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1.
Minimum energy geometries and electron density distributions, ϱ(r), for ∼40 polyatomic oxide molecules containing first and second row M-cations have been calculated at the Hartree-Fock level with a 6-311++G** basis set. The nature of the bonded interactions
in these molecules is examined in terms of the relative electronegativities, χ
M
, of the M-cations and the properties of the electron density distribution, ϱ(r
c
), evaluated at the bond critical points, r
c
, along each MO bond. As ϱ(r
c
) and the Laplacian of ϱ(r
c
) increase, χ
M
increases indicating an increase in the covalent character of the bonded interactions between M and O. The ratios of the curvatures of ϱ(r
c
) indicate that the NO bond is predominantly covalent, that the CO and SO bonds are of intermediate type and that the remaining
MO bonds are indicated to be predominantly ionic in character. A comparison of the critical point properties of ϱ(r
c
) and χ
M
indicates that the minimum energy MO bond length is an important determinate of the properties of ϱ(r
c
) and the character of the MO bonds.
On the other hand, values of the local energy density, H(r
c
), indicate that the LiO, BeO, NaO, MgO and AlO bonds are predominantly ionic and that the BO, CO, NO, SiO, PO and SO bonds
are predominantly covalent in character. The χ
M
-values provided by the properties of ϱ(r
c
) indicate that the covalent component of a bond increases with decreasing bond length, coordination number and increasing
bond strength. Each MO bond seems to represent a unique entity and to possess a distinct set of ϱ(r
c
) properties, the distinction being greater for the more electronegative cations.
The bonded radius of the oxide ion, r
b
(O), and the χ
M
-values determined from ϱ(r
c
) correlate with values determined from promolecule electron density distributions. In addition, r
b
(O) and χ
M
-values determined from experimental electron density distributions for crystals correlate with values determined from procrystal
electron density distributions. The number of critical points and bond paths are modeled rather faithfully by procrystal and
promolecule electron density distributions, despite the neglect of the binding forces in their constructions.
Received: October 15, 1996/Revised, accepted: February 10, 1997 相似文献
2.
Maximum and minimum void ratios (emax and emin) of granular soils are commonly used as indicators of many engineering properties. However, few methods, apart from laboratory tests, are available to provide a rapid estimation of both emax and emin. In this study, we present a theoretical model to map the densest and the loosest packing configurations of granular soils onto the void space. A corresponding numerical procedure that can predict both emax and emin of granular soils with arbitrary grain size distributions is proposed. The capacity of the proposed method is evaluated by predicting the maximum and minimum void ratios of medium to fine mixed graded sands with different contents of fines. The influence of the grain size distribution, characterized quantitatively by uniformity parameter and the fractal dimension, on emax and emin is discussed using the proposed method. Moreover, application of this method in understanding the controlling mechanism for the void ratio change during grain crushing is presented.
相似文献3.
Sampling exploration of uncertain functions to locate critical contour levels is most effective if sampling decisions are made sequentially. A simple sequential exploration strategy, based on pseudo-Bayesian second-moment analysis, is proposed and compared with non-sequential systematic sampling. Repeated application to functions simulated pseudorandomly from stationary random processes on the line and on the plane indicates uniform superiority of the sequential strategy. The method is particularly advantageous when the function of interest,h(X), has an uncertain trend, and in general when the random process that quantifies prior uncertainty onh(X) is highly correlated. 相似文献
4.
S. Feth G. V. Gibbs M. B. Boisen Jr. F. C. Hill 《Physics and Chemistry of Minerals》1998,25(3):234-241
Bond critical point properties calculated for the MN bonds in a number of geometry optimized nitride molecules containing first- and second-row M cations are compared with those calculated for a number of oxide molecules. As reported for the oxides, the value of the
electron density, ρ(r
c
), at the bond critical points, r
c
, increases with decreasing bond length while for the more electronegative cations, the local energy density, H(r
c
) decreases nonlinearly in value as the relative electronegativities of the M-cations, χ
M
, tend to increase. In the majority of cases, χM, |λ1|/λ3 and ∇2ρ(r
c
) increase with decreasing minimum energy bond lengths. The bond lengths adopted by the molecules are indicated to be an important
determinant of the critical point properties of the electron density distributions. The relative electronegativities derived
from the electron density distributions of the nitrides agree with those derived for the oxides and Pauling’s electronegativities
to within ∼5%, on average.
Received: 3 February 1997 / Revised, accepted: 11 July 1997 相似文献
5.
近年来光释光测年在单颗粒技术上的研究取得了一系列重要进展,极大地提高了测年精度,为地质考古测年提供了更大的空间,研究者们对全球重要考古遗址点进行了详细的单颗粒测年,取得诸多考古新发现。单颗粒释光技术是在光释光单片技术上发展而来,对样品的单个石英或长石颗粒进行独立测试,基于单个颗粒测量结果,结合误差理论、统计学分析和样品地质沉积特征分析获得样品的准确年龄。本文结合大量地质考古样品的单颗粒测年数据,重点阐述了单颗粒释光测年技术的原理、发展历程、实验流程、筛选条件和年龄模型。单颗粒释光技术为地质考古的精确定年提供了可能性,尤其是对由于晒退不充分等原因导致的等效剂量分散的样品,如过度分散值(OD)高达20%甚至超过50%的地质考古样品,提供了新的方法和及时支持。通过开展释光测年信号分析,选择不同的单颗粒样品年龄模型分析,可以得到较为可靠的年龄,为诸多地质考古遗迹建立年代学框架。 相似文献
6.
The variance-based cross-variogram between two spatial processes, Z1
(·) and Z2
(·), is var (Z1
(
u
) – Z2
(
v
)), expressed generally as a bivariate function of spatial locations
uandv. It characterizes the cross-spatial dependence between Z1
(·) and Z2
(·) and can be used to obtain optimal multivariable predictors (cokriging). It has also been called the pseudo cross-variogram; here we compare its properties to that of the traditional (covariance-based) cross-variogram, cov (Z1
(
u
) – Z1
(
v
), Z2
(
u
) – Z2
(
v
)). One concern with the variance-based cross-variogram has been that Z1
(·) and Z2
(·) might be measured in different units (apples and oranges). In this note, we show that the cokriging predictor based on variance-based cross-variograms can handle any units used for Z1
(·) and Z2
(·); recommendations are given for an appropriate choice of units. We review the differences between the variance-based cross-variogram and the covariance-based cross-variogram and conclude that the former is more appropriate for cokriging. In practice, one often assumes that variograms and cross-variograms are functions of
uandv
only through the difference
u – v. This restricts the types of models that might be fitted to measures of cross-spatial dependence. 相似文献
7.
Xi-Yao Li Yan-Hui Suo Li-Ming Dai Ling-Li Guo Feng-Jian Ge 《International Geology Review》2018,60(11-14):1721-1743
ABSTRACTSoutheastern China is characterized by an extensive Late Mesozoic (Yanshanian) tectono-magmatic-metallogenic event. Although Late Cretaceous volcanism gradually weakened during the epilogue of the Yanshanian event, its petrogenesis and geodynamic processes remain unclear. In this study, we present new zircon U–Pb–Hf isotopic, whole-rock elemental, and Sr–Nd isotopic compositions data, for volcanic rocks from the Zhaixia Formation of the Shimaoshan Group in Fujian Province. The lower member of the Zhaixia Formation consists of basalts and rhyolites, and the upper member is only rhyolites. These volcanic rocks erupted in the early stage of Late Cretaceous, with basalts erupting earlier (ca. 99–98 Ma) than rhyolites (ca. 98–94 Ma). These basalts record high-K calc-alkaline to shoshonitic, light rare earth element (LREE)- and LILE-enrichment, high field strength element (HFSE)depletion with negligible Eu anomalies, and uniform whole-rock εNd(t) (–3 to –6) and zircon εHf(t) (–3.3 to –14.1) values. The overlying rhyolites record peraluminous and high-K calc-alkaline characteristics, LREE- and LILE-enrichment with negative Eu anomalies, and Nb–Ta depletion. The whole-rock εNd(t) and zircon εHf(t) values of these rhyolites both increase from the lower member (εNd(t), –1.5 to –4.7; εHf(t), –5.1 to –16.1) to the upper member (εNd(t), –0.5 to 0.1; εHf(t), –0.3 to –4.3). The features imply that these basalts were derived from the partial melting of the enriched lithospheric mantle and the overlying rhyolites from the melting of the crustal components, respectively. Data from the rhyolites in the upper member indicate that more juvenile, Nd–Hf isotopically depleted materials were injected into their source. During the Late Cretaceous, the new, fast rollback of the subducting slab triggered lithospheric extension and asthenospheric upwelling beneath the coastal regions, which induced the melting of lithospheric mantle and crustal components. As continued, the new round of basaltic underplating provided necessary heat to cause partial melting of the deep crust, including the younger, juvenile, and isotopically depleted crustal components. 相似文献
8.
Zircon Lu-Hf systematics and the evolution of the Archean crust in the southern Superior Province,Canada 总被引：2，自引：0，他引：2
Patrick E. Smith Mitsunobo Tatsumoto Ronald M. Farquhar 《Contributions to Mineralogy and Petrology》1987,97(1):93-104
A combined Lu-Hf and U-Th-Pb isotopic study was made of 25 zircons and 2 whole rocks from the late Archean crust (2,888-2,668 Ma) in the southern Superior Province, Canada. The relative abundances of U, Th, Lu and Hf in zircons from the low grade Michipicoten and Gamitagama greenstone belts show variable patterns which in part reflect the bulk compositional differences of their parent rocks. Zircons from the high grade lower crustal regions adjacent to these belts (Kapuskasing Structural Zone) are distinguished from the low grade zircons by their strong depletions of Lu and Hf. The low Hf contents imply that the growth of metamorphic zircon involves a significant fractionation of the Zr/Hf ratio.Initial Hf isotope ratios for Hf in zircons from the low grade rocks are correlated with silica enrichment of their host rocks. e
Hf varies from +9.2 to –1.3 and data from similar rock types exhibit correlations of e
Hf with time. Whole rock basalt analyses yield e
Hf values of +8.7 and +11.3 suggesting their derivation from a depleted mantle. The basalt data fall on an evolution trend which implies that differentiation from a chondritic mantle occurred at 3,100-2,900 Ma. Low e
Hf values (–1.3 to +1.4) for rhyolites and granites are consistent with a derivation involving remelting of old crust similar to a 2,888 Ma granite with e
HF of +0.5. Significantly higher values (+1.4 to +3.9) are found in zircons from 2,748-2,682 Ma dacites and tonalites suggesting that their parent rocks had higher Lu/Hf ratios. This may indicate that their parent rocks were mafic. However, there is some evidence that the possible lower crustal source reservoirs of these rocks may have undergone processes early in their histories which increased their Lu/ Hf ratios. This would give rise to the higher e
Hf values observed in their derivatives. 相似文献
9.
Jason B. Burt Nancy L. Ross G. V. Gibbs George R. Rossman Kevin M. Rosso 《Physics and Chemistry of Minerals》2007,34(5):295-306
Potential protonation sites for, kyanite, sillimanite, and andalusite, located in a mapping of the (3, −3) critical points
displayed by their L(r) = −∇2ρ(r) distributions, are compared with polarized single-crystal FTIR spectra of kyanite and sillimanite determined earlier and
with andalusite measured in this study. For andalusite, seven peaks were observed when the electric vector, E, is parallel to [100]: four intense ones at 3,440, 3,460, 3,526, and 3,597 cm−1 and three weaker ones at 3,480, 3,520, and 3,653 cm−1. Six peaks, three intense ones at 3,440, 3,460, and 3,526 cm−1 and three weaker ones at 3,480, 3,520, and 3,653 cm−1 when E parallels [010]. No peaks were observed when E is parallel to [001]. The concentration of water in andalusite varies between 110 and 168 ppm by weight % H2O. Polarized FTIR spectra indicate that the OH vector is parallel to (001) in andalusite and sillimanite and
in kyanite. Examination of the L(r) (3, −3) critical points in comparison with the polarized FTIR indicates that H prefers to bond to the oxygen atoms O1 and
O2 in andalusite and O2 and O4 in sillimanite which correspond to the underbonded oxygen atoms and those with the largest
L(r) maxima. In kyanite, comparison of the FTIR spectrum and the critical points indicates that H will preferentially bond to
the two 4-coordinated O2 and O6 atoms. 相似文献
10.
《Georisk: Assessment and Management of Risk for Engineered Systems and Geohazards》2013,7(3-4):163-172
We present a series of simple approximate methods for up-scaling the cumulative distribution function of spatially correlated variables by using an effective number n e of independent variables. Methods are based on the property of distribution permanence of the gamma and inverse Gaussian distributions under averaging, bootstrap sampling and expansions about the normal and gamma distributions. A stochastic simulation study is used to validate each method, and simple parameters are defined to identify respective ranges of applicability. A practical example is presented where core sample rock strength data are up-scaled to shaft size for probabilistic (risk-based) deep foundation design. Supplemental material is available online. 相似文献
11.
TORE P°SSE 《Sedimentology》1997,44(6):1011-1014
The grain size distribution within a unimodal sediment can be described as a lognormal distribution when the distribution is formed by only one process. However, most sediments are formed by more than one process giving polymodal sediments. Polymodal sediments have to be described as the sum of several normal distributions, one for each process involved within the formation. Grain size distributions are usually interpreted with the help of graphical methods. Interpretations of polymodal sediments require mathematical methods. In mathematical terms a unimodal sediment can be described as a tangential hyperbolic function (tanh) and a polymodal sediment can generally be described by the sum of two or three tanh-functions. The tanh-method is a tool for identifying and estimating the number of modes within a grain size distribution and helps interpret the processes involved within the formation of a deposit. The mathematical method can also be used to computerize sediment data, allowing storage with just a few numbers. Different samples can easily be compared and classified. Also, this method could be a valuable tool for calculations of various sediment parameters both in geotechnology and hydrogeology. 相似文献
12.
目前研究萃取分离富集镓大多偏向在强酸性体系中,一定程度上给操作带来安全风险,另需耐酸器皿设备,易污染,空白背景值高。本文开发了一种在弱酸性条件下萃取分离富集痕量镓的方法。以大孔吸附树脂为载体,十六烷基三甲基溴化铵调节其表面极性,热固化负载2-乙基己基磷酸(2-乙基己基)酯,制备了镓的萃取树脂。动态考察了固相萃取镓的吸附容量,优化选择固相萃取分离富集条件,实验表明萃取条件温和,分离富集痕量镓效果理想。当溶液酸度为pH 2.5时,Ga(Ⅲ)达到最大的回收率99%,并确定了掺氧空气乙炔火焰原子吸收光谱法(FAAS)测定镓的最佳参数,提升了常规空气乙炔FAAS测定镓的灵敏度。方法检出限(3σ)为2.6ng/mL,相对标准偏差(RSD,n=7)为2.87%,加标回收率在95.7%～102.0%之间,理论富集倍数为40。本方法已应用于自来水、中药材和水培蔬菜样品中痕量镓的测定,简便、快速、可靠。 相似文献
13.
ABSTRACT Based on a two-segment plate flexural modelling, we investigated the effective elastic thickness of global subducting oceanic lithosphere. Our results show that for the plate age of 0 to 50 Ma, the seaward effective elastic thickness T e M values are located between 600 and 900°C isotherms, and do not track any isotherm, while the majority of the trenchward effective elastic thickness T e m values are located between 300 and 600°C isotherms. For the plate age older than 50 Ma, T e M values basically matches the 600°C isotherm with some fluctuations for the age older than 110 Ma, while T e m values mainly fall between 200 and 400°C isotherms. The reduction in effective elastic thickness (T e M-T e m) varies from 2.6 to 30.1 km, or 11–68% of seaward T e M. Thus, the absolute value of the decrease in the effective elastic thicknesses (T e M-T e m) increases with the plate age, while the percentage reduction in the effective elastic thickness (1-T e m/T e M) has no obvious relationship with the age, but more related to the curvature of bending plate. Almost all bending-related earthquakes occurred above the T e M line, but many normal-faulting earthquakes are deeper than the T e M-T e m line, implying that the plate may still retain some thickness of an elastic property core in the areas (depth) where earthquakes occur. 相似文献
14.
Tony D. Peterson 《Contributions to Mineralogy and Petrology》1996,124(3-4):395-405
Log-normal size distributions are of the form n=noe−L/α, where n=number density, L=crystal length, and α is a constant. A method for measuring three-dimensional log-normal crystal
or grain size distributions (CSDs) in thin section has been deduced from computer experiments, in which 2D sections were cut
through assemblages of 3D solids. The size ranges and distributions studied were appropriate for igneous microphenocryst to
megacryst populations. Conversion from 2D to 3D is based on an exact correction for spheres of uniform diameter. Cumulate
numbers of polygons with length≥L (N2D) are converted to N3D by the equation:
ln(N3D)=ln(N2D/[L·S])+ln(γ)−β/[L·S]
The number density is then obtained as n=−dN/dL. The parameters S and γ correct the measured lengths and no (no=number density at L=0) respectively, and are functions of crystal shape. The parameter β is a weak function of the degree
of spatial orientation of the crystals. Highly symmetrical shapes such as cubes, octahedra, and elongated prisms can be accurately
measured when randomly oriented; however, rectangular solids with a≠b≠c cannot be accurately measured because they produce
bimodal length distributions in cross section. Strongly oriented textures (trachytic or lineated) can be accurately measured
regardless of crystal shape. New CSD data from alkaline rocks and a kimberlite give examples of CSDs modified by megacryst
retention, xenocryst addition, phenocryst accumulation, and groundmass nucleation.
Received: 25 November 1994 / Accepted: 14 November 1995 相似文献
15.
Based on the fracture trace length distribution, conditions for the existence, uniqueness, and correctness of the fracture diameter distribution are given using Warburton’s fracture model. In particular, a solution for the fracture diameter distribution exists and is unique for all trace length probability density functions, h A (y), such that \(h_{A}(y)/\sqrt{y^{2}-x^{2}}\) is Lebesgue integrable on [x,∞). This condition is met by the uniform, exponential, gamma, lognormal, and power-law trace length distributions as well as by the trace length distributions that arise from a deterministic fracture diameter or from a discontinuous fracture diameter length distribution. Exponential, gamma, lognormal, and power-law trace length distributions satisfy necessary conditions for the diameter distribution to be non-negative, and necessary and sufficient conditions for the distribution to have unit integral over the real line. Negative values of the fracture diameter distribution arise when the trace has a uniform distribution and the lower bound of the fracture trace is greater than zero. 相似文献
16.
There is no single method available for estimating the seismic risk in a given area, and as a result most studies are based
on some statistical model. If we denote by Z the random variable that measures the maximum magnitude of earthquakes per unit time, the seismic risk of a value m is the probability that this value will be exceeded in the next time units, that is, R(m)=P(Z>m). Several approximations can be made by adjusting different theoretical distributions to the function R, assuming different distributions for the magnitude of earthquakes. A related method used to treat this problem is to consider
the difference between the times of occurrence of consecutive earthquakes, or inter-event times. The hazard function, or failure
rate function, of this variable measures the instantaneous risk of occurrence of a new earthquake, supposing that the last
earthquake happened at time 0. In this paper, we will consider the estimation of the variable that measures the inter-event
time and apply nonparametric techniques; that is, we do not consider any theoretical distribution. Moreover, because the stochastic
process associated with this variable can sometimes be non-stationary, we condition each time by the previous ones. We then
work with a multidimensional estimation, and consider each multidimensional variable as a functional datum. Functional data
analysis deals with data consisting of curves or multidimensional variables. Nonparametric estimation can be applied to functional
data, to describe the behavior of seismic zones and their associated instantaneous risk. The applications of estimation techniques
are shown by applying them to two different regions and data catalogues: California and southern Spain. 相似文献
17.
Fan Zhang 《International Geology Review》2020,62(7-8):859-886
ABSTRACT We quantify flexural deformation of subducting oceanic plates at a global array of 15 ocean trenches, using a new approach of modelling spatial variations in flexural bending shape and curvature. The investigated trenches are chosen to represent a diverse range of subducting plate age of 24–150 Ma, including the Middle America, Peru, Chile, West and East Aleutian, Sumatra, North and South Philippine, Tonga, Kermadec, Kuril, Japan, Izu-Bonin, and South and North Mariana. The studied trenches show systematic intra- and inter-trench variability in the calculated flexural bending curvature, stress distribution, extensional brittle yield zone, and effective elastic plate thickness Te of the subducting plates. We find that subducting plate age is a critical factor controlling the bending curvature and the corresponding extensional yield zone. The width, depth, and area of the extensional yield zone are all calculated to increase systematically with the subducting plate age. The newly-developed curvature analysis can yield continuously varying apparent Te(x) from the trench axis to outer rise. The calculated extensional yield zones from the curvature analysis are in general consistent with the observed normal faulting earthquakes of magnitude≥6.0 at the 15 global trenches. Our analyses also reveal that the five deepest regions of the global trenches, i.e. the Challenger, Horizon, Serena, and Scholl Deeps and Galathea Depth, are associated with relatively large flexural bending and calculated yield zones comparing to their respective adjacent trench segments. The Serena and Challenger Deeps of the S. Mariana trench are calculated to have the largest flexural bending among the five deeps. 相似文献
18.
二十年来,国内外相继建立了多种金属（铁铜锌镁钙锂钼硒汞铬镉矾钡钛等）同位素的分析方法。金属同位素分析中的样品处理包括两个过程：样品的消解和样品中待测元素的分离纯化。为了获得真实、准确的金属同位素数据,样品处理过程必须遵守两个基本原则：①不引入待测元素以及可能会对待测元素同位素分析产生干扰的元素;②待测元素不发生损失。金属同位素分析常用的样品消解方法是酸溶法（包括高压闷罐法和微波消解法）。待测元素的分离纯化主要使用离子交换分离法。相同的树脂可以用于不同元素的化学分离,同一种元素也可以使用不同的树脂进行化学分离。不同类型样品的基质差异较大,需要不同的流程对待测元素进行分离。研究人员可以通过改变前人的分离流程,包括改变树脂的用量、变换淋洗液或用量、增加分离步骤等方法来满足不同样品的分离要求。本文提出了金属同位素样品处理中需要注意的一些细节：①如果消解样品时使用了高氯酸,必须将高氯酸在高温下彻底去除,因为残余的高氯酸具有强氧化性会使后续化学分离中使用的离子交换树脂失效,影响分离效果;②同一体积的树脂放入不同内径的交换柱中,树脂柱越细越长,淋洗液流速越慢、洗脱时间越长,并且待测元素洗脱出来越滞后;③离子交换过程中,每次加入的试剂体积越小,淋洗出来的元素越集中,分离效果越好。 相似文献
19.
The Owen Conglomerate comprises coarse-grained siliciclastics that were deposited in response to Late Cambrian extension. The identification of normal faults that host thickened accumulations of siliciclastics is used here to support interpretation of syn-fill extension. Local mapping and section construction have identified a series of north-trending, en échelon, segmented normal faults that exhibit changes in along-strike polarity. The Late Cambrian faults are adjacent to sedimentary packages that define half-graben geometries, with an unconformity that defines basal contacts with underlying Mt Read Volcanics and onlap geometries onto the opposing basin margin. Faults that were active during deposition of the Owen Conglomerate were subsequently reversed during D1 Middle Devonian deformation, with reverse displacement controlling the development of inversion structures defined by north-trending fold structures. Pervasive northwest-trending D2 deformation extensively overprints earlier deformation features, and has led to the spectacular development of type 1 interference patterns that largely control outcrop distributions along the West Coast Range. Field evidence is documented in support for a simple structural history that accounts for geometries associated with Late Cambrian extension, prior to Middle Devonian inversion (D1) and subsequent shortening (D2). 相似文献
20.
Based on the radii and masses of degenerate dwarfs derived from HIPPARCOS and other observations, we estimate the microscopic
parameters of a Chandrasekhar model (the relativistic parameter at the stellar center x
0, and the chemical-composition parameter μ
e
= A/Z, where A is the mass number and Z is the nuclear charge). We have obtained analytical expressions for the macroscopic characteristics (mass, radius, energy)
as functions of x
0 and μ
e
. From the calculated dependence of the energy on these parameters, we have found constraints on the range of variability
of x
0, which are in good agreement with the observed radius distribution of dwarfs. The critical value of x
0 at which stability breaks down due to general-relativisitc effects is found more accurately than previously. We propose a
generalized model with an inhomogeneous (coordinate-dependent) chemical composition, with μ
e
= μ
e
(r). 相似文献