109 research outputs found
Characterization of denture acrylic resin surfaces modified by glow discharges
Resin samples prepared by compression molding using a poly (methyl methacrylate) (PMMA) denture base material were exposed to radio-frequency (rf) glow discharges to improve the wettability of the material. Fourier transform infrared (FT-IR) reflectance, X-ray photoelectron spectroscopy (XPS), and contact-angle measurements have been employed to characterize the changes introduced by the glow discharge plasma. FT-IR measurements cannot detect any modification. XPS reveals an increase in the O/C atomic ratio. Contact angles of the plasma-treated samples are always lower when compared with untreated ones. The increased O atomic concentration is attributed to formation of -COH groups on the surface during plasma treatment. The O/C atomic ratio decreases upon heating the samples in vacuum to 100 °C for 1-2 min and exposing the samples to liquid CH2Cl2 for 1-2 min. Exposure to distilled water for prolonged periods causes a slight decrease during the initial 1-20 days but levels off to a constant value up to a period of 60 days. Plasma treatment seems to offer a durable increase in the wettability for these materials left in air or distilled water
Heat-damage assessment of carbon-fiber-reinforced polymer composites by diffuse reflectance infrared spectroscopy
Diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy was used to assess the effects of heat damage on carbon-fiber-reinforced polymer composites. Moisture-saturated graphite-epoxy laminates with a quasi-isotropic lay-up were heat-damaged above their upper service temperatures. The loss of matrix-dominated mechanical properties due to heat exposure was investigated in the laboratory under environmental testing conditions with mechanical tests, ultrasonic C-scanning, and DRIFT spectroscopy. The reduction of the mechanical strength of the composite materials was accompanied by an increase in the carbonyl band integral and a decrease in the phenyl ratio and hydroxyl and hydrocarbon band integrals, as shown by the DRIFT spectra. DRIFT was confirmed to be more effective than ultrasonic inspection in evaluating the extent of heat damage, and a good correlation was found between the mechanical test results and DRIFT spectra. © 2005 Wiley Periodicals, Inc
Rotationally Invariant Hamiltonians for Nuclear Spectra Based on Quantum Algebras
The rotational invariance under the usual physical angular momentum of the
SUq(2) Hamiltonian for the description of rotational nuclear spectra is
explicitly proved and a connection of this Hamiltonian to the formalisms of
Amal'sky and Harris is provided. In addition, a new Hamiltonian for rotational
spectra is introduced, based on the construction of irreducible tensor
operators (ITO) under SUq(2) and use of q-deformed tensor products and
q-deformed Clebsch-Gordan coefficients. The rotational invariance of this
SUq(2) ITO Hamiltonian under the usual physical angular momentum is explicitly
proved, a simple closed expression for its energy spectrum (the ``hyperbolic
tangent formula'') is introduced, and its connection to the Harris formalism is
established. Numerical tests in a series of Th isotopes are provided.Comment: 34 pages, LaTe
High fidelity replication of surface texture and geometric form of a high aspect ratio aerodynamic test component
This paper details, assesses and validates a technique for the replication of a titanium wind tunnel test
aerofoil in polyurethane resin. Existing resin replication techniques are adapted to overcome the
technical difficulties associated with casting a high aspect ratio component. The technique is shown to
have high replication fidelity over all important length-scales. The blade chord was accurate to 0.02%,
and the maximum blade thickness was accurate to 2.5%. Important spatial and amplitude areal
surface texture parameter were accurate to within 2%. Compared to an existing similar system using
correlation areal parameters the current technique is shown to have lower fidelity and this difference is
discussed. The current technique was developed for the measurement of boundary layer flowâlaminar
to turbulentâ transition for gas turbine compressor blade profiles and this application is illustrated
Alpha decay and proton-neutron correlations
We study the influence of proton-neutron (p-n) correlations on alpha-decay
width. It is shown from the analysis of alpha Q values that the p-n
correlations increase the penetration of the alpha particle through the Coulomb
barrier in the treatment following Gamow's formalism, and enlarges the total
alpha-decay width significantly.
In particular, the isoscalar p-n interactions play an essential role in
enlarging the alpha-decay width.
The so-called "alpha-condensate" in Z > 84 isotopes are related to the strong
p-n correlations.Comment: 5 pages, 6 figures, accepted for publication in Phys. Rev. C (R.C.
Ground- band coupling in heavy deformed nuclei and SU(3) contraction limit
We derive analytic expressions for the energies and -transition
probabilities in the states of the ground and bands of heavy deformed
nuclei within a collective Vector-Boson Model with SU(3) dynamical symmetry. On
this basis we examine the analytic behavior of the SU(3) energy splitting and
the B(E2) interband transition ratios in the SU(3) contraction limits of the
model. The theoretical analyses outline physically reasonable ways in which the
ground- band coupling vanishes. The experimental data on the lowest
collective states of even-even rare earth nuclei and actinides strongly support
the theoretical results. They suggest that a transition from the
ground- band coupling scheme to a scheme in which the ground band is
situated in a separate irreducible representation of SU(3) should be realized
towards the midshell regions. We propose that generally the SU(3) group
contraction process should play an important role for such a kind of
transitions in any collective band coupling scheme in heavy deformed nuclei.Comment: 24 pages (LaTeX), 7 figures (12 postscript files
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