Engineering topics

Lim, Jeremy

Publications and source records attributed to Lim, Jeremy.

5 records

DOE OSTI2024

Free-electron crystals for enhanced X-ray radiation

Abstract Bremsstrahlung—the spontaneous emission of broadband radiation from free electrons that are deflected by atomic nuclei—contributes to the majority of X-rays emitted from X-ray tubes and used in applications ranging from medical imaging to semiconductor chip inspection. Here, we show that the bremsstrahlung intensity can be enhanced significantly—by more than three orders of magnitude—through shaping the electron wavefunction to periodically overlap with atoms in crystalline materials. Furthermore, we show how to shape the bremsstrahlung X-ray emission pattern into arbitrary angular emission profiles for purposes such as unidirectionality and multi-directionality. Importantly, we find that these enhancements and shaped emission profiles cannot be attributed solely to the spatial overlap between the electron probability distribution and the atomic centers, as predicted by the paraxial and non-recoil theory for free electron light emission. Our work highlights an unprecedented regime of free electron light emission where electron waveshaping provides multi-dimensional control over practical radiation processes like bremsstrahlung. Our results pave the way towards greater versatility in table-top X-ray sources and improved fundamental understanding of quantum electron-light interactions.

47 OTHER INSTRUMENTATION↗

NASA NTRS2015

Multigenerational Independent Colony for Extraterrestrial Habitation, Autonomy, and Behavior Health (MICEHAB): An Investigation of a Long Duration, Partial Gravity, Autonomous Rodent Colony

The path from Earth to Mars requires exploration missions to be increasingly Earth-independent as the foundation is laid for a sustained human presence in the following decades. NASA pioneering of Mars will expand the boundaries of human exploration, as a sustainable presence on the surface requires humans to successfully reproduce in a partial gravity environment independent from Earth intervention. Before significant investment is made in capabilities leading to such pioneering efforts, the challenges of multigenerational mammalian reproduction in a partial gravity environment need be investigated. The Multi-generational Independent Colony for Extraterrestrial Habitation, Autonomy, and Behavior health is designed to study these challenges. The proposed concept is a conceptual, long duration, autonomous habitat designed to house rodents in a partial gravity environment with the goal of understanding the effects of partial gravity on mammalian reproduction over multiple generations and how to effectively design such a facility to operate autonomously while keeping the rodents healthy in order to achieve multiple generations. All systems are designed to feed forward directly to full-scale human missions to Mars. This paper presents the baseline design concept formulated after considering challenges in the mission and vehicle architectures such as: vehicle automation, automated crew health management/medical care, unique automated waste disposal and hygiene, handling of deceased crew members, reliable long-duration crew support systems, and radiation protection. This concept was selected from an architectural trade space considering the balance between mission science return and robotic and autonomy capabilities. The baseline design is described in detail including: transportation and facility operation constraints, artificial gravity system design, habitat design, and a full-scale mock-up demonstration of autonomous rodent care facilities. The proposed concept has the potential to integrate into existing mission architectures in order to achieve exploration objectives, and to demonstrate and mature common capabilities that enable a range of destinations and missions.

Rodgers, Erica M.↗

NASA NTRS1997

From Top to Bottom - the Multiwavelength Campaign of V824 Ara (HD 155555)

A great deal of progress has been made in recent years in decomposing the 2-D structure in the atmospheres of late-type stars. Doppler images of many photospheres single stars, T Tauri stars, Algols, RS CV(sub n) binaries to name a few - are regularly published (Strassmeier 1996; Richards and Albright 1996; Rice and Strassmeier 1996; Kuerster et al. 1994). Ultraviolet spectral images of chromospheres appear in the literature (e.g., Walter et al. 1987; Neff et al. 1989) but are less common owing to the difficult nature of obtaining complete phase coverage. Zeeman doppler images of magnetic fields are now feasible (e.g., Donati et al. 1992). Performing Doppler imaging of the same targets over many seasons has also been accomplished (e.g, Vogt et al. 1997). Even when a true image reconstruction is not possible due to poor spectral resolution, we can still infer a great deal about spatial structure if enough phases are observed. However, it is increasingly apparent that to make sense of recent results, many different spectral features spanning a range of formation temperature and density must be observed simultaneously for a coherent picture to emerge. Here we report on one such campaign. In 1996, we observed the southern hemisphere RS CV(sub n) binary V824 Ara (P=1(sup d).68, G5IV+K0V-IV-IV) over one complete stellar rotation with the Hubble Space Telescope and EUVE. In conjunction, radio and optical photometry and spectroscopy were obtained from the ground. Unique to this campaign is the complete phase coverage of a number of activity proxy indicators that cover source temperatures ranging from the photosphere to the corona.

Dempsey, Robert↗

NASA NTRS1994

Directivity of the radio emission from the K1 dwarf star AB Doradus

We present measurements of the spectrum and polarization of the flaring radio emission from the K1 dwarf star AB Doradus, together with previously reported single frequency measurements (with no polarization information) on 3 other days. On all 4 days spanning a 6 month period, the emission was strong and, when folded with the stellar rotation period, showed similar time variations with two prominant peaks at phase 0.35 and 0.75. These peaks coincide in longitude with two large starspots identified from the stellar optical light curve and have half-powe widths as small as 0.1 rotations and no larger than 0.2 rotations. The modulated emission shows no measurable circular polarization, and its two peaks have different turnover frequencies.

Lim, Jeremy↗

NASA NTRS1994

Imaging spectroscopy of solar microwave radiation. 1: Flaring emission

We present observations of an impulsive microwave burst on the Sun with both high spatial and spectral resolution, made with the Solar Array at the Owens Valley Radio Observatory (OVRO). We used the measured brightness temperature spectrum to infer the emission process responsible for each microwave source, and to derive physical conditions in the source region. We confimed our predictions using soft X-ray measurements from Geostationary Operational Environmental Satellite (GOES), soft X-ray images from Yohkoh, and H-alpha flare images together with sunspots and magnetogram images from the Big Bear Solar Observatory.

Lim, Jeremy↗