342 research outputs found
Theory for Nonlinear Spectroscopy of Vibrational Polaritons
Molecular polaritons have gained considerable attention due to their
potential to control nanoscale molecular processes by harnessing
electromagnetic coherence. Although recent experiments with liquid-phase
vibrational polaritons have shown great promise for exploiting these effects,
significant challenges remain in interpreting their spectroscopic signatures.
In this letter, we develop a quantum-mechanical theory of pump-probe
spectroscopy for this class of polaritons based on the quantum Langevin
equations and the input-output theory. Comparison with recent experimental data
shows good agreement upon consideration of the various vibrational
anharmonicities that modulate the signals. Finally, a simple and intuitive
interpretation of the data based on an effective mode-coupling theory is
provided. Our work provides a solid theoretical framework to elucidate
nonlinear optical properties of molecular polaritons as well as to analyze
further multidimensional spectroscopy experiments on these systems
Experimental study of THGEM detector with mini-rim
The gas gain and energy resolution of single and double THGEM detectors
(5{\times}5cm2 effective area) with mini-rims (rim is less than 10{\mu}m) were
studied. The maximum gain can reach 5{\times}103 and 2{\times}105 for single
and double THGEM respectively, while the energy resolution of 5.9 keV X-ray
varied from 18% to 28% for both single and double THGEM detectors of different
hole sizes and thicknesses.All the experiments were investigated in mixture of
noble gases(argon,neon) and small content of other gases(iso-butane,methane) at
atmospheric pressure.Comment: 4pages,6figures, it has been submitted to Chinese Physics
Divacancy-induced Ferromagnetism in Graphene Nanoribbons
Zigzag graphene nanoribb ons have spin-polarized edges,
anti-ferromagnetically coupled in the ground state with total spin zero.
Customarily, these ribbons are made ferromagnetic by producing an imbalance
between the two sublattices. Here we show that zigzag ribbons can be
ferromagnetic due to the presence of reconstructed divacancies near one edge.
This effect takes place despite the divacancies are produced by removing two
atoms from opposite sublattices, being balanced before reconstruction to 5-8-5
defects. We demonstrate that there is a strong interaction between the
defect-localized and edge bands which mix and split away from the Fermi level.
This splitting is asymmetric, yielding a net edge spin-polarization. Therefore,
the formation of reconstructed divacancies close to the edges of the
nanoribbons can be a practical way to make them partially ferromagnetic
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Direct observation of the intermediate in an ultrafast isomerization.
Using a combination of two-dimensional infrared (2D IR) and variable temperature Fourier transform infrared (FTIR) spectroscopies the rapid structural isomerization of a five-coordinate ruthenium complex is investigated. In methylene chloride, three exchanging isomers were observed: (1) square pyramidal equatorial, (1); (2) trigonal bipyramidal, (0); and (3) square pyramidal apical, (2). Exchange between 1 and 0 was found to be an endergonic process (ΔH = 0.84 (0.08) kcal mol-1, ΔS = 0.6 (0.4) eu) with an isomerization time constant of 4.3 (1.5) picoseconds (ps, 10-12 s). Exchange between 0 and 2 however was found to be exergonic (ΔH = -2.18 (0.06) kcal mol-1, ΔS = -5.3 (0.3) eu) and rate limiting with an isomerization time constant of 6.3 (1.6) ps. The trigonal bipyramidal complex was found to be an intermediate, with an activation barrier of 2.2 (0.2) kcal mol-1 and 2.4 (0.2) kcal mol-1 relative to the equatorial and apical square pyramidal isomers respectively. This study provides direct validation of the mechanism of Berry pseudorotation - the pairwise exchange of ligands in a five-coordinate complex - a process that was first described over fifty years ago. This study also clearly demonstrates that the rate of pseudorotation approaches the frequency of molecular vibrations
Signaling pathways in the development of infantile hemangioma
Infantile hemangioma (IH), which is the most common tumor in infants, is a benign vascular neoplasm resulting from the abnormal proliferation of endothelial cells and pericytes. For nearly a century, researchers have noted that IH exhibits diverse and often dramatic clinical behaviors. On the one hand, most lesions pose no threat or potential for complication and resolve spontaneously without concern in most children with IH. On the other hand, approximately 10% of IHs are destructive, disfiguring and even vision- or life-threatening. Recent studies have provided some insight into the pathogenesis of these vascular tumors, leading to a better understanding of the biological features of IH and, in particular, indicating that during hemangioma neovascularization, two main pathogenic mechanisms prevail, angiogenesis and vasculogenesis. Both mechanisms have been linked to alterations in several important cellular signaling pathways. These pathways are of interest from a therapeutic perspective because targeting them may help to reverse, delay or prevent hemangioma neovascularization. In this review, we explore some of the major pathways implicated in IH, including the VEGF/VEGFR, Notch, β-adrenergic, Tie2/angiopoietins, PI3K/AKT/mTOR, HIF-α-mediated and PDGF/PDGF-R-β pathways. We focus on the role of these pathways in the pathogenesis of IH, how they are altered and the consequences of these abnormalities. In addition, we review the latest preclinical and clinical data on the rationally designed targeted agents that are now being directed against some of these pathways
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