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At least 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Search for X ( 3872 ) → π + π - π 0 at Belle

We present a search for the decay X⁡(3872) → π + ⁢π -⁢ π 0 in the (772 ±11) ×10 6 Y⁡(4⁢S)→B⁢$\overline{B}$ data sample collected at the Belle detector, where the X⁡(3872) is produced in B ± → K ± X⁢⁡(3872) and B 0 →K$^{0}_{S}$X(3872) decays. We do not observe a signal, and set 90% credible upper limits for two different models of the decay processes: if the decay products are distributed uniformly in phase space, $\mathscr{B}$⁡(X⁡(3872) → π + ⁢π -⁢ π 0 )<1.3%, and if M⁡(π + ⁢π - ) is concentrated near the mass of the D 0 ⁢$\overline{D}$ 0 pair in the process X⁡(3872) → D 0 ⁢$\overline{D}$ *0 + c.c. → D 0 ⁢$\overline{D}$ 0 ⁢π 0 → π + ⁢π - π 0 , $\mathscr{B}$⁡⁡(X⁡(3872) → π + ⁢π -⁢ π 0 )<1.2×10 -3 .

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
NASA NTRS1974

Particle distribution functions in modulation theory

Development of a simple formulation of the cosmic ray modulation problem which involves the use of the omnidirectional part of the distribution function in phase space, and the magnitude of the momentum or the rigidity. It is shown that, by employing the proposed formulation, the Compton-Getting factor is greatly simplified, and the well-known force-field equation is reduced to a one-dimensional Vlasov equation. In addition, another Vlasov equation can be written for the very low energy galactic particles which are convected by the solar wind.

Forman, M. A.↗
NASA NTRS2020

Beam Propagation Through Atmospheric Turbulence Using an Altitude-Dependent Structure Profile with Non-Uniformly Distributed Phase Screens

For free-space optical communication systems, numerical wave optics simulations provide a useful technique for modeling turbulence-induced beam degradation when the analytical theory is insufficient for characterizing the atmospheric channel. Motivated by such applications we use a split-step method modeling the turbulence as a series of random phase screens using the Hufnagel-Valley turbulence profile. We employ a space-to-ground case study to examine the irradiance and phase statistics for uniformly and non-uniformly located screens and find better agreement with theory using a non-uniform discretization minimizing the contribution of each screen to the total scintillation. In this poster, we summarize the method and the results of the case study including a comparison to layered models used in astronomical imaging applications.

Chahine, Yousef K.↗
NASA NTRS2015

The Dependence of Cirrus Gamma Size Distributions Expressed as Volumes in N(sub 0)-Lambda-Mu Phase Space and Bulk Cloud Properties on Environmental Conditions: Results from the Small Ice Particles in Cirrus Experiment (SPARTICUS)

The variability of cirrus ice microphysical properties is investigated using observations obtained during the Small Particles in Cirrus (SPARTICUS) campaign. An existing approach that represents a size distribution (SD) as a single gamma function using an ellipsoid of equally realizable solutions in (N(sub 0), lambda, mu) phase space is modified to automatically identify multiple modes in SDs and characterize each mode by such an ellipsoid. The modified approach is applied to ice crystals with maximum dimension D greater than15 micrometers collected by the 2-D stereo and 2-D precipitation probes on the Stratton Park Engineering Company Learjet. The dependencies of N(sub 0), mu, and lambda from each mode, total number concentration, bulk extinction, ice water content (IWC), and mass median maximum dimension D(sub mm) as a function of temperature T and cirrus type are then analyzed. The changes in the observed codependencies between N(sub 0), mu, and lambda, bulk extinction, IWC, and D(sub mm) with environmental conditions indicate that particles were larger at higher T during SPARTICUS. At most two modes were observed in any SD during SPARTICUS, with the average boundary between them at 115 micrometers, similar to past studies not using probes with shatter mitigating tips and artifact removal algorithms. The bimodality of the SDs increased with T. This and the differences in N(sub 0), mu, and lambda between the modes suggest that particles with smaller D nucleated more recently than particles with larger D, which grew via vapor deposition and aggregation. Because smaller crystals, whose concentrations are uncertain, make marginal contributions to higher order moments, the use of higher moments for evaluating model fields is suggested.

Ellipsoids↗
NASA NTRS1994

Energetic electrons in the magnetophere of Saturn

The energy spectra and angular distributions of electrons observed by Pioneer 11 as a function of radial distance in the inner magnetosphere of Saturn are reanalyzed and phase space densities are then calculated. The radial dependence of phase space density requires a distributed loss process. The loss is greatest in the region of the E ring (5.5 less than L less than 8.5) and is attributed to collisions with the ring particles in agreement with earlier work by Van Allen et al. (1980b). Quantitative analysis yields the following properties of the E ring: the particle radii are in the range of 4 x 10(exp -5) to 3.2 x 10(exp -4) cm and the thickness of the ring is approximately 3 R(sub s). Between the inner edge of the E ring (5.5 R(sub s)) and the outer edge of the A ring (2.3 R(sub s)) there are more energetic electrons than can be supplied by radial diffusion from an external source. Detailed calculations show that a cosmic ray albedo neutron decay (CRAND) source in the A and B rings is a plausible source for this excess. The radial diffusion coefficient required to explain the E ring absorption and CRAND source for electrons is 1 x 10(exp -12) greater than D(sub 0) greater than 3 x 10(exp -12) R(sub s)(exp 2)/s, assuming that D(sub LL) = D(sub 0)L(exp 3). As part of the reanalysis program, a method for the deconvolution of pitch angle distributions observed by simple detectors on a rotating spacecraft is developed. This process removes the instrumental response and rotational smear due to finite sampling periods and yields true angular distributions.

Randall, B. A.↗
NASA NTRS1994

Energetic electrons in the magnetosphere of Saturn

The energy spectra and angular distributions of electrons observed by Pioneer 11 as a function of radial distance in the inner magnetosphere of Saturn are reanalyzed and phase space densities are then calculated. The radial dependence of phase space density requires a distributed loss process. The loss is greatest in the region of the E ring (5.5 less than L less than 8.5) and is attributed to collisions with the ring particles in agreement with earlier work by Van Allen et al. (1980). Quantitative analysis yields the following properties of the E ring: the particle radii are in the range of 4 x 10(exp -5) to 3.2 x 10(exp -4) cm and the thickness of the ring is approximately 3 R(sub s). Between the inner edge of the E ring (5.5 R(sub s)) and the outer edge of the A ring (2.3 R(sub s)) there are more energetic electrons than can be supplied by radial diffusion from an external source. Detailed calculations show that a cosmic ray albedo neutron decay (CRAND) source in the A and B rings is a plausible source for this excess. The radial diffusion coefficient required to explain the E ring absorption and CRAND source for electrons is 1 x 10(exp -12) greater than D(sub 0) greater than 3 x 10(exp -12) R(exp 2, sub s)/s, assuming that D(sub LL) = D(sub 0)L(exp 3). As part of the reanalysis program, a method for the deconvolution of pitch angle distributions observed by simple detectors on a rotating spacecraft is developed. This process removes the instrumental response and rotational smear due to finite sampling periods and yields true angular distributions.

Randall, B. A.↗
NASA NTRS1986

Analyses of convective flows and spatial gradients in energetic ion observations

Based on the measured anisotropy of three-dimensional energetic ion distributions obtained from the Medium Energy Particle Instrument experiment of the ISEE 1 spacecraft, bulk flow, epsilon x B convection, and pressure gradients in magnetospheric plasmas are measured with two techniques. In the first technique, using a Compton-Getting transform into the appropriate rest frame in an iterative fashion and converging to the unique velocity that removes the first-order anisotropy from the flux angular distribution, the actual measured angular distribution, and spectrum at each angle, are employed. The second technique uses a first moment of the distribution function in which the shift in velocity space of the distribution function is obtained at two phase space density values. The convection contribution to the velocity shift is assumed to be perpendicular to the pressure gradient contribution if an MHD generator condition is assumed, rendering the two shifts separable, and a gradient scale and a lower limit to the convection electric field are derived in one calculation.

Mitchell, D. G.↗
NASA NTRS2010

Directivity of a Sparse Array in the Presence of Atmospheric-Induced Phase Fluctuations for Deep Space Communications

Widely distributed (sparse) ground-based arrays have been utilized for decades in the radio science community for imaging celestial objects, but have only recently become an option for deep space communications applications with the advent of the proposed Next Generation Deep Space Network (DSN) array. But whereas in astronomical imaging, observations (receive-mode only) are made on the order of minutes to hours and atmospheric-induced aberrations can be mostly corrected for in post-processing, communications applications require transmit capabilities and real-time corrections over time scales as short as fractions of a second. This presents an unavoidable problem with the use of sparse arrays for deep space communications at Ka-band which has yet to be successfully resolved, particularly for uplink arraying. In this paper, an analysis of the performance of a sparse antenna array, in terms of its directivity, is performed to derive a closed form solution to the expected array loss in the presence of atmospheric-induced phase fluctuations. The theoretical derivation for array directivity degradation is validated with interferometric measurements for a two-element array taken at Goldstone, California. With the validity of the model established, an arbitrary 27-element array geometry is defined at Goldstone, California, to ascertain its performance in the presence of phase fluctuations. It is concluded that a combination of compact array geometry and atmospheric compensation is necessary to ensure high levels of availability.

Nessel, James A.↗
NASA NTRS1986

Space station 20-kHz power management and distribution system

During the conceptual design phase a 20-kHz power distribution system was selected as the reference for the space station. The system is single-phase 400 VRMS, with a sinusoidal wave form. The initial user power level will be 75 kW with growth to 300 kW. The high-frequency system selection was based upon considerations of efficiency, weight, safety, ease of control, interface with computers, and ease of paralleling for growth. Each of these aspects will be discussed as well as the associated trade-offs involved. An advanced development program has been instituted to accelerate the maturation of the high-frequency system. Some technical aspects of the advanced development will be discussed.

Hansen, I. G.↗
NASA NTRS1986

Space Station 20-kHz power management and distribution system

During the conceptual design phase a 20-kHz power distribution system was selected as the reference for the Space Station. The system is single-phase 400 VRMS, with a sinusoidal wave form. The initial user power level will be 75 kW with growth to 300 kW. The high-frequency system selection was based upon considerations of efficiency, weight, safety, ease of control, interface with computers, and ease of paralleling for growth. Each of these aspects will be discussed as well as the associated trade-offs involved. An advanced development program has been instituted to accelerate the maturation of the high-frequency system. Some technical aspects of the advanced development will be discussed.

Hansen, Irving G.↗
NASA NTRS1990

Viscosity and mass transport in nonuniform Keplerian disks

A quantitative formalism for Keplerian particulate disk dynamics having its basis in a heuristic description of viscous transport is presently applied to the case of a ring with optical thickness radial gradient. A steady-state velocity distribution solution directly yields both the radial mass transport and the viscosity. The analytical method employed involves the solution of a novel form of the Krook equation through the separation of the phase-space collisional-products distribution into a symmetrical component and a delta function-approachable remainder. While this model is simplified for the case treated, its general approach may be extended to less artificially restricted cases.

Ojakangas, G. W.↗
NASA NTRS1993

Hypervelocity impact testing of the Space Station utility distribution system carrier

A two-phase, joint JSC and McDonnell Douglas Aerospace-Huntington Beach hypervelocity impact (HVI) test program was initiated to develop an improved understanding of how meteoroid and orbital debris (M/OD) impacts affect the Space Station Freedom (SSF) avionic and fluid lines routed in the Utility Distribution System (UDS) carrier. This report documents the first phase of the test program which covers nonpowered avionic line segment and pressurized fluid line segment HVI testing. From these tests, a better estimation of avionic line failures is approximately 15 failures per year and could very well drop to around 1 or 2 avionic line failures per year (depending upon the results of the second phase testing of the powered avionic line at White Sands). For the fluid lines, the initial McDonnell Douglas analysis calculated 1 to 2 line failures over a 30 year period. The data obtained from these tests indicate the number of predicted fluid line failures increased slightly to as many as 3 in the first 10 years and up to 15 for the entire 30 year life of SSF.

Lazaroff, Scott↗
DOE OSTI2023

Phase diagram of twisted bilayer graphene at filling factor $v = ±3$

Here, we study the correlated insulating phases of twisted bilayer graphene (TBG) in the absence of lattice strain at integer filling $v = ±3$. Using the self-consistent Hartree-Fock method on a particle-hole symmetric model and allowing translation symmetry breaking terms, we obtain the phase diagram with respect to the ratio of AA interlayer hopping (w 0 ) and AB interlayer hopping (w 1 ). When the interlayer hopping ratio is close to the chiral limit (w 0 /w 1 ≲ 0.5), a quantum anomalous Hall state with Chern number v c = ±1 can be observed consistent with previous studies. Around the realistic value w 0 /w 1 ≈ 0.8, we find a spin and valley polarized, translation symmetry breaking, state with C 2⁢z T symmetry, a charge gap and a doubling of the moiré unit cell, dubbed theC 2⁢z T stripe phase. The real-space total charge distribution of this C 2⁢z T stripe phase in the flat band limit does not have modulation between different moiré unit cells, although the charge density in each layer is modulated, and the translation symmetry is strongly broken. Other symmetries, including C 2⁢z , C 2⁢x , particle-hole symmetry P, and the topology of the C 2⁢z T stripe phase, are also discussed in detail. We observed braiding and annihilation of the Dirac nodes by continuously turning on the order parameter to its fully self-consistent value, and provide a detailed explanation of the mechanism for the charge gap opening despite preserving C 2⁢z T and valley U⁡(1) symmetries. In the transition region between the quantum anomalous Hall phase and the C 2⁢z T stripe phase, we find an additional competing state with comparable energy corresponding to a phase with a tripling of the moiré unit cell.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

The cosmic waltz of Coma Berenices and Latyshev 2 (Group X)

Context. Open clusters (OCs) are fundamental benchmarks where theories of star formation and stellar evolution can be tested and validated. Coma Berenices (Coma Ber) and Latyshev 2 (Group X) are the second and third OCs closest to the Sun, making them excellent targets to search for low-mass stars and ultra-cool dwarfs. In addition, this pair will experience a flyby in 10–16 Myr, making it a benchmark to test pair interactions of OCs. Aims. We aim to analyse the membership, luminosity, mass, phase-space (i.e. positions and velocities), and energy distributions for Coma Ber and Latyshev 2 and test the hypothesis of the mixing of their populations at the encounter time. Methods. We developed a new phase-space membership methodology and applied it to Gaia data. With the recovered members, we inferred the phase-space, luminosity, and mass distributions using publicly available Bayesian inference codes. Then, with a publicly available orbit integration code and members’ positions and velocities, we integrated their orbits 20 Myr into the future. Results. In Coma Ber, we identified 302 candidate members distributed in the core and tidal tails. The tails are dynamically cold and asymmetrically populated. The stellar system called Group X is made of two structures: the disrupted OC Latyshev 2 (186 candidate members) and a loose stellar association called Mecayotl 1 (146 candidate members), and both of them will fly by Coma Ber in 11.3 ± 0.5 Myr and 14.0 ± 0.6 Myr, respectively, and each other in 8.1 ± 1.3 Myr. Conclusions. We study the dynamical properties of the core and tails of Coma Ber and also confirm the existence of the OC Latyshev 2 and its neighbour stellar association Mecayotl 1. Although these three systems will experience encounters, we find no evidence supporting the mixing of their populations.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1983

Voyager observations of Saturnian ion and electron phase space densities

Voyager 1 and 2 low-energy charged particle (LECP) observations of 30-keV to 2-MeV electron and ion energy spectra and angular distributions have been used to calculate phase space densities at constant first and second adiabatic invariants in the Saturnian magnetosphere. The results are generally consistent with inward radial diffusion from an external source. The data obtained also indicate a source of ions located within the orbital distance of Enceladus capable of producing 10- to 40-MeV/Gauss ions as well as a source of electrons at about 3.5 Saturn radii which produces particles at 100 to 200 MeV/Gauss. Higher magnetic moment (200-400 MeV/Gauss) ions extend from the sunward boundary between a plasma mantle and the region of durable trapping at the Saturn radius; the behavior of the phase space density suggests inward diffusion of these particles from a source at the boundary. The identification of sources of low (10 to 200 MeV/Gauss) magnetic moment particles deep in the Saturnian magnetosphere is a new result of this work. Several analyses of the observed phase space densities in terms of time-independent radial diffusion are presented.

Armstrong, T. P.↗
NASA NTRS1989

The velocity distributions of cometary protons picked up by the solar wind

Velocity space distributions of picked up cometary protons were measured by the ion mass spectrometer on the Giotto spacecraft upstream of the Halley bow shock. Large pitch angle anisotropies were observed at all distances greater than 1.2 x 10 to the 6th km from the comet. As expected, pitch angle diffusion was much more rapid than energy diffusion. When the field was quasi-parallel to the solar wind velocity vector, it was possible to discern the effect of pitch angle scattering by sunward propagating, field-aligned hydromagnetic waves, but there is evidence for other scattering modes as well. For quasi-perpendicular geometries, the pitch angle distribution was very asymmetric with phase space density peaks near pitch angles of 180 deg. It is suggested that the asymmetric pitch angle distribution may be caused by global rather than local wave-particle interactions. Just outside the shock, the pitch angle distribution was nearly isotropic and the radius of the pickup shell increased significantly.

Neugebauer, M.↗
DOE OSTI2022

Simulation of convective transport during frequency chirping of a TAE using the MEGA code

Here, we present a procedure to examine energetic particle phase-space during long range frequency chirping phenomena in tokamak plasmas. To apply the proposed method, we have performed self-consistent simulations using the MEGA code and analyzed the simulation data. We demonstrate a traveling wave in phase-space and that there exist specific slices of phase-space on which the resonant particles lie throughout the wave evolution. For non-linear evolution of an n = 6 toroidicity-induced Alfvén eigenmode (TAE), our results reveal the formation of coherent phase-space structures (holes/clumps) after coarse-graining of the distribution function. These structures cause a convective transport in phase-space which implies a radial drift of the resonant particles. We also demonstrate that the rate of frequency chirping increases with the TAE damping rate. Our observations of the TAE behavior and the corresponding phase-space dynamics are consistent with the Berk–Breizman theory.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Regulation of Solar Wind Electron Temperature Anisotropy by Collisions and Instabilities

Abstract Typical solar wind electrons are modeled as being composed of a dense but less energetic thermal “core” population plus a tenuous but energetic “halo” population with varying degrees of temperature anisotropies for both species. In this paper, we seek a fundamental explanation of how these solar wind core and halo electron temperature anisotropies are regulated by combined effects of collisions and instability excitations. The observed solar wind core/halo electron data in ( β ∥ , T ⊥ / T ∥ ) phase space show that their respective occurrence distributions are confined within an area enclosed by outer boundaries. Here, T ⊥ / T ∥ is the ratio of perpendicular and parallel temperatures and β ∥ is the ratio of parallel thermal energy to background magnetic field energy. While it is known that the boundary on the high- β ∥ side is constrained by the temperature anisotropy-driven plasma instability threshold conditions, the low- β ∥ boundary remains largely unexplained. The present paper provides a baseline explanation for the low- β ∥ boundary based upon the collisional relaxation process. By combining the instability and collisional dynamics it is shown that the observed distribution of the solar wind electrons in the ( β ∥ , T ⊥ / T ∥ ) phase space is adequately explained, both for the “core” and “halo” components.

Yoon, Peter H. (ORCID:0000000181343790)↗