Donor Concentration Research Articles

H2S improves growth of tomato seedlings involving the MAPK signaling

As a signal molecule, hydrogen sulfide (H2S) plays an important role in plant growth. In this study, the effect of different concentration of H2S donor, sodium hydrosulfide (NaHS), on growth of tomato seedlings was tested in hydroponic culture. The effects of 50 μM NaHS on tomato seedlings were not significant, compared with the control. After 100 μM NaHS treatment, plant height, shoot fresh weight and dry weight increased significantly. However, 300, 500 and 1000 μM NaHS had inhibitory effect on tomato seedlings, especially 1000 μM NaHS. 100 μM NaHS could increase chlorophyll a, chlorophyll b, and total chlorophyll content, stomatal conductance, net photosynthetic rate, transpiration rate and intercellular CO2 concentration. The activities of nitrate reductase, glutamate synthase and glutamine synthase, and L-cysteine demethylase (LCD), and nitrate content, were increased significantly after 100 μM NaHS treatment. The microarray results showed that 9122 genes changed after treated with 100 μM NaHS for 3 h, and 430 genes changed more than 2 times. These genes were grouped into metabolism, signal transduction, stress resistance, transcription factors, transport, protein synthesis and degradation, hormone response, and cell wall related genes in tomato seedlings. RT-PCR analysis showed that the expression of some MAPK family genes changed significantly when exogenous NaHS was added, especially SlMAPK3 and SlMAPK13. The MAPK inhibitor PD98059 reduce the LCD activity and H2S content in tomato seedlings, which indicated that MAPK signaling pathway was involved in the process of H2S promoting tomato seedling growth.

On the permittivity of titanium dioxide

Conductive rutile TiO2 has received considerable attention recently due to multiple applications. However, the permittivity in conductive, reduced or doped TiO2 appears to cause controversy with reported values in the range 100–10,000. In this work, we propose a method for measurements of the permittivity in conductive, n-type TiO2 that involves: (i) hydrogen ion-implantation to form a donor concentration peak at a known depth, and (ii) capacitance–voltage measurements for donor profiling. We cannot confirm the claims stating an extremely high permittivity of single crystalline TiO2. On the contrary, the permittivity of conductive, reduced single crystalline TiO2 is similar to that of insulating TiO2 established previously, with a Curie–Weiss type temperature dependence and the values in the range 160–240 along with the c-axis.

Modeling the spatial control over point defect spin states via processing variables

Contemporary models that are used to search for solid-state point defects for quantum-information applications tend to focus on the defect’s intrinsic properties rather than the range of conditions in which they will form. In this work, a first-principles based multi-scale device model is used to explore how the conditions (i.e., growth temperature, doping concentration, unintentional impurity concentration) influence the formation of a neutral aluminum vacancy complexed with an oxygen impurity at a neighboring nitrogen site vAl-1ON in an Si/Mg:AlN homojunction. Varying the donor (Si) concentration is predicted to lead to the greatest change in both the maximum height and shape of the (vAl-1ON)0 profile. The shape is found to depend on the acceptor (Mg) concentration as well, and a critical ratio between the acceptor and unintentional impurities below which the (vAl-1ON)0 center would not form was identified. A detailed analysis of the electrostatic potential, electric field, and defect chemistry obtained with the model was used to reveal the underlying causes of these changes. These results show the potential of varying processing parameters to manipulate the local electronic structure as a means to control the properties of point defects for quantum-information applications.

Increasing electron donor concentration does not accelerate complete microbial reductive dechlorination in contaminated sediment with native organic carbon.

Experiments with Fe(III)-rich, chloroethene-contaminated sediment demonstrated that trichloroethylene (TCE) and vinyl chloride (VC) were completely reduced to ethene regardless of whether electron donor(s) were added at 1 × stoichiometry or 10 × stoichiometry relative to all-electron acceptors. Unamended controls uniformly reduced TCE to ethene with a mean time to complete dechlorination (operationally defined as the presence of stoichiometric ethene production) of 79days. Adding 1 × and 10 × acetate hindered the rate and extent of TCE and VC reduction relative to unamended controls, with several only partially reduced when the experiments were terminated. Adding high molecular mass (soybean oil derivative) substrates did not increase microbial reductive dechlorination relative to unamended incubations, and in many cases, hindered microbial dechlorination in favor of methanogenesis. The mean time to complete dechlorination was comparable between low (× 1) and high (× 10) electron donor concentration for all lipid-based electron donors tested. Those tested included Newman Zone® Standard without sodium lactate (96 vs. 75days, respectively), CAP 18 ME (85 vs. 94days, respectively), EOS 598B42 (68 vs. 72days, respectively), and acetate (134 vs. 125days, respectively). These data suggest that the addition of an electron donor does not always increase the rate and extent of reductive dechlorination but will increase costs. In particular, increasing the concentration of electron donors higher than the stoichiometric demand only decreased complete microbial reductive dechlorination, which is the opposite of most standard "more time and more electrons" approaches. These data argue that site-specific electron donor demands must be evaluated, and in some cases, a monitored natural attenuation (MNA) approach is most favorable.

Charge Carrier Transport in Van Der Waals Semiconductor InSe Intercalated with RbNO3 Probed by Direct Current Methods

Layered van der Waals (vdW) semiconductors show great promise to overcome limitations imposed by traditional semiconductor materials. The synergistic combination of vdW semiconductors with other functional materials can offer novel working principles and device concepts for future nano- and optoelectronics. Herein, we investigate the influence of the intercalation of semiconducting n-type InSe vdW crystals with ferroelectric rubidium nitrate (RbNO3) on the transport of charge carriers along and across the layers. The apparent maxima in the temperature dependences of the Hall coefficient are explained in the framework of a model that predicts, along with three-dimensional carriers, the existence of two-dimensional ones contributing only to the conductivity along the layers. The revealed increase of the conductivity anisotropy and its activation variation with temperature, which is mainly due to a decrease of the conductivity across the layers, confirm a two-dimensionalization of electron gas in n-InSe after insertion of the ferroelectric. From the numerical analysis, we determined the densities of carriers of both types, concentrations of donors and acceptors, as well as the value of the interlayer barrier.

Neutron irradiation induced defects in oxides and their impact on the oxide properties

Understanding the irradiation-induced defects in oxides is of interest for a wide range of applications. ZnO is an interesting oxide with mixed ionic and covalent bonding that contains a variety of point defect structures—making it an excellent model for studying irradiation-induced defects and their impact on properties. Here, we investigate the effects of neutron irradiation on the formation of defects and on the structural, optical, and electrical properties of ZnO single crystals. We observe the formation of vacancies and voids via positron annihilation spectroscopy. Neutron irradiation led to a significant deterioration of the ZnO structure and formed a high concentration of point defects, vacancy clusters, and voids with large disparities in their structure across variable irradiation times. It also led to significant changes in the optical properties and sample color. Irradiation for 444 h induced a high concentration of Cu acceptors as well as a high concentration of Ga donors. Temperature-dependent Hall effect measurements revealed the competing production of donors and acceptors and showed an increase in the slope of the carrier freeze-out curve with increasing irradiation dose. This work demonstrates the combined effects of neutron irradiation in producing a wide range of structural defects, impurities, and dopants in oxides and their enormous impact on modifying the oxide structure and both the optical and electronic properties. It particularly emphasizes the importance of considering the production of new impurities and dopants during the neutron irradiation of oxides.

Effect of MoS2 interlayer on performances of copper-barium-tin-sulfur thin film solar cells via theoretical simulation

Cu2BaSn(S,Se)4 (CBTSSe) solar cells are emerging photovoltaic devices due to their high theoretical efficiencies of ~31%, environment-friendly and earth-abundant composition, low density of non-recombination defects, and so on. However, the record efficiency of CBTSSe solar cell is only 5.2%, showing the importance of studying their performance via numerical analysis to further enhance their practical efficiencies. In this paper, the effect of absorber and buffer layers on performances of Cu2BaSnS4 (CBTS) solar cells are firstly systematically studied via the SCAPS-1D software to provide a platform for the study of the effect of MoS2 interlayer on the performances of CBTS solar cells. The highest PCE of CBTS solar cell with a 30 nm CdS buffer layer is 11.87%. The PCE of CBTS solar cell with a 0.8 μm CBTS absorb layer is 12.51%, indicating that the CBTS solar cell is a potential low-cost solar cell due to its large optical absorption coefficient (α > 104 cm−1). The efficiency of CBTS solar cell is improved to 16.47% when the carrier concentration of CBTS is 1016 cm−3. The relationship between the performance of solar cell and the band gap, thickness, donor concentration, acceptor concentration of MoS2 interlayer is systematically investigated on the basis of the optimized efficiency. It is found that MoS2 interlayer plays an important role in the performance of CBTS solar cell. The p-type MoS2 has a beneficial effect on the efficiency improvement while the n-type MoS2 has a negative effect on the efficiency enhancement. The highest PCE of CBTS solar cell is as high as 18.28% when the thickness and the acceptor concentration of MoS2 are 4 nm and 1019 cm−3, respectively. Our simulation result provides a promising research direction to further improve the actual efficiency of the CBTS solar cell.

Kinetic study on liquid propylene polymerization using a modified heat flow reaction calorimeter

Bulk phase polymerization of propylene with a 4th generation of Ziegler-Natta catalyst was kinetically investigated by means of heat flow calorimetry. The assumptions and modifications on isothermal calorimetric method were demonstrated. Our calibration method showed that heat exchange with the reactor cover plate is not constant over time. Therefore, the dynamic of cover plate temperature was considered in the calorimetric method. The polymerization rate profiles depending on hydrogen and external electron donor concentration have been investigated. Normalized polymerization profiles (Rp /Rpmax) are plotted and expressed as an exponential function of time. Effects of hydrogen and external electron donor (ED) concentration on Rpmax and polymerization rate were investigated as well. The results showed that by increasing hydrogen concentration, initial polymerization rate (Rpmax) increased. Hydrogen increased productivity by increasing the initial polymerization rate, while it had no negative effect on the rates of decay or its effect was small. The ED concentration was optimized so that the catalyst deactivation rate was at its lowest level. Also, changes in the ratio of activation to inactivation with ED concentration were examined, and a proportional change was observed.

Electron mobility along 〈0001〉 and 〈11̅00〉 directions in 4H-SiC over a wide range of donor concentration and temperature

We investigated the Hall electron mobility in 4H-SiC along and perpendicular to the c-axis (μ H,// and μ H,⊥) using Hall bar structures fabricated on n-type SiC() epitaxial layers over a wide range of donor concentration (2.1 × 1015–3.2 × 1018 cm−3) and temperature (298–600 K). We obtained μ H,// of 1160 cm2 V−1s−1, which is the highest electron mobility ever reported for SiC measured at room temperature. The anisotropy of drift mobility becomes smaller at higher temperature and with higher donor concentration. This result can be qualitatively explained by smaller anisotropy of electron effective mass in the high-energy region of the conduction band.

Structure, Optical and Electrical Properties of the High Doped ZnO Thin Films Deposited By RF Magnetron Sputtering of Powder Target in Methane Ambient

The ZnO thin films were deposited by RF-magnetron sputtering of ZnO powder target using pure argon, argon with hydrogen and argon with methane as reactive gas. Surface morphology and crystalline structure of the films were studied by SEM, XRD and XRR techniques. Chemical composition and optical properties were investigated by SIMS, Raman scattering spectroscopy (RSS), PL spectroscopy and spectral ellipsometry. Electrical measurements were performed on the ZnO films deposited on SiO2-Si and silicon wafers n- and p-type with Ni contacts by TLM, IV, CV characteristics, admittance spectroscopy, Van der Pauw and Hall methods. It was found that growth morphology, crystalline structure, optical and electrical properties of the films are strongly affected by adding methane to argon during the deposition process. Adding of methane resulted in a destruction of hexagonal phase texture and considerable increase a size of ZnO nanocrystallites (from 50 nm for argon to 200 nm for argon/methane working gas). SIMS measurements demonstrated that methane promoted hydrogen incorporation into the ZnO film that was more than an order of magnitude larger in comparison with adding molecular hydrogen in the gas mixture at the same concentration. Adding of methane resulted in a high energy shift of near band edge ultraviolet photoluminescence band, quenching of deep level emission in the visible spectral range and increase of optical band gap from 3.24 to 3.45 eV. The strongest effect of methane has been found for electrical resistivity that reduced by 3 orders of magnitude in comparison with films deposited in pure argon. Additionally, electrical conductance of the ZnO film deposited at high methane concentration does not depend on measurement temperature. Hall method with combination with Van der Pauw resistivity measurements shows: strong n-type doping of the film; donor concentration more than 1020 cm-3 slightly depending on methane concentration; maximum electron mobility about 7 cm2/V s. The direct comparison of resistivity and donor concentration of the films deposited using methane and molecular hydrogen as doping precursors has demonstrated that doping efficiency of methane is about an order of magnitude larger than that of molecular hydrogen under similar deposition conditions. On the other hand, methane addition in working gas resulted in an intensity decrease of the E2L (100 cm-1) and E2H (438 cm-1) lines in the RSS that can be associated with some disturbance of the ZnO structure. Additionally a peak at 71 cm-1 was observed in some films that can be related to the metallic Zn. The possible mechanisms of the ZnO film formation, nature of the doping and electron transport mechanisms will be discussed.

Heterologous Expression of Cyclodextrin Glycosyltransferase my20 in Escherichia coli and Its Application in 2-O-α-D-Glucopyranosyl-L-Ascorbic Acid Production.

In this study, the cgt gene my20, which encodes cyclodextrin glycosyltransferase (CGTase) and was obtained by the metagenome sequencing of marine microorganisms from the Mariana Trench, was codon optimized and connected to pET-24a for heterologous expression in Escherichia coli BL21(DE3). Through shaking flask fermentation, the optimized condition for recombinant CGTase expression was identified as 20°C for 18 h with 0.4 mM of isopropyl β-D-L-thiogalactopyranoside. The recombinant CGTase was purified by Ni2+-NTA resin, and the optimum pH and temperature were identified as pH 7 and 80°C, respectively. Activity was stable over wide temperature and pH ranges. After purification by Ni2+-NTA resin, the specific activity of the CGTase was 63.3 U/mg after 67.3-fold purification, with a final yield of 43.7%. In addition, the enzyme was used to transform L-ascorbic acid into 2-O-α-D-glucopyranosyl-L-ascorbic acid (AA-2G). The maximal AA-2G production reached 28 g/L, at 40°C, pH 4, 24 h reaction time, 50 g/L donor concentration, and 50 U/g enzyme dosage. The superior properties of recombinant CGTase strongly facilitate the industrial production of AA-2G.

Tunable tunnel barriers in a semiconductor via ionization of individual atoms

We report scanning tunneling microscopy (STM) studies of individual adatoms deposited on an InSb(110) surface. The adatoms can be reproducibly dropped off from the STM tip by voltage pulses, and impact tunneling into the surface by up to ∼100×. The spatial extent and magnitude of the tunneling effect are widely tunable by imaging conditions such as bias voltage, set current and photoillumination. We attribute the effect to occupation of a (+/0) charge transition level, and switching of the associated adatom-induced band bending. The effect in STM topographic images is well reproduced by transport modeling of filling and emptying rates as a function of the tip position. STM atomic contrast and tunneling spectra are in good agreement with density functional theory calculations for In adatoms. The adatom ionization effect can extend to distances greater than 50 nm away, which we attribute to the low concentration and low binding energy of the residual donors in the undoped InSb crystal. These studies demonstrate how individual atoms can be used to sensitively control current flow in nanoscale devices.

Microneedle-mediated transdermal delivery of naloxone hydrochloride for treatment of opioid overdose

Naloxone (NAL) is administered parenterally or intranasally for treating opioid overdose. The short duration of action of NAL calls for frequent re-dosing which may be eliminated by the development of a transdermal system. This study aimed to assess the effect of microneedles on improving the skin permeation of NAL hydrochloride. In vitro permeation of NAL across intact and microneedle-treated (Dr. Pen™ Ultima A6) porcine skin was evaluated. The effect of microneedle length and application duration, and donor concentration on NAL permeation were investigated. In-vitro in-vivo correlation of the permeation results was done to predict the plasma concentration kinetics of NAL in patients. In vitro passive permeation of NAL after 6 h was observed to be 8.25±1.06 µg/cm2. A 56- and 37-fold enhancement was observed with 500 and 250 µm needles applied for 1 min, respectively. Application of 500 µm MNs for 2 min significantly reduced the lag time to ~ 8 min and increasing the donor concentration for the same treatment group doubled the permeation (p < 0.05). Modeling simulations demonstrated the attainment of pharmacokinetic profile of NAL comparable to those obtained with the FDA-approved intramuscular and intranasal devices. Microneedle-mediated transdermal delivery holds potential for rapid and sustained NAL delivery for opioid overdose treatment.

Charge and spin transport over record distances in GaAs metallic n -type nanowires

We have investigated charge and spin transport in $n$-type metallic GaAs nanowires ($\ensuremath{\approx}{10}^{17}\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$ doping level) grown by hydride vapor phase epitaxy (HVPE) on Si substrates. For this doping level, charge and spin transport might appear difficult because of the expected localization of minority holes in the valence band potential fluctuations generated by statistical fluctuations of the donor concentration. In contrast with these expectations, it is found, using spatially and spectrally resolved investigation of the luminescence intensity and circular polarization under laser excitation, that (i) establishment of a charge thermodynamic equilibrium between the photoelectrons and the Fermi sea occurs over a distance from the excitation spot of $2\phantom{\rule{0.28em}{0ex}}\ensuremath{\mu}\mathrm{m}$. At this distance, the spin polarization is still observed, implying that photoelectrons have preserved their spin orientation and that the two spin reservoirs remain distinct. (ii) Charge can be transported over record distances larger than $20\phantom{\rule{4pt}{0ex}}\ensuremath{\mu}\mathrm{m}$ at 6 K. (iii) Spatially-resolved investigations show that a photoelectron spin polarization of $20%$ can be transported over a record distance of more than $20\phantom{\rule{0.28em}{0ex}}\ensuremath{\mu}\mathrm{m}$. This long distance transport occurs because of the presence of large internal electric fields of ambipolar origin, further enhanced by the spatial redistribution of the Fermi sea. These findings have potential applications for long distance spin transport in $n$-type doped nanowires.

Electrical properties and structural defects of p-type GaN layers grown by halide vapor phase epitaxy

The electrical properties and structural defects of p-type GaN layers with Mg concentrations from 8.0 × 1018 to 8.3 × 1019 cm−3 grown by halide vapor phase epitaxy (HVPE) were investigated. In all samples, p-type conduction was confirmed at room temperature. The hole concentration at room temperature decreased in a heavily Mg-doped sample. By analyzing the results of Hall-effect measurements at various temperatures, the acceptor concentration decreased in a heavily Mg-doped sample, whereas the compensating donor concentration increased. These results affect the decrease in the hole concentration. The hole mobility decreased with increasing acceptor concentration. In the heavily Mg-doped sample, pyramidal inversion domains (PIDs) were formed. The size of each PID in an HVPE-grown sample is in good agreement with that Mg-doped GaN layers grown by metalorganic vapor phase epitaxy (MOVPE). Thus, the formation mechanism of PIDs in HVPE-grown samples is possibly the same as that in MOVPE-grown samples. Energy-dispersive X-ray spectroscopy shows that Mg atoms accumulate in PIDs, which suggests that Mg atoms in PIDs are electrically inactive, inhibiting the increase in the acceptor concentration. These results are useful guidelines for fabricating p-type GaN layers with higher hole concentrations by HVPE.

Extracellular electron transfer influences the transport and retention of ferrihydrite nanoparticles in quartz sand coated with Shewanella oneidensis biofilm

Microbial biofilm has been found to impact the mobility of nanoparticles in saturated porous media by altering physicochemical properties of collector surface. However, little is known about the influence of biofilm’s biological activity on nanoparticle transport and retention. Here, the transport of ferrihydrite nanoparticles (FhNPs) was studied in quartz sands coated with biofilm of Shewanella oneidensis MR-1 that is capable of reducing Fe(III) through extracellular electron transfer (EET). It was found that MR-1 biofilm coating enhanced FhNPs’ deposition under different pH/ionic strength conditions and humic acid concentrations. More importantly, when the influent electron donor (glucose) concentration was increased to promote biofilm’s EET activity, the breakthrough of FhNPs in biofilm-coated sands was inhibited. A lack of continuous and stable supply of electron donor, on the contrary, led to remobilization and release of the originally retained FhNPs. Column experiments with biofilm of EET-deficient MR-1 mutants (ΔomcA/ΔmtrC and ΔcymA) further indicated that the impairment of EET activity decreased the retention of FhNPs. It is proposed that the effective surface binding and adhesion of FhNPs that is required by direct EET cannot be neglected when evaluating the transport of FhNPs in sands coated with electroactive biofilm.

Stemness of Human Pluripotent Cells: Hypoxia-Dependent Effect of Nitric Oxide

Optimization of conditions to promote in vitro the stemness of pluripotent cells is instrumental for their use in advanced therapies. We show here that exposure of human (iPSC) and human (ESC) to low concentrations of the chemical NO donor DETA/NO leads to stabilization of hypoxia-inducible factors (HIF-1α and HIF-2α) under normoxia, this effect being dependent on diminished Pro 402 hydroxylation and decreased degradation by the proteasome. Moreover, the master genes of pluripotency NANOG and OCT4 were upregulated. NO also induces a shift in the metabolic profile of PSCs with increased expression of hypoxia response genes in glycolysis. Furthermore, a reduction in the mitochondrial membrane potential with lower oxygen consumption and increased expression of mitochondrial fusion regulators, such as DRP1 was observed. The results reported here indicate that NO mimics hypoxia response in human PSCs and enhances their stemness properties when cultured under normoxic conditions.

Tunable local and global piezopotential properties of graded InGaN nanowires

Owing to the continuously tunable physical properties, composition-graded wurtzite nanowires (NWs) recently become an attractive class of materials with potential applications in novel nanodevices. In this paper, the piezopotential properties of graded InGaN NWs are studied through multiscale modeling. Our atomic-scale simulations show that the structural and material parameters of graded InGaN NWs are dependent on the NW position, which are well described by the analytic expressions based on the Vegard’s law. The non-uniform distribution of structural and material parameters triggers the flexoelectric effect in graded InGaN NWs that can enhance the polarization components in NWs. The modified electromechanical theory incorporating the flexoelectric effect and analytic expressions of the position-dependent structural and material parameters is employed in the finite element calculations of piezopotential. The piezopotential in graded InGaN NWs is found to be asymmetric to NW center, which is different to the symmetric piezopotential distribution observed in binary wurtzite NWs. Both the local piezopotential and the global piezopotential difference of graded InGaN NWs are enhanced due to the flexoelectric effect, which becomes more significant as the concentration of donors grows. In addition, the piezopotential distribution in graded InGaN NWs can be significantly affected by the length of graded InGaN region, while it almost has no influence on the piezopotential difference. However, both the local piezopotential and the global piezopotential difference of graded InGaN NWs can be greatly enhanced by increasing the maximum In composition. • Piezopotential of graded InGaN NWs is studied by multiscale modeling technique. • Material properties of graded InGaN NWs depend on the NW position. • Flexoelectric effect can increase the piezopotential of graded InGaN NWs. • Graded InGaN NWs have tunable local and global piezopotential properties.

Cholesterol Disrupts H 2 S‐Mediated Vasodilation in Large Arteries

Small resistance size arteries are key players in vascular resistance and overall blood pressure control. We previously demonstrated that within endothelial cells (EC), H2S-mediated vasodilation involves activation of transient receptor potential cation channel subfamily V member 4 (TRPV4)-dependent Ca2+ influx to activate nearby large-conductance Ca2+-activated potassium (BK) channel in resistance-size arteries. Comparison of vasodilatory responses in large and small (resistance-size) arteries show that small arteries dilate at lower concentrations of H2S donors vs large arteries. The importance of endogenous H2S in endothelium-dependent vasodilatory responses in small resistance size arteries highlights a role for H2S in regulating blood pressure and flow. However, little is known of the differences in H2S signaling in large and small arteries and how these differences modulate vasodilation. Based on previous reports that cell membrane cholesterol negatively regulates TRPV4 mobility and BK activity, we hypothesized that H2S-mediated vasodilation is disrupted by elevated EC membrane cholesterol in large arteries. We first verified EC plasma membrane cholesterol content was higher in large vs small arteries by immunofluorescence using the cholesterol stain, filipin III (20 µg/ml) in EC labeled with the glycocalyx marker tomato lectin (20 µg/ml) and the nuclear stain SYTOX green (large 145.20 ± 13.67, small: 59.85 ± 5.50, p = 0.0004, n = 5 animals/group). Next, we examined the effect of cholesterol depletion using methyl β cyclodextrin (MBCD, 100 μM), on dilatory responses to H2S in large (300-380 μm) and small (60-130 μm) mesenteric arteries using the H2S donor, NaHS (1, 10 or 100 μM). In large arteries, MBCD pretreatment significantly enhanced H2S-mediated vasodilation (10 μM +vehicle: 0.72% ± 2.17, +MBCD: 9.71% ± 2.710, p = 0.026), (100 μM +vehicle: 2.25% ± 5.74, +MBCD: 20.55% ± 7.687, p < 0.0001) n = 5 animals/group. Although NaHS dilated small arteries more than large arteries, there was no effect of cholesterol depletion in small arteries (1 μM +vehicle: 16.25% ± 2.36, +MBCD: 16.29% ± 4.44, NS), (10 μM +vehicle: 33.22% ± 7.10, +MBCD: 39.00% ± 5.85, NS), (100 μM +vehicle: 59.84% ±5.98, +MBCD: 63.18% ± 4.639, NS) n = 3 animals/group. Additionally, immunofluorescence studies of EC TRPV4 expression showed no difference between large and small arteries (large 39.6 ± 12.9, small 41.8 ± 14.1, NS) n =3 animals/group. These studies suggest that membrane cholesterol disrupts H2S-mediated vasodilation and contributes to the relative differences in sensitivity to H2S-mediated vasodilation in large and small arteries.

Curie–Weiss behavior of the low-temperature paramagnetic susceptibility of semiconductors doped and compensated with hydrogen-like impurities

For the first time, a quantitative model of the Curie–Weiss behavior of a low-temperature paramagnetic susceptibility of electrically neutral donors in n-type diamagnetic covalent semiconductors is proposed. The exchange interaction between nearest two neutral donors was calculated with the use of the Heitler–London model. In this model, we take into account the change in the thermal ionization energy of donors due to the shift of the bottom of the conduction band to the bandgap with doping and compensation. The energy of the exchange spin–spin interaction between electrons localized on donors is calculated as a function of the donor concentration and the degree of their compensation by acceptors. The broadening of the donor band due to the Coulomb interaction of the nearest impurity ions was taken into account. We considered crystals of n-type germanium doped with arsenic up to the concentration close to the insulator–metal phase transition (Mott transition) and compensated with gallium. The compensation ratio K is the ratio of the concentration of compensating acceptors KN to the concentration of doping donors N. The model predicts a change in the sign of the Curie–Weiss temperature from minus to plus (a transition from the antiferromagnetic to ferromagnetic local ordering of electron spins on donors) for K ≈ 0.15–0.3, reaching its maximum positive values of ≈1.3 K for K ≈ 0.5 with the following decrease (a transition to paramagnetism) for K &amp;gt; 0.85. The calculated behavior of the paramagnetic susceptibility of donors is consistent with the experimental data for compensated n-Ge:As,Ga samples close to the Mott transition.