Template-free sonochemical synthesis of flower-like ZnO nanostructures

Flower-like ZnO nanostructures have been successfully synthesized via a facile and template-free sonochemical method, using zinc acetate and potassium hydroxide as reactants only. The as-synthesized flower-like ZnO nanostructures were composed of nanorods with the width of ∼300–400 nm$\sim 300\text{–}400\text{nm}$ and the length of ∼2–3 μm$\sim 2\text{–}3\text{μm}$. The structures, morphologies and optical properties of the as-prepared products were characterized by X-ray diffraction, scanning electron microscope, transmission electron microscopy, UV-Vis spectrophotometry and Raman-scattering spectroscopy. A plausible formation mechanism of flower-like ZnO nanostructures was studied by SEM which monitors an intermediate morphology transformation of the product at the different ultrasonic time (t=80,90,95,105, and 120 min$t=80,90,95,105\text{, and}120\text{min}$).     

Electron dynamics in CaB6 induced by one- and two-color femtosecond laser

We simulate nonlinear electron dynamics in CaB₆ crystal within the framework of time-dependent density functional theory (TDDFT) under one-color femtosecond laser fields (400 nm, 800 nm) and two-color cases (400 nm+800 nm$400\text{nm}+800\text{nm}$) with different relative phases of ?=0$?=0$, ?=π/4$?=\pi /4$, ?=π/2$?=\pi /2$. The time-dependent Kohn–Sham equation (TDKS) is solved in real-time and real-space evolution scheme. We investigate the energy absorption and the electron excitation of CaB₆ crystal in detail. Besides, the electron density distributions and occupations are shown after each external field ends. Computational results indicate that for one-color case, the excitation behaviors are distinct due to the different frequencies; for two-color laser, we adjust the phase and obtain the asymmetric field, which causes the change of the dynamics response comparing with the symmetric field. At the end of laser, the electron occupation is broadly distributed in the energy range of 2.4–42.4 eV, which means a high excitation rate in the narrow-gap semiconductor under intense laser field. The occurrence of the breakdown is also checked for each case in the Letter.     

First principle study on phase stability and electronic structure of YCu

The phase stability and electronic structure of YCu were studied by self-consistent full-potential linearized augmented plane wave method (FP_LAPW) on the basis of the density functional theory (DFT). The calculated equilibrium volumes are 41.963 and 173.21 Å³$173.21{\text{Å}}^3$ for B2 and B27 structures respectively, which are in good agreement with the experimental values. The total energy of the B27 phase is about 0.03 eV lower than that of the B2 phase. The formation energies are −1.173 and −1.204 eV$-1.204\text{eV}$ for B2 and B27 structures respectively. The density of state at the Fermi energy, N(EF)$N(E_F)$, is 1.08 states/eV$1.08\text{states}/\text{eV}$ for B2 phase and 0.92 states/eV$0.92\text{states}/\text{eV}$ for B27 phase, respectively. These results indicate that the B27 phase is the thermodynamic ground state equilibrium phase of YCu at low temperatures, as observed experimentally. However, our calculations also predict that a pressure-induced B27 to B2 phase transition exists in YCu.     

Ambiguities on structure analysis of Fe–N thin films

Fe–N thin films with good soft magnetic properties were prepared by RF sputtering and vacuum annealed at 250°C under 12000 A/m magnetic field for 4 h. The structure of α′ in thin films deposited at room temperature is different from α′ formed through the Bain mechanism in bulk samples. In thin films, the lattice parameters of α′ are $\text{c=2.866+1.559}\text{C}{}_{\mathrm{<mtext>N</mtext>}}{}^{\mathrm{<mtext>\alpha </mtext><mtext>\prime </mtext>}}\text{,a=2.864+0.181}\text{C}{}_{\mathrm{<mtext>N</mtext>}}{}^{\mathrm{<mtext>\alpha </mtext><mtext>\prime </mtext>}}$.     

WIMP dark matter from gravitino decays and leptogenesis

The spontaneous breaking of B−L$B-L$ symmetry naturally accounts for the small observed neutrino masses via the seesaw mechanism. We have recently shown that the cosmological realization of B−L$B-L$ breaking in a supersymmetric theory can successfully generate the initial conditions of the hot early universe, i.e. entropy, baryon asymmetry and dark matter, if the gravitino is the lightest superparticle (LSP). This implies relations between neutrino and superparticle masses. Here we extend our analysis to the case of very heavy gravitinos which are motivated by hints for the Higgs boson at the LHC. We find that the nonthermal production of ‘pure’ wino or higgsino LSPs, i.e. weakly interacting massive particles (WIMPs), in heavy gravitino decays can account for the observed amount of dark matter while simultaneously fulfilling the constraints imposed by primordial nucleosynthesis and leptogenesis within a range of LSP, gravitino and neutrino masses. For instance, a mass of the lightest neutrino of 0.05 eV$0.05\text{eV}$ would require a higgsino mass below 900 GeV$900\text{GeV}$ and a gravitino mass of at least 10 TeV$10\text{TeV}$.     

Enhanced x-ray emissions from low-density high-Z mixture plasmas generated with intense nanosecond laser

Enhancement of x-ray emissions from laser-produced plasmas is imperative for various applications. Low-density Au–Gd mixture was proposed to enhance the x-ray emissions. X-ray emissions were simulated for the laser-irradiated gold and Au–Gd mixtures with different initial densities. It was shown that 1.34 times conversion efficiency has been achieved for the 0.05 g/cm³$0.05\text{g}/{\text{cm}}^3$ Au–Gd (6/4)$(6/4)$ mixture comparing with the 10 g/cm³$10\text{g}/{\text{cm}}^3$ gold. The enhancement is attributed to higher Rosseland mean opacities of the mixture and reduction of the ion kinetic energy caused by the lower initial density.     

First observation of electronic structure of the even parity boron acceptor states in diamond

We use electronic Raman scattering for studying the band structure of the ns$\mathrm{n}s$ boron acceptor states in diamond. For the first time, the spin–orbit splitting of these acceptor states and the 1s→ns$1s\to \mathrm{n}s$ Lyman series of transitions are observed. The spin–orbit splitting linearly increases with n number. Lyman series exhibit fine structure consisting of four bands each. The energy spacing between series is equal to ∼13 meV$\sim 13\text{meV}$. Evolution of Raman spectra of the boron-doped diamond with increasing boron concentration is shown. Mott transition is revealed in Raman spectrum. Correct values of Luttinger parameters for diamond are specified.     

125 GeV Higgs,type III seesaw and gauge–Higgs unification

Recently, both the ATLAS and CMS experiments have observed an excess of events that could be the first evidence for a 125 GeV Higgs boson. This is a few GeV below the (absolute) vacuum stability bound on the Higgs mass in the Standard Model (SM), assuming a Planck mass ultraviolet (UV) cutoff. In this Letter, we study some implications of a 125 GeV Higgs boson for new physics in terms of the vacuum stability bound. We first consider the seesaw extension of the SM and find that in type III seesaw, the vacuum stability bound on the Higgs mass can be as low as 125 GeV for the seesaw scale around a TeV. Next we discuss some alternative new physics models which provide an effective ultraviolet cutoff lower than the Planck mass. An effective cutoff Λ?10¹¹ GeV$\Lambda ?{10}^{11}\text{GeV}$ leads to a vacuum stability bound on the Higgs mass of 125 GeV. In a gauge–Higgs unification scenario with five-dimensional flat spacetime, the so-called gauge–Higgs condition can yield a Higgs mass of 125 GeV, with the compactification scale of the extra-dimension being identified as the cutoff scale Λ?10¹¹ GeV$\Lambda ?{10}^{11}\text{GeV}$. Identifying the compactification scale with the unification scale of the SM SU(2) gauge coupling and the top quark Yukawa coupling yields a Higgs mass of 121±2 GeV$121\pm 2\text{GeV}$.     

A simple explanation of the PVLAS anomaly in spontaneously broken mirror models

The PVLAS anomaly can be explained if there exist millicharged particles of mass ?0.1 eV$?0.1\text{eV}$ and electric charge ?∼¹⁰⁻⁶e$\mathrm{?}\sim {10}^{\mathrm{-6}}e$. We point out that such particles occur naturally in spontaneously broken mirror models. We argue that this interpretation of the PVLAS anomaly is not in conflict with astrophysical constraints due to the self interactions of the millicharged particles which lead them to be trapped within stars. This conclusion also holds for a generic paraphoton model.