Theoretical structure and surface energy of the reconstructed {01.2} form of calcite (CaCO3) crystal

Two different reconstructions of the (01.2) face (Ca or CO₃ terminated) of calcite (CaCO₃) were studied: (i) R1 reconstruction: the outermost layer is based on the [0 1 0] × 1/3[2 1 1] rectangular mesh, which is symmetrical with respect to the c glide plane of the crystal, thus fulfilling the 2D symmetry of the face and (ii) R2 reconstruction: the outermost layer is based on a lozenge shaped mesh that does not respect the 2D symmetry of the face.The , , and slabs geometry optimizations of calcite (CaCO₃) were performed either at DFT level or by using empirical potentials; the results obtained with these two different calculation methodologies are in good agreement. With respect to their arrangement in the bulk, the CO₃ groups of the outermost layer are significantly rotated about the crystallographic a-axis and about the normal to the 01.2 plane; further, the thickness of the outermost layer is significantly lower than that of the underneath ones.The surfaces energies (γ) at 0 K, for relaxed and unrelaxed , , and faces, were determined either at DFT level or by using empirical potentials. Independently of the method of calculation employed, the stability order of the relaxed faces is < < < . Concerning the unrelaxed faces, whose energies were evaluated by using empirical potentials only, the stability order is instead < < < ; such different ordering shows the importance of geometry relaxation in the calculation of the surface energy. The values of the relaxed surface energies are , , and erg/cm².     

Structure of light hypernuclei

The structure of light hypernuclei with strangeness S=−1 and −2 is investigated with the microscopic cluster model and the Gaussian expansion method (GEM). We emphasize that the cluster picture as well as the mean-field picture is invaluable to understand the structure of Λ hypernuclei, Σ hypernuclei and double Λ hypernuclei. A variety of aspects of Λ hypernuclei is demonstrated through a systematic study of p-shell hypernuclei (,, , , , , ) and sd-shell ones (, ): for example, the appearance of genuine hypernuclear states with new spatial symmetry which cannot be seen in ordinary nuclei, the glue-like role of the Λ particle which shrinks the size of nuclear core and thus reduces the B(E2) value, and the halo and skin structures in and etc. The typical light hypernucleus is thoroughly investigated, including its production, structure and decay. Precise three-body and four-body calculations of , and using GEM provide important information on the spin structure of the underlying ΛN interaction, by comparing with recent experimental data from γ-ray hypernuclear spectroscopy. The Λ–Σ coupling effect is studied in and . The binding mechanism of is discussed together with the possible existence of , emphasizing the fact that the study of is useful for extracting information on the ΣN interaction differing from that from . A systematic study of double-Λ hypernuclei, constrained by the NAGARA data () within a four-body cluster model indicates that the recently observed Demachi–Yanagi event can be interpreted as the 2⁺ state of . The effect of hyperon mixing in and is investigated using one-boson-exchange potentials and quark-cluster-model interactions for the S=−2 sector. A close relation between nuclear deep hole states and hypernuclei is discussed, emphasizing the selection rule for fragmentation of the s-hole in light nuclei, which is promising for understanding the production mechanism of double-Λ and twin-Λ hypernuclei via Ξ-atomic capture.     

Korringa-like nuclear spin–lattice relaxation in a 2DES at

Via a resistively detected NMR technique, the nuclear spin–lattice relaxation time T₁ of ⁷¹Ga has been measured in a GaAs/AlGaAs heterostructure containing two weakly coupled 2D electron systems (2DES) at low temperatures, each at Landau level filling . Incomplete electronic spin polarization, which has been reported previously for low density 2DESs at , should facilitate hyperfine-coupled nuclear spin relaxation owing to the presence of both electron spin states at the Fermi level. Composite fermion theory suggests a Korringa-law temperature dependence: T₁T=constant is expected for temperatures . Our measurements show that for temperatures in the range , T₁ rises less rapidly with falling temperature than this law predicts. This may suggest the existence of alternate nuclear spin relaxation mechanisms in this system. Also, our data allows for an estimate of the composite fermion mass.     

Tree-level contributions to the rare decays , , and in the Standard Model

The tree-level contributions to the rare decays , , and are analyzed and compared to those occurring in , , and . It is shown that these purely long-distance contributions, arising from the exchange of a charged lepton, can be significant in B⁺ decays for an intermediate τ, potentially blurring the distinction between the modes used to extract B⁺→τ⁺ν_τ and those used to probe the genuine short-distance and FCNC transitions. Numerically, the tree-level contributions are found to account for 98%, 12% and 14% of the total , , and rates, respectively.     

Step formation on hydrogen-etched 6H-SiC{0 0 0 1} surfaces

The formation of step bunches and/or facets on hydrogen-etched 6H-SiC(0 0 0 1) and () surfaces has been studied, using both nominally on-axis and intentionally miscut (i.e. vicinal) substrates. It is found that small miscuts on the (0 0 0 1) surface produce full unit-cell high steps, while half unit-cell high steps are observed on the () surface. The observed step normal direction is found to be for both surfaces. Hence, for intentionally miscut material, a miscut oriented towards this direction produces much better order in the step array compared to a miscut oriented towards a direction. For (0 0 0 1) vicinal surfaces that are miscut towards the direction, the formation of surface ripples is observed for 3° miscut and the development of small facets (nanofacets) is found for higher miscut angles. Much less faceting is observed on miscut () surfaces. Additionally, the (0 0 01) surface is found to have a much larger spatial anisotropy in step energies than the () surface.     

Absolute photoionization cross sections with ultra-high energy resolution for Ar, Kr, Xe and N2 in inner-shell ionization regions

The high-resolution absolute photoionization cross sections for Ar, Kr, Xe and N₂ in the inner-shell ionization region have been measured using a multi-electrode ion chamber and monochromatized synchrotron radiation. The energy ranges of the incident photons for the target gases were as follows: Ar: 242–252 eV (2p Rydberg excitation), Kr: 1650–1770 eV (near the 2p ionization thresholds), Xe: 665–720 eV (near the 3d ionization thresholds) and 880–1010 eV (near the 3p ionization thresholds), N₂: 400–425 eV (N 1s excitation and ionization). It is the first time to measure the absolute ionization cross sections of Ar, Kr, Xe and N₂ over the present energy ranges with the energy resolution of over 10,000. The natural lifetime widths of , , and resonances for Ar, resonance for Xe, and resonance for N₂ have been obtained based on the cross sections determined. The ionization energies into the Ar⁺ (), Ar⁺ () and Xe⁺ () ionic states are also determined using the Rydberg formula.     

Observation of the state of CH2 by optical–optical double resonance

We report the observation of levels in the state of CH₂ via optical–optical double resonance spectroscopy. Direct transitions between the lowest singlet state and the state are allowed by symmetry, but weak because they correspond to a two electron excitation in the single configuration approximation to the electronic wavefunction. The observed transitions involve sequential single photon absorptions at visible and near infrared wavelengths using state intermediate levels. Recent ab initio results (S.N. Yurchenko et al., J. Mol. Spectrosc. 208 (2001), 136) predicted the positions of some of the levels which are confirmed by the present results. The new spectra provide accurate energies for rotational levels in the , l = 0 level of the state.     

Boundary Lax pairs for the Toda field theories

Based on the recent formulation of a general scheme to construct boundary Lax pairs, we develop this systematic construction for the affine Toda field theories (ATFT). We work out explicitly the first two models of the hierarchy, i.e. the sine-Gordon () and the models. The Toda theory is the first non-trivial example of the hierarchy that exhibits two distinct types of boundary conditions. We provide here novel expressions of boundary Lax pairs associated to both types of boundary conditions.     

Optical characterization of the heating performance of microchannel fluid flow

The temperature dependent quantum efficiency of fluorescent dyes can be used to measure changes in temperature of the fluorescent dye molecules. This paper describes the use of Rhodamine dye as a temperature sensitive based fluorescence indicator for the characterization of heating in a pressure driven microfluidic device with high spatial resolution. A microheating element is used to control the temperature of the fluid in order to create localized heating in the microchannel. The temperature dependent fluorescence intensity of Rhodamine 6G for a concentration of is characterized with a 5th order polynomial then used to detect the temperature of the fluid in a microchannel. Fluid temperatures in the range of 20– are measured with an uncertainty of using a confocal fluorescence microscope. This method enables the characterization, imaging and mapping of three-dimensional temperature gradients within a microchannel.     

Electro-optic measurement system with high spatial resolution utilizing poled polymer film as external probe tip

A new external electro-optic probing technology has been first demonstrated using a poling electro-optic (EO) polymer film, spin-coated on 20 nm thick grounding perspective aluminum layer which sputtered on a piece of ITO glass as a probe tip, the aluminum layer which has 30% reflectance ratio is also a reference coating. A interdigital electrode was measured, and the spatial resolution of less than was obtained. Voltage sensitivity was approximately . The probing beam reflected from the metal line is phase-modulated by the signal electric field in the EO polymer film, and then converted to amplitude modulation by interference with the reference beam reflected from the 30% reflective coating. The reference electrode makes sure that the most signal voltage drops down in the EO polymer film.     

First-principles study of benzene on noble metal surfaces: Adsorption states and vacuum level shifts

We have studied the interaction of benzene with Cu(1 1 1), Ag(1 1 1) and Au(1 1 1) surfaces using density functional theory (DFT) within a generalized gradient approximation (GGA) and the van der Waals density functional [vdW-DF; M. Dion, H. Rydberg, E. Schröder, D.C. Langreth, B.I. Lundqvist, Phys. Rev. Lett. 92 (2004) 246401]. The adsorption energies using vdW-DF are significantly more accurate than those using GGA, while the equilibrium adsorption distances between benzene and metal substrates () calculated by both GGA and vdW-DF are almost identical. The work function changes induced by the adsorption of benzene are significantly underestimated compared with the experimental values, as a result of the overestimation of by both GGA and vdW-DF. Instead of determining the values from first-principles calculations, we deduced the most probable adsorption distances in such a way as to reproduce the experimentally-observed work function changes. The deduced adsorption distance () is shortest on Cu(1 1 1) while it is longest on Ag(1 1 1), reflecting the strength of the interactions between benzene and the metal surfaces. It turns out that the substrate dependence of the work function change is mainly ascribed to the difference in the benzene–metal distance (Z_C). Charge transfer and work function changes by the adsorption of benzene were analyzed by means of the induced density of interface states (IDIS) model [H. Vázquez, R. Qszwaldowski, P. Pou, J. Ortega, R. Pérez, F. Flores, A. Kahn, Europhys. Lett. 65 (2004) 802], and compared with the self-consistent GGA calculations. The vacuum level shifts estimated by the IDIS model agree with the GGA results for . On the other hand, the discrepancy between the two methods becomes larger for , where the back donation from the metal substrates to the adsorbate becomes significant. We show that the IDIS model reasonably works well for benzene on Cu(1 1 1), Ag(1 1 1) and Au(1 1 1) surfaces because on all surfaces. However, our analysis reveals that the actual charge density redistribution induced by the adsorption of benzene is more complicated than that assumed in the IDIS model.     

Theoretical study of optical recording with a solid immersion lens illuminated by focused double-ring-shaped radially-polarized beam

Based on the Richards–Wolf vector diffraction theory, the intensity distributions in the recording sample near a solid immersion lens are calculated for two different radially-polarized beams ( and modes). Numerical results show that a double-ring-shaped mode focusing has some excellent features in near-field optical storage, compared with a single-ring-shaped mode focusing. The recording density is markedly improved, the focal depth of the near-field recording system is substantially increased, and a subsurface recording is effectively obtained using the mode focusing.     

Widely tunable high power OPO based on a periodically poled MgO doped lithium niobate crystal

An optical parametric oscillator (OPO) based on a highly MgO doped periodically poled lithium niobate (PPMgLN) crystal was experimentally demonstrated and the result is presented in this report. The PPMgLN wafer was fabricated from a MgO doped (with 6 mol% doping concentration) lithium niobate crystal by means of high voltage pulse trigged domain reversal technique and has 20 domain reversal periods from 27.8 to with a step of between the neighbor periods. An acousto-optic (AO) Q-switched Nd³⁺:YVO₄ laser was used as the pumping laser. A maximum laser output power of 4.8 W has been achieved for the OPO when the pumping power is 10.8 W and it corresponds to an optic-optic conversion efficiency of 44%. By shifting the PPMgLN wafer, the periods of the domain structure on the PPMgLN wafer can be changed, thus enabling a wide spectral tuning range of the laser output from 1.42 to (for the signal light) and from 2.76 to (for the idler light).     

Search for the rare decays , , and

Rare decay modes , J/ψ→D⁻π⁺+c.c., and are searched for using events collected with the BESII detector at the BEPC. No signal above background is observed. We present upper limits on the branching fractions of , B(J/ψ→D⁻π⁺)<7.5×10⁻⁵, and at the 90% confidence level.     

Quantum-dot size dependence of exciton fine-structure splitting

A systematic variation of the exciton fine-structure splitting with quantum dot size in single MOCVD-grown self-organized InAs/GaAs quantum dots is observed, ranging from several tens to as much as , thus covering more than one order of magnitude. Piezoelectricity is identified to be the dominant factor governing the observed trend. A change in sign of the fine-structure splitting is reported for the first time, originating from quantum dots with confinement potentials elongated in the and crystal direction, respectively.     

The observation of hot bands in the 288 nm system of the FeCl2 radical

The 288 nm band system of FeCl₂ has been recorded with a sample produced in a warmed, free-jet expansion at moderately high resolution (with a linewidth of 0.28 cm⁻¹). Under these conditions, several hot bands are observed involving excitation of the symmetric and anti-symmetric stretching vibrations. The wavenumbers determined as a result for FeCl₂ in its ground ⁵Δ_g,4 state are and . No hot, sequence bands in the bending vibration were observed. The most likely explanation is that the wavenumber for ν₂ is essentially the same in both the electronic states involved (88 cm⁻¹). Additional strong hot bands are observed that are unrelated to the previously assigned electronic transitions; they appear to emanate from a low-lying electronic state of FeCl₂.     

Optical–optical double resonance spectroscopy of the transition of CaOH

The state of CaOH was investigated using optical–optical double resonance spectroscopy. A combined least-squares fit of the double resonance transition data along with optical transition data and the millimeter-wave pure rotational data of the state was performed using an effective Hamiltonian. The spin–rotation constant was determined for the state for the first time. An analysis of these constants showed that the Ca–O bond length and spin–rotation parameter of the state have the smallest values of all the observed ²Σ⁺ states of CaOH. This evidence suggests the assignment of the state as arising from a Ca⁺ atomic orbital of mainly 5sσ character. This atomic orbital assignment was shown to be consistent with both previous work on CaF and recent theoretical calculations on CaOH.     

Three equations of state for solids considering thermal effect

 The Einstein model to consider thermal effect in universal equations of state (UEOS) is modified. It is proposed that the zero-point vibration term should be deleted in a thermal UEOS, and the parameters cannot be directly taken as experimental data at a reference temperature, V_R, B_R, and , but their values at absolute zero temperature, V₀, B₀, and . An approach is proposed to solve V₀, B₀, and from V_R, B_R, and . The approaches are applied to three typical universal EOSs, including the Baonza, mGLJ and Morse EOSs. The numerical results show that the solved values of parameters are almost identical for different EOSs. And the thermo-physical properties predicted through different EOSs are almost identical at zero- and low-pressure conditions, once the same approach and input experimental data are used to solve the parameters. It is concluded that the prediction of thermo-physical properties at zero- and low-pressure conditions cannot be taken as the criteria to judge the applicability of a universal EOS.     

Measurements of the isotopic composition of water vapor using a DFG-based spectrometer at

We report on absorption measurements of the isotopic composition of water in a demineralized sample by means of wavelength modulation spectroscopy of H₂O lines in the spectral region around . The mid-IR radiation was obtained by difference-frequency mixing of the radiation of an extended cavity diode laser () and that of a diode-pumped monolithic Nd–YAG laser. Preliminary tests indicate the possibility of obtaining a precision for the ¹⁸O/¹⁶O, ¹⁷O/¹⁶O and ²H/¹⁶O isotope ratio measurements of the order of 1 per mil.