Quantification of the directional detection capability of the DRIFT-IIe dark matter search detector via the range of nuclear recoil tracks in two dimensions

2021 Spring.Includes bibliographical references.Evidence suggests that 83% of the matter content of the universe is dark matter. Despite its ubiquity, the identity of this matter is unknown. It is thought that a halo of dark matter surrounds and is distributed throughout our galaxy. The Weakly Interacting Massive Particle (WIMP) has been a popular dark matter candidate. As we move through this halo it should appear as a wind of WIMPs incident upon us. A properly-placed detector could have this wind blow through its top face at one time in the day, and through a side face 12 sidereal hours later. DRIFT-IIe is a low-pressure gas negative-ion time projection chamber designed for direct and directional detection of WIMPs elastically scattering from gas nuclei. Partial directional information of a WIMP recoil could be extracted by measuring the range of the track of ionization that it produces in two dimensions. To study this signature, the detector was exposed to a source of neutrons in a series of runs. In one run the source was placed above the detector and in a second run the source was placed to the side of the detector. Neutron recoils mimic those expected from WIMPs, and the source placement mimics a specific WIMP wind direction. For the two runs, the range information was compared with a Monte Carlo resampling test. It was found on average 302 +/- 4 neutron recoils, sampled with WIMP-like energy spectra, are required along each of these axes to discern the two populations with a significance of 3σ

Time and Nationhood: The United States and Indigenous Nations

This study examines the temporal rhetoric and discourse in documents of the Indian Removal debate of the late 1820s and early 1830s. The national narratives of both the United States and Cherokee nation are found to be inherently temporal. This study analyzes four key documents of the Removal debate in the form of memorials, speeches before congress, addresses to the people of the United States, and court cases.Time is found not only to help build nations in the minds of its members, but in the case of the United States, it is also found to help maintain the colonial-nation-state and to imagine erasure by presenting indigenous communities as fading away or moving into a state of degradation. Demonstrating more variation in the use of time between sources, the Cherokee documents present a variety of temporal arguments to support their claims for recognition as an indigenous nation. The overall findings show variation in the use of time with each source producing a different temporal argument of a nation passing through this medium. As a result, the study offers an increased understanding of these specific print narrative conceptions of colonialism, nationhood, and temporality

Space robotics: Recent accomplishments and opportunities for future research

The Langley Guidance, Navigation, and Control Technical Committee (GNCTC) was one of six technical committees created in 1991 by the Chief Scientist, Dr. Michael F. Card. During the kickoff meeting Dr. Card charged the chairmen to: (1) establish a cross-Center committee; (2) support at least one workshop in a selected discipline; and (3) prepare a technical paper on recent accomplishments in the discipline and on opportunities for future research. The Guidance, Navigation, and Control Committee was formed and selected for focus on the discipline of Space robotics. This report is a summary of the committee's assessment of recent accomplishments and opportunities for future research. The report is organized as follows. First is an overview of the data sources used by the committee. Next is a description of technical needs identified by the committee followed by recent accomplishments. Opportunities for future research ends the main body of the report. It includes the primary recommendation of the committee that NASA establish a national space facility for the development of space automation and robotics, one element of which is a telerobotic research platform in space. References 1 and 2 are the proceedings of two workshops sponsored by the committee during its June 1991, through May 1992 term. The focus of the committee for the June 1992 - May 1993 term will be to further define to the recommended platform in space and to add an additional discipline which includes aircraft related GN&C issues. To the latter end members performing aircraft related research will be added to the committee. (A preliminary assessment of future opportunities in aircraft-related GN&C research has been included as appendix A.

Motivating Students to Learn a Programming Language: Applying a Second Language Acquisition Approach in a Blended Learning Environment

Learning a programming language typically involves acquisition of new vocabulary, punctuation, and grammatical structures to communicate with a computer. In other words, learning a programming language is like learning a human language. A recent study showed that programmers use language regions of the brain when understanding source code and found little activation in other regions of the brain devoted to mathematical thinking. Even though programming code involved mathematical operations, conditionals, and loop iterations, researchers found that programming had less in common with mathematics and more in common with human language

A Spitzer c2d Legacy Survey to Identify and Characterize Disks with Inner Dust Holes

Understanding how disks dissipate is essential to studies of planet formation. However, identifying exactly how dust and gas dissipates is complicated due to difficulty in finding objects clearly in the transition of losing their surrounding material. We use Spitzer IRS spectra to examine 35 photometrically-selected candidate cold disks (disks with large inner dust holes). The infrared spectra are supplemented with optical spectra to determine stellar and accretion properties and 1.3mm photometry to measure disk masses. Based on detailed SED modeling, we identify 15 new cold disks. The remaining 20 objects have IRS spectra that are consistent with disks without holes, disks that are observed close to edge-on, or stars with background emission. Based on these results, we determine reliable criteria for identifying disks with inner holes from Spitzer photometry and examine criteria already in the literature. Applying these criteria to the c2d surveyed star-forming regions gives a frequency of such objects of at least 4% and most likely of order 12% of the YSO population identified by Spitzer. We also examine the properties of these new cold disks in combination with cold disks from the literature. Hole sizes in this sample are generally smaller than for previously discovered disks and reflect a distribution in better agreement with exoplanet orbit radii. We find correlations between hole size and both disk and stellar masses. Silicate features, including crystalline features, are present in the overwhelming majority of the sample although 10 micron feature strength above the continuum declines for holes with radii larger than ~7 AU. In contrast, PAHs are only detected in 2 out of 15 sources. Only a quarter of the cold disk sample shows no signs of accretion, making it unlikely that photoevaporation is the dominant hole forming process in most cases.Comment: 24 pages, 18 figures and 8 tables. Fixed a typo in Table