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91.
A 36-year-old man with a history of hypertrophic obstructive cardiomyopathy presented to the emergency room with "stabbing" chest pain. He had undergone dual-chamber pacemaker implantation in 1993 using an atrial lead (Accufix; Telectronics; Englewood, Colo) and a myomectomy in 1996 during which the distal portion of the atrial lead was removed. Digital fluoroscopy revealed that the retention wire had migrated out of the remaining atrial lead and perforated the right atrium. The retention wire was successfully removed percutaneously. The need for complete removal of the retention wire in the Accufix lead at the time of open-heart surgery is emphasized.  相似文献   
92.
The complex hierarchical structure of lamellar bone makes understanding structure–mechanical function relations, very difficult. We approach the problem by first using the relatively simple structure of parallel-fibred bone to construct a mathematical model for calculating Young's moduli in three-dimensions. Parallel-fibred bone is composed essentially of arrays of mineralized collagen fibrils, which are also the basic structural motif of the individual lamellae of lamellar bone. Parallel-fibred bone structure has orthotropic symmetry. As the sizes and shapes of crystals in bone are not well known, the model is also used to compare the cases of platelet-, ribbon- and sheet-reinforced composites. The far more complicated rotated plywood structure of lamellar bone results in the loss of the orthotropic symmetry of individual lamellae. The mathematical model used circumvents this problem by sub-dividing the lamellar unit into a thin lamella, thick lamella, transition zone between them, and the recently observed back-flip lamella. Each of these is regarded as having orthotropic symmetry. After the calculation of their Young's moduli they are rotated in space in accordance with the rotated plywood model, and then the segments are combined to present the overall modulus values in three-dimensions. The calculated trends compare well with the trends in microhardness values measured for circumferential lamellar bone. Microhardness values are, as yet, the only measurements available for direct comparison. Although the model is not directly applicable to osteonal bone, which is composed of many hollow cylinders of lamellar bone, the range of calculated modulus values and the trends observed for off-axis calculations, compare well with measured values. © 1998 Chapman & Hall  相似文献   
93.
Plant class I glucan endo-1,3-beta-glucosidases (beta-1,3-glucanase; 1,3-beta-D-glucan glucanohydrolase, EC 3.2.1.39) have been implicated in development and defense against pathogen attack. Nevertheless, beta-1,3-glucanase deficiencies generated by antisense transformation of Nicotiana sylvestris and tobacco have little biological effect. We report here that another beta-1,3-glucanase activity is induced in these deficient mutants after infection with necrotizing viruses. Induction of class I beta-1,3-glucanase was markedly inhibited in leaves of N. sylvestris and tobacco antisense transformants infected with tobacco necrosis virus and tobacco mosaic virus, respectively. A serologically distinct beta-1,3-glucanase activity was present in the infected antisense transformants but was absent in both healthy and infected control plants and in antisense transformants treated with the stress hormone ethylene. Immunoblot analyses, localization studies, and measurements of antibody specificity indicate that this compensatory beta-1,3-glucanase activity is an intracellular enzyme different from known tobacco beta-1,3-glucanases. Therefore, plants can compensate for a deficiency in enzyme activity by producing a functionally equivalent replacement--i.e., "ersatz"--protein or proteins. The fact that compensation for beta-1,3-glucanase activity occurs in response to infection argues strongly for an important role of these enzymes in pathogenesis.  相似文献   
94.
OBJECTIVES: The effect of Mg2+ on the developed force and concentrations of high energy phosphate metabolites in isolated human atrial trabeculae has been investigated. METHODS: Human atrial trabeculae, obtained from right atrial appendages of patients undergoing cardiac surgery requiring cardiopulmonary bypass, were dissected at room temperature in modified Krebs-Henseleit buffer containing 1.2 or 16 mM Mg2+, mounted on muscle stands, and rewarmed to 34 degrees C in the same buffer. After 30 minutes, their mechanical function was assessed. At the end of the protocol, trabeculae were fast frozen for measurement of concentrations of metabolites of high energy phosphates. RESULTS: Trabeculae collected and rewarmed in 16 mM Mg2+ Krebs-Henseleit buffer showed significantly higher mean developed force (0.59(SEM 0.10) g, p < 0.01) than those rewarmed in 1.2 mM Mg2+ Krebs-Henseleit buffer (0.32(0.03) g). Trabeculae that had a developed force > or = 0.8 g, a resting force < or = 0.7 g, and a cross sectional area < or = 1 mm2 ("functional" trabeculae) were selected for further comparison. New reverse phase high performance liquid chromatography techniques developed for the analysis of small samples (0.5-5 mg dry weight) were used to measure nucleotide, nucleoside, and creatine compounds. Total adenylate (ATP+ADP+AMP) concentrations in trabeculae revived in the presence of 16 mM Mg2+ (15.4(1.1) mumol.g-1 dry weight) were significantly higher (p < 0.01) than in those revived with 1.2 mM Mg2+ (11.8(1.0) mumol.g-1), but lower (p < 0.01) than in trabeculae fast frozen immediately after removal from the patient (22.6(1.0) mumol.g-1). There were no significant differences in NAD and total creatine (phosphocreatine+creatine) concentrations between the three groups. CONCLUSIONS: The presence of high Mg2+ during the rewarming of human atrial trabecular preparations maintains a significantly higher developed force and a significantly higher total adenylate pool than does collection and rewarming with normal concentrations of Mg2+.  相似文献   
95.
The main features of a passive thin film display cell based on the electrochemically reversible formation of a tungsten bronze according to the reaction
(colourless) WO3 + xM+ + xe? ? MxWO3(blue)
where 0 < x < 1 are considered. Chemical analysis of an electrochemically coloured WO3 film has confirmed the presence of M. It is shown that a critical requirement of these cells is that Dτ(qCm/Q)2 ≈ 1, where the symbols are, in order, the M+ diffusion coefficient, the required device response time, the electronic charge, the maximum practical volume concentration of M in the WO3 film and lastly the area colouring charge. Typical energy requirements might be about 10 mJ cm?2 per complete cycle in a favourable case.Ionic injection overpotentials and ionic diffusion both appear to play a significant role in determining cell currents. Preliminary diffusion coefficient results for Li+ in r.f. sputtered WO3 films are reported, and their predicted dependence of film structure is discussed. The optical absorption of coloured WO3 films is presented, and it is interpreted as being predominantly due to free-electron intraband transitions.  相似文献   
96.
Infection of KB cells at 39.5 degrees C with H5ts147, a temperature-sensitive (ts) mutant of type 5 adenovirus, resulted in the cytoplasmic accumulation of hexon antigen; all other virion proteins measured, however, were normally transported into the nucleus. Immunofluorescence techniques were used to study the intracellular location of viral proteins. Genetic studies revealed that H5ts147 was the single member of a nonoverlapping complementation group and occupied a unique locus on the adenovirus genetic map, distinct from mutants that failed to produce immunologically reactive hexons at 39.5 degrees C ("hexon-minus" mutants). Sedimentation studies of extracts of H5ts147-infected cells cultured and labeled at 39.5 degrees C revealed the production of 12S hexon capsomers (the native, trimeric structures), which were immunoprecipitable to the same extent as hexons synthesized in wild type (WT)-infected cells. In contrast, only 3.4S polypeptide chains were found in extracts of cells infected with the class of mutants unable to produce immunologically reactive hexon protein at 39.5 degrees C. Hexons synthesized in H5ts147-infected cells at 39.5 degrees C were capable of being assembled into virions, to the same extent as hexons synthesized in WT-infected cells, when the temperature was shifted down to the permissive temperature, 32 degrees C. Infectious virus production was initiated within 2 to 6 h after shift-down to 32 degrees C; de novo protein synthesis was required to allow this increase in viral titer. If ts147-infected cells were shifted up to 39.5 degrees C late in the viral multiplication cycle, viral production was arrested within 1 to 2 h. The kinetics of shutoff was similar to that of a WT-infected culture treated with cycloheximide at the time of shift-up. The P-VI nonvirion polypeptide, the precursor to virion protein VI, was unstable at 39.5 degrees C, whereas the hexon polypeptide was not degraded during the chase. It appears that there is a structural requirement for the transport of hexons into the nucleus more stringent than the acquisition of immunological reactivity and folding into the 12S form.  相似文献   
97.
Cytogenetic studies were done on 18 patients with myelofibrosis or the closely related syndrome, undifferentiated myeloproliferative disorder (MPD). Clones of cells with chromosome abnormalities were demonstrated in the blood of eight individuals, including two with a history of radiation therapy and two with "acute myelofibrosis". Trisomy 8 was present in the latter two patients, but otherwise, there was no consistent cytogenetic pattern or correlation with specific hematologic findings. Sixteen of these patients have been followed for more than 1 year or until death; none has progressed to leukemia. The results indicate that chromosome abnormalities are relatively common in this disorder, but as with polycythemia vera, and unlike some other "preleukemic" states, the aberrant clones in myelofibrosis do not appear to indicate that clinical leukemia is imminent.  相似文献   
98.
The concept of cardiac reconditioning centers for the prevention and rehabilitation of coronary patients has been tremendously successful in Germany over the past 20 years. At least 40 such centers are located throughout the country. Physicians, nurses, and physical therapists work closely together in the various facets of the rehabilitation process. The financial backing for these facilities is primarily through governmental and regional insurance companies, whose officials are apparently convinced that in the long run supporting preventive measures is financially sound. Objective data supporting their convictions come from studies such as that of Brusis, who showed that such as that of 1,500 employees was diminished by nearly 70 percent during a two-year period after cardiac reconditioning, as compared to a similar time period before the rehabilitation experience. Subjective benefits, which are extremely difficult to quantitate in meaningful terms, were nonetheless expressed by nearly all the patients with whom I conversed. Perhaps they have experienced the same feelings that Mark Twain did when he observed that "all frets and worries and chafings sank to sleep in the presence of the benignant serenity of the Alps; the Great Spirit of the Mountains breathed his own peace upon their hurt minds and sore hearts and healed them."  相似文献   
99.
The synthesis and properties of sulfur-doped nanocrystalline diamond films were investigated. The films were deposited by hot-filament chemical vapor deposition on Mo substrates using methane, hydrogen, and hydrogen disulfide. The nanocrystalline nature of the material arises from the induction of continuous secondary nucleation in the chemical vapor deposition environment. Complementary characterization tools were employed in order to obtain a comprehensive and coherent understanding of the correlations between the structural and electronic properties. In particular, sulfur-doped nanocrystalline diamond films show n-type Hall conductivity, enhanced field emission properties, and insensitivity to ion radiation. It was found that n-type doping of the tetragonally-bonded carbon matrix together with a nano network of trigonally-bonded carbon are crucial elements for enhanced field emission from nanocrystalline diamond. These conclusions and the corresponding supporting evidence are discussed.  相似文献   
100.
A dual stage process of depositing bamboo-like carbon nanotubes (BCNTs) by hot filament chemical vapor deposition (HFCVD) and coating Si using Radio frequency sputtering (RFS) technique. The films were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and electron field emission studies (EFE). SEM results suggest a dense network of homogeneous silicon-coated BCNTs. From the comprehensive analysis of the results provided by these techniques emerges the picture of Si encapsulated BCNTs.  相似文献   
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