Graphene Quantum Hall Effect Devices for AC and DC Electrical Metrology.

A new type of graphene-based quantum Hall standards is tested for electrical quantum metrology applications at alternating current (ac) and direct current (dc). The devices are functionalized with Cr(CO)3 to control the charge carrier density and have branched Hall contacts based on NbTiN superconducting material. The work is an in-depth study about the characteristic capacitances and related losses in the ac regime of the devices and about their performance during precision resistance measurements at dc and ac.

Hydrogen Uptake and Embrittlement of Carbon Steels in Various Environments.

To avoid failures due to hydrogen embrittlement, it is important to know the amount of hydrogen absorbed by certain steel grades under service conditions. When a critical hydrogen content is reached, the material properties begin to deteriorate. The hydrogen uptake and embrittlement of three different carbon steels (API 5CT L80 Type 1, P110 and 42CrMo4) was investigated in autoclave tests with hydrogen gas (H2) at elevated pressure and in ambient pressure tests with hydrogen sulfide (H2S). H2 gas with a pressure of up to 100 bar resulted in an overall low but still detectable hydrogen absorption, which did not cause any substantial hydrogen embrittlement in specimens under a constant load of 90% of the specified minimum yield strength (SMYS). The amount of hydrogen absorbed under conditions with H2S was approximately one order of magnitude larger than under conditions with H2 gas. The high hydrogen content led to failures of the 42CrMo4 and P110 specimens.

Fetal development of complex autonomic control evaluated from multiscale heart rate patterns.

Development of the fetal autonomic nervous system's integrative capacity in relation to gestational age and emerging behavioral pattern is reflected in fetal heart rate patterns. Conventional indices of vagal and sympathetic rhythms cannot sufficiently reflect their complex interrelationship. Universal behavioral indices of developing complex systems may provide additional information regarding the maturating complex autonomic control. We investigated fetal magnetocardiographic recordings undertaken at 10-min intervals in active (n = 248) and quiet (n = 111) states between 22 and 39 wk gestational age. Standard deviation of heartbeat intervals, skewness, contribution of particular rhythms to the total power, and multiscale entropy were analyzed. The multiscale entropy methodology was validated for 10-min data sets. Age dependence was analyzed by linear regression. In the quiet state, contribution of sympathovagal rhythms and their complexity over a range of corresponding short scales increased with rising age, and skewness shifted from negative to positive values. In the active state, age dependencies were weaker. Skewness as the strongest parameter shifted in the same direction. Fluctuation amplitude and the complexity of scales associated with sympathovagal rhythms increased. We conclude that in the quiet state, stable complex organized rhythms develop. In the active state, however, increasing behavioral variability due to multiple internal coordinations, such as movement-related heart rate accelerations, and external influences develop. Hence, the state-selective assessment in association with developmental indices used herein may substantially improve evaluation of maturation age and early detection and interpretation of developmental problems in prenatal diagnosis.

Development of integrative autonomic nervous system function: an investigation based on time correlation in fetal heart rate patterns.

OBJECTIVE: To describe the development of the integrative capacity of the fetal autonomic nervous system (ANS) according to gestational age and emerging behavioral states, assuming that developing integrative ANS functions are reflected in increasing autocorrelation of fetal heart rate and fetal heart rate variability markers. METHODS: Magnetocardiograms of 114 healthy fetuses (21-40 weeks of gestation) were recorded. Level of fetal activity (quiet/active sleep) was estimated according to characteristic heart rate patterns. Autocorrelation functions of (i) fetal heart rate and (ii) time patterns of SDNN (standard deviation of normal-to-normal intervals) and RMSSD (root mean square of successive differences in normal-to-normal intervals) were calculated and autocorrelation was determined over different time scales. Age and activity related changes were examined using linear regression and non-parametric tests. RESULTS: During pregnancy, autocorrelation increased in fetal heart rate signals and time patterns of SDNN and RMSSD. Short-time correlation (0-20 s) changed between 21 and 31 gestational weeks. Long-time correlation (75-300 s) accelerated later in pregnancy and did not increase in quiet heart rate patterns. Strong state-dependent changes were found with time patterns of SDNN. CONCLUSIONS: Emerging integrative ANS functions are reflected in increasing autocorrelation of fetal heart rate fluctuations over increasing time scales. The period from 21 to 31 gestational weeks seems to be critical to ANS development. Increasing long-time correlation is specific to active sleep states.

Fetal development assessed by heart rate patterns--time scales of complex autonomic control.

The increasing functional integrity of the organism during fetal maturation is connected with increasing complex internal coordination. We hypothesize that time scales of complexity and dynamics of heart rate patterns reflect the increasing inter-dependencies within the fetal organism during its prenatal development. We investigated multi-scale complexity, time irreversibility and fractal scaling from 73 fetal magnetocardiographic 30min recordings over the third trimester. We found different scale dependent complexity changes, increasing medium scale time irreversibility, and increasing long scale fractal correlations (all changes p<0.05). The results confirm the importance of time scales to be considered in fetal heart rate based developmental indices.