Application strategies for Sechura phosphate rock use on permanent pasture

At two phosphate (P) responsive sites in hill country the effectiveness of Sechura phosphate rock (SPR) as a direct application P fertilizer for permanent pasture was evaluated. Sechura was applied at two rates, in three different application strategies. The treatments were 16.7 and 50 kgP ha^–1 annually, 25 and 75 kgP ha^–1 biennially, and 50 and 150 kgP ha^–1 triennially giving a total of 50 and 150 kgP ha^–1, respectively, over three years. Single superphosphate (SSP) served as the standard P fertilizer. A comparison was also made between SPR and Chatham Rise phosphorite (CRP), another reactive PR. Total pasture and legume production and P uptake by pasture was measured with all fertilizer treatments over a three year period.In the year of application, SPR was as effective as SSP in stimulating total pasture and legume production and P uptake by pasture. This reflects the very reactive nature of this PR. In the second and third years of measurement, SPR did not show superior residual efffects to SSP. The ability of CRP to stimulate legume growth more than SPR in the second year following application demonstrates the danger of generalizing about the residual effects of reactive PR materials. Of the application strategies evaluated, a biennial appplication of 25 kgP ha^–1 as SPR maintained legume growth at a higher level than a smaller (16.7 kgP ha^–1) annual dressing. The biennial strategy also increased total pasture yield, in addition to legume production to a greater extent in the second and third years than a single (50 kgP ha^–1) triennial application.     

Matrilineal inheritance of complex I dysfunction in a multigenerational Parkinson's disease family

Recent data suggesting complex I dysfunction in Parkinson's disease (PD) arises from mitochondrial DNA (mtDNA) mutation does not conclusively answer whether the responsible genetic lesion is inherited (primary) or somatic (secondary). To address this question, we identified a family in which multiple members over three generations are affected with PD through exclusively maternal lines. Cytoplasmic hybrids (cybrids) were created for 15 family members over two generations by transferring each individual's mtDNA to mtDNA-depleted human neuroblastoma cells. Eight of the 15 cybrid lines contained mtDNA obtained from maternally descended family members and seven contained mtDNA from paternally descended family members. After 6 weeks of culture, cybrid cell lines were assayed for complex I activity and oxidative stress, and mitochondrial morphology was analyzed by electron microscopy. Compared with the cybrid lines containing mtDNA from paternal descendants, cybrid lines containing mtDNA from maternal descendants had lower complex I activity, increased reactive oxygen species production, increased radical scavenging enzyme activities, and more abnormal mitochondrial morphologic features. These findings were present in cybrid lines containing mtDNA from maternal descendants with PD as well as in currently asymptomatic young maternal descendants, and support a precedent for inherited mtDNA mutation in some persons with PD.     

Source Apportionment of Individual Carbonaceous Particles Using 14C and Laser Microprobe Mass Spectrometry

An exploratory study of laser microprobe mass spectra of individual atmospheric soot particles has been made in search of a potential combustion source tracer index. A tentative “cluster ratio index” (CRI = C₄ ^?/C₂ ^?) has been found and compared with bulk measurements of ¹⁴C in a set of ambient samples exhibiting varying impacts from woodburning and motor vehicle exhaust. A CRI-¹⁴C calibration curve resulted, and it led to the conclusion that, at the present level of precision, three particles (or agglomerates) of micrometer size or about 3 pg of carbon would be required for discrimination between the two pure sources. Mixture samples, such as those reported here, would require about 40 times as much. Classification of small set of individual particles from the mixed source ambient samples, suggests preservation of carbonaceous source identity at the single particle level.     

Optical and electrical characterization of GaAs-based high-speed and high-sensitivity delta-doped resonant cavity-enhanced HMSM photodetector

We have previously reported an AlGaAs-GaAs-based delta modulation doped resonant cavity-enhanced, heterostructure metal-semiconductor-metal (HMSM) photodetector design with wavelength selectivity, high sensitivity, and high-speed properties. In this paper, the influences of the resonant cavity and the delta modulation-doped layer on the optical and electrical performances of HMSM photodetectors have been studied by using the transmission line model and Ramo's theorem, respectively. The microcavity offers narrow spectral bandwidth detection accompanied by a drastic increase of the optical field at the resonant wavelength, solving the tradeoff between high efficiency and high speed with the thinner absorption regions. The top AlGaAs delta modulation-doped layer presents an enhanced barrier height associated with the vertically oriented two-dimensional potential and field profiles rather than the horizontally oriented ones, providing very low dark current values and an increase in device responsivity and speed of the response. Optimizing the optical and electric field simultaneously results in high-performance photodetection without further scaling down the devices. Two separate groups of photodetectors with various geometries have been fabricated, characterized, and simulated: One with a delta modulation-doped structure, the other without this doped layer. Delta-doped photodetectors show wavelength selectivity at 850 nm with about a 30-nm full width at half-maximum (FWHM), 9.2 fA//spl mu/m/sup 2/ dark current, less than 30 fF capacitance, 10.6-ps FWHM, and 18.4-ps fall time. Photocurrent spectral response, dark current, time response, and capacitance-voltage measurements consistently show that the delta-doped detectors have the better optical and electrical performances over the undoped ones.     

A Critical Evaluation of Interlaboratory Data on Total,Elemental, and Isotopic Carbon in the Carbonaceous Particle Reference Material,NIST SRM 1649a

Because of increased interest in the marine and atmospheric sciences in elemental carbon (EC), or black carbon (BC) or soot carbon (SC), and because of the difficulties in analyzing or even defining this pervasive component of particulate carbon, it has become quite important to have appropriate reference materials for intercomparison and quality control. The NIST “urban dust” Standard Reference Material^® SRM 1649a is useful in this respect, in part because it comprises a considerable array of inorganic and organic species, and because it exhibits a large degree of (¹⁴C) isotopic heterogeneity, with biomass carbon source contributions ranging from about 2 % (essentially fossil aliphatic fraction) to about 32 % (polar fraction).A primary purpose of this report is to provide documentation for the new isotopic and chemical particulate carbon data for the most recent (31 Jan. 2001) SRM 1649a Certificate of Analysis. Supporting this is a critical review of underlying international intercomparison data and methodologies, provided by 18 teams of analytical experts from 11 institutions. Key results of the intercomparison are: (1) a new, Certified Value for total carbon (TC) in SRM 1649a; (2) ¹⁴C Reference Values for total carbon and a number of organic species, including for the first time 8 individual PAHs; and (3) elemental carbon (EC) Information Values derived from 13 analytical methods applied to this component. Results for elemental carbon, which comprised a special focus of the intercomparison, were quite diverse, reflecting the confounding of methodological-matrix artifacts, and methods that tended to probe more or less refractory regions of this universal, but ill-defined product of incomplete combustion. Availability of both chemical and ¹⁴C speciation data for SRM 1649a holds great promise for improved analytical insight through comparative analysis (e.g., fossil/biomass partition in EC compared to PAH), and through application of the principle of isotopic mass balance.     

Evaluation of a modified EC Four Plate Method to detect antimicrobial drugs.

This paper describes a modification of the EC Four Plate Method based on microbial growth inhibition of Bacillus subtilis on agar medium at pH 6.0, 7.2 and 8.0 and Micrococcus luteus at pH 8.0 developed to cope with large numbers of samples. The method's performance was evaluated by determining the Minimum Inhibitory Concentrations of 66 commonly used drugs and determining the between-assay variation of antimicrobial control standards. The modified method proved particularly sensitive for beta-lactams, tetracyclines, quinolones, marcrolides and lincosamides and least sensitive for anticoccidials and nitrofurans. The pH 6.0 and 7.2 plates were more sensitive for 39 of the 66 antimicrobials (59%) whereas the two pH 8.0 plates (B. subtilis, M. luteus) were the most sensitive for 27 (41%). Muscle samples were taken from 1830 routine meat inspection investigations between 1994 and 1996. Of the 38 (2%) positive meat inspection carcasses, the following antimicrobials were confirmed above the MRL: penicillin G (10), oxytetracycline (16), sulphadimidine and sulphadiazine in combination (4) and chlortetracycline (1). The method as described is technically simple, cost effective, robust, suitable for large sample throughput and for frozen, thawed or fresh tissues. When all four plates are used the pattern of inhibition can reduce unnecessary confirmatory assays by indicating the antimicrobial group most likely to be present.     

Impedance studies of polycrystalline tin oxide

Polycrystalline SnO₂ samples prepared in the laboratory were irradiated with 2 MeV He ions having doses of 3.62 × 10¹⁵ ion/cm². The ac small-signal electrical data acquired for the polycrystalline SnO₂ in the frequency (f) range 100 Hz ≤ f ≤ 1 MHz and temperature (T) range 26°C ≤ T ≤ 100°C revealed one semicircular relaxation in the impedance plane for the He implanted sample. However, two semicircular relaxations were obtained in the same plane for the samples without He implantation. The He implantation indicated enhancement in the donor density in the polycrystalline SnO₂ as depicted via terminal conductance (or resistance). An erratum to this article can be found at