro activity of tea-tree oil against clinical skin isolates of meticillin-resistant and -sensitive Staphylococcus aureus and coagulase-negative staphylococci growing planktonically and as biofilms

The susceptibility of Staphylococcus aureus [meticillin-resistant (MRSA) and meticillin-sensitive (MSSA)] and coagulase-negative staphylococci (CoNS), which respectively form part of the transient and commensal skin flora, to tea-tree oil (TTO) was compared using broth microdilution and quantitative in vitro time-kill test methods. MRSA and MSSA isolates were significantly less susceptible than CoNS isolates, as measured by both MIC and minimum bactericidal concentration. A significant decrease in the mean viable count of all isolates in comparison with the control was seen at each time interval in time-kill assays. However, the only significant difference in the overall mean log(10) reduction in viable count between the groups of isolates was between CoNS and MSSA at 3 h, with CoNS isolates demonstrating a significantly lower mean reduction. To provide a better simulation of in vivo conditions on the skin, where bacteria are reported to grow as microcolonies encased in glycocalyx, the bactericidal activity of TTO against isolates grown as biofilms was also compared. Biofilms formed by MSSA and MRSA isolates were completely eradicated following exposure to 5 % TTO for 1 h. In contrast, of the biofilms formed by the nine CoNS isolates tested, only five were completely killed, although a reduction in viable count was apparent for the other four isolates. These results suggest that TTO exerts a greater bactericidal activity against biofilm-grown MRSA and MSSA isolates than against some biofilm-grown CoNS isolates.