Showing papers by "Dalian University of Technology published in 2009"

Central and autonomic nervous system interaction is altered by short-term meditation

Abstract: Five days of integrative body–mind training (IBMT) improves attention and self-regulation in comparison with the same amount of relaxation training. This paper explores the underlying mechanisms of this finding. We measured the physiological and brain changes at rest before, during, and after 5 days of IBMT and relaxation training. During and after training, the IBMT group showed significantly better physiological reactions in heart rate, respiratory amplitude and rate, and skin conductance response (SCR) than the relaxation control. Differences in heart rate variability (HRV) and EEG power suggested greater involvement of the autonomic nervous system (ANS) in the IBMT group during and after training. Imaging data demonstrated stronger subgenual and adjacent ventral anterior cingulate cortex (ACC) activity in the IBMT group. Frontal midline ACC theta was correlated with high-frequency HRV, suggesting control by the ACC over parasympathetic activity. These results indicate that after 5 days of training, the IBMT group shows better regulation of the ANS by a ventral midfrontal brain system than does the relaxation group. This changed state probably reflects training in the coordination of body and mind given in the IBMT but not in the control group. These results could be useful in the design of further specific interventions.

A Soluble and Highly Conductive Ionomer for High‐Performance Hydroxide Exchange Membrane Fuel Cells

Abstract: Hydrogen proton exchange membrane fuel cells (PEMFCs) have been demonstrated to have high power density and reasonable energy density. Their commercialization, however, has been hampered by the high cost and low durability of their electrocatalysts. By switching from an acidic medium to a basic one, hydroxide (OH ) exchange membrane fuel cells (HEMFCs) have the potential to solve the problems of catalyst cost and durability while achieving high power and energy density. In a basic environment, the cathode oxygen reduction over-potential can be significantly reduced, leading to high fuel cell efficiency, and catalysts in basic medium are also more durable. In addition, the facile cathode kinetics allows nonprecious metals to be used as catalysts, thus drastically reducing the cost of the fuel cell. Further, HEMFCs can offer fuel flexibility (e.g., methanol, ethanol, ethylene glycol, etc.) because of their low overpotential for hydrocarbon fuel oxidation and reduced fuel crossover. One of the most significant problems for HEMFCs is the lack of a soluble ionomer that can be used in the catalyst layer to build an efficient three-phase boundary and thus drastically improve the utilization of the catalyst particles and reduce the internal resistance. One of the most desirable properties of an ionomer for use in the catalyst layer is high solubility in low-boiling-point water-soluble solvents such as ethanol and (nor 2-)propanol, because these solvents are easy and safe to handle and remove during the electrode preparation. The ionomer should also have high hydroxide conductivity and alkaline stability. For PEMFCs, Nafion has been the ionomer of choice because it meets these requirements. But for HEMFCs, the most commonly used material for the hydroxide exchange membrane (HEM) is a quaternary ammonium hydroxide containing polymer that has poor solubility in the aforementioned simple solvents, low hydroxide conductivity, and poor alkaline stability. For example, Tokuyama Co. very recently reported two types of soluble quaternary ammonium hydroxide containing polymers (product code: A3Ver2, soluble in tetrahydrofuran or n-propanol, and AS-4, soluble in n-propanol); however, as a result of their low hydroxide conductivity, their incorporation into the catalyst layers of HEMFCs only led to a moderate improvement in performance. In another case, Park et al. prepared an ionomer solution of the trimethylamine (TMA) and N,N,N’,N’-tetramethyl-1,6-hexanediamine (TMHDA) based polysulfone– methylene quaternary ammonium hydroxide (T/TPQAOH) in dimethylacetamide (DMAc, b.p. 166 8C). Similar to the Tokuyama results, the low hydroxide conductivity of the ionomer significantly limited the improvement in fuel cell performance, and in addition, removal of the high-boilingpoint solvent is considered difficult and unsafe in the presence of finely dispersed catalysts. Owing to the lack of a soluble highly conductive solid ionomer, aqueous solutions of KOH or NaOH have been previously used in the electrodes, where the introduction of metal cations (M) offsets the key advantages of a HEMFC over traditional liquid-electrolytebased alkaline fuel cells (AFCs). Furthermore, owing to the lack of a good ionomer as the binder, non-ionic conductive PTFE and proton-conductive Nafion ionomers were used as substitutes in the electrodes, even though these materials were known to have no hydroxide conductivity. Recently, Varcoe et al. reported a TMHDA-based polyvinylbenzylcrosslinked quaternary ammonium hydroxide (TPCQAOH) electrochemical interface to enhance HEMFC performance. Because the polymer used was not soluble in ionomer form, one could question its ability to form an efficient three-phase-boundary structure in the catalyst layer, thereby limiting performance. Moreover, the hydroxide conductivity and stability of the electrochemical interface are still of concern because it is based on quaternary ammonium hydroxide groups. Quaternary phosphonium containing polymers showed excellent solubility in methanol. The strong basicity of the tertiary phosphine suggests that quaternary phosphonium hydroxides are very strong bases. Therefore in this work, we synthesized a new quaternary phosphonium based ionomer that is soluble in low-boiling-point water-soluble solvents and is highly hydroxide conductive: tris(2,4,6-trimethoxyphenyl) polysulfone-methylene quaternary phosphonium hydroxide (TPQPOH; Scheme 1). The TPQPOH ionomer exhibits excellent solubility in pure methanol, ethanol, and n-propanol and in their aqueous solutions (50 wt% in water, see Table S1 in the Supporting Information). On the other hand, the TPQPOH is insoluble in pure water, even at 80 8C, suggesting that it can be used in the [*] Dr. S. Gu, Dr. R. Cai, T. Luo, Dr. Z. Chen, M. Sun, Y. Liu, Prof. Dr. Y. S. Yan Department of Chemical and Environmental Engineering University of California—Riverside Riverside, CA 92521 (USA) Fax: (+1)951-827-5696 E-mail: yushan.yan@ucr.edu Homepage: http://www.engr.ucr.edu/faculty/chemenv/ yushanyan.html

Graphene oxide as an ideal substrate for hydrogen storage.

Abstract: Organometallic nanomaterials hold the promise for molecular hydrogen (H(2)) storage by providing nearly ideal binding strength to H(2) for room-temperature applications Synthesizing such materials, however, faces severe setbacks due to the problem of metal clustering Inspired by a recent experimental breakthrough ( J Am Chem Soc 2008 , 130 , 6992 ), which demonstrates enhanced H(2) binding in Ti-grafted mesoporous silica, we propose combining the graphene oxide (GO) technique with Ti anchoring to overcome the current synthesis bottleneck for practical storage materials Similar to silica, GO contains ample hydroxyl groups, which are the active sites for anchoring Ti atoms GO can be routinely synthesized and is much lighter than silica Hence, higher gravimetric storage capacity can be readily achieved Our first-principles computations suggest that GO is primarily made of low-energy oxygen-containing structural motifs on the graphene sheet The Ti atoms bind strongly to the oxygen sites with binding energies as high as 450 kJ/mol This is comparable to that of silica and is indeed enough to prevent the Ti atoms from clustering Each Ti can bind multiple H(2) with the desired binding energies (14-41 kJ/mol-H(2)) The estimated theoretical gravimetric and volumetric densities are 49 wt % and 64 g/L, respectively

Recent developments in the chemical synthesis of inorganic porous capsules

Abstract: The preparation of hollow inorganic capsules of defined shape, composition and with tailored properties is of immense scientific and technological interest. This article mainly features recent research progress towards various methods for preparing porous inorganic capsules. By choosing some typical inorganic porous capsules as examples, we present a comprehensive overview of synthetic strategies for inorganic capsules, and some typical organic capsules are also included. The available strategies are broadly categorized into three themes, i.e., hard-templating, soft-templating, and template-free routes, and each includes several well-established methods. The current methods show great success in controlling the size, composition, thickness, permeability and function of the finally achieved porous capsules. Applications of porous capsules in biomedicine, energy resources, environment protection and catalysis are also discussed. It is the intention of this contribution to provide a brief account of these research activities.

Mechanistic Aspects of the Copolymerization of CO2 with Epoxides Using a Thermally Stable Single-Site Cobalt(III) Catalyst

Abstract: The mechanism of the copolymerization of CO(2) and epoxides to afford the corresponding polycarbonates catalyzed by a highly active and thermally stable cobalt(III) complex with 1,5,7-triabicyclo[4,4,0] dec-5-ene (designated as TBD, a sterically hindered organic base) anchored on the ligand framework has been studied by means of electrospray ionization mass spectrometry (ESI-MS) and Fourier transform infrared spectroscopy (FTIR). The single-site, cobalt-based catalyst exhibited excellent activity and selectivity for polymer formation during CO(2)/propylene oxide (PO) copolymerization even at temperatures up to 100 degrees C and high [epoxide]/[catalyst] ratios, and/or low CO(2) pressures. The anchored TBD on the ligand framework plays an important role in maintaining thermal stability and high activity of the catalyst. ESI-MS and FTIR studies, in combination with some control experiments, confirmed the formation of the carboxylate intermediate with regard to the anchored TBD on the catalyst ligand framework. This analysis demonstrated that the formed carboxylate intermediate helped to stabilize the active Co(III) species against decomposition to inactive Co(II) by reversibly intramolecular Co-O bond formation and dissociation. Previous studies of binary catalyst systems based on Co(III)-Salen complexes did not address the role of these nucleophilic cocatalysts in stabilizing active Co(III) species during the copolymerization. The present study provides a new mechanistic understanding of these binary catalyst systems in which alternating chain-growth and dissociation of propagating carboxylate species derived from the nucleophilic axial anion and the nucleophilic cocatalyst take turns at both sides of the Co(III)-Salen center. This significantly increases the reaction rate and also helps to stabilize the active SalenCo(III) against decomposition to inactive SalenCo(II) even at low CO(2) pressures and/or relatively high temperatures.

Athermal Silicon-on-insulator ring resonators by overlaying a polymer cladding on narrowed waveguides

Abstract: Athermal silicon ring resonators are experimentally demonstrated by overlaying a polymer cladding on narrowed silicon wires. The ideal width to achieve athermal condition for the TE mode of 220 nm-height SOI waveguides is found to be around 350 nm. After overlaying a polymer layer, the wavelength temperature dependence of the silicon ring resonator is reduced to less than 5 pm/degrees C, almost eleven times less than that of normal silicon waveguides. The optical loss of a 350-nm bent waveguide (with a radius of 15 microm) is extracted from the ring transmission spectrum. The scattering loss is reduced to an acceptable level of about 50 dB/cm after overlaying a polymer cladding.

Towards an explanatory and computational theory of scientific discovery

Abstract: We propose an explanatory and computational theory of transformative discoveries in science. The theory is derived from a recurring theme found in a diverse range of scientific change, scientific discovery, and knowledge diffusion theories in philosophy of science, sociology of science, social network analysis, and information science. The theory extends the concept of structural holes from social networks to a broader range of associative networks found in science studies, especially including networks that reflect underlying intellectual structures such as co-citation networks and collaboration networks. The central premise is that connecting otherwise disparate patches of knowledge is a valuable mechanism of creative thinking in general and transformative scientific discovery in particular.

Robust Fault Detection for Switched Linear Systems With State Delays

Abstract: This correspondence deals with the problem of robust fault detection for discrete-time switched systems with state delays under an arbitrary switching signal. The fault detection filter is used as the residual generator, in which the filter parameters are dependent on the system mode. Attention is focused on designing the robust fault detection filter such that, for unknown inputs, control inputs, and model uncertainties, the estimation error between the residuals and faults is minimized. The problem of robust fault detection is converted into an H infin-filtering problem. By a switched Lyapunov functional approach, a sufficient condition for the solvability of this problem is established in terms of linear matrix inequalities. A numerical example is provided to demonstrate the effectiveness of the proposed method.

A Color‐Tunable Europium Complex Emitting Three Primary Colors and White Light

Abstract: The manufacture of new full-color displays is one of the main tasks in flat-panel display systems and lighting technology. Different applications place different demands on emitted light: in some cases a white-light source is needed, and in others pure colors are necessary. Thus, white emission should ideally be composed of three (blue, green, and red) or two (blue and yellow) primary colors and cover the whole visible range from 400 to 700 nm, and the emitter should have the ability to emit the primary colors simultaneously with equal intensities to produce white light and the pure colors separately in a tunable way. Considerable interest exists for such color-tunable materials, which can be used to define or modify environments, moods, and brands. Traditional methods of such white light generation typically rely on mixing various primary colors from different emitting materials. An alternative approach for the generation of efficient (white) light sources is to use a single-component emitter, which can have advantages such as greater stability, better reproducibility, no phase separation, and simpler fabrication processes. 8] Although a few materials show white-light emission as a single-emitting component, none has been reported to produce well-separated blue, green, and red emissions beside white light. Since energy transfer typically quenches one or more of the emission pathways and thereby restricts the transitions that define the output spectrum, the design of color tunable single-component emitters requires readily tailorable different fluorophores and fine-tuning of the energy-transfer processes between the different fluorophores. On the other hand, lanthanide-containing materials, which exhibit excellent sharp-emission luminescence properties with suitable sensitization, have attracted considerable interest and been effectively used in designing white-emitting nanoparticles. With judiciously chosen red(Eu, Pr, Sm), green(Tb, Er), and blue-emissive (Tm , Ce, Dy) ions doped in an suitable host, it is possible to obtain phosphors which emit across the entire visible spectrum with high color purity. Specifically, an Eu-containing singlecomponent complex has been reported to offer white-light emission in a carefully designed system which only allows partial energy transfer between the sensitizing fluorophore and the Eu center. Herein we report the design and synthesis of a new fluorophore that exhibits tunable emission of three primary colors (blue, green, and red) and white light, by combining an Eu moiety as the origin of red light with an organic ligand that comprises a blue-emitting coumarin fluorophore and a green-emitting Rhodamine 6G fluorophore. Coumarin-Rhodamine CR1 was synthesized by reaction of 7-diethylamino-2-oxo-2H-chromen-3-carboxylic chloride and N-(Rhodamine-6G)lactamethylenediamine and recrystallized from ethanol as yellow crystals. Single-crystal X-ray structural analysis confirms the coexistence of two fluorophores in CR1 (Supporting Information Figure S1), whereby the Rhodamine 6G moiety is in a luminescence-inactive ringclosed tautomeric form. Europium compound CR1-Eu (1) was prepared by refluxing ligand CR1 and [Eu(tta)3] in THF (tta = 1,1,1-trifluoro-3-(2-thenoyl)acetone) and purified by recrystallization as an amorphous yellow powder. Elemental analysis and H NMR spectroscopic characterization suggest the chemical formula [Eu(tta)2(CR1)2](tta) for 1 (Figure 1).

Photoeletrocatalytic activity of a Cu2O-loaded self-organized highly oriented TiO2 nanotube array electrode for 4-chlorophenol degradation.

Abstract: Differently sized Cu2O nanoparticles have been assembled photocatalytically on the surface of self-organized highly oriented TiO2 nanotubes obtained by anodization of a Ti sheet in fluoride-containing electrolytes. X-ray diffraction analysis identifies an anatase structure and fine preferential orientation of (101) planes. The UV-vis absorption edge of the TiO2 nanotube arrays shift to lower energy after Cu2O loading. The composite array electrode exhibits a higher photovoltage response than the TiO2 powders directly deposited on a Ti sheet. The highest photoconversion efficiencies observed for the Cu2O-loaded electrode are 17.2% and 0.82% under UV light and visible light irradiation, respectively. Especially, the composite array electrode shows a higher efficiency than the nonloaded one for the photoelectrocatalytic decomposition of 4-chlorophenol. The improved photoeletrocatalytic activity of the TiO2/Cu2O composite array electrode is attributed to the synergistic effect of Cu2O nanoparticles and TiO2 nanotube arrays. The Cu2O nanoparticles could enhance the efficiency of photon harvesting and reduce the chances of electron-hole recombination by sending the electrons to the conduction band of TiO2 nanotubes. The accumulated electrons in the conduction band of TiO2 nanotubes would reduce oxygen to form peroxides for enhanced advanced oxidation. The byproducts were identified by high-performance liquid chromatography.

Light-driven hydrogen production catalysed by transition metal complexes in homogeneous systems

Abstract: The development of heterogeneous catalytic systems for hydrogen production from water under light irradiation has been investigated during last three decades Homogeneous photocatalysts, however, are very attractive in sense that their chemical and photochemical properties can be understood and tuned on molecular level Moreover, in homogeneous systems catalysts may be covalently bound to photosensitizers, which leads to more efficient electron transfer Molecular devices for water splitting based on such a systems are of great interest In this review, we summarize recent progresses in the synthesis, properties and application of metal-based molecular catalysts for photoinduced hydrogen evolution in homogeneous systems

Tuning the intramolecular charge transfer of alkynylpyrenes: effect on photophysical properties and its application in design of OFF-ON fluorescent thiol probes.

Abstract: Green and yellow-emitting 1,6- and 1,8-bis(phenylethynyl) pyrenes (dyes 7, 8, 9, and 10) with different intramolecular charge transfer (ICT) feature were synthesized and the effect of ICT on the photophysical properties of these derivatives were studied by UV−vis absorption spectra, fluorescence emission spectra, and DFT/TDDFT calculations. For the dyes with electron-pushing group (e.g., -dimethylamino, dye 8 and dye 10), structureless and solvent polarity-sensitive fluorescence emission spectra were observed. Conversely, dye with electron-withdrawing group (e.g., −CN, dye 7) shows structured and solvent polarity-independent emission spectra. OFF−ON fluorescent thiol probes 11 and 12 with 2,4-dinitrobenzenesulfonyl protected ethynylpyrene fluorophore were designed based on DFT/TDDFT calculations, which predicts dark state (S1) for these thiol probes (e.g., oscillator strength f = 0.0086 for S1←S0 transition of the probe 11). This dark state is induced by the ICT effect with ethynylated pyrene fluorophore ...

Hormone Activity of Hydroxylated Polybrominated Diphenyl Ethers on Human Thyroid Receptor-β: In Vitro and In Silico Investigations

Abstract: BackgroundHydroxylated polybrominated diphenyl ethers (HO-PBDEs) may disrupt thyroid hormone status because of their structural similarity to thyroid hormone. However, the molecular mechanisms of i...

Nucleophilic attack of hydroxide on a Mn(V) oxo complex: a model of the O-O bond formation in the oxygen evolving complex of photosystem II.

Abstract: A manganese(III) corrole complex, 1, has been synthesized and used to study a potential mechanism for oxidation of water to molecular oxygen. Oxidation by t-BuOOH gave the Mn-V=O complex 2. Additio ...

Continuum topology optimization with non-probabilistic reliability constraints based on multi-ellipsoid convex model

Abstract: Using a quantified measure for non-probab ilistic reliability based on the multi-ellipsoid convex model, the topology optimization of continuum structures in presence of uncertain-but-bounded parameters is investigated. The problem is formulated as a double-loop optimization one. The inner loop handles evaluation of the non-probabilistic reliability index, and the outer loop treats the optimum material distribution using the results from the inner loop for checking feasibility of the reliability constraints. For circumventing the numerical difficulties arising from its nested nature, the topology optimization problem with reliability constraints is reformulated into an equivalent one with constraints on the concerned performance. In this context, the adjoint variable schemes for sensitivity analysis with respect to uncertain variables as well as design variables are discussed. The structural optimization problem is then solved by a gradient-based algorithm using the obtained sensitivity. In the present formulation, the uncertain-but bounded uncertain variations of material properties, geometrical dimensions and loading conditions can be realistically accounted for. Numerical investigations illustrate the applicability and the validity of the present problem statement as well as the proposed numerical techniques. The computational results also reveal that non-probabilistic reliability-based topology optimization may yield more reasonable material layouts than conventional deterministic approaches. The proposed method can be regarded as an attractive supplement to the stochastic reliability-based topology optimization.