36,826 research outputs found
Microscopic Description of Deeply Virtual Compton Scattering off Spin-0 Nuclei
We evaluate within a microscopic calculation the contributions of both
coherent and incoherent deeply virtual Compton scattering from a spin-0
nucleus. The coherent contribution is obtained when the target nucleus recoils
as a whole, whereas for incoherent scattering break-up configurations for the
final nucleus into a an outgoing nucleon and an system are considered.
The two processes encode different characteristics of generalized parton
distributions.Comment: 7 pages, 3 figure
Cerenkov counters for high energy nuclei: Some new developments
A method to determine with gas Cerenkov counters the Lorentz factor, gamma = E/mc, of cosmic ray nuclei with high accuracy over the range gamma approx. 20 to 100 is discussed. The measurement of the Cerenkov emission angle theta, by use of a suitable imaging system is considered. Imaging counters, the ring imaging Cerenkov counters (RICH), were developed for use on accelerators. The image of off-axis particles to determine the amount of image distortion as a function of the direction of the incoming nucleus is examined and an acceptance solid angle, relative to the optical axis, within which the nucleus produces an image with an acceptable level of distortion is defined. The properties of the image, which becomes elliptical, for off-axis particles are analyzed
Nuclear Medium Modifications of Hadrons from Generalized Parton Distributions
We study the structure of generalized parton distributions in spin 0 nuclei
within a microscopic approach for nuclear dynamics. GPDs can be used on one
side as tools to unravel the deep inelastic transverse structure of nuclei in
terms of both transverse spatial and transverse momentum degrees of freedom. On
the other, one can obtain information on GPDs themselves by observing how they
become modified in the nuclear environment. We derive the structure of the
nuclear deeply virtual Compton scattering tensor and generalized parton
distributions at leading order in in a field-theoretical framework. The
nuclear generalized parton distributions are calculated using a two step
process -- the convolution approach -- where the scattering process happens
from a quark inside a nucleon, itself inside a nucleus, disregarding final
state interactions with both the nuclear and nucleon debris. We point out that
details of the nuclear long range interactions such as two-body currents, can
be disregarded compared to the deep inelastic induced modifications of the
bound GPDs. We show how the pattern of nuclear modifications predicted, and in
particular the deviations of off-shell effects from the longitudinal
convolution provide clear signals to be sought in experimental measurements.
Finally, we find interesting relationships by studying Mellin moments in
nuclei: in particular we predict the -dependence for the -term of GPDs
within a microscopic approach, and the behavior with of the total momentum
carried by quarks in a nucleus. The latter provides an important element for
the evaluation of nuclear hadronization phenomena which are vital for
interpreting current and future data at RHIC, HERMES and Jefferson Lab.Comment: 29 pages, 10 figure
Indigenous sovereignties: relational ontologies and environmental management
© 2019 Institute of Australian Geographers Indigenous nations have always and continue to assert their sovereignties to resist colonialism. This paper makes explicit the ways in which environmental management has been and continues to act as a tool of colonialism, particularly by privileging Western science, institutions, and administrative procedures. We argue that to decolonise environmental management, it is crucial to understand and challenge the power relations that underlie itâasking who makes decisions and on what worldview those decisions are based. Indigenous ways of being deeply challenge the foundations of environmental management and the colonising power structures that underlie it, and invite further thought about posthuman and relational ontologies. We provide a range of case studies that showcase the role of Indigenous nations in redefining and reimagining environmental management based on Indigenous sovereignties, knowledges, and ways of being. The case studies emphasise the crucial connection between Indigenous decision-making authority and self-governance for the enhanced protection and health of the environment. We argue that Indigenous agency, grounded in Indigenous governance and sovereignties, is driving innovation and decolonising environmental management by making space for new ways of thinking and being âin placeâ
Solvable senescence model with positive mutations
We build upon our previous analytical results for the Penna model of
senescence to include positive mutations. We investigate whether a small but
non-zero positive mutation rate gives qualitatively different results to the
traditional Penna model in which no positive mutations are considered. We find
that the high-lifespan tail of the distribution is radically changed in
structure, but that there is not much effect on the bulk of the population. Th
e mortality plateau that we found previously for a stochastic generalization of
the Penna model is stable to a small positive mutation rate.Comment: 3 figure
Carrier scattering, mobilities and electrostatic potential in mono-, bi- and tri-layer graphenes
The carrier density and temperature dependence of the Hall mobility in mono-,
bi- and tri-layer graphene has been systematically studied. We found that as
the carrier density increases, the mobility decreases for mono-layer graphene,
while it increases for bi-layer/tri-layer graphene. This can be explained by
the different density of states in mono-layer and bi-layer/tri-layer graphenes.
In mono-layer, the mobility also decreases with increasing temperature
primarily due to surface polar substrate phonon scattering. In
bi-layer/tri-layer graphene, on the other hand, the mobility increases with
temperature because the field of the substrate surface phonons is effectively
screened by the additional graphene layer(s) and the mobility is dominated by
Coulomb scattering.
We also find that the temperature dependence of the Hall coefficient in
mono-, bi- and tri-layer graphene can be explained by the formation of electron
and hole puddles in graphene. This model also explains the temperature
dependence of the minimum conductance of mono-, bi- and tri-layer graphene. The
electrostatic potential variations across the different graphene samples are
extracted.Comment: 18 pages, 7 figure
Self-reported domain-specific and accelerometer-based physical activity and sedentary behaviour in relation to psychological distress among an urban Asian population
Background: The interpretation of previous studies on the association of physical activity and sedentary behaviour with psychological health is limited by the use of mostly self-reported physical activity and sedentary behaviour, and a focus on Western populations. We aimed to explore the association of self-reported and devise-based measures of physical activity and sedentary behaviour domains on psychological distress in an urban multi-ethnic Asian population.
Methods: From a population-based cross-sectional study of adults aged 18-79 years, data were used from an overall sample (n = 2653) with complete self-reported total physical activity/sedentary behaviour and domain-specific physical activity data, and a subsample (n = 703) with self-reported domain-specific sedentary behaviour and accelerometry data. Physical activity and sedentary behaviour data were collected using the Global Physical Activity Questionnaire (GPAQ), a domain-specific sedentary behaviour questionnaire and accelerometers. The Kessler Screening Scale (K6) and General Health Questionnaire (GHQ-12) were used to assess psychological distress. Logistic regression models were used to calculate odds ratios (ORs) and 95% confidence intervals, adjusted for socio-demographic and lifestyle characteristics.
Results: The sample comprised 45.0% men (median age = 45.0 years). The prevalence of psychological distress based on the K6 and GHQ-12 was 8.4% and 21.7%, respectively. In the adjusted model, higher levels of self-reported moderate-to-vigorous physical activity (MVPA) were associated with significantly higher odds for K6 (OR = 1.47 [1.03-2.10]; p-trend = 0.03) but not GHQ-12 (OR = 0.97 [0.77-1.23]; p-trend = 0.79), when comparing the highest with the lowest tertile. Accelerometry-assessed MVPA was not significantly associated with K6 (p-trend = 0.50) nor GHQ-12 (p-trend = 0.74). The highest tertile of leisure-time physical activity, but not work- or transport-domain activity, was associated with less psychological distress using K6 (OR = 0.65 [0.43-0.97]; p-trend = 0.02) and GHQ-12 (OR = 0.72 [0.55-0.93]; p-trend = 0.01). Self-reported sedentary behaviour was not associated with K6 (p-trend = 0.90) and GHQ-12 (p-trend = 0.33). The highest tertile of accelerometry-assessed sedentary behaviour was associated with significantly higher odds for K6 (OR = 1.93 [1.00-3.75]; p-trend = 0.04), but not GHQ-12 (OR = 1.34 [0.86-2.08]; p-trend = 0.18).
Conclusions: Higher levels of leisure-time physical activity and lower levels of accelerometer-based sedentary behaviour were associated with lower psychological distress. This study underscores the importance of assessing accelerometer-based and domain-specific activity in relation to mental health, instead of solely focusing on total volume of activity
Dynamics of the Solar Magnetic Network. II. Heating the Magnetized Chromosphere
We consider recent observations of the chromospheric network, and argue that
the bright network grains observed in the Ca II H & K lines are heated by an as
yet unidentified quasi-steady process. We propose that the heating is caused by
dissipation of short-period magnetoacoustic waves in magnetic flux tubes
(periods less than 100 s). Magnetohydrodynamic (MHD) models of such waves are
presented. We consider wave generation in the network due to two separate
processes: (a) by transverse motions at the base of the flux tube; and (b) by
the absorption of acoustic waves generated in the ambient medium. We find that
the former mechanism leads to an efficient heating of the chromosphere by slow
magnetoacoustic waves propagating along magnetic field lines. This heating is
produced by shock waves with a horizontal size of a few hundred kilometers. In
contrast, acoustic waves excited in the ambient medium are converted into
transverse fast modes that travel rapidly through the flux tube and do not form
shocks, unless the acoustic sources are located within 100 km from the tube
axis. We conclude that the magnetic network may be heated by magnetoacoustic
waves that are generated in or near the flux tubes.Comment: 30 pages, 8 figures, Accepted in Astrophysical Journa
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