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

Final state interactions in the decay B0→ηcK∗B^0 \to \eta_c K^*

In this article, we study the final-state rescattering effects in the decay $B^0 \to \eta_cK^*$, the numerical results indicate the corrections are comparable with the contribution from the naive factorizable amplitude, and the total amplitudes can accommodate the experimental data.Comment: 11 pages, 1 figure, revised version, to appear in EPJ

A_4 Symmetry and Lepton Masses and Mixing

Stimulated by Ma's idea which explains the tribimaximal neutrino mixing by assuming an A_4 flavor symmetry, a lepton mass matrix model is investigated. A Frogatt-Nielsen type model is assumed, and the flavor structures of the masses and mixing are caused by the VEVs of SU(2)_L-singlet scalars \phi_i^u and \phi_i^d (i=1,2,3), which are assigned to {\bf 3} and ({\bf 1}, {\bf 1}',{\bf 1}'') of A_4, respectively.Comment: 13 pages including 1 table, errors in Sec.7 correcte

On Two-Body Decays of A Scalar Glueball

We study two body decays of a scalar glueball. We show that in QCD a spin-0 pure glueball (a state only with gluons) cannot decay into a pair of light quarks if chiral symmetry holds exactly, i.e., the decay amplitude is chirally suppressed. However, this chiral suppression does not materialize itself at the hadron level such as in decays into $\pi^+\pi^-$ and $K^+K^-$, because in perturbative QCD the glueball couples to two (but not one) light quark pairs that hadronize to two mesons. Using QCD factorization based on an effective Lagrangian, we show that the difference of hadronization into $\pi\pi$ and $KK$ already leads to a large difference between ${\rm Br} (\pi^+\pi^-)$ and ${\rm Br}(K^+K^-)$, even the decay amplitude is not chirally suppressed. Moreover, the small ratio of $R={\rm Br}(\pi\pi)/{\rm Br}(K\bar K)$ of $f_0(1710)$ measured in experiment does not imply $f_0(1710)$ to be a pure glueball. With our results it is helpful to understand the partonic contents if ${\rm Br}(\pi\pi)$ or ${\rm Br}(K\bar K)$ is measured reliably.Comment: revised versio

Lepton flavor violation decays τ−→μ−P1P2\tau^-\to \mu^- P_1 P_2 in the topcolor-assisted technicolor model and the littlest Higgs model with TT parity

The new particles predicted by the topcolor-assisted technicolor ($TC2$) model and the littlest Higgs model with T-parity (called $LHT$ model) can induce the lepton flavor violation ($LFV$) couplings at tree level or one loop level, which might generate large contributions to some $LFV$ processes. Taking into account the constraints of the experimental data on the relevant free parameters, we calculate the branching ratios of the $LFV$ decay processes $\tau^-\to\mu^- P_1 P_2$ with $P_1 P_2$ = $\pi^+\pi^-$, $K^+K^-$ and $K^0\bar{K^0}$ in the context of these two kinds of new physics models. We find that the $TC2$ model and the $LHT$ model can indeed produce significant contributions to some of these $LFV$ decay processes.Comment: 24 pages, 7 figure

Measurement of the Atmospheric Muon Spectrum from 20 to 3000 GeV

The absolute muon flux between 20 GeV and 3000 GeV is measured with the L3 magnetic muon spectrometer for zenith angles ranging from 0 degree to 58 degree. Due to the large exposure of about 150 m2 sr d, and the excellent momentum resolution of the L3 muon chambers, a precision of 2.3 % at 150 GeV in the vertical direction is achieved. The ratio of positive to negative muons is studied between 20 GeV and 500 GeV, and the average vertical muon charge ratio is found to be 1.285 +- 0.003 (stat.) +- 0.019 (syst.).Comment: Total 32 pages, 9Figure

Precison Measurements of the Mass, the Widths of ψ(3770)\psi(3770) Resonance and the Cross Section σ[e+e−→ψ(3770)]\sigma[e^+e^-\to \psi(3770)] at Ecm=3.7724E_{\rm cm}=3.7724 GeV

By analyzing the $R$ values measured at 68 energy points in the energy region between 3.650 and 3.872 GeV reported in our previous paper, we have precisely measured the mass, the total width, the leptonic width and the leptonic decay branching fraction of the $\psi(3770)$ to be ${M}_{\psi(3770)}=3772.4 \pm 0.4 \pm 0.3$ MeV, $\Gamma_{\psi(3770)}^{\rm tot} = 28.6 \pm 1.2 \pm 0.2$ MeV, $\Gamma_{\psi(3770)}^{ee} = 279 \pm 11 \pm 13$ eV and $B[\psi(3770)\to e^+e^-]=(0.98\pm 0.04\pm 0.04)\times 10^{-5}$, respectively, which result in the observed cross section $\sigma^{\rm obs}[e^+e^-\to \psi(3770)]=7.25\pm 0.27 \pm 0.34$ nb at $\sqrt{s}=3772.4$ MeV. We have also measured $R_{\rm uds}=2.121\pm 0.023 \pm 0.084$ for the continuum light hadron production in the region from 3.650 to 3.872 GeV.Comment: 5 pages, 2 figure

Comparative cellular analysis of motor cortex in human, marmoset and mouse

The primary motor cortex (M1) is essential for voluntary fine-motor control and is functionally conserved across mammals(1). Here, using high-throughput transcriptomic and epigenomic profiling of more than 450,000 single nuclei in humans, marmoset monkeys and mice, we demonstrate a broadly conserved cellular makeup of this region, with similarities that mirror evolutionary distance and are consistent between the transcriptome and epigenome. The core conserved molecular identities of neuronal and non-neuronal cell types allow us to generate a cross-species consensus classification of cell types, and to infer conserved properties of cell types across species. Despite the overall conservation, however, many species-dependent specializations are apparent, including differences in cell-type proportions, gene expression, DNA methylation and chromatin state. Few cell-type marker genes are conserved across species, revealing a short list of candidate genes and regulatory mechanisms that are responsible for conserved features of homologous cell types, such as the GABAergic chandelier cells. This consensus transcriptomic classification allows us to use patch-seq (a combination of whole-cell patch-clamp recordings, RNA sequencing and morphological characterization) to identify corticospinal Betz cells from layer 5 in non-human primates and humans, and to characterize their highly specialized physiology and anatomy. These findings highlight the robust molecular underpinnings of cell-type diversity in M1 across mammals, and point to the genes and regulatory pathways responsible for the functional identity of cell types and their species-specific adaptations.Cardiovascular Aspects of Radiolog