Search

The effects of steps on the transition of laminar boundary layers were measured on a flat plate for low Reynolds numbers with critical and subcritical step heights. The transition position was measured by determining the intermittency distribution in streamwise direction, including the characteristic length of the transitional region. The results are compared with formulations of a critical step Reynolds number Re h , i.e., the step height that will instantly trigger transition at the step position, and—for subcritical step heights—with Δ N -formulations from the literature. For backward-facing steps, the concept of a step Reynolds number can be used to distinguish between subcritical and critical step heights, whereas for forward-facing steps there seems not to be one unique Re h . Furthermore, for subcritical backward-facing steps the concept of a Δ N -approximation gives a reasonable description of the experimental observations. Again in contrast, for forward-facing steps a Δ N -approach scattered a lot and no clear dependency was found between the reduction in the critical N-factor of transition and the relative step height. [ABSTRACT FROM AUTHOR]

We discuss a method to quantify the supersonic discharge of airbag cold gas inflators. Since one primary quantity of interest, the mass flow with time, is not directly measurable, a combined experimental and numerical approach was chosen. Shadowgraph and schlieren images visualize the gas dynamic process. Pressure measurements were conducted inside the inflator and downstream of the outlets in the supersonic jet. In this context, a method to measure the pressure of the flow without effects of shock reflection is presented. The temperature inside the inflator was estimated using a fast response heat flux probe and assuming different scenarios for the unknown heat transfer coefficient. Then, a numerical model of the inflator was created. The experimental results served as boundary conditions and some basic sensitivities remaining unknown from the measurements were studied to verify the numerical outcome. The numerical model was verified using experimental results. Finally, the mass flow rate was derived from the numerical model and compared to an analytical model. The method can reconstruct the temporal evolution of the mass flow discharging from the inflator, the pressure and the topology of the flow field within acceptable bounds. Furthermore, the method can deliver inflow data for subsequent airbag inflation studies. [ABSTRACT FROM AUTHOR]

The two most important measurement categories in production are temperature and load. Therefore commercial sensors are applied in machinery as near as possible to the working parts. For a cost efficient production the integration of sensor elements directly on top of the surface in the heavily loaded regions is essential to get the real temperature and load distributions during the production process. Therefore a new multifunctional thin film sensor system is in development. This multilayer system combines thermoresistive sensor structures with piezoresistive ones and exists out of wear resistant carbon based layers (Bewilogua and Hofmann, Surf Coat Technol 242:214-225, 2014; Biehl et al. Thin Solid Films 515:1171-1175, 2006; Biehl et al. Microsystem Technologies, Springer, 2010; Biehl et al. Microsystem Technologies, Springer, 2014; Robertson, Daim Relat Mater 12:79-84, 2003). The sensor data will lead to a deeper process understanding, to optimization of simulation tools, to reduction of rejects and to an improvement of flexibility in production. [ABSTRACT FROM AUTHOR]

The flow in a high aspect ratio generic cooling duct is described for different Reynolds numbers and for adiabatic as well as non-adiabatic conditions. The Reynolds number is varied in a range from 39,000 to 111,000. The generic cooling duct facility allows for applying a constant temperature on the duct's lower wall, and it ensures having well-defined boundary conditions. The high-quality, optical noninvasive measurement methods, namely Particle Image Velocimetry (2C2D-PIV, i.e., two velocity components in a plane), Stereo Particle Image Velocimetry (3C2D-PIV, i.e., three velocity components in a plane) and Volumetric Particle Tracking Velocimetry (3C3D-PTV, i.e., three velocity components in a volume), are used to characterize the flow in detail. Pressure transducers are installed for measuring the pressure losses. The repeatability and the validity of the data are discussed in detail. For that purpose, modifications in the test facility and in the experimental setup as well as comparisons between the different measurement methods are given. A focus lies on the average velocity distribution and on the turbulent statistics. The longitudinal velocity profile is analyzed in detail for Reynolds number variations. Secondary flows are identified with velocities of two orders of magnitude smaller than the longitudinal velocity. Reynolds stress distributions are given for several different cases. The Reynolds number dependency of $$\overline{u'^2}$$ and $$\overline{v'^2}$$ is shown, and a comparison between the adiabatic and the heated case is given. $$\overline{u'^2}$$ changes significantly when the lower wall heat flux is applied, whereas $$\overline{v'^2}$$ and $$\overline{u'v'}$$ almost stay constant. [ABSTRACT FROM AUTHOR]

The generation, insertion, pressurization and use of oil-based tracer particles is qualified for the application in heated flow facilities, typically hypersonic facilities such as Ludwieg tubes. The operative challenges are to ensure a sub-critical amount of seeding material in the heated part, to qualify the methods that are used to generate the seeding, pressurize it to storage tube pressure, as well as to test specific oil types. The mass of the seeding material is held below the lower explosion limit such that operation is safe. The basis for the tracers is qualified in off-situ particle size measurements. In the main part different methods and operational procedures are tested with respect to their ability to generate a suitable amount of seeding in the test section. For the best method the relaxation time of the tracers is qualified by the oblique shock wave test. The results show that the use of a special temperature resistant lubricant oil 'Plantfluid' is feasible under the conditions of a Mach-6 Ludwieg tube with heated storage tube. The method gives high-quality tracers with high seeding densities. Although the experimental results of the oblique shock wave test differ from theoretical predictions of relaxation time, still the relaxation time of 3.2 μs under the more dense tunnel conditions with 18 bar storage tube pressure is low enough to allow the use of the seeding for meaningful particle image velocimetry studies. [ABSTRACT FROM AUTHOR]

The global wall shear stress measurement technique using shear-sensitive liquid crystal (SSLC) is extended to wind tunnel measurements. Simple and common everyday equipment is used in the measurement; in particular a tungsten-halogen light bulb provides illumination and a saturation of SSLC coating color change with time is found. Spatial wall shear stress distributions of several typical flows are obtained using this technique, including wall-jet flow, vortex flow generated by a delta wing and junction flow behind a thin cylinder, although the magnitudes are not fully calibrated. The results demonstrate that SSLC technique can be extended to wind tunnel measurements with no complicated facilities used. [ABSTRACT FROM AUTHOR]

Experiments are conducted to evaluate the ability of various schemes to correct for pressure distortion caused by a finite tubing length between the pressure tap and the transducer. This study focuses on relatively short tubes, such as those encountered in multi-hole probes. Experimentally determined dynamic response is compared to the analytical model of Berg and Tijdeman with and without the Wiener filter. Bench-top experiments show that, for pneumatic systems with relatively short tubes, the addition of the Wiener filter carries no advantage over the Berg and Tijdeman model. The true advantage of the Wiener deconvolution method is observed for pressure tubes longer than ∼150 mm. Finally, the mean axial velocity and three Reynolds stress distributions from three correction schemes are compared to particle image velocimetry (PIV) results in a shear flow experiment. The statistical results ascertain the advantage of the Berg and Tijdeman and the Wiener deconvolution method over the generally noise-dominated inverse transfer function method. [ABSTRACT FROM AUTHOR]

Radiation protection is a topic of great public concern and of many scientific investigations, because ionizing radiation is an established risk factor for leukaemia and many solid tumours. Exposure of the public to ionizing radiation includes exposure to background radiation, as well as medical and occupational exposures. A large fraction of the exposure from diagnostic procedures comes from medical imaging. Computed tomography (CT) is the major single contributor of diagnostic radiation exposure. An increase in the use of CTs has been reported over the last decades in many countries. Children have smaller bodies and lower shielding capacities, factors that affect the individual organ doses due to medical imaging. Several risk models have been applied to estimate the cancer burden caused by ionizing radiation from CT. All models predict higher risks for cancer among children exposed to CT as compared to adults. However, the cancer risk associated with CT has not been assessed directly in epidemiological studies. Here, plans are described to conduct an historical cohort study to investigate the cancer incidence in paediatric patients exposed to CT before the age of 15 in Germany. Patients will be recruited from radiology departments of several hospitals. Their individual exposure will be recorded, and time-dependent cumulative organ doses will be calculated. Follow-up for cancer incidence via the German Childhood Cancer Registry will allow computation of standardized incidence ratios using population-based incidence rates for childhood cancer. Dose-response modelling and analyses for subgroups of children based on the indication for and the result of the CT will be performed. [ABSTRACT FROM AUTHOR]

A previously determined surface shear stress measurement technique using shear-sensitive liquid crystal (SSLC) coating is extended for use in wind tunnel-like conditions. Simple and common everyday equipment is used in the measurement; in particular a tungsten halogen light bulb provides illumination. The color change characteristics of two SSLC mixtures, BCN192 and BN/R50C, are investigated. BCN/192 is found sensitive to both magnitude and direction of the shear stress at different shear stress levels with little noise, and is suitable for surface shear stress distribution measurements. The spatial shear stress vector distribution beneath a tangential jet is obtained using BCN/192, although the magnitude is not fully calibrated. BN/R50C is found to be sensitive to shear stress magnitude, but only slightly sensitive to shear stress direction at both low and high levels. Moreover, jumps in the reflected hue are found when the viewing orientation is perpendicular to the shear stress direction. These characteristics render the use of BN/R50C for surface shear stress measurement difficult. [ABSTRACT FROM AUTHOR]

Shear sensitive liquid crystal coating (SSLCC) can measure surface shear stress vector distribution efficiently with a high spatial resolution. The purpose of the present paper is to modify and extend the surface shear stress measurement technique determined by Reda et al. to wind tunnel studies. All the facilities employed in the technique are very common and simple. The measurement technique is applied to surface flow beneath a tangential jet and surface flow in a turbulence wedge generated by a small cylinder in windtunnel flow. Spatially resolved shear stresses over planar surface are obtained, although the magnitude is not fully calibrated. [ABSTRACT FROM AUTHOR]

In this contribution, it is shown that perfect synchroneous specifications can be partitioned to and implemented on a distributed processor network. To this end, we introduce a lean visual formalism, called μ-charts, that is similar to the specification language Statecharts. This formalism consists of fewer syntactic constructs than Statecharts. Further syntax like hierarchical decomposition can be derived by means of syntactic abbreviation. μ-charts' semantics is based on the assumption of perfect synchrony. This paper is one of several contributions in this context; it gives a formal background and concentrates on the question how to use perfect synchroneous, state-based description techniques as a basis for distributed implementations. The main contribution presented in this article is that the (formal and compositional) semantics of a perfect synchroneous specification is preserved when it is partitioned and implemented on distributed processors. We prove a theorem which guarantees that the communication flow between distributed parts of a perfect synchroneous specification stabilizes in a fixed point, i.e.$ terminates, independently of the processor speeds. [ABSTRACT FROM AUTHOR]

Increasing stimulation rate increases function in cardiac myocytes and nitric oxide and cyclic GMP inhibit this effect. We tested the hypothesis that myocyte stunning would blunt both the effects of increases in rate and of nitric oxide and cyclic GMP. Ventricular myocytes from 11 rabbits were used to determine maximum rate of shortening (Rmax, µm/s) and %shortening during control and after simulated ischemia [15 min 95% N2- 5% CO2] and reperfusion [reoxygenation]. Measurements were obtained at 1–4 Hz with vehicle, 1H[1,2,4]oxadiazolo[4,3,alpha] quinoxaline-1-one (ODQ) 10–6 M, soluble guanylyl cyclase inhibitor, or NG-nitro-L-arginine methyl ester, nitric oxide synthase inhibitor (L-NAME) 10–5 M. In control, increases in rate increased Rmax from 69 ± 3 to 254±12 and %shortening from 5.3 ± 0.3 to 8.7 ± 0.5. Both ODQ and L-NAME shifted values higher. With stunning, the effects of pacing on Rmax and %shortening were blunted and ODQ and L-NAME failed to alter these values. Cyclic GMP was 322±37 pmol/105 myocytes at baseline and these values were lowered by ODQ (244 ± 31) and LNAME (207 ± 23), and similar changes were observed in stunned myocytes. Increasing frequency increased function, and reducing nitric oxide/cyclic GMP enhanced this relationship. The effect of nitric oxide was diminished by stunning, but this was not related to altered cyclic GMP levels. This suggested changes in effects of cyclic GMP downstream to its production during myocardial stunning. [ABSTRACT FROM AUTHOR]

Objective: The purpose of this study was to investigate the plasma levels of tumor necrosis factor (TNF)-alpha, its soluble p55 and p75 receptors, ex vivo lipopolysaccharide (LPS)-stimulated TNF-alpha production, and plasma levels of interleukin 6, interleukin 1, and interleukin 10 during a 7-day oral administration of iloprost in patients with active rheumatoid arthritis. Methods: During oral 7-day administration of the prostacyclin analog iloprost, the plasma levels of TNF-alpha, soluble p55, and p75 TNF-alpha receptors, IL-1, IL-6, and IL-10 and C-reactive protein (CRP) in serum were determined on days –1, 1, 3, 4, 6, and 8 and after a treatment-free follow-up on day 15. In addition, the ex vivo TNF-alpha production in whole blood under LPS-stimulated and -unstimulated conditions were measured. Fifteen patients with active rheumatoid arthritis and baseline TNF-alpha plasma levels of ≥2 pg/ml were included in independent groups receiving 50 µg, 100 µg, or 150 µg iloprost per day in addition to their conventional antirheumatic therapy. The respective dose was given once daily from days 1 to 3 and doubled from days 4 to 7. The tender and swollen joint count (28 joints) and the patients' assessments of pain severity and general feeling (10-cm visual analog scale) were performed on days –1, 4, and 8 (end of treatment) and after a 7-day follow-up. Results: The patients showed decreased TNF-alpha levels during iloprost administration. The decrease in the ex vivo LPS-stimulated TNF-alpha production and plasma levels of the p75 TNF receptor were found to be associated with a decrease in the number of tender joints. Additionally, IL-6 was downregulated. Conclusion: A 7-day oral administration of iloprost resulted in a change of in vivo and ex vivo cellular cytokine production, with reductions in TNF-alpha and p75 TNF receptor plasma levels. These changes were associated with clinical improvements in active rheumatoid arthritis. [ABSTRACT FROM AUTHOR]

We tested the hypothesis that in isolated cardiac myocytes, the negative functional effects of cyclic GMP would be blunted when the level of cyclic AMP was increased and that this interaction would be altered in renal hypertensive (One-Kidney-One-Clip, 1K1C) cardiac hypertrophic rabbits. Using isolated control and 1K1C ventricular myocytes, cyclic AMP and cell shortening (%) data were collected: 1) at baseline, 2) after the addition of 8-Br-cGMP 10-7, -6, -5 M, and 3) after forskolin (10-6 M), and adenylate cyclase activator, followed by 8-Br-cGMP 10-7, -6,-5 M. Basal levels of cyclic AMP were similar in control vs. 1K1C myocytes (10.2 ± 1.6 vs. 11.3 ± 2.6 pmol/105 myocytes). We found that 8-Br-cGMP decreased the percent shortening in a dose related manner in both control myocytes (5.1 ± 0.6 to 3.2 ± 0.4%) and hypertrophic myocytes (5.2 ± 0.4 to 3.6 ± 0.5). The level of cyclic AMP significantly increased after the addition of 8-Br-cGMP in control myocytes (14.1 ± 2.1), but not in 1K1C myocytes. Forskolin increased the percent shortening in the control myocytes (3.8 ± 0.1 to 4.8 ± 0.4), but no significant increase was noted in the hypertrophic myocytes (3.6 ± 0.3 to 3.7 ± 0.3). The level of cyclic AMP significantly increased after the addition of forskolin in both control (13.9 ± 2.0), and 1K1C cells (14.6 ± 3.8). Forskolin attenuated the negative functional effects of 8-Br-cGMP in the control (4.8 ± 0.4 to 3.2 ± 0.1) and 1K1C myocytes (3.7 ± 0.3 to 2.7 ± 0.3). The adition of 8-Br-cGMP did not affect the level of cyclic AMP after forskolin in either control (13.9 ± 2.0 to 14.8 ± 2.5) or 1K1C myocytes (14.6 ± 3.8 to 13.8 ± 1.9). These data indicated that in hypertrophic cardiac myocytes the negative functional effects of 8-Br-cGMP were similar to control, but the positive functional effects of cyclic AMP were blunted. There was an increase in cyclic AMP levels after addition of 8-Br-cGMP in control but not 1K1C cells. We conclude that in control and hypertrophic myocytes, the effects of cyclic GMP were blunted after forskolin, but this did not seem to be related to cyclic AMP phosphodiesterase activity. [ABSTRACT FROM AUTHOR]

We recently demonstrated that rapid ventricular pacing caused cardiac failure (Failure) in dogs with aortic stenosis-induced left ventricular hypertrophy (Hypertrophy) and isoproterenol caused no significant increases in function, O2 consumption and intracellular cyclic AMP level in the failing hypertrophied hearts. We tested the hypothesis that alterations in the β1-adrenoceptor-signal transduction pathway would correlate with the reduced functional and metabolic responses to β-adrenergic stimulation during the transition from the compensated hypertrophy to failure. Pressure overload-induced left ventricular hypertrophy was created using aortic valve plication in 10 dogs over a 6-month period. Five months after aortic valve plication, congestive heart failure was induced in 5 dogs by rapid ventricular pacing at 240 bpm for 4 weeks. The density of myocardial β1-adrenoceptors (fmoles/mg membrane protein; fmoles/g wet tissue) was significantly reduced in the Failure dogs (176 ± 19; 755 ± 136) when compared to those of the Control (344 ± 51; 1,551 ± 203) and the Hypertrophy (298 ± 33; 1,721 ± 162) dogs. The receptor affinities were not significantly different among all groups. There was a small but significant decrease in the percentage of β1-adrenoceptors of the failing hypertrophied hearts (62 ± 3%) when compared to that of the hypertrophied hearts (77 ± 5%). The basal myocardial adenylyl cyclase activity (rmoles/mg protein/min) was significantly lower in the Failure dogs (45 ± 4) than in the Control (116 ± 14) and Hypertrophy (86 ± 6) dogs. The forskolin (0.1 mM)-stimulated adenylyl cyclase activity was also significantly lower in the Failure dogs (158 ± 17) than in the Control dogs (296 ± 35) and slightly lower than in the Hypertrophy dogs (215 ± 10). There were no significant differences in low Km cyclic AMP-phosphodiesterase activities among all groups. We conclude that down regulation of β1-adrenoceptors and reduced adenylyl cyclase activities contribute to the decreases in myocardial functions and β-adrenergic responses in the failing hypertrophied hearts induced by rapid ventricular pacing. [ABSTRACT FROM AUTHOR]

We tested the hypothesis that increasing myocardial cyclic GMP would attenuate cyclic AMP induced positive inotropy and O2 consumption, in part, through changes in cyclic AMP and that renal hypertension-induced cardiac hypertrophy (HYP) would alter this relationship. Anesthetized, open chest rabbits (N = 48) were divided into four groups of control (CON) and HYP animals which received vehicle (VEH), isoproterenol 10-6M (ISO), 3-morpholinosyndnonimine 10-4M, (SIN-1), or a combination of ISO+SIN-1. Coronary blood flow (micro-spheres) and O2 extraction (microspectrophotometry) were used to determine O2 consumption in both subepicardium (EPI) and subendocardium (ENDO). Left ventricular change in wall thickness (%) was increased significantly by ISO in both CON (16 ± 4 to 31 ± 6) and HYP (17 ± 2 to 24 ±3). Percent change in wall thickness was similar in the CON, SIN-1, and ISO+SIN-1 groups. Myocardial O2 consumption (ml O2/min/100 g) was increased by ISO in CON (10.3 ± 1.0 to 13.6 ± 2.0 EPI; 10.9 ± 1.0 17.1 ±1.7 ENDO) and HYP (8.2 ± 1.4 to 12.3 ± 2.2 EPI; 6.6 ± 1.4 to 14.8 ± 1.8 ENDO). Oxygen consumption was unaffected by SIN-1 in CON and HYP animals. ISO+SIN-1 caused attenuated ISO-induced increases in O2 consumption in CON in EPI and ENDO, and in EPI in HYP. Cyclic GMP (pmol/g) was unchanged by ISO in CON and HYP, and increased by SIN-1 in CON (8.1 ± 1.3 to 19.2 ± 2.3 EPI) and HYP (9.1 ± 1.5 to 12.8 ± 2.0 EPI). Cyclic GMP remained elevated with ISO+SIN-1 in both groups. Cyclic AMP (pmol/g) was increased significantly by ISO in CON (496 ± 43 to 725 ± 106 EPI; 534 ± 44 to 756 ± 148 ENDO) and insignificantly in HYP (435 ± 50 to 566 ± 35 EPI; 497 ± 51 to 583 ± 47 ENDO). Cyclic AMP levels were unaffected by SIN-1 in either group. Isoproterenol induced increases in cyclic AMP were blunted by ISO+SIN-1 in CON (496 ± 43 to 537 ± 59 EPI) and not affected in HYP. The current study demonstrated attenuation of cyclic AMP mediated increased inotropy and O2 consumption by increasing cyclic GMP, which appeared, in part, related to cyclic GMP-induced reduction in cyclic AMP. This effect of cyclic GMP on cyclic AMP was not observed in myocardial hypertrophy. [ABSTRACT FROM AUTHOR]

Copyright of Informatik Spektrum is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

We tested the hypothesis that preventing cyclic GMP degradation with zaprinast, (a selective cyclic GMP-phosphodiesterase inhibitor) would produce a blunted reduction in myocardial O2 consumption in renal hypertension (One Kidney-One Clip, 1K1C)-induced cardiac hypertrophy. Four groups of anesthetized open-chest New Zealand white rabbits (n = 26) were utilized. Either vehicle or zaprinast (3×10-3 M) was applied topically to the left ventricular surface of control or 1K1C rabbits. Coronary blood flow (radioactive microspheres) and O2 extraction (microspectrophotometry) were used to determine O2 consumption. Myocardial cyclic GMP levels were determined by radioimmunoassay. The 1K1C rabbits had a greater heart weight-to-body weight ratio (2.94±0.08 g/kg) than controls (2.58±0.17). Systolic blood pressure was higher in 1K1C (102±9 mm Hg) than in controls (86±3). Zaprinast significantly and similarly increased cyclic GMP in both control (3.90±0.47 to 4.66±0.89 pmol/g) subepicardium (EPI) and (5.08±0.69 to 7.06±1.36) subendocardium (ENDO) and 1K1C hearts (5.53±0.61 to 7.48±1.51 EPI and 6.48±0.42 to 8.88±1.08 ENDO). Myocardial O2 consumption (ml O2/min/ 100 g) was significantly lower in controls treated with zaprinast (EPI: 8.8±0.1; ENDO: 9.5±1.9) than in controls treated with vehicle (EPI: 13.6±1.3; ENDO: 16.2±2.9). This effect was diminished in 1K1C rabbits treated with zaprinast (EPI: 10.3±2.4; ENDO: 11.2±2.6) compared with the vehicle-treated 1K1C group (EPI: 13.3±1.2; ENDO: 14.5±2.4). There was a similar increase in myocardial cyclic GMP after treatment with zaprinast, but a greater depression of myocardial O2 consumption in control animals than in 1K1C after treatment with zaprinast. This suggested that the reduction in myocardial O2 consumption, related to increases in cyclic GMP caused by cyclic GMP-phosphodiesterase blockade, was less in 1K1C cardiac hypertrophy. [ABSTRACT FROM AUTHOR]

Short-term co-cultivation of blastemal cells from 12-day-old mouse limb buds and human rheumatoid synovial fluid cells in high density cultures (Trowell culture system) resulted, depending on when co-cultivation started, either in (1) an inhibition of chondrogenesis (co-cultivation right from the start) or in (2) an extensive breakdown of cartilaginous matrix (co-cultivation after formation of embryonic cartilage). These synovial effects were markedly impeded if Avarol (a dioxygenase inhibitor) was applied singly or in combination with PAI-2 (a u-PA-inhibitor). PAI-2 alone, however, had no effect on the synovial-induced inhibition of chondrogenesis, but produced a pronounced inhibitory effect on matrix breakdown. The effects of both inhibitors were studied electron microscopically and biochemically (determination of sulfated-glycosaminoglycans in the high density cultures by Alcian Blue binding assay). The results of this study are consistent with the presumption that rheumatoid synovial cells are capable of inhibiting chondrogenesis and enhancing the breakdown of the cartilaginous matrix. Amongst others, the possible mediators involved are prostaglandins and plasminogen activators. The response to the inhibitors Avarol and PAI-2 is compatible with their mode of action. The chondroprotective action of these substances may be useful in developing potential antirheumatic drugs. [ABSTRACT FROM AUTHOR]