Two-Electron Linear Intersubband Light Absorption in a Biased Quantum Well

We point out a novel manifestation of many-body correlations in the linear optical response of electrons confined in a quantum well. Namely, we demonstrate that along with conventional absorption peak at frequency close to intersubband energy, there exists an additional peak at double frequency. This new peak is solely due to electron-electron interactions, and can be understood as excitation of two electrons by a single photon. The actual peak lineshape is comprised of a sharp feature, due to excitation of pairs of intersubband plasmons, on top of a broader band due to absorption by two single-particle excitations. The two-plasmon contribution allows to infer intersubband plasmon dispersion from linear absorption experiments.Comment: 4 pages, 3 figures; published versio

The Possible Interpretations of Y(4260)

The recently observed Y(4260) lies far above the decay threshold with a width less than 100 MeV. We argue that it's very difficult to accommodate Y(4260) as a conventional $c\bar c$ radial excitation or a D-wave state. It can't be a hadronic molecule. Its production mechanism and special decay pattern do not favor the glueball interpretation. If Y(4260) is a scalar tetraquark, it must be produced by the I=0 component of the virtual photon. Then the $I=1, I_z=0$ component of the virtual photon should have produced its isovector partner $Y^\prime (4260)$, which may be searched for in the decay channel $\pi^+\pi^-\pi^0 J/\psi$ using exactly the same database from the initial state radiation process. The observation/non-observation of $Y^\prime (4260)$ can easily confirm/reject the tetraquark hypothesis. However, a tetraquark far above threshold can fall apart into $D\bar D, D^\ast\bar D$ very easily. Its not-so-large width and the non-observation of $D\bar D$ mode tend to disfavor the tetraquark hypothesis. Hence the only feasible interpretation is a hybrid charmonium if Y(4260) is {\sl NOT} an experimental artifact. At present, none of the experimental information from BABAR measurement is in conflict with the hybrid charmonium picture.Comment: some references adde

Synthesis of VO_2 Nanowire and Observation of the Metal-Insulator Transition

We have fabricated crystalline nanowires of VO_2 using a new synthetic method. A nanowire synthesized at 650^oC shows the semiconducting behavior and a nanowire at 670^oC exhibits the first-order metal-insulator transition which is not the one-dimensional property. The temperature coefficient of resistance in the semiconducting nanowire is 7.06 %/K at 300 K, which is higher than that of commercial bolometer.Comment: 3 pages, 4 figures, This was presented in NANOMAT 2006 "International workshop on nanostructed materials" on June 21-23th of 2006 in Antalya/TURKE

Enhanced performance of supercritical fluid foaming of natural-based polymers by deep eutetic solvents

Natural deep eutetic solvents (NADES) are defined as a mixture of two or more solid or liquid components, which at a particular composition present a high melting point depression becoming liquids at room temperature. NADES are constituted by natural molecules and fully represent the green chemistry principles. For these reasons, the authors believe that the submit manuscript is a highly valuable contribution to the field of green chemistry and chemical engineering. For the first time, the possibility to use NADES as enhancers of supercritical fluid tecnology is revealed.The research leading to these results has received funding from Fundacao da Ciencia e Tecnologia (FCT) through the project ENIGMA-PTDC/EQU-EPR/121491/2010 and the project PEst-C/EQB/LA0006/2013. The funding from the European Union's Seventh Framework Programme (FP7/2007-2013) under grant agreement no REGPOT-CT2012-316331-POLARIS and from Project "Novel smart and biomimetic materials for innovative regenerative medicine approaches (Ref.: RL1 - ABMR - NORTE-01-0124-FEDER-000016)" cofinanced by North Portugal Regional Operational Programme (ON.2 - O Novo Norte), under the National Strategic Reference Framework (NSRF), through the European Regional Development Fund (ERDF) and FEDER are also acknowledged. Marta Martins, Rita Craveiro and Alexandre Paiva are grateful for financial support from Fundacao da Ciencia e Tecnologia (FCT) through the grants BIM/PTDC/EQU-EPR/121491/2010/ENIGMA and SFRH/BPD/44946/2008

Non-leptonic two-body decays of the Bc meson in light-front quark model and QCD factorization approach

We study exclusive non-leptonic two-body $B_c\to(D_{(s)},\eta_c,B_{(s)})+F$ decays with $F$(pseudoscalar or vector meson) being factored out in QCD factorization approach. The non-leptonic decay amplitudes are related to the product of meson decay constants and the form factors for semileptonic $B_c$ decays. As inputs in obtaining the branching ratios for a large set of non-leptonic $B_c$ decays, we use the weak form factors for the semileptonic $B_c\to(D_{(s)},\eta_c,B_{(s)})$ decays in the whole kinematical region and the unmeasured meson decay constants obtained from our previous light-front quark model. We compare our results of the branching ratios with those of other theoretical studies.Comment: 11 pages, 3 figures, minor corrections, version to appear in PR