Strain sensors based on carbon nanotubes-cuprous oxide composite

This paper presents the design, fabrication and experimental results of carbon nanotubes-cuprous oxide (CNTs-Cu₂O) composite based strain sensors. The press-tablets were fabricated from the blend of CNTs (25 wt%) and Cu₂O (75 wt%) at a pressure of 353 MPa. The diameter of multiwalled carbon nanotubes (MWCNTs) varied between 10 and 30 nm. The sizes of Cu₂O micro-particles were in the range of 3-4 μm. The thickness of the press-tablets was 1 mm. The samples were installed on the polymer elastic beam by glue. The electric contacts to the samples were made by silver paste. The inter-electrodes distance (length) and diameter of the surface-type samples were in the range of 6-8 mm and 10 mm, respectively. The DC resistance of the strain sensors increases under tension and decreases under compression, while the average strain sensitivities are in the range of 44-46 and 24-28 for tension and compression, respectively. The simulation is in good agreement with the experimental results.     

Determination of selenium in animal tissue samples using radioisotope induced X-ray fluorescence

A summary of sources of background affecting gamma-ray spectrometers and methods for eliminating each are discussed, along with practical cost/benefit ratios. Background contributed by samples generally defines practical levels for system background. The practical bottom line can be obtained for relatively modest costs. A realistic bottom line is attained in underground systems when the major contributions to the background come from cosmogenically produced⁶⁸Ge and double-beta decay of⁷⁶Ge in the detector. The true bottom line is reached with isotopically enriched detectors that eliminate these two chemically inseparable radioactive impurities. Data from isotopically enriched detectors are presented.     

The photochemistry of proaporphines: a new route to the aporphines

Proaporphines undergo light catalyzed rearrangement. Pakistanamine ($\text{1}$) is thus converted into lumipakistanine ($\text{2}$), while pronuciferine ($\text{7}$) and N-acetylnorpronuciferine ($\text{8}$) afford the corresponding C-9 hydroxylated aporphines $\text{9}$ and $\text{10}$. Possible biogenetic schemes for the formation of C-8, C-9-, and C-8,9-substituted aporphines are presented.     

Thermal analysis of mercury(I) sulfate and mercury(II) sulfate

The thermal decomposition of mercury(I) and (II) sulfates has been investigated by thermogravimetry. The solid-state decomposition products have been characterized by infrared and Raman spectroscopy, mass spectrometry and an X-ray diffraction method. It is concluded that mercury(I) sulfate decomposes in two steps, initially forming a mixture of metallic mercury and mercury(II) sulfate — the latter subsequently decomposes without forming a stable intermediate. The stoichiometry of disproportionation of mercury(I) sulfate and the thermal stability range of mercury(I) and mercury(II) sulfates have been established.

---

Zusammenfassung Die thermische Zersetzung von Quecksilber(I) und (II)-sulfaten wurde durch Thermogravimetrie untersucht. Die Festphasen-Zersetzungsprodukte wurden durch Infrarot- und Ramanspektroskopie, Massenspektrometrie und Röntgendiffraktion charakterisiert. Es wurde gefolgert, dass Quecksilber(I)sulfat in zwei Stufen zersetzt wird, unter anfänglicher Bildung eines Gemisches von metallischem Quecksilber und Quecksilber(II)-sulfat, welches in der Folge ohne Bildung eines stabilen Zwischenproduktes zersetzt wird. Die Stöchiometrie der Disproportionierung des Quecksilber(I)sulfats und der Bereich der Thermostabilität der Quecksilber(I) und Quecksilber(II)sulfate wurden ermittelt.

---

Résumé La décomposition thermique des sulfates de mercure(I) et de mercure(II) a été suivie par TG. On a caractérisé les produits de la décomposition en phase solide par spectroscopies infrarouge et Raman, spectrométrie de masse et diffraction des rayons X. On en a conclu que le sulfate de mercure(I) se décompose en deux étapes, formant initialement un mélange de mercure métallique et de sulfate de mercure(II), ce dernier se décomposant ensuite sans formation d'un intermédiaire stable. Les proportions stoechiométriques de la dismutation du sulfate de mercure(I) et de l'intervalle de stabilité thermique des sulfates de mercure(I) et de mercure(II) ont été établis.

---

- . , , . , , (), - . - .

     

Modification of amyloid-beta peptide aggregation via photoactivation of strained Ru(ii) polypyridyl complexes

Alzheimer''s disease (AD) is a chronic neurodegenerative disorder characterized by progressive and irreversible damage to the brain. One of the hallmarks of the disease is the presence of both soluble and insoluble aggregates of the amyloid beta (Aβ) peptide in the brain, and these aggregates are considered central to disease progression. Thus, the development of small molecules capable of modulating Aβ peptide aggregation may provide critical insight into the pathophysiology of AD. In this work we investigate how photoactivation of three distorted Ru(ii) polypyridyl complexes (Ru1–3) alters the aggregation profile of the Aβ peptide. Photoactivation of Ru1–3 results in the loss of a 6,6′-dimethyl-2,2′-bipyridyl (6,6′-dmb) ligand, affording cis-exchangeable coordination sites for binding to the Aβ peptide. Both Ru1 and Ru2 contain an extended planar imidazo[4,5-f][1,10]phenanthroline ligand, as compared to a 2,2′-bipyridine ligand for Ru3, and we show that the presence of the phenanthroline ligand promotes covalent binding to Aβ peptide His residues, and in addition, leads to a pronounced effect on peptide aggregation immediately after photoactivation. Interestingly, all three complexes resulted in a similar aggregate size distribution at 24 h, forming insoluble amorphous aggregates as compared to significant fibril formation for peptide alone. Photoactivation of Ru1–3 in the presence of pre-formed Aβ_1–42 fibrils results in a change to amorphous aggregate morphology, with Ru1 and Ru2 forming large amorphous aggregates immediately after activation. Our results show that photoactivation of Ru1–3 in the presence of either monomeric or fibrillar Aβ_1–42 results in the formation of large amorphous aggregates as a common endpoint, with Ru complexes incorporating the extended phenanthroline ligand accelerating this process and thereby limiting the formation of oligomeric species in the initial stages of the aggregation process that are reported to show considerable toxicity.

Photoactivation of a series of Ru(ii) polypyridyl complexes leads to ligand exchange and modulation of amyloid-beta peptide aggregation of relevance to Alzheimer''s disease.     

Chimeric streptogramin-tyrocidine antibiotics that overcome streptogramin resistance

Streptogramin antibiotics are comprised of two distinct chemical components: the type A polyketides and the type B cyclic depsipeptides. Clinical resistance to the type B streptogramins can occur via enzymatic degradation catalyzed by the lyase Vgb or by target modification through the action of Erm ribosomal RNA methyltransferases. We have prepared through chemical and chemo-enzymatic approaches a series of chimeric antibiotics composed of elements of type B streptogramins and the membrane-active antibiotic tyrocidine that evade these resistance mechanisms. These new compounds show broad antibiotic activity against gram-positive bacteria including a number of important pathogens, and chimeras appear to function by a mechanism that is distinct from their parent antibiotics. These results allow for the development of a brand new class of antibiotics with the ability to evade type B streptogramin-resistance mechanisms.     

Simultaneous Determination of Caffeine and Paracetamol in Commercial Formulations Using Greener Normal-Phase and Reversed-Phase HPTLC Methods: A Contrast of Validation Parameters

There has been no assessment of the greenness of the described analytical techniques for the simultaneous determination (SMD) of caffeine and paracetamol. As a result, in comparison to the greener normal-phase high-performance thin-layer chromatography (HPTLC) technique, this research was conducted to develop a rapid, sensitive, and greener reversed-phase HPTLC approach for the SMD of caffeine and paracetamol in commercial formulations. The greenness of both techniques was calculated using the AGREE method. For the SMD of caffeine and paracetamol, the greener normal-phase and reversed-phase HPTLC methods were linear in the 50–500 ng/band and 25–800 ng/band ranges, respectively. For the SMD of caffeine and paracetamol, the greener reversed-phase HPTLC approach was more sensitive, accurate, precise, and robust than the greener normal-phase HPTLC technique. For the SMD of caffeine paracetamol in commercial PANEXT and SAFEXT tablets, the greener reversed-phase HPTLC technique was superior to the greener normal-phase HPTLC approach. The AGREE scores for the greener normal-phase and reversed-phase HPTLC approaches were estimated as 0.81 and 0.83, respectively, indicated excellent greenness profiles for both analytical approaches. The greener reversed-phase HPTLC approach is judged superior to the greener normal-phase HPTLC approach based on numerous validation parameters and pharmaceutical assays.     

Syntheses of Substituted Indan 1 ones and Indenes

Ｉｎｔｒｏｄｕｃｔｉｏｎ１－Ｉｎｄａｎｏｎｅｉｓａｎｉｍｐｏｒｔａｎｔｃｌａｓｓｏｆｃｏｍｐｏｕｎｄｓ．Ａｆｔｅｒｒｅｄｕｃｔｉｏｎａｎｄｄｅｈｙｄｒａｔｉｏｎｔｈｅｙｆｏｒｍｉｎｄｅｎｅａｎｉｍｐｏｒｔａｎｔｐｒｅｃｕｒｓｏｒｆｏｒｐｒｅｐａｒｉｎｇｍｅｔａｌｌｏｃｅｎｅｓ［１］．Ｍｅｔａｌｌｏｃｅｎｅｓｍａｙｂｅｕｓｅｄａｓｃａｔａｌｙｓｔｓｆｏｒｏｌｅｆｉｎｐｏｌｙｍｅｒｉｚａｔｉｏｎ［２］;ｔｈｅｙｆｏｒｍａｎｉｍｐｏｒｔａｎｔｆｉｅｌｄｉｎｐｏｌｙｍｅｒｃｈｅｍｉｓｔｒｙａｎｄｏｒｇａ…     

Impact of Charge Transfer Complex on the Dielectric Relaxation Processes in Poly(methyl methacrylate) Polymer

The impact of the charge transfer complex on the dielectric relaxation processes in free poly(methyl methacrylate) (PMMA) polymer sheets was investigated. The frequency dependence of dielectric properties was obtained over the frequency range 0.1 Hz–1 MHz at temperatures ranging between 303 K and 373 K for perylene dye and acceptors (picric acid (PA) and chloranilic acid (CLA)) in an in situ PMMA polymer. The TG/dTG technique was used to investigate the thermal degradation of the synthesized polymeric sheets. Additionally, the kinetic parameters have been assessed using the Coats–Redfern relation. The dielectric relaxation spectroscopy of the synthesized polymeric sheets was analyzed in terms of complex dielectric constant, dielectric loss, electrical modulus, electrical conductivity, and Cole–Cole impedance spectroscopy. α- and β-relaxation processes were detected and discussed. The σ(ω) dispersion curves of the synthesized polymeric sheets show two distinct regions with increasing frequency. The impedance data of the synthesized polymeric sheets can be represented by the equivalent circuit (parallel RC).     

Cluster structure of <Superscript>16</Superscript>O

A folding potential describing the -scattering on ¹⁶O over a broad energy range 25.8-146.0 MeV is constructed on the basis of -like cluster and unclustered-nucleon configurations of ¹⁶O. The resulting potential does not need any renormalization to fit the angular distribution of elastic cross-sections. The effects of the repulsive part of - and -nucleon interactions are investigated. The analysis suggests that both the - repulsive potential and the unclustered nucleonic configuration in the target are important to describe the scattering data over a broad range of incident energies. The root-mean-square radius for the ¹⁶O nucleus is deduced.Received: 5 December 2002, Published online: 9 October 2003PACS: 25.55.Ci Elastic and inelastic scattering - 24.10.Ht Optical and diffraction models - 21.60.Gx Cluster models