Excess Resistance Research Articles

GC-ToF-MS Profiling and In Vitro Inhibitory Effects of Selected South African Plants against Important Mycotoxigenic Phytopathogens.

The harmful effects following the ingestion of mycotoxin-contaminated food include the induction of cancers, mutagenicity, immune suppression, and toxicities that target organs of the digestive, cardiovascular, and central nervous systems. Synthetic fungicides are generally associated with a high toxic residue in food and the development of excessive fungal resistance. This study aimed to determine the antifungal activities against mycotoxigenic fungi of selected South African plant leaves and potentially develop plant-derived bio-fungicides, and, furthermore, to explore the in vitro antioxidant activity and the phytochemical spectra of the compounds of the selected medicinal plant extracts. The extracts were tested for antifungal activity against phytopathogenic strains using a microdilution broth assay. Bauhinia galpinii extracts exhibited the lowest minimum inhibitory concentration (MIC) against C. cladospoides and P. haloterans at 24 h incubation periods. C. caffrum had good antioxidant activity against 2,2-diphenyl-1-picrylhydrazyl (DPPH) with 50% inhibitory concentration (IC50) values of 0.013 mg/mL while B. galpini had IC50 values of 0.053 against free radicals of 2,2'-azinobis (3-ethylbenzthiazoline-6-suphonic acid (ABTS). The antimycotoxigenic and antioxidant activity exerted by both B. galpinii and C. caffrum may well be attributed to high TPC. In the GC-ToF-MS analysis, all the selected medicinal plants exhibited the presence of Hexadecanoic acid at varying % areas, while both B. galpinii and C. caffum exhibited the presence of lupeol at % area 2.99 and 3.96, respectively. The compounds identified, particularly the ones with higher % area, may well explain the biological activity observed. Although the selected medicinal plants exhibited a notable biological activity, there is a need to explore the safety profiles of these plants, both in vitro and in vivo.

Rational Design of High-Performance Nanomaterials for Electric Vehicle Tires

In today's society, the market limitations of electric vehicle tires are relatively poor wear resistance and rolling resistance. These two problems restrict the further development of electric vehicles, accelerate energy consumption and environmental pollution, and bring hidden dangers to users. In this paper, the principle of tire wear resistance and the cause of excessive rolling resistance related to tire deformation are analyzed from the perspective of materials. At present, these two problems can be improved by adding nanomaterials to automobile tire materials (natural rubber and synthetic rubber). The tire's thermal conductivity and wear resistance can be improved by inserting Silica and a small amount of nano-diamond. This paper will also discuss the unique advantages of carbon black with different particle sizes as filler by analyzing the effects of modified Silica and carbon black on the molecular rubber chain. On this basis, this paper will also explain the drawbacks of nanofiller materials.

Pigment Epithelium-Derived Factor, a Novel Adipokine, Contributes to Gestational Diabetes Mellitus.

Excessive insulin resistance, inadequate insulin compensation, or both could result in gestational diabetes mellitus (GDM). Levels of pigment epithelium-derived factor (PEDF), a novel adipokine that could induce insulin resistance, are high in patients with obesity and diabetes. However, the impact of PEDF in pregnancy remains unknown. This study aimed to elucidate the role of PEDF on insulin resistance and compensatory elevation of insulin levels during normal pregnancy and in patients with GDM. In this population-based and cohort study, logistic regression analysis was performed to determine the association of PEDF/adiponectin/leptin levels with the risk of developing GDM and to predict postpartum prediabetes. PEDF protein, PEDF transgenic mice, PEDF knockout mice, and PEDF-neutralized antibodies were used to observe changes in insulin resistance and insulin levels with pregnancy. Plasma PEDF levels were increased in normal pregnancy and higher in GDM women. Higher PEDF levels were associated with the increased risk of developing GDM and emerged as a significant independent determinant of postpartum prediabetes in GDM women. Mechanistically, in vivo and in vitro experiments revealed that PEDF induced insulin resistance by inhibiting the insulin signaling pathway. In addition to insulin resistance and upregulated insulin levels in normal pregnancy and GDM, aberrant PEDF levels can serve as a "fingerprint" of metabolic abnormalities during pregnancy. Thus, PEDF is a valuable biomarker but could interfere with the time course for early diagnosis and prognosis of GDM.

Inhibiting Polyamide Intrusion of Thin Film Composite Membranes: Strategies and Environmental Implications.

Thin film composite polyamide (TFC) nanofiltration (NF) membranes represent extensive applications at the water-energy-environment nexus, which motivates unremitting efforts to explore membranes with higher performance. Intrusion of polyamide into substrate pores greatly restricts the overall membrane permeance because of the excessive hydraulic resistance, while the effective inhibition of intrusion remains technically challenging. Herein, we propose a synergetic regulation strategy of pore size and surface chemical composition of the substrate to optimize selective layer structure, achieving the inhibition of polyamide intrusion effective for the membrane separation performance enhancement. Although reducing the pore size of the substrate prevented polyamide intrusion at the intrapore, the membrane permeance was adversely affected due to the exacerbated "funnel effect". Optimizing the polyamide structure via surface chemical modification of the substrate, where reactive amino sites were in situ introduced by the ammonolysis of polyethersulfone substrate, allowed for maximum membrane permeance without reducing the substrate pore size. The optimal membrane exhibited excellent water permeance, ion selectivity, and emerging contaminants removal capability. The accurate optimization of selective layer is anticipated to provide a new avenue for the state-of-the-art membrane fabrication, which opens opportunities for promoting more efficient membrane-based water treatment applications.

Influence of outrigger truss system on the seismic fragility of super high-rise braced mega frame-core tube structure

The braced mega frame-core tube (BMFCT) structure is an efficient seismic structural system for super high-rise buildings of over 500 m high. The outrigger truss (OT) system has become a commonly adopted design option for the super high-rise BMFCT structure, however, its influence on the seismic performance is not clear. In this study, the seismic responses and collapse risks of the 590-m-high BMFCT structures with and without OT system were analyzed. An efficient elasto-plastic modeling method was introduced to establish the accurate FE models. Based on the incremental dynamic analysis-based (IDA) fragility analysis, the deformation responses, energy dissipations, collapse risks and collapse resistance capacities, etc. were researched. The results indicate the average top displacements under earthquakes of ‘one-degree-higher’ rare intensities are reduced by the OT from 1286.51 mm to 1348.31 mm by 4.6%. The OT system can effectively limit the story drift ratios of the BMFCT under earthquakes with the lower intensity. With the increasing seismic intensity, the OT presents an unfavorable effect on the lateral deformations. The OT system increases the proportion of damping energy dissipation from 68.28% to 70.24%, and decreases that of plastic deformation energy dissipation from 20.74% to 20.12%, both by less than 2%. The OT system causes the slope of IDA curves to rise first and then fall, which is the opposite of that without OT. The OT system is detrimental to the structural collapse resistance capacity, reducing the collapse margin ratio from 8.46 to 7.41 by about 14%. The OT's function can effectively reduce the cross-sectional dimensions of main components and ensure the architectural functionality and view-transparency. In the seismic design of BMFCT structures, the OT system should be given more attention, especially in the earthquakes stronger than rare intensity, and recommended to be designed to meet the basic structural stiffness requirement and not to provide excessive lateral stiffness resistance.

The DEAD-box RNA helicase, DDX60, Suppresses immunotherapy and promotes malignant progression of pancreatic cancer

Excessive proliferation, invasion, metastasis, and immune resistance in pancreatic cancer (PC) makes it one of the most lethal malignant tumors. Recently, DDX60 was found to be involved in the development of various tumors and in immunotherapy. Therefore, we aimed to investigate whether DDX60 is a new factor involved in PC immunotherapy. The DDX60 mRNA was screened using transcriptome sequencing (RNA-seq). The Cox and survival analysis of DDX60 was performed using the Gene Expression Omnibus (GEO) and The Cancer Genome Atlas (TCGA) databases. In addition, clinical and immune infiltration data in the databases were analyzed and plotted using the R language. Clinical samples and in vitro experiments were used to determine the molecular evolution of DDX60 during PC progression. We found that DDX60 was upregulated in PC tissues (P value = 0.0083) and was associated with poor prognosis and short survival time of patients with PC. Results of Gene Ontology, Kyoto Encyclopedia of Genes and Genomes, and gene set variation analyses showed that viral defense, tumor, and immune-related pathways were significantly enriched in samples with high DDX60 expression. The Pearson correlation test demonstrated that DDX60 expression correlated strongly with immune checkpoint and immune system-related metagene clusters. Our results indicated that DDX60 promoted cell proliferation, migration, and invasion and was related to poor prognosis and immune resistance. Therefore, DDX60 may be a promising novel target for PC immunotherapy.

Genome-wide association studies categorized by class of anti-hypertensive drugs reveal complex pathogenesis of hypertension with drug resistance.

Resistant hypertension is defined as uncontrolled blood pressure despite the use of three or more anti-hypertensive drugs of different classes. Though genetic factors may greatly contribute to hypertension with resistance to multiple drug classes, more than for general hypertension, its pathogenesis remains unknown. To reveal the genetic background of resistant hypertension, we categorized 32,239 patients whose data were obtained from the BioBank Japan Project, by prescription of seven classes of anti-hypertensive drugs and performed genome-wide association studies. Our genome-wide association studies identified four loci with significant association (P < 5×10-8 ): rs6445583 in CACNA1D and rs12308051 in the intergenic region on chromosome 12 for ARBs, rs35497065 in FOXA3 for CCBs, and rs11066280 in HECTD4 for α-blockers. Since these loci are known to be susceptibility loci for hypertension and/or blood pressure, our results indicate that resistant hypertension is caused by a combination of excessive blood pressure and drug resistance to each anti-hypertensive pharmacological class. Furthermore, to investigate the genetic difference between BP traits and the treatment effectiveness of anti-hypertensive drugs, we performed gene-set analysis and calculated the genetic correlation continuously. Most of the genetic factors were in common between BP traits and anti-hypertensive effectiveness, but it seems that the genetic architecture of the drug response to anti-hypertensive treatment is more complicated than BP traits. This corresponds to the well-known mosaic theory of hypertension. Our findings reveal the complex pathogenesis of hypertension with resistance to multiple classes of anti-hypertensive drugs.

Homogenizing fluid transport in stratified porous media using an elastic flow instability

Many key environmental, industrial and energy processes rely on controlling fluid transport within subsurface porous media. These media are typically structurally heterogeneous, often with vertically layered strata of distinct permeabilities – leading to uneven partitioning of flow across strata, which can be undesirable. Here, using directin situvisualization, we demonstrate that polymer additives can homogenize this flow by inducing a purely elastic flow instability that generates random spatio-temporal fluctuations and excess flow resistance in individual strata. In particular, we find that this instability arises at smaller imposed flow rates in higher-permeability strata, diverting flow towards lower-permeability strata and helping to homogenize the flow. Guided by the experiments, we develop a parallel-resistor model that quantitatively predicts the flow rate at which this homogenization is optimized for a given stratified medium. Thus, our work provides a new approach to homogenizing fluid and passive scalar transport in heterogeneous porous media.

Glucocorticoid excess and insulin resistance in aged spontaneously hypertensive rats/stroke-prone

Vascular diseases cause chronic cerebral hypoperfusion and neuronal injury and are the second most common cause of dementia. A significant cause of chronic cerebral hypoperfusion is hypertension. Insulin resistance is an important risk factor for hypertension. Aside from age, insulin resistance is also the most important risk factor for the development of dementia. While Insulin resistance is considered an important risk factor for the development of hypertension and dementia, little consideration has been given to the idea that hypertension could initiate insulin resistance and fuel a destructive cycle that hastens dementia. We hypothesized that hypertension initiates insulin resistance through sustained activation of the hypothalamic-pituitary-adrenal axis. To test this hypothesis, we measured corticosterone and the expression of steroid biosynthetic genes in six-month-old spontaneously hypertensive rat/stroke-prone (SHRSP) and normotensive Sprague Dawley (SD) rats. To measure glycemic control, rats were subjected to glucose tolerance and insulin tolerance tests. SHRSP were hypertensive and cognitively impaired. SHRSPs had increased corticosterone compared to SD (Male SD vs. SHRSP: 167±29 pg/g vs.1091±166 pg/g, P&lt;0.0001; Female SD vs. SHRSP: 134±19 pg/g vs. 376±47 pg/g, P=0.0017). Adrenal CYP11B1 mRNA expression was increased in SHRSP (Males 14.44±1.44, P=0.0009; Females 710±59, P=0.0016). STARD1 mRNA expression provided a marker of HPA negative feedback. Male SHRSPs had decreased STARD1 mRNA expression (0.56±0.09, P = 0.0217). However, female SHRSPs had increased STARD1 mRNA expression (12.5± 2.25, P=0.0028). Female, but not male, SHRSPs had increased fasting blood glucose, decreased fasting insulin, and reduced rates of glucose clearance (SD vs. SHRSP: 73±6 vs. 92±4 mg/dL glucose, P=0.0045; 33±2.0 vs. 12±5 pmol/L insulin, P=0.0111; AUC 185±37 vs. 279±27 mg/dL/h, P=0.0368). When fasting rats were challenged with insulin, both male and female SHRSPs had decreased clearance of glucose compared to SDs (Male SD vs. SHRSP AUC 87 ± 2 vs. 58 ± 4 mg/dL/h, P&lt; 0.0001, Female SD vs. SHRSP AUC 82 ± 2 vs. 68 ± 3 mg/dL/h, P=0.0007). These results indicate that hypertension is associated with impaired HPA function and insulin resistance, with female SHRSP succumbing faster to hyperglycemia than males. Alzheimer's Association Research Fellowship This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

A CASE CONTROL STUDY TO ASSESS C-REACTIVE PROTEIN/ALBUMIN RATIO IN WOMEN WITH AND WITHOUT POLYCYSTIC OVARIAN SYNDROME

A. AIM &amp; OBJECTIVE: To compare C-reactive protein/Albumin ratio in women with or without polycystic ovarian syndrome. The present study is a hospital based comparative study conducted SMS B. METHODOLOGY: Medical College, Jaipur Rajasthan. Total 168 subjects divided into two groups with case comprising of 84 subjects diagnosed on the basis of Rotterdam's criteria and 84 controls. The study aimed to nd CRP/Albumin ratio in women with and without PCOS. Mean CRP/albumin ratio C. RESULT: was higher in PCOS cases (0.437 ± 0.222) as compared to controls (0.086 ± 0.112). A high AUC of 0.861 suggest that CRP is a good marker of PCOS (p&lt;0.001). At a cutoff value for CRP &gt; 9.15 mg/dl, it identied PCOS with a sensitivity of73.8% and specicity of 83.3%. The AUC for CRP/Albumin Ratio was higher (AUC=0.890), indicating that CRP/Albumin Ratio is a good marker of PCOS (p&lt;0.001). At a cutoff value for &gt; 0.103, CRP/Albumin Ratio identied PCOS with a sensitivity of 77.4% and specicity of 90.5%. CRP/albumin ratio, a D. CONCLUSION: marker for inammation related to metabolic dysfunction, was found to have a stronger association with PCOS than either androgen excess or Insulin resistance. Inammation is known to be inuenced by adiposity, but relative to controls, women with PCOS have higher levels of CRP/albumin ratio irrespective of BMI. This supports the view that inammation may play a central role in the pathophysiology of PCOS.

Targeting a novel apoptotic pathway in human disease.

Apoptotic pathways have always been regarded as a key-player in preserving tissue and organ homeostasis. Excessive activation or resistance to activation of cell death signaling may indeed be responsible for several mechanisms of disease, including malignancy and chronic degenerative diseases. Therefore, targeting apoptotic factors gained more and more attention in the scientific community and novel strategies emerged aimed at selectively blocking or stimulating cell death signaling. This is also the case for the TMEM219 death receptor, which is activated by a circulating ligand, the Insulin-like growth factor binding protein 3 (IGFBP3) and induces a caspase-8-dependent apoptosis of the target cells. Interestingly, stimulation of the IGFBP3/TMEM219 axis exerts an anti-proliferative effect, while blockade of the TMEM219 deleterious signal protects TMEM219-expressing cells of the endocrine pancreas, lung, and intestine from damage and death. Here, we summarize the most updated reports on the role of the IGFBP3/TMEM219 apoptotic axis in disease conditions, including intestinal disorders and diabetes, and we describe the advancements in designing and testing novel TMEM219-based targeting approaches in emerging potential clinical applications.

Sulfonated graphene oxide-based pervaporation membranes inspired by a tortuous brick and mortar structure for enhanced resilience against silica scaling and organic fouling

A novel tortuous brick-and-mortar structure utilizing intercalation of polyvinyl alcohol (PVA) on sulfonated graphene oxide (SGO) membranes was specifically tailored for brine treatment by pervaporation to ensure excessive resistance to silica scaling and organic fouling, as well as ultrafast water transport without compromising salt rejection. The synthesized SGO membrane showed a smoother surface morphology, improved zeta potential, and a higher hydration capacity than the graphene oxide (GO) membrane. Further intercalation of PVA through glutaraldehyde (GA) crosslinking, confirmed by Fourier transform infrared spectroscopy and X-ray diffraction analysis, conferred increased cohesiveness, and the SGO-PVA-GA membrane was therefore able to withstand ultrasonication tests without any erosion of the coating layer. According to a pervaporative desalination test, the SGO-PVA-GA membrane exhibited 62 kg m−2 h−1 of permeate flux, with an extraordinary salt rejection of 99.99% for a 10 wt% NaCl feed solution at 65 °C. The 72 h organic fouling, silica scaling, and combined fouling and scaling tests proved that the SGO-PVA-GA membrane sustains a stable flux with less scaling and fouling than the GO-PVA-GA membrane, attributable to dense surface negative charges and great hydration capacities caused by sulfonic acid. Thus, the SGO-PVA-GA membrane offers superlative advantages for long-term brine treatment by pervaporation, related to its ability to withstand silica scaling and organic fouling.

Serving Two Masters: Effect of Escherichia coli Dual Resistance on Antibiotic Susceptibility

The prevalence of multidrug-resistant bacteria and their increased pathogenicity has led to a growing interest in metallic antimicrobial materials and bacteriophages as potential alternatives to conventional antibiotics. This study examines how resistance to excess iron (III) influences the evolution of bacteriophage resistance in the bacterium Escherichia coli. We utilized experimental evolution in E. coli to test the effect of the evolution of phage T7 resistance on populations resistant to excess iron (III) and populations without excess iron resistance. Phage resistance evolved rapidly in both groups. Dual-resistant (iron (III)/phage) populations were compared to their controls (excess iron (III)-resistant, phage-resistant, no resistance to either) for their performance against each stressor, excess iron (III) and phage; and correlated resistances to excess iron (II), gallium (III), silver (I) and conventional antibiotics. Excess iron (III)/phage-resistant populations demonstrated superior 24 h growth compared to all other populations when exposed to increasing concentrations of iron (II, III), gallium (III), ampicillin, and tetracycline. No differences in 24 h growth were shown between excess iron (III)/phage-resistant and excess iron (III)-resistant populations in chloramphenicol, sulfonamide, and silver (I). The genomic analysis identified selective sweeps in the iron (III) resistant (rpoB, rpoC, yegB, yeaG), phage-resistant (clpX →/→ lon, uvaB, yeaG, fliR, gatT, ypjF, waaC, rpoC, pgi, and yjbH) and iron (III)/phage resistant populations (rcsA, hldE, rpoB, and waaC). E. coli selected for resistance to both excess iron (III) and T7 phage showed some evidence of a synergistic effect on various components of fitness. Dual selection resulted in correlated resistances to ionic metals {iron (II), gallium (III), and silver (I)} and several conventional antibiotics. There is a likelihood that this sort of combination antimicrobial treatment may result in bacterial variants with multiple resistances.

Don't sugar coat it: The independent and synergistic impacts of obesity and gestational diabetes on placental parameters.

Don't sugar coat it: The independent and synergistic impacts of obesity and gestational diabetes on placental parameters.

Intermittent fasting for the management of NAFLD: Is there enough evidence?

Abstract The pathogenesis of the non-alcoholic fatty liver disease (NAFLD) has been described as multifactorial, with genetic and environmental factors acting synergistically and causing excessive hepatic lipid accumulation, insulin resistance, and downstream pathogenetic insults. High-calorie diets, particularly those rich in foods with high (saturated) fat and sugar content, and sugar-sweetened beverages, are among the behavioral risk factors with a crucial role in the disease pathogenesis. In addition, meal frequency and meal timing appear to be relevant factors associated with NAFLD. Current guidelines recommend a hypocaloric, preferably Mediterranean diet as the main dietary intervention approach, but various other dietary models have been evaluated in patients with NAFLD. Among these, several intermittent fasting regimens have shown promising results. Diets based on Time-Restricted Feeding and Intermittent Energy Restriction have demonstrated some improvements in body adiposity, liver enzymes, and hepatic steatosis, but most studies included a small number of subjects, were of relatively short-duration, and used surrogate markers of NAFLD. The best intermittent fasting regimen for NAFLD is not yet known, and further well-designed research that evaluates the feasibility (mainly on long-term), safety and efficacy outcomes of these dietary interventions is still needed. Our review has evaluated the up-to-date information regarding the intermittent fasting dietary intervention in NAFLD and generated some key-point messages that are relevant to physicians and dietitians involved in the care of patients with NAFLD.

Hydrogen‐Bond‐Mediated Surface Functionalization of Boron Nitride Micro‐Lamellae toward High Thermal Conductive Papers

AbstractWide‐bandgap, layered hexagonal boron nitride (h‐BN) possesses excellent electrical insulation and ultrahigh thermal conductivity simultaneously, offering a perfect candidate for the growing demands of heating dissipations in modern chip industries and power electronics. Hybrids of h‐BN with polymers fulfill the thermal management materials (TMMs) requirement of flexibility, while the composite poses severe challenges in the interfacial bonding and excess thermal resistance. To date, the practical bonding between h‐BN intrinsic surfaces and polymer matrices remains elusive. This work reports on the effective alignment of h‐BN micro‐lamellae by introducing nitrogen‐atoms‐containing polymers as inter‐lamellae bridging mediums. Based on theoretical calculations the hydrogen bonding between polymer chains and the BN surface is revealed by differential charge densities mapping. It is shown experimentally that the neuron‐like polymer bundles strongly bonding surfaces of two neighboring h‐BN platelets as direct, microscopic evidence of the structure models. An extra alignment of h‐BN induced by this strong interfacial interaction leads to a higher degree of h‐BN stacking order, boosting the thermal conduction by eight times. These results reveal one unprecedented method to non‐covalently functionalize the h‐BN surface and expand the TMMs family in the dimension of the filler size, paving the way for exploring the larger‐sized ceramic TMMs.

Basal boundary conditions for granular surface flows over fragile and brittle erodible beds

Many granular surface flows occur as shear flows of finite thickness, over erodible beds composed of the same granular material. Such beds may be fragile, and offer no more resistance to erosion than to sustained shear. Or they may be brittle, and offer instead an excess resistance to erosion. To take this contrast into account, new basal boundary conditions are proposed. Their implications for parallel flows down infinite slopes are then examined for three different cases: stationary flows; starting; and stopping transients. For all three cases, flow behaviour is altered significantly when beds present an excess resistance to erosion. For stationary flows, non-unique velocity profiles are obtained, implying hysteresis or history-dependence. For starting transients, a power law growth of the flow thickness is predicted, instead of the jump to finite or infinite depth that would otherwise occur. For stopping transients, flows start to decelerate with a finite basal shear rate, even over erodible substrates. Analytical solutions to the corresponding free and moving boundary problems are obtained, and checked against numerical results. Model predictions are then compared with experimental measurements. Overall, good agreement is obtained. In particular, the model describes well the very different erosional responses observed for fragile and brittle beds.

Study on Polypropylene Twisted Bundle Fiber Reinforced Lightweight Foamed Concrete

Recent industrial developments have focused more and more on the applications of lightweight foamed concrete (LFC) in the construction industry, having advantages over normal-strength concrete. LFC, however, has several drawbacks including brittleness, high porosity, excessive drying shrinkage, rapid cracking, and low deformation resistance. Practical engineering typically chooses steel fiber or polymer fiber to increase the tensile and fracture resistance of LFC. The polypropylene twisted bundle fiber (PTBF) was added to the LFC with varying weight fractions of 0.0%, 0.5%, 1.0%, 1.5%, 2.0% and 2.5%. Three low densities of LFC were prepared, specifically 500 kg/m3, 700 kg/m3 and 900 kg/m3. The mechanical and durability properties of PTBF-reinforced LFC were determined through compression, flexural, splitting tensile, flow table, porosity, and water absorption tests. The results show that the addition of PTBF in LFC significantly improves the strength properties (compressive, flexural, and splitting tensile strengths) and reduces the water absorption capacity and porosity. The optimal weight fraction of PTBF was between 1.5 and 2.0% for mechanical properties enhancement. The inclusion of PTBF increased the ductility of LFC, and the specimens remain intact from loading to failure. The PTBF reduces the original cracks of the LFC and inhibits the development of further cracks in the LFC.

Microwave volt-impedance spectroscopy of semiconductor structure

Microwave voltage-impedance spectroscopy is used to study a semiconductor structure in the form of a doped n-GaAs film grown on a conducting n^+-GaAs substrate with a buffer sublayer. A system of concentric barrier contacts is formed on the structure surface. A technique has been developed for measuring complex impedance spectrum Z(f,U) of the sample as a function of DC bias voltage U. Spectra Z(f,U) were measured using a Cascade Microtech probe station in the frequency range 0.01-40 GHz with a lateral resolution of 15-30 μm at U=0-10 V. The main electrophysical characteristics of a semiconductor film were determined from the spectra: type, concentration and mobility of free charge carriers, electrical conductivity. An excess resistance was found in the range f=0.1-20 GHz. This effect is interpreted as the deep states (traps) recharging for two types of traps --- low-frequency l and high-frequency h with characteristic time tau_l=10-9 s, tau_h=4.2·10-11 s. A model description is proposed that explains the characteristic shape of the trap resistance spectrum, its dependence on the contact area and voltage U. Keywords: microwave band, near field, impedance, semiconductor, barier contact, deep states, electrophysical characteristics.

Микроволновая вольт-импедансная спектроскопия полупроводниковой структуры

Microwave voltage-impedance spectroscopy is used to study a semiconductor structure in the form of a doped n-GaAs film grown on a conducting n+-GaAs substrate with a buffer sublayer. A system of concentric barrier contacts is formed on the structure surface. A technique has been developed for measuring complex impedance spectrum Z(f,U) of the sample as a function of DC bias voltage U. Spectra Z(f,U) were measured using a Cascade Microtech probe station in the frequency range 0.01 – 40 GHz with a lateral resolution of 15 – 30 μm at U = 0 – 10 V. The main electrophysical characteristics of a semiconductor film were determined from the spectra: type, concentration and mobility of free charge carriers, electrical conductivity. An excess resistance was found in the range f = 0.1 – 20 GHz. This effect is interpreted as the deep states (traps) recharging for two types of traps – low-frequency l and high-frequency h with characteristic time τl = 10^(-9) s, τh = 4.2∙10^(-11) s. A model description is proposed that explains the characteristic shape of the trap resistance spectrum, its dependence on the contact area and voltage U.