筛选条件 共查询到13条结果
排序方式
Electrical Property and Biocompatibility of Polyvinylidene Fluoride Films Modified by Polypyrrole

期刊: CHINA SURFACE ENGINEERING, 2019; 32 (5)

Polyvinylidene fluoride (PVDF) has attracted much attention due to its biocompatibility, piezoelectric and favourable mechanical properties. The modification of polypyrrole coating on the surface of the PVDF film by electrochemical method was studied. The surface morphology of the nanostructured polypyrrole coating modified PVDF film was observed by scanning electron microscopy (SEM) and atomic force microscope (AFM). The surface contact angle analyzer and AFM were used to study the hydrophilicity and electrical properties of the PVDF membrane modified by the nano structure polypyrrole coating. The biocompatibility of the nanostructured polypyrrole coating modified PVDF membrane was investigated by in vitro mineralization, cell viability staining and CCK-8 assay, respectively. The results show that the surface hydrophilicity, surface potential distribution and biocompatibility of PVDF films are significantly improved by the modification of the nanostructured polypyrrole coating, and more conducive to the surface bone mineral deposition and cell adhesion and proliferation. In addition, the PVDF membrane modified by polypyrrole nanowire has higher hydrophilicity and surface potential distribution, which is more conducive to cell adhesion and proliferation.

Polypyrrole Nanocones and Dynamic Piezoelectric Stimulation-Induced Stem Cell Osteogenic Differentiation

期刊: ACS BIOMATERIALS SCIENCE & ENGINEERING, 2019; 5 (9)

Imitating the physiological microenvironment of living cell and tissues opens new avenues of research into the application of electricity to medical therapies. In this study, dynamic piezoelectric stimulation is generated in a dynamic culture because of the piezoelectric effect of the poly(vinylidene fluoride)-polypyrrole (PVDF-PPy) electroactive composite. Combined with PPy nanocones, dynamic piezoelectric signals are effectively and continuously provided to cells. In the presence of dynamic piezoelectric stimulation and PPy nanocones, PPy-PVDF NS samples show promoted bone mesenchymal stem cell (BMSCs) adhesion, spreadin, and osteogenic differentiation. On the basis of the results of this study, PPy nanocones and dynamic piezoelectric stimulation can be administered to modulate cell behavior, paving the way for the exploration of cellular responses to dynamic electrical stimulation.

IF:4.51

The Gaussian Wave Packet Transform for the Semi-Classical Schrodinger Equation with Vector Potentials

期刊: COMMUNICATIONS IN COMPUTATIONAL PHYSICS, 2019; 26 (2)

In this paper, we reformulate the semi-classical Schrodinger equation in the presence of electromagnetic field by the Gaussian wave packet transform. With this approach, the highly oscillatory Schrodinger equation is equivalently transformed into another Schrodinger type wave equation, the omega equation, which is essentially not oscillatory and thus requires much less computational effort. We propose two numerical methods to solve the w equation, where the Hamiltonian is either divided into the kinetic, the potential and the convection part, or into the kinetic and the potential-convection part. The convection, or the potential-convection part is treated by a semi-Lagrangian method, while the kinetic part is solved by the Fourier spectral method. The numerical methods are proved to be unconditionally stable, spectrally accurate in space and second order accurate in time, and in principle they can be extended to higher order schemes in time. Various one dimensional and multidimensional numerical tests are provided to justify the properties of the proposed methods.

IF:1.81

pH Controlled Intersystem Crossing and Singlet Oxygen Generation of 8-Azaadenine in Aqueous Solution

期刊: CHEMPHYSCHEM, 2019; 20 (5)

Azabases are intriguing DNA and RNA analogues and have been used as effective antiviral and anticancer medicines. However, photosensitivity of these drugs has also been reported. Here, pH-controlled intersystem crossing (ISC) process of 9H 8-azaadenine (8-AA) in aqueous solution is reported. Broadband transient absorption measurements reveal that the hydrogen atom at N9 position can greatly affect ISC of 8-AA and ISC is more favorable when 8-AA is in its neutral form in aqueous solution. The initial excited pi pi* (S-2) state evolves through ultrafast internal conversion (IC) (4.2 ps) to the lower-lying n pi* state (S-1), which further stands as a door way state for ISC with a time constant of 160 ps. The triplet state has a lifetime of 6.1 mu s. On the other hand, deprotonation at N9 position promotes the IC from the pi pi* (S-2) state to the ground state (S-0) and the lifetime of the S-2 state is determined to be 10 ps. The experimental results are further supported by time-dependent density functional theory (TDDFT) calculations. Singlet oxygen generation yield is measured to be 13.8 % for the neutral 8-AA while the deprotonated one exhibit much lower yield (<2 %), implying that this compound could be a potential pH-sensitized photodynamic therapy agent.

IF:3.08

Direct observation of an intramolecular charge transfer state in epigenetic nucleobase N6-methyladenine

期刊: PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 2019; 21 (13)

N6-Methyladenine (6MeAde), the most abundant internal modification in mRNA, has proved to be an important epigenetic biomarker for gene regulation just like 5-methylcytosine in DNA. Recently, a unique UV-induced response of 6MeAde was reported, which makes it instructive and intriguing to reveal the excited state relaxation mechanism in this methylated adenine and its derivatives. In this work, we investigated 6MeAde and its ribose species N6-methyladenosine (6MeAdo) by using femtosecond time-resolved fluorescence up-conversion (FUC) and broadband transient absorption (TA) spectroscopy. Both 6MeAde and 6MeAdo exhibit a hundreds of femtoseconds lifetime, which originates from the efficient depletion of the pi pi* (L-a) state. A several picoseconds lifetime is also observed and it should be attributed to the pi pi* (L-b) state. Surprisingly, dual peak fluorescence emission is observed in 6MeAde and the long wavelength emission is ascribed to an intramolecular charge transfer (ICT) state. The lifetime of this ICT state is determined to be 107 ps. The kinetic isotope effect shows that the ICT state is closely associated with the solute-solvent H-bonding in aqueous solution. In 6MeAdo, the ICT state is apparently quenched and adenine-like excited state dynamics suggests that DNA/RNA containing such modification could still possess excellent photostability under UV irradiation. Our results contain an important insight for understanding excited state properties in epigenetic modified DNA/RNA.

IF:3.57

Study on Electrochemical Corrosion Rate of Braided Wire Rope

期刊: 2019 3RD INTERNATIONAL WORKSHOP ON RENEWABLE ENERGY AND DEVELOPMENT (IWRED 2019), 2019; 267 ()

Taking 8x19 traction galvanized Braided steel wire rope as the research object, we carried out the electrochemical corrosion test of the steel wire rope matrix and the galvanized layer. And the response surface method was used to examine the influence of the interaction of three factors on the corrosion rate of steel wire rope. The results show that the corrosion rate of the braided steel wire rope matrix and the galvanized layer increases with the increase of temperature and the decrease of pH value, and increases first and then decreases with the increase of Cl- concentration. There is a nonlinear relationship between corrosion rate and temperature, Cl- concentration and pH value. In the same corrosive environment, the corrosion rate of the galvanized layer of the wire rope is greater than the corrosion rate of the matrix. The influence degree of the three factors on the corrosion rate of the steel wire rope matrix and the galvanized layer under the interaction is: pH>temperature>Cl- concentration.

Martensite transformation, mechanical properties and shape memory effects of Ni-Mn-In-Mg shape memory alloys

期刊: PROGRESS IN NATURAL SCIENCE-MATERIALS INTERNATIONAL, 2018; 28 (1)

The martensite transformation (MT), mechanical properties and shape memory effect (SME) of (Ni50Mn35In15)((1-x))Mg-x (x = 0%, 0.08%, 0.3%, 0.6% at%) alloys were comprehensively investigated. The results showed that due to Mg doping the MT temperature shifted to higher temperatures and a worm-like secondphase precipitated at grain boundaries and inside the grains. With increasing Mg content, the amount of precipitates gradually increased, the thermal hysteresis was almost invariant, and the SME was not obviously affected at 3% pre-strain, even when the volume of the second phase reached up to 28.75%. Compressive stress and strain experiments showed that both the strain and strength of the Ni-Mn-In-Mg alloys were improved substantially (by 46.9% and 53.4%, respectively, at x = 0.6%) compared with those of the pure Ni50Mn35In15 alloy; this effect is nearly the same as that achieved by the directional solidification method. Because Mg is nonmagnetic, the magnetization difference of the alloy with Mg doping is much lower than that of the alloy without Mg doping. Overall, the results confirm that adding a small amount of Mg is a potentially viable method for improving the mechanical properties of Ni-Mn-In alloys without adversely damaging their functional properties.

IF:3.31

Martensitic transformations and kinetics in Ni-Mn-In-Mg shape memory alloys

期刊: INTERMETALLICS, 2018; 92 ()

The martensitic transformation (MT) and its kinetics in Ni-Mn-In-Mg shape memory alloys (SMAs) were calculated for the first time. The differences in the phase transition processes of alloys with various Mg contents were analyzed using two different models, and their microstructures were investigated using differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). As the Mg content increased, the grain size decreased, and the MT temperature and activation energy increased significantly due to the grain refinement of the second phase. The Johnson-Mehl-Avrami-Kolmogorov (JMAK) equation was used to simulate the MT time temperature-transformation (TTT) curves of the alloys, which exhibited the same trends as the DSC test results. To study the dependence of the activation energy on the heating rate, DSC studies were conducted using nine different heating rates to study the kinetics of the thermally induced transformation process. It was clarified that the heating rate could adjust the phase transition temperature and significantly affect the activation energy, indicating that the heating rate can be used as a method for adjusting the phase change parameters. Moreover, for the same alloy system, using the same heating rate is a useful means of comparing activation energies. This study provides a reference for designing and calculating the kinetics of Ni-Mn-In memory alloys.

IF:3.35

Cauda equina syndrome secondary to leptomeningeal metastases from recurrent primary peritoneal carcinoma

期刊: ECANCERMEDICALSCIENCE, 2018; 12 ()

The patient is a 42-year-old woman with metastatic primary peritoneal carcinoma and known brain metastases, who subsequently developed cauda equina syndrome after presenting with ataxia, lower extremity weakness, and bowel and bladder incontinence secondary to leptomeningeal metastasis after treatment with neoadjuvant chemotherapy, surgical debulking, and adjuvant chemotherapy. Metastases to the central nervous system (CNS) and leptomeninges are rare events in epithelial ovarian and primary peritoneal carcinomas as these tumours do not have a predilection for the CNS. Cauda equina syndrome is often characterised by gait disturbances, bowel and bladder dysfunction, saddle anaesthesia, and lower extremity muscle weakness. In patients with known metastatic gynaecologic carcinomas presenting with nonspecific neurologic symptoms, cauda equina syndrome should remain high in the differential diagnosis.

Internal friction behaviors of Ni-Mn-In magnetic shape memory alloy with two-step structural transformation

期刊: PROGRESS IN NATURAL SCIENCE-MATERIALS INTERNATIONAL, 2017; 27 (3)

The internal friction (IF) behaviors of dual-phase Ni52Mn32In16 alloy with two-step structural transformation were investigated by dynamic mechanical analyzer. The IF peak for the martensite transformation (MT) is an asymmetric shoulder rather than those sharp peaks for other shape memory alloys. The intermartensitic transformation (IMT) peak has the maximum IF value. As the heating rate increases, the height of the IMT peak increases and its position is shifted to higher temperatures. In comparison with the IMT peak, the MT peak is independent on the heating rate. The starting temperatures of the IMT peak are strongly dependent on frequency, while the MT peak is weakly dependent. Meanwhile, the heights of both the MT and IMT peak rapidly decrease with increasing the frequency. This work also throws new light on their structural transformation mechanisms.

IF:2.57

Ultrafast Excited-State Dynamics of Cytosine Aza-Derivative and Analogues

期刊: JOURNAL OF PHYSICAL CHEMISTRY A, 2017; 121 (14)

Excited state dynamics of 5-azacytosine (5-AC), 2,4-diamino-1,3,5-triazine (2,4-DT), and 2-amino-1,3,5-triazine (2-AT) were comprehensively investigated by steady state absorption, fluorescence, and femtosecond transient absorption measurements. Time-dependent density functional theory (TDDFT) calculations were performed to help assign the absorption bands and understand the excited state decay mechanisms. The experimental results of excited singlet state dynamics for 5-AC, 2,4-DT, and 2-AT with femtosecond time resolution were reported for the first time. Two distinct decay pathways, with similar to 1 ps and tens of picosecond lifetimes, were observed in 5-AC. Only one decay pathway with 17 ps lifetime was observed in 2,4-DT while an emissive state was found in 2 AT. TDDFT calculations suggest that 5-AC has a dark n pi* (S-1) state below the first allowed pi pi* (S-2) state, which leads to the ultrafast decay of the ire state. In 2,4-DT, there is no dark n pi* state below the bright pi pi* (S-1) state and the 17 ps lifetime is assigned to the relaxation from the pi pi* (S-1) state to ground state. Two dark n pi* states (Si and S2) were found in 2-AT, which exhibits much more complex excited state dynamics compared with the other two. Photoluminescence in 2-AT has been confirmed to be fluorescence emission from its bright pi pi* (S-3) state. Our results strongly suggest that electronic structures are very sensitive to the substitution on the triazine ring and that the photophysical properties of nucleic acid analogues depend highly on their molecular structures.

IF:2.84

共13条页码: 1/1页15条/页