16 research outputs found
Conservation of the Windover (8Br246) Textiles
No full textAbstractThe excavations at the Windover Bog site (8BR246) in 1986 and 1987 yielded 87 specimens of technologically sophisticated textiles and other perishables from 37 human burials. The assemblage currently represents the oldest known textiles from this hemisphere. Unfortunately, microscopic examination has demonstrated that substantial cellular degradation has occurred in these artifacts. In fact, these items are but the dimmest reflections or more accurately skeletons of their former predepositional states. Although traditional consolidants ensured a minimum of warpage and shrinkage with subsequent freeze drying, they produced an undesirable surficial film. Additionally, the resultant products were extremely brittle and required further treatment. To this end, several leading authorities suggested the testing of Parylene gas phase polymer technology on the Windover specimens. The senior author introduced Parylene gas phase technology to the conservation field in 1984. Since that time, numerous evaluation programs have been undertaken at major institutions. Important artifacts as well as extremely ancient natural history materials have been successfully treated utilizing Parylene technology [1]. This paper specifically addresses the application of Parylene gas phase polymer technology to the consolidation and preservation of the unique textile materials recovered from the Windover site. Major areas of discussion are: historical background, early conservation efforts, evaluation and decision to use Parylene technology, properties of the Parylene family of polymers, the method of deposition and treatment, and final conclusions on the consolidation of the treated textiles.</jats:p
The Calibration of Laboratory X‐Ray Diffraction Equipment Using NIST Standard Reference Materials
No full textDEoptim: An R Package for Global Optimization by Differential Evolution
No full textThis article describes the R package DEoptim, which implements the differential evolution algorithm for global optimization of a real-valued function of a real-valued parameter vector. The implementation of differential evolution in DEoptim interfaces with C code for efficiency. The utility of the package is illustrated by case studies in fitting a Parratt model for X-ray reflectometry data and a Markov-switching generalized autoregressive conditional heteroskedasticity model for the returns of the Swiss Market Index
DEoptim: An R Package for Global Optimization by Differential Evolution
No full textThis article describes the R package DEoptim which implements the differential evolution algorithm for the global optimization of a real-valued function of a real-valued parameter vector. The implementation of differential evolution in DEoptim interfaces with C code for efficiency. The utility of the package is illustrated via case studies in fitting a Parratt model for X-ray reflectometry data and a Markov-Switching Generalized
AutoRegressive Conditional Heteroskedasticity (MSGARCH) model for the returns of the Swiss Market Index
DEoptim: An R Package for Global Optimization by Differential Evolution
No full textThis article describes the R package DEoptim which implements the differential evolution algorithm for the global optimization of a real-valued function of a real-valued parameter vector. The implementation of differential evolution in DEoptim interfaces with C code for efficiency. The utility of the package is illustrated via case studies in fitting a Parratt model for X-ray reflectometry data and a Markov-Switching Generalized AutoRegressive Conditional Heteroskedasticity (MSGARCH) model for the returns of the Swiss Market Index.global optimization; evolutionary algorithm; differential evolution; R software
"Non-destructive" dimensional metrology of EUV resist gratings (Conference Presentation)
No full textX-ray scattering critical dimensional metrology using a compact x-ray source for next generation semiconductor devices
No full text
The Application of the Fundamental Parameters Approach as Implemented in TOPAS to Divergent Beam Powder Diffraction Data
No full textThe fundamental parameters approach (FPA) as implemented in TOPAS is investigated for analyses of conventional X-ray powder diffraction (XRPD) data. The FPA involves the convolution of a series of models, each one constituting an individual contribution to the geometric portion of the instrument profile function (IPF). Parameters within each model are refined by least squares to yield a presumably accurate description of the experiment. If one wishes to interrogate the functionality of said models, a diffractometer wherein the uncertainties in optical character are minimized is required. To this end, a diffractometer was built at NIST which featured conventional divergent beam optics in conjunction with a well aligned, stiff, and accurate goniometer assembly. Initial results indicated that the detector arm was flexing; this problem has been addressed with the fabrication and installation of a new arm and counterweight assembly. Data collected from NIST Standard Reference Material (SRM) 660a, lanthanum hexaboride, are analyzed using the FPA method to yield conclusions on the validity of the models with respect to shape and position of the diffraction profiles.</jats:p
