474 research outputs found
The Phase-space analysis of scalar fields with non-minimally derivative coupling
We perform a dynamical analysis for the exponential scalar field with
non-minimally derivative coupling. For the quintessence case, the stable fixed
points are the same with and without the non-minimally derivative coupling. For
the phantom case, the attractor with dark energy domination exists for the
minimal coupling only. For the non-minimally derivative coupling without the
standard canonical kinetic term, only the de-Sitter attractor exists, and the
dark matter solution is unstable.Comment: v2, minor correction, EPJC in pres
Thermodynamics of scalar-tensor theory with non-minimally derivative coupling
With the usual definitions for the entropy and the temperature associated
with the apparent horizon, we show that the unified first law on the apparent
horizon is equivalent to the Friedmann equation for the scalar--tensor theory
with non-minimally derivative coupling. The second law of thermodynamics on the
apparent horizon is also satisfied. The results support a deep and fundamental
connection between gravitation, thermodynamics, and quantum theory.Comment: 12 pages, no figure, minor correction
ISSUES OF WATER RESOURCE MANAGEMENT IN CHINA: IMPLICATIONS ON AGRICULTURE AND FOOD SECURITY IN THE GUANGXI PROVINCE OF SOUTH CHINA
Despite China’s great stride in technology development and economic recovery, water remains a major issue of concern. Water has a direct impact on agriculture and food production, hence, water management is critical to achieving food security. This paper reviews in a broader perspective the relationship between water resource management and food security in China, and assesses water resource management interms of water use, pollution and influence of government policies, as well as social and economic systems. It also highlights the challenges of water resource management and its implications on agriculture and food security in the Guangxi province of South China. The review also sets a background upon which further studies and frameworks could be developed to help provide a sustainable solution to regional water management challenges, with a view to achieving improved agricultural production and food security in China and other countries with similar issues. Thus, in the growing quest for economic growth, and owing to the growing need for water in the country, the government of China should ensure through a properly monitored policy framework that water resources are not exploited by a particular sector or region at the expense of other regions in the country
Intergenerational transmission of education in China: New evidence from the Chinese Cultural Revolution
This paper estimates the effect of parental education on children’s education by using instruments generated by the Chinese Cultural Revolution, and further explores the mechanisms of this causal relationship. Several important findings stand out from our empirical analyses. We find a larger intergenerational persistence in education for higher level in urban areas but for a lower level of education in rural areas. The main results from instrumental variable estimation show that the nurture effect is larger and more significant for fathers than for mothers. A deeper investigation of the mechanism behind this nurture effect informs us that a father’s education passes on to his children’s education partly through the income channel. Another notable finding is that even after controlling for fathers’ income, parental education still has a significantly positive effect on children’s education through the nurture effect. This indicates that beyond the income channel, there may exist other channels such as better home environment, which deserve to be explored in future research.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/147763/1/rode12558_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/147763/2/rode12558.pd
Weak antilocalization and electron-electron interaction in coupled multiple-channel transport in a BiSe thin film
Electron transport properties of a topological insulator BiSe thin
film are studied in Hall-bar geometry. The film with a thickness of 10 nm is
grown by van der Waals epitaxy on fluorophlogopite mica and Hall-bar devices
are fabricated from the as-grown film directly on the mica substrate. Weak
antilocalization and electron-electron interaction effects are observed and
analyzed at low temperatures. The phase-coherence length extracted from the
measured weak antilocalization characteristics shows a strong power-law
increase with decreasing temperature and the transport in the film is shown to
occur via coupled multiple (topological surface and bulk states) channels. The
conductivity of the film shows a logarithmically decrease with decreasing
temperature and thus the electron-electron interaction plays a dominant role in
quantum corrections to the conductivity of the film at low temperatures.Comment: 12 pages, 5 figure
Thermodynamic properties of higher-dimensional dS black holes in dRGT massive gravity
On the basis of the state parameter of de Sitter space-time satisfying the
first law of thermodynamics,we can derive some effective thermodynamic
quantities.When the temperature of the black hole horizon is equal to that of
the cosmological horizon, we think that the effective temperature of the
space-time should have the same value. Using this condition, we obtain a
differential equation of the entropy of the de Sitter black hole in the
higherdimensional de Rham, Gabadadze and Tolley (dRGT) massive gravity. Solving
the differential equation, we obtain the corrected entropy and effective
thermodynamic quantities of the de Sitter black hole. The results show that for
multiparameter black holes, the entropy satisfied differential equation is
invariable with different independent state parameters. Therefore, the entropy
of higher-dimensional dS black holes in dRGT massive gravity is only a function
of the position of the black hole horizon, and is independent of other state
parameters. It is consistent with the corresponding entropy of the black hole
horizon and the cosmological horizon. The thermodynamic quantities of
self-consistent de Sitter spacetime are given theoretically, and the equivalent
thermodynamic quantities have the second-order phase transformation similar to
AdS black hole, but unlike AdS black hole, the equivalent temperature of de
Sitter space-time has a maximum value. By satisfying the requirement of
thermodynamic equilibrium and stability of space-time, the conditions for the
existence of dS black holes in the universe are obtained.Comment: 11 pages, 6 figure
Strong spin-orbit interaction and magnetotransport in semiconductor BiOSe nanoplates
Semiconductor BiOSe nanolayers of high crystal quality have been
realized via epitaxial growth. These two-dimensional (2D) materials possess
excellent electron transport properties with potential application in
nanoelectronics. It is also strongly expected that the 2D BiOSe
nanolayers could be of an excellent material platform for developing spintronic
and topological quantum devices, if the presence of strong spin-orbit
interaction in the 2D materials can be experimentally demonstrated. Here, we
report on experimental determination of the strength of spin-orbit interaction
in BiOSe nanoplates through magnetotransport measurements. The
nanoplates are epitaxially grown by chemical vapor deposition and the
magnetotransport measurements are performed at low temperatures. The measured
magnetoconductance exhibits a crossover behavior from weak antilocalization to
weak localization at low magnetic fields with increasing temperature or
decreasing back gate voltage. We have analyzed this transition behavior of the
magnetoconductance based on an interference theory which describes the quantum
correction to the magnetoconductance of a 2D system in the presence of
spin-orbit interaction. Dephasing length and spin relaxation length are
extracted from the magnetoconductance measurements. Comparing to other
semiconductor nanostructures, the extracted relatively short spin relaxation
length of ~150 nm indicates the existence of strong spin-orbit interaction in
BiOSe nanolayers.Comment: 14 pages, 4 figures, and 5 pages of Supplementary Material
Acute resource pulses from periodical cicadas propagate to belowground food webs but do not affect tree performance
Acute resource pulses can have dramatic legacies for organismal growth, but the legacy effects of resource pulses on broader aspects of community structure and ecosystem processes are less understood. Mass emergence of periodical cicadas (Magicicada spp.) provides an excellent opportunity to shed light on the influence of resource pulses on community and ecosystem dynamics: the adults emerge every 13 or 17 years in vast numbers over much of eastern North America, with a smaller but still significant number becoming incorporated into forest food webs. To study the potential effects of such arthropod resource pulse on primary production and belowground food webs, we added adult cicada bodies to the soil surface surrounding sycamore trees and assessed soil carbon and nitrogen concentrations, plant-available nutrients, abundance and community composition of soil fauna occupying various trophic levels, decomposition rate of plant litter after 50 and 100 days, and tree performance for 4 years. Contrary to previous studies, we did not find significant cicada effects on tree performance despite observing higher plant-available nutrient levels on cicada addition plots. Cicada addition did change the community composition of soil nematodes and increased the abundance of bacterial- and fungal-feeding nematodes, while plant feeders, omnivores, and predators were not influenced. Altogether, acute resource pulses from decomposing cicadas propagated belowground to soil microbial-feeding invertebrates and stimulated nutrient mineralization in the soil, but these effects did not transfer up to affect tree performance. We conclude that, despite their influence on soil food web and processes they carry out, even massive resource pulses from arthropods do not necessarily translate to NPP, supporting the view that ephemeral nutrient pulses can be attenuated relatively quickly despite being relatively large in magnitude.Peer reviewe
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