Influence of stator and rotor pole number combinations on the electromagnetic performance of stator slot-opening PM hybrid-excited machine

A new type of three-phase stator hybrid excited machine with permanent magnets (PMs) located at the slot openings of field winding slots is presented in this paper. It has the advantage of good flux regulation capability due to the field excitation. The machines with different stator/rotor pole combinations, i.e., 6-stator pole and 7-/8-/10-/11-/13-/14-rotor poles, have been comparatively investigated in terms of the open-circuit and on-load characteristics, as well as the influence of dc current and the unbalanced magnetic forces. The 2-D finite element analysis (FEA) has been employed for analysis and optimization of the machines together with experimental validation

Characteristics and Sensing Properties of the La1-xNdxCo0.3Fe0.7O3 System for CO Gas Sensors

A series of nanostructured La1-xNdxCo0.3Fe0.7O3 perovskite-type (x ranging from 0 to 1) were prepared using the co-precipitation method. CO gas sensing properties of La1-xNdxCo0.3Fe0.7O3 sensors were performed. La0.7Nd0.3Co0.3Fe0.7O3 sensor showed the highest response at 250 °C (S=52.8)

Influence of magnetic saturation and rotor eccentricity on back EMF of novel hybrid-excited stator slot opening permanent magnet machine

This paper introduces a novel hybrid-excited stator slot opening permanent magnet (PM) machine (HSSPMM). The operation principle of the machine is described and the effects of rotor eccentricity and magnetic saturation due to PMs on electromagnetic performance, with particular emphasis on back electromotive force (EMF), are analyzed by finite element method (FEM). It shows that different from the conventional PM machines, the open-circuit back EMF in this novel HSSPMM should be zero but may become non-zero if significant magnetic saturation exists, and furthermore, the rotor eccentricity has a detrimental effect on the waveforms, amplitudes, and symmetries of three-phase back EMFs, as confirmed by FEM and tests

Nonfactorizable contributions to B→D(∗)MB \to D^{(*)} M decays

While the factorization assumption works well for many two-body nonleptonic $B$ meson decay modes, the recent measurement of $\bar B\to D^{(*)0}M^0$ with $M=\pi$, $\rho$ and $\omega$ shows large deviation from this assumption. We analyze the $B\to D^{(*)}M$ decays in the perturbative QCD approach based on $k_T$ factorization theorem, in which both factorizable and nonfactorizable contributions can be calculated in the same framework. Our predictions for the Bauer-Stech-Wirbel parameters, $|a_2/a_1|= 0.43\pm 0.04$ and $Arg(a_2/a_1)\sim -42^\circ$ and $|a_2/a_1|= 0.47\pm 0.05$ and $Arg(a_2/a_1)\sim -41^\circ$, are consistent with the observed $B\to D\pi$ and $B\to D^*\pi$ branching ratios, respectively. It is found that the large magnitude $|a_2|$ and the large relative phase between $a_2$ and $a_1$ come from color-suppressed nonfactorizable amplitudes. Our predictions for the ${\bar B}^0\to D^{(*)0}\rho^0$, $D^{(*)0}\omega$ branching ratios can be confronted with future experimental data.Comment: 25 pages with Latex, axodraw.sty, 6 figures and 5 tables, Version published in PRD, Added new section 5 and reference

Kaluza-Klein Cosmology With Modified Holographic Dark Energy

We investigate the compact Kaluza-Klein cosmology in which modified holographic dark energy is interacting with dark matter. Using this scenario, we evaluate equation of state parameter as well as equation of evolution of the modified holographic dark energy. Further, it is shown that the generalized second law of thermodynamics holds without any constraint.Comment: 13 pages, accepted for publication in Gen. Relativ. Gravi

The transition form factors for semi-leptonic weak decays of J/ψJ/\psi in QCD sum rules

Within the Standard Model, we investigate the semi-leptonic weak decays of $J/\psi$. The various form factors of $J/\psi$ transiting to a single charmed meson ($D^{(*)}_{(d,s)}$) are studied in the framework of the QCD sum rules. These form factors fully determine the rates of the weak semi-leptonic decays of $J/\psi$ and provide valuable information about the non-perturbative QCD effects. Our results indicate that the decay rate of the semi-leptonic weak decay mode $J/\psi \to D^{(*)-}_{s}+e^{+}+\nu_{e}$ is at order of $10^{-10}$.Comment: 28 pages, 6 figures, revised version to be published in Eur.Phys.J.

Observation of Two New N* Peaks in J/psi -> ppi−nˉp pi^- \bar n and pˉπ+n\bar p\pi^+n Decays

The $\pi N$ system in decays of $J/\psi\to\bar NN\pi$ is limited to be isospin 1/2 by isospin conservation. This provides a big advantage in studying $N^*\to \pi N$ compared with $\pi N$ and $\gamma N$ experiments which mix isospin 1/2 and 3/2 for the $\pi N$ system. Using 58 million $J/\psi$ decays collected with the Beijing Electron Positron Collider, more than 100 thousand $J/\psi \to p \pi^- \bar n + c.c.$ events are obtained. Besides two well known $N^*$ peaks at 1500 MeV and 1670 MeV, there are two new, clear $N^*$ peaks in the $p\pi$ invariant mass spectrum around 1360 MeV and 2030 MeV. They are the first direct observation of the $N^*(1440)$ peak and a long-sought "missing" $N^*$ peak above 2 GeV in the $\pi N$ invariant mass spectrum. A simple Breit-Wigner fit gives the mass and width for the $N^*(1440)$ peak as $1358\pm 6 \pm 16$ MeV and $179\pm 26\pm 50$ MeV, and for the new $N^*$ peak above 2 GeV as $2068\pm 3^{+15}_{-40}$ MeV and $165\pm 14\pm 40$ MeV, respectively

Inquiry web-based learning to enhance information problem solving competences in science

Early research on using web information indicates that secondary students fail to explore much web tools, use them naively and have serious difficulties to understand and integrate web information. In response to these challenges, the main goal of this research has been to design, implement and evaluate an instructional approach that helps students learn from web information. We have developed on-line learning materials which focus on specific curricular contents and provide specific scaffolds to help students accomplish web-based tasks and develop specific information problem-solving competencies. These scaffolds have intended to give support to students involved in information-seeking activities as they were asked questions, searched for information, organised and assessed their findings, and created rich representations of their newly-constructed understandings. We have designed a one year long study to investigate the depth and accuracy of 127 secondary students, as regards their content understanding as well as their development of information problem-solving competencies when using on-line resources to solve instructional tasks. Our research demonstrates that the experimental group performed computer-based activities statistically better than the control group. Our findings also suggest that students were able to develop accurate and in-depth understanding from web information if they could appropriately use search and managerial strategies. This research lends evidence to questions regarding the value of students engaging in on-line inquiry web-based learning to enhance content understanding and to develop more efficient information problem-solving competencies in secondary education

Branching ratios of B+→D(∗)+K(∗)0B^+ \to D^{(*)+}K^{(*)0} decays in perturbative QCD approach

We study the rare decays $B^+ \to D^{(*)+}K^{(*)0}$, which can occur only via annihilation type diagrams in the standard model. We calculate all of the four modes, $B \to PP, VP, PV, VV$, in the framework of perturbative QCD approach and give the branching ratios of the order about $10^{-6}$.Comment: 18 pages, 1 figure, Revte