N‐Heterocyclic Carbene‐Mediated Organocatalytic Transfer of Tin onto Aldehydes: An Easy Access to syn‐Diols and Mechanistic Studies

An update of our preliminary communication concerning an efficient organocatalytic procedure for the transfer of tin onto aldehydes is presented. This update combines (i) a full study of the preparation of γ‐silyloxyallylstannanes from β‐substituted enals, (ii) a “one‐pot” sequence (in inter‐ and intramolecular version) including N‐heterocyclic carbene (NHC)‐catalyzed silylstannation reaction/Lewis acid‐promoted allylstannation reaction to furnish the corresponding syn‐diols, and (iii) mechanistic studies on the organocatalytic 1,2‐addition.     

含间隙的翅翼机构运动稳定性的研究

在分析了常用的运动稳定性分析方法优缺点和局限性的基础上,应用Floquet-Lyapunov理论对以连续接触模型建立的含间隙翅翼机构动力学方程周期解的稳定性进行分析.研究结果表明,当间隙值大于某一值时,机构的周期运动将是不稳定的.     

Probabilistic analysis of the replacement thickness of the in-cuts roadbed in permafrost regions

Limited to terrain and road longitudinal gradient, it is inevitable to excavate permafrost for linearity engineering in permafrost regions such as railway and highway. It is a very complicated process for freezing-thawing cycle of the active layer due to parameters variability and complex climate. Moreover, there are scarce data for ground temperature and deformation in in-cuts roadbed. A probabilistic approach may consider the influences of the variation of each significant parameter upon the factor of safety and has the particular advantages over the classical approach. So it is frequently used to give a more rational assessment of the risks. A probabilistic model is put forward to evaluate the replacement thickness of in-cuts roadbed in the permafrost regions, and the procedure is validated by the observation data in cutting of Qinghai-Tibetan railway. The analysis results show that the thermal stability of the roadbed cannot be ensured if in-cuts roadbed is only displaced by coarse-grained soils. The reliability can be improved greatly if the thermal-insulated material is embedded in the replacement layer. The calculation results show that the maximum thawed depth of in-cuts roadbed will not be deeper than the replacement layer if the Extruded Polystyrenes (EPS) with a thickness of 10.0 cm is embedded at the depth of 0.8 m below the surface of the imported fill layer. The computation results also indicate that the in-cuts roadbed design in the Qinghai-Tibetan railway can protect the permafrost under the replacement layer from thawing and ensure the in-cuts roadbed stability in the coming fifty year. The Monte Carlo simulation and the first-order second moment method are applied to establish the limit-state function of probabilistic analysis of the replacement thickness. The calculated results indicate that probabilistic approach can be used to determine the replacement thickness and can provide more reasonable suggestions for engineering application than the classical approach.     

An active protein kinase A (PKA) is involved in meiotic arrest of rat growing oocytes

Reinitiation of meiosis in meiotically competent, fully grown mammalian oocytes is governed by a fall in intraoocyte cAMP concentrations and the subsequent inactivation of protein kinase A (PKA). A similar reduction in intraoocyte cAMP concentrations in growing, meiotically incompetent rat oocytes not leading to resumption of meiosis, questions the involvement of PKA in the regulation of meiosis at this early stage of oocyte development. We examined the possibility of whether PKA activity maintains growing oocytes in meiotic arrest and further explored the mode of activation of PKA under conditions of relatively low cAMP concentrations. Our experiment demonstrated that inactivation of PKA stimulates growing rat oocytes to resume meiosis, and elevates the activity of their maturation-promoting factor (MPF). We also found that the expressions of type I and type II regulatory subunits (RI and RII) of PKA are higher in growing and fully grown oocytes, respectively. In addition, we revealed that the common 1:1 ratio between the regulatory (R) and catalytic (C) subunits of PKA is apparently not abrogated and, in accordance PKA activity in growing oocyte-cell extract is fully dependent on cAMP. Finally, we identified in growing oocytes, the A kinase anchoring protein (AKAP) 140, which was previously depicted in fully grown oocytes. We conclude that an active PKA prevents growing oocytes from resuming meiosis. Our findings further suggest that relatively high abundance of the PKAI isoform and/or its subcellular compartmentalization, through interaction with AKAP140, could possibly account for the high basal PKA activity at relatively low intraoocyte cAMP concentrations.     

A miniature concentrating photovoltaic and thermal system

A novel miniature concentrating PV (MCPV) system is presented and analyzed. The system is producing both electrical and thermal energy, which is supplied to a nearby consumer. In contrast to PV/thermal (PV/T) flat collectors, the heat from an MCPV collector is not limited to low-temperature applications. The work reported here refers to the evaluation and preliminary design of the MCPV approach. The heat transport system, the electric and thermal performance, the manufacturing cost, and the resulting cost of energy in case of domestic water heating have been analyzed. The results show that the new approach has promising prospects.     

Nanoscale Defect Engineering and the Resulting Effects on Domain Wall Dynamics in Ferroelectric Thin Films

Defect engineering is one of the cornerstones of the modern electronics industry. Almost all electronic devices include materials that have been doped by ion bombardment. For materials where crystallinity is essential, such as ferroelectrics, defect type and concentration can vastly influence properties and are often used to optimize device performance. This study shows a method to effectively control the density and position on the nanoscale of defect sites in thin films of Pb(Zr,Ti)O₃ via focused ion beam microscopy. This allows for exceptional clarity of observation of the role of defects in nucleation, polarization switching, and domain wall interaction through investigation with piezoresponse force microscopy and transmission electron microscopy, adding insight to accepted but seldom‐demonstrated facts on defect‐induced effects. This nanoscale defect engineering can be used as a tool to control material properties, and furthermore, a route is demonstrated toward a practical application.     

Negative dielectric relaxation of hot electrons in CdTe

A direct measurement of negative dielectric relaxation in CdTe at room temperature is presented at electric fields where electrons exhibit negative differential mobility. Data have been obtained with the time-of-flight technique, which is suitable to investigate electron diffusion process and space charge effects by means of an analysis of the time and space evolution of an electron charge layer drifting in a semiconductor material exhibiting either positive or negative differential mobility.     

Enzymes in gastric juice. An aid in the diagnosis of gastric cancer

In the present study we measured the activities of the following enzymes: LDH (lactic dehydrogenase), beta-glucuronidase, acid maltase, phosphohexoseisomerase (PHI) and acid proteases in the gastric juice of patients with gastric cancer (n = 50) (Case Group), in endoscopically normal subjects (n = 50) and in subjects with different non tumor-like digestive pathologies (n = 55) (Control Groups). In the patients with gastric carcinoma we found a significant increase in LDH, beta-glucuronidase, PHI and acid maltase activities and a decreased activity of acid proteases. The results agree with previous findings from other workers. The variations of enzyme activities in gastric juice can help to differentiate between malignant and benign processes of the gastric mucosa.     

The generalized Hartree-Fock theory of nonmagnetic high-temperature superconductors

The Eliashberg equations are generalized to apply to high-temperature superconductors without spin correlations. The generalization assumes any general electronic density of states. Consequently, it treats the Coulomb interaction dynamically, and takes into account the averaged momentum dependence of the self-energy and of the interactions. Unlike in the conventional Eliashberg equation, the bare Coulomb interaction yields a frequency-independent term in the renormalization function. This term breaks the symmetry of the self-energy, and changes the renormalization.