Influence of a Strain Rate and Temperature on the Crack Tip Stress and Microstructure Evolution of Monocrystalline Nickel: a Molecular Dynamics Simulation

The effect of a strain rate and temperature on the crack tip stress and microstructure evolution ahead of a growing crack in monocrystalline nickel are studied by molecular dynamics simulations. The correlation between the microstructure evolution and stress field near the crack tip is also explored. The results indicate that the crack tip stress distribution characteristics and crack propagation dynamics are closely related to the microstructure evolution caused by the change of the strain rate and temperature. At a lower strain rate and temperature, the crack propagates by the brittle mechanism without inducing the change in atomic configuration near the crack tip. The stress concentration occurs at the crack tip of a growing crack. The crack propagation exhibits a gradual brittle-to-ductile transition with an increase in temperature and a strain rate. The peak stress is accompanied by the microstructure evolution ahead of the crack tip.Влияние скорости деформации и температуры на напряжение у вершины трещины и развитие микроструктуры вблизи распространяющейся трещины в монокристаллическом никеле исследовали с помощью моделирования методом молекулярной динамики. Исследовали корреляцию между развитием микроструктуры и полем напряжений у вершины трещины. Результаты продемонстрировали, что характеристика распределения напряжений у вершины трещины и динамика распространения трещины тесно связаны с развитием микроструктуры, обусловленной изменением скорости деформации и температуры. При низких скорости деформации и температуре трещина распространяется по механизму хрупкого разрушения без воздействия на изменение расположения атомов у ее вершины. Концентрация напряжений возникает у вершины распространяющейся трещины. Распространение трещины характеризуется постепенным переходом от хрупкого разрушения к пластичному с увеличением температуры и скорости деформации. Максимальное напряжение сопровождается развитием микроструктуры у вершины трещины.Вплив швидкості деформації і температури на напруження у вістрі тріщини і розвиток мікроструктури поблизу тріщини, що розповсюджується, в монокристалічному нікелі досліджували за допомогою моделювання методом молекулярної динаміки. Досліджували кореляцію між розвитком мікроструктури і полем напружень у вістрі тріщини. Результати показали, що характеристика розподілу напружень у вістрі тріщини і динаміка поширення тріщини тісно пов’язані з розвитком мікроструктури, зумовленої зміною швидкості деформації і температури. За низьких швидкості деформації і температури тріщина поширюється по механізму крихкого руйнування без впливу на зміну розташування атомів у її вістрі. Концентрація напружень виникає у вістрі тріщини, що поширюється. Поширення тріщини характеризується поступовим переходом від крихкого руйнування до пластичного з підвищенням температури і швидкості деформації. Максимальне напруження супроводжується розвитком мікроструктури у вістрі тріщини

Magnetic resonance imaging of glutamate in neuroinflammation

AbstractInflammation in central nervous system (CNS) is one of the most severe diseases, and also plays an impellent role in some neurodegenerative diseases. Glutamate (Glu) has been considered relevant to the pathogenesis of neuroinflammation. In order to diagnose neuroinflammation incipiently and precisely, we review the pathobiological events in the early stages of neuroinflammation, the interactions between Glu and neuroinflammation, and two kinds of magnetic resonance techniques of imaging Glu (chemical exchange saturation transfer and magnetic resonance spectroscopy)

Hawking radiation, W-infinity algebra and trace anomalies

We apply the "trace anomaly method" to the calculation of moments of the Hawking radiation of a Schwarzschild black hole. We show that they can be explained as the fluxes of chiral currents forming a W-infinity algebra. Then we construct the covariant version of these currents and verify that up to order 6 they are not affected by any trace anomaly. Using cohomological methods we show that actually, for the fourth order current, no trace anomalies can exist. The results reported here are strictly valid in two dimensions.Comment: 22 pages, typos correcte

Influence of DC winding configuration on its induced voltage in wound field machines

DC winding induced voltage pulsation in the wound field synchronous machines (WFSMs) will cause dc winding current ripple, challenge the dc power supply, and deteriorate the control performance, especially at high speed. In this paper, the influence of dc winding configuration including the dc coil number and the parallel branch number on its induced voltage pulsation is investigated for WFSMs. Based on the modeling of both open-circuit and on-load dc winding induced voltages, the preferred dc winding configurations for WFSMs having various stator/rotor pole number combinations with double layer or single layer ac windings are obtained and validated by finite element (FE) analysis on four typical partitioned stator WFSMs (PS-WFSMs). A PS-WFSM prototype is built and tested to validate both analytical and FE analyses

Reduction of open-circuit dc-winding-induced voltage in wound field switched flux machines by skewing

In this paper, the open-circuit dc-winding-induced voltage in a wound field switched flux (WFSFs) machines is analyzed. The phenomenon of open-circuit dc-winding-induced voltage is illustrated and the mechanism is explained. Rotor skewing is proposed to reduce the open-circuit dc-winding-induced voltage, and the optimal skewing angle is analytically derived based on the analytically deduced harmonic orders of the open-circuit dc-winding-induced voltage. Finite-element (FE) analyses show that the open-circuit dc-winding-induced voltages in the analyzed 12-stator-pole partitioned stator WFSF machines having 10-, 11-, 13-, and 14-rotor-pole rotors can be effectively reduced by >94%, while the ac-winding phase-fundamental back-EMFs can be maintained by >95%. Twelve/ten-stator/rotor-pole prototypes with skewed and nonskewed rotors are built and tested to verify the analytical and FE results

Thermodynamics of charged and rotating black strings

We study thermodynamics of cylindrically symmetric black holes. Uncharged as well as charged and rotating objects have been discussed. We derive surface gravity and hence the Hawking temperature and entropy for all these cases. We correct some results in the literature and present new ones. It is seen that thermodynamically these black configurations behave differently from spherically symmetric objects

Performance Comparison between Consequent-Pole and Inset Modular Permanent Magnet Machines

This paper proposes some consequent-pole modular permanent magnet machines with different flux gap widths and slot/pole number combinations. The corresponding inset modular permanent magnet machines having the same magnet volume are also presented for comparison. It has been demonstrated that the output torques of the consequent pole modular machines are always higher than those of the inset modular machines regardless of flux gap widths and slot/pole number combinations. Other electromagnetic performances such as back-EMF, cogging torque, and iron losses, etc. are calculated by 2D FEA software and compared as well. The advantages and disadvantages of consequent and inset modular permanent magnet machines are summarized in this paper

Charmless Bs→PP,PV,VVB_s\to PP, PV, VV Decays Based on the six-quark Effective Hamiltonian with Strong Phase Effects II

We provide a systematic study of charmless $B_s \to PP, PV, VV$ decays ($P$ and $V$ denote pseudoscalar and vector mesons, respectively) based on an approximate six-quark operator effective Hamiltonian from QCD. The calculation of the relevant hard-scattering kernels is carried out, the resulting transition form factors are consistent with the results of QCD sum rule calculations. By taking into account important classes of power corrections involving "chirally-enhanced" terms and the vertex corrections as well as weak annihilation contributions with non-trivial strong phase, we present predictions for the branching ratios and CP asymmetries of $B_s$ decays into PP, PV and VV final states, and also for the corresponding polarization observables in VV final states. It is found that the weak annihilation contributions with non-trivial strong phase have remarkable effects on the observables in the color-suppressed and penguin-dominated decay modes. In addition, we discuss the SU(3) flavor symmetry and show that the symmetry relations are generally respected

Weak Phase γ\gamma and Strong Phase δ\delta from CP Averaged B→ππB\to \pi\pi and πK\pi K Decays

Assuming SU(3) symmetry for the strong phases in the four decay modes B\rarrow \pi^-\pi^+, \pi^0 \pi^+, \pi^- K^+, \pi^- \bar{K}^0 and ignoring the relative small electroweak penguin effects in those decays, the weak phase $\gamma$ and the strong phase $\delta$ can be determined in a model independent way by the CP-averaged branching ratios of the four decay modes. It appears that the current experimental data for $B\to \pi\pi$ and $\pi K$ decays prefer a negative value of $\cos\gamma\cos\delta$. By combining with the other constraints from $V_{ub}$, $B^{0}_{d,s}-\bar{B}^{0}_{d,s}$ mixings and indirect CP-violating parameter $\epsilon_K$ within the standard model, two favorable solutions for the phases $\gamma$ and $\delta$ are found to lie in the region: 35^{\circ}\alt\gamma\alt 62^{\circ} and 106^{\circ}\alt \delta \alt 180^{\circ} or 86^{\circ}\alt\gamma\alt 151^{\circ} and 0^{\circ}\alt\delta\alt 75^{\circ} within 1$\sigma$ standard deviation. It is noted that if allowing the standard deviation of the data to be more than 1$\sigma$, the two solutions could approach to one solution with a much larger region for the phases $\gamma$ and $\delta$. Direct CP asymme try $a_{\epsilon''}^{(\pi^- K^+)}$ in B\rarrow \pi^-K^+ decay can be as large as the present experimental upper bound. Direct CP asymmetry $a_{\epsilon''}^{(\pi^+\pi^-)}$ in B\rarrow \pi^-\pi^+ decay can reach up to about 40% at 1$\sigma$ level.Comment: 14 Pages, ReVTeX, 5 figures, one figure (Fig.3) is correcte

Anomaly analysis of Hawking radiation from Kaluza-Klein black hole with squashed horizon

Considering gravitational and gauge anomalies at the horizon, a new method that to derive Hawking radiations from black holes has been developed by Wilczek et al. In this paper, we apply this method to non-rotating and rotating Kaluza-Klein black holes with squashed horizon, respectively. For the rotating case, we found that, after the dimensional reduction, an effective U(1) gauge field is generated by an angular isometry. The results show that the gauge current and energy-momentum tensor fluxes are exactly equivalent to Hawking radiation from the event horizon.Comment: 15 pages, no figures, the improved version, accepted by Eur. Phys. J.