Modeling Changes in Measured Conductance of Thin Boron Carbide Semiconducting Films Under Irradiation

Semiconducting, p-type, amorphous partially dehydrogenated boron carbide films (a-B10C2+x:Hy) were deposited utilizing plasma enhanced chemical vapor deposition (PECVD) onto n-type silicon thus creating a heterojunction diode. A model was developed for the conductance of the device as a function of perturbation frequency (��) that incorporates changes of the electrical properties for both the a-B10C2+x:Hy film and the silicon substrate when irradiated. The virgin model has 3 independent variables (R1, C1, R3), and 1 dependent variable (��). Samples were then irradiated with 200 keV He+ ions, and the conductance model was matched to the measured data. It was found that initial irradiation (0.1 displacements per atom (dpa) equivalent) resulted in a decrease in the parallel junction resistance parameter from 6032 Ω to 2705 Ω. Further irradiation drastically increased the parallel junction resistance parameter to 39000 Ω (0.2 dpa equivalent), 77440 Ω (0.3 dpa equivalent), and 190000 Ω (0.5 dpa equivalent). It is believed that the initial irradiation causes type inversion of the silicon substrate changing the original junction from a p-n to a p-p+ with a much lower barrier height leading to a lower junction resistance component between the a-B10C2+x:Hy and irradiated silicon. Additionally, it was found that after irradiation, a second parallel resistor and capacitor component is required for the model, introducing 2 additional independent variables (R2, C2). This is interpreted as the junction between the irradiated and virgin silicon near ion end of range

An absorption event in the X-ray lightcurve of NGC 3227

We have monitored the Seyfert galaxy NGC 3227 with the Rossi X-ray Timing Explorer (RXTE) since January 1999. During late 2000 and early 2001 we observed an unusual hardening of the 2-10 keV X-ray spectrum which lasted several months. The spectral hardening was not accompanied by any correlated variation in flux above 8 keV. We therefore interpret the spectral change as transient absorption by a gas cloud of column density 2.6 10^23 cm^-2 crossing the line of sight to the X-ray source. A spectrum obtained by XMM-Newton during an early phase of the hard-spectrum event confirms the obscuration model and shows that the absorbing cloud is only weakly ionised. The XMM-Newton spectrum also shows that ~10% of the X-ray flux is not obscured, but this unabsorbed component is not significantly variable and may be scattered radiation from a large-scale scattering medium. Applying the spectral constraints on cloud ionisation parameter and assuming that the cloud follows a Keplerian orbit, we constrain the location of the cloud to be R~10-100 light-days from the central X-ray source, and its density to be n_H~10^8cm^-3, implying that we have witnessed the eclipse of the X-ray source by a broad line region cloud.Comment: 5 pages, 6 figures, accepted for publication in MNRAS letter

Practical quantum key distribution over a 48-km optical fiber network

The secure distribution of the secret random bit sequences known as "key" material, is an essential precursor to their use for the encryption and decryption of confidential communications. Quantum cryptography is a new technique for secure key distribution with single-photon transmissions: Heisenberg's uncertainty principle ensures that an adversary can neither successfully tap the key transmissions, nor evade detection (eavesdropping raises the key error rate above a threshold value). We have developed experimental quantum cryptography systems based on the transmission of non-orthogonal photon states to generate shared key material over multi-kilometer optical fiber paths and over line-of-sight links. In both cases, key material is built up using the transmission of a single-photon per bit of an initial secret random sequence. A quantum-mechanically random subset of this sequence is identified, becoming the key material after a data reconciliation stage with the sender. Here we report the most recent results of our optical fiber experiment in which we have performed quantum key distribution over a 48-km optical fiber network at Los Alamos using photon interference states with the B92 and BB84 quantum key distribution protocols.Comment: 13 pages, 7 figures, .pdf format submitted to Journal of Modern Optic

Animal waste management

"71/1M""Livestock producers have asked for guidelines on animal waste management that will be feasible and enduring. The Missouri Water Pollution Board has been aware of the need for improvements in methods of handling waste from confined feeding operations and for guidelines for producers. Chapter 204 of Missouri Statutes, as amended, gives the Water Pollution Board the responsibility and authority to correct and/or prevent "pollution" of "waters of the state." These terms are defined in the law and discussed briefly in the first section. With these facts in mind, staff engineers of the Water Pollution Board held a series of meetings with staff members of the Extension Division and Department of Agricultural Engineering of the University of Missouri-Columbia to develop guidelines for disposing of waste from confinement feeding operations. This report is a result of their combined efforts. Others assisting with various phases of development of these guidelines included: School of Engineering, University of Missouri-Columbia; State Department of Health, and the Soil Conservation Service. Research data and experience in handling livestock wastes have been used to develop the guidelines for planning, design, construction, and management of alternative systems of livestock waste management. The information and design guidelines herein are intended primarily for the use of personnel in agencies concerned with animal waste management problems." --PrefaceMissouri Water Pollution Board and Extension Division, University of Missouri - Columbia

The Ursinus Weekly, June 4, 1917

Wonderful concert by Music Society • Seniors entertained by alumni club • Baccalaureate theme brotherhood of man • Unveiling of portraits impressive ceremony • Senior programs in literary societies • Real Christian work for next year • Successful season for college quartet • Pupils\u27 recital • A letter from Fort Niagarahttps://digitalcommons.ursinus.edu/weekly/2596/thumbnail.jp

A Spectroscopic and Photometric Study of Short-Timescale Variability in NGC5548

Results of a ground-based optical monitoring campaign on NGC5548 in June 1998 are presented. The broad-band fluxes (U,B,V), and the spectrophotometric optical continuum flux F_lambda(5100 A) monotonically decreased in flux while the broad-band R and I fluxes and the integrated emission-line fluxes of Halpha and Hbeta remained constant to within 5%. On June 22, a short continuum flare was detected in the broad band fluxes. It had an amplitude of about ~18% and it lasted only ~90 min. The broad band fluxes and the optical continuum F_lambda(5100 A) appear to vary simultaneously with the EUV variations. No reliable delay was detected for the broad optical emission lines in response to the EUVE variations. Narrow Hbeta emission features predicted as a signature of an accretion disk were not detected during this campaign. However, there is marginal evidence for a faint feature at lambda = 4962 A with FWHM=~6 A redshifted by Delta v = 1100 km/s with respect to Hbeta_narrow.Comment: 12 pages, 7 figures, accepted for publishing in A&

Retention of Salmon-derived N and P by Bryophytes and Microbiota in Mesocosm Streams

Annual migrations of anadromous salmon are an important source of nutrients for many coastal streams. Much of the current research on salmon-derived nutrients has focused on nutrient retention via carcass consumption by mammals, birds, and macroinvertebrates, whereas retention and transfer of nutrients by microbiota has received less attention. Our research objective was to investigate nutrient movement from decomposing salmon tissue into periphyton, bryophytes, leaf-pack microbiota, and amphipods in laboratory mesocosm streams. We measured δ15N of microbiota growing on unglazed tiles (periphyton), microbiota growing on leaf packs, bryophytes on partially submerged stones, and amphipods; C:N and C:P ratios of microbiota and bryophytes; and periphyton biomass (ash-free dry mass and chlorophyll a) in channels with and without decomposing salmon tissue. Periphyton, bryophytes, and leafpack microbiota had lower C:N ratios and leaf-pack microbiota had lower C:P ratios in salmon channels than in reference channels. These results indicate increased nutrient quality in salmon channels. Periphyton ash-free dry mass and chlorophyll a were greater in salmon channels than in reference channels. δ15N values for periphyton, leaf-pack microbiota, and bryophytes were more enriched in salmon channels than in reference channels, a result that demonstrates that salmon-derived nutrients can be retained in streams through multiple mechanisms. Transfer of salmon-derived nutrients through leaf-pack microbiota to a higher trophic level was evidenced by higher δ15N in amphipods from salmon channels than from reference channels. Last, higher P concentrations (as much as 90% higher) in biota from salmon channels than from reference channels indicate uptake of salmon-derived P in salmon channels. These results suggest that periphyton, leaf-pack microbiota, and bryophytes might play a critical role in capturing salmon-derived nutrients

Simultaneous Ultraviolet and X-ray Observations of the Seyfert Galaxy NGC 4151. I. Physical Conditions in the X-ray Absorbers

We present a detailed analysis of the intrinsic X-ray absorption in the Seyfert 1 galaxy NGC 4151 using Chandra/HETGS data obtained 2002 May, as part of a program which included simultaneous UV spectra using HST/STIS and FUSE. NGC 4151 was in a relatively low flux state during the observations reported here, although roughly 2.5 times as bright in the 2 --10 keV band as during a Chandra observation in 2000. The soft X-ray band was dominated by emission lines, which show no discernible variation in flux between the two observations. The 2002 data show the presence of a very highly ionized absorber, in the form of H-like and He-like Mg, Si, and S lines, as well as lower ionization gas via the presence of inner-shell absorption lines from lower-ionization species of these elements. The former is too highly ionized to be radiatively accelerated in a sub-Eddington source such as NGC 4151. We find that the lower ionization gas had a column density a factor of ~ 3 higher during the 2000 observation. If due to bulk motion, we estimate that this component must have a velocity of more than 1250 km/sec transverse to our line-of-sight. We suggest that these results are consistent with a magneto-hydrodynamic flow.Comment: 42 pages, 14 figures. Accepted for publication in The Astrophysical Journa

Practical quantum cryptography for secure free-space communications

Quantum cryptography is an emerging technology in which two parties may simultaneously generate shared, secret cryptographic key material using the transmission of quantum states of light. The security of these transmissions is based on the inviolability of the laws of quantum mechanics and information-theoretically secure post-processing methods. An adversary can neither successfully tap the quantum transmissions, nor evade detection, owing to Heisenberg's uncertainty principle. In this paper we describe the theory of quantum cryptography, and the most recent results from our experimental free-space system with which we have demonstrated for the first time the feasibility of quantum key generation over a point-to-point outdoor atmospheric path in daylight. We achieved a transmission distance of 0.5 km, which was limited only by the length of the test range. Our results provide strong evidence that cryptographic key material could be generated on demand between a ground station and a satellite (or between two satellites), allowing a satellite to be securely re-keyed on orbit. We present a feasibility analysis of surface-to-satellite quantum key generation.Comment: 12 pages, 4 figure