A novel voltage sensorless control technique for a bidirectional AC/DC converter

A novel voltage sensorless control technique for a bidirectional AC/DC converter is presented. Only a single current sensor that measures the inductor current is needed in the whole system. The sensed inductor current is used for two functions. The first one is for shaping the current waveform at the AC side and the second one is for deriving the inductor voltage by determining the rate of change of the inductor current. The AC-side and DC-side voltages, which are used for AC current synchronization and DC voltage regulation, respectively, are obtained by extracting the envelopes of the derived inductor voltage. Apart from reducing the number of sensing elements, the proposed method has additional advantages of: (1) inherent electrical isolation and reducing noise coupling between the power circuit and the controller; (2) wide operating range. Design criteria for the differentiator and the envelope detector circuit has been described. The applicability of the proposed method is verified with the experimental results of a laboratory prototype.     

5-[4′-正庚基-氧-联苯基-4-氧-羰基]基-1-正戊炔的晶体结构研究

由于共轭聚合物的光致发光和电致发光性能,有望成为制造全塑性发光二极管的材料,因此近年来已引起人们的研究兴趣[1].聚乙炔是一种典型的共轭聚合物,其不稳定性和难加工性限制了它的应用.而含联苯液晶基元的取代聚乙炔,不仅其难加工性得到了改善,提高了稳定性,而且赋予了聚合物液晶性,因此有望开发出一批新型的高性能材料[2].目前对这类新型取代乙炔聚合物及其单体的凝聚态结构的报道还较少.本文通过WAXD,TEM和AFM等手段对小分子液晶5-[4′-正庚基-氧-联苯基-4-氧-羰基]基-1-正戊炔(A3E′O7)的晶体结构进行了研究.1实验部分1.1样品及…     

Launching of the HE11 surface-wave mode on a dielectric rod

The fields excited by a point electric dipole situated on, but oriented perpendicularly to, the axis of an infinitely long dielectric rod are examined. A technique, which involves expressing the fields and the source in a Fourier integral in the z direction and a Fourier series in the ? direction in a cylindrical co-ordinate system (p, ? z), is adopted for the analysis. Only the dominant HE11 dipole modes are found to be excited. Some preliminary numerical results for the dispersion characteristics and the surface-wave power are presented.     

Liposomes as protective capsules for active silica sol-gel biocomposite synthesis

Using liposome to shield an enzyme from hostile chemical environments during the sol-gel formation process has resulted in a novel approach to synthesizing silica sol-gel biocomposite materials. By reporting the encapsulation of horseradish peroxidase and firefly luciferase, we demonstrate that this new protocol can produce silica biocomposites that are more active than trapping the enzymes directly into hydrogels.     

Improvement of duty-cycle heating compensation in NMR spin relaxation experiments

To reliably measure NMR relaxation properties of macromolecules is a prerequisite for precise experiments that identify subtle variations in relaxation rates, as required for the determination of rotational diffusion anisotropy, CSA tensor determination, advanced motional modeling or entropy difference estimations. An underlying problem with current NMR relaxation measurement protocols is maintaining constant sample temperature throughout the execution of the relaxation series especially when rapid data acquisition is required. Here, it is proposed to use a combination of a heating compensation and a proton saturation sequence at the beginning of the NMR relaxation pulse scheme. This simple extension allows reproducible, robust and rapid acquisition of NMR spin relaxation data sets. The method is verified with (15)N spin relaxation measurements for human ubiquitin.     

Van hove self-correlation function of a hard-disk fluid: Enskog theory and computer simulation

The van Hove self-correlation function in a hard-disk fluid is analyzed using the Lorentz-Enskog kinetic equation and the kinetic model method of solution. Numerical convergence of the model solutions is demonstrated and accurate model results are used to interpret molecular dynamics simulation data at finite wave numbers. It is found that at about 60% of freezing density the error in the Enskog theory can be mainly attributed to an underestimate of the effective self-diffusion coefficient, but at 90% freezing density a theory which treats correlated collisions is needed to describe the width behavior of the singleparticle density fluctuation spectrum.     

Pulse broadening compensation in fibre-optical links

Modal dispersion can be reduced by splicing together over-and undercompensated fibres. A similar effect is obtained when the modes are inverted in the middle of their paths. A mode convertor made of a ring-shaped graded-index fibre is proposed.     

On the anisotropy of multi-chance, high-spin fission

Inclusion of the fission-fragment anisotropy in statistical-model analyses is shown to provide significant constraints on the spin and chance distributions for high-spin fission. Selective anisotropy measurements which should enhance sensitivity to shell or pairing corrections in the late stages of compound-nucleus decay are suggested.     

Rationalized Hadamard-Haar transform

A hybrid version of Haar transforms (HT) and Walsh-Hadamard transforms (WHT), called the Hadamard-Haar transform (HHT), has been developed, which effectively combines the advantages of both the transforms. Recently the HT has been rationalized so that the powers of √2 are replaced by integer powers of 2 [11-13]. In addition, the rationalized HT(RHT) retains also the properties of the HT. Similarly to the RHT, the (HHT), is now rationalized. Fast algorithms for efficient implementation of rationalized HHT [(RHHT)], based on sparse matrix factors, have now been developed. Also by using pipeline structure real-time digital processors have now been designed. These hardware utilize only adders subtractors and delay units.     

Polymerization of allyl phenyl ether

Allyl phenyl ether polymerized rapidly and quantitatively to a resin with a structure similar to a phenolic thermoset in the presence of boron trifluoride etherate at 50°C. The structure and properties of this polyphenol were studied. A reaction mechanism involving rearrangement was discussed.