Steroidogenesis and cyclic adenosine 3', 5'-monophosphate accumulation in rat adrenal cells: divergent effects of adrenocorticotropin and its o-nitrophenyl sulfenyl derivative

Both adrenocorticotropin (ACTH) and its o-nitrophenyl sulfenyl derivative (NPS-ACTH) in which the single tryptophan residue of the hormone is modified, were able to stimulate corticosterone synthesis to the same maximal rate in isolated rat adrenal cells. The concentration of NPS-ACTH required for half-maximal steroidogenesis was approximately 70 times that of ACTH. Although both ACTH and NPS-ACTH stimulated cyclic AMP accumulation, the effect of NPS-ACTH was marginal; the maximal stimulation of cyclic adenosine 3',5'-monophosphate (cyclic AMP) accumulation in response to ACTH was 30 to 100-fold greater than that due to NPS-ACTH. Apparently ACTH increased cyclic AMP accumulation well beyond that required for the stimulation of maximal steroidogenesis. NPS-ACTH appeared to inhibit in a competitive manner the effect of ACTH on cyclic AMP production but not steroid synthesis. The continued presence of ACTH or NPS-ACTH was necessary for the continued stimulation of steroidogenesis indicating that the factor (or factors) mediating the steroidogenic response must be present throughout the time of stimulation. The relationship between steroid synthesis and cyclic AMP accumulation was different for ACTH and NPS-ACTH. Much less cyclic AMP was produced when NPS-ACTH stimulated steroid synthesis to 75% of the maximal level than when ACTH enhanced steroidogenesis half-maximally. Even though cyclic AMP was found to leave the cells during the time of incubation, the same lack of correlation between cyclic AMP generation and rate of steroid synthesis mentioned above was found whether intracellular or total cyclic AMP was measured. These results suggest that there may be two receptors for ACTH in the adrenal cell population which may be in the same cell or in different cell types. NPS-ACTH stimulates one of these receptors but inhibits the other. Furthermore, these results imply that either very small amounts of cyclic AMP are required for the stimulation of steroidogenesis or factor (or factors) besides cyclic AMP may be involved in mediating this function of ACTH

Magnetic fluctuations and superconducting properties of CaKFe4As4 studied by 75As NMR

We report $^{75}$As nuclear magnetic resonance (NMR) studies on a new iron-based superconductor CaKFe$_4$As$_4$ with $T_{\rm c}$ = 35 K. $^{75}$As NMR spectra show two distinct lines corresponding to the As(1) and As(2) sites close to the K and Ca layers, respectively, revealing that K and Ca layers are well ordered without site inversions. We found that nuclear quadrupole frequencies $\nu_{\rm Q}$ of the As(1) and As(2) sites show an opposite temperature ($T$) dependence. Nearly $T$ independent behavior of the Knight shifts $K$ are observed in the normal state, and a sudden decrease in $K$ in the superconducting (SC) state clearly evidences spin-singlet Cooper pairs. $^{75}$As spin-lattice relaxation rates 1/$T_1$ show a power law $T$ dependence with different exponents for the two As sites. The isotropic antiferromagnetic spin fluctuations characterized by the wavevector ${\bf q}$ = ($\pi$, 0) or (0, $\pi$) in the single-iron Brillouin zone notation are revealed by 1/$T_1T$ and $K$ measurements. Such magnetic fluctuations are necessary to explain the observed temperature dependence of the $^{75}$As quadrupole frequencies, as evidenced by our first-principles calculations. In the SC state, 1/$T_1$ shows a rapid decrease below $T_{\rm c}$ without a Hebel-Slichter peak and decreases exponentially at low $T$, consistent with an $s^{\pm}$ nodeless two-gap superconductor.Comment: 9 pages, 6 figures, accepted for publication in Phys.Rev.

Optimization of the crystal growth of the superconductor CaKFe4As4 from solution in the FeAs−CaFe2As2−KFe2As2 system

Measurements of the anisotropic properties of single crystals play a crucial role in probing the physics of new materials. Determining a growth protocol that yields suitable high-quality single crystals can be particularly challenging for multicomponent compounds. Here we present a case study of how we refined a procedure to grow single crystals of CaKFe4As4 from a high temperature, quaternary liquid solution rich in iron and arsenic (“FeAs self-flux”). Temperature dependent resistance and magnetization measurements are emphasized, in addition to the x-ray diffraction, to detect intergrown CaKFe4As4, CaFe2As2, and KFe2As2 within what appear to be single crystals. Guided by the rules of phase equilibria and these data, we adjusted growth parameters to suppress formation of the impurity phases. The resulting optimized procedure yielded phase-pure single crystals of CaKFe4As4. This optimization process offers insight into the growth of quaternary compounds and a glimpse of the four-component phase diagram in the pseudoternary FeAs−CaFe2As2−KFe2As2 system

Numerical simulation and experimental validation of a large-area capacitive strain sensor for fatigue crack monitoring

A large-area electronics in the form of a soft elastomeric capacitor (SEC) has shown great promise as a strain sensor for fatigue crack monitoring in steel structures. The SEC sensors are inexpensive, easy to fabricate, highly stretchable, and mechanically robust. It is a highly scalable technology, capable of monitoring deformations on mesoscale systems. Preliminary experiments verified the SEC sensor’s capability in detecting, localizing, and monitoring crack growth in a compact specimen. Here, a numerical simulation method is proposed to simulate accurately the sensor’s performance under fatigue cracks. Such a method would provide a direct link between the SEC’s signal and fatigue crack geometry, extending the SEC’s capability to dense network applications on mesoscale structural components. The proposed numerical procedure consists of two parts: (1) a finite element (FE) analysis for the target structure to simulate crack growth based on an element deletion method; (2) an algorithm to compute the sensor’s capacitance response using the FE analysis results. The proposed simulation method is validated based on test data from a compact specimen. Results from the numerical simulation show good agreement with the SEC’s response from the laboratory tests as a function of the crack size. Using these findings, a parametric study is performed to investigate how the SEC would perform under different geometries. Results from the parametric study can be used to optimize the design of a dense sensor network of SECs for fatigue crack detection and localizatio