Substitution effects on the stereochemical outcome of bisspiroketalization on the C1-C17 carbon backbone of azaspiracid is presented. A possible explanation is offered to explain the observed stereochemical outcome. 相似文献
The formation of local moments and the effect of charge carrriers in dilute magnetic semiconductors can be well understood using local probe techniques like Mossbauer Spectroscopy. We report here on Mossbauer studies in the systems Fe0.008Ge1 ? xDx (D = As, Bi), Fe0.008Ge1 ? xInx, and Fe0.008Ge1 ? xSnx. At room temperature magnetic interactions were observed for donor (D) impurities at the Fe site in the Fe0.008Ge system. No such magnetic ordering was observed for acceptor (In) or neutral (Sn) impurities. 相似文献
The ground state masses of thirty-nine neutronrich nuclei from51Ca to72Ni have been measured using the Time-of-Flight Isochronous (TOFI) spectrometer. Eight of these masses have been measured for the first time and thirty-one are remeasurements of neutron-rich nuclei previously reported. Good agreement between these results and a previous TOFI experiment was observed except for the most neutron-rich isotopes of vanadium through iron with the present results being more bound and in better agreement with theory. The low binding energy of68Ni, as indicated by an unreasonably low two-neutron separation energy, suggests the presence of a high-lying, long-lived isomeric state in this nucleus. 相似文献
A new methodology for the determination of the fluorescence quantum yield of dyes adsorbed onto microcrystalline cellulose is presented and applied to rhodamine 101, cresyl violet and auramine O. It is based on a previously reported method by Ruetten and Thomas (J. Phys. Chem., 1998, 102, 598-606), which is not applicable to the dyes used in the present study. It uses ground-state diffuse reflectance spectra obtained with and without filters, which prevents the luminescence of the dye from reaching the integrating sphere and the photodetector. New equations are presented here, correcting for the fluorescence emission of the dye, which depends on the detector sensitivity. Cut-on filters, which have a transmittance close to unity in the absorption region, and close to zero in the emission region, of the dye are used to obtain corrected reflectance spectra. The influence of the substrate was also taken into account. This methodology may be applied to other probes and surfaces or emissions of a different nature (i.e., phosphorescence or delayed fluorescence), and constitutes a very simple and general procedure to solve the important problem of luminescence quantum yield determination of probes adsorbed onto solid powdered surfaces. 相似文献
This paper presents the analysis of stress and strain data acquired with the finite element method and with tests that used
post-yielding strain gages bonded onto the external surface of pipes that suffered thickness metal loss and that had been
loaded with internal pressure. These metal loss areas were produced by three different processes: actual internal corrosion,
careful machining of external patches by spark-erosion, and milling of internal or external patches to simulate limited or
extensive strip corrosion defects with depths up to 70% of the pipe’s thickness. Results show that: (1) the extensive longitudinal
internal or external defect areas behave as extensive strips with a high degree of freedom to deform elastically and plastically
in the circumferential and thickness directions, and (2) large restraints are offered to the longitudinal strains by the non-corroded
thick walls parallel to the strip. Using the above experimental observation, a simple mathematical model was developed to
predict the burst pressure of pipes with longitudinal extensive and reasonably constant depths of metal loss. This model employed
thin-pipe-strength-of-material equations associated to a bulging correction factor, the material’s uniaxial ultimate strength
and the von Mises criterion. The onset of plastic collapse predicted by the simple model was successfully compared with results
determined from actual hydrostatic tests that were carried out with full scale pipe specimens and from finite element results
generated by the use of a commercial program. The developed model was also helpful in showing that the yield and burst behaviors
of new or corroded pipeline specimens under laboratory test conditions can be directly compared and extended to the yield
and burst behaviors of buried pipeline in field operation. 相似文献
Proteins and protein‐based assemblies represent the most structurally and functionally diverse molecules found in nature. Protein cages, viruses and bacterial microcompartments are highly organized structures that are composed primarily of protein building blocks and play important roles in molecular ion storage, nucleic acid packaging and catalysis. The outer and inner surface of protein cages can be modified, either chemically or genetically, and the internal cavity can be used to template, store and arrange molecular cargo within a defined space. Owing to their structural, morphological, chemical and thermal diversity, protein cages have been investigated extensively for applications in nanotechnology, nanomedicine and materials science. Here we provide a concise overview of the most common icosahedral viral and nonviral assemblies, their role in nature, and why they are highly attractive scaffolds for the encapsulation of functional materials. 相似文献
Despite significant progress in development of bioanalytical devices cost, complexity, access to reagents and lack of infrastructure have prevented use of these technologies in resource‐limited regions. To provide a sustainable tool in the global effort to combat infectious diseases the diagnostic device must be low cost, simple to operate and read, robust, and have sensitivity and specificity comparable to laboratory analysis. In this mini‐review we describe recent work using laser machined plastic laminates to produce diagnostic devices that are capable of a wide variety of bioanalytical measurements and show great promise towards future use in low‐resource environments. 相似文献
Imaging mobile zinc in acidic environments remains challenging because most small-molecule optical probes display pH-dependent fluorescence. Here we report a reaction-based sensor that detects mobile zinc unambiguously at low pH. The sensor responds reversibly and with a large dynamic range to exogenously applied Zn2+ in lysosomes of HeLa cells, endogenous Zn2+ in insulin granules of MIN6 cells, and zinc-rich mossy fiber boutons in hippocampal tissue from mice. This long-wavelength probe is compatible with the green-fluorescent protein, enabling multicolor imaging, and facilitates visualization of mossy fiber boutons at depths of >100 μm, as demonstrated by studies in live tissue employing two-photon microscopy. 相似文献
Hetero-dimeric magnetic nanoparticles of the type Au-Fe3O4 have been synthesised from separately prepared, differently shaped (spheres and cubes), monodisperse nanoparticles. This synthesis was achieved by the following steps: (a) Mono-functionalising each type of nanoparticles with aldehyde functional groups through a solid support approach, where nanoparticle decorated silica nanoparticles were fabricated as an intermediate step; (b) Derivatising the functional faces with complementary functionalities (e.g. amines and carboxylic acids); (c) Dimerising the two types of particles via amide bond formation. The resulting hetero-dimers were characterised by high-resolution TEM, Fourier transform IR spectroscopy and other appropriate methods.