Evolving Guide Subdivision

To overcome the well-known shape deficiencies of bi-cubic subdivision surfaces, Evolving Guide subdivision (EG subdivision) generalizes C² bi-quartic (bi-4) splines that approximate a sequence of piecewise polynomial surface pieces near extraordinary points. Unlike guided subdivision, which achieves good shape by following a guide surface in a two-stage, geometry-dependent process, EG subdivision is defined by five new explicit subdivision rules. While formally only C¹ at extraordinary points, EG subdivision applied to an obstacle course of inputs generates surfaces without the oscillations and pinched highlight lines typical for Catmull-Clark subdivision. EG subdivision surfaces join C² with bi-3 surface pieces obtained by interpreting regular sub-nets as bi-cubic tensor-product splines and C² with adjacent EG surfaces. The EG subdivision control net surrounding an extraordinary node can have the same structure as Catmull-Clark subdivision: two rings of 4-sided facets around each extraordinary nodes so that extraordinary nodes are separated by at least one regular node.     

Effect of finite grating, waveguide width, and end-facet geometry on resonant subwavelength grating reflectivity

Resonant subwavelength gratings (RSGs) offer narrowband high reflectivity with low-reflectivity sidebands. Analysis with the commonly used rigorous coupled-wave analysis assumes an RSG with infinite lateral extent and illumination by plane waves. This analysis is performed with a finite-difference semivectorial high-order accurate two-dimensional Helmholtz code that is able to simulate the entire finite RSG structure in the dimension of the grating vector. We study the effect of finite beam size on RSG reflectivity, resonant wavelength, and spectral response width. Independently, we study the effect of a finite RSG by varying the waveguide length and number of grating periods while fixing the beam size. We show that the placement of the waveguide end facets relative to the termination of the grating has a significant effect on the reflectivity and response width.     

Electrophoretic deposition of polyetheretherketone (PEEK) and PEEK/Bioglass® coatings on NiTi shape memory alloy wires

Polyetheretherketone (PEEK) and PEEK/Bioglass® coatings were produced on shape memory alloy (NiTi, Nitinol®) wires using electrophoretic deposition (EPD). Best results were achieved with suspensions of PEEK powders in ethanol in the range (1–6 wt%), using a deposition time of 5 minutes and applied voltage of 20 Volts. EPD using these parameters led to high quality PEEK coatings with a homogeneous microstructure along the wire length and a uniform thickness of up to 15 μm without development of cracks or the presence of large voids. Suspensions of PEEK powders in ethanol with addition of Bioglass® particles (0.5–2 wt%) (size < 5 μm) were used to produce PEEK/Bioglass® coatings. Sintering was carried out as a post EPD process in order to densify the coatings and to improve the adhesion of the coatings to the substrate. The sintering temperature was 340 °C, sintering time 20 min and heating rate 300 °C/h. Sintering led to uniform and dense PEEK and PEEK/Bioglass® coatings without any cracks. The bioactive behaviour of PEEK/Bioglass® composite coatings was investigated by immersion in acellular simulated body fluid (SBF) for up to two weeks. As expected, hydroxyapatite crystals formed on the surface of the coated wires after 1 week in SBF, confirming the bioactive character of the coatings. The results have demonstrated for the first time that EPD is a very convenient method to obtain homogeneous and uniform bioactive PEEK and PEEK/Bioglass® coatings on Nitinol® wires for biomedical applications.     

Fabrication of reconfigurable protein matrices by cracking

The interface between extracellular matrices and cells is a dynamic environment that is crucial for regulating important cellular processes such as signal transduction, growth, differentiation, motility and apoptosis. In vitro cellular studies and the development of new biomaterials would benefit from matrices that allow reversible modulation of the cell adhesive signals at a scale that is commensurate with individual adhesion complexes. Here, we describe the fabrication of substrates containing arrays of cracks in which cell-adhesive proteins are selectively adsorbed. The widths of the cracks (120-3,200 nm) are similar in size to individual adhesion complexes (typically 500-3,000 nm) and can be modulated by adjusting the mechanical strain applied to the substrate. Morphology of cells can be reversibly manipulated multiple times through in situ adjustment of crack widths and hence the amount of the cell-adhesive proteins accessible to the cell. These substrates provide a new tool for assessing cellular responses associated with exposure to matrix proteins.     

Laboratory batch experiments of the combined effects of ultrasound and air stripping in removing CCl4 and 1,1,1-TCA from water

Ultrasonic and air-stripping techniques for removal of carbon tetrachloride (CCl₄) and 1,1,1-trichloroethane (1,1,1-TCA) from water were studied in batch experiments. Ultrasound (US) is effective for destroying organic compounds in aqueous solutions whereas air stripping (AS) efficiently transfers volatile compounds from the liquid to the gas phase. In simultaneous US and AS experiments, synergistic effects were observed and attributed to the effect of US on the mass transfer process. Using a photographic method, ultrasonic break up of gas bubbles and changes in gas holdup ratios were examined. In the two different gas-sparging systems studied, ultrasonic waves did not break up gas bubbles. In contrast, bubbles from the smaller porous size diffuser were coalesced due to sonication. In addition, both photographic and gas holdup experiments demonstrated that ultrasonic irradiation increased the gas holdup ratio. The enhancement observed in the removal of the compounds appeared to be due to this greater ultrasonic gas holdup ratio.     

Neutron transmission probability through a revolving slit for a continuous source and a divergent neutron beam

An analytical calculation for the transmission probability of neutrons travelling through a revolving slit is presented here. For the first time, two effects have been taken into account in the same approach, that is, on the one hand, the fact that the neutron beam might be divergent and, on the other hand, that neutrons from a continuous source can arrive at different times at the chopper. Furthermore, the neutron distribution at a given distance behind the chopper has been calculated and these theoretical results have been compared with simulated data obtained with the VITESS simulation program. The theoretical and the simulated curves are in good agreement.     

Encoding mechanical design features for recognition via neural nets

Within mechanical computer-aided design (CAD), pattern-recognition techniques are fundamental to feature recognition. The use of neural net software as the pattern-recognition element depends upon encoding schemes which extract critical information from candidate geometric subsets. The trained memory can then determine if a particular candidate geometric subset corresponds to a feature of interest. Successful experiments with particular encoding schemes over a restricted class of features will be presented. Neural nets were chosen with the long-term view toward a feature-recognition architecture where the end-user could customize the domain of features that can be recognized. The training of the neural net memory would be achieved through a graceful graphics interface. Extensive programming and knowledge bases would be avoided. This envisioned architecture will be presented to provide a context for the encoding schemes.     

Topological properties that model feature-based representation conversions within concurrent engineering

One of the fundamental axioms of concurrent engineering is that undertaking functional design without foreseeing the manufacturing process leads to production delays and increased costs. This widely accepted concurrent engineering principle is given a formal basis by development of a mathematical model for the conversion of a feature-based design representation to a manufacturing representation. Within the domain of thin-walled components, it is shown that the conversion to tooling cost representations can result in a discontinuous function when the sets of design and manufacturing representations have been formulated as topological spaces. This discontinuity formally reflects the folklore that a small design change can significantly increase product cost. The mathematical sophistication required within this model is suggestive of why manufacturability evaluations can be quite difficult.     

Summary of the Intercomparison of the Force Standard Machines of the National Institute of Standards and Technology,USA, and the Physikalisch-Technische Bundesanstalt,Germany

A comparison of force measurements performed at the National Institute of Standards and Technology, USA, and at the Physikalisch-Technische Bundesanstalt, Germany is reported. The focus of the study was the intercomparison of the forces realized by the two Institutes rather than the measurement process. The transfer standards used in the comparison consisted of force transducers and associated readout instrumentation. The results of the intercomparison reveal that over a range of 50 kN to 4.5 MN, the forces realized at NIST and at PTB compare favorably. For forces up to 900 kN the agreement is within ±40 ppm; above 900 kN the agreement is within ± 100 ppm.