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51.
Among the terrestrial epilithic cyanobacteria isolated from Roman hypogea at extremely low light intensity, a non-heterocystous strain, belonging to the genus Leptolyngbya, showed a marked photobehavior. These red cyanobacteria possess an orange spot at the tip of the apical cell. Micro-spectrophotometric analysis of this tip showed an absorption spectrum with two bands, centered at 456 and 504 nm, respectively. Experiments on photo-orientation impairment of these cells, and micro-spectrophotometric analysis of the tip of impaired trichomes showed that a rhodopsin-like protein might be present in this structure. All these data could support the hypothesis of the presence of a complex photoreceptive system in this prokaryote. 相似文献
52.
Gabriella Gualtieri 《Zeitschrift für Angewandte Mathematik und Physik (ZAMP)》1982,33(6):826-832
The radiation heat flux in a plane slab of an absorbing medium is evaluated by determining upper and lower bounds via complementary variational principles. The results obtained are in excellent agreement with those corresponding to other more cumbersome solution procedures (for small values of the spacing parameterd).
Riassunto Si valuta il trasporto di energia raggiante in una lastra piana di un mezzo assorbente, determinandone limiti superiori ed inferiori, mediante principi variazionali complementari. I risultati ottenuti sono in eccellente accordo con quelli ottenuti mediante tecniche risolutive più complesse (per piccoli valori del parametrod).相似文献
53.
Tubular-shaped stoichiometric chrysotile nanocrystals 总被引:5,自引:0,他引:5
Falini G Foresti E Gazzano M Gualtieri AF Leoni M Lesci IG Roveri N 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(12):3043-3049
Stoichiometric chrysotile tubular nanocrystals have been synthesized as possible starting materials for applications toward nanotechnology, and as a standard reference sample for the investigation of the molecular interactions between chrysotile, the most utilized asbestos, and biological systems. Chrysotile nanocrystals have been synthesized under controlled hydrothermal conditions, and have been characterized by chemical, morphological, structural, spectroscopic and microcalorimetric analyses. They show a constant "cylinder-in-cylinder" morphology constituted by two or three concentric subunits. Each single nanocrystal has a tubular shape of about 49+/-1 nm in outer maximum diameter, and a hollow core of about 7+/-1 nm. Structural investigation carried out on an X-ray powder pattern allowed to improve the structural model proposed for chrysotile mineral samples. Synthetic chrysotile crystallizes in the monoclinic Cc space group with a=0.5340(1) nm, b=0.9241(1) nm, and c=1.4689(2) nm, beta=93.66(3) degrees. 相似文献
54.
We present a study of the preparation procedure for stepped MgO surfaces which can be used as templates for the deposition of metallic nanostructures. A cleaved sample of MgO(0 0 1) was mechanically polished to reach the desired miscut angle along the [1 1 0] direction. Then a thermal annealing was performed. The effect of an intermediate chemical etching has been also studied. The surface was analyzed by means of contact AFM in air, LEED and XPS in UHV. The role of the chemical etching and the dependence of the final morphology on the annealing time and temperature were investigated. The influence of the miscut angle on the final surface topography is also briefly discussed. 相似文献
55.
Luca Guandalini Silvia Dei Fulvio Gualtieri MariaNovella Romanelli Serena Scapecchi Elisabetta Teodori Katia Varani 《Helvetica chimica acta》2002,85(1):96-107
Two hexahydropyrindine derivatives, 1,2,3,4,6,7‐hexahydro‐2‐methyl‐5H‐cyclopenta[c]pyridin‐5‐one ( 1 ) and 1,2,3,4,5,6‐hexahydro‐2‐methyl‐7H‐cyclopenta[c]pyridin‐7‐one ( 2 ), and their methiodides 14 and 26 , respectively, were synthesized. They can be considered rigid analogues of the known nicotinic agonists arecolone (=1‐(1,2,5,6‐tetrahydro‐1‐methylpyridin‐3‐yl)ethanone) and isoarecolone (=1‐(1,2,3,6‐tetrahydro‐1‐methylpyridin‐4‐yl)ethanone). The affinity for the central nicotinic receptor were measured on rat cerebral cortex. Although only the methiodide 14 , among the four conformationally restricted compounds, shows an appreciable affinity, the results obtained provide useful information on the molecular requirements at the interaction site of the central nicotinic receptors. 相似文献
56.
Small scale clustering of inertial particles and relative velocity of particle pairs have been fully characterized for statistically steady homogeneous isotropic flows. Depending on the particle Stokes relaxation time, the spatial distribution of the disperse phase results in a multi-scale manifold characterized by local particle concentration and voids and, because of finite inertia, the two nearby particles have high probability to exhibit large relative velocities. Both effects might explain the speed-up of particle collision rate in turbulent flows. Recently it has been shown that the large scale geometry of the flow plays a crucial role in organizing small scale particle clusters. For instance, a mean shear preferentially orients particle patterns. In this case, depending on the Stokes time, anisotropic clustering may occur even in the inertial range of scales where the turbulent fluctuations which drive the particles have already recovered isotropy. Here we consider the statistics of particle pair relative velocity in the homogeneous shear flow, the prototypical flow which manifests anisotropic clustering at small scales. We show that the mean shear, by imprinting anisotropy on the large scale velocity fluctuations, dramatically affects the particle relative velocity distribution even in the range of small scales where the anisotropic mechanisms of turbulent kinetic energy production are sub-dominant with respect to the inertial energy transfer which drives the carrier fluid velocity towards isotropy. We find that the particles’ populations which manifest strong anisotropy in their relative velocities are the same which exhibit small scale clustering. In contrast to any Kolmogorov-like picture of turbulent transport these phenomena may persist even below the smallest dissipative scales where the residual level of anisotropy may eventually blow-up. The observed anisotropy of particle relative velocity and spatial configuration is suggested to influence the directionality of the collision probability, as inferred on the basis of the so-called “ghost collision” model. 相似文献
57.
58.
In order to get information about the role of the oxygen atom in position 1 of dioxolane I and thus about the corresponding binding site of the muscarinic receptor, Elferink and Salemink2 have synthesized the sulfur analog II as a cis/trans mixture in a 4:1 or 8:1 ratio, depending upon the synthetic method. This compound proved to be very active as muscarinic agent and might provide useful tool in Structure-Activity Relationship (SAR) studies on muscarinic receptor, if it were available as a pure cis form3. 相似文献
59.
Francesco A. Costabile Maria Italia Gualtieri 《Integral Transforms and Special Functions》2019,30(2):112-127
In this paper the set of general polynomial sequences is considered. An elementary systematic approach is proposed. In fact a structure of group is given and for every element of this group recurrence relations and determinant forms are derived. Applications of the derived determinant forms are considered. In particular, the general linear interpolation and bounds of the zeros of each polynomial of the sequence are sketched. Finally, as an illustrative example, the shifted (with respect to the degree) Genocchi polynomial sequence is analyzed. 相似文献
60.
Electron Paramagnetic Resonance (EPR) spectroscopy is useful to archeologists in recognizing and dating sites. This non-destructive technique of analysis gives information on material composition, on paramagnetic impurities, on firing techniques and on surface oxidation. In this paper it is shown how to recover information about firing techniques from a fragment of ceramic pot, dating from the 9th century B.C. The internal brown-black layer showed a strong g anisotropy whilst the external reddish layer showed hardly any. This indicates a non-homogeneous rapid firing of the pot, due probably to primitive firing techniques. 相似文献