The symmetry energy γ parameter of relativistic mean-field models

The relativistic mean-field models tested in previous works against nuclear matter experimental values,critical parameters and macroscopic stellar properties are revisited and used in the evaluation of the symmetry energyγ parameter obtained in three different ways. We have checked that, independent of the choice made to calculate theγ values, a trend of linear correlation is observed between γ and the symmetry energy(S_0) and a more clear linear relationship is established between γ and the slope of the symmetry energy(L_0). These results directly contribute to the arising of other linear correlations between γ and the neutron star radii of R_(1.0) and R_(1.4), in agreement with recent findings. Finally, we have found that short-range correlations induce two specific parametrizations, namely,IU-FSU and DD-MEδ, simultaneously compatible with the neutron star mass constraint of 1.93≤M_(max)/M_☉≤2.05 and with the overlap band for the L_0 ×S_0 region, to present γ in the range of γ=0.25±0.05.     

Examining metal nanoparticle surface chemistry using hollow-core, photonic-crystal, fiber-assisted SERS

In this Letter, we demonstrate the efficacy of hollow core photonic crystal fibers (HCPCFs) as a surface-enhanced Raman spectroscopy (SERS) platform for investigating the ligand exchange process on the surface of gold nanoparticles. Raman measurements carried out using this platform show the capability to monitor minute amounts of surface ligands on gold nanoparticles used as an SERS substrate. The SERS signal from an HCPCF exhibits a tenfold enhancement compared to that in a direct sampling scheme using a cuvette. Using exchange of cytotoxic cetyltrimethylammonium bromide with α-methoxy-ω-mercaptopoly(ethylene glycol) on the surface of gold nanorods as an exemplary system, we show the feasibility of using HCPCF SERS to monitor the change in surface chemistry of nanoparticles.     

Finite-Wavelength Stability¶of Capillary-Gravity Solitary Waves

We consider the Euler equations describing nonlinear waves on the free surface of a two-dimensional inviscid, irrotational fluid layer of finite depth. For large surface tension, Bond number larger than 1/3, and Froude number close to 1, the system possesses a one-parameter family of small-amplitude, traveling solitary wave solutions. We show that these solitary waves are spectrally stable with respect to perturbations of finite wave-number. In particular, we exclude possible unstable eigenvalues of the linearization at the soliton in the long-wavelength regime, corresponding to small frequency, and unstable eigenvalues with finite but bounded frequency, arising from non-adiabatic interaction of the infinite-wavelength soliton with finite-wavelength perturbations. Received: 7 February 2001 / Accepted: 6 October 2001     

Dissociative excitation of HD+, D2+ , and DT+ by electron impact

In the framework of the Multi-Channel Quantum Defect Theory (MQDT), a theoretical study of the dissociative excitation is presented. Numerical results for the dissociative excitation cross sections of HD ⁺, D ₂⁺, and DT ⁺ with electrons of energy between 2 and 12 eV are reported. The contribution of the vibrational continua of the two lowest electronic states as explicit ionization channels has been considered. Within a quasi-diabatic representation of the molecular electronic states, the Born expansion of second order is done in the K-matrix evaluation.     

Studies on terbium activated yttrium based tantalate phosphors

Terbium activated yttrium niobium tantalate phosphors were prepared by solid-state reaction and were characterized by photoluminescence measurements, X-ray diffraction and scanning electron microscopy. Photoluminescence (PL) of Y_0.95Tb_0.05Ta_1?xNb_xO₄ phosphors (x = 0–1) are influenced by the host-lattice composition, degree of crystalline order and particle morphology and size. The effect of the morpho-structural properties on PL characteristics of Y(Ta,Nb)O₄:Tb powders is reported.     

Morpho-structural and luminescence investigations on yttrium silicate based phosphors prepared with different precipitating agents

Yttrium silicate doped with cerium (Y₂SiO₅:Ce) was obtained from Y-Ce-Si based precursors prepared by the simultaneous addition of reagents (SimAdd) technique. The synthesis of the precursors was done in well controlled conditions using ammonium oxalate, ammonium carbonate or urea as precipitating agents. Results regarding the influence of precipitating agents on the morpho structural and photoluminescent characteristics of Y₂SiO₅:Ce are reported. The TG analysis in correlation with EGA, FT-IR and XRD investigations reveals the formation of oxalate, hydroxy-carbonate or hydroxy-nitrate based compounds, the same as the conversion of the precursors to well crystallized yttrium silicate. XRD patterns show that the precursors are amorphous except for the sample prepared with ammonium oxalate. Depending on the precipitation conditions, the phosphors phase composition varies from single phase (X2-Y₂SiO₅) to a mixture of phases (X2-Y₂SiO₅, X1-Y₂SiO₅, Y₂O₃). Under UV excitation, phosphors exhibit the specific blue emission of cerium with an intensity that varies from 175.8% (urea) to 96.0% (ammonium carbonate) and to 78.5% (ammonium oxalate). The emission intensity depends on the phase purity and order degree of the phosphors. PACS Classification codes:78.55 Hx, 81.20Fw      

Electrical properties study of multi-walled carbon nanotubes/hybrid-glass nanocomposites

Electrical properties of multi-walled carbon nanotubes (MWNTs)/hybrid-glass nanocomposites prepared by the fast-sol–gel reaction were investigated in light of percolation theory. A good correlation was found between the experimental results and the theory. We obtained a percolation threshold ? _c  = 0.22 wt%, and a critical exponent of t = 1.73. These values are reported for the first time for a silica-based system. The highest conductivity measured on the MWNT/hybrid-glass nanocomposites was σ ≈ 10^?3(Ω cm)^?1 for 2 wt% carbon nanotube (CNT) loading. The electrical conductivity was at least 12 orders of magnitude higher than that of pure silica. Electrostatic force microscopy and conductive-mode atomic force microscopy studies demonstrated conductivity at the micro-level, which was attributed to the CNT dispersed in the matrix. It appears that the dispersion in our MWNT/hybrid-glass system yields a particularly low percolation threshold compared with that of a MWNT/silica-glass system. Materials with electrical conductivities described in this work can be exploited for anti-static coating.