Proton magnetic resonance imaging of lipid in pecan embryos

Magnetic resonance images of plant tissues typically are manifestations of water protons in tissues. Within oilseeds, however, lipids contain a major portion of the mobile protons, which should enable specific imaging of lipids. In this study, experiments were done to demonstrate spin-echo imaging (SEI) and chemical-shift imaging (CSI) of lipid within nonimbibed and imbibed embryos of pecan (Carya illinoensis), a high-lipid seed. Magnetic resonance spectra of airdry embryos contained a single major peak for lipid, whereas those of imbibed embryos contained separate peaks for water and lipid. This separation of spectral peaks enabled CSI of distributions of either lipids or water in imbibed embryos. A longer spin-spin relaxation time of lipid protons than of water protons in imbibed embryos allowed selective SEI of lipids in those embryos. SEI of normal, dry embryos revealed fairly uniform distribution of lipids across tissues. Similar images of embryos damaged by the fungusPhoma exocarpina or the insectZerara viridula were less intense than those of a normal embryo, reflecting the lower oil contents of the damaged embryos. Magnetic resonance imaging should provide a useful technology for studying lipid distribution and metabolism within oil seeds.     

主客体掺杂的分子偶极聚合物驻极体材料的空间和偶极电荷的性质研究

以主客体掺杂型DR1／PMMA（分散红1号／聚甲基丙烯酸甲脂）体系为例，通过表面电位等温衰减研究了材料极化后空间电荷的脱阱及异性电荷的补偿导致的衰减行为，由开路和短路的热刺激放电及电光效应实验探讨了样品内空间和偶极电荷的性质。     

On the stability of neural networks with arbitrary weights

Dynamical properties of a general neural network are discussed. A condition for the neural activation dynamics being stable is derived. The stability condition does not put any symmetry restriction on the weights. The transitions from stable to non-stable dynamics are analysed and their analogy to phase transitions in statistical mechanics discussed. In general, the network dynamics can violate the stability condition. To avoid that happening, a method is introduced which makes the dynamics adaptive such that the stability condition is sustained. Relations to some previous works on stability are discussed.     

有源扩散方程的一种解和“双滤纸法”测氢的换算公式

文章从流速场中级联衰变下气载核素的扩散规律出发,提出了强吸附性壁圆管内氡子体扩散方程的完整定解问题,求出了等速分布廓线时的方程的精密解,弥补了C.W.Tan这部分工作的不足。引进了新的物理量m(μ),导出了等速分布条件下m(μ)与F(μ)的互换关系式。从测量氡子体的α计数出发,通过放射性平衡比m(μ)给出了“双滤膜法”测氡的换算公式。由J·W·Thomas的精密实验数据,取镭-A扩散系数D=0.07cm~2·s~(-1)时,理论与实验十分吻合。     

压力对X线胶片潜影衰退的影响

对压力引起X线胶片潜影衰退的影响进行研究 ,得出压力越大、受压时间越长、潜影衰退越甚。表现在经显影后影像密度越低。拍摄好的X线胶片应避免受到挤压和弯曲     

防辐射复合材料的性能研究

本文介绍的是利用交联反应工艺制成的一种防辐射复合新材料的性能。通过实测数据的列举和运用比较的方法,从比重、对x、r射线的防护作用、耐辐射能力、物理特性等方面证实了这种新材料的良好使用效果。在辐射技术和环境保护等领域有广泛的应用前途和开发价值。     

Characterization of Radon Decay Products in a Domestic Environment

Field measurements of the concentration and activity size distribution of radon decay products were conducted in a one-story house located in the Princeton, NJ area. Radon concentration and particle number concentration were also measured. The concentration and activity-weighted size distribution of radon decay products were determined using a microcomputer-controlled, semi-continuous screen diffusion battery system with 6 parallel sampler/detector units. A condensation nuclei counter was used for the measurements of indoor panicle number concentration. Several measurements were made in the living room as well as more than one hundred measurements in the master bedroom of the Princeton house. Aerosols were generated from taking a shower, burning a candle, smoldering a cigarette, vacuuming, and cooking. Therefore, the influence of various indoor panicle sources on the behavior of radon decay products was investigated. With panicles generated from typical household activities, Potential Alpha Energy Concentration (PAEC) increases and the unattached fraction decreases. Larger panicles generated from cigarette smoke and cooking dramatically shifted most of the radon decay products into the attached mode (15-500 nm). With regard to the higher attachment rate, the size distributions of radon decay products remained stable for long periods of time after particle generation. On the other hand, aerosols produced from candle burning and vacuuming were much smaller, with an average attachment diameter of 15 nm. These panicles did decrease the unattached fraction, especially during the aerosol generation period. However, the size distributions of radon decay products returned to the background condition within ISO minutes after the end of particle generation. In these cases, the panicles had a higher deposition rate and a lower attachment rate. The dose of alpha radiation per unit radon concentration resulting from each of these aerosol conditions was calculated using the measured activity size distributions and the most recent James dosimetric model. These doses to basal cells at a breathing rate of 0.45 m³ hr¹ ranged from 3 to 14 μGy Bq^?1 hr while the dose to secretory cells at a breathing rate of 1.5 m³ hr¹ ranged from 13 to 77 μGy Bq^?1 hr for the various aerosol conditions.     

α-CuPc/PVK体系光电性能的研究

研究了α-CuPc/PVK体系的伏安特性及等温衰减电流(IDC)。观察到低场欧姆区与高场非欧姆区,其转折场强为1.2×10~4V/cm。在非欧姆区1g(I/V)与V~(1/2)成线性关系,其系数为1.5×10~(-4)eV/(V/cm)~(1/2),符合Poole-Frenkel效应。用简单的弛豫过程处理了不同场强和不同温度的IDC实验结果,得到的活化能随场强增加而减小,符合Poole-Frenkel效应。并用Garofano等人推导的电流密度与弛豫时间的关系式,计算了被陷载流子密度和与温度无关的逸出频率。     

Studies on the polymerization of propylene using high activity ziegler-natta catalysts. 1: Kinetic models for rate decay in ziegler-natta polymerization

Kinetic models for describing the time dependence of the polymerization rate and active centre concentration for high activity Ziegler-Natta catalyst systems are discussed. It is demonstrated that the decay in the rate of polymerization and in the concentration of active centres with time for the polymerization of propylene with the heterogeneous catalyst system MgCl₂/EB/TiCl₄? Al(i-Bu)₃/EB can be represented better by a modified multi-centre first order decay model than by the other models which are considered.     

A study of the Pd/C catalyst for synthesis of hydroxylamine

Palladium dispersed on active carbon (Pd/C) is used as a catalyst in the synthesis of hydroxylamine. Alkaline precipitation was used to prepare the catalyst. It was found that the controlling factor was the size of palladium crystal, which in turn was chiefly determined by the PdCl₄^2-/Pd(OH)₂ conversion stage. The sintering and crystal growth of Pd was the main reason for the decay of the catalyst. The sintering mechanism was found to follow the Ostwald ripening model.