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The anharmonicity of lattice vibration is mainly responsible for the coefficient of thermal expansion (CTE) of materials. External stimuli, such as magnetic and electric fields, thus cannot effectively change the CTE, much less the sign variation from positive to negative or vice versa. In this study, we report significant magnetic field effects on the CTE of zircon- and scheelite-type DyCrO4 prepared at ambient and high pressures, respectively. At zero field, the zircon-type DyCrO4 exhibits a negative CTE below the ferromagnetic-order temperature of 23 K. With increasing field up to ≥1.0 T, however, the sign of the CTE changes from negative to positive. In the scheelite phase, magnetic field can change the initially positive CTE to be negative with a field up to 2.0 T, and then a reentrant positive CTE is induced by enhanced fields ≥3.5 T. Both zircon and scheelite phases exhibit considerable magnetostrictive effects with the absolute values as high as ~800 ppm at 2 K and 10 T. The strong spin-lattice coupling is discussed to understand the unprecedented sign changes of the CTE caused by applying magnetic fields. The current DyCrO4 provides the first example of field-induced sign change of thermal expansion, opening up a way to readily control the thermal expansion beyond the conventional chemical substitution.

The achievable precision of parameter estimation plays a significant role in evaluating a strategy of metrology. In practice, one may employ approximations in a theoretical model development for simplicity, which, however, will cause systematic error and lead to a loss of precision. We derive the error of maximum likelihood estimation in the weak-value amplification technique where the linear approximation of the coupling parameter is used. We show that this error is positively related to the coupling strength and can be effectively suppressed by improving the Fisher information. Considering the roles played by weak values and initial meter states in the weak-value amplification, we also point out that the estimation error can be decreased by several orders of magnitude by averaging the estimations resulted from different initial meter states or weak values. These results are finally illustrated in a numerical example where an extended linear response regime to the parameter is observed.

Previous works on personalized recommendation mostly emphasize modeling peoples' diversity in potential favorites into a uniform recommender. However, these recommenders always ignore the heterogeneity of users at an individual level. In this study, we propose an individualized recommender that can satisfy every user with a customized parameter. Experimental results on four benchmark datasets demonstrate that the individualized recommender can significantly improve the accuracy of recommendation. The work highlights the importance of the user heterogeneity in recommender design.

Al$^+$ ions optical clock is a very promising optical frequency standard candidate due to its extremely small blackbody radiation shift. It has been successfully demonstrated with indirect cooled, quantum-logic-based spectroscopy technique. Its accuracy is limited by second-order Doppler shift, and its stability is limited by the number of ions that can be probed in quantum logic processing. We propose a direct laser cooling scheme of Al$^+$ ions optical clocks where both the stability and accuracy of the clocks are greatly improved. In the proposed scheme, two Al$^+$ ions traps are utilized. The first trap is used to trap a large number of Al$^+$ ions to improve the stability of the clock laser, while the second trap is used to trap a single Al$^+$ ions to provide the ultimate accuracy. Both traps are cooled with a continuous wave 167 nm laser. The expected clock laser stability can reach $9.0\times10^{-17}/\sqrt{\tau}$. For the second trap, in addition to 167 nm laser Doppler cooling, a second stage pulsed 234 nm two-photon cooling laser is utilized to further improve the accuracy of the clock laser. The total systematic uncertainty can be reduced to about $1\times10^{-18}$. The proposed Al$^+$ ions optical clock has the potential to become the most accurate and stable optical clock., Comment: 17 pages, 2 figures

We apply perturbative QCD to the radiative decays of charmonia $J/\psi$ and $\chi_{cJ}$ into light mesons. We perform a complete numerical calculation for the quark-gluon loop diagrams involved in these processes. The calculated $J/\psi$ decay branching ratios to P-wave mesons $f_2(1270)$ and $f_1(1285)$ fit the data well, while that of $f_0(980)$ (if treated as an $s\bar s$ meson) is predicted to be $1.6\times 10^{-4}$, which implies that $f_0(1710)$ can not be the $s\bar s$ or $(u\bar u+d\bar d)/\sqrt{2}$ meson. Decays of P-wave charmonia $\chi_{cJ}\to \rho(\omega, \phi)\gamma$ (J=0,1,2) are also studied, and the branching ratio of $\chi_{c1}\to \rho\gamma$ is predicted to be $1.4\times 10^{-5}$, which may be tested by CLEO-c and BESIII with future experiments., Comment: journal version; a note on the f_2(1270) helicity added

An x-ray laser shadowgraphy experiment was conducted on Xingguang-II laser facility in 1996. A multi-layer spherical mirror was used as an imaging element and a high sensitivity CCD camera as a detector. We measured the near-field image of the Ti x-ray laser beam. With a Ti x-ray laser beam as a backlight source, we obtained a clear Cu mesh image, demonstrating the potential as advanced diagnostic measurements to study high density plasmas in inertial confinement fusion research.

Reflections of a Korteweg-de Vries (KdV) solitary wave and an envelope solitary wave are studied by using the particle-in-cell simulation method. Defining the phase shift of the reflected solitary wave, we notice that there is a phase shift of the reflected KdV solitary wave, while there is no phase shift for an envelope solitary wave. It is also noted that the reflection of a KdV solitary wave at a solid boundary is equivalent to the head-on collision between two identical amplitude solitary waves.

The pseudorapidity distribution of charged particles produced in p-p collisions at 400 GeV/c was measured by using the Lexan bubble chamber films offered by the CERN NA27 collaboration. The scaled factorial cumulant moments have been calculated. The results show that the second order cumulants have positive values, while the cumulants of higher order are consistent with zero except for the case with nch ≥ 4 events, where the third-order cumulants have small positive values beyond the statistical uncertainties. From Monte Carlo events with the same single particle spectrum and no correlations, we observed that for broad mixed-multiplicity distributions, a significant part of K2 is coming from the single-particle fluctuation due to the fluctuation multiplicity.

The influence of a node in a network can be characterized by its macroscopic properties such as eigenvector centrality. An issue of significant theoretical and practical interest is to modify the influence or roles of the nodes in a network, and recent advances indicate that this can be achieved by just controlling a subset of nodes: the so-called controllers. However, the relationship between the structural properties of a network and its controllability, e.g., the control of node importance, is still not well understood. Here we systematically explore this relationship by constructing scale-free networks with a fixed degree sequence and tunable network characteristics. We calculate the relative size (nC*) of the minimal controlling set required to control the importance of each individual node in a network. It is found that while clustering has no significant impact on nC*, changes in degree–degree correlations, heterogeneity and the average degree of networks demonstrate a discernible impact on its controllability.

The local surface plasmon resonances (LSPRs) of dielectric-Ag core-shell nanospheres are studied by the discretedipole approximation method. The result shows that LSPRs are sensitive to the surrounding medium refractive index, which shows a clear red-shift with the increasing surrounding medium refractive index. A dielectric-Ag core-shell nanosphere exhibits a strong coupling between the core and shell plasmon resonance modes. LSPRs depend on the shell thickness and the composition of dielectric-core and metal-shell. LSPRs can be tuned over a longer wavelength range by changing the ratio of core to shell value. The lower energy mode ω− shows a red-shift with the increasing dielectric-core value and the inner core radius, while blue-shifted with the increasing outer shell thickness. The underlying mechanisms are analyzed with the plasmon hybridization theory and the phase retardation effect.

The pseudorapidity and azimuthal angle distributions for charged particle produced in pp collisions at 400 GeV/c have been measured by using the LEBC films offered by CERN NA27 collaboration. The split-bin correlation functions have been calculated. The results show that the correlations are produced by resonance-like processes.

Electron and bremsstrahlung photon number spectra formulas are presented for relativistic laser-plasma interactions. The relevant electron-positron and neutron productions are demonstrated by recent available laser intensities to be possible through high-energy superthermal electrons interacting with solid-targets. The result implys that the further amelioration to optimal conditions of target is significant for increasing particle yield in photon-induced nuclear reactions.

Intense lasing at 18.9 and 20.3 nm in nickel-like molybdenum and niobium ions has been observed by using two 200 ps laser pulses with total energy of 50 J at 1.053 μm from XingGuang II laser facility. Their gain coefficients were measured to be 1.6 and 1.5 cm-1, respectively. This shows the possibility of extending Ni-like x-ray lasing in low-Z elements and paves the way towards small scale x-ray lasers for applications at university laboratories.

Quantum cosmology with complex 6 fields at finite temperature for the Vilenkin boundary conditions and Hartle-Hawking boundary conditions has been studied in this paper. The corresponding Wheeler-DeWitt equations and the Universe wave functions are obtained. At the same time, the probability density distribution is calculated and the effect of temperature on probability density distribution is found.

Relativistic momentum and energy equations of electrons in an intense laser field are derived with Hamilton-Jacobi equation. For initial electrons in non-equilibrium or Maxwellian equilibrium distributions in preplasmas, suprathermal electron energy distributions are obtained analytically and numerically. The calculation results agree well with the experiments.

The gamma-rays with energies up to 300 keV have been observed from:plasmas produced by femtosecond laser pulses at a focused intensity of 5 x 10(15) W.cm(-2).mu m(2) irradiating Ta, Mo, and Cu targets. By introducing an 8% prepulse of 70 ps before the main pulse, the fraction of high energy gamma-ray photons (hv >100 keV) was significantly enhanced relative to low energy photons (hv

Co2MnSi thin films are made by magnetron sputtering onto MgO (001) substrates. The crystalline quality is improved by increasing depositing temperature and/or annealing temperature. The sample deposited at 550°C and subsequently annealed at 550°C (sample I) exhibits a pseudo-epitaxial growth with partially ordered L21 phase. Sample I shows a four-fold magnetic anisotropy, in addition to a relatively weak uniaxial anisotropy. The Gilbert damping factor of sample I is smaller than 0.001, much smaller than reported ones. The possible reasons responsible for the small Gilbert damping factor are discussed, including weak spin-orbit coupling, small density of states at Fermi level, and so on.

Time-resolved electron diffraction employing MeV electron beams is demonstrated experimentally at the center for ultrafast diffraction and microscopy of Shanghai Jiao Tong University. A high-quality diffraction pattern is recorded by a single shot of electron pulse. Synchronization between the pump laser and the probe electron beam is achieved through measurement of electron deflection caused by the laser-induced plasmas in a metal tip. We study the ultrafast structural dynamics of the gold lattice excited by a femtosecond laser through tracing the change of Bragg peaks intensity at different time delays. It is expected that the combination of MeV ultrashort electron beams and femtosecond laser pulses will open many new opportunities in the ultrafast and ultrasmall world.

UV laser induced reaction between C60 and W(CO)60 in benzene solution was studied by infrared absorption spectroscopy. The reversible formation of a C60 complex of W(CO)5, presumably (η2-C60)W(CO)5, was observed.

We investigate charged hadron production at RHIC and LHC energies in the framework of color glass condensate. Our study gives a very good description of the experimental data of inclusive charged hadron production in proton—proton collisions at both RHIC and LHC energies. The saturation scale is treated as a free parameter, which will reduce the uncertainties from fitting low-energy experimental data and the modeling of the saturation momentum. We find a reasonable value of the saturation scale Qs ~ 1 GeV, which is consistent with the theoretical findings. The running coupling effect is taken into account, and it is found that it plays an important role in the description of the experimental data. We provide quantitative predictions of the rapidity dependence of the inclusive charged hadron production for the upcoming LHC experiment in proton—proton collisions at √s = 14TeV.

The pseudo-rapidity distribution of charged hadron multiplicity in Pb+Pb collisions at √s = 2.76 TeV is studied by using Color Glass Condensate dynamics in the fixed coupling case. We fit the HERA experimental data with heavy parton mass effect to obtain saturation exponent λ = 0.22. It is found that the charged hadron multiplicity can only describe after including heavy parton mass effect due to a large amount of heavy partons produced at large hadron collider (LHC) energy. The pomeron loop effect contribution to hadron production is also investigated. It shows that charged hadron multiplicity is underestimated by including the pomeron loop effect, which indicates that the pomeron loop effect may not exist at LHC energy.

We study the statistical properties of leaders in growing networks with age. A leader of a network is defined as the node with the largest degree and the age of the node is trivially labeled by its index, i.e., the time it joins the network. As networks evolve with the addition of new nodes connecting to old ones with the possibility that is proportional to the index of the target, we investigate both the average number and index of leaders as well as the degree distribution of nodes. The average number of leaders first increases quickly with time and then saturates to a finite value and the average index of leaders increases algebraically with time. Both features result from the degree distribution with an exponential tail. Analytical calculations based on the rate equation are verified by numerical simulations.

We provide a theoretical analysis of node importance from the perspective of dynamical processes on networks. In particular, using Markov chain analysis of the susceptible-infected-susceptible (SIS) epidemic model on networks, we derive the node importance in terms of dynamical behaviors on network in a theoretical way. It is found that this quantity happens to be the eigenvector centrality under some conditions, which bridges the topological centrality measure of the nodes with the dynamical influence of the nodes for the dynamical process. We furthermore discuss the condition under which the eigenvector centrality is valid for dynamical phenomena on networks.

We propose a new single-shot method for measuring terahertz pulses using a linearly chirped optical pulse interferogram. Modulated frequency domain phase information can be extracted by the interferogram recorded on imaging spectrographs. The terahertz pulse waveform is obtained from the phase information. We overcome the energy fluctuation problem by using the phase information, making a reference shot unnecessary and the terahertz detection more flexible and convincing.