104 research outputs found
Modelling of atmospheric boundary layer: Generation of shear.
Roughness length, z0 and friction velocity, u* are the defining parameters of wind log profile that must be matched in wind tunnel simulation. To fully understand the role of these parameters, the basics and review from the primitive equations and its relation to the logarithmic profile obtained for wind tunnel conditions were discussed. The problem of roughness, although well known, still needs to be addressed more rigorously especially when determining values of z0 and u* from wind tunnel data and their relation to the roughness element geometry. A review of classic literature and new published material were carried out, focusing on the applicability to wind tunnel modelling
Differential image motion in the short exposure regime
Whole atmosphere seeing \beta_0 is the most important parameter in site
testing measurements. Estimation of the seeing from a variance of differential
image motion is always biased by a non-zero DIMM exposure, which results in a
wind smoothing. In the paper, the wind effects are studied within short
exposure approximation, i.e. when the wind shifts turbulence during exposure by
distance lesser than device aperture. The method of correction for this effect
on the base of image motion correlation between adjacent frames is proposed. It
is shown that the correlation can be used for estimation of the mean wind speed
V_2 and atmospheric coherence time \tau_0. Total power of longitudinal and
transverse image motion is suggested for elimination of dependence on the wind
direction. Obtained theoretical results were tested on the data obtained on
Mount Shatdjatmaz in 2007--2010 with MASS/DIMM device and good agreement was
found.Comment: 11 pages, 8 figures. Accepted for publication in MNRA
An evidence-based socioecological framework to understand men’s use of anabolic androgenic steroids and inform interventions in this area
Research into men’s use of anabolic androgenic steroids (AAS) over the past three decades has identified many factors that contribute to decision making in this area. However there are limited theoretical frameworks to synthesize this research and guide practice, such as interventions to prevent use or reduce health risks. To address this gap a socioecological framework is presented based upon the international literature examining AAS use. Socioecological models recognize that individuals and behaviors exist within complex physical and social systems and are useful tools for guiding interventions to ensure consideration is given to multiple influential factors. This framework proposes that use of AAS is the result of the interaction of a range of factors at the individual, social network, institutional, community and societal levels that are likely to change over time and with experience. Viewed through this framework it becomes clear that AAS use can be a complex behavior with many influential environments and relationships impacting on a diverse population in different ways and at different times. The implications of findings for engaging with people who use AAS and delivering interventions are discussed, such as the identification of important transition times and influencing norms within social groups and communities
Diamond Surface Functionalization via Visible Light-Driven C-H Activation for Nanoscale Quantum Sensing
Nitrogen-vacancy centers in diamond are a promising platform for nanoscale
nuclear magnetic resonance sensing. Despite significant progress towards using
NV centers to detect and localize nuclear spins down to the single spin level,
NV-based spectroscopy of individual, intact, arbitrary target molecules remains
elusive. NV molecular sensing requires that target molecules are immobilized
within a few nanometers of NV centers with long spin coherence time. The inert
nature of diamond typically requires harsh functionalization techniques such as
thermal annealing or plasma processing, limiting the scope of functional groups
that can be attached to the surface. Solution-phase chemical methods can be
more readily generalized to install diverse functional groups, but they have
not been widely explored for single-crystal diamond surfaces. Moreover,
realizing shallow NV centers with long spin coherence times requires highly
ordered single-crystal surfaces, and solution-phase functionalization has not
yet been shown to be compatible with such demanding conditions. In this work,
we report a versatile strategy to directly functionalize C-H bonds on
single-crystal diamond surfaces under ambient conditions using visible light.
This functionalization method is compatible with charge stable NV centers
within 10 nm of the surface with spin coherence times comparable to the state
of the art. As a proof of principle, we use shallow ensembles of NV centers to
detect nuclear spins from functional groups attached to the surface. Our
approach to surface functionalization based on visible light-driven C-H bond
activation opens the door to deploying NV centers as a broad tool for chemical
sensing and single-molecule spectroscopy
Modern optical astronomy: technology and impact of interferometry
The present `state of the art' and the path to future progress in high
spatial resolution imaging interferometry is reviewed. The review begins with a
treatment of the fundamentals of stellar optical interferometry, the origin,
properties, optical effects of turbulence in the Earth's atmosphere, the
passive methods that are applied on a single telescope to overcome atmospheric
image degradation such as speckle interferometry, and various other techniques.
These topics include differential speckle interferometry, speckle spectroscopy
and polarimetry, phase diversity, wavefront shearing interferometry,
phase-closure methods, dark speckle imaging, as well as the limitations imposed
by the detectors on the performance of speckle imaging. A brief account is
given of the technological innovation of adaptive-optics (AO) to compensate
such atmospheric effects on the image in real time. A major advancement
involves the transition from single-aperture to the dilute-aperture
interferometry using multiple telescopes. Therefore, the review deals with
recent developments involving ground-based, and space-based optical arrays.
Emphasis is placed on the problems specific to delay-lines, beam recombination,
polarization, dispersion, fringe-tracking, bootstrapping, coherencing and
cophasing, and recovery of the visibility functions. The role of AO in
enhancing visibilities is also discussed. The applications of interferometry,
such as imaging, astrometry, and nulling are described. The mathematical
intricacies of the various `post-detection' image-processing techniques are
examined critically. The review concludes with a discussion of the
astrophysical importance and the perspectives of interferometry.Comment: 65 pages LaTeX file including 23 figures. Reviews of Modern Physics,
2002, to appear in April issu
The new enclosures: critical perspectives on corporate land deals
The contributions to this collection use the tools of agrarian political economy to
explore the rapid growth and complex dynamics of large-scale land deals in recent
years, with a special focus on the implications of big land deals for property and
labour regimes, labour processes and structures of accumulation. The first part of
this introductory essay examines the implications of this agrarian political
economy perspective. First we explore the continuities and contrasts between
historical and contemporary land grabs, before examining the core underlying
debate around large- versus small-scale farming futures. Next, we unpack the
diverse contexts and causes of land grabbing today, highlighting six overlapping
mechanisms. The following section turns to assessing the crisis narratives that
frame the justifications for land deals, and the flaws in the argument around there
being excess, empty or idle land available. Next the paper turns to an examination
of the impacts of land deals, and the processes of inclusion and exclusion at play,
before looking at patterns of resistance and constructions of alternatives. The
final section introduces the papers in the collection.ESR
Replacing Conventional Carbon Nucleophiles with Electrophiles: Nickel-Catalyzed Reductive Alkylation of Aryl Bromides and Chlorides
HiRadMat Low Intensity Beam Commissioning
On Wednesday 22 June 2011, proton beam was sent for the first time through the HiRadMat primary beam line, onto the beam dump located in the HiRadMat experimental cavern. The aims of the beam commissioning were to check the beam line geometry and design validity, the correct functioning of all beam line equipment and to verify the beam parameters. At the first trial, the proton beam reached the end of the primary beam line and the preliminary checks allowed confirming that all beam equipment and parameters are within the specification
- …