Sweetgum (Liquidambar styraciflua L.): Extraction of Shikimic Acid Coupled to Dilute Acid Pretreatment

Liquidambar styraciflua L., also known as sweetgum, is an understory hardwood species that has widespread distribution in the southeast USA, especially in pine plantations. In addition to being a possible biorefinery feedstock, sweetgum contains shikimic acid, which is a precursor for the drug Tamiflu®. Sweetgum bark was extracted with 65 °C water and yielded 1.7 mg/g of shikimic acid, while sweetgum de-barked wood yielded 0.2 mg/g of shikimic acid. Because shikimic acid can be extracted with water, the coupling of the phytochemical hot water extraction with dilute acid pretreatment was examined. The addition of a 65 °C shikimic acid extraction step coupled to pretreatment with 0.98% H₂SO₄ at 130 °C for 50 min resulted in 21% and 17% increases in xylose percent recovery from bark and de-barked wood, respectively. These results indicate that, in addition to recovering a high value product, the 65 °C wash step also increases xylose recovery.     

Effect of guided resonance modes on emission from GaN core–shell nanorod arrays

We model the process of incoherent emission from \(\hbox {In}_{x}\hbox {Ga}_{1-x}\hbox {N/GaN}\) quantum wells in GaN core–shell nanorod arrays using finite-difference time-domain simulations. We find that high-intensity features in the emitted field correspond to guided resonance modes near the \(\varGamma \) -point of the photonic band structure. We identify one \(\varGamma \) -point mode whose electric field intensity profile is ideal for core–shell nanorod array geometries. Using this mode, we are able to simultaneously enhance the radiative recombination rate and extraction efficiency relative to an in-filled slab. We determine the conditions on radiative and nonradiative recombination rates for which the nanorod array has a higher internal and external quantum efficiency than a reference slab. We present one nanorod array geometry where the external quantum efficiency is enhanced up to a factor of 25.     

A finite field method for calculating molecular polarizability tensors for arbitrary multipole rank

A finite field method for calculating spherical tensor molecular polarizability tensors α_lm;l′m′ = ?Δ_lm/??_l′m′* by numerical derivatives of induced molecular multipole Δ_lm with respect to gradients of electrostatic potential ?_l′m′* is described for arbitrary multipole ranks l and l′. Interconversion formulae for transforming multipole moments and polarizability tensors between spherical and traceless Cartesian tensor conventions are derived. As an example, molecular polarizability tensors up to the hexadecapole–hexadecapole level are calculated for water using the following ab initio methods: Hartree–Fock (HF), Becke three‐parameter Lee‐Yang‐Parr exchange‐correlation functional (B3LYP), Møller–Plesset perturbation theory up to second order (MP2), and Coupled Cluster theory with single and double excitations (CCSD). In addition, intermolecular electrostatic and polarization energies calculated by molecular multipoles and polarizability tensors are compared with ab initio reference values calculated by the Reduced Variation Space method for several randomly oriented small molecule dimers separated by a large distance. It is discussed how higher order molecular polarizability tensors can be used as a tool for testing and developing new polarization models for future force fields. © 2011 Wiley Periodicals, Inc. J Comput Chem, 2011     

Polymers and molecular solids: New frontiers in surface science

A brief review is given of the present state of knowledge of the surface properties of polymers and molecular solids. These materials are shown to exhibit surface phenomena which are dramatically different from those characteristic of metals and covalent solids. The origin of these differences resides in the combined occurrence both of large electronic and atomic polarizabilities and of small probabilities for the transfer of an electronic excitation from one molecular site to another. The interplay of these two quantities leads to a diversity in the character of the resulting electronic excitations, ranging from localized molecular ion states in aromatic pendant-group polymers to quasi-one-dimensional metallic behavior in certain charge transfer salts and polymers. The primary role of the surface in such materials is the introduction of large, inhomogeneous fluctuations in the relaxation energies associated with the polarization of the solid by an excitation. These fluctuations produce a number of novel phenomena including localized surface states in the absence of dangling bonds, inhomogeneous broadening of photo-emission spectra, and alterations of the charge state of surface molecules. A simple, unified theoretical framework is developed for the interpretation of these phenomena.     

The influence of electron exchange and relativistic corrections on elastic low energy electron diffraction from compound semiconductors

The model of the electron-solid interaction used for dynamical low energy electron diffraction (LEED) calculations is extended to include both an energy dependent local exchange interaction and relativistically computed ion-core charge densities. These extensions of earlier work based on non-relativistic, local exchange models are tested for the (110) surfaces of InP, ZnTe and InSb. Calculations reveal discernible differences between LEED intensities computed using the energy dependent exchange force and those obtained using energy independent local exchange forces. The replacement of the non-relativistic ion-core potential with a relativistic one produces smaller changes which are most apparent when the energy dependent exchange force is used for compound semiconductors containing one or more components from the fifth row or lower in the periodic table (e.g., Cd, In, Sb or Te).     

Nondestructive evaluation of model adhesive joints by PVDF piezoelectric film sensors

Metallized poly(vinylidene fluoride) (PVDF) films can be etched into nondestructive evaluation (NDE) sensor devices. Since these sensors are relatively inexpensive, thin and lightweight, they can be attached permanently to adhesively bonded joints, laminated composites, and other structures to measure structural integrity. The present study has addressed techniques to design, attach, and utilize such sensors for adhesive joint and laminated composite applications. PVDF sensors have been successfully used as NDE transducers in pulse-echo, through-transmission, and acousto-ultrasonic techniques to monitor curing, and to detect porosity and crack propagation in different model joint geometries. Feasibility of several applications has been demonstrated, although several problems remain. The potential of using these techniques for practical bonded structures is also suggested.