Constant time steady gradient NMR diffusometry using the secondary stimulated echo

A pulse sequence producing a second stimulated echo is suggested for the compensation of relaxation and residual dipolar interaction effects in steady gradient spin echo diffusometry. Steady field gradients of considerable strength exist in the fringe field of NMR magnets, for instance. While the absolute echo time of the second stimulated echo is kept constant throughout the experiment, the interval between the first two radiofrequency pulses is augmented leading to a modulation of the amplitude of that second stimulated echo by self-diffusion only. The unique feature of this technique is that it is of a single-scan/single-echo-signal nature. That is, no reference signals neither of the same pulse sequence nor of separate experiments are needed. The new method was tested with poly(ethylene oxide) melts and proved to provide reliable data for (time dependent) self-diffusion coefficients down to the physical limit (D approximately 10(-15)m(2)/s) when flip-flop spin diffusion starts to become effective.     

Edge-wave-driven durable variations in the thickness of the surfactant film and concentration of surface floats

By employing a simple model for small-scale linear edge waves propagating along a homogeneous sloping beach, we demonstrate that certain combinations of linear wave components may lead to durable changes in the thickness of the surfactant film, equivalently, in the concentration of various substances (debris, litter) floating on the water surface. Such changes are caused by high-amplitude transient elevations that resemble rogue waves and occur during dispersive focusing of wave fields with a continuous spectrum. This process can be treated as an intrinsic mechanism of production of patches in the surface layer of an otherwise homogeneous coastal environment impacted by linear edge waves.     

High sensitivity CW-Cavity Ring Down Spectroscopy of N2O near 1.5 μm (II)

We present the second part of the investigation of the high sensitivity absorption spectrum of nitrous oxide by CW-Cavity Ring Down Spectroscopy near 1.5 μm. In a first paper [A.W. Liu, S. Kassi, P. Malara, D. Romanini, V.I. Perevalov, S.A. Tashkun, S.M. Hu, A. Campargue, J. Mol. Spectrosc. 244 (2007) 33-47] devoted to the 6000-6833 cm⁻¹ region, more than 6000 line positions of five isotopologues (¹⁴N₂¹⁶O, ¹⁵N¹⁴N¹⁶O, ¹⁴N¹⁵N¹⁶O, ¹⁴N₂¹⁷O, and ¹⁴N₂¹⁸O), were rovibrationally assigned to a total of 68 bands. The achieved noise equivalent absorption (α_min ∼ 2 × 10⁻¹⁰ cm⁻¹) allowed for the detection of lines with intensity weaker than 2 × 10⁻²⁹ cm/molecule. In this contribution, the investigated region was extended down to 5905 cm⁻¹ and additional recordings allowed accessing small spectral sections uncovered in our preceding recordings. A deeper analysis based on the predictions of the effective Hamiltonian model has allowed assigning a total of 3149 transitions and lowering the percentage of lines left unassigned from 51% to 28%. It led to the analysis of 35, 6, 7, and 6 bands for the ¹⁴N₂¹⁶O, ¹⁵N¹⁴N¹⁶O, ¹⁴N¹⁵N¹⁶O, and ¹⁴N₂¹⁸O isotopologues, respectively. Forty-two of these 54 bands are newly observed, while the rotational analysis of the twelve others is significantly extended and improved. Most of the bands were found unperturbed and their line positions could be reproduced within the experimental uncertainty (about 1 × 10⁻³ cm⁻¹). The corresponding spectroscopic parameters are reported. Local rovibrational perturbations induced by either intrapolyad or interpolyad couplings were found to affect five hot bands of ¹⁴N₂¹⁶O. Their detailed analysis is presented.     

Epitaxial growth of cobalt clusters on the bare and the oxide film grown on NiAl(1 0 0) surfaces

The structure of the nano-sized cobalt clusters on bare NiAl(1 0 0) and an oxidized NiAl(1 0 0) surfaces have been investigated by AES, LEED and RHEED. The deposition of Co onto bare NiAl(1 0 0) at room temperature led to small crystalline Co grains and surface asperities of substrate. The latter is likely induced by replacement of surface Al, Ni atoms by Co deposit. At 800 K Co particles aggregate to form clusters, but incorporation of Co into bulk NiAl(1 0 0) could occur upon annealing at 900 K. On the other hand, pure face-centered cubic (fcc) phase of Co crystallites of ≈1 nm in diameter with inclusion of smaller-sized particles (D < 1 nm) are observed on Θ-Al₂O₃ after Co deposition at room temperature. After annealing the Co nano-clusters grow larger at expense of small particles (D ≈ 3 nm), where the [1 1 0] and [−1 1 0] axis of the Co(0 0 1) facets are parallel to the [1 0 0] and [0 1 0] directions of (0 0 1)oxide, respectively. The in-plane lattice constant of Co clusters is ca. 4% larger than that of bulk Co, yielding less strain at the Co/oxide interface. A 15° ± 10% random orientation of the normal to (0 0 1) facet of Co clusters with respect to (0 0 1)oxide surface was deduced from the “arc”-shape reflection spots in RHEED. These results suggest that both orientation and phase of Co clusters are strongly affected by the nature and structure of oxide surface.     

一种新型叠层光敏全息记录软片

通过化学反应，在三醋酸纤维素睛基的正反两面同时生成具有感光活性的光敏层的方法，获得了一种具有叠层光敏性的全息记录软片：重铬酸盐－三醋酸纤维素酯。由该软片记录的叠层体积全息光栅，具有迄今为止，最高的一级实验衍射效率（５４％）。     

A non-thermal chemical synthesis of hydrophilic and amorphous cobalt oxide films for supercapacitor application

Present work explored a room temperature, simple and low cost chemical route for the preparation of hydrophilic cobalt oxide films from alkaline cobalt chloride (CoCl₂:6H₂O) and double distilled water precursor solutions. As-deposited cobalt oxide films showed amorphous nature, which is one of the prime requirements for supercapacitor, as confirmed from X-ray diffraction studies. Changes in direct band gap energy and electrical resistivity of as-deposited cobalt oxide films were confirmed after annealing. Spherical grains of about 40-50 nm diameters were uniformly distributed over the substrate surface. Surface wettability studied in contact with liquid interface, showed hydrophilic nature as water contact angle was <90°. Finally, presence of cobalt-oxygen covalent bond was observed from Raman shift experiment.     

Nd:YAG laser synthesis of nanostructural V2O5 from vanadium oxide sols: Morphological and structural characterizations

Vanadium oxide thin films were prepared by sol-gel method, then subjected to Nd:YAG laser (CW, 1064 nm) radiation. The characteristics of the films were changed by varying the intensity of the laser radiation. The nanocrystalline films were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). XRD revealed that above 102 W/cm² the original xerogel structure disappears and above 129 W/cm² the films become totally polycrystalline with an orthorhombic structure. From TEM observations, we can see that due to laser radiation, the originally fibrillar-like particles disappear and irregular shaped, layer structured V₂O₅ particles are created. From XPS spectra we can conclude that due to laser radiation the O/V ratio increased with higher intensities.     

薄膜光学常数的模拟退火算法研究

在薄膜的光学参数拟合时，操作者给定的模型初值对拟合结果有很大的关系。采用广泛用于求解复杂系统优化问题的模拟退火算法来求解薄膜光学常数，降低了操作者给定拟合模型初值的要求。通过对常规的模拟退火算法以及非常快速的模拟退火方法(Very Fast Stimulated Annealing，VFSA)分析，针对性地在模型扰动及退火计划上存在的缺陷作了改进，提高了VFSA算法的计算稳健性。通过大量的拟合实践，验证了提出的改进模拟退火方法的有效性。     

Infrared combination and difference bands of the NO dimer

The mid-infrared (1500-3800 cm⁻¹) absorption spectrum of gaseous nitric oxide has been studied at low temperature (99 K) with a long absorption path (160 m) in order to observe weak combination, difference, and overtone bands of the NO dimer. About ten new bands were assigned with greater or lesser certainty. Combined with previous results, they lead to a set of 12 secure and 7 tentative vibrational term values for (NO)₂, essentially doubling our knowledge of NO dimer vibrational states. The strongest non-fundamental bands in this region, other than the ν₁ (symmetric N-O stretch) + ν₅ (asymmetric N-O stretch) overtone, involve combinations of ν₅ with ν₃ (intermolecular stretch). Excitation of ν₅ results in increased frequencies for the intermolecular modes ν₂, ν₃, and ν₄. A new value of 155.5 cm⁻¹ was obtained for ν₄, the elusive infrared-inactive out-of-plane fundamental vibration.     

Dynamics of gold clusters on amorphous carbon films induced by annealing in a transmission electron microscope

The change of the size distribution of Au clusters induced by annealing was studied in situ by transmission electron microscopy. Starting from statistically distributed Au clusters on a thin amorphous carbon film, “islands” are formed within a few months storage at room temperature, which consist of Au clusters with sizes <4 nm embedded in a thin Au film. These islands cover originally areas with sizes around 25 × 70 nm². If the temperature is increased in the transmission electron microscope two different processes can be clearly distinguished that lead to the coarsening of the cluster size distribution: cluster coalescence and (contactless) Ostwald ripening. The degree and rate of the coarsening are found to depend on the underlying surface (Au film or amorphous carbon) and the exposure to the high-flux high-energy electron beam, which can be estimated to lead to high-temperature excursions in a cluster on a 10⁻¹² s time scale. The experimental findings are confirmed by Monte-Carlo simulations using the many-body Gupta potentials in order to calculate the Au/Au interaction. Moreover, the results of MC simulations suggest an electron-beam induced formation of a “quasi-two-dimensional gas” of small highly mobile Au species on the Au film, which promotes Ostwald ripening.