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241.
To investigate isotope effects in the hydroxylation of [3′,5′-2H2]-α-methyl- and [3′,5′-2H2]-N-methyl-l-tyrosine, they were synthesised using acid catalysed isotope exchange at high temperature. The kinetic and solvent deuterium isotope effects on Vmax and Vmax/Km parameters of tyrosinase in its action on methylated derivatives of l-tyrosine were determined using the non-competitive spectrophotometric method. Lineweaver–Burk plots were used to consider the inhibition type of O-methyl-l-tyrosine, revealing that it is an uncompetitive inhibitor of tyrosinase. 相似文献
242.
Suspensions of polydimethylsiloxane (PDMS) containing low amounts (1 wt.% or less) of a highly conducting carbon black (CB)
filler are rendered conductive and exhibit electrorheological (ER) responses under shear flow when exposed to an externally
applied AC electric field. The presence of columnar structures, consisting of CB particles aligned in the direction of the
electric field is evidenced through optical microscopy experiments. The appearance of yielding behavior and positive ER response,
manifested by an increase in the viscosity of the suspensions, depend strongly on the filler loading, strength of the electric
field, magnitude of the shear field, and viscosity of the medium. The responses are stronger at low filler loadings, below
the percolation threshold, and at very low shear rates, where the microstructure of the dispersed phase remains intact. At
higher shear rates, corresponding to Mason numbers (Mn) above 1, the structure is disrupted and thus does not contribute to
the observed shear stress. The rheological characterization is accompanied with admittance measurements, to demonstrate that
the induced polarization forces between particles lead to the formation of electrically conductive structures within the polymer
matrix. A critical comparison with the qualitative predictions based on the theory of induced dipole–dipole interactions shows
that the theory is valid for these dilute systems. 相似文献
243.
G. Carbone M. Scaraggi U. Tartaglino 《The European physical journal. E, Soft matter》2009,30(1):65-74
The authors have employed a numerical procedure to analyse the adhesive contact between a soft elastic layer and a rough rigid
substrate. The solution to the problem, which belongs to the class of the free boundary problems, is obtained by calculating
Green’s function which links the pressure distribution to the normal displacements at the interface. The problem is then formulated
in the form of a Fredholm integral equation of the first kind with a logarithmic kernel. The boundaries of the contact area
are calculated by requiring the energy of the system to be stationary. This methodology has been employed to study the adhesive
contact between an elastic semi-infinite solid and a randomly rough rigid profile with a self-affine fractal geometry. We
show that, even in the presence of adhesion, the true contact area still linearly depends on the applied load. The numerical
results are then critically compared with the predictions of an extended version of Persson’s contact mechanics theory, which
is able to handle anisotropic surfaces, as 1D interfaces. It is shown that, for any given load, Persson’s theory underestimates
the contact area by about 50% in comparison with our numerical calculations. We find that this discrepancy is larger than
for 2D rough surfaces in the case of adhesionless contact. We argue that this increased difference might be explained, at
least partially, by considering that Persson’s theory is a mean-field theory in spirit, so it should work better for 2D rough
surfaces rather than for 1D rough surfaces. We also observe that the predicted value of separation is in agreement with our
numerical results as well as the exponents of the power spectral density of the contact pressure distribution and of the elastic
displacement of the solid. Therefore, we conclude that Persson’s theory captures almost exactly the main qualitative behaviour
of the rough contact phenomena. 相似文献
244.
Antonella Greco Luca Sorriso-Valvo Vincenzo Carbone Stefano Cidone 《Physica A》2008,387(16-17):4272-4284
We investigate the time behaviour of the Italian MIB30 stock index collected every minute during two months in the period from May 17, 2006, up to July 24, 2006. We find short-range correlations in the price returns and, on the contrary, a long persistent time lag and slow decay in the autocorrelation functions of volatility. Besides, we find that the probability density functions (PDFs) of returns show fat tails, which are well fit by the log-normal model of Castaing [B. Castaing, Y. Gagne, E.J. Hopfinger, Physica D 46 (1990) 177], and a convergence toward a normal distribution for large time scales; we also find that the PDFs of volatility, for short time horizons, fit better with a log-normal distribution than with a Gaussian. Most of these features characterize the indexes and stocks of the largest American, European and Asian markets.We also investigate the distribution of stochastic separation between isolated strong events in the volatility signal. This is interesting because this gives us a deeper understanding about the price formation process. By using a test for the occurrence of local Poisson hypothesis, we show that the process we examined strongly departs from a Poisson statistics, the origin of this failure stemming from the presence of temporal clustering and of a certain amount of memory. 相似文献
245.
Sarra Bouchelaghem Sourav Das Romen Singh Naorem Lilla Czuni Gbor Papp Marianna Kocsis 《Molecules (Basel, Switzerland)》2022,27(2)
Propolis is a natural bee product that is widely used in folk medicine. This study aimed to evaluate the antimicrobial and antibiofilm activities of ethanolic extract of propolis (EEP) on methicillin-resistant and sensitive Staphylococcus aureus (MRSA and MSSA). Propolis samples were collected from six regions in Hungary. The minimum inhibitory concentrations (MIC) values and the interaction of EEP-antibiotics were evaluated by the broth microdilution and the chequerboard broth microdilution methods, respectively. The effect of EEP on biofilm formation and eradication was estimated by crystal violet assay. Resazurin/propidium iodide dyes were applied for simultaneous quantification of cellular metabolic activities and dead cells in mature biofilms. The EEP1 sample showed the highest phenolic and flavonoid contents. The EEP1 successfully prevented the growth of planktonic cells of S. aureus (MIC value = 50 µg/mL). Synergistic interactions were shown after the co-exposition to EEP1 and vancomycin at 108 CFU/mL. The EEP1 effectively inhibited the biofilm formation and caused significant degradation of mature biofilms (50–200 µg/mL), as a consequence of the considerable decrement of metabolic activity. The EEP acts effectively as an antimicrobial and antibiofilm agent on S. aureus. Moreover, the simultaneous application of EEP and vancomycin could enhance their effect against MRSA infection. 相似文献
246.
Alberto Porta Francesca Gelpi Vlasta Bari Beatrice Cairo Beatrice De Maria Cora May Panzetti Noemi Cornara Enrico Giuseppe Bertoldo Valentina Fiolo Edward Callus Carlo De Vincentiis Marianna Volpe Raffaella Molfetta Valeria Pistuddi Marco Ranucci 《Entropy (Basel, Switzerland)》2022,24(1)
Cerebrovascular control is carried out by multiple nonlinear mechanisms imposing a certain degree of coupling between mean arterial pressure (MAP) and mean cerebral blood flow (MCBF). We explored the ability of two nonlinear tools in the information domain, namely cross-approximate entropy (CApEn) and cross-sample entropy (CSampEn), to assess the degree of asynchrony between the spontaneous fluctuations of MAP and MCBF. CApEn and CSampEn were computed as a function of the translation time. The analysis was carried out in 23 subjects undergoing recordings at rest in supine position (REST) and during active standing (STAND), before and after surgical aortic valve replacement (SAVR). We found that at REST the degree of asynchrony raised, and the rate of increase in asynchrony with the translation time decreased after SAVR. These results are likely the consequence of the limited variability of MAP observed after surgery at REST, more than the consequence of a modified cerebrovascular control, given that the observed differences disappeared during STAND. CApEn and CSampEn can be utilized fruitfully in the context of the evaluation of cerebrovascular control via the noninvasive acquisition of the spontaneous MAP and MCBF variability. 相似文献
247.
Marianna Raczyk Katarzyna Polanowska Bartosz Kruszewski Anna Grygier Dorota Michaowska 《Molecules (Basel, Switzerland)》2022,27(2)
Taking into account that many advantages have been associated with the consumption of spirulina (microalgae) in terms of antioxidant capacity, anticancer, anti-inflammatory, and anti-aging activities, the study focuses on spirulina supplementation of semolina-based pasta. Fresh pasta was prepared by mixing semolina flour (Triticum durum) with an addition of 3, 5, 7, and 10% (w/w) of spirulina (Arthrospira platensis) powder. Physicochemical and nutritional analyses were done on raw materials, and on fresh pasta before and after cooking. Sensorial analysis was done shortly after cooking pastas. Spirulina had a high content of protein (71.34%), with all the essential amino acids, a high total fiber (8.45%), as well as ash content (5.93%), which significantly increased the nutritional value of the obtained fresh pasta. Supplemented pastas have a significantly better amino acid profile and higher total fiber content (up to 2.99 g/100 g d.m.) than the control sample. Moreover, the addition of spirulina had a significant effect on the pasta’s color, weight gain, and cooking loss after being cooked. The addition of spirulina also affected the scores obtained for the individual parameters (texture, color, flavor, taste, and overall acceptability) of the sensory evaluation. 相似文献
248.
249.
Barbara Parrino Virginia Spanò Anna Carbone Alessandra Montalbano Paola Barraja Peter Màtyus Girolamo Cirrincione Patrizia Diana 《Tetrahedron》2014
‘Interrupted’ diazotization of 3-aminoindoles and 3-aminopyrroles, achieved by quenching with cold water immediately after the addition of nitrite, led, in good yields, to stable compounds whose structures were identified to be the diazonium species with nitrate as the counter ion, which show no saline character. 相似文献
250.
Summary The minimum-variance analysis reveals a strong anisotropy in the magnetic fluctuations measured in the interplanetary space.
Using a typical spectral shape for the energy fluctuations, previously derived in the framework of incompressible anisotropic
MHD turbulence, we relate the measured anisotropy to the free spectral parameters. Some constraints on the correlation lengths,
characteristic of the energy spectrum, are then derived.
Paper presented at the V Cosmic Physics National Conference, S. Miniato, November 27–30, 1990. 相似文献