3,798 research outputs found
Electrical conductivity cell and method for fabricating the same
A flask having a threaded neck and a cap adapted for threaded engagement on the neck are used. A laminated disc between the cap and the neck forms a gas tight seal and the cap has a central opening that exposes a medial region of the disc. Piercing the disc through the opening are two electrodes, the inner ends of which contact the sample within the flask and the outer ends of which can be connected to test equipment. Cylindric glass tubes are fitted over the external portion of the electrodes to provide physical support and silicone rubber or a similar material serves to retain the glass cylinders in place and form a gas tight seal between the cylinders and the electrodes. Shrinkable tubing is shrunk over the glass tubes to afford further mechanical support and sealing. A final relatively large diameter shrinkable tube is shrunk over both electrodes and their associated glass cylinders. The support and sealing means for the electrodes is confined to a limited portion of the medial region of the disc so that the remainder of such region can be punctured by a hollow needle to introduce a test sample within the flask
Controlled nanochannel lattice formation utilizing prepatterned substrates
Solid substrates can be endued with self-organized regular stripe patterns of
nanoscopic lengthscale by Langmuir-Blodgett transfer of organic monolayers.
Here we consider the effect of periodically prepatterned substrates on this
process of pattern formation. It leads to a time periodic forcing of the
oscillatory behavior at the meniscus. Utilizing higher order synchronization
with this forcing, complex periodic patterns of predefined wavelength can be
created. The dependence of the synchronization on the amplitude and the
wavelength of the wetting contrast is investigated in one and two spatial
dimensions and the resulting patterns are discussed. Furthermore, the effect of
prepatterned substrates on the pattern selection process is investigated
Spectroscopic Evidence for the Specific Na+ and K+ Interactions with the Hydrogen-bonded Water Molecules at the Electrolyte Aqueous Solution Surfaces
Sum frequency generation vibrational spectra of the water molecules at the
NaF and KF aqueous solution surfaces showed significantly different spectral
features and different concentration dependence. This result is the first
direct observation of the cation effects of the simple alkali cations, which
have been believed to be depleted from the aqueous surface, on the hydrogen
bonding structure of the water molecules at the electrolyte solution surfaces.
These observations may provide important clue to understand the fundamental
phenomenon of ions at the air/water interface.Comment: 15 pages, 2 figure
Wall-liquid and wall-crystal interfacial free energies via thermodynamic integration: A molecular dynamics simulation study
A method is proposed to compute the interfacial free energy of a
Lennard-Jones system in contact with a structured wall by molecular dynamics
simulation. Both the bulk liquid and bulk face-centered-cubic crystal phase
along the (111) orientation are considered. Our approach is based on a
thermodynamic integration scheme where first the bulk Lennard-Jones system is
reversibly transformed to a state where it interacts with a structureless flat
wall. In a second step, the flat structureless wall is reversibly transformed
into an atomistic wall with crystalline structure. The dependence of the
interfacial free energy on various parameters such as the wall potential, the
density and orientation of the wall is investigated. The conditions are
indicated under which a Lennard-Jones crystal partially wets a flat wall.Comment: 15 pages, 11 figure
Kinetics of Surfactant Adsorption at Fluid/Fluid Interfaces: Non-ionic Surfactants
We present a model treating the kinetics of adsorption of soluble
surface-active molecules at the interface between an aqueous solution and
another fluid phase. The model accounts for both the diffusive transport inside
the solution and the kinetics taking place at the interface using a free-energy
formulation. In addition, it offers a general method of calculating dynamic
surface tensions. Non-ionic surfactants are shown, in general, to undergo a
diffusion-limited adsorption, in accord with experimental findings.Comment: 6 pages, 3 figures, see also cond-mat/960814
Detecting Hidden Differences via Permutation Symmetries
We present a method for describing and characterizing the state of N
particles that may be distinguishable in principle but not in practice due to
experimental limitations. The technique relies upon a careful treatment of the
exchange symmetry of the state among experimentally accessible and
experimentally inaccessible degrees of freedom. The approach we present allows
a new formalisation of the notion of indistinguishability and can be
implemented easily using currently available experimental techniques. Our work
is of direct relevance to current experiments in quantum optics, for which we
provide a specific implementation.Comment: 8 pages, 1 figur
Transonic small-disturbance theory for lightly loaded cascades
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76863/1/AIAA-7841-736.pd
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
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