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At least 1,567 records · Page 87
All sourcesNASA NTRSDOE OSTI
DOE OSTI2011

FORMATION OF PEPTIDE BONDS IN SPACE: A COMPREHENSIVE STUDY OF FORMAMIDE AND ACETAMIDE IN Sgr B2(N)

Extensive observations of acetamide (CH{sub 3}CONH{sub 2}) and formamide (NH{sub 2}CHO) have been conducted toward Sgr B2(N) at 1, 2, and 3 mm using the Submillimeter Telescope (SMT) and the 12 m antenna of the Arizona Radio Observatory. Over the frequency range 65-280 GHz, 132 transitions of acetamide have been observed as individual, distinguishable features, although in some cases they are partially blended. The unblended transitions in acetamide indicate V{sub LSR} = 63.2 {+-} 2.8 km s{sup -1} and {Delta}V{sub 1/2} = 12.5 {+-} 2.9 km s{sup -1}, line parameters that are very similar to that of formamide (NH{sub 2}CHO) and other organic species in Sgr B2(N). For formamide, 79 individual transitions were identified over the same frequency region. Rotational diagram analyses indicate the presence of two components for both species in Sgr B2(N). For acetamide, the colder component (E{sub u} < 40 K) exhibits a rotational temperature of T{sub rot} = 17 {+-} 4 K and a column density of N{sub tot} = 5.2 {+-} 3.5 Multiplication-Sign 10{sup 13} cm{sup -2}; the higher energy component has T{sub rot} = 171 {+-} 4 K and N{sub tot} = 6.4 {+-} 4.7 Multiplication-Sign 10{sup 14} cm{sup -2}. In the case of formamide, T{sub rot} = 26 {+-} 4 K and N{sub tot} = 1.6 {+-} 0.7 Multiplication-Sign 10{sup 14} cm{sup -2} for the colder component with T{sub rot} = 134 {+-} 17 K and N{sub tot} = 4.0 {+-} 1.2 Multiplication-Sign 10{sup 14} cm{sup -2} for the warmer region. The fractional abundances of acetamide are f (H{sub 2}) = 1.7 Multiplication-Sign 10{sup -11} and 2.1 Multiplication-Sign 10{sup -10} for the cold and warm components, and in formamide, f (H{sub 2}) = 5.3 Multiplication-Sign 10{sup -11} and 1.3 Multiplication-Sign 10{sup -10}. The similarity between the abundances and distributions of CH{sub 3}CONH{sub 2} and NH{sub 2}CHO suggests a synthetic connection. The abundance of acetamide, moreover, is only a factor of three lower than that of formaldehyde, and very similar to acetaldehyde and ketene. CH{sub 3}CONH{sub 2} is therefore one of the most abundant complex organic species in Sgr B2(N), and could be a possible source of larger peptide molecules, as opposed to amino acids.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1978

Radar backscatter from the ocean - Dependence on surface friction velocity

From the mid 1960s to the present, the normalized radar cross-section (NRCS) of the ocean has been measured using airborne radars operating over a frequency range of 0.4 to 14 GHz. Analyses of these data have shown that the NRCS was proportional to the ocean surface wind speed raised to some power, but the values of the exponent remained in dispute. This paper extends previous work and uses these NRCS measurements to demonstrate that to the first order, the NRCS is a function of only the friction velocity at the ocean's surface. Further analyses characterize the dependence of the NRCS on radar variables such as frequency, incidence angle, polarization, etc. Finally, recommendations are made for using Ku-band radars at large incidence angles for remote sensing of the wind friction velocity vector.

Jones, W. L.↗
NASA NTRS2021

Springer Handbook of Atmospheric Measurements: Chapter 39: Airborne Radar

Ground-based radar systems have been used to observe clouds and precipitation since the 1940s. While weather radars that use centimeter waves can observe precipitation several hundred kilometers away, radars that are dedicated to cloud observations use millimeter waves and have limited ranges of just a few tens of kilometers. Airborne radars have the advantages that they can perform measurements close to the region of interest and they provide radar information on regions that ground-based radars cannot access. There is no such thing as a standard airborne radar system; all systems are tailored for use on specific research aircraft, although some of them are designed to be modular so that they can be mounted on various aircraft. Airborne radar systems use frequencies ranging from those in the X band to those in the W band. Radars that use shorter wavelengths are preferred due to spatial restrictions on antenna size in aircraft, but C-band systems are also being considered for installation in large aircraft. Besides reflectivity (the backscatter signal), the radial motions of scattering particles can be measured and used to retrieve atmospheric motion. In addition, several airborne radars are able to measure dual-polarization backscatter signals that can be employed to identify different types of hydrometeors.

Martin Hagen↗
DOE OSTI2016

Optical properties of A Fe 2 As 2 ( A = Ca , Sr, and Ba) single crystals

The detailed optical properties have been determined for the iron-based materials A Fe 2 As 2 , where A = Ca , Sr, and Ba, for light polarized in the iron-arsenic (a-b) planes over a wide frequency range, above and below the magnetic and structural transitions at T N = 138 , 195, and 172 K, respectively. The real and imaginary parts of the complex conductivity are fit simultaneously using two Drude terms in combination with a series of oscillators. Above T N , the free-carrier response consists of a weak, narrow Drude term, and a strong, broad Drude term, both of which show only a weak temperature dependence. Below T N there is a slight decrease of the plasma frequency but a dramatic drop in the scattering rate for the narrow Drude term, and for the broad Drude term there is a significant decrease in the plasma frequency, while the decrease in the scattering rate, albeit significant, is not as severe. The small values observed for the scattering rates for the narrow Drude term for T $\ll$ T N may be related to the Dirac conelike dispersion of the electronic bands. Below T N new features emerge in the optical conductivity that are associated with the reconstruction Fermi surface and the gapping of bands at Δ 1 ≃ 45 – 80 meV, and Δ 2 ≃ 110 – 210 meV. In conclusion, the reduction in the spectral weight associated with the free carriers is captured by the gap structure; specifically, the spectral weight from the narrow Drude term appears to be transferred into the low-energy gap feature, while the missing weight from the broad term shifts to the high-energy gap.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Production of Ba(Zn{sub 1/3}Nb{sub 2/3})O{sub 3} ceramic by coprecipitation

A simple coprecipitation technique was successfully applied for the preparation of pure, nanosized, single phase Ba(Zn{sub 1/3}Nb{sub 2/3})O{sub 3} microwave dielectric ceramic powders. Barium, zinc and niobium ions were precipitated as hydroxide under basic conditions using aqueous sodium hydroxide solution and single phase Ba(Zn{sub 1/3}Nb{sub 2/3})O{sub 3} ceramic was produced at 800 Degree-Sign C. TEM revealed an average particle size of around 100 nm for the calcined powders. The samples sintered at 1250 Degree-Sign C for 4 h had a relatively high density and fine grain sizes. While the dielectric constant of ceramics varied between 37.5 and 39.8 the dielectric losses were lower than 4 Multiplication-Sign 10{sup -3} at frequency range of 1 kHz-2 MHz between 20 and 200 Degree-Sign C. - Highlights: Black-Right-Pointing-Pointer Production of BZN by coprecipitation. Black-Right-Pointing-Pointer Nanoscale BZN powder. Black-Right-Pointing-Pointer Dielectric properties of BZN.

36 MATERIALS SCIENCE↗
DOE OSTI2015

INERTIAL RANGE TURBULENCE OF FAST AND SLOW SOLAR WIND AT 0.72 AU AND SOLAR MINIMUM

We investigate Venus Express observations of magnetic field fluctuations performed systematically in the solar wind at 0.72 Astronomical Units (AU), between 2007 and 2009, during the deep minimum of solar cycle 24. The power spectral densities (PSDs) of the magnetic field components have been computed for time intervals that satisfy the data integrity criteria and have been grouped according to the type of wind, fast and slow, defined for speeds larger and smaller, respectively, than 450 km s{sup −1}. The PSDs show higher levels of power for the fast wind than for the slow. The spectral slopes estimated for all PSDs in the frequency range 0.005–0.1 Hz exhibit a normal distribution. The average value of the trace of the spectral matrix is −1.60 for fast solar wind and −1.65 for slow wind. Compared to the corresponding average slopes at 1 AU, the PSDs are shallower at 0.72 AU for slow wind conditions suggesting a steepening of the solar wind spectra between Venus and Earth. No significant time variation trend is observed for the spectral behavior of both the slow and fast wind.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Axisymmetric global Alfvén eigenmodes within the ellipticity-induced frequency gap in the Joint European Torus

Alfvén eigenmodes (AEs) with toroidal mode number n = 0 (i.e., axisymmetric) have been observed in the ellipticity-induced frequency range in the Joint European Torus. The axisymmetric modes are of interest because they can be used to diagnose fast particle energy distributions at the mode location. The modes were identified here as global Alfvén eigenmodes (GAEs), with the ellipticity of the plasma cross-section preventing strong continuum damping of the modes. The MHD codes CSCAS, MISHKA, and AEGIS were used to compute the n = 0 Alfvén continuum, eigenmode structure, and continuum damping. For zero ellipticity, a single mode exists at a frequency below the Alfvén continuum branch. This mode has two dominant poloidal harmonics with poloidal mode numbers m = ±1 that have the same polarity; therefore, it is an even mode. For finite ellipticity, the continuum branch splits into two branches and the single GAE splits into two modes. An even mode exists below the minimum of the top continuum branch, and the frequency of this mode coincides with the experimentally observed AE frequency. The other mode is found below the lower continuum branch with opposite signs between the two poloidal harmonics (an odd mode structure). This mode was not excited in our experiment. Analytical theory for the n = 0 GAE in an elliptical cylinder shows the n = 0 Alfvén continuum agrees with the numerical modelling.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1989

High-frequency electrostatic waves near earth's bow shock

Electrostatic wave measurements from the Active Magnetospheric Particle Tracer Explorer Ion Release Module have been used to investigate the wave modes and their possible generation mechanisms in the earth's bow shock and magnetosheath. It is demonstrated that electrostatic waves are present in the bow shock and magnetosheath with frequencies above the maximum frequency for Doppler-shifted ion acoustic waves, yet below the plasma frequency. Waves in this frequency range are tentatively identified as electron beam mode waves. Data from 45 bow shock crossings are then used to investigate possible correlations between the electrostatic wave properties and the near-shock plasma parameters. The most significant relationships found are anticorrelations with Alfven Mach number and electron beta. Mechanisms which might produce electron beams in the shock and magnetosheath are discussed in terms of the correlation study results. These mechanisms include acceleration by the cross-shock electric field and by lower hybrid frequency waves. A magnetosheath 'time of flight' mechanism, in analogy to the electron foreshock region, is introduced as another possible beam generation mechanism.

Onsager, T. G.↗
NASA NTRS1991

Analysis of airframe/engine interactions in integrated flight and propulsion control

An analysis framework for the assessment of dynamic cross-coupling between airframe and engine systems from the perspective of integrated flight/propulsion control is presented. This analysis involves to determining the significance of the interactions with respect to deterioration in stability robustness and performance, as well as critical frequency ranges where problems may occur due to these interactions. The analysis illustrated here investigates both the airframe's effects on the engine control loops and the engine's effects on the airframe control loops in two case studies. The second case study involves a multi-input/multi-output analysis of the airframe. Sensitivity studies are performed on critical interactions to examine the degradations in the system's stability robustness and performance. Magnitudes of the interactions required to cause instabilities, as well as the frequencies at which the instabilities occur are recorded. Finally, the analysis framework is expanded to include control laws which contain cross-feeds between the airframe and engine systems.

Schierman, John D.↗
NASA NTRS1994

Energy transfer between energetic ring current H(+) and O(+) by electromagnetic ion cyclotron waves

Electromagnetic ion cyclotron (EMIC) waves in the frequency range below the helium gyrofrequency can be excited in the equatorial region of the outer magnetosphere by cyclotron resonant instability with anisotropic ring current H(+) ions. As the unducted waves propagate to higher latitudes, the wave normal should become highly inclined to the ambient magnetic field. Under such conditions, wave energy can be absorbed by cyclotron resonant interactions with ambient O(+), leading to ion heating perpendicular to the ambient magnetic field. Resonant wave absorption peaks in the vicinity of the bi-ion frequency and the second harmonic of the O(+) gyrofrequrency. This absorption should mainly occur at latitudes between 10 deg and 30 deg along auroral field lines (L is greater than or equal to 7) in the postnoon sector. The concomitant ion heating perpendicular to the ambient magnetic field can contribute to the isotropization and geomagnetic trapping of collapsed O(+) ion conics (or beams) that originate from a low-altitude ionospheric source region. During geomagnetic storms when the O(+) content of the magnetosphere is significantly enhanced, the absorption of EMIC waves should become more efficient, and it may contribute to the observed acceleration of O(+) ions of ionospheric origin up to ring current energies.

Thorne, Richard M.↗
NASA NTRS2013

Low Noise Amplifiers for 140 Ghz Wide-Band Cryogenic Receivers

We report S-parameter and noise measurements for three different Indium Phosphide 35-nanometer-gate-length High Electron Mobility Transistor (HEMT) Low Noise Amplifier (LNA) designs operating in the frequency range centered on 140 gigahertz. When packaged in a Waveguide Rectangular-6.1 waveguide housing, the LNAs have an average measured noise figure of 3.0 decibels - 3.6 decibels over the 122-170 gigahertz band. One LNA was cooled to 20 degrees Kelvin and a record low noise temperature of 46 Kelvin, or 0.64 decibels noise figure, was measured at 152 gigahertz. These amplifiers can be used to develop receivers for instruments that operate in the 130-170 gigahertz atmospheric window, which is an important frequency band for ground-based astronomy and millimeter-wave imaging applications.

High Electron Mobility Transistors (HEMTs)↗
DOE OSTI2017

The Detectability of Radio Auroral Emission from Proxima b

Magnetically active stars possess stellar winds whose interactions with planetary magnetic fields produce radio auroral emission. We examine the detectability of radio auroral emission from Proxima b, the closest known exosolar planet orbiting our nearest neighboring star, Proxima Centauri. Using the radiometric Bode’s law, we estimate the radio flux produced by the interaction of Proxima Centauri’s stellar wind and Proxima b’s magnetosphere for different planetary magnetic field strengths. For plausible planetary masses, Proxima b could produce radio fluxes of 100 mJy or more in a frequency range of 0.02–3 MHz for planetary magnetic field strengths of 0.007–1 G. According to recent MHD models that vary the orbital parameters of the system, this emission is expected to be highly variable. This variability is due to large fluctuations in the size of Proxima b’s magnetosphere as it crosses the equatorial streamer regions of dense stellar wind and high dynamic pressure. Using the MHD model of Garraffo et al. for the variation of the magnetosphere radius during the orbit, we estimate that the observed radio flux can vary nearly by an order of magnitude over the 11.2-day period of Proxima b. The detailed amplitude variation depends on the stellar wind, orbital, and planetary magnetic field parameters. We discuss observing strategies for proposed future space-based observatories to reach frequencies below the ionospheric cutoff (∼10 MHz), which would be required to detect the signal we investigate.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Battery inverter experimental data

The increase in power electronic based generation sources require accurate modeling of inverters. Accurate modeling requires experimental data over wider operation range. We used 30 kW off-the-shelf grid following battery inverter in the experiments. We used controllable AC supply and controllable DC supply to emulate AC and DC side characteristics. The experiments were performed at NREL's Energy Systems Integration Facility. Inverter is tested under 100%, 75%, 50%, 25% load conditions. In the first dataset, for each operating condition, controllable AC source voltage is varied from 0.9 to 1.1 per unit (p.u) with a step value of 0.025 p.u while keeping the frequency at 60 Hz. In the second dataset, under similar load conditions (100%, 75%, 50%, 25% ), the frequency of the controllable AC source voltage was varied from 59 Hz to 61 Hz with a step value of 0.2 Hz. Voltage and frequency range is chosen based on inverter protection. Voltages and currents on DC and AC side are included in the dataset.

24 POWER TRANSMISSION AND DISTRIBUTION↗
NASA NTRS1988

Leading edge vortex dynamics on a pitching delta wing

The leading edge flow structure was investigated on a 70 deg flat plate delta wing which was pitched about its 1/2 chord position, to increase understanding of the high angle of attack aerodynamics on an unsteady delta wing. The wing was sinusoidally pitched at reduced frequencies ranging from k being identical with 2pi fc/u = 0.05 to 0.30 at chord Reynolds numbers between 90,000 and 350,000, for angle of attack ranges of alpha = 29 to 39 deg and alpha = 0 to 45 deg. The wing was also impulsively pitched at an approximate rate of 0.7 rad/s. During these dynamic motions, visualization of the leading edge vorticies was obtained by entraining titanium tetrachloride into the flow at the model apex. The location of vortex breakdown was recorded using 16mm high speed motion picture photography. When the wing was sinusoidally pitched, a hysteresis was observed in the location of breakdown position. This hysteresis increased with reduced frequency. The velocity of breakdown propagation along the wing, and the phase lag between model motion and breakdown location were also determined. When the wing was impulsively pitched, several convective times were required for the vortex flow to reach a steady state. Detailed information was also obtained on the oscillation of breakdown position in both static and dynamic cases.

Lemay, Scott P.↗
DOE OSTI2024

Validation of a Tapered Impact Damper for Traffic Signal Structure Vibrations Using the Method of Harmonic Balance

Significant vibration amplitudes and cycles can be produced when traffic signal structures with low inherent damping are excited near one of their natural frequencies. For the mitigation of wind-induced vibrations, dynamic vibration absorbers coupled to the structure are often used. Here, this research investigates the performance of a tapered impact damper, consisting of a hanging spring-mass oscillator inside a housing capable of reducing vibration amplitude over a broader frequency range than the conventional tuned mass damper. A nonlinear, two degree-of-freedom model is developed with coordinates representing the traffic structure and the tapered impact damper. This research focuses on the application of the harmonic balance method to approximate the periodic solutions of the nonlinear equations to compute the nonlinear dynamics of the damped traffic signal structure. After designing and manufacturing a tapered impact damper, the traffic signal structure is tested with and without the damper using free vibration snapback tests. The experimental frequency and damping backbone curves are used to validate the analytical model, and the effectiveness of the damper is discussed.

42 ENGINEERING↗
DOE OSTI2012

Electromagnetic and microwave-absorbing properties of magnetite decorated multiwalled carbon nanotubes prepared with poly(N-vinyl-2-pyrrolidone)

Graphical abstract: The Fe{sub 3}O{sub 4}/MWNTs hybrids prepared with PVP achieve a maximum reflection loss is -35.8 dB at 8.56 GHz, and the bandwidth below -10 dB is more than 2.32 GHz. More importantly, a new reflection loss peak occurs at the frequency of 14.6 GHz, which indicates that the Fe{sub 3}O{sub 4}/MWNTs hybrids have better absorption properties in the high-frequency range. Highlight: Black-Right-Pointing-Pointer The Fe{sub 3}O{sub 4} decorated MWNTs hybrids were prepared using PVP as dispersant. Black-Right-Pointing-Pointer Many more Fe{sub 3}O{sub 4} particles were attached homogeneously on the surface of MWNTs. Black-Right-Pointing-Pointer The Fe{sub 3}O{sub 4}/MWNTs hybrids achieve a maximum reflection loss of -35.8 dB at 8.56 GHz. Black-Right-Pointing-Pointer A new reflection loss peak occurs at the high-frequency of 14.6 GHz. -- Abstract: The magnetite (Fe{sub 3}O{sub 4}) decorated multiwalled carbon nanotubes (MWNTs) hybrids were prepared by an in situ chemical precipitation method using poly(N-vinyl-2-pyrrolidone) (PVP) as dispersant. The structure and morphology of hybrids are characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and transmission electron-microscopy (TEM). The TEM investigation shows that the Fe{sub 3}O{sub 4}/MWNTs hybrids exhibit less entangled structure and many more Fe{sub 3}O{sub 4} particles are attached homogeneously on the surface of MWNTs, which indicated that PVP can indeed help MWNTs to disperse in isolated form. The electromagnetic and absorbing properties were investigated in a frequency of 2-18 GHz. The results show that the Fe{sub 3}O{sub 4}/MWNTs hybrids exhibit a superparamagnetic behavior and possess a saturation magnetization of 22.9 emu/g. The maximum reflection loss is -35.8 dB at 8.56 GHz, and the bandwidth below -10 dB is more than 2.32 GHz. More importantly, a new reflection loss peak occurs at the frequency of 14.6 GHz, which indicates that the Fe{sub 3}O{sub 4}/MWNTs hybrids have better absorption properties in the high-frequency.

36 MATERIALS SCIENCE↗
DOE OSTI2019

A THz driven split-ring resonator based ultrafast relativistic electron streak camera

The use of sub-wavelength metal structures to locally enhance high frequency electromagnetic fields, generally known as plasmonics, enables breakthrough opportunities across diverse fields of research such as nonlinear optics, biosensing, photovoltaics and others. Here we study the application of sub-wavelength metallic resonators tuned in the THz frequency range for manipulation and diagnostics of relativistic electron beams. In this work, we report on the use of a double-sided split-ring structure driven by a near single cycle THz field generated by optical rectification to impart a time-dependent angular deviation (streak) on a 4.5 MeV electron beam. Electrons passing through the small gap reveal field enhancement factors larger than 10, in good agreement with finite difference time domain simulations. This work paves the way for further application of high frequency metallic structures in compact particle accelerators such as for THz-based relativistic electron streaking at fs and sub-fs temporal resolution.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1974

Observations of interplanetary plasma waves, spacecraft noise, and sheath phenomena on Imp 7

The Imp 7 plasma wave instrument measures electric and magnetic wave components of plasma oscillations over the frequency range from 10 Hz to 100 kHz. The instrumentation and relevant external characteristics of the spacecraft that appear to be responsible for some in-flight disturbance effects are briefly described. It is shown that as each one of the 16 solar panel flats rotates into shadow or sunlight, the array transients produce fluctuating magnetic fields that are detected on the magnetic loop mounted 3.4 m from the spacecraft. These transients occur 16 times per spin period, and the corresponding magnetic noise has a high frequency on the rapidly spinning Imp 7 spacecraft. The analysis suggests that some Imp magnetic threshold levels measured 3-4 m from the spacecraft are determined by the solar array current transient effects associated with the discrete 16-sided geometry of the spacecraft. The geometry also influences the response of the electric dipole antenna by modulating the sheath.

Scarf, F. L.↗