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At least 199 records · Page 11

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NASA NTRS2009

Solar Spicules near and at The Limb, Observed from Hinode

Solar spicules appear as narrow jets emanating from the chromosphere and extending into the corona. They have been observed for over a hundred years,mainly in chromospheric spectral lines such as H-alpha. Because they are at the limit of visibility of ground-based instruments, their nature has long been a puzzle. In recent years however, vast progress has been made in understanding them both theoretically and observationally. Most recently, spicule studies have undergone revolution because of the superior resolution, time cadence, and atmosphere-free observations from the Solar Optical Telescope (SOT) instrument on the Hinode spacecraft. Here we present observations of spicules from {\sl Hinode} SOT, and consider how the observations from Hinode compare with historical observations. We include data taken in the blue and red wings of Halpha, where the spicules have widths of a few approx.100 kms, and the longest ones reach about 10(exp 4) km in extent,similar to sizes long reported from ground-based instruments. Their dynamics are not easy to generalize, with many showing the upward movement followed by falling or fading, as traditionally reported, but with others showing more dynamic or even ejective aspects. There is a strong transverse component to their motion, as extensively reported previously from the Hinode data as evidence for Alfven waves.

Sterling, Alphonse C.↗

NASA NTRS2008

Role of Gravity Waves in Determining Cirrus Cloud Properties

Cirrus clouds are important in the Earth's radiation budget. They typically exhibit variable physical properties within a given cloud system and from system to system. Ambient vertical motion is a key factor in determining the cloud properties in most cases. The obvious exception is convectively generated cirrus (anvils), but even in this case, the subsequent cloud evolution is strongly influenced by the ambient vertical motion field. It is well know that gravity waves are ubiquitous in the atmosphere and occur over a wide range of scales and amplitudes. Moreover, researchers have found that inclusion of statistical account of gravity wave effects can markedly improve the realism of simulations of persisting large-scale cirrus cloud features. Here, we use a 1 -dimensional (z) cirrus cloud model, to systematically examine the effects of gravity waves on cirrus cloud properties. The model includes a detailed representation of cloud microphysical processes (bin microphysics and aerosols) and is run at relatively fine vertical resolution so as to adequately resolve nucleation events, and over an extended time span so as to incorporate the passage of multiple gravity waves. The prescribed gravity waves "propagate" at 15 m s (sup -1), with wavelengths from 5 to 100 km, amplitudes range up to 1 m s (sup -1)'. Despite the fact that the net gravity wave vertical motion forcing is zero, it will be shown that the bulk cloud properties, e.g., vertically-integrated ice water path, can differ quite significantly from simulations without gravity waves and that the effects do depend on the wave characteristics. We conclude that account of gravity wave effects is important if large-scale models are to generate realistic cirrus cloud property climatology (statistics).

OCStarr, David↗

DOE OSTI2022

Multimode Strong Coupling in Cavity Optomechanics

Optomechanical systems show great potential as quantum transducers and information storage devices for use in future hybrid quantum networks. In this context, optomechanical strong coupling can enable efficient, high-bandwidth, and deterministic transfer of quantum states. While optomechanical strong coupling has been realized at optical frequencies, it has proven difficult to identify a robust optomechanical system that features the low loss and high coupling rates required for more sophisticated control of mechanical motion. In this paper, we demonstrate strong coupling in a Brillouin-based bulk cavity optomechanical system in both the single-mode and the multimode strong-coupling regime, which leads to a useful device both for applications in quantum information and for investigating decoherence phenomena in bulk acoustic wave resonators. Using nontrivial mode hybridizations in the strong-coupling regime, we create hybridized photonic-phononic modes with lifetimes that are significantly longer than those of the uncoupled system. This surprising lifetime enhancement, which results from the interference of decay channels, showcases the use of multimode strong coupling as a general strategy to control extrinsic decoherence mechanisms. Moreover, phonons supported by such bulk-acoustic-wave resonators have a collection of properties, including high frequencies, long coherence times, and robustness against thermal decoherence, that make this optomechanical system particularly enticing for applications such as quantum transduction and memories. Hence, this system provides access to phenomena in a previously unexplored regime of optomechanical interactions and could serve as an important building block for future quantum devices.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2020

Mixed quantum–classical approach to model non-adiabatic electron–nuclear dynamics: Detailed balance and improved surface hopping method

We develop a density matrix formalism to describe coupled electron–nuclear dynamics. To this end, we introduce an effective Hamiltonian formalism that describes electronic transitions and small (quantum) nuclear fluctuations along a classical trajectory of the nuclei. Using this Hamiltonian, we derive equations of motion for the electronic occupation numbers and for the nuclear coordinates and momenta. We show that, in the limit, when the number of nuclear degrees of freedom coupled to a given electronic transition is sufficiently high (i.e., the strong decoherence limit), the equations of motion for the electronic occupation numbers become Markovian. Furthermore, the transition rates in these (rate) equations are asymmetric with respect to the lower-to-higher energy transitions and vice versa. In thermal equilibrium, such asymmetry corresponds to the detailed balance condition. We also study the equations for the electronic occupations in the non-Markovian regime and develop a surface hopping algorithm based on our formalism. To treat the decoherence effects, we introduce additional “virtual” nuclear wave packets whose interference with the “real” (physical) wave packets leads to the reduction in coupling between the electronic states (i.e., decoherence) as well as to the phase shifts that improve the accuracy of the numerical approach. Remarkably, the same phase shifts lead to the detailed balance condition in the strong decoherence limit.

74 ATOMIC AND MOLECULAR PHYSICS↗

NASA NTRS1999

Dependence of Cumulus Anvil Radiative Properties on Environmental Conditions in the Tropical West Pacific

Areally extensive, optically thick anvil clouds associated with mesoscale convective clusters dominate the shortwave cloud forcing in the tropics and provide longwave forcing comparable to that of thin cirrus. Changes in the cover and optical thickness of tropical anvils as climate warms can regulate the sign of cloud feedback. As a prelude to the study of MMCR data from the ARM TWP sites, we analyze ISCCP-derived radiative characteristics of anvils observed in the tropical west Pacific during the TOGA-COARE IOP. Anvils with radius greater than 100 km were identified and tracked from inception to decay using the Machado-Rossow algorithm. Corresponding environmental conditions just prior to the start of the convectove event were diagnosed using the Lin-Johnson objective analysis product. Small clusters (100-200 km radius) are observed to have a broad range of optical thicknesses (10-50), while intermediate optical thickness clusters are observed to range in size from 100 km to almost 1000 km. Large-size clusters appear to be favored by strong pre-storm large scale upward motion throughout the troposphere, moist low-to-midlevel relative humidities, environments with slightly higher CAPE than those for smaller clusters, and strong front-to-rear flow. Optically thick anvils are favored in situations of strong low-level moisture convergence and strong upper-level shear.

Ye, B.↗

NASA NTRS1992

The formation of the wall region - Consequences in the near earth magnetotail

This paper discusses important new findings obtained from global kinetic simulations of magnetotail plasma. A region of strongly nonadiabatic ion acceleration (known as the wall region) exists in the near earth tail and demarcates two very different regimes of ion motion: adiabatic and quasi-adiabatic. A strong enhancement of the cross-tail current occurs on the tailward side of the wall. A comparison of numerical and adiabatic pressure profiles indicates that nonadiabatic processes operating in this region may contribute significantly to a pressure balance relief in the course of quasi-steady magnetospheric convection.

Ashour-Abdalla, Maha↗

NASA NTRS1991

Incipient torsional stall flutter aerodynamic experiments on a swept three-dimensional wing

The aerodynamics of small amplitude pitching motions near stall have been studied experimentally in order to improve understanding of the torsional stall flutter problem for propeller blades. A model wing was oscillated in pitch at several small amplitudes over a wide and representative range of conditions. Unsteady surface pressures were measured and integrated to determine the aerodynamic damping at five spanwise stations. Strong negative damping was found for motions centered near static stall for all studied reduced frequencies, Mach numbers, and sweep angles. The 30-deg sweptback configuration was found to become negatively damped over the entire span nearly simultaneously, while the unswept model exhibited local regions of negative damping that moved toward the wing tip as the mean angle of attack was increased.

Lorber, Peter F.↗

DOE OSTI2022

An “Eddy β-Spiral” mechanism for vertical velocity dipole patterns of isolated oceanic mesoscale eddies

Oceanic eddies accompanied by a significant vertical velocity ( w ) are known to be of great importance for the vertical transport of various climatically, biologically or biogeochemically relevant properties. Using quasi-geostrophic w -thinking to extend the classic “ β -spiral” w -theory for gyre circulations to isolated and nearly symmetric oceanic mesoscale eddies, we propose that their w motion will be dominated by a strong east-west dipole pattern with deep ocean penetrations. Contrasting numerical simulations of idealized isolated eddies together with w -equation diagnostics confirm that the w -dipole is indeed dominated by the “eddy β -spiral” mechanism in the β -plane simulation, whereas this w -dipole expectedly disappears in the f -plane simulation. Analyses of relatively isolated warm and cold eddy examples show good agreement with the proposed mechanism. Our studies further clarify eddy vertical motions, have implications for ocean mixing and vertical transport, and inspire further studies.

58 GEOSCIENCES↗

NASA NTRS1996

Resolving High Amplitude Surface Motion with Diffusing Light

A new technique has been developed for the purpose of imaging high amplitude surface motion. With this method one can quantitatively measure the transition to ripple wave turbulence. In addition, one can measure the phase of the turbulent state. These experiments reveal strong coherent structures in turbulent range of motion.

Wright, W.↗

DOE OSTI2021

Strong-field ionization of water: Nuclear dynamics revealed by varying the pulse duration

Polyatomic molecules in strong laser fields can undergo substantial nuclear motion within tens of femtoseconds. Ion imaging methods based on dissociation or Coulomb explosion therefore have difficulty faithfully recording the geometry dependence of the field ionization that initiates the dissociation process. Here we compare the strong-field double ionization and subsequent dissociation of water (both H 2 O and D 2 O) in 10-fs and 40-fs 800-nm laser pulses. We find that 10-fs pulses turn off before substantial internuclear motion occurs, whereas rapid internuclear motion can take place during the double ionization process for 40-fs pulses. The short-pulse measurements are consistent with a simple tunnel ionization picture whose predictions help interpret the motion observed in the long-pulse measurements.

74 ATOMIC AND MOLECULAR PHYSICS↗

DOE OSTI2021

Pathways to fluorescence via restriction of intramolecular motion in substituted tetraphenylethylenes

The design of materials with enhanced luminescence properties is a fast-developing field due to the potential applicability of these materials as light-emitting diodes or for bioimaging. A transparent way to enhance the emission properties of interesting molecular candidates is blocking competing and unproductive non-radiative relaxation pathways by the restriction of intramolecular motions. Rationalized functionalization is an important possibility to achieve such restrictions. Using time-dependent density functional theory (TD-DFT) based on the ωB97XD functional and the semiempirical tight-binding method including long-range corrections (TD-LC-DFTB), this work investigates the effect of functionalization of the paradigmatic tetraphenylethylene (TPE) on achieving restricted access to conical intersections (RACI). Photodynamical surface hopping simulations have been performed on a larger set of compounds including TPE and ten functionalized TPE compounds. Functionalization has been achieved by means of electron-withdrawing groups, bulky groups which block the relaxation channels via steric hindrance and groups capable of forming strong hydrogen bonds, which restrict the motion via the formation of hydrogen bond channels. Most of the investigated functionalized TPE candidates show ultrafast deactivation to the ground state due to their still existing structural flexibility, but two examples, one containing –CN and –CF 3 groups and a second characterized by a network of hydrogen bonds, have been identified as interesting candidates for creating efficient luminescence properties in solution.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

NASA NTRS2011

Relationship Between Optimal Gain and Coherence Zone in Flight Simulation

In motion simulation the inertial information generated by the motion platform is most of the times different from the visual information in the simulator displays. This occurs due to the physical limits of the motion platform. However, for small motions that are within the physical limits of the motion platform, one-to-one motion, i.e. visual information equal to inertial information, is possible. It has been shown in previous studies that one-to-one motion is often judged as too strong, causing researchers to lower the inertial amplitude. When trying to measure the optimal inertial gain for a visual amplitude, we found a zone of optimal gains instead of a single value. Such result seems related with the coherence zones that have been measured in flight simulation studies. However, the optimal gain results were never directly related with the coherence zones. In this study we investigated whether the optimal gain measurements are the same as the coherence zone measurements. We also try to infer if the results obtained from the two measurements can be used to differentiate between simulators with different configurations. An experiment was conducted at the NASA Langley Research Center which used both the Cockpit Motion Facility and the Visual Motion Simulator. The results show that the inertial gains obtained with the optimal gain are different than the ones obtained with the coherence zone measurements. The optimal gain is within the coherence zone.The point of mean optimal gain was lower and further away from the one-to-one line than the point of mean coherence. The zone width obtained for the coherence zone measurements was dependent on the visual amplitude and frequency. For the optimal gain, the zone width remained constant when the visual amplitude and frequency were varied. We found no effect of the simulator configuration in both the coherence zone and optimal gain measurements.

Gracio, Bruno Jorge Correia↗

NASA NTRS1980

Tangential mode combustion instability of solid propellant rocket motors. 2: Pressure, frequency, and burning rate histories

The relationships among excursions of mean chamber pressure, high frequency pressure oscillations and accelerations associated with tangential mode combustion instability are considered. A data reduction procedure was devised to utilize the precise pressure time data as input to a numerical solution of the chamber mass balance relationships. The results indicate that both elevated burning rate induced by the tangential wave motions and variable nozzle blockage due to passage of vortical flow through the nozzle throat must act together to generate the large mean pressure peaks observed in the tests. There is strong correlation between the amplitude of wave motions and the level of mean pressure rise. Evidence for the presence of traveling tangential waves at the time of the D.C. shift was found by use of dual Kistler pressure transducers mounted at the head end of the burner. A very unusual frequency history was found to accompany the high amplitude disturbances. This was consistent from test to test and may represent an additional source of information regarding the complicated flow combustion interactions within the propellant burning zone.

Flandro, G. A.↗

NASA NTRS1988

Vestibular factors influencing the biomedical support of humans in space

This paper will describe the biomedical support aspects of humans in space with respect to the vestibular system. The vestibular system is thought to be the primary sensory system involved in the short-term effects of space motion sickness although there is increasing evidence that many factors play a role in this complex set of symptoms. There is the possibility that an individual's inner sense of orientation may be strongly coupled with the susceptibility to space motion sickness. A variety of suggested countermeasures for space motion sickness will be described. Although there are no known ground-based tests that can predict space motion sickness, the search should go on. The long term effects of the vestibular system in weightlessness are still relatively unknown. Some preliminary data has shown that the otoconia are irregular in size and distribution following extended periods of weightlessness. The ramifications of this data are not yet known and because the data was obtained on lower order animals, definitive studies and results must wait until the space station era when higher primates can be studied for long durations. This leads us to artificial gravity, the last topic of this paper. The vestibular system is intimately tied to this question since it has been shown on Earth that exposure to a slow rotating room causes motion sickness for some period of time before adaptation occurs. If the artificial gravity is intermittent, will this mean that people will get sick every time they experience it? The data from many astronauts returning to Earth indicates that a variety of sensory illusions are present, especially immediately upon return to a 1-g environment. Oscillopsia or apparent motion of the visual surround upon head motion along with inappropriate eye motions for a given head motion, all indicate that there is much to be studied yet about the vestibular and CNS systems reaction to a sudden application of a steady state acceleration field like 1-g. From the above information it is obvious that the vestibular system does have unique requirements when it comes to the biomedical support of space flight. This is not to say that other areas such as cardiovascular, musculo-skeletal, immunological and hematological systems do not have their own unique requirements but that possible solutions to one system can provide continuing problems to another system. For example, artificial gravity might be helpful for long term stabilization of bone demineralization or cardiovascular deconditioning but might introduce a new set of problems in orientation, vestibular conflict and just plain body motion in a rotating space vehicle.

Non-NASA Center↗

NASA NTRS1992

Kinetic treatment of nonlinear magnetized plasma motions - General geometry and parallel waves

The expansion of kinetic equations in the limit of a strong magnetic field is presented. This gives a natural description of the motions of magnetized plasmas, which are slow compared to the particle gyroperiods and gyroradii. Although the approach is 3D, this very general result is used only to focus on the parallel propagation of nonlinear Alfven waves. The derivative nonlinear Schroedinger-like equation is obtained. Two new terms occur compared to earlier treatments, a nonlinear term proportional to the heat flux along the magnetic field line and a higher-order dispersive term. It is shown that kinetic description avoids the singularities occurring in magnetohydrodynamic or multifluid approaches, which correspond to the degenerate case of sound speeds equal to the Alfven speed, and that parallel heat fluxes cannot be neglected, not even in the case of low parallel plasma beta. A truly stationary soliton solution is derived.

Khabibrakhmanov, I. KH.↗

NASA NTRS2003

High-Resolution Simulation of Hurricane Bonnie (1998): The Organization of Vertical Motion - Part 1

Hurricanes are well known for their strong winds and heavy rainfall, particularly in the intense rainband (eyewall) surrounding the calmer eye of the storm. In some hurricanes, the rainfall is distributed evenly around the eye so that it has a donut shape on radar images. In other cases, the rainfall is concentrated on one side of the eyewall and nearly absent on the other side and is said to be asymmetric. This study examines how the vertical air motions that produce the rainfall are distributed within the eyewall of an asymmetric hurricane and the factors that cause this pattern of rainfall. We use a sophisticated numerical forecast model to simulate Hurricane Bonnie, which occurred in late August of 1998 during a special NASA field experiment designed to study hurricanes. The simulation results suggest that vertical wind shear (a rapid change in wind speed or direction with height) caused the asymmetric rainfall and vertical air motion patterns by tilting the hurricane vortex and favoring upward air motions in the direction of tilt. Although the rainfall in the hurricane eyewall may surround more than half of the eye, the updrafts that produce the rainfall are concentrated in very small-scale, intense updraft cores that occupy only about 10% of the eyewall area. The model simulation suggests that the timing and location of individual updraft cores are controlled by intense, small-scale vortices (regions of rapidly swirling flow) in the eyewall and that the updrafts form when the vortices encounter low-level air moving into the eyewall.

Braun, Scott A.↗

DOE OSTI2025

Decoherence and Brownian motion of a polarizable particle near a medium

Optically levitated nanoparticles are ideal experimental testbeds for investigating macroscopic superpositions and microscopic thermodynamics. Integrating such levitated nanoparticles with photonic structures can enable strong coupling between their center-of-mass motion and guided photonic modes, facilitating enhanced control and probing of their motion. When coupling a particle to a photonic structure, such as a waveguide, the effects of fluctuations become prominent at nanoscales. In this work, we analyze the classical and quantized center-of-mass motion of a polarizable particle interacting with the fluctuations of the electromagnetic field in the presence of a medium. We derive a position localization master equation for the particle's quantized center of mass, and examine its classical center-of-mass momentum diffusion, elucidating correspondences between classical and quantum Brownian motion of polarizable particles near media. We study the decoherence rate of the particle in the presence of a planar surface as a function of temperature and distance from the surface, comparing it to common sources of decoherence. Our results are pertinent to experiments aimed at preparing levitated nanospheres in macroscopic quantum states and investigating their Brownian dynamics.

Brownian motion↗

NASA NTRS1992

Cloud motions on Neptune from Voyager 2 images

The puzzle presented by Neptune's circulation is evidenced by its wide spectrum of wind speeds and differences between the drift rate of its longest lived features and its finer scale cloud forms, unlike Jupiter or Saturn. Neptune's clouds appear dynamic and show strong evidence of atmospheric waves, making cloud motion measurements somewhat difficult and requiring some departures from the methods which have been traditionally used to determine atmospheric circulations. New measurements of cloud motions of Neptune that confirm the general characteristics reported by Smith et al. (1989) are presented below. Besides greater number of measurements from a higher time resolution data set, the new results reveal the shape of the westerly jet at 72 deg S latitude.

Limaye, S. S.↗