Acetaldehyde adsorption and catalytic decomposition on Pd(1 1 0) and the dissolution of carbon

The reaction of acetaldehyde with the Pd(1 1 0) surface has been studied using a molecular beam reactor, TPD and LEED. Below 270 K acetaldehyde sticks to the surface with a high initial probability (∼0.8), but no gas phase products evolve. When the reaction is run at >270 K, hydrogen evolves into the gas phase early in the reaction together with methane in a non-steady-state fashion, but above 300 K there is a very efficient steady-state catalytic reaction at the surface; this reaction is the decarbonylation of acetaldehyde to produce methane and carbon monoxide in the gas phase. This behaviour continues up to about 400 K. However, when acetaldehyde is dosed at 423 K, the reaction rate slowly evolves through a maximum to a very low catalytic rate. Upon carrying out reactor experiments at 473 K and above, the reaction mechanism changes to total dehydrogenation, and CO and H₂ are produced at high steady-state rate, not withstanding the fact that carbon is continually being deposited onto the surface. This carbon does not appear to affect the reaction, which takes place on a surface with a c(2 × 2)-C layer present, since the extra carbon is lost from the reaction zone by diffusion into the bulk of the crystal.     

Surface site dependence to negative ion formation

The processes of electron transfer and dissociative scattering are explored for collisions of hyperthermal NO⁺ on GaAs(110). The experiments reveal a marked angular dependence to O⁻ emergence. A strong correlation between the O⁻ scattering angle and the final atom-surface interaction site provides a map of the lateral dependence to reactivity. The results are modeled by sequential neutralization, dissociation, and electron attachment steps. Classical trajectory calculations, in conjunction with an empirical opacity function, accurately reproduce the experimental results. The opacity function is interpreted as the probability that an electron will attach to a departing O fragment as a function of the last surface site the atom impacts. The experiments indicate that O⁻ emergence occurs predominantly for oxygen atoms which come in close contact with the localized dangling bond states of GaAs(110).     

Luminescent molecular hybrid system derived from 2-furancarboxylic acid and silylated monomer coordinated to rare earth ions

In this study, silica-based organic-inorganic hybrids were prepared by the sol-gel method. Tetraethoxysilane (abbreviated as TEOS) and a kind of monomer (abbreviated as FA-APES) derived from modified 2-furancarboxylic acid (abbreviated as FA) with (3-aminopropyl)triethoxysilane (abbreviated as APES) were used as the inorganic and organic fragments, respectively. Coordination reaction between lanthanides (europium and terbium ions) and CO group of the monomer happened simultaneously. And after days of aging process the resultant materials showed characteristic luminescence of lanthanides. The enhancement of luminescence can be seen by the comparison with simply doped lanthanide hybrid systems. And it can be explained by the coordination ability of the organic counterpart. IR, NMR, UV-vis absorption, low-temperature phosphorescence spectroscopy and fluorescence spectroscopy were applied to characterize and the above spectroscopic data revealed that the triplet state energy of organic ligand matches with the emissive energy level of lanthanides (especially of Tb³⁺).     

Molecular depth profiling of organic and biological materials

Atomic depth profiling using secondary ion mass spectrometry, SIMS, is common in the field micro-electronics; however, the generation of molecular information as a function of sample depth is difficult due to the accumulation of damage both on and beneath the sample surface. The introduction of polyatomic ion beams such as SF₅ and C₆₀ have raised the possibility of overcoming this problem as they deposit the majority of their energy in the upper surface of the sample resulting in increased sputter yields but with a complimentary reduction in sub-surface damage accumulation. In this paper we report the depth profile analysis of the bio-polymer polycaprolactone, PCL, using the polyatomic ions and and the monoatomic Au⁺. Results are compared to recent analysis of a similar sample using . depth profiling of cellulose is also demonstrated, an experiment that has been reported as unsuccessful when attempted with implications for biological analysis are discussed.     

Strain relaxation and surface morphology of high indium content InAlAs metamorphic buffers with reverse step

Low-temperature step-graded high indium content InAlAs (In% = 0.75) metamorphic buffer layers with reverse step layer grown on GaAs substrate by molecular beam epitaxy are investigated in this paper. The composition and the strain relaxation of the top InAlAs layer are determined by high-resolution triple-axis X-ray diffraction measurements, which show that the top InAlAs layer is nearly fully relaxed and the growth parameters for these samples have little influence on the strain relaxation ratio. Surface morphology is observed by reflection high-energy electron diffraction pattern and atomic force microscopy. The surface morphology is found to depend strongly on both the growth temperature and the As flux. Compared with other samples, the sample growth under the optimized conditions has the smallest value of root mean square surface roughness. Furthermore, the ω − 2θ and ω scans of the triple-axis X-ray diffraction and transmission electron microscopy result also show the sample grown under the optimized conditions has good crystalline quality.     

Interaction of nobiletin with human serum albumin studied using optical spectroscopy and molecular modeling methods

The binding of nobiletin to human serum albumin (HSA) was investigated by fluorescence, UV-vis, FT-IR, CD, and molecular modeling. Fluorescence data revealed the presence of a single class of binding site on HSA and its binding constants (K) at four different temperatures (289, 296, 303 and 310 K) were 4.054, 4.769, 5.646 and 7.044×10⁴ M⁻¹, respectively. The enthalpy change (ΔH⁰) and the entropy changes (ΔS⁰) were calculated to be 1.938 kJ mol⁻¹ and 155.195 J mol⁻¹ K⁻¹ according to the Van’t Hoff equation. The binding average distance, r, between the donor (HSA) and the acceptor (nobiletin) was evaluated and found to be 2.33 nm according to the Förster's theory of non-radiation energy transfer. Changes in the CD and FT-IR spectra were observed upon ligand binding along with a significant degree of tryptophan fluorescence quenching on complex formation. Computational mapping of the possible binding sites of nobiletin revealed the molecule to be bound in the large hydrophobic cavity of subdomain IIA.     

Rotational analysis of the (4, 8) band in the A-X system of Cl2

Thirty-four rovibronic spectral lines of the Ω=1/2 component of the (4, 8) band in the A-X system of ³⁵Cl₂⁺ were observed in the range of 16,940-17,010 cm⁻¹, employing optical heterodyne-enhanced velocity modulation spectroscopy. Nonlinear least-squares fitting the effective Hamiltonians results in precise band origin and other molecular constants of the levels involved.     

Reliable computing with unreliable components: Using separable environments to stabilize long-term information storage

How, in the face of both intrinsic and extrinsic volatility, can unconventional computing fabrics store information over arbitrarily long periods? Here, we argue that the predictable structure of many realistic environments, both natural and artificial, can be used to maintain useful categorical boundaries even when the computational fabric itself is inherently volatile and the inputs and outputs are partially stochastic. As a concrete example, we consider the storage of binary classifications in connectionist networks, although the underlying principles should be applicable to other unconventional computing paradigms. Specifically, we demonstrate that an unsupervised, activity dependent plasticity rule, AHAH (Anti-Hebbian-And-Hebbian), allows binary classifications to remain stable even when the underlying synaptic weights are subject to random noise. When embedded in environments composed of separable features, the weight vector is restricted by the AHAH rule to local attractors representing stable partitions of the input space, allowing unsupervised recovery of stored binary classifications following random perturbations that leave the system in the same basin of attraction. We conclude that the stability of long-term memories may depend not so much on the reliability of the underlying substrate, but rather on the reproducible structure of the environment itself, suggesting a new paradigm for reliable computing with unreliable components.     

Molecular dynamics of the intramolecular 1, 3-dipolar ene reaction of a nitrile oxide and an alkene: non-statistical behavior of a reaction involving a diradical intermediate*

ABSTRACT

Potential energy surfaces and molecular dynamics of the intramolecular 1, 3-dipolar cycloaddition and ene reaction of a nitrile oxide with an alkene were performed in the gas phase and in dichloromethane with density functional theory. One hundred trajectories were propagated in the gas phase and in dichloromethane, respectively. Twenty percent of the trajectories in the gas phase involve bicyclic intermediate and the mean time gap is 472fs. A dynamically stepwise reaction is observed. In dichloromethane, more reactive trajectories were obtained and the time gap is larger than that in the gas phase.