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991.
Numerical calculations of the excitonic absorption spectra in a strained CdxZn1−xO/ZnO quantum dot are investigated for various Cd contents. We calculate the quantized energies of the exciton as a function of dot radius for various confinement potentials and thereby the interband emission energy is computed considering the internal electric field induced by the spontaneous and piezoelectric polarizations. The optical absorption as a function of photon energy for different dot radii is discussed. Decrease of exciton binding energy and the corresponding optical band gap with the Cd concentration imply that the confinement of carriers decreases with composition x. The main results show that the confined energies and the transition energies between the excited levels are significant for smaller dots. Non-linearity band gap with the increase in Cd content is observed for smaller dots in the strong confinement region and the magnitude of the absorption spectra increases for the transitions between the higher excited levels. 相似文献
992.
Lim Tae Woo Son Yong Yang Dong-Yol Kong Hong-Jin Lee Kwang-Sup 《Applied Physics A: Materials Science & Processing》2011,103(4):1111-1116
The two-photon stereolithography (TPS) process has strong merits for the direct fabrication of 2-D and 3-D microstructures
with sub-100-nm resolution. In this paper, we report an effective fabrication process in which selective ablation-assisted
TPS (SA-TPS) was used to ameliorate some of the limitations of the TPS process. In SA-TPS, two processes (namely, an additive
process of two-photon induced photocuring and a subtractive process of selective laser ablation) were performed sequentially
using a single femtosecond laser optical scanning system. The effectiveness of the proposed process was demonstrated in several
applications, including precise high-resolution patterning at resolution levels higher than those achievable using the TPS
process, and the fabrication of structures with high mechanical sensitivity. 相似文献
993.
Woo M Khan NZ Royce J Mehta U Gagnon B Ramaswamy S Soice N Morelli M Cheng KS 《Journal of chromatography. A》2011,1218(32):5386-5392
A novel anion exchange membrane adsorber is presented which shows excellent impurity removal under different buffer conductivities ranging from 2 to 2 7mS/cm. The membrane utilizes a primary amine ligand (polyallylamine) and was designed specifically to bind impurities at high salt concentrations. Studies with DNA, endotoxin, and virus spiked into buffer at varying salt conditions were done, resulting in clearance of >3, 4, and 4 LRV, respectively, with negligible change on increasing salt up to 27 mS/cm conductivities. Verification of virus removal in mAb feedstocks is also shown. The data are compared with other membrane adsorbers and a conventional resin which utilize traditional chemistries to demonstrate improved purification performance with the primary amine ligand. Additional data on scale-up of the membrane adsorber device is discussed. A stacked flat-sheet design was implemented to ensure linear scale-up of performance using bovine serum albumin (BSA) as a model. The linearly scalable device, coupled with the highly effective membrane for virus, DNA, and endotoxin removal, represents a step forward in polishing technology for the purification of monoclonal antibodies and recombinant proteins. 相似文献
994.
Sung?Bin?ParkEmail author Dong?Wook?Cho Moon?Sik?Woo Sung?Chan?Hwang Young?Ho?Kang Jeong?Guk?Kim Hansoo?Lee 《Journal of Radioanalytical and Nuclear Chemistry》2011,287(2):603-608
Uranium dendrites which were deposited at a solid cathode of an electrorefiner contained a certain amount of salts. These
salts should be removed for the recovery of pure metal using a cathode processor. In the uranium deposits from the electrorefining
process, there are actinide chlorides and rare earth chlorides in addition to uranium chloride in the LiCl–KCl eutectic salt.
The evaporation behaviors of the actinides and rare earth chlorides in the salts should be investigated for the removal of
salts in the deposits. Experiments on the salt evaporation of rare earth chlorides in a LiCl–KCl eutectic salt were carried
out. Though the vapor pressures of the rare earth chlorides were lower than those of the LiCl and KCl, the rare earth chlorides
were co-evaporized with the LiCl–KCl eutectic salt. The Hertz–Langmuir relation was applied for this evaporation, and also
the evaporation rates of the salt were obtained. The co-evaporation of the rare earth chlorides and LiCl–KCl eutectic were
also discussed. 相似文献
995.
996.
997.
On the mechanism of enhanced oxygen reduction reaction in nitrogen-doped graphene nanoribbons 总被引:2,自引:0,他引:2
Nitrogen (N)-doped carbon materials were shown in recent studies to have promising catalytic activity for oxygen reduction reaction (ORR) as a metal-free alternative to platinum, but the underlying molecular mechanism or even the active sites for high catalytic efficiency are still missing or controversial both experimentally and theoretically. We report here the results of periodic density functional theory (DFT) calculations about the ORR at the edge of a graphene nanoribbon (GNR). The edge structure and doped-N near the edge are shown to enhance the oxygen adsorption, the first electron transfer, and also the selectivity toward the four-electron, rather than the two-electron, reduction pathway. We find that the outermost graphitic nitrogen site in particular gives the most desirable characteristics for improved ORR activity, and hence the active site. However, the latter graphitic nitrogen becomes pyridinic-like in the next electron and proton transfer reaction via the ring-opening of a cyclic C-N bond. This inter-conversion between the graphitic and pyridinic sites within a catalytic cycle may reconcile the controversy whether the pyridinic, graphitic, or both nitrogens are active sites. 相似文献
998.
We recently proposed an ultrafast DNA sequencing method that electrically distinguishes different nucleobases on a graphene nanoribbon (GNR), utilizing π-π interaction. Analyzing the molecular orbitals (MOs) and the features of dips in conductance for our GNR-based sequencing device, we prove that the Fano resonance is responsible for the characteristic dips of each nucleobase. 相似文献
999.
Fujii A Hayashi H Park JW Kazama T Mikami N Tsuzuki S 《Physical chemistry chemical physics : PCCP》2011,13(31):14131-14141
The CH/π interaction energies in benzene-alkane model clusters were precisely determined by laser spectroscopy and theoretical calculations. Two-color resonant two-photon ionization spectroscopy was employed to experimentally determine the interaction energies with isomer selectivity. High precision ab initio calculations were also performed to evaluate the CCSD(T) level interaction energies of various isomers at the basis set limit. Binary clusters of benzene with ethane, propane, n-butane, iso-butane, and cyclohexane were studied. The experimental interaction energies were well reproduced by the theoretical evaluations. The magnitude of the interaction energy clearly correlates with the average polarizability of the alkane moiety, demonstrating that the CH/π interaction energy is dominated by the dispersion interaction. On the other hand, the number of C-H groups in contact with the phenyl ring has no relation to the magnitude of the interaction energy, and it indicates that the role of the hydrogen atom in the CH/π interaction is essentially different from that in hydrogen bonds. 相似文献
1000.
Recently, Wolfe-Simon has discovered a bacterium which is able to survive using arsenic(V) rather than phosphorus(V) in its DNA. Thus it is important to investigate some important structural and chemical similarities and dissimilarities between phosphate and arsenate. We compared the monohydrated structures and the alkali/alkaline-earth metal (Na(+), K(+), Mg(2+) and Ca(2+)) complexes of the arsenic acid/anions with those of the phosphoric acid/anions [i.e., H(m)PO(4)(-(3-m)) vs H(m)AsO(4)(-(3-m)) (m = 1-3)]. We carried out geometry optimization along with harmonic frequency calculations using ab initio calculations. Despite the increased van der Waals radius of As, the hydrated structures of both P and As systems show very close similarity (within 0.25 ? in the P/As···O(water) distance and within a few kJ/mol in binding energy) because of the increased induction energies by more polar arsenic acid/anons and slightly increased dispersion energy by a larger size of the As atom. In the metal complexes, the arsenic acid has a slightly larger binding distance (by 0.07-1.0 ?) and weaker binding energy because the As(V) ion has a slightly larger radius than the P(V) ion, and the electrostatic interaction is the dominating feature in these systems. 相似文献