4,848 research outputs found
The creeping motion of liquid drops through a circular tube of comparable diameter
The creeping motion through a circular tube of neutrally buoyant Newtonian drops which have an undeformed radius comparable to that of the tube was studied experimentally. Both a Newtonian and a viscoelastic suspending fluid were used in order to determine the influence of viscoelasticity. The extra pressure drop owing to the presence of the suspended drops, the shape and velocity of the drops, and the streamlines of the flow are reported for various viscosity ratios, total flow rates and drop sizes
Migration of rigid spheres in a two-dimensional unidirectional shear flow of a second-order fluid
The lateral migration of a neutrally buoyant rigid sphere suspended in a second-order fluid is studied theoretically for unidirectional two-dimensional flows. The results demonstrate the existence of migration induced by normal stresses whenever there is a lateral variation of the shear rate in the undisturbed flow. The migration occurs in the direction of decreasing absolute shear rate, which is towards the centre-line for a plane Poiseuille flow and towards the outer cylinder wall for Couette flow. The direction of migration agrees with existing experimental data for a viscoelastic suspending fluid, and qualitative agreement is found between the theoretically predicted and experimentally measured sphere trajectories
The motion of a deformable drop in a second-order fluid
The cross-stream migration of a deformable drop in a unidirectional shear flow of a second-order fluid is considered. Expressions for the particle velocity due to the separate effects of deformation and viscoelastic rheology are obtained. The direction and magnitude of migration are calculated for the particular cases of Poiseuille flow and simple shear flow and compared with experimental data
Electromagnetism and multiple-valued loop-dependent wave functionals
We quantize the Maxwell theory in the presence of a electric charge in a
"dual" Loop Representation, i.e. a geometric representation of magnetic
Faraday's lines. It is found that the theory can be seen as a theory without
sources, except by the fact that the wave functional becomes multivalued. This
can be seen as the dual counterpart of what occurs in Maxwell theory with a
magnetic pole, when it is quantized in the ordinary Loop Representation. The
multivaluedness can be seen as a result of the multiply-connectedness of the
configuration space of the quantum theory.Comment: 5 page
Automated Identification and Classification of Stereochemistry: Chirality and Double Bond Stereoisomerism
Stereoisomers have the same molecular formula and the same atom connectivity
and their existence can be related to the presence of different
three-dimensional arrangements. Stereoisomerism is of great importance in many
different fields since the molecular properties and biological effects of the
stereoisomers are often significantly different. Most drugs for example, are
often composed of a single stereoisomer of a compound, and while one of them
may have therapeutic effects on the body, another may be toxic. A challenging
task is the automatic detection of stereoisomers using line input
specifications such as SMILES or InChI since it requires information about
group theory (to distinguish stereoisomers using mathematical information about
its symmetry), topology and geometry of the molecule. There are several
software packages that include modules to handle stereochemistry, especially
the ones to name a chemical structure and/or view, edit and generate chemical
structure diagrams. However, there is a lack of software capable of
automatically analyzing a molecule represented as a graph and generate a
classification of the type of isomerism present in a given atom or bond.
Considering the importance of stereoisomerism when comparing chemical
structures, this report describes a computer program for analyzing and
processing steric information contained in a chemical structure represented as
a molecular graph and providing as output a binary classification of the isomer
type based on the recommended conventions. Due to the complexity of the
underlying issue, specification of stereochemical information is currently
limited to explicit stereochemistry and to the two most common types of
stereochemistry caused by asymmetry around carbon atoms: chiral atom and double
bond. A Webtool to automatically identify and classify stereochemistry is
available at http://nams.lasige.di.fc.ul.pt/tools.ph
Buoyancy-driven motion of a deformable drop toward a planar wall at low Reynolds number
The slow viscous motion of a deformable drop moving normal to a planar wall is studied numerically. In particular, a boundary integral technique employing the Green's function appropriate to a no-slip planar wall is used. Beginning with spherical drop shapes far from the wall, highly deformed and ‘dimpled’ drop configurations are obtained as the planar wall is approached. The initial stages of dimpling and their evolution provide information and insight into the basic assumptions of film-drainage theory
Stability of a horizontal viscous fluid layer in a vertical time periodic electric field
The stability of a horizontal interface between two viscous fluids, one of
which is conducting and the other is dielectric, acted upon by a vertical
time-periodic electric field is considered. The two fluids are bounded by
electrodes separated by a finite distance. By means of Floquet theory, the
marginal stability curves are obtained, thereby elucidating the dependency of
the critical voltage and wavenumber upon the fluid viscosities. The limit of
vanishing viscosities is shown to be in excellent agreement with the marginal
stability curves predicted by means of a Mathieu equation. The methodology to
obtain the marginal stability curves developed here is applicable to any
arbitrary but time periodic-signal, as demonstrated for the case of a signal
with two different frequencies. As a special case, the marginal stability
curves for an applied ac voltage biased by a dc voltage are depicted. It is
shown that the mode coupling caused by the normal stress at the interface due
to the electric field leads to appearance of harmonic modes and subharmonic
modes. This is in contrast to the application of a voltage with a single
frequency which always leads to a harmonic mode. Whether a harmonic or
subharmonic mode is the most unstable one depends on details of the excitation
signal. It is also shown that the electrode spacing has a distinct effect on
the stability bahavior of the system
Treatment of bimodality in proficiency test of pH in bioethanol matrix
The pH value in bioethanol is a quality control parameter related to its
acidity and to the corrosiveness of vehicle engines when it is used as fuel. In
order to verify the comparability and reliability of the measurement of pH in
bioethanol matrix among some experienced chemical laboratories, reference
material (RM) of bioethanol developed by Inmetro - the Brazilian National
Metrology Institute - was used in a proficiency testing (PT) scheme. There was
a difference of more than one unit in the value of the pH measured due to the
type of internal filling electrolytic solutions (potassium chloride, KCl or
lithium chloride, LiCl) from the commercial pH combination electrodes used by
the participant laboratories. Therefore, bimodal distribution has occurred from
the data of this PT scheme. This work aims to present the possibilities that a
PT scheme provider can use to overcome the bimodality problem. Data from the PT
of pH in bioethanol were treated by two different statistical approaches:
kernel density model and the mixture of distributions. Application of these
statistical treatments improved the initial diagnoses of PT provider, by
solving bimodality problem and contributing for a better performance evaluation
in measuring pH of bioethanol.Comment: 20 pages, 6 figures, Accepted for publication in Accreditation and
Quality Assurance (ACQUAL
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