Estimation of critical convergence and rock load in coal mine roadways — an approach based on rock mass rating     

C. N. Ghosh  A. K. Ghose 《Geotechnical and Geological Engineering》1992,10(3):185-202

Summary Based on field instrumentation in eight different coal mines representing varying depths and strata conditions, a relation for obtaining the critical convergence value has been established. In development heading for bord and pillar workings this relation can be used successfully to control the premature collapse of the roof. An empirical relation for rock load has been established. This can be utilized for optimum design of support system. The roofs have been categorized as stable, short-term stable and unstable. Proper attention should be provided for an unstable roof and the support design is to be changed before the convergence reaches the critical value.  相似文献   

Ferroelastic phase transition in cryolite,Na3AlF6, a mixed fluoride perovskite: High temperature single crystal X-ray diffraction study and symmetry analysis of the transition mechanism     

Hexiong Yang  Subrata Ghose  Dorian M. Hatch 《Physics and Chemistry of Minerals》1993,19(8):528-544

Cryolite, Na₃AlF₆[ = 2Na⁺(Na_0.5 ⁺Al_0.5 ³⁺)F₃] is a mixed fluoride perovskite, in which the corner-sharing octahedral framework is formed by alternating [NaF₆] and [AlF₆] octahedra and the cavities are occupied by Na⁺ ions. At 295 K, it is monoclinic (α phase), space group P2 ₁/n with a = 5.4139 (7), b = 5.6012 (5) and c = 7.7769 (8) Å and β = 90.183 (3)°, Z = 2. A high temperature single crystal X-ray diffraction study in the range 295–900 K indicates a fluctuation-induced first-order phase transition from monoclinic to orthorhombic symmetry at T ₀ ～ 885 K, in contrast to a previous report that it becomes cubic at ～823 K. The space group of the high temperature β phase is Immm with a = 5.632 (4), b = 5.627 (3) and c = 7.958 (4) Å, Z = 2 at 890 K. Above T ₀, the coordination number of the Na⁺ ion in the cavity increases from eight to twelve and the zigzag Na1 — Al octahedral chains parallel to c become straight with the Na1-F-Al angle = 180 °. The phase transition is driven by two coupled primary order parameters. The first corresponds to the rotation of the nearly rigid [AlF₆] group and transforms according to the Γ ₄ ⁺ irreducible representation of Immm. Coupled to the [AlF₆] rotation is a second primary order parameter corresponding to the displacement of the Na2⁺ ion in the cavity from its equilibrium position. This order parameter transforms according to the X ₃ ⁺ irreducible representation of Immm. Following Immm → P2 ₁ /n phase transition, four equivalent domains of P2 ₁/n are determined relative to Immm, which are in an antiphase and/or twin relationship. The abrupt shortening of the octahedral Al-F and Na-F bonds and a sudden change in orientations of the atomic thermal vibration ellipsoids above T ₀ indicate a crossover from displacive to an order-disorder mechanism near the transition temperature. The β phase is interpreted as a dynamic average of four micro-twin and -antiphase domains of the a phase. This view is consistent with the entropy of phase transition, ΔS_trans (11.43 JK^?1 mol^?1) calculated from heat capacity measurements (Anovitz et al. 1987), which corresponds closely to R ln4 (11.53 JK^?1 mol^?1), where 4 is the number of domains formed during the phase transition. The dynamic nature of the β phase is independently confirmed from a considerable narrowing of the ²⁷Al nuclear magnetic resonance (NMR) line-shape above T ₀ (Stebbins et al. 1992).  相似文献   

Spatiotemporal trends of temperature extremes in Bangladesh under changing climate using multi-statistical techniques     

Mallick  Javed  Islam  Abu Reza Md. Towfiqul  Ghose  Bonosri  Islam  H. M. Touhidul  Rana  Yousuf  Hu  Zhenghua  Bhat  Shakeel Ahmed  Pal  Subodh Chandra  Ismail  Zulhilmi Bin 《Theoretical and Applied Climatology》2022,147(1-2):307-324

Theoretical and Applied Climatology - The rise in the frequency and magnitude of extreme temperature phenomena across the globe has led to the recurrent incidence of global climate hazards, which...  相似文献   

Impact Assessment of GIS Based Land Resource Inventory Towards Optimizing Agricultural Land Use Plan in Dandakaranya and Easternghats Physiographic Confluence of India     

Birendra Nath Ghosh  Krishnendu Das  Siladitya Bandyopadhyay  Subrata Mukhopadhyay  Dulal Chandra Nayak  Surendra Kumar Singh 《Journal of the Indian Society of Remote Sensing》2018,46(4):641-654

GIS based land resource inventory (LRI) with fine resolution imagery is considered as most authentic tool for soil resource mapping. Soil resource mapping using the concept of soil series in a smaller scale limits its wide application and also its impact assessment for crop suitability is controversial. In this study, we attempted to develop LRI at large scale (1:10,000 scale) at block level land use planning (LUP) in Dandakaranya and Easternghats physiographic confluence of India. The concept of land management unit was introduced in this endeavour. The impact assessment of LRI based LUP was exercised to develop efficient crop planning with best possible management practices. The study area comprised six landforms with slope gradient ranging from very gentle (1–3%) to steep slopes (15–25%). The very gently sloping young alluvial plains occupied maximum areas (19.95% of TGA). The single cropped (paddy) land appears to dominate the land use systems (40.0% of TGA). Thirty three landscape ecological units were resulted by GIS-overlay. Eighteen soils mapping units were generated. The area was broadly under two soil orders (Inceptisols and Alfisols); three great group (Haplaquepts, Rhodustalfs and Endoaquepts) and ten soil series. Crop suitability based impact assessment of LRI based LUP revealed that average yield of different crops increased by 39.2 and 14.5% in Kharif (rainy season) and Rabi (winter) seasons respectively and annual net returns by 83.4% for the cropping system, compared to traditional practices. Productivity and net returns can be increased several folds if customized recommended practices are adopted by the farmers. Informations generated from the study emphasized the potentiality of LRI towards optimizing LUP and exhibited an ample scope to use the methodology as a tool to assess in other physiographic regions in India and abroad.  相似文献   

A neutron powder diffraction study of the crystal and magnetic structures of ilvaite from 305 K to 5 K — a mixed valence iron silicate with an electronic transition     

Subrata Ghose  A. W. Hewat  M. Marezio 《Physics and Chemistry of Minerals》1984,11(2):67-74

The crystal and magnetic structures of ilvaite Ca(Fe²⁺, Fe³⁺)Fe²⁺Si₂O₇O(OH) have been obtained by profile refinement of high resolution neutron powder data from a natural sample from Seriphos, Greece. Below about 400 K an electronic transition from an itinerant to an ordered state is expected, with the structure changing from orthorhombic to monoclinic. The structure remains monoclinic P2 ₁/a down to 5 K, with Fe²⁺ almost completely ordered on one of the A-sites and Fe³⁺ on the other: the ordering may increase with decreasing temperature. The B-site contains Fe²⁺ plus a small amount of Mn²⁺ impurity. There are two magnetic transitions, at 116 K and 40 K: at 80 K the Fe²⁺ and Fe³⁺ spins on the A-sites along one infinite c-axis chain are parallel, and antiparallel to those along the adjoined edge-sharing centrosymmetrically related chain. The spin vectors are all perpendicular to the plane of these chains, i.e. almost parallel to the crystallographic b-axis. At 5 K, this order is maintained, but the Fe²⁺ spins on the B-sites order antiferromagnetically as well, again almost along the b-axis. These results explain the earlier Mössbauer and magnetisation measurements.  相似文献   

Magnetic order in grunerite,Fe7Si8O22(OH)2A quasi-one dimensional antiferromagnet with a spin canting transition     

Subrata Ghose  D. E. Cox  N. Van Dang 《Physics and Chemistry of Minerals》1987,14(1):36-44

Magnetization and neutron diffraction measurements have been made on grunerite, Fe₇Si₈O₂₂(OH)₂, a monoclinic double-chain silicate with Fe²⁺ octahedral bands. The mineral orders antiferromagnetically at 47K into a collinear structure with a second transition at 8K to a canted arrangement. The magnetic susceptibility follows a Curie-Weiss Law above 120K, with a paramagnetic Curie temeprature ?_p=67K. Magnetization measurements below 47K indicate a spin-flop or metamagnetic transition in an applied field of about 12KOe. Powder neutron diffraction measurements between 8–45K reveal that all the Fe²⁺ spins within an octahedral band are ferromagnetically coupled parallel to the b axis, with each band antiferromagnetically coupled to neighboring bands. Below 8K Fe²⁺ spins at the M1 and M4 sites are canted away from the b axis, whereas those at the M2 and M3 sites are not significantly affected. The ordered Fe²⁺ moment on the M4 site is substantially lower than those on the other sites, most likely indicating strong covalency effects, i.e. considerable spin transfer to neighboring oxygen atoms.  相似文献   

A rock mass classification model for caving roofs     

A. K. Ghose  D. Dutta 《Geotechnical and Geological Engineering》1987,5(3):257-271

Summary Evaluation of the caving behaviour of longwall roof rocks has thus far been based on a pot-pourri of classification systems, which ignore basic caving criteria. The paper outlines a new classification model of roof strata namely cavability using fuzzy set methodology and linguistic variables to assign ratings for individual roof beds. A microcomputer program has been developed to evaluate the decision ratings for cavability and the model applied to ten longwall case-histories from Indian coalfields. The classification model has excellent potential for being used as a standard tool for the evaluation of caving behaviour of longwall roof rocks.  相似文献   

Comparison of wave hindcasts at weather station “J” for North Atlantic storm of December, 1959     

Peter H. Feldhausen  Subrata K. Chakrabarti  Basil W. Wilson 《Ocean Dynamics》1973,26(1):10-16

  相似文献   

Geochemistry of thermal metamorphic and granitization processes in the aureole rocks around Richughuta,Dt. Palamau,Bihar, India     

Dr. N. C. Ghose 《International Journal of Earth Sciences》1970,59(2):686-724

The Archaean metasediments represented by pelitic, semi-pelitic, calcareous and psammitic rocks around Richughuta have been thermally metamorphosed around a granite-granodiorite pluton. A detailed account of chemical and mineralogical studies from both the affected and unaffected representatives of the various rock units was carried out. It is found that the trend of chemical changes across the contact varies under similar physico-chemical conditions in different lithological set-up. Such a diversity in the thermal effect of the aureole rocks is caused due to the difference in chemical potential, geological setting, macro- and micro-structure of the affected rocks, nature of contact, prevailing vapour pressure and temperature in the system and lastly on the original silica content of the rock. The mechanism which controlled the migration of the cations was chiefly a two-way diffusion process and the history of the movement of cation changes, during the entire period of metamorphism.  相似文献   

The α-β phase transition in cristobalite,SiO2     

Dorian M. Hatch  Subrata Ghose 《Physics and Chemistry of Minerals》1991,17(6):554-562

Cristobalite, a high temperature phase of silica, SiO₂, undergoes a (metastable) first-order phase transition from a cubic, , to a tetragonal, P4₃2₁2 (or P4₁2₁2), structure at around 220° C. The cubic C9-type structure for -cristobalite (Wyckoff 1925) is improbable because of two stereochemically unfavorable features: a 180° Si-O-Si angle and an Si-O bond length of 1.54 Å, whereas the corresponding values in tetragonal -cristobalite are 146° and 1.609 Å respectively. The structure of the -phase is still controversial. To resolve this problem, a symmetry analysis of the (or P4₁2₁2) transition in cristobalite has been carried out based on the Landau formalism and projection operator methods. The starting point is the ideal cubic ( ) C9-type structure with the unit cell dimension a (7.432 Å) slightly larger than the known a dimension (7.195 Å at 205° C) of -cristobalite, such that the Si-O-Si angle is still 180°, but the Si-O bond length is 1.609 Å. The six-component order parameter driving the phase transition transforms according to the X₄ representation. The transition mechanism essentially involves a simultaneous translation and rotation of the silicate tetrahedra coupled along 110. A Landau free-energy expression is given as well as a listing of the three types of domains expected in -cristobalite from the transition. These domains are: (i) transformation twins from a loss of 3-fold axes, (ii) enantiomorphous twins from a loss of the inversion center, and (iii) antiphase domains from a loss of translation vectors 1/2 110 (FP). These domains are macroscopic and static in -cristobalite, and microscopic and dynamic in -cristobalite. The order parameter , couples with the strain components as ², which initiates the structural fluctuations, thereby causing the domain configurations to dynamically interchange in the -phase. Hence, the - cristobalite transition is a fluctuation-induced first-order transition and the -phase is a dynamic average of -type domains.  相似文献