4,643 research outputs found
The effect of manganese oxide on the sinterability of hydroxyapatite
The sinterability of manganese oxide (MnO2) doped hydroxyapatite (HA) ranging from 0.05 to 1 wt% was investigated. Green samples were prepared and sintered in air at temperatures ranging from 1000 to 1400 °C. Sintered bodies were characterized to determine the phase stability, grain size, bulk density, hardness, fracture toughness and Young's modulus. XRD analysis revealed that the HA phase stability was not disrupted throughout the sintering regime employed. In general, samples containing less than 0.5 wt% MnO2 and when sintered at lower temperatures exhibited higher mechanical properties than the undoped HA. The study revealed that all the MnO2-doped HA achieved >99% relative density when sintered at 1100–1250 °C as compared to the undoped HA which could only attained highest value of 98.9% at 1150 °C. The addition of 0.05 wt% MnO2 was found to be most beneficial as the samples exhibited the highest hardness of 7.58 GPa and fracture toughness of 1.65 MPam1/2 as compared to 5.72 GPa and 1.22 MPam1/2 for the undoped HA when sintered at 1000 °C. Additionally, it was found that the MnO2-doped samples attained E values above 110 GPa when sintered at temperature as low as 1000 °C if compared to 1050 °C for the undoped HA
Comparative study of microwave radiation-induced magnetoresistive oscillations induced by circularly- and linearly- polarized photo-excitation
A comparative study of the radiation-induced magnetoresistance oscillations
in the high mobility GaAs/AlGaAs heterostructure two dimensional electron
system (2DES) under linearly- and circularlypolarized microwave excitation
indicates a profound difference in the response observed upon rotating the
microwave launcher for the two cases, although circularly polarized microwave
radiation induced magnetoresistance oscillations observed at low magnetic
fields are similar to the oscillations observed with linearly polarized
radiation. For the linearly polarized radiation, the magnetoresistive response
is a strong sinusoidal function of the launcher rotation (or linear
polarization) angle, {\theta}. For circularly polarized radiation, the
oscillatory magnetoresistive response is hardly sensitive to {\theta}
Observations and models for needle-tissue interactions
The asymmetry of a bevel-tip needle results in the needle naturally bending when it is inserted into soft tissue. In this study we present a mechanics-based model that calculates the deflection of the needle embedded in an elastic medium. Microscopic observations for several needle- gel interactions were used to characterize the interactions at the bevel tip and along the needle shaft. The model design was guided by microscopic observations of several needle- gel interactions. The energy-based model formulation incor- porates tissue-specific parameters such as rupture toughness, nonlinear material elasticity, and interaction stiffness, and needle geometric and material properties. Simulation results follow similar trends (deflection and radius of curvature) to those observed in macroscopic experimental studies of a robot- driven needle interacting with different kinds of gels. These results contribute to a mechanics-based model of robotic needle steering, extending previous work on kinematic models
Determining Object Orientations from Run Length Encodings
Run length codes are widely used for image compression, and efficient algorithms have been devised for identifying objects and calculating geometric features directly from these codes. However, if the image objects are rotated it can be difficult to determine their orientation and position so that they can be grasped by manipulators. This paper describes a method for structural determination of object orientation directly from the run length codes of successive image scan lines. An algorithm is described that makes use of the equations of object boundary segments to form hypotheses about object orientations that are refined as scanning progresses. 2-dimensional polygonal objects are discussed, and it is assumed that objects do not touch or overlap, although the algorithm could be extended to include those situations
Axisymmetric Self-Similar Equilibria of Self-Gravitating Isothermal Systems
All axisymmetric self-similar equilibria of self-gravitating, rotating,
isothermal systems are identified by solving the nonlinear Poisson equation
analytically. There are two families of equilibria: (1) Cylindrically symmetric
solutions in which the density varies with cylindrical radius as R^(-alpha),
with 0 <= alpha <= 2. (2) Axially symmetric solutions in which the density
varies as f(theta)/r^2, where `r' is the spherical radius and `theta' is the
co-latitude. The singular isothermal sphere is a special case of the latter
class with f(theta)=constant. The axially symmetric equilibrium configurations
form a two-parameter family of solutions and include equilibria which are
surprisingly asymmetric with respect to the equatorial plane. The asymmetric
equilibria are, however, not force-free at the singular points r=0, infinity,
and their relevance to real systems is unclear. For each hydrodynamic
equilibrium, we determine the phase-space distribution of the collisionless
analog.Comment: 13 pages, 7 figures, uses emulateapj.sty. Submitted to Ap
Effect of quantum nuclear motion on hydrogen bonding
This work considers how the properties of hydrogen bonded complexes,
D-H....A, are modified by the quantum motion of the shared proton. Using a
simple two-diabatic state model Hamiltonian, the analysis of the symmetric
case, where the donor (D) and acceptor (A) have the same proton affinity, is
carried out. For quantitative comparisons, a parametrization specific to the
O-H....O complexes is used. The vibrational energy levels of the
one-dimensional ground state adiabatic potential of the model are used to make
quantitative comparisons with a vast body of condensed phase data, spanning a
donor-acceptor separation (R) range of about 2.4-3.0 A, i.e., from strong to
weak bonds. The position of the proton and its longitudinal vibrational
frequency, along with the isotope effects in both are discussed. An analysis of
the secondary geometric isotope effects, using a simple extension of the
two-state model, yields an improved agreement of the predicted variation with R
of frequency isotope effects. The role of the bending modes in also considered:
their quantum effects compete with those of the stretching mode for certain
ranges of H-bond strengths. In spite of the economy in the parametrization of
the model used, it offers key insights into the defining features of H-bonds,
and semi-quantitatively captures several experimental trends.Comment: 12 pages, 8 figures. Notation clarified. Revised figure including the
effect of bending vibrations on secondary geometric isotope effect. Final
version, accepted for publication in Journal of Chemical Physic
Generation of a train of ultrashort pulses using periodic waves in tapered photonic crystal fibres
Funding This work was supported by the Ministry of Education , Nigeria for financial support through the TETFUND scholarship 55 scheme; CSIR [grant number 03(1264)/12/EMR-II].Peer reviewedPostprin
Transaction Cost of Offsite Construction (OSC): A New Zealand Study
Offsite construction (OSC) has been put forward as a solution to many prevailing challenges facing the construction industry, including but not limited to low productivity, housing shortage, lack of innovation, and poor-quality outputs. The uptake of OSC is relatively slow in the New Zealand construction industry. With only 10% of all the new builds using the OSC approach, it is evident that the potential of this construction approach is under-utilised. Many barriers have been identified as responsible for low uptake, including cost-related barriers. This study investigates the transaction cost of OSC, which is an extra cost to the project development cost and is generally overlooked in the project planning and development stage. This study aims to identify the factors that contribute to the transaction cost of OSC in New Zealand, alongside investigating the impact of transaction cost on overall project delivery and factors that can minimise the transaction cost. A questionnaire survey was conducted involving OSC practitioners in New Zealand. It was noted that consultation with building consent authority, the complexity of interface design, limited capacity of offsite manufacturers, and highly skilled workforce requirements contribute to transition cost during concept design, technical design and procurement, manufacturing, and on-site assembly stages. Consequently, disputes between stakeholders, uncertainty, an overall increase in project cost, and reluctance to use OSC may occur. It is noted that the use of innovation like automation, building information modeling, design for manufacturing and assembly, and consenting process to suit OSC holds the potential to reduce the transaction cost.fals
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