962 resultados para single electron transfer (SET)
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"June 1977."
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"7 November 1961."
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[Ensian caption: "Bob Penska escorts Johnson downfield" Johnson rushed for a record 349 yards]
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Type 1 diabetes (TID) susceptibility locus, IDDM8, has been accurately mapped to 200 kilobases at the terminal end of chromosome 6q27. This is within the region which harbours a cluster of three genes encoding proteasome subunit beta 1 (PMSB1), TATA-box binding protein (TBP) and a homologue of mouse programming cell death activator 2 (PDCD2). In this study, we evaluated whether these genes contribute to TID susceptibility using the transmission disequilibrium test of the data set from 114 affected Russian simplex families. The A allele of the G/A1180 single nucleotide polymorphism (SNP) at the PDCD2 gene, which was significant in its preferential transfer from parents to diabetic children (75 transmissions vs. 47 non-transmissionS, x(2) = 12.85, P corrected = 0.0038), was found to be associated with T1D. G/A1180 dimorphism and two other SNPs, C/T771 TBP and G/T(-271) PDCD2, were shown to share three common haplotypes, two of which (A-T-G and A-T-T) have been associated with higher development risk of TID. The third haplotype (G-T-G) was related to having a lower risk of disease. These findings suggest that the PDCD2 gene is a likely susceptibility gene for TID within IDDM8. However, it was not possible to exclude the TBP gene from being another putative susceptibility gene in this region. (c) 2005 Elsevier Ltd. All rights reserved.
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A specially-designed vertical wind tunnel was used to freely suspend individual liquid drops of 5 mm initial diameter to investigate drop dynamics, terminal velocity and heat and mass transfer rates. Droplets of distilled, de-ionised water, n-propanol, iso-butanol, monoethanolamine and heptane were studied over a temperature range of 50oC to 82oC. The effects of substances that may provide drop surface rigidity (e.g. surface active agents, binders and polymers) on mass transfer rates were investigated by doping distilled de-ionised water drops with sodium di-octyl sulfo-succinate surfactant. Mass transfer rates decreased with reduced drop oscillation as a result of surfactant addition, confirming the importance of droplet surface instability. Rigid naphthalene spheres and drops which formed a skin were also studied; the results confirmed the reduced transfer rates in the absence of drop fluidity. Following consideration of fundamental drop dynamics in air and experimental results from this study, a novel dimensionless group, the Oteng-Attakora, (OT), number was included in the mass transfer equation to account for droplet surface behaviour and for prediction of heat and mass transfer rates from single drops which exhibit surface instability at Re>=500. The OT number and the modified mass transfer equation are respectively: OT=(ava2/d).de1.5(d/) Sh = 2 + 0.02OT0.15Re0.88Sc0.33 Under all conditions drop terminal velocity increased linearly with the square root of drop diameter and the drag coefficient was 1. The data were correlated with a modified equation by Finlay as follows: CD=0.237.((Re/P0.13)1.55(1/We.P0.13) The relevance of the new model to practical evaporative spray processes is discussed.
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The literature relating to the performance of pulsed sieve plate liquid-liquid extraction columns and the relevant hydrodynamic phenomenon have been surveyed. Hydrodynamic behaviour and mass transfer characteristics of droplets in turbulent and non-turbulent conditions have also been reviewed. Hydrodynamic behaviour, i.e. terminal and characteristic velocity of droplets, droplet size and droplet breakup processes, and mass transfer characteristics of single droplets (d≤0.6 cm) were investigated under pulsed (mixer-settler & transitional regimes) and non-pulsed conditions in a 5.0 cm diameter, 100 cm high, pulsed sieve plate column with three different sieve plate types and variable plate spacing. The system used was toluene (displaced) - acetone - distilled water. Existing photographic techniques for following and recording the droplet behaviour, and for observing the parameters of the pulse and the pulse shape were further developed and improved. A unique illumination technique was developed by which a moving droplet could be photographed using cine or video photography with good contrast without using any dye. Droplet size from a given nozzle and droplet velocity for a given droplet diameter are reduced under pulsing condition, and it was noted that this effect is enhanced in the presence of sieve plate. The droplet breakup processes are well explained by reference to an impact-breakup mechanism. New correlations to predict droplet diameter based on this mechanism are given below.vskip 1.0cm or in dimensionless groups as follows:- (We)crit= 3.12 - 1.79 (Eo)crit A correlation based on the isotropic turbulence theory was developed to calculate droplet diameter in the emulsion regime.vskip 1.0cm Experimental results show that in the mixer-settler and transitional regimes, pulsing parameters had little effect on the overall dispersed phase mass transfer coefficient during the droplet formation and unhindered travel periods.
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The literature relating to evaporation from single droplets of pure liquids and the drying of solution and slurry droplets, and of droplet sprays has been reviewed. The heat and mass transfer rates for individual droplets suspended in free-flight, were investigated using a specially-designed vertical wind tunnel, to simulate conditions in a spray drier. The technique represented a unique alternative method for investigating evaporation from unrestrained single droplets with variable residence times. The experiments covered droplets of pure liquid allowbreak (water, isopropanol) allowbreak and of significantly different solutions (sucrose, potassium sulphate) over a range of temperatures of 37oC to 97oC, initial concentrations of 5 to 40wt/wt% , and initial drop sizes of 2.8 to 4.6mm. Drop behaviour was recorded photographically and dried particles were examined by Scanning Electron Microscopy. Correlations were developed for mass transfer coefficients for pure water droplets in free-flight; (i) experiencing oscillations, rotation and deformation, Sh = -105 + 3.9 [Ta - Td/Tamb]0.18Re0.5Sc033 for Re approx. > 1380 (ii) when these movements had ceased or diminished, Sh = 2.0 + 0.71 [Ta - Td/Tamb]0.18Re0.5Sc033 for Re approx. < 1060. Data for isopropanol drops were correlated resonably well by these equations. The heat transfer data showed a similar transition range. The drying rate curves for drops of sucrose and potassium sulphate solution exhibited three distinct stages; an initial increase in the drying rate as drop temperature reduced to the wet-bulb temperature, a short constant-rate period and a falling-rate period characterised by formation of a crust which controlled the mass transfer rate. Due to drop perturbation the rates in the high Re number region were up to 5 times greater than predicted from theory for spherical droplets. In the case of sucrose solution a `skin' formed over the drop surface prior to crust formation. This provided an additional resistance to mass transfer and resulted in extended drying times and a smooth crust of low porosity. The relevance of the results to practical spray drying operations is discussed.
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This investigation looks critically at conventional magnetic lenses in the light of present-day technology with the aim of advancing electron microscopy in its broadest sense. By optimising the cooling arrangements and heat transfer characteristics of lens windings it was possible to increase substantially the current density in the winding, and achieve a large reduction in the size of conventional magnetic electron lenses. Following investigations into the properties of solenoidal lenses, a new type of lens with only one pole-piece was developed. The focal properties of such lenses, which differ considerably from those.of conventional lenses, have been derived from a combination of mathematical models and experimentally measured axial flux density distributions. These properties can be profitably discussed with reference to "half-lenses". Miniature conventional twin pole-piece lenses and the proposed radial field single pole-piece lenses have been designed and constructed and both types of lenses have been evaluated by constructing miniature electron optical columns. A miniature experimental transmission electron microscope (TEM), a miniature scanning electron microscope (SEM) and a scanning transmission microscope (STEM) have been built. A single pole-piece miniature one million volt projector lens of only lOcm diameter and weighing 2.lkg was designed, built and tested at 1 million volts in a commercial electron microscope. iii. Preliminary experiments indicate that in single pole lenses it is possible to extract secondary electrons from the specimen in spite of the presence of the magnetic field of the probe-forming lens. This may well be relevant for the SEM in which it is desirable to examine a large specimen at a moderately good resolution.
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Permafrost degradation influences the morphology, biogeochemical cycling and hydrology of Arctic landscapes over a range of time scales. To reconstruct temporal patterns of early to late Holocene permafrost and thermokarst dynamics, site-specific palaeo-records are needed. Here we present a multi-proxy study of a 350-cm-long permafrost core from a drained lake basin on the northern Seward Peninsula, Alaska, revealing Lateglacial to Holocene thermokarst lake dynamics in a central location of Beringia. Use of radiocarbon dating, micropalaeontology (ostracods and testaceans), sedimentology (grain-size analyses, magnetic susceptibility, tephra analyses), geochemistry (total nitrogen and carbon, total organic carbon, d13Corg) and stable water isotopes (d18O, dD, d excess) of ground ice allowed the reconstruction of several distinct thermokarst lake phases. These include a pre-lacustrine environment at the base of the core characterized by the Devil Mountain Maar tephra (22 800±280 cal. a BP, Unit A), which has vertically subsided in places due to subsequent development of a deep thermokarst lake that initiated around 11 800 cal. a BP (Unit B). At about 9000 cal. a BP this lake transitioned from a stable depositional environment to a very dynamic lake system (Unit C) characterized by fluctuating lake levels, potentially intermediate wetland development, and expansion and erosion of shore deposits. Complete drainage of this lake occurred at 1060 cal. a BP, including post-drainage sediment freezing from the top down to 154 cm and gradual accumulation of terrestrial peat (Unit D), as well as uniform upward talik refreezing. This core-based reconstruction of multiple thermokarst lake generations since 11 800 cal. a BP improves our understanding of the temporal scales of thermokarst lake development from initiation to drainage, demonstrates complex landscape evolution in the ice-rich permafrost regions of Central Beringia during the Lateglacial and Holocene, and enhances our understanding of biogeochemical cycles in thermokarst-affected regions of the Arctic.
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This is a comprehensive study of protein-mediated membrane fusion through single-molecule fluorescence resonance energy transfer (smFRET). Membrane fusion is one of the important cellular processes by which two initially distinct lipid bilayers merge their hydrophobic cores, resulting in one interconnected structure. For example, exocytosis, fertilization of an egg by a sperm and communication between neurons are a few among many processes that rely on some form of fusion. Proteins called soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) play a central role in fusion processes which is also regulated by many accessory proteins, such as synaptotagmin, complexin and Munc18. By a new lipid mixing method at the single-vesicle level, we are able to accurately detect different stages of SNARE-mediated membrane fusion including docking, hemi and full fusion via FRET value of single donor/acceptor vesicle pair. Through this single-vesicle lipid mixing assay, we discovered the vesicle aggregation induced by C2AB/Ca2+, the dual function of complexin, and the fusion promotion role of Munc18/SNARE-core binding mode. While this new method provides the information regarding the extent of the ensemble lipid mixing, the fusion pore opening between two vesicular cavities and the interaction between proteins cannot be detected. In order to overcome these limitations, we then developed a single-vesicle content mixing method to reveal the key factor of pore expansion by detecting the FRET change of dual-labeled DNA probes encapsulated in vesicles. Through our single-vesicle content mixing assay, we found the fusion pore expansion role of yeast SNAREs as well as neuronal SNAREs plus synaptotagmin 1.
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Developments in theory and experiment have raised the prospect of an electronic technology based on the discrete nature of electron tunnelling through a potential barrier. This thesis deals with novel design and analysis tools developed to study such systems. Possible devices include those constructed from ultrasmall normal tunnelling junctions. These exhibit charging effects including the Coulomb blockade and correlated electron tunnelling. They allow transistor-like control of the transfer of single carriers, and present the prospect of digital systems operating at the information theoretic limit. As such, they are often referred to as single electronic devices. Single electronic devices exhibit self quantising logic and good structural tolerance. Their speed, immunity to thermal noise, and operating voltage all scale beneficially with junction capacitance. For ultrasmall junctions the possibility of room temperature operation at sub picosecond timescales seems feasible. However, they are sensitive to external charge; whether from trapping-detrapping events, externally gated potentials, or system cross-talk. Quantum effects such as charge macroscopic quantum tunnelling may degrade performance. Finally, any practical system will be complex and spatially extended (amplifying the above problems), and prone to fabrication imperfection. This summarises why new design and analysis tools are required. Simulation tools are developed, concentrating on the basic building blocks of single electronic systems; the tunnelling junction array and gated turnstile device. Three main points are considered: the best method of estimating capacitance values from physical system geometry; the mathematical model which should represent electron tunnelling based on this data; application of this model to the investigation of single electronic systems. (DXN004909)
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The aim of this study was to evaluate the effectiveness of 17% ethylene-diamine-tetra-acetic acid (EDTA) used alone or associated with 2% chlorhexidine gel (CHX) on intracanal medications (ICM) removal. Sixty single-rooted human teeth with fully formed apex were selected. The cervical and middle thirds of each canal were prepared with Gates Glidden drills and rotary files. The apical third was shaped with hand files. The specimens were randomly divided into two groups depending on the ICM used after instrumentation: calcium hydroxide Ca(OH)(2) +CHX or Ca(OH)(2) +sterile saline (SS). After seven days, each group was divided into subgroups according to the protocol used for ICM removal: instrumentation and irrigation either with EDTA, CHX+EDTA, or SS (control groups). All specimens were sectioned and processed for observation of the apical thirds by using scanning electron microscopy. Two calibrated evaluators attributed scores to each specimen. The differences between the protocols for ICM removal were analyzed with Kruskal-Wallis and Mann-Whitney U tests. Friedman and Wilcoxon signed rank tests were used for comparison between the score of debris obtained in each root canal third. Remains of Ca(OH)(2) were found in all specimens independently of the protocol and ICM used (P > 0.05). Seventeen percent EDTA showed the best results in removing ICM when used alone (P < 0.05), particularly in those associated with CHX. It was concluded that the chelating agent 17% EDTA significantly improved the removal of ICM when used alone. Furthermore, the type of the vehicle associated with Ca(OH)(2) also plays a role in the ICM removal.