3,662 research outputs found
An investigation of adhesive/adherend and fiber matrix interactions
Research during the report period focused on continued scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) of lap shear samples and flatwise tensile specimens and on the surface characterization of TiO2, Ti 6-4, and Ti powders with particular emphasis on their interaction with primer solutions of both polyphenylquinoxaline and LaRC-13 polyimide. The use of SEM and XPS in the analysis of Ti 6-4 adherend surfaces is described as well as differences in Ti 6-4 surface composition after different chemical pretreatments. Analysis of fractured surfaces is used to established the failure mode. The surface acidity of Ti 6-4 coupons can be established by reflectance visible spectroscopy using indicator dyes
Editorial: Language of Possibilities and Sense of the 1m/possible in Art Education
Schooling in the United States is increasingly defined by arthritic traditionalisms of standardized assessments and testing, school and teacher accountabilities, models of exacerbated efficiency and tracking, and even more strident state and federal calls for more of the same (Kanpol, 1997, p. ix). Mired in escalating restricted conventional practices that deny humanistic and democratic possibilities, many art educators are frequently unaware of what, in reality, is possible with/in art/ education. Moreover, our praxis continues to reflect dispositions and actions that are oftentimes bereft of the language of possibility or hope. Using the language of possibility, we transform our thinking from how it has been to how it could be. Those who achieve the impossible tend to focus their thoughts and energies on possibilities rather than limitations. Possibilities encompass the big picture, and provide hope for the future. To predict the future, we are obliged to actively create it. Even impossibilities give way to possibilities when we exhibit conduct, habits, or ways that lead to success. What we envision today with/in art/education, raising the quality of education, equity of opportunity in education, social responsibility, research, and possible initiatives, will give birth to worlds of possibilities
Continuity of symplectically adjoint maps and the algebraic structure of Hadamard vacuum representations for quantum fields on curved spacetime
We derive for a pair of operators on a symplectic space which are adjoints of
each other with respect to the symplectic form (that is, they are sympletically
adjoint) that, if they are bounded for some scalar product on the symplectic
space dominating the symplectic form, then they are bounded with respect to a
one-parametric family of scalar products canonically associated with the
initially given one, among them being its ``purification''. As a typical
example we consider a scalar field on a globally hyperbolic spacetime governed
by the Klein-Gordon equation; the classical system is described by a symplectic
space and the temporal evolution by symplectomorphisms (which are
symplectically adjoint to their inverses). A natural scalar product is that
inducing the classical energy norm, and an application of the above result
yields that its ``purification'' induces on the one-particle space of the
quantized system a topology which coincides with that given by the two-point
functions of quasifree Hadamard states. These findings will be shown to lead to
new results concerning the structure of the local (von Neumann)
observable-algebras in representations of quasifree Hadamard states of the
Klein-Gordon field in an arbitrary globally hyperbolic spacetime, such as local
definiteness, local primarity and Haag-duality (and also split- and type
III_1-properties). A brief review of this circle of notions, as well as of
properties of Hadamard states, forms part of the article.Comment: 42 pages, LaTeX. The Def. 3.3 was incomplete and this has been
corrected. Several misprints have been removed. All results and proofs remain
unchange
pH-sensitivity of YFP provides an intracellular indicator of programmed cell death.
BACKGROUND: Programmed cell death (PCD) is an essential process for the life cycle of all multicellular organisms. In higher plants however, relatively little is known about the cascade of genes and signalling molecules responsible for the initiation and execution of PCD. To aid with the discovery and analysis of plant PCD regulators, we have designed a novel cell death assay based on low cytosolic pH as a marker of PCD. RESULTS: The acidification that occurs in the cytosol during plant PCD was monitored by way of the extinction of YFP fluorescence at low pH. This fluorescence was recovered experimentally when bringing the intracellular pH back to 7, demonstrating that there was no protein degradation of YFP. Because it uses YFP, the assay is none-destructive, does not interfere with the PCD process and allows time-lapse studies to be carried out. In addition, changes of sub-cellular localisation can be visualised during PCD using the protein of interest fused to RFP. Coupled to a transient expression system, this pH-based assay can be used to functionally analyse genes involved in PCD, using point mutations or co-expressing PCD regulators. Transfecting mBAX and AtBI-1in onion epidermal cells showed that the pH shift is downstream of PCD suppression by AtBI-1. In addition, this method can be used to score PCD in tissues of stably transformed transgenic lines. As proof of principle, we show the example of YFP extinction during xylogenesis in Arabidopsis. This demonstrates that the assay is applicable to PCD studies in a variety of tissues. CONCLUSIONS: The observation that YFP fluorescence is lost during the plant PCD process provides a new tool to study the genetic regulation and cell biology of the process. In addition, plant cell biologists should make a note of this effect of PCD on YFP fluorescence to avoid misinterpretation of their data and to select a pH insensitive reporter if appropriate. This method represents an efficient and streamlined tool expected to bring insights on the process leading to the pH shift occurring during PCD
"Massless" vector field in de Sitter Universe
In the present work the massless vector field in the de Sitter (dS) space has
been quantized. "Massless" is used here by reference to conformal invariance
and propagation on the dS light-cone whereas "massive" refers to those dS
fields which contract at zero curvature unambiguously to massive fields in
Minkowski space. Due to the gauge invariance of the massless vector field, its
covariant quantization requires an indecomposable representation of the de
Sitter group and an indefinite metric quantization. We will work with a
specific gauge fixing which leads to the simplest one among all possible
related Gupta-Bleuler structures. The field operator will be defined with the
help of coordinate independent de Sitter waves (the modes) which are simple to
manipulate and most adapted to group theoretical matters. The physical states
characterized by the divergencelessness condition will for instance be easy to
identify. The whole construction is based on analyticity requirements in the
complexified pseudo-Riemanian manifold for the modes and the two-point
function.Comment: 33 pages, 3 figure
Causality, particle localization and positivity of the energy
Positivity of the Hamiltonian alone is used to show that particles, if
initially localized in a finite region, immediately develop infinite tails.Comment: To appear in: Irreversibility and Causality in Quantum Theory --
Semigroups and Rigged Hilbert Spaces, edited by A. Bohm, H.-D. Doebner and P.
Kielanowski, Springer Lecture Notes in Physics, Vol. 504 (1998
Relativistic Operator Description of Photon Polarization
We present an operator approach to the description of photon polarization,
based on Wigner's concept of elementary relativistic systems. The theory of
unitary representations of the Poincare group, and of parity, are exploited to
construct spinlike operators acting on the polarization states of a photon at
each fixed energy momentum. The nontrivial topological features of these
representations relevant for massless particles, and the departures from the
treatment of massive finite spin representations, are highlighted and
addressed.Comment: Revtex 9 page
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