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排序方式: 共有172条查询结果,搜索用时 15 毫秒
111.
Per?Erik?Vullum Mark?Pitt John?Walmsley Bj?rn?Hauback Randi?Holmestad 《Applied Physics A: Materials Science & Processing》2009,94(4):787-793
Transmission electron microscopy has been used to study ball milled and H cycled NaAlH4 with 10 mol% TiCl3. Isolated from the main phases in this hydrogen storage system, nanocrystalline aggregates of fcc TiH x (0≤x<0.67) were found. The value of x was determined based on the assumption of a linear increase of the TiH x lattice parameter by increasing H content. The size of the TiH x crystallites was in the range 10 to 20 nm, and the lattice parameter decreased from 4.22 Å in TiH0.67 to 4.10 Å in pure fcc Ti. Non-equilibrium ball milling and subsequent H cycling in combination with a small crystallite size are believed to make the TiH x phase stable. The present results are the first observations of fcc TiH x with low hydrogen content, and the measured fcc lattice parameter of Ti matches first-principles calculations. 相似文献
112.
Goodwin RJ Pitt AR Harrison D Weidt SK Langridge-Smith PR Barrett MP Logan Mackay C 《Rapid communications in mass spectrometry : RCM》2011,25(7):969-972
Mass spectrometry imaging (MSI) is a powerful tool in metabolomics and proteomics for the spatial localization and identification of pharmaceuticals, metabolites, lipids, peptides and proteins in biological tissues. However, sample preparation remains a crucial variable in obtaining the most accurate distributions. Common washing steps used to remove salts, and solvent-based matrix application, allow analyte spreading to occur. Solvent-free matrix applications can reduce this risk, but increase the possibility of ionisation bias due to matrix adhesion to tissue sections. We report here the use of matrix-free MSI using laser desorption ionisation performed on a 12 T Fourier transform ion cyclotron resonance (FTICR) mass spectrometer. We used unprocessed tissue with no post-processing following thaw-mounting on matrix-assisted laser desorption ionisation (MALDI) indium-tin oxide (ITO) target plates. The identification and distribution of a range of phospholipids in mouse brain and kidney sections are presented and compared with previously published MALDI time-of-flight (TOF) MSI distributions. 相似文献
113.
Ghaleb A. Husseini Natalya Y. Rapoport Douglas A. Christensen John D. Pruitt William G. Pitt 《Colloids and surfaces. B, Biointerfaces》2002,24(3-4):253-264
The aim of this research was to measure and model the kinetics of acoustic release and subsequent re-encapsulation of Doxorubicin (DOX) from Pluronic P105 micelles. A fluorescence detection ultrasound exposure chamber was used. Experimental data showed that no significant release was observed when DOX loaded in Pluronic P105 micelles was exposed to ultrasound for less than 0.1 s at a power density of 58 mW/cm2 and a frequency of 20 kHz. Above this threshold, the amount of release was shown to increase as the pulse length increased up to 0.6 s. The same experiments showed that it requires at least 0.1 s of no ultrasound for measurable re-encapsulation to occur. Release and re-encapsulation are completed within about 0.6 s of the beginning of the ON and OFF phases of pulsed ultrasound. Several physical models and their corresponding mathematical solutions were analyzed to see which most closely fit the data. The model of zero-order release with first-order re-encapsulation appears to represent data from this polymeric system better than other models. This technique has possible applications in site-specific chemotherapy. 相似文献
114.
The effect of a small amount of poly(ethylene naphthalate) (PEN) in its blends with poly(trimethylene terephthalate) (PTT) on isothermal melt-crystallization kinetics and spherulitic morphology of the blends was thoroughly investigated. The maximum PEN content in the blends was 9 wt%. Due to the single composition-dependent glass transition temperature (Tg) that was observed for each blend, these blends appeared to be miscible in the amorphous state. After isothermal crystallization from the melt state, the neat PTT and its blends with PEN exhibited either double or triple melting endotherms. The triple endothermic peaks were observed in both the neat PTT and the blends when being crystallized at crystallization temperatures (Tc) of less than or equal to 195 °C. The equilibrium melting temperature () for the neat PTT was determined based on the linear Hoffman–Weeks extrapolative method to be 248 °C. Such values for the blends were found to decrease with the addition and increasing amount of PEN. Both the neat PTT and the blends were isothermally crystallized over the Tc range of 190–205 °C. At a given Tc, the 97PTT/3PEN blend exhibited a half-time of crystallization (t0.5) value that was lower, while it exhibited reciprocal half-time (), Avrami rate constant (KA), and spherulitic growth rate (G) values that were greater, than those of the neat PTT. With further increase in the PEN content, the t0.5 value increased, while the , KA, and G values decreased. Analysis of the G values based on the Lauritzen–Hoffman's (LH) secondary nucleation theory showed that the neat PTT and the 91PTT/9PEN blend exhibited a regime II→III transition at 194 °C (467.2 K), while no regime transition was observed for the other two blends. The lateral and the fold surface free energies (σ and σe) and the work of chain folding (q) for the neat PTT and the blends were 19.4, 30.2–46.3 erg cm−2, and 2.4–3.6 kcal mol−1, respectively. Lastly, the effect of both the Tc and the PEN content on morphology and texture of the PTT spherulites was also investigated and the results showed that the texture of the spherulites became coarser with increasing Tc and PEN content. 相似文献
115.
Minh-Ngoc Tran Paolo Giordani Xiuyan Mun Robert Kohn Michael K. Pitt 《Journal of computational and graphical statistics》2013,22(4):1163-1178
Copulas are popular as models for multivariate dependence because they allow the marginal densities and the joint dependence to be modeled separately. However, they usually require that the transformation from uniform marginals to the marginals of the joint dependence structure is known. This can only be done for a restricted set of copulas, for example, a normal copula. Our article introduces copula-type estimators for flexible multivariate density estimation which also allow the marginal densities to be modeled separately from the joint dependence, as in copula modeling, but overcomes the lack of flexibility of most popular copula estimators. An iterative scheme is proposed for estimating copula-type estimators and its usefulness is demonstrated through simulation and real examples. The joint dependence is modeled by mixture of normals and mixture of normal factor analyzer models, and mixture of t and mixture of t-factor analyzer models. We develop efficient variational Bayes algorithms for fitting these in which model selection is performed automatically. Based on these mixture models, we construct four classes of copula-type densities which are far more flexible than current popular copula densities, and outperform them in a simulated dataset and several real datasets. Supplementary material for this article is available online. 相似文献
116.
K-hasuwan PR Pavasant P Supaphol P 《Langmuir : the ACS journal of surfaces and colloids》2011,27(17):10938-10946
The use of electrospun fibrous matrices as substrates for cell/tissue culture has usually been confined to those consisting of smooth fibers. Here, we demonstrated that in vitro responses of mouse-calvaria-derived preosteoblastic cells (MC3T3-E1) that had been cultured on electrospun fibrous substrates made from blend solutions of 50/50 w/w poly(ε-caprolactone) (PCL) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) of varying concentrations, ranging from 4 to 14 wt %, depended strongly on the topography of the individual fibers. As the concentration of the blend solutions increased from 4 to 14 wt %, the topography of the individual fibers changed from discrete beads/smooth fibers to beaded fibers/smooth fibers and finally to smooth fibers, and the average diameter of the individual, smooth fibers increased from ~0.4 to ~1.8 μm. The results clearly showed that MC3T3-E1 preferred the smooth hydrophilic surface of the fibrous substrate from 10 wt % PCL/PHBV solution because the cells appeared to attach, proliferate, and differentiate on the surface of this substrate particularly well. 相似文献
117.
Kelly JG Ahmadzai AA Hermansen P Pitt MA Saidan Z Martin-Hirsch PL Martin FL 《Analytical and bioanalytical chemistry》2011,401(3):957-967
Fine needle aspirates (FNAs) of suspicious breast lesions are often used to aid the diagnosis of female breast cancer. Biospectroscopy
tools facilitate the acquisition of a biochemical cell fingerprint representative of chemical bonds present in a biological
sample. The mid-infrared (IR; 4,000–400 cm−1) is absorbed by the chemical bonds present, allowing one to derive an absorbance spectrum. Complementary to IR spectroscopy,
Raman spectroscopy measures the scattering by chemical bonds following excitation by a laser to generate an intensity spectrum.
Our objective was to apply these methods to determine whether a biospectroscopy approach could objectively segregate different
categories of FNAs. FNAs of breast tissue were collected (n = 48) in a preservative solution and graded into categories by a cytologist as C1 (non-diagnostic), C2 (benign), C3 (suspicious,
probably benign) or C5 (malignant) [or C4 (suspicious, probably malignant); no samples falling within this category were identified
during the collection period of the study]. Following washing, the cellular material was transferred onto BaF2 (IR-transparent) slides for interrogation by Raman or Fourier-transform IR (FTIR) microspectroscopy. In some cases where
sufficient material was obtained, this was transferred to low-E (IR-reflective) glass slides for attenuated total reflection–FTIR
spectroscopy. The spectral datasets produced from these techniques required multivariate analysis for data handling. Principal
component analysis followed by linear discriminant analysis was performed independently on each of the spectral datasets for
only C2, C3 and C5. The resulting scores plots revealed a marked overlap of C2 with C3 and C5, although the latter pair were
both significantly segregated (P < 0.001) in the Raman spectra. Good separation was observed between C3 and C5 in all three spectral datasets. Analysis performed
on the average spectra showed the presence of three distinct cytological groups. Our findings suggest that biospectroscopy
tools coupled with multivariate analysis may support the current FNA tests whilst increasing the sensitivity and associated
reliability for improved diagnostics. 相似文献
118.
Wang R Allmendinger P Zhu L Gröhn AJ Wegner K Frankevich V Zenobi R 《Journal of the American Society for Mass Spectrometry》2011,22(7):1234-1241
In this work, we investigated the role of the nebulizer gas flow in electrosonic spray ionization (ESSI), by systematically
studying the relation between the flow and the ion signals of proteins, such as cytochrome c and holomyoglobin using ESSI-mass spectrometry (MS). When a neutral solution was delivered with a small sample flow rate
(≤5 μL/min), no obvious transition from electrospray ionization (ESI) to ESSI was found as the gas velocity varies from subsonic
to supersonic speed. Droplets mostly experienced acceleration instead of breakup by the high-speed nebulizer gas. On the contrary,
using particular experimental conditions, such as an acidic solution or high sample flow rate (≥200 μL/min), more folded protein
ions appear to be kept in droplets of diminishing size due to breakup by the high-speed nebulizer gas in ESSI compared with
ESI. Theoretical analyses and numerical simulations were also performed to explain the observed phenomena. These systematic
studies clarify the ionization mechanism of ESSI and provide valuable insight for optimizing ESSI and other popular pneumatically
assisted electrospray ionization methods for future applications. 相似文献
119.
120.
The synthesis and characterization of (Me3Si)2AsCH2RCH2As(SiMe3)2 [R = CH2 ( 1 ), SiMe2 ( 2 )] is described. Compound 1 reacts with four equivalents of Ph2GaCl to produce (3), whose structure was deduced by use of 1H and 13C{1H} NMR spectroscopy. 相似文献