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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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Shock-wave sputtering of lead surface has been investigated. The dynamics of motion of particles has been determined by laser interferometric photon Doppler velocimetry (PDV) method, and their size has been calculated from the law of deceleration in a gaseous medium.
It is shown that a rapid deceleration of alpha particles in matter of electron temperature up to 100 keV leads a strong suppression of the chain nuclear fusion reaction on the basis of the p+{sup 11}B reaction with the reproduction of fast protons in the α+{sup 11}B and n+{sup 10}B reactions. The statement that the chain nuclear fusion reaction based on the p+{sup 11}B reaction with an acceleration of {sup 11}B nuclei because of elastic alpha-particle scattering manifests itself in experiments at the PALS (Prague Asterix Laser System) facility is analyzed.
Temporal reflection is a process where an optical pulse reflects off a moving boundary with different refractive indices across it. In a dispersive medium, this process creates a reflected pulse with a frequency shift that changes its speed. Such frequency shifts depend on the speed of the moving boundary. In this work, we propose and experimentally show that it is possible to probe the trajectory of the boundary by measuring the frequency shifts while changing the initial delay between the incident pulse and the boundary. We demonstrate this effect by reflecting a probe pulse off a short soliton, acting as a moving boundary that decelerates inside a photonic crystal fiber because of intrapulse Raman scattering. We deduce trajectory of the soliton from the measured spectral data for the reflected pulse.
This presentation describes cylindrical targets, which are designed with the laser package in xRAGE, and experiments will test code predictions for deceleration RTI.
The nature of dark energy can be probed by the derivative Q=dq(z)/dz|{sub 0} at redshift z = 0 of the deceleration parameter q(z). It is probably static if Q<1 or dynamic if Q>2.5, supporting ΛCDM or Λ=(1−q)H{sup 2}, respectively, where H denotes the Hubble parameter. We derive q=1−(4πa{sub 0}/cH){sup 2}, enabling a determination of q(z) by measuring Milgrom’s parameter, a{sub 0}(z), in galaxy rotation curves, equivalent to the coefficient A in the Tully–Fisher relation V{sub c}{sup 4}=AM{sub b} between a rotation velocity V {sub c} and a baryonic mass M {sub b}. We infer that dark matter should be extremely light, with clustering limited to the size of galaxy clusters. The associated transition radius to non-Newtonian gravity can conceivably be probed in a freefall Cavendish-type experiment in space.
We compile an updated list of 38 measurements of the Hubble parameter $H(z)$ between redshifts 0.07 $≤ z ≤$ 2.36 and use them to place constraints on model parameters of constant and time-varying dark energy cosmological models, both spatially flat and curved. We use five models to measure the redshift of the cosmological deceleration–acceleration transition, $z_{da}$, from these H(z) data. Within the error bars, the measured zda are insensitive to the model used, depending only on the value assumed for the Hubble constant $H_0$. The weighted mean of our measurements is $z_{da}$ = 0.72 ± 0.05 (0.84 ± 0.03) for $H_0$ = 68 ± 2.8 (73.24 ± 1.74) km s -1 Mpc -1 and should provide a reasonably model-independent estimate of this cosmological parameter. The H(z) data are consistent with the standard spatially flat ΛCDM cosmological model but do not rule out nonflat models or dynamical dark energy models.
We construct a complete collection of reliable Hubble parameter H(z) data to redshift z ≤ 2.36 and use them with the Gaussian Process approach to determine continuous H(z) functions for various data subsets. From these continuous H(z)'s, summarizing across the data subsets considered, we find H 0 ~ 67 ± 4 km s–1 Mpc–1, more consistent with the recent lower values observed using a variety of techniques. In most data subsets, we see a cosmological deceleration–acceleration transition at 2σ significance, with the data subsets transition redshifts varying over $0.33\lt {z}_{\mathrm{da}}\lt 1.0$ at 1σ significance. We discover that the flat-ΛCDM model is consistent with the H(z) data to a z of 1.5 to 2.0, depending on data subset considered, with 2σ deviations from flat-ΛCDM above this redshift range. Using the continuous H(z) with baryon acoustic oscillation distance-redshift observations, we constrain the current spatial curvature density parameter to be ${{\rm{\Omega }}}_{K0}=-0.03\pm 0.21$, consistent with a flat universe, but the large error bar does not rule out small values of spatial curvature that are now under debate.
While the extended main-sequence turnoffs (eMSTOs) found in almost all 1–2 Gyr old star clusters in the Magellanic Clouds are often explained by postulating extended star formation histories (SFHs), the tight subgiant branches (SGBs) seen in some clusters challenge this popular scenario. Puzzlingly, the SGB of the eMSTO cluster NGC 419 is significantly broader at bluer than at redder colors. We carefully assess and confirm the reality of this observational trend. If we would assume that the widths of the features in color–magnitude space were entirely owing to a range in stellar ages, the SFHs of the eMSTO stars and the blue SGB region would be significantly more prolonged than that of the red part of the SGB. This cannot be explained by assuming an internal age spread. We show that rotational deceleration of a population of rapidly rotating stars, a currently hotly debated alternative scenario, naturally explains the observed trend along the SGB. Our analysis shows that a “converging” SGB could be produced if the cluster is mostly composed of rapidly rotating stars that slow down over time owing to the conservation of angular momentum during their evolutionary expansion from main-sequence turnoff stars to red giants.
At a distance of about 4.22 ly, it would take about 100,000 years for humans to visit our closest stellar neighbor Proxima Centauri using modern chemical thrusters. New technologies are now being developed that involve high-power lasers firing at 1 gram solar sails in near-Earth orbits, accelerating them to 20% the speed of light ( c ) within minutes. Although such an interstellar probe could reach Proxima 20 years after launch, without propellant to slow it down it would traverse the system within hours. Here we demonstrate how the stellar photon pressures of the stellar triple α Cen A, B, and C (Proxima) can be used together with gravity assists to decelerate incoming solar sails from Earth. The maximum injection speed at α Cen A to park a sail with a mass-to-surface ratio ( σ ) similar to graphene (7.6 × 10{sup −4} gram m{sup −2}) in orbit around Proxima is about 13,800 km s{sup −1} (4.6% c ), implying travel times from Earth to α Cen A and B of about 95 years and another 46 years (with a residual velocity of 1280 km s{sup −1}) to Proxima. The size of such a low- σ sail required to carry a payload of 10 grams is about 10{sup 5} m{sup 2} = (316 m){sup 2}. Such a sail could use solar photons instead of an expensive laser system to gain interstellar velocities at departure. Photogravitational assists allow visits of three stellar systems and an Earth-sized potentially habitable planet in one shot, promising extremely high scientific yields.
Heat transfer and melting ablation about decelerating spherical bodies during planetary atmosphere entry
In operating a hoist to transport delicate or fragile components, an automatic stopping device is adjusted to impose a predetermined deceleration rate during stopping.
Analyzing emergency deceleration and descent of XB-70-1 airplane due to engine damage resulting from structural failure for supersonic transport data
Deceleration, aerodynamic heating and weight factors in feasibility study of hot air balloon recovery system for large boosters
Heat transfer and melting ablation about decelerating spherical bodies during planetary atmosphere entry
Adiabatic deceleration effect on cosmic ray spectrum, noting particle momentum and energy change, diffusion coefficient independent of energy, etc
Radar observations of meteor deceleration when encountering atmospheric drag
Drag generation theory, design, and drop tests for high altitude Stokes flow decelerator
Maximum drop diameters for atomization of liquid jets injected concurrently into accelerating or decelerating gas streams