Characteristics of a conditioned response in human subjects during extinction trials following a single traumatic conditioning trial.

A single experience of respiratory paralysis can be used to establish a conditioned response (CR) to a hitherto neutral stimulus. Respiratory paralysis to those undergoing it is horrific but not painful. The CR does not extinguish but becomes stronger as time passes despite repeated extinction trials. The skeletal aspects of the response are more variable than the autonomic aspects and do not provide any constant stimulus input. The results do not fit an "anxiety-reduction" explanation for the inextinguishability of traumatically conditioned responses but suggest that these responses have characteristics not mediated by reinforcement. (20 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

关于空气间隔棱镜空气隙厚度的再研究

空气间隔偏振棱镜的气隙厚度可无穷减小,以获得大的半视场角,但其消光比将受到严重影响。本文给出获得高消光比的条件。     

Aversive Pavlovian conditioning in childhood anxiety disorders: Impaired response inhibition and resistance to extinction.

Learning-based models of anxiety disorders emphasize the role of aversive conditioning and retarded extinction in the etiology and maintenance of anxiety disorders. Yet few studies have examined these underlying processes in children, despite that some anxiety disorders typically onset during childhood. The authors examined the acquisition and extinction of conditioned responses in 17 anxious children and 18 nonanxious control children between 8 and 12 years old using a discriminative Pavlovian conditioning procedure. One geometric shape conditional stimulus was paired with an unpleasant loud tone unconditional stimulus (CS+) whereas another geometric shape was presented alone (CS?). In the context of similar levels of discriminative conditioning in both groups, anxious children showed larger skin conductance responses to the CS+ and the CS? during acquisition and evaluated the CS+ as more arousing than the CS? compared with control children. They also showed greater resistance to extinction in skin conductance responses but not in arousal ratings to the CS+ vs. the CS? relative to control children. Results suggest that deficits in response inhibition to safety cues and retarded extinction may underlie learning processes involved in the pathogenesis of childhood anxiety disorders. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Delayed extinction attenuates conditioned fear renewal and spontaneous recovery in humans.

This study investigated whether the retention interval after an aversive learning experience influences the return of fear after extinction training. After fear conditioning, participants underwent extinction training either 5 min or 1 day later and in either the same room (same context) or a different room (context shift). The next day, conditioned fear was tested in the original room. When extinction took place immediately, fear renewal was robust and prolonged for context-shift participants, and spontaneous recovery was observed in the same-context participants. Delayed extinction, by contrast, yielded a brief form of fear renewal that reextinguished within the testing session for context-shift participants, and there was no spontaneous recovery in the same-context participants. The authors conclude that the passage of time allows for memory consolidation processes to promote the formation of distinct yet flexible emotional memory traces that confer an ability to recall extinction, even in an alternate context, and minimize the return of fear. Furthermore, immediate extinction can yield spontaneous recovery and prolong fear renewal. These findings have potential implications for ameliorating fear relapse in anxiety disorders. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The effects of FG7142 on overexpectation of Pavlovian fear conditioning.

Six experiments studied the role of GABAA receptor activation in expression of overexpectation of Pavlovian fear conditioning. After separate pairings of CSA and CSB with shock in Stage I, rats received pairings of the compound AB with shock in Stage II, producing overexpectation of fear. The expression of overexpectation was attenuated, in a dose-dependent manner, by the benzodiazepine partial inverse agonist FG7142. FG7142 had no effect on responding to a CS paired with a low magnitude US or a CS subjected to associative blocking. These results suggest that the negative prediction error generated during overexpectation training may impose a mask on fear rather than erasing the original fear learning. They support claims that overexpectation shares features with extinction. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Spontaneous recovery of excitation and inhibition.

In two conditioned suppression experiments with rats as subjects, the authors examined two classes of accounts of spontaneous recovery of excitation and inhibition. One view suggests that spontaneous recovery occurs due to greater temporal instability of inhibitory associations, whereas the other posits that spontaneous recovery occurs due to greater temporal instability of second-learned associations. These accounts diverge in predictions concerning spontaneous recovery when the first-learned association is inhibitory and the second-learned association is excitatory. Using different designs, Experiments 1 and 2 found spontaneous recovery of both excitation and inhibition. The results support the view that spontaneous recovery occurs due to faster waning of second-learned associations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Angstrom turbidity and ozone column estimations from spectral solar irradiance in a semi-desertic environment in Spain

Angstrom parameters are commonly used for modelling the solar radiation extinction by aerosols. Detailed knowledge of these parameters in as many places as possible is desirable since many applications need this kind of information: satellite products assessment, clear sky models benchmarking, spectral modelling, etc. Experimental determinations of the Angstrom turbidity and wavelength exponent have been made for a semi-desertic area in the south-east of Spain using a double monochromator spectroradiometer. Experimental measurements of direct-beam spectral irradiance have been made about every 20 min during one year (from october 2005 to september 2006). Angstrom turbidity has a noticeable variability during the year, showing a seasonal characteristic behaviour. Low turbidity values were found during autumn and winter and quite large values can be observed in spring and summer days. The eventual values of high turbidity with low wavelength exponent found could indicate Saharan dust outbreaks events. In addition, total ozone column have been experimentally estimated from spectral measurements in the Huggins absorption band. The results showed a general agreement with the values extracted from the TOMS web site.     

稀释燃烧的火焰稳定性

采用实验研究的方法探讨了反应物预热温度与稀释率两个因素对稀释燃烧火焰稳定性的影响.实验以氮气稀释的甲烷-空气对冲扩散火焰为研究对象,确定了不同反应物预热温度与氧化剂稀释率(氧气体积分数)时火焰的熄火极限,结果表明,增大反应物预热温度拓宽了火焰稳定燃烧区域,而增加氧化剂稀释率(降低氧气体积分数)会降低稀释火焰的稳定性,二者对火焰稳定性的影响作用相反.为了进一步分析反应物预热温度与稀释率对火焰稳定性的影响程度,引入了估算的Damkohler数,分析表明,在实验研究范围内,反应物预热温度对火焰稳定性的影响比稀释率的影响显著,是火焰稳定性的主要影响因素.     

钝体驻定湍流扩散火焰局部熄火的PDF模拟

用标量联合的概率密度函数(PDF)方法对钝体驻定的湍流射流扩散Sydney火焰HM3进行数值模拟,速度场用一个修正的LRR-IP雷诺应力模型求解.采用3种不同层次的甲烷反应动力学机理对火焰的宏观结构和熄火特征进行比较研究,并结合当地自适应建表方法加速化学反应计算.结果表明,计算值和实验数据吻合较好,在回流区内,不同反应机理的预测值差别不大,但在颈部区域,C2机理相对C1机理可以更准确地模拟标量场的变化和局部熄火现象.     

添加氢气的甲烷/空气预混火焰结构的数值预测

针对添加氢气的甲烷/空气预混火焰的重要特性进行了计算研究.不同含氢比、稀释比以及不同当量比下的绝热燃烧速率模拟结果与目前国际上相关的研究结果相吻合.从稀燃到等当量比范围,采用的模型较好地重构了NO浓度变化,但在浓混合气时,预测结果与Coppens等的研究结果不同.计算结果表明,添加氢气对炭黑生成无明显的作用;同时,以反向对称双火焰为模拟背景,计算获得了不同含氢比下的熄火拉伸率和对应的燃烧温度,证明了添加氢气可以增强稀薄燃烧的稳定性以及扩大稀燃极限.