1,903 research outputs found
The medicine hat block and the early paleoproterozoic assembly of Western Laurentia
© 2020 by the authors. Licensee MDPI, Basel, Switzerland. The accretion of the Wyoming, Hearne, and Superior Provinces to form the Archean core of western Laurentia occurred rapidly in the Paleoproterozoic. Missing from Hoffmanâs (1988) original rapid aggregation model was the Medicine Hat block (MHB). The MHB is a structurally distinct, complex block of Precambrian crystalline crust located between the Archean Wyoming Craton and the Archean Hearne Province and overlain by an extensive Phanerozoic cover. It is distinguished on the basis of geophysical evidence and limited geochemical data from crustal xenoliths and drill core. New UâPb ages and LuâHf data from zircons reveal protolith crystallization ages from 2.50 to 3.28 Ga, magmatism/metamorphism at 1.76 to 1.81 Ga, and ΔHfT values from â23.3 to 8.5 in the Archean and Proterozoic rocks of the MHB. These data suggest that the MHB played a pivotal role in the complex assembly of western Laurentia in the Paleoproterozoic as a conjugate or extension to the Montana Metasedimentary Terrane (MMT) of the northwestern Wyoming Province. This MMTâMHB connection likely existed in the Mesoarchean, but it was broken sometime during the earliest Paleoproterozoic with the formation and closure of a small ocean basin. Closure of the ocean led to formation of the Little Belt arc along the southern margin of the MHB beginning at approximately 1.9 Ga. The MHB and MMT reâjoined at this time as they amalgamated into the supercontinent Laurentia during the Great Falls orogeny (1.7â1.9 Ga), which formed the Great Falls tectonic zone (GFTZ). The GFTZ developed in the same timeframe as the betterâknown TransâHudson orogen to the east that marks the merger of the Wyoming, Hearne, and Superior Provinces, which along with the MHB, formed the Archean core of western Laurentia
Hexa-ÎŒ-chlorido-hexaÂchlorido(η6-hexaÂmethylÂbenzene)trialuminium(III)lanthanum(III) benzene solvate
In the title compound, [Al3LaCl12(C12H18)]·C6H6, all molÂecules are located on a mirror plane. Three chloridoaluminate groups and a hexaÂmethylÂbenzene molÂecule are bound to the central lanthanum(III) ion, forming a distorted pentaÂgonal bipyramid with the η6-coordinated arene located at the apical position. The hexaÂmethylÂbenzene ligand disordered between two orientations in a 1:1 ratio is also involved in parallel-slipped ÏâÏ stacking interÂmolecular interÂactions with a benzene solvent molÂecule [centroidâcentroid distance 3.612â
(4)â
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]
Probing theories of gravity with phase space-inferred potentials of galaxy clusters
Modified theories of gravity provide us with a unique opportunity to generate innovative tests of gravity. In Chameleon f(R) gravity, the gravitational potential differs from the weak-field limit of general relativity (GR) in a mass dependent way. We develop a probe of gravity which compares high mass clusters, where Chameleon effects are weak, to low mass clusters, where the effects can be strong. We utilize the escape velocity edges in the radius/velocity phase space to infer the gravitational potential profiles on scales of 0.3â1 virial radii. We show that the escape edges of low mass clusters are enhanced compared to GR, where the magnitude of the difference depends on the background field value |fR0ÂŻÂŻÂŻÂŻÂŻ|. We validate our probe using N-body simulations and simulated light cone galaxy data. For a Dark Energy Spectroscopic Instrument Bright Galaxy Sample, including observational systematics, projection effects, and cosmic variance, our test can differentiate between GR and Chameleon f(R) gravity models, |fR0ÂŻÂŻÂŻÂŻÂŻ|=4Ă10â6 (2Ă10â6) at >5Ï (>2Ï), more than an order of magnitude better than current cluster-scale constraints
Deterministic Partial Differential Equation Model for Dose Calculation in Electron Radiotherapy
Treatment with high energy ionizing radiation is one of the main methods in
modern cancer therapy that is in clinical use. During the last decades, two
main approaches to dose calculation were used, Monte Carlo simulations and
semi-empirical models based on Fermi-Eyges theory. A third way to dose
calculation has only recently attracted attention in the medical physics
community. This approach is based on the deterministic kinetic equations of
radiative transfer. Starting from these, we derive a macroscopic partial
differential equation model for electron transport in tissue. This model
involves an angular closure in the phase space. It is exact for the
free-streaming and the isotropic regime. We solve it numerically by a newly
developed HLLC scheme based on [BerCharDub], that exactly preserves key
properties of the analytical solution on the discrete level. Several numerical
results for test cases from the medical physics literature are presented.Comment: 20 pages, 7 figure
Taking up the cudgels against gay rights? Trends and trajectories in African Christian theologies on homosexuality
Against the background of the HIV epidemic and the intense public controversy on homosexuality in African societies, this article investigates the discourses of academic African Christian theologians on homosexuality. Distinguishing some major strands in African theology, that is, inculturation, liberation, womenâs and reconstruction theology, the article examines how the central concepts of culture, liberation, justice, and human rights function in these discourses. On the basis of a qualitative analysis of a large number of publications, the article shows that stances of African theologians are varying from silence and rejection to acceptance. Although many African theologians have taken up the cudgels against gay rights, some âdissident voicesâ break the taboo and develop more inclusive concepts of African identity and African Christianity
Solving the riddle of the bright mismatches: hybridization in oligonucleotide arrays
HDONA technology is predicated on two ideas. First, the differential between
high-affinity (perfect match, PM) and lower-affinity (mismatch, MM) probes is
used to minimize cross-hybridization. Second, several short probes along the
transcript are combined, introducing redundancy. Both ideas have shown problems
in practice: MMs are often brighter than PMs, and it is hard to combine the
pairs because their brightness often spans decades. Previous analysis suggested
these problems were sequence-related; publication of the probe sequences has
permitted us an in-depth study of this issue. Our results suggest that
fluorescently labeling the nucleotides interferes with mRNA binding, causing a
catch-22 since, to be detected, the target mRNA must both glow and stick to its
probe: without labels it cannot be seen even if bound, while with too many it
won't bind. We show that this conflict causes much of the complexity of HDONA
raw data, suggesting that an accurate physical understanding of hybridization
by incorporating sequence information is necessary to perfect microarray
analysis.Comment: 4 figure
Measuring urban social sustainability:Scale development and validation
Despite the significant role of social sustainability in the sustainable development agenda, there is a lack of research to clearly define and fully operationalise the concept of urban social sustainability. The aim of this study is to contribute to the existing literature by developing a comprehensive measurement scale to assess urban social sustainability at the neighbourhood level. We argue that urban social sustainability is a multidimensional concept that incorporates six main dimensions of social interaction, sense of place, social participation, safety, social equity and neighbourhood satisfaction. Failure to consider each of these dimensions may lead to an incomplete picture of social sustainability. Validity, reliability and dimensionality of the urban social sustainability scale are examined using factor analysis. We also illustrate the application of the urban social sustainability scale by investigating the influence of quality of design, as one of the least studied factors of urban form, on different dimensions of social sustainability. The paper uses data collected from the household questionnaire survey in a sample of 251 respondents from five case study neighbourhoods of Dunedin city, New Zealand. This study provides new evidence on the significance of improving neighbourhood quality of design and its positive and significant relationship with different dimensions of social sustainability and the overall social sustainability
The extraordinary evolutionary history of the reticuloendotheliosis viruses
The reticuloendotheliosis viruses (REVs) comprise several closely related amphotropic retroviruses isolated from birds. These viruses exhibit several highly unusual characteristics that have not so far been adequately explained, including their extremely close relationship to mammalian retroviruses, and their presence as endogenous sequences within the genomes of certain large DNA viruses. We present evidence for an iatrogenic origin of REVs that accounts for these phenomena. Firstly, we identify endogenous retroviral fossils in mammalian genomes that share a unique recombinant structure with REVsâunequivocally demonstrating that REVs derive directly from mammalian retroviruses. Secondly, through sequencing of archived REV isolates, we confirm that contaminated Plasmodium lophurae stocks have been the source of multiple REV outbreaks in experimentally infected birds. Finally, we show that both phylogenetic and historical evidence support a scenario wherein REVs originated as mammalian retroviruses that were accidentally introduced into avian hosts in the late 1930s, during experimental studies of P. lophurae, and subsequently integrated into the fowlpox virus (FWPV) and gallid herpesvirus type 2 (GHV-2) genomes, generating recombinant DNA viruses that now circulate in wild birds and poultry. Our findings provide a novel perspective on the origin and evolution of REV, and indicate that horizontal gene transfer between virus families can expand the impact of iatrogenic transmission events
Vortices in multicomponent Bose-Einstein condensates
We review the topic of quantized vortices in multicomponent Bose-Einstein
condensates of dilute atomic gases, with an emphasis on that in two-component
condensates. First, we review the fundamental structure, stability and dynamics
of a single vortex state in a slowly rotating two-component condensates. To
understand recent experimental results, we use the coupled Gross-Pitaevskii
equations and the generalized nonlinear sigma model. An axisymmetric vortex
state, which was observed by the JILA group, can be regarded as a topologically
trivial skyrmion in the pseudospin representation. The internal, coherent
coupling between the two components breaks the axisymmetry of the vortex state,
resulting in a stable vortex molecule (a meron pair). We also mention
unconventional vortex states and monopole excitations in a spin-1 Bose-Einstein
condensate. Next, we discuss a rich variety of vortex states realized in
rapidly rotating two-component Bose-Einstein condensates. We introduce a phase
diagram with axes of rotation frequency and the intercomponent coupling
strength. This phase diagram reveals unconventional vortex states such as a
square lattice, a double-core lattice, vortex stripes and vortex sheets, all of
which are in an experimentally accessible parameter regime. The coherent
coupling leads to an effective attractive interaction between two components,
providing not only a promising candidate to tune the intercomponent interaction
to study the rich vortex phases but also a new regime to explore vortex states
consisting of vortex molecules characterized by anisotropic vorticity. A recent
experiment by the JILA group vindicated the formation of a square vortex
lattice in this system.Comment: 69 pages, 25 figures, Invited review article for International
Journal of Modern Physics
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