15,720 research outputs found
On Secular Resonances of Small Bodies in the Planetary Systems
We investigate the secular resonances for massless small bodies and
Earth-like planets in several planetary systems. We further compare the results
with those of Solar System. For example, in the GJ 876 planetary system, we
show that the secular resonances and (respectively, resulting
from the inner and outer giant planets) can excite the eccentricities of the
Earth-like planets with orbits 0.21 AU 0.50 AU and eject them out of
the system in a short timescale. However, in a dynamical sense, the potential
zones for the existence of Earth-like planets are in the area 0.50 AU 1.00 AU, and there exist all stable orbits last up to yr with low
eccentricities. For other systems, e.g., 47 UMa, we also show that the
Habitable Zones for Earth-like planets are related to both secular resonances
and mean motion resonances in the systems.Comment: 8 pages, 3 figures, accepted to IAU236. Proceeding of IAU 236: Near
Earth Objects, Our Celestial Neighbors: Opportunity and Risk, in pres
Metastable Flux Configurations and de Sitter Spaces
We derive stability conditions for the critical points of the no-scale scalar
potential governing the dynamics of the complex structure moduli and the
axio-dilaton in compactifications of type IIB string theory on Calabi-Yau
three-folds. We discuss a concrete example of a T^6 orientifold. We then
consider the four-dimensional theory obtained from compactifications of type
IIB string theory on non-geometric backgrounds which are mirror to rigid
Calabi-Yau manifolds and show that the complex structure moduli fields can be
stabilized in terms of H_{RR} only, i.e. with no need of orientifold
projection. The stabilization of all the fields at weak coupling, including the
axio-dilaton, may require to break supersymmetry in the presence of H_{NS} flux
or corrections to the scalar potential.Comment: 24 page
Target-mass corrections and the Bloom-Gilman duality of the nucleon structure function
The occurrence of the Bloom-Gilman local duality in the low-order moments of
the nucleon structure function is investigated for values of the squared
four-momentum transfer Q**2 between ~ 0.5 and 10 (GeV/c)**2. At variance with
previous analyses truncated Cornwall-Norton moments, limited to the
nucleon-resonance production regions, are considered. The role played by
target-mass corrections is illustrated, showing that target-mass effects are
necessary (but not sufficient) for producing the observed Bloom-Gilman duality
of the nucleon structure function. The possibility of a local duality between
the unphysical region at large values of the Nachtmann variable and the nucleon
elastic peak contribution is analyzed. It is found that the proton magnetic
form factor extracted assuming local duality is significantly below the
experimental data at low and intermediate values of Q**2.Comment: final version with minor modifications, to appear in Phys. Lett.
Recent Results from Jefferson Lab
Recent results on studies of the structure of nucleons and nuclei in the
regime of strong interaction QCD are discussed. Use of high current polarized
electron beams, polarized targets, and recoil polarimeters, in conjunction with
modern spectrometers and detector instrumentation allow much more detailed
studies of nucleon and nuclear structure than has been possible in the past.
The CEBAF accelerator at Jefferson Lab was build to study the internal
structure of hadrons in a regime where confinement is important and strong
interaction QCD is the relevant theory. I discuss how the first experiments
already make significant contributions towards an improved understanding of
hadronic structure.Comment: Lecture presented at the International School of Nuclear Physics,
Erice, Sicily, Italy, September 17 - 25, 199
New Green Theories of Urban Development in China
China’s rapid urbanisation has already led to the development of more large-scale cities than ever before. One result is that China is now the largest carbon emitter in the world. Meanwhile, China is facing enormous challenges in respect to environmental degradation, and limiting the use of natural resources in urban areas when it comes to balancing rapid economic development and environmental protection. To address this issue, China has to explore a new approach to urban development, namely green urban development.
Various green urban theories are in the process of being formulated in China due to the difference in the responsibility of the central government and the gradual changes in national policies. The lack of a clear vision and target is a common barrier to green urban development in China. This paper reviews three new concepts and approaches to green urban development in China, and analyses how these concepts and approaches have been adopted, defined and developed within the Chinese context. Three typical projects are then selected to illustrate green city development in order to develop a better understanding of the application of the green theories of urban development in China. Finally, methods of future green urban development in China are proposed
Overview of nucleon structure studies
A brief overview of the recent activity in the measurement of the elastic
electromagnetic proton and neutron form factors is presented. It is discussed
how the quality of the data has been greatly improved by performing double
polarization experiments, and the role of two-photon exchange processes will be
highlighted. The spatial information on the quark charge distribibutions in the
nucleon resulting from the form factors measurements will be discussed, as well
as the steady rate of improvements made in the lattice QCD calculations. It is
discussed how generalized parton distributions have emerged as a unifying theme
in hadron physics linking the spatial densities extracted from form factors
with the quark momentum distribution information residing in quark structure
functions. The recent progress in the electromagnetic excitation of the
resonance will also briefly be discussed.Comment: prepared for Proceedings of International Nuclear Physics Conference
(INPC07), typos corrected + references adde
Recommended from our members
HNRNPK maintains epidermal progenitor function through transcription of proliferation genes and degrading differentiation promoting mRNAs.
Maintenance of high-turnover tissues such as the epidermis requires a balance between stem cell proliferation and differentiation. The molecular mechanisms governing this process are an area of investigation. Here we show that HNRNPK, a multifunctional protein, is necessary to prevent premature differentiation and sustains the proliferative capacity of epidermal stem and progenitor cells. To prevent premature differentiation of progenitor cells, HNRNPK is necessary for DDX6 to bind a subset of mRNAs that code for transcription factors that promote differentiation. Upon binding, these mRNAs such as GRHL3, KLF4, and ZNF750 are degraded through the mRNA degradation pathway, which prevents premature differentiation. To sustain the proliferative capacity of the epidermis, HNRNPK is necessary for RNA Polymerase II binding to proliferation/self-renewal genes such as MYC, CYR61, FGFBP1, EGFR, and cyclins to promote their expression. Our study establishes a prominent role for HNRNPK in maintaining adult tissue self-renewal through both transcriptional and post-transcriptional mechanisms
Resource allocation for Lagrangian tracking
Author Posting. © American Meteorological Society, 2016. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Atmospheric and Oceanic Technology 33 (2016): 1225-1235, doi:10.1175/JTECH-D-15-0115.1.Accurate estimation of the transport probabilities among regions in the ocean provides valuable information for understanding plankton transport, the spread of pollutants, and the movement of water masses. Individual-based particle-tracking models simulate a large ensemble of Lagrangian particles and are a common method to estimate these transport probabilities. Simulating a large ensemble of Lagrangian particles is computationally expensive, and appropriately allocating resources can reduce the cost of this method. Two universal questions in the design of studies that use Lagrangian particle tracking are how many particles to release and how to distribute particle releases. A method is presented for tailoring the number and the release location of particles to most effectively achieve the objectives of a study. The method detailed here is a sequential analysis procedure that seeks to minimize the number of particles that are required to satisfy a predefined metric of result quality. The study assesses the result quality as the precision of the estimates for the elements of a transport matrix and also describes how the method may be extended for use with other metrics. Applying this methodology to both a theoretical system and a particle transport model of the Gulf of Maine results in more precise estimates of the transport probabilities with fewer particles than from uniformly or randomly distributing particle releases. The application of this method can help reduce the cost of and increase the robustness of results from studies that use Lagrangian particles.This research was supported by the Department of Defense (DoD) through the National Defense Science and Engineering Graduate Fellowship (NDSEG) program and the National Science Foundation through Grant OCE-1459133 and Grant OCE-1031256.2016-12-0
Found: High Surface Brightness Compact Galaxies
We are using the 2dF spectrograph to make a survey of all objects (`stars'
and `galaxies') in a 12 sq.deg region towards the Fornax cluster. We have
discovered a population of compact emission-line galaxies unresolved on
photographic sky survey plates and therefore missing in most galaxy surveys
based on such material. These galaxies are as luminous as normal field
galaxies. Using H-alpha to estimate star formation they contribute at least an
additional 5 per cent to the local star formation rate.Comment: To appear in "The Low Surface Brightness Universe", IAU Coll 171,
eds. J.I. Davies et al., A.S.P. Conference Series. 3 pages, LaTex, 1
encapsulated ps-figure, requires paspconf.st
Biodiversity assessment across a dynamic riverine system: A comparison of eDNA metabarcoding versus traditional fish surveying methods
While many studies have considered the ability of eDNA to assess animal communities in lacustrine settings, fewer have considered riverine systems, particularly those spanning the environmental gradients present in large river basins. Such dynamic systems are challenging for eDNA biomonitoring due to differing eDNA transport distances in rivers and the effects of river chemistry. To address this challenge, we focused on the Thames River system, UK, which has exceptional historical fish records providing a baseline to test the accuracy of eDNA metabarcoding in recovering fish community structure across both fresh and tidal zones. Two primer sets targeting 12S and CO1 regions were used to capture fish communities across the Thames catchment, from the upper freshwaters to the mid estuary. eDNA was collected at 35Â sites, 14 of which were simultaneously paired with traditional fish surveys for direct comparison. We demonstrated that eDNA metabarcoding consistently detected more freshwater species than traditional methods, despite extensive sampling effort using the latter. In contrast, metabarcoding did not perform as well as traditional approaches in estuarine waters, although results included the novel detection of the protected sea lamprey. We further demonstrated that minor variations in the recovery of all approaches would not impact on the assessment of simple ecological models of community structure and, thus, some variability between approaches should not be viewed as a serious hindrance to uptake. Rather, our findings support a growing consensus that eDNA can reliably detect fish communities across dynamic freshwater habitats
- …