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181.
182.
Bhattacharyya I Maze JT Ewing GE Jarrold MF 《The journal of physical chemistry. A》2011,115(23):5723-5728
Film droplets formed from the bursting of 2.4 mm diameter bubbles on the surface of pure water are predominantly negatively charged. The charge generated per bubble varies chaotically; a few bubbles generate more than -3 × 10(6) elementary charges (e) but the vast majority generate much less. The average is -5 × 10(4)e/bubble, and it is not significantly affected by bubbling rate or temperature. The charge diminishes with increasing salt concentration and vanishes for concentrations above 10(-3) M. We propose a mechanism consistent with the observed charge separation. The model relies on the assumption that the surface of pure water has a slight excess of hydroxide ions. The charge separation results when water with entrained counterions (H(3)O(+)) flows out of the thinning film of the bubble cap, leaving behind the excess OH(-) on the surface. Addition of salt reduces the Debye length, and the charge separation mechanism becomes less effective as the Debye length becomes small compared with the film thickness. The excess charge near the surface of pure water is very small, around -4 nC/m(2). 相似文献
183.
Advances in electrochemical methodology over the past 30?years have allowed chemical measurements to be made with decreasing amounts of analyte and at smaller spatial dimensions. This has allowed the investigation of single cells and single vesicles in cells either during release of chemical transmitter or separately. The cellular event called exocytosis can be measured with amperometry or cyclic voltammetry as discovered by Wightman and first published in 1990. In addition, the measurement of vesicle contents with electrochemistry is a new approach we have termed electrochemical cytometry. This involves isolation of intact vesicles, separation of the vesicles, and then lysing followed by coulometric analysis of the electroactive vesicle content. In this review, we will highlight work done by us and by others to discuss measurements of exocytosis at single cells and measurements at artificial cell models for studying the biophysical properties of vesicle membrane dynamics and lipid nanotubes connecting artificial cells using electrochemical methods. 相似文献
184.
Svensson FR Abrahamsson M Strömberg N Ewing AG Lincoln P 《The journal of physical chemistry letters》2011,2(5):397-401
Ruthenium dipyridophenazine (dppz) complexes are sensitive luminescent probes for hydrophobic environments. Here, we apply multiple-frequency fluorescence lifetime imaging microscopy (FLIM) to Δ and Λ enantiomers of lipophilic ruthenium dppz complexes in live and fixed cells, and their different lifetime staining patterns are related to conventional intensity-based microscopy. Excited state lifetimes of the enantiomers determined from FLIM measurements correspond well with spectroscopically measured emission decay curves in pure microenvironments of DNA, phospholipid membrane or a model protein. We show that FLIM can be applied to monitor the long-lived excited states of ruthenium complex enantiomers and, combined with confocal microscopy, give new insight into their biomolecular binding and reveal differences in the microenvironment probed by the complexes. 相似文献
185.
R. Senger J. Ewing K. Zhang J. Avis P. Marschall I. Gaus 《Transport in Porous Media》2011,90(1):113-133
In low/intermediate-level waste (L/ILW) repositories, anaerobic corrosion of metals and degradation of organic materials produce
mainly hydrogen, methane, and carbon dioxide. The Swiss reference concept for the L/ILW repository consists of parallel caverns
sealed off from a single access tunnel in a deep low-permeability claystone formation. The potential buildup of excess gas
pressures in the backfilled emplacement caverns was investigated in a series of two-phase flow models. In the first step,
a large-scale model was constructed, implementing the 3D radial tunnel and cavern geometry with a simplified rectangular geometry.
In the second step, the potential impact of the detailed geometry of the engineered barrier system (EBS) and the associated
heterogeneity inside the cavern was examined using detailed models of the repository caverns, tunnel seals, access tunnel,
and surrounding host rock. The simulation results from the large-scale 3D repository model show that during the early post-closure
period simulated pressures can vary significantly between different parts of the repository. The simulated pressure increase
in the emplacement caverns remained below the fracture pressure of the rock for realistic assumptions. Gas flow is largely
limited to the EBS and the excavation disturbed zone (EDZ); thus, gas flows through and around the repository seal into the
adjacent tunnel system, which is also demonstrated in the detailed repository-cavern model. The repository seal model described
the detailed two-phase flow pattern of early time resaturation of the repository by water inflow from the ramp and subsequent
counter flow associated with the gas flow from the repository cavern. Overall, the results of the detailed models complement
and confirmed the results of the large-scale 3D model in terms of the timing of the pressure peaks and the migration of gas
from the cavern into the surrounding host rock and through the repository seal. 相似文献
186.
The selective syntheses of new classes of decaboranyl ethers containing a range of functional groups substituted at the B5 or B6 positions were achieved through the reaction of alcohols with halodecaboranes. The surprising regioselectivity of the reaction, where the reaction of the 6-halodecaboranes (6-X-B(10)H(13)) with alcohols yielded the 5-substituted decaboranyl ethers (5-RO-B(10)H(13)) and the reaction with 5-halodecaboranes (5-X-B(10)H(13)) gave the 6-substituted decaboranyl ethers (6-RO-B(10)H(13)), was confirmed by NMR and X-ray crystallographic analyses. The crystallographic determinations also showed that the decaboranyl ethers had shortened B-O bonds and apparent sp(2) hybridization at oxygen indicating significant π-backbonding from oxygen to the cage boron. A possible substitution mechanism was computationally identified involving: (1) initial nucleophilic attack by the alcohol-oxygen at a site adjacent to the 5- or 6-halo-substituted boron, (2) movement of the terminal hydrogen at the point of attack to a bridging position, (3) formation of a 5-membered (B-O-H-Cl-B) cyclic transition state allowing the acidic methanolic-hydrogen to bond to the halogen, (4) release of HX, and finally (5) movement of a bridging hydrogen into the vacated terminal position. Deuterium labeling studies confirmed the movement of hydrogen from a bridging position of the halodecaborane into the halogen-vacated terminal position on the decaboranyl ether product. The relative reaction rates of the 6-X-B(10)H(13) compounds (X = F, Cl, Br, I) with alcohols were likewise found to be consistent with this mechanism. 相似文献
187.
A. G. Hunt T. E. Skinner R. P. Ewing B. Ghanbarian-Alavijeh 《The European Physical Journal B - Condensed Matter and Complex Systems》2011,80(4):411-432
A recently introduced theory of solute transport in porous media is tested
by comparison with experiment. The solute transport is predicted using an
adaptation of the cluster statistics of percolation theory to critical path
analysis together with knowledge of how the structure of such percolation
clusters affects the time of transport across them. Only the effects of a
single scale of medium heterogeneity are incorporated, and a minimal amount
of information regarding the structure of the medium is required. This
framework is used to find effectively the distributions of solute velocities
and travel distances and thus generate arrival time distributions. The
comparison with experiment focuses on the dispersivity (the ratio of the
second to the first moment of the spatial solute distribution). The
predictions of the theory in the absence of diffusion are verified by
comparing with over 2200 experiments over length scales from a few microns
to 100 km. At larger length scales (centimeters on up) about 95% of the
data lie within our predicted bounds. At smaller length scales approximately
99.8% of the data lie where we predict. These comparisons are not trivial
as the typical values of the dispersivity increase by ten orders of
magnitude over ten orders of magnitude of length scale. Noteworthy is that
the classical advection-dispersion (ADE) equation predicts that the
dispersivity should be independent of length scale! This agreement with
experiment requires rethinking of the relevance of diffusion and multi-scale
heterogeneity and would also appear to signal the complete inappropriateness
of using the classical ADE or any of its derivatives to model solute
transport. 相似文献
188.
189.
190.
Damon Bahr Eula Ewing Monroe Mark Balzotti Dennis Eggett 《School science and mathematics》2009,109(4):223-236
A 2‐year school‐based mathematics professional development program is described and evaluated after its first year of implementation. Included in this program as its first course was a unique methods course in elementary education involving both preservice students and inservice teachers who cooperatively studied and applied reform pedagogy. The program resulted from the collaborative efforts of two institutions of higher education, a neighboring school district, the principal and teachers of one school within that district, and the state office of education. Evaluation of the first year of the program consisted of assessing the beliefs and perceptions of both preservice students and inservice teachers, along with an assessment of the mathematical achievement of the children within the classes of those teachers. Pre‐ and post‐assessments of the preservice students and inservice teachers' beliefs regarding reform pedagogy were administered using the IMAP [Integrating Mathematics and Pedagogy] Web‐Based Beliefs Survey (2006). Likert scale surveys were used to assess perceptions regarding course climate and participant relationships from both teacher groups. The mathematical achievement of children was assessed in three ways: The Wide Range Achievement Test‐3 ( Stone, Jastak, & Wilkinson, 1995 ), the Utah state criterion‐referenced assessment, and performance assessments developed specifically for use at the school. Data obtained from all sources indicated positive effects upon teachers and children, thus providing substantial evidence in support of both the value of the methods course itself and the overall professional development program. An additional evaluation will be conducted following the second year of the program. 相似文献