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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.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2011

Shell and cluster states of {sub {Lambda}}{sup 21}Ne studied with antisymmetrized molecular dynamics

The low-lying states of {sub {Lambda}}{sup 21}Ne are studied with antisymmetrized molecular dynamics for hypernuclei. We have obtained ten rotational bands where the number of bands are increased compared to {sup 20}Ne by adding a {Lambda} hyperon. Among them, we focus on the K{sup {pi}=}0{sub 1}{sup +} x {Lambda}{sub s} and K{sup {pi}=}0{sub 1}{sup -} x {Lambda}{sub s} bands. The former has a shell-model-like structure that has {Lambda} in an s wave coupled to the ground band of {sup 20}Ne. The latter is a cluster state that has a {alpha}+{sub {Lambda}}{sup 17}O dicluster structure. The difference between their structures leads to the binding energy of {Lambda} particle B{sub {Lambda}} and reduction of the E2 transition probabilities B(E2).

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2013

Measurement of neutral strange particle production in the underlying event in proton-proton collisions at sqrt(s) = 7 TeV

Measurements are presented of the production of primary K(S)0 and Lambda particles in proton-proton collisions at sqrt(s) = 7 TeV in the region transverse to the leading charged-particle jet in each event. The average multiplicity and average scalar transverse momentum sum of K(S)0 and Lambda particles measured at pseudorapidities abs(eta) < 2 rise with increasing charged-particle jet pt in the range 1-10 GeV and saturate in the region 10-50 GeV. The rise and saturation of the strange particle yields and transverse momentum sums in the underlying event are similar to those observed for inclusive charged particles, which confirms the impact-parameter picture of multiple parton interactions. The results are compared to recent tunes of the PYTHIA Monte Carlo event generator. The PYTHIA simulations underestimate the data by 15-30% for K(S)0 mesons and by about 50% for Lambda baryons, a deficit similar to that observed for the inclusive strange particle production in non-single-diffractive proton-proton collisions. The constant strange- to charged-particle activity ratios and the similar trends for mesons and baryons indicate that the multiparton-interaction dynamics is decoupled from parton hadronization, which occurs at a later stage.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Deformation of hypernuclei studied with antisymmetrized molecular dynamics

An extended version of antisymmetrized molecular dynamics was developed to study the structure of p-sd shell hypernuclei. By using an effective {Lambda}N interaction, we investigated the energy curves of {sub {Lambda}}{sup 9}Be, {sub {Lambda}}{sup 13}C, and {sub {Lambda}}{sup 20,21}Ne as a function of nuclear quadrupole deformation. The changes to nuclear deformation caused by {Lambda} particles are discussed. We found that {Lambda} in the p wave enhances nuclear deformation, while that in the s wave reduces it. This effect is most prominent in {sub {Lambda}}{sup 13}C. The possibility of parity inversion in {sub {Lambda}}{sup 20}Ne is also examined.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2015

Hypernuclei and the hyperon problem in neutron stars

The likely presence of $\Lambda$ baryons in dense hadronic matter tends to soften the equation of state to an extend that the observed heaviest neutron stars are difficult to explain. Here we analyze this "hyperon problem" with a phenomenological approach. First, we review what can be learned about the interaction of $\Lambda$ particle with dense matter from the observed hypernuclei and extend this phenomenological analysis to asymmetric matter. We add to this the current knowledge on non-strange dense matter, including its uncertainties, to conclude that the interaction between $\Lambda$s and dense matter has to become repulsive at densities below three times the nuclear saturation density.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

Collisionless losses of fast ions in the Divertor Tokamak Test due to toroidal field ripple

In this paper we analyze fast ion motion in the Divertor Tokamak Test device. DTT is planned to be heated through a mix of 45 MW heating power, including 15 MW negative-ion-based Neutral Beam heating (NNBI) which is currently being developed by Consorzio RFX in Padova, Italy. An issue for DTT is that a Toroidal Field (TF) ripple with a maximum value of about 0.42% (with respect to the on-axis magnetic field $B_0$) is expected on the low-field side (LFS), and this ripple interacts with fast ions through rather well-known phenomena of ripple-precession resonances, in addition to prompt losses of ions which do not complete a full orbit in the poloidal plane. We will show that, with the planned geometry of NNBI, prompt losses are negligible, and ripple-precession losses amount to a maximum 0.15%. The calculations are performed with the guiding center code ORBIT using two different equilibria, and a beam with energy 400 keV and injection angle $\alpha_{inj} = 40^{\circ}$ (measured w.r.t. the first wall), which corresponds to a pitch of injected particles $\lambda = v_{\parallel}/v \approx \sin{\alpha_{inj}} = 0.65$. Main resonances are of the form $\omega_b - n N \omega_d = 0$, $\omega_b$ and $\omega_d$ being the bounce and precession frequency, respectively, $N=18$ the ripple periodicity and $3 \le n \le 6$ are the toroidal wavenumbers of the resonances. Although collisionless interaction with the TF ripple does not pose a serious threat to the NNBI project, an open question remains whether the presence of these resonances will interact with fast particles accelerated by \alfven eigenmodes, and if stochastization of the resonances is possible in DTT, as it was observed in the past in TORE SUPRA.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS2011

Jovian Chromophore Characteristics from Multispectral HST Images

The chromophores responsible for coloring the jovian atmosphere are embedded within Jupiter's vertical aerosol structure. Sunlight propagates through this vertical distribution of aerosol particles, whose colors are defined by omega-bar (sub 0)(lambda), and we remotely observe the culmination of the radiative transfer as I/F(lambda). In this study, we employed a radiative transfer code to retrieve omega-bar (sub 0)(lambda) for particles in Jupiter's tropospheric haze at seven wavelengths in the near-UV and visible regimes. The data consisted of images of the 2008 passage of Oval BA to the south of the Great Red Spot obtained by the Wide Field Planetary Camera 2 on-board the Hubble Space Telescope. We present derived particle colors for locations that were selected from 14 weather regions, which spanned a large range of observed colors. All omega-bar (sub 0)(lambda) curves were absorbing in the blue, and omega-bar (sub 0)(lambda) increased monotonically to approximately unity as wavelength increased. We found accurate fits to all omega-bar (sub 0)(lambda) curves using an empirically derived functional form: omega-bar (sub 0)(lambda) = 1 A exp(-B lambda). The best-fit parameters for the mean omega-bar (sub 0)(lambda) curve were A = 25.4 and B = 0.0149 for lambda in units of nm. We performed a principal component analysis (PCA) on our omega-bar (sub 0)(lambda) results and found that one or two independent chromophores were sufficient to produce the variations in omega-bar (sub 0)(lambda). A PCA of I/F(lambda) for the same jovian locations resulted in principal components (PCs) with roughly the same variances as the omega-bar (sub 0)(lambda) PCA, but they did not result in a one-to-one mapping of PC amplitudes between the omega-bar (sub 0)(lambda) PCA and I/F(lambda) PCA. We suggest that statistical analyses performed on I/ F(lambda) image cubes have limited applicability to the characterization of chromophores in the jovian atmosphere due to the sensitivity of 1/ F(lambda) to horizontal variations in the vertical aerosol distribution.

Strycker, Paul D.↗
DOE OSTI2015

On Baryon-Antibaryon Cross Sections from Initial State Radiation Processes at BABAR and their Surprising Threshold Behavior

BABAR has measured with unprecedented accuracy the e + e - → pp-bar and e + e - → ΛΛ-bar cross sections by means of the initial state radiation technique, which has the advantages of good efficiency and energy resolution, and full angular acceptance in the threshold region. A striking feature of these cross sections is their non-vanishing values at threshold. In the case of charged baryons, the phenomenon is well understood in terms of the Coulomb interaction between the outgoing baryon and antibaryon. However, such an effect is not expected for neutral baryons. We suggest a simple explanation for both charged and neutral baryon pairs based on Coulomb interactions at the valence quark level.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Theoretical investigation of the formation of K{sup -}K{sup -}pp in high-energy proton-proton collisions

We have formulated and calculated the differential cross section for the formation of the simplest double-K nuclear cluster system, K{sup -}K{sup -}pp, in the reaction process p+p{yields}K{sup +}+K{sup +}+{Lambda}*+{Lambda}*{yields}K{sup +}+K{sup +}+K{sup -}K{sup -}pp, where {Lambda}* is a quasibound K{sup -}p state corresponding to the {Lambda}(1405) resonance. From a comprehensive study of the calculated effects of the binding and density of K{sup -}K{sup -}pp on the cross section, we find that the bound-state peak of K{sup -}K{sup -}pp dominates over the spectrum when and only when the system is dense. This is understood as meaning that the two {Lambda}* doorway particles interact immediately within a short distance, assisted by a large momentum transfer ({approx} 1.8 GeV/c) and a short collision length ({approx} 0.3 fm), which helps to enlarge the {Lambda}*-{Lambda}* sticking into a dense K{sup -}K{sup -}pp system. This mechanism is similar to that for a single K cluster (K{sup -}pp) formation, which has just been proven by a DISTO experiment. The K{sup -}K{sup -} repulsion causes an energy shift to somewhat lower binding and a reduction in the peak cross section, but does not change the basic character of this reaction.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

Transverse momentum distributions of strange hadrons produced in p–p collisions at √s{sub NN} = 200 GeV

The mid-rapidity transverse momentum spectra of strange hadrons (K{sup +},K{sup −},K{sup −}/K{sup +},Λ,Λ̄,Ξ{sup −},Ξ{sup +}, and Ω) produced in p–p collisions at the highest RHIC energy √s{sub NN} = 200 GeV have been studied using a statistical unified thermal freeze-out model. The calculated results are found to be in good agreement with the experimental data taken from STAR and BRAHMS experiments. The fits of the transverse momentum spectra to the model calculations provide the thermal freeze-out conditions in terms of the temperature and collective flow effect parameters for different particle species. The model incorporates a longitudinal and a transverse hydrodynamic flow. The rapidity distributions of kaons and their ratios are also reproduced successfully, which reveals the presence of partial nuclear transparency effects in p–p collisions at √s{sub NN} = 200 GeV. The contributions from heavier decay resonances are also taken into account.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

Investigation of Nuclear Partonic Structure. Final Report

Our research program had two primary goals during the period of this grant, to search for new and rare particles produced in high-energy nuclear collisions and to understand the internal structure of nuclear matter. We have developed electronics to pursue these goals at the Relativistic Heavy Ion Collider (RHIC) in the Solenoidal Tracker at RHIC (STAR) experiment and the AnDY experiment. Our results include discovery of the anti-hyper-triton, anti- 3 Λ-bar H, which opened a new branch on the chart of the nuclides, and the anti-alpha, anti- 4 He, the heaviest form of anti-matter yet seen, as well as uncovering hints of gluon saturation in cold nuclear matter and observation of jets in polarized proton-proton collisions that will be used to probe orbital motion inside protons.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Hypernuclear spectroscopy

A program of hypernuclear spectroscopy experiments encompassing many hypernuclei has been undertaken in both Halls A and C using complimentary approaches. Spectra with sub-MeV resolution have been obtained for Li, B, and N in Hall A, while results from Hall C include He, B, and Al with new data still under analysis for He, Li, Be, B and V. High resolution and high precision in the determination of the single Λ binding energy at various shell levels has been the key success of these experiments using the (e,e'K+) reaction to produce Λ hypernuclei.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2015

The EOS of neutron matter, and the effect of Lambda hyperons to neutron star structure

The following topics are addressed: the model and the method; equation of state of neutron matter, role of three-neutron force; symmetry energy; Λ-hypernuclei; Λ-neutron matter; and neutron star structure. In summary, quantum Monte Carlo methods are useful to study nuclear systems in a coherent framework; the three-neutron force is the bridge between E sym and neutron star structure; and neutron star observations are becoming competitive with experiments. Λ-nucleon data are very limited, but ΛNN is very important. The role of Λ in neutron stars is far from understood; more ΛN data are needed. The author's conclusion: We cannot conclude anything with present models.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
NASA NTRS2003

Effects of Non-Sphericity on Mineral Dust Modeling

The dependency of non-sphericity on gravitational settling of mineral dust particles is parameterized for prolate ellipsoids and Reynolds number lower than 2. The settling speed is numerically solved from the momentum equation as a function of particle diameter and aspect ratio. The reduction of settling speed due to non-sphericity is included in the GO-CART model to simulate dust size distribution for April 2001. Two numerical schemes for solving sedimentation are compared. For particles of diameter greater than 5 micron the simulated size distribution is sensitive to the numerical sedimentation scheme. Changing the particle shape from spherical to non-spherical with lambda=2, makes little difference to the simulated surface concentration and size distribution except at the periphery of the dust sources. However, when very elongated particles (lambda=5) are simulated the differences between non-spherical and spherical particles are significant. With limited in-situ measurements reporting most frequent lambda around 1.5, the overall effects on global modeling is rather negligible and the essential benefit is to relax the CFL condition of Eulerian settling schemes.

Ginoux, Paul↗
DOE OSTI2011

Strange Particle Production in pp Collisions at sqrt(s) = 0.9 and 7 TeV

The spectra of strange hadrons are measured in proton-proton collisions, recorded by the CMS experiment at the CERN LHC, at centre-of-mass energies of 0.9 and 7 TeV. The K0_s, Lambda, and Xi^- particles and their antiparticles are reconstructed from their decay topologies and the production rates are measured as functions of rapidity and transverse momentum. The results are compared to other experiments and to predictions of the PYTHIA Monte Carlo program. The transverse momentum distributions are found to differ substantially from the PYTHIA results and the production rates exceed the predictions by up to a factor of three.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2024

Kinetic stability of Chapman–Enskog plasmas

In this paper, we investigate the kinetic stability of classical, collisional plasma – that is, plasma in which the mean-free-path $\lambda$ of constituent particles is short compared with the length scale $L$ over which fields and bulk motions in the plasma vary macroscopically, and the collision time is short compared with the evolution time. Fluid equations are typically used to describe such plasmas, since their distribution functions are close to being Maxwellian. The small deviations from the Maxwellian distribution are calculated via the Chapman–Enskog (CE) expansion in $\lambda /L \ll 1$ , and determine macroscopic momentum and heat fluxes in the plasma. Such a calculation is only valid if the underlying CE distribution function is stable at collisionless length scales and/or time scales. We find that at sufficiently high plasma $\beta$ , the CE distribution function can be subject to numerous microinstabilities across a wide range of scales. For a particular form of the CE distribution function arising in strongly magnetised plasma ( viz. plasma in which the Larmor periods of particles are much smaller than collision times), we provide a detailed analytic characterisation of all significant microinstabilities, including peak growth rates and their associated wavenumbers. Of specific note is the discovery of several new microinstabilities, including one at sub-electron-Larmor scales (the ‘whisper instability’) whose growth rate in certain parameter regimes is large compared with other instabilities. Our approach enables us to construct the kinetic stability maps of classical, two-species collisional plasma in terms of $\lambda$ , the electron inertial scale $d_e$ and the plasma $\beta$ . This work is of general consequence in emphasising the fact that high- $\beta$ collisional plasmas can be kinetically unstable; for strongly magnetised CE plasmas, the condition for instability is $\beta \gtrsim L/\lambda$ . In this situation, the determination of transport coefficients via the standard CE approach is not valid.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗