Gamma–ray spectroscopy with single–carrier collection in high–resistivity semiconductors

With the standard plane–parallel configuration of semiconductor detectors, good γ–ray spectra can only be obtained when both electrons and holes are completely collected. We show by calculations (and experiments) that with contacts of hemispherical configuration one can obtain γ–ray spectra of adequate resolution and with signal heights of nearly full amplitude even when only one type of carrier is collected. Experiments with CdTe detectors for which the µτ product for electrons is about 10^(3) times that of the holes confirm these calculations. The adoption of hemispherical contacts thus widens the range of high–resistivity semiconductors potentially acceptable for γ–ray detection at room temperature

Humidification Factors from Laboratory Studies of Fresh Smoke from Biomass Fuels

Measurements of smoke aerosol humidification factors were performed in a laboratory for different biomass fuel types and burn conditions. Two nephelometers simultaneously measured dry and humidified light scattering coefficients (bsp(dry) and bsp(RH), respectively), providing the first observations of the temporal evolution of the humidification factor (f(RH) = bsp(RH)/bsp(dry)) for fresh (minutes-old) smoke. Hygroscopic characteristics of the smoke aerosols varied with fuel type and fire conditions, with the mean f(RH) ranging from 1.01 to 1.95 for fresh minutes-old smoke for the relative humidity (RH) range of 70-94%. These f(RH) values exhibited temporal variability, with some fuels alternating from hygroscopic to nonhygroscopic within minutes. Humidograms were also obtained, demonstrating that smoke from different fuels begins to take up water at different RH values. Humidification factors for hour-old smoke ranged from 1.10 to 1.51 for RH \u3e 90%. Finally, light-absorbing carbon mass measured with a multiwavelength aethalometer demonstrated different spectral responses as a function of fuel type. These laboratory experiments demonstrate the complexity of smoke hygroscopicity from young fires and are essential for understanding the radiative effects of biomass burning in the ambient atmosphere

Detection of X-ray Emission from Gravitationally Lensed Submillimeter Sources in the Field of Abell 370

We report the detection by Chandra of SMM J02399-0134 and SMM J02399-0136, two distant (z=1.06 and z=2.81, respectively) submillimeter sources gravitationally magnified by the galaxy cluster Abell 370. These are high-significance (> 7-sigma) X-ray detections of the high-redshift submillimeter source population. The X-ray positions are coincident with the optical positions to within one arcsecond. The X-ray spectra, while of low signal-to-noise ratio, are quite hard. Absorbed power law models with fixed photon indices of $\Gamma=2.0$ imply local absorbing columns $>2 \times 10^{23}$ cm$^{-2}$ and unabsorbed luminosities $>10^{44}$ erg s$^{-1}$ in both sources. These results imply that nuclear activity is responsible for the bulk of the luminosity in SMM J02399-0134, and for at least 20% of the luminosity of SMM J02399-0136, consistent with previous optical observations. We also place an upper limit on the X-ray flux of a third submillimeter source, SMM J02400-0134. Considered together with previously published Chandra upper limits on X-ray flux from submillimeter sources, our results imply that $20^{+30}_{-16}$ % of submillimeter sources exhibit X-ray emission from AGN (90% confidence), consistent with expectations of their contribution to the diffuse X-ray background.Comment: Corrected typos in Figure 1 labels; Accepted for publication in ApJ Letters, 6 pages, 2 figures, latex requires emulateapj5.st

Relative Contributions of Fossil and Contemporary Carbon sources to PM 2.5 Aerosols at Nine IMPROVE Network Sites

Particulate matter aerosols contribute to haze diminishing vistas and scenery at National Parks and Wilderness Areas within the United States. To increase understanding of the sources of carbonaceous aerosols at these settings, the total carbon loading and {sup 14}C/C ratio of PM 2.5 aerosols at nine IMPROVE (Interagency Monitoring for Protection Of Visual Environments) network sites were measured. Aerosols were collected weekly in the summer and winter at one rural site, two urban sites, five sites located in National Parks and one site located in a Wildlife Preserve. The carbon measurements together with the absence of {sup 14}C in fossil carbon materials and the known {sup 14}C/C levels in contemporary carbon materials were used to derive contemporary and fossil carbon contents of the particulate matter. Contemporary and fossil carbon aerosol loadings varied across the sites and suggest different percentages of carbon source inputs. The urban sites had the highest fossil carbon loadings that comprised around 50% of the total carbon aerosol loading. The Wildlife Preserve and National Park sites together with the rural site had much lower fossil carbon loading components. At these sites, variations in the total carbon aerosol loading were dominated by non-fossil carbon sources. This suggests that reduction of anthroprogenic sources of fossil carbon aerosols may result in little decrease in carbonaceous aerosol loading at many National Parks and rural areas

Enhancing Classroom Interaction in Distance Education Utilizing the World Wide Web

study utilized the World Wide Web and a Class Page to evaluate interaction strategies in a distance education setting. Participants were primarily elementary school teachers (n= 47 graduate students) who completed survey instruments concerning their participation on the Class Page , interactions with both the instructor and other students, and utilization of linked Web resources. An initial survey regarding students’ computer literacy skills and usage proficiencies was followed by seven additional surveys which focused upon Page ” use and interaction patterns. Among the findings were: student views regarding the value of getting to know fellow classmates shifted from zero percent (Week 2) to 88 percent (Week 15); students judging they were able freely to express their views went from 11 percent (Week 2) to 91 percent (Week 15). Increases were also noted concerning student out-of-class participation, enjoyment using the Internet, use of e-mail, and appreciation of the distance environment tools for encouraging involvement and interaction. Although many students questioned the usefulness of the Page at the beginning of the semester, the final survey found all students viewed the Page as beneficial. Analysis of the data found both interaction and class involvement were greatly enhanced through the Class Page and the Web based tools which supported the “Page” in this distance education environment

Enhancing Elementary Curricula through Internet Technology

Radical advancements in Internet technology over the last decade have created endless opportunities to expand the realm of the elementary classroom. The World Wide Web (WWW), e-mail, Newsgroups, and Internet Relay Chat (IRC) are four of the most prominent utilizations of Internet technology. This paper demonstrates how one mid-western, suburban elementary classroom has enhanced its curriculum and improved classroom interaction by maximizing Internet technology. In addition to reviewing the merits of this case study, the reader will also: (a) be presented with a rationale for utilizing Internet technology with existing curricula, (b) examine the current debate on the issue of networking schools, (c) compare and contrast the pros and cons of utilizing Internet technology in elementary classrooms, and (d) consider the coalescence of curriculum and technology. An overview regarding the current application of Internet technology in an elementary setting highlights its true benefits: students conducting research on a topic of interest, communication and collaborative projects between students around the world, and the opportunity for students to publish original work