拉-压预应力混凝土梁的设计

阐述拉—压预应力混凝土结构的基本原理，以预应力筋两个阶段工作原理为基础，建立拉—压预应力混凝土结构的计算方法。     

切合并联电容器组暂态过电压问题的研究

采用EMTP电磁暂态程序,考虑在最不利的运行条件下,计算得出切合并联电容器组暂态过电压水平,并给出降低暂态过电压的措施。     

热探测法监测岩石应力变化的实验研究

为了探测岩石在受力过程中温度的变化特征，用接触式测温仪对花岗岩和大理岩试件进行了单轴加压条件下的测温试验，同时用红外热像仪作为辅助监测．结果表明：在加载与卸载过程中都有温度的变化，并有一定的可逆性，即，加载升温，卸载降温；岩石在破坏前存在温度奇变点，温度变化能够显示岩石破坏的前兆信息，80％抗压强度附近是岩石破坏的临界前兆点；红外热图也可以显示出破坏前的温度异常．热探测法对于矿山岩体应力变化监测是实用和有效的．     

Tickcon专家系统中的不确定性问题的研究

不确定性问题是人工智能和专家系统中的难点和核心研究课题，文章着重讨论Tickcon专家系统中的一个典型的不确定性问题的分析并提出了一个解决方案。     

脉冲筛板柱萃取分离钍鈾的研究(Ⅰ)——钍铀分离脉冲筛板柱的流体力学性能

在2英寸脉冲筛板柱中,结合钍铀分离的Thorex过程,研究了30％TBP-煤油/水和30％TBP-煤油/Th(NO_3)_4-UO_2(NO_3)_2-HNO_3-H_2O体系脉冲筛板柱的流体力学性能。通过实验对液泛通量、分散相存留分数等流体力学参数,并用改进的Pratt公式对两相流体力学流体力学行为进行了关联,得到了较为满意的结果。通过对脉冲筛板柱流体力学性能的研究,获得了最优操作条件,为进一步的传质实验研究奠定了基础。     

Cutting edge: novel RNA ligands able to bind CD4 antigen and inhibit CD4+ T lymphocyte function

The value of high affinity-specific reagents in immunology is exemplified by the use of mAbs. Recent in vitro selection methods suggested that oligonucleotides may provide a useful alternative, especially where Abs have been insufficient thus far. We used a systematic evolution of ligands by exponential enrichment (SELEX) procedure to derive high affinity oligonucleotide ligands (aptamers) recognizing CD4. These RNase-resistant aptamers bound with high affinity and specificity as demonstrated using BIAcore (Stevenage, U.K.) technology. They also bound native CD4 on rat lymphocytes and specifically interfered with labeling by high affinity mAbs. All aptamers recognized the same binding site in the CDR2-like region in domain 1 of CD4. The applicability of these aptamers for immunologic studies was clearly demonstrated by their ability to block a fully allogeneic MLR in a CD4-specific manner. The high affinity and stability of aptamers point to their value in the analysis and functional manipulation of the immune system.     

The effect of changing excitation frequency on parallel conductance in different sized hearts

OBJECTIVE: An important component of the ventricular volume measured using the conductance catheter technique is due to parallel conductance (Vc), which results from the extension of the electric field beyond the ventricular blood pool. Parallel conductance volume is normally estimated using the saline dilution method (Vc(saline dilution)), in which the conductivity of blood in the ventricle is transiently increased by injection of hypertonic saline. A simpler alternative has been reported by Gawne et al. [12]. Vc(dual frequency) is estimated from the difference in total conductance measured at two exciting frequencies and the method is based on the assumption that parallel conductance is mainly capacitive and hence is negligible at low frequency. The objective of this study was to determine whether the dual frequency technique could be used to substitute the saline dilution method to estimate Vc in different sized hearts. METHODS: The accuracy and linearity of a custom-built conductance catheter (CC) system was initially assessed in vitro. Subsequently, a CC and micromanometer were inserted into the left ventricle of seven 5 kg pigs (group 1) and six 50 kg pigs (group 2). Cardiac output was determined using thermodilution (group 1) and an ultrasonic flow probe (group 2) from which the slope coefficient (alpha) was determined. Steady state measurements and Vc estimated using saline dilution were performed at frequencies in the range of 5-40 kHz. All measurements were made at end-expiration. Finally, Vc was estimated from the change in end-systolic conductance between 5 kHz and 40 kHz using the dual frequency technique of Gawne et al. [12]. RESULTS: There was no change in measured volume of a simple insulated cylindrical model when the stimulating frequency was varied from 5-40 kHz. Vc(saline dilution) varied significantly with frequency in group 1 (8.63 +/- 2.74 ml at 5 kHz; 11.51 +/- 2.65 ml at 40 kHz) (p = 0.01). Similar results were obtained in group 2 (69.43 +/- 27.76 ml at 5 kHz; 101.24 +/- 15.21 ml at 40 kHz) (p < 0.001). However, the data indicate that the resistive component of the parallel conductance is substantial (Vc at 0 Hz estimated as 8.01 ml in group 1 and 62.3 ml in group 2). There was an increase in alpha with frequency in both groups but this did not reach significance. The correspondence between Vc(dual frequency) and Vc(saline dilution) methods was poor (group 1 R2 = 0.69; group 2 R2 = 0.22). CONCLUSION: At a lower excitation frequency of 5 kHz a smaller percentage of the electric current extends beyond the blood pool so parallel conductance is reduced. While parallel conductance is frequency dependent, it has a substantial resistive component. The dual frequency method is based on the assumption that parallel conductance is negligible at low frequencies and this is clearly not the case. The results of this study confirm that the dual frequency technique cannot be used to substitute the saline dilution technique.     

Effect of trial-by-trial variation in center frequency on detection of interaural temporal and intensitive differences in bands of noise

Sensitivity to interaural temporal disparities (ITDs) and interaural intensitive disparities (IIDs) was measured as a function of duration in conditions where the center frequency (CF) of the stimuli was constant and, separately, in conditions where the CF of the stimuli was varied on a trial-by-trial basis. Stimuli were bands of noise centered at either 300, 1200, 2400, or 4800 Hz with the bandwidth of the noise being 40% of their CF. The largest effects of shortening duration and varying center CF of the stimuli were degradations of sensitivity to ITDs for stimuli centered at 2400 or 4800 Hz. Overall, the data confirm and extend previous findings which indicate that ITDs and IIDs are processed separately within the central nervous system.     

Peroxidase activity of ferritin in aerosol OT reversed micelles in heptane

The aim of the present investigation was to determine spin lock (SL) relaxation parameters for the normal brain tissues and thus, to provide basis for optimizing the imaging contrast at 0.1 T. 68 healthy volunteers were included. On-resonance spin lock relaxation time (T1rho) and off-resonance spin lock relaxation parameters (T1rho(off), Me/Mo), MT parameters (T1sat, Ms/Mo), and T1, T2 were determined for the cortical gray matter, and for the frontal and parietal white matters. The T1rho for the frontal and parietal white matters ranged from 110 to 133 ms and from 122 to 155 ms with locking field strengths from 50 microT to 250 microT, respectively. Accordingly, the values for the gray matter ranged from 127 to 155 ms. With a locking field strength of 50 microT, T1rho(off) for the frontal and parietal white matters were from 114 to 217 ms and from 126 to 219 ms, and for the gray matter from 136 to 267 ms with the angle between the effective magnetic field (B(eff)) and the z-axis (theta) ranging from 60 degrees to 15 degrees, respectively. The T1rho of the white and gray matters increased significantly with increasing locking field amplitude (p < 0.001). The T1rho(off) decreased significantly with increasing theta (p < 0.001). T1rho and T1rho(off) with theta > or = 30 degrees were statistically significantly shorter in the frontal than in the parietal white matters (p < 0.05). The duration, amplitude and theta of the locking pulse provide additional parameters to optimize contrast in brain SL imaging.