Boron carbide (B4C) is one of the main products from the primary combustion of boron (B)-based propellants and has a significant influence on the secondary combustion of B. To systematically evaluate its effects on the secondary combustion of B, mixtures of B4C and B in different mass ratios were prepared. To study the ignition temperatures and combustion flames of the samples, a xenon lamp ignition experimental system and a flame shape test system were designed, respectively. A thermogravimetry–differential scanning calorimetry–Fourier transform infrared spectroscopy combined thermal analysis system was used to study the thermal oxidation characteristics and analyze the gaseous products of the samples. The results indicate that B4C reduces the heat absorption at the beginning of the ignition, but subsequently prevents the rapid rise of sample temperature. During the stable combustion stage, the maximum flame length under optical density 10−4 (OD4) filter was 20.4 mm, and the maximum flame length under 580 nm + OD4 filters (represents the combustion of B element) was 16.7 mm. The samples contained a small amount of HBO2 and H3BO3, which led to slight mass loss during the low temperature section of the thermal oxidation process. During the high temperature section, the oxidation of B and B4C caused considerable mass gain. The gaseous products of the thermal oxidation process include CO2, CO, and H2O. In general, the B content of 60% was the most beneficial to decrease the oxidation temperature, increase the combustion intensity, and improve the heat-releasing ability of the samples.
The Raman spectroscopic data in the range 500-1800 cm−1 for a series of 15 rare earth double-deckers with tervalent rare earths MIII[Pc(MeOPhO)8]2 (M = Y, La, …, Lu, except Ce, Pr and Pm), reduced state HPr[Pc(MeOPhO)8]2 and intermediate-valent cerium Ce[Pc(MeOPhO)8]2 have been collected using laser excitation source emitting at 632.8 nm. With excitation at 632.8 nm, which is in close resonance with the main Q absorption band of the phthalocyanine ligand, typical Raman marker bands of the monoanion radical [Pc(MeOPhO)8]− were observed at 1500-1528 cm−1 as very strong bands resulting from the coupling of pyrrole CC and aza CN stretchings. For Ce[Pc(MeOPhO)8]2 and HPr[Pc(MeOPhO)8]2, a very strong band at 1499 cm−1 with contributions from both pyrrole CC and aza CN stretchings and also isoindole stretching was the marker Raman band of [Pc(MeOPhO)8]2−. In addition, the influence of ionic radius of the rare earth metal and substituent species on the Raman scatting characteristics of sandwich-type compounds has also been tentatively studied. 相似文献
In a recent work [Gao et al., Appl. Phys. Lett. 134, 113902 (2007)], we reported a novel DNA separation method by tethering DNA chains to a solid surface and then stretching the DNA chains with an electric field. The anchor is such designed that the critical force to detach a DNA chain is independent of its length. Because the stretching force is proportional to the DNA net charge, a gradual increase of the electric field leads to size-based removal of the DNA strands from the surface and thus DNA separation. Originally proposed for separation of long double-stranded DNA chains (>10 000 bps), this method has been proven useful also for short single-stranded DNA fragments (<100 bases) for which the fluctuation force induced by the solvent becomes significant. Here we show that the fluctuation force can be approximately represented by a gaussian model for tethered DNA chains. Analytical expressions have been derived to account for the dependence of the fluctuation force on the surface confinement, the polymer chain length, and the DNA tethering potential. The theoretical predictions are found to coincide with experiment. 相似文献
We report on a highly sensitive aptameric assay system for the determination of IgE, where a special chemiluminescence (CL) reagent, 3,4,5-trimethoxylphenylglyoxal (TMPG), acts as the signaling molecule and polystyrene beads as the amplification platform. Briefly, a "sandwich-type" detection strategy is employed in our design, where magnetic beads functionalized with a capture antibody were reacted with the target protein IgE, and then sandwiched with the aptamer-barcodes which were prepared by assembling polystyrene beads with IgE aptamer. The target immunoreaction event could be sensitively detected via an instantaneous derivatization reaction between TMPG and the guanine (G) nucleotides within the aptamer-barcodes to form an unstable CL intermediate for the generation of light. Further signal amplification is achieved by extending the G nucleotide-rich domain on the aptamer backbone for second amplification. Such simple amplified CL transduction allows the detection of IgE down to the 4.6 pM level, which is better than most previous aptameric methods for IgE detection. This new protocol also provides a good capability in discriminating IgE from nontarget proteins such as IgG, IgA, IgM, interferon and thrombin. The practical application of the proposed aptamer-barcode based immunoassay was successfully carried out for the determination of IgE in 20 human serum samples. It is straightforward to adapt this strategy to detect a spectrum of other proteins by using different aptamers, thus this method may offer a new direction in designing high-performance CL aptasensors for early diagnoses of diseases. 相似文献
The object of this research aims at the hydraulic generator unit rotor system. According to fault problems of the generator
rotor local rubbing caused by the parallel misalignment and mass eccentricity, a dynamic model for the rotor system coupled
with misalignment and rub-impact is established. The dynamic behaviors of this system are investigated using numerical integral
method, as the parallel misalignment, mass eccentricity and bearing stiffness vary. The nonlinear dynamic responses of the
generator rotor and turbine rotor with coupling faults are analyzed by means of bifurcation diagrams, Poincaré maps, axis
orbits, time histories and amplitude spectrum diagrams. Various nonlinear phenomena in the system, such as periodic, three-periodic
and quasi-periodic motions, are studied with the change of the parallel misalignment. The results reveal that vibration characteristics
of the rotor system with coupling faults are extremely complex and there are some low frequencies with large amplitude in
the 0.3–0.4× components. As the increase in mass eccentricity, the interval of nonperiodic motions will be continuously moved
forward. It suggests that the reduction in mass eccentricity or increase in bearing stiffness could preclude nonlinear vibration.
These might provide some important theory references for safety operating and exact identification of the faults in rotating
machinery. 相似文献
Methods of nonnegative tensor factorization (NTF), such as NTF1, NTF2, etc., are extension of nonnegative matrix factorization (NMF) for multi-way data analysis. As an existing NTF method, nonnegative Tucker3 decomposition (NTD) is researched for three-way decomposition in this paper. Firstly, an approach utilizing matrix exponentials built on Tikhonov-type regularization to enforce sparseness is proposed to extract image features instead of exclusively using Tucker tensor decomposition. Meanwhile, updating algorithms, derived from updating rules of NMF, are allowed to efficiently implement updating of mode matrices and core tensors alternatively for accuracy. Then, experimental cases of alternating least squares (ALS) and conjugate nonnegative constraints, called nonnegative alternating least squares (NALS), are studied to remedy data overfitting in computing procedures. Lastly, the proposed method exhibits more advantageous results than other algorithms of Tucker3 for feature extraction, thanks to computer simulations performed in the context of data analysis. 相似文献