2,753 research outputs found

    The Cosmic Ray Observatory Project: A Statewide Outreach and Education Experiment in Nebraska

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    The Cosmic Ray Observatory Project (CROP) is a statewide education and research experiment involving Nebraska high school students, teachers and university undergraduates in the study of extensive cosmic-ray air showers. A network of high school teams construct, install, and operate school-based detectors in coordination with University of Nebraska physics professors and graduate students. The detector system at each school is an array of scintillation counters recycled from the Chicago Air Shower Array in weather-proof enclosures on the school roof, with a GPS receiver providing a time stamp for cosmic-ray events. The detectors are connected to triggering electronics and a data-acquisition PC inside the building. Students share data via the Internet to search for time coincidences with other sites. Funded by the National Science Foundation, CROP has enlisted 29 schools with the aim of expanding to the 314 high schools in the state over several years. This report highlights both the scientific and professional development achievements of the project to date.Comment: 4 pages, 4 figures, submitted to the 2007 International Cosmic Ray Conference (ICRC2007), Merida, Mexico, July 200

    The Cosmic Ray Observatory Project: A Statewide Outreach and Education Ex-periment in Nebraska

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    Abstract: The Cosmic Ray Observatory Project (CROP) is a statewide education and research ex-periment involving Nebraska high school students, teachers and university undergraduates in the study of extensive cosmic-ray air showers. A network of high school teams construct, install, and op-erate school-based detectors in coordination with University of Nebraska physics professors and graduate students. The detector system at each school is an array of scintillation counters recycled from the Chicago Air Shower Array in weather-proof enclosures on the school roof, with a GPS re-ceiver providing a time stamp for cosmic-ray events. The detectors are connected to triggering elec-tronics and a data-acquisition PC inside the building. Students share data via the Internet to search for time coincidences with other sites. Funded by the National Science Foundation, CROP has enlisted 29 schools with the aim of expanding to the 314 high schools in the state over several years. This report highlights both the scientific and professional development achievements of the project to date

    Multi-messenger Observations of a Binary Neutron Star Merger

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    On 2017 August 17 a binary neutron star coalescence candidate (later designated GW170817) with merger time 12:41:04 UTC was observed through gravitational waves by the Advanced LIGO and Advanced Virgo detectors. The Fermi Gamma-ray Burst Monitor independently detected a gamma-ray burst (GRB 170817A) with a time delay of ~1.7 s with respect to the merger time. From the gravitational-wave signal, the source was initially localized to a sky region of 31 deg2 at a luminosity distance of 40 8 8 - + Mpc and with component masses consistent with neutron stars. The component masses were later measured to be in the range 0.86 to 2.26 M. An extensive observing campaign was launched across the electromagnetic spectrum leading to the discovery of a bright optical transient (SSS17a, now with the IAU identification of AT 2017gfo) in NGC 4993 (at ~40 Mpc) less than 11 hours after the merger by the One- Meter, Two Hemisphere (1M2H) team using the 1 m Swope Telescope. The optical transient was independently detected by multiple teams within an hour. Subsequent observations targeted the object and its environment. Early ultraviolet observations revealed a blue transient that faded within 48 hours. Optical and infrared observations showed a redward evolution over ∌10 days. Following early non-detections, X-ray and radio emission were discovered at the transient’s position ~9 and ~16 days, respectively, after the merger. Both the X-ray and radio emission likely arise from a physical process that is distinct from the one that generates the UV/optical/near-infrared emission. No ultra-high-energy gamma-rays and no neutrino candidates consistent with the source were found in follow-up searches. These observations support the hypothesis that GW170817 was produced by the merger of two neutron stars in NGC4993 followed by a short gamma-ray burst (GRB 170817A) and a kilonova/macronova powered by the radioactive decay of r-process nuclei synthesized in the ejecta

    Geo 585 Field Methods: Edge Effects [in the Gordon Natural Area]

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    On the size distribution of newly formed grains in red supergiant atmospheres

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    Theoretical ultraviolet extinction curves have been calculated for comparison with observed curves for circumstellar dust in M supergiants. The theoretical curves assumed a silicate grain composition, because silicate grains are expected in the oxygen-rich environments that are observed. Calculations were performed with and without the inclusion of scattering into the beam, with largely similar results. A comparison of the computed curves with the observed ultraviolet extinction curve for circumstellar dust in Scorpii indicates that the size distribution of the circumstellar grains must cut off near 800 Å that is, there are few or no grains smaller than this. Our conclusion is that smaller interstellar silicate grains, where they exist, must come from other sources such as grain fragmentation in shocks

    Section properties for cellular decks subjected to negative bending

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    Cellular decks are formed by attaching cold-formed “hat-shaped” deck sections on top of cold-formed steel sheets. The attachment is typically made using resistance spot welds spaced at a specific interval. The void left underneath the deck flutes and above the steel sheet provides a convenient means for the distribution of wiring and data cables throughout building systems. The section properties of cellular decks subjected to positive bending can be determined using the provisions of Chapter B of the 2001 AISI Specification (AISI, 2001). However, the provisions of Chapter B do not apply to cellular decks subjected to negative bending unless a specific weld spacing requirement is met. This requirement, set by Section D1.2 Spacing of Connections in Compression Elements (AISI, 2001), limits weld spacing so as to completely prevent column-like buckling between welds and provide adequate resistance to horizontal shear forces. Using section D1.2 limits weld spacing to a range of 1 in. to 2 in. for most cellular decks. It is standard industry practice to space cellular deck welds at 4 in. to 8 in. on center, exceeding the limits of Section D1.2. If the spacing limits of Section D1.2 are exceeded, the 2001 AISI Specification requires that the steel sheet be neglected when determining the section properties of cellular deck in negative bending. This is done because column-like buckling is likely to occur in the sheet when it is subjected to compression forces. Although the 2001 AISI Specification has provisions in place to account for the effects of local buckling, it has no provisions in place to account for the post column-like buckling strength of the steel sheet. However, a procedure for determining the post-buckling strength of cellular decks was developed by Luttrell and Balaji (1992), and is based on the results of 82 negative bending tests performed on six cellular deck profiles. The procedure developed by Luttrell and Balaji (1992) utilizes a dimensional reduction factor, ρm, which is used to determine the effective width of the steel sheet when column-like buckling is an issue. The factors having the greatest influence on ρm include steel sheet thickness, steel sheet yield strength, weld spacing, and the depth of the deck. Although the method correlated well with the 82 bending tests performed, a ballot containing his method was not passed by AISI. The principal reason for its rejection was 2 that the reduction factor, ρm, was dimensional, which violates an AISI directive that all equations be non-dimensional so they apply to both US Standard and SI units. The primary objective of this research was to modify the method developed by Luttrell and Balaji such that the dimensional reduction factor is non-dimensional. Using Luttrell\u27s method, section properties for 49 of the 82 cellular decks tested in negative bending were determined. Section properties were not determined for the remaining 33 ECP266 and EPC3 cellular decks due to a lack of information with regard to the deck dimensions. However, a dimensionless reduction factor was developed based on the section properties of the EP-type cellular deck. The equation used to predict the reduction factor was optimized so as to reduce the error between observed and theoretical bending strength to a minimum

    Strength of arc-spot welds made in single and multiple steel sheets

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    The objective of this research was to establish a relationship between arc spot weld shear strength and the arc time used to form the weld. Lap shear tests were performed on both 3/4 in. and 5/8 in. nominal diameter welds. Each weld was formed in one-, two-, or four-layers of sheet steel ranging from 22 gauge (0.028 in.) to 16 gauge (.057 in.). Three distinct time series were tested for each unique weld size, thickness of sheet steel and layer configuration. The first of these series were the full-time welds. The two remaining series, 2/3-time and 1/3-time welds, had arc times equal to 2/3 and 1/3 of the average full-time weld arc time, respectively. Both weld shear strength tests and weld sectioning were performed for each series of weld. Strength tests were performed on a minimum of three specimens from every weld series. If the strength of any specimen deviated by over ten percent from the mean strength, an additional specimen was tested, helping to better understand the true behavior of the weld. Comparisons were made between the strengths of full-time, 2/3- time and 1/3-time welds. Comparisons were also made between the observed strength of each weld and the strengths calculated using the 2001 AISI Specification. Each sectioning test involved measuring and documenting the visual diameter, average diameter and effective diameter of the weld. Weld penetrations were also documented as sufficient or insufficient and any porosity was noted. A single sectioning test was performed for each full-time series, while three were performed for every 2/3- time and 1/3-time series. The data taken from the strength tests and the sectioning samples proved that welds formed using reduced arc times were considerably smaller and weaker than fulltime welds. The tests also proved that proper penetration is not dependent on the arc time, but is instead a function of the welding current and sheet steel thickness

    Diffuse band profiles in the Rho Ophiuchi cloud

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    High-resolution, high signal-to-noise ratio line profiles are presented for the 5780 and 5797 A diffuse interstellar bands toward six stars in the Rho Oph dark cloud. Target stars were chosen to exhibit a wide range of interstellar grain properties, as measured by grain polarization and far-UV extinction. The extreme case of the heavily reddened star HD 147889 is included; this star has one of the highest known lambdamax values, indicative of unusually large grains. Despite the differences in the grain properties, the line profiles and central wavelengths for the 5780 A band were found to be essentially identical for all lines of sight. This finding is in contradiction to the results of the embedded cavity grain model for diffuse bands, which predicts changes in both profile and central wavelength with grain size and impurity concentration. Results therefore support a molecular origin for the diffuse bands
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