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At least 919 records · Page 51
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Di-nucleons do not form bound states at heavy pion mass

We perform a high-statistics lattice QCD calculation of the low-energy two-nucleon scattering amplitudes. In order to address discrepancies in the literature, the calculation is performed at a heavy pion mass in the limit that the light quark masses are equal to the physical strange quark mass, $m_π= m_K \simeq 714 $ MeV. Using a state-of-the-art momentum space method, we rule out the presence of a bound di-nucleon in both the isospin 0 (deuteron) and 1 (di-neutron) channels, in contrast with many previous results that made use of compact hexaquark creation operators. In order to diagnose the discrepancy, we add such hexaquark interpolating operators to our basis and find that they do not affect the determination of the two-nucleon finite volume spectrum, and thus they do not couple to deeply bound di-nucleons that are missed by the momentum-space operators. Further, we perform a high-statistics calculation of the HAL QCD potential on the same gauge ensembles and find qualitative agreement with our main results. We conclude that two-nucleons do not form bound states at heavy pion masses and that previous identification of deeply bound di-nucleons must have arisen from a misidentification of the spectrum from off-diagonal elements of a correlation function.

FOS: Physical sciences↗
DOE OSTI2025

Confined and deconfined chaos in classical spin systems

Weakly perturbed integrable many-body systems are typically chaotic, and thermal at late times. However, there are distinct relationships between the timescales for thermalization and chaos. The typical relationship is confined chaos: when trajectories are still confined to regions in phase space with constant conserved quantities (actions), the conjugate angle variables are already unstable. Chaotic instabilities thus far precede thermalization. In a different relationship, which we term deconfined chaos, chaotic instabilities and thermalization occur on the same timescale. We investigate these two qualitatively distinct scenarios through numerical and analytical studies of two perturbed integrable classical spin models: the Ishimori spin chain (confined chaos), and the central spin model with XX interactions (deconfined chaos). We analytically establish (super)-integrability in the latter model in a microcanonical shell. Deconfined chaos emerges through the separation of phase space into large quasi-integrable regions and a thin chaotic manifold. The latter leads to chaos and thermalization on the fastest possible timescale, which is proportional to the inverse perturbation strength. This behavior is reminiscent of the quantum SYK models and strange metals.

Chaotic Dynamics (nlin.CD)↗
DOE OSTI2012

Statistical hadronization with exclusive channels in e + e - annihilation

We present a systematic analysis of exclusive hadronic channels in e + e - collisions at centre-of-mass energies between 2.1 and 2.6 GeV within the statistical hadronization model. Because of the low multiplicities involved, calculations have been carried out in the full microcanonical ensemble, including conservation of energy-momentum, angular momentum, parity, isospin, and all relevant charges. We show that the data is in an overall good agreement with the model for an energy density of about 0.5 GeV/fm 3 and an extra strangeness suppression parameter γ S 0:7, essentially the same values found with fits to inclusive multiplicities at higher energy.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2022

Searching for the QCD Critical Point Along the Pseudo-critical/Freeze-out Line Using Padé-resummed Taylor Expansions of Cumulants of Conserved Charge Fluctuations

Using high-statistics datasets generated in (2+1)-flavor QCD calculations at finite temperature we construct estimators for the radius of convergence from an eighth order series expansion of the pressure as well as the number density. We show that the estimator for pressure and number density will be identical in the asymptotic limit. In the vicinity of the pseudo-critical temperature, T pc ≃ 156.5 MeV, we find the estimator of the radius of convergence to be µ B /T ≳ 3 for strangeness-neutral matter. We also present results for the pole structure of the Pad´e approximants for the pressure at non-zero values of the baryon chemical potential and show that the pole structure of the [4,4] Pad´e is consistent with not having a critical point at temperatures larger than 135 MeV and a baryon chemical potential smaller than µ B /T ~ 2.5.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2014

Spectroscopic Research of Lambda Hypdernuclei at JLab Hall C

A Lambda hyperon which has a strangeness can be bound in deep inside of a nucleus since a Λ does not suffer from the Pauli exclusion principle from nucleons. Thus, a Λ could be a useful tool to investigate inside of a nucleus. Since 2000, Lambda hypernuclear spectroscopic experiments by the (e,e'k) reaction have been performed at the experimental hall C in Thomas Jefferson National Accelerator Facility (JLab Hall C). An experiment, JLab E05-115 was carried out to investigate Lambda hypernuclei with a wide mass range (the mass number, A = 7, 9, 10, 12, 52). The latest analysis status of JLab E05-115 experiment is discussed in the present article.

Gogami, Toshiyuki↗
DOE OSTI2021

Intertwined States at Finite Temperatures in the Hubbard Model

We report significant advances in numerical techniques have enabled recent breakthroughs in the study of various properties of the Hubbard model - a seemingly simple, yet complex model of correlated electrons that has been a focus of study for more than half a century. In particular, it captures the essence of strong correlations, and is believed to possess various emergent, low energy states and collective excitations characteristic of cuprate high-temperature superconducting materials. While a thorough review of all activity is not possible here, we have focused the discussion on our recent work using unbiased, numerically exact, “brute force”, finite temperature quantum Monte Carlo methods. Our various studies reveal a rich variety of quantum liquid crystal phases, and complementary transport properties, which answer some questions, but certainly raise others concerning “strange metal” behavior and the ultimate fate of quasiparticles in the Hubbard model.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1962

EFFECT OF STERILIZATION IN SPACECRAFT DESIGN

Modern spacecraft design no longer involves only the Engineering Sciences. To get "the bugs" out of a system must now be taken literally to signify eradication of actual free-living microorganisms. A severe impact of a non-sterilized space vehicle could result in overt, reckless contamination, virtually eliminating a celestial body as a scientific base for the exobiological phases of space exploration. Recognizing the potentially damaging effects of septic launches, the National Aeronautics and Space Administration in December, 1960 authorized spacecraft sterilization and decontamination as National policy, thereby elevating the space effort onto a higher scientific plane. In the NASA directive, the basic reasons for sterilization were established, viz., "to preserve clues to the origin of life and of the universe, which may be hidden beneath the lunar strata or under the atmospheres of strange planets, to prevent inadvertent seeding of extraterrestrial surfaces by earth-life cultures, and to protect the earth from mutual contamination." In light of the foregoing, spacecraft sterilization should be regarded as the most significant single mission as well as design requirement of planetary space exploration --- especially if our objectives are primarily scientific.

Ranger project↗
NASA NTRS1962

LOW-ALTITUDE REPEATER SATELLITES

The new perspective that is forced upon us by the Space Age is oddly evident in the title of this paper. The key adjective is "low-altitude," evoking, perhaps, a picture of objects flying just above the rooftops. In the strange new realm of space, however, we are using a different order of measurement. The low-altitude satellites that I shall discuss will be moving in orbits anywhere from a few hundred to more than ten thousand miles above the Earth.

Low altitude↗
NASA NTRS1976

Spectrum of carbonaceous-chondrite fission xenon

Estimations of the fission spectrum in xenon isotopes from the progenitor of the strange carbonaceous-chondrite xenon must take account of p-process nucleosynthesis if the latter is the source of anomalous Xe-124, 126. Sample calculations of the p-process yields illustrate the magnitude of the effect, which can greatly increase the estimated Xe-132 fission yield.

Clayton, D. D.↗
NASA NTRS1977

Skylab 2 crew observations and summary

Signs and symptoms experienced during weightlessness ranged from a sensation of fullness in the head to a strange body posture and the sensation of fluid drainage out of the legs. There was no vestibular sense of the upright whatsoever unless the crewmember happened to look at the earth; motion sickness was not a clinical problem. The ability to maintain physical fitness through exercise and the caloric demand remained just about the same as they do on the ground after initial adjustment.

Kerwin, J. P.↗
NASA NTRS1978

Infrared radiation of Venusian clouds

The thermal infrared emission of Venus measured by Venera-9 and Venera-10 is analyzed. The emission of the night side corresponds to a brightness temperature of 244 K. The brightest temperature of the day side is 233-234 K. The extent of the upper layer of clouds, in which the thermal emission is formed, is 4-6 km. The altitude of the emitting layer above the surface of the planet (64-67 km) is determined from the brightness temperature and the existing models of the atmosphere of Venus. In some cases, correlation is noted between the inhomogeneity and the details of the ultraviolet image. The day side temperatures strangely coincide with the freezing point of sulfuric acid at a concentration of 66-77%.

Ksanfomaliti, L. V.↗
NASA NTRS1980

Strouhal number influence on flight effects on jet noise radiated from convecting quadrupoles

The paper reports a complementary extension of previous work to include the high-frequency features reflected in the discussion of the higher Strouhal number influence on flight effects. It is found that, in addition to the usual features of flight effects on noise from ordinary flows, the high Strouhal number flows exhibit some more interesting features which are uniquely characteristic to them. The additional features are as follows: (1) Flight effects are more favorable to hot jets than to cold jets; (2) the higher the Strouhal number of the jet flow, the lesser the forward arc amplification due to flight; (3) as the Strouhal number increases, the peak amplification angle in the forward quadrant and the peak suppression angle in the aft quadrant move toward 90 deg and get closer, thus reducing the amplification exposure to a constricted angular region; (4) the silence zone is disturbed and displaced from its normal position parallel to the jet flow to give rise to multiple crossings of flight curves with the static line; and (5) the occurrence of multiple crossings is a strange phenomenon solely characteristic of high Strouhal number with high subcritical jet flows in flight.

Dash, R.↗
NASA NTRS1980

The geology and morphology of Ina

The lunar feature Ina, an unusual D-shaped depression, is located in Lacus Felicitatis north of Mare Vaporum. Attention was drawn to the feature because of its strange 'blistered' appearance. Using detailed topographic data available from the Lunar Topographic Orthophotomap (LTO) series, it is now possible to depict the morphology and structure of Ina and the surrounding region more accurately than was previously feasible. The maps employed in the study are 41C3 and 41C4 at 1:250,000 scale, and 41C3S1 (Ina) at 1:10,000 scale. Attention is given to the regional setting, and the morphologic characteristics and origins of features. It is concluded that Ina is an apparently unique volcanic feature. It rests on a dome displaying evidence of episodic extrusive activity. Its odd D-shape is probably related to a local fracture pattern, since the straight edge is aligned with other small lineaments in the area. Ina's floor exhibits several volcanic units.

Strain, P. L.↗
NASA NTRS1982

Internal stresses in Phobos and other triaxial bodies

The unusual dynamical behavior of Phobos, its strange appearance, and its mysterious network of grooves all make it an intriguing object. Geophysical studies, though, have been hampered by the lack of suitable theories applicable to nonspherical bodies. In this paper the Martian satellites are modeled as homogeneous, elastic triaxial ellipsoids subject to tidal, rotational, and self-gravitational stresses. A novel semianalytical treatment then gives the stress and strain fields throughout their interiors. Yield phenomena and their possible surface expressions are also investigated. The results indicate that Phobos and Deimos have always been stable with respect to tidal fracture or disruption, but that Phobos will probably break up before colliding with Mars. Applications of the new formulation to other nonspherical bodies in the solar system are also discussed.

Dobrovolskis, A. R.↗
NASA NTRS1984

Nonlinear problems in flight dynamics

A comprehensive framework is proposed for the description and analysis of nonlinear problems in flight dynamics. Emphasis is placed on the aerodynamic component as the major source of nonlinearities in the flight dynamic system. Four aerodynamic flows are examined to illustrate the richness and regularity of the flow structures and the nature of the flow structures and the nature of the resulting nonlinear aerodynamic forces and moments. A framework to facilitate the study of the aerodynamic system is proposed having parallel observational and mathematical components. The observational component, structure is described in the language of topology. Changes in flow structure are described via bifurcation theory. Chaos or turbulence is related to the analogous chaotic behavior of nonlinear dynamical systems characterized by the existence of strange attractors having fractal dimensionality. Scales of the flow are considered in the light of ideas from group theory. Several one and two degree of freedom dynamical systems with various mathematical models of the nonlinear aerodynamic forces and moments are examined to illustrate the resulting types of dynamical behavior. The mathematical ideas that proved useful in the description of fluid flows are shown to be similarly useful in the description of flight dynamic behavior.

Chapman, G. T.↗
NASA NTRS1985

Observations, theoretical ideas and modeling of turbulent flows: Past, present and future

Turbulence was analyzed in a historical context featuring the interactions between observations, theoretical ideas, and modeling within three successive movements. These are identified as predominantly statistical, structural and deterministic. The statistical movement is criticized for its failure to deal with the structural elements observed in turbulent flows. The structural movement is criticized for its failure to embody observed structural elements within a formal theory. The deterministic movement is described as having the potential of overcoming these deficiencies by allowing structural elements to exhibit chaotic behavior that is nevertheless embodied within a theory. Four major ideas of this movement are described: bifurcation theory, strange attractors, fractals, and the renormalization group. A framework for the future study of turbulent flows is proposed, based on the premises of the deterministic movement.

Chapman, G. T.↗