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排序方式: 共有283条查询结果,搜索用时 15 毫秒
51.
H. Zhu R. Venkataraman N. Menaa W. Mueller S. Croft A. Berlizov 《Journal of Radioanalytical and Nuclear Chemistry》2008,278(2):359-363
When radionuclides decay by cascading photons, the accuracy of the measured nuclide activity may be affected by true coincidence
summing effects. The effects can be quantified by Monte Carlo simulations that can handle correlated γ-and X-ray emissions
from a radionuclide. Analysis techniques are also available commercially to correct for the effects due to cascading γ-rays.
The MCNP-CP code was used to compute the effects in high purity germanium detectors for several commonly used nuclides and
geometries and the results were compared to measurements and an analysis technique. Excellent agreement in true coincidence
summing corrections predicted by MCNP-CP and the analysis technique was obtained. In addition, the X-ray true coincidence
summing effects were evaluated. 相似文献
52.
A general synthetic methodology has been developed for the synthesis of a conformationally locked, bridged diselena-bicyclo[3.2.1]octane skeleton by regio- and stereospecific tandem nucleophilic ring opening of cis-1,4-aziridino-epoxides with tetraethylammonium tetraselenotungstate [Et4N]2WSe4, 1, in a one-pot synthesis. Some correlations have been made on the physicochemical characteristics of the diselenides with a change in the dihedral angles. 相似文献
53.
Sureshkumar D Gunasundari T Ganesh V Chandrasekaran S 《The Journal of organic chemistry》2007,72(6):2106-2117
A comprehensive study of a general and effective one-step procedure for the synthesis of beta-sulfonamidodisulfides directly from N-tosyl aziridines in a regio- and stereospecific manner under neutral conditions without the use of any Lewis acid or base has been reported. This methodology is extended to the synthesis of an optically pure cyclic seven-membered disulfide 29. Synthesis of a variety of beta-sulfonamidosulfides involving tandem, multistep reactions in one pot is also reported. 相似文献
54.
Spori DM Venkataraman NV Tosatti SG Durmaz F Spencer ND Zürcher S 《Langmuir : the ACS journal of surfaces and colloids》2007,23(15):8053-8060
A series of alkyl phosphates with alkyl chain lengths ranging from C10 to C18 have been synthesized. Self-assembled monolayers (SAMs) of these molecules were prepared on titanium oxide surfaces by immersion of the substrates in alkyl phosphate solutions of 0.5 mM concentration in n-heptane/isopropanol. The SAMs were characterized by means of dynamic water contact angle (dCA) measurements, variable-angle spectroscopic ellipsometry (VASE), X-ray photoelectron spectroscopy (XPS), and polarization-modulated infrared reflection-absorption spectroscopy (PM-IRRAS). A higher degree of order and packing density within the monolayers was found for alkyl phosphates with alkyl chain lengths exceeding 15 carbon atoms. This is reflected in a lower dCA hysteresis, as well as a film thickness measured by VASE and XPS close to the expected values for SAMs with an average alkyl chain tilt angle of 30 degrees to the surface normal. Additionally a shift of the symmetric and antisymmetric C-H stretching modes in the PM-IRRAS spectra to lower wave numbers was observed. These findings imply a higher two-dimensional crystallinity of the films derived from alkyl phosphates with a longer alkyl chain length. 相似文献
55.
56.
Joseph A. Loo Peifeng Hu Patrick McConnell W. Tom Mueller Tomi K. Sawyer Venkataraman Thanabal 《Journal of the American Society for Mass Spectrometry》1997,8(3):234-243
The noncovalent binding of various peptide ligands to pp60src (Src) SH2 (Src homology 2) domain protein (12.9 ku) has been used as a model system for development of electrospray ionization mass spectrometry (ESI-MS) as a tool to study noncovalently bound complexes. SH2 motifs in proteins are critical in the signal transduction pathways of the tyrosine kinase growth factor receptors and recognize phosphotyrosine-containing proteins and peptides. ESI-MS with a magnetic sector instrument and array detection has been used to detect the protein-peptide complex with low-picomole sensitivity. The relative abundances of the multiply charged ions for the complex formed between Src SH2 protein and several nonphosphorylated and phosphorylated peptides have been compared. The mass spectrometry data correlate well to the measured binding constants derived from solution-based methods, indicating that the mass spectrometry-based method can be used to assess the affinity of such interactions. Solution-phase equilibrium constants may be determined by measuring the amount of bound and unbound species as a function of concentration for construction of a Scatchard graph. ESI-MS of a solution containing Src SH2 with a mixture of phosphopeptides showed the expected protein-phosphopeptide complex as the dominant species in the mass spectrum, demonstrating the method’s potential for screening mixtures from peptide libraries. 相似文献
57.
Zhongzhi Tang Matthew B. Abrams John C. Mauro Leon R. Zoeller Natesan Venkataraman Guangli Hu 《Applied Physics A: Materials Science & Processing》2014,116(2):471-477
Thermally or chemically strengthened glass is more resistant to damage and breakage compared to non-strengthened glass. Both strengthening mechanisms are based on incorporation of a compressive stress profile in the surface of the glass, which must be balanced by an equivalent amount of integrated tensile stress in the interior of the glass. This tensile stress is believed to affect the kinetics of Stage III crack propagation upon fracture of the sample. In this study, we use a high-speed camera to perform direct measurement of the kinetics of Stage III fracture in a strengthened glass sample. Data including crack propagation speed, crack bifurcation distance, and bifurcation angles are collected at a rate of 500,000 frames per second and then characterized. The authors believe that these data will provide a foundation for understanding the physics of Stage III fracture in strengthened glass samples. 相似文献
58.
Beurer E Venkataraman NV Sommer M Spencer ND 《Langmuir : the ACS journal of surfaces and colloids》2012,28(6):3159-3166
An orthogonal, charge-density-versus-net-charge, surface-chemical gradient, composed of ternary mixed self-assembled monolayers, has been prepared from three hydrophilic components: positively chargeable amine-terminated, negatively chargeable carboxylic-acid-terminated, and hydroxyl-terminated alkanethiols, with the latter bearing a slight negative charge in electrolytes. The chemical composition and its distribution have been monitored by X-ray photoelectron spectroscopy. The adsorption behavior of negatively charged SiO(2) nanoparticles and positively charged amine-modified SiO(2) nanoparticles has been studied. Additionally, negatively charged proteins (bovine serum albumin and fibrinogen) and positively charged proteins (lysozyme) were adsorbed on the gradients. Negatively charged nanoparticles and proteins adsorb mainly in the positively charged region and vice versa, illustrating that the adsorption behavior is mainly influenced by electrostatic interactions, and showing the potential of the gradient for sorting applications. Despite literature reports to the contrary, no area was found that was completely resistant to protein adsorption. 相似文献
59.
Saptarshi Chattopadhyay Sheryl H. Ehrman Jayesh Bellare Chandra Venkataraman 《Journal of nanoparticle research》2012,14(4):779
Small liposome suspensions (hydrodynamic diameter, 80–130 nm) were nebulised, and the resulting changes in morphology and
bilayer integrity were found to be related to surface properties controlled by bilayer composition. Four separate liposome
compositions (or liposome types) were investigated using three different phospholipids with unique properties. Morphological
changes were studied using light scattering and imaging of liposomes before and after nebulisation, and structural integrity
was investigated on the basis of the retention of an encapsulated dye (probe molecule). Nebulisation generated droplets contained
liposomes. The liposome particles generated on droplet evaporation had a hollow structure as evidenced by electron imaging,
indicating that the lipid bilayer does not collapse on evaporation. The particles of all compositions had mobility diameters
between 50 and 90 nm, 1.4–1.6 times smaller than their diameters (hydrodynamic) measured before nebulisation, implying considerable
volume shrinkage. Liposomes that had polymer-conjugated lipids covering their external surface underwent aggregation during
nebulisation, evidenced by increased diameter after nebulisation. Incorporation of charged lipids reduced nebulisation-induced
aggregation, but induced greater membrane rupture during aerosol generation, causing leakage of encapsulated probe molecules.
Incorporation of both cholesterol and charged lipids prevented aggregation, but also preserved bilayer integrity, evidenced
by the maximum retention of encapsulated dye observed in these conditions (>85%). The findings suggest that liposome bilayer
composition can be manipulated to improve the efficiency of liposome aerosol delivery. 相似文献
60.
The ethyl acetate extracts of the bark and leaves of Ficus coronata were separated by column chromatography and the resulting fractions tested for their bioactivity toward methicillin-resistant-Staphylococcus aureus (MRSA) and M. luteus. The bioactive column chromatography fractions were further separated by preparative thin layer chromatography (TLC) and the resulting bands investigated by high-performance liquid chromatography-electrospray ionization-ion trap mass spectrometry (HPLC-ESI-MS(n) ) and ESI-MS(n) . The resulting retention times, molecular masses, their fragmentation patterns, and the chemnet database (www.chemnetbase.com) were then used in the dereplication process by structural elucidation of some of the compounds when compared with known structures of natural origin. Some molecular masses and the corresponding fragmentations were found that did not correlate with any known compounds thus revealing potentially novel natural products that could be investigated on a larger scale and could ultimately find application as new drugs against MRSA and other multidrug-resistant microorganisms. Structures are also proposed for known compounds that have not been previously reported for F. coronata. 相似文献