Estimation of Generic Subslab Attenuation Factors for Vapor Intrusion Investigations     

Roger Brewer  Josh Nagashima  Mark Rigby  Martin Schmidt  Harry O'Neill 《Ground Water Monitoring & Remediation》2014,34(4):79-92

Generic indoor air:subslab soil gas attenuation factors (SSAFs) are important for rapid screening of potential vapor intrusion risks in buildings that overlie soil and groundwater contaminated with volatile chemicals. Insufficiently conservative SSAFs can allow high‐risk sites to be prematurely excluded from further investigation. Excessively conservative SSAFs can lead to costly, time‐consuming, and often inconclusive actions at an inordinate number of low‐risk sites. This paper reviews two of the most commonly used approaches to develop SSAFs: (1) comparison of paired, indoor air and subslab soil gas data in empirical databases and (2) comparison of estimated subslab vapor entry rates and indoor air exchange rates (IAERs). Potential error associated with databases includes interference from indoor and outdoor sources, reliance on data from basements, and seasonal variability. Heterogeneity in subsurface vapor plumes combined with uncertainty regarding vapor entry points calls into question the representativeness of limited subslab data and diminishes the technical defensibility of SSAFs extracted from databases. The use of reasonably conservative vapor entry rates and IAERs offers a more technically defensible approach for the development of generic SSAF values for screening. Consideration of seasonal variability in building leakage rates, air exchange rates, and interpolated vapor entry rates allows for the development of generic SSAFs at both local and regional scales. Limitations include applicability of the default IAERs and vapor entry rates to site‐specific vapor intrusion investigations and uncertainty regarding applicability of generic SSAFs to assess potential short‐term (e.g., intraday) variability of impacts to indoor air.  相似文献   

Modulation of galactic cosmic ray anisotropy in heliomagnetosphere: Seasonal variation of sidereal daily variation     

K. Nagashima  I. Morishita  S. Yasue 《Planetary and Space Science》1983,31(11):1259-1268

In the previous paper (Nagashima et al., 1982), we have reported the yearly averaged modulation of galactic cosmic ray anisotropy in the heliomagnetosphere. In the present paper, we analyze the seasonal (annual) dependence of the modulation, using the frequency modulation method. The seasonal variation of the sidereal daily variation produced from the anisotropy is resolved into variations with proper sideband frequencies, such as solar and anti-sidereal variations. These side-band variations are predominant in the rigidity region of 10² ～' 10³ GV and show the following characteristics.(1) Being similar to the average sidereal variation, they are strongly dependent on the polarity state (‘positive’ or ‘negative’) of the heliomagnetosphere.(2) The side-band variations with frequencies lower than the sidereal frequency (366 cycle/year) generally predominate over those with higher frequencies. The most predominant variations are produced from the component of the uni-directional anisotropy projected to the Earth's rotation axis and could be observed as the solar and anti-sidereal diurnal variations.(3) If the flat neutral sheet of the heliomagnetosphere is replaced with the wavy neutral sheet, side-band variations in the positive state tend to diminish with the increase of the heliolatitudinal extent of the wavy neutral sheet, while those in the negative state almost retain their magnitude.(4) These variations depend also on the observation periods when the Earth is located either in the “toward” field or in the “away” field. This T-A dependence changes with the transition from the positive state to the negative and increases with the increase of the heliolatitudinal extent of the wavy neutral sheet. The most remarkable T-A dependence is observed in solar diurnal variation arising from the component of the unidirectional anisotropy projected to the Earth's rotation axis and can be used for the determination of the direction of the anisotropy.  相似文献   

Twenty-two year modulation of cosmic rays associated with polarity reversal of polar magnetic field of the sun     

K. Nagashima  I. Morishita 《Planetary and Space Science》1980,28(2):195-205

The existence of the 22-year modulation of cosmic ray intensity is pointed out, using data of the ion chamber at Huancayo and the neutron monitors at Ottawa and Deep River for about four solar cycles. The modulation consists of two discrete states (high and low intensities), corresponding respectively to those of the polarity of the polar magnetic field of the Sun. This can be interpreted on the basis of the following hypothesis; when the polar magnetic field of the Sun is nearly parallel to the galactic magnetic field, they could easily connect with each other, so that galactic cosmic rays could intrude more easily into the heliomagnetosphere along the magnetic line of force, as compared with those in the anti-parallel state of the magnetic fields. The observed intensity difference between two states is about 4.3 ± 0.2% for neutron monitor (P_c = 1.5GV). The abnormal increase in proton (0.28–0.42 GV) and electron (0.41-3.24 GV) fluxes in the 20th solar cycle and the sudden appearance of anomalous components (He⁺, etc.) since 1972 can be also explained on the basis of the present hypothesis. The transition between the two states has a time lag behind the polarity reversal, depending on the cosmic ray rigidity, such as about 1 year for the neutron monitor (P_c = 1.5 GV) and about 3.5 years for low rigidity components (P < 1 GV). These time lags could be explained on the basis of the generalized Simpson's coasting solar wind model and the general diffusion-convection theory on some assumptions.  相似文献   

Distribution of Fe among octahedral sites and its effect on the crystal structure of pumpellyite     

Mariko Nagashima  Takahiro Ishida  Masahide Akasaka 《Physics and Chemistry of Minerals》2006,33(3):178-191

Two pumpellyites with the general formula W ₈ X ₄ Y ₈ Z ₁₂O_56-n (OH) _n were studied using ⁵⁷Fe Mössbauer spectroscopic and X-ray Rietveld methods to investigate the relationship between the crystal chemical behavior of iron and structural change. The samples are ferrian pumpellyite-(Al) collected from Mitsu and Kouragahana, Shimane Peninsula, Japan. Rietveld refinements gave Fe(X):Fe(Y) ratios (%) of 41.5(4):58.5(4) for the Mitsu pumpellyite and 46(1):54(1) for the Kouragahana pumpellyite, where Fe(X) and Fe(Y) represent Fe content at the X and Y sites, respectively. The Mössbauer spectra consisted of two Fe²⁺ and two Fe³⁺ doublets for the Mitsu pumpellyite, and one Fe²⁺ and two Fe³⁺ doublets for the Kouragahana pumpellyite. In terms of the area ratios of the Mössbauer doublets and the Fe(X):Fe(Y) ratios determined by the Rietveld refinements, Fe²⁺(X):Fe³⁺(X):Fe³⁺(Y) ratios are determined to be 22:14:64 for the Mitsu pumpellyite and 27:8:65 for the Kouragahana pumpellyite. By applying the Fe²⁺:Fe³⁺-ratio determined by the Mössbauer analysis and the site occupancies of Fe at the X and Y sites given by the Rietveld method together with chemical analysis, the resulting formula of the Mitsu and Kouragahana pumpellyites are established as Ca₈(Fe _0.88 ²⁺ Mg_0.68Fe _0.77 ³⁺ Al_1.66)_Σ3.99(Al_5.67Fe _2.34 ³⁺ )_Σ8.01Si₁₂O_42.41(OH)_13.59 and Ca₈(Mg_1.24Fe _0.65 ²⁺ Fe _0.46 ³⁺ Al_1.66)_Σ4.01(Al_6.71Fe _1.29 ³⁺ )_Σ8.00Si₁₂O_42.14(OH)_13.86, respectively. Mean Y–O distances and volumes of the YO₆ octahedra increase with increasing mean ionic radii, i.e., the Fe³⁺→Al substitution at the Y site. However, change of the sizes of XO₆ octahedra against the mean ionic radii at the X site is not distinct, and tends to depend on the volume change of the YO₆ octahedra. Thus, the geometrical change of the YO₆ octahedra with Fe³⁺→Al substitution at the Y site is essential for the structural changes of pumpellyite. The expansion of the YO₆ octahedra by the ionic substitution of Fe³⁺ for Al causes gradual change of the octahedra to more symmetrical and regular forms.  相似文献   

Calcium-aluminum-rich inclusion found in the Ivuna CI chondrite: Are CI chondrites a good proxy for the bulk composition of the solar system?     

David R. Frank  Gary R. Huss  Michael E. Zolensky  Kazuhide Nagashima  Loan Le 《Meteoritics & planetary science》2023,58(10):1495-1511

Cosmochemists have relied on CI carbonaceous chondrites as proxies for chemical composition of the non-volatile elements in the solar system because these meteorites are fine-grained, chemically homogeneous, and have well-determined bulk compositions that agree with that of the solar photosphere, within uncertainties. Here we report the discovery of a calcium-aluminum-rich inclusion (CAI) in the Ivuna CI chondrite. CAIs are chemically highly fractionated compared to CI composition, consisting of refractory elements and having textures that either reflect condensation from nebular gas or melting in a nebular environment. The CAI we found is a compact type A CAI with typical ¹⁶O-rich oxygen. However, it shows no evidence of ²⁶Al, which was present when most CAIs formed. Finding a CAI in a CI chondrite raises serious questions about whether CI chondrites are a reliable proxy for the bulk composition of the solar system. Too much CAI material would show up as mismatches between the CI composition and the composition of the solar photosphere. Although small amounts of refractory material have previously been identified in CI chondrites, this material is not abundant enough to significantly perturb the bulk compositions of CI chondrites. The agreement between the composition of the solar photosphere and CI chondrites allows no more than ~0.5 atom% of CAI-like material to have been added to CI chondrites. As the compositions of CI chondrites, carbonaceous asteroids, and the solar photosphere are better determined, we will be able to reduce the uncertainties in our estimates of the composition of the solar system.  相似文献   

Revisiting 26Al‐26Mg systematics of plagioclase in H4 chondrites     

M. Telus  G. R. Huss  K. Nagashima  R. C. Ogliore 《Meteoritics & planetary science》2014,49(6):929-945

Zinner and Göpel ( 1992 , 2002 ) found clear evidence for the former presence of ²⁶Al in the H4 chondrites Ste. Marguerite and Forest Vale. They assumed that the ²⁶Al‐²⁶Mg systematics of these chondrites date “metamorphic cooling of the H4 parent body.” Plagioclase in these chondrites can have very high Al/Mg ratios and low Mg concentrations, making these ion probe analyses susceptible to ratio bias, which is inversely proportional to the number of counts of the denominator isotope (Ogliore et al. 2011 ). Zinner and Göpel ( 2002 ) used the mean of the ratios to calculate the isotope ratios, which exacerbates this problem. We analyzed the Al/Mg ratios and Mg isotopic compositions of plagioclase grains in thin sections of Ste. Marguerite, Forest Vale, Beaver Creek, and Sena to evaluate the possible influence of ratio bias on the published initial ²⁶Al/²⁷Al ratios for these meteorites. We calculated the isotope ratios using total counts, a less biased method of calculating isotope ratios. The results from our analyses are consistent with those from Zinner and Göpel ( 2002 ), indicating that ratio bias does not significantly affect ²⁶Al‐²⁶Mg results for plagioclase in these chondrites. Ste. Marguerite has a clear isochron with an initial ²⁶Al/²⁷Al ratio indicating that it cooled to below 450 °C 5.2 ± 0.2 Myr after CAIs. The isochrons for Forest Vale and Beaver Creek also show clear evidence that ²⁶Al was alive when they cooled, but the initial ²⁶Al/²⁷Al ratios are not well constrained. Sena does not show evidence that ²⁶Al was alive when it cooled to below the Al‐Mg closure temperature. Given that metallographic cooling rates for Ste. Marguerite, Forest Vale, and Beaver Creek are atypical (>5000 °C/Myr at 500 °C) compared with most H4s, including Sena, which have cooling rates of 10–50 °C/Myr at 500 °C (Scott et al. 2014 ), we conclude that the Al‐Mg systematics for Ste. Marguerite, Forest Vale, and Beaver Creek are the result of impact excavation of these chondrites and cooling at the surface of the parent body, instead of undisturbed cooling at depth in the H chondrite parent body, like many have assumed.  相似文献   

Structural variation of babingtonite depending on cation distribution at the octahedral sites     

Mariko Nagashima  Keiko Mitani  Masahide Akasaka 《Mineralogy and Petrology》2014,108(2):287-301

Babingtonite, Ca₂Fe²⁺Fe³⁺[Si₅O₁₄(OH)] (Z?=?2, space group $ P\overline{1} $ ) from Yakuki mine (Japan), Grönsjöberget (Sweden), Kandivali Quarry (India), Baveno Quarry (Italy), Bråstad Mine (Norway), and Kouragahana (Japan), and manganbabingtonite, Ca₂(Mn²⁺, Fe²⁺)Fe³⁺[Si₅O₁₄(OH)], from Iron Cap mine (USA) were studied using electron-microprobe analysis (EMPA), ⁵⁷Fe Mössbauer analysis and single-crystal X-ray diffraction methods to determine the cation distribution at M1 and M2 and to analyze its effect on the crystal structure of babingtonite. Although all studied babingtonite crystals are relatively homogeneous, chemical zonation due to mainly Fe ? Mn substitution is observed in manganbabingtonite. Mössbauer spectra consist of two doublets with isomer shift (I.S.)?=?1.16–1.22 mm/s and quadrupole splitting (Q.S.)?=?2.33–2.50 mm/s and with I.S.?=?0.38–0.42 mm/s and Q.S.?=?0.82–0.90 mm/s, assigned to Fe²⁺ and Fe³⁺ at the M1 and M2 octahedral sites, respectively. The determined ratio of Fe²⁺/total Fe in manganbabingtonite (0.26) was smaller than that in the others (0.35–0.44) because of high Mn²⁺ content instead of Fe²⁺. The unit-cell parameters of babingtonite are a?=?7.466–7.478, b?=?11.624–11.642, c?=?6.681–6.690 Å, α?=?91.53–91.59, β?=?93.86–93.94, γ?=?104.20–104.34º, and V?=?560.2–562.3 Å³, and those of manganbabingtonite are a?=?7.4967(3), b?=?11.6632(4), c?=?6.7014(2) Å, α?=?91.602(2), β?=?93.989(2), γ?=?104.574(3)º, and V =565.09(5) ų. Structural refinements converged to R ₁ values of 1.64–3.16 %. The <M1-O> distance was lengthened due to the substitution of large octahedral cations such as Mn²⁺ for Fe²⁺. The increase of the M1-O8, M1-O8’ and M1-O13 lengths with mean ionic radii is slightly more pronounced than of the other M1-Oi lengths. The lengthened M1-O13 distance leads the positive correlation between Si5-O15-Si1 angle and M1-O13 distance. The increase of Si2-O3-Si1 and Si5-O12-Si4 angles due to the increase of mean ionic radius of M2 is also observed.  相似文献   

日本琵琶湖中微囊藻水华形成机理的再认识     

Antonio Quesa  Jean-Jacques Frenette  早川和秀  熊谷道夫 《湖泊科学》1998,10(S1):341-345

Blooms of cyanobacteria are responsible for many problems in freshwater ecosystems. The massive growth of these microorganisms may limit the utilization of freshwater for human requirements since, apart from other problems, the production of toxic substances has been found to occur frequently during blooming periods. Ecologically, cyanobacterial blooms can modify dramatically the ecosystem through their low edibility within the food web and the huge primary production. Thus, saprobic processes are stimulated and the characteristics related to anaerobic conditions are also more extreme.Cyanobacterial blooms are many times explained as the consequence of the eutrophication of waterbodies. However, factors promoting bloom formation and ecological succession of cyanobacteria are not well understood yet.  相似文献   

Variable gain feedback control technique of active mass damper and its application to hybrid structural control     

Ichiro Nagashima  Yuzo Shinozaki 《地震工程与结构动力学》1997,26(8):815-838

A systematic design procedure and an algorithm are devised for variable gain feedback (VGF) control of buildings with active mass damper (AMD) systems. The limit of the stroke length of the auxiliary mass, which is considered to be one of the most important physical constraints for application of AMD systems to actual structures, is studied. A set of variable feedback gains is designed as a function of a single variable that indicates a trade-off between the reduction of the building response and the amplitude of the auxiliary mass stroke, and this variable is on-line controlled to keep the amplitude of the auxiliary mass stroke constant, and within its limits. A design method of static output feedback controller for modal control of buildings with non-classical damping is also presented. Next, an efficient control method for hybrid structural control is developed, with combined use of the VGF control and the static output feedback control. It is shown through numerical examples that the proposed control method effectively adapts the control performance according to the variation in the intensity level of the external excitations in such a manner that the amplitude of the auxiliary mass stroke is kept within its limits and the control power is restrained as well. The application range of the AMD systems is thereby improved significantly. © 1997 John Wiley & Sons, Ltd.  相似文献