Energy Conditions and Constraints on the Generalized Non-Local Gravity Model

We study and derive the energy conditions in generalized non-local gravity, which is the modified theory of general relativity obtained by adding a term m2n-2R□-nRto the Einstein-Hilbert action. Moreover, to obtain some insight on the meaning of the energy conditions, we illustrate the evolutions of four energy conditions with the model parameter ε for different n. By analysis we give the constraints on the model parameters ε.

Direct impacts and spatial spillovers:How does the multilateral resistance affect China-Africa agricultural trade?

The changes of one region’s trade barriers will affect other regions’trade volume.These spatial correlations caused by explanatory variables also constitute another part of“the multilateral resistance”,which tend to be ignored in traditional gravity equations.This paper takes this inconsistency between theoretical basis and empirical analysis as the breakthrough point of research.A multilateral gravity model is built,which has the feature of generalized spatial correlation.Then,frontier techniques of spatial econometrics are used to construct an empirical equation,and to conduct an empirical analysis,which scientifically estimate the magnitudes of bilateral direct impacts and the magnitudes of spatial spillovers on multilateral neighbors.The decomposition of the effects that provides reference for the directional operations of trade policy shows as follows:The negative factors that have significant spatial spillover effects would bring about multilateral resistance on China-Africa agricultural trade,which are caused by relatively poor social and economic conditions,corruption,and ethnic conflicts in some African countries.Energy production may cause crowding-out effects on agriculture of neighboring regions.In addition,the conflicts between African countries would hinder the development of agricultural trade between China and African countries not only because they have negative direct impacts on China-African agricultural trade but also because they have significant spatial spillover effects.When China promotes China-Africa agricultural trade by means of investment or aid,China should pay close attention to some direct or indirect impacts on the stable development of the China-African agricultural trade,which are caused by factors such as the developments of non-agricultural industries,peace,cultural consensus and efficient government.