118 research outputs found
Spherically symmetric solution of f(R,G) gravity at low energy
No full textThe weak-field and slow-motion limit of f(R,G) gravity is developed up to (v/c)(4) order in a spherically symmetric background. Considering the Taylor expansion of a general function f around vanishing values of R and G, we present general vacuum solutions up to (v/c)(4) order for the gravitational field generated by a ball-like source. The spatial behaviors at (v/c)(2) order are the same for f(R,G) gravity and f(R) gravity, and their corresponding real valued static behaviors are presented and compared with the one in general relativity. The static Yukawa-like behavior is proved to be compatible with the previous result of the most general fourth-order theory. At (v/c)(4) order, the static corrections to the Yukawa-like behavior for f(R,G) gravity, f(R) gravity, and the Starobinsky gravity are presented and compared with the one in general relativity.National Natural Science Foundation of China [11120101004, 11475006]SCI(E)[email protected]; [email protected]
Spatiotemporal changes of China's carbon emissions
No full textSpatiotemporal changes in China's carbon emissions during the 11th and 12th Five‐Year Plan periods are quantified for the first time through a reconstructed nationwide high‐resolution gridded data set. The hot spots of carbon emissions in China have expanded by 28.5% (toward the west) in the north and shrunk by 18.7% in the south; meanwhile, the emission densities in North and South China have increased by 15.7% and 49.9%, respectively. This suggests a clear transition to a more intensive economic growth model in South China as a result of the energy conservation and emission reduction policies, while the expanded carbon hot spots in North China are mainly dominated by the Grand Western Development Program. The results also show that China's carbon emissions exhibit a typical spatially intensive, high‐emission pattern, which has undergone a slight relaxation (up to 3%) from 2007 to 2012 due to a typical urbanization process
Investigation of Unclamped Inductive Switch Characteristics in 4H-SiC MOSFETs With Different Cell Topologies
No full textTo investigate the unclamped inductive switch (UIS) characteristics, 1200 V silicon carbide (SiC) planar MOSFETs with four cell topologies of linear, current sharing linear, square, and hexagon are designed and manufactured. The experimental platform was built and tested. The results show that the single pulse avalanche energy density of the linear cell topology is 1.69 times higher than that of the square and 1.49 times that of the hexagon. Further, the UIS process is simulated by using physical simulation, which shows that the avalanche energy was concentrated near the corner of the P-base region in the UIS mode. From this, the avalanche energy distribution differences of the four cell topologies were analyzed and compared. A theoretical model of avalanche heating per unit area is proposed, which shows that the avalanche energy density is inversely proportional to the proportion of avalanche energy concentration region. This study may contribute to the cell topology design of SiC MOSFETs under the application scenario with high avalanche reliability requirements.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Electronic Components, Technology and Material
Multipole analysis for linearized<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>f</mml:mi><mml:mo stretchy="false">(</mml:mo><mml:mi>R</mml:mi><mml:mo stretchy="false">)</mml:mo></mml:math>gravity with irreducible Cartesian tensors
No full textMultipole analysis for linearized
No full textThe field equations of gravity are rewritten in the form of obvious wave equations with the stress–energy pseudotensor of the matter fields and the gravitational field as its source under the de Donder condition. The linearized field equations of gravity are the same as those of linearized f(R) gravity, and thus, their multipole expansions under the de Donder condition are also the same. It is also shown that the Gauss–Bonnet curvature scalar does not contribute to the effective stress–energy tensor of gravitational waves in linearized gravity, though plays an important role in the nonlinear effects in general. Further, by applying the 1 / r expansion in the distance to the source to the linearized gravity, the energy, momentum, and angular momentum carried by gravitational waves in linearized gravity are provided, which shows that , unlike the nonlinear term in the gravitational Lagrangian, does not contribute to them either
The gravitational field outside a spatially compact stationary source in a generic fourth-order theory of gravity
No full textBy applying the symmetric and trace-free formalism in terms of the
irreducible Cartesian tensors, the metric for the external gravitational field
of a spatially compact stationary source is provided in gravity, a
generic fourth-order theory of gravity, where is Ricci scalar,
is Ricci square, and
is Riemann square. A new type of
gauge condition is proposed so that the linearized gravitational field
equations of gravity are greatly simplified, and then, the
stationary metric in the region exterior to the source is derived. In the
process of applying the result, integrations are performed only over the domain
occupied by the source. The multipole expansion of the metric potential in
gravity for a spatially compact stationary source is also presented.
In the expansion, the corrections of gravity to General Relativity
are Yukawa-like ones, dependent on two characteristic lengths. Two additional
sets of mass-type source multipole moments appear in the corrections and the
salient feature characterizing them is that the integrations in their
expressions are always modulated by a common radial factor related to the
source distribution.Comment: 11 pages,accepted by JHE
Multipole analysis in the radiation field for linearized <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mi>f</mml:mi><mml:mo stretchy="false">(</mml:mo><mml:mi>R</mml:mi><mml:mo stretchy="false">)</mml:mo></mml:mrow></mml:math> gravity with irreducible Cartesian tensors
No full textMultipole expansion of the gravitational field in a general class of fourth-order theories of gravity and the application in gyroscopic precession
No full textA viable weak-field and slow-motion approximation method is constructed in
gravity,
a general class of fourth-order theories of gravity. By applying this method,
the metric, presented in the form of the multipole expansion, outside a
spatially compact source up to order is provided, and the closed-form
expressions for the source multipole moments are all presented explicitly. The
metric consists of the massless tensor part, the massive scalar part, and the
massive tensor part, where the former is exactly the metric in General
Relativity, and the latter two are the corrections to it. It is shown that the
corrections bear the Yukawa-like dependence on the two massive parameters and
predict the appearance of six additional sets of source multipole moments,
which indicates that up to order, there exist six degrees of freedom
beyond General Relativity within gravity. By means of the metric, for
a gyroscope moving around the source without experiencing any torque, the
multipole expansions of its spin's angular velocities of the Thomas precession,
the geodetic precession, and the Lense-Thirring precession are derived, and
from them, the corrections to the angular velocities of the three types of
precession in General Relativity can be read off. These results indicate that
differently from or gravity, the most salient feature
of the general gravity is that it gives the
nonvanishing correction to the gyroscopic spin's angular velocity of the
Lense-Thirring precession in General Relativity.Comment: 46 pages,0 figure,accepted by JCA
Successful biological control of Chromolaena odorata (Asteraceae) by the gall fly Cecidochares connexa (Diptera: Tephritidae) in Papua New Guinea
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