238 research outputs found
Relativistic Quark Spin Coupling Effects in the Nucleon Electromagnetic Form Factors
We investigate the effect of different forms of relativistic spin coupling of
constituent quarks in the nucleon electromagnetic form factors. The
four-dimensional integrations in the two-loop Feynman diagram are reduced to
the null-plane, such that the light-front wave function is introduced in the
computation of the form factors. The neutron charge form factor is very
sensitive to different choices of spin coupling schemes, once its magnetic
moment is fitted to the experimental value. The scalar coupling between two
quarks is preferred by the neutron data, when a reasonable fit of the proton
magnetic momentum is found.Comment: 13 pages, needs axodraw.ps and axodraw.sty for diagrams of Fig.
The VLA Frontier Field Survey: A Comparison of the Radio and UV/Optical Size of 0.3 ≲ z ≲ 3 Star-forming Galaxies
o investigate the growth history of galaxies, we measure the rest-frame radio, ultraviolet (UV), and optical sizes of 98 radio-selected, star-forming galaxies (SFGs) distributed over 0.3 ≲ z ≲ 3 with a median stellar mass of . We compare the size of galaxy stellar disks, traced by rest-frame optical emission, relative to the overall extent of star formation activity that is traced by radio continuum emission. Galaxies in our sample are identified in three Hubble Frontier Fields: MACS J0416.1−2403, MACS J0717.5+3745, and MACS J1149.5+2223. Radio continuum sizes are derived from 3 and 6 GHz radio images (≲0farcs6 resolution, ≈0.9 μJy beam−1 noise level) from the Karl G. Jansky Very Large Array. Rest-frame UV and optical sizes are derived using observations from the Hubble Space Telescope and the Advanced Camera for Surveys and Wide Field Camera 3 instruments. We find no clear dependence between the 3 GHz radio size and stellar mass of SFGs, which contrasts with the positive correlation between the UV/optical size and stellar mass of galaxies. Focusing on SFGs with , we find that the radio/UV/optical emission tends to be more compact in galaxies with high star formation rates (≳100 M⊙ yr−1), suggesting that a central, compact starburst (and/or an active galactic nucleus) resides in the most luminous galaxies of our sample. We also find that the physical radio/UV/optical size of radio-selected SFGs with log(M⋆/M⊙) > 10 increases by a factor of 1.5–2 from z ≈ 3 to z ≈ 0.3, yet the radio emission remains two to three times more compact than that from the UV/optical. These findings indicate that these massive, radio-selected SFGs at 0.3 ≲ z ≲ 3 tend to harbor centrally enhanced star formation activity relative to their outer disks
Relativistic Quark Spin Coupling Effects in the Correlations Between Nucleon Electroweak Properties
We investigate the effect of different relativistic spin couplings of
constituent quarks on nucleon electroweak properties. Within each quark spin
coupling scheme the correlations between static electroweak observables are
found to be independent of the particular shape of the momentum part of the
nucleon light-front wave function. The neutron charge form factor is very
sensitive to different choices of spin coupling schemes once the magnetic
moment is fitted to the experimental value. However, it is found rather
insensitive to the details of the momentum part of the three-quark wave
function model.Comment: 23 pages, 13 figures, requires axodraw.sty 1 figure corrected, 1
refs. added, some changes in tex
An Exploration of Cross-Cultural and Gender Differences in East Asia, South Asia and Southeast Asia
QUBIC: The QU Bolometric Interferometer for Cosmology
One of the major challenges of modern cosmology is the detection of B-mode
polarization anisotropies in the CMB. These originate from tensor fluctuations
of the metric produced during the inflationary phase. Their detection would
therefore constitute a major step towards understanding the primordial
Universe. The expected level of these anisotropies is however so small that it
requires a new generation of instruments with high sensitivity and extremely
good control of systematic effects. We propose the QUBIC instrument based on
the novel concept of bolometric interferometry, bringing together the
sensitivity advantages of bolometric detectors with the systematics effects
advantages of interferometry. Methods: The instrument will directly observe the
sky through an array of entry horns whose signals will be combined together
using an optical combiner. The whole set-up is located inside a cryostat.
Polarization modulation will be achieved using a rotating half-wave plate and
interference fringes will be imaged on two focal planes (separated by a
polarizing grid) tiled with bolometers. We show that QUBIC can be considered as
a synthetic imager, exactly similar to a usual imager but with a synthesized
beam formed by the array of entry horns. Scanning the sky provides an
additional modulation of the signal and improve the sky coverage shape. The
usual techniques of map-making and power spectrum estimation can then be
applied. We show that the sensitivity of such an instrument is comparable with
that of an imager with the same number of horns. We anticipate a low level of
beam-related systematics thanks to the fact that the synthesized beam is
determined by the location of the primary horns. Other systematics should be
under good control thanks to an autocalibration technique, specific to our
concept, that will permit the accurate determination of most of the systematics
parameters.Comment: 12 pages, 10 figures, submitted to Astronomy and Astrophysic
Proton Extraction from IHEP Accelerator Using Bent Crystals
IHEP Protvino has pioneered the wide practical use of bent crystals as
optical elements in high-energy beams for beam extraction and deflection on
permanent basis since 1989. In the course of IHEP experiments, crystal
channeling has been developed into efficient instrument for particle steering
at accelerators, working in predictable, reliable manner with beams of very
high intensity over years. Crystal systems extract 70 GeV protons from IHEP
main ring with efficiency of 85% at intensity of 1.E12, basing on multi-pass
mechanism of channeling proposed theoretically and realised experimentally at
IHEP. Today, six locations on the IHEP 70-GeV main ring of the accelerator
facility are equipped by crystal extraction systems, serving mostly for routine
applications rather than for research and allowing a simultaneous run of
several particle physics experiments, thus significantly enriching the IHEP
physics program. The long successful history of large-scale crystal
exploitation at IHEP should help to incorporate channeling crystals into
accelerator systems worldwide in order to create unique systems for beam
delivery. We report recent results from the research and exploitation of
crystal extraction systems at IHEP.Comment: Invited talk at the International workshop "Relativistic Channeling
and Related Coherent Phenomena", Frascati (Rome) 23-26 March 200
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The challenges of applying planetary boundaries as a basis for strategic decision-making in companies with global supply chains
The Planetary Boundaries (PB) framework represents a significant advance in specifying the ecological constraints on human development. However, to enable decision-makers in business and public policy to respect these constraints in strategic planning, the PB framework needs to be developed to generate practical tools. With this objective in mind, we analyse the recent literature and highlight three major scientific and technical challenges in operationalizing the PB approach in decision-making: first, identification of thresholds or boundaries with associated metrics for different geographical scales; second, the need to frame approaches to allocate fair shares in the 'safe operating space' bounded by the PBs across the value chain and; third, the need for international bodies to co-ordinate the implementation of the measures needed to respect the Planetary Boundaries. For the first two of these challenges, we consider how they might be addressed for four PBs: climate change, freshwater use, biosphere integrity and chemical pollution and other novel entities. Four key opportunities are identified: (1) development of a common system of metrics that can be applied consistently at and across different scales; (2) setting 'distance from boundary' measures that can be applied at different scales; (3) development of global, preferably open-source, databases and models; and (4) advancing understanding of the interactions between the different PBs. Addressing the scientific and technical challenges in operationalizing the planetary boundaries needs be complemented with progress in addressing the equity and ethical issues in allocating the safe operating space between companies and sectors
Monitoring and moderating extreme indoor temperatures in low-income urban communities
Climate change presents significant threats to human health, especially for low-income urban
communities in the Global South. Despite numerous studies of heat stress, surprisingly little is
known about the temperatures actually encountered by people in their homes, or the benefits of
affordable adaptations. This paper examines indoor air temperature measurements gathered from
47 living rooms within eight low-income communities of Accra and Tamale, Ghana. Using
multiple temperature indices and a tiered analysis, we evaluate indoor temperature variations
linked to roof type, ceiling insulation, presence of fans, and tree shade, for different housing types
and locations. Our data reveal indoor temperatures in the range 22.4 ◦C to 45.9 ◦C for Accra, and
22.2 ◦C to 43.0 ◦C in Tamale. Using dummy regression analysis, we find that tree shade reduces the
number of very hot days (>40 ◦C) and nights (>30 ◦C) by about 12 and 15 d per year, respectively.
Building materials also strongly moderate indoor temperatures but in opposing ways: rooms with
traditional mud walls and thatch roofs are on average 4.5 ◦C cooler than rooms in concrete block
houses with uninsulated metal roofs during the day but are 1.5 ◦C warmer at night; rooms with
ceiling insulation are on average 6.9 ◦C cooler in the day but 1.4 ◦C warmer at night. We conclude
that sub-daily data are necessary for reporting extreme indoor temperatures, and that trade-offs
between minimum and maximum temperatures require interventions to be assessed carefully
before attempting to counter extreme heat inside homes
The Einstein polarization interferometer for cosmology (EPIC) and the millimeter-wave bolometric interferometer (MBI)
We provide an overview of a mission concept study underway for the Einstein Inflation Probe (EIP). Our study investigates the advantages and tradeoffs of using an interferometer (EPIC) for the mission. We also report on the status of the millimeter-wave bolometric interferometer (MBI), a ground-based pathfinder optimized for degree-scale CMB polarization measurements at 90 GHz
Early above- and below-ground responses of subboreal conifer seedlings to various levels of deciduous canopy removal
We examined the growth of understory conifers, following partial or complete deciduous canopy removal, in a field study established in two regions in Canada. In central British Columbia, we studied the responses of three species (Pseudotsuga menziesii var. glauca (Beissn.) Franco, Picea glauca (Moench) Voss x Picea engelmannii Parry ex Engelm., and Abies lasiocarpa (Hook.) Nutt.), and in northwestern Quebec, we studied one species (Abies balsamea (L.) Mill.). Stem and root diameter and height growth were measured 5 years before and 3 years after harvesting. Both root and stem diameter growth increased sharply following release but seedlings showed greater root growth, suggesting that in the short term, improvement in soil resource capture and transport, and presumably stability, may be more important than an increase in stem diameter and height growth. Response was strongly size dependent, which appears to reflect greater demand for soil resources as well as higher light levels and greater tree vigour before release for taller individuals. Growth ratios could not explain the faster response generally attributed to true fir species or the unusual swift response of spruces. Good prerelease vigour of spruces, presumably favoured by deciduous canopies, could explain their rapid response to release
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