新疆天池"96·7"暴雨洪水分析

1996年7月16～20日,新疆天山中、东部地区大范围连降暴雨,天山两侧几十条河流及山沟发生了较大洪水.分析了天池"96·7"暴雨洪水的成因、洪水特性,并根据进出天池的水量以及本地区的洪水参数,对本次洪水进行了合理分析.     

闽江“98·6”特大暴雨洪水分析

就1998年6月闽江发生的本世纪内最大一场暴雨洪水的天气成因、发展过程及特性作了简要的介绍与分析。"98·6"洪水是由历时17天的暴雨过程形成的,雨峰多且相互衔接,从而形成这场峰高、量大、多峰的特大洪水过程。     

新疆天池“96·7”暴雨洪水分析

1996年7月16～20日,新疆天山中、东部地区大范围连降暴雨,天山两侧几十条河流及山沟发生了较大洪水。分析了天池“96·7”暴雨洪水的成因、洪水特性,并根据进出天池的水量以及本地区的洪水参数,对本次洪水进行了合理分析。     

山东潍河"99·8"特大暴雨洪水分析

１９９年８月９～１３日,山东省潍河流域发生了该省有降雨观测记载以来罕见的特大暴雨洪水（以下简称“９９．８”暴雨中心三里庄水库雨量达７１１．４ｍｍ,最大２４小时雨量达５９９．６ｍｍ。致使三里庄水库上游山洪暴发,水位暴涨,入库洪峰达３０１０ｍ＾３／ｓ,洪水总量达８５３０万ｍ＾３,最大泄量７００ｍ＾３／ｓ。对这次暴雨洪水的特性进行了分析。     

陕南"2002·6"暴雨洪水分析

2002年6月8-9日，陕西省南部突降特大暴雨，致使子午河、旬河发生了特大洪水。分析了本次特大暴雨洪水的特性及洪灾成因，提出了关于防御局地暴雨洪水的几点建议。     

河北省中南部"96·8"暴雨洪水特性分析

分析了发生在河北省中南部的"96·8"暴雨洪水的天气系统、暴雨特点和洪水形成特性,并与历史上发生的"56·8"、"63·8"暴雨洪水进行了比较,有助于人们对该地区暴雨洪水的进一步认识.     

松辽流域东南部地区“95．7”特大洪水分析

从降水过程，暴雨时空分布，洪水发生时间及过程，洪水组成特征和洪水稀遇程度等几方面，分析了1995年7月中，下旬发生在松辽流域东南部地区的特大洪水。     

泾河洪水特性分析

泾河是渭河最大支流,灾害性洪水频发。通过收集泾河历史洪水资料,采用水文学方法,统计、分类、归纳,分析泾河洪水特点及洪水形成、组合、演变规律。分析得出泾河洪水主要发生在7、8、9月,洪水过程有单峰和复式峰,一次洪水历时5~7天,泾河洪水年际变化不稳定,上游河段年际变化幅度大于下游河段。洪水主要由夏季暴雨水形成,来自泾河杨家坪、马莲河雨落坪以上区域,可分为干流型洪水、支流型和混合型洪水。     

天山北坡三工河流域暴雨洪水及其对自然环境的影响

天山北坡的三工河孕育着新疆著名风景区天山"天池", 当来自西方路径的水汽在沿天山东移过程中遇"博峰"西北侧迎风坡阻挡, 使气流强迫抬升, 并通过山口气流绕流效应、山谷峡管效应、气流爬坡上升运动等造成的水汽垂直输送, 在天山南北坡形成暴雨, 三工河上游是暴雨活动中心频繁的地区.观测了天池上游96.7暴雨洪水, 调查了天池下游三工河05.8特大暴雨洪水的过程. 近百年来三工河曾在1915年、 1946年、 2003年和2005年发生过4次较大洪水;其中2005年洪水是1946年以来第1位的洪水, 洪水重现期定为61 a一遇. 三工河流域属于冰雪融水、降水补给为主的河流, 自20世纪80年代中后期以来, 年均气温呈上升趋势,降水则表现为明显增大的趋势, 洪旱灾害的发生频率加大. 这些气候和环境变化导致上游山区水土流失加剧, 暴雨洪水及洪旱灾害交替发生, 引起该区域水文环境、地表径流、流域水资源功能的恶性循环, 进而引发暴雨洪水灾害对风景区自然生态环境造成破坏并产生深远影响.     

广西郁江2001年7月暴雨洪水分析

分析了2001年7月发生在广西郁江的暴雨洪水的成因及发展过程、暴雨特性、洪水过程、洪水来源及组成、洪水特点及重现期,对于掌握该流域暴雨、洪水的形成条件和变化规律是十分有益的。     

Low-temperature heat capacities of MgAl<Subscript>2</Subscript>O<Subscript>4</Subscript> and spinels of the MgCr<Subscript>2</Subscript>O<Subscript>4</Subscript>–MgAl<Subscript>2</Subscript>O<Subscript>4</Subscript> solid solution

We present results from low-temperature heat capacity measurements of spinels along the solid solution between MgAl₂O₄ and MgCr₂O₄. The data also include new low-temperature heat capacity measurements for MgAl₂O₄ spinel. Heat capacities were measured between 1.5 and 300 K, and thermochemical functions were derived from the results. No heat capacity anomaly was observed for MgAl₂O₄ spinel; however, we observe a low-temperature heat capacity anomaly for Cr-bearing spinels at temperatures below 15 K. From our data we calculate standard entropies (298.15 K) for Mg(Cr,Al)₂O₄ spinels. We suggest a standard entropy for MgAl₂O₄ of 80.9 ± 0.6 J mol⁻¹ K⁻¹. For the solid solution between MgAl₂O₄ and MgCr₂O₄, we observe a linear increase of the standard entropies from 80.9 J mol⁻¹ K⁻¹ for MgAl₂O₄ to 118.3 J mol⁻¹ K⁻¹ for MgCr₂O₄.     

Point defects and cation tracer diffusion in (Ti<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> Fe<Subscript><Emphasis Type="Italic">1−x</Emphasis></Subscript>)<Subscript>3−δ</Subscript>O<Subscript>4</Subscript>. II. Cation tracer diffusion

 Cation tracer diffusion coefficients, D_Me ^*, for Me=Fe, Mn, Co and Ti, were measured using radioactive isotopes in the spinel solid solution (Ti _x Fe _1−x )_3−δO₄ as a function of the oxygen activity. Experiments were performed at different cationic compositions (x=0, 0.1, 0.2 and 0.3) at 1100, 1200, 1300 and 1400 °C. The oxygen activity dependence of all data for D_Me ^* at constant temperature and cationic composition can be described by equations of the type D_Me ^*=D^∘ _Me[V]. C_V·a _O2 ^2/3+D_Me[I] ^∘·a _O2 ^−2/3·D_Me[V] ^∘ and D_Me[I] ^∘ are constants and C_V is a factor of the order of unity which decreases with increasing δ. All log D_Me ^* vs. loga _O2 curves obtained for different values of x and for different temperatures go through a minimum due to a change in the type of point defects dominating the cation diffusion with oxygen activity. Cation vacancies prevail for the cation diffusion at high oxygen activities while cation interstitials become dominant at low oxygen activities. At constant values of x, D_Me[V] ^∘ decreases with increasing temperature while D_Me[I] ^∘ increases.     

LiFeSi<Subscript>2</Subscript>O<Subscript>6</Subscript> and NaFeSi<Subscript>2</Subscript>O<Subscript>6</Subscript> at low temperatures: an infrared spectroscopic study

 Synthetic aegirine LiFeSi₂O₆ and NaFeSi₂O₆ were characterized using infrared spectroscopy in the frequency range 50–2000 cm⁻¹, and at temperatures between 20 and 300 K. For the C2/c phase of LiFeSi₂O₆, 25 of the 27 predicted infrared bands and 26 of 30 predicted Raman bands are recorded at room temperature. NaFeSi₂O₆ (with symmetry C2/c) shows 25 infrared and 26 Raman bands. On cooling, the C2/c–P2₁/c structural phase transition of LiFeSi₂O₆ is characterized by the appearance of 13 additional recorded peaks. This observation indicates the enlargement of the unit cell at the transition point. The appearance of an extra band near 688 cm⁻¹ in the monoclinic P2₁/c phase, which is due to the Si–O–Si vibration in the Si₂O₆ chains, indicates that there are two non-equivalent Si sites with different Si–O bond lengths. Most significant spectral changes appear in the far-infrared region, where Li–O and Fe–O vibrations are mainly located. Infrared bands between 300 and 330 cm⁻¹ show unusually dramatic changes at temperatures far below the transition. Compared with the infrared data of NaFeSi₂O₆ measured at low temperatures, the change in LiFeSi₂O₆ is interpreted as the consequence of mode crossing in the frequency region. A generalized Landau theory was used to analyze the order parameter of the C2/c–P2₁/c phase transition, and the results suggest that the transition is close to tricritical. Received: 21 January 2002 / Accepted: 22 July 2002     

Pressure induced phase transition in Pb<Subscript>6</Subscript>Bi<Subscript>2</Subscript>S<Subscript>9</Subscript>

The crystal structure of Pb₆Bi₂S₉ is investigated at pressures between 0 and 5.6 GPa with X-ray diffraction on single-crystals. The pressure is applied using diamond anvil cells. Heyrovskyite (Bbmm, a = 13.719(4) Å, b = 31.393(9) Å, c = 4.1319(10) Å, Z = 4) is the stable phase of Pb₆Bi₂S₉ at ambient conditions and is built from distorted moduli of PbS-archetype structure with a low stereochemical activity of the Pb²⁺ and Bi³⁺ lone electron pairs. Heyrovskyite is stable until at least 3.9 GPa and a first-order phase transition occurs between 3.9 and 4.8 GPa. A single-crystal is retained after the reversible phase transition despite an anisotropic contraction of the unit cell and a volume decrease of 4.2%. The crystal structure of the high pressure phase, β-Pb₆Bi₂S₉, is solved in Pna2 ₁ (a = 25.302(7) Å, b = 30.819(9) Å, c = 4.0640(13) Å, Z = 8) from synchrotron data at 5.06 GPa. This structure consists of two types of moduli with SnS/TlI-archetype structure in which the Pb and Bi lone pairs are strongly expressed. The mechanism of the phase transition is described in detail and the results are compared to the closely related phase transition in Pb₃Bi₂S₆ (lillianite).     

BaCO<Subscript>3</Subscript>: high-temperature crystal structures and the <Emphasis Type="Italic">Pmcn</Emphasis>→<Emphasis Type="Italic">R</Emphasis>3<Emphasis Type="Italic">m</Emphasis> phase transition at 811°C

The temperature (T) evolution of the barium carbonate (BaCO₃) structure was studied using Rietveld structure refinements based on synchrotron X-ray diffraction and a powdered synthetic sample. BaCO₃ transforms from an orthorhombic, Pmcn, α phase to a trigonal, R3m, β phase at 811°C. The orthorhombic BaCO₃ structure is isotypic with aragonite, CaCO₃. In trigonal R3m BaCO₃, the CO₃ group occupies one orientation and shows no rotational disorder. The average <Ba–O> distances increase while the <C–O> distances decrease linearly with T in the orthorhombic phase. After the 811°C phase transition, the <Ba–O> distances increase while C–O distances decrease. There is also a significant volume change of 2.8% at the phase transition.     

Atomistic model of diopside-K-jadeite (CaMgSi<Subscript>2</Subscript>O<Subscript>6</Subscript>-KAlSi<Subscript>2</Subscript>O<Subscript>6</Subscript>) solid solution

Atomistic model was proposed to describe the thermodynamics of mixing in the diopside-K-jadeite solid solution (CaMgSi₂O6-KAlSi₂O₆). The simulations were based on minimization of the lattice energies of 800 structures within a 2 × 2 × 4 supercell of C2/c diopside with the compositions between CaMgSi₂O₆ and KAlSi₂O₆ and with variable degrees of order/disorder in the arrangement of Ca/K cations in M2 site and Mg/Al in Ml site. The energy minimization was performed with the help of a force-field model. The results of the calculations were used to define a generalized Ising model, which included 37 pair interaction parameters. Isotherms of the enthalpy of mixing within the range of 273–2023 K were calculated with a Monte Carlo algorithm, while the Gibbs free energies of mixing were obtained by thermodynamic integration of the enthalpies of mixing. The calculated T-X diagram for the system CaMgSi₂O₆-KAlSi₂O₆ at temperatures below 1000 K shows several miscibility gaps, which are separated by intervals of stability of intermediate ordered compounds. At temperatures above 1000 K a homogeneous solid solution is formed. The standard thermodynamic properties of K-jadeite (KAlSi₂O₆) evaluated from quantum mechanical calculations were used to determine location of several mineral reactions with the participation of the diopside-K-jadeite solid solution. The results of the simulations suggest that the low content of KalSi₂O₆ in natural clinopyroxenes is not related to crystal chemical factors preventing isomorphism, but is determined by relatively high standard enthalpy of this end member.     

The crystal structure of alumoklyuchevskite,K<Subscript>3</Subscript>Cu<Subscript>3</Subscript>AlO<Subscript>2</Subscript>(SO<Subscript>4</Subscript>)<Subscript>4</Subscript>

The crystal structure of the unstable mineral alumoklyuchevskite K₃Cu₃AlO₂(SO₄)₄ [monoclinic, I2, a = 18.772(7), b = 4.967(2), c = 18.468(7) Å, β = 101.66(1)°, V = 1686(1) Å] was refined to R ₁ = 0.131 for 2450 unique reflections with F ≥ 4σF _hkl. The structure is based on oxocentered tetrahedrons (OAlCu ₃ ⁷⁺ ) linked into chains via edges. Each chain is surrounded by SO₄ tetrahedrons forming a structural complex. Each complex is elongated along the b axis. This type of crystal structure was also found in other fumarole minerals of the Great Tolbachik Fissure Eruption (GTFE, Kamchatka Peninsula, Russia, 1975–1976), klyuchevskite, K₃Cu₃Fe³⁺O₂(SO₄)₄; and piypite, K₂Cu₂O(SO₄)₂.     

Performance of elevated tanks in<Emphasis Type="Italic">M</Emphasis><Subscript><Emphasis Type="Italic">w</Emphasis></Subscript> 7.7 Bhuj earthquake of january 26th, 2001

The current designs of supporting structures of elevated water tanks are extremely vulnerable under lateral forces due to an earthquake and the Bhuj earthquake provided another illustration when a great many water tank stagings suffered damage and a few collapsed. The more popular shaft type stagings suffer from poor ductility of thin shell sections besides low redundancy and toughness whereas framed stagings consist of weak members and poor brace-column joints. A strength analysis of a few damaged shaft type stagings clearly shows that all of them either met or exceeded the strength requirements of IS:1893-1984, however, they were all found deficient when compared with requirements of the International Building Code. IS:1893-1984 is unjustifiably low for these systems which do not have the advantage of ductility and redundancy and are currently being underestimated at least by a factor of 3 and need an upward revision of forces immediately.     

High-pressure Raman studies and heat capacity measurements on the MgSiO<Subscript>3</Subscript> analogue CaIr<Subscript>0.5</Subscript>Pt<Subscript>0.5</Subscript>O<Subscript>3</Subscript>

Raman spectroscopy and heat capacity measurements have been used to study the post-perovskite phase of CaIr_0.5Pt_0.5O₃, recovered from synthesis at a pressure of 15 GPa. Laser heating CaIr_0.5Pt_0.5O₃ to 1,900 K at 60 GPa produces a new perovskite phase which is not recoverable and reverts to the post-perovskite polymorph between 20 and 9 GPa on decompression. This implies that Pt-rich CaIr_1−xPt_xO₃ perovskites including the end member CaPtO₃ cannot easily be recovered to ambient pressure from high P–T synthesis. We estimate an increase in the thermodynamic Grüneisen parameter across the post-perovskite to perovskite transition of 34%, of similar magnitude to those for (Mg,Fe)SiO₃ and MgGeO₃, suggesting that CaIr_0.5Pt_0.5O₃ is a promising analogue for experimental studies of the competition in energetics between perovskite and post-perovskite phases of magnesium silicates in Earth’s lowermost mantle. Low-temperature heat capacity measurements show that CaIrO₃ has a significant Sommerfeld coefficient of 11.7 mJ/mol K² and an entropy change of only 1.1% of Rln2 at the 108 K Curie transition, consistent with the near-itinerant electron magnetism. Heat capacity results for post-perovskite CaIr_0.5Rh_0.5O₃ are also reported.