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1.
<正> An experimental study was carried out to investigate the effects of coupling agents on the rheological properties of kaolin filled polyamide 6(PA6). We have investigated the state of dispersion and interfacial interaction of the filled systems, using ’h:anning electron microscopy (SEM) and Molau test, respectively. It is found that the addition of the coupling agents to the PA6/ kaolin (20 wt percent) significantly decreases the melt viscosity and the melt elasticity (first normal stress difference). Moreover, the states of dispersion and the polymer/filler interactions have significant influences on the rheological properties of kaolin/PA6 systems. The rheological behavior of KH550 kaolin /PA6 system is different from that of KH560 kaolin/PA6 system, although chemical reactions have taken place between the surface of KH550 kaolin (or KH560 kaolin) and PA6 matrix during melt processing. This is attributable, in part, to the differences in the state of dispersion of kaolins in PA6 matrix and, to a great extent, to the differences in the extent of chemical reactions that have taken place between the filler and polymer matrix.  相似文献   

2.
The effect of solar irradiation on the percentage of motile cells, their average speed and their phototactic orientation to white actinic light was studied in the flagellate, Euglena gracilis. Unfiltered solar radiation in midsummer during mid-day at a location near Lisboa, Portugal, was found to impair motility within 2 h. This effect is exclusively due to the UV-B component of the radiation and not due to UV-A, visible light or a temperature increase. Likewise, phototactic orientation was drastically impaired. Reduction of the solar UV-B irradiation by insertion of an ozone-Hooded plexiglass cuvette partially reduced the inhibition and covering the cuvettes with glass prevented any decrease in motility and photoorientation. Similar results were found with artificial irradiation (Xe lamps). After inoculation the motility of the population follows an optimum curve (optimum at 8 days). Also, the UV-B effect on motility was smallest after about one week and increased for younger and older cultures.  相似文献   

3.
Abstract— Vascular stasis and tissue ischemia are known to cause tumor cell death in several experimental models after photodynamic therapy (PDT); however, the mechanisms leading to this damage remain unclear. Because previous studies indicated that thromboxane release is implicated in vessel damage, we further examined the role of throm-boxane in PDT. Rats bearing chondrosarcoma were injected with 25 mg/kg Photofrin® (intravenously) 24 h before treatment. Light (135 J/cm 2 , 630 nm) was delivered to thc tumor area after injection of one of the following inhibitors: (1) R68070: a thromboxane synthetase inhibitor; (2) SQ-29548: a thromboxane receptor antagonist; and (3) Flunarizine: an inhibitor of platelet shape change. Systemic thromboxane levels were determined. Vessel constriction and leakage were evaluated by intravital microscopy. Tumor response was assessed after treatment. Thromboxane levels were decreased more than 50% with SQ-29548 as compared to controls. Thromboxane levels in animals given R68070 and Flunarizine remained at baseline levels. SQ-29548 and R68070 reduced vessel constriction compared to controls, while Flunarizine totally prevented vessel constriction. R68070 and SQ-29548 inhibited vessel permeability compared to PDT controls; Flunarizine did not. Animals given these inhibitors showed markedly reduced tumor cure. These results indicate that the release of thromboxane is linked to the vascular response in PDT.  相似文献   

4.
Abstract— Charge effects on the quenching of tryptophan fluorescence in small peptides by iodide ion have been analyzed by the conventional "static" quenching model and by a recently proposed competitive quenching model. The former involves a fit of the quenching data using two quenching parameters—one for dynamic and one for static quenching contributions. The latter model involves a single parameter fit in which the fitting parameter is the characteristic rate constant for quenching of the fluorescent state. Both models indicate a clear charge effect on the efficiency of quenching by iodide ion. However, the static model results are obscured by the interdependence of the two fitting parameters and the fact that the true physical meaning of the static parameter is uncertain. Rate constants derived from the competitive model can be converted into relative quenching efficiencies. These efficiencies, which vary by more than a factor of two for the molecules studied, are greatest when the positive charge is on the tryptophan and least when this residue contains a negative charge.  相似文献   

5.
ON THE MECHANISM OF QUENCHING OF SINGLET OXYGEN IN SOLUTION   总被引:2,自引:0,他引:2  
Abstract— Bimolecular rate constants for the quenching of singlet oxygen O*2(1Δg), have been obtained for several transition-metal complexes and for β-carotene. Laser photolysis experiments of aerated solutions, in which triplet anthracene is produced and quenched by oxygen, yielding singlet oxygen which then sensitizes absorption due to triplet carotene, firmly establishes diffusion-controlled energy transfer from singlet oxygen as the quenching mechanism in the case of β-carotene. The efficient quenching of singlet oxygen by two trans-planar Schiff-base Ni(II) complexes, which have low-lying triplet ligand-field states, most probably also occurs as a result of electronic energy transfer, since an analogous Pd(II) complex and ferrocene, which both have lowest-lying triplet states at higher energies than the O*2(1Δg), state, quench much less effectively.  相似文献   

6.
复方新诺明系磺胺甲基异噁唑(Sulfamethoxazole,简称SMZ)和甲氧苄氨嘧啶(Trime-thoprim,简称TMP)的复方制剂,用于抗脑膜炎球菌、肺炎球菌、溶血性链球菌及革蓝氏阴性杆菌,为临床广泛使用的磺胺类抗菌药物之一。药典规定用永停滴定法,重氮化外指示剂法进行含量测定。文献报道也有用三波长分光光度法、双波长法、吸收度比值法,核磁共振法等。本文根据SMZ的结构  相似文献   

7.
Abstract— The interpretation of the viscosity dependence of anthracene triplet decay is shown to be complexed by the effects of the macroscopic and the microscopic viscosity of the system on the translational diffusion coefficient. The second order rate constant for the decay of the anthracene triplet as measured by flash photolysis is equal to 2.45plusmn;.30×1091. mole-1sec-1 for nearly a one hundredfold change in the viscosity of cyclohexane-polyisobutylene solutions. The translational diffusion coefficient is unaffected by the presence of the polymer, and the local viscosity of the polymer solutions is identical to that of the pure solvent.  相似文献   

8.
9.
Abstract— Perimycin, ouabain and elevation of extracellular K+ concentrations cause an increase in the fluence rate thresholds (white light) for the step-up photophobic response in Peranema trichophorum . Elevation of extracellular Na+ concentration decreases the thresholds for this response in comparison to the control level. The fluence rate threshold of perimycin-treated cells increases before the side effect of an antibiotic action appears. Removal of K+ ions from the medium of K+-treated cells to a concentration of 1 mM depresses the threshold for the step-up response to the control level. By addition of K+ or Na + ions to perimycin- or ouabain-treated cells the threshold returns to the control value. It is suggested that the flagellar and cell membrane are responsible for changes of P. trichophorum photosensitivity.  相似文献   

10.
Abstract— The photolysis in aqueous neutral solutions of 5-nitrofurfural (NFA), an important metabolite of nitrofurans used as medicines, was investigated. Upon UV-A irradiation NFA loses up to 70 mol % nitrite, with formation of 5-hydroxymethylene-2(5H)-furanone, a new substance. When Cl−1 is present 5-chlorofurfural is an important photoproduct. Photo-induced addition of either OH or CI−1, followed by thermochemical elimination of NO2−1, is the proposed mechanism. Furthermore, NFA reacts with nitrite yielding nifuroxim. The possible role of the NFA photolysis in the occurrence of (photo)biological effects of NFA is discussed.  相似文献   

11.
Abstract —The effects of various light/dark schedules on the time course of CO2 output by axenic cultures of the short-day plant Lemna perpusilla 6746 differ substantially depending on whether the medium is N-less or contains NH4 or NO3 as the sole N source. The steady-state pattern achieved with a daily 1/4 h light pulse in N-less medium is essentially the same whether the light is red or far-red; on NO3 or NH4, however, the red and far-red patterns differ in form and suggest the action of a ‘Pfr-hourglass’ timer. In darkness, following either continuous light or entrainment to kh red light daily, CO2 output oscillates for three or more circadian cycles on NH4 medium and for at least two on N-less, but damps after a single cycle on NO3. A schedule of 1/4 h red light every 12 h elicits a 24 h periodicity on NO3 or NH4 media and a 12 h periodicity on N-less medium, while a similar far-red schedule elicits a 12 h periodicity on all three. CO2 output patterns on each of the media respond differently to varying the daily span of light from 1/4 to 6 to 12 h. These results are probably due to differential effects of changing N status on the proportion of total C O2 arising from various metabolic reactions. They suggest that, rather than being a simple, unitary indicator, CO2 output can be made to reflect different processes on different media, increasing its value as a real-time indicator of events underlying photoperiodism.  相似文献   

12.
Abstract —D-α-tocopherol was found to be an effective quencher of 1O2 molecules ( k = 2.5 times 108→mol-1 s-1 in pyridine) by measuring its effect on the autosensitized photooxidation of rubrene. The quenching process was shown to be almost entirely 'physical', that is, α-tocopherol deactivated about 120 1O2 molecules before being destroyed. The results suggest that this process may be a mechanism for the protective effect of α - tocopherol in photodynamic action.  相似文献   

13.
We measured concentration changes of the fluorescence quantum yield eta/eta 0 of flavomononucleotide (FMN) in glycerine-water solutions of various viscosities. The results obtained show that FMN dimers are traps for the exciting light energy as well as the energy transferred non-radiatively. Very good agreement between the experimental and theoretical eta/eta 0 results was obtained. It has been shown that in the investigated solutions non-radiative energy transfer from monomers to dimers takes place, preceded by the migration of energy. It has been stated that no monomer quenching occurs in these solutions. The contribution of the individual fluorescence concentration quenching mechanisms has been determined.  相似文献   

14.
The measurements of the emission anisotropy r/r0 of flavomononucleotide (FMN) within a range of concentrations of 10(-5)-10(-1) mol/L in glycerine-water solutions of different viscosities--0.056 Pa/s (system I) and 0.256 Pa/s (system II) have been carried out. In the range of high concentrations the repolarization effect due to the sharp drop of the quantum yield has been observed. The experimental results have been compared with theoretical expressions evaluated by taking into account both concentration and rotation depolarization. A good agreement on the values of the theoretical parameters obtained from independent measurements has been found. It has been stated that in the investigated systems the excitation energy transfer may be treated as a Markov process.  相似文献   

15.
THE BIOLOGICAL EFFECTS OF UV-B ON THE EYE   总被引:1,自引:0,他引:1  
–The adverse effects of ultraviolet-B (UV-B) radiation on the eye have been suspected but only recently have they been quantified by epidemiologic studies in humans. These studies became possible as methods to qualify individual ocular UV-B exposure were developed. A consistent dose-dependent association between ocular UV-B exposure and two common types of cataract (cortical and posterior subcapsular) has been shown. Although suggested by experimental studies, at present, evidence does not exist to link UV-B exposure to senile macular degeneration. Ocular exposure to UV-B is also associated with several corneal changes, pterygium, climatic droplet keratopathy, and acute photokeratitis (snow blindness). Significant reduction in ocular UV-B exposure results from the use of eyeglasses and hats.  相似文献   

16.
Crystallization phenomena and processes may be greatly affected by the addition of surfactants, which play an important rote in nucleation and growth kinetics and can substantially modify both habit and size distribution of crystal products. Moreover, scaling in industrial equipments and caking in storage tanks can be reduced and re-dissolution more easily accomplished. All these effects are related to adsorption of surfactant molecules onto crystal faces. Other applications of surfactants in crystallization processes involve nucleation induced by amphiphilic films, and micelle or microemulsion solubilization of nuclei. The above aspects are thoroughly reviewed through literature data.  相似文献   

17.
Abstract— –The presumed photoreceptor for phototaxis, the paraflagellar body, in the flagellate Euglena gracilis , was isolated still attached to the flagellum. After solubilization, fast protein liquid chromatography (FPLC) analysis yielded four major protein fractions with the chromophoric groups still attached. Fluorescence spectra showed that three fractions had excitation peaks at 380 nm and emission peaks around 450 nm indicative of pterins, while the fourth chromoprotein had a fluorescence emission at 520 nm and an excitation peak at 450 nm, indicative of a flavin. The separated proteins were analyzed by gel electrophoresis: the pterin binding proteins have apparent molecular masses between 27 000 and 31 600 and the flavin binding protein has an apparent molecular mass of 33 500.  相似文献   

18.
Abstract— The effect of relative humidity on the survival and sensitivity to radiations of Streptococcus liquefaciens has been studied. The micro-organism was found to be little affected by dehydration in aerosols and its sensitivity to the lethal action of 2537 Å light to be unaffected by changes in the relative humidity at which the cells were held during irradiation. The cells were more stable to the lethal action of 3200–4000 Å, however, when they were held at 70% relative humidity than at 50 or 30% relative humidity. Mutant cells unable to liquify gelatine were induced by semi-dehydration at 50% relative humidity and their numbers were increased by concomitant irradiation with 3200–4000 Å light. This type of mutant was not observed when the cells were irradiated with 2537 Å light. Mutant cells which had a different response from that of the parent cell to the presence of oxygen in their growth medium were produced by both wavebands of light, but only when the cells were held at 50% relative humidity. It is proposed that semi-dehydration stresses the cell membrane and damages those parts of the bacterial DNA associated with the membrane. Concomitant irradiation is suggested to enhance this particular effect.  相似文献   

19.
吖啶红荧光猝灭法测定痕量亚硝酸根   总被引:5,自引:0,他引:5  
研究了在稀硫酸介质中亚硝酸根与吖啶红发生的亚硝化反应,建立了测定痕量亚硝酸根的荧光猝灭法。方法的测定范围为0.01~0.70μg·ml-1。方法用于环境水样中痕量亚硝酸根的测定,结果满意。  相似文献   

20.
In order to systematically investigate the effects of simulated weightlessness on thefunction state of human brain, 15° head-down tilt (HDT) was used to simulate weightless-ness, and the response changes of event-related EEG power spectra, medium-frequencysynchronous potentials and slow-waves were examined in the present study. It was foundthat HDT had characteristic effects on the above EEG responses, suggesting that the ef-fects mainly occurred in the brain's regulatory system, therefore, resulting in changes ofthe brain function state.  相似文献   

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