Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “weak scaling”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 523 records · Page 29
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Galaxy blending effects in deep imaging cosmic shear probes of cosmology

ABSTRACT Upcoming deep imaging surveys such as the Vera C. Rubin Observatory Legacy Survey of Space and Time will be confronted with challenges that come with increased depth. One of the leading systematic errors in deep surveys is the blending of objects due to higher surface density in the more crowded images; a considerable fraction of the galaxies which we hope to use for cosmology analyses will overlap each other on the observed sky. In order to investigate these challenges, we emulate blending in a mock catalogue consisting of galaxies at a depth equivalent to 1.3 yr of the full 10-yr Rubin Observatory that includes effects due to weak lensing, ground-based seeing, and the uncertainties due to extraction of catalogues from imaging data. The emulated catalogue indicates that approximately 12 per cent of the observed galaxies are ‘unrecognized’ blends that contain two or more objects but are detected as one. Using the positions and shears of half a billion distant galaxies, we compute shear–shear correlation functions after selecting tomographic samples in terms of both spectroscopic and photometric redshift bins. We examine the sensitivity of the cosmological parameter estimation to unrecognized blending employing both jackknife and analytical Gaussian covariance estimators. An ∼0.025 decrease in the derived structure growth parameter S8 = σ8(Ωm/0.3)0.5 is seen due to unrecognized blending in both tomographies with a slight additional bias for the photo-z-based tomography. This bias is greater than the 2σ statistical error in measuring S8.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2004

Small-scale Interstellar Structure Toward the Open Cluster Chi Persei; Program ID: BO29 (Cycle 2)

The primary objective of this program was to obtain FUSE observations of the interstellar H2 absorption toward six early-type stars in the core of the open star cluster Chi Persei. High resolution optical observations of the interstellar Na I absorption toward these stars and others in the core of Chi Per have revealed a rich variety of small-scale diffuse ISM structure in both the distant Perseus and more local Orion spiral arms. At the 1 arc minute angular scales typically probed by the separations of these stars, this structure corresponds to respective physical length scales of 0.6 and 0.15 pc in the Perseus and Orion arm gas. The principal scientific goal of the FUSE observations was to determine if this small-scale Na I structure toward the core of Chi Per was reflected in the abundance and/or excitation of interstellar H2. In September 2001, we obtained FUSE observations of the Chi Per stars BD +56 563, BD +56 571, BD +56 573, BD +56 574, BD +56 575, and BD +56 578 for this program. The data reveal that the Perseus arm gas exhibits significant small-scale variations in the strength of its molecular hydrogen absorption while the Orion arm H2 absorption is relatively uniform. We presented these results at the January 2003 American Astronomical Society meeting in Seattle, WA (points, Meyer, Lauroesch, Nguyen, and Friedman 2002, Bulletin of the American Astronomical Society, 34,1229). Since Na I is not a dominant ion in H I clouds, the variations detected in the Perseus arm Na I line profiles could be due to spatial differences in either the physical structure or the physical conditions in the gas. Although many of the H2 absorption profiles are too saturated or too weak to be definitive in this regard, it is clear that small-scale variations are present in H2 gas with excitation as high as the J=4 rotational level. In contrast, lower spatial resolution H I 21 cm studies of the Perseus arm gas across the face of the h and Chi Per double cluster have shown smoother, continuous variations on the larger scale. In order to investigate if the global velocity structure of H2 toward h and Chi Per more closely follows the chaotic structure seen in interstellar Na I absorption or the smoother, continuous H I structure, we have expanded our FUSE study with a Cycle 4 program (D902, PI: Points) to survey the H2 absorption toward a number of other stars across the face of the double cluster. We have obtained FUSE spectra of 14 additional h and Chi Per stars through this program and are now combining all of the data into a comprehensive study that will be submitted for publication next year.

Meyer, David M.↗
NASA NTRS1994

Equatorial wave activity derived from fluctuations in observed convection

The spectrum of equatorial wave activity propagating vertically into the stratosphere is calculated from high-resolution imagery of the global convective pattern. Synoptic Global Cloud Imagery (GCI), constructed from six satellites simultaneously observing the earth, is used to diabatically force the linearized primitive equations. Having resolution of 0.5 deg and 3 h, that imagery captures the dominant scales of organized convection, including several harmonics of the diurnal cycle. Its global coverage with high space-time resolution allows the GCI to represent heating variability and dynamical behavior excited by it over a wide range of scales. The dynamical response above the heating is evaluated globally in terms of a space-time spectrum of Hough modes, one which includes planetary-scale Kelvin waves, Rossby waves, and gravity waves down to the resolution of the GCI. The geopotential response, which is indicative of temperature fluctuations observed by satellite, is very red in frequency. Therefore, planetary-scale waves with periods longer than two days dominate the spectrum of geopotential, while high-frequency gravity waves make a comparatively small contribution. Some 80% of the geopotential variance is accounted for by the Kelvin and gravest-symmetric Rossby modes, while the Rossby-gravity mode is comparatively weak. In horizontal eddy motion, the excited wave spectrum is still dominated by planetary-scale components. However, meridional wind fluctuations associated with the Rossby-gravity mode have variance comparable to that of zonal wind fluctuations associated with the Kelvin mode, even though the Rossby-gravity mode is nearly invisible in the geopotential response. Estimates of tropospheric heating lead to amplitudes and propagation characteristics that are broadly consistent with satellite and radiosonde observations of wave activity in the lower stratosphere. The space-time spectrum of EP flux is significantly whiter than the response in either geopotential or motion. Gravity waves of small scale and high frequency carry a large fraction of the upward flux. Although it dominates eastward variance of geopotential and motion, the Kelvin mode carries only about 50% of the eastward EP flux at phase speeds of 20-40 m/s and only 35% of the total eastward flux transmitted to the stratosphere. The remainder is carried by the gravity wave spectrum, which carries nearly all of the westward flux at phase speeds greater than 20 m/s. The gravity wave spectrum also contributes significantly at phase speeds of 10-20 m/s, where only 25% of the flux is accounted for by zonal wavenumbers less than 20. The broad nature of the gravity wave spectrum suggests its absorption at critical levels will be distributed over a deep layer of the middle atmosphere.

Bergman, John W.↗
DOE OSTI2022

Transitioning from Stage-III to Stage-IV: cosmology from galaxy×CMB lensing and shear×CMB lensing

ABSTRACT We examine the cosmological constraining power from two cross-correlation probes between galaxy and cosmic microwave background (CMB) surveys: the cross-correlation of lens galaxy density with CMB lensing convergence 〈δgκCMB〉, and source galaxy weak lensing shear with CMB lensing convergence 〈γκCMB〉. These two cross-correlation probes provide an independent cross-check of other large-scale structure constraints and are insensitive to galaxy-only or CMB-only systematic effects. In addition, when combined with other large-scale structure probes, the cross-correlations can break degeneracies in cosmological and nuisance parameters, improving both the precision and robustness of the analysis. In this work, we study how the constraining power of 〈δgκCMB〉 + 〈γκCMB〉 changes from Stage-III (ongoing) to Stage-IV (future) surveys. Given the flexibility in selecting the lens galaxy sample, we also explore systematically the impact on cosmological constraints when we vary the redshift range and magnitude limit of the lens galaxies using mock galaxy catalogs. We find that in our setup, the contribution to cosmological constraints from 〈δgκCMB〉 and 〈γκCMB〉 are comparable in the Stage-III data sets; but in Stage-IV surveys, the noise in 〈δgκCMB〉 becomes subdominant to cosmic variance, preventing 〈δgκCMB〉 to further improve the constraints. This implies that to maximize the cosmological constraints from future 〈δgκCMB〉 + 〈γκCMB〉 analyses, we should focus more on the requirements on 〈γκCMB〉 instead of 〈δgκCMB〉. Furthermore, the selection of the lens sample should be optimized in terms of our ability to characterize its redshift or galaxy bias instead of its number density.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2003

Characteristics of Mini-Magnetospheres Formed by Paleo-Magnetic Fields of Mars

The intensely and non-uniformly magnetized crustal sources generate an effective large-scale magnetic field. In the Southern hemisphere the strongest crustal fields lead to the formation of large-scale mini-magnetospheres. In the Northern hemisphere, the crustal fields are rather weak and there are only isolated mini-magnetospheres. Re-connection with the interplanetary magnetic field (IMF) occurs in many localized regions. This may occur not only in cusp-like structures above nearly vertical field anomalies but also in halos extending several hundreds of kilometers from these sources. Re-connection will permit solar wind (SW) and more energetic particles to precipitate into and heat the neutral atmosphere. Electron density profiles of the ionosphere of Mars derived from radio occultation data obtained by the Radio Science Mars Global Surveyor (MGS) experiment are concentrated in the near polar regions. The effective scale-height of the neutral atmosphere density in the vicinity of the ionization peak has been derived for each of the profiles studied. The effective scale-heights have been compared with the crustal magnetic fields measured by the MGS Magnetometer/Electron Reflectometer (MAG/ER) experiment. A significant difference between the large-scale mini-magnetospheres and regions outside of them has been found. The neutral atmosphere is cooler inside the large-scale mini-magnetospheres. It appears that outside of the cusps the strong crustal magnetic fields prevent additional heating of the neutral atmosphere by direct interaction of the SW. The scale-height of the neutral atmosphere density derived from the experiment with the MGS Accelerometer has been compared with MAG/ER data. The scale-height was found to be usually larger than mean value near the boundaries of potential mini-magnetospheres and around cusps . It may indicate that the paleo-magnetic/IMF field re-connection is characteristic of the mini-magnetospheres at Mars.

N F Ness↗
DOE OSTI2022

Combining Planck and SPT Cluster Catalogs: Cosmological Analysis and Impact on the Planck Scaling Relation Calibration

We provide the first combined cosmological analysis of the South Pole Telescope (SPT) and Planck cluster catalogs. The aim is to provide an independent calibration for Planck scaling relations, exploiting the cosmological constraining power of the SPT-SZ cluster catalog and its dedicated weak lensing (WL) and X-ray follow-up observations. We build a new version of the Planck cluster likelihood. In the νΛ CDM scenario, focusing on the mass slope and mass bias of Planck scaling relations, we find ${\alpha }_{\mathrm{SZ}}={1.49}_{-0.10}^{+0.07}$ and ${\left(1-b\right)}_{\mathrm{SZ}}={0.69}_{-0.14}^{+0.07}$, respectively. The results for the mass slope show a ~4 σ departure from the self-similar evolution, α SZ ~ 1.8. This shift is mainly driven by the matter density value preferred by SPT data, Ωm = 0.30 ± 0.03, lower than the one obtained by Planck data alone, ${{\rm{\Omega }}}_{m}={0.37}_{-0.06}^{+0.02}$. The mass bias constraints are consistent both with outcomes of hydrodynamical simulations and external WL calibrations, (1 – b) ~ 0.8, and with results required by the Planck cosmic microwave background cosmology, (1 – b) ~ 0.6. From this analysis, we obtain a new catalog of Planck cluster masses M 500 . We estimate the ratio between the published Planck M SZ masses and our derived masses M 500 , as a "measured mass bias," ${\left(1-b\right)}_{M}$. We analyze the mass, redshift, and detection noise dependence of ${\left(1-b\right)}_{M}$, finding an increasing trend toward high redshift and low mass. These results mimic the effect of departure from self-similarity in cluster evolution, showing different dependencies for the low-mass, high-mass, low-z, and high-z regimes.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2020

The Atacama Cosmology Telescope: A CMB lensing mass map over 2100 square degrees of sky and its cross-correlation with BOSS-CMASS galaxies

We construct cosmic microwave background lensing mass maps using data from the 2014 and 2015 seasons of observations with the Atacama Cosmology Telescope (ACT). These maps cover 2100 square degrees of sky and overlap with a wide variety of optical surveys. The maps are signal dominated on large scales and have fidelity such that their correlation with the cosmic infrared background is clearly visible by eye. We also create lensing maps with thermal Sunyaev-Zel’dovich contamination removed using a novel cleaning procedure that only slightly degrades the lensing signal-to-noise ratio. The cross-spectrum between the cleaned lensing map and the BOSS CMASS galaxy sample is detected at 10-σ significance, with an amplitude of A = 1.02±0.10 relative to the Planck best-fit LCDM cosmological model with fiducial linear galaxy bias. Our measurement lays the foundation for lensing cross-correlation science with current ACT data and beyond.

gravitational lensing↗
NASA NTRS1978

Detection of a weak maser emission pedestal associated with the SiO maser

Results are reported for high-spectral-resolution observations of the v = 1, J = 1-0 SiO maser sources at 43,122.027 MHz (6.95 mm wavelength) associated with the variable stars Omega Cet, NML Tau, VY CMa, R Leo, W Hya, VX Sgr, NML Cyg, and R Cas. A weak underlying maser emission pedestal is clearly observed in the spectra of all but NML Cyg and R Cas. The data indicate that the underlying pedestal of SiO emission appears to originate in a shell-like region around the star, has a thermal appearance even though it must be due to weak maser emission, and appears to be part of the spectral signature of SiO maser emission from late-type stars. It is found that the center velocities of the pedestals may be used to determine stellar radial velocities. Observations of large-scale time variations in the intensity of the Ori A SiO maser and the detection of weak maser pedestals associated with each of the two strong emission-feature groups in Orion are also discussed. It is suggested that the Orion molecular cloud might contain two late-type long-period variable stars that may be semiregular variables.

Snyder, L. E.↗
NASA NTRS2011

Microphysics in the Multi-Scale Modeling Systems with Unified Physics

In recent years, exponentially increasing computer power has extended Cloud Resolving Model (CRM) integrations from hours to months, the number of computational grid points from less than a thousand to close to ten million. Three-dimensional models are now more prevalent. Much attention is devoted to precipitating cloud systems where the crucial 1-km scales are resolved in horizontal domains as large as 10,000 km in two-dimensions, and 1,000 x 1,000 km2 in three-dimensions. Cloud resolving models now provide statistical information useful for developing more realistic physically based parameterizations for climate models and numerical weather prediction models. It is also expected that NWP and mesoscale model can be run in grid size similar to cloud resolving model through nesting technique. Recently, a multi-scale modeling system with unified physics was developed at NASA Goddard. It consists of (l) a cloud-resolving model (Goddard Cumulus Ensemble model, GCE model), (2) a regional scale model (a NASA unified weather research and forecast, WRF), (3) a coupled CRM and global model (Goddard Multi-scale Modeling Framework, MMF), and (4) a land modeling system. The same microphysical processes, long and short wave radiative transfer and land processes and the explicit cloud-radiation, and cloud-surface interactive processes are applied in this multi-scale modeling system. This modeling system has been coupled with a multi-satellite simulator to use NASA high-resolution satellite data to identify the strengths and weaknesses of cloud and precipitation processes simulated by the model. In this talk, the microphysics developments of the multi-scale modeling system will be presented. In particular, the results from using multi-scale modeling system to study the heavy precipitation processes will be presented.

Tao, Wei-Kuo↗
DOE OSTI2020

Transverse momentum broadening of a jet in quark-gluon plasma: an open quantum system EFT

We utilize the technology of open quantum systems in conjunction with the recently developed effective field theory for forward scattering to address the question of massless jet propagation through a weakly-coupled quark-gluon plasma in thermal equilibrium. We discuss various possible hierarchies of scales that may appear in this problem, by comparing thermal scales of the plasma with relevant scales in the effective field theory. Starting from the Lindblad equation, we derive and solve a master equation for the trans- verse momentum distribution of a massless quark jet, at leading orders both in the strong coupling and in the power counting of the effective field theory. Markovian approximation is justified in the weak coupling limit. Using the solution to the master equation, we study the transverse momentum broadening of a jet as a function of the plasma temperature and the time of propagation. We discuss the physical origin of infrared sensitivity that arises in the solution and a way to handle it in the effective field theory formulation. We suspect that the final measurement constraint can only cut-off leading infrared singularities and the solution to the Markovian master equation resums a logarithmic series. This work is a stepping stone towards understanding jet quenching and jet substructure observables on both light and heavy quark jets as probes of the quark-gluon plasma.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
NASA NTRS1994

Toward a theory of interstellar turbulence. 1: Weak Alfvenic turbulence

We study weak Alfvenic turbulence of an incompressible, magnetized fluid in some detail, with a view to developing a firm theoretical basis for the dynamics of small-scale turbulence in the interstellar medium. We prove that resonant 3-wave interactions are absent. We also show that the Iroshnikov-Kraichnan theory of incompressible, magnetohydrodynamic turbulence -- which is widely accepted -- describes weak 3-wave turbulence; consequently, it is incorrect. Physical arguments, as well as detailed calculations of the coupling coefficients are used to demonstrate that these interactions are empty. We then examine resonant 4-wave interactions, and show that the resonance relations forbid energy transport to small spatial scales along the direction of the mean magnetic field, for both the shear Alfven wave and the pseudo Alfven wave. The three-dimensional inertial-range energy spectrum of 4-wave shear Alfven turbulence guessed from physical arguments reads E(k(sub z), k(sub perpendicular)) approximately V(sub A)v(sub L)L(exp -1/3)k(sub perpendicular)(exp -10/3), where V(sub A) is the Alfven speed, and v(sub L) is the velocity difference across the outer scale L. Given this spectrum, the velocity difference across lambda(sub perpendicular) approximately k(sub perpendicular exp -1) is v(sub lambda (sub perpendicular)) is approximately v(sub L)(lambda(sub perpendicular)/L)(exp 2/3). We derive a kinetic equation, and prove that this energy spectrum is a stationary solution and that it implies a positive flux of energy in k-space, along directions perpendicular to the mean magnetic field. Using this energy spectrum, we deduce that 4-wave interactions strengthen as the energy cascades to small, perpendicular spatial scales; beyond an upper bound in perpendicular wavenumber, k(sub perpendicular)L is approximately (V(sub A)/v(sub L))(exp 3/2), weak turbulence theory ceases to be valid. Energy excitation amplitudes must be very small for the 4-wave inertial-range to be substantial. When the excitation is strong, the width of the 4-wave inertial-range shrinks to zero. This seems likely to be the case in the interstellar medium.

Sridhar, S.↗
DOE OSTI2021

BPS Wilson loop in $\mathcal{N}$ = 2 superconformal SU(N) “orientifold” gauge theory and weak-strong coupling interpolation

We consider the expectation value \( \left\langle \mathcal{W}\right\rangle \) of the circular BPS Wilson loop in \( \mathcal{N} \) = 2 superconformal SU( N ) gauge theory containing a vector multiplet coupled to two hypermultiplets in rank-2 symmetric and antisymmetric representations. This theory admits a regular large N expansion, is planar-equivalent to \( \mathcal{N} \) = 4 SYM theory and is expected to be dual to a certain orbifold/orientifold projection of AdS 5 × S 5 superstring theory. On the string theory side \( \left\langle \mathcal{W}\right\rangle \) is represented by the path integral expanded near the same AdS 2 minimal surface as in the maximally supersymmetric case. Following the string theory argument in [5], we suggest that as in the \( \mathcal{N} \) = 4 SYM case and in the \( \mathcal{N} \) = 2 SU( N ) × SU( N ) superconformal quiver theory discussed in [19], the coefficient of the leading non-planar 1/ N 2 correction in \( \left\langle \mathcal{W}\right\rangle \) should have the universal λ 3/2 scaling at large ’t Hooft coupling. We confirm this prediction by starting with the localization matrix model representation for \( \left\langle \mathcal{W}\right\rangle \) . We complement the analytic derivation of the λ 3/2 scaling by a numerical high-precision resummation and extrapolation of the weak-coupling expansion using conformal mapping improved Padé analysis.

1/N Expansion↗
NASA NTRS2015

Constraints on Cumulus Parameterization from Simulations of Observed MJO Events

Two recent activities offer an opportunity to test general circulation model (GCM) convection and its interaction with large-scale dynamics for observed Madden-Julian oscillation (MJO) events. This study evaluates the sensitivity of the Goddard Institute for Space Studies (GISS) GCM to entrainment, rain evaporation, downdrafts, and cold pools. Single Column Model versions that restrict weakly entraining convection produce the most realistic dependence of convection depth on column water vapor (CWV) during the Atmospheric Radiation Measurement MJO Investigation Experiment at Gan Island. Differences among models are primarily at intermediate CWV where the transition from shallow to deeper convection occurs. GCM 20-day hindcasts during the Year of Tropical Convection that best capture the shallow–deep transition also produce strong MJOs, with significant predictability compared to Tropical Rainfall Measuring Mission data. The dry anomaly east of the disturbance on hindcast day 1 is a good predictor of MJO onset and evolution. Initial CWV there is near the shallow–deep transition point, implicating premature onset of deep convection as a predictor of a poor MJO simulation. Convection weakly moistens the dry region in good MJO simulations in the first week; weakening of large-scale subsidence over this time may also affect MJO onset. Longwave radiation anomalies are weakest in the worst model version, consistent with previous analyses of cloud/moisture greenhouse enhancement as the primary MJO energy source. The authors’ results suggest that both cloud-/moisture-radiative interactions and convection–moisture sensitivity are required to produce a successful MJO simulation.

Madden-Julian Oscillation↗
DOE OSTI2022

Dark Energy Survey Year 3 results: marginalization over redshift distribution uncertainties using ranking of discrete realizations

ABSTRACT Cosmological information from weak lensing surveys is maximized by sorting source galaxies into tomographic redshift subsamples. Any uncertainties on these redshift distributions must be correctly propagated into the cosmological results. We present hyperrank, a new method for marginalizing over redshift distribution uncertainties, using discrete samples from the space of all possible redshift distributions, improving over simple parametrized models. In hyperrank, the set of proposed redshift distributions is ranked according to a small (between one and four) number of summary values, which are then sampled, along with other nuisance parameters and cosmological parameters in the Monte Carlo chain used for inference. This approach can be regarded as a general method for marginalizing over discrete realizations of data vector variation with nuisance parameters, which can consequently be sampled separately from the main parameters of interest, allowing for increased computational efficiency. We focus on the case of weak lensing cosmic shear analyses and demonstrate our method using simulations made for the Dark Energy Survey (DES). We show that the method can correctly and efficiently marginalize over a wide range of models for the redshift distribution uncertainty. Finally, we compare hyperrank to the common mean-shifting method of marginalizing over redshift uncertainty, validating that this simpler model is sufficient for use in the DES Year 3 cosmology results presented in companion papers.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1971

Proposed characterization of tornadoes and hurricanes by area and intensity

Results of the 1968 through 1970 Tornado Watch Experiment conducted jointly by NASA and NOAA suggested the necessity of characterizing individual tornadoes in order to improve the identity of tornado-producing nephsystems. An attempt was made, therefore, to categorize each tornado by its intensity and area. Fujita-scale wind and corresponding damage categories were devised to classify tornadoes as Gale (F0), Weak (F1), Strong (F2), Severe (F3), Devastating (F4), and Incredible (F5). Additionally, individual tornado areas were also categorized as Trace (TR), Decimicro (DM), Micro (MI), Meso (ME), Marco (MA), Giant (GI), and Decagiant (DG), thus permitting characterizing of a tornado by a combination of intensity and area, such as weak decimicro tornado, severe meso tornado, or incredible giant tornado. A test characterization of 156 Japanese tornadoes in 1950-69 was accomplished for comparison with 893 U.S. tornadoes in 1965. Unexpectedly, the percentage distribution of intensity and individual area of U.S. and Japanese tornadoes is very similar except for large and/or intense ones. Intensity distribution within the Dallas and Fargo tornadoes of 1957 was also studied in detail. It was also found that the F-scale variation along the paths of family tornadoes shows an intensity oscillation with a 45-min interval.

Fujita, T. T.↗
DOE OSTI2025

New Constraints on Cosmic Ray-Boosted Dark Matter from the LUX-ZEPLIN Experiment

While dual-phase xenon time projection chambers have driven the sensitivity toward weakly interacting massive particles at the GeV/c 2 to TeV/c 2 mass scale, the scope for sub-GeV/c 2 dark matter particles is hindered by a limited nuclear recoil energy detection threshold. One approach to probe for lighter candidates is to consider cases where they have been boosted by collisions with cosmic rays in the Milky Way, such that the additional kinetic energy lifts their induced signatures above the nominal threshold. In this Letter, we report first results of a search for cosmic ray-boosted dark matter (CRDM) with a combined 4.2 metric ton/yr exposure from the LUX-ZEPLIN experiment. We observe no excess above the expected backgrounds and establish world-leading constraints on the spin-independent CRDM-nucleon cross section as small as 3.9×10 −33 cm 2 at 90% confidence level for sub-GeV/c 2 masses.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
NASA NTRS2012

Anomalously Weak Solar Convection

Convection in the solar interior is thought to comprise structures on a spectrum of scales. This conclusion emerges from phenomenological studies and numerical simulations, though neither covers the proper range of dynamical parameters of solar convection. Here, we analyze observations of the wavefield in the solar photosphere using techniques of time-distance helioseismology to image flows in the solar interior. We downsample and synthesize 900 billion wavefield observations to produce 3 billion cross-correlations, which we average and fit, measuring 5 million wave travel times. Using these travel times, we deduce the underlying flow systems and study their statistics to bound convective velocity magnitudes in the solar interior, as a function of depth and spherical- harmonic degree l..Within the wavenumber band l < 60, convective velocities are 20-100 times weaker than current theoretical estimates. This constraint suggests the prevalence of a different paradigm of turbulence from that predicted by existing models, prompting the question: what mechanism transports the heat flux of a solar luminosity outwards? Advection is dominated by Coriolis forces for wavenumbers l < 60, with Rossby numbers smaller than approximately 10(exp −2) at r∕R-solar = 0.96, suggesting that the Sun may be a much faster rotator than previously thought, and that large-scale convection may be quasi-geostrophic. The fact that isorotation contours in the Sun are not coaligned with the axis of rotation suggests the presence of a latitudinal entropy gradient.

Sun↗
NASA NTRS1983

Quasi-steady solar wind dynamics

Progress in understanding the large scale dynamics of quasisteady, corotating solar wind structure was reviewed. The nature of the solar wind at large heliocentric distances preliminary calculations from a 2-D MHD model are used to demonstrate theoretical expectations of corotating structure out to 30 AU. It is found that the forward and reverse shocks from adjacent CIR's begin to interact at about 10 AU, producing new shock pairs flanking secondary CIR's. These sawtooth secondary CIR's interact again at about 20 AU and survive as visible entities to 30 AU. The model predicts the velocity jumps at the leading edge of the secondary CIR's at 30 AU should be very small but there should still be sizable variations in the thermodynamic and magnetic parameters. The driving dynamic mechanism in the distant solar wind is the relaxation of pressure gradients. The second topic is the influence of weak, nonimpulsive time dependence in quasisteady dynamics. It is suggested that modest large scale variations in the coronal flow speed on periods of several hours to a day may be responsible for many of the remaining discrepancies between theory and observation. Effects offer a ready explanation for the apparent rounding of stream fronts between 0.3 and 1.0 AU discovered by Helios.

Pizzo, V. J.↗