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排序方式: 共有473条查询结果,搜索用时 15 毫秒
361.
362.
Debuigne A Champouret Y Jérôme R Poli R Detrembleur C 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(13):4046-4059
Over the past few years, cobalt-mediated radical polymerization (CMRP) has proved efficient in controlling the radical polymerization of very reactive monomers, such as vinyl acetate (VAc). However, the reason for this success and the intimate mechanism remained basically speculative. Herein, two mechanisms are shown to coexist: the reversible termination of the growing poly(vinyl acetate) chains by the Co(acac)2 complex (acac: acetylacetonato), and a degenerative chain-transfer process. The importance of one contribution over the other strongly depends on the polymerization conditions, including complexation of cobalt by ligands, such as water and pyridine. This significant progress in the CMRP mechanism relies on the isolation and characterization of the very first cobalt adducts formed in the polymerization medium and their use as CMRP initiators. The structure proposed for these adducts was supported by DFT calculations. Beyond the control of the VAc polymerization, which is the best ever achieved by CMRP, extension to other monomers and substantial progress in macromolecular engineering are now realistic forecasts. 相似文献
363.
Poli AL Batista T Schmitt CC Gessner F Neumann MG 《Journal of colloid and interface science》2008,325(2):386-390
This paper reports on the effect of sonication on SAz-1 and SWy-1 montmorillonite suspensions. Changes in the size of the particles of these materials and modifications of their properties have been investigated. The variation of the particle size has been analyzed by DLS (dynamic light scattering). In all cases the clay particles show a bimodal distribution. Sonication resulted in a decrease of the larger modal diameter, as well as a reduction of its volume percentage. Simultaneously, the proportion of the smallest particles increases. After 60 min of sonication, SAz-1 presented a very broad particle size distribution with a modal diameter of 283 nm. On the other hand, the SWy-1 sonicated for 60 min presents a bimodal distribution of particles at 140 and 454 nm. Changes in the properties of the clay suspensions due to sonication were evaluated spectroscopically from dye-clay interactions, using Methylene Blue. The acidic sites present in the interlamellar region, which are responsible for dye protonation, disappeared after sonication of the clay. The changes in the size of the scattering particles and the lack of acidic sites after sonication suggest that sonication induces delamination of the clay particles. 相似文献
364.
A. Surpi F. Poli D. Pelliccia I. Bukreeva S. Lagomarsino 《Optics Communications》2008,281(11):3217-3220
Surface roughness is a key point for all X-ray reflective optics, and is in general obtained through careful polishing and surface finishing. Here we propose a simple and inexpensive procedure to drastically reduce surface roughness: using sol-gel silica coatings. The motivation for this work is the improvement of X-ray mirrors obtained on Si substrate using micro-fabrication technology, where the usual polishing methods cannot be applied. Sol-gel silica layers dramatically reduce surface roughness and enhance the X-ray reflectivity up to acceptable values. The proof-of-principle presented in this paper can be further improved and applied to systems of different nature. 相似文献
365.
D. Hojman M.A. Cardona D.R. Napoli S.M. Lenzi C.A. Ur G. Lo Bianco C.M. Petrache M. Axiotis D. Bazzacco J. Davidson M. Davidson M. De Poli G. de Angelis E. Farnea T. Kroell S. Lunardi N. Marginean T. Martınez R. Menegazzo B. Quintana C. Rossi Alvarez 《The European Physical Journal A - Hadrons and Nuclei》2001,10(3):245-248
High-spin states in 178Ir were investigated by means of in-beam γ-ray spectroscopy techniques using the multidetector array GASP. Excited states
of 178Ir were populated through the 159Tb(24Mg, 5n) fusion-evaporation reaction at E(24
Mg) = 131-141 MeV. Several rotational bands were observed. Among them, the πi
13/2⊗νi
13/2 structure has been identified up to spin 36 ?. This band exhibits an anomalous signature splitting and a signature inversion
around spin 25 ?.
Received: 13 December 2000 / Accepted: 11 April 2001 相似文献
366.
N. Mărginean D. Bucurescu C.A. Ur D. Bazzacco S.M. Lenzi S. Lunardi C. Rossi Alvarez M. Ionescu-Bujur A. Iordăchescu G. de Angelis M. De Poli E. Farnea A. Gadea D.R. Napoli P. Spolaore A. Buscemi 《The European Physical Journal A - Hadrons and Nuclei》1999,4(4):311-312
The nucleus 84Nb has been studied with the 58Ni(28Si,pnγ) reaction at 90 MeV. Several rotational structures are established and connected to an irregular low-energy level scheme
which includes one isomeric level whose decay was observed before.
Received: 23 July 1998 / Revised version: 30 November 1998 相似文献
367.
C N Davids P J Woods D Seweryniak A A Sonzogni J C Batchelder C R Bingham T Davinson D J Henderson R J Irvine G L Poli J Uusitalo W B Walters 《Pramana》1999,53(3):631-631
The proton drip line defines one of the fundamental limits to nuclear stability. Nuclei lying beyond this line are energetically unbound to the emission of a constituent proton from their ground states. For near-spherical nuclei in the region of the drip line between Z=69 (Tm) and Z=81 (T1), proton decay transition rates have been shown to be well reproduced by WKB calculations using spectroscopic factors derived from a low-seniority shell model calculation [2]. Another approach using spectroscopic factors obtained from the independent quasiparticle approximation has also proved successful in this region [3]. These interpretations have allowed the extraction of nuclear structure information from nuclei well beyond the proton drip line. 相似文献
368.
C N Davids P J Woods D Seweryniak A A Sonzogni J C Batchelder C R Bingham T Davinson D J Henderson R J Irvine G L Poli J Uusitalo W B Walters 《Pramana》1999,53(3):631
The proton drip line defines one of the fundamental limits to nuclear stability. Nuclei lying beyond this line are energetically
unbound to the emission of a constituent proton from their ground states.
For near-spherical nuclei in the region of the drip line between Z=69 (Tm) and Z=81 (T1), proton decay transition rates have been shown to be well reproduced by WKB calculations using spectroscopic factors
derived from a low-seniority shell model calculation [2]. Another approach using spectroscopic factors obtained from the independent
quasiparticle approximation has also proved successful in this region [3]. These interpretations have allowed the extraction
of nuclear structure information from nuclei well beyond the proton drip line.
The rare-earth proton emitters 141Ho and 131Eu have recently been observed [4], and their decay rates can only be explained by assuming large deformation for these nuclei.
In addition to providing information on the wavefunctions and deformations of these nuclei, these results offer the opportunity
to study the phenomenon of quantum mechanical tunneling through a deformed potential barrier.
Work supported by the U.S. Department of Energy, Nuclear Physics Division, under contract W-31-109-ENG-38. 相似文献
369.
Cristina Occhiuto Gianluigi Aliberto Mariarosaria Ingegneri Domenico Trombetta Clara Circosta Antonella Smeriglio 《Molecules (Basel, Switzerland)》2022,27(11)
Recently, there has been a growing interest in the recovery of agri-food waste within the circular economy perspective. In this study, the nutritional, phytochemical, and biological features of the cold-pressed hempseed oil (HSO) and hempseed meal (HSM) of two industrial hemp varieties (USO 31 and Futura 75, THC ≤ 0.2%) were evaluated. The HSOs showed a high total phenols and flavonoid content, which were confirmed by LC-DAD-ESI-MS analysis, with rutin as the most abundant compound (56.93–77.89 µg/100 FW). They also proved to be a rich source of tocopherols (81.69–101.45 mg/100 g FW) and of a well-balanced ω-6 to ω-3 fatty acid ratio (3:1) with USO 31, which showed the best phytochemical profile and consequently the best antioxidant activity (about two times higher than Futura 75). The HSMs still retained part of the phytochemicals identified in the HSOs (polyphenols, tocopherols, and the preserved ω-6/ω-3 fatty acids ratio) and a modest antioxidant activity. Furthermore, they showed a very interesting nutritional profile, which was very rich in proteins (29.88–31.44 g/100 g FW), crude fibers (18.39–19.67 g/100 g), and essential and non-essential amino acids. Finally, only a restrained amount of anti-nutritional factors (trypsin inhibitors, phytic acid, and condensed tannins) was found, suggesting a promising re-use of these byproducts in the nutraceutical field. 相似文献
370.
Gianluigi De Falco Ingrid El Helou Pedro M. de Oliveira Mariano Sirignano Ruoyang Yuan Andrea D'Anna Epaminondas Mastorakos 《Proceedings of the Combustion Institute》2021,38(2):2691-2699
There is a need to better understand particle size distributions (PSDs) from turbulent flames from a theoretical, practical and even regulatory perspective. Experiments were conducted on a sooting turbulent non-premixed swirled ethylene flame with secondary (dilution) air injection to investigate exhaust and in-burner PSDs measured with a Scanning Mobility Particle Sizer (SMPS) and soot volume fractions (fv) using extinction measurements. The focus was to understand the effect of systematically changing the amount and location of dilution air injection on the PSDs and fv inside the burner and at the exhaust. The PSDs were also compared with planar Laser Induced Incandescence (LII) calibrated against the average fv. LII provides some supplemental information on the relative soot amounts and spatial distribution among the various flow conditions that helps interpret the results. For the flame with no air dilution, fv drops gradually along the centreline of the burner towards the exhaust and the PSD shows a shift from larger particles to smaller. However, with dilution air fv reduces sharply where the dilution jets meet the burner axis. Downstream of the dilution jets fv reduces gradually and the PSDs remain unchanged until the exhaust. At the exhaust, the flame with no air dilution shows significantly more particles with an fv one to two orders of magnitude greater compared to the Cases with dilution. This dataset provides insights into soot spatial and particle size distributions within turbulent flames of relevance to gas turbine combustion with differing dilution parameters and the effect dilution has on the particle size. Additionally, this work measures fv using both ex situ and in situ techniques, and highlights the difficulties associated with comparing results across the two. The results are useful for validating advanced models for turbulent combustion. 相似文献