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Search Results: 1 - 10 of 27058 matches for " Peng Meng "
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Palatini formulation of modified gravity with squared scalar curvature
Xinhe Meng,Peng Wang
Physics , 2003, DOI: 10.1023/B:GERG.0000048981.40061.63
Abstract: In this paper we derive the Modified Friedmann equation in the Palatini formulation of $R^2$ gravity. Then we use it to discuss the problem of whether in Palatini formulation a $R^2$ term can drive an inflation. We show that the Palatini formulation of $R^2$ gravity cannot lead to gravity-driven inflation. If considering no zero radiation and matter energy densities, we show that only under rather restrictive assumption about the radiation and matter energy densities there will be a mild power-law inflation $a\sim t^2$.
Cosmological Evolution in 1/R-Gravity Theory
Xinhe Meng,Peng Wang
Physics , 2003, DOI: 10.1088/0264-9381/21/4/015
Abstract: Recently, corrections of the $L(R)$ type to Einstein-Hilbert action that become important at small curvature are proposed. Those type of models intend to explain the observed cosmic acceleration without dark energy. We derive the full Modified Friedmann equation in the Palatini formulation of those modified gravity model of the $L(R)$ type. Then, we discuss various cosmological predictions of the Modified Friedmann equation.
Modified Friedmann Equations in R$^{-1}$-Modified Gravity
Xinhe Meng,Peng Wang
Physics , 2003, DOI: 10.1088/0264-9381/20/22/018
Abstract: Recently, corrections to Einstein-Hilbert action that become important at small curvature are proposed. We discuss the first order and second order approximations to the field equations derived by the Palatini variational principle. We work out the first and second order Modified Friedmann equations and present the upper redshift bounds when these approximations are valid. We show that the second order effects can be neglected on the cosmological predictions involving only the Hubble parameter itself, e.g. the various cosmological distances, but the second order effects can not be neglected in the predictions involving the derivatives of the Hubble parameter. Furthermore, the Modified Friedmann equations fit the SN Ia data at an acceptable level.
A Control Mechanism of Stream Media Based on 3G Network  [PDF]
Wei Jiang, Liming Meng, Songxiang Ying, Hong Peng, Zhijiang Xu
Journal of Software Engineering and Applications (JSEA) , 2012, DOI: 10.4236/jsea.2012.512B002
Abstract: In this paper, we use RTP/RTCP over unreliable UDP to realize the transportation of real time streaming. Meanwhile, according to the transmission feedback and network parameters, we analyze and calculate the network delay, packet loss and RTT (round trip time) to determine the network state. Finally, we propose a streaming media transmission   control scheme which could sense the network state and quickly adjust the rate of the sending side. It takes congestion, packet loss rate into comprehensive consideration and improves the overall performance of 3G network stream media.
Interlayer Prediction Method for Braid River Reservoirs in Offshore Oil Field  [PDF]
Wei Wang, Peng Meng, Jie Tan, Dongdong Yang, Dong Zhang
Open Journal of Geology (OJG) , 2019, DOI: 10.4236/ojg.2019.95017
Abstract: The interlayer structure of braid river reservoirs is complex and the interwell prediction is difficult in offshore oil field. Taking CFD11-1 oilfield of NgⅢ sand as an example, based on layer contrasting, the interlayer is divided into muddy interlayer, clay boulder interlayer, and physical interlayer according to lithology. Under the guidance of sedimentary model, we use the geology statistical inversion method to predict the clay boulder interlayer, consistent with the dynamic characteristics of oil production which is used for the prior quality control. The results of this study can objectively reveal the characteristics of interlayer space distribution. Compared with the traditional multi-well comparison and stochastic simulation model, this method is applied to the offshore oil field which is character with wide well space, sparse well network, which has very high application value in predicting the interlayer and deploying of inter-well encryption in the similar oilfield.
Palatini formulation of the $R^{-1}$modified gravity with an additionally squared scalar curvature term
Xin He Meng,Peng Wang
Physics , 2004, DOI: 10.1088/0264-9381/22/1/002
Abstract: In this paper by deriving the Modified Friedmann equation in the Palatini formulation of $R^2$ gravity, first we discuss the problem of whether in Palatini formulation an additional $R^2$ term in Einstein's General Relativity action can drive an inflation. We show that the Palatini formulation of $R^2$ gravity cannot lead to the gravity-driven inflation as in the metric formalism. If considering no zero radiation and matter energy densities, we obtain that only under rather restrictive assumption about the radiation and matter energy densities there will be a mild power-law inflation $a(t)\sim t^2$, which is obviously different from the original vacuum energy-like driven inflation. Then we demonstrate that in the Palatini formulation of a more generally modified gravity, i.e., the $1/R+R^2$ model that intends to explain both the current cosmic acceleration and early time inflation, accelerating cosmic expansion achieved at late Universe evolution times under the model parameters satisfying $\alpha\ll\beta$.
Lobectomy with Bronchoplasty and Reconstruction of Pulmonary Artery by Minitrauma-technique for Lung Cancer
Zhongmin PENG,Meng LI,Long MENG,Jiajun DU
Chinese Journal of Lung Cancer , 2009,
Abstract: Background and objective To research the effect and practicalbility of lobectomy with bronchoplasty and reconstruction of pulmonary artery by minitrauma-technique for lung cancer. Methods We retrospectibely reviewed our experience on 61 cases being lobectomy with bronchoplasty and bronchoplasty with or without video assisted thoracic small incision surgery for lung cancer from July 2005 to June 2009 from Shandong Provincal Hospital and 46 cases simultaneously by routine posterolateral incision. All patients whose bronchus and/or pulmonary artery were involved underwent the operation and experienced the bronchial sleeve/wedge resection or reconstruction of the pulmonary artery. Results All patients were done operation successfully and there were no operative mortality and no occurrence of anastomosis stenosis as well as fistula. The small incisions’ length was from 8 cm-15 cm while the routine posterolateral incision’s length was 25 cm-35 cm. The patients done the operation of small incision had less postoperative shoulder joint dysfunction and had better quality of life compaired to the patients done the routine posterolateral incision. Conclusion Lobectomy with bronchoplasty and reconstruction of pulmonary artery by minitrauma-technique for lung cancer could finished the same work with the traditional thoracic lateral incision and had less trauma, less pain, less recovery time.
Description of Chiral Doublets in $A\sim130$ Nuclei and the Possible Chiral Doublets in $A\sim100$ Nuclei
J. Peng,J. Meng,S. Q. Zhang
Physics , 2003, DOI: 10.1103/PhysRevC.68.044324
Abstract: The chiral doublets for nuclei in $A\sim100$ and $A\sim130$ regions have been studied with the particle-rotor model. The experimental spectra of chiral partners bands for four N=75 isotones in $A\sim130$ region have been well reproduced by the calculation with the configuration $\pi h_{11/2}\otimes\nu h_{11/2}^{-1}$. The possible chiral doublets in $A\sim100$ region have been predicted by the PRM model with the configuration $\pi g_{9/2}\otimes\nu g_{9/2}^{-1}$ based on the analysis of the spectra, the $\omega$-I relation, the $B(M1)$ and $B(E2)$ transition probabilities, and the structure of the wave functions. The possible chiral doublets for nuclei with asymmetric particle and hole configuration are also discussed.
$R^2$ corrections to the cosmological dynamics of inflation in the Palatini formulation
Xin-He Meng,Peng Wang
Physics , 2004, DOI: 10.1088/0264-9381/21/8/008
Abstract: We investigate the corrections to the inflationary cosmological dynamics due to a $R^2$ term in the Palatini formulation which may arise as quantum corrections to the effective Lagrangian in early universe. We found that the standard Friedmann equation will not be changed when the scalar field is in the potential energy dominated era. However, in the kinetic energy dominated era, the standard Friedmann equation will be modified and in the case of closed and flat universe, the Modified Friedmann equation will automatically require that the initial kinetic energy density of the scalar field must be in sub-Planckian scale.
Gravitational potential in Palatini formulation of modified gravity
Xin-He Meng,Peng Wang
Physics , 2003, DOI: 10.1023/B:GERG.0000036052.81522.fe
Abstract: General Relativity has so far passed almost all the ground-based and solar-system experiments. Any reasonable extended gravity models should consistently reduce to it at least in the weak field approximation. In this work we derive the gravitational potential for the Palatini formulation of the modified gravity of the L(R) type which admits a de Sitter vacuum solution. We conclude that the Newtonian limit is always obtained in those class of models and the deviations from General Relativity is very small for a slowly moving source.
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