Viscoelasticity of living cells allows high resolution imaging by tapping mode atomic force microscopy

Application of atomic force microscopy (AFM) to biological objects and processes under physiological conditions has been hampered so far by the deformation and destruction of the soft biological materials invoked. Here we describe a new mode of operation in which the standard V-shaped silicon nitride cantilever is oscillated under liquid and damped by the interaction between AFM tip and sample surface. Because of the viscoelastic behavior of the cellular surface, cells effectively "harden" under such a tapping motion at high frequencies and become less susceptible to deformation. Images obtained in this way primarily reveal the surface structure of the cell. It is now possible to study physiological processes, such as cell growth, with a minimal level of perturbation and high spatial resolution (approximately 20 nm).     

Presence of acetyl coenzyme A (CoA) carboxylase and propionyl-CoA carboxylase in autotrophic Crenarchaeota and indication for operation of a 3-hydroxypropionate cycle in autotrophic carbon fixation

The pathway of autotrophic CO2 fixation was studied in the phototrophic bacterium Chloroflexus aurantiacus and in the aerobic thermoacidophilic archaeon Metallosphaera sedula. In both organisms, none of the key enzymes of the reductive pentose phosphate cycle, the reductive citric acid cycle, and the reductive acetyl coenzyme A (acetyl-CoA) pathway were detectable. However, cells contained the biotin-dependent acetyl-CoA carboxylase and propionyl-CoA carboxylase as well as phosphoenolpyruvate carboxylase. The specific enzyme activities of the carboxylases were high enough to explain the autotrophic growth rate via the 3-hydroxypropionate cycle. Extracts catalyzed the CO2-, MgATP-, and NADPH-dependent conversion of acetyl-CoA to 3-hydroxypropionate via malonyl-CoA and the conversion of this intermediate to succinate via propionyl-CoA. The labelled intermediates were detected in vitro with either 14CO2 or [14C]acetyl-CoA as precursor. These reactions are part of the 3-hydroxypropionate cycle, the autotrophic pathway proposed for C. aurantiacus. The investigation was extended to the autotrophic archaea Sulfolobus metallicus and Acidianus infernus, which showed acetyl-CoA and propionyl-CoA carboxylase activities in extracts of autotrophically grown cells. Acetyl-CoA carboxylase activity is unexpected in archaea since they do not contain fatty acids in their membranes. These aerobic archaea, as well as C. aurantiacus, were screened for biotin-containing proteins by the avidin-peroxidase test. They contained large amounts of a small biotin-carrying protein, which is most likely part of the acetyl-CoA and propionyl-CoA carboxylases. Other archaea reported to use one of the other known autotrophic pathways lacked such small biotin-containing proteins. These findings suggest that the aerobic autotrophic archaea M. sedula, S. metallicus, and A. infernus use a yet-to-be-defined 3-hydroxypropionate cycle for their autotrophic growth. Acetyl-CoA carboxylase and propionyl-CoA carboxylase are proposed to be the main CO2 fixation enzymes, and phosphoenolpyruvate carboxylase may have an anaplerotic function. The results also provide further support for the occurrence of the 3-hydroxypropionate cycle in C. aurantiacus.     

基于降阶模型的斜拉索振动的半主动神经网络控制

根据模态降阶理论,获得了斜拉索-阻尼器系统的降阶模型,有效地缩减了系统的自由度.根据ER/MR阻尼器特性和主动控制中LQG控制理论,建立了面向速度剪切的半主动LQG控制方法,并获得了很好的控制效果.本文设计了神经网络的观测器,使用的传感器数目大大减少,根据智能控制理论,设计了神经网络控制器,并提出采用该神经网络作斜拉索半主动控制的控制算法.振动仿真的结果表明,经过离线训练后的神经网络观测器和控制器,有效地抑制了斜拉索的振动.     

Performance of simple cross-interleaved Reed-Solomon decoding strategies for compact disc players

The complexity and performance of three simple error detection and correction strategies frequently used for the decoding of the cross-interleaved Reed-Solomon codes in digital compact disc ( CD) are compared. It is assumed that the number of byte errors in the input codeword is always a multiple of l a positive integer. By varying l from 1 to 32, the random to burst error performance of the various strategies is obtained. Specifically, it is shown that unless random errors are the main cause of concern, the best strategies seem to be those using erasure corrections. The results presented will be useful for deciding the decoding strategies to be adopted for CD players as well as in potential applications such as optical mass storage devices using the CD format     

Subarachnoid neurocysticercosis with occlusion of the major intracranial arteries: case report

Cysticercosis is the most common parasitic disease affecting the central nervous system. Stroke is a recognized complication of neurocysticercosis, occurring in 2 to 12% of cases, mostly in the form of small lacunar infarcts. We report a case of hemiparesis and aphasia in a 51-year-old Hispanic woman, which was secondary to complete occlusion of the left internal carotid and bilateral anterior cerebral arteries. Magnetic resonance imaging demonstrated the presence of enhancing subarachnoid material surrounding these occluded cerebral arteries, providing antemortem, noninvasive documentation of the inflammatory meningeal cysticercotic reaction that was presumably responsible for the occlusive arteritis causing the cerebral infarction. This represents the third reported case of internal carotid artery occlusion and the first reported case of anterior cerebral artery occlusion secondary to neurocysticercosis.