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We consider the one-dimensional steady-state semiconductor deviceequations modelling a pnpn device. There are two relevant scalingsof the equations corresponding to small and large applied voltages.In both scalings, the semiconductor equations can be consideredas singularly perturbed. It turns out that the small-voltagescaling breaks down for current values between two saturationcurrents. In that interval, the large-voltage scaling has tobe employed. For both scalings, we derive the first-order termsof an asymptotic expansion and show that the reduced problemhas a solution. An example verifies that the current-voltagecurves obtained have the expected qualitative structure. 相似文献
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Döbereiner HG Gompper G Haluska CK Kroll DM Petrov PG Riske KA 《Physical review letters》2003,91(4):048301
The bending elasticity of a fluid membrane is characterized by its modulus and spontaneous curvature. We present a new method, advanced flicker spectroscopy of giant nonspherical vesicles, which makes it possible to simultaneously measure both parameters for the first time. Our analysis is based on the generation of a large set of reference data from Monte Carlo simulations of randomly triangulated surfaces. As an example of the potential of the procedure, we monitor thermal trajectories of vesicle shapes and discuss the elastic response of zwitterionic membranes to transmembrane pH gradients. Our technique makes it possible to easily characterize membrane curvature as a function of environmental conditions. 相似文献
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Background
The effects of negative emotion on different processing periods in spatial and verbal working memory (WM) and the possible brain mechanism of the interaction between negative emotion and WM were explored using a high-time resolution event-related potential (ERP) technique and time-locked delayed matching-to-sample task (DMST). 相似文献5.
PLD-assisted VLS growth of aligned ferrite nanorods, nanowires, and nanobelts-synthesis, and properties 总被引:4,自引:0,他引:4
Morber JR Ding Y Haluska MS Li Y Liu JP Wang ZL Snyder RL 《The journal of physical chemistry. B》2006,110(43):21672-21679
We report here a systematic synthesis and characterization of aligned alpha-Fe2O3 (hematite), epsilon-Fe2O3, and Fe3O4 (magnetite) nanorods, nanobelts, and nanowires on alumina substrates using a pulsed laser deposition (PLD) method. The presence of spherical gold catalyst particles at the tips of the nanostructures indicates selective growth via the vapor-liquid-solid (VLS) mechanism. Through a series of experiments, we have produced a primitive "phase diagram" for growing these structures based on several designed pressure and temperature parameters. Transmission electron microscopy (TEM) analysis has shown that the rods, wires, and belts are single-crystalline and grow along <111>m or <110>h directions. X-ray diffraction (XRD) measurements confirm phase and structural analysis. Superconducting quantum interference device (SQUID) measurements show that the iron oxide structures exhibit interesting magnetic behavior, particularly at room temperature. This work is the first known report of magnetite 1D nanostructure growth via the vapor-liquid-solid (VLS) mechanism without using a template, as well as the first known synthesis of long epsilon-Fe2O3 nanobelts and nanowires. 相似文献
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Ahmad G Dickerson MB Cai Y Jones SE Ernst EM Vernon JP Haluska MS Fang Y Wang J Subramanyam G Naik RR Sandhage KH 《Journal of the American Chemical Society》2008,130(1):4-5
A 12-mer peptide, identified through phage display biopanning, has been used for the first time to induce the rapid formation of ferroelectric (tetragonal) nanocrystalline BaTiO3 at room temperature from an aqueous salt precursor solution at near neutral pH. BaTiO3 is widely used in capacitors, thermistors, displays, and sensors owing to its attractive dielectric, ferroelectric, pyroelectric, optical, and electrochemical properties. Two 12-mer peptides (BT1 and BT2) were selected from a phage-displayed peptide library via binding to tetragonal BaTiO3 powder. While these peptides possessed various types of amino acids, 8 of the 12 amino acids were common to both peptides. Each of these peptides induced the formation of faceted nanoparticles (50-100 nm diameter) from an aqueous precursor solution. X-ray diffraction and selected area electron diffraction patterns obtained from these faceted nanoparticles were consistent with the BaTiO3 compound. Rietveld analyses of the X-ray diffraction patterns yielded good fits to tetragonal crystal structures, with the BaTiO3 formed in the presence of the BT2 peptide exhibiting the most tetragonal character. A coating of the latter BaTiO3 nanoparticles exhibited polarization hysteresis (a well-known characteristic of ferroelectric materials) at room temperature and a relative permittivity of 2200. Such rapid, peptide-induced precipitation at room temperature provides new opportunities for direct BaTiO3 formation on low-melting or reactive materials (e.g., plastics, cloths, bio-organics) and the low temperature integration of BaTiO3 into electronic devices (e.g., on silicon or flexible polymer substrates). 相似文献
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Hydrogen storage in sonicated carbon materials 总被引:6,自引:0,他引:6
M. Hirscher M. Becher M. Haluska U. Dettlaff-Weglikowska A. Quintel G.S. Duesberg Y.-M. Choi P. Downes M. Hulman S. Roth I. Stepanek P. Bernier 《Applied Physics A: Materials Science & Processing》2001,72(2):129-132
The hydrogen storage in purified single-wall carbon nanotubes (SWNTs), graphite and diamond powder was investigated at room
temperature and ambient pressure. The samples were sonicated in 5 M HNO3 for various periods of time using an ultrasonic probe of the alloy Ti-6Al-4V. The goal of this treatment was to open the
carbon nanotubes. The maximum value of overall hydrogen storage was found to be 1.5 wt %, as determined by thermal desorption
spectroscopy. The storage capacity increases with sonication time. The sonication treatment introduces particles of the Ti
alloy into the samples, as shown by X-ray diffraction, transmission electron microscopy, and chemical analysis. All of the
hydrogen uptake can be explained by the assumption that the hydrogen is only stored in the Ti-alloy particles. The presence
of Ti-alloy particles does not allow the determination of whether a small amount of hydrogen possibly is stored in the SWNTs
themselves, and the fraction of nanotubes opened by the sonication treatment is unknown.
Received: 18 December 2000 / Accepted: 18 December 2000 / Published online: 9 February 2001 相似文献
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Krishnan Kumar Elias Saion M. K. Halimah Yap CK Muhd Suhaimi Hamzah 《Journal of Radioanalytical and Nuclear Chemistry》2014,301(3):667-676
A study is carried out on the concentrations of rare earth element (REE) elements present in surface mangrove sediments from 10 locations throughout west coast Malaysia. In carrying out the analysis, the best and most convenient method being the instrumental neutron activation analysis (INAA). Samples were obtained, dried, crushed to powdery form and samples prepared for INAA. All the samples for analysis were weighted approximately 150 mg for short irradiation and 200 mg for long irradiation time. As calibration and quality control procedures, blank samples, standard reference material SL-1 were then irradiated with thermal neutron flux of 4 × 1012 cm?2 s?1 at the MINT TRIGA Mark II research reactor which operated at 750 kW by using a pneumatic transport facility. The REE elements of surface sediment samples in this study are Dy, Sm, Eu,Yb, Lu, Tb, La and Ce. It was found that the level of concentrations of all the REE elements varies in the range (0.35–117.4 mg/kg). The geochemical behavior of REEs in surface sediments and normalized pattern (chondrite and shale) has been studied. The degree of sediments contaminations were computed using an enrichment factor. The results showed that the enrichment factor varied in the range (0.75–6.75). 相似文献
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Robert J. Koch Indunil N. Lokuhewa Jiawanjun Shi Michael S. Haluska Scott T. Misture 《Journal of Sol-Gel Science and Technology》2012,64(3):612-618
A group of three-layered Aurivillius compounds with composition Bi2A2TiM2O12, where A?=?Ca, Sr, Ba and M?=?Nb and Ta, have been synthesized as nanoscale powders using two variants of the complex polymerization method. A new modified method is presented that yields single phase powders using reaction temperatures as low as 700?°C and accommodates a wide range of chemical substitutions. The resulting crystallites have dimensions below 100?nm and surface area ~10?m2/g. In situ analysis of the decomposition of the polymeric precursor shows that the polymer yields a three-phase mixture consisting of Bi2A2TiM2O12 and the metastable ??- and ??-polymorphs of Bi2O3 upon heating under flowing air. Full kinetics analysis of a 2-step solid state synthesis method was used to demonstrate that the crystallization of ?? Bi2O3 in the sol?Cgel method greatly accelerates the conversion to the Aurivillius phase. The fluorite structure of ?? Bi2O3 is the same as that of the [Bi2O2]2+ layer in the Aurivillius phase, facilitating rapid and low-temperature crystallization of the Aurivillius phase from the ?? Bi2O3 template. 相似文献