Exciton recurrence motion in aggregate systems in the presence of quantized optical fields

The exciton dynamics of model aggregate systems, dimer, trimer, and pentamer, composed of two-state monomers is computationally investigated in the presence of three types of quantized optical fields, i.e., coherent, amplitude-squeezed, and phase-squeezed fields, in comparison with the case of classical laser fields. The constituent monomers are assumed to interact with each other by the dipole-dipole interaction, and the two-exciton model, which takes into account both the one- and two-exciton generations, is employed. As shown in previous studies, near-degenerate exciton states in the presence of a (near) resonant classical laser field create quantum superposition states and thus cause the spatial exciton recurrence motion after cutting the applied field. In contrast, continuously applied quantized optical fields turn out to induce similar exciton recurrence motions in the quiescent region between the collapse and revival behaviors of Rabi oscillation. The spatial features of exciton recurrence motions are shown to depend on the architecture of aggregates. It is also found that the coherent and amplitude-squeezed fields tend to induce longer-term exciton recurrence behavior than the phase-squeezed field. These features have a possibility for opening up a novel creation and control scheme of exciton recurrence motions in aggregate systems under the quantized optical fields.     

Photodissociation dynamics of ClN3 at 193 nm

Photofragment translational spectroscopy was used to identify the primary and secondary reaction pathways in 193 nm photodissociation of chlorine azide (ClN(3)) under collision-free conditions. Both the molecular elimination (NCl+N(2)) and the radical bond rupture channel (Cl+N(3)) were investigated and compared with earlier results at 248 nm. The radical channel strongly dominates, just as at 248 nm. At 193 nm, the ClN(3) (C (1)A(")) state is excited, rather than the B (1)A(') state that is accessed at 248 nm, resulting in different photofragment angular distributions. The chlorine translational energy distribution probing the dynamics of the radical bond rupture channel shows three distinct peaks, with the two fastest peaks occurring at the same translational energies as the two peaks seen at 248 nm that were previously assigned to linear and "high energy" N(3). Hence, nearly all the additional photon energy relative to 248 nm appears as N(3) internal excitation rather than as translational energy, resulting in considerably more spontaneous dissociation of N(3) to N(2)+N.     

Coordination complexes of 2,6-diarylpyrazines with copper(II) acetate

The coordination chemistry of a series of 2,6- and 2,3-diarylpyrazines with copper(II) acetate is reported. The 2:2 coordination complexes formed between two 2,6-diarylpyrazines and copper(II) acetate are characterized by X-ray crystallography. The structure (2,6-bis(3,5-dimethylphenyl)pyrazine)copper(II) acetate acetonitrile solvate, (C₄₈H₅₂Cu₂N₄O₈) (C₂H₃N) is triclinic, P 1, with a = 7.9685(10), b = 13.1893(16), c = 13.8267(17) Å, = 107.585(3)°, = 103.921(3)° and = 96.759(3)°. The structure of (2-(2,6-dimethylphenyl)-6-(3,5-dimethylphenyl)pyrazine)copper(II) acetate, C₄₈H₅₂Cu₂N₄O₈, is monoclinic, P2₁/c, with a = 8.2196(7), b = 12.5174(11), c = 21.7325(19) Å and = 96.201(2)°.     

Dictionary Learning and Non-Asymptotic Bounds for Geometric Multi-Resolution Analysis

Data sets in high-dimensional spaces are often concentrated near low-dimensional sets. Geometric Multi-Resolution Analysis (Allard, Chen, Maggioni, 2012) was introduced as a method for approximating (in a robust, multiscale fashion) a low-dimensional set around which data may concentrated and also providing dictionary for sparse representation of the data. Moreover, the procedure is very computationally efficient. We introduce an estimator for low-dimensional sets supporting the data constructed from the GMRA approximations. We exhibit (near optimal) finite sample bounds on its performance, and demonstrate the robustness of this estimator with respect to noise and model error. In particular, our results imply that, if the data is supported on a low-dimensional manifold, the proposed sparse representations result in an error which depends only on the intrinsic dimension of the manifold. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

The effects of α-cellulose extraction and blue-stain fungus on retrospective studies of carbon and oxygen isotope variation in live and dead trees

Tree‐ring carbon and oxygen isotope ratios from live and recently dead trees may reveal important mechanisms of tree mortality. However, wood decay in dead trees may alter the δ¹³C and δ¹⁸O values of whole wood obscuring the isotopic signal associated with factors leading up to and including physiological death. We examined whole sapwood and α‐cellulose from live and dead specimens of ponderosa pine (Pinus ponderosa), one‐seed juniper (Juniperous monosperma), piñon pine (Pinus edulis) and white fir (Abies concolor), including those with fungal growth and beetle frass in the wood, to determine if α‐cellulose extraction is necessary for the accurate interpretation of isotopic compositions in the dead trees. We found that the offset between the δ¹³C or δ¹⁸O values of α‐cellulose and whole wood was the same for both live and dead trees across a large range of inter‐annual and regional climate differences. The method of α‐cellulose extraction, whether Leavitt‐Danzer or Standard Brendel modified for small samples, imparts significant differences in the δ¹³C (up to 0.4‰) and δ¹⁸O (up to 1.2‰) of α‐cellulose, as reported by other studies. There was no effect of beetle frass or blue‐stain fungus (Ophiostoma) on the δ¹³C and δ¹⁸O of whole wood or α‐cellulose. The relationships between whole wood and α‐cellulose δ¹³C for ponderosa, piñon and juniper yielded slopes of ~1, while the relationship between δ¹⁸O of whole wood and α‐cellulose was less clear. We conclude that there are few analytical or sampling obstacles to retrospective studies of isotopic patterns of tree mortality in forests of the western United States. Published in 2011 by John Wiley & Sons, Ltd.