177 research outputs found
X-ray study of the electric double layer at the n-hexane/nanocolloidal silica interface
The spatial structure of the transition region between an insulator and an
electrolyte solution was studied with x-ray scattering.The electron density
profile across the n-hexane/silica sol interface (solutions with 5-nm, 7-nm,
and 12-nm colloidal particles) agrees with the theory of the electrical double
layer and shows separation of positive and negative charges. The interface
consists of three layers, i.e., a compact layer of Na+, a loose monolayer of
nanocolloidal particles as part of a thick diffuse layer, and a low-density
layer sandwiched between them. Its structure is described by a model in which
the potential gradient at the interface reflects the difference in the
potentials of "image forces" between the cationic Na+ and anionic nanoparticles
and the specific adsorption of surface charge. The density of water in the
large electric field (1-10 GV/m) of the transition region and the layering of
silica in the diffuse layer is discussed.Comment: 9 pages, 9 figure
The Kinetics of the Adiabatic and Nonadiabatic Reactions at the Metal and Semiconductor Electrodes
The basic results of the correct quantum-mechanical calculqtions
of the probability of the elementary act of adiabatic homogeneous
reactions are summarized. The calculations are carried
out for the model of the one-dimensional potential energy curves
without using the perturbation theory. The adiabatic and nonadiabatic electrochemical reactions at the metal and semiconductor electrodes are considered. The physical picture of the process is discussed. The adiabatic electrochemical process is shown to be of the many-electron character. The expressions for the transition probability is derived for the
metal and semiconductor electrodes. The redox reactions at the
semiconductor are considered in the presence of the surface states
The Kinetics of the Adiabatic and Nonadiabatic Reactions at the Metal and Semiconductor Electrodes
The basic results of the correct quantum-mechanical calculqtions
of the probability of the elementary act of adiabatic homogeneous
reactions are summarized. The calculations are carried
out for the model of the one-dimensional potential energy curves
without using the perturbation theory. The adiabatic and nonadiabatic electrochemical reactions at the metal and semiconductor electrodes are considered. The physical picture of the process is discussed. The adiabatic electrochemical process is shown to be of the many-electron character. The expressions for the transition probability is derived for the
metal and semiconductor electrodes. The redox reactions at the
semiconductor are considered in the presence of the surface states
Crystals of Na+ ions at the surface of a silica hydrosol
I used x-ray grazing incidence diffraction to measure the spatial
correlations between sodium ions adsorbed with Bjerrum's density at the surface
of a monodispersed 22-nm-particle colloidal silica solution stabilized by NaOH
with a total bulk concentration mol/L. My findings show that the surface
compact layer is in a two-dimensional crystalline state (symmetry p2), with
four ions forming the unit cell and a ~30 Angstrom translational correlation
length between sodium ions.Comment: 13 pages, 4 figure
Ion-Size Effect at the Surface of a Silica Hydrosol
The author used synchrotron x-ray reflectivity to study the ion-size effect
for alkali ions (Na, K, Rb, and Cs), with densities as high as
m, suspended above the surface of a
colloidal solution of silica nanoparticles in the field generated by the
surface electric-double layer. According to the data, large alkali ions
preferentially accumulate at the sol's surface replacing smaller ions, a
finding that qualitatively agrees with the dependence of the Kharkats-Ulstrup
single-ion electrostatic free energy on the ion's radius.Comment: 17 pages, 4 figure
Torsional fluctuations in columnar DNA assemblies
In columnar assemblies of helical bio-molecules the azimuthal degrees of
freedom, i.e. rotations about the long axes of molecules, may be important in
determining the structure of the assemblies especially when the interaction
energy between neighbouring molecules explicitly depends on their relative
azimuthal orientations. For DNA this leads to a rich variety of mesophases for
columnar assemblies, each categorized by a specific azimuthal ordering. In a
preceding paper [A. Wynveen, D. J. Lee, and A. A. Kornyshev, Eur. Phys. J. E,
16, 303 (2005)] a statistical mechanical theory was developed for the
assemblies of torsionally rigid molecues in order to determine how thermal
fluctuations influence the structure of these mesophases. Here we extend this
theory by including torsional fluctuations of the molecules, where a DNA
molecule may twist about its long axis at the cost of torsional elastic energy.
Comparing this with the previous study, we find that inclusion of torsional
fluctuations further increases the density at which the transition between the
hexagonal structure and the predicted rhombic phase occurs and reduces the
level of distortion in the rhombic phase. As X-ray diffraction may probe the
2-D lattice structure of such assemblies and provide information concerning the
underlying interaction between molecules, we have also calculated correlation
functions for the azimuthal ordering which are manifest in an x-ray scattering
intensity profiles.Comment: 33 pages, 8 figure
Long-range intramolecular electron transfer in aromatic radical anions and binuclear transition metal complexes
Linear response in theory of electron transfer reactions as an alternative to the molecular harmonic oscillator model
Ionic liquids at electrified interfaces
Until recently, âroom-temperatureâ (<100â150 °C) liquid-state electrochemistry was mostly electrochemistry of diluted electrolytes(1)â(4) where dissolved salt ions were surrounded by a considerable amount of solvent molecules. Highly concentrated liquid electrolytes were mostly considered in the narrow (albeit important) niche of high-temperature electrochemistry of molten inorganic salts(5-9) and in the even narrower niche of âfirst-generationâ room temperature ionic liquids, RTILs (such as chloro-aluminates and alkylammonium nitrates).(10-14) The situation has changed dramatically in the 2000s after the discovery of new moisture- and temperature-stable RTILs.(15, 16) These days, the âlater generationâ RTILs attracted wide attention within the electrochemical community.(17-31) Indeed, RTILs, as a class of compounds, possess a unique combination of properties (high charge density, electrochemical stability, low/negligible volatility, tunable polarity, etc.) that make them very attractive substances from fundamental and application points of view.(32-38) Most importantly, they can mix with each other in âcocktailsâ of oneâs choice to acquire the desired properties (e.g., wider temperature range of the liquid phase(39, 40)) and can serve as almost âuniversalâ solvents.(37, 41, 42) It is worth noting here one of the advantages of RTILs as compared to their high-temperature molten salt (HTMS)(43) âsister-systemsâ.(44) In RTILs the dissolved molecules are not imbedded in a harsh high temperature environment which could be destructive for many classes of fragile (organic) molecules
Epidemiology, practice of ventilation and outcome for patients at increased risk of postoperative pulmonary complications
BACKGROUND Limited information exists about the epidemiology and outcome of surgical patients at increased risk of postoperative pulmonary complications (PPCs), and how intraoperative ventilation was managed in these patients.
OBJECTIVES To determine the incidence of surgical patients at increased risk of PPCs, and to compare the intraoperative ventilation management and postoperative outcomes with patients at low risk of PPCs.
DESIGN This was a prospective international 1-week observational study using the âAssess Respiratory Risk in Surgical Patients in Catalonia risk scoreâ (ARISCAT score) for PPC for risk stratification.
PATIENTS AND SETTING Adult patients requiring intraoperative ventilation during general anaesthesia for surgery in 146 hospitals across 29 countries.
MAIN OUTCOME MEASURES The primary outcome was the incidence of patients at increased risk of PPCs based on the ARISCAT score. Secondary outcomes included intraoperative ventilatory management and clinical outcomes.
RESULTS A total of 9864 patients fulfilled the inclusion criteria. The incidence of patients at increased risk was 28.4%. The most frequently chosen tidal volume (VT) size was 500 ml, or 7 to 9 ml kg1 predicted body weight, slightly lower in patients at increased risk of PPCs. Levels of positive end-expiratory pressure (PEEP) were slightly higher in patients at increased risk of PPCs, with 14.3% receiving more than 5 cmH2O PEEP compared with 7.6% in patients at low risk of PPCs (P < 0.001). Patients with a predicted preoperative increased risk of PPCs developed PPCs more frequently: 19 versus 7%, relative risk (RR) 3.16 (95% confidence interval 2.76 to 3.61), P < 0.001) and had longer hospital stays. The only ventilatory factor associated with the occurrence of PPCs was the peak pressure.
CONCLUSION The incidence of patients with a predicted increased risk of PPCs is high. A large proportion of patients receive high VT and low PEEP levels. PPCs occur frequently in patients at increased risk, with worse clinical outcome
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