Hypothesis generation guided by co-word clustering

Co-word analysis was applied to keywords assigned to MEDLINE documents contained in sets of complementary but disjoint literatures. In strategical diagrams of disjoint literatures, based on internal density and external centrality of keyword-containing clusters, intermediate terms (linking the disjoint partners) were found in regions of below-median centrality and density. Terms representing the disjoint literature themes were found in close vicinity in strategical diagrams of intermediate literatures. Based on centrality-density ratios, characteristic values were found which allow a rapid identification of clusters containing possible intermediate and disjoint partner terms. Applied to the already investigated disjoint pairs Raynaud"s Disease - Fish Oil, Migraine - Magnesium, the method readily detected known and unknown (but relevant) intermediate and disjoint partner terms. Application of the method to the literature on Prions led to Manganese as possible disjoint partner term. It is concluded that co-word clustering is a powerful method for literature-based hypothesis generation and knowledge discovery.     

Temperature derivative of the pressure of4He at the superfluid transition

We present new measurements of the temperature derivative of the pressure along the superfluid transition line in ⁴ He near saturated vapor pressure. These results indicate that the second derivative (₂P/PT) is finite at saturated vapor pressure. The data agree with earlier measurements by Kierstead.     

A High-Resolution Thermometer for the Range 1.6 to 5 K

This paper presents a detailed design, a theoretical analysis, and experimental tests of a high-resolution thermometer for use in the temperature range from 1.6 to 5 K. The device uses a dc-SQUID magnetometer to determine the change in magnetization with temperature of a paramagnetic salt in a magnetic field. The field is provided by a small permanent magnet attached to the thermometer. Measurements of the sensitivity of the device agree well with the theoretical analysis. Near 2.17 K (the superfluid transition of ⁴ He at saturated vapor pressure) the thermometer has a specific sensitivity of 4000 ₀ /K Gauss. There it achieves a temperature resolution better than 10 ^–9 K when it is charged with a field of about 300 Gauss. At 4.2 K, the specific sensitivity is smaller by a factor of 50, but should still allow temperature measurements with a resolution better than 10 ^–7 K. Near 2.17 K, drifts of the device are below the level of 10 ^–13 K/s. The thermometer has a small mass of about 7 g (excluding the magnet), and thus the advantage of relatively small cosmic radiation heating during microgravity experiments in Earth orbit.     

Second sound very near Tλ

The results of an experimental investigation of the evolution of planar, non-linear, second-sound pulses in superfluid⁴He, to within 650 nK of the -transition, are presented. A new method for extracting the second-sound velocity and damping is demonstrated. As predicted from two-fluid hydrodynamics, the pulses are well modeled by the solutions of Burgers' equation. The second-sound velocity (u ₂₀) and damping (D ₂) are extracted from fits of the model to the data. Damping data are obtained in this fashion to 3×10^–7 in reduced temperature at saturated vapor pressure; nearly two decades closer to T then any previous measurements. The superfluid density is extracted from theu ₂₀ measurements and the critical exponent, , is determined. A study of very large amplitude pulses near T is also presented. These pulses extend well beyond the range of validity of Burgers' equation. The amplitude of the shock that forms at the trailing edge of the pulse is observed to saturate as a function of heater power and then decrease suddenly, as has been previously observed away from T. However, the pulse shapes are quite different from any previously observed.     

Multistage and tandem mass spectrometry of glycosylated triterpenoid saponins isolated from Bacopa monnieri: comparison of the information content provided by different techniques

Whereas all state-of-the-art techniques in mass spectrometry (MS) have been extensively applied to oligosaccharides derived from glycoproteins, less effort has been devoted to the analysis of smaller glycoconjugates. In the present study, the application of a variety of MS techniques for the analysis of two dammarane-type triterpenoid saponins isolated from B. monnieri is reported. The structural information provided by ESI-ion trap (IT)-, AP-MALDI-IT-, and MALDI-IT/reflectron time-of-flight (RTOF)-MS, all utilizing low-energy collision-induced dissociation (CID), and MALDI-TOF/RTOF-MS, facilitating postsource decay and high-energy CID analysis, was compared. The applied desorption/ionization technique does not influence the fragmentation of identical precursor ions in low-energy CID. All three fragmentation techniques clearly yield the sequence and branching of the glycan moiety as well as the molecular mass of the intact aglycon. Cross-ring cleavage of the branching sugar, which gives some information about the sugar linkages, was mainly observed in low-energy CID. High-energy CID, on the other hand, yielded some additional diagnostic fragment ions from the aglycon moiety. Internal cleavage ions are formed by alternative mechanisms in high-energy CID and are assumed to be diagnostic for some linkages. However, none of the applied MS techniques facilitates the identification of those saponins that differ only by their aglycon moiety (i.e., jujubogenin or pseudojujubogenin).     

Finite-size Effects on the Thermal Resistivity of 4He Near the Superfluid Transition

We present measurements of the thermal resistivity () near the superfluid transition temperature of ⁴He at saturated vapor pressure and confined in glass capillary arrays with rectangular capillary cross-sections of spacing L = 1 μm, width m, and length mm. We expect the finite-size effect in this rectangular geometry to provide a good approximation to that in the ideal parallel-plate geometry. The data coincide within our resolution with previous measurements for cylindrical capillaries of 1 m radius, indicating that the finite-size scaling-functions for these two geometries are indistinguishable. This stands in contrast to the scaling functions for static properties which, near the transition temperature, depend on the dimensionality of the confinement. The results are consistent with recent Monte Carlo and spin-dynamics simulations, and with renormalization-group calculations for capillaries with square cross section and .     

Carbon nanotube coating improves neuronal recordings

Implanting electrical devices in the nervous system to treat neural diseases is becoming very common. The success of these brain-machine interfaces depends on the electrodes that come into contact with the neural tissue. Here we show that conventional tungsten and stainless steel wire electrodes can be coated with carbon nanotubes using electrochemical techniques under ambient conditions. The carbon nanotube coating enhanced both recording and electrical stimulation of neurons in culture, rats and monkeys by decreasing the electrode impedance and increasing charge transfer. Carbon nanotube-coated electrodes are expected to improve current electrophysiological techniques and to facilitate the development of long-lasting brain-machine interface devices.     

环保型12-40．5kV的C-GIS非SF6/少SF6N2S／N2X的研发和一些比较

本文描述了基于紧凑型、低气压、环保的理念,通过精确设计和综合了薄板箱体的激光切割、焊接及氦检漏技术的高精密制造技术而成功制造的。符合IEC／GB／DL标准的,12／24／36／40．5kV-630／1250／2000／2500／3150A-25／31．5／40kA N2S／N2X系列的箱式气体绝缘开关柜的最新进展。其中12kV等级的产品采用大气压力下的N2,24／36／40．5kV等级采用尽量少的SF6和N2混合,减少了温室气体SF8的使用,减少了开关柜制造中材料的消耗和柜体占地面积,更值得一提的是节省了在服务期间的能源消耗。 相比较空气绝缘柜以及其他的SF6绝缘的C—GIS开关柜,N2S／N2X系列对于各种工业系统中的中压配电而言更为稳定可靠和更好的性价比,从而为用户降低在整个产品期内的使用成本。     

Systematic analysis of yeast strains with possible defects in lipid metabolism

Lipids are essential components of all living cells because they are obligate components of biological membranes, and serve as energy reserves and second messengers. Many but not all genes encoding enzymes involved in fatty acid, phospholipid, sterol or sphingolipid biosynthesis of the yeast Saccharomyces cerevisiae have been cloned and gene products have been functionally characterized. Less information is available about genes and gene products governing the transport of lipids between organelles and within membranes or the turnover and degradation of complex lipids. To obtain more insight into lipid metabolism, regulation of lipid biosynthesis and the role of lipids in organellar membranes, a group of five European laboratories established methods suitable to screen for novel genes of the yeast Saccharomyces cerevisiae involved in these processes. These investigations were performed within EUROFAN (European Function Analysis Network), a European initiative to identify the functions of unassigned open reading frames that had been detected during the Yeast Genome Sequencing Project. First, the methods required for the complete lipid analysis of yeast cells based on chromatographic techniques were established and standardized. The reliability of these methods was demonstrated using tester strains with established defects in lipid metabolism. During these investigations it was demonstrated that different wild‐type strains, among them FY1679, CEN.PK2‐1C and W303, exhibit marked differences in lipid content and lipid composition. Second, several candidate genes which were assumed to encode proteins involved in lipid metabolism were selected, based on their homology to genes of known function. Finally, lipid composition of mutant strains deleted of the respective open reading frames was determined. For some genes we found evidence suggesting a possible role in lipid metabolism. Copyright © 1999 John Wiley & Sons, Ltd.