3,224 research outputs found
Experiments and modeling of shear-driven film separation
Dynamic thin liquid films driven by an adjacent gas flow have been subject to many investigations due to the presence of such films in many engineering applications. More specifically though, the behavior of such films at a sharply expanding corner has received little attention, but can be observed in internal combustion engines, liquid atomizer systems, refrigerant flows in evaporators, and film drag over wetted surfaces. Efforts to validate computational models of the propagation and separation of films are limited by the lack of reliable non-intrusive techniques to measure and analyze dynamic film parameters. In this study, film propagation models and film separation models were validated separately using experimental film thickness and separation measurements. These experimental measurements were performed in an experimental facility that enabled controlled development of a shear-driven thin liquid film and allowed for subsequent film analysis --Abstract, page iii
VADA: A transformation-based system for variable dependence analysis
Variable dependence is an analysis problem in which the aim is to determine the set of input variables that can affect the values stored in a chosen set of intermediate program variables. This paper shows the relationship between the variable dependence analysis problem and slicing and describes VADA, a system that implements variable dependence analysis. In order to cover the full range of C constructs and features, a transformation to a core language is employed Thus, the full analysis is required only for the core language, which is relatively simple. This reduces the overall effort required for dependency analysis. The transformations used need preserve only the variable dependence relation, and therefore need not be meaning preserving in the traditional sense. The paper describes how this relaxed meaning further simplifies the transformation phase of the approach. Finally, the results of an empirical study into the performance of the system are presented
Numerical Investigation of Light Scattering off Split-Ring Resonators
Recently, split ring-resonators (SRR's) have been realized experimentally in
the near infrared (NIR) and optical regime. In this contribution we numerically
investigate light propagation through an array of metallic SRR's in the NIR and
optical regime and compare our results to experimental results.
We find numerical solutions to the time-harmonic Maxwell's equations by using
advanced finite-element-methods (FEM). The geometry of the problem is
discretized with unstructured tetrahedral meshes. Higher order, vectorial
elements (edge elements) are used as ansatz functions. Transparent boundary
conditions and periodic boundary conditions are implemented, which allow to
treat light scattering problems off periodic structures.
This simulation tool enables us to obtain transmission and reflection spectra
of plane waves which are incident onto the SRR array under arbitrary angles of
incidence, with arbitrary polarization, and with arbitrary
wavelength-dependencies of the permittivity tensor. We compare the computed
spectra to experimental results and investigate resonances of the system.Comment: 9 pages, 8 figures (see original publication for images with a better
resolution
Numerical calculations of effective elastic properties of two cellular structures
Young's moduli of regular two-dimensional truss-like and eye-shape-like
structures are simulated by using the finite element method. The structures are
the idealizations of soft polymeric materials used in the electret
applications. In the simulations size of the representative smallest units are
varied, which changes the dimensions of the cell-walls in the structures. A
power-law expression with a quadratic as the exponential term is proposed for
the effective Young's moduli of the systems as a function of the solid volume
fraction. The data is divided into three regions with respect to the volume
fraction; low, intermediate and high concentrations. The parameters of the
proposed power-law expression in each region are later represented as a
function of the structural parameters, unit-cell dimensions. The presented
expression can be used to predict structure/property relationship in materials
with similar cellular structures. It is observed that the structures with
volume fractions of solid higher than 0.15 exhibit the importance of the
cell-wall thickness contribution in the elastic properties. The cell-wall
thickness is the most significant factor to predict the effective Young's
modulus of regular cellular structures at high volume fractions of solid. At
lower concentrations of solid, eye-like structure yields lower Young's modulus
than the truss-like structure with the similar anisotropy. Comparison of the
numerical results with those of experimental data of poly(propylene) show good
aggreement regarding the influence of cell-wall thickness on elastic properties
of thin cellular films.Comment: 7 figures and 2 table
The extrinsic proteins of Photosystem II
Years of genetic, biochemical, and structural work have provided a number of insights into the oxygen evolving complex (OEC) of Photosystem II (PSII) for a variety of photosynthetic organisms. However, questions still remain about the functions and interactions among the various subunits that make up the OEC. After a brief introduction to the individual subunits Psb27, PsbP, PsbQ, PsbR, PsbU, and PsbV, a current picture of the OEC as a whole in cyanobacteria, red algae, green algae, and higher plants will be presented. Additionally, the role that these proteins play in the dynamic life cycle of PSII will be discussed. © 2006 Springer Science+Business Media B.V
Magnetic polarons and magnetoresistance in EuB6
EuB6 is a low carrier density ferromagnet which exhibits large
magnetoresistance, positive or negative depending on temperature. The formation
of magnetic polarons just above the magnetic critical temperature has been
suggested by spin-flip Raman scattering experiments. We find that the fact that
EuB6 is a semimetal has to be taken into account to explain its electronic
properties, including magnetic polarons and magnetoresistance.Comment: 6 pages, 1 figur
Ανάδειξη της αγροτικής παραγωγής στην αστική καθημερινότητα. _προβολή _ εμπόριο _ ενημέρωση στην Θήβα
An 'aggregate economic' value (H), which is a combination of genetic control and relative economic value of traits, for all traits in the breeding objective was developed to aid in multitrait selection of strawberry cultivars in the subtropical southeast Queensland program. A profitability index for 12 traits was calculated from the effect of unit changes in each trait on changes in production costs and profitability. The index was applied to the breeding values of 3008 genotypes to produce estimates of H. H was validated by its high correlation (R=0.77) with year of selection (1945-1998) for commercial cultivars. H values for 3008 genotypes ranged from -0.36 to +0.28, when the zero value was set to the value of the cultivar 'Festival', which is the main cultivar grown in southeast Queensland. Modelling indicated that the gross margins were highly linearly related (R0.98) to H values where the genotype occupied less than 50% of total area planted in the industry, but this relationship became quadratic when the genotype occupied higher percentages of the total area planted to strawberries, and variation in gross margin increased as H values increased. H is efficient in identifying economically superior genotypes, but, when deploying new genotypes with high H, impacts on farm gross margin due to high adoption rates should also be considered
Magnetic metamaterials at telecommunication and visible frequencies
Arrays of gold split-rings with 50-nm minimum feature size and with an LC
resonance at 200-THz frequency (1500-nm wavelength) are fabricated. For normal
incidence conditions, they exhibit a pronounced fundamental magnetic mode,
arising from a coupling via the electric component of the incident light. For
oblique incidence, a coupling via the magnetic component is demonstrated as
well. Moreover, we identify a novel higher-order magnetic resonance at around
370 THz (800-nm wavelength) that evolves out of the Mie resonance for oblique
incidence. Comparison with theory delivers good agreement and also shows that
the structures allow for a negative magnetic permeability.Comment: 4 pages, 3 figure
Understanding the dynamics of photoionization-induced solitons in gas-filled hollow-core photonic crystal fibers
We present in detail our developed model [Saleh et al., Phys. Rev. Lett. 107]
that governs pulse propagation in hollow-core photonic crystal fibers filled by
an ionizing gas. By using perturbative methods, we find that the
photoionization process induces the opposite phenomenon of the well-known Raman
self-frequency red-shift of solitons in solid-core glass fibers, as was
recently experimentally demonstrated [Hoelzer et al., Phys. Rev. Lett. 107].
This process is only limited by ionization losses, and leads to a constant
acceleration of solitons in the time domain with a continuous blue-shift in the
frequency domain. By applying the Gagnon-B\'{e}langer gauge transformation,
multi-peak `inverted gravity-like' solitary waves are predicted. We also
demonstrate that the pulse dynamics shows the ejection of solitons during
propagation in such fibers, analogous to what happens in conventional
solid-core fibers. Moreover, unconventional long-range non-local interactions
between temporally distant solitons, unique of gas plasma systems, are
predicted and studied. Finally, the effects of higher-order dispersion
coefficients and the shock operator on the pulse dynamics are investigated,
showing that the resonant radiation in the UV [Joly et al., Phys. Rev. Lett.
106] can be improved via plasma formation.Comment: 9 pages, 10 figure
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