943 research outputs found
The P-C phase transition of synthetic amphiboles in the NCMSH system: an FTIR study
No full textDuring the last years, a series of experimental studies have been done to characterize the structural features of synthetic amphiboles in the Li2O-Na2O-MgO-SiO2-H2O (LNMSH system) under different T, P and X conditions. Camára et al. (2003) and Iezzi et al. (2004) showed that the Li-free Na0.8(Na0.8Mg1.2)Mg5Si8O22(OH)2 compound is P21/m at room-T, and Camára et al. (2003) characterized the displacive P21/m C2/m phase-transition by single-crystal XRD. The phase transition of this amphibole has a macroscopic second order character, with a transition temperature (TC) of 257 °C.
Iezzi et al. (2005) did a similar investigation on the Na(LiMg)Mg5Si8O22(OH)2 composition by means of synchrotron radiation HT-XRPD, and showed that this compound also undergoes a displacive phase transition as a function of T, but the transition has a tricritical character and TC = 326 °C. Furthermore Iezzi et al. (2006) showed that all amphiboles in the LNMSH system, independently of their Na-Li contents at the B site, have the P21/m symmetry at room conditions.
Natural Group 5 amphiboles which belong to the B(Na,Li)2, B(Na,Mn)2 and B(Ca,Mn)2 solid-solutions, whether their A site is filled or empty, have monoclinic C2/m symmetry. In contrast, the A-site filled synthetic samples belonging to the B(Na,Mg)2 and B(Li,Mg)2 solid-solutions, have P21/m symmetry at room T, and undergo phase-transitions at variable TC, depending on their chemical composition (Welch et al. 2007). The P21/m symmetry is restricted to amphiboles with a double-chain composition close to Si8 and is probably stabilized by small cations only at the B-group sites or by a B compositions where large monovalent cation (Na) and a small divalent cation (Mg) have a ratio close to 1:1. However, the dimension of the C-group cations also play a significant role in determining the transition behavior (cf. Welch et al. 2007 for more discussion).
In this work, we explore the effects on the phase transitions of a large divalent cation as Ca which progressively replaces BMg. The amphibole symmetry was monitored using in situ low- and high-T FTIR spectroscopy. Samples were prepared as conventional KBr disks (Iezzi et al., 2006); low-T spectra were collected using a nitrogen-cooled cryostat, while high-T spectra were collected using a Specac microfurnace. Previous work (Iezzi et al., 2004, 2006) show that OH-stretching FTIR spectroscopy is particularly useful in characterizing the symmetry changes associated with the P C transition in these amphiboles. For varying T conditions there are well-defined modifications of the room-T pattern, consisting of progressive band broadening and band splitting. Inspection of the data shows that for increasing BCa in the amphibole structure there is a linear decrease of the transition temperature TC for the Mg-richer samples, as also evidenced by the companion X-Ray diffraction study (Iezzi et al., this meeting).
References
Cámara F., Oberti R., Iezzi G., Della Ventura G. (2003) Phys. Chem. Miner., 30, 570-581.
Della Ventura G., Iezzi G., Bellatreccia F., Càmara F., Oberti R. (2004). Mitt. Oster. Min. Ges., 149: 23.
Iezzi G., Della Ventura G., Oberti R., Cámara F., Holtz F. (2004) Am. Miner., 89, 640–646.
Iezzi G., Tribaudino M., Della Ventura G., Nestola G., Bellatreccia F. (2005) Phys. Chem. Miner., 32, 515–523.
Iezzi G., Della Ventura G., Tribaudino M. (2006) Am. Miner., 91, 425-429.
Welch M.D., Cámara F., Della Ventura G., Iezzi G. (2007) Rev. Mineral. Geochem., 67, in press
Yi ge shufazhuiyizhe Luo Qi 一个书法主义者 洛齐 (A Practitioner of Calligraphyism: Luo Qi)
No full text在《一个书法主义者 洛齐》中,作者阐述了洛齐书法创作的心路历程,并仔细分析了书法主义的概念。
洛齐作为中国当代最重要、最有影响力的艺术家之一。在本书中,洛齐的创作风格和影响进行了比较全面的阐述和评析,见解深刻,评论精到。他的作品展现了书法作为一种多才多艺的艺术,并收到了西方艺术和中国现代书法的互相影响。在他的创作的同时,还以著述文章的方式思考着书法的未来。
书法主义是洛齐革命的艺术理论。在本书中,作者探索书法主义的理论与实践。以书法主义为探论主题,内容涉及书法主义的建构。作者也选录了近年来国内国外艺术家所创作的书法主义作品。
这本书分为五章:一、中国当代书法,二、洛齐艺术传记,三、洛齐作品解析,四、书法主义,五,洛齐艺术的访谈。《洛齐访谈录》包括洛齐访谈和有名艺术家谈洛齐艺术的访谈。读者通过本书可感受洛齐的艺术生活和洒脱风采,也可探寻书法主义的本质。
《一个书法主义者 洛齐》是10 卷本《书法主义文献丛书》中的一本,洛齐教授(中国美术学院)是这套丛书的主编。由于这套丛书是当代艺术研究的成果,具有很高的科学学术价值,它将在中华人民共和国的所有公共图书馆和大学分发,并将在全国范围内广泛传播。这套丛书是中国第一套关于书法文化和艺术领域获得中国国家图书最高学术奖的书,阿德丽亚娜·叶星(Adriana Iezzi)博士也是获得最高学术奖的作者。In this book, the author explores in detail the theory and practice of “Calligraphyism” (Shufazhuyi), the most important Chinese post-modern calligraphic movement, reconstructing its history and its diffusion in China and abroad. At the same time, the author deeply analyses the artistic production and theoretical thoughts of the founder of this movement, Prof. Luo Qi (Hangzhou, 1960). Prof. Luo Qi is one of the most important and influential calligraphers in contemporary China. In his works, calligraphy is used as a versatile art, receiving the mutual influence of Western art and "Modern Chinese Calligraphic Movement" (Zhongguo xiandai shufa), while in his theoretical writings, he thinks about the future of calligraphy, expanding the concept of Calligraphyism globally.
The book is divided into five chapters: 1. The Art of Calligraphy in Contemporary China; 2. Luo Qi's biography; 3. Luo Qi's works; 4. Calligraphyism; 5. Interviews about Luo Qi's art. A large number of images of calligraphic artworks and contemporary exhibitions enrich and expand the content of the book.
This book is included in a series of 10 books entitled “Calligraphyism. A Series of Books.” Prof. Luo Qi (China Academy of Art) is the editor of this series. Due to the high scientific value of this series, it will be distributed in all public libraries of the People's Republic of China and it will have a very wide diffusion throughout the Chinese territory. This series of books has been the first in China to win the highest academic award for Chinese National Books in the field of calligraphy, culture and art, and Dr. Adriana Iezzi has obtained this highest academic award as author of the book entitled “A Practitioner of Calligraphyism: Luo Qi”
Analisi della transizione università-lavoro in Italia: obiettivi e prospettive dei laureati in Scienze Statistiche
No full textHollywood Ulteriore (o Post-Hollywood)
No full textIl cinema nordamericano - cioè statunitense-hollywoodiano, il più "grande" del mondo, e canadese, piccolo ma con punte qualitative - è in questo volume esposto nella concretezza dei suoi autori e delle sue immagini. A sfilare è un vasto repertorio di figure creative e professionali: soprattutto di registi, nel loro complesso contesto culturale-produttivo e con il loro bagaglio di tanti film (formativi di tanta parte dell'immaginario mondiale) qui sondati in gratificante profondità
Synthesis and solid-solution in rubidium richterite, Rb(NaCa)Mg5Si8O22(OH,F)2
No full textThe OH–F substitution in “synthetic Rb-richterite” has been investigated along the join Rb(NaCa)Mg5Si8O22(OH)2–Rb(NaCa)
Mg5Si8O22(F)2. Syntheses were done by conventional hydrothermal techniques (Tuttle-type vessels) at 800 °C, 1 kbar P(
H2O).
SEM microscopy showed very high yields of acicular to prismatic amphibole crystals up to XF = F/(F + OH) = 0.6. Beyond
this value, a micaceous phase and a very fine-grained granular phase were present. Powder X-ray diffraction patterns show
a single amphibole phase below XF = 0.6; above XF = 0.6, a distinct peak at d = 12.18 Å indicates the presence of a mica
and there is a broad hump starting at ~ 20o 2θ and ~ 15o wide, both features increasing in intensity with increasing XF.
Cell
dimensions at XF = 0 are compatible with an ideal amphibole composition Rb(NaCa)Mg5Si8O22(OH)2 and evolve with
increasing XF up to XF = 0.6, where there is a sharp discontinuity in a, β and V. The infrared OH-stretching spectrum of the
OH end-member shows a main band at 3732 cm−1 which is assigned to the local MgMgMg–OH→ Rb arrangement, and a
minor band at 3670 cm−1 assigned to the local MgMgMg–OH→ □ arrangement. This latter band indicates a slight departure
toward tremolite. Intermediate OH–F compositions show the appearance of a second band at 3718 cm−1, whose intensity
is proportional to the F content in the system, in accord with OH−OH and OH–F arrangements across the filled A-site. For
XF > 0.6, the OH-stretching spectra are complicated by the appearance of two more peaks at 3705 and 3685 cm−1. Additional
bands at lower wavenumbers, centered around 3595, 3540 and 3475 cm−1, respectively, are better resolved by collecting the
spectra on disks heated at 250 °C to remove the adsorbed moisture in the pellet. Combining the behavior of unit-cell dimensions
and the infrared spectra with mass-balance arguments indicates that at high XF values, Na replaces part of the Rb at the
A-site in the amphibole and the tremolite component of the amphibole increases, while “Rb tetrasilicic magnesium mica”
crystallizes, along with semi-amorphous nanophases. The variation in band intensities as a function of XF indicates that OH
and F randomly occupy local pairs of O(3) sites across a (filled) A-site, and that there is no short-range order of OH and F.Published759–7703V. Proprietà chimico-fisiche dei magmi e dei prodotti vulcaniciJCR Journa
The analysis of fibrous amphiboles by FTIR spectroscopy in the OH-stretching region
No full textThe mechanism through which fibrous amphiboles may give rise to mesothelioma is still not completely understood. Several factors have been taken into account, and these include the morphological aspect (length:width ratio), the chemical composition, and a variety of surface properties which are ultimately responsible for the mineral-cellule interactions (e.g. van Oss et al., 1999). Studies in vitro demonstrate that the morphology of the fiber has a strong role in determining its biological danger, because very thin and long crystallites are hardly eliminated by the alveolar macrophages. However, a second factor which seems to influence the biological attack of a fiber is its Fe content; iron can in fact be involved in complex biochemical reactions with oxygen and cause DNA damages. It follows that the rapid determination of the chemical composition of a fiber, and of its Mg/Fe ratio in particular, is extremely important in environmental studies. The direct analysis can be achieved only by micro-chemical tools such as by EDS- or WDS-equipped electron microscopes. However, these techniques are extremely expensive and often unsuitable when dealing with extremely fibrous (diameter 2+ at the OH-coordinated M(1,3) sites (Della Ventura et al. 1996, 1997, Iezzi et al. 2005, 2007). The digitized spectra were fitted by interactive optimization followed by least-squares refinement; all bands were modelled as symmetric Gaussians. Della Ventura et al. (1996, 1997) showed that the binary site-occupancies at M(1) and M(3) in the amphibole structure are related to the observed intensities of the four (A to D) components in the principal IR OH-stretching spectrum. Using the original equations of Burns and Strens (1966):
M(1,3)Mg = 3IA + 2IB + IC and M(1,3)M2+ = IB + 2IC + 3ID (with M2+ = Fe2+)
where IA-ID are the intensities measured for the corresponding A to D bands, one can derive the (Mg, M2+) site populations at M(1,3) with a high degree of confidence. This method is particularly suitable for asbestiform materials which cannot be properly characterized by EMP. The present work shows that the above spectroscopic tool can be applied to a large variety of amphibole types. For species were significant (Mg, Fe) are present at M(4) (i.e. anthophyllite –cummingtonite - grunerite) an additional information (e.g. Mössbauer) is however required for a complete characterization of the sample.
References
Burns, R.G. and Strens, R.G.J. (1966) Science, 153, 890-892.
Della Ventura, G., Robert, J.-L., Hawthorne, F.C. (1996) Geochimica and Cosmochimica Acta, vol. spec. 5, 55-63.
Della Ventura, G., Robert, J.-L., Raudsepp, M., Hawthorne, F.C., Welch, M. (1997) American Mineralogist, 82, 291-301.
Iezzi, G., Della Ventura, G., Hawthorne, F.C., Pedrazzi, G., Robert, J.-L., Novembre, D. (2005) European Journal of Mineralogy, 17, 733-740.
Iezzi, G., Della Ventura, G., Bellatreccia, F., Lo Mastro, S., Gunther, M., Bandly, (2007) Mineralogical Magazine, in press.
van Oss, C.J., Naim, J.O., Costanza, P.M., Giese, R.F. Jr., Wu, W., Sorling, A.F. (1999) Clays and Clay Minerals, 47, 697-707
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