Biarc approximation of NURBS curves

An algorithm for approximating arbitrary NURBS curves with biarcs is presented. The main idea is to approximate the NURBS curve with a polygon, and then to approximate the polygon with biarcs to within the required tolerance. The method uses a parametric formulation of biarcs appropriate in geometric design using parametric curves. The method is most useful in numerical control to drive the cutter along straight line or circular paths.     

Product property and production rate control of styrene polymerization

A multivariable multi-rate nonlinear model predictive control (NMPC) strategy is applied to styrene polymerization. The NMPC algorithm incorporates a multi-rate Extended Kalman Filter (EKF) to handle state variable and parameter estimation. A fundamental model is developed for the styrene polymerization CSTR, and control of polymer properties such as number average molecular weight (NAMW) and polydispersity is considered. These properties characterize the final polymer distribution and are strong indicators of the polymer qualities of interest. Production rate control is also demonstrated. Temperature measurements are available frequently while laboratory measurements of concentration and molecular weight distribution are available infrequently with substantial time delays between sampling and analysis. Observability analysis of the augmented system provides guidelines for the design of the augmented disturbance model for use in estimation using the multi-rate EKF. The observability analysis links measurement sets and corresponding observable disturbance models, and shows that measurements of moments of the polymer distribution are essential for good estimation and control. The CSTR is operated at an open-loop unstable steady state. Control simulations are performed under conditions of plant-model structural mismatch and in the presence of parameter uncertainty and disturbances, and the proposed multi-rate NMPC algorithm is shown to provide superior performance compared to linear multi-rate and nonlinear single-rate MPC algorithms. The major contributions of this work are the development of the multi-rate estimator and the measurement design study based on the observability analysis.     

Solubility Limit of MgO in Al2O3 at 1600°C

The solubility of Mg in alumina was measured using wavelength-dispersive spectroscopy mounted on a scanning electron microscope. Careful calibration of the microscope's working conditions was performed in order to optimize the detection limit and accuracy. Measurements were conducted on water-quenched and furnace-cooled samples, without any thermal or chemical etching to avoid alteration of the bulk concentration. The results indicate the solubility limit of Mg in alumina to be 132±11 ppm at 1600°C.     

Structure and digestibility of tissues in normal and brown midrib pearl millet (Pennisetum glaucum)

The tissues in leaf blades, midribs, sheaths and stems of normal (N), 5848, and two brown midrib (bmr) mutants, 5753 and 5778, of pearl millet (Pennisetum glaucum (L) R Br) were examined for structural characteristics related to digestibility. The anatomies of the various plant parts were not substantially different between N and bmr plants. The more rigid, lignified tissues such as vascular bundles in all plant parts and the rind of stems were not digested after incubation for 7 days in N or bmr plants, indicating that modifications in these tissues were not sufficient to affect biodegradation. Modifications in the digestible tissues resulted in faster and more extensive degradation in bmr plants, and these changes appear to be the most significant in relation to biodegradation. The parenchyma of midveins and stems, which occupies c 70 and 60% of the cross-sectional area of these respective parts, were the sites where modification in phenolics resulted in the greatest improvement in digestibility.     

Multicast support for mobile hosts using Mobile IP: Design issues and proposed architecture

In this paper, we consider the problem of providing multicast to mobile hosts using Mobile IP for network routing support. Providing multicast in an internetwork with mobile hosts is made difficult because many multicast protocols are inefficient when faced with frequent membership or location changes. This basic difficulty can be handled in a number of ways, but three main problems emerge with most solutions. The tunnel convergence problem, the duplication problem, and the scoping problem are identified in this paper and a set of solutions are proposed. The paper describes an architecture to support IP multicast for mobile hosts using Mobile IP. The basic unicast routing capability of Mobile IP is used to serve as the foundation for the design of a multicast service facility for mobile hosts. We believe that our scheme is transparent to higher layers, simple, flexible, robust, scalable, and, to the extent possible, independent of the underlying multicast routing facility. For example, our scheme could interoperate with DVMRP, MOSPF, CBT, or PIM in the current Internet. Where differences exist between the current version of IP (IPv4) and the next generation protocol (IPv6), these differences and any further optimizations are discussed. This revised version was published online in June 2006 with corrections to the Cover Date.     

Atomistic simulations of the surfaces of thin films of random copolymers

Amorphous thin films of styrene-butadiene and styrene-butadiene-acrylonitrile copolymers containing a small amount of acrylic acid are generated using molecular dynamics and energy minimization simulations. The structure of the films shows an interior region of bulk density and a thin outer surface layer where the density falls to zero. The surface layer over which the density changes is approximately 5 Å in thickness. The film mass density at its center of mass is close to the bulk values. The orientation function parameter of the backbone carbon-carbon bonds, averaged over the ensemble of representative cells, shows a random nature in the dense region and an inclination towards an orientation somewhat along the plane of the surface layer in the external parts of the film. The styrene rings are mostly located in the bulk region, with random spatial and orientation distributions. The polar groups in the acrylonitrile segment of the SBA films are mostly found in the surface region, where they contribute to the marked enhancement in the surface energy for SBA films compared to SB films. The surface energy values deduced from the models are systematically slightly lower than independent estimates.     

Uncle Sam's crypto road show

State Department documents released to the Electronic Privacy Information Center (EPIC) illustrate the extensive travels of Ambassador David Aaron, President Clinton's former Special Envoy for Cryptography, during 1996 and 1997. On 6 November 1996, Aaron became the Under Secretary of Commerce for international trade. Aaron was charged by the Clinton administration with selling the concept of the unpopular key escrow/key recovery initiatives to governments around the world. This was in addition to his other duties as Permanent Representative to the Organization for Economic Cooperation and Development (OECD) in Paris.     

The Scintillation Mechanism in Thallium Doped Alkali Halides

In the scintillation mechanism for alkali iodides doped with thallous iodide: 1. Most of the luminescence, and possibly all of it, is from recombination and therefore energy transfer is predominantly from charge transport to thallium. 2. There are two modes of recombination at thallium which differ in the sequence of charge trapping at Tl+. The electron may be trapped before a mobile hole recombines with it, or the hole may be trapped before recombination with a free electron. 3. Thermal hole diffusion is an important process at room temperature and determines which mode a recombination event follows. 4. Both modes of recombination are active. 5. There is non-thermal hole trapping which is a significant part of the scintillator mechanism.     

Dimensionality in the measurement of authoritarian and political attitudes.

Administered 300 items from major inventories of authoritarian and political attitudes (e.g., the Rokeach Dogmatism Scale) to 135 undergraduates. The 300 items were reduced to 77 by selecting those with major factor loadings. Refactoring the 77 produced 25 1st-order factors and 10 2nd-order factors. The 1st-order factors typically referred to groupings of specific attitudes while 2nd-order factors referred to broad patterns which transcend a variety of attitudes. 4 major 2nd-order factors were identified as Religiosity, Political-Economic Liberalism, Authoritarianism, and Restrictiveness; these were found to differentiate Ss according to political and religious affiliations. Examination of items loading on the factors was considered to support the concept of the authoritarian personality but provided less support for M. Rokeach's concepts. The Melvin-Eysenck 2-factor model did not offer enough dimensions to account for the major sources of authoritarian and political attitudes. (French summary) (17 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)