Optimum multiple- and single-stress accelerated life tests

We consider the optimal design of Accelerated Life Tests (ALT) with Type II censored data. It is assumed that the time-to-failure, or a transformation of it, follows a location scale Gumbel distribution. The location parameter of this distribution is assumed to be of the form;(DIAGRAM, TABLE OR GRAPHIC OMITTED...PLEASE SEE DAI);where the (beta)(,j)\u27s are unknown and the f(,j)\u27s are functions of the stresses x. The scale parameter, (sigma), of the distribution is assumed to be independent of the stresses x;We estimate the parameters in the model using a linear model inwhich the dependent variables are observed order statistics at thepoints of the design. We give general formulae for the Best LinearUnbiased Estimator (BLUE), Y(,p), of the 100pth percentile, Y(,p), of the(\u27 )Gumbel distribution at the design stress x(,D). Also, a general expression for Var(Y(,p)) is derived.(\u27 );For designs in k+1 points, we use asymptotic theory to express^Var(Y(,p)) as a function of the number of allocated units and the(\u27 )^proportion of censoring at each of the k+1 stress levels in the^design. The primary objective is to find designs that minimize^Var(Y(,p)). However, this minimization is complicated by the lack of(\u27 )^closed form expressions for the expected values of the order^statistics and the variance-covariance matrix of the error term in^the linear model. Thus, we propose to restrict the optimization to^designs that minimize one of the components of Var(Y(,p)); in practical(\u27 )situations, this component is usually the dominant term of Var(Y(,p)).(\u27 )We prove that the proposed minimization is equivalent to a problemof optimal extrapolation under a linear model with uncorrelated errors;In the case of a single accelerating stress, we present a characterization of optimal designs in k+1 points when the functions f(,0),...,f(,k) are a T-system in a finite interval a,b;In the case of two or more accelerating stresses and uniform proportion of censoring at each point in the design, we present optimal designs for diverse forms of the regression function;(DIAGRAM, TABLE OR GRAPHIC OMITTED...PLEASE SEE DAI);In particular, these forms include: regression in two variables with first order terms and the cross product, polynomials in r dimension of degree less than or equal to s, and polynomials in three variables with first order terms and cross products of second order

Layer by Layer, Nano-particle "Only" Surface Modification of Filtration Membranes

Layer by Layer (LbL) deposition using primarily inorganic silica nanoparticles is employed for the modification of polymeric micro and ultrafiltration (MF/UF) membranes to produce thin film composites (TFC) with potential nanofiltration (NF) and reverse osmosis (RO) capabilities.. A variety of porous substrate membranes with different membrane surface characteristics are employed, but exhibiting in common that wicking of water does not readily occur into the pore structure, including polycarbonate track etched (PCTE), polyethersulfone (PES) and sulfonated PES (SPEES) MF/UF membranes. Both spherical (cationic/anionic) and eccentric elongated (anionic) silica nanoparticles are deposited using conditions similar to those reported by Lee et al.1 Appropriate selection of the pH's for anionic and cationic particle deposition enables the construction of nanoparticle only layers 100 -1200 nm in thickness atop the original membrane substrates. The surface layer thickness varies monotonically with the number of bilayers (anionic/cationic deposition cycles) as expected. The deposition process is optimized to eliminate drying induced cracking and to improve mechanical durability via thickness control and post-deposition hydro-thermal treatment. The hydrodynamic permeability of these TFC membranes is measured to evaluate their performance under typical NF operating conditions using dead-end permeation experiments and their performance compared quantitatively with realistic hydrodynamic models, with favorable results. For track etched polycarbonate MF substrates, surface modification causes a permeability reduction of approximately two orders of magnitude with respect to the bare substrates, to values comparable to those for typical commercial NF membranes. Good quantitative agreement with hydrodynamic models with no adjustable parameters was also established for this case, providing indirect confirmation that the LbL deposited surface layers are largely defect (crack) free. Imaging of our TFC membranes after permeation tests confirmed that no significant mechanical damage resulted, indicating integrity and robustness of the LbL deposited surface layers in typical applications. The selectivity of these novel TFC membranes was also tested using standard "rejection" tests normally used to characterize NF and RO membranes for their capabilities in typical applications, such as water softening or desalination. We report the dextran standards molecular weight "cut-off" (MWCO) using mixed dextrans from 1.5 to 500 KDa in dead-end stir cells, and the percentage of rejection of standard bivalent and monovalent salt solutions using steady cross flow permeation experiments. The results confirm rejection of at least 60% of even the smallest dextrans, an estimated dextran MWCO of 20 KDa, and rejection of 10% and 20% for monovalent (NaCl) and bivalent (MgSO4) salts, respectively, for all the TFC membranes studied, while the unmodified membranes showed no rejection capability at all. The work supports that nanoparticle based LbL surface modification of MF/UF membranes can produce filtration quality media for important water purification applications, such as nanofiltration (NF) softening processes, natural organic matter (NOM) elimination and possibly reverse osmosis (RO) desalination

Apuntes a la organización de documentos: bases teóricas y consideraciones prácticas

To address the organization of documents, requires a comprehensive management of archival theory, due to its planning is influenced not only by the phase of assessment and selection, but also by identification, classification, arrangement, description and installation aspects. In line with this approach, concepts and theories presented in this text, condense the experiences of the lead entity concerning the application of archival policy in Colombia (AGN), and of some national and international theorists, who, in the author´s point of view, provide judgment elements for the organization nd administration of documents

Tablas de retención documental enfocada a procesos (TRDP): una propuesta emergente en tiempos de cambio

This article aims to give the reader an introductory idea of the terms identification and evaluation of documents, because in recent years has been a constant called the national and international archival community, the set limits and boundaries for one or other concept. It then seeks to draw attention to the time of proposing and drafting tables with document retention-TRDP process approach, because your gear requires the car to explore and wonder what is the most suitable for archiving tool, here proposed, and finally, to publicize the experience of the Universidad de La Salle around document management and quality management

Profane Rites. Contemporary Argentine Literature

Indexación: Revista UNAB.Este artículo propone una lectura en torno a ciertos modos de representación del rito religioso popular en dos novelas argentinas –La Virgen Cabeza, Gabriela Cabezón Cámara; Santería de Leonardo Oyola– y en una crónica –Cuando me muera quiero que me toquen cumbia de Cristián Alarcón–. En este corpus se interpreta el rito profano desde una lógica contraespectacular que implica el cruce, despliegue y desborde de cuerpos, lenguaje, marginalidad e imágenes.This article proposes an interpretation around certain modes of representation of the popular religious rite in two argentinian novels: La Virgen Cabeza by Gabriela Cabezón Cámara, Santería by Leonardo Oyola and in the chronicle: Cuando me muera quiero que me toquen cumbia by Cristián Alarcón. The profane rite is interpreted as a contraspectacular way that implies the crossing, unfolding and overflowing of bodies, language, marginality and images