Two procedures for the calibration of an electron capture detector (ECD) for peroxyacetyl nitrate (PAN) are discussed. One is based on the first-order decay rate of the the PAN mixing ratio in conditioned glass storage vessels. The other method makes use of the photochemical generation of PAN in mixtures of acetone and NO2 in air. For this purpose a Penray Hg lamp was inserted into a glass vessel filled with 1 atmosphere of air containing 10 ppm NO2 and 1% acetone. After 3 min of irradiation, the average PAN mixing ratio formed was 8.87±0.25 ppmv as determined in six separate runs. 相似文献
Observations of nocturnal slope flow have been made at two sites with quite different topography and vegetation. In both cases, continuous measurements of wind and temperature profiles were made from towers that extended through the depth of the katabatic flow. At the simpler site, which approximates a tilted plane, three towers were located at different distances down the slope to measure the development of slope flow with downslope distance.Slope flow depth, downslope wind speed, and temperature deficit are found to change with downslope distance at rates that are consistent with the predictions of Manins and Sawford's (1979) layer-averaged model of slope flow, while measured entrainment rates are found to be comparable to those predicted by Ellison and Turner's (1959) laboratory experiments. The depth of slope flow is found to be roughly 0.05 times the vertical drop from the top of the slope, a relationship that also follows from combining Manins and Sawford's model and Ellison and Turner's laboratory data. Analysis of the wind spectra and a simple numerical model suggest that the turbulent kinetic energy profiles in slope flow are dependent on the speed and direction of the ambient wind and can differ substantially from those found over flat terrain. At the more complex of the two measurement sites, the occurrence of slope flow was found to correlate well with a dimensionless number 5 that is a function of the ridge-top wind speed and of the strength and depth of the inversion and that is an estimate of the ratio of the buoyancy deficit to the external horizontal pressure gradient.Prepared for the U.S. Department of Energy under Contract DE-AC06-76RLO 1830 相似文献
Blanfordite (I), winchite (II), and juddite (III), all showing vivid colors and pleochroism, from highly oxidized parageneses of Indian gondites were studied by microprobe, Mössbauer, and microscope-spectrophotometric techniques and by X-ray structure refinements. The compositions of the Mn-bearing minerals were close to diopsideacmite (I) and magnesio-arfvedsonite to magnesio-riebeckite (II and III). Transition metal ions are located inM(1)-octahedra (I) or predominantlyM(2)-octahedra (II, III). Mössbauer spectra of57Fe(IS, ΔEQ) are typical of octahedral Fe3+ only. Polarized absorption spectra in the UV/VIS/NIR ranges explain color and pleochroism of the minerals. The position of the UV-“edge” is correlated with Fe3+-contents of the minerals, except for judditeE ∥Z, where the edge shows an unusual low energy position. This is most likely due to Mie-scattering of submicroscopic inclusions of braunite with nearly uniform dimensions. In the VIS range, the spectra are dominated by a complex band system between 15,000 and 20,000 cm?1. Energies and ?-values of component bands are compatible with those of Mn3+d-d transitions in other Mn3+-bearing silicates. The polarization behavior of component bands can best be explained by aC2(C2″) symmetry of the crystal field. The Jahn-Teller splitting (<9,000 cm?1) of the5Eg ground state of Mn3+ inOh crystal fields is appreciably smaller than in other Mn3+-silicates. Crystal field parameters 10Dq, (I) 13,650, (II) ca. 11,640, and (III) 11,925 cm?1, are near to that in piemontite. The crystal field stabilization energy of Mn3+, (I) 146, (II) ca. 140, (III) 142 \({{{\text{kJ}}} \mathord{\left/ {\vphantom {{{\text{kJ}}} {\text{g}}}} \right. \kern-0em} {\text{g}}}{\text{ - atom}}_{{\text{Mn}}^{{\text{3 + }}} } \) , is appreciably smaller than that found in other Mn3+-silicates (piemontites and manganian andalusites, viridines and kanonaite). 相似文献
Transmission electron microscopic study of synthetic CaAl2Ge2O8-feldspar revealed two types of antiphase domains: type “b”-antiphase domains with the displacement vector 1/2 [110] and type “c”-antiphase domains with the displacement vector 1/2 [111]. The “b”-domains were on the order of 0.1 μm in size, while the “c”-domains displayed wall to wall distances mostly between 0.1 and 1 μm. The formation of the two types of antiphase domains is due to reductions in translational symmetry associated with the phase transitions \(C\bar 1 \to I\bar 1 \to P\bar 1\) . The antiphase domain textures of CaAl2Ge2O8-feldspar are very similar to the textures found in natural and synthetic anorthite, CaAl2Si2O8. 相似文献
Salt-loaded effluents were introduced into the river Wipper during the mining period for almost a century. Beginning with the year 1990, the waste water load was strongly reduced due to the termination of the potash industry. Prior to 1990, monthly means of the chloride concentrations at times exceeded 6,000 mg l−1 in the strongly polluted sections. Maximum concentrations reached twice these values. Up to 1998, mean annual chloride concentrations decreased to values below 2,000 mg l−1. This led to more balanced fluctuations in salinity which had been pronounced before, depending on discharge and short-term changes in production. Similarly, the physiologically adverse ion conditions improved due to decrasing potassium and increasing calcium proportions.
In 1963/64, 1986 and 1998, samples of epilithic, epiphytic and epipsammic diatoms were taken at locations of different salinities along the river and examined for the effects of the salinization on the structure of the diatom assemblages. These structures changed in dependence on salinity. Increasing salt concentrations coincided with decreasing oligohalophilic and increasing mesohalophilic and polyhalophilic species numbers. Above a chloride concentration of about 3,000 mg l−1, the proportion of the latter exceed that of the former (halobion index > 50). Corresponding to different conditions of salinization along the river, characteristic diatom assemblages occur differring from each other and which are specific for the river section. Spring and autumn aspects of the diatom assemblages show also salt-dependent differences. The assemblages found in 1998 after decrease of salinization have changed markedly in comparison to those from 1963/64 and 1986. Halobiontic species predominating formerly occurred only occasionally or not at all. They were replaced by oligohalobic-indifferent forms.
An ecological assessment of the changes was performed based on the halobion index calculated from all the samples. For the strongly salinized section of the river Wipper, a shift from -mesohalobic/polyhalobic conditions in 1963/64 and 1986 to -oligohalobic/β-mesohalobic conditions in 1998 was found. However, constant -oligohalobic conditions are still not given. With regard to the transition from -oligohalobic (limnetic) to β-mesohalobic (brackish) conditions, a maximum chloride concentration of 600 mg l−1 was found. To guarantee -oligohalobic conditions, a maximum chloride concentration of 400 mg l−1 should not be exceeded. 相似文献
Polarized electronic single crystal spectra of natural Fe2+ ion-bearing oxygen-based minerals, in which ferrous ions enter octahedral sites of different symmetry and distortion (olivine,
cordierite, ortho- and clinopyroxene, amphibole), eightfold sites in garnet (almandine) and clinopyroxene (M2), and tetrahedral
sites in spinel, were studied at temperatures from 300 to ca. 600 K. In the minerals studied, the spin-allowed bands of Fe2+ display rather variable temperature behaviour. In most cases, due to the thermal expansion of the Fe2+-bearing polyhedra, bands shift to lower energies upon increasing temperature, though there are some exceptions to this rule:
in cases of other than sixfold octahedral or close to octahedral coordination, in almandine and spinel the bands shift to
higher energies, which can be explained by an increase in distortions of the Fe2+-bearing polyhedra. Splitting of the excited 5Eg-level of Fe2+ ions usually, but not always, increases with temperature, reflecting thermally induced increase in distortion of the Fe2+-bearing sites in the minerals studied. Integral intensities of the bands in question do not always obey the general rule,
according to which intensity should increase with temperature, when the 3dN-centred site is centrosymmetric, or should remain unchanged when the 3dN site lacks an inversion centre. The experimental results show that the response of the characteristics of absorption bands
such as width, intensity and energy caused by dd transitions of Fe2+ in oxygen-based minerals to increasing temperature is not always uniform and is at variance with expectation. This temperature
dependence cannot be used directly to solve band assignment problems, as earlier proposed in the literature.
Received: 22 December 1999 / Accepted: 30 October 2000 相似文献
Polarized near-UV spectra have been recorded on 20 μm diameter spots on oriented crystals of microprobe-analyzed olivines
from Baikhal Rift, Fa8.8 (I) and Seberget, Fa9.3 (II), which have formed under different fO2 and, therefore, are expected to contain Fe3+-bearing point defects in different concentrations. These should be reflected in the UV-spectra of such minerals (Cemic et
al. 1986). The spectra obtained confirm these predictions: The difference in αY, 26500 in both samples indicates a difference in Fe3+-site fractions of ΔXFe. = 1.78-10−4, which may be related to an fO2 about ten times higher for the formation of olivine II compared to I. 相似文献