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81.
Let (ℋ
t
)
t≥0 be the Ornstein-Uhlenbeck semigroup on ℝ
d
with covariance matrix I and drift matrix −λ(I+R), where λ>0 and R is a skew-adjoint matrix and denote by γ
∞ the invariant measure for (ℋ
t
)
t≥0. Semigroups of this form are the basic building blocks of Ornstein-Uhlenbeck semigroups which are normal on L
2(γ
∞). We investigate the weak type 1 estimate of the Riesz transforms for (ℋ
t
)
t≥0. We prove that if the matrix R generates a one-parameter group of periodic rotations then the first order Riesz transforms are of weak type 1 with respect
to the invariant measure γ
∞. We also prove that the Riesz transforms of any order associated to a general Ornstein-Uhlenbeck semigroup are bounded on
L
p
(γ
∞) if 1<p<∞.
The authors have received support by the Italian MIUR-PRIN 2005 project “Harmonic Analysis” and by the EU IHP 2002-2006 project
“HARP”. 相似文献
82.
Fernando Cruz Moraes Sonia Tomie Tanimoto Giancarlo Richard Salazar‐Banda Sergio Antonio Spinola Machado Lucia Helena Mascaro 《Electroanalysis》2009,21(9):1091-1098
The electrochemical detection of the hazardous pollutant 4‐nitrophenol (4‐NP) at low potentials, in order to avoid matrix interferences, is an important research challenge. This study describes the development, electrochemical characterization and utilization of a multiwall carbon nanotube (MWCNT) film electrode for the quantitative determination of 4‐NP in natural water. Electrochemical impedance spectroscopy measurements showed that the modified surface exhibits a decrease of ca. 13 times in the charge transfer resistance when compared with a bare glassy carbon (GC) surface. Voltammetric experiments showed the possibility to oxidize a hydroxylamine layer (produced by the electrochemical reduction of 4‐NP on the GC/MWNCT surface) in a potential region which is approximately 700 mV less positive than that needed to oxidize 4‐NP, thus minimizing the interference of matrix components. The limit of detection for 4‐NP obtained using square‐wave voltammetry (0.12 μmol L?1) was lower than the value advised by EPA. A natural water sample from a dam located in São Carlos (Brazil) was spiked with 4‐NP and analyzed by the standard addition method using the GC/MWCNT electrode, without any further purification step. The recovery procedure yielded a value of 96.5% for such sample, thus confirming the suitability of the developed method to determine 4‐NP in natural water samples. The electrochemical determination was compared with that obtained by HPLC with UV‐vis detection. 相似文献
83.
84.
85.
N-Propargylic beta-enaminones have been used as common intermediates for the synthesis of polysubstituted pyrroles and pyridines. Best results have been obtained using DMSO as solvent. In the presence of Cs(2)CO(3) N-propargylic beta-enaminones are cyclized to pyrroles in good to high yields, whereas omitting bases and using CuBr leads to the selective formation of pyridines. 相似文献
86.
87.
Giancarlo Masci Marco Diociaiuti Vittorio Crescenzi 《Journal of polymer science. Part A, Polymer chemistry》2008,46(14):4830-4842
Thermosensitive anionic block copolymers of sodium 2‐acrylamido‐2‐methylpropanesulfonate (AMPS) and N‐isopropylacrylamide (NIPAAM) with different block lengths were prepared by atom transfer radical polymerization (ATRP). Controlled polymerization was achieved by using ethyl 2‐chloropropionate (ECP) as initiator and CuCl/CuCl2/tris(2‐dimethylaminoethyl)amine (Me6TREN) catalytic system in DMF:water 50:50 (v/v) mixtures at 20 °C. Blocks lengths ranging from 36 to 98 repeating units were obtained. The association properties in aqueous solutions at different NaCl ionic strengths were studied as a function of temperature and polymer concentration by dynamic light scattering, fluorescence spectroscopy, and energy‐filtered transmission electron microscopy. The block copolymers with a higher pNIPAAM/pAMPS ratio formed spherical core‐shell type micelles independently of the ionic strength. The block copolymers with lower pNIPAAM/pAMPS ratio formed core‐shell type micelles at high ionic strength. Larger particles were observed at low ionic strength, which could be due to the formation of vesicles or compound micelles/micellar clusters. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4830–4842, 2008 相似文献
88.
Giancarlo Verardo Irene Duse Alessandro Callea 《Rapid communications in mass spectrometry : RCM》2009,23(11):1607-1618
Underivatized oligosaccharides were analyzed by electrospray ionization (ESI) using a linear ion trap mass spectrometer in the negative ion mode with post‐column addition of an aqueous solution of formic acid. Under these conditions all oligosaccharides showed the presence of the corresponding formate adduct [M + HCOO]? with high intensity and easy subsequent low‐energy collision‐induced dissociation (CID) fragmentation using successive MSn experiments. A careful examination of the mass spectra obtained from these MSn experiments pointed out some significant differences useful to identify and quantify the single components in mixtures of coeluted disaccharides. This new sensitive and rapid method was successfully applied to the quantification of oligosaccharides in some juices minimizing sample handling. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
89.
Bunyamin Karagoz Giancarlo Galli Hakan Durmaz Gurkan Hizal Umit Tunca Niyazi Bicak 《Colloid and polymer science》2010,288(5):535-542
A novel strategy was developed for tailoring of SiO2 and TiO2 nanoparticle surfaces with poly(ε-caprolactone) (PCL). Thus, a self-curable polyester, poly(2-hydroxypropylene maleate) was
adsorbed on the nanoparticle surfaces and heated to 180 °C to give a cross-linked polyester layer with residual hydroxyalkyl
groups on their surfaces. Surface-initiated polymerization of ε-caprolactone from hydroxyalkyl groups on the surfaces yielded
core-shell nanoparticles with cross-linked core and PCL shells (22.2–71.4%). The organic shell layers around the nanoparticle
cores were evidenced by transmission electron microscopy, dynamic light scattering, and thermogravimetric analyses techniques.
The core-shell nanoparticles were then employed in preparing the stable and the homogenous dispersions with poly(methyl methacrylate-stat-butyl acrylate) solutions. An application of the solutions onto glass substrates yielded uniform and nearly transparent free
standing films (40–60 μm) with good homogeneity as inferred from scanning electron microscopy pictures. 相似文献
90.
Seydou Yao Giancarlo DellaVentura Cyril Petibois 《Analytical and bioanalytical chemistry》2010,397(6):2079-2089
Asbestos is a fiber causing lung diseases such as asbestosis and mesothelioma. Although the process involving these diseases
remains to be elucidated for developing drugs and treatments, direct consequences of fiber exposure in humans have been clearly
demonstrated. These diseases are first characterized by histological heterogeneity and combine chronic inflammation with fibrosis
and cellular alterations. As a consequence, asbestosis is usually diagnosed at advanced stages of the disease and treatments
are usually inefficient to cure the patients. Here, we review the links established between asbestos fiber chemistry and morphology
with the occurrence of associated lung diseases. Cytological and histological aspects of diseases are described with respect
to current analytical capabilities, notably for microscopy techniques. 相似文献