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排序方式: 共有211条查询结果,搜索用时 15 毫秒
1.
Michael Dickson 《Foundations of Physics》2015,45(10):1330-1340
2.
Experimental analysis, modeling, and theoretical design of McMaster pore-filled nanofiltration membranes 总被引:1,自引:0,他引:1
A side-by-side comparison of the performance of McMaster pore-filled (MacPF) and commercial nanofiltration (NF) membranes is presented here. The single-salt and multi-component performance of these membranes is studied using experimental data and using a mathematical model. The pseudo two-dimensional model is based on the extended Nernst–Planck equation, a modified Poisson–Boltzmann equation, and hydrodynamic calculations. The model includes four structural properties of the membrane: pore radius, pure water permeability, surface charge density and the ratio of effective membrane thickness to water content. The analysis demonstrates that the rejection and transport mechanisms are the same in the commercial and MacPF membranes with different contributions from each type of mechanism (convection, diffusion and electromigration). Solute rejection in NF membranes is determined primarily by a combination of steric and electrostatic effects. The selectivity of MacPF membranes is primarily determined by electrostatic effects with a significantly smaller contribution of steric effects compared to commercial membranes. Hence, these membranes have the ability to reject ions while remaining highly permeable to low molecular weight organics. Additionally, a new theoretical membrane design approach is presented. This design procedure potentially offers the optimization of NF membrane performance by tailoring the membrane structure and operating variables to the specific process, simultaneously. The procedure is validated at the laboratory scale. 相似文献
3.
The amount of chemiluminescence (CL) or light that is emitted from human polymorphonuclear leukocytes (PMN) during phagocytosis or activation by soluble stimuli is dependent on the emission of photons from the oxidation of particulate or bystander molecules. Because the compounds luminol and lucigenin yield photons with high quantum efficiency these agents have been introduced to sensitively assess PMN-CL. Since there is limited information about the pathways involved in the chemiluminescence of these compounds, we investigated the role of both myeloperoxidase (MPO) and superoxide anion (· O2?) in luminol-and lucigenin-PMN-CL. We compared the CL between normal and MPO- deficient PMN using zymosan for phagocytosis and N-formylmethionyleucylphenylalanine (FMLP) as a soluble stimulus. Our data demonstrated that luminol-CL was dependent on the presence of MPO and independent of · O2? generation during phagocytosis but independent of MPO during FMLP activation. In contrast lucigenin-CL was independent of MPO during both phagocytosis and FMLP activation and appeared to reflect · O2? production. Consequently, dependent on the type of activation, it appears that luminol- and lucigenin-CL are generated via different oxidative pathways and may serve as potentially useful tools to differentiate the redox activity of phagocytic cells. 相似文献
4.
DNA-templated Ag nanocluster formation 总被引:2,自引:0,他引:2
The high affinity of Ag+ for DNA bases has enabled creation of short oligonucleotide-encapsulated Ag nanoclusters without formation of large nanoparticles. Time-dependent formation of cluster sizes ranging from Ag1 to Ag4/oligonucleotide were observed with strong, characteristic electronic transitions between 400 and 600 nm. The slow nanocluster formation kinetics enables observation of specific aqueous nanocluster absorptions that evolve over a period of 12 h. Induced circular dichroism bands confirm that the nanoclusters are associated with the chiral ss-DNA template. Fluorescence, absorption, mass, and NMR spectra all indicate that multiple species are present, but that their creation is both nucleotide- and time-dependent. 相似文献
5.
Balest R Cho K Ford WT Lohner M Park H Rankin P Smith JG Alexander JP Bebek C Berger BE Berkelman K Bloom K Browder TE Cassel DG Cho HA Coffman DM Crowcroft DS Dickson M Drell PS Dumas DJ Ehrlich R Elia R Gaidarev P Garcia-Sciveres M Gittelman B Gray SW Hartill DL Heltsley BK Henderson S Jones CD Jones SL Kandaswamy J Katayama N Kim PC Kreinick DL Lee T Liu Y Ludwig GS Masui J Mevissen J Mistry NB Ng CR Nordberg E Patterson JR Peterson D Riley D Soffer A Avery P Freyberger A Lingel K Prescott C 《Physical review letters》1995,75(21):3809-3813
6.
Bartelt J Csorna SE Egyed Z Jain V Gibaut D Kinoshita K Pomianowski P Barish B Chadha M Chan S Cowen DF Eigen G Miller JS O'Grady C Urheim J Weinstein AJ Würthwein F Asner DM Athanas M Bliss DW Brower WS Masek G Paar HP Gronberg J Korte CM Kutschke R Menary S Morrison RJ Nakanishi S Nelson HN Nelson TK Qiao C Richman JD Roberts D Ryd A Tajima H Witherell MS Balest R Cho K Ford WT Lohner M Park H Rankin P Smith JG Alexander JP Bebek C Berger BE Berkelman K Bloom K Browder TE Cassel DG Cho HA 《Physical review D: Particles and fields》1995,52(9):4860-4867
7.
Asner DM Athanas M Bliss DW Brower WS Masek G Paar HP Gronberg J Korte CM Kutschke R Menary S Morrison RJ Nakanishi S Nelson HN Nelson TK Qiao C Richman JD Roberts D Ryd A Tajima H Witherell MS Balest R Cho K Ford WT Lohner M Park H Rankin P Smith JG Alexander JP Bebek C Berger BE Berkelman K Bloom K Browder TE Cassel DG Cho HA Coffman DM Crowcroft DS Dickson M Drell PS Dumas DJ Ehrlich R Elia R Gaidarev P Garcia-Sciveres M Gittelman B Gray SW Hartill DL Heltsley BK Henderson S Jones CD 《Physical review D: Particles and fields》1996,53(3):1039-1050
8.
Ron S. Dickson Gary S. Evans Gary D. Fallon 《Journal of organometallic chemistry》1982,236(2):C49-C52
The complexes (η-C5Me5)2Rh2(μ-CO) {μ-η2,η2-C(O)CRCR} are obtained from reactions between (η-C5Me5)2Rh2(CO)2 and the alkynes RCCR (R CF3, CO2Me, or Ph) at 25°C. The molecular geometry of the complex with R CF3 has been established by X-ray diffraction; the bridging 'ene-one' unit adopts a μ-η2,η2 conformation. Other complexes isolated from these reactions include (η-C5Me5)Rh(C6R6) (R CF3, CO2Me), (η-C5Me)2Rh2(C4R4) (R CO2Me) and (η-C5Me5)2Rh2(CO2C2R2) (R Ph). The reaction between (η-C5Me5)2Rh2(CO)2 and C6F5CCC6F5 gives (η-C5Me5)2Rh2(CO)2(C6F5C2C6F5). Mononuclear complexes such as (η-C5Me5)Co(C4R4CO) are the major products isolated from reactions between (η-C5Me5)2CO2(CO)2 and alkynes at 25°C. 相似文献
9.
A recent exact-exchange-based density-functional model of nondynamical and dynamical correlation [A.D. Becke, J. Chem. Phys. 122, 064101 (2005)] is tested on 70 barrier heights for a variety of reaction types: hydrogen transfer reactions, heavy-atom transfer reactions, nucleophilic substitutions, association reactions, and unimolecular rearrangements, including both even- and odd-electron systems. The mean absolute error with respect to accurate reference data is 1.4 kcal/mol. This is achieved without any refitting of the parameters of the model to the barrier height data. 相似文献
10.
Pan PW Dickson RJ Gordon HL Rothstein SM Tanaka S 《The Journal of chemical physics》2005,122(3):34904
Functionally relevant motion of proteins has been associated with a number of atoms moving in a concerted fashion along so-called "collective coordinates." We present an approach to extract collective coordinates from conformations obtained from molecular dynamics simulations. The power of this technique for differentiating local structural fluctuations between classes of conformers obtained by clustering is illustrated by analyzing nanosecond-long trajectories for the response regulator protein Spo0F of Bacillus subtilis, generated both in vacuo and using an implicit-solvent representation. Conformational clustering is performed using automated histogram filtering of the inter-C(alpha) distances. Orthogonal (varimax) rotation of the vectors obtained by principal component analysis of these interresidue distances for the members of individual clusters is key to the interpretation of collective coordinates dominating each conformational class. The rotated loadings plots isolate significant variation in interresidue distances, and these are associated with entire mobile secondary structure elements. From this we infer concerted motions of these structural elements. For the Spo0F simulations employing an implicit-solvent representation, collective coordinates obtained in this fashion are consistent with the location of the protein's known active sites and experimentally determined mobile regions. 相似文献