NASA Astrophysics Data System (ADS)
Piran, Tsvi
1997-11-01
The concepts of negative gravitational mass and gravitational repulsion are alien to general relativity. Still, we show here that small negative fluctuations~--- small dimples in the primordial density field~--- that act as if they have an effective negative gravitational mass, play a dominant role in shaping our Universe. These initially tiny perturbations repel matter surrounding them, expand and grow to become voids in the galaxy distribution. These voids~--- regions with a diameter of $40h^{-1}$ Mpc which are almost devoid of galaxies~--- are the largest objects in the Universe.
Gravitational Repulsion and Dirac Antimatter
NASA Astrophysics Data System (ADS)
Kowitt, Mark E.
1996-03-01
Based on an analogy with electron and hole dynamics in semiconductors, Dirac's relativistic electron equation is generalized to include a gravitational interaction using an electromagnetic-type approximation of the gravitational potential. With gravitational and inertial masses decoupled, the equation serves to extend Dirac's deduction of antimatter parameters to include the possibility of gravitational repulsion between matter and antimatter. Consequences for general relativity and related “antigravity” issues are considered, including the nature and gravitational behavior of virtual photons, virtual pairs, and negative-energy particles. Basic cosmological implications of antigravity are explored—in particular, potential contributions to inflation, expansion, and the general absence of detectable antimatter. Experimental and observational tests are noted, and new ones suggested.
NASA Astrophysics Data System (ADS)
Xiong, Hongwei
2015-08-01
We consider the gravitational effect of quantum wave packets when quantum mechanics, gravity, and thermodynamics are simultaneously considered. Under the assumption of a thermodynamic origin of gravity, we propose a general equation to describe the gravitational effect of quantum wave packets. In the classical limit, this equation agrees with Newton's law of gravitation. For quantum wave packets, however, it predicts a repulsive gravitational effect. We propose an experimental scheme using superfluid helium to test this repulsive gravitational effect. Our studies show that, with present technology such as superconducting gravimetry and cold atom interferometry, tests of the repulsive gravitational effect for superfluid helium are within experimental reach.
NASA Astrophysics Data System (ADS)
Nyambuya, Golden Gadzirayi
2010-11-01
This paper is part of a series on the Azimuthally Symmetric Theory of Gravitation (ASTG). This theory is built on Laplace-Poisson's well known equation and it has been shown that the ASTG is capable of explaining, from a purely classical physics standpoint, the precession of the perihelion of solar planets as a consequence of the azimuthal symmetry emerging from the spin of the Sun. This symmetry has and must have an influence on the emergent gravitational field. We show herein that the emergent equations from the ASTG, under some critical conditions determined by the spin, do possess repulsive gravitational fields in the polar regions of the gravitating body in question. This places the ASTG on an interesting pedestal to infer the origins of outflows as a repulsive gravitational phenomenon. Outflows are a ubiquitous phenomenon found in star forming systems and their true origin is a question yet to be settled. Given the current thinking on their origin, the direction that the present paper takes is nothing short of an asymptotic break from conventional wisdom; at the very least, it is a complete paradigm shift because gravitation is not at all associated with this process, but rather it is thought to be an all-attractive force that only tries to squash matter together onto a single point. Additionally, we show that the emergent Azimuthally Symmetric Gravitational Field from the ASTG strongly suggests a solution to the supposed Radiation Problem that is thought to be faced by massive stars in their process of formation. That is, at ~ 8-10 , radiation from the nascent star is expected to halt the accretion of matter. We show that in-falling material will fall onto the equatorial disk and from there, this material will be channeled onto the forming star via the equatorial plane, thus accretion of mass continues well past the value of ~ 8-10 , albeit via the disk. Along the equatorial plane, the net force (with the radiation force included) on any material there
Gravitational waves during inflation from a 5D large-scale repulsive gravity model
NASA Astrophysics Data System (ADS)
Reyes, Luz M.; Moreno, Claudia; Madriz Aguilar, José Edgar; Bellini, Mauricio
2012-10-01
We investigate, in the transverse traceless (TT) gauge, the generation of the relic background of gravitational waves, generated during the early inflationary stage, on the framework of a large-scale repulsive gravity model. We calculate the spectrum of the tensor metric fluctuations of an effective 4D Schwarzschild-de Sitter metric on cosmological scales. This metric is obtained after implementing a planar coordinate transformation on a 5D Ricci-flat metric solution, in the context of a non-compact Kaluza-Klein theory of gravity. We found that the spectrum is nearly scale invariant under certain conditions. One interesting aspect of this model is that it is possible to derive the dynamical field equations for the tensor metric fluctuations, valid not just at cosmological scales, but also at astrophysical scales, from the same theoretical model. The astrophysical and cosmological scales are determined by the gravity-antigravity radius, which is a natural length scale of the model, that indicates when gravity becomes repulsive in nature.
Gravitational repulsion within a black hole using the Stueckelberg quantum formalism
Ludwin, D. M.; Horwitz, L. P.
2011-01-15
We wish to study an application of Stueckelberg's relativistic quantum theory in the framework of general relativity. We study the form of the wave equation of a massive body in the presence of a Schwarzschild gravitational field. We treat the mathematical behavior of the wavefunction also around and beyond the horizon (r= 2M). Classically, within the horizon, the time component of the metric becomes spacelike and distance from the origin singularity becomes timelike, suggesting an inevitable propagation of all matter within the horizon to a total collapse at r=0. However, the quantum description of the wavefunction provides a different understanding of the behavior of matter within the horizon. We find that a test particle can almost never be found at the origin and is more probable to be found at the horizon. Matter outside the horizon has a very small wavelength and therefore interference effects can be found only on a very small atomic scale. However, within the horizon, matter becomes totally 'tachyonic' and is potentially 'spread' over all space. Small location uncertainties on the atomic scale become large around the horizon, and different mass components of the wavefunction can therefore interfere on a stellar scale. This interference phenomenon, where the probability of finding matter decreases as a function of the distance from the horizon, appears as an effective gravitational repulsion.
NASA Astrophysics Data System (ADS)
Qadir, Asghar
1983-12-01
It is pointed out that there was an error in the recent paper by Grøn claiming that there is no electro-gravitic repulsion in the Reissner-Nordstrom geometry. It is concluded that the earlier result of Mahajan, Qadir and Valanju still stands.
NASA Astrophysics Data System (ADS)
Jannson, Tomasz; Wang, Wenjian; Hodelin, Juan; Forrester, Thomas; Romanov, Volodymyr; Kostrzewski, Andrew
2016-05-01
In this paper, Bayesian Binary Sensing (BBS) is discussed as an effective tool for Bayesian Inference (BI) evaluation in interdisciplinary areas such as ISR (and, C3I), Homeland Security, QC, medicine, defense, and many others. In particular, Hilbertian Sine (HS) as an absolute measure of BI, is introduced, while avoiding relativity of decision threshold identification, as in the case of traditional measures of BI, related to false positives and false negatives.
A repulsive force in the Einstein theory
NASA Astrophysics Data System (ADS)
Gorkavyi, Nick; Vasilkov, Alexander
2016-09-01
The Laser Interferometer Gravitational-Wave Observatory (LIGO) detection of gravitational waves that take away 5 per cent of the total mass of two merging black holes points out on the importance of considering varying gravitational mass of a system in the framework of the Einstein general theory of relativity. We calculate the acceleration of a particle in the non-stationary field of a quasi-spherical system composed of a large number of objects emitting gravitational waves. It is shown that reduction of the gravitational mass of the system due to emitting gravitational waves leads to a repulsive gravitational force that diminishes with time but never disappears. This repulsive force may be related to the observed expansion of the Universe.
Neji, Radhouène; Besbes, Ahmed; Komodakis, Nikos; Deux, Jean-François; Maatouk, Mezri; Rahmouni, Alain; Bassez, Guillaume; Fleury, Gilles; Paragios, Nikos
2009-01-01
In this paper, we present a manifold clustering method fo the classification of fibers obtained from diffusion tensor images (DTI) of the human skeletal muscle. Using a linear programming formulation of prototype-based clustering, we propose a novel fiber classification algorithm over manifolds that circumvents the necessity to embed the data in low dimensional spaces and determines automatically the number of clusters. Furthermore, we propose the use of angular Hilbertian metrics between multivariate normal distributions to define a family of distances between tensors that we generalize to fibers. These metrics are used to approximate the geodesic distances over the fiber manifold. We also discuss the case where only geodesic distances to a reduced set of landmark fibers are available. The experimental validation of the method is done using a manually annotated significant dataset of DTI of the calf muscle for healthy and diseased subjects. PMID:19694249
Magnetic Repulsion: An Introductory Experiment
ERIC Educational Resources Information Center
Romer, Alfred
1973-01-01
Discusses the use of a balance assembled from standard laboratory components to conduct an experiment on the repulsion between two bar magnets. Includes an analysis of data on the two-pole and four-pole models. (CC)
Indians Repulse British With Rocket
NASA Technical Reports Server (NTRS)
2004-01-01
During the early introduction of rockets to Europe, they were used only as weapons. Enemy troops in India repulsed the British with rockets. Later, in Britain, Sir William Congreve developed a rocket that could fire to about 9,000 feet. The British fired Congreve rockets against the United States in the War of 1812.
Repulsive Casimir force: Sufficient conditions
Rosa, Luigi; Lambrecht, Astrid
2010-09-15
In this paper the Casimir energy of two parallel plates made by materials of different penetration depth and no medium in between is derived. We study the Casimir force density and derive analytical constraints on the two penetration depths which are sufficient conditions to ensure repulsion. Compared to other methods our approach needs no specific model for dielectric or magnetic material properties and constitutes a complementary analysis.
Characterizing repulsive gravity with curvature eigenvalues
NASA Astrophysics Data System (ADS)
Luongo, Orlando; Quevedo, Hernando
2014-10-01
Repulsive gravity has been investigated in several scenarios near compact objects by using different intuitive approaches. Here, we propose an invariant method to characterize regions of repulsive gravity, associated to black holes and naked singularities. Our method is based upon the behavior of the curvature tensor eigenvalues, and leads to an invariant definition of a repulsion radius. The repulsion radius determines a physical region, which can be interpreted as a repulsion sphere, where the effects due to repulsive gravity naturally arise. Further, we show that the use of effective masses to characterize repulsion regions can lead to coordinate-dependent results whereas, in our approach, repulsion emerges as a consequence of the spacetime geometry in a completely invariant way. Our definition is tested in the spacetime of an electrically charged Kerr naked singularity and in all its limiting cases. We show that a positive mass can generate repulsive gravity if it is equipped with an electric charge or an angular momentum. We obtain reasonable results for the spacetime regions contained inside the repulsion sphere whose size and shape depend on the value of the mass, charge and angular momentum. Consequently, we define repulsive gravity as a classical relativistic effect by using the geometry of spacetime only.
Repulsive force actuated rotary micromirror
NASA Astrophysics Data System (ADS)
He, Siyuan; Ben Mrad, Ridha
2004-09-01
In this paper, a novel repulsive force based rotary micromirror is proposed. A repulsive force is produced in the rotary micromirror and the mirror plate is pushed up and away from the substrate. Therefore the rotation angle of the micromirror is not limited to the space underneath the mirror plate and thus the "pull-in" effect is completely circumvented. The novel rotary micromirror can achieve a large rotation angle with a large mirror plate. In addition the novel micromirror has a very simple structure and can be fabricated by standard surface micromachining technology. Numerical simulation is used to verify the working principle of the novel micromirror. A prototype of the novel rotary micromirror is fabricated by a commercially available surface microfabrication process called MUMPs. The prototype has a mirror size of 300μm x 300μm. The experimental measurements show that the prototype can achieve a mechanical rotation of 2.25 degrees (an optical angle of 4.5 degrees) at a driving voltage of 170 volts. A conventional surface micromachined attractive force based rotary micromirror of the same size can only achieve an angle of 0.1~0.2 degree.
Competition, Competitive Repulsion, and Coexistence
Darlington, P. J.
1972-01-01
This manuscript is concerned with concepts rather than abstruse details or mathematics. Discussed are: competition; extended competition, proposed for competition in the strict sense, extended and modified by all related interactions including predation, parasitism, disease, and even cooperation, all of which can be “weapons of competition”; competitive repulsion, proposed for the sum of forces that determine spacings, including ecologic spacings, of individuals and populations; Darwin (biotic) equilibriums; competitive extinction, Gause's principle, limited and limiting resources, and single-resource competition; de facto coexistence of competing species, exemplified by green plants competing for sunlight; niche competition; the two concepts of competitive exclusion; devision of resources and of their utilizers; cause and effect in real situations; and niches, niche overlap, and coexistence. Stressed is the complexity of the real world, and the confusion that can and does arise from modeling it too simply. PMID:4508308
Rheology and dynamics of repulsive clathrates
NASA Astrophysics Data System (ADS)
Eroshenko, V. A.; Lazarev, Yu. F.
2012-01-01
The physical and thermodynamic properties of a repulsive clathrate used as a working body for the dissipation, storage, and conversion of energy in thermomechanical systems are studied. In repulsive clathrates, use is made for the first time of the molecular repulsive forces acting in large interfacial areas in a system consisting of a fluid and a capillary-porous matrix not wetted by this fluid. Based on experimental studies of a car damper with a repulsive clathrate, a rheological model of energy dissipation was developed which can be used to design compact high-performance dampers for different purposes and anti-seismic systems of new generation.
Repulsion between Oppositely Charged Planar Macroions
Jho, YongSeok; Brown, Frank L. H.; Kim, MahnWon; Pincus, Philip A.
2013-01-01
The repulsive interaction between oppositely charged macroions is investigated using Grand Canonical Monte Carlo simulations of an unrestricted primitive model, including the effect of inhomogeneous surface charge and its density, the depth of surface charge, the cation size, and the dielectric permittivity of solvent and macroions, and their contrast. The origin of the repulsion is a combination of osmotic pressure and ionic screening resulting from excess salt between the macroions. The excess charge over-reduces the electrostatic attraction between macroions and raises the entropic repulsion. The magnitude of the repulsion increases when the dielectric constant of the solvent is lowered (below that of water) and/or the surface charge density is increased, in good agreement with experiment. Smaller size of surface charge and the cation, their discreteness and mobility are other factors that enhance the repulsion and charge inversion phenomenons. PMID:23940518
Gauge approach to gravitation and regular Big Bang theory
NASA Astrophysics Data System (ADS)
Minkevich, A. V.
2006-03-01
Field theoretical scheme of regular Big Bang in 4-dimensional physical space-time, built in the framework of gauge approach to gravitation, is discussed. Regular bouncing character of homogeneous isotropic cosmological models is ensured by gravitational repulsion effect at extreme conditions without quantum gravitational corrections. The most general properties of regular inflationary cosmological models are examined. Developing theory is valid, if energy density of gravitating matter is positive and energy dominance condition is fulfilled.
Equivalent Activities of Repulsive Axon Guidance Receptors
Long, Hong; Yoshikawa, Shingo
2016-01-01
Receptors on the growth cone at the leading edge of elongating axons play critical guidance roles by recognizing cues via their extracellular domains and transducing signals via their intracellular domains, resulting in changes in direction of growth. An important concept to have emerged in the axon guidance field is the importance of repulsion as a major guidance mechanism. Given the number and variety of different repulsive receptors, it is generally thought that there are likely to be qualitative differences in the signals they transduce. However, the nature of these possible differences is unknown. By creating chimeras using the extracellular and intracellular domains of three different Drosophila repulsive receptors, Unc5, Roundabout (Robo), and Derailed (Drl) and expressing them in defined cells within the embryonic nervous system, we examined the responses elicited by their intracellular domains systematically. Surprisingly, we found no qualitative differences in growth cone response or axon growth, suggesting that, despite their highly diverged sequences, each intracellular domain elicits repulsion via a common pathway. In terms of the signaling pathway(s) used by the repulsive receptors, mutations in the guanine nucleotide exchange factor Trio strongly enhance the repulsive activity of all three intracellular domains, suggesting that repulsion by Unc5, Robo, and Drl, and perhaps repulsion in general, involves Trio activity. SIGNIFICANCE STATEMENT A prevailing concept that has emerged in the axon guidance field is the importance of repulsion as a guidance mechanism for steering axons to their appropriate targets. Given the number and variety of different repulsive receptors, it is generally thought that there are differences in the signals that they transduce. However, this has never been tested directly. We have used the advanced genetics of Drosophila to compare directly the outputs of different repulsive receptors. Surprisingly, we found no qualitative
Enhancing Casimir repulsion via topological insulator multilayers
NASA Astrophysics Data System (ADS)
Zeng, Ran; Chen, Liang; Nie, Wenjie; Bi, Meihua; Yang, Yaping; Zhu, Shiyao
2016-08-01
We propose to observe the enhanced Casimir repulsion between two parallel multilayer walls made of alternating layers of a topological insulator (TI) and a normal insulator. Based on the transfer matrix method, the Fresnel coefficients matrix is generalized to apply to the TI multilayer structure. The Casimir repulsion under the influence of the magnetization orientation in the magnetic coatings on TI layer surfaces, the layer thicknesses, and the topological magnetoelectric polarizability, is investigated. We show that, for the multilayer structures with parallel magnetization on the TI layer surfaces, it is possible to enhance the repulsion by increasing the TI layer number, which is due to the accumulation of the contribution to the repulsion from the polarization rotation effect occurring on each TI layer surface. Generally, in the distance region where there is Casimir attraction between semi-infinite TIs, the force may turn into repulsion in TI multilayer structure, and in the region of repulsion for semi-infinite TI, the repulsive force can be enhanced in magnitude, the enhancement tends to a maximum while the structure contains sufficiently many layers.
Casimir Repulsion between Metallic Objects in Vacuum
Levin, Michael; McCauley, Alexander P.; Rodriguez, Alejandro W.; Reid, M. T. Homer; Johnson, Steven G.
2010-08-27
We give an example of a geometry in which two metallic objects in vacuum experience a repulsive Casimir force. The geometry consists of an elongated metal particle centered above a metal plate with a hole. We prove that this geometry has a repulsive regime using a symmetry argument and confirm it with numerical calculations for both perfect and realistic metals. The system does not support stable levitation, as the particle is unstable to displacements away from the symmetry axis.
Repulsive Casimir force in chiral metamaterials.
Zhao, R; Zhou, J; Koschny, Th; Economou, E N; Soukoulis, C M
2009-09-01
We demonstrate theoretically that one can obtain repulsive Casimir forces and stable nanolevitations by using chiral metamaterials. By extending the Lifshitz theory to treat chiral metamaterials, we find that a repulsive force and a minimum of the interaction energy possibly exist for strong chirality, under realistic frequency dependencies and correct limiting values (for zero and infinite frequencies) of the permittivity, permeability, and chiral coefficients. PMID:19792309
Thermal fluctuations and stability of a particle levitated by a repulsive Casimir force in a liquid.
Inui, Norio; Goto, Kosuke
2013-11-01
We study the vertical Brownian motion of a gold particle levitated by a repulsive Casimir force to a silica plate immersed in bromobenzene. The time evolution of the particle distribution starting from an equilibrium position, where the Casimir force and gravitational force are balanced, is considered by solving the Langevin equation using the Monte Carlo method. When the gold particle is very close to the silica plate, the Casimir force changes from repulsive to attractive, and the particle eventually sticks to the surface. The escape rate from a metastable position is calculated by solving the Fokker-Plank equation; it agrees with the value obtained by Kramers' escape theory. The duration of levitation increases as the particle radius increases up to around 2.3 μm. As an example, we show that a 1-μm-diameter gold particle can be levitated for a significantly long time by the repulsive Casimir force at room temperature. PMID:24329240
Modified entropic gravitation in superconductors
NASA Astrophysics Data System (ADS)
de Matos, Clovis Jacinto
2012-01-01
Verlinde recently developed a theoretical account of gravitation in terms of an entropic force. The central element in Verlinde’s derivation is information and its relation with entropy through the holographic principle. The application of this approach to the case of superconductors requires to take into account that information associated with superconductor’s quantum vacuum energy is not stored on Planck size surface elements, but in four volume cells with Planck-Einstein size. This has profound consequences on the type of gravitational force generated by the quantum vacuum condensate in superconductors, which is closely related with the cosmological repulsive acceleration responsible for the accelerated expansion of the Universe. Remarkably this new gravitational type force depends on the level of breaking of the weak equivalence principle for cooper pairs in a given superconducting material, which was previously derived by the author starting from similar principles. It is also shown that this new gravitational force can be interpreted as a surface force. The experimental detection of this new repulsive gravitational-type force appears to be challenging.
Repulsive Casimir force between Weyl semimetals
NASA Astrophysics Data System (ADS)
Wilson, Justin H.; Allocca, Andrew A.; Galitski, Victor
2015-06-01
Weyl semimetals are a class of topological materials that exhibit a bulk Hall effect due to time-reversal symmetry breaking. We show that for the idealized semi-infinite case, the Casimir force between two identical Weyl semimetals is repulsive at short range and attractive at long range. Considering plates of finite thickness, we can reduce the size of the long-range attraction even making it repulsive for all distances when thin enough. In the thin-film limit, we study the appearance of an attractive Casimir force at shorter distances due to the longitudinal conductivity. Magnetic field, thickness, and chemical potential provide tunable nobs for this effect, controlling the Casimir force: whether it is attractive or repulsive, the magnitude of the effect, and the positions and existence of a trap and antitrap.
The repulsive Casimir effect in Weyl semimetals
NASA Astrophysics Data System (ADS)
Wilson, Justin; Allocca, Andrew; Galitski, Victor
2015-03-01
Weyl semimetals are a proposed topological material with broken time-reversal symmetry. Due to this, they experience a particular bulk Hall effect as well as a weak longitudinal conductance. In such a situation, one can see a repulsive Casimir effect between two Weyl semimetals (similar to what has been studied for topological insulators and quantum hall materials), and the effect can be tuned from attractive to repulsive with chemical potential or magnetic field. We consider, separately, a simplified bulk description and a thin film geometry taking into account the band structure. This work is supported by JQI-PFC.
Electron attraction mediated by Coulomb repulsion
NASA Astrophysics Data System (ADS)
Hamo, A.; Benyamini, A.; Shapir, I.; Khivrich, I.; Waissman, J.; Kaasbjerg, K.; Oreg, Y.; von Oppen, F.; Ilani, S.
2016-07-01
One of the defining properties of electrons is their mutual Coulomb repulsion. However, in solids this basic property may change; for example, in superconductors, the coupling of electrons to lattice vibrations makes the electrons attract one another, leading to the formation of bound pairs. Fifty years ago it was proposed that electrons can be made attractive even when all of the degrees of freedom in the solid are electronic, by exploiting their repulsion from other electrons. This attraction mechanism, termed ‘excitonic’, promised to achieve stronger and more exotic superconductivity. Yet, despite an extensive search, experimental evidence for excitonic attraction has yet to be found. Here we demonstrate this attraction by constructing, from the bottom up, the fundamental building block of the excitonic mechanism. Our experiments are based on quantum devices made from pristine carbon nanotubes, combined with cryogenic precision manipulation. Using this platform, we demonstrate that two electrons can be made to attract each other using an independent electronic system as the ‘glue’ that mediates attraction. Owing to its tunability, our system offers insights into the underlying physics, such as the dependence of the emergent attraction on the underlying repulsion, and the origin of the pairing energy. We also demonstrate transport signatures of excitonic pairing. This experimental demonstration of excitonic pairing paves the way for the design of exotic states of matter.
Electron attraction mediated by Coulomb repulsion.
Hamo, A; Benyamini, A; Shapir, I; Khivrich, I; Waissman, J; Kaasbjerg, K; Oreg, Y; von Oppen, F; Ilani, S
2016-07-21
One of the defining properties of electrons is their mutual Coulomb repulsion. However, in solids this basic property may change; for example, in superconductors, the coupling of electrons to lattice vibrations makes the electrons attract one another, leading to the formation of bound pairs. Fifty years ago it was proposed that electrons can be made attractive even when all of the degrees of freedom in the solid are electronic, by exploiting their repulsion from other electrons. This attraction mechanism, termed 'excitonic', promised to achieve stronger and more exotic superconductivity. Yet, despite an extensive search, experimental evidence for excitonic attraction has yet to be found. Here we demonstrate this attraction by constructing, from the bottom up, the fundamental building block of the excitonic mechanism. Our experiments are based on quantum devices made from pristine carbon nanotubes, combined with cryogenic precision manipulation. Using this platform, we demonstrate that two electrons can be made to attract each other using an independent electronic system as the 'glue' that mediates attraction. Owing to its tunability, our system offers insights into the underlying physics, such as the dependence of the emergent attraction on the underlying repulsion, and the origin of the pairing energy. We also demonstrate transport signatures of excitonic pairing. This experimental demonstration of excitonic pairing paves the way for the design of exotic states of matter. PMID:27443742
Repulsive and attractive Casimir interactions in liquids
Phan, Anh D.; Viet, N. A.
2011-12-15
The Casimir interactions in solid-liquid-solid systems as a function of separation distance have been studied by the Lifshitz theory. The dielectric permittivity functions for a wide range of materials are described by Drude, Drude-Lorentz, and oscillator models. We find that the Casimir forces between gold and silica or MgO materials are both repulsive and attractive. We also find the stable forms for the systems. Our studies would provide good guidance for future experimental studies on dispersion interactions.
Coulomb Repulsion in Miniature Ion Mobility Spectrometry
Xu, J.; Whitten, W.B.; Ramsey, J.M.
1999-08-08
We have undertaken a study of ion mobility resolution in a miniature ion mobility spectrometer with a drift channel 1.7 mm in diameter and 35 mm in length. The device attained a maximum resolution of 14 in separating ions of NO, O{sub 2}, and methyl iodine. The ions were generated by pulses from a frequency-quadrupled Nd:YAG laser. Broadening due to Coulomb repulsion was modeled theoretically and shown experimentally to have a major effect on the resolution of the miniature device.
Complex phase behavior induced by repulsive interactions
Velasco; Mederos; Navascues; Hemmer; Stell
2000-07-01
For a solid in which the interactions have a hard core plus a simple soft repulsive tail we show, using a perturbation theory, that the possible stable crystalline structures give rise to a rich phase behavior. We find two concomitant critical points each corresponding to phase transitions separating bcc and fcc structures, respectively, and the occurrence of a transition between fcc and bcc phases without change in density. This novel phenomenology may be relevant to the behavior of some metallic systems, colloids, and to water. PMID:10991174
NASA Technical Reports Server (NTRS)
Weiss, R.; Muehlner, D. J.; Benford, R. L.; Owens, D. K.; Pierre, N. A.; Rosenbluh, M.
1972-01-01
Balloon measurements were made of the far infrared background radiation. The radiometer used and its calibration are discussed. An electromagnetically coupled broadband gravitational antenna is also considered. The proposed antenna design and noise sources in the antenna are reviewed. A comparison is made between interferometric broadband and resonant bar antennas for the detection of gravitational wave pulses.
Sterically stabilized colloids with tunable repulsions.
van Gruijthuijsen, Kitty; Obiols-Rabasa, Marc; Heinen, Marco; Nägele, Gerhard; Stradner, Anna
2013-09-10
When studying tunable electrostatic repulsions in aqueous suspensions of charged colloids, irreversible colloid aggregation or gelation may occur at high salt concentrations. For many commonly used synthetic colloids, such as polystyrene and silica particles, the reason for coagulation is the presence of unbalanced, strongly attractive, and short-ranged van der Waals (VDW) forces. Here, we present an aqueous polystyrene model colloid that is sterically stabilized against VDW attractions. We show that the synthesis procedure, based on a neutral initiator couple and a nonionic surfactant, introduces surface charges that can be further increased by the addition of charged comonomer methacrylic acid. Thus, the interactions between the polystyrene spheres can be conveniently tuned from hard-sphere-like to charge-stabilized with long-ranged electrostatic repulsions described by a Yukawa-type pair potential. The particle size, grafting density, core-shell structure, and surface charge are characterized by light and neutron scattering. Using X-ray and neutron scattering in combination with an accurate analytic integral equation scheme for the colloidal static structure factor, we deduce effective particle charges for colloid volume fractions ≥0.1 and salt concentrations in the range of 1.5 to 50 mM. PMID:23937718
Attraction by Repulsion: Pairing Electrons using Electrons
NASA Astrophysics Data System (ADS)
Ilani, Shahal
One of the fundamental properties of electrons is their mutual Columbic repulsion. If electrons are placed in a solid, however, this basic property may change. A famous example is that of superconductors, where coupling to lattice vibrations makes electrons attractive and leads to the formation of bound pairs. But what if all the degrees of freedom in the solid are electronic? Is it possible to make electrons attract each other only by their repulsion to other electrons? Such an `excitonic' mechanism for attraction was proposed fifty years ago by W. A. Little, with the hope that it could lead to better and more exotic superconductivity. Yet, despite many efforts to synthesize materials that possess this unique property, to date there is still no evidence for electronic-based attraction. In this talk I will present our recent experiments that observe this unusual electronic attraction using a different, bottom-up approach. Our experiments are based on a new generation of quantum devices made from pristine carbon nanotubes, combined with precision cryogenic manipulation. Using this setup we can now assemble the fundamental building block of the excitonic attraction and demonstrate that two electrons that naturally repel each other can be made attractive using an independent electronic system as the binding glue. I will discuss the lessons learned from these experiments on what is achievable with plain electrostatics, and on the possibility to use the observed mechanism for creating exotic states of matter.
Turbine blade cooling using Coulomb repulsion
NASA Astrophysics Data System (ADS)
Breidenthal, Robert; Colannino, Joseph; Dees, John; Goodson, David; Krichtafovitch, Igor; Prevo, Tracy
2012-11-01
Video photography and thermocouples reveal the effect of an electric field on the flow around a stationary, idealized turbine blade downstream of a combustor. The hot products of combustion naturally include positive ions. When the blade is an electrode and elevated to a positive potential, it tends to attract the free electrons and repel the positive ions. Due to their lower mass, the light electrons are rapidly swept toward the blade, while the positive ions are repelled. As they collide with the neutrals in the hot gas, the positive ions transfer their momentum so that a Coulomb body force is exerted on the hot gas. Cool, compressed air is injected out of the stationary blade near its leading edge to form a layer of film cooling. In contrast to the hot combustion products, the cool air is not ionized. At the interface between the hot gas and the cool air, the Coulomb repulsion force acts on the former but not the latter, analogous to gravity at a stratified interface. An effective Richardson number representing the ratio of potential to kinetic energy characterizes the topography of the interface. When the electric field is turned on, the repulsion of the hot gas from the idealized blade is evident in video recordings and thermocouple measurements.
Cellular cooperation with shift updating and repulsion
Pavlogiannis, Andreas; Chatterjee, Krishnendu; Adlam, Ben; Nowak, Martin A.
2015-01-01
Population structure can facilitate evolution of cooperation. In a structured population, cooperators can form clusters which resist exploitation by defectors. Recently, it was observed that a shift update rule is an extremely strong amplifier of cooperation in a one dimensional spatial model. For the shift update rule, an individual is chosen for reproduction proportional to fecundity; the offspring is placed next to the parent; a random individual dies. Subsequently, the population is rearranged (shifted) until all individual cells are again evenly spaced out. For large population size and a one dimensional population structure, the shift update rule favors cooperation for any benefit-to-cost ratio greater than one. But every attempt to generalize shift updating to higher dimensions while maintaining its strong effect has failed. The reason is that in two dimensions the clusters are fragmented by the movements caused by rearranging the cells. Here we introduce the natural phenomenon of a repulsive force between cells of different types. After a birth and death event, the cells are being rearranged minimizing the overall energy expenditure. If the repulsive force is sufficiently high, shift becomes a strong promoter of cooperation in two dimensions. PMID:26602306
Shnir, Ya. M.
2015-12-15
We construct solutions of the 3 + 1 dimensional Faddeev–Skyrme model coupled to Einstein gravity. The solutions are static and asymptotically flat. They are characterized by a topological Hopf number. We investigate the dependence of the ADM masses of gravitating Hopfions on the gravitational coupling. When gravity is coupled to flat space solutions, a branch of gravitating Hopfion solutions arises and merges at a maximal value of the coupling constant with a second branch of solutions. This upper branch has no flat space limit. Instead, in the limit of a vanishing coupling constant, it connects to either the Bartnik–McKinnon or a generalized Bartnik–McKinnon solution. We further find that in the strong-coupling limit, there is no difference between the gravitating solitons of the Skyrme model and the Faddeev–Skyrme model.
Gravitational waves from gravitational collapse
Fryer, Christopher L; New, Kimberly C
2008-01-01
Gravitational wave emission from stellar collapse has been studied for nearly four decades. Current state-of-the-art numerical investigations of collapse include those that use progenitors with more realistic angular momentum profiles, properly treat microphysics issues, account for general relativity, and examine non-axisymmetric effects in three dimensions. Such simulations predict that gravitational waves from various phenomena associated with gravitational collapse could be detectable with ground-based and space-based interferometric observatories. This review covers the entire range of stellar collapse sources of gravitational waves: from the accretion induced collapse of a white dwarf through the collapse down to neutron stars or black holes of massive stars to the collapse of supermassive stars.
The Electron-Pair Repulsion Model for Molecular Geometry
ERIC Educational Resources Information Center
Gillespie, R. J.
1970-01-01
Describes how the electron-pair repulsion model qualitatively explains the size and shape of molecular orbitals. Briefly discusses trigonal bipyramidal molecules, three-center bonds, and transition elements. Describes cluster compounds and finishes with a discussion of the exceptions to the model and effects of ligand-ligand repulsions. (RR)
Hard-Core Repulsion and Supersolid Cluster Crystals
NASA Astrophysics Data System (ADS)
Boninsegni, Massimo
2016-09-01
We study the effect of a short-ranged hard-core repulsion on the stability and superfluid properties of the cluster crystal phase of two-dimensional (2D) soft-core bosons. Results of Quantum Monte Carlo simulations on a cogent test case suggest that the main physical properties of the phase remain unaltered if the range d of the inner repulsive core is sufficiently short, even if the strength of the repulsion is several orders of magnitude greater than the outer soft-core barrier. Only if d is an appreciable fraction of the size of the clusters ([InlineEquation not available: see fulltext.] 5 %) does a sufficiently strong hard-core repulsion cause the crystal to break down into a homogeneous superfluid; a moderate inner core repulsion enhances the superfluid response of the crystalline phase.
Hard-Core Repulsion and Supersolid Cluster Crystals
NASA Astrophysics Data System (ADS)
Boninsegni, Massimo
2016-06-01
We study the effect of a short-ranged hard-core repulsion on the stability and superfluid properties of the cluster crystal phase of two-dimensional (2D) soft-core bosons. Results of Quantum Monte Carlo simulations on a cogent test case suggest that the main physical properties of the phase remain unaltered if the range d of the inner repulsive core is sufficiently short, even if the strength of the repulsion is several orders of magnitude greater than the outer soft-core barrier. Only if d is an appreciable fraction of the size of the clusters ([InlineEquation not available: see fulltext.] 5 %) does a sufficiently strong hard-core repulsion cause the crystal to break down into a homogeneous superfluid; a moderate inner core repulsion enhances the superfluid response of the crystalline phase.
Directional Noncovalent Interactions: Repulsion and Dispersion.
El Kerdawy, Ahmed; Murray, Jane S; Politzer, Peter; Bleiziffer, Patrick; Heßelmann, Andreas; Görling, Andreas; Clark, Timothy
2013-05-14
The interaction energies between an argon atom and the dihalogens Br2, BrCl, and BrF have been investigated using frozen core CCSD(T)(fc)/aug-cc-pVQZ calculations as reference values for other levels of theory. The potential-energy hypersurfaces show two types of minima: (1) collinear with the dihalogen bond and (2) in a bridging position. The former represent the most stable minima for these systems, and their binding energies decrease in the order Br > Cl > F. Isotropic atom-atom potentials cannot reproduce this binding pattern. Of the other levels of theory, CCSD(T)(fc)/aug-cc-pVTZ reproduces the reference data very well, as does MP2(fc)/aug-cc-pVDZ, which performs better than MP2 with the larger basis sets (aug-cc-pVQZ and aug-cc-pvTZ). B3LYP-D3 and M06-2X reproduce the binding patterns moderately well despite the former using an isotropic dispersion potential correction. B3LYP-D3(bj) performs even better. The success of the B3LYP-D3 methods is because polar flattening of the halogens allows the argon atom to approach more closely in the direction collinear with the bond, so that the sum of dispersion potential and repulsion is still negative at shorter distances than normally possible and the minimum is deeper at the van der Waals distance. Core polarization functions in the basis set and including the core orbitals in the CCSD(T)(full) calculations lead to a uniform decrease of approximately 20% in the magnitudes of the calculated interaction energies. The EXXRPA+@EXX (exact exchange random phase approximation) orbital-dependent density functional also gives interaction energies that correlate well with the highest level of theory but are approximately 10% low. The newly developed EXXRPA+@dRPA functional represents a systematic improvement on EXXRPA+@EXX. PMID:26583720
Universal three-body repulsion suggested by neutron stars
Takatsuka, T.; Nishizaki, S.; Tamagaki, R.
2008-04-29
Because of a serious inconsistency between theory and observation for the mass of hyperon-mixed neutron stars, it is suggested that some 'extra repulsion' is needed in hypernuclear systems. A 3-body force repulsion is tested for two cases, a 2{pi}-exchange via {delta}-excitation type (2{pi}{delta}) and a string-junction model (SJM) for the quark structure of baryons. It is found that the 2{pi}{delta} model generates an increasing repulsion with increasing density but cannot produce the 'extra repulsion' in hyperon-mixed neutron stars because it does not work on a {lambda} due to the lack of {lambda}{lambda}{pi} direct coupling. It is pointed out that the 'extra repulsion' should act universally, i.e., independent of baryon species. The SJM 3-body repulsion can satisfy the condition of universality because of the flavor-independence and the {l_brace}2{pi}{delta}+SJM{r_brace} scheme is shown to be a promising candidate for the 'extra repulsion', maintaining consistency with the empirical saturation property of nuclear matter.
Axelrod models of social influence with cultural repulsion
NASA Astrophysics Data System (ADS)
Radillo-Díaz, Alejandro; Pérez, Luis A.; Del Castillo-Mussot, Marcelo
2009-12-01
Since both attractive and repulsive effects among agents are important in social systems, we present simulations of two models based on Axelrod’s homogenization mechanism that includes repulsion. These models are the repulsive model, where all individuals can repel, and the partially repulsive model where only a fraction of repelling agents are considered. In these two models, attractive dynamics is implemented for agents with the ability to repel each other only if the number of features shared by them is greater than a threshold parameter. Otherwise, repelling dynamics is used. In the repulsive model, the transition from a monocultural state to a fragmented one often occurs abruptly from one cultural-variability value to the next one and a second transition emerges. For the partially repulsive model, there are also two different transitions present: the initial one being as abrupt as the one found for the repulsive model, whereas the second one follows a less abrupt behavior and resembles that of the original Axelrod model. However, the second transition for this model occurrs from a partially fragmented state and not from a monocultural one.
Lincoln, Don
2015-06-24
In a long line of intellectual triumphs, Einstein’s theory of general relativity was his greatest and most imaginative. It tells us that what we experience as gravity can be most accurately described as the bending of space itself. This idea leads to consequences, including gravitational lensing, which is caused by light traveling in this curved space. This is works in a way analogous to a lens (and hence the name). In this video, Fermilab’s Dr. Don Lincoln explains a little general relativity, a little gravitational lensing, and tells us how this phenomenon allows us to map out the matter of the entire universe, including the otherwise-invisible dark matter.
Turner, E.L.
1988-07-01
For several years astronomers have devoted considerable effort to finding and studying a class of celestial phenomena whose very existence depends on rare cosmic accidents. These are gravitational-lens events, which occur when two or more objects at different distances from the earth happen to lie along the same line of sight and so coincide in the sky. The radiation from the more distant object, typically a quasar, is bent by the gravitational field of the foreground object. The bending creates a cosmic mirage: distorted or multiple images of the background object. Such phenomena may reveal many otherwise undetectable features of the image source, of the foreground object and of the space lying between them. Such observations could help to resolve several fundamental questions in cosmology. In the past decade theoretical and observational research on gravitational lenses has grown rapidly and steadily. At this writing at least 17 candidate lens systems have been discussed in the literature. Of the 17 lens candidates reported so far in professional literature, only five are considered to have been reliably established by subsequent observations. Another three are generally regarded as weak or speculative cases with less than 50 percent chance of actually being lens systems. In the remaining nine cases the evidence is mixed or is sparse enough so that the final judgment could swing either way. As might be concluded, little of the scientific promise of gravitational lenses has yet been realized. The work has not yielded a clear value for the proportionality constant or any of the other fundamental cosmological parameter. 7 figs.
NASA Astrophysics Data System (ADS)
Saha, P.; Murdin, P.
2000-11-01
Gravity bends light rays in a way analogous to, but quantitatively different from, the way it bends trajectories of passing particles. If light from some bright object passes close enough to some foreground mass, that object's image will be altered. The effect is more like a piece of bathroom glass in the sky than a precision-ground and well-focused lens, but the terms `gravitational lensing' or ...
On the possibility of Casimir repulsion using metamaterials
Da Rosa, Felipe S
2008-01-01
It is well known that the Casimir force between two half-spaces is dictated by their electromagnetic properties. In particular, when one of the half-spaces is mainly metallic or dielectric and the other is mainly magnetic, it is possible to show that the force is repulsive. This has attracted lots of interest towards the study of metamaterials (MMs) in the context of Casimir effect, as their magnetic activity might help bring the idea of Casimir repulsion from the theoretical realm to experimental verification. In this paper we investigate the possibility of repulsion when the MM magnetic permeability is given not by a Drude-Lorentz behavior, but by a model put forward by Pendry et al. [16]. After introducing the model and deriving the necessary formulas, we show that it is impossible to achieve repulsion with such a model and present a qualitative discussion of why this is so.
NASA Astrophysics Data System (ADS)
Lämmerzahl, Claus; di Virgilio, Angela
2016-06-01
100 years after the invention of General Relativity (GR) and 110 years after the development of Special Relativity (SR) we have to state that until now no single experiment or observation allows any doubt about the validity of these theories within the accuracy of the available data. Tests of GR can be divided into three categories: (i) test of the foundations of GR, (ii) tests of the consequences of GR, and (iii) test of the interplay between GR and quantum mechanics. In the first category, we have tests of the Einstein Equivalence Principle and the structure of the Newton axioms, in the second category we have effects like the gravitational redshift, light defection, gravitational time delay, the perihelion shift, the gravitomagnetic effects as the Lense-Thirring and Schiff effect, and gravitational waves. Tests of the effects of gravity on quantum systems are a first step towards experiments searching for a quantum gravity theory. In this paper, we also highlight practical applications in positioning, geodesy, and the International Atomic Time. After 100 years, GR can now definitely be regarded also as practical and applied science.
Metastable states of a composite system tunneling through repulsive barriers
NASA Astrophysics Data System (ADS)
Gusev, A. A.; Vinitsky, S. I.; Chuluunbaatar, O.; Derbov, V. L.; Góźdź, A.; Krassovitskiy, P. M.
2016-01-01
We consider a method for solving the problem of quantum tunneling through repulsive potential barriers for a composite system consisting of several identical particles coupled via pair oscillator-type potentials in the oscillator symmetrized-coordinate representation. We confirm the efficiency of the proposed approach by calculating complex energy values and analyzing metastable states of composite systems of three, four, and five identical particles on a line, which leads to the effect of quantum transparency of the repulsive barriers.
Sparse repulsive coupling enhances synchronization in complex networks.
Leyva, I; Sendiña-Nadal, I; Almendral, J A; Sanjuán, M A F
2006-11-01
Through the last years, different strategies to enhance synchronization in complex networks have been proposed. In this work, we show that synchronization of nonidentical dynamical units that are attractively coupled in a small-world network is strongly improved by just making phase-repulsive a tiny fraction of the couplings. By a purely topological analysis that does not depend on the dynamical model, we link the emerging dynamical behavior with the structural properties of the sparsely coupled repulsive network. PMID:17279973
Repulsive Synchronization in an Array of Phase Oscillators
NASA Astrophysics Data System (ADS)
Tsimring, L. S.; Rulkov, N. F.; Larsen, M. L.; Gabbay, M.
2005-06-01
We study the dynamics of a repulsively coupled array of phase oscillators. For an array of globally coupled identical oscillators, repulsive coupling results in a family of synchronized regimes characterized by zero mean field. If the number of oscillators is sufficiently large, phase locking among oscillators is destroyed, independently of the coupling strength, when the oscillators’ natural frequencies are not the same. In locally coupled networks, however, phase locking occurs even for nonidentical oscillators when the coupling strength is sufficiently strong.
Elastic repulsion from polymer brush layers exhibiting high protein repellency.
Inoue, Yuuki; Nakanishi, Tomoaki; Ishihara, Kazuhiko
2013-08-27
Hydrophilic poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) and poly(2-hydroxyethyl methacrylate) (PHEMA) brush layers with different thicknesses and graft densities were prepared to construct a model surface to elucidate protein-surface interactions. In particular, we focused on the steric repulsion of hydrophilic polymer layers as one of the surface properties that strongly influence protein adsorption and employed force-versus-distance (f-d) curve measurements obtained via atomic force microscopy to quantitatively evaluate the steric repulsion force, which is also referred to as the "elastic repulsion energy." We also analyzed direct interactions between the surface and proteins via the f-d curve, because these interactions trigger the protein-adsorption phenomenon. Protein-surface interactions were extremely suppressed at surfaces with high elastic repulsion energies and highly dense polymer brush structures, which is in contrast to those at surfaces with low elastic repulsion energies and low density of the grafted polymer layers. These results indicate that the elastic repulsion from the grafted polymer layer at the surface is an important parameter for controlling protein-surface interactions and protein adsorption phenomenon. PMID:23898820
Coulomb repulsion and the electron beam directed energy weapon
NASA Astrophysics Data System (ADS)
Retsky, Michael W.
2004-09-01
Mutual repulsion of discrete charged particles or Coulomb repulsion is widely considered to be an ultimate hard limit in charged particle optics. It prevents the ability to finely focus high current beams into small spots at large distances from defining apertures. A classic example is the 1970s era "Star Wars" study of an electron beam directed energy weapon as an orbiting antiballistic missile device. After much analysis, it was considered physically impossible to focus a 1000-amp 1-GeV beam into a 1-cm diameter spot 1000-km from the beam generator. The main reason was that a 1-cm diameter beam would spread to 5-m diameter at 1000-km due to Coulomb repulsion. Since this could not be overcome, the idea was abandoned. But is this true? What if the rays were reversed? That is, start with a 5-m beam converging slightly with the same nonuniform angular and energy distribution as the electrons from the original problem were spreading at 1000-km distance. Could Coulomb repulsion be overcome? Looking at the terms in computational studies, some are reversible while others are not. Based on estimates, the nonreversible terms should be small - of the order of 0.1 mm. If this is true, it is possible to design a practical electron beam directed weapon not limited by Coulomb repulsion.
An anisotropic hydrogel with electrostatic repulsion between cofacially aligned nanosheets.
Liu, Mingjie; Ishida, Yasuhiro; Ebina, Yasuo; Sasaki, Takayoshi; Hikima, Takaaki; Takata, Masaki; Aida, Takuzo
2015-01-01
Machine technology frequently puts magnetic or electrostatic repulsive forces to practical use, as in maglev trains, vehicle suspensions or non-contact bearings. In contrast, materials design overwhelmingly focuses on attractive interactions, such as in the many advanced polymer-based composites, where inorganic fillers interact with a polymer matrix to improve mechanical properties. However, articular cartilage strikingly illustrates how electrostatic repulsion can be harnessed to achieve unparalleled functional efficiency: it permits virtually frictionless mechanical motion within joints, even under high compression. Here we describe a composite hydrogel with anisotropic mechanical properties dominated by electrostatic repulsion between negatively charged unilamellar titanate nanosheets embedded within it. Crucial to the behaviour of this hydrogel is the serendipitous discovery of cofacial nanosheet alignment in aqueous colloidal dispersions subjected to a strong magnetic field, which maximizes electrostatic repulsion and thereby induces a quasi-crystalline structural ordering over macroscopic length scales and with uniformly large face-to-face nanosheet separation. We fix this transiently induced structural order by transforming the dispersion into a hydrogel using light-triggered in situ vinyl polymerization. The resultant hydrogel, containing charged inorganic structures that align cofacially in a magnetic flux, deforms easily under shear forces applied parallel to the embedded nanosheets yet resists compressive forces applied orthogonally. We anticipate that the concept of embedding anisotropic repulsive electrostatics within a composite material, inspired by articular cartilage, will open up new possibilities for developing soft materials with unusual functions. PMID:25557713
Order disorder alternations in the populations of faulty repulsive agents
NASA Astrophysics Data System (ADS)
Collet, Jacques Henri
2007-12-01
We study the spatio-temporal evolution of populations made up from a few tens to thousands of monokinetic repulsive agents moving through a two-dimensional grid. We adopt the behavioral description of agents, in which each agent executes an action following a state automaton. In the first step, the agents follow the repulsion rule of a deterministic automaton. Collective behaviors are calculated from the application of the evolution mechanisms for each individual. We show that, depending on the repulsion law and on the presence of borders, the agents become organized into a square or a condensed hexagonal stationary lattice, which maximizes the potential function of the distribution. Thus, the repulsion may force the condensation to the same site. Then, we study the collective behaviors when the agents are faulty and randomly violate the repulsion law. When the number of agents is small (say, for population involving a few tens of agents), we observe fast and random alternations between the ordered lattice phase and a strongly disorganized state. These alternations are essentially averaged and disappear in the large populations, resulting in a partially ordered homogeneous distribution.
An anisotropic hydrogel with electrostatic repulsion between cofacially aligned nanosheets
NASA Astrophysics Data System (ADS)
Liu, Mingjie; Ishida, Yasuhiro; Ebina, Yasuo; Sasaki, Takayoshi; Hikima, Takaaki; Takata, Masaki; Aida, Takuzo
2015-01-01
Machine technology frequently puts magnetic or electrostatic repulsive forces to practical use, as in maglev trains, vehicle suspensions or non-contact bearings. In contrast, materials design overwhelmingly focuses on attractive interactions, such as in the many advanced polymer-based composites, where inorganic fillers interact with a polymer matrix to improve mechanical properties. However, articular cartilage strikingly illustrates how electrostatic repulsion can be harnessed to achieve unparalleled functional efficiency: it permits virtually frictionless mechanical motion within joints, even under high compression. Here we describe a composite hydrogel with anisotropic mechanical properties dominated by electrostatic repulsion between negatively charged unilamellar titanate nanosheets embedded within it. Crucial to the behaviour of this hydrogel is the serendipitous discovery of cofacial nanosheet alignment in aqueous colloidal dispersions subjected to a strong magnetic field, which maximizes electrostatic repulsion and thereby induces a quasi-crystalline structural ordering over macroscopic length scales and with uniformly large face-to-face nanosheet separation. We fix this transiently induced structural order by transforming the dispersion into a hydrogel using light-triggered in situ vinyl polymerization. The resultant hydrogel, containing charged inorganic structures that align cofacially in a magnetic flux, deforms easily under shear forces applied parallel to the embedded nanosheets yet resists compressive forces applied orthogonally. We anticipate that the concept of embedding anisotropic repulsive electrostatics within a composite material, inspired by articular cartilage, will open up new possibilities for developing soft materials with unusual functions.
Quasiparticle-continuum level repulsion in a quantum magnet
Plumb, K. W.; Hwang, Kyusung; Qiu, Y.; Harriger, Leland W.; Granroth, G. Â E.; Kolesnikov, Alexander I.; Shu, G. J.; Chou, F. C.; Rüegg, Ch.; Kim, Yong Baek; Kim, Young-June
2015-11-30
When the energy eigenvalues of two coupled quantum states approach each other in a certain parameter space, their energy levels repel each other and level crossing is avoided. Such level repulsion, or avoided level crossing, is commonly used to describe the dispersion relation of quasiparticles in solids. But, little is known about the level repulsion when more than two quasiparticles are present; for example, in a strongly interacting quantum system where a quasiparticle can spontaneously decay into a many-particle continuum. Here we show that even in this case level repulsion exists between a long-lived quasiparticle state and a continuum. Here, we observe a renormalization of the quasiparticle dispersion relation due to the presence of the continuum of multi-quasiparticle states, in our fine-resolution neutron spectroscopy study of magnetic quasiparticles in the frustrated quantum magnet BiCu_{2}PO_{6}.
Quasiparticle-continuum level repulsion in a quantum magnet
Plumb, K. W.; Hwang, Kyusung; Qiu, Y.; Harriger, Leland W.; Granroth, G. Â E.; Kolesnikov, Alexander I.; Shu, G. J.; Chou, F. C.; Rüegg, Ch.; Kim, Yong Baek; et al
2015-11-30
When the energy eigenvalues of two coupled quantum states approach each other in a certain parameter space, their energy levels repel each other and level crossing is avoided. Such level repulsion, or avoided level crossing, is commonly used to describe the dispersion relation of quasiparticles in solids. But, little is known about the level repulsion when more than two quasiparticles are present; for example, in a strongly interacting quantum system where a quasiparticle can spontaneously decay into a many-particle continuum. Here we show that even in this case level repulsion exists between a long-lived quasiparticle state and a continuum. Here,more » we observe a renormalization of the quasiparticle dispersion relation due to the presence of the continuum of multi-quasiparticle states, in our fine-resolution neutron spectroscopy study of magnetic quasiparticles in the frustrated quantum magnet BiCu2PO6.« less
Quasiparticle-continuum level repulsion in a quantum magnet
NASA Astrophysics Data System (ADS)
Plumb, K. W.; Hwang, Kyusung; Qiu, Y.; Harriger, Leland W.; Granroth, G. E.; Kolesnikov, Alexander I.; Shu, G. J.; Chou, F. C.; Rüegg, Ch.; Kim, Yong Baek; Kim, Young-June
2016-03-01
When the energy eigenvalues of two coupled quantum states approach each other in a certain parameter space, their energy levels repel each other and level crossing is avoided. Such level repulsion, or avoided level crossing, is commonly used to describe the dispersion relation of quasiparticles in solids. However, little is known about the level repulsion when more than two quasiparticles are present; for example, in a strongly interacting quantum system where a quasiparticle can spontaneously decay into a many-particle continuum. Here we show that even in this case level repulsion exists between a long-lived quasiparticle state and a continuum. In our fine-resolution neutron spectroscopy study of magnetic quasiparticles in the frustrated quantum magnet BiCu2PO6, we observe a renormalization of the quasiparticle dispersion relation due to the presence of the continuum of multi-quasiparticle states.
Schee, J.; Stuchlík, Z.; Petrásek, M. E-mail: zdenek.stuchlik@fpf.slu.cz
2013-12-01
It has been recently shown that the cosmic repulsion can have a highly significant influence on the motion of Magellanic Clouds (MC) in the gravitational field of Milky Way, treated in the framework of the Cold Dark Matter (CDM) halo model. However, there is an alternative to the CDM halo explanation of the rotation curves in the periphery of spiral galaxies, based on MOdified Newtonian Dynamics (MOND). Therefore, we study the role of the cosmic repulsion in the framework of the MOND theory applied to determine the MC motion. Our results demonstrate that in the MOND framework the influence of the cosmic repulsion on the motion of both Small and Large MC is also highly significant, but it is of a different character than in the framework of the CDM halo model. Moreover, we demonstrate that the MC motion in the framework of the CDM halo and MOND models is subtantially different and can serve as a test of these fundamentally different approaches to the explanation of the phenomena related to galaxies and the motion of satellite galaxies.
Repulsive Casimir-Polder potential by a negative reflecting surface
NASA Astrophysics Data System (ADS)
Yuan, Qi-Zhang
2015-07-01
We present a scheme to generate an all-range long repulsive Casimir-Polder potential between a perfect negative reflecting surface and a ground-state atom. The repulsive potential is stable and does not decay with time. The Casimir-Polder potential is proportional to z-2 at short atom-surface distances and to z-4 at long atom-surface distances. Because of these advantages, this potential can help in building quantum reflectors, quantum levitating devices, and waveguides for matter waves.
Teaching Valence Shell Electron Pair Repulsion (VSEPR) Theory
ERIC Educational Resources Information Center
Talbot, Christopher; Neo, Choo Tong
2013-01-01
This "Science Note" looks at the way that the shapes of simple molecules can be explained in terms of the number of electron pairs in the valence shell of the central atom. This theory is formally known as valence shell electron pair repulsion (VSEPR) theory. The article explains the preferred shape of chlorine trifluoride (ClF3),…
Can Coulomb repulsion for charged particle beams be overcome?
NASA Astrophysics Data System (ADS)
Retsky, Michael W.
2004-01-01
Mutual repulsion of discrete charged particles or Coulomb repulsion is widely considered to be an ultimate hard limit in charged particle optics. It prevents the ability to finely focus high current beams into a small spots at large distances from the defining apertures. A classic example is the 1970s era "Star Wars" study of an electron beam directed energy weapon as an orbiting antiballistic missile device. After much analysis, it was considered physically impossible to focus a 1000-amp 1-GeV beam into a 1-cm diameter spot 1000-km from the beam generator. The main reason was that a 1-cm diameter beam would spread to 5-m diameter at 1000-km due to Coulomb repulsion. Since this could not be overcome, the idea was abandoned. But is this true? What if the rays were reversed? That is, start with a 5-m beam converging slightly with the same nonuniform angular and energy distribution as the electrons from the original problem were spreading at 1000-km distance. Could Coulomb repulsion be overcome? Looking at the terms in computational studies, some are reversible while others are not. Since the nonreversible terms should be small, it might be possible to construct an electron beam directed energy weapon.
The Pauli Principle and Electronic Repulsion in Helium
ERIC Educational Resources Information Center
Snow, Richard L.; Bills, James L.
1974-01-01
The authors indicate that several recent textbooks in quantum chemistry use a discussion of the excited states of the helium atom to demonstrate the importance of the Pauli principle in determining electronic repulsions. They present data suggesting "Pauli forces" do not keep electrons of parallel spins separated in space. (RH)
Spontaneous symmetry breaking in vortex systems with two repulsive lengthscales.
Curran, P J; Desoky, W M; Milosević, M V; Chaves, A; Laloë, J-B; Moodera, J S; Bending, S J
2015-01-01
Scanning Hall probe microscopy (SHPM) has been used to study vortex structures in thin epitaxial films of the superconductor MgB2. Unusual vortex patterns observed in MgB2 single crystals have previously been attributed to a competition between short-range repulsive and long-range attractive vortex-vortex interactions in this two band superconductor; the type 1.5 superconductivity scenario. Our films have much higher levels of disorder than bulk single crystals and therefore both superconducting condensates are expected to be pushed deep into the type 2 regime with purely repulsive vortex interactions. We observe broken symmetry vortex patterns at low fields in all samples after field-cooling from above Tc. These are consistent with those seen in systems with competing repulsions on disparate length scales, and remarkably similar structures are reproduced in dirty two band Ginzburg-Landau calculations, where the simulation parameters have been defined by experimental observations. This suggests that in our dirty MgB2 films, the symmetry of the vortex structures is broken by the presence of vortex repulsions with two different lengthscales, originating from the two distinct superconducting condensates. This represents an entirely new mechanism for spontaneous symmetry breaking in systems of superconducting vortices, with important implications for pinning phenomena and high current density applications. PMID:26492969
Electrostatic Repulsion Governs TDP-43 C-terminal Domain Aggregation.
Mompeán, Miguel; Chakrabartty, Avijit; Buratti, Emanuele; Laurents, Douglas V
2016-04-01
TDP-43 is a protein that forms aggregates implicated in amyotrophic lateral sclerosis. In response to a recent study, this Formal Comment argues that the pH-dependent solubility of this protein is better explained by the mutual repulsion of charged groups than by the formation of hydrogen bonds. PMID:27096426
Electron Pairing, Repulsion, and Correlation: A Simplistic Approach
ERIC Educational Resources Information Center
Olsson, Lars-Fride; Kloo, Lars
2004-01-01
The interplay between a nucleus and an electron pair is explained through a basic application of an electrostatic and balanced model to determine the correlated and repulsive movements of the electron pair. The stable correlation depends on the positive charge produced by the combined force, which in turn establishes a negative potential energy.
Spontaneous symmetry breaking in vortex systems with two repulsive lengthscales
Curran, P. J.; Desoky, W. M.; Milos̆ević, M. V.; Chaves, A.; Laloë, J.-B.; Moodera, J. S.; Bending, S. J.
2015-01-01
Scanning Hall probe microscopy (SHPM) has been used to study vortex structures in thin epitaxial films of the superconductor MgB2. Unusual vortex patterns observed in MgB2 single crystals have previously been attributed to a competition between short-range repulsive and long-range attractive vortex-vortex interactions in this two band superconductor; the type 1.5 superconductivity scenario. Our films have much higher levels of disorder than bulk single crystals and therefore both superconducting condensates are expected to be pushed deep into the type 2 regime with purely repulsive vortex interactions. We observe broken symmetry vortex patterns at low fields in all samples after field-cooling from above Tc. These are consistent with those seen in systems with competing repulsions on disparate length scales, and remarkably similar structures are reproduced in dirty two band Ginzburg-Landau calculations, where the simulation parameters have been defined by experimental observations. This suggests that in our dirty MgB2 films, the symmetry of the vortex structures is broken by the presence of vortex repulsions with two different lengthscales, originating from the two distinct superconducting condensates. This represents an entirely new mechanism for spontaneous symmetry breaking in systems of superconducting vortices, with important implications for pinning phenomena and high current density applications. PMID:26492969
Gravitational lens time delays and gravitational waves
Frieman, J.A. Department of Astronomy Astrophysics, University of Chicago, Chicago, Illinois 60637 ); Harari, D.D.; Surpi, G.C. )
1994-10-15
Using Fermat's principle, we analyze the effects of very long wavelength gravitational waves upon the images of a gravitationally lensed quasar. We show that the lens equation in the presence of gravity waves is equivalent to that of a lens with a different alignment between source, deflector, and observer in the absence of gravity waves. Contrary to a recent claim, we conclude that measurements of time delays in gravitational lenses cannot serve as a method to detect or constrain a stochastic background of gravitational waves of cosmological wavelengths, because the wave-induced time delay is observationally indistinguishable from an intrinsic time delay due to the lens geometry.
Detectors of gravitational waves
NASA Astrophysics Data System (ADS)
Pizzella, G.
Gravitational waves Motion of test bodies in a g.w. field Energy carried by gravitational waves Gravitational-wave sources Spinning star Double-star systems Fall into a Schwarzschild black hole Radiation from gravitational collapse Gravitational-wave detectors The nonresonant detectors The resonant detectors Electromechnical transducers Piezoelectric ceramic The capacitor The inductor Data analysis The Brownian noise The back-action The wide-band noise, data analysis and optimization The resonant transducer The Wiener-Kolmogoroff filter The cross-section and the effective temperature The antenna bandwidth The gravitational-wave experiments in the world The laser interferometers The resonant detectors
Modeling and strain gauging of eddy current repulsion deicing systems
NASA Technical Reports Server (NTRS)
Smith, Samuel O.
1993-01-01
Work described in this paper confirms and extends work done by Zumwalt, et al., on a variety of in-flight deicing systems that use eddy current repulsion for repelling ice. Two such systems are known as electro-impulse deicing (EIDI) and the eddy current repulsion deicing strip (EDS). Mathematical models for these systems are discussed for their capabilities and limitations. The author duplicates a particular model of the EDS. Theoretical voltage, current, and force results are compared directly to experimental results. Dynamic strain measurements results are presented for the EDS system. Dynamic strain measurements near EDS or EIDI coils are complicated by the high magnetic fields in the vicinity of the coils. High magnetic fields induce false voltage signals out of the gages.
Synergistic effect of repulsive inhibition in synchronization of excitatory networks
NASA Astrophysics Data System (ADS)
Belykh, Igor; Reimbayev, Reimbay; Zhao, Kun
2015-06-01
We show that the addition of pairwise repulsive inhibition to excitatory networks of bursting neurons induces synchrony, in contrast to one's expectations. Through stability analysis, we reveal the mechanism underlying this purely synergistic phenomenon and demonstrate that it originates from the transition between different types of bursting, caused by excitatory-inhibitory synaptic coupling. This effect is generic and observed in different models of bursting neurons and fast synaptic interactions. We also find a universal scaling law for the synchronization stability condition for large networks in terms of the number of excitatory and inhibitory inputs each neuron receives, regardless of the network size and topology. This general law is in sharp contrast with linearly coupled networks with positive (attractive) and negative (repulsive) coupling where the placement and structure of negative connections heavily affect synchronization.
Ferromagnetism in a repulsive atomic Fermi gas with correlated disorder
NASA Astrophysics Data System (ADS)
Pilati, S.; Fratini, E.
2016-05-01
We investigate the zero-temperature ferromagnetic behavior of a two-component repulsive Fermi gas in the presence of a correlated random field that represents an optical speckle pattern. The density is tuned so that the (noninteracting) Fermi energy is close to the mobility edge of the Anderson localization transition. We employ quantum Monte Carlo simulations to determine various ground-state properties, including the equation of state, the magnetic susceptibility, and the energy of an impurity immersed in a polarized Fermi gas (repulsive polaron). In the weakly interacting limit, the magnetic susceptibility is found to be suppressed by disorder. However, it rapidly increases with the interaction strength, and it diverges at a much weaker interaction strength compared to the clean gas. Both the transition from the paramagnetic phase to the partially ferromagnetic phase, and the one from the partially to the fully ferromagnetic phase, are strongly favored by disorder, indicating a case of order induced by disorder.
Dynamics of chaotic systems with attractive and repulsive couplings.
Chen, Yuehua; Xiao, Jinghua; Liu, Weiqing; Li, Lixiang; Yang, Yixian
2009-10-01
Together with attractive couplings, repulsive couplings play crucial roles in determining important evolutions in natural systems, such as in learning and oscillatory processes of neural networks. The complex interactions between them have great influence on the systems. A detailed understanding of the dynamical properties under this type of couplings is of practical significance. In this paper, we propose a model to investigate the dynamics of attractive and repulsive couplings, which give rise to rich phenomena, especially for amplitude death (AD). The relationship among various dynamics and possible transitions to AD are illustrated. When the system is in the maximally stable AD, we observe the transient behavior of in-phase (high frequency) and out-of-phase (low frequency) motions. The mechanism behind the phenomenon is given. PMID:19905414
General continuum approach for dissipative systems of repulsive particles
NASA Astrophysics Data System (ADS)
Vieira, César M.; Carmona, Humberto A.; Andrade, José S.; Moreira, André A.
2016-06-01
We propose a general coarse-graining method to derive a continuity equation that describes any dissipative system of repulsive particles interacting through short-ranged potentials. In our approach, the effect of particle-particle correlations is incorporated to the overall balance of energy, and a nonlinear diffusion equation is obtained to represent the overdamped dynamics. In particular, when the repulsive interaction potential is a short-ranged power law, our approach reveals a distinctive correspondence between particle-particle energy and the generalized thermostatistics of Tsallis for any nonpositive value of the entropic index q . Our methodology can also be applied to microscopic models of superconducting vortices and complex plasma, where particle-particle correlations are pronounced at low concentrations. The resulting continuum descriptions provide elucidating and useful insights on the microdynamical behavior of these physical systems. The consistency of our approach is demonstrated by comparison with molecular dynamics simulations.
First-principles study of Casimir repulsion in metamaterials.
Yannopapas, Vassilios; Vitanov, Nikolay V
2009-09-18
We examine theoretically the Casimir effect between a metallic plate and several types of magnetic metamaterials in pursuit of Casimir repulsion, by employing a rigorous multiple-scattering theory for the Casimir effect. We first examine metamaterials in the form of two-dimensional lattices of inherently nonmagnetic spheres such as spheres made from materials possessing phonon-polariton and exciton-polariton resonances. Although such systems are magnetically active in infrared and optical regimes, the force between finite slabs of these materials and metallic slabs is plainly attractive since the effective electric permittivity is larger than the magnetic permeability for the studied spectrum. When lattices of magnetic spheres made from superparamagnetic composites are employed, we achieve not only Casimir repulsion but almost total suppression of the Casimir effect itself in the micrometer scale. PMID:19792414
Molecular evolution of hemojuvelin and the repulsive guidance molecule family.
Camus, Laura Marie; Lambert, Lisa A
2007-07-01
Repulsive guidance molecules (RGMs) are found in vertebrates and chordates and are involved in embryonic development and iron homeostasis. Members of this family are GPI-linked membrane proteins that contain an N-terminal signal peptide, a C-terminal propeptide, and a conserved RGD motif. Vertebrates are known to possess three paralogues; RGMA and RGMB (sometimes called Dragon) are expressed in the nervous system and are thought to play various roles in neural development. Hemojuvelin (HJV; also called repulsive guidance molecule c, RGMC) is the third member of this family, and mutations in this gene result in a form of juvenile hemochromatosis (type 2A). Phylogenetic analyses of 55 different RGM family sequences from 21 different species support the existence of a novel gene, found only in fish, which we have labeled RGMD. The pattern of conserved residues in each family identifies new candidates for important functional roles, including ligand binding. PMID:17593421
General continuum approach for dissipative systems of repulsive particles.
Vieira, César M; Carmona, Humberto A; Andrade, José S; Moreira, André A
2016-06-01
We propose a general coarse-graining method to derive a continuity equation that describes any dissipative system of repulsive particles interacting through short-ranged potentials. In our approach, the effect of particle-particle correlations is incorporated to the overall balance of energy, and a nonlinear diffusion equation is obtained to represent the overdamped dynamics. In particular, when the repulsive interaction potential is a short-ranged power law, our approach reveals a distinctive correspondence between particle-particle energy and the generalized thermostatistics of Tsallis for any nonpositive value of the entropic index q. Our methodology can also be applied to microscopic models of superconducting vortices and complex plasma, where particle-particle correlations are pronounced at low concentrations. The resulting continuum descriptions provide elucidating and useful insights on the microdynamical behavior of these physical systems. The consistency of our approach is demonstrated by comparison with molecular dynamics simulations. PMID:27415187
Phosphatidylglycerol Flip-Flop Suppression due to Headgroup Charge Repulsion.
Brown, Krystal L; Conboy, John C
2015-08-13
The kinetics and thermodynamics of 1,2-distearoyl-sn-glycero-3-[phospho(1'-rac-glycerol)] (DSPG) flip-flop in 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) membranes were examined by sum-frequency vibrational spectroscopy (SFVS). The effect of DSPG concentration in the membrane and the influence of electrolyte concentration were examined in an attempt to decipher the role the anionic PG headgroup plays in dictating the dynamics of PG flip-flop for this biologically important lipid species. DSPG flip-flop dynamics and the activation barrier to exchange were found to be directly dependent on the amount of DSPG present in the bilayer. Analysis of the activation free energy for DSPG flip-flop in mixed DSPG + DSPC bilayers reveals that charge repulsion between neighboring PG headgroups modulates the free energy barrier and subsequently, the rate of translocation. Specifically, when DSPG comprises a small portion of the bilayer, the electrostatic potential of neighboring PG lipids are effectively shielded from each other under high ionic strength conditions and little to no charge repulsion occurs. When DSPG lipids are close enough to experience charge repulsion from neighboring PG lipids, as in bilayers containing a large fraction of DSPG, or for bilayers in low ionic strength solutions, the influence of charge repulsion on the energetics of lipid flip-flop are measurable. For biological membranes, where the concentration of PG is relatively low, the neighboring PG lipids are spaced far enough apart that their anionic charges are effectively shielded, such that under physiological conditions the charged nature of the headgroup does little to modulate its lipid flip-flop energetics and corresponding rate of translocation. PMID:26202012
Effective Reduction of Coulomb Repulsion in Charged Granular Matter
NASA Astrophysics Data System (ADS)
Scheffler, T.; Werth, J.; Wolf, D. E.
2000-04-01
This paper is an extension to a previous article by Scheffler and Wolfs.6 We study the rate of energy dissipation due to inelastic collisions in a charged granular gas. One observes that the electrostatic repulsion of two particles is effectively reduced by nearest neighbor interactions in a dense granular gas. We study the radial distribution function for dense systems, which leads to a better expression for the reduced energy barrier.
A magnetic bearing based on eddy-current repulsion
NASA Technical Reports Server (NTRS)
Nikolajsen, J. L.
1987-01-01
This paper describes a new type of electromagnetic bearing, called the Eddy-Current Bearing, which works by repulsion between fixed AC-electromagnets and a conducting rotor. The following advantages are expected: inherent stability, higher load carrying capacity than DC-electromagnetic bearings, simultaneous radial, angular and thrust support, motoring and generating capability, and backup mode of operation in case of primary power failure. A prototype is under construction.
Attractive and repulsive Fermi polarons in two dimensions.
Koschorreck, Marco; Pertot, Daniel; Vogt, Enrico; Fröhlich, Bernd; Feld, Michael; Köhl, Michael
2012-05-31
The dynamics of a single impurity in an environment is a fundamental problem in many-body physics. In the solid state, a well known case is an impurity coupled to a bosonic bath (such as lattice vibrations); the impurity and its accompanying lattice distortion form a new entity, a polaron. This quasiparticle plays an important role in the spectral function of high-transition-temperature superconductors, as well as in colossal magnetoresistance in manganites. For impurities in a fermionic bath, studies have considered heavy or immobile impurities which exhibit Anderson's orthogonality catastrophe and the Kondo effect. More recently, mobile impurities have moved into the focus of research, and they have been found to form new quasiparticles known as Fermi polarons. The Fermi polaron problem constitutes the extreme, but conceptually simple, limit of two important quantum many-body problems: the crossover between a molecular Bose-Einstein condensate and a superfluid with BCS (Bardeen-Cooper-Schrieffer) pairing with spin-imbalance for attractive interactions, and Stoner's itinerant ferromagnetism for repulsive interactions. It has been proposed that such quantum phases (and other elusive exotic states) might become realizable in Fermi gases confined to two dimensions. Their stability and observability are intimately related to the theoretically debated properties of the Fermi polaron in a two-dimensional Fermi gas. Here we create and investigate Fermi polarons in a two-dimensional, spin-imbalanced Fermi gas, measuring their spectral function using momentum-resolved photoemission spectroscopy. For attractive interactions, we find evidence for a disputed pairing transition between polarons and tightly bound dimers, which provides insight into the elementary pairing mechanism of imbalanced, strongly coupled two-dimensional Fermi gases. Additionally, for repulsive interactions, we study novel quasiparticles--repulsive polarons--the lifetime of which determines the
Pattern formation in annular systems of repulsive particles
NASA Astrophysics Data System (ADS)
Marschler, Christian; Starke, Jens; Sørensen, Mads P.; Gaididei, Yuri B.; Christiansen, Peter L.
2016-01-01
General particle models with symmetric and asymmetric repulsion are studied and investigated for finite-range and exponential interaction in an annulus. In the symmetric case transitions from one- to multi-lane behavior including multistability are observed for varying particle density and for a varying curvature with fixed density. Hence, the system cannot be approximated by a periodic channel. In the asymmetric case, which is important in pedestrian dynamics, we reveal an inhomogeneous new phase, a traveling wave reminiscent of peristaltic motion.
When do we need attractive-repulsive intermolecular potentials?
Venkattraman, Ayyaswamy
2014-12-09
The role of attractive-repulsive interactions in direct simulation Monte Carlo (DSMC) simulations is studied by comparing with traditional purely repulsive interactions. The larger collision cross section of the long-range LJ potential is shown to result in a higher collision frequency and hence a lower mean free path, by at least a factor of two, for given conditions. This results in a faster relaxation to equilibrium as is shown by comparing the fourth and sixth moments of the molecular velocity distribution obtained using 0-D DSMC simulations. A 1-D Fourier-Couette flow with a large temperature and velocity difference between the walls is used to show that matching transport properties will result in identical solutions using both LJPA and VSS models in the near-continuum regime. However, flows in the transitional regime with Knudsen number, Kn ∼ 0.5 show a dependence on the intermolecular potential in spite of matching the viscosity coefficient due to differences in the collision frequency. Attractive-repulsive potentials should be used when both transport coefficients and collision frequencies should be matched.
Measured long-range repulsive Casimir–Lifshitz forces
Munday, J. N.; Capasso, Federico; Parsegian, V. Adrian
2014-01-01
Quantum fluctuations create intermolecular forces that pervade macroscopic bodies1–3. At molecular separations of a few nanometres or less, these interactions are the familiar van der Waals forces4. However, as recognized in the theories of Casimir, Polder and Lifshitz5–7, at larger distances and between macroscopic condensed media they reveal retardation effects associated with the finite speed of light. Although these long-range forces exist within all matter, only attractive interactions have so far been measured between material bodies8–11. Here we show experimentally that, in accord with theoretical prediction12, the sign of the force can be changed from attractive to repulsive by suitable choice of interacting materials immersed in a fluid. The measured repulsive interaction is found to be weaker than the attractive. However, in both cases the magnitude of the force increases with decreasing surface separation. Repulsive Casimir–Lifshitz forces could allow quantum levitation of objects in a fluid and lead to a new class of switchable nanoscale devices with ultra-low static friction13–15. PMID:19129843
TOPICAL REVIEW Gravitational lensing
NASA Astrophysics Data System (ADS)
Bartelmann, Matthias
2010-12-01
Gravitational lensing has developed into one of the most powerful tools for the analysis of the dark universe. This review summarizes the theory of gravitational lensing, its main current applications and representative results achieved so far. It has two parts. In the first, starting from the equation of geodesic deviation, the equations of thin and extended gravitational lensing are derived. In the second, gravitational lensing by stars and planets, galaxies, galaxy clusters and large-scale structures is discussed and summarized.
ERIC Educational Resources Information Center
Ridgely, Charles T.
2011-01-01
When two gravitating bodies reside in a material medium, Newton's law of universal gravitation must be modified to account for the presence of the medium. A modified expression of Newton's law is known in the literature, but lacks a clear connection with existing gravitational theory. Newton's law in the presence of a homogeneous material medium…
Gravitational mass of relativistic matter and antimatter
NASA Astrophysics Data System (ADS)
Kalaydzhyan, Tigran
2015-12-01
The universality of free fall, the weak equivalence principle (WEP), is a cornerstone of the general theory of relativity, the most precise theory of gravity confirmed in all experiments up to date. The WEP states the equivalence of the inertial, m, and gravitational, mg, masses and was tested in numerous occasions with normal matter at relatively low energies. However, there is no confirmation for the matter and antimatter at high energies. For the antimatter the situation is even less clear - current direct observations of trapped antihydrogen suggest the limits - 65
NASA Astrophysics Data System (ADS)
Fontana, Giorgio
2005-02-01
There is only one experimental proof that gravitational waves exist. With such a limitation, it may seem premature to suggest the possibility that gravitational waves can became a preferred space propulsion technique. The present understanding of the problem indicates that this is not the case. The emission of gravitational waves from astrophysical sources has been confirmed by observation, the respective detection at large distance from the source is difficult and actually we have no confirmation of a successful detection. Therefore the required preliminary discovery has been already made. This opinion is enforced by many different proposals for building the required powerful gravitational wave generators that have recently appeared in the literature and discussed at conferences. It is no longer reasonable to wait for additional confirmation of the existence of gravitational waves to start a program for building generators and testing their possible application to space travel. A vast literature shows that gravitational waves can be employed for space propulsion. Gravitational wave rockets have been proposed, non-linearity of Einstein equations allows the conversion of gravitational waves to a static gravitational field and ``artificial gravity assist'' may become a new way of travelling in space-time. Different approaches to gravitational wave propulsion are reviewed and compared. Gravitational wave propulsion is also compared to traditional rocket propulsion and an undeniable advantage can be demonstrated in terms of efficiency and performance. Testing the predictions will require gravitational wave generators with high power and wavelength short enough for producing high energy densities. Detectors designed for the specific application must be developed, taking into account that non-linearity effects are expected. The study and development of Gravitational wave propulsion is a very challenging endeavor, involving the most complex theories, sophisticated
Electrostatic Repulsion during Ferritin Assembly and Its Screening by Ions.
Sato, Daisuke; Takebe, Satsuki; Kurobe, Atsushi; Ohtomo, Hideaki; Fujiwara, Kazuo; Ikeguchi, Masamichi
2016-01-26
Escherichia coli non-heme-binding ferritin A (EcFtnA) is a spherical cagelike protein that is composed of 24 identical subunits. EcFtnA dissociates into 2-mers under acidic conditions and can reassemble into the native structure when the pH is increased. To understand how electrostatic interactions influence the assembly reaction, the dependence of the process on ionic strength and pH was investigated. The assembly reaction was initiated by stopped-flow mixing of the acid-dissociated EcFtnA solution and high-pH buffer solutions and monitored by time-resolved small-angle X-ray scattering. The rate of assembly increased with increasing ionic strength and decreased with increasing pH from 6 to 8. These dependences were thought to originate from repulsion between assembly units (2-mer in the case of EcFtnA) with the same net charge sign; therefore, to test this assumption, mutants with different net charges (net-charge mutants) were prepared. In buffers with a low ionic strength, the rate of assembly increased with a decreasing net charge. Thus, repulsion between the assembly unit net charges was demonstrated to be an important factor determining the rate of assembly. However, the difference in the assembly rate among net-charge mutants was not significant in buffers with an ionic strength of >0.1. Notably, under such high-ionic strength conditions, the assembly rate increased with an increasing ionic strength, suggesting that local electrostatic interactions are also responsible for the ionic strength dependence of the rate of assembly and are repulsive on average. PMID:26716350
NASA Astrophysics Data System (ADS)
Zheng, Sheng Ming
2012-10-01
In the natural world, people have discovered four kinds of forces: electromagnetic force, gravitation, weak force, and strong force. Although the gravitation has been discovered more than three hundred years, its mechanism of origin is unclear until today. While investigating the origin of gravitation, I do some experiments discover the moving photons produce gravitation. This discovery shows the origin of gravitation. Meanwhile I do some experiments discover the light interference fringes are produced by the gravitation: my discovery demonstrate light is a particle, but is not a wave-particle duality. Furthermore, applications of this discovery to other moving particles show a similar effect. In a word: the micro particle moving produce gravitation and electromagnetic force. Then I do quantity experiment get a general formula: Reveal the essence of gravitational mass and the essence of electric charge; reveal the origin of gravitation and the essence of matter wave. Along this way, I unify the gravitation and electromagnetic force. Namely I find a natural law that from atomic world to star world play in moving track. See website: https://www.lap-publishing.com/catalog/details/store/gb/book/978-3-8473-2658-8/mechanism-of-interaction-in-moving-matter
Semiflexible polymers under good solvent conditions interacting with repulsive walls
NASA Astrophysics Data System (ADS)
Egorov, Sergei A.; Milchev, Andrey; Virnau, Peter; Binder, Kurt
2016-05-01
Solutions of semiflexible polymers confined by repulsive planar walls are studied by density functional theory and molecular dynamics simulations, to clarify the competition between the chain alignment favored by the wall and the depletion caused by the monomer-wall repulsion. A coarse-grained bead-spring model with a bond bending potential is studied, varying both the contour length and the persistence length of the polymers, as well as the monomer concentration in the solution (good solvent conditions are assumed throughout, and solvent molecules are not included explicitly). The profiles of monomer density and pressure tensor components near the wall are studied, and the surface tension of the solution is obtained. While the surface tension slightly decreases with chain length for flexible polymers, it clearly increases with chain length for stiff polymers. Thus, at fixed density and fixed chain length, the surface tension also increases with increasing persistence length. Chain ends always are enriched near the wall, but this effect is much larger for stiff polymers than for flexible ones. Also the profiles of the mean square gyration radius components near the wall and the nematic order parameter are studied to clarify the conditions where wall-induced nematic order occurs.
Semiflexible polymers under good solvent conditions interacting with repulsive walls.
Egorov, Sergei A; Milchev, Andrey; Virnau, Peter; Binder, Kurt
2016-05-01
Solutions of semiflexible polymers confined by repulsive planar walls are studied by density functional theory and molecular dynamics simulations, to clarify the competition between the chain alignment favored by the wall and the depletion caused by the monomer-wall repulsion. A coarse-grained bead-spring model with a bond bending potential is studied, varying both the contour length and the persistence length of the polymers, as well as the monomer concentration in the solution (good solvent conditions are assumed throughout, and solvent molecules are not included explicitly). The profiles of monomer density and pressure tensor components near the wall are studied, and the surface tension of the solution is obtained. While the surface tension slightly decreases with chain length for flexible polymers, it clearly increases with chain length for stiff polymers. Thus, at fixed density and fixed chain length, the surface tension also increases with increasing persistence length. Chain ends always are enriched near the wall, but this effect is much larger for stiff polymers than for flexible ones. Also the profiles of the mean square gyration radius components near the wall and the nematic order parameter are studied to clarify the conditions where wall-induced nematic order occurs. PMID:27155651
Swarming and pattern formation due to selective attraction and repulsion
Romanczuk, Pawel; Schimansky-Geier, Lutz
2012-01-01
We discuss the collective dynamics of self-propelled particles with selective attraction and repulsion interactions. Each particle, or individual, may respond differently to its neighbours depending on the sign of their relative velocity. Thus, it is able to distinguish approaching (coming closer) and retreating (moving away) individuals. This differentiation of the social response is motivated by the response to looming visual stimuli and may be seen as a generalization of the previously proposed escape and pursuit interactions motivated by empirical evidence for cannibalism as a driving force of collective migration in locusts and Mormon crickets. The model can account for different types of behaviour such as pure attraction, pure repulsion or escape and pursuit, depending on the values (signs) of the different response strengths. It provides, in the light of recent experimental results, an interesting alternative to previously proposed models of collective motion with an explicit velocity–alignment interaction. We discuss the derivation of a coarse-grained description of the system dynamics, which allows us to derive analytically the necessary condition for emergence of collective motion. Furthermore, we analyse systematically the onset of collective motion and clustering in numerical simulations of the model for varying interaction strengths. We show that collective motion arises only in a subregion of the parameter space, which is consistent with the analytical prediction and corresponds to an effective escape and/or pursuit response. PMID:24312728
Effects of Agent's Repulsion in 2d Flocking Models
NASA Astrophysics Data System (ADS)
Moussa, Najem; Tarras, Iliass; Mazroui, M'hammed; Boughaleb, Yahya
In nature many animal groups, such as fish schools or bird flocks, clearly display structural order and appear to move as a single coherent entity. In order to understand the complex behavior of these systems, many models have been proposed and tested so far. This paper deals with an extension of the Vicsek model, by including a second zone of repulsion, where each agent attempts to maintain a minimum distance from the others. The consideration of this zone in our study seems to play an important role during the travel of agents in the two-dimensional (2D) flocking models. Our numerical investigations show that depending on the basic ingredients such as repulsion radius (R1), effect of density of agents (ρ) and noise (η), our nonequilibrium system can undergo a kinetic phase transition from no transport to finite net transport. For different values of ρ, kinetic phase diagrams in the plane (η ,R1) are found. Implications of these findings are discussed.
Interaction Versus Entropic Repulsion for Low Temperature Ising Polymers
NASA Astrophysics Data System (ADS)
Ioffe, Dmitry; Shlosman, Senya; Toninelli, Fabio Lucio
2015-03-01
Contours associated to many interesting low-temperature statistical mechanics models (2D Ising model, (2+1)D SOS interface model, etc) can be described as self-interacting and self-avoiding walks on . When the model is defined in a finite box, the presence of the boundary induces an interaction, that can turn out to be attractive, between the contour and the boundary of the box. On the other hand, the contour cannot cross the boundary, so it feels entropic repulsion from it. In various situations of interest (in Caputo et al. Ann. Probab., arXiv:1205.6884, J. Eur. Math. Soc., arXiv:1302.6941, arXiv:1406.1206, Ioffe and Shlosman, in preparation), a crucial technical problem is to prove that entropic repulsion prevails over the pinning interaction: in particular, the contour-boundary interaction should not modify significantly the contour partition function and the related surface tension should be unchanged. Here we prove that this is indeed the case, at least at sufficiently low temperature, in a quite general framework that applies in particular to the models of interest mentioned above.
Friction and Hydration Repulsion Between Hydrogen-Bonding Surfaces
NASA Astrophysics Data System (ADS)
Netz, Roland
2012-02-01
The dynamics and statics of polar surfaces are governed by the hydrogen-bonding network and the interfacial water layer properties. Insight can be gained from all-atomistic simulations with explicit water that reach the experimentally relevant length and time scales. Two connected lines of work will be discussed: 1) On surfaces, the friction coefficient of bound peptides is very low on hydrophobic substrates, which is traced back to the presence of a depletion layer between substrate and water that forms a lubrication layer. Conversely, friction forces on hydrophilic substrates are large. A general friction law is presented and describes the dynamics of hydrogen-bonded matter in the viscous limit. 2) The so-called hydration repulsion between polar surfaces in water is studied using a novel simulation technique that allows to efficiently determine the interaction pressure at constant water chemical potential. The hydration repulsion is shown to be caused by a mixture of water polarization effects and the desorption of interfacial water.
Dissociative ionization of sodium molecules via repulsive Rydberg states
NASA Astrophysics Data System (ADS)
Chen, Hong
In this thesis, an investigation of two color resonance multiphoton ionization (REMPI) and fragmentation processes in Na2 has been performed in combination with Linear Time-of-Flight Mass Spectrometry technique. The ionization and dissociative ionizations channels in the energy range up to 2500cm -1 above the dissociative ionization threshold into Na(3s)+Na ++e have been studied. After a mild supersonic expansion from the beam source, neutral sodium dimers in the ground state have been produced. Two tunable, pulsed lasers excite Na2 molecules via the intermediate A1S+u state to a single ro-vibrational level of the second intermediate 21pig state. Following absorption of a third photon, the total energy is above the dissociation limit into Na(3s) + Na+ + e. Typically, a small portion of atomic ions is produced under our experimental conditions. By varying the total available energy below and through the doubly excited states correlating with the Na(3p)+Na(4s) atom pair, there is no evidence that the doubly excited states positioned in the ionic continuum get involved. By calculation of the expected transition probabilities for all possible channels which can decay directly and indirectly into atomic ions, I find that direct dissociative ionization via 12S+u is impossible. The transition probabilities for dissociative ionization via the repulsive Rydberg states with principal quantum numbers n from 5˜12 converging toward the 12S+u state are three to four orders of magnitude larger than those for direct ionization into the continuum of the X2S+g ground state. These repulsive Rydberg states are much more likely to play a role in the photo-ionization through the intermediate 21Pg state. A semi-classical model which was originally developed for negative ion dissociative attachment (O'MAL'67) describes how dissociative ionization occurs along the repulsive Rydberg states. Its prediction concerning the ratio of atomic to molecular ion production as a function of initial
Astrometric detection of gravitational effects of quantum vacuum
NASA Astrophysics Data System (ADS)
Vecchiato, Alberto; Gai, Mario; Hajdukovic, Dragan
2015-08-01
In a series of recent papers it was suggested that the pairs of virtual particles-antiparticles composing the Quantum Vacuum (QV) can behave like gravitational dipoles with both attractive and repulsive interaction. If verified, this hypothesis would give raise to a series of gravitational effects at different scale length not yet considered in current gravity theories, and it may support galactic and cosmological models alternative to those involving Dark Matter and Dark Energy.Within the boundaries of the Solar System, the most promising targets for testing the gravitational QV conjecture are the binary trans-neptunian objects (TNOs). The gravitational action of the QV, in fact, would manifest itself as an external force inducing an anomalous precession, i.e. an excess shift of the longitude of the pericenter in the orbit of the TNO satellite which, e.g., for the UX25 candidate and under reasonable working hypothesis, was estimated to be about 0.23 arcsec per orbit.In this work we analyze in some detail the feasibility of testing the gravitational QV hypothesis estimating the above effect with ground-based and spaceborne astrometric observations. Several observing scenarios are explored here, including those using conventional and adaptive optics telescopes from ground, some spaceborne telescopes, and by exploring a list of possible candidates.
Gravitational mass of positron from LEP synchrotron losses
NASA Astrophysics Data System (ADS)
Kalaydzhyan, Tigran
2016-07-01
General relativity(GR) is the current description of gravity in modern physics. One of the cornerstones of GR, as well as Newton’s theory of gravity, is the weak equivalence principle (WEP), stating that the trajectory of a freely falling test body is independent of its internal structure and composition. WEP is known to be valid for the normal matter with a high precision. However, due to the rarity of antimatter and weakness of the gravitational forces, the WEP has never been confirmed for antimatter. The current direct bounds on the ratio between the gravitational and inertial masses of the antihydrogen do not rule out a repulsive nature for the antimatter gravity. Here we establish an indirect bound of 0.13% on the difference between the gravitational and inertial masses of the positron (antielectron) from the analysis of synchrotron losses at the Large Electron-Positron collider (LEP). This serves as a confirmation of the conventional gravitational properties of antimatter without common assumptions such as, e.g., coupling of gravity to virtual particles, dynamics of distant astrophysical sources and the nature of absolute gravitational potentials.
Gravitational mass of positron from LEP synchrotron losses
Kalaydzhyan, Tigran
2016-01-01
General relativity(GR) is the current description of gravity in modern physics. One of the cornerstones of GR, as well as Newton’s theory of gravity, is the weak equivalence principle (WEP), stating that the trajectory of a freely falling test body is independent of its internal structure and composition. WEP is known to be valid for the normal matter with a high precision. However, due to the rarity of antimatter and weakness of the gravitational forces, the WEP has never been confirmed for antimatter. The current direct bounds on the ratio between the gravitational and inertial masses of the antihydrogen do not rule out a repulsive nature for the antimatter gravity. Here we establish an indirect bound of 0.13% on the difference between the gravitational and inertial masses of the positron (antielectron) from the analysis of synchrotron losses at the Large Electron-Positron collider (LEP). This serves as a confirmation of the conventional gravitational properties of antimatter without common assumptions such as, e.g., coupling of gravity to virtual particles, dynamics of distant astrophysical sources and the nature of absolute gravitational potentials. PMID:27461548
Gravitational mass of positron from LEP synchrotron losses.
Kalaydzhyan, Tigran
2016-01-01
General relativity(GR) is the current description of gravity in modern physics. One of the cornerstones of GR, as well as Newton's theory of gravity, is the weak equivalence principle (WEP), stating that the trajectory of a freely falling test body is independent of its internal structure and composition. WEP is known to be valid for the normal matter with a high precision. However, due to the rarity of antimatter and weakness of the gravitational forces, the WEP has never been confirmed for antimatter. The current direct bounds on the ratio between the gravitational and inertial masses of the antihydrogen do not rule out a repulsive nature for the antimatter gravity. Here we establish an indirect bound of 0.13% on the difference between the gravitational and inertial masses of the positron (antielectron) from the analysis of synchrotron losses at the Large Electron-Positron collider (LEP). This serves as a confirmation of the conventional gravitational properties of antimatter without common assumptions such as, e.g., coupling of gravity to virtual particles, dynamics of distant astrophysical sources and the nature of absolute gravitational potentials. PMID:27461548
Superconductivity from a Long-Range Repulsive Interaction
NASA Astrophysics Data System (ADS)
Onari, S.; Arita, R.; Kuroki, K.; Aoki, H.
2006-09-01
The lattice model with short-range interactions (exemplified by the Hubbard model) is known to exhibit quite different features from those in the electron gas with the long-range Coulomb interaction. In order to explore how they cross over to each other, we have studied an extended Hubbard model which includes repulsions up to the 12th neighbors with the simplified fluctuation exchange (FLEX) approximation for the square lattice. We have found that (i) in the most dilute density region, spin and charge fluctuations become comparable, and s- and p-waves superconductivity become dominant, in agreement with the result for the electron gas by Takada, while (ii) the dominant spin fluctuation and its reflection on dx2-y2 and dxy pairing, both the effect of lattice structure, persists well away (n ≳ 0.2) from the half filling. 2006 American Institute of Physics
Phantom energy mediates a long-range repulsive force.
Amendola, Luca
2004-10-29
Scalar field models with nonstandard kinetic terms have been proposed in the context of k inflation, of Born-Infeld Lagrangians, of phantom energy and, more in general, of low-energy string theory. In general, scalar fields are expected to couple to matter inducing a new interaction. In this Letter I derive the cosmological perturbation equations and the Yukawa correction to gravity for such general models. I find three interesting results: first, when the field behaves as phantom energy (equation of state less than -1), then the coupling strength is negative, inducing a long-range repulsive force; second, the dark-energy field might cluster on astrophysical scales; third, applying the formalism to a Brans-Dicke theory with a general kinetic term it is shown that its Newtonian effects depend on a single parameter that generalizes the Brans-Dicke constant. PMID:15525149
Repulsive effects of hydrophobic diamond thin films on biomolecule detection
NASA Astrophysics Data System (ADS)
Ruslinda, A. Rahim; Ishiyama, Y.; Penmatsa, V.; Ibori, S.; Kawarada, H.
2015-02-01
The repulsive effect of hydrophobic diamond thin film on biomolecule detection, such as single-nucleotide polymorphisms and human immunodeficiency virus type 1 trans-activator of transcription peptide protein detection, was investigated using a mixture of a fluorine-, amine-, and hydrogen-terminated diamond surfaces. These chemical modifications lead to the formation of a surface that effectively resists the nonspecific adsorption of proteins and other biomolecules. The effect of fluorine plasma treatment on elemental composition was also investigated via X-ray photoelectron spectroscopy (XPS). XPS results revealed a fluorocarbon layer on the diamond thin films. The contact angle measurement results indicated that the fluorine-treated diamond thin films were highly hydrophobic with a surface energy value of ∼25 mN/m.
Nonperturbative effects on the ferromagnetic transition in repulsive Fermi gases
NASA Astrophysics Data System (ADS)
He, Lianyi; Huang, Xu-Guang
2012-04-01
It is generally believed that a dilute spin-(1)/(2) Fermi gas with repulsive interactions can undergo a ferromagnetic phase transition to a spin-polarized state at a critical gas parameter (kFa)c. Previous theoretical predictions of the ferromagnetic phase transition have been based on the perturbation theory, which treats the gas parameter as a small number. On the other hand, Belitz, Kirkpatrick, and Vojta (BKV) have argued that the phase transition in clean itinerant ferromagnets is generically of first order at low temperatures, due to the correlation effects that lead to a nonanalytic term in the free energy. The second-order perturbation theory predicts a first-order phase transition at (kFa)c=1.054, consistent with the BKV argument. However, since the critical gas parameter is expected to be of order O(1), perturbative predictions may be unreliable. In this paper we study the nonperturbative effects on the ferromagnetic phase transition by summing the particle-particle ladder diagrams to all orders in the gas parameter. We consider a universal repulsive Fermi gas where the effective range effects can be neglected, which can be realized in a two-component Fermi gas of 6Li atoms by using a nonadiabatic field switch to the upper branch of a Feshbach resonance with a positive s-wave scattering length. Our theory predicts a second-order phase transition, which indicates that ferromagnetic transition in dilute Fermi gases is possibly a counterexample to the BKV argument. The predicted critical gas parameter (kFa)c=0.858 is in good agreement with the recent quantum Monte Carlo result (kFa)c=0.86 for a nearly zero-range potential [S. Pilati , Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.105.030405 105, 030405 (2010)]. We also compare the spin susceptibility with the quantum Monte Carlo result and find good agreement.
From repulsive to attractive glass: A rheological investigation.
Zhou, Zhi; Jia, Di; Hollingsworth, Javoris V; Cheng, He; Han, Charles C
2015-12-21
Linear rheological properties and yielding behavior of polystyrene core and poly (N-isopropylacrylamide) (PNIPAM) shell microgels were investigated to understand the transition from repulsive glass (RG) to attractive glass (AG) and the A3 singularity. Due to the volume phase transition of PNIPAM in aqueous solution, the microgel-microgel interaction potential gradually changes from repulsive to attractive. In temperature and frequency sweep experiments, the storage modulus (G') and loss modulus (G″) increased discontinuously when crossing the RG-to-AG transition line, while G' at low frequency exhibited a different volume fraction (Φ) dependence. By fitting the data of RG and AG, and then extrapolating to high volume fraction, the difference between RG and AG decreased and the existence of A3 singularity was verified. Dynamic strain sweep experiments were conducted to confirm these findings. RG at 25 °C exhibited one-step yielding, whereas AG at 40 °C showed a typical two-step yielding behavior; the first yielding strain remained constant and the second one gradually decreased as the volume fraction increased. By extrapolating the second yield strain to that of the first one, the predicted A3 singularity was at 0.61 ± 0.02. At 37 °C, when Φeff = 0.59, AG showed one step yielding as the length of the attractive bond increased. The consistency and agreement of the experimental results reaffirmed the existence of A3 singularity, where the yielding behavior of RG and AG became identical. PMID:26696073
Those Elusive Gravitational Waves
ERIC Educational Resources Information Center
MOSAIC, 1976
1976-01-01
The presence of gravitational waves was predicted by Einstein in his theory of General Relativity. Since then, scientists have been attempting to develop a detector sensitive enough to measure these cosmic signals. Once the presence of gravitational waves is confirmed, scientists can directly study star interiors, galaxy cores, or quasars. (MA)
Advanced Gravitational Wave Detectors
NASA Astrophysics Data System (ADS)
Blair, D. G.; Howell, E. J.; Ju, L.; Zhao, C.
2012-02-01
Part I. An Introduction to Gravitational Wave Astronomy and Detectors: 1. Gravitational waves D. G. Blair, L. Ju, C. Zhao and E. J. Howell; 2. Sources of gravitational waves D. G. Blair and E. J. Howell; 3. Gravitational wave detectors D. G. Blair, L. Ju, C. Zhao, H. Miao, E. J. Howell, and P. Barriga; 4. Gravitational wave data analysis B. S. Sathyaprakash and B. F. Schutz; 5. Network analysis L. Wen and B. F. Schutz; Part II. Current Laser Interferometer Detectors: Three Case Studies: 6. The Laser Interferometer Gravitational-Wave Observatory P. Fritschel; 7. The VIRGO detector S. Braccini; 8. GEO 600 H. Lück and H. Grote; Part III. Technology for Advanced Gravitational Wave Detectors: 9. Lasers for high optical power interferometers B. Willke and M. Frede; 10. Thermal noise, suspensions and test masses L. Ju, G. Harry and B. Lee; 11. Vibration isolation: Part 1. Seismic isolation for advanced LIGO B. Lantz; Part 2. Passive isolation J-C. Dumas; 12. Interferometer sensing and control P. Barriga; 13. Stabilizing interferometers against high optical power effects C. Zhao, L. Ju, S. Gras and D. G. Blair; Part IV. Technology for Third Generation Gravitational Wave Detectors: 14. Cryogenic interferometers J. Degallaix; 15. Quantum theory of laser-interferometer GW detectors H. Miao and Y. Chen; 16. ET. A third generation observatory M. Punturo and H. Lück; Index.
Solitary state at the edge of synchrony in ensembles with attractive and repulsive interactions.
Maistrenko, Yuri; Penkovsky, Bogdan; Rosenblum, Michael
2014-06-01
We discuss the desynchronization transition in networks of globally coupled identical oscillators with attractive and repulsive interactions. We show that, if attractive and repulsive groups act in antiphase or close to that, a solitary state emerges with a single repulsive oscillator split up from the others fully synchronized. With further increase of the repulsing strength, the synchronized cluster becomes fuzzy and the dynamics is given by a variety of stationary states with zero common forcing. Intriguingly, solitary states represent the natural link between coherence and incoherence. The phenomenon is described analytically for phase oscillators with sine coupling and demonstrated numerically for more general amplitude models. PMID:25019710
Progress in gravitational wave detection
NASA Astrophysics Data System (ADS)
Cheng, Jing-Quan; Yang, De-Hua
2005-09-01
General theory of Einstein's relativity predicts the existence of gravitational wave when mass is accelerated. However, no material has direct effect when the gravitational wave passes. Therefore, gravitational wave can only be detected indirectly. The effort in gravitational wave detection was started in the 60s of last century by using a huge cylinder of aluminum. This paper introduced all the relevant projects in the gravitational wave detection. These projects include Weber's bar, Laser interferometer Gravitational wave Detector (LGD), Laser Interferometer Gravitational wave Observatory (LIGO), GEO600, VIRGO, TAMA300, Advanced LIGO, Large scale Cryogenic Gravitational wave Telescope (LCGO), and Laser Interferometer Space Antenna (LISA).
NASA Astrophysics Data System (ADS)
Conklin, John
2016-03-01
With the expected direct detection of gravitational waves by Advanced LIGO and pulsar timing arrays in the near future, and with the recent launch of LISA Pathfinder this can arguably be called the decade of gravitational waves. Low frequency gravitational waves in the mHz range, which can only be observed from space, provide the richest science and complement high frequency observatories on the ground. A space-based observatory will improve our understanding of the formation and growth of massive black holes, create a census of compact binary systems in the Milky Way, test general relativity in extreme conditions, and enable searches for new physics. LISA, by far the most mature concept for detecting gravitational waves from space, has consistently ranked among the nation's top priority large science missions. In 2013, ESA selected the science theme ``The Gravitational Universe'' for its third large mission, L3, under the Cosmic Visions Program, with a planned launch date of 2034. NASA has decided to join with ESA on the L3 mission as a junior partner and has recently assembled a study team to provide advice on how NASA might contribute to the European-led mission. This talk will describe these efforts and the activities of the Gravitational Wave Science Interest Group and the L3 Study Team, which will lead to the first space-based gravitational wave observatory.
Electrostatic repulsion of charged pith balls hanging from strings
NASA Astrophysics Data System (ADS)
Mungan, Carl E.
2011-01-01
Two positively charged pith balls hang from a nail at the end of equal-length strings in Earth's surface gravitational field. The problem consists in finding each of the hanging angles when the balls do not necessarily have the same mass or charge. The solution is an excellent exercise in developing two skills: wisely choosing the coordinate axes in a free-body diagram, and correctly interpreting the roots and limits of a numerical solution. The treatment is accessible to undergraduate physics majors in their first or second year of physics courses.
Gravitational scaling dimensions
Hamber, Herbert W.
2000-06-15
A model for quantized gravitation based on simplicial lattice discretization is studied in detail using a comprehensive finite size scaling analysis combined with renormalization group methods. The results are consistent with a value for the universal critical exponent for gravitation, {nu}=1/3, and suggest a simple relationship between Newton's constant, the gravitational correlation length and the observable average space-time curvature. Some perhaps testable phenomenological implications of these results are discussed. To achieve a high numerical accuracy in the evaluation of the lattice path integral a dedicated parallel machine was assembled. (c) 2000 The American Physical Society.
Solid-solid transitions induced by repulsive interactions revisited.
Navascués, G; Velasco, E; Mederos, L
2016-10-19
We revisit a problem already studied 15 years ago by us in collaboration with Stell and Hemmer: the isostructural solid-solid transitions induced by repulsive particle interactions exhibited by classical systems interacting via the Stell-Hemmer potentials. The full phase diagram in the crystal region is obtained by applying a perturbation theory for classical solids used during our collaboration with Stell. Also, the performance of such a theory is now tested by comparing the perturbative phase diagram with that obtained from computer simulations. The latter was calculated using a recently refined method to obtain the free-energy of crystals by means of Monte Carlo simulations. The perturbation theory captures the correct topology and correctly identifies the stable, fcc and bcc, phases. In addition, the theory predicts the occurrence of special points: a point where the two stable structures coexist at the same density, and two critical points terminating the corresponding isostructural phase transitions for fcc and bcc phases. The location of some of these features in the phase diagram is predicted almost quantitatively. However, phase boundaries involving the non-compact bcc phase are much less accurate, a problem that can be traced to the poor representation used for the bcc phase of the reference, hard-sphere, system. PMID:27546295
A gradient field defeats the inherent repulsion between magnetic nanorods
Gu, Yu; Burtovyy, Ruslan; Custer, John; Luzinov, Igor; Kornev, Konstantin G.
2014-01-01
When controlling the assembly of magnetic nanorods and chains of magnetic nanoparticles, it is extremely challenging to bring them together side by side while keeping a desired spacing between their axes. We show that this challenge can be successfully resolved by using a non-uniform magnetic field that defeats an inherent repulsion between nanorods. Nickel nanorods were suspended in a viscous film and a non-uniform field was used to control their placement. The in-plane movement of nanorods was tracked with a high-speed camera and a detailed image analysis was conducted to quantitatively characterize the behaviour of the nanorods. The analysis focused on the behaviour of a pair of neighbour nanorods, and a corresponding dynamic model was formulated and investigated. The complex two-dimensional dynamics of a nanorod pair was analysed analytically and numerically, and a phase portrait was constructed. Using this phase portrait, we classified the nanorod behaviour and revealed the experimental conditions in which nanorods could be placed side by side. Dependence of the distance between a pair of neighbour nanorods on physical parameters was analysed. With the aid of the proposed theory, one can build different lattices and control their spacing by applying different field gradients. PMID:26064550
Highly effective photonic cue for repulsive axonal guidance.
Black, Bryan J; Gu, Ling; Mohanty, Samarendra K
2014-01-01
In vivo nerve repair requires not only the ability to regenerate damaged axons, but most importantly, the ability to guide developing or regenerating axons along paths that will result in functional connections. Furthermore, basic studies in neuroscience and neuro-electronic interface design require the ability to construct in vitro neural circuitry. Both these applications require the development of a noninvasive, highly effective tool for axonal growth-cone guidance. To date, a myriad of technologies have been introduced based on chemical, electrical, mechanical, and hybrid approaches (such as electro-chemical, optofluidic flow and photo-chemical methods). These methods are either lacking in desired spatial and temporal selectivity or require the introduction of invasive external factors. Within the last fifteen years however, several attractive guidance cues have been developed using purely light based cues to achieve axonal guidance. Here, we report a novel, purely optical repulsive guidance technique that uses low power, near infrared light, and demonstrates the guidance of primary goldfish retinal ganglion cell axons through turns of up to 120 degrees and over distances of ∼90 µm. PMID:24717339
Highly Effective Photonic Cue for Repulsive Axonal Guidance
Black, Bryan J.; Gu, Ling; Mohanty, Samarendra K.
2014-01-01
In vivo nerve repair requires not only the ability to regenerate damaged axons, but most importantly, the ability to guide developing or regenerating axons along paths that will result in functional connections. Furthermore, basic studies in neuroscience and neuro-electronic interface design require the ability to construct in vitro neural circuitry. Both these applications require the development of a noninvasive, highly effective tool for axonal growth-cone guidance. To date, a myriad of technologies have been introduced based on chemical, electrical, mechanical, and hybrid approaches (such as electro-chemical, optofluidic flow and photo-chemical methods). These methods are either lacking in desired spatial and temporal selectivity or require the introduction of invasive external factors. Within the last fifteen years however, several attractive guidance cues have been developed using purely light based cues to achieve axonal guidance. Here, we report a novel, purely optical repulsive guidance technique that uses low power, near infrared light, and demonstrates the guidance of primary goldfish retinal ganglion cell axons through turns of up to 120 degrees and over distances of ∼90 µm. PMID:24717339
Kinematic Repulsions Between Inertial Systems in AN Expanding Inflationary Universe
NASA Astrophysics Data System (ADS)
Savickas, D.
2013-09-01
The cosmological background radiation is observed to be isotropic only within a coordinate system that is at rest relative to its local Hubble drift. This indicates that the Hubble motion describes the recessional motion of an inertial system that is at rest relative to its local Hubble drift. It is shown that when the Hubble parameter is kinematically defined directly in terms of the positions and velocities of mass particles in the universe, it then also defines inertial systems themselves in terms of the distribution and motion of mass particles. It is independent of the velocity of photons because photons always have a speed c relative to the inertial system in which they are located. Therefore the definition of their velocity depends on the definition of the Hubble parameter itself and cannot be used to define H. The derivative of the kinematically defined Hubble parameter with respect to time is shown to always be positive and highly repulsive at the time of the origin of the universe. A model is used which describes a universe that is balanced at the time of its origin so that H approaches zero as the universe expands to infinity.
Cell adhesion. Competition between nonspecific repulsion and specific bonding.
Bell, G I; Dembo, M; Bongrand, P
1984-01-01
We develop a thermodynamic calculus for the modeling of cell adhesion. By means of this approach, we are able to compute the end results of competition between the formation of specific macromolecular bridges and nonspecific repulsion arising from electrostatic forces and osmotic (steric stabilization) forces. Using this calculus also allows us to derive in a straightforward manner the effects of cell deformability, the Young's modulus for stretching of bridges, diffusional mobility of receptors, heterogeneity of receptors, variation in receptor number, and the strength of receptor-receptor binding. The major insight that results from our analysis concerns the existence and characteristics of two phase transitions corresponding, respectively, to the onset of stable cell adhesion and to the onset of maximum cell-cell or cell-substrate contact. We are also able to make detailed predictions of the equilibrium contact area, equilibrium number of bridges, and the cell-cell or cell-substrate separation distance. We illustrate how our approach can be used to improve the analysis of experimental data, by means of two concrete examples. PMID:6743742
Twisted toroidal vortex solitons in inhomogeneous media with repulsive nonlinearity.
Kartashov, Yaroslav V; Malomed, Boris A; Shnir, Yasha; Torner, Lluis
2014-12-31
Toroidal modes in the form of so-called Hopfions, with two independent winding numbers, a hidden one (twist s), which characterizes a circular vortex thread embedded into a three-dimensional soliton, and the vorticity around the vertical axis (m), appear in many fields, including field theory, ferromagnetics, and semi- and superconductors. Such topological states are normally generated in multicomponent systems, or as trapped quasilinear modes in toroidal potentials. We uncover that stable solitons with this structure can be created, without any linear potential, in the single-component setting with the strength of repulsive nonlinearity growing fast enough from the center to the periphery, for both steep and smooth modulation profiles. Toroidal modes with s=1 and vorticity m=0, 1, 2 are produced. They are stable for m≤1, and do not exist for s>1. An approximate analytical solution is obtained for the twisted ring with s=1, m=0. Under the application of an external torque, it rotates like a solid ring. The setting can be implemented in a Bose-Einstein condensate (BEC) by means of the Feshbach resonance controlled by inhomogeneous magnetic fields. PMID:25615341
On long-range forces of repulsion between biological cells
NASA Astrophysics Data System (ADS)
Derjaguin, B. V.; Golovanov, M. V.
1992-05-01
We have established experimentally that when biological cells, for example, blood, are suspended in concentrated solutions of inorganic electrolytes (for instance, in a 15% solution of sodium chloride) then around some cells (leucocytes, especially tumour cells) there form haloes, i.e., circular spaces free from background cells (erythrocytes, yeast cells, colloidal particles of Indian ink). In the medium made up of erythrocytes the haloes form during 5-10 min as a result of the background cells drawing apart from the central halo-forming cell (HFC) at a distance of 10-100 μm and more. In the medium made of the Indian ink particles, the haloes form during 2-4 s and attain a thickness of about 10-20 μm. The erythrocytes and the haloes forming in their medium can be preserved for about three to five days at room temperature. It has been established that, when tumour HFCs are present at sufficient concentrations, they form hexagonal periodic structures having a mean spacing between cells of up to 60 μm. The authors put forward as one probable suggestion that the formation of haloes is largely determined by long-range repulsive forces arising from the phenomenon of diffusiophoresis generated by the diffusion currents that emerge from the surface of halo-forming cells.
Superfluid state of repulsively interacting three-component fermionic atoms in optical lattices
NASA Astrophysics Data System (ADS)
Suga, Sei-Ichiro; Inaba, Kensuke
2013-03-01
We investigate the superfluid state of repulsively interacting three-component (color) fermionic atoms in optical lattices using Feynman diagrammatic approaches and the dynamical mean field theory. When the anisotropy of the three repulsive interactions is strong, atoms of two of the three colors form Cooper pairs and atoms of the third color remain a Fermi liquid. This superfluid emerges close to half filling at which the Mott insulating state characteristic of the three-component repulsive fermions appears. An effective attractive interaction is induced by density fluctuations of the third-color atoms. The superfluid state is stable against the phase separation that occurs in the strongly repulsive region. We determine the phase diagrams in terms of temperature, filling, and the anisotropy of the repulsive interactions. This work was supported by Grant-in-Aid for Scientific Research (C) (No. 23540467) from the Japan Society for the Promotion of Science.
FLRT Structure: Balancing Repulsion and Cell Adhesion in Cortical and Vascular Development
Seiradake, Elena; del Toro, Daniel; Nagel, Daniel; Cop, Florian; Härtl, Ricarda; Ruff, Tobias; Seyit-Bremer, Gönül; Harlos, Karl; Border, Ellen Clare; Acker-Palmer, Amparo; Jones, E. Yvonne; Klein, Rüdiger
2014-01-01
Summary FLRTs are broadly expressed proteins with the unique property of acting as homophilic cell adhesion molecules and as heterophilic repulsive ligands of Unc5/Netrin receptors. How these functions direct cell behavior and the molecular mechanisms involved remain largely unclear. Here we use X-ray crystallography to reveal the distinct structural bases for FLRT-mediated cell adhesion and repulsion in neurons. We apply this knowledge to elucidate FLRT functions during cortical development. We show that FLRTs regulate both the radial migration of pyramidal neurons, as well as their tangential spread. Mechanistically, radial migration is controlled by repulsive FLRT2-Unc5D interactions, while spatial organization in the tangential axis involves adhesive FLRT-FLRT interactions. Further, we show that the fundamental mechanisms of FLRT adhesion and repulsion are conserved between neurons and vascular endothelial cells. Our results reveal FLRTs as powerful guidance factors with structurally encoded repulsive and adhesive surfaces. PMID:25374360
NASA Astrophysics Data System (ADS)
seyithocuk; jjeherrera; eltodesukane; GrahamRounce; rloldershaw; Beaker, Dr; Sandhu, G. S.; Ophiuchi
2016-03-01
In reply to the news article on the LIGO collaboration's groundbreaking detection of gravitational waves, first predicted by Einstein 100 years ago, from two black holes colliding (pp5, 6-7 and http://ow.ly/Ylsyt).
Observation of Gravitational Waves
NASA Astrophysics Data System (ADS)
Gonzalez, Gabriela
2016-06-01
On September 14 2015, the two LIGO gravitational wave detectors in Hanford, Washington and Livingston, Louisiana registered a nearly simultaneous signal with time-frequency properties consistent with gravitational-wave emission by the merger of two massive compact objects. Further analysis of the signals by the LIGO Scientific Collaboration and Virgo Collaboration revealed that the gravitational waves detected by LIGO came from the merger of a binary black hole (BBH) system approximately 420 Mpc distant (z=0.09) with constituent masses of 36 and 29 M_sun. I will describe the details of the observation, the status of ground-based interferometric detectors, and prospects for future observations in the new era of gravitational wave astronomy.
Relativistic theory of gravitation
Logunov, A.A.; Mestvirishvili, M.A.
1986-01-01
In the present paper a relativistic theory of gravitation (RTG) is unambiguously constructed on the basis of the special relativity and geometrization principle. In this a gravitational field is treated as the Faraday--Maxwell spin-2 and spin-0 physical field possessing energy and momentum. The source of a gravitational field is the total conserved energy-momentum tensor of matter and of a gravitational field in Minkowski space. In the RTG the conservation laws are strictly fulfilled for the energy-moment and for the angular momentum of matter and a gravitational field. The theory explains the whole available set of experiments on gravity. By virtue of the geometrization principle, the Riemannian space in our theory is of field origin, since it appears as an effective force space due to the action of a gravitational field on matter. The RTG leads to an exceptionally strong prediction: The universe is not closed but just ''flat.'' This suggests that in the universe a ''missing mass'' should exist in a form of matter.
NASA Astrophysics Data System (ADS)
Finn, Lee Samuel
2012-03-01
If two black holes collide in a vacuum, can they be observed? Until recently, the answer would have to be "no." After all, how would we observe them? Black holes are "naked" mass: pure mass, simple mass, mass devoid of any matter whose interactions might lead to the emission of photons or neutrinos, or any electromagnetic fields that might accelerate cosmic rays or leave some other signature that we could observe in our most sensitive astronomical instruments. Still, black holes do have mass. As such, they interact—like all mass—gravitationally. And the influence of gravity, like all influences, propagates no faster than that universal speed we first came to know as the speed of light. The effort to detect that propagating influence, which we term as gravitational radiation or gravitational waves, was initiated just over 50 years ago with the pioneering work of Joe Weber [1] and has been the object of increasingly intense experimental effort ever since. Have we, as yet, detected gravitational waves? The answer is still "no." Nevertheless, the accumulation of the experimental efforts begun fifty years ago has brought us to the point where we can confidently say that gravitational waves will soon be detected and, with that first detection, the era of gravitational wave astronomy—the observational use of gravitational waves, emitted by heavenly bodies—will begin. Data analysis for gravitational wave astronomy is, today, in its infancy and its practitioners have much to learn from allied fields, including machine learning. Machine learning tools and techniques have not yet been applied in any extensive or substantial way to the study or analysis of gravitational wave data. It is fair to say that this owes principally to the fields relative youth and not to any intrinsic unsuitability of machine learning tools to the analysis problems the field faces. Indeed, the nature of many of the analysis problems faced by the field today cry-out for the application of
Water anomalous thermodynamics, attraction, repulsion, and hydrophobic hydration
NASA Astrophysics Data System (ADS)
Cerdeiriña, Claudio A.; Debenedetti, Pablo G.
2016-04-01
A model composed of van der Waals-like and hydrogen bonding contributions that simulates the low-temperature anomalous thermodynamics of pure water while exhibiting a second, liquid-liquid critical point [P. H. Poole et al., Phys. Rev. Lett. 73, 1632 (1994)] is extended to dilute solutions of nonionic species. Critical lines emanating from such second critical point are calculated. While one infers that the smallness of the water molecule may be a relevant factor for those critical lines to move towards experimentally accessible regions, attention is mainly focused on the picture our model draws for the hydration thermodynamics of purely hydrophobic and amphiphilic non-electrolyte solutes. We first focus on differentiating solvation at constant volume from the corresponding isobaric process. Both processes provide the same viewpoint for the low solubility of hydrophobic solutes: it originates from the combination of weak solute-solvent attractive interactions and the specific excluded-volume effects associated with the small molecular size of water. However, a sharp distinction is found when exploring the temperature dependence of hydration phenomena since, in contrast to the situation for the constant-V process, the properties of pure water play a crucial role at isobaric conditions. Specifically, the solubility minimum as well as enthalpy and entropy convergence phenomena, exclusively ascribed to isobaric solvation, are closely related to water's density maximum. Furthermore, the behavior of the partial molecular volume and the partial molecular isobaric heat capacity highlights the interplay between water anomalies, attraction, and repulsion. The overall picture presented here is supported by experimental observations, simulations, and previous theoretical results.
Water anomalous thermodynamics, attraction, repulsion, and hydrophobic hydration.
Cerdeiriña, Claudio A; Debenedetti, Pablo G
2016-04-28
A model composed of van der Waals-like and hydrogen bonding contributions that simulates the low-temperature anomalous thermodynamics of pure water while exhibiting a second, liquid-liquid critical point [P. H. Poole et al., Phys. Rev. Lett. 73, 1632 (1994)] is extended to dilute solutions of nonionic species. Critical lines emanating from such second critical point are calculated. While one infers that the smallness of the water molecule may be a relevant factor for those critical lines to move towards experimentally accessible regions, attention is mainly focused on the picture our model draws for the hydration thermodynamics of purely hydrophobic and amphiphilic non-electrolyte solutes. We first focus on differentiating solvation at constant volume from the corresponding isobaric process. Both processes provide the same viewpoint for the low solubility of hydrophobic solutes: it originates from the combination of weak solute-solvent attractive interactions and the specific excluded-volume effects associated with the small molecular size of water. However, a sharp distinction is found when exploring the temperature dependence of hydration phenomena since, in contrast to the situation for the constant-V process, the properties of pure water play a crucial role at isobaric conditions. Specifically, the solubility minimum as well as enthalpy and entropy convergence phenomena, exclusively ascribed to isobaric solvation, are closely related to water's density maximum. Furthermore, the behavior of the partial molecular volume and the partial molecular isobaric heat capacity highlights the interplay between water anomalies, attraction, and repulsion. The overall picture presented here is supported by experimental observations, simulations, and previous theoretical results. PMID:27131551
Repulsive interactions in quantum Hall systems as a pairing problem
NASA Astrophysics Data System (ADS)
Ortiz, G.; Nussinov, Z.; Dukelsky, J.; Seidel, A.
2013-10-01
A subtle relation between quantum Hall physics and the phenomenon of pairing is unveiled. By use of second quantization, we establish a connection between (i) a broad class of rotationally symmetric two-body interactions within the lowest Landau level and (ii) integrable hyperbolic Richardson-Gaudin-type Hamiltonians that arise in (px+ipy) superconductivity. Specifically, we show that general Haldane pseudopotentials (and their sums) can be expressed as a sum of repulsive noncommuting (px+ipy)-type pairing Hamiltonians. The determination of the spectrum and individual null spaces of each of these noncommuting Richardson-Gaudin-type Hamiltonians is nontrivial yet is Bethe ansatz solvable. For the Laughlin sequence, it is observed that this problem is frustration free and zero-energy ground states lie in the common null space of all of these noncommuting Hamiltonians. This property allows for the use of a new truncated basis of pairing configurations in which to express Laughlin states at general filling factors. We prove separability of arbitrary Haldane pseudopotentials, providing explicit expressions for their second quantized forms, and further show by explicit construction how to exploit the topological equivalence between different geometries (disk, cylinder, and sphere) sharing the same topological genus number, in the second quantized formalism, through similarity transformations. As an application of the second quantized approach, we establish a “squeezing principle” that applies to the zero modes of a general class of Hamiltonians, which includes but is not limited to Haldane pseudopotentials. We also show how one may establish (bounds on) “incompressible filling factors” for those Hamiltonians. By invoking properties of symmetric polynomials, we provide explicit second quantized quasihole generators; the generators that we find directly relate to bosonic chiral edge modes and further make aspects of dimensional reduction in the quantum Hall systems
Sources of gravitational waves
NASA Technical Reports Server (NTRS)
Schutz, Bernard F.
1989-01-01
Sources of low frequency gravitational radiation are reviewed from an astrophysical point of view. Cosmological sources include the formation of massive black holes in galactic nuclei, the capture by such holes of neutron stars, the coalescence of orbiting pairs of giant black holes, and various means of producing a stochastic background of gravitational waves in the early universe. Sources local to our Galaxy include various kinds of close binaries and coalescing binaries. Gravitational wave astronomy can provide information that no other form of observing can supply; in particular, the positive identification of a cosmological background originating in the early universe would be an event as significant as was the detection of the cosmic microwave background.
Gravitational signatures of antiparticles:a cosmic perspective
NASA Astrophysics Data System (ADS)
Al Dallal, Shawqi
The gravitational signature of antimatter has received growing interest during the past few decades. Much of the theoretical work in ordinary tensor gravity rules out any difference in the gravitational interaction of matter and antimatter. In field theories the exchange of even-spin bosons, such as the spin-2 graviton or its spin-0 partner, generates attractive forces, while the exchange of odd bosons, such as the photon or the postulated spin-1 graviton generates repulsive forces. The CPT theorem is at the origin of the argument that the exchange of even-spin bosons produces a universally attractive force field. So far, it has been impossible to construct a CPT-violating theory in flat spacetime. However, in curved spacetime, no generalization of the CPT theorem has been unequivocally demonstrated and its validity is open to question. Recently, experiments at the LEAR (Low Energy Accumulating Ring) at CERN have shown a surprising result for a fraction (3%) of antiprotons annihilated by protons of He3 nuclei. The annihilation process was retarded by as much as 10 to the power 8 times the value derived from theoretical calculations of Enrico Fermi and Edward Teller. These results are in good agreement with a formula introduced earlier by certain authors describing the time annihilation of anti-atoms by atoms. The motivation for investigating this problem is that a repulsive field between matter and antimatter may have drastic consequences on certain cosmic issues, such as the early phase of the Big Bang, Hawking radiation, and virtual particle production and annihilation. In the first part of this work we discuss the various theoretical arguments supporting or refuting the gravitational attraction between matter and antimatter, with emphasis on the CPT theorem. In the second part, we address the consequences of certain cosmic issues that arise from this problem. Finally, we propose an experimental test to clarify the nature of matter-antimatter interactions.
Pioneering in gravitational physiology
NASA Technical Reports Server (NTRS)
Soffen, G. A.
1983-01-01
Gravity affects biology at almost all levels above that of the cell organelle. Attention is presently given to progress made in the understanding of gravitational effects through studies employing centrifuges, clinostats, inverted preparations, linear devices, water immersion, free fall, and short- and long-term spaceflight. The cardiovascular changes which cause malaise and illness during the first few days of extended space missions are the direct result of fluid translocation from the lower extremities. Upon reentry, there is hypovolumnia and a cardiovascular deconditioning that can include tachycardia, changes in arterial blood pressure, narrow pulse pressure, and syncope. Attention is also given to NASA's gravitational physiology reseach program.
Gravitation: Foundations and Frontiers
NASA Astrophysics Data System (ADS)
Padmanabhan, T.
2010-01-01
1. Special relativity; 2. Scalar and electromagnetic fields in special relativity; 3. Gravity and spacetime geometry: the inescapable connection; 4. Metric tensor, geodesics and covariant derivative; 5. Curvature of spacetime; 6. Einstein's field equations and gravitational dynamics; 7. Spherically symmetric geometry; 8. Black holes; 9. Gravitational waves; 10. Relativistic cosmology; 11. Differential forms and exterior calculus; 12. Hamiltonian structure of general relativity; 13. Evolution of cosmological perturbations; 14. Quantum field theory in curved spacetime; 15. Gravity in higher and lower dimensions; 16. Gravity as an emergent phenomenon; Notes; Index.
NASA Astrophysics Data System (ADS)
Mottola, Emil
2016-03-01
General Relativity receives quantum corrections relevant at macroscopic distance scales and near event horizons. These arise from the conformal scalar degree of freedom in the extended effective field theory (EFT) of gravity generated by the trace anomaly of massless quantum fields in curved space. Linearized around flat space this quantum scalar degree of freedom combines with the conformal part of the metric and predicts the existence of scalar spin-0 ``breather'' propagating gravitational waves in addition to the transverse tensor spin-2 waves of classical General Relativity. Estimates of the expected strength of scalar gravitational radiation from compact astrophysical sources are given.
Supersymmetry and gravitational duality
Argurio, Riccardo; Dehouck, Francois; Houart, Laurent
2009-06-15
We study how the supersymmetry algebra copes with gravitational duality. As a playground, we consider a charged Taub-Newman-Unti-Tamburino(NUT) solution of D=4, N=2 supergravity. We find explicitly its Killing spinors, and the projection they obey provides evidence that the dual magnetic momenta necessarily have to appear in the supersymmetry algebra. The existence of such a modification is further supported using an approach based on the Nester form. In the process, we find new expressions for the dual magnetic momenta, including the NUT charge. The same expressions are then rederived using gravitational duality.
NASA Technical Reports Server (NTRS)
Kelly, Bernard J.
2010-01-01
Einstein's General Theory of Relativity is our best classical description of gravity, and informs modern astronomy and astrophysics at all scales: stellar, galactic, and cosmological. Among its surprising predictions is the existence of gravitational waves -- ripples in space-time that carry energy and momentum away from strongly interacting gravitating sources. In my talk, I will give an overview of the properties of this radiation, recent breakthroughs in computational physics allowing us to calculate the waveforms from galactic mergers, and the prospect of direct observation with interferometric detectors such as LIGO and LISA.
Level repulsion of GHz phononic surface waves in quartz substrate with finite-depth holes.
Yeh, Sih-Ling; Lin, Yu-Ching; Tsai, Yao-Chuan; Ono, Takahito; Wu, Tsung-Tsong
2016-09-01
This paper presents numerical and experimental results on the level repulsion of gigahertz surface acoustic waves in an air/ST-cut quartz phononic structure with finite-depth holes. The colorful dispersion with the parameter of the in-plane (sagittal plane) ratio of polarization was adopted to determine the Rayleigh wave bandgap induced by the level repulsion. The results of numerical analyses showed that the frequency and width of the bandgap induced by the level repulsion strongly depend on the geometry of the air holes in the phononic structure. In the experiment, a pair of slanted interdigital transducers with frequency in the gigahertz range was designed and fabricated to generate and receive broadband Rayleigh waves, whereas the reactive ion etching process with electron-beam lithography was used to fabricate submicrometer phononic structures. The measured results of the bandgap induced by the level repulsion agreed favorably with the numerical prediction. PMID:27300272
Gravitational Waves: The Evidence Mounts
ERIC Educational Resources Information Center
Wick, Gerald L.
1970-01-01
Reviews the work of Weber and his colleagues in their attempts at detecting extraterrestial gravitational waves. Coincidence events recorded by special detectors provide the evidence for the existence of gravitational waves. Bibliography. (LC)
Extragalactic Gravitational Collapse
NASA Astrophysics Data System (ADS)
Rees, Martin J.
After some introductory "numerology", routes towards black hole formation are briefly reviewed; some properties of black holes relevant to theories for active galactic nuclei are then described. Applications are considered to specific models for energy generation and the production of relativistic beams. The paper concludes with a discussion of extragalactic sources of gravitational waves.
Probing gravitational dark matter
NASA Astrophysics Data System (ADS)
Ren, Jing; He, Hong-Jian
2015-03-01
So far all evidences of dark matter (DM) come from astrophysical and cosmological observations, due to the gravitational interactions of DM. It is possible that the true DM particle in the universe joins gravitational interactions only, but nothing else. Such a Gravitational DM (GDM) may act as a weakly interacting massive particle (WIMP), which is conceptually simple and attractive. In this work, we explore this direction by constructing the simplest scalar GDM particle χs. It is a Bbb Z2 odd singlet under the standard model (SM) gauge group, and naturally joins the unique dimension-4 interaction with Ricci curvature, ξsχs2Script R, where ξs is the dimensionless nonminimal coupling. We demonstrate that this gravitational interaction ξsχs2Script R, together with Higgs-curvature nonminimal coupling term ξhH†HScript R, induces effective couplings between χs2 and SM fields, and can account for the observed DM thermal relic abundance. We analyze the annihilation cross sections of GDM particles and derive the viable parameter space for realizing the DM thermal relic density. We further study the direct/indirect detections and the collider signatures of such a scalar GDM. These turn out to be highly predictive and testable.
New Perspectives on Gravitation
NASA Astrophysics Data System (ADS)
Zhang, Yikun
2003-04-01
Based on radiation mechanics, a new rational mechanics proposed by the author, we can prove Newton's gravitational law and its conditions of validity. The gravitational coefficient is not a universal constant, but affected by many factors and can be both positive and negative. It is further shown how the gravitational coefficients are different for the planets in the solar system. The new rational mechanics expounds that the force causing an apple falling from a tree is not the same force causing the Earth revolving about the Sun. The gravitational force is the combining effect of shielding and shooting of gravitons between the Sun and Earth, whereas a dropped apple falling from a tree is due to the surface adsorption of Earth, called the blowing force. From this, we can rigorously prove that all electrically neutral bodies must fall with the same acceleration. However, any electrically charged bodies fall with different accelerations. It is also deduced that the weight of a magnet and its acceleration of falling depend on its orientation. So we have to distinguish weight and gravity. Moreover, the weight of a body may not be a conservative force on a planet.
Research on gravitational physiology
NASA Technical Reports Server (NTRS)
Brown, A. H.; Dahl, A. O.
1974-01-01
The topic of gravitational plant physiology was studied through aspects of plant development (in ARABIDOPSIS) and of behavior (in HELIANTHUS) as these were affected by altered g experience. The effect of increased g levels on stem polarity (in COLEUS) was also examined.
Probing gravitational dark matter
Ren, Jing; He, Hong-Jian
2015-03-27
So far all evidences of dark matter (DM) come from astrophysical and cosmological observations, due to the gravitational interactions of DM. It is possible that the true DM particle in the universe joins gravitational interactions only, but nothing else. Such a Gravitational DM (GDM) may act as a weakly interacting massive particle (WIMP), which is conceptually simple and attractive. In this work, we explore this direction by constructing the simplest scalar GDM particle χ{sub s}. It is a ℤ{sub 2} odd singlet under the standard model (SM) gauge group, and naturally joins the unique dimension-4 interaction with Ricci curvature, ξ{sub s}χ{sub s}{sup 2}R, where ξ{sub s} is the dimensionless nonminimal coupling. We demonstrate that this gravitational interaction ξ{sub s}χ{sub s}{sup 2}R, together with Higgs-curvature nonminimal coupling term ξ{sub h}H{sup †}HR, induces effective couplings between χ{sub s}{sup 2} and SM fields, and can account for the observed DM thermal relic abundance. We analyze the annihilation cross sections of GDM particles and derive the viable parameter space for realizing the DM thermal relic density. We further study the direct/indirect detections and the collider signatures of such a scalar GDM. These turn out to be highly predictive and testable.
NASA Astrophysics Data System (ADS)
Pires, Sandrine; Starck, Jean-Luc; Leonard, Adrienne; Réfrégier, Alexandre
2012-03-01
This chapter reviews the data mining methods recently developed to solve standard data problems in weak gravitational lensing. We detail the different steps of the weak lensing data analysis along with the different techniques dedicated to these applications. An overview of the different techniques currently used will be given along with future prospects. Until about 30 years ago, astronomers thought that the Universe was composed almost entirely of ordinary matter: protons, neutrons, electrons, and atoms. The field of weak lensing has been motivated by the observations made in the last decades showing that visible matter represents only about 4-5% of the Universe (see Figure 14.1). Currently, the majority of the Universe is thought to be dark, that is, does not emit electromagnetic radiation. The Universe is thought to be mostly composed of an invisible, pressure less matter - potentially relic from higher energy theories - called "dark matter" (20-21%) and by an even more mysterious term, described in Einstein equations as a vacuum energy density, called "dark energy" (70%). This "dark" Universe is not well described or even understood; its presence is inferred indirectly from its gravitational effects, both on the motions of astronomical objects and on light propagation. So this point could be the next breakthrough in cosmology. Today's cosmology is based on a cosmological model that contains various parameters that need to be determined precisely, such as the matter density parameter Omega_m or the dark energy density parameter Omega_lambda. Weak gravitational lensing is believed to be the most promising tool to understand the nature of dark matter and to constrain the cosmological parameters used to describe the Universe because it provides a method to directly map the distribution of dark matter (see [1,6,60,63,70]). From this dark matter distribution, the nature of dark matter can be better understood and better constraints can be placed on dark energy
Gravitational wave astronomy and cosmology
NASA Astrophysics Data System (ADS)
Hughes, Scott A.
2014-09-01
The first direct observation of gravitational waves' action upon matter has recently been reported by the BICEP2 experiment. Advanced ground-based gravitational-wave detectors are being installed. They will soon be commissioned, and then begin searches for high-frequency gravitational waves at a sensitivity level that is widely expected to reach events involving compact objects like stellar mass black holes and neutron stars. Pulsar timing arrays continue to improve the bounds on gravitational waves at nanohertz frequencies, and may detect a signal on roughly the same timescale as ground-based detectors. The science case for space-based interferometers targeting millihertz sources is very strong. The decade of gravitational-wave discovery is poised to begin. In this writeup of a talk given at the 2013 TAUP conference, we will briefly review the physics of gravitational waves and gravitational-wave detectors, and then discuss the promise of these measurements for making cosmological measurements in the near future.
NASA Astrophysics Data System (ADS)
Finn, L. S.
Astronomers rely on a multiplicity of observational perspectives in order to infer the nature of the Universe. Progress in astronomy has historically been associated with new or improved observational perspectives. Gravitational wave detectors now under construction will provide us with a perspective on the Universe fundamentally different from any we have come to know. With this new perspective comes the hope of new insights and understanding, not just of exotic astrophysical processes, but of "bread-and-butter" astrophysics: e.g., stars and stellar evolution, galaxy formation and evolution, neutron star structure, and cosmology. In this report the author discusses briefly a small subset of the areas of conventional, "bread-and-butter" astrophysics where we can reasonably hope that gravitational wave observations will provide us with valuable new insights and understandings.
The gravitational wave experiment
NASA Technical Reports Server (NTRS)
Bertotti, B.; Ambrosini, R.; Asmar, S. W.; Brenkle, J. P.; Comoretto, G.; Giampieri, G.; Less, L.; Messeri, A.; Wahlquist, H. D.
1992-01-01
Since the optimum size of a gravitational wave detector is the wave length, interplanetary dimensions are needed for the mHz band of interest. Doppler tracking of Ulysses will provide the most sensitive attempt to date at the detection of gravitational waves in the low frequency band. The driving noise source is the fluctuations in the refractive index of interplanetary plasma. This dictates the timing of the experiment to be near solar opposition and sets the target accuracy for the fractional frequency change at 3.0 x 10 exp -14 for integration times of the order of 1000 sec. The instrumentation utilized by the experiment is distributed between the radio systems on the spacecraft and the seven participating ground stations of the Deep Space Network and Medicina. Preliminary analysis is available of the measurements taken during the Ulysses first opposition test.
NASA Astrophysics Data System (ADS)
Cook, Paul P.; Fleming, Michael
2014-07-01
The algebra A {/D - 3 + + +} dimensionally reduces to the E D-1 symmetry algebra of (12 - D)-dimensional supergravity. An infinite set of five-dimensional gravitational objects embedded in D-dimensions is constructed by identifying the null geodesic motion on cosets embedded in the generalised Kac-Moody algebra A {/D - 3 + + +}. By analogy with super-gravity these are bound states of dual gravitons. The metric interpolates continuously between exotic gravitational solutions generated by the action of an affine sub-group. We investigate mixed-symmetry fields in the brane sigma model, identify actions for the full interpolating bound state and investigate the dualisation of the bound state to a solution of the Einstein-Hilbert action via the Hodge dual on multiforms. We conclude that the Hodge dual is insufficient to reconstruct solutions to the Einstein-Hilbert action from mixed-symmetry tensors.
Gravitationally induced quantum transitions
NASA Astrophysics Data System (ADS)
Landry, A.; Paranjape, M. B.
2016-06-01
In this paper, we calculate the probability for resonantly inducing transitions in quantum states due to time-dependent gravitational perturbations. Contrary to common wisdom, the probability of inducing transitions is not infinitesimally small. We consider a system of ultracold neutrons, which are organized according to the energy levels of the Schrödinger equation in the presence of the Earth's gravitational field. Transitions between energy levels are induced by an oscillating driving force of frequency ω . The driving force is created by oscillating a macroscopic mass in the neighborhood of the system of neutrons. The neutron lifetime is approximately 880 sec while the probability of transitions increases as t2. Hence, the optimal strategy is to drive the system for two lifetimes. The transition amplitude then is of the order of 1.06 ×10-5, and hence with a million ultracold neutrons, one should be able to observe transitions.
Linked Gravitational Radiation
NASA Astrophysics Data System (ADS)
Thompson, Amy; Swearngin, Joseph; Wickes, Alexander; Willem Dalhuisen, Jan; Bouwmeester, Dirk
2013-04-01
The electromagnetic knot is a topologically nontrivial solution to the vacuum Maxwell equations with the property that any two field lines belonging to either the electric, magnetic, or Poynting vector fields are closed and linked exactly once [1]. The relationship between the vacuum Maxwell and linearized Einstein equations, as expressed in the form of the spin-N massless field equations, suggests that gravitational radiation possesses analogous topologically nontrivial field configurations. Using twistor methods we find the analogous spin-2 solutions of Petrov types N, D, and III. Aided by the concept of tendex and vortex lines as recently developed for the physical interpretation of solutions in general relativity [2], we investigate the physical properties of these knotted gravitational fields by characterizing the topology of their associated tendex and vortex lines.[4pt] [1] Ranada, A. F. and Trueba, J. L., Mod. Nonlinear Opt. III, 119, 197 (2002).[2] Nichols, D. A., et al., Phys. Rev. D, 84 (2011).
Gravitational vacuum condensate stars
Mazur, Pawel O.; Mottola, Emil
2004-01-01
A new final state of gravitational collapse is proposed. By extending the concept of Bose–Einstein condensation to gravitational systems, a cold, dark, compact object with an interior de Sitter condensate pv = -ρv and an exterior Schwarzschild geometry of arbitrary total mass M is constructed. These regions are separated by a shell with a small but finite proper thickness ℓ of fluid with equation of state p = +ρ, replacing both the Schwarzschild and de Sitter classical horizons. The new solution has no singularities, no event horizons, and a global time. Its entropy is maximized under small fluctuations and is given by the standard hydrodynamic entropy of the thin shell, which is of the order kBℓMc/, instead of the Bekenstein–Hawking entropy formula, SBH = 4πkBGM2/c. Hence, unlike black holes, the new solution is thermodynamically stable and has no information paradox. PMID:15210982
Gravitational lensing by gravastars
NASA Astrophysics Data System (ADS)
Kubo, Tomohiro; Sakai, Nobuyuki
2016-04-01
As a possible method to detect gravastars (gravitational-vacuum-star), which was originally proposed by Mazur and Mottola, we study their gravitational lensing effects. Specifically, we adopt a spherical thin-shell model of a gravastar developed by Visser and Wiltshire, which connects interior de Sitter geometry and exterior Schwarzschild geometry, and assume that its surface is optically transparent. We calculate the image of a companion which rotates around the gravastar; we find that some characteristic images appear, depending on whether the gravastar possess unstable circular orbits of photons (Model 1) or not (Model 2). For Model 2, we calculate the total luminosity change, which is called microlensing effects; the maximal luminosity could be considerably larger than the black hole with the same mass.
Towers of Gravitational Theories
NASA Astrophysics Data System (ADS)
Goldberger, Walter D.; Rothstein, Ira Z.
In this essay, we introduce a theoretical framework designed to describe black hole dynamics. The difficulties in understanding such dynamics stems from the proliferation of scales involved when one attempts to simultaneously describe all of the relevant dynamical degrees of freedom. These range from the modes that describe the black hole horizon, which are responsible for dissipative effects, to the long wavelength gravitational radiation that drains mechanical energy from macroscopic black hole bound states. We approach the problem from a Wilsonian point of view, by building a tower of theories of gravity each of which is valid at different scales. The methodology leads to multiple new results in diverse topics including phase transitions of Kaluza-Klein black holes and the interactions of spinning black hole in non-relativistic orbits. Moreover, our methods tie together speculative ideas regarding dualities for black hole horizons to real physical measurements in gravitational wave detectors.
Towers of gravitational theories
NASA Astrophysics Data System (ADS)
Goldberger, Walter D.; Rothstein, Ira Z.
2006-11-01
In this essay we introduce a theoretical framework designed to describe black hole dynamics. The difficulties in understanding such dynamics stems from the proliferation of scales involved when one attempts to simultaneously describe all of the relevant dynamical degrees of freedom. These range from the modes that describe the black hole horizon, which are responsible for dissipative effects, to the long wavelength gravitational radiation that drains mechanical energy from macroscopic black hole bound states. We approach the problem from a Wilsonian point of view, by building a tower of theories of gravity each of which is valid at different scales. The methodology leads to multiple new results in diverse topics including phase transitions of Kaluza-Klein black holes and the interactions of spinning black hole in non-relativistic orbits. Moreover, our methods tie together speculative ideas regarding dualities for black hole horizons to real physical measurements in gravitational wave detectors.
Gravitational properties of antimatter
Goldman, T.; Nieto, M.M.
1985-01-01
Quantum gravity is at the forefront of modern particle physics, yet there are no direct tests, for antimatter, of even the principle of equivalence. We note that modern descriptions of gravity, such as fibre bundles and higher dimensional spacetimes, allow violations of the commonly stated form of the principle of equivalence, and of CPT. We review both indirect arguments and experimental tests of the expected gravitational properties of CPT-conjugate states. We conclude that a direct experimental test of the gravitational properties of antimatter, at the 1% (or better) level, would be of great value. We identify some experimental reasons which make the antiproton a prime candidate for this test, and we strongly urge that such an experiment be done at LEAR. 21 references.
Gravitational Condensate Stars
NASA Astrophysics Data System (ADS)
Mazur, P.; Mottola, E.
The issue of the final state of the gravitational collapse will be addressed. Ishall present physical arguments to the effect that the remnant of the gravitationalcollapse of super-massive stars is a cold and dark super-dense object which isthermodynamically and dynamically stable: a Gravitational Condensate Star orQuasi Black Hole (QBH). A QBH is characterized by a huge, but not an infinite,surface redshift. This surface redshift depends universally on the total mass of aQBH and the proper thickness of a thin shell of an exotic matter described bythe Zel'dovich equation of state p = c2 . The velocity of sound in a thin shell isequal to the velocity of light. Hence, this thin shell replaces the event horizon of amathematical black hole ( = 0). Inside a thin shell the zero entropy gravitationalcondensate characterized by the cosmological equation of state p = -c2 resides.A QBH is described by a new static and spherically symmetric solution of Ein-stein's equations supplemented with the proper boundary conditions based on mi-crophysics considerations. The new solution has no singularities and no eventhorizons. Its entropy is maximized under small fluctuations and is given by thestandard hydrodynamic entropy of the thin shell which is proportional to the to-tal mass instead of the Bekenstein-Hawking entropy which is proportional to thesquare of the total mass. This resolves the paradox of an excessively high en-tropy of black holes as compared to their progenitors. The formation of such acold gravitational condensate stellar remnant very likely would require a violentcollapse process with an explosive output of energy. Some observational conse-quences of the formation of gravitational condensate stars will be described.
Interatomic repulsion softness directly controls the fragility of supercooled metallic melts.
Krausser, Johannes; Samwer, Konrad H; Zaccone, Alessio
2015-11-10
We present an analytic scheme to connect the fragility and viscoelasticity of metallic glasses to the effective ion-ion interaction in the metal. This is achieved by an approximation of the short-range repulsive part of the interaction, combined with nonaffine lattice dynamics to obtain analytical expressions for the shear modulus, viscosity, and fragility in terms of the ion-ion interaction. By fitting the theoretical model to experimental data, we are able to link the steepness of the interionic repulsion to the Thomas-Fermi screened Coulomb repulsion and to the Born-Mayer valence electron overlap repulsion for various alloys. The result is a simple closed-form expression for the fragility of the supercooled liquid metal in terms of few crucial atomic-scale interaction and anharmonicity parameters. In particular, a linear relationship is found between the fragility and the energy scales of both the screened Coulomb and the electron overlap repulsions. This relationship opens up opportunities to fabricate alloys with tailored thermoelasticity and fragility by rationally tuning the chemical composition of the alloy according to general principles. The analysis presented here brings a new way of looking at the link between the outer shell electronic structure of metals and metalloids and the viscoelasticity and fragility thereof. PMID:26504208
NASA Astrophysics Data System (ADS)
Kruppa, Tobias; Neuhaus, Tim; Messina, René; Löwen, Hartmut
2012-04-01
A binary mixture of particles interacting via long-ranged repulsive forces is studied in gravity by computer simulation and theory. The more repulsive A-particles create a depletion zone of less repulsive B-particles around them reminiscent to a bubble. Applying Archimedes' principle effectively to this bubble, an A-particle can be lifted in a fluid background of B-particles. This "depletion bubble" mechanism explains and predicts a brazil-nut effect where the heavier A-particles float on top of the lighter B-particles. It also implies an effective attraction of an A-particle towards a hard container bottom wall which leads to boundary layering of A-particles. Additionally, we have studied a periodic inversion of gravity causing perpetuous mutual penetration of the mixture in a slit geometry. In this nonequilibrium case of time-dependent gravity, the boundary layering persists. Our results are based on computer simulations and density functional theory of a two-dimensional binary mixture of colloidal repulsive dipoles. The predicted effects also occur for other long-ranged repulsive interactions and in three spatial dimensions. They are therefore verifiable in settling experiments on dipolar or charged colloidal mixtures as well as in charged granulates and dusty plasmas.
Two-dimensional colloidal mixtures in magnetic and gravitational fields
NASA Astrophysics Data System (ADS)
Löwen, H.; Horn, T.; Neuhaus, T.; ten Hagen, B.
2013-11-01
This mini-review is concerned with two-dimensional colloidal mixtures exposed to various kinds of external fields. By a magnetic field perpendicular to the plane, dipole moments are induced in paramagnetic particles which give rise to repulsive interactions leading to complex crystalline alloys in the composition-asymmetry diagram. A quench in the magnetic field induces complex crystal nucleation scenarios. If exposed to a gravitational field, these mixtures exhibit a brazil-nut effect and show a boundary layering which is explained in terms of a depletion bubble picture. The latter persists for time-dependent gravity ("colloidal shaking"). Finally, we summarize crystallization effects when the second species is frozen in a disordered matrix which provides obstacles for the crystallizing component.
Relativistic Transverse Gravitational Redshift
NASA Astrophysics Data System (ADS)
Mayer, A. F.
2012-12-01
The parametrized post-Newtonian (PPN) formalism is a tool for quantitative analysis of the weak gravitational field based on the field equations of general relativity. This formalism and its ten parameters provide the practical theoretical foundation for the evaluation of empirical data produced by space-based missions designed to map and better understand the gravitational field (e.g., GRAIL, GRACE, GOCE). Accordingly, mission data is interpreted in the context of the canonical PPN formalism; unexpected, anomalous data are explained as similarly unexpected but apparently real physical phenomena, which may be characterized as ``gravitational anomalies," or by various sources contributing to the total error budget. Another possibility, which is typically not considered, is a small modeling error in canonical general relativity. The concept of the idealized point-mass spherical equipotential surface, which originates with Newton's law of gravity, is preserved in Einstein's synthesis of special relativity with accelerated reference frames in the form of the field equations. It was not previously realized that the fundamental principles of relativity invalidate this concept and with it the idea that the gravitational field is conservative (i.e., zero net work is done on any closed path). The ideal radial free fall of a material body from arbitrarily-large range to a point on such an equipotential surface (S) determines a unique escape-velocity vector of magnitude v collinear to the acceleration vector of magnitude g at this point. For two such points on S separated by angle dφ , the Equivalence Principle implies distinct reference frames experiencing inertial acceleration of identical magnitude g in different directions in space. The complete equivalence of these inertially-accelerated frames to their analogous frames at rest on S requires evaluation at instantaneous velocity v relative to a local inertial observer. Because these velocity vectors are not parallel, a
Emergence of amplitude death scenario in a network of oscillators under repulsive delay interaction
NASA Astrophysics Data System (ADS)
Bera, Bidesh K.; Hens, Chittaranjan; Ghosh, Dibakar
2016-07-01
We report the existence of amplitude death in a network of identical oscillators under repulsive mean coupling. Amplitude death appears in a globally coupled network of identical oscillators with instantaneous repulsive mean coupling only when the number of oscillators is more than two. We further investigate that, amplitude death may emerge even in two coupled oscillators as well as network of oscillators if we introduce delay time in the repulsive mean coupling. We have analytically derived the region of amplitude death island and find out how strength of delay controls the death regime in two coupled or a large network of coupled oscillators. We have verified our results on network of delayed Mackey-Glass systems where parameters are set in hyperchaotic regime. We have also tested our coupling approach in two paradigmatic limit cycle oscillators: Stuart-Landau and Van der Pol oscillators.
Contact repulsion controls the dispersion and final distribution of Cajal-Retzius cells
Villar-Cerviño, Verona; Molano-Mazón, Manuel; Catchpole, Timothy; Valdeolmillos, Miguel; Henkemeyer, Mark; Martínez, Luis M.; Borrell, Víctor; Marín, Oscar
2012-01-01
Summary Cajal-Retzius (CR) cells play a fundamental role in the development of the mammalian cerebral cortex. They control the formation of cortical layers by regulating the migration of pyramidal cells through the release of Reelin. The function of CR cells critically depends on their regular distribution throughout the surface of the cortex, but little is known about the events controlling this phenomenon. Using time-lapse video microscopy in vivo and in vitro, we found that movement of CR cells is regulated by repulsive interactions, which leads to their random dispersion throughout the cortical surface. Mathematical modeling reveals that contact repulsion is both necessary and sufficient for this process, which demonstrates that complex neuronal assemblies may emerge during development through stochastic events. At the molecular level, we found that contact repulsion is mediated by Eph/ephrin interactions. Our observations reveal a novel mechanism that controls the even distribution of neurons in the developing brain. PMID:23395373
Quantum vacuum photon modes and repulsive Lifshitz-van der Waals interactions
NASA Astrophysics Data System (ADS)
Dellieu, Louis; Deparis, Olivier; Muller, Jérôme; Kolaric, Branko; Sarrazin, Michaël
2015-12-01
The bridge between quantum vacuum photon modes and properties of patterned surfaces is currently being established on solid theoretical grounds. Based on these foundations, the manipulation of quantum vacuum photon modes in a nanostructured cavity is theoretically shown to be able to change the Lifshitz-van der Waals forces from attractive to repulsive regime. Since this concept relies on surface nanopatterning instead of chemical composition changes, it drastically relaxes the usual conditions for achieving repulsive Lifshitz-van der Waals forces. As a case study, the potential interaction energy between a nanopatterned polyethylene slab and a flat polyethylene slab with water as the intervening medium is calculated. Extremely small corrugation heights (<10 nm) are shown to be able to change the Lifshitz-van der Waals force from attractive to repulsive, the interaction strength being controlled by the corrugation height. This new approach could lead to various applications in surface science.
Slow relaxation mode in concentrated oil-in-water microemulsions consisting of repulsive droplets
NASA Astrophysics Data System (ADS)
Hattori, Y.; Ushiki, H.; Courbin, L.; Panizza, P.
2007-02-01
The present contribution reports on the observation of two diffusive relaxation modes in a concentrated microemulsion made of repulsive droplets. These two modes can be interpreted in the frame of Weissman’s and Pusey’s theoretical pioneering works. The fast mode is associated to the collective diffusion of droplets whereas the slow one corresponds to the relaxation of droplet concentration fluctuations associated with composition and/or size. We show that (i) repulsive interactions considerably slow down the latter and (ii) a generalized Stokes Einstein relationship between its coefficient of diffusion and the Newtonian viscosity of the solutions, similar to the Walden’s rule for electrolytes, holds for concentrated microemulsion systems made of repulsive droplets.
Concentration Fluctuations of a Semidilute Polymer Solution in Good Solvent Near a Repulsive Surface
NASA Astrophysics Data System (ADS)
Yeh, Catherine; Pincus, Philip; Zidovska, Alexandra
2012-02-01
The concentration profile of a semidilute polymer solution in good solvent near a repulsive surface has been previously calculated.ootnotetextJ. F. Joanny, L. Leibler, P.-G. de Gennes, J. Polym. Sci. 17, 1073 (1979) In this work we consider fluctuation corrections to the mean field concentration profile in the presence of a repulsive surface using the Cahn-Hilliard square-gradient approach extended to polymer interfaces. Our results predict that at strongly repulsive surfaces, a polymer in good solvent exhibits concentration fluctuations associated with the surface in addition to fluctuations of the bulk polymer solution. We compare our predictions with current experiments which have measured fluctuations in the concentration of interphase chromatin (DNA with its associated proteins) inside the nucleus of mammalian cells in vivo using ultrafast high space resolution spinning disc confocal microscopy.
Müller, Thomas; Trommer, Isabel; Muhlack, Siegfried; Mueller, Bernhard K
2016-04-01
Exposure to free radicals influences synthesis, degradation and function of proteins, such as repulsive guidance molecule A. Decay of this protein is essential for neuronal maintenance and recovery. Levodopa elevates oxidative stress. Therefore levodopa may impact repulsive guidance molecule A metabolism. Objectives were to investigate plasma concentrations of repulsive guidance molecule A, levodopa, cysteine and cysteinyl-glycine before and 1 h after levodopa application in patients with Parkinson's disease. Cysteine and cysteinyl-glycine as biomarkers for oxidative stress exposure decreased, repulsive guidance molecule A and levodopa rose. Repulsive guidance molecule A remained unchanged in levodopa naïve patients, but particularly went up in patients on a prior chronic levodopa regimen. Decay of cysteine specifically cysteinyl-glycine results from an elevated glutathione generation with rising cysteine consumption respectively from the alternative glutathione transformation to its oxidized form glutathione disulfide after free radical scavenging. Repulsive guidance molecule A rise may inhibit physiologic mechanisms for neuronal survival. PMID:26880022
Recent Developments in Gravitation - Proceedings of the Relativity Meeting - 89
NASA Astrophysics Data System (ADS)
Verdaguer, E.; Garriga, J.; Céspedes, J.
1990-10-01
The Table of Contents for the full book PDF is as follows: * Foreword * I. INVITED LECTURES * Low Energy Effects of Quantum Gravity * Rigid Motion lnvariance of Newtonian and Einatein's Theories of General Relativity * General Relativity and the Early Universe * Computer Algebra and Exact Solutions of the Einstein Equations * Gravitational Waves * II. REVIEW TALKS * Classical Relativistic Particles with Spin * Testing Flux Conservative Methods in Numerical Relativity * Symmetries in General Relativity and the Problem of Symmetry Inheritance * Clifford Algebra Approach to Gravitation: Applications to Symmetries and to Twisting, Type-N Fields * Unusual Frames of the Space-Time * Massive Photon Modes in Q.E.D. and Abnormal e+ e- Pair Production * Repulsive Gravity: A Current State of Understanding * Physics versus Metaphysics in Collision between Plane Gravitational Waves * Primordial Black Holes and FRW Cosmology * What Does Morphological Segregation of Galaxies Tell Us about Galaxy Formation? * III. SHORT COMMUNICATIONS * A Demianski Cavity with Small Rotation Parameter in a Dust Universe with Cosmological Constant * Relation between Quasirigidity and Weak Rigidity in Weak Fields * Almost-Product Structures in Relativity * On the Solutions of Quantum Field Equations in Curved Space-Time * Perturbative Methods for Type D Space-Time * The Energy-Momentum Tensor of Two Perfect Fluids * Two Fluids Solutions of Einstein Equations * Gravitational Wave Detection: The Problem of Estimating a Signal's Arrival Time * Quantum Particles Produced during Cosmic String Formation * Electric Neutrality and the Jordan-Thiry Scalar Field * Why Do Spinors Appear in Relativity? * Variational Principles and Quantum Gravity * A Nelson Like Approach to Quantum Mechanics on a Maximally Symmetric Manifold * A Note on the Scalar Product in Relativistic Quantum Mechanics * On the Tolman Bondi Solution of Einstein's Equations. Numerical Applications * The Dirac Equation in Two Rectilinear
NASA Astrophysics Data System (ADS)
Lee, Sang-Rock; Choi, Seung-Hyun; Oh, Jong-Seok; Choi, Seung-Bok
2015-02-01
This paper proposes a novel technique for predicting a repulsive force in a haptic interface. The goal of many haptic systems is to reflect a desired repulsive force to an operator. However, there is no way of describing a repulsive force mathematically. This means that the force-reflection performance of haptic systems cannot be simulated at the design process. Even though reflecting a repulsive force to an operator is the purpose of the systems, many haptic systems have been designed without knowing how an operator perceives a repulsive force during manipulation. Such design process unavoidably entails a lot of trials and errors and increases development time and costs. Here we show that the repulsive force can be predicted by establishing an optimal controller. 1-Degree of freedom lever system is designed with light and heavy inertia in order to reflect inertial variation. The dynamics of the system is derived and an optimal controller is established based on the system dynamics. The optimal controller predicts the repulsive forces under three different position trajectories. After manufacturing the lever system, actual repulsive force data is collected under the same position trajectories. The predicted repulsive forces are then compared with the actual repulsive forces. To demonstrate the effectiveness of the proposed method, a correlation coefficient between the predicted repulsive force and the actual one is presented. In addition, the mean value and standard deviation of the force error are provided. After showing that a repulsive force can be predicted by an optimal controller, a steering-wheel simulator is designed and manufactured to show that the proposed method is applicable to a haptic system’s design as well.
Quantum Emulation of Gravitational Waves
Fernandez-Corbaton, Ivan; Cirio, Mauro; Büse, Alexander; Lamata, Lucas; Solano, Enrique; Molina-Terriza, Gabriel
2015-01-01
Gravitational waves, as predicted by Einstein’s general relativity theory, appear as ripples in the fabric of spacetime traveling at the speed of light. We prove that the propagation of small amplitude gravitational waves in a curved spacetime is equivalent to the propagation of a subspace of electromagnetic states. We use this result to propose the use of entangled photons to emulate the evolution of gravitational waves in curved spacetimes by means of experimental electromagnetic setups featuring metamaterials. PMID:26169801
Quantum Emulation of Gravitational Waves.
Fernandez-Corbaton, Ivan; Cirio, Mauro; Büse, Alexander; Lamata, Lucas; Solano, Enrique; Molina-Terriza, Gabriel
2015-01-01
Gravitational waves, as predicted by Einstein's general relativity theory, appear as ripples in the fabric of spacetime traveling at the speed of light. We prove that the propagation of small amplitude gravitational waves in a curved spacetime is equivalent to the propagation of a subspace of electromagnetic states. We use this result to propose the use of entangled photons to emulate the evolution of gravitational waves in curved spacetimes by means of experimental electromagnetic setups featuring metamaterials. PMID:26169801
Repulsive Casimir forces between solid materials with high-refractive-index intervening liquids
Zwol, P. J. van; Palasantzas, G.
2010-06-15
In order to explore repulsive Casimir or van der Waals forces between solid materials with liquid as the intervening medium, we analyze dielectric data for a wide range of materials as, for example, (p)olytetrafluoroethylene, polystyrene, silica, and more than 20 liquids. Although significant variation in the dielectric data from different sources exists, we provide a scheme based on measured static dielectric constants, refractive indices, and applying Kramers-Kronig consistency to dielectric data to create accurate dielectric functions at imaginary frequencies. The latter is necessary for more accurate force calculations via the Lifshitz theory, thereby allowing reliable predictions of repulsive Casimir forces.
Phase behavior of a simple lattice model with a two-scale repulsive interaction
NASA Astrophysics Data System (ADS)
Høye, J. S.; Lomba, E.
2008-07-01
The properties of a simple one-dimensional lattice model with two repulsive ranges are studied in terms of its analytic solution. Its phase behavior is characterized by the presence of a disorder-order-disorder transition (or a fluid-solid-fluid transition in lattice gas language). A similar situation was discussed by Hemmer and Stell [Phys. Rev. Lett. 24, 1284 (1970)] when considering the purely repulsive version of their ramp potential. The melting of the solid phase, when pressure is increased along an isotherm, is a feature common to both models and one of the characteristic features of water.
Gravitational collapse of Vaidya spacetime
NASA Astrophysics Data System (ADS)
Vertogradov, Vitalii
2016-03-01
The gravitational collapse of generalized Vaidya spacetime is considered. It is known that the endstate of gravitational collapse, as to whether a black hole or a naked singularity is formed, depends on the mass function M(v,r). Here we give conditions for the mass function which corresponds to the equation of the state P = αρ where α ∈ (0, 1 3] and according to these conditions we obtain either a black hole or a naked singularity at the endstate of gravitational collapse. Also we give conditions for the mass function when the singularity is gravitationally strong.
NASA Astrophysics Data System (ADS)
Yang, Chao Yuan
2012-05-01
Anomalous decelerations of spacecraft Pioneer-10,11,etc could be interpreted as signal delay effect between speed of gravity and that of light as reflected in virtual scale, similar to covarying virtual scale effect in relative motion (http://arxiv.org/html/math-ph/0001019v5).A finite speed of gravity faster than light could be inferred (http://arXiv.org/html/physics/0001034v2). Measurements of gravitational variations by paraconical pendulum during a total solar eclipse infer the same(http://arXiv.org/html/physics/0001034v9). A finite Superluminal speed of gravity is the necessary condition to imply that there exists gravitational horizon (GH). Such "GH" of our Universe would stretch far beyond the cosmic event horizon of light. Dark energy may be owing to mutually interactive gravitational horizons of cousin universes. Sufficient condition for the conjecture is that the dark energy would be increasing with age of our Universe since accelerated expansion started about 5 Gyr ago, since more and more arrivals of "GH" of distant cousin universes would interact with "GH" of our Universe. The history of dark energy variations between then and now would be desirable(http://arXiv.org/html/physics/0001034). In "GH" conjecture, the neighborhood of cousin universes would be likely boundless in 4D-space-time without begining or end. The dark energy would keep all universes in continually accelerated expansion to eventual fragmentation. Fragments would crash and merge into bangs, big or small, to form another generation of cousin universes. These scenarios might offer a clue to what was before the big bang.
Gravitational Physics Research
NASA Technical Reports Server (NTRS)
Wu, S. T.
2000-01-01
Gravitational physics research at ISPAE is connected with NASA's Relativity Mission (Gravity Probe B (GP-B)) which will perform a test of Einstein's General Relativity Theory. GP-B will measure the geodetic and motional effect predicted by General Relativity Theory with extremely stable and sensitive gyroscopes in an earth orbiting satellite. Both effects cause a very small precession of the gyroscope spin axis. The goal of the GP-B experiment is the measurement of the gyroscope precession with very high precision. GP-B is being developed by a team at Stanford University and is scheduled for launch in the year 2001. The related UAH research is a collaboration with Stanford University and MSFC. This research is focussed primarily on the error analysis and data reduction methods of the experiment but includes other topics concerned with experiment systems and their performance affecting the science measurements. The hydrogen maser is the most accurate and stable clock available. It will be used in future gravitational physics missions to measure relativistic effects such as the second order Doppler effect. The HMC experiment, currently under development at the Smithsonian Astrophysical Observatory (SAO), will test the performance and capability of the hydrogen maser clock for gravitational physics measurements. UAH in collaboration with the SAO science team will study methods to evaluate the behavior and performance of the HMC. The GP-B data analysis developed by the Stanford group involves complicated mathematical operations. This situation led to the idea to investigate alternate and possibly simpler mathematical procedures to extract the GP-B measurements form the data stream. Comparison of different methods would increase the confidence in the selected scheme.
Gravitational lens observations
NASA Astrophysics Data System (ADS)
Burke, B. F.; Roberts, D. H.; Hewitt, J. N.; Greenfield, P. E.; Dupree, A. K.
1983-06-01
The structure of the gravitational lens 0957 + 561 provides strong constraints on allowable lens models. Here, the modeling constraints for the lens are summarized, and it is shown that, for the foreground cluster, mass-to-luminosity ratio with a well-defined locus can be given. Constraints on other images in the radio map are then discussed, and it is concluded that a third quasar image has not yet been identified convincingly, but perturbations of the B quasar image are consistent with the partial jet image predicted by Greenfield (1981). Finally, polarization studies of the A and B images are reported.
Regular gravitational lagrangians
NASA Astrophysics Data System (ADS)
Dragon, Norbert
1992-02-01
The Einstein action with vanishing cosmological constant is for appropriate field content the unique local action which is regular at the fixed point of affine coordinate transformations. Imposing this regularity requirement one excludes also Wess-Zumino counterterms which trade gravitational anomalies for Lorentz anomalies. One has to expect dilatational and SL (D) anomalies. If these anomalies are absent and if the regularity of the quantum vertex functional can be controlled then Einstein gravity is renormalizable. On leave of absence from Institut für Theoretische Physik, Universität Hannover, W-3000 Hannover 1, FRG.
Octonic Gravitational Field Equations
NASA Astrophysics Data System (ADS)
Demir, Süleyman; Tanişli, Murat; Tolan, Tülay
2013-08-01
Generalized field equations of linear gravity are formulated on the basis of octons. When compared to the other eight-component noncommutative hypercomplex number systems, it is demonstrated that associative octons with scalar, pseudoscalar, pseudovector and vector values present a convenient and capable tool to describe the Maxwell-Proca-like field equations of gravitoelectromagnetism in a compact and simple way. Introducing massive graviton and gravitomagnetic monopole terms, the generalized gravitational wave equation and Klein-Gordon equation for linear gravity are also developed.
Gravitational vacuum condensate stars.
Mazur, Pawel O; Mottola, Emil
2004-06-29
A new final state of gravitational collapse is proposed. By extending the concept of Bose-Einstein condensation to gravitational systems, a cold, dark, compact object with an interior de Sitter condensate p(v) = -rho(v) and an exterior Schwarzschild geometry of arbitrary total mass M is constructed. These regions are separated by a shell with a small but finite proper thickness l of fluid with equation of state p = +rho, replacing both the Schwarzschild and de Sitter classical horizons. The new solution has no singularities, no event horizons, and a global time. Its entropy is maximized under small fluctuations and is given by the standard hydrodynamic entropy of the thin shell, which is of the order k(B)lMc/Planck's over 2 pi, instead of the Bekenstein-Hawking entropy formula, S(BH) = 4 pi k(B)GM(2)/Planck's over 2 pi c. Hence, unlike black holes, the new solution is thermodynamically stable and has no information paradox. PMID:15210982
Burinskii, A.
2015-08-15
The Kerr–Newman (KN) black hole (BH) solution exhibits the external gravitational and electromagnetic field corresponding to that of the Dirac electron. For the large spin/mass ratio, a ≫ m, the BH loses horizons and acquires a naked singular ring creating two-sheeted topology. This space is regularized by the Higgs mechanism of symmetry breaking, leading to an extended particle that has a regular spinning core compatible with the external KN solution. We show that this core has much in common with the known MIT and SLAC bag models, but has the important advantage of being in accordance with the external gravitational and electromagnetic fields of the KN solution. A peculiar two-sheeted structure of Kerr’s gravity provides a framework for the implementation of the Higgs mechanism of symmetry breaking in configuration space in accordance with the concept of the electroweak sector of the Standard Model. Similar to other bag models, the KN bag is flexible and pliant to deformations. For parameters of a spinning electron, the bag takes the shape of a thin rotating disk of the Compton radius, with a ring–string structure and a quark-like singular pole formed at the sharp edge of this disk, indicating that the considered lepton bag forms a single bag–string–quark system.
NASA Astrophysics Data System (ADS)
Burinskii, A.
2015-08-01
The Kerr-Newman (KN) black hole (BH) solution exhibits the external gravitational and electromagnetic field corresponding to that of the Dirac electron. For the large spin/mass ratio, a ≫ m, the BH loses horizons and acquires a naked singular ring creating two-sheeted topology. This space is regularized by the Higgs mechanism of symmetry breaking, leading to an extended particle that has a regular spinning core compatible with the external KN solution. We show that this core has much in common with the known MIT and SLAC bag models, but has the important advantage of being in accordance with the external gravitational and electromagnetic fields of the KN solution. A peculiar two-sheeted structure of Kerr's gravity provides a framework for the implementation of the Higgs mechanism of symmetry breaking in configuration space in accordance with the concept of the electroweak sector of the Standard Model. Similar to other bag models, the KN bag is flexible and pliant to deformations. For parameters of a spinning electron, the bag takes the shape of a thin rotating disk of the Compton radius, with a ring-string structure and a quark-like singular pole formed at the sharp edge of this disk, indicating that the considered lepton bag forms a single bag-string-quark system.
General Relativity and Gravitation
NASA Astrophysics Data System (ADS)
Ashtekar, Abhay; Berger, Beverly; Isenberg, James; MacCallum, Malcolm
2015-07-01
Part I. Einstein's Triumph: 1. 100 years of general relativity George F. R. Ellis; 2. Was Einstein right? Clifford M. Will; 3. Cosmology David Wands, Misao Sasaki, Eiichiro Komatsu, Roy Maartens and Malcolm A. H. MacCallum; 4. Relativistic astrophysics Peter Schneider, Ramesh Narayan, Jeffrey E. McClintock, Peter Mészáros and Martin J. Rees; Part II. New Window on the Universe: 5. Receiving gravitational waves Beverly K. Berger, Karsten Danzmann, Gabriela Gonzalez, Andrea Lommen, Guido Mueller, Albrecht Rüdiger and William Joseph Weber; 6. Sources of gravitational waves. Theory and observations Alessandra Buonanno and B. S. Sathyaprakash; Part III. Gravity is Geometry, After All: 7. Probing strong field gravity through numerical simulations Frans Pretorius, Matthew W. Choptuik and Luis Lehner; 8. The initial value problem of general relativity and its implications Gregory J. Galloway, Pengzi Miao and Richard Schoen; 9. Global behavior of solutions to Einstein's equations Stefanos Aretakis, James Isenberg, Vincent Moncrief and Igor Rodnianski; Part IV. Beyond Einstein: 10. Quantum fields in curved space-times Stefan Hollands and Robert M. Wald; 11. From general relativity to quantum gravity Abhay Ashtekar, Martin Reuter and Carlo Rovelli; 12. Quantum gravity via unification Henriette Elvang and Gary T. Horowitz.
Polymer Brushes that Mimic Repulsive Properties of the Boundary Lubricant Glycoprotein Lubricin
NASA Astrophysics Data System (ADS)
Torres, Jahn; Jay, Gregory; Ni, Qian; Bello, David; Bothun, Geoffrey; Kim, Kyung-Suk
2011-03-01
This is a report on the design of tailored functional groups which mimic the repulsive forces at work in the natural-joint boundary lubricant known as lubricin. Lubricin, an amphiphilic polyelectrolyte biomolecule, decreases friction and cellular adhesion by exhibiting surface force fields based on steric hindrance, Debye electrostatic double layer repulsion and hydration repulsive forces. We have identified a physically and chemically stable candidate polymers for anti-fouling coatings that will mimic lubricin's repulsive properties. Synthetic polymer brushes mimicking lubricin have been produced using these polymers grafted onto a glass surfaces. The average adhesive forces for the polymer brushes measured through atomic force microscopy are as low (56.796 +/- 0.796 mN/m), similar to those exhibited by lubricin coated surfaces and on the same order of magnitude as superhydrophobic surfaces. This work was supported by the Coatings/Biofouling Program and the Maritime Sensing Program of the Office of Naval Research as well as the ILIR Program of the Naval Undersea Warfare Center DIVNPT.
Electronic Structure in Pi Systems: Part I. Huckel Theory with Electron Repulsion.
ERIC Educational Resources Information Center
Fox, Marye Anne; Matsen, F. A.
1985-01-01
Pi-CI theory is a simple, semi-empirical procedure which (like Huckel theory) treats pi and pseudo-pi orbitals; in addition, electron repulsion is explicitly included and molecular configurations are mixed. Results obtained from application of pi-CI to ethylene are superior to either the Huckel molecular orbital or valence bond theories. (JN)
Mass, Energy, Space And Time Systemic Theory ---MEST--- repulsion and gravity
NASA Astrophysics Data System (ADS)
Cao, Dayong
2009-10-01
Things have their physical system of the mass, energy, space and time of themselves-MEST. Sun can give the planets the repulsion and the gravity. It decided the relationship between the mass-energy and space-time of the planets. The repulsion of the planets ``equal'' its gravity. So them get a balanceable system and a inertial system. The planets lie in the wave like the boat being in the water. When sun radiate light, it can produce the repulsion. It decided the relationship between the mass-energy and space-time of the radiate light. When the radiate light condense to the condensed light (gravity wave), and it come back to the sun. It can produce the gravity. It decided the relationship between the mass-energy and space-time of the gravity wave. Both of the radiate light and the gravity wave act on the planets. There are their physical model which is about their mass-energy relation and their mass-energy wave equation. In the solar system, there are a lot of the dark matter-energy (wave) which is from the black hole. The dark matter-energy would go into the solar system and could give the sun the press force like the gravity. In sun, sun's nuclear fusion can produce repulsion. Sun is control nuclear fusion. It is controlled by the dark matter-energy.
Discontinuous nature of the repulsive-to-attractive colloidal glass transition
van de Laar, T.; Higler, R.; Schroën, K.; Sprakel, J.
2016-01-01
In purely repulsive colloidal systems a glass transition can be reached by increasing the particle volume fraction beyond a certain threshold. The resulting glassy state is governed by configurational cages which confine particles and restrict their motion. A colloidal glass may also be formed by inducing attractive interactions between the particles. When attraction is turned on in a repulsive colloidal glass a re-entrant solidification ensues. Initially, the repulsive glass melts as free volume in the system increases. As the attraction strength is increased further, this weakened configurational glass gives way to an attractive glass in which motion is hindered by the formation of physical bonds between neighboring particles. In this paper, we study the transition from repulsive-to-attractive glasses using three-dimensional imaging at the single-particle level. We show how the onset of cage weakening and bond formation is signalled by subtle changes in local structure. We then demonstrate the discontinuous nature of the solid-solid transition, which is marked by a critical onset at a threshold bonding energy. Finally, we highlight how the interplay between bonding and caging leads to complex and heterogeneous dynamics at the microscale. PMID:26940737
Discontinuous nature of the repulsive-to-attractive colloidal glass transition.
van de Laar, T; Higler, R; Schroën, K; Sprakel, J
2016-01-01
In purely repulsive colloidal systems a glass transition can be reached by increasing the particle volume fraction beyond a certain threshold. The resulting glassy state is governed by configurational cages which confine particles and restrict their motion. A colloidal glass may also be formed by inducing attractive interactions between the particles. When attraction is turned on in a repulsive colloidal glass a re-entrant solidification ensues. Initially, the repulsive glass melts as free volume in the system increases. As the attraction strength is increased further, this weakened configurational glass gives way to an attractive glass in which motion is hindered by the formation of physical bonds between neighboring particles. In this paper, we study the transition from repulsive-to-attractive glasses using three-dimensional imaging at the single-particle level. We show how the onset of cage weakening and bond formation is signalled by subtle changes in local structure. We then demonstrate the discontinuous nature of the solid-solid transition, which is marked by a critical onset at a threshold bonding energy. Finally, we highlight how the interplay between bonding and caging leads to complex and heterogeneous dynamics at the microscale. PMID:26940737
Discontinuous nature of the repulsive-to-attractive colloidal glass transition
NASA Astrophysics Data System (ADS)
van de Laar, T.; Higler, R.; Schroën, K.; Sprakel, J.
2016-03-01
In purely repulsive colloidal systems a glass transition can be reached by increasing the particle volume fraction beyond a certain threshold. The resulting glassy state is governed by configurational cages which confine particles and restrict their motion. A colloidal glass may also be formed by inducing attractive interactions between the particles. When attraction is turned on in a repulsive colloidal glass a re-entrant solidification ensues. Initially, the repulsive glass melts as free volume in the system increases. As the attraction strength is increased further, this weakened configurational glass gives way to an attractive glass in which motion is hindered by the formation of physical bonds between neighboring particles. In this paper, we study the transition from repulsive-to-attractive glasses using three-dimensional imaging at the single-particle level. We show how the onset of cage weakening and bond formation is signalled by subtle changes in local structure. We then demonstrate the discontinuous nature of the solid-solid transition, which is marked by a critical onset at a threshold bonding energy. Finally, we highlight how the interplay between bonding and caging leads to complex and heterogeneous dynamics at the microscale.
Singh, R; Ho, S Y
2000-06-01
Dissimilarity and similarity between attitudes of the participants and a stranger were manipulated across two sets of issues to test the attraction, repulsion and similarity-dissimilarity asymmetry hypotheses. Participants (N = 192) judged social (liking, enjoyment of company) and intellectual (intelligence, general knowledge) attractiveness of the stranger. The similarity in the first set of attitudes x similarity in the second set of attitudes effect emerged in social attraction, but not in intellectual attraction. Stated simply, dissimilarity had a greater weight than similarity in social attraction, but equal weight in intellectual attraction. These results support the similarity-dissimilarity asymmetry hypothesis that predicts dissimilarity-repulsion to be stronger than similarity-attraction. However, they reject (1) the attraction hypothesis that dissimilarity and similarity produce equal and opposite effects on social attraction; and (2) the repulsion hypothesis that only dissimilar attitudes affect social attraction by leading to repulsion. An equal weighting of dissimilarity and similarity in intellectual attraction further suggested that the similarity-dissimilarity asymmetry on social attraction is reflective of a stronger avoidance response in the Darwinian sense. PMID:10907095
ERIC Educational Resources Information Center
Speight, Suzette L.; Vera, Elizabeth M.
1997-01-01
Summarizes issues relevant to empirical investigations of client and counselor preferences. Explores the effects of similarity and difference on relationship development and focuses on the attraction and repulsion hypotheses' applicability to multicultural counseling research and theory. It is hoped that differences between counseling and social…
Regardless-of-Speed Superconducting LSM Controlled-Repulsive MAGLEV Vehicle
NASA Technical Reports Server (NTRS)
Yoshida, Kinjiro; Egashira, Tatsuya; Hirai, Ryuichi
1996-01-01
This paper proposes a new repulsive Maglev vehicle which a superconducting linear synchronous motor (LSM) can levitate and propel simultaneously, independently of the vehicle speeds. The combined levitation and propulsion control is carried out by controlling mechanical-load angle and armature-current. Dynamic simulations show successful operations with good ride-quality by using a compact control method proposed here.
The gravitational properties of antimatter
Goldman, T.; Hughes, R.J.; Nieto, M.M.
1986-09-01
It is argued that a determination of the gravitational acceleration of antimatter towards the earth is capable of imposing powerful constraints on modern quantum gravity theories. Theoretical reasons to expect non-Newtonian non-Einsteinian effects of gravitational strength and experimental suggestions of such effects are reviewed. 41 refs. (LEW)
Shh signaling guides spatial pathfinding of raphespinal tract axons by multidirectional repulsion
Song, Lijuan; Liu, Yuehui; Yu, Yang; Duan, Xin; Qi, Shening; Liu, Yaobo
2012-01-01
Relatively little is known about the molecular mechanisms underlying spatial pathfinding in the descending serotonergic raphespinal tract (RST) in the developing spinal cord, one of the most important nerve pathways for pain, sensory and motor functions. We provide evidence that ventral floor plate-secreted Sonic hedgehog (Shh) is responsible for the establishment of decreasing gradients in both the anterior-to-posterior (A-P) and the medial-to-lateral (M-L) directions in the ventral spinal cord during serotonergic RST axon projection. Downstream components of the Shh pathway, Patched 1 (Ptch1) and Smoothened (Smo), were expressed in the serotonergic caudal raphe nuclei and enriched in the descending serotonergic RST axons. Diffusible Shh repulsion of serotonergic RST axons was shown to be mediated by Shh-Ptch1 interactions and derepression of Smo. Using a co-culture assay, we showed that A-P graded repulsion mediated by Shh signaling pushed the serotonergic axons caudally through the ventral spinal cord and M-L graded repulsion mediated by Shh signaling simultaneously restricted the serotonergic axons to the ventral and ventral-lateral funiculus. Prominent pathfinding errors of serotonergic RST axons were observed in various Shh, Ptch1 and Smo mutants. We conclude that Shh signaling-mediated multidirectional repulsion is required to push descending serotonergic RST axons in the A-P direction, and to restrict these axons to the ventral and ventral-lateral funiculus in the M-L direction. This is the first demonstration that Shh signaling-mediated multidirectional repulsion of serotonergic RST axons maintains spatial axon pathfinding in the developing spinal cord. PMID:22064698
Gravitational correction to vacuum polarization
NASA Astrophysics Data System (ADS)
Jentschura, U. D.
2015-02-01
We consider the gravitational correction to (electronic) vacuum polarization in the presence of a gravitational background field. The Dirac propagators for the virtual fermions are modified to include the leading gravitational correction (potential term) which corresponds to a coordinate-dependent fermion mass. The mass term is assumed to be uniform over a length scale commensurate with the virtual electron-positron pair. The on-mass shell renormalization condition ensures that the gravitational correction vanishes on the mass shell of the photon, i.e., the speed of light is unaffected by the quantum field theoretical loop correction, in full agreement with the equivalence principle. Nontrivial corrections are obtained for off-shell, virtual photons. We compare our findings to other works on generalized Lorentz transformations and combined quantum-electrodynamic gravitational corrections to the speed of light which have recently appeared in the literature.
Boutros, C P; Koenig, J B
2001-04-01
The 3rd maxillary molar is a difficult tooth to remove by extraction or repulsion. A combined frontal and maxillary approach provides good exposure for repulsion of this tooth, debridement of the sinuses, and placement of an alveolar seal. The improved exposure should minimize operative difficulties and postoperative complications. PMID:11326631
Gravitational mass and Newton's universal gravitational law under relativistic conditions
NASA Astrophysics Data System (ADS)
Vayenas, Constantinos G.; Fokas, Athanasios; Grigoriou, Dimitrios
2015-09-01
We discuss the predictions of Newton's universal gravitational law when using the gravitational, mg, rather than the rest masses, mo, of the attracting particles. According to the equivalence principle, the gravitational mass equals the inertial mass, mi, and the latter which can be directly computed from special relativity, is an increasing function of the Lorentz factor, γ, and thus of the particle velocity. We consider gravitationally bound rotating composite states, and we show that the ratio of the gravitational force for gravitationally bound rotational states to the force corresponding to low (γ ≈ 1) particle velocities is of the order of (mPl/mo)2 where mpi is the Planck mass (ħc/G)1/2. We also obtain a similar result, within a factor of two, by employing the derivative of the effective potential of the Schwarzschild geodesics of GR. Finally, we show that for certain macroscopic systems, such as the perihelion precession of planets, the predictions of this relativistic Newtonian gravitational law differ again by only a factor of two from the predictions of GR.
Atomic and gravitational clocks
NASA Technical Reports Server (NTRS)
Canuto, V. M.; Goldman, I.
1982-01-01
Atomic and gravitational clocks are governed by the laws of electrodynamics and gravity, respectively. While the strong equivalence principle (SEP) assumes that the two clocks have been synchronous at all times, recent planetary data seem to suggest a possible violation of the SEP. Past analysis of the implications of an SEP violation on different physical phenomena revealed no disagreement. However, these studies assumed that the two different clocks can be consistently constructed within the framework. The concept of scale invariance, and the physical meaning of different systems of units, are now reviewed and the construction of two clocks that do not remain synchronous - whose rates are related by a non-constant function beta sub a - is demonstrated. The cosmological character of beta sub a is also discussed.
Frontiers in gravitational physics
NASA Astrophysics Data System (ADS)
Dutta, Koushik
In this thesis we present three research projects in classical General Relativity and Cosmology. In the first part of the thesis we investigate the definition of gravitational charge corresponding to the asymptotic boost symmetry of a spacetime and derive its role in the first law of black hole thermodynamics. In the cosmology part, we investigate the role of a scalar field in the early and late time evolution of the Universe. We find out observational constraints on the pseudo Nambu Goldstone Boson quintessence model using the latest supernova and Cosmic Microwave Background (CMB) data. In an attempt to explain a particular anomaly in the latest CMB data, we propose a modification to the standard single field inflation based on the initial kinetic energy domination with anisotropic initial conditions. Predictions of this mechanism can be tested in future data analysis.
Gravitational adaptation of animals
NASA Technical Reports Server (NTRS)
Smith, A. H.; Burton, R. R.
1982-01-01
The effect of gravitational adaptation is studied in a group of five Leghorn cocks which had become physiologically adapted to 2 G after 162 days of centrifugation. After this period of adaptation, they are periodically exposed to a 2 G field, accompanied by five previously unexposed hatch-mates, and the degree of retained acceleration adaptation is estimated from the decrease in lymphocyte frequency after 24 hr at 2 G. Results show that the previously adapted birds exhibit an 84% greater lymphopenia than the unexposed birds, and that the lymphocyte frequency does not decrease to a level below that found at the end of 162 days at 2 G. In addition, the capacity for adaptation to chronic acceleration is found to be highly heritable. An acceleration tolerant strain of birds shows lesser mortality during chronic acceleration, particularly in intermediate fields, although the result of acceleration selection is largely quantitative (a greater number of survivors) rather than qualitative (behavioral or physiological changes).
Earth Gravitational Model 2020
NASA Astrophysics Data System (ADS)
Barnes, D.; Factor, J. K.; Holmes, S. A.; Ingalls, S.; Presicci, M. R.; Beale, J.; Fecher, T.
2015-12-01
The National Geospatial-Intelligence Agency [NGA], in conjunction with its U.S. and international partners, has begun preliminary work on its next Earth Gravitational Model, to replace EGM2008. The new 'Earth Gravitational Model 2020' [EGM2020] has an expected public release date of 2020, and will likely retain the same harmonic basis and resolution as EGM2008. As such, EGM2020 will be essentially an ellipsoidal harmonic model up to degree (n) and order (m) 2159, but will be released as a spherical harmonic model to degree 2190 and order 2159. EGM2020 will benefit from new data sources and procedures. Updated satellite gravity information from the GOCE and GRACE mission, will better support the lower harmonics, globally. Multiple new acquisitions (terrestrial, airborne and shipborne) of gravimetric data over specific geographical areas, will provide improved global coverage and resolution over the land, as well as for coastal and some ocean areas. Ongoing accumulation of satellite altimetry data as well as improvements in the treatment of this data, will better define the marine gravity field, most notably in polar and near-coastal regions. NGA and partners are evaluating different approaches for optimally combining the new GOCE/GRACE satellite gravity models with the terrestrial data. These include the latest methods employing a full covariance adjustment. NGA is also working to assess systematically the quality of its entire gravimetry database, towards correcting biases and other egregious errors where possible, and generating improved error models that will inform the final combination with the latest satellite gravity models. Outdated data gridding procedures have been replaced with improved approaches. For EGM2020, NGA intends to extract maximum value from the proprietary data that overlaps geographically with unrestricted data, whilst also making sure to respect and honor its proprietary agreements with its data-sharing partners.
Weight, gravitation, inertia, and tides
NASA Astrophysics Data System (ADS)
Pujol, Olivier; Lagoute, Christophe; Pérez, José-Philippe
2015-11-01
This paper deals with the factors that influence the weight of an object near the Earth's surface. They are: (1) the Earth's gravitational force, (2) the centrifugal force due to the Earth's diurnal rotation, and (3) tidal forces due to the gravitational field of the Moon and Sun, and other solar system bodies to a lesser extent. Each of these three contributions is discussed and expressions are derived. The relationship between weight and gravitation is thus established in a direct and pedagogical manner readily understandable by undergraduate students. The analysis applies to the Newtonian limit of gravitation. The derivation is based on an experimental (or operational) definition of weight, and it is shown that it coincides with the Earth’s gravitational force modified by diurnal rotation around a polar axis and non-uniformity of external gravitational bodies (tidal term). Two examples illustrate and quantify these modifications, respectively the Eötvös effect and the oceanic tides; tidal forces due to differential gravitation on a spacecraft and an asteroid are also proposed as examples. Considerations about inertia are also given and some comments are made about a widespread, yet confusing, explanation of tides based on a centrifugal force. Finally, the expression of the potential energy of the tide-generating force is established rigorously in the appendix.
Gravitational lensing of gravitational waves from merging neutron star binaries
Wang, Yun; Stebbins, Albert; Turner, Edwin L.
1996-05-01
We discuss the gravitational lensing of gravitational waves from merging neutron star binaries, in the context of advanced LIGO type gravitational wave detectors. We consider properties of the expected observational data with cut on the signal-to-noise ratio \\rho, i.e., \\rho>\\rho_0. An advanced LIGO should see unlensed inspiral events with a redshift distribution with cut-off at a redshift z_{\\rm max} < 1 for h \\leq 0.8. Any inspiral events detected at z>z_{\\rm max} should be lensed. We compute the expected total number of events which are present due to gravitational lensing and their redshift distribution for an advanced LIGO in a flat Universe. If the matter fraction in compact lenses is close to 10\\%, an advanced LIGO should see a few strongly lensed events per year with \\rho >5.
An overview of gravitational physiology
NASA Technical Reports Server (NTRS)
Miquel, Jaime; Souza, Kenneth A.
1991-01-01
The focus of this review is on the response of humans and animals to the effects of the near weightless condition occurring aboard orbiting spacecraft. Gravity is an omnipresent force that has been a constant part of our lives and of the evolution of all living species. Emphasis is placed on the general mechanisms of adaptation to altered gravitational fields and vectors, i.e., both hypo- and hypergravity. A broad literature review of gravitational biology was conducted and the general state of our knowledge in this area is discussed. The review is specifically targeted at newcomers to the exciting and relatively new area of space and gravitational biology.
Gravitation. [Book on general relativity
NASA Technical Reports Server (NTRS)
Misner, C. W.; Thorne, K. S.; Wheeler, J. A.
1973-01-01
This textbook on gravitation physics (Einstein's general relativity or geometrodynamics) is designed for a rigorous full-year course at the graduate level. The material is presented in two parallel tracks in an attempt to divide key physical ideas from more complex enrichment material to be selected at the discretion of the reader or teacher. The full book is intended to provide competence relative to the laws of physics in flat space-time, Einstein's geometric framework for physics, applications with pulsars and neutron stars, cosmology, the Schwarzschild geometry and gravitational collapse, gravitational waves, experimental tests of Einstein's theory, and mathematical concepts of differential geometry.
Gravitational radiation quadrupole formula is valid for gravitationally interacting systems
NASA Technical Reports Server (NTRS)
Walker, M.; Will, C. M.
1980-01-01
An argument is presented for the validity of the quadrupole formula for gravitational radiation energy loss in the far field of nearly Newtonian (e.g., binary stellar) systems. This argument differs from earlier ones in that it determines beforehand the formal accuracy of approximation required to describe gravitationally self-interacting systems, uses the corresponding approximate equation of motion explicitly, and evaluates the appropriate asymptotic quantities by matching along the correct space-time light cones.
Dipole gravitational radiation in the nonsymmetric gravitational theory of Moffat
NASA Astrophysics Data System (ADS)
Krisher, Timothy P.
1985-07-01
The generation of gravitational radiation in the nonsymmetric gravitational theory (NGT) of Moffat is analyzed. It is shown that the theory predicts the emission of dipole gravitational radiation from a binary system. The source of the dipole radiation is a vector density S postulated to be proportional to the number density of fermion particles in the components of the system. This radiation is shown to result in a secular decrease in the orbital period of a binary system in addition to that predicted by general relativity. The size of the effect is proportional to the reduced mass of the system and to the square of the difference in l2/[mass] between the two components of the system, where l is a parameter having units of [length] that is related to the number of fermion particles in each component. As part of the analysis, the stress-energy pseudotensor of the NGT, expanded to quadratic order in the gravitational fields, and the NGT gravitational-wave luminosity formula are derived for the first time. With a perfect-fluid model of matter, results are also given for the post-Newtonian expansions of the source densities of the gravitational fields. The results of this analysis are then applied to the binary pulsar system PSR 1913+16 which contains a pulsar orbiting an unobserved companion. With gravitational radiation attributed as the cause of the observed secular decrease in the orbital period, this system provides a test of the prediction by the NGT of dipole gravitational radiation. It is shown that the NGT can only fit the observations of this system provided the l parameter of the unseen companion is <~350 km.
Gravitational Stokes parameters. [for electromagnetic and gravitational radiation in relativity
NASA Technical Reports Server (NTRS)
Anile, A. M.; Breuer, R. A.
1974-01-01
The electromagnetic and gravitational Stokes parameters are defined in the general theory of relativity. The general-relativistic equation of radiative transfer for polarized radiation is then derived in terms of the Stokes parameters for both high-frequency electromagnetic and gravitational waves. The concept of Stokes parameters is generalized for the most general class of metric theories of gravity, where six (instead of two) independent states of polarization are present.
Dissipation of modified entropic gravitational energy through gravitational waves
NASA Astrophysics Data System (ADS)
de Matos, Clovis Jacinto
2012-01-01
The phenomenological nature of a new gravitational type interaction between two different bodies derived from Verlinde's entropic approach to gravitation in combination with Sorkin's definition of Universe's quantum information content, is investigated. Assuming that the energy stored in this entropic gravitational field is dissipated under the form of gravitational waves and that the Heisenberg principle holds for this system, one calculates a possible value for an absolute minimum time scale in nature tau=15/16 Λ^{1/2}hbar G/c4˜9.27×10^{-105} seconds, which is much smaller than the Planck time t P =( ħG/ c 5)1/2˜5.38×10-44 seconds. This appears together with an absolute possible maximum value for Newtonian gravitational forces generated by matter Fg=32/30c7/Λ hbar G2˜ 3.84× 10^{165} Newtons, which is much higher than the gravitational field between two Planck masses separated by the Planck length F gP = c 4/ G˜1.21×1044 Newtons.
Gravitation toward Walls among Human Subjects
ERIC Educational Resources Information Center
Dabbs, James M., Jr.; Wheeler, Patricia A.
1976-01-01
In two studies, college students (N=34) in a classroom corridor who walked near the wall ("gravitators") were contrasted with those who walked near the center ("non-gravitators"). Gravitators were lower than non-gravitators on Autonomy and Defendence and appeared to be less responsive to other persons. (Author)
Quantum Opportunities in Gravitational Wave Detectors
Mavalvala, Negris
2012-03-14
Direct observation of gravitational waves should open a new window into the Universe. Gravitational wave detectors are the most sensitive position meters ever constructed. The quantum limit in gravitational wave detectors opens up a whole new field of study. Quantum opportunities in gravitational wave detectors include applications of quantum optics techniques and new tools for quantum measurement on truly macroscopic (human) scales.
Testing local Lorentz invariance with gravitational waves
NASA Astrophysics Data System (ADS)
Kostelecký, V. Alan; Mewes, Matthew
2016-06-01
The effects of local Lorentz violation on dispersion and birefringence of gravitational waves are investigated. The covariant dispersion relation for gravitational waves involving gauge-invariant Lorentz-violating operators of arbitrary mass dimension is constructed. The chirp signal from the gravitational-wave event GW150914 is used to place numerous first constraints on gravitational Lorentz violation.
NASA Astrophysics Data System (ADS)
Wang, Peng-Fei; Ruan, Xiao-Dong; Xu, Zhong-Bin; Fu, Xin
2015-11-01
The Hong-Strogatz (HS) model of globally coupled phase oscillators with attractive and repulsive interactions reflects the fact that each individual (oscillator) has its own attitude (attractive or repulsive) to the same environment (mean field). Previous studies on HS model focused mainly on the stable states on Ott-Antonsen (OA) manifold. In this paper, the eigenvalues of the Jacobi matrix of each fixed point in HS model are explicitly derived, with the aim to understand the local dynamics around each fixed point. Phase transitions are described according to relative population and coupling strength. Besides, the dynamics off OA manifold is studied. Supported by the National Basic Research Program of China under Grant No. 2015CB057301, the Applied Research Project of Public Welfare Technology of Zhejiang Province under Grant No. 201SC31109 and China Postdoctoral Science Foundation under Grant No. 2014M560483
Development of a simple 2.45 GHz microwave plasma with a repulsive double hexapole configuration
Arciaga, Marko; Ulano, April; Lee, Henry Jr.; Lledo, Rumar; Ramos, Henry; Tumlos, Roy
2008-09-15
A simple and inexpensive 2.45 GHz microwave plasma source with a repulsive double hexapole configuration is described and characterized. In this work, the operation of the source is shown to be flexible in terms of electron density, electron temperature, and plasma uniformity even at low-pressures (approximately millitorr). It allows for easy control of the electron temperature (2-3.8 eV) and density ({approx}10{sup 9}-10{sup 10} cm{sup -3}) by removing either of the two hexapoles or by varying the separation distance between the two hexapoles. Characterization was done via information gathered from the usual Langmuir probe measurements for electron temperature and density. The source makes a resonant surface with its repulsive double hexapole magnetic configuration providing an additional longitudinal confinement near the walls midway between the two hexapoles. Magnetic field maps are presented for varying double hexapole distances. Power delivery for various settings is also presented.
Hydration Repulsion between Carbohydrate Surfaces Mediated by Temperature and Specific Ions
NASA Astrophysics Data System (ADS)
Chen, Hsieh; Cox, Jason R.; Ow, Hooisweng; Shi, Rena; Panagiotopoulos, Athanassios Z.
2016-06-01
Stabilizing colloids or nanoparticles in solution involves a fine balance between surface charges, steric repulsion of coating molecules, and hydration forces against van der Waals attractions. At high temperature and electrolyte concentrations, the colloidal stability of suspensions usually decreases rapidly. Here, we report a new experimental and simulation discovery that the polysaccharide (dextran) coated nanoparticles show ion-specific colloidal stability at high temperature, where we observed enhanced colloidal stability of nanoparticles in CaCl2 solution but rapid nanoparticle-nanoparticle aggregation in MgCl2 solution. The microscopic mechanism was unveiled in atomistic simulations. The presence of surface bound Ca2+ ions increases the carbohydrate hydration and induces strongly polarized repulsive water structures beyond at least three hydration shells which is farther-reaching than previously assumed. We believe leveraging the binding of strongly hydrated ions to macromolecular surfaces represents a new paradigm in achieving absolute hydration and colloidal stability for a variety of materials, particularly under extreme conditions.
NASA Astrophysics Data System (ADS)
Yoon, Kyung-Beom; Park, Won-Hee
2015-04-01
The convective heat transfer coefficient and surface emissivity before and after flame occurrence on a wood specimen surface and the flame heat flux were estimated using the repulsive particle swarm optimization algorithm and cone heater test results. The cone heater specified in the ISO 5660 standards was used, and six cone heater heat fluxes were tested. Preservative-treated Douglas fir 21 mm in thickness was used as the wood specimen in the tests. This study confirmed that the surface temperature of the specimen, which was calculated using the convective heat transfer coefficient, surface emissivity and flame heat flux on the wood specimen by a repulsive particle swarm optimization algorithm, was consistent with the measured temperature. Considering the measurement errors in the surface temperature of the specimen, the applicability of the optimization method considered in this study was evaluated.
Classical and quantum analysis of repulsive singularities in four-dimensional extended supergravity
NASA Astrophysics Data System (ADS)
Gaida, I.; Hollmann, H. R.; Stewart, J. M.
1999-07-01
Non-minimal repulsive singularities (`repulsons') in extended supergravity theories are investigated. The short-distance antigravity properties of the repulsons are tested at the classical and the quantum level by a scalar test-particle. Using a partial wave expansion it is shown that the particle is totally reflected at the origin. A high-frequency incoming particle undergoes a phase shift of icons/Journals/Common/pi" ALT="pi" ALIGN="TOP"/>/2. However, the phase shift for a low-frequency particle depends upon the physical data of the repulson. The curvature singularity at a finite distance rh turns out to be transparent for the scalar test-particle and the coordinate singularity at the origin serves as the repulsive barrier to bounce back the particles.
Effect of interdots electronic repulsion in the Majorana signature for a double dot interferometer
NASA Astrophysics Data System (ADS)
Ricco, L. S.; Marques, Y.; Dessotti, F. A.; de Souza, M.; Seridonio, A. C.
2016-04-01
We investigate theoretically the features of the Majorana hallmark in the presence of Coulomb repulsion between two quantum dots describing a spinless double dot interferometer, where one of the dots is strongly coupled to a Kitaev wire within the topological phase. Such a system has been originally proposed without Coulomb interaction in Dessotti et al. (2014 [16]) . Our findings reveal that for dots in resonance, the ratio between the strength of Coulomb repulsion and the dot-wire coupling changes the width of the Majorana zero-bias peak for both Fano regimes studied, indicating thus that the electronic interdots correlation influences the Majorana state lifetime in the dot hybridized with the wire. Moreover, for the off-resonance case, the swap between the energy levels of the dots also modifies the width of the Majorana peak, which does not happen for the noninteracting case. The results obtained here can guide experimentalists that pursuit a way of revealing Majorana signatures.
Ground-state densities of repulsive two-component Fermi gases
NASA Astrophysics Data System (ADS)
Trappe, Martin-Isbjörn; Grochowski, Piotr; Brewczyk, Mirosław; Rzążewski, Kazimierz
2016-02-01
We investigate separations of trapped balanced two-component atomic Fermi gases with repulsive contact interaction. Candidates for ground-state densities are obtained from the imaginary-time evolution of a nonlinear pseudo-Schrödinger equation in three dimensions, rather than from the cumbersome variational equations of the underlying energy density functional. With the employed hydrodynamical approach, gradient corrections to the Thomas-Fermi approximation are conveniently included and are shown to be vital for reliable density profiles. We provide critical repulsion strengths that mark the onset of phase transitions in a harmonic trap. We present transitions from identical density profiles of the two fermion species towards isotropic and anisotropic separations for various confinements, including harmonic and double-well-type traps. Our proposed method is suited for arbitrary trap geometries and can be straightforwardly extended to study dynamics in the light of ongoing experiments on degenerate Fermi gases.
Development of a simple 2.45 GHz microwave plasma with a repulsive double hexapole configuration.
Arciaga, Marko; Tumlos, Roy; Ulano, April; Lee, Henry; Lledo, Rumar; Ramos, Henry
2008-09-01
A simple and inexpensive 2.45 GHz microwave plasma source with a repulsive double hexapole configuration is described and characterized. In this work, the operation of the source is shown to be flexible in terms of electron density, electron temperature, and plasma uniformity even at low-pressures (approximately millitorr). It allows for easy control of the electron temperature (2-3.8 eV) and density ( approximately 10(9)-10(10) cm(-3)) by removing either of the two hexapoles or by varying the separation distance between the two hexapoles. Characterization was done via information gathered from the usual Langmuir probe measurements for electron temperature and density. The source makes a resonant surface with its repulsive double hexapole magnetic configuration providing an additional longitudinal confinement near the walls midway between the two hexapoles. Magnetic field maps are presented for varying double hexapole distances. Power delivery for various settings is also presented. PMID:19044416
Ferromagnetism of a repulsive atomic Fermi gas in an optical lattice: a quantum Monte Carlo study.
Pilati, S; Zintchenko, I; Troyer, M
2014-01-10
Using continuous-space quantum Monte Carlo methods, we investigate the zero-temperature ferromagnetic behavior of a two-component repulsive Fermi gas under the influence of periodic potentials that describe the effect of a simple-cubic optical lattice. Simulations are performed with balanced and with imbalanced components, including the case of a single impurity immersed in a polarized Fermi sea (repulsive polaron). For an intermediate density below half filling, we locate the transitions between the paramagnetic, and the partially and fully ferromagnetic phases. As the intensity of the optical lattice increases, the ferromagnetic instability takes place at weaker interactions, indicating a possible route to observe ferromagnetism in experiments performed with ultracold atoms. We compare our findings with previous predictions based on the standard computational method used in material science, namely density functional theory, and with results based on tight-binding models. PMID:24483906
Monomolecular adsorption on nanoparticles with repulsive interactions: a Monte Carlo study.
Pinto, O A; López de Mishima, B A; Leiva, E P M; Oviedo, O A
2016-06-01
In the present work, we study the adsorption of different monomolecular species on nanoparticles with different sizes and geometries using a grand canonical Monte Carlo method. These species are characterized by repulsive lateral interactions between themselves, as takes place in the case of the adsorption of partially charged atoms or molecules. Nanosize effects are analyzed in terms of adsorption on edge and facet sites. The energy minimization in these systems comes out as a complex conjugation of the repulsive lateral interactions between the adsorbates and the attractive interactions of the adsorbates with the nanoparticle. The phenomenon is analyzed as a function of the occurrence of different ordered structures being formed on the surface of the nanoparticle. We find that layers with different structures may coexist on different facets of the nanoparticle. Finally, a discussion of deposition on flat surfaces and in finite systems is given. PMID:27181601
NASA Astrophysics Data System (ADS)
Jeon, Hyungkook; Lee, Horim; Kang, Kwan Hyoung; Lim, Geunbae
2013-12-01
We proposed a novel separation method, which is the first report using ion concentration polarization (ICP) to separate particles continuously. We analyzed the electrical forces that cause the repulsion of particles in the depletion region formed by ICP. Using the electrical repulsion, micro- and nano-sized particles were separated based on their electrophoretic mobilities. Because the separation of particles was performed using a strong electric field in the depletion region without the use of internal electrodes, it offers the advantages of simple, low-cost device fabrication and bubble-free operation compared with conventional continuous electrophoretic separation methods, such as miniaturizing free-flow electrophoresis (μ-FFE). This separation device is expected to be a useful tool for separating various biochemical samples, including cells, proteins, DNAs and even ions.
Synchronization and beam forming in an array of repulsively coupled oscillators
NASA Astrophysics Data System (ADS)
Rulkov, N. F.; Tsimring, L.; Larsen, M. L.; Gabbay, M.
2006-11-01
We study the dynamics of an array of Stuart-Landau oscillators with repulsive coupling. Autonomous network with global repulsive coupling settles on one from a continuum of synchronized regimes characterized by zero mean field. Driving this array by an external oscillatory signal produces a nonzero mean field that follows the driving signal even when the oscillators are not locked to the external signal. At sufficiently large amplitude the external signal synchronizes the oscillators and locks the phases of the array oscillations. Application of this system as a beam-forming element of a phase array antenna is considered. The phase dynamics of the oscillator array synchronization is used to reshape the phases of signals received from the phase array antenna and improve its beam pattern characteristics.
Long-range repulsion of colloids driven by ion exchange and diffusiophoresis
Florea, Daniel; Musa, Sami; Huyghe, Jacques M. R.; Wyss, Hans M.
2014-01-01
Interactions between surfaces and particles in aqueous suspension are usually limited to distances smaller than 1 μm. However, in a range of studies from different disciplines, repulsion of particles has been observed over distances of up to hundreds of micrometers, in the absence of any additional external fields. Although a range of hypotheses have been suggested to account for such behavior, the physical mechanisms responsible for the phenomenon still remain unclear. To identify and isolate these mechanisms, we perform detailed experiments on a well-defined experimental system, using a setup that minimizes the effects of gravity and convection. Our experiments clearly indicate that the observed long-range repulsion is driven by a combination of ion exchange, ion diffusion, and diffusiophoresis. We develop a simple model that accounts for our data; this description is expected to be directly applicable to a wide range of systems exhibiting similar long-range forces. PMID:24748113
Residual entropy and waterlike anomalies in the repulsive one dimensional lattice gas
Silva, Fernando Barbosa V. da; Oliveira, Fernando Albuquerque; Barbosa, Marco Aurélio A.
2015-04-14
The thermodynamics and kinetics of the one dimensional lattice gas with repulsive interaction are investigated using transfer matrix technique and Monte Carlo simulations. This simple model is shown to exhibit waterlike anomalies in density, thermal expansion coefficient, and self-diffusion. An unified description for the thermodynamic anomalies in this model is achieved based on the ground state residual entropy which appears in the model due to mixing entropy in a ground state phase transition.
Pioneer midbrain longitudinal axons navigate using a balance of Netrin attraction and Slit repulsion
2014-01-01
Background Longitudinal axons grow parallel to the embryonic midline to connect distant regions of the central nervous system. Previous studies suggested that repulsive midline signals guide pioneer longitudinal axons by blocking their entry into the floor plate; however, the role of midline attractants, and whether attractant signals may cooperate with repulsive signals, remains unclear. In this study we investigated the navigation of a set of pioneer longitudinal axons, the medial longitudinal fasciculus, in mouse embryos mutant for the Netrin/Deleted in Colorectal Cancer (DCC) attractants, and for Slit repellents, as well as the responses of explanted longitudinal axons in vitro. Results In mutants for Netrin1 chemoattractant or DCC receptor signaling, longitudinal axons shifted away from the ventral midline, suggesting that Netrin1/DCC signals act attractively to pull axons ventrally. Analysis of mutants in the three Slit genes, including Slit1/2/3 triple mutants, suggest that concurrent repulsive Slit/Robo signals push pioneer axons away from the ventral midline. Combinations of mutations between the Netrin and Slit guidance systems provided genetic evidence that the attractive and repulsive signals balance against each other. This balance is demonstrated in vitro using explant culture, finding that the cues can act directly on longitudinal axons. The explants also reveal an unexpected synergy of Netrin1 and Slit2 that promotes outgrowth. Conclusions These results support a mechanism in which longitudinal trajectories are positioned by a push-pull balance between opposing Netrin and Slit signals. Our evidence suggests that longitudinal axons respond directly and simultaneously to both attractants and repellents, and that the combined signals constrain axons to grow longitudinally. PMID:25056828
Gravitational Many-Body Problem
Makino, J.
2008-04-29
In this paper, we briefly review some aspects of the gravitational many-body problem, which is one of the oldest problems in the modern mathematical science. Then we review our GRAPE project to design computers specialized to this problem.
Tidal radiation. [relativistic gravitational effects
NASA Technical Reports Server (NTRS)
Mashhoon, B.
1977-01-01
The general theory of tides is developed within the framework of Einstein's theory of gravitation. It is based on the concept of Fermi frame and the associated notion of tidal frame along an open curve in spacetime. Following the previous work of the author an approximate scheme for the evaluation of tidal gravitational radiation is presented which is valid for weak gravitational fields. The emission of gravitational radiation from a body in the field of a black hole is discussed, and for some cases of astrophysical interest estimates are given for the contributions of radiation due to center-of-mass motion, purely tidal deformation, and the interference between the center of mass and tidal motions.
Gravitational quantum states of Antihydrogen
Voronin, A. Yu.; Froelich, P.; Nesvizhevsky, V. V.
2011-03-15
We present a theoretical study of the motion of the antihydrogen atom (H) in the gravitational field of Earth above a material surface. We predict that the H atom, falling in the gravitational field of Earth above a material surface, would settle into long-lived quantum states. We point out a method of measuring the difference in the energy of H in such states. The method allows for spectroscopy of gravitational levels based on atom-interferometric principles. We analyze the general feasibility of performing experiments of this kind. We point out that such experiments provide a method of measuring the gravitational force (Mg) acting on H and that they might be of interest in the context of testing the weak equivalence principle for antimatter.
Gravitational scattering of electromagnetic radiation
NASA Technical Reports Server (NTRS)
Brooker, J. T.; Janis, A. I.
1980-01-01
The scattering of electromagnetic radiation by linearized gravitational fields is studied to second order in a perturbation expansion. The incoming electromagnetic radiation can be of arbitrary multipole structure, and the gravitational fields are also taken to be advanced fields of arbitrary multipole structure. All electromagnetic multipole radiation is found to be scattered by gravitational monopole and time-varying dipole fields. No case has been found, however, in which any electromagnetic multipole radiation is scattered by gravitational fields of quadrupole or higher-order multipole structure. This lack of scattering is established for infinite classes of special cases, and is conjectured to hold in general. The results of the scattering analysis are applied to the case of electromagnetic radiation scattered by a moving mass. It is shown how the mass and velocity may be determined by a knowledge of the incident and scattered radiation.
Relativistic Gravitational Experiments in Space
NASA Technical Reports Server (NTRS)
Hellings, Ronald W. (Editor)
1989-01-01
The results are summarized of a workshop on future gravitational physics space missions. The purpose of the workshop was to define generic technological requirements for such missions. NASA will use the results to direct its program of advanced technology development.
Mechanism of vibration-induced repulsion force on a particle in a viscous fluid cell.
Saadatmand, Mehrrad; Kawaji, Masahiro
2013-08-01
Space platforms such as the Space Shuttle and International Space Station have been considered an ideal environment for production of protein and semiconductor crystals of superior quality due to the negligible gravity-induced convection. Although it was believed that under microgravity environment diffusive mass transport would dominate the growth of the crystals, some related experiments have not shown satisfactory results possibly due to the movement of the growing crystals in fluid cells caused by small vibrations present in the space platforms called g-jitter. In ground-based experiments, there have been clear observations of attraction and repulsion of a solid particle with respect to a nearby wall of the fluid cell due to small vibrations. The present work is a numerical investigation on the physical mechanisms responsible for the repulsion force, which has been predicted to increase with the cell vibration frequency and amplitude, as well as the fluid viscosity. Moreover, the simulations have revealed that the repulsion force occurs mostly due to the increased pressure in the narrow gap between the particle and the nearest wall. PMID:24032936
Mechanism of vibration-induced repulsion force on a particle in a viscous fluid cell
NASA Astrophysics Data System (ADS)
Saadatmand, Mehrrad; Kawaji, Masahiro
2013-08-01
Space platforms such as the Space Shuttle and International Space Station have been considered an ideal environment for production of protein and semiconductor crystals of superior quality due to the negligible gravity-induced convection. Although it was believed that under microgravity environment diffusive mass transport would dominate the growth of the crystals, some related experiments have not shown satisfactory results possibly due to the movement of the growing crystals in fluid cells caused by small vibrations present in the space platforms called g-jitter. In ground-based experiments, there have been clear observations of attraction and repulsion of a solid particle with respect to a nearby wall of the fluid cell due to small vibrations. The present work is a numerical investigation on the physical mechanisms responsible for the repulsion force, which has been predicted to increase with the cell vibration frequency and amplitude, as well as the fluid viscosity. Moreover, the simulations have revealed that the repulsion force occurs mostly due to the increased pressure in the narrow gap between the particle and the nearest wall.
Construction of exchange repulsion in terms of the wave functions at QM/MM boundary region
Takahashi, Hideaki Umino, Satoru; Morita, Akihiro
2015-08-28
We developed a simple method to calculate exchange repulsion between a quantum mechanical (QM) solute and a molecular mechanical (MM) molecule in the QM/MM approach. In our method, the size parameter in the Buckingham type potential for the QM solute is directly determined in terms of the one-electron wave functions of the solute. The point of the method lies in the introduction of the exchange core function (ECF) defined as a Slater function which mimics the behavior of the exterior electron density at the QM/MM boundary region. In the present paper, the ECF was constructed in terms of the Becke-Roussel (BR) exchange hole function. It was demonstrated that the ECF yielded by the BR procedure can faithfully reproduce the radial behavior of the electron density of a QM solute. The size parameter of the solute as well as the exchange repulsion are, then, obtained using the overlap model without any fitting procedure. To examine the efficiency of the method, it was applied to calculation of the exchange repulsions for minimal QM/MM systems, hydrogen-bonded water dimer, and H{sub 3}O{sup +}–H{sub 2}O. We found that our approach is able to reproduce the potential energy curves for these systems showing reasonable agreements with those given by accurate full quantum chemical calculations.
Quantum liquid of repulsively bound pairs of particles in a lattice
Petrosyan, David; Schmidt, Bernd; Anglin, James R.; Fleischhauer, Michael
2007-09-15
Repulsively interacting particles in a periodic potential can form bound composite objects, whose dissociation is suppressed by a band gap. Nearly pure samples of such repulsively bound pairs of cold atoms--'dimers'--have recently been prepared by Winkler et al. [Nature (London) 441, 853 (2006)]. We here derive an effective Hamiltonian for a lattice loaded with dimers only and discuss its implications for the many-body dynamics of the system. We find that the dimer-dimer interaction includes strong on-site repulsion and nearest-neighbor attraction which always dominates over the dimer kinetic energy at low temperatures. The dimers then form incompressible, minimal-surface 'droplets' of a quantum lattice liquid. For low lattice filling, the effective Hamiltonian can be mapped onto the spin-1/2 XXZ model with fixed total magnetization which exhibits a first-order phase transition from the droplet to a gas phase. This opens the door to studying first-order phase transitions using highly controllable ultracold atoms.
Steric repulsions, rotation barriers, and stereoelectronic effects: a real space perspective.
Pendás, A Martín; Blanco, M A; Francisco, E
2009-01-15
Widely used chemical concepts like Pauli repulsion or hyperconjugation, and their role in determining rotation barriers or stereoelectronic effects, are analyzed from the real space perspective of the interacting quantum atoms approach (IQA). IQA emerges from the quantum theory of atoms in molecules (QTAIM), but is free from the equilibrium geometry constraint of the former. A framework with both electronically unrelaxed and relaxed wavefunctions is presented that leads to an approximate correspondence between the IQA concepts and those used in the EDA (energy decomposition analysis) or NBO (natural bond orbital) procedures. We show that no net force acts upon the electrons in an electronically relaxed system, so that any reasonable definition of Pauli repulsion must involve unrelaxed state functions. Using antisymmetrized fragments clarifies that Pauli repulsions are energetically connected to the IQA deformation energies, leaving footprints in the finally relaxed states. Similarly, EDA or NBO hyperconjugative stabilizations are found to be naturally related to the IQA electron delocalization patterns. Applications to the rotation barrier of ethane and other simple systems are presented, and the very often forgotten role of electrostatic contributions in determining preferred conformations is highlighted. PMID:18536054
Mueller, Bernhard K; Yamashita, Toshihide; Schaffar, Gregor; Mueller, Reinhold
2006-01-01
During the development of the nervous system, outgrowing axons often have to travel long distances to reach their target neurons. In this process, outgrowing neurites tipped with motile growth cones rely on guidance cues present in their local environment. These cues are detected by specific receptors expressed on growth cones and neurites and influence the trajectory of the growing fibres. Neurite growth, guidance, target innervation and synapse formation and maturation are the processes that occur predominantly but not exclusively during embryonic or early post-natal development in vertebrates. As a result, a functional neural network is established, which is usually remarkably stable. However, the stability of the neural network in higher vertebrates comes at an expensive price, i.e. the loss of any significant ability to regenerate injured or damaged neuronal connections in their central nervous system (CNS). Most importantly, neurite growth inhibitors prevent any regenerative growth of injured nerve fibres. Some of these inhibitors are associated with CNS myelin, others are found at the lesion site and in the scar tissue. Traumatic injuries in brain and spinal cord of mammals induce upregulation of embryonic inhibitory or repulsive guidance cues and their receptors on the neurites. An example for embryonic repulsive directional cues re-expressed at lesion sites in both the rat and human CNS is provided with repulsive guidance molecules, a new family of directional guidance cues. PMID:16939972
NASA Astrophysics Data System (ADS)
Koyama, Tomonori; Kaiho, Katsuyuki; Yamaguchi, Iwao; Yanabu, Satoru
Using a high-temperature superconductor, we constructed and tested a model superconducting fault current limiter (SFCL). The superconductor and vacuum interrupter as the commutation switch were connected in parallel using a bypass coil. When the fault current flows in this equipment, the superconductor is quenched and the current is then transferred to the parallel coil due to the voltage drop in the superconductor. This large current in the parallel coil actuates the magnetic repulsion mechanism of the vacuum interrupter and the current in the superconductor is broken. Using this equipment, the current flow time in the superconductor can be easily minimized. On the other hand, the fault current is also easily limited by large reactance of the parallel coil. This system has many merits. So, we introduced to electromagnetic repulsion switch. There is duty of high speed re-closing after interrupting fault current in the electrical power system. So the SFCL should be recovered to superconducting state before high speed re-closing. But, superconductor generated heat at the time of quench. It takes time to recover superconducting state. Therefore it is a matter of recovery time. In this paper, we studied recovery time of superconductor. Also, we proposed electromagnetic repulsion switch with reclosing system.
Bera, Mrinal K.; Qiao, Baofu; Seifert, Soenke; Burton-Pye, Benjamin P.; Monica Olvera de la Cruz; Antonio, Mark R.
2015-12-15
Charged colloids and proteins in aqueous solutions interact via short-range attractions and long-range repulsions (SALR) and exhibit complex structural phases. These include homogeneously dispersed monomers, percolated monomers, clusters, and percolated clusters. We report the structural architectures of simple charged systems in the form of spherical, Keggin-type heteropolyanions (HPAs) by small-angle X-ray scattering (SAXS) and molecular dynamics (MD) simulations. Structure factors obtained from the SAXS measurements show that the HPAs interact via SALR. Concentration and temperature dependences of the structure factors for HPAs with –3e (e is the charge of an electron) charge are consistent with a mixture of nonassociated monomersmore » and associated randomly percolated monomers, whereas those for HPAs with –4e and –5e charges exhibit only nonassociated monomers in aqueous solutions. Our experiments show that the increase in magnitude of the charge of the HPAs increases their repulsive interactions and inhibits their aggregation in aqueous solutions. MD simulations were done to reveal the atomistic scale origins of SALR between HPAs. As a result, the short-range attractions result from water or proton-mediated hydrogen bonds between neighboring HPAs, whereas the long-range repulsions are due to the distributions of ions surrounding the HPAs.« less
Bera, Mrinal K.; Qiao, Baofu; Seifert, Soenke; Burton-Pye, Benjamin P.; Monica Olvera de la Cruz; Antonio, Mark R.
2015-12-15
Charged colloids and proteins in aqueous solutions interact via short-range attractions and long-range repulsions (SALR) and exhibit complex structural phases. These include homogeneously dispersed monomers, percolated monomers, clusters, and percolated clusters. We report the structural architectures of simple charged systems in the form of spherical, Keggin-type heteropolyanions (HPAs) by small-angle X-ray scattering (SAXS) and molecular dynamics (MD) simulations. Structure factors obtained from the SAXS measurements show that the HPAs interact via SALR. Concentration and temperature dependences of the structure factors for HPAs with –3e (e is the charge of an electron) charge are consistent with a mixture of nonassociated monomers and associated randomly percolated monomers, whereas those for HPAs with –4e and –5e charges exhibit only nonassociated monomers in aqueous solutions. Our experiments show that the increase in magnitude of the charge of the HPAs increases their repulsive interactions and inhibits their aggregation in aqueous solutions. MD simulations were done to reveal the atomistic scale origins of SALR between HPAs. As a result, the short-range attractions result from water or proton-mediated hydrogen bonds between neighboring HPAs, whereas the long-range repulsions are due to the distributions of ions surrounding the HPAs.
From hydration repulsion to dry adhesion between asymmetric hydrophilic and hydrophobic surfaces
Kanduč, Matej; Netz, Roland R.
2015-01-01
Using all-atom molecular dynamics (MD) simulations at constant water chemical potential in combination with basic theoretical arguments, we study hydration-induced interactions between two overall charge-neutral yet polar planar surfaces with different wetting properties. Whether the water film between the two surfaces becomes unstable below a threshold separation and cavitation gives rise to long-range attraction, depends on the sum of the two individual surface contact angles. Consequently, cavitation-induced attraction also occurs for a mildly hydrophilic surface interacting with a very hydrophobic surface. If both surfaces are very hydrophilic, hydration repulsion dominates at small separations and direct attractive force contribution can—if strong enough—give rise to wet adhesion in this case. In between the regimes of cavitation-induced attraction and hydration repulsion we find a narrow range of contact angle combinations where the surfaces adhere at contact in the absence of cavitation. This dry adhesion regime is driven by direct surface–surface interactions. We derive simple laws for the cavitation transition as well as for the transition between hydration repulsion and dry adhesion, which favorably compare with simulation results in a generic adhesion state diagram as a function of the two surface contact angles. PMID:26392526
Hemmerle, Arnaud; Malaquin, Linda; Charitat, Thierry; Lecuyer, Sigolène; Fragneto, Giovanna; Daillant, Jean
2012-01-01
Understanding interactions between membranes requires measurements on well-controlled systems close to natural conditions, in which fluctuations play an important role. We have determined, by grazing incidence X-ray scattering, the interaction potential between two lipid bilayers, one adsorbed on a solid surface and the other floating close by. We find that interactions in this highly hydrated model system are two orders of magnitude softer than in previously reported work on multilayer stacks. This is attributed to the weak electrostatic repulsion due to the small fraction of ionized lipids in supported bilayers with a lower number of defects. Our data are consistent with the Poisson–Boltzmann theory, in the regime where repulsion is dominated by the entropy of counter ions. We also have unique access to very weak entropic repulsion potentials, which allowed us to discriminate between the various models proposed in the literature. We further demonstrate that the interaction potential between supported bilayers can be tuned at will by applying osmotic pressure, providing a way to manipulate these model membranes, thus considerably enlarging the range of biological or physical problems that can be addressed. PMID:23169650
Tuning the Formation and Rupture of Single Ligand-Receptor Bonds by Hyaluronan-Induced Repulsion
Robert, Philippe; Sengupta, Kheya; Puech, Pierre-Henri; Bongrand, Pierre; Limozin, Laurent
2008-01-01
We used a combination of laminar flow chamber and reflection interference microscopy to study the formation and rupture of single bonds formed between Fc-ICAM-1 attached to a substrate and anti-ICAM-1 carried by micrometric beads in the presence of a repulsive hyaluronan (HA) layer adsorbed onto the substrate. The absolute distance between the colloids and the surface was measured under flow with an accuracy of a few nanometers. We could verify the long-term prediction of classical lubrication theory for the movement of a sphere near a wall in a shear flow. The HA polymer layer exerted long-range repulsive steric force on the beads and the hydrodynamics at the boundary remained more or less unchanged. By incubating HA at various concentrations, the thickness of the layer, as estimated by beads most probable height, was tuned in the range 20–200 nm. Frequency of bond formation was decreased by more than one order of magnitude by increasing the thickness of the repulsive layer, while the lifetime of individual bonds was not affected. This study opens the way for further quantitative studies of the effect of molecular environment and separation distance on ligand-receptor association and dissociation. PMID:18599637
Diamagnetic repulsion--a versatile tool for label-free particle handling in microfluidic devices.
Peyman, Sally A; Kwan, Er Yee; Margarson, Oliver; Iles, Alexander; Pamme, Nicole
2009-12-25
We report the exploration of diamagnetic repulsion forces for the selective manipulation of microparticles inside microfluidic devices. Diamagnetic materials such as polymers are repelled from magnetic fields, an effect greatly enhanced by suspending a diamagnetic object in a paramagnetic Mn(2+) solution. The versatility of diamagnetic repulsion is demonstrated for the trapping, focussing and deflection of polystyrene particles for three example applications. Firstly, magnet pairs with unlike poles facing each other were arranged along a microcapillary to trap plugs of differently functionalised particles for a simultaneous surface-based assay in which biotin was selectively bound to a plug of streptavidin coated particles utilising only 22nL of reagent. Secondly, by slightly modifying the magnetic field design, the rapid focussing of particles into a narrow central stream at a flow rate of 650microms(-1) was accomplished for particle pre-concentration. In a third application, 5 and 10microm polystyrene particles were separated from each other in continuous flow by passing the particle mixture through a microfluidic chamber with a perpendicular magnetic field, a method termed diamagnetophoresis. The separation was investigated between flow rates of 20-100microL h(-1), with full resolution of the particle populations being achieved at 20microL h(-1). These experiments show the potential of diamagnetic repulsion for simple, label-free manipulation of particles and other diamagnetic objects such as cells for a range of bioanalytical techniques. PMID:19592004
Construction of exchange repulsion in terms of the wave functions at QM/MM boundary region
NASA Astrophysics Data System (ADS)
Takahashi, Hideaki; Umino, Satoru; Morita, Akihiro
2015-08-01
We developed a simple method to calculate exchange repulsion between a quantum mechanical (QM) solute and a molecular mechanical (MM) molecule in the QM/MM approach. In our method, the size parameter in the Buckingham type potential for the QM solute is directly determined in terms of the one-electron wave functions of the solute. The point of the method lies in the introduction of the exchange core function (ECF) defined as a Slater function which mimics the behavior of the exterior electron density at the QM/MM boundary region. In the present paper, the ECF was constructed in terms of the Becke-Roussel (BR) exchange hole function. It was demonstrated that the ECF yielded by the BR procedure can faithfully reproduce the radial behavior of the electron density of a QM solute. The size parameter of the solute as well as the exchange repulsion are, then, obtained using the overlap model without any fitting procedure. To examine the efficiency of the method, it was applied to calculation of the exchange repulsions for minimal QM/MM systems, hydrogen-bonded water dimer, and H3O+-H2O. We found that our approach is able to reproduce the potential energy curves for these systems showing reasonable agreements with those given by accurate full quantum chemical calculations.
Gravitational-wave sensitivity curves
NASA Astrophysics Data System (ADS)
Moore, C. J.; Cole, R. H.; Berry, C. P. L.
2015-01-01
There are several common conventions in use by the gravitational-wave community to describe the amplitude of sources and the sensitivity of detectors. These are frequently confused. We outline the merits of and differences between the various quantities used for parameterizing noise curves and characterizing gravitational-wave amplitudes. We conclude by producing plots that consistently compare different detectors. Similar figures can be generated on-line for general use at http://rhcole.com/apps/GWplotter.