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Recent Measurements (recent + measurement)
Selected AbstractsDynamical mechanisms controlling the vertical redistribution of dust and the thermodynamic structure of the West Saharan atmospheric boundary layer during summerATMOSPHERIC SCIENCE LETTERS, Issue 1 2009Juan Cuesta Abstract The Saharan atmospheric boundary layer (SABL) plays a significant role in the atmospheric global circulation and directly affects the vertical redistribution of dust originated in the Sahara, the world's largest dust source. Recent measurements have revealed a variety of new dynamical mechanisms that control the structure of the SABL, which are responsible for exchange between the Saharan convective and residual boundary layers. Using new space-borne laser remote sensing data (CALIPSO) and recently published results, we provide an overview of the following known dynamical mechanisms: diurnal vertical mixing, dynamical lifting (density currents and cold air outbreaks) and topographic effects (mountains and albedo anomalies). Copyright © 2009 Royal Meteorological Society [source] Hard X-ray emission of the Earth's atmosphere: Monte Carlo simulationsMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2007S. Sazonov ABSTRACT We perform Monte Carlo simulations of cosmic ray-induced hard X-ray radiation from the Earth's atmosphere. We find that the shape of the spectrum emergent from the atmosphere in the energy range 25,300 keV is mainly determined by Compton scatterings and photoabsorption, and is almost insensitive to the incident cosmic ray spectrum. We provide a fitting formula for the hard X-ray surface brightness of the atmosphere as would be measured by a satellite-borne instrument, as a function of energy, solar modulation level, geomagnetic cut-off rigidity and zenith angle. A recent measurement by the INTEGRAL observatory of the atmospheric hard X-ray flux during the occultation of the cosmic X-ray background by the Earth agrees with our prediction within 10 per cent. This suggests that Earth observations could be used for in-orbit calibration of future hard X-ray telescopes. We also demonstrate that the hard X-ray spectra generated by cosmic rays in the crusts of the Moon, Mars and Mercury should be significantly different from that emitted by the Earth's atmosphere. [source] Longitudinal PSA changes in men with and without prostate cancer: Assessment of prostate cancer riskTHE PROSTATE, Issue 3 2005Andreas P. Berger Abstract BACKGROUND To determine longitudinal PSA changes over a period of 10 years in patients with and without prostate cancer. METHODS Serial PSA measurements performed over 10 years were evaluated in 353 men who eventually developed prostate cancer and in 2.462 participants of a screening program without prostatic malignancy. RESULTS In men with cancer, mean tPSA increased from 2.28 ng/ml at 10 years before diagnosis to 6.37 ng/ml at the time of postive biopsy (PSA velocity: 0.409 ng/ml/year). PSA velocity was significantly associated with Gleason scores and pathologic stage. In the benign group (n,=,2.462), mean tPSA increased from 1.18 to 1.49 ng/ml over a period of 10 years (PSA velocity of 0.03 ng/ml/year). Of the subjects with tPSA levels of 2 ng/ml or less, 2 years prior to cancer diagnosis, 11.4% had tPSA values of more than 4 ng/ml at the time of biopsy. Of the 972 men with tPSA below 1 ng/ml 2 years before the most recent measurement was obtained, 966 (99.4%) had no evidence of prostate cancer 2 years later, while six were found to have malignancies (0.6%). CONCLUSIONS Longitudinal PSA changes in men with and without prostate cancer are significantly different. Annual testing may not be required in men with baseline tPSA levels of 1 ng/ml or below, whereas in patients with levels higher than 1 ng/ml, it seems to be indicated because of the significant percentage of men presenting with tPSA levels of more than 4 ng/ml two years later. © 2005 Wiley-Liss, Inc. [source] A thermodynamics-based estimation model for adsorption of organic compounds by carbonaceous materials in environmental sorbentsENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 6 2003Paul C. M. van Noort Abstract A model was developed to estimate Langmuir affinities for adsorption of low-polarity organic compounds from either water or air by carbonaceous sorbents. Sorption enthalpies and entropies provided the basic information for the description of sorption affinities in terms of the entropy of melting and either solubility in water or vapor pressure. For m -xylene, polycyclic aromatic hydrocarbons (PAHs) and chlorobenzenes on 10 different sorbents, 80% of the measured sorption affinities fall within a factor of four of the model estimates. Equations for the limiting distribution coefficients in terms of either octanol,air (KOA) or octanol,water partition (Kow) coefficients were derived from regressions of calculated affinities combined with an estimated relation between experimental Langmuir sorption capacities and Kow. Estimated soot,water distribution coefficients were within a factor of three of measured data for polychlorobiphenyls (PCBs) and lower molecular weight PAHs on automotive soot samples and captured the dependence of PCB distribution coefficients on the extent of ortho substitution. For higher molecular weight PAHs, sorption was underestimated. For soot in sediment,water distribution coefficients of PAHs and PCBs, estimated values captured both the trend of measured data with Kow and the dependence on sorbate planarity. Tentative application to aerosol,air distribution explained the observed independence of distribution coefficient,KOA relations for PCBs on the extent of ortho substitution and suggested nonequilibrium conditions for PAHs in comparison with recent measurements. [source] OH concentration time histories in n -alkane oxidationINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 12 2001D. F. Davidson OH radical concentration time histories were measured behind reflected shocks in the oxidation of four n -alkanes: propane, n -butane, n -heptane, and n -decane. Initial reflected shock conditions of these measurements were 1357,1784 K, 2.02,3.80 atm, with fuel concentrations of 300,2000 ppm, and equivalence ratios from 0.8 to 1.2. OH concentrations were measured using narrow-linewidth ring-dye laser absorption of the R1(5) line of the A,X (0,0) transition at 306.5 nm. These concentration time-history measurements were compared to the modeled predictions of eight large n -alkane oxidation mechanisms currently available in the literature and the kinetic implications of these measurements are discussed. These data, in conjunction with recent measurements of n -alkane ignition times and ethylene yields in n -alkane pyrolysis experiments, also performed in this laboratory, provide a unique database of species concentration time histories for n -alkane mechanism validation. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 775,783, 2001 [source] Two-way interactions between ocean biota and climate mediated by biogeochemical cyclesISRAEL JOURNAL OF CHEMISTRY, Issue 1 2002Hezi Gildor Some of the two-way interactions between ocean biota and climate are mediated by biogeochemical cycles that link the different components of the climate system. As suggested by proxy records extracted from ice and ocean cores, by recent measurements, and by numerical models, such two-way interactions were likely major players in past climate variability on glacial,interglacial timescales, and may act to amplify or moderate an anthropogenically induced climate change in the near future. At present, our lack of understanding of these interactions hampers our ability to anticipate the consequences of possible anthropogenic climate change. In this article, we highlight some of the possible feedbacks between ocean biota and climate, reviewing some key biogeochemical processes and discussing mechanisms of two-way interactions. We also outline the need and strategies for continuing research aimed at advancing our understanding of these feedbacks and discuss their significance. [source] Modification of the gamma-ray spectra by internal absorption in optically violently variable blazars: the example cases of 3C 273 and 3C 279MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2008J. Sitarek ABSTRACT Recent observations with the low-threshold Cherenkov telescopes proved that sub-TeV ,-rays are able to arrive from active galaxies at relatively large distances in spite of the expected severe absorption in the extragalactic background light (EBL). We calculate the ,-ray spectra at TeV energies from two example optically violently variable quasars, 3C 273 and 3C 279, assuming that ,-rays are injected in the inner parts of the jets launched by the accretion discs. It is assumed that ,-rays in the broad energy range (from MeV up to TeV) are produced in these blazars with a power-law spectrum with the spectral index as observed from these objects by the EGRET telescope at GeV energies. We take into account the internal absorption of these ,-rays by considering a number of models for the radiation field surrounding the jet. The classical picture of a relativistic blob in a jet for the injection of primary ,-rays is considered, with the injection rate of ,-rays as observed by the EGRET telescope in the GeV energy range. The results of calculations are compared with positive detection and the upper limits on the sub-TeV ,-ray fluxes from these two sources. It is concluded that, even with the Stecker EBL model, the level of ,-ray emission from 3C 279 is close to the recent measurements in the sub-TeV ,-ray energies, provided that the injected ,-ray spectrum extends from the GeV energies over the next two decades with this same spectral index. We also suggest that a flare with a time-scale of a few days from 3C 273 could be detected by the MAGIC II stereo telescopes. [source] Cluster correlations in redshift spaceMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2002N.D. Padilla We test an analytic model for the two-point correlations of galaxy clusters in redshift space using the Hubble volume N -body simulations. The correlation function of clusters shows no enhancement along the line of sight, owing to the lack of any virialized structures in the cluster distribution. However, the distortion of the clustering pattern arising from coherent bulk motions is clearly visible. The distribution of cluster peculiar motions is well described by a Gaussian, except in the extreme high-velocity tails. The simulations produce a small but significant number of clusters with large peculiar motions. The form of the redshift-space power spectrum is strongly influenced by errors in measured cluster redshifts in extant surveys. When these errors are taken into account, the model reproduces the power spectrum recovered from the simulation to an accuracy of 15 per cent or better over a decade in wavenumber. We compare our analytic predictions with the power spectrum measured from the APM cluster redshift survey. The cluster power spectrum constrains the amplitude of density fluctuations, as measured by the linear rms variance in spheres of radius 8 h,1 Mpc, denoted by ,8. When combined with the constraints on ,8 and the density parameter , derived from the local abundance of clusters, we find a best-fitting cold dark matter model with and , for a power spectrum shape that matches that measured for galaxies. However, for the best-fitting value of , and given the value of Hubble's constant from recent measurements, the assumed shape of the power spectrum is incompatible with the most readily motivated predictions from the cold dark matter paradigm. [source] Correction of mass spectrometric isotope ratio measurements for isobaric isotopologues of O2, CO, CO2, N2O and SO2RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 24 2008Jan Kaiser Gas isotope ratio mass spectrometers usually measure ion current ratios of molecules, not atoms. Often several isotopologues contribute to an ion current at a particular mass-to-charge ratio (m/z). Therefore, corrections have to be applied to derive the desired isotope ratios. These corrections are usually formulated in terms of isotope ratios (R), but this does not reflect the practice of measuring the ion current ratios of the sample relative to those of a reference material. Correspondingly, the relative ion current ratio differences (expressed as , values) are first converted into isotopologue ratios, then into isotope ratios and finally back into elemental , values. Here, we present a reformulation of this data reduction procedure entirely in terms of , values and the ,absolute' isotope ratios of the reference material. This also shows that not the absolute isotope ratios of the reference material themselves, but only product and ratio combinations of them, are required for the data reduction. These combinations can be and, for carbon and oxygen have been, measured by conventional isotope ratio mass spectrometers. The frequently implied use of absolute isotope ratios measured by specially calibrated instruments is actually unnecessary. Following related work on CO2, we here derive data reduction equations for the species O2, CO, N2O and SO2. We also suggest experiments to measure the required absolute ratio combinations for N2O, SO2 and O2. As a prelude, we summarise historic and recent measurements of absolute isotope ratios in international isotope reference materials. Copyright © 2008 John Wiley & Sons, Ltd. [source] Modelling the impact of oxygenated VOC and meteorology upon the boundary layer photochemistry at the South PoleATMOSPHERIC SCIENCE LETTERS, Issue 1 2007P. D. Hamer Abstract A chemistry box model is used to explore implications of recent measurements of methyl hydroperoxide (MHP) across Antarctica and their influence upon high ozone events in the South Pole boundary layer. To reconcile, recent data models suggest that chemistry and meteorology play an important role. Copyright © 2007 Royal Meteorological Society [source] Teil 2: Trittschalldämmung , Flankentrittschallpegel und TrittschallminderungBAUPHYSIK, Issue 2 2004Elmar Sälzer Dipl.-Ing. Im Teil 1 [1] der insgesamt dreiteiligen Darstellung des Schallschutzes von Hohlraumböden wurde über die geschichtliche Entwicklung der seit Anfang der 1980er Jahre auf den Markt gekommenen Hohlraumböden, die wesentlichen Konstruktionsprinzipien solcher Böden und über die Schallängsdämmung, dargestellt durch die bewertete Norm-Flankenpegeldifferenz, berichtet. Im vorliegenden zweiten Teil werden die beiden Aspekte der Trittschalldämmung, und zwar des Flankentrittschallpegels , der früher auch als horizontale Trittschalldämmung bezeichnet wurde , und der Trittschallminderung (früher Trittschallverbesserung) dargestellt. Der nachfolgenden Darstellung der beiden Parameter der Trittschalldämmung liegen ca. 150 Messungen im schalltechnischen Labor zu Grunde, die zum großen Teil noch nach DIN 52 210 [3], in jüngerer Zeit selbstverständlich nach DIN EN ISO 140-12 [4] durchgeführt wurden. Sound protection of cavity floors. Part 2: Impact sound insulation , namely impact sound flanking level and impact sound reduction In part 1 [1] of this three-part report on cavity floor sound protection, the history of the development of cavity floors introduced on the market since the early 1980s, the main design principles of such floors, and the concepts of flanking level reduction and weighted standard flanking level difference were illustrated. This second part examines two aspects of impact sound insulation, namely impact sound flanking level , previously sometimes referred to as horizontal impact sound insulation , and impact sound reduction. The following discussion of these two impact sound insulation parameters is based on approximately 150 measurements in an acoustics laboratory. The bulk of the measurements was carried out according to DIN 52 210 [3], more recent measurements according to DIN EN ISO 140-12 [4]. [source] | ||||||||||