Report condemns pressure to publish     

Powell D 《Science (New York, N.Y.)》1994,264(5166):1662

  相似文献   

Isotopic composition of strontium in volcanic rocks from oahu     

Powell JL  Delong SE 《Science (New York, N.Y.)》1966,153(3741):1239-1242

Analysis of several well-documented specimens from each of the three volcanic series on Oahu gives the following mean ratios of Sr(87) to Sr(86): the Waianae series, 0.7030 +/- 0.00010 (sigma); the Koolau series, 0.70385+/- 0.00009 (sigma); and the Honolulu series, 0.7029 ++/- 0.00006 ( sigma). The mean ratio of Sr(87) to Sr(86) of the Koolau series specimens is significantly higher than the means of the other two series. With one exception, significant differences in Sr(87)/ Sr(86) within a series were not found, even though some large compositional differences existed.  相似文献   

Letter to the editor     

Powell BJ 《Science (New York, N.Y.)》1967,158(3809):1625

  相似文献   

Drosophila in its ecosystem: ecological genetics and evolution     

Powell JR 《Science (New York, N.Y.)》1983,221(4618):1367

  相似文献   

Ecology. Synthesizing U.S. river restoration efforts     

Bernhardt ES  Palmer MA  Allan JD  Alexander G  Barnas K  Brooks S  Carr J  Clayton S  Dahm C  Follstad-Shah J  Galat D  Gloss S  Goodwin P  Hart D  Hassett B  Jenkinson R  Katz S  Kondolf GM  Lake PS  Lave R  Meyer JL  O'donnell TK  Pagano L  Powell B  Sudduth E 《Science (New York, N.Y.)》2005,308(5722):636-637

  相似文献   

Photographic Tracking of Elementary Particles     

Powell CF 《Science (New York, N.Y.)》1960,132(3434):1134-1136

  相似文献   

An empirical approach to target DNA quantification in environmental samples using real-time polymerase chain reactions     

Robert H. Gulden  David Levy-Booth  Jeff R. Powell  Kari E. Dunfield  K. Peter Pauls  Clarence J. Swanton 《Soil biology & biochemistry》2007,39(8):1956-1967

Recent advances in molecular techniques have allowed for the routine examination of nucleic acids in environmental samples. Although current methodologies are very sensitive, accurate target DNA quantification from environmental samples remains challenging. To facilitate high-throughput DNA quantification from environmental samples, we developed a novel DNA quantification method based on a non-linear curve-fitting approach to extract additional information from quantitative PCR amplification curves and used the fitted parameters to develop multiple regression standard equations for target DNA quantification. A 3-parameter sigmoidal function performed superior to a 4-parameter Weibull function for generating the multiple regression standard equations. In a verification experiment, target DNA was quantified in a series of ‘unknown’ samples in three soils using this approach and the results were compared to target DNA values determined using corrected and uncorrected Ct-based (threshold cycle) methods. For each method, the deviations from the expected target DNA content were determined. Results clearly showed that over all DNA concentrations, target DNA content determined by the non-linear curve-fitting method was more accurate and more precise than values predicted by all other methods. Analysis of variance conducted on the predicted DNA contents also revealed fewer statistical artifacts with the non-linear curve fitting method compared to the conventional Ct-based methods. The novel approach described here is accurate, inexpensive, and very amenable for automation and high-throughput applications.  相似文献   

Anthropogenic Vanadium-Chromium-Iron and Cerium-Lanthanum-Iron Particles in Settled Urban House Dust: CCSEM Identification and Analysis     

Powell  J. W. D.  Hunt  A.  Abraham  J. L. 《Water, air, and soil pollution》2002,135(1-4):207-217

There is continuing concern over the health threat posed by theinhalation of ambient, transition-metal-containing particulatematter. Here, we report on the collection of two types ofanthropogenic, airborne particles, composed of iron with vanadiumand chromium (FeVCr) and iron with the rare earth metals ceriumand lanthanum (FeCeLa), respectively. Bi-weekly deposition platesamples were collected on indoor window sills of residentiallocations in inner-city Syracuse, NY. Sampling was continuous ateach location for two months during the spring of 1999. Themetal-bearing particles were identified, analyzed, and sizedin situ on each deposition plate using computer controlledscanning electron microscopy (CCSEM). Approximately 17% of thoseanalyzed by CCSEM fell into the inhalable size fraction. Particle loading varied between locations and changed over time.This was probably a function of various factors affectingparticle deposition rates. Notwithstanding, the plate loadingsfor the FeVCr-bearing particles tended to peak during the middleof the sampling period, suggesting that a single source/processwas operating to produce the FeVCr particles. The large sizeattained by some of these particles (greater than 50 μm inaggregates) suggest that long range transport was probably notinvolved.  相似文献   

Quantitation of the nitrosamine 2-ethylhexyl-4-(N-methyl-N-nitrosoamino) benzoate (NPABAO) in sunscreen products.     

T A Meyer  J B Powell 《Journal of the Association of Official Analytical Chemists》1991,74(5):766-771

We have devised a method to quantitate the nitrosamine, 2-ethylhexyl-4-(N-methyl-N-nitrosoamino) benzoate (NPABAO), in commercial products containing the sunscreen ingredient, Padimate O. The method involves a minimum of cleanup steps to afford a nonaqueous extract from product emulsions suitable for analysis by a liquid chromatograph interfaced to a thermal energy analyzer (LC/TEA). The method is applicable to lotions, creams, and gels. Oils are normally soluble in the mobile phase and can be analyzed directly on the LC/TEA without additional cleanup procedures. The method has a minimum detectable limit of about 30 ppb and yields greater than 80% recovery. It is highly reproducible and generates no NPABAO artifactually prior to quantitation on the LC/TEA. Application of the method to 22 different commercial product formulas disclosed that the level of NPABAO in each of the products is below 250 ppb, with 18 of the products containing less than 100 ppb. Of interest was the observation that musk ketone, a common fragrance constituent, produces a false-positive TEA response that can interfere with accurate analysis of NPABAO content in typical commercial products.  相似文献   

A Notable Evolution     

Powell EP 《Science (New York, N.Y.)》1888,12(292):120

  相似文献