Biomedical subjects

Zheng Xu

Publications and source records attributed to Zheng Xu.

At least 55 records · Page 3Linked to original sources

PubMed2005

[Investigations on the movement of pigment particles in the electrophoretic liquids].

In the present report, the authors studied the movement of pigment particles which decide the display status, enduced the equation of the motion and the expression of reflectivity, and estimated the value of the delay time. Combining the above theoretical conclusion with the experimental results, the authors discussed the feasibility of the passive matrix addressing of electrophoretic image displays, and provided good advice on how to acquire display devices of good quality.

Algorithms↗

PubMed2005

[Study of water-sol core-shell CdSe/CdS quantum dots].

Water-sol core/shell CdSe/CdS quantum dots (QDs) were synthesized in aqueous solution by using mercapto-acetate acid as stabilizer. The UV-Vis absorption and emission spectra were studied. The size of the SdSe-core was about 2 nm estimated by absorption edge and X-ray powder diffraction(XRD). The structure was also characterized by X-ray photoelectron spectroscopy(XPS). The intensity of luminescence of the quantum dots was greatly enhanced after the surface was modified with CdS shell. Red shift of the peak was shown in both the emission and absorption spectra.

Algorithms↗

PubMed2005

[The study of electroplex emission based on PVK/BCP].

Electroplex emission based on poly(N-vinylcarbazole) (PVK) and 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) has been studied. A emission peak at 595 nm was observed in EL spectrum but not in PL spectra in the devices. The emission originates from the transition between the excited state of BCP and the ground state of PVK. Because of the increase of emission zone, the device of PVK: BCP blend exhibited stronger electroplex emission. The emission of electronplex was enhanced for both of PVK/BCP double layer device and PVK:BCP blend device, and it is stronger for blend devices. At higher drive voltage, only electroplex emission was observed in the blend device.

Algorithms↗

PubMed2005

[Influence of some extrinsic factors on the stability of water-soluble carboxymethyl chitosan].

Water-soluble carboxymethyl chitosan was prepared from dried shrimp shells. The intrinsic viscosities of its samples were measured to evaluate the stability of carboxymethyl chitosan. The influential factors of stability, such as heat, pH, ionic strength, ultraviolet radiation, and sterilization were studied. The results demonstrate that the intrinsic viscosities of water-soluble chitosan will be influenced, to a certain extent, by the change of pH and ionic strength. Ultraviolet radiation and sterilized processes not only exept influence on the degradation of chitosan, but also have prominent effects on the molecular structure of it. Besides, temperature will also affect the speed of degradation, and chitosan can be stored at a temperature as low as 2 degrees C-8 degrees C.

Chitosan↗

PubMed2005

[Study of PVK: TPB thin film by using stable spectra].

The energy transfer between PVK and TPB in PVK:TPB thin film in different concentrations was studied by emission spectra, excitation spectra, and absorption spectra. It is proved that the energy can be transfered from PVK to TPB in a wide concentration range and the transfer is most efficient at the concentration of 5% wt. A model Hamitonian based on a single chain model including the dopant was proposed to simulate the experiment. This model can be used to explain the experimental results very well.

English Abstract↗

PubMed2005

[Upconversion luminescence properties of YLiF4:Er, Tm, Yb synthesized by hydrothermal method].

YLiF4 codoped with Er3+, Tm3+ and Yb3+ ions was synthesized by hydrothermal method. The absorption spectra and upconversion spectra excited at 980 nm were investigated. Under the excitation of infrared photons, strong white emission can be obtained. According to the value of n obtained from the power law, the 484 nm blue emission, 524 and 552 nm green emission, and 665 nm red emission are all due to two photon process, while the UV emission is attributed to three photon process. The authors also analyzed the upconversion mechanism and process.

English Abstract↗

PubMed2005

[Studies on photoluminescence spectra of polyfluorene under modulation of electric field].

The photoluminescence of polyfluorene thin film modulated by an electric field are studied. The results show that the photoluminescence from polyfluorene film can obviously quenched by the extra electric field, which is attributed to the electric field-induced dissociation of photogeneration excitons. The dependence of the exciton dissociation rate constant on the intensity of electric filed is fitted. The average hopping distance of element charge is 0.68 nm in PFO. This volume is comparable with the reported results in Alq3 and polymers. The spectral dependence of the factor of EFIQP is given. The dissociation of hot-exciton is deduced, which influences on the spectral dependence of the EFIQP factor slightly.

Algorithms↗

PubMed2005

[Simultaneous determination of rate ratio of recombination to capture and trap depth from thermo-luminescence of ZnS:Cu, Co].

The recombination luminescence is in nature a bimolecular process but, the decay rule may be changing from that of mono-molecular to bimolecular rule, i.e., from exponential to hyperbolic rule, depending on the behavior of conduction electrons. This behavior is represented by relative rate of recombination with ionized centers to that of capture by traps. This relative rate depends partly on the intrinsic parameters of the specified materials, and partly on the concentration of conduction electrons supplied by traps. Each point of the TL curve is related to the material parameters and the release of electrons from traps. The ratio of relative rate of recombination to that of capture gamma(epsilon) = sigma0(n0)/sigma(nu - n) involves the parameter epsilon. They are inseparable and must be determined at the same time. In the present report, starting from the same sample ZnS:Cu, Co which has only one peak in its TL(i. e., only one kind of luminescent center and only one kind of traps), and the experimental value of sigma/sigma0 = 0.005, the authors use thermo-luminescence kinetics models and some mathematic tools to exactly estimate the ratio sigma0(n0)/sigma(nu) and the trap depth epsilon simultaneously from the glow curve. The authors found that sigma0(n0)/sigma(nu) = -2.6 and epsilon = 0.86 eV.

Cobalt↗

PubMed2005

[Proof of solid state cathodoluminescence by using brightness waveform].

Three different inorganic-organic hetero-junctions (A: ITO/SiO2/Alq3/Al, B: ITO/Alq3/SiO2/Al and C: ITO/SiO2/Alq3/SiO2/Al) were fabricated. The emission can be observed only under positive bias in devices A and B, but under both biases in device C according to their brightness waveforms. With increasing voltage, the increase in blue emission in devices B and C is faster than that in green emission. This is because that the recombination of hot electrons and holes, i.e., electron-hole pairs, produced blue emission in devices B and C, and the recombination of electrons injected from Al with the accumulated holes, which are excited by hot electrons, produced green emission in device A. Hence, the emissions of the devices are attributed to not only the recombination of electrons and accumulated holes, but also the cathodoluminescence-like (CL-like) emission.

English Abstract↗

PubMed2005

[Photostimulated luminescence properties of KCl:Cu+ after UV excitation].

KCl:Cu+ powder sample was prepared with high temperature solid reaction process. After being excited by UV, the sample shows near ultraviolet blue luminescence by stimulation with 560 nm light. The research result indicates that Cu+ acts as a luminous center, and Cu+ does not change into Cu2+ by UV irradiation. So, Cu+ ions do not act as hole traps, while anion vacancies act as electron traps. Once UV excited sample is stimulated, electrons from F center combine with hole trapping center or VK center, and cause subsequent energy transfer to Cu+ ion. Then, a character emission attributed to d-s transition of Cu+ in lattice occurs.

English Abstract↗

PubMed2005

[Donor concentration dependence of upconversion luminescence in YLiF4: Er3+, Yb3+].

YLiF4 :Er3+, Yb3+ was synthesized by hydrothermal method. The concentration of Er3+ was 2 mol%, and Yb3+ changed from 0 to 7 mol%. At room temperature the absorbance of YLiF4: Er3+, Yb3+ in all samples was measured from 200 to 1 200 nm. The absorbance around 980 nm increased with increasing Yb3+ concentration. The result shows that the upconversion intensity excited at 980 nm was enhanced. The enhanced intensity is dependent on the Yb3+ concentration. The excitation spectra and photoluminescence spectra were measured in the sample with Yb3+ concentration of 2 mol%. The red and green luminescence came from the transition 4F(9/2) --> 2 I(15/2), and 4 S(3/2) -->2 I(15/2) and 2H(11/2) --> 2 I(15/2), respectively.

English Abstract↗

PubMed2004

Intervertebral disc replacement maintains cervical spine kinetics.

STUDY DESIGN: An in vitro biomechanical study of C4-C5 intervertebral disc replacement using a cadaveric model. OBJECTIVES: To investigate the degree of motion afforded by a ball-and-socket cervical intervertebral disc prosthesis design. SUMMARY OF BACKGROUND DATA: Intervertebral disc prostheses designs attempt to restore or maintain cervical disc motion after anterior cervical discectomy and reduce the likelihood of accelerated degeneration in adjacent discs by maintaining normal motion at the affected disc level. Surprisingly, the actual kinetic and biomechanical effects that cervical disc arthroplasty imparts on the spine have not been widely reported. Accordingly, we investigated what effect implanting a cervical disc prosthesis has on the range of motion at the affected level as well as how it changes the coupled motion patterns at the level of implantation. METHODS: Six fresh-frozen human cadaveric cervical spines (C2-C7) were used in this study. We evaluated two different spinal conditions: intact and after disc replacement at C4-C5. Compression (using the follower load concept) and pure moment loading were applied to the specimen. Range of motion was measured using an optical tracking system. Statistical differences between the intact and replaced condition range of motion was determined using analysis of variance with post hoc comparisons (alpha = 0.05). RESULTS: The data indicate that the intervertebral disc prosthesis approximated the intact motion in all three rotation planes at the affected level. Finally, changes in cervical coupled rotations, specifically lateral bending during axial rotation loading and axial rotation during lateral bending loading, were not statistically significant between the two tested conditions. CONCLUSIONS: Our data demonstrate that a ball-and-socket design can replicate physiologic motion at the affected and adjacent levels. More importantly, the data indicate that motion coupling, which is most dramatic in the cervical spine and plays an important biomechanical role, is maintained.

Arthroplasty, Replacement↗

PubMed2004

Characterization and biological evaluation of a microparticle adjuvant formulation for plasmid DNA vaccines.

We describe the physiochemical characterization and immunological evaluation of plasmid DNA vaccine formulations containing a nonionic triblock copolymer adjuvant (CRL1005) in the presence and absence of a cationic surfactant, benzalkonium chloride (BAK). CRL1005 forms particles of 1-10 microns upon warming above its phase-transition temperature (approximately 6-8 degrees C) and the physical properties of the particles are altered by BAK. DNA/CRL1005 vaccines formulated with and without BAK were evaluated in rhesus macaques to determine the effect of CRL1005 and BAK on the ability of plasmid DNA to induce a cellular immune response. Immunogenicity results indicate that the addition of CRL1005 to human immunodeficiency virus-1 gag plasmid DNA formulated in phosphate-buffered saline leads to an enhancement in the gag-specific cellular immune response. Moreover, the addition of BAK to human immunodeficiency virus-1 gag plasmid DNA/CRL1005 formulations produces an additional enhancement in gag-specific cellular immunity. In vitro characterization studies of DNA/CRL1005 formulations indicate no detectable binding of DNA to CRL1005 particles in the absence of BAK, suggesting that the enhancement of cellular immunity induced by DNA/CRL1005 formulations is not due to enhanced DNA delivery. In the presence of BAK, however, results indicate that BAK binds to CRL1005 particles, producing cationic microparticles that bind DNA through electrostatic interactions. If BAK is present at the phase-transition temperature, it reduces the particle size from approximately 2 microns to approximately 300 nm, presumably by binding to hydrophobic surfaces during particle formation. Zeta potential measurements indicate that the surface charge of CRL1005-BAK particles changes from positive to negative upon DNA binding, and DNA bound to the surface of CRL1005-BAK particles was visualized by fluorescence microscopy. These results indicate that the addition of BAK to DNA/CRL1005 formulations leads to the formation of approximately 300 nm CRL1005-BAK-DNA particles that enhance the cellular immune response in rhesus monkeys.

Adjuvants, Pharmaceutic↗

PubMed2004

[The luminescence characteristic of a new novel coprecipitate rare earths complexes].

A new novel coprecipitate rare earths complexes La0.6Eu0.4(BSA)3phen has been synthesized and was chosen as the emitter material in the organic electroluminescent devices: ITO/PVK: La0.6Eu0.4(BSA)3phen/Alq/Al where PVK was used to improve the film-forming and hole-transporting property of the La0.6Eu0.4(BSA)3phen. It has been proved that it exists Förster energy transfer process from La3+ to Eu3+. This device has also been compared with the devices: ITO/PVK: Eu(BSA)3phen/Alq/Al and ITO/PVK: Tb0.6Eu0.4(BSA)3phen/Alq/Al. From the data, it indicated the device has the good purity of red color and good commutation property. The maximum EL brightness of 102 cd x m(-2) had been got.

English Abstract↗

PubMed2004

[Electroluminescence property of MEH-PPV/ZnO nano-crystal structure].

A new structure with II-VI nano-crystal ZnO film as the electron transport layer and MEH-PPV as the hole transport layer and emitting layer was fabricated. The new structure's brightness and efficiency were improved markedly compared with that of the single MEH-PPV layer structure. And a new peak at 620 nm was found in the ITO/MEH-PPV/ZnO/Al structure's electroluminescence spectrum, which should resulted from ZnO layer. In addition, the turning-on voltage of the two-layer structure decreased from 9 V of the single layer structure to 4 V. From the I-V curve, the authors concluded that the emitting area was around the interface of MEH-PPV/ZnO and the combination area could shift with changing the voltage.

English Abstract↗

PubMed2004

[The influence of thickness of SiO2 on the electron acceleration in cathodluminescence-like emission].

The authors investigated the property of cathodluminescence-like (CL-like) emission in the device of MEH-PPV sandwiched between two SiO2 layers. The authors observed in addition to the inherent electroluminescence of MEH-PPV, a shorter emission peak which is considered to be corresponding to HOMO-LUMO transition. From the relative change of these two peaks with the variation of the thickness of SiO2, The authors studied the electron acceleration ability of SiO2.

English Abstract↗

PubMed2004

[Photoexcitation mechanism of photoconductive device by organic/inorganic thin-film heteropairing].

Photoconductive devices with organic (polyvinylcarbazole-PVK)/inorganic (zinc-sulfide--ZnS) thin-film heteropairing were fabricated. In external field, the excitation profile of the steady-state photoconductivity and the primary photoexcitation process of hybrid devices were presented and discussed. Comparison of photoconductivity of the devices and absorption spectra of PVK and ZnS implied that both layers absorption contributes to the photocurrent, but the effective part is at the interface of PVK and ZnS. The dependence of maximum photocurrent on the applied voltage and the dark and illuminated current spectra indicates the ultrafast charge transfer at the interface.

Electrochemistry↗

PubMed2004

[Luminescence properties of a new kind of rare earth complexes Tb(m-benzoicacid)3].

The luminescence properties of a new kind of rare earth complex Tb(m-benzoicacid)3 were studied. With the new complex as the dopant and PVK as the host, the film of the mixed system was made, from whose spectra the authors learned that a highly efficient energy transfer process exists. The energy transfer is related to the mass proportion, and the more the mass proportion of Tb in the doped system, the more the emission proportion, and at the same time the emission of PVK is relatively weak. When the mass proportion of Tb(m-benzoicacid)3:PVK is higher than 20%, the emission of Tb is stronger than that of PVK, and plays the main role, while the emission of PVK disappears. The authors used the PVK:Tb(m-benzoicacid)3 system as the emission layer and Alq as the electron-transfer layer, thus the device, whose structure is ITO/PVK:Tb(m-benzoicacid)3/Alq/LiF/Al was formed. From the spectrum of this device, the characteristic emission of Tb can be observed. At the bias voltage of 21 V, a brightness 311 cd x m(-2) was achieved.

English Abstract↗