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1.
Interstitial and intracavity 252Cf sources have been used to treat a number of tumor types with encouraging results. In particular these tumors include a variety of cervical, head-and-neck, and oral-cavity cancers and possible malignant gliomas. As a neutron source, 252Cf offers certain theoretical advantages over photon therapy (i.e., in treating tumors with significant hypoxic or necrotic components). With the recent availability of 10B-labeled tumor-seeking compounds, the usefulness of 252Cf may be further improved by augmenting the 252Cf dose to the tumor with an additional dose due to the fission (following thermal neutron capture) of 10B located in the tumor itself. While the high mean neutron energy permits 252Cf to deliver a high-LET, low-OER dose to the tumor on a macroscopic scale, thermalization of neutrons followed by 10B capture may augment this dose at the cellular level if adequate loading of tumor cells with 10B is possible. This paper presents results of a Monte Carlo simulation study investigating the dosimetric characteristics of linear 252Cf sources both with and without the quantitative increase in tumor dose possible with the addition of 10B. Results are displayed in the form of "along and away" tables and dose profiles in a water phantom. Comparisons of Monte Carlo results with experimental and analytical dosimetry data available in the literature are also presented.  相似文献   

2.
Fusion peptides mimic the membrane fusion activities of the larger viral proteins from which they derive their sequences. A possible mode of activity involves their oblique insertion into lipid bilayers, causing membrane disruption by promoting highly curved hemifusion intermediates, leading to fusion. We have determined the location and orientation of the simian immunodeficiency virus (SIV) fusion peptide in planar lipid bilayers using neutron lamellar diffraction. The helical axis of the peptide adopts an angle of 55 degrees relative to the membrane normal, while it positions itself nearest the lipid bilayer surface. This is the first direct observation of the structural interaction between a fusion peptide and a phospholipid bilayer.  相似文献   

3.
A concept of the divertor and the technology for organizing the edge plasma in a fusion neutron source based on a spherical tokamak (FNS-ST) are described. The experimental data on the characteristics of the peripheral plasma in modern tokamaks are extrapolated to the FNS-ST conditions with the help of semi-analytical models. The effects depending on the magnetic configuration and on the geometry and materials of the divertor and the first-wall elements are considered. Possible designs of the FNS-ST divertor and the first wall are described. Using an original model, it is shown that the maximum density of the heat flux at the divertor plates in a double-null magnetic configuration does not exceed 5?C6 MW/m2, which complies with modern engineering capabilities. Methods for further improvement of the FNS-ST divertor concept are analyzed.  相似文献   

4.
Summary For our program on the transfer of cytoplasmic male sterility (CMS) by cybridization inBeta vulgaris L. (sugar beet), we have developed a procedure for the isolation and culture of mesophyll protoplasts of sugar beet followed by shoot regeneration. A prerequisite proved to be the presence in the media of n-propylgallate (nPG), a lipoxygenase inhibitor. Sustained divisions were found in all accessions that were tested. Plating efficiencies and regeneration ability varied greatly from one experiment to the other and appeared to be accession-dependent. Shoots could be easily transferred to soil. A majority of the regenerants (72%) retained the diploid chromosome number. Somaclonar variation in phenotype was low (4.9%). Mitochondrial DNA probes, capable of discriminating different cytoplasms ofBeta spp. showed no rearrangements due to the protoplast and in vitro culture phase, indicating that these probes can be used to identify cybrids after asymmetric fusions. The data presented here open up possibilities for genetic engineering using protoplasts in one of the world's most important arable crops.  相似文献   

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Two thiophosphoroate radiation protectors (WR-2721 and WR-151327) were assessed for their ability to modify the effects of neutron or gamma irradiation on the gastrointestinal tract. Three neutron sources (DOSAR, JANUS, and FERMILAB) were compared to the response obtained after 60Co irradiation. The end points studied were intestinal stem cell survival and LD50(6). DOSAR and JANUS, both fission-spectrum neutrons, showed somewhat different gut sensitivities [LD50(6)] of about 240 and 400 cGy respectively. The intestinal LD50 obtained with FERMILAB neutrons (25 meV) was closer (875 cGy) to that obtained after 60Co (1068 cGy) irradiation. WR-151327 protected against the lethal effects of fission neutron (DOSAR and JANUS) to a greater degree (DMF = 2.2) than with lower LET sources such as FERMILAB neutrons (DMF = 1.7) or 60Co (DMF = 1.7). The results did not correlate with the intestinal stem cell assays where WR-2721 when compared to WR-151327 showed either similar (DOSAR; fission spectrum neutrons) or somewhat better (60Co and FERMILAB neutrons) protection. Possible explanations for the differing results are discussed.  相似文献   

8.
In a population with overlapping generations, intense selection can perturb the age distribution and thus affect the rate of increase of an advantageous allele. We found that the age-specific nature of intense selection, such as that generated by many diseases, can affect the outcome of selection on loci, such as those conferring disease resistance. We also found that the temporal dynamics of selection alter the speed of evolution, particularly when selection is intense, and even more so when it is age-specific. We relate our model and results to selection for disease resistance, although the results have broader implications for inferences about past selection pressures in general.  相似文献   

9.
以一株表达人胰高血糖素样肽-1融合蛋白的重组大肠杆菌为研究对象,首先通过摇瓶实验对碳源种类进行了初步选择,发现葡萄糖和甘油对菌体生长以及GLP-1融合蛋白表达较为适宜。进一步在5 L反应器上对初始葡萄糖及甘油浓度进行了考察,发现高浓度碳源有利于菌体生长却抑制GLP-1融合蛋白表达,但能提高GLP-1融合蛋白的体积得率。在0.25%初始葡萄糖或甘油存在的条件下,在培养过程中流加葡萄糖或甘油维持其在发酵液中的浓度,比较了两者对菌体生长以及GLP-1融合蛋白表达的影响,结果发现,以甘油为碳源时,菌体生长以及GLP-1融合蛋白的表达量均高于以葡萄糖为碳源的结果,最终发酵液的菌浓(OD_(600))可达到25.4,较葡萄糖为碳源时19.1提高了33.0%,GLP-1融合蛋白表达水平和体积得率分别可达到22.4%和1.051 g/L,较葡萄糖为碳源的15.8%和0.504 g/L分别提高41.8%和108.5%。该结果对GLP-1融合蛋白表达菌株发酵条件的进一步优化提供了依据。  相似文献   

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A method for calculating and optimizing the composition of materials for soft X-ray sources used in research on inertial confinement fusion is described. For a target-converter, a material composition is determined with which the conversion of laser light into X radiation is highly efficient. A comparative analysis is carried out of the efficiencies of generation of soft X-ray emission in the plasmas of some composite materials of thin conductors (wires) used as loads in X-and Z-pinches. Numerical calculations of the optical plasma properties are reported whose results make it possible to judge the emissivity of plasmas of different materials. The results obtained are compared to the data from other studies.  相似文献   

12.
There are conflicts between the effects of free radical over-production induced by exercise on neurotrophins and brain oxidative metabolism. The objective of this study was to investigate the effects of intense physical training on brain-derived neurotrophic factor (BDNF) levels, COX activity, and lipoperoxidation levels in mice brain cortex. Twenty-seven adult male CF1 mice were assigned to three groups: control untrained, intermittent treadmill exercise (3 × 15 min/day) and continuous treadmill exercise (45 min/day). Training significantly (P < 0.05) increased citrate synthase activity when compared to untrained control. Blood lactate levels classified the exercise as high intensity. The intermittent training significantly (P < 0.05) reduced in 6.5% the brain cortex COX activity when compared to the control group. BDNF levels significantly (P < 0.05) decreased in both exercise groups. Besides, continuous and intermittent exercise groups significantly (P < 0.05) increased thiobarbituric acid reactive species levels in the brain cortex. In summary, intense exercise promoted brain mitochondrial dysfunction due to decreased BDNF levels in the frontal cortex of mice.  相似文献   

13.
目的:观察新型强脉冲光治疗雀斑的疗效。方法:采用飞顿辉煌激光360嫩肤系统(以色列飞顿公司),波长570~950nm,光斑面积10mm×30mm,脉宽10、12、15ms,能量14~19J/cm~2。治疗40例雀斑患者,每三周一次,共治疗5次,末次治疗后评价患者雀斑的疗效。结查:40例患者经过治疗后,18例(45%)基本完全消退,14例(35%)明显消退,8例(20%)好转,总有效率为100%。所有患者面部治疗区域皮肤质地较以前更光滑、细腻,无严重不良反应出现。结论:采用新型强脉冲光治疗雀斑疗效显著、安全,副作用少。  相似文献   

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A combination iron-mordant fixative in which propionic acid is substituted for acetic acid has been found useful in preparing small plant chromosomes for carmine stained squashes. Propionic acid is better than acetic acid because it holds more iron in stable solution. The fixative is a 3:1 mixture of 95% alcohol and pure propionic acid which contains 400 mg. of Fe(OH)3 per 100 ml. of propionic acid. The latter is previously prepared by dissolving the dry freshly prepared Fe(OH)3 in it. To each 10 ml. vial of fixative is added a few drops of carmine stain. Standard aceto-carmine squashes of material fixed in this mixture show quick intense staining and are especially useful for differentiated chromosomes at mitotic prophase.  相似文献   

16.
What changes occur when a natural protein that had been under low mutation rates is subjected to a neutral drift at high mutational loads, thus generating genetically diverse (polymorphic) gene ensembles that all maintain the protein's original function and structure? To address this question we subjected large populations of TEM-1 beta-lactamase to a prolonged neutral drift, applying high mutation rates and purifying selection to maintain TEM-1's existing penicillinase activity. Purging of deleterious mutations and enrichment of beneficial ones maintained the sequence of these ensembles closer to TEM-1's family consensus and inferred ancestor. In particular, back-to-consensus/ancestor mutations that increase TEM-1's kinetic and thermodynamic stability were enriched. These acted as global suppressors and enabled the tolerance of a broad range of deleterious mutations, thus further increasing the genetic diversity of the drifting populations. The probability of a new function emerging (cefotaxime degradation) was also substantially increased in these ensembles owing to the presence of many gene variants carrying the global suppressors. Our findings indicate the unique features of large, polymorphic neutral ensembles generated under high mutational loads and prompt the speculation that the progenitors of today's proteins may have evolved under high mutational loads. The results also suggest that predictable back-to-consensus/ancestor changes can be used in the laboratory to generate highly diverse and evolvable gene libraries.  相似文献   

17.
In neurons, spike timing is determined by integration of synaptic potentials in delicate concert with intrinsic properties. Although the integration time is functionally crucial, it remains elusive during network activity. While mechanisms of rapid processing are well documented in sensory systems, agility in motor systems has received little attention. Here we analyze how intense synaptic activity affects integration time in spinal motoneurons during functional motor activity and report a 10-fold decrease. As a result, action potentials can only be predicted from the membrane potential within 10 ms of their occurrence and detected for less than 10 ms after their occurrence. Being shorter than the average inter-spike interval, the AHP has little effect on integration time and spike timing, which instead is entirely determined by fluctuations in membrane potential caused by the barrage of inhibitory and excitatory synaptic activity. By shortening the effective integration time, this intense synaptic input may serve to facilitate the generation of rapid changes in movements.  相似文献   

18.
目的:研究多功能光子治疗机对面部痤疮的治疗效果。方法:采用多功能光子治疗机对30例面部痤疮患者进行6-8次治疗,每周治疗2次。观察并记录治疗前后痤疮的各种皮损的改变情况。结果:经过6-8次治疗,黑头粉刺、白头粉刺、丘疹、脓疱、结节、扩张的毛细血管、痤疮疤痕、色素异常、粗大毛孔的有效率分别为80%、88.9%、86.7%、80%、100%、83.3%、57.9%、74.1%、68.2%。约83.3%患者感觉皮肤较以前细腻光滑,肤质有明显改善。结论:多功能光子治疗机是治疗面部痤疮的一种安全有效的方法。  相似文献   

19.
G J Storr 《Radiation research》1992,131(3):235-242
The discrete-ordinates transport computer code DORT has been used to develop a two-dimensional cylindrical phantom model for use as a tool to assess beam design and dose distributions for boron neutron capture therapy. The model uses an S8 approximation for angular fluxes and a P3 Legendre approximation for scattering cross sections. A one-dimensional discrete-ordinates model utilizing the computer code ANISN was used to validate the energy-group structure used in the two-dimensional calculations. In the two-dimensional model the effects of varying basic parameters such as aperture width, neutron source energy, and tissue composition have been studied. Identical results were obtained when comparing narrow beam calculations to fine-mesh higher-order Sn treatments (up to S32), and with P5 cross sections. It is shown that, when the correct assessment volume is used, narrow beams will give little or no advantage for therapy even with an optimum-energy ideal neutron beam.  相似文献   

20.
Results are presented from experimental studies of the parameters of an X-pinch-based neutron source made of 70- to 80-μm-diameter deuterated polyethylene fibers. At currents of up to 1.7 MA and a current rise time of ~150 ns, hot plasma spots were observed in the fiber crossing region. The formation of hot spots was accompanied by the generation of short soft X-ray pulses with a duration of 2–4 ns, as well as by neutron emission. The neutron energy was measured using the time-of-flight technique in four directions, at 0°, 90°, 180°, and 270° with respect to the load axis. The mean energy of the neutrons emitted along the axis towards the anode and cathode was found to be 2.0 ± 0.2 and 2.6 ± 0.1 MeV, respectively, and that of neutrons emitted in two opposite directions along the radius, 2.5 ± 0.1 and 2.4 ± 0.1 MeV. The maximum neutron yield at a current amplitude of 1.6 MA was of 1010 neutrons per shot.  相似文献   

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