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71.
Nick Schiavon Tilde De Caro Alemayehu Kiros Ana Teresa Caldeira Isabella Erica Parisi Cristina Riccucci Giovanni Ettore Gigante 《Applied Physics A: Materials Science & Processing》2013,113(4):843-854
A multianalytical approach combining Optical Microscopy (OM), Backscattered Variable Pressure Scanning Electron Microscopy + Energy Dispersive X-ray Spectroscopy (VP-BSEM + EDS), Powder X-ray Diffractometry (PXRD), Raman Spectroscopy, and Microbiological techniques has been applied to characterize decay products and processes occurring at the surface of two rock-hewn churches (Bete Gyorgis and Bete Amanuel) at the UNESCO’s World Heritage site of Lalibela, Northern Ethiopia. The two churches were carved into volcanic scoria deposits of basaltic composition. In their geological history, the Lalibela volcanic rocks underwent late to post-magmatic hydrothermal alteration together with partial laterization and are therefore characterized by a decay-prone highly vesicular microtexture with late stage to post-magmatic precipitation of secondary mineral phases (calcite–zeolite–smectite). The main objective of the study was to gain a better insight into the weathering products and mechanisms affecting the surface of the stone monuments and to assess the relative contribution of natural “geological” weathering processes versus biological/salt attack in stone decay at this unique heritage site. Results indicate that while the main cause of bulk rock deterioration and structural failure could be related to the stone inherited “geological” features, biological attack by micro- (bacteria) and/or macro- (lichens) organisms is currently responsible for severe stone surface physical and chemical weathering leading to significant weakening of the stone texture and to material loss at the surface of the churches walls. A prompt and careful removal of the biological patinas with the correct biocidal treatment is therefore recommended. 相似文献
72.
Sonication of aqueous solutions causes cavitation in the liquid which results in the formation of H· and ·OH radical species that can be used to reduce or oxidize certain chemical compounds. This article focuses on the effect of ultrasounds in homogeneous reactions to examine the type of chemistry that ensues. It also deals with a rather novel method of using ultrasounds in combination with photochemical methods of inducing chemical reactions; this sonophotochemical technique remains to be explored and exploited. Finally, we examine and explore the potential utilization of ultrasounds to convert environmental hazardous substances into more benign substrates, or better still to mineralize organics into carbon dioxide. 相似文献
73.
The notion of n-fold Čech derived functors is introduced and studied. This is illustrated using the n-fold Čech derived functors of the nilization functors Zk. This gives a new purely algebraic method for the investigation of the Brown–Ellis generalised Hopf formula for the higher
integral group homology and for its further generalisation. The paper ends with an application to algebraic K-theory.
(Received: December 2004) 相似文献
74.
Nick Wright 《Journal of Functional Analysis》2005,220(2):265-303
The C0 coarse structure on a metric space is a refinement of the bounded structure and is closely related to the topology of the space. In this paper we will prove the C0 version of the coarse Baum–Connes conjecture and show that K*(C*X0) is a topological invariant for a broad class of metric spaces. Using this result we construct a ‘geometric’ obstruction group to the coarse Baum–Connes conjecture for the bounded coarse structure. We then show under the assumption of finite asymptotic dimension that the obstructions vanish, and hence we obtain a new proof of the coarse Baum–Connes conjecture in this context. 相似文献
75.
76.
Jeffrey A. Jackson Howard S. Derman Richard L. Harper M.Robert Willcott Joseph J. Ford Nicholas J. Schneiders John A. McCrary Anne Kelly R.Nick Bryan 《Magnetic resonance imaging》1984,2(3):227-233
A patient presented with an 8-month history of a progressive left homonymous visual field deficit, left hemiparesis, and a left thalamocortical sensory deficit that was not detectable by repeated conventional neurodiagnostic evaluations. Proton nuclear magnetic resonance (NMR) imaging revealed a right parietal lesion characterized by a prolonged T2 (spin-spin relaxation time). At surgery, the mass proved to be an anaplastic astrocytoma. NMR appears to be more sensitive than x-ray computerized tomography scanning in some patients with malignant gliomas and offers the clinician an additional probe with which to evaluate these patients. 相似文献
77.
78.
We study Riesz transforms associated with a sublaplacian H on a solvable Lie group G, where G has polynomial volume growth. It is known that the standard second order Riesz transforms corresponding to H are generally unbounded in Lp(G). In this paper, we establish boundedness in Lp for modified second order Riesz transforms, which are defined using derivatives on a nilpotent group GN associated with G. Our method utilizes a new algebraic approach which associates a distinguished choice of Cartan subalgebra with the sublaplacian
H. We also obtain estimates for higher derivatives of the heat kernel of H, and give a new proof (without the use of homogenization theory) of the boundedness of first order Riesz transforms. Our
results can be generalized to an arbitrary (possibly non-solvable) Lie group of polynomial growth. 相似文献
79.
Gareth J. Brown Des S. Creasey Nick J. Miles 《Particle & Particle Systems Characterization》1996,13(4):260-263
The avalanching behaviour of two coal types was determined, one of good and the other of poor handleability characteristics. This revealed significant differences in the nature of flow of the coals. Analysis of the strange attractors of the weight series of avalanches enabled quanitification of this difference, and the establishment of practical, relative criteria for the measurement of coal handleability. These criteria will now enable a structured study of the variables that affect handleability, for example proportion of fines and moisture content, and industrial consumers of coal to specify minimum acceptable limits for its transport characteristics. 相似文献
80.
Don Coppersmith Nick Howgrave-Graham Phong Q. NguyêÜn Igor E. Shparlinski 《Journal of Discrete Algorithms》2006,4(2):324-335
Given two k element subsets , we give a quasi-linear algorithm to either find such that S=λT or prove that no such λ exists.This question is closely related to isomorphism testing of circulant graphs and has recently been studied in the literature. 相似文献