计算化学在生物质气化研究中的应用

从可再生的生物质得到的替代能源是解决石油资源枯竭的方法之一。但生物质能的制备过程复杂,包括热解和反应速率较慢的气化过程。为了研究其反应机理,必须从实验和理论两方面入手。本综述介绍了生物质气化过程研究中应用的计算理论,并讨论了理论模型的类型、大小及电子结构的影响。此外,还对气化过程中的吸附、重排、迁移和解吸进行了综述。     

Phase separation in immiscible silver–copper alloy thin films

Far from equilibrium, immiscible nanocrystalline Ag–Cu alloy thin films of nominal composition Ag–40 at.% Cu have been deposited by co-sputter deposition. Both X-ray and electron diffraction studies indicate that the as-deposited films largely consist of nanocrystalline grains of a single alloyed face-centered cubic (fcc) phase. However, detailed three-dimensional atom probe tomography studies on the same films give direct evidence of a nanoscale phase separation within the columnar grains of the as-deposited Ag–Cu films. Subsequent annealing of these films at 200 °C leads to two effects; a more pronounced nanoscale separation of the Ag and Cu phases, as well as the early stages of recrystallization leading to the breakdown of the columnar grain morphology. Finally, annealing at a higher temperature of 390 °C for a long period of time leads to complete recrystallization, grain coarsening, and a complete phase separation into fcc Cu and fcc Ag phases.     

Initial analyses of naltriben, a delta opioid receptor antagonist, as a putative medicine for treating cocaine abuse.

The authors explored naltriben's (NTB, a delta opioid antagonist) potential to be a pharmacotherapy for cocaine abuse. NTB (3–6 mg/kg) reduced rats' (Rattus norvegicus) intravenous, self-administration of cocaine, daily, across 5 days. NTB did not, however, interfere with rats' pressing for water. NTB (3 mg/kg) blocked cocaine's facilitation of pressing for brain stimulation, daily, for 5 days. As doses of NTB were explored, it was found that 10 mg/kg of NTB was lethal for about one third of the rats. Smaller doses (e.g., 3 mg/kg) gave some indications of toxicity as indexed by NTB's tendency to reduce pressing for brain stimulation by itself. NTB (3 mg/kg) induced a mild conditioned taste aversion but had no negative effects on rats' ability to learn and remember a sequence of mazes. Taken together, these results lead to the suggestion that opioidergic processes play an important role in mediating cocaine's reinforcement. Although NTB may not be the ideal opioid antagonist for treating people, it has many positive properties supporting further investigation of opioid antagonists as agents for treating cocaine addiction. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A general multilevel SEM framework for assessing multilevel mediation.

Several methods for testing mediation hypotheses with 2-level nested data have been proposed by researchers using a multilevel modeling (MLM) paradigm. However, these MLM approaches do not accommodate mediation pathways with Level-2 outcomes and may produce conflated estimates of between- and within-level components of indirect effects. Moreover, these methods have each appeared in isolation, so a unified framework that integrates the existing methods, as well as new multilevel mediation models, is lacking. Here we show that a multilevel structural equation modeling (MSEM) paradigm can overcome these 2 limitations of mediation analysis with MLM. We present an integrative 2-level MSEM mathematical framework that subsumes new and existing multilevel mediation approaches as special cases. We use several applied examples and accompanying software code to illustrate the flexibility of this framework and to show that different substantive conclusions can be drawn using MSEM versus MLM. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Thermodynamic approach to enhanced dispersion and physical properties in a carbon nanotube/polypeptide nanocomposite

A high molecular weight synthetic polypeptide has been designed which exhibits favorable interactions with single wall carbon nanotubes (SWCNTs). The enthalpic and entropic penalties of mixing between these two molecules are reduced due to the polypeptide's aromatic sidechains and helical secondary structure, respectively. These enhanced interactions result in a well dispersed SWCNT/Poly (l-Leucine-ran-l-Phenylalanine) nanocomposite with enhanced mechanical and electrical properties using only shear mixing and sonication. At 0.5 wt% loading of SWCNT filler, the nanocomposite exhibits simultaneous increases in the Young's modulus, failure strain, and toughness of 8%, 120%, and 144%, respectively. At 1 kHz, the same nanotube loading level also enhances the dielectric constant from 2.95 to 22.81, while increasing the conductivity by four orders of magnitude.     

Fibromyalgia: The role of sleep in affect and in negative event reactivity and recovery.

Objective: Fibromyalgia (FM) syndrome is a chronic pain condition characterized by diffuse muscle pain, increased negative mood, and sleep disturbance. Until recently, sleep disturbance in persons with FM has been modeled as the result of the disease process or its associated pain. The current study examined sleep disturbance (i.e., sleep duration and sleep quality) as a predictor of daily affect, stress reactivity, and stress recovery. Design and Measures: A hybrid of daily diary and ecological momentary assessment methodology was used to evaluate the psychosocial functioning of 89 women with FM. Participants recorded numeric ratings of pain, fatigue, and positive and negative affect 3 times throughout the day for 30 consecutive days. At the end of each day, participants completed daily diary records of positive and negative life events. In addition, participants reported on their sleep duration and sleep quality each morning. Results: After accounting for the effects of positive events, negative events, and pain on daily affect scores, it was found that sleep duration and quality were prospectively related to affect and fatigue. Furthermore, the effects of inadequate sleep on negative affect were cumulative. In addition, an inadequate amount of sleep prevented affective recovery from days with a high number of negative events. Conclusions: These results lend support to the hypothesis that sleep is a component of allostatic load and has an upstream role in daily functioning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Secondhand smoke exposure and C-reactive protein levels in youth.

Using data from the National Health and Nutrition Examination Survey (NHANES, 1999-2002), we examined the association of secondhand tobacco exposure, estimated by serum cotinine, with serum C-reactive protein (CRP) concentrations in nonsmoking participants, aged 6-18 years. The association between serum cotinine and serum CRP was analyzed using multiple linear regression, with adjustment for other study variables. All analyses used weighted data and adjustments for design effects. Multiple regression analysis indicated that a change in serum cotinine of 0.5 ng/ml was associated with a 0.96 mg/dl change in CRP (95% CI=0.93-1.00), even after adjustment for age, white blood cell count, and body mass index percentile. We found a significant association between secondhand smoke exposure, assessed by serum cotinine, and elevated serum CRP among nonsmoking youth. Secondhand smoke exposure may pose an important long-term cardiovascular risk for children and adolescents.     

Design of an optical thermal sensor for proton exchange membrane fuel cell temperature measurement using phosphor thermometry

Internal temperatures in a proton exchange membrane (PEM) fuel cell govern the ionic conductivities of the polymer electrolyte, influence the reaction rate at the electrodes, and control the water vapor pressure inside the cell. It is vital to fully understand thermal behavior in a PEM fuel cell if performance and durability are to be optimized. The objective of this research was to design, construct, and implement thermal sensors based on the principles of the lifetime-decay method of phosphor thermometry to measure temperatures inside a PEM fuel cell. Five sensors were designed and calibrated with a maximum uncertainty of ±0.6 °C. Using these sensors, surface temperatures were measured on the cathode gas diffusion layer of a 25 cm² PEM fuel cell. The test results demonstrate the utility of the optical temperature sensor design and provide insight into the thermal behavior found in a PEM fuel cell.     

Improved ion mobility resolving power with increased buffer gas pressure

Security and military applications of analytical techniques demand a small, rugged, reliable instrument that has traditionally been served well by atmospheric pressure ion mobility spectrometry (IMS) systems. Modern threats stipulate these instruments must reliably operate in increasingly complex environments. Previous work has demonstrated that increasing the pressure of an IMS drift tube has the potential to increase the resolving power of IMS, but operation at low temperatures resulted in a leveling of the measured resolving power as a function of pressure. By creating a novel aperture grid/Faraday plate design, a high-pressure IMS (HPIMS) system has been created that maintains a resolving power efficiency of 80% regardless of the pressure applied to the cell. This allows previously unattainable resolving powers to be achieved utilizing a small (10.7 cm) IMS cell. Using high pressure, a stand-alone IMS cell of 10.7 cm length has demonstrated a resolving power of 102 when operated at 2.5 atm. An increase in peak-to-peak resolution was also noted as pressure increased. Finally, the slope of the resulting inverse mobility/pressure curve for a single analyte has been shown to be proportional to the collision-cross-section of the analyte of interest, providing a novel method for the calculation of collision-cross-section of target ions from the HPIMS data.