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排序方式: 共有155条查询结果,搜索用时 15 毫秒
1.
2.
McMillan SA Haubein NC Snurr RQ Broadbelt LJ 《Journal of chemical information and computer sciences》2003,43(6):1820-1828
Moderate to large size molecules in solution have complex energy surfaces due to intramolecular (conformational) and intermolecular (many-body) interactions. The first principles Monte Carlo (FPMC) method, previously shown to effectively locate minimum-energy structures for systems with only many-body complexity, has been extended to address conformational flexibility by adding three new Monte Carlo move types. The primary advantage of the FPMC method is the ability to efficiently locate minimum energy structures of molecules with conformational flexibility in the presence of explicit solvent molecules using highly accurate quantum chemical calculations. The additions to FPMC were validated by studying conformers of glycerol, glyceraldehyde, and a large humic acid monomer unit. The structure of glyceraldehyde in the presence of one and two water molecules was also explored to demonstrate the power of FPMC to study systems with both conformational and many-body degrees of freedom. 相似文献
3.
McMillan RA Howard J Zaluzec NJ Kagawa HK Mogul R Li YF Paavola CD Trent JD 《Journal of the American Chemical Society》2005,127(9):2800-2801
Self-assembling biomolecules that form highly ordered structures have attracted interest as potential alternatives to conventional lithographic processes for patterning materials. Here, we introduce a general technique for patterning nanoparticle arrays using two-dimensional crystals of genetically modified hollow protein structures called chaperonins. Constrained chemical synthesis of transition metal nanoparticles is initiated using templates functionalized with polyhistidine sequences. These nanoparticles are ordered into arrays because the template-driven synthesis is constrained by the nanoscale structure of the crystallized protein. We anticipate that this system may be used to pattern different classes of nanoparticles based on the growing library of sequences shown to specifically bind or direct the growth of materials. 相似文献
4.
Schmidt Sherry L. Myers Michele D. Kelley Stephen S. McMillan James D. Padukone Nandan 《Applied biochemistry and biotechnology》1997,(1):469-482
The use of membrane processes for the recovery of fermentation products has been gaining increased acceptance in recent years.
Pervaporation has been studied in the past as a process for simultaneous fermentation and recovery of volatile products such
as ethanol and butanol. However, membrane fouling and low permeate fluxes have imposed limitations on the effectiveness of
the process. In this study, we characterize the performance of a substituted polyacetylene membrane, poly[(l-trimethylsilyl)-l-propyne]
(PTMSP), in the recovery of ethanol from aqueous mixtures and fermentation broths. Pervaporation using PTMSP membranes shows
a distinct advantage over conventional poly(dimethyl siloxane) (PDMS) membranes in ethanol removal. The flux with PTMSP is
about threefold higher and the concentration factor is about twofold higher than the corresponding performance achieved with
PDMS under similar conditions. The performance of PTMSP with fermentation broths shows a reduction in both flux and concentration
factor relative to ethanol-water mixtures. However, the PTMSP membranes indicate initial promise of increased fouling resistance
in operation with cell-containing fermentation broths. 相似文献
5.
P. M. Pollard J. W. McMillan D. J. Malcolme-Lawes 《Journal of Radioanalytical and Nuclear Chemistry》1982,70(1-2):349-370
Sensitive and selective nuclear reaction methods have been sought for the nuclear microprobe measurement of the spatial distributions
of13C and13C/12C ratios. The13C(α, n)16O reaction, with neutron detection, is the most selective for13C, and has a sensitivity of ca. 100 ppm. The reactions13C(d, p)14C and12C(d, p)13C, with proton detection, are the most sensitive for the simultaneous measurement of13C and12C, with detection limits of 30 and 2 ppm respectively. Less sensitive alternative reaction pairs are;13C(3He, p)15N and12C(3He, p)14N;13C(d, nγ)14N and12C(d, pγ)13C;13C(3He, pγ)15N and12C(3He, pγ)14N. The conditions governing their use, particularly light element interferences, are detailed. 相似文献
6.
J. W. McMillan F. C. W. Pummery 《Journal of Radioanalytical and Nuclear Chemistry》1977,38(1-2):51-66
A nuclear microprobe method has been developed for the simultaneous determination of silicon and nitrogen concentration profiles
in metals. The method was based on the reactions28Si(d, p0)29Si and14N(d, p0)15N plus14N(d, β0)12C with measurement of emitted charged particles during irradiation with 1.9 MeV deuterons. The nitrogen sensitivity was ten
times that for silicon and the minimum concentrations detected were 0.002% and 0.03% respectively. The method was successfully
applied to the measurement of silicon and nitrogen profiles in alloys contacted with silicon nitride at high temperature. 相似文献
7.
A comprehensive review of techniques for the experimental characterisation of the fracture toughness associated with the translaminar (fibre-breaking) failure modes of continuously reinforced laminated composites is presented. The collection of work relating to tensile failure reveals a varied approach in terms of specimen configuration, size and data reduction, despite the existence of an ASTM standard. Best practices are identified and suggestions for extending the scope of the current standard are made. Works on compressive failure are found to be less comprehensive. Measurement of the toughness associated with initiation of the failure mode in isolation has been achieved, but this review finds that significant research steps need to be taken before a resistance curve can be fully characterised. 相似文献
8.
Subramanian S Devasahayam N McMillan A Matsumoto S Munasinghe JP Saito K Mitchell JB Chandramouli GV Krishna MC 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2012,214(1):244-251
Oxygen maps derived from electron paramagnetic resonance spectral-spatial imaging (EPRI) are based upon the relaxivity of molecular oxygen with paramagnetic spin probes. This technique can be combined with MRI to facilitate mapping of pO(2) values in specific anatomic locations with high precision. The co-registration procedure, which matches the physical and digital dimensions of EPR and MR images, may present the pO(2) map at the higher MRI resolution, exaggerating the spatial resolution of oxygen, making it difficult to precisely distinguish hypoxic regions from normoxic regions. The latter distinction is critical in monitoring the treatment of cancer by radiation and chemotherapy, since it is well-established that hypoxic regions are three or four times more resistant to treatment compared to normoxic regions. The aim of this article is to describe pO(2) maps based on the intrinsic resolution of EPRI. A spectral parameter that affects the intrinsic spatial resolution of EPRI is the full width at half maximum (FWHM) height of the gradient-free EPR absorption line in frequency-encoded imaging. In single point imaging too, the transverse relaxation times (T(2)(?)) limit the resolution since the signal decays by exp(-t(p)/T(2)(?)) where the delay time after excitation pulse, t(p), is related to the resolution. Although the spin densities of two point objects may be resolved at this separation, it is inadequate to evaluate quantitative changes of pO(2) levels since the linewidths are proportionately affected by pO(2). A spatial separation of at least twice this resolution is necessary to correctly identify a change in pO(2) level. In addition, the pO(2) values are blurred by uncertainties arising from spectral dimensions. Blurring due to noise and low resolution modulates the pO(2) levels at the boundaries of hypoxic and normoxic regions resulting in higher apparent pO(2) levels in hypoxic regions. Therefore, specification of intrinsic resolution and pO(2) uncertainties are necessary to interpret digitally processed pO(2) illustrations. 相似文献
9.
Craig L. Bull Tetsuya Kawashima Paul F. McMillan Denis Machon Dominik Daisenberger E. Takayama-Muromachi 《Journal of solid state chemistry》2006,179(6):1762-1767
We prepared samples of cubic γ-MoNx (x∼0.5) by high-pressure-high-temperature synthesis. N atom site occupancies within the defect rock salt structure were determined from time-of-flight neutron diffraction and powder X-ray diffraction data by Rietveld analysis. The results show that N atoms occupy only octahedral sites within the structure. The semi-metallic compound is a superconductor, with determined by SQUID magnetometry. The compressibility of the material was determined by synchrotron X-ray diffraction measurements at high pressure in the diamond anvil cell. The vibrational density of states was studied by Raman scattering spectroscopy. 相似文献
10.
Sodium orthonitrate (Na3NO4) is an unusual phase containing the first example of isolated tetrahedrally bonded NO43− groups. This compound was obtained originally by heating together mixtures of Na2O and NaNO3 for periods extending up to >14 days in evacuated chambers. Considering the negative volume change between reactants and products, it was inferred that a high-pressure synthesis route might favor the formation of the Na3NO4 compound. We found that the recovered sample is likely to be a high-pressure polymorph, containing NO43− groups as evidenced by Raman spectroscopy. The high-pressure behavior of Na3NO4 was studied using Raman spectroscopy and synchrotron X-ray diffraction in a diamond anvil cell above 60 GPa. We found no evidence for major structural transformations, even following laser heating experiments carried out at high pressure, although broadening of the Raman peaks could indicate the onset of disordering at higher pressure. 相似文献