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101.
102.
The author discusses the concept that data sampled beyond the Nyquist frequency is meaningless. A simple signal processing scheme to extend resolution to nearly twice the Nyquist without the problem of alias emerged. It starts by placing one-dimensional signals into a simulated sample-and-hold process in a Mathcad application 相似文献
103.
Advances in instrumentation have made it possible in recent years to study the microstructure of inorganic materials at atomic resolution using the technique of high-resolution electron microscopy (HREM). Details of instrumentation have been described elsewhere [l], and applications and trends for HREM have recently been reviewed [2]. Although HREM is primarily a technique for studying bulk defects, it is increasingly also being applied in the profile-imaging mode to derive information about surfaces [3]. The high spatial resolution of the electron microscope makes it a valuable tool for the characterization of heterogeneous catalysts. This is evidenced by the growing number of studies wherein electron micrographs are being used to describe the morphology of a particular catalyst. Profile imaging is proving particularly useful in this regard for following changes in surface structure as a function of treatment conditions [4]. 相似文献
104.
Dream work in therapeutic environments is reviewed, exploring the benefits and limitations of dreams. The application of dreams to groups and the impact of the work on group process and interaction is discussed. The integration of dream-work models within various group psychotherapeutic approaches is examined. A meta-classification of dream-work concludes the review. 相似文献
105.
106.
To examine the separate effects of viscosity and sweetness on astringency, aqueous solutions of grape seed tannin (GST) were thickened with carboxymethyl cellulose (CMC) from 2 to 45 cP (experiment 1) or sweetened with 0 to 1.8 g/L aspartame (experiment 2). Trained subjects continuously rated astringency and bitterness in duplicate. Subjects were categorized by the salivary flow induced by citric acid and ability to taste n-propyl thiouracil (PROP). In experiment 1, maximum intensity and total duration of astringency were significantly decreased as viscosity rose, although time to maximum intensity of astringency was not affected. Maximum intensity and total duration of bitterness were not significantly affected by increasing viscosity; however, the onset of bitterness was significantly delayed. In experiment 2, increasing sweetness had no affect on any astringency parameter, although maximum intensity of bitterness was significantly decreased. Neither PROP nor salivary flow-status had any effect on perception of bitterness or astringency in either experiment. 相似文献
107.
D. P. Papadopoulos D. V. Bandekas J. R. Smith 《Electrical Engineering (Archiv fur Elektrotechnik)》1992,75(3):215-222
Contents The control-canonical-form (CCF) method is introduced for the purpose of applying it to high-order state-space single-input single or multiple-output (SISO or SIMO) and multiple-input multiple-output (MIMO) linear time-invariant system models to determine closed-loop systems (i.e. design robust controllers) from which enchanced dynamic stability characteristics and overall performance of these systems is achieved. The method has been applied successfully to a SISO 6th-order linearized state-space open-loop model (representing a simplified hydro power system), and to a MIMO 8th-order linearized state-space open-loop model (representing an 87.5 kVA synchronous machine with conventional exciter supplying power to an electric utility system through an interconnection network)
Anwendung der kanonischen Form der Zustandsrückführung auf Erzeugersysteme zur Verbesserung der dynamischen Stabilitätseigenschaften
Übersicht Die Methode der kanonischen Form wird auf lineare zeitinvariante Systeme höherer Ordnung im Zustandsraum angewendet, die eine oder mehrere Eingangsgrößen bei einer oder mehreren Ausgangsgrößen aufweisen. Damit werden robuste Regler entworfen, welche die dynamische Stabilität und das gesamte Betriebsverhalten verbessern. Die Methode wurde erfolgreich auf ein linearisiertes Modell sechster Ordnung mit einem Eingang und einem Ausgang angewendet, das vereinfachend eine Wasserkraftanlage darstellt; außerdem auf ein linearisiertes Zustandsmodell achter Ordnung einer Synchronmaschine 87,5kVA mit konventioneller Erregung, die über ein Verbindungsnetzwerk in das öffentliche Netz einspeist.相似文献
108.
DG Robertson TK Braden ER Urda ND Lalwani FA de la Iglesia 《Canadian Metallurgical Quarterly》1998,72(6):362-371
Tetrahydroaminoacridine (tacrine) causes morphological and functional changes in the endoplasmic reticulum, ribosomes, and mitochondria in the liver of humans and animals. In order to investigate species differences as well as to understand the morphological changes, we examined the effects of tacrine on respiration and electron transport in mitochondria isolated from rat, dog, monkey, and human liver. Tacrine produced significantly decreased respiratory control ratios (RCR) in all species at concentrations ranging from 5 to 25 microg/ml. Human mitochondria were more sensitive to tacrine effects with RCR decreased 24% at 5 microg/ml while other species were unaffected at this concentration. The tacrine effects were characterized by increased hepatic mitochondrial State 4 respiration in rats and decreased State 3 respiration in humans. Mitochondria from aged rats were more sensitive to the effects of tacrine than mitochondria from young animals, with significantly decreased RCR at 10 microg/ml in aged rats while mitochondria from young rats were unaffected at this concentration. Concomitant with the respiratory changes, mitochondrial DNA synthesis was impaired. Since tacrine undergoes extensive biotransformation, we also explored the possibility that metabolites could exert detrimental effects. The ranking order of potency for decreasing RCR caused by monohydroxylated metabolites was: tacrine > 4-OH and 7-OH > 2-OH, 1-OH, and velnacrine with the latter group of metabolites having no effect on mitochondrial respiration at concentrations up to 50 microg/ml. In vivo administration of 20 mg/kg tacrine to rats for up to 20 days caused a paradoxical increase in RCR and P/O on Day 1 and decreased RCR on Days 9 and 20, the later findings being consistent with in vitro data. From these data we propose that tacrine does not necessarily have to be metabolized to exert effects on mitochondria at different sites in the electron transport chain that differ among species. These effects are exacerbated in mitochondria from older animals and humans appear to be more sensitive than the laboratory animals studied. 相似文献
109.
It is known that the phosphorylation of two serine residues on the NH2-terminal extension specific to cardiac troponin-I (Tn-I) modulates the calcium-dependent activation of the myofilaments. The process by which this occurs remains an unsolved puzzle. We have applied a dissective approach to study the effect of this phosphorylation on the interactions between Tn-I and its partner proteins, actin and troponin-C (Tn-C). Using N-[14C]ethylmaleimide-labelled Tn-I in sedimentation assays with F-actin, we found that the dephosphorylated Tn-I binds to F-actin with pronounced positive cooperativity, both in the absence and the presence of tropomyosin. Phosphorylation of the protein slightly weakens the interaction in the absence of tropomyosin, but the cooperativity remained. In the presence of tropomyosin, phosphorylation of the Tn-I also appeared to slightly weaken the interaction as well but, more significantly, the cooperativity was eliminated. These data can only be explained simply by a cooperative interaction between the monomer units in the actin filament. The interactions between cardiac Tn-I and Tn-C were studied by labelling the Tn-C with the fluorescent probe dansyl aziridine. As expected, the binding of the dephosphorylated Tn-I to Tn-C was strengthened by over 20-fold upon the addition of calcium to the assay. Phosphorylation of the protein, however, had a dramatic effect on the interaction in that it appeared to desensitise the complex to the effect of calcium: the Ka values obtained for both interactions (+/- Ca2+) were almost identical. These results clearly indicate that the phosphorylation of Tn-I in the cardiac system has dramatic effects on the isolated inter-protein interactions. We also discuss the possible significance of such an effect on the interactions of the isolated proteins in their roles within the intact cardiac regulatory complex. 相似文献
110.
JL Alcorn ME Smith JF Smith LR Margraf CR Mendelson 《Canadian Metallurgical Quarterly》1997,17(6):672-682
Studies of the regulation of surfactant lipoprotein metabolism and secretion and surfactant protein gene expression have been hampered by the lack of a cell culture system in which the phenotypic properties of type II cells are maintained. We have developed a primary culture system that facilitates the maintenance of a number of morphologic and biochemical properties of type II pneumonocytes for up to 2 wk. Cells were isolated by collagenase digestion of midgestation human fetal lung tissue that had been maintained in organ culture in the presence of dibutyryl cyclic AMP (Bt2cAMP) for 5 days. The isolated cells were enriched for epithelial components by treatment with DEAE-dextran, plated on an extracellular matrix (ECM) derived from Madin-Darby canine kidney (MDCK) cells, and incubated at an air/liquid interface in a minimal amount of culture medium containing Bt2cAMP. The cell cultures were comprised of islands of round epithelial-like cells containing numerous dense osmiophilic granules, surrounded by sparse spindle-shaped cells with the appearance of fibroblasts. Ultrastructural examination revealed that the osmiophilic granules had the appearance of lamellar bodies, the distinguishing feature of type II pneumonocytes. Additionally, the cultures maintained elevated levels of SP-A gene expression for up to 2 wk. The expression of mRNAs encoding SP-A, SP-B, and SP-C were regulated in the cultured cells by glucocorticoids and cyclic AMP in a manner similar to that observed in fetal lung tissue in organ culture. The differentiated phenotype was most apparent when the cells were cultured at an air/liquid interface. In order to utilize the cultured type II cells for study of the effects of overexpression of various proteins and for promoter analysis, it is of essence to transfect DNA constructs into these cells with high efficiency. Unfortunately, we found the cells to be refractory to efficient transfer of DNA using conventional methods (i.e., lipofection, electroporation, or calcium phosphate-mediated transfection). However, replication-defective recombinant human adenoviruses were found to provide a highly efficient means of introducing DNA into the type II pneumonocytes. Furthermore, we observed in type II cell-enriched cultures infected with recombinant adenoviruses containing the lacZ gene under control of a cytomegalovirus promoter, that beta-galactosidase was expressed uniformly in the islands of type II cells and surrounding fibroblasts. By contrast, in cultures infected with recombinant adenoviruses containing the human growth hormone (hGH) gene under control of the SP-A gene promoter and 5'-flanking region, hGH was expressed only in the type II cells. Thus, this culture system provides an excellent means for identifying genomic elements that mediate type II cell-specific gene expression. 相似文献