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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
NASA NTRS2019

Universal Expansion with Spatially Varying G

We calculate the expansion of the Universe under the assumptions that G varies in space and the radial size r of the Universe is very large (we call this the MOND regime of varying-G gravity). The inferred asymptotic behaviour turns out to be different from that found by McCrea & Milne in 1934 and our equations bear no resemblance to those of the relativistic case. In this cosmology, the scale factor R(t) increases linearly with time t, the radial velocity is driven by inertia, and gravity is incapable of hindering the expansion. Yet, Hubble’s law is borne out without any additional assumptions. When we include a repulsive acceleration a(sub de) due to dark energy, the resulting universal expansion is then driven totally by this new term and the solutions for a(sub de) → 0 do not reduce to those of the a(sub de) ≡ 0 case. This is a realization of a new Thom catastrophe: The inclusion of the new term alters the conservation of energy and the dark energy solutions are not reducible to those in the case without dark energy.

Christodoulou, Dimitris M.↗
NASA NTRS1986

Galaxy distances and deviations from universal expansion; Proceedings of the NATO Advanced Research Workshop, Kona, HI, Jan. 13-17, 1986

A collection of papers on galaxy distances and deviations from universal expansion is presented. Individual topics addressed include: new results on the distance scale and the Hubble constant, Magellanic Clouds and the distance scale, CCD observations of Cepheids in nearby galaxies, distances using A supergiant stars, infrared calibration of the Cepheid distance scale, two stepping stones to the Hubble constant, physical models of supernovae and the distance scale, 21 cm line widths and distances of spiral galaxies, infrared color-luminosity relations for field galaxies, minimizing the scatter in the Tully-Fisher relation, photometry of galaxies and the local peculiar motion, elliptical galaxies and nonuniformities in the Hubble flow, and large-scale anisotropy in the Hubble flow. Also discussed are: improved distance indicator for elliptical galaxies, anisotropy of galaxies detected by IRAS, the local gravitational field, measurements of the CBR, measure of cosmological times, ages from nuclear cosmochronology, extragalactic gas at high redshift, supercluster infall models, Virgo infall and the mass density of the universe, dynamics of superclusters and Omega(0), distribution of galaxies versus dark matter, peculiar velocities and galaxy formation, cosmological shells and blast waves.

Madore, Barry F.↗
NASA NTRS2016

Pressurized Adapter for "Shirt-Sleeves" Transfer and Universal Base Expansion (PASSTUBE)

Proposed is a scalable, six-degree-of-freedom, pressurized docking adapter that can connect multiple volumes while resolving all forces within itself. In a large space outpost pass-through connection is needed between multiple volumes to maintain a continuous pressurized cabin for crew access, translation, and egress. Zero-g docking and berthing of elements can be done using robotic arms, thrusters, and simple docking interface hardware because orthogonal mating is only governed by position, orientation, and momentum, but soft capture / hard docking techniques would not work in a gravity environment because modules cannot be brought in square with each other. Gravity docking is problematic in that any two elements have a gravity vector and it is not practical to provide a perfectly flat surface for them to rest on. Any stretch of natural or graded terrain still has surface fluctuations - maneuvering one element in respect to another would constantly be working against a gravity vector, where uneven surfaces would cause modules to come to rest in odd configurations in respect to each other. Manipulation of heavy elements, such as habitats will be difficult to do with precision -- elements may be placed as close as the mobility system can handle but would still leave the elements not in square with each other. The proposed Pressurized Adapter for "Shirt-Sleeve" Transfer and Universal Base Expansion (PASSTUBE) element will connect non-square and skewed elements while resolving all forces internal to itself.

Howe, A. Scott↗
NASA NTRS1971

Qualitative cosmology - Diagrammatic solutions for Bianchi type IX universes with expansion, rotation, and shear. II.

The investigation of expanding, rotating, shearing Bianchi type IX universes is extended to the most general case possible. Use is made of the techniques of Arnowitt et al. (1962). It is shown that the conclusion reached by Arnowitt et al. regarding the small effect of rotation on the singularity of type IX universes is true in general. The superspace approach to the motion of the universe is discussed in an appendix.

Ryan, M. P., Jr.↗
NASA NTRS1989

Evolution of domain walls in the early universe

The evolution of domain walls in the early universe is studied via 2-D computer simulation. The walls are initially configured on a triangular lattice and then released from the lattice, their evolution driven by wall curvature and by the universal expansion. The walls attain an average velocity of about 0.3c and their surface area per volume (as measured in comoving coordinates) goes down with a slope of -1 with respect to conformal time, regardless of whether the universe is matter or radiation dominated. The additional influence of vacuum pressure causes the energy density to fall away from this slope and steepen, thus allowing a situation in which domain walls can constitute a significant portion of the energy density of the universe without provoking an unacceptably large perturbation upon the microwave background.

Kawano, Lawrence↗
DOE OSTI2025

Selection Effect in Dark Energy Survey Y1

The discovery that the Universe expansion is accelerated poses one of the most profound mysteries in physics. Cosmic acceleration could be a sign of the fact that General Relativity breaks down on cosmological scales and has to be replaced, or it could arise from an unknown form of energy that currently dominates our Universe. That is what we call dark energy and in this case the problem moves to the discovery of its nature. Dark Energy Survey aims to study the nature of dark energy and to test General Relativity and cosmological models. The cluster analysis of the first run of DES leads to results which are incomparable with what other surveys have obtained. In particular it turns out that the matter density of the Universe is $Ω_m = 0.179^{+0.031}_{−0.038}$, very different from the 0.3 value expected. In this work we build a procedure that can be followed in order to understand whether the solution of DES Y1 problem could be a selection effect or not.

43 PARTICLE ACCELERATORS↗
NASA NTRS1999

Simulation of Unsteady Hypersonic Combustion Around Projectiles in an Expansion Tube

The temporal evolution of combustion flowfields established by the interaction between wedge-shaped bodies and explosive hydrogen-oxygen-nitrogen mixtures accelerated to hypersonic speeds in an expansion tube is investigated. The analysis is carried out using a fully implicit, time-accurate, computational fluid dynamics code that we developed recently for solving the Navier-Stokes equations for a chemically reacting gas mixture. The numerical results are compared with experimental data from the Stanford University expansion tube for two different gas mixtures at Mach numbers of 4.2 and 5.2. The experimental work showed that flow unstart occurred for the Mach 4.2 cases. These results are reproduced by our numerical simulations and, more significantly, the causes for unstart are explained. For the Mach 5.2 mixtures, the experiments and numerical simulations both produced stable combustion. However, the computations indicate that in one case the experimental data were obtained during the transient phase of the flow; that is, before steady state had been attained.

Yungster, S.↗
NASA NTRS1979

The problems of cosmology

Three examples that illustrate the expected role of the Space Telescope in cosmological investigations are described addressing the distribution of globular star clusters, universe expansion, and other classical cosmological problems.

Peebles, P. J. E.↗
DOE OSTI2025

Isotropy of Hubble Expansion in the Early and Late Universe

We test the isotropy of Hubble expansion by combining several probes for the first time, constructing full-sky maps of expansion rate variation using Type Ia supernovae, fundamental plane galaxies, and cosmic microwave background (CMB) temperature fluctuations. We find no hint of anisotropy or correlation between early- and late-Universe expansion across all systematic models. The 99% confidence upper limits on expansion rate anisotropy are 0.39% for low-redshift supernovae, 0.95% for high-redshift CMB, and 0.37% when combined at a 60-degree smoothing scale. A significant anomaly in the fundamental plane residual map may reflect systematics in the current dark energy spectroscopic instrument dataset, as evidenced by the absence of cross-correlation with other tracers and its correlation with spatial density variations.

Zhou, Alan Junzhe [Chicago U.; Chicago U., KICP] (↗
NASA NTRS1972

Dissipative effects in the expansion of the universe. I, II.

Consideration of dissipative processes in anisotropic homogeneous world models, showing that dissipation reduces the anisotropy. The viscosity approximation and its range of applicability is discussed. Examples are presented which have been calculated by the use of a simple approximation to the collision-time method, using the cross section appropriate to weak interaction neutrino scattering. It is found that such dissipation is quite effective except for one particular cosmological model which is axisymmetric and in which the entire expansion of the model is taken up by expansion along the axis. A detailed multicomponent model is developed for dissipative processes in Euclidean homogeneous cosmological models. These processes involve neutrinos which might have long mean free times in interaction with other constituents which are thermalized by electromagnetic interactions, and whose weak interactions produce thermal neutrinos.

Matzner, R. A.↗
DOE OSTI2021

Evolution of decaying particles and decay products in various scenarios for the future expansion of the Universe

We examine nonrelativistic particles that decay into relativistic products in big rip, little rip, and pseudorip models for the future evolution of the Universe. In contrast to decays that occur in standard ΛCDM, the evolution of the ratio r of the energy density of the relativistic decay products to the energy density of the initially decaying particles can decrease with time in all of these models. In big rip and little rip models, r always goes to zero asymptotically, while this ratio evolves to infinity or a constant in pseudorip models.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2022

How slowly can the early Universe expand?

When the expansion of the Universe is dominated by a perfect fluid with equation of state parameter w and a sound speed c s satisfying w = $c^{2}_{s}$ ≤ 1 , the Hubble parameter H and time t satisfy the bound Ht ≥ 1/3 . There has been recent interest in “ultraslow” expansion laws with Ht <1/3 (sometimes described as “fast expanding” models). Here, we examine various models that can produce ultraslow expansion: scalar fields with negative potentials, barotropic fluids, braneworld models, or a loitering phase in the early Universe. Scalar field models and barotropic models for ultraslow expansion are unstable to evolution toward w = 1 or w → ∞ in the former case and w → ∞ in the latter case. Braneworld models can yield ultraslow expansion but require an expansion law beyond the standard Friedman equation. Loitering early universe models can produce a quasistatic expansion phase in the early Universe but require an exotic negative-density component. These results suggest that appeals to an ultraslow expansion phase in the early Universe should be approached with some caution, although the loitering early universe may be worthy of further investigation. These results do not apply to ultraslow contracting models.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

Snowmass2021 Cosmic Frontier White Paper: Future Gravitational-Wave Detector Facilities

The next generation of gravitational-wave observatories can explore a wide range of fundamental physics phenomena throughout the history of the universe. These phenomena include access to the universe's binary black hole population throughout cosmic time, to the universe's expansion history independent of the cosmic distance ladders, to stochastic gravitational-waves from early-universe phase transitions, to warped space-time in the strong-field and high-velocity limit, to the equation of state of nuclear matter at neutron star and post-merger densities, and to dark matter candidates through their interaction in extreme astrophysical environments or their interaction with the detector itself. We present the gravitational-wave detector concepts than can drive the future of gravitational-wave astrophysics. We summarize the status of the necessary technology, and the research needed to be able to build these observatories in the 2030s.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
NASA NTRS2005

National Aeronautics and Space Administration Training Grant Supplement

The following section summarizes the impact of the Ohio Space Grant Consortium (OSGC) in Ohio and to NASA over the last four-year period (February 1, 2001 to April 30, 2005) and highlights the important accomplishments of the consortium. The strength of the OSGC network of universities, community colleges, government agencies, industry, and outreach affiliates is well-established and is growing. The OSGC Consortium Management Structure was designed and remains committed to using the talents and diversity of everyone within this collaborative network, and operational policies and procedures are such that all consortium members are active contributors resulting in quality OSGC programs in research, education and service, while receiving a relatively small amount of NASA funds. The number of quality activities, both on- and off-campus, and collaborations/partnerships that OSGC has established with NASA and government agencies, state and local government, educational institutions, and private industry, has been impressive. Further desired university affiliate expansion requires additional funds. Diversity is shown in the OSGC 12-member Executive Committee by the presence of three campus representatives from Central State University, Wilberforce University, and The Ohio State University (two underrepresented minority, one female). One additional female campus representative (Cleveland State University) is currently on sabbatical leave and a valuable alternate member attends. Other additional female and underrepresented minority members are on the larger OSGC Advisory committee. All committee members participate fully in all consortium management and policy decisions. The OSGC Executive Committee strives to achieve and communicate a culture of trust, respect, teamwork, open communication, creativity, and empowerment. These programs have shown results and impact by their visibility and importance to Ohio and to NASA, resulting in strategic alliances created throughout Ohio. These alliances have improved over the last 4 years.

DeWitt, Kenneth J.↗
DOE OSTI2023

Systematic Study of Projection Biases in Weak Lensing Analysis

The nature of Dark Energy is possibly one of the most fundamental questions in Physics today. Comprising 70% of the energy density of the Universe, and being responsible for the accelerated expansion of the Universe, this mysterious form of energy with negative pressure is challenging our current understanding of the fundamental laws of nature. Cosmological parameters like total relative matter Density Ωm, the normalization of power spectrum σ8 and their combination S8 = σ8 p Ωm/0.3 are used to quantify our understanding of the evolution of the large-scale structure in the Universe and shed light on the accelerated expansion, caused by the Dark Energy, that started about halfway through the life of the Universe. Sky surveys, like Dark Energy Survey (DES), utilize weak lensing analysis to use the observations of galaxies and their shapes and extract these cosmological parameters. By doing an exhaustive study and quantifying the projection biases in the weak lensing statistics, the research work presented in this dissertation aims to contribute to the precise measurements of the cosmological parameters Ωm, σ8, and S8. For the analysis, we used the standard cosmological model that includes dark energy as the cosmological constant. And, we used the data taken by the DES experiment, which is one of the most complete, deep, and wide field surveys of the sky today.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2020

The First Three Seconds: a Review of Possible Expansion Histories of the Early Universe

It is commonly assumed that the energy density of the Universe was dominated by radiation between reheating after inflation and the onset of matter domination 54,000 years later. While the abundance of light elements indicates that the Universe was radiation dominated during Big Bang Nucleosynthesis (BBN), there is scant evidence that the Universe was radiation dominated prior to BBN. It is therefore possible that the cosmological history was more complicated, with deviations from the standard radiation domination during the earliest epochs. Indeed, several interesting proposals regarding various topics such as the generation of dark matter, matter-antimatter asymmetry, gravitational waves, primordial black holes, or microhalos during a nonstandard expansion phase have been recently made. In this paper, we review various possible causes and consequences of deviations from radiation domination in the early Universe - taking place either before or after BBN - and the constraints on them, as they have been discussed in the literature during the recent years.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2025

Measuring type Ia supernova angular-diameter distances with intensity interferometry

This paper investigates the potential of intensity interferometry, based on the Hanbury Brown-Twiss effect, for measuring supernova sizes and distances. With optimized telescope positioning, observing strategy, and advancements in single-photon detection technology, this method can provide precise angular size measurements of supernovae with apparent magnitudes as bright as 12 mag. For type Ia supernovae, this limiting brightness corresponds to a local volume extending to redshift z∼0.004 and an anticipated discovery rate of approximately 1 event per year. The combination of angular size data with known physical dimensions enables accurate distance determination. Multiple telescope pairs at different relative positions allow tomographic mapping of the ejecta structure while reducing distance uncertainties. As type Ia supernovae serve as standardizable candles for measuring the Universe’s expansion history, combining intensity interferometry distances with the supernova Hubble diagram facilitates measurements of the Hubble constant H0.

cosmological parameters↗