Ozone exposure, uptake, and response of different-sized black cherry trees

Differences in exposure, uptake and relative sensitivity to ozone between seedling, sapling, and canopy black cherry (Prunus serotina Ehrh.) trees were characterized during two growing seasons in north central Pennsylvania. Open-grown trees of all sizes received a similar amount of ozone exposure. Seedlings had greater foliar ozone injury, expressed as adaxial stipple and early leaf senescence, than larger trees, which was correlated with their higher rates of stomatal conductance and greater rates of ozone uptake. The higher stomatal conductance and ozone uptake of seedlings was proportional to their higher (less negative) predawn xylem water potentials. Seedlings appeared to have some ability to compensate for injury because their free growth habit reduced exposure per unit leaf area compared to larger trees whose leaves were exposed to ozone throughout the entire growing season

Resonant inelastic x-ray scattering study of holon-antiholon continuum in SrCuO2

We report a resonant inelastic x-ray scattering study of charge excitations in the quasi-one-dimensional Mott insulator SrCuO2. We observe a continuum of low-energy excitations, in which a highly dispersive feature with a large sinusoidal dispersion (~1.1 eV) resides. We have also measured the optical conductivity, and studied the dynamic response of the extended Hubbard model with realistic parameters, using a dynamical density-matrix renormalization group method. In contrast to earlier work, we do not find a long-lived exciton, but rather these results suggest that the excitation spectrum comprises a holon-antiholon continuum together with a broad resonance.Comment: Final version to be published in Phys. Rev. Let

Symmetry energy of dense matter in holographic QCD

We study the nuclear symmetry energy of dense matter using holographic QCD. To this end, we consider two flavor branes with equal quark masses in a D4/D6/D6 model. We find that at all densities the symmetry energy monotonically increases. At small densities, it exhibits a power law behavior with the density, $E_{\rm sym} \sim \rho^{1/2}$.Comment: 9 pages, 3 figure

Ab Initio Calculation of Crystalline Electric Fields and Kondo Temperatures in Ce-Compounds

We have calculated the band-$f$ hybridizations for Ce$_x$La$_{1-x}$M$_3$ compounds ($x=1$ and $x\rightarrow 0$; M=Pb, In, Sn, Pd) within the local density approximation and fed this into a non-crossing approximation for the Anderson impurity model applied to both dilute and concentrated limits. Our calculations produce crystalline electric field splittings and Kondo temperatures with trends in good agreement with experiment and demonstrate the need for detailed electronic structure information on hybridization to describe the diverse behaviors of these Ce compounds.Comment: 13 pages(RevTeX), 3 Postscript figure

Optical-phonon resonances with saddle-point excitons in twisted-bilayer graphene

Twisted-bilayer graphene (tBLG) exhibits van Hove singularities in the density of states that can be tuned by changing the twisting angle $\theta$. A $\theta$-defined tBLG has been produced and characterized with optical reflectivity and resonance Raman scattering. The $\theta$-engineered optical response is shown to be consistent with persistent saddle-point excitons. Separate resonances with Stokes and anti-Stokes Raman scattering components can be achieved due to the sharpness of the two-dimensional saddle-point excitons, similar to what has been previously observed for one-dimensional carbon nanotubes. The excitation power dependence for the Stokes and anti-Stokes emissions indicate that the two processes are correlated and that they share the same phonon.Comment: 5 pages, 6 figure

Gyroid-Structured 3D ZnO Networks Made by Atomic Layer Deposition

3D continuous ZnO morphologies with characteristic feature sizes on the 10 nm length scale are attractive for electronic device manufacture. However, their synthesis remains a challenge because of the low crystallization temperature of ZnO. Here, we report a method for the robust and reliable synthesis of fully crystalline 3D mesoporous ZnO networks by means of atomic layer deposition (ALD) of ZnO into a self-assembled block copolymer template. By carefully optimizing the processing conditions we are able to synthesize several-micrometer-thick layers of mesoporous ZnO networks with a strut width of 30 nm. Two 3D mesoporous morphologies are manufactured: a periodic gyroid structure and a random worm-like morphology. Exploiting the ALD property to conformally coat complex surfaces of high aspect ratio, the channel network of a 3D continuous channel network of a self-assembled block copolymer is replicated into ZnO. X-ray photoemission spectroscopy and x-ray diffraction measurements reveal that the chemical composition of the mesoporous structures is uniform and consists of wurtzite-ZnO throughout the film. Scanning electron microscopy reveals an average pore dimension of 30 nm. The potential of this material for a hybrid photovoltaic application is demonstrated by the manufacture of a poly(3-hexylthiophene)/ZnO solar cell

Modular and predictable assembly of porous organic molecular crystals

Nanoporous molecular frameworks are important in applications such as separation, storage and catalysis. Empirical rules exist for their assembly but it is still challenging to place and segregate functionality in three-dimensional porous solids in a predictable way. Indeed, recent studies of mixed crystalline frameworks suggest a preference for the statistical distribution of functionalities throughout the pores rather than, for example, the functional group localization found in the reactive sites of enzymes. This is a potential limitation for 'one-pot' chemical syntheses of porous frameworks from simple starting materials. An alternative strategy is to prepare porous solids from synthetically preorganized molecular pores. In principle, functional organic pore modules could be covalently prefabricated and then assembled to produce materials with specific properties. However, this vision of mix-and-match assembly is far from being realized, not least because of the challenge in reliably predicting three-dimensional structures for molecular crystals, which lack the strong directional bonding found in networks. Here we show that highly porous crystalline solids can be produced by mixing different organic cage modules that self-assemble by means of chiral recognition. The structures of the resulting materials can be predicted computationally, allowing in silico materials design strategies. The constituent pore modules are synthesized in high yields on gram scales in a one-step reaction. Assembly of the porous co-crystals is as simple as combining the modules in solution and removing the solvent. In some cases, the chiral recognition between modules can be exploited to produce porous organic nanoparticles. We show that the method is valid for four different cage modules and can in principle be generalized in a computationally predictable manner based on a lock-and-key assembly between modules

Symmetry Energy and Universality classes of holographic QCD

We study nuclear symmetry energy of dense matter using holographic QCD. We calculate it in a various holographic QCD models and show that the scaling index of the symmetry energy in dense medium is almost invariant under the smooth deformation of the metric as well as the embedding shape of the probe brane. We find that the scaling index depends only on the dimensionality of the branes and space-time. Therefore the scaling index of the symmetry energy characterizes the universality classes of holographic QCD models. We suggest that the scaling index might be also related to the non-fermi liquid behavior of the interacting nucleons.Comment: 23 pages, 17 figure