Structural,electronic, and magnetic properties of heterofullerene C58Si with odd number of atoms and a near planar tetracoordinate Si atom

Density functional calculations and minimization techniques have been employed to characterize the structural and electronic properties of [5,6]-heterofullerene-C₅₈Si-C_2v. Since it has odd number of atoms and a near planar tetracoordinate Si atom on the skeleton of the cage, it has odd number of atoms assembling a cage and is a novel molecule. Vibrational frequencies of the molecule have been calculated at the B3LYP/6-31G* level of theory. The absence of imaginary vibrational frequency confirms that the molecule corresponds to a true minimum on the potential energy hypersurface. Sixteen ¹³C nuclear magnetic resonance (NMR) spectral signals of C₅₈Si are characterized, and its heat of formation was estimated in this work.     

Theoretical prediction of maximum capacity of C80 and Si80 fullerenes for noble gas storage

In this paper, we try to demonstrate that how many helium, neon and argon atoms can be trapped into fullerene cages until the pressure becomes large enough to break the C₈₀ and Si₈₀ frameworks. The maximum number of helium, neon and argon atoms which can be encapsulated into C₈₀ fullerene, is found with 46, 24 and 10 atoms respectively. Having investigated the mechanism of C₈₀ opening, we found that if the number of helium and argon atoms reaches to 50 and 12 respectively, the CC bonds of C₈₀ are broken and the gas molecules escaped from the fullerene cage. The final optimization geometries of latter complexes are similar to the shopping cart. Therefore, this appearance is named as molecular cart. Moreover, the maximum capacity of Si₈₀ fullerene for encapsulated noble gas atoms is found 95, 56 and 22 for helium, neon and argon atoms correspondingly. It is worth highlighting that the new phenomenon of trapping argon atoms into Si₈₀ cage is observed, when a Si atom randomly added to the center of Ar₁₉@Si₈₀ structures. In this case, the SiSi bonds of Si₈₀ are broken and two argon atoms will escape from the cage. After that, the framework rebuilds its structure like the initial one. This phenomenon is introduced as molecular cesarean section. The estimated internal pressure of Ng atoms trapped into the fullerene cages is also investigated. Results show that the maximum calculated internal pressure is related to He₄₆@C₈₀ and He₉₅@Si₈₀ structures with 212.3 and 144.1 GPa respectively.     

Theoretical study on the cylinder-shaped N78 cage

Recent theoretical studies have suggested that the stabilizing factors for large nitrogen cages tend to favor more five-membered rings, more three-membered rings and cylindrical structure with large numbers of layers. Further studies of relative stability of the all-nitrogen molecule have prompted to figure out what brings about the stabilizing factors. Herein, the cylinder-shaped molecule of N(78) (D(3h)) has been studied in detail. The geometry and energies are examined at B3LYP/cc-pVDZ and single point energy calculations at MP2/cc-pVDZ are carried out for the purposes of determining relative thermodynamic stability. NBO analysis and AIM analysis are applied to investigate the bonding properties of the cage molecule. The major result of this study is the identification of intra-molecular interactions, whether it is at B3LYP/cc-pVDZ or at MP2/cc-pVDZ, as the dominant stabilizing factor for the large all-nitrogen cage. The length of the cylinder-shaped molecule is about 2.5nm. N(78) (D(3h)) might be one novel nanomaterial which is environment-friendly and as a beeline nanotube or a beeline "nano-bar", it is expected to impact a wide range of applications.     

Application of the independent molecule model to elucidate the dynamics of structure I methane hydrate

Raman spectroscopy has exhibited the C–H stretch (A₁ mode) frequency ν₁ of hydrated methanes at 2915 cm⁻¹ for the 5¹² cage and 2905 cm⁻¹ for the 5¹²6² cage. These values are lower than the frequency of 2916.5 cm⁻¹ in gaseous methane. In this paper, we theoretically examine the Raman spectra observed in methane hydrate by normal mode analysis using the independent molecule model. By a breakdown of the symmetry, the four frequencies in modes A₁, E, T₂ and T₂ observed in gaseous methane are separated into nine frequencies in the hydrate. It is necessary to consider the anharmonic potential energy within methane and hydrogen bonding between methane hydrogen and water oxygen in order to get a result in qualitative agreement with experiment. The frequency in the 5¹²6² cage is shifted downward in comparison to the one in 5¹², and the frequencies in the both cages are also shifted downward compared with the frequencies in gas. Calculations are also reported for the isotopic methane (CD₄, ¹³CH₄) hydrates.     

Application of the independent molecule model to elucidate the dynamics of structure I methane hydrate: a second report

Two model systems of methane hydrate are constructed. One has a small cage surrounded by 12 large cages. The other has a large cage surrounded by four small cages and ten large cages. Three different H-bonding network patterns between waters are formed, and three random configurations of methane in each cage are chosen. A new method called the surface water fixed model is presented in which the energy minimum conformations for both model systems are preserved close to the X-ray crystallized structure. With normal mode analysis, we calculated frequencies of 2916.6 cm⁻¹ for a small cage at a centre, 2915.9 cm⁻¹ not at a centre, and 2911.7 cm⁻¹ for a large cage at a centre, and 2911.3 cm⁻¹ not at a centre. These frequencies are in moderate agreement with the corresponding Raman spectra, though not adequate. With our new method, however, it should be possible to improve agreement with the Raman spectra, if a model system vastly larger than the present model systems were constructed.     

Weighted HOMO-LUMO energy separations of properly closed-shell fullerene isomers

The HOMO-LUMO energy separation has been used as an index of kinetic stability for fullerenes. However, its utility is rather limited, in that a larger fullerene molecule in general has a smaller HOMO-LUMO energy separation even if it is kinetically stable. The T value, i.e., the HOMO-LUMO energy separation weighted with the number of carbon atoms, is free from this kind of difficulty. Properly closed-shell isomers of fullerenes with antibonding LUMOs were found to have an exceptionally large T value irrespective of the number of constituent carbon atoms and are hence predicted to be kinetically very stable. Thus, the antibonding character of the LUMOs is one of the determinants for kinetically stabilizing fullerene molecules.     

Efficient parallel algorithms for solvent accessible surface areaof proteins

We present faster sequential and parallel algorithms for computing the solvent accessible surface area (ASA) of protein molecules. The ASA is computed by finding the exposed surface areas of the spheres obtained by increasing the van der Waals radii of the atoms with the van der Waals radius of the solvent. Using domain specific knowledge, we show that the number of sphere intersections is only O(n), where n is the number of atoms in the protein molecule. For computing sphere intersections, we present hash-based algorithms that run in O(n) expected sequential time and O(n/p) expected parallel time and sort-based algorithms that run in worst-case O(n log n) sequential time and O(n log n/p) parallel time. These are significant improvements over previously known algorithms which take O(n²) time sequentially and O(n²/p) time in parallel. We present a Monte Carlo algorithm for computing the solvent accessible surface area. The basic idea is to generate points uniformly at random on the surface of spheres obtained by increasing the van der Waals radii of the atoms with the van der Waals radius of the solvent molecule and to test the points for accessibility. We also provide error bounds as a function of the sample size. Experimental verification of the algorithms is carried out using an IBM SP-2     

P改性ZSM-5分子筛的结构及酸性变化

P-ZSM-5分子筛通常用来催化甲醇转化制轻烯烃,乙醇脱水制乙烯,芳烃的烷基化或者歧化等反应。目前,P-ZSM-5分子筛中磷和分子筛之间的相互作用仍不清楚。本文通过密度泛函理论（Density Functional Theory,DFT）计算了ZSM-5分子筛改性前后的结构及酸性变化。结果发现P骨架外改性后,磷酸分子的氢原子和分子筛骨架氧原子形成氢键作用,并且O₄,H_a和0_zeo总是保持在一条直线上,这是稳定的骨架外改性结构;骨架改性后,分子筛优化前后的结构发生较大变化,这是因为固定了8T模型中的终止氢原子,分子筛的骨架结构阻止了H₂PO₃基团的插入。本文还计算了磷酸分子和分子筛的酸性位之间的关系,研究发现,分子筛中引入P后,其酸性降低,且骨架改性后酸性减弱的程度更大。这一结果可以进一步指导实验,制备出不同酸性的分子筛。     

Computations of model narrow nanotubes closed by fragments of smaller fullerenes and quasi-fullerenes

New type of carbon nanotubes—narrow nanotubes—has recently been observed with diameters of 4–5 Å. It has been postulated that the narrow nanotubes are closed by fullerene fragments of C₂₀ and C₃₆. This paper presents computational results on related model nanotubes with stoichiometries such as C₈₀, C₈₄, C₉₆, C₁₀₈, or C₁₂₀. The computations were carried out at the PM3, AM1, SAM1, HF/3-21G, HF/4-31G, and B3LYP/6-31G^* levels. Two C₃₆ fullerenes were considered, D_6h and D_2d. At the PM3 level and with the C₈₄ nanotube stoichiometry, the D_2d cage closure gave a lower energy (by 185 kcal/mol and a diameter of 5.42 Å). There is another possible candidate, a C₃₂ cage with D_4d symmetry (two four-membered rings). At the PM3 level and with the C₉₆ nanotube stoichiometry, the D_4d closure (with a diameter of 5.43 Å) had energy lower by 210 kcal/mol than that of the D_6h nanotube closure. On the other hand, four-membered rings should not play a significant role for narrow nanotubes with a diameter of 4 Å, where the dodecahedron-related closure should be exclusive. Still narrower nanotubes are briefly discussed.     

Stability of feedback systems containing a single odd monotonic nonlinearity

In this paper the stability of a feedback system with a single odd monotonic nonlinearity is considered. It is shown that if a multiplierZ(s)having a specific form exists so thatG(s) Z^{pm1}(s)is positive real, the feedback system is asymptotically stable for every odd monotonic function lying in the first and third quadrants. The multiplierZ(s)suggested can have both complex poles and complex zesro. A simple example is included to demonstrate the applicability of the criterion developed.     

Gas response dependence on gate metal morphology of field-effect devices

The dependence of the gas response on the gate metal morphology of field-effect gas sensors has been investigated in a new systematic way by using a scanning light pulse technique (SLPT) together with fabrication of metal gates where the metal morphology is continuously varied over the gate area. With the SLPT the local gas response at different points of the gate area can be measured. Furthermore, a mass spectrometric local gas sampling technique has been applied in combination with the local gas response measurements, which gives complementary information about the surface chemistry and how it changes with the morphology of the metal gate.

Three different gate metals, Pd, Pt and Ir, have been studied by analysing the morphology and the gas response to five different gases, H₂, NH₃, C₂H₅OH, C₂H₄ and CH₃CHO. Morphological aspects such as crack coverage, concentration of cracks and the length of the crack boundary, have been calculated from acquired scanning electron microscopy (SEM) images. Different possible response mechanisms are discussed in order to explain the observed responses and to understand the role of the morphology and the choice of the catalytic metal.

Only in the case of ammonia a direct correlation between the morphological aspects, e.g. crack coverage, and the response was found. For Pd large changes in the local water pressure close to the metal gate surface have been measured at different parts of the metal gate by using the local gas sampling technique and a correlation is observed with the simultaneously measured gas response. Of the response mechanisms discussed in this contribution only a dissociative mechanism, where hydrogen atoms trapped at the interface between the metal gate and the insulator gives the response of the device, is consistent with all obtained results.     

Fabrication of thick Si resonators with a frontside-releaseetch-diffusion process

A frontside-release etch-diffusion process has been developed to create released single-crystalline Si microstructures without the need for wafer bonding. This frontside-release process is simple and requires only a single mask. A deep dry etch in an electron cyclotron resonance source is used to define the structures, followed by a short boron diffusion to convert them to p⁺⁺ Si. A short etch in ethylenediamine pyrocatechol (EDP) is then used to undercut and release the structures from the frontside of the Si wafer. The structures are isolated from the substrate using a reverse-biased p⁺⁺/n junction. Since the structures have a high aspect ratio, beams longer than 1 mm can be released without sticking to the substrate, and thick resonators are flat with no bending due to stresses. Resonant microstructures with thicknesses ranging from 10 to 55 μm thick have been fabricated using this process and their resonant frequency has been measured. For typical clamped-clamped beam resonators that were 24 μm thick, 5 μm wide, and 400 μm long, with 2-μm comb gaps, a resonant frequency of 90.6 kHz and a quality factor of 362 were measured in air     

Systematic studies on responses of metal-oxide sensor surfaces to straight chain alkanes, alcohols, aldehydes, ketones, acids and esters using the SOMMSA approach

Metal oxide sensors are widely used in the so-called “electronic noses”, and it is proposed that these equipment can be used to objectify food aromas.

Due to the fact that, up to now, systematic approaches to correlate the intensity of sensor responses with the structure of a given volatile have scarcely been performed [K. Suzuki, T. Takada, Highly sensitive odour sensors using various SnO₂ thick films, Sens. Actuators, B 24–25 (1995) 773–776; B. Lalauze et al., High sensitivity materials for gas detection, Sens. Actuators, B 8 (1992) 237–243; K. Fukui, Detection and measurement of odor by sintered tin oxide gas sensor, Sens. Actuators, B 5 (1991) 27–32; J.W. Gardner, A. Pike et al., Integrated array sensor for detecting organic solvents, Sens. Actuators, B 13–14 (1993) 355–357.], it is as yet not possible to predict the sensitivity and the specivity of metal oxide preparations vs. a given chemical structure.

Using the SOMMSA approach [T. Hofmann et al., High resolution gas chromatography/selective odorant measurement by multisensor array (HRGC/SOMSA): a useful approach to standardize multisensor arrays for the use in the detection of key food odorants, Sens. Actuators, B 41 (1997) 81–87.], mixtures of alkanes, alcohols, aldehydes (all with chain length of 8–14 carbon atoms) and acids (chain length of 2–10 carbon atoms) were applied to different self-prepared metal oxide mixtures and the signal intensities were monitored. In addition, quantitative experiments were performed to determine the detection threshold of sensors. E.g. (E,E)-2,4-nonadienal, one of the most important odorants in fresh cucumbers, could be clearly detected at a level below 4.0 ng/ml (He) by a sensor containing a mixture of ZnO and SnO₂.     

Computing smooth molecular surfaces

We consider how we set out to formulate a parallel analytical molecular surface algorithm that has expected linear complexity with respect to the total number of atoms in a molecule. To achieve this goal, we avoided computing the complete 3D regular triangulation over the entire set of atoms, a process that takes time O(n log n), where n is the number of atoms in the molecule. We aim to compute and display these surfaces at interactive rates, by taking advantage of advances in computational geometry, making further algorithmic improvements and parallelizing the computations     

量子化学方法研究阴离子表面活性剂在气液界面上的吸附

用量子化学方法中的密度泛函理论,在B3LYP/6-3IG水平上,对十二烷基硫酸钠（SDS）阴离子表面活性剂与水分子形成的水合物CH₃（CH₂）₁₁OSO₃ˉ（H₂O）_n（n=0～7）进行结构优化和频率计算。从分子水平上研究了CH₃（CH₂）₁₁OSO₃ˉ在气液界面上与水分子的相互作用。计算结果表明:（1）7个水分子与极性头均采用1:1型和2:1型,即极性头中一个氧原子或2个氧原子与水分子以氢键形式构成水合层;（2）CH₃（CH₂）₁₁OSO₃中的氧原子与水分子中的氧原子最短氢键的键长（O-O键长）在0.27～0.31 nm之间,H…O键长在0.19～0.21 nm之间,O-H…O键角在140°～167°之间,均属于中强氢键:（3）水合物R（S-O）平均键长比表面活性剂单体分子分别增长了,说明形成水合物后S-O间的键减弱;（4）结合能D₀从64.04 kJ/mol增加到.428.29 kJ/mol,说明随着水分子数的增加,所获得的7种水合物的稳定性依次增强,表明最终形成的水合层是稳定的:（5）随着水分子数增加疏水基链长收缩,亲水基总电荷增加,C12-O13-S14的键角增大;（6）由于烷烃链带有了弱电荷,使胶束内核带有了部分极性,此种极性介于烷烃油相和水相的极性之间,利于表面活性剂在溶液中的聚集。     

Integration of Speech Recognition and Machine Translation in Computer-Assisted Translation

Parallel integration of automatic speech recognition (ASR) models and statistical machine translation (MT) models is an unexplored research area in comparison to the large amount of works done on integrating them in series, i.e., speech-to-speech translation. Parallel integration of these models is possible when we have access to the speech of a target language text and to its corresponding source language text, like a computer-assisted translation system. To our knowledge, only a few methods for integrating ASR models with MT models in parallel have been studied. In this paper, we systematically study a number of different translation models in the context of the $N$-best list rescoring. As an alternative to the $N$ -best list rescoring, we use ASR word graphs in order to arrive at a tighter integration of ASR and MT models. The experiments are carried out on two tasks: English-to-German with an ASR vocabulary size of 17 K words, and Spanish-to-English with an ASR vocabulary of 58 K words. For the best method, the MT models reduce the ASR word error rate by a relative of 18% and 29% on the 17 K and the 58 K tasks, respectively.      

The pseudo-self-similar traffic model: application and validation

Since the early 1990s, a variety of studies have shown that network traffic, both for local- and wide-area networks, has self-similar properties. This led to new approaches in network traffic modelling because most traditional traffic approaches result in the underestimation of performance measures of interest. Instead of developing completely new traffic models, a number of researchers have proposed to adapt traditional traffic modelling approaches to incorporate aspects of self-similarity. The motivation for doing so is the hope to be able to reuse techniques and tools that have been developed in the past and with which experience has been gained. One such approach is the so-called pseudo-self-similar traffic (PSST) model. This model is appealing, as it is easy to understand and easily embedded in Markovian performance evaluation studies.

In applying this model in a number of cases, we have perceived various problems which we initially thought were particular to these specific cases. However, we recently have been able to show that these problems are fundamental to the PSST model.

In this paper we review the PSST model, validate it experimentally and discuss its shortcomings. As far as we know, this is the first paper that discusses these shortcomings formally. We also report on ongoing work to overcome some of these problems.     

囊泡表面氨基酸信号分子与维生素B6衍生物受体反应平衡常数的估计

为了构建一个新的以维生素B₆衍生物(PL⁺C₁₆)为受体、氨基酸为信号分子的人工细胞信号转导超分子体系,测定在40℃、pH值分别为7.0、8.0及9.0的缓冲液体系下,4种信号分子（甘氨酸、β-丙氨酸、γ-氨基丁酸、天冬氨酸）在不同初始浓度下与受体PL⁺C₁₆反应的吸光度,通过用MATLAB模型拟合工具包将其实验数据进行非线性拟合,估计反应的平衡常数K,定量考察了4种信号分子到达人工细胞膜载体表面与受体分子的结合能力。结果表明:不同pH值下,同一氨基化合物与受体PL⁺C₁₆反应的平衡常数K有明显差异,而在同一pH值下,不同氨基酸与受体的K值也有很大差别,其中pH值为9.0时,天冬氨酸的K值最大,与受体PL⁺C₁₆的结合能力最强。     

A family of network topologies with multiple loops and logarithmic diameter

A new family of network topologies containing multiple loops is discussed in this paper. In the proposed structure, N processors are interconnected to form a graph G(m, N), m 3, where m is a parameter of the graph such that N is an even multiple of m and (m − 1) × 2[(^{m− l)/2}]+ < N m × 2[^m/2]+1. The graph G(m, N) is hamiltonian with an average node degree (3 + l/m), when m is even and exactly 3 when m is odd. Whereas, the maximum node degree is 4. The diameter of G(m, N) is upper bounded by [11m/8]+ 1. A point to point routing algorithm has been presented. Implementation of ASCEND/DESCEND algorithms in O(m) time has been discussed. It has been shown that in case of a single node failure, the diameter increases by at most 6.     

CH基团替代N对Nn（CH）8-nH8（n=0-7）结构与性质影响的理论研究

采用密度泛函理论的B3LYP方法在6-311++G^**基组水平上优化了,用等电子体-CH-基团逐个取代N8H8环状异构体中最稳定的分子构型中的N原子,得到32种N_n（CH）_8-nH₈（n=0-7）的异构体,应用自然键轨道理论NBO和分子中的原子理论AIM分析了这些化合物成键特征和相对稳定性,G3MP2方法计算了各异构体的能量及生成热。研究结果表明:N原子孤对电子到相邻的碳氮键的超共轭作用是影响碳氮键长变化的主要因素;随着等电子体-CH-基团取代分子中氮原子的个数的增加,分子的生产热逐渐减小,而分子的能量将逐渐升高,且有很好的线性相关性。