Molecular-scale Study of Cr(VI) Adsorption onto Lepidocrocite Facets by EXAFS, In Situ ATR-FTIR, Theoretical Frequency Calculations and DFT+U Techniques

Lepidocrocite, as a ubiquitous iron mineral, is widely detected as different morphologies in natural environments, controlling the mobility and availability of heavy metal ions (HMIs). These different morphologies of lepidocrocite...

DC-DC 3SSC-A-Based Boost Converter: Analysis, Design, and Experimental Validation

A detailed analysis and validation of the DC-DC boost converter based on the three-state switching cell (3SSC) type-A are presented in this paper. The study of this topology is justified by the small amount of research that employs 3SSC-A and the advantages inherent to 3SSC-based converters, such as the division of current stresses between the semiconductors, the distribution of thermal losses, and the high-density power. Therefore, a complete static analysis of the converter is described, as well as the study of all voltage and current stresses in the semiconductors, the development of a loss model in all components, and a comparison with other step-up structures. Additionally, the small-signal model validation is accomplished by comparing the theoretical frequency response and the simulated AC sweep analysis. Finally, implementing a simple controller structure, the converter is experimentally validated through a 600 W prototype, where its overall efficiency is examined for various load conditions, reaching 96.8% at nominal load.

A Novel Simulation Method of Micro-Topography for Grinding Surface

A novel simulation method of microtopography for grinding surface was proposed in this paper. Based on the theory of wavelet analysis, multiscale decomposition of the measured topography was conducted. The topography was divided into high frequency band (HFB), theoretical frequency band (TFB), and low frequency band (LFB) by wavelet energy method. The high-frequency and the low-frequency topography were extracted to obtain the digital combination model. Combined with the digital combination model and the theoretical topography obtained by geometric simulation method, the simulation topography of grinding surface can be generated. Moreover, the roughness parameters of the measured topography and the simulation topography under different machining parameters were compared. The maximum relative error of Sa, Sq, Ssk and Sku were 1.79%, 2.24%, 4.69% and 4.73%, respectively, which verifies the feasibility and accuracy of the presented method.

Deuterium-depletion has no significant impact on the mutation rate of Escherichia coli, invalidating the Double D-Bridge Hypothesis

Deuterium (D), the second most abundant isotope of hydrogen is present in natural waters at an approximate concentration of 145-155 ppm (cca. 1.5E-4 atom/atom). D is known to influence various biological processes due to its physical and chemical properties, which significantly differ from those of hydrogen. For example, increasing D-concentration to >1000-fold above its natural abundance has been shown to increase the frequency of genetic mutations in several species. The Double D-Bridge Hypothesis, formulated with the intent of explaining the mechanism of D-mutagenicity is based on the calculation that the theoretical frequency of A:T base pairs that comprise two D-bridges instead of H-bridges is 2E-8, which is equal to the mutation rate of certain species. To experimentally challenge this hypothesis, and to infer the mutagenicity of D present at natural concentrations, we investigated the effect of a nearly 100-fold reduction of D concentration on the bacterial mutation rate. Using fluctuation tests, we measured the mutation rate of three Escherichia coli genes (cycA, ackA and galK) in media containing D at either <2 ppm or 150 ppm concentrations. Out of 15 pair-wise fluctuation analyses, nine indicated a significant decrease, while three marked the significant increase of the mutation/culture value upon D-depletion. Overall, growth in D-depleted minimal medium led to a geometric mean of 0.663-fold (95% confidence interval: 0.483-0.911) change in the mutation rate. This falls nowhere near the expected 10,000-fold reduction, indicating that the Double D-Bridge Hypothesis does not hold. In addition, the combined results did not display a statistically significant change in the mutation/culture value, the mutation rate or the mutant frequency upon D-depletion. The potential mutagenic effect of D present at natural concentrations on E. coli is therefore below the limit of detection using the indicated methods.

The Influence of the Expansive Grout on Theoretical Bandwidth for the Measurement of Strain Waves by Borehole Tensor Strainmeters

The scattering model of incident seismic waves by an empty borehole has been presented to investigate the theoretical frequency response and the corresponding bandwidth of borehole tensor strainmeters. Inner-diameter changes of the stainless steel instrument casing are measured by horizontal extensometers (gauges), after the borehole tensor strainmeter is installed at a certain depth of the borehole and boned by expansive grout with the surrounding rock. There is, however, no answer for the difference between this case and the empty case. In this paper, the scattering model of incident elastic seismic waves by a two-ring borehole is introduced to investigate the influence of the expansive grout on theoretical bandwidth for the measurement of strain waves by borehole tensor strainmeters. The calculation of wave fields in the surrounding rock and the two rings by wave function expansion gives the inner-diameter changes of the stainless steel instrument casing. Several cases show that the mechanical parameters of the expansive grout have great influence on the frequency responses of borehole tensor strainmeters for different gauge combinations, but little influence on the bandwidth, which means that the high-frequency bandwidth promises the quantitative measurability of strain waves in the acoustical frequency range for borehole tensor strainmeters.

Theoretical Frequency Response and Corresponding Bandwidth of an Empty Borehole for The Measurement of Strain Waves in Borehole Tensor Strainmeters

Borehole tensor strainmeters such as the RZB tensor strainmeter, YRY tensor strainmeter, and Gladwin tensor strainmeter are highly sensitive to ground deformation over periods of minutes to months, bridging the gap in the sensitivity and frequency between Global Positioning System and seismic measurements. To discuss the possibility of quantitatively measuring seismic strain waves by borehole tensor strainmeters, a model of the scattering of plane elastic P and S waves by an empty borehole is introduced to investigate the theoretical frequency response and corresponding bandwidth of an empty borehole for borehole tensor strainmeters. The calculation of scattering waves around the empty borehole gives the changes in the diameter of the borehole. Different gauge combinations are introduced to reflect the areal strain and the maximum shear strain of the incident waves. The theoretical frequency responses for different gauge combinations are determined by the nondimensional wavenumber of the incident wave, the Poisson’s ratio of the surrounding rock, and the difference between the azimuth angle of the first gauge and the incident angle of the incident wave. Theoretical‐frequency‐response analysis of different gauge combinations for an empty borehole confirms that different gauge combinations serve as low‐pass filters. The 1% bandwidth of the gauge combinations shows that borehole tensor strainmeters could quantitatively measure seismic strain waves in the acoustic frequency range if the instrumental effective bandwidth of the gauge is sufficiently large, which will advance high‐frequency seismology and benefit in situ calibration of borehole tensor strainmeters.