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排序方式: 共有146条查询结果,搜索用时 15 毫秒
1.
DC and microwave measurements on AlSb/InAs HEMTs with a gate length of 0.21 μm are reported. The reverse gate characteristics exhibit relatively low gate leakage current and gate-drain breakdown voltages as high as 5 V. Equivalent circuit modelling yields an fT of 110 GHz after removal of the gate bonding pad capacitance. The bias dependence of fmax is examined indicating a significant reduction in the unilateral gain due to impact ionisation 相似文献
2.
Miriama Simunkova Zuzana Barbierikova Klaudia Jomova Lenka Hudecova Peter Lauro Saleh H. Alwasel Ibrahim Alhazza Christopher J. Rhodes Marian Valko 《International journal of molecular sciences》2021,22(4)
Kaempferol is a flavonoid that occurs in tea and in many vegetables and fruits, including broccoli, cabbage, beans, grapes, apples, and strawberries. The efficacy of Kaempferol has been demonstrated in the treatment of breast, esophageal, cervical, ovarian, and liver cancers and leukemia, which very likely arises from its prooxidant properties and the activation of pro-apoptotic pathways. Indeed, this matter has already been the focus of a number of published studies and reviews. The aim of the present study was to elucidate the antioxidant vs. prooxidant properties of flavonoids in the presence of the redox-active metal, copper (II) ion, by means of the Fenton reaction. The specific motivation of this work is that, since an increased level of Cu(II) ions is known to be associated with many disease states such as neurological conditions (Alzheimer’s disease) and cancer, any interaction between these ions and flavonoids might affect the outcome of therapeutic uses of the latter. The structure of the Cu-kaempferol complex in DMSO was investigated by means of low temperature EPR spectroscopy, which confirmed the existence of at least two distinct coordination environments around the copper (II) ion. UV vis-spectra of kaempferol and its Cu(II) complex in DMSO revealed an interaction between the 5-OH (A ring) group and the 4-CO (C ring) group of kaempferol with Cu(II) ions. An ABTS assay confirmed that kaempferol acted as an effective radical scavenger, and that this effect was further enhanced in the form of the Cu(II)-kaempferol complex. Quantitative EPR spin trapping experiments, using DMPO as the spin trap, confirmed suppression of the formation of a mixture of hydroxyl, superoxide, and methyl radicals, in a Fenton reaction system, upon coordination of kaempferol to the redox-active Cu(II) ions, by 80% with respect to the free Cu(II) ions. A viscometric study revealed a better DNA-intercalating ability of the Cu-kaempferol complex than for free kaempferol, essential for conferring anticancer activity of these substances. The results of the viscometric measurements were compared with those from a DNA damage study of Cu-kaempferol complexes in a Fenton reaction system, using gel electrophoresis. At low concentrations of kaempferol (Cu–kaempferol ratios of 1:1 and 1:2), a very weak protective effect on DNA was noted, whereas when kaempferol was present in excess, a significant DNA-protective effect was found. This can be explained if the weakly intercalated kaempferol molecules present at the surface of DNA provide protection against attack by ROS that originate from the Fenton reaction involving intercalated Cu(II)-kaempferol complexes. Following the application of ROS scavengers, L-histidine, DMSO, and SOD, gel electrophoresis confirmed the formation of singlet oxygen, hydroxyl radicals, and superoxide radical anions, respectively. We propose that the prooxidant properties of Cu-kaempferol complexes may provide anticancer activity of these substances. When present in excess, kaempferol displays antioxidant properties under Cu-Fenton conditions. This suggests that kaempferol might prove a suitable candidate for the prevention or treatment of oxidative stress related medical conditions that involve a disturbed metabolism of redox metals such as copper, for example, Menkes disease, and neurological disorders, including Alzheimer’s disease. For the potential use of kaempferol in clinical practice, it will be necessary to optimize the dose size and critical age of the patient so that this flavonoid may be beneficial as a preventive drug against cancer and neurological disorders. 相似文献
3.
Klaudia Zeranska-Chudek Anna Lapinska Agnieszka Siemion Agnieszka M. Jastrzębska Mariusz Zdrojek 《应用聚合物科学杂志》2021,138(10):49962
The rising demand for faster and more efficient electronic devices forces electronics industry to shift toward terahertz frequencies. Therefore there is a growing need for efficient, lightweight, and easy to produce absorbing materials in the terahertz range for electromagnetic interference (EMI) shielding and related applications. This study presents a study on basic optical properties of two types polymer-based composites loaded with two-dimensional structures—graphene and MXene phases (Ti2C). In said range, total EMI shielding efficiency (SE) and its components, the absorption coefficient (α ), refractive index, and complex dielectric function are investigated. The ratio of SE absorption component to reflection component (SEABS :SER ) of fabricated composites is equal or higher than 30:1 in over 80% of studied range. The fabricated composites exhibit low (<0.1) loss tangent in studied range. The addition of 1 wt% of graphene increases the composite α over 10-fold in respect to pure polymer–up to 60 cm−1 for frequency higher than 2 THz. 相似文献
4.
Itzhak I. Maor Katharina Kruppa Adi Rozencweig Amir Sterzer Frank Steinbach Vadim Beilin Bernd Breidenstein Gennady E. Shter Meirav Mann-Lahav Armin Feldhoff Gideon S. Grader 《Advanced functional materials》2023,33(49):2304464
Calcium cobaltite Ca3Co4−xO9+δ (CCO) is a promising p-type thermoelectric (TE) material for high-temperature applications in air. The grains of the material exhibit strong anisotropic properties, making texturing and nanostructuring mostly favored to improve thermoelectric performance. On the one hand multitude of interfaces are needed within the bulk material to create reflecting surfaces that can lower the thermal conductivity. On the other hand, low residual porosity is needed to improve the contact between grains and raise the electrical conductivity. In this study, CCO fibers with 100% flat cross sections in a stacked, compact form are electrospun. Then the grains within the nanoribbons in the plane of the fibers are grown. Finally, the nanoribbons are electrospun into a textured ceramic that features simultaneously a high electrical conductivity of 177 S cm−1 and an immensely enhanced Seebeck coefficient of 200 µV K−1 at 1073 K are assembled. The power factor of 4.68 µW cm−1 K−2 at 1073 K in air surpasses all previous CCO TE performances of nanofiber ceramics by a factor of two. Given the relatively high power factor combined with low thermal conductivity, a relatively large figure-of-merit of 0.3 at 873 K in the air for the textured nanoribbon ceramic is obtained. 相似文献
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6.
Acrylic bone cements modified with poly(ethylene glycol)‐based biocompatible phase‐change materials
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The high polymerization temperature of acrylic bone cements used in hip replacement implantation may cause thermal necrosis of surrounding tissues. In order to reduce the polymerization temperature, acrylic bone cement has been modified with a biocompatible polymeric phase‐change material (PCM) based on poly(ethylene glycol) (PEG) of different molecular weights and stabilized with potato starch. Structural and morphological studies were performed, and the thermal and mechanical properties were investigated. The incorporation of PEG‐based PCM led to a decrease in the polymerization temperature of bone cement from 70 °C for unmodified cement to 58 °C for modified cement. Modified cement materials were stable in incubation tests, although acoustic analysis data revealed a decrease in propagation speed after incubation, which indicates formation of material defects (pores, cracks, voids, etc.) due to water activity. However, in the regeneration process, these defects can be filled by freshly grown bone tissue leading to better incorporation of bone cement replacements into tissue. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43898. 相似文献
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8.
Florian Stieglitz Ralf Gerhard Rabea Hnig Klaudia Giehl Andreas Pich 《International journal of molecular sciences》2022,23(8)
A Clostridioides difficile infection (CDI) is the most common nosocomial infection worldwide. The main virulence factors of pathogenic C. difficile are TcdA and TcdB, which inhibit small Rho-GTPases. The inhibition of small Rho-GTPases leads to the so-called cytopathic effect, a reorganization of the actin cytoskeleton, an impairment of the colon epithelium barrier function and inflammation. Additionally, TcdB induces a necrotic cell death termed pyknosis in vitro independently from its glucosyltransferases, which are characterized by chromatin condensation and ROS production. To understand the underlying mechanism of this pyknotic effect, we conducted a large-scale phosphoproteomic study. We included the analysis of alterations in the phosphoproteome after treatment with TcdA, which was investigated for the first time. TcdA exhibited no glucosyltransferase-independent necrotic effect and was, thus, a good control to elucidate the underlying mechanism of the glucosyltransferase-independent effect of TcdB. We found RAS to be a central upstream regulator of the glucosyltransferase-independent effect of TcdB. The inhibition of RAS led to a 68% reduction in necrosis. Further analysis revealed apolipoprotein C-III (APOC3) as a possible crucial factor of CDI-induced inflammation in vivo. 相似文献
9.
Tomasz Charytoniuk Klaudia Sztolsztener Patrycja Bielawiec Adrian Chabowski Karolina Konstantynowicz-Nowicka Ewa Harasim-Symbor 《International journal of molecular sciences》2022,23(4)
It is known that metabolic disturbances, including obesity, predispose to an increased incidence of cardiovascular diseases. Elevated consumption of dietary fat results in intramyocardial accumulation of lipids and their biologically active derivatives, which can disrupt the contractile function of the heart, its metabolism, and intracellular signaling pathways. Therefore, alternative methods, such as phytocannabinoids, are being sought for the treatment of obesity-related effects. In a model of rodent obesity (seven weeks of high-fat-diet (HFD) regime), we used cannabidiol—CBD therapy (intraperitoneal injections for 14 days; 10 mg/kg). High-performance and gas-liquid chromatographies were applied in order to determine sphingolipids in the heart and plasma as well as Western blotting for protein expression. Two-week CBD administration significantly inhibited the de novo ceramide synthesis pathway in the heart of HFD fed rats by lowering sphinganine and sphinganine-1-phosphate contents. The above reductions were accompanied by markedly diminished expressions of myocardial serine palmitoyltransferase 1 and 2 as well as ceramide synthase 5 and 6 in the HFD group with 2-week CBD treatment. To our knowledge, this research is the first that reveals unknown effects of CBD treatment on the heart, i.e., amelioration of de novo ceramide synthesis pathway in obese rats. 相似文献
10.
Two new applications using multiple ion isolations in the cell of a Fourier transform-ion cyclotron resonance mass spectrometer equipped with an electrospray ionization source are described. A procedure that uses multiple ion isolations of an analyte and calibrants for internal calibration at each stage in a MSn experiment, under high-resolution exact-mass conditions, for structural characterization/elucidation of angiotensin I and rapamycin is illustrated. Fragment ion mass accuracies < 1.0 ppm are demonstrated and routinely achieved. Purification of a mixture is illustrated by isolating multiple charge states of a protein-drug complex from residual protein for further MSn studies to elucidate the site of covalent drug bonding using IRMPD for a mixture of epidermal growth factor receptor (EGFr) protein and EGFr-drug complex. The procedure developed for multiple ion isolations is referred to as multi-CHEF, multiple correlated harmonic excitation fields, in which tailored waveforms are used to notch out multiple mass regions of a spectrum with minimal off-resonance excitation. 相似文献