各种引气剂以及抑泡剂对混凝土经时变化状态等的影响

众所周知,采用粉煤灰制备混凝土,因粉煤灰成分中含有未燃炭等微粒子,容易造成阴离子型引气剂吸附在这些微粒子上,导致含气量经时损失.同时在混凝土的制备、运输过程中,因受采用的材料、拌和状态等物理因素影响,还会发生含气量经时增加的现象.所以在制备、管理混凝土时,如何保证出机初期一定的含气量、缓解含气量的经时损失或经时增加,是一项极其关键的技术.本文将就采用能改善上述状态的引气剂、抑泡剂拌和混凝土,对混凝土的经时变化以及抗冻融性等特征产生的影响进行论述.     

Non-curated distributed databases for experimental data and models in neuroscience

Neuroscience is generating vast amounts of highly diverse data which is of potential interest to researchers beyond the laboratories in which it is collected. In particular, quantitative neuroanatomical data is relevant to a wide variety of areas, including studies of development, aging, pathology and in biophysically oriented computational modelling. Moreover, the relatively discrete and well-defined nature of the data make it an ideal application for developing systems designed to facilitate data archiving, sharing and reuse. At present, the only widely used forms of dissemination are figures and tables in published papers which suffer from inaccessibility and the loss of machine readability. They may also present only an averaged or otherwise selected subset of the available data. Numerous database projects are in progress to address these shortcomings. They employ a variety of architectures and philosophies, each with its own merits and disadvantages. One axis on which they may be distinguished is the degree of top-down control, or curation, involved in data entry. Here we consider one extreme of this scale in which there is no curation, minimal standardization and a wide degree of freedom in the form of records used to document data. Such a scheme has advantages in the ease of database creation and in the equitable assignment of perceived intellectual property by keeping the control of data in the hands of the experts who collected it. It does, however, require a more sophisticated infrastructure than conventional databases since the software must be capable of organizing diverse and differently documented data sets in an effective way. Several components of a software system to provide this infrastructure are now in place. Examples are presented, showing how these tools can be used to archive and publish neuronal morphology data, and how they can give an integrated view of data stored at many different sites.     

On the temperature sensitivity of 1.5-/spl mu/m GaInNAsSb lasers

We analyze the temperature sensitivity of 1.5-/spl mu/m GaInNAsSb lasers grown on GaAs. Building on the method of Tansu and coworkers, we find evidence that the characteristic temperatures for the threshold current T/sub 0/ and external efficiency T/sub 1/ are balanced by a combination of monomolecular recombination and temperature destabilizing mechanism(s) near room temperature. At elevated temperatures, the destabilizing process(es) dominate, due to increased threshold current density J/sub th/. While it is difficult to definitively identify carrier leakage, Auger recombination, or a combination of the two as the responsible mechanism(s), results indicate that carrier leakage certainly plays a role. Evidence of intervalence band absorption was also found; T/sub 1/ was reduced, but J/sub th/ and T/sub 0/ were not significantly degraded. Conclusions are corroborated by supporting measurements of the Z-parameter with bias, spontaneous emission spectrum, and band-offsets. Spontaneous emission measurements show evidence of weak Fermi-level pinning within the active region at threshold, indicating a form of carrier leakage. This is consistent with the characteristic temperature analysis and a leakage mechanism is proposed. This process is partially responsible for the greater temperature sensitivity of device parameters and the poor internal efficiency. Methods for reducing the effects of each parasitic mechanism are also described.     

一种高精度超声测距方法的研究

本文介绍了一种基于超声波循环反射测量原理的高精度超声测距方法 ,并给出了以单片机为核心的测距系统的组成 .本测量法克服了多次反射法中对回波脉冲个数的限制 ,经温度补偿后测量精度得到了明显改善 .     

Stoichiometrically bound beta-carotene in the cytochrome b6f complex of oxygenic photosynthesis protects against oxygen damage

The cytochrome b6f complex of oxygenic photosynthesis carries out "dark reactions" of electron transfer that link the light-driven reactions of the reaction centers, and coupled proton transfer that generates part of the electrochemical potential utilized for ATP synthesis. In contrast to the bc1 complex of the respiratory chain, with which there are many structural and functional homologies, the b6f complex contains bound pigment molecules. Along with the specifically bound chlorophyll a previously found to be bound stoichiometrically in the dimeric b6f complex, it was found in the present study that beta-carotene is also present in the b6f complex at stoichiometric levels or nearly so. Chlorophyll and carotenoid pigments were quantitatively extracted from b6f complex purified from (i) the thermophilic cyanobacterium, Mastigocladus laminosus, (ii) spinach chloroplasts, and (iii) the green alga, Chlamydomonas reinhardtii. Visible and mass spectra showed the carotenoid to be a beta-carotene of molecular weight = 536, with a stoichiometry of 1. 0:1 relative to cytochrome f in the highly active M. laminosus complex but somewhat lower stoichiometries, 0.77 and 0.55, in the b6f complex obtained from spinach chloroplasts and C. reinhardtii. A photoprotective function for the beta-carotene was inferred from the findings that the rate of photobleaching of the chlorophyll a bound in the complex was found to vary inversely with beta-carotene content and to decrease markedly in the presence of ambient N2 instead of air. The presence of beta-carotene in the b6f complex, and not in the related bc1 complexes of the mitochondrial respiratory chain and photosynthetic bacteria, suggests that an additional function is to protect the protein complexes in oxygenic photosynthetic membranes against toxic effects of intramembrane singlet O2.     

Solution structure of the sodium channel inactivation gate

The sodium channel initiates action potentials by opening in response to membrane depolarization. Fast channel inactivation, which is required for proper physiological function, is mediated by a cytoplasmic loop proposed to occlude the ion pore via a hinged lid mechanism with the triad IFM serving as a hydrophobic "latch". The NMR solution structure of the isolated inactivation gate reveals a stably folded core comprised of an alpha-helix capped by an N-terminal turn, supporting a model in which the tightly folded core containing the latch motif pivots on a more flexible hinge region to occlude the pore during inactivation. The structure, in combination with substituted cysteine mutagenesis experiments, indicates that the IFM triad and adjacent Thr are essential components of the latch and suggests differing roles for the residues of the IFMT motif in fast inactivation.     

The t(5;17) variant of acute promyelocytic leukemia expresses a nucleophosmin-retinoic acid receptor fusion

The classical action of the hormone 1,25-dihydroxyvitamin D3 (VD) is the regulation of calcium metabolism. In contrast, the peptide hormone atrial natriuretic factor (ANF) is one of the few known nonclassical VD responding genes. We screened the promoter of the rat ANF gene and identified a typical VD receptor (VDR) binding site formed by a direct repeat of two hexameric core binding motifs spaced by three nucleotides, between positions -907 and -891. Like most of the DR3-type VD response elements this sequence is bound with high affinity (Kd = 0.53 nM) by a heterodimer formed by VDR and retinoid X receptor. In a heterologous promoter context one copy of this sequence mediated an about fourfold gene activation by VD and a half-maximal activation (EC50) value of 0.48 nM VD. This characterizes the identified sequence as one of the most potent VD response elements.     

Non-steroidal anti-inflammatory drugs and the protective activity of valproate and diphenylhydantoin against maximal electroshock-induced seizures in mice--an interaction

OBJECTIVE: To discuss the clinical implications of systemic lupus erythematosus (SLE) as a complication of a urological condition. METHODS: Herein we describe a patient who presented with acute pyelonephritis due to ureteropelvic juntion stenosis, and a superimposed activation of SLE that had not been previously detected. RESULTS: This form of presentation led to a delay in making the diagnosis since it was focused urologically. The diagnosis of SLE was based on the clinical features, determination of antinuclear antibodies (ANA) and a decrease in serum complement. CONCLUSION: When a patient consults with fever arising from a urological condition that is refractory to conventional therapy, it is mandatory to make the differential diagnosis from other disease entities, as shown in this case.