The activities of Na2O and K2O dissolved in mixed-alkali Na–K–(β+β")-Al2O3 (NKBA) have been determined by using yttria stabilized zirconia (YSZ) as a solid electrolyte in the following galvanic cells: The approach enables to verify in situ the establishment and maintenance of the β/β"-equilibrium, and to characterize it as a function of the phase composition of NKBA. The results can be expressed as follows: 相似文献
Poly-p-phenylene (PPP) was synthesized from benzene according to the Kovacic method. Electrodes were made from this electronic insulator by cold- or hot-pressing of the loose, brown powder, under the addition of 7.5 wt. % soot (Corax L®, Degussa AG). The electrochemical insertion and removal of anions HSO−4, ClO−4 in this material in aqueous solutions of the corresponding acids was investigated by slow cyclic voltammetry.
Initially, only a surface layer of about 0.1 mm thickness takes part in the electrochemical processes, which are reversible. A maximum concentration of anions in the solid of [(−C6H4−)+7 A−] is attainable. The maximum degree of insertion is equal to 0.14. The insertion potential UI shifts strongly into the negative direction with increasing concentration c of the acid. A linear UI/c relationship is observed as in the case of graphite, where the intercalation potential is more positive by 20–200 mV for the same electrolyte. The round trip current efficiency for the insertion/removal cycle increases with increasing acid concentration attaining 100% in 14 M H2SO4 or 11.3 M CHlO4. For a given concentration, increases in the same order as with graphite (H2SO4 < HClO4 < HBF4), being somewhat lower for a given electrolyte composition. From anodic current limitation (jlim = 5–10 mA cm−2), a diffusion coefficient of about D = 2 × 10−7 cm2 s−1 is derived for the transport of anions in the bulk of PPP. The striking similarity of our results to former findings with graphite is thoroughly discussed. Some general conclusions are derived thereof. 相似文献
Electrochemical dressing of fine-grained metal-bonded diamond grinding wheels enables to grind hard and brittle materials
in the ductile mode. Optical surfaces can be manufactured by grinding, which reduces the need for subsequent, time-consuming
polishing work. When using metal-bonded grinding wheels, the emerging oxides regulate the electrochemical dissolution. Bronze-bonded
grinding wheels are more suitable for grinding cemented carbides and ceramics than iron-bonded grinding wheels, as it is easier
to modify their chemical composition to suit a specific grinding task. They can also be sintered at lower temperatures, which
reduces the risk of thermal damage to the diamond. In this paper, the dissolution and the oxidation of different bronze alloys
are characterized for the electrochemical dressing process. The relevant evaluation criteria are the oxide layer thickness,
the electrical behavior and the different emerging bronze alloy oxides.
This work is funded by the German Research Association DFG within the Transregional Collaborative Research Center SFB/TR4
“Process Chains for the Replication of Complex Optical Elements”. 相似文献
Abstract Beginning as an innovative idea in the early 1970s, the third-party maintenance industry realized revenues in 1986 of $1.4 billion. This flourishing industry offers opportunities for vendors and customers alike. 相似文献
Medical data mining is currently actively pursued in computer science and statistical research but not in medical practice.
The reasons therefore lie in the difficulties of handling and statistically analyzing medical data. We have developed a system
that allows practitioners in the field to interactively analyze their data without assistance of statisticians or data mining
experts. In the course of this paper we will introduce data mining of medical data and show how this can be achieved for survival
data. We will demonstrate how to solve common problems of interactive survival analysis by presenting the Online Clinical
Data Mining (OCDM) system. Thereby the main focus is on similarity based queries, a new method to select similar cases based
on their covariables and the influence of these on their survival. 相似文献
BACKGROUND: Calculations on the basis of the LQ-model have been focussed on the possible radiobiological equivalence between common continuous low dose rate irradiation (CLDR) and a superfractionated irradiation (PDR = pulsed dose rate) provided that the same total dose will be prescribed in the same overall time as with the low doserate. A clinically usable fractionation scheme for brachytherapy was recommended by Brenner and Hall and should replace the classical CLDR brachytherapy with line sources with an afterloading technique using a stepping source. The hypothes is that LDR equivalency can be achieved by superfractionation was tested by means of in vitro experiments on V79 cells in monolayer and spheroid cultures as well as on HeLa monolayers. MATERIALS AND METHODS: Simulating the clinical situation in PDR brachytherapy, fractionation experiments were carried out in the dose rate gradient of afterloading sources. Different dose levels were produced with the same number of fractions in the same overall incubation time. The fractionation schedules which were to be compared with a CLDR reference curve were: 40 x 0.47 Gy, 20 x 0.94 Gy, 10 x 1.88 Gy, 5 x 3.76 Gy, 2 x 9.4 Gy given in a period of 20 h and 1 x 18.8 Gy as a "single dose" exposition. As measured by flow cytometry, the influence of the dose rate in the pulse on cell survival and on cell cycle distribution under superfractionation was examined on V79 cells. RESULTS: V79 spheroids as a model for a slowly growing tumor, reacted according to the radiobiological calculations, as a CLDR equivalency was achieved with increasing fractionation. Rapidly growing V79 monolayer cells showed an inverse fractionation effect. A superfractionated irradiation with pulses of 0.94 Gy/h respectively 0.47 Gy/0.5 h was significantly more effective than the CLDR irradiation. This inverse fractionation effect in log-phase V79 cells could be attributed to the accumulation of cycling cells in the radiosensitive G2/M phase (G2 block) during protected exposure which was drastically more pronounced for the pulsed scheme. HeLa cells were rather insensitive to changes of fractionation. Superfractionation as well as hypofractionation yielded CLDR equivalent survival curves. CONCLUSIONS: The fractionation scheme, derived from the PDR theory to achieve CLDR equivalent effects, is valid for many cell lines, however not for all. Proliferation and dose rate dependend cell cycle effects modify predictions derived from the sublethal damage recovery model and can influence acute irradiation effects significantly. Dose rate sensitivity and rapid proliferation favour cell cycle effects and substantiate, applied to the clinical situation, the possibility of a higher effectiveness of the pulsed irradiation on rapidly growing tumors. 相似文献
Temperature of the tympanic membrane is recommended as a "gold standard" of core-temperature recording. However, use of temperature probes in the auditory canal may lead to damage of tympanic membrane. Temperature measurement in the auditory canal with infrared thermometry does not pose this risk. Furthermore it is easy to perform and not very time-consuming. For this reason infrared thermometry of the auditory canal is becoming increasingly popular in clinical practice. We evaluated two infrared thermometers-the Diatek 9000 Thermoguide and the Diatek 9000 Instatemp-regarding factors influencing agreement with conventional tympanic temperature measurement and other core-temperature recording sites. In addition, we systematically evaluated user dependent factors that influence the agreement with the tympanic temperature. MATERIALS AND METHODS: In 20 volunteers we evaluated the influence of three factors: duration of the devices in the auditory canal before taking temperature (0 or 5 s), interval between two following recordings (30, 60, 90, 120, 180 s) and positioning of the grip relative to the auditory-canal axis (0, 60, 180 and 270 degrees). Agreement with tympanic contact probes (Mon-a-therm tympanic) in the contralateral ear was investigated in 100 postoperative patients. Comparative readings with rectal (YSI series 400) and esophageal (Mon-a-therm esophageal stethoscope with temperature sensor) probes were done in 100 patients in the ICU. The method of Bland and Altman was taken for comparison. RESULTS: Shortening of the interval between two consecutive readings led to increasing differences between the two measurements with the second reading decreasing. A similar effect was seen when positioning the infrared thermometers in the auditory canal before taking temperatures: after 5 s the recorded temperatures were significantly lower than temperature recordings taken immediately. Rotation of the devices out of the telephone handle position led to increasing lack of agreement between infrared thermometry and contact probes. Mean differences between infrared thermometry (Instatemp and Thermoguide, CAL-Mode) and tympanic probes were -0.41 +/- 0.67 degree C (2 SD) and -0.43 +/- 0.70 degree C, respectively. Mean differences between the Thermoquide (Rectal-Mode) and rectal probe were -0.19 +/- 0.72 degree C, and between the Thermoguide (Core Mode) and esophageal probe -0.13 +/- 0.74 degree C. DISCUSSION: Although easy to use, infrared thermometry requires careful handling. To obtain optimal recordings, the time between two consecutive readings should not be less than two min. Recordings should be taken immediately after positioning the devices in the auditory canal. Best results are obtained in the 60 degrees position with the grip of the devices following the ramus mandibulae (telephone handle position). The lower readings of infrared thermometry compared with tympanic contact probes indicate that the readings obtained represent the temperature of the auditory canal rather than of the tympanic membrane itself. To compensate for underestimation of core temperature by infrared thermometry, the results obtained are corrected and transferred into core-equivalent temperatures. This data correction reduces mean differences between infrared recordings and traditional core-temperature monitoring, but leaves limits of agreement between the two methods uninfluenced. 相似文献
In this paper we describe the successful application of the ProB tool for data validation in several industrial applications. The initial case study centred on the San Juan metro system
installed by Siemens. The control software was developed and formally proven with B. However, the development contains certain
assumptions about the actual rail network topology which have to be validated separately in order to ensure safe operation.
For this task, Siemens has developed custom proof rules for Atelier B. Atelier B, however, was unable to deal with about 80
properties of the deployment (running out of memory). These properties thus had to be validated by hand at great expense,
and they need to be revalidated whenever the rail network infrastructure changes. In this paper we show how we were able to
use ProB to validate all of the about 300 properties of the San Juan deployment, detecting exactly the same faults automatically in
a few minutes that were manually uncovered in about one man-month. We have repeated this task for three ongoing projects at
Siemens, notably the ongoing automatisation of the line 1 of the Paris Métro. Here again, about a man month of effort has
been replaced by a few minutes of computation. This achievement required the extension of the ProB kernel for large sets as well as an improved constraint propagation algorithm. We also outline some of the effort and features
that were required in moving from a tool capable of dealing with medium-sized examples towards a tool able to deal with actual
industrial specifications. We also describe the issue of validating ProB, so that it can be integrated into the SIL4 development chain at Siemens. 相似文献
The largest group of Lie symmetries that a third-order ordinary differential equation (ode) may allow has seven parameters.
Equations sharing this property belong to a single equivalence class with a canonical representative v′′′(u)=0. Due to this simple canonical form, any equation belonging to this equivalence class may be identified in terms of certain
constraints for its coefficients. Furthermore a set of equations for the transformation functions to canonical form may be
set up for which large classes of solutions may be determined algorithmically. Based on these steps a solution algorithm is described for any equation with this symmetry type which resembles a similar
scheme for second order equations with projective symmetry group.
Received March 9, 2000; revised June 8, 2000 相似文献