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Pranowo, Waskito, and Sonny Winardhi. "Application of Velocity Variation with Angle (VVA) Method on an Anisotropic Model with Thomsen Delta Anisotropy Parameters." Jurnal Geofisika 16, no. 2 (September 19, 2018): 6. http://dx.doi.org/10.36435/jgf.v16i2.371.
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Anisotropic properties will influence seismic propagation, for example it will affect wave velocity. One of well-known anisotropi equation for Transversaly Isotropic media is weak anisotropy with Thomsen's notation. Supriyono [2011] tried to estimate all of these variables by using velocity variation with angle (VVA) attribute. This research uses synthetic data, which is CMP Gather to know limitations of VVA attribute, to identify the error values, and to determine the best indicator of anisotropic eect. This research also uses another analysis method, which is grid search inversion to estimate VP0. From this research, Both VVA and grid search invesion still produce signcant error. The effects which will appear because of anisotropic property's presence are hockey-stick and over NMO-stretching.
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Rongkonusa, Melisa, Gerald Tamuntuan, and Guntur Pasau. "Analisis Anisotropi Suseptibilitas Magnetik Batuan Beku Lengan Utara Sulawesi." Jurnal MIPA 6, no. 1 (May 2, 2017): 8. http://dx.doi.org/10.35799/jm.6.1.2017.15846.
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Telah dilakukan penelitian untuk menentukan pola anisotropi suseptibilitas magnetik dan status singkapan batuan beku dari pola yang diperoleh. Pengukuran anisotropi suseptibilitas magnetic dilakukan pada lima sampel batuan beku dari Sulawesi Utara menggunakan Bartington MS2B. Arah pengukuran sampel disesuaikan dengan desain Tauxe. Hasilnya menunjukkan bahwa suseptibilitas maksimum terdistribusi disekitar arah utara dan timur. Sedangkan suseptibilitas intermediet dan minimum terdistribusi disekitar Utara-Timur dan Timur-Selatan. Elipsoida suseptibilitas cenderung prolate atau lebih lonjong. Batuan beku yang dianalisis merupakan kelompok batuan terobosan yang mekanisme lelehannya terjadi secara vertikal.A research has been conducted to determine the anisotropic pattern of magnetic susceptibility and the status of igneous rocks exposure from the obtained pattern. We have measured the anisotropy of magnetic susceptibility on five samples of igneous rock from North Sulawesi by Bartington MS2B. The position of samples were adjusted according to the Tauxe’s design. The result shows that the maximum susceptibility is distributed around northward and eastward, while the intermediate and minimum susceptibility are distributed around nortward-eastward and eastward-southward. The susceptibility ellipsoid tends to be prolate or more oval. This shows that the igneous rocks that have been analyzed are group of intrusive rocks which melting mechanism occurs through vertical fracture.enetie
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Luthfin, Ahmad, Adi Susilo, and Teguh Suroso. "PEMODELAN BAWAH PERMUKAAN METODE PRE-STACK TIME MIGRATION (PSTM) ISOTROPY DAN METODE PSTM ANISOTROPY HIGH ORDER MOVEOUT (HOM)." JURNAL NEUTRINO 8, no. 2. APRIL (May 2, 2016): 58. http://dx.doi.org/10.18860/neu.v8i2.3265.
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Struktur bawah permukaan memiliki perlapisan yang sangat komplek, sehingga memungkinkan penjalaran gelombang seismik memiliki kecepatan yang berbeda tergantung arah rambatnya. Hal inilah yang mendasari perlunya proses pengolahan data dengan melibatkan parameter anisotropi (<em>η</em>). Umumnya data seismik memiliki nilai anisotropi dengan presentase tertentu, sehingga tidak semua data harus diproses dengan proses anisotropi. Ketepatan metode migrasi yang digunakan dapat menghasilkan gambar penampang struktur bawah permukaan dengan resolusi yang tinggi. Penelitian ini bertujuan untuk memodelkan struktur bawah permukaan dengan menggunakan metode PSTM isotopi (lapisan isotropi) sedangkan untuk lapisan anisotropi dimodelkan dengan metode PSTM anisotropi HOM. Hasil dari metode PSTM isotropi berupa citra, dimana lapisan pertama pada CMP 2073-CMP 2413 hasilnya jelek (beresolusi rendah), tetapi untuk lapisan kedua dan ketiga tampak bagus (beresolusi tinggi). Pada saat diproses dengan PSTM anisotropi, peneliti menggunakan nilai (<em>η) </em>sekitar 0,25 pada lapisan pertama. Berdasarkan hasil PSTM anisotropi pada CMP 2073-CMP 2413 model lapisan pertama menghasilkan citra beresolusi lebih tinggi (lebih bagus), sedangkan model lapisan kedua dan ketiga tidak mengalami kenaikan resolusi yang signifikan. Hal ini karena rasio <em>far offset</em> dan kedalaman lapisan pertama besar menyebabkan lapisan pertama mengalami efek anisotropi, sedangkan lapisan kedua dan ketiga tidak mengalami efek anisotropi
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Febriardi, Julius, and Wahyu Triyoso. "Estimasi Parameter Koreksi Anisotropi Seismik Melalui Pendekatan Nonhyperbolic Moveout Pada Gather Konvensional, DMO, dan CRS." Jurnal Geofisika 15, no. 1 (November 18, 2019): 15. http://dx.doi.org/10.36435/jgf.v15i1.404.
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Sifat anisotropi pada suatu medium menyebabkan adanya perbedaan kecepatan rambat gelombang berdasarkan arah rambatnya. Medium bersifat transvere isotropy memiliki nilai kecepatan yang berbeda ke arah lateral dan vertikal. Medium bersifat vertical transverse isotropy (VTI) memiliki kecepatan lateral yang lebih besar daripada kecepatan vertikal. Perbedaan ini menyebabkan timbulnya efek hockey stick, terutama pada offset jauh. Karena informasi pada offset jauh amat penting, maka efek ini perlu dikoreksi terlebih dahulu sebelum melanjutkan ke tahapan pemrosesan data selanjutnya. Untuk mendapat pemahaman yang lebih baik, maka dibuat model sintetik VTI yang diproses menggunakan normal moveout (NMO), dip moveout (DMO) dan common reflection surface (CRS). Untuk menghilangkan efek dipping dan agar didapatkan hasil velocity analysis yang baik, DMO dan CRS dilakukan. Pilihan ini atas pertimbangan bahwa metode DMO dapat menghilangkan sifat dip- dependent pada gather seismik, dan analisis kecepatan paling mudah dilakukan pada metode CRS. Hasil perbandingan metode DMO dan CRS menunjukkan bahwa CRS menunjukkan S/N ratio yang lebih baik dan memiliki ketidakpastian yang lebih kecil dalam analisis kecepatan yang berpengaruh langsung dalam estimasi parameter koreksi anisotropi. Nilai parameter koreksi anisotropi diestimasi pada CDP yang ditentukan menggunakan pendekatan nonhyperbolic moveout. Nilai rata-rata yang diperoleh pada masing-masing metode menunjukkan hasil yang berbeda. Nilai ηeff yang paling mendekati nilai η model adalah pada metode DMO dan CRS.
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Nurhasan, Abdullah, Dadang Ramdan, Zuardin Azzaino, Alexis Badai Samudra, and Rino Saputra. "Fault Related Stress and Fractures Analysis using the Anisotropy Signatures from Azimuthal Amplitude Variation in Lematang Trend, South Sumatera Basin." Jurnal Geofisika 18, no. 2 (December 22, 2020): 27. http://dx.doi.org/10.36435/jgf.v18i2.444.
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Evaluasi reservoir terrekahkan harus didasari pengetahuan tentang arah rekah dominan dan stress horizontal yang berlaku pada area studi demi mendapatkan rekomendasi arah pengeboran yang optimal. Namun demikian, informasi tentang stress yang banyak ditemukan adalah pada skala regional, global, maupun skala sumuran. Dalam hal pemodelan pada skala reservoir, data seismic dapat dijadikan penghubung kedua skala yang berjauhan tersebut.
Kehadiran rekahan dan stress pada batuan dapat menyebabkan karakter anisotropi di reservoir. Pada skala seismic, sifat anisotropi sebuah media dapat diamati dari perubahan amplitude dan waktu tempuh terhadap azimuth rambat dan pantulan gelombang seismic. Pada makalah ini, kami menggunakan data seismic pre-stack selangkah di depan metode Amplitude Versus Offset (AVO) dan Extended Elastic Impedance (EEI) yang masih mengandalkan perubahan amplitude terhadap sudut pantul, dengan mengamati perubahan amplitude terhadap azimuth (AVAZ). Untuk pencapai tujuan tersebut, kami memproses ulang data seismic 3D dengan menggunakan metode Offset Vector Tile (OVT) sehingga informasi azimuth tersimpan dengan baik.
Informasi yang digunakan untuk menginterpretasi orientasi rewkahan dan tress horizontal maximum adalah orientasi dan magnitude anisotropi. Hasil studi ini menunjukkan rekahan dan stress yang bersifat local dapat dengan yang bersifat regional dan global. Hal ini menunjukkan bahwa arah pengeboran optimal tidak harus dikontrol oleh arah stress global.
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Xiong, Zonghou. "Electromagnetic fields of electric dipoles embedded in a stratified anisotropic earth." GEOPHYSICS 54, no. 12 (December 1989): 1643–46. http://dx.doi.org/10.1190/1.1442633.
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The anisotropy of electrical conductivity in earth formations may be caused by crystal anisotropies of minerals, as well as by minilayers which occur frequently in sedimentary environments. The effects of anisotropy on the propagation of electromagnetic (EM) fields have been studied by many geophysicists. For instance, Kong (1972) and Wait (1981) solved the EM propagation problem for vertically anisotropic layered earths; O’Brien and Morrison (1967), for a horizontally anisotropic multilayer half‐space; Chetayev (1960), as well as Reddy and Rankin (1971), for media of dipping anisotropies; and Al’tgauzen (1969), for more complicated anisotropic media with a tensor dielectric constant of five components.
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Febriyanti, Eka, Amin Suhadi, Dedi Priadi, and Rini Riastuti. "ANALISIS MAMPU BENTUK BAHAN BAKU SELONGSONG MUNISI Cu-Zn 70/30 SETELAH DEFORMASI PADA SUHU 500ºC = ANALYSIS FORMABILITY OF RAW MATERIALS CU - ZN MUNITIONS CASINGS 70/30 AFTER DEFORMATION AT TEMPERATURE 500ºC." Majalah Ilmiah Pengkajian Industri 9, no. 3 (September 5, 2015): 175–78. http://dx.doi.org/10.29122/mipi.v9i3.1648.
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casing because both processes have important role to derive raw material into the required form, dimensions and characteristics. Cu-Zn 70/30 alloy is raw material which normally used as munition casing however, its formability after deformation and heat treatment is not widely known. Therefore, this research has an objective to study the effect of deformation at warm temperature on cold formability by introducing thermomechanical controlled processed in warm rolling. Warm rolling have been conducted by double pass reversible method on 25% x 2, 30% x 2, and 35% x 2 at temperature 500oC. Evaluation of formability have been done by limited tensile test up to 20% elongation and full tensile test until rupture. The result of this research indicates that the best formability of Cu-Zn 70/30 is obtained on specimen which are deformed by warm rolling at actual degree of deformation 38.7%. Formability testing result for his specimen under designated warm rolling parameter has an elongation 10 % with strain hardening coefficient 0.00228, average normal anisotropy value 0.5452, and plannar anisotropy value Δr<1 is: -0.42. ABSTRAKDeformasi dan perlakuan panas selalu menyertai proses pembuatan selongsong peluru karena kedua proses tersebutlah yang mampu mengatur bahan baku menjadi bentuk dan dimensi yang diinginkan serta sesuai dengan karakteristik yang dikehendaki. Padaun Cu-Zn 70/30 adalah bahan baku yang digunakan untuk pembuatan selongsong peluru, namun mampu bentuk paduan ini akibat deformasi dan perlakuan panas belum banyak diketahui. Oleh karena itu pada penelitian ini bertujuan untuk mempelajari pengaruh deformasi yang dilakukan pada suhu hangat terhadap mampu bentuk dingin dengan metode thermomechanical controlled processed menggunakan teknologi canai hangat. Teknologi canai hangat dilakukan dengan metode double pass reversible sebanyak 25% x 2, 30% x 2, dan 35% x 2 pada suhu 500oC. Pengamatan mampu bentuk dilakukan dengan pengujian tarik hanya sampai perpanjangan 20% serta uji tarik sampai putus. Hasil dari penelitian menunjukkan bahwa sifat mampu bentuk terbaik diperoleh pada benda uji yang dideformasi canai hangat di temperatur 500oC dengan derajat deformasi aktual sebesar 38.7%. Apabila dilihat dari sifat mampu bentuknya maka benda uji yang dideformasi canai hangat pada kondisi parameter penelitian ini memiliki nilai elongasi sebesar 10 % dengan nilai koefisien pengerasan regang yang tinggi sebesar 0.00228, nilai anisotropi normal rata-rata sebesar 0.5452, dan nilai anisotropi planar yaitu Δr<1 sebesar -0.42.
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Hood, J. A. "A simple method for decomposing fracture‐induced anisotropy." GEOPHYSICS 56, no. 8 (August 1991): 1275–79. http://dx.doi.org/10.1190/1.1443149.
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A heterogeneous mixture of isotropic elements may appear homogeneous and anisotropic when the scale of its fabric is smaller than the seismic wavelengths that measure it (Backus, 1962). These fabrics can result from thin layering or from oriented microcracks or fractures. In many situations the anisotropy is quite complex, resulting, for example, from fractures in previously anisotropic media. Since these anisotropies combine, the effect of each must be separated to permit the study of either the fractures or the preexisting anisotropy.
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Ramadhan, Muhammad Gilang, Ayuna Santika Putri, Andang Kurniawan, and Amir Mustofa Irawan. "PRIORITAS ARAH PENEMPATAN TITIK PENGAMATAN KECEPATAN VERTIKAL DI KALIMANTAN MENGGUNAKAN ANALISIS ANISOTROPI." Jurnal Meteorologi Klimatologi dan Geofisika 5, no. 3 (April 29, 2019): 63–71. http://dx.doi.org/10.36754/jmkg.v5i3.76.
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Keberadaan hutan sebagai paru-paru dunia berperan penting dalam menghasilkan gas oksigen. Pulau Kalimantan merupakan salah satu paru-paru dunia karena luas hutannya yang mencapai 40,8 juta hektar. Namun, pada saat ini kualitas dan kuantitas hutan di Pulau Kalimantan mengalami penurunan drastis akibat adanya deforestasi dan kebakaran hutan. Kebakaran hutan di Pulau Kalimantan menjadi sorotan dunia karena persebaran asapnya menyebabkan polusi udara di berbagai wilayah Indonesia. Dampak dari persebaran asap kebakaran hutan dipengaruhi oleh kecepatan angin vertikal pada daerah tersebut. Penelitian ini bertujuan untuk menambah bahan pertimbangan dalam menentukan titik pengamatan kecepatan vertikal angin di Pulau Kalimantan, sehingga dapat diketahui prioritas sebaran penempatan titik pengamatan yang dapat digunakan sebagai upaya mitigasi persebaran asap kebakaran hutan. Data kecepatan angin vertikal Pulau Kalimantan pada bulan Juni sampai Oktober mulai tahun 2008 – 2017 disajikan dalam bentuk spasial. Analisis data angin tersebut menggunakan metode variogram permukaan dengan piranti lunak SAGA. Berdasarkan analisis anisotropi, diperoleh hasil bahwa pengamatan kecepatan vertikal angin di Pulau Kalimantan cenderung mempunyai prioritas arah Timur-Barat pada bulan Juni sampai Agustus, prioritas arah Tenggara-Barat Laut pada bulan September, dan prioritas arah Timur Laut-Barat Daya pada Bulan Oktober. Analisis dan pemodelan kecepatan angin vertikal pada Pulau Kalimantan secara umum mendapatkan pola dominan prioritas arah Timur-Barat, sehingga prioritas penempatan titik pengamatan kecepatan vertikal pada Pulau Kalimantan efektif jika membentuk pola oval yang memanjang dari Utara ke Selatan.
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Yu, Jing, Yongmei Zhang, Yuhong Zhao, and Yue Ma. "Anisotropies in Elasticity, Sound Velocity, and Minimum Thermal Conductivity of Low Borides VxBy Compounds." Metals 11, no. 4 (April 1, 2021): 577. http://dx.doi.org/10.3390/met11040577.
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Anisotropies in the elasticity, sound velocity, and minimum thermal conductivity of low borides VB, V5B6, V3B4, and V2B3 are discussed using the first-principles calculations. The various elastic anisotropic indexes (AU, Acomp, and Ashear), three-dimensional (3D) surface contours, and their planar projections among different crystallographic planes of bulk modulus, shear modulus, and Young’s modulus are used to characterize elastic anisotropy. The bulk, shear, and Young’s moduli all show relatively strong degrees of anisotropy. With increased B content, the degree of anisotropy of the bulk modulus increases while those of the shear modulus and Young’s modulus decrease. The anisotropies of the sound velocity in the different planes show obvious differences. Meanwhile, the minimum thermal conductivity shows little dependence on crystallographic direction.
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KRAUS, L. "LOCAL MAGNETIC ANISOTROPY AND MAGNETOANELASTIC EFFECT IN AMORPHOUS AND NANOCRYSTALLINE ALLOYS." International Journal of Modern Physics B 07, no. 01n03 (January 1993): 916–21. http://dx.doi.org/10.1142/s0217979293001979.
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Anelastic deformation of amorphous and nanocrystalline metals results in an anisotropic distribution of atomic pair bonds. This mechanism can lead to rather strong macroscopic magnetic anisotropy in some alloys. Experimental results show that the creep-induced magnetic anisotropy of amorphous and nanocrystalline Fe- and Co-based alloys essentially depends both on TM and metalloid elements. This is a clear evidence that the random local magnetic anisotropy in these materials is closely related to the details of electronic structure. Based on this conclusion a model of bond -orientational anisotropy taking into account the distribution of local anisotropies in TM-based alloys is proposed.
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Janhunen, P., A. Olsson, H. Laakso, and A. Vaivads. "Middle-energy electron anisotropies in the auroral region." Annales Geophysicae 22, no. 1 (January 1, 2004): 237–49. http://dx.doi.org/10.5194/angeo-22-237-2004.
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Abstract. Field-aligned anisotropic electron distribution functions of T∥ > T⊥ type are observed on auroral field lines at both low and high altitudes. We show that typically the anisotropy is limited to a certain range of energies, often below 1keV, although sometimes extending to slightly higher energies as well. Almost always there is simultaneously an isotropic electron distribution at higher energies. Often the anisotropies are up/down symmetrical, although cases with net upward or downward electron flow also occur. For a statistical analysis of the anisotropies we divide the energy range into low (below 100eV), middle (100eV–1keV) and high (above 1keV) energies and develop a measure of anisotropy expressed in density units. The statistical magnetic local time and invariant latitude distribution of the middle-energy anisotropies obeys that of the average auroral oval, whereas the distributions of the low and high energy anisotropies are more irregular. This suggests that it is specifically the middle-energy anisotropies that have something to do with auroral processes. The anisotropy magnitude decreases monotonically with altitude, as one would expect, because electrons have high mobility along the magnetic field and thus, the anisotropy properties spread rapidly to different altitudes. Key words. Magnetospheric physics (auroral phenomena). Space plasma physics (wave-particle interactions; changed particle motion and acceleration)
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Bouknia, Mohamed Lamine, Chemseddine Zebiri, Djamel Sayad, Issa Elfergani, Jonathan Rodriguez, Mohammad Alibakhshikenari, Raed A. Abd-Alhameed, Francisco Falcone, and Ernesto Limiti. "Theoretical Study of the Input Impedance and Electromagnetic Field Distribution of a Dipole Antenna Printed on an Electrical/Magnetic Uniaxial Anisotropic Substrate." Electronics 10, no. 9 (April 29, 2021): 1050. http://dx.doi.org/10.3390/electronics10091050.
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The present work considers the investigation of the effects of both electrical and magnetic uniaxial anisotropies on the input impedance, resonant length, and fields distribution of a dipole printed on an anisotropic grounded substrate. In this study, the associated integral equation, based on the derivation of the Green’s functions in the spectral domain, is numerically solved employing the method of moments. In order to validate the computing method and the evaluated calculation code, numerical results are compared with available data in the literature treating particular cases of electrical uniaxial anisotropy; reasonable agreements are reported. Novel results of the magnetic uniaxial anisotropy effects on the input impedance and the evaluated electromagnetic field are presented and discussed. This work will serve as a stepping stone for further works for a better understanding of the electromagnetic field behavior in complex anisotropic and bi-anisotropic media.
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Castro, Caio Leandro Perdigão, José Jadsom Sampaio de Figueiredo, and Isadora Augusta Soares de Macedo. "COMPARING TWO APPROACHES ON THE ESTIMATIVE ANISOTROPIC PARAMETERSFROM WELL LOGS: AN APPLICATION ON THE NORNE FIELD DATASET." Revista Brasileira de Geofísica 36, no. 4 (December 21, 2018): 1. http://dx.doi.org/10.22564/rbgf.v36i4.1971.
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ABSTRACT. Estimating the elastic properties of the rocks in the subsurface is a task with many challenges. The main goal of this work is to estimate the Thomsen anisotropic parameters from the inversion of elastic stiffness coefficients using data from five wells of the Norne Field, located at Norway. We compare the results of these parameters with the Backus average, using Li’s empirical method. Further, aspect ratio and crack density are calculated from the results of the elastic stiffness coefficients. It is considered a transversely isotropic medium. The results from the two methods showed similarities in estimating anisotropic parameters, aspect ratio and fracture density. The anisotropy of the study area is weak with some regions with moderate anisotropy. Some patterns suggest the possibility of calculating the anisotropic parameters for the adjacent wells and interpolate values for use in seismic processing.Keywords: Transversally isotropic medium, well logs, Thomsen parameters, Backus AverageRESUMO. Estimar as propriedades elásticas das rochas em subsurperfície é uma tarefa com muitos desafios. O principal objetivo deste trabalho é estimar os parâmetros de anisotropia de Thomsen a partir da inversão dos coeficientes de rigidez elástica, utilizando dados de cinco diferentes poços do campo de Norne, localizado na Noruega. Comparamos os resultados obtidos para esses parâmetros com a média de Backus, usando o método empírico de Li. Em seguida, a razão de aspecto e a densidade de fratura foram calculadas a partir dos resultados dos coeficientes de rigidez elástica. O meio transversalmente isotrópico é considerado neste trabalho. Os resultados obtidos a partir dos dois métodos mostraram similaridades na estimativa dos parâmetros de anisotropia, razão de aspecto e densidade de fratura. A anisotropia da área de estudo é fraca com algumas regiões de anisotropia moderada. Alguns padrões encontrados sugerem a possibilidade de calcular os parâmetros de anisotropia para os poços vizinhos e interpolá-los para uso futuro no processamento sísmico.Palavras-chave: Meios transversalmente isotrópicos, perfis de poços, parâmetros de Thomsen, média de Backus 1UFPA,
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Djuraidah, Anik, Septian Rahardiantoro, and Azizah Desiwari. "PENERAPAN METODE COKRIGING DENGAN VARIOGRAM ISOTROPI DAN ANISOTROPI DALAM MEMPREDIKSI CURAH HUJAN BULANAN JAWA BARAT." Jurnal Meteorologi dan Geofisika 20, no. 1 (August 21, 2019): 39. http://dx.doi.org/10.31172/jmg.v20i1.594.
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<p>Curah hujan merupakan salah satu unsur iklim yang penting dalam pertanian. Informasi mengenai ukuran curah hujan dapat diketahui dari pos hujan pada suatu wilayah. Permasalahan yang dihadapi adalah tidak semua wilayah memiliki pos hujan, sehingga metode interpolasi spasial dapat digunakan dalam memprediksi besarnya curah hujan pada suatu wilayah. Metode <em>cokriging </em>merupakan salah satu metode interpolasi spasial yang bersifat <em>Best Linear Unbiased Prediction</em> (BLUP) dengan melibatkan minimum dua peubah. Peubah yang digunakan dalam penelitian ini dipilih berdasarkan keeratan hubungannya, yaitu peubah curah hujan dan elevasi pos hujan. Data yang digunakan dalam penelitian ini adalah curah hujan bulanan tahun 1981 hingga 2013 pada 38 pos hujan di wilayah Jawa Barat. Metode analisis diawali dengan menetukan variogram isotropi yang ditentukan berdasarkan jarak spasial dan variogram anisotropi yang ditentukan berdasarkan jarak dan arah pada kedua peubah. Selanjutnya, variogram yang terbaik digunakan untuk prediksi curah hujan. Hasil penelitian menunjukkan variogram terbaik adalah variogram isotropi dengan hasil prediksi curah hujan bulanan yang mempunyai nilai <em>reduced means square error</em> berkisar antara 0.54 sampai dengan 1.46 dan nilai <em>average error</em> hampir 0.</p><p><em><br /></em></p><p><em>Rainfall is one of the important climatic elements in agriculture. The information on the amount of rainfall can be known from the weather station in a region. The problem faced is not all regions have its own weather station, so that spatial interpolation can be used to predict the amount of rainfall in a region. Cokriging is one of spatial interpolation that has properties BLUP (Best Linear Unbiased Prediction) that involved at least two variables. In this study, the variables used were the amount of rainfall and elevation of the weather station because these variables have a correlation. The data used in this study were monthly rainfall from 1981 to 2013 at 38 weather stations in West Java. The first step in analysis data was determined isotropy variogram determined based on spatial distance and anisotropic variogram determined based on distance and direction in the two variables. Furthermore, the best variogram was used for the rainfall prediction. The results showed the best variogram is isotropy with the results of monthly rainfall predictions with the cokriging method having reduced means square error values ranging from 0.54 to 1.46 and the average error value of almost 0. </em></p>
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Kolomiets, I. S. "Studying anisotropic properties of longitudinal inhomogeneous nondepolarizing media with elliptical phase anisotropy." Semiconductor Physics Quantum Electronics and Optoelectronics 16, no. 4 (December 16, 2013): 366–73. http://dx.doi.org/10.15407/spqeo16.04.366.
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Sharma, M. D. "Rayleigh wave at the surface of a general anisotropic poroelastic medium: derivation of real secular equation." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 474, no. 2211 (March 2018): 20170589. http://dx.doi.org/10.1098/rspa.2017.0589.
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A secular equation governs the propagation of Rayleigh wave at the surface of an anisotropic poroelastic medium. In the case of anisotropy with symmetry, this equation is obtained as a real irrational equation. But, in the absence of anisotropic symmetries, this secular equation is obtained as a complex irrational equation. True surface waves in non-dissipative materials decay only with depth. That means, propagation of Rayleigh wave in anisotropic poroelastic solid should be represented by a real phase velocity. In this study, the determinantal system leading to the complex secular equation is manipulated to obtain a transformed equation. Even for arbitrary (triclinic) anisotropy, this transformed equation remains real for the propagation of true surface waves. Such a real secular equation is obtained with the option of boundary pores being opened or sealed. A numerical example is solved to study the existence and propagation of Rayleigh waves in porous media for the top three (i.e. triclinic, monoclinic and orthorhombic) anisotropies.
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Krūminiene, I. "ANALYSIS OF ANISOTROPIC VARIOGRAM MODELS FOR PREDICTION OF THE CURONIAN LAGOON DATA." Mathematical Modelling and Analysis 11, no. 1 (March 31, 2006): 73–86. http://dx.doi.org/10.3846/13926292.2006.9637303.
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The anisotropy in particular environmental phenomena is detected when behavior of a physical process differs in different directions. In this paper geometric and zonal anisotropies are considered. Various methods of geostatistical analysis, also isotropic and geometrical anisotropic variogram models are compared and applied for the Curonian lagoon depth data. The results demonstrate that after robust estimation, i.e. elimination of outliers and after elimination of geometric anisotropy the precision of prediction and adequacy of models are much better. All computations have been performed by means of gstat, base and spatial packages of R system. Prediction results are compared with the results of research where outliers and geometric anisotropy were not eliminated.
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Mannion, Damien J., J. Scott McDonald, and Colin W. G. Clifford. "Orientation Anisotropies in Human Visual Cortex." Journal of Neurophysiology 103, no. 6 (June 2010): 3465–71. http://dx.doi.org/10.1152/jn.00190.2010.
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Representing the orientation of features in the visual image is a fundamental operation of the early cortical visual system. The nature of such representations can be informed by considering anisotropic distributions of response across the range of orientations. Here we used functional MRI to study modulations in the cortical activity elicited by observation of a sinusoidal grating that varied in orientation. We report a significant anisotropy in the measured blood-oxygen level-dependent activity within visual areas V1, V2, V3, and V3A/B in which horizontal orientations evoked a reduced response. These visual areas and hV4 showed a further anisotropy in which increased responses were observed for orientations that were radial to the point of fixation. We speculate that the anisotropies in cortical activity may be related to anisotropies in the prevalence and behavioral relevance of orientations in typical natural environments.
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Shaaban, S. M., M. Lazar, R. A. López, and R. F. Wimmer-Schweingruber. "On the interplay of solar wind proton and electron instabilities: linear and quasi-linear approaches." Monthly Notices of the Royal Astronomical Society 503, no. 3 (March 31, 2021): 3134–44. http://dx.doi.org/10.1093/mnras/stab075.
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ABSTRACT Important efforts are currently being made to understand the so-called kinetic instabilities, driven by the anisotropy of different species of plasma particles present in the solar wind and terrestrial magnetosphere. These instabilities are fast enough to efficiently convert the free energy of plasma particles into enhanced (small-scale) fluctuations, with multiple implications, regulating the anisotropy of plasma particles. In this paper we use both linear and quasi-linear (QL) frameworks to describe complex unstable regimes, which realistically combine different temperature anisotropies of electrons and ions (protons). Thus various instabilities are parametrized, for example the proton and electron firehose, electromagnetic ion cyclotron and whistler instabilities, showing that their main linear properties are markedly altered by the interplay of anisotropic electrons and protons. Linear theory may predict the strong competition of two instabilities of different natures when their growth rates are comparable. In the QL phase, wave fluctuations grow and saturate at different levels and temporal scales, in comparison to results for the individual excitation of the proton or electron instabilities. In addition, the cumulative effects of the combined proton- and electron-induced fluctuations can markedly stimulate the relaxation of their temperature anisotropies. Only whistler fluctuations inhibit the efficiency of proton firehose fluctuations in the relaxation of anisotropic protons. These results offer valuable premises for further investigations in numerical simulations to decode the full spectrum of kinetic instabilities resulting from the interplay of anisotropic electrons and protons in space plasmas.
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Hagiwara, Teruhiko. "Apparent dip and apparent anisotropy from multifrequency triaxial induction measurements." GEOPHYSICS 76, no. 1 (January 2011): F1—F13. http://dx.doi.org/10.1190/1.3511349.
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The triaxial (or multicomponent) induction log is used to measure not only the resistivity anisotropy of an anisotropic formation but also the relative dip of the tool with respect to the formation. The anisotropic resistivity and the relative dip of layered formations are also inverted from the triaxial induction-log measurements at a depth by assuming a homogeneous anisotropic formation or at multiple depths by assuming a multilayered formation model. When the triaxial induction log is run at multiple frequencies, multifrequency focusing can be applied to the log measurements. Then, the apparent dip is algebraically defined from the frequency-focused triaxial induction measurements at a depth. The apparent dip yields the true dip in an anisotropic formation. The algebraically calculated apparent dip may be used to determine the effective dip in layered formations. The apparent dip yields the true dip in thinly bedded formations. The apparentdip also yields the true dip in thick anisotropic formations. However, the apparent dip yields a smaller dip than the true dip when the anisotropy is small (the anisotropy effect). It yields a much smaller dip in thick isotropic formations. Like the apparent dip, the apparent anisotropy is algebraically defined from the frequency-focused triaxial induction measurements at a depth. The apparent anisotropy yields the true anisotropy in an anisotropic formation. The algebraically calculated apparent anisotropy may be applied to layered formations. The apparent anisotropic resistivity (horizontal and vertical) can likewise be determined algebraically from the frequency-focused triaxial data. In contrast to the apparent dip, which yields the true dip in thinly bedded formations but not in thicker formations, the apparent anisotropy yields the true anisotropy in thick anisotropic formations but not in thinner anisotropic formations. The apparent anisotropy is affected by the shoulder-bed anisotropy when the formation is not thick (the shoulder-bed effect).
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Purnama, Budi, Ismail Ismail, and Suharyana Suharyana. "Kajian Simulasi Mikromagnetik: Ketergantungan Medan Koersif dengan Besaran Intrinsik Nano-Dot Magnetik dengan Anisotropi Tegak Lurus." Jurnal Fisika dan Aplikasinya 9, no. 1 (January 15, 2013): 30. http://dx.doi.org/10.12962/j24604682.v9i1.835.
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Shaaban, S. M., M. Lazar, P. H. Yoon, and S. Poedts. "Quasilinear approach of the cumulative whistler instability in fast solar wind: Constraints of electron temperature anisotropy." Astronomy & Astrophysics 627 (July 2019): A76. http://dx.doi.org/10.1051/0004-6361/201935515.
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Context. Solar outflows are a considerable source of free energy that accumulates in multiple forms such as beaming (or drifting) components, or temperature anisotropies, or both. However, kinetic anisotropies of plasma particles do not grow indefinitely and particle-particle collisions are not efficient enough to explain the observed limits of these anisotropies. Instead, self-generated wave instabilities can efficiently act to constrain kinetic anisotropies, but the existing approaches are simplified and do not provide satisfactory explanations. Thus, small deviations from isotropy shown by the electron temperature (T) in fast solar winds are not explained yet. Aims. This paper provides an advanced quasilinear description of the whistler instability driven by the anisotropic electrons in conditions typical for the fast solar winds. The enhanced whistler-like fluctuations may constrain the upper limits of temperature anisotropy A ≡ T⊥/T∥ > 1, where ⊥, ∥ are defined with respect to the magnetic field direction. Methods. We studied self-generated whistler instabilities, cumulatively driven by the temperature anisotropy and the relative (counter)drift of electron populations, for example, core and halo electrons. Recent studies have shown that quasi-stable states are not bounded by linear instability thresholds but an extended quasilinear approach is necessary to describe these quasi-stable states in this case. Results. Marginal conditions of stability are obtained from a quasilinear theory of cumulative whistler instability and approach the quasi-stable states of electron populations reported by the observations. The instability saturation is determined by the relaxation of both the temperature anisotropy and relative drift of electron populations.
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Garemstani, Hamid, Dong Sheng Li, and Moe A. Khaleel. "Microstructure Sensitive Design and Quantitative Prediction of Effective Conductivity in Fuel Cell Design." Materials Science Forum 561-565 (October 2007): 315–18. http://dx.doi.org/10.4028/www.scientific.net/msf.561-565.315.
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Statistical continuum approach is used to predict effective conductivity of anisotropic random porous heterogeneous media using two-point correlation functions. Probability functions play a critical role in describing the statistical distribution of different constituents in a heterogeneous media. In this study a 3-dimensional two-point correlation function is utilized to characterize the anisotropic porous media of a Cathode materials to incorporate all the details of the microstructure. These correlation functions are then linked to the effective properties using homogenization relations. An anisotropioc Green’s function solution is used to solve the set of field equations. Examples in this study demonstrated how the model captured the anisotropy in effective conductivity of the random heterogeneous media. Predicted results showed the influence of microstructure on the effective conductivity tensor.
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MOHAPATRA, RANJITA K., P. S. SAUMIA, and AJIT M. SRIVASTAVA. "ANALYZING FLOW ANISOTROPIES WITH EXCURSION SETS IN RELATIVISTIC HEAVY-ION COLLISIONS." Modern Physics Letters A 27, no. 29 (September 17, 2012): 1250168. http://dx.doi.org/10.1142/s0217732312501684.
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We show that flow anisotropies in relativistic heavy-ion collisions can be analyzed using a certain technique of shape analysis of excursion sets recently proposed by us for CMBR fluctuations to investigate anisotropic expansion history of the universe. The technique analyzes shapes (sizes) of patches above (below) certain threshold value for transverse energy/particle number (the excursion sets) as a function of the azimuthal angle and rapidity. Modeling flow by imparting extra anisotropic momentum to the momentum distribution of particles from HIJING, we compare the resulting distributions for excursion sets at two different azimuthal angles. Angles with maximum difference in the two distributions identify the event plane, and the magnitude of difference in the two distributions relates to the magnitude of momentum anisotropy, i.e. elliptic flow.
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Wu, Feng Min, and Yuh Zhang Fang. "Anisotropic Growth of Metal Chains on Anisotropic Substrate." Solid State Phenomena 121-123 (March 2007): 1129–32. http://dx.doi.org/10.4028/www.scientific.net/ssp.121-123.1129.
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Based on the exchange mechanism of metal islands growth on anisotropic metal surfaces, the growth processes of anisotropic Cu islands on the anisotropic Pd (110) surface are investigated by Monte Carlo simulations with realistic growth model and physical parameters. The anisotropic diffusion and anisotropic sticking of Cu adatoms are included in the simulation model after being considered the anisotropy of Pd (110) surface and compared to the experiments. It is found that the larger diffusion rate along the [110] channels of Pd (110) surface gives rise to a slower growth rate of Cu island in this direction, unless special effect of the anisotropic sticking is invoked. The simulation results show that the shape anisotropy of Cu islands is mainly due to the sticking anisotropy rather than the diffusion anisotropy.
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OTÁLORA, FERMÍN, and JUANMA GARCÍA-RUIZ. "THE ANISOTROPY OF ON-LATTICE SIMULATIONS OF AGGREGATE GROWTH." Fractals 01, no. 04 (December 1993): 867–74. http://dx.doi.org/10.1142/s0218348x93000897.
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The origin of anisotropy in on-lattice simulations of cluster growth is investigated by quantifying the anisotropic behavior of the two processes involved in the simulation: transport and aggregation of nutrient particles. Three different anisotropic effects are described: anisotropic surface kinetics, anisotropic concentration profiles and anisotropic screening. The relevance of these sources of anisotropy in natural systems is discussed.
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Zhou, Jian Ping, Jin Xia Liu, Wen Yang Gao, Zhi Wen Cui, Wei Guo Lv, and Ke Xie Wang. "Effect of Anisotropy on Shear Wave Velocity in Wood." Advanced Materials Research 535-537 (June 2012): 1923–26. http://dx.doi.org/10.4028/www.scientific.net/amr.535-537.1923.
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The velocities of shear waves propagating along radial direction of birch and elmwood specimens are measured in order to study the effect of anisotropy on shear wave velocity. The relationship between the shear wave velocity and the oscillation direction is examined by rotating an ultrasonic sensor. The results indicate that the effect of anisotropy on shear wave velocity in birch and elmwood specimens is similar to Japanese magnolia specimen. When the oscillation direction of the shear wave corresponds to the certain anisotropic direction of the wood specimen, the shear wave velocity decreases sharply and the relationship between shear wave velocity and rotation angle tends to become discontinuous. The intrinsic birefringence due to the anisotropy of birch and elmwood woods is observed. Their texture anisotropies are strong. In an isotropic nylon, on the contrary, the value of shear wave velocity was similar to a circular ring. This investigation is significant meanings in architectural and civil engineering field.
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Šoltis, Tomáš, and Jozef Brestenský. "Magnetoconvection in a plane layer rotating about the horizontal axis: The effect of anisotropic diffusivities." Contributions to Geophysics and Geodesy 43, no. 4 (December 1, 2013): 271–303. http://dx.doi.org/10.2478/congeo-2013-0017.
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Abstract A linear stability analysis of convection arising in a horizontal plane layer rotating about the horizontal axis and permeated by a homogeneous horizontal magnetic field perpendicular to the rotation axis is performed. Resulting horizontal convective rolls are inclined to the magnetic field at an angle dependent on the dimensionless numbers − the Elsasser, Ekman and Roberts numbers, and moreover on the anisotropy parameter, the ratio of horizontal and vertical diffusion coefficients (which are the viscosity and thermal diffusivity; magnetic diffusivity is considered isotropic). Two types of anisotropies, SA andBM, are considered and compared with the isotropic case of diffusion coefficients. In the stratification anisotropy, SA, of the Sa and So types, diffusivities in the horizontal directions are, respectively, smaller and greater than the vertical ones. In the BM anisotropy (Braginsky and Meytlis, 1990), the diffusivities in the directions of rotation axis and magnetic field - in the horizontal directions are greater than in vertical direction, thus identically as in So type anisotropy. Results of this H case, the model with the horizontal rotation axis, are compared with the V case of a similar model with the vertical rotation axis. The modes of instabilities are much more sensitive to viscosity and various anisotropies in the H case than in the V case. Results indicate that the effects of anisotropic diffusivities on the Earth’s core magnetoconvection and geodynamo processes should be studied more thoroughly in simpler models than is usually done.
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Shaaban, S. M., and M. Lazar. "Whistler instabilities from the interplay of electron anisotropies in space plasmas: a quasi-linear approach." Monthly Notices of the Royal Astronomical Society 492, no. 3 (December 28, 2019): 3529–39. http://dx.doi.org/10.1093/mnras/stz3569.
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ABSTRACT Recent statistical studies of observational data unveil relevant correlations between whistler fluctuations and the anisotropic electron populations present in space plasmas, e.g. solar wind and planetary magnetospheres. Locally, whistlers can be excited by two sources of free energy associated with anisotropic electrons, i.e. temperature anisotropies and beaming populations carrying the heat flux. However, these two sources of free energy and the resulting instabilities are usually studied independently preventing a realistic interpretation of their interplay. This paper presents the results of a parametric quasi-linear study of the whistler instability cumulatively driven by two counter-drifting electron populations and their anisotropic temperatures. By comparison to individual regimes dominated either by beaming population or by temperature anisotropy, in a transitory regime the instability becomes highly conditioned by the effects of both these two sources of free energy. Cumulative effects stimulate the instability and enhance the resulting fluctuations, which interact with electrons and stimulate their diffusion in velocity space, leading to a faster and deeper relaxation of the beaming velocity associated with a core heating in perpendicular direction and a thermalization of the beaming electrons. In particular, the relaxation of temperature anisotropy to quasi-stable states below the thresholds conditions predicted by linear theory may explain the observations showing the accumulation of these states near the isotropy and equipartition of energy.
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Dudkowiak, Alina, Danuta Frackowiak, Ewa Teślak, Zygmunt Gryczyński, and Ignacy Gryczyński. "Orientation and spectral properties of two stilbazolium merocyanine dyes in stretched and unstretched polyvinyl alcohol films." Acta Biochimica Polonica 54, no. 3 (September 18, 2007): 647–56. http://dx.doi.org/10.18388/abp.2007_3238.
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Spectral properties (anisotropy coefficients calculated for absorption, emission and fluorescence decay time) of two stilbazolium merocyanine dyes have been determined to evaluate the applicability of these dyes as sensitizers in photodynamic therapy. The dyes were embedded in an anisotropic polymer matrix. Analysis of the emission decay components measured in polarized light provides information on the interactions of the dye molecules with the polymer matrix being a model of an anisotropic biological system. Different values of the emission anisotropies obtained from various polarized components of fluorescence decays have shown that the orientations of the dye molecules influence their interactions with the polymer. This means that differently oriented dye molecules located in biological systems should exhibit different interactions with membranes. The chain length and type of side groups attached as well as the salt form of the dye molecule were shown to influence the dye-polymer interactions and should be taken into account before the application of merocyanine dyes in medicine. These dyes seem to be promising optical sensors with spectral properties, including the calculated anisotropy coefficients, sensitive to the molecular environment, useful to study orientation and interaction with neighbouring molecules in biological membranes.
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Tsvankin, Ilya, and Leon Thomsen. "Nonhyperbolic reflection moveout in anisotropic media." GEOPHYSICS 59, no. 8 (August 1994): 1290–304. http://dx.doi.org/10.1190/1.1443686.
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The standard hyperbolic approximation for reflection moveouts in layered media is accurate only for relatively short spreads, even if the layers are isotropic. Velocity anisotropy may significantly enhance deviations from hyperbolic moveout. Nonhyperbolic analysis in anisotropic media is also important because conventional hyperbolic moveout processing on short spreads is insufficient to recover the true vertical velocity (hence the depth). We present analytic and numerical analysis of the combined influence of vertical transverse isotropy and layering on long‐spread reflection moveouts. Qualitative description of nonhyperbolic moveout on “intermediate” spreads (offset‐to‐depth ratio x/z < 1.7–2) is given in terms of the exact fourth‐order Taylor series expansion for P, SV, and P‐SV traveltime curves, valid for multilayered transversely isotropic media with arbitrary strength of anisotropy. We use this expansion to provide an analytic explanation for deviations from hyperbolic moveout, such as the strongly nonhyperbolic SV‐moveout observed numerically in the case where δ < ε. With this expansion, we also show that the weak anisotropy approximation becomes inadequate (to describe nonhyperbolic moveout) for surprisingly small values of the anisotropies δ and ε. However, the fourth‐order Taylor series rapidly loses numerical accuracy with increasing offset. We suggest a new, more general analytical approximation, and test it against several transversely isotropic models. For P‐waves, this moveout equation remains numerically accurate even for substantial anisotropy and large offsets. This approximation provides a fast and effective way to estimate the behavior of long‐spread moveouts for layered anisotropic models.
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Silva, Bruno dos Santos, and Ellen de Nazaré Souza Gomes. "LOCAL ANISOTROPY ESTIMATION FROM QP-WAVE VSP DATA: ANALYSIS OF 3D SURVEY DESIGN." Brazilian Journal of Geophysics 37, no. 1 (March 27, 2019): 29. http://dx.doi.org/10.22564/rbgf.v37i1.1987.
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ABSTRACT. In the world, many unconventional hydrocarbon reservoirs have been found. This type of reservoir generally has anisotropic properties. The estimation of the anisotropy of the medium can give useful information about the reservoir, for example, one can obtain the information on the direction of fractures, these are related to the preferential flow. This information is important in deciding which direction to drill the well. Measurements of slowness and polarization of qP-wave obtained from VSP (vertical seismic profile) experiments allow estimating the anisotropy in the vicinity of a geophones inside the borehole. Using the perturbation theory, a weakly anisotropic medium can be modeled by first-order perturbation around an isotropic reference medium. The inversion scheme is based on a linear approximation which expresses the slowness and polarization in terms of WA (weak anisotropy) parameters. These parameters characterize the deviations of the anisotropic medium from a reference isotropic medium. In presented inversion scheme, we use the three components of the polarization, since we consider 3C (three-components) geophones, and only one of the slowness components, the one along the borehole direction, where is located the receiver array. In this work, the inversion scheme using VSP data of slowness and polarization from direct wave qP for the estimation of the parameters of weak anisotropy WA is analyzed considering the orientation of the horizontal borehole. Three different configurations for the sources are analyzed. The results are compared with results from vertical borehole. It has been found that only a group of components of the tensor of the WA parameters is well estimated and this group depend on the orientation of the borehole. On the other hand, the phase velocity determined from the WA parameter tensor is always well estimated in a 30_ cone around the borehole, regardless of the borehole orientation.Keywords: Local anisotropy, VSP multiazimuthal, linear inversion, survey design.RESUMO. Muitos reservatórios de hidrocarbonetos não convencionais tem sido encontrados. Esse tipo de reservatório geralmente tem propriedades anisotrópicas. A estimativa da anisotropia do meio pode fornecer informações úteis sobre o reservatório, como por exemplo, informações sobre a direção das fraturas que estão relacionadas a direção de fluxo preferencial. Esta informação é importante para decidir que direção furar o poço. Medidas de vagarosidade e polarização de ondas qP obtidas em levantamentos de VSP (vertical seismic profile) permitem estimar a anisotropia na vizinhança de um geofone dentro do poço. Usando a teoria da perturbação, um meio fracamente anisotrópico pode ser modelado como uma perturbação de primeira ordem em torno de um meio isotrópico de referência. O esquema de inversão baseia-se numa aproximação linear que expressa a vagarosidade e polarização em termos do parâmetros WA (fraca anisotropia). Esses parâmetros caracterizam os desvios do meio anisotrópico a partir de um meio isotrópico de referência. No esquema de inversão são usadas as três componentes do vetor de polarização, esta-se considerando geofones 3C (três componentes) e apenas uma componente do vetor de vagarosidade, a componente ao longo da direção de orientação do poço, onde estão localizados os receptores. Neste trabalho, é analisado o esquema de inversão são usados dados de vagarosidade e polarização de ondas qP diretas em experimentos de VSP considerando a orientação do poço horizontal. Três diferentes configurações para as fontes são estudadas. Os resultados foram comparados com os resultados obtidos considerando o poço vertical. Verifica-se que apenas um grupo de componentes do tensor dos parâmetros elásticos WA é bem estimado. Este grupo depende da orientação do poço. Por outro lado, a velocidade de fase determinada a partir dos parâmetros WA é sempre bem estimada em um cone de 30_ torno do poço, independente de sua orientação. Palavras-chave: Anisotropia Local, VSP multiazimutal, inversão linear, desenho de experimento.
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Martins, Jorge L. "Elastic impedance in weakly anisotropic media." GEOPHYSICS 71, no. 3 (May 2006): D73—D83. http://dx.doi.org/10.1190/1.2195448.
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The original formulation for the P-wave elastic impedance (EI) equation ignores seismic anisotropy. Incorporation of anisotropy effects into the EI formula requires a suitable approximation for reflection coefficients. In order to derive an anisotropic EI equation, this paper uses an approximation for PP-wave reflection [Formula: see text] coefficients which holds for weak-contrast interfaces separating weakly anisotropic media of arbitrary symmetry. Inserting the chosen [Formula: see text] coefficient approximation into the original formalism provides an anisotropic EI formula, which is written as a product of two terms: a modified version for the isotropic EI equation and a correction because of weak anisotropy. The latter term shows dependence of the anisotropic EI formula on the so-called weak anisotropy (WA) parameters, on a reference isotropic medium, and on the azimuthal and incident phase angles. Numerical tests show the performance of the EI formula in calculating anisotropic [Formula: see text] coefficients and in constructing azimuthal far-offset EI logs. Since EI allows applying poststack algorithms without modification, an inversion methodology can be designed for investigating anisotropy in sedimentary formations.
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Mastio, Nicolas, Pierre Thore, Marianne Conin, and Guillaume Caumon. "Determination of a stress-dependent rock-physics model using anisotropic time-lapse tomographic inversion." GEOPHYSICS 85, no. 4 (June 10, 2020): C141—C152. http://dx.doi.org/10.1190/geo2019-0526.1.
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In the petroleum industry, time-lapse (4D) studies are commonly used for reservoir monitoring, but they are also useful to perform risk assessment for potential overburden deformations (e.g., well shearing, cap-rock integrity). Although complex anisotropic velocity changes are predicted in the overburden by geomechanical studies, conventional time-lapse inversion workflows only deal with vertical velocity changes. To retrieve the geomechanically induced anisotropy, we have adopted a reflection traveltime tomography method coupled with a time-shift estimation algorithm of prestack data of the baseline and monitor simultaneously. For the 2D approach, we parameterize the anisotropy using five coefficients, enough to cover any type of anisotropy. Before applying the workflow to a real data set, we first study a synthetic data set based on the real data set and include velocity variations between baseline and monitor found in the literature (vertical P-wave velocity decrease in the cap rock and isotropic P-wave velocity change in the reservoir). On the synthetics, we measure the angular ray coverage necessary to retrieve the target anisotropy and observe that the retrieved anisotropies depend on the offset range. Based on a synthetic experiment, we believe that the acquisition of the real case study is suitable for performing tomographic inversion. The anisotropic velocity changes obtained on three inlines separated by 375 m are consistent and show a strong positive anomaly in the cap rock along the 45° direction (the [Formula: see text] parameter in Thomsen notation), whereas the vertical velocity change is surprisingly almost negligible. We adopt a rock-physics explanation compatible with these observations and geologic considerations: a reactivation of water-filled subvertical cracks.
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VanderBeek, Brandon P., and Manuele Faccenda. "Imaging upper mantle anisotropy with teleseismic P-wave delays: insights from tomographic reconstructions of subduction simulations." Geophysical Journal International 225, no. 3 (March 1, 2021): 2097–119. http://dx.doi.org/10.1093/gji/ggab081.
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SUMMARY Despite the well-established anisotropic nature of Earth’s upper mantle, the influence of elastic anisotropy on teleseismic P-wave imaging remains largely ignored. Unmodelled anisotropic heterogeneity can lead to substantial isotropic velocity artefacts that may be misinterpreted as compositional heterogeneities. Recent studies have demonstrated the possibility of inverting P-wave delay times for the strength and orientation of seismic anisotropy. However, the ability of P-wave delay times to constrain complex anisotropic patterns, such as those expected in subduction settings, remains unclear as synthetic testing has been restricted to the recovery of simplified block-like structures using ideal self-consistent data (i.e. data produced using the assumptions built into the tomography algorithm). Here, we present a modified parametrization for imaging arbitrarily oriented hexagonal anisotropy and test the method by reconstructing geodynamic simulations of subduction. Our inversion approach allows for isotropic starting models and includes approximate analytic finite-frequency sensitivity kernels for the simplified anisotropic parameters. Synthetic seismic data are created by propagating teleseismic waves through an elastically anisotropic subduction zone model created via petrologic-thermomechanical modelling. Delay times across a synthetic seismic array are measured using conventional cross-correlation techniques. We find that our imaging algorithm is capable of resolving large-scale features in subduction zone anisotropic structure (e.g. toroidal flow pattern and dipping fabrics associated with the descending slab). Allowing for arbitrarily oriented anisotropy also results in a more accurate reconstruction of isotropic slab structure. In comparison, models created assuming isotropy or only azimuthal anisotropy contain significant isotropic and anisotropic imaging artefacts that may lead to spurious interpretations. We conclude that teleseismic P-wave traveltimes are a useful observable for probing the 3-D distribution of upper mantle anisotropy and that anisotropic inversions should be explored to better understand the nature of isotropic velocity anomalies particularly in subduction settings.
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Thomsen, Leon. "Weak elastic anisotropy." GEOPHYSICS 51, no. 10 (October 1986): 1954–66. http://dx.doi.org/10.1190/1.1442051.
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Most bulk elastic media are weakly anisotropic. The equations governing weak anisotropy are much simpler than those governing strong anisotropy, and they are much easier to grasp intuitively. These equations indicate that a certain anisotropic parameter (denoted δ) controls most anisotropic phenomena of importance in exploration geophysics, some of which are nonnegligible even when the anisotropy is weak. The critical parameter δ is an awkward combination of elastic parameters, a combination which is totally independent of horizontal velocity and which may be either positive or negative in natural contexts.
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Banik, N. C. "An effective anisotropy parameter in transversely isotropic media." GEOPHYSICS 52, no. 12 (December 1987): 1654–64. http://dx.doi.org/10.1190/1.1442282.
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An interesting physical meaning is presented for the anisotropy parameter δ, previously introduced by Thomsen to describe weak anisotropy in transversely isotropic media. Roughly, δ is the difference between the P-wave and SV-wave anisotropies of the medium. The observed systematic depth errors in the North Sea are reexamined in view of the new interpretation of the moveout velocity through δ. The changes in δ at an interface adequately describe the effects of transverse isotropy on the P-wave reflection amplitude, The reflection coefficient expression is linearized in terms of changes in elastic parameters. The linearized expression clearly shows that it is the variation of δ at the interface that gives the anisotropic effects at small incidence angles. Thus, δ effectively describes both the moveout velocity and the reflection amplitude variation, two very important pieces of information in reflection seismic prospecting, in the presence of transverse isotropy.
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Secco, R. A., and P. S. Balog. "On the possibility of anisotropic heat flow in the inner core." Canadian Journal of Earth Sciences 38, no. 6 (June 1, 2001): 975–82. http://dx.doi.org/10.1139/e00-116.
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We consider the possibility of anisotropic heat flow in the inner core by examining the potential for anisotropic thermal conductivity of hexagonal close-packed (hcp-)Fe. Because hcp-Fe exists only at pressures above 13 GPa at room temperature, we investigate thermal conductivity anisotropy in analog material Gd by measuring the electrical conductivity and applying the WiedemannFranz Law to determine thermal conductivity (k). The electrical conductivity anisotropy of Gd was measured at pressures up to 1.4 GPa and temperatures up to 873 K in the hcp phase range. At elevated pressure, the variation with temperature of anisotropic thermal conductivity of Gd single crystal resembles the anisotropic behavior at high temperature and 1 atm observed in earlier work. The temperature range of anisotropy of thermal conductivity of Gd, where kc > ka, is extended by pressure, but the anisotropy disappears before the high temperature hcp[Formula: see text]bcc (body-centered cubic) transformation. Our results on hcp-Gd lead us to raise the question of the possibility of hcp-Fe exhibiting anisotropy of thermal conductivity. Together with the known seismic anisotropy of the inner core, and the inferred textural alignment of hcp crystals causing it, we suggest some implications that an anisotropy of thermal conductivity of hcp-Fe, and a concomitant anisotropy of inner core heat flow, could have on thermally driven core processes.
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Brito, P., and M. Mechetti. "Determination of dipole moment values of anisotropic molecules using Brot's formalism." Canadian Journal of Chemistry 68, no. 9 (September 1, 1990): 1523–26. http://dx.doi.org/10.1139/v90-234.
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A method for the determination of dipole moment values based on Brot's theory is proposed. It takes into account the influence of the molecular anisotropies of shape and polarizability on the permittivity of a mixture. Starting from measurements performed on dilute solutions and from the knowledge of the molecular structure of some chlorinated derivatives of α-cyanostilbene and 1,3 derivatives of benzene, the best parameters of an ellipsoid used for the representation of a polar anisotropic molecule are determined. The dipole moments obtained, using benzene and tetrachloromethane as solvents, are finally compared to values from the literature. Keywords: dipole moment, Brot's formalism, molecular anisotropy.
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ACHARYYA, MUKTISH. "AXIAL AND OFF-AXIAL DYNAMIC TRANSITIONS IN UNIAXIALLY ANISOTROPIC HEISENBERG FERROMAGNET: A COMPARISON." International Journal of Modern Physics C 14, no. 01 (January 2003): 49–59. http://dx.doi.org/10.1142/s0129183103004206.
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Uniaxially anisotropic Heisenberg ferromagnet, in the presence of a magnetic field varying sinusoidally in time, is studied by Monte Carlo simulation. The axial (field applied only along the direction of anisotropy) and off-axial (field applied only along the direction which is perpendicular to the direction of anisotropy) dynamic transitions are studied. By studying the distribution of the dynamic order parameter component, it is observed that the axial transition is discontinuous for low anisotropy and becomes continuous in high anisotropy. The off-axial transition is found to be continuous for all values of anisotropy. In the infinite anisotropy limit, both types of transitions are compared with that observed in an Ising ferromagnet for the same value of the field and frequency. The infinitely anisotropic axial transition and dynamic transition in the Ising ferromagnet occur at different temperatures, whereas the infinitely anisotropic off-axial transition and the equilibrium ferro-para transition in the Ising model occur at the same temperature.
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Yuan, S. P., and R. M. C. So. "Turbulent rotating flow calculations: An assessment of two-equation anisotropic and Reynolds stress models." Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering 212, no. 3 (March 1, 1998): 193–212. http://dx.doi.org/10.1243/0954410981532270.
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The stress field in a rotating turbulent internal flow is highly anisotropic. This is true irrespective of whether the axis of rotation is aligned with or normal to the mean flow plane. Consequently, turbulent rotating flow is very difficult to model. This paper attempts to assess the relative merits of three different ways to account for stress anisotropies in a rotating flow. One is to assume an anisotropic stress tensor, another is to model the anisotropy of the dissipation rate tensor, while a third is to solve the stress transport equations directly. Two different near-wall two-equation models and one Reynolds stress closure are considered. All the models tested are asymptotically consistent near the wall. The predictions are compared with measurements and direct numerical simulation data. Calculations of turbulent flows with inlet swirl numbers up to 1.3, with and without a central recirculation, reveal that none of the anisotropic two-equation models tested is capable of replicating the mean velocity field at these swirl numbers. This investigation, therefore, indicates that neither the assumption of anisotropic stress tensor nor that of an anisotropic dissipation rate tensor is sufficient to model flows with medium to high rotation correctly. It is further found that, at very high rotation rates, even the Reynolds stress closure fails to predict accurately the extent of the central recirculation zone.
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Grech, M. Graziella Kirtland, Don C. Lawton, and Samuel H. Gray. "A multioffset vertical seismic profiling experiment for anisotropy analysis and depth imaging." GEOPHYSICS 67, no. 2 (March 2002): 348–54. http://dx.doi.org/10.1190/1.1468595.
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A multioffset vertical seismic profile (VSP) was carried out in the Rocky Mountain foothills of southern Alberta, Canada. The purpose of this experiment was to investigate whether the dipping shale strata exhibit P‐wave velocity anisotropy and, if so, to calculate the Thomsen anisotropy parameters for use in anisotropic depth migration. Traveltime inversion of first‐arrival data from the multioffset VSP revealed that the dipping Mesozoic clastics in the area exhibit seismic velocity anisotropy of about 10%. The anisotropy parameters derived from this experiment were then used in anisotropic prestack depth migration of data from a surface seismic line close to the VSP well. Comparison of the anisotropic migration with the corresponding isotropic prestack depth migration showed that the target was imaged incorrectly in the isotropic case; a lateral shift of 180 m in the updip direction of the overlying beds was observed. The image obtained with an anisotropic velocity model was also better focused than that obtained assuming isotropic velocities.
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Thomsen, Leon. "Reflection seismology over azimuthally anisotropic media." GEOPHYSICS 53, no. 3 (March 1988): 304–13. http://dx.doi.org/10.1190/1.1442464.
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Recent surveys have shown that azimuthal anisotropy (due most plausibly to aligned fractures) has an important effect on seismic shear waves. Previous work had discussed these effects on VSP data; the same effects are seen in surface recording of reflections at small to moderate angles of incidence. The anisotropic effects on different polarization components of vertically traveling shear waves permit the recognition and estimation of very small degrees of azimuthal anisotropy (of order ⩾1 percent), as in an interferometer. Anisotropic effects on traveltime yield estimates of anisotropy which are averages over large depth intervals. Often, raw field data must be corrected for these effects before the reflectors may be imaged; two variations of a rotational algorithm to determine the “principal time series” are derived. Anisotropic effects on moveout lead to abnormal moveout unless the survey line is parallel to the fractures. Anisotropic effects on reflection amplitude permit the recognition and estimation of anisotropy (hence fracture intensity) differences at the reflecting horizon, i.e., with high vertical resolution.
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Chang, Hui, and George McMechan. "3D 3-C full-wavefield elastic inversion for estimating anisotropic parameters: A feasibility study with synthetic data." GEOPHYSICS 74, no. 6 (November 2009): WCC159—WCC175. http://dx.doi.org/10.1190/1.3204766.
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Traveltime-based inversions cannot solve for all of the anisotropy parameters for orthorhombic media. Vertical velocities cannot be recovered simultaneously with the dimensionless anisotropy parameters. Also, the density cannot be solved because it does not affect the normal moveout of P and S reflections. These limitations can be overcome using full-wavefield inversion for anisotropy parameters for orthorhombic media and for transversely isotropic media with vertical and horizontal symmetry axes. Tsvankin’s parameters and the orientation of the local (anisotropic) coordinates are inverted from three-component, wide-azimuth data sets containing P reflected and PS converted waves. The inversions are performed in two steps. The first step uses only reflections from the top of an anisotropic layer, whichdoes not constrain the trade-offs between the vertical velocities, the anisotropies, and density, as shown by parameter correlation analysis. The results from the first step are refined by using them as the starting model for the second step, which fits reflections from the top and bottom of the layer. The properties of the target layer influence the amplitudes of top and bottom reflections as well as the traveltime of the bottom reflections; when all these data are used, the inversion is highly overdetermined and all model parameters are estimated accurately. When Gaussian noise is added, the inversion results are very similar to those for the noise-free data because only the coherent signal is fitted. The residual at convergence for the noisy data corresponds to the noise level. Concurrent inversion of data from multiple sources increases the azimuthal illumination of a target.
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Tramsen, Halvor T., Stanislav N. Gorb, Hao Zhang, Poramate Manoonpong, Zhendong Dai, and Lars Heepe. "Inversion of friction anisotropy in a bio-inspired asymmetrically structured surface." Journal of The Royal Society Interface 15, no. 138 (January 2018): 20170629. http://dx.doi.org/10.1098/rsif.2017.0629.
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Friction anisotropy is an important property of many surfaces that usually facilitate the generation of motion in a preferred direction. Such surfaces are very common in biological systems and have been the templates for various bio-inspired materials with similar tribological properties. So far friction anisotropy is considered to be the result of an asymmetric arrangement of surface nano- and microstructures. However, here we show by using bio-inspired sawtooth-structured surfaces that the anisotropic friction properties are not only controlled by an asymmetric surface topography, but also by the ratio of the sample–substrate stiffness, the aspect ratio of surface structures, and by the substrate roughness. Systematically modifying these parameters, we were able to demonstrate a broad range of friction anisotropies, and for specific sample–substrate combinations even an inversion of the anisotropy. This result highlights the complex interrelation between the different material and topographical parameters on friction properties and sheds new light on the conventional design paradigm of tribological systems. Finally, this result is also of great importance for understanding functional principles of biological materials and surfaces, as such inversion of friction anisotropy may correlate with gait pattern and walking behaviour in climbing animals, which in turn may be used in robotic applications.
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Song, Honghua, Yixin Zhao, Yaodong Jiang, and Jiehao Wang. "Scale Effect on the Anisotropy of Acoustic Emission in Coal." Shock and Vibration 2018 (December 18, 2018): 1–11. http://dx.doi.org/10.1155/2018/8386428.
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Acoustic emission (AE) in coal is anisotropic. In this paper, we investigate the microstructure-related scale effect on the anisotropic AE feature in coal at unconfined loading process. A series of coal specimens were processed with diameters of 25 mm, 38 mm, 50 mm, and 75 mm (height to diameter ratio of 2) and anisotropic angles of 0°, 15°, 30°, 45°, 60°, and 90°. The cumulative AE counts and energy dissipation increase with the specimen size, while the energy dissipation per AE count behaves in the opposite way. This may result from the increasing amount of both preexisting discontinuities and cracks (volume/number) needed for specimen failure and the lower energy dissipation AE counts generated by them. The effect of microstructures on the anisotropies of AE weakens with the increasing specimen size. The TRFD and its anisotropy reduce as the specimen size increases, and the reduction of fractal dimension is most pronounced at the anisotropic angle of 45°. The correlation between TRFD and cumulative AE energy in the specimens with different sizes are separately consistent with the negative exponential equation proposed by Xie and Pariseau. With the specimen size gain, the reduction of the TRFD weakens with the increasing amount of cumulative absolute AE energy.
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Vladimirov, Ivaylo N., and Stefanie Reese. "Prediction of Springback in Unconstrained Bending by a Model for Evolving Elastic and Plastic Anisotropy." Key Engineering Materials 554-557 (June 2013): 2330–37. http://dx.doi.org/10.4028/www.scientific.net/kem.554-557.2330.
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Sheet metals exhibit anisotropic plastic behavior due to the large plastic deformations that occur during the rolling of the sheet and which induce texture and are responsible for the initial anisotropy. There exist various possibilities to introduce plastic anisotropy into the finite element modelling of sheet metal forming. The initial yield anisotropy can be incorporated either through an anisotropic yield surface or directly by means of a crystallographic texture model. Here, one basically differentiates between empirical and phenomenological anisotropic yield function equations, where the anisotropy coefficients can be obtained from mechanical tests, and texture-based models the coefficients of which are directly determined based on experimentally obtained orientation distributions. Another type of anisotropy that can be usually found in anisotropic materials is the elastic anisotropy. In metal plasticity one often considers the effect of elastic anisotropy significantly smaller than the effect of plastic anisotropy. Consequently, elastic isotropic expressions are often used for elastic stored energy functions with anisotropic yield criteria. However, the influence of elastic anisotropy in the elastoplastic behavior can be very important especially during elastic recovery processes during unloading after forming and springback. This research focuses, therefore, on the study of the influence of elastic anisotropy on the amount of springback in bending processes such as e.g. unconstrained bending. We discuss a finite strain material model for evolving elastic and plastic anisotropy combining nonlinear isotropic and kinematic hardening. The evolution of elastic anisotropy is described by representing the Helmholtz free energy as a function of a family of evolving structure tensors. In addition, plastic anisotropy is modelled via the dependence of the yield surface on the same family of structure tensors. Exploiting the dissipation inequality leads to the interesting result that all tensor-valued internal variables are symmetric. Thus, the integration of the evolution equations can be efficiently performed by means of an algorithm that automatically retains the symmetry of the internal variables in every time step. The material model has been implemented as a user material subroutine UMAT into the commercial finite element software ABAQUS/Standard and has been applied to the simulation of springback of unconstrained bending.
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Ben Slimane, Mourad. "Anisotropic Two-Microlocal Spaces and Regularity." Journal of Function Spaces 2014 (2014): 1–10. http://dx.doi.org/10.1155/2014/505796.
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We defineD-u-anisotropic two-microlocal spaces by decay conditions on anisotropic wavelet coefficients on anyD-u-anisotropic wavelet basis ofL2(Rd). We prove that these spaces allow the characterizing of pointwise anisotropic Hölder regularity. We also prove an anisotropic wavelet criterion for anisotropic uniform regularity. We finally prove that both this criterion and anisotropicD-u-two-microlocal spaces are independent of the chosen anisotropicD-u-orthonormal wavelet basis.
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Han, Han. "Influence of Material Anisotropy and Friction on Ring Deformation." Journal of Tribology 124, no. 3 (May 31, 2002): 637–44. http://dx.doi.org/10.1115/1.1473144.
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The influence of material anisotropy and friction on ring deformation has been examined in relation to the distribution of normal pressure and frictional shear stress, deformed ring shapes, and estimated errors in the coefficient of friction. Based on the flow rule associated with von Mises’ and Hill’s yield criteria, the analyses have been carried out with the finite element method (FEM) for three cases, namely, (1) an anisotropic ring oriented 90 deg to the axis of rotational symmetrical anisotropy under uniform coefficient of friction; (2) an isotropic ring under frictional anisotropy condition; and (3) an anisotropic ring oriented 0 deg to the axis of rotational symmetrical anisotropy under uniform coefficient of friction. In the first two cases, the results show that the influence of anisotropy on ring deformation is quite similar to that obtained by changing the frictional condition. Therefore, in the third case, if the anisotropic behavior is mistakenly attributed to friction, the possible estimated error for the coefficient of friction can be as high as 80 percent for a pronounced anisotropic material. Deformed ring shapes have been verified in experiments using the extruded annealed aluminum alloy AA6082 (Al-Si1Mg0.9Mn0.1).