Potassium and oxygen diffusion and segregation in nickel

Nickel is used as catalyst in alkaline electrochemical systems like batteries, electrolyzers and fuel cells. Adsorption experiments from potassium on a thin NiO(100) epitactic layer on an Ag(100)-single crystal substrate showed that potassium intrudes in that NiO-layer where at a temperature of 350 K a mixed oxide phase was built. At 120 K metallic potassium was adsorbed on the NiO surface. A symmetric K2p-peak showed that potassium is in the oxidized state compared to the asymmetric peak of metallic potassium. No potassium diffused into metallic nickel at a temperature of 450 K. The electrochemically oxidized surface layer consisted of nickel, oxygen and also potassium. After heating and ion-etching no more potassium was detectable by x-ray photoelectron spectroscopy (XPS) and energy dispersive x-ray spectroscopy (EDX). But it was visible again after oxidizing and heating of the sample to 670 K. Therefore, the potassium must have been in the bulk. It diffused to the surface if there was oxygen at sufficiently high temperatures. Further heating reduces the surface and the potassium also disappeared. Received: 6 September 1998 / Revised: 1 April 1999 / Accepted: 16 April 1999     

Evaluation of split/splitless operation and rapid heating of a multi-bed sorption trap used for gas chromatography analysis of large-volume air samples

The effects of split-flow operation and rapid trap heating on injection-plug widths from an electrically heated, microscale, multibed sorption trap were evaluated. The sorption trap has been designed to quantitatively collect volatile organic compounds from large-volume vapor samples and inject them into a gas chromatograph. Previous trap designs resulted in injection-plug widths of typically a second or more, and this significantly degraded chromatographic resolution, particularly for early-eluting sample components and for high-speed separations. Injection-plug widths are determined by the heating rate of the trap during sample desorption and the volumetric flow rate of carrier gas through the trap. The effects of the heating rate of the trap and carrier gas velocity through the trap on the injection-plug widths of pentane, octane, and undecane were studied. Carrier gas velocity through the trap was increased by splitting the flow coming from the trap between the column and a vent. This decreases transport time from the trap to the column, and thus decreases injection-plug widths. The heating rate for the trap was increased by increasing the applied voltage in the range from 4 to 30 V. Increasing the heating rate decreases the time required to desorb the analytes from the sorbent bed, thus decreasing injection-plug width. Injection-plug widths as small as 89, 210, and 520 ms were obtained in the split mode with very fast heating rates for n-pentane, noctane, and n-undecane, respectively. The effect of split ratio on resolving power, peak height, and peak width was also evaluated.     

Surface-Enhanced Raman Scattering (SERS) on transition metal and semiconductor nanostructures

Surface-Enhanced Raman Scattering (SERS) spectroscopy has experienced a rapid growth over the past 30 years, and has become a valuable tool in various research areas. In conjunction with recent explosive development of nanoscience and nanotechnology, the SERS-active substrates have also expanded from traditional Group 11 metals (Au, Ag, Cu) to non-Group 11 nanostructures. This paper gives an overview of historical advances in the use of non-Group 11 nanostructures as substrates for SERS. Several possible mechanisms and important factors for SERS from non-Group 11 nanostructures are discussed in detail. The SERS from non-Group 11 nanostructures provides many significant applications in surface, interface analysis and biochemical detection. It is reasonable to believe that the advancement in the non-Group 11 nanostructures-based SERS-active substrates will lead to a more promising future for the SERS technology in surface science, spectroscopy and biomedicine.     

POSSIBLE CAUSES OF COUNTERCLOCKWISE LOOP OF TROPICAL CYCLONES

The counterclockwise loop of a moving tropical cyclone in the model atmosphere is clearly shown in the numerical experiment by six sets of time integrations over periods longer than seven days in terms of a barotropical quasi-geostrophic model containing terms of environmental heating and dissipation. Numerical investigation is performed of the dependence of the abnormal path stability upon the computational domain size and the disturbance of the heat source, initial value and iterative precision, indicating that this type of path is a stabler form of motion for the cyclone in the model atmosphere. And the possible causes are presented.     

At-column heating and a resistively heated, liquid-cooled thermal modulator for a low-resource bench-top GC x GC

A transportable GC x GC instrument is under development for on-site applications that would benefit from the enhanced resolution and powers of detection, which can be achieved by this method. In the present study, a low-resource GC x GC instrument using an electrically heated and liquid-cooled single-stage thermal modulator that requires no cryogenic materials is evaluated. The instrument also uses at-column heating, thus eliminating the need for a convection oven to house the two columns. The stainless-steel modulator tube is coated with PDMS, which can be heated to 350 degrees C for sample injection into the second-dimension column. The modulator is cooled to -30 degrees C by a 100 mL/min flow of PEG by means of a commercial liquid chiller and a small recirculating pump. Resistive heating of the modulator tube is provided by a programmable power supply, which uses a voltage program that results in increasing modulator temperature during an analysis. This, together with more rapid cooling by the use of a liquid cooling medium, results in reduced solute breakthrough following each heating cycle as the modulator cools to a temperature where quantitative trapping resumes. As a result, modulated peak widths at half-height of less than 40 ms are observed. Design and performance details are presented along with chromatograms of gasoline and an essential oil sample.     

DSC study of stabilization reactions in poly(acrylonitrile-co-itaconic acid) with peak-resolving method

The effect of itaconic acid (IA) content and heating rate on the stabilization reactions in poly(acrylonitrile-co-itaconic acid) (P(AN-co-IA)) was investigated by differential scanning calorimetry (DSC) with peak-resolving method. Increasing IA content was effective in decreasing the initial temperature and the heat evolved, and found to enhance oxidative reactions to some extent. While, promoting heating rate resulted in a shift of the exotherm to a higher temperature and a more rapid liberation of heat. The percentage of area of the first exothermic peak increased with increasing heating rate, which would be attributed to the enhancement of the free radical cyclization reactions.     

Studies on preparation of HDPE/CB composites including a novel oriented structure by the microwave heating and their characterization

Microwave heating has several advantages over traditional methods of heating, including rapid and uniform heating, greater penetration depth of heat into material, lower power costs and selective heating within the material and so on. In this paper, effects of microwave heating on the properties of high‐density polyethylene/carbon black (HDPE/CB) composites were studied. The results show that the HDPE/CB composites can be heated via microwave irradiation, and composites with different CB concentration exhibit different microwave heatability. The 20 wt% CB composites have the most rapid heating rate, and its temperature reaches 78°C after 10 sec, and 159°C after 150 sec, respectively. Meanwhile, microwave heating improves the mechanical properties of HDPE/CB composites. Scanning Electron Microscopy (SEM) analysis shows a better combination between CB particles and HDPE after microwave irradiation. Furthermore, selective heating of microwave was used to prepare a novel oriented structure, which the core layer has preferential orientation and the surface layer has little orientation. Characterization of the novel oriented structure was also studied. Wide angle X‐ray diffraction (WAXD) analysis of 25 wt% CB composites with the novel oriented structure shows that the diffraction peaks of the surface layer are obviously weaker than those of the core layer, which indicates that orientation in the core layer is more intensive than that in the surface layer. The novel oriented structure is different to the traditional skin‐core structure, in which the surface layer has preferential orientation and the core layer has little orientation. Copyright © 2009 John Wiley & Sons, Ltd.     

The mechanism of thermally stimulated delayed fluorescence

Rapid heating of isotopic mixed crystalline hexadeuterobenzene at 4.2°K causes an intense peak in the emission of delayed fluorescence (DF). This behaviour can be explained by the rapid depopulation of triplet exciton traps during thermal stimulation. which is followed by annihilation of excitons.Rapid heating was performed either by IR radiation or by electrical heating of the sample. The peak height of the DF emission was found to be dependent on the initial temperature via the square of occupied-trap concentration and proportional to the heating rate during stimulation. This agrees with a kinetic analysis of thermally stimulated DF. For this only one type of trap was assumed. Since weak excitation only was presumed, nonlinear terms in the rate equations were neglected.     

Uranium-235 fallout from the nuclear-powered satellite Cosmos-1402

The presence of excess uranium-235 was detected in many of the rain samples collected at Fayetteville (36°N, 94°W), Arkansas, during the period between April 1983 and March 1984. The experimental data indicate that the uranium-235 originated from the nuclear reactor on board the Soviet satellite Cosmos-1402, which fell over the South Atlantic Ocean on 7 February 1983.This investigation was supported by the National Science Foundation under Grant ATM 82-06718 and ATM 84-07618.     

Simulation of a movement of dispersed particles in view of a second gas circulation in a cyclone

The gas flow in the cyclone was simulated in view of a constant component of a gas velocity directed from periphery to center of a cyclone. An influence of this component of the gas velocity makes it possible a judgment that with an increase in a value of the radial flowing off the particle velocity can shift and achieve outside wall of a vortex body. Its occurrence was not observed earlier and its forecast was difficult since the radial flowing off was directed to other side. As shown from computations at certain intensity of the second circulation such a critical size of the particles occurs that the particles transfer from suspension to rapid movement toward the outside wall of the vortex chamber.     

Non-isothermal unfolding/denaturing kinetics of egg white protein

Egg protein is an important part of our food to get protein in our daily diet, and makes this protein more important to researchers to understand its kinetic behavior to understand the energy involved in the digestion of the egg protein. Hence, the present study explores the denaturing kinetics of the protein obtained from the hen??s egg white (EW) using high resolution calorimetric technique. Fresh EW was scanned for heating and cooling to see the thermodynamics from 10 to 100?°C at different heating ramp rates varying from 1 to 20?°C?min^?1. An endothermic peak was found on heating scan showing denaturing of protein which was found absent at the cooling indicating the absence of any residue after heating. The denature peak shifted towards higher temperature as ramp rate increases following Arrhenius behavior and shows an activated denaturing kinetics of the egg protein. This peak was also compared with the water to avoid water effects. Behavior of denaturing peak can be explained in terms of Arrhenius theory and further discussed to get the energy involved in digestion.     

竹材非等温热解动力学

利用热重分析技术对竹材在高纯N2条件下,从室温至1273K进行了非等温热解分析,研究了升温速率(5、10、20和40K/min)对热解过程的影响,探讨了其热解机理。研究表明,竹材非等温热解过程主要分为失水干燥、快速热解和缓慢分解三个阶段组成,其中第二阶段是整个过程的主要阶段,析出大量挥发分造成明显失重。升温速率对热解过程有显著影响,随着升温速率的增加,最大热解速度增大,对应的峰值温度升高,热滞后现象加重,热解各阶段向高温侧移动。热解机理满足一维扩散Parabolic法则,反应机理函数为g(α)=α2。不同升温速率下活化能为75.32-82.99kJ.mol-1,指前因子为1.17×105-1.12×106min-1。     

Temperature requirements for thermal modulation in comprehensive two-dimensional gas chromatography

Temperature requirements for trapping and release of compounds in a cryogenic gas loop-type GC x GC modulator were determined. Maximum trapping temperatures on the uncoated, deactivated modulator capillary were determined for compounds from C4 (bp -0.5 degrees C) to C40 (bp 522 degrees C). The liquid-nitrogen cooled gas flow rate was reduced from a high of 15.5 to 1.5 SLPM over the range to achieve the required trapping temperature. Excessive cold jet flow rates caused irreversible trapping and peak tailing for semi-volatile compounds above C26. Alternate cold jet coolants were investigated. An ice water-cooled jet was able to trap compounds with boiling points from C18 (bp 316 degrees C) to C40 and a room temperature air-cooled jet was able to trap compounds from C20 (bp 344 degrees C) to C40. The hot jet produced launch temperatures approximately 40 degrees C hotter than the elution temperature with heating time constants of 8 to 27 ms. Modulated compound peaks were symmetrical with half-height peak widths of 43 to 56 ms for compounds with little second column retention, and 70 to 75 ms for compounds with more second column retention. The liquid nitrogen-cooled loop modulator with gas flow programming was used to produce a GC x GC chromatogram for a crude oil that contained compounds from C7 to C47.     

Rapid, sensitive DNT vapor detection with UV-assisted photo-chemically synthesized gold nanoparticle SERS substrates

We report rapid, sensitive, and direct detection of 2,4-dinitrotoluene (DNT) vapor using tailored gold nanoparticles (Au-NPs) as the SERS substrate. The Au-NPs were synthesized using the UV-assisted photo-chemical reduction method and subsequently formed a monolayer on the glass slide through polymer-mediated self-assembly. The SERS substrate such prepared has high SERS enhancement, high affinity towards DNT vapor, and rapid response to the DNT adsorption/desorption. We systematically studied the effect of the Au-NP size and surface density on the SERS performance such as enhancement factor and response time. With the optimized SERS substrate, an enhancement factor over 5.6 × 10(6) was achieved. Furthermore, real-time detection of DNT vapor with only 0.35 second data acquisition time was demonstrated using a 12 mW laser. Compared to previously reported results, we achieved two orders of magnitude reduction in detection time and more than one order of magnitude reduction in excitation laser power. The detection limit is estimated to be 0.4 attogram, which corresponds to a sub-ppb DNT concentration in air. This work will lead to the development of ultra-fast and ultra-sensitive SERS devices for explosive identification and monitoring.     

Thermal desorption and vapor transport characteristics in an explosive trace detector

Swipe-based explosive trace detectors rely on thermal desorption to vaporize explosive particles collected on a swipe. The vaporized material is carried by air flows from the desorption unit to the inlet of the chemical analyzer, typically an ion mobility spectrometer. We have observed that the amount of explosives detected from a swipe varies with the physical location of explosives collected on the swipe. There are two issues that may contribute to this effect: inhomogeneous or insufficient heating of the swipe during desorption and low velocity air flows that inefficiently transport desorbed vapor during the instruments analysis time. To better characterize this effect, we have simulated the air movements within a generic desorption unit using commercially available computational fluid dynamics software. Simulations are three dimensional, symmetric and solved under steady, laminar flow conditions. The calculated velocity field correlates directly with experimental detector response to the high explosive RDX. Results suggest that the limiting factor in this model thermal desorption unit is the flow-field around the swipe and flow rate into the detector, rather than heat transfer to the swipe itself. Buoyancy effects due to heating dominate the flow-field and produce a vertical bulk fluid motion within the domain that opposes much of the flow drawn into the analyzer.     

Inside-out disruption of silica/gold core-shell nanoparticles by pulsed laser irradiation

Near-infrared (NIR) femtosecond laser irradiation of metallodielectric core-shell silica-gold (SiO(2)-Au) nanoparticles can induce extreme local heating prior to the rapid dissipation of energy caused by the large surface area/volume ratio of nanometer-scale objects. At low pulse intensities, the dielectric silica core is removed, leaving an incomplete gold shell behind. The gold shells with water inside and out still efficiently absorb NIR light from subsequent pulses, showing that a complete shell is not necessary for absorption. At higher pulse intensities, the gold shell itself is melted and disrupted, leading to smaller, approximately 20-nm gold nanoparticles. Spectroscopic measurements show that this disruption is accompanied by optical hole burning of the peak at 730 nm and formation of a new peak at 530 nm. The silica removal and gold shell disruption confirms significant temperature rise of the core-shall nanoparticle. However, the entire process leads to minimal heating of the bulk solution due to the low net energy input.     

The CaO?MgO?P2O5 System at 1000°C for P2O5 ⩽ 33.3 mole %

The quasi ternary phase diagram CaO-MgO-P₂O₅ at 1000°C for P₂O₅ ? 33.3 mole-% is determined by heating some 140 compositions prepared from the appropriate ones of 4 starting chemicals (reagent grade CaHPO₄, CaCO₃, MgO, and MgHPO₄ · 3 aq.). Products were investigated with X-ray diffraction and heating was continued until no more changes in phase composition and peak positions in the X-ray diffraction pattern were observed, leading occasionally to heating times of over 1000 hours. There are three major regions of solid solution: for the whitlockite phase, and for the ternary compounds on the pyro- and the ortho-phosphate join. The extent of solid solution of the ternary pyrophosphate compound was determined by the change in peak position in the X-ray diffraction pattern with composition and was found to be 15.9–27.5 mole-% MgO. Two and three phase areas were determined using the change in peak position data for the whitlockite and ternary pyrophosphate compound. The experiments were carried out in air. However additional experiments in a CO₂ atmosphere revealed no changes in the X-ray diffraction patterns, apart from those in which apatite was involved. The apatite phase did not incorporate detectable amounts of Mg, not on heating in air nor on heating in a carbondioxide atmosphere.     

Galactomannans from two species ofGleditsia studied by13C NMR

Galactomannans isolated from the seeds ofGleditsia macracantha (GMM) andGleditsia texana (GMT) have molecular masses (MM) of 750.000 and 795.000 and galactose to mannose ratios of 1.0∶4.9 and 1.0∶3.8, respectively. GMT and GMM are depolymerized to fragments of MM 25 and 19 kDa with retention of the primary structure and are studied by¹³C NMR spectroscopy. The principal chains of GMM and GMT are β-1-4-mannopyranose residues in which the hydroxyl groups of C-6 are substituted by single α-D-galactopyranose units. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 566–569, September–October, 1999.     

THREE-DIMENSIONAL NUMERICAL SIMULATION OF TROPICAL CYCLONE AND THE EFFECTS OF RADIATIVE PROCESSES ON IT

In this paper, a three-dimensional primitive equation numerical model includingvarious physical processes is constructed. Using this model, the development and thestructure of the tropical cyclone (typhoon) are first successfully simulated. Then theeffects of radiative processes on the development of the cyclone are investigated. Theradiative processes and their parameterization include long wave, short wave radiationand cloud type and cloudiness respectively. The results show that the tropical cyclonewill develop earlier and more quickly after the effect of radiative processes isincorporated, but the differences in intensity between the two cases with and withoutradiative processes at the final state are not evident. Only at the developing stage hasthe cyclone affected by radiation a sharper decrease in the surface pressure, a strongerwind and upward motion. a more obvious eye and eyewall, etc. All the results showthat the radiative processes are important in the earlier development stage of thetropica     

On-Line SPE Coupled with LC�CAPCI�CMS for the Determination of Trace Explosives in Water

In this study, a rapid, sensitive, and fully automated on-line solid phase extraction (SPE)?Cliquid chromatography (LC)?Cmass spectrometry (MS) method for the analysis of explosive residues in water, was systematically investigated. First, separation of explosive residues was achieved by reverse-phase chromatography using an XDB-C18 column in 30 min with an eluent containing 0.1% acetic acid, 5 mM ammonium acetate, and methanol. Secondly, atmospheric pressures chemical ionization (APCI) and electrospray ionization (ESI) interfaced with the MS detector were used to examine the explosive residues, indicating that APCI?CMS was more suitable than ESI?CMS for the detection of explosives. Thirdly, the conditions for on-line SPE, including solvent pH and sample injected volume, were optimized. The calibration curves obtained for all explosives studied were linear in the concentration range 0.5?C50 ??g L^?1. The detection limits of this method ranged from 0.05 to 0.5 ??g L^?1 when 4000 ??L of sample was on-line pre-concentrated on C18 enrichment column. The recoveries from lake waters spiked with explosive standard solution ranged from 90.5 to 108.0%. The proposed method is simple, fast, and could be applied successfully to the analysis of explosive residues in contaminated water without any further pretreatment.