Wert, Daniel; Körding, Konrad
2010-01-01
We constantly make small errors during movement and use them to adapt our future movements. Movement experiments often probe this error-driven learning by perturbing movements and analyzing the after-effects. Past studies have applied perturbations of varying nature such as visual disturbances, position- or velocity-dependent forces and modified inertia properties of the limb. However, little is known about how the specific nature of a perturbation influences subsequent movements. For a single perturbation trial, the nature of a perturbation may be highly uncertain to the nervous system, given that it receives only noisy information. One hypothesis is that the nervous system can use this rough estimate to partially correct for the perturbation on the next trial. Alternatively, the nervous system could ignore uncertain information about the nature of the perturbation and resort to a nonspecific adaptation. To study how the brain estimates and responds to incomplete sensory information, we test these two hypotheses using a trial-by-trial adaptation experiment. On each trial, the nature of the perturbation was chosen from six distinct types, including a visuomotor rotation and different force fields. We observed that corrective forces aiming to oppose the perturbation in the following trial were independent of the nature of the perturbation. Our results suggest that the nervous system uses a nonspecific strategy when it has high uncertainty about the nature of perturbations during trial-by-trial learning. PMID:20861427
Natural arsenic contaminated diets perturb reproduction in fish.
Boyle, David; Brix, Kevin V; Amlund, Heidi; Lundebye, Anne-Katrine; Hogstrand, Christer; Bury, Nic R
2008-07-15
The toxicological effect of natural diets elevated in metals on reproduction in fish is poorly understood. The reproductive output of zebrafish fed the polychaete Nereis diversicolor collected from a metal-impacted estuary, Restronguet Creek, Cornwall, UK, was compared to fish fed N. diversicolor collected from a nonmetal impacted estuary, Blackwater, Essex, UK. Fish fed the metal laden N. diversicolorfor 68 days showed reduced reproductive output, characterized by reduced cumulative egg production (47%), cumulative number of spawns (30%), as well as reduced average number of eggs produced per spawn and % hatch rate. The mRNA transcript levels of the egg-yolk protein vitellogenin was also reduced 1.5 fold in the livers of female fish fed metal-laden N. diversicolor. No difference was seen between the lipid, protein, or moisture content of the two diets and no difference in growth was seen between the two fish populations. The Restronguet Creek polychaetes have elevated arsenic, cadmium, copper, zinc, lead, and silver body burdens, but the only element found to accumulate in the tissues of zebrafish fed this diet was As. The As in these N. diversicolor was found to be predominantly potentially toxic inorganic As species, 58% of total As content, which is unusual for aquatic organisms where arsenic is typically biotransformed into less toxic organoarsenical compounds. These results demonstrate that reproduction in fish is a sensitive target of exposure to a natural diet contaminated with As and this exposure route could be of significance to the health of fish populations. PMID:18754393
NASA Astrophysics Data System (ADS)
Cupiał, Piotr
2015-09-01
The paper discusses a perturbation solution of the natural frequencies and mode shapes of a piezoelectric rectangular plate modelled as a three-dimensional body. The coupled theory of piezoelectricity is used, with the governing equations consisting of one electrostatic and three mechanical equations coupled through the piezoelectric effect. Analytical perturbation formulas up to the first-order terms have been derived and used. An important difference of the present analysis as compared to the classical perturbation method consists in that the small parameter enters not only the governing equations but the boundary conditions as well. To address this complication an efficient new approach that makes use of generalized functions has been proposed. Results of the natural frequencies and mode shapes obtained by the perturbation method are discussed for a thin piezoelectric rectangular plate, a thick plate and a piezoelectric parallelepiped. All the results obtained using the perturbation method have been compared with the exact solutions of the coupled electromechanical problem. The proposed perturbation approach furnishes an efficient approximate method of studying the coupled piezoelectric vibration problem. The main advantage of the method derives from the fact that only the elastic solution is required, the effect of piezoelectric coupling being accounted for at a post-processing stage.
Long-term Dynamical Behavior of Highly Perturbed Natural and Artificial Celestial Bodies
NASA Astrophysics Data System (ADS)
Rosengren, Aaron J.
This thesis explores the dynamical evolution of celestial bodies, both natural and artificial, which are strongly perturbed by solar radiation pressure---a non-gravitational force that has played an increasingly important role in celestial mechanics since the early 1900s. The particular focus is on the high area-to-mass ratio (HAMR) space debris discovered in near geosynchronous Earth orbit (GEO) through optical observations in 2004, and on micron-sized circumplanetary dust particles in the outer Saturnian system. The formalism developed can also be applied to---and, indeed, was unquestionably influenced by---the orbital motion of spacecraft about small bodies (asteroids and comets). The chief difficulties which arise in getting an accurate understanding of the motion of such bodies in highly perturbed dynamical environments come, in part, from the nonlinearity of the dynamical system, but more so from the inadequacy of the classical approaches and methods. While modern formulations based on numerical integrations can give "precise" solutions for specific initial conditions, these afford little insight into the nature of the problem or the essential dependence of the perturbed motion on the system parameters. The predominant perturbations acting on HAMR objects and circumplanetary dust grains are solar radiation pressure, planetary oblateness, and third-body gravitational interactions induced by the Sun and nearby natural satellites. We developed first-order averaged models, based on the Milankovitch formulation of perturbation theory, which govern the long-term evolution of orbits subject to these perturbing forces. The unexpectedly rich results obtained by the use of this vector formalism are due to certain important circumstances in celestial and quantum mechanics which gave rise to its origin and development. An attempt has been made to trace these historical developments and to put them into the perspective of the present. The averaged equations of motion hold
NASA Astrophysics Data System (ADS)
Komjathy, A.; Yang, Y. M.; Meng, X.; Verkhoglyadova, O. P.; Mannucci, A. J.; Langley, R. B.
2015-12-01
Natural hazards, including earthquakes, volcanic eruptions, and tsunamis, have been significant threats to humans throughout recorded history. The Global Positioning System satellites have become primary sensors to measure signatures associated with such natural hazards. These signatures typically include GPS-derived seismic deformation measurements, co-seismic vertical displacements, and real-time GPS-derived ocean buoy positioning estimates. Another way to use GPS observables is to compute the ionospheric total electron content (TEC) to measure and monitor post-seismic ionospheric disturbances caused by earthquakes, volcanic eruptions, and tsunamis. Research at the University of New Brunswick (UNB) laid the foundations to model the three-dimensional ionosphere at NASA's Jet Propulsion Laboratory by ingesting ground- and space-based GPS measurements into the state-of-the-art Global Assimilative Ionosphere Modeling (GAIM) software. As an outcome of the UNB and NASA research, new and innovative GPS applications have been invented including the use of ionospheric measurements to detect tiny fluctuations in the GPS signals between the spacecraft and GPS receivers caused by natural hazards occurring on or near the Earth's surface.We will show examples for early detection of natural hazards generated ionospheric signatures using ground-based and space-borne GPS receivers. We will also discuss recent results from the U.S. Real-time Earthquake Analysis for Disaster Mitigation Network (READI) exercises utilizing our algorithms. By studying the propagation properties of ionospheric perturbations generated by natural hazards along with applying sophisticated first-principles physics-based modeling, we are on track to develop new technologies that can potentially save human lives and minimize property damage. It is also expected that ionospheric monitoring of TEC perturbations might become an integral part of existing natural hazards warning systems.
Detection of Natural Hazards Generated TEC Perturbations and Related New Applications
NASA Astrophysics Data System (ADS)
Komjathy, A.; Yang, Y.; Langley, R. B.
2013-12-01
Natural hazards, including earthquakes, volcanic eruptions, and tsunamis, have been significant threats to humans throughout recorded history. The Global Positioning System satellites have become primary sensors to measure signatures associated with such natural hazards. These signatures typically include GPS-derived seismic deformation measurements, co-seismic vertical displacements, and real-time GPS-derived ocean buoy positioning estimates. Another way to use GPS observables is to compute the ionospheric total electron content (TEC) to measure and monitor post-seismic ionospheric disturbances caused by earthquakes, volcanic eruptions, and tsunamis. Research at the University of New Brunswick (UNB) laid the foundations to model the three-dimensional ionosphere at NASA's Jet Propulsion Laboratory by ingesting ground- and space-based GPS measurements into the state-of-the-art Global Assimilative Ionosphere Modeling (GAIM) software. As an outcome of the UNB and NASA research, new and innovative GPS applications have been invented including the use of ionospheric measurements to detect tiny fluctuations in the GPS signals between the spacecraft and GPS receivers caused by natural hazards occurring on or near the Earth's surface. This continuing research is expected to provide early warning for tsunamis, earthquakes, volcanic eruptions, and meteor impacts, for example, using GPS and other global navigation satellite systems. We will demonstrate new and upcoming applications including recent natural hazards and artificial explosions that generated TEC perturbations to perform state-of-the-art imaging and modeling of earthquakes, tsunamis and meteor impacts. By studying the propagation properties of ionospheric perturbations generated by natural hazards along with applying sophisticated first-principles physics-based modeling, we are on track to develop new technologies that can potentially save human lives and minimize property damage.
Natural and Anthropogenically Perturbed Biogenic Aerosol over Tropical South East Asia
NASA Astrophysics Data System (ADS)
Coe, H.; Robinson, N.; Allan, J. D.; Hewitt, C. N.
2014-12-01
Tropical forested regions are of interest as sources of atmospheric aerosol since they cover very large areas of the tropics and are a source of a large amount of volatile organic compounds which act as precursors for particle formation. Natural forest regions offer the potential to study the background state of the tropics and so potentially gain some insight into the pre-perturbed atmosphere. However, over the last decade in South East Asia, a considerable fraction of the native tropical deciduous forest has been deforested and replanted with palm oil plantations. This changes the range of volatile organic compounds that are emitted and act as sources of secondary organic aerosol. A suite of intensive ground and airborne measurements were made over both tropical forest and oil palm plantations in Sabah, Malaysia as part of the "Oxidant and Particle Photochemical Processes above a South East Asian tropical rainforest (OP3) during 2008. These data will be used together with recent improvements in our understanding of aerosol formation from biogenic compounds to discuss aerosol formation in tropical regions and the influence of human influence through widespread palm oil agriculture.
Vision and photoentrainment in fishes: the effects of natural and anthropogenic perturbation.
Collin, Shaun P; Hart, Nathan S
2015-01-01
Vision and photoentrainment in fishes are vital for feeding, avoiding predation, spatial orientation, navigation, social communication and the synchronization of many homeostatic functions such as activity patterns and sleep. The camera-like (image-forming) eyes of fishes are optimized to provide a clear view of their preferred ecological niche, while non-visual photoreceptors provide irradiance detection that mediates circadian photoentrainment, an endogenous time-keeping mechanism (biological clock) to respond to predictable changes in environmental conditions. Fish and fisheries are under pressure from both natural and anthropogenic perturbation, which in many cases alters the intensity and spectral composition of the light environment on which they depend for their survival. This review examines the effects of a changing light environment and turbidity on the health of fishes within a developmental and ecological context. Understanding the sensory environment of fishes is vital to predicting their responses and, ultimately, their resilience to environmental change and the potential for maintaining sustainable levels of biodiversity. PMID:24919443
Cleansing of the atmosphere: smoke removal under natural and perturbed conditions
Hallett, J.
1987-01-01
The overall cleansing of the atmosphere can be related to the efficiency of the precipitation system, which is small for individual cumulus clouds (O), intermediate for air mass thunderstorms (20%), and larger for a steady-state system such as a supercell or a depression (70%). Air processed by the storm is cleaned of its aerosol loading, depending on the detail of the microphysical process. It follows that in any disaster scenario whereby large amounts of smoke are emitted into the troposphere - volcanic eruption, comet impact, nuclear exchange fires - the immediate cloud forming and precipitation processes are of major importance in determining the scavenging rate and overall scavenging efficiency. Even in the unpolluted atmosphere, removal by any precipitation process depends critically on the likelihood of the aerosol containing air passing into a suitable precipitation system. In the case of Chernobyl, with iodine-activated soot, its removals is more likely as it passes into an ice-forming precipitation system, to be removed directly by ice nucleation. In the present atmosphere, statistics of parcel trajectory can give a mean removal rate; in the case of the perturbed atmosphere, major uncertainties remain on the nature and scale of the initial circulations.
NASA Astrophysics Data System (ADS)
McMahon, Jay W.
Solar radiation pressure is the largest non-gravitational perturbation for most satellites in the solar system, and can therefore have a significant influence on their orbital dynamics. This work presents a new method for representing the solar radiation pressure force acting on a satellite, and applies this theory to natural and artificial satellites. The solar radiation pressure acceleration is modeled as a Fourier series which depends on the Sun's location in a body-fixed frame; a new set of Fourier coefficients are derived for every latitude of the Sun in this frame, and the series is expanded in terms of the longitude of the Sun. The secular effects due to the solar radiation pressure perturbations are given analytically through the application of averaging theory when the satellite is in a synchronous orbit. This theory is then applied to binary asteroid systems to explain the Binary YORP effect. Long term predictions of the evolution of the near-Earth asteroid 1999 KW4 are discussed under the influence of solar radiation pressure, J2, and 3rd body gravitational effects from the Sun. Secular effects are shown to remain when the secondary asteroid becomes non-synchronous due to a librational motion. The theory is also applied to Earth orbiting spacecraft, and is shown to be a valuable tool for improved orbit determination. The Fourier series solar radiation pressure model derived here is shown to give comparable results for orbit determination of the GPS IIR-M satellites as JPL's solar radiation pressure model. The theory is also extended to incorporate the effects of the Earth's shadow analytically. This theory is briefly applied to the evolution of orbital debris to explain the assumptions that are necessary in order to use the cannonball model for debris orbit evolution, as is common in the literature. Finally, the averaging theory methodology is applied to a class of Earth orbiting solar sail spacecraft to show the orbital effects when the sails are made
The nature and energetics of AGN-driven perturbations in the hot gas in the Perseus Cluster
Zhuravleva, I.; Churazov, E.; Arevalo, P.; Schekochihin, A. A.; Forman, W. R.; Allen, S. W.; Simionescu, A.; Sunyaev, R.; Vikhlinin, A.; Werner, N.
2016-03-07
In this paper, cores of relaxed galaxy clusters are often disturbed by AGN. Their Chandra observations revealed a wealth of structures induced by shocks, subsonic gas motions, bubbles of relativistic plasma, etc. In this paper, we determine the nature and energy content of gas fluctuations in the Perseus core by probing statistical properties of emissivity fluctuations imprinted in the soft- and hard-band X-ray images. About 80 per cent of the total variance of perturbations on ~8–70 kpc scales in the core have an isobaric nature, i.e. are consistent with subsonic displacements of the gas in pressure equilibrium with the ambientmore » medium. The observed variance translates to the ratio of energy in perturbations to thermal energy of ~13 per cent. In the region dominated by weak ‘ripples’, about half of the total variance is associated with isobaric perturbations on scales of a few tens of kpc. If these isobaric perturbations are induced by buoyantly rising bubbles, then these results suggest that most of the AGN-injected energy should first go into bubbles rather than into shocks. Using simulations of a shock propagating through the Perseus atmosphere, we found that models reproducing the observed features of a central shock have more than 50 per cent of the AGN-injected energy associated with the bubble enthalpy and only about 20 per cent is carried away with the shock. Such energy partition is consistent with the AGN-feedback model, mediated by bubbles of relativistic plasma, and supports the importance of turbulence in the cooling–heating balance.« less
The nature and energetics of AGN-driven perturbations in the hot gas in the Perseus Cluster
NASA Astrophysics Data System (ADS)
Zhuravleva, I.; Churazov, E.; Arévalo, P.; Schekochihin, A. A.; Forman, W. R.; Allen, S. W.; Simionescu, A.; Sunyaev, R.; Vikhlinin, A.; Werner, N.
2016-05-01
Cores of relaxed galaxy clusters are often disturbed by AGN. Their Chandra observations revealed a wealth of structures induced by shocks, subsonic gas motions, bubbles of relativistic plasma, etc. In this paper, we determine the nature and energy content of gas fluctuations in the Perseus core by probing statistical properties of emissivity fluctuations imprinted in the soft- and hard-band X-ray images. About 80 per cent of the total variance of perturbations on ˜8-70 kpc scales in the core have an isobaric nature, i.e. are consistent with subsonic displacements of the gas in pressure equilibrium with the ambient medium. The observed variance translates to the ratio of energy in perturbations to thermal energy of ˜13 per cent. In the region dominated by weak `ripples', about half of the total variance is associated with isobaric perturbations on scales of a few tens of kpc. If these isobaric perturbations are induced by buoyantly rising bubbles, then these results suggest that most of the AGN-injected energy should first go into bubbles rather than into shocks. Using simulations of a shock propagating through the Perseus atmosphere, we found that models reproducing the observed features of a central shock have more than 50 per cent of the AGN-injected energy associated with the bubble enthalpy and only about 20 per cent is carried away with the shock. Such energy partition is consistent with the AGN-feedback model, mediated by bubbles of relativistic plasma, and supports the importance of turbulence in the cooling-heating balance.
Riley, Kevin E.; Hobza, Pavel
2008-01-12
In recent years it has been recognized that, because of their unique properties, halogen bonds have tremendous potential in the development of new pharmaceutical compounds and materials. In this study we investigate the phenomenon of halogen bonding by carrying out ab initio calculations on the halomethane-formaldehyde complexes as well as the fluorine substituted FnH₃-nCX---OCH₂ dimers, where the halogen bonding halogens (X) are chlorine, bromine, and iodine. Coupled cluster (CCSD(T)/aug-cc-pVTZ) calculations indicate that the binding energies for these type of interactions lie in the range between -1.05 kcal/mol (H₃CCl---OCH₂) and -3.72 kcal/mol (F₃CI---OCH₂). One of the most important findings in this study is that, according to symmetry adapted perturbation theory (SAPT) analyses, halogen bonds are largely dependent on both electrostatic and dispersion type interactions. As the halogen atom involved in halogen bonding becomes larger the interaction strength for this type of interaction also gets larger and, interestingly, more electrostatic (and less dispersive) in character. Halogen bonding interactions also become stronger and more electrostatic upon substitution of (the very electronegative) fluorines onto the halomethane molecule.
Chingangbam, Pravabati; Park, Changbom E-mail: cbp@kias.re.kr
2009-12-01
We simulate CMB maps including non-Gaussianity arising from cubic order perturbations of the primordial gravitational potential, characterized by the non-linearity parameter g{sub NL}. The maps are used to study the characteristic nature of the resulting non-Gaussian temperature fluctuations. We measure the genus and investigate how it deviates from Gaussian shape as a function of g{sub NL} and smoothing scale. We find that the deviation of the non-Gaussian genus curve from the Gaussian one has an antisymmetric, sine function like shape, implying more hot and more cold spots for g{sub NL} > 0 and less of both for g{sub NL} < 0. The deviation increases linearly with g{sub NL} and also exhibits mild increase as the smoothing scale increases. We further study other statistics derived from the genus, namely, the number of hot spots, the number of cold spots, combined number of hot and cold spots and the slope of the genus curve at mean temperature fluctuation. We find that these observables carry signatures of g{sub NL} that are clearly distinct from the quadratic order perturbations, encoded in the parameter f{sub NL}. Hence they can be very useful tools for distinguishing not only between non-Gaussian temperature fluctuations and Gaussian ones but also between g{sub NL} and f{sub NL} type non-Gaussianities.
Ver, L.M.B.; Mackenzie, F.T.; Lerman, A.
1999-07-01
In the past three centuries, human perturbations of the environment have affected the biogeochemical behavior of the global carbon cycle and that of the other three nutrient elements closely coupled to carbon: nitrogen, phosphorus, and sulfur. The partitioning of anthropogenic CO{sub 2} among its various sinks in the past, for the present, and for projections into the near future is controlled by the interactions of these four elemental cycles within the major environmental domains of the land, atmosphere, coastal oceanic zone, and open ocean. The authors analyze the past, present, and future behavior of the global carbon cycle using the Terrestrial-Ocean-aTmosphere Ecosystem Model (TOTEM), a unique process-based model of the four global coupled biogeochemical cycles of carbon, nitrogen, phosphorus, and sulfur. They find that during the past 300 yrs, anthropogenic CO{sub 2} was mainly stored in the atmosphere and in the open ocean. Human activities on land caused an enhanced loss of mass from the terrestrial organic matter reservoirs (phytomass and humus) mainly through deforestation and consequently increased humus remineralization, erosion, and transport to the coastal margins by rivers and runoff. Photosynthetic uptake by the terrestrial phytomass was enhanced owing to fertilization by increasing atmospheric CO{sub 2} concentrations and supported by nutrients remineralized from organic matter. TOTEM results indicate that through most of the past 300 yrs, the loss of C from deforestation and other land-use activities was greater than the gain from the enhanced photosynthetic uptake. Since pre-industrial time (since 1700), the net flux of CO{sub 2} from the coastal waters has decreased by 40%, from 0.20 Gt C/yr to 0.12 Gt C/yr. TOTEM analyses of atmospheric CO{sub 2} concentrations for the 21st century were based on the fossil-fuel emission projections of IPCC (business as usual scenario) and of the more restrictive UN 1997 Kyoto Protocol. By the mid-21st century
NASA Astrophysics Data System (ADS)
Yang, Y. M.; Komjathy, A.; Meng, X.; Verkhoglyadova, O. P.; Langley, R. B.; Mannucci, A. J.
2015-12-01
Traveling ionospheric disturbances (TIDs) induced by acoustic-gravity waves in the neutral atmosphere have significant impact on trans-ionospheric radio waves such as Global Navigation Satellite System (GNSS, including Global Position System (GPS)) measurements. Natural hazards and solid Earth events, such as earthquakes, tsunamis and volcanic eruptions are actual sources that may trigger acoustic and gravity waves resulting in traveling ionospheric disturbances (TIDs) in the upper atmosphere. Trans-ionospheric radio wave measurements sense the total electron content (TEC) along the signal propagation path. In this research, we introduce a novel GPS-based detection and estimation technique for remote sensing of atmospheric wave-induced TIDs including space weather phenomena induced by major natural hazard events, using TEC time series collected from worldwide ground-based dual-frequency GNSS (including GPS) receiver networks. We demonstrate the ability of using ground- and space-based dual-frequency GPS measurements to detect and monitor tsunami wave propagation from the 2011 Tohoku-Oki earthquake and tsunami. Major wave trains with different propagation speeds and wavelengths were identified through analysis of the GPS remote sensing observations. Dominant physical characteristics of atmospheric wave-induced TIDs are found to be associated with specific tsunami propagations and oceanic Rayleigh waves. In this research, we compared GPS-based observations, corresponding model simulations and tsunami wave propagation. Results are shown to lead to a better understanding of the tsunami-induced ionosphere responses. Based on current distribution of Plate Boundary Observatory GPS stations, the results indicate that tsunami-induced TIDs may be detected about 60 minutes prior to tsunamis arriving at the U.S. west coast. It is expected that this GNSS-based technology will become an integral part of future early-warning systems.
NASA Astrophysics Data System (ADS)
Gupta, Mohan Lal
The original Oslo 2-dimensional global tropospheric photochemical model is modified by extending its vertical domain to 24.5 km with new transport coefficients to deduce the annual global source strengths of parent hydrocarbons (C-1 to C-3, or LHCs) and to study the role of photochemistry of these hydrocarbons and isoprene (rm C _5H_8) on the chemical composition of natural and perturbed troposphere. Model transport features are studied by comparing simulated atmospheric distributions and trends of CFC-11, CFC-12 and ^{85}Kr with corresponding long term observations. Four different photochemical schemes PC-1, PC -2, PC-3, and PC-5, that include C-1, C-2, C-3 hydrocarbons and rm C_5H_8 respectively, are developed. OH radical distributions calculated using these schemes and averaged surface observation data of LHCs as their respective lower boundary conditions are validated by comparing simulated atmospheric distribution and trends of rm CH_3CCl_3 with ALE/GAGE observations. Annual steady state source strengths of LHCs and rm C_2Cl _4 are calculated from their surface observations and above stated OH distributions. Comparison of modeled concentrations of C-2 and C-3 hydrocarbons in the lowest model layer with their corresponding observations shows that the sources of these species are seasonal in nature. The effects of photochemistry of light nonmethane hydrocarbons (NMHCs) on distributions of selected tropospheric species and ratio distributions of key species and on the budgets of O_3, CO, NOx and HNO _3 are also evaluated. Simulations of multiple changes in individual source strengths of NOx, CH_4, CO, NMHCs suggest that per molecule injected, NOx from aircraft emissions is the most efficient, the magnitude of which decreases with increase in emissions, in changing the global averaged O_3 concentration. Among NMHCs, changes in propane and ethane emissions are the most effective in changing the global average O _3 concentration and steady state lifetime of CH_4
NASA Astrophysics Data System (ADS)
Plaksin, Igor; Guiruis, Raafat; Rodrigues, Luis; Mendes, Ricardo; Plaksin, Svyatoslav; Fernandes, Eduardo; Ferreira, Claudia
2015-06-01
Ejecting debris from free surface of liner is of considerable interest at optimization of explosive devices, in which the PBX-driven liner effects shock compression of gaseous matter. Following factors were historically considered as main drivers of material ejection: granular microstructure of liner material, roughness and surface defects of liner, and shock pressure time history in PBX-driven liner. In contrast to existing models, we are considering the small scale fluctuations of detonation flow as probable dominating factor of surface jetting in the PBX-driven collapsing liners. Obtained experimental evidence is indicative that jetting from the liners is caused by meso-scale perturbations of PBX detonations, which are identified as (1) ejecta of overdriven detonation products through detonation front, (2) ejecta-driven detonation cells, and (3) galloping detonation front motion. Spatially resolved scenarios of each of phenomena (1-3) were obtained in experiments with copper-liners and HMX-based PBXs fabricated on maximum packing density of crystalline constituents. Both the DRZ-induced perturbations translated to a PBX-driven liner and the ejected debris were recorded and quantitatively measured in the mesoscale range with application of the 96-channel optical analyzer MCOA-UC. Work was supported by the ONR and ONR Global Grants N00014-12-1-0477 and N62909-12-1-7131 with Drs. Clifford Bedford and John Zimmerman Program Managers.
Dehayes, D. )
1994-06-01
Winter injury occurs frequently to current-year needles of red spruce in the northern Appalachians and appears to be caused by subfreezing temperatures rather than foliar desiccation. Under ambient conditions, the maximum depth of cold tolerance achieved by red spruce needles in midwinter is barely sufficient to avoid freezing injury at common winter temperatures. Therefore, any perturbation that would decrease midwinter cold tolerance by just a few degrees substantially increases the probability of freezing injury. Laboratory and field experiments have demonstrated that extended winter thaws and exposure to ambient and simulated acidic cloud water increase the freezing sensitivity of red spruce. Repeated experiments have been unable to demonstrate a consistent negative influence of ambient or elevated ozone concentrations or elevated N on cold tolerance or freezing injury susceptibility. Rapid freezing, especially following solar heating of needles, has also resulted in some injury to both current-year and year-old needles, under laboratory conditions. Visible freezing injury and winter cold tolerance appear to be associated with relatively low foliar Ca concentrations. It is hypothesized that Ca leaching by acidic cloud water could increase freezing susceptibility by modifying membrane structure and/or permeability.
NASA Astrophysics Data System (ADS)
Yang, Y.; Komjathy, A.; Mannucci, A. J.
2013-12-01
Traveling ionospheric disturbances (TIDs) induced by acoustic-gravity waves in the neutral atmosphere have significant impact on trans-ionospheric Global Navigation Satellite System (GNSS) measurements. Natural hazard events, such as earthquakes, tsunamis and volcano eruptions are actual sources that may trigger acoustic and gravity waves resulting in disturbances in the upper atmosphere. GNSS measurements sense the integrated electron content (IEC) along the signal propagation path. Methods from the previous space weather related research may be applied to detect disturbances in IEC time series. In our work, we use wavelet-based detection and a novel estimation technique for remote sensing of atmospheric wave-induced TIDs including space weather phenomenon using dual frequency IEC time series collected form worldwide GNSS networks of ground and space-based GNSS measurements corresponding to major natural hazard events. Through the analysis from the GNSS sounding, we are able to find major wave trains that may be observable in the measurements using ground networks and spaceborne GNSS receivers. The dominant frequencies are seen to be associated with the selected nature hazard events. Furthermore, a comparison of space and ground-based GNSS observations, corresponding model simulations and other geophysical measurements will be shown to get a better understanding of the atmosphere-ionosphere responses due to major natural hazards. We anticipate that observations from GNSS remote sensing of thermosphere-ionosphere disturbances will become cornerstones for future applications in natural hazard monitoring and it is expected to become integral part of existing early-warning systems.
Technology Transfer Automated Retrieval System (TEKTRAN)
Perturbing lignification is possible in multiple and diverse ways. Without obvious growth/development phenotypes, transgenic angiosperms can have lignin levels reduced to half the normal level, can have compositions ranging from very high-guaiacyl/low-syringyl to almost totally syringyl, and can eve...
NASA Astrophysics Data System (ADS)
Jansing, C.; Mertins, H. C.; Gaupp, A.; Sokolov, A.; Gilbert, M. C.; Wahab, H.; Timmers, H.
2016-05-01
Reflectivity measurements on graphitic materials such as graphene at energies across the carbon K-edge are frustrated by significant intensity loss due to adventitious carbon on beamline mirrors. Such intensity reduction enhances effects due to perturbing high-order harmonics in the beam. These effects distort the actual structure of the reflectance curve. In order to overcome this limitation, a correction technique has been developed and demonstrated first with measurements for highly ordered pyrolytic graphite. The same approach may be applied to other graphitic materials such as graphene and it may be used with other synchrotron beamlines. The fraction of high-order harmonics was determined by passing the incident beam through a 87 nm thin silicon nitride absorber that can be well modeled. Using the corrected measurements the x-ray natural linear dichroism of the sample has been determined.
NASA Astrophysics Data System (ADS)
Lesgourges, J.
2013-08-01
We present a self-contained summary of the theory of linear cosmological perturbations. We emphasize the effect of the six parameters of the minimal cosmological model, first, on the spectrum of Cosmic Microwave Background temperature anisotropies, and second, on the linear matter power spectrum. We briefly review at the end the possible impact of a few non-minimal dark matter and dark energy models.
On dark energy isocurvature perturbation
Liu, Jie; Zhang, Xinmin; Li, Mingzhe E-mail: limz@nju.edu.cn
2011-06-01
Determining the equation of state of dark energy with astronomical observations is crucially important to understand the nature of dark energy. In performing a likelihood analysis of the data, especially of the cosmic microwave background and large scale structure data the dark energy perturbations have to be taken into account both for theoretical consistency and for numerical accuracy. Usually, one assumes in the global fitting analysis that the dark energy perturbations are adiabatic. In this paper, we study the dark energy isocurvature perturbation analytically and discuss its implications for the cosmic microwave background radiation and large scale structure. Furthermore, with the current astronomical observational data and by employing Markov Chain Monte Carlo method, we perform a global analysis of cosmological parameters assuming general initial conditions for the dark energy perturbations. The results show that the dark energy isocurvature perturbations are very weakly constrained and that purely adiabatic initial conditions are consistent with the data.
Kopeliovich, B. Z.; Pirner, H.-J.; Potashnikova, I. K.; Schmidt, Ivan; Tarasov, A. V.
2008-03-01
The Berger model of perturbative fragmentation of quarks to pions is improved by providing an absolute normalization and keeping all terms in a (1-z) expansion, which makes the calculation valid at all values of fractional pion momentum z. We also replace the nonrelativistic wave function of a loosely bound pion by the more realistic procedure of projecting to the light-cone pion wave function, which in turn is taken from well known models. The full calculation does not confirm the (1-z){sup 2} behavior of the fragmentation function (FF) predicted in [E. L. Berger, Z. Phys. C 4, 289 (1980); Phys. Lett. 89B, 241 (1980] for z>0.5, and only works at very large z>0.95, where it is in reasonable agreement with phenomenological FFs. Otherwise, we observe quite a different z-dependence which grossly underestimates data at smaller z. The disagreement is reduced after the addition of pions from decays of light vector mesons, but still remains considerable. The process dependent higher twist terms are also calculated exactly and found to be important at large z and/or p{sub T}.
Causal compensated perturbations in cosmology
NASA Technical Reports Server (NTRS)
Veeraraghavan, Shoba; Stebbins, Albert
1990-01-01
A theoretical framework is developed to calculate linear perturbations in the gravitational and matter fields which arise causally in response to the presence of stiff matter sources in a FRW cosmology. It is shown that, in order to satisfy energy and momentum conservation, the gravitational fields of the source must be compensated by perturbations in the matter and gravitational fields, and the role of such compensation in containing the initial inhomogeneities in their subsequent evolution is discussed. A complete formal solution is derived in terms of Green functions for the perturbations produced by an arbitrary source in a flat universe containing cold dark matter. Approximate Green function solutions are derived for the late-time density perturbations and late-time gravitational waves in a universe containing a radiation fluid. A cosmological energy-momentum pseudotensor is defined to clarify the nature of energy and momentum conservation in the expanding universe.
Perturbations i have Known and Loved
NASA Astrophysics Data System (ADS)
Field, Robert W.
2011-06-01
A spectroscopic perturbation is a disruption of a ^1Σ-^1Σ-like regular pattern that can embody level-shifts, extra lines, and intensity anomalies. Once upon a time, when a band was labeled ``perturbed,'' it was considered worthless because it could at best yield molecular constants unsuited for archival tables. Nevertheless, a few brave spectroscopists, notably Albin Lagerqvist and Richard Barrow, collected perturbations because they knew that the pattern of multiple perturbations formed an intricate puzzle that would eventually reveal the presence and electronic symmetry of otherwise unobservable electronic states. There are many kinds of patterns of broken patterns. In my PhD thesis I showed how to determine absolute vibrational assignments for the perturber from patterns among the observed values of perturbation matrix elements. When a ^3Π state is perturbed, its six (Ω, parity) components capture a pattern of level shifts and intensity anomalies that reveals more about the nature of the perturber than a simple perturbation of the single component of a ^1Σ state. In perturbation-facilitated OODR, a perturbed singlet level acts as a spectroscopic doorway through which the entire triplet manifold may be systematically explored. For polyatomic molecule vibrations, a vibrational polyad (a group of mutually perturbing vibrational levels, among which the perturbation matrix elements are expected to follow harmonic oscillator scaling rules) can contain more components than a ^3Π state and intrapolyad patterns can be exquisitely sensitive not merely to the nature of an interloper within the polyad but also to the eigenvector character of the vibronic state from which the polyad is viewed. Variation of scaled polyad interaction parameters from one polyad to the next, a pattern of patterns, can signal proximity to an isomerization barrier. Everything in Rydberg-land seems to scale as N⋆-3, yet a trespassing valence state causes all scaling and propensity rules go
NASA Astrophysics Data System (ADS)
Rangel, Tonatiuh; Sharifzadeh, Sahar; Rinn, Andre; da Jornada, Felipe H.; Shao, Meiyue; Witte, Gregor; Yang, Chao; Louie, Steven G.; Chatterjee, Sangaam; Kronik, Leeor; Neaton, Jeffrey B.
Organic semiconductors have attracted attention due to their potential for optoelectronics and novel phenomena, such as singlet fission. Here, we use many-body perturbation theory to simulate neutral excitations in acene and perylene crystals. By diagonalizing the full Bethe-Salpether (BSE) Hamiltonian beyond the Tamm Dancoff approximation (TDA), we find that both low-lying excitation energies and oscillator strengths are in improved agreement with experiments relative to the TDA. We characterize the low-lying excitons, focusing in the degree of charge-transfer and spatial delocalization, connecting their relevance to singlet fission. For perylene, we find overall good agreement with absorption measurements, and we see evidence for the formation of an ``exciton-polariton'' band in β-perylene. This work is supported by the DOE.
Palenik, Mark C.; Dunlap, Brett I.
2015-07-28
Despite the fundamental importance of electron density in density functional theory, perturbations are still usually dealt with using Hartree-Fock-like orbital equations known as coupled-perturbed Kohn-Sham (CPKS). As an alternative, we develop a perturbation theory that solves for the perturbed density directly, removing the need for CPKS. This replaces CPKS with a true Hohenberg-Kohn density perturbation theory. In CPKS, the perturbed density is found in the basis of products of occupied and virtual orbitals, which becomes ever more over-complete as the size of the orbital basis set increases. In our method, the perturbation to the density is expanded in terms of a series of density basis functions and found directly. It is possible to solve for the density in such a way that it makes the total energy stationary even if the density basis is incomplete.
Automated Lattice Perturbation Theory
Monahan, Christopher
2014-11-01
I review recent developments in automated lattice perturbation theory. Starting with an overview of lattice perturbation theory, I focus on the three automation packages currently "on the market": HiPPy/HPsrc, Pastor and PhySyCAl. I highlight some recent applications of these methods, particularly in B physics. In the final section I briefly discuss the related, but distinct, approach of numerical stochastic perturbation theory.
Frame independent cosmological perturbations
Prokopec, Tomislav; Weenink, Jan E-mail: j.g.weenink@uu.nl
2013-09-01
We compute the third order gauge invariant action for scalar-graviton interactions in the Jordan frame. We demonstrate that the gauge invariant action for scalar and tensor perturbations on one physical hypersurface only differs from that on another physical hypersurface via terms proportional to the equation of motion and boundary terms, such that the evolution of non-Gaussianity may be called unique. Moreover, we demonstrate that the gauge invariant curvature perturbation and graviton on uniform field hypersurfaces in the Jordan frame are equal to their counterparts in the Einstein frame. These frame independent perturbations are therefore particularly useful in relating results in different frames at the perturbative level. On the other hand, the field perturbation and graviton on uniform curvature hypersurfaces in the Jordan and Einstein frame are non-linearly related, as are their corresponding actions and n-point functions.
Calculating nonadiabatic pressure perturbations during multifield inflation
NASA Astrophysics Data System (ADS)
Huston, Ian; Christopherson, Adam J.
2012-03-01
Isocurvature perturbations naturally occur in models of inflation consisting of more than one scalar field. In this paper, we calculate the spectrum of isocurvature perturbations generated at the end of inflation for three different inflationary models consisting of two canonical scalar fields. The amount of nonadiabatic pressure present at the end of inflation can have observational consequences through the generation of vorticity and subsequently the sourcing of B-mode polarization. We compare two different definitions of isocurvature perturbations and show how these quantities evolve in different ways during inflation. Our results are calculated using the open source Pyflation numerical package which is available to download.
NASA Astrophysics Data System (ADS)
Rong, Shu-Jun; Liu, Qiu-Yu
2012-04-01
The puma model on the basis of the Lorentz and CPT violation may bring an economical interpretation to the conventional neutrinos oscillation and part of the anomalous oscillations. We study the effect of the perturbation to the puma model. In the case of the first-order perturbation which keeps the (23) interchange symmetry, the mixing matrix element Ue3 is always zero. The nonzero mixing matrix element Ue3 is obtained in the second-order perturbation that breaks the (23) interchange symmetry.
Guo, Yang; Sivalingam, Kantharuban; Valeev, Edward F; Neese, Frank
2016-03-01
Multi-reference (MR) electronic structure methods, such as MR configuration interaction or MR perturbation theory, can provide reliable energies and properties for many molecular phenomena like bond breaking, excited states, transition states or magnetic properties of transition metal complexes and clusters. However, owing to their inherent complexity, most MR methods are still too computationally expensive for large systems. Therefore the development of more computationally attractive MR approaches is necessary to enable routine application for large-scale chemical systems. Among the state-of-the-art MR methods, second-order N-electron valence state perturbation theory (NEVPT2) is an efficient, size-consistent, and intruder-state-free method. However, there are still two important bottlenecks in practical applications of NEVPT2 to large systems: (a) the high computational cost of NEVPT2 for large molecules, even with moderate active spaces and (b) the prohibitive cost for treating large active spaces. In this work, we address problem (a) by developing a linear scaling "partially contracted" NEVPT2 method. This development uses the idea of domain-based local pair natural orbitals (DLPNOs) to form a highly efficient algorithm. As shown previously in the framework of single-reference methods, the DLPNO concept leads to an enormous reduction in computational effort while at the same time providing high accuracy (approaching 99.9% of the correlation energy), robustness, and black-box character. In the DLPNO approach, the virtual space is spanned by pair natural orbitals that are expanded in terms of projected atomic orbitals in large orbital domains, while the inactive space is spanned by localized orbitals. The active orbitals are left untouched. Our implementation features a highly efficient "electron pair prescreening" that skips the negligible inactive pairs. The surviving pairs are treated using the partially contracted NEVPT2 formalism. A detailed comparison
NASA Astrophysics Data System (ADS)
Guo, Yang; Sivalingam, Kantharuban; Valeev, Edward F.; Neese, Frank
2016-03-01
Multi-reference (MR) electronic structure methods, such as MR configuration interaction or MR perturbation theory, can provide reliable energies and properties for many molecular phenomena like bond breaking, excited states, transition states or magnetic properties of transition metal complexes and clusters. However, owing to their inherent complexity, most MR methods are still too computationally expensive for large systems. Therefore the development of more computationally attractive MR approaches is necessary to enable routine application for large-scale chemical systems. Among the state-of-the-art MR methods, second-order N-electron valence state perturbation theory (NEVPT2) is an efficient, size-consistent, and intruder-state-free method. However, there are still two important bottlenecks in practical applications of NEVPT2 to large systems: (a) the high computational cost of NEVPT2 for large molecules, even with moderate active spaces and (b) the prohibitive cost for treating large active spaces. In this work, we address problem (a) by developing a linear scaling "partially contracted" NEVPT2 method. This development uses the idea of domain-based local pair natural orbitals (DLPNOs) to form a highly efficient algorithm. As shown previously in the framework of single-reference methods, the DLPNO concept leads to an enormous reduction in computational effort while at the same time providing high accuracy (approaching 99.9% of the correlation energy), robustness, and black-box character. In the DLPNO approach, the virtual space is spanned by pair natural orbitals that are expanded in terms of projected atomic orbitals in large orbital domains, while the inactive space is spanned by localized orbitals. The active orbitals are left untouched. Our implementation features a highly efficient "electron pair prescreening" that skips the negligible inactive pairs. The surviving pairs are treated using the partially contracted NEVPT2 formalism. A detailed comparison
NASA Astrophysics Data System (ADS)
Tiburzi, Brian C.
The era of high-precision lattice QCD has led to synergy between lattice computations and phenomenological input from chiral perturbation theory. We provide an introduction to chiral perturbation theory with a bent towards understanding properties of the nucleon and other low-lying baryons. Four main topics are the basis for this chapter. We begin with a discussion of broken symmetries and the procedure to construct the chiral Lagrangian. The second topic concerns specialized applications of chiral perturbation theory tailored to lattice QCD, such as partial quenching, lattice discretization, and finite-volume effects. We describe inclusion of the nucleon in chiral perturbation theory using a heavy-fermion Euclidean action. Issues of convergence are taken up as our final topic. We consider expansions in powers of the strange-quark mass, and the appearance of unphysical singularities in the heavy-particle formulation. Our aim is to guide lattice practitioners in understanding the predictions chiral perturbation theory makes for baryons, and show how the lattice will play a role in testing the rigor of the chiral expansion at physical values of the quark masses.
NASA Technical Reports Server (NTRS)
Criminale, W. O.; Lasseigne, D. G.; Jackson, T. L.
1995-01-01
An initial value approach is used to examine the dynamics of perturbations introduced into a vortex under strain. Both the basic vortex considered and the perturbations are taken as fully three-dimensional. An explicit solution for the time evolution of the vorticity perturbations is given for arbitrary initial vorticity. Analytical solutions for the resulting velocity components are found when the initial vorticity is assumed to be localized. For more general initial vorticity distributions, the velocity components are determined numerically. It is found that the variation in the radial direction of the initial vorticity disturbance is the most important factor influencing the qualitative behavior of the solutions. Transient growth in the magnitude of the velocity components is found to be directly attributable to the compactness of the initial vorticity.
Cosmological perturbations in antigravity
NASA Astrophysics Data System (ADS)
Oltean, Marius; Brandenberger, Robert
2014-10-01
We compute the evolution of cosmological perturbations in a recently proposed Weyl-symmetric theory of two scalar fields with oppositely signed conformal couplings to Einstein gravity. It is motivated from the minimal conformal extension of the standard model, such that one of these scalar fields is the Higgs while the other is a new particle, the dilaton, introduced to make the Higgs mass conformally symmetric. At the background level, the theory admits novel geodesically complete cyclic cosmological solutions characterized by a brief period of repulsive gravity, or "antigravity," during each successive transition from a big crunch to a big bang. For simplicity, we consider scalar perturbations in the absence of anisotropies, with potential set to zero and without any radiation. We show that despite the necessarily wrong-signed kinetic term of the dilaton in the full action, these perturbations are neither ghostlike nor tachyonic in the limit of strongly repulsive gravity. On this basis, we argue—pending a future analysis of vector and tensor perturbations—that, with respect to perturbative stability, the cosmological solutions of this theory are viable.
Liouvillian perturbations of black holes
NASA Astrophysics Data System (ADS)
Couch, W. E.; Holder, C. L.
2007-10-01
We apply the well-known Kovacic algorithm to find closed form, i.e., Liouvillian solutions, to the differential equations governing perturbations of black holes. Our analysis includes the full gravitational perturbations of Schwarzschild and Kerr, the full gravitational and electromagnetic perturbations of Reissner-Nordstrom, and specialized perturbations of the Kerr-Newman geometry. We also include the extreme geometries. We find all frequencies ω, in terms of black hole parameters and an integer n, which allow Liouvillian perturbations. We display many classes of black hole parameter values and their corresponding Liouvillian perturbations, including new closed-form perturbations of Kerr and Reissner-Nordstrom. We also prove that the only type 1 Liouvillian perturbations of Schwarzschild are the known algebraically special ones and that type 2 Liouvillian solutions do not exist for extreme geometries. In cases where we do not prove the existence or nonexistence of Liouvillian perturbations we obtain sequences of Diophantine equations on which decidability rests.
Perturbations in bouncing and cyclic models
NASA Astrophysics Data System (ADS)
Biswas, Tirthabir; Mayes, Riley; Lattyak, Colleen
2016-03-01
Being able to reliably track perturbations across bounces and turnarounds in cyclic and bouncing cosmology lies at the heart of being able to compare the predictions of these models with the cosmic microwave background observations. This has been a challenging task due to the unknown nature of the physics involved during the bounce as well as the technical challenge of matching perturbations precisely between the expansion and contraction phases. In this paper, we present some general techniques (analytical and numerical) that can be applied to understand the physics of the fluctuations, especially those with "long" wavelengths, and apply our techniques to nonsingular cosmological models such as the bounce inflation and cyclic inflation.
Topology and perturbation theory
NASA Astrophysics Data System (ADS)
Manjavidze, J.
2000-08-01
This paper contains description of the fields nonlinear modes successive quantization scheme. It is shown that the path integrals for absorption part of amplitudes are defined on the Dirac (δ-like) functional measure. This permits arbitrary transformation of the functional integral variables. New form of the perturbation theory achieved by mapping the quantum dynamics in the space WG of the (action, angle)-type collective variables. It is shown that the transformed perturbation theory contributions are accumulated exactly on the boundary ∂WG. Abilities of the developed formalism are illustrated by the Coulomb problem. This model is solved in the WC=(angle, angular momentum, Runge-Lentz vector) space and the reason of its exact integrability is emptiness of ∂WC.
Renormalized Lie perturbation theory
Rosengaus, E.; Dewar, R.L.
1981-07-01
A Lie operator method for constructing action-angle transformations continuously connected to the identity is developed for area preserving mappings. By a simple change of variable from action to angular frequency a perturbation expansion is obtained in which the small denominators have been renormalized. The method is shown to lead to the same series as the Lagrangian perturbation method of Greene and Percival, which converges on KAM surfaces. The method is not superconvergent, but yields simple recursion relations which allow automatic algebraic manipulation techniques to be used to develop the series to high order. It is argued that the operator method can be justified by analytically continuing from the complex angular frequency plane onto the real line. The resulting picture is one where preserved primary KAM surfaces are continuously connected to one another.
Intermolecular perturbation theory
NASA Astrophysics Data System (ADS)
Hayes, I. C.; Hurst, G. J. B.; Stone, A. J.
The new intermolecular perturbation theory described in the preceding papers is applied to some van der Waals molecules. HeBe is used as a test case, and the perturbation method converges well at interatomic distances down to about 4 a0, giving results in excellent agreement with supermolecule calculations. ArHF and ArHCl have been studied using large basis sets, and the results agree well with experimental data. The ArHX configuration is favoured over the ArXH configuration mainly because of larger polarization and charge-transfer contributions. In NeH2 the equilibrium geometry is determined by a delicate balance between opposing effects; with a double-zeta-polarization basis the correct configuration is predicted.
Aspects of perturbative unitarity
NASA Astrophysics Data System (ADS)
Anselmi, Damiano
2016-07-01
We reconsider perturbative unitarity in quantum field theory and upgrade several arguments and results. The minimum assumptions that lead to the largest time equation, the cutting equations and the unitarity equation are identified. Using this knowledge and a special gauge, we give a new, simpler proof of perturbative unitarity in gauge theories and generalize it to quantum gravity, in four and higher dimensions. The special gauge interpolates between the Feynman gauge and the Coulomb gauge without double poles. When the Coulomb limit is approached, the unphysical particles drop out of the cuts and the cutting equations are consistently projected onto the physical subspace. The proof does not extend to nonlocal quantum field theories of gauge fields and gravity, whose unitarity remains uncertain.
Rolling axions during inflation: perturbativity and signatures
NASA Astrophysics Data System (ADS)
Peloso, Marco; Sorbo, Lorenzo; Unal, Caner
2016-09-01
The motion of a pseudo-scalar field X during inflation naturally induces a significant amplification of the gauge fields to which it is coupled. The amplified gauge fields can source characteristic scalar and tensor primordial perturbations. Several phenomenological implications have been discussed in the cases in which (i) X is the inflaton, and (ii) X is a field different from the inflaton, that experiences a temporary speed up during inflation. In this second case, visible sourced gravitational waves (GW) can be produced at the CMB scales without affecting the scalar perturbations, even if the scale of inflation is several orders of magnitude below what is required to produce a visible vacuum GW signal. Perturbativity considerations can be used to limit the regime in which these results are under perturbative control. We revised limits recently claimed for the case (i), and we extend these considerations to the case (ii). We show that, in both cases, these limits are satisfied by the applications that generate signals at CMB scales. Applications that generate gravitational waves and primordial black holes at much smaller scales are at the limit of the validity of this perturbativity analysis, so we expect those results to be valid up to possibly order one corrections.
Baryon chiral perturbation theory
NASA Astrophysics Data System (ADS)
Scherer, S.
2012-03-01
We provide a short introduction to the one-nucleon sector of chiral perturbation theory and address the issue of power counting and renormalization. We discuss the infrared regularization and the extended on-mass-shell scheme. Both allow for the inclusion of further degrees of freedom beyond pions and nucleons and the application to higher-loop calculations. As applications we consider the chiral expansion of the nucleon mass to order Script O(q6) and the inclusion of vector and axial-vector mesons in the calculation of nucleon form factors. Finally, we address the complex-mass scheme for describing unstable particles in effective field theory.
Discrete reductive perturbation technique
Levi, Decio; Petrera, Matteo
2006-04-15
We expand a partial difference equation (P{delta}E) on multiple lattices and obtain the P{delta}E which governs its far field behavior. The perturbative-reductive approach is here performed on well-known nonlinear P{delta}Es, both integrable and nonintegrable. We study the cases of the lattice modified Korteweg-de Vries (mKdV) equation, the Hietarinta equation, the lattice Volterra-Kac-Van Moerbeke equation and a nonintegrable lattice KdV equation. Such reductions allow us to obtain many new P{delta}Es of the nonlinear Schroedinger type.
Dynamics of free surface perturbations along an annular viscous film
NASA Astrophysics Data System (ADS)
Smolka, Linda B.; North, Justin; Guerra, Bree K.
2008-03-01
It is known that the free surface of an axisymmetric viscous film flowing down the outside of a thin vertical fiber under the influence of gravity becomes unstable to interfacial perturbations. We present an experimental study using fluids with different densities, surface tensions, and viscosities to investigate the growth and dynamics of these interfacial perturbations and to test the assumptions made by previous authors. We find that the initial perturbation growth is exponential, followed by a slower phase as the amplitude and wavelength saturate in size. Measurements of the perturbation growth for experiments conducted at low and moderate Reynolds numbers are compared to theoretical predictions developed from linear stability theory. Excellent agreement is found between predictions from a long-wave Stokes flow model [Craster and Matar, J. Fluid Mech. 553, 85 (2006)] and data, while fair to excellent agreement (depending on fiber size) is found between predictions from a moderate-Reynolds-number model [Sisoev , Chem. Eng. Sci. 61, 7279 (2006)] and data. Furthermore, we find that a known transition in the longer-time perturbation dynamics from unsteady to steady behavior at a critical flow rate Qc is correlated with a transition in the rate at which perturbations naturally form along the fiber. For Q
Canonical floquet perturbation theory
NASA Astrophysics Data System (ADS)
Pohlen, David J.
1992-12-01
Classical Floquet theory is examined in order to generate a canonical transformation to modal variables for periodic system. This transformation is considered canonical if the periodic matrix of eigenvectors is symplectic at the initial time. Approaches for symplectic normalization of the eigenvectors had to be examined for each of the different Poincare eigenvalue cases. Particular attention was required in the degenerate case, which depended on the solution of a generalized eigenvector. Transformation techniques to ensure real modal variables and real periodic eigenvectors were also needed. Periodic trajectories in the restricted three-body case were then evaluated using the canonical Floquet solution. The system used for analyses is the Sun-Jupiter system. This system was especially useful since it contained two of the more difficult Poincare eigenvalue cases, the degenerate case and the imaginary eigenvalue case. The perturbation solution to the canonical modal variables was examined using both an expansion of the Hamiltonian and using a representation that was considered exact. Both methods compared quite well for small perturbations to the initial condition. As expected, the expansion solution failed first due to truncation after the third order term of the expansion.
Perturbative Lagrangian approach to gravitational instability.
NASA Astrophysics Data System (ADS)
Bouchet, F. R.; Colombi, S.; Hivon, E.; Juszkiewicz, R.
1995-04-01
This paper deals with the time evolution in the matter era of perturbations in Friedman-Lemaitre models with arbitrary density parameter {OMEGA}, with either a zero cosmological constant, {LAMBDA}=0, or with a non-zero cosmological constant in a spatially flat Universe. Unlike the classical Eulerian approach where the density contrast is expanded in a perturbative series, this analysis relies instead on a perturbative expansion of particles trajectories in Lagrangian coordinates. This brings a number of advantages over the classical analysis. In particular, it enables the description of stronger density contrasts. Indeed the linear term in the Lagrangian perturbative series is the famous Zeldovich approximate solution (1970). The idea to consider the higher order terms was introduced by Moutarde et al. (1991), generalized by Bouchet et al. (1992), and further developed by many others. We present here a systematic and detailed account of this approach. We give analytical results (or fits to numerical results) up to the third order (which is necessary to compute, for instance, the four point spatial correlation function or the corrections to the linear evolution of the two-point correlation function, as well as the secondary temperature anisotropies of the Cosmic Microwave Background). We then proceed to explore the link between the Lagrangian description and statistical measures. We show in particular that Lagrangian perturbation theory provides a natural framework to compute the effect of redshift distortions, using the skewness of the density distribution function as an example. Finally, we show how well the second order theory does as compared to other approximations in the case of spherically symmetric perturbations. We also compare this second order approximation and Zeldovich solution to N-body simulations with scale-free (n=-2) Gaussian initial conditions. We find that second order theory is both simple and powerful.
Flatbands under correlated perturbations.
Bodyfelt, Joshua D; Leykam, Daniel; Danieli, Carlo; Yu, Xiaoquan; Flach, Sergej
2014-12-01
Flatband networks are characterized by the coexistence of dispersive and flatbands. Flatbands (FBs) are generated by compact localized eigenstates (CLSs) with local network symmetries, based on destructive interference. Correlated disorder and quasiperiodic potentials hybridize CLSs without additional renormalization, yet with surprising consequences: (i) states are expelled from the FB energy E_{FB}, (ii) the localization length of eigenstates vanishes as ξ∼1/ln(E-E_{FB}), (iii) the density of states diverges logarithmically (particle-hole symmetry) and algebraically (no particle-hole symmetry), and (iv) mobility edge curves show algebraic singularities at E_{FB}. Our analytical results are based on perturbative expansions of the CLSs and supported by numerical data in one and two lattice dimensions. PMID:25526142
Flatbands under Correlated Perturbations
NASA Astrophysics Data System (ADS)
Bodyfelt, Joshua D.; Leykam, Daniel; Danieli, Carlo; Yu, Xiaoquan; Flach, Sergej
2014-12-01
Flatband networks are characterized by the coexistence of dispersive and flatbands. Flatbands (FBs) are generated by compact localized eigenstates (CLSs) with local network symmetries, based on destructive interference. Correlated disorder and quasiperiodic potentials hybridize CLSs without additional renormalization, yet with surprising consequences: (i) states are expelled from the FB energy EFB, (ii) the localization length of eigenstates vanishes as ξ ˜1 /ln (E -EFB) , (iii) the density of states diverges logarithmically (particle-hole symmetry) and algebraically (no particle-hole symmetry), and (iv) mobility edge curves show algebraic singularities at EFB . Our analytical results are based on perturbative expansions of the CLSs and supported by numerical data in one and two lattice dimensions.
Discrete Newtonian cosmology: perturbations
NASA Astrophysics Data System (ADS)
Ellis, George F. R.; Gibbons, Gary W.
2015-03-01
In a previous paper (Gibbons and Ellis 2014 Discrete Newtonian cosmology Class. Quantum Grav. 31 025003), we showed how a finite system of discrete particles interacting with each other via Newtonian gravitational attraction would lead to precisely the same dynamical equations for homothetic motion as in the case of the pressure-free Friedmann-Lemaître-Robertson-Walker cosmological models of general relativity theory, provided the distribution of particles obeys the central configuration equation. In this paper we show that one can obtain perturbed such Newtonian solutions that give the same linearized structure growth equations as in the general relativity case. We also obtain the Dmitriev-Zel’dovich equations for subsystems in this discrete gravitational model, and show how it leads to the conclusion that voids have an apparent negative mass.
Perturbed effects at radiation physics
NASA Astrophysics Data System (ADS)
Külahcı, Fatih; Şen, Zekâi
2013-09-01
Perturbation methodology is applied in order to assess the linear attenuation coefficient, mass attenuation coefficient and cross-section behavior with random components in the basic variables such as the radiation amounts frequently used in the radiation physics and chemistry. Additionally, layer attenuation coefficient (LAC) and perturbed LAC (PLAC) are proposed for different contact materials. Perturbation methodology provides opportunity to obtain results with random deviations from the average behavior of each variable that enters the whole mathematical expression. The basic photon intensity variation expression as the inverse exponential power law (as Beer-Lambert's law) is adopted for perturbation method exposition. Perturbed results are presented not only in terms of the mean but additionally the standard deviation and the correlation coefficients. Such perturbation expressions provide one to assess small random variability in basic variables.
Controlling chaos in a high dimensional system with periodic parametric perturbations
Mirus, K.A.; Sprott, J.C.
1998-10-01
The effect of applying a periodic perturbation to an accessible parameter of a high-dimensional (coupled-Lorenz) chaotic system is examined. Numerical results indicate that perturbation frequencies near the natural frequencies of the unstable periodic orbits of the chaotic system can result in limit cycles or significantly reduced dimension for relatively small perturbations.
First order perturbations of the Einstein-Straus and Oppenheimer-Snyder models
Mars, Marc; Mena, Filipe C.; Vera, Rauel
2008-10-15
We derive the linearly perturbed matching conditions between a Schwarzschild spacetime region with stationary and axially symmetric perturbations and a Friedmann-Lemaitre-Robertson-Walker (FLRW) spacetime with arbitrary perturbations. The matching hypersurface is also perturbed arbitrarily and, in all cases, the perturbations are decomposed into scalars using the Hodge operator on the sphere. This allows us to write down the matching conditions in a compact way. In particular, we find that the existence of a perturbed (rotating, stationary, and vacuum) Schwarzschild cavity in a perturbed FLRW universe forces the cosmological perturbations to satisfy constraints that link rotational and gravitational wave perturbations. We also prove that if the perturbation on the FLRW side vanishes identically, then the vacuole must be perturbatively static and hence Schwarzschild. By the dual nature of the problem, the first result translates into links between rotational and gravitational wave perturbations on a perturbed Oppenheimer-Snyder model, where the perturbed FLRW dust collapses in a perturbed Schwarzschild environment which rotates in equilibrium. The second result implies, in particular, that no region described by FLRW can be a source of the Kerr metric.
First order perturbations of the Einstein-Straus and Oppenheimer-Snyder models
NASA Astrophysics Data System (ADS)
Mars, Marc; Mena, Filipe C.; Vera, Raül
2008-10-01
We derive the linearly perturbed matching conditions between a Schwarzschild spacetime region with stationary and axially symmetric perturbations and a Friedmann-Lemaître-Robertson-Walker (FLRW) spacetime with arbitrary perturbations. The matching hypersurface is also perturbed arbitrarily and, in all cases, the perturbations are decomposed into scalars using the Hodge operator on the sphere. This allows us to write down the matching conditions in a compact way. In particular, we find that the existence of a perturbed (rotating, stationary, and vacuum) Schwarzschild cavity in a perturbed FLRW universe forces the cosmological perturbations to satisfy constraints that link rotational and gravitational wave perturbations. We also prove that if the perturbation on the FLRW side vanishes identically, then the vacuole must be perturbatively static and hence Schwarzschild. By the dual nature of the problem, the first result translates into links between rotational and gravitational wave perturbations on a perturbed Oppenheimer-Snyder model, where the perturbed FLRW dust collapses in a perturbed Schwarzschild environment which rotates in equilibrium. The second result implies, in particular, that no region described by FLRW can be a source of the Kerr metric.
Cosmological perturbations in massive bigravity
Lagos, Macarena; Ferreira, Pedro G. E-mail: p.ferreira1@physics.ox.ac.uk
2014-12-01
We present a comprehensive analysis of classical scalar, vector and tensor cosmological perturbations in ghost-free massive bigravity. In particular, we find the full evolution equations and analytical solutions in a wide range of regimes. We show that there are viable cosmological backgrounds but, as has been found in the literature, these models generally have exponential instabilities in linear perturbation theory. However, it is possible to find stable scalar cosmological perturbations for a very particular choice of parameters. For this stable subclass of models we find that vector and tensor perturbations have growing solutions. We argue that special initial conditions are needed for tensor modes in order to have a viable model.
Canonical density matrix perturbation theory.
Niklasson, Anders M N; Cawkwell, M J; Rubensson, Emanuel H; Rudberg, Elias
2015-12-01
Density matrix perturbation theory [Niklasson and Challacombe, Phys. Rev. Lett. 92, 193001 (2004)] is generalized to canonical (NVT) free-energy ensembles in tight-binding, Hartree-Fock, or Kohn-Sham density-functional theory. The canonical density matrix perturbation theory can be used to calculate temperature-dependent response properties from the coupled perturbed self-consistent field equations as in density-functional perturbation theory. The method is well suited to take advantage of sparse matrix algebra to achieve linear scaling complexity in the computational cost as a function of system size for sufficiently large nonmetallic materials and metals at high temperatures. PMID:26764847
On the divergences of inflationary superhorizon perturbations
Enqvist, K; Nurmi, S; Podolsky, D; Rigopoulos, G I E-mail: sami.nurmi@helsinki.fi E-mail: gerasimos.rigopoulos@helsinki.fi
2008-04-15
We discuss the infrared divergences that appear to plague cosmological perturbation theory. We show that, within the stochastic framework, they are regulated by eternal inflation so that the theory predicts finite fluctuations. Using the {Delta}N formalism to one loop, we demonstrate that the infrared modes can be absorbed into additive constants and the coefficients of the diagrammatic expansion for the connected parts of two-and three-point functions of the curvature perturbation. As a result, the use of any infrared cutoff below the scale of eternal inflation is permitted, provided that the background fields are appropriately redefined. The natural choice for the infrared cutoff would, of course, be the present horizon; other choices manifest themselves in the running of the correlators. We also demonstrate that it is possible to define observables that are renormalization-group-invariant. As an example, we derive a non-perturbative, infrared finite and renormalization point-independent relation between the two-point correlators of the curvature perturbation for the case of the free single field.
Do cosmological perturbations have zero mean?
Armendariz-Picon, Cristian
2011-03-01
A central assumption in our analysis of cosmic structure is that cosmological perturbations have a constant ensemble mean, which can be set to zero by appropriate choice of the background. This property is one of the consequences of statistical homogeneity, the invariance of correlation functions under spatial translations. In this article we explore whether cosmological perturbations indeed have zero mean, and thus test one aspect of statistical homogeneity. We carry out a classical test of the zero mean hypothesis against a class of alternatives in which primordial perturbations have inhomogeneous non-vanishing means, but homogeneous and isotropic covariances. Apart from Gaussianity, our test does not make any additional assumptions about the nature of the perturbations and is thus rather generic and model-independent. The test statistic we employ is essentially Student's t statistic, applied to appropriately masked, foreground-cleaned cosmic microwave background anisotropy maps produced by the WMAP mission. We find evidence for a non-zero mean in a particular range of multipoles, but the evidence against the zero mean hypothesis goes away when we correct for multiple testing. We also place constraints on the mean of the temperature multipoles as a function of angular scale. On angular scales smaller than four degrees, a non-zero mean has to be at least an order of magnitude smaller than the standard deviation of the temperature anisotropies.
Controlling chaos in low and high dimensional systems with periodic parametric perturbations
Mirus, K.A.; Sprott, J.C.
1998-06-01
The effect of applying a periodic perturbation to an accessible parameter of various chaotic systems is examined. Numerical results indicate that perturbation frequencies near the natural frequencies of the unstable periodic orbits of the chaotic systems can result in limit cycles for relatively small perturbations. Such perturbations can also control or significantly reduce the dimension of high-dimensional systems. Initial application to the control of fluctuations in a prototypical magnetic fusion plasma device will be reviewed.
Resumming the string perturbation series
NASA Astrophysics Data System (ADS)
Grassi, Alba; Mariño, Marcos; Zakany, Szabolcs
2015-05-01
We use the AdS/CFT correspondence to study the resummation of a perturbative genus expansion appearing in the type II superstring dual of ABJM theory. Although the series is Borel summable, its Borel resummation does not agree with the exact non-perturbative answer due to the presence of complex instantons. The same type of behavior appears in the WKB quantization of the quartic oscillator in Quantum Mechanics, which we analyze in detail as a toy model for the string perturbation series. We conclude that, in these examples, Borel summability is not enough for extracting non-perturbative information, due to non-perturbative effects associated to complex instantons. We also analyze the resummation of the genus expansion for topological string theory on local , which is closely related to ABJM theory. In this case, the non-perturbative answer involves membrane instantons computed by the refined topological string, which are crucial to produce a well-defined result. We give evidence that the Borel resummation of the perturbative series requires such a non-perturbative sector.
Life expectancy change in perturbed communities: derivation and qualitative analysis.
Dambacher, Jeffrey M; Levins, Richard; Rossignol, Philippe A
2005-09-01
Pollution, loss of habitat, and climate change are introducing dramatic perturbations to natural communities and affecting public health. Populations in perturbed communities can change dynamically, in both abundance and age structure. While analysis of the community matrix can predict changes in population abundance arising from a sustained or press perturbation, perturbations also have the potential to modify life expectancy, which adds yet another means to falsify experimental hypotheses and to monitor management interventions in natural systems. In some instances, an input to a community will produce no change in the abundance of a population but create a major shift in its mean age. We present an analysis of change in both abundance and life expectancy, leading to a formal quantitative assessment as well as qualitative predictions, and illustrate the usefulness of the technique through general examples relating to vector-borne disease and fisheries. PMID:16043195
Computing singularities of perturbation series
Kvaal, Simen; Jarlebring, Elias; Michiels, Wim
2011-03-15
Many properties of current ab initio approaches to the quantum many-body problem, both perturbational and otherwise, are related to the singularity structure of the Rayleigh-Schroedinger perturbation series. A numerical procedure is presented that in principle computes the complete set of singularities, including the dominant singularity which limits the radius of convergence. The method approximates the singularities as eigenvalues of a certain generalized eigenvalue equation which is solved using iterative techniques. It relies on computation of the action of the Hamiltonian matrix on a vector and does not rely on the terms in the perturbation series. The method can be useful for studying perturbation series of typical systems of moderate size, for fundamental development of resummation schemes, and for understanding the structure of singularities for typical systems. Some illustrative model problems are studied, including a helium-like model with {delta}-function interactions for which Moeller-Plesset perturbation theory is considered and the radius of convergence found.
Axion inflation with cross-correlated axion isocurvature perturbations
NASA Astrophysics Data System (ADS)
Kadota, Kenji; Kobayashi, Tatsuo; Otsuka, Hajime
2016-01-01
We study the inflation scenarios, in the framework of superstring theory, where the inflaton is an axion producing the adiabatic curvature perturbations while there exists another light axion producing the isocurvature perturbations. We discuss how the non-trivial couplings among string axions can generically arise, and calculate the consequent cross-correlations between the adiabatic and isocurvature modes through concrete examples. Based on the Planck analysis on the generally correlated isocurvature perturbations, we show that there is a preference for the existence of the correlated isocurvature modes for the axion monodromy inflation while the natural inflation disfavors such isocurvature modes.
A general analysis of non-gaussianity from isocurvature perturbations
Kawasaki, Masahiro; Nakayama, Kazunori; Sekiguchi, Toyokazu; Suyama, Teruaki; Takahashi, Fuminobu E-mail: nakayama@icrr.u-tokyo.ac.jp E-mail: teruaki.suyama@uclouvain.be
2009-01-15
Light scalars may be ubiquitous in nature, and their quantum fluctuations can produce large non-Gaussianity in the cosmic microwave background temperature anisotropy. The non-Gaussianity may be accompanied with a small admixture of isocurvature perturbations, which often have correlations with the curvature perturbations. We present a general method to calculate the non-Gaussianity in the adiabatic and isocurvature perturbations with and without correlations, and see how it works in several explicit examples. We also show that they leave distinct signatures on the bispectrum of the cosmic microwave background temperature fluctuations.
Statistical anisotropy of the curvature perturbation from vector field perturbations
Dimopoulos, Konstantinos; Karciauskas, Mindaugas; Lyth, David H.; Rodriguez, Yeinzon E-mail: m.karciauskas@lancaster.ac.uk E-mail: yeinzon.rodriguez@uan.edu.co
2009-05-15
The {delta}N formula for the primordial curvature perturbation {zeta} is extended to include vector as well as scalar fields. Formulas for the tree-level contributions to the spectrum and bispectrum of {zeta} are given, exhibiting statistical anisotropy. The one-loop contribution to the spectrum of {zeta} is also worked out. We then consider the generation of vector field perturbations from the vacuum, including the longitudinal component that will be present if there is no gauge invariance. Finally, the {delta}N formula is applied to the vector curvaton and vector inflation models with the tensor perturbation also evaluated in the latter case.
Geometric perturbation theory and plasma physics
Omohundro, S.M.
1985-04-04
Modern differential geometric techniques are used to unify the physical asymptotics underlying mechanics, wave theory and statistical mechanics. The approach gives new insights into the structure of physical theories and is suited to the needs of modern large-scale computer simulation and symbol manipulation systems. A coordinate-free formulation of non-singular perturbation theory is given, from which a new Hamiltonian perturbation structure is derived and related to the unperturbed structure. The theory of perturbations in the presence of symmetry is developed, and the method of averaging is related to reduction by a circle group action. The pseudo-forces and magnetic Poisson bracket terms due to reduction are given a natural asymptotic interpretation. Similar terms due to changing reference frames are related to the method of variation of parameters, which is also given a Hamiltonian formulation. These methods are used to answer a question about nearly periodic systems. The answer leads to a new secular perturbation theory that contains no ad hoc elements. Eikonal wave theory is given a Hamiltonian formulation that generalizes Whitham's Lagrangian approach. The evolution of wave action density on ray phase space is given a Hamiltonian structure using a Lie-Poisson bracket. The relationship between dissipative and Hamiltonian systems is discussed. A new type of attractor is defined which attracts both forward and backward in time and is shown to occur in infinite-dimensional Hamiltonian systems with dissipative behavior. The theory of Smale horseshoes is applied to gyromotion in the neighborhood of a magnetic field reversal and the phenomenon of reinsertion in area-preserving horseshoes is introduced. The central limit theorem is proved by renormalization group techniques. A natural symplectic structure for thermodynamics is shown to arise asymptotically from the maximum entropy formalism.
Cosmological perturbations during radion stabilization
NASA Astrophysics Data System (ADS)
Ashcroft, P. R.; van de Bruck, C.; Davis, A.-C.
2005-01-01
We consider the evolution of cosmological perturbations during radion stabilization, which we assume to happen after a period of inflation in the early universe. Concentrating on the Randall-Sundrum brane world scenario, we find that, if matter is present both on the positive and negative tension branes, the coupling of the radion to matter fields could have significant impact on the evolution of the curvature perturbation and on the production of entropy perturbations. We investigate both the case of a long-lived and a short-lived radion and outline similarities and differences to the curvaton scenario.
Tubulin-perturbing naphthoquinone spiroketals.
Balachandran, Raghavan; Hopkins, Tamara D; Thomas, Catherine A; Wipf, Peter; Day, Billy W
2008-02-01
Several natural and synthetic naphthoquinone spiroketals are potent inhibitors of the thioredoxin-thioredoxin reductase redox system. Based on the antimitotic and weak antitubulin actions noted for SR-7 ([8-(furan-3-ylmethoxy)-1-oxo-1,4-dihydronaphthalene-4-spiro-2'-naphtho[1'',8''-de][1',3'][dioxin]), a library of related compounds was screened for tubulin-perturbing properties. Two compounds, TH-169 (5'-hydroxy-4'H-spiro[1,3-dioxolane-2,1'-naphthalen]-4'-one) and TH-223 (5'-methoxy-4'H-spiro[1,3-dioxane-2,1'-naphthalen]-4'-one), had substantial effects on tubulin assembly and were antiproliferative at low micromolar concentrations. TH-169 was the most potent at blocking GTP-dependent polymerization of 10 mum tubulin in vitro with a remarkable 50% inhibitory concentration of ca. 400 nm. It had no effect on paclitaxel-induced microtubule assembly and did not cause microtubule hypernucleation. TH-169 failed to compete with colchicine for binding to beta-tubulin. The 50% antiproliferative concentration of TH-169 against human cancer cells was at or slightly below 1 mum. Flow cytometry showed that 1 mum TH-169 caused an increase in G(2)/M and hypodiploid cells. TH-169 eliminated the PC-3 cells' polyploid population and increased their expression of p21(WAF1) and Hsp70 in a concentration-dependent manner. The antiproliferative effect of TH-169 was irreversible and independent of changes in caspases, actin, tubulin, glyceraldehyde phosphate dehydrogenase or Bcl-x(S/L). This structurally simple naphthoquinone spiroketal represents a small molecule, tubulin-interactive agent with a novel apoptotic pathway and attractive biological function. PMID:18194192
Isocurvature perturbations in extra radiation
Kawasaki, Masahiro; Miyamoto, Koichi; Nakayama, Kazunori; Sekiguchi, Toyokazu E-mail: miyamone@icrr.u-tokyo.ac.jp E-mail: oyokazu.sekiguchi@nagoya-u.jp
2012-02-01
Recent cosmological observations, including measurements of the CMB anisotropy and the primordial helium abundance, indicate the existence of an extra radiation component in the Universe beyond the standard three neutrino species. In this paper we explore the possibility that the extra radiation has isocurvatrue fluctuations. A general formalism to evaluate isocurvature perturbations in the extra radiation is provided in the mixed inflaton-curvaton system, where the extra radiation is produced by the decay of both scalar fields. We also derive constraints on the abundance of the extra radiation and the amount of its isocurvature perturbation. Current observational data favors the existence of an extra radiation component, but does not indicate its having isocurvature perturbation. These constraints are applied to some particle physics motivated models. If future observations detect isocurvature perturbations in the extra radiation, it will give us a hint to the origin of the extra radiation.
Robust stability under additive perturbations
NASA Technical Reports Server (NTRS)
Bhaya, A.; Desoer, C. A.
1985-01-01
A MIMO linear time-invariant feedback system 1S(P,C) is considered which is assumed to be U-stable. The plant P is subjected to an additive perturbation Delta P which is proper but not necessarily stable. It is proved that the perturbed system is U-stable if and only if Delta P(I + Q x Delta P) exp -1 is U-stable.
Using Lagrangian perturbation theory for precision cosmology
Sugiyama, Naonori S.
2014-06-10
We explore the Lagrangian perturbation theory (LPT) at one-loop order with Gaussian initial conditions. We present an expansion method to approximately compute the power spectrum LPT. Our approximate solution has good convergence in the series expansion and enables us to compute the power spectrum in LPT accurately and quickly. Non-linear corrections in this theory naturally satisfy the law of conservation of mass because the relation between matter density and the displacement vector of dark matter corresponds to the conservation of mass. By matching the one-loop solution in LPT to the two-loop solution in standard perturbation theory, we present an approximate solution of the power spectrum which has higher order corrections than the two-loop order in standard perturbation theory with the conservation of mass satisfied. With this approximation, we can use LPT to compute a non-linear power spectrum without any free parameters, and this solution agrees with numerical simulations at k = 0.2 h Mpc{sup –1} and z = 0.35 to better than 2%.
Dark matter dispersion tensor in perturbation theory
NASA Astrophysics Data System (ADS)
Aviles, Alejandro
2016-03-01
We compute the dark matter velocity dispersion tensor up to third order in perturbation theory using the Lagrangian formalism, revealing growing solutions at the third and higher orders. Our results are general and can be used for any other perturbative formalism. As an application, corrections to the matter power spectrum are calculated, and we find that some of them have the same structure as those in the effective field theory of large-scale structure, with "EFT-like" coefficients that grow quadratically with the linear growth function and are further suppressed by powers of the logarithmic linear growth factor f ; other corrections present additional k dependence. Due to the velocity dispersions, there exists a free-streaming scale that suppresses the whole 1-loop power spectrum. Furthermore, we find that as a consequence of the nonlinear evolution, the free-streaming length is shifted towards larger scales, wiping out more structure than that expected in linear theory. Therefore, we argue that the formalism developed here is better suited for a perturbation treatment of warm dark matter or neutrino clustering, where the velocity dispersion effects are well known to be important. We discuss implications related to the nature of dark matter.
Evolution equation for non-linear cosmological perturbations
Brustein, Ram; Riotto, Antonio E-mail: Antonio.Riotto@cern.ch
2011-11-01
We present a novel approach, based entirely on the gravitational potential, for studying the evolution of non-linear cosmological matter perturbations. Starting from the perturbed Einstein equations, we integrate out the non-relativistic degrees of freedom of the cosmic fluid and obtain a single closed equation for the gravitational potential. We then verify the validity of the new equation by comparing its approximate solutions to known results in the theory of non-linear cosmological perturbations. First, we show explicitly that the perturbative solution of our equation matches the standard perturbative solutions. Next, using the mean field approximation to the equation, we show that its solution reproduces in a simple way the exponential suppression of the non-linear propagator on small scales due to the velocity dispersion. Our approach can therefore reproduce the main features of the renormalized perturbation theory and (time)-renormalization group approaches to the study of non-linear cosmological perturbations, with some possibly important differences. We conclude by a preliminary discussion of the nature of the full solutions of the equation and their significance.
Boundary Layer Instabilities Generated by Freestream Laser Perturbations
NASA Technical Reports Server (NTRS)
Chou, Amanda; Schneider, Steven P.
2015-01-01
A controlled, laser-generated, freestream perturbation was created in the freestream of the Boeing/AFOSR Mach-6 Quiet Tunnel (BAM6QT). The freestream perturbation convected downstream in the Mach-6 wind tunnel to interact with a flared cone model. The geometry of the flared cone is a body of revolution bounded by a circular arc with a 3-meter radius. Fourteen PCB 132A31 pressure transducers were used to measure a wave packet generated in the cone boundary layer by the freestream perturbation. This wave packet grew large and became nonlinear before experiencing natural transition in quiet flow. Breakdown of this wave packet occurred when the amplitude of the pressure fluctuations was approximately 10% of the surface pressure for a nominally sharp nosetip. The initial amplitude of the second mode instability on the blunt flared cone is estimated to be on the order of 10 -6 times the freestream static pressure. The freestream laser-generated perturbation was positioned upstream of the model in three different configurations: on the centerline, offset from the centerline by 1.5 mm, and offset from the centerline by 3.0 mm. When the perturbation was offset from the centerline of a blunt flared cone, a larger wave packet was generated on the side toward which the perturbation was offset. The offset perturbation did not show as much of an effect on the wave packet on a sharp flared cone as it did on a blunt flared cone.
Generating ekpyrotic curvature perturbations before the big bang
Lehners, Jean-Luc; Turok, Neil; McFadden, Paul; Steinhardt, Paul J.
2007-11-15
We analyze a general mechanism for producing a nearly scale-invariant spectrum of cosmological curvature perturbations during a contracting phase preceding a big bang, which can be entirely described using 4D effective field theory. The mechanism, based on first producing entropic perturbations and then converting them to curvature perturbations, can be naturally incorporated in cyclic and ekpyrotic models in which the big bang is modeled as a brane collision, as well as other types of cosmological models with a pre-big bang phase. We show that the correct perturbation amplitude can be obtained and that the spectral tilt n{sub s} tends to range from slightly blue to red, with 0.97
Gravitational waves from perturbed stars
NASA Astrophysics Data System (ADS)
Ferrari, V.
2011-12-01
Non radial oscillations of neutron stars are associated with the emission of gravitational waves. The characteristic frequencies of these oscillations can be computed using the theory of stellar perturbations, and they are shown to carry detailed information on the internal structure of the emitting source. Moreover, they appear to be encoded in various radiative processes, as for instance, in the tail of the giant flares of Soft Gamma Repeaters. Thus, their determination is central to the theory of stellar perturbation. A viable approach to the problem consists in formulating this theory as a problem of resonant scattering of gravitational waves incident on the potential barrier generated by the spacetime curvature. This approach discloses some unexpected correspondences between the theory of stellar perturbations and the theory of quantum mechanics, and allows us to predict new relativistic effects.
Gravitational waves from perturbed stars
NASA Astrophysics Data System (ADS)
Ferrari, V.
2011-03-01
Non radial oscillations of neutron stars are associated with the emission of gravitational waves. The characteristic frequencies of these oscillations can be computed using the theory of stellar perturbations, and they are shown to carry detailed information on the internal structure of the emitting source. Moreover, they appear to be encoded in various radiative processes, as for instance in the tail of the giant flares of Soft Gamma Repeaters. Thus, their determination is central to the theory of stellar perturbation. A viable approach to the problem consists in formulating this theory as a problem of resonant scattering of gravitational waves incident on the potential barrier generated by the spacetime curvature. This approach discloses some unexpected correspondences between the theory of stellar perturbations and the theory of quantum mechanics, and allows us to predict new relativistic effects.
Poulsen, P; Kuklo, R M
2001-03-01
We have previously reported the degree of attenuation and perturbation by a Cu jet passing through Comp B explosive. Similar tests have now been performed with high explosive (HE) targets having CJ pressures higher than and lower than the CJ pressure of Comp B. The explosives were LX-14 and TNT, respectively. We found that the measured exit velocity of the jet where it transitions from perturbed to solid did not vary significantly as a function of HE type for each HE thickness. The radial momentum imparted to the perturbed jet segment did vary as a function of HE type, however, and we report the radial spreading of the jet and the penetration of a downstream target as a function of HE type and thickness.
Perturbed motion at small eccentricities
NASA Astrophysics Data System (ADS)
Emel'yanov, N. V.
2015-09-01
In the study of the motion of planets and moons, it is often necessary to have a simple approximate analytical motion model, which takes into account major perturbations and preserves almost the same accuracy at long time intervals. A precessing ellipse model is used for this purpose. In this paper, it is shown that for small eccentricities this model of the perturbed orbit does not correspond to body motion characteristics. There is perturbed circular motion with a constant zero mean anomaly. The corresponding solution satisfies the Lagrange equations with respect to Keplerian orbital elements. There are two families of solutions with libration and circulation changes in the mean anomaly close to this particular solution. The paper shows how the eccentricity and mean anomaly change in these solutions. Simple analytical models of the motion of the four closest moons of Jupiter consistent with available ephemerides are proposed, which in turn are obtained by the numerical integration of motion equations and are refined by observations.
Thermal perturbation of the Sun
NASA Technical Reports Server (NTRS)
Twigg, L. W.; Endal, A. S.
1981-01-01
An investigation of thermal perturbations of the solar convective zone via changes in the mixing length parameter were carried out, with a view toward understanding the possible solar radius and luminosity changes cited in the literature. The results show that: (a) a single perturbation of alpha is probably not the cause of the solar radius change and (b) the parameter W = d lambda nR./d lambda nL. can not be characterized by a single value, as implied in recent work.
Magnetic perturbations as a viable tool for edge turbulence modification
NASA Astrophysics Data System (ADS)
Vianello, N.; Rea, C.; Agostini, M.; Cavazzana, R.; Ciaccio, G.; De Masi, G.; Martines, E.; Mazzi, A.; Momo, B.; Spizzo, G.; Scarin, P.; Spolaore, M.; Zanca, P.; Zuin, M.; Carraro, L.; Innocente, P.; Marrelli, L.; Puiatti, M. E.; Terranova, D.
2015-01-01
A complete description of the effects of magnetic perturbation on the edge region of RFX-mod is here reported. The flexibility of the RFX-mod device [1] allows for the operation of the machine both as a reversed field pinch (RFP, with maximum current 2 MA) and as a low-current, circular ohmic tokamak (Ip,max = 0.15 MA). The present paper summarizes the most recent results obtained in both configurations with either spontaneous or induced edge radial magnetic perturbation. Emphasis will be devoted to the experimental characterization of the edge flow, focusing on the phase relation between flow and perturbed magnetic field. These informations are provided for natural and stimulated helical discharges in RFPs, and for tokamak safely operated, thanks to the unique RFX-mod MHD control system, in a wide range of edge safety factor 1.9 ≲ q(a) ⩽ 3.4 with externally imposed helical boundary. For the first time a detailed comparison between this phenomenology in tokamaks and RFPs will be presented, providing experimental measurement of the streamline of E × B flow around the magnetic perturbation and of the density modulation which exhibits the same periodicity of the perturbation. Strong new indication of the modification of the small scale turbulence in presence of magnetic perturbation is reported: this modification is deeply connected to the variation of turbulence induced particle transport.
VHS Movies: Perturbations for Morphogenesis.
ERIC Educational Resources Information Center
Holmes, Danny L.
This paper discusses the concept of a family system in terms of an interactive system of interrelated, interdependent parts and suggests that VHS movies can act as perturbations, i.e., change promoting agents, for certain dysfunctional family systems. Several distinct characteristics of a family system are defined with particular emphasis on…
Adaptation Strategies in Perturbed /s/
ERIC Educational Resources Information Center
Brunner, Jana; Hoole, Phil; Perrier, Pascal
2011-01-01
The purpose of this work is to investigate the role of three articulatory parameters (tongue position, jaw position and tongue grooving) in the production of /s/. Six normal speakers' speech was perturbed by a palatal prosthesis. The fricative was recorded acoustically and through electromagnetic articulography in four conditions: (1) unperturbed,…
NASA Astrophysics Data System (ADS)
Bartels, Jochen
2006-06-01
I summarize the present status of the AGK cutting rules in perturbative QCD. Particular attention is given to the application of the AGK analysis to diffraction and multiple scattering in DIS at HERA and to pp collisions at the LHC. I also discuss the bootstrap conditions which appear in pQCD.
Seven topics in perturbative QCD
Buras, A.J.
1980-09-01
The following topics of perturbative QCD are discussed: (1) deep inelastic scattering; (2) higher order corrections to e/sup +/e/sup -/ annihilation, to photon structure functions and to quarkonia decays; (3) higher order corrections to fragmentation functions and to various semi-inclusive processes; (4) higher twist contributions; (5) exclusive processes; (6) transverse momentum effects; (7) jet and photon physics.
Generalized perturbations in neutrino mixing
NASA Astrophysics Data System (ADS)
Liao, Jiajun; Marfatia, D.; Whisnant, K.
2015-10-01
We derive expressions for the neutrino mixing parameters that result from complex perturbations on (1) the Majorana neutrino mass matrix (in the basis of charged lepton mass eigenstates) and on (2) the charged lepton mass matrix, for arbitrary initial (unperturbed) mixing matrices. In the first case, we find that the phases of the elements of the perturbation matrix, and the initial values of the Dirac and Majorana phases, strongly impact the leading-order corrections to the neutrino mixing parameters and phases. For experimentally compatible scenarios wherein the initial neutrino mass matrix has μ -τ symmetry, we find that the Dirac phase can take any value under small perturbations. Similarly, in the second case, perturbations to the charged lepton mass matrix can generate large corrections to the mixing angles and phases of the Pontecorvo-Maki-Nakagawa-Sakata (PMNS) matrix. As an illustration of our generalized procedure, we apply it to a situation in which nonstandard scalar and nonstandard vector interactions simultaneously affect neutrino oscillations.
Basics of QCD perturbation theory
Soper, D.E.
1997-06-01
This is an introduction to the use of QCD perturbation theory, emphasizing generic features of the theory that enable one to separate short-time and long-time effects. The author also covers some important classes of applications: electron-positron annihilation to hadrons, deeply inelastic scattering, and hard processes in hadron-hadron collisions. 31 refs., 38 figs.
Timescales of fluvial response to climate and tectonic perturbations
NASA Astrophysics Data System (ADS)
Castelltort, Sebastien
2015-04-01
Earth's landscapes are composed of connected elements such as hillslopes, bedrock and alluvial rivers, alluvial fans and floodplains for example. Because these entities are dominated by different processes, they might respond in different ways and at different rates to external forcings depending on the nature, magnitude and time scale of changes. Knowledge of those response times is fundamental if we want to extract past climate and tectonics from landscape forms and sedimentary archives. Moreover, the interactions between different landscape elements and their response times also control the response of the landscape as a whole, and the delivery of sediment flux to the basins. Here we review the timescales of fluvial response to perturbations in bedrock and alluvial rivers and discuss the implications for delivery of sediment to basins over multi-millenial timescales. We first use existing relationships for bedrock rivers to study their response to climatic and tectonic perturbations. For alluvial rivers, we consider a simple 1D alluvial reach with a single grain size and an equilibrium slope determined by classical bedload relations. Upstream perturbations of grain size, sediment concentration and water discharge induce river aggradation or degradation according to their effect on river equilibrium slope. While minimum aggradation time can be computed analytically as a function of slope change and sediment supply, the time necessary to degrade to a lower equilibrium slope may be only a function of the timescale of the perturbation in a transport-limited system. We explore the field of natural rivers and their possible response to upstream perturbations.
NEXCADE: Perturbation Analysis for Complex Networks
Yadav, Gitanjali; Babu, Suresh
2012-01-01
Recent advances in network theory have led to considerable progress in our understanding of complex real world systems and their behavior in response to external threats or fluctuations. Much of this research has been invigorated by demonstration of the ‘robust, yet fragile’ nature of cellular and large-scale systems transcending biology, sociology, and ecology, through application of the network theory to diverse interactions observed in nature such as plant-pollinator, seed-dispersal agent and host-parasite relationships. In this work, we report the development of NEXCADE, an automated and interactive program for inducing disturbances into complex systems defined by networks, focusing on the changes in global network topology and connectivity as a function of the perturbation. NEXCADE uses a graph theoretical approach to simulate perturbations in a user-defined manner, singly, in clusters, or sequentially. To demonstrate the promise it holds for broader adoption by the research community, we provide pre-simulated examples from diverse real-world networks including eukaryotic protein-protein interaction networks, fungal biochemical networks, a variety of ecological food webs in nature as well as social networks. NEXCADE not only enables network visualization at every step of the targeted attacks, but also allows risk assessment, i.e. identification of nodes critical for the robustness of the system of interest, in order to devise and implement context-based strategies for restructuring a network, or to achieve resilience against link or node failures. Source code and license for the software, designed to work on a Linux-based operating system (OS) can be downloaded at http://www.nipgr.res.in/nexcade_download.html. In addition, we have developed NEXCADE as an OS-independent online web server freely available to the scientific community without any login requirement at http://www.nipgr.res.in/nexcade.html. PMID:22870252
NEXCADE: perturbation analysis for complex networks.
Yadav, Gitanjali; Babu, Suresh
2012-01-01
Recent advances in network theory have led to considerable progress in our understanding of complex real world systems and their behavior in response to external threats or fluctuations. Much of this research has been invigorated by demonstration of the 'robust, yet fragile' nature of cellular and large-scale systems transcending biology, sociology, and ecology, through application of the network theory to diverse interactions observed in nature such as plant-pollinator, seed-dispersal agent and host-parasite relationships. In this work, we report the development of NEXCADE, an automated and interactive program for inducing disturbances into complex systems defined by networks, focusing on the changes in global network topology and connectivity as a function of the perturbation. NEXCADE uses a graph theoretical approach to simulate perturbations in a user-defined manner, singly, in clusters, or sequentially. To demonstrate the promise it holds for broader adoption by the research community, we provide pre-simulated examples from diverse real-world networks including eukaryotic protein-protein interaction networks, fungal biochemical networks, a variety of ecological food webs in nature as well as social networks. NEXCADE not only enables network visualization at every step of the targeted attacks, but also allows risk assessment, i.e. identification of nodes critical for the robustness of the system of interest, in order to devise and implement context-based strategies for restructuring a network, or to achieve resilience against link or node failures. Source code and license for the software, designed to work on a Linux-based operating system (OS) can be downloaded at http://www.nipgr.res.in/nexcade_download.html. In addition, we have developed NEXCADE as an OS-independent online web server freely available to the scientific community without any login requirement at http://www.nipgr.res.in/nexcade.html. PMID:22870252
Perturbative quantum gravity in double field theory
NASA Astrophysics Data System (ADS)
Boels, Rutger H.; Horst, Christoph
2016-04-01
We study perturbative general relativity with a two-form and a dilaton using the double field theory formulation which features explicit index factorisation at the Lagrangian level. Explicit checks to known tree level results are performed. In a natural covariant gauge a ghost-like scalar which contributes even at tree level is shown to decouple consistently as required by perturbative unitarity. In addition, a lightcone gauge is explored which bypasses the problem altogether. Using this gauge to study BCFW on-shell recursion, we can show that most of the D-dimensional tree level S-matrix of the theory, including all pure graviton scattering amplitudes, is reproduced by the double field theory. More generally, we argue that the integrand may be reconstructed from its single cuts and provide limited evidence for off-shell cancellations in the Feynman graphs. As a straightforward application of the developed technology double field theory-like expressions for four field string corrections are derived.
Harmonically Perturbed Gas-Solid Fluidized System
NASA Astrophysics Data System (ADS)
Nix, S. T.; Muller, M. R.
1996-11-01
Experiments were performed on a harmonically perturbed gas-solid fluidized system, to determine the extent to which the total system behaved as a liquid in regards to the aspects of resonant frequency, wave shapes, and damping effects. The fluidized system consists of a cylindrical alumina oxide/air fluidized bed which is vertically perturbed in a symmetrical fashion by externally vibrating the entire vessel. The external vibrations were carried out over various flow rates, amplitudes, and frequencies. The results obtained could then be compared to the natural frequencies of water for the same governing parameters by analytical means. The effects of excitations on the formation of voidage disturbances or "gas bubbles" was also investigated. Data acquisition enabled the determination of both the amplitude and frequency of the waves generated in the bath. Results indicate that external vertical vibration caused the mean surface level of the bed to drop. This can be attributed to a closer packing of the particles along with a decrease in the number and size of gas bubbles in the bed.
Vector perturbations of galaxy number counts
NASA Astrophysics Data System (ADS)
Durrer, Ruth; Tansella, Vittorio
2016-07-01
We derive the contribution to relativistic galaxy number count fluctuations from vector and tensor perturbations within linear perturbation theory. Our result is consistent with the the relativistic corrections to number counts due to scalar perturbation, where the Bardeen potentials are replaced with line-of-sight projection of vector and tensor quantities. Since vector and tensor perturbations do not lead to density fluctuations the standard density term in the number counts is absent. We apply our results to vector perturbations which are induced from scalar perturbations at second order and give numerical estimates of their contributions to the power spectrum of relativistic galaxy number counts.
Density perturbations from modulated decay of the curvaton
Langlois, David; Takahashi, Tomo E-mail: tomot@cc.saga-u.ac.jp
2013-04-01
We study density perturbations, including their non-Gaussianity, in models in which the decay rate of the curvaton depends on another light scalar field, denoted the modulaton. Although this model shares some similarities with the standard curvaton and modulated reheating scenarios, it exhibits interesting predictions for f{sub NL} and g{sub NL} that are specific to this model. We also discuss the possibility that both modulaton and curvaton fluctuations contribute to the final curvature perturbation. Our results naturally include the standard curvaton and modulated reheating scenarios as specific limits and are thus useful to present a unified treatment of these models and their variants.
Cosmological perturbations in unimodular gravity
Gao, Caixia; Brandenberger, Robert H.; Cai, Yifu; Chen, Pisin E-mail: rhb@hep.physics.mcgill.ca E-mail: chen@slac.stanford.edu
2014-09-01
We study cosmological perturbation theory within the framework of unimodular gravity. We show that the Lagrangian constraint on the determinant of the metric required by unimodular gravity leads to an extra constraint on the gauge freedom of the metric perturbations. Although the main equation of motion for the gravitational potential remains the same, the shift variable, which is gauge artifact in General Relativity, cannot be set to zero in unimodular gravity. This non-vanishing shift variable affects the propagation of photons throughout the cosmological evolution and therefore modifies the Sachs-Wolfe relation between the relativistic gravitational potential and the microwave temperature anisotropies. However, for adiabatic fluctuations the difference between the result in General Relativity and unimodular gravity is suppressed on large angular scales. Thus, no strong constraints on the theory can be derived.
Neptune's story. [Triton's orbit perturbation
NASA Technical Reports Server (NTRS)
Goldreich, P.; Murray, N.; Longaretti, P. Y.; Banfield, D.
1989-01-01
It is conjectured that Triton was captured from a heliocentric orbit as the result of a collision with what was then one of Neptune's regular satellites. The immediate post-capture orbit was highly eccentric. Dissipation due to tides raised by Neptune in Triton caused Triton's orbit to evolve to its present state in less than one billion years. For much of this time Triton was almost entirely molten. While its orbit was evolving, Triton cannibalized most of the regular satellites of Neptune and also perturbed Nereid, thus accounting for that satellite's highly eccentric and inclined orbit. The only regular satellites of Neptune that survived were those that formed well within 5 Neptune radii, and they move on inclined orbits as the result of chaotic perturbations forced by Triton.
Gas hydrate inhibition by perturbation of liquid water structure.
Sa, Jeong-Hoon; Kwak, Gye-Hoon; Han, Kunwoo; Ahn, Docheon; Lee, Kun-Hong
2015-01-01
Natural gas hydrates are icy crystalline materials that contain hydrocarbons, which are the primary energy source for this civilization. The abundance of naturally occurring gas hydrates leads to a growing interest in exploitation. Despite their potential as energy resources and in industrial applications, there is insufficient understanding of hydrate kinetics, which hinders the utilization of these invaluable resources. Perturbation of liquid water structure by solutes has been proposed to be a key process in hydrate inhibition, but this hypothesis remains unproven. Here, we report the direct observation of the perturbation of the liquid water structure induced by amino acids using polarized Raman spectroscopy, and its influence on gas hydrate nucleation and growth kinetics. Amino acids with hydrophilic and/or electrically charged side chains disrupted the water structure and thus provided effective hydrate inhibition. The strong correlation between the extent of perturbation by amino acids and their inhibition performance constitutes convincing evidence for the perturbation inhibition mechanism. The present findings bring the practical applications of gas hydrates significantly closer, and provide a new perspective on the freezing and melting phenomena of naturally occurring gas hydrates. PMID:26082291
Gas hydrate inhibition by perturbation of liquid water structure
NASA Astrophysics Data System (ADS)
Sa, Jeong-Hoon; Kwak, Gye-Hoon; Han, Kunwoo; Ahn, Docheon; Lee, Kun-Hong
2015-06-01
Natural gas hydrates are icy crystalline materials that contain hydrocarbons, which are the primary energy source for this civilization. The abundance of naturally occurring gas hydrates leads to a growing interest in exploitation. Despite their potential as energy resources and in industrial applications, there is insufficient understanding of hydrate kinetics, which hinders the utilization of these invaluable resources. Perturbation of liquid water structure by solutes has been proposed to be a key process in hydrate inhibition, but this hypothesis remains unproven. Here, we report the direct observation of the perturbation of the liquid water structure induced by amino acids using polarized Raman spectroscopy, and its influence on gas hydrate nucleation and growth kinetics. Amino acids with hydrophilic and/or electrically charged side chains disrupted the water structure and thus provided effective hydrate inhibition. The strong correlation between the extent of perturbation by amino acids and their inhibition performance constitutes convincing evidence for the perturbation inhibition mechanism. The present findings bring the practical applications of gas hydrates significantly closer, and provide a new perspective on the freezing and melting phenomena of naturally occurring gas hydrates.
Identifying Network Perturbation in Cancer.
Grechkin, Maxim; Logsdon, Benjamin A; Gentles, Andrew J; Lee, Su-In
2016-05-01
We present a computational framework, called DISCERN (DIfferential SparsE Regulatory Network), to identify informative topological changes in gene-regulator dependence networks inferred on the basis of mRNA expression datasets within distinct biological states. DISCERN takes two expression datasets as input: an expression dataset of diseased tissues from patients with a disease of interest and another expression dataset from matching normal tissues. DISCERN estimates the extent to which each gene is perturbed-having distinct regulator connectivity in the inferred gene-regulator dependencies between the disease and normal conditions. This approach has distinct advantages over existing methods. First, DISCERN infers conditional dependencies between candidate regulators and genes, where conditional dependence relationships discriminate the evidence for direct interactions from indirect interactions more precisely than pairwise correlation. Second, DISCERN uses a new likelihood-based scoring function to alleviate concerns about accuracy of the specific edges inferred in a particular network. DISCERN identifies perturbed genes more accurately in synthetic data than existing methods to identify perturbed genes between distinct states. In expression datasets from patients with acute myeloid leukemia (AML), breast cancer and lung cancer, genes with high DISCERN scores in each cancer are enriched for known tumor drivers, genes associated with the biological processes known to be important in the disease, and genes associated with patient prognosis, in the respective cancer. Finally, we show that DISCERN can uncover potential mechanisms underlying network perturbation by explaining observed epigenomic activity patterns in cancer and normal tissue types more accurately than alternative methods, based on the available epigenomic data from the ENCODE project. PMID:27145341
Perturbation growth in accreting filaments
NASA Astrophysics Data System (ADS)
Clarke, S. D.; Whitworth, A. P.; Hubber, D. A.
2016-05-01
We use smoothed particle hydrodynamic simulations to investigate the growth of perturbations in infinitely long filaments as they form and grow by accretion. The growth of these perturbations leads to filament fragmentation and the formation of cores. Most previous work on this subject has been confined to the growth and fragmentation of equilibrium filaments and has found that there exists a preferential fragmentation length-scale which is roughly four times the filament's diameter. Our results show a more complicated dispersion relation with a series of peaks linking perturbation wavelength and growth rate. These are due to gravo-acoustic oscillations along the longitudinal axis during the sub-critical phase of growth. The positions of the peaks in growth rate have a strong dependence on both the mass accretion rate onto the filament and the temperature of the gas. When seeded with a multiwavelength density power spectrum, there exists a clear preferred core separation equal to the largest peak in the dispersion relation. Our results allow one to estimate a minimum age for a filament which is breaking up into regularly spaced fragments, as well as an average accretion rate. We apply the model to observations of filaments in Taurus by Tafalla & Hacar and find accretion rates consistent with those estimated by Palmeirim et al.
R evolution: Improving perturbative QCD
NASA Astrophysics Data System (ADS)
Hoang, André H.; Jain, Ambar; Scimemi, Ignazio; Stewart, Iain W.
2010-07-01
Perturbative QCD results in the MS¯ scheme can be dramatically improved by switching to a scheme that accounts for the dominant power law dependence on the factorization scale in the operator product expansion. We introduce the “MSR scheme” which achieves this in a Lorentz and gauge invariant way and has a very simple relation to MS¯. Results in MSR depend on a cutoff parameter R, in addition to the μ of MS¯. R variations can be used to independently estimate (i.) the size of power corrections, and (ii.) higher-order perturbative corrections (much like μ in MS¯). We give two examples at three-loop order, the ratio of mass splittings in the B*-B and D*-D systems, and the Ellis-Jaffe sum rule as a function of momentum transfer Q in deep inelastic scattering. Comparing to data, the perturbative MSR results work well even for Q˜1GeV, and power corrections are reduced compared to MS¯.
R evolution: Improving perturbative QCD
Hoang, Andre H.; Jain, Ambar; Stewart, Iain W.; Scimemi, Ignazio
2010-07-01
Perturbative QCD results in the MS scheme can be dramatically improved by switching to a scheme that accounts for the dominant power law dependence on the factorization scale in the operator product expansion. We introduce the ''MSR scheme'' which achieves this in a Lorentz and gauge invariant way and has a very simple relation to MS. Results in MSR depend on a cutoff parameter R, in addition to the {mu} of MS. R variations can be used to independently estimate (i.) the size of power corrections, and (ii.) higher-order perturbative corrections (much like {mu} in MS). We give two examples at three-loop order, the ratio of mass splittings in the B*-B and D*-D systems, and the Ellis-Jaffe sum rule as a function of momentum transfer Q in deep inelastic scattering. Comparing to data, the perturbative MSR results work well even for Q{approx}1 GeV, and power corrections are reduced compared to MS.
Path integral for inflationary perturbations
NASA Astrophysics Data System (ADS)
Prokopec, Tomislav; Rigopoulos, Gerasimos
2010-07-01
The quantum theory of cosmological perturbations in single-field inflation is formulated in terms of a path integral. Starting from a canonical formulation, we show how the free propagators can be obtained from the well-known gauge-invariant quadratic action for scalar and tensor perturbations, and determine the interactions to arbitrary order. This approach does not require the explicit solution of the energy and momentum constraints, a novel feature which simplifies the determination of the interaction vertices. The constraints and the necessary imposition of gauge conditions is reflected in the appearance of various commuting and anticommuting auxiliary fields in the action. These auxiliary fields are not propagating physical degrees of freedom but need to be included in internal lines and loops in a diagrammatic expansion. To illustrate the formalism we discuss the tree-level three-point and four-point functions of the inflaton perturbations, reproducing the results already obtained by the methods used in the current literature. Loop calculations are left for future work.
New Representations of the Perturbative S Matrix.
Baadsgaard, Christian; Bjerrum-Bohr, N E J; Bourjaily, Jacob L; Caron-Huot, Simon; Damgaard, Poul H; Feng, Bo
2016-02-12
We propose a new framework to represent the perturbative S matrix which is well defined for all quantum field theories of massless particles, constructed from tree-level amplitudes and integrable term by term. This representation is derived from the Feynman expansion through a series of partial fraction identities, discarding terms that vanish upon integration. Loop integrands are expressed in terms of "Q-cuts" that involve both off-shell and on-shell loop momenta, defined with a precise contour prescription that can be evaluated by ordinary methods. This framework implies recent results found in the scattering equation formalism at one loop, and it has a natural extension to all orders--even nonplanar theories without well-defined forward limits or good ultraviolet behavior. PMID:26918978
Estimation of velocity perturbations in satellite fragmentation events
NASA Technical Reports Server (NTRS)
Tan, Arjun
1989-01-01
The magnitude, variance and directionality of the velocity perturbations of the fragments of a satellite can shed valuable information regarding the nature and intensity of the fragmentation. Up until now, the only method used to calculate the three orthogonal components of the velocity change consisted of inverting the process of evaluating the changes in the orbital elements of the fragments due to velocity perturbing forces. But the traditional method failed in five different cases: (1) when the parent satellite's orbit was circular; (2) and (3) when the true anomaly of the parent was either 0 deg or 180 deg; and (4) and (5) when the argument of latitude of the parent was 90 deg or 270 deg. Described here is a new method of calculating the velocity perturbations which is free from the shortcomings of the traditional method and could be used in all occasions, provided the fragmentation data and the orbital elements data are consistent with one another.
Local Perturbations Do Not Affect Stability of Laboratory Fruitfly Metapopulations
Dey, Sutirth; Joshi, Amitabh
2007-01-01
Background A large number of theoretical studies predict that the dynamics of spatially structured populations (metapopulations) can be altered by constant perturbations to local population size. However, these studies presume large metapopulations inhabiting noise-free, zero-extinction environments, and their predictions have never been empirically verified. Methodology/Principal Findings Here we report an empirical study on the effects of localized perturbations on global dynamics and stability, using fruitfly metapopulations in the laboratory. We find that constant addition of individuals to a particular subpopulation in every generation stabilizes that subpopulation locally, but does not have any detectable effect on the dynamics and stability of the metapopulation. Simulations of our experimental system using a simple but widely applicable model of population dynamics were able to recover the empirical findings, indicating the generality of our results. We then simulated the possible consequences of perturbing more subpopulations, increasing the strength of perturbations, and varying the rate of migration, but found that none of these conditions were expected to alter the outcomes of our experiments. Finally, we show that our main results are robust to the presence of local extinctions in the metapopulation. Conclusions/Significance Our study shows that localized perturbations are unlikely to affect the dynamics of real metapopulations, a finding that has cautionary implications for ecologists and conservation biologists faced with the problem of stabilizing unstable metapopulations in nature. PMID:17311100
Observations of Seismo-Ionospheric Perturbations Using Wavelet Analysis
NASA Astrophysics Data System (ADS)
Revathi, R.; Ramesh, K. S.; Gopal Rao, M. Venu; Sri Chaitanya, G. Rama; Jasmitha, A.; Tejasw, G.; Rekha, A. Vijaya
2014-07-01
Electromagnetic signals generated before and during the Earthquakes lie in a broad range of frequencies from MHz to Qasi DC frequencies (Darcy Karakelian et.,al 2000). These signals reach higher altitudes and perturb the background atmosphere by dumping their energy (V.V. Hegai et.,al 2006, Tadahiko Ogawa et.,al 2012). These electromagnetic signals cause perturbations in the ion content of the ionosphere. The study of these perturbations is important to understand their evolution mechanisms. The ionospheric variability is measured in terms of ionospheric Total Electron content (TEC). The complex time varying and non-linear characteristics of Seismo-ionospheric perturbations are different from other disturbances ( Li-ming He et.,al, 2011). The earthquake which occurred in Indonesian region on 1st Sepember 2013 with a magnitude M>6 is considered for the present study. The time frequency analysis of narrow transition regions of these signals are analyzed using Wavelets (Gwal A.K., et., al 2002, Michael E. Contadakis et.,al 2012) . Analysis of the non-stationary data using wavelets provides time localized alternatives and complex wavelets are useful in accurate detection and recognition of transient signals. The results show that these perturbations are observed three days before the Earthquake and are increasing in nature. The observed periodicities on the Earthquake day may represent that there is possible transfer of momentum and energy from lower atmosphere to upper atmosphere.
The bispectrum of matter perturbations from cosmic strings
NASA Astrophysics Data System (ADS)
Regan, Donough; Hindmarsh, Mark
2015-03-01
We present the first calculation of the bispectrum of the matter perturbations induced by cosmic strings. The calculation is performed in two different ways: the first uses the unequal time correlators (UETCs) of the string network - computed using a Gaussian model previously employed for cosmic string power spectra. The second approach uses the wake model, where string density perturbations are concentrated in sheet-like structures whose surface density grows with time. The qualitative and quantitative agreement of the two gives confidence to the results. An essential ingredient in the UETC approach is the inclusion of compensation factors in the integration with the Green's function of the matter and radiation fluids, and we show that these compensation factors must be included in the wake model also. We also present a comparison of the UETCs computed in the Gaussian model, and those computed in the unconnected segment model (USM) used by the standard cosmic string perturbation package CMBACT. We compare numerical estimates for the bispectrum of cosmic strings to those produced by perturbations from an inflationary era, and discover that, despite the intrinsically non-Gaussian nature of string-induced perturbations, the matter bispectrum is unlikely to produce competitive constraints on a population of cosmic strings.
Geometric Hamiltonian structures and perturbation theory
Omohundro, S.
1984-08-01
We have been engaged in a program of investigating the Hamiltonian structure of the various perturbation theories used in practice. We describe the geometry of a Hamiltonian structure for non-singular perturbation theory applied to Hamiltonian systems on symplectic manifolds and the connection with singular perturbation techniques based on the method of averaging.
Cosmological perturbations: Vorticity, isocurvature and magnetic fields
NASA Astrophysics Data System (ADS)
Christopherson, Adam J.
2014-10-01
In this paper, I review some recent, interlinked, work undertaken using cosmological perturbation theory — a powerful technique for modeling inhomogeneities in the universe. The common theme which underpins these pieces of work is the presence of nonadiabatic pressure, or entropy, perturbations. After a brief introduction covering the standard techniques of describing inhomogeneities in both Newtonian and relativistic cosmology, I discuss the generation of vorticity. As in classical fluid mechanics, vorticity is not present in linearized perturbation theory (unless included as an initial condition). Allowing for entropy perturbations, and working to second order in perturbation theory, I show that vorticity is generated, even in the absence of vector perturbations, by purely scalar perturbations, the source term being quadratic in the gradients of first order energy density and isocurvature, or nonadiabatic pressure perturbations. This generalizes Crocco's theorem to a cosmological setting. I then introduce isocurvature perturbations in different models, focusing on the entropy perturbation in standard, concordance cosmology, and in inflationary models involving two scalar fields. As the final topic, I investigate magnetic fields, which are a potential observational consequence of vorticity in the early universe. I briefly review some recent work on including magnetic fields in perturbation theory in a consistent way. I show, using solely analytical techniques, that magnetic fields can be generated by higher order perturbations, albeit too small to provide the entire primordial seed field, in agreement with some numerical studies. I close this paper with a summary and some potential extensions of this work.
Superconvergent perturbation method in quantum mechanics
Scherer, W. )
1995-02-27
An analog of Kolmogorov's superconvergent perturbation theory in classical mechanics is constructed for self-adjoint operators. It is different from the usual Rayleigh-Schroedinger perturbation theory and yields expansions for eigenvalues and eigenvectors in terms of functions of the perturbation parameter.
C. ALLEN
2000-08-01
We consider halo formation in continuous beams oscillating at natural modes by inspecting particle trajectories. Trajectory equations containing field nonlinearities are derived from a weighted polynomial expansion. We then use perturbational techniques to further analyze particle motion.
NASA Astrophysics Data System (ADS)
Sadlej, A. J.; Snijders, J. G.; van Lenthe, E.; Baerends, E. J.
1995-01-01
By combining the ideas of the direct perturbation theory approach to the solution of the Dirac equation with those underlying the regular expansion as used to obtain the two-component Chang-Pélissier-Durand Hamiltonian, a four-component form of the regular expansion is proposed. This formulation lends itself naturally to systematic improvement by a nonsingular form of perturbation theory. Alternatively it can be viewed as a double perturbation version of direct perturbation theory, where relativistic effects on the Hamiltonian and the metric are considered separately and the Hamiltonian perturbation is summed to infinite order. The scaling procedure that was earlier shown to be exact in the case of a hydrogenic potential and that greatly improved the core orbital energies, is found to follow naturally from the current formulation. The accuracy of the various approximations to the wave functions is assessed with respect to several radial expectation values weighing different regions in the uranium atom as a test case.
Identifying Network Perturbation in Cancer
Logsdon, Benjamin A.; Gentles, Andrew J.; Lee, Su-In
2016-01-01
We present a computational framework, called DISCERN (DIfferential SparsE Regulatory Network), to identify informative topological changes in gene-regulator dependence networks inferred on the basis of mRNA expression datasets within distinct biological states. DISCERN takes two expression datasets as input: an expression dataset of diseased tissues from patients with a disease of interest and another expression dataset from matching normal tissues. DISCERN estimates the extent to which each gene is perturbed—having distinct regulator connectivity in the inferred gene-regulator dependencies between the disease and normal conditions. This approach has distinct advantages over existing methods. First, DISCERN infers conditional dependencies between candidate regulators and genes, where conditional dependence relationships discriminate the evidence for direct interactions from indirect interactions more precisely than pairwise correlation. Second, DISCERN uses a new likelihood-based scoring function to alleviate concerns about accuracy of the specific edges inferred in a particular network. DISCERN identifies perturbed genes more accurately in synthetic data than existing methods to identify perturbed genes between distinct states. In expression datasets from patients with acute myeloid leukemia (AML), breast cancer and lung cancer, genes with high DISCERN scores in each cancer are enriched for known tumor drivers, genes associated with the biological processes known to be important in the disease, and genes associated with patient prognosis, in the respective cancer. Finally, we show that DISCERN can uncover potential mechanisms underlying network perturbation by explaining observed epigenomic activity patterns in cancer and normal tissue types more accurately than alternative methods, based on the available epigenomic data from the ENCODE project. PMID:27145341
Hadronic Structure from Perturbative Dressing
NASA Astrophysics Data System (ADS)
Arash, Firooz
2005-09-01
Perturbative dressing of a valence quark in QCD produces the internal structure of an extended object, the so-called Valon. The valon structure is universal and independent of the hosting hadron. Polarized and unpolarized proton and pion structure functions are calculated in the valon representation. One finds that although all the available data on g1p,n,d are easily reproduced, a sizable orbital angular momentum associated with the partonic structure of the valon is required in order to have a spin 1/2 valon.
"Phonon" scattering beyond perturbation theory
NASA Astrophysics Data System (ADS)
Qiu, WuJie; Ke, XueZhi; Xi, LiLi; Wu, LiHua; Yang, Jiong; Zhang, WenQing
2016-02-01
Searching and designing materials with intrinsically low lattice thermal conductivity (LTC) have attracted extensive consideration in thermoelectrics and thermal management community. The concept of part-crystalline part-liquid state, or even part-crystalline part-amorphous state, has recently been proposed to describe the exotic structure of materials with chemical- bond hierarchy, in which a set of atoms is weakly bonded to the rest species while the other sublattices retain relatively strong rigidity. The whole system inherently manifests the coexistence of rigid crystalline sublattices and fluctuating noncrystalline substructures. Representative materials in the unusual state can be classified into two categories, i.e., caged and non-caged ones. LTCs in both systems deviate from the traditional T -1 relationship ( T, the absolute temperature), which can hardly be described by small-parameter-based perturbation approaches. Beyond the classical perturbation theory, an extra rattling-like scattering should be considered to interpret the liquid-like and sublattice-amorphization-induced heat transport. Such a kind of compounds could be promising high-performance thermoelectric materials, due to the extremely low LTCs. Other physical properties for these part-crystalline substances should also exhibit certain novelty and deserve further exploration.
Perturbations of vortex ring pairs
NASA Astrophysics Data System (ADS)
Gubser, Steven S.; Horn, Bart; Parikh, Sarthak
2016-02-01
We study pairs of coaxial vortex rings starting from the action for a classical bosonic string in a three-form background. We complete earlier work on the phase diagram of classical orbits by explicitly considering the case where the circulations of the two vortex rings are equal and opposite. We then go on to study perturbations, focusing on cases where the relevant four-dimensional transfer matrix splits into two-dimensional blocks. When the circulations of the rings have the same sign, instabilities are mostly limited to wavelengths smaller than a dynamically generated length scale at which single-ring instabilities occur. When the circulations have the opposite sign, larger wavelength instabilities can occur.
Matter perturbations in scaling cosmology
NASA Astrophysics Data System (ADS)
Fuño, A. Romero; Hipólito-Ricaldi, W. S.; Zimdahl, W.
2016-04-01
A suitable nonlinear interaction between dark matter with an energy density ρM and dark energy with an energy density ρX is known to give rise to a non-canonical scaling ρM ∝ ρXa-ξ, where ξ is a parameter which generally deviates from ξ = 3. Here, we present a covariant generalization of this class of models and investigate the corresponding perturbation dynamics. The resulting matter power spectrum for the special case of a time-varying Lambda model is compared with data from the Sloan Digital Sky Survey (SDSS) DR9 catalogue (Ahn et al.). We find a best-fitting value of ξ = 3.25 which corresponds to a decay of dark matter into the cosmological term. Our results are compatible with the Lambda Cold Dark Matter model at the 2σ confidence level.
Perturbativity in the seesaw mechanism
NASA Astrophysics Data System (ADS)
Asaka, Takehiko; Tsuyuki, Takanao
2016-02-01
We consider the Standard Model extended by right-handed neutrinos to explain massive neutrinos through the seesaw mechanism. The new fermion can be observed when it has a sufficiently small mass and large mixings to left-handed neutrinos. If such a particle is the lightest right-handed neutrino, its contribution to the mass matrix of active neutrinos needs to be canceled by that of a heavier one. Yukawa couplings of the heavier one are then larger than those of the lightest one. We show that the perturbativity condition gives a severe upper bound on the mixing of the lightest right-handed neutrino, depending on the masses of heavier ones. Models of high energy phenomena, such as leptogenesis, can be constrained by low energy experiments.
Sudakov safety in perturbative QCD
NASA Astrophysics Data System (ADS)
Larkoski, Andrew J.; Marzani, Simone; Thaler, Jesse
2015-06-01
Traditional calculations in perturbative quantum chromodynamics (pQCD) are based on an order-by-order expansion in the strong coupling αs. Observables that are calculable in this way are known as "safe." Recently, a class of unsafe observables was discovered that do not have a valid αs expansion but are nevertheless calculable in pQCD using all-orders resummation. These observables are called "Sudakov safe" since singularities at each αs order are regulated by an all-orders Sudakov form factor. In this paper, we give a concrete definition of Sudakov safety based on conditional probability distributions, and we study a one-parameter family of momentum sharing observables that interpolate between the safe and unsafe regimes. The boundary between these regimes is particularly interesting, as the resulting distribution can be understood as the ultraviolet fixed point of a generalized fragmentation function, yielding a leading behavior that is independent of αs.
Robust control with structured perturbations
NASA Technical Reports Server (NTRS)
Keel, Leehyun
1988-01-01
Two important problems in the area of control systems design and analysis are discussed. The first is the robust stability using characteristic polynomial, which is treated first in characteristic polynomial coefficient space with respect to perturbations in the coefficients of the characteristic polynomial, and then for a control system containing perturbed parameters in the transfer function description of the plant. In coefficient space, a simple expression is first given for the l(sup 2) stability margin for both monic and non-monic cases. Following this, a method is extended to reveal much larger stability region. This result has been extended to the parameter space so that one can determine the stability margin, in terms of ranges of parameter variations, of the closed loop system when the nominal stabilizing controller is given. The stability margin can be enlarged by a choice of better stabilizing controller. The second problem describes the lower order stabilization problem, the motivation of the problem is as follows. Even though the wide range of stabilizing controller design methodologies is available in both the state space and transfer function domains, all of these methods produce unnecessarily high order controllers. In practice, the stabilization is only one of many requirements to be satisfied. Therefore, if the order of a stabilizing controller is excessively high, one can normally expect to have a even higher order controller on the completion of design such as inclusion of dynamic response requirements, etc. Therefore, it is reasonable to have a lowest possible order stabilizing controller first and then adjust the controller to meet additional requirements. The algorithm for designing a lower order stabilizing controller is given. The algorithm does not necessarily produce the minimum order controller; however, the algorithm is theoretically logical and some simulation results show that the algorithm works in general.
Cosmological perturbations in f(T) gravity
Chen, Shih-Hung; Dent, James B.; Dutta, Sourish; Saridakis, Emmanuel N.
2011-01-15
We investigate the cosmological perturbations in f(T) gravity. Examining the pure gravitational perturbations in the scalar sector using a diagonal vierbein, we extract the corresponding dispersion relation, which provides a constraint on the f(T) Ansaetze that lead to a theory free of instabilities. Additionally, upon inclusion of the matter perturbations, we derive the fully perturbed equations of motion, and we study the growth of matter overdensities. We show that f(T) gravity with f(T) constant coincides with General Relativity, both at the background as well as at the first-order perturbation level. Applying our formalism to the power-law model we find that on large subhorizon scales (O(100 Mpc) or larger), the evolution of matter overdensity will differ from {Lambda}CDM cosmology. Finally, examining the linear perturbations of the vector and tensor sectors, we find that (for the standard choice of vierbein) f(T) gravity is free of massive gravitons.
Natural and anthropogenic perturbations of the stratospheric ozone layer
NASA Technical Reports Server (NTRS)
Brasseur, Guy P.
1992-01-01
The paper reviews potential causes for reduction in the ozone abundance. The response of stratospheric ozone to solar activity is discussed. Ozone changes are simulated in relation with the potential development of a fleet of high-speed stratospheric aircraft and the release in the atmosphere of chlorofluorocarbons. The calculations are performed by a two-dimensional chemical-radiative-dynamical model. The importance of heterogeneous chemistry in polar stratospheric clouds and in the Junge layer (sulfate aerosol) is emphasized. The recently reported ozone trend over the last decade is shown to have been largely caused by the simultaneous effects of increasing concentrations of chlorofluorocarbons and heterogeneous chemistry. The possibility for a reduction in stratospheric ozone following a large volcanic eruption such as that of Mount Pinatubo in 1991 is discussed.
Kato expansion in quantum canonical perturbation theory
NASA Astrophysics Data System (ADS)
Nikolaev, Andrey
2016-06-01
This work establishes a connection between canonical perturbation series in quantum mechanics and a Kato expansion for the resolvent of the Liouville superoperator. Our approach leads to an explicit expression for a generator of a block-diagonalizing Dyson's ordered exponential in arbitrary perturbation order. Unitary intertwining of perturbed and unperturbed averaging superprojectors allows for a description of ambiguities in the generator and block-diagonalized Hamiltonian. We compare the efficiency of the corresponding computational algorithm with the efficiencies of the Van Vleck and Magnus methods for high perturbative orders.
Singularity perturbed zero dynamics of nonlinear systems
NASA Technical Reports Server (NTRS)
Isidori, A.; Sastry, S. S.; Kokotovic, P. V.; Byrnes, C. I.
1992-01-01
Stability properties of zero dynamics are among the crucial input-output properties of both linear and nonlinear systems. Unstable, or 'nonminimum phase', zero dynamics are a major obstacle to input-output linearization and high-gain designs. An analysis of the effects of regular perturbations in system equations on zero dynamics shows that whenever a perturbation decreases the system's relative degree, it manifests itself as a singular perturbation of zero dynamics. Conditions are given under which the zero dynamics evolve in two timescales characteristic of a standard singular perturbation form that allows a separate analysis of slow and fast parts of the zero dynamics.
Singular perturbation applications in neutron transport
Losey, D.C.; Lee, J.C.
1996-09-01
This is a paper on singular perturbation applications in neutron transport for submission at the next ANS conference. A singular perturbation technique was developed for neutron transport analysis by postulating expansion in terms of a small ordering parameter {eta}. Our perturbation analysis is carried, without approximation, through {Omicron}({eta}{sup 2}) to derive a material interface correction for diffusion theory. Here we present results from an analytical application of the perturbation technique to a fixed source problem and then describe and implementation of the technique in a computational scheme.
Cosmological perturbations in coherent oscillating scalar field models
NASA Astrophysics Data System (ADS)
Cembranos, J. A. R.; Maroto, A. L.; Jareño, S. J. Núñez
2016-03-01
The fact that fast oscillating homogeneous scalar fields behave as perfect fluids in average and their intrinsic isotropy have made these models very fruitful in cosmology. In this work we will analyse the perturbations dynamics in these theories assuming general power law potentials V( ϕ) = λ| ϕ| n /n. At leading order in the wavenumber expansion, a simple expression for the effective sound speed of perturbations is obtained c eff 2 = ω = ( n - 2)/( n + 2) with ω the effective equation of state. We also obtain the first order correction in k 2/ ω eff 2 , when the wavenumber k of the perturbations is much smaller than the background oscillation frequency, ω eff. For the standard massive case we have also analysed general anharmonic contributions to the effective sound speed. These results are reached through a perturbed version of the generalized virial theorem and also studying the exact system both in the super-Hubble limit, deriving the natural ansatz for δϕ; and for sub-Hubble modes, exploiting Floquet's theorem.
Environmental and genetic perturbations reveal different networks of metabolic regulation
Greenberg, Anthony J; Hackett, Sean R; Harshman, Lawrence G; Clark, Andrew G
2011-01-01
Progress in systems biology depends on accurate descriptions of biological networks. Connections in a regulatory network are identified as correlations of gene expression across a set of environmental or genetic perturbations. To use this information to predict system behavior, we must test how the nature of perturbations affects topologies of networks they reveal. To probe this question, we focused on metabolism of Drosophila melanogaster. Our source of perturbations is a set of crosses among 92 wild-derived lines from five populations, replicated in a manner permitting separate assessment of the effects of genetic variation and environmental fluctuation. We directly assayed activities of enzymes and levels of metabolites. Using a multivariate Bayesian model, we estimated covariance among metabolic parameters and built fine-grained probabilistic models of network topology. The environmental and genetic co-regulation networks are substantially the same among five populations. However, genetic and environmental perturbations reveal qualitative differences in metabolic regulation, suggesting that environmental shifts, such as diet modifications, produce different systemic effects than genetic changes, even if the primary targets are the same. PMID:22186737
Phase-averaged measurements of perturbations introduced into boundary layers
NASA Technical Reports Server (NTRS)
Watmuff, Jonathan H.
1991-01-01
Large-scale structures in turbulent and transitional wall-bounded flows make a significant contribution to the Reynolds stress and turbulent energy. The behavior of these structures is examined. Small perturbations are introduced into a laminar and a turbulent boundary layer to trigger the formation of large-scale features. Both flows use the same inlet unit Reynolds number, and they experience the same pressure gradient history, i.e. a favorable pressure gradient (FPG) followed by an adverse pressure gradient (APG). The perturbation consists of a small short duration flow repetitively introduced through a hole in the wall located at the C(sub p) minimum. Hot-wire data are averaged on the basis of the phase of the disturbance, and automation of the experiment was used to obtain measurements on large spatially dense grids. In the turbulent boundary, the perturbation evolves into a vortex loop which retains its identity for a considerable streamwise distance. In the laminar layer, the perturbation decays to a very small magnitude before growing rapidly and triggering the transition process in the APG. The 'time-like' animations of the phase-averaged data are used to gain insight into the naturally occurring physical mechanisms in each flow.
Perturbation theory in light-cone quantization
Langnau, A.
1992-01-01
A thorough investigation of light-cone properties which are characteristic for higher dimensions is very important. The easiest way of addressing these issues is by analyzing the perturbative structure of light-cone field theories first. Perturbative studies cannot be substituted for an analysis of problems related to a nonperturbative approach. However, in order to lay down groundwork for upcoming nonperturbative studies, it is indispensable to validate the renormalization methods at the perturbative level, i.e., to gain control over the perturbative treatment first. A clear understanding of divergences in perturbation theory, as well as their numerical treatment, is a necessary first step towards formulating such a program. The first objective of this dissertation is to clarify this issue, at least in second and fourth-order in perturbation theory. The work in this dissertation can provide guidance for the choice of counterterms in Discrete Light-Cone Quantization or the Tamm-Dancoff approach. A second objective of this work is the study of light-cone perturbation theory as a competitive tool for conducting perturbative Feynman diagram calculations. Feynman perturbation theory has become the most practical tool for computing cross sections in high energy physics and other physical properties of field theory. Although this standard covariant method has been applied to a great range of problems, computations beyond one-loop corrections are very difficult. Because of the algebraic complexity of the Feynman calculations in higher-order perturbation theory, it is desirable to automatize Feynman diagram calculations so that algebraic manipulation programs can carry out almost the entire calculation. This thesis presents a step in this direction. The technique we are elaborating on here is known as light-cone perturbation theory.
Non-perturbative approach for curvature perturbations in stochastic δ N formalism
Fujita, Tomohiro; Kawasaki, Masahiro; Tada, Yuichiro E-mail: kawasaki@icrr.u-tokyo.ac.jp
2014-10-01
In our previous paper [1], we have proposed a new algorithm to calculate the power spectrum of the curvature perturbations generated in inflationary universe with use of the stochastic approach. Since this algorithm does not need the perturbative expansion with respect to the inflaton fields on super-horizon scale, it works even in highly stochastic cases. For example, when the curvature perturbations are very large or the non-Gaussianities of the curvature perturbations are sizable, the perturbative expansion may break down but our algorithm enables to calculate the curvature perturbations. We apply it to two well-known inflation models, chaotic and hybrid inflation, in this paper. Especially for hybrid inflation, while the potential is very flat around the critical point and the standard perturbative computation is problematic, we successfully calculate the curvature perturbations.
Non-Perturbative Field Theories.
NASA Astrophysics Data System (ADS)
Stephenson, David
Available from UMI in association with The British Library. Requires signed TDF. Some non-perturbative aspects of field theories are studied by applying lattice gauge theory techniques. The low-lying hadronic mass spectrum is calculated numerically using quenched lattice quantum chromodynamics. The results of large numerical simulations performed on a distributed array processor are presented and analysed. Particular emphasis is stressed upon the understanding of systematic and statistical errors in the calculation. In addition, the pion decay constant and the chiral condensate are evaluated. An attempt is made to relate the numerical findings to the experimentally measured quantities. A pioneering attempt to understand Yukawa couplings is discussed. A toy Fermion-Higgs system is studied numerically on a transputer array. Dynamical fermions are included in the investigation of the behavior of the system over a wide range of Yukawa couplings. A phase diagram is found for the model which shows evidence of spontaneous chiral symmetry breaking transitions. Extensions of the model are discussed together some speculations concerning the behaviour of Yukawa couplings in general. The possibility of using the lattice as a model for space-time is investigated by studying the propagation of particles on a fractal lattice. In addition, the use of truncated fractals as novel regulators is studied numerically in the hope that the problem of fermion doubling will be alleviated.
Quantum field perturbation theory revisited
NASA Astrophysics Data System (ADS)
Matone, Marco
2016-03-01
Schwinger's formalism in quantum field theory can be easily implemented in the case of scalar theories in D dimension with exponential interactions, such as μDexp (α ϕ ). In particular, we use the relation exp (α δ/δ J (x ) )exp (-Z0[J ])=exp (-Z0[J +αx]) with J the external source, and αx(y )=α δ (y -x ). Such a shift is strictly related to the normal ordering of exp (α ϕ ) and to a scaling relation which follows by renormalizing μ . Next, we derive a new formulation of perturbation theory for the potentials V (ϕ )=λ/n ! :ϕn: , using the generating functional associated to :exp (α ϕ ):. The Δ (0 )-terms related to the normal ordering are absorbed at once. The functional derivatives with respect to J to compute the generating functional are replaced by ordinary derivatives with respect to auxiliary parameters. We focus on scalar theories, but the method is general and similar investigations extend to other theories.
Perturbative theory for Brownian vortexes
NASA Astrophysics Data System (ADS)
Moyses, Henrique W.; Bauer, Ross O.; Grosberg, Alexander Y.; Grier, David G.
2015-06-01
Brownian vortexes are stochastic machines that use static nonconservative force fields to bias random thermal fluctuations into steadily circulating currents. The archetype for this class of systems is a colloidal sphere in an optical tweezer. Trapped near the focus of a strongly converging beam of light, the particle is displaced by random thermal kicks into the nonconservative part of the optical force field arising from radiation pressure, which then biases its diffusion. Assuming the particle remains localized within the trap, its time-averaged trajectory traces out a toroidal vortex. Unlike trivial Brownian vortexes, such as the biased Brownian pendulum, which circulate preferentially in the direction of the bias, the general Brownian vortex can change direction and even topology in response to temperature changes. Here we introduce a theory based on a perturbative expansion of the Fokker-Planck equation for weak nonconservative driving. The first-order solution takes the form of a modified Boltzmann relation and accounts for the rich phenomenology observed in experiments on micrometer-scale colloidal spheres in optical tweezers.
Chiral perturbation theory with nucleons
Meissner, U.G.
1991-09-01
I review the constraints posed on the interactions of pions, nucleons and photons by the spontaneously broken chiral symmetry of QCD. The framework to perform these calculations, chiral perturbation theory, is briefly discussed in the meson sector. The method is a simultaneous expansion of the Greens functions in powers of external moments and quark masses around the massless case, the chiral limit. To perform this expansion, use is made of a phenomenological Lagrangian which encodes the Ward-identities and pertinent symmetries of QCD. The concept of chiral power counting is introduced. The main part of the lectures of consists in describing how to include baryons (nucleons) and how the chiral structure is modified by the fact that the nucleon mass in the chiral limit does not vanish. Particular emphasis is put on working out applications to show the strengths and limitations of the methods. Some processes which are discussed are threshold photopion production, low-energy compton scattering off nucleons, {pi}N scattering and the {sigma}-term. The implications of the broken chiral symmetry on the nuclear forces are briefly described. An alternative approach, in which the baryons are treated as very heavy fields, is touched upon.
Perturbative theory for Brownian vortexes.
Moyses, Henrique W; Bauer, Ross O; Grosberg, Alexander Y; Grier, David G
2015-06-01
Brownian vortexes are stochastic machines that use static nonconservative force fields to bias random thermal fluctuations into steadily circulating currents. The archetype for this class of systems is a colloidal sphere in an optical tweezer. Trapped near the focus of a strongly converging beam of light, the particle is displaced by random thermal kicks into the nonconservative part of the optical force field arising from radiation pressure, which then biases its diffusion. Assuming the particle remains localized within the trap, its time-averaged trajectory traces out a toroidal vortex. Unlike trivial Brownian vortexes, such as the biased Brownian pendulum, which circulate preferentially in the direction of the bias, the general Brownian vortex can change direction and even topology in response to temperature changes. Here we introduce a theory based on a perturbative expansion of the Fokker-Planck equation for weak nonconservative driving. The first-order solution takes the form of a modified Boltzmann relation and accounts for the rich phenomenology observed in experiments on micrometer-scale colloidal spheres in optical tweezers. PMID:26172698
Cosmological perturbations across an S-brane
Brandenberger, Robert H.; Kounnas, Costas; Partouche, Hervé; Patil, Subodh P.; Toumbas, Nicolaos E-mail: kounnas@lpt.ens.fr E-mail: subodh.patil@cern.ch
2014-03-01
Space-filling S-branes can mediate a transition between a contracting and an expanding universe in the Einstein frame. Following up on previous work that uncovered such bouncing solutions in the context of weakly coupled thermal configurations of a certain class of type II superstrings, we set up here the formalism in which we can study the evolution of metric fluctuations across such an S-brane. Our work shows that the specific nature of the S-brane, which is sourced by non-trivial massless thermal string states and appears when the universe reaches a maximal critical temperature, allows for a scale invariant spectrum of curvature fluctuations to manifest at late times via a stringy realization of the matter bounce scenario. The finite energy density at the transition from contraction to expansion provides calculational control over the propagation of the curvature perturbations through the bounce, furnishing a working proof of concept that such a stringy universe can result in viable late time cosmology.
Phase perturbation measurements through a heated ionosphere
NASA Technical Reports Server (NTRS)
Frey, A.; Gordon, W. E.
1982-01-01
High frequency radiowaves incident on an overdense (i.e., HF-frequency penetration frequency) ionosphere produce electron density irregularities. The effect of such ionospheric irregularities on the phase of UHF-radiowaves was determined. For that purpose the phase of radiowaves originating from celestial radio sources was observed with two antennas. The radiosources were chosen such that the line of sight to at least one of the antennas (usually both) passed through the modified volume of the ionosphere. Observations at 430 MHz and at 2380 MHz indicate that natural irregularities have a much stronger effect on the UHF phase fluctuations than the HF-induced irregularities for presently achieved HF-power densities of 20-80 uW/sq m. It is not clear whether some of the effects observed are the result of HF-modification of the ionosphere. Upper limits on the phase perturbations produced by HF-modification are 10 deg at 2380 MHz and 80 deg at 430 MHz.
Scalar Quantum Electrodynamics: Perturbation Theory and Beyond
Bashir, A.; Gutierrez-Guerrero, L. X.; Concha-Sanchez, Y.
2006-09-25
In this article, we calculate scalar propagator in arbitrary dimensions and gauge and the three-point scalar-photon vertex in arbitrary dimensions and Feynman gauge, both at the one loop level. We also discuss constraints on their non perturbative structure imposed by requirements of gauge invariance and perturbation theory.
Degenerate Open Shell Density Perturbation Theory
NASA Astrophysics Data System (ADS)
Palenik, Mark; Dunlap, Brett
The density perturbation theory (DPT) methodology we have developed applies the Hohenberg-Kohn theorem to perturbations in density functional theory. At each order, the energy is directly minimized with respect to the density at all lower orders. The difference between the perturbed and unperturbed densities is expanded in terms of a finite number of basis functions, and a single matrix inversion in this space reduces the complexity of the problem to that of non-interacting perturbation theory. For open-shell systems with symmetry, however, the situation becomes more complex. Typically, the perturbation will break the symmetry leading to a zeroth-order shift in the Kohn-Sham potential. Because the symmetry breaking is independent of the strength of the perturbation, the mapping from the initial to the perturbed KS potential is discontinuous and techniques from perturbation theory for noninteracting particles fail. We describe a rigorous formulation of DPT for use in systems that display an initial degeneracy, such as atoms and Fe55Cp*12 clusters and present initial calculations on these systems.
Intelligent perturbation algorithms for space scheduling optimization
NASA Technical Reports Server (NTRS)
Kurtzman, Clifford R.
1991-01-01
Intelligent perturbation algorithms for space scheduling optimization are presented in the form of the viewgraphs. The following subject areas are covered: optimization of planning, scheduling, and manifesting; searching a discrete configuration space; heuristic algorithms used for optimization; use of heuristic methods on a sample scheduling problem; intelligent perturbation algorithms are iterative refinement techniques; properties of a good iterative search operator; dispatching examples of intelligent perturbation algorithm and perturbation operator attributes; scheduling implementations using intelligent perturbation algorithms; major advances in scheduling capabilities; the prototype ISF (industrial Space Facility) experiment scheduler; optimized schedule (max revenue); multi-variable optimization; Space Station design reference mission scheduling; ISF-TDRSS command scheduling demonstration; and example task - communications check.
Covariant generalization of cosmological perturbation theory
Enqvist, Kari; Hoegdahl, Janne; Nurmi, Sami; Vernizzi, Filippo
2007-01-15
We present an approach to cosmological perturbations based on a covariant perturbative expansion between two worldlines in the real inhomogeneous universe. As an application, at an arbitrary order we define an exact scalar quantity which describes the inhomogeneities in the number of e-folds on uniform density hypersurfaces and which is conserved on all scales for a barotropic ideal fluid. We derive a compact form for its conservation equation at all orders and assign it a simple physical interpretation. To make a comparison with the standard perturbation theory, we develop a method to construct gauge-invariant quantities in a coordinate system at arbitrary order, which we apply to derive the form of the nth order perturbation in the number of e-folds on uniform density hypersurfaces and its exact evolution equation. On large scales, this provides the gauge-invariant expression for the curvature perturbation on uniform density hypersurfaces and its evolution equation at any order.
Analysis of structural perturbations in systems via cost decomposition methods
NASA Technical Reports Server (NTRS)
Skelton, R. E.
1983-01-01
It has long been common practice to analyze linear dynamic systems by decomposing the total response in terms of individual contributions which are easier to analyze. Examples of this philosophy include the expansion of transfer functions using: (1) the superposition principle, (2) residue theory and partial fraction expansions, (3) Markov parameters, Hankel matrices, and (4) regular and singular perturbations. This paper summarizes a new and different kind of expansion designed to decompose the norm of the response vector rather than the response vector itself. This is referred to as "cost-decomposition' of the system. The notable advantages of this type of decomposition are: (a) easy application to multi-input, multi-output systems, (b) natural compatibility with Linear Quadratic Gaussian Theory, (c) applicability to the analysis of more general types of structural perturbations involving inputs, outputs, states, parameters. Property (c) makes the method suitable for problems in model reduction, measurement/actuator selections, and sensitivity analysis.
Quantifying human mobility perturbation and resilience in Hurricane Sandy.
Wang, Qi; Taylor, John E
2014-01-01
Human mobility is influenced by environmental change and natural disasters. Researchers have used trip distance distribution, radius of gyration of movements, and individuals' visited locations to understand and capture human mobility patterns and trajectories. However, our knowledge of human movements during natural disasters is limited owing to both a lack of empirical data and the low precision of available data. Here, we studied human mobility using high-resolution movement data from individuals in New York City during and for several days after Hurricane Sandy in 2012. We found the human movements followed truncated power-law distributions during and after Hurricane Sandy, although the β value was noticeably larger during the first 24 hours after the storm struck. Also, we examined two parameters: the center of mass and the radius of gyration of each individual's movements. We found that their values during perturbation states and steady states are highly correlated, suggesting human mobility data obtained in steady states can possibly predict the perturbation state. Our results demonstrate that human movement trajectories experienced significant perturbations during hurricanes, but also exhibited high resilience. We expect the study will stimulate future research on the perturbation and inherent resilience of human mobility under the influence of hurricanes. For example, mobility patterns in coastal urban areas could be examined as hurricanes approach, gain or dissipate in strength, and as the path of the storm changes. Understanding nuances of human mobility under the influence of such disasters will enable more effective evacuation, emergency response planning and development of strategies and policies to reduce fatality, injury, and economic loss. PMID:25409009
Quantifying Human Mobility Perturbation and Resilience in Hurricane Sandy
Wang, Qi; Taylor, John E.
2014-01-01
Human mobility is influenced by environmental change and natural disasters. Researchers have used trip distance distribution, radius of gyration of movements, and individuals' visited locations to understand and capture human mobility patterns and trajectories. However, our knowledge of human movements during natural disasters is limited owing to both a lack of empirical data and the low precision of available data. Here, we studied human mobility using high-resolution movement data from individuals in New York City during and for several days after Hurricane Sandy in 2012. We found the human movements followed truncated power-law distributions during and after Hurricane Sandy, although the β value was noticeably larger during the first 24 hours after the storm struck. Also, we examined two parameters: the center of mass and the radius of gyration of each individual's movements. We found that their values during perturbation states and steady states are highly correlated, suggesting human mobility data obtained in steady states can possibly predict the perturbation state. Our results demonstrate that human movement trajectories experienced significant perturbations during hurricanes, but also exhibited high resilience. We expect the study will stimulate future research on the perturbation and inherent resilience of human mobility under the influence of hurricanes. For example, mobility patterns in coastal urban areas could be examined as hurricanes approach, gain or dissipate in strength, and as the path of the storm changes. Understanding nuances of human mobility under the influence of such disasters will enable more effective evacuation, emergency response planning and development of strategies and policies to reduce fatality, injury, and economic loss. PMID:25409009
Transient dynamics of perturbations in astrophysical disks
NASA Astrophysics Data System (ADS)
Razdoburdin, D. N.; Zhuravlev, V. V.
2015-11-01
We review some aspects of a major unsolved problem in understanding astrophysical (in particular, accretion) disks: whether the disk interiors can be effectively viscous in spite of the absence of magnetorotational instability. A rotational homogeneous inviscid flow with a Keplerian angular velocity profile is spectrally stable, making the transient growth of perturbations a candidate mechanism for energy transfer from regular motion to perturbations. Transient perturbations differ qualitatively from perturbation modes and can grow substantially in shear flows due to the nonnormality of their dynamical evolution operator. Because the eigenvectors of this operator, also known as perturbation modes, are not pairwise orthogonal, they can mutually interfere, resulting in the transient growth of their linear combinations. Physically, a growing transient perturbation is a leading spiral whose branches are shrunk as a result of the differential rotation of the flow. We discuss in detail the transient growth of vortex shearing harmonics in the spatially local limit, as well as methods for identifying the optimal (fastest growth) perturbations. Special attention is given to obtaining such solutions variationally by integrating the respective direct and adjoint equations forward and backward in time. The presentation is intended for experts new to the subject.
Vector perturbations in a contracting Universe
Battefeld, T.J.; Brandenberger, R.
2004-12-15
In this note we show that vector perturbations exhibit growing mode solutions in a contracting Universe, such as the contracting phase of the pre big bang or the cyclic/ekpyrotic models of the Universe. This is not a gauge artifact and will in general lead to the breakdown of perturbation theory--a severe problem that has to be addressed in any bouncing model. We also comment on the possibility of explaining, by means of primordial vector perturbations, the existence of the observed large-scale magnetic fields. This is possible since they can be seeded by vorticity.
Cosmological perturbations and the Weinberg theorem
NASA Astrophysics Data System (ADS)
Akhshik, Mohammad; Firouzjahi, Hassan; Jazayeri, Sadra
2015-12-01
The celebrated Weinberg theorem in cosmological perturbation theory states that there always exist two adiabatic scalar modes in which the comoving curvature perturbation is conserved on super-horizon scales. In particular, when the perturbations are generated from a single source, such as in single field models of inflation, both of the two allowed independent solutions are adiabatic and conserved on super-horizon scales. There are few known examples in literature which violate this theorem. We revisit the theorem and specify the loopholes in some technical assumptions which violate the theorem in models of non-attractor inflation, fluid inflation, solid inflation and in the model of pseudo conformal universe.
HIV-associated memory B cell perturbations
Hu, Zhiliang; Luo, Zhenwu; Wan, Zhuang; Wu, Hao; Li, Wei; Zhang, Tong; Jiang, Wei
2015-01-01
Memory B-cell depletion, hyperimmunoglobulinemia, and impaired vaccine responses are the hallmark of B cell perturbations inhuman immunodeficiency virus (HIV) disease. Although B cells are not the targets for HIV infection, there is evidence for B cell, especially memory B cell dysfunction in HIV disease mediated by other cells or HIV itself. This review will focus on HIV-associated phenotypic and functional alterations in memory B cells. Additionally, we will discuss the mechanism underlying these perturbations and the effect of anti-retroviral therapy (ART) on these perturbations. PMID:25887082
Perturbing macroscopic magnetohydrodynamic stability for toroidal plasmas
NASA Astrophysics Data System (ADS)
Comer, Kathryn J.
We have introduced a new perturbative technique to rapidly explore the dependence of long wavelength ideal magnetohydrodynamic (MHD) instabilities on equilibrium profiles, shaping properties, and wall parameters. Traditionally, these relations are studied with numerical parameter scans using computationally intensive stability codes. Our perturbative technique first finds the equilibrium and stability using traditional methods. Subsequent small changes in the original equilibrium parameters change the stability. We quickly find the new stability with an expansion of the energy principle, rather than with another run of the stability codes. We first semi-analytically apply the technique to the screw pinch after eliminating compressional Alfven wave effects. The screw pinch results validate the approach, but also indicate that allowable perturbations to equilibria with certain features may be restricted. Next, we extend the approach to toroidal geometry using experimental equilibria and a simple constructed equilibrium, with the ideal MHD stability code GATO. Stability properties are successfully predicted from perturbed toroidal equilibria when only the vacuum beyond the plasma is perturbed (through wall parameter variations), rather than the plasma itself. Small plasma equilibrium perturbations to both experimental and simple equilibria result in very large errors to the predicted stability, and valid results are found only over a narrow range of most perturbations. Despite the large errors produced when changing plasma parameters, the wall perturbations revealed two useful applications of this technique. Because the calculations are non-iterative matrix multiplications, the convergence issues that can disrupt a full MHD stability code are absent. Marginal stability, therefore, is much easier to find with the perturbative technique. Also, the perturbed results can be input as the initial guess for the eigenvalue for a full stability code, and improve subsequent
Evolution of non-spherical perturbations.
NASA Astrophysics Data System (ADS)
Boschan, P.
1995-06-01
In this paper I investigate the evolution of primordial non-spherical positive and negative fluctuations. They can be calculated by second order of perturbation theory. I solved analytically the second order equation for arbitrary density parameter {OMEGA}_M0_ and cosmological constant {LAMBDA} using the approximation introduced by Martell & Freundling (???). The second order solution is compared with the exact one in the spherical case. I find that the initial deformation grows rapidly for positive perturbations, while the negative perturbations (voids) are stable against deformations.
Perturbation calculation of thermodynamic density of states
Brown, Greg; Schulthess, Thomas C; Nicholson, Don M; Eisenbach, Markus; Stocks, George Malcolm
2011-01-01
The density of states g( ) is frequently used to calculate the temperature-dependent properties of a thermodynamic system. Here a derivation is given for calculating the warped density of states g ( ) resulting from the addition of a perturbation. The method is validated for a classical Heisenberg model of bcc Fe and the errors in the free energy are shown to be second order in the perturbation. Taking the perturbation to be the difference between a first-principles quantum-mechanical energy and a corresponding classical energy, this method can significantly reduce the computational effort required to calculate g( ) for quantum systems using the Wang-Landau approach.
A Model for Gaussian Perturbations of Graphene
NASA Astrophysics Data System (ADS)
Dodson, C. T. J.
2015-11-01
Graphene consists nominally of a regular planar hexagonal carbon lattice monolayer. However, its structure experiences perturbations in the presence of external influences, whether from substrate properties, thermal or electromagnetic fields, or ambient fluid movement. Here we give an information geometric model to represent the state space of perturbations as a Riemannian pseudosphere with scalar curvature close to -1/2. This would allow the representation of a trajectory of states under a given ambient or process change, so opening the possibility for geometrically formulated dynamical models to link structural perturbations to the physics.
Detector dose response in megavoltage small photon beams. II. Pencil beam perturbation effects
Bouchard, Hugo Duane, Simon; Kamio, Yuji; Palmans, Hugo; Seuntjens, Jan
2015-10-15
Purpose: To quantify detector perturbation effects in megavoltage small photon fields and support the theoretical explanation on the nature of quality correction factors in these conditions. Methods: In this second paper, a modern approach to radiation dosimetry is defined for any detector and applied to small photon fields. Fano’s theorem is adapted in the form of a cavity theory and applied in the context of nonstandard beams to express four main effects in the form of perturbation factors. The pencil-beam decomposition method is detailed and adapted to the calculation of perturbation factors and quality correction factors. The approach defines a perturbation function which, for a given field size or beam modulation, entirely determines these dosimetric factors. Monte Carlo calculations are performed in different cavity sizes for different detection materials, electron densities, and extracameral components. Results: Perturbation effects are detailed with calculated perturbation functions, showing the relative magnitude of the effects as well as the geometrical extent to which collimating or modulating the beam impacts the dosimetric factors. The existence of a perturbation zone around the detector cavity is demonstrated and the approach is discussed and linked to previous approaches in the literature to determine critical field sizes. Conclusions: Monte Carlo simulations are valuable to describe pencil beam perturbation effects and detail the nature of dosimetric factors in megavoltage small photon fields. In practice, it is shown that dosimetric factors could be avoided if the field size remains larger than the detector perturbation zone. However, given a detector and beam quality, a full account for the detector geometry is necessary to determine critical field sizes.
NASA Astrophysics Data System (ADS)
Chagelishvili, George; Hau, Jan-Niklas; Khujadze, George; Oberlack, Martin
2016-08-01
The linear dynamics of perturbations in smooth shear flows covers the transient exchange of energies between (1) the perturbations and the basic flow and (2) different perturbations modes. Canonically, the linear exchange of energies between the perturbations and the basic flow can be described in terms of the Orr and the lift-up mechanisms, correspondingly for two-dimensional (2D) and three-dimensional (3D) perturbations. In this paper the mechanical basis of the linear transient dynamics is introduced and analyzed for incompressible plane constant shear flows, where we consider the dynamics of virtual fluid particles in the framework of plane perturbations (i.e., perturbations with plane surfaces of constant phase) for the 2D and 3D case. It is shown that (1) the formation of a pressure perturbation field is the result of countermoving neighboring sets of incompressible fluid particles in the flow, (2) the keystone of the energy exchange mechanism between the basic flow and perturbations is the collision of fluid particles with the planes of constant pressure in accordance with the classical theory of elastic collision of particles with a rigid wall, making the pressure field the key player in this process, (3) the interplay of the collision process and the shear flow kinematics describes the transient growth of plane perturbations and captures the physics of the growth, and (4) the proposed mechanical picture allows us to reconstruct the linearized Euler equations in spectral space with a time-dependent shearwise wave number, the linearized Euler equations for Kelvin modes. This confirms the rigor of the presented analysis, which, moreover, yields a natural generalization of the proposed mechanical picture of the transient growth to the well-established linear phenomenon of vortex-wave-mode coupling.
The Tidal Perturbations of the Galilean Satellites
NASA Astrophysics Data System (ADS)
Jacobson, Robert A.; Folkner, William M.
2014-11-01
To support the Juno mission currently enroute to Jupiter and preproject studies for the Europa Clipper mission, we developed new ephemerides for the Jovian satellites (the Galileans and four inners). The ephemerides are based on orbits that were determined by fitting a data set that included Earth-based astrometry from 1891 through 2013, Galilean satellite mutual events from 1973 through 2009, Galilean satellite eclipse timings from 1878 to 2013, and data acquired by the Pioneer, Voyager, Ulysses, Cassini, Galileo, and New Horizons spacecraft. As a part of the data fit we also redetermined the Jovian system gravity parameters and the spacecraft trajectories to be consistent with the satellite orbits. The dynamical model for the satellite orbits did not include tidal perturbations. Lainey et al. (2009 Nature 459, 957) determined tidal parameters for Jupiter and Io from a fit of the Galilean satellite orbits to Earth-based astrometry from 1891 to 2007 and mutual events from 1973 to 2003; he estimated only the satellite states and the tidal parameters. Subsequent to our ephemeris development, we activated the tide model and repeated our orbit analysis adding the determination of the tidal parameters. We found that if we omitted the spacecraft data and estimated only satellite states and tidal parameters, we obtained results similar to Lainey. However, when we included the spacecraft data in the fit, the tidal acceleration on Io was smaller but still caused a positive secular acceleration. The remaining task is to discriminate between the effects of the tide raised on Jupiter by Io and that raised on Io by Jupiter.
Flexoelectricity from density-functional perturbation theory
NASA Astrophysics Data System (ADS)
Stengel, Massimiliano
2013-11-01
We derive the complete flexoelectric tensor, including electronic and lattice-mediated effects, of an arbitrary insulator in terms of the microscopic linear response of the crystal to atomic displacements. The basic ingredient, which can be readily calculated from first principles in the framework of density-functional perturbation theory, is the quantum-mechanical probability current response to a long-wavelength acoustic phonon. Its second-order Taylor expansion in the wave vector q around the Γ (q=0) point in the Brillouin zone naturally yields the flexoelectric tensor. At order one in q we recover Martin's theory of piezoelectricity [Martin, Phys. Rev. B 5, 1607 (1972)], thus providing an alternative derivation thereof. To put our derivations on firm theoretical grounds, we perform a thorough analysis of the nonanalytic behavior of the dynamical matrix and other response functions in a vicinity of Γ. Based on this analysis, we find that there is an ambiguity in the specification of the “zero macroscopic field” condition in the flexoelectric case; such arbitrariness can be related to an analytic band-structure term, in close analogy to the theory of deformation potentials. As a by-product, we derive a rigorous generalization of the Cochran-Cowley formula [Cochran and Cowley, J. Phys. Chem. Solids 23, 447 (1962)] to higher orders in q. This can be of great utility in building reliable atomistic models of electromechanical phenomena, as well as for improving the accuracy of the calculation of phonon dispersion curves. Finally, we discuss the physical interpretation of the various contributions to the flexoelectric response, either in the static or dynamic regime, and we relate our findings to earlier theoretical works on the subject.
Casimir energy for perturbed surfaces of revolution
NASA Astrophysics Data System (ADS)
Morales-Almazan, Pedro
2016-03-01
In this paper, we explore the zeta function arising from a small perturbation on a surface of revolution and the effect of this on the functional determinant and on the change of the Casimir energy associated with the surface.
SHARP ENTRYWISE PERTURBATION BOUNDS FOR MARKOV CHAINS
THIEDE, ERIK; VAN KOTEN, BRIAN; WEARE, JONATHAN
2015-01-01
For many Markov chains of practical interest, the invariant distribution is extremely sensitive to perturbations of some entries of the transition matrix, but insensitive to others; we give an example of such a chain, motivated by a problem in computational statistical physics. We have derived perturbation bounds on the relative error of the invariant distribution that reveal these variations in sensitivity. Our bounds are sharp, we do not impose any structural assumptions on the transition matrix or on the perturbation, and computing the bounds has the same complexity as computing the invariant distribution or computing other bounds in the literature. Moreover, our bounds have a simple interpretation in terms of hitting times, which can be used to draw intuitive but rigorous conclusions about the sensitivity of a chain to various types of perturbations. PMID:26491218
Cosmological perturbations in mimetic Horndeski gravity
NASA Astrophysics Data System (ADS)
Arroja, Frederico; Bartolo, Nicola; Karmakar, Purnendu; Matarrese, Sabino
2016-04-01
We study linear scalar perturbations around a flat FLRW background in mimetic Horndeski gravity. In the absence of matter, we show that the Newtonian potential satisfies a second-order differential equation with no spatial derivatives. This implies that the sound speed for scalar perturbations is exactly zero on this background. We also show that in mimetic G3 theories the sound speed is equally zero. We obtain the equation of motion for the comoving curvature perturbation (first order differential equation) and solve it to find that the comoving curvature perturbation is constant on all scales in mimetic Horndeski gravity. We find solutions for the Newtonian potential evolution equation in two simple models. Finally we show that the sound speed is zero on all backgrounds and therefore the system does not have any wave-like scalar degrees of freedom.
Perturbations of black p-branes
Abdalla, Elcio; Fernandez Piedra, Owen Pavel; Oliveira, Jeferson de; Molina, C.
2010-03-15
We consider black p-brane solutions of the low-energy string action, computing scalar perturbations. Using standard methods, we derive the wave equations obeyed by the perturbations and treat them analytically and numerically. We have found that tensorial perturbations obtained via a gauge-invariant formalism leads to the same results as scalar perturbations. No instability has been found. Asymptotically, these solutions typically reduce to a AdS{sub (p+2)}xS{sup (8-p)} space which, in the framework of Maldacena's conjecture, can be regarded as a gravitational dual to a conformal field theory defined in a (p+1)-dimensional flat space-time. The results presented open the possibility of a better understanding the AdS/CFT correspondence, as originally formulated in terms of the relation among brane structures and gauge theories.
The Perturbational MO Method for Saturated Systems.
ERIC Educational Resources Information Center
Herndon, William C.
1979-01-01
Summarizes a theoretical approach using nonbonding MO's and perturbation theory to correlate properties of saturated hydrocarbons. Discussion is limited to correctly predicted using this method. Suggests calculations can be carried out quickly in organic chemistry. (Author/SA)
Controlling roll perturbations in fruit flies.
Beatus, Tsevi; Guckenheimer, John M; Cohen, Itai
2015-04-01
Owing to aerodynamic instabilities, stable flapping flight requires ever-present fast corrective actions. Here, we investigate how flies control perturbations along their body roll angle, which is unstable and their most sensitive degree of freedom. We glue a magnet to each fly and apply a short magnetic pulse that rolls it in mid-air. Fast video shows flies correct perturbations up to 100° within 30 ± 7 ms by applying a stroke-amplitude asymmetry that is well described by a linear proportional-integral controller. For more aggressive perturbations, we show evidence for nonlinear and hierarchical control mechanisms. Flies respond to roll perturbations within 5 ms, making this correction reflex one of the fastest in the animal kingdom. PMID:25762650
Controlling roll perturbations in fruit flies
Beatus, Tsevi; Guckenheimer, John M.; Cohen, Itai
2015-01-01
Owing to aerodynamic instabilities, stable flapping flight requires ever-present fast corrective actions. Here, we investigate how flies control perturbations along their body roll angle, which is unstable and their most sensitive degree of freedom. We glue a magnet to each fly and apply a short magnetic pulse that rolls it in mid-air. Fast video shows flies correct perturbations up to 100° within 30 ± 7 ms by applying a stroke-amplitude asymmetry that is well described by a linear proportional–integral controller. For more aggressive perturbations, we show evidence for nonlinear and hierarchical control mechanisms. Flies respond to roll perturbations within 5 ms, making this correction reflex one of the fastest in the animal kingdom. PMID:25762650
Non Perturbative Aspects of Field Theory
Bashir, A.
2009-04-20
For any quantum field theory (QFT), there exists a set of Schwinger-Dyson equations (SDE) for all its Green functions. However, it is not always straight forward to extract quantitatively exact physical information from this set of equations, especially in the non perturbative regime. The situation becomes increasingly complex with growing number of external legs. I give a qualitative account of the hunt for the non perturbative Green functions in gauge theories.
On perturbations of a quintom bounce
Cai Yifu; Qiu Taotao; Zhang Xinmin; Brandenberger, Robert; Piao Yunsong E-mail: qiutt@mail.ihep.ac.cn E-mail: yspiao@gucas.ac.cn
2008-03-15
A quintom universe with an equation of state crossing the cosmological constant boundary can provide a bouncing solution dubbed the quintom bounce and thus resolve the big bang singularity. In this paper, we investigate the cosmological perturbations of the quintom bounce both analytically and numerically. We find that the fluctuations in the dominant mode in the post-bounce expanding phase couple to the growing mode of the perturbations in the pre-bounce contracting phase.
Brevity of haptic force perturbations induces heightened adaptive sensitivity
Wanda, Paul A.; Fine, Michael S.; Weeks, Heidi M.; Gross, Andrew M.; Macy, Jenny L.; Thoroughman, Kurt A.
2013-01-01
We have exposed human participants to both full-movement and pulsatile viscous force perturbations to study the effect of force duration on the incremental transformation of sensation into adaptation. Traditional views of movement biomechanics could suggest that pulsatile forces would largely be attenuated as stiffness and viscosity act as a natural low-pass filter. Sensory transduction, however, tends to react to changes in stimuli and therefore could underlie heightened sensitivity to briefer, pulsatile forces. Here, participants adapted within perturbation duration conditions in a manner proportionate to sensed force and positional errors. Across perturbation conditions, we found participants had greater adaptive sensitivity when experiencing pulsatile forces rather than full-movement forces. In a follow-up experiment, we employed error-clamped, force channel trials to determine changes in predictive force generation. We found that while participants learned to closely compensate for the amplitude and breadth of full-movement forces, they exhibited a persistent mismatch in amplitude and breadth between adapted motor output and experienced pulsatile forces. This mismatch could generate higher salience of error signals that contribute to heightened sensitivity to pulsatile forces. PMID:23468159
Finite element structural redesign by large admissible perturbations
NASA Technical Reports Server (NTRS)
Bernitsas, Michael M.; Beyko, E.; Rim, C. W.; Alzahabi, B.
1991-01-01
In structural redesign, two structural states are involved; the baseline (known) State S1 with unacceptable performance, and the objective (unknown) State S2 with given performance specifications. The difference between the two states in performance and design variables may be as high as 100 percent or more depending on the scale of the structure. A Perturbation Approach to Redesign (PAR) is presented to relate any two structural states S1 and S2 that are modeled by the same finite element model and represented by different values of the design variables. General perturbation equations are derived expressing implicitly the natural frequencies, dynamic modes, static deflections, static stresses, Euler buckling loads, and buckling modes of the objective S2 in terms of its performance specifications, and S1 data and Finite Element Analysis (FEA) results. Large Admissible Perturbation (LEAP) algorithms are implemented in code RESTRUCT to define the objective S2 incrementally without trial and error by postprocessing FEA results of S1 with no additional FEAs. Systematic numerical applications in redesign of a 10 element 48 degree of freedom (dof) beam, a 104 element 192 dof offshore tower, a 64 element 216 dof plate, and a 144 element 896 dof cylindrical shell show the accuracy, efficiency, and potential of PAR to find an objective state that may differ 100 percent from the baseline design.
Particle Motion and Perturbed Dynamical System in Warped Product Spacetimes
NASA Astrophysics Data System (ADS)
Bhattacharya, Pinaki; Guha, Sarbari
2016-07-01
In this paper we have used the dynamical systems analysis to study the dynamics of a five-dimensional universe in the form of a warped product spacetime with a spacelike dynamic extra dimension. We have decomposed the geodesic equations to get the motion along the extra dimension and have studied the associated dynamical system when the cross-diagonal element of the Einstein tensor vanishes, and also when it is non-vanishing. Introducing the concept of an energy function along the phase path in terms of the extra-dimensional coordinate, we have examined how the energy function depends on the warp factor. The energy function serves as a measure of the amount of perturbation of geodesic paths along the extra dimension in the region close to the brane. Then we studied the geodesic motion under a conventional metric perturbation in the form of homothetic motion and conformal motion and examined the nature of critical points for a Mashhoon-Wesson-type metric, for timelike and null geodesics when the cross-diagonal term of the Einstein tensor vanishes. Finally we investigated the motion for null and timelike geodesics under the condition when the cross-diagonal element of the Einstein tensor is non-vanishing and examined the effects of perturbation on the critical points of the dynamical system.
Dynamics near a periodically-perturbed robust heteroclinic cycle
NASA Astrophysics Data System (ADS)
Tsai, Tsung-Lung; Dawes, Jonathan H. P.
2013-11-01
Robust heteroclinic cycles (RHCs) arise naturally in collections of symmetric differential equations derived as dynamical models in many fields, including fluid mechanics, game theory and population dynamics. In this paper, we present a careful study of the complicated dynamics generated by small amplitude periodic perturbations of a stable robust heteroclinic cycle (RHC). We give a detailed derivation of the Poincaré map for trajectories near the RHC, asymptotically correct in the limit of small amplitude perturbations. This reduces the nonautonomous system in R3 to a 2D map. We identify three distinct dynamical regimes. The distinctions between these regimes depend subtly on different distinguished limits of the two small parameters in the problem. The first regime corresponds to the RHC being only weakly attracting: here we show that the system is equivalent to a damped nonlinear pendulum with a constant torque. In the second regime the periodically-perturbed RHC is more strongly attracting and the system dynamics corresponds to that of a (non-invertible or invertible) circle map. In the third regime, of yet stronger attraction, the dynamics of the return map is chaotic and no longer reducible to a one-dimensional map. This third regime has been noted previously; our analysis in this paper focusses on providing quantitative results in the first two regimes.
Shock-induced perturbation evolution in planar laser targets
NASA Astrophysics Data System (ADS)
Aglitskiy, Y.; Karasik, M.; Velikovich, A. L.; Serlin, V.; Weaver, J. L.; Kessler, T. J.; Schmitt, A. J.; Obenschain, S. P.; Metzler, N.; Oh, J.
2013-10-01
Experimental studies of hydrodynamic perturbation evolution triggered by a laser-driven shock wave in a planar target done on the KrF Nike laser facility are reported. The targets were made of solid plastic and/or plastic foam with single mode sinusoidal perturbation on the front or back surface or plastic/foam interface. Two specific cases are discussed. When a planar solid plastic target rippled at the front side is irradiated with a 350 ps long laser pulse, ablative Richtmyer-Meshkov (RM) oscillation of its areal mass modulation amplitude is detected while the laser is on, followed by observed strong oscillations of the areal mass in the unsupported shock flow after the laser pulse ends. When the target is rippled at the rear side, the nature of the perturbation evolution after the shock breakout is determined by the strength of the laser-driven shock wave. At pressure below 1 Mbar shock interaction with rear-surface ripples produces planar collimated jets manifesting the development of a classical RM instability in a weakly compressible shocked fluid. At shock pressure ~ 8 Mbar sufficient for vaporizing the shocked target material we observed instead the strong areal mass oscillations characteristic of a rippled centered rarefaction wave. Work supported by US DOE, Defense Programs.
Rapid eco-evolutionary responses in perturbed phytoplankton communities.
Thibodeau, Geneviève; Walsh, David A; Beisner, Beatrix E
2015-09-01
Biodiversity currently faces unprecedented threats owing to species extinctions. Ecologically, compensatory dynamics can ensure stable community biomass following perturbation. However, whether there is a contribution of genetic diversity to community responses is an outstanding question. To date, the contribution of evolutionary processes through genotype shifts has not been assessed in naturally co-occurring multi-species communities in the field. We examined the mechanisms contributing to the response of a lake phytoplankton community exposed to either a press or pulse acidification perturbation in lake mesocosms. To assess community shifts in the ecological response of morphospecies, we identified taxa microscopically. We also assessed genotype shifts by sequencing the ITS2 region of ribosomal DNA. We observed ecological and genetic contributions to community responses. The ecological response was attributed to compensatory morphospecies dynamics and occurred primarily in the Pulse perturbation treatment. In the Press treatments, in addition to compensatory dynamics, we observed evidence for genotype selection in two species of chlorophytes, Desmodesmus cuneatus and an unidentified Chlamydomonas. Our study demonstrates that while genotype selection may be rare, it is detectable and occurs especially when new environmental conditions are maintained for long enough to force selection processes on standing variation. PMID:26311667
Lipid Bilayer Membrane Perturbation by Embedded Nanopores: A Simulation Study.
Garcia-Fandiño, Rebeca; Piñeiro, Ángel; Trick, Jemma L; Sansom, Mark S P
2016-03-22
A macromolecular nanopore inserted into a membrane may perturb the dynamic organization of the surrounding lipid bilayer. To better understand the nature of such perturbations, we have undertaken a systematic molecular dynamics simulation study of lipid bilayer structure and dynamics around three different classes of nanopore: a carbon nanotube, three related cyclic peptide nanotubes differing in the nature of their external surfaces, and a model of a β-barrel nanopore protein. Periodic spatial distributions of several lipid properties as a function of distance from the nanopore were observed. This was especially clear for the carbon nanotube system, for which the density of lipids, the bilayer thickness, the projection of lipid head-to-tail vectors onto the membrane plane, and lipid lateral diffusion coefficients exhibited undulatory behavior as a function of the distance from the surface of the channel. Overall, the differences in lipid behavior as a function of the nanopore structure reveal local adaptation of the bilayer structure and dynamics to different embedded nanopore structures. Both the local structure and dynamic behavior of lipids around membrane-embedded nanopores are sensitive to the geometry and nature of the outer surface of the macromolecule/molecular assembly forming the pore. PMID:26943498
Thermally unstable perturbations in stratified conducting atmospheres
NASA Astrophysics Data System (ADS)
Reale, Fabio; Serio, Salvatore; Peres, Giovanni
1994-10-01
We investigate the thermal stability of isobaric perturbations in a stratified isothermal background atmosphere with solar abundances, as resulting from the competition of optically thin plasma radiative cooling and of heating conducted from the surrounding atmosphere. We have analyzed the threshold line between stable and unstable perturbations, in the plane of the two important control parameters: the initial size of the perturbation and the temperature of the unperturbed medium; this line changes with the pressure of the unperturbed atmosphere. We have extended the results of linear perturbation analysis by means of numerical calculations of the evolution of spherical isobaric perturbations, using a two-dimensional hydrodynamic code including Spitzer heat conduction. We explore a wide range of the parameters appropriate to the solar and stellar upper atmospheres: the background uniform temperature is between 105 K and 107 K, the initial pressure betweeen 0.1 and 10 dyn/sq cm, and the perturbation size between 105 and 1010 cm. The numerical results are in substantial agreement with the linear analysis. We discuss possible implications of our results also in terms of observable effects, especially concerning plasma downflows, and propose thermal instability as a possible candidate to explain the observed redshifts in solar and stellar transition region lines.
Perturbative Solutions of the Einstein Klein-Gordon Equations
NASA Astrophysics Data System (ADS)
Puliti, Gianluca; Jennings, Mara; Mamo, Vincent; Vuille, Chris
2005-11-01
As the Klein-Gordon equation is important in quantum theory and describes spin-0 particles, it is of interest to discover the nature of the gravity field such particles would be expected to create. In this paper, we solve the static, massive Einstein-Klein-Gordon (EKG) equations in perturbation, and compare the results with a similar calculation developed for the Einstein-Proca system. Subsequently, we study the massless static Klein-Gordon equation, and compare the result to the Reissner-Nordstrom metric.
NASA Astrophysics Data System (ADS)
Hajian, K.; Seraj, A.; Sheikh-Jabbari, M. M.
2014-10-01
In [1] we formulated and derived the three universal laws governing Near Horizon Extremal Geometries (NHEG). In this work we focus on the Entropy Perturbation Law (EPL) which, similarly to the first law of black hole thermodynamics, relates perturbations of the charges labeling perturbations around a given NHEG to the corresponding entropy perturbation. We show that field perturbations governed by the linearized equations of motion and symmetry conditions which we carefully specify, satisfy the EPL. We also show that these perturbations are limited to those coming from difference of two NHEG solutions (i.e. variations on the NHEG solution parameter space). Our analysis and discussions shed light on the "no-dynamics" statements of [2, 3].
Statistics and dynamics of the perturbed universe
NASA Astrophysics Data System (ADS)
Lemson, G.
1995-09-01
In the not too distant past, our theorizing about the nature of the Universe we live in, was not much limited by observational constraints. Consequently, no true science could be developed dealing with the nature of the Universe at large: its origin, its present state and its future. This was the realm of religion and philosophy. In this century, revolutionary developments in physics have provided the framework within which to describe the Universe as a whole and which finally made it possible to obtain tentative answers to questions we have only recently learned to ask. In this thesis, I present investigations that deal with a small part of the theory of cosmology. In particular, I have investigated certain aspects of the theory of structure formation in the Universe. This subject has been extensively studied in the last few decennia. It originated from the realization that the Universe has not always been the same as observed at present. The Universe as we observe it today is filled with objects of a great variety of sizes and shapes. In the 2nd and 3rd decade of this century Hubble discovered that our Universe is expanding. This implies that in the past the Universe was smaller and therefore denser. All the structures we observe nowadays, if also existing in the past, would have been closer and at some time would have touched and overlapped. Furthermore, the theories that were developed to describe such an expanding Universe in quantitative detail, required that the Universe be homogeneous and isotropic, i.e. it should look the same at every position and in every direction. All mass and radiation must once have been distributed uniformly throughout space. With these theories, Gamov (1946, 1948ab) predicted that in the past the Universe must have been much hotter than presently, and that the afterglow of this epoch should still be observable as a faint radio signal at a temperature a few degrees above the absolute zero point. In the early sixties, Penzias and
Perturbations of the Robertson-Walker space
NASA Astrophysics Data System (ADS)
Hwang, Jai Chan
This dissertation contains three parts consisting of thirteen chapters. Each chapter is self-contained, and can be read independently. In chapter 1, we have presented a complete set of cosmological perturbation equations using the covariant equations. We also present an explicit solution for the evolution of large scale cosmological density perturbations assuming a perfect fluid. In chapter 2, two independent gauge-invariant variables are derived which are continuous at any transition where there is a discontinuous change in pressure. In chapter 3, we present a Newtonian counterpart to the general relativistic covariant approach to cosmological perturbations. In chapter 4, we present a simple way of deriving cosmological perturbation equations in generalized gravity theories which accounts for metric perturbations in gauge-invariant way. We apply this approach to the f(phi,R)-omega(phi)phi, cphi;c Lagrangian. In chapter 5, we have derived second order differential equations for cosmological perturbations in a Robertson-Walker space, for each of the following gravity theories: f(R) gravity, generalized scalar-tensor gravity, gravity with non-minimally coupled scalar field, and induced gravity. Asymptotic solutions are derived for the large and small scale limits. In chapter 6, classical evolution of density perturbations in the large scale limit is clarified in the generalized gravity theories. In chapter 7, we apply our method to a theory with the Lagrangian L approximately f(R) + gamma RR;c;c. In chapter 8, T(M)ab;b equals 0 is shown in a general ground. In chapter 9, the origin of the Friedmann-like behavior of the perturbed model in the large scale limit is clarified in a comoving gauge. Thus, when the imperfect fluid contributions are negligible, the large scale perturbations in a nearly flat background evolve like separate Friedmann models. In chapter 10, we generalize the perturbation equations applicable to a class of generalized gravity theories with multi
Non-hard sphere thermodynamic perturbation theory
NASA Astrophysics Data System (ADS)
Zhou, Shiqi
2011-08-01
A non-hard sphere (HS) perturbation scheme, recently advanced by the present author, is elaborated for several technical matters, which are key mathematical details for implementation of the non-HS perturbation scheme in a coupling parameter expansion (CPE) thermodynamic perturbation framework. NVT-Monte Carlo simulation is carried out for a generalized Lennard-Jones (LJ) 2n-n potential to obtain routine thermodynamic quantities such as excess internal energy, pressure, excess chemical potential, excess Helmholtz free energy, and excess constant volume heat capacity. Then, these new simulation data, and available simulation data in literatures about a hard core attractive Yukawa fluid and a Sutherland fluid, are used to test the non-HS CPE 3rd-order thermodynamic perturbation theory (TPT) and give a comparison between the non-HS CPE 3rd-order TPT and other theoretical approaches. It is indicated that the non-HS CPE 3rd-order TPT is superior to other traditional TPT such as van der Waals/HS (vdW/HS), perturbation theory 2 (PT2)/HS, and vdW/Yukawa (vdW/Y) theory or analytical equation of state such as mean spherical approximation (MSA)-equation of state and is at least comparable to several currently the most accurate Ornstein-Zernike integral equation theories. It is discovered that three technical issues, i.e., opening up new bridge function approximation for the reference potential, choosing proper reference potential, and/or using proper thermodynamic route for calculation of fex - ref, chiefly decide the quality of the non-HS CPE TPT. Considering that the non-HS perturbation scheme applies for a wide variety of model fluids, and its implementation in the CPE thermodynamic perturbation framework is amenable to high-order truncation, the non-HS CPE 3rd-order or higher order TPT will be more promising once the above-mentioned three technological advances are established.
Mathematical inference and control of molecular networks from perturbation experiments
NASA Astrophysics Data System (ADS)
Mohammed-Rasheed, Mohammed
One of the main challenges facing biologists and mathematicians in the post genomic era is to understand the behavior of molecular networks and harness this understanding into an educated intervention of the cell. The cell maintains its function via an elaborate network of interconnecting positive and negative feedback loops of genes, RNA and proteins that send different signals to a large number of pathways and molecules. These structures are referred to as genetic regulatory networks (GRNs) or molecular networks. GRNs can be viewed as dynamical systems with inherent properties and mechanisms, such as steady-state equilibriums and stability, that determine the behavior of the cell. The biological relevance of the mathematical concepts are important as they may predict the differentiation of a stem cell, the maintenance of a normal cell, the development of cancer and its aberrant behavior, and the design of drugs and response to therapy. Uncovering the underlying GRN structure from gene/protein expression data, e.g., microarrays or perturbation experiments, is called inference or reverse engineering of the molecular network. Because of the high cost and time consuming nature of biological experiments, the number of available measurements or experiments is very small compared to the number of molecules (genes, RNA and proteins). In addition, the observations are noisy, where the noise is due to the measurements imperfections as well as the inherent stochasticity of genetic expression levels. Intra-cellular activities and extra-cellular environmental attributes are also another source of variability. Thus, the inference of GRNs is, in general, an under-determined problem with a highly noisy set of observations. The ultimate goal of GRN inference and analysis is to be able to intervene within the network, in order to force it away from undesirable cellular states and into desirable ones. However, it remains a major challenge to design optimal intervention strategies
Cohomology Methods in Causal Perturbation Theory
NASA Astrophysics Data System (ADS)
Grigore, D. R.
2010-01-01
Various problems in perturbation theory of (quantum) gauge models can be rephrased in the language of cohomology theory. This was already noticed in the functional formulation of perturbative gauge theories. Causal perturbation theory is a fully quantum approach: is works only with the chronological products which are defined as operator-valued distributions in the Fock space of the model. The use of causal perturbation theory leads to similar cohomology problems; the main difference with respect to the functional methods comes from the fact that the gauge transformation of the causal approach is, essentially, the linear part of the non-linear BRST transformation. Using these methods it is possible to give a nice determination of the interaction Lagrangians for gauge models (Yang-Mills and gravitation in the linear approximation); one obtains with this method the unicity of the interaction Lagrangian up to trivial terms. The case of quantum gravity is highly non-trivial and can be generalized with this method to the massive graviton case. Going to higher orders of perturbation theory one finds quantum anomalies. Again the cohomological methods can be used to determine the generic form of these anomalies. Finally, one can investigate the arbitrariness of the chronological products in higher orders and reduce this problem to cohomology methods also.
Supersymmetry restoration in superstring perturbation theory
NASA Astrophysics Data System (ADS)
Sen, Ashoke
2015-12-01
Superstring perturbation theory based on the 1PI effective theory approach has been useful for addressing the problem of mass renormalization and vacuum shift. We derive Ward identities associated with space-time supersymmetry transformation in this approach. This leads to a proof of the equality of renormalized masses of bosons and fermions and identities relating fermionic amplitudes to bosonic amplitudes after taking into account the effect of mass renormalization. This also relates unbroken supersymmetry to a given order in perturbation theory to absence of tadpoles of massless scalars to higher order. The results are valid at the perturbative vacuum as well as in the shifted vacuum when the latter describes the correct ground state of the theory. We apply this to SO(32) heterotic string theory on Calabi-Yau 3-folds where a one loop Fayet-Iliopoulos term apparently breaks supersymmetry at one loop, but analysis of the low energy effective field theory indicates that there is a nearby vacuum where supersymmetry is restored. We explicitly prove that the perturbative amplitudes of this theory around the shifted vacuum indeed satisfy the Ward identities associated with unbroken supersymmetry. We also test the general arguments by explicitly verifying the equality of bosonic and fermionic masses at one loop order in the shifted vacuum, and the appearance of two loop dilaton tadpole in the perturbative vacuum where supersymmetry is expected to be broken.
Mode coupling of Schwarzschild perturbations: Ringdown frequencies
Pazos, Enrique; Brizuela, David; Martin-Garcia, Jose M.; Tiglio, Manuel
2010-11-15
Within linearized perturbation theory, black holes decay to their final stationary state through the well-known spectrum of quasinormal modes. Here we numerically study whether nonlinearities change this picture. For that purpose we study the ringdown frequencies of gauge-invariant second-order gravitational perturbations induced by self-coupling of linearized perturbations of Schwarzschild black holes. We do so through high-accuracy simulations in the time domain of first and second-order Regge-Wheeler-Zerilli type equations, for a variety of initial data sets. We consider first-order even-parity (l=2, m={+-}2) perturbations and odd-parity (l=2, m=0) ones, and all the multipoles that they generate through self-coupling. For all of them and all the initial data sets considered we find that--in contrast to previous predictions in the literature--the numerical decay frequencies of second-order perturbations are the same ones of linearized theory, and we explain the observed behavior. This would indicate, in particular, that when modeling or searching for ringdown gravitational waves, appropriately including the standard quasinormal modes already takes into account nonlinear effects.
Improved WKB analysis of cosmological perturbations
Casadio, Roberto; Luzzi, Mattia; Venturi, Giovanni; Finelli, Fabio
2005-02-15
Improved Wentzel-Kramers-Brillouin (WKB)-type approximations are presented in order to study cosmological perturbations beyond the lowest order. Our methods are based on functions which approximate the true perturbation modes over the complete range of the independent (Langer) variable, from subhorizon to superhorizon scales, and include the region near the turning point. We employ both a perturbative Green's function technique and an adiabatic (or semiclassical) expansion (for a linear turning point) in order to compute higher order corrections. Improved general expressions for the WKB scalar and tensor power spectra are derived for both techniques. We test our methods on the benchmark of power-law inflation, which allows comparison with exact expressions for the perturbations, and find that the next-to-leading order adiabatic expansion yields the amplitude of the power spectra with excellent accuracy, whereas the next-to-leading order with the perturbative Green's function method does not improve the leading order result significantly. However, in more general cases, either or both methods may be useful.
Local perturbations perturb—exponentially–locally
De Roeck, W. Schütz, M.
2015-06-15
We elaborate on the principle that for gapped quantum spin systems with local interaction, “local perturbations [in the Hamiltonian] perturb locally [the groundstate].” This principle was established by Bachmann et al. [Commun. Math. Phys. 309, 835–871 (2012)], relying on the “spectral flow technique” or “quasi-adiabatic continuation” [M. B. Hastings, Phys. Rev. B 69, 104431 (2004)] to obtain locality estimates with sub-exponential decay in the distance to the spatial support of the perturbation. We use ideas of Hamza et al. [J. Math. Phys. 50, 095213 (2009)] to obtain similarly a transformation between gapped eigenvectors and their perturbations that is local with exponential decay. This allows to improve locality bounds on the effect of perturbations on the low lying states in certain gapped models with a unique “bulk ground state” or “topological quantum order.” We also give some estimate on the exponential decay of correlations in models with impurities where some relevant correlations decay faster than one would naively infer from the global gap of the system, as one also expects in disordered systems with a localized groundstate.
Cosmological perturbations on the phantom brane
NASA Astrophysics Data System (ADS)
Bag, Satadru; Viznyuk, Alexander; Shtanov, Yuri; Sahni, Varun
2016-07-01
We obtain a closed system of equations for scalar perturbations in a multi-component braneworld. Our braneworld possesses a phantom-like equation of state at late times, weff < ‑1, but no big-rip future singularity. In addition to matter and radiation, the braneworld possesses a new effective degree of freedom—the `Weyl fluid' or `dark radiation'. Setting initial conditions on super-Hubble spatial scales at the epoch of radiation domination, we evolve perturbations of radiation, pressureless matter and the Weyl fluid until the present epoch. We observe a gradual decrease in the amplitude of the Weyl-fluid perturbations after Hubble-radius crossing, which results in a negligible effect of the Weyl fluid on the evolution of matter perturbations on spatial scales relevant for structure formation. Consequently, the quasi-static approximation of Koyama and Maartens provides a good fit to the exact results during the matter-dominated epoch. We find that the late-time growth of density perturbations on the brane proceeds at a faster rate than in ΛCDM. Additionally, the gravitational potentials Φ and Ψ evolve differently on the brane than in ΛCDM, for which Φ = Ψ. On the brane, by contrast, the ratio Φ/Ψ exceeds unity during the late matter-dominated epoch (z lesssim 50). These features emerge as smoking gun tests of phantom brane cosmology and allow predictions of this scenario to be tested against observations of galaxy clustering and large-scale structure.
Cosmological perturbations in teleparallel Loop Quantum Cosmology
NASA Astrophysics Data System (ADS)
Haro, Jaime
2013-11-01
Cosmological perturbations in Loop Quantum Cosmology (LQC) are usually studied incorporating either holonomy corrections, where the Ashtekar connection is replaced by a suitable sinus function in order to have a well-defined quantum analogue, or inverse-volume corrections coming from the eigenvalues of the inverse-volume operator. In this paper we will develop an alternative approach to calculate cosmological perturbations in LQC based on the fact that, holonomy corrected LQC in the flat Friedmann-Lemaître-Robertson-Walker (FLRW) geometry could be also obtained as a particular case of teleparallel F(T) gravity (teleparallel LQC). The main idea of our approach is to mix the simple bounce provided by holonomy corrections in LQC with the non-singular perturbation equations given by F(T) gravity, in order to obtain a matter bounce scenario as a viable alternative to slow-roll inflation. In our study, we have obtained an scale invariant power spectrum of cosmological perturbations. However, the ratio of tensor to scalar perturbations is of order 1, which does not agree with the current observations. For this reason, we suggest a model where a transition from the matter domination to a quasi de Sitter phase is produced in order to enhance the scalar power spectrum.
Perturbed vortex lattices and the stability of nucleated topological phases
NASA Astrophysics Data System (ADS)
Lahtinen, Ville; Ludwig, Andreas W. W.; Trebst, Simon
2014-02-01
We study the stability of nucleated topological phases that can emerge when interacting non-Abelian anyons form a regular array. The studies are carried out in the context of Kitaev's honeycomb model, where we consider three distinct types of perturbations in the presence of a lattice of Majorana mode binding vortices—spatial anisotropy of the vortices, dimerization of the vortex lattice, and local random disorder. While all the nucleated phases are stable with respect to weak perturbations of each kind, strong perturbations are found to result in very different behavior. Anisotropy of the vortices stabilizes the strong-pairing-like phases, while dimerization can recover the underlying non-Abelian phase. Local random disorder, on the other hand, can drive all the nucleated phases into a gapless thermal metal state. We show that all these distinct behaviors can be captured by an effective staggered tight-binding model for the Majorana modes. By studying the pairwise interactions between the vortices, i.e., the amplitudes for the Majorana modes to tunnel between vortex cores, the locations of phase transitions and the nature of the resulting states can be predicted. We also find that, due to oscillations in the Majorana tunneling amplitude, lattices of Majorana modes may exhibit a Peierls-like instability, where a dimerized configuration is favored over a uniform lattice. As the nature of the nucleated phases depends only on the Majorana tunneling, our results are expected to apply also to other system supporting localized Majorana mode arrays, such as Abrikosov lattices in p-wave superconductors, Wigner crystals in Moore-Read fractional quantum Hall states, or arrays of topological nanowires.
Dynamic response of ramjet inlets to downstream perturbations
NASA Astrophysics Data System (ADS)
Sajben, M.; Bogar, T. J.; Kroutil, J. C.
1983-01-01
An external-compression inlet with high-aspect-ratio, rectangular cross sections was investigated in a semi-freejet arrangement at M(infinity) = 1.84 and zero incidence, over a wide range of super- and subcritical conditions. The response of the inlet flows to periodic perturbations imposed at the downstream end was determined. The perturbations were created by mechanical modulation of the choked exhaust area at frequencies from 20 to 360 Hz. The amplitude of the pressure fluctuations induced at the downstream end of the inlet was varied up to 8% of the time-mean static pressure at the same location. The observed oscillations were categorized according to position ranges associated with the shock motion. In supercritical oscillations, the pressure fluctuation amplitudes within the inlet were found to be linearly proportional to the fluctuation intensity at the exit station, establishing the latter as the appropriate quantity for normalization. In subcritical conditions, the inlet displays a large-amplitude natural oscillation (buzz). Superimposed excitation may couple with the natural oscillations in two distinctly different ways, both strongly nonlinear. Combinations of mean flow condition, excitation amplitude, and frequency that cause the terminal shock to move upstream of the cowl or the ramp were determined.
An Aircraft Separation Algorithm with Feedback and Perturbation
NASA Technical Reports Server (NTRS)
White, Allan L.
2010-01-01
A separation algorithm is a set of rules that tell aircraft how to maneuver in order to maintain a minimum distance between them. This paper investigates demonstrating that separation algorithms satisfy the FAA requirement for the occurrence of incidents by means of simulation. Any demonstration that a separation algorithm, or any other aspect of flight, satisfies the FAA requirement is a challenge because of the stringent nature of the requirement and the complexity of airspace operations. The paper begins with a probability and statistical analysis of both the FAA requirement and demonstrating meeting it by a Monte Carlo approach. It considers the geometry of maintaining separation when one plane must change its flight path. It then develops a simple feedback control law that guides the planes on their paths. The presence of feedback control permits the introduction of perturbations, and the stochastic nature of the chosen perturbation is examined. The simulation program is described. This paper is an early effort in the realistic demonstration of a stringent requirement. Much remains to be done.
Non-gravitational perturbations and satellite geodesy
Milani, A.; Nobill, A.M.; Farinella, P.
1987-01-01
This book presents the basic ideas of the physics of non-gravitational perturbations and the mathematics required to compute their orbital effects. It conveys the relevance of the different problems that must be solved to achieve a given level of accuracy in orbit determination and in recovery of geophysically significant parameters. Selected Contents are: Orders of Magnitude of the Perturbing Forces, Tides and Apparent Forces, Tools from Celestial Mechanics, Solar Radiation Pressure-Direct Effects: Satellite-Solar Radiation Interaction, Long-Term Effects on Semi-Major Axis, Radiation Pressure-Indirect Effects: Earth-Reflected Radiation Pressure, Anisotropic Thermal Emission, Drag: Orbital Perturbations by a Drag-Like Force, and Charged Particle Drag.
Perturbations in a regular bouncing universe
Battefeld, T.J.; Geshnizjani, G.
2006-03-15
We consider a simple toy model of a regular bouncing universe. The bounce is caused by an extra timelike dimension, which leads to a sign flip of the {rho}{sup 2} term in the effective four dimensional Randall Sundrum-like description. We find a wide class of possible bounces: big bang avoiding ones for regular matter content, and big rip avoiding ones for phantom matter. Focusing on radiation as the matter content, we discuss the evolution of scalar, vector and tensor perturbations. We compute a spectral index of n{sub s}=-1 for scalar perturbations and a deep blue index for tensor perturbations after invoking vacuum initial conditions, ruling out such a model as a realistic one. We also find that the spectrum (evaluated at Hubble crossing) is sensitive to the bounce. We conclude that it is challenging, but not impossible, for cyclic/ekpyrotic models to succeed, if one can find a regularized version.
Non-perturbative quantum geometry III
NASA Astrophysics Data System (ADS)
Krefl, Daniel
2016-08-01
The Nekrasov-Shatashvili limit of the refined topological string on toric Calabi-Yau manifolds and the resulting quantum geometry is studied from a non-perturbative perspective. The quantum differential and thus the quantum periods exhibit Stokes phenomena over the combined string coupling and quantized Kähler moduli space. We outline that the underlying formalism of exact quantization is generally applicable to points in moduli space featuring massless hypermultiplets, leading to non-perturbative band splitting. Our prime example is local ℙ1 + ℙ1 near a conifold point in moduli space. In particular, we will present numerical evidence that in a Stokes chamber of interest the string based quantum geometry reproduces the non-perturbative corrections for the Nekrasov-Shatashvili limit of 4d supersymmetric SU(2) gauge theory at strong coupling found in the previous part of this series. A preliminary discussion of local ℙ2 near the conifold point in moduli space is also provided.
Interactions of Blast Waves with Perturbed Interfaces
NASA Astrophysics Data System (ADS)
Henry de Frahan, Marc; Johnsen, Eric
2015-11-01
Richtmyer-Meshkov and Rayleigh-Taylor instabilities induce hydrodynamic mixing in many important physical systems such as inertial confinement fusion, supernova collapse, and scramjet combustion. Blast waves interacting with perturbed interfaces are prevelant in such applications and dictate the mixing dynamics. This study increases our understanding of blast-driven hydrodynamic instabilities by providing models for the time-dependent perturbation growth and vorticity production mechanisms. The strength and length of the blast wave determine the different growth regimes and the importance of the Richtmyer-Meshkov or Rayleigh-Taylor growth. Our analysis is based on simulations of a 2D planar blast wave, modeled by a shock (instantaneous acceleration) followed by a rarefaction (time-dependent deceleration), interacting with a sinusoidal perturbation at an interface between two fluids. A high-order accurate Discontinuous Galerkin method is used to solve the multifluid Euler equations.
Perturbation analysis of electromagnetic geodesic acoustic modes
Ren, Haijun
2014-06-15
Lagrangian displacement and magnetic field perturbation response to the geodesic acoustic mode is analyzed by using the ideal magnetohydrodynamic equations in a large-aspect-ratio tokamak. δB{sub θ}, the poloidal component of magnetic field perturbation, has poloidal wave number m = 2 created by the poloidal displacement ξ{sub θ}. The parallel perturbation of magnetic field, δB{sub ∥}, has a poloidally asymmetric structure with m = 1 and is on the same order of magnitude with δB{sub θ} to the leading order. The radial displacement ξ{sub r} is of order O(βϵξ{sub θ}) but plays a significant role in determining δB{sub ∥}, where β is the plasma/magnetic pressure ratio and ϵ is the inverse aspect ratio.
Elementary theorems regarding blue isocurvature perturbations
NASA Astrophysics Data System (ADS)
Chung, Daniel J. H.; Yoo, Hojin
2015-04-01
Blue CDM-photon isocurvature perturbations are attractive in terms of observability and may be typical from the perspective of generic mass relations in supergravity. We present and apply three theorems useful for blue isocurvature perturbations arising from linear spectator scalar fields. In the process, we give a more precise formula for the blue spectrum associated with the axion model of Kasuya and Kawasaki [Axion Isocurvature Fluctuations with Extremely Blue Spectrum, Phys. Rev. D 80, 023516 (2009).], which can in a parametric corner give a factor of O (10 ) correction. We explain how a conserved current associated with Peccei-Quinn symmetry plays a crucial role and explicitly plot several example spectra including the breaks in the spectra. We also resolve a little puzzle arising from a naive multiplication of isocurvature expression that sheds light on the gravitational imprint of the adiabatic perturbations on the fields responsible for blue isocurvature fluctuations.
Perturbation measurement of waveguides for acoustic thermometry
NASA Astrophysics Data System (ADS)
Lin, H.; Feng, X. J.; Zhang, J. T.
2013-09-01
Acoustic thermometers normally embed small acoustic transducers in the wall bounding a gas-filled cavity resonator. At high temperature, insulators of transducers loss electrical insulation and degrade the signal-to-noise ratio. One essential solution to this technical trouble is to couple sound by acoustic waveguides between resonator and transducers. But waveguide will break the ideal acoustic surface and bring perturbations(Δf+ig) to the ideal resonance frequency. The perturbation model for waveguides was developed based on the first-order acoustic theory in this paper. The frequency shift Δf and half-width change g caused by the position, length and radius of waveguides were analyzed using this model. Six different length of waveguides (52˜1763 mm) were settled on the cylinder resonator and the perturbation (Δf+ig) were measured at T=332 K and p=250˜500 kPa. The experiment results agreed with the theoretical prediction very well.
Hypersurface-invariant approach to cosmological perturbations
NASA Astrophysics Data System (ADS)
Salopek, D. S.; Stewart, J. M.
1995-01-01
Using Hamilton-Jacobi theory, we develop a formalism for solving semiclassical cosmological perturbations which does not require an explicit choice of time hypersurface. The Hamilton-Jacobi equation for gravity interacting with matter (either a scalar or dust field) is solved by making an ansatz which includes all terms quadratic in the spatial curvature. Gravitational radiation and scalar perturbations are treated on an equal footing. Our technique encompasses linear perturbation theory and it also describes some mild nonlinear effects. As a concrete example of the method, we compute the galaxy-galaxy correlation function as well as large-angle microwave background fluctuations for power-law inflation, and we compare with recent observations.
Instability of charged Lovelock black holes: Vector perturbations and scalar perturbations
NASA Astrophysics Data System (ADS)
Takahashi, Tomohiro
2013-01-01
We examine the stability of charged Lovelock black hole solutions under vector-type and scalar-type perturbations. We find suitable master variables for the stability analysis; the equations for these variables are Schrödinger-type equations with two components, and these Schrödinger operators are symmetric. By these master equations, we show that charged Lovelock black holes are stable under vector-type perturbations. For scalar-type perturbations, we show the criteria for instability and check these numerically. In our previous paper [T. Takahashi, Prog. Theor. Phys. 125, 1289 (2011)], we have shown that nearly extreme black holes show instability under tensor-type perturbations. In this paper, we find that black holes with a small charge show instability under scalar-type perturbations even if they have a relatively large mass.
CHARACTERIZATION OF THE RESONANT CAUSTIC PERTURBATION
Chung, Sun-Ju
2009-11-01
Four of nine exoplanets found by microlensing were detected by the resonant caustic, which represents the merging of the planetary and central caustics at the position when the projected separation of a host star and a bounded planet is s approx 1. One of the resonant caustic lensing events, OGLE-2005-BLG-169, was a caustic-crossing high-magnification event with A {sub max}approx 800 and the source star was much smaller than the caustic, nevertheless the perturbation was not obviously apparent on the light curve of the event. In this paper, we investigate the perturbation pattern of the resonant caustic to understand why the perturbations induced by the caustic do not leave strong traces on the light curves of high-magnification events despite a small source/caustic size ratio. From this study, we find that the regions with small magnification excess around the center of the resonant caustic are rather widely formed, and the event passing the small-excess region produces a high-magnification event with a weak perturbation that is small relative to the amplification caused by the star and thus does not noticeably appear on the light curve of the event. We also find that the positive excess of the inside edge of the resonant caustic and the negative excess inside the caustic become stronger and wider as q increases, and thus the resonant caustic-crossing high-magnification events with the weak perturbation occur in the range of q <= 10{sup -4}. We determine the probability of the occurrence of events with the small excess |epsilon| <= 3% in high-magnification events induced by a resonant caustic. As a result, we find that for Earth-mass planets with a separation of approx2.5 AU the resonant caustic high-magnification events with the weak perturbation can occur with a significant frequency.
Nonlinear Growth of Singular Vector Based Perturbations
NASA Astrophysics Data System (ADS)
Reynolds, C. A.
2002-12-01
The nonlinearity of singular vector-based perturbation growth is examined within the context of a global atmospheric forecast model. The characteristics of these nonlinearities and their impact on the utility of SV-based diagnostics are assessed both qualitatively and quantitatively. Nonlinearities are quantified by examining the symmetry of evolving positive and negative "twin" perturbations. Perturbations initially scaled to be consistent with estimates of analysis uncertainty become significantly nonlinear by 12 hours. However, the relative magnitude of the nonlinearities is a strong function of scale and metric. Small scales become nonlinear very quickly while synoptic scales can remain significantly linear out to three day. Small shifts between positive and negative perturbations can result in significant nonlinearities even when the basic anomaly patterns are quite similar. Thus, singular vectors may be qualitatively useful even when nonlinearities are large. Post-time pseudo-inverse experiments show that despite significant nonlinear perturbation growth, the nonlinear forecast corrections are similar to the expected linear corrections, even at 72 hours. When the nonlinear correction does differ significantly from the expected linear correction, the nonlinear correction is usually better, indicating that in some cases the pseudo-inverse correction effectively suppresses error growth outside the subspace defined by the leading (dry) singular vectors. Because a significant portion of the nonlinear growth occurs outside of the dry singular vector subspace, an a priori nonlinearity index based on the full perturbations is not a good predictor of when pseudo-inverse based corrections will be ineffective. However, one can construct a reasonable predictor of pseudo-inverse ineffectiveness by focusing on nonlinearities in the synoptic scales or in the singular vector subspace only.
Death to perturbative QCD in exclusive processes?
Eckardt, R.; Hansper, J.; Gari, M.F.
1994-04-01
The authors discuss the question of whether perturbative QCD is applicable in calculations of exclusive processes at available momentum transfers. They show that the currently used method of determining hadronic quark distribution amplitudes from QCD sum rules yields wave functions which are completely undetermined because the polynomial expansion diverges. Because of the indeterminacy of the wave functions no statement can be made at present as to whether perturbative QCD is valid. The authors emphasize the necessity of a rigorous discussion of the subject and the importance of experimental data in the range of interest.
Perturbative approach to Markovian open quantum systems
Li, Andy C. Y.; Petruccione, F.; Koch, Jens
2014-01-01
The exact treatment of Markovian open quantum systems, when based on numerical diagonalization of the Liouville super-operator or averaging over quantum trajectories, is severely limited by Hilbert space size. Perturbation theory, standard in the investigation of closed quantum systems, has remained much less developed for open quantum systems where a direct application to the Lindblad master equation is desirable. We present such a perturbative treatment which will be useful for an analytical understanding of open quantum systems and for numerical calculation of system observables which would otherwise be impractical. PMID:24811607
Evolution of perturbations in an inflationary universe
NASA Technical Reports Server (NTRS)
Frieman, J. A.; Will, C. M.
1982-01-01
The evolution of inhomogeneous density perturbations in a model of the very early universe that is dominated for a time by a constant energy density of a false quantum-mechanical vacuum is analyzed. During this period, the universe inflates exponentially and supercools exponentially, until a phase transition back to the true vacuum reheats the matter and radiation. Focus is on the physically measurable, coordinate-independent modes of inhomogeneous perturbations of this model and it is found that all modes either are constant or are exponentially damped during the inflationary era.
Continuum methods in lattice perturbation theory
Becher, Thomas G
2002-11-15
We show how methods of continuum perturbation theory can be used to simplify perturbative lattice calculations. We use the technique of asymptotic expansions to expand lattice loop integrals around the continuum limit. After the expansion, all nontrivial dependence on momenta and masses is encoded in continuum loop integrals and the only genuine lattice integrals left are tadpole integrals. Using integration-by-parts relations all of these can be expressed in terms of a small number of master integrals. Four master integrals are needed for bosonic one loop integrals, sixteen in QCD with Wilson or staggered fermions.
Robustness of braneworld scenarios against tensorial perturbations
NASA Astrophysics Data System (ADS)
Bazeia, D.; Losano, L.; Menezes, R.; Olmo, Gonzalo J.; Rubiera-Garcia, D.
2015-11-01
Inspired by the peculiarities of the effective geometry of crystalline structures, we reconsider thick brane scenarios from a metric-affine perspective. We show that for a rather general family of theories of gravity, whose Lagrangian is an arbitrary function of the metric and the Ricci tensor, the background and scalar field equations can be written in first-order form, and tensorial perturbations have a non negative definite spectrum, which makes them stable under linear perturbations regardless of the form of the gravity Lagrangian. We find, in particular, that the tensorial zero modes are exactly the same as predicted by Einstein’s theory regardless of the scalar field and gravitational Lagrangians.
Conservative perturbation theory for nonconservative systems
NASA Astrophysics Data System (ADS)
Shah, Tirth; Chattopadhyay, Rohitashwa; Vaidya, Kedar; Chakraborty, Sagar
2015-12-01
In this paper, we show how to use canonical perturbation theory for dissipative dynamical systems capable of showing limit-cycle oscillations. Thus, our work surmounts the hitherto perceived barrier for canonical perturbation theory that it can be applied only to a class of conservative systems, viz., Hamiltonian systems. In the process, we also find Hamiltonian structure for an important subset of Liénard system—a paradigmatic system for modeling isolated and asymptotic oscillatory state. We discuss the possibility of extending our method to encompass an even wider range of nonconservative systems.
Perturbative renormalization of the electric field correlator
NASA Astrophysics Data System (ADS)
Christensen, C.; Laine, M.
2016-04-01
The momentum diffusion coefficient of a heavy quark in a hot QCD plasma can be extracted as a transport coefficient related to the correlator of two colour-electric fields dressing a Polyakov loop. We determine the perturbative renormalization factor for a particular lattice discretization of this correlator within Wilson's SU(3) gauge theory, finding a ∼ 12% NLO correction for values of the bare coupling used in the current generation of simulations. The impact of this result on existing lattice determinations is commented upon, and a possibility for non-perturbative renormalization through the gradient flow is pointed out.
Non-Gaussianity from isocurvature perturbations
Kawasaki, Masahiro; Nakayama, Kazunori; Sekiguchi, Toyokazu; Suyama, Teruaki; Takahashi, Fuminobu E-mail: nakayama@icrr.u-tokyo.ac.jp E-mail: suyama@icrr.u-tokyo.ac.jp
2008-11-15
We develop a formalism for studying non-Gaussianity in both curvature and isocurvature perturbations. It is shown that non-Gaussianity in the isocurvature perturbation between dark matter and photons leaves distinct signatures in the cosmic microwave background temperature fluctuations, which may be confirmed in future experiments, or possibly even in the currently available observational data. As an explicit example, we consider the quantum chromodynamics axion and show that it can actually induce sizable non-Gaussianity for the inflationary scale, H{sub inf} = O(10{sup 9}-10{sup 11}) GeV.
Computing model independent perturbations in dark energy and modified gravity
Battye, Richard A.; Pearson, Jonathan A. E-mail: jonathan.pearson@durham.ac.uk
2014-03-01
We present a methodology for computing model independent perturbations in dark energy and modified gravity. This is done from the Lagrangian for perturbations, by showing how field content, symmetries, and physical principles are often sufficient ingredients for closing the set of perturbed fluid equations. The fluid equations close once ''equations of state for perturbations'' are identified: these are linear combinations of fluid and metric perturbations which construct gauge invariant entropy and anisotropic stress perturbations for broad classes of theories. Our main results are the proof of the equation of state for perturbations presented in a previous paper, and the development of the required calculational tools.
Gauge-invariant cosmological perturbation theory with seeds
Durrer, R. )
1990-10-15
Gauge-invariant cosmological perturbation theory is extended to handle perturbations induced by seeds. A calculation of the Sachs-Wolfe effect is presented. A second-order differential equation for the growth of density perturbations is derived and the perturbation of Liouville's equation for collisionless particles is also given. The results are illustrated by a simple analytic example of a single texture knot, where we calculate the induced perturbations of the energy of microwave photons, of baryonic matter, and of collisionless particles.
Collective response to perturbations in a data-driven fish school model
Calovi, Daniel S.; Lopez, Ugo; Schuhmacher, Paul; Chaté, Hugues; Sire, Clément; Theraulaz, Guy
2015-01-01
Fish schools are able to display a rich variety of collective states and behavioural responses when they are confronted by threats. However, a school's response to perturbations may be different depending on the nature of its collective state. Here we use a previously developed data-driven fish school model to investigate how the school responds to perturbations depending on its different collective states, we measure its susceptibility to such perturbations, and exploit its relation with the intrinsic fluctuations in the school. In particular, we study how a single or a small number of perturbing individuals whose attraction and alignment parameters are different from those of the main population affect the long-term behaviour of a school. We find that the responsiveness of the school to the perturbations is maximum near the transition region between milling and schooling states where the school exhibits multistability and regularly shifts between these two states. It is also in this region that the susceptibility, and hence the fluctuations, of the polarization order parameter is maximal. We also find that a significant school's response to a perturbation only happens below a certain threshold of the noise to social interactions ratio. PMID:25631571
Plume Diagnostics of the RSRM Static Firings for the Pressure Perturbation Studies
NASA Technical Reports Server (NTRS)
Mathias, Edward C.; Sambamurthi, Jay K.; Alvarado, Alexis
1995-01-01
During the STS-54 launch (RSRM-29), the right hand solid rocket motor experienced a 13.9 psi chamber pressure perturbation at 67 seconds into the motor operation. This pressure augmentation equated to a thrust change of 51 klb. Concerns were raised regarding the adverse effects of this thrust imbalance on the shuttle system and the overall thrust into the external tank structural elements. Pressure perturbations have been observed in solid rocket motors due to expulsion of igniter or insulation materials; the motor thrust during such events drop abruptly before rising. However, the RSRM motors do not exhibit such behavior during the large chamber pressure perturbation events. Several scenarios were investigated to explain these pressure perturbations in the RSRM motors based on a fault tree developed after STS-54. Of these, the expulsion of the slag accumulated in the submerged nozzle region appeared to be the most plausible scenario to explain the observations. Slag is a natural combustion product of aluminized solid rocket motors. The RSRM propellant contains 16% by weight of aluminum. Any ejection of this slag mass during nozzle vectoring or other side loads on the motor will result in the chamber pressure perturbation. Two RSRM static firings were instrumented extensively to further understand the slag expulsion phenomenon in the RSRM and the associated pressure perturbations.
Statistics and dynamics of the perturbed universe
NASA Astrophysics Data System (ADS)
Lemson, G.
1995-09-01
In the not too distant past, our theorizing about the nature of the Universe we live in, was not much limited by observational constraints. Consequently, no true science could be developed dealing with the nature of the Universe at large: its origin, its present state and its future. This was the realm of religion and philosophy. In this century, revolutionary developments in physics have provided the framework within which to describe the Universe as a whole and which finally made it possible to obtain tentative answers to questions we have only recently learned to ask. In this thesis, I present investigations that deal with a small part of the theory of cosmology. In particular, I have investigated certain aspects of the theory of structure formation in the Universe. This subject has been extensively studied in the last few decennia. It originated from the realization that the Universe has not always been the same as observed at present. The Universe as we observe it today is filled with objects of a great variety of sizes and shapes. In the 2nd and 3rd decade of this century Hubble discovered that our Universe is expanding. This implies that in the past the Universe was smaller and therefore denser. All the structures we observe nowadays, if also existing in the past, would have been closer and at some time would have touched and overlapped. Furthermore, the theories that were developed to describe such an expanding Universe in quantitative detail, required that the Universe be homogeneous and isotropic, i.e. it should look the same at every position and in every direction. All mass and radiation must once have been distributed uniformly throughout space. With these theories, Gamov (1946, 1948ab) predicted that in the past the Universe must have been much hotter than presently, and that the afterglow of this epoch should still be observable as a faint radio signal at a temperature a few degrees above the absolute zero point. In the early sixties, Penzias and
Staggered heavy baryon chiral perturbation theory
NASA Astrophysics Data System (ADS)
Bailey, Jon A.
2008-03-01
Although taste violations significantly affect the results of staggered calculations of pseudoscalar and heavy-light mesonic quantities, those entering staggered calculations of baryonic quantities have not been quantified. Here I develop staggered chiral perturbation theory in the light-quark baryon sector by mapping the Symanzik action into heavy baryon chiral perturbation theory. For 2+1 dynamical quark flavors, the masses of flavor-symmetric nucleons are calculated to third order in partially quenched and fully dynamical staggered chiral perturbation theory. To this order the expansion includes the leading chiral logarithms, which come from loops with virtual decuplet-like states, as well as terms of O(mπ3), which come from loops with virtual octet-like states. Taste violations enter through the meson propagators in loops and tree-level terms of O(a2). The pattern of taste symmetry breaking and the resulting degeneracies and mixings are discussed in detail. The resulting chiral forms are appropriate to lattice results obtained with operators already in use and could be used to study the restoration of taste symmetry in the continuum limit. I assume that the fourth root of the fermion determinant can be incorporated in staggered chiral perturbation theory using the replica method.
Aharonov-Bohm Effect in Perturbation Theory.
ERIC Educational Resources Information Center
Purcell, Kay M.; Henneberger, Walter C.
1978-01-01
The Aharonov-Bohn effect is obtained in first-order perturbation theory. It is shown that the effect occurs only when the initial state is a superposition of eigenstates of Lz corresponding to eigenvalues having opposite sign. (Author/GA)
Entropy perturbations in N-flation
Cai Ronggen; Hu Bin; Piao Yunsong
2009-12-15
In this paper we study the entropy perturbations in N-flation by using the {delta}N formalism. We calculate the entropy corrections to the power spectrum of the overall curvature perturbation P{sub {zeta}}. We obtain an analytic form of the transfer coefficient T{sub RS}{sup 2}, which describes the correlation between the curvature and entropy perturbations, and investigate its behavior numerically. It turns out that the entropy perturbations cannot be neglected in N-flation because the amplitude of entropy components is approximately in the same order as the adiabatic one at the end of inflation T{sub RS}{sup 2}{approx}O(1). The spectral index n{sub S} is calculated and it becomes smaller after the entropy modes are taken into account, i.e., the spectrum becomes redder, compared to the pure adiabatic case. Finally we study the modified consistency relation of N-flation, and find that the tensor-to-scalar ratio (r{approx_equal}0.006) is greatly suppressed by the entropy modes, compared to the pure adiabatic one (r{approx_equal}0.017) at the end of inflation.
What Perturbs the ggrdgr Rings of Uranus?
French, R G; Kangas, J A; Elliot, J L
1986-01-31
The gamma and delta rings have by far the largest radial perturbations of any of the nine known Uranian rings. These two rings deviate from Keplerian orbits, having typical root-mean-square residuals of about 3 kilometers (compared to a few hundred meters for the other seven known rings). Possible causes for the perturbations include nearby shepherd satellites and Lindblad resonances. If shepherd satellites are responsible, they could be as large as several tens of kilometers in diameter. The perturbation patterns of the gamma and delta rings have been examined for evidence of Lindblad resonances of azimuthal wave number m = 0, 1, 2, 3, and 4. The beta ring radial residuals are well matched by a 2:1 Lindblad resonance. If this represents a real physical phenomenon and is not an artifact of undersampling, then the most plausible interpretation is that there is an undiscovered satellite orbiting 76,522 +/- 8 kilometers from Uranus, with an orbital period of 15.3595 +/- 0.0001 hours and a radius of 75 to 100 kilometers. Such a satellite would be easily detected by the Voyager spacecraft when it encounters Uranus. The 2:1 resonance location is 41 +/- 9 kilometers inside the delta ring, which makes it unlikely that the resonance is due to a viscous instability within the ring. In contrast, no low-order Lindblad resonance matches the gamma ring perturbations, which are probably caused by one or more shepherd satellites large enough to be clearly visible in Voyager images. PMID:17776019
Circumstellar Debris Disks: Diagnosing the Unseen Perturber
NASA Astrophysics Data System (ADS)
Nesvold, Erika R.; Naoz, Smadar; Vican, Laura; Farr, Will M.
2016-07-01
The first indication of the presence of a circumstellar debris disk is usually the detection of excess infrared emission from the population of small dust grains orbiting the star. This dust is short-lived, requiring continual replenishment, and indicating that the disk must be excited by an unseen perturber. Previous theoretical studies have demonstrated that an eccentric planet orbiting interior to the disk will stir the larger bodies in the belt and produce dust via interparticle collisions. However, motivated by recent observations, we explore another possible mechanism for heating a debris disk: a stellar-mass perturber orbiting exterior to and inclined to the disk and exciting the disk particles’ eccentricities and inclinations via the Kozai–Lidov mechanism. We explore the consequences of an exterior perturber on the evolution of a debris disk using secular analysis and collisional N-body simulations. We demonstrate that a Kozai–Lidov excited disk can generate a dust disk via collisions and we compare the results of the Kozai–Lidov excited disk with a simulated disk perturbed by an interior eccentric planet. Finally, we propose two observational tests of a dust disk that can distinguish whether the dust was produced by an exterior brown dwarf or stellar companion or an interior eccentric planet.
Degenerate adiabatic perturbation theory: Foundations and applications
NASA Astrophysics Data System (ADS)
Rigolin, Gustavo; Ortiz, Gerardo
2014-08-01
We present details and expand on the framework leading to the recently introduced degenerate adiabatic perturbation theory [Phys. Rev. Lett. 104, 170406 (2010), 10.1103/PhysRevLett.104.170406], and on the formulation of the degenerate adiabatic theorem, along with its necessary and sufficient conditions [given in Phys. Rev. A 85, 062111 (2012), 10.1103/PhysRevA.85.062111]. We start with the adiabatic approximation for degenerate Hamiltonians that paves the way to a clear and rigorous statement of the associated degenerate adiabatic theorem, where the non-Abelian geometric phase (Wilczek-Zee phase) plays a central role to its quantitative formulation. We then describe the degenerate adiabatic perturbation theory, whose zeroth-order term is the degenerate adiabatic approximation, in its full generality. The parameter in the perturbative power-series expansion of the time-dependent wave function is directly associated to the inverse of the time it takes to drive the system from its initial to its final state. With the aid of the degenerate adiabatic perturbation theory we obtain rigorous necessary and sufficient conditions for the validity of the adiabatic theorem of quantum mechanics. Finally, to illustrate the power and wide scope of the methodology, we apply the framework to a degenerate Hamiltonian, whose closed-form time-dependent wave function is derived exactly, and also to other nonexactly solvable Hamiltonians whose solutions are numerically computed.
Cell cycle population effects in perturbation studies
O'Duibhir, Eoghan; Lijnzaad, Philip; Benschop, Joris J; Lenstra, Tineke L; van Leenen, Dik; Groot Koerkamp, Marian JA; Margaritis, Thanasis; Brok, Mariel O; Kemmeren, Patrick; Holstege, Frank CP
2014-01-01
Growth condition perturbation or gene function disruption are commonly used strategies to study cellular systems. Although it is widely appreciated that such experiments may involve indirect effects, these frequently remain uncharacterized. Here, analysis of functionally unrelated Saccharyomyces cerevisiae deletion strains reveals a common gene expression signature. One property shared by these strains is slower growth, with increased presence of the signature in more slowly growing strains. The slow growth signature is highly similar to the environmental stress response (ESR), an expression response common to diverse environmental perturbations. Both environmental and genetic perturbations result in growth rate changes. These are accompanied by a change in the distribution of cells over different cell cycle phases. Rather than representing a direct expression response in single cells, both the slow growth signature and ESR mainly reflect a redistribution of cells over different cell cycle phases, primarily characterized by an increase in the G1 population. The findings have implications for any study of perturbation that is accompanied by growth rate changes. Strategies to counter these effects are presented and discussed. PMID:24952590
On-Shell Methods in Perturbative QCD
Bern, Zvi; Dixon, Lance J.; Kosower, David A.
2007-04-25
We review on-shell methods for computing multi-parton scattering amplitudes in perturbative QCD, utilizing their unitarity and factorization properties. We focus on aspects which are useful for the construction of one-loop amplitudes needed for phenomenological studies at the Large Hadron Collider.
Partially Quenched Chiral Perturbation Theory to NNLO
Laehde, Timo; Bijnens, Johan; Danielsson, Niclas
2006-07-11
This paper summarizes the recent calculations of the masses and decay constants of the pseudoscalar mesons at the two-loop level, or NNLO, in Partially Quenched Chiral Perturbation theory (PQ{chi}PT). Possible applications include chiral extrapolations of Lattice QCD, as well as the determination of the low-energy constants (LEC:s) of QCD.
Magnetic perturbation inspection of inner bearing races
NASA Technical Reports Server (NTRS)
Barton, J. R.; Lankford, J.
1972-01-01
Approximately 100 inner race bearings were inspected nondestructively prior to endurance testing. Two of the bearings which failed during testing spalled at the sites of subsurface inclusions previously detected by using magnetic field perturbation. At other sites initially judged to be suspect, subsurface inclusion-nucleated cracking was observed. Inspection records and metallurgical sectioning results are presented and discussed.
The General Necessary Condition for the Validity of Dirac's Transition Perturbation Theory
NASA Technical Reports Server (NTRS)
Quang, Nguyen Vinh
1996-01-01
For the first time, from the natural requirements for the successive approximation the general necessary condition of validity of the Dirac's method is explicitly established. It is proved that the conception of 'the transition probability per unit time' is not valid. The 'super-platinium rules' for calculating the transition probability are derived for the arbitrarily strong time-independent perturbation case.
Interpretation of perturbed angular distribution results for19F implanted into diamond
NASA Astrophysics Data System (ADS)
Connell, S.; Sellschop, J. P. F.; Stemmet, M. C.; Appel, H.; Bharuth-Ram, K.; Verwoerd, W. S.
1990-08-01
Perturbed Angular Distribution measurements have been made on natural diamond using recoil implanted fluorine ions as probes. Two distinct lattice sites for fluorine in diamond were found. Site identifications prompted by theoretical cluster calculations are presented. The PAD data are well described by a texture theory, though the origin of the texture effects is presently not known.
NASA Technical Reports Server (NTRS)
Buccello-Stout, Regina R.; Cromwell, Ronita L.; Bloomberg, Jacob J.
2009-01-01
A main contributor of fractures in older adults is from a lateral fall. The decline in sensory systems results in difficulty maintaining balance stability. Head stabilization contributes to postural control by serving as a stable platform for the sensory systems. The purpose of this study was to characterize the head stabilization response to a lateral perturbation while walking. A total of 16 healthy older adults, aged 66-81 years, walked across a foam pathway 6 times. One piece of the foam pathway covered a movable platform that translated to the left when the subject stepped on the foam. Three trials were randomized in which the platform shifted. Angular rate sensors placed on the center of mass of the head and trunk collected head and trunk movement in all three planes of motion. The roll plane was analyzed to examine motion in the plane of the perturbation. Subjects stepped onto the platform with the right foot. Recovery step time and distance were recorded. The first trial was analyzed to capture the novelty of the perturbation. Results indicate a significant difference in footfall distance t=0.004, p<0.05, as well as the speed of foot recovery t=0.001, p<0.05, between natural and perturbed walking. Results indicate that the head t=0.005, p<0.05, and trunk t=0.0001, p<0.05, velocities increase during perturbed compared to natural walking. Older adults place their recovery foot down faster when perturbed to re-establish their base of support. Head and trunk segments are less stable and move with greater velocities to reestablish stability when perturbed.
Transverse, propagating velocity perturbations in solar coronal loops
NASA Astrophysics Data System (ADS)
De Moortel, I.; Pascoe, D. J.; Wright, A. N.; Hood, A. W.
2016-01-01
As waves and oscillations carry both energy and information, they have enormous potential as a plasma heating mechanism and, through seismology, to provide estimates of local plasma properties which are hard to obtain from direct measurements. Being sufficiently near to allow high-resolution observations, the atmosphere of the Sun forms a natural plasma laboratory. Recent observations have revealed that an abundance of waves and oscillations is present in the solar atmosphere, leading to a renewed interest in wave heating mechanisms. This short review paper gives an overview of recently observed transverse, propagating velocity perturbations in coronal loops. These ubiquitous perturbations are observed to undergo strong damping as they propagate. Using 3D numerical simulations of footpoint-driven transverse waves propagating in a coronal plasma with a cylindrical density structure, in combination with analytical modelling, it is demonstrated that the observed velocity perturbations can be understood in terms of coupling of different wave modes in the inhomogeneous boundaries of the loops. Mode coupling in the inhomogeneous boundary layers of the loops leads to the coupling of the transversal (kink) mode to the azimuthal (Alfvén) mode, observed as the decay of the transverse kink oscillations. Both the numerical and analytical results show the spatial profile of the damped wave has a Gaussian shape to begin with, before switching to exponential decay at large heights. In addition, recent analysis of CoMP (Coronal Multi-channel Polarimeter) Doppler shift observations of large, off-limb, trans-equatorial loops shows that Fourier power at the apex appears to be higher in the high-frequency part of the spectrum than expected from theoretical models. This excess high-frequency FFT power could be tentative evidence for the onset of a cascade of the low-to-mid frequency waves into (Alfvénic) turbulence.
High-order primordial perturbations with quantum gravitational effects
NASA Astrophysics Data System (ADS)
Zhu, Tao; Wang, Anzhong; Kirsten, Klaus; Cleaver, Gerald; Sheng, Qin
2016-06-01
In this paper, we provide a systematic investigation of high-order primordial perturbations with nonlinear dispersion relations due to quantum gravitational effects in the framework of uniform asymptotic approximations. Because of these effects, the equation of motion of the mode function in general has multiple turning points. After obtaining analytically approximated solutions to any order in different regions, associated with different types of turning points, we match them to the third one. To this order the errors are less than 0.15%. General expressions of the power spectra of the primordial tensor and scalar perturbations are derived explicitly. We also investigate effects of backreactions of the quantum gravitational corrections, and make sure that inflation lasts long enough in order to solve the underlying problems, such as flatness, horizon, and monopole. Then we study various features of the spectra that are observationally relevant. In particular, under a moderate assumption about the energy scale of the underlying theory of quantum gravity, we have shown that the quantum gravitational effects may alter significantly the ratio between the tensor and scalar power spectra, thereby providing a natural mechanism to alleviate the tension between observations and certain inflationary models, including the one with a quadratic potential.
Sensitivity analysis of state-specific multireference perturbation theory
NASA Astrophysics Data System (ADS)
Szabados, Ágnes
2011-05-01
State-specific multireference perturbation theory (SS-MRPT) developed by Mukherjee et al. [Int. J. Mol. Sci. 3, 733 (2002)] is examined focusing on the dependence of the perturbed energy on the initial model space coefficients. It has been observed earlier, that non-physical kinks may appear on the potential energy surface obtained by SS-MRPT while related coupled-cluster methods may face convergence difficulties. Though exclusion or damping of the division by small coefficients may alleviate the problem, it is demonstrated here that the effect does not originate in an ill-defined division. It is shown that non-negligible model space coefficients may also be linked with the problem. Sensitivity analysis is suggested as a tool for detecting the coefficient responsible. By monitoring the singular values of sensitivity matrices, orders of magnitude increase is found in the largest value, in the vicinity of the problematic geometry point on the potential energy surface. The drastic increase of coefficient sensitivities is found to be linked with a degeneracy of the target root of the effective Hamiltonian. The nature of the one-electron orbitals has a profound influence on the picture: a rotation among active orbitals may screen or worsen the effect.
Stability and Perturbation Analysis on a Model of Cell Chemotaxis
NASA Astrophysics Data System (ADS)
McCann, Colin; Skupsky, Ron; Losert, Wolfgang; Nossal, Ralph
2006-03-01
Many eukaryotic cells respond with directional movement to spatial and/or temporal gradients of small molecules that bind to cell surface receptors. The computational model of a chemotaxing cell developed in [1], which models cells such as neutrophils or Dictyostelium discoideum, is investigated with regard to stability and response to perturbations. A formal stability analysis finds that, when placed in an initial linear gradient, the model is most sensitive to perturbations at a 60-90 degree offset from the direction of the initial gradient. The model also responds most quickly and strongly to external point sources placed in that direction. These responses hold for all four of the model variants developed in [1]. This suggests that the observed `zigzag' behavior of real cell movement in a gradient may be influenced by the nature of the biochemical reactions that control a cell's chemotactic response. This research was funded in by the National Institutes of Health (NIH) and the National Institute of Standards and Technology (NIST). [1] Skupsky, R., W. Losert, and R.J. Nossal. 2005. ``Distinguishing modes of eukaryotic gradient sensing''. Biophys. J. 89:2806--2823
Non-adiabatic perturbations in multi-component perfect fluids
Koshelev, N.A.
2011-04-01
The evolution of non-adiabatic perturbations in models with multiple coupled perfect fluids with non-adiabatic sound speed is considered. Instead of splitting the entropy perturbation into relative and intrinsic parts, we introduce a set of symmetric quantities, which also govern the non-adiabatic pressure perturbation in models with energy transfer. We write the gauge invariant equations for the variables that determine on a large scale the non-adiabatic pressure perturbation and the rate of changes of the comoving curvature perturbation. The analysis of evolution of the non-adiabatic pressure perturbation has been made for several particular models.
Evolution of the curvature perturbations during warm inflation
Matsuda, Tomohiro
2009-06-15
This paper considers warm inflation as an interesting application of multi-field inflation. Delta-N formalism is used for the calculation of the evolution of the curvature perturbations during warm inflation. Although the perturbations considered in this paper are decaying after the horizon exit, the corrections to the curvature perturbations sourced by these perturbations can remain and dominate the curvature perturbations at large scales. In addition to the typical evolution of the curvature perturbations, inhomogeneous diffusion rate is considered for warm inflation, which may lead to significant non-Gaussianity of the spectrum.
Singular perturbations of nonlinear degenerate parabolic PDEs: a general convergence result
NASA Astrophysics Data System (ADS)
Imbert, Cyril; Monneau, Régis
2008-01-01
In this paper, we present a result of homogenization of first-order Hamilton Jacobi equations with (u/\\varepsilon)-periodic Hamiltonians. On the one hand, under a coercivity assumption on the Hamiltonian (and some natural regularity assumptions), we prove an ergodicity property of this equation and the existence of nonperiodic approximate correctors. On the other hand, the proof of the convergence of the solution, usually based on the introduction of a perturbed test function in the spirit of Evans’s work, uses here a twisted perturbed test function for a higher-dimensional problem.
Bred vectors with customizable scale: 'À la carte' ensemble perturbations
NASA Astrophysics Data System (ADS)
Homar Santaner, V.; Stensrud, D. J.
2009-09-01
Short-range forecasts of severe weather are one of the most challenging tasks faced by the atmospheric science community. Our persistent failure to generate accurate numerical forecasts of tornadoes, large hail, heavy precipitation or strong wind events is caused by two fundamental aspects of numerical forecast systems: the chaotic nature of the governing equations and the large uncertainties in both the atmospheric state and the models that govern its evolution. Currently, we cope with both sources of error by describing the state of the atmosphere in a probabilistic manner. In this framework, forecasting becomes predicting the probability density function (pdf) of future states, given the pdf of initial states that are compatible with available observations and previous forecasts. This probabilistic perspective is often created by generating ensembles of deterministic predictions that are aimed at sampling the most important sources of uncertainty in the forecasting system. The ensemble generation/sampling strategy is a crucial aspect of their performance and various methods have been proposed. Although global forecasting offices have been using ensembles of perturbed initial conditions for medium-range operational forecasts since 1994, no consensus exists regarding the optimum sampling strategy for high resolution short-range ensemble forecasts with predicting skill in the mesoscale. Bred vectors, however, have been hypothesized to better capture the growing modes in the highly nonlinear mesoscale dynamics of severe episodes than singular vectors or observation perturbations. Yet even this technique is not able to produce enough diversity in the ensembles to accurately and routinely predict extreme phenomena such as severe weather. Thus, we propose a new method to generate ensembles of initial conditions perturbations that is based on the breeding technique. Given a standard bred mode, a set of customized perturbations is derived with specified amplitudes and
Thermostat-Like Perturbations of an Oscillator
NASA Astrophysics Data System (ADS)
Freidlin, Mark
2016-07-01
We consider an oscillator with one degree of freedom perturbed by a deterministic thermostat-like perturbation and another system, in particular, another oscillator, coupled with the first one. If the Hamiltonian of the first system has saddle points, the whole system has, in a sense, a stochastic behavior on long time intervals. Under certain conditions, one can introduce the relative entropy and describe metastability and other large deviation effects in this deterministic system. If the coupled system is also an oscillator, the long time evolution of the energy of this oscillator has a diffusion approximation. To get these results one has to regularize the system. But the results are, to some extent, independent of the regularization: the stochasticity is due to instabilities at saddle points of the original system.
Resummation Approach in QCD Analytic Perturbation Theory
NASA Astrophysics Data System (ADS)
Bakulev, Alexander P.; Potapova, Irina V.
2011-10-01
We discuss the resummation approach in QCD Analytic Perturbation Theory (APT). We start we a simple example of asymptotic ower series for a zero-dimensional analog of the scalar g φ model. Then we give a short historic preamble of APT and show that renormgroup improvement of the QCD perturbation theory dictates to use the Fractional APT (FAPT). After that we discuss the (F)PT resummation of nonpower series and provide the one-, two-, and three-loop resummation recipes. We show the results of applications of these recipes to the estimation of the Adler function D(Q) in the N=4 region of Q and of the Higgs-boson-decay width Γ(mH2) for M=100-180 GeV.
A Renormalisation Group Method. III. Perturbative Analysis
NASA Astrophysics Data System (ADS)
Bauerschmidt, Roland; Brydges, David C.; Slade, Gordon
2015-05-01
This paper is the third in a series devoted to the development of a rigorous renormalisation group method for lattice field theories involving boson fields, fermion fields, or both. In this paper, we motivate and present a general approach towards second-order perturbative renormalisation, and apply it to a specific supersymmetric field theory which represents the continuous-time weakly self-avoiding walk on . Our focus is on the critical dimension . The results include the derivation of the perturbative flow of the coupling constants, with accompanying estimates on the coefficients in the flow. These are essential results for subsequent application to the 4-dimensional weakly self-avoiding walk, including a proof of existence of logarithmic corrections to their critical scaling. With minor modifications, our results also apply to the 4-dimensional -component spin model.
Perturbative type II amplitudes for BPS interactions
NASA Astrophysics Data System (ADS)
Basu, Anirban
2016-02-01
We consider the perturbative contributions to the {{ R }}4, {D}4{{ R }}4 and {D}6{{ R }}4 interactions in toroidally compactified type II string theory. These BPS interactions do not receive perturbative contributions beyond genus three. We derive Poisson equations satisfied by these moduli dependent string amplitudes. These T-duality invariant equations have eigenvalues that are completely determined by the structure of the integrands of the multi-loop amplitudes. The source terms are given by boundary terms of the moduli space of Riemann surfaces corresponding to both separating and non-separating nodes. These are determined directly from the string amplitudes, as well as from U-duality constraints and logarithmic divergences of maximal supergravity. We explicitly solve these Poisson equations in nine and eight-dimensions.
Inflationary tensor perturbations after BICEP2.
Caligiuri, Jerod; Kosowsky, Arthur
2014-05-16
The measurement of B-mode polarization of the cosmic microwave background at large angular scales by the BICEP experiment suggests a stochastic gravitational wave background from early-Universe inflation with a surprisingly large amplitude. The power spectrum of these tensor perturbations can be probed both with further measurements of the microwave background polarization at smaller scales and also directly via interferometry in space. We show that sufficiently sensitive high-resolution B-mode measurements will ultimately have the ability to test the inflationary consistency relation between the amplitude and spectrum of the tensor perturbations, confirming their inflationary origin. Additionally, a precise B-mode measurement of the tensor spectrum will predict the tensor amplitude on solar system scales to 20% accuracy for an exact power-law tensor spectrum, so a direct detection will then measure the running of the tensor spectral index to high precision. PMID:24877926
(Perturbed angular correlations in zirconia ceramics)
Not Available
1990-01-01
This is the progress report for the first year of the currently-approved three year funding cycle. We have carried on a vigorous program of experimental and theoretical research on microscopic properties of zirconia and ceria using the Perturbed Angular Correlation (PAC) experimental technique. The experimental method was described in the original proposal and in a number of references as well as several of the technical reports that accompany this progress report.
Intelligent perturbation algorithms to space scheduling optimization
NASA Technical Reports Server (NTRS)
Kurtzman, Clifford R.
1991-01-01
The limited availability and high cost of crew time and scarce resources make optimization of space operations critical. Advances in computer technology coupled with new iterative search techniques permit the near optimization of complex scheduling problems that were previously considered computationally intractable. Described here is a class of search techniques called Intelligent Perturbation Algorithms. Several scheduling systems which use these algorithms to optimize the scheduling of space crew, payload, and resource operations are also discussed.
Stability of SIRS system with random perturbations
NASA Astrophysics Data System (ADS)
Lu, Qiuying
2009-09-01
Epidemiological models with bilinear incidence rate λSI usually have an asymptotically stable trivial equilibrium corresponding to the disease-free state, or an asymptotically stable non-trivial equilibrium (i.e. interior equilibrium) corresponding to the endemic state. In this paper, we consider an epidemiological model, which is an SIRS model with or without distributed time delay influenced by random perturbations. We present the stability conditions of the disease-free equilibrium of the associated stochastic SIRS system.
Study of the spectrum of inflaton perturbations
Glenz, Matthew M.; Parker, Leonard
2009-09-15
We examine the spectrum of inflaton fluctuations resulting from any given long period of exponential inflation. Infrared and ultraviolet divergences in the inflaton dispersion summed over all modes do not appear in our approach. We show how the scale invariance of the perturbation spectrum arises. We also examine the spectrum of scalar perturbations of the metric that is created by the inflaton fluctuations that have left the Hubble sphere during inflation and the spectrum of density perturbations that they produce at reentry after inflation has ended. When the inflaton dispersion spectrum is renormalized during the expansion, we show (for the case of the quadratic inflaton potential) that the density perturbation spectrum approaches a mass-independent limit as the inflaton mass approaches zero, and remains near that limiting value for masses less than about 1/4 of the inflationary Hubble constant. We show that this limiting behavior does not occur if one only makes the Minkowski space subtraction, without the further adiabatic subtractions that involve time derivatives of the expansion scale factor a(t). We also find a parametrized expression for the energy density produced by the change in a(t) as inflation ends. If the end of inflation were sufficiently abrupt, then the temperature corresponding to this energy density could be very significant. We also show that fluctuations of the inflaton field that are present before inflation starts are not dissipated during inflation and could have a significant observational effect today. The mechanism for this is caused by the initial fluctuations through stimulated emission from the vacuum.
Tests of Chiral Perturbation Theory with COMPASS
Friedrich, Jan
2010-12-28
The COMPASS experiment at CERN studies with high precision pion-photon induced reactions on nuclear targets via the Primakoff effect. This offers the possibility to test chiral perturbation theory (ChPT) in various channels: Pion Compton scattering allows to clarify the longstanding question of the pion polarisabilities, single neutral pion production is related to the chiral anomaly, and for the two-pion production cross sections exist as yet untested ChPT predictions.
Perturbations of nested branes with induced gravity
Sbisà, Fulvio; Koyama, Kazuya E-mail: kazuya.koyama@port.ac.uk
2014-06-01
We study the behaviour of weak gravitational fields in models where a 4D brane is embedded inside a 5D brane equipped with induced gravity, which in turn is embedded in a 6D spacetime. We consider a specific regularization of the branes internal structures where the 5D brane can be considered thin with respect to the 4D one. We find exact solutions corresponding to pure tension source configurations on the thick 4D brane, and study perturbations at first order around these background solutions. To perform the perturbative analysis, we adopt a bulk-based approach and we express the equations in terms of gauge invariant and master variables using a 4D scalar-vector-tensor decomposition. We then propose an ansatz on the behaviour of the perturbation fields when the thickness of the 4D brane goes to zero, which corresponds to configurations where gravity remains finite everywhere in the thin limit of the 4D brane. We study the equations of motion using this ansatz, and show that they give rise to a consistent set of differential equations in the thin limit, from which the details of the internal structure of the 4D brane disappear. We conclude that the thin limit of the ''ribbon'' 4D brane inside the (already thin) 5D brane is well defined (at least when considering first order perturbations around pure tension configurations), and that the gravitational field on the 4D brane remains finite in the thin limit. We comment on the crucial role of the induced gravity term on the 5D brane.
Perturbation Theory for Superfluid in Nonuniform Potential
NASA Astrophysics Data System (ADS)
Koshida, Shinji; Kato, Yusuke
2016-05-01
Perturbation theory of superfluid fraction in terms of nonuniform potential is constructed. We find that the coefficient of the leading term is determined by the dynamical structure factor or density fluctuation of the system. The results for the ideal Bose gas and the interacting Bose system with linear dispersion are consistent to implications from Landau's criterion. We also find that the superfluidity of Tomonaga-Luttinger liquid with K>2 is shown to be stable against nonuniform potential.