Danckwerts’ law for mean residence time revisited

This paper shows that Danckwerts’ law for mean residence time in a vessel with continuous and steady throughflow holds for a stochastic model based on a Markov chain for the particle spatial position, under a set of three very general conditions on the transfer probabilities. These are natural conditions and represent mass balance conditions on the transfer between spatial regions in the process. It is shown that a stochastic model for particle residence time distribution with these three conditions may describe almost any physical flow configuration, and also covers published mathematical RTD models, independent of their mathematical form or the nature of the associated boundary conditions, models for which Danckwert's law has hitherto been shown to be satisfied on a case-by-case basis. Two examples, namely those birth-death Markov chains and fluidized bed models are discussed.     

Conditions of Liquid Steel Treatment for Near Net‐Shape Casting Processes

Slab casting for hot rolled steel and strip casting using the twin roll casting (TRC) method are compared in terms of inclusions evolution. There are differences of the processes, mainly the use of casting flux in CC of slabs, or pool shapes and sizes in terms of TRC, particularly when roll diameters vary. The inclusion evolution of alumina in a low carbon steel grade was estimated. By modelling particle growth rate, coagulation and deposition, an ‘agglomeration index’ was created to describe the probability of clogging in the SEN. Similarly the growth of secondary alumina precipitation during cooling of the melt in the pool by Stokes collision and turbulent collision was estimated in terms of forming large particles which are able to float‐up. Influences of melt superheat or caster size were taken into account.     

A Numerical Treatment of the rf SQUID: I. General Properties and Noise Energy

We investigate the characteristics and noise performance of rf Superconducting Quantum Interference Devices (SQUIDs) by solving the corresponding Langevin equations numerically and optimizing the model parameters with respect to noise energy. After introducing the basic concepts of the numerical simulations, we give a detailed discussion of the performance of the SQUID as a function of all relevant parameters. The best performance is obtained in the crossover region between the dispersive and dissipative regimes, characterized by an inductance parameter β′ _L ≡2π LI ₀/Φ ₀≈1; L is the loop inductance, I ₀ the critical current of the Josephson junction, and Φ ₀ the flux quantum. In this regime, the lowest (intrinsic) values of noise energy are a factor of about 2 above previous estimates based on analytical approaches. However, several other analytical predictions, such as the inverse proportionality of the noise energy on the tank circuit quality factor and the square of the coupling coefficient between the tank circuit and the SQUID loop, could not be well reproduced. The optimized intrinsic noise energy of the rf SQUID is superior to that of the dc SQUID at all temperatures. Although for technologically achievable parameters this advantage shrinks, particularly at low thermal fluctuation levels, we give examples for realistic parameters that lead to a noise energy comparable to that of the dc SQUID even in this regime.      

Modern Teaching and Training in Metallurgical Engineering

This contribution deals with advanced educational technologies needed to equip customers from higher education institutions, research and industry with efficient tools supporting their work and operating new skills‐training methods. The challenges are reducing the training costs, improving quality and increasing the number of graduates in engineering departments. The concept of a Virtual Lab based on the combination of various teaching methods and tools is presented. Principles of mathematisation in metallurgical education and training are discussed. An example of online course designed in the form of Virtual Lab is demonstrated.     

Effect of progressive systemic sclerosis on antral myoelectrical activity and gastric emptying

In patients with progressive systemic sclerosis (PSS) suffering from chronic dyspepsia the stomach may be affected by this disease. The objective of this study was to investigate both antral myoelectrical activity and gastric emptying in PSS patients. Electrogastrography (EGG) was performed in 17 PSS patients (16 female, one male, median age 58 years, range 32-74 years) with chronic dyspepsia. After an overnight fast during one hour in the fasting and one hour in the fed state after ingestion of a liquid-solid test meal (370 kcal; liquid phase labeled with 0.5 mCi 99mTc-colloid) antral electrical activity was measured by one pair of electrodes sonographically placed on the skin overlying the gastric antrum. Several EGG parameters including dominant frequency (DF), percentages of DF in the normal range (2-4 cycles per minute [cpm]), bradygastria (< 2 cpm) and tachygastria (4-10 cpm), dominant frequency instability coefficient (DFIC), and postprandial to preprandial power ratio (PR) were calculated. The data were correlated to results obtained in 20 age- and gender-matched healthy subjects. In addition, the data were compared to gastric retention of the radionuclide at 60 min measured by simultaneous scintigraphy. The PSS patients did not reveal electrical disturbances. They even exhibited a significant postprandial decrease in DFIC, bradygastria, and tachygastria (ns) compared to healthy subjects. Over 50% of the PSS patients showed a delayed gastric emptying. However, EGG did not correlate to radioscintigraphy significantly. Our results reflect an absent relationship between antral myoelectrical activity in EGG and gastric emptying. Therefore, electrogastrography is unsuitable to assess gastric involvement in PSS.     

Influence of Threshold Stress on the Estimation of the Weibull Statistics

The influence of threshold stress on the estimation of the Weibull statistics is discussed in terms of the Akaike information criterion. Numerical simulations show that, if sample data are limited in number and threshold stress is not too large, the two-parameter Weibull distribution is still a preferred choice. For example, the fit of strength data of glass and ceramics to the two- and three-parameter Weibull distributions is compared.     

Effect of hemofiltration on hemodynamics and systemic concentrations of anaphylatoxins and cytokines in human sepsis

OBJECTIVE: To determine whether hemofiltration (HF) can eliminate cytokines and complement components and alter systemic hemodynamics in patients with severe sepsis. DESIGN: Prospective observation study. SETTING: Surgical intensive care unit of a university hospital. PATIENTS: 16 patients with severe sepsis. INTERVENTIONS: Continuous zero-balanced HF without dialysis (ultrafiltrate rate 2 l/h) was performed in addition to pulmonary artery catheterization, arterial cannulation, and standard intensive care treatment. MEASUREMENTS AND MAIN RESULTS: Plasma and ultrafiltrate concentrations of cytokines (the interleukins IL-1 beta, IL-6, IL-8, and tumor necrosis factor alpha) and of complement components (C3adesArg, C5adesArg) were measured after starting HF (t0) and 4 h (t4) and 12 h later (t12). Hemodynamic variables including mean arterial pressure (MAP), mean central venous pressure, mean pulmonary artery pressure, pulmonary capillary wedge pressure, and cardiac output were serially determined. During HF, cytokine plasma concentrations remained constant. However, C3adesArg and C5adesArg plasma concentrations showed a significant decline during 12-h HF (C3adesArg: t0 = 676.9 +/- 99.7 ng/ml vs t12 = 467.8 +/- 71, p < 0.01; C5adesArg: 26.6 +/- 4.7 ng/ml vs 17.6 +/- 6.2, p < 0.01). HF resulted in a significant increase over time in systemic vascular resistance (SVR) and MAP (SVR at t0: 669 +/- 85 dyne.s/cm5 vs SVR at t12: 864 +/- 75, p < 0.01; MAP at t0: 69.9 +/- 3.5 mmHg vs MAP at t12: 82.2 +/- 3.7, p < 0.01). CONCLUSIONS: HF effectively eliminated the anaphylatoxins C3adesArg and C5adesArg during sepsis. There was also a significant rise in SVR and MAP during high volume HF. Therefore, HF may represent a new modality for removal of anaphylatoxins and may, thereby, deserve clinical testing in patients with severe sepsis.