14 CFR 27.27 - Center of gravity limits.
2010-01-01
... 14 Aeronautics and Space 1 2010-01-01 2010-01-01 false Center of gravity limits. 27.27 Section 27... AIRWORTHINESS STANDARDS: NORMAL CATEGORY ROTORCRAFT Flight General § 27.27 Center of gravity limits. The extreme forward and aft centers of gravity and, where critical, the extreme lateral centers of gravity must...
14 CFR 29.27 - Center of gravity limits.
2010-01-01
... 14 Aeronautics and Space 1 2010-01-01 2010-01-01 false Center of gravity limits. 29.27 Section 29... AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY ROTORCRAFT Flight General § 29.27 Center of gravity limits. The extreme forward and aft centers of gravity and, where critical, the extreme lateral centers of...
14 CFR 27.1519 - Weight and center of gravity.
2010-01-01
... 14 Aeronautics and Space 1 2010-01-01 2010-01-01 false Weight and center of gravity. 27.1519 Section 27.1519 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION... Operating Limitations § 27.1519 Weight and center of gravity. The weight and center of gravity...
14 CFR 29.1519 - Weight and center of gravity.
2010-01-01
... 14 Aeronautics and Space 1 2010-01-01 2010-01-01 false Weight and center of gravity. 29.1519 Section 29.1519 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION... Operating Limitations § 29.1519 Weight and center of gravity. The weight and center of gravity...
14 CFR 25.27 - Center of gravity limits.
2010-01-01
... 14 Aeronautics and Space 1 2010-01-01 2010-01-01 false Center of gravity limits. 25.27 Section 25... AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY AIRPLANES Flight General § 25.27 Center of gravity limits. The extreme forward and the extreme aft center of gravity limitations must be established for each...
The Effect of Center of Gravity and Anthropometrics on Human Performance in Simulated Lunar Gravity
Mulugeta, Lealem; Chappell, Steven P.; Skytland, Nicholas G.
2009-01-01
NASA EVA Physiology, Systems and Performance (EPSP) Project at JSC has been investigating the effects of Center of Gravity and other factors on astronaut performance in reduced gravity. A subset of the studies have been performed with the water immersion technique. Study results show correlation between Center of Gravity location and performance. However, data variability observed between subjects for prescribed Center of Gravity configurations. The hypothesis is that Anthropometric differences between test subjects could be a source of the performance variability.
14 CFR 23.1519 - Weight and center of gravity.
2010-01-01
... 14 Aeronautics and Space 1 2010-01-01 2010-01-01 false Weight and center of gravity. 23.1519 Section 23.1519 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION... Limitations and Information § 23.1519 Weight and center of gravity. The weight and center of...
Effect of Changing the Center of Gravity on Human Performance in Simulated Lunar Gravity
Chappell, Steven P.; Norcross, Jason R.; Gernhardt, Michael L.
2010-01-01
The presentation slides include: Moving Past Apollo, Testing in Analog Environments, NEEMO/NBL CG (center of gravity) Studies, Center of Gravity Test Design and Methods, CG Suited Locations and Results, CG Individual Considerations, CG Shirt-Sleeve Locations and Results.
46 CFR 170.200 - Estimated lightweight vertical center of gravity.
2010-10-01
... 46 Shipping 7 2010-10-01 2010-10-01 false Estimated lightweight vertical center of gravity. 170... Centers of Gravity § 170.200 Estimated lightweight vertical center of gravity. (a) Each tank vessel that... calculations required by §§ 170.170 and 172.065, the vertical center of gravity of a tank vessel in...
14 CFR 25.523 - Design weights and center of gravity positions.
2010-01-01
... 14 Aeronautics and Space 1 2010-01-01 2010-01-01 false Design weights and center of gravity... Design weights and center of gravity positions. (a) Design weights. The water load requirements must be...) must be used. (b) Center of gravity positions. The critical centers of gravity within the limits...
14 CFR 23.523 - Design weights and center of gravity positions.
2010-01-01
... 14 Aeronautics and Space 1 2010-01-01 2010-01-01 false Design weights and center of gravity... Structure Water Loads § 23.523 Design weights and center of gravity positions. (a) Design weights. The water... water taxi and takeoff run) must be used. (b) Center of gravity positions. The critical centers...
14 CFR 27.29 - Empty weight and corresponding center of gravity.
2010-01-01
... 14 Aeronautics and Space 1 2010-01-01 2010-01-01 false Empty weight and corresponding center of gravity. 27.29 Section 27.29 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF... and corresponding center of gravity. (a) The empty weight and corresponding center of gravity must...
14 CFR 29.29 - Empty weight and corresponding center of gravity.
2010-01-01
... 14 Aeronautics and Space 1 2010-01-01 2010-01-01 false Empty weight and corresponding center of gravity. 29.29 Section 29.29 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF... weight and corresponding center of gravity. (a) The empty weight and corresponding center of gravity...
14 CFR 25.29 - Empty weight and corresponding center of gravity.
2010-01-01
... 14 Aeronautics and Space 1 2010-01-01 2010-01-01 false Empty weight and corresponding center of gravity. 25.29 Section 25.29 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF... and corresponding center of gravity. (a) The empty weight and corresponding center of gravity must...
14 CFR 25.1519 - Weight, center of gravity, and weight distribution.
2010-01-01
... 14 Aeronautics and Space 1 2010-01-01 2010-01-01 false Weight, center of gravity, and weight... Information Operating Limitations § 25.1519 Weight, center of gravity, and weight distribution. The airplane weight, center of gravity, and weight distribution limitations determined under §§ 25.23 through...
14 CFR 135.185 - Empty weight and center of gravity: Currency requirement.
2010-01-01
... 14 Aeronautics and Space 3 2010-01-01 2010-01-01 false Empty weight and center of gravity... ON BOARD SUCH AIRCRAFT Aircraft and Equipment § 135.185 Empty weight and center of gravity: Currency... gravity are calculated from values established by actual weighing of the aircraft within the preceding...
14 CFR 23.29 - Empty weight and corresponding center of gravity.
2010-01-01
... gravity. 23.29 Section 23.29 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF... Flight General § 23.29 Empty weight and corresponding center of gravity. (a) The empty weight and corresponding center of gravity must be determined by weighing the airplane with— (1) Fixed ballast;...
Combination of monthly gravity field solutions from different processing centers
Jean, Yoomin; Meyer, Ulrich; Jäggi, Adrian
2015-04-01
Currently, the official GRACE Science Data System (SDS) monthly gravity field solutions are generated independently by the Centre for Space Research (CSR) and the German Research Centre for Geosciences (GFZ). Additional GRACE SDS monthly fields are provided by the Jet Propulsion Laboratory (JPL) for validation and outside the SDS by a number of other institutions worldwide. Although the adopted background models and processing standards have been harmonized more and more by the various processing centers during the past years, notable differences still exist and the users are more or less left alone with a decision which model to choose for their individual applications. Combinations are well-established in the area of other space geodetic techniques, such as the Global Navigation Satellite Systems (GNSS), Satellite Laser Ranging (SLR), and Very Long Baseline Interferometry (VLBI), where regular comparisons and combinations of space-geodetic products have tremendously increased the usefulness of the products in a wide range of disciplines and scientific applications. In the frame of the recently started Horizon 2020 project European Gravity Service for Improved Emergency Management (EGSIEM), a scientific combination service shall therefore be established to deliver the best gravity products for applications in Earth and environmental science research based on the unified knowledge of the European GRACE community. In a first step the large variety of available monthly GRACE gravity field solutions shall be mutually compared spatially and spectrally. We assess the noise of the raw as well as filtered solutions and compare the secular and seasonal periodic variations fitted to the monthly solutions. In a second step we will explore ways to generate combined solutions, e.g., based on a weighted average of the individual solutions using empirical weights derived from pair-wise comparisons. We will also assess the quality of such a combined solution and discuss the
Three-Dimensional Center of Gravity Detection for Trucks Hauling Marine Containers
Directory of Open Access Journals (Sweden)
Runan Dang
2016-01-01
Full Text Available Difficulty in preventing rollover accidents of marine containers derives from various load conditions of cargoes inside the containers. Heavier cargoes are widely regarded as presenting greater danger of rollover accidents. However, this presupposition is severely misleading because lighter cargoes having a higher center of gravity such as machinery with an upper mass can also cause rollover accidents. Rollover accidents are explainable fundamentally as follows. The center of gravity of a truck loading a marine container conflicts with the centrifugal force in cornering. A truck is unstable, causing a rollover accident when the moment originating from the centrifugal force exceeds that originating from the force of gravity. Such a truck might cause a rollover accident at a lower driving speed when the center of gravity is positioned higher. The question is therefore how to find the center of gravity of trucks with marine containers. Conditions of cargoes inside the containers differ greatly. Moreover, it is practically impossible to calculate those conditions by measuring all cargoes piece-by-piece in a container unless the time and cost to do so are unlimited. Without knowing what is inside a container, there is no way to detect the center of gravity after a truck starts moving. An important invention by the second author of this paper was produced to solve that difficulty. Detection of the Three Dimensional Center of Gravity (D3DCG can ascertain the position of the center of gravity while trucks are moving. Soon after starting to move, vertical and rolling motions are measured onboard the trucks in half a minute. Then D3DCG is activated, instantly assessing the position of the center of gravity. D3DCG assumes that the center of gravity causes unique motions depending on its position on the truck. Therefore there is no need to know what is inside the container. This paper first demonstrated the precision of D3DCG running an experiment by which
16 CFR Figure 10 to Part 1203 - Center of Gravity for Drop Assembly
2010-01-01
... 16 Commercial Practices 2 2010-01-01 2010-01-01 false Center of Gravity for Drop Assembly 10 Figure 10 to Part 1203 Commercial Practices CONSUMER PRODUCT SAFETY COMMISSION CONSUMER PRODUCT SAFETY... Gravity for Drop Assembly ER10MR98.010...
Japanese Oceanographic Data Center Japan Land Gravity
National Oceanic and Atmospheric Administration, Department of Commerce — The gravity station data (4,381 records) were compiled by the Japanese Oceanographic Data Center. This data base was received in July 1988. The data are in the...
Romero-Franco, Natalia; Martínez-López, Emilio; Lomas-Vega, Rafael; Hita-Contreras, Fidel; Martínez-Amat, Antonio
2012-08-01
The purpose of this study was to determinate the effect of a 6-week specific-sprinter proprioceptive training program on core stability and gravity center control in sprinters. Thirty-three athletes (age = 21.82 ± 4.84 years, height = 1.76 ± 0.07 m, weight = 67.82 ± 08.04 kg, body mass index = 21.89 ± 2.37 kg · m(-2)) from sprint disciplines were divided into a control (n = 17) and experimental (n = 16) groups. A 30-minute proprioceptive training program was included in the experimental group training sessions, and it was performed for 6 weeks, 3 times each week. This program included 5 exercises with the BOSU and Swiss ball as unstable training tools that were designed to reproduce different moments of the technique of a sprint race. Stability with eyes open (EO) and eyes closed, postural stability, and gravity center control were assessed before and after the training program. Analyses of covariance (α = 0.05) revealed significant differences in stability in the medial-lateral plane with EO, gravity center control in the right direction and gravity center control in the back direction after the exercise intervention in the experimental athletes. Nevertheless, no other significant differences were demonstrated. A sprinter-specific proprioceptive training program provided postural stability with EO and gravity center control measures improvements, although it is not clear if the effect of training would transfer to the general population. PMID:21997455
Romero-Franco, Natalia; Martínez-López, Emilio; Lomas-Vega, Rafael; Hita-Contreras, Fidel; Martínez-Amat, Antonio
2012-08-01
The purpose of this study was to determinate the effect of a 6-week specific-sprinter proprioceptive training program on core stability and gravity center control in sprinters. Thirty-three athletes (age = 21.82 ± 4.84 years, height = 1.76 ± 0.07 m, weight = 67.82 ± 08.04 kg, body mass index = 21.89 ± 2.37 kg · m(-2)) from sprint disciplines were divided into a control (n = 17) and experimental (n = 16) groups. A 30-minute proprioceptive training program was included in the experimental group training sessions, and it was performed for 6 weeks, 3 times each week. This program included 5 exercises with the BOSU and Swiss ball as unstable training tools that were designed to reproduce different moments of the technique of a sprint race. Stability with eyes open (EO) and eyes closed, postural stability, and gravity center control were assessed before and after the training program. Analyses of covariance (α = 0.05) revealed significant differences in stability in the medial-lateral plane with EO, gravity center control in the right direction and gravity center control in the back direction after the exercise intervention in the experimental athletes. Nevertheless, no other significant differences were demonstrated. A sprinter-specific proprioceptive training program provided postural stability with EO and gravity center control measures improvements, although it is not clear if the effect of training would transfer to the general population.
Mulugeta, Lealem; Chappell, Steven P.
2009-01-01
Drawing from the experiences of the Apollo missions, it is evident that the off nominal center of gravity (CG) induced by the portable life support system (PLSS) had significant impact on the locomotion stability of the crew. This in turn is believed to have been a major contributor to the high numbers of falls and high metabolic rates experienced by the crew, and thus significantly hampered the crew s performance. With this in mind, the EVA Physiology, Systems and Performance (EPSP) group at the NASA Johnson Space Center (JSC) has been conducting tests to assess how spacesuit CG location impacts human performance in simulated lunar and Mars gravity. The results acquired to date show correlations between CG location and performance. However, noticeable variations in the performance data have been observed across subjects for fixed CG configurations. Consequently, it was hypothesized that this variability may be attributed to the anthropometrics of the different test subjects. It was further hypothesized that trunk-to-height ratio (THR) may be directly correlated to performance in reduced gravity; i.e. subjects with increased THR may have increased performance. To test this hypothesis, lunar and Mars gravity test data acquired over three years during NASA Neural Buoyancy Lab (NBL) tests and NASA Extreme Environment Missions Operation (NEEMO) missions were analyzed against THR, height, trunk length, and subject body mass/weight. The results of the study supported the hypothesis relating THR and performance, while the other three anthropometric parameters did not provide consistent correlations with performance. This in turn suggests that human performance in reduced gravity may be more dependent on anthropometric proportions than on body segment lengths and mass/weight.
Landi, Gregorio
2003-01-01
The center of gravity as an algorithm for position measurements is analyzed for a two-dimensional geometry. Several mathematical consequences of discretization for various types of detector arrays are extracted. Arrays with rectangular, hexagonal, and triangular detectors are analytically studied, and tools are given to simulate their discretization properties. Special signal distributions free of discretized error are isolated. It is proved that some crosstalk spreads are able to eliminate the center of gravity discretization error for any signal distribution. Simulations, adapted to the CMS em-calorimeter and to a triangular detector array, are provided for energy and position reconstruction algorithms with a finite number of detectors.
Clustering-boundary-detection algorithm based on center-of-gravity of neighborhood
Directory of Open Access Journals (Sweden)
Wang Gui Zhi
2013-07-01
Full Text Available The cluster boundary is a useful model, in order to identify the boundary effectively, according to the uneven distribution of data points int the epsilon neighborhood of boundary objects, this paper proposes a boundary detection algorithm ---- S-BOUND. Firstly, all the points in the epsilon neighborhood of the data objects are projected onto the boundary of the convex hull of the neighborhood, and then calculate the center of gravity of the neighborhood. Finally, detect the boundary object according to the degree of deviation of the center of gravity of the neighborhood with the object. The experimental results show that the S-BOUND algorithm can accurately detect a variety of clustering boundary and remove the noises, the time of performance is also better.
The Self as a Center of Ethical Gravity
DEFF Research Database (Denmark)
Hjortkær, Christian; Willert, Søren
2013-01-01
This paper examines the striking similarity between Kierkegaard’s and Mead’s theories of the self as relation, reflection and process as well as the normativity behind these theories. It is claimed that the theologian and the social psychologist share the view that the human being is an ethical...... the Other. It is argued that differences in professions can be overcome: While reading Kierkegaard in the light of Mead helps to underline the relational character of Kierkegaard’s ethical notions, reading Mead in the light of Kierkegaard underlines the normative aspect of Mead’s social psychology....
A Difference Method of the Gravity Center with Double Pilots for the MC-CDMA System
Institute of Scientific and Technical Information of China (English)
无
2000-01-01
A carrier recovery method of the power spectrum center difference adapting to the mobile channel of the MC-CDMA system with serious Doppler shift using double pilots is presented. In the transmitter, two pilots of equal frequency distance to the carrier with one putting on the left position and the other on the right position of the carrier frequency are used. Even if a continuous sine wave is transmitted, the power spectrum is expanded to a Doppler band in the receiver owing to the multi-path transmission and the Doppler shift. The pilot spectrum is made to pass through two narrow band filters which are transformed to the base band with local carrier wave in the receiver. The frequency difference between the local carrier and the transmitter carrier is obtained when the difference of the gravity centers of the two pilot spectra is computed.
Pilot Study: Measuring the Effects of Center of Gravity Shift on Postural Stability
Times-Marshall, Chelsea; Reschke, Millard
2009-01-01
It has been shown that astronauts returning from space often experience postural instability due to the stimulus rearrangement of the visual, vestibular, and proprioceptive systems. However, postural control may also be influenced by the head-ward shift in their center of gravity (CG) that occurs as a result of the expansion of their spinal column by as much as two inches during long duration space flight, as well as the CG shift that occurs from the Life Support Pack on the extra-vehicular activity (EVA) suit. This study investigated the effect on postural stability after (1) an immediate shift in the CG towards the head, (2) a 30 minute adaptation to the shifted CG, and (3) immediate shift of the CG back to normal, accomplished by donning and removing a modified backpack. We hypothesized that at each immediate shift in CG, postural performance will be compromised.
Portfolio Evaluation Based on Efficient Frontier Superiority Using Center of Gravity
Directory of Open Access Journals (Sweden)
Omar Samat
2010-01-01
Full Text Available Investing in portfolio of assets is the best way to reduce the investment risk. The most desired portfolio can be obtained when investors chose to invest in the portfolios that lay on the portfolio’s efficient frontier. However, the superiorities of the portfolios are difficult to differentiate especially when the efficient frontier curves are overlapping. This paper proposed the portfolio’s efficient frontier center of gravity (CoG and Euclidean distance to identify its superiority. A sample of 49 stocks of large-cap and small-cap were used to construct two hypothetical portfolios and its efficient frontiers. The Euclidean distance showed that the large-cap portfolio is superior and having wider feasible solutions compared to the small-cap portfolio. The results of new tool introduced are consistent with the conventional methods. Here the theoretical and practical implications are provided in light of the findings.
Cloud's Center of Gravity – a compact approach to analyze convective cloud development
Directory of Open Access Journals (Sweden)
I. Koren
2009-01-01
Full Text Available As cloud resolving models become more detailed, with higher resolution outputs, it is often complicated to isolate the physical processes that control the cloud attributes. Moreover, due to the high dimensionality and complexity of the model output, the analysis and interpretation of the results can be very complicated. Here we suggest a novel approach to convective cloud analysis that yields more insight into the physical and temporal evolution of clouds, and is compact and efficient. The different (3-D cloud attributes are weighted and projected onto a single point in space and in time, that has properties of, or similar to, the Center Of Gravity (COG. The location, magnitude and spread of this variable are followed in time. The implications of the COG approach are demonstrated for a study of aerosol effects on a warm convective cloud. We show that in addition to reducing dramatically the dimensionality of the output, such an approach often enhances the signal, adds more information, and makes the physical description of cloud evolution clearer, allowing unambiguous comparison of clouds evolving in different environmental conditions. This approach may also be useful for analysis of cloud data retrieved from surface or space-based cloud radars.
Cloud's center of gravity – a compact approach to analyze convective cloud development
Directory of Open Access Journals (Sweden)
I. Koren
2008-07-01
Full Text Available As cloud resolving models become more detailed, with higher resolution outputs, it is often complicated to isolate the physical processes that control the cloud attributes. Moreover, due to the high dimensionality and complexity of the model output, the analysis and interpretation of the results can be very complicated. Here we suggest a novel approach to convective cloud analysis that yields more insight into the physical and temporal evolution of clouds, and is compact and efficient. The different (3-D cloud attributes are weighted and projected onto a single point in space and in time, that has properties of, or similar to, the Center Of Gravity (COG. The location, magnitude and spread of this variable are followed in time. The implications of the COG approach are demonstrated for a study of aerosol effects on a warm convective cloud. We show that in addition to reducing dramatically the dimensionality of the output, such an approach often enhances the signal, adds more information, and makes the physical description of cloud evolution clearer, allowing unambiguous comparison of clouds evolving in different environmental conditions. This approach may also be useful for analysis of cloud data retrieved from surface or space-based cloud radars.
Santoso, Agus; Sismanto, Setiawan, Ary; Pramumijoyo, Subagyo
2016-05-01
Ancient eruption centers can be determined by detecting the position of the ancient volcanic material, it is important to understand the elements of ancient volcanic material by studying the area geologically and prove the existence of an ancient volcanic eruption centers using geophysics gravity method. The measuring instrument is Lacoste & Romberg gravimeter type 1115, the number of data are 900 points. The area 60×40 kilometers, the modeling 3D software is reaching depth of 15 km at the south of the island of Java subduction zone. It is suported by geological data in the field that are found as the following: 1. Pyroclastic Fall which is a product of volcanic eruptions, and lapilli tuff with felsic mineral. 2. Pyroclastic flow with Breccia, tuffaceous sandstone and tuff breccia. 3. Hot springs near Parangwedang Parangtritis. 4. Igneous rock with scoria structure in Parang Kusumo, structured amigdaloida which is the result of the eruption of lava/volcanic eruptions, and Pillow lava in the shows the flowing lava into the sea. Base on gravity anomaly shows that there are strong correlationship between those geological data to the gravity anomaly. The gravblox modeling (3D) shows the position of ancient of volcanic eruption in this area clearly.
Yoo, Won-gyu
2015-01-01
[Purpose] This study developed a backpack with a low center of gravity (LCG) and investigated the effects of the LCG backpack on the trunk stability of mountaineers while ascending and descending. [Subjects and Methods] Ten males aged 20–32 years were recruited. The subjects ascended and descended a road with an inclination of 30 degrees wearing the standard or LCG backpack, and trunk acceleration was measured using a tri-axial accelerometer. [Results] The anterior-posterior (AP) and medial-l...
Yoo, Won-Gyu
2015-10-01
[Purpose] This study developed a backpack with a low center of gravity (LCG) and investigated the effects of the LCG backpack on the trunk stability of mountaineers while ascending and descending. [Subjects and Methods] Ten males aged 20-32 years were recruited. The subjects ascended and descended a road with an inclination of 30 degrees wearing the standard or LCG backpack, and trunk acceleration was measured using a tri-axial accelerometer. [Results] The anterior-posterior (AP) and medial-lateral (ML) trunk acceleration while ascending and descending with the LCG backpack were significantly lower than those with the standard backpack. [Conclusion] The results suggest that the LCG backpack could prevent falling injuries during mountaineering and mountain-related activities. PMID:26644687
Directory of Open Access Journals (Sweden)
Marinichev M. B.
2015-01-01
Full Text Available The subjects of the study are the foundations of buildings with a high center of gravity, in particular, the foundations of high-rise buildings with developed upper floors due to the large consoles. From a set of loads, transferred to the high-rise building with a high center of gravity, we can highlight the most significant impacts, affecting the distribution of forces in the elements of the foundation. We reveal the factors playing a special role in the choice of design solutions for the foundations. The practical significance of this research is due to the demand for ground areas in the cities which are being developed, although they were previously considered unsuitable for construction. Today, one of the primary tasks for engineers and architects is increasing technical and economic performance of construction projects and meeting customers' requirements in the individual architecture. As a variant of increasing technical and economic performance of buildings in dense city building conditions is to use the arm structures in their design solutions that both low-rise and high-rise building can achieve the architectural attractiveness of the building and significantly increase the usable floor area. In the research, two types of the foundations were projected for the object which is an eight-apartment building in the ground conditions of Sochi. The analysis was carried out with such software as PC ING +. After receiving the results of numerical analyses we performed a comparative analysis of pile-slab and slab foundation with the seismicity of the construction site. Therefore, we have identified the most rational of two types of foundations
Center of Gravity Compensation for Dynamically-Balanced Two-Wheeled Wheelchair System
Acar, Cihan; Murakami, Toshiyuki
Two-wheeled systems have many advantages compared to statically stable systems. This paper describes a control strategy of dynamically-balanced two-wheeled wheelchair system that does not have any front casters. In this system, rider can sit the seat and control the motion of the system by adjusting CoG of his/her body. Unlike other commercial two-wheeled systems, CoG position of the upper body is mainly determined by the position of the user. Thus, there is a possibility that CoG position may not overlap with the wheel axis. In that case, sensor information cannot be used to measure the exact position of the CoG. This paper shows an estimation of method of the unknown CoG position for Two-Wheeled Dynamically-Balanced Wheelchair (TWDBW) is considered. Gravity torque observer with a compliance control is utilized to realize stable compensation according to the variable CoG position. Backstepping based nonlinear control design is applied to regulate and track the CoG motion of the upper body in the TWDBW. The validity of proposed method is verified by simulation and experimental results.
Study of Migration of Population Gravity Center in North Xinjiang Region%北疆城镇区域人口重心迁移研究
Institute of Scientific and Technical Information of China (English)
张婷; 段汉明; 张芳
2013-01-01
This paper makes emphases on the study of the characteristics of the migration of population gravity center in the North Xinjiang Region. Using population gravity center model and GIS technology ,the study is finished on the based of the Xinjiang Statistical Yearbook 2003-2012. The results show that the migration trajectory of the population gravity center of North Xinjiang Region in the past 10 years gradually moved to Urumqi with a continuous single direction. The migration of population gravity center in North Xinjiang Region is mainly affected by many factors such as nature , sociol economic devel-opment fact and changes in infrastructure conditions ,etc.%采用人口重心模型结合GIS，以2003-2012年新疆统计年鉴为基础，对北疆城镇区域人口重心的迁移特征进行了探究。结果显示，近10年来北疆城镇区域人口重心的迁移轨迹呈连续单一方向逐步向乌鲁木齐市移动，人口重心的迁移受到自然环境条件、社会经济发展和基础设施条件等诸多因素的影响。
TR-GRAV: National Center for Turkish Gravity Field
Simav, Mehmet; Akpınar, İlyas; Sezen, Erdinc; Cingöz, Ayhan; Yıldız, Hasan
2016-04-01
TR-GRAV, the National Center for Turkish Gravity Field (TR-GRAV) that has recently become operational,is a national center that collects, processes and distributes Absolute Gravimetry,Relative Gravimetry, Airborne Gravimetry,Shipborne Gravimetry,Satellite Gravimetry, GNSS/Levelling, Astrogeodetic Vertical Deflection data to model and improve regional gravity field for the Turkish territory and its surrounding regions and to provide accurate, consistent and value-added data & products to the scientific and engineering communities. In this presentation, we will introduce the center web portal and give some details about the database.
Exponential Growth and the Shifting Global Center of Gravity of Science Production, 1900-2011
Zhang, Liang; Powell, Justin J. W.; Baker, David P.
2015-01-01
Long historical trends in scientific discovery led mid-20th century scientometricians to mark the advent of "big science"--extensive science production--and predicted that over the next few decades, the exponential growth would slow, resulting in lower rates of increase in production at the upper limit of a logistic curve. They were…
Study of the Migration Economy Gravity Center in Jinhua City Based on GIS%基于GIS的经济重心迁移研究——以金华市为例
Institute of Scientific and Technical Information of China (English)
张明霞; 陈雄
2012-01-01
The paper using GIS technology,based on the meaning of the concept of gravity and economy gravity center,analyzing the technical route of migration research of gravity center.Based on economy gravity center model,this paper makes emphases on the study of the characteristics of the migration of economy gravity center from 1999 to 2008 in Jinhua city.At last,based on view of the system of administrative division,analyzes why the economy gravity center migrated.The results show that the economy gravity center approaches the geometry center in Jinhua city,the trend that economy gravity center moves from west to east is obvious,and the migration orbit of economy gravity center demonstrates certain fluctuation.%在GIS技术支持下,对重心及经济重心概念的理解上,分析了经济重心的技术路线,并通过经济重心模型的应用,着重对1999～2008年金华市经济重心迁移特征进行研究,最后基于行政区划体制的视角分析了经济重心迁移的原因。结果显示,金华市的经济重心总体接近几何中心,经济重心自西向东方向迁移的趋势明显,经济重心移动轨迹呈现出一定的曲折和波动。
Z-2 Suit Support Stand and MKIII Suit Center of Gravity Test
Nguyen, Tuan Q.
2014-01-01
NASA's next generation spacesuits are the Z-Series suits, made for a range of possible exploration missions in the near future. The prototype Z-1 suit has been developed and assembled to incorporate new technologies that has never been utilized before in the Apollo suits and the Extravehicular Mobility Unit (EMU). NASA engineers tested the Z-1 suit extensively in order to developed design requirements for the new Z-2 suit. At the end of 2014, NASA will be receiving the new Z-2 suit to perform more testing and to further develop the new technologies of the suit. In order to do so, a suit support stand will be designed and fabricated to support the Z-2 suit during maintenance, sizing, and structural leakage testing. The Z-2 Suit Support Stand (Z2SSS) will be utilized for these purposes in the early testing stages of the Z-2 suit.
Barkin, Yury
2010-05-01
The summary. On the basis of geodynamic model of the forced relative displacement of the centers of mass of the core and the mantle of the Earth the secular variations of a gravity and heights of some gravimetry stations on a surface of the Earth have ben studied. At the account of secular drift of the center of mass of the Earth which on our geodynamic model is caused by the unidirectional drift of the core of the Earth relatively to the mantle, the full explanation is given to observable secular variations of a gravity at stations Ny-Alesund (Norway), Churchill (Canada), Medicine (Italy), Sayowa (Antarctica), Strastburg (France), Membach (Belgium), Wuhan (China) and Metsahovi (Finland). Two new methods of determination of secular drift of the center of mass of the Earth, alternative to classical method of a space geodesy are offered: 1) on the basis of gravimetry data about secular trends of a gravity at the stations located on all basic regions of the Earth; 2) on the basis of the comparative analysis of altimetry and coastal data about secular changes of sea level also in basic regions of ocean. 1. Secular drift of the center of mass of the core and the center of mass of the Earth. A secular drift of the center of mass of the Earth to the North relatively to special center O on an axis of rotation of the Earth for which the coefficient of third zonal harmonic J3' = 0, has been predicted in the author work [1]. A drift in a direction to a geographical point (pole P) 70°0 N and 104°3 E has been established for the first time theoretically - as a result of the analysis of the global directed redistribution of masses of the Earth, explaining the observed secular drift of the pole of an axis of rotation of the Earth and not tidal acceleration of its axial rotation [2]. In [1] velocity of drift it has been estimated in 1-2 cm/yr. For specified center O the figure of a planet is as though deprived of pure-shaped form (J3' = 0). And in this sense the point O can be
International Nuclear Information System (INIS)
The center of buoyancy of an arbitrary shaped body is defined in analogy to the center of gravity. The definitions of the buoyant force and center of buoyancy in terms of integrals over the area of the body are converted to volume integrals and shown to have simple intuitive interpretations
Heiblum, Reuven H.; Altaratz, Orit; Koren, Ilan; Feingold, Graham; Kostinski, Alexander B.; Khain, Alexander P.; Ovchinnikov, Mikhail; Fredj, Erick; Dagan, Guy; Pinto, Lital; Yaish, Ricki; Chen, Qian
2016-06-01
In Part I of this work a 3-D cloud tracking algorithm and phase space of center of gravity altitude versus cloud liquid water mass (CvM space) were introduced and described in detail. We showed how new physical insight can be gained by following cloud trajectories in the CvM space. Here this approach is used to investigate aerosol effects on cloud fields of warm cumuli. We show a clear effect of the aerosol loading on the shape and size of CvM clusters. We also find fundamental differences in the CvM space between simulations using bin versus bulk microphysical schemes, with the bin scheme precipitation expressing much higher sensitivity to changes in aerosol concentrations. Using the bin microphysical scheme, we find that the increase in cloud center of gravity altitude with increase in aerosol concentrations occurs for a wide range of cloud sizes. This is attributed to reduced sedimentation, increased buoyancy and vertical velocities, and increased environmental instability, all of which are tightly coupled to inhibition of precipitation processes and subsequent feedbacks of clouds on their environment. Many of the physical processes shown here are consistent with processes typically associated with cloud invigoration.
Directory of Open Access Journals (Sweden)
Animesh Mukherjee
1991-01-01
Full Text Available Based upon Biot's [1965] theory of initial stresses of hydrostatic nature produced by the effect of gravity, a study is made of surface waves in higher order visco-elastic media under the influence of gravity. The equation for the wave velocity of Stonely waves in the presence of viscous and gravitational effects is obtained. This is followed by particular cases of surface waves including Rayleigh waves and Love waves in the presence of viscous and gravity effects. In all cases the wave-velocity equations are found to be in perfect agreement with the corresponding classical results when the effects of gravity and viscosity are neglected.
Aspects of multimetric gravity
International Nuclear Information System (INIS)
We present a class of gravity theories containing N ≥ 2 metric tensors and a corresponding number of standard model copies. In the Newtonian limit gravity is attractive within each standard model copy, but different standard model copies mutually repel each other. We discuss several aspects of these multimetric gravity theories, including cosmology, structure formation, the post-Newtonian limit and gravitational waves. The most interesting feature we find is an accelerating expansion of the universe that naturally becomes small at late times.
美国战略重心东移的特点%The Characteristics of America Strategic Center of Gravity Eastward
Institute of Scientific and Technical Information of China (English)
徐明达
2015-01-01
Since the Obama administration took office, American began to implement the strategic center of gravity ,eastward policy. The strategic focus from Europe, the Middle East to the Asia Pacific Region. In a series of strategic initiatives, America gradually show characteristics of revealing its strategic focus eastward. This article from the strategic perspective, analyzes the characteristics of the strategic center of gravity eastward of USA.%自奥巴马政府上台以来，美国开始推行战略重心东移政策，将战略重点从欧洲、中东地区转向亚太。在一系列的战略举措中，美国渐渐展露出其战略重心东移的特点。本篇文章将从大战略的视角，对美国战略重心东移的特点进行剖析。
Consistency of orthodox gravity
Energy Technology Data Exchange (ETDEWEB)
Bellucci, S. [INFN, Frascati (Italy). Laboratori Nazionali di Frascati; Shiekh, A. [International Centre for Theoretical Physics, Trieste (Italy)
1997-01-01
A recent proposal for quantizing gravity is investigated for self consistency. The existence of a fixed-point all-order solution is found, corresponding to a consistent quantum gravity. A criterion to unify couplings is suggested, by invoking an application of their argument to more complex systems.
Kan, Nahomi; Maki, Takuya; Shiraishi, Kiyoshi
2016-10-01
We propose a model of gravity in which a General Relativity metric tensor and an effective metric generated from a single scalar formulated in geometric scalar gravity are mixed. We show that the model yields the exact Schwarzschild solution, along with accelerating behavior of scale factors in cosmological solutions.
Topological Aspects of Quantum Gravity
Weis, Morten
1998-01-01
This thesis discusses the topological aspects of quantum gravity, focusing on the connection between 2D quantum gravity and 2D topological gravity. The mathematical background for the discussion is presented in the first two chapters. The possible gauge formulations of 2D topological gravity as a BF or a Super BF theory are presented and compared against 2D quantum gravity in the dynamical triangulation scheme. A new identification between topological gravity in the Super BF formulation and t...
Heiblum, Reuven H.; Altaratz, Orit; Koren, Ilan; Feingold, Graham; Kostinski, Alexander B.; Khain, Alexander P.; Ovchinnikov, Mikhail; Fredj, Erick; Dagan, Guy; Pinto, Lital; Yaish, Ricki; Chen, Qian
2016-06-01
We study the evolution of warm convective cloud fields using large eddy simulations of continental and trade cumulus. Individual clouds are tracked a posteriori from formation to dissipation using a 3-D cloud-tracking algorithm, and results are presented in the phase space of center of gravity altitude versus cloud liquid water mass (CvM space). The CvM space is shown to contain rich information on cloud field characteristics, cloud morphology, and common cloud development pathways, together facilitating a comprehensive understanding of the cloud field. In this part we show how the meteorological (thermodynamic) conditions that determine the cloud properties are projected on the CvM phase space and how changes in the initial conditions affect the clouds' trajectories in this space. This part sets the stage for a detailed microphysical analysis that will be shown in part II.
Institute of Scientific and Technical Information of China (English)
李如友; 黄常州
2015-01-01
运用重心模型，定量分析了2001—2012年江苏省旅游经济时空格局的演进过程。江苏省旅游外汇收入重心持续北上，国内旅游收入重心则先南下、后北上，旅游总收入重心的演化路径与国内旅游收入较为相似；江苏省旅游外汇收入重心、国内旅游收入重心和旅游总收入重心都明显偏离几何中心，但呈缓慢趋同态势；旅游外汇收入重心与入境旅游客流重心、国内旅游收入重心与国内旅游客流重心、旅游总收入重心与旅游客流总量重心均呈现出显著的空间分离特征。从资源开发、政策支持、经济基础、对外开放和事件影响等方面深入剖析了江苏省旅游经济重心移动的驱动机制。旅游资源的开发利用是旅游经济重心移动的关键驱动因素，政府的区域发展政策是旅游经济重心移动的直接驱动因素，经济发展的区域格局及其变化促进旅游经济重心的移动，对外开放的全面推进成为旅游经济重心移动的助推剂，重大事件驱动旅游经济重心变化趋势发生短暂性偏离。%With the gravity center model, this paper analyzed the changes of the tourist economy pattern in Jiangsu Province from 2001 to 2012.The gravity centers of tourism foreign exchange earnings moved north, but the gravity center of domestic tourism revenue moved south before turned north, which was similar to the evolving pat-tern of the gravity center of total tourism revenue.The gravity centers of tourism foreign exchange earnings, domes-tic tourism revenue and the total tourism revenue all deviated from the geometric center obviously, and the moving tendencies of them trended to be close slowly.The spatial mismatch between the gravity center of tourism foreign exchange earnings and inbound tourist flow is found, just as the spatial mismatch between the gravity centers of do-mestic tourism revenue and domestic tourist flow.The driving forces of the
Institute of Scientific and Technical Information of China (English)
秦显平
2015-01-01
针对卫星质心测量误差影响编队卫星基线的问题，首先从编队卫星相对定轨的原理出发，分析了卫星质心误差的影响，然后考虑到编队卫星有效基线通常为载荷天线之间的基线，提出了天线基线与质心基线的定义。采用2015-12-08两颗编队卫星的实测数据，计算分析了卫星质心测量误差对质心基线和天线基线的影响，结果表明：卫星质心测量误差对质心基线的影响明显大于对天线基线的影响；卫星质心测量误差对天线基线的影响约为质心测量误差的10％。%To the question of the influence of satellite center-of-gravity measurement error on the baseline of formation fly-ing satellites,the influence of satellite center-of-gravity measurement error was analyzed from the principle of formation flying satellites relative orbit determination firstly.Then,in view of the useful baseline is usually the distance between the payload in-struments of two satellites,the definition of the baseline of two payload instruments antennas and the baseline of two satellites center-of-gravity were established.The baseline of two formation flying satellites center-of-gravity and the baseline of two an-tennas were computed by using the global positioning system data observed December 8,2005.The results of computation show that the measurement error of the satellite center-of-gravity makes the baseline error of two satellites center-of-gravity greatly than that of two antennas.The two antennas baseline error is about 10 percent of the two satellites center-of-gravity baseline error.
BRST symmetry of Unimodular Gravity
Upadhyay, S.; Oksanen, M.; Bufalo, R.
2015-01-01
We derive the BRST symmetry for two versions of unimodular gravity, namely, fully diffeomorphism-invariant unimodular gravity and unimodular gravity with fixed metric determinant. The BRST symmetry is generalized further to the finite field-dependent BRST, in order to establish the connection between different gauges in each of the two versions of unimodular gravity.
Gravity Plant Physiology Facility (GPPF) Team in the Spacelab Payload Operations Control Center (SL
1992-01-01
The primary payload for Space Shuttle Mission STS-42, launched January 22, 1992, was the International Microgravity Laboratory-1 (IML-1), a pressurized manned Spacelab module. The goal of IML-1 was to explore in depth the complex effects of weightlessness of living organisms and materials processing. Around-the-clock research was performed on the human nervous system's adaptation to low gravity and effects of microgravity on other life forms such as shrimp eggs, lentil seedlings, fruit fly eggs, and bacteria. Materials processing experiments were also conducted, including crystal growth from a variety of substances such as enzymes, mercury iodide, and a virus. The Huntsville Operations Support Center (HOSC) Spacelab Payload Operations Control Center (SL POCC) at the Marshall Space Flight Center (MSFC) was the air/ground communication channel used between the astronauts and ground control teams during the Spacelab missions. Featured is the Gravity Plant Physiology Facility (GPPF) team in the SL POCC during the IML-1 mission.
Massive gravity as a limit of bimetric gravity
Martin-Moruno, Prado; Baccetti, Valentina; Visser, Matt
2013-01-01
Massive gravity may be viewed as a suitable limit of bimetric gravity. The limiting procedure can lead to an interesting interplay between the "background" and "foreground" metrics in a cosmological context. The fact that in bimetric theories one always has two sets of metric equations of motion continues to have an effect even in the massive gravity limit. Thus, solutions of bimetric gravity in the limit of vanishing kinetic term are also solutions of massive gravity, but the contrary statem...
Jain, Bhuvnesh
2010-01-01
Modifications of general relativity provide an alternative explanation to dark energy for the observed acceleration of the universe. We review recent developments in modified gravity theories, focusing on higher dimensional approaches and chameleon/f(R) theories. We classify these models in terms of the screening mechanisms that enable such theories to approach general relativity on small scales (and thus satisfy solar system constraints). We describe general features of the modified Friedman equation in such theories. The second half of this review describes experimental tests of gravity in light of the new theoretical approaches. We summarize the high precision tests of gravity on laboratory and solar system scales. We describe in some detail tests on astrophysical scales ranging from ~kpc (galaxy scales) to ~Gpc (large-scale structure). These tests rely on the growth and inter-relationship of perturbations in the metric potentials, density and velocity fields which can be measured using gravitational lensi...
Energy Technology Data Exchange (ETDEWEB)
Abele, Hartmut; Bittner, Thomas; Cronenberg, Gunther; Filter, Hanno; Jenke, Tobias; Lemmel, Hartmut; Thalhammer, Martin [Atominstitut TU Wien, Wien (Austria); Geltenbort, Peter [Institut Laue-Langevin, Grenoble (France)
2012-07-01
This talk is about a test of the Newtons Inverse Square Law of Gravity at micron distances by quantum interference with ultra-cold neutrons deep into the theoretically interesting regime. The method is based on a new resonance spectroscopy technique related to Rabi spectroscopy, but it has been adapted to gravitationally bound quantum systems. By coupling such a quantum system to mechanical vibrations, we observe resonant transitions, devoid of electromagnetic interaction. As Newtonian gravity and hypothetical Fifth Forces evolve with different phase information, the experiment has the potential to test the equivalence principle and Newtons gravity law at the micron scale. This experiment can therefore test speculations on large extra dimensions of sub-millimetre size of space-time or the origin of the cosmological constant in the universe, where effects are predicted in the interesting range of this experiment and might give a signal in an improved setup.
Deser, S; Ong, Y C; Waldron, A
2014-01-01
The method of characteristics is a key tool for studying consistency of equations of motion; it allows issues such as predictability, maximal propagation speed, superluminality, unitarity and acausality to be addressed without requiring explicit solutions. We review this method and its application to massive gravity theories to show the limitations of these models' physical viability: Among their problems are loss of unique evolution, superluminal signals, matter coupling inconsistencies and micro-acausality (propagation of signals around local closed timelike/causal curves). We extend previous no-go results to the entire three-parameter range of massive gravity theories. It is also argued that bimetric models suffer a similar fate.
National Oceanic and Atmospheric Administration, Department of Commerce — The National Geophysical Data Center (NGDC) of NOAA, in cooperation with the National Geodetic Survey of NOAA, have published a Gravity CD-ROM containing observed...
De Aquino, Fran
2016-01-01
A new type of device for controlling gravity is here proposed. This is a quantum device because results from the behaviour of the matter and energy at subatomic length scale (10 m).-20 From the technical point of view this device is easy to build, and can be used to develop several devices for controlling gravity. Introduction Some years ago I wrote a paper [1] where a correlation between gravitational mass and inertial mass was obtained. In the paper I pointed out that the relationship betwe...
Gamow, George
2003-01-01
A distinguished physicist and teacher, George Gamow also possessed a special gift for making the intricacies of science accessible to a wide audience. In Gravity, he takes an enlightening look at three of the towering figures of science who unlocked many of the mysteries behind the laws of physics: Galileo, the first to take a close look at the process of free and restricted fall; Newton, originator of the concept of gravity as a universal force; and Einstein, who proposed that gravity is no more than the curvature of the four-dimensional space-time continuum.Graced with the author's own draw
Zero-gravity venting of three refrigerants
Labus, T. L.; Aydelott, J. C.; Amling, G. E.
1974-01-01
An experimental investigation of venting cylindrical containers partially filled with initially saturated liquids under zero-gravity conditions was conducted in the NASA Lewis Research Center 5-second zero-gravity facility. The effect of interfacial mass transfer on the ullage pressure response during venting was analytically determined, based on a conduction analysis applied to an infinitely planer (flat) liquid-vapor interface. This pressure response was compared with both the experimental results and an adiabatic decompression computation.
Bergshoeff, Eric A.; Hohm, Olaf; Rosseel, Jan; Townsend, Paul K.
2011-01-01
The physical modes of a recently proposed D-dimensional "critical gravity'', linearized about its anti-de Sitter vacuum, are investigated. All "log mode'' solutions, which we categorize as "spin-2'' or "Proca'', arise as limits of the massive spin-2 modes of the noncritical theory. The linearized Ei
Banerjee, Rabin; Majhi, Bibhas Ranjan
2010-01-01
Starting from the definition of entropy used in statistical mechanics we show that it is proportional to the gravity action. For a stationary black hole this entropy is expressed as $S = E/ 2T$, where $T$ is the Hawking temperature and $E$ is shown to be the Komar energy. This relation is also compatible with the generalised Smarr formula for mass.
Newburgh, Ronald
2010-01-01
It's both surprising and rewarding when an old, standard problem reveals a subtlety that expands its pedagogic value. I realized recently that the role of gravity in the range equation for a projectile is not so simple as first appears. This realization may be completely obvious to others but was quite new to me.
SATELLITE GRAVITY SURVEYING TECHNOLOGY AND RESEARCH OF EARTH'S GRAVITY FIELD
Institute of Scientific and Technical Information of China (English)
Ning Jinsheng
2003-01-01
This is a summarized paper. Two topics are discussed: Firstly, the concept, development and application of four kinds of satellite gravity surveying technology are introduced; Secondly, some problems of theory and method, which must be considered in the study of the Earth's gravity field based on satellite gravity data, are expounded.
On the no-gravity limit of gravity
Kowalski-Glikman, J.; Szczachor, M.
2012-01-01
We argue that Relative Locality may arise in the no gravity $G\\rightarrow0$ limit of gravity. In this limit gravity becomes a topological field theory of the BF type that, after coupling to particles, may effectively deform its dynamics. We briefly discuss another no gravity limit with a self dual ground state as well as the topological ultra strong $G\\rightarrow\\infty$ one.
Graviresponses of osteocytes under altered gravity
Di, S. M.; Qian, A. R.; Qu, L. N.; Zhang, W.; Wang, Z.; Ding, C.; Li, Y. H.; Ren, H. G.; Shang, P.
2011-09-01
Single cell was capable of sensing and responding to alterations of gravity. Osteocytes, as the most abundant cells of the bone tissue playing an important role in the bone mechanotransduction, are very sensitive to mechanical stimuli. However, the effect of altered gravity on osteocytes so far is less known according to the public papers. Further study on this issue will help to verify and develop the theory of how cells perceive and respond to gravity. It also brings new ideas to the study of space bone loss. In our study, Osteocyte-like MLO-Y4 cells were exposed to 30 parabolic flights three times on ZERO-G airbus A300 to investigate the comprehensive effect on osteocytes stimulated by hyper- and hypo-gravity forces. It showed that the cell morphology, as well as cell area and height, was not changed significantly by hyper-gravity and hypo-gravity. However, the cytoskeleton was reorganized. In flight cells, F-actin polymerization was enhanced at the cell periphery and microtubule organizing center disappeared, but no apoptotic feathers were detected. The results of western blot showed that connexin 43 (Cx43) expression was down-regulated, indicating an decrease of gap-junction. In conclusion, hyper- and hypo-gravity stimulation altered the cytoskeleton architecture and suppressed gap-junction of osteocyte-like MLO-Y4 cells.
Institute of Scientific and Technical Information of China (English)
金娇辉; 梁建生
2012-01-01
The sea-going steel fishery administration ship is to be standardization and humanization.The estimation of lightweight and center of gravity is essential for the preliminary design.This paper collected most of data of existing fishery administration ships,and analyzed lightweight and center of gravity of fishery administration ships,then put forward formulas for calculating lightweight and center of gravity.The empirical equations was based on the ship design theory and regression analysis of fishery administration ship data.Compared the calculated result with the real test one,the relative error is adequate for preliminary design.%在实船资料统计分析和基于船舶基本原理基础上,提出了适合渔政船设计初期空船重量及重心的估算公式,以此分析、整理出的回归方程更具有针对性.将空船重量、重心高度、重心纵向位置的公式计算结果与实船倾斜试验所得值相比较后发现,相对误差符合工程要求,重心纵向位置值亦在允许范围内.本估算方法可以给设计者以前期估算参考.
Quantum theory of two-dimensional gravity
International Nuclear Information System (INIS)
We discuss local O(2,1)-invariant two-dimensional gravity interacting with scalar matter fields. Quantum constraints of lapse and shift functions are obtained by demanding the conformal algebra without a center. From the constraints and the covariant conservation law, we derive the semiclassical expectation value of the energy-momentum tensor of matter
Geometric scalar theory of gravity
Energy Technology Data Exchange (ETDEWEB)
Novello, M.; Bittencourt, E.; Goulart, E.; Salim, J.M.; Toniato, J.D. [Instituto de Cosmologia Relatividade Astrofisica ICRA - CBPF Rua Dr. Xavier Sigaud 150 - 22290-180 Rio de Janeiro - Brazil (Brazil); Moschella, U., E-mail: novello@cbpf.br, E-mail: eduhsb@cbpf.br, E-mail: Ugo.Moschella@uninsubria.it, E-mail: egoulart@cbpf.br, E-mail: jsalim@cbpf.br, E-mail: toniato@cbpf.br [Università degli Studi dell' Insubria - Dipartamento di Fisica e Matematica Via Valleggio 11 - 22100 Como - Italy (Italy)
2013-06-01
We present a geometric scalar theory of gravity. Our proposal will be described using the ''background field method'' introduced by Gupta, Feynman, Deser and others as a field theory formulation of general relativity. We analyze previous criticisms against scalar gravity and show how the present proposal avoids these difficulties. This concerns not only the theoretical complaints but also those related to observations. In particular, we show that the widespread belief of the conjecture that the source of scalar gravity must be the trace of the energy-momentum tensor — which is one of the main difficulties to couple gravity with electromagnetic phenomenon in previous models — does not apply to our geometric scalar theory. From the very beginning this is not a special relativistic scalar gravity. The adjective ''geometric'' pinpoints its similarity with general relativity: this is a metric theory of gravity. Some consequences of this new scalar theory are explored.
Bergshoeff, Eric A; Rosseel, Jan; Townsend, Paul K
2011-01-01
The physical modes of a recently proposed D-dimensional "critical gravity", linearized about its anti-de Sitter vacuum, are investigated. All "log mode" solutions, which we categorize as `spin 2' or `Proca', arise as limits of the massive spin 2 modes of the non-critical theory. The linearized Einstein tensor of a spin 2 log mode is itself a 'non-gauge' solution of the linearized Einstein equations whereas the linearized Einstein tensor of a Proca mode takes the form of a linearized general coordinate transformation. Our results suggest the existence of a holographically dual logarithmic conformal field theory.
Renormalization of Horava Gravity
Barvinsky, Andrei O; Herrero-Valea, Mario; Sibiryakov, Sergey M; Steinwachs, Christian F
2016-01-01
We prove perturbative renormalizability of projectable Horava gravity. The key element of the argument is the choice of a gauge which ensures the correct anisotropic scaling of the propagators and their uniform falloff at large frequencies and momenta. This guarantees that the counterterms required to absorb the loop divergences are local and marginal or relevant with respect to the anisotropic scaling. Gauge invariance of the counterterms is achieved by making use of the background-covariant formalism. We also comment on the difficulties of this approach when addressing the renormalizability of the non-projectable model.
Cosmological tests of modified gravity.
Koyama, Kazuya
2016-04-01
We review recent progress in the construction of modified gravity models as alternatives to dark energy as well as the development of cosmological tests of gravity. Einstein's theory of general relativity (GR) has been tested accurately within the local universe i.e. the Solar System, but this leaves the possibility open that it is not a good description of gravity at the largest scales in the Universe. This being said, the standard model of cosmology assumes GR on all scales. In 1998, astronomers made the surprising discovery that the expansion of the Universe is accelerating, not slowing down. This late-time acceleration of the Universe has become the most challenging problem in theoretical physics. Within the framework of GR, the acceleration would originate from an unknown dark energy. Alternatively, it could be that there is no dark energy and GR itself is in error on cosmological scales. In this review, we first give an overview of recent developments in modified gravity theories including f(R) gravity, braneworld gravity, Horndeski theory and massive/bigravity theory. We then focus on common properties these models share, such as screening mechanisms they use to evade the stringent Solar System tests. Once armed with a theoretical knowledge of modified gravity models, we move on to discuss how we can test modifications of gravity on cosmological scales. We present tests of gravity using linear cosmological perturbations and review the latest constraints on deviations from the standard [Formula: see text]CDM model. Since screening mechanisms leave distinct signatures in the non-linear structure formation, we also review novel astrophysical tests of gravity using clusters, dwarf galaxies and stars. The last decade has seen a number of new constraints placed on gravity from astrophysical to cosmological scales. Thanks to on-going and future surveys, cosmological tests of gravity will enjoy another, possibly even more, exciting ten years. PMID:27007681
Institute of Scientific and Technical Information of China (English)
WU Ning
2006-01-01
It is well known that energy-momentum is the source of gravitational field. For a long time, it is generally believed that only stars with huge masses can generate strong gravitational field. Based on the unified theory of gravitational interactions and electromagnetic interactions, a new mechanism of the generation of gravitational field is studied. According to this mechanism, in some special conditions, electromagnetic energy can be directly converted into gravitational energy, and strong gravitational field can be generated without massive stars. Gravity impulse found in experiments is generated by this mechanism.
Astrophysical aspects of Weyl gravity
Kazanas, Demosthenes
1991-01-01
This paper discusses the astrophysical implications and applications of Weyl gravity, which is the theory resulting from the unique action allowed under the principle of local scale invariance in Einstein gravity. These applications include galactic dynamics, the mass-radius relation, the cosmological constant, and the 'Modified Newtonian Dynamics' proposed by Milgrom (1983). The relation of Weyl gravity to other scale-invariant theories is addressed.
Teleparallel equivalent of Lovelock gravity
González, P. A.; Vásquez, Yerko
2015-12-01
There is a growing interest in modified gravity theories based on torsion, as these theories exhibit interesting cosmological implications. In this work inspired by the teleparallel formulation of general relativity, we present its extension to Lovelock gravity known as the most natural extension of general relativity in higher-dimensional space-times. First, we review the teleparallel equivalent of general relativity and Gauss-Bonnet gravity, and then we construct the teleparallel equivalent of Lovelock gravity. In order to achieve this goal, we use the vielbein and the connection without imposing the Weitzenböck connection. Then, we extract the teleparallel formulation of the theory by setting the curvature to null.
Symmetries of Quantum Nonsymmetric Gravity
Mebarki, N; Boudine, A; Benslama, A
1999-01-01
Symmetries of Quantum Nonsymmetric gravity are studied and the corresponding generators are constructed . The related equal time canonical (and non canonical) (anti) commutation relations are established.
Observable Effects of Quantum Gravity
Chang, Lay Nam; Sun, Chen; Takeuchi, Tatsu
2016-01-01
We discuss the generic phenomenology of quantum gravity and, in particular, argue that the observable effects of quantum gravity, associated with new, extended, non-local, non-particle-like quanta, and accompanied by a dynamical energy-momentum space, are not necessarily Planckian and that they could be observed at much lower and experimentally accessible energy scales.
Bailey, Quentin G
2016-01-01
In this talk, the gravity sector of the effective field theory description of local Lorentz violation is discussed, including minimal and nonminimal curvature couplings. Also, recent experimental and observational analyses including solar-system ephemeris and short-range gravity tests are reviewed.
The role of information in gravity
Spaans, M.
2009-01-01
It is argued that particle-specific information on energy-momentum adjusts the strength of gravity. This form of gravity has no free parameters, preserves Einstein gravity locally and predicts 6 times stronger accelerations on galaxy scales.
Jankiewicz, Marcin
2007-12-01
This thesis summarizes research projects that I have been involved in during my graduate studies at Vanderbilt University. My research spanned different areas of theoretical high energy physics with gravity as a common denominator. I explore both fundamental and phenomenological aspects of: (i) mathematical physics where I have studied relations between partition functions of certain class of conformal field theories and Fischer-Griess Monster group; (ii) cosmology, where I performed a numerical study of a horizon size modes of scalar field; (iii) a black hole physics project involving possible extensions of the non-hair theorem in a presence of exotic types of scalar field; and (iv) a study of phenomenological space-time foam models and their relation to Planck scale physics.
基于重力模型的中国金融中心体系识别%Discernment of Chinese Financial Center System: Gravity Model Approach
Institute of Scientific and Technical Information of China (English)
程婧瑶; 樊杰; 陈东
2013-01-01
The Financial Center (FC) is one of the most important topics in New Economic Geography, in which the discernment of FC is the primary task and basic work. This paper is focus on the formation and discernment of FC based on the Financial Geography Theory. Firstly, it's discussed that the relationship between FC and its information hinterland to find different effects of technical progress and deregulation on two types of financial center on the basis of information category. Then, geographic element is added to traditional methodology used to only containing scale elements by means of "gravity model approach". Finally, take mainland China as a case to explore the discernment method of FC system, and the results showed as followed: (l)Concerning Chinese FC system, two major regional FC system have formed, the southern system centralized with Shanghai and northern one with Beijing, containing 4 regional FCs and 27 local FCs.(2) Almost every province has 1 or 2 FCs, except Hebei and Inner Mongolia in the northern system, geographical proximity to Beijing.(3)Comparing to Northern system, Southern one have absolute advantage in financial scale, hinterland size, structure complexity and evolution trend, and have formed muti-layer structure inside.%金融中心是新经济地理学研究的重要领域,金融中心识别是金融中心研究的基础性工作.沿袭金融地理学的分析脉络,从“信息”的角度解释金融中心的形成与演化机制,探究金融中心与信息腹地的关系,以及技术进步和放松管制对不同类型金融中心的影响.引入“重力模型”,将空间要素纳入到金融中心体系识别框架中,对我国金融中心体系进行识别.通过模拟全国、省域两大尺度城市空间金融联系,确定金融中心及其腹地范围,识别并划分我国南、北两大区域金融中心体系,最终得到区域金融中心4个,省域金融中心27个.通过对两大区域体系的对比分析,结果显示
International Nuclear Information System (INIS)
It has been shown by Atkinson (1965) that there is a rigorously exact euclidean interpretation of the general relativity field equations if certain arbitrary definitions of mass (m) and the velocity of light (c) are invoked. With a preferred (euclidean) frame postulated ab initio, a particularly simple explanation in terms of classical physics may be found for very similar definitions of m and c. It is not unexpected that with this scheme, all the usual tests of general relativity (light deflexion, perihelion motion, gravitational redshift, and radar delay time) are immediately satisfied. The preferred frame is however identified with a real aether and this requires a return to the Lorentzian interpretation of the special relativistic transformations of space and time variables. It is shown that gravity may be attributed to the action of a temperature gradient in the aether and an explanation of its origin in terms of an ideal relativistic gas is proposed. The temperature gradients are thermodynamically stable and do not diffuse if the relativistic aether (γsub(A)) is effectively adiabatic and matter is fundamentally a species of aether with instantaneous motion at high γ (>γsub(A)) relative to the aethereal rest frame. To be consistent with such a picture, it is necessary to assume aether particles are capable of forming temporary associations (not recognized as matter) which take on some of the properties of crystalline solids and thereby become the means of transmitting electromagnetic radiation through space. A number of specific predictions arising from this theory of gravity are indicated and these may serve to discriminate it from general relativity. (Auth.)
The structure of local gravity theories
Dupre, Maurice J.
2014-01-01
We discuss the structure of local gravity theories as resulting from the idea that locally gravity must be physically characterized by tidal acceleration, and show how this relates to both Newtonian gravity and Einstein's general relativity.
Geometric Formulation of Gauge Theory of Gravity
Institute of Scientific and Technical Information of China (English)
WUNing; ZHANGDa-Hua; RUANTu-Nan
2003-01-01
DitTerential geometric formulation of quantum gauge theory of gravity is studied in this paper. The quantum gauge theory of gravity is formulated completely in the framework of traditional quantum field theory. In order to study the relationship between quantum gauge theory of gravity and traditional quantum gravity which is formulated in curved space, it is important to set up the geometry picture of quantum gauge theory of gravity. The correspondence between quantum gauge theory of gravity and differential geometry is discussed and the geometry picture of quantum gauge theory of gravity is studied.
Geometric Formulation of Gauge Theory of Gravity
Institute of Scientific and Technical Information of China (English)
WU Ning; ZHANG Da-Hua; RUAN Tu-Nan
2003-01-01
Differential geometric formulation of quantum gauge theory of gravity is studied in this paper. The quantumgauge theory of gravity is formulated completely in the framework of traditional quantum field theory. In order to studythe relationship between quantum gauge theory of gravity and traditional quantum gravity which is formulated in curvedspace, it is important to set up the geometry picture of quantum gauge theory of gravity. The correspondence betweenquantum gauge theory of gravity and differential geometry is discussed and the geometry picture of quantum gaugetheory of gravity is studied.
Teleparallel Equivalent of Lovelock Gravity
Gonzalez, P A
2015-01-01
There is a growing interest in modified gravity theories based on torsion due to these theories prove to exhibit interesting cosmological implications. In this work, inspired by the teleparallel formulation of General Relativity we present its extension to Lovelock Gravity known as the most natural extension of general relativity in higher-dimensional spacetimes. First, we review Teleparallel Equivalent of General Relativity and Teleparallel Equivalent of Gauss-Bonnet Gravity, and then we construct Teleparallel Equivalent of Lovelock Gravity. In order to achieve this goal we use the vielbein and the connection, without imposing the Weitzenb\\"ock connection. Then, we extract the teleparallel formulation of the theory by setting the curvature to be null.
Giannakis, Ioannis
1996-01-01
Two-dimensional gravity in the light-cone gauge was shown to exhibit an underlying sl(2,R) current algebra. It is the purpose of this note to offer a possible explanation about the origin of this important algebra. The essential point is that two-dimensional gravity is governed by a topological field theory. The gauge group is sl(2,R) and it is this enhanced gauge group that yields Polyakov's current algebra.
Institute of Scientific and Technical Information of China (English)
刘怀金; 邓晓东
2012-01-01
The key in modern dance technique is constant shifting gravity center in body, by which the whole body may move in inertia to form a moving inertial flow. And the key to forming mobile body inertia flow is that body weight transfer can be achieved by feet movement which droved by skeleton movement resulting from muscle tissue contraction under the control of the central nervous system in body trunk. In these processes, weight trans- fer can be conducted by body trunk, with mobile pivot formed by firming waist and hip, as well as balanced shift of gravity center by foot corresponding motion.%摩登舞技巧中最重要的环节是控制身体重心的不断转换，整个形体在惯性中移动，形成移动惯性流量。形体移动惯性流量的形成，关键在于身体躯干在中枢神经系统的控制下，由肌肉收缩牵引骨骼来带动腿脚移动实现重心移动到位。在此过程中，身体躯干主导着重心转移，腰胯稳固形成移动的枢纽，脚底联动实现重心的平衡转移。
Users Guide for NASA Lewis Research Center DC-9 Reduced-Gravity Aircraft Program
Neumann, Eric S.; Withrow, James P.; Yaniec, John S.
1996-01-01
The document provides guidelines and information for users of the DC-9 Reduced-Gravity Aircraft Program. It describes the facilities, requirements for test personnel, equipment design and installation, mission preparation, and in-flight procedures. Those who have used the KC-135 reduced-gravity aircraft will recognize that many of the procedures and guidelines are the same.
Cutoff for extensions of massive gravity and bi-gravity
Matas, Andrew
2016-04-01
Recently there has been interest in extending ghost-free massive gravity, bi-gravity, and multi-gravity by including non-standard kinetic terms and matter couplings. We first review recent proposals for this class of extensions, emphasizing how modifications of the kinetic and potential structure of the graviton and modifications of the coupling to matter are related. We then generalize existing no-go arguments in the metric language to the vielbein language in second-order form. We give an ADM argument to show that the most promising extensions to the kinetic term and matter coupling contain a Boulware-Deser ghost. However, as recently emphasized, we may still be able to view these extensions as effective field theories below some cutoff scale. To address this possibility, we show that there is a decoupling limit where a ghost appears for a wide class of matter couplings and kinetic terms. In particular, we show that there is a decoupling limit where the linear effective vielbein matter coupling contains a ghost. Using the insight we gain from this decoupling limit analysis, we place an upper bound on the cutoff for the linear effective vielbein coupling. This result can be generalized to new kinetic interactions in the vielbein language in second-order form. Combined with recent results, this provides a strong uniqueness argument on the form of ghost-free massive gravity, bi-gravity, and multi-gravity.
Phillips, W. P.
1984-01-01
Aerodynamic characteristics at M=5.97 for the 140 A/B Space Shuttle Orbiter configuration and for the configuration modified by geometric changes in the wing planform fillet region and the fuselage forebody are presented. The modifications, designed to extend the orbiter's longitudinal trim capability to more forward center of gravity locations, include reshaping the baseline wing fillet, changing the fuselage forebody camber, and adding canards. The Langley 20 inch Mach 6 Tunnel at a Reynolds number of approximately 6 million based on fuselage reference length was used. The angle of attack range of the investigation varied from about 15 deg to 35 deg at 0 deg and -5 deg sideslip angles. Data are obtained with the elevators and body flap deflected at appropriate negative and positive conditions to assess the trim limits.
PPN-limit of Fourth Order Gravity inspired by Scalar-Tensor Gravity
Capozziello, S.; Troisi, A.
2005-01-01
Based on the {\\it dynamical} equivalence between higher order gravity and scalar-tensor gravity the PPN-limit of fourth order gravity is discussed. We exploit this analogy developing a fourth order gravity version of the Eddington PPN-parameters. As a result, Solar System experiments can be reconciled with higher order gravity, if physical constraints descending from experiments are fulfilled.
Empirical Foundations of Relativistic Gravity
Ni, W T
2005-01-01
In 1859, Le Verrier discovered the mercury perihelion advance anomaly. This anomaly turned out to be the first relativistic-gravity effect observed. During the 141 years to 2000, the precisions of laboratory and space experiments, and astrophysical and cosmological observations on relativistic gravity have been improved by 3 orders of magnitude. In 1999, we envisaged a 3-6 order improvement in the next 30 years in all directions of tests of relativistic gravity. In 2000, the interferometric gravitational wave detectors began their runs to accumulate data. In 2003, the measurement of relativistic Shapiro time-delay of the Cassini spacecraft determined the relativistic-gravity parameter gammaγ with a 1.5-order improvement. In October 2004, Ciufolini and Pavlis reported a measurement of the Lense-Thirring effect on the LAGEOS and LAGEOS2 satellites to 10 percent of the value predicted by general relativity. In April 2004, Gravity Probe B was launched and has been accumulating science data for more than ...
Lorentz violation of quantum gravity
Energy Technology Data Exchange (ETDEWEB)
Moffat, J W, E-mail: john.moffat@utoronto.c [Perimeter Institute for Theoretical Physics, Waterloo, Ontario, N2J 2W9 (Canada); Department of Physics, University of Waterloo, Waterloo, Ontario N2Y 2L5 (Canada)
2010-07-07
A quantum gravity theory which becomes renormalizable at short distances due to a spontaneous symmetry breaking of Lorentz invariance and diffeomorphism invariance is studied. A breaking of Lorentz invariance with the breaking patterns SO(3, 1) {yields} O(3) and SO(3, 1) {yields} O(2), describing 3 + 1 and 2 + 1 quantum gravity, respectively, is proposed. A complex time-dependent Schroedinger equation (generalized Wheeler-DeWitt equation) for the wavefunction of the universe exists in the spontaneously broken symmetry phase at Planck energy and in the early universe, uniting quantum mechanics and general relativity. An explanation of the second law of thermodynamics and the spontaneous creation of matter in the early universe can be obtained in the symmetry broken phase of gravity.
A Possible Mechanism of Gravity
Lev, F M
2003-01-01
We consider systems of two free particles in de Sitter invariant quantum theory and calculate the mean value of the mass operator for such systems. It is shown that, in addition to the well known relativistic contribution (and de Sitter antigravity which is small when the de Sitter radius is large), there also exists a contribution caused by the fact that certain decomposition coefficients have different phases. Such a contribution is negative and proportional to the particle masses in the nonrelativistic approximation. In particular, for a class of two-body wave functions the mean value is described by standard Newtonian gravity and post Newtonian corrections in General Relativity. This poses the problem whether gravity can be explained without using the notion of interaction at all. We discuss a hypothesis that gravity is a manifestation of Galois fields in quantum physics.
Probing Quantum Aspects of Gravity
Adunas, G Z; Ahluwalia, D V
2000-01-01
We emphasize that a specific aspect of quantum gravity is the absence of a super-selection rule that prevents a linear superposition of different gravitational charges. As an immediate consequence, we obtain a tiny, but observable, violation of the equivalence principle, provided, inertial and gravitational masses are not assumed to be operationally identical objects. In this framework, the cosmic gravitational environment affects local experiments. A range of terrestrial experiments, from neutron interferometry to neutrino oscillations, can serve as possible probes to study the emergent quantum aspects of gravity.
The Breakdown of Classical Gravity?
Hernandez, X; Allen, C
2011-01-01
Assuming Newton's gravity and GR to be valid at all scales, leads to the dark matter hypothesis as a forced requirement demanded by the observed dynamics and measured baryonic content at galactic and extra galactic scales. Alternatively, one can propose a contrasting scenario where gravity exhibits a change of regime at acceleration scales $a
Cellular basis of gravity resistance in plants
Hoson, Takayuki; Matsumoto, Shouhei; Inui, Kenichi; Zhang, Yan; Soga, Kouichi; Wakabayashi, Kazuyuki; Hashimoto, Takashi
Mechanical resistance to the gravitational force is a principal gravity response in plants distinct from gravitropism. In the final step of gravity resistance, plants increase the rigidity of their cell walls via modifications to the cell wall metabolism and apoplastic environment. We studied cellular events that are related to the cell wall changes under hypergravity conditions produced by centrifugation. Hypergravity induced reorientation of cortical microtubules from transverse to longitudinal directions in epidermal cells of stem organs. In Arabidopsis tubulin mutants, the percentage of cells with longitudinal microtubules was high even at 1 g, and it was further increased by hypergravity. Hypocotyls of tubulin mutants also showed either left-handed or right-handed helical growth at 1 g, and the degree of twisting phenotype was intensified under hypergravity conditions. The left-handed helical growth mutants had right-handed microtubule arrays, whereas the right-handed mutant had left-handed arrays. There was a close correlation between the alignment angle of epidermal cell files and the alignment of cortical microtubules. Gadolinium ions suppressed both the twisting phenotype and reorientation of microtubules in tubulin mutants. These results support the hypothesis that cortical microtubules play an es-sential role in maintenance of normal growth phenotype against the gravitational force, and suggest that mechanoreceptors are involved in modifications to morphology and orientation of microtubule arrays by hypergravity. Actin microfilaments, in addition to microtubules, may be involved in gravity resistance. The nucleus of epidermal cells of azuki bean epicotyls, which is present almost in the center of the cell at 1 g, was displaced to the cell bottom by increasing the magnitude of gravity. Cytochalasin D stimulated the sedimentation by hypergravity of the nu-cleus, suggesting that the positioning of the nucleus is regulated by actin microfilaments, which is
Gravity Data for the State of Nevada
National Oceanic and Atmospheric Administration, Department of Commerce — Gravity data for the entire state of Nevada and adjacent parts of California, Utah, and Arizona are presented. About 80,000 gravity stations were compiled primarily...
Narlikar, Jayant Vishnu
1996-10-01
From the drop of an apple to the stately dance of the galaxies, gravity is omnipresent in the Cosmos. Even with its high profile, gravity is the most enigmatic of all the known basic forces in nature. The Lighter Side of Gravity presents a beautifully clear and completely nontechnical introduction to the phenomenon of this force in all its manifestations. Astrophysicist Jayant Narlikar begins with an historical background to the discovery of the law of gravitation by Isaac Newton in the seventeenth century. Using familiar analogies, interesting anecdotes, and numerous illustrations to get across subtle effects and difficult points to readers, he goes on to describe the general theory of relativity and some of its strange and unfamiliar ideas such as curved spacetime, the bending of light, and black holes. Since first publication in 1982 (W.H. Freeman), Dr. Narlikar has brought his book completely up to date and expanded it to include the discovery of gigantic gravitational lenses in space, the findings of the Cosmic Background Explorer (COBE) satellite, the detection of dark matter in galaxies, the investigation of the very early Universe, and other new ideas in cosmology. This lucid and stimulating book presents a clear approach to the intriguing phenomenon of gravity for everyone who has ever felt caught in its grip. Jayant Narlikar is the winner of many astronomical prizes and the author of Introduction to Cosmology (Cambridge University Press, 1993).
On the Synchronization of Acoustic Gravity Waves
Lonngren, Karl E.; Bai, Er-Wei
Using the model proposed by Stenflo, we demonstrate that acoustic gravity waves found in one region of space can be synchronized with acoustic gravity waves found in another region of space using techniques from modern control theory.
Gravity Data for portions of Ohio
National Oceanic and Atmospheric Administration, Department of Commerce — The gravity station data (1,037 records) were compiled by Doctor Stierman. This data base was received in June 1992. Principal gravity parameters include Free-Air...
Gravity Data For The State of Ohio
National Oceanic and Atmospheric Administration, Department of Commerce — The gravity station data (6,591 records) were compiled by the U. S. Geological Survey. This data base was received on February 23, 1993. Principal gravity...
Gravity Data For The State of Utah
National Oceanic and Atmospheric Administration, Department of Commerce — The gravity station data (41,960 records) were compiled by the U. S. Geological Survey. This data base was received on February 23, 1993. Principal gravity...
Preparation of dynamic gravity testing system
Bowin, Carl
Bowin's interest at WHOI is to obtain the most accurate gravity and gravity gradient measurements possible. The Navy's interest is to have the most accurate navigation possible. Neither can have one without the other. Through Zarak Corporation, Bowin has proposed to the Navy Air System Command to develop a dynamic navigational gravity/gravity gradient (NAV/GRAV) system utilizing superconducting squid gravity and tensor gravity gradient sensors for high precision performance. The proposed system development incorporates that inter-dependency, not only to provide the best estimates of both, but also to provide estimates of the quality of the results obtained. Zarak is pursuing funds for the development of superconducting gravity and gravity gradient sensors. Such sensors, when available, will then be utilized in this palletized system for higher accuracy navigation, gravity and gravity gradient determination. It is desired that initial testing utilize Vibrating String Accelerometers (VSA) gravity sensors and readout systems available at WHOI. This way the development and testing of the NAV/GRAV system can proceed using the VSA sensors while the superconducting gravity sensors are being fabricated. Initial dynamic systems tests will be in a van vehicle for convenience and practicality. The system units will be palletized, and therefore they shall be easily transferable, and thus also be usable in aircraft and ships. It is planned that WHOI will have loan of prototype systems for about two months each year for earth research use.
Thermodynamic properties of modified gravity theories
Bamba, Kazuharu
2016-06-01
We review thermodynamic properties of modified gravity theories, such as F(R) gravity and f(T) gravity, where R is the scalar curvature and T is the torsion scalar in teleparallelism. In particular, we explore the equivalence between the equations of motion for modified gravity theories and the Clausius relation in thermodynamics. In addition, thermodynamics of the cosmological apparent horizon is investigated in f(T) gravity. We show both equilibrium and nonequilibrium descriptions of thermodynamics. It is demonstrated that the second law of thermodynamics in the universe can be met, when the temperature of the outside of the apparent horizon is equivalent to that of the inside of it.
Nonlocal Modification of Newtonian Gravity
Blome, Hans-Joachim; Hehl, Friedrich W; Mashhoon, Bahram
2010-01-01
The Newtonian regime of a recent nonlocal extension of general relativity (GR) is investigated. Nonlocality is introduced via a scalar "constitutive" kernel in a special case of the translational gauge theory of gravitation, namely, the teleparallel equivalent of GR. In this theory, the nonlocal aspect of gravity simulates dark matter. A nonlocal and nonlinear generalization of Poisson's equation of Newtonian gravitation is presented. The implications of nonlocality for the gravitational physics in the solar system are briefly studied.
Hammer, Katrin
2015-01-01
We consider the recently introduced mimetic gravity, which is a Weyl-symmetric extension of the General Relativity and which can play a role of an imperfect fluid-like Dark Matter with a small sound speed. In this paper we discuss in details how this higher- derivative scalar-tensor theory goes beyond the construction by Horndeski, keeping only one scalar degree of freedom on top of two standard graviton polarizations. In particular, we consider representations of the theory in different sets of Weyl-invariant variables and connect this framework to the singular Brans-Dicke theory. Further, we find solution of equations of motion for the mimetic gravity in the synchronous reference frame in a general curved spacetime. This solution is exact in the test-field approximation or in the case of a shear-free spacetime without any other matter.
Minimal theory of massive gravity
De Felice, Antonio
2016-01-01
We propose a new theory of massive gravity with only two propagating degrees of freedom. After defining the theory in the unitary gauge in the vielbein language, we shall perform a Hamiltonian analysis to count the number of physical degrees of freedom, and then study some phenomenologies. While the homogeneous and isotropic background cosmology and the tensor linear perturbations around it are described by exactly the same equations as those in the de Rham - Gabadadze - Tolley (dRGT) massive gravity, the scalar and vector gravitational degrees of freedom are absent in the new theory at the fully nonlinear level. Hence the new theory provides a stable nonlinear completion of the self-accelerating cosmological solution that was originally found in the dRGT theory.
Polarization of instantons and gravity
Kuchiev, M Yu; Kuchiev, M Yu; Ioffe, A F
1994-01-01
Gravity can arise in a conventional non-Abelian gauge theory in which a specific phenomenon takes place. Suppose there is a condensation of polarized instantons and antiinstantons in the vacuum state. Then the excitations of the gauge field in the classical approximation are described through the variables of Riemann geometry satisfying the Einstein equations of general relativity. There are no dimensional coupling constants in the theory.
Institute of Scientific and Technical Information of China (English)
杜小沛; 纪莹; 陆海涛; 张婷婷; 邱伟
2016-01-01
目的：调查混合牙列期身体重心动摇与咬合力之间的关系。方法56名处于Hellman咬合发育Ⅲ期A阶段的健康小学生纳入研究。通过检查咬合平衡中点与中线的距离( X)关系,X≤5 mm被划分为正中组,X>5 mm被划分为偏移组。使用自动姿态分析系统测定了身体平衡相关开闭眼时的重心动摇距离、重心动摇面积。使用牙齿压力感应装置Dental Prescale®测定了咬合接触面积、平均咬合力、最大咬合压力,咬合力和咬合平衡。结果咬合接触面积和咬合力的测试结果男女分别为18.1 mm2、712.2 N和14.1 mm2、541.8 N,差异均具有统计学意义(P<0.05)。咬合平衡中点正中组与偏移组的咬合接触面积、咬合力之间差异具有统计学意义(P <0.05)。咬合平衡中点正中组开、闭眼时期的重心动摇距离、面积明显小于偏移组,咬合平衡与开、闭眼时期的重心动摇距离、面积有关且具有统计学意义(P<0.05)。重心动摇稳定组的咬合接触面积大于动摇组,两者差异具有统计学意义(P<0.05)。结论 Hellman咬合发育Ⅲ期A阶段儿童咬合平衡和人体重心动摇存在相关性,咬合接触面积与身体重心动摇相互影响。%Objective To investigate the relationship between gravity center movement and bite force during the mixed dentition period. Methods Fifty-six healthy children with Hellman's Dental AgeⅢ A were selected from an ele-mentary school. The body balance, distance and area of gravity center movement ( GCM) were measured with automatic posture analytical devices. Occlusal abilities were measured with pressure-sensitive sheets ( Dental Prescale® ) , including occlusal contacts area, average occlusal pressure, maximum occlusal pressure, occlusal force and occlusal balance. Re-sults The occlusal contact area and bite force test results of male and female group were 18. 1 mm2 , 712. 2 N and 14. 1 mm2, 541. 8 N, The differences were statistically
Institute of Scientific and Technical Information of China (English)
无
2006-01-01
The nesting problem involves arranging pieces on a plate to maximize use of material. A new scheme for 2D irregular-shaped nesting problem is proposed. The new scheme is based on the NFP (No Fit Polygon) algorithm and a new placement principle for pieces. The novel placement principle is to place a piece to the position with lowest gravity center based on NFP. In addition, genetic algorithm (GA) is adopted to find an efficient nesting sequence. The proposed scheme can deal with pieces with arbitrary rotation and containing region with holes, and achieves competitive results in experiment on benchmark datasets.
Institute of Scientific and Technical Information of China (English)
皋宇翔; 黄伟芬; 马爱军; 刘巍; 张磊
2013-01-01
目的 测试水下训练航天服(含受试者)的重心、浮心间距.方法 水下试验中,采用移动活动配重的方法改变服装前倾角度,通过图像采集与处理,计算出水下训练航天服的重心、浮心间距.结果 某水下训练航天服的重心、浮心间距为3.52 cm.结论 本文提出了一种水下训练航天服重心、浮心间距的测试方法,首次对服装中性浮力状态进行了定量分析.建议水下训练航天服各运动组成部分应分别达到中性浮力状态,并提出了进一步的研究思路.%Objective To test the interval between centers of gravity and buoyancy of underwater training space-suit (including the training subject). Methods The pitch angle of the training spacesuit will change when moving the portable lead mass during underwater experiments, so the interval can be calculated by analyzing the images taken before and after the lead mass' s moving. Results The interval between the two centers in one underwater spacesuit is 3. 52 cm. Conclusion The test method is the first quantitative analysis of the neutral buoyancy status of the underwater training spacesuit. It is suggested that every movable part of the training spacesuit should be designed to achieve the neutral buoyancy status for the better weightlessness environment simulation, and some ideas for further researches are proposed in the end.
Perturbative Quantization of Gravity Theories
Bern, Z.
2001-01-01
We discuss string theory relations between gravity and gauge theory tree amplitudes. Together with $D$-dimensional unitarity, these relations can be used to perturbatively quantize gravity theories, i.e. they contain the necessary information for calculating complete gravity $S$-matrices to any loop orders. This leads to a practical method for computing non-trivial gravity $S$-matrix elements by relating them to much simpler gauge theory ones. We also describe arguments that N=8 D=4 supergrav...
Establishment of Absolute Gravity Datum in CMONOC and Its Application
XING Lelin; LI Hui; Li, Jianguo; Zhang, Weimin; HE Zhitang
2016-01-01
The high accuracy absolute gravity datum covered the Chinese mainland area is established by using absolute gravity measurement data of one hundred stations in CMONOC(Crustal Movement Observation Network of China), the accuracy of each station is better than 5.0 μGal/a. The high accuracy gravity datum can be used for relative gravity measurements in adjustment, and the real gravity value can be determined from relative gravity measurement data of adjustment by using the gravity datum to avoid...
Equivalence of modified gravity equation to the Clausius relation
Bamba, Kazuharu; Nojiri, Shin'ichi; Odintsov, Sergei D
2009-01-01
We show that the equations of motion for modified gravity theories are equivalent to the Clausius relation in thermodynamics. For modified gravity theories, we study $F(R)$-gravity, the scalar-Gauss-Bonnet gravity, $F(\\mathcal{G})$-gravity and the non-local gravity. In addition, we discuss the relation between the expression of the entropy and the contribution from the modified gravity as well as the matter to the definition of the energy flux (heat).
The meaning of quantum gravity
International Nuclear Information System (INIS)
The authors of this book take the Bohr-Rosenfeld analysis of quantum electrodynamics as their starting point and develop arguments in support of Einstein's own thesis that, due to the validity of the strong principle of equivalence, the General Theory cannot be rigorously quantized. They show that the concept of gravitons is an approximate formalization only, which has its use in the harmonization of the gravitational equations with the matter field, but which does not predict any effect that may be used to distinguish quantum from classical gravity. Furthermore, it is argued that, when using Planck units, it is senseless to attempt quantization of the General Theory. 154 refs.; 4 figs
UCN and gravity: ideas of new experiments
International Nuclear Information System (INIS)
Some new experiments for the investigation of neutron gravity properties and for the test of the weak equivalence principle are discussed. They are the experiment for the measurement of the free-fall gravity acceleration with the accuracy exceeding the present level on one-two orders of magnitude, the experiment for the observation of quantum effects occurring when the UCNs are trapped in the potential well formed in the Earth gravity field above the Vladimirskii magnetic mirror and Cavendish experiment with neutrons
Algebraic definition of topological W gravity
International Nuclear Information System (INIS)
In this paper, the authors propose a definition of the topological W gravity using some properties of the principal three-dimensional subalgebra of a simple Lie algebra due to Kostant. In the authors' definition, structures of the two-dimensional topological gravity are naturally embedded in the extended theories. In accordance with the definition, the authors will present some explicit calculations for the W3 gravity
Renormalizable Quantum Gauge Theory of Gravity
Institute of Scientific and Technical Information of China (English)
WU Ning
2002-01-01
The quantum gravity is formulated based on the principle of local gauge invariance. The model discussedin this paper has local gravitational gauge symmetry, and gravitational field is represented by gauge field. In the leading-order approximation, it gives out classical Newton's theory of gravity. In the first-order approximation and for vacuum,it gives out Einstein's general theory of relativity. This quantum gauge theory of gravity is a renormalizable quantumtheory.
Modelling of gravity changes in mining areas
Energy Technology Data Exchange (ETDEWEB)
Szostak-Chrzanowski, A.; Chrzanowski, A.; Popiolek, E. [University of New Brunswick, Fredericton, NB (Canada). Department of Geodesy and Geomatics Engineering
1995-10-01
The numerical modelling of gravity changes resulting from the simultaneous effects of mass relocation and rock deformation is described. The method is supported by FEMMA (Finite Element Method for Multipurpose Applications) software, and has been used for modelling expected gravity changes in a large open pit coal mine in Poland. The results are in good agreement with conventional calculations of gravity changes for a simple geometry of relocated mass. 10 refs., 6 figs., 2 tabs.
Gravity duals of boundary cones
Camps, Joan
2016-01-01
The replica trick defines Renyi entropies as partition functions on conically singular geometries. We discuss their gravity duals: regular bulk solutions to the Einstein equations inducing conically singular metrics at the boundary. When the conical singularity is supported on a flat or spherical surface, these solutions are rewritings of the hyperbolic black hole. For more general shapes, these solutions are new. We construct them perturbatively in a double expansion in the distance and strength of the conical singularity, and extract the vacuum polarisation due to the cone. Recent results about the structure of logarithmic divergences of Renyi entropies are reproduced ---in particular, $f_b\
Quantum aspects of massive gravity
Park, Minjoon
2011-05-01
We consider the effect of quantum interactions on Pauli-Fierz massive gravity. With generic graviton cubic interactions, we observe that the 1-loop counterterms do not conform to the tree level structure of Pauli-Fierz action, resulting in the reappearance of the sixth mode ghost. Then to explore the quantum effects to the full extent, we calculate the resummed graviton propagator with an arbitrary interaction and analyze its complete structure, from which a minimal condition for the absence of the ghost is obtained.
Goradia, Shantilal
2008-04-01
We postulate that every particle has a Planck size quantum mouth it stretches to interact with other particles, making all interactions between quantum mouths and the probability of an interaction between two particles is inversely proportional to the square of the statistical number of Planck lengths separating the particles [1], linking entropy, fine-structure constant and cosmological constant, explaining quantum tunneling, dark energy and some other issues consistent with some great minds. This was presented at the ``Concepts of Entropy and Their Applications'' conference in Melbourne, Australia on Dec 29, 2007. The natural logarithm connects the statistical entropy to thermodynamic and makes it consistent with the observed expansion of the universe with Hubble constant. [1] http://www.arXiv.org/physics/0210040
Airborne Gravity Gradiometry Resolves a Full Range of Gravity Frequencies
Mataragio, J.; Brewster, J.; Mims, J.
2007-12-01
Airborne Full Tensor Gradiometry (Air\\-FTGR) was flown at high altitude coincident with Airborne Gravity (AG) flown in 2003 in West Arnhem Land, Australia. A preliminary analysis of two data sets indicates that the Air\\-FTGR system has the capability of resolving intermediate to long wavelengths features that may be associated with relatively deeper geological structures. A comparison of frequency filtered slices and power spectral density (PSD) for both data sets using the short (> 5 km), intermediate (10 km) and long (20 km) wavelengths reveals that high altitude Air\\-FTGR data show greater response in high frequency anomalies than a conventional Airborne Gravity and matches well with the AG even at the longest wavelengths anomalies. The effect of line spacing and target resolution was examined between the two data sets. Reprocessed gradient and AG data at 2, 4 and 6 km line spacing suggest that Air\\-FTGR could be effectively flown at a comparatively wider line spacing to resolve similar targets the AG would resolve with tighter line spacing. Introduction Airborne Full Tensor Gradiometry (Air\\-FTGR) data have been available to the mining industry since 2002 and their use for geologic applications is well established. However, Air\\-FTGR data has been mostly considered and used in mapping and delineation of near surface geological targets. This is due to the fact that gravity gradiometer measurements are well suited to capture the high frequency signal associated with near\\-surface targets ( Li, 2001). This is possible because the gradiometer signal strength falls off with the cube of the distance to the target. Nonetheless, in recent years there has been an increasing demand from the mining, oil, and gas industry in utilizing Full Tensor Gravity Gradiometer as a mapping tool for both regional and prospect level surveys. Air\\-FTGR as a Regional Mapping Tool Several, relatively low altitude surveys have been successfully flown in Brazil, Canada and Australia
Comparison of various isostatic marine gravity disturbances
Indian Academy of Sciences (India)
Robert Tenzer; Mohammad Bagherbandi; Lars E Sjöberg
2015-08-01
We present and compare four types of the isostatic gravity disturbances compiled at sea level over the world oceans and marginal seas. These isostatic gravity disturbances are computed by applying the Airy–Heiskanen (AH), Pratt–Hayford (PH) and Vening Meinesz–Moritz (VMM) isostatic models. In addition, we compute the complete crust-stripped (CCS) isostatic gravity disturbances which are defined based on a principle of minimizing their spatial correlation with the Moho geometry. We demonstrate that each applied compensation scheme yields a distinctive spatial pattern in the resulting isostatic marine gravity field. The AH isostatic gravity disturbances provide the smoothest gravity field (by means of their standard deviation). The AH and VMM isostatic gravity disturbances have very similar spatial patterns due to the fact that the same isostatic principle is applied in both these definitions expect for assuming a local (in the former) instead of a global (in the latter) compensation mechanism. The PH isostatic gravity disturbances are highly spatially correlated with the ocean-floor relief. The CCS isostatic gravity disturbances reveal a signature of the ocean-floor spreading characterized by an increasing density of the oceanic lithosphere with age.
Palsingh, S. (Inventor)
1975-01-01
An educational toy useful in demonstrating fundamental concepts regarding the laws of gravity is described. The device comprises a sphere 10 of radius r resting on top of sphere 12 of radius R. The center of gravity of sphere 10 is displaced from its geometrical center by distance D. The dimensions are so related that D((R+r)/r) is greater than r. With the center of gravity of sphere 10 lying on a vertical line, the device is in equilibrium. When sphere 10 is rolled on the surface of sphere 12 it will return to its equilibrium position upon release. This creates an illusion that sphere 10 is defying the laws of gravity. In reality, due to the above noted relationship of D, R, and r, the center of gravity of sphere 10 rises from its equilibrium position as it rolls a short distance up or down the surface of sphere 12.
Cosmological solution of Machian gravity
Das, Santanu
2012-01-01
The standard model of cosmology predicts that more than 95% matter in the universe consists of dark components namely dark matter and dark energy. In spite of several attempts to measure these components, there is not a single direct observational evidence for these components till date. Hence, different alternate models of cosmology have been put forward by different authors. However, most of these models have their own problems. Therefore, in this paper, a new cosmological model has been proposed. This model is based on the Machian gravity model, which will be discussed in detail in a later paper. The model can provide an exactly similar cosmology as that of the standard cosmological model without demanding any ad-hoc dark matter or dark energy components. The paper shows that when the field equations from Machian gravity (a 5 dimensional model) are projected to the 4-dimensional space-time, some new mathematical terms arise in the equations that behave exactly like dark matter and dark energy. These mathem...
Simultaneous measurement of gravity acceleration and gravity gradient with an atom interferometer
Energy Technology Data Exchange (ETDEWEB)
Sorrentino, F.; Lien, Y.-H.; Rosi, G.; Tino, G. M. [Dipartimento di Fisica e Astronomia and LENS, Universita di Firenze, INFN Sezione di Firenze, via Sansone 1, I-50019 Sesto Fiorentino (Italy); Bertoldi, A. [Laboratoire Charles Fabry de l' Institut d' Optique, CNRS and Universite Paris-Sud Campus Polytechnique, RD 128, F-91127 Palaiseau cedex (France); Bodart, Q. [Dipartimento di Fisica e Astronomia and LENS, Universita di Firenze, INFN Sezione di Firenze, via Sansone 1, I-50019 Sesto Fiorentino (Italy); European Space Agency, Research and Scientific Support Department, Keplerlaan 1, 2201 AZ Noordwijk (Netherlands); Cacciapuoti, L. [European Space Agency, Research and Scientific Support Department, Keplerlaan 1, 2201 AZ Noordwijk (Netherlands); Angelis, M. de [Istituto di Fisica Applicata ' Nello Carrara' CNR, via Madonna del Piano 10, I-50019 Sesto Fiorentino (Italy); Prevedelli, M. [Dipartimento di Fisica dell' Universita di Bologna, Via Irnerio 46, I-40126, Bologna (Italy)
2012-09-10
We demonstrate a method to measure the gravitational acceleration with a dual cloud atom interferometer; the use of simultaneous atom interferometers reduces the effect of seismic noise on the gravity measurement. At the same time, the apparatus is capable of accurate measurements of the vertical gravity gradient. The ability to determine the gravity acceleration and gravity gradient simultaneously and with the same instrument opens interesting perspectives in geophysical applications.
In favor of a Newtonian quantum gravity
International Nuclear Information System (INIS)
Arguments for creating a unified theory of Newtonian gravity and quantum mechanics are listed. This nonrelativistic level is historically bypassed, however, conceptional problems anticipating some features of relativistic quantum gravity may come up. Starting from Wigner's analysis on measurability in the relativistic case, a genuine uncertainty of the Newton potential is verified leading to the breakdown of the Schroedinger equation outside microscopic regions. (author)
Energy Technology Data Exchange (ETDEWEB)
Rahaman, F [Department of Mathematics, Jadavpur University, Kolkata 700032 (India); Kuhfittig, P K F [Department of Mathematics, Milwaukee School of Engineering, Milwaukee, WI 53202-3109 (United States); Kalam, M [Department of Physics, Aliah University, Sector V, Salt Lake, Kolkata 700091 (India); Usmani, A A [Department of Physics, Aligarh Muslim University, Aligarh 202002, Uttar Pradesh (India); Ray, S, E-mail: farook-rahaman@yahoo.com, E-mail: kuhfitti@msoe.edu, E-mail: mehedikalam@yahoo.co.in, E-mail: anisul@iucaa.ernet.in, E-mail: saibal@iucaa.ernet.in [Department of Physics, Govt College of Engineering and Ceramic Technology, Kolkata 700010 (India)
2011-08-07
In this paper, we have constructed a new class of thin-shell wormholes from black holes in Horava-Lifshitz gravity. Particular emphasis is placed on those aspects that allow a comparison of Horava-Lifshitz gravity to Einstein gravity. The former enjoys a number of advantages for small values of the throat radius.
Gravity, Magnetism, and "Down": Non-Physics College Students' Conceptions of Gravity
Asghar, Anila; Libarkin, Julie C.
2010-01-01
This study investigates how students enrolled in entry-level geology, most of whom would graduate from college without university-level physics courses, thought about and applied the concept of gravity while solving problems concerning gravity. The repercussions of students' gravity concepts are then considered in the context of non-physics…
Directory of Open Access Journals (Sweden)
R. A. Arko
1999-06-01
Full Text Available The U.S. National Science Foundation (NSF has agreed to support the development of a new generation gravity map of Antarctica (ADGRAV - Antarctic Digital Gravity Synthesis, funding the development of a web based access tool. The goal of this project is the creation of an on-line Antarctic gravity database which will facilitate access to improved high resolution satellite gravity models, in conjunction with shipboard, airborne, and land based gravity measurements for the continental regions. This database will complement parallel projects underway to develop new continental bedrock (BEDMAP and magnetic (ADMAP maps of Antarctica.
Fixed points of quantum gravity
Litim, D.F.(Department of Physics and Astronomy, University of Sussex, Brighton, BN1 9QH, UK)
2004-01-01
Euclidean quantum gravity is studied with renormalisation group methods. Analytical results for a non-trivial ultraviolet fixed point are found for arbitrary dimensions and gauge fixing parameter in the Einstein-Hilbert truncation. Implications for quantum gravity in four dimensions are discussed.
SATELLITE GRAVITY SURVEYING TECHNOLOGY AND RESEARCH OF EARTH＇S GRAVITY FIELD
Institute of Scientific and Technical Information of China (English)
NingJinsheng
2003-01-01
This is a summarized paper.Two topics are discussed:Firstly,the comcept,development and application of four kinds of satellite gravity surveying technology are introduced；Secondly,some problems of theory and method,which must be considered in the study lf the Earth's gravity field based on satellite gravity data,are expounded.
Development of the Newtonian Gravity Concept Inventory
Williamson, Kathryn E.; Willoughby, Shannon; Prather, Edward E.
2013-01-01
We introduce the Newtonian Gravity Concept Inventory (NGCI), a 26-item multiple-choice instrument to assess introductory general education college astronomy ("Astro 101") student understanding of Newtonian gravity. This paper describes the development of the NGCI through four phases: Planning, Construction, Quantitative Analysis, and…
Thermodynamic properties of modified gravity theories
Bamba, Kazuharu
2016-01-01
We review thermodynamic properties of modified gravity theories such as $F(R)$ gravity and $f(T)$ gravity, where $R$ is the scalar curvature and $T$ is the torsion scalar in teleparallelism. In particular, we explore the equivalence between the equations of motion for modified gravity theories and the Clausius relation in thermodynamics. In addition, thermodynamics of the cosmological apparent horizon is investigated in $f(T)$ gravity. We show both equilibrium and non-equilibrium descriptions of thermodynamics. It is demonstrated that the second law of thermodynamics in the universe can be met when the temperature of the outside of the apparent horizon is equivalent to that of the inside of it.
Comparison of Present SST Gravity Field Models
Institute of Scientific and Technical Information of China (English)
LUO Jia; SHI Chuang; ZOU Xiancai; WANG Haihong
2006-01-01
Taking the main land of Europe as the region to be studied, the potential of the new satellite gravity technique: satellite-to-satellite tracking (SST) and improving the accuracy of regional gravity field model with the SST models are investigated. The drawbacks of these models are discussed. With GPM98C as the reference, the gravity anomaly residuals of several other models, the latest SST global gravity field models (EIGEN series and GGM series), were computed and compared. The results of the comparison show that in the selected region, some systematic errors with periodical properties exist in the EIGEN and GGM's S series models in the high degree and order. Some information that was not shown in the classic gravity models is detected in the low and middle degree and order of EIGEN and GGM's S series models. At last, the effective maximum degrees and orders of SST models are suggested.
A Dialogue on the Nature of Gravity
Padmanabhan, T
2009-01-01
I describe the conceptual and mathematical basis of an approach which describes gravity as an emergent phenomenon. Combining principle of equivalence and principle of general covariance with known properties of local Rindler horizons, perceived by observers accelerated with respect to local inertial frames, one can prove that the field equations describing gravity in any diffeomorphism invariant theory can be given a thermodynamic re-interpretation. This fact, in turn, leads us to the possibility of deriving the field equations of gravity by maximising a suitably defined entropy functional, without using the metric tensor as a dynamical variable. The approach synthesises concepts from quantum theory, thermodynamics and gravity leading to a fresh perspective on the nature of gravity. The description is presented here in the form of a dialogue, thereby addressing several frequently-asked-questions.
The Necessity of Quantizing Gravity
Adelman, Jeremy
2015-01-01
The Eppley Hannah thought experiment is often cited as justification for attempts by theorists to develop a complete, consistent theory of quantum gravity. A modification of the earlier "Heisenberg microscope" argument for the necessity of quantized light, the Eppley-Hannah thought experiment purports to show that purely classical gravitational waves would either not conserve energy or else allow for violations of the uncertainty principle. However, several subsequent papers have cast doubt as to the validity of the Eppley-Hannah argument. In this paper, we attempt to resurrect the Eppley-Hannah thought experiment by modifying the original argument in such a manner as to render it immune to the present criticisms levied against it.
Equivalence of modified gravity equation to the Clausius relation
Bamba, Kazuharu; Geng, Chao-Qiang; Nojiri, Shin'ichi; Odintsov, Sergei D.
2009-01-01
We explicitly show that the equations of motion for modified gravity theories of $F(R)$-gravity, the scalar-Gauss-Bonnet gravity, $F(\\mathcal{G})$-gravity and the non-local gravity are equivalent to the Clausius relation in thermodynamics. In addition, we discuss the relation between the expression of the entropy and the contribution from the modified gravity as well as the matter to the definition of the energy flux (heat).
Institute of Scientific and Technical Information of China (English)
王介勇; 刘彦随
2009-01-01
通过构建粮食产量重心模型,定量分析了1990年～2005年中国粮食生产时空格局演进过程.结果表明:中国粮食产量重心呈现出"北上西进"的态势,粮食产量重心移动的速率不断增大,粮食产量增长的空间波动性逐渐增强,产量优势区的空间格局尚不稳定.从资源、经济、技术、政策等方面深入剖析了粮食产量重心移动的驱动机制.耕地资源的空间格局及其变动趋势是驱动粮食产量重心移动的客观基础,北方地下水资源开发利用是粮食产量重心移动的关键因素,食物消费结构变化是粮食产量重心移动的直接因素,科技进步、农村经济发展不平衡以及区域化的粮食支持政策是粮食产量重心移动的重要驱动力量.最后探讨了粮食产量重心移动的区域环境、经济及社会效应.%Grain security is a considerable challenge to the world in the 21 century, especially to China. The pattern of grain-output has changed greatly since the reform of the grain market, the accelerating urbanization and fast industrialization. In this paper, the model for the center of gravity of grain-output was built, and the change of grain-output pattern was analyzed from 1990 to 2005 with the model. The results showed that: 1) from 1990 to 1998, the grain-output center-of-gravity moved towards northeast at the speed of 7.6 km/year. In total, it moved 60.8km northward and 6.4km eastward; 2) In the period of 1998 to 2003, the grain-output center-of-gravity moved towards southwest at a speed of 16 km/year. Therefore, it moved 63.8km southward and 48.1km westward in all; 3) In the last period of 2003 to 2005, the grain-output center-of-gravity moved back to northeast at the speed odf 41.2 km/year. In other words, it moved 82.3 km northward and 46.8km eastward in all; 4) During the entire period of 1990 to 2005, the grain-output center-of-gravity moved remarkably from the south and east to the north and west of China, and
Validation of the EGSIEM combined monthly GRACE gravity fields
Li, Zhao; van Dam, Tonie; Chen, Qiang; Weigelt, Matthias; Güntner, Andreas; Jäggi, Adrian; Meyer, Ulrich; Jean, Yoomin; Altamimi, Zuheir; Rebischung, Paul
2016-04-01
Observations indicate that global warming is affecting the water cycle. Here in Europe predictions are for more frequent high precipitation events, wetter winters, and longer and dryer summers. The consequences of these changes include the decreasing availability of fresh water resources in some regions as well as flooding and erosion of coastal and low-lying areas in other regions. These weather related effects impose heavy costs on society and the economy. We cannot stop the immediate effects global warming on the water cycle. But there may be measures that we can take to mitigate the costs to society. The Horizon2020 supported project, European Gravity Service for Improved Emergency Management (EGSIEM), will add value to EO observations of variations in the Earth's gravity field. In particular, the EGSIEM project will interpret the observations of gravity field changes in terms of changes in continental water storage. The project team will develop tools to alert the public water storage conditions could indicate the onset of regional flooding or drought. As part of the EGSIEM project, a combined GRACE gravity product is generated, using various monthly GRACE solutions from associated processing centers (ACs). Since each AC follows a set of common processing standards but applies its own independent analysis method, the quality, robustness, and reliability of the monthly combined gravity fields should be significantly improved as compared to any individual solution. In this study, we present detailed and updated comparisons of the combined EGSIEM GRACE gravity product with GPS position time series, hydrological models, and existing GRACE gravity fields. The GPS residuals are latest REPRO2 station position residuals, obtained by rigorously stacking the IGS Repro 2 , daily solutions, estimating, and then restoring the annual and semi-annual signals.
Schreiber, L; Robert, C; Diolaiti, E; Conan, J -M; Lombini, M
2009-01-01
Over the last few years increasing consideration has been given to the study of Laser Guide Stars (LGS) for the measurement of the disturbance introduced by the atmosphere in optical and near-infrared astronomical observations from the ground. A possible method for the generation of a LGS is the excitation of the Sodium layer in the upper atmosphere at approximately 90 km of altitude. Since the Sodium layer is approximately 10 km thick, the artificial reference source looks elongated, especially when observed from the edge of a large aperture. The spot elongation strongly limits the performance of the most common wavefront sensors. The centroiding accuracy in a Shack-Hartmann wavefront sensor, for instance, decreases proportionally to the elongation (in a photon noise dominated regime). To compensate for this effect a straightforward solution is to increase the laser power, i.e. to increase the number of detected photons per subaperture. The scope of the work presented in this paper is twofold: an analysis of...
Consistency of canonical formulation of Horava gravity
Energy Technology Data Exchange (ETDEWEB)
Soo, Chopin, E-mail: cpsoo@mail.ncku.edu.tw [Department of Physics, National Cheng Kung University, Tainan, Taiwan (China)
2011-09-22
Both the non-projectable and projectable version of Horava gravity face serious challenges. In the non-projectable version, the constraint algebra is seemingly inconsistent. The projectable version lacks a local Hamiltonian constraint, thus allowing for an extra graviton mode which can be problematic. A new formulation (based on arXiv:1007.1563) of Horava gravity which is naturally realized as a representation of the master constraint algebra (instead of the Dirac algebra) studied by loop quantum gravity researchers is presented. This formulation yields a consistent canonical theory with first class constraints; and captures the essence of Horava gravity in retaining only spatial diffeomorphisms as the physically relevant non-trivial gauge symmetry. At the same time the local Hamiltonian constraint is equivalently enforced by the master constraint.
Directory of Open Access Journals (Sweden)
Katsuya Hasegawa
2014-04-01
Full Text Available The ability to maintain the body relative to the external environment is important for adaptation to altered gravity. However, the physiological limits for adaptation or the disruption of body orientation are not known. In this study, we analyzed postural changes in mice upon exposure to various low gravities. Male C57BL6/J mice (n = 6 were exposed to various gravity-deceleration conditions by customized parabolic flight-maneuvers targeting the partial-gravity levels of 0.60, 0.30, 0.15 and μ g (<0.001 g. Video recordings of postural responses were analyzed frame-by-frame by high-definition cineradiography and with exact instantaneous values of gravity and jerk. As a result, the coordinated extension of the neck, spine and hindlimbs was observed during the initial phase of gravity deceleration. Joint angles widened to 120%–200% of the reference g level, and the magnitude of the thoracic-curvature stretching was correlated with gravity and jerk, i.e., the gravity deceleration rate. A certain range of jerk facilitated mouse skeletal stretching efficiently, and a jerk of −0.3~−0.4 j (g/s induced the maximum extension of the thoracic-curvature. The postural response of animals to low gravity may undergo differential regulation by gravity and jerk.
Willamette (AO91812-1), a high-yielding, round, white-skinned variety with good chipping qualities, was released in 2003 by the Oregon, Idaho and Washington Agricultural Experiment Stations and the United States Department of Agriculture-Agricultural Research Service. Willamette was selected at Powe...
Hasegawa, Katsuya; de Campos, Priscila S; Zeredo, Jorge L; Kumei, Yasuhiro
2014-01-01
The ability to maintain the body relative to the external environment is important for adaptation to altered gravity. However, the physiological limits for adaptation or the disruption of body orientation are not known. In this study, we analyzed postural changes in mice upon exposure to various low gravities. Male C57BL6/J mice (n = 6) were exposed to various gravity-deceleration conditions by customized parabolic flight-maneuvers targeting the partial-gravity levels of 0.60, 0.30, 0.15 and μ g (definition cineradiography and with exact instantaneous values of gravity and jerk. As a result, the coordinated extension of the neck, spine and hindlimbs was observed during the initial phase of gravity deceleration. Joint angles widened to 120%-200% of the reference g level, and the magnitude of the thoracic-curvature stretching was correlated with gravity and jerk, i.e., the gravity deceleration rate. A certain range of jerk facilitated mouse skeletal stretching efficiently, and a jerk of -0.3~-0.4 j (g/s) induced the maximum extension of the thoracic-curvature. The postural response of animals to low gravity may undergo differential regulation by gravity and jerk. PMID:25370191
Gauge Theory of Gravity and Spacetime
Hehl, Friedrich W
2012-01-01
The advent of general relativity settled it once and for all that a theory of spacetime is inextricably linked to the theory of gravity. From the point of view of the gauge principle of Weyl and Yang-Mills-Utiyama, it became manifest around the 1960s (Sciama--Kibble) that gravity is closely related to the Poincare group acting in Minkowski space. The gauging of this external group induces a Riemann-Cartan geometry on spacetime. If one generalizes the gauge group of gravity, one finds still more involved spacetime geometries. If one specializes it to the translation group, one finds a specific Riemann-Cartan geometry with teleparallelism (Weitzenbock geometry).
Modified gravity models of dark energy
Tsujikawa, Shinji
2011-01-01
We review recent progress of modified gravity models of dark energy--based on f(R) gravity, scalar-tensor theories, braneworld gravity, Galileon gravity, and other theories. In f(R) gravity and Brans-Dicke theory it is possible to design viable models consistent with local gravity constraints under a chameleon mechanism, while satisfying conditions for the cosmological viability. The Dvali-Gabadazde-Porrati braneworld model can be compatible with local gravity constraints through a nonlinear field self-interaction arising from a brane-bending mode, but the self-accelerating solution contains a ghost mode in addition to the tension with observational data about the cosmic expansion history. The extension of the field self-interaction to more general forms satisfying a Galilean symmetry in the flat space-time allows a possibility to avoid the appearance of ghosts and Laplacian instabilities, while the late-time cosmic acceleration can be realized by the field kinetic energy. We study the evolution of cosmologic...
Center of Gravity Analysis and Operational Design
DEFF Research Database (Denmark)
Barfoed, Jacob
USA er god at til vinde sine militære kampagner, men fejler i sikringen af den efterfølgende fred. Der er behov for en interagency strategisk analysemodel, der kan medvirke til at sikre sammenhæng mellem de politiske mål og den militære kampagne. Dette paper giver et bud på en sådan model....
Gauge Theory of Gravity and Supergravity
Kaul, Romesh K.
2006-01-01
We present a formulation of gravity in terms of a theory based on complex SU(2) gauge fields with a general coordinate invariant action functional quadratic in the field strength. Self-duality or anti-self-duality of the field strength emerges as a constraint from the equations of motion of this theory. This in turn leads to Einstein gravity equations for a dilaton and an axion conformally coupled to gravity for the self-dual constraint. The analysis has also been extended to N=1 and 2 super ...
Fractal Structure of Loop Quantum Gravity
Modesto, Leonardo
2008-01-01
In this paper we have calculated the spectral dimension of loop quantum gravity (LQG) using simple arguments coming from the area spectrum at different length scales. We have obtained that the spectral dimension of the spatial section runs from 2 to 3, across a 1.5 phase, when the energy of a probe scalar field decrees from high to low energy. We have calculated the spectral dimension of the space-time also using results from spin-foam models, obtaining a 2-dimensional effective manifold at hight energy. Our result is consistent with other two approach to non perturbative quantum gravity: causal dynamical triangulation and asymptotic safety quantum gravity.
Gravity Field Atlas of the S. Ocean
National Oceanic and Atmospheric Administration, Department of Commerce — This Gravity Field Atlas of the Southern Ocean from GEOSAT is MGG Report 7. In many areas of the global ocean, the depth of the seafloor is not well known because...
Toward a gauge field theory of gravity.
Yilmaz, H.
Joint use of two differential identities (Bianchi and Freud) permits a gauge field theory of gravity in which the gravitational energy is localizable. The theory is compatible with quantum mechanics and is experimentally viable.
The Gravity of Giraffe Physiology
Hargens, Alan R.; Holton, Emily M. (Technical Monitor)
1997-01-01
By virtue of its tallness and terrestrial environment, the giraffe is a uniquely sensitive African animal to investigate tissue adaptations to gravitational stress. One decade ago, we studied transcapillary fluid balance and local tissue adaptations to high cardiovascular and musculoskeletal loads in adult and fetal giraffes. Previous studies by Goetz, Pattersson, Van Citters, Warren and their colleagues revealed that arterial pressure near the giraffe heart is about twice that in humans, to provide more normal blood pressure and perfusion to the brain. Another important question is how giraffes avoid pooling of blood and tissue fluid (edema) in dependent tissue of the extremities. As monitored by radiotelemetry, the blood and tissue fluid pressures that govern transcapillary exchange vary greatly with exercise. These pressures, combined with a tight skin layer, move fluid upward against gravity. Other mechanisms that prevent edema include precapillary vasoconstriction and low permeability of capillaries to plasma proteins. Other anatomical adaptations in dependent tissues of giraffes represent developmental adjustments to high and variable gravitational forces. These include vascular wall hypertrophy, thickened capillary basement membrane and other connective tissue adaptations. Our results in giraffe suggest avenues of future gravitational research in other animals including humans.
Gravity and Nonequilibrium Thermodynamics of Classical Matter
Hu, B L
2010-01-01
Renewed interest in deriving gravity (more precisely, the Einstein equations) from thermodynamics considerations [1, 2] is stirred up by a recent proposal that 'gravity is an entropic force' [3] (see also [4]). Even though I find the arguments justifying such a claim in this latest proposal rather ad hoc and simplistic compared to the original one I would unreservedly support the call to explore deeper the relation between gravity and thermodynamics, this having the same spirit as my long-held view that general relativity is the hydrodynamic limit [5, 6] of some underlying theories for the microscopic structure of spacetime - all these proposals, together with that of [7, 8], attest to the emergent nature of gravity [9]. In this first paper of two we set the modest goal of studying the nonequilibrium thermodynamics of classical matter only, bringing afore some interesting prior results, without invoking any quantum considerations such as Bekenstein-Hawking entropy, holography or Unruh effect. This is for the ...
Evaporation Time of Horava Gravity Black Holes
International Nuclear Information System (INIS)
Recently it has been a lot of interest in the theory proposed by Horava because is a remormalizable theory of gravity and may be a candidate for the UV completion of Einstein gravity. In the present work we study thermodynamical properties of black hole type solutions in this setup. In particular we are able to obtain times of evaporation for black hole solution in this formalism.
6D Interpretation of 3D Gravity
Herfray, Yannick; Scarinci, Carlos
2016-01-01
We show that 3D gravity, in its pure connection formulation, admits a natural 6D interpretation. The 3D field equations for the connection are equivalent to 6D Hitchin equations for the Chern-Simons 3-form in the total space of the principal bundle over the 3-dimensional base. Turning this construction around one gets an explanation of why the pure connection formulation of 3D gravity exists. More generally, we interpret 3D gravity as the dimensional reduction of the 6D Hitchin theory. To this end, we show that any SU(2) invariant closed 3-form in the total space of the principal SU(2) bundle can be parametrised by a connection together with a 2-form field on the base. The dimensional reduction of the 6D Hitchin theory then gives rise to 3D gravity coupled to a topological 2-form field.
Toward an invariant definition of repulsive gravity
Luongo, Orlando; Quevedo, Hernando
2010-01-01
A remarkable property of naked singularities in general relativity is their repulsive nature. The effects generated by repulsive gravity are usually investigated by analyzing the trajectories of test particles which move in the effective potential of a naked singularity. This method is, however, coordinate and observer dependent. We propose to use the properties of the Riemann tensor in order to establish in an invariant manner the regions where repulsive gravity plays a dominant role. In par...
Emergent gravity: From statistical point of view
Majhi, Bibhas Ranjan
2012-01-01
Near the event horizon of a black hole, the effective theory is two dimensional conformal theory. Here we show that the holographic modes characterising this underlying conformal symmetry and the basic definition of entropy $S$ in statistical mechanics lead the equipartition law of energy. We also show that $S$ is proportional to the gravity action which suggests the emergent nature of gravity. This is further bolstered by expressing the generalised Smarr formula as a thermodynamic relation, ...
Evolution of spiral galaxies in modified gravity
Tiret, O; Combes, F
2007-01-01
We compare N-body simulations of isolated galaxies performed in both frameworks of modified Newtonian dynamics (MOND) and Newtonian gravity with dark matter (DM). We have developed a multigrid code able to efficiently solve the modified Poisson equation derived from the Lagrangian formalism AQUAL. We take particular care of the boundary conditions that are a crucial point in MOND. The 3-dimensional dynamics of initially identical stellar discs is studied in both models. In Newtonian gravity t...
Gravity as the breakdown of conformal invariance
Amelino-Camelia, Giovanni; Gubitosi, Giulia; Magueijo, Joao
2015-01-01
We propose that at the beginning of the universe gravity existed in a limbo either because it was switched off or because it was only conformally coupled to all particles. This picture can be reverse-engineered from the requirement that the cosmological perturbations be (nearly) scale-invariant without the need for inflation. It also finds support in recent results in quantum gravity suggesting that spacetime becomes two-dimensional at super-Planckian energies. We advocate a novel top-down approach to cosmology based on the idea that gravity and the Big Bang Universe are relics from the mechanism responsible for breaking the fundamental conformal invariance. Such a mechanism should leave clear signatures in departures from scale-invariance in the primordial power spectrum and the level of gravity waves generated.
Katsuya Hasegawa; de Campos, Priscila S.; Zeredo, Jorge L.; Yasuhiro Kumei
2014-01-01
The ability to maintain the body relative to the external environment is important for adaptation to altered gravity. However, the physiological limits for adaptation or the disruption of body orientation are not known. In this study, we analyzed postural changes in mice upon exposure to various low gravities. Male C57BL6/J mice (n = 6) were exposed to various gravity-deceleration conditions by customized parabolic flight-maneuvers targeting the partial-gravity levels of 0.60, 0.30, 0.15 and...
FEM structural analysis of ITER gravity supports
International Nuclear Information System (INIS)
Because of the complexity of the load cases, the gravity support of ITER endures several large forces during operation besides the dead weight of the magnet system, such as electromagnetic force on the magnets, thermal load and seismic loads (SL). In order to verify the reliability of the design, and make the gravity support operate safely under the various load cases, it is very important to analyze the applied force on the gravity support in different load cases. In this paper, finite-element-method (FEM) is used for the structural analysis. 3-D FEM models of the overall gravity support system, with 20 degree sector and 360 degree respectively, are created by ANSYS according to different load cases. The 20 degree model in the torus is used for the structural analysis of the gravity support system under the several symmetric load combinations, and the 360 degree model is used for the structural analysis under the load combinations with the asymmetric SL. The analysis results are given, such as the static structural analysis and the buckling analysis for the different load combinations, and the modal analysis for the natural frequencies. The calculation results reveal that all of the gravity support components have enough safety margins against various load combinations. (authors)
Unification of Gravity and Electromagnetism and Cosmology
Ghose, Partha
2016-01-01
It is first argued that radiation by a uniformly accelerated charge in flat space-time indicates the need for a unified geometric theory of gravity and electromagnetism. Such a theory, based on a metric-affine $U_4$ manifold, is constructed with the torsion pseudo-vector $\\Gamma_\\mu$ linking gravity and electromagnetism. This conceptually simple extension results in (i) Einstein's equations being modified by a vacuum energy $\\Gamma_\\mu\\Gamma_\
Forward Modeling of Gravity, Gravity Gradients,and Magnetic Anomalies due to Complex Bodies
Institute of Scientific and Technical Information of China (English)
Luo Yao; Yao Changli
2007-01-01
On the basis of the results of improved analytical expression of computation of gravity anomalies due to a homogeneous polyhedral body composed of polygonal facets, and applying the forward theory with the coordinate transformation of vectors and tensors, we deduced both the analytical expressions for gravity gradient tensors and for magnetic anomalies of a polygon, and obtained new analytical expressions for computing vertical gradients of gravity anomalies and vertical component of magnetic anomalies caused by a polyhedral body. And also we developed explicitly the complete unified expressions for the calculation of gravity anomalies, gravity gradient, and magnetic anomalies due to the homogeneous polyhedron. Furthermore, we deduced new analytical expressions for computing vertical gradients of gravity anomalies due to a finite rectangular prism by applying the newly obtained expressions for gravity gradient tensors due to a polyhedral target body. Comparison with forward calculation of models shows the correctness of these new expressions. It will reduce forward calculation time of gravity-magnetic anomalies and improve computational efficiency by applying our unified expressions for joint forward modeling of gravity-magnetic anomalies due to homogeneous polyhedral bodies.
The Branching of Graphs in 2-d Quantum Gravity
Harris, M. G.
1996-01-01
The branching ratio is calculated for three different models of 2d gravity, using dynamical planar phi-cubed graphs. These models are pure gravity, the D=-2 Gaussian model coupled to gravity and the single spin Ising model coupled to gravity. The ratio gives a measure of how branched the graphs dominating the partition function are. Hence it can be used to estimate the location of the branched polymer phase for the multiple Ising model coupled to 2d gravity.
Gravity Analysis of the Jeffera Basin, Tunisia
Mickus, K.; Gabtni, H.; Jallouli, C.
2004-12-01
Southern Tunisia consists of two main tectonic provinces: 1) the Saharan Platform and 2) the folded Atlasic domain, separated by the North Saharan Flexure. The Saharan Platform, which contains the Ghadames Basin and the Telemzane Arch, consists of gently dipping Paleozoic strata overlain by Triassic to Cretaceous sediments. The Atlasic domain consists of a thicker sequence of mainly Mesozoic and younger rock with less complete sequences of Paleozoic strata. Within the Atlasic domain are the still actively subsiding Chotts and Jeffera basins. The Jeffera basin, which occurs to the east of the Telemzane Arch contains at least eight kilometers of Paleozoic and younger sediment that were formed during numerous subsidence episodes since Carboniferous time. The Jeffera basin is dominated by tilted fault blocks that were formed during numerous tectonic episodes. Several unpublished seismic reflection profiles and well data exist for the Jeffera basin, however a deep structural analysis of the basin has not been published. We examined the existing gravity data in conjunction with available well and geologic data to determine structural features within the basin. The Bouguer gravity anomaly map shows that the Jeffera basin is dominated by a narrow northwest-trending gravity minimum. However, a more detailed analysis consisting of wavelength filtering and edge enhancements indicate that the structure of the basin is more complicated than indicated by the Bouguer gravity anomaly map. A residual gravity anomaly map indicates that the Jeffera basin consists of at least three and maybe four subbasins. Additionally, the Jeffera Fault marks the boundary between northwest-trending gravity anomalies to its northeast and east-trending anomalies over the Saharan Platform. The above observation is amplified by the construction of the enhanced horizontal derivatives (EHG) of both the complete Bouguer gravity and the residual gravity anomaly maps. The EHG maps highlight the lateral
Reduction of gravity-matter and dS gravity to hypersurface
Park, I.Y.
2015-01-01
The quantization scheme based on reduction of the physical states \\cite{Park:2014tia} is extended to two gravity-matter systems and pure dS gravity. For the gravity-matter systems we focus on quantization in a flat background for simplicity, and renormalizability is established through conversion of matter degrees of freedom to the metric degrees of freedom. Quantization of pure dS gravity has several new novel features. It is noted that the infrared divergence does not arise in the present s...
Equations of motion in relativistic gravity
Lämmerzahl, Claus; Schutz, Bernard
2015-01-01
The present volume aims to be a comprehensive survey on the derivation of the equations of motion, both in General Relativity as well as in alternative gravity theories. The topics covered range from the description of test bodies, to self-gravitating (heavy) bodies, to current and future observations. Emphasis is put on the coverage of various approximation methods (e.g., multipolar, post-Newtonian, self-force methods) which are extensively used in the context of the relativistic problem of motion. Applications discussed in this volume range from the motion of binary systems -- and the gravitational waves emitted by such systems -- to observations of the galactic center. In particular the impact of choices at a fundamental theoretical level on the interpretation of experiments is highlighted. This book provides a broad and up-do-date status report, which will not only be of value for the experts working in this field, but also may serve as a guideline for students with background in General Relativity who ...
Directory of Open Access Journals (Sweden)
Claudia de Rham
2014-08-01
Full Text Available We review recent progress in massive gravity. We start by showing how different theories of massive gravity emerge from a higher-dimensional theory of general relativity, leading to the Dvali–Gabadadze–Porrati model (DGP, cascading gravity, and ghost-free massive gravity. We then explore their theoretical and phenomenological consistency, proving the absence of Boulware–Deser ghosts and reviewing the Vainshtein mechanism and the cosmological solutions in these models. Finally, we present alternative and related models of massive gravity such as new massive gravity, Lorentz-violating massive gravity and non-local massive gravity.
Polar ring galaxies as tests of gravity
Lüghausen, F; Kroupa, P; Angus, G; Combes, F; Gentile, G; Tiret, O; Zhao, H
2013-01-01
Polar ring galaxies are ideal objects with which to study the three-dimensional shapes of galactic gravitational potentials since two rotation curves can be measured in two perpendicular planes. Observational studies have uncovered systematically larger rotation velocities in the extended polar rings than in the associated host galaxies. In the dark matter context, this can only be explained through dark halos that are systematically flattened along the polar rings. Here, we point out that these objects can also be used as very effective tests of gravity theories, such as those based on Milgromian dynamics (MOND). We run a set of polar ring models using both Milgromian and Newtonian dynamics to predict the expected shapes of the rotation curves in both planes, varying the total mass of the system, the mass of the ring with respect to the host, as well as the size of the hole at the center of the ring. We find that Milgromian dynamics not only naturally leads to rotation velocities being typically higher in th...
Extreme neutron stars from Extended Theories of Gravity
Energy Technology Data Exchange (ETDEWEB)
Astashenok, Artyom V. [I. Kant Baltic Federal University, Institute of Physics and Technology, Nevskogo st. 14, Kaliningrad, 236041 (Russian Federation); Capozziello, Salvatore [Dipartimento di Fisica, Università di Napoli ' ' Federico II' ' , Via Cinthia, 9, Napoli, I-80126 Italy (Italy); Odintsov, Sergei D., E-mail: artyom.art@gmail.com, E-mail: capozziello@na.infn.it, E-mail: odintsov@ieec.uab.es [Instituciò Catalana de Recerca i Estudis Avançats (ICREA), Barcelona (Spain)
2015-01-01
We discuss neutron stars with strong magnetic mean fields in the framework of Extended Theories of Gravity. In particular, we take into account models derived from f(R) and f(G) extensions of General Relativity where functions of the Ricci curvature invariant R and the Gauss-Bonnet invariant G are respectively considered. Dense matter in magnetic mean field, generated by magnetic properties of particles, is described by assuming a model with three meson fields and baryons octet. As result, the considerable increasing of maximal mass of neutron stars can be achieved by cubic corrections in f(R) gravity. In principle, massive stars with M > 4M{sub ☉} can be obtained. On the other hand, stable stars with high strangeness fraction (with central densities ρ{sub c} ∼ 1.5–2.0 GeV/fm{sup 3}) are possible considering quadratic corrections of f(G) gravity. The magnetic field strength in the star center is of order 6–8 × 10{sup 18} G. In general, we can say that other branches of massive neutron stars are possible considering the extra pressure contributions coming from gravity extensions. Such a feature can constitute both a probe for alternative theories and a way out to address anomalous self-gravitating compact systems.
Extreme neutron stars from Extended Theories of Gravity
International Nuclear Information System (INIS)
We discuss neutron stars with strong magnetic mean fields in the framework of Extended Theories of Gravity. In particular, we take into account models derived from f(R) and f(G) extensions of General Relativity where functions of the Ricci curvature invariant R and the Gauss-Bonnet invariant G are respectively considered. Dense matter in magnetic mean field, generated by magnetic properties of particles, is described by assuming a model with three meson fields and baryons octet. As result, the considerable increasing of maximal mass of neutron stars can be achieved by cubic corrections in f(R) gravity. In principle, massive stars with M > 4M☉ can be obtained. On the other hand, stable stars with high strangeness fraction (with central densities ρc ∼ 1.5–2.0 GeV/fm3) are possible considering quadratic corrections of f(G) gravity. The magnetic field strength in the star center is of order 6–8 × 1018 G. In general, we can say that other branches of massive neutron stars are possible considering the extra pressure contributions coming from gravity extensions. Such a feature can constitute both a probe for alternative theories and a way out to address anomalous self-gravitating compact systems
Institute of Scientific and Technical Information of China (English)
赵海霞; 蒋晓威; 崔建鑫
2014-01-01
工业污染重心路径演变是制造业转移过程中形成的环境空间响应形式,为探明经济发达的泛长三角地区工业污染重心对制造业转移的响应关系,采用2000~2010年工业污染排放数据,运用重心模型,测算各年份工业废水、废气和固废排放重心坐标,分析工业污染重心转移路径及演变规律,探讨重心演变的驱动机制.结果表明：①泛长三角地区的工业污染重心发生了偏移,其中工业固废偏移距离最大,为180.18 km,而工业废水、废气偏移的方向最大,分别为0.40°、0.17°；②工业污染重心轨迹偏移受多种因素的驱动影响.其中,安徽、江西地区重工业的高速发展加剧了污染重心朝西部偏移；以江苏、上海、浙江为代表的长三角地区产业结构优化与调整在一定程度上缓解了该地区的工业污染,安徽、江西地区高污染产业份额的增加及宽松的宏观区域政策助推了工业污染向西部地区偏移；而大规模的清洁化生产、较强的环境治理力度和完善的环保监测制度在一定程度上减缓了工业污染朝东部地区偏移.%Shifting path of industrial pollution gravity centers is the response of environmental special formation during the industry transfer process, in order to prove the responding of industrial pollution gravity centers to industry transfer in economically developed areas, this paper calculates the gravity centers of industrial wastewater, gas and solid patterns and reveals the shifting path and its driving mechanism, using the data of industrial pollution in the Pan-Yangtze River Delta from 2000 to 2010. The results show that the gravity center of the industrial waste in Pan-Yangtze River Delta shifts for sure in the last 10 years, and gravity center of solid waste shifts the maximum distance within the three wastes, which was 180. 18 km, and shifting distances for waste gas and waste water were 109. 51 km and 85. 92 km
Effects of gravity modulation on convection in a horizontal annulus
Energy Technology Data Exchange (ETDEWEB)
Dyko, Mark P. [Aircraft Braking Systems Corporation, Akron, Ohio (United States). Research and Technology; Vafai, Kambiz [University of California, Riverside, CA (United States). Department of Mechanical Engineering
2007-01-15
Convection in the annulus between two horizontal coaxial cylinders resulting from gravity modulation in a microgravity environment is investigated for the first time. The three-dimensional transient equations of fluid motion and heat transfer are solved to study the unsteady flow structures in a large-gap annulus. The gravity fluctuations are shown to induce recirculating flows that reverse direction of rotation in response to the gravitational reversals. Except for a short period of time following flow reversal, at low modulation frequencies the centers of rotation of these flows are below and above the horizontal angular plane when the acceleration acts in the upward and downward directions, respectively, whereas at high frequencies they are above and below this plane. The effects of gravity modulation on development of secondary flows that arise in narrow- and moderate-gap annuli owing to thermal instability are also investigated. It is found that supercritical transverse rolls repeatedly form, dissipate, and re-form in the upper and lower regions of a narrow-gap annulus as a result of the fluctuating gravity field. At the same frequency, the supercritical rolls in a moderate-gap annulus are much slower to develop between flow reversals. The results show that gravity modulation has a stabilizing effect on the secondary flows compared to the case of a constant gravity force, and this effect diminishes with reduction in either frequency or annulus radius ratio R. The effects of frequency on heat transfer in large-, moderate-, and narrow-gap annuli are also studied. It is found that the time-averaged Nusselt number approaches that of pure conduction at high frequencies and increases toward that for terrestrial natural convection as frequency is reduced. As R is decreased, the increase in time-averaged Nusselt number brought about by reducing frequency becomes a smaller percentage of the value for terrestrial natural convection. The results for large-, moderate
Effect of gravity on vertical eye position.
Pierrot-Deseilligny, C
2009-05-01
There is growing evidence that gravity markedly influences vertical eye position and movements. A new model for the organization of brainstem upgaze pathways is presented in this review. The crossing ventral tegmental tract (CVTT) could be the efferent tract of an "antigravitational" pathway terminating at the elevator muscle motoneurons in the third nerve nuclei and comprising, upstream, the superior vestibular nucleus and y-group, the flocculus, and the otoliths. This pathway functions in parallel to the medial longitudinal fasciculus pathways, which control vertical eye movements made to compensate for all vertical head movements and may also comprise the "gravitational" vestibular pathways, involved in the central reflection of the gravity effect. The CVTT could provide the upgaze system with the supplement of tonic activity required to counteract the gravity effect expressed in the gravitational pathway, being permanently modulated according to the static positions of the head (i.e., the instantaneous gravity vector) between a maximal activity in the upright position and a minimal activity in horizontal positions. Different types of arguments support this new model. The permanent influence of gravity on vertical eye position is strongly suggested by the vertical slow phases and nystagmus observed after rapid changes in hypo- or hypergravity. The chin-beating nystagmus, existing in normal subjects with their head in the upside-down position, suggests that gravity is not compensated for in the downgaze system. Upbeat nystagmus due to brainstem lesions, most likely affecting the CVTT circuitry, is improved when the head is in the horizontal position, suggesting that this circuitry is involved in the counteraction of gravity between the upright and horizontal positions of the head. In downbeat nystagmus due to floccular damage, in which a permanent hyperexcitation of the CVTT could exist, a marked influence of static positions of the head is also observed. Finally
Measurement of absolute gravity acceleration in Firenze
Directory of Open Access Journals (Sweden)
M. de Angelis
2011-01-01
Full Text Available This paper reports the results from the accurate measurement of the acceleration of gravity g taken at two separate premises in the Polo Scientifico of the University of Firenze (Italy. In these laboratories, two separate experiments aiming at measuring the Newtonian constant and testing the Newtonian law at short distances are in progress. Both experiments require an independent knowledge on the local value of g. The only available datum, pertaining to the italian zero-order gravity network, was taken more than 20 years ago at a distance of more than 60 km from the study site. Gravity measurements were conducted using an FG5 absolute gravimeter, and accompanied by seismic recordings for evaluating the noise condition at the site. The absolute accelerations of gravity at the two laboratories are (980 492 160.6 ± 4.0 μGal and (980 492 048.3 ± 3.0 μGal for the European Laboratory for Non-Linear Spectroscopy (LENS and Dipartimento di Fisica e Astronomia, respectively. Other than for the two referenced experiments, the data here presented will serve as a benchmark for any future study requiring an accurate knowledge of the absolute value of the acceleration of gravity in the study region.
Measurement of absolute gravity acceleration in Firenze
de Angelis, M.; Greco, F.; Pistorio, A.; Poli, N.; Prevedelli, M.; Saccorotti, G.; Sorrentino, F.; Tino, G. M.
2011-01-01
This paper reports the results from the accurate measurement of the acceleration of gravity g taken at two separate premises in the Polo Scientifico of the University of Firenze (Italy). In these laboratories, two separate experiments aiming at measuring the Newtonian constant and testing the Newtonian law at short distances are in progress. Both experiments require an independent knowledge on the local value of g. The only available datum, pertaining to the italian zero-order gravity network, was taken more than 20 years ago at a distance of more than 60 km from the study site. Gravity measurements were conducted using an FG5 absolute gravimeter, and accompanied by seismic recordings for evaluating the noise condition at the site. The absolute accelerations of gravity at the two laboratories are (980 492 160.6 ± 4.0) μGal and (980 492 048.3 ± 3.0) μGal for the European Laboratory for Non-Linear Spectroscopy (LENS) and Dipartimento di Fisica e Astronomia, respectively. Other than for the two referenced experiments, the data here presented will serve as a benchmark for any future study requiring an accurate knowledge of the absolute value of the acceleration of gravity in the study region.
The Center of Mass of a Soft Spring
Serna, Juan D.; Joshi, Amitabh
2011-01-01
This article uses calculus to find the center of mass of a soft, vertically suspended, cylindrical helical spring, which necessarily is stretched non-uniformly by the action of gravity. A general expression for the vertical position of the center of mass is obtained and compared with other results in the literature.
Semiclassical analysis of loop quantum gravity
Energy Technology Data Exchange (ETDEWEB)
Conrady, F.
2005-10-17
In this Ph.D. thesis, we explore and develop new methods that should help in determining an effective semiclassical description of canonical loop quantum gravity and spin foam gravity. A brief introduction to loop quantum gravity is followed by three research papers that present the results of the Ph.D. project. In the first article, we deal with the problem of time and a new proposal for implementing proper time as boundary conditions in a sum over histories: we investigate a concrete realization of this formalism for free scalar field theory. In the second article, we translate semiclassical states of linearized gravity into states of loop quantum gravity. The properties of the latter indicate how semiclassicality manifests itself in the loop framework, and how this may be exploited for doing semiclassical expansions. In the third part, we propose a new formulation of spin foam models that is fully triangulation- and background-independent: by means of a symmetry condition, we identify spin foam models whose triangulation-dependence can be naturally removed. (orig.)
Semiclassical analysis of loop quantum gravity
International Nuclear Information System (INIS)
In this Ph.D. thesis, we explore and develop new methods that should help in determining an effective semiclassical description of canonical loop quantum gravity and spin foam gravity. A brief introduction to loop quantum gravity is followed by three research papers that present the results of the Ph.D. project. In the first article, we deal with the problem of time and a new proposal for implementing proper time as boundary conditions in a sum over histories: we investigate a concrete realization of this formalism for free scalar field theory. In the second article, we translate semiclassical states of linearized gravity into states of loop quantum gravity. The properties of the latter indicate how semiclassicality manifests itself in the loop framework, and how this may be exploited for doing semiclassical expansions. In the third part, we propose a new formulation of spin foam models that is fully triangulation- and background-independent: by means of a symmetry condition, we identify spin foam models whose triangulation-dependence can be naturally removed. (orig.)
Gravity and Anti-gravity of Fermions: the Unification of Dark Matter and Dark Energy
Chen, X S
2005-01-01
Massive gravity with second and fourth derivatives is shown to give both attractive and repulsive gravity between fermions. In contrast to the attractive gravity correlated with energy-momentum tensor, the repulsive gravity is proportional to the graviton mass. Therefore, weakly interacting fermions with energy smaller than the graviton mass are both dark matter and dark energy: Their overall gravity is attractive with normal matter but repulsive among themselves. Detailed analyses reveal that this unified dark scenario can properly account for the observed dark matter/energy phenomena: galaxy rotation curves, transition from early cosmic deceleration to recent acceleration; and naturally overcome other dark scenarios' difficulties: the substructure and cuspy core problems, the difference of dark halo distributions in galaxies and clusters, and the cosmic coincidence.
Aspects of general higher-order gravities
Bueno, Pablo; Min, Vincent S; Visser, Manus R
2016-01-01
We study several aspects of higher-order gravities constructed from general contractions of the Riemann tensor and the metric in arbitrary dimensions. First, we use the fast-linearization procedure presented in arXiv:1607.06463 to obtain the equations satisfied by the metric perturbation modes on a maximally symmetric background in the presence of matter and to classify $\\mathcal{L}($Riemann$)$ theories according to their spectrum. Then, we linearize all theories up to quartic order in curvature and use this result to construct quartic versions of Einsteinian cubic gravity (ECG). In addition, we show that the most general cubic gravity constructed in a dimension-independent way and which does not propagate the ghost-like spin-2 mode (but can propagate the scalar) is a linear combination of $f($Lovelock$)$ invariants, plus the ECG term, plus a New ghost-free gravity term. Next, we construct the generalized Newton potential and the Post-Newtonian parameter $\\gamma$ for general $\\mathcal{L}($Riemann$)$ gravities...
Conformal classes of Brans-Dicke gravity
Quirós, I
1999-01-01
A classification of Brans-Dicke theories of gravitation, based on the behaviour of the dimensionless gravitational coupling constant, is given. It is noted that the discussion takes place in the current literature, about which of the two distinguished conformal frames in which scalar-tensor theories of gravity can be formulated: the Jordan frame and the Einstein frame, is the physical one, may, in most cases, be meaningless for both frames may belong to the same conformal class. It is also noted that the Jordan frame formulation of Brans-Dicke gravity with ordinary matter nonminimally coupled is scale-invariant, unlike the situation with the Jordan frame formulation of Brans-Dicke gravity with matter minimally coupled (the original formulation of Brans-Dicke theory), where the presence of nonzero mass ordinary matter breaks the scale-invariance of the theory.
Simulation of Gravity Currents Using VOF Model
Institute of Scientific and Technical Information of China (English)
邹建锋; 黄钰期; 应新亚; 任安禄
2002-01-01
By the Volume of Fluid (VOF) multiphase flow model two-dimensional gravity currents with three phases including air are numerically simulated in this article. The necessity of consideration of turbulence effect for high Reynolds numbers is demonstrated quantitatively by LES (the Large Eddy Simulation) turbulence model. The gravity currents are simulated for h ≠ H as well as h = H, where h is the depth of the gravity current before the release and H is the depth of the intruded fluid. Uprising of swell occurs when a current flows horizontally into another lighter one for h ≠ H. The problems under what condition the uprising of swell occurs and how long it takes are considered in this article. All the simulated results are in reasonable agreement with the experimental results available.
Virtual Gravity and the Duality of Reality
Harokopos, E
2003-01-01
It is shown that a hypothesis about gravity having a virtual cause implies there are two primary reference frames, a reality and a functional virtual reality and an equivalence principle relating the two is postulated. A mathematical expression relating the primary reference frames to the state of reality provides an explanation of particle-wave duality and resolves the controversy about the speed of gravity. A model for motion, time and particle formation is briefly discussed, in which the hypothesis about the virtual cause of gravity and supporting postulates are valid. It is further shown that such model provides solutions to unsolved paradoxes and a unification of consistent but contradictory ancient theories of matter and motion. Finally, a reference is made about the basis for devising experiments and testing the predictions of the model.
Gravity-Off-loading System for Large-Displacement Ground Testing of Spacecraft Mechanisms
Han, Olyvia; Kienholz, David; Janzen, Paul; Kidney, Scott
2010-01-01
Gravity-off-loading of deployable spacecraft mechanisms during ground testing is a long-standing problem. Deployable structures which are usually too weak to support their own weight under gravity require a means of gravity-off-loading as they unfurl. Conventional solutions to this problem have been helium-filled balloons or mechanical pulley/counterweight systems. These approaches, however, suffer from the deleterious effects of added inertia or friction forces. The changing form factor of the deployable structure itself and the need to track the trajectory of the center of gravity also pose a challenge to these conventional technologies. This paper presents a novel testing apparatus for high-fidelity zero-gravity simulation for special application to deployable space structures such as solar arrays, magnetometer booms, and robotic arms in class 100,000 clean room environments
Thermodynamics of black holes in rainbow gravity
Banerjee, Ritwick
2016-01-01
In this paper, we investigate the thermodynamic properties of black holes under the influence of rainbow gravity. In the metric of Schwarzschild, Reissner-Nordstrom and Reissner-Nordstrom-de-Sitter black hole surrounded by quintessence, we consider a rainbow function and derive the existence of remnant and critical masses of a black hole. Using the Hawking temperature relation we derive the heat capacity and the entropy of the rainbow gravity inspired black holes and closely study the relation between entropy and area of the horizon for different values of n of the rainbow function.
Fermion's tunnelling with effects of quantum gravity
Chen, Deyou; Yang, Haitang
2013-01-01
In this paper, using Hamilton-Jacobi method, we address the tunnelling of fermions in a 4-dimensional Schwarzschild spacetime. Base on the generalized uncertainty principle, we introduce the influence of quantum gravity. After solving the equation of motion of the spin 1/2 field, we derive the corrected Hawking temperature. It turns out that the correction depends not only on the black hole's mass but also on the mass (energy) of emitted fermions. It is of interest that, in our calculation, the quantum gravity correction decelerates the temperature increase during the radiation explicitly. This observation then naturally leads to the remnants in black hole evaporation. Our calculation shows that the residue mass is $\\gtrsim M_p/\\beta_0$, where $M_p$ is the Planck mass and $\\beta_0$ is a dimensionless parameter accounting for quantum gravity effects. The evaporation singularity is then avoided.
A Hamiltonian Formulation of Topological Gravity
Waelbroeck, Henri
2009-01-01
Topological gravity is the reduction of Einstein's theory to spacetimes with vanishing curvature, but with global degrees of freedom related to the topology of the universe. We present an exact Hamiltonian lattice theory for topological gravity, which admits translations of the lattice sites as a gauge symmetry. There are additional symmetries, not present in Einstein's theory, which kill the local degrees of freedom. We show that these symmetries can be fixed by choosing a gauge where the torsion is equal to zero. In this gauge, the theory describes flat space-times. We propose two methods to advance towards the holy grail of lattice gravity: A Hamiltonian lattice theory for curved space-times, with first-class translation constraints.
Modifications of Einstein's theory of gravity at large distances
2015-01-01
In the last few years modified gravity theories have been proposed as extensions of Einstein's theory of gravity. Their main motivation is to explain the latest cosmological and astrophysical data on dark energy and dark matter. The study of general relativity at small scales has already produced important results (cf e.g. LNP 863 Quantum Gravity and Quantum Cosmology) while its study at large scales is challenging because recent and upcoming observational results will provide important information on the validity of these modified theories. In this volume, various aspects of modified gravity at large scales will be discussed: high-curvature gravity theories; general scalar-tensor theories; Galileon theories and their cosmological applications; F(R) gravity theories; massive, new massive and topologically massive gravity; Chern-Simons modifications of general relativity (including holographic variants) and higher-spin gravity theories, to name but a few of the most important recent developments. Edite...
Spectral analysis of the full gravity tensor
Rummel, R.; van Gelderen, M.
1992-10-01
It is shown that, when the five independent components of the gravity tensor are grouped into (Gamma-zz), (Gamma-xz, Gamma-yz), and (Gamma-xx - Gamma-yy, 2Gamma-xy) sets and expanded into an infinite series of pure-spin spherical harmonic tensors, it is possible to derive simple eigenvalue connections between these three sets and the spherical harmonic expansion of the gravity potential. The three eigenvalues are (n + 1)(n + 2), -(n + 2) sq rt of n(n + 1), and sq rt of (n - 1)n(n + 1)(n + 2). The joint ESA and NASA Aristoteles mission is designed to measure with high precision the tensor components Gamma-zz, Gamma-yz, and Gamma-yy, which will make it possible to determine the global gravity field in six months time with a high precision.
Geoid of Nepal from airborne gravity survey
DEFF Research Database (Denmark)
Forsberg, René; Olesen, Arne Vestergaard; Einarsson, Indriði;
2011-01-01
An airborne gravity survey of Nepal was carried out December 2010 in a cooperation between DTU-Space, Nepal Survey Department, and NGA, USA. The entire country was flown with survey lines spaced 6 nm with a King Air aircraft, with a varying flight altitude from 4 to 10 km. The survey operations...... were a major challenge due to excessive jet streams at altitude as well as occasional excessive mountain waves. Despite the large 400 mGal+ range of gravity anomaly changes from the Indian plains to the Tibetan Plateau, results appear accurate to a few mGal, with proper evaluation from cross...... as well as recent GPS-heights of Mt. Everest. The new airborne data also provide an independent validation of GOCE gravity field results at the local ~100 km resolution scale....
Thermodynamics of gravity favours Weak Censorship Conjecture
Acquaviva, Giovanni; Hamid, Aymen I M; Maharaj, Sunil D
2015-01-01
We use the formulation of thermodynamics of gravity as proposed by Clifton, Ellis and Tavakol on the gravitational collapse of dustlike matter, that violates the strong or weak cosmic censorship conjecture depending on the initial data. We transparently demonstrate that the gravitational entropy prefers the scenario where the stronger version is violated but the weak censorship conjecture is satisfied. This is a novel result, showing the weak cosmic censorship and hence the future asymptotically simple structure of spacetime, is being validated by the nature of gravity, without imposing any extra constraint on the form of matter.
Cui, Weiguang; Yang, Xiaohu
2010-01-01
A large fraction of cosmological information on dark energy and gravity is encoded in the nonlinear regime. Precision cosmology thus requires precision modeling of nonlinearities in general dark energy and modified gravity models. We modify the Gadget-2 code and run a series of N-body simulations on modified gravity cosmology to study the nonlinearities. The modified gravity model that we investigate in the present paper is characterized by a single parameter \\zeta, which determines the enhancement of particle acceleration with respect to general relativity (GR), given the identical mass distribution (\\zeta = 1 in GR). The first nonlinear statistics we investigate is the nonlinear matter power spectrum at k < 3h/Mpc, which is the relevant range for robust weak lensing power spectrum modeling at l < 2000. In this study, we focus on the relative difference in the nonlinear power spectra at corresponding redshifts where different gravity models have the same linear power spectra. This particular statistics...
Violation of Energy Bounds in Designer Gravity
Hertog, Thomas
2006-01-01
We continue our study of the stability of designer gravity theories, where one considers anti-de Sitter gravity coupled to certain tachyonic scalars with boundary conditions defined by a smooth function W. It has recently been argued there is a lower bound on the conserved energy in terms of the global minimum of W, if the scalar potential arises from a superpotential P and the scalar reaches an extremum of P at infinity. We show, however, there are superpotentials for which these bounds do n...
Eddington's theory of gravity and its progeny.
Bañados, Máximo; Ferreira, Pedro G
2010-07-01
We resurrect Eddington's proposal for the gravitational action in the presence of a cosmological constant and extend it to include matter fields. We show that the Newton-Poisson equation is modified in the presence of sources and that charged black holes show great similarities with those arising in Born-Infeld electrodynamics coupled to gravity. When we consider homogeneous and isotropic space-times, we find that there is a minimum length (and maximum density) at early times, clearly pointing to an alternative theory of the big bang. We thus argue that the modern formulation of Eddington's theory, Born-Infeld gravity, presents us with a novel, nonsingular description of the Universe.
Nonlinear Properties of Vielbein Massive Gravity
Nibbelink, S G; Sexton, M; Nibbelink, Stefan Groot; Peloso, Marco; Sexton, Matthew
2006-01-01
We consider a special theory of massive gravity, which is obtained in a decoupling limit from a bi-gravity theory in the vielbein formulation, with only cosmological constant-like interactions between the two gravitational sectors. We investigate this theory using the Stueckelberg method, and construct a 't Hooft-Feynman gauge fixing in which the tensor, vector and scalar Stueckelberg fields are decoupled. We prove that this model has the softest possible ultraviolet behavior which can be expected from any generic (Lorentz invariant) theory of massive gravity, namely that it becomes strong only at the scale Lambda_3 = (m_g^2 M_P)^{1/3} . Finally, we confirm that also this model is plagued by a ghost instability, which, in the Stueckelberg formalism, arises from quartic scalar-vector and scalar-tensor interactions.
On Poincaré gauge theory of gravity, its equations of motion, and Gravity Probe B
International Nuclear Information System (INIS)
We discuss the structure of the Poincaré gauge theory of gravity (PG) that can be considered as the standard theory of gravity with torsion. We reconfirm that torsion, in the context of PG, couples only to the elementary particle spin and under no circumstances to the orbital angular momentum of test particles. We conclude that, unfortunately, the investigations of Mao et al. (2007) and March et al. (2011)—who claimed a coupling of torsion to orbital angular momentum, in particular in the context of the Gravity Probe B (GPB) experiment—do not yield any information on torsion
On Poincaré gauge theory of gravity, its equations of motion, and Gravity Probe B
Energy Technology Data Exchange (ETDEWEB)
Hehl, Friedrich W., E-mail: hehl@thp.uni-koeln.de [Institute for Theoretical Physics, University of Cologne, 50923 Köln (Germany); Department of Physics and Astronomy, University of Missouri, Columbia, MO 65211 (United States); Obukhov, Yuri N., E-mail: yo@thp.uni-koeln.de [Theoretical Physics Laboratory, Nuclear Safety Institute, Russian Academy of Sciences, B. Tulskaya 52, 115191 Moscow (Russian Federation); Puetzfeld, Dirk, E-mail: dirk.puetzfeld@zarm.uni-bremen.de [ZARM, University of Bremen, Am Fallturm, 28359 Bremen (Germany)
2013-10-30
We discuss the structure of the Poincaré gauge theory of gravity (PG) that can be considered as the standard theory of gravity with torsion. We reconfirm that torsion, in the context of PG, couples only to the elementary particle spin and under no circumstances to the orbital angular momentum of test particles. We conclude that, unfortunately, the investigations of Mao et al. (2007) and March et al. (2011)—who claimed a coupling of torsion to orbital angular momentum, in particular in the context of the Gravity Probe B (GPB) experiment—do not yield any information on torsion.
On unification of gravity and gauge interactions
Chamseddine, Ali; Mukhanov, Viatcheslav
2016-01-01
Considering a higher dimensional Lorentz group as the symmetry of the tangent space, we unify gravity and gauge interactions in a natural way. The spin connection of the gauged Lorentz group is then responsible for both gravity and gauge fields, and the action for the gauged fields becomes part of the spin curvature squared. The realistic group which unifies all known particles and interactions is the SO(1, 13) Lorentz group whose gauge part leads to SO(10) grand unified theory and contains d...
Stability of the Einstein static universe in modified theories of gravity
Boehmer, Christian G.; Hollenstein, Lukas; Lobo, Francisco S N; Seahra, Sanjeev S.
2010-01-01
We present a brief overview of the stability analysis of the Einstein static universe in various modified theories of gravity, like f(R) gravity, Gauss-Bonnet or f(G) gravity, and Horava-Lifshitz gravity.
Symmetries of linearized gravity from adjoint operators
Aksteiner, Steffen
2016-01-01
Using a covariant formulation it is shown that the Teukolsky equation and the Teukolsky-Starobinsky identities for spin-1 and linearized gravity on a vacuum type D background are self-adjoint. This fact is used to construct symmetry operators for each of the four cases. We find both irreducible second order symmetry operators for spin-1, a known fourth order, and a new sixth order symmetry operator for linearized gravity. The results are connected to Hertz and Debye potentials and to the separability of the Teukolsky equation.
Institute of Scientific and Technical Information of China (English)
程战员; 郑思莉; 宋宁宁
2012-01-01
This paper first presents an evaluation index system of symmetry factors and verified its rationality and scientific.And then established the mathematical optimization model of maximize mate selection satisfaction based on the trapezoidal fuzzy number and fuzzy theory of gravity.Finally,the model has been verified by a practical example and seeks out the best matrimony object.%构造了一种择偶因素的评价指标体系,并对构造的合理性与科学性进行了验证,基于梯形模糊数和模糊重心理论建立了择偶满意度最大化的数学优化模型。对模型进行了实践验证,求出了最佳的婚配对象。
Effect of Gravity on Surface Tension
Weislogel, M. M.; Azzam, M. O. J.; Mann, J. A.
1998-01-01
Spectroscopic measurements of liquid-vapor interfaces are made in +/- 1-g environments to note the effect of gravity on surface tension. A slight increase is detected at -1-g0, but is arguably within the uncertainty of the measurement technique. An increased dependence of surface tension on the orientation and magnitude of the gravitational vector is anticipated as the critical point is approached.
Loop formulation of gauge theory and gravity
Loll, R.
1993-01-01
This chapter contains a overview of the loop formulation of Yang-Mills theory and 3+1-dimensional gravity in the Ashtekar form. Since the configuration space of these theories are spaces of gauges potentials, their classical and quantum descriptions may be given in terms of gauges-invariant Wilson
Extremal Black Hole in a Nonlinear Newtonian Theory of Gravity
Good, Michael R R
2008-01-01
This work investigates an upper-limit of charge for a black hole in a nonlinear Newtonian theory of gravity. The charge is accumulated via protons fired isotropically at the black hole. This theoretical study of gravity (known as `pseudo-Newtonian') is a forced merger of special relativity and Newtonian gravity. Whereas the source of Newton's gravity is purely mass, pseudo-Newtonian gravity includes effects of fields around the mass, giving a more complete picture of how gravity behaves. Interestingly, pseudo-Newtonian gravity predicts such relativistic phenomena as black holes and deviations from Kepler's laws, but of course, provides a less accurate picture than general relativity. Though less accurate, it offers an easier approach to understanding some results of general relativity, and merits interest due to its simplicity. The method of study applied here examines the predictions of pseudo-Newtonian gravity for a particle interacting with a highly charged black hole. A black hole with a suitable charge w...
Moduli Space of Topological 2-form Gravity
Abe, Mitsuko; Nakamichi, A.; Ueno, T.
1993-01-01
We propose a topological version of four-dimensional (Euclidean) Einstein gravity, in which anti-self-dual 2-forms and an SU(2) connection are used as fundamental fields. The theory describes the moduli space of conformally self-dual Einstein manifolds. In the presence of a cosmological constant, we evaluate the index of the elliptic complex associated with the moduli space.
Gravity Data for the State of New Mexico
National Oceanic and Atmospheric Administration, Department of Commerce — The gravity station data (21,242 records) were compiled by the University of Texas at El Paso. This data base was received in October 1984. Principal gravity...
Multiphase Flow: The Gravity of the Situation
Hewitt, Geoffrey F.
1996-01-01
A brief survey is presented of flow patterns in two-phase, gas-liquid flows at normal and microgravity, the differences between them being explored. It seems that the flow patterns in zero gravity are in general much simpler than those in normal gravity with only three main regimes (namely bubbly, slug and annular flows) being observed. Each of these three regimes is then reviewed, with particular reference to identification of areas of study where investigation of flows at microgravity might not only be interesting in themselves, but also throw light on mechanisms at normal earth gravity. In bubbly flow, the main area of interest seems to be that of bubble coalescence. In slug flow, the extension of simple displacement experiments to the zero gravity case would appear to be a useful option, supplemented by computational fluid dynamics (CFD) studies. For annular flow, the most interesting area appears to be the study of the mechanisms of disturbance waves; it should be possible to extend the region of investigation of the onset and behavior of these waves to much low gas velocities where measurements are clearly much easier.
Initial value formulation of Newtonian gravity
Natario, J
2004-01-01
We show that there exists a remarkable analogy between the initial value formulation of General Relativity and Newton's gravity theory, which can be recast as an evolution problem for a flat metric in R^3. We identify conditions for solutions of both evolution problems to coincide and present examples, including a Newtonian analogue of the warp drive.
On a broken - symmetric theory of gravity
International Nuclear Information System (INIS)
A theory of gravity recently proposed by Zee is examined. The propagation of the special scalar field introduced by this theory is studied in cosmological models, and some problems are pointed out, connected with the possibility of a time-dependent vacuum expectation value for this scalar field. (Author)
Phenomenology of quantum gravity black holes
Energy Technology Data Exchange (ETDEWEB)
Nicolini, Piero [Johann Wolfgang Goethe Universitaet, Frankfurt am Main (Germany); Mureika, Jonas [Loyola Marymount University, Los Angeles, CA (United States); Spallucci, Euro [Universita di Trieste (Italy); INFN, Trieste (Italy); Winstanley, Elizabeth [University of Sheffield, Sheffield (United Kingdom)
2012-07-01
In this contribution we present a new scenario for the production and the evaporation of microscopic black holes in the presence of a quantum gravity induced fundamental length. After a brief analysis of the existing families of quantum gravity improved black hole geometries, we focus on their common thermodynamic behavior, namely the presence of a phase transition to a positive heat capacity cooling down in the final stages of the evaporation even in the non-rotating, neutral case. This fact has important repercussions of the evaporation spectra in terms of new profiles of grey body factors. Quantum gravity black holes would emit soft particles mainly on the brane, a distinctive signatures in marked contrast to results obtained with classical metrics. Then we present a first step in modeling black hole production in a post-semiclassical limit, by employing an effective ultraviolet cut off. We show that the new cross sections approach the usual ''black disk'' form at high energy, while they differ significantly near the fundamental scale. If this behavior is confirmed by all the class of quantum gravity black holes, such novel phenomenology is beyond the reach of current accelerators experiments, but is still potentially observable in ultra-high energy cosmic ray collisions.
Sub-subleading soft gravitons: New symmetries of quantum gravity?
Campiglia, Miguel; Laddha, Alok
2016-01-01
Due to seminal works of Weinberg, Cachazo and Strominger we know that tree level quantum gravity amplitudes satisfy three factorization constraints. Building on previous works which relate two of these constraints to symmetries of quantum gravity at null infinity, we present rather strong evidence that the third constraint is also equivalent to a new set of symmetries of (perturbative) quantum gravity. Our analysis implies that the symmetry group of quantum gravity may be even richer than the...
Gravity Independence of Microchannel Two-Phase Flow Project
National Aeronautics and Space Administration — Most of the amassed two-phase flow and heat transfer knowledge comes from experiments conducted in Earth’s gravity. Space missions span varying gravity...
Scaling of Two-Phase Systems Across Gravity Levels Project
National Aeronautics and Space Administration — There is a defined need for long term earth based testing for the development and deployment of two-phase flow systems in reduced-gravity, including lunar gravity,...
Constraining Gravity with LISA Detections of Binaries
Canizares, Priscilla; Sopuerta, Carlos F
2012-01-01
General Relativity (GR) describes gravitation well at the energy scales which we have so far been able to achieve or detect. However, we do not know whether GR is behind the physics governing stronger gravitational field regimes, such as near neutron stars or massive black-holes (MBHs). Gravitational-wave (GW) astronomy is a promising tool to test and validate GR and/or potential alternative theories of gravity. The information that a GW waveform carries not only will allow us to map the strong gravitational field of its source, but also determine the theory of gravity ruling its dynamics. In this work, we explore the extent to which we could distinguish between GR and other theories of gravity through the detection of low-frequency GWs from extreme-mass-ratio inspirals (EMRIs) and, in particular, we focus on dynamical Chern-Simons modified gravity (DCSMG). To that end, we develop a framework that enables us, for the first time, to perform a parameter estimation analysis for EMRIs in DCSMG. Our model is descr...
The mechanics of gravity-driven faulting
Directory of Open Access Journals (Sweden)
L. Barrows
2010-04-01
Full Text Available Faulting can result from either of two different mechanisms. These involve fundamentally different energetics. In elastic rebound, locked-in elastic strain energy is transformed into the earthquake (seismic waves plus work done in the fault zone. In force-driven faulting, the forces that create the stress on the fault supply work or energy to the faulting process. Half of this energy is transformed into the earthquake and half goes into an increase in locked-in elastic strain. In elastic rebound the locked-in elastic strain drives slip on the fault. In force-driven faulting it stops slip on the fault.
Tectonic stress is reasonably attributed to gravity acting on topography and the Earth's lateral density variations. This includes the thermal convection that ultimately drives plate tectonics. Mechanical analysis has shown the intensity of the gravitational tectonic stress that is associated with the regional topography and lateral density variations that actually exist is comparable with the stress drops that are commonly associated with tectonic earthquakes; both are in the range of tens of bar to several hundred bar.
The gravity collapse seismic mechanism assumes the fault fails and slips in direct response to the gravitational tectonic stress. Gravity collapse is an example of force-driven faulting. In the simplest case, energy that is released from the gravitational potential of the stress-causing topography and lateral density variations is equally split between the earthquake and the increase in locked-in elastic strain.
The release of gravitational potential energy requires a change in the Earth's density distribution. Gravitational body forces are solely dependent on density so a change in the density distribution requires a change in the body forces. This implies the existence of volumetric body-force displacements. The volumetric body-force displacements are in addition to displacements generated by slip on
Tests of modified gravity with dwarf galaxies
International Nuclear Information System (INIS)
In modified gravity theories that seek to explain cosmic acceleration, dwarf galaxies in low density environments can be subject to enhanced forces. The class of scalar-tensor theories, which includes f(R) gravity, predict such a force enhancement (massive galaxies like the Milky Way can evade it through a screening mechanism that protects the interior of the galaxy from this ''fifth'' force). We study observable deviations from GR in the disks of late-type dwarf galaxies moving under gravity. The fifth-force acts on the dark matter and HI gas disk, but not on the stellar disk owing to the self-screening of main sequence stars. We find four distinct observable effects in such disk galaxies: 1. A displacement of the stellar disk from the HI disk. 2. Warping of the stellar disk along the direction of the external force. 3. Enhancement of the rotation curve measured from the HI gas compared to that of the stellar disk. 4. Asymmetry in the rotation curve of the stellar disk. We estimate that the spatial effects can be up to 1 kpc and the rotation velocity effects about 10 km/s in infalling dwarf galaxies. Such deviations are measurable: we expect that with a careful analysis of a sample of nearby dwarf galaxies one can improve astrophysical constraints on gravity theories by over three orders of magnitude, and even solar system constraints by one order of magnitude. Thus effective tests of gravity along the lines suggested by Hui, Nicolis, and Stubbs (2009) and Jain (2011) can be carried out with low-redshift galaxies, though care must be exercised in understanding possible complications from astrophysical effects
The strange equation of quantum gravity
Rovelli, Carlo
2015-01-01
Appeared in the Classical and Quantum Gravity Focus issue: Milestones of general relativity. 7 pages International audience Disavowed by one its fathers, ill defined, never empirically tested, the Wheeler-DeWitt equation has nevertheless had a powerful influence on fundamental physics. A well deserved one.
Quantum Gravity: A Brief History of Ideas and Some Prospects
Carlip, Steven; Ni, Wei-Tou; Woodard, Richard
2015-01-01
We present a bird's-eye survey on the development of fundamental ideas of quantum gravity, placing emphasis on perturbative approaches, string theory, loop quantum gravity, and black hole thermodynamics. The early ideas at the dawn of quantum gravity as well as the possible observations of quantum gravitational effects in the foreseeable future are also briefly discussed.
Nonequilibrium / nonlinear chemical oscillation in the virtual absence of gravity
Fujieda, S.; Mogami, Y.; Moriyasu, K.; Mori, Y.
1999-01-01
The Belousov-Zhabotinsky (BZ) reactions were used as typical examples of a nonlinear system far from equilibrium in connection with biological evolution. The virtual absence of gravity in the present work was given from the free-fall facility of Japan Microgravity Center (JAMIC) in Hokkaido. The reaction solution of BZ reaction was composed of bromate in sulfuric acid, 1,4-cyclohexanedione and ferroin to visualize the time development of patterns of chemical oscillations in the reaction-diffusion system. It is a bubble-free constitution in the aging of the reaction. Therefore, the setup constructed to collect image data via CCD cameras was simplified. The operation sequences of necessary devices were comprised of simple solid state relays which were started by a command from the operation room of JAMIC. The propagation profile of chemical patterns under microgravity of 10-5 g was collected as image data for 9.8 s, and processed by a software of STM-STS2. In the aqueous solutions, propagation velocity of chemical patterns under microgravity was decreased to 80.9 % of that under normal gravity, owing to suppression of convection. On the other hand, in gel matrix, gravity did not influence the propagation velocity.
Exact solutions of three dimensional black holes: Einstein gravity vs F(R) gravity
Hendi, S H; Saffari, R
2014-01-01
In this paper, we consider Einstein gravity in the presence of a class of nonlinear electrodynamics, called power Maxwell invariant (PMI). We take into account $(2+1)$-dimensional spacetime in Einstein-PMI gravity and obtain its black hole solutions. Then, we regard pure $F(R)$ gravity as well as $F(R)$-conformally invariant Maxwell theory to obtain exact solutions of the field equations with black hole interpretation. Finally, we investigate the conserved and thermodynamic quantities and discuss about the first law of thermodynamics for the mentioned gravitational models.
Violation of the Holographic Principle in the Loop Quantum Gravity
Sargın, Ozan
2015-01-01
In this paper, we analyze the holographic principle using loop quantum gravity (LQG). This will be done by analysing a simple quantum mechanical system using polymeric quantization. As the polymeric quantization is the characteristic feature of loop quantum gravity, we will argue that this calculation will indicate the effect on the holographic principle from the loop quantum gravity. Thus, we will be able to explicitly demonstrate the violation of the holographic principle in the loop quantum gravity.
The Cauchy problem of f(R) gravity
Lanahan-Tremblay, Nicolas; Faraoni, Valerio
2007-01-01
The initial value problem of metric and Palatini f(R)gravity is studied by using the dynamical equivalence between these theories and Brans-Dicke gravity. The Cauchy problem is well-formulated for metric f(R)gravity in the presence of matter and well-posed in vacuo. For Palatini f(R)gravity, instead, the Cauchy problem is not well-formulated.
The perception of verticality in lunar and Martian gravity conditions
Winkel, K.N. de; Clément, G.; Groen, E.L.; Werkhoven, P.J.
2012-01-01
Although the mechanisms of neural adaptation to weightlessness and re-adaptation to Earth-gravity have received a lot of attention since the first human space flight, there is as yet little knowledge about how spatial orientation is affected by partial gravity, such as lunar gravity of 0.16. g or Ma
2006 Compilation of Alaska Gravity Data and Historical Reports
Saltus, Richard W.; Brown, Philip J., II; Morin, Robert L.; Hill, Patricia L.
2008-01-01
Gravity anomalies provide fundamental geophysical information about Earth structure and dynamics. To increase geologic and geodynamic understanding of Alaska, the U.S. Geological Survey (USGS) has collected and processed Alaska gravity data for the past 50 years. This report introduces and describes an integrated, State-wide gravity database and provides accompanying gravity calculation tools to assist in its application. Additional information includes gravity base station descriptions and digital scans of historical USGS reports. The gravity calculation tools enable the user to reduce new gravity data in a consistent manner for combination with the existing database. This database has sufficient resolution to define the regional gravity anomalies of Alaska. Interpretation of regional gravity anomalies in parts of the State are hampered by the lack of local isostatic compensation in both southern and northern Alaska. However, when filtered appropriately, the Alaska gravity data show regional features having geologic significance. These features include gravity lows caused by low-density rocks of Cenozoic basins, flysch belts, and felsic intrusions, as well as many gravity highs associated with high-density mafic and ultramafic complexes.
Kanzow, Torsten; Flechtner, F.; Chave, A; R. Schmidt; P. Schwintzer; Send, Uwe
2005-01-01
The Gravity Recovery and Climate Experiment (GRACE) processing centers at the GeoForschungsZentrum Potsdam (GFZ) and the University of Texas Center for Space Research (UTCSR) provide time series of monthly gravity field solutions covering the period since mission launch in March 2002. Although the achieved accuracy still remains an order of magnitude below the mission's baseline goal, these time series have successfully been used to study terrestrial phenomena such as water storage variations...
Phillips, W. P.; Fournier, R. H.
1985-01-01
Wind-tunnel tests were conducted at Mach 1.5 to 2.5 to determine the effect of modifications designed to extend the forward center-of-gravity trim capability on the static longitudal and lateral directional characteristics of a Space shuttle 140 A/B orbiter model (0.01 scale). The modifications consisted of a forward-extended wing fillet, a flat plate canard, and a blended canard. The investigation was conducted in the low Mach number test section of the Langley unitary plan wind tunnel at a Reynolds number of approximately 2.15 million based on the fuselage reference length. The test angle of attack range was -1 deg to 32 deg and the sideslip angles were 0 deg and 5 deg.
Evaluation of recent Earth's global gravity field models with terrestrial gravity data
Karpik, Alexander P.; Kanushin, Vadim F.; Ganagina, Irina G.; Goldobin, Denis N.; Kosarev, Nikolay S.; Kosareva, Alexandra M.
2016-03-01
In the context of the rapid development of environmental research technologies and techniques to solve scientific and practical problems in different fields of knowledge including geosciences, the study of Earth's gravity field models is still important today. The results of gravity anomaly modelling calculated by the current geopotential models data were compared with the independent terrestrial gravity data for the two territories located in West Siberia and Kazakhstan. Statistical characteristics of comparison results for the models under study were obtained. The results of investigations show that about 70% of the differences between the gravity anomaly values calculated by recent global geopotential models and those observed at the points in flat areas are within ±10 mGal, in mountainous areas are within ±20 mGal.
Einstein Gravity and Beyond: Aspects of Higher-Curvature Gravity and Black Holes
Chatterjee, Saugata
This thesis explores the different aspects of higher curvature gravity. The "membrane paradigm" of black holes in Einstein gravity is extended to black holes in f(R) gravity and it is shown that the higher curvature effects of f( R) gravity causes the membrane fluid to become non-Newtonian. Next a modification of the null energy condition in gravity is provided. The purpose of the null energy condition is to filter out ill-behaved theories containing ghosts. Conformal transformations, which are simple redefinitions of the spacetime, introduces serious violations of the null energy condition. This violation is shown to be spurious and a prescription for obtaining a modified null energy condition, based on the universality of the second law of thermodynamics, is provided. The thermodynamic properties of the black holes are further explored using merger of extremal black holes whose horizon entropy has topological contributions coming from the higher curvature Gauss-Bonnet term. The analysis refutes the prevalent belief in the literature that the second law of black hole thermodynamics is violated in the presence of the Gauss-Bonnet term in four dimensions. Subsequently a specific class of higher derivative scalar field theories called the galileons are obtained from a Kaluza-Klein reduction of Gauss-Bonnet gravity. Galileons are null energy condition violating theories which lead to violations of the second law of thermodynamics of black holes. These higher derivative scalar field theories which are non-minimally coupled to gravity required the development of a generalized method for obtaining the equations of motion. Utilizing this generalized method, it is shown that the inclusion of the Gauss-Bonnet term made the theory of gravity to become higher derivative, which makes it difficult to make any statements about the connection between the violation of the second law of thermodynamics and the galileon fields.
Dykowski, Przemyslaw; Krynski, Jan
2015-04-01
The establishment of modern gravity control with the use of exclusively absolute method of gravity determination has significant advantages as compared to the one established mostly with relative gravity measurements (e.g. accuracy, time efficiency). The newly modernized gravity control in Poland consists of 28 fundamental stations (laboratory) and 168 base stations (PBOG14 - located in the field). Gravity at the fundamental stations was surveyed with the FG5-230 gravimeter of the Warsaw University of Technology, and at the base stations - with the A10-020 gravimeter of the Institute of Geodesy and Cartography, Warsaw. This work concerns absolute gravity determinations at the base stations. Although free of common relative measurement errors (e.g. instrumental drift) and effects of network adjustment, absolute gravity determinations for the establishment of gravity control require advanced corrections due to time dependent factors, i.e. tidal and ocean loading corrections, atmospheric corrections and hydrological corrections that were not taken into account when establishing the previous gravity control in Poland. Currently available services and software allow to determine high accuracy and high temporal resolution corrections for atmospheric (based on digital weather models, e.g. ECMWF) and hydrological (based on hydrological models, e.g. GLDAS/Noah) gravitational and loading effects. These corrections are mostly used for processing observations with Superconducting Gravimeters in the Global Geodynamics Project. For the area of Poland the atmospheric correction based on weather models can differ from standard atmospheric correction by even ±2 µGal. The hydrological model shows the annual variability of ±8 µGal. In addition the standard tidal correction may differ from the one obtained from the local tidal model (based on tidal observations). Such difference at Borowa Gora Observatory reaches the level of ±1.5 µGal. Overall the sum of atmospheric and
Measurement of the Gravity-Field Curvature by Atom Interferometry
Rosi, G; Sorrentino, F; Menchetti, M; Prevedelli, M; Tino, G M
2015-01-01
We present the first direct measurement of the gravity-field curvature based on three conjugated atom interferometers. Three atomic clouds launched in the vertical direction are simultaneously interrogated by the same atom interferometry sequence and used to probe the gravity field at three equally spaced positions. The vertical component of the gravity-field curvature generated by nearby source masses is measured from the difference between adjacent gravity gradient values. Curvature measurements are of interest in geodesy studies and for the validation of gravitational models of the surrounding environment. The possibility of using such a scheme for a new determination of the Newtonian constant of gravity is also discussed.
Geoid change over Australia: analysis of the GRACE gravity field solution
Kevin Fleming; Martinec, Z.; Ingo Sasgen;
2006-01-01
The Gravity Recovery and Climate Experiment (GRACE) has so far seen around 4 years worth of monthly gravity-field solutions being released to the scientific community. These are provided in the form of Stokes potential coefficients by the GRACE Science Data Service centers; the Center for Space Research, University of Texas (CSR), the GeoForschungsZentrum Potsdam (GFZ) and the Jet Propulsion Laboratory (JPL), as well as the Centre National d'Études Spatiales (CNES). We make use of the release...
Gravity Field, Topography, and Interior Structure of Amalthea
Anderson, J. D.; Anabtawi, A.; Jacobson, R. A.; Johnson, T. V.; Lau, E. L.; Moore, W. B.; Schubert, G.; Taylor, A. H.; Thomas, P. C.; Weinwurm, G.
2002-12-01
A close Galileo flyby of Jupiter's inner moon Amalthea (JV) occurred on 5 November 2002. The final aimpoint was selected by the Galileo Radio Science Team on 5 July 2002. The closest approach distance for the selected aimpoint was 221 km from the center of mass, the latitude was - 45.23 Deg and the west longitude was 266.41 Deg (IAU/IAG/COSPAR cartographic coordinate system). In order to achieve an acceptable impact probability (0.15%), and yet fly close to Amalthea, the trajectory was selected from a class of trajectories running parallel to Amalthea's long axis. The Deep Space Network (DSN) had the capability to generate continuous coherent radio Doppler data during the flyby. Such data can be inverted to obtain information on Amalthea's gravity field. Amalthea is irregular and neither a triaxial ellipsoid nor an equilibrium body. It has a volume of about 2.4 x 106 km3, and its best-fit ellipsoid has dimensions 131x73x67 km. Its mass can be determined from the 2002 flyby, and in combination with the volume, a density can be obtained accurate to about 5%, where the error is dominated by the volume uncertainty. Similarly, gravity coefficients (Cnm Snm) can be detected up to fourth degree and order, and the second degree field (quadrupole) can be measured. Topography data are available from Voyager imaging and from images taken with Galileo's solid state imaging system at various times between February and June 1997. By combining the gravity and topography data, new information can be obtained on Amalthea's interior. For example if the gravity coefficients agree with those calculated from the topography, assuming constant density, we can conclude that Amalthea is homogeneous. On the other hand, if the gravity coefficients are smaller than predicted from topography, we can conclude that there is a concentration of mass toward Amalthea's center. We are presenting preliminary pre-publication results at the Fall meeting. This work was sponsored by the Galileo Project
Cosmological singularities and modified theories of gravity
Fernández Jambrina, Leonardo; Lazkoz, Ruth
2009-01-01
We consider perturbative modifications of the Friedmann equations in terms of energy density corresponding to modified theories of gravity proposed as an alternative route to comply with the observed accelerated expansion of the universe. Assuming that the present matter content of the universe is a pressureless fluid, the possible singularities that may arise as the final state of the universe are surveyed. It is shown that, at most, two coefficients of the perturbative expansion of the Frie...
EGSIEM: Combination of GRACE monthly gravity models on normal equation level
Meyer, Ulrich; Jean, Yoomin; Jäggi, Adrian; Mayer-Gürr, Torsten; Neumayer, Hans; Lemoine, Jean-Michel
2016-04-01
One of the three geodetic services to be realized in the frame of the EGSIEM project is a scientific combination service. Each associated processing center (AC) will follow a set of common processing standards but will apply its own, independent analysis method. Therefore the quality, robustness and reliability of the combined monthly gravity fields is expected to improve significantly compared to the individual solutions. The Monthly GRACE gravity fields of all ACs are combined on normal equation level. The individual normal equations are weighted depending on pairwise comparisons of the individual gravity field solutions. To derive these weights and for quality control of the individual contributions first a combination of the monthly gravity fields on solution level is performed. The concept of weighting and of the combination on normal equation level is introduced and the formats used for normal equation exchange and gravity field solutions is described. First results of the combination on normal equation level are presented and compared to the corresponding combinations on solution level. EGSIEM has an open data policy and all processing centers of GRACE gravity fields are invited to participate in the combination.
Lopsidedness of cluster galaxies in modified gravity
International Nuclear Information System (INIS)
We point out an interesting theoretical prediction for elliptical galaxies residing inside galaxy clusters in the framework of modified Newtonian dynamics (MOND), that could be used to test this paradigm. Apart from the central brightest cluster galaxy, other galaxies close enough to the centre experience a strong gravitational influence from the other galaxies of the cluster. This influence manifests itself only as tides in standard Newtonian gravity, meaning that the systematic acceleration of the centre of mass of the galaxy has no consequence. However, in the context of MOND, a consequence of the breaking of the strong equivalence principle is that the systematic acceleration changes the own self-gravity of the galaxy. We show here that, in this framework, initially axisymmetric elliptical galaxies become lopsided along the external field's direction, and that the centroid of the galaxy, defined by the outer density contours, is shifted by a few hundreds parsecs with respect to the densest point
Novel Probes of Gravity and Dark Energy
Jain, Bhuvnesh; Thompson, Rodger; Upadhye, Amol; Battat, James; Brax, Philippe; Davis, Anne-Christine; de Rham, Claudia; Dodelson, Scott; Erickcek, Adrienne; Gabadadze, Gregory; Hu, Wayne; Hui, Lam; Huterer, Dragan; Kamionkowski, Marc; Khoury, Justin; Koyama, Kazuya; Li, Baojui; Linder, Eric; Schmidt, Fabian; Scoccimarro, Roman; Starkman, Glenn; Stubbs, Chris; Takada, Masahiro; Tolley, Andrew; Trodden, Mark; Uzan, Jean-Philippe; Vikram, Vinu; Weltman, Amanda; Wyman, Mark; Zaritsky, Dennis; Zhao, Gongbo
2013-01-01
The discovery of cosmic acceleration has stimulated theorists to consider dark energy or modifications to Einstein's General Relativity as possible explanations. The last decade has seen advances in theories that go beyond smooth dark energy -- modified gravity and interactions of dark energy. While the theoretical terrain is being actively explored, the generic presence of fifth forces and dark sector couplings suggests a set of distinct observational signatures. This report focuses on observations that differ from the conventional probes that map the expansion history or large-scale structure. Examples of such novel probes are: detection of scalar fields via lab experiments, tests of modified gravity using stars and galaxies in the nearby universe, comparison of lensing and dynamical masses of galaxies and clusters, and the measurements of fundamental constants at high redshift. The observational expertise involved is very broad as it spans laboratory experiments, high resolution astronomical imaging and sp...
Reissner Nordstrom Metric in Unimodular Theory of Gravity
Chaturvedi, Pankaj; Singh, Dharm Veer
2016-01-01
We study the modified Reissner Nordstrom metric in the unimodular gravity. So far the spherically symmetric Einstein field equation in unimodular gravity has been studied in the absence of any source. We consider static electric and magnetic charge as source. We solve for Maxwell equations in unimodular gravitational background. We show that in unimodular gravity the electromagnetic field strength tensor is modified. We also show that the solution in unimodular gravity differs from the usual R-N metric in Einstein gravity with some corrections. We further study the thermodynamical properties of the R-N black-hole solution in this theory.
Holographic Theory of Gravity and Cosmology
Ng, Y Jack
2016-01-01
According to the holographic principle, the maximum amount of information stored in a region of space scales as the area of its two-dimensional surface, like a hologram. We show that the holographic principle can be understood heuristically as originated from quantum fluctuations of spacetime. Applied to cosmology, this consideration leads to a dynamical cosmological constant $\\Lambda$ of the observed magnitude, in agreement with the result obtained for the present and recent cosmic eras, by using unimodular gravity and causal-set theory. By generalizing the concept of entropic gravity, we find a critical acceleration parameter related to $\\Lambda$ in galactic dynamics, and we construct a phenomenological model of dark matter which we call "modified dark matter" (MDM). We provide successful observational tests of MDM at both the galactic and cluster scales. We also discuss the possibility that the quanta of both dark energy and dark matter obey the quantum Boltzmann statistics or infinite statistics as descri...
Ghost and singularity free theories of gravity
Buoninfante, L; Mazumdar, A
2016-01-01
Albert Einstein's General Relativity (GR) from 1916 has become the widely accepted theory of gravity and been tested observationally to a very high precision at different scales of energy and distance. At the same time, there still remain important questions to resolve. The presence of cosmological and black hole singularities are examples of problems at the classical level which strongly suggest the incompleteness of GR at short distances (high energy). Furthermore, at the quantum level GR is not UV complete, namely it is not perturbatively renormalizable. These two kind of questions, classical and quantum, could be closely related as both concern short-distance (high energy) physics. Most of the work try to solve these problems modifying GR by considering finite higher order derivative terms. Fourth Order Gravity, for example, turns out to be renormalizable, but at the same time it introduces ghost. To avoid both UV divergence and presence of ghost one could consider an infinite set of higher derivative ter...
f(R) gravity equation of state
International Nuclear Information System (INIS)
The f(R) gravity field equations are derived as an equation of state of local space-time thermodynamics. Jacobson's arguments are nontrivially extended, by means of a more general definition of local entropy, for which Wald's definition of dynamic black hole entropy is used, as well as the concept of an effective Newton constant for graviton exchange, which recently appeared in the literature.
F(R) gravity equation of state
Elizalde, Emilio; Silva, Pedro J.
2008-01-01
The ${\\bf f}(R)$ gravity field equations are derived as an equation of state of local space-time thermodynamics. Jacobson's arguments are non-trivially extended, by means of a more general definition of local entropy, for which Wald's definition of dynamic black hole entropy is used, as well as the concept of an effective Newton constant for graviton exchange, recently appeared in the literature.
Experimental Indications of Electro-Gravity
Datta, T; Dimofte, A; Bleiweiss, M C; Cai, Z; Yin, Ming; Dimofte, Andreea; Cai, Zhihua
2005-01-01
Recent results from our on going experimental investigation of the influence of space dependant electric fields on the weight of test particles are reported. Test particles were gold coated metal spheres of same size but of different masses. Data collected from a number of runs over several years continue to indicate an intriguing effect. For experimental parameters in question this effect is manifested as a ppm level sample mass dependent force additional to expected electrostatic forces. A force that is proportional to mass is the unique signature of gravity furthermore it is non-zero only when the field is applied; hence these observations may be further evidence in support of electro-gravity.
Entropic-gravity derivation of MOND
Klinkhamer, F. R.
2012-01-01
A heuristic entropic-gravity derivation has previously been given of the gravitational two-body force of modified Newtonian dynamics (MOND). Here, it is shown that also another characteristic of MOND can be recovered, namely, the external field effect (implying a violation of the Strong Equivalence Principle). In fact, the derivation gives precisely the modified Poisson equation which Bekenstein and Milgrom proposed as a consistent nonrelativistic theory of MOND.
Cosmological Solutions of $f(T)$ Gravity
Paliathanasis, Andronikos; Leach, P G L
2016-01-01
In the cosmological scenario in $f\\left( T\\right) $ gravity, we find analytical solutions for an isotropic and homogeneous universe containing a dust fluid and radiation and for an empty anisotropic Bianchi I universe. The method that we apply is that of movable singularities of differential equations. For the isotropic universe, the solutions are expressed in terms of a Laurent expansion, while for the anisotropic universe we find a family of exact Kasner-like solutions in vacuum. Finally, we discuss when a nonlinear $f\\left( T\\right) $-gravity theory provides solutions for the teleparallel equivalence of general relativity and derive conditions for exact solutions of general relativity to solve the field equations of an $f(T)$ theory.
Finsler geometric extension of Einstein gravity
Pfeifer, Christian
2011-01-01
We construct gravitational dynamics for Finsler spacetimes in terms of an action integral on the unit tangent bundle. These spacetimes are generalizations of Lorentzian metric manifolds which satisfy necessary causality properties. A coupling procedure for matter fields to Finsler gravity completes our new theory that consistently becomes equivalent to Einstein gravity in the limit of metric geometry. We provide a precise geometric definition of observers and their measurements, and show that the transformations by means of which different observers communicate form a groupoid that generalizes the usual Lorentz group. Moreover, we discuss the implementation of Finsler spacetime symmetries. We use our results to analyze a particular spacetime model that leads to Finsler geometric refinements of the linearized Schwarzschild solution.
Finsler geometric extension of Einstein gravity
Pfeifer, Christian; Wohlfarth, Mattias N. R.
2012-03-01
We construct gravitational dynamics for Finsler spacetimes in terms of an action integral on the unit tangent bundle. These spacetimes are generalizations of Lorentzian metric manifolds which satisfy necessary causality properties. A coupling procedure for matter fields to Finsler gravity completes our new theory that consistently becomes equivalent to Einstein gravity in the limit of metric geometry. We provide a precise geometric definition of observers and their measurements and show that the transformations, by means of which different observers communicate, form a groupoid that generalizes the usual Lorentz group. Moreover, we discuss the implementation of Finsler spacetime symmetries. We use our results to analyze a particular spacetime model that leads to Finsler geometric refinements of the linearized Schwarzschild solution.
f(Lovelock) theories of gravity
Bueno, Pablo; A., Oscar Lasso; Ramirez, Pedro F
2016-01-01
f(Lovelock) gravities are simple generalizations of the usual f(R) and Lovelock theories in which the gravitational action depends on some arbitrary function of the corresponding dimensionally-extended Euler densities. In this paper we study several aspects of these theories in general dimensions. We start by identifying the generalized boundary term which makes the gravitational variational problem well-posed. Then, we show that these theories are equivalent to certain scalar-tensor theories and how this relation is characterized by the Hessian of f. We also study the linearized equations of the theory on general maximally symmetric backgrounds. Remarkably, we find that these theories do not propagate the usual ghost-like massive gravitons characteristic of higher-derivative gravities on such backgrounds. In some non-trivial cases, the additional scalar associated to the trace of the metric perturbation is also absent, being the usual graviton the only dynamical field. In those cases, the linearized equation...
Conceptual Aspects of Gauge/Gravity Duality
de Haro, Sebastian; Butterfield, Jeremy
2015-01-01
We give an introductory review of gauge/gravity duality, and associated ideas of holography, emphasising the conceptual aspects. The opening Sections gather the ingredients, viz. anti-de Sitter spacetime, conformal field theory and string theory, that we need for presenting, in Section 5, the central and original example: Maldacena's AdS/CFT correspondence. Sections 6 and 7 develop the ideas of this example, also in applications to condensed matter systems, QCD, and hydrodynamics. Sections 8 and 9 discuss the possible extensions of holographic ideas to de Sitter spacetime and to black holes. Section 10 discusses the bearing of gauge/gravity duality on two philosophical topics: the equivalence of physical theories, and the idea that spacetime, or some features of it, are emergent.
Conceptual Aspects of Gauge/Gravity Duality
De Haro, Sebastian; Mayerson, Daniel R.; Butterfield, Jeremy N.
2016-07-01
We give an introductory review of gauge/gravity duality, and associated ideas of holography, emphasising the conceptual aspects. The opening sections gather the ingredients, viz. anti-de Sitter spacetime, conformal field theory and string theory, that we need for presenting, in Sect. 5, the central and original example: Maldacena's AdS/CFT correspondence. Sections 6 and 7 develop the ideas of this example, also in applications to condensed matter systems, QCD, and hydrodynamics. Sections 8 and 9 discuss the possible extensions of holographic ideas to de Sitter spacetime and to black holes. Section 10 discusses the bearing of gauge/gravity duality on two philosophical topics: the equivalence of physical theories, and the idea that spacetime, or some features of it, are emergent.
The extended loop representation of quantum gravity
Di Bartolo, C; Griego, J R
1995-01-01
A new representation of Quantum Gravity is developed. This formulation is based on an extension of the group of loops. The enlarged group, that we call the Extended Loop Group, behaves locally as an infinite dimensional Lie group. Quantum Gravity can be realized on the state space of extended loop dependent wavefunctions. The extended representation generalizes the loop representation and contains this representation as a particular case. The resulting diffeomorphism and hamiltonian constraints take a very simple form and allow to apply functional methods and simplify the loop calculus. In particular we show that the constraints are linear in the momenta. The nondegenerate solutions known in the loop representation are also solutions of the constraints in the new representation. The practical calculation advantages allows to find a new solution to the Wheeler-DeWitt equation. Moreover, the extended representation puts in a precise framework some of the regularization problems of the loop representation. We sh...
Gravity and topography. [of planet Mars
Esposito, P. B.; Banerdt, W. B.; Lindal, G. F.; Sjogren, W. L.; Slade, M. A.; Bills, B. G.; Smith, D. E.; Balmino, G.
1992-01-01
The paper summarizes the fundamental gravity field constants for Mars and a brief historical review of early determinations and current-day accurate estimates. These include the planetary gravitational constant, global figure, dynamical oblateness, mean density, and rotational period. Topographic results from data acquired from the 1967 opposition to the most recent, 1988, opposition are presented. Both global and selected local topographic variations and features are discussed. The inertia tensor and the nonhydrostatic component of Mars are examined in detail. The dimensionless moment of inertia about the rotational axis is 0.4 for a body of uniform density and 0.37621 if Mars were in hydrostatic equilibrium. By comparing models of both gravity and topography, inferences are made about the degree and depth of compensation in the interior and stresses in the lithosphere.
Continuous record of the gravity changes at Mt. Vesuvius
Directory of Open Access Journals (Sweden)
U. Riccardi
1997-06-01
Full Text Available High precision relative and absolute gravity measurements are periodically carried out at Mt. Vesuvius (Southern Italy to monitor the changes in the gravity field caused by the internal dynamics of the volcano. Moreover, a recording gravity station is also operating at the Osservatorio Vesuviano (Old Building aimed at measuring in continuous mode the time variations of the gravity and the tidal parameters, possibly due to changes in the physical state of the volcano. The analysis carried out on an hourly data set spanning the 1994-1996 time interval and a comparison of the results with those previously obtained, exhibit a change in the tidal parameters which occurred between 1991 and 1994. A gravity decrease of about 60 µGal was observed during the same time interval in the same area. Consistent with relative and absolute gravity observations, no significant variations have been detected since 1994 in the tidal parameters and gravity residuals.
Modeling of Earth's Gravity Fields Visualization Based on Quad Tree
Institute of Scientific and Technical Information of China (English)
LUO Zhicai; LI Zhenhai; ZHONG Bo
2010-01-01
The problems of the earth's gravity fields' visualization are both focus and puzzle currently. Aiming at multiresolution rendering, modeling of the Earth's gravity fields' data is discussed in the paper by using LOD algorithm based on Quad Tree. First,this paper employed the method of LOD based on Quad Tree to divide up the regional gravity anomaly data, introduced the combined node evaluation system that was composed of viewpoint related and roughness related systems, and then eliminated the T-cracks that appeared among the gravity anomaly data grids with different resolutions. The test results demonstrated that the gravity anomaly data grids' rendering effects were living, and the computational power was low. Therefore, the proposed algorithm was a suitable method for modeling the gravity anomaly data and has potential applications in visualization of the earth's gravity fields.
A special fermionic generalization of lineal gravity
Institute of Scientific and Technical Information of China (English)
无
2006-01-01
The central extension of the (1+1)-dimensional Poincaré algebra by including fermionic charges which obey not supersymmetric algebra, but a special graded algebra containing in the right hand side a central element only is obtained. The corresponding theory being the fermionic extension of the lineal gravity is proposed. We considered the algebra of generators, the field transformations and found Lagrangian and equation of motion, then we derived the Casimir operator and obtained the constant black hole mass.
Asymptotic dynamics of three-dimensional gravity
Donnay, Laura
2016-01-01
These are the lectures notes of the course given at the Eleventh Modave Summer School in Mathematical Physics, 2015, aimed at PhD candidates and junior researchers in theoretical physics. We review in details the result of Coussaert-Henneaux-van Driel showing that the asymptotic dynamics of $(2+1)$- dimensional gravity with negative cosmological constant is described at the classical level by Liouville theory. Boundary conditions implement the asymptotic reduction in two steps: the first set reduces the $SL(2,\\mathbb R)\\times SL(2,\\mathbb R)$ Chern-Simons action, equivalent to the Einstein action, to a non-chiral $SL(2,\\mathbb R)$ Wess-Zumino-Witten model, while the second set imposes constraints on the WZW currents that reduce further the action to Liouville theory. We discuss the issues of considering the latter as an effective description of the dual conformal field theory describing AdS$_3$ gravity beyond the semi-classical regime.
Meyers, D. G.; Farmer, J. M.
1982-01-01
Gravity receptors of Dephnia magna were discovered on the basal segment of the swimming antennae and were shown to respond to upward water currents that pass the animal as it sinks between swimming strokes. Sensitivity of the gravity perceiving mechanism was tested by subjecting daphnids to a series of five decreasingly dense aqueous solutions (neutral density to water) in darkness (to avoid visual cues). Three-dimensional, video analysis of body position (pitch, yaw and roll) and swimming path (hop and sink, vertical and horizontal patterns) revealed a gradual threshold that occurred near a density difference between the animal and its environment of less than 0.25%. Because daphnids do not sink but continue to slide after stroking in the increased density solutions, gravity perception appears to occur during a vertical swing of the longitudinal body axis to the vertical plane, about their center of gravity, and, thereby, implies a multidirectional sensitivity for the antennal-socket setae.
The physics of orographic gravity wave drag
Directory of Open Access Journals (Sweden)
MiguelA CTeixeira
2014-07-01
Full Text Available The drag and momentum fluxes produced by gravity waves generated in flow over orography are reviewed, focusing on adiabatic conditions without phase transitions or radiation effects, and steady mean incoming flow. The orographic gravity wave drag is first introduced in its simplest possible form, for inviscid, linearized, non-rotating flow with the Boussinesq and hydrostatic approximations, and constant wind and static stability. Subsequently, the contributions made by previous authors (primarily using theory and numerical simulations to elucidate how the drag is affected by additional physical processes are surveyed. These include the effect of orography anisotropy, vertical wind shear, total and partial critical levels, vertical wave reflection and resonance, non-hydrostatic effects and trapped lee waves, rotation and nonlinearity. Frictional and boundary layer effects are also briefly mentioned. A better understanding of all of these aspects is important for guiding the improvement of drag parametrization schemes.
Geophysical interpretation of Venus gravity data
Reasenberg, R. D.
1985-01-01
The investigation of the subsurface mass distribution of Venus through the analysis of the data from Pioneer Venus Orbiter (PVO) is presented. The Doppler tracking data was used to map the gravitational potential, which was compared to the topographic data from the PVO radar (ORAD). In order to obtain an unbiased comparison, the topography obtained from the PVO-ORAD was filtered to introduce distortions which are the same as those of our gravity models. The last major software package that was required in order to determine the spectral admittance Z (lambda) was used. This package solves the forward problem: given the topography and its density, and assuming no compensation, find the resulting spacecraft acceleration along a given nominal trajectory. The filtered topography is obtained by processing these accelerations in the same way (i.e., with the same geophysical inverter) as the Doppler-rate data that we use to estimate the gravity maps.
Cosmological consequences of Modified Gravity (MOG)
Toth, Viktor T
2010-01-01
As an alternative to the LCDM concordance model, Scalar-Tensor-Vector Modified Gravity (MOG) theory reproduces key cosmological observations without postulating the presence of an exotic dark matter component. MOG is a field theory based on an action principle, with a variable gravitational constant and a repulsive vector field with variable range. MOG yields a phenomenological acceleration law that includes strong tensorial gravity partially canceled by a repulsive massive vector force. This acceleration law can be used to model the CMB acoustic spectrum and the matter power spectrum yielding good agreement with observation. A key prediction of MOG is the presence of strong baryonic oscillations, which will be detectable by future surveys. MOG is also consistent with Type Ia supernova data. We also describe on-going research of the coupling between MOG and continuous matter, consistent with the weak equivalence principle and solar system observations.
Analysis on Gravity Center Transfer Technique in Modern Dance%摩登舞重心移动技术探讨
Institute of Scientific and Technical Information of China (English)
邓晓东; 刘怀金
2012-01-01
The key in modern dance technique is constant shifting gravity center in body, by which the whole body may move in inertia to form a moving inertial flow. And the key to forming mobile body inertia flow is that body weight transfer can be achieved by feet movement which is driven by skeleton movement resulting from muscle tissue contraction under the control of the central nervous system in body trunk. In these processes, weight transfer can be conducted by body trunk, with mobile pivot formed by firming waist and hip, as well as balanced shift of gravity center by foot corresponding motion.%摩登舞技巧中最重要的环节是控制身体重心的不断转换，整个形体在惯性中移动，形成移动惯性流量。形体移动惯性流量的形成，关键在于身体躯干在中枢神经系统的控制下，由肌肉收缩牵引骨骼来带动腿脚移动实现重心移动到位。在此过程中，身体躯干主导着重心转移，腰胯稳固形成移动的枢纽，脚底联动实现重心的平衡转移。
Low Gravity Rapid Thermal Analysis of Glass
Tucker, Dennis S.; Ethridge, Edwin C.; Smith, Guy A.
2004-01-01
It has been observed by two research groups that ZrF4-BaF2-LaF3-AlF3-NaF (ZBLAN) glass crystallization is suppressed in microgravity. The mechanism for this phenomenon is unknown at the present time. In order to better understand the mechanism, an experiment was performed on NASA's KC135 reduced gravity aircraft to obtain quantitative crystallization data. An apparatus was designed and constructed for performing rapid thermal analysis of milligram quantities of ZBLAN glass. The apparatus employs an ellipsoidal furnace allowing for rapid heating and cooling. Using this apparatus nucleation and crystallization kinetic data was obtained leading to the construction of time-temperature-transformation curves for ZBLAN in microgravity and unit gravity.
Cause of winter gravity wave spectrum saturation
Institute of Scientific and Technical Information of China (English)
WU; Yongfu; XU; Jiyao
2005-01-01
This paper utilizes horizontal velocity measurements observed from 19 chaff rockets and nearly simultaneous temperature measurements collected from 19 falling sphere rockets to study the cause of winter gravity wave spectrum saturation. Results suggest that strong horizontal velocity shears larger than 0.04 s-1 are observed to be present at various heights near the winter mesopause. On one single chaff rocket flight, an extremely strong horizontal velocity shear as high as 0.33 s-1 is observed at 87.4 km and is believed to be the strongest value ever measured in the mesosphere. These strong horizontal velocity shears, together with Brunt-V(a)is(a)l(a) frequency squared obtained from the temperature profile, act collectively to yield two dynamical instability regions of Richardson number smaller than 1/4, suggesting that the saturated gravity wave spectrum observed by the chaff rockets in winter is a result of dynamical instability.
Tests of Modified Gravity with Dwarf Galaxies
Jain, Bhuvnesh
2011-01-01
In modified gravity theories that seek to explain cosmic acceleration, dwarf galaxies in low density environments can be subject to enhanced forces. The class of scalar-tensor theories, which includes f(R) gravity, predict such a force enhancement (massive galaxies like the Milky Way can evade it through a screening mechanism that protects the interior of the galaxy from this "fifth" force). We study observable deviations from GR in the disks of late-type dwarf galaxies moving under gravity. The fifth-force acts on the dark matter and HI gas disk, but not on the stellar disk owing to the self-screening of main sequence stars. We find four distinct observable effects in such disk galaxies: 1. A displacement of the stellar disk from the HI disk. 2. Warping of the stellar disk along the direction of the external force. 3. Enhancement of the rotation curve measured from the HI gas compared to that of the stellar disk. 4. Asymmetry in the rotation curve of the stellar disk. We estimate that the spatial effects can...
Gauge theory of gravity and matter
Kerr, Steven
2014-01-01
It is shown how to write the first order action for gravity in a gauge theoretic formalism where the spin connection and frame field degrees of freedom are assimilated together into a gauge connection. It is then shown how to couple the theory to spin-0, 1/2, 1 and 3/2 fields in a gauge invariant fashion. The results hold in any number of spacetime dimensions.
Observation of solid precipitation using satellite gravity
Seo, K.; Waliser, D. E.; Ryu, D.; Tian, B.; Kim, B.
2009-12-01
Understanding hydrological processes in the arctic region and their variation are emerging and important issues in the association with global climate changes. Solid precipitation is particularly important because it plays a major role in controlling the winter hydrological cycle and spring discharge. Nevertheless, observations of winter snowfall in high latitudes is challenging due to sharply decreasing numbers of precipitation gauges and gauge measurement biases. In addition, conventional satellite methods that work well in low-latitudes are unsuitable for the high latitude conditions. In this study, we present a new method of estimating winter snowfall in the arctic region with GRACE time varying gravity measurements. In northern high latitudes, it is very cold in winter, and thus solid precipitation accumulates with very limited melting and evapotranspiration. Therefore, observed gravity increments during winter mainly result from solid precipitation. We estimate amount of solid precipitation during winter (DJF) from four major arctic basins, Mackenzie, Lena, Yenisei and Ob. New estimates using satellite gravity are compared to global satellite and reanalysis precipitation products , which are GPCP, CMAP, NCEP/NCAR, ECMWF and JCDAS. GRACE-based estimates of snowfall are very close to those of CMAP, ECMWF and JCDAS. We extend the methodology to examine spatial distribution of solid precipitation in the pan-arctic land areas, which shows a good agreement with JCDAS. This new measurement of solid precipitation can provide an altogether new form of observations for hydrological cycle research studies, model and precipitation product evaluation and data assimilation efforts.
Mechanical Nature of Gravity and Tectonic Forces
Institute of Scientific and Technical Information of China (English)
Liu Ruixun; Lü Guxian; Wang Fangzheng; Wei Changshan; Guo Chusun
2004-01-01
There are two models of ultrahigh pressure metamorphism (UHPM) zone in Dabie: the model of under thrusting-returning which even arrives at the mantle and the superimposed model of tectonics in the crust. There are two points of view in the argument about formation depth of ultrahigh pressure metamorphism: (1) the depth can be calculated by hydrostatic equation; (2) the high pressure was composed of gravity, tectonic and other forces instead of merely gravity force. Some misunderstandings of mechanical conceptions presented in the paper showing the hydrostatic viewpoints should be open to question. The main conceptions are: (1) the confining pressure was only formed by gravity, and the differential stress was only formed by tectonic force; (2) the differential stress is not big enough to lead to form ultrahigh pressure metamorphism; (3) once tectonic overpressure goes beyond the limited strength of rocks the tectonic force would disappear and the rocks would be broken or rheomorphied at the same time. A short discussion in basic mechanics is made in this paper for a perfect process for discussing the argument.
Constraining Gravity with LISA Detections of Binaries
Canizares, P.; Gair, J. R.; Sopuerta, C. F.
2013-01-01
General Relativity (GR) describes gravitation well at the energy scales which we have so far been able to achieve or detect. However, we do not know whether GR is behind the physics governing stronger gravitational field regimes, such as near neutron stars or massive black-holes (MBHs). Gravitational-wave (GW) astronomy is a promising tool to test and validate GR and/or potential alternative theories of gravity. The information that a GW waveform carries not only will allow us to map the strong gravitational field of its source, but also determine the theory of gravity ruling its dynamics. In this work, we explore the extent to which we could distinguish between GR and other theories of gravity through the detection of low-frequency GWs from extreme-mass-ratio inspirals (EMRIs) and, in particular, we focus on dynamical Chern-Simons modified gravity (DCSMG). To that end, we develop a framework that enables us, for the first time, to perform a parameter estimation analysis for EMRIs in DCSMG. Our model is described by a 15-dimensional parameter space, that includes the Chern-Simons (CS) parameter which characterises the deviation between the two theories, and our analysis is based on Fisher information matrix techniques together with a (maximum-mismatch) criterion to assess the validity of our results. In our analysis, we study a 5-dimensional parameter space, finding that a GW detector like the Laser Interferometer Space Antenna (LISA) or eLISA (evolved LISA) should be able to discriminate between GR and DCSMG with fractional errors below 5%, and hence place bounds four orders of magnitude better than current Solar System bounds.
Establishment of National Gravity Base Network of Iran
Hatam Chavari, Y.; Bayer, R.; Hinderer, J.; Ghazavi, K.; Sedighi, M.; Luck, B.; Djamour, Y.; Le Moign, N.; Saadat, R.; Cheraghi, H.
2009-04-01
A gravity base network is supposed to be a set of benchmarks uniformly distributed across the country and the absolute gravity values at the benchmarks are known to the best accessible accuracy. The gravity at the benchmark stations are either measured directly with absolute devices or transferred by gravity difference measurements by gravimeters from known stations. To decrease the accumulation of random measuring errors arising from these transfers, the number of base stations distributed across the country should be as small as possible. This is feasible if the stations are selected near to the national airports long distances apart but faster accessible and measurable by a gravimeter carried in an airplane between the stations. To realize the importance of such a network, various applications of a gravity base network are firstly reviewed. A gravity base network is the required reference frame for establishing 1st , 2nd and 3rd order gravity networks. Such a gravity network is used for the following purposes: a. Mapping of the structure of upper crust in geology maps. The required accuracy for the measured gravity values is about 0.2 to 0.4 mGal. b. Oil and mineral explorations. The required accuracy for the measured gravity values is about 5 µGal. c. Geotechnical studies in mining areas for exploring the underground cavities as well as archeological studies. The required accuracy is about 5 µGal and better. d. Subsurface water resource explorations and mapping crustal layers which absorb it. An accuracy of the same level of previous applications is required here too. e. Studying the tectonics of the Earth's crust. Repeated precise gravity measurements at the gravity network stations can assist us in identifying systematic height changes. The accuracy of the order of 5 µGal and more is required. f. Studying volcanoes and their evolution. Repeated precise gravity measurements at the gravity network stations can provide valuable information on the gradual
Accuracy evaluation of pendulum gravity measurements of Robert von Sterneck
Directory of Open Access Journals (Sweden)
Alena Pešková
2015-06-01
Full Text Available The accuracy of first pendulum gravity measurements in the Czech territory was determined using both original surveying notebooks of Robert Daublebsky von Sterneck and modern technologies. Since more accurate methods are used for gravity measurements nowadays, our work is mostly important from the historical point of view. In previous works, the accuracy of Sterneck’s gravity measurements was determined using only a small dataset. Here we process all Sterneck’s measurements from the Czech territory (a dataset ten times larger than in the previous works, and we complexly assess the accuracy of these measurements. Locations of the measurements were found with the help of original notebooks. Gravity in the site was interpolated using actual gravity models. Finally, the accuracy of Sterneck’s measurements was evaluated as the difference between the measured and interpolated gravity.
Dynamics of generalized Palatini theories of gravity
International Nuclear Information System (INIS)
It is known that in f(R) theories of gravity with an independent connection which can be both nonmetric and nonsymmetric, this connection can always be algebraically eliminated in favor of the metric and the matter fields, so long as it is not coupled to the matter explicitly. We show here that this is a special characteristic of f(R) actions, and it is not true for actions that include other curvature invariants. This contradicts some recent claims in the literature. We clarify the reasons for this contradiction.
Sneddon, Andrew
2013-01-01
Gravity is a cross-disciplinary research project in Fine Art at Sheffield Institute of the Arts (SIA) in partnership with Sheffield Galleries and Museums. Gravity is led by Penny McCarthy, Dr Becky Shaw and Andrew Sneddon. Gravity begins with a series of lectures designed to examine the wider context of practice and discourse. Gravity examines the contemporary condition of the art object or artefact, and the relations between maker, medium, site of production and systems of dissemination. ...
Damping performance of bean bag dampers in zero gravity environments
Zhang, Chao; Chen, Tianning; Wang, Xiaopeng
2016-06-01
Bean bag dampers (BBDs), developed from impact damping technology, have been widely applied in engineering field to attenuate the vibration of a structural system. The damping effect of a BBD on vibration control in ground gravity environments is good, but its performance in zero gravity environments is not clear, and there are few studies on it. Therefore, the damping effect of BBDs in zero gravity environments was investigated based on the discrete element method (DEM) in this paper. Firstly, a three-dimensional DEM model of a BBD was established, and the damping effects of the single degree of freedom (SDOF) systems with BBDs and non-obstructive particle dampers (NOPDs) in zero gravity environments were compared. Moreover, the influences of the diameter of the inner ball, the tightness of BBD, the vibration frequency of SDOF system and the gap between BBD and cavity on the vibration reduction effect of BBD in zero gravity environments were also studied, and the results were compared with the system with BBD in ground gravity environments. There are optimum ranges of the diameter of the inner ball, tightness and gap for BBD, and the effects of these parameters on the damping performances of BBD in gravity and zero gravity environments are similar in evolving trends, and the values are without big differences in the optimum ranges. Thereby the parameter selection in BBD design in zero gravity environments is similar to that in gravity environments. However, the diameter of BBD should be a slightly larger than the size of the cavity when the structures with BBD work in zero gravity environments. The BBD is supposed to be picked tightly when the vibration frequency is high, and the BBD has better to be picked more tightly in zero gravity environments. These results can be used as a guide in the design of BBDs in zero gravity environments.
A Spin Gauge Formulation of Gravity and a New View of Gravity-Matter Interactions
Ivancevic, Nicolas
2011-01-01
A first-order formulation of gravity is developed in which the fundamental fields consist of an SL(2,C) connection and two spinor-valued 1-forms. It is shown that the first term of an expansion of the Einstein-Hilbert action leads to an action for these fields which consists of dynamic L2 inner products of their covariant derivatives, resembling reasonable generalisations of the terms found in the actions of typical gauge theories on Minkowski spacetime. If additional terms corresponding to other forces and matter, formulated in the same manner, are then included, this approach may shed new light on interactions of gravity with matter and other force carriers.
Claudia de Rham
2014-01-01
We review recent progress in massive gravity. We start by showing how different theories of massive gravity emerge from a higher-dimensional theory of general relativity, leading to the Dvali–Gabadadze–Porrati model (DGP), cascading gravity, and ghost-free massive gravity. We then explore their theoretical and phenomenological consistency, proving the absence of Boulware–Deser ghosts and reviewing the Vainshtein mechanism and the cosmological solutions in these models. Finally, we present alt...
Barriot, J. P.; Balmino, G.
1992-01-01
A novel method is presented for mapping line-of-sight gravity data (LOSGD) joining planetary probes and observers during Doppler tracking operations, with a view to geodetic and geophysical applications. LOSGD are in this case mapped as gravity anomalies along a radial direction, at constant altitude, using an inversion procedure in conjunction with a Tikhonov-Arsenine regularization method. The application of different regularization-parameter choices to a synthetic case is followed by application to the real case of Pioneer-Venus orbiter data for Venus' Gula Mons.
The dark side of gravity: Modified theories of gravity
Lobo, Francisco S N
2008-01-01
Modern astrophysical and cosmological models are faced with two severe theoretical difficulties, that can be summarized as the dark energy and the dark matter problems. Relative to the former, it has been stated that cosmology has entered a 'golden age', in which high-precision observational data have confirmed with startling evidence that the Universe is undergoing a phase of accelerated expansion. Several candidates, responsible for this expansion, have been proposed in the literature, in p...
Quantum Cosmology of f( R, T) gravity
Xu, Min-Xing; Harko, Tiberiu; Liang, Shi-Dong
2016-08-01
Modified gravity theories have the potential of explaining the recent acceleration of the Universe without resorting to the mysterious concept of dark energy. In particular, it has been pointed out that matter-geometry coupling may be responsible for the recent cosmological dynamics of the Universe, and matter itself may play a more fundamental role in the description of the gravitational processes that usually assumed. In the present paper we study the quantum cosmology of the f( R, T) theory of gravity, in which the effective Lagrangian of the gravitational field is given by an arbitrary function of the Ricci scalar, and the trace of the matter energy-momentum tensor, respectively. For the background geometry we adopt the Friedmann-Robertson-Walker metric, and we assume that matter content of the Universe consists of a perfect fluid. In this framework we obtain the general form of the gravitational Hamiltonian, of the quantum potential, and of the canonical momenta, respectively. This allows us to formulate the full Wheeler-de Witt equation describing the quantum properties of this modified gravity model. As a specific application we consider in detail the quantum cosmology of the f(R,T)=F^0(R)+θ RT model, in which F^0(R) is an arbitrary function of the Ricci scalar, and θ is a function of the scale factor only. The Hamiltonian form of the equations of motion, and the Wheeler-de Witt equations are obtained, and a time parameter for the corresponding dynamical system is identified, which allows one to formulate the Schrödinger-Wheeler-de Witt equation for the quantum-mechanical description of the model under consideration. A perturbative approach for the study of this equation is developed, and the energy levels of the Universe are obtained by using a twofold degenerate perturbation approach. A second quantization approach for the description of quantum time is also proposed and briefly discussed.
Cosmological implications of modified gravity induced by quantum metric fluctuations
Liu, Xing; Harko, Tiberiu; Liang, Shi-Dong
2016-01-01
We investigate the cosmological implications of modified gravities induced by the quantum fluctuations of the gravitational metric. If the metric can be decomposed as the sum of the classical and of a fluctuating part, of quantum origin, then the corresponding Einstein quantum gravity generates at the classical level modified gravity models with a nonminimal coupling between geometry and matter. As a first step in our study, after assuming that the expectation value of the quantum correction ...
Arctic marine gravity and bathymetry from 3 years of Cryosat-2 SAR altimetry (DTU13 Gravity)
DEFF Research Database (Denmark)
Andersen, Ole Baltazar; Stenseng, Lars; Knudsen, Per;
The accuracy of the Arctic marine gravity field has for many been severely limited by the availability and accuracy of altimeter data in the Arctic Ocean. Until recently only ERS-1 provided non-repeat (0.9 year) geodetic mission altimetry in the Arctic Ocean and only up to 82N. With the launch...... of Cryosat-2 three years ago a new source of high quality altimetric data has become available. The Cryosat-2 delay Doppler altimeter offers a factor of 20 improvements in along track resolution, an along-track footprint length that does not vary with wave height (sea state) and at least a factor of two......1 SAR altimetry in the Arctic Ocean for gravity field determination. Extensive testing, interpretation and improvement of methods to handles the new class of data has been investigated and the first result from a new Arctic Ocean wide gravity field will be presented as well as initial test...
Classical limit of quantum gravity in an accelerating universe
Energy Technology Data Exchange (ETDEWEB)
Schuller, Frederic P. [Perimeter Institute for Theoretical Physics, 31 Caroline Street N, Waterloo N2L 2Y5 (Canada)]. E-mail: fschuller@perimeterinstitute.ca; Wohlfarth, Mattias N.R. [II. Institut fuer Theoretische Physik, Universitaet Hamburg, Luruper Chaussee 149, 22761 Hamburg (Germany)]. E-mail: mattias.wohlfarth@desy.de
2005-04-21
A one-parameter deformation of Einstein-Hilbert gravity with an inverse Riemann curvature term is derived as the classical limit of quantum gravity compatible with an accelerating universe. This result is based on the investigation of semi-classical theories with sectional curvature bounds which are shown not to admit static spherically symmetric black holes if otherwise of phenomenological interest. We discuss the impact on the canonical quantization of gravity, and observe that worldsheet string theory is not affected.
The Gravity Fields of the Saturnian Satellites
Iess, L.
2011-12-01
In its tour of the Saturnian system, begun on July 1st, 2004, the Cassini spacecraft had many close flybys of Saturn's main satellites. However, due to impossibility to carry out simultaneously remote sensing observations and microwave tracking from ground, only a small fraction of those flybys could be exploited for gravity measurements. So far, the quadrupole field has been mapped only for Titan, Rhea and Enceladus, while for Hyperion and Iapetus the mass was the only accessible parameter. For Titan and Enceladus, the only satellites targeted more than once for gravity observations, also a rough geoid to degree and order 3 has been determined. Satellite gravity investigations rely upon accurate measurements of the spacecraft range rate, enabled by coherent, two-way radio links at X and Ka band (8.4 and 32.5 GHz). The use of hydrogen masers frequency standards at the ground station and the consid-erable suppression of plasma noise at X and Ka band frequen-cies provide range rate accuracies of 10-30 micron/s at integra-tion times of 60 s. Thanks to the higher frequency of the radio link, these measurement accuracies are in the average a factor of 10 better than those attained by Galileo in its tour of the Jovian system. However, in order to attain a reliable determination of the low degree field, good measurements must be combined with appropriate flyby geometries and adequate sampling, a condition that necessarily requires multiple flybys. We review the main results obtained so far by Cassini for Titan, Rhea and Enceladus, and discuss the methods of analysis used by the Radio Science Team.
Wavelet approach to the determination of gravity tide parameters
Institute of Scientific and Technical Information of China (English)
柳林涛; 许摩泽; 孙和平; 郝兴华
2000-01-01
A new approach is proposed for the determination of gravity tide parameters. Three pairs of compactly supported wavelet filters are introduced in the approach. They can efficiently extract the objective tides from the gravity observation series. The new approach guarantees a direct and precise analysis on the tidal gravity records of any sampling length. The new approach is applied to the harmonic analysis on Wuhan superconducting gravimeter records. The results clearly show the resonant effects of the Earth Nearly Diurnal Free Wobble (NDFW).
Classical limit of quantum gravity in an accelerating universe
Schuller, F P; Schuller, Frederic P.; Wohlfarth, Mattias N.R.
2005-01-01
A one-parameter deformation of Einstein-Hilbert gravity with an inverse curvature term is derived as the classical limit of quantum gravity compatible with an accelerating universe. This result is based on the investigation of semi-classical theories with sectional curvature bounds which are shown not to admit static black holes if otherwise of phenomenological interest. Consequences for classical gravity and the canonical quantization program are briefly discussed.
A new quasidilaton theory of massive gravity
Mukohyama, Shinji
2014-01-01
We present a new quasidilaton theory of Poincare invariant massive gravity, based on the recently proposed framework of matter coupling that makes it possible for the kinetic energy of the quasidilaton scalar to couple to both physical and fiducial metrics simultaneously. We find a scaling-type exact solution that expresses a self-accelerating de Sitter universe, and then analyze linear perturbations around it. It is shown that in a range of parameters all physical degrees of freedom have non-vanishing quadratic kinetic terms and are stable in the subhorizon limit, while the effective Newton's constant for the background is kept positive.
Getting the Swing of Surface Gravity
Thomas, Brian C
2012-01-01
Sports are a popular and effective way to illustrate physics principles. Baseball in particular presents a number of opportunities to motivate student interest and teach concepts. Several articles have appeared in this journal on this topic, illustrating a wide variety of areas of physics. In addition, several websites and an entire book are available. In this paper we describe a student-designed project that illustrates the relative surface gravity on the Earth, Sun and other solar-system bodies using baseball. We describe the project and its results here as an example of a simple, fun, and student-driven use of baseball to illustrate an important physics principle.
Hamiltonian formulation of teleparallel gravity
Ferraro, Rafael
2016-01-01
The Hamiltonian formulation of the teleparallel equivalent of general relativity (TEGR) is developed from an ordinary second-order Lagrangian, which is written as a quadratic form of the coefficients of anholonomy of the orthonormal frames (vielbeins). We analyze the structure of eigenvalues of the multi-index matrix entering the (linear) relation between canonical velocities and momenta to obtain the set of primary constraints. The canonical Hamiltonian is then built with the Moore-Penrose pseudo-inverse of that matrix. The set of constraints, including the subsequent secondary constraints, completes a first class algebra. This means that all of them generate gauge transformations. The gauge freedoms are basically the diffeomorphisms, and the (local) Lorentz transformations of the vielbein. In particular, the ADM algebra of general relativity is recovered as a sub-algebra.
Halo Scale Predictions of Symmetron Modified Gravity
Clampitt, Joseph; Khoury, Justin
2011-01-01
We offer predictions of symmetron modified gravity in the neighborhood of realistic dark matter halos. The predictions for the fifth force are obtained by solving the nonlinear symmetron equation of motion in the spherical NFW approximation. In addition, we compare the three major known screening mechanisms: Vainshtein, Chameleon, and Symmetron around such dark matter sources, emphasizing the significant differences between them and highlighting observational tests which exploit these differences. Finally, we demonstrate the host halo environmental screening effect ("blanket screening") on smaller satellite halos by solving for the modified forces around a density profile which is the sum of satellite and approximate host components.
Quantum gravity extension of the inflationary scenario.
Agullo, Ivan; Ashtekar, Abhay; Nelson, William
2012-12-21
Since the standard inflationary paradigm is based on quantum field theory on classical space-times, it excludes the Planck era. Using techniques from loop quantum gravity, the paradigm is extended to a self-consistent theory from the Planck scale to the onset of slow roll inflation, covering some 11 orders of magnitude in energy density and curvature. This preinflationary dynamics also opens a small window for novel effects, e.g., a source for non-Gaussianities, which could extend the reach of cosmological observations to the deep Planck regime of the early Universe.
Asymptotics of loop quantum gravity fusion coefficients
Energy Technology Data Exchange (ETDEWEB)
Alesci, Emanuele; Bianchi, Eugenio; Magliaro, Elena; Perini, Claudio, E-mail: alesci@fis.uniroma3.i, E-mail: e.bianchi@sns.i, E-mail: elena.magliaro@gmail.co, E-mail: claude.perin@libero.i [Centre de Physique Theorique de Luminy , case 907, F-13288 Marseille (France)
2010-05-07
The fusion coefficients from SO(3) to SO(4) play a key role in the definition of spin foam models for the dynamics in loop quantum gravity. In this paper we give a simple analytic formula of the Engle-Pereira-Rovelli-Livine fusion coefficients. We study the large spin asymptotics and show that they map SO(3) semiclassical intertwiners into SU(2){sub L} x SU(2){sub R} semiclassical intertwiners. This non-trivial property opens the possibility for an analysis of the semiclassical behavior of the model.
The generalized second law of thermodynamics in generalized gravity theories
Wu, Shao-Feng; Wang, Bin; Yang, Guo-Hong; Zhang, Peng-Ming
2008-01-01
We investigate the generalized second law of thermodynamics (GSL) in generalized theories of gravity. We examine the total entropy evolution with time including the horizon entropy, the non-equilibrium entropy production, and the entropy of all matter, field and energy components. We derive a universal condition to protect the generalized second law and study its validity in different gravity theories. In Einstein gravity, (even in the phantom-dominated universe with a Schwarzschild black hol...
Contribution of satellite laser ranging to combined gravity field models
Maier, A.; Krauss, S.; Hausleitner, W.; Baur, O.
2012-02-01
In the framework of satellite-only gravity field modeling, satellite laser ranging (SLR) data is typically exploited to recover long-wavelength features. This contribution provides a detailed discussion of the SLR component of GOCO02S, the latest release of combined models within the GOCO series. Over a period of five years (January 2006 to December 2010), observations to LAGEOS-1, LAGEOS-2, Ajisai, Stella, and Starlette were analyzed. We conducted a series of closed-loop simulations and found that estimating monthly sets of spherical harmonic coefficients beyond degree five leads to exceedingly ill-posed normal equation systems. Therefore, we adopted degree five as the spectral resolution for real data analysis. We compared our monthly coefficient estimates of degree two with SLR and Gravity Recovery and Climate Experiment (GRACE) time series provided by the Center for Space Research (CSR) at Austin, Texas. Significant deviations in C20 were noted between SLR and GRACE; the agreement is better for the non-zonal coefficients. Fitting sinusoids together with a linear trend to our C20 time series yielded a rate of (-1.75 ± 0.6) × 10-11/yr; this drift is equivalent to a geoid change from pole to equator of 0.35 ± 0.12 mm/yr or an apparent Greenland mass loss of 178.5 ± 61.2 km3/yr. The mean of all monthly solutions, averaged over the five-year period, served as input for the satellite-only model GOCO02S. The contribution of SLR to the combined gravity field model is highest for C20, and hence is essential for the determination of the Earth's oblateness.
Directory of Open Access Journals (Sweden)
Galin Tihanov
2012-11-01
Full Text Available I propose to take the grotesque, both as a discursive genre and a cultural attitude and practice, as a point of departure that allows us to comment more widely on Bakhtin‘s Rabelais book and its significance for current debates on subjectivity. In carnival, the epic reverberates in humanity‘s boundless memory ―of cosmic perturbations in the distant past, while the novelistic lives in the grotesque fluctuation and removal of distance, and in the irreverent and joyful celebration of resilience through laughter. Like the epic, carnival is about the maintaining of traditional practices, but in an open and charitably insecure, ―novelistic‖ way. The book on Rabelais seems to be the point where, on reconciling and synthesizing culture and life in the acts of the human body, reworking and redrawing the boundaries of cultural taboos, and championing a symbiosis between the epic and the novelistic, Bakhtin sponsors a new sense of tradition inscribed in the irreverent life of folk (community culture. This celebration of the people re-opens the vexing question about the political implications of Bakhtin‘s pronouncements on the epic and the novelistic, on communitarian and individual culture, and on their desired synthesis. But it also enables us to locate Bakhtin‘s style of thinking and his specific brand of decentred, indeed dislocated, humanism.
Symmetries of Quantum Nonsymmetric Gravity
Mebarki, N.; Maireche, A.; Boudine, A.; Benslama, A
1999-01-01
Withdrawn by arXiv administration because authors have forged affiliations and acknowledgements, and have not adequately responded to charges [hep-th/9912039] of unattributed use of verbatim material.
Sub-subleading soft gravitons: New symmetries of quantum gravity?
Campiglia, Miguel
2016-01-01
Due to seminal works of Weinberg, Cachazo and Strominger we know that tree level quantum gravity amplitudes satisfy three factorization constraints. Building on previous works which relate two of these constraints to symmetries of quantum gravity at null infinity, we present rather strong evidence that the third constraint is also equivalent to a new set of symmetries of (perturbative) quantum gravity. Our analysis implies that the symmetry group of quantum gravity may be even richer than the BMS group (or infinite dimensional extension thereof) previously considered.
Institute of Scientific and Technical Information of China (English)
徐崇温
2012-01-01
In the past few years, there appears a trend, which accelerated during the period of international fi- nancial crisis, of shift of the world＇ s center of gravity from the West to the East. This shift is illustrated not only by the redistribution of power in world production, financial structure, and global governance structure, but also by the transformation of civilizations. Its primary reason is the pathology and maldevelopment of financial capital under neo -liberalism and the frenetic mode of living on debt for consumption. The direct results of change in global balance of power caused by the shift of the world ＇ s center of gravity to the East are primarily the change between the devel- oped countries and developing countries and emerging economies, and the change between the capitalist United States and the socialist China. The ＂converse＂ methods such as ＂returning manufacturing＂ and ＂reindustrializa- tion＂ employed by the capitalist countries in Europe and America to reverse the trend of center shift and power change will be futile.%近年来出现的世界重心由西方向东方转移的发展趋势,在国际金融危机期间得到了加速。这种重心的转移表现在世界生产、金融格局、全球治理结构中权力的再分配乃至文明的转换上。主要原因是新自由主义主导下金融资本的病变和畸形发展,以及狂热的借贷消费的生存方式。由世界重心东移所直接产生的全球力量对比的改变,主要是发达国家同发展中国家、新兴经济体之间力量对比的改变,资本主义美国同社会主义中国之间力量对比的改变;欧美资本主义国家通过＂制造业回归＂、＂再工业化＂等＂逆向＂举措,去扭转世界重心转移和全球力量对比改变的大趋势的企图,是徒劳的。
Cosmological solutions of emergent noncommutative gravity.
Klammer, Daniela; Steinacker, Harold
2009-06-01
Matrix models of the Yang-Mills type lead to an emergent gravity theory, which does not require fine-tuning of a cosmological constant. We find cosmological solutions of the Friedmann-Robertson-Walker type. They generically have a big bounce, and an early inflationlike phase with graceful exit. The mechanism is purely geometrical; no ad hoc scalar fields are introduced. The solutions are stabilized through vacuum fluctuations and are thus compatible with quantum mechanics. This leads to a Milne-like universe after inflation, which appears to be in remarkably good agreement with observation and may provide an alternative to standard cosmology.
Electronic states of germanium grown under micro-gravity condition
Energy Technology Data Exchange (ETDEWEB)
Sugahara, A. [Department of Physics, Graduate School of Science, Osaka University, 1-1 Machikaneyama, Toyonaka, Osaka 560-0043 (Japan)]. E-mail: sugahara@tsurugi.phys.sci.osaka-u.ac.jp; Ogawa, T. [Department of Physics, Graduate School of Science, Osaka University, 1-1 Machikaneyama, Toyonaka, Osaka 560-0043 (Japan); Fujii, K. [Department of Physics, Graduate School of Science, Osaka University, 1-1 Machikaneyama, Toyonaka, Osaka 560-0043 (Japan); Ohyama, T. [Liberal Arts, Fukui University of Technology, 3-6-1 Gakuen, Fukui, Fukui 910-8505 (Japan); Nakata, J. [Kyoto Semiconductor Corp. 418-9 Yodo Saime-cho, Fushimi-ku, Kyoto 613-0915 (Japan)
2006-04-01
Magneto-optical absorption measurements of Sb-doped germaniums grown under micro-gravity condition were carried out to investigate the influence of the gravity on crystal growth, using far-infrared laser and microwave. For comparison, we prepared two germanium crystals grown in the same conditions except the gravity conditions. In spite of the quite short growth period, the germanium grown under micro-gravity has a quite good quality. The lineshape analysis of Zeeman absorption peaks due to donor electrons indicates the existence of residual thermal acceptors.
Liouville gravity from Einstein gravity
Grumiller, D.; Jackiw, R.
2007-01-01
We show that Liouville gravity arises as the limit of pure Einstein gravity in 2+epsilon dimensions as epsilon goes to zero, provided Newton's constant scales with epsilon. Our procedure - spherical reduction, dualization, limit, dualizing back - passes several consistency tests: geometric properties, interactions with matter and the Bekenstein-Hawking entropy are as expected from Einstein gravity.
Gravity Dual of Spatially Modulated Phase
Nakamura, Shin; Park, Chang-Soon
2009-01-01
We show that the five-dimensional Maxwell theory with the Chern-Simons term is tachyonic in the presence of a constant electric field. When coupled to gravity, a sufficiently large Chern-Simons coupling causes instability of the Reissner-Nordstrom black holes in anti-de Sitter space. The instability happens only at non-vanishing momenta, suggesting a spatially modulated phase in the holographically dual quantum field theory in 3+1 dimensions, with spontaneous current generation in a helical configuration. The three-charge extremal black hole in the type IIB superstring theory on AdS_5 x S^5 barely satisfies the stability condition.
Review of lattice supersymmetry and gauge-gravity duality
International Nuclear Information System (INIS)
We review the status of recent investigations on validating the gauge-gravity duality conjecture through numerical simulations of strongly coupled maximally supersymmetric thermal gauge theories. In the simplest setting, the gauge-gravity duality connects systems of D0-branes and black hole geometries at finite temperature to maximally supersymmetric gauged quantum mechanics at the same temperature. Recent simulations show that non-perturbative gauge theory results give excellent agreement with the quantum gravity predictions, thus proving strong evidence for the validity of the duality conjecture and more insight into quantum black holes and gravity.
Review of lattice supersymmetry and gauge-gravity duality
Energy Technology Data Exchange (ETDEWEB)
Joseph, Anosh [Deutsches Elektronen-Synchrotron (DESY), Zeuthen (Germany). John von Neumann-Inst. fuer Computing NIC; Cambridge Univ. (United Kingdom). Dept. of Applied Mathematics and Theoretical Physics (DAMTP)
2015-12-15
We review the status of recent investigations on validating the gauge-gravity duality conjecture through numerical simulations of strongly coupled maximally supersymmetric thermal gauge theories. In the simplest setting, the gauge-gravity duality connects systems of D0-branes and black hole geometries at finite temperature to maximally supersymmetric gauged quantum mechanics at the same temperature. Recent simulations show that non-perturbative gauge theory results give excellent agreement with the quantum gravity predictions, thus proving strong evidence for the validity of the duality conjecture and more insight into quantum black holes and gravity.
From Extended theories of Gravity to Dark Matter
Choudhury, Sayantan; Sadhukhan, Soumya
2016-01-01
In this work, we propose different models of extended theories of gravity, which are minimally coupled to the SM fields, to explain the possibility of a dark matter (DM) candidate, without ad-hoc additions to the Standard Model (SM). We modify the gravity sector by allowing quantum corrections motivated from local $f(R)$ gravity, and non-minimally coupled gravity with SM sector and dilaton field. Using an effective field theory (EFT) framework, we constrain the scale of the EFT and DM mass. We consider two cases-Light DM (LDM) and Heavy DM (HDM), and deduce upper bounds on the DM annihilation cross section to SM particles.
Jiang, Tao; Wang, Yan Ming
2016-07-01
One of the challenges for geoid determination is the combination of heterogeneous gravity data. Because of the distinctive spectral content of different data sets, spectral combination is a suitable candidate for its solution. The key to have a successful combination is to determine the proper spectral weights, or the error degree variances of each data set. In this paper, the error degree variances of terrestrial and airborne gravity data at low degrees are estimated by the aid of a satellite gravity model using harmonic analysis. For higher degrees, the error covariances are estimated from local gravity data first, and then used to compute the error degree variances. The white and colored noise models are also used to estimate the error degree variances of local gravity data for comparisons. Based on the error degree variances, the spectral weights of satellite gravity models, terrestrial and airborne gravity data are determined and applied for geoid computation in Texas area. The computed gravimetric geoid models are tested against an independent, highly accurate geoid profile of the Geoid Slope Validation Survey 2011 (GSVS11). The geoid computed by combining satellite gravity model GOCO03S and terrestrial (land and DTU13 altimetric) gravity data agrees with GSVS11 to ±1.1 cm in terms of standard deviation along a line of 325 km. After incorporating the airborne gravity data collected at 11 km altitude, the standard deviation is reduced to ±0.8 cm. Numerical tests demonstrate the feasibility of spectral combination in geoid computation and the contribution of airborne gravity in an area of high quality terrestrial gravity data. Using the GSVS11 data and the spectral combination, the degree of correctness of the error spectra and the quality of satellite gravity models can also be revealed.
On the biological role of gravity.
Gazenko, O G; Gurjian, A A
1965-01-01
The paper is dedicated to the memory of Galileo Galilei whose work is a great contribution to the development of a new branch of science--gravitation biology. Penetration of man into outer space necessitates a study of the role of gravity in the onto- and phylogenetic development of living organisms. This allows one to get insight into the biological action of weightlessness under the conditions of long-term space flight. The paper summarizes some results of the investigation of weightlessness effects in experiments on animals and during flights of Soviet and American astronauts. The rearing of animals in a special centrifuge under the conditions of prolonged action of accelerations simulating an increased gravity affects noticeably the formation of vegetative (height, weight, metabolism) and animal (vestibulo-tonic reflexes) functions as well as reactivity of the organism. Experiments employing the rearing of animals in a centrifuge represent one of the most promising methods of studying the urgent problem--biological action of increased and decreased gravitation conditions. PMID:12035804
On the biological role of gravity.
Gazenko, O G; Gurjian, A A
1965-01-01
The paper is dedicated to the memory of Galileo Galilei whose work is a great contribution to the development of a new branch of science--gravitation biology. Penetration of man into outer space necessitates a study of the role of gravity in the onto- and phylogenetic development of living organisms. This allows one to get insight into the biological action of weightlessness under the conditions of long-term space flight. The paper summarizes some results of the investigation of weightlessness effects in experiments on animals and during flights of Soviet and American astronauts. The rearing of animals in a special centrifuge under the conditions of prolonged action of accelerations simulating an increased gravity affects noticeably the formation of vegetative (height, weight, metabolism) and animal (vestibulo-tonic reflexes) functions as well as reactivity of the organism. Experiments employing the rearing of animals in a centrifuge represent one of the most promising methods of studying the urgent problem--biological action of increased and decreased gravitation conditions.
Effect of Crustal Density Structures on GOCE Gravity Gradient Observables
Directory of Open Access Journals (Sweden)
Robert Tenzer and Pavel Novák
2013-01-01
Full Text Available We investigate the gravity gradient components corrected for major known anomalous density structures within the _ crust. Heterogeneous mantle density structures are disregarded. The gravimetric forward modeling technique is utilized to compute the gravity gradients based on methods for a spherical harmonic analysis and synthesis of a gravity field. The _ gravity gradient components are generated using the global geopotential model GOCO-03s. The topographic and stripping gravity corrections due to the density contrasts of the ocean and ice are computed from the global topographic/bathymetric model DTM2006.0 (which also includes the ice-thickness dataset. The discrete data of sediments and crust layers taken from the CRUST2.0 global crustal model are then used to apply the additional stripping corrections for sediments and remaining anomalous crustal density structures. All computations are realized globally on a one arc-deg geographical grid at a mean satellite elevation of 255 km. The global map of the consolidated crust-stripped gravity gradients reveals distinctive features which are attributed to global tectonics, lithospheric plate configuration, lithosphere structure and mantle dynamics (e.g., glacial isostatic adjustment, mantle convection. The Moho signature, which is the most pronounced signal in these refined gravity gradients, is superimposed over a weaker gravity signal of the lithospheric mantle. An interpretational quality of the computed (refined gravity gradient components is mainly limited by a low accuracy and resolution of the CRUST2.0 sediment and crustal layer data and unmodeled mantle structures.
Generalised Boundary for Higher Derivative Theories of Gravity
Teimouri, Ali; Edholm, James; Mazumdar, Anupam
2016-01-01
In this paper we wish to find the corresponding Gibbons-Hawking-York term for the most general quadratic in curvature gravity by using Coframe slicing within the Arnowitt-Deser-Misner (ADM) decomposition of spacetime in four dimensions. In order to make sure that the higher derivative gravity is ghost and tachyon free at a perturbative level, one requires infinite covariant derivatives, which yields a generalised covariant infinite derivative theory of gravity. We will be exploring the boundary term for such a covariant infinite derivative theory of gravity.
Impact Of GOCE On The Nordic Gravity Field Modelling
DEFF Research Database (Denmark)
Yidiz, Hasan; Forsberg, René; Tscherning, C. C.;
2011-01-01
GOCE level-2 Tzz and Txx gravity gradients at satellite altitude are used in combination as input data to predict surface free air gravity anomalies over the Nordic region using Least Square Collocation. We test the performance of using covariance functions created separately from Tzz gradients...... and surface free air gravity anomalies to predict terrestrial gravity anomalies with a direct comparison of 19 mgal level and much better (7-8 mgal) when surface data are filtered at the GOCE resolution. We found that the results are slightly dependent of covariance function. Combined with DTU10 Mean Sea...
Violation of the holographic principle in the loop quantum gravity
Sargın, Ozan; Faizal, Mir
2016-02-01
In this paper, we analyze the holographic principle using loop quantum gravity (LQG). This will be done by using polymeric quantization for analysing Yurtsever's holographic bound on the entropy, which is obtained from local quantum field theories. As the polymeric quantization is the characteristic feature of loop quantum gravity, we will argue that this calculation will indicate the effect of loop quantum gravity on the holographic principle. Thus, we will be able to explicitly demonstrate the violation of the holographic principle in the loop quantum gravity.
Universality of testing ghost-free gravity
Edholm, James; Mazumdar, Anupam
2016-01-01
In this paper we show that there is a universal prediction for the Newtonian potential for an infinite derivative, ghost-free, quadratic curvature gravity. We show that in order to make such a theory ghost-free at a perturbative level, the Newtonian potential always falls-off as 1/r in the infrared limit, while at short distances the potential becomes non-singular. We provide examples which can potentially test the scale of gravitational non-locality up to 0.01 eV.
Note on the relationship between the speed of light and gravity in the bi-metric theory of gravity
Kopeikin, Sergei
2005-01-01
Relationship between the speed of gravity c_g and the speed of light c_e in the bi-metric theory of gravity is discussed. We reveal that the speed of light is a function of the speed of gravity which is a primary fundamental constant. Thus, experimental measurement of relativistic bending of light propagating in time-dependent gravitational field directly compares the speed of gravity versus the speed of light and tests if there is any aether associated with the gravitational field considered...
Embeddings of the "New Massive Gravity"
Dalmazi, D.; Mendonça, E. L.
2016-07-01
Here we apply different types of embeddings of the equations of motion of the linearized "New Massive Gravity" in order to generate alternative and even higher-order (in derivatives) massive gravity theories in D=2+1. In the first part of the work we use the Weyl symmetry as a guiding principle for the embeddings. First we show that a Noether gauge embedding of the Weyl symmetry leads to a sixth-order model in derivatives with either a massive or a massless ghost, according to the chosen overall sign of the theory. On the other hand, if the Weyl symmetry is implemented by means of a Stueckelberg field we obtain a new scalar-tensor model for massive gravitons. It is ghost-free and Weyl invariant at the linearized level around Minkowski space. The model can be nonlinearly completed into a scalar field coupled to the NMG theory. The elimination of the scalar field leads to a nonlocal modification of the NMG. In the second part of the work we prove to all orders in derivatives that there is no local, ghost-free embedding of the linearized NMG equations of motion around Minkowski space when written in terms of one symmetric tensor. Regarding that point, NMG differs from the Fierz-Pauli theory, since in the latter case we can replace the Einstein-Hilbert action by specific f(R,Box R) generalizations and still keep the theory ghost-free at the linearized level.
Einstein's theory of gravity and the problem of missing mass.
Ferreira, Pedro G; Starkman, Glenn D
2009-11-01
The observed matter in the universe accounts for just 5% of the observed gravity. A possible explanation is that Newton's and Einstein's theories of gravity fail where gravity is either weak or enhanced. The modified theory of Newtonian dynamics (MOND) reproduces, without dark matter, spiral-galaxy orbital motions and the relation between luminosity and rotation in galaxies, although not in clusters. Recent extensions of Einstein's theory are theoretically more complete. They inevitably include dark fields that seed structure growth, and they may explain recent weak lensing data. However, the presence of dark fields reduces calculability and comes at the expense of the original MOND premise, that the matter we see is the sole source of gravity. Observational tests of the relic radiation, weak lensing, and the growth of structure may distinguish modified gravity from dark matter. PMID:19892973
Einstein's theory of gravity and the problem of missing mass.
Ferreira, Pedro G; Starkman, Glenn D
2009-11-01
The observed matter in the universe accounts for just 5% of the observed gravity. A possible explanation is that Newton's and Einstein's theories of gravity fail where gravity is either weak or enhanced. The modified theory of Newtonian dynamics (MOND) reproduces, without dark matter, spiral-galaxy orbital motions and the relation between luminosity and rotation in galaxies, although not in clusters. Recent extensions of Einstein's theory are theoretically more complete. They inevitably include dark fields that seed structure growth, and they may explain recent weak lensing data. However, the presence of dark fields reduces calculability and comes at the expense of the original MOND premise, that the matter we see is the sole source of gravity. Observational tests of the relic radiation, weak lensing, and the growth of structure may distinguish modified gravity from dark matter.
The f(R gravity function of the Linde quintessence
Directory of Open Access Journals (Sweden)
Sergei V. Ketov
2015-02-01
Full Text Available We calculate the f(R gravity function in the dual gravity description of the quintessence model with a quadratic (Linde scalar potential and a positive cosmological constant. We find that in the large curvature regime relevant to chaotic inflation in Early Universe, the dual f(R gravity is well approximated by the (matter loop-corrected Starobinsky inflationary model. In the small curvature regime relevant to dark energy in the Present Universe, the f(R gravity function reduces to the Einstein–Hilbert one with a positive cosmological constant.
A Simple Theory of Quantum Gravity
Horndeski, Gregory W
2015-01-01
A novel theory of Quantum Gravity is presented in which the real gravitons manifest themselves as holes in space. In general, these holes propagate at the speed of light through an expanding universe with boundary denoted by U, which is comprised of pulsating cells. These holes can form bound and semi-bound states. The geometry of U is non-Euclidean on a small scale, but there are indications that it can become Euclidean on a large scale. The motions of elementary particles through U are governed by probability 4 and 7-vectors, which are related to the momentum vectors in Minkowski space. The connection of this theory to Newtonian gravity is discussed, and an expression for the gravitational redshift of photons is derived which relates the redshift to the probability that a photon absorbs a virtual graviton. The theory also provides a possible explanation of dark matter and dark energy as gravitational phenomena, which do not require the introduction of any new particles. A quantum cosmology is presented in w...
Fabrication of gravity-driven microfluidic device
Yamada, H.; Yoshida, Y.; Terada, N.; Hagihara, S.; Komatsu, T.; Terasawa, A.
2008-12-01
We have studied the micro total analysis system as a blood test. A microfluidic device with a three-pronged microchannel and artificial capillary vessels was fabricated. The microchannel is to transport blood, focus blood cells, and line them up. The vessels are to observe red blood cell deformation. An excimer laser was used to form grooves and so on. Numbers of thermosetting resin film and fluororesin were piled up on a cover glass. A laser fabricated part of the channel at the each film every lamination, and then a three-dimensional structure microchannel was fabricated. The channel sizes have widths of 50-150 μm and depths of 45 μm. Through holes used as artificial capillary vessels are made in the fluororesin having a minimum diameter of 5 μm and a length of 100 μm. As blood and a physiological saline are injected into the microchannel, the device stands upward facing the channel, and blood cells go into the vessels by the force of gravity and sheath flow of the saline. By gravity various groove patterns were made changing the width and length for measurement of blood focusing. Moreover, the red blood cell deformation was observed in the vessels with a microscope.
Motion in alternative theories of gravity
Esposito-Farese, Gilles
2009-01-01
Although general relativity (GR) passes all present experimental tests with flying colors, it remains important to study alternative theories of gravity for several theoretical and phenomenological reasons that we recall in these lecture notes. The various possible ways of modifying GR are presented, and we notably show that the motion of massive bodies may be changed even if one assumes that matter is minimally coupled to the metric as in GR. This is illustrated with the particular case of scalar-tensor theories of gravity, whose Fokker action is discussed, and we also mention the consequences of the no-hair theorem on the motion of black holes. The finite size of the bodies modifies their motion with respect to pointlike particles, and we give a simple argument showing that the corresponding effects are generically much larger in alternative theories than in GR. We also discuss possible modifications of Newtonian dynamics (MOND) at large distances, which have been proposed to avoid the dark matter hypothesi...
Phenomenology in minimal theory of massive gravity
De Felice, Antonio
2015-01-01
We investigate the minimal theory of massive gravity (MTMG) recently introduced. After reviewing the original construction based on its Hamiltonian in the vielbein formalism, we reformulate it in terms of its Lagrangian in both the vielbein and the metric formalisms. It then becomes obvious that, unlike previous attempts in the literature, not only the potential but also the kinetic structure of the action is modified from the de Rham-Gabadadze-Tolley (dRGT) massive gravity theory. We confirm that the number of physical degrees of freedom in MTMG is two at fully nonlinear level. This proves the absence of various possible pathologies such as superluminality, acausality and strong coupling. Afterwards, we discuss the phenomenology of MTMG in the presence of a dust fluid. We find that on a flat homogeneous and isotropic background we have two branches. One of them (self-accelerating branch) naturally leads to acceleration without the genuine cosmological constant or dark energy. For this branch both the scalar ...
Capozziello, S; Salzano, V
2008-01-01
It is nowadays accepted that the universe is undergoing a phase of accelerated expansion as tested by the Hubble diagram of Type Ia Supernovae (SNeIa) and several LSS observations. Future SNeIa surveys and other probes will make it possible to better characterize the dynamical state of the universe renewing the interest in cosmography which allows a model independent analysis of the distance - redshift relation. On the other hand, fourth order theories of gravity, also referred to as $f(R)$ gravity, have attracted a lot of interest since they could be able to explain the accelerated expansion without any dark energy. We show here how it is possible to relate the cosmographic parameters (namely the deceleration $q_0$, the jerk $j_0$, the snap $s_0$ and the lerk $l_0$ parameters) to the present day values of $f(R)$ and its derivatives $f^{(n)}(R) = d^nf/dR^n$ (with $n = 1, 2, 3$) thus offering a new tool to constrain such higher order models. Our analysis thus offers the possibility to relate the model independ...
LHC Signals of Pure Gravity Mediation
Directory of Open Access Journals (Sweden)
Feldstein Brian
2013-05-01
Full Text Available Evidence is mounting that natural supersymmetry at the weak scale is not realized in nature. This evidence comes from collider searches, a lack of new flavor changing neutral current effects, and now also the size of the measured Higgs mass. On the other hand, string theory suggests that supersymmetry might be present at some energy scale, and gauge coupling unification and dark matter imply that that energy scale may be relatively low. The simplest model to address all of these hints is arguably “pure gravity mediation”, in which the scalar superpartner masses are taken to be perhaps 100 TeV, with gauginos automatically acquiring loop factor suppressed masses of order TeV. The gauginos might then be the only superpartners accessible to the LHC. Unification and LSP dark matter are maintained (with a wino LSP at the cost of a 10−5 or 10−6 fine tuning. Here I will discuss the structure and LHC phenomenology of pure gravity mediation.
Institute of Scientific and Technical Information of China (English)
卢飞; 蒙永胜; 刘明辉
2016-01-01
The essence of constant promotion of the Silk Road Economic Belt needs people’s supports ,and places emphasis on residents’ higher income and regional coordination .The dis-crete distribution of elements and the economic or social development is a new perspective to learn about regional differences .Based on A HP and entropy method ,this paper designs an analytical framework to describe the regional differences by the application of gravity principle .Then it ex-plores the barycenter moving track of factors such as resources ,environment ﹠ population ,and economy ﹠ society in Xinjiang Uygur autonomous region from 1998 to 2013 ,identifies the con-vergent and discrete trends among factors from the perspectives of spatial distribution correlation and matching between factors and economy ﹠ society ,and then analyzes the evolution of regional differences in Xinjiang Uygur autonomous region .It arrives at the results as follows :firstly ,pop-ulation distribution’s center of gravity dislocates economy and society ’s center of gravity ,and the mismatching degree widens ;secondly ,resources and environment play a common role in the distribution of the center of gravity and track changes of society and population :resources affect the distribution of the center of gravity ,environment affects track changes ,and the effect of re-sources is more significant ;thirdly , the effectiveness of the role of fiscal control in regional differences is not sound ,and a series of projects of the Silk Road Economic Belt in the short term are difficult to make up the development weakness of the south Xinjiang Uygur autonomous re-gion ,but in the long term (2030) the differences among districts may weaken .In order to coordi-nate the core area development of the Silk Road Economic Belt ,governments should help to ad-vance the long-term stability of the strategy of the Silk Road Economic Belt through differentiated policies of talents ,investment ﹠ openness and effective
Modeling Human Perception of Orientation in Altered Gravity
Directory of Open Access Journals (Sweden)
Torin K. Clark
2015-05-01
Full Text Available Altered gravity environments, such as those experienced by astronauts, impact spatial orientation perception and can lead to spatial disorientation and sensorimotor impairment. To more fully understand and quantify the impact of altered gravity on orientation perception, several mathematical models have been proposed. The utricular shear, tangent, and the idiotropic vector models aim to predict static perception of tilt in hyper-gravity. Predictions from these prior models are compared to the available data, but are found to systematically err from the perceptions experimentally observed. Alternatively, we propose a modified utricular shear model for static tilt perception in hyper-gravity. Previous dynamic models of vestibular function and orientation perception are limited to 1 G. Specifically, they fail to predict the characteristic overestimation of roll tilt observed in hyper-gravity environments. To address this, we have proposed a modification to a previous observer-type canal otolith interaction model based upon the hypothesis that the central nervous system treats otolith stimulation in the utricular plane differently than stimulation out of the utricular plane. Here we evaluate our modified utricular shear and modified observer models in four altered gravity motion paradigms: a static roll tilt in hyper-gravity, b static pitch tilt in hyper-gravity, c static roll tilt in hypo-gravity, and d static pitch tilt in hypo-gravity. The modified models match available data in each of the conditions considered. Our static modified utricular shear model and dynamic modified observer model may be used to help quantitatively predict astronaut perception of orientation in altered gravity environments.
DEFF Research Database (Denmark)
Rapetti Serra, David Angelo
2011-01-01
Using measurements of the abundance of galaxy clusters we obtain constraints on dark energy and gravity at cosmological scales. Our data set consists of 238 cluster detections drawn from the ROSAT All-Sky Survey and X-ray follow-up observations of 94 of those clusters. Using a new statistical...... framework we self-consistently and simultaneously constrain cosmology and observable-mass scaling relations accounting for survey biases, parameter covariances and systematic uncertainties. Allowing the linear growth index and the dark energy equation of state to take any constant values, we find...
Oscillating cosmological solutions within gauge theories of gravity
Vereshchagin, G.
2003-01-01
New type of nonsingular oscillating solutions for the Universe described by cosmological equations of gauge theories of gravity is presented. Advantages of these solutions with respect to existing nonsingular solutions within framework of general relativity and gauge gravity are discussed. It is shown in particular that these solutions have nonzero measure and stable on contraction stage unlike usual nonsingular solutions.
Eigenvalues of the volume operator in loop quantum gravity
Energy Technology Data Exchange (ETDEWEB)
Meissner, Krzysztof A [Institute of Theoretical Physics, Warsaw University, Hoza 69, 00-681 Warsaw (Poland); Theoretical Division, CERN, Geneva (Switzerland)
2006-02-07
We present a simple method to calculate certain sums of the eigenvalues of the volume operator in loop quantum gravity. We derive the asymptotic distribution of the eigenvalues in the classical limit of very large spins, which turns out to be of a very simple form. The results can be useful for example in the statistical approach to quantum gravity.
Stochastic cosmology, theories of perturbations and Lifshitz gravity
Khalatnikov, I. M.; Kamenshchik, A. Yu.
2015-01-01
We review some works of E M Lifshitz connected with gravity and cosmology and also some later works, connected with his ideas. The main topics of this review are the stochastic cosmology of an anisotropic universe and of an isotropic universe with the scalar field, the quasi-isotropic (gradient) expansion in cosmology and Horava-Lifshitz gravity and cosmology.
Gravity-driven clustering of inertial particles in turbulence.
Park, Yongnam; Lee, Changhoon
2014-06-01
We report a different kind of particle clustering caused purely by gravity, discovered in our simulation of particle-laden turbulence. Clustering in a vertical strip pattern forms when strong gravity acts on heavy particles. This phenomenon is explained by the skewness of the flow velocity gradient in the gravitational direction experienced by particles, which causes horizontal convergence of particles.
Specific gravity and API gravity of biodiesel and ultra-low sulfur diesel (ULSD) blends
Biodiesel is an alternative fuel made from vegetable oils and animal fats. In 2006, the U. S. Environmental Protection Agency mandated a maximum sulfur content of 15 ppm in on-road diesel fuels. Processing to produce the new ultra-low sulfur petrodiesel (ULSD) alters specific gravity (SG) and othe...
A regional gravity survey of the Cuyuna Iron Range, Minnesota
Durfee, George Austin
1957-01-01
A regional gravity survey of the Cuyuna Iron Range, Minnesota, was conducted during the summer of 1955 by the U. S. Geological Survey. It was believed that gravity data would aid in the understanding of the major structures of the range. It was found that synclinal and steeply dipping structures produced positive gravity anomalies while anilclinal structures produced negative anomalies. This principle was noted in areas of well known geology and then applied to outlying areas of the district. The outstanding gravity feature is a narrow positive anomaly extending from south of Brainerd eastward through Aitkin, the axis of the anomaly being somewhat south of the South Range. This gives support to the theory that the Biwabik formation passes under the stratigraphically higher South Range member as a synclinal structure. However, this anomaly is also explained using one main iron formation and assuming an anticlinal structure between the North and South Ranges and a syncline between the South Range and Bay Lake. A large magnitude negative gravity anomaly north of Mille Lacs is postulated to result from an intrusive mass extending to the erosion surface. Aeromagnetics are used to strengthen the gravity interpretation. The need is realized for additional regional gravity coverage to the east of the area Included in this survey and a detailed gravity study of the area between the North and South Ranges.
Mechanics of Apparent Horizon in Two Dimensional Dilaton Gravity
Cai, Rong-Gen
2016-01-01
In this article, we give a definition of apparent horizon in a two dimensional general dilaton gravity theory. With this definition, we construct the mechanics of the apparent horizon by introducing a quasi-local energy of the theory. Our discussion generalizes the apparent horizons mechanics in general spherically symmetric spactimes in four or higher dimensions to the two dimensional dilaton gravity case.
Hamiltonian Analysis of Mixed Derivative Horava-Lifshitz Gravity
Kluson, J
2016-01-01
This short note is devoted to the canonical analysis of the Horava-Lifshitz gravity with mixed derivative terms that was proposed in arXiv:1604.04215. We determine the algebra of constraints and we show that there is one additional scalar degree of freedom with respect to the non-projectable Horava-Lifshitz gravity.
Stochastic filtering for determining gravity variations for decade-long time series of GRACE gravity
Wang, Lei; Davis, James L.; Hill, Emma M.; Tamisiea, Mark E.
2016-04-01
We present a new stochastic filter technique for statistically rigorous separation of gravity signals and correlated "stripe" noises in a series of monthly gravitational spherical harmonic coefficients (SHCs) produced by the Gravity Recovery and Climate Experiment (GRACE) satellite mission. Unlike the standard destriping process that removes the stripe contamination empirically, the stochastic approach simultaneously estimates gravity signals and correlated noises relying on covariance information that reflects both the spatial spectral features and temporal correlations among them. A major benefit of the technique is that by estimating the stripe noise in a Bayesian framework, we are able to propagate statistically rigorous covariances for the destriped GRACE SHCs, i.e. incorporating the impact of the destriping on the SHC uncertainties. The Bayesian approach yields a natural resolution for the gravity signal that reflects the correlated stripe noise, and thus achieve a kind of spatial smoothing in and of itself. No spatial Gaussian smoothing is formally required although it might be useful for some circumstances. Using the stochastic filter, we process a decade-length series of GRACE monthly gravity solutions, and compare the results with GRACE Tellus data products that are processed using the "standard" destriping procedure. The results show that the stochastic filter is able to remove the correlated stripe noise to a remarkable degree even without an explicit smoothing step. The estimates from the stochastic filter for each destriped GRACE field are suitable for Bayesian integration of GRACE with other geodetic measurements and models, and the statistically rigorous estimation of the time-varying rates and seasonal cycles in GRACE time series.
Economics of data center optics
Huff, Lisa
2016-03-01
Traffic to and from data centers is now reaching Zettabytes/year. Even the smallest of businesses now rely on data centers for revenue generation. And, the largest data centers today are orders of magnitude larger than the supercomputing centers of a few years ago. Until quite recently, for most data center managers, optical data centers were nice to dream about, but not really essential. Today, the all-optical data center - perhaps even an all-single mode fiber (SMF) data center is something that even managers of medium-sized data centers should be considering. Economical transceivers are the key to increased adoption of data center optics. An analysis of current and near future data center optics economics will be discussed in this paper.
Boundary Dynamics of Higher Dimensional Chern-Simons Gravity
Gegenberg, J.; Kunstatter, G.
2000-01-01
We review the relevance to the black hole entropy problem of boundary dynamics in Chern-Simons gravity. We then describe a recent derivation of the action induced on the four dimensional boundary in a five dimensional Chern-Simons gravity theory with gauge invariant, anti-deSitter boundary conditions.
Gravity dependence at the bottom of the main sequence
Viti, Serena; Jones, Hugh R. A.
1999-11-01
We investigate the effects of gravity on the infrared spectra of objects around the M dwarf to brown dwarf transition. We focus on observations of the very low-mass objects TVLM 513-46546 and GJ 569B from 1 to 2.5 mu m. These objects have very similar spectral types and colours but they differ by more than a magnitude in luminosity; this indicates that their surface gravities differ by around 0.5 dex. We compare their spectra and present line identifications in the infrared. We investigate at low resolution the sensitivity of some of the atomic features to changes in surface gravities and make comparisons with recent atmospheric models. We identify seven surface gravity sensitive features. We find that the difference in surface gravity between the spectra are consistent with GJ 569B having a lower surface gravity than TVLM by at least 0.5 dex which suggests GJ 569B is a brown dwarf. Because of the relatively few surface gravity features which can be identified at low resolution, confirmation of this result should be made with observations at higher resolution which would enable more gravity sensitive features to be identified with better precision.
Local effects of gravity wave propagation and saturation
Fritts, D. C.
1985-01-01
In recent years, gravity waves were recognized to play a major role in the dynamics of the middle atmosphere. Perhaps the major effect of such motions are the reversal of the vertical shear of the mean zonal wind and the occurrence of a large turbulent diffusivity in the mesosphere due to gravity wave saturation. Yet, despite the importance of these gravity wave effects, the processes and the consequences of gravity wave propagation and saturation are only beginning to be understood in detail. The linear saturation theory predicts drag and turbulent diffusion due to saturating wave motion. This theory, however, fails to address a number of issues that are certain to be important for gravity wave propagation and saturation in the middle atmosphere. These issues, including wave transience, wave superposition, local convective adjustment, and nonlinearity, are discussed.
Bending of light in conformal Weyl gravity
Sultana, Joseph; Kazanas, Demosthenes
2010-06-01
We reexamine the bending of light issue associated with the metric of the static, spherically symmetric solution of Weyl gravity discovered by Mannheim and Kazanas (1989). To this end we employ the procedure used recently by Rindler and Ishak to obtain the bending angle of light by a centrally concentrated spherically symmetric matter distribution in a Schwarzschild-de Sitter background. In earlier studies the term γr in the metric led to the paradoxical result of a bending angle proportional to the photon impact parameter, when using the usual formalism appropriate to asymptotically flat space-times. However, employing the approach of light bending of Rindler and Ishak we show that the effects of this term are in fact insignificant, with the discrepancy between the two procedures attributed to the definition of the bending angle between the asymptotically flat and nonflat spaces.
Eddy diffusivities of inertial particles under gravity
Afonso, Marco Martins; Muratore-Ginanneschi, Paolo
2011-01-01
The large-scale/long-time transport of inertial particles of arbitrary mass density under gravity is investigated by means of a formal multiple-scale perturbative expansion in the scale-separation parametre between the carrier flow and the particle concentration field. The resulting large-scale equation for the particle concentration is determined, and is found to be diffusive with a positive-definite eddy diffusivity. The calculation of the latter tensor is reduced to the resolution of an auxiliary differential problem, consisting of a coupled set of two differential equations in a (6+1)-dimensional coordinate system (3 space coordinates plus 3 velocity coordinates plus time). Although expensive, numerical methods can be exploited to obtain the eddy diffusivity, for any desirable non-perturbative limit (e.g. arbitrary Stokes and Froude numbers). The aforementioned large-scale equation is then specialized to deal with two different relevant perturbative limits: i) vanishing of both Stokes time and sedimenting...
Crossing of the phantom divide in modified gravity
Bamba, Kazuharu; Nojiri, Shin'ichi; Odintsov, Sergei D
2009-01-01
We reconstruct an explicit model of modified gravity in which a crossing of the phantom divide can be realized. It is shown that the Big Rip singularity appears in the model of modified gravity, whereas that the (finite-time) Big Rip singularity in modified gravity is transformed to the infinite-time singularity in the corresponding scalar field theory obtained through the conformal transformation. Furthermore, we investigate the relations between the scalar field theories realizing a crossing of the phantom divide and the corresponding modified gravitational theories by using the inverse conformal transformation. It is demonstrated that the scalar field theories describing the non-phantom phase (phantom one with the Big Rip) can be represented as the theories of real (complex) $F(R)$ gravity through the inverse (complex) conformal transformation. We also study a viable model of modified gravity in which the transition from the de Sitter universe to the phantom phase can occur.
Determination of Antarctic geoid by using global gravity field
Institute of Scientific and Technical Information of China (English)
无
2000-01-01
With Chinese latest global gravity field model WDM94, the authors providethe geoid height and mean free-air gravity anomaly of Antarctica (The range of latitude is from—60° to—90°). In order to conclude and analyze the characters of Antarctic geoid roundly, the authors collect the latest oversea global gravity field model OSU91 (to degree and order 360) and JGMOSU (to degree and order 360), get the corresponding geoid height and mean free-air gravity anomaly. The results arecompared with the results got from WDM94, thus we get the difference. The standard deviation of geoid height between WDM94 and OSU91 is ± 1.90 re;the deviation of geoid between WDM9 and JGMOSU is ± 2.09 m. The standard deviation of mean gravity anomaly are±8.97 mGal and ± 9.32 mGal respectively.
Hamiltonian analysis of Einstein-Chern-Simons gravity
Avilés, L.; Salgado, P.
2016-06-01
In this work we consider the construction of the Hamiltonian action for the transgressions field theory. The subspace separation method for Chern-Simons Hamiltonian is built and used to find the Hamiltonian for five-dimensional Einstein-Chern-Simons gravity. It is then shown that the Hamiltonian for Einstein gravity arises in the limit where the scale parameter l approaches zero.
Impact of Gravity on Vacuum Stability
Branchina, Vincenzo; Zappala, Dario
2016-01-01
In a pioneering paper on the role of gravity on false vacuum decay, Coleman and De Luccia showed that a strong gravitational field can stabilize the false vacuum, suppressing the formation of true vacuum bubbles. This result is obtained for the case when the energy density difference between the two vacua is small, the so called thin wall regime, but is considered of more general validity. Here we show that when this condition does not hold, however, {\\it even a very strong gravitational field (Planckian physics) cannot suppress the formation of true vacuum bubbles}. Contrary to common expectations then, gravitational physics at the Planck scale {\\it does not stabilize the false vacuum}. These results are of crucial importance for the stability analysis of the electroweak vacuum and for searches of new physics beyond the Standard Model.
Acoustic levitation in the presence of gravity
Collas, P.; Barmatz, M.; Shipley, C.
1989-01-01
The method of Gor'kov (1961) has been applied to derive general expressions for the total potential and force on a small spherical object in a resonant chamber in the presence of both acoustic and gravitational force fields. The levitation position is also determined in rectangular resonators for the simultaneous excitation of up to three acoustic modes, and the results are applied to the triple-axis acoustic levitator. The analysis is applied to rectangular, spherical, and cylindrical single-mode levitators that are arbitrarily oriented relative to the gravitational force field. Criteria are determined for isotropic force fields in rectangular and cylindrical resonators. It is demonstrated that an object will be situated within a volume of possible levitation positions at a point determined by the relative strength of the acoustic and gravitational fields and the orientation of the chamber relative to gravity.
Extended Scalar-Tensor Theories of Gravity
Crisostomi, Marco; Tasinato, Gianmassimo
2016-01-01
We determine new consistent scalar-tensor theories of gravity, with potentially interesting cosmological applications. We develop a general method to find the conditions for the existence of a primary constraint, which is necessary to prevent the propagation of an additional dangerous mode associated with higher order equations of motion. We then classify the most general, consistent scalar-tensor theories that are at most quadratic in the second derivatives of the scalar field. In addition, we investigate the possible connection between these theories and (beyond) Horndeski through conformal and disformal transformations. Finally, we point out that these theories can be associated with new operators in the effective field theory of dark energy, which might open up new possibilities to test dark energy models in future surveys.
Kruglov, S I
2015-01-01
The new model of modified $F(R)$ gravity theory with the function $F(R) = R+(a/\\gamma) \\arcsin(\\gamma R)$ is suggested and investigated. Constant curvature solutions corresponding to the extremum of the effective potential are obtained. We consider both the Jordan and Einstein frames, and the potential and the mass of the scalar degree of freedom are found. It was shown that the de Sitter space-time is unstable but the flat space-time is stable. We calculate the slow-roll parameters $\\epsilon$, $\\eta$, and the $e$-fold number of the model. Critical points of autonomous equations for the de Sitter phase and the matter dominated epoch are obtained and learned.
Stellar Structure and Tests of Modified Gravity
Chang, Philip
2010-01-01
Theories that attempt to explain cosmic acceleration by modifying gravity typically introduces a long-range scalar force that needs to be screened on small scales. One common screening mechanism is the chameleon, where the scalar force is screened in environments with a sufficiently deep gravitational potential, but acts unimpeded in regions with a shallow gravitational potential. This leads to a variation in the overall gravitational G with environment. We show such a variation can occur within a star itself, significantly affecting its evolution and structure, provided that the host galaxy is unscreened. The effect is most pronounced for red giants, which would be smaller by a factor of tens of percent and thus hotter by 100's of K, depending on the parameters of the underlying scalar-tensor theory. Careful measurements of these stars in suitable environments (nearby dwarf galaxies not associated with groups or clusters) would provide constraints on the chameleon mechanism that are four orders of magnitude ...
Dynamics of Gravity in a Higgs Phase
Arkani-Hamed, N; Luty, M A; Mukohyama, S; Wiseman, T; Arkani-Hamed, Nima; Cheng, Hsin-Chia; Luty, Markus A.; Mukohyama, Shinji; Wiseman, Toby
2007-01-01
We investigate the universal low-energy dynamics of the simplest Higgs phase for gravity, `ghost condensation.' We show that the nonlinear dynamics of the `ghostone' field dominate for all interesting gravitational sources. Away from caustic singularities, the dynamics is equivalent to the irrotational flow of a perfect fluid with equation of state p \\propto \\rho^2, where the fluid particles can have negative mass. We argue that this theory is free from catastrophic instabilities due to growing modes, even though the null energy condition is violated. Numerical simulations show that solutions generally have singularities in which negative energy regions shrink to zero size. We exhibit partial UV completions of the theory in which these singularities are smoothly resolved, so this does not signal any inconsistency in the effective theory. We also consider the bounds on the symmetry breaking scale M in this theory. We argue that the nonlinear dynamics cuts off the Jeans instability of the linear theory, and all...
The Structural Foundations of Quantum Gravity
International Nuclear Information System (INIS)
The core of the collection of papers that form the book originates from a workshop on 'Structural Aspects of Quantum Gravity' held in Milwaukee, WI, in 2002. But the collection also includes contributions from philosophers and scientists who did not attend the meeting. The book is presented with a structuralist agenda: to emphasize the idea that 'relational structures are of equal or more fundamental ontological status than objects'. The goal of the editors is, as they put it, to 'suggest' a possible 'interpretative and ontological perspective from which to view quantum gravity physics'. Attention to structure rather than objects is a long-standing tradition. It played a major role in anthropology and linguistics, from which it fertilized numerous other disciplines. In the recent philosophy of science, when criticism of the dominant positivism of the beginning of the century has begun to pile up, several thinkers have steered towards more realist positions. The conceptual problems of quantum gravity are illustrated and discussed in detail throughout the book, often from different perspectives, and sometimes with discordant conclusions. At times, the book reads almost as a dialogue, where different thinkers present different sides of the issue. Perhaps it is our full conceptualization of reality that evolves, not just its ontology: our knowledge of the world's structures (and equations) persists and changes historically as much as our knowledge of the world's objects. Efforts to find a fixed ground on which to anchor our beliefs often fail; I think the scientific picture of the world is credible because it captures the best that we know today, not because it captures something definitive. Still, I find the ideas underlying the structural proposal challenging and very intriguing. Notions such as object, entity or substance keep playing a fundamental role in physics, but continue also to show their limits: a physicist often thinks that the prototypical 'object' is
Gravitational collapse of massless scalar field in $f(R)$ gravity
Zhang, Cheng-Yong; Wang, Bin
2016-01-01
We study the spherically symmetric gravitational collapse of massless scalar matter field in asymptotic flat spacetime in $f(R)$ gravity. In the Einstein frame of $f(R)$ gravity, an additional scalar field arises due to the conformal transformation. We find that besides the usual competition between gravitational energy and kinetic energy in the process of gravitational collapse, the new scalar field brought by the conformal transformation adds one more competing force in the dynamical system. The dynamical competition can be controlled by tuning the amplitudes of the initial perturbations of the new scalar field and the matter field. To understand the physical reasons behind these phenomena, we analyze the gravitational potential behavior and calculate the Ricci scalar at center with the change of initial amplitudes of perturbations. We find rich physics on the formation of black holes through gravitational collapse in $f(R)$ gravity.
Possible formation of compact stars in f(R,T) gravity
Zubair, M.; Abbas, G.; Noureen, I.
2016-01-01
This paper reports on the investigations regarding the possible formation of compact stars in f(R,T) theory of gravity, where R is the Ricci scalar and T is the trace of the energy-momentum tensor. In this connection, we use the analytic solution of the Krori and Barua metric (Krori and Barua in J. Phys. A., Math. Gen. 8:508, 1975) for a spherically symmetric anisotropic star in the context of f(R,T) gravity. The masses and radii of compact star models, namely Model 1, Model 2, and Model 3, are employed to incorporate the unknown constants in the Krori and Barua metric. The physical features such as regularity at the center, the anisotropy measure, causality, and the well-behaved condition of the above-mentioned class of compact starts are analyzed. Moreover, we also discuss the energy conditions, stability, and surface redshift in f(R,T) gravity.
Possible Formation of Compact Stars in $f(R,T)$ Gravity
Zubair, M; Noureen, Ifra
2015-01-01
This paper constitutes the investigations regarding possible formation of compact stars in $f(R,T)$ theory of gravity, where $R$ is Ricci scalar and $T$ is trace of energy momentum tensor. In this connection, we use analytic solution of Krori and Barua metric (Krori and Barua 1975)to spherically symmetric anisotropic star in context of $f(R,T)$ gravity. The masses and radii of compact stars models namely model $1$, model$ 2$ and model $3$ are employed to incorporate with unknown constants in Krori and Barua metric. The physical features such as regularity at center, anisotropy measure, casuality and well-behaved condition of above mentioned class of compact starts are analyzed. Moreover, we have also discussed energy conditions, stability and surface redshift in $f(R,T)$ gravity.
Molecular mechanisms of gravity perception and signal transduction in plants.
Kolesnikov, Yaroslav S; Kretynin, Serhiy V; Volotovsky, Igor D; Kordyum, Elizabeth L; Ruelland, Eric; Kravets, Volodymyr S
2016-07-01
Gravity is one of the environmental cues that direct plant growth and development. Recent investigations of different gravity signalling pathways have added complexity to how we think gravity is perceived. Particular cells within specific organs or tissues perceive gravity stimulus. Many downstream signalling events transmit the perceived information into subcellular, biochemical, and genomic responses. They are rapid, non-genomic, regulatory, and cell-specific. The chain of events may pass by signalling lipids, the cytoskeleton, intracellular calcium levels, protein phosphorylation-dependent pathways, proteome changes, membrane transport, vacuolar biogenesis mechanisms, or nuclear events. These events culminate in changes in gene expression and auxin lateral redistribution in gravity response sites. The possible integration of these signalling events with amyloplast movements or with other perception mechanisms is discussed. Further investigation is needed to understand how plants coordinate mechanisms and signals to sense this important physical factor. PMID:26215561
Mechanism of gravity-dependent atelectasis
International Nuclear Information System (INIS)
The purpose of this study was to determine whether airway collapse was concerned in the development of gravity-dependent atelectasis (GDA) in an experimental animal model. After uniform reduction of lung volume in 9 rabbits by artificially-induced pneumoperitoneum, dynamic inhalation CT was performed using 50% nonradioactive xenon. Time-CT attenuation value curves were fitted to an exponential function, y=P-Qxe-RX, and Q value, which is build up of CT attenuation value, was calculated by regression analysis. GDA occurred only in 4/9 rabbits. In this group, Q values in the dorsal regions were decreasing, but enhancement was still recognized until just prior to the appearance of GDA. GDA was not caused by airway collapse. (author)
Gravity study of Libya;Evaluation and Integration with Geological Data
Ben Suleman, abdunnur; Saheel, Ahmed
2016-04-01
Libya is located on the Mediterranean foreland of the African Shield and covers an area of approximately 1.8 million square kilometers. Since Early Paleozoic time, Libya has been a site of deposition of large sheets of continental clastics and several transgressions and regressions by the seas with consequent accumulations of a wide variety of sedimentary rocks. Several tectonic cycles affected the area and shaped the geological setting of the country. However, the regional geology and the structural framework have been highly influenced by the Caledonian, Hercynian, and Alpine tectonic events. As a result, a total of seven sedimentary basins, namely Ghadames, Murzuq, Al Kufra, Al Butnan, Sirt, and the Offshore Pelagian Basin, were developed and were separated by intervening uplifts and platforms ( Gargaf, Tibesti, Nafusah and Cyrenaica platform). Apart from Sirt and the offshore basins, all the above mentioned basins are active since Early Paleozoic time and received several thousand feet of sediments. The capability of providing regional information on the structure of sedimentary basins makes gravity mapping, in conjunction with geological information, potentially powerful tools. In this study we used gravity mapping as our primary tool of investigation however, we also used all available geological information to better understand the regional tectonics. The gravity dataset that were used in the Gravity compilation project of Libya is not homogenous. As a result, some irregularities, apparent spikes or misties, and large shifts were obtained and were taken into consideration. Evaluation of gravity Maps of Libya and their integration with geological data provide a better understanding of the role that gravity mapping plays in the geological exploration of sedimentary basins. Results confirm the known Sirt Basin regional tectonic elements and the possible presence of NW-SE lateral wrench tectonics, crossing Ajdabiya Trough at the center of Sirt Basin. The
Canonical quantization of gravity without 'frozen formalism'
International Nuclear Information System (INIS)
We write down a quantum gravity equation which generalizes the Wheeler-DeWitt one in view of including a time dependence in the wave functional. The obtained equation provides a consistent canonical quantization of the 3-geometries resulting from a 'gauge-fixing' (3+1)-slicing of the space-time. Our leading idea relies on a criticism to the possibility that, in a quantum space-time, the notion of a (3+1)-slicing formalism (underlying the Wheeler-DeWitt approach) has yet a precise physical meaning. As solution to this problem we propose of adding to the gravity-matter action the so-called kinematical action (indeed in its reduced form, as implemented in the quantum regime), and then we impose the new quantum constraints. As consequence of this revised approach, the quantization procedure of the 3-geometries takes place in a fixed reference frame and the wave functional acquires a time evolution along a one-parameter family of spatial hypersurfaces filling the space-time. We show how the states of the new quantum dynamics can be arranged into an Hilbert space, whose associated inner product induces a conserved probability notion for the 3-geometries. Finally, since the constraints we quantize violate the classical symmetries (i.e., the vanishing nature of the super-Hamiltonian), then a key result is to find a (non-physical) restriction on the initial wave functional phase, ensuring that general relativity outcomes when taking the appropriate classical limit. However, we propose a physical interpretation of the kinematical variables which, based on the analogy with the so-called Gaussian reference fluid, makes allowance even for such classical symmetry violation
Seismic response of uplifting concrete gravity dams
International Nuclear Information System (INIS)
The foundation interaction effects on the seismic response of dam-foundation systems have generally been studied using the linear elastic finite element models. In reality, the foundation can not develop effective tensile stresses to a significant degree along the interface. A two-dimensional finite element model, in which nonlinear gap elements are used at the dam-foundation interface to determine the uplift response of concrete gravity dams subjected to seismic loads, is presented. Time domain analyses were performed for a wide range of modelling assumptions such as dam height, interface uplift pressure, interface mesh density, and earthquake input motions, that were systematically varied to find their influence on the seismic response. The nonlinear interface behavior generally reduces the seismic response of dam-foundation systems acting as a seismic isolation mechanism, and may increase the safety against sliding by reducing the base shear transmitted to the foundation. 4 refs., 5 figs., 6 tabs
On the gravity field processing of next generation satellite gravity missions
Daras, Ilias; Pail, Roland
2016-04-01
Dedicated gravity field missions delivering observations for a period longer than 16 years have drastically contributed in improving our knowledge of mass transport processes in the Earth system. At the same time, they have left a precious heritage for the design of next generation satellite gravity missions to be launched in the mid-term future. Main subject of this study is the gravity field processing of future Low-Low Satellite-to-Satellite Tracking (LL-SST) missions. We perform assessment of the contribution of all error sources and develop methods for reducing their effect at the level of gravity field processing. Advances in metrology of sensors such as the inter-satellite ranging instrument, may raise the demands for processing accuracy. We show that gravity field processing with double precision may be a limiting factor for exploiting the nm-level accuracy of a laser interferometer that future missions are expected to carry. An enhanced numerical precision processing scheme is proposed instead, where double and quadruple precision is used in different parts of the processing chain. It is demonstrated that processing with enhanced precision can efficiently handle laser measurements and take full advantage of their accuracy, while keeping the computational times within reasonable levels (Daras, 2015). However, error sources of considerably larger impact are expected to affect future missions, with the accelerometer instrument noise and temporal aliasing effects being the most significant ones. The effect of time-correlated noise such as the one present in accelerometer measurements can be efficiently handled by frequency dependent data weighting. Residual time series that contain the effect of system errors and propagated accelerometer and laser noise, is considered as a noise realization with stationary stochastic properties. The weight matrix is constructed from the auto-correlation functions of these residuals. Applying the weight matrix to a noise case
Fragility Analysis of Concrete Gravity Dams
Tekie, Paulos B.; Ellingwood, Bruce R.
2002-09-01
Concrete gravity dams are an important part ofthe nation's infrastructure. Many dams have been in service for over 50 years, during which time important advances in the methodologies for evaluation of natural phenomena hazards have caused the design-basis events to be revised upwards, in some cases significantly. Many existing dams fail to meet these revised safety criteria and structural rehabilitation to meet newly revised criteria may be costly and difficult. A probabilistic safety analysis (PSA) provides a rational safety assessment and decision-making tool managing the various sources of uncertainty that may impact dam performance. Fragility analysis, which depicts fl%e uncertainty in the safety margin above specified hazard levels, is a fundamental tool in a PSA. This study presents a methodology for developing fragilities of concrete gravity dams to assess their performance against hydrologic and seismic hazards. Models of varying degree of complexity and sophistication were considered and compared. The methodology is illustrated using the Bluestone Dam on the New River in West Virginia, which was designed in the late 1930's. The hydrologic fragilities showed that the Eluestone Dam is unlikely to become unstable at the revised probable maximum flood (PMF), but it is likely that there will be significant cracking at the heel ofthe dam. On the other hand, the seismic fragility analysis indicated that sliding is likely, if the dam were to be subjected to a maximum credible earthquake (MCE). Moreover, there will likely be tensile cracking at the neck of the dam at this level of seismic excitation. Probabilities of relatively severe limit states appear to be only marginally affected by extremely rare events (e.g. the PMF and MCE). Moreover, the risks posed by the extreme floods and earthquakes were not balanced for the Bluestone Dam, with seismic hazard posing a relatively higher risk.
Gauge aspect of tetrad field in gravity
Zhou, Tao
2016-01-01
In general relativity, an inertial frame can only be established in a small region of spacetime, and a locally inertial frame is mathematically represented by a tetrad field in gravity. The tetrad field is not unique due to the freedom to perform a local Lorentz transformation in an inertial frame, and there exists freedom to choose the locally inertial frame at each spacetime. The local Lorentz transformations are known as non-Abelian gauge transformations for the tetrad field, and to fix the gauge freedom, corresponding to the Lorentz gauge $\\partial^\\mu\\mathcal{A}_\\mu=0$ and Coulomb gauge $\\partial^i\\mathcal{A}_i=0$ in electrodynamics, the Lorentz gauge and Coulomb gauge for the tetrad field are proposed in the present work. Moreover, properties of the Lorentz gauge and Coulomb gauge for tetrad field are discussed, which show the similarities to those in electromagnetic field.
The Gravity Dual of Boundary Causality
Engelhardt, Netta
2016-01-01
In gauge/gravity duality, points which are not causally related on the boundary cannot be causally related through the bulk; this is the statement of boundary causality. By the Gao-Wald theorem, the averaged null energy condition in the bulk is sufficient to ensure this property. Here we proceed in the converse direction: we derive a necessary as well as sufficient condition for the preservation of boundary causality under perturbative (quantum or stringy) corrections to the bulk. The condition that we find is a (background-dependent) constraint on the amount by which light cones can "open" over all null bulk geodesics. We show that this constraint is weaker than the averaged null energy condition.
Hamiltonian dynamics of gauge theories of gravity
International Nuclear Information System (INIS)
We investigate the Hamiltonian structure of gauge theories of gravity based on arbitrary gravitational and matter field Lagrangians. The gauge group of the theory in question is the semisimple product of the local Lorentz group and the group of diffeomorphisms of spacetime (the local Poincare group). We derive formulas for the symplectic two-form Ω, the translational E, and the rotational J generators. The Hamilton equations expressed in terms of Ω, E, and J are equivalent to the variational Euler-Lagrange equations. The ten constraint equations of the theory are closely related both to properties of the symplectic two-form Ω and to an action of the gauge group in the space of solutions. The dynamical generators E and J can be expressed by the left-hand sides of the constraint equations, that is, the constraints generate the dynamics by means of the Hamilton equations for the functions E and J. On the other hand, the action of the gauge group in the set of initial data determines their ''time'' evolution. We show that this evolution is in a one-to-one correspondence with that generated by the Hamilton equations
Critical behaviors of gravity under quantum perturbations
Directory of Open Access Journals (Sweden)
ZHANG Hongsheng
2014-02-01
Full Text Available Phase transition and critical phenomenon is a very interesting topic in thermodynamics and statistical mechanics. Gravity is believed to have deep and inherent relation to thermodynamics. Near the critical point,the perturbation becomes significant. Thus for ordinary matter (governed by interactions besides gravity the critical behavior will become very different if we ignore the perturbations around the critical point,such as mean field theory. We find that the critical exponents for RN-AdS spacetime keep the same values even when we consider the full quantum perturbations. This indicates a key difference between gravity and ordinary thermodynamic system.
Perturbations of cosmological and black hole solutions in massive gravity and bi-gravity
Kobayashi, Tsutomu; Siino, Masaru; Yamaguchi, Masahide; Yoshida, Daisuke
2016-10-01
We investigate perturbations of a class of spherically symmetric solutions in massive gravity and bi-gravity. The background equations of motion for the particular class of solutions we are interested in reduce to a set of the Einstein equations with a cosmological constant. Thus, the solutions in this class include all the spherically symmetric solutions in general relativity, such as the Friedmann-Lemaître-Robertson-Walker solution and the Schwarzschild (-de Sitter) solution, though the one-parameter family of two parameters of the theory admits such a class of solutions. We find that the equations of motion for the perturbations of this class of solutions also reduce to the perturbed Einstein equations at first and second order. Therefore, the perturbative stability of the solutions coincides with that of the corresponding solutions in general relativity at least up to the second-order perturbations.
Major results of gravity and magnetic studies at Yucca Mountain, Nevada
International Nuclear Information System (INIS)
About 4000 gravity stations have been obtained at Yucca Mountain and vicinity since the beginning of radioactive-waste studies there in 1978. These data have been integrated with data from about 29,000 stations previously obtained in the surrounding region to produce a series of Bouguer and isostatic-residual-gravity maps of the Nevada Test Site and southeastern Nevada. Yucca Mountain is characterized by a WNW-dipping gravity gradient whereby residual values of -10 mGal along the east edge of Yucca Mountain decrease to about -38 mGal over Crater Flat. Using these gravity data, two-dimensional modeling predicted the depth to pre-Cenozoic rocks near the proposed repository to be about 1220 ± 150 m, an estimate that was subsequently confirmed by drilling to be 1244 m. Three-dimensional modeling of the gravity low over Crater Flat indicates the thickness of Cenozoic volcanic rocks and alluvial cover to be about 3000 m. Considerable aeromagnetic coverage of southwestern Nevada was obtained in 1978--1979 to help characterize Yucca Mountain and vicinity. One significant result is the discovery of a series of circular magnetic anomalies in Crater Flat and the northern Amargosa Desert that suggest the presence of buried volcanic centers there. Elongate magnetic highs and associated lows over Yucca Mountain correlate with mapped faults, some of which are only partially exposed. Thus, the data provide inforamtion on the extent and continuity of these faults. 31 refs., 3 figs
Compact stars in alternative theories of gravity. Einstein-Dilaton-Gauss-Bonnet gravity
Pani, Paolo; Cardoso, Vitor; Read, Jocelyn
2011-01-01
We develop a theoretical framework to study slowly rotating compact stars in a rather general class of alternative theories of gravity, with the ultimate goal of investigating constraints on alternative theories from electromagnetic and gravitational-wave observations of compact stars. Our Lagrangian includes as special cases scalar-tensor theories (and indirectly f(R) theories) as well as models with a scalar field coupled to quadratic curvature invariants. As a first application of the formalism, we discuss (for the first time in the literature) compact stars in Einstein-Dilaton-Gauss-Bonnet gravity. We show that compact objects with central densities typical of neutron stars cannot exist for certain values of the coupling constants of the theory. In fact, the existence and stability of compact stars sets more stringent constraints on the theory than the existence of black hole solutions. This work is a first step in a program to systematically rule out (possibly using Bayesian model selection) theories tha...
Cosmology and modifications of gravity at large distances
International Nuclear Information System (INIS)
In the framework of General Relativity, the observed current acceleration of the expansion of the Universe requires the presence of a Dark Energy component, whose nature is not well understood. In order to explain the acceleration of the Universe without introducing such a tantalizing source of energy, other gravitation theories have been designed. This thesis is devoted to the study of some of these modified gravity theories, as well as to the observation methods that could constrain them. The first part of this thesis presents a review of modified gravity theories and their motivations. The second part is devoted to the study of the massive gravity theories and of the so-called Vainshtein's mechanism, which allows some of the solutions of Massive Gravity to strongly differ from General Relativity at cosmological scales while satisfying the experimental constraints inside the solar system. For the first time, the validity of the Vainshtein's mechanism is demonstrated, through the study of specific spherically symmetric solutions. The third part deals with scalar modification of gravity; a new model of this sort is presented, inspired by the Vainshtein's mechanism in Massive Gravity. Finally, the fourth part discusses local, astrophysical and cosmological observations that might constrain modified gravity theories. (author)
Extended N = 2 superconformal structure of gravity and W-gravity coupled to matter
Bershadsky, M.; Lerche, W.; Nemeschansky, D.; Warner, N. P.
1993-07-01
We show that almost all string theories, including the bosonic string, the superstring and W-string theories, possess a twisted N = 2 superconformal symmetry. This enables us to establish a connection between topological gravity and the field theoretical description of matter coupled to gravity. We also show how the BRST operators of the W n-string can be obtained by hamiltonian reduction of SL( n|; n-1). The tachyonic and ground ring states of W-strings are described in the light of the N = 2 superconformal structure, and the ground ring generators for the non-critical W 3-string are explicitly constructed. The relationship to G/G models and quantum integrable systems is also briefly described.
The Other Side of Gravity and Geometry: Antigravity and Anticurvature
Directory of Open Access Journals (Sweden)
M. I. Wanas
2012-01-01
Full Text Available Gravity is one of the four known fundamental interactions used to study and interpret physical phenomenae. It governs diverse phenomenae, especially those connected with large-scale structures. From more than one decade, existing gravity theories have suffered from some problems, when confronting their predictions with the results of some experiments and observations. This situation has led to many suggestions, none of which is final, so far. Here, we show that the assumption of existence of another side of gravity, a repulsive gravity or antigravity, together with its attractive side, may give a satisfactory solution to gravity problems. We caught here two pieces of evidence for the existence of antigravity in nature. The first is on the laboratory scale, the COW experiment, and the second is on the cosmic scale, SN type Ia observation. On the other hand, we show how gravity theories can predict antigravity, using a new defined geometric object called Parameterized anticurvature. This shows clearly how Einstein's geometrization philosophy can solve recent gravity problems in a satisfactory and easy way. Also, it may throw some light on the mystery of physical nature of “Dark Energy.”
Einstein Gravity from Conformal Gravity
Maldacena, Juan
2011-01-01
We show that that four dimensional conformal gravity plus a simple Neumann boundary condition can be used to get the semiclassical (or tree level) wavefunction of the universe of four dimensional asymptotically de-Sitter or Euclidean anti-de Sitter spacetimes. This simple Neumann boundary condition selects the Einstein solution out of the more numerous solutions of conformal gravity. It thus removes the ghosts of conformal gravity from this computation. In the case of a five dimensional pure ...
Quantum Gravity Corrections to the Tunneling Radiation of Scalar Particles
Wang, Peng; Yang, Haitang; Ying, Shuxuan
2016-05-01
The original derivation of Hawking radiation shows the complete evaporation of black holes. However, theories of quantum gravity predict the existence of the minimal observable length. In this paper, we investigate the tunneling radiation of the scalar particles by introducing the quantum gravity effects influenced by the generalized uncertainty principle. The Hawking temperatures are not only determined by the properties of the black holes, but also affected by the quantum numbers of the emitted particles. The quantum gravity corrections slow down the increase of the temperatures. The remnants are found during the evaporation.
Resource Letter PTG-1: Precision Tests of Gravity
Will, Clifford M
2010-01-01
This resource letter provides an introduction to some of the main current topics in experimental tests of general relativity as well as to some of the historical literature. It is intended to serve as a guide to the field for upper-division undergraduate and graduate students, both theoretical and experimental, and for workers in other fields of physics who wish learn about experimental gravity. The topics covered include alternative theories of gravity, tests of the principle of equivalence, solar-system and binary-pulsar tests, searches for new physics in gravitational arenas, and tests of gravity in new regimes, involving astrophysics and gravitational radiation.
Impact of gravity waves on long-range infrasound propagation
Millet, Christophe; Lott, François; De La Camara, Alvaro
2016-04-01
In this work we study infrasound propagation in acoustic waveguides that support a finite number of propagating modes. We analyze the effects of gravity waves on these acoustic waveguides. Testing sound propagation in such perturbed fields can potentially be used to improve the gravity wave models. A linear solution modeling the interaction between an incoming acoustic wave and a randomly perturbed atmosphere is developed, using the forward-scattering approximation. The wave mode structure is determined by the effective sound speed profile which is strongly affected by gravity wave breaking. The random perturbations are described by a stochastic field predicted by a multiwave stochastic parameterization of gravity waves, which is operational in the LMDz climate model. The justification for this approach is two fold. On the one hand, the use of a few monochromatic waves mimics the observations of rather narrow-banded gravity wave packets in the lower stratosphere. On the other hand, the stochastic sampling of the gravity wave field and the random choice of wave properties deals with the inherent unpredictability of mesoscale dynamics from large scale conditions provided by the meteorological reanalysis. The transmitted acoustic signals contain a stable front and a small-amplitude incoherent coda. A general expression for the stable front is derived in terms of saddle-point contributions. The saddle-points are obtained from a WKB approximation of the vertical eigenvalue problem. This approach extract the dominant effects in the acoustic - gravity wave interaction. We present results that show how statistics of the transmitted signal are related to a few saddle-points and how the GW field can trigger large deviations in the acoustic signals. While some of the characteristics of the stable front can be directly related to that of a few individual gravity waves, it is shown that the amount of the launched gravity waves included in climate models can be estimated using
Software Analysis of New Space Gravity Data for Geophysics and Climate Research
Deese, Rupert; Ivins, Erik R.; Fielding, Eric J.
2012-01-01
Both the Gravity Recovery and Climate Experiment (GRACE) and Gravity field and steady-state Ocean Circulation Explorer (GOCE) satellites are returning rich data for the study of the solid earth, the oceans, and the climate. Current software analysis tools do not provide researchers with the ease and flexibility required to make full use of this data. We evaluate the capabilities and shortcomings of existing software tools including Mathematica, the GOCE User Toolbox, the ICGEM's (International Center for Global Earth Models) web server, and Tesseroids. Using existing tools as necessary, we design and implement software with the capability to produce gridded data and publication quality renderings from raw gravity data. The straight forward software interface marks an improvement over previously existing tools and makes new space gravity data more useful to researchers. Using the software we calculate Bouguer anomalies of the gravity tensor's vertical component in the Gulf of Mexico, Antarctica, and the 2010 Maule earthquake region. These maps identify promising areas of future research.
Intercomparison of stratospheric gravity wave observations with AIRS and IASI
Directory of Open Access Journals (Sweden)
L. Hoffmann
2014-08-01
Full Text Available Gravity waves are an important driver for the atmospheric circulation and have substantial impact on weather and climate. Satellite instruments offer excellent opportunities to study gravity waves on a global scale. This study focuses on observations from the Atmospheric Infrared Sounder (AIRS onboard the National Aeronautics and Space Administration's Aqua satellite and the Infrared Atmospheric Sounding Interferometer (IASI onboard the European MetOp satellites. The main aim of this study is an intercomparison of stratospheric gravity wave observations of both instruments. In particular, we analyzed AIRS and IASI 4.3 μm brightness temperature measurements, which directly relate to stratospheric temperature. Three case studies showed that AIRS and IASI provide a clear and consistent picture of the temporal development of individual gravity wave events. Statistical comparisons based on a five-year period of measurements (2008–2012 showed similar spatial and temporal patterns of gravity wave activity. However, the statistical comparisons also revealed systematic differences of variances between AIRS and IASI (about 45% that we attribute to the different spatial measurement characteristics of both instruments. We also found differences between day- and nighttime data (about 30% that are partly due to the local time variations of the gravity wave sources. While AIRS has been used successfully in many previous gravity wave studies, IASI data are applied here for the first time for that purpose. Our study shows that gravity wave observations from different hyperspectral infrared sounders such as AIRS and IASI can be directly related to each other, if instrument-specific characteristics such as different noise levels and spatial resolution and sampling are carefully considered. The ability to combine observations from different satellites provides an opportunity to create a long-term record, which is an exciting prospect for future climatological
Intercomparison of stratospheric gravity wave observations with AIRS and IASI
Directory of Open Access Journals (Sweden)
L. Hoffmann
2014-12-01
Full Text Available Gravity waves are an important driver for the atmospheric circulation and have substantial impact on weather and climate. Satellite instruments offer excellent opportunities to study gravity waves on a global scale. This study focuses on observations from the Atmospheric Infrared Sounder (AIRS onboard the National Aeronautics and Space Administration Aqua satellite and the Infrared Atmospheric Sounding Interferometer (IASI onboard the European MetOp satellites. The main aim of this study is an intercomparison of stratospheric gravity wave observations of both instruments. In particular, we analyzed AIRS and IASI 4.3 μm brightness temperature measurements, which directly relate to stratospheric temperature. Three case studies showed that AIRS and IASI provide a clear and consistent picture of the temporal development of individual gravity wave events. Statistical comparisons based on a 5-year period of measurements (2008–2012 showed similar spatial and temporal patterns of gravity wave activity. However, the statistical comparisons also revealed systematic differences of variances between AIRS and IASI that we attribute to the different spatial measurement characteristics of both instruments. We also found differences between day- and nighttime data that are partly due to the local time variations of the gravity wave sources. While AIRS has been used successfully in many previous gravity wave studies, IASI data are applied here for the first time for that purpose. Our study shows that gravity wave observations from different hyperspectral infrared sounders such as AIRS and IASI can be directly related to each other, if instrument-specific characteristics such as different noise levels and spatial resolution and sampling are carefully considered. The ability to combine observations from different satellites provides an opportunity to create a long-term record, which is an exciting prospect for future climatological studies of stratospheric
Nonstationary Gravity Wave Forcing of the Stratospheric Zonal Mean Wind
Alexander, M. J.; Rosenlof, K. H.
1996-01-01
The role of gravity wave forcing in the zonal mean circulation of the stratosphere is discussed. Starting from some very simple assumptions about the momentum flux spectrum of nonstationary (non-zero phase speed) waves at forcing levels in the troposphere, a linear model is used to calculate wave propagation through climatological zonal mean winds at solstice seasons. As the wave amplitudes exceed their stable limits, a saturation criterion is imposed to account for nonlinear wave breakdown effects, and the resulting vertical gradient in the wave momentum flux is then used to estimate the mean flow forcing per unit mass. Evidence from global, assimilated data sets are used to constrain these forcing estimates. The results suggest the gravity-wave-driven force is accelerative (has the same sign as the mean wind) throughout most of the stratosphere above 20 km. The sense of the gravity wave forcing in the stratosphere is thus opposite to that in the mesosphere, where gravity wave drag is widely believed to play a principal role in decelerating the mesospheric jets. The forcing estimates are further compared to existing gravity wave parameterizations for the same climatological zonal mean conditions. Substantial disagreement is evident in the stratosphere, and we discuss the reasons for the disagreement. The results suggest limits on typical gravity wave amplitudes near source levels in the troposphere at solstice seasons. The gravity wave forcing in the stratosphere appears to have a substantial effect on lower stratospheric temperatures during southern hemisphere summer and thus may be relevant to climate.
Research recommendations of the ESA Topical Team on Artificial Gravity
Clément, Gilles; Bukley, Angie
Many experts believe that artificial gravity will be required for an interplanetary mission. However, despite its attractiveness as an efficient, multi-system countermeasure and its potential for simplifying operational activities, much still needs to be learned regarding the human response to rotating environments before artificial gravity can be successfully implemented. The European Space Agency (ESA) Topical Team on Artificial Gravity recommended a comprehensive program to determine the gravity threshold required to reverse or prevent the detrimental effects of microgravity and to evaluate the effects of centrifugation on various physiological functions. Part of the required research can be accomplished using animal models on a dedicated centrifuge in low Earth orbit. Studies of human responses to centrifugation could be performed during ambulatory, short- and long-duration bed rest, and in-flight studies. Artificial-gravity scenarios should not be a priori discarded in Moon and Mars mission designs. One major step is to determine the relationship between the artificial gravity dose level, duration, and frequency and the physiological responses of the major body functions affected by spaceflight. Once its regime characteristics are defined and a dose-response curve is established, artificial gravity should serve as the standard against which all other countermeasure candidates are evaluated, first on Earth and then in space.
Gravity research on plants: use of single cell experimental models
Directory of Open Access Journals (Sweden)
Youssef eChebli
2011-09-01
Full Text Available Future space missions and implementation of permanent bases on Moon and Mars will greatly depend on the availability of ambient air and sustainable food supply. Therefore, understanding the effects of altered gravity conditions on plant metabolism and growth is vital for space missions and extra-terrestrial human existence. In this mini-review we summarize how plant cells are thought to perceive changes in magnitude and orientation of the gravity vector. The particular advantages of several single celled model systems for gravity research are explored and an overview over recent advancements and potential use of these systems is provided.
Effects of gravity on transpiration of plant leaves.
Hirai, Hiroaki; Kitaya, Yoshiaki
2009-04-01
To clarify effects of gravity on the water vapor exchange between plants and the ambient air, we evaluated the transpiration rate of plant leaves at 0.01, 1.0, and 2.0 g for 20 s each during parabolic airplane flights. The transpiration rates of a strawberry leaf and a replica leaf made of wet cloth were determined using a chamber method with humidity sensors. Absolute humidity at 3 and 8 mm below the lower surface of leaves was measured to evaluate the effect of gravity on humidity near leaves and estimate their transpiration rate. The transpiration rate of the replica leaf decreased by 42% with decreasing gravity levels from 1.0 to 0.01 g and increased by 31% with increasing gravity levels from 1.0 to 2.0 g. Absolute humidity near the intact strawberry leaf was 5 g m(-3) at ambient absolute humidity of 2.3 g m(-3) and gravity of 1.0 g. The absolute humidity increased by 2.5 g m(-3) with decreasing gravity levels from 1.0 to 0.01 g. The transpiration rate of the intact leaf decreased by 46% with decreasing gravity levels from 1.0 to 0.01 g and increased by 32% with increasing gravity levels from 1.0 to 2.0 g. We confirmed that the transpiration rate of leaves was suppressed by retarding the water vapor transfer due to restricted free air convection under microgravity conditions.
Hogg, Charlie A. R.; Dalziel, Stuart B.; Huppert, Herbert E.; Imberger, Jörg
2015-09-01
In many important natural and industrial systems, gravity currents of dense fluid feed basins. Examples include lakes fed by dense rivers and auditoria supplied with cooled air by ventilation systems. As we will show, the entrainment into such buoyancy driven currents can be influenced by viscous forces. Little work, however, has examined this viscous influence and how entrainment varies with the Reynolds number, Re. Using the idea of an entrainment coefficient, E, we derive a mathematical expression for the rise of the front at the top of the dense fluid ponding in a basin, where the horizontal cross-sectional area of the basin varies linearly with depth. We compare this expression to experiments on gravity currents with source Reynolds numbers, Res, covering the broad range 100 < Res < 1500. The form of the observed frontal rises was well approximated by our theory. By fitting the observed frontal rises to the theoretical form with E as the free parameter, we find a linear trend for E(Res) over the range 350 < Res < 1100, which is in the transition to turbulent flow. In the experiments, the entrainment coefficient, E, varied from 4 × 10-5 to 7 × 10-2. These observations show that viscous damping can be a dominant influence on gravity current entrainment in the laboratory and in geophysical flows in this transitional regime.
Characteristic of gravity waves resolved in ECMWF
Preusse, Peter; Eckermann, Stephen; Ern, Manfred; Riese, Martin
Gravity waves (GWs) influence the circulation of the atmosphere on global scale. Because of insufficient measurements and the difficulty to involve all relevant scales in a single model run, they are one of the chief uncertainties in climate and weather prediction. More information, in particular on global scale, is required. Can we employ global models such as the ECMWF high-resolution GCM to infer quantities of resolved GWs? Does this give us insight for the characteristics and relative importance of real GW sources? And can we use such data safely for, e.g., planning measurement campaigns on GWs? Also trajectory studies of cloud formation (cirrus in the UTLS, PSCs) and related dehydration and denitrification rely heavily on realistic temperature structures due to GWs. We here apply techniques developed for an ESA study proving the scientifc break-through which could be reached by a novel infrared limb imager. The 3D temperature structure of mesoscale GWs is exploited to determine amplitudes and 3D wave vectors of GWs at different levels (25km, 35km and 45km altitude) in the stratosphere. Similar to real observations, GW momentum flux is largest in the winter polar vortex and exhibits a second maximum in the summer subtropics. Based on the 3D wavevectors backward ray-tracing is employed to characterize specific sources. For instance, we find for the northern winter strong GW momentum flux (GWMF) associated with mountain waves from Norway and Greenland as well as waves emitted in the lower troposphere from a storm approaching Norway. Waves from these sources spread up to several thousand km in the stratosphere. Together these three events form a burst in the total hemispheric GWMF of a factor of 3. Strong mountain wave events are also found e.g. at Tierra del Fuego and the Antarctic Peninsula, regions which are in the focus of observational and modeling studies for a decade. Gravity waves in the tropical region are associated with deep convection in the upper
A spin-4 analog of 3D massive gravity
Bergshoeff, Eric A; Rosseel, Jan; Townsend, Paul K; Yin, Yihao
2011-01-01
A 6th-order, but ghost-free, gauge-invariant action is found for a 4th-rank symmetric tensor potential in a three-dimensional (3D) Minkowski spacetime. It propagates two massive modes of spin 4 that are interchanged by parity, and is thus a spin-4 analog of linearized "new massive gravity". Also found are ghost-free spin-4 analogs of linearized "topologically massive gravity" and "new topologically massive gravity", of 5th- and 8th-order respectively.
Wavelet approach to the determination of gravity tide parameters
Institute of Scientific and Technical Information of China (English)
无
2000-01-01
A new approach is proposed for the determination of gravity tide parameters.Three pairs of compactly supported wavelet filters are introduced in the approach.They can efficiently extract the objective tides from the gravity observation series.The new approach guarantees a direct and precise analysis on the tidal gravity records of any sampling length.The new approach is applied to the harmonic analysis on Wuhan superconducting gravimeter records.The results clearly show the resonant effects of the Earth Nearly Diurnal Free Wobble (NDFW).
Kim, Jinsoo; Lee, Youngcheol; Cha, Sungyeoul; Choi, Chuluong; Lee, Seongkyu
2013-07-12
This paper proposes a smartphone-based network real-time kinematic (RTK) positioning and gravity-surveying application (app) that allows semi-real-time measurements using the built-in Bluetooth features of the smartphone and a third-generation or long-term evolution wireless device. The app was implemented on a single smartphone by integrating a global navigation satellite system (GNSS) controller, a laptop, and a field-note writing tool. The observation devices (i.e., a GNSS receiver and relative gravimeter) functioned independently of this system. The app included a gravity module, which converted the measured relative gravity reading into an absolute gravity value according to tides; meter height; instrument drift correction; and network adjustments. The semi-real-time features of this app allowed data to be shared easily with other researchers. Moreover, the proposed smartphone-based gravity-survey app was easily adaptable to various locations and rough terrain due to its compact size.
Born-Infeld Type Extension of (Non-)Critical Gravity
Yi, Sang-Heon
2012-01-01
We consider the Born-Infeld type extension of (non-)critical gravity which is higher curvature gravity on Anti de-Sitter space with specific combinations of scalar curvature and Ricci tensor. This theory may also be viewed as a natural extension of three-dimensional Born-Infeld new massive gravity to arbitrary dimensions. We show that this extension is consistent with holographic $c$-theorem and scalar graviton modes are absent in this theory. After showing that ghost modes in the theory can ...
Gravity evolution and earthquake activities of the northeastern edge of Qinghai-Xizang block
Institute of Scientific and Technical Information of China (English)
祝意青; 李辉; 朱桂芝; 徐云马
2004-01-01
The relationship between temporal-spatial evolution of gravity and earthquake activity during 1992～2001 has beenanalyzed systematically byintegrally adjusting the gravity observation data of the northeastern edge of Qinghai-Xizang (Qingzang) block. The result shows that the gravity observation data of the northeastern edge of Qingzangblock obtained by using the uniform starting datum can completely reflect the precursory gravity informationappearing during the seismogenic process. In the genesis stage of an earthquake, regional gravity anomaly appearsin a large area, resulting in related local gravity anomaly. The dynamic image of gravity field can clearly reflect theorderly evolution and earthquake activity.
Emergent perspective of gravity and dark energy
Padmanabhan, T.
2012-08-01
There is sufficient amount of internal evidence in the nature of gravitational theories to indicate that gravity is an emergent phenomenon like, e.g, elasticity. Such an emergent nature is most apparent in the structure of gravitational dynamics. It is, however, possible to go beyond the field equations and study the space itself as emergent in a well-defined manner in (and possibly only in) the context of cosmology. In the first part of this review, I describe various pieces of evidence which show that gravitational field equations are emergent. In the second part, I describe a novel way of studying cosmology in which I interpret the expansion of the universe as equivalent to the emergence of space itself. In such an approach, the dynamics evolves towards a state of holographic equipartition, characterized by an equality in the number of bulk and surface degrees of freedom in a region bounded by the Hubble radius. This principle correctly reproduces the standard evolution of a Friedmann universe. Further, (a) it demands the existence of an early inflationary phase as well as late time acceleration for its successful implementation and (b) allows us to link the value of late time cosmological constant to the e-folding factor during inflation.
Emergent perspective of gravity and dark energy
Institute of Scientific and Technical Information of China (English)
T.Padmanabhan
2012-01-01
There is sufficient amount of internal evidence in the nature of gravitational theories to indicate that gravity is an emergent phenomenon like,e.g,elasticity.Such an emergent nature is most apparent in the structure of gravitational dynamics.It is,however,possible to go beyond the field equations and study the space itself as emergent in a well-defined manner in (and possibly only in) the context of cosmology.In the first part of this review,I describe various pieces of evidence which show that gravitational field equations are emergent.In the second part,I describe a novel way of studying cosmology in which I interpret the expansion of the universe as equivalent to the emergence of space itself.In such an approach,the dynamics evolves towards a state of holographic equipartition,characterized by an equality in the number of bulk and surface degrees of freedom in a region bounded by the Hubble radius.This principle correctly reproduces the standard evolution of a Friedmann universe.Further,(a) it demands the existence of an early inflationary phase as well as late time acceleration for its successful implementation and (b) allows us to link the value of late time cosmological constant to the e-folding factor during inflation.
Emergent perspective of Gravity and Dark Energy
Padmanabhan, T
2012-01-01
There is sufficient amount of internal evidence in the nature of gravitational theories to indicate that gravity is an emergent phenomenon like, e.g, elasticity. Such an emergent nature is most apparent in the structure of gravitational dynamics. It is, however, possible to go beyond the field equations and study the space itself as emergent in a well-defined manner in (and possibly only in) the context of cosmology. In the first part of this review, I describe various pieces of evidence which show that gravitational field equations are emergent. In the second part, I describe a novel way of studying cosmology in which I interpret the expansion of the universe as equivalent to the emergence of space itself. In such an approach, the dynamics evolves towards a state of holographic equipartition, characterized by the equality of number of bulk and surface degrees of freedom in a region bounded by the Hubble radius. This principle correctly reproduces the standard evolution of a Friedmann universe. Further, (a) i...
On chains of centered valuations
Directory of Open Access Journals (Sweden)
Rachid Chibloun
2003-01-01
Full Text Available We study chains of centered valuations of a domain A and chains of centered valuations of A [X1,…,Xn] corresponding to valuations of A. Finally, we make some applications to chains of valuations centered on the same ideal of A [X1,…,Xn] and extending the same valuation of A.
A case study of gravity waves in noctilucent clouds
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P. Dalin
2004-06-01
Full Text Available We present a case study of a noctilucent cloud (NLC display appearing on 10-11 August 2000 over Northern Sweden. Clear wave structures were visible in the clouds and time-lapse photography was used to derive the parameters characterising the gravity waves which could account for the observed NLC modulation. Using two nearby atmospheric radars, the Esrange MST Radar data and Andoya MF radar, we have identified gravity waves propagating upward from the upper stratosphere to NLC altitudes. The wave parameters derived from the radar measurements support the suggestion that gravity waves are responsible for the observed complex wave dynamics in the NLC.
Effects of gravity and posture on the human lung
Rohdin, Malin
2004-01-01
The presence of the gravitational force at the surface of Earth affects all of the organ systems in landliving creatures. The function of the lung is particularly susceptible to changes in the direction and magnitude of gravity because of the elastic structure of this organ. Gravity-dependent deformation of lung tissue in turn is an important determinant of gas transfer between the gas and the blood in the lungs. For example, the impaired arterial oxygenation characteristic ...
Bouguer Gravity Anomaly Map of Bangladesh (grav8bg)
U.S. Geological Survey, Department of the Interior — This coverage includes arcs and arc labels that hold the Bouguer Gravity anomaly value for contours and type contours of the original map of Bangladesh with the...
One-loop renormalization of a gravity-scalar system
Park, I Y
2016-01-01
Extending the renormalizability proposal of 4D Einstein gravity, we have recently proposed renormalizability of gravity-matter systems. The main goal of the present work is to conduct systematic one-loop renormalization of a gravity-matter system by applying our foliation-based quantization scheme. In this work we explicitly carry out renormalization of a gravity-scalar system with a Higgs-type potential. With the fluctuation part of the scalar field gauged away, the system becomes renormalizable through a metric field redefinition. We use dimensional regularization throughout. One of the salient aspects of our analysis is how the graviton propagator acquires the"mass" term. One-loop calculations lead to renormalization of the cosmological and Newton's constants. We discuss other implications of our results as well: time-varying vacuum energy density and masses of the elementary particles as well as the potential relevance of Neumann boundary condition for black hole information.
Embeddings of the "New Massive Gravity"
Dalmazi, D
2016-01-01
Using different types of embeddings of equations of motion we investigate the existence of generalizations of the "New Massive Gravity" (NMG) model with the same particle content (massive gravitons). By using the Weyl symmetry as a guiding principle for the embeddings we show that the Noether gauge embedding approach leads us to a sixth order model in derivatives with either a massive or a massless ghost. If the Weyl symmetry is implemented by means of a Stueckelberg field we obtain a new scalar-tensor model for massive gravitons. It is ghost free and Weyl invariant at linearized level. The model can be nonlinearly completed into a scalar field coupled to the NMG theory. The elimination of the scalar field leads to a nonlocal modification of the NMG. We also prove to all orders in derivatives that there is no local, ghost free embedding of the linearized NMG equations of motion around Minkowski space when written in terms of one symmetric tensor. Regarding that point, NMG differs from the Fierz-Pauli theory, ...
An Efficient Representation of Euclidean Gravity I
Lee, Jungjai; Yang, Hyun Seok
2011-01-01
We explore how the topology of spacetime fabric is encoded into the local structure of Riemannian metrics using the gauge theory formulation of Euclidean gravity. In part I, we provide a rigorous mathematical foundation to prove that a general Einstein manifold arises as the sum of SU(2)_L Yang-Mills instantons and SU(2)_R anti-instantons where SU(2)_L and SU(2)_R are normal subgroups of the four-dimensional Lorentz group Spin(4) = SU(2)_L x SU(2)_R. Our proof relies only on the general properties in four dimensions: The Lorentz group Spin(4) is isomorphic to SU(2)_L x SU(2)_R and the six-dimensional vector space of two-forms splits canonically into the sum of three-dimensional vector spaces of self-dual and anti-self-dual two-forms. Consolidating these two, it turns out that the splitting of Spin(4) is deeply correlated with the decomposition of two-forms on four-manifold which occupies a central position in the theory of four-manifolds.
Testing Alternative Theories of Gravity using LISA
Will, Clifford M
2004-01-01
We investigate the possible bounds which could be placed on alternative theories of gravity using gravitational wave detection from inspiralling compact binaries with the proposed LISA space interferometer. Specifically, we estimate lower bounds on the coupling parameter \\omega of scalar-tensor theories of the Brans-Dicke type and on the Compton wavelength of the graviton \\lambda_g in hypothetical massive graviton theories. In these theories, modifications of the gravitational radiation damping formulae or of the propagation of the waves translate into a change in the phase evolution of the observed gravitational waveform. We obtain the bounds through the technique of matched filtering, employing the LISA Sensitivity Curve Generator (SCG), available online. For a neutron star inspiralling into a 10^3 M_sun black hole in the Virgo Cluster, in a two-year integration, we find a lower bound \\omega > 3 * 10^5. For lower-mass black holes, the bound could be as large as 2 * 10^6. The bound is independent of LISA arm...
Ghost dark energy in $f(R)$ model of gravity
Saaidi, Kh; Sabet, B
2012-01-01
We study a correspondence between $f(R)$ model of gravity and a phenomenological kind of dark energy (DE), which is known as QCD ghost dark energy. Since this kind of dark energy is not stable in the context of Einsteinian theory of gravity and Brans-Dicke model of gravity, we consider two kinds of correspondence between modified gravity and DE. By studding the dynamical evolution of model and finding relevant quantities such as, equation of state parameter, deceleration parameter, dimensionless density parameter, we show that the model can describe the present Universe and also the EoS parameter can cross the phantom divide line without needs to any kinetic energy with negative sign. Furthermore, by obtaining the adiabatic squared sound speed of the model for different cases of interaction, we show that this model is stable.
Gravity dual of dynamically broken supersymmetry
Cottrell, William; Hashimoto, Akikazu
2013-01-01
We study a renormalization group flow of ABJM theory embedded into the warped A_8 geometry and explore the dependence of the vacuum structure on the parameters of the theory. This model has a product group gauge structure U(N)xU(n+l) and comes equipped with discrete parameters N, l and k, a continuous parameter b related to the ratio of the Yang-Mills coupling for the two gauge groups, and one dimensionful parameter gYM^2 setting the overall scale. A supersymmetric supergravity solution exists when Q=N-l(l-k)/2k-k/24 is positive and is interpretable as a RG flow from a Yang-Mills like UV fixed point to a superconformal IR fixed point with free energy of order Q^3/2. The fate of the theory when Q is taken to be negative is less clear. We explore the structure of the possible gravity solution for small negative Q by considering the linearized gravitational back reaction from adding a small number of anti-branes on the Q=0 background. Following the work of Bena, et.al., we find that a sensible solution satisfyin...
Gravity influences the visual representation of object tilt in parietal cortex.
Rosenberg, Ari; Angelaki, Dora E
2014-10-22
Sensory systems encode the environment in egocentric (e.g., eye, head, or body) reference frames, creating inherently unstable representations that shift and rotate as we move. However, it is widely speculated that the brain transforms these signals into an allocentric, gravity-centered representation of the world that is stable and independent of the observer's spatial pose. Where and how this representation may be achieved is currently unknown. Here we demonstrate that a subpopulation of neurons in the macaque caudal intraparietal area (CIP) visually encodes object tilt in nonegocentric coordinates defined relative to the gravitational vector. Neuronal responses to the tilt of a visually presented planar surface were measured with the monkey in different spatial orientations (upright and rolled left/right ear down) and then compared. This revealed a continuum of representations in which planar tilt was encoded in a gravity-centered reference frame in approximately one-tenth of the comparisons, intermediate reference frames ranging between gravity-centered and egocentric in approximately two-tenths of the comparisons, and in an egocentric reference frame in less than half of the comparisons. Altogether, almost half of the comparisons revealed a shift in the preferred tilt and/or a gain change consistent with encoding object orientation in nonegocentric coordinates. Through neural network modeling, we further show that a purely gravity-centered representation of object tilt can be achieved directly from the population activity of CIP-like units. These results suggest that area CIP may play a key role in creating a stable, allocentric representation of the environment defined relative to an "earth-vertical" direction.
Seismic performance evaluation of concrete gravity dams
Energy Technology Data Exchange (ETDEWEB)
Yamaguchi, Y.; Sasaki, T.; Kanenawa, K. [Public Works Research Institute, Tsukuba City (Japan); Hall, R.; Yule, D. [United States Army Engineer Research and Development Center, Vicksburg, MS (United States); Matheu, E. [Louisiana State Univ., Baton Rouge, LA (United States); Chudgar, A. [United States Army Corps of Engineers, Washington, DC (United States)
2004-07-01
This paper addresses technical issues related to seismic design practices and current evaluation methods in Japan and the United States. Nonlinear analysis procedures can identify the ultimate capacity of existing concrete dams, taking into account the most critical nonlinear phenomena controlling the response. A numerical model of a non-overflow monolith of Koyna Dam, subject to earthquake motion, is used as a case study to compare the different approaches for seismic evaluation of concrete gravity dams currently employed in the two countries. The complexity of nonlinear analysis procedures and the scarcity of appropriate calibration strategies force analysts to frequently interpret results using their own judgment. It was concluded that the influence of the input parameters and ground excitation on the nonlinear dynamic response should be investigated in order to identify the most critical conditions. It was also suggested that methodologies for qualitative damage estimation based on results from linear analyses could be used to develop a systematic assessment tool and reference framework for the adequate interpretation of results. 14 refs., 2 tabs., 13 figs.
Dynamics of galaxies and clusters in \\textit{refracted gravity}
Matsakos, Titos
2016-01-01
We investigate the proof of concept and the implications of \\textit{refracted gravity}, a novel modified gravity aimed to solve the discrepancy between the luminous and the dynamical mass of cosmic structures without resorting to dark matter. Inspired by the behavior of electric fields in matter, refracted gravity introduces a gravitational permittivity that depends on the local mass density and modifies the standard Poisson equation. The resulting gravitational field can become more intense than the Newtonian field and can mimic the presence of dark matter. We show that the refracted gravitational field correctly describes (1) the rotation curves and the Tully-Fisher relation of disk galaxies; and (2) the observed temperature profile of the X-ray gas of galaxy clusters. According to these promising results, we conclude that refracted gravity deserves further investigation.
Stability Aspects of Wormholes in $R^2$ Gravity
Dent, James B; Kephart, Thomas W; White, Sara C
2016-01-01
We study radial perturbations of a wormhole in $R^2$ gravity to determine regions of stability. We also investigate massive and massless particle orbits and tidal forces in this space-time for a radially infalling observer.
Comparison of surface and satellite gravity data
Rapp, R. H.
1978-01-01
Satellite derived potential coefficients (GEM 9) are compared to terrestrial gravity data by degree in terms of coefficient differences and in terms of mean anomaly differences. The root mean square undulation difference (to degree 20) was 9 + or - m and the anomaly difference was + or - 7 mgals with GEM 9 commission errors of + or - 1.7 m and + or - 3.8 mgals. The standard deviations of the GEM 9 implied undulations increased from + or - 4 cm at degree 2 to + or - 53 cm at degree 20. The corresponding values implied by a recent (June 1978) terrestrial 5 deg field were + or - 2.53 m and + or - 0.38 m (at degree 20). Comparisons between Geos-3 altimeter derived anomalies and 1 deg X 1 Deg terrestrial data showed that + or - 6-8 mgals is a reasonable accuracy estimate for the altimeter derived anomalies. Anomalies derived from satellite to satellite tracking data indicate an accuracy of about + or - 6 mgals for the recovery of 5 deg equal area blocks.
On the cosmology of massive gravity
De Felice, Antonio; Lin, Chunshan; Mukohyama, Shinji
2013-01-01
We present a review of cosmological solutions in non-linear massive gravity, focusing on the stability of perturbations. Although homogeneous and isotropic solutions have been found, these are now known to suffer from either Higuchi ghost or a new non-linear ghost instability. We discuss two approaches to alleviate this issue. By relaxing the symmetry of the background by e.g. breaking isotropy in the hidden sector, it is possible to accommodate a stable cosmological solution. Alternatively, extending the theory to allow for new dynamical degrees of freedom can also remove the conditions which lead to the instability. As examples for this case, we study the stability of self-accelerating solutions in the quasi-dilatonic extension and generic cosmological solutions in the varying mass extension. While the quasi-dilaton case turns out to be unstable, the varying mass case allows stable regimes of parameters. Viable self-accelerating solutions in the varying mass theory yet remain to be found.
Dynamics of gravity in a Higgs phase
Arkani-Hamed, Nima; Cheng, Hsin-Chia; Luty, Markus A.; Mukohyama, Shinji; Wiseman, Toby
2007-01-01
We investigate the universal low-energy dynamics of the simplest Higgs phase for gravity, `ghost condensation.' We show that the nonlinear dynamics of the `ghostone' field dominate for all interesting gravitational sources. Away from caustic singularities, the dynamics is equivalent to the irrotational flow of a perfect fluid with equation of state pproptoρ2, where the fluid particles can have negative mass. We argue that this theory is free from catastrophic instabilities due to growing modes, even though the null energy condition is violated. Numerical simulations show that solutions generally have singularities in which negative energy regions shrink to zero size. We exhibit partial UV completions of the theory in which these singularities are smoothly resolved, so this does not signal any inconsistency in the effective theory. We also consider the bounds on the symmetry breaking scale M in this theory. We argue that the nonlinear dynamics cuts off the Jeans instability of the linear theory, and allows M lesssim 100 GeV.
On the parameterization scheme of gravity wave drag effect on the mean zonal flow of mesosphere
Institute of Scientific and Technical Information of China (English)
无
2003-01-01
Based on McFarlane's parameterization scheme of gravity wave drag, a refined gravity-wave-drag scheme is presented. Both the drag effect of the momentum flux and the dissipation effect of gravity wave breaking on the mean zonal flow are included in the refined parameterization scheme. The dissipation effect can be formulated with the gravity wave numbers and the mean quantities. The refined parameterization scheme may represent a complete drag effect of stationary gravity wave breaking on the mean zonal flow.
Thermodynamic instability of nonlinearly charged black holes in gravity's rainbow
Hendi, S H; Panah, B Eslam; Momennia, M
2015-01-01
Motivated by the violation of Lorentz invariancy in quantum gravity, we study black hole solutions in gravity's rainbow in the context of Einstein gravity coupled with various models of nonlinear electrodynamics. We regard an energy dependent spacetime and obtain related metric functions and electric fields. We show that there is an essential singularity at the origin which is covered with an event horizon. We also compute the conserved and thermodynamical quantities and examine the validity of the first law of thermodynamics in the presence of rainbow functions. Finally we investigate thermal stability conditions for these black hole solutions in context of canonical ensemble. We show that although there is not physical small black hole, large black holes are physical and enjoy thermal stability in gravity's rainbow.
Evolution of universes in quadratic theories of gravity
International Nuclear Information System (INIS)
We use a dynamical systems approach to investigate Bianchi type I and II universes in quadratic theories of gravity. Because of the complicated nature of the equations of motion we focus on the stability of exact solutions and find that there exists an isotropic Friedmann-Robertson-Walker (FRW) universe acting as a past attractor. This may indicate that there is an isotropization mechanism at early times for these kind of theories. We also discuss the Kasner universes, elucidate the associated center manifold structure, and show that there exists a set of nonzero measure which has the Kasner solutions as a past attractor. Regarding the late-time behavior, the stability shows a dependence of the parameters of the theory. We give the conditions under which the de Sitter solution is stable and also show that for certain values of the parameters there is a possible late-time behavior with phantomlike behavior. New types of anisotropic inflationary behavior are found which do not have counterparts in general relativity
Time delays across saddles as a test of modified gravity
Magueijo, Joao
2012-01-01
Modified gravity theories can produce strong signals in the vicinity of the saddles of the total gravitational potential. In a sub-class of these models this translates into diverging time-delays for echoes crossing the saddles. Such models arise from the possibility that gravity might be infrared divergent or confined, and if suitably designed they are very difficult to rule out. We show that Lunar Laser Ranging during an eclipse could probe the time-delay effect within meters of the saddle, thereby proving or excluding these models. Very Large Baseline Interferometry, instead, could target delays across the Jupiter-Sun saddle. Such experiments would shed light on the infrared behaviour of gravity and examine the puzzling possibility that there might be well-hidden regions of strong gravity and even singularities inside the solar system.
Transient response of a rectangular cavity to pulsed gravity conditions
International Nuclear Information System (INIS)
Increasing space engineering applications necessitates a complete and thorough understanding of fluid flow in low-gravity environments. To identify and clearly define meaningful low-gravity fluid problems it is necessary first to study the effects of gravity and its consequences on fluids. Heat transfer through fluids in a closed container at nominal gravity is under extensive study. The influence of gravitational magnitude and direction on natural convection is the subject of previous study. This paper analyzes the fluid transient response to a step change in gravitational magnitude. Such a transient response will play a critical role in safety analyses of nuclear space reactors as this situation will result from any change in the orbit of the reactor station. The case described in this paper indicates overshoot and undershoot in heat transfer during a change in natural convection transient. There also is a finite time, governed by some time constant, for reaching new steady-state conditions
Thermodynamics of spherically symmetric spacetimes in loop quantum gravity
Mäkelä, Jarmo
2015-06-01
The choice of the area operator in loop quantum gravity is by no means unique. In addition to the area operator commonly used in loop quantum gravity there is also an area operator introduced by Krasnov in 1998, which gives uniformly spaced area spectra for the horizons of spacetime. Using Krasnov's area operator we consider the thermodynamics of spherically symmetric spacetimes equipped with horizons in loop quantum gravity. Among other things, our approach implies, in a pretty simple manner, that every horizon of spacetime emits thermal radiation and possesses entropy which, in the natural units, is one-quarter of its area. When applied to the de Sitter spacetime loop quantum gravity provides an explanation both to the presence and the smallness of the cosmological constant.
Discussion of the Entanglement Entropy in Quantum Gravity
Ma, Chen-Te
2016-01-01
Quantum gravity needs to be satisfied by the holographic principle, and the entanglement entropy already has holographic evidences via anti-de Sitter/ Conformal field theory correspondence. Thus, we explore principles of quantum gravity via the entanglement entropy. We compute the entanglement entropy in two dimensional Einstein-Hilbert action to understand quantum geometry and area law. Then we also discuss two dimensional conformal field theory because we expect strongly coupled conformal field theory can describe perturbative quantum gravity theory. We find universal terms of the entanglement entropy is independent of a choice of an entangling surface in two dimensional conformal field theory for one interval and some cases of multiple intervals. To extend our discussion to generic multiple intervals, we use a geometric method to determine the entanglement entropy. Finally, we argue translational invariance possibly be a necessary condition in quantum gravity theory from ruing out volume law of the entangl...
National Oceanic and Atmospheric Administration, Department of Commerce — The NGS Absolute Gravity data (78 stations) was received in July 1993. Principal gravity parameters include Gravity Value, Uncertainty, and Vertical Gradient. The...
National Oceanic and Atmospheric Administration, Department of Commerce — This data base (14,559 records) was received in January 1986. Principal gravity parameters include elevation and observed gravity. The observed gravity values are...
Gerrard, Andrew J.; Kane, Timothy J.; Eckermann, Stephen D.; Thayer, Jeffrey P.
2004-01-01
We conducted gravity wave ray-tracing experiments within an atmospheric region centered near the ARCLITE lidar system at Sondrestrom, Greenland (67N, 310 deg E), in efforts to understand lidar observations of both upper stratospheric gravity wave activity and mesospheric clouds during August 1996 and the summer of 2001. The ray model was used to trace gravity waves through realistic three-dimensional daily-varying background atmospheres in the region, based on forecasts and analyses in the troposphere and stratosphere and climatologies higher up. Reverse ray tracing based on upper stratospheric lidar observations at Sondrestrom was also used to try to objectively identify wave source regions in the troposphere. A source spectrum specified by reverse ray tracing experiments in early August 1996 (when atmospheric flow patterns produced enhanced transmission of waves into the upper stratosphere) yielded model results throughout the remainder of August 1996 that agreed best with the lidar observations. The model also simulated increased vertical group propagation of waves between 40 km and 80 km due to intensifying mean easterlies, which allowed many of the gravity waves observed at 40 km over Sondrestrom to propagate quasi-vertically from 40-80 km and then interact with any mesospheric clouds at 80 km near Sondrestrom, supporting earlier experimentally-inferred correlations between upper stratospheric gravity wave activity and mesospheric cloud backscatter from Sondrestrom lidar observations. A pilot experiment of real-time runs with the model in 2001 using weather forecast data as a low-level background produced less agreement with lidar observations. We believe this is due to limitations in our specified tropospheric source spectrum, the use of climatological winds and temperatures in the upper stratosphere and mesosphere, and missing lidar data from important time periods.
Comprehensive Evaluation of Tahe Medium Gravity Crude
Institute of Scientific and Technical Information of China (English)
Li Li; Zou Ying; Weng Huixin
2008-01-01
The comprehensive evaluation of Tahe medium gravity crude has demonstrated that this type of crude belongs to a intermediate base sour crude, featuring high vanadium content (103ppm), high carbon residue content, low pour point, and low acid value. Based on the crude processing conditions at SINOPEC Luoyang Petrochemical Branch Company, a proposal on the appropriate process flow scheme for processing Tahe crude oil has been raised with the main ideas presented as follows. The IBP-175 ℃ fraction is not an ideal feedstock for catalytic reforming; the 75-250℃ fraction is a qualified feedstock for zeolite de-waxing; the 140-230℃ fraction can be used to manufacture the No. 3 jet fuel through appropriate distillation range adjustment and product refining; the 175-350℃ fraction can be directly used to manufacture No.-10 diesel through proper refining; the atmospheric resid boiling over 350℃ is not suited to be used as the RFCC feedstock; the 350-520℃ vacuum distillate oil can be used as the FCC feedstock; and the vacuum residuum boiling over 520℃ is a good feedstock for manufacture of asphalt.
Stability of Modified Gravity Coupled by the Weyl Tensor
Ghanaatian, M.; A. Gharaati; Milani, F.
2016-01-01
In this paper, we try to consider the stability conditions of a modified gravity coupled by Weyl tensor. In this way, we indicate the suitable conditions for a successful bounce while the equation of state (EoS) parameter crosses the phantom divider for our new corrected modified gravity. In the spatially flat Friedmann-Lema\\^{\\i}tre-Robertson-Walker (FLRW) universe, according to the ordinary version of the holographic dark energy (HDE) model, describing accelerated expansion of the universe,...
Nonlocal theories of gravity: the flat space propagator
Biswas, Tirthabir; Mazumdar, Anupam
2013-01-01
It was recently found that there are classes of nonlocal gravity theories that are free of ghosts and singularities in their Newtonian limit [PRL, 108 (2012), 031101]. In these proceedings, a detailed and pedagogical derivation of a main result, the flat space propagator for an arbitrary covariant metric theory of gravitation, is presented. The result is applied to analyse f(R) models, Gauss-Bonnet theory, Weyl-squared gravity and the potentially asymptotically free nonlocal theories.
Gravitational luminosity of a hot plasma in R^2 gravity
Niri, B Nadiri; Corda, C
2016-01-01
The R^{2}-gravity contribution to energy loss of a hot plasma due to the gravitational bremsstrahlung is calculated in the linearized theory on the basis of classical Coulomb scattering of plasma constituents in small-angle scattering approximation. The explicit dependence of the gravitational luminosity on the plasma temperature is derived and its relevance to the Einstein gravity is demonstrated. The result when applied to the Sun as a hot plasma, shows very good agreement with available data.
Design of a gravity corer for near shore sediment sampling
Digital Repository Service at National Institute of Oceanography (India)
Bhat, S.T.; Sonawane, A; Nayak, B.U.
For the purpose of geotechnical investigation a gravity corer has been designed and fabricated to obtain undisturbed sediment core samples from near shore waters. The corer was successfully operated at 75 stations up to water depth 30 m. Simplicity...
A lecture of the hierarchy problem and gravity
International Nuclear Information System (INIS)
In this lecture we shall briefly review some motivations for physics beyond the Standard Model. We focus our attention on the hierarchy problem and discuss the role of gravity in defining and solving this problem. (author)
LINEAR GRAVITY WAVES ON MAXWELL FLUIDS OF FINITE DEPTH
Institute of Scientific and Technical Information of China (English)
ZHANG Qinghe; SUN Yabin
2004-01-01
Linear surface gravity waves on Maxwell viscoelastic fluids with finite depth are studied in this paper. A dispersion equation describing the spatial decay of the gravity wave in finite depth is derived. A dimensionless memory (time) number θ is introduced. The dispersion equation for the pure viscous fluid will be a specific case of the dispersion equation for the viscoelastic fluid as θ = 0. The complex dispersion equation is numerically solved to investigate the dispersion relation. The influences of θ and water depth on the dispersion characteristics and wave decay are discussed. It is found that the role of elasticity for the Maxwell fluid is to make the surface gravity wave on the Maxwell fluid behave more like the surface gravity wave on the inviscid fluid.
Atom Interferometry for detection of Gravity Waves-a Project
National Aeronautics and Space Administration — Atom interferometers are more sensitive to inertial effects. This is because atoms in their inertial frame are ideal test masses for detection of gravity effects...
Former Soviet Union (FSU) Gravity Data
National Oceanic and Atmospheric Administration, Department of Commerce — Gridded gravity anomaly data for the Former Soviet Union (FSU) and Eastern Europe has been received by the National Geophysical Data Center(NGDC). The data file...
Thermodynamics of cosmological horizons in $f(T)$ gravity
Bamba, Kazuharu
2011-01-01
We explore thermodynamics of the apparent horizon in $f(T)$ gravity with both equilibrium and non-equilibrium descriptions. We find the same dual equilibrium/non-equilibrium formulation for $f(T)$ as for $f(R)$ gravity. In particular, we show that the second law of thermodynamics can be satisfied for the universe with the same temperature of the outside and inside the apparent horizon.
Crossing of Phantom Divide in $F(R)$ Gravity
Bamba, Kazuharu; Nojiri, Shin'ichi; Odintsov, Sergei D
2010-01-01
An explicit model of $F(R)$ gravity with realizing a crossing of the phantom divide is reconstructed. In particular, it is shown that the Big Rip singularity may appear in the reconstructed model of $F(R)$ gravity. Such a Big Rip singularity could be avoided by adding $R^2$ term or non-singular viable $F(R)$ theory to the model because phantom behavior becomes transient.
Consistent Extension of Hořava Gravity
Blas, D; Sibiryakov, SLPHE, Lausanne
2010-01-01
We propose a natural extension of Horava's model for quantum gravity, which is free from the notorious pathologies of the original proposal. The new model endows the scalar graviton mode with a regular quadratic action and remains power-counting renormalizable. At low energies, it reduces to a Lorentz-violating scalar-tensor gravity theory. The deviations with respect to general relativity can be made weak by an appropriate choice of parameters.
Gravity wave turbulence revealed by horizontal vibrations of the container.
Issenmann, B; Falcon, E
2013-01-01
We experimentally study the role of forcing on gravity-capillary wave turbulence. Previous laboratory experiments using spatially localized forcing (vibrating blades) have shown that the frequency power-law exponent of the gravity wave spectrum depends on the forcing parameters. By horizontally vibrating the whole container, we observe a spectrum exponent that does not depend on the forcing parameters for both gravity and capillary regimes. This spatially extended forcing leads to a gravity spectrum exponent in better agreement with the theory than by using a spatially localized forcing. The role of the vessel shape has been also studied. Finally, the wave spectrum is found to scale linearly with the injected power for both regimes whatever the forcing type used.
Towards Nonperturbation Theory of Emergent Gravity
Kar, Supriya
2016-01-01
We investigate an emergent gravity in $(4+1)$ dimensions underlying a geometric torsion ${\\cal H}_3$ in $1.5$ order formulation. We show that an emergent pair-symmetric $4$th order curvature tensor underlying a NS field theory governs a torsion free geometry and is identified as the Riemann type tensor. Interestingly a pair anti-symmetric $4$th order tensor is shown to incorporate a dynamical correction underlying a ${\\cal H}_3$ gauge potential and is identified with a non-perturbative correction. The non-perturbative term in the emergent action is shown to be described by a $U(1)$ gauge invariant ${\\cal F}_4$ in a second order theory underlying an onshell ${\\cal H}_3$ in a first order. A complete emergent theory is elegantly described with an axion, and hence a quintessence, coupling to the Riemann type geometries. The curvatures are appropriately worked out to obtain a $12D$ emergent $F$ theory. Further investigation reveals that a pair of $(M{\\bar M})_{10}$-brane are created across an event horizon. We obt...
Role of Gravity Waves in Determining Cirrus Cloud Properties
OCStarr, David; Singleton, Tamara; Lin, Ruei-Fong
2008-01-01
Cirrus clouds are important in the Earth's radiation budget. They typically exhibit variable physical properties within a given cloud system and from system to system. Ambient vertical motion is a key factor in determining the cloud properties in most cases. The obvious exception is convectively generated cirrus (anvils), but even in this case, the subsequent cloud evolution is strongly influenced by the ambient vertical motion field. It is well know that gravity waves are ubiquitous in the atmosphere and occur over a wide range of scales and amplitudes. Moreover, researchers have found that inclusion of statistical account of gravity wave effects can markedly improve the realism of simulations of persisting large-scale cirrus cloud features. Here, we use a 1 -dimensional (z) cirrus cloud model, to systematically examine the effects of gravity waves on cirrus cloud properties. The model includes a detailed representation of cloud microphysical processes (bin microphysics and aerosols) and is run at relatively fine vertical resolution so as to adequately resolve nucleation events, and over an extended time span so as to incorporate the passage of multiple gravity waves. The prescribed gravity waves "propagate" at 15 m s (sup -1), with wavelengths from 5 to 100 km, amplitudes range up to 1 m s (sup -1)'. Despite the fact that the net gravity wave vertical motion forcing is zero, it will be shown that the bulk cloud properties, e.g., vertically-integrated ice water path, can differ quite significantly from simulations without gravity waves and that the effects do depend on the wave characteristics. We conclude that account of gravity wave effects is important if large-scale models are to generate realistic cirrus cloud property climatology (statistics).
The Hamiltonian Form of Three-Dimensional Chern-Simons-like Gravity Models
Bergshoeff, Eric A; Merbis, Wout; Routh, Alasdair J; Townsend, Paul K
2014-01-01
A wide class of three-dimensional gravity models can be put into ``Chern-Simons-like'' form. We perform a Hamiltonian analysis of the general model and then specialise to Einstein-Cartan Gravity, General Massive Gravity, the recently proposed Zwei-Dreibein Gravity and a further parity violating generalisation combining the latter two.
27 CFR 30.25 - Use of precision specific gravity hydrometers.
2010-04-01
... gravity hydrometers. 30.25 Section 30.25 Alcohol, Tobacco Products and Firearms ALCOHOL AND TOBACCO TAX... precision specific gravity hydrometers. The provisions of § 30.23 respecting the care, handling, and use of... specific gravity hydrometers. Specific gravity hydrometers shall be read to the nearest...
Regional gravity and tectonic study of the Ouachita system
Energy Technology Data Exchange (ETDEWEB)
Kruger, J.M.; Keller, G.R.
1984-04-01
A regional study of the Ouachita system has been undertaken using gravity and deep-drilling data. An integrated analysis of gravity maps, computer models, and geologic data suggests that the crust beneath the Gulf coastal plain is variably attenuated continental crust. The transition zone between this crust and the craton, which is marked by a steep gravity gradient that lies along the trend of the Ouachita system, may have been created by Mesozoic reactivation of a crustal zone of weakness inherited from a plate collision during the late Paleozoic Ouachita orogeny. Gravity minima along the frontal zone of the Ouachita system are due to a thick sedimentary rock pile in conjunction with a gulfward dipping intracrustal or crust/mantle boundary in some areas. The arcuate Ouachita gravity maximum is the result of denser (metamorphic) rocks of the interior zone, with uplifts and upper crustal mafic intrusions making contributions in some areas. Gravity anomalies in the Gulf coastal plain are a combined effect of variable crustal attenuation, subsidence, and densification of the upper crust. Maxima in the southern Oklahoma aulacogen area are the result of uplifts and upper crustal mafic intrusions and/or lower crustal upwarps.
Thermodynamics of cosmological horizons in f(T) gravity
Energy Technology Data Exchange (ETDEWEB)
Bamba, Kazuharu; Geng, Chao-Qiang, E-mail: bamba@kmi.nagoya-u.ac.jp, E-mail: geng@phys.nthu.edu.tw [Department of Physics, National Tsing Hua University, Hsinchu, Taiwan 300 (China)
2011-11-01
We explore thermodynamics of the apparent horizon in f(T) gravity with both equilibrium and non-equilibrium descriptions. We find the same dual equilibrium/non-equilibrium formulation for f(T) as for f(R) gravity. In particular, we show that the second law of thermodynamics can be satisfied for the universe with the same temperature outside and inside the apparent horizon.
Design and prototype of Variable Gravity Compensation Mechanism (VGCM)
Takesue, Naoyuki; Ikematsu, Takashi; Murayama, Hideyuki; Fujimoto, Hideo
2011-01-01
A machine moving vertically requires strong gravitational resistance. Gravity compensation mechanisms devised to reduce actuator force mostly compensate for constant weight, but practical use requires that the mechanism compensate for weight variations. This paper presents a Variable Gravity Compensation Mechanism (VGCM) that uses two types of linear springs and changes the equilibrium position of one. The mechanism principle is described and the prototype is designed. Performance is experime...
Spacetime-noncommutativity regime of Loop Quantum Gravity
AMELINO-CAMELIA, Giovanni; da Silva, Malú Maira; Ronco, Michele; Cesarini, Lorenzo; Lecian, Orchidea Maria
2016-01-01
A recent study by Bojowald and Paily provided a path toward the identification of an effective quantum-spacetime picture of Loop Quantum Gravity, applicable in the "Minkowski regime", the regime where the large-scale (coarse-grained) spacetime metric is flat. A pivotal role in the analysis is played by Loop-Quantum-Gravity-based modifications to the hypersurface deformation algebra, which leave a trace in the Minkowski regime. We here show that the symmetry-algebra results reported by Bojowal...
Energy Technology Data Exchange (ETDEWEB)
Grugel, R.N. [Universities Space Research Association, Huntsville, AL (United States). Marshall Space Flight Center; Brush, L.N. [Univ. of Washington, Seattle, WA (United States). Dept. of Materials Science and Engineering
1996-12-31
Highly segregated macrostructures tend to develop during processing of hypermonotectic alloys because of the density difference existing between the two liquid phases. The {approximately}4.6 seconds of low-gravity provided by Marshall Space Flight Center`s 105 meter drop tube was utilized to minimize density-driven separation and promote uniform microstructures in hypermonotectic Ag-Ni and Ag-Mn alloys. For the Ag-Ni alloys a numerical model was developed to track heat flow and solidification of the bi-metal drop configuration. Results, potential applications, and future work are presented.
Cluster gas fraction as a test of gravity
Li, Baojiu; Gao, Liang
2015-01-01
We propose a new cosmological test of gravity, by using the observed mass fraction of X-ray emitting gas in massive galaxy clusters. The cluster gas fraction, believed to be a fair sample of the average baryon fraction in the Universe, is a well-understood observable, which has previously mainly been used to constrain background cosmology. In some modified gravity models, such as $f(R)$ gravity, gas temperature in a massive cluster is determined by the effective mass of that cluster, which can be larger than its true mass. On the other hand, X-ray luminosity is determined by the true gas density, which in both modified gravity and $\\Lambda$CDM models depends mainly on $\\Omega_{\\rm b}/\\Omega_{\\rm m}$ and hence the true total cluster mass. As a result, the standard practice of combining gas temperatures and X-ray surface brightnesses of clusters to infer their gas fractions can, in modified gravity models, lead to a larger - in $f(R)$ gravity this can be $1/3$ larger - value of $\\Omega_{\\rm b}/\\Omega_{\\rm m}$ t...
Renormalization of 3d quantum gravity from matrix models
Ambjørn, Jan; Loll, R
2004-01-01
Lorentzian simplicial quantum gravity is a non-perturbatively defined theory of quantum gravity which predicts a positive cosmological constant. Since the approach is based on a sum over space-time histories, it is perturbatively non-renormalizable even in three dimensions. By mapping the three-dimensional theory to a two-matrix model with ABAB interaction we show that both the cosmological and the (perturbatively) non-renormalizable gravitational coupling constant undergo additive renormalizations consistent with canonical quantization.
International Nuclear Information System (INIS)
In this paper, we consider two first order corrections to both the gravity and the gauge sides of the Einstein-Maxwell gravity: Gauss-Bonnet gravity and quadratic Maxwell invariant as corrections. We obtain horizonless magnetic solutions by implying a metric representing a topological defect. We analyze the geometric properties of the solutions and investigate the effects of both corrections, and find that these solutions may be interpreted as magnetic branes. We study the singularity condition and find a nonsingular spacetime with a conical geometry. We also investigate the effects of different parameters on the deficit angle of spacetime near the origin. (orig.)
Gravity and Magnetotelluric Modeling of the Santo Domingo Basin, Northern New Mexico
Zamudio, K. D.; Keithline, N.; Blum, C.; Cunningham, E.; Fromont, A.; Jorgensen, M.; Lee, R.; McBride, K.; Saez Berrios, P.; Harper, C.; Pellerin, L.; McPhee, D.; Ferguson, J. F.
2015-12-01
The Santo Domingo Basin, one of a series of basins within the Rio Grande Rift, is located between Santa Fe and Albuquerque, NM, and has been the focus of research by the Summer of Geophysical Experience (SAGE) program since 2000. Gravity, magnetotelluric (MT), and seismic data have been collected throughout the region, although we are concentrating on gravity and MT data collected during SAGE 2014 and 2015. The study area is located in the center of the Santo Domingo basin, an extensional, Miocene age, rift basin, in an area that was minimally involved in the preceding local Laramide orogenic activity. Rift sediments (~3.5 km thick) are underlain by Eocene age sediments that were shed from adjacent uplifts. Up to 3 km of Mesozoic and Paleozoic sediments are preserved above the Precambrian basement. Geologic outcrop, borehole and seismic reflection data, and known density values were used in the construction of a ~100 km-long, generalized geologic cross section from which a gravity response was calculated. The modeled gravity response makes fairly definitive predictions about the geometry of the basin as well as the stratigraphy and faulting within and bounding the basin. MT data was collected at ten stations within the basin. The MT sounding curves exhibit one-dimensional behavior at short periods (1000 ohm-m) at ~ 3.5-4 km. Conductivities of the major stratigraphic units have been determined from well logs and previous MT modeling. Forward and inverse MT models constrained by the gravity-modeled geologic cross section are used to develop a conductivity model consistent with the geology, and are a step towards a better unified treatment of MT, seismic and gravity data.
AIUB-RL02: an improved time-series of monthly gravity fields from GRACE data
Meyer, U.; Jäggi, A.; Jean, Y.; Beutler, G.
2016-05-01
The new release AIUB-RL02 of monthly gravity models from GRACE GPS and K-Band range-rate data is based on reprocessed satellite orbits referring to the reference frame IGb08. The release is consistent with the IERS2010 conventions. Improvements with respect to its predecessor AIUB-RL01 include the use of reprocessed (RL02) GRACE observations, new atmosphere and ocean dealiasing products (RL05), an upgraded ocean tide model (EOT11A), and the interpolation of shallow ocean tides (admittances). The stochastic parametrization of AIUB-RL02 was adapted to include daily accelerometer scale factors, which drastically reduces spurious signal at the 161 d period in C20 and at other low degree and order gravity field coefficients. Moreover, the correlation between the noise in the monthly gravity models and solar activity is considerably reduced in the new release. The signal and the noise content of the new AIUB-RL02 monthly gravity fields are studied and calibrated errors are derived from their non-secular and non-seasonal variability. The short-period time-variable signal over the oceans, mostly representing noise, is reduced by 50 per cent with respect to AIUB-RL01. Compared to the official GFZ-RL05a and CSR-RL05 monthly models, the AIUB-RL02 stands out by its low noise at high degrees, a fact emerging from the estimation of seasonal variations for selected river basins and of mass trends in polar regions. Two versions of the monthly AIUB-RL02 gravity models, with spherical harmonics resolution of degree and order 60 and 90, respectively, are available for the time period from March 2003 to March 2014 at the International Center for Global Earth Models or from ftp://ftp.unibe.ch/aiub/GRAVITY/GRACE (last accessed 22 March 2016).
AIUB-RL02: an improved time series of monthly gravity fields from GRACE data
Meyer, U.; Jäggi, A.; Jean, Y.; Beutler, G.
2016-03-01
The new release AIUB-RL02 of monthly gravity models from GRACE GPS and K-Band range-rate data is based on reprocessed satellite orbits referring to the reference frame IGb08. The release is consistent with the IERS2010 conventions. Improvements with respect to its predecessor AIUB-RL01 include the use of reprocessed (RL02) GRACE observations, new atmosphere and ocean dealiasing products (RL05), an upgraded ocean tide model (EOT11A), and the interpolation of shallow ocean tides (admittances). The stochastic parametrization of AIUB-RL02 was adapted to include daily accelerometer scale factors, which drastically reduces spurious signal at the 161 day period in C20 and at other low degree and order gravity field coefficients. Moreover, the correlation between the noise in the monthly gravity models and solar activity is considerably reduced in the new release. The signal and the noise content of the new AIUB-RL02 monthly gravity fields are studied and calibrated errors are derived from their non-secular and non-seasonal variability. The short-period time-variable signal over the oceans, mostly representing noise, is reduced by 50% with respect to AIUB-RL01. Compared to the official GFZ-RL05a and CSR-RL05 monthly models, the AIUB-RL02 stands out by its low noise at high degrees, a fact emerging from the estimation of seasonal variations for selected river basins and of mass trends in polar regions. Two versions of the monthly AIUB-RL02 gravity models, with spherical harmonics resolution of degree and order 60 and 90, respectively, are available for the time period from March 2003 to March 2014 at the International Center for Global Earth Models (ICGEM) or from ftp://ftp.unibe.ch/aiub/GRAVITY/GRACE
Study of two-phase flows in reduced gravity
Roy, Tirthankar
Study of gas-liquid two-phase flows under reduced gravity conditions is extremely important. One of the major applications of gas-liquid two-phase flows under reduced gravity conditions is in the design of active thermal control systems for future space applications. Previous space crafts were characterized by low heat generation within the spacecraft which needed to be redistributed within the craft or rejected to space. This task could easily have been accomplished by pumped single-phase loops or passive systems such as heat pipes and so on. However with increase in heat generation within the space craft as predicted for future missions, pumped boiling two-phase flows are being considered. This is because of higher heat transfer co-efficients associated with boiling heat transfer among other advantages. Two-phase flows under reduced gravity conditions also find important applications in space propulsion as in space nuclear power reactors as well as in many other life support systems of space crafts. Two-fluid model along with Interfacial Area Transport Equation (IATE) is a useful tool available to predict the behavior of gas-liquid two-phase flows under reduced gravity conditions. It should be noted that considerable differences exist between two-phase flows under reduced and normal gravity conditions especially for low inertia flows. This is because due to suppression of the gravity field the gas-liquid two-phase flows take a considerable time to develop under reduced gravity conditions as compared to normal gravity conditions. Hence other common methods of analysis applicable for fully developed gas-liquid two-phase flows under normal gravity conditions, like flow regimes and flow regime transition criteria, will not be applicable to gas-liquid two-phase flows under reduced gravity conditions. However the two-fluid model and the IATE need to be evaluated first against detailed experimental data obtained under reduced gravity conditions. Although lot of studies
Gravity of cosmological perturbations in the CMB
International Nuclear Information System (INIS)
We, first, attempt to single out the measures of cosmological perturbations that are least afflicted by gauge artifacts and directly connect inhomogeneous large-scale evolution with microscopic kinetics and interactions. We seek perturbation measures (i) whose dynamics is completely specified by the physics within the local Hubble volume and (ii) which are practically applicable on microscopic scales and retain their microscopic physical meaning on all scales in any homogeneous and isotropic geometry. We identify such natural measures for linear perturbations of species' density, and for nonlinear perturbations of phase-space distribution and radiation intensity. When these measures are applied to linear evolution in the Newtonian gauge, the equations acquire an explicit Cauchy structure and nonsingular superhorizon limit, while their solutions simplify. We prove that all measures of linear overdensity that satisfy (i) and (ii) coincide in the superhorizon limit. We then show that, contrary to the prevailing view, the perturbations of the cosmic microwave background (CMB) are not resonantly boosted by their self-gravity at horizon entry in the radiation era. This explains the mildness of the CMB signatures caused by the dark species which may be abundant in the radiation era, e.g. neutrinos or early quintessence. Such species can still be well constrained due to their characteristic nondegenerate signatures on scales l(greater-or-similar sign)200, where the cosmic variance is low. We find, on the other hand, that the dark matter inhomogeneities in the matter era gravitationally suppress large-angle CMB anisotropy by an order of magnitude stronger than previously stated. (In a cosmology dominated by pressureless matter, the suppression of CMB temperature autocorrelation Cl is 25-fold.) Hence, despite the larger cosmic variance at the affected l(less-or-similar sign)200, the CMB anisotropy on these scales is a useful probe of the dark sectors in the matter era
Matters of Gravity, a newsletter for the gravity community, Number 5
Pullin, J
1995-01-01
Table of contents: -Editorial and Correspondents Gravity news: -LISA Recommended to ESA as Possible New Cornerstone Mission, Peter Bender. -LIGO Project News, Stan Whitcomb. Research briefs: -Some Recent Work in General Relativistic Astrophysics, John Friedman. -Pair Creation of Black Holes, Gary Horowitz. -Conformal Field Equations and Global Properties of Spacetimes, Bernd Schmidt Conference reports: -Aspen Workshop on Numerical Investigations of Singularities in GR, Susan Scott -Second Annual Penn State Conference: Quantum Geometry, Abhay Ashtekar -First Samos Meeting, Spiros Cotsakis and Dieter Brill -Aspen Conference on Gravitational Waves and Their Detection, Syd Meshkov
Three years of practical use of airborne gravity gradiometry
van Leeuwen, E.
2003-04-01
BHP Billiton has successfully built and deployed three airborne gravity gradiometer (AGG) systems, (Newton, Einstein and Galileo) based upon the Bell Airspace (now Lockheed Martin) Gravity Gradient Instruments developed for the United States Department of Defense. A second-generation gradiometer (Feynman) is presently nearing completion. The GGI technology is based on groups of four (4) accelerometers where the accelerometers are equi-spaced on a circle. The configuration successfully rejects both common mode accelerations and rotations about the axis perpendicular to the plane of the complement. The GGI is mounted within an aircraft in a specially designed, inertially stabilized platform, which significantly reduces sensitivity to noise and turbulence. The BHP Billiton AGG Technology provides high quality gravity maps with a resolution and sensitivity to map gravity anomalies associated with both minerals and hydrocarbon deposits. To date the purpose built and designed hardware and data processing algorithms, in conjunction with several other geophysical survey instruments, have been deployed against a broad range of mineral and hydrocarbon targets, a total of over 300,000km of operational flights having been made. Data will also be presented on the in-flight sensitivity of a gravity gradiometer to the airborne environment. It will also outline some of the many unexpected problems that were encountered in the 18-month flight trials required to achieve satisfactory airborne operation.
Requirements analysis of airborne gravity gradiometry on moving-based platform
Tu, L.; Li, Z.; Wu, W.
2014-12-01
Airborne gravity and gravity gradient measurement are the most effective ways for the earth gravitational field measurement. Gravity gradient is a derivative of gravity acceleration, due to the high order feature of gravity gradient, it is more sensitive to short wave component, and can reflect the details of the source so that the gravity gradient measurement has wide applications in geophysical science, resource exploration, and inertial navigation. Airborne gravity gradient measurement uses the plane or ship as the platform, and it is efficient and high precision. In this paper, We compared the gravity and gravity gradient measurement, and analyzed the advantages of the gravity gradient measurement compared with gravity measurement. The airborne gravity gradient measurement system and the inertial stabilization platform were discussed. By setting a goal sensitivity of the gravity gradient measurement being 1 E/√Hz, the key factors of the stabilized platform, namely the pointing accuracy, pointing stability, and gyroscope random drift, are 0.5°, 0.01°/hr/√Hz, and 0.01°/hr respectively. Compared with the airborne gravity measurement whose goal sensitivity is 1mGal/√Hz, the requirements of moving-based gravity gradient measurement on the inertial stabilization platform is significantly lower and hence easy to realize, and the major reason is the differential measurement mode being used.
The influence of gravity on structure and function of animals
Ross, M. D.
1984-01-01
Gravity is the only environmental parameter that has remained constant during the period of evolution of living matter on earth. Thus, it must have been a major force in shaping living things. The influence of gravitational loading on evolution of the vertebrate skeleton is well recognized, and scale effects have been studied. This paper, however, considers in addition four pivotal events in early evolution that would seem to have been significant for the later success and diversifcation of animal life. These are evolution of the cytoskeleton, cell motility (flagellae and cilia), gravity detecting devices (accelerometers), and biomineralization. All are functionally calcium dependent in eukaryotes and all occurred or were foreshadowed in prokaryotes. A major question is why calcium was selected as an ion of great importance to the structure and function of living matter; another is whether gravity played a role in its selection.
Affine generalizations of gravity in the light of modern cosmology
Filippov, A T
2010-01-01
We discuss new models of an `affine' theory of gravity in multidimensional space-times with symmetric connections. We use and develop ideas of Weyl, Eddington, and Einstein, in particular, Einstein's proposal to specify the space - time geometry by use of the Hamilton principle. More specifically, the connection coefficients are determined using a `geometric' Lagrangian that is an arbitrary function of the generalized (non-symmetric) Ricci curvature tensor (and, possibly, of other fundamental tensors) expressed in terms of the connection coefficients regarded as independent variables. Such a theory supplements the standard Einstein gravity with dark energy (the cosmological constant, in the first approximation), a neutral massive (or tachyonic) vector field (vecton), and massive (or tachyonic) scalar fields. These fields couple only to gravity and can generate dark matter and/or inflation. The new field masses (real or imaginary) have a geometric origin and must appear in any concrete model. The concrete choi...
Modeling and estimation of a low degree geopotential model from terrestrial gravity data
Pavlis, Nikolaos K.
1988-01-01
The development of appropriate modeling and adjustment procedures for the estimation of harmonic coefficients of the geopotential, from surface gravity data was studied, in order to provide an optimum way of utilizing the terrestrial gravity information in combination solutions currently developed at NASA/Goddard Space Flight Center, for use in the TOPEX/POSEIDON mission. The mathematical modeling was based on the fundamental boundary condition of the linearized Molodensky boundary value problem. Atmospheric and ellipsoidal corrections were applied to the surface anomalies. Terrestrial gravity solutions were found to be in good agreement with the satellite ones over areas which are well surveyed (gravimetrically), such as North America or Australia. However, systematic differences between the terrestrial only models and GEMT1, over extended regions in Africa, the Soviet Union, and China were found. In Africa, gravity anomaly differences on the order of 20 mgals and undulation differences on the order of 15 meters, over regions extending 2000 km in diameter, occur. Comparisons of the GEMT1 implied undulations with 32 well distributed Doppler derived undulations gave an RMS difference of 2.6 m, while corresponding comparison with undulations implied by the terrestrial solution gave RMS difference on the order of 15 m, which implies that the terrestrial data in that region are substantially in error.
Geophysical investigations of buried volcanic centers near Yucca Mountain, Southwest Nevada
International Nuclear Information System (INIS)
Several aeromagnetic dipolar anomalies occur over flat, alluvial areas near Yucca Mountain that resemble anomalies typically associated with subaerial basaltic volcanic centers. Detailed gravity and ground magnetic data were collected along a surveyed traverse across an aeromagnetic anomaly in Amargosa Valley, south of Yucca Mountain, Nevada. Modeling of the ground magnetic data collected over the largest of these anomalies, the Lathrop Wells aeromagnetic anomaly, indicates that the top of the causative body, most likely basalt, is less than 250 m below the surface. Gravity data indicate an apparent lack of an associated gravity anomaly and suggest that either the causative body may be tuff rather than basalt, or the volume of the body is small. Both drilling and collection of more magnetic and gravity data are necessary because ages and volumes of buried volcanic centers are important constraints for estimating the probability of potential volcanism near the proposed nuclear waste repository at Yucca Mountain
Collisional origin of asteroid families: effects of the target's gravity
International Nuclear Information System (INIS)
The outcomes of asteroidal catastrophic collisions are strongly affected by the target asteroid's gravity, since only the fragments escaping with initial velocities higher than the target's escape velocity are not reaccumulated into 'rubble pile' remnants. This idea can be compared with the observational evidence on the properties of family asteroids in several ways: (1) the shape and spin period of the 'reaccumulated' family asteroids will roughly fit the relationships valid for self-gravitating fluid bodies; (2) the relative velocities of the few escaping fragments arising from a breakup event marginally overcoming self-gravity will often have an anisotropic distribution, affecting the final distribution of orbital elements; (3) the amount of mass which in a given family escaped to 'infinity' will be correlated with the target's size, since only for objects larger than approx. 100 km self-gravity plays an important role. These predictions are discussed and compared with the available data. (Auth.)
Role of actin in auxin transport and transduction of gravity
Hu, S.; Basu, S.; Brady, S.; Muday, G.
Transport of the plant hormone auxin is polar and the direction of the hormone movement appears to be controlled by asymmetric distribution of auxin transport protein complexes. Changes in the direction of auxin transport are believed to drive asymmetric growth in response to changes in the gravity vector. To test the possibility that asymmetric distribution of the auxin transport protein complex is mediated by attachment to the actin cytoskeleton, a variety of experimental approaches have been used. The most direct demonstration of the role of the actin cytoskeleton in localization of the protein complex is the ability of one protein in this complex to bind to affinity columns containing actin filaments. Additionally, treatments of plant tissues with drugs that fragment the actin c toskeleton reducey polar transport. In order to explore this actin interaction and the affect of gravity on auxin transport and developmental polarity, embryos of the brown alga, Fucus have been examined. Fucus zygotes are initially symmetrical, but develop asymmetry in response to environmental gradients, with light gradients being the best- characterized signal. Gravity will polarize these embryos and gravity-induced polarity is randomized by clinorotation. Auxin transport also appears necessary for environmental controls of polarity, since auxin efflux inhibitors perturb both photo- and gravity-polarization at a very discrete temporal window within six hours after fertilization. The actin cytoskeleton has previously been shown to reorganize after fertilization of Fucus embryos leading to formation of an actin patch at the site of polar outgrowth. These actin patches still form in Fucus embryos treated with auxin efflux inhibitors, yet the position of these patches is randomized. Together, these results suggest that there are connections between the actin cytoskeleton, auxin transport, and gravity oriented growth and development. (Supported by NASA Grant: NAG2-1203)
Interaction of modulated gravity water waves of finite depth
Giannoulis, Ioannis
2016-10-01
We consider the capillary-gravity water wave problem of finite depth with a flat bottom of one or two horizontal dimensions. We derive the modulation equations of leading and next-to-leading order in the hyperbolic scaling for three weakly amplitude-modulated plane wave solutions of the linearized problem in the absence of quadratic and cubic resonances. We justify the derived system of macroscopic equations in the case of gravity waves using the stability of the finite depth water wave problem on the time scale O (1 / ɛ).
Aerodynamic heating of ballistic missile including the effects of gravity
Indian Academy of Sciences (India)
S N Maitra
2000-10-01
The aerodynamic heating of a ballistic missile due to only convection is analysed taking into consideration the effects of gravity. The amount of heat transferred to the wetted area and to the nose region has been separately determined, unlike A Miele's treatise without consideration of gravity. The peak heating ratesto the wetted area and to the nose of the missile are also investigated. Finally four numerical examples are cited to estimate the errors, in heat transfers and heating ratesto both wetted area and nose region of the missile, arising out of neglecting the gravitational forces.
New gravity and magnetics map of eastern part of Azores
Dehghani, Ali
2014-05-01
The Azores are of volcanic origin and the volcanic activities are still occurs in the area. The main tectonic features in the eastern part of Azores are the Gloria Fault (GF) and São Miguel volcanic Island. The GF is an E-W strike-slip fault and can be traced by bathymetry. In the past decade many geological and geophysical investigations were dedicated to the study of tectonic features in the eastern part of Azores. Two of these cruises were organized by the Institute of Geophysics, University of Hamburg, Germany, in the years 2009 and 2012. In 2009 during the Meteor cruise M79-2 a total of 5500 km new Gravity and 2000 km new magnetic data were collected along some 60 Profiles. During the Poseidon cruise in the year 2012 some 2000 km new gravity and magnetic data were collected along two E-W profiles in the eastern part of Azores. The new gravity data were recorded with the modern Air-Sea-Gravimeter of Bodenseewerk KSS 31M and the new magnetic date with the Gradiometer SeaSpy. All new potential date were combined with the available data of the data base GEODAS and the new gravity anomaly maps (Free-Air and Bouguer) and the new magnetic anomaly map were produced. The maps show clearly the tectonic features in the area. The GF can be traced very well on both gravity and magnetic anomaly maps. Most of the small hills around the São Miguel Island are shown up in the magnetic anomaly map as strong magnetic anomaly. The new gravity and magnetic maps and the interpretation of them will be presented. The results of some 2-D modeling along some interesting profiles will be also presented and discussed.
Design of Superconducting Gravity Gradiometer Cryogenic System for Mars Mission
Li, X.; Lemoine, F. G.; Paik, H. J.; Zagarola, M.; Shirron, P. J.; Griggs, C. E.; Moody, M. V.; Han, S.-C.
2016-01-01
Measurement of a planet's gravity field provides fundamental information about the planet's mass properties. The static gravity field reveals information about the internal structure of the planet, including crustal density variations that provide information on the planet's geological history and evolution. The time variations of gravity result from the movement of mass inside the planet, on the surface, and in the atmosphere. NASA is interested in a Superconducting Gravity Gradiometer (SGG) with which to measure the gravity field of a planet from orbit. An SGG instrument is under development with the NASA PICASSO program, which will be able to resolve the Mars static gravity field to degree 200 in spherical harmonics, and the time-varying field on a monthly basis to degree 20 from a 255 x 320 km orbit. The SGG has a precision two orders of magnitude better than the electrostatic gravity gradiometer that was used on the ESA's GOCE mission. The SGG operates at the superconducting temperature lower than 6 K. This study developed a cryogenic thermal system to maintain the SGG at the design temperature in Mars orbit. The system includes fixed radiation shields, a low thermal conductivity support structure and a two-stage cryocooler. The fixed radiation shields use double aluminized polyimide to emit heat from the warm spacecraft into the deep space. The support structure uses carbon fiber reinforced plastic, which has low thermal conductivity at cryogenic temperature and very high stress. The low vibration cryocooler has two stages, of which the high temperature stage operates at 65 K and the low temperature stage works at 6 K, and the heat rejection radiator works at 300 K. The study also designed a second option with a 4-K adiabatic demagnetization refrigerator (ADR) and two-stage 10-K turbo-Brayton cooler.
Energy Technology Data Exchange (ETDEWEB)
NONE
1997-03-01
The effect of micro-gravity on bio-functions and vital reaction was studied using the facility of Underground Gravity-free Experiment Center Co. On the effect on osteoblast shape and gene expression, although fluorochrome reacting with Ca was well taken into cells, no significant difference in Ca content in cells was observed before/after falling. Expression of genes related to cell propagation was controlled under micro-gravity. Protoplast fusion of Lentinus was unaffected by micro-gravity. The mRNA fragments of gravity sensitive mutant of rice plant were affected by micro-gravity. Paramecium was set swimming in solutions with different specific gravities. The reaction behavior of Paramecium was affected by the difference in specific gravity between cell bodies and solutions. The water content metabolism functions of a mouse with needle stimulus, in particular excretory, were slightly promoted by micro- gravity. The cortisol level in blood of a falling mouse group rose showing strong stress. As the preliminary study on the geotaxis of insects, motion of bagworm was observed. 12 refs., 38 figs., 4 tabs.
Juergen Neumeyer; Schäfer, U.; Kremer, J; Hartmut Pflug; Guochang Xu;
2009-01-01
Derivation of gravity anomalies from Airborne Gravimeter, IMU recordings - validation with regional analytic models using ground and satellite gravity data GERMANY (Neumeyer, Jurgen) GERMANY Received: 2008-03-31 Revised: 2008-08-01 Accepted: 2008-08-21
Gravitation. [consideration of black holes in gravity theories
Fennelly, A. J.
1978-01-01
Investigations of several problems of gravitation are discussed. The question of the existence of black holes is considered. While black holes like those in Einstein's theory may not exist in other gravity theories, trapped surfaces implying such black holes certainly do. The theories include those of Brans-Dicke, Lightman-Lee, Rosen, and Yang. A similar two-tensor theory of Yilmaz is investigated and found inconsistent and nonviable. The Newman-Penrose formalism for Riemannian geometries is adapted to general gravity theories and used to implement a search for twisting solutions of the gravity theories for empty and nonempty spaces. The method can be used to find the gravitational fields for all viable gravity theories. The rotating solutions are of particular importance for strong field interpretation of the Stanford/Marshall gyroscope experiment. Inhomogeneous cosmologies are examined in Einstein's theory as generalizations of homogeneous ones by raising the dimension of the invariance groups by one more parameter. The nine Bianchi classifications are extended to Rosen's theory of gravity for homogeneous cosmological models.
Study of Thermodynamic Quantities in Generalized Gravity Theories
Chattopadhyay, Surajit; Bhattacharya, Samarpita
2011-01-01
In this work, we have studied the thermodynamic quantities like temperature of the universe, heat capacity and squared speed of sound in generalized gravity theories like Brans-Dicke, Ho$\\check{\\text r}$ava-Lifshitz and $f(R)$ gravities. We have considered the universe filled with dark matter and dark energy. Also we have considered the equation of state parameters for open, closed and flat models. We have observed that in all cases the equation of state behaves like quintessence. The temperature and heat capacity of the universe are found to decrease with the expansion of the universe in all cases. In Brans-Dicke and $f(R)$ gravity theories the squared speed of sound is found to exhibit increasing behavior for open, closed and flat models and in Ho$\\check{\\text r}$ava-Lifshitz gravity theory it is found to exhibit decreasing behavior for open and closed models with the evolution of the universe. However, for flat universe, the squared speed of sound remains constant in Ho$\\check{\\text r}$ava-Lifshitz gravity...
Gravitons from a loop representation of linearised gravity
Varadarajan, M
2002-01-01
Loop quantum gravity is based on a classical formulation of 3+1 gravity in terms of a real SU(2) connection. Linearization of this classical formulation about a flat background yields a description of linearised gravity in terms of a {\\em real} $U(1)\\times U(1)\\times U(1)$ connection. A `loop' representation, in which holonomies of this connection are unitary operators, can be constructed. These holonomies are not well defined operators in the standard graviton Fock representation. We generalise our recent work on photons and U(1) holonomies to show that Fock space gravitons are associated with distributional states in the $U(1)\\times U(1)\\times U(1)$ loop representation. Our results may illuminate certain aspects of the much deeper (and as yet unkown,) relation between gravitons and states in nonperturbative loop quantum gravity. This work leans heavily on earlier seminal work by Ashtekar, Rovelli and Smolin (ARS) on the loop representation of linearised gravity using {\\em complex} connections. In the last p...
Effects of artificial gravity on the cardiovascular system: Computational approach
Diaz Artiles, Ana; Heldt, Thomas; Young, Laurence R.
2016-09-01
Artificial gravity has been suggested as a multisystem countermeasure against the negative effects of weightlessness. However, many questions regarding the appropriate configuration are still unanswered, including optimal g-level, angular velocity, gravity gradient, and exercise protocol. Mathematical models can provide unique insight into these questions, particularly when experimental data is very expensive or difficult to obtain. In this research effort, a cardiovascular lumped-parameter model is developed to simulate the short-term transient hemodynamic response to artificial gravity exposure combined with ergometer exercise, using a bicycle mounted on a short-radius centrifuge. The model is thoroughly described and preliminary simulations are conducted to show the model capabilities and potential applications. The model consists of 21 compartments (including systemic circulation, pulmonary circulation, and a cardiac model), and it also includes the rapid cardiovascular control systems (arterial baroreflex and cardiopulmonary reflex). In addition, the pressure gradient resulting from short-radius centrifugation is captured in the model using hydrostatic pressure sources located at each compartment. The model also includes the cardiovascular effects resulting from exercise such as the muscle pump effect. An initial set of artificial gravity simulations were implemented using the Massachusetts Institute of Technology (MIT) Compact-Radius Centrifuge (CRC) configuration. Three centripetal acceleration (artificial gravity) levels were chosen: 1 g, 1.2 g, and 1.4 g, referenced to the subject's feet. Each simulation lasted 15.5 minutes and included a baseline period, the spin-up process, the ergometer exercise period (5 minutes of ergometer exercise at 30 W with a simulated pedal cadence of 60 RPM), and the spin-down process. Results showed that the cardiovascular model is able to predict the cardiovascular dynamics during gravity changes, as well as the expected
Extended Theories of Gravity in cosmological and astrophysical applications
Wojnar, Aneta
2016-01-01
The main subjects of the PhD dissertation concern cosmological models considered in Palatini f(R) gravity and scalar-tensor theories. We introduce a simple generalization of the LCDM model based on Palatini modified gravity with quadratic Starobinsky term. A matter source is provided by generalized Chaplygin gas. The statistical analysis of our model is investigated. We use dynamical system approach to study the evolution of the Universe. The model reaches a very good agreement with the newest experimental data and yields an inflationary epoch caused by a singularity of the type III. The present-day accelerated expansion is also provided by the model. We also show that the Lie and Noether symmetry approaches are very useful tools in cosmological considerations. We examine two other models of Extended Theories of Gravity (ETGs): the novel hybrid metric-Palatini gravity and a minimally coupled to gravity scalar field. The first one is applied to homogeneous and isotropic model while in the scalar-tensor theory ...
Sensitivity study of high eccentricity orbits for Mars gravity recovery
International Nuclear Information System (INIS)
By linear perturbation theory, a sensitivity study is presented to calculate the contribution of the Mars gravity field to the orbital perturbations in velocity for spacecrafts in both low eccentricity Mars orbits and high eccentricity orbits (HEOs). In order to improve the solution of some low degree/order gravity coefficients, a method of choosing an appropriate semimajor axis is often used to calculate an expected orbital resonance, which will significantly amplify the magnitude of the position and velocity perturbations produced by certain gravity coefficients. We can then assess to what degree/order gravity coefficients can be recovered from the tracking data of the spacecraft. However, this existing method can only be applied to a low eccentricity orbit, and is not valid for an HEO. A new approach to choosing an appropriate semimajor axis is proposed here to analyze an orbital resonance. This approach can be applied to both low eccentricity orbits and HEOs. This small adjustment in the semimajor axis can improve the precision of gravity field coefficients and does not affect other scientific objectives. (research papers)
Higher derivative gravity: Field equation as the equation of state
Dey, Ramit; Liberati, Stefano; Mohd, Arif
2016-08-01
One of the striking features of general relativity is that the Einstein equation is implied by the Clausius relation imposed on a small patch of locally constructed causal horizon. The extension of this thermodynamic derivation of the field equation to more general theories of gravity has been attempted many times in the last two decades. In particular, equations of motion for minimally coupled higher-curvature theories of gravity, but without the derivatives of curvature, have previously been derived using a thermodynamic reasoning. In that derivation the horizon slices were endowed with an entropy density whose form resembles that of the Noether charge for diffeomorphisms, and was dubbed the Noetheresque entropy. In this paper, we propose a new entropy density, closely related to the Noetheresque form, such that the field equation of any diffeomorphism-invariant metric theory of gravity can be derived by imposing the Clausius relation on a small patch of local causal horizon.
Higher derivative gravity: field equation as the equation of state
Dey, Ramit; Mohd, Arif
2016-01-01
One of the striking features of general relativity is that the Einstein equation is implied by the Clausius relation imposed on a small patch of locally constructed causal horizon. Extension of this thermodynamic derivation of the field equation to more general theories of gravity has been attempted many times in the last two decades. In particular, equations of motion for minimally coupled higher curvature theories of gravity, but without the derivatives of curvature, have previously been derived using a thermodynamic reasoning. In that derivation the horizon slices were endowed with an entropy density whose form resembles that of the Noether charge for diffeomorphisms, and was dubbed the Noetheresque entropy. In this paper, we propose a new entropy density, closely related to the Noetheresque form, such that the field equation of any diffeomorphism invariant metric theory of gravity can be derived by imposing the Clausius relation on a small patch of local causal horizon.
The interpretation of gravity anomaly on lunar Apennines
Institute of Scientific and Technical Information of China (English)
无
2009-01-01
The lunar Apennines,located in the southeast of Mare Imbrium,is the largest range on the Moon. The gravity anomalies on profiles across the mountains reveal evidence of a great fault zone characteristic. The deep crustal structures of lunar Apennines are analyzed on the basis of topographic data from Chang’E-1 satellite and gravity data from Lunar Prospector. The inverted crust-mantle models indicate the presence of a lithosphere fault beneath the mountains. Inverted results of gravity and the hypothe-sis of lunar thermal evolution suggest that the lunar lithosphere might be broken ～3.85 Ga ago due to a certain dynamic lateral movement and compression of lunar lithosphere. This event is associated with the history of magma filling and lithosphere deformation in the mountain zone and adjacent area. Moreover,the formation and evolution of Imbrium basin impose this effect on the process.
Unraveling the nature of Gravity through our clumpy Universe
Baghram, Shant; Habibi, Farhang; Mohayaee, Roya; Silk, Joseph
2014-01-01
We propose a new probe to test the nature of gravity at various redshifts through large-scale cosmological observations. We use our void catalog, extracted from the Sloan Digital Sky Survey (SDSS, DR10), to trace the distribution of matter along the lines of sight to SNe Ia that are selected from the Union 2 catalog. We study the relation between SNe Ia luminosities and convergence and also the peculiar velocities of the sources. We show that the effects, on SNe Ia luminosities, of convergence and of peculiar velocities predicted by the theory of general relativity and theories of modified gravities are different and hence provide a new probe of gravity at various redshifts. We show that the present sparse large-scale data does not allow us to determine any statistically- significant deviation from the theory of general relativity but future more comprehensive surveys should provide us with means for such an exploration.
Cosmological implications of modified gravity induced by quantum metric fluctuations
Liu, Xing; Liang, Shi-Dong
2016-01-01
We investigate the cosmological implications of modified gravities induced by the quantum fluctuations of the gravitational metric. If the metric can be decomposed as the sum of the classical and of a fluctuating part, of quantum origin, then the corresponding Einstein quantum gravity generates at the classical level modified gravity models with a nonminimal coupling between geometry and matter. As a first step in our study, after assuming that the expectation value of the quantum correction can be generally expressed in terms of an arbitrary second order tensor constructed from the metric and from the thermodynamic quantities characterizing the matter content of the Universe, we derive the (classical) gravitational field equations in their general form. We analyze in detail the cosmological models obtained by assuming that the quantum correction tensor is given by the coupling of a scalar field and of a scalar function to the metric tensor, and by a term proportional to the matter energy-momentum tensor. For...
The interpretation of gravity anomaly on lunar Apennines
Institute of Scientific and Technical Information of China (English)
CHEN Chao; CHEN Bo; PING JinSong; LIANG Qing; HUANG Qian; ZHAO WenJin; ZHANG ChangDa
2009-01-01
The lunar Apennines, located in the southeast of Mare Imbrium, is the largest range on the Moon. The gravity anomalies on profiles across the mountains reveal evidence of a great fault zone characteristic.The deep crustal structures of lunar Apennines are analyzed on the basis of topographic data from Chang'E-1 satellite and gravity data from Lunar Prospector. The inverted crust-mantle models indicate the presence of a lithosphere fault beneath the mountains. Inverted results of gravity and the hypothesis of lunar thermal evolution suggest that the lunar lithosphere might be broken ～3.85 Ga ago due to a certain dynamic lateral movement and compression of lunar lithosphere. This event is associated with the history of magma filling and lithosphere deformation in the mountain zone and adjacent area. Moreover, the formation and evolution of Imbrium basin impose this effect on the process.
Institute of Scientific and Technical Information of China (English)
XU; Jiyao(徐寄遥); MA; Ruiping(马瑞平); A.K.Smith
2002-01-01
A nonlinear, compressible, non-isothermal gravity wave model that involves photochemistry is used to study the effects of gravity wave on atmospheric chemical species distributions in this paper. The changes in the distributions of oxygen compound and hydrogen compound density induced by gravity wave propagation are simulated. The results indicate that when a gravity wave propagates through a mesopause region, even if it does not break, it can influence the background distributions of chemical species. The effect of gravity wave on chemical species at night is larger than in daytime.
Inviscid evolution of large amplitude filaments in a uniform gravity field
International Nuclear Information System (INIS)
The inviscid evolution of localized density stratifications under the influence of a uniform gravity field in a homogeneous, ambient background is studied. The fluid is assumed to be incompressible, and the stratification, or filament, is assumed to be initially isotropic and at rest. It is shown that the center of mass energy can be related to the center of mass position in a form analogous to that of a solid object in a gravity field g by introducing an effective gravity field geff, which is less than g due to energy that goes into the background and into non-center of mass motion of the filament. During the early stages of the evolution, geff is constant in time and can be determined from the solution of a 1D differential equation that depends on the initial, radially varying density profile of the filament. For small amplitude filaments such that ρ0 ≪ 1, where ρ0 is the relative amplitude of the filament to the background, the early stage geff scales linearly with ρ0, but as ρ0→∞, geff→g and is thus independent of ρ0. Fully nonlinear simulations are performed for the evolution of Gaussian filaments, and it is found that the time tmax, which is defined as the time for the center of mass velocity to reach its maximum value Umax, occurs very soon after the constant acceleration phase and so Umax≈geff(t=0)tmax. The simulation results show that Umax∼1/tmax∼√(ρ0) for ρ0 ≪ 1, in agreement with theory and results from previous authors, but that Umax and tmax both scale approximately with √(ρ0) for ρ0 ≫ 1. The fact that Umax and tmax have the same scaling with ρ0 for large amplitude filaments is in agreement with the theory presented in this paper
Galactic space-times in modified theories of gravity
Dey, Dipanjan; Sarkar, Tapobrata
2014-01-01
We study Bertrand space-times (BSTs), which have been proposed as viable models of space-times seeded by galactic dark matter, in modified theories of gravity. We first critically examine the issue of galactic rotation curves in General Relativity, and establish the usefulness of BSTs to fit experimental data in this context. We then study BSTs in metric $f(R)$ gravity and in Brans-Dicke theories. For the former, the nature of the Newtonian potential is established, and we also compute the effective equation of state and show that it can provide good fits to some recent experimental results. For the latter, we calculate the Brans-Dicke scalar analytically in some limits and numerically in general, and find interesting constraints on the parameters of the theory. Our results provide evidence for the physical nature of Bertrand space-times in modified theories of gravity.
Sketches of emergent geometry in the gauge/gravity duality
Energy Technology Data Exchange (ETDEWEB)
Berenstein, D. [Physics Department, University of California, Santa Barbara, CA 93106 (United States)
2014-09-11
In this paper three notions of emergent geometry arising from the study of gauge/gravity duals are discussed. The unifying theme behind these notions of emergent geometry is that one can derive properties of the effective action of a probe or excitation around some configuration in gauge theory which can be argued to be localized at a particular position in the gravity dual, and match this description to various degrees of accuracy in the gravity dual. The three examples discussed are giant gravitons in AdS{sub 5} x S{sup 5}, open strings stretching between these giants and the probe dynamics of a D0 brane in the presence of a thermal matrix configuration of the BFSS matrix model. (Copyright copyright 2014 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)
Algebraic quantum gravity (AQG): IV. Reduced phase space quantization of loop quantum gravity
International Nuclear Information System (INIS)
We perform a canonical, reduced phase space quantization of general relativity by loop quantum gravity (LQG) methods. The explicit construction of the reduced phase space is made possible by the combination of (a) the Brown-Kuchar mechanism in the presence of pressure-free dust fields which allows to deparametrize the theory and (b) Rovelli's relational formalism in the extended version developed by Dittrich to construct the algebra of gauge-invariant observables. Since the resulting algebra of observables is very simple, one can quantize it using the methods of LQG. Basically, the kinematical Hilbert space of non-reduced LQG now becomes a physical Hilbert space and the kinematical results of LQG such as discreteness of spectra of geometrical operators now have physical meaning. The constraints have disappeared; however, the dynamics of the observables is driven by a physical Hamiltonian which is related to the Hamiltonian of the standard model (without dust) and which we quantize in this paper.
Deterrents to a Theory of Quantum Gravity
Rabinowitz, M
2006-01-01
As shown in my previous paper, quantum mechanics (QM) directly violates the weak equivalence principle (WEP) in general, and thus indirectly violates the strong equivalence principle (SEP) in all dimensions. The present paper shows that quantum mechanics also directly violates the SEP unless it is arbitrarily abetted in hindsight. Vital domains are shown to exist in which quantum gravity would be non-applicable. There are classical subtleties in which the SEP appears to be violated, but is not. Neutron free fall interference experiments in a gravitational field are examined, as is Galileo's falling body assertion and the misconception it leads to.
Atom interferometer as a selective sensor of rotation or gravity
Dubetsky, B
2006-01-01
In the presence of Earth gravity and gravity-gradient forces, centrifugal and Coriolis forces caused by the Earth rotation, the phase of the time-domain atom interferometers is calculated with accuracy up to the terms proportional to the fourth degree of the time separation between pulses. We considered double-loop atom interferometers and found appropriate condition to eliminate their sensitivity to acceleration to get atomic gyroscope, or to eliminate the sensitivity to rotation to increase accuracy of the atomic gravimeter. Consequent use of these interferometers allows one to measure all components of the acceleration and rotation frequency projection on the plane perpendicular to gravity acceleration. Atom interference on the Raman transition driving by non-counterpropagating optical fields is proposed to exclude stimulated echo processes which can affect the accuracy of the atomic gyroscopes. Using non-counterpropagating optical fields allows one to get new type of the Ramsey fringes arising in the unid...
Effect of gravity convection on interface morphology during solidification
Institute of Scientific and Technical Information of China (English)
2007-01-01
An experimental apparatus consisting of a crystal growth room and a crystal growth observation system was developed for the study of the effect of the gravity convection perpendicular to the growth direction on the growth process by use of model alloy succinonitrile (SCN)-5wt%ethanol. It was found that the convection improves the stability of the interface and causes the downstream alternation of the cell growth direction because of the dual effect of the Stokes force and the gravity. The second dendrite arm facing the flow comes into being earlier than that at an- other side when the interface transforms cell to dendrite. Then the dendrite at the side facing the flow comes into being earlier. The second dendrite arm facing the flow grows faster and is more developed than that at another side. In addition, the primary dendrite arm spacing increases and the dendrite tip radius decreases un- der the gravity convection.
A Simple Theory of Capillary-Gravity Wave Turbulence
Glazman, Roman E.
1995-01-01
Employing a recently proposed 'multi-wave interaction' theory, inertial spectra of capillary gravity waves are derived. This case is characterized by a rather high degree of nonlinearity and a complicated dispersion law. The absence of scale invariance makes this and some other problems of wave turbulence (e.g., nonlinear inertia gravity waves) intractable by small-perturbation techniques, even in the weak-turbulence limit. The analytical solution obtained in the present work for an arbitrary degree of nonlinearity is shown to be in reasonable agreement with experimental data. The theory explains the dependence of the wave spectrum on wind input and describes the accelerated roll-off of the spectral density function in the narrow sub-range separating scale-invariant regimes of purely gravity and capillary waves, while the appropriate (long- and short-wave) limits yield power laws corresponding to the Zakharov-Filonenko and Phillips spectra.
Consistency of matter models with asymptotically safe quantum gravity
Donà, P; Percacci, Roberto
2014-01-01
We discuss the compatibility of quantum gravity with dynamical matter degrees of freedom. Specifically, we present bounds we obtained in [1] on the allowed number and type of matter fields within asymptotically safe quantum gravity. As a novel result, we show bounds on the allowed number of spin-3/2 (Rarita-Schwinger) fields, e.g., the gravitino. These bounds, obtained within truncated Renormalization Group flows, indicate the compatibility of asymptotic safety with the matter fields of the standard model. Further, they suggest that extensions of the matter content of the standard model are severely restricted in asymptotic safety. This means that searches for new particles at colliders could provide experimental tests for this particular approach to quantum gravity.
The metric-affine formalism of f(R) gravity
International Nuclear Information System (INIS)
Recently a class of alternative theories of gravity which goes under the name f(R) gravity, has received considerable attention, mainly due to its interesting applications in cosmology. However, the phenomenology of such theories is not only relevant to cosmological scales, especially when it is treated within the framework of the so called Palatini variation, an independent variation with respect to the metric and the connection, which is not considered a priori to be the Levi-Civita connection of the metric. If this connection has its standard geometrical meaning the resulting theory will be a metric-affine theory of gravity, as will be discussed in this talk. The general formalism will be presented and several aspects of the theory will be covered, mainly focusing on the enriched phenomenology that such theories exhibit with respect to General Relativity, relevant not only to large scales (cosmology) but also to small scales (e.g. torsion)
Gravity Currents in a Vegetated Valley of Trapezoidal Shape
Directory of Open Access Journals (Sweden)
Evangelos Keramaris
2016-01-01
Full Text Available In this study lock-exchange experiments are performed in a tank of rectangular upper cross section and a lower vegetated valley of trapezoidal shape to study the effect of drag resistance, due to vegetation, on gravity currents. Many natural and man-made channels are approximately trapezoidal. For the simulation of the vegetation the bed is covered by flexible grass vegetation (height of vegetation, hv=2.0cm of different submergence ratio hν/H (hν=height of vegetation, H=water depth. The motion of the gravity current is monitored with a digital video of high definition, the front velocity is measured and the height of the front is captured. Twenty four experiments are performed, twelve inside the trapezoidal section (H/Htr=0.4, 0.6 or 0.8 and twelve over the trapezoidal section (H/Htr=1.2, 1.4 or 1.6. The initial Reynolds number, based on the height of the valley and the reduced gravity, is greater than 10000 for all cases indicating that the gravity currents are turbulent. Results are compared with those of similar experiments without vegetation (Keramaris and Prinos, 2010 and hence the effect of the vegetation drag resistance on the motion of the current is investigated. The main conclusion of this study is that the shape of the tank plays a significant role in the propagation of gravity currents. The presence of trapezoidal increases the velocity of gravity currents in comparison with triangular or orthogonal shape.
Oriti, Daniele
2009-03-01
Preface; Part I. Fundamental Ideas and General Formalisms: 1. Unfinished revolution C. Rovelli; 2. The fundamental nature of space and time G. 't Hooft; 3. Does locality fail at intermediate length scales R. Sorkin; 4. Prolegomena to any future quantum gravity J. Stachel; 5. Spacetime symmetries in histories canonical gravity N. Savvidou; 6. Categorical geometry and the mathematical foundations of quantum gravity L. Crane; 7. Emergent relativity O. Dreyer; 8. Asymptotic safety R. Percacci; 9. New directions in background independent quantum gravity F. Markopoulou; Questions and answers; Part II: 10. Gauge/gravity duality G. Horowitz and J. Polchinski; 11. String theory, holography and quantum gravity T. Banks; 12. String field theory W. Taylor; Questions and answers; Part III: 13. Loop Quantum Gravity T. Thiemann; 14. Covariant loop quantum gravity? E. LIvine; 15. The spin foam representation of loop quantum gravity A. Perez; 16. 3-dimensional spin foam quantum gravity L. Freidel; 17. The group field theory approach to quantum gravity D. Oriti; Questions and answers; Part IV. Discrete Quantum Gravity: 18. Quantum gravity: the art of building spacetime J. Ambjørn, J. Jurkiewicz and R. Loll; 19. Quantum Regge calculations R. Williams; 20. Consistent discretizations as a road to quantum gravity R. Gambini and J. Pullin; 21. The causal set approach to quantum gravity J. Henson; Questions and answers; Part V. Effective Models and Quantum Gravity Phenomenology: 22. Quantum gravity phenomenology G. Amelino-Camelia; 23. Quantum gravity and precision tests C. Burgess; 24. Algebraic approach to quantum gravity II: non-commutative spacetime F. Girelli; 25. Doubly special relativity J. Kowalski-Glikman; 26. From quantum reference frames to deformed special relativity F. Girelli; 27. Lorentz invariance violation and its role in quantum gravity phenomenology J. Collins, A. Perez and D. Sudarsky; 28. Generic predictions of quantum theories of gravity L. Smolin; Questions and
Recovering MOND from extended metric theories of gravity
International Nuclear Information System (INIS)
We show that the Modified Newtonian Dynamics (MOND) regime can be fully recovered as the weak-field limit of a particular theory of gravity formulated in the metric approach. This is possible when Milgrom's acceleration constant is taken as a fundamental quantity which couples to the theory in a very consistent manner. As a consequence, the scale invariance of the gravitational interaction is naturally broken. In this sense, Newtonian gravity is the weak-field limit of general relativity and MOND is the weak-field limit of that particular extended theory of gravity. We also prove that a Noether's symmetry approach to the problem yields a conserved quantity coherent with this relativistic MONDian extension. (orig.)
Observations of gravity wave scales, fluxes, and saturation during MAP
Reid, I. M.
1989-01-01
During the MAP/MAC period, considerable improvements in instrumentation and experimental technique have occurred, and many hitherto unavailable parameters relating to gravity waves have become available. Studies of individual wave events and simultaneous observations made with a variety of techniques have provided insight into wave saturation mechanisms. In addition, long data sets of upper middle atmosphere winds were collected at a number of widely spaced sites, allowing climatological investigations of gravity wave amplitudes, wave number spectra, polarization, mean flow acceleration, and other saturation effects to be undertaken. Observations of gravity wave scales, momentum fluxes, saturation and saturation effects obtained during MAP/MAC, made on both a statistical and case study basis are reviewed.
Lujan, Richard E.
2001-01-01
A mechanical gravity brake that prevents hoisted loads within a shaft from free-falling when a loss of hoisting force occurs. A loss of hoist lifting force may occur in a number of situations, for example if a hoist cable were to break, the brakes were to fail on a winch, or the hoist mechanism itself were to fail. Under normal hoisting conditions, the gravity brake of the invention is subject to an upward lifting force from the hoist and a downward pulling force from a suspended load. If the lifting force should suddenly cease, the loss of differential forces on the gravity brake in free-fall is translated to extend a set of brakes against the walls of the shaft to stop the free fall descent of the gravity brake and attached load.
Critical behavior of charged black holes in Gauss-Bonnet gravity`s rainbow
Hendi, Seyed Hossein; Panah, Behzad Eslam; Faizal, Mir; Momennia, Mehrab
2016-01-01
Following an earlier study regarding Gauss-Bonnet-Maxwell black holes in the presence of gravity's rainbow [S. H. Hendi and M. Faizal, Phys. Rev. D 92, 044027 (2015)], in this paper, we will consider all constants as energy dependent ones. The geometrical and thermodynamical properties of this generalization are studied and the validation of the first law of thermodynamics is examined. Next, through the use of proportionality between cosmological constant and thermodynamical pressure, van der Waals-like behavior of these black holes in extended phase space is investigated. An interesting critical behavior for sets of rainbow functions in this case is reported. Also, the critical behavior of uncharged and charged solutions is analyzed and it is shown that the generalization to a charged case puts an energy dependent restriction on values of different parameters.