Composites comprised of chitosan (CS) and multiwalled carbon nanotubes (MWCNTs) were fabricated by milling and ultrasonication dispersion methods. Scanning electron microscopy images showed homogeneous dispersion of MWCNTs throughout the CS matrix for samples prepared by either ultrasonication or milling methods. Further, the crystallinity of the CS component was found to decrease with the addition of MWCNTs, although the decomposition temperature and the storage modulus (E′) of the samples were improved. The decomposition temperature for the composite prepared by milling was 7°C higher than that by the ultrasonication. Meanwhile, the E′ decreased relatively slowly with temperature in the dynamic mechanical analysis measurements. In addition, IR analysis implied an interaction between CS and MWCNTs, which likely originated from hydrogen bonds between the amino, hydroxyl, and carboxyl groups of the two components. Compared with the ultrasonication, milling was more effective to promote the formation of the hydrogen bonds between CS and the MWCNTs and thus enhance the thermal stability of CS. 相似文献
The transformation method provides an efficient way to control wave propagation by materials. However, the degree to which this transformation concept can be applied to other physical phenomena remains an open question. Recently, Hu et al. presented a general framework for determining the transformation relations of the physical quantities in an arbitrary partial differential equation (PDE) in its application scope according to the idea of the transformation method. In this paper, we will review the main concepts of this general theory, particularly the difference between this idea and usual methods. The flexibility of this method is shown using an example. 相似文献
Two ruthenium complexes containing a new ligand phipz (phipz = 2‐(1,10‐phenanthroline)‐1H‐imidazo[4,5‐b]phenazine) were designed and synthesized. These complexes were found to inhibit the DNA supercoiled relaxation mediated by topoisomerase I (topo I), cleave DNA under irradiation and bind to calf thymus DNA through intercalative mode. Furthermore, complex 2 shows higher photocleavage activity, topo I inhibition activity and DNA affinity than complex 1 . Additionally, introduction of phenazine unit may be the reason that two complexes exhibit DNA ‘light switch’ behavior. The present work shows that two complexes might be potential as new DNA ‘light switches’, DNA photocleavers and topo I inhibitors. 相似文献
Rotating radio transients(RRATs) are peculiar astronomical objects whose emission mechanism remains under investigation.In this paper, we present observations of three RRATs, J1538+2345, J1854+0306 and J1913+1330, carried out with the Fivehundred-meter Aperture Spherical radio Telescope(FAST). Specifically, we analyze the mean pulse profiles and temporal flux density evolutions of the RRATs. Owing to the high sensitivity of FAST, the derived burst rates of the three RRATs are higher than those in previous reports. RRAT J1854+0306 exhibited a time-dynamic mean pulse profile, whereas RRAT J1913+1330 showed distinct radiation and nulling segments on its pulse intensity trains. The mean pulse profile variation with frequency is also studied for RRAT J1538+2345 and RRAT J1913+1330, and the profiles at different frequencies could be well fitted with a cone-core model and a conal-beam model, respectively. 相似文献
Research about two-dimensional (2D) materials is growing exponentially across various scientific and engineering disciplines due to the wealth of unusual physical phenomena that occur when charge transport is confined to a plane. The applications of 2D materials are highly affected by the electrical properties of these materials, including current distribution, surface potential, dielectric response, conductivity, permittivity, and piezoelectric response. Hence, it is very crucial to characterize these properties at the nanoscale. The Atomic Force Microscopy (AFM)-based techniques are powerful tools that can simultaneously characterize morphology and electrical properties of 2D materials with high spatial resolution, thus being more and more extensively used in this research field. Here, the principles of these AFM techniques are reviewed in detail. After that, their representative applications are further demonstrated in the local characterization of various 2D materials’ electrical properties.
High pressure can effectively control the phase transition of MoTe2 in experiment, but the mechanism is still unclear. In this work, we show by first-principles calculations that the phase transition is suppressed and phase becomes more stable under high pressure, which originates from the pressure-induced change of the interlayer band occupancies near the Fermi energy. Specifically, the interlayer states of phase tend to be fully occupied under high pressure, while they keep partially occupied for the phase. The increase of the band occupancies makes the phase more favorable in energy and prevents the structure changing from to phase. Moreover, we also analyze the superconductivity under high pressure based on BCS theory by calculating the density of states and phonon spectra. Our results may shed some light on understanding the relationship between the interlayer band occupancy and crystal stability of MoTe2 under high pressures. 相似文献
Notoginsenoside R1 (NGR1), a diagnostic protopanaxatriol‐type (ppt‐type) saponin in Panax notoginseng, possesses potent biological activities including antithrombotic, anti‐inflammatory, neuron protection and improvement of microcirculation, yet its pharmacokinetics and metabolic characterization as an individual compound remain unclear. The aim of this study was to investigate the exposure profile of NGR1 in rats after oral and intravenous administration and to explore the metabolic characterization of NGR1. A simple and sensitive ultra‐fast liquid chromatographic–tandem mass spectrometric method was developed and validated for the quantitative determination of NGR1 and its major metabolites, and for characterization of its metabolic profile in rat plasma. The blood samples were precipitated with methanol, quantified in a negative multiple reaction monitoring mode and analyzed within 6.0 min. Validation parameters (linearity, precision and accuracy, recovery and matrix effect, stability) were within acceptable ranges. After oral administration, NGR1 exhibited dose‐independent exposure behaviors with t1/2 over 8.0 h and oral bioavailability of 0.25–0.29%. A total of seven metabolites were characterized, including two pairs of epimers, 20(R)‐notoginsenoside R2/20(S)‐notoginsenoside R2 and 20(R)‐ginsenoside Rh1/20(S)‐ginsenoside Rh1, with the 20(R) form of saponins identified for the first time in rat plasma. Five deglycometabolites were quantitatively determined, among which 20(S)‐notoginsenoside R2, ginsenoside Rg1, ginsenoside F1 and protopanaxatriol displayed relatively high exploration, which may partly explain the pharmacodynamic diversity of ginsenosides after oral dose. 相似文献
A sensitive and accurate LC–MS/MS method was established for quantifying salvianolic acid B (Sal B), rosmarinic acid (Ros A) and Danshensu (DA) in rat plasma. Salvia miltiorrhiza polyphenolic acid (SMPA), active water‐soluble ingredients isolated and purified from Salvia miltiorrhiza Bge included Sal B, Ros A and DA. The pharmacokinetic analysis of Sal B, Ros A and DA after pulmonary administration of SMPA solution to rat was performed by LC–MS/MS. Results from the pharmacokinetic studies showed that the peak concentration of DA was 21.85 ± 6.43 and 65.39 ± 3.83 ng/mL after pulmonary and intravenous administration, respectively. DA was not detected at 2 h after administration. The absolute bioavailabilities of Sal B and Ros A were respectively 50.37 ± 27.04 and 89.63 ± 12.16% after pulmonary administration of 10 mg/kg SMPA solution in rats. The absolute bioavailability of Sal B increased at least 10‐fold after pulmonary administration, compared with oral administration. It was concluded that the newly established LC–MS/MS method was suitable for describing the pharmacokinetic characteristics of Sal B, Ros A and DA in rat after pulmonary administration of SMPA solution. The data from this study will provide a preclinical insight into the feasibility of pulmonary administration of SMPA. 相似文献