538 research outputs found
Multi-use lunar telescopes
The objective of multi-use telescopes is to reduce the initial and operational costs of space telescopes to the point where a fair number of telescopes, a dozen or so, would be affordable. The basic approach is to develop a common telescope, control system, and power and communications subsystem that can be used with a wide variety of instrument payloads, i.e., imaging CCD cameras, photometers, spectrographs, etc. By having such a multi-use and multi-user telescope, a common practice for earth-based telescopes, development cost can be shared across many telescopes, and the telescopes can be produced in economical batches
Project management : learning by breaking the rules
The paper explores project management in action in a large public research organisation – NLAT which decided to change its internal organisation from team-based to project-based organisation a few years ago. A systematic and comparative analysis of 8 projects reveals that adherence to the ISO 9000’s standardized rules of project management - specific staffing and project leaders, definition of milestones ex ante, procedure manuals, and formalized learning accumulation mechanisms - had little to do with the organisations success over recent years: Looking for explanations for this success, the paper focuses on the process of transferring from one project to another, enhancing organisational learning through rules breaking. We identify three elements which encourage the accumulation of knowledge and competencies, as organisational learning: low project core staffing levels which stimulates the circulation of engineers and researchers between projects and blurs project boundaries, implementing and managing thematic projects which build on specific competencies developed in dedicated projects and encouraging ‘bricolage’ to hybridise project management with traditional hierarchical management practices.PROJECT MANAGEMENT;R&D;HIGH TECH;MANAGEMENT PRACTICES
Weak Measurements of Light Chirality with a Plasmonic Slit
We examine, both experimentally and theoretically, an interaction of tightly
focused polarized light with a slit on a metal surface supporting
plasmon-polariton modes. Remarkably, this simple system can be highly sensitive
to the polarization of the incident light and offers a perfect
quantum-weak-measurement tool with a built-in post-selection in the
plasmon-polariton mode. We observe the plasmonic spin Hall effect in both
coordinate and momentum spaces which is interpreted as weak measurements of the
helicity of light with real and imaginary weak values determined by the input
polarization. Our experiment combines advantages of (i) quantum weak
measurements, (ii) near-field plasmonic systems, and (iii) high-numerical
aperture microscopy in employing spin-orbit interaction of light and probing
light chirality.Comment: 5 pages, 3 figure
Influence of water adsorbed on gold on van der Waals/Casimir forces
In this paper we investigate the influence of ultra thin water layer (1-1.5
nm) on the van der Waals/Casimir force between gold surfaces. Adsorbed water is
inevitably present on gold surfaces at ambient conditions as jump-up-to contact
during adhesion experiments demonstrate. Calculations based on the Lifshitz
theory give very good agreement with the experiment in absence of any water
layer for surface separations d>10 nm. However, a layer of thickness h<1.5 nm
is allowed by the error margin in force measurements. At shorter separations,
d<10 nm, the water layer can have a strong influence as calculations show for
flat surfaces. Nonetheless, in reality the influence of surface roughness must
also be considered, and it can overshadow any water layer influence at
separations comparable to the total sphere-plate rms roughness w_{shp}+w.Comment: 8 pages, 5 figure, to be published in Phys. Rev.
Casimir interaction between a dielectric nanosphere and a metallic plane
We study the Casimir interaction between a dielectric nanosphere and a
metallic plane, using the multiple scattering theory. Exact results are
obtained with the dielectric described by a Sellmeier model and the metal by a
Drude model. Asymptotic forms are discussed for small spheres, large or small
distances. The well-known Casimir-Polder formula is recovered at the limit of
vanishingly small spheres, while an expression better behaved at small
distances is found for any finite value of the radius. The exact results are of
particular interest for the study of quantum states of nanospheres in the
vicinity of surfaces.Comment: 6 pages, 5 figure
Development of a protocol for standardized use of a water-soluble contrast agent with polyethylene glycol in post-mortem CT angiography.
Computed tomography angiography (PMCTA) is increasingly used in postmortem cases. Standardized validated protocols permit to compare different PMCTA images and make it more easily to defend a case in court. In addition to the well-known technique by Grabherr et al. (2011) which is using paraffin oil as a carrier substance, water-soluble polyethylene glycol 200 (PEG200) can be used in combination with the contrast agent Accupaque® 300. As to date, there exists no standardized protocol for the use of this contrast agent mixture, the aim of this study was to develop a protocol using it. Between 2012 and 2022, 23 PMCTA with PEG200 and Accupaque®300 were performed at the University Centre of Legal Medicine Lausanne (Switzerland) and the Institute of Forensic Medicine Munich (Germany). The images obtained were evaluated regarding the opacification of the vessels and possible artefacts. The best image quality was obtained with a mixing ratio of 1:15 (Accupaque®300:PEG200) and a perfusion volume of 1000 ml in the arterial, 1400 ml in the venous and 350 ml in the dynamic phase. The infusion rates described by Grabherr et al. were confirmed for the three phases. Overall, the opacification of the vessels was diagnostically sufficient. In 13 cases no opacification of the right coronary artery was observed due to a stratification artefact. By using the PMCTA protocol with PEG200 as a carrier, a good overall image quality can be achieved. This protocol offers the possibility to standardize PMCTA with PEG200
Three-dimensional enantiomeric recognition of optically trapped single chiral nanoparticles
We optically trap freestanding single metallic chiral nanoparticles using a
standing-wave optical tweezer. We also incorporate within the trap a
polarimetric setup that allows to perform in situ chiral recognition of single
enantiomers. This is done by measuring the S_3 component of the Stokes vector
of a light beam scattered off the trapped nanoparticle in the forward
direction. This unique combination of optical trapping and chiral recognition,
all implemented within a single setup, opens new perspectives towards the
control, recognition, and manipulation of chiral objects at nanometer scales.Comment: 8 pages, including Supplemental Material, 7 figure
Casimir energy and entropy between dissipative mirrors
We discuss the Casimir effect between two identical, parallel slabs,
emphasizing the role of dissipation and temperature. Starting from quite
general assumptions, we analyze the behavior of the Casimir entropy in the
limit T->0 and link it to the behavior of the slab's reflection coefficients at
low frequencies. We also derive a formula in terms of a sum over modes, valid
for dissipative slabs that can be interpreted in terms of a damped quantum
oscillator.Comment: 8 pages, 1 figur
The Scattering Approach to the Casimir Force
We present the scattering approach which is nowadays the best tool for
describing the Casimir force in realistic experimental configurations. After
reminders on the simple geometries of 1d space and specular scatterers in 3d
space, we discuss the case of stationary arbitrarily shaped mirrors in
electromagnetic vacuum. We then review specific calculations based on the
scattering approach, dealing for example with the forces or torques between
nanostructured surfaces and with the force between a plane and a sphere. In
these various cases, we account for the material dependence of the forces, and
show that the geometry dependence goes beyond the trivial {\it Proximity Force
Approximation} often used for discussing experiments.Comment: Proceedings of the QFEXT'09 conference (Oklahoma, 2009
UBVJHKLM photometry and modeling of R Coronae Borealis
We present the results of UBVJHKLM photometry of R CrB spanning the period
from 1976 to 2001. Studies of the optical light curve have shown no evidence of
any stable harmonics in the variations of the stellar emission. In the L band
we found semi-regular oscillations with the two main periods of ~3.3 yr and
11.9 yr and the full amplitude of ~0.8 mag and ~0.6 mag, respectively. The
colors of the warm dust shell (resolved by Ohnaka et al. 2001) are found to be
remarkably stable in contrast to its brightness. This indicates that the inner
radius is a constant, time-independent characteristic of the dust shell. The
observed behavior of the IR light curve is mainly caused by the variation of
the optical thickness of the dust shell within the interval \tau(V)= 0.2-0.4.
Anticorrelated changes of the optical brightness (in particular with P ~ 3.3
yr) have not been found. Their absence suggests that the stellar wind of R CrB
deviates from spherical symmetry. The light curves suggest that the stellar
wind is variable. The variability of the stellar wind and the creation of dust
clouds may be caused by some kind of activity on the stellar surface. With some
time lag, periods of increased mass-loss cause an increase in the dust
formation rate at the inner boundary of the extended dust shell and an increase
in its IR brightness. We have derived the following parameters of the dust
shell (at mean brightness) by radiative transfer modeling: inner dust shell
radius r_in ~ 110 R_*, temperature T_dust(r_in) ~ 860 K, dust density
\rho_dust(r_in) ~ 1.1x10^{-20} g cm^-3, optical depth \tau(V) ~ 0.32 at 0.55
micron, mean dust formation rate [dM/dt]_dust ~ 3.1x10^-9 M_sun / yr, mass-loss
rate [dM/dt]_gas ~ 2.1x10^-7 M_sun / yr, size of the amorphous carbon grains
<(~) 0.01 micron, and B-V ~ -0.28.Comment: 9 pages, 6 figures, accepted for publication in A&
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