Sample records for modified gravity lessons

  1. Nonlocal Gravity and Structure in the Universe

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Dodelson, Scott; Park, Sohyun

    2014-08-26

    The observed acceleration of the Universe can be explained by modifying general relativity. One such attempt is the nonlocal model of Deser and Woodard. Here we fix the background cosmology using results from the Planck satellite and examine the predictions of nonlocal gravity for the evolution of structure in the universe, confronting the model with three tests: gravitational lensing, redshift space distortions, and the estimator of gravitymore » $$E_G$$. Current data favor general relativity (GR) over nonlocal gravity: fixing primordial cosmology with the best fit parameters from Planck leads to weak lensing results favoring GR by 5.9 sigma; redshift space distortions measurements of the growth rate preferring GR by 7.8 sigma; and the single measurement of $$E_G$$ favoring GR, but by less than 1-sigma. The significance holds up even after the parameters are allowed to vary within Planck limits. The larger lesson is that a successful modified gravity model will likely have to suppress the growth of structure compared to general relativity.« less

  2. Canonical structure of general relativity with a limiting curvature and its relation to loop quantum gravity

    NASA Astrophysics Data System (ADS)

    Bodendorfer, N.; Schäfer, A.; Schliemann, J.

    2018-04-01

    Chamseddine and Mukhanov recently proposed a modified version of general relativity that implements the idea of a limiting curvature. In the spatially flat, homogeneous, and isotropic sector, their theory turns out to agree with the effective dynamics of the simplest version of loop quantum gravity if one identifies their limiting curvature with a multiple of the Planck curvature. At the same time, it extends to full general relativity without any symmetry assumptions and thus provides an ideal toy model for full loop quantum gravity in the form of a generally covariant effective action known to all orders. In this paper, we study the canonical structure of this theory and point out some interesting lessons for loop quantum gravity. We also highlight in detail how the two theories are connected in the spatially flat, homogeneous, and isotropic sector.

  3. Low Gravity Guidance System for Airborne Microgravity Research

    NASA Technical Reports Server (NTRS)

    Rieke, W. J.; Emery, E. F.; Boyer, E. O.; Hegedus, C.; ODonoghue, D. P.

    1996-01-01

    Microgravity research techniques have been established to achieve a greater understanding of the role of gravity in the fundamentals of a variety of physical phenomena and material processing. One technique in use at the NASA Lewis Research Center involves flying Keplarian trajectories with a modified Lear Jet and DC-9 aircraft to achieve a highly accurate Microgravity environment by neutralizing accelerations in all three axis of the aircraft. The Low Gravity Guidance System (LGGS) assists the pilot and copilot in flying the trajectories by displaying the aircraft acceleration data in a graphical display format. The Low Gravity Guidance System is a microprocessor based system that acquires and displays the aircraft acceleration information. This information is presented using an electroluminescent display mounted over the pilot's instrument panel. The pilot can select the Microgravity range that is required for a given research event. This paper describes the characteristics, design, calibration and testing of the Low Gravity Guidance System Phase 3, significant lessons from earlier systems and the developmental work on future systems.

  4. Effects of the f(R) and f(G) Gravities and the Exotic Particle on Primordial Nucleosynthesis

    NASA Astrophysics Data System (ADS)

    Kusakabe, Motohiko; Koh, Seoktae; Kim, K. S.; Cheoun, Myung-Ki; Kajino, Toshitaka; Mathews, Grant J.

    A plateau Li/H abundance of metal-poor stars is smaller than those predicted in the standard big bang nucleosynthesis (BBN) model by a factor of ˜3, for the baryon density determined from Planck. This discrepancy may be caused by a non-standard cosmic thermal history or reactions of a hypothetical particle. We consider the BBN in specific modified gravity models characterized by f(R) and f(G) terms in the gravitational actions. These models have cosmic expansion rates different from that in the standard model, and abundances of all light elements are affected. The modified gravities are constrained mainly from observational deuterium abundances. No solution is found for the Li problem because a significant modification of the expansion rate results in a large change of D abundance. This result is quite a contrast to that of a BBN model including a long-lived negatively charged massive particle X-. The 7Be nuclide is destroyed via the recombination with an X- followed by the radiative proton capture. The X- particle selectively decreases the abundance of 7Be, and the primordial abundance of 7Li originating from the electron capture of 7Be is reduced. We have an important theoretical lesson: Some physical process must have operated preferentially on 7Be nuclei.

  5. Motor imagery: lessons learned in movement science might be applicable for spaceflight

    PubMed Central

    Bock, Otmar; Schott, Nadja; Papaxanthis, Charalambos

    2015-01-01

    Before participating in a space mission, astronauts undergo parabolic-flight and underwater training to facilitate their subsequent adaptation to weightlessness. Unfortunately, similar training methods can’t be used to prepare re-adaptation to planetary gravity. Here, we propose a quick, simple and inexpensive approach that could be used to prepare astronauts both for the absence and for the renewed presence of gravity. This approach is based on motor imagery (MI), a process in which actions are produced in working memory without any overt output. Training protocols based on MI have repeatedly been shown to modify brain circuitry and to improve motor performance in healthy young adults, healthy seniors and stroke victims, and are routinely used to optimize performance of elite athletes. We propose to use similar protocols preflight, to prepare for weightlessness, and late inflight, to prepare for landing. PMID:26042004

  6. Is There Gravity in Space?

    ERIC Educational Resources Information Center

    Bar, Varda; And Others

    1997-01-01

    Investigates students' ideas about gravity beyond the earth's surface. Presents a lesson plan designed to help students understand that gravity can act beyond Earth's atmosphere. Also helps students gain a more adequate intuitive understanding of how natural and artificial satellites stay in orbit. Reports that this strategy changed some students'…

  7. Constraints on modified gravity models from white dwarfs

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Banerjee, Srimanta; Singh, Tejinder P.; Shankar, Swapnil, E-mail: srimanta.banerjee@tifr.res.in, E-mail: swapnil.shankar@cbs.ac.in, E-mail: tpsingh@tifr.res.in

    Modified gravity theories can introduce modifications to the Poisson equation in the Newtonian limit. As a result, we expect to see interesting features of these modifications inside stellar objects. White dwarf stars are one of the most well studied stars in stellar astrophysics. We explore the effect of modified gravity theories inside white dwarfs. We derive the modified stellar structure equations and solve them to study the mass-radius relationships for various modified gravity theories. We also constrain the parameter space of these theories from observations.

  8. Modeling human perception of orientation in altered gravity

    PubMed Central

    Clark, Torin K.; Newman, Michael C.; Oman, Charles M.; Merfeld, Daniel M.; Young, Laurence R.

    2015-01-01

    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 (CNS) 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. PMID:25999822

  9. High Gain Antenna System Deployment Mechanism Integration, Characterization, and Lessons Learned

    NASA Technical Reports Server (NTRS)

    Parong, Fil; Russell, Blair; Garcen, Walter; Rose, Chris; Johnson, Chris; Huber, Craig

    2014-01-01

    The integration and deployment testing of the High Gain Antenna System (HGAS) for the Global Precipitation Measurement mission is summarized. The HGAS deployment mechanism is described. The gravity negation system configuration and its influence on vertical, ground-based deployment tests are presented with test data and model predictions. A focus is made on the late discovery and resolution of a potentially mission-degrading deployment interference condition. The interaction of the flight deployment mechanism, gravity-negation mechanism, and use of dynamic modeling is described and lessons learned presented

  10. High Gain Antenna System Deployment Mechanism Integration, Characterization, and Lessons Learned

    NASA Technical Reports Server (NTRS)

    Parong, Fil; Russell, Blair; Garcen, Walter; Rose, Chris; Johnson, Chris; Huber, Craig

    2014-01-01

    The integration and deployment testing of the High Gain Antenna System for the Global Precipitation Measurement mission is summarized. The HGAS deployment mechanism is described. The gravity negation system configuration and its influence on vertical, ground-based, deployment tests are presented with test data and model predictions. A focus is made on the late discovery and resolution of a potentially mission degrading deployment interference condition. The interaction of the flight deployment mechanism, gravity negation mechanism, and use of dynamic modeling is described and lessons learned presented.

  11. Clear and Measurable Signature of Modified Gravity in the Galaxy Velocity Field

    NASA Astrophysics Data System (ADS)

    Hellwing, Wojciech A.; Barreira, Alexandre; Frenk, Carlos S.; Li, Baojiu; Cole, Shaun

    2014-06-01

    The velocity field of dark matter and galaxies reflects the continued action of gravity throughout cosmic history. We show that the low-order moments of the pairwise velocity distribution v12 are a powerful diagnostic of the laws of gravity on cosmological scales. In particular, the projected line-of-sight galaxy pairwise velocity dispersion σ12(r) is very sensitive to the presence of modified gravity. Using a set of high-resolution N-body simulations, we compute the pairwise velocity distribution and its projected line-of-sight dispersion for a class of modified gravity theories: the chameleon f(R) gravity and Galileon gravity (cubic and quartic). The velocities of dark matter halos with a wide range of masses would exhibit deviations from general relativity at the (5-10)σ level. We examine strategies for detecting these deviations in galaxy redshift and peculiar velocity surveys. If detected, this signature would be a "smoking gun" for modified gravity.

  12. COLA with scale-dependent growth: applications to screened modified gravity models

    NASA Astrophysics Data System (ADS)

    Winther, Hans A.; Koyama, Kazuya; Manera, Marc; Wright, Bill S.; Zhao, Gong-Bo

    2017-08-01

    We present a general parallelized and easy-to-use code to perform numerical simulations of structure formation using the COLA (COmoving Lagrangian Acceleration) method for cosmological models that exhibit scale-dependent growth at the level of first and second order Lagrangian perturbation theory. For modified gravity theories we also include screening using a fast approximate method that covers all the main examples of screening mechanisms in the literature. We test the code by comparing it to full simulations of two popular modified gravity models, namely f(R) gravity and nDGP, and find good agreement in the modified gravity boost-factors relative to ΛCDM even when using a fairly small number of COLA time steps.

  13. Age versus size determination of radial variation in wood specific gravity : lessons from eccentrics

    Treesearch

    G. Bruce Williamson; Michael C. Wiemann

    2011-01-01

    Radial increases in wood specific gravity have been shown to characterize early successional trees from tropical forests. Here, we develop and apply a novel method to test whether radial increases are determined by tree age or tree size. The method compares the slopes of specific gravity changes across a short radius and a long radius of trees with eccentric trunks. If...

  14. Physics for First-Graders.

    ERIC Educational Resources Information Center

    Hagerott, Steven G.

    1997-01-01

    A Lockheed flight controls engineer describes how, as an undergraduate, he taught first graders basic lessons in physics and engineering by using slides, monkey bars, and other playground equipment to demonstrate principles like gravity, friction, force, and inertia. The children learned more about lift and gravity by constructing and flying paper…

  15. Unimodular F ( R ) gravity

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Nojiri, S.; Odintsov, S.D.; Oikonomou, V.K., E-mail: nojiri@gravity.phys.nagoya-u.ac.jp, E-mail: odintsov@ieec.uab.es, E-mail: v.k.oikonomou1979@gmail.com

    2016-05-01

    We extend the formalism of the Einstein-Hilbert unimodular gravity in the context of modified F ( R ) gravity. After appropriately modifying the Friedmann-Robertson-Walker metric in a way that it becomes compatible to the unimodular condition of having a constant metric determinant, we derive the equations of motion of the unimodular F ( R ) gravity by using the metric formalism of modified gravity with Lagrange multiplier constraint. The resulting equations are studied in frames of reconstruction method, which enables us to realize various cosmological scenarios, which was impossible to realize in the standard Einstein-Hilbert unimodular gravity. Several unimodular Fmore » ( R ) inflationary scenarios are presented, and in some cases, concordance with Planck and BICEP2 observational data can be achieved.« less

  16. Weighted density fields as improved probes of modified gravity models

    NASA Astrophysics Data System (ADS)

    Llinares, Claudio; McCullagh, Nuala

    2017-11-01

    When it comes to searches for extensions to general relativity, large efforts are being dedicated to accurate predictions for the power spectrum of density perturbations. While this observable is known to be sensitive to the gravitational theory, its efficiency as a diagnostic for gravity is significantly reduced when Solar system constraints are strictly adhered to. We show that this problem can be overcome by studying weighted density fields. We propose a transformation of the density field for which the impact of modified gravity on the power spectrum can be increased by more than a factor of three. The signal is not only amplified, but the modified gravity features are shifted to larger scales that are less affected by baryonic physics. Furthermore, the overall signal-to-noise ratio increases, which in principle makes identifying signatures of modified gravity with future galaxy surveys more feasible. While our analysis is focused on modified gravity, the technique can be applied to other problems in cosmology, such as the detection of neutrinos, the effects of baryons or baryon acoustic oscillations.

  17. On holographic Rényi entropy in some modified theories of gravity

    NASA Astrophysics Data System (ADS)

    Dey, Anshuman; Roy, Pratim; Sarkar, Tapobrata

    2018-04-01

    We perform a detailed analysis of holographic entanglement Rényi entropy in some modified theories of gravity with four dimensional conformal field theory duals. First, we construct perturbative black hole solutions in a recently proposed model of Einsteinian cubic gravity in five dimensions, and compute the Rényi entropy as well as the scaling dimension of the twist operators in the dual field theory. Consistency of these results are verified from the AdS/CFT correspondence, via a corresponding computation of the Weyl anomaly on the gravity side. Similar analyses are then carried out for three other examples of modified gravity in five dimensions that include a chemical potential, namely Born-Infeld gravity, charged quasi-topological gravity and a class of Weyl corrected gravity theories with a gauge field, with the last example being treated perturbatively. Some interesting bounds in the dual conformal field theory parameters in quasi-topological gravity are pointed out. We also provide arguments on the validity of our perturbative analysis, whenever applicable.

  18. Results and Lessons Learned from Performance Testing of Humans in Spacesuits in Simulated Reduced Gravity

    NASA Technical Reports Server (NTRS)

    Chappell, Steven P.; Norcross, Jason R.; Gernhardt, Michael L.

    2010-01-01

    The Apollo lunar EVA experience revealed challenges with suit stability and control-likely a combination of mass, mobility, and center of gravity (CG) factors. The EVA Physiology, Systems and Performence (EPSP) Project is systematically working with other NASA projects, labs, and facilities to lead a series of studies to understand the role of suit mass, weight, CG, and other parameters on astronaut performance in partial gravity environments.

  19. Robert Dicke and the naissance of experimental gravity physics, 1957-1967

    NASA Astrophysics Data System (ADS)

    Peebles, Phillip James Edwin

    2017-06-01

    The experimental study of gravity became much more active in the late 1950s, a change pronounced enough be termed the birth, or naissance, of experimental gravity physics. I present a review of developments in this subject since 1915, through the broad range of new approaches that commenced in the late 1950s, and up to the transition of experimental gravity physics to what might be termed a normal and accepted part of physical science in the late 1960s. This review shows the importance of advances in technology, here as in all branches of natural science. The role of contingency is illustrated by Robert Dicke's decision in the mid-1950s to change directions in mid-career, to lead a research group dedicated to the experimental study of gravity. The review also shows the power of nonempirical evidence. Some in the 1950s felt that general relativity theory is so logically sound as to be scarcely worth the testing. But Dicke and others argued that a poorly tested theory is only that, and that other nonempirical arguments, based on Mach's Principle and Dirac's Large Numbers hypothesis, suggested it would be worth looking for a better theory of gravity. I conclude by offering lessons from this history, some peculiar to the study of gravity physics during the naissance, some of more general relevance. The central lesson, which is familiar but not always well advertised, is that physical theories can be empirically established, sometimes with surprising results.

  20. Modified gravity and the CMB

    NASA Astrophysics Data System (ADS)

    Brax, Philippe; Davis, Anne-Christine

    2012-01-01

    We consider the effect of modified gravity on the peak structure of the cosmic microwave background (CMB) spectrum. We focus on simple models of modified gravity mediated by a massive scalar field coupled to both baryons and cold dark matter. This captures the features of chameleon, symmetron, dilaton, and f(R) models. We find that the CMB peaks can be affected in three independent ways provided the Compton radius of the massive scalar is not far-off the sound horizon at last scattering. When the coupling of the massive scalar to cold dark matter is large, the anomalous growth of the cold dark matter perturbation inside the Compton radius induces a change in the peak amplitudes. When the coupling to baryons is moderately large, the speed of sound is modified and the peaks shifted to higher momenta. Finally when both couplings are nonvanishing, a new contribution proportional to the Newton potential appears in the Sachs-Wolfe temperature and increases the peak amplitudes. We also show how, given any temporal evolution of the scalar field mass, one can engineer a corresponding modified gravity model of the chameleon type. This opens up the possibility of having independent constraints on modified gravity from the CMB peaks and large scale structures at low redshifts.

  1. What Makes a Superhero "Super"? Graphic Novels Inspire a Gravity Investigation

    ERIC Educational Resources Information Center

    Gross, Lisa A.; Bradbury, Leslie Upson; Frye, Elizabeth M.; Watkins, Bonnie

    2016-01-01

    To further students' understanding about gravity, forces, and motion, multiple types of text were integrated into instruction. As part of a 5E lesson (Bybee et al. 2006), the authors used a selection from Capstone Press's Graphic Science series, "A Crash Course in Forces and Motion with Max Axiom" (Sohn and Barnett 2007) to support…

  2. Gravity. Learning in Science Project. Working Paper No. 20.

    ERIC Educational Resources Information Center

    Stead, Keith; Osborne, Roger

    One area explored in the second (in-depth) phase of the Learning in Science Project was "children's science," defined as views of the world and the meanings for words that children have and bring with them to science lessons. The investigation reported focuses on students' thinking regarding their views on gravity. Students (N=42) were…

  3. Gravity Thickening. Sludge Treatment and Disposal Course #166. Instructor's Guide [and] Student Workbook.

    ERIC Educational Resources Information Center

    Klopping, Paul H.

    The basic operation of the gravity thickener is described in this lesson, focusing on the theory of operation, components found in a typical thickener, and the parameters which must be understood in optimizing the opeation of the thickener. Attention is given to mathematics concepts which are used in controlling hydraulic loading, detention time,…

  4. Exploring plane-symmetric solutions in f(R) gravity

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Shamir, M. F., E-mail: farasat.shamir@nu.edu.pk

    2016-02-15

    The modified theories of gravity, especially the f(R) gravity, have attracted much attention in the last decade. This paper is devoted to exploring plane-symmetric solutions in the context of metric f(R) gravity. We extend the work on static plane-symmetric vacuum solutions in f(R) gravity already available in the literature [1, 2]. The modified field equations are solved using the assumptions of both constant and nonconstant scalar curvature. Some well-known solutions are recovered with power-law and logarithmic forms of f(R) models.

  5. Ciencias 3. Caderno de Exercicios. (Science 3. Workbook).

    ERIC Educational Resources Information Center

    Raposo, Lucilia

    This workbook contains 47 activities and exercises which reinforce lesson topics found in the grade 3 science textbook. These lesson topics, presented in nine sections in the textbook, focus on such areas as: (1) solar energy, electricity, and light; (2) solar system, planets, earth motions, and phases of the moon; (3) gravity, rocks, and erosion;…

  6. Cosmological bound from the neutron star merger GW170817 in scalar-tensor and F(R) gravity theories

    NASA Astrophysics Data System (ADS)

    Nojiri, Shin'ichi; Odintsov, Sergei D.

    2018-04-01

    We consider the evolution of cosmological gravitational waves in scalar-tensor theory and F (R) gravity theory as typical models of the modified gravity. Although the propagation speed is not changed from the speed of light, the propagation phase changes when we compare the propagation in these modified gravity theories with the propagation in the ΛCDM model. The phase change might be detected in future observations.

  7. de Sitter and power-law solutions in some models of modified gravity

    NASA Astrophysics Data System (ADS)

    Zhong, Yi; Elizalde, Emilio

    2016-11-01

    Inspired by some recent works of Lovelock Brans-Dicke (BD) gravity and mimetic gravity, cosmology solutions in extensions of these two modified gravities are investigated. A nonlocal term is added to the Lovelock BD action and Gauss-Bonnet (GB) terms to the mimetic action, correspondingly. de Sitter and power scale factor solutions are then obtained in both theories. They can provide natural new approaches to a more accurate description of the unverse evolution.

  8. Tensor-vector-scalar-modified gravity: from small scale to cosmology.

    PubMed

    Bekenstein, Jacob D

    2011-12-28

    The impressive success of the standard cosmological model has suggested to many that its ingredients are all that one needs to explain galaxies and their systems. I summarize a number of known problems with this programme. They might signal the failure of standard gravity theory on galaxy scales. The requisite hints as to the alternative gravity theory may lie with the modified Newtonian dynamics (MOND) paradigm, which has proved to be an effective summary of galaxy phenomenology. A simple nonlinear modified gravity theory does justice to MOND at the non-relativistic level, but cannot be consistently promoted to relativistic status. The obstacles were first side-stepped with the formulation of tensor-vector-scalar theory (TeVeS), a covariant-modified gravity theory. I review its structure, its MOND and Newtonian limits, and its performance in the face of galaxy phenomenology. I also summarize features of TeVeS cosmology and describe the confrontation with data from strong and weak gravitational lensing.

  9. Modified gravity in Arnowitt-Deser-Misner formalism

    NASA Astrophysics Data System (ADS)

    Gao, Changjun

    2010-02-01

    Motivated by Hořava-Lifshitz gravity theory, we propose and investigate two kinds of modified gravity theories, the f(R) kind and the K-essence kind, in the Arnowitt-Deser-Misner (ADM) formalism. The f(R) kind includes one ultraviolet (UV) term and one infrared (IR) term together with the Einstein-Hilbert action. We find that these two terms naturally present the ultraviolet and infrared modifications to the Friedmann equation. The UV and IR modifications can avoid the past Big-Bang singularity and the future Big-Rip singularity, respectively. Furthermore, the IR modification can naturally account for the current acceleration of the Universe. The Lagrangian of K-essence kind modified gravity is made up of the three-dimensional Ricci scalar and an arbitrary function of the extrinsic curvature term. We find the cosmic acceleration can also be naturally interpreted without invoking any kind of dark energy. The static, spherically symmetry and vacuum solutions of both theories are Schwarzschild or Schwarzschild-de Sitter solution. Thus these modified gravity theories are viable for solar system tests.

  10. General Relativity solutions in modified gravity

    NASA Astrophysics Data System (ADS)

    Motohashi, Hayato; Minamitsuji, Masato

    2018-06-01

    Recent gravitational wave observations of binary black hole mergers and a binary neutron star merger by LIGO and Virgo Collaborations associated with its optical counterpart constrain deviation from General Relativity (GR) both on strong-field regime and cosmological scales with high accuracy, and further strong constraints are expected by near-future observations. Thus, it is important to identify theories of modified gravity that intrinsically possess the same solutions as in GR among a huge number of theories. We clarify the three conditions for theories of modified gravity to allow GR solutions, i.e., solutions with the metric satisfying the Einstein equations in GR and the constant profile of the scalar fields. Our analysis is quite general, as it applies a wide class of single-/multi-field scalar-tensor theories of modified gravity in the presence of matter component, and any spacetime geometry including cosmological background as well as spacetime around black hole and neutron star, for the latter of which these conditions provide a necessary condition for no-hair theorem. The three conditions will be useful for further constraints on modified gravity theories as they classify general theories of modified gravity into three classes, each of which possesses i) unique GR solutions (i.e., no-hair cases), ii) only hairy solutions (except the cases that GR solutions are realized by cancellation between singular coupling functions in the Euler-Lagrange equations), and iii) both GR and hairy solutions, for the last of which one of the two solutions may be selected dynamically.

  11. DOE Office of Scientific and Technical Information (OSTI.GOV)

    Winther, Hans A.; Koyama, Kazuya; Wright, Bill S.

    We present a general parallelized and easy-to-use code to perform numerical simulations of structure formation using the COLA (COmoving Lagrangian Acceleration) method for cosmological models that exhibit scale-dependent growth at the level of first and second order Lagrangian perturbation theory. For modified gravity theories we also include screening using a fast approximate method that covers all the main examples of screening mechanisms in the literature. We test the code by comparing it to full simulations of two popular modified gravity models, namely f ( R ) gravity and nDGP, and find good agreement in the modified gravity boost-factors relative tomore » ΛCDM even when using a fairly small number of COLA time steps.« less

  12. Cosmological tests of modified gravity.

    PubMed

    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.

  13. Noether symmetry approach in f(G,T) gravity

    NASA Astrophysics Data System (ADS)

    Shamir, M. Farasat; Ahmad, Mushtaq

    2017-01-01

    We explore the recently introduced modified Gauss-Bonnet gravity (Sharif and Ikram in Eur Phys J C 76:640, 2016), f(G,T) pragmatic with G, the Gauss-Bonnet term, and T, the trace of the energy-momentum tensor. Noether symmetry approach has been used to develop some cosmologically viable f(G,T) gravity models. The Noether equations of modified gravity are reported for flat FRW universe. Two specific models have been studied to determine the conserved quantities and exact solutions. In particular, the well known deSitter solution is reconstructed for some specific choice of f(G,T) gravity model.

  14. Blue Sky Below My Feet: Daycamp & After School Programs--9 to 11 Year Olds. Leader's Manual.

    ERIC Educational Resources Information Center

    California Univ., Berkeley. Cooperative Extension Service.

    This manual presents a 10-day lesson plan for day camp and after-school program leaders. The activities and experiments described in the manual focus on nutrition and space exploration. Topics covered by the lesson plan and specific projects include: (1) gravity; (2) food spoilage; (3) model rocket building and launching; (4) the basic food…

  15. Neutron stars in a perturbative f(R) gravity model with strong magnetic fields

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Cheoun, Myung-Ki; Deliduman, Cemsinan; Güngör, Can

    2013-10-01

    In Kaluza-Klein electromagnetism it is natural to associate modified gravity with strong electromagnetic fields. Hence, in this paper we investigate the combined effects of a strong magnetic field and perturbative f(R) gravity on the structure of neutron stars. The effect of an interior strong magnetic field of about 10{sup 17−18} G on the equation of state is derived in the context of a quantum hadrodynamics (QHD) equation of state (EoS) including effects of the magnetic pressure and energy along with occupied Landau levels. Adopting a random orientation of interior field domains, we solve the modified spherically symmetric hydrostatic equilibrium equationsmore » derived for a gravity model with f(R) = R+αR{sup 2}. Effects of both the finite magnetic field and the modified gravity are detailed for various values of the magnetic field and the perturbation parameter α along with a discussion of their physical implications. We show that there exists a parameter space of the modified gravity and the magnetic field strength, in which even a soft equation of state can accommodate a large ( > 2 M{sub s}un) maximum neutron star mass.« less

  16. Constraining modified gravitational theories by weak lensing with Euclid

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Martinelli, Matteo; Calabrese, Erminia; De Bernardis, Francesco

    2011-01-15

    Future proposed satellite missions such as Euclid can offer the opportunity to test general relativity on cosmic scales through mapping of the galaxy weak-lensing signal. In this paper we forecast the ability of these experiments to constrain modified gravity scenarios such as those predicted by scalar-tensor and f(R) theories. We find that Euclid will improve constraints expected from the Planck satellite on these modified theories of gravity by 2 orders of magnitude. We discuss parameter degeneracies and the possible biases introduced by modifications to gravity.

  17. Unified cosmic history in modified gravity: From F(R) theory to Lorentz non-invariant models

    NASA Astrophysics Data System (ADS)

    Nojiri, Shin'Ichi; Odintsov, Sergei D.

    2011-08-01

    The classical generalization of general relativity is considered as the gravitational alternative for a unified description of the early-time inflation with late-time cosmic acceleration. The structure and cosmological properties of a number of modified theories, including traditional F(R) and Hořava-Lifshitz F(R) gravity, scalar-tensor theory, string-inspired and Gauss-Bonnet theory, non-local gravity, non-minimally coupled models, and power-counting renormalizable covariant gravity are discussed. Different representations of and relations between such theories are investigated. It is shown that some versions of the above theories may be consistent with local tests and may provide a qualitatively reasonable unified description of inflation with the dark energy epoch. The cosmological reconstruction of different modified gravities is provided in great detail. It is demonstrated that eventually any given universe evolution may be reconstructed for the theories under consideration, and the explicit reconstruction is applied to an accelerating spatially flat Friedmann-Robertson-Walker (FRW) universe. Special attention is paid to Lagrange multiplier constrained and conventional F(R) gravities, for latter F(R) theory, the effective ΛCDM era and phantom divide crossing acceleration are obtained. The occurrences of the Big Rip and other finite-time future singularities in modified gravity are reviewed along with their solutions via the addition of higher-derivative gravitational invariants.

  18. Separating Dark Physics from Physical Darkness: Minimalist Modified Gravity vs. Dark Energy

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Huterer, Dragan; Linder, Eric V.

    The acceleration of the cosmic expansion may be due to a new component of physical energy density or a modification of physics itself. Mapping the expansion of cosmic scales and the growth of large scale structure in tandem can provide insights to distinguish between the two origins. Using Minimal Modified Gravity (MMG) - a single parameter gravitational growth index formalism to parameterize modified gravity theories - we examine the constraints that cosmological data can place on the nature of the new physics. For next generation measurements combining weak lensing, supernovae distances, and the cosmic microwave background we can extend themore » reach of physics to allow for fitting gravity simultaneously with the expansion equation of state, diluting the equation of state estimation by less than 25percent relative to when general relativity is assumed, and determining the growth index to 8percent. For weak lensing we examine the level of understanding needed of quasi- and nonlinear structure formation in modified gravity theories, and the trade off between stronger precision but greater susceptibility to bias as progressively more nonlinear information is used.« less

  19. Separating dark physics from physical darkness: Minimalist modified gravity versus dark energy

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Huterer, Dragan; Linder, Eric V.

    The acceleration of the cosmic expansion may be due to a new component of physical energy density or a modification of physics itself. Mapping the expansion of cosmic scales and the growth of large scale structure in tandem can provide insights to distinguish between the two origins. Using Minimal Modified Gravity (MMG) - a single parameter gravitational growth index formalism to parametrize modified gravity theories - we examine the constraints that cosmological data can place on the nature of the new physics. For next generation measurements combining weak lensing, supernovae distances, and the cosmic microwave background we can extend themore » reach of physics to allow for fitting gravity simultaneously with the expansion equation of state, diluting the equation of state estimation by less than 25% relative to when general relativity is assumed, and determining the growth index to 8%. For weak lensing we examine the level of understanding needed of quasi- and nonlinear structure formation in modified gravity theories, and the trade off between stronger precision but greater susceptibility to bias as progressively more nonlinear information is used.« less

  20. Neutron stars in screened modified gravity: Chameleon versus dilaton

    NASA Astrophysics Data System (ADS)

    Brax, Philippe; Davis, Anne-Christine; Jha, Rahul

    2017-04-01

    We consider the scalar field profile around relativistic compact objects such as neutron stars for a range of modified gravity models with screening mechanisms of the chameleon and Damour-Polyakov types. We focus primarily on inverse power law chameleons and the environmentally dependent dilaton as examples of both mechanisms. We discuss the modified Tolman-Oppenheimer-Volkoff equation and then implement a relaxation algorithm to solve for the scalar profiles numerically. We find that chameleons and dilatons behave in a similar manner and that there is a large degeneracy between the modified gravity parameters and the neutron star equation of state. This is exemplified by the modifications to the mass-radius relationship for a variety of model parameters.

  1. Mali and Islamic Extremism: Applying Lessons Learned from Afghanistan

    DTIC Science & Technology

    2016-11-21

    Stability operations use the pop- ulation as the center of gravity.40 U.S. military doctrine directs us to review political, military, economic ...military success or lasting stability . This article addresses the similar contexts between the two countries and how lessons from Afghanistan can be...applied to Mali to improve chances for lasting stability . Keywords: Africa, Mali, Azawad, asymmetric warfare, belligerent forces, jihad, Islamic

  2. A class of minimally modified gravity theories

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Lin, Chunshan; Mukohyama, Shinji, E-mail: chunshan.lin@yukawa.kyoto-u.ac.jp, E-mail: shinji.mukohyama@yukawa.kyoto-u.ac.jp

    We investigate the Hamiltonian structure of a class of gravitational theories whose actions are linear in the lapse function. We derive the necessary and sufficient condition for a theory in this class to have two or less local physical degrees of freedom. As an application we then find several concrete examples of modified gravity theories in which the total number of local physical degrees of freedom in the gravity sector is two.

  3. Modified first-order Hořava-Lifshitz gravity: Hamiltonian analysis of the general theory and accelerating FRW cosmology in a power-law F(R) model

    NASA Astrophysics Data System (ADS)

    Carloni, Sante; Chaichian, Masud; Nojiri, Shin'Ichi; Odintsov, Sergei D.; Oksanen, Markku; Tureanu, Anca

    2010-09-01

    We propose the most general modified first-order Hořava-Lifshitz gravity, whose action does not contain time derivatives higher than the second order. The Hamiltonian structure of this theory is studied in all the details in the case of the spatially-flat Friedmann-Robertson-Walker (FRW) space-time, demonstrating many of the features of the general theory. It is shown that, with some plausible assumptions, including the projectability of the lapse function, this model is consistent. As a large class of such theories, the modified Hořava-Lifshitz F(R) gravity is introduced. The study of its ultraviolet properties shows that its z=3 version seems to be renormalizable in the same way as the original Hořava-Lifshitz proposal. The Hamiltonian analysis of the modified Hořava-Lifshitz F(R) gravity shows that it is in general a consistent theory. The F(R) gravity action is also studied in the fixed-gauge form, where the appearance of a scalar field is particularly illustrative. Then the spatially-flat FRW cosmology for this F(R) gravity is investigated. It is shown that a special choice of parameters for this theory leads to the same equations of motion as in the case of traditional F(R) gravity. Nevertheless, the cosmological structure of the modified Hořava-Lifshitz F(R) gravity turns out to be much richer than for its traditional counterpart. The emergence of multiple de Sitter solutions indicates the possibility of unification of early-time inflation with late-time acceleration within the same model. Power-law F(R) theories are also investigated in detail. It is analytically shown that they have a quite rich cosmological structure: early-/late-time cosmic acceleration of quintessence, as well as of phantom types. Also it is demonstrated that all the four known types of finite-time future singularities may occur in the power-law Hořava-Lifshitz F(R) gravity. Finally, a covariant proposal for (renormalizable) F(R) gravity within the Hořava-Lifshitz spirit is presented.

  4. Structure formation in f(T) gravity and a solution for H0 tension

    NASA Astrophysics Data System (ADS)

    Nunes, Rafael C.

    2018-05-01

    We investigate the evolution of scalar perturbations in f(T) teleparallel gravity and its effects on the cosmic microwave background (CMB) anisotropy. The f(T) gravity generalizes the teleparallel gravity which is formulated on the Weitzenböck spacetime, characterized by the vanishing curvature tensor (absolute parallelism) and the non-vanishing torsion tensor. For the first time, we derive the observational constraints on the modified teleparallel gravity using the CMB temperature power spectrum from Planck's estimation, in addition to data from baryonic acoustic oscillations (BAO) and local Hubble constant measurements. We find that a small deviation of the f(T) gravity model from the ΛCDM cosmology is slightly favored. Besides that, the f(T) gravity model does not show tension on the Hubble constant that prevails in the ΛCDM cosmology. It is clear that f(T) gravity is also consistent with the CMB observations, and undoubtedly it can serve as a viable candidate amongst other modified gravity theories.

  5. S2 like Star Orbits near the Galactic Center in Rn and Yukawa Gravity

    NASA Astrophysics Data System (ADS)

    Borka, Dusko; Jovanović, Predrag; Jovanović Vesna Borka; Zakharov, Alexander F.

    2015-01-01

    In this chapter we investigate the possibility to provide theoretical explanation for the observed deviations of S2 star orbit around the Galactic Center using gravitational potentials derived from extended gravity models, but in absence of dark matter. Extended Theories of Gravity are alternative theories of gravitational interaction developed from the exact starting points investigated first by Einstein and Hilbert and aimed from one side to extend the positive results of General Relativity and, on the other hand, to cure its shortcomings. One of the aims of these theories is to explain galactic and extragalactic dynamics without introduction of dark matter. They are based on straightforward generalizations of the Einstein theory where the gravitational action (the Hilbert-Einstein action) is assumed to be linear in the Ricci curvature scalar R. The f(R) gravity is a type of modified gravity which generalizes Einstein's General Relativity, i.e. the simplest case is just the General Relativity. It is actually a family of models, each one defined by a different function of the Ricci scalar. Here, we consider Rn (power-law fourth-order theories of gravity) and Yukawa-like modified gravities in the weak field limit and discuss the constrains on these theories. For that purpose we simulate the orbit of S2 star around the Galactic Center in Rn and Yukawa-like gravity potentials and compare it with New Technology Telescope/Very Large Telescope (NTT/VLT) as well as by Keck telescope observations. Our simulations result in strong constraints on the range of gravity interaction and showed that both Rn and Yukawa gravity could satisfactorily explain the observed orbits of S2 star. However, we concluded that parameters of Rn and Yukawa gravity theories must be very close to those corresponding to the Newtonian limit of the theory. Besides, in contrast to Newtonian gravity, these two modified theories induce orbital precession, even in the case of point-like central mass. The approach we are proposing seems to be sufficiently reliable to constrain the modified gravity models from stellar orbits around Galactic Center.

  6. Extreme gravity tests with gravitational waves from compact binary coalescences: (I) inspiral-merger

    NASA Astrophysics Data System (ADS)

    Berti, Emanuele; Yagi, Kent; Yunes, Nicolás

    2018-04-01

    The observation of the inspiral and merger of compact binaries by the LIGO/Virgo collaboration ushered in a new era in the study of strong-field gravity. We review current and future tests of strong gravity and of the Kerr paradigm with gravitational-wave interferometers, both within a theory-agnostic framework (the parametrized post-Einsteinian formalism) and in the context of specific modified theories of gravity (scalar-tensor, Einstein-dilaton-Gauss-Bonnet, dynamical Chern-Simons, Lorentz-violating, and extra dimensional theories). In this contribution we focus on (i) the information carried by the inspiral radiation, and (ii) recent progress in numerical simulations of compact binary mergers in modified gravity.

  7. Designing to Sample the Unknown: Lessons from OSIRIS-REx Project Systems Engineering

    NASA Technical Reports Server (NTRS)

    Everett, David; Mink, Ronald; Linn, Timothy; Wood, Joshua

    2017-01-01

    On September 8, 2016, the third NASA New Frontiers mission launched on an Atlas V 411. The Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer (OSIRIS-REx) will rendezvous with asteroid Bennu in 2018, collect a sample in 2020, and return that sample to Earth in September 2023. The development team has overcome a number of challenges in order to design and build a system that will make contact with an unexplored, airless, low-gravity body. This paper will provide an overview of the mission, then focus in on the system-level challenges and some of the key system-level processes. Some of the lessons here are unique to the type of mission, like discussion of operating at a largely-unknown, low-gravity object. Other lessons, particularly from the build phase, have broad implications. The OSIRIS-REx risk management process was particularly effective in achieving an on-time and under-budget development effort. The systematic requirements management and verification and the system validation also helped identify numerous potential problems. The final assessment of the OSIRIS-REx performance will need to wait until the sample is returned in 2023, but this post-launch assessment will capture some of the key systems-engineering lessons from the development team.

  8. Probing hybrid modified gravity by stellar motion around Galactic Center

    NASA Astrophysics Data System (ADS)

    Borka, D.; Capozziello, S.; Jovanović, P.; Borka Jovanović, V.

    2016-06-01

    We consider possible signatures for the so called hybrid gravity within the Galactic Central Parsec. This modified theory of gravity consists of a superposition of the metric Einstein-Hilbert Lagrangian with an f(R) term constructed à la Palatiniand can be easily reduced to an equivalent scalar-tensor theory. Such an approach is introduced in order to cure the shortcomings related to f(R) gravity, in general formulated either in metric or in metric-affine frameworks. Hybrid gravity allows to disentangle the further gravitational degrees of freedom with respect to those of standard General Relativity. The present analysis is based on the S2 star orbital precession around the massive compact dark object at the Galactic Center where the simulated orbits in hybrid modified gravity are compared with astronomical observations. These simulations result with constraints on the range of hybrid gravity interaction parameter ϕ0, showing that in the case of S2 star it is between -0.0009 and -0.0002. At the same time, we are also able to obtain the constraints on the effective mass parameter mϕ, and found that it is between -0.0034 and -0.0025 AU-1 for S2 star. Furthermore, the hybrid gravity potential induces precession of S2 star orbit in the same direction as General Relativity. In previous papers, we considered other types of extended gravities, like metric power law f(R)∝Rn gravity, inducing Yukawa and Sanders-like gravitational potentials, but it seems that hybrid gravity is the best among these models to explain different gravitational phenomena at different astronomical scales.

  9. The dark-baryonic matter mass relation for observational verification in Verlinde's emergent gravity

    NASA Astrophysics Data System (ADS)

    Shen, Jian Qi

    2018-06-01

    Recently, a new interesting idea of origin of gravity has been developed by Verlinde. In this scheme of emergent gravity, where horizon entropy, microscopic de Sitter states and relevant contribution to gravity are involved, an entropy displacement resulting from matter behaves as a memory effect and can be exhibited at sub-Hubble scales, namely, the entropy displacement and its "elastic" response would lead to emergent gravity, which gives rise to an extra gravitational force. Then galactic dark matter effects may origin from such extra emergent gravity. We discuss some concepts in Verlinde's theory of emergent gravity and point out some possible problems or issues, e.g., the gravitational potential caused by Verlinde's emergent apparent dark matter may no longer be continuous in spatial distribution at ordinary matter boundary (such as a massive sphere surface). In order to avoid the unnatural discontinuity of the extra emergent gravity of Verlinde's apparent dark matter, we suggest a modified dark-baryonic mass relation (a formula relating Verlinde's apparent dark matter mass to ordinary baryonic matter mass) within this framework of emergent gravity. The modified mass relation is consistent with Verlinde's result at relatively small scales (e.g., R<3h_{70}^{-1} Mpc). However, it seems that, compared with Verlinde's relation, at large scales (e.g., gravitating systems with R>3h_{70}^{-1} Mpc), the modified dark-baryonic mass relation presented here might be in better agreement with the experimental curves of weak lensing analysis in the recent work of Brouwer et al. Galactic rotation curves are compared between Verlinde's emergent gravity and McGaugh's recent model of MOND (Modified Newtonian Dynamics established based on recent galaxy observations). It can be found that Verlinde rotational curves deviate far from those of McGaugh MOND model when the MOND effect (or emergent dark matter) dominates. Some applications of the modified dark-baryonic mass relation inspired by Verlinde's emergent gravity will be addressed for galactic and solar scales. Potential possibilities to test this dark-baryonic mass relation as well as apparent dark matter effects, e.g., planetary perihelion precession at Solar System scale, will be considered. This may enable to place some constraints on the magnitudes of the MOND characteristic acceleration at the small solar scale.

  10. Testing modified gravity with globular clusters: the case of NGC 2419

    NASA Astrophysics Data System (ADS)

    Llinares, Claudio

    2018-05-01

    The dynamics of globular clusters has been studied in great detail in the context of general relativity as well as with modifications of gravity that strongly depart from the standard paradigm such as Modified Newtonian Dynamics. However, at present there are no studies that aim to test the impact that less extreme modifications of gravity (e.g. models constructed as alternatives to dark energy) have on the behaviour of globular clusters. This Letter presents fits to the velocity dispersion profile of the cluster NGC 2419 under the symmetron-modified gravity model. The data show an increase in the velocity dispersion towards the centre of the cluster which could be difficult to explain within general relativity. By finding the best-fitting solution associated with the symmetron model, we show that this tension does not exist in modified gravity. However, the best-fitting parameters give a model that is inconsistent with the dynamics of the Solar system. Exploration of different screening mechanisms should give us the chance to understand if it is possible to maintain the appealing properties of the symmetron model when it comes to globular clusters and at the same time recover the Solar system dynamics properly.

  11. Lessons Learned from Performance Testing of Humans in Spacesuits in Simulated Reduced Gravity

    NASA Technical Reports Server (NTRS)

    Norcross, Jason R.; Chappell, Steven P.; Gernhardt, Michael L.

    2010-01-01

    Introduction: The overarching objective of the Integrated Suit Test (IST) series is to evaluate suited human performance using reduced-gravity analogs and learn what aspects of an EVA suit system affect human performance. For this objective to be successfully achieved, the testing methodology should be valid and reproducible, and the partial-gravity simulations must be as accurate and realistic as possible. Objectives: To highlight some of the key lessons learned about partial-gravity analogs and testing methodology, and to suggest considerations for optimizing the effectiveness and quality of results of future tests. Methods: Performance testing of suited and unsuited subjects was undertaken in different reduced-gravity analogs including the Space Vehicle Mockup Facility s Partial Gravity Simulator (POGO), parabolic flight on the C-9 aircraft, underwater environments including NASA s Extreme Environment Mission Operations (NEEMO) and the Neutral Buoyancy Lab (NBL), and in field analogs including Desert Research and Technology Studies (RATS), the Haughton Mars Project (HMP), and the JSC Rock Pile. Subjects performed level walking, incline/decline walking, running, shoveling, picking up and transferring rocks, kneeling/standing, and task boards. Lessons Learned Analogs: No single analog will properly simulate all aspects of the true partial-gravity environment. The POGO is an ideal environment from the standpoint that there are no time limits or significant volumetric constraints, but it does have several limitations. It allows only 2 translational degrees of freedom (DOF) and applies true partial-gravity offload only through the subject s center of gravity (CG). Also, when a subject is doing non-stationary tasks, significant overhead inertia from the lift column seems to have a negative impact on performance. Parabolic flight allows full translational and rotational DOF and applies offload to all parts of the body, but the simulation lasts less than 30 seconds. When this is coupled with the volumetric constraints of the plane, both task selection and data collection options are significantly limited. The underwater environments also allow all 6 DOF and allow off-loading to be applied throughout the body, but the data collection capabilities are limited to little more than subjective ratings. In addition, water drag negatively affects performance of tasks requiring dynamic motion. Field analogs provide the ability to simulate lunar terrain and more realistic mission-like objectives, but all of them operate at 1-g, so suited human performance testing generally must utilize a reduced-mass or "mockup" suit, depending on study objectives. In general, the ground-based overhead-suspension partial-gravity analogs like POGO allow the most diverse data collection methods possible while still simulating partial gravity. However, as currently designed, the POGO has significant limitations. Design of the Active Response Gravity Offload System (ARGOS) has begun and is focusing on adding full x,y,z translational DOF, improved offload accuracy, increased lift capacity, and active control of the x and y axes to minimize offload system inertia. Additionally, a new gimbal is being designed to reduce mass and inertia and to be able to work with different suits, as the current gimbal only supports suited testing with the Mark III Technology Demonstrator Suit (MKIII).

  12. Parametrized modified gravity and the CMB bispectrum

    NASA Astrophysics Data System (ADS)

    Di Valentino, Eleonora; Melchiorri, Alessandro; Salvatelli, Valentina; Silvestri, Alessandra

    2012-09-01

    We forecast the constraints on modified theories of gravity from the cosmic microwave background (CMB) anisotropies bispectrum that arises from correlations between lensing and the Integrated Sachs-Wolfe effect. In models of modified gravity the evolution of the metric potentials is generally altered and the contribution to the CMB bispectrum signal can differ significantly from the one expected in the standard cosmological model. We adopt a parametrized approach and focus on three different classes of models: Linder’s growth index, Chameleon-type models, and f(R) theories. We show that the constraints on the parameters of the models will significantly improve with future CMB bispectrum measurements.

  13. Cosmic ray production in modified gravity

    NASA Astrophysics Data System (ADS)

    Arbuzova, E. V.; Dolgov, A. D.; Reverberi, L.

    2018-06-01

    This paper is a reply to the criticism of our work on particle production in modified gravity by Gorbunov and Tokareva. We show that their arguments against efficient particle production are invalid. F( R) theories can lead to an efficient generation of high energy cosmic rays in contracting systems.

  14. Understanding Preservice Teacher Skills to Construct Lesson Plans

    ERIC Educational Resources Information Center

    Lim, Woong; Son, Ji-Won; Kim, Dong-Joong

    2018-01-01

    This study examined preservice teachers' (PSTs) capacity for lesson planning in a university-based teacher preparation program in the USA Participants (n = 126) wrote lesson plans in three approaches: synthesis, creation, and modification. Findings indicate that PSTs who modified preexisting lesson plans produced better lesson plans than their…

  15. Physical Activity in Physical Education: Are Longer Lessons Better?

    PubMed Central

    Smith, Nicole J.; Monnat, Shannon M.; Lounsbery, Monica A.F.

    2015-01-01

    BACKGROUND The purpose of this study was to compare physical activity (PA) outcomes in a sample of high school physical education (PE) lessons from schools that adopted traditional versus modified block schedule formats. METHODS We used the System for Observing Fitness Instruction Time (SOFIT) to conduct observations of 168 high school (HS) PE lessons delivered by 22 PE teachers in 4 schools. We used t-tests and multilevel models were used to explore variability in moderate PA and vigorous PA. RESULTS PA outcomes were significantly different between modified block and traditional schools. Students who attended traditional schools engaged in more vigorous PA in PE lessons. Modified block lessons lost more scheduled lesson time due to poor transition to and from the locker room. PA outcomes were positively associated with fitness and teacher promotion of PA and negatively associated with lost time, class size, management, and knowledge. CONCLUSIONS Though PE proponents widely advocate for more PE minutes, this study showed that greater time scheduled in PE does not necessarily result in more student accrual of MVPA minutes. PMID:25611935

  16. Model-independent constraints on modified gravity from current data and from the Euclid and SKA future surveys

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Taddei, Laura; Martinelli, Matteo; Amendola, Luca, E-mail: taddei@thphys.uni-heidelberg.de, E-mail: martinelli@lorentz.leidenuniv.nl, E-mail: amendola@thphys.uni-heidelberg.de

    2016-12-01

    The aim of this paper is to constrain modified gravity with redshift space distortion observations and supernovae measurements. Compared with a standard ΛCDM analysis, we include three additional free parameters, namely the initial conditions of the matter perturbations, the overall perturbation normalization, and a scale-dependent modified gravity parameter modifying the Poisson equation, in an attempt to perform a more model-independent analysis. First, we constrain the Poisson parameter Y (also called G {sub eff}) by using currently available f σ{sub 8} data and the recent SN catalog JLA. We find that the inclusion of the additional free parameters makes the constraintsmore » significantly weaker than when fixing them to the standard cosmological value. Second, we forecast future constraints on Y by using the predicted growth-rate data for Euclid and SKA missions. Here again we point out the weakening of the constraints when the additional parameters are included. Finally, we adopt as modified gravity Poisson parameter the specific Horndeski form, and use scale-dependent forecasts to build an exclusion plot for the Yukawa potential akin to the ones realized in laboratory experiments, both for the Euclid and the SKA surveys.« less

  17. Unscreening Modified Gravity in the Matter Power Spectrum.

    PubMed

    Lombriser, Lucas; Simpson, Fergus; Mead, Alexander

    2015-06-26

    Viable modifications of gravity that may produce cosmic acceleration need to be screened in high-density regions such as the Solar System, where general relativity is well tested. Screening mechanisms also prevent strong anomalies in the large-scale structure and limit the constraints that can be inferred on these gravity models from cosmology. We find that by suppressing the contribution of the screened high-density regions in the matter power spectrum, allowing a greater contribution of unscreened low densities, modified gravity models can be more readily discriminated from the concordance cosmology. Moreover, by variation of density thresholds, degeneracies with other effects may be dealt with more adequately. Specializing to chameleon gravity as a worked example for screening in modified gravity, employing N-body simulations of f(R) models and the halo model of chameleon theories, we demonstrate the effectiveness of this method. We find that a percent-level measurement of the clipped power at k<0.3h/Mpc can yield constraints on chameleon models that are more stringent than what is inferred from Solar System tests or distance indicators in unscreened dwarf galaxies. Finally, we verify that our method is also applicable to the Vainshtein mechanism.

  18. Action growth for black holes in modified gravity

    NASA Astrophysics Data System (ADS)

    Sebastiani, Lorenzo; Vanzo, Luciano; Zerbini, Sergio

    2018-02-01

    The general form of the action growth for a large class of static black hole solutions in modified gravity which includes F (R ) -gravity models is computed. The cases of black hole solutions with nonconstant Ricci scalar are also considered, generalizing the results previously found and valid only for black holes with constant Ricci scalar. An argument is put forward to provide a physical interpretation of the results, which seem tightly connected with the generalized second law of black hole thermodynamics.

  19. Modifying gravity: you cannot always get what you want.

    PubMed

    Starkman, Glenn D

    2011-12-28

    The combination of general relativity (GR) and the Standard Model of particle physics disagrees with numerous observations on scales from our Solar System up. In the canonical concordance model of Lambda cold dark matter (ΛCDM) cosmology, many of these contradictions between theory and data are removed or alleviated by the introduction of three completely independent new components of stress energy--the inflaton, dark matter and dark energy. Each of these in its turn is meant to have dominated (or to currently dominate) the dynamics of the Universe. There is, until now, no non-gravitational evidence for any of these dark sectors, nor is there evidence (though there may be motivation) for the required extension of the Standard Model. An alternative is to imagine that it is GR that must be modified to account for some or all of these disagreements. Certain coincidences of scale even suggest that one might expect not to make independent modifications of the theory to replace each of the three dark sectors. Because they must address the most different types of data, attempts to replace dark matter with modified gravity are the most controversial. A phenomenological model (or family of models), modified Newtonian dynamics, has, over the last few years, seen several covariant realizations. We discuss a number of challenges that any model that seeks to replace dark matter with modified gravity must face: the loss of Birkhoff's theorem, and the calculational simplifications it implies; the failure to explain clusters, whether static or interacting, and the consequent need to introduce dark matter of some form, whether hot dark matter neutrinos or dark fields that arise in new sectors of the modified gravity theory; the intrusion of cosmological expansion into the modified force law, which arises precisely because of the coincidence in scale between the centripetal acceleration at which Newtonian gravity fails in galaxies and the cosmic acceleration. We conclude with the observation that, although modified gravity may indeed manage to replace dark matter, it is likely to do so by becoming or at least incorporating a dark matter theory itself.

  20. Science Notes.

    ERIC Educational Resources Information Center

    Piearce, Trevor; And Others

    1988-01-01

    Provides explanations of 15 experiments, laboratory activities, demonstrations, and lessons for use in instruction. Includes information on Daphnia, wild garlic, crystals, gas chromatographs, bleaches, alcohols, reactivity series, chemistry formula, electronic keyboards and waveforms, interference and diffraction gravity, Moire fringe patterns,…

  1. Cosmic Tsunamis in Modified Gravity: Disruption of Screening Mechanisms from Scalar Waves.

    PubMed

    Hagala, R; Llinares, C; Mota, D F

    2017-03-10

    Extending general relativity by adding extra degrees of freedom is a popular approach for explaining the accelerated expansion of the Universe and to build high energy completions of the theory of gravity. The presence of such new degrees of freedom is, however, tightly constrained from several observations and experiments that aim to test general relativity in a wide range of scales. The viability of a given modified theory of gravity, therefore, strongly depends on the existence of a screening mechanism that suppresses the extra degrees of freedom. We perform simulations, and find that waves propagating in the new degrees of freedom can significantly impact the efficiency of some screening mechanisms, thereby threatening the viability of these modified gravity theories. Specifically, we show that the waves produced in the symmetron model can increase the amplitude of the fifth force and the parametrized post Newtonian parameters by several orders of magnitude.

  2. Cosmic Tsunamis in Modified Gravity: Disruption of Screening Mechanisms from Scalar Waves

    NASA Astrophysics Data System (ADS)

    Hagala, R.; Llinares, C.; Mota, D. F.

    2017-03-01

    Extending general relativity by adding extra degrees of freedom is a popular approach for explaining the accelerated expansion of the Universe and to build high energy completions of the theory of gravity. The presence of such new degrees of freedom is, however, tightly constrained from several observations and experiments that aim to test general relativity in a wide range of scales. The viability of a given modified theory of gravity, therefore, strongly depends on the existence of a screening mechanism that suppresses the extra degrees of freedom. We perform simulations, and find that waves propagating in the new degrees of freedom can significantly impact the efficiency of some screening mechanisms, thereby threatening the viability of these modified gravity theories. Specifically, we show that the waves produced in the symmetron model can increase the amplitude of the fifth force and the parametrized post Newtonian parameters by several orders of magnitude.

  3. Reconstructing f(R) modified gravity with dark energy parametrization

    NASA Astrophysics Data System (ADS)

    Morita, Masaaki; Takahashi, Hirotaka

    2014-03-01

    We demonstrate the reconstruction of f(R) modified gravity theory with late-time accelerated cosmic expansion. A second-order differential equation for Lagrangian density is obtained from the field equation, and is solved as a function of the cosmic scale factor in two cases. First we begin with the case of a wCDM cosmological model, in which a dark-energy equation-of-state parameter w is constant, for simplicity. Next we extend the method to a case in which the parameter w is epoch-dependent and is expressed as the Chevallier-Polarski-Linder parametrization. Thus we can represent Lagrangian density of f(R) modified gravity theory in terms of dark energy parameters.

  4. New classes of modified teleparallel gravity models

    NASA Astrophysics Data System (ADS)

    Bahamonde, Sebastian; Böhmer, Christian G.; Krššák, Martin

    2017-12-01

    New classes of modified teleparallel theories of gravity are introduced. The action of this theory is constructed to be a function of the irreducible parts of torsion f (Tax ,Tten ,Tvec), where Tax ,Tten and Tvec are squares of the axial, tensor and vector components of torsion, respectively. This is the most general (well-motivated) second order teleparallel theory of gravity that can be constructed from the torsion tensor. Different particular second order theories can be recovered from this theory such as new general relativity, conformal teleparallel gravity or f (T) gravity. Additionally, the boundary term B which connects the Ricci scalar with the torsion scalar via R = - T + B can also be incorporated into the action. By performing a conformal transformation, it is shown that the two unique theories which have an Einstein frame are either the teleparallel equivalent of general relativity or f (- T + B) = f (R) gravity, as expected.

  5. On the stability conditions for theories of modified gravity in the presence of matter fields

    NASA Astrophysics Data System (ADS)

    De Felice, Antonio; Frusciante, Noemi; Papadomanolakis, Georgios

    2017-03-01

    We present a thorough stability analysis of modified gravity theories in the presence of matter fields. We use the Effective Field Theory framework for Dark Energy and Modified Gravity to retain a general approach for the gravity sector and a Sorkin-Schutz action for the matter one. Then, we work out the proper viability conditions to guarantee in the scalar sector the absence of ghosts, gradient and tachyonic instabilities. The absence of ghosts can be achieved by demanding a positive kinetic matrix, while the lack of a gradient instability is ensured by imposing a positive speed of propagation for all the scalar modes. In case of tachyonic instability, the mass eigenvalues have been studied and we work out the appropriate expressions. For the latter, an instability occurs only when the negative mass eigenvalue is much larger, in absolute value, than the Hubble parameter. We discuss the results for the minimally coupled quintessence model showing for a particular set of parameters two typical behaviours which in turn lead to a stable and an unstable configuration. Moreover, we find that the speeds of propagation of the scalar modes strongly depend on matter densities, for the beyond Horndeski theories. Our findings can be directly employed when testing modified gravity theories as they allow to identify the correct viability space.

  6. ISW-galaxy cross-correlation in K-mouflage

    NASA Astrophysics Data System (ADS)

    Benevento, G.; Bartolo, N.; Liguori, M.

    2018-01-01

    Cross-correlations between the cosmic microwave background and the galaxy distribution can probe the linear growth rate of cosmic structures, thus providing a powerful tool to investigate different Dark Energy and Modified Gravity models. We explore the possibility of using this observable to probe a particular class of Modified Gravity models, called K-mouflage.

  7. Dynamical spacetimes in conformal gravity

    NASA Astrophysics Data System (ADS)

    Zhang, Hongsheng; Zhang, Yi; Li, Xin-Zhou

    2017-08-01

    The conformal gravity remarkably boosts our prehension of gravity theories. We find a series of dynamical solutions in the W2-conformal gravity, including generalized Schwarzschild-Friedmann-Robertson-Walker (GSFRW), charged generalized Schwarzschild-Friedmann-Robertson-Walker (CGSFRW), especially rotating Friedmann-Robertson-Walker (RFRW), charged rotating Friedmann-Robertson-Walker (CRFRW), and a dynamical cylindrically symmetric solutions. The RFRW, CRFRW and the dynamical cylindrically symmetric solutions are never found in the Einstein gravity and modified gravities. The GSFRW and CGSFRW solutions take different forms from the corresponding solutions in the Einstein gravity.

  8. Cosmological Constant: A Lesson from Bose-Einstein Condensates

    NASA Astrophysics Data System (ADS)

    Finazzi, Stefano; Liberati, Stefano; Sindoni, Lorenzo

    2012-02-01

    The cosmological constant is one of the most pressing problems in modern physics. We address this issue from an emergent gravity standpoint, by using an analogue gravity model. Indeed, the dynamics of the emergent metric in a Bose-Einstein condensate can be described by a Poisson-like equation with a vacuum source term reminiscent of a cosmological constant. The direct computation of this term shows that in emergent gravity scenarios this constant may be naturally much smaller than the naive ground-state energy of the emergent effective field theory. This suggests that a proper computation of the cosmological constant would require a detailed understanding about how Einstein equations emerge from the full microscopic quantum theory. In this light, the cosmological constant appears as a decisive test bench for any quantum or emergent gravity scenario.

  9. Cosmological constant: a lesson from Bose-Einstein condensates.

    PubMed

    Finazzi, Stefano; Liberati, Stefano; Sindoni, Lorenzo

    2012-02-17

    The cosmological constant is one of the most pressing problems in modern physics. We address this issue from an emergent gravity standpoint, by using an analogue gravity model. Indeed, the dynamics of the emergent metric in a Bose-Einstein condensate can be described by a Poisson-like equation with a vacuum source term reminiscent of a cosmological constant. The direct computation of this term shows that in emergent gravity scenarios this constant may be naturally much smaller than the naive ground-state energy of the emergent effective field theory. This suggests that a proper computation of the cosmological constant would require a detailed understanding about how Einstein equations emerge from the full microscopic quantum theory. In this light, the cosmological constant appears as a decisive test bench for any quantum or emergent gravity scenario.

  10. Looking for empty topological wormhole spacetimes in F(R)-modified gravity

    NASA Astrophysics Data System (ADS)

    Di Criscienzo, R.; Myrzakulov, R.; Sebastiani, L.

    2013-12-01

    Much attention has been recently devoted to modified theories of gravity, the simplest models of which overcome General Relativity simply by replacing R with F(R) in the Einstein-Hilbert action. Unfortunately, such models typically lack most of the beautiful solutions discovered in Einstein’s gravity. Nonetheless, in F(R) gravity, it has been possible to get at least few black holes, but still we do not know any empty wormhole-like spacetime solution. This paper aims to explain why it is so hard to get such solutions (given that they exist!). Few solutions are derived in the simplest cases, while only an implicit form has been obtained in the non-trivial case.

  11. Probing Modified Gravity with Double Pulsars

    NASA Astrophysics Data System (ADS)

    Deng, Xue-Mei; Xie, Yi; Huang, Tian-Yi

    2015-01-01

    Although Einstein's general relativity has passed all the tests so far, alternative theories are still required for deeper understanding of the nature of gravity. Double pulsars provide us a significant opportunity to test them. In order to probe some modified gravities which try to explain some astrophysical phenomena without dark matter, we use periastron advance dot ω of four binary pulsars (PSR B1913+16, PSR B1534+12, PSR J0737-3039 and PSR B2127+11C) to constrain their Yukawa parameters: λ = (3.97 ± 0.01) × 108m and α = (2.40 ± 0.02) × 10-8. It might help us to distinguish different gravity theories and get closer to the new physics.

  12. Superbounce and loop quantum ekpyrotic cosmologies from modified gravity: F(R) , F(G) and F(T) theories

    NASA Astrophysics Data System (ADS)

    Odintsov, S. D.; Oikonomou, V. K.; Saridakis, Emmanuel N.

    2015-12-01

    We investigate the realization of two bouncing paradigms, namely of the superbounce and the loop quantum cosmological ekpyrosis, in the framework of various modified gravities. In particular, we focus on the F(R) , F(G) and F(T) gravities, and we reconstruct their specific subclasses which lead to such universe evolutions. These subclasses constitute from power laws, polynomials, or hypergeometric ansatzes, which can be approximated by power laws. The qualitative similarity of the different effective gravities which realize the above two bouncing cosmologies, indicates that a universality might be lying behind the bounce. Finally, performing a linear perturbation analysis, we show that the obtained solutions are conditionally or fully stable.

  13. Cosmological applications of F (T ,TG) gravity

    NASA Astrophysics Data System (ADS)

    Kofinas, Georgios; Saridakis, Emmanuel N.

    2014-10-01

    We investigate the cosmological applications of F (T ,TG) gravity, which is a novel modified gravitational theory based on the torsion invariant T and the teleparallel equivalent of the Gauss-Bonnet term TG. F (T ,TG) gravity differs from both F (T ) theories as well as from F (R ,G ) class of curvature modified gravity, and thus its corresponding cosmology proves to be very interesting. In particular, it provides a unified description of the cosmological history from early-times inflation to late-times self-acceleration, without the inclusion of a cosmological constant. Moreover, the dark energy equation-of-state parameter can be quintessence or phantomlike, or experience the phantom-divide crossing, depending on the parameters of the model.

  14. Unifying inflation with ΛCDM epoch in modified f(R) gravity consistent with Solar System tests

    NASA Astrophysics Data System (ADS)

    Nojiri, Shin'ichi; Odintsov, Sergei D.

    2007-12-01

    We suggest two realistic f(R) and one F(G) modified gravities which are consistent with local tests and cosmological bounds. The typical property of such theories is the presence of the effective cosmological constant epochs in such a way that early-time inflation and late-time cosmic acceleration are naturally unified within single model. It is shown that classical instability does not appear here and Newton law is respected. Some discussion of possible anti-gravity regime appearance and related modification of the theory is done.

  15. Human Factors Engineering. A Self-Paced Text, Lessons 21-25,

    DTIC Science & Technology

    1981-08-01

    the moon’ mission really consists of several unitary missions, such as: (1) Supersonic speed (2) Orbit earth (3) Re-enter earth’s gravity , and so on...radar antenna height to clear surrounding obstructions raises the ship’s center of gravity and, therefore, makes it less stable in the water. While... meterial is documented in the Letter Requirement (LR), which is an abbreviated version of the LOA used for acquisition of low-cost items. The Outline

  16. Science Teaching to Fire the Imagination.

    ERIC Educational Resources Information Center

    Sandford, Diana; Fleetwood, Julie

    1997-01-01

    Presents a range of exciting ideas for encouraging active learning, for illuminating new concepts, and for making science lessons fun. Topics include modeling, matter, heat, diffusion, changes of state, heat transfer, energy changes, atomic structure, waves, gravity, enzymes, and habitats. (JRH)

  17. Batter's Choice: Lessons for Teaching Tactics in a Modified Striking/Fielding Game

    ERIC Educational Resources Information Center

    Sinclair, Christina

    2004-01-01

    When played in their standard form, striking/fielding games are often a favorite among elementary students; yet they allow for only limited participation, which is contradictory to quality physical education. This article presents a sequence of lessons leading to Batter's Choice, a modified striking/fielding game, designed to maximize the…

  18. On the stability conditions for theories of modified gravity in the presence of matter fields

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    De Felice, Antonio; Frusciante, Noemi; Papadomanolakis, Georgios, E-mail: antonio.defelice@yukawa.kyoto-u.ac.jp, E-mail: fruscian@iap.fr, E-mail: papadomanolakis@lorentz.leidenuniv.nl

    We present a thorough stability analysis of modified gravity theories in the presence of matter fields. We use the Effective Field Theory framework for Dark Energy and Modified Gravity to retain a general approach for the gravity sector and a Sorkin-Schutz action for the matter one. Then, we work out the proper viability conditions to guarantee in the scalar sector the absence of ghosts, gradient and tachyonic instabilities. The absence of ghosts can be achieved by demanding a positive kinetic matrix, while the lack of a gradient instability is ensured by imposing a positive speed of propagation for all themore » scalar modes. In case of tachyonic instability, the mass eigenvalues have been studied and we work out the appropriate expressions. For the latter, an instability occurs only when the negative mass eigenvalue is much larger, in absolute value, than the Hubble parameter. We discuss the results for the minimally coupled quintessence model showing for a particular set of parameters two typical behaviours which in turn lead to a stable and an unstable configuration. Moreover, we find that the speeds of propagation of the scalar modes strongly depend on matter densities, for the beyond Horndeski theories. Our findings can be directly employed when testing modified gravity theories as they allow to identify the correct viability space.« less

  19. Lessons for Teaching Art Criticism.

    ERIC Educational Resources Information Center

    Barrett, Terry, Ed.; Clark, Gilbert, Ed.

    This collection of lessons is meant to be a practical guide to help teachers engage children in art criticism. The lessons generally follow a similar format. Most suggest an age group but may be modified for use with younger or older students. Several authors suggest variations and extensions for lessons that include studio activities. A broad…

  20. Strange stars in f( R) theories of gravity in the Palatini formalism

    NASA Astrophysics Data System (ADS)

    Panotopoulos, Grigoris

    2017-05-01

    In the present work we study strange stars in f( R) theories of gravity in the Palatini formalism. We consider two concrete well-known cases, namely the R+R^2/(6 M^2) model as well as the R-μ ^4/R model for two different values of the mass parameter M or μ . We integrate the modified Tolman-Oppenheimer-Volkoff equations numerically, and we show the mass-radius diagram for each model separately. The standard case corresponding to the General Relativity is also shown in the same figure for comparison. Our numerical results show that the interior solution can be vastly different depending on the model and/or the value of the parameter of each model. In addition, our findings imply that (i) for the cosmologically interesting values of the mass scales M,μ the effect of modified gravity on strange stars is negligible, while (ii) for the values predicting an observable effect, the modified gravity models discussed here would be ruled out by their cosmological effects.

  1. Initial conditions for cosmological N-body simulations of the scalar sector of theories of Newtonian, Relativistic and Modified Gravity

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Valkenburg, Wessel; Hu, Bin, E-mail: valkenburg@lorentz.leidenuniv.nl, E-mail: hu@lorentz.leidenuniv.nl

    2015-09-01

    We present a description for setting initial particle displacements and field values for simulations of arbitrary metric theories of gravity, for perfect and imperfect fluids with arbitrary characteristics. We extend the Zel'dovich Approximation to nontrivial theories of gravity, and show how scale dependence implies curved particle paths, even in the entirely linear regime of perturbations. For a viable choice of Effective Field Theory of Modified Gravity, initial conditions set at high redshifts are affected at the level of up to 5% at Mpc scales, which exemplifies the importance of going beyond Λ-Cold Dark Matter initial conditions for modifications of gravitymore » outside of the quasi-static approximation. In addition, we show initial conditions for a simulation where a scalar modification of gravity is modelled in a Lagrangian particle-like description. Our description paves the way for simulations and mock galaxy catalogs under theories of gravity beyond the standard model, crucial for progress towards precision tests of gravity and cosmology.« less

  2. No slip gravity

    NASA Astrophysics Data System (ADS)

    Linder, Eric V.

    2018-03-01

    A subclass of the Horndeski modified gravity theory we call No Slip Gravity has particularly interesting properties: 1) a speed of gravitational wave propagation equal to the speed of light, 2) equality between the effective gravitational coupling strengths to matter and light, Gmatter and Glight, hence no slip between the metric potentials, yet difference from Newton's constant, and 3) suppressed growth to give better agreement with galaxy clustering observations. We explore the characteristics and implications of this theory, and project observational constraints. We also give a simple expression for the ratio of the gravitational wave standard siren distance to the photon standard candle distance, in this theory and others, and enable a direct comparison of modified gravity in structure growth and in gravitational waves, an important crosscheck.

  3. New insights on the matter-gravity coupling paradigm.

    PubMed

    Delsate, Térence; Steinhoff, Jan

    2012-07-13

    The coupling between matter and gravity in general relativity is given by a proportionality relation between the stress tensor and the geometry. This is an oriented assumption driven by the fact that both the stress tensor and the Einstein tensor are divergenceless. However, general relativity is in essence a nonlinear theory, so there is no obvious reason why the coupling to matter should be linear. On another hand, modified theories of gravity usually affect the vacuum dynamics, yet keep the coupling to matter linear. In this Letter, we address the implications of consistent nonlinear gravity-matter coupling. The Eddington-inspired Born-Infeld theory recently introduced by Bañados and Ferreira provides an enlightening realization of such coupling modifications. We find that this theory coupled to a perfect fluid reduces to general relativity coupled to a nonlinearly modified perfect fluid, leading to an ambiguity between modified coupling and modified equation of state. We discuss observational consequences of this degeneracy and argue that such a completion of general relativity is viable from both an experimental and theoretical point of view through energy conditions, consistency, and singularity-avoidance perspectives. We use these results to discuss the impact of changing the coupling paradigm.

  4. Systematic simulations of modified gravity: chameleon models

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Brax, Philippe; Davis, Anne-Christine; Li, Baojiu

    2013-04-01

    In this work we systematically study the linear and nonlinear structure formation in chameleon theories of modified gravity, using a generic parameterisation which describes a large class of models using only 4 parameters. For this we have modified the N-body simulation code ecosmog to perform a total of 65 simulations for different models and parameter values, including the default ΛCDM. These simulations enable us to explore a significant portion of the parameter space. We have studied the effects of modified gravity on the matter power spectrum and mass function, and found a rich and interesting phenomenology where the difference withmore » the ΛCDM paradigm cannot be reproduced by a linear analysis even on scales as large as k ∼ 0.05 hMpc{sup −1}, since the latter incorrectly assumes that the modification of gravity depends only on the background matter density. Our results show that the chameleon screening mechanism is significantly more efficient than other mechanisms such as the dilaton and symmetron, especially in high-density regions and at early times, and can serve as a guidance to determine the parts of the chameleon parameter space which are cosmologically interesting and thus merit further studies in the future.« less

  5. Mimetic compact stars

    NASA Astrophysics Data System (ADS)

    Momeni, D.; Moraes, P. H. R. S.; Gholizade, H.; Myrzakulov, R.

    Modified gravity models have been constantly proposed with the purpose of evading some standard gravity shortcomings. Recently proposed by Chamseddine and Mukhanov, the Mimetic Gravity arises as an optimistic alternative. Our purpose in this work is to derive Tolman-Oppenheimer-Volkoff equations and solutions for such a gravity theory. We solve them numerically for quark star and neutron star cases. The results are carefully discussed.

  6. DOE Office of Scientific and Technical Information (OSTI.GOV)

    Shamir, M. F., E-mail: farasat.shamir@nu.edu.pk

    Modified theories of gravity have attracted much attention of the researchers in the recent years. In particular, the f(R) theory has been investigated extensively due to important f(R) gravity models in cosmological contexts. This paper is devoted to exploring an anisotropic universe in metric f(R) gravity. A locally rotationally symmetric Bianchi type I cosmological model is considered for this purpose. Exact solutions of modified field equations are obtained for a well-known f(R) gravity model. The energy conditions are also discussed for the model under consideration. The viability of the model is investigated via graphical analysis using the present-day values ofmore » cosmological parameters. The model satisfies null energy, weak energy, and dominant energy conditions for a particular range of the anisotropy parameter while the strong energy condition is violated, which shows that the anisotropic universe in f(R) gravity supports the crucial issue of accelerated expansion of the universe.« less

  7. Membrane paradigm of black holes in Chern-Simons modified gravity

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Zhao, Tian-Yi; Wang, Towe, E-mail: zhaotianyi5566@foxmail.com, E-mail: twang@phy.ecnu.edu.cn

    2016-06-01

    The membrane paradigm of black hole is studied in the Chern-Simons modified gravity. Derived with the action principle a la Parikh-Wilczek, the stress tensor of membrane manifests a rich structure arising from the Chern-Simons term. The membrane stress tensor, if related to the bulk stress tensor in a special form, obeys the low-dimensional fluid continuity equation and the Navier-Stokes equation. This paradigm is applied to spherically symmetric static geometries, and in particular, the Schwarzschild black hole, which is a solution of a large class of dynamical Chern-Simons gravity.

  8. Reconstruction of cosmological matter perturbations in modified gravity

    NASA Astrophysics Data System (ADS)

    Gonzalez, J. E.

    2017-12-01

    The analysis of perturbative quantities is a powerful tool to distinguish between different dark energy models and gravity theories degenerated at the background level. In this work, we generalize the integral solution of the matter density contrast for general relativity gravity [V. Sahni and A. Starobinsky, Int. J. Mod. Phys. D 15, 2105 (2006)., 10.1142/S0218271806009704, U. Alam, V. Sahni, and A. A. Starobinsky, Astrophys. J. 704, 1086 (2009)., 10.1088/0004-637X/704/2/1086] to a wide class of modified gravity (MG) theories. To calculate this solution, it is necessary to have prior knowledge of the Hubble rate, the density parameter at the present epoch (Ωm 0), and the functional form of the effective Newton's constant that characterizes the gravity theory. We estimate in a model-independent way the Hubble expansion rate by applying a nonparametric reconstruction method to model-independent cosmic chronometer data and high-z quasar data. In order to compare our generalized solution of the matter density contrast, using the nonparametric reconstruction of H (z ) from observational data, with a purely theoretical one, we choose a parametrization of the screened modified gravity and the Ωm 0 from WMAP-9 Collaborations. Finally, we calculate the growth index for the analyzed cases, finding very good agreement between theoretical values and the obtained ones using the approach presented in this work.

  9. Lessons learned in stepped chute research

    USDA-ARS?s Scientific Manuscript database

    Early research on stepped chutes focused on steep gravity style stepped chutes. Today, the research trend has shifted to stepped chutes applied to more moderate slopes like those for aging embankment dams. Research contributions have been made on hydraulic properties of stepped chutes including ai...

  10. Integrating a Gravity Simulation and Groundwater Modeling on the Calibration of Specific Yield for Choshui Alluvial Fan

    NASA Astrophysics Data System (ADS)

    Chang, Liang Cheng; Tsai, Jui pin; Chen, Yu Wen; Way Hwang, Chein; Chung Cheng, Ching; Chiang, Chung Jung

    2014-05-01

    For sustainable management, accurate estimation of recharge can provide critical information. The accuracy of estimation is highly related to uncertainty of specific yield (Sy). Because Sy value is traditionally obtained by a multi-well pumping test, the available Sy values are usually limited due to high installation cost. Therefore, this information insufficiency of Sy may cause high uncertainty for recharge estimation. Because gravity is a function of a material mass and the inverse square of the distance, gravity measurement can assist to obtain the mass variation of a shallow groundwater system. Thus, the groundwater level observation data and gravity measurements are used for the calibration of Sy for a groundwater model. The calibration procedure includes four steps. First, gravity variations of three groundwater-monitoring wells, Si-jhou, Tu-ku and Ke-cuo, are observed in May, August and November 2012. To obtain the gravity caused by groundwater variation, this study filters the noises from other sources, such as ocean tide and land subsidence, in the collected data The refined data, which are data without noises, are named gravity residual. Second, this study develops a groundwater model using MODFLOW 2005 to simulate the water mass variation of the groundwater system. Third, we use Newton gravity integral to simulate the gravity variation caused by the simulated water mass variation during each of the observation periods. Fourth, comparing the ratio of the gravity variation between the two data sets, which are observed gravity residuals and simulated gravities. The values of Sy is continuously modified until the gravity variation ratios of the two data sets are the same. The Sy value of Si-jhou is 0.216, which is obtained by the multi-well pumping test. This Sy value is assigned to the simulation model. The simulation results show that the simulated gravity can well fit the observed gravity residual without parameter calibration. This result indicates that the proposed approach is correct and reasonable. In Tu-ku and Ke-cuo, the ratios of the gravity variation between observed gravity residuals and simulated gravities are approximate 1.8 and 50, respectively. The Sy values of these two stations are modified 1.8 and 50 times the original values. These modified Sy values are assigned to the groundwater morel. After the parameter re-assignment, the simulated gravities meet the gravity residuals in these two stations. In conclusion, the study results show that the proposed approach has the potential to identify Sy without installing wells. Therefore, the proposed approach can be used to increase the spatial density of Sy and can conduct the recharge estimation with low uncertainty.

  11. DOE Office of Scientific and Technical Information (OSTI.GOV)

    Song, Yong-Seon; Institute of Cosmology and Gravitation, University of Portsmouth, Dennis Sciama Building, Portsmouth, PO1 3FX; Zhao Gongbo

    We explore the complementarity of weak lensing and galaxy peculiar velocity measurements to better constrain modifications to General Relativity. We find no evidence for deviations from General Relativity on cosmological scales from a combination of peculiar velocity measurements (for Luminous Red Galaxies in the Sloan Digital Sky Survey) with weak lensing measurements (from the Canadian France Hawaii Telescope Legacy Survey). We provide a Fisher error forecast for a Euclid-like space-based survey including both lensing and peculiar velocity measurements and show that the expected constraints on modified gravity will be at least an order of magnitude better than with present data,more » i.e. we will obtain {approx_equal}5% errors on the modified gravity parametrization described here. We also present a model-independent method for constraining modified gravity parameters using tomographic peculiar velocity information, and apply this methodology to the present data set.« less

  12. Dark stars in Starobinsky's model

    NASA Astrophysics Data System (ADS)

    Panotopoulos, Grigoris; Lopes, Ilídio

    2018-01-01

    In the present work we study non-rotating dark stars in f (R ) modified theory of gravity. In particular, we have considered bosonic self-interacting dark matter modeled inside the star as a Bose-Einstein condensate, while as far as the modified theory of gravity is concerned we have assumed Starobinsky's model R +a R2. We solve the generalized structure equations numerically, and we obtain the mass-to-ratio relation for several different values of the parameter a , and for two different dark matter equation-of-states. Our results show that the dark matter stars become more compact in the R-squared gravity compared to general relativity, while at the same time the highest star mass is slightly increased in the modified gravitational theory. The numerical value of the highest star mass for each case has been reported.

  13. A general framework to test gravity using galaxy clusters - I. Modelling the dynamical mass of haloes in f(R) gravity

    NASA Astrophysics Data System (ADS)

    Mitchell, Myles A.; He, Jian-hua; Arnold, Christian; Li, Baojiu

    2018-06-01

    We propose a new framework for testing gravity using cluster observations, which aims to provide an unbiased constraint on modified gravity models from Sunyaev-Zel'dovich (SZ) and X-ray cluster counts and the cluster gas fraction, among other possible observables. Focusing on a popular f(R) model of gravity, we propose a novel procedure to recalibrate mass scaling relations from Λ cold dark matter (ΛCDM) to f(R) gravity for SZ and X-ray cluster observables. We find that the complicated modified gravity effects can be simply modelled as a dependence on a combination of the background scalar field and redshift, fR(z)/(1 + z), regardless of the f(R) model parameter. By employing a large suite of N-body simulations, we demonstrate that a theoretically derived tanh fitting formula is in excellent agreement with the dynamical mass enhancement of dark matter haloes for a large range of background field parameters and redshifts. Our framework is sufficiently flexible to allow for tests of other models and inclusion of further observables, and the one-parameter description of the dynamical mass enhancement can have important implications on the theoretical modelling of observables and on practical tests of gravity.

  14. Mysterious Anti-Gravity and Dark-Essence

    NASA Astrophysics Data System (ADS)

    Gu, Je-An

    2013-12-01

    The need of anti-gravity and dark-essence in cosmology is the greatest scientific mystery in the 21st century. This paper presents a personal view of several relevant issues, including the long-standing cosmological constant problem, the newly emerging dark radiation issue, and the basic stability issue of the general-relativity limit in modified gravity.

  15. Mysterious Anti-Gravity and Dark-Essence

    NASA Astrophysics Data System (ADS)

    Gu, Je-An

    2013-01-01

    The need of anti-gravity and dark-essence in cosmology is the greatest scientific mystery in the 21st century. This paper presents a personal view of several relevant issues, including the long-standing cosmological constant problem, the newly emerging dark radiation issue, and the basic stability issue of the general-relativity limit in modified gravity.

  16. Efficient simulations of large-scale structure in modified gravity cosmologies with comoving Lagrangian acceleration

    NASA Astrophysics Data System (ADS)

    Valogiannis, Georgios; Bean, Rachel

    2017-05-01

    We implement an adaptation of the cola approach, a hybrid scheme that combines Lagrangian perturbation theory with an N-body approach, to model nonlinear collapse in chameleon and symmetron modified gravity models. Gravitational screening is modeled effectively through the attachment of a suppression factor to the linearized Klein-Gordon equations. The adapted cola approach is benchmarked, with respect to an N-body code both for the Λ cold dark matter (Λ CDM ) scenario and for the modified gravity theories. It is found to perform well in the estimation of the dark matter power spectra, with consistency of 1% to k ˜2.5 h /Mpc . Redshift space distortions are shown to be effectively modeled through a Lorentzian parametrization with a velocity dispersion fit to the data. We find that cola performs less well in predicting the halo mass functions but has consistency, within 1 σ uncertainties of our simulations, in the relative changes to the mass function induced by the modified gravity models relative to Λ CDM . The results demonstrate that cola, proposed to enable accurate and efficient, nonlinear predictions for Λ CDM , can be effectively applied to a wider set of cosmological scenarios, with intriguing properties, for which clustering behavior needs to be understood for upcoming surveys such as LSST, DESI, Euclid, and WFIRST.

  17. A parametrisation of modified gravity on nonlinear cosmological scales

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Lombriser, Lucas, E-mail: llo@roe.ac.uk

    2016-11-01

    Viable modifications of gravity on cosmological scales predominantly rely on screening mechanisms to recover Einstein's Theory of General Relativity in the Solar System, where it has been well tested. A parametrisation of the effects of such modifications in the spherical collapse model is presented here for the use of modelling the modified nonlinear cosmological structure. The formalism allows an embedding of the different screening mechanisms operating in scalar-tensor theories through large values of the gravitational potential or its first or second derivatives as well as of linear suppression effects or more general transitions between modified and Einstein gravity limits. Eachmore » screening or suppression mechanism is parametrised by a time, mass, and environment dependent screening scale, an effective modified gravitational coupling in the fully unscreened limit that can be matched to linear theory, the exponent of a power-law radial profile of the screened coupling, determined by derivatives, symmetries, and potentials in the scalar field equation, and an interpolation rate between the screened and unscreened limits. Along with generalised perturbative methods, the parametrisation may be used to formulate a nonlinear extension to the linear parametrised post-Friedmannian framework to enable generalised tests of gravity with the wealth of observations from the nonlinear cosmological regime.« less

  18. Testing modified gravity at large distances with the HI Nearby Galaxy Survey's rotation curves

    NASA Astrophysics Data System (ADS)

    Mastache, Jorge; Cervantes-Cota, Jorge L.; de la Macorra, Axel

    2013-03-01

    Recently a new—quantum motivated—theory of gravity has been proposed that modifies the standard Newtonian potential at large distances when spherical symmetry is considered. Accordingly, Newtonian gravity is altered by adding an extra Rindler acceleration term that has to be phenomenologically determined. Here we consider a standard and a power-law generalization of the Rindler modified Newtonian potential. The new terms in the gravitational potential are hypothesized to play the role of dark matter in galaxies. Our galactic model includes the mass of the integrated gas, and stars for which we consider three stellar mass functions (Kroupa, diet-Salpeter, and free mass model). We test this idea by fitting rotation curves of seventeen low surface brightness galaxies from the HI Nearby Galaxy Survey (THINGS). We find that the Rindler parameters do not perform a suitable fit to the rotation curves in comparison to standard dark matter profiles (Navarro-Frenk-White and Burkert) and, in addition, the computed parameters of the Rindler gravity show a high spread, posing the model as a nonacceptable alternative to dark matter.

  19. Cosmic growth signatures of modified gravitational strength

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Denissenya, Mikhail; Linder, Eric V., E-mail: mikhail.denissenya@nu.edu.kz, E-mail: evlinder@lbl.gov

    2017-06-01

    Cosmic growth of large scale structure probes the entire history of cosmic expansion and gravitational coupling. To get a clear picture of the effects of modification of gravity we consider a deviation in the coupling strength (effective Newton's constant) at different redshifts, with different durations and amplitudes. We derive, analytically and numerically, the impact on the growth rate and growth amplitude. Galaxy redshift surveys can measure a product of these through redshift space distortions and we connect the modified gravity to the observable in a way that may provide a useful parametrization of the ability of future surveys to testmore » gravity. In particular, modifications during the matter dominated era can be treated by a single parameter, the ''area'' of the modification, to an accuracy of ∼0.3% in the observables. We project constraints on both early and late time gravity for the Dark Energy Spectroscopic Instrument and discuss what is needed for tightening tests of gravity to better than 5% uncertainty.« less

  20. Astrophysical black holes in screened modified gravity

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Davis, Anne-Christine; Jha, Rahul; Muir, Jessica

    2014-08-01

    Chameleon, environmentally dependent dilaton, and symmetron gravity are three models of modified gravity in which the effects of the additional scalar degree of freedom are screened in dense environments. They have been extensively studied in laboratory, cosmological, and astrophysical contexts. In this paper, we present a preliminary investigation into whether additional constraints can be provided by studying these scalar fields around black holes. By looking at the properties of a static, spherically symmetric black hole, we find that the presence of a non-uniform matter distribution induces a non-constant scalar profile in chameleon and dilaton, but not necessarily symmetron gravity. Anmore » order of magnitude estimate shows that the effects of these profiles on in-falling test particles will be sub-leading compared to gravitational waves and hence observationally challenging to detect.« less

  1. Causal properties of nonlinear gravitational waves in modified gravity

    NASA Astrophysics Data System (ADS)

    Suvorov, Arthur George; Melatos, Andrew

    2017-09-01

    Some exact, nonlinear, vacuum gravitational wave solutions are derived for certain polynomial f (R ) gravities. We show that the boundaries of the gravitational domain of dependence, associated with events in polynomial f (R ) gravity, are not null as they are in general relativity. The implication is that electromagnetic and gravitational causality separate into distinct notions in modified gravity, which may have observable astrophysical consequences. The linear theory predicts that tachyonic instabilities occur, when the quadratic coefficient a2 of the Taylor expansion of f (R ) is negative, while the exact, nonlinear, cylindrical wave solutions presented here can be superluminal for all values of a2. Anisotropic solutions are found, whose wave fronts trace out time- or spacelike hypersurfaces with complicated geometric properties. We show that the solutions exist in f (R ) theories that are consistent with Solar System and pulsar timing experiments.

  2. Semi-Infinite Geology Modeling Algorithm (SIGMA): a Modular Approach to 3D Gravity

    NASA Astrophysics Data System (ADS)

    Chang, J. C.; Crain, K.

    2015-12-01

    Conventional 3D gravity computations can take up to days, weeks, and even months, depending on the size and resolution of the data being modeled. Additional modeling runs, due to technical malfunctions or additional data modifications, only compound computation times even further. We propose a new modeling algorithm that utilizes vertical line elements to approximate mass, and non-gridded (point) gravity observations. This algorithm is (1) magnitudes faster than conventional methods, (2) accurate to less than 0.1% error, and (3) modular. The modularity of this methodology means that researchers can modify their geology/terrain or gravity data, and only the modified component needs to be re-run. Additionally, land-, sea-, and air-based platforms can be modeled at their observation point, without having to filter data into a synthesized grid.

  3. Cosmological footprints of loop quantum gravity.

    PubMed

    Grain, J; Barrau, A

    2009-02-27

    The primordial spectrum of cosmological tensor perturbations is considered as a possible probe of quantum gravity effects. Together with string theory, loop quantum gravity is one of the most promising frameworks to study quantum effects in the early universe. We show that the associated corrections should modify the potential seen by gravitational waves during the inflationary amplification. The resulting power spectrum should exhibit a characteristic tilt. This opens a new window for cosmological tests of quantum gravity.

  4. f(R) gravity on non-linear scales: the post-Friedmann expansion and the vector potential

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Thomas, D.B.; Bruni, M.; Koyama, K.

    2015-07-01

    Many modified gravity theories are under consideration in cosmology as the source of the accelerated expansion of the universe and linear perturbation theory, valid on the largest scales, has been examined in many of these models. However, smaller non-linear scales offer a richer phenomenology with which to constrain modified gravity theories. Here, we consider the Hu-Sawicki form of f(R) gravity and apply the post-Friedmann approach to derive the leading order equations for non-linear scales, i.e. the equations valid in the Newtonian-like regime. We reproduce the standard equations for the scalar field, gravitational slip and the modified Poisson equation in amore » coherent framework. In addition, we derive the equation for the leading order correction to the Newtonian regime, the vector potential. We measure this vector potential from f(R) N-body simulations at redshift zero and one, for two values of the f{sub R{sub 0}} parameter. We find that the vector potential at redshift zero in f(R) gravity can be close to 50% larger than in GR on small scales for |f{sub R{sub 0}}|=1.289 × 10{sup −5}, although this is less for larger scales, earlier times and smaller values of the f{sub R{sub 0}} parameter. Similarly to in GR, the small amplitude of this vector potential suggests that the Newtonian approximation is highly accurate for f(R) gravity, and also that the non-linear cosmological behaviour of f(R) gravity can be completely described by just the scalar potentials and the f(R) field.« less

  5. Factors Considered by Elementary Teachers When Developing and Modifying Mathematical Tasks to Support Children's Mathematical Thinking

    NASA Astrophysics Data System (ADS)

    Fredenberg, Michael Duane

    The idea that problems and tasks play a pivotal role in a mathematics lesson has a long standing in mathematics education research. Recent calls for teaching reform appeal for training teachers to better understand how students learn mathematics and to employ students' mathematical thinking as the basis for pedagogy (CCSSM, 2010; NCTM, 2000; NRC 1999). The teaching practices of (a) developing a task for a mathematics lesson and, (b) modifying the task for students while enacting the lesson fit within the scope of supporting students' mathematical thinking. Surprisingly, an extensive search of the literature did not yield any research aimed to identify and refine the constituent parts of the aforementioned teaching practices in the manner called for by Grossman and xiii colleagues (2009). Consequently, my research addresses the two questions: (a) what factors do exemplary elementary teachers consider when developing a task for a mathematics lesson? (b) what factors do they consider when they modify a task for a student when enacting a lesson? I conducted a multiple case study involving three elementary teachers, each with extensive training in the area of Cognitively Guided Instruction (CGI), as well as several years experience teaching mathematics following the principles of CGI (Carpenter et al., 1999). I recorded video of three mathematics lessons with each participant and after each lesson I conducted a semi-structured stimulated recall interview. A subsequent follow-up clinical interview was conducted soon thereafter to further explore the teacher's thoughts (Ginsberg, 1997). In addition, my methodology included interjecting myself at select times during a lesson to ask the teacher to explain her reasoning. Qualitative analysis led to a framework that identified four categories of influencing factors and seven categories of supporting objectives for the development of a task. Subsets of these factors and objectives emerged as particularly relevant when the teachers decided to modify a task. Moreover, relationships between and among the various factors were identified. The emergent framework from this study offers insight into decompositions of the two teaching practices of interest, and, in particular, the utility of the number choices made by the teachers.

  6. Teaching Science. A Weighty Gravity Lesson.

    ERIC Educational Resources Information Center

    Leyden, Michael B.

    1996-01-01

    Describes an activity that uses a candle, a scale, and an elevator to demonstrate the concept of weightlessness in space, showing that astronauts are not truly weightless. Activity includes an exploration phase, a concept introduction phase, and a concept application phase. Provides guidelines and safety measures for conducting the activity. (JW)

  7. On Gauge Invariant Cosmological Perturbations in UV-modified Hořava Gravity: A Brief Introduction

    NASA Astrophysics Data System (ADS)

    Park, Mu-In

    2018-01-01

    We revisit gauge invariant cosmological perturbations in UV-modified, z = 3 Hořava gravity with one scalar matter field, which has been proposed as a renormalizable gravity theory without the ghost problem in four dimensions. We confirm that there is no extra graviton modes and general relativity is recovered in IR, which achieves the consistency of the model. From the UV-modification terms which break the detailed balance condition in UV, we obtain scale-invariant power spectrums for non-inflationary backgrounds, like the power-law expansions, without knowing the details of early expansion history of Universe. This could provide a new framework for the Big Bang cosmology.

  8. Interpreting the results of a modified gravity model: examining access to primary health care physicians in five Canadian provinces and territories.

    PubMed

    Crooks, Valorie A; Schuurman, Nadine

    2012-08-01

    Primary health care (PHC) encompasses an array of health and social services that focus on preventative, diagnostic, and basic care measures to maintain wellbeing and address illnesses. In Canada, PHC involves the provision of first-contact health care services by providers such as family physicians and general practitioners - collectively referred as PHC physicians here. Ensuring access is a key requirement of effective PHC delivery. This is because having access to PHC has been shown to positively impact a number of health outcomes. We build on recent innovations in measuring potential spatial access to PHC physicians using geographic information systems (GIS) by running and then interpreting the findings of a modified gravity model. Elsewhere we have introduced the protocol for this model. In this article we run it for five selected Canadian provinces and territories. Our objectives are to present the results of the modified gravity model in order to: (1) understand how potential spatial access to PHC physicians can be interpreted in these Canadian jurisdictions, and (2) provide guidance regarding how findings of the modified gravity model should be interpreted in other analyses. Regarding the first objective, two distinct spatial patterns emerge regarding potential spatial access to PHC physicians in the five selected Canadian provinces: (1) a clear north-south pattern, where southern areas have greater potential spatial access than northern areas; and (2) while gradients of potential spatial access exist in and around urban areas, access outside of densely-to-moderately populated areas is fairly binary. Regarding the second objective, we identify three principles that others can use to interpret the findings of the modified gravity model when used in other research contexts. Future applications of the modified gravity model are needed in order to refine the recommendations we provide on interpreting its results. It is important that studies are undertaken that can help administrators, policy-makers, researchers, and others with characterizing the state of access to PHC, including potential spatial access. We encourage further research to be done using GIS in order to offer new, spatial perspectives on issues of access to health services given the increased recognition that the place-based nature of health services can benefit from the use of the capabilities of GIS to enhance the role that visualization plays in decision-making.

  9. Interpreting the results of a modified gravity model: examining access to primary health care physicians in five Canadian provinces and territories

    PubMed Central

    2012-01-01

    Background Primary health care (PHC) encompasses an array of health and social services that focus on preventative, diagnostic, and basic care measures to maintain wellbeing and address illnesses. In Canada, PHC involves the provision of first-contact health care services by providers such as family physicians and general practitioners – collectively referred as PHC physicians here. Ensuring access is a key requirement of effective PHC delivery. This is because having access to PHC has been shown to positively impact a number of health outcomes. Methods We build on recent innovations in measuring potential spatial access to PHC physicians using geographic information systems (GIS) by running and then interpreting the findings of a modified gravity model. Elsewhere we have introduced the protocol for this model. In this article we run it for five selected Canadian provinces and territories. Our objectives are to present the results of the modified gravity model in order to: (1) understand how potential spatial access to PHC physicians can be interpreted in these Canadian jurisdictions, and (2) provide guidance regarding how findings of the modified gravity model should be interpreted in other analyses. Results Regarding the first objective, two distinct spatial patterns emerge regarding potential spatial access to PHC physicians in the five selected Canadian provinces: (1) a clear north–south pattern, where southern areas have greater potential spatial access than northern areas; and (2) while gradients of potential spatial access exist in and around urban areas, access outside of densely-to-moderately populated areas is fairly binary. Regarding the second objective, we identify three principles that others can use to interpret the findings of the modified gravity model when used in other research contexts. Conclusions Future applications of the modified gravity model are needed in order to refine the recommendations we provide on interpreting its results. It is important that studies are undertaken that can help administrators, policy-makers, researchers, and others with characterizing the state of access to PHC, including potential spatial access. We encourage further research to be done using GIS in order to offer new, spatial perspectives on issues of access to health services given the increased recognition that the place-based nature of health services can benefit from the use of the capabilities of GIS to enhance the role that visualization plays in decision-making. PMID:22852816

  10. Extrasolar planets as a probe of modified gravity

    NASA Astrophysics Data System (ADS)

    Vargas dos Santos, Marcelo; Mota, David F.

    2017-06-01

    We propose a new method to test modified gravity theories, taking advantage of the available data on extrasolar planets. We computed the deviations from the Kepler third law and use that to constrain gravity theories beyond General Relativity. We investigate gravity models which incorporate three screening mechanisms: the Chameleon, the Symmetron and the Vainshtein. We find that data from exoplanets orbits are very sensitive to the screening mechanisms putting strong constraints in the parameter space for the Chameleon models and the Symmetron, complementary and competitive to other methods, like interferometers and solar system. With the constraints on Vainshtein we are able to work beyond the hypothesis that the crossover scale is of the same order of magnitude than the Hubble radius rc ∼ H0-1, which makes the screening work automatically, testing how strong this hypothesis is and the viability of other scales.

  11. Speed of gravitational waves and black hole hair

    NASA Astrophysics Data System (ADS)

    Tattersall, Oliver J.; Ferreira, Pedro G.; Lagos, Macarena

    2018-04-01

    The recent detection of GRB 170817A and GW170817 constrains the speed of gravity waves cT to be that of light, which severely restricts the landscape of modified gravity theories that impact the cosmological evolution of the Universe. In this work, we investigate the presence of black hole hair in the remaining viable cosmological theories of modified gravity that respect the constraint cT=1 . We focus mainly on scalar-tensor theories of gravity, analyzing static, asymptotically flat black holes in Horndeski, Beyond Horndeski, Einstein-scalar-Gauss-Bonnet, and Chern-Simons theories. We find that in all of the cases considered here, theories that are cosmologically relevant and respect cT=1 do not allow for hair, or have negligible hair. We further comment on vector-tensor theories including Einstein-Yang-Mills, Einstein-Aether, and generalized Proca theories, as well as bimetric theories.

  12. New Class of Quasinormal Modes of Neutron Stars in Scalar-Tensor Gravity

    NASA Astrophysics Data System (ADS)

    Mendes, Raissa F. P.; Ortiz, Néstor

    2018-05-01

    Detection of the characteristic spectrum of pulsating neutron stars can be a powerful tool not only to probe the nuclear equation of state but also to test modifications to general relativity. However, the shift in the oscillation spectrum induced by modified theories of gravity is often small and degenerate with our ignorance of the equation of state. In this Letter, we show that the coupling to additional degrees of freedom present in modified theories of gravity can give rise to new families of modes, with no counterpart in general relativity, which could be sufficiently well resolved in frequency space to allow for clear detection. We present a realization of this idea by performing a thorough study of radial oscillations of neutron stars in massless scalar-tensor theories of gravity. We anticipate astrophysical scenarios where the presence of this class of quasinormal modes could be probed with electromagnetic and gravitational wave measurements.

  13. The New Era of Precision Cosmology: Testing Gravity at Large Scales

    NASA Technical Reports Server (NTRS)

    Prescod-Weinstein, Chanda

    2011-01-01

    Cosmic acceleration may be the biggest phenomenological mystery in cosmology today. Various explanations for its cause have been proposed, including the cosmological constant, dark energy and modified gravities. Structure formation provides a strong test of any cosmic acceleration model because a successful dark energy model must not inhibit the development of observed large-scale structures. Traditional approaches to studies of structure formation in the presence of dark energy ore modified gravity implement the Press & Schechter formalism (PGF). However, does the PGF apply in all cosmologies? The search is on for a better understanding of universality in the PGF In this talk, I explore the potential for universality and talk about what dark matter haloes may be able to tell us about cosmology. I will also discuss the implications of this and new cosmological experiments for better understanding our theory of gravity.

  14. Modified gravity (MOG), the speed of gravitational radiation and the event GW170817/GRB170817A

    NASA Astrophysics Data System (ADS)

    Green, M. A.; Moffat, J. W.; Toth, V. T.

    2018-05-01

    Modified gravity (MOG) is a covariant, relativistic, alternative gravitational theory whose field equations are derived from an action that supplements the spacetime metric tensor with vector and scalar fields. Both gravitational (spin 2) and electromagnetic waves travel on null geodesics of the theory's one metric. MOG satisfies the weak equivalence principle and is consistent with observations of the neutron star merger and gamma ray burster event GW170817/GRB170817A.

  15. N-body simulations in modified Newtonian dynamics

    NASA Astrophysics Data System (ADS)

    Nipoti, C.; Londrillo, P.; Ciotti, L.

    We describe some results obtained with N-MODY, a code for N-body simulations of collisionless stellar systems in modified Newtonian dynamics (MOND). We found that a few fundamental dynamical processes are profoundly different in MOND and in Newtonian gravity with dark matter. In particular, violent relaxation, phase mixing and galaxy merging take significantly longer in MOND than in Newtonian gravity, while dynamical friction is more effective in a MOND system than in an equivalent Newtonian system with dark matter.

  16. Ultra faint dwarf galaxies: an arena for testing dark matter versus modified gravity

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Lin, Weikang; Ishak, Mustapha, E-mail: wxl123830@utdallas.edu, E-mail: mishak@utdallas.edu

    2016-10-01

    The scenario consistent with a wealth of observations for the missing mass problem is that of weakly interacting dark matter particles. However, arguments or proposals for a Newtonian or relativistic modified gravity scenario continue to be made. A distinguishing characteristic between the two scenarios is that dark matter particles can produce a gravitational effect, in principle, without the need of baryons while this is not the case for the modified gravity scenario where such an effect must be correlated with the amount of baryonic matter. We consider here ultra-faint dwarf (UFD) galaxies as a promising arena to test the twomore » scenarios based on the above assertion. We compare the correlation of the luminosity with the velocity dispersion between samples of UFD and non-UFD galaxies, finding a significant loss of correlation for UFD galaxies. For example, we find for 28 non-UFD galaxies a strong correlation coefficient of −0.688 which drops to −0.077 for the 23 UFD galaxies. Incoming and future data will determine whether the observed stochasticity for UFD galaxies is physical or due to systematics in the data. Such a loss of correlation (if it is to persist) is possible and consistent with the dark matter scenario for UFD galaxies but would constitute a new challenge for the modified gravity scenario.« less

  17. Galaxy cluster lensing masses in modified lensing potentials

    DOE PAGES

    Barreira, Alexandre; Li, Baojiu; Jennings, Elise; ...

    2015-10-28

    In this study, we determine the concentration–mass relation of 19 X-ray selected galaxy clusters from the Cluster Lensing and Supernova Survey with Hubble survey in theories of gravity that directly modify the lensing potential. We model the clusters as Navarro–Frenk–White haloes and fit their lensing signal, in the Cubic Galileon and Nonlocal gravity models, to the lensing convergence profiles of the clusters. We discuss a number of important issues that need to be taken into account, associated with the use of non-parametric and parametric lensing methods, as well as assumptions about the background cosmology. Our results show that the concentrationmore » and mass estimates in the modified gravity models are, within the error bars, the same as in Λ cold dark matter. This result demonstrates that, for the Nonlocal model, the modifications to gravity are too weak at the cluster redshifts, and for the Galileon model, the screening mechanism is very efficient inside the cluster radius. However, at distances ~ [2–20] Mpc/h from the cluster centre, we find that the surrounding force profiles are enhanced by ~ 20–40% in the Cubic Galileon model. This has an impact on dynamical mass estimates, which means that tests of gravity based on comparisons between lensing and dynamical masses can also be applied to the Cubic Galileon model.« less

  18. Lensing-induced morphology changes in CMB temperature maps in modified gravity theories

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Munshi, D.; Coles, P.; Hu, B.

    2016-04-01

    Lensing of the Cosmic Microwave Background (CMB) changes the morphology of pattern of temperature fluctuations, so topological descriptors such as Minkowski Functionals can probe the gravity model responsible for the lensing. We show how the recently introduced two-to-two and three-to-one kurt-spectra (and their associated correlation functions), which depend on the power spectrum of the lensing potential, can be used to probe modified gravity theories such as f ( R ) theories of gravity and quintessence models. We also investigate models based on effective field theory, which include the constant-Ω model, and low-energy Hořava theories. Estimates of the cumulative signal-to-noise formore » detection of lensing-induced morphology changes, reaches O(10{sup 3}) for the future planned CMB polarization mission COrE{sup +}. Assuming foreground removal is possible to ℓ{sub max}=3000, we show that many modified gravity theories can be rejected with a high level of significance, making this technique comparable in power to galaxy weak lensing or redshift surveys. These topological estimators are also useful in distinguishing lensing from other scattering secondaries at the level of the four-point function or trispectrum. Examples include the kinetic Sunyaev-Zel'dovich (kSZ) effect which shares, with lensing, a lack of spectral distortion. We also discuss the complication of foreground contamination from unsubtracted point sources.« less

  19. Testing local Lorentz invariance with short-range gravity

    DOE PAGES

    Kostelecký, V. Alan; Mewes, Matthew

    2017-01-10

    The Newton limit of gravity is studied in the presence of Lorentz-violating gravitational operators of arbitrary mass dimension. The linearized modified Einstein equations are obtained and the perturbative solutions are constructed and characterized. We develop a formalism for data analysis in laboratory experiments testing gravity at short range and demonstrate that these tests provide unique sensitivity to deviations from local Lorentz invariance.

  20. Crossing of the phantom divide using tachyon-Gauss-Bonnet gravity

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Sadeghi, J.; Banijamali, A.; Milani, F.

    2009-06-15

    In this paper we consider two models. First, we study tachyon-Gauss-Bonnet gravity and obtain the condition of the equation of state crossing -1. Second, we discuss the modified Gauss-Bonnet gravity with the tachyon field and show the condition of {omega} crossing -1. Also, we plot figures for {omega} numerically in special potential and coupling function.

  1. [Gravity resistance, another graviresponse in plants--function of anti-gravitational polysaccharides].

    PubMed

    Hoson, Takayuki; Wakabayashi, Kazuyuki; Soga, Kouichi

    2003-08-01

    The involvement of anti-gravitational polysaccharides in gravity resistance, one of two major gravity responses in plants, was discussed. In dicotyledons, xyloglucans are the only cell wall polysaccharides, whose level, molecular size, and metabolic turnover were modified under both hypergravity and microgravity conditions, suggesting that xyloglucans act as anti-gravitational polysaccharides. In monocotyledonous Poaceae, (1-->3),(1-->4)-beta glucans, instead of xyloglucans, were shown to play a role as anti-gravitational polysaccharides. These polysaccharides are also involved in plant responses to other environmental factors, such as light and temperature, and to some phytohormones, such as auxin and ethylene. Thus, the type of anti-gravitational polysaccharides is different between dicotyledons and Poaceae, but such polysaccharides are universally involved in plant responses to environmental and hormonal signals. In gravity resistance, the gravity signal may be received by the plasma membrane mechanoreceptors, transformed and transduced within each cell, and then may modify the processes of synthesis and secretion of the anti-gravitational polysaccharides and the cell wall enzymes responsible for their degradation, as well as the apoplastic pH, leading to the cell wall reinforcement. A series of events inducing gravity resistance are quite independent of those leading to gravitropism.

  2. The Role of Photoblogs in Social Studies Classroom: Learning about the People of the Civil War

    ERIC Educational Resources Information Center

    Barrow, Elizabeth; Anderson, Janice; Horner, Martinette

    2017-01-01

    Using the of Humans of New York photoblog concept, the exemplar lesson plan described in this article incorporated technology and the replacement, amplification, and transformation framework to modify a traditional social studies lesson on the American Civil War into an engaging and inquiry-based lesson. Students researched individuals who lived…

  3. Testing Modified Gravity Theories via Wide Binaries and GAIA

    NASA Astrophysics Data System (ADS)

    Pittordis, Charalambos; Sutherland, Will

    2018-06-01

    The standard ΛCDM model based on General Relativity (GR) including cold dark matter (CDM) is very successful at fitting cosmological observations, but recent non-detections of candidate dark matter (DM) particles mean that various modified-gravity theories remain of significant interest. The latter generally involve modifications to GR below a critical acceleration scale ˜10-10 m s-2. Wide-binary (WB) star systems with separations ≳ 5 kAU provide an interesting test for modified gravity, due to being in or near the low-acceleration regime and presumably containing negligible DM. Here, we explore the prospects for new observations pending from the GAIA spacecraft to provide tests of GR against MOND or TeVes-like theories in a regime only partially explored to date. In particular, we find that a histogram of (3D) binary relative velocities, relative to equilibrium circular velocity predicted from the (2D) projected separation predicts a rather sharp feature in this distribution for standard gravity, with an 80th (90th) percentile value close to 1.025 (1.14) with rather weak dependence on the eccentricity distribution. However, MOND/TeVeS theories produce a shifted distribution, with a significant increase in these upper percentiles. In MOND-like theories without an external field effect, there are large shifts of order unity. With the external field effect included, the shifts are considerably reduced to ˜0.04 - 0.08, but are still potentially detectable statistically given reasonably large samples and good control of contaminants. In principle, followup of GAIA-selected wide binaries with ground-based radial velocities accurate to ≲ 0.03 { km s^{-1}} should be able to produce an interesting new constraint on modified-gravity theories.

  4. New post-Newtonian parameter to test Chern-Simons gravity.

    PubMed

    Alexander, Stephon; Yunes, Nicolas

    2007-12-14

    We study Chern-Simons (CS) gravity in the parametrized post-Newtonian (PPN) framework through a weak-field solution of the modified field equations. We find that CS gravity possesses the same PPN parameters as general relativity, except for the inclusion of a new term, proportional to the CS coupling and the curl of the PPN vector potential. This new term leads to a modification of frame dragging and gyroscopic precession and we provide an estimate of its size. This correction might be used in experiments, such as Gravity Probe B, to bound CS gravity and test string theory.

  5. Detection of Directions of Gravity by Organisms and Contributions to SmaggIce

    NASA Technical Reports Server (NTRS)

    Dill, Loren H.

    2003-01-01

    Research covers the following: In the Microgravity Environment and Telescience Branch, a study wasI extended thar focused upon a flagellated alga or other swimming microbe and the effect of gravity upon its swimming direction. It has long been known that many organisms tend to swim up or down on Earth. How organisms detect the direction of gravity is a question not fully resolved. The response of such organisms to reduced gravity or the absence of gravity is also of interest, particularly because the expected modified behavior may affect the health of astronauts.

  6. Gauss-Bonnet cosmology unifying late and early-time acceleration eras with intermediate eras

    NASA Astrophysics Data System (ADS)

    Oikonomou, V. K.

    2016-07-01

    In this paper we demonstrate that with vacuum F(G) gravity it is possible to describe the unification of late and early-time acceleration eras with the radiation and matter domination era. The Hubble rate of the unified evolution contains two mild singularities, so called Type IV singularities, and the evolution itself has some appealing features, such as the existence of a deceleration-acceleration transition at late times. We also address quantitatively a fundamental question related to modified gravity models description of cosmological evolution: Is it possible for all modified gravity descriptions of our Universe evolution, to produce a nearly scale invariant spectrum of primordial curvature perturbations? As we demonstrate, the answer for the F(G) description is no, since the resulting power spectrum is not scale invariant, in contrast to the F(R) description studied in the literature. Therefore, although the cosmological evolution can be realized in the context of vacuum F(G) gravity, the evolution is not compatible with the observational data, in contrast to the F(R) gravity description of the same cosmological evolution.

  7. Stealth configurations in vector-tensor theories of gravity

    NASA Astrophysics Data System (ADS)

    Chagoya, Javier; Tasinato, Gianmassimo

    2018-01-01

    Studying the physics of compact objects in modified theories of gravity is important for understanding how future observations can test alternatives to General Relativity. We consider a subset of vector-tensor Galileon theories of gravity characterized by new symmetries, which can prevent the propagation of the vector longitudinal polarization, even in absence of Abelian gauge invariance. We investigate new spherically symmetric and slowly rotating solutions for these systems, including an arbitrary matter Lagrangian. We show that, under certain conditions, there always exist stealth configurations whose geometry coincides with solutions of Einstein gravity coupled with the additional matter. Such solutions have a non-trivial profile for the vector field, characterized by independent integration constants, which extends to asymptotic infinity. We interpret our findings in terms of the symmetries and features of the original vector-tensor action, and on the number of degrees of freedom that it propagates. These results are important to eventually describe gravitationally bound configurations in modified theories of gravity, such as black holes and neutron stars, including realistic matter fields forming or surrounding the object.

  8. The Soccer-Ball Problem

    NASA Astrophysics Data System (ADS)

    Hossenfelder, Sabine

    2014-07-01

    The idea that Lorentz-symmetry in momentum space could be modified but still remain observer-independent has received quite some attention in the recent years. This modified Lorentz-symmetry, which has been argued to arise in Loop Quantum Gravity, is being used as a phenomenological model to test possibly observable effects of quantum gravity. The most pressing problem in these models is the treatment of multi-particle states, known as the 'soccer-ball problem'. This article briefly reviews the problem and the status of existing solution attempts.

  9. Stability of cylindrical thin shell wormholes supported by MGCG in f(R) gravity

    NASA Astrophysics Data System (ADS)

    Eid, A.

    2018-02-01

    In the framework of f(R) modified theory of gravity, the dynamical equations of motion of a cylindrical thin shell wormholes supported by a modified generalized Chaplygin gas are constructed, using the cut and paste scheme (Darmois Israel formalism). The mechanical stability analysis of a cylindrical thin shell wormhole is discussed using a linearized radial perturbation around static solutions at the wormhole throat. The presence of stable static solutions depends on the suitable values of some parameters of dynamical shell.

  10. Evaluating Material Flammability in Microgravity and Martian Gravity Compared to the NASA Standard Normal Gravity Test

    NASA Technical Reports Server (NTRS)

    Oslon, Sandra. L.; Ferkul, Paul

    2012-01-01

    Drop tower tests are conducted at Martian gravity to determine the flammability of three materials compared to previous tests in other normal gravity and reduced gravity environments. The comparison is made with consideration of a modified NASA standard test protocol. Material flammability limits in the different gravity and flow environments are tabulated to determine the factor of safety associated with normal gravity flammability screening. Previous testing at microgravity and Lunar gravity indicated that some materials burned to lower oxygen concentrations in low gravity than in normal gravity, although the low g extinction limit criteria are not the same as 1g due to time constraints in drop testing. Similarly, the data presented in this paper for Martian gravity suggest that there is a gravity level below Earth s at which materials burn more readily than on Earth. If proven for more materials, this may indicate the need to include a factor of safety on 1g flammability limits.

  11. I've Just Seen a Face: Portraits. [Lesson Plan].

    ERIC Educational Resources Information Center

    National Endowment for the Humanities (NFAH), Washington, DC.

    Image has always been important to the powerful. Their portraits have traditionally been designed to impress people with the gravity of the subject, but changing sensibilities and media have tended to introduce more intimacy and spontaneity. Creating visual and literary representations of people has proved to be an enduring human activity. This…

  12. Gravity Can Do What?

    ERIC Educational Resources Information Center

    Schnittka, Christine

    2017-01-01

    Many students (and adults) do not understand a basic tenet of energy literacy: how electricity is produced. They do not know how coal or other fossil fuels are used to make electricity, nor do they understand how nuclear power, hydroelectric power, and wind power work. The author developed a series of lessons to help students understand how…

  13. Testing general relativity with compact-body orbits: a modified Einstein–Infeld–Hoffmann framework

    NASA Astrophysics Data System (ADS)

    Will, Clifford M.

    2018-04-01

    We describe a general framework for analyzing orbits of systems containing compact objects (neutron stars or black holes) in a class of Lagrangian-based alternative theories of gravity that also admit a global preferred reference frame. The framework is based on a modified Einstein–Infeld–Hoffmann (EIH) formalism developed by Eardley and by Will, generalized to include the possibility of Lorentz-violating, preferred-frame effects. It uses a post-Newtonian N-body Lagrangian with arbitrary parameters that depend on the theory of gravity and on ‘sensitivities’ that encode the effects of the bodies’ internal structure on their motion. We determine the modified EIH parameters for the Einstein-Æther and Khronometric vector-tensor theories of gravity. We find the effects of motion relative to a preferred universal frame on the orbital parameters of binary systems containing neutron stars, such as a class of ultra-circular pulsar-white dwarf binaries; the amplitudes of the effects depend upon ‘strong-field’ preferred-frame parameters \\hatα1 and \\hatα2 , which we relate to the fundamental modified EIH parameters. We also determine the amplitude of the ‘Nordtvedt effect’ in a triple system containing the pulsar J0337+1715 in terms of the modified EIH parameters.

  14. Dark energy and modified gravity in the Effective Field Theory of Large-Scale Structure

    NASA Astrophysics Data System (ADS)

    Cusin, Giulia; Lewandowski, Matthew; Vernizzi, Filippo

    2018-04-01

    We develop an approach to compute observables beyond the linear regime of dark matter perturbations for general dark energy and modified gravity models. We do so by combining the Effective Field Theory of Dark Energy and Effective Field Theory of Large-Scale Structure approaches. In particular, we parametrize the linear and nonlinear effects of dark energy on dark matter clustering in terms of the Lagrangian terms introduced in a companion paper [1], focusing on Horndeski theories and assuming the quasi-static approximation. The Euler equation for dark matter is sourced, via the Newtonian potential, by new nonlinear vertices due to modified gravity and, as in the pure dark matter case, by the effects of short-scale physics in the form of the divergence of an effective stress tensor. The effective fluid introduces a counterterm in the solution to the matter continuity and Euler equations, which allows a controlled expansion of clustering statistics on mildly nonlinear scales. We use this setup to compute the one-loop dark-matter power spectrum.

  15. A modified oxic-settling-anaerobic activated sludge process using gravity thickening for excess sludge reduction

    NASA Astrophysics Data System (ADS)

    Wang, Jun; Li, Shi-Yu; Jiang, Feng; Wu, Ke; Liu, Guang-Li; Lu, Hui; Chen, Guang-Hao

    2015-09-01

    Oxic-settling-anaerobic process (OSA) was known as a cost-effective way to reduce the excess sludge production with simple upgrade of conventional activated sludge process (CAS). A low oxidation-reduction potential (ORP) level was the key factor to sludge decay and lysis in the sludge holding tank of the OSA process. However, the ORP control with nitrogen purge or chemical dosing in the OSA process would induce extra expense and complicate the operation. Hence, in this study, a sludge holding tank using gravity thickening was applied to OSA process to reduce the excess sludge production without any ORP control. Results showed that the modified OSA process not only reduced the excess sludge production effectively but also improved the sludge settleability without affected the treatment capacity. The reduction of the excess sludge production in the modified OSA process resulted from interactions among lots of factors. The key element of the process was the gravity thickening sludge holding tank.

  16. The reconstruction of f(ϕ)R and mimetic gravity from viable slow-roll inflation

    NASA Astrophysics Data System (ADS)

    Odintsov, S. D.; Oikonomou, V. K.

    2018-04-01

    In this work, we extend the bottom-up reconstruction framework of F (R) gravity to other modified gravities, and in particular for f (ϕ) R and mimetic F (R) gravities. We investigate which are the important conditions in order for the method to work, and we study several viable cosmological evolutions, focusing on the inflationary era. Particularly, for the f (ϕ) R theory case, we specify the functional form of the Hubble rate and of the scalar-to-tensor ratio as a function of the e-foldings number and accordingly, the rest of the physical quantities and also the slow-roll and the corresponding observational indices can be calculated. The same method is applied in the mimetic F (R) gravity case, and in both cases we thoroughly analyze the resulting free parameter space, in order to show that the viability of the models presented is guaranteed and secondly that there is a wide range of values of the free parameters for which the viability of the models occurs. In addition, the reconstruction method is also studied in the context of mimetic F (R) = R gravity. As we demonstrate, the resulting theory is viable, and also in this case, only the scalar-to-tensor ratio needs to be specified, since the rest follow from this condition. Finally, we discuss in brief how the reconstruction method could function for other modified gravities.

  17. Beyond δ : Tailoring marked statistics to reveal modified gravity

    NASA Astrophysics Data System (ADS)

    Valogiannis, Georgios; Bean, Rachel

    2018-01-01

    Models that seek to explain cosmic acceleration through modifications to general relativity (GR) evade stringent Solar System constraints through a restoring, screening mechanism. Down-weighting the high-density, screened regions in favor of the low density, unscreened ones offers the potential to enhance the amount of information carried in such modified gravity models. In this work, we assess the performance of a new "marked" transformation and perform a systematic comparison with the clipping and logarithmic transformations, in the context of Λ CDM and the symmetron and f (R ) modified gravity models. Performance is measured in terms of the fractional boost in the Fisher information and the signal-to-noise ratio (SNR) for these models relative to the statistics derived from the standard density distribution. We find that all three statistics provide improved Fisher boosts over the basic density statistics. The model parameters for the marked and clipped transformation that best enhance signals and the Fisher boosts are determined. We also show that the mark is useful both as a Fourier and real-space transformation; a marked correlation function also enhances the SNR relative to the standard correlation function, and can on mildly nonlinear scales show a significant difference between the Λ CDM and the modified gravity models. Our results demonstrate how a series of simple analytical transformations could dramatically increase the predicted information extracted on deviations from GR, from large-scale surveys, and give the prospect for a much more feasible potential detection.

  18. Comparing dark matter models, modified Newtonian dynamics and modified gravity in accounting for galaxy rotation curves

    NASA Astrophysics Data System (ADS)

    Li, Xin; Tang, Li; Lin, Hai-Nan

    2017-05-01

    We compare six models (including the baryonic model, two dark matter models, two modified Newtonian dynamics models and one modified gravity model) in accounting for galaxy rotation curves. For the dark matter models, we assume NFW profile and core-modified profile for the dark halo, respectively. For the modified Newtonian dynamics models, we discuss Milgrom’s MOND theory with two different interpolation functions, the standard and the simple interpolation functions. For the modified gravity, we focus on Moffat’s MSTG theory. We fit these models to the observed rotation curves of 9 high-surface brightness and 9 low-surface brightness galaxies. We apply the Bayesian Information Criterion and the Akaike Information Criterion to test the goodness-of-fit of each model. It is found that none of the six models can fit all the galaxy rotation curves well. Two galaxies can be best fitted by the baryonic model without involving nonluminous dark matter. MOND can fit the largest number of galaxies, and only one galaxy can be best fitted by the MSTG model. Core-modified model fits about half the LSB galaxies well, but no HSB galaxies, while the NFW model fits only a small fraction of HSB galaxies but no LSB galaxies. This may imply that the oversimplified NFW and core-modified profiles cannot model the postulated dark matter haloes well. Supported by Fundamental Research Funds for the Central Universities (106112016CDJCR301206), National Natural Science Fund of China (11305181, 11547305 and 11603005), and Open Project Program of State Key Laboratory of Theoretical Physics, Institute of Theoretical Physics, Chinese Academy of Sciences, China (Y5KF181CJ1)

  19. Speeding up N-body simulations of modified gravity: chameleon screening models

    NASA Astrophysics Data System (ADS)

    Bose, Sownak; Li, Baojiu; Barreira, Alexandre; He, Jian-hua; Hellwing, Wojciech A.; Koyama, Kazuya; Llinares, Claudio; Zhao, Gong-Bo

    2017-02-01

    We describe and demonstrate the potential of a new and very efficient method for simulating certain classes of modified gravity theories, such as the widely studied f(R) gravity models. High resolution simulations for such models are currently very slow due to the highly nonlinear partial differential equation that needs to be solved exactly to predict the modified gravitational force. This nonlinearity is partly inherent, but is also exacerbated by the specific numerical algorithm used, which employs a variable redefinition to prevent numerical instabilities. The standard Newton-Gauss-Seidel iterative method used to tackle this problem has a poor convergence rate. Our new method not only avoids this, but also allows the discretised equation to be written in a form that is analytically solvable. We show that this new method greatly improves the performance and efficiency of f(R) simulations. For example, a test simulation with 5123 particles in a box of size 512 Mpc/h is now 5 times faster than before, while a Millennium-resolution simulation for f(R) gravity is estimated to be more than 20 times faster than with the old method. Our new implementation will be particularly useful for running very high resolution, large-sized simulations which, to date, are only possible for the standard model, and also makes it feasible to run large numbers of lower resolution simulations for covariance analyses. We hope that the method will bring us to a new era for precision cosmological tests of gravity.

  20. Disentangling dark energy and cosmic tests of gravity from weak lensing systematics

    NASA Astrophysics Data System (ADS)

    Laszlo, Istvan; Bean, Rachel; Kirk, Donnacha; Bridle, Sarah

    2012-06-01

    We consider the impact of key astrophysical and measurement systematics on constraints on dark energy and modifications to gravity on cosmic scales. We focus on upcoming photometric ‘stage III’ and ‘stage IV’ large-scale structure surveys such as the Dark Energy Survey (DES), the Subaru Measurement of Images and Redshifts survey, the Euclid survey, the Large Synoptic Survey Telescope (LSST) and Wide Field Infra-Red Space Telescope (WFIRST). We illustrate the different redshift dependencies of gravity modifications compared to intrinsic alignments, the main astrophysical systematic. The way in which systematic uncertainties, such as galaxy bias and intrinsic alignments, are modelled can change dark energy equation-of-state parameter and modified gravity figures of merit by a factor of 4. The inclusion of cross-correlations of cosmic shear and galaxy position measurements helps reduce the loss of constraining power from the lensing shear surveys. When forecasts for Planck cosmic microwave background and stage IV surveys are combined, constraints on the dark energy equation-of-state parameter and modified gravity model are recovered, relative to those from shear data with no systematic uncertainties, provided fewer than 36 free parameters in total are used to describe the galaxy bias and intrinsic alignment models as a function of scale and redshift. While some uncertainty in the intrinsic alignment (IA) model can be tolerated, it is going to be important to be able to parametrize IAs well in order to realize the full potential of upcoming surveys. To facilitate future investigations, we also provide a fitting function for the matter power spectrum arising from the phenomenological modified gravity model we consider.

  1. Constraints on deviations from ΛCDM within Horndeski gravity

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Bellini, Emilio; Cuesta, Antonio J.; Jimenez, Raul

    2016-02-01

    Recent anomalies found in cosmological datasets such as the low multipoles of the Cosmic Microwave Background or the low redshift amplitude and growth of clustering measured by e.g., abundance of galaxy clusters and redshift space distortions in galaxy surveys, have motivated explorations of models beyond standard ΛCDM. Of particular interest are models where general relativity (GR) is modified on large cosmological scales. Here we consider deviations from ΛCDM+GR within the context of Horndeski gravity, which is the most general theory of gravity with second derivatives in the equations of motion. We adopt a parametrization in which the four additional Horndeskimore » functions of time α{sub i}(t) are proportional to the cosmological density of dark energy Ω{sub DE}(t). Constraints on this extended parameter space using a suite of state-of-the art cosmological observations are presented for the first time. Although the theory is able to accommodate the low multipoles of the Cosmic Microwave Background and the low amplitude of fluctuations from redshift space distortions, we find no significant tension with ΛCDM+GR when performing a global fit to recent cosmological data and thus there is no evidence against ΛCDM+GR from an analysis of the value of the Bayesian evidence ratio of the modified gravity models with respect to ΛCDM, despite introducing extra parameters. The posterior distribution of these extra parameters that we derive return strong constraints on any possible deviations from ΛCDM+GR in the context of Horndeski gravity. We illustrate how our results can be applied to a more general frameworks of modified gravity models.« less

  2. Constraining Modified Theories of Gravity with Gravitational-Wave Stochastic Backgrounds

    NASA Astrophysics Data System (ADS)

    Maselli, Andrea; Marassi, Stefania; Ferrari, Valeria; Kokkotas, Kostas; Schneider, Raffaella

    2016-08-01

    The direct discovery of gravitational waves has finally opened a new observational window on our Universe, suggesting that the population of coalescing binary black holes is larger than previously expected. These sources produce an unresolved background of gravitational waves, potentially observable by ground-based interferometers. In this Letter we investigate how modified theories of gravity, modeled using the parametrized post-Einsteinian formalism, affect the expected signal, and analyze the detectability of the resulting stochastic background by current and future ground-based interferometers. We find the constraints that Advanced LIGO would be able to set on modified theories, showing that they may significantly improve the current bounds obtained from astrophysical observations of binary pulsars.

  3. Centrifuges in gravitational physiology research

    NASA Technical Reports Server (NTRS)

    Ballard, Rodney W.; Davies, Phil; Fuller, Charles A.

    1993-01-01

    Data from space flight and ground based experiments have clearly demonstrated the importance of Earth gravity for normal physiological function in man and animals. Gravitational Physiology is concerned with the role and influence of gravity on physiological systems. Research in this field examines how we perceive and respond to gravity and the mechanisms underlying these responses. Inherent in our search for answers to these questions is the ability to alter gravity, which is not physically possible without leaving Earth. However, useful experimental paradigms have been to modify the perceived force of gravity by changing either the orientation of subjects to the gravity vector (i.e., postural changes) or by applying inertial forces to augment the magnitude of the gravity vector. The later technique has commonly been used by applying centripetal force via centrifugation.

  4. Matter scattering in quadratic gravity and unitarity

    NASA Astrophysics Data System (ADS)

    Abe, Yugo; Inami, Takeo; Izumi, Keisuke; Kitamura, Tomotaka

    2018-03-01

    We investigate the ultraviolet (UV) behavior of two-scalar elastic scattering with graviton exchanges in higher-curvature gravity theory. In Einstein gravity, matter scattering is shown not to satisfy the unitarity bound at tree level at high energy. Among some of the possible directions for the UV completion of Einstein gravity, such as string theory, modified gravity, and inclusion of high-mass/high-spin states, we take R_{μν}^2 gravity coupled to matter. We show that matter scattering with graviton interactions satisfies the unitarity bound at high energy, even with negative norm states due to the higher-order derivatives of metric components. The difference in the unitarity property of these two gravity theories is probably connected to that in another UV property, namely, the renormalizability property of the two.

  5. Nonsingular rainbow universes

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Awad, Adel; Ali, Ahmed Farag; Majumder, Barun, E-mail: aawad@zewailcity.edu.eg, E-mail: ahmed.ali@fsc.bu.edu.eg, E-mail: barunbasanta@iitgn.ac.in

    2013-10-01

    In this work, we study FRW cosmologies in the context of gravity rainbow. We discuss the general conditions for having a nonsingular FRW cosmology in gravity rainbow. We propose that gravity rainbow functions can be fixed using two known modified dispersion relation (MDR), which have been proposed in literature. The first MDR was introduced by Amelino-Camelia, et el. in [9] and the second was introduced by Magueijo and Smolin in [24]. Studying these FRW-like cosmologies, after fixing the gravity rainbow functions, leads to nonsingular solutions which can be expressed in exact forms.

  6. Einstein-Yang-Mills-Dirac systems from the discretized Kaluza-Klein theory

    NASA Astrophysics Data System (ADS)

    Wali, Kameshwar; Viet, Nguyen Ali

    2017-01-01

    A unified theory of the non-Abelian gauge interactions with gravity in the framework of a discretized Kaluza-Klein theory is constructed with a modified Dirac operator and wedge product. All the couplings of chiral spinors to the non-Abelian gauge fields emerge naturally as components of the coupling of the chiral spinors in the generalized gravity together with some new interactions. In particular, the currently prevailing gravity-QCD quark and gravity-electroweak-quark and lepton models are shown to follow as special cases of the general framework.

  7. Teleparallel equivalent of Lovelock gravity

    NASA Astrophysics Data System (ADS)

    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.

  8. Beyond the growth rate of cosmic structure: Testing modified gravity models with an extra degree of freedom

    NASA Astrophysics Data System (ADS)

    Burrage, Clare; Parkinson, David; Seery, David

    2017-08-01

    In "modified" gravity the observed acceleration of the universe is explained by changing the gravitational force law or the number of degrees of freedom in the gravitational sector. Both possibilities can be tested by measurements of cosmological structure formation. In this paper we elaborate the details of such tests using the Galileon model as a case study. We pay attention to the possibility that each new degree of freedom may have stochastically independent initial conditions, generating different types of potential well in the early universe and breaking complete correlation between density and velocity power spectra. This "stochastic bias" can confuse schemes to parametrize the predictions of modified gravity models, such as the use of the growth parameter f alone. Using data from the WiggleZ Dark Energy Survey we show that it will be possible to obtain constraints using information about the cosmological-scale force law embedded in the multipole power spectra of redshift-space distortions. As an example, we obtain an upper limit on the strength of the conformal coupling to matter in the cubic Galileon model, giving |1 /M |≲200 /MP . This allows the fifth-force to be stronger than gravity, but is consistent with zero coupling.

  9. Modified Einstein's gravity as a possible missing link between sub- and super-Chandrasekhar type Ia supernovae

    NASA Astrophysics Data System (ADS)

    Das, Upasana; Mukhopadhyay, Banibrata

    2015-05-01

    We explore the effect of modification to Einstein's gravity in white dwarfs for the first time in the literature, to the best of our knowledge. This leads to significantly sub- and super-Chandrasekhar limiting masses of white dwarfs, determined by a single model parameter. On the other hand, type Ia supernovae (SNeIa), a key to unravel the evolutionary history of the universe, are believed to be triggered in white dwarfs having mass close to the Chandrasekhar limit. However, observations of several peculiar, under- and over-luminous SNeIa argue for exploding masses widely different from this limit. We argue that explosions of the modified gravity induced sub- and super-Chandrasekhar limiting mass white dwarfs result in under- and over-luminous SNeIa respectively, thus unifying these two apparently disjoint sub-classes and, hence, serving as a missing link. Our discovery raises two fundamental questions. Is the Chandrasekhar limit unique? Is Einstein's gravity the ultimate theory for understanding astronomical phenomena? Both the answers appear to be no!

  10. MODELING THE NONLINEAR CLUSTERING IN MODIFIED GRAVITY MODELS. I. A FITTING FORMULA FOR THE MATTER POWER SPECTRUM OF f(R) GRAVITY

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Zhao, Gong-Bo, E-mail: gongbo@icosmology.info; Institute of Cosmology and Gravitation, University of Portsmouth, Portsmouth PO1 3FX

    2014-04-01

    Based on a suite of N-body simulations of the Hu-Sawicki model of f(R) gravity with different sets of model and cosmological parameters, we develop a new fitting formula with a numeric code, MGHalofit, to calculate the nonlinear matter power spectrum P(k) for the Hu-Sawicki model. We compare the MGHalofit predictions at various redshifts (z ≤ 1) to the f(R) simulations and find that the relative error of the MGHalofit fitting formula of P(k) is no larger than 6% at k ≤ 1 h Mpc{sup –1} and 12% at k in (1, 10] h Mpc{sup –1}, respectively. Based on a sensitivitymore » study of an ongoing and a future spectroscopic survey, we estimate the detectability of a signal of modified gravity described by the Hu-Sawicki model using the power spectrum up to quasi-nonlinear scales.« less

  11. An exact solution for a rotating black hole in modified gravity

    NASA Astrophysics Data System (ADS)

    Filippini, Francesco; Tasinato, Gianmassimo

    2018-01-01

    Exact solutions describing rotating black holes can offer important tests for alternative theories of gravity, motivated by the dark energy and dark matter problems. We present an analytic rotating black hole solution for a class of vector-tensor theories of modified gravity, valid for arbitrary values of the rotation parameter. The new configuration is characterised by parametrically large deviations from the Kerr-Newman geometry, controlled by non-minimal couplings between vectors and gravity. It has an oblate horizon in Boyer-Lindquist coordinates, and it can rotate more rapidly and have a larger ergosphere than black holes in General Relativity (GR) with the same asymptotic properties. We analytically investigate the features of the innermost stable circular orbits for massive objects on the equatorial plane, and show that stable orbits lie further away from the black hole horizon with respect to rotating black holes in GR. We also comment on possible applications of our findings for the extraction of rotational energy from the black hole.

  12. MOND as a regime of quantum gravity

    NASA Astrophysics Data System (ADS)

    Smolin, Lee

    2017-10-01

    We propose that there is a regime of quantum gravity phenomena, for the case that the cosmological constant is small and positive, which concerns physics at temperatures below the de Sitter temperature, or length scales larger than the horizon. We observe that the standard form of the equivalence principle does not apply in this regime; we consider instead that a weakened form of the equivalence principle might hold in which the ratio of gravitational to inertial mass is a function of environmental parameters. We consider possible principles to determine that function. These lead to behavior that, in the limit of ℏ→0 and c →∞ , reproduces the modifications of Newtonian dynamics first proposed by Milgrom. Thus modified newtonian dynamics is elucidated as coding the physics of a novel regime of quantum gravity phenomena. We propose also an effective description of this regime in terms of a bimetric theory, valid in the approximation where the metric is static. This predicts a new effect, which modifies gravity for radial motions.

  13. GR 20 parallel session A3: modified gravity

    NASA Astrophysics Data System (ADS)

    Hořava, Petr; Mohd, Arif; Melby-Thompson, Charles M.; Shawhan, Peter

    2014-05-01

    The parallel session (A3), on "Modified Gravity", enjoyed one on the largest number of abstract submissions (over 80), resulting in the selection of 24 oral presentations. The three short papers presented in the following sections are based on the session talks by Arif Mohd on thermodynamics of universal horizons in Einstein-Æther theory, Conformal anomalies in Hořava-Lifshitz gravity by Charles Melby-Thompson and detectability of scalar gravitational waves by LIGO and Virgo by Peter Shawhan. They have been selected as a representative sample, to illustrate some of the best in the remarkable and encouraging variety of topics discussed in the session—ranging from highly theoretical, to phenomenological, observational, and experimental—with all these areas playing an integral part in our quest to understand the limits of standard general relativity.

  14. Exploring the Use of Lesson Study to Develop Elementary Preservice Teachers' Pedagogical Content Knowledge for Teaching Nature of Science

    ERIC Educational Resources Information Center

    Akerson, Valarie L.; Pongsanon, Khemmawadee; Park Rogers, Meredith A.; Carter, Ingrid; Galindo, Enrique

    2017-01-01

    This study explored a modified version of Japanese Lesson Study to determine whether and how it influenced preservice elementary teachers in their abilities to deliver science lessons that included nature of science (NOS) to their own students. We used a case study approach that focused on one subset of a cohort of preservice elementary teachers…

  15. Linear and non-linear Modified Gravity forecasts with future surveys

    NASA Astrophysics Data System (ADS)

    Casas, Santiago; Kunz, Martin; Martinelli, Matteo; Pettorino, Valeria

    2017-12-01

    Modified Gravity theories generally affect the Poisson equation and the gravitational slip in an observable way, that can be parameterized by two generic functions (η and μ) of time and space. We bin their time dependence in redshift and present forecasts on each bin for future surveys like Euclid. We consider both Galaxy Clustering and Weak Lensing surveys, showing the impact of the non-linear regime, with two different semi-analytical approximations. In addition to these future observables, we use a prior covariance matrix derived from the Planck observations of the Cosmic Microwave Background. In this work we neglect the information from the cross correlation of these observables, and treat them as independent. Our results show that η and μ in different redshift bins are significantly correlated, but including non-linear scales reduces or even eliminates the correlation, breaking the degeneracy between Modified Gravity parameters and the overall amplitude of the matter power spectrum. We further apply a Zero-phase Component Analysis and identify which combinations of the Modified Gravity parameter amplitudes, in different redshift bins, are best constrained by future surveys. We extend the analysis to two particular parameterizations of μ and η and consider, in addition to Euclid, also SKA1, SKA2, DESI: we find in this case that future surveys will be able to constrain the current values of η and μ at the 2-5% level when using only linear scales (wavevector k < 0 . 15 h/Mpc), depending on the specific time parameterization; sensitivity improves to about 1% when non-linearities are included.

  16. Strategic career planning for physician-scientists.

    PubMed

    Shimaoka, Motomu

    2015-05-01

    Building a successful professional career in the physician-scientist realm is rewarding but challenging, especially in the dynamic and competitive environment of today's modern society. This educational review aims to provide readers with five important career development lessons drawn from the business and social science literatures. Lessons 1-3 describe career strategy, with a focus on promoting one's strengths while minimizing fixing one's weaknesses (Lesson 1); effective time management in the pursuit of long-term goals (Lesson 2); and the intellectual flexibility to abandon/modify previously made decisions while embracing emerging opportunities (Lesson 3). Lesson 4 explains how to maximize the alternative benefits of English-language fluency (i.e., functions such as signaling and cognition-enhancing capabilities). Finally, Lesson 5 discusses how to enjoy happiness and stay motivated in a harsh, zero-sum game society.

  17. No Presentism in Quantum Gravity

    NASA Astrophysics Data System (ADS)

    Wüthrich, Christian

    This essay offers a reaction to the recent resurgence of presentism in the philosophy of time. What is of particular interest in this renaissance is that a number of recent arguments supporting presentism are crafted in an untypically naturalistic vein, breathing new life into a metaphysics of time with a bad track record of co-habitation with modern physics. Against this trend, the present essay argues that the pressure on presentism exerted by special relativity and its core lesson of Lorentz symmetry cannot easily be shirked. A categorization of presentist responses to this pressure is offered. As a case in point, I analyze a recent argument by Monton (Presentism and quantum gravity, 263-280, 2006) presenting a case for the compatibility of presentism with quantum gravity. Monton claims that this compatibility arises because there are quantum theories of gravity that use fixed foliations of spacetime and that such fixed foliations provide a natural home for a metaphysically robust notion of the present. A careful analysis leaves Monton's argument wanting. In sum, the prospects of presentism to be alleviated from the stress applied by fundamental physics are faint.

  18. Kinetic models for batch ethanol production from sweet sorghum juice under normal and high gravity fermentations: Logistic and modified Gompertz models.

    PubMed

    Phukoetphim, Niphaphat; Salakkam, Apilak; Laopaiboon, Pattana; Laopaiboon, Lakkana

    2017-02-10

    The aim of this study was to model batch ethanol production from sweet sorghum juice (SSJ), under normal gravity (NG, 160g/L of total sugar) and high gravity (HG, 240g/L of total sugar) conditions with and without nutrient supplementation (9g/L of yeast extract), by Saccharomyces cerevisiae NP 01. Growth and ethanol production increased with increasing initial sugar concentration, and the addition of yeast extract enhanced both cell growth and ethanol production. From the results, either logistic or a modified Gompertz equation could be used to describe yeast growth, depending on information required. Furthermore, the modified Gompertz model was suitable for modeling ethanol production. Both the models fitted the data very well with coefficients of determination exceeding 0.98. The results clearly showed that these models can be employed in the development of ethanol production processes using SSJ under both NG and HG conditions. The models were also shown to be applicable to other ethanol fermentation systems employing pure and mixed sugars as carbon sources. Copyright © 2016 Elsevier B.V. All rights reserved.

  19. Terrestrial Sagnac delay constraining modified gravity models

    NASA Astrophysics Data System (ADS)

    Karimov, R. Kh.; Izmailov, R. N.; Potapov, A. A.; Nandi, K. K.

    2018-04-01

    Modified gravity theories include f(R)-gravity models that are usually constrained by the cosmological evolutionary scenario. However, it has been recently shown that they can also be constrained by the signatures of accretion disk around constant Ricci curvature Kerr-f(R0) stellar sized black holes. Our aim here is to use another experimental fact, viz., the terrestrial Sagnac delay to constrain the parameters of specific f(R)-gravity prescriptions. We shall assume that a Kerr-f(R0) solution asymptotically describes Earth's weak gravity near its surface. In this spacetime, we shall study oppositely directed light beams from source/observer moving on non-geodesic and geodesic circular trajectories and calculate the time gap, when the beams re-unite. We obtain the exact time gap called Sagnac delay in both cases and expand it to show how the flat space value is corrected by the Ricci curvature, the mass and the spin of the gravitating source. Under the assumption that the magnitude of corrections are of the order of residual uncertainties in the delay measurement, we derive the allowed intervals for Ricci curvature. We conclude that the terrestrial Sagnac delay can be used to constrain the parameters of specific f(R) prescriptions. Despite using the weak field gravity near Earth's surface, it turns out that the model parameter ranges still remain the same as those obtained from the strong field accretion disk phenomenon.

  20. Modified Process Reduces Porosity when Soldering in Reduced Gravity Environments

    NASA Technical Reports Server (NTRS)

    Watson, Kevin; Struk, Peter; Pettegrew, Richard; Downs, Robert; Haylett, Daniel

    2012-01-01

    A modified process yields lower levels of internal porosity for solder joints produced in reduced-gravity environments. The process incorporates both alternative materials and a modified procedure. The process provides the necessary cleaning action to enable effective bonding of the applied solder alloy with the materials to be joined. The modified process incorporates a commercially available liquid flux that is applied to the solder joint before heating with the soldering iron. It is subsequently heated with the soldering iron to activate the cleaning action of the flux and to evaporate most of the flux, followed by application of solder alloy in the form of commercially available solid solder wire (containing no flux). Continued heating ensures adequate flow of the solder alloy around and onto the materials to be joined. The final step is withdrawal of the soldering iron to allow alloy solidification and cooling of the solder joint.

  1. Goce and Its Role in Combined Global High Resolution Gravity Field Determination

    NASA Astrophysics Data System (ADS)

    Fecher, T.; Pail, R.; Gruber, T.

    2013-12-01

    Combined high-resolution gravity field models serve as a mandatory basis to describe static and dynamic processes in system Earth. Ocean dynamics can be modeled referring to a high-accurate geoid as reference surface, solid earth processes are initiated by the gravity field. Also geodetic disciplines such as height system determination depend on high-precise gravity field information. To fulfill the various requirements concerning resolution and accuracy, any kind of gravity field information, that means satellite as well as terrestrial and altimetric gravity field observations have to be included in one combination process. A key role is here reserved for GOCE observations, which contribute with its optimal signal content in the long to medium wavelength part and enable a more accurate gravity field determination than ever before especially in areas, where no high-accurate terrestrial gravity field observations are available, such as South America, Asia or Africa. For our contribution we prepare a combined high-resolution gravity field model up to d/o 720 based on full normal equation including recent GOCE, GRACE and terrestrial / altimetric data. For all data sets, normal equations are set up separately, relative weighted to each other in the combination step and solved. This procedure is computationally challenging and can only be performed using super computers. We put special emphasis on the combination process, for which we modified especially our procedure to include GOCE data optimally in the combination. Furthermore we modified our terrestrial/altimetric data sets, what should result in an improved outcome. With our model, in which we included the newest GOCE TIM4 gradiometry results, we can show how GOCE contributes to a combined gravity field solution especially in areas of poor terrestrial data coverage. The model is validated by independent GPS leveling data in selected regions as well as computation of the mean dynamic topography over the oceans. Further, we analyze the statistical error estimates derived from full covariance propagation and compare them with the absolute validation with independent data sets.

  2. Radiation of quantum black holes and modified uncertainty relation

    NASA Astrophysics Data System (ADS)

    Kamali, A. D.; Pedram, P.

    In this paper, using a deformed algebra [X,P] = iℏ/(1 ‑ λ2P2) which is originated from various theories of gravity, we study thermodynamical properties of quantum black holes (BHs) in canonical ensembles. We exactly calculate the modified internal energy, entropy and heat capacity. Moreover, we investigate a tunneling mechanism of massless particle in phase space. In this regard, the tunneling radiation of BH receives new corrections and the exact radiant spectrum is no longer precisely thermal. In addition, we show that our results are compatible with other quantum gravity (QG) approaches.

  3. Modified Gravity and its test on galaxy clusters

    NASA Astrophysics Data System (ADS)

    Nieuwenhuizen, Theodorus M.; Morandi, Andrea; Limousin, Marceau

    2018-05-01

    The MOdified Gravity (MOG) theory of J. Moffat assumes a massive vector particle which causes a repulsive contribution to the tensor gravitation. For the galaxy cluster A1689 new data for the X-ray gas and the strong lensing properties are presented. Fits to MOG are possible by adjusting the galaxy density profile. However, this appears to work as an effective dark matter component, posing a serious problem for MOG. New gas and strong lensing data for the cluster A1835 support these conclusions and point at a tendency of the gas alone to overestimate the lensing effects in MOG theory.

  4. Nonsingular universe in massive gravity's rainbow

    NASA Astrophysics Data System (ADS)

    Hendi, S. H.; Momennia, M.; Eslam Panah, B.; Panahiyan, S.

    2017-06-01

    One of the fundamental open questions in cosmology is whether we can regard the universe evolution without singularity like a Big Bang or a Big Rip. This challenging subject stimulates one to regard a nonsingular universe in the far past with an arbitrarily large vacuum energy. Considering the high energy regime in the cosmic history, it is believed that Einstein gravity should be corrected to an effective energy dependent theory which could be acquired by gravity's rainbow. On the other hand, employing massive gravity provided us with solutions to some of the long standing fundamental problems of cosmology such as cosmological constant problem and self acceleration of the universe. Considering these aspects of gravity's rainbow and massive gravity, in this paper, we initiate studying FRW cosmology in the massive gravity's rainbow formalism. At first, we show that although massive gravity modifies the FRW cosmology, but it does not itself remove the big bang singularity. Then, we generalize the massive gravity to the case of energy dependent spacetime and find that massive gravity's rainbow can remove the early universe singularity. We bring together all the essential conditions for having a nonsingular universe and the effects of both gravity's rainbow and massive gravity generalizations on such criteria are determined.

  5. Theoretical model of gravitational perturbation of current collector axisymmetric flow field

    NASA Astrophysics Data System (ADS)

    Walker, John S.; Brown, Samuel H.; Sondergaard, Neal A.

    1989-03-01

    Some designs of liquid metal collectors in homopolar motors and generators are essentially rotating liquid metal fluids in cylindrical channels with free surfaces and will, at critical rotational speeds, become unstable. The role of gravity in modifying this ejection instability is investigated. Some gravitational effects can be theoretically treated by perturbation techniques on the axisymmetric base flow of the liquid metal. This leads to a modification of previously calculated critical current collector ejection values neglecting gravity effects. The derivation of the mathematical model which determines the perturbation of the liquid metal base flow due to gravitational effects is documented. Since gravity is a small force compared with the centrifugal effects, the base flow solutions can be expanded in inverse powers of the Froude number and modified liquid flow profiles can be determined as a function of the azimuthal angle. This model will be used in later work to theoretically study the effects of gravity on the ejection point of the current collector. A rederivation of the hydrodynamic instability threshold of a liquid metal current collector is presented.

  6. Theoretical model of gravitational perturbation of current collector axisymmetric flow field

    NASA Astrophysics Data System (ADS)

    Walker, John S.; Brown, Samuel H.; Sondergaard, Neal A.

    1990-05-01

    Some designs of liquid-metal current collectors in homopolar motors and generators are essentially rotating liquid-metal fluids in cylindrical channels with free surfaces and will, at critical rotational speeds, become unstable. An investigation at David Taylor Research Center is being performed to understand the role of gravity in modifying this ejection instability. Some gravitational effects can be theoretically treated by perturbation techniques on the axisymmetric base flow of the liquid metal. This leads to a modification of previously calculated critical-current-collector ejection values neglecting gravity effects. The purpose of this paper is to document the derivation of the mathematical model which determines the perturbation of the liquid-metal base flow due to gravitational effects. Since gravity is a small force compared with the centrifugal effects, the base flow solutions can be expanded in inverse powers of the Froude number and modified liquid-flow profiles can be determined as a function of the azimuthal angle. This model will be used in later work to theoretically study the effects of gravity on the ejection point of the current collector.

  7. Modified Einstein's gravity as a possible missing link between sub- and super-Chandrasekhar type Ia supernovae

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Das, Upasana; Mukhopadhyay, Banibrata, E-mail: upasana@physics.iisc.ernet.in, E-mail: bm@physics.iisc.ernet.in

    2015-05-01

    We explore the effect of modification to Einstein's gravity in white dwarfs for the first time in the literature, to the best of our knowledge. This leads to significantly sub- and super-Chandrasekhar limiting masses of white dwarfs, determined by a single model parameter. On the other hand, type Ia supernovae (SNeIa), a key to unravel the evolutionary history of the universe, are believed to be triggered in white dwarfs having mass close to the Chandrasekhar limit. However, observations of several peculiar, under- and over-luminous SNeIa argue for exploding masses widely different from this limit. We argue that explosions of themore » modified gravity induced sub- and super-Chandrasekhar limiting mass white dwarfs result in under- and over-luminous SNeIa respectively, thus unifying these two apparently disjoint sub-classes and, hence, serving as a missing link. Our discovery raises two fundamental questions. Is the Chandrasekhar limit unique? Is Einstein's gravity the ultimate theory for understanding astronomical phenomena? Both the answers appear to be no!.« less

  8. Global stability of self-gravitating discs in modified gravity

    NASA Astrophysics Data System (ADS)

    Ghafourian, Neda; Roshan, Mahmood

    2017-07-01

    Using N-body simulations, we study the global stability of a self-gravitating disc in the context of modified gravity (MOG). This theory is a relativistic scalar-tensor-vector theory of gravity and it is presented to address the dark matter problem. In the weak field limit, MOG possesses two free parameters α and μ0, which have already been determined using the rotation curve data of spiral galaxies. The evolution of a stellar self-gravitating disc and, more specifically, the bar instability in MOG are investigated and compared to a Newtonian case. Our models have exponential and Mestel-like surface densities as Σ ∝ exp (-r/h) and Σ ∝ 1/r. It is found that, surprisingly, the discs are more stable against the bar mode in MOG than in Newtonian gravity. In other words, the bar growth rate is effectively slower than the Newtonian discs. Also, we show that both free parameters (I.e. α and μ0) have stabilizing effects. In other words, an increase in these parameters will decrease the bar growth rate.

  9. On gauge invariant cosmological perturbations in UV-modified Hořava gravity

    NASA Astrophysics Data System (ADS)

    Shin, Sunyoung; Park, Mu-In

    2017-12-01

    We consider gauge invariant cosmological perturbations in UV-modified, z = 3 (non-projectable) Hořava gravity with one scalar matter field, which has been proposed as a renormalizable gravity theory without the ghost problem in four dimensions. In order to exhibit its dynamical degrees of freedom, we consider the Hamiltonian reduction method and find that, by solving all the constraint equations, the degrees of freedom are the same as those of Einstein gravity: one scalar and two tensor (graviton) modes when a scalar matter field presents. However, we confirm that there is no extra graviton modes and general relativity is recovered in IR, which achieves the consistency of the model. From the UV-modification terms which break the detailed balance condition in UV, we obtain scale-invariant power spectrums for non-inflationary backgrounds, like the power-law expansions, without knowing the details of early expansion history of Universe. This could provide a new framework for the Big Bang cosmology. Moreover, we find that tensor and scalar fluctuations travel differently in UV, generally. We present also some clarifying remarks about confusing points in the literatures.

  10. KSC-07pd0964

    NASA Image and Video Library

    2007-04-26

    KENNEDY SPACE CENTER, FLA. -- Peter Diamandis (left), founder of the Zero Gravity Corp., and noted physicist Stephen Hawking move away from Zero G's modified Boeing 727 on the runway at the Kennedy Space Center's Shuttle Landing Facility. Hawking enjoyed his first zero gravity flight provided by Zero G. At the celebration of his 65th birthday on January 8 this year, Hawking announced his plans for a zero-gravity flight to prepare for a sub-orbital space flight in 2009 on Virgin Galactic's space service. Photo credit: NASA/Kim Shiflett

  11. Resolving the issue of branched Hamiltonian in modified Lanczos-Lovelock gravity

    NASA Astrophysics Data System (ADS)

    Ruz, Soumendranath; Mandal, Ranajit; Debnath, Subhra; Sanyal, Abhik Kumar

    2016-07-01

    The Hamiltonian constraint H_c = N{H} = 0, defines a diffeomorphic structure on spatial manifolds by the lapse function N in general theory of relativity. However, it is not manifest in Lanczos-Lovelock gravity, since the expression for velocity in terms of the momentum is multivalued. Thus the Hamiltonian is a branch function of momentum. Here we propose an extended theory of Lanczos-Lovelock gravity to construct a unique Hamiltonian in its minisuperspace version, which results in manifest diffeomorphic invariance and canonical quantization.

  12. Radion tunneling in modified theories of gravity

    NASA Astrophysics Data System (ADS)

    Paul, Tanmoy; SenGupta, Soumitra

    2018-04-01

    We consider a five dimensional warped spacetime where the bulk geometry is governed by higher curvature F( R) gravity. In this model, we determine the modulus potential originating from the scalar degree of freedom of higher curvature gravity. In the presence of this potential, we investigate the possibility of modulus (radion) tunneling leading to an instability in the brane configuration. Our results reveal that the parametric regions where the tunneling probability is highly suppressed, corresponds to the parametric values required to resolve the gauge hierarchy problem.

  13. White Dwarf Critical Tests for Modified Gravity.

    PubMed

    Jain, Rajeev Kumar; Kouvaris, Chris; Nielsen, Niklas Grønlund

    2016-04-15

    Scalar-tensor theories of gravity can lead to modifications of the gravitational force inside astrophysical objects. We exhibit that compact stars such as white dwarfs provide a unique setup to test beyond Horndeski theories of G^{3} type. We obtain stringent and independent constraints on the parameter ϒ characterizing the deviations from Newtonian gravity using the mass-radius relation, the Chandrasekhar mass limit, and the maximal rotational frequency of white dwarfs. We find that white dwarfs impose stronger constraints on ϒ than red and brown dwarfs.

  14. Black holes in massive gravity as heat engines

    NASA Astrophysics Data System (ADS)

    Hendi, S. H.; Eslam Panah, B.; Panahiyan, S.; Liu, H.; Meng, X.-H.

    2018-06-01

    The paper at hand studies the heat engine provided by black holes in the presence of massive gravity. The main motivation is to investigate the effects of massive gravity on different properties of the heat engine. It will be shown that massive gravity parameters modify the efficiency of engine on a significant level. Furthermore, it will be pointed out that it is possible to have a heat engine for non-spherical black holes in massive gravity, and therefore, we will study the effects of horizon topology on the properties of heat engine. Surprisingly, it will be shown that the highest efficiency for the heat engine belongs to black holes with the hyperbolic horizon, while the lowest one belongs to the spherical black holes.

  15. Physical Activity in Physical Education: Are Longer Lessons Better?

    ERIC Educational Resources Information Center

    Smith, Nicole J.; Monnat, Shannon M.; Lounsbery, Monica A. F.

    2015-01-01

    Background: The purpose of this study was to compare physical activity (PA) outcomes in a sample of high school (HS) physical education (PE) lessons from schools that adopted "traditional" versus "modified block" schedule formats. Methods: We used the System for Observing Fitness Instruction Time (SOFIT) to conduct observations…

  16. This Is Inquiry ... Right?

    ERIC Educational Resources Information Center

    Zangori, Laura; Forbes, Cory; Biggers, Mandy

    2012-01-01

    Many teachers have taught their share of science lessons that needed improvements. For the past eight years, the authors have been working with elementary teachers to implement quick and easy strategies to modify existing science lessons to make them more inquiry-based. Elementary teachers can use these strategies to adapt existing science lessons…

  17. Shells. Modified Primary. Revised. Anchorage School District Elementary Science Program.

    ERIC Educational Resources Information Center

    Defendorf, Jean, Ed.

    This publication provides information and activities for teaching about seashells and process skills including observing, classifying, collecting and interpreting data, inferring, measuring, and predicting. There are 10 lessons. Lessons 1 through 5 deal with an introduction to shells, why animals have shells, observing and classifying shells, the…

  18. Early-time cosmology with stiff era from modified gravity

    NASA Astrophysics Data System (ADS)

    Odintsov, S. D.; Oikonomou, V. K.

    2017-11-01

    In this work, we shall incorporate a stiff era in the Universe's evolution in the context of F (R ) gravity. After deriving the vacuum F (R ) gravity, which may realize a stiff evolution, we combine the stiff F (R ) gravity with an R2 model, and we construct a qualitative model for the inflationary and stiff era, with the latter commencing after the end of the inflationary era. We assume that the baryogenesis occurs during the stiff era, and we calculate the baryon to entropy ratio, which effectively constraints the functional form of the stiff F (R ) gravity. Further constraints on the stiff F (R ) gravity may come from the primordial gravitational waves, and particularly their scalar mode, which is characteristic of the F (R ) gravity theory. The stiff era presence does not contradict the standard cosmology era, namely, inflation, and the radiation-matter domination eras. Furthermore, we investigate which F (R ) gravity may realize a dust and stiff matter dominated Einstein-Hilbert evolution.

  19. A universal test for gravitational decoherence

    PubMed Central

    Pfister, C.; Kaniewski, J.; Tomamichel, M.; Mantri, A.; Schmucker, R.; McMahon, N.; Milburn, G.; Wehner, S.

    2016-01-01

    Quantum mechanics and the theory of gravity are presently not compatible. A particular question is whether gravity causes decoherence. Several models for gravitational decoherence have been proposed, not all of which can be described quantum mechanically. Since quantum mechanics may need to be modified, one may question the use of quantum mechanics as a calculational tool to draw conclusions from the data of experiments concerning gravity. Here we propose a general method to estimate gravitational decoherence in an experiment that allows us to draw conclusions in any physical theory where the no-signalling principle holds, even if quantum mechanics needs to be modified. As an example, we propose a concrete experiment using optomechanics. Our work raises the interesting question whether other properties of nature could similarly be established from experimental observations alone—that is, without already having a rather well-formed theory of nature to make sense of experimental data. PMID:27694976

  20. Acceleration estimation using a single GPS receiver for airborne scalar gravimetry

    NASA Astrophysics Data System (ADS)

    Zhang, Xiaohong; Zheng, Kai; Lu, Cuixian; Wan, Jiakuan; Liu, Zhanke; Ren, Xiaodong

    2017-11-01

    Kinematic acceleration estimated using the global positioning system (GPS) is significant for airborne scalar gravimetry. As the conventional approach based on the differential global positioning system (DGPS) presents several drawbacks, including additional cost or the impracticality of setting up nearby base stations in challenging environments, we introduce an alternative approach, Modified Kin-VADASE (MKin-VADASE), based on a modified Kin-VADASE approach without the requirement to have ground-base stations. In this approach, the aircraft velocities are first estimated with the modified Kin-VADASE. Then the accelerations are obtained from velocity estimates using the Taylor approximation differentiator. The impact of carrier-phase measurement noise and satellite ephemeris errors on acceleration estimates are investigated carefully in the frequency domain with the Fast Fourier Transform Algorithm (FFT). The results show that the satellite clock products have a significant impact on the acceleration estimates. Then, the performance of MKin-VADASE, PPP, and DGPS are validated using flight tests carried out in Shanxi Province, China. The accelerations are estimated using the three approaches, then used to calculate the gravity disturbances. Finally, the analysis of crossover difference and the terrestrial gravity data are used to evaluate the accuracy of gravity disturbance estimates. The results show that the performances of MKin-VADASE, PPP and DGPS are comparable, but the computational complexity of MKin-VADASE is greatly reduced with regard to PPP and DGPS. For the results of the three approaches, the RMS of crossover differences of gravity disturbance estimates is approximately 1-1.5 mGal at a spatial resolution of 3.5 km (half wavelength) after crossover adjustment, and the accuracy is approximately 3-4 mGal with respect to terrestrial gravity data.

  1. The gravitational wave stress–energy (pseudo)-tensor in modified gravity

    NASA Astrophysics Data System (ADS)

    Saffer, Alexander; Yunes, Nicolás; Yagi, Kent

    2018-03-01

    The recent detections of gravitational waves by the advanced LIGO and Virgo detectors open up new tests of modified gravity theories in the strong-field and dynamical, extreme gravity regime. Such tests rely sensitively on the phase evolution of the gravitational waves, which is controlled by the energy–momentum carried by such waves out of the system. We here study four different methods for finding the gravitational wave stress–energy pseudo-tensor in gravity theories with any combination of scalar, vector, or tensor degrees of freedom. These methods rely on the second variation of the action under short-wavelength averaging, the second perturbation of the field equations in the short-wavelength approximation, the construction of an energy complex leading to a Landau–Lifshitz tensor, and the use of Noether’s theorem in field theories about a flat background. We apply these methods in general relativity, Jordan–Fierz–Brans–Dicky theoy, and Einstein-Æther theory to find the gravitational wave stress–energy pseudo-tensor and calculate the rate at which energy and linear momentum is carried away from the system. The stress–energy tensor and the rate of linear momentum loss in Einstein-Æther theory are presented here for the first time. We find that all methods yield the same rate of energy loss, although the stress–energy pseudo-tensor can be functionally different. We also find that the Noether method yields a stress–energy tensor that is not symmetric or gauge-invariant, and symmetrization via the Belinfante procedure does not fix these problems because this procedure relies on Lorentz invariance, which is spontaneously broken in Einstein-Æther theory. The methods and results found here will be useful for the calculation of predictions in modified gravity theories that can then be contrasted with observations.

  2. Sink or Float. Modified Primary. Revised. Anchorage School District Elementary Science Program.

    ERIC Educational Resources Information Center

    Defendorf, Jean, Ed.

    This publication provides information and activities for teaching about water, whether certain objects will sink or float, and process skills including observing, classifying, inferring, measuring, predicting, and collecting and interpreting data. There are 14 lessons in the unit. The first four lessons deal with the classification of objects and…

  3. Supporting English Language Learners in Math Class, Grades 6-8

    ERIC Educational Resources Information Center

    Melanese, Kathy; Chung, Luz; Forbes, Cheryl

    2011-01-01

    This new addition to Math Solutions "Supporting English Language Learners in Math Class series" offers a wealth of lessons and strategies for modifying grades 6-8 instruction. Section I presents an overview of teaching math to English learners: the research, the challenges, the linguistic demands of a math lesson, and specific strategies and…

  4. Cultivating Mindfulness with Third Grade Students via Classroom-Based Interventions

    ERIC Educational Resources Information Center

    Kielty, Michele; Gilligan, Tammy; Staton, Renee; Curtis, Nicholas

    2017-01-01

    Forty-five third grade students, from six different classrooms at a local elementary school, participated in our 3-year study. We delivered three 30-min classroom lessons on mindfulness using a curriculum that included modified lessons from the "Mindful Schools" and "MindUp" curricula as well as material we developed. We also…

  5. Mystery Powders. [Modified Primary]. Revised. Anchorage School District Elementary Science Program.

    ERIC Educational Resources Information Center

    Anchorage School District, AK.

    This publication provides information and activities for identifying objects using the five senses and process skills including observing, classifying, collecting and interpreting data, inferring, and predicting. Lessons 1 through 3 deal with the identification of an unknown substance and the physical properties of powders. Lessons 4 through 6 are…

  6. There's More to Light than Meets the Eye

    ERIC Educational Resources Information Center

    McCann, Florence; Pedersen, Jon; Falsarella, Carell; McCann, Patrick

    2008-01-01

    This investigation was part of a multi-lesson unit that gave students direct experience using increasingly sophisticated tools to make more detailed observations and measurements of light. Through these lessons, students experienced a key aspect of the nature of science (McComas 2004), namely how scientists constantly refine and modify theories as…

  7. Precursor SSF utilization: The MODE experiments

    NASA Technical Reports Server (NTRS)

    Crawley, Edward F.

    1992-01-01

    The MIT Space Engineering Research Center is the principal investigator for a series of experiments which utilize the Shuttle Middeck as an engineering dynamics laboratory. The first, which flew on STS-48 in Sep. 1991, was the Middeck O-gravity Dynamics Experiment (MODE). This experiment focused on the dynamics of a scaled deployable truss, similar to that of SSF, and contained liquids in tanks. MODE will be reflown in the fall of 1993. In mid-1994, the Middeck Active Control Experiment (MACE) will examine the issues associated with predicting and verifying the closed loop behavior of a controlled structure in zero gravity. The paper will present experiment background, planning, operational experience, results, and lessons learned from these experiments which are pertinent to SSF utilization.

  8. Testing modified gravity using a marked correlation function

    NASA Astrophysics Data System (ADS)

    Armijo, Joaquí n.; Cai, Yan-Chuan; Padilla, Nelson; Li, Baojiu; Peacock, John A.

    2018-05-01

    In theories of modified gravity with the chameleon screening mechanism, the strength of the fifth force depends on environment. This induces an environment dependence of structure formation, which differs from ΛCDM. We show that these differences can be captured by the marked correlation function. With the galaxy correlation functions and number densities calibrated to match between f(R) and ΛCDM models in simulations, we show that the marked correlation functions from using either the local galaxy number density or halo mass as the marks encode extra information, which can be used to test these theories. We discuss possible applications of these statistics in observations.

  9. An Evaluation of Cosmological Models from the Expansion and Growth of Structure Measurements

    NASA Astrophysics Data System (ADS)

    Zhai, Zhongxu; Blanton, Michael; Slosar, Anže; Tinker, Jeremy

    2017-12-01

    We compare a large suite of theoretical cosmological models to observational data from the cosmic microwave background, baryon acoustic oscillation measurements of expansion, Type Ia supernova measurements of expansion, redshift space distortion measurements of the growth of structure, and the local Hubble constant. Our theoretical models include parametrizations of dark energy as well as physical models of dark energy and modified gravity. We determine the constraints on the model parameters, incorporating the redshift space distortion data directly in the analysis. To determine whether models can be ruled out, we evaluate the p-value (the probability under the model of obtaining data as bad or worse than the observed data). In our comparison, we find the well-known tension of H 0 with the other data; no model resolves this tension successfully. Among the models we consider, the large-scale growth of structure data does not affect the modified gravity models as a category particularly differently from dark energy models; it matters for some modified gravity models but not others, and the same is true for dark energy models. We compute predicted observables for each model under current observational constraints, and identify models for which future observational constraints will be particularly informative.

  10. Anamorphic quasiperiodic universes in modified and Einstein gravity with loop quantum gravity corrections

    NASA Astrophysics Data System (ADS)

    Amaral, Marcelo M.; Aschheim, Raymond; Bubuianu, Laurenţiu; Irwin, Klee; Vacaru, Sergiu I.; Woolridge, Daniel

    2017-09-01

    The goal of this work is to elaborate on new geometric methods of constructing exact and parametric quasiperiodic solutions for anamorphic cosmology models in modified gravity theories, MGTs, and general relativity, GR. There exist previously studied generic off-diagonal and diagonalizable cosmological metrics encoding gravitational and matter fields with quasicrystal like structures, QC, and holonomy corrections from loop quantum gravity, LQG. We apply the anholonomic frame deformation method, AFDM, in order to decouple the (modified) gravitational and matter field equations in general form. This allows us to find integral varieties of cosmological solutions determined by generating functions, effective sources, integration functions and constants. The coefficients of metrics and connections for such cosmological configurations depend, in general, on all spacetime coordinates and can be chosen to generate observable (quasi)-periodic/aperiodic/fractal/stochastic/(super) cluster/filament/polymer like (continuous, stochastic, fractal and/or discrete structures) in MGTs and/or GR. In this work, we study new classes of solutions for anamorphic cosmology with LQG holonomy corrections. Such solutions are characterized by nonlinear symmetries of generating functions for generic off-diagonal cosmological metrics and generalized connections, with possible nonholonomic constraints to Levi-Civita configurations and diagonalizable metrics depending only on a time like coordinate. We argue that anamorphic quasiperiodic cosmological models integrate the concept of quantum discrete spacetime, with certain gravitational QC-like vacuum and nonvacuum structures. And, that of a contracting universe that homogenizes, isotropizes and flattens without introducing initial conditions or multiverse problems.

  11. Magnetized string cosmological models of accelerated expansion of the Universe in f(R,T) theory of gravity

    NASA Astrophysics Data System (ADS)

    Pradhan, Anirudh; Jaiswal, Rekha

    A class of spatially homogeneous and anisotropic Bianchi-V massive string models have been studied in the modified f(R,T)-theory of gravity proposed by Harko et al. [Phys. Rev. D 84:024020, 2011] in the presence of magnetic field. For a specific choice of f(R,T)=f1(R) + f2(T), where f1(R) = ν1R and f2(T) = ν2T; ν1, ν2 being arbitrary parameters, solutions of modified gravity field equations have been generated. To find the deterministic solution of the field equations, we have considered the time varying deceleration parameter which is consistent with observational data of standard cosmology (SNIa, BAO and CMB). As a result to study the transit behavior of Universe, we consider a law of variation for the specifically chosen scale factor, which yields a time-dependent deceleration parameter comprising a class of models that depicts a transition of the Universe from the early decelerated phase to the recent accelerating phase. In this context, for the model of the Universe, the field equations are solved and corresponding cosmological aspects have been discussed. The Energy conditions in this modified gravity theory are also studied. Stability analysis of the solutions through cosmological perturbation is performed and it is concluded that the expanding solution is stable against the perturbation with respect to anisotropic spatial direction. Some physical and geometric properties of the models are also discussed.

  12. Thin-shell wormholes in rainbow gravity

    NASA Astrophysics Data System (ADS)

    Amirabi, Z.; Halilsoy, M.; Mazharimousavi, S. Habib

    2018-03-01

    At the Planck scale of length ˜10‑35 m where the energy is comparable with the Planck energy, the quantum gravity corrections to the classical background spacetime results in gravity’s rainbow or rainbow gravity. In this modified theory of gravity, geometry depends on the energy of the test particle used to probe the spacetime, such that in the low energy limit, it yields the standard general relativity. In this work, we study the thin-shell wormholes in the spherically symmetric rainbow gravity. We find the corresponding properties in terms of the rainbow functions which are essential in the rainbow gravity and the stability of such thin-shell wormholes are investigated. Particularly, it will be shown that there are exact solutions in which high energy particles crossing the throat will encounter less amount of total exotic matter. This may be used as an advantage over general relativity to reduce the amount of exotic matter.

  13. Inflation from higher dimensions

    NASA Astrophysics Data System (ADS)

    Nakada, Hiroshi; Ketov, Sergei V.

    2017-12-01

    We derive the scalar potential in four spacetime dimensions from an eight-dimensional (R +γ R4-2 Λ -F42) gravity model in the presence of the 4-form F4, with the (modified gravity) coupling constant γ and the cosmological constant Λ , by using the flux compactification of four extra dimensions on a 4-sphere with the warp factor. The scalar potential depends upon two scalar fields: the scalaron and the 4-sphere volume modulus. We demonstrate that it gives rise to a viable description of cosmological inflation in the early universe, with the scalaron playing the role of inflaton and the volume modulus to be (almost) stabilized at its minimum. We also speculate about a possibility of embedding our model in eight dimensions into a modified eight-dimensional supergavity that, in its turn, arises from a modified eleven-dimensional supergravity.

  14. The first Australian gravimetric quasigeoid model with location-specific uncertainty estimates

    NASA Astrophysics Data System (ADS)

    Featherstone, W. E.; McCubbine, J. C.; Brown, N. J.; Claessens, S. J.; Filmer, M. S.; Kirby, J. F.

    2018-02-01

    We describe the computation of the first Australian quasigeoid model to include error estimates as a function of location that have been propagated from uncertainties in the EGM2008 global model, land and altimeter-derived gravity anomalies and terrain corrections. The model has been extended to include Australia's offshore territories and maritime boundaries using newer datasets comprising an additional {˜ }280,000 land gravity observations, a newer altimeter-derived marine gravity anomaly grid, and terrain corrections at 1^' ' }× 1^' ' } resolution. The error propagation uses a remove-restore approach, where the EGM2008 quasigeoid and gravity anomaly error grids are augmented by errors propagated through a modified Stokes integral from the errors in the altimeter gravity anomalies, land gravity observations and terrain corrections. The gravimetric quasigeoid errors (one sigma) are 50-60 mm across most of the Australian landmass, increasing to {˜ }100 mm in regions of steep horizontal gravity gradients or the mountains, and are commensurate with external estimates.

  15. Satellite borne gravity gradiometer study

    NASA Technical Reports Server (NTRS)

    Metzger, E.; Jircitano, A.; Affleck, C.

    1976-01-01

    Gravity gradiometry is recognized to be a very difficult instrumentation problem because extremely small differential acceleration levels have to be measured, 0.1 EU corresponds to an acceleration of 10 to the minus 11th power g at two points 1 meter apart. A feasibility model of a gravity gradiometer is being developed for airborne applications using four modified versions of the proven Model VII accelerometers mounted on a slowly rotating fixture. Gravity gradients are being measured to 1.07 EU in a vertical rotation axis orientation. Equally significant are the outstanding operational characteristics such as fast reaction time, low temperature coefficients and high degree of bias stability over long periods of time. The rotating accelerometer gravity gradiometer approach and its present status is discussed and it is the foundation for the orbital gravity gradiometer analyzed. The performance levels achieved in a 1 g environment of the earth and under relatively high seismic disturbances, lend the orbital gravity gradiometer a high confidence level of success.

  16. The New Zealand gravimetric quasigeoid model 2017 that incorporates nationwide airborne gravimetry

    NASA Astrophysics Data System (ADS)

    McCubbine, J. C.; Amos, M. J.; Tontini, F. C.; Smith, E.; Winefied, R.; Stagpoole, V.; Featherstone, W. E.

    2017-12-01

    A one arc-minute resolution gravimetric quasigeoid model has been computed for New Zealand, covering the region 25°S -60°S and 160°E -170°W . It was calculated by Wong and Gore modified Stokes integration using the remove-compute-restore technique with the EIGEN-6C4 global gravity model as the reference field. The gridded gravity data used for the computation consisted of 40,677 land gravity observations, satellite altimetry-derived marine gravity anomalies, historical shipborne marine gravity observations and, importantly, approximately one million new airborne gravity observations. The airborne data were collected with the specific intention of reinforcing the shortcomings of the existing data in areas of rough topography inaccessible to land gravimetry and in coastal areas where shipborne gravimetry cannot be collected and altimeter-derived gravity anomalies are generally poor. The new quasigeoid has a nominal precision of ± 48 mm on comparison with GPS-levelling data, which is approximately 14 mm less than its predecessor NZGeoid09.

  17. Chameleon f(R) gravity on the Virgo cluster scale

    NASA Astrophysics Data System (ADS)

    Moran, C. Corbett; Teyssier, R.; Li, B.

    2015-03-01

    Models of modified gravity offer promising alternatives to the concordance Λ cold dark matter (ΛCDM) cosmology to explain the late-time acceleration of the universe. A popular such model is f(R) gravity, in which the Ricci scalar in the Einstein-Hilbert action is replaced by a general function of it. We study the f(R) model of Hu & Sawicki, which recovers standard general relativity in high-density regimes, while reproducing the desired late time acceleration at cosmological scales. We run a suite of high-resolution zoom simulations using the ECOSMOG code to examine the effect of f(R) gravity on the properties of a halo that is analogous to the Virgo cluster. We show that the velocity dispersion profiles can potentially discriminate between f(R) models and ΛCDM, and provide complementary analysis of lensing signal profiles to explore the possibility to further distinguish the different f(R) models. Our results confirm the techniques explored by Cabré et al. to quantify the effect of environment in the behaviour of f(R) gravity, and we extend them to study halo satellites at various redshifts. We find that the modified gravity effects in our models are most observable at low redshifts, and that effects are generally stronger for satellites far from the centre of the main halo. We show that the screening properties of halo satellites trace very well that of dark matter particles, which means that low-resolution simulations in which subhaloes are not very well resolved can in principle be used to study satellite properties. We discuss observables, particularly for halo satellites, that can potentially be used to constrain the observational viability of f(R) gravity.

  18. Testing gravity with EG: mapping theory onto observations

    NASA Astrophysics Data System (ADS)

    Leonard, C. Danielle; Ferreira, Pedro G.; Heymans, Catherine

    2015-12-01

    We present a complete derivation of the observationally motivated definition of the modified gravity statistic EG. Using this expression, we investigate how variations to theory and survey parameters may introduce uncertainty in the general relativistic prediction of EG. We forecast errors on EG for measurements using two combinations of upcoming surveys, and find that theoretical uncertainties may dominate for a futuristic measurement. Finally, we compute predictions of EG under modifications to general relativity in the quasistatic regime, and comment on the pros and cons of using EG to test gravity with future surveys.

  19. KSC-07pd0961

    NASA Image and Video Library

    2007-04-26

    KENNEDY SPACE CENTER, FLA. -- Noted physicist Stephen Hawking (center) returns to the Kennedy Space Center Shuttle Landing Facility after a zero gravity flight. At far left is Peter Diamandis, founder of the Zero Gravity Corp. that provided the flight aboard its modified Boeing 727. Hawking suffers from amyotrophic lateral sclerosis (also known as Lou Gehrig's disease). At the celebration of his 65th birthday on January 8 this year, Hawking announced his plans for a zero-gravity flight to prepare for a sub-orbital space flight in 2009 on Virgin Galactic's space service. Photo credit: NASA/Kim Shiflett

  20. Modeling corewood-outerwood transition in loblolly pine using wood specific gravity

    Treesearch

    Christian R. Mora; H. Lee Allen; Richard F. Daniels; Alexander Clark

    2007-01-01

    A modified logistic function was used for modeling specific-gravity profiles obtained from X-ray densitometry analysis in 675 loblolly pine (Pinus taeda L.) trees in four regeneration trials. Trees were 21 or 22 years old at the time of the study. The function was used for demarcating corewood, transitional, and outerwood zones. Site and silvicultural effects were...

  1. Numerical study of gravity effects on phase separation in a swirl chamber.

    PubMed

    Hsiao, Chao-Tsung; Ma, Jingsen; Chahine, Georges L

    2016-01-01

    The effects of gravity on a phase separator are studied numerically using an Eulerian/Lagrangian two-phase flow approach. The separator utilizes high intensity swirl to separate bubbles from the liquid. The two-phase flow enters tangentially a cylindrical swirl chamber and rotate around the cylinder axis. On earth, as the bubbles are captured by the vortex formed inside the swirl chamber due to the centripetal force, they also experience the buoyancy force due to gravity. In a reduced or zero gravity environment buoyancy is reduced or inexistent and capture of the bubbles by the vortex is modified. The present numerical simulations enable study of the relative importance of the acceleration of gravity on the bubble capture by the swirl flow in the separator. In absence of gravity, the bubbles get stratified depending on their sizes, with the larger bubbles entering the core region earlier than the smaller ones. However, in presence of gravity, stratification is more complex as the two acceleration fields - due to gravity and to rotation - compete or combine during the bubble capture.

  2. Photon and graviton mass limits

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Nieto, Michael; Goldhaber Scharff, Alfred

    2008-01-01

    We review past and current studies of possible long-distance, low-frequency deviations from Maxwell electrodynamics and Einstein gravity. Both have passed through three phases: (1) Testing the inverse-square laws of Newton and Coulomb, (2) Seeking a nonzero value for the rest mass of photon or graviton, and (3) Considering more degrees of freedom, allowing mass while preserving gauge or general-coordinate invariance. For electrodynamics there continues to be no sign of any deviation. Since our previous review the lower limit on the photon Compton wavelength (associated with weakening of electromagnetic fields in vacuum over large distance scale) has improved by four ordersmore » of magnitude, to about one astronomical unit. Rapid current progress in astronomical observations makes it likely that there will be further advances. These ultimately could yield a bound exceeding galactic dimensions, as has long been contemplated. Meanwhile, for gravity there have been strong arguments about even the concept of a graviton rest mass. At the same time there are striking observations, commonly labeled 'dark matter' and 'dark energy' that some argue imply modified gravity. This makes the questions for gravity much more interesting. For dark matter, which involves increased attraction at large distances, any explanation by modified gravity would be qualitatively different from graviton mass. Because dark energy is associated with reduced attraction at large distances, it might be explained by a graviton-mass-like effect.« less

  3. A Mixed Methods Comparison of Teachers' Lunar Modeling Lesson Implementation and Student Learning Outcomes

    ERIC Educational Resources Information Center

    Lamar, Mary F.; Wilhelm, Jennifer Anne; Cole, Merryn

    2018-01-01

    The authors compare three teachers' adaptations and implementation of a lunar modeling lesson to explain marked differences in student learning outcomes on a spatial-scientific lunar assessment. They used a modified version of the Practices of Science Observation Protocol (P-SOP; Forbes, Biggers, & Zangori, 2013) to identify ways in which…

  4. 77 FR 5853 - In the Matter of Entergy Nuclear Operations Inc; Confirmatory Order Modifying License (Effective...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-02-06

    ... portable fit test machine. iv. Required RP technicians to complete focused training to remediate the work... that lessons learned from these events, is extended to the Entergy fleet and to the industry: A... lessons learned from the event that formed the basis for the Confirmatory Order (CO), regarding both...

  5. Classrooms with Growing Room. Playing Smart: Enrichment in the Home. Lessons without Limits.

    ERIC Educational Resources Information Center

    Kanevsky, Lannie

    Three papers by the same author address: (1) educational methods for gifted children in the regular classroom; (2) principles of enriching the gifted child's development in the home; and (3) modifying lessons to optimally challenge gifted students. The first paper is titled, "Classrooms with Growing Room." It stresses the need for gifted children…

  6. Infrared lessons for ultraviolet gravity: the case of massive gravity and Born-Infeld

    NASA Astrophysics Data System (ADS)

    Beltrán Jiménez, Jose; Heisenberg, Lavinia; Olmo, Gonzalo J.

    2014-11-01

    We generalize the ultraviolet sector of gravitation via a Born-Infeld action using lessons from massive gravity. The theory contains all of the elementary symmetric polynomials and is treated in the Palatini formalism. We show how the connection can be solved algebraically to be the Levi-Civita connection of an effective metric. The non-linearity of the algebraic equations yields several branches, one of which always reduces to General Relativity at low curvatures. We explore in detail a minimal version of the theory, for which we study solutions in the presence of a perfect fluid with special attention to the cosmological evolution. In vacuum we recover Ricci-flat solutions, but also an additional physical solution corresponding to an Einstein space. The existence of two physical branches remains for non-vacuum solutions and, in addition, the branch that connects to the Einstein space in vacuum is not very sensitive to the specific value of the energy density. For the branch that connects to the General Relativity limit we generically find three behaviours for the Hubble function depending on the equation of state of the fluid, namely: either there is a maximum value for the energy density that connects continuously with vacuum, or the energy density can be arbitrarily large but the Hubble function saturates and remains constant at high energy densities, or the energy density is unbounded and the Hubble function grows faster than in General Relativity. The second case is particularly interesting because it could offer an interesting inflationary epoch even in the presence of a dust component. Finally, we discuss the possibility of avoiding certain types of singularities within the minimal model.

  7. Chern-Simons Modified Gravity

    NASA Astrophysics Data System (ADS)

    Efstratiou, P.

    2013-09-01

    This presentation will be based on my, undergraduate, thesis at Aristotle University of Thessoliniki with the same subject, supervised by Professor Demetrios Papadopoulos. I will first present the general mathematical formulation of the Chern-Simons (CS) modified gravity, which is split in a dynamical and a non-dynamical context, and the different physical theories which suggest this modification. Then proceed by examing the possibility that the CS theory shares solutions with General Relativity in both contexts. In the non-dynamical context I will present a new, undocumented solution as well as all the other possible solutions found to date. I will conclude by arguing that General Relativity and CS Theory share any solutions in the dynamical context.

  8. Radiative corrections in the (varying power)-law modified gravity

    NASA Astrophysics Data System (ADS)

    Hammad, Fayçal

    2015-06-01

    Although the (varying power)-law modified gravity toy model has the attractive feature of unifying the early- and late-time expansions of the Universe, thanks to the peculiar dependence of the scalar field's potential on the scalar curvature, the model still suffers from the fine-tuning problem when used to explain the actually observed Hubble parameter. Indeed, a more correct estimate of the mass of the scalar field needed to comply with actual observations gives an unnaturally small value. On the other hand, for a massless scalar field the potential would have no minimum and hence the field would always remain massless. What solves these issues are the radiative corrections that modify the field's effective potential. These corrections raise the field's effective mass, rendering the model free from fine-tuning, immune against positive fifth-force tests, and better suited to tackle the dark matter sector.

  9. Fate of Large-Scale Structure in Modified Gravity After GW170817 and GRB170817A

    NASA Astrophysics Data System (ADS)

    Amendola, Luca; Kunz, Martin; Saltas, Ippocratis D.; Sawicki, Ignacy

    2018-03-01

    The coincident detection of gravitational waves (GW) and a gamma-ray burst from a merger of neutron stars has placed an extremely stringent bound on the speed of GWs. We showed previously that the presence of gravitational slip (η ) in cosmology is intimately tied to modifications of GW propagation. This new constraint implies that the only remaining viable source of gravitational slip is a conformal coupling to gravity in scalar-tensor theories, while viable vector-tensor theories cannot now generate gravitational slip at all. We discuss structure formation in the remaining viable models, demonstrating that (i) the dark-matter growth rate must now be at least as fast as in general relativity (GR), with the possible exception of that beyond the Horndeski model, and (ii) if there is any scale dependence at all in the slip parameter, it is such that it takes the GR value at large scales. We show a consistency relation that must be violated if gravity is modified.

  10. Time varying G and \\varLambda cosmology in f(R,T) gravity theory

    NASA Astrophysics Data System (ADS)

    Tiwari, R. K.; Beesham, A.; Singh, Rameshwar; Tiwari, L. K.

    2017-08-01

    We have studied the time dependence of the gravitational constant G and cosmological constant Λ by taking into account an anisotropic and homogeneous Bianchi type-I space-time in the framework of the modified f(R,T) theory of gravity proposed by Harko et al. (Phys. Rev. D 84:024020, 2011). For a specific choice of f(R,T)=R+2f(T) where f(T)=-λ T, two solutions of the modified gravity field equations have been generated with the help of a variation law between the expansion anisotropy ({σ}/{θ}) and the scale factor (S), together with a general non-linear equation of state. The solution for m≠3 corresponds to singular model of the universe whereas the solution for m=3 represents a non-singular model. We infer that the models entail a constant value of the deceleration parameter. A careful analysis of all the physical parameters of the models has also been carried out.

  11. Using ion flows parallel and perpendicular to gravity to modify dust acoustic waves

    NASA Astrophysics Data System (ADS)

    Thomas, E.; Fisher, R.

    2008-11-01

    Recent studies of dust acoustic waves have shown that the dust kinetic temperature can play an important role in determining the resulting dispersion relation [M. Rosenberg, et al., Phys. Plasmas, 15, 073701 (2008)]. In these studies, it is believed that ion flows play a dominant role in determining both the kinetic temperature of the charged microparticles as well as providing the source of energy for triggering the waves. In this presentation, results will be presented on the effects of ion flow on spatial structure and velocity distribution of dust acoustic waves. Here, the waves will be formed in dusty plasmas consisting of 3 ± 1 micron diameter silica microspheres. Two separate electrodes will be used to modify the ion flow in the plasma -- one parallel to the direction of gravity and one perpendicular to the direction of gravity. Particle image velocimetry (PIV) techniques will be used to observe the particles and to measure their velocity distributions.

  12. Emergent cosmology revisited

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Bag, Satadru; Sahni, Varun; Shtanov, Yuri

    We explore the possibility of emergent cosmology using the effective potential formalism. We discover new models of emergent cosmology which satisfy the constraints posed by the cosmic microwave background (CMB). We demonstrate that, within the framework of modified gravity, the emergent scenario can arise in a universe which is spatially open/closed. By contrast, in general relativity (GR) emergent cosmology arises from a spatially closed past-eternal Einstein Static Universe (ESU). In GR the ESU is unstable, which creates fine tuning problems for emergent cosmology. However, modified gravity models including Braneworld models, Loop Quantum Cosmology (LQC) and Asymptotically Free Gravity result inmore » a stable ESU. Consequently, in these models emergent cosmology arises from a larger class of initial conditions including those in which the universe eternally oscillates about the ESU fixed point. We demonstrate that such an oscillating universe is necessarily accompanied by graviton production. For a large region in parameter space graviton production is enhanced through a parametric resonance, casting serious doubts as to whether this emergent scenario can be past-eternal.« less

  13. Anisotropic strange stars under simplest minimal matter-geometry coupling in the f (R ,T ) gravity

    NASA Astrophysics Data System (ADS)

    Deb, Debabrata; Guha, B. K.; Rahaman, Farook; Ray, Saibal

    2018-04-01

    We study strange stars in the framework of f (R ,T ) theory of gravity. To provide exact solutions of the field equations it is considered that the gravitational Lagrangian can be expressed as the linear function of the Ricci scalar R and the trace of the stress-energy tensor T , i.e. f (R ,T )=R +2 χ T , where χ is a constant. We also consider that the strange quark matter (SQM) distribution inside the stellar system is governed by the phenomenological MIT bag model equation of state (EOS), given as pr=1/3 (ρ -4 B ) , where B is the bag constant. Further, for a specific value of B and observed values of mass of the strange star candidates we obtain the exact solution of the modified Tolman-Oppenheimer-Volkoff (TOV) equation in the framework of f (R ,T ) gravity and have studied in detail the dependence of the different physical parameters, like the metric potentials, energy density, radial and tangential pressures and anisotropy etc., due to the chosen different values of χ . Likewise in GR, as have been shown in our previous work [Deb et al., Ann. Phys. (Amsterdam) 387, 239 (2017), 10.1016/j.aop.2017.10.010] in the present work also we find maximum anisotropy at the surface which seems an inherent property of the strange stars in modified f (R ,T ) theory of gravity. To check the physical acceptability and stability of the stellar system based on the obtained solutions we have performed different physical tests, viz., the energy conditions, Herrera cracking concept, adiabatic index etc. In this work, we also have explained the effects, those are arising due to the interaction between the matter and the curvature terms in f (R ,T ) gravity, on the anisotropic compact stellar system. It is interesting to note that as the values of χ increase the strange stars become more massive and their radius increase gradually so that eventually they gradually turn into less dense compact objects. The present study reveals that the modified f (R ,T ) gravity is a suitable theory to explain massive stellar systems like recent magnetars, massive pulsars and super-Chandrasekhar stars, which cannot be explained in the framework of GR. However, for χ =0 the standard results of Einsteinian gravity are retrieved.

  14. KSC-07pd0957

    NASA Image and Video Library

    2007-04-26

    KENNEDY SPACE CENTER, FLA. -- At the Kennedy Space Center Shuttle Landing Facility, a modified Boeing 727 aircraft owned by Zero Gravity Corp. takes off with its well-known passenger, physicist Stephen Hawking. Zero Gravity Corp. is a commercial company licensed to provide the public with weightless flight experiences. Hawking will be making his first zero-gravity flight. Hawking developed amyotrophic lateral sclerosis disease in the 1960s, a type of motor neuron disease which would cost him the loss of almost all neuromuscular control. At the celebration of his 65th birthday on January 8 this year, Hawking announced his plans for a zero-gravity flight to prepare for a sub-orbital space flight in 2009 on Virgin Galactic's space service. Photo credit: NASA/Jack Pfaller

  15. KSC-07pd0951

    NASA Image and Video Library

    2007-04-26

    KENNEDY SPACE CENTER, FLA. -- At the Kennedy Space Center Shuttle Landing Facility, Peter Diamandis, founder of the Zero Gravity Corp., talks to the media about physicist Stephen Hawking's (in the wheelchair) first zero-gravity flight. The flight will be aboard a modified Boeing 727 aircraft owned by Zero Gravity Corp., a commercial company licensed to provide the public with weightless flight experiences. Hawking developed amyotrophic lateral sclerosis disease in the 1960s, a type of motor neuron disease which would cost him the loss of almost all neuromuscular control. At the celebration of his 65th birthday on January 8 this year, Hawking announced his plans for a zero-gravity flight to prepare for a sub-orbital space flight in 2009 on Virgin Galactic's space service. Photo credit: NASA/Kim Shiflett

  16. KSC-07pd0956

    NASA Image and Video Library

    2007-04-26

    KENNEDY SPACE CENTER, FLA. -- At the Kennedy Space Center Shuttle Landing Facility, a modified Boeing 727 aircraft owned by Zero Gravity Corp. is ready to take off with its well-known passenger, physicist Stephen Hawking. Zero Gravity Corp. is a commercial company licensed to provide the public with weightless flight experiences. Hawking will be making his first zero-gravity flight. Hawking developed amyotrophic lateral sclerosis disease in the 1960s, a type of motor neuron disease which would cost him the loss of almost all neuromuscular control. At the celebration of his 65th birthday on January 8 this year, Hawking announced his plans for a zero-gravity flight to prepare for a sub-orbital space flight in 2009 on Virgin Galactic's space service. Photo credit: NASA/Kim Shiflett

  17. Lunar Bouguer gravity anomalies - Imbrian age craters

    NASA Technical Reports Server (NTRS)

    Dvorak, J.; Phillips, R. J.

    1978-01-01

    The Bouguer gravity of mass anomalies associated with four Imbrian age craters, analyzed in the present paper, are found to differ considerably from the values of the mass anomalies associated with some young lunar craters. Of the Imbrian age craters, only Piccolomini exhibits a negative gravity anomaly (i.e., a low density region) which is characteristic of the young craters studied. The Bouguer gravity anomalies are zero for each of the remaining Imbrian age craters. Since, Piccolomini is younger, or at least less modified, than the other Imbrian age craters, it is suggested that the processes responsible for the post-impact modification of the Imbrian age craters may also be responsible for removing the negative mass anomalies initially associated with these features.

  18. Power law f(𝒢,T) gravity models supporting wormhole solutions

    NASA Astrophysics Data System (ADS)

    Shamir, M. Farasat; Ahmad, Mushtaq

    This work provides some feasible regions for the existence of traversable wormhole geometries in modified f(𝒢,T) gravity. For this purpose, three different matter contents have been studied with special emphasis on anisotropic fluid by considering a specific f(𝒢,T) gravity power law model. It has been shown that the null energy conditions for the effective energy-momentum tensor are widely violated for the ordinary matter content. However, some small feasible regions to support the wormhole solutions have been noted. Furthermore, the stability of the anisotropic feasible regions for the wormhole solutions has been discussed. It is concluded that the wormhole geometries threaded by the ordinary matter actually exist and are well stable in f(𝒢,T) gravity.

  19. New Agegraphic Pilgrim Dark Energy in f(T, TG) Gravity

    NASA Astrophysics Data System (ADS)

    Jawad, Abdul; Debnath, Ujjal

    2015-08-01

    In this work, we briefly discuss a novel class of modified gravity like f(T, TG) gravity. In this background, we assume the new agegraphic version of pilgrim dark energy and reconstruct f(T, TG) models for two specific values of s. We also discuss the equation of state parameter, squared speed of sound and wDE-w‧DE plane for these reconstructed f(T, TG) models. The equation of state parameter provides phantom-like behavior of the universe. The wDE-w‧DE plane also corresponds to ΛCDM limit, thawing and freezing regions for both models.

  20. Piloting a Dispersed and Inter-Professional Lesson Study Using Technology to Link Team Members at a Distance

    ERIC Educational Resources Information Center

    Koutsouris, George; Norwich, Brahm; Fujita, Taro; Ralph, Thomas; Adlam, Anna; Milton, Fraser

    2017-01-01

    This article presents an evaluation of distance technology used in a novel Lesson Study (LS) approach involving a dispersed LS team for inter-professional purposes. A typical LS model with only school teachers as team members was modified by including university-based lecturers with the school-based teachers, using video-conferencing and online…

  1. An Evaluation of Cosmological Models from the Expansion and Growth of Structure Measurements

    DOE PAGES

    Zhai, Zhongxu; Blanton, Michael; Slosar, Anze; ...

    2017-12-01

    Here, we compare a large suite of theoretical cosmological models to observational data from the cosmic microwave background, baryon acoustic oscillation measurements of expansion, Type Ia supernova measurements of expansion, redshift space distortion measurements of the growth of structure, and the local Hubble constant. Our theoretical models include parametrizations of dark energy as well as physical models of dark energy and modified gravity. We determine the constraints on the model parameters, incorporating the redshift space distortion data directly in the analysis. To determine whether models can be ruled out, we evaluate the p-value (the probability under the model of obtainingmore » data as bad or worse than the observed data). In our comparison, we find the well-known tension of H 0 with the other data; no model resolves this tension successfully. Among the models we consider, the large-scale growth of structure data does not affect the modified gravity models as a category particularly differently from dark energy models; it matters for some modified gravity models but not others, and the same is true for dark energy models. We compute predicted observables for each model under current observational constraints, and identify models for which future observational constraints will be particularly informative.« less

  2. An Evaluation of Cosmological Models from the Expansion and Growth of Structure Measurements

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Zhai, Zhongxu; Blanton, Michael; Slosar, Anze

    Here, we compare a large suite of theoretical cosmological models to observational data from the cosmic microwave background, baryon acoustic oscillation measurements of expansion, Type Ia supernova measurements of expansion, redshift space distortion measurements of the growth of structure, and the local Hubble constant. Our theoretical models include parametrizations of dark energy as well as physical models of dark energy and modified gravity. We determine the constraints on the model parameters, incorporating the redshift space distortion data directly in the analysis. To determine whether models can be ruled out, we evaluate the p-value (the probability under the model of obtainingmore » data as bad or worse than the observed data). In our comparison, we find the well-known tension of H 0 with the other data; no model resolves this tension successfully. Among the models we consider, the large-scale growth of structure data does not affect the modified gravity models as a category particularly differently from dark energy models; it matters for some modified gravity models but not others, and the same is true for dark energy models. We compute predicted observables for each model under current observational constraints, and identify models for which future observational constraints will be particularly informative.« less

  3. General virial theorem for modified-gravity MOND

    NASA Astrophysics Data System (ADS)

    Milgrom, Mordehai

    2014-01-01

    An important and useful relation is known to hold in two specific MOND theories. It pertains to low-acceleration, isolated systems of pointlike masses, mp, at positions rp, subject to gravitational forces Fp. It reads ∑prp·Fp=-(2/3)(Ga0)1/2 [(∑pmp)3/2-∑p mp3/2]; a0 is the MOND acceleration constant. Here I show that this relation holds in the nonrelativistic limit of any modified-gravity MOND theory. It follows from only the basic tenets of MOND, which include departure from standard dynamics at accelerations below a0, and space-time scale invariance in the nonrelativistic, low-acceleration limit. This implies space-dilatation invariance of the static, gravitational-field equations, which, in turn, leads to the above point-mass virial relation. Thus, the various MOND predictions and tests based on this relation hold in any modified-gravity MOND theory. Since we do not know that any of the existing MOND theories point in the right direction, it is important to identify such predictions that hold in a much larger class of theories. Among these predictions are the MOND two-body force for arbitrary masses, and a general mass-velocity-dispersion relation of the form σ2=(2/3)(MGa0)1/2[1-∑p(mp/M)3/2], where M = ∑p mp.

  4. TRACKING GENE FLOW FROM A GENETICALLY MODIFIED CREEPING BENTGRASS -- METHODS, MEASURES AND LESSONS LEARNED

    EPA Science Inventory

    Creeping bentgrass (CBG) expressing an engineered gene for resistance to glyphosate herbicide is one of the first genetically modified (GM) perennial crops to undergo regulatory review for commercial release by the US Department of Agriculture Animal Plant Health and Inspection S...

  5. Improvement of the GPS/A system for extensive observation along subduction zones around Japan

    NASA Astrophysics Data System (ADS)

    Fujimoto, H.; Kido, M.; Tadokoro, K.; Sato, M.; Ishikawa, T.; Asada, A.; Mochizuki, M.

    2011-12-01

    Combined high-resolution gravity field models serve as a mandatory basis to describe static and dynamic processes in system Earth. Ocean dynamics can be modeled referring to a high-accurate geoid as reference surface, solid earth processes are initiated by the gravity field. Also geodetic disciplines such as height system determination depend on high-precise gravity field information. To fulfill the various requirements concerning resolution and accuracy, any kind of gravity field information, that means satellite as well as terrestrial and altimetric gravity field observations have to be included in one combination process. A key role is here reserved for GOCE observations, which contribute with its optimal signal content in the long to medium wavelength part and enable a more accurate gravity field determination than ever before especially in areas, where no high-accurate terrestrial gravity field observations are available, such as South America, Asia or Africa. For our contribution we prepare a combined high-resolution gravity field model up to d/o 720 based on full normal equation including recent GOCE, GRACE and terrestrial / altimetric data. For all data sets, normal equations are set up separately, relative weighted to each other in the combination step and solved. This procedure is computationally challenging and can only be performed using super computers. We put special emphasis on the combination process, for which we modified especially our procedure to include GOCE data optimally in the combination. Furthermore we modified our terrestrial/altimetric data sets, what should result in an improved outcome. With our model, in which we included the newest GOCE TIM4 gradiometry results, we can show how GOCE contributes to a combined gravity field solution especially in areas of poor terrestrial data coverage. The model is validated by independent GPS leveling data in selected regions as well as computation of the mean dynamic topography over the oceans. Further, we analyze the statistical error estimates derived from full covariance propagation and compare them with the absolute validation with independent data sets.

  6. Human Locomotion under Reduced Gravity Conditions: Biomechanical and Neurophysiological Considerations

    PubMed Central

    Sylos-Labini, Francesca; Ivanenko, Yuri P.

    2014-01-01

    Reduced gravity offers unique opportunities to study motor behavior. This paper aims at providing a review on current issues of the known tools and techniques used for hypogravity simulation and their effects on human locomotion. Walking and running rely on the limb oscillatory mechanics, and one way to change its dynamic properties is to modify the level of gravity. Gravity has a strong effect on the optimal rate of limb oscillations, optimal walking speed, and muscle activity patterns, and gait transitions occur smoothly and at slower speeds at lower gravity levels. Altered center of mass movements and interplay between stance and swing leg dynamics may challenge new forms of locomotion in a heterogravity environment. Furthermore, observations in the lack of gravity effects help to reveal the intrinsic properties of locomotor pattern generators and make evident facilitation of nonvoluntary limb stepping. In view of that, space neurosciences research has participated in the development of new technologies that can be used as an effective tool for gait rehabilitation. PMID:25247179

  7. A test of Hořava gravity: the dark energy

    NASA Astrophysics Data System (ADS)

    Park, Mu-In

    2010-01-01

    Recently Hořava proposed a renormalizable gravity theory with higher spatial derivatives in four dimensions which reduces to Einstein gravity with a non-vanishing cosmological constant in IR but with improved UV behaviors. Here, I consider a non-trivial test of the new gravity theory in FRW universe by considering an IR modification which breaks ``softly'' the detailed balance condition in the original Hořava model. I separate the dark energy parts from the usual Einstein gravity parts in the Friedman equations and obtain the formula of the equations of state parameter. The IR modified Hořava gravity seems to be consistent with the current observational data but we need some more refined data sets to see whether the theory is really consistent with our universe. From the consistency of our theory, I obtain some constraints on the allowed values of w0 and wa in the Chevallier, Polarski, and Linder's parametrization and this may be tested in the near future, by sharpening the data sets.

  8. Gravitational decoherence

    NASA Astrophysics Data System (ADS)

    Bassi, Angelo; Großardt, André; Ulbricht, Hendrik

    2017-10-01

    We discuss effects of loss of coherence in low energy quantum systems caused by or related to gravitation, referred to as gravitational decoherence. These effects, resulting from random metric fluctuations, for instance, promise to be accessible by relatively inexpensive table-top experiments, way before the scales where true quantum gravity effects become important. Therefore, they can provide a first experimental view on gravity in the quantum regime. We will survey models of decoherence induced both by classical and quantum gravitational fluctuations; it will be manifest that a clear understanding of gravitational decoherence is still lacking. Next we will review models where quantum theory is modified, under the assumption that gravity causes the collapse of the wave functions, when systems are large enough. These models challenge the quantum-gravity interplay, and can be tested experimentally. In the last part we have a look at the state of the art of experimental research. We will review efforts aiming at more and more accurate measurements of gravity (G and g) and ideas for measuring conventional and unconventional gravity effects on nonrelativistic quantum systems.

  9. Einstein's 1919 View

    NASA Astrophysics Data System (ADS)

    Goradia, Shantilal

    2012-10-01

    When Rutherford discovered the nuclear force in 1919, he felt the force he discovered reflected some deviation of Newtonian gravity. Einstein too in his 1919 paper published the failure of the general relativity and Newtonian gravity to explain nuclear force and, in his concluding remarks, he retracted his earlier introduction of the cosmological constant. Consistent with his genius, we modify Newtonian gravity as probabilistic gravity using natural Planck units for a realistic study of nature. The result is capable of expressing both (1) nuclear force [strong coupling], and (2) Newtonian gravity in one equation, implying in general, in layman's words, that gravity is the cumulative effect of all quantum mechanical forces which are impossible to measure at long distances. Non discovery of graviton and quantum gravity silently support our findings. Continuing to climb on the shoulders of the giants enables us to see horizons otherwise unseen, as reflected in our book: ``Quantum Consciousness - The Road to Reality,'' and physics/0210040, where we derive the fine structure constant as a function of the age of the universe in Planck times consistent with Gamow's hint, using natural logarithm consistent with Feynman's hint.

  10. Optimizing Spectroscopic and Photometric Galaxy Surveys: Same-Sky Benefits for Dark Energy and Modified Gravity

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Kirk, Donnacha; Lahav, Ofer; Bridle, Sarah

    The combination of multiple cosmological probes can produce measurements of cosmological parameters much more stringent than those possible with any individual probe. We examine the combination of two highly correlated probes of late-time structure growth: (i) weak gravitational lensing from a survey with photometric redshifts and (ii) galaxy clustering and redshift space distortions from a survey with spectroscopic redshifts. We choose generic survey designs so that our results are applicable to a range of current and future photometric redshift (e.g. KiDS, DES, HSC, Euclid) and spectroscopic redshift (e.g. DESI, 4MOST, Sumire) surveys. Combining the surveys greatly improves their power tomore » measure both dark energy and modified gravity. An independent, non-overlapping combination sees a dark energy figure of merit more than 4 times larger than that produced by either survey alone. The powerful synergies between the surveys are strongest for modified gravity, where their constraints are orthogonal, producing a non-overlapping joint figure of merit nearly 2 orders of magnitude larger than either alone. Our projected angular power spectrum formalism makes it easy to model the cross-correlation observable when the surveys overlap on the sky, producing a joint data vector and full covariance matrix. We calculate a same-sky improvement factor, from the inclusion of these cross-correlations, relative to non-overlapping surveys. We find nearly a factor of 4 for dark energy and more than a factor of 2 for modified gravity. The exact forecast figures of merit and same-sky benefits can be radically affected by a range of forecasts assumption, which we explore methodically in a sensitivity analysis. We show that that our fiducial assumptions produce robust results which give a good average picture of the science return from combining photometric and spectroscopic surveys.« less

  11. Studies into the nature of cosmic acceleration: Dark energy or a modification to gravity on cosmological scales

    NASA Astrophysics Data System (ADS)

    Dossett, Jason Nicholas

    Since its discovery more than a decade ago, the problem of cosmic acceleration has become one of the largest in cosmology and physics as a whole. An unknown dark energy component of the universe is often invoked to explain this observation. Mathematically, this works because inserting a cosmic fluid with a negative equation of state into Einstein's equations provides an accelerated expansion. There are, however, alternative explanations for the observed cosmic acceleration. Perhaps the most promising of the alternatives is that, on the very largest cosmological scales, general relativity needs to be extended or a new, modified gravity theory must be used. Indeed, many modified gravity models are not only able to replicate the observed accelerated expansion without dark energy, but are also more compatible with a unified theory of physics. Thus it is the goal of this dissertation to develop and study robust tests that will be able to distinguish between these alternative theories of gravity and the need for a dark energy component of the universe. We will study multiple approaches using the growth history of large-scale structure in the universe as a way to accomplish this task. These approaches include studying what is known as the growth index parameter, a parameter that describes the logarithmic growth rate of structure in the universe, which describes the rate of formation of clusters and superclusters of galaxies over the entire age of the universe. We will explore the effectiveness of this parameter to distinguish between general relativity and modifications to gravity physics given realistic expectations of results from future experiments. Next, we will explore the modified growth formalism wherein deviations from the growth expected in general relativity are parameterized via changes to the growth equations, i.e. the perturbed Einstein's equations. We will also explore the impact of spatial curvature on these tests. Finally, we will study how dark energy with some unusual properties will affect the conclusiveness of these tests.

  12. Improved artificial bee colony algorithm based gravity matching navigation method.

    PubMed

    Gao, Wei; Zhao, Bo; Zhou, Guang Tao; Wang, Qiu Ying; Yu, Chun Yang

    2014-07-18

    Gravity matching navigation algorithm is one of the key technologies for gravity aided inertial navigation systems. With the development of intelligent algorithms, the powerful search ability of the Artificial Bee Colony (ABC) algorithm makes it possible to be applied to the gravity matching navigation field. However, existing search mechanisms of basic ABC algorithms cannot meet the need for high accuracy in gravity aided navigation. Firstly, proper modifications are proposed to improve the performance of the basic ABC algorithm. Secondly, a new search mechanism is presented in this paper which is based on an improved ABC algorithm using external speed information. At last, modified Hausdorff distance is introduced to screen the possible matching results. Both simulations and ocean experiments verify the feasibility of the method, and results show that the matching rate of the method is high enough to obtain a precise matching position.

  13. Improved Artificial Bee Colony Algorithm Based Gravity Matching Navigation Method

    PubMed Central

    Gao, Wei; Zhao, Bo; Zhou, Guang Tao; Wang, Qiu Ying; Yu, Chun Yang

    2014-01-01

    Gravity matching navigation algorithm is one of the key technologies for gravity aided inertial navigation systems. With the development of intelligent algorithms, the powerful search ability of the Artificial Bee Colony (ABC) algorithm makes it possible to be applied to the gravity matching navigation field. However, existing search mechanisms of basic ABC algorithms cannot meet the need for high accuracy in gravity aided navigation. Firstly, proper modifications are proposed to improve the performance of the basic ABC algorithm. Secondly, a new search mechanism is presented in this paper which is based on an improved ABC algorithm using external speed information. At last, modified Hausdorff distance is introduced to screen the possible matching results. Both simulations and ocean experiments verify the feasibility of the method, and results show that the matching rate of the method is high enough to obtain a precise matching position. PMID:25046019

  14. Multi-Scale Modeling of Liquid Phase Sintering Affected by Gravity: Preliminary Analysis

    NASA Technical Reports Server (NTRS)

    Olevsky, Eugene; German, Randall M.

    2012-01-01

    A multi-scale simulation concept taking into account impact of gravity on liquid phase sintering is described. The gravity influence can be included at both the micro- and macro-scales. At the micro-scale, the diffusion mass-transport is directionally modified in the framework of kinetic Monte-Carlo simulations to include the impact of gravity. The micro-scale simulations can provide the values of the constitutive parameters for macroscopic sintering simulations. At the macro-scale, we are attempting to embed a continuum model of sintering into a finite-element framework that includes the gravity forces and substrate friction. If successful, the finite elements analysis will enable predictions relevant to space-based processing, including size and shape and property predictions. Model experiments are underway to support the models via extraction of viscosity moduli versus composition, particle size, heating rate, temperature and time.

  15. KSC-07pd0955

    NASA Image and Video Library

    2007-04-26

    KENNEDY SPACE CENTER, FLA. -- At the Kennedy Space Center Shuttle Landing Facility, noted physicist Stephen Hawking, in the wheelchair, is ready to get onboard a modified Boeing 727 aircraft owned by Zero Gravity Corp. for his first zero-gravity flight. Zero Gravity Corp. is a commercial company licensed to provide the public with weightless flight experiences. At right is Peter Diamandis, founder of the Zero Gravity Corp. Behind Hawking is Nicola O'Brien, a nurse practitioner who is Hawking's aide. Hawking developed amyotrophic lateral sclerosis disease in the 1960s, a type of motor neuron disease which would cost him the loss of almost all neuromuscular control. At the celebration of his 65th birthday on January 8 this year, Hawking announced his plans for a zero-gravity flight to prepare for a sub-orbital space flight in 2009 on Virgin Galactic's space service. Photo credit: NASA/Kim Shiflett

  16. New observational constraints on f ( T ) gravity from cosmic chronometers

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Nunes, Rafael C.; Pan, Supriya; Saridakis, Emmanuel N., E-mail: nunes@ecm.ub.edu, E-mail: span@iiserkol.ac.in, E-mail: Emmanuel_Saridakis@baylor.edu

    2016-08-01

    We use the local value of the Hubble constant recently measured with 2.4% precision, as well as the latest compilation of cosmic chronometers data, together with standard probes such as Supernovae Type Ia and Baryon Acoustic Oscillation distance measurements, in order to impose constraints on the viable and most used f ( T ) gravity models, where T is the torsion scalar in teleparallel gravity. In particular, we consider three f ( T ) models with two parameters, out of which one is independent, and we quantify their deviation from ΛCDM cosmology through a sole parameter. Our analysis reveals thatmore » for one of the models a small but non-zero deviation from ΛCDM cosmology is slightly favored, while for the other models the best fit is very close to ΛCDM scenario. Clearly, f ( T ) gravity is consistent with observations, and it can serve as a candidate for modified gravity.« less

  17. Analyzing after-action reports from Hurricanes Andrew and Katrina: repeated, modified, and newly created recommendations.

    PubMed

    Knox, Claire Connolly

    2013-01-01

    Thirteen years after Hurricane Andrew struck Homestead, FL, Hurricane Katrina devastated the Gulf Coast of Mississippi, Alabama, and southeastern Louisiana. Along with all its destruction, the term "catastrophic" was redefined. This article extends the literature on these hurricanes by providing a macrolevel analysis of The Governor's Disaster Planning and Response Review Committee Final Report from Hurricane Andrew and three federal after-action reports from Hurricane Katrina, as well as a cursory review of relevant literature. Results provide evidence that previous lessons have not been learned or institutionalized with many recommendations being repeated or modified. This article concludes with a discussion of these lessons, as well as new issues arising during Hurricane Katrina.

  18. Characterization of heat transfer in nutrient materials, part 2

    NASA Technical Reports Server (NTRS)

    Cox, J. E.; Bannerot, R. B.; Chen, C. K.; Witte, L. C.

    1973-01-01

    A thermal model is analyzed that takes into account phase changes in the nutrient material. The behavior of fluids in low gravity environments is discussed along with low gravity heat transfer. Thermal contact resistance in the Skylab food heater is analyzed. The original model is modified to include: equivalent conductance due to radiation, radial equivalent conductance, wall equivalent conductance, and equivalent heat capacity. A constant wall-temperature model is presented.

  19. Comments on MacDowell-Mansouri gravity and torsion

    NASA Astrophysics Data System (ADS)

    López-Domínguez, J. C.; Rosales-Quintero, J. E.; Sabido, M.

    Starting with the MacDowell-Mansouri formulation of gravity with a SO(4, 1) gauge group, we introduce new parameters into the action to include the nondynamical Holst term, and the topological Nieh-Yan and Pontryagin classes. Then, we consider the new parameters as fields and analyze the solutions coming from their equations of motion. The new fields introduce torsional contributions to the theory that modify Einstein’s equations.

  20. Finding Horndeski theories with Einstein gravity limits

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    McManus, Ryan; Lombriser, Lucas; Peñarrubia, Jorge, E-mail: ryanm@roe.ac.uk, E-mail: llo@roe.ac.uk, E-mail: jorpega@roe.ac.uk

    The Horndeski action is the most general scalar-tensor theory with at most second-order derivatives in the equations of motion, thus evading Ostrogradsky instabilities and making it of interest when modifying gravity at large scales. To pass local tests of gravity, these modifications predominantly rely on nonlinear screening mechanisms that recover Einstein's Theory of General Relativity in regions of high density. We derive a set of conditions on the four free functions of the Horndeski action that examine whether a specific model embedded in the action possesses an Einstein gravity limit or not. For this purpose, we develop a new andmore » surprisingly simple scaling method that identifies dominant terms in the equations of motion by considering formal limits of the couplings that enter through the new terms in the modified action. This enables us to find regimes where nonlinear terms dominate and Einstein's field equations are recovered to leading order. Together with an efficient approximation of the scalar field profile, one can then further evaluate whether these limits can be attributed to a genuine screening effect. For illustration, we apply the analysis to both a cubic galileon and a chameleon model as well as to Brans-Dicke theory. Finally, we emphasise that the scaling method also provides a natural approach for performing post-Newtonian expansions in screened regimes.« less

  1. Differences in Perceived Competence and Physical Activity Levels during Single-Gender Modified Basketball Game Play in Middle School Physical Education

    ERIC Educational Resources Information Center

    Slingerland, Menno; Haerens, Leen; Cardon, Greet; Borghouts, Lars

    2014-01-01

    Creating environments in physical education (PE) that foster perceived competence and physical activity during gender-mixed game play lessons is a challenge, especially with adolescent girls. This study is a small experiment in one PE lesson that aimed to increase the perceived competence and in-class physical activity in girls, by applying a…

  2. Quasinormal modes of modified gravity (MOG) black holes

    NASA Astrophysics Data System (ADS)

    Manfredi, Luciano; Mureika, Jonas; Moffat, John

    2018-04-01

    The Quasinormal modes (QNMs) for gravitational and electromagnetic perturbations are calculated in a Scalar-Tensor-Vector (Modified Gravity) spacetime, which was initially proposed to obtain correct dynamics of galaxies and galaxy clusters without the need for dark matter. It is found that for the increasing model parameter α, both the real and imaginary parts of the QNMs decrease compared to those for a standard Schwarzschild black hole. On the other hand, when taking into account the 1 / (1 + α) mass re-scaling factor present in MOG, Im (ω) matches almost identically that of GR, while Re (ω) is higher. These results can be identified in the ringdown phase of massive compact object mergers, and are thus timely in light of the recent gravitational wave detections by LIGO.

  3. Binary Mixture of Perfect Fluid and Dark Energy in Modified Theory of Gravity

    NASA Astrophysics Data System (ADS)

    Shaikh, A. Y.

    2016-07-01

    A self consistent system of Plane Symmetric gravitational field and a binary mixture of perfect fluid and dark energy in a modified theory of gravity are considered. The gravitational field plays crucial role in the formation of soliton-like solutions, i.e., solutions with limited total energy, spin, and charge. The perfect fluid is taken to be the one obeying the usual equation of state, i.e., p = γρ with γ∈ [0, 1] whereas, the dark energy is considered to be either the quintessence like equation of state or Chaplygin gas. The exact solutions to the corresponding field equations are obtained for power-law and exponential volumetric expansion. The geometrical and physical parameters for both the models are studied.

  4. Dark matter admixed strange quark stars in the Starobinsky model

    NASA Astrophysics Data System (ADS)

    Lopes, Ilídio; Panotopoulos, Grigoris

    2018-01-01

    We compute the mass-to-radius profiles for dark matter admixed strange quark stars in the Starobinsky model of modified gravity. For quark matter, we assume the MIT bag model, while self-interacting dark matter inside the star is modeled as a Bose-Einstein condensate with a polytropic equation of state. We numerically integrate the structure equations in the Einstein frame, adopting the two-fluid formalism, and we treat the curvature correction term nonperturbatively. The effects on the properties of the stars of the amount of dark matter as well as the higher curvature term are investigated. We find that strange quark stars (in agreement with current observational constraints) with the highest masses are equally affected by dark matter and modified gravity.

  5. Exploiting the Modified Colombo-Nyquist Rule for Co-estimating Sub-monthly Gravity Field Solutions from a GRACE-like Mission

    NASA Astrophysics Data System (ADS)

    Devaraju, B.; Weigelt, M.; Mueller, J.

    2017-12-01

    In order to suppress the impact of aliasing errors on the standard monthly GRACE gravity-field solutions, co-estimating sub-monthly (daily/two-day) low-degree solutions has been suggested as a solution. The maximum degree of the low-degree solutions is chosen via the Colombo-Nyquist rule of thumb. However, it is now established that the sampling of satellites puts a restriction on the maximum estimable order and not the degree - modified Colombo-Nyquist rule. Therefore, in this contribution, we co-estimate low-order sub-monthly solutions, and compare and contrast them with the low-degree sub-monthly solutions. We also investigate their efficacies in dealing with aliasing errors.

  6. Reconstruction scenario in modified Horava-Lifshitz F( R) gravity with well-known scale factors

    NASA Astrophysics Data System (ADS)

    Jawad, Abdul; Rani, Shamaila

    2015-05-01

    In this paper, we analyze the behavior of pilgrim dark energy with G-O cutoff scale in modified Horava-Lifshitz F( R) gravity through correspondence scenario. We consider three well-known scale factors in which one scale factor describes the unification of matter dominated and accelerated phases and others are intermediate and bouncing forms. We obtain the models for these scale factors and obtain increasing behavior with the passage of time. We also extract equation of state parameter corresponding to these models. We observe that this parameter shows transition from phantom towards quintessence by crossing the phantom divide line in all cases. We also give comparison of our results of equation of state parameter with observational constraints.

  7. Modified floating-zone growth of organic single crystals

    NASA Astrophysics Data System (ADS)

    Kou, S.; Chen, C. P.

    1994-04-01

    For organic materials floating-zone crystal growth is superior to other melt growth processes in two significant respects: (1) the absence of crucible-induced mechanical damage and (2) minimum heating-induced chemical degradation. Due to the rather low surface tension of organic melts, however, floating-zone crystal growth under normal gravity has not been possible so far but microgravity is ideal for such a purpose. With the help of a modified floating-zone technique, organic single crystals of small cross-sections were test grown first under normal gravity. These small crystals were round and rectangular single crystals of benzil and salol, up to about 7 cm long and 6 mm in diameter or 9 mm × 3 mm in cross-section.

  8. Clustering of galaxies with f(R) gravity

    NASA Astrophysics Data System (ADS)

    Capozziello, Salvatore; Faizal, Mir; Hameeda, Mir; Pourhassan, Behnam; Salzano, Vincenzo; Upadhyay, Sudhaker

    2018-02-01

    Based on thermodynamics, we discuss the galactic clustering of expanding Universe by assuming the gravitational interaction through the modified Newton's potential given by f(R) gravity. We compute the corrected N-particle partition function analytically. The corrected partition function leads to more exact equations of state of the system. By assuming that the system follows quasi-equilibrium, we derive the exact distribution function that exhibits the f(R) correction. Moreover, we evaluate the critical temperature and discuss the stability of the system. We observe the effects of correction of f(R) gravity on the power-law behaviour of particle-particle correlation function also. In order to check the feasibility of an f(R) gravity approach to the clustering of galaxies, we compare our results with an observational galaxy cluster catalogue.

  9. Gravitational dynamics of biosystems - Some speculations

    NASA Technical Reports Server (NTRS)

    Kessler, J. O.; Bier, M.

    1976-01-01

    The response of organisms to gravity is generally discussed in terms of hypotheses involving sedimentation and other static effects. This paper considers several complex, inhomogeneous fluid-containing systems that are intended to model some possible dynamic effects of gravity on biosystems. It is shown that the presence of gravity may result in modified long range transport, concentration oscillations, and broken symmetries. The magnitude of density-gradient-driven convective transport times, and their ratios to diffusive transport times, are calculated for cell dimensions of six different plant varieties. The results indicate that further investigation of gravitational convection effects may be realistic in some cases and is definitely not in others. The results of this paper should aid in the planning of 'zero-gravity' experiments concerning plant geotropism and bio-materials processing.

  10. Constraining the loop quantum gravity parameter space from phenomenology

    NASA Astrophysics Data System (ADS)

    Brahma, Suddhasattwa; Ronco, Michele

    2018-03-01

    Development of quantum gravity theories rarely takes inputs from experimental physics. In this letter, we take a small step towards correcting this by establishing a paradigm for incorporating putative quantum corrections, arising from canonical quantum gravity (QG) theories, in deriving falsifiable modified dispersion relations (MDRs) for particles on a deformed Minkowski space-time. This allows us to differentiate and, hopefully, pick between several quantization choices via testable, state-of-the-art phenomenological predictions. Although a few explicit examples from loop quantum gravity (LQG) (such as the regularization scheme used or the representation of the gauge group) are shown here to establish the claim, our framework is more general and is capable of addressing other quantization ambiguities within LQG and also those arising from other similar QG approaches.

  11. Testing gravity with E{sub G}: mapping theory onto observations

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Leonard, C. Danielle; Ferreira, Pedro G.; Heymans, Catherine, E-mail: danielle.leonard@physics.ox.ac.uk, E-mail: p.ferreira1@physics.ox.ac.uk, E-mail: heymans@roe.ac.uk

    We present a complete derivation of the observationally motivated definition of the modified gravity statistic E{sub G}. Using this expression, we investigate how variations to theory and survey parameters may introduce uncertainty in the general relativistic prediction of E{sub G}. We forecast errors on E{sub G} for measurements using two combinations of upcoming surveys, and find that theoretical uncertainties may dominate for a futuristic measurement. Finally, we compute predictions of E{sub G} under modifications to general relativity in the quasistatic regime, and comment on the pros and cons of using E{sub G} to test gravity with future surveys.

  12. Eddington's theory of gravity and its progeny.

    PubMed

    Bañados, Máximo; Ferreira, Pedro G

    2010-07-02

    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.

  13. Instability of meridional axial system in f( R) gravity

    NASA Astrophysics Data System (ADS)

    Sharif, M.; Yousaf, Z.

    2015-05-01

    We analyze the dynamical instability of a non-static reflection axial stellar structure by taking into account the generalized Euler equation in metric f( R) gravity. Such an equation is obtained by contracting the Bianchi identities of the usual anisotropic and effective stress-energy tensors, which after using a radial perturbation technique gives a modified collapse equation. In the realm of the gravity model, we investigate instability constraints at Newtonian and post-Newtonian approximations. We find that the instability of a meridional axial self-gravitating system depends upon the static profile of the structure coefficients, while f( R) extra curvature terms induce the stability of the evolving celestial body.

  14. Gravitational waves in modified teleparallel theories of gravity.

    PubMed

    Abedi, Habib; Capozziello, Salvatore

    2018-01-01

    Teleparallel theory of gravity and its modifications have been studied extensively in literature. However, gravitational waves has not been studied enough in the framework of teleparallelism. In the present study, we discuss gravitational waves in general theories of teleparallel gravity containing the torsion scalar T , the boundary term B and a scalar field ϕ . The goal is to classify possible new polarizations generalizing results presented in Bamba et al. (Phys Lett B 727:194-198, arXiv:1309.2698, 2013). We show that, if the boundary term is minimally coupled to the torsion scalar and the scalar field, gravitational waves have the same polarization modes of General Relativity.

  15. Gravitational waves in modified teleparallel theories of gravity

    NASA Astrophysics Data System (ADS)

    Abedi, Habib; Capozziello, Salvatore

    2018-06-01

    Teleparallel theory of gravity and its modifications have been studied extensively in literature. However, gravitational waves has not been studied enough in the framework of teleparallelism. In the present study, we discuss gravitational waves in general theories of teleparallel gravity containing the torsion scalar T, the boundary term B and a scalar field φ . The goal is to classify possible new polarizations generalizing results presented in Bamba et al. (Phys Lett B 727:194-198, arXiv:1309.2698, 2013). We show that, if the boundary term is minimally coupled to the torsion scalar and the scalar field, gravitational waves have the same polarization modes of General Relativity.

  16. KSC-07pd0962

    NASA Image and Video Library

    2007-04-26

    KENNEDY SPACE CENTER, FLA. -- Well-wishers greet noted physicist Stephen Hawking (in the wheelchair) at the Kennedy Space Center Shuttle Landing Facility after a zero gravity flight. Next to him at left are Peter Diamandis, founder of the Zero Gravity Corp. that provided the flight aboard its modified Boeing 727, and Nicola O'Brien, a nurse practitioner who is Hawking's aide. Hawking suffers from amyotrophic lateral sclerosis (also known as Lou Gehrig's disease). At the celebration of his 65th birthday on January 8 this year, Hawking announced his plans for a zero-gravity flight to prepare for a sub-orbital space flight in 2009 on Virgin Galactic's space service. Photo credit: NASA/Kim Shiflett

  17. KSC-07pd0963

    NASA Image and Video Library

    2007-04-26

    KENNEDY SPACE CENTER, FLA. -- Well-wishers greet noted physicist Stephen Hawking (in the wheelchair) at the Kennedy Space Center Shuttle Landing Facility after a zero gravity flight. Next to him at left are Peter Diamandis, founder of the Zero Gravity Corp. that provided the flight aboard its modified Boeing 727, and Nicola O'Brien, a nurse practitioner who is Hawking's aide. Hawking suffers from amyotrophic lateral sclerosis (also known as Lou Gehrig's disease). At the celebration of his 65th birthday on January 8 this year, Hawking announced his plans for a zero-gravity flight to prepare for a sub-orbital space flight in 2009 on Virgin Galactic's space service. Photo credit: NASA/Kim Shiflett

  18. Gravity Bias in Young and Adult Chimpanzees ("Pan Troglodytes"): Tests with a Modified Opaque-Tubes Task

    ERIC Educational Resources Information Center

    Tomonaga, Masaki; Imura, Tomoko; Mizuno, Yuu; Tanaka, Masayuki

    2007-01-01

    Young human children at around 2 years of age fail to predict the correct location of an object when it is dropped from the top of an S-shape opaque tube. They search in the location just below the releasing point (Hood, 1995). This type of error, called a "gravity bias", has recently been reported in dogs and monkeys. In the present study, we…

  19. Microgravity

    NASA Image and Video Library

    2004-04-15

    The Reduced-Gravity Program provides the unique weightless or zero-g environment of space flight for testing and training of human and hardware reactions. The reduced-gravity environment is obtained with a specially modified KC-135A turbojet transport which flies parabolic arcs to produce weightless periods of 20 to 25 seconds. KC-135A cargo bay test area is approximately 60 feet long, 10 feet wide, and 7 feet high. The image shows KC-135A in flight.

  20. Improving Student Group Marketing Presentations: A Modified Pecha Kucha Approach

    ERIC Educational Resources Information Center

    Oliver, Jason; Kowalczyk, Christine

    2013-01-01

    Student presentations can often seem like a formality rather than a lesson in representing oneself or group in a professional manner. To improve the quality of group presentations, the authors modified the popular presentation style of Pecha Kucha (20 slides, 20 seconds per slide) for marketing courses to help students prepare and deliver…

  1. Lessons from the GP-B Experience for Future Fundamental Physics Missions in Space

    NASA Technical Reports Server (NTRS)

    Kolodziejczak, Jeffery

    2006-01-01

    Gravity Probe B launched in April 2004 and completed its science data collection in September 2005, with the objective of sub-milliarcsec measurement of two General Relativistic effects on the spin axis orientation of orbiting gyroscopes. Much of the technology required by GP-B has potential application in future missions intended to make precision measurements. The philosophical approach and experiment design principles developed for GP-B are equally adaptable to these mission concepts. This talk will discuss GP-B's experimental approach and the technological and philosophical lessons learned that apply to future experiments in fundamental physics. Measurement of fundamental constants to high precision, probes of short-range forces, searches for equivalence principle violations, and detection of gravitational waves are examples of concepts and missions that will benefit kern GP-B's experience.

  2. Energy scale of Lorentz violation in Rainbow Gravity

    NASA Astrophysics Data System (ADS)

    Nilsson, Nils A.; Dąbrowski, Mariusz P.

    2017-12-01

    We modify the standard relativistic dispersion relation in a way which breaks Lorentz symmetry-the effect is predicted in a high-energy regime of some modern theories of quantum gravity. We show that it is possible to realise this scenario within the framework of Rainbow Gravity which introduces two new energy-dependent functions f1(E) and f2(E) into the dispersion relation. Additionally, we assume that the gravitational constant G and the cosmological constant Λ also depend on energy E and introduce the scaling function h(E) in order to express this dependence. For cosmological applications we specify the functions f1 and f2 in order to fit massless particles which allows us to derive modified cosmological equations. Finally, by using Hubble+SNIa+BAO(BOSS+Lyman α)+CMB data, we constrain the energy scale ELV to be at least of the order of 1016 GeV at 1 σ which is the GUT scale or even higher 1017 GeV at 3 σ. Our claim is that this energy can be interpreted as the decoupling scale of massless particles from spacetime Lorentz violating effects.

  3. Scalar-tensor theories and modified gravity in the wake of GW170817

    NASA Astrophysics Data System (ADS)

    Langlois, David; Saito, Ryo; Yamauchi, Daisuke; Noui, Karim

    2018-03-01

    Theories of dark energy and modified gravity can be strongly constrained by astrophysical or cosmological observations, as illustrated by the recent observation of the gravitational wave event GW170817 and of its electromagnetic counterpart GRB 170817A, which showed that the speed of gravitational waves, cg , is the same as the speed of light, within deviations of order 10-15 . This observation implies severe restrictions on scalar-tensor theories, in particular theories whose action depends on second derivatives of a scalar field. Working in the very general framework of degenerate higher-order scalar-tensor (DHOST) theories, which encompass Horndeski and beyond Horndeski theories, we present the DHOST theories that satisfy cg=c . We then examine, for these theories, the screening mechanism that suppresses scalar interactions on small scales, namely the Vainshtein mechanism, and compute the corresponding gravitational laws for a nonrelativistic spherical body. We show that it can lead to a deviation from standard gravity inside matter, parametrized by three coefficients which satisfy a consistency relation and can be constrained by present and future astrophysical observations.

  4. Finite length-scale anti-gravity and observations of mass discrepancies in galaxies

    NASA Astrophysics Data System (ADS)

    Sanders, R. H.

    1986-01-01

    The modification of Newtonian attraction suggested by Sanders (1984) contains a repulsive Yukawa component which is characterised by two physical parameters: a coupling constant, α, and a length scale, r0. Although this form of the gravitational potential can result in flat rotation curves for a galaxy (or a point mass) it is not obvious that any modification of gravity associated with a definite length scale can reproduce the observed rotation curves of galaxies covering a wide range of mass and size. Here it is shown that the rotation curves of galaxies ranging in size from 5 to 40 kpc can be reproduced by this modified potential. Moreover, the implied mass-to-light ratios for a larger sample of galaxies are reasonable (one to three) and show no systematic trend with the size of the galaxy. The observed infrared Tully-Fisher law is shown to be consistent with the prediction of this revised gravity. The modified potential permits the X-ray emitting halos observed around elliptical galaxies to be bound without the addition of dark matter.

  5. Predicting airborne particle deposition by a modified Markov chain model for fast estimation of potential contaminant spread

    NASA Astrophysics Data System (ADS)

    Mei, Xiong; Gong, Guangcai

    2018-07-01

    As potential carriers of hazardous pollutants, airborne particles may deposit onto surfaces due to gravitational settling. A modified Markov chain model to predict gravity induced particle dispersion and deposition is proposed in the paper. The gravity force is considered as a dominant weighting factor to adjust the State Transfer Matrix, which represents the probabilities of the change of particle spatial distributions between consecutive time steps within an enclosure. The model performance has been further validated by particle deposition in a ventilation chamber and a horizontal turbulent duct flow in pre-existing literatures. Both the proportion of deposited particles and the dimensionless deposition velocity are adopted to characterize the validation results. Comparisons between our simulated results and the experimental data from literatures show reasonable accuracy. Moreover, it is also found that the dimensionless deposition velocity can be remarkably influenced by particle size and stream-wise velocity in a typical horizontal flow. This study indicates that the proposed model can predict the gravity-dominated airborne particle deposition with reasonable accuracy and acceptable computing time.

  6. Parametrizing growth in dark energy and modified gravity models

    NASA Astrophysics Data System (ADS)

    Resco, Miguel Aparicio; Maroto, Antonio L.

    2018-02-01

    It is well known that an extremely accurate parametrization of the growth function of matter density perturbations in Λ CDM cosmology, with errors below 0.25%, is given by f (a )=Ωmγ(a ) with γ ≃0.55 . In this work, we show that a simple modification of this expression also provides a good description of growth in modified gravity theories. We consider the model-independent approach to modified gravity in terms of an effective Newton constant written as μ (a ,k )=Geff/G and show that f (a )=β (a )Ωmγ(a ) provides fits to the numerical solutions with similar accuracy to that of Λ CDM . In the time-independent case with μ =μ (k ), simple analytic expressions for β (μ ) and γ (μ ) are presented. In the time-dependent (but scale-independent) case μ =μ (a ), we show that β (a ) has the same time dependence as μ (a ). As an example, explicit formulas are provided in the Dvali-Gabadadze-Porrati (DGP) model. In the general case, for theories with μ (a ,k ), we obtain a perturbative expansion for β (μ ) around the general relativity case μ =1 which, for f (R ) theories, reaches an accuracy below 1%. Finally, as an example we apply the obtained fitting functions in order to forecast the precision with which future galaxy surveys will be able to measure the μ parameter.

  7. Thought-Experiments About Gravity in the History of Science and in Research into Children's Thinking

    NASA Astrophysics Data System (ADS)

    Blown, E. J.; Bryce, T. G. K.

    2013-03-01

    This article examines the main strands of thinking about gravity through the ages and the continuity of thought-experiments, from the early Greeks, through medieval times, to Galileo, Newton and Einstein. The key ideas are used to contextualise an empirical study of 247 children's ideas about falling objects carried out in China and New Zealand, including the use of scenarios involving thrown and dropped items, and objects falling down deep well holes (as in Carroll's Alice in Wonderland). The sample included 68 pre-school pupils, 68 primary school pupils, 56 middle school students, and 55 high school students; with approximately equal numbers in each group and of boys and girls in each group in each culture. The methodology utilised Piagetian interviews with three media (verbal language, drawing, and play-dough), a shadow stick; and everyday items including model people and soft model animals. The data from each group was categorised and analysed with Kolmogorov- Smirnov Two- Sample Tests and Spearman r s coefficients. It was hypothesised and confirmed (at K- S alpha levels .05; r s : p < .001) that cross-age and cross-cultural research and analysis would reveal that (a) an intuitive sense of gravity is present from an early age and develops in association with concepts like Earth shape and motion; (b) the development of concepts of gravity is similar in cultures such as China and New Zealand where teachers hold a scientific world view; and (c) children's concepts of Earth motion, Earth shape, and gravity are coherent rather than fragmented. It was also demonstrated that multi-media interviews together with concrete experiences and thought-experiments afforded children the opportunity to share their emerging concepts of gravity. The findings provide information that teachers might use for lessons at an appropriate level.

  8. DOE Office of Scientific and Technical Information (OSTI.GOV)

    Frusciante, Noemi; Papadomanolakis, Georgios; Silvestri, Alessandra, E-mail: fruscian@iap.fr, E-mail: papadomanolakis@lorentz.leidenuniv.nl, E-mail: silvestri@lorentz.leidenuniv.nl

    We present a generalization of the effective field theory (EFT) formalism for dark energy and modified gravity models to include operators with higher order spatial derivatives. This allows the extension of the EFT framework to a wider class of gravity theories such as Hořava gravity. We present the corresponding extended action, both in the EFT and the Arnowitt-Deser-Misner (ADM) formalism, and proceed to work out a convenient mapping between the two, providing a self contained and general procedure to translate a given model of gravity into the EFT language at the basis of the Einstein-Boltzmann solver EFTCAMB. Putting this mappingmore » at work, we illustrate, for several interesting models of dark energy and modified gravity, how to express them in the ADM notation and then map them into the EFT formalism. We also provide for the first time, the full mapping of GLPV models into the EFT framework. We next perform a thorough analysis of the physical stability of the generalized EFT action, in absence of matter components. We work out viability conditions that correspond to the absence of ghosts and modes that propagate with a negative speed of sound in the scalar and tensor sector, as well as the absence of tachyonic modes in the scalar sector. Finally, we extend and generalize the phenomenological basis in terms of α-functions introduced to parametrize Horndeski models, to cover all theories with higher order spatial derivatives included in our extended action. We elaborate on the impact of the additional functions on physical quantities, such as the kinetic term and the speeds of propagation for scalar and tensor modes.« less

  9. Large-scale structure in brane-induced gravity. I. Perturbation theory

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Scoccimarro, Roman

    2009-11-15

    We study the growth of subhorizon perturbations in brane-induced gravity using perturbation theory. We solve for the linear evolution of perturbations taking advantage of the symmetry under gauge transformations along the extra-dimension to decouple the bulk equations in the quasistatic approximation, which we argue may be a better approximation at large scales than thought before. We then study the nonlinearities in the bulk and brane equations, concentrating on the workings of the Vainshtein mechanism by which the theory becomes general relativity (GR) at small scales. We show that at the level of the power spectrum, to a good approximation, themore » effect of nonlinearities in the modified gravity sector may be absorbed into a renormalization of the gravitational constant. Since the relation between the lensing potential and density perturbations is entirely unaffected by the extra physics in these theories, the modified gravity can be described in this approximation by a single function, an effective gravitational constant for nonrelativistic motion that depends on space and time. We develop a resummation scheme to calculate it, and provide predictions for the nonlinear power spectrum. At the level of the large-scale bispectrum, the leading order corrections are obtained by standard perturbation theory techniques, and show that the suppression of the brane-bending mode leads to characteristic signatures in the non-Gaussianity generated by gravity, generic to models that become GR at small scales through second-derivative interactions. We compare the predictions in this work to numerical simulations in a companion paper.« less

  10. Cosmology based on f(R) gravity with O(1) eV sterile neutrino

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Chudaykin, Anton S.; Gorbunov, Dmitry S.; Starobinsky, Alexei A.

    2015-05-01

    We address the cosmological role of an additional O(1) eV sterile neutrino in modified gravity models. We confront the present cosmological data with predictions of the FLRW cosmological model based on a variant of f(R) modified gravity proposed by one of the authors previously. This viable cosmological model which deviation from general relativity with a cosmological constant Λ decreases as R{sup −2n} for large, but not too large values of the Ricci scalar R (while no Λ is introduced by hand at small R) provides an alternative explanation of present dark energy and the accelerated expansion of the Universe (themore » case n=2 is considered in the paper). Various up-to-date cosmological data sets exploited include measurements of the cosmic microwave background (CMB) anisotropy, the CMB lensing potential, the baryon acoustic oscillations (BAO), the cluster mass function and the Hubble constant. We find that the CMB+BAO constraints strongly restrict the sum of neutrino masses from above. This excludes values of the model parameter λ∼ 1 for which distinctive cosmological features of the model are mostly pronounced as compared to the ΛCDM model, since then free streaming damping of perturbations due to neutrino rest masses is not sufficient to compensate their extra growth occurring in f(R) modified gravity. Thus, in the gravity sector we obtain λ>8.2 (2σ) with the account of systematic uncertainties in galaxy cluster mass function measurements and λ>9.4 (2σ) without them. At the same time in the latter case we find for the sterile neutrino mass 0.47 eV < m{sub ν, sterile} < 1 eV (2σ) assuming that the sterile neutrinos are thermalized and the active neutrinos are massless, not significantly larger than in the standard ΛCDM with the same data set: 0.45 eV < m{sub ν, sterile} < 0.92 eV (2σ). However, a possible discovery of a sterile neutrino with the mass m{sub ν, sterile} ≈ 1.5 eV motivated by various anomalies in neutrino oscillation experiments would favor cosmology based on f(R) gravity rather than the ΛCDM model.« less

  11. KSC-07pd0950

    NASA Image and Video Library

    2007-04-26

    KENNEDY SPACE CENTER, FLA. -- At the Kennedy Space Center Shuttle Landing Facility, Space Florida president Steve Kohler (left) talks to the media about physicist Stephen Hawking's (in the wheelchair) first zero-gravity flight. The flight will be aboard a modified Boeing 727 aircraft owned by Zero Gravity Corp., a commercial company licensed to provide the public with weightless flight experiences. At right is Peter Diamandis, founder of the Zero Gravity Corp. Hawking developed amyotrophic lateral sclerosis disease in the 1960s, a type of motor neuron disease which would cost him the loss of almost all neuromuscular control. At the celebration of his 65th birthday on January 8 this year, Hawking announced his plans for a zero-gravity flight to prepare for a sub-orbital space flight in 2009 on Virgin Galactic's space service. Photo credit: NASA/Kim Shiflett

  12. New observational constraints on f ( R ) gravity from cosmic chronometers

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Nunes, Rafael C.; Pan, Supriya; Saridakis, Emmanuel N.

    We use the recently released cosmic chronometer data and the latest measured value of the local Hubble parameter, combined with the latest joint light curves of Supernovae Type Ia, and Baryon Acoustic Oscillation distance measurements, in order to impose constraints on the viable and most used f ( R ) gravity models. We consider four f ( R ) models, namely the Hu-Sawicki, the Starobinsky, the Tsujikawa, and the exponential one, and we parametrize them introducing a distortion parameter b that quantifies the deviation from ΛCDM cosmology. Our analysis reveals that a small but non-zero deviation from ΛCDM cosmology ismore » slightly favored, with the corresponding fittings exhibiting very efficient AIC and BIC Information Criteria values. Clearly, f ( R ) gravity is consistent with observations, and it can serve as a candidate for modified gravity.« less

  13. Inclination Angles of Black Hole X-Ray Binaries Manifest Strong Gravity around Black Holes

    NASA Technical Reports Server (NTRS)

    Zhang, S. N.; Zhang, Xiao-Ling; Yao, Yangsen

    2002-01-01

    System inclination angles have been determined for about 15 X-ray binaries, in which stellar mass black holes are considered to exist. These inclination angles range between 25 degrees and 80 degrees, but peaked between 60-70 degrees. This peak is not explained in the frame work of Newtonian gravity. However, this peak is reproduced naturally if we model the observed X-ray radiations as being produced in the accretion disks very close to the black hole horizons, where the extremely strong general and special relativistic effects, caused by the extremely strong gravity near the black hole horizons, modify the local radiation significantly as the X-rays propagate to the remote observer. Therefore the peak of the inclination angle distribution provides evidence or strong gravity around stellar mass black holes.

  14. Anisotropic singularities in modified gravity models

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Figueiro, Michele Ferraz; Saa, Alberto; Departamento de Matematica Aplicada, IMECC-UNICAMP, C.P. 6065, 13083-859 Campinas, SP

    2009-09-15

    We show that the common singularities present in generic modified gravity models governed by actions of the type S={integral}d{sup 4}x{radical}(-g)f(R,{phi},X), with X=-(1/2)g{sup ab}{partial_derivative}{sub a}{phi}{partial_derivative}{sub b}{phi}, are essentially the same anisotropic instabilities associated to the hypersurface F({phi})=0 in the case of a nonminimal coupling of the type F({phi})R, enlightening the physical origin of such singularities that typically arise in rather complex and cumbersome inhomogeneous perturbation analyses. We show, moreover, that such anisotropic instabilities typically give rise to dynamically unavoidable singularities, precluding completely the possibility of having physically viable models for which the hypersurface ({partial_derivative}f/{partial_derivative}R)=0 is attained. Some examples are explicitly discussed.

  15. Modified QCD ghost f(T,TG) gravity

    NASA Astrophysics Data System (ADS)

    Jawad, Abdul; Rani, Shamaila; Chattopadhyay, Surajit

    2015-12-01

    In this paper, we explore the reconstruction scenario of modified QCD ghost dark energy model and newly proposed f(T,TG) gravity in flat FRW universe. We consider the well-known assumption of scale factor, i.e., power law form. We construct the f(T,TG) model and discuss its cosmological consequences through various cosmological parameters such as equation of state parameter, squared speed of sound and ω_{DE}-ω '_{DE}. The equation of state parameter provides the quintom-like behavior of the universe. The squared speed of sound exhibits the stability of model in the later time. Also, ω_{DE}- ω '_{DE} corresponds to freezing as well as thawing regions. It is also interesting to remark here that the results of equation of state parameter and w_{DE}-w'_{DE} coincide with the observational data.

  16. [An assessment approach to the adequacy of peritoneal dialysis based on modified MART2 network].

    PubMed

    Zhang, Mei; Zhao, Jing; Hu, Yueming

    2009-06-01

    Against the large number of assessment indices to the adequacy peritoneal dialysis and incompatibility of some indices, an intelligent assessment approach to the peritoneal dialysis adequacy based on MART2 (modified from ART2) network is proposed. After non-dimension and weighting preconditioning, the assessment indices were put to MART2 and sorted into many clusters. The center-of-gravity of each cluster was identified as adequacy or inadequacy according to the assessment criteria of dialysis adequacy, and the adequacy of each cluster could be determined by the adequacy of corresponding center-of-gravity when the network threshold was high. Finally, the peritoneal dialysis adequacy of each patient could be judged according to the adequacy of cluster to which the patients' indices belong. Experimental results demounstrate its effectiveness.

  17. FLRW cosmological models with quark and strange quark matters in f(R,T) gravity

    NASA Astrophysics Data System (ADS)

    Nagpal, Ritika; Singh, J. K.; Aygün, S.

    2018-06-01

    In this paper, we have studied the magnetized quark matter (QM) and strange quark matter (SQM) distributions in the presence of f(R,T) gravity in the background of Friedmann-Lemaître-Robertson-Walker (FLRW) metric. To get exact solutions of modified field equations we have used f(R,T ) = R + 2 f(T) model given by Harko et al. with two different parametrization of geometrical parameters i.e. the parametrization of the deceleration parameter q , and the scale factor a in hybrid expansion form. Also, we have obtained Einstein Static Universe (ESU) solutions for QM and SQM distributions in f(R,T) gravity and General Relativity (GR). All models in f(R,T) gravity and GR for FRW and ESU Universes with QM also SQM distributions, we get zero magnetic field. These results agree with the solutions of Aktaş and Aygün in f(R,T) gravity. However, we have also discussed the physical consequences of our obtained models.

  18. Digital holographic microscopy long-term and real-time monitoring of cell division and changes under simulated zero gravity.

    PubMed

    Pan, Feng; Liu, Shuo; Wang, Zhe; Shang, Peng; Xiao, Wen

    2012-05-07

    The long-term and real-time monitoring the cell division and changes of osteoblasts under simulated zero gravity condition were succeed by combing a digital holographic microscopy (DHM) with a superconducting magnet (SM). The SM could generate different magnetic force fields in a cylindrical cavity, where the gravitational force of biological samples could be canceled at a special gravity position by a high magnetic force. Therefore the specimens were levitated and in a simulated zero gravity environment. The DHM was modified to fit with SM by using single mode optical fibers and a vertically-configured jig designed to hold specimens and integrate optical device in the magnet's bore. The results presented the first-phase images of living cells undergoing dynamic divisions and changes under simulated zero gravity environment for a period of 10 hours. The experiments demonstrated that the SM-compatible DHM setup could provide a highly efficient and versatile method for research on the effects of microgravity on biological samples.

  19. Using a Modified Simple Pendulum to Find the Variations in the Value of “g”

    NASA Astrophysics Data System (ADS)

    Arnold, Jonathan P.; Efthimiou, C.

    2007-05-01

    The simple pendulum is one of the most known and studied system of Newtonian Mechanics. It also provides one of the most elegant and simple devices to measure the acceleration of gravity at any location. In this presentation we will revisit the problem of measuring the acceleration of gravity using a simple pendulum and will present a modification to the standard technique that increases the accuracy of the measurement.

  20. Inverse scattering method and soliton double solution family for the general symplectic gravity model

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Gao Yajun

    A previously established Hauser-Ernst-type extended double-complex linear system is slightly modified and used to develop an inverse scattering method for the stationary axisymmetric general symplectic gravity model. The reduction procedures in this inverse scattering method are found to be fairly simple, which makes the inverse scattering method applied fine and effective. As an application, a concrete family of soliton double solutions for the considered theory is obtained.

  1. Relation Between Motility, Accelerated Aging and Gene Expression in Selected Drosophila Strains under Hypergravity Conditions

    NASA Astrophysics Data System (ADS)

    Serrano, Paloma; van Loon, Jack J. W. A.; Medina, F. Javier; Herranz, Raúl

    2013-02-01

    Motility and aging in Drosophila have proven to be highly modified under altered gravity conditions (both in space and ground simulation facilities). In order to find out how closely connected they are, five strains with altered geotactic response or survival rates were selected and exposed to an altered gravity environment of 2 g. By analysing the different motile and behavioural patterns and the median survival rates, we show that altered gravity leads to changes in motility, which will have a negative impact on the flies' survival. Previous results show a differential gene expression between sessile samples and adults and confirm that environmentally-conditioned behavioural patterns constrain flies' gene expression and life span. Therefore, hypergravity is considered an environmental stress factor and strains that do not respond to this new environment experience an increment in motility, which is the major cause for the observed increased mortality also under microgravity conditions. The neutral-geotaxis selected strain (strain M) showed the most severe phenotype, unable to respond to variations in the gravitational field. Alternatively, the opposite phenotype was observed in positive-geotaxis and long-life selected flies (strains B and L, respectively), suggesting that these populations are less sensitive to alterations in the gravitational load. We conclude that the behavioural response has a greater contribution to aging than the modified energy consumption in altered gravity environments.

  2. The Amateur Scientist.

    ERIC Educational Resources Information Center

    Walker, Jearl

    1980-01-01

    Describes an inexpensive apparatus for the detection of gravity waves traveling through the ionosphere. The detector consists of a modified transistor radio with a ferrite-core antenna. Numerous diagrams accompany a lengthy description. (CS)

  3. Membrane Fluidity Changes, A Basic Mechanism of Interaction of Gravity with Cells?

    NASA Astrophysics Data System (ADS)

    Kohn, Florian; Hauslage, Jens; Hanke, Wolfgang

    2017-10-01

    All life on earth has been established under conditions of stable gravity of 1g. Nevertheless, in numerous experiments the direct gravity dependence of biological processes has been shown on all levels of organization, from single molecules to humans. According to the underlying mechanisms a variety of questions, especially about gravity sensation of single cells without specialized organelles or structures for gravity sensing is being still open. Biological cell membranes are complex structures containing mainly lipids and proteins. Functional aspects of such membranes are usually attributed to membrane integral proteins. This is also correct for the gravity dependence of cells and organisms which is well accepted since long for a wide range of biological systems. However, it is as well established that parameters of the lipid matrix are directly modifying the function of proteins. Thus, the question must be asked, whether, and how far plain lipid membranes are affected by gravity directly. In principle it can be said that up to recently no real basic mechanism for gravity perception in single cells has been presented or verified. However, it now has been shown that as a basic membrane parameter, membrane fluidity, is significantly dependent on gravity. This finding might deliver a real basic mechanism for gravity perception of living organisms on all scales. In this review we summarize older and more recent results to demonstrate that the finding of membrane fluidity being gravity dependent is consistent with a variety of published laboratory experiments. We additionally point out to the consequences of these recent results for research in the field life science under space condition.

  4. Cosmological reconstruction and Om diagnostic analysis of Einstein-Aether theory

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Pasqua, Antonio; Chattopadhyay, Surajit; Momeni, Davood

    In this paper, we analyze the cosmological models in Einstein-Aether gravity, which is a modified theory of gravity in which a time-like vector field breaks the Lorentz symmetry. We use this formalism to analyse different cosmological models with different behavior of the scale factor. In this analysis, we use a certain functional dependence of the Dark Energy (DE) on the Hubble parameter H . It will be demonstrated that the Aether vector field has a non-trivial effect on these cosmological models. We also perform the Om diagnostic in Einstein-Aether gravity and we fit the parameters of the cosmological models usingmore » recent observational data.« less

  5. Higgs mechanism for gravity. II. Higher spin connections

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Boulanger, Nicolas; Kirsch, Ingo; Jefferson Laboratory of Physics, Harvard University, Cambridge, Massachusetts 02138

    We continue the work of [Phys. Rev. D 72, 024001 (2005)] in which gravity is considered as the Goldstone realization of a spontaneously broken diffeomorphism group. We complete the discussion of the coset space Diff (d,R)/SO(1,d-1) formed by the d-dimensional group of analytic diffeomorphisms and the Lorentz group. We find that this coset space is parametrized by coordinates, a metric, and an infinite tower of higher-spin or generalized connections. We then study effective actions for the corresponding symmetry breaking which gives mass to the higher spin connections. Our model predicts that gravity is modified at high energies by the exchangemore » of massive higher spin particles.« less

  6. Constraints on Yukawa parameters by double pulsars

    NASA Astrophysics Data System (ADS)

    Deng, Xue-Mei; Xie, Yi; Huang, Tian-Yi

    2013-03-01

    Although Einstein's general relativity has passed all the tests so far, alternative theories are still required for deeper understanding of the nature of gravity. Double pulsars provide us a significant opportunity to test them. In order to probe some modified gravities which try to explain some astrophysical phenomena without dark matter, we use periastron advance dot{ω} of four binary pulsars (PSR B1913+16, PSR B1534+12, PSR J0737-3039 and PSR B2127+11C) to constrain their Yukawa parameters: λ = (3.97 ± 0.01) × 108m and α = (2.40 ± 0.02) × 10-8. It might help us to distinguish different gravity theories and get closer to the new physics.

  7. KSC-07pd0946

    NASA Image and Video Library

    2007-04-26

    KENNEDY SPACE CENTER, FLA. -- Noted physicist Stephen Hawking arrives at the Kennedy Space Center Shuttle Landing Facility for his first zero-gravity flight. The flight will be aboard a modified Boeing 727 aircraft owned by Zero Gravity Corp., a commercial company licensed to provide the public with weightless flight experiences. Hawking developed amyotrophic lateral sclerosis disease in the 1960s, a type of motor neuron disease which would cost him the loss of almost all neuromuscular control. At the celebration of his 65th birthday on January 8 this year, Hawking announced his plans for a zero-gravity flight to prepare for a sub-orbital space flight in 2009 on Virgin Galactic's space service. Photo credit: NASA/Kim Shiflett

  8. Covariant generalized holographic dark energy and accelerating universe

    NASA Astrophysics Data System (ADS)

    Nojiri, Shin'ichi; Odintsov, S. D.

    2017-08-01

    We propose the generalized holographic dark energy model where the infrared cutoff is identified with the combination of the FRW universe parameters: the Hubble rate, particle and future horizons, cosmological constant, the universe lifetime (if finite) and their derivatives. It is demonstrated that with the corresponding choice of the cutoff one can map such holographic dark energy to modified gravity or gravity with a general fluid. Explicitly, F( R) gravity and the general perfect fluid are worked out in detail and the corresponding infrared cutoff is found. Using this correspondence, we get realistic inflation or viable dark energy or a unified inflationary-dark energy universe in terms of covariant holographic dark energy.

  9. One gravitational potential or two? Forecasts and tests.

    PubMed

    Bertschinger, Edmund

    2011-12-28

    The metric of a perturbed Robertson-Walker space-time is characterized by three functions: a scale-factor giving the expansion history and two potentials that generalize the single potential of Newtonian gravity. The Newtonian potential induces peculiar velocities and, from these, the growth of matter fluctuations. Massless particles respond equally to the Newtonian potential and to a curvature potential. The difference of the two potentials, called the gravitational slip, is predicted to be very small in general relativity, but can be substantial in modified gravity theories. The two potentials can be measured, and gravity tested on cosmological scales, by combining weak gravitational lensing or the integrated Sachs-Wolfe effect with galaxy peculiar velocities or clustering.

  10. KSC-07pd0960

    NASA Image and Video Library

    2007-04-26

    KENNEDY SPACE CENTER, FLA. -- Noted physicist Stephen Hawking (center) returns to the Kennedy Space Center Shuttle Landing Facility after a zero gravity flight. At his side is Nicola O'Brien, a nurse practitioner who is Hawking's aide. At far left on the truck's tail gate is Peter Diamandis, founder of the Zero Gravity Corp. that provided the flight aboard its modified Boeing 727. Hawking suffers from amyotrophic lateral sclerosis (also known as Lou Gehrig's disease). At the celebration of his 65th birthday on January 8 this year, Hawking announced his plans for a zero-gravity flight to prepare for a sub-orbital space flight in 2009 on Virgin Galactic's space service. Photo credit: NASA/Kim Shiflett

  11. Modification of the gravity model and application to the metropolitan Seoul subway system.

    PubMed

    Goh, Segun; Lee, Keumsook; Park, Jong Soo; Choi, M Y

    2012-08-01

    The Metropolitan Seoul Subway system is examined through the use of the gravity model. Exponents describing the power-law dependence on the time distance between stations are obtained, which reveals a universality for subway lines of the same topology. In the short (time) distance regime the number of passengers between stations does not grow with the decrease in the distance, thus deviating from the power-law behavior. It is found that such reduction in passengers is well described by the Hill function. Further, temporal fluctuations in the passenger flow data, fitted to the gravity model modified by the Hill function, are analyzed to reveal the Yule-type nature inherent in the structure of Seoul.

  12. Lessons from obesity prevention for the prevention of mental disorders: the primordial prevention approach.

    PubMed

    Hayward, Joshua; Jacka, Felice N; Waters, Elizabeth; Allender, Steven

    2014-09-10

    Emerging evidence supports a relationship between risk factors for obesity and the genesis of the common mental disorders, depression and anxiety. This suggests common mental disorders should be considered as a form of non-communicable disease, preventable through the modification of lifestyle behaviours, particularly diet and physical activity. Obesity prevention research since the 1970's represents a considerable body of knowledge regarding strategies to modify diet and physical activity and so there may be clear lessons from obesity prevention that apply to the prevention of mental disorders. For obesity, as for common mental disorders, adolescence represents a key period of vulnerability. In this paper we briefly discuss relationships between modifiable lifestyle risk factors and mental health, lifestyle risk factor interventions in obesity prevention research, the current state of mental health prevention, and the implications of current applications of systems thinking in obesity prevention research for lifestyle interventions. We propose a potential focus for future mental health promotion interventions and emphasise the importance of lessons available from other lifestyle modification intervention programmes.

  13. Preservice teachers' use of lesson study in teaching nature of science

    NASA Astrophysics Data System (ADS)

    McDowell, Amy Virginia

    The purpose of this study was to explore preservice teachers' lived experiences in a lesson study focused on teaching and learning nature of science (NOS). The body of knowledge about shifting pre- and in-service novice NOS understandings is substantial. The focus of science education research is now exploring ways to move these informed NOS understandings into classroom practice (Abd-El-Khalick & Lederman, 2000b). The research questions guiding the study were (a) how do preservice teachers' understandings of NOS shift as a result of the lesson study experience?, and (b) how does the reflective practice that occurs in lesson study influence preservice teachers' transition of NOS tenets into classroom practice? The participants in this study represented a sample of graduate preservice teachers, who were part of a middle and secondary science teaching alternative certification program in a southeastern university. In the first summer semester of this certification program, the participants were immersed in reform based science instruction; a section of which included NOS teachings (INTASC, 2002). In the following semester, participants were placed in a practicum setting; where the exploration of the preservice teachers' teaching of NOS was supported through the modified lesson study framework. Data sources included the Views on Nature of Science-Form B (VNOS-b), interviews, and lesson study portfolios. Analysis of NOS understandings was guided by instruments found in literature associated with the VNOS-b (Lederman et al., 2002) and reflection (Ward & McCotter, 2004). Results showed successful transfer of NOS into classroom practice using the modified lesson study framework, with less success in the deepening of participants' NOS understandings. Of particular significance was that results indicated a deepening of NOS pedagogical content knowledge for those participants functioning at higher levels of reflection. The study's results contributes to two knowledge bases. First it provides insight to how lesson study can be used in the United States in alterative teacher preparation programs. Second, it contributes to what is understood about how to support the transition of NOS understandings into classroom practice.

  14. Gravity Probe B data system description

    NASA Astrophysics Data System (ADS)

    Bennett, Norman R.

    2015-11-01

    The Gravity Probe B data system, developed, integrated, and tested by Lockheed Missiles & Space Company, and later Lockheed Martin Corporation, included flight and ground command, control, and communications software. The development was greatly facilitated, conceptually and by the transfer of key personnel, through Lockheed’s earlier flight and ground test software development for the Hubble Space Telescope (HST). Key design challenges included the tight mission timeline (17 months, 9 days of on-orbit operation), the need to tune the system once on-orbit, and limited 2 Kbps real-time data rates and ground asset availability. The result was a completely integrated space vehicle and Stanford mission operations center, which successfully collected and archived 97% of the ‘guide star valid’ data to support the science analysis. Lessons learned and incorporated from the HST flight software development and on-orbit support experience, and Lockheed’s independent research and development effort, will be discussed.

  15. Test and On-Orbit Experiences of FalconSAT-3

    NASA Astrophysics Data System (ADS)

    Saylor, W. W.; France, M. E. B.

    2008-08-01

    The fundamental objectives of the capstone design project in the Department of Astronautics at the United States Air Force Academy (USAFA) are for cadets to learn important engineering lessons by executing a real space mission on a Department of Defense-funded satellite project. FalconSAT-3 is a 50 kg, gravity gradient-stabilized designed and built by cadets and launched March 2007 on the first ESPA (Enhanced extended launch vehicle Satellite Payload Adapter) mission. FalconSAT-3 was one of six satellites integrated onto the launch vehicle and the nature of the mission made it that the satellite was subject to the full formality of testing requirements. Two successive gravity gradient booms failed either design requirements or environmental testing; design requirements grew dramatically during the design phase; ambiguous thermal vacuum test results led to uncertainty at launch; and after launch it was not possible to contact the satellite for several weeks.

  16. Exploration of plant growth and development using the European Modular Cultivation System facility on the International Space Station.

    PubMed

    Kittang, A-I; Iversen, T-H; Fossum, K R; Mazars, C; Carnero-Diaz, E; Boucheron-Dubuisson, E; Le Disquet, I; Legué, V; Herranz, R; Pereda-Loth, V; Medina, F J

    2014-05-01

    Space experiments provide a unique opportunity to advance our knowledge of how plants respond to the space environment, and specifically to the absence of gravity. The European Modular Cultivation System (EMCS) has been designed as a dedicated facility to improve and standardise plant growth in the International Space Station (ISS). The EMCS is equipped with two centrifuges to perform experiments in microgravity and with variable gravity levels up to 2.0 g. Seven experiments have been performed since the EMCS was operational on the ISS. The objectives of these experiments aimed to elucidate phototropic responses (experiments TROPI-1 and -2), root gravitropic sensing (GRAVI-1), circumnutation (MULTIGEN-1), cell wall dynamics and gravity resistance (Cell wall/Resist wall), proteomic identification of signalling players (GENARA-A) and mechanism of InsP3 signalling (Plant signalling). The role of light in cell proliferation and plant development in the absence of gravity is being analysed in an on-going experiment (Seedling growth). Based on the lessons learned from the acquired experience, three preselected ISS experiments have been merged and implemented as a single project (Plant development) to study early phases of seedling development. A Topical Team initiated by European Space Agency (ESA), involving experienced scientists on Arabidopsis space research experiments, aims at establishing a coordinated, long-term scientific strategy to understand the role of gravity in Arabidopsis growth and development using already existing or planned new hardware. © 2014 German Botanical Society and The Royal Botanical Society of the Netherlands.

  17. Lumpy Janus

    NASA Image and Video Library

    2013-07-01

    The Cassini spacecraft catches a glimpse of Janus, an irregularly shaped moon. Lacking sufficient gravity to pull itself into a round shape, Janus has had its lumpy primordial shape only slightly modified by impacts since its formation.

  18. Teaching Technical Competencies for Fluid Mechanics Research

    NASA Astrophysics Data System (ADS)

    Tagg, Randall

    2014-11-01

    We are developing an ``on demand'' framework for students to learn techniques used in fluid mechanics research. The site for this work is a university-grade laboratory situated next to Gateway High School in Aurora, Colorado. Undergraduate university students work with K-12 students on research and technical innovation projects. Both groups need customized training as their projects proceed. A modular approach allows particular competencies such as pump selection, construction of flow piping and channels, flow visualization, and specific flow measurement methods to be acquired through focused lessons. These lessons can be learned in either a stand-alone fashion or assembled into units for formal courses. A research example was a student project on diffusion of infectious material in micro-gravity in the event of an intestinal puncture wound. A curriculum example is a 9-week quarter of high-school instruction on instrumentation that uses small-scale water treatment systems as a case study.

  19. How an inquiry-based classroom lesson intervenes in science efficacy, career-orientation and self-determination

    NASA Astrophysics Data System (ADS)

    Schmid, S.; Bogner, F. X.

    2017-11-01

    Three subscales of the 'Science Motivation Questionnaire II' (SMQII; motivational components: career motivation, self-efficacy and self-determination), with 4 items each, were applied to a sample of 209 secondary school students to monitor the impact of a 3-hour structured inquiry lesson. Four testing points (before, immediately after, 6 and 12 weeks after) were applied. The modified SMQII was factor-analyzed at each testing cycle and the structure confirmed. Only self-determination was shown to be influenced by an inquiry course, while self-efficacy and career motivation did not. Only self-efficacy and career motivation were intercorrelated and also correlated with science subject grades and subsequent achievement. Implications for using the modified SMQII subscales for research and teaching in secondary school are discussed.

  20. Is Cosmic Acceleration Telling Us Something About Gravity?

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Trodden, Mark

    2006-03-02

    Among the possible explanations for the observed acceleration of the universe, perhaps the boldest is the idea that new gravitational physics might be the culprit. In this colloquium I will discuss some of the challenges of constructing a sensible phenomenological extension of General Relativity, give examples of some candidate models of modified gravity and survey existing observational constraints on this approach. I will conclude by discussing how we might hope to distinguish between modifications of General Relativity and dark energy as competing hypotheses to explain cosmic acceleration.

  1. Is Cosmic Acceleration Telling Us Something About Gravity?

    ScienceCinema

    Trodden, Mark

    2018-05-11

    Among the possible explanations for the observed acceleration of the universe, perhaps the boldest is the idea that new gravitational physics might be the culprit. In this colloquium I will discuss some of the challenges of constructing a sensible phenomenological extension of General Relativity, give examples of some candidate models of modified gravity and survey existing observational constraints on this approach. I will conclude by discussing how we might hope to distinguish between modifications of General Relativity and dark energy as competing hypotheses to explain cosmic acceleration.

  2. Wormhole solutions in f(R) gravity satisfying energy conditions

    NASA Astrophysics Data System (ADS)

    Mazharimousavi, S. Habib; Halilsoy, M.

    2016-10-01

    Without reference to exotic sources construction of viable wormholes in Einstein’s general relativity remained ever a myth. With the advent of modified theories, however, specifically the f(R) theory, new hopes arose for the possibility of such objects. From this token, we construct traversable wormholes in f(R) theory supported by a fluid source which respects at least the weak energy conditions. We provide an example (Example 1) of asymptotically flat wormhole in f(R) gravity without ghosts.

  3. Magnetofluid dynamics in curved spacetime

    NASA Astrophysics Data System (ADS)

    Bhattacharjee, Chinmoy; Das, Rupam; Mahajan, S. M.

    2015-03-01

    A grand unified field Mμ ν is constructed from Maxwell's field tensor and an appropriately modified flow field, both nonminimally coupled to gravity, to analyze the dynamics of hot charged fluids in curved background space-time. With a suitable 3 +1 decomposition, this new formalism of the hot fluid is then applied to investigate the vortical dynamics of the system. Finally, the equilibrium state for plasma with nonminimal coupling through Ricci scalar R to gravity is investigated to derive a double Beltrami equation in curved space-time.

  4. f (T ) gravity after GW170817 and GRB170817A

    NASA Astrophysics Data System (ADS)

    Cai, Yi-Fu; Li, Chunlong; Saridakis, Emmanuel N.; Xue, Ling-Qin

    2018-05-01

    The combined observation of GW170817 and its electromagnetic counterpart GRB170817A reveals that gravitational waves propagate at the speed of light in high precision. We apply the standard analysis of cosmological perturbations, as well as the effective field theory approach, to investigate the experimental consequences for the theory of f (T ) gravity. Our analysis verifies for the first time that the speed of gravitational waves within f (T ) gravity is equal to the light speed, and hence, the constraints from GW170817 and GRB170817A are trivially satisfied. Nevertheless, by examining the dispersion relation and the frequency of cosmological gravitational waves, we observe a deviation from the results of general relativity, quantified by a new parameter. Although its value is relatively small in viable f (T ) models, its possible future measurement in advancing gravitational-wave astronomy would be the smoking gun of testing this type of modified gravity.

  5. KSC-07pd0947

    NASA Image and Video Library

    2007-04-26

    KENNEDY SPACE CENTER, FLA. -- The media surround noted wheelchair-bound physicist Stephen Hawking after his arrival at the Kennedy Space Center Shuttle Landing Facility for his first zero-gravity flight. Behind Hawking, at left, is Space Florida president Steve Kohler. In the center, striding toward Hawking, is Zero Gravity Corp. founder Peter Diamandis. The flight will be aboard a modified Boeing 727 aircraft owned by Zero Gravity, a commercial company licensed to provide the public with weightless flight experiences. Hawking developed amyotrophic lateral sclerosis disease in the 1960s, a type of motor neuron disease which would cost him the loss of almost all neuromuscular control. At the celebration of his 65th birthday on January 8 this year, Hawking announced his plans for a zero-gravity flight to prepare for a sub-orbital space flight in 2009 on Virgin Galactic's space service. Photo credit: NASA/Kim Shiflett

  6. Stringy Gravity: Solving the Dark Problems at `short' distance

    NASA Astrophysics Data System (ADS)

    Park, Jeong-Hyuck

    2018-01-01

    Dictated by Symmetry Principle, string theory predicts not General Relativity but its own gravity which assumes the entire closed string massless sector to be geometric and thus gravitational. In terms of R/(MG), i.e. the dimensionless radial variable normalized by mass, Stringy Gravity agrees with General Relativity toward infinity, but modifies it at short distance. At far short distance, gravitational force can be even repulsive. These may solve the dark matter and energy problems, as they arise essentially from small R/(MG) observations: long distance divided by much heavier mass. We address the pertinent differential geometry for Stringy Gravity, stringy Equivalence Principle, stringy geodesics and the minimal coupling to the Standard Model. We highlight the notion of `doubled-yet-gauged' coordinate system, in which a gauge orbit corresponds to a single physical point and proper distance is defined between two gauge orbits by a path integral.

  7. Gravitational time advancement under gravity's rainbow

    NASA Astrophysics Data System (ADS)

    Deng, Xue-Mei; Xie, Yi

    2017-09-01

    Under gravity's rainbow, we investigate its effects on the gravitational time advancement, which is a natural consequence of measuring proper time span for a photon's round trip. This time advancement can be complementary to the time delay for testing the gravity's rainbow, because they are sensitive to different modified dispersion relations (MDRs). Its observability on ranging a spacecraft far from the Earth by two radio and a laser links is estimated at superior conjunction (SC) and inferior conjunction (IC). We find that (1) the IC is more favorable than the SC for measurement on the advancement caused by the rainbow; (2) a specific type of MDR has a significantly larger effect on the advancement than others in both SC and IC cases; and (3) a combination of available optical clocks and the realization of planetary laser ranging in the future will benefit distinguishing the gravity's rainbow from GR by measuring the gravitational time advancement.

  8. Phase space of modified Gauss-Bonnet gravity.

    PubMed

    Carloni, Sante; Mimoso, José P

    2017-01-01

    We investigate the evolution of non-vacuum Friedmann-Lemaître-Robertson-Walker (FLRW) spacetimes with any spatial curvature in the context of Gauss-Bonnet gravity. The analysis employs a new method which enables us to explore the phase space of any specific theory of this class. We consider several examples, discussing the transition from a decelerating into an acceleration universe within these theories. We also deduce from the dynamical equations some general conditions on the form of the action which guarantee the presence of specific behaviours like the emergence of accelerated expansion. As in f ( R ) gravity, our analysis shows that there is a set of initial conditions for which these models have a finite time singularity which can be an attractor. The presence of this instability also in the Gauss-Bonnet gravity is to be ascribed to the fourth-order derivative in the field equations, i.e., is the direct consequence of the higher order of the equations.

  9. KSC-07pd0952

    NASA Image and Video Library

    2007-04-26

    KENNEDY SPACE CENTER, FLA. -- At the Kennedy Space Center Shuttle Landing Facility, noted physicist Stephen Hawking, in the wheelchair, arrives at the runway for his first zero-gravity flight. The flight will be aboard a modified Boeing 727 aircraft owned by Zero Gravity Corp., a commercial company licensed to provide the public with weightless flight experiences. At left is Peter Diamandis, founder of the Zero Gravity Corp. Behind Hawking is Nicola O'Brien, a nurse practitioner who is Hawking's aide. Hawking developed amyotrophic lateral sclerosis disease in the 1960s, a type of motor neuron disease which would cost him the loss of almost all neuromuscular control. At the celebration of his 65th birthday on January 8 this year, Hawking announced his plans for a zero-gravity flight to prepare for a sub-orbital space flight in 2009 on Virgin Galactic's space service. Photo credit: NASA/Kim Shiflett

  10. KSC-07pd0954

    NASA Image and Video Library

    2007-04-26

    KENNEDY SPACE CENTER, FLA. -- At the Kennedy Space Center Shuttle Landing Facility, noted physicist Stephen Hawking, in the wheelchair, arrives at the runway for his first zero-gravity flight. The flight will be aboard a modified Boeing 727 aircraft owned by Zero Gravity Corp., a commercial company licensed to provide the public with weightless flight experiences. At left is Peter Diamandis, founder of the Zero Gravity Corp. At center is Nicola O'Brien, a nurse practitioner who is Hawking's aide. Hawking developed amyotrophic lateral sclerosis disease in the 1960s, a type of motor neuron disease which would cost him the loss of almost all neuromuscular control. At the celebration of his 65th birthday on January 8 this year, Hawking announced his plans for a zero-gravity flight to prepare for a sub-orbital space flight in 2009 on Virgin Galactic's space service. Photo credit: NASA/Kim Shiflett

  11. KSC-07pd0953

    NASA Image and Video Library

    2007-04-26

    KENNEDY SPACE CENTER, FLA. -- At the Kennedy Space Center Shuttle Landing Facility, noted physicist Stephen Hawking, in the wheelchair, arrives at the runway for his first zero-gravity flight. The flight will be aboard a modified Boeing 727 aircraft owned by Zero Gravity Corp., a commercial company licensed to provide the public with weightless flight experiences. At left is Peter Diamandis, founder of the Zero Gravity Corp. At center is Nicola O'Brien, a nurse practitioner who is Hawking's aide. Hawking developed amyotrophic lateral sclerosis disease in the 1960s, a type of motor neuron disease which would cost him the loss of almost all neuromuscular control. At the celebration of his 65th birthday on January 8 this year, Hawking announced his plans for a zero-gravity flight to prepare for a sub-orbital space flight in 2009 on Virgin Galactic's space service. Photo credit: NASA/Kim Shiflett

  12. Ellipsoidal corrections for geoid undulation computations using gravity anomalies in a cap

    NASA Technical Reports Server (NTRS)

    Rapp, R. H.

    1981-01-01

    Ellipsoidal correction terms have been derived for geoid undulation computations when the Stokes equation using gravity anomalies in a cap is combined with potential coefficient information. The correction terms are long wavelength and depend on the cap size in which its gravity anomalies are given. Using the regular Stokes equation, the maximum correction for a cap size of 20 deg is -33 cm, which reduces to -27 cm when the Stokes function is modified by subtracting the value of the Stokes function at the cap radius. Ellipsoidal correction terms were also derived for the well-known Marsh/Chang geoids. When no gravity was used, the correction could reach 101 cm, while for a cap size of 20 deg the maximum correction was -45 cm. Global correction maps are given for a number of different cases. For work requiring accurate geoid computations these correction terms should be applied.

  13. R 2 inflation to probe non-perturbative quantum gravity

    NASA Astrophysics Data System (ADS)

    Koshelev, Alexey S.; Sravan Kumar, K.; Starobinsky, Alexei A.

    2018-03-01

    It is natural to expect a consistent inflationary model of the very early Universe to be an effective theory of quantum gravity, at least at energies much less than the Planck one. For the moment, R + R 2, or shortly R 2, inflation is the most successful in accounting for the latest CMB data from the PLANCK satellite and other experiments. Moreover, recently it was shown to be ultra-violet (UV) complete via an embedding into an analytic infinite derivative (AID) non-local gravity. In this paper, we derive a most general theory of gravity that contributes to perturbed linear equations of motion around maximally symmetric space-times. We show that such a theory is quadratic in the Ricci scalar and the Weyl tensor with AID operators along with the Einstein-Hilbert term and possibly a cosmological constant. We explicitly demonstrate that introduction of the Ricci tensor squared term is redundant. Working in this quadratic AID gravity framework without a cosmological term we prove that for a specified class of space homogeneous space-times, a space of solutions to the equations of motion is identical to the space of backgrounds in a local R 2 model. We further compute the full second order perturbed action around any background belonging to that class. We proceed by extracting the key inflationary parameters of our model such as a spectral index ( n s ), a tensor-to-scalar ratio ( r) and a tensor tilt ( n t ). It appears that n s remains the same as in the local R 2 inflation in the leading slow-roll approximation, while r and n t get modified due to modification of the tensor power spectrum. This class of models allows for any value of r < 0.07 with a modified consistency relation which can be fixed by future observations of primordial B-modes of the CMB polarization. This makes the UV complete R 2 gravity a natural target for future CMB probes.

  14. TALARIS project update: Overview of flight testing and development of a prototype planetary surface exploration hopper

    NASA Astrophysics Data System (ADS)

    Rossi, Christopher; Cunio, Phillip M.; Alibay, Farah; Morrow, Joe; Nothnagel, Sarah L.; Steiner, Ted; Han, Christopher J.; Lanford, Ephraim; Hoffman, Jeffrey A.

    2012-12-01

    The TALARIS (Terrestrial Artificial Lunar And Reduced GravIty Simulator) project is intended to test GNC (Guidance, Navigation, and Control) algorithms on a prototype planetary surface exploration hopper in a dynamic environment with simulated reduced gravity. The vehicle is being developed by the Charles Stark Draper Laboratory and Massachusetts Institute of Technology in support of efforts in the Google Lunar X-Prize contest. This paper presents progress achieved since September 2010 in vehicle development and flight testing. Upgrades to the vehicle are described, including a redesign of the power train for the gravity-offset propulsion system and a redesign of key elements of the spacecraft emulator propulsion system. The integration of flight algorithms into modular flight software is also discussed. Results are reported for restricted degree of freedom (DOF) tests used to tune GNC algorithms on the path to a full 6-DOF hover-hop flight profile. These tests include 3-DOF tests on flat surfaces restricted to horizontal motion, and 2-DOF vertical tests restricted to vertical motion and 1-DOF attitude control. The results of tests leading up to full flight operations are described, as are lessons learned and future test plans.

  15. Partial gravity habitat study

    NASA Technical Reports Server (NTRS)

    Capps, Stephen; Lorandos, Jason; Akhidime, Eval; Bunch, Michael; Lund, Denise; Moore, Nathan; Murakawa, Kiosuke

    1989-01-01

    The purpose of this study is to investigate comprehensive design requirements associated with designing habitats for humans in a partial gravity environment, then to apply them to a lunar base design. Other potential sites for application include planetary surfaces such as Mars, variable-gravity research facilities, and a rotating spacecraft. Design requirements for partial gravity environments include locomotion changes in less than normal earth gravity; facility design issues, such as interior configuration, module diameter, and geometry; and volumetric requirements based on the previous as well as psychological issues involved in prolonged isolation. For application to a lunar base, it is necessary to study the exterior architecture and configuration to insure optimum circulation patterns while providing dual egress; radiation protection issues are addressed to provide a safe and healthy environment for the crew; and finally, the overall site is studied to locate all associated facilities in context with the habitat. Mission planning is not the purpose of this study; therefore, a Lockheed scenario is used as an outline for the lunar base application, which is then modified to meet the project needs. The goal of this report is to formulate facts on human reactions to partial gravity environments, derive design requirements based on these facts, and apply the requirements to a partial gravity situation which, for this study, was a lunar base.

  16. Beyond δ: Tailoring marked statistics to reveal modified gravity

    NASA Astrophysics Data System (ADS)

    Valogiannis, Georgios; Bean, Rachel

    2018-01-01

    Models which attempt to explain the accelerated expansion of the universe through large-scale modifications to General Relativity (GR), must satisfy the stringent experimental constraints of GR in the solar system. Viable candidates invoke a “screening” mechanism, that dynamically suppresses deviations in high density environments, making their overall detection challenging even for ambitious future large-scale structure surveys. We present methods to efficiently simulate the non-linear properties of such theories, and consider how a series of statistics that reweight the density field to accentuate deviations from GR can be applied to enhance the overall signal-to-noise ratio in differentiating the models from GR. Our results demonstrate that the cosmic density field can yield additional, invaluable cosmological information, beyond the simple density power spectrum, that will enable surveys to more confidently discriminate between modified gravity models and ΛCDM.

  17. Statefinder diagnostic for modified Chaplygin gas cosmology in f(R,T) gravity with particle creation

    NASA Astrophysics Data System (ADS)

    Singh, J. K.; Nagpal, Ritika; Pacif, S. K. J.

    In this paper, we have studied flat Friedmann-Lemaître-Robertson-Walker (FLRW) model with modified Chaplygin gas (MCG) having equation of state pm = Aρ ‑ B ργ, where 0 ≤ A ≤ 1, 0 ≤ γ ≤ 1 and B is any positive constant in f(R,T) gravity with particle creation. We have considered a simple parametrization of the Hubble parameter H in order to solve the field equations and discussed the time evolution of different cosmological parameters for some obtained models showing unique behavior of scale factor. We have also discussed the statefinder diagnostic pair {r,s} that characterizes the evolution of obtained models and explore their stability. The physical consequences of the models and their kinematic behaviors have also been scrutinized here in some detail.

  18. Late-time cosmic acceleration: ABCD of dark energy and modified theories of gravity

    NASA Astrophysics Data System (ADS)

    Sami, M.; Myrzakulov, R.

    2016-10-01

    We briefly review the problems and prospects of the standard lore of dark energy. We have shown that scalar fields, in principle, cannot address the cosmological constant problem. Indeed, a fundamental scalar field is faced with a similar problem dubbed naturalness. In order to keep the discussion pedagogical, aimed at a wider audience, we have avoided technical complications in several places and resorted to heuristic arguments based on physical perceptions. We presented underlying ideas of modified theories based upon chameleon mechanism and Vainshtein screening. We have given a lucid illustration of recently investigated ghost-free nonlinear massive gravity. Again, we have sacrificed rigor and confined to the basic ideas that led to the formulation of the theory. The review ends with a brief discussion on the difficulties of the theory applied to cosmology.

  19. Optimizing future imaging survey of galaxies to confront dark energy and modified gravity models

    NASA Astrophysics Data System (ADS)

    Yamamoto, Kazuhiro; Parkinson, David; Hamana, Takashi; Nichol, Robert C.; Suto, Yasushi

    2007-07-01

    We consider the extent to which future imaging surveys of galaxies can distinguish between dark energy and modified gravity models for the origin of the cosmic acceleration. Dynamical dark energy models may have similar expansion rates as models of modified gravity, yet predict different growth of structure histories. We parametrize the cosmic expansion by the two parameters, w0 and wa, and the linear growth rate of density fluctuations by Linder’s γ, independently. Dark energy models generically predict γ≈0.55, while the Dvali-Gabadadze-Porrati (DGP) model γ≈0.68. To determine if future imaging surveys can constrain γ within 20% (or Δγ<0.1), we perform the Fisher matrix analysis for a weak-lensing survey such as the ongoing Hyper Suprime-Cam (HSC) project. Under the condition that the total observation time is fixed, we compute the figure of merit (FoM) as a function of the exposure time texp. We find that the tomography technique effectively improves the FoM, which has a broad peak around texp≃several˜10min; a shallow and wide survey is preferred to constrain the γ parameter. While Δγ<0.1 cannot be achieved by the HSC weak-lensing survey alone, one can improve the constraints by combining with a follow-up spectroscopic survey like Wide-field Fiber-fed Multi-Object Spectrograph (WFMOS) and/or future cosmic microwave background (CMB) observations.

  20. Equivalent off-diagonal cosmological models and ekpyrotic scenarios in -modified, massive, and einstein gravity

    NASA Astrophysics Data System (ADS)

    Vacaru, Sergiu I.

    2015-04-01

    We reinvestigate how generic off-diagonal cosmological solutions depending, in general, on all spacetime coordinates can be constructed in massive and -modified gravity using the anholonomic frame deformation method. New classes of locally anisotropic and (in-) homogeneous cosmological metrics are constructed with open and closed spatial geometries. By resorting to such solutions, we show that they describe the late time acceleration due to effective cosmological terms induced by nonlinear off-diagonal interactions, possible modifications of the gravitational action and graviton mass. The cosmological metrics and related Stückelberg fields are constructed in explicit form up to nonholonomic frame transforms of the Friedmann-Lamaître-Robertson-Walker (FLRW) coordinates. The solutions include matter, graviton mass, and other effective sources modeling nonlinear gravitational and matter field interactions with polarization of physical constants and deformations of metrics, which may explain dark energy and dark matter effects. However, we argue that it is not always necessary to modify gravity if we consider the effective generalized Einstein equations with nontrivial vacuum and/or non-minimal coupling with matter. Indeed, we state certain conditions when such configurations mimic interesting solutions in general relativity and modifications, for instance, when we can extract the general Painlevé-Gullstrand and FLRW metrics. In a more general context, we elaborate on a reconstruction procedure for off-diagonal cosmological solutions which describe cyclic and ekpyrotic universes. Finally, open issues and further perspectives are discussed.

  1. Genetic Analysis of Gravity Signal Transduction in Arabidopsis thaliana Seedlings

    NASA Astrophysics Data System (ADS)

    Boonsirichai, K.; Harrison, B.; Stanga, J.; Young, L.-S.; Neal, C.; Sabat, G.; Murthy, N.; Harms, A.; Sedbrook, J.; Masson, P.

    The primary roots of Arabidopsis thaliana seedlings respond to gravity stimulation by developing a tip curvature that results from differential cellular elongation on opposite flanks of the elongation zone. This curvature appears modulated by a lateral gradient of auxin that originates in the gravity-perceiving cells (statocytes) of the root cap through an apparent lateral repositioning of a component the auxin efflux carrier complex within these cells (Friml et al, 2002, Nature 415: 806-809). Unfortunately, little is known about the molecular mechanisms that govern early phases of gravity perception and signal transduction within the root-cap statocytes. We have used a molecular genetic approach to uncover some of these mechanisms. Mutations in the Arabidopsis ARG1 and ARL2 genes, which encode J-domain proteins, resulted in specific alterations in root and hypocotyl gravitropism, without pleiotropic phenotypes. Interestingly, ARG1 and ARL2 appear to function in the same genetic pathway. A combination of molecular genetic, biochemical and cell-biological approaches were used to demonstrate that ARG1 functions in early phases of gravity signal transduction within the root and hypocotyl statocytes, and is needed for efficient lateral auxin transport within the cap. The ARG1 protein is associated with components of the secretory and/or endosomal pathways, suggesting its role in the recycling of components of the auxin efflux carrier complex between plasma membrane and endosome (Boonsirichai et al, 2003, Plant Cell 15:2612-2625). Genetic modifiers of arg1-2 were isolated and shown to enhance the gravitropic defect of arg1-2, while resulting in little or no gravitropic defects in a wild type ARG1 background. A slight tendency for arg1-2;mar1-1 and arg1-2;mar2-1 double-mutant organs to display an opposite gravitropic response compared to wild type suggests that all three genes contribute to the interpretation of the gravity-vector information by seedling organs. The molecular structure of these new loci is being investigated. Furthermore, a proteomic approach is being developed to characterize root-tip proteins that are differentially expressed, modified or targeted in response to gravity stimulation. We acknowledge funding by NASA and NSF.

  2. Effects of mechanostimulation on gravitropism and signal persistence in flax roots.

    PubMed

    John, Susan P; Hasenstein, Karl H

    2011-09-01

    Gravitropism describes curvature of plants in response to gravity or differential acceleration and clinorotation is commonly used to compensate unilateral effect of gravity. We report on experiments that examine the persistence of the gravity signal and separate mechanostimulation from gravistimulation. Flax roots were reoriented (placed horizontally for 5, 10 or 15 min) and clinorotated at a rate of 0.5 to 5 rpm either vertically (parallel to the gravity vector and root axis) or horizontally (perpendicular to the gravity vector and parallel to the root axis). Image sequences showed that horizontal clinorotation did not affect root growth rate (0.81 ± 0.03 mm h-1) but vertical clinorotation reduced root growth by about 7%. The angular velocity (speed of clinorotation) did not affect growth for either direction. However, maximal curvature for vertical clinorotation decreased with increasing rate of rotation and produced straight roots at 5 rpm. In contrast, horizontal clinorotation increased curvature with increasing angular velocity. The point of maximal curvature was used to determine the longevity (memory) of the gravity signal, which lasted about 120 min. The data indicate that mechanostimulation modifies the magnitude of the graviresponse but does not affect memory persistence.

  3. New Probe of Departures from General Relativity Using Minkowski Functionals.

    PubMed

    Fang, Wenjuan; Li, Baojiu; Zhao, Gong-Bo

    2017-05-05

    The morphological properties of the large scale structure of the Universe can be fully described by four Minkowski functionals (MFs), which provide important complementary information to other statistical observables such as the widely used 2-point statistics in configuration and Fourier spaces. In this work, for the first time, we present the differences in the morphology of the large scale structure caused by modifications to general relativity (to address the cosmic acceleration problem), by measuring the MFs from N-body simulations of modified gravity and general relativity. We find strong statistical power when using the MFs to constrain modified theories of gravity: with a galaxy survey that has survey volume ∼0.125(h^{-1}  Gpc)^{3} and galaxy number density ∼1/(h^{-1}  Mpc)^{3}, the two normal-branch Dvali-Gabadadze-Porrati models and the F5 f(R) model that we simulated can be discriminated from the ΛCDM model at a significance level ≳5σ with an individual MF measurement. Therefore, the MF of the large scale structure is potentially a powerful probe of gravity, and its application to real data deserves active exploration.

  4. Self-completeness and the generalized uncertainty principle

    NASA Astrophysics Data System (ADS)

    Isi, Maximiliano; Mureika, Jonas; Nicolini, Piero

    2014-03-01

    The generalized uncertainty principle discloses a self-complete characteristic of gravity, namely the possibility of masking any curvature singularity behind an event horizon as a result of matter compression at the Planck scale. In this paper we extend the above reasoning in order to overcome some current limitations to the framework, including the absence of a consistent metric describing such Planck-scale black holes. We implement a minimum-size black hole in terms of the extremal configuration of a neutral non-rotating metric, which we derived by mimicking the effects of the generalized uncertainty principle via a short scale modified version of Einstein gravity. In such a way, we find a self- consistent scenario that reconciles the self-complete character of gravity and the generalized uncertainty principle.

  5. Self-completeness and the generalized uncertainty principle

    NASA Astrophysics Data System (ADS)

    Isi, Maximiliano; Mureika, Jonas; Nicolini, Piero

    2013-11-01

    The generalized uncertainty principle discloses a self-complete characteristic of gravity, namely the possibility of masking any curvature singularity behind an event horizon as a result of matter compression at the Planck scale. In this paper we extend the above reasoning in order to overcome some current limitations to the framework, including the absence of a consistent metric describing such Planck-scale black holes. We implement a minimum-size black hole in terms of the extremal configuration of a neutral non-rotating metric, which we derived by mimicking the effects of the generalized uncertainty principle via a short scale modified version of Einstein gravity. In such a way, we find a self-consistent scenario that reconciles the self-complete character of gravity and the generalized uncertainty principle.

  6. KSC-07pd0948

    NASA Image and Video Library

    2007-04-26

    KENNEDY SPACE CENTER, FLA. — Noted physicist Stephen Hawking greets the media after his arrival at the Kennedy Space Center Shuttle Landing Facility for his first zero-gravity flight. The flight will be aboard a modified Boeing 727 aircraft owned by Zero Gravity Corp., a commercial company licensed to provide the public with weightless flight experiences. Hawking developed amyotrophic lateral sclerosis disease in the 1960s, a type of motor neuron disease which would cost him the loss of almost all neuromuscular control. At the celebration of his 65th birthday on January 8 this year, Hawking announced his plans for a zero-gravity flight to prepare for a sub-orbital space flight in 2009 on Virgin Galactic's space service. Photo credit: NASA/Kim Shiflett

  7. Constraining inverse-curvature gravity with supernovae.

    PubMed

    Mena, Olga; Santiago, José; Weller, Jochen

    2006-02-03

    We show that models of generalized modified gravity, with inverse powers of the curvature, can explain the current accelerated expansion of the Universe without resorting to dark energy and without conflicting with solar system experiments. We have solved the Friedmann equations for the full dynamical range of the evolution of the Universe and performed a detailed analysis of supernovae data in the context of such models that results in an excellent fit. If we further include constraints on the current expansion of the Universe and on its age, we obtain that the matter content of the Universe is 0.07

  8. DOE Office of Scientific and Technical Information (OSTI.GOV)

    Bose, Sownak; Li, Baojiu; He, Jian-hua

    We describe and demonstrate the potential of a new and very efficient method for simulating certain classes of modified gravity theories, such as the widely studied f ( R ) gravity models. High resolution simulations for such models are currently very slow due to the highly nonlinear partial differential equation that needs to be solved exactly to predict the modified gravitational force. This nonlinearity is partly inherent, but is also exacerbated by the specific numerical algorithm used, which employs a variable redefinition to prevent numerical instabilities. The standard Newton-Gauss-Seidel iterative method used to tackle this problem has a poor convergencemore » rate. Our new method not only avoids this, but also allows the discretised equation to be written in a form that is analytically solvable. We show that this new method greatly improves the performance and efficiency of f ( R ) simulations. For example, a test simulation with 512{sup 3} particles in a box of size 512 Mpc/ h is now 5 times faster than before, while a Millennium-resolution simulation for f ( R ) gravity is estimated to be more than 20 times faster than with the old method. Our new implementation will be particularly useful for running very high resolution, large-sized simulations which, to date, are only possible for the standard model, and also makes it feasible to run large numbers of lower resolution simulations for covariance analyses. We hope that the method will bring us to a new era for precision cosmological tests of gravity.« less

  9. Reducing NPR 7120.5D to Practice: Transitioning from Design Reviews to the SIR Hardware Review

    NASA Technical Reports Server (NTRS)

    Taylor, Randall

    2011-01-01

    The Gravity Recovery And Interior Laboratory (GRAIL) mission was the first Jet Propulsion Laboratory (JPL) project initiated under NASA's revised rules for space flight project management, NPR 7120.5D, "NASA Space Flight Program and Project Management Requirements." NASA selected GRAIL through a competitive Announcement of Opportunity process and funded its Phase B Preliminary Design effort. The team's first major milestone was a JPL institutional milestone, the Project Mission System Review (PMSR), which proved an excellent tune-up for the end-of-Phase-B NASA life-cycle review, the Preliminary Design Review (PDR). Building on JPL experience on the Prometheus and Juno projects, the team successfully organized for and conducted these reviews on an aggressive schedule. For the Project Critical Design Review (CDR), lessons learned from the PDR and updated Standing Review Board (SRB) practices from the Agency were factored into the review preparation effort. Additionally, the review was held at the Principal Investigator's institution, the Massachusetts Institute of Technology, rather than at the project management center (JPL), which necessitated additional cross-country coordination steps. The PMSR, PDR, and CDR were design reviews and largely paper-oriented. For the System Integration Review (SIR), the project needed to transition to a hardware review and deal with paper in a very different manner. While many of the practices employed for the design reviews were modified and retained (e.g., review preparation team, gate products management, pre-reviews, SRB coordination), the review agenda, presentation style, and slide templates were significantly changed. A key success factor concerned the handling of project open paper, which was succinctly and effectively communicated to the SRB in presentations.This paper provides a brief overview of the GRAIL mission and its project management challenges, provides a detailed description of project SIR preparation and execution activities, including positive and negative lessons learned and identifies recommendations for future NASA (and non- NASA) project teams.

  10. A new monthly gravity field model based on GRACE observations computed by the modified dynamic approach

    NASA Astrophysics Data System (ADS)

    Zhou, H.; Luo, Z.; Li, Q.; Zhong, B.

    2016-12-01

    The monthly gravity field model can be used to compute the information about the mass variation within the system Earth, i.e., the relationship between mass variation in the oceans, land hydrology, and ice sheets. For more than ten years, GRACE has provided valuable information for recovering monthly gravity field model. In this study, a new time series of GRACE monthly solution, which is truncated to degree and order 60, is computed by the modified dynamic approach. Compared with the traditional dynamic approach, the major difference of our modified approach is the way to process the nuisance parameters. This type of parameters is mainly used to absorb low-frequency errors in KBRR data. One way is to remove the nuisance parameters before estimating the geo-potential coefficients, called Pure Predetermined Strategy (PPS). The other way is to determine the nuisance parameters and geo-potential coefficients simultaneously, called Pure Simultaneous Strategy (PSS). It is convenient to detect the gross error by PPS, while there is also obvious signal loss compared with the solutions derived from PSS. After comparing the difference of practical calculation formulas between PPS and PSS, we create the Filter Predetermine Strategy (FPS), which can combine the advantages of PPS and PSS efficiently. With FPS, a new monthly gravity field model entitled HUST-Grace2016s is developed. The comparisons of geoid degree powers and mass change signals in the Amazon basin, the Greenland and the Antarctic demonstrate that our model is comparable with the other published models, e.g., the CSR RL05, JPL RL05 and GFZ RL05 models. Acknowledgements: This work is supported by China Postdoctoral Science Foundation (Grant No.2016M592337), the National Natural Science Foundation of China (Grant Nos. 41131067, 41504014), the Open Research Fund Program of the State Key Laboratory of Geodesy and Earth's Dynamics (Grant No. SKLGED2015-1-3-E).

  11. Effects of acute altered gravity during parabolic flight and/or vestibular loss on cell proliferation in the rat dentate gyrus.

    PubMed

    Zheng, Yiwen; Gliddon, Catherine M; Aitken, Phillip; Stiles, Lucy; Machado, Marie-Laure; Philoxene, Bruno; Denise, Pierre; Smith, Paul F; Besnard, Stephane

    2017-07-27

    Both parabolic flight, i.e. a condition of altered gravity, and loss of vestibular function, have been suggested to affect spatial learning and memory, which is known to be influenced by neurogenesis in the hippocampus. In this study we investigated whether short alternated micro- and hyper-gravity stimulations during parabolic flight and/or loss of vestibular function, would alter cell proliferation in the hippocampal dentate gyrus of rats, by measuring the number of bromodeoxyuridine (BrdU)-incorporated cells. Rats were randomly allocated to the following experimental groups: (1) sham transtympanic saline injection only (n=5); (2) bilateral vestibular deafferentation (BVD) by sodium arsanilate transtympanic injection only (n=5); (3) sham treatment and parabolic flight (n=5); (4) BVD and parabolic flight (n=6). Forty-two days following transtympanic injection, the animals were subjected to parabolic flight in an awake restrained condition after habituation. A modified Airbus A300 aircraft was flown on a parabolic path, creating 20s of 1.8G during both climbing and descending and 22s of 0G at the apex of each parabola. The no flight animals were subjected to the same housing for the same duration. Immediately after the parabolic flight or control ground condition, animals were injected with BrdU (300mg/kg, i.p). Twenty-four hs after BrdU injection, rats were sacrificed. BrdU immunolabelling was performed and the number of BrdU +ve cells in the dentate gyrus of the hippocampus was quantified using a modified fractionator method. BVD caused a large and significant reduction in the number of BrdU-positive cells compared to sham animals (P≤0.0001); however, flight and all interactions were non-significant. These results indicate that BVD significantly decreased cell proliferation irrespective of the short exposure to altered/modified gravity. Copyright © 2017 Elsevier B.V. All rights reserved.

  12. de Sitter limit analysis for dark energy and modified gravity models

    NASA Astrophysics Data System (ADS)

    De Felice, Antonio; Frusciante, Noemi; Papadomanolakis, Georgios

    2017-07-01

    The effective field theory of dark energy and modified gravity is supposed to well describe, at low energies, the behavior of the gravity modifications due to one extra scalar degree of freedom. The usual curvature perturbation is very useful when studying the conditions for the avoidance of ghost instabilities as well as the positivity of the squared speeds of propagation for both the scalar and tensor modes, or the Stückelberg field performs perfectly when investigating the evolution of linear perturbations. We show that the viable parameter space identified by requiring no-ghost instabilities and positive squared speeds of propagation does not change by performing a field redefinition, while the requirement of the avoidance of tachyonic instability might instead be different. Therefore, we find it interesting to associate to the general modified gravity theory described in the effective field theory framework, a perturbation field which will inherit all of the properties of the theory. In the present paper we address the following questions: (1) how can we define such a field? and (2) what is the mass of such a field as the background approaches a final de Sitter state? We define a gauge-invariant quantity which identifies the density of the dark energy perturbation field valid for any background. We derive the mass associated to the gauge-invariant dark energy field on a de Sitter background, which we retain to be still a good approximation also at very low redshift (z ≃0 ). On this background we also investigate the value of the speed of propagation and we find that there exist classes of theories which admit a nonvanishing speed of propagation, even in the Horndeski model, for which a zero speed of sound has previously been found in the literature. We finally apply our results to specific well-known models.

  13. Correction of Cardy–Verlinde formula for Fermions and Bosons with modified dispersion relation

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Sadatian, S. Davood, E-mail: sd-sadatian@um.ac.ir; Dareyni, H.

    Cardy–Verlinde formula links the entropy of conformal symmetry field to the total energy and its Casimir energy in a D-dimensional space. To correct black hole thermodynamics, modified dispersion relation can be used which is proposed as a general feature of quantum gravity approaches. In this paper, the thermodynamics of Schwarzschild four-dimensional black hole is corrected using the modified dispersion relation for Fermions and Bosons. Finally, using modified thermodynamics of Schwarzschild four-dimensional black hole, generalization for Cardy–Verlinde formula is obtained. - Highlights: • The modified Cardy–Verlinde formula obtained using MDR for Fermions and Bosons. • The modified entropy of the blackmore » hole used to correct the Cardy–Verlinde formula. • The modified entropy of the CFT has been obtained.« less

  14. Learning on Jupiter, learning on the Moon: the dark side of the G-force. Effects of gravity changes on neurovascular unit and modulation of learning and memory

    PubMed Central

    Porte, Yves; Morel, Jean-Luc

    2012-01-01

    On earth, gravity vector conditions the development of all living beings by physically imposing an axis along which to build their organism. Thus, during their whole life, they have to fight against this force not only to maintain their architectural organization but also to coordinate the communication between organs and keep their physiology in a balanced steady-state. In space, astronauts show physiological, psychological, and cognitive deregulations, ranging from bone decalcification or decrease of musculature, to depressive-like disorders, and spatial disorientation. Nonetheless, they are confronted to a great amount of physical changes in their environment such as solar radiations, loss of light-dark cycle, lack of spatial landmarks, confinement, and obviously a dramatic decrease of gravity force. It is thus very hard to selectively discriminate the strict role of gravity level alterations on physiological, and particularly cerebral, dysfunction. To this purpose, it is important to design autonomous models and apparatuses for behavioral phenotyping utilizable under modified gravity environments. Our team actually aims at working on this area of research. PMID:23015785

  15. Partial gravity habitat study: With application to lunar base design

    NASA Technical Reports Server (NTRS)

    Capps, Stephen; Lorandos, Jason; Akhidime, Eval; Bunch, Michael; Lund, Denise; Moore, Nathan; Murakawa, Kio; Bell, Larry; Trotti, Guillermo; Neubek, Deb

    1989-01-01

    Comprehensive design requirements associated with designing habitats for humans in a partial gravity environment were investigated and then applied to a lunar base design. Other potential sites for application include planetary surfaces such as Mars, variable gravity research facilities, or a rotating spacecraft. Design requirements for partial gravity environments include: (1) locomotion changes in less than normal Earth gravity; (2) facility design issues, such as interior configuration, module diameter and geometry; and (3) volumetric requirements based on the previous as well as psychological issues involved in prolonged isolation. For application to a Lunar Base, it was necessary to study the exterior architecture and configuration to insure optimum circulation patterns while providing dual egress. Radiation protection issues were addressed to provide a safe and healthy environment for the crew, and finally, the overall site was studied to locate all associated facilities in context with the habitat. Mission planning was not the purpose of this study; therefore, a Lockheed scenario was used as an outline for the Lunar Base application, which was then modified to meet the project needs.

  16. Lunar gravitational field estimation and the effects of mismodeling upon lunar satellite orbit prediction. M.S. Thesis

    NASA Technical Reports Server (NTRS)

    Davis, John H.

    1993-01-01

    Lunar spherical harmonic gravity coefficients are estimated from simulated observations of a near-circular low altitude polar orbiter disturbed by lunar mascons. Lunar gravity sensing missions using earth-based nearside observations with and without satellite-based far-side observations are simulated and least squares maximum likelihood estimates are developed for spherical harmonic expansion fit models. Simulations and parameter estimations are performed by a modified version of the Smithsonian Astrophysical Observatory's Planetary Ephemeris Program. Two different lunar spacecraft mission phases are simulated to evaluate the estimated fit models. Results for predicting state covariances one orbit ahead are presented along with the state errors resulting from the mismodeled gravity field. The position errors from planning a lunar landing maneuver with a mismodeled gravity field are also presented. These simulations clearly demonstrate the need to include observations of satellite motion over the far side in estimating the lunar gravity field. The simulations also illustrate that the eighth degree and order expansions used in the simulated fits were unable to adequately model lunar mascons.

  17. Extravehicular Activity Testing in Analog Environments: Evaluating the Effects of Center of Gravity and Environment on Human Performance

    NASA Technical Reports Server (NTRS)

    Gernhardt, M.L.; Chappell, S.P.

    2009-01-01

    The EVA Physiology, Systems and Performance (EPSP) Project is performing tests in different analog environments to understand human performance during Extravehicular Activity (EVA) with the aim of developing more safe and efficient systems for lunar exploration missions and the Constellation Program. The project is characterizing human EVA performance in studies using several test beds, including the underwater NASA Extreme Environment Mission Operations (NEEMO) and Neutral Buoyancy Laboratory (NBL) facilities, JSC fs Partial Gravity Simulator (POGO), and the NASA Reduced Gravity Office (RGO) parabolic flight aircraft. Using these varied testing environments, NASA can gain a more complete understanding of human performance issues related to EVA and the limitations of each testing environment. Tests are focused on identifying and understanding the EVA system factors that affect human performance such as center of gravity (CG), inertial mass, ground reaction forces (GRF), suit weight, and suit pressure. The test results will lead to the development of lunar EVA systems operations concepts and design requirements that optimize human performance and exploration capabilities. METHODS: Tests were conducted in the NBL and during NEEMO missions in the NOAA Aquarius Habitat. A reconfigurable back pack with repositionable mass was used to simulate Perfect, Low, Forward, High, Aft and NASA Baseline CG locations. Subjects performed simulated exploration tasks that included ambulation, kneel and recovery, rock pick-up, and shoveling. Testing using POGO, that simulates partial gravity via pneumatic weight offload system and a similar reconfigurable rig, is underway for a subset of the same tasks. Additionally, test trials are being performed on the RGO parabolic flight aircraft. Subject performance was assessed using a modified Cooper-Harper scale to assess operator compensation required to achieve desired performance. All CG locations are based on the assumption of a standardized 6 ft 180 lb subject. RESULTS: The modified Cooper-Harper Scale assesses desired task performance described as performance in a reduced gravity environment as compared to a 1G environment. Modified Cooper-Harper ratings of . 3 indicate no improvements are needed, ratings of 4-6 indicate improvements are desirable, and ratings . 7 indicate improvements are mandatory. DISCUSSION: Differences were noted in suited CH results based on environment at the same CG and suit pressure. Additionally, results suggest that CG location affects unsuited human performance. Subjects preferred locations near their natural CG over those that are high, aft, or a combination of high and aft. Further testing and analyses are planned to compare these unsuited results to suited performance.

  18. Capturing student mathematical engagement through differently enacted classroom practices: applying a modification of Watson's analytical tool

    NASA Astrophysics Data System (ADS)

    Patahuddin, Sitti Maesuri; Puteri, Indira; Lowrie, Tom; Logan, Tracy; Rika, Baiq

    2018-04-01

    This study examined student mathematical engagement through the intended and enacted lessons taught by two teachers in two different middle schools in Indonesia. The intended lesson was developed using the ELPSA learning design to promote mathematical engagement. Based on the premise that students will react to the mathematical tasks in the forms of words and actions, the analysis focused on identifying the types of mathematical engagement promoted through the intended lesson and performed by students during the lesson. Using modified Watson's analytical tool (2007), students' engagement was captured from what the participants' did or said mathematically. We found that teachers' enacted practices had an influence on student mathematical engagement. The teacher who demonstrated content in explicit ways tended to limit the richness of the engagement; whereas the teacher who presented activities in an open-ended manner fostered engagement.

  19. Student Understanding of Time in an Introductory Astronomy Laboratory

    NASA Astrophysics Data System (ADS)

    Traxler, A. L.; Batuski, D. J.; Comins, N. F.; Thompson, J. R.

    2005-09-01

    The astronomy lab at the University of Maine consists of discrete weekly lessons in which students work in small groups. Individual pretests and post-tests accompany each lesson. The lesson studied here covers the topic of time, including sidereal time, Apparent Solar Time, and time zones. The pretest consists of four multiple-choice questions, which are also administered after instruction as a post-test. In the fall 2004 semester, the pretest was rewritten to focus on some major conceptual components of the lab, while the lesson materials were not modified from previous years. Examination of class performance (n = 96) revealed no significant improvements in score from pre- to post-lesson. In the spring 2005 semester, the lesson was altered to incorporate the Starry Night software for simulating the sky instead of the celestial sphere models previously used. The goal of the change was to give students a more interactive environment for completing the laboratory exercise, which was otherwise altered as little as possible. Data from the spring semester show some gains on the pre/post-test questions covering sidereal time and Daylight Savings Time. Results to date have informed planned modifications to the lesson. A. L. T. was supported during this research by the University of Maine through a Provost Fellowship.

  20. Cutting thin sections of bone

    NASA Technical Reports Server (NTRS)

    Ashley, W. W.

    1972-01-01

    Medical equipment for obtaining repetitive planoparallel sections of bone to study healing of bone structure under high gravity stress is described. Device consists of modified saw with diamond cutting edges. Construction of device and manner of use are explained.

  1. Dark matter (energy) may be indistinguishable from modified gravity (MOND)

    NASA Astrophysics Data System (ADS)

    Sivaram, C.

    For Newtonian dynamics to hold over galactic scales, large amounts of dark matter (DM) are required which would dominate cosmic structures. Accounting for the strong observational evidence that the universe is accelerating requires the presence of an unknown dark energy (DE) component constituting about 70% of the matter. Several ingenious ongoing experiments to detect the DM particles have so far led to negative results. Moreover, the comparable proportions of the DM and DE at the present epoch appear unnatural and not predicted by any theory. For these reasons, alternative ideas like MOND and modification of gravity or general relativity over cosmic scales have been proposed. It is shown in this paper that these alternate ideas may not be easily distinguishable from the usual DM or DE hypotheses. Specific examples are given to illustrate this point that the modified theories are special cases of a generalized DM paradigm.

  2. Motion and gravity effects in the precision of quantum clocks.

    PubMed

    Lindkvist, Joel; Sabín, Carlos; Johansson, Göran; Fuentes, Ivette

    2015-05-19

    We show that motion and gravity affect the precision of quantum clocks. We consider a localised quantum field as a fundamental model of a quantum clock moving in spacetime and show that its state is modified due to changes in acceleration. By computing the quantum Fisher information we determine how relativistic motion modifies the ultimate bound in the precision of the measurement of time. While in the absence of motion the squeezed vacuum is the ideal state for time estimation, we find that it is highly sensitive to the motion-induced degradation of the quantum Fisher information. We show that coherent states are generally more resilient to this degradation and that in the case of very low initial number of photons, the optimal precision can be even increased by motion. These results can be tested with current technology by using superconducting resonators with tunable boundary conditions.

  3. DOE Office of Scientific and Technical Information (OSTI.GOV)

    Bose, Benjamin; Koyama, Kazuya, E-mail: benjamin.bose@port.ac.uk, E-mail: kazuya.koyama@port.ac.uk

    We develop a code to produce the power spectrum in redshift space based on standard perturbation theory (SPT) at 1-loop order. The code can be applied to a wide range of modified gravity and dark energy models using a recently proposed numerical method by A.Taruya to find the SPT kernels. This includes Horndeski's theory with a general potential, which accommodates both chameleon and Vainshtein screening mechanisms and provides a non-linear extension of the effective theory of dark energy up to the third order. Focus is on a recent non-linear model of the redshift space power spectrum which has been shownmore » to model the anisotropy very well at relevant scales for the SPT framework, as well as capturing relevant non-linear effects typical of modified gravity theories. We provide consistency checks of the code against established results and elucidate its application within the light of upcoming high precision RSD data.« less

  4. Motion and gravity effects in the precision of quantum clocks

    PubMed Central

    Lindkvist, Joel; Sabín, Carlos; Johansson, Göran; Fuentes, Ivette

    2015-01-01

    We show that motion and gravity affect the precision of quantum clocks. We consider a localised quantum field as a fundamental model of a quantum clock moving in spacetime and show that its state is modified due to changes in acceleration. By computing the quantum Fisher information we determine how relativistic motion modifies the ultimate bound in the precision of the measurement of time. While in the absence of motion the squeezed vacuum is the ideal state for time estimation, we find that it is highly sensitive to the motion-induced degradation of the quantum Fisher information. We show that coherent states are generally more resilient to this degradation and that in the case of very low initial number of photons, the optimal precision can be even increased by motion. These results can be tested with current technology by using superconducting resonators with tunable boundary conditions. PMID:25988238

  5. Mechanotransduction as an Adaptation to Gravity

    PubMed Central

    Najrana, Tanbir; Sanchez-Esteban, Juan

    2016-01-01

    Gravity has played a critical role in the development of terrestrial life. A key event in evolution has been the development of mechanisms to sense and transduce gravitational force into biological signals. The objective of this manuscript is to review how living organisms on Earth use mechanotransduction as an adaptation to gravity. Certain cells have evolved specialized structures, such as otoliths in hair cells of the inner ear and statoliths in plants, to respond directly to the force of gravity. By conducting studies in the reduced gravity of spaceflight (microgravity) or simulating microgravity in the laboratory, we have gained insights into how gravity might have changed life on Earth. We review how microgravity affects prokaryotic and eukaryotic cells at the cellular and molecular levels. Genomic studies in yeast have identified changes in genes involved in budding, cell polarity, and cell separation regulated by Ras, PI3K, and TOR signaling pathways. Moreover, transcriptomic analysis of late pregnant rats have revealed that microgravity affects genes that regulate circadian clocks, activate mechanotransduction pathways, and induce changes in immune response, metabolism, and cells proliferation. Importantly, these studies identified genes that modify chromatin structure and methylation, suggesting that long-term adaptation to gravity may be mediated by epigenetic modifications. Given that gravity represents a modification in mechanical stresses encounter by the cells, the tensegrity model of cytoskeletal architecture provides an excellent paradigm to explain how changes in the balance of forces, which are transmitted across transmembrane receptors and cytoskeleton, can influence intracellular signaling pathways and gene expression. PMID:28083527

  6. Testing Universal Relations of Neutron Stars with a Nonlinear Matter-Gravity Coupling Theory

    NASA Astrophysics Data System (ADS)

    Sham, Y.-H.; Lin, L.-M.; Leung, P. T.

    2014-02-01

    Due to our ignorance of the equation of state (EOS) beyond nuclear density, there is still no unique theoretical model for neutron stars (NSs). It is therefore surprising that universal EOS-independent relations connecting different physical quantities of NSs can exist. Lau et al. found that the frequency of the f-mode oscillation, the mass, and the moment of inertia are connected by universal relations. More recently, Yagi and Yunes discovered the I-Love-Q universal relations among the mass, the moment of inertia, the Love number, and the quadrupole moment. In this paper, we study these universal relations in the Eddington-inspired Born-Infeld (EiBI) gravity. This theory differs from general relativity (GR) significantly only at high densities due to the nonlinear coupling between matter and gravity. It thus provides us an ideal case to test how robust the universal relations of NSs are with respect to the change of the gravity theory. Due to the apparent EOS formulation of EiBI gravity developed recently by Delsate and Steinhoff, we are able to study the universal relations in EiBI gravity using the same techniques as those in GR. We find that the universal relations in EiBI gravity are essentially the same as those in GR. Our work shows that, within the currently viable coupling constant, there exists at least one modified gravity theory that is indistinguishable from GR in view of the unexpected universal relations.

  7. Testing universal relations of neutron stars with a nonlinear matter-gravity coupling theory

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Sham, Y.-H.; Lin, L.-M.; Leung, P. T., E-mail: yhsham@phy.cuhk.edu.hk, E-mail: lmlin@phy.cuhk.edu.hk, E-mail: ptleung@phy.cuhk.edu.hk

    Due to our ignorance of the equation of state (EOS) beyond nuclear density, there is still no unique theoretical model for neutron stars (NSs). It is therefore surprising that universal EOS-independent relations connecting different physical quantities of NSs can exist. Lau et al. found that the frequency of the f-mode oscillation, the mass, and the moment of inertia are connected by universal relations. More recently, Yagi and Yunes discovered the I-Love-Q universal relations among the mass, the moment of inertia, the Love number, and the quadrupole moment. In this paper, we study these universal relations in the Eddington-inspired Born-Infeld (EiBI)more » gravity. This theory differs from general relativity (GR) significantly only at high densities due to the nonlinear coupling between matter and gravity. It thus provides us an ideal case to test how robust the universal relations of NSs are with respect to the change of the gravity theory. Due to the apparent EOS formulation of EiBI gravity developed recently by Delsate and Steinhoff, we are able to study the universal relations in EiBI gravity using the same techniques as those in GR. We find that the universal relations in EiBI gravity are essentially the same as those in GR. Our work shows that, within the currently viable coupling constant, there exists at least one modified gravity theory that is indistinguishable from GR in view of the unexpected universal relations.« less

  8. Mechanotransduction as an Adaptation to Gravity.

    PubMed

    Najrana, Tanbir; Sanchez-Esteban, Juan

    2016-01-01

    Gravity has played a critical role in the development of terrestrial life. A key event in evolution has been the development of mechanisms to sense and transduce gravitational force into biological signals. The objective of this manuscript is to review how living organisms on Earth use mechanotransduction as an adaptation to gravity. Certain cells have evolved specialized structures, such as otoliths in hair cells of the inner ear and statoliths in plants, to respond directly to the force of gravity. By conducting studies in the reduced gravity of spaceflight (microgravity) or simulating microgravity in the laboratory, we have gained insights into how gravity might have changed life on Earth. We review how microgravity affects prokaryotic and eukaryotic cells at the cellular and molecular levels. Genomic studies in yeast have identified changes in genes involved in budding, cell polarity, and cell separation regulated by Ras, PI3K, and TOR signaling pathways. Moreover, transcriptomic analysis of late pregnant rats have revealed that microgravity affects genes that regulate circadian clocks, activate mechanotransduction pathways, and induce changes in immune response, metabolism, and cells proliferation. Importantly, these studies identified genes that modify chromatin structure and methylation, suggesting that long-term adaptation to gravity may be mediated by epigenetic modifications. Given that gravity represents a modification in mechanical stresses encounter by the cells, the tensegrity model of cytoskeletal architecture provides an excellent paradigm to explain how changes in the balance of forces, which are transmitted across transmembrane receptors and cytoskeleton, can influence intracellular signaling pathways and gene expression.

  9. Estimating aquifer properties using time-lapse, high precision gravity surveys and groundwater modeling

    NASA Astrophysics Data System (ADS)

    Keating, E.; Cogbill, A. H.; Ferguson, J. F.

    2003-12-01

    In the past, gravity methods have had limited application for monitoring aquifers, primarily due to the poor drift characteristics of relative gravimeters, which made long-term gravity studies of aquifers prohibitively expensive. Recent developments in portable, very accurate, absolute gravity instruments having essentially zero long-term drift have reawakened interest in using gravity methods for hydrologic monitoring. Such instruments have accuracies of 7 microGals or better and can acquire measurements at the rate of better than one station per hour. Theoretically, temporal changes in gravity can be used to infer storage characteristics and fluxes into and out of the aquifer. The sensitivity of the method to scaling effects, temporal lags between recharge/discharge and changes in storage, and to uncertainties in aquifer structure are poorly understood. In preparation for interpreting a basin-scale, time-lapse gravity data set, we have established a network of gravity stations within the Espanola Basin in northern New Mexico, a semi-arid region which is experiencing rapid population growth and groundwater resource use. We are using an existing basin-scale groundwater flow model to predict changes in mass, given our current level of understanding of inflows, outflows, and aquifer properties. Preliminary model results will be used to examine scaling issues related to the spatial density of the gravity station network and depths to the regional water table. By modeling the gravitational response to water movement in the aquifer, we study the sensitivity of gravity measurements to aquifer storage properties, given other known uncertainties in basin-scale fluxes. Results will be used to evaluate the adequacy of the existing network and to modify its design, if necessary.

  10. A Factor of 2-4 Improvement in Marine Gravity and Predicted Bathymetry from CryoSat, Jason-1, and Envisat Radar Altimetry: Arctic and Coastal Regions

    DTIC Science & Technology

    2013-09-30

    dsandwell@ucsd.edu Award Number: N00014-12-1-0111 http://topex.ucsd.edu LONG-TERM GOALS • Improve our understanding of the ocean basins for...scientific research and Naval operations. OBJECTIVES • Improve global marine gravity maps by a factor of 2 in deep ocean areas and a factor of 4 in...arcsecond bathymetry model (SRTM30_PLUS). • Prepare the next generation of scientists for ocean research. APPROACH 1. Modify waveform

  11. A Factor of 2-4 Improvement in Marine Gravity and Predicted Bathymetry from CryoSat, Jason-1, and Envisat Radar Altimetry: Arctic and Coastal Regions

    DTIC Science & Technology

    2012-09-30

    ucsd.edu Award Number: N00014-12-1-0111 http://topex.ucsd.edu LONG-TERM GOALS • Improve our understanding of the ocean basins for...scientific research and Naval operations. OBJECTIVES • Improve global marine gravity maps by a factor of 2 in deep ocean areas and a factor of 4 in the...arcsecond bathymetry model (SRTM30_PLUS). • Prepare the next generation of scientists for ocean research. APPROACH 1. Modify waveform retracking

  12. Human habitat positioning system for NASA's space flight environmental simulator

    NASA Technical Reports Server (NTRS)

    Caldwell, W. F.; Tucker, J.; Keas, P.

    1998-01-01

    Artificial gravity by centrifugation offers an effective countermeasure to the physiologic deconditioning of chronic exposure to microgravity; however, the system requirements of rotational velocity, radius of rotation, and resultant centrifugal acceleration require thorough investigation to ascertain the ideal human-use centrifuge configuration. NASA's Space Flight Environmental Simulator (SFES), a 16-meter (52-foot) diameter, animal-use centrifuge, was recently modified to accommodate human occupancy. This paper describes the SFES Human Habitat Positioning System, the mechanism that facilitates radius of rotation variability and alignment of the centrifuge occupants with the artificial gravity vector.

  13. Massive gravity and the suppression of anisotropies and gravitational waves in a matter-dominated contracting universe

    NASA Astrophysics Data System (ADS)

    Lin, Chunshan; Quintin, Jerome; Brandenberger, Robert H.

    2018-01-01

    We consider a modified gravity model with a massive graviton, but which nevertheless only propagates two gravitational degrees of freedom and which is free of ghosts. We show that non-singular bouncing cosmological background solutions can be generated. In addition, the mass term for the graviton prevents anisotropies from blowing up in the contracting phase and also suppresses the spectrum of gravitational waves compared to that of the scalar cosmological perturbations. This addresses two of the main problems of the matter bounce scenario.

  14. Gravitational wave probes of parity violation in compact binary coalescences

    NASA Astrophysics Data System (ADS)

    Alexander, Stephon H.; Yunes, Nicolás

    2018-03-01

    Is gravity parity violating? Given the recent observations of gravitational waves from coalescing compact binaries, we develop a strategy to find an answer with current and future detectors. We identify the key signatures of parity violation in gravitational waves: amplitude birefringence in their propagation and a modified chirping rate in their generation. We then determine the optimal binaries to test the existence of parity violation in gravity, and prioritize the research in modeling that will be required to carry out such tests before detectors reach their design sensitivity.

  15. Open-Ended, Problem-Solving Investigations--Getting Started.

    ERIC Educational Resources Information Center

    Lock, Roger

    1991-01-01

    Ways in which linear lesson sequences can be modified to provide increased opportunities for open-ended activities especially with problem solving are considered. Examples drawn from chemistry and plant reproduction, seeds, and germination are given. (KR)

  16. Anisotropic neutron stars in R2 gravity

    NASA Astrophysics Data System (ADS)

    Folomeev, Vladimir

    2018-06-01

    We consider static neutron stars within the framework of R2 gravity. The neutron fluid is described by three different types of realistic equations of state (soft, moderately stiff, and stiff). Using the observational data on the neutron star mass-radius relation, it is demonstrated that the characteristics of the objects supported by the isotropic fluid agree with the observations only if one uses the soft equation of state. We show that the inclusion of the fluid anisotropy enables one also to employ more stiff equations of state to model configurations that will satisfy the observational constraints sufficiently. Also, using the standard thin accretion disk model, we demonstrate potentially observable differences, which allow us to distinguish the neutron stars constructed within the modified gravity framework from those described in Einstein's general relativity.

  17. Testing Quantum Gravity Induced Nonlocality via Optomechanical Quantum Oscillators.

    PubMed

    Belenchia, Alessio; Benincasa, Dionigi M T; Liberati, Stefano; Marin, Francesco; Marino, Francesco; Ortolan, Antonello

    2016-04-22

    Several quantum gravity scenarios lead to physics below the Planck scale characterized by nonlocal, Lorentz invariant equations of motion. We show that such nonlocal effective field theories lead to a modified Schrödinger evolution in the nonrelativistic limit. In particular, the nonlocal evolution of optomechanical quantum oscillators is characterized by a spontaneous periodic squeezing that cannot be generated by environmental effects. We discuss constraints on the nonlocality obtained by past experiments, and show how future experiments (already under construction) will either see such effects or otherwise cast severe bounds on the nonlocality scale (well beyond the current limits set by the Large Hadron Collider). This paves the way for table top, high precision experiments on massive quantum objects as a promising new avenue for testing some quantum gravity phenomenology.

  18. Spherical collapse in chameleon models

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Brax, Ph.; Rosenfeld, R.; Steer, D.A., E-mail: brax@spht.saclay.cea.fr, E-mail: rosenfel@ift.unesp.br, E-mail: daniele.steer@apc.univ-paris7.fr

    2010-08-01

    We study the gravitational collapse of an overdensity of nonrelativistic matter under the action of gravity and a chameleon scalar field. We show that the spherical collapse model is modified by the presence of a chameleon field. In particular, we find that even though the chameleon effects can be potentially large at small scales, for a large enough initial size of the inhomogeneity the collapsing region possesses a thin shell that shields the modification of gravity induced by the chameleon field, recovering the standard gravity results. We analyse the behaviour of a collapsing shell in a cosmological setting in themore » presence of a thin shell and find that, in contrast to the usual case, the critical density for collapse in principle depends on the initial comoving size of the inhomogeneity.« less

  19. Metric Theories of Gravity: Perturbations and Conservation Laws

    NASA Astrophysics Data System (ADS)

    Petrov, Alexander N.; Kopeikin, Sergei M.; Lompay, Robert R.; Tekin, Bayram

    2017-04-01

    By focusing on the mostly used variational methods, this monograph aspires to give a unified description and comparison of various ways of constructing conserved quantities for perturbations and to study symmetries in general relativity and modified theories of gravity. The main emphasis lies on the field-theoretical covariant formulation of perturbations, the canonical Noether approach and the Belinfante procedure of symmetrisation. The general formalism is applied to build the gauge-invariant cosmological perturbation theory, conserved currents and superpotentials to describe physically important solutions of gravity theories. Meticulous attention is given to the construction of conserved quantities in asymptotically-flat spacetimes as well as in asymptotically constant curvature spacetimes such as the Anti-de Sitter space. Significant part of the book can be used in graduate courses on conservation laws in general relativity.

  20. Determining the depth of certain gravity sources without a priori specification of their structural index

    NASA Astrophysics Data System (ADS)

    Zhou, Shuai; Huang, Danian

    2015-11-01

    We have developed a new method for the interpretation of gravity tensor data based on the generalized Tilt-depth method. Cooper (2011, 2012) extended the magnetic Tilt-depth method to gravity data. We take the gradient-ratio method of Cooper (2011, 2012) and modify it so that the source type does not need to be specified a priori. We develop the new method by generalizing the Tilt-depth method for depth estimation for different types of source bodies. The new technique uses only the three vertical tensor components of the full gravity tensor data observed or calculated at different height plane to estimate the depth of the buried bodies without a priori specification of their structural index. For severely noise-corrupted data, our method utilizes different upward continuation height data, which can effectively reduce the influence of noise. Theoretical simulations of the gravity source model with and without noise illustrate the ability of the method to provide source depth information. Additionally, the simulations demonstrate that the new method is simple, computationally fast and accurate. Finally, we apply the method using the gravity data acquired over the Humble Salt Dome in the USA as an example. The results show a good correspondence to the previous drilling and seismic interpretation results.

  1. Moment of inertia of neutron star crust in alternative and modified theories of gravity

    NASA Astrophysics Data System (ADS)

    Staykov, Kalin V.; Ekşi, K. Yavuz; Yazadjiev, Stoytcho S.; Türkoǧlu, M. Metehan; Arapoǧlu, A. Savaş

    2016-07-01

    The glitch activity of young pulsars arises from the exchange of angular momentum between the crust and the interior of the star. Recently, it was inferred that the moment of inertia of the crust of a neutron star is not sufficient to explain the observed glitches. Such estimates are presumed in Einstein's general relativity in describing the hydrostatic equilibrium of neutron stars. The crust of the neutron star has a spacetime curvature of 14 orders of magnitude larger than that probed in solar system tests. This makes gravity the weakest constrained physics input in the crust-related processes. We calculate the ratio of the crustal to the total moment of inertia of neutron stars in the scalar-tensor theory of gravity and the nonperturbative f (R )=R +a R2 gravity. We find for the former that the crust-to-core ratio of the moment of inertia does not change significantly from what is inferred in general relativity. For the latter, we find that the ratio increases significantly from what is inferred in general relativity in the case of high mass objects. Our results suggest that the glitch activity of pulsars may be used to probe gravity models, although the gravity models explored in this work are not appropriate candidates.

  2. Statistical aspects of the Klein-Gordon oscillator in the frame work of GUP

    NASA Astrophysics Data System (ADS)

    Khosropour, B.

    2018-01-01

    Investigation in perturbative string theory and quantum gravity suggest that there is a measurable minimal length in nature. In this work, according to generalized uncertainty principle, we study the statistical characteristics of Klein-Gordon Oscillator (KLO). The modified energy spectrum of the KLO are obtained. The generalized thermodynamical quantities of the KLO such as partition function, mean energy and entropy are calculated by using the modified energy spectrum.

  3. Femur-bending properties as influenced by gravity. V - Strength vs. calcium and gravity in rats exposed for 2 weeks

    NASA Technical Reports Server (NTRS)

    Wunder, Charles C.; Cook, Kenneth M.; Watkins, Stanley R.; Moressi, William J.

    1987-01-01

    The dependence of gravitationally related changes in femur bone strength on the comparable changes in calcium content was investigated in rats exposed to chronic simulations of altered gravity from the 28th to 42nd day of age. Zero G was simulated by harness suspension and 3 G by centrifugation. Bone strength (S) was determined by bending (using modified quasi-static cantilever bending methods and equipment described by Wunder et al., 1977 and 1979) and Ca content (C, by mass pct) determined by atomic absorption spectrometry; results were compared with data obtained on both normal and harnessed control animals at 1 G. Multiple regression showed significant dependence of S upon earth's gravity, independent from C, for which there was no significant coefficient of partial regression. It is suggested that the lack of S/C correlation might have been due to the fact that considerable fraction of the calcium in these young, developing bones has not yet crystallized into the hydroxyapatite which provides strength.

  4. Post-Newtonian parameter γ in generalized non-local gravity

    NASA Astrophysics Data System (ADS)

    Zhang, Xue; Wu, YaBo; Yang, WeiQiang; Zhang, ChengYuan; Chen, BoHai; Zhang, Nan

    2017-10-01

    We investigate the post-Newtonian parameter γ and derive its formalism in generalized non-local (GNL) gravity, which is the modified theory of general relativity (GR) obtained by adding a term m 2 n-2 R☐-n R to the Einstein-Hilbert action. Concretely, based on parametrizing the generalized non-local action in which gravity is described by a series of dynamical scalar fields ϕ i in addition to the metric tensor g μν, the post-Newtonian limit is computed, and the effective gravitational constant as well as the post-Newtonian parameters are directly obtained from the generalized non-local gravity. Moreover, by discussing the values of the parametrized post-Newtonian parameters γ, we can compare our expressions and results with those in Hohmann and Järv et al. (2016), as well as current observational constraints on the values of γ in Will (2006). Hence, we draw restrictions on the nonminimal coupling terms F̅ around their background values.

  5. Metric-affine f (R ,T ) theories of gravity and their applications

    NASA Astrophysics Data System (ADS)

    Barrientos, E.; Lobo, Francisco S. N.; Mendoza, S.; Olmo, Gonzalo J.; Rubiera-Garcia, D.

    2018-05-01

    We study f (R ,T ) theories of gravity, where T is the trace of the energy-momentum tensor Tμ ν, with independent metric and affine connection (metric-affine theories). We find that the resulting field equations share a close resemblance with their metric-affine f (R ) relatives once an effective energy-momentum tensor is introduced. As a result, the metric field equations are second-order and no new propagating degrees of freedom arise as compared to GR, which contrasts with the metric formulation of these theories, where a dynamical scalar degree of freedom is present. Analogously to its metric counterpart, the field equations impose the nonconservation of the energy-momentum tensor, which implies nongeodesic motion and consequently leads to the appearance of an extra force. The weak field limit leads to a modified Poisson equation formally identical to that found in Eddington-inspired Born-Infeld gravity. Furthermore, the coupling of these gravity theories to perfect fluids, electromagnetic, and scalar fields, and their potential applications are discussed.

  6. Current Space Station Experiments Investigating Component Level Electronics Repair

    NASA Technical Reports Server (NTRS)

    Easton, John W.; Struk, Peter M.

    2010-01-01

    The Soldering in a Reduced Gravity Experiment (SoRGE) and Component Repair Experiment (CRE)-1 are tests performed on the International Space Station to determine the techniques, tools, and training necessary to allow future crews to perform manual electronics repairs at the component level. SoRGE provides information on the formation and internal structure of through-hole solder joints, illustrating the challenges and implications of soldering in reduced gravity. SoRGE showed a significant increase in internal void defects for joints formed in low gravity compared to normal gravity. Methods for mitigating these void defects were evaluated using a modified soldering process. CRE-1 demonstrated the removal, cleaning, and replacement of electronics components by manual means on functional circuit boards. The majority of components successful passed a post-repair functional test demonstrating the feasibility of component-level repair within the confines of a spacecraft. Together, these tasks provide information to recommend material and tool improvements, training improvements, and future work to help enable electronics repairs in future space missions.

  7. Classical aspects of higher spin topologically massive gravity

    NASA Astrophysics Data System (ADS)

    Chen, Bin; Long, Jiang; Zhang, Jian-Dong

    2012-10-01

    We study the classical solutions of three-dimensional topologically massive gravity (TMG) and its higher spin generalization, in the first-order formulation. The action of higher spin TMG has been proposed by Chen and Long (2011 J. High Energy Phys. JHEP12(2011)114) to be of a Chern-Simons-like form. The equations of motion are more complicated than the ones in pure higher spin AdS3 gravity, but are still tractable. As all the solutions in higher spin gravity are automatically the solutions of higher spin TMG, we focus on other solutions. We manage to find the AdS pp-wave solutions with higher spin hair and find that the non-vanishing higher spin fields may or may not modify the pp-wave geometry. In order to discuss the warped spacetime, we introduce the notion of a special Killing vector, which is defined to be the symmetry on the frame-like fields. We reproduce various warped spacetimes of TMG in our framework, with the help of special Killing vectors.

  8. Novel symmetries in Weyl-invariant gravity with massive gauge field

    NASA Astrophysics Data System (ADS)

    Abhinav, K.; Shukla, A.; Panigrahi, P. K.

    2016-11-01

    The background field method is used to linearize the Weyl-invariant scalar-tensor gravity, coupled with a Stückelberg field. For a generic background metric, this action is found not to be invariant, under both a diffeomorphism and generalized Weyl symmetry, the latter being a combination of gauge and Weyl transformations. Interestingly, the quadratic Lagrangian, emerging from a background of Minkowski metric, respects both transformations independently. The Becchi-Rouet-Stora-Tyutin symmetry of scalar-tensor gravity coupled with a Stückelberg-like massive gauge particle, possessing a diffeomorphism and generalized Weyl symmetry, reveals that in both cases negative-norm states with unphysical degrees of freedom do exist. We then show that, by combining diffeomorphism and generalized Weyl symmetries, all the ghost states decouple, thereby removing the unphysical redundancies of the theory. During this process, the scalar field does not represent any dynamic mode, yet modifies the usual harmonic gauge condition through non-minimal coupling with gravity.

  9. Momentum and charge transport in non-relativistic holographic fluids from Hořava gravity

    NASA Astrophysics Data System (ADS)

    Davison, Richard A.; Grozdanov, Sašo; Janiszewski, Stefan; Kaminski, Matthias

    2016-11-01

    We study the linearized transport of transverse momentum and charge in a conjectured field theory dual to a black brane solution of Hořava gravity with Lifshitz exponent z = 1. As expected from general hydrodynamic reasoning, we find that both of these quantities are diffusive over distance and time scales larger than the inverse temperature. We compute the diffusion constants and conductivities of transverse momentum and charge, as well the ratio of shear viscosity to entropy density, and find that they differ from their relativistic counterparts. To derive these results, we propose how the holographic dictionary should be modified to deal with the multiple horizons and differing propagation speeds of bulk excitations in Hořava gravity. When possible, as a check on our methods and results, we use the covariant Einstein-Aether formulation of Hořava gravity, along with field redefinitions, to re-derive our results from a relativistic bulk theory.

  10. White dwarfs and revelations

    NASA Astrophysics Data System (ADS)

    Saltas, Ippocratis D.; Sawicki, Ignacy; Lopes, Ilidio

    2018-05-01

    We use the most recent, complete and independent measurements of masses and radii of white dwarfs in binaries to bound the class of non-trivial modified gravity theories, viable after GW170817/GRB170817, using its effect on the mass-radius relation of the stars. We show that the uncertainty in the latest data is sufficiently small that residual evolutionary effects, most notably the effect of core composition, finite temperature and envelope structure, must now accounted for if correct conclusions about the nature of gravity are to be made. We model corrections resulting from finite temperature and envelopes to a base Hamada-Salpeter cold equation of state and derive consistent bounds on the possible modifications of gravity in the stars' interiors, finding that the parameter quantifying the strength of the modification Y< 0.14 at 95% confidence, an improvement of a factor of three with respect to previous bounds. Finally, our analysis reveals some fundamental degeneracies between the theory of gravity and the precise chemical makeup of white dwarfs.

  11. Logarithmic entropy of Kehagias-Sfetsos black hole with self-gravitation in asymptotically flat IR modified Hořava gravity

    NASA Astrophysics Data System (ADS)

    Liu, Molin; Lu, Junwang

    2011-05-01

    Motivated by recent logarithmic entropy of Hořava-Lifshitz gravity, we investigate Hawking radiation for Kehagias-Sfetsos black hole from tunneling perspective. After considering the effect of self-gravitation, we calculate the emission rate and entropy of quantum tunneling by using Kraus-Parikh-Wilczek method. Meanwhile, both massless and massive particles are considered in this Letter. Interestingly, two types tunneling particles have the same emission rate Γ and entropy Sb whose analytical formulae are Γ=exp[π(rin2-rout2)/2+π/αln rin/rout] and Sb=A/4+π/αln(A/4), respectively. Here, α is the Hořava-Lifshitz field parameter. The results show that the logarithmic entropy of Hořava-Lifshitz gravity could be explained well by the self-gravitation, which is totally different from other methods. The study of this semiclassical tunneling process may shed light on understanding the Hořava-Lifshitz gravity.

  12. Users Guide to the JPL Doppler Gravity Database

    NASA Technical Reports Server (NTRS)

    Muller, P. M.; Sjogren, W. L.

    1986-01-01

    Local gravity accelerations and gravimetry have been determined directly from spacecraft Doppler tracking data near the Moon and various planets by the Jet Propulsion Laboratory. Researchers in many fields have an interest in planet-wide global gravimetric mapping and its applications. Many of them use their own computers in support of their studies and would benefit from being able to directly manipulate these gravity data for inclusion in their own modeling computations. Pubication of some 150 Apollo 15 subsatellite low-altitude, high-resolution, single-orbit data sets is covered. The doppler residuals with a determination of the derivative function providing line-of-sight-gravity are both listed and plotted (on microfilm), and can be ordered in computer readable forms (tape and floppy disk). The form and format of this database as well as the methods of data reduction are explained and referenced. A skeleton computer program is provided which can be modified to support re-reductions and re-formatted presentations suitable to a wide variety of research needs undertaken on mainframe or PC class microcomputers.

  13. Dr. Tulp's Anatomy Lesson by Rembrandt: the third day hypothesis.

    PubMed

    Afek, Arnon; Friedman, Tal; Kugel, Chen; Barshack, Iris; Lurie, Doron J

    2009-07-01

    An autopsy was an important event in 17th century Holland. Autopsies were held in an 'anatomy theater' and performed according to a fixed protocol that often took up to 3 days to complete. Of the five group portraits painted by Rembrandt over the course of his career, two were anatomy lessons given by Dr. Tulp and Dr. Deyman. An examination of Rembrandt's painting Dr. Tulp's Anatomy Lesson (1632) and an X-ray image of the painting, as compared to other paintings of anatomy lessons from the same period, reveal interesting differences, such as positioning, and light and shadow. Not only was the autopsy not performed according to the usual protocol, but in this painting Rembrandt created a unique dramatic scene in his effort to tell a story. We suggest that Dr. Tulp and Rembrandt "modified" the painting of Dr. Tulp's anatomy lesson to emphasize Dr. Tulp's position as the greatest anatomist of his era--"Vesalius of Amsterdam," and as a way of demonstrating God's greatness by highlighting the hand as a symbol of the most glorious of God's creations.

  14. Confirmation of general relativity on large scales from weak lensing and galaxy velocities.

    PubMed

    Reyes, Reinabelle; Mandelbaum, Rachel; Seljak, Uros; Baldauf, Tobias; Gunn, James E; Lombriser, Lucas; Smith, Robert E

    2010-03-11

    Although general relativity underlies modern cosmology, its applicability on cosmological length scales has yet to be stringently tested. Such a test has recently been proposed, using a quantity, E(G), that combines measures of large-scale gravitational lensing, galaxy clustering and structure growth rate. The combination is insensitive to 'galaxy bias' (the difference between the clustering of visible galaxies and invisible dark matter) and is thus robust to the uncertainty in this parameter. Modified theories of gravity generally predict values of E(G) different from the general relativistic prediction because, in these theories, the 'gravitational slip' (the difference between the two potentials that describe perturbations in the gravitational metric) is non-zero, which leads to changes in the growth of structure and the strength of the gravitational lensing effect. Here we report that E(G) = 0.39 +/- 0.06 on length scales of tens of megaparsecs, in agreement with the general relativistic prediction of E(G) approximately 0.4. The measured value excludes a model within the tensor-vector-scalar gravity theory, which modifies both Newtonian and Einstein gravity. However, the relatively large uncertainty still permits models within f(R) theory, which is an extension of general relativity. A fivefold decrease in uncertainty is needed to rule out these models.

  15. Confirmation of general relativity on large scales from weak lensing and galaxy velocities

    NASA Astrophysics Data System (ADS)

    Reyes, Reinabelle; Mandelbaum, Rachel; Seljak, Uros; Baldauf, Tobias; Gunn, James E.; Lombriser, Lucas; Smith, Robert E.

    2010-03-01

    Although general relativity underlies modern cosmology, its applicability on cosmological length scales has yet to be stringently tested. Such a test has recently been proposed, using a quantity, EG, that combines measures of large-scale gravitational lensing, galaxy clustering and structure growth rate. The combination is insensitive to `galaxy bias' (the difference between the clustering of visible galaxies and invisible dark matter) and is thus robust to the uncertainty in this parameter. Modified theories of gravity generally predict values of EG different from the general relativistic prediction because, in these theories, the `gravitational slip' (the difference between the two potentials that describe perturbations in the gravitational metric) is non-zero, which leads to changes in the growth of structure and the strength of the gravitational lensing effect. Here we report that EG = 0.39+/-0.06 on length scales of tens of megaparsecs, in agreement with the general relativistic prediction of EG~0.4. The measured value excludes a model within the tensor-vector-scalar gravity theory, which modifies both Newtonian and Einstein gravity. However, the relatively large uncertainty still permits models within f() theory, which is an extension of general relativity. A fivefold decrease in uncertainty is needed to rule out these models.

  16. The integrated bispectrum in modified gravity theories

    NASA Astrophysics Data System (ADS)

    Munshi, Dipak

    2017-01-01

    Gravity-induced non-Gaussianity can provide important clues to Modified Gravity (MG) Theories. Several recent studies have suggested using the Integrated Bispectrum (IB) as a probe for squeezed configuration of bispectrum. Extending previous studies on the IB, we include redshift-space distortions to study a class of (parametrised) MG theories that include the string-inspired Dvali, Gabadadze & Porrati (DGP) model. Various contributions from redshift-space distortions are derived in a transparent manner, and squeezed contributions from these terms are derived separately. Results are obtained using the Zel'dovich Approximation (ZA). Results are also presented for projected surveys (2D). We use the Press-Schechter (PS) and Sheth-Tormen (ST) mass functions to compute the IB for collapsed objects that can readily be extended to peak-theory based approaches. The cumulant correlators (CCs) generalise the ordinary cumulants and are known to probe collapsed configurations of higher order correlation functions. We generalise the concept of CCs to halos of different masses. We also introduce a generating function based approach to analyse more general non-local biasing models. The Fourier representations of the CCs, the skew-spectrum, or the kurt-spctra are discussed in this context. The results are relevant for the study of the Minkowski Functionals (MF) of collapsed tracers in redshift-space.

  17. Off-diagonal ekpyrotic scenarios and equivalence of modified, massive and/or Einstein gravity

    NASA Astrophysics Data System (ADS)

    Vacaru, Sergiu I.

    2016-01-01

    Using our anholonomic frame deformation method, we show how generic off-diagonal cosmological solutions depending, in general, on all spacetime coordinates and undergoing a phase of ultra-slow contraction can be constructed in massive gravity. In this paper, there are found and studied new classes of locally anisotropic and (in)homogeneous cosmological metrics with open and closed spatial geometries. The late time acceleration is present due to effective cosmological terms induced by nonlinear off-diagonal interactions and graviton mass. The off-diagonal cosmological metrics and related Stückelberg fields are constructed in explicit form up to nonholonomic frame transforms of the Friedmann-Lamaître-Robertson-Walker (FLRW) coordinates. We show that the solutions include matter, graviton mass and other effective sources modeling nonlinear gravitational and matter fields interactions in modified and/or massive gravity, with polarization of physical constants and deformations of metrics, which may explain certain dark energy and dark matter effects. There are stated and analyzed the conditions when such configurations mimic interesting solutions in general relativity and modifications and recast the general Painlevé-Gullstrand and FLRW metrics. Finally, we elaborate on a reconstruction procedure for a subclass of off-diagonal cosmological solutions which describe cyclic and ekpyrotic universes, with an emphasis on open issues and observable signatures.

  18. Fixing extensions to general relativity in the nonlinear regime

    NASA Astrophysics Data System (ADS)

    Cayuso, Juan; Ortiz, Néstor; Lehner, Luis

    2017-10-01

    The question of what gravitational theory could supersede General Relativity has been central in theoretical physics for decades. Many disparate alternatives have been proposed motivated by cosmology, quantum gravity and phenomenological angles, and have been subjected to tests derived from cosmological, solar system and pulsar observations typically restricted to linearized regimes. Gravitational waves from compact binaries provide new opportunities to probe these theories in the strongly gravitating/highly dynamical regimes. To this end however, a reliable understanding of the dynamics in such a regime is required. Unfortunately, most of these theories fail to define well posed initial value problems, which prevents at face value from meeting such challenge. In this work, we introduce a consistent program able to remedy this situation. This program is inspired in the approach to "fixing" viscous relativistic hydrodynamics introduced by Israel and Stewart in the late 70's. We illustrate how to implement this approach to control undesirable effects of higher order derivatives in gravity theories and argue how the modified system still captures the true dynamics of the putative underlying theories in 3 +1 dimensions. We sketch the implementation of this idea in a couple of effective theories of gravity, one in the context of Noncommutative Geometry, and one in the context of Chern-Simons modified General Relativity.

  19. Linearization instability for generic gravity in AdS spacetime

    NASA Astrophysics Data System (ADS)

    Altas, Emel; Tekin, Bayram

    2018-01-01

    In general relativity, perturbation theory about a background solution fails if the background spacetime has a Killing symmetry and a compact spacelike Cauchy surface. This failure, dubbed as linearization instability, shows itself as non-integrability of the perturbative infinitesimal deformation to a finite deformation of the background. Namely, the linearized field equations have spurious solutions which cannot be obtained from the linearization of exact solutions. In practice, one can show the failure of the linear perturbation theory by showing that a certain quadratic (integral) constraint on the linearized solutions is not satisfied. For non-compact Cauchy surfaces, the situation is different and for example, Minkowski space having a non-compact Cauchy surface, is linearization stable. Here we study, the linearization instability in generic metric theories of gravity where Einstein's theory is modified with additional curvature terms. We show that, unlike the case of general relativity, for modified theories even in the non-compact Cauchy surface cases, there are some theories which show linearization instability about their anti-de Sitter backgrounds. Recent D dimensional critical and three dimensional chiral gravity theories are two such examples. This observation sheds light on the paradoxical behavior of vanishing conserved charges (mass, angular momenta) for non-vacuum solutions, such as black holes, in these theories.

  20. The integrated bispectrum in modified gravity theories

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Munshi, Dipak, E-mail: D.Munshi@sussex.ac.uk

    2017-01-01

    Gravity-induced non-Gaussianity can provide important clues to Modified Gravity (MG) Theories. Several recent studies have suggested using the Integrated Bispectrum (IB) as a probe for squeezed configuration of bispectrum. Extending previous studies on the IB, we include redshift-space distortions to study a class of (parametrised) MG theories that include the string-inspired Dvali, Gabadadze and Porrati (DGP) model. Various contributions from redshift-space distortions are derived in a transparent manner, and squeezed contributions from these terms are derived separately. Results are obtained using the Zel'dovich Approximation (ZA). Results are also presented for projected surveys (2D). We use the Press-Schechter (PS) and Sheth-Tormenmore » (ST) mass functions to compute the IB for collapsed objects that can readily be extended to peak-theory based approaches. The cumulant correlators (CCs) generalise the ordinary cumulants and are known to probe collapsed configurations of higher order correlation functions. We generalise the concept of CCs to halos of different masses. We also introduce a generating function based approach to analyse more general non-local biasing models. The Fourier representations of the CCs, the skew-spectrum, or the kurt-spctra are discussed in this context. The results are relevant for the study of the Minkowski Functionals (MF) of collapsed tracers in redshift-space.« less

  1. Adaptive changes in the angular VOR: duration of gain changes and lack of effect of nodulo-uvulectomy.

    PubMed

    Yakushin, Sergei B; Bukharina, Svetlana E; Raphan, Theodore; Buttner-Ennever, Jean; Cohen, Bernard

    2003-10-01

    Alterations in the gain of the vertical angular vestibulo-ocular reflex (VOR) are dependent on the head position in which the gain changes were produced. We determined how long gravity-dependent gain changes last in monkeys after four hours of adaptation, and whether the adaptation is mediated through the nodulus and uvula of the vestibulocerebellum. Vertical VOR gains were adaptively modified by rotation about an interaural axis, in phase or out of phase with the visual surround. Vertical VOR gains were modified with the animals in one of three orientations: upright, left-side down, or right-side down. Monkeys were tested in darkness for up to four days after adaptation using sinusoidal rotation about an interaural axis that was incrementally tilted in 10 degrees steps from vertical to side down positions. Animals were unrestrained in their cages in normal light conditions between tests. Gravity-dependent gain changes lasted for a day or less after adaptation while upright, but persisted for two days or more after on-side adaptation. These data show that gravity-dependent gain changes can last for prolonged periods after only four hours of adaptation in monkeys, as in humans. They also demonstrate that natural head movements made while upright do not provide an adequate stimulus for rapid recovery of vertical VOR gains that were induced on side. In two animals, the nodulus and uvula were surgically ablated. Vertical gravity-dependent gain changes were not significantly different before and after surgery, indicating that the nodulus and uvula do not have a critical role in producing them.

  2. Modification in CSF specific gravity in acutely decompensated cirrhosis and acute on chronic liver failure independent of encephalopathy, evidences for an early blood-CSF barrier dysfunction in cirrhosis.

    PubMed

    Weiss, Nicolas; Rosselli, Matteo; Mouri, Sarah; Galanaud, Damien; Puybasset, Louis; Agarwal, Banwari; Thabut, Dominique; Jalan, Rajiv

    2017-04-01

    Although hepatic encephalopathy (HE) on the background of acute on chronic liver failure (ACLF) is associated with high mortality rates, it is unknown whether this is due to increased blood-brain barrier permeability. Specific gravity of cerebrospinal fluid measured by CT is able to estimate blood-cerebrospinal fluid-barrier permeability. This study aimed to assess cerebrospinal fluid specific gravity in acutely decompensated cirrhosis and to compare it in patients with or without ACLF and with or without hepatic encephalopathy. We identified all the patients admitted for acute decompensation of cirrhosis who underwent a brain CT-scan. Those patients could present acute decompensation with or without ACLF. The presence of hepatic encephalopathy was noted. They were compared to a group of stable cirrhotic patients and healthy controls. Quantitative brain CT analysis used the Brainview software that gives the weight, the volume and the specific gravity of each determined brain regions. Results are given as median and interquartile ranges and as relative variation compared to the control/baseline group. 36 patients presented an acute decompensation of cirrhosis. Among them, 25 presented with ACLF and 11 without ACLF; 20 presented with hepatic encephalopathy grade ≥ 2. They were compared to 31 stable cirrhosis patients and 61 healthy controls. Cirrhotic patients had increased cerebrospinal fluid specific gravity (CSF-SG) compared to healthy controls (+0.4 %, p < 0.0001). Cirrhotic patients with ACLF have decreased CSF-SG as compared to cirrhotic patients without ACLF (-0.2 %, p = 0.0030) that remained higher than in healthy controls. The presence of hepatic encephalopathy did not modify CSF-SG (-0.09 %, p = 0.1757). Specific gravity did not differ between different brain regions according to the presence or absence of either ACLF or HE. In patients with acute decompensation of cirrhosis, and those with ACLF, CSF specific gravity is modified compared to both stable cirrhotic patients and healthy controls. This pattern is observed even in the absence of hepatic encephalopathy suggesting that blood-CSF barrier impairment is manifest even in absence of overt hepatic encephalopathy.

  3. Using the Earth as a guide to martian mass movement processes: From form to process

    NASA Astrophysics Data System (ADS)

    Lanza, N.; Newsom, H. E.; Osterloo, M. M.; Okubo, C. H.

    2011-12-01

    The discovery of gully features on Mars has led to renewed interest in hillslope processes on that planet, in particular mass movement and the morphologies that it produces. Mass movement is a collection of gravity-driven processes that act to move materials down a hillslope. Here, we examine how mass movements on hillslopes may be expected to differ on Earth and Mars as the result of gravity differences between these planets. Downslope movement of unconsolidated materials is generally controlled by the bulk shear strength of these materials. Although the relationship between gravity and shear strength is largely dependent on variables that are independent of gravity, the lower gravity on Mars is expected to produce some systematic changes in mass movement behaviors that may in turn create morphological features that are observably different from their terrestrial counterparts. After scaling for gravity and modifying empirically derived relationships, we may expect the following differences on martian hillslopes when compared to their terrestrial counterparts: ==On Mars, hillslopes may have steeper angles of repose in fine grained (< ~2 mm) materials, even when dry. No change in angle of repose is expected for larger particles; ==An increase in soil moisture content (e.g., excess pore pressure) is expected to weaken unconsolidated slope materials more on Mars for a particular regolith type, which in turn may produce --An increase in creep rates for a given pore pressure, and --An increase in effectiveness of frost heave to transport materials downslope; ==Processes triggered by saturation may occur at lower pore pressures on Mars; --A smaller amount of fluid is needed to achieve failure; ==Shorter runout lengths are expected for rapid mass movements; ==On Mars, overland flow will exert a proportionally lower shear stress on slope materials; --In cohesive materials, the same volume of water will detach sediments of smaller sizes. On Earth, mass movement processes may be directly observed and measured as they occur, whereas on Mars only the resultant landforms may be studied at present. By understanding how martian hillslope processes are expected to be modified by lower gravity, the interpretation of martian landforms may be greatly aided. Examples of observations that support some of these predicted differences will be presented, with a focus on saturation-triggered events in unconsolidated materials.

  4. The Gravity of LBNP Exercise: Lessons Learned from Identical Twins in Bed for 30 Days

    NASA Technical Reports Server (NTRS)

    Hargens, Alan R.; Groppo, Eli R.; Lee, Stuart M. C.; Watenpaugh, Donald; Schneider, Suzanne; O'Leary, Deborah; Smith, Scott M.; Steinbach, Gregory C.; Tanaka, Kunihiko; Kimura, Shinji; hide

    2002-01-01

    Microgravity leads to cardiovascular deconditioning in humans, which is manifested by post-flight reduction of orthostatic tolerance and upright exercise capacity. During upright posture on Earth, blood pressures are greater in the feet than at heart or head levels due to gravity's effects on columns of blood in the body. During exposure to Microgravity, all gravitational blood pressures disappear. Presently, there is no exercise hardware available for space flight to provide gravitational blood pressures to tissues of the lower body. We hypothesized that 40 minutes of supine treadmill running per day in a LBNP chamber at 1.0 to 1.2 body weight (approximately 50 - 60 mm Hg LBNP) with a 5 min resting, nonexercise LBNP exposure at 50 mm Hg after the exercise session will maintain aerobic fitness orthostatic tolerance, and selected parameters of musculoskeletal function during 30 days of bed rest (simulated microgravity). This paper is an interim report of some of our findings on 16 subjects.

  5. Active Control of a Pneumatic Isolation System,

    DTIC Science & Technology

    A pneumatically isolated test platform has been modified to provide active control to the local gravity vector. A combination of sensors , including... tiltmeters , angular accelerometers, seismometers, and a gyrocompass measure total platform motion between 0 and 100 Hz. Electrical-to-pressure

  6. MOG without anomaly

    NASA Astrophysics Data System (ADS)

    Sepehri, Alireza; Ghaffary, Tooraj; Naimi, Yaghoob

    2018-03-01

    We obtain the action of Moffat's Modified Gravity (MOG), a scalar-tensor-vector theory of gravitation, by generalizing the Horava-Witten mechanism to fourteen dimensions. We show that the resulting theory is anomaly-free. We propose an extended version of MOG that includes fermionic fields.

  7. Crickets in space

    NASA Astrophysics Data System (ADS)

    Horn, Eberhard; Böser, Sybille; Förster, Susanne; Riewe, Pascal; Sebastian, Claudia; Agricola, Hans

    2001-08-01

    "Crickets in Space" (CRISP) was a Neurolab experiment by which the balance between genetic programs and the gravitational environment for the development of a gravity sensitive neuronal system was studied. The model character of crickets was justified by their external gravity receptors, identified position-sensitive interneurons (PSI) and gravity-related compensatory head response, and by the specific relation of this behavior to neuronal activation systems. These advantages allowed us to study the impact of modified gravity on cellular processes in a complex organism. Eggs, 1 st, 4 th and 6 th stage larvae of Acheta domesticus were used. Post-flight experiments revealed a low susceptibility of the behavior to microgravity (μg) and hypergravity (hg) while the physiology of the PSI was significantly affected. Immunocytological investigations revealed a stage-dependent sensitivity of thoracic GABAergic motoneurons to 3g-conditions concerning their soma sizes but not their topographical arrangement. Peptidergic neurons from cerebral sensorimotor centers revealed no significant modifications by microgravity. The contrary physiological and behavioral results indicate a facilitation of 1g-readaptation by accessory gravity, proprioceptive and visual sense organs. Absence of anatomical modifications point to an effective time window of μg- or hg-exposure related to the period of neuronal proliferation.

  8. Extending Newton's Universal Theory of Gravity

    NASA Astrophysics Data System (ADS)

    Aisenberg, Sol

    2011-11-01

    This should remove the mystery of Dark Matter. Newton's universal theory of gravity only used the observations of the motion of planets in our solar system. Hubble later used observations of fixed stars in the universe, and showed that the fixed stars were actually galaxies with very large numbers of stars. Newton's universal law of gravity could not explain these new observations without the mystery of dark matter for the additional gravity. In science, when a theory is not able to explain new observations it is necessary to modify the theory or abandon the theory. Rubin observed flat (constant velocity) rotation curves for stars in spiral galaxies. Dark matter was proposed to provide the missing gravity. The equation balancing gravitational force and centripetal force is M*G=v*v*r and for the observed constant velocity v this requires M*G to be a linear function of distance r. If the linear dependence is instead assigned to G instead of M to give a new value for Gn as G+A*r, this will explain the observations in the cosmos and also in our solar system for small r. See ``The Misunderstood Universe'' for more details.

  9. Testing Chern-Simons modified gravity with observations of extreme-mass-ratio binaries

    NASA Astrophysics Data System (ADS)

    Canizares, P.; Gair, J. R.; Sopuerta, C. F.

    2012-06-01

    Extreme-Mass-Ratio Inspirals (EMRIs) are one of the most promising sources of gravitational waves (GWs) for space-based detectors like the Laser Interferometer Space Antenna (LISA). EMRIs consist of a compact stellar object orbiting around a massive black hole (MBH). Since EMRI signals are expected to be long lasting (containing of the order of hundred thousand cycles), they will encode the structure of the MBH gravitational potential in a precise way such that features depending on the theory of gravity governing the system may be distinguished. That is, EMRI signals may be used to test gravity and the geometry of black holes. However, the development of a practical methodology for computing the generation and propagation of GWs from EMRIs in theories of gravity different than General Relativity (GR) has only recently begun. In this paper, we present a parameter estimation study of EMRIs in a particular modification of GR, which is described by a four-dimensional Chern-Simons (CS) gravitational term. We focus on determining to what extent a space-based GW observatory like LISA could distinguish between GR and CS gravity through the detection of GWs from EMRIs.

  10. The Matter-Gravity Entanglement Hypothesis

    NASA Astrophysics Data System (ADS)

    Kay, Bernard S.

    2018-03-01

    I outline some of my work and results (some dating back to 1998, some more recent) on my matter-gravity entanglement hypothesis, according to which the entropy of a closed quantum gravitational system is equal to the system's matter-gravity entanglement entropy. The main arguments presented are: (1) that this hypothesis is capable of resolving what I call the second-law puzzle, i.e. the puzzle as to how the entropy increase of a closed system can be reconciled with the asssumption of unitary time-evolution; (2) that the black hole information loss puzzle may be regarded as a special case of this second law puzzle and that therefore the same resolution applies to it; (3) that the black hole thermal atmosphere puzzle (which I recall) can be resolved by adopting a radically different-from-usual description of quantum black hole equilibrium states, according to which they are total pure states, entangled between matter and gravity in such a way that the partial states of matter and gravity are each approximately thermal equilibrium states (at the Hawking temperature); (4) that the Susskind-Horowitz-Polchinski string-theoretic understanding of black hole entropy as the logarithm of the degeneracy of a long string (which is the weak string coupling limit of a black hole) cannot be quite correct but should be replaced by a modified understanding according to which it is the entanglement entropy between a long string and its stringy atmosphere, when in a total pure equilibrium state in a suitable box, which (in line with (3)) goes over, at strong-coupling, to a black hole in equilibrium with its thermal atmosphere. The modified understanding in (4) is based on a general result, which I also describe, which concerns the likely state of a quantum system when it is weakly coupled to an energy-bath and the total state is a random pure state with a given energy. This result generalizes Goldstein et al.'s `canonical typicality' result to systems which are not necessarily small.

  11. Tackling non-linearities with the effective field theory of dark energy and modified gravity

    NASA Astrophysics Data System (ADS)

    Frusciante, Noemi; Papadomanolakis, Georgios

    2017-12-01

    We present the extension of the effective field theory framework to the mildly non-linear scales. The effective field theory approach has been successfully applied to the late time cosmic acceleration phenomenon and it has been shown to be a powerful method to obtain predictions about cosmological observables on linear scales. However, mildly non-linear scales need to be consistently considered when testing gravity theories because a large part of the data comes from those scales. Thus, non-linear corrections to predictions on observables coming from the linear analysis can help in discriminating among different gravity theories. We proceed firstly by identifying the necessary operators which need to be included in the effective field theory Lagrangian in order to go beyond the linear order in perturbations and then we construct the corresponding non-linear action. Moreover, we present the complete recipe to map any single field dark energy and modified gravity models into the non-linear effective field theory framework by considering a general action in the Arnowitt-Deser-Misner formalism. In order to illustrate this recipe we proceed to map the beyond-Horndeski theory and low-energy Hořava gravity into the effective field theory formalism. As a final step we derived the 4th order action in term of the curvature perturbation. This allowed us to identify the non-linear contributions coming from the linear order perturbations which at the next order act like source terms. Moreover, we confirm that the stability requirements, ensuring the positivity of the kinetic term and the speed of propagation for scalar mode, are automatically satisfied once the viability of the theory is demanded at linear level. The approach we present here will allow to construct, in a model independent way, all the relevant predictions on observables at mildly non-linear scales.

  12. The Matter-Gravity Entanglement Hypothesis

    NASA Astrophysics Data System (ADS)

    Kay, Bernard S.

    2018-05-01

    I outline some of my work and results (some dating back to 1998, some more recent) on my matter-gravity entanglement hypothesis, according to which the entropy of a closed quantum gravitational system is equal to the system's matter-gravity entanglement entropy. The main arguments presented are: (1) that this hypothesis is capable of resolving what I call the second-law puzzle, i.e. the puzzle as to how the entropy increase of a closed system can be reconciled with the asssumption of unitary time-evolution; (2) that the black hole information loss puzzle may be regarded as a special case of this second law puzzle and that therefore the same resolution applies to it; (3) that the black hole thermal atmosphere puzzle (which I recall) can be resolved by adopting a radically different-from-usual description of quantum black hole equilibrium states, according to which they are total pure states, entangled between matter and gravity in such a way that the partial states of matter and gravity are each approximately thermal equilibrium states (at the Hawking temperature); (4) that the Susskind-Horowitz-Polchinski string-theoretic understanding of black hole entropy as the logarithm of the degeneracy of a long string (which is the weak string coupling limit of a black hole) cannot be quite correct but should be replaced by a modified understanding according to which it is the entanglement entropy between a long string and its stringy atmosphere, when in a total pure equilibrium state in a suitable box, which (in line with (3)) goes over, at strong-coupling, to a black hole in equilibrium with its thermal atmosphere. The modified understanding in (4) is based on a general result, which I also describe, which concerns the likely state of a quantum system when it is weakly coupled to an energy-bath and the total state is a random pure state with a given energy. This result generalizes Goldstein et al.'s `canonical typicality' result to systems which are not necessarily small.

  13. Evolution of intelligent transportation systems for mobility management and coordination serving California's rural frontier.

    DOT National Transportation Integrated Search

    2012-01-01

    This report documents the evolution, development, and lessons learned while attempting to identify, modify, and deploy Intelligent Transportation System (ITS) and advanced technology tools to facilitate coordination of public transit and social (huma...

  14. Topographical scattering of gravity waves

    NASA Astrophysics Data System (ADS)

    Miles, J. W.; Chamberlain, P. G.

    1998-04-01

    A systematic hierarchy of partial differential equations for linear gravity waves in water of variable depth is developed through the expansion of the average Lagrangian in powers of [mid R:][nabla del, Hamilton operator][mid R:] (h=depth, [nabla del, Hamilton operator]h=slope). The first and second members of this hierarchy, the Helmholtz and conventional mild-slope equations, are second order. The third member is fourth order but may be approximated by Chamberlain & Porter's (1995) ‘modified mild-slope’ equation, which is second order and comprises terms in [nabla del, Hamilton operator]2h and ([nabla del, Hamilton operator]h)2 that are absent from the mild-slope equation. Approximate solutions of the mild-slope and modified mild-slope equations for topographical scattering are determined through an iterative sequence, starting from a geometrical-optics approximation (which neglects reflection), then a quasi-geometrical-optics approximation, and on to higher-order results. The resulting reflection coefficient for a ramp of uniform slope is compared with the results of numerical integrations of each of the mild-slope equation (Booij 1983), the modified mild-slope equation (Porter & Staziker 1995), and the full linear equations (Booij 1983). Also considered is a sequence of sinusoidal sandbars, for which Bragg resonance may yield rather strong reflection and for which the modified mild-slope approximation is in close agreement with Mei's (1985) asymptotic approximation.

  15. Cell Wall Assembly and Intracellular Trafficking in Plant Cells Are Directly Affected by Changes in the Magnitude of Gravitational Acceleration

    PubMed Central

    Chebli, Youssef; Pujol, Lauranne; Shojaeifard, Anahid; Brouwer, Iman; van Loon, Jack J. W. A.; Geitmann, Anja

    2013-01-01

    Plants are able to sense the magnitude and direction of gravity. This capacity is thought to reside in selected cell types within the plant body that are equipped with specialized organelles called statoliths. However, most plant cells do not possess statoliths, yet they respond to changes in gravitational acceleration. To understand the effect of gravity on the metabolism and cellular functioning of non-specialized plant cells, we investigated a rapidly growing plant cell devoid of known statoliths and without gravitropic behavior, the pollen tube. The effects of hyper-gravity and omnidirectional exposure to gravity on intracellular trafficking and on cell wall assembly were assessed in Camellia pollen tubes, a model system with highly reproducible growth behavior in vitro. Using an epi-fluorescence microscope mounted on the Large Diameter Centrifuge at the European Space Agency, we were able to demonstrate that vesicular trafficking is reduced under hyper-gravity conditions. Immuno-cytochemistry confirmed that both in hyper and omnidirectional gravity conditions, the characteristic spatial profiles of cellulose and callose distribution in the pollen tube wall were altered, in accordance with a dose-dependent effect on pollen tube diameter. Our findings suggest that in response to gravity induced stress, the pollen tube responds by modifying cell wall assembly to compensate for the altered mechanical load. The effect was reversible within few minutes demonstrating that the pollen tube is able to quickly adapt to changing stress conditions. PMID:23516452

  16. Extreme gravity tests with gravitational waves from compact binary coalescences: (II) ringdown

    NASA Astrophysics Data System (ADS)

    Berti, Emanuele; Yagi, Kent; Yang, Huan; Yunes, Nicolás

    2018-05-01

    The LIGO/Virgo detections of binary black hole mergers marked a watershed moment in astronomy, ushering in the era of precision tests of Kerr dynamics. We review theoretical and experimental challenges that must be overcome to carry out black hole spectroscopy with present and future gravitational wave detectors. Among other topics, we discuss quasinormal mode excitation in binary mergers, astrophysical event rates, tests of black hole dynamics in modified theories of gravity, parameterized "post-Kerr" ringdown tests, exotic compact objects, and proposed data analysis methods to improve spectroscopic tests of Kerr dynamics by stacking multiple events.

  17. An atlas of Rapp's 180-th order geopotential.

    NASA Astrophysics Data System (ADS)

    Melvin, P. J.

    1986-08-01

    Deprit's 1979 approach to the summation of the spherical harmonic expansion of the geopotential has been modified to spherical components and normalized Legendre polynomials. An algorithm has been developed which produces ten fields at the users option: the undulations of the geoid, three anomalous components of the gravity vector, or six components of the Hessian of the geopotential (gravity gradient). The algorithm is stable to high orders in single precision and does not treat the polar regions as a special case. Eleven contour maps of components of the anomalous geopotential on the surface of the ellipsoid are presented to validate the algorithm.

  18. Exact solutions and phenomenological constraints from massive scalars in a gravity's rainbow spacetime

    NASA Astrophysics Data System (ADS)

    Bezerra, V. B.; Christiansen, H. R.; Cunha, M. S.; Muniz, C. R.

    2017-07-01

    We obtain the exact (confluent Heun) solutions to the massive scalar field in a gravity's rainbow Schwarzschild metric. With these solutions at hand, we study the Hawking radiation resulting from the tunneling rate through the event horizon. We show that the emission spectrum obeys nonextensive statistics and is halted when a certain mass remnant is reached. Next, we infer constraints on the rainbow parameters from recent LHC particle physics experiments and Hubble STIS astrophysics measurements. Finally, we study the low frequency limit in order to find the modified energy spectrum around the source.

  19. A special class of solutions in F( R)-gravity

    NASA Astrophysics Data System (ADS)

    Calzà, Marco; Rinaldi, Massimiliano; Sebastiani, Lorenzo

    2018-03-01

    We consider a special class of vacuum F( R)-modified gravity models. The form of their Lagrangian is such that the field equations are trivially satisfied when the Ricci scalar is constant. There are many interesting F( R)-models for inflation and dark energy that fall in this class. However, little is known outside the domain of cosmology therefore we aim to explore the class of solutions that are static and spherically symmetric. After some general considerations, we investigate in more detail black hole solutions, traversable wormhole metrics and, finally, configurations that can match the anomalous rotation curves of galaxies.

  20. KSC-07pd0949

    NASA Image and Video Library

    2007-04-26

    KENNEDY SPACE CENTER, FLA. -- The media surround noted wheelchair-bound physicist Stephen Hawking after his arrival at the Kennedy Space Center Shuttle Landing Facility for his first zero-gravity flight. Behind Hawking, at left, are Zero Gravity Corporation founder Peter Diamandis and Space Florida president Steve Kohler. The flight will be aboard a modified Boeing 727 aircraft owned by Zero G, a commercial company licensed to provide the public with weightless flight experiences. Hawking developed amyotrophic lateral sclerosis disease in the 1960s, a type of motor neuron disease which would cost him the loss of almost all neuromuscular control. At the celebration of his 65th birthday on January 8 this year, Hawking announced his plans for a zero-gravity flight to prepare for a sub-orbital space flight in 2009 on Virgin Galactic's space service. Photo credit: NASA/Kim Shiflett

  1. AdS charged black holes in Einstein-Yang-Mills gravity's rainbow: Thermal stability and P - V criticality

    NASA Astrophysics Data System (ADS)

    Hendi, Seyed Hossein; Momennia, Mehrab

    2018-02-01

    Motivated by the interesting non-abelian gauge field, in this paper, we look for the analytical solutions of Yang-Mills theory in the context of gravity's rainbow. Regarding the trace of quantum gravity in black hole thermodynamics, we examine the first law of thermodynamics and also thermal stability in the canonical ensemble. We show that although the rainbow functions and Yang-Mills charge modify the solutions, the first law of thermodynamics is still valid. Based on the phenomenological similarities between the adS black holes and van der Waals liquid/gas systems, we study the critical behavior of the Yang-Mills black holes in the extended phase space thermodynamics. We also investigate the effects of various parameters on thermal instability as well as critical properties by using appropriate figures.

  2. Generalized uncertainty principle and quantum gravity phenomenology

    NASA Astrophysics Data System (ADS)

    Bosso, Pasquale

    The fundamental physical description of Nature is based on two mutually incompatible theories: Quantum Mechanics and General Relativity. Their unification in a theory of Quantum Gravity (QG) remains one of the main challenges of theoretical physics. Quantum Gravity Phenomenology (QGP) studies QG effects in low-energy systems. The basis of one such phenomenological model is the Generalized Uncertainty Principle (GUP), which is a modified Heisenberg uncertainty relation and predicts a deformed canonical commutator. In this thesis, we compute Planck-scale corrections to angular momentum eigenvalues, the hydrogen atom spectrum, the Stern-Gerlach experiment, and the Clebsch-Gordan coefficients. We then rigorously analyze the GUP-perturbed harmonic oscillator and study new coherent and squeezed states. Furthermore, we introduce a scheme for increasing the sensitivity of optomechanical experiments for testing QG effects. Finally, we suggest future projects that may potentially test QG effects in the laboratory.

  3. Chameleon halo modeling in f(R) gravity

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Li Yin; Department of Physics, University of Chicago, Chicago Illinois 60637; Hu, Wayne

    2011-10-15

    We model the chameleon effect on cosmological statistics for the modified gravity f(R) model of cosmic acceleration. The chameleon effect, required to make the model compatible with local tests of gravity, reduces force enhancement as a function of the depth of the gravitational potential wells of collapsed structure and so is readily incorporated into a halo model by including parameters for the chameleon mass threshold and rapidity of transition. We show that the abundance of halos around the chameleon mass threshold is enhanced by both the merging from below and the lack of merging to larger masses. This property alsomore » controls the power spectrum in the nonlinear regime and we provide a description of the transition to the linear regime that is valid for a wide range of f(R) models.« less

  4. Brane universes with Gauss-Bonnet-induced-gravity

    NASA Astrophysics Data System (ADS)

    Brown, Richard A.

    2007-04-01

    The DGP brane world model allows us to get the observed late time acceleration via modified gravity, without the need for a “dark energy” field. This can then be generalised by the inclusion of high energy terms, in the form of a Gauss-Bonnet bulk. This is the basis of the Gauss-Bonnet-Induced-Gravity (GBIG) model explored here with both early and late time modifications to the cosmological evolution. Recently the simplest GBIG models (Minkowski bulk and no brane tension) have been analysed. Two of the three possible branches in these models start with a finite density “Big-Bang” and with late time acceleration. Here we present a comprehensive analysis of more general models where we include a bulk cosmological constant and brane tension. We show that by including these factors it is possible to have late time phantom behaviour.

  5. Development of the Vibration Isolation System for the Advanced Resistive Exercise Device

    NASA Technical Reports Server (NTRS)

    Niebuhr, Jason H.; Hagen, Richard A.

    2011-01-01

    This paper describes the development of the Vibration Isolation System for the Advanced Resistive Exercise Device from conceptual design to lessons learned. Maintaining a micro-g environment on the International Space Station requires that experiment racks and major vibration sources be isolated. The challenge in characterizing exercise loads and testing the system in the presence of gravity led to a decision to qualify the system by analysis. Available data suggests that the system is successful in attenuating loads, yet there has been a major component failure and several procedural issues during its 3 years of operational use.

  6. Cosmic Catastrophes

    NASA Astrophysics Data System (ADS)

    Wheeler, J. Craig

    2014-08-01

    Preface; 1. Setting the stage: star formation and hydrogen burning in single stars; 2. Stellar death: the inexorable grip of gravity; 3. Dancing with stars: binary stellar evolution; 4. Accretion disks: flat stars; 5. White Dwarfs: quantum dots; 6. Supernovae: stellar catastrophes; 7. Supernova 1987A: lessons and enigmas; 8. Neutron stars: atoms with attitude; 9. Black holes in theory: into the abyss; 10. Black holes in fact: exploring the reality; 11. Gamma-ray bursts, black holes and the universe: long, long ago and far, far away; 12. Supernovae and the universe; 13. Worm holes and time machines: tunnels in space and time; 14. Beyond: the frontiers; Index.

  7. Cosmic Catastrophes

    NASA Astrophysics Data System (ADS)

    Wheeler, J. Craig

    2007-01-01

    Preface; 1. Setting the stage: star formation and hydrogen burning in single stars; 2. Stellar death: the inexorable grip of gravity; 3. Dancing with stars: binary stellar evolution; 4. Accretion disks: flat stars; 5. White Dwarfs: quantum dots; 6. Supernovae: stellar catastrophes; 7. Supernova 1987A: lessons and enigmas; 8. Neutron stars: atoms with attitude; 9. Black holes in theory: into the abyss; 10. Black holes in fact: exploring the reality; 11. Gamma-ray bursts, black holes and the universe: long, long ago and far, far away; 12. Supernovae and the universe; 13. Worm holes and time machines: tunnels in space and time; 14. Beyond: the frontiers; Index.

  8. Making Inexpensive 3-D Models

    NASA Astrophysics Data System (ADS)

    Manos, Harry

    2016-03-01

    Visual aids are important to student learning, and they help make the teacher's job easier. Keeping with the TPT theme of "The Art, Craft, and Science of Physics Teaching," the purpose of this article is to show how teachers, lacking equipment and funds, can construct a durable 3-D model reference frame and a model gravity well tailored to specific class lessons. Most of the supplies are readily available in the home or at school: rubbing alcohol, a rag, two colors of spray paint, art brushes, and masking tape. The cost of these supplies, if you don't have them, is less than 20.

  9. Parameterized post-Newtonian cosmology

    NASA Astrophysics Data System (ADS)

    Sanghai, Viraj A. A.; Clifton, Timothy

    2017-03-01

    Einstein’s theory of gravity has been extensively tested on solar system scales, and for isolated astrophysical systems, using the perturbative framework known as the parameterized post-Newtonian (PPN) formalism. This framework is designed for use in the weak-field and slow-motion limit of gravity, and can be used to constrain a large class of metric theories of gravity with data collected from the aforementioned systems. Given the potential of future surveys to probe cosmological scales to high precision, it is a topic of much contemporary interest to construct a similar framework to link Einstein’s theory of gravity and its alternatives to observations on cosmological scales. Our approach to this problem is to adapt and extend the existing PPN formalism for use in cosmology. We derive a set of equations that use the same parameters to consistently model both weak fields and cosmology. This allows us to parameterize a large class of modified theories of gravity and dark energy models on cosmological scales, using just four functions of time. These four functions can be directly linked to the background expansion of the universe, first-order cosmological perturbations, and the weak-field limit of the theory. They also reduce to the standard PPN parameters on solar system scales. We illustrate how dark energy models and scalar-tensor and vector-tensor theories of gravity fit into this framework, which we refer to as ‘parameterized post-Newtonian cosmology’ (PPNC).

  10. Lorentz violation and gravity

    NASA Astrophysics Data System (ADS)

    Bailey, Quentin G.

    2007-08-01

    This work explores the theoretical and experimental aspects of Lorentz violation in gravity. A set of modified Einstein field equations is derived from the general Lorentz-violating Standard-Model Extension (SME). Some general theoretical implications of these results are discussed. The experimental consequences for weak-field gravitating systems are explored in the Earth- laboratory setting, the solar system, and beyond. The role of spontaneous Lorentz-symmetry breaking is discussed in the context of the pure-gravity sector of the SME. To establish the low-energy effective Einstein field equations, it is necessary to take into account the dynamics of 20 coefficients for Lorentz violation. As an example, the results are compared with bumblebee models, which are general theories of vector fields with spontaneous Lorentz violation. The field equations are evaluated in the post- newtonian limit using a perfect fluid description of matter. The post-newtonian metric of the SME is derived and compared with some standard test models of gravity. The possible signals for Lorentz violation due to gravity-sector coefficients are studied. Several new effects are identified that have experimental implications for current and future tests. Among the unconventional effects are a new type of spin precession for a gyroscope in orbit and a modification to the local gravitational acceleration on the Earth's surface. These and other tests are expected to yield interesting sensitivities to dimensionless gravity- sector coefficients.

  11. Uneven flows: On cosmic bulk flows, local observers, and gravity

    NASA Astrophysics Data System (ADS)

    Hellwing, Wojciech A.; Bilicki, Maciej; Libeskind, Noam I.

    2018-05-01

    Using N -body simulations we study the impact of various systematic effects on the low-order moments of the cosmic velocity field: the bulk flow (BF) and the cosmic Mach number (CMN). We consider two types of systematics: those related to survey properties and those induced by the observer's location in the Universe. In the former category we model sparse sampling, velocity errors, and survey incompleteness (radial and geometrical). In the latter, we consider local group (LG) analogue observers, placed in a specific location within the cosmic web, satisfying various observational criteria. We differentiate such LG observers from Copernican ones, who are at random locations. We report strong systematic effects on the measured BF and CMN induced by sparse sampling, velocity errors and radial incompleteness. For BF most of these effects exceed 10% for scales R ≲100 h-1 Mpc . For CMN some of these systematics can be catastrophically large (i.e., >50 %) also on bigger scales. Moreover, we find that the position of the observer in the cosmic web significantly affects the locally measured BF (CMN), with effects as large as ˜20 % (30 % ) at R ≲50 h-1 Mpc for a LG-like observer as compared to a random one. This effect is comparable to the sample variance at the same scales. Such location-dependent effects have not been considered previously in BF and CMN studies and here we report their magnitude and scale for the first time. To highlight the importance of these systematics, we additionally study a model of modified gravity with ˜15 % enhanced growth rate (compared to general relativity). We found that the systematic effects can mimic the modified gravity signal. The worst-case scenario is realized for a case of a LG-like observer, when the effects induced by local structures are degenerate with the enhanced growth rate fostered by modified gravity. Our results indicate that dedicated constrained simulations and realistic mock galaxy catalogs will be absolutely necessary to fully benefit from the statistical power of the forthcoming peculiar velocity data from surveys such as TAIPAN, WALLABY, COSMICFLOWS-4 and SKA.

  12. MODTOHAFSD — A GUI based JAVA code for gravity analysis of strike limited sedimentary basins by means of growing bodies with exponential density contrast-depth variation: A space domain approach

    NASA Astrophysics Data System (ADS)

    Chakravarthi, V.; Sastry, S. Rajeswara; Ramamma, B.

    2013-07-01

    Based on the principles of modeling and inversion, two interpretation methods are developed in the space domain along with a GUI based JAVA code, MODTOHAFSD, to analyze the gravity anomalies of strike limited sedimentary basins using a prescribed exponential density contrast-depth function. A stack of vertical prisms all having equal widths, but each one possesses its own limited strike length and thickness, describes the structure of a sedimentary basin above the basement complex. The thicknesses of prisms represent the depths to the basement and are the unknown parameters to be estimated from the observed gravity anomalies. Forward modeling is realized in the space domain using a combination of analytical and numerical approaches. The algorithm estimates the initial depths of a sedimentary basin and improves them, iteratively, based on the differences between the observed and modeled gravity anomalies within the specified convergence criteria. The present code, works on Model-View-Controller (MVC) pattern, reads the Bouguer gravity anomalies, constructs/modifies regional gravity background in an interactive approach, estimates residual gravity anomalies and performs automatic modeling or inversion based on user specification for basement topography. Besides generating output in both ASCII and graphical forms, the code displays (i) the changes in the depth structure, (ii) nature of fit between the observed and modeled gravity anomalies, (iii) changes in misfit, and (iv) variation of density contrast with iteration in animated forms. The code is used to analyze both synthetic and real field gravity anomalies. The proposed technique yielded information that is consistent with the assumed parameters in case of synthetic structure and with available drilling depths in case of field example. The advantage of the code is that it can be used to analyze the gravity anomalies of sedimentary basins even when the profile along which the interpretation is intended fails to bisect the strike length.

  13. Dualities and emergent gravity: Gauge/gravity duality

    NASA Astrophysics Data System (ADS)

    de Haro, Sebastian

    2017-08-01

    In this paper I develop a framework for relating dualities and emergence: two notions that are close to each other but also exclude one another. I adopt the conception of duality as 'isomorphism', from the physics literature, cashing it out in terms of three conditions. These three conditions prompt two conceptually different ways in which a duality can be modified to make room for emergence; and I argue that this exhausts the possibilities for combining dualities and emergence (via coarse-graining). I apply this framework to gauge/gravity dualities, considering in detail three examples: AdS/CFT, Verlinde's scheme, and black holes. My main point about gauge/gravity dualities is that the theories involved, qua theories of gravity, must be background-independent. I distinguish two senses of background-independence: (i) minimalistic and (ii) extended. I argue that the former is sufficiently strong to allow for a consistent theory of quantum gravity; and that AdS/CFT is background-independent on this account; while Verlinde's scheme best fits the extended sense of background-independence. I argue that this extended sense should be applied with some caution: on pain of throwing the baby (general relativity) out with the bath-water (extended background-independence). Nevertheless, it is an interesting and potentially fruitful heuristic principle for quantum gravity theory construction. It suggests some directions for possible generalisations of gauge/gravity dualities. The interpretation of dualities is discussed; and the so-called 'internal' vs. 'external' viewpoints are articulated in terms of: (i) epistemic and metaphysical commitments; (ii) parts vs. wholes. I then analyse the emergence of gravity in gauge/gravity dualities in terms of the two available conceptualisations of emergence; and I show how emergence in AdS/CFT and in Verlinde's scenario differ from each other. Finally, I give a novel derivation of the Bekenstein-Hawking black hole entropy formula based on Verlinde's scheme; the derivation sheds light on several aspects of Verlinde's scheme and how it compares to Bekenstein's original calculation.

  14. Computational Simulation of a Water-Cooled Heat Pump

    NASA Technical Reports Server (NTRS)

    Bozarth, Duane

    2008-01-01

    A Fortran-language computer program for simulating the operation of a water-cooled vapor-compression heat pump in any orientation with respect to gravity has been developed by modifying a prior general-purpose heat-pump design code used at Oak Ridge National Laboratory (ORNL).

  15. Distinguishing modified gravity models

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Brax, Philippe; Davis, Anne-Christine, E-mail: philippe.brax@cea.fr, E-mail: A.C.Davis@damtp.cam.ac.uk

    2015-10-01

    Modified gravity models with screening in local environments appear in three different guises: chameleon, K-mouflage and Vainshtein mechanisms. We propose to look for differences between these classes of models by considering cosmological observations at low redshift. In particular, we analyse the redshift dependence of the fine structure constant and the proton to electron mass ratio in each of these scenarios. When the absorption lines belong to unscreened regions of space such as dwarf galaxies, a time variation would be present for chameleons. For both K-mouflage and Vainshtein mechanisms, the cosmological time variation of the scalar field is not suppressed inmore » both unscreened and screened environments, therefore enhancing the variation of constants and their detection prospect. We also consider the time variation of the redshift of distant objects using their spectrocopic velocities. We find that models of the K-mouflage and Vainshtein types have very different spectroscopic velocities as a function of redshift and that their differences with the Λ-CDM template should be within reach of the future ELT-HIRES observations.« less

  16. Modified Holographic Ricci Dark Energy in Chameleon Brans-Dicke Cosmology and Its Thermodynamic Consequence

    NASA Astrophysics Data System (ADS)

    Jawad, A.; Chattopadhyay, S.; Bhattacharya, S.; Pasqua, A.

    2015-04-01

    The objective of this paper is to discuss the Chameleon Brans-Dicke gravity with non-minimally matter coupling of scalar field. We take modified Holographic Ricci dark energy model in this gravity with its energy density in interaction with energy density of cold dark matter. We assume power-law ansatz for scale factor and scalar field to discuss potential as well as coupling functions in the evolving universe. These reconstructed functions are plotted versus scalar field and time for different values of power component of scale factor n. We observe that potential and coupling functions represent increasing behavior, in particular, consistent results for a specific value of n. Finally, we have examined validity of the generalized second law of thermodynamics and we have observed its validity for all values of n. The financial Supported from Department of Science and Technology, Govt. of India under Project Grant No. SR/FTP/PS-167/2011 is thankfully acknowledged by SC

  17. A marked correlation function for constraining modified gravity models

    NASA Astrophysics Data System (ADS)

    White, Martin

    2016-11-01

    Future large scale structure surveys will provide increasingly tight constraints on our cosmological model. These surveys will report results on the distance scale and growth rate of perturbations through measurements of Baryon Acoustic Oscillations and Redshift-Space Distortions. It is interesting to ask: what further analyses should become routine, so as to test as-yet-unknown models of cosmic acceleration? Models which aim to explain the accelerated expansion rate of the Universe by modifications to General Relativity often invoke screening mechanisms which can imprint a non-standard density dependence on their predictions. This suggests density-dependent clustering as a `generic' constraint. This paper argues that a density-marked correlation function provides a density-dependent statistic which is easy to compute and report and requires minimal additional infrastructure beyond what is routinely available to such survey analyses. We give one realization of this idea and study it using low order perturbation theory. We encourage groups developing modified gravity theories to see whether such statistics provide discriminatory power for their models.

  18. Generalized Entanglement Entropy and Holography

    NASA Astrophysics Data System (ADS)

    Obregón, O.

    2018-04-01

    A nonextensive statistical mechanics entropy that depends only on the probability distribution is proposed in the framework of superstatistics. It is based on a Γ(χ 2) distribution that depends on β and also on pl . The corresponding modified von Neumann entropy is constructed; it is shown that it can also be obtained from a generalized Replica trick. We address the question whether the generalized entanglement entropy can play a role in the gauge/gravity duality. We pay attention to 2dCFT and their gravity duals. The correction terms to the von Neumann entropy result more relevant than the usual UV (for c = 1) ones and also than those due to the area dependent AdS 3 entropy which result comparable to the UV ones. Then the correction terms due to the new entropy would modify the Ryu-Takayanagi identification between the CFT entanglement entropy and the AdS entropy in a different manner than the UV ones or than the corrections to the AdS 3 area dependent entropy.

  19. [Research on the Kosmos biosatellites].

    PubMed

    Il'in, E A

    1984-01-01

    In the last decade the USSR has launched six biosatellites of the Cosmos series. The duration of the first flight was 6 days and of the five subsequent flights 18 to 21 days. The major goals of the flight studies were: investigation of adaptation of living systems to weightlessness, identification of the modifying effect of weightlessness on radiosensitivity, and detection of the biological effect of artificial gravity. The examinations were performed on 37 biological species, with most of them on rats. The exposure to weightlessness gave rise to moderate stress reactions and specific changes, particularly in the musculo-skeletal system (muscle atrophy, reduced bone strength, etc). Artificial gravity of 1 g generated inflight helped maintain the normal function of most physiological systems. The exposure of mammals (rats) to 137Ce irradiation did not reveal a modifying effect of weightlessness on radiation sickness. Distinct manifestations of the effects of weightlessness on intracellular processes were not observed. Dissimilar results were obtained with respect to the growth and development of living organisms in weightlessness.

  20. Renormalization group scale-setting from the action—a road to modified gravity theories

    NASA Astrophysics Data System (ADS)

    Domazet, Silvije; Štefančić, Hrvoje

    2012-12-01

    The renormalization group (RG) corrected gravitational action in Einstein-Hilbert and other truncations is considered. The running scale of the RG is treated as a scalar field at the level of the action and determined in a scale-setting procedure recently introduced by Koch and Ramirez for the Einstein-Hilbert truncation. The scale-setting procedure is elaborated for other truncations of the gravitational action and applied to several phenomenologically interesting cases. It is shown how the logarithmic dependence of the Newton's coupling on the RG scale leads to exponentially suppressed effective cosmological constant and how the scale-setting in particular RG-corrected gravitational theories yields the effective f(R) modified gravity theories with negative powers of the Ricci scalar R. The scale-setting at the level of the action at the non-Gaussian fixed point in Einstein-Hilbert and more general truncations is shown to lead to universal effective action quadratic in the Ricci tensor.

  1. Entropy corrected holographic dark energy models in modified gravity

    NASA Astrophysics Data System (ADS)

    Jawad, Abdul; Azhar, Nadeem; Rani, Shamaila

    We consider the power law and the entropy corrected holographic dark energy (HDE) models with Hubble horizon in the dynamical Chern-Simons modified gravity. We explore various cosmological parameters and planes in this framework. The Hubble parameter lies within the consistent range at the present and later epoch for both entropy corrected models. The deceleration parameter explains the accelerated expansion of the universe. The equation of state (EoS) parameter corresponds to quintessence and cold dark matter (ΛCDM) limit. The ωΛ-ωΛ‧ approaches to ΛCDM limit and freezing region in both entropy corrected models. The statefinder parameters are consistent with ΛCDM limit and dark energy (DE) models. The generalized second law of thermodynamics remain valid in all cases of interacting parameter. It is interesting to mention here that our results of Hubble, EoS parameter and ωΛ-ωΛ‧ plane show consistency with the present observations like Planck, WP, BAO, H0, SNLS and nine-year WMAP.

  2. Lorentz symmetry violation with higher-order operators and renormalization

    NASA Astrophysics Data System (ADS)

    Nascimento, J. R.; Petrov, A. Yu; Reyes, C. M.

    2018-01-01

    Effective field theory has shown to be a powerful method in searching for quantum gravity effects and in particular for CPT and Lorentz symmetry violation. In this work we study an effective field theory with higher-order Lorentz violation, specifically we consider a modified model with scalars and modified fermions interacting via the Yukawa coupling. We study its renormalization properties, that is, its radiative corrections and renormalization conditions in the light of the requirements of having a finite and unitary S-matrix.

  3. Galaxy-galaxy weak gravitational lensing in f(R) gravity

    NASA Astrophysics Data System (ADS)

    Li, Baojiu; Shirasaki, Masato

    2018-03-01

    We present an analysis of galaxy-galaxy weak gravitational lensing (GGL) in chameleon f(R) gravity - a leading candidate of non-standard gravity models. For the analysis, we have created mock galaxy catalogues based on dark matter haloes from two sets of numerical simulations, using a halo occupation distribution (HOD) prescription which allows a redshift dependence of galaxy number density. To make a fairer comparison between the f(R) and Λ cold dark matter (ΛCDM) models, their HOD parameters are tuned so that the galaxy two-point correlation functions in real space (and therefore the projected two-point correlation functions) match. While the f(R) model predicts an enhancement of the convergence power spectrum by up to ˜ 30 per cent compared to the standard ΛCDM model with the same parameters, the maximum enhancement of GGL is only half as large and less than 5 per cent on separations above ˜1-2 h-1 Mpc, because the latter is a cross-correlation of shear (or matter, which is more strongly affected by modified gravity) and galaxy (which is weakly affected given the good match between galaxy autocorrelations in the two models) fields. We also study the possibility of reconstructing the matter power spectrum by combination of GGL and galaxy clustering in f(R) gravity. We find that the galaxy-matter cross-correlation coefficient remains at unity down to ˜2-3 h-1 Mpc at relevant redshifts even in f(R) gravity, indicating joint analysis of GGL and galaxy clustering can be a powerful probe of matter density fluctuations in chameleon gravity. The scale dependence of the model differences in their predictions of GGL can potentially allows us to break the degeneracy between f(R) gravity and other cosmological parameters such as Ωm and σ8.

  4. Ontogeny of mouse vestibulo-ocular reflex following genetic or environmental alteration of gravity sensing.

    PubMed

    Beraneck, Mathieu; Bojados, Mickael; Le Séac'h, Anne; Jamon, Marc; Vidal, Pierre-Paul

    2012-01-01

    The vestibular organs consist of complementary sensors: the semicircular canals detect rotations while the otoliths detect linear accelerations, including the constant pull of gravity. Several fundamental questions remain on how the vestibular system would develop and/or adapt to prolonged changes in gravity such as during long-term space journey. How do vestibular reflexes develop if the appropriate assembly of otoliths and semi-circular canals is perturbed? The aim of present work was to evaluate the role of gravity sensing during ontogeny of the vestibular system. In otoconia-deficient mice (ied), gravity cannot be sensed and therefore maculo-ocular reflexes (MOR) were absent. While canals-related reflexes were present, the ied deficit also led to the abnormal spatial tuning of the horizontal angular canal-related VOR. To identify putative otolith-related critical periods, normal C57Bl/6J mice were subjected to 2G hypergravity by chronic centrifugation during different periods of development or adulthood (Adult-HG) and compared to non-centrifuged (control) C57Bl/6J mice. Mice exposed to hypergravity during development had completely normal vestibulo-ocular reflexes 6 months after end of centrifugation. Adult-HG mice all displayed major abnormalities in maculo-ocular reflexe one month after return to normal gravity. During the next 5 months, adaptation to normal gravity occurred in half of the individuals. In summary, genetic suppression of gravity sensing indicated that otolith-related signals might be necessary to ensure proper functioning of canal-related vestibular reflexes. On the other hand, exposure to hypergravity during development was not sufficient to modify durably motor behaviour. Hence, 2G centrifugation during development revealed no otolith-specific critical period.

  5. f(T) teleparallel gravity and cosmology.

    PubMed

    Cai, Yi-Fu; Capozziello, Salvatore; De Laurentis, Mariafelicia; Saridakis, Emmanuel N

    2016-10-01

    Over recent decades, the role of torsion in gravity has been extensively investigated along the main direction of bringing gravity closer to its gauge formulation and incorporating spin in a geometric description. Here we review various torsional constructions, from teleparallel, to Einstein-Cartan, and metric-affine gauge theories, resulting in extending torsional gravity in the paradigm of f (T) gravity, where f (T) is an arbitrary function of the torsion scalar. Based on this theory, we further review the corresponding cosmological and astrophysical applications. In particular, we study cosmological solutions arising from f (T) gravity, both at the background and perturbation levels, in different eras along the cosmic expansion. The f (T) gravity construction can provide a theoretical interpretation of the late-time universe acceleration, alternative to a cosmological constant, and it can easily accommodate with the regular thermal expanding history including the radiation and cold dark matter dominated phases. Furthermore, if one traces back to very early times, for a certain class of f (T) models, a sufficiently long period of inflation can be achieved and hence can be investigated by cosmic microwave background observations-or, alternatively, the Big Bang singularity can be avoided at even earlier moments due to the appearance of non-singular bounces. Various observational constraints, especially the bounds coming from the large-scale structure data in the case of f (T) cosmology, as well as the behavior of gravitational waves, are described in detail. Moreover, the spherically symmetric and black hole solutions of the theory are reviewed. Additionally, we discuss various extensions of the f (T) paradigm. Finally, we consider the relation with other modified gravitational theories, such as those based on curvature, like f (R) gravity, trying to illuminate the subject of which formulation, or combination of formulations, might be more suitable for quantization ventures and cosmological applications.

  6. Ontogeny of Mouse Vestibulo-Ocular Reflex Following Genetic or Environmental Alteration of Gravity Sensing

    PubMed Central

    Beraneck, Mathieu; Bojados, Mickael; Le Séac’h, Anne; Jamon, Marc; Vidal, Pierre-Paul

    2012-01-01

    The vestibular organs consist of complementary sensors: the semicircular canals detect rotations while the otoliths detect linear accelerations, including the constant pull of gravity. Several fundamental questions remain on how the vestibular system would develop and/or adapt to prolonged changes in gravity such as during long-term space journey. How do vestibular reflexes develop if the appropriate assembly of otoliths and semi-circular canals is perturbed? The aim of present work was to evaluate the role of gravity sensing during ontogeny of the vestibular system. In otoconia-deficient mice (ied), gravity cannot be sensed and therefore maculo-ocular reflexes (MOR) were absent. While canals-related reflexes were present, the ied deficit also led to the abnormal spatial tuning of the horizontal angular canal-related VOR. To identify putative otolith-related critical periods, normal C57Bl/6J mice were subjected to 2G hypergravity by chronic centrifugation during different periods of development or adulthood (Adult-HG) and compared to non-centrifuged (control) C57Bl/6J mice. Mice exposed to hypergravity during development had completely normal vestibulo-ocular reflexes 6 months after end of centrifugation. Adult-HG mice all displayed major abnormalities in maculo-ocular reflexe one month after return to normal gravity. During the next 5 months, adaptation to normal gravity occurred in half of the individuals. In summary, genetic suppression of gravity sensing indicated that otolith-related signals might be necessary to ensure proper functioning of canal-related vestibular reflexes. On the other hand, exposure to hypergravity during development was not sufficient to modify durably motor behaviour. Hence, 2G centrifugation during development revealed no otolith-specific critical period. PMID:22808156

  7. Using voids to unscreen modified gravity

    NASA Astrophysics Data System (ADS)

    Falck, Bridget; Koyama, Kazuya; Zhao, Gong-Bo; Cautun, Marius

    2018-04-01

    The Vainshtein mechanism, present in many models of gravity, is very effective at screening dark matter haloes such that the fifth force is negligible and general relativity is recovered within their Vainshtein radii. Vainshtein screening is independent of halo mass and environment, in contrast to e.g. chameleon screening, making it difficult to test. However, our previous studies have found that the dark matter particles in filaments, walls, and voids are not screened by the Vainshtein mechanism. We therefore investigate whether cosmic voids, identified as local density minima using a watershed technique, can be used to test models of gravity that exhibit Vainshtein screening. We measure density, velocity, and screening profiles of stacked voids in cosmological N-body simulations using both dark matter particles and dark matter haloes as tracers of the density field. We find that the voids are completely unscreened, and the tangential velocity and velocity dispersion profiles of stacked voids show a clear deviation from Λ cold dark matter at all radii. Voids have the potential to provide a powerful test of gravity on cosmological scales.

  8. Analysis of the Yukawa gravitational potential in f (R ) gravity. II. Relativistic periastron advance

    NASA Astrophysics Data System (ADS)

    De Laurentis, Mariafelicia; De Martino, Ivan; Lazkoz, Ruth

    2018-05-01

    Alternative theories of gravity may serve to overcome several shortcomings of the standard cosmological model but, in their weak field limit, general relativity must be recovered so as to match the tight constraints at the Solar System scale. Therefore, testing such alternative models at scales of stellar systems could give a unique opportunity to confirm or rule them out. One of the most straightforward modifications is represented by analytical f (R )-gravity models that introduce a Yukawa-like modification to the Newtonian potential thus modifying the dynamics of particles. Using the geodesics equations, we have illustrated the amplitude of these modifications. First, we have integrated numerically the equations of motion showing the orbital precession of a particle around a massive object. Second, we have computed an analytic expression for the periastron advance of systems having their semimajor axis much shorter than the Yukawa-scale length. Finally, we have extended our results to the case of a binary system composed of two massive objects. Our analysis provides a powerful tool to obtain constraints on the underlying theory of gravity using current and forthcoming data sets.

  9. Plasma Component of Self-gravitating Disks and Relevant Magnetic Configurations

    NASA Astrophysics Data System (ADS)

    Bertin, G.; Coppi, B.

    2006-04-01

    Astrophysical disks in which the disk self-gravity is more important than the gravity force associated with the central object can have significant plasma components where appreciable toroidal current densities are produced. When the vertical confinement of the plasma rotating structures that can form is kept by the Lorentz force rather than by the vertical component of the gravity force, the disk self-gravity remains important only in the radial equilibrium condition, modifying the rotation curve from the commonly considered Keplerian rotation. The equilibrium equations that are solved involve the vertical and the horizontal components of the total momentum conservation equations, coupled with the lowest order form of the gravitational Poisson's equation. The resulting poloidal field configuration can be visualized as a sequence [1] of Field Reverse Configurations, in the radial direction, consisting of pairs of oppositely directed current channels. The plasma density thus acquires a significant radial modulation that may grow to the point where plasma rings can form [2]. [1] B. Coppi, Phys. Plasmas, 12, 057302 (2005) [2] B. Coppi and F. Rousseau, to be published in Astrophys. J. (April 2006)

  10. Disformal theories of gravity: from the solar system to cosmology

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Sakstein, Jeremy, E-mail: j.a.sakstein@damtp.cam.ac.uk

    This paper is concerned with theories of gravity that contain a scalar coupled both conformally and disformally to matter through the metric. By systematically deriving the non-relativistic limit, it is shown that no new non-linear screening mechanisms are present beyond the Vainshtein mechanism and chameleon-like screening. If one includes the cosmological expansion of the universe, disformal effects that are usually taken to be absent can be present in the solar system. When the conformal factor is absent, fifth-forces can be screened on all scales when the cosmological field is slowly-rolling. We investigate the cosmology of these models and use localmore » tests of gravity to place new constraints on the disformal coupling and find M ∼> O(eV), which is not competitive with laboratory tests. Finally, we discuss the future prospects for testing these theories and the implications for other theories of modified gravity. In particular, the Vainshtein radius of solar system objects can be altered from the static prediction when cosmological time-derivatives are non-negligible.« less

  11. Born-Infeld inspired modifications of gravity

    NASA Astrophysics Data System (ADS)

    Beltrán Jiménez, Jose; Heisenberg, Lavinia; Olmo, Gonzalo J.; Rubiera-Garcia, Diego

    2018-01-01

    General Relativity has shown an outstanding observational success in the scales where it has been directly tested. However, modifications have been intensively explored in the regimes where it seems either incomplete or signals its own limit of validity. In particular, the breakdown of unitarity near the Planck scale strongly suggests that General Relativity needs to be modified at high energies and quantum gravity effects are expected to be important. This is related to the existence of spacetime singularities when the solutions of General Relativity are extrapolated to regimes where curvatures are large. In this sense, Born-Infeld inspired modifications of gravity have shown an extraordinary ability to regularise the gravitational dynamics, leading to non-singular cosmologies and regular black hole spacetimes in a very robust manner and without resorting to quantum gravity effects. This has boosted the interest in these theories in applications to stellar structure, compact objects, inflationary scenarios, cosmological singularities, and black hole and wormhole physics, among others. We review the motivations, various formulations, and main results achieved within these theories, including their observational viability, and provide an overview of current open problems and future research opportunities.

  12. On the cosmology of scalar-tensor-vector gravity theory

    NASA Astrophysics Data System (ADS)

    Jamali, Sara; Roshan, Mahmood; Amendola, Luca

    2018-01-01

    We consider the cosmological consequences of a special scalar-tensor-vector theory of gravity, known as MOG (for MOdified Gravity), proposed to address the dark matter problem. This theory introduces two scalar fields G(x) and μ(x), and one vector field phiα(x), in addition to the metric tensor. We set the corresponding self-interaction potentials to zero, as in the standard form of MOG. Then using the phase space analysis in the flat Friedmann-Robertson-Walker background, we show that the theory possesses a viable sequence of cosmological epochs with acceptable time dependency for the cosmic scale factor. We also investigate MOG's potential as a dark energy model and show that extra fields in MOG cannot provide a late time accelerated expansion. Furthermore, using a dynamical system approach to solve the non-linear field equations numerically, we calculate the angular size of the sound horizon, i.e. θs, in MOG. We find that 8× 10‑3rad<θs<8.2× 10‑3 rad which is way outside the current observational bounds. Finally, we generalize MOG to a modified form called mMOG, and we find that mMOG passes the sound-horizon constraint. However, mMOG also cannot be considered as a dark energy model unless one adds a cosmological constant, and more importantly, the matter dominated era is still slightly different from the standard case.

  13. Dipolar dark matter with massive bigravity

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Blanchet, Luc; Heisenberg, Lavinia; Department of Physics & The Oskar Klein Centre, AlbaNova University Centre,Roslagstullsbacken 21, 10691 Stockholm

    2015-12-14

    Massive gravity theories have been developed as viable IR modifications of gravity motivated by dark energy and the problem of the cosmological constant. On the other hand, modified gravity and modified dark matter theories were developed with the aim of solving the problems of standard cold dark matter at galactic scales. Here we propose to adapt the framework of ghost-free massive bigravity theories to reformulate the problem of dark matter at galactic scales. We investigate a promising alternative to dark matter called dipolar dark matter (DDM) in which two different species of dark matter are separately coupled to the twomore » metrics of bigravity and are linked together by an internal vector field. We show that this model successfully reproduces the phenomenology of dark matter at galactic scales (i.e. MOND) as a result of a mechanism of gravitational polarisation. The model is safe in the gravitational sector, but because of the particular couplings of the matter fields and vector field to the metrics, a ghost in the decoupling limit is present in the dark matter sector. However, it might be possible to push the mass of the ghost beyond the strong coupling scale by an appropriate choice of the parameters of the model. Crucial questions to address in future work are the exact mass of the ghost, and the cosmological implications of the model.« less

  14. Dipolar dark matter with massive bigravity

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Blanchet, Luc; Heisenberg, Lavinia, E-mail: blanchet@iap.fr, E-mail: laviniah@kth.se

    2015-12-01

    Massive gravity theories have been developed as viable IR modifications of gravity motivated by dark energy and the problem of the cosmological constant. On the other hand, modified gravity and modified dark matter theories were developed with the aim of solving the problems of standard cold dark matter at galactic scales. Here we propose to adapt the framework of ghost-free massive bigravity theories to reformulate the problem of dark matter at galactic scales. We investigate a promising alternative to dark matter called dipolar dark matter (DDM) in which two different species of dark matter are separately coupled to the twomore » metrics of bigravity and are linked together by an internal vector field. We show that this model successfully reproduces the phenomenology of dark matter at galactic scales (i.e. MOND) as a result of a mechanism of gravitational polarisation. The model is safe in the gravitational sector, but because of the particular couplings of the matter fields and vector field to the metrics, a ghost in the decoupling limit is present in the dark matter sector. However, it might be possible to push the mass of the ghost beyond the strong coupling scale by an appropriate choice of the parameters of the model. Crucial questions to address in future work are the exact mass of the ghost, and the cosmological implications of the model.« less

  15. DOE Office of Scientific and Technical Information (OSTI.GOV)

    Wright, Bill S.; Winther, Hans A.; Koyama, Kazuya, E-mail: bill.wright@port.ac.uk, E-mail: hans.winther@port.ac.uk, E-mail: kazuya.koyama@port.ac.uk

    The effect of massive neutrinos on the growth of cold dark matter perturbations acts as a scale-dependent Newton's constant and leads to scale-dependent growth factors just as we often find in models of gravity beyond General Relativity. We show how to compute growth factors for ΛCDM and general modified gravity cosmologies combined with massive neutrinos in Lagrangian perturbation theory for use in COLA and extensions thereof. We implement this together with the grid-based massive neutrino method of Brandbyge and Hannestad in MG-PICOLA and compare COLA simulations to full N -body simulations of ΛCDM and f ( R ) gravity withmore » massive neutrinos. Our implementation is computationally cheap if the underlying cosmology already has scale-dependent growth factors and it is shown to be able to produce results that match N -body to percent level accuracy for both the total and CDM matter power-spectra up to k ∼< 1 h /Mpc.« less

  16. Cosmic transit and anisotropic models in f(R,T) gravity

    NASA Astrophysics Data System (ADS)

    Sahu, S. K.; Tripathy, S. K.; Sahoo, P. K.; Nath, A.

    2017-06-01

    Accelerating cosmological models are constructed in a modified gravity theory dubbed as $f(R,T)$ gravity at the backdrop of an anisotropic Bianchi type-III universe. $f(R,T)$ is a function of the Ricci scalar $R$ and the trace $T$ of the energy-momentum tensor and it replaces the Ricci scalar in the Einstein-Hilbert action of General Relativity. The models are constructed for two different ways of modification of the Einstein-Hilbert action. Exact solutions of the field equations are obtained by a novel method of integration. We have explored the behaviour of the cosmic transit from an decelerated phase of expansion to an accelerated phase to get the dynamical features of the universe. Within the formalism of the present work, it is found that, the modification of the Einstein-Hilbert action does not affect the scale factor. However the dynamics of the effective dark energy equation of state is significantly affected.

  17. Magnetic solutions in Einstein-massive gravity with linear and nonlinear fields

    NASA Astrophysics Data System (ADS)

    Hendi, Seyed Hossein; Panah, Behzad Eslam; Panahiyan, Shahram; Momennia, Mehrab

    2018-06-01

    The solutions of U(1) gauge-gravity coupling is one of the interesting models for analyzing the semi-classical nature of spacetime. In this regard, different well-known singular and nonsingular solutions have been taken into account. The paper at hand investigates the geometrical properties of the magnetic solutions by considering Maxwell and power Maxwell invariant (PMI) nonlinear electromagnetic fields in the context of massive gravity. These solutions are free of curvature singularity, but have a conic one which leads to presence of deficit/surplus angle. The emphasize is on modifications that these generalizations impose on deficit angle which determine the total geometrical structure of the solutions, hence, physical/gravitational properties. It will be shown that depending on the background spacetime [being anti de Sitter (AdS) or de Sitter (dS)], these generalizations present different effects and modify the total structure of the solutions differently.

  18. COLA with massive neutrinos

    NASA Astrophysics Data System (ADS)

    Wright, Bill S.; Winther, Hans A.; Koyama, Kazuya

    2017-10-01

    The effect of massive neutrinos on the growth of cold dark matter perturbations acts as a scale-dependent Newton's constant and leads to scale-dependent growth factors just as we often find in models of gravity beyond General Relativity. We show how to compute growth factors for ΛCDM and general modified gravity cosmologies combined with massive neutrinos in Lagrangian perturbation theory for use in COLA and extensions thereof. We implement this together with the grid-based massive neutrino method of Brandbyge and Hannestad in MG-PICOLA and compare COLA simulations to full N-body simulations of ΛCDM and f(R) gravity with massive neutrinos. Our implementation is computationally cheap if the underlying cosmology already has scale-dependent growth factors and it is shown to be able to produce results that match N-body to percent level accuracy for both the total and CDM matter power-spectra up to klesssim 1 h/Mpc.

  19. Cylindrically symmetric cosmological model of the universe in modified gravity

    NASA Astrophysics Data System (ADS)

    Mishra, B.; Vadrevu, Samhita

    2017-02-01

    In this paper, we have constructed the cosmological models of the universe in a cylindrically symmetric space time in two classes of f(R,T) gravity (Harko et al. in Phys. Rev. D 84:024020, 2011). We have discussed two cases: one in the linear form and the other in the quadratic form of R. The matter is considered to be in the form of perfect fluid. It is observed that in the first case, the pressure and energy density remain the same, which reduces to a Zeldovich fluid. In the second case we have studied the quadratic function of f(R,T) gravity in the form f(R)=λ(R+R2) and f(T)=λ T. In the second case the pressure is in the negative domain and the energy density is in the positive domain, which confirms that the equation of state parameter is negative. The physical properties of the constructed models are studied.

  20. Diffusive-convective physical vapor transport of PbTe from a Te-rich solid source

    NASA Technical Reports Server (NTRS)

    Zoutendyk, J.; Akutagawa, W.

    1982-01-01

    Crystal growth of PbTe by physical vapor transport (sublimation) in a closed ampoule is governed by the vapor species in thermal equilibrium with the solid compound. Deviations from stoichiometry in the source material cause diffusion limitation of the transport rate, which can be modified by natural (gravity-driven) convection. Mass-transport experiments have been performed using Te-rich material wherein sublimation rates have been measured in order to study the effects of natural convection in diffusion-limited vapor transport. Linear velocities for both crystal growth and evaporation (back sublimation) have been measured for transport in the direction of gravity, horizontally, and opposite to gravity. The experimental results are discussed in terms of both the one-dimensional diffusive-advective model and current, more sophisticated theory which includes natural convection. There is some evidence that convection effects from radial temperature gradients and solutal density gradients have been observed.

  1. Binding of alpha-fetoprotein by immobilized monoclonal antibodies during episodes of zero-gravity obtained by parabolic flight

    NASA Technical Reports Server (NTRS)

    Spooner, Brian S.; Guikema, James A.; Barnes, Grady

    1990-01-01

    Alpha-fetoprotein (AFP), a single-chain polypeptide which is synthesized by the liver and yolk sac of the human fetus, provided a model ligand for assessing the effects of microgravity on ligand binding to surface-immobilized model receptor molecules. Monoclonal antibodies, used as receptors for AFP, were immobilized by covalent attachment to latex microparticles. Zero gravity environment was obtained by parabolic flight aboard NASA 930, a modified KC-135 aircraft. Buring the onset of an episode of zero gravity, ligand and receptor were mixed. Timed incubation (20 s) was terminated by centrifugation, the supernatant removed, and microparticies were assessed for bound AFP by immunochemical methods. The extent of binding was not influenced by microgravity, when compared with 1-G controls, which suggests that aberrant cellular activities observed in microgravity are not the simple expression of altered macromolecular interactions.

  2. Large scale structure constraints for a class of f(R) theories of gravity

    NASA Astrophysics Data System (ADS)

    Abebe, Amare; de la Cruz-Dombriz, Álvaro; Dunsby, Peter K. S.

    2013-08-01

    Over the past few years much attention has been given to the study of modified gravity theories in order to find a more natural explanation for the late time acceleration of the Universe. Nevertheless, a comparison of the matter power spectrum predictions made by these theories with available data has not yet been subjected to a detailed analysis. In the context of f(R) theories of gravity we study the predicted power spectra using both a dynamical systems approach for the background and solving for the matter perturbations without using the quasistatic approximation, comparing the theoretical results with several Sloan Digital Sky Survey data. The importance of studying the first order perturbed equations by assuming the correct background evolution and the relevance of the initial conditions are also stressed. We determine the statistical significance in relation to the observational data and demonstrate their conflict with existing observations.

  3. Charged BTZ black holes in the context of massive gravity's rainbow

    NASA Astrophysics Data System (ADS)

    Hendi, S. H.; Panahiyan, S.; Upadhyay, S.; Eslam Panah, B.

    2017-04-01

    Banados, Teitelboim, and Zanelli (BTZ) black holes are excellent laboratories for studying black hole thermodynamics, which is a bridge between classical general relativity and the quantum nature of gravitation. In addition, three-dimensional gravity could have equipped us for exploring some of the ideas behind the two-dimensional conformal field theory based on the AdS3/CFT2 . Considering the significant interest in these regards, we examine charged BTZ black holes. We consider the system contains massive gravity with energy dependent spacetime to enrich the results. In order to make high curvature (energy) BTZ black holes more realistic, we modify the theory by energy dependent constants. We investigate thermodynamic properties of the solutions by calculating heat capacity and free energy. We also analyze thermal stability and study the possibility of the Hawking-Page phase transition. At last, we study the geometrical thermodynamics of these black holes and compare the results of various approaches.

  4. Cap integration in spectral gravity forward modelling: near- and far-zone gravity effects via Molodensky's truncation coefficients

    NASA Astrophysics Data System (ADS)

    Bucha, Blažej; Hirt, Christian; Kuhn, Michael

    2018-04-01

    Spectral gravity forward modelling is a technique that converts a band-limited topography into its implied gravitational field. This conversion implicitly relies on global integration of topographic masses. In this paper, a modification of the spectral technique is presented that provides gravity effects induced only by the masses located inside or outside a spherical cap centred at the evaluation point. This is achieved by altitude-dependent Molodensky's truncation coefficients, for which we provide infinite series expansions and recurrence relations with a fixed number of terms. Both representations are generalized for an arbitrary integer power of the topography and arbitrary radial derivative. Because of the altitude-dependency of the truncation coefficients, a straightforward synthesis of the near- and far-zone gravity effects at dense grids on irregular surfaces (e.g. the Earth's topography) is computationally extremely demanding. However, we show that this task can be efficiently performed using an analytical continuation based on the gradient approach, provided that formulae for radial derivatives of the truncation coefficients are available. To demonstrate the new cap-modified spectral technique, we forward model the Earth's degree-360 topography, obtaining near- and far-zone effects on gravity disturbances expanded up to degree 3600. The computation is carried out on the Earth's surface and the results are validated against an independent spatial-domain Newtonian integration (1 μGal RMS agreement). The new technique is expected to assist in mitigating the spectral filter problem of residual terrain modelling and in the efficient construction of full-scale global gravity maps of highest spatial resolution.

  5. Brane-World Gravity.

    PubMed

    Maartens, Roy; Koyama, Kazuya

    2010-01-01

    The observable universe could be a 1+3-surface (the "brane") embedded in a 1+3+ d -dimensional spacetime (the "bulk"), with Standard Model particles and fields trapped on the brane while gravity is free to access the bulk. At least one of the d extra spatial dimensions could be very large relative to the Planck scale, which lowers the fundamental gravity scale, possibly even down to the electroweak (∼ TeV) level. This revolutionary picture arises in the framework of recent developments in M theory. The 1+10-dimensional M theory encompasses the known 1+9-dimensional superstring theories, and is widely considered to be a promising potential route to quantum gravity. At low energies, gravity is localized at the brane and general relativity is recovered, but at high energies gravity "leaks" into the bulk, behaving in a truly higher-dimensional way. This introduces significant changes to gravitational dynamics and perturbations, with interesting and potentially testable implications for high-energy astrophysics, black holes, and cosmology. Brane-world models offer a phenomenological way to test some of the novel predictions and corrections to general relativity that are implied by M theory. This review analyzes the geometry, dynamics and perturbations of simple brane-world models for cosmology and astrophysics, mainly focusing on warped 5-dimensional brane-worlds based on the Randall-Sundrum models. We also cover the simplest brane-world models in which 4-dimensional gravity on the brane is modified at low energies - the 5-dimensional Dvali-Gabadadze-Porrati models. Then we discuss co-dimension two branes in 6-dimensional models.

  6. Interpolation of Superconducting Gravity Observations Using Least-Squares Collocation Method

    NASA Astrophysics Data System (ADS)

    Habel, Branislav; Janak, Juraj

    2014-05-01

    A pre-processing of the gravity data measured by superconducting gravimeter involves removing of spikes, offsets and gaps. Their presence in observations can limit the data analysis and degrades the quality of obtained results. Short data gaps are filling by theoretical signal in order to get continuous records of gravity. It requires the accurate tidal model and eventually atmospheric pressure at the observed site. The poster presents a design of algorithm for interpolation of gravity observations with a sampling rate of 1 min. Novel approach is based on least-squares collocation which combines adjustment of trend parameters, filtering of noise and prediction. It allows the interpolation of missing data up to a few hours without necessity of any other information. Appropriate parameters for covariance function are found using a Bayes' theorem by modified optimization process. Accuracy of method is improved by the rejection of outliers before interpolation. For filling of longer gaps the collocation model is combined with theoretical tidal signal for the rigid Earth. Finally, the proposed method was tested on the superconducting gravity observations at several selected stations of Global Geodynamics Project. Testing demonstrates its reliability and offers results comparable with the standard approach implemented in ETERNA software package without necessity of an accurate tidal model.

  7. Modeling and Testing Dark Energy and Gravity with Galaxy Cluster Data

    NASA Astrophysics Data System (ADS)

    Rapetti, David; Cataneo, Matteo; Heneka, Caroline; Mantz, Adam; Allen, Steven W.; Von Der Linden, Anja; Schmidt, Fabian; Lombriser, Lucas; Li, Baojiu; Applegate, Douglas; Kelly, Patrick; Morris, Glenn

    2018-06-01

    The abundance of galaxy clusters is a powerful probe to constrain the properties of dark energy and gravity at large scales. We employed a self-consistent analysis that includes survey, observable-mass scaling relations and weak gravitational lensing data to obtain constraints on f(R) gravity, which are an order of magnitude tighter than the best previously achieved, as well as on cold dark energy of negligible sound speed. The latter implies clustering of the dark energy fluid at all scales, allowing us to measure the effects of dark energy perturbations at cluster scales. For this study, we recalibrated the halo mass function using the following non-linear characteristic quantities: the spherical collapse threshold, the virial overdensity and an additional mass contribution for cold dark energy. We also presented a new modeling of the f(R) gravity halo mass function that incorporates novel corrections to capture key non-linear effects of the Chameleon screening mechanism, as found in high resolution N-body simulations. All these results permit us to predict, as I will also exemplify, and eventually obtain the next generation of cluster constraints on such models, and provide us with frameworks that can also be applied to other proposed dark energy and modified gravity models using cluster abundance observations.

  8. Dark Energy After GW170817: Dead Ends and the Road Ahead.

    PubMed

    Ezquiaga, Jose María; Zumalacárregui, Miguel

    2017-12-22

    Multimessenger gravitational-wave (GW) astronomy has commenced with the detection of the binary neutron star merger GW170817 and its associated electromagnetic counterparts. The almost coincident observation of both signals places an exquisite bound on the GW speed |c_{g}/c-1|≤5×10^{-16}. We use this result to probe the nature of dark energy (DE), showing that a large class of scalar-tensor theories and DE models are highly disfavored. As an example we consider the covariant Galileon, a cosmologically viable, well motivated gravity theory which predicts a variable GW speed at low redshift. Our results eliminate any late-universe application of these models, as well as their Horndeski and most of their beyond Horndeski generalizations. Three alternatives (and their combinations) emerge as the only possible scalar-tensor DE models: (1) restricting Horndeski's action to its simplest terms, (2) applying a conformal transformation which preserves the causal structure, and (3) compensating the different terms that modify the GW speed (to be robust, the compensation has to be independent on the background on which GWs propagate). Our conclusions extend to any other gravity theory predicting varying c_{g} such as Einstein-Aether, Hořava gravity, Generalized Proca, tensor-vector-scalar gravity (TEVES), and other MOND-like gravities.

  9. Dark Energy After GW170817: Dead Ends and the Road Ahead

    NASA Astrophysics Data System (ADS)

    Ezquiaga, Jose María; Zumalacárregui, Miguel

    2017-12-01

    Multimessenger gravitational-wave (GW) astronomy has commenced with the detection of the binary neutron star merger GW170817 and its associated electromagnetic counterparts. The almost coincident observation of both signals places an exquisite bound on the GW speed |cg/c -1 |≤5 ×10-16 . We use this result to probe the nature of dark energy (DE), showing that a large class of scalar-tensor theories and DE models are highly disfavored. As an example we consider the covariant Galileon, a cosmologically viable, well motivated gravity theory which predicts a variable GW speed at low redshift. Our results eliminate any late-universe application of these models, as well as their Horndeski and most of their beyond Horndeski generalizations. Three alternatives (and their combinations) emerge as the only possible scalar-tensor DE models: (1) restricting Horndeski's action to its simplest terms, (2) applying a conformal transformation which preserves the causal structure, and (3) compensating the different terms that modify the GW speed (to be robust, the compensation has to be independent on the background on which GWs propagate). Our conclusions extend to any other gravity theory predicting varying cg such as Einstein-Aether, Hořava gravity, Generalized Proca, tensor-vector-scalar gravity (TEVES), and other MOND-like gravities.

  10. Results and Lessons Learned from Performance Testing of Humans in Spacesuits in Simulated Reduced Gravity

    NASA Technical Reports Server (NTRS)

    Chappell, Steven P.; Norcross, Jason R.; Gernhardt, Michael L.

    2009-01-01

    NASA's Constellation Program has plans to return to the Moon within the next 10 years. Although reaching the Moon during the Apollo Program was a remarkable human engineering achievement, fewer than 20 extravehicular activities (EVAs) were performed. Current projections indicate that the next lunar exploration program will require thousands of EVAs, which will require spacesuits that are better optimized for human performance. Limited mobility and dexterity, and the position of the center of gravity (CG) are a few of many features of the Apollo suit that required significant crew compensation to accomplish the objectives. Development of a new EVA suit system will ideally result in performance close to or better than that in shirtsleeves at 1 G, i.e., in "a suit that is a pleasure to work in, one that you would want to go out and explore in on your day off." Unlike the Shuttle program, in which only a fraction of the crew perform EVA, the Constellation program will require that all crewmembers be able to perform EVA. As a result, suits must be built to accommodate and optimize performance for a larger range of crew anthropometry, strength, and endurance. To address these concerns, NASA has begun a series of tests to better understand the factors affecting human performance and how to utilize various lunar gravity simulation environments available for testing.

  11. High-energy photon-hadron scattering in holographic QCD

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Nishio, Ryoichi; Institute for the Physics and Mathematics of the Universe, University of Tokyo, Kashiwano-ha 5-1-5, 277-8583; Watari, Taizan

    2011-10-01

    This article provides an in-depth look at hadron high-energy scattering by using gravity dual descriptions of strongly coupled gauge theories. Just like deeply inelastic scattering (DIS) and deeply virtual Compton scattering (DVCS) serve as clean experimental probes into nonperturbative internal structure of hadrons, elastic scattering amplitude of a hadron and a (virtual) photon in gravity dual can be exploited as a theoretical probe. Since the scattering amplitude at sufficiently high energy (small Bjorken x) is dominated by parton contributions (=Pomeron contributions) even in strong coupling regime, there is a chance to learn a lesson for generalized parton distribution (GPD) bymore » using gravity dual models. We begin with refining derivation of the Brower-Polchinski-Strassler-Tan (BPST) Pomeron kernel in gravity dual, paying particular attention to the role played by the complex spin variable j. The BPST Pomeron on warped spacetime consists of a Kaluza-Klein tower of 4D Pomerons with nonlinear trajectories, and we clarify the relation between Pomeron couplings and the Pomeron form factor. We emphasize that the saddle-point value j* of the scattering amplitude in the complex j-plane representation is a very important concept in understanding qualitative behavior of the scattering amplitude. The total Pomeron contribution to the scattering is decomposed into the saddle-point contribution and at most a finite number of pole contributions, and when the pole contributions are absent (which we call saddle-point phase), kinematical variable (q,x,t)-dependence of ln(1/q) evolution and ln(1/x) evolution parameters {gamma}{sub eff} and {lambda}{sub eff} in DIS and t-slope parameter B of DVCS in HERA experiment are all reproduced qualitatively in gravity dual. All of these observations shed a new light on modeling of GPD. Straightforward application of those results to other hadron high-energy scattering is also discussed.« less

  12. Ghost Condensation and Modification of Gravity at Long distances

    NASA Astrophysics Data System (ADS)

    Luty, Markus

    2004-05-01

    This talk will describe the physics of a "ghost condensate", a new kind of cosmological fluid that can fill the universe and give rise to novel gravitational effects. The fluid has a preferred rest frame, but is nonetheless compatible with maximally symmetric spacetimes such as flat space or de Sitter. In the presence of a ghost condensate, gravity is modified in a nontrivial way at large distances and late times. New phenomena include new contributions to dark energy and dark matter, antigravity, new spin-dependent forces, and oscillatory potentials. All of this new physics can be described by a completely explicit and consistent effective field theory.

  13. Phantom-like behavior of a DGP-inspired Scalar-Gauss-Bonnet gravity

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Nozari, Kourosh; Azizi, Tahereh; Setare, M.R., E-mail: knozari@umz.ac.ir, E-mail: t.azizi@umz.ac.ir, E-mail: rezakord@ipm.ir

    2009-10-01

    We study the phantom-like behavior of a DGP-inspired braneworld scenario where curvature correction on the brane is taken into account. We include a possible modification of the induced gravity on the brane by incorporating higher order curvature terms of Gauss-Bonnet type. We investigate the cosmological implications of the model and we show that the normal branch of the scenario self-accelerates in this modified scenario without introducing any dark energy component. Also, a phantom-like behavior can be realized in this model without introducing any phantom field that suffers from serious difficulties such as violation of the null energy condition.

  14. Topology and dark energy: testing gravity in voids.

    PubMed

    Spolyar, Douglas; Sahlén, Martin; Silk, Joe

    2013-12-13

    Modified gravity has garnered interest as a backstop against dark matter and dark energy (DE). As one possible modification, the graviton can become massive, which introduces a new scalar field--here with a Galileon-type symmetry. The field can lead to a nontrivial equation of state of DE which is density and scale dependent. Tension between type Ia supernovae and Planck could be reduced. In voids, the scalar field dramatically alters the equation of state of DE, induces a soon-observable gravitational slip between the two metric potentials, and develops a topological defect (domain wall) due to a nontrivial vacuum structure for the field.

  15. Generalizing the bms3 and 2D-conformal algebras by expanding the Virasoro algebra

    NASA Astrophysics Data System (ADS)

    Caroca, Ricardo; Concha, Patrick; Rodríguez, Evelyn; Salgado-Rebolledo, Patricio

    2018-03-01

    By means of the Lie algebra expansion method, the centrally extended conformal algebra in two dimensions and the bms3 algebra are obtained from the Virasoro algebra. We extend this result to construct new families of expanded Virasoro algebras that turn out to be infinite-dimensional lifts of the so-called Bk, Ck and Dk algebras recently introduced in the literature in the context of (super)gravity. We also show how some of these new infinite-dimensional symmetries can be obtained from expanded Kač-Moody algebras using modified Sugawara constructions. Applications in the context of three-dimensional gravity are briefly discussed.

  16. Remediation of trichloroethylene-contaminated groundwater by three modifier-coated microscale zero-valent iron.

    PubMed

    Han, Jun; Xin, Jia; Zheng, Xilai; Kolditz, Olaf; Shao, Haibing

    2016-07-01

    Building a microscale zero-valent iron (mZVI) reaction zone is a promising in situ remediation technology for restoring groundwater contaminated by trichloroethylene (TCE). In order to determine a suitable modifier that could not only overcome gravity sedimentation of mZVI but also improve its remediation efficiency for TCE, the three biopolymers xanthan gum (XG), guargum (GG), and carboxymethyl cellulose (CMC) were employed to coat mZVI for surface modification. The suspension stability of the modified mZVI and its TCE removal efficiency were systematically investigated. The result indicated that XG as a shear-thinning fluid showed the most remarkable efficiency of preventing mZVI from gravity sedimentation and enhancing the TCE removal efficiency by mZVI. In a 480-h experiment, the presence of XG (3 g L(-1)) increased the TCE removal efficiency by 31.85 %, whereas GG (3 g L(-1)) and CMC (3 g L(-1)) merely increased by 15.61 and 9.69 % respectively. The pH value, Eh value, and concentration of ferrous ion as functions of the reaction time were recorded in all the reaction systems, which indicated that XG worked best in buffering the pH value of the solution and inhibiting surface passivation of mZVI.

  17. Modeling the liquid filling in capillary well microplates for analyte preconcentration.

    PubMed

    Yu, Yang; Wang, Xuewei; Ng, Tuck Wah

    2012-06-15

    An attractive advantage of the capillary well microplate approach is the ability to conduct evaporative analyte preconcentration. We advance the use of hydrophobic materials for the wells which apart from reducing material loss through wetting also affords self entry into the well when the droplet size reduces below a critical value. Using Surface Evolver simulation without gravity, we find the critical diameters D(c) fitting very well with theoretical results. When simulating the critical diameters D(c)(G) with gravity included, the gravitational effect could only be ignored when the liquid volumes were small (difference of 5.7% with 5 μL of liquid), but not when the liquid volumes were large (differences of more than 22% with 50 μL of liquid). From this, we developed a modifying equation from a series of simulation results made to describe the gravitational effect. This modifying equation fitted the simulation results well in our simulation range (100°≤θ≤135° and 1 μL≤V≤200 μL). In simulating the condition of multiple wells underneath each droplet, we found that having more holes did not alter the critical diameters significantly. Consequently, the modifying relation should also generally express the critical diameter for multiple wells under a droplet. Crown Copyright © 2012. Published by Elsevier Inc. All rights reserved.

  18. The Black Forest in a Bamboo Garden: Missionary Kindergartens in Japan, 1868-1912.

    ERIC Educational Resources Information Center

    Wollons, Roberta

    1993-01-01

    Traces the history of kindergartens in Japan. Maintains that the Japanese government embraced the concept and modified it to encourage modernization. Includes 10 photographs of wood block prints showing how Friedrich Froebel's moral lessons were replicated in Japanese settings. (CFR)

  19. Study of Critical Heat Flux and Two-Phase Pressure Drop Under Reduced Gravity

    NASA Technical Reports Server (NTRS)

    Abdollahian, Davood; Quintal, Joseph; Barez, Fred; Zahm, Jennifer; Lohr, Victor

    1996-01-01

    The design of the two-phase flow systems which are anticipated to be utilized in future spacecraft thermal management systems requires a knowledge of two-phase flow and heat transfer phenomena in reduced gravities. This program was funded by NASA headquarters in response to NRA-91-OSSA-17 and was managed by Lewis Research Center. The main objective of this program was to design and construct a two-phase test loop, and perform a series of normal gravity and aircraft trajectory experiments to study the effect of gravity on the Critical Heat Flux (CHF) and onset of instability. The test loop was packaged on two aircraft racks and was also instrumented to generate data for two-phase pressure drop. The normal gravity tests were performed with vertical up and downflow configurations to bound the effect of gravity on the test parameters. One set of aircraft trajectory tests was performed aboard the NASA DC-9 aircraft. These tests were mainly intended to evaluate the test loop and its operational performance under actual reduced gravity conditions, and to produce preliminary data for the test parameters. The test results were used to demonstrate the applicability of the normal gravity models for prediction of the two-phase friction pressure drop. It was shown that the two-phase friction multipliers for vertical upflow and reduced gravity conditions can be successfully predicted by the appropriate normal gravity models. Limited critical heat flux data showed that the measured CHF under reduced gravities are of the same order of magnitude as the test results with vertical upflow configuration. A simplified correlation was only successful in predicting the measured CHF for low flow rates. Instability tests with vertical upflow showed that flow becomes unstable and critical heat flux occurs at smaller powers when a parallel flow path exists. However, downflow tests and a single reduced gravity instability experiment indicated that the system actually became more stable with a parallel single-phase flow path. Several design modifications have been identified which will improve the system performance for generating reduced gravity data. The modified test loop can provide two-phase flow data for a range of operating conditions and can serve as a test bed for component evaluation.

  20. On the hitchhiker Robot Operated Materials Processing System: Experiment data system

    NASA Technical Reports Server (NTRS)

    Kizhner, Semion; Jenstrom, Del

    1995-01-01

    The Space Shuttle Discovery STS-64 mission carried the first American autonomous robot into space, the Robot Operated Materials Processing System (ROMPS). On this mission ROMPS was the only Hitchhiker experiment and had a unique opportunity to utilize all Hitchhiker space carrier capabilities. ROMPS conducted rapid thermal processing of the one hundred semiconductor material samples to study how micro gravity affects the resulting material properties. The experiment was designed, built and operated by a small GSFC team in cooperation with industry and university based principal investigators who provided the material samples and data interpretation. ROMPS' success presents some valuable lessons in such cooperation, as well as in the utilization of the Hitchhiker carrier for complex applications. The motivation of this paper is to share these lessons with the scientific community interested in attached payload experiments. ROMPS has a versatile and intelligent material processing control data system. This paper uses the ROMPS data system as the guiding thread to present the ROMPS mission experience. It presents an overview of the ROMPS experiment followed by considerations of the flight and ground data subsystems and their architecture, data products generation during mission operations, and post mission data utilization. It then presents the lessons learned from the development and operation of the ROMPS data system as well as those learned during post-flight data processing.

  1. Effect of the Earth's inner structure on the gravity in definitions of height systems

    NASA Astrophysics Data System (ADS)

    Tenzer, Robert; Foroughi, Ismael; Pitoňák, Martin; Šprlák, Michal

    2017-04-01

    In context of the vertical datum unification, the geoid-to-quasi-geoid separation has been of significant interest in recent years, because most of existing local vertical datums are realized in the system of either normal or orthometric heights. Nevertheless, the normal-orthometric heights are still used in many other countries where the normal gravity values along leveling lines were adopted instead of the observed gravity. Whereas the conversion between the orthometric and normal heights is defined by means of the mean gravity disturbances (i.e. differences between the mean values of the actual and normal gravity) along the plumbline within the topography, differences between the normal and normal-orthometric heights can be described by means of the surface gravity disturbances. Since the normal gravity field does not reflect the topographic masses and actual mass density distribution inside the Earth, the definition of gravity represents a principal aspect for a realization of particular vertical datum. To address this issue in this study, we investigate effects of the Earth's inner density structure on the surface and mean gravity disturbances, and discuss their impact on the vertical datum realization. These two gravity field quantities are computed globally with a spectral resolution complete to a spherical harmonic degree 2160 using the global gravity, terrain, ice-thickness, inland bathymetry and crustal structure models. Our results reveal that both, the surface and mean gravity disturbances mostly comprise the gravitational signal of topography and masses distributed below the geoid surface. Moreover, in polar areas, a significant contribution comes from large glaciers. In contrast, the contributions of anomalous density distribution within the topography attributed to major lakes, sediments and bedrock density variations are much less pronounced. We also demonstrate that the mean gravity disturbances within the topography are significantly modified compared to the corresponding surface values mainly due to topographic elevation and terrain geometry as well as the presence of large glaciers in polar regions. Changes of the vertical gravity gradient within the topography attributed to the masses distributed below the geoid (dominated mainly by the isostatic signature and the long-wavelength gravitational signature of deep mantle density heterogeneities) are, on the other hand, relatively small. Despite differences between the normal and normal-orthometric heights could directly be assessed from the surface gravity disturbances only when taken along leveling lines with information about the spirit leveling height differences, our results indicate that differences between these two height systems can be significant.

  2. Constraints on Born-Infeld gravity from the speed of gravitational waves after GW170817 and GRB 170817A

    NASA Astrophysics Data System (ADS)

    Jana, Soumya; Chakravarty, Girish Kumar; Mohanty, Subhendra

    2018-04-01

    The observations of gravitational waves from the binary neutron star merger event GW170817 and the subsequent observation of its electromagnetic counterparts from the gamma-ray burst GRB 170817A provide us a significant opportunity to study theories of gravity beyond general relativity. An important outcome of these observations is that they constrain the difference between the speed of gravity and the speed of light to less than 10-15c . Also, the time delay between the arrivals of gravitational waves at different detectors constrains the speed of gravity at the Earth to be in the range 0.55 c

  3. Self-accelerated Universe Induced by Repulsive Effects as an Alternative to Dark Energy and Modified Gravities

    NASA Astrophysics Data System (ADS)

    Luongo, Orlando; Quevedo, Hernando

    2018-01-01

    The existence of current-time universe's acceleration is usually modeled by means of two main strategies. The first makes use of a dark energy barotropic fluid entering by hand the energy-momentum tensor of Einstein's theory. The second lies on extending the Hilbert-Einstein action giving rise to the class of extended theories of gravity. In this work, we propose a third approach, derived as an intrinsic geometrical effect of space-time, which provides repulsive regions under certain circumstances. We demonstrate that the effects of repulsive gravity naturally emerge in the field of a homogeneous and isotropic universe. To this end, we use an invariant definition of repulsive gravity based upon the behavior of the curvature eigenvalues. Moreover, we show that repulsive gravity counterbalances the standard gravitational attraction influencing both late and early times of the universe evolution. This phenomenon leads to the present speed up and to the fast expansion due to the inflationary epoch. In so doing, we are able to unify both dark energy and inflation in a single scheme, showing that the universe changes its dynamics when {\\ddot{H}\\over H}=-2 \\dot{H}, at the repulsion onset time where this condition is satisfied. Further, we argue that the spatial scalar curvature can be taken as vanishing because it does not affect at all the emergence of repulsive gravity. We check the goodness of our approach through two cosmological fits involving the most recent union 2.1 supernova compilation.

  4. Propulsion Ground Testing with High Test Peroxide: Lessons Learned

    NASA Technical Reports Server (NTRS)

    Bruce, Robert; Taylor, Gary; Taliancich, Paula

    2002-01-01

    Propulsion Ground Testing with High Test Peroxide (85 to 98% concentration) began at the NASA John C. Stennis Space Center in calendar year 1998, when the E3 Test Facility was modified to accomodate hydrogen peroxide (H2O2) in order to suport the research and development testing of the USAF Upper Stage Flight Experiment rocket engine. Since that time, efforts have continued to provide actual and planned test services to various customers, both U.S. Government and Commercial, in the ground test of many test articles, ranging from gas generators, to catalyst beds, to turbomachinery, to main injectors, to combustion chambers, to integrated rocket engines, to integrated stages. Along this path, and over the past 4 years, there has been both the rediscovery of previously learned lessons, through literature search, archive review, and personal interviews, as well as the learning of many new lessons as new areas are explored and new endeavors are tried. This paper will summarize those lessons learned in an effort to broaden the knowledge base as High Test Peroxide is considered more widely for use in rocket propulsion applications.

  5. NASA's Next Solar Sail: Lessons Learned from NanoSail - D2

    NASA Technical Reports Server (NTRS)

    Katan, Chelsea

    2012-01-01

    NanoSail-D2 unfurled January 17th, 2011 and commenced a nine month Low Earth Orbit path to reentry to evaluate a sail's capacity to deploy in space and deorbit satellites. The orbit was strongly affected by variables including but not limited to: initial attitude, orbit lighting, solar radiation pressure, aerodynamic drag, gravity, and Center of Pressure offsets. The effects of these variables were evaluated through a 3-DOF rigid body simulation. The sail experienced stability in orbits which were continuously lit, i.e. did not orbit behind Earth. Probable drag area experienced by the sail for the mission is also estimated from orbital data and compared to the attitude simulation results. Analysis focuses on sail behavior in full lighting conditions to establish the limits of the sails stability in full lighting. Solar radiation pressure, aerodynamic drag, and gravity torque effects are described. Lastly, a reasonable upper bound on the variation of the Center of Pressure from the geometric center of the sail plane is established. Each of these results contributes to the design requirements for future solar sails.

  6. Lessons from the decoupling limit of Hořava gravity

    NASA Astrophysics Data System (ADS)

    Kimpton, Ian; Padilla, Antonio

    2010-07-01

    We consider the so-called “healthy” extension of Hořava gravity in the limit where the Stuckelberg field decouples from the graviton. We verify the alleged strong coupling problem in this limit, under the assumption that no large dimensionless parameters are put in by hand. This follows from the fact that the dispersion relation for the Stuckelberg field does not have the desired z = 3 anisotropic scaling in the UV. To get the desired scaling and avoid strong coupling one has to introduce a low scale of Lorentz violation and retain some coupling between the graviton and the Stuckelberg field. We also make use of the foliation preserving symmetry to show how the Stuckelberg field couples to some violation of energy conservation. We source the Stuckelberg field using a point particle with a slowly varying mass and show that two such particles feel a constant attractive force. In this particular example, we see no Vainshtein effect, and violations of the Equivalence Principle. The latter is probably generic to other types of source and could potentially be used to place lower bounds on the scale of Lorentz violation.

  7. Catalog of Apollo experiment operations

    NASA Technical Reports Server (NTRS)

    Sullivan, Thomas A.

    1994-01-01

    This catalog reviews Apollo mission reports, preliminary science reports, technical crew debriefings, lunar surface operations plans, and various relevant lunar experiment documents, collecting engineering- and operation-specific information by experiment. It is organized by discrete experimental and equipment items emplaced or operated on the lunar surface or at zero gravity during the Apollo missions. It also attempts to summarize some of the general problems encountered on the surface and provides guidelines for the design of future lunar surface experiments with an eye toward operations. Many of the problems dealt with on the lunar surface originated from just a few novel conditions that manifested themselves in various nasty ways. Low gravity caused cables to stick up and get caught on feet, and also made it easy for instruments to tip over. Dust was a problem and caused abrasion, visibility, and thermal control difficulties. Operating in a pressure suit limited a person's activity, especially in the hands. I hope to capture with this document some of the lessons learned from the Apollo era to make the jobs of future astronauts, principle investigators, engineers, and operators of lunar experiments more productive.

  8. Combat Trauma Lessons Learned from Military Operations of 2001 - 2013

    DTIC Science & Technology

    2015-03-09

    and fentanyl citrate lozenges as described in the TCCC “triple-option analgesia” plan. - Documentation of care by using TCCC Casualty Cards and TCCC...o Meloxicam/acetaminophen o Oral transmucosal fentanyl citrate o Ketamine  Modified tactical combat casualty care (TCCC) measures to optimize

  9. KURDISH READERS. PART I, NEWSPAPER KURDISH.

    ERIC Educational Resources Information Center

    ABDULLA, JAMAL JALAL; MCCARUS, ERNEST N.

    ASSUMING A MASTERY OF THE CONTENTS OF THE "BASIC COURSE IN KURDISH" (BY THE SAME AUTHORS), THIS READER PRESENTS A VARIETY OF 28 ARTICLES SELECTED FROM THE IRAQI NEWSPAPERS "ZHIN" AND "KHEBAT." EACH LESSON BEGINS WITH A SELECTION WRITTEN IN KURDISH (MODIFIED ARABIC-PERSIAN) SCRIPT, FOLLOWED BY PHONEMIC TRANSCRIPTION…

  10. Weed Control Strategies for Organic Peanut Production and Transition: A Lesson in Basic Agronomy

    USDA-ARS?s Scientific Manuscript database

    Weed control in organic peanut production is difficult and costly. The only production inputs that consistently improved weed management in organic peanut production were modified production practices and intense cultivation with a tine weeder. Research trials evaluated row patterns, seeding rates...

  11. Ant Homes under the Ground. Teacher's Guide.

    ERIC Educational Resources Information Center

    Echols, Jean C.; And Others

    This teacher's guide features step-by-step instructions for activities that use easily-obtained and inexpensive materials as well as background information, literature connections, and assessment ideas. The activities are designed for children in preschool through first grade. Lesson descriptions include suggestions for modifying the activities to…

  12. Performance of Regolith Feed Systems for Analog Field Tests of In-Situ Resource Utilization Oxygen Production Plants in Mauna Kea, Hawaii

    NASA Technical Reports Server (NTRS)

    Townsend, Ivan I.; Mueller, Robert P.; Mantovani, James G.; Zacny, Kris A.; Craft, Jack

    2010-01-01

    This paper focuses on practical aspects of mechanical auger and pneumatic regolith conveying system feeding In-Situ Resource Utilization Oxygen production plants. The subsystems of these feedstock delivery systems include an enclosed auger device, pneumatic venturi educator, jet-lift regolith transfer, innovative electro-cyclone gas-particle separation/filtration systems, and compressors capable of dealing with hot hydrogen and/or methane gas re-circulating in the system. Lessons learned from terrestrial laboratory, reduced gravity and field testing on Mauna Kea Volcano in Hawaii during NASA lunar analog field tests will be discussed and practical design tips will be presented.

  13. Life sciences on-line: A study in hypermedia application

    NASA Technical Reports Server (NTRS)

    Christman, Linda A.; Hoang, Nam V.; Proctor, David R.

    1990-01-01

    The main objective was to determine the feasibility of using a computer-based interactive information recall module for the Life Sciences Project Division (LSPD) at NASA, Johnson Space Center. LSPD personnel prepare payload experiments to test and monitor physiological functions in zero gravity. Training refreshers and other types of online help are needed to support personnel in their tasks during mission testing and in flight. Results of a survey of other hypermedia and multimedia developers and lessons learned by the developer of the LSPD prototype module are presented. Related issues and future applications are also discussed and further hypermedia development within the LSPD is recommended.

  14. Materials Research Conducted Aboard the International Space Station: Facilities Overview, Operational Procedures, and Experimental Outcomes

    NASA Technical Reports Server (NTRS)

    Grugel, Richard N.; Luz, Paul; Smith, Guy; Spivey, Reggie; Jeter, Linda; Gillies, Donald; Hua, Fay; Anikumar, A. V.

    2007-01-01

    The Microgravity Science Glovebox (MSG) and Maintenance Work Area (MWA) are facilities aboard the International Space Station (ISS) that were used to successfully conduct experiments in support of, respectively, the Pore Formation and Mobility Investigation (PFMI) and the In-Space Soldering Investigation (ISSI). The capabilities of these facilities are briefly discussed and then demonstrated by presenting "real-time" and subsequently down-linked video-taped examples from the abovementioned experiments. Data interpretation, ISS telescience, some lessons learned, and the need of such facilities for conducting work in support of understanding materials behavior, particularly fluid processing and transport scenarios, in low-gravity environments is discussed.

  15. Materials Research Conducted Aboard the International Space Station: Facilities Overview, Operational Procedures, and Experimental Outcomes

    NASA Technical Reports Server (NTRS)

    Grugel, R. N.; Luz, P.; Smith, G. A.; Spivey, R.; Jeter, L.; Gillies, D. C.; Hua, F.; Anilkumar, A. V.

    2006-01-01

    The Microgravity Science Glovebox (MSG) and Maintenance Work Area (MWA) are facilities aboard the International Space Station (ISS) that were used to successfully conduct experiments in support of, respectively, the Pore Formation and Mobility Investigation (PFMI) and the In-Space Soldering Investigation (ISSI). The capabilities of these facilities are briefly discussed and then demonstrated by presenting real-time and subsequently down-linked video-taped examples from the abovementioned experiments. Data interpretation, ISS telescience, some lessons learned, and the need of such facilities for conducting work in support of understanding materials behavior, particularly fluid processing and transport scenarios, in low-gravity environments is discussed.

  16. [Life lessons of eight families donating organs of deceased family members].

    PubMed

    Avilés R, Lissette; Rivera M, M Soledad; Catoni S, María Isabel

    2014-06-01

    Most organ donors are already death. Therefore family members become an essential link in the final decision for organ donation. To get acquainted about the life lessons of people who accepted donating an organ of a deceased family member. Qualitative research, in depth interviews to eight families that accepted donating an organ of a deceased family member. The interviews were analyzed using the method proposed by Streubert et al and modified by Rivera. The life lessons are described in six comprehensive categories. The painful experience changed towards the feeling that the loved one remains alive. This sensation generated a sense of pride in family members and sensitized them towards the painful experience of other people. Therefore, a desire to help and improve as humans beings was awakened. A compassionate approach towards families donating organs with improve organ donation and humanize the process.

  17. Feeling Gravity's Pull: Gravity Modeling. The Gravity Field of Mars

    NASA Technical Reports Server (NTRS)

    Lemoine, Frank; Smith, David; Rowlands, David; Zuber, Maria; Neumann, G.; Chinn, Douglas; Pavlis, D.

    2000-01-01

    Most people take the constant presence of gravitys pull for granted. However, the Earth's gravitational strength actually varies from location to location. This variation occurs because mass, which influences an object's gravitational pull, is not evenly distributed within the planet. Changes in topography, such as glacial movement, an earthquake, or a rise in the ocean level, can subtly affect the gravity field. An accurate measurement of the Earth's gravity field helps us understand the distribution of mass beneath the surface. This insight can assist us in locating petroleum, mineral deposits, ground water, and other valuable substances. Gravity mapping can also help notice or verify changes in sea surface height and other ocean characteristics. Such changes may indicate climate change from polar ice melting and other phenomena. In addition, gravity mapping can indicate how land moves under the surface after earthquakes and other plate tectonic processes. Finally, changes in the Earth's gravity field might indicate a shift in water distribution that could affect agriculture, water supplies for population centers, and long-term weather prediction. Scientists can map out the Earth's gravity field by watching satellite orbits. When a satellite shifts in vertical position, it might be passing over an area where gravity changes in strength. Gravity is only one factor that may shape a satellite's orbital path. To derive a gravity measurement from satellite movement, scientists must remove other factors that might affect a satellite's position: 1. Drag from atmospheric friction. 2. Pressure from solar radiation as it heads toward Earth and. as it is reflected off the surface of the Earth 3. Gravitational pull from the Sun, the Moon, and other planets in the Solar System. 4. The effect of tides. 5. Relativistic effects. Scientists must also correct for the satellite tracking process. For example, the tracking signal must be corrected for refraction through the atmosphere of the Earth. Supercomputers can calculate the effect of gravity for specific locations in space following a mathematical process known as spherical harmonics, which quantifies the gravity field of a planetary body. The process is based on Laplace's fundamental differential equation of gravity. The accuracy of a spherical harmonic solution is rated by its degree and order. Minute variations in gravity are measured against the geoid, a surface of constant gravity acceleration at mean sea level. The geoid reference gravity model strength includes the central body gravitational attraction (9.8 m/sq s) and a geopotential variation in latitude partially caused by the rotation of the Earth. The rotational effect modifies the shape of the geoid to be more like an ellipsoid, rather than a perfect, circle. Variations of gravity strength from the ellipsoidal reference model are measured in units called milli-Galileos (mGals). One mGal equals 10(exp -5) m/sq s. Research projects have also measured the gravity fields of other planetary bodies, as noted in the user profile that follows. From this information, we may make inferences about our own planet's internal structure and evolution. Moreover, mapping the gravity fields of other planets can help scientists plot the most fuel-efficient course for spacecraft expeditions to those planets.

  18. What was the programme theory of New Labour's Health System Reforms?

    PubMed

    Millar, Ross; Powell, Martin; Dixon, Anna

    2012-01-01

    To examine whether the Health System Reforms delivered the promise of being a coherent and mutually supporting reform programme; to identify the underlying programme theory of the reform programme; to reflect on whether lessons have been learned. Documentary analysis mapping the implicit and explicit programme theories about how the reforms intended to achieve its goals and outcomes. Semi-structured interviews with policy-makers to further understand the programme theory. The Health System Reforms assumed a 'one size fits all' approach to policy implementation with little recognition that some contexts can be more receptive than others. There was evidence of some policy evolution and rebalancing between the reform streams as policy-makers became aware of some perverse incentives and unforeseen consequences. Later elements aimed to restore balance to the system. The Health System Reforms do not appear to comprise a coherent and mutually supportive set of levers and incentives. They appear unbalanced with the centre of gravity favouring suppliers over commissioners. However, recent reform changes have sought to redress this imbalance to some extent, suggesting that lessons have been learned and policies have been adapted over time.

  19. N-MODY: A Code for Collisionless N-body Simulations in Modified Newtonian Dynamics

    NASA Astrophysics Data System (ADS)

    Londrillo, Pasquale; Nipoti, Carlo

    2011-02-01

    N-MODY is a parallel particle-mesh code for collisionless N-body simulations in modified Newtonian dynamics (MOND). N-MODY is based on a numerical potential solver in spherical coordinates that solves the non-linear MOND field equation, and is ideally suited to simulate isolated stellar systems. N-MODY can be used also to compute the MOND potential of arbitrary static density distributions. A few applications of N-MODY indicate that some astrophysically relevant dynamical processes are profoundly different in MOND and in Newtonian gravity with dark matter.

  20. Meso-beta scale numerical simulation studies of terrain-induced jet streak mass/momentum perturbations

    NASA Technical Reports Server (NTRS)

    Lin, Yuh-Lang; Kaplan, Michael L.

    1995-01-01

    Mesoscale model simulations provide insight into the complex jet streak adjustments on 11-12 July 1981 that preceded the first of two significant gravity wave events to have been generated over the Rocky Mountains in Montana. Simulations employing a variety of terrain treatments indicate that prior to wave formation, geostrophic adjustment processes modified the structure of the mid-upper tropospheric jet streak by creating secondary jetlets to the southeast of the polar jet streak in proximity to the gravity wave generation region. This simulated restructuring of the mid-upper tropospheric jet streak is the result of a four stage process. During stage 1, the wind adjusts to the mass field as the jet streak exit region propagates into the inflection point between the upstream trough and downstream ridge in the height field. Stage 2 is initiated as the mass field is forced to adjust to the new ageostrophic wind field created during stage 1. Stage 3 is defined by a second geostrophic adjustment process occurring in a similar manner but to the south and east of the adjustment which occurs during stage 1. A low-level mesoscale jetlet is formed during stage 4 in response to the low-level pressure falls that are established during stage 3. The perturbation of this jetlet, caused by orographically-induced adiabatic and diabatic physical processes, is the likely mechanism responsible for the generation of the first and second episode of observed gravity waves. The dynamics responsible for this wave episode are discussed as differential surface sensible heating inducing an orographically-forced mountain-plains solenoid, resulting in the formation of additional mesoscale jetlets and internal gravity waves. Also discussed is how convective latent heating modifies the numerically simulated terrain-induced internal gravity waves, especially their amplitude and phase velocities, which provide better agreement with those wave characteristics observed in nature. Finally, the three-dimensional linear response of a zonally uniform barotropic flow in a vertically unbounded, continuously stratified, Boussinesq atmosphere which is perturbed from geostrophic equilibrium is investigated.

  1. Hierarchical clustering in chameleon f(R) gravity

    NASA Astrophysics Data System (ADS)

    Hellwing, Wojciech A.; Li, Baojiu; Frenk, Carlos S.; Cole, Shaun

    2013-11-01

    We use a suite of high-resolution state-of-the-art N-body dark matter simulations of chameleon f(R) gravity to study the higher order volume-averaged correlation functions overline{ξ _n} together with the hierarchical nth-order correlation amplitudes S_n=overline{ξ }_n/overline{ξ }_2^{n-1} and density distribution functions (PDF). We show that under the non-linear modifications of gravity the hierarchical scaling of the reduced cumulants is preserved. This is however characterized by significant changes in the values of both overline{ξ _n} and Sn and their scale dependence with respect to General Relativity gravity (GR). In addition, we measure a significant increase of the non-linear σ8 parameter reaching 14, 5 and 0.5 per cent in excess of the GR value for the three flavours of our f(R) models. We further note that the values of the reduced cumulants up to order n = 9 are significantly increased in f(R) gravity for all our models at small scales R ≲ 30 h-1 Mpc. In contrast, the values of the hierarchical amplitudes, Sn, are smaller in f(R) indicating that the modified gravity density distribution functions are deviating from the GR case. Furthermore, we find that the redshift evolution of relative deviations of the f(R) hierarchical correlation amplitudes is fastest at high and moderate redshifts 1 ≤ z ≤ 4. The growth of these deviations significantly slows down in the low-redshift universe. We also compute the PDFs and show that for scales below ˜20 h-1 Mpc, they are significantly shifted in f(R) gravity towards the low densities. Finally, we discuss the implications of our theoretical predictions for measurements of the hierarchical clustering in galaxy redshift surveys, including the important problems of the galaxy biasing and redshift space distortions.

  2. The DESIRE Airborne gravity project in the Dead Sea Basin and 3D numerical gravity modeling

    NASA Astrophysics Data System (ADS)

    Choi, S.; Goetze, H.; Meyer, U.; Group, D.

    2008-12-01

    This geo-scientific research focuses on the geological setting of the Dead Sea Transform (DST) and the Dead Sea Basin (DSB) and its resulting pull-apart basins. Since the late 1970s, crustal scale geophysical experiments have been carried out in this region. However, the nature of the crust underlying the eastern and western shoulders of the DSB and underneath the DST itself is still a hotly debated topic among researchers. To address one of the central questions of plate tectonics - How do large transform systems work and what are their typical features? - An international geoscientific Dead Sea Integrated Research project (DESIRE) is being conducted by colleagues from Germany, Israel, Palestine, and Jordan. In order to provide a high resolution gravity database that support 3D numerical modeling and hence a more comprehensive understanding of the nature and segmentation of the DST, an airborne gravity survey as a part of the DESIRE project has been carried out from February to March 2007. The airborne gravity survey covered the DST from Elat/Aqaba in the South to the northern rim of the Dead Sea. The low speed and terrain-following helicopter gravity flights were performed to acquire the highest possible data quality. In total, 32 north-south profiles and 16 west-east profiles crossing the DST have been measured. Most of the profiles concentrated in areas that lacked terrestrial gravity data coverage, e. g. over the shoulders of the DSB. The airborne gravity data are merged with existing conventional (terrestrial) data sets to provide a seamless gravity map of the area of interest. Using that combined gravity dataset and DESIRE wide angle refractions seismic interpretation we modified density structures in the DSB. As results we estimated that (1) the Moho depth varies from 26 km in the Israel side to 34 km in the Jordan side. (2) The maximum thickness of the Dead Sea sediment Basin is about 15 km. (3) The salt rock with an average thickness of about 5 km is present not only in the southern part of the DSB but also in northern part underlying the entire Dead Sea.

  3. Hacking Say and Reviving ELIZA: Lessons from Virtual Environments

    ERIC Educational Resources Information Center

    Mazar, Rochelle; Nolan, Jason

    2009-01-01

    As text-based predecessors to Second Life, MOOs can offer educators important insights on managing virtual communities to create rich, meaningful learning experiences. Rochelle Mazar and Jason Nolan outline two instructional experiments in MOOs that have implications for current educational practice in Second Life. One involves modifying and…

  4. Putting New Life in an Old Lesson

    ERIC Educational Resources Information Center

    Veal, William; Sneed, Kevin

    2014-01-01

    The Next Generation Science Standards ("NGSS") were developed by teachers, scientists, and leaders in science and science education from around the country and are endorsed by the National Science Teachers Association (NSTA), a partner in the development of the "NGSS." This article presents an example of how to modify a lab to…

  5. Modified Delphi Investigation of Lesson Planning Concepts for Physical Education Teacher Education

    ERIC Educational Resources Information Center

    Sager, Jack W.

    2012-01-01

    Improving the methods of instructing future educators, through program evaluation and improvement, should be a goal of all teacher education programs. In physical education, the National Association for Sport & Physical Education created standards for initial preparation of physical education teachers. The six standards for preparation include…

  6. Teaching Evolution through Inquiry-Based Lessons of Uncontroversial Science

    ERIC Educational Resources Information Center

    DeSantis, Larisa R. G.

    2009-01-01

    Antibiotic resistance, genetically modified produce, avian flu, and invasive species persistence are just a few scientific issues pulled from the headlines that affect society on a daily basis. Understanding these issues requires knowledge of evolutionary processes. Educating students about evolution may never have been as necessary as it is…

  7. Root gravitropism is regulated by a transient lateral auxin gradient controlled by a tipping-point mechanism

    PubMed Central

    Band, Leah R.; Wells, Darren M.; Larrieu, Antoine; Sun, Jianyong; Middleton, Alistair M.; French, Andrew P.; Brunoud, Géraldine; Sato, Ethel Mendocilla; Wilson, Michael H.; Péret, Benjamin; Oliva, Marina; Swarup, Ranjan; Sairanen, Ilkka; Parry, Geraint; Ljung, Karin; Beeckman, Tom; Garibaldi, Jonathan M.; Estelle, Mark; Owen, Markus R.; Vissenberg, Kris; Hodgman, T. Charlie; Pridmore, Tony P.; King, John R.; Vernoux, Teva; Bennett, Malcolm J.

    2012-01-01

    Gravity profoundly influences plant growth and development. Plants respond to changes in orientation by using gravitropic responses to modify their growth. Cholodny and Went hypothesized over 80 years ago that plants bend in response to a gravity stimulus by generating a lateral gradient of a growth regulator at an organ's apex, later found to be auxin. Auxin regulates root growth by targeting Aux/IAA repressor proteins for degradation. We used an Aux/IAA-based reporter, domain II (DII)-VENUS, in conjunction with a mathematical model to quantify auxin redistribution following a gravity stimulus. Our multidisciplinary approach revealed that auxin is rapidly redistributed to the lower side of the root within minutes of a 90° gravity stimulus. Unexpectedly, auxin asymmetry was rapidly lost as bending root tips reached an angle of 40° to the horizontal. We hypothesize roots use a “tipping point” mechanism that operates to reverse the asymmetric auxin flow at the midpoint of root bending. These mechanistic insights illustrate the scientific value of developing quantitative reporters such as DII-VENUS in conjunction with parameterized mathematical models to provide high-resolution kinetics of hormone redistribution. PMID:22393022

  8. Root gravitropism is regulated by a transient lateral auxin gradient controlled by a tipping-point mechanism.

    PubMed

    Band, Leah R; Wells, Darren M; Larrieu, Antoine; Sun, Jianyong; Middleton, Alistair M; French, Andrew P; Brunoud, Géraldine; Sato, Ethel Mendocilla; Wilson, Michael H; Péret, Benjamin; Oliva, Marina; Swarup, Ranjan; Sairanen, Ilkka; Parry, Geraint; Ljung, Karin; Beeckman, Tom; Garibaldi, Jonathan M; Estelle, Mark; Owen, Markus R; Vissenberg, Kris; Hodgman, T Charlie; Pridmore, Tony P; King, John R; Vernoux, Teva; Bennett, Malcolm J

    2012-03-20

    Gravity profoundly influences plant growth and development. Plants respond to changes in orientation by using gravitropic responses to modify their growth. Cholodny and Went hypothesized over 80 years ago that plants bend in response to a gravity stimulus by generating a lateral gradient of a growth regulator at an organ's apex, later found to be auxin. Auxin regulates root growth by targeting Aux/IAA repressor proteins for degradation. We used an Aux/IAA-based reporter, domain II (DII)-VENUS, in conjunction with a mathematical model to quantify auxin redistribution following a gravity stimulus. Our multidisciplinary approach revealed that auxin is rapidly redistributed to the lower side of the root within minutes of a 90° gravity stimulus. Unexpectedly, auxin asymmetry was rapidly lost as bending root tips reached an angle of 40° to the horizontal. We hypothesize roots use a "tipping point" mechanism that operates to reverse the asymmetric auxin flow at the midpoint of root bending. These mechanistic insights illustrate the scientific value of developing quantitative reporters such as DII-VENUS in conjunction with parameterized mathematical models to provide high-resolution kinetics of hormone redistribution.

  9. Stellar equilibrium configurations of white dwarfs in the f( R, T) gravity

    NASA Astrophysics Data System (ADS)

    Carvalho, G. A.; Lobato, R. V.; Moraes, P. H. R. S.; Arbañil, José D. V.; Otoniel, E.; Marinho, R. M.; Malheiro, M.

    2017-12-01

    In this work we investigate the equilibrium configurations of white dwarfs in a modified gravity theory, namely, f( R, T) gravity, for which R and T stand for the Ricci scalar and trace of the energy-momentum tensor, respectively. Considering the functional form f(R,T)=R+2λ T, with λ being a constant, we obtain the hydrostatic equilibrium equation for the theory. Some physical properties of white dwarfs, such as: mass, radius, pressure and energy density, as well as their dependence on the parameter λ are derived. More massive and larger white dwarfs are found for negative values of λ when it decreases. The equilibrium configurations predict a maximum mass limit for white dwarfs slightly above the Chandrasekhar limit, with larger radii and lower central densities when compared to standard gravity outcomes. The most important effect of f( R, T) theory for massive white dwarfs is the increase of the radius in comparison with GR and also f( R) results. By comparing our results with some observational data of massive white dwarfs we also find a lower limit for λ , namely, λ >- 3× 10^{-4}.

  10. Numerical simulation and experimental validation of the dynamics of multiple bubble merger during pool boiling under microgravity conditions.

    PubMed

    Abarajith, H S; Dhir, V K; Warrier, G; Son, G

    2004-11-01

    Numerical simulation and experimental validation of the growth and departure of multiple merging bubbles and associated heat transfer on a horizontal heated surface during pool boiling under variable gravity conditions have been performed. A finite difference scheme is used to solve the equations governing mass, momentum, and energy in the vapor liquid phases. The vapor-liquid interface is captured by a level set method that is modified to include the influence of phase change at the liquid-vapor interface. Water is used as test liquid. The effects of reduced gravity condition and orientation of the bubbles on the bubble diameter, interfacial structure, bubble merger time, and departure time, as well as local heat fluxes, are studied. In the experiments, multiple vapor bubbles are produced on artificial cavities in the 2-10 micrometer diameter range, microfabricated on the polished silicon wafer with given spacing. The wafer was heated electrically from the back with miniature strain gage type heating elements in order to control the nucleation superheat. The experiments conducted in normal Earth gravity and in the low gravity environment of KC-135 aircraft are used to validate the numerical simulations.

  11. Chaos in a dynamic model of traffic flows in an origin-destination network.

    PubMed

    Zhang, Xiaoyan; Jarrett, David F.

    1998-06-01

    In this paper we investigate the dynamic behavior of road traffic flows in an area represented by an origin-destination (O-D) network. Probably the most widely used model for estimating the distribution of O-D flows is the gravity model, [J. de D. Ortuzar and L. G. Willumsen, Modelling Transport (Wiley, New York, 1990)] which originated from an analogy with Newton's gravitational law. The conventional gravity model, however, is static. The investigation in this paper is based on a dynamic version of the gravity model proposed by Dendrinos and Sonis by modifying the conventional gravity model [D. S. Dendrinos and M. Sonis, Chaos and Social-Spatial Dynamics (Springer-Verlag, Berlin, 1990)]. The dynamic model describes the variations of O-D flows over discrete-time periods, such as each day, each week, and so on. It is shown that when the dimension of the system is one or two, the O-D flow pattern either approaches an equilibrium or oscillates. When the dimension is higher, the behavior found in the model includes equilibria, oscillations, periodic doubling, and chaos. Chaotic attractors are characterized by (positive) Liapunov exponents and fractal dimensions.(c) 1998 American Institute of Physics.

  12. Evanescent effects can alter ultraviolet divergences in quantum gravity without physical consequences

    DOE PAGES

    Bern, Zvi; Cheung, Clifford; Chi, Huan -Hang; ...

    2015-11-17

    Evanescent operators such as the Gauss-Bonnet term have vanishing perturbative matrix elements in exactly D = 4 dimensions. Similarly, evanescent fields do not propagate in D = 4; a three-form field is in this class, since it is dual to a cosmological-constant contribution. In this Letter, we show that evanescent operators and fields modify the leading ultraviolet divergence in pure gravity. To analyze the divergence, we compute the two-loop identical-helicity four-graviton amplitude and determine the coefficient of the associated (nonevanescent) R 3 counterterm studied long ago by Goroff and Sagnotti. We compare two pairs of theories that are dual inmore » D = 4: gravity coupled to nothing or to three-form matter, and gravity coupled to zero-form or to two-form matter. Duff and van Nieuwenhuizen showed that, curiously, the one-loop trace anomaly—the coefficient of the Gauss-Bonnet operator—changes under p-form duality transformations. In addition, we concur and also find that the leading R 3 divergence changes under duality transformations. Nevertheless, in both cases, the physical renormalized two-loop identical-helicity four-graviton amplitude can be chosen to respect duality. In particular, its renormalization-scale dependence is unaltered.« less

  13. Evanescent Effects can Alter Ultraviolet Divergences in Quantum Gravity without Physical Consequences.

    PubMed

    Bern, Zvi; Cheung, Clifford; Chi, Huan-Hang; Davies, Scott; Dixon, Lance; Nohle, Josh

    2015-11-20

    Evanescent operators such as the Gauss-Bonnet term have vanishing perturbative matrix elements in exactly D=4 dimensions. Similarly, evanescent fields do not propagate in D=4; a three-form field is in this class, since it is dual to a cosmological-constant contribution. In this Letter, we show that evanescent operators and fields modify the leading ultraviolet divergence in pure gravity. To analyze the divergence, we compute the two-loop identical-helicity four-graviton amplitude and determine the coefficient of the associated (nonevanescent) R^{3} counterterm studied long ago by Goroff and Sagnotti. We compare two pairs of theories that are dual in D=4: gravity coupled to nothing or to three-form matter, and gravity coupled to zero-form or to two-form matter. Duff and van Nieuwenhuizen showed that, curiously, the one-loop trace anomaly-the coefficient of the Gauss-Bonnet operator-changes under p-form duality transformations. We concur and also find that the leading R^{3} divergence changes under duality transformations. Nevertheless, in both cases, the physical renormalized two-loop identical-helicity four-graviton amplitude can be chosen to respect duality. In particular, its renormalization-scale dependence is unaltered.

  14. Local Lunar Gravity Field Analysis over the South Pole-aitken Basin from SELENE Farside Tracking Data

    NASA Technical Reports Server (NTRS)

    Goossens, Sander Johannes; Ishihara, Yoshiaki; Matsumoto, Koji; Sasaki, Sho

    2012-01-01

    We present a method with which we determined the local lunar gravity field model over the South Pole-Aitken (SPA) basin on the farside of the Moon by estimating adjustments to a global lunar gravity field model using SELENE tracking data. Our adjustments are expressed in localized functions concentrated over the SPA region in a spherical cap with a radius of 45deg centered at (191.1 deg E, 53.2 deg S), and the resolution is equivalent to a 150th degree and order spherical harmonics expansion. The new solution over SPA was used in several applications of geophysical analysis. It shows an increased correlation with high-resolution lunar topography in the frequency band l = 40-70, and admittance values are slightly different and more leveled when compared to other, global gravity field models using the same data. The adjustments expressed in free-air anomalies and differences in Bouguer anomalies between the local solution and the a priori global solution correlate with topographic surface features. The Moho structure beneath the SPA basin is slightly modified in our solution, most notably at the southern rim of the Apollo basin and around the Zeeman crater

  15. Exploring the Planets: A Mathematical Journey

    NASA Astrophysics Data System (ADS)

    Campbell, M. B.; Johnson, C. L.

    2002-12-01

    We have developed a series of lessons, designed to teach and reinforce mathematics through lessons about Earth and the bodies that most resemble it in the solar system: Mars, Venus, and the Moon. All lessons are based on California mathematics standards and also cover some Earth science content standards. The overall goal is to achieve cross-curricular learning objectives by showing how math and science work together. While the lessons are designed for a 7th grade math class, they could easily be adapted for a science class, or even modified for different grade levels. The lessons are designed to make recent discoveries in planetary science accessible to students in under-resourced schools. The set of five lessons makes up one unit to be taught consecutively. All the lessons are designed for the alternate day 1 hr and 50 min block scheduling, however the activities could be divided up over two days to accommodate a traditional schedule. There are a total of five lessons, plus a unit test and alternative assessment activities to be given on the sixth day of the unit. In a normal block schedule, the unit should take three weeks. The lessons are available on the web at http://mahi.ucsd.edu/johnson/mathjourney. Each lesson plan comprises the lesson objectives (along with the relevant California 7th grade mathematics standards), a warm-up activity, a vocabulary list (containing words that may be unfamiliar to students, especially those who are learning English), materials required for the class, the lesson structure plus sample dialogue, and in-class and homework activities and worksheets. The in-class activities and worksheets give students the opportunity to master concepts, and can also be useful as a formative assessment tool for the teacher. The mid-unit quiz, final test, and final project can be used as summative assessments. The lessons will be tested this fall by the first author at Davis Middle School, Compton, CA. They will also be disseminated among Teach For America corps members to enable a broader impact in a range of urban and rural under-resourced schools. We have also been using the capabilities of the Scripps Institution of Oceanography Visualization Center to produce fly-throughs of large planetary data sets. These are exported as QuickTime movies, making them available as educational tools.

  16. Gravitational radiation from compact binary systems in screened modified gravity

    NASA Astrophysics Data System (ADS)

    Zhang, Xing; Liu, Tan; Zhao, Wen

    2017-05-01

    Screened modified gravity (SMG) is a kind of scalar-tensor theory with screening mechanisms, which can suppress the fifth force in dense regions and allow theories to evade the solar system and laboratory tests. In this paper, we investigate how the screening mechanisms in SMG affect the gravitational radiation damping effects, calculate in detail the rate of the energy loss due to the emission of tensor and scalar gravitational radiations, and derive their contributions to the change in the orbital period of the binary system. We find that the scalar radiation depends on the screened parameters and the propagation speed of scalar waves, and the scalar dipole radiation dominates the orbital decay of the binary system. For strongly self-gravitating bodies, all effects of scalar sector are strongly suppressed by the screening mechanisms in SMG. By comparing our results to observations of binary system PSR J 1738 +0333 , we place the stringent constraints on the screening mechanisms in SMG. As an application of these results, we focus on three specific models of SMG (chameleon, symmetron, and dilaton), and derive the constraints on the model parameters, respectively.

  17. STELLAR STRUCTURE AND TESTS OF MODIFIED GRAVITY

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Chang, Philip; Hui, Lam, E-mail: pchang@cita.utoronto.ca, E-mail: lhui@astro.columbia.edu

    2011-05-01

    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 that 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,more » which would be smaller by a factor of tens of percent and thus hotter by hundreds of Kelvin, 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 better than current large-scale structure limits and two orders of magnitude better than present solar system tests.« less

  18. f(T) gravity and energy distribution in Landau-Lifshitz prescription

    NASA Astrophysics Data System (ADS)

    Ganiou, M. G.; Houndjo, M. J. S.; Tossa, J.

    We investigate in this paper the Landau-Lifshitz energy distribution in the framework of f(T) theory view as a modified version of Teleparallel theory. From some important Teleparallel theory results on the localization of energy, our investigations generalize the Landau-Lifshitz prescription from the computation of the energy-momentum complex to the framework of f(T) gravity as it is done in the modified versions of General Relativity. We compute the energy density in the first step for three plane-symmetric metrics in vacuum. We find for the second metric that the energy density vanishes independently of f(T) models. We find that the Teleparallel Landau-Lifshitz energy-momentum complex formulations for these metrics are different from those obtained in General Relativity for the same metrics. Second, the calculations are performed for the cosmic string spacetime metric. It results that the energy distribution depends on the mass M and the radius r of cosmic string and it is strongly affected by the parameter of the considered quadratic and cubic f(T) models. Our investigation with this metric induces interesting results susceptible to be tested with some astrophysics hypothesis.

  19. SKA weak lensing - I. Cosmological forecasts and the power of radio-optical cross-correlations

    NASA Astrophysics Data System (ADS)

    Harrison, Ian; Camera, Stefano; Zuntz, Joe; Brown, Michael L.

    2016-12-01

    We construct forecasts for cosmological parameter constraints from weak gravitational lensing surveys involving the Square Kilometre Array (SKA). Considering matter content, dark energy and modified gravity parameters, we show that the first phase of the SKA (SKA1) can be competitive with other Stage III experiments such as the Dark Energy Survey and that the full SKA (SKA2) can potentially form tighter constraints than Stage IV optical weak lensing experiments, such as those that will be conducted with LSST, WFIRST-AFTA or Euclid-like facilities. Using weak lensing alone, going from SKA1 to SKA2 represents improvements by factors of ˜10 in matter, ˜10 in dark energy and ˜5 in modified gravity parameters. We also show, for the first time, the powerful result that comparably tight constraints (within ˜5 per cent) for both Stage III and Stage IV experiments, can be gained from cross-correlating shear maps between the optical and radio wavebands, a process which can also eliminate a number of potential sources of systematic errors which can otherwise limit the utility of weak lensing cosmology.

  20. Lensing convergence in galaxy clustering in ΛCDM and beyond

    NASA Astrophysics Data System (ADS)

    Villa, Eleonora; Di Dio, Enea; Lepori, Francesca

    2018-04-01

    We study the impact of neglecting lensing magnification in galaxy clustering analyses for future galaxy surveys, considering the ΛCDM model and two extensions: massive neutrinos and modifications of General Relativity. Our study focuses on the biases on the constraints and on the estimation of the cosmological parameters. We perform a comprehensive investigation of these two effects for the upcoming photometric and spectroscopic galaxy surveys Euclid and SKA for different redshift binning configurations. We also provide a fitting formula for the magnification bias of SKA. Our results show that the information present in the lensing contribution does improve the constraints on the modified gravity parameters whereas the lensing constraining power is negligible for the ΛCDM parameters. For photometric surveys the estimation is biased for all the parameters if lensing is not taken into account. This effect is particularly significant for the modified gravity parameters. Conversely for spectroscopic surveys the bias is below one sigma for all the parameters. Our findings show the importance of including lensing in galaxy clustering analyses for testing General Relativity and to constrain the parameters which describe its modifications.

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