11,703 research outputs found
The study of comets, part 1
Papers are presented dealing with observations of comets. Topic discussed include: photometry, polarimetry, and astrometry of comets; detection of water and molecular transitions in comets; ion motions in comet tails; determination of comet brightness and luminosity; and evolution of cometary orbits. Emphasis is placed on analysis of observations of comet Kohoutek
Radiative corrections to the pressure and the one-loop polarization tensor of massless modes in SU(2) Yang-Mills thermodynamics
We compute the one-loop polarization tensor for the on-shell, massless
mode in a thermalized SU(2) Yang-Mills theory being in its deconfining phase.
Postulating that SU(2), we discuss
's effect on the low-momentum part of the black-body spectrum at
temperatures where K.
A table-top experiment is proposed to test the above postulate. As an
application, we point out a possible connection with the stability of dilute,
cold, and old innergalactic atomic hydrogen clouds. We also compute the
two-loop correction to the pressure arising from the instantaneous massless
mode in unitary-Coulomb gauge, which formerly was neglected, and present
improved estimates for subdominant corrections.Comment: 25 pages, 17 figs, v4: consequences of a modification of the
evolution equation for the effectice coupling implemented, no qualitative
change of the physic
Middle-up-down and top-down approaches: Strategy implementation, uncertainty, structure, and foodservice segment
This study explores the relationship between various profiles of the strategy implementation process and managers\u27 perception of the task environment, complexity and dynamism. This study addresses the following research questions: Do differences exist between levels of perceived environmental change/uncertainty and users of middle-up-down and top-down strategy implementation approaches? And, does this relationship become more meaningful when ownership, firm structure and foodservice segment characteristics are considered? There has been very little research on the food service industry that assesses the relationship between eleven task environment measures of complexity and dynamism and the use of a predominately top-down or middle-up-down approach to the implementation of strategies. Using a sample of food industry managers, multiple discriminate analysis (MDA) was used to predict the use of implementation strategies. Substantive differences appear to exist between levels of perceived environmental change/uncertainty and users of middle-up-down and top-down strategy implementation approaches for foodservice firms. The ability to correctly classify users of middle-up-down and top-down approaches using a multivariate combination of environmental variables is improved radically when ownership, firm structure, and market segment classifications were are considered. Taken as a whole, the findings are most convincing and support the basic hypotheses. Study findings indicate that a broad brushstroke approach to determining whether a middle-updown or top-down is used or appropriate based on the perceived task environment may not be valuable. The results support previous findings in other industries in that the prediction is better for market segments served and the public versus private nature of the firms involved
Study of a small solar probe /sunblazer/. part ii- spacecraft and payload design progress report, jul. 1, 1964 - jun. 30, 1965
Design considerations for Sunblazer solar probe and payloa
Towards a systematic design of isotropic bulk magnetic metamaterials using the cubic point groups of symmetry
In this paper a systematic approach to the design of bulk isotropic magnetic
metamaterials is presented. The role of the symmetries of both the constitutive
element and the lattice are analyzed. For this purpose it is assumed that the
metamaterial is composed by cubic SRR resonators, arranged in a cubic lattice.
The minimum symmetries needed to ensure an isotropic behavior are analyzed, and
some particular configurations are proposed. Besides, an equivalent circuit
model is proposed for the considered cubic SRR resonators. Experiments are
carried out in order to validate the proposed theory. We hope that this
analysis will pave the way to the design of bulk metamaterials with strong
isotropic magnetic response, including negative permeability and left-handed
metamaterials.Comment: Submitted to Physical Review B, 23 page
Vibration Suppression of a Spacecraft Flexible Appendages Using Smart Material
The article of record as published may be found at http://dx.doi.org/10..1088/0964-1726/7/1/011This paper presents the results of positive position feedback (PPF)
control and linear–quadratic Gaussian (LQG) control for vibration suppression of a
flexible structure using piezoceramics. Experiments were conducted on the US
Naval Postgraduate School’s flexible spacecraft simulator (FSS), which is
comprised of a rigid central body and a flexible appendage. The objective of this
research is to suppress the vibration of the flexible appendage. Experiments show
that both control methods have unique advantages for vibration suppression. PPF
control is effective in providing high damping for a particular mode and is easy to
implement. LQG control provides damping to all modes; however, it cannot provide
high damping for a specific mode. LQG control is very effective in meeting specific
requirements, such as minimization of tip motion of a flexible beam, but at a higher
implementation cost.This paper presents the results of positive position feedback (PPF)
control and linear–quadratic Gaussian (LQG) control for vibration suppression of a
flexible structure using piezoceramics. Experiments were conducted on the US
Naval Postgraduate School’s flexible spacecraft simulator (FSS), which is
comprised of a rigid central body and a flexible appendage. The objective of this
research is to suppress the vibration of the flexible appendage. Experiments show
that both control methods have unique advantages for vibration suppression. PPF
control is effective in providing high damping for a particular mode and is easy to
implement. LQG control provides damping to all modes; however, it cannot provide
high damping for a specific mode. LQG control is very effective in meeting specific
requirements, such as minimization of tip motion of a flexible beam, but at a higher
implementation cost.This paper presents the results of positive position feedback (PPF)
control and linear–quadratic Gaussian (LQG) control for vibration suppression of a
flexible structure using piezoceramics. Experiments were conducted on the US
Naval Postgraduate School’s flexible spacecraft simulator (FSS), which is
comprised of a rigid central body and a flexible appendage. The objective of this
research is to suppress the vibration of the flexible appendage. Experiments show
that both control methods have unique advantages for vibration suppression. PPF
control is effective in providing high damping for a particular mode and is easy to
implement. LQG control provides damping to all modes; however, it cannot provide
high damping for a specific mode. LQG control is very effective in meeting specific
requirements, such as minimization of tip motion of a flexible beam, but at a higher
implementation cost
Electromagnetic multipole theory for optical nanomaterials
Optical properties of natural or designed materials are determined by the
electromagnetic multipole moments that light can excite in the constituent
particles. In this work we present an approach to calculate the multipole
excitations in arbitrary arrays of nanoscatterers in a dielectric host medium.
We introduce a simple and illustrative multipole decomposition of the electric
currents excited in the scatterers and link this decomposition to the classical
multipole expansion of the scattered field. In particular, we find that
completely different multipoles can produce identical scattered fields. The
presented multipole theory can be used as a basis for the design and
characterization of optical nanomaterials
Supporting Primary and Secondary Beginning Teachers Online: Key findings of the Education Alumni Support Project
During 2005, the Education Alumni Support Project (EdASP) (Maxwell, Smith, Baxter, Boyd, Harrington, Jenkins, Sargeant & Tamatea 2006) provided online support for University of New England (UNE) graduand, and later, graduate, teachers as they commenced their careers. The project was based on research which reported that many beginning teachers did not get the support they needed as permanent or contract workers, or, as casual, relief or support teachers, and that small scale trials had shown that online support could be effective. One third of beginning teachers who were alumni of UNE in 2004, reported they did not receive adequate or any mentoring. UNE web-based technologies provided the teachers and mentors with online environments for professional and social interaction, and resource sharing. We found that support was especially sought by the project participants in their first school term, and there were differences in the levels of online support sought by secondary and primary beginning teachers. The project raises implications for on-going systemic support for beginning teachers, the issue of transition from students to teachers, as well as questions about teacher education students’ preparation. This paper provides the key findings of the project. Detailed description of the project structure, data collection and data analysis are available in Maxwell et al. (2006)
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