期刊文献+
共找到3,300篇文章
< 1 2 165 >
每页显示 20 50 100
The “Dead Universe” Theory: Natural Separation of Galaxies Driven by the Remnants of a Supermassive Dead Universe
1
作者 Joel Almeida 《Natural Science》 2024年第6期65-101,共37页
This article explores the dead universe theory as a novel interpretation for the origin and evolution of the universe, suggesting that our cosmos may have originated from the remnants of a preceding universe. This per... This article explores the dead universe theory as a novel interpretation for the origin and evolution of the universe, suggesting that our cosmos may have originated from the remnants of a preceding universe. This perspective challenges the conventional Big Bang theory, particularly concerning dark matter, the expansion of the universe, and the interpretation of phenomena such as gravitational waves. 展开更多
关键词 Dead Universe theory Heat Death of the Universe Big Bang theory Universe’s Ultimate Fate Universe Expansion Big Freeze Universe Cosmological Models End of Universe theories Natural Galaxy Drift Future of the Universe Universe Cooling Down Cosmology and Entropy
下载PDF
On the Proof of the Contradiction of Set Theory
2
作者 Yury M. Volin 《Advances in Pure Mathematics》 2024年第3期139-159,共21页
The article is devoted to proving the inconsistency of set theory arising from the existence of strange trees. All steps of the proof rely on common informal set-theoretic reasoning, but they take into account the pro... The article is devoted to proving the inconsistency of set theory arising from the existence of strange trees. All steps of the proof rely on common informal set-theoretic reasoning, but they take into account the prohibitions that were introduced into axiomatic set theories in order to overcome the difficulties encountered by the naive Cantor set theory. Therefore, in fact, the article is about proving the inconsistency of existing axiomatic set theories, in particular, the ZFC theory. 展开更多
关键词 Set theory Inconsistency TREE Strange Tree Through way Almost through way ISOMORPHISM Almost Isomorphism Isomorphism Tree Place Plane Superposition of Trees on the Place Plane Disposition of Trees on the Place Plane
下载PDF
Physical Experiments and Mechanism Study on the Occurrence State of Hydrogen in Clay Minerals
3
作者 WANG Lu JIN Zhijun 《Acta Geologica Sinica(English Edition)》 SCIE CAS CSCD 2024年第S01期70-71,共2页
In recent years,natural hydrogen has been discovered in various geological environments both domestically and internationally,which has sparked a global interest among geologists and led to a surge in the exploration ... In recent years,natural hydrogen has been discovered in various geological environments both domestically and internationally,which has sparked a global interest among geologists and led to a surge in the exploration of hydrogen gas(Klein et al.,2019;Prinzhofer et al.,2019;Moretti and Webber,2021;Scott,2021;Bezruchko,2022).However,there is a lack of research on the occurrence state of natural hydrogen gas,which hinders a deeper understanding of its behavior in underground storage and migration. 展开更多
关键词 natural hydrogen clay minerals hydrogen adsorption density functional theory natural hydrogen exploration grand canonical Monte Carlo
下载PDF
A symmetric substructuring method for analyzing the natural frequencies of conical origami structures
4
作者 Chenhao Lu Yao Chen +2 位作者 Weiying Fan Jian Feng Pooya Sareh 《Theoretical & Applied Mechanics Letters》 CAS CSCD 2024年第3期203-210,共8页
Conical origami structures are characterized by their substantial out-of-plane stiffness and energy-absorptioncapacity.Previous investigations have commonly focused on the static characteristics of these lightweight s... Conical origami structures are characterized by their substantial out-of-plane stiffness and energy-absorptioncapacity.Previous investigations have commonly focused on the static characteristics of these lightweight struc-tures.However,the efficient analysis of the natural vibrations of these structures is pivotal for designing conicalorigami structures with programmable stiffness and mass.In this paper,we propose a novel method to analyzethe natural vibrations of such structures by combining a symmetric substructuring method(SSM)and a gener-alized eigenvalue analysis.SSM exploits the inherent symmetry of the structure to decompose it into a finiteset of repetitive substructures.In doing so,we reduce the dimensions of matrices and improve computationalefficiency by adopting the stiffness and mass matrices of the substructures in the generalized eigenvalue analysis.Finite element simulations of pin-jointed models are used to validate the computational results of the proposedapproach.Moreover,the parametric analysis of the structures demonstrates the influences of the number of seg-ments along the circumference and the radius of the cone on the structural mass and natural frequencies of thestructures.Furthermore,we present a comparison between six-fold and four-fold conical origami structures anddiscuss the influence of various geometric parameters on their natural frequencies.This study provides a strategyfor efficiently analyzing the natural vibration of symmetric origami structures and has the potential to contributeto the efficient design and customization of origami metastructures with programmable stiffness. 展开更多
关键词 Natural structural vibration Origami design Group theory Symmetric substructuring method(SSM) Generalized eigenvalue analysis
下载PDF
Fundamental Issues Towards Unified Design Theory of Recycled and Natural Aggregate Concrete Components 被引量:1
5
作者 Jianzhuang Xiao Kaijian Zhang +2 位作者 Tao Ding Qingtian Zhang Xuwen Xiao 《Engineering》 SCIE EI CAS CSCD 2023年第10期188-197,共10页
In the past 20 years,recycled aggregate concrete(RAC),as a type of low-carbon concrete,has become a worldwide focus of research.However,the design methodology for RAC structural components remains a challenge.Conseque... In the past 20 years,recycled aggregate concrete(RAC),as a type of low-carbon concrete,has become a worldwide focus of research.However,the design methodology for RAC structural components remains a challenge.Consequently,demands for a unified design of natural aggregate concrete(NAC)and RAC components have been presented.Accordingly,this study analyses the necessity of a unified design theory and provides an in-depth demonstration of the strength determination,compressive constitutive relationship,and design method of concrete components.The coefficient of variation of RAC strength is found to be generally higher than that of NAC strength.The compressive and tensile strengths of RAC can be defined and determined using the same method as that used for NAC.The uniaxial compressive constitutive relationship between NAC and RAC has a unified mathematical expression.However,the elastic modulus of RAC decreases,and its brittleness exhibits an increasing trend compared with that of NAC.Finally,to unify the design formulae of RAC and NAC components for bearing capacity,modification factors for RAC components are proposed considering safety and reliability.Additionally,the feasibility of the proposed unified time-dependent design theory is demonstrated in terms of conceptual design and structural measures considering the effects of strength degradation and reinforcement corrosion.It is believed that this study enriches and develops the basic theory of concrete structures. 展开更多
关键词 Recycled aggregate concrete(RAC) Natural aggregate concrete(NAC) Strength determination Constitutive relation Reliability Unified design theory
下载PDF
About the Strange Tree Paradox and Possible Inconsistency of Set Theory
6
作者 Yury M. Volin 《Advances in Pure Mathematics》 2023年第10期694-713,共20页
The existence of “strange trees” is proven and their paradoxical nature is discussed, due to which set theory is suspected of being contradictory. All proofs rely on informal set-theoretic reasoning, but without usi... The existence of “strange trees” is proven and their paradoxical nature is discussed, due to which set theory is suspected of being contradictory. All proofs rely on informal set-theoretic reasoning, but without using elements that were prohibited in axiomatic set theories in order to overcome the difficulties encountered by Cantor’s naive set theory. Therefore, in fact, the article deals with the possible inconsistency of existing axiomatic set theories, in particular, the ZFC theory. Strange trees appear when uncountable cardinals appear. 展开更多
关键词 Set theory INCONSISTENCY TREE Strange Tree Through way Almost Through way ISOMORPHISM Almost Isomorphism
下载PDF
On the Natures of English Passive Construction Based on Theta Theory
7
作者 王丽 《海外英语》 2016年第22期186-187,共2页
The study of English passive construction has always been one of the hot topics in the literature of Generative Grammar. Although many attempts have been made, the study of this structure is still not systematic enoug... The study of English passive construction has always been one of the hot topics in the literature of Generative Grammar. Although many attempts have been made, the study of this structure is still not systematic enough especially in terms of its essential natures. The present study is designed to give a full explanation of natures of English passive construction from the perspective of theta theory, which can provide English learners with a deeper understanding of passive structure. 展开更多
关键词 passive structure theta theory natures
下载PDF
Density functional theory study on natural hydrophobicity of sulfide surfaces 被引量:5
8
作者 赵翠华 陈建华 +1 位作者 吴伯增 龙贤灏 《Transactions of Nonferrous Metals Society of China》 SCIE EI CAS CSCD 2014年第2期491-498,共8页
Adsorption of water on sulfide surfaces and natural floatability of sulfide minerals were studied using density functional theory (DFT) method. All computational models were built in a vacuum environment to eliminat... Adsorption of water on sulfide surfaces and natural floatability of sulfide minerals were studied using density functional theory (DFT) method. All computational models were built in a vacuum environment to eliminate the effects of oxygen and other factors. H2O molecule prefers to stay with pyrite and sphalerite surfaces rather than water, whereas for galena, chalcocite, stibnite, and molybdenite, H2O molecule prefers to stay with water rather than the mineral surfaces. On the other hand, pyrite surface favors N2 more than water, while sphalerite surface cannot adsorb N2. These results show that galena, stibnite, chalcocite, and molybdenite are hydrophobic, while sphalerite is hydrophilic. Although pyrite has certain hydrophilicity, it tends to be aerophilic because the reaction of pyrite with H2O is weaker than pyrite with N2. Thus, pyrite, galena, chalcocite, stibnite and molybdenite all have natural floatability. 展开更多
关键词 sulfide minerals water adsorption natural floatability density functional theory
下载PDF
Investigating the tourism image of mountain scenic spots in China through the lens of tourist perception 被引量:2
9
作者 LI Feng-jiao LIAO Xia +3 位作者 LIU Jia-ming JIANG Li-li WANG Meng-di LIU Jin-feng 《Journal of Mountain Science》 SCIE CSCD 2023年第8期2298-2314,共17页
A favorable tourism image of high-quality mountain scenic spots(HQMSS)is crucial for tourism prosperity and sustainability.This paper establishes a framework for investigating the tourism image based on cognitive-emot... A favorable tourism image of high-quality mountain scenic spots(HQMSS)is crucial for tourism prosperity and sustainability.This paper establishes a framework for investigating the tourism image based on cognitive-emotion theory and uses natural language processing(NLP)tools to clarify the cognition,emotion,and overall tourist image of the HQMSS in China from the perspective of tourist perception.This paper examines the multi-dimensional spatial differentiation of China's overall image,including province,scenic spot scales,as well as the spatial pattern of the overall comprehensive tourism image.Strategies for comprehensively improving HQMSS's tourism image are also formulated.The results show that:(1)The cognitive image of Chinese HQMSS is categorized into core and marginal images,and the core images such as scenery and cable car are the expression of the uniqueness of mountainous scenic spots.Additionally,the cognitive image is classified into six dimensions:tourism environment,tourism supporting facilities,tourism experience,tourism price,tourism service,and tourism safety.(2)Positive emotions are the dominant mood type of HQMSS in China,followed by neutral emotions,with negative emotions being the least frequent.Emotional images vary across dimensions,with tourism environment and tourism experience evoking relatively higher emotion.(3)The spatial pattern of HQMSS for each dimension at the national,provincial,and scenic scales is diversifying.This article provides a multidimensional perspective for investigating the tourism image of mountainous scenic spots,proposes targeted recommendations to improve the overall image of HQMSS in China,and can greatly contribute to the sustainable development of mountain tourism. 展开更多
关键词 Mountain scenic spot Tourism image Spatial differentiation Natural language processing Cognitive-emotion theory Tourist perception
下载PDF
A theoretical insight about co-pyrolysis reaction of natural gas and coal
10
作者 Mingjun Pan Chengkai Jin +3 位作者 Bingying Han Runping Ye Rongbin Zhang Gang Feng 《Chinese Journal of Chemical Engineering》 SCIE EI CAS CSCD 2023年第11期220-225,共6页
The co-pyrolysis of natural gas and coal is a promising way for the production of acetylene due to its high efficiency for energy and hydrogen utilization.This work investigated the thermodynamics for the copyrolysis ... The co-pyrolysis of natural gas and coal is a promising way for the production of acetylene due to its high efficiency for energy and hydrogen utilization.This work investigated the thermodynamics for the copyrolysis reaction of natural gas and coal using density functional theory.The favorable reaction conditions are presented in the form of phase diagrams.The calculation results show that the extra amount of methane may benefit the production of acetylene in the co-pyrolysis reaction,and the C/H ratio of 1:1,temperature around 3000 K and pressure at 0.1 MPa are most favorable.The results would provide basic data for related industrial process for the production of acetylene. 展开更多
关键词 Natural gas theRMODYNAMICS Hydrocarbons CO-PYROLYSIS Gibbs free energy Density functional theory
下载PDF
The Thought of the Oneness Between Man and Nature in Walden
11
作者 田烨 《科技信息》 2010年第1期162-163,共2页
From the view of the ecological theory, this paper tries to analyze that Thoreau uses Chinese traditional philosophical thought--- the oneness of man and nature to deal with the relationship of human beings and the na... From the view of the ecological theory, this paper tries to analyze that Thoreau uses Chinese traditional philosophical thought--- the oneness of man and nature to deal with the relationship of human beings and the nature in Walden. 展开更多
关键词 沃尔登 中国 传统哲学 发展现状
下载PDF
Free vibration analysis of functionally graded material beams based on Levinson beam theory 被引量:6
12
作者 Xuan WANG Shirong LI 《Applied Mathematics and Mechanics(English Edition)》 SCIE EI CSCD 2016年第7期861-878,共18页
Free vibration response of functionally graded material (FGM) beams is studied based on the Levinson beam theory (LBT). Equations of motion of an FGM beam are derived by directly integrating the stress-form equati... Free vibration response of functionally graded material (FGM) beams is studied based on the Levinson beam theory (LBT). Equations of motion of an FGM beam are derived by directly integrating the stress-form equations of elasticity along the beam depth with the inertial resultant forces related to the included coupling and higherorder shear strain. Assuming harmonic response, governing equations of the free vibration of the FGM beam are reduced to a standard system of second-order ordinary differential equations associated with boundary conditions in terms of shape functions related to axial and transverse displacements and the rotational angle. By a shooting method to solve the two-point boundary value problem of the three coupled ordinary differential equations, free vibration response of thick FGM beams is obtained numerically. Particularly, for a beam with simply supported edges, the natural frequency of an FGM Levinson beam is analytically derived in terms of the natural frequency of a corresponding homogenous Euler-Bernoulli beam. As the material properties are assumed to vary through the depth according to the power-law functions, the numerical results of frequencies are presented to examine the effects of the material gradient parameter, the length-to-depth ratio, and the boundary conditions on the vibration response. 展开更多
关键词 functionally graded material (FGM) beam Levinson beam theory (LBT) free vibration shooting method natural frequency
下载PDF
Quantization of light energy directly from classical electromagnetic theory in vacuum 被引量:2
13
作者 佘卫龙 《Chinese Physics B》 SCIE EI CAS CSCD 2005年第12期2514-2521,共8页
It is currently believed that light quantum or the quantization of light energy is beyond classical physics, and the picture of wave-particle duality, which was criticized by Einstein but has attracted a number of exp... It is currently believed that light quantum or the quantization of light energy is beyond classical physics, and the picture of wave-particle duality, which was criticized by Einstein but has attracted a number of experimental researches, is necessary for the description of light. It is shown in this paper, however, that the quantization of light energy in vacuum, which is the same as that in quantum electrodynamics, can be derived directly from the classical electromagnetic theory through the consideration of statistics based on classical physics. Therefore, the quantization of energy is an intrinsic property of light as a classical electromagnetic wave and has no need of being related to particles. 展开更多
关键词 the nature of light quantization of light energy classical electromagnetic theory consideration of statistics
下载PDF
THEORY AND PRACTICE FOR COMPILING THE ATLAS OF NATURAL DISASTERS IN CHINA 被引量:1
14
作者 Wang Jingai(Department of Resources and Environmental Sciences, Bejing Normal University, Beijing 100875 People’s Republic of China) 《Journal of Geographical Sciences》 SCIE CSCD 1994年第Z2期103-111,共9页
This article inquires into theoretical and practical problems on compilation of an atlas of regional natural disasters. (1) The basic theory of compiling an atlas of regional disasters has been founded on the combinat... This article inquires into theoretical and practical problems on compilation of an atlas of regional natural disasters. (1) The basic theory of compiling an atlas of regional disasters has been founded on the combination of the sciences of disasters, cartography and regional geogrphy. The content structure of a regional disaster atlas should be composed of at least the following five parts:hazard-formative environments and hazard-affected bodies,hazards, disaster effects, monitoring and warning system for natural disasters, and countermeasures for natural disaster reduction. (2) Contents of cartographic design of a regional disaster atlas should be composed of at least the following five parts: base map system, cartographic representation, Symbol System, color system, map edition and map layout system. (3) Based on theory and cartographic design of compiling an atlas of regional disaster, the Atlas of Natural Disater in China, which reveals objectively the temporal and spaial pattern of regional natural disasters of China,has been compiled and published. 展开更多
关键词 atlas compilation natural disaster theory PRACTICE
下载PDF
Community Regeneration Based on CPTED Theory: A Case Study of Rosengard Residential Area in Sweden 被引量:1
15
作者 GU Zhixin 《Journal of Landscape Research》 2016年第5期7-10,14,共5页
With urban development and social transformation, residential areas in some western countries have been faced with safety problems and community deterioration. In order to solve these problems through community planni... With urban development and social transformation, residential areas in some western countries have been faced with safety problems and community deterioration. In order to solve these problems through community planning, Crime Prevention through Environmental Design(CPTED) theory had been applied to practice. Rosengard residential area in Malmo, Sweden was a typical example of underclass community with physical and social problems. However, regeneration programme based on CPTED theory aimed to change the community from a problematical area to a safe and attractive neighborhood. Multidimensional analysis was carried out to illustrate the relationship between environmental improvement and security from community image, traffic system, territoriality and natural surveillance perspectives. This study could be considered as a referential approach for community construction and regeneration in China. 展开更多
关键词 Community regeneration CPTED theory Natural surveillance Residential area
下载PDF
An R(x)-orthonormal theory for the vibration performance of a non-smooth symmetric composite beam with complex interface 被引量:2
16
作者 Chein-Shan Liu Bo-Tong Li 《Acta Mechanica Sinica》 SCIE EI CAS CSCD 2019年第1期228-241,I0007,共15页
A composite beam is symmetric if both the material property and support are symmetric with respect to the middle point. In order to study the free vibration performance of the symmetric composite beams with different ... A composite beam is symmetric if both the material property and support are symmetric with respect to the middle point. In order to study the free vibration performance of the symmetric composite beams with different complex nonsmooth/discontinuous interfaces, we develop an R(x)-orthonormal theory, where R(x) is an integrable flexural rigidity function. The R(x)-orthonormal bases in the linear space of boundary functions are constructed, of which the second-order derivatives of the boundary functions are asked to be orthonormal with respect to the weight function R(x). When the vibration modes of the symmetric composite beam are expressed in terms of the R(x)-orthonormal bases we can derive an eigenvalue problem endowed with a special structure of the coefficient matrix A :=[aij ],aij= 0 if i + j is odd. Based on the special structure we can prove two new theorems, which indicate that the characteristic equation of A can be decomposed into the product of the characteristic equations of two sub-matrices with dimensions half lower. Hence, we can sequentially solve the natural frequencies in closed-form owing to the specialty of A. We use this powerful new theory to analyze the free vibration performance and the vibration modes of symmetric composite beams with three different interfaces. 展开更多
关键词 SYMMETRIC composite beams R(x)-orthogonality of second-order derivatives of boundary functions R(x)-orthonormal theory Non-smooth/discontinuous interface Sequentially closed-from natural frequencies
下载PDF
The Practical Significance of Marx's Theory of Natural Force Resources 被引量:1
17
作者 Jiefang ZHU 《Asian Agricultural Research》 2020年第3期64-67,74,共5页
Marx's theory of natural force resources is an indispensable part of Marx's economic theory.Natural force resources,as a kind of natural elements that do not cost a penny,are added to the production process fr... Marx's theory of natural force resources is an indispensable part of Marx's economic theory.Natural force resources,as a kind of natural elements that do not cost a penny,are added to the production process free of charge,and play a special role in the production process.Grasping and understanding the scientific connotation of Marx's theory of natural force resources is of great theoretical value and practical significance for promoting the harmonious unity of man and nature and adhering to the strategy of sustainable economic development. 展开更多
关键词 Marx theory of NATURAL FORCE RESOURCE Practical SIGNIFICANCE
下载PDF
Analysis of Marx's Theory of Natural Forces 被引量:1
18
作者 Jiefang ZHU 《Meteorological and Environmental Research》 CAS 2022年第4期37-39,共3页
Marx’s theory of natural forces is an indispensable part of Marx’s economic theory.As a natural element that does not need to spend a penny,natural forces are added to the production process free of charge,and play ... Marx’s theory of natural forces is an indispensable part of Marx’s economic theory.As a natural element that does not need to spend a penny,natural forces are added to the production process free of charge,and play a special restrictive role in the production process.Mastering and applying the scientific connotation of Marx’s theory has very important theoretical value and practical significance for adhering to the sustainable development of nature,economy and society. 展开更多
关键词 Marx theory of natural forces Sustainable development
下载PDF
“Extreme utilization”development theory of unconventional natural gas 被引量:1
19
作者 MA Xinhua 《Petroleum Exploration and Development》 CSCD 2021年第2期381-394,共14页
In the process of unconventional natural gas development practice,the"extreme utilization"concept that focuses on"continuously breaking through the limit of development technology"is gradually form... In the process of unconventional natural gas development practice,the"extreme utilization"concept that focuses on"continuously breaking through the limit of development technology"is gradually formed,and supports the scale benefit exploration of unconventional gas in China.On this basis,the development theory of"extreme utilization"is proposed,its theoretical connotation together with development technologies of unconventional natural gas are clarified.The theoretical connotation is that,aiming at"extreme gas reservoirs","extreme techniques"are utilized to build subsurface connected bodies,expand the discharge area,and enlarge the production range,to obtain the maximum single-well production,extreme recovery,and eventually achieve the"extreme effect"of production.The series of development technologies include micro/nano-scale reservoir evaluation,"sweet spot"prediction,unconventional percolation theory and production capacity evaluation,optimization of grid well pattern,optimal-fast drilling and volume fracturing,and working regulation optimization and"integrated"organizing system.The"extreme utilization"development theory has been successfully applied in the development of unconventional gas reservoirs such as Sulige tight gas,South Sichuan shale gas,and Qinshui coalbed methane.Such practices demonstrate that,the"extreme utilization"development theory has effectively promoted the development of unconventional gas industry in China,and can provide theoretical guidance for effective development of other potential unconventional and difficult-to-recovery resources. 展开更多
关键词 unconventional natural gas extreme gas reservoir extreme development theory of extreme utilization subsurface connected body production capacity evaluation grid well pattern drainage and extraction optimization
下载PDF
Questions of Theory and Practice: To Synthesis, Analysis and Evaluation Natural Systems of Pacific Russia Based on Models of Landscape Geosystems
20
作者 V. T. Starozhilov 《Journal of Geoscience and Environment Protection》 2019年第1期81-92,共12页
The results of long-term author’s scientific research in the field of geological and geographical study and landscape mapping of large regional links, such as Sikhote-Alinsky, Sakhalinsky, Kamchatsky, Anadyrsky, loca... The results of long-term author’s scientific research in the field of geological and geographical study and landscape mapping of large regional links, such as Sikhote-Alinsky, Sakhalinsky, Kamchatsky, Anadyrsky, located in the Pacific landscape belt of Russia, are considered (Starozhilov, 2013). The studies were conducted at the medium scale (1:500,000) and were accompanied by landscape mapping (Starozhilov, 2016). The proposed article discusses the theory and practice of the overall results and the strategic vision of applying the landscape approach with selected examples. The wide range of possibilities of applying the landscape approach in studying the interaction of nature and society is emphasized. The importance and the indisputable need for the synthesis, analysis and assessment of natural systems based on the mapping of landscape geosystems to assess the environmental management of not only regional territories, but also of Pacific Russia as a whole are noted. 展开更多
关键词 SYNtheSIS Analysis Assessment nature LANDSCAPE Geosystems theory Practice
下载PDF
上一页 1 2 165 下一页 到第
使用帮助 返回顶部