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Estimates of atomic concentration ionosphere from radar backscatter and rocket probe measurements of electron and ion temperatures and electron concentration
The principal objectives of the Smithsonian Astrophysical Observatory cold maser research programs are given. This work is aimed principally at understanding more about the interaction of hydrogen atoms with wall coatings of fluorinated ethylene propylene (Dupont Teflon FEP-120 co-polymer) and of carbon tetrafluoride (CE4). The principal measured quantity in these experiments is the wall shift of the maser's output frequency. The wall shift per atomic collision was calculated from the measured wall frequency shift. This assumes that the wall surface area is smooth on a molecular scale.
For this study, a femtosecond two-photon-absorption laser-induced-fluorescence (TALIF) diagnostic was designed, installed, and operated on the Princeton-Field-Reversed Configuration-2 device to provide non-invasive measurements of the time and spatially resolved neutral-atom densities in its plasmas. Calibration of the H o density was accomplished by comparison with Kr TALIF. Measurements on plasmas formed of either H 2 or Kr fill gases allowed examination of nominally long and short ionization mean-free-path regimes. With multi-kW plasma heating and H 2 fill gas, a spatially uniform H o density of order 10 17 m –3 was measured with better than ±2 mm and 10 µs resolution. Under similar plasma conditions but with Kr fill gas, a 3-fold decrease in the in-plasma Kr density was observed.
Atomic hydrogen (H) generated by atmospheric pressure radio frequency (RF) plasma jet is investigated by two-photon absorption laser induced fluorescence in a He-H 2 mixture. The reported time and spatially resolved H density profiles enable a detailed analysis of the species generation, transport and decay along the axis of symmetry of the jet. Here, the H density distribution for a continuous RF plasma jet corresponds well with the outcome of a Pseudo-1D plug flow model. In addition, RF power modulation has a strong effect on the H density in the active discharge region but has a negligible effect on the H density in the far effluent.
Frequency stability, tuning, coupling and tolerances of atomic hydrogen masers
Reactive oxygen species are one of the most important species produced in a plasma. In particular the role of atomic oxygen and the hydroxyl radical OH has attracted many studies ranging from plasma medicine to plasma-driven biocatalysis and water treatment. Atomic oxygen and the hydroxyl radical OH are very reactive and react unselectively with many different substrates. The quantification of atomic oxygen and OH is challenging because of their reactivity and unknown reactions and rate constants.
The J = 0 left arrow 1 fine-structure transition in atomic sulfur (S I) in its ground (3)P state has been detected in the laboratory by far-infrared laser magnetic resonance. The fine-structure interval has been measured accurately as 5,322,492.9 +/- 2.8 MHz which corresponds to a wavelength of 56.325572 +/- 0.000030 micrometers.
Simultaneous measurements of catalytic efficiency and atom concentration in hypersonic gas flow by self calibrating probes
It is proposed that the thermal velocity of a single atom could be measured in real time using a laser time-of-flight velocimeter (LTV) operating on the principle of laser resonance fluorescence. Theoretical data are presented for several atomic species that have resonances within the range of available dye-laser systems. It is shown that measurements in the subsonic region are certainly feasible. The atoms could be either in vacuum or in a buffer gas, e.g., at atmospheric pressure. Measurements in the transonic and supersonic region also appear possible. One potential application is the measurement of flow speeds in wind tunnels, perhaps as high as Mach 45.
This study introduces the integration of dynamic computer vision–enabled imaging with electron energy loss spectroscopy (EELS) in scanning transmission electron microscopy (STEM). This approach involves real-time discovery and analysis of atomic structures as they form, allowing us to observe the evolution of material properties at the atomic level, capturing transient states traditional techniques often miss. Rapid object detection and action system enhances the efficiency and accuracy of STEM-EELS by autonomously identifying and targeting only areas of interest. This machine learning (ML)–based approach differs from classical ML in that it must be executed on the fly, not using static data. We apply this technology to V-doped MoS 2 , uncovering insights into defect formation and evolution under electron beam exposure. This approach opens uncharted avenues for exploring and characterizing materials in dynamic states, offering a pathway to increase our understanding of dynamic phenomena in materials under thermal, chemical, and beam stimuli.
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Thermospheric atomic hydrogen concentration temporal variations in situ measurement by Explorer 32 satellite
It is noted that recently developed atomic hydrogen masers have achieved stability well into the 10 to the -16th domain for averaging time intervals beyond 1000 sec and that further improvements are in prospect. These devices are highly adaptable for space use in very high precision measurements of angle through Very Long Baseline Interferometry (VLBI) and of range and range-rate through Doppler techniques. Space missions that will use these clocks for measuring the sun's gravity field distribution and for testing gravitation and relativity (a project that will include a search for pulsed low-frequency gravitational waves) are discussed. Estimates are made of system performance capability, and the accuracy capability of relativistic measurements is evaluated in terms of the results from the 1976 NASA/SAO spaceborne clock test of the Einstein Equivalence Principle.
We present the Migdal In Galactic Dark mAtter expLoration (MIGDAL) experiment aiming at the unambiguous observation and study of the so-called Migdal effect induced by fast-neutron scattering. It is hoped that this elusive atomic process can be exploited to enhance the reach of direct dark matter search experiments to lower masses, but it is still lacking experimental confirmation. Our goal is to detect the predicted atomic electron emission which is thought to accompany nuclear scattering with low, but calculable, probability, by deploying an Optical Time Projection Chamber filled with a low-pressure gas based on CF 4 . Initially, pure CF 4 will be used, and then in mixtures containing other elements employed by leading dark matter search technologies — including noble species, plus Si and Ge. High resolution track images generated by a Gas Electron Multiplier stack, together with timing information from scintillation and ionisation readout, will be used for 3D reconstruction of the characteristic event topology expected for this process — an arrangement of two tracks sharing a common vertex, with one belonging to a Migdal electron and the other to a nuclear recoil. Different energy-loss rate distributions along both tracks will be used as a powerful discrimination tool against background events. In this article we present the design of the experiment, informed by extensive particle and track simulations and detailed estimations of signal and background rates. In pure CF 4 we expect to observe 8.9 (29.3) Migdal events per calendar day of exposure to an intense D–D (D–T) neutron generator beam at the NILE facility located at the Rutherford Appleton Laboratory (UK). With our nominal assumptions, 5σ median discovery significance can be achieved in under one day with either generator.
An apparatus for the study of differential angular scattering of atomic projectiles by gas targets is described. The design facilitates system alignment and provides for accurate reproducible location of components. The performance of the instrument is studied for scattering of H+ at 5-25 keV energies by helium and argon targets. Differential cross sections for elastic scattering and charge transfer are presented as well as total charge transfer cross sections. The coefficients for secondary electron ejection by impact of H and H+ on a metal surface are compared.
This publication contains written versions of most of the invited talks presented at the workshop on Atomic Data Needs for X-ray Astronomy which was held at NASA's Goddard Space Flight Center on December 16-1 7 1999. The idea of hosting such a workshop emerged from an imminent need to update and complete current atomic datasets in anticipation of a new era of high quality X-ray spectra starting with the launching of Chandra and XMM-Newton observatories. At first, our vision of the workshop was of a short and limited attendance event, given the specialization of the topic. But it, was soon realized, from the response to the first workshop announcement, that the topic was of much interest, to researchers working in X-ray spectra (physicists and astronomers). As a result, the workshop grew to approximately 120 participants from several countries. The kind of atomic data that interests us are those parameters needed for analysis and modeling of spectra shortward of about about 100 A and relevant to ionic species of astronomical interest. The physical mechanisms of interest in the formation of spectra include photoionization. collisional ionization, recombination (radiative and dielectronic). collisional excitation (by electrons and protons). and radiative deexcitation. Unique to X-ray spectroscopy are the ionization and excitation processes from inner-closed shells. in addition to the challenges in interpret,ing the medium resolution (epsilon/delta epsilon is about 0.05 - 0.1) data obtained by current X-ray astronomy experiments. Line wavelengths are of interest too, particularly owing to the high resolution spectra from the new experiments. The workshop was divided into five major areas: Observational Spectroscopy, Theoretical Calculations of Atomic Data, Laboratory Measurements of Atomic Parameters. Spectra Modeling, and Atomic Databases. One comforting finding from the work shop is that the enthusiasm felt by X-ray astronomers about the new observational missions seems to be shared by theoretical and experimental physicists. Talks were presented about several exciting new projects and experimental and theoretical techniques devoted to X-ray spectroscopy. Simultaneously, several new tools for spectral analysis and modeling have recently been developed, together with improved atomic databases. These proceeding are expected to be of interests to producers and users of atomic data. Moreover. the contributions presented here have been written in a way that can be used by a general audience of scientists and graduate students in X-ray astronomy, modelling, and in computational and experimental atomic physics.
This publication contains written versions of most of the invited talks presented at the workshop on "Atomic Data Needs for X-ray Astronomy," which was held at NASA's Goddard Space Flight Center on December 16-17, 1999. The workshop was divided into five major areas: Observational Spectroscopy, Theoretical Calculations of Atomic Data, Laboratory Measurements of Atomic Parameters, Spectra Modeling, and Atomic Databases. These proceedings are expected to be of interest to producers and users of atomic data. Moreover, the contributions presented here have been written in a way that can be used by a general audience of scientists and graduate students in X-ray astronomy, modelling, and in computational and experimental atomic physics.
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