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31.
We report the first experimental test of an analytic image reconstruction algorithm for optical tomography with large data sets. Using a continuous-wave optical tomography system with 10(8) source-detector pairs, we demonstrate the reconstruction of an absorption image of a phantom consisting of a highly scattering medium containing absorbing inhomogeneities. 相似文献
32.
Natalia Shevchenko Galina Pankova Boris Shabsels Vadim Baigildin Alexander Khoshkin Timofei Ukleev 《Journal of Dispersion Science and Technology》2019,40(6):802-810
Monodisperse dye-containing crosslinked particles are promising for application in novel optical chemical sensors due to their intrinsic sensitivity. However, preparation of these particles in aqueous media still remains a challenge, since luminophores inhibit radical processes or else cannot embed into polymer chains because of difference in monomer reactivity ratios. In this work, novel dye-containing monodisperse crosslinked particles were prepared and characterized. In order to obtain dye-containing monodisperse crosslinked particles, we studied seed copolymerization of styrene in the presence of divinylbenzene. The influence of nature and concentration of the used comonomers and co-solvents on shape, size distributions and surface characteristics of the particles formed was investigated. Shapes and diameters of the particles were analyzed by DLS, TEM and SEM. The data of SEM and optical spectroscopy studies demonstrated that the synthesized particles were able to self-assemble into thin-film three-dimensional ordered structures. Finally, the structures under study are promising for development of sensor devices with optical response to acetone. 相似文献
33.
Alexander V. Pastukhov Maria P. Tsyurupa Vadim A. Davankov 《Journal of Polymer Science.Polymer Physics》1999,37(17):2324-2333
Deformation and relaxation properties of hypercrosslinked polystyrene networks have been studied by thermomechanical method at a uniaxial compression using individual spherical beads of the polymer. The networks examined were prepared by postcrosslinking of highly swollen beads of a styrene‐0.3% DVB copolymer with 0.3–0.75 mole of monochlorodimethyl ether, which results in the introduction of 0.6–1.5 methylene bridges between each two polystyrene phenyl rings. The polymers obtained are shown to belong neither to typical glassy materials, nor to typical elastomers. Though no characteristic plateau of rubberlike elasticity was observed on the deformation curves of the beads, the polymers exhibit two fundamentally important features of the rubberlike state: The deformations are large (up to 30–40% of the initial diameter) and reversible. Relaxation of residual deformations, however, requires prolonged heating of the sample, or a cycle of swelling and drying. The deformation can start in the temperature range from −70 to +150°C depending on pressure applied. The crosslinking degree in the range from 40–100% and higher does not affect noticeably the behavior of the hypercrosslinked polystyrene. Nature of the high mobility of the hypercrosslinked network is discussed. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2324–2333, 1999 相似文献
34.
Nicolay Yu. Adonin Dmitrii E. Babushkin Vadim V. Bardin Vasiliy I. Mashukov 《Tetrahedron》2008,64(25):5920-5924
The effect of N-heterocyclic carbene (NHC) ligands on the catalytic activity of in situ generated palladium complexes in the model cross-coupling reaction of K[C6F5BF3] with 4-FC6H4I was studied. Based on the obtained results, a series of pentafluorobiphenyls C6F5C6H4X were prepared from K[C6F5BF3] and XC6H4I or 4-CF3C6H4Br in high yields under aerobic conditions. 相似文献
35.
36.
Gaspar AB Ksenofontov V Reiman S Gütlich P Thompson AL Goeta AE Muñoz MC Real JA 《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(36):9289-9298
The crystal structure of the complex [{Fe(bt)(NCS)(2)}(2)bpym] (1) (bt=2,2'-bithiazoline, bpym=2,2'-bipyrimidine) has been solved at 293, 240, 175 and 30 K. At all four temperatures the crystal remains in the P space group with a=8.7601(17), b=9.450(2), c=12.089(3) A, alpha=72.77(2), beta=79.150(19), gamma=66.392(18) degrees , V=873.1(4) Angstrom(3) (data for 293 K structure). The structure consists of centrosymmetric dinuclear units in which each iron(II) atom is coordinated by two NCS(-) ions in the cis position and two nitrogen atoms of the bridging bpym ligand, with the remaining positions occupied by the peripheral bt ligand. The iron atom is in a severely distorted octahedral FeN(6) environment. The average Fe--N bond length of 2.15(9) Angstrom indicates that compound 1 is in the high-spin state (HS-HS) at 293 K. Crystal structure determinations at 240, 175 and 30 K gave a cell comparable to that seen at 293 K, but reduced in volume. At 30 K, the average Fe--N distance is 1.958(4) Angstrom, showing that the structure is clearly low spin (LS-LS). At 175 K the average Fe--N bond length of 2.052(11) Angstrom suggests that there is an intermediate phase. M?ssbauer investigations of the light-induced excited spin state trapping (LIESST) effect (lambda=514 nm, 25 mW cm(-2)) in 1 (4.2 K, H(ext)=50 kOe) show that the excited spin states correspond to the HS-HS and HS-LS pairs. The dynamics of the relaxation of the photoexcited states studied at 4.2 K and H(ext)=50 kOe demonstrate that HS-HS pairs revert with time to both HS-LS and LS-LS configurations. The HS-LS photoexcited pairs relax with time back to the ground LS-LS configuration. Complex [{Fe(0.15)Zn(0.85)(bt)(NCS)(2)}(2)bpym] (2) exhibits a continuous spin transition centred around 158 K in contrast to the two-step transition observed for 1. The different spin-crossover behaviour observed for 2 is due to the decrease of cooperativity (intermolecular interactions) imposed by the matrix of Zn(II) ions. This clearly demonstrates the role of the intermolecular interactions in the stabilization of the HS-LS intermediate state in 1. 相似文献
37.
Previously unknown polyfluorocyclohexenyl, and acyclic perfluoroalkenyliodine tetrafluorides were prepared in high yields. Perfluorocyclohex-1-enyliodine tetrafluoride was obtained from pentafluoroiodobenzene using XeF2-NbF5 in aHF. The reaction of C6F5I with the weaker fluorooxidant XeF2-BF3 in 1,1,1,3,3-pentafluorobutane (PFB) yielded C6F5IF2, perfluorocyclohexa-1,4-dienyliodine difluoride, C6F5IF4, perfluorocyclohexa-1,4, and 1,3-dienyliodine tetrafluoride as intermediate products on parallel reaction routes. Both perfluoroalkenyl iodides, cis- and trans-(CF3)2CFCFCFI, reacted with XeF2-BF3 in PFB to give the corresponding perfluoroalkenyliodine tetrafluorides, cis- and trans-(CF3)2CFCFCFIF4. Even perfluoroalkyl iodides can be fluorinated by this reagent as was demonstrated by the preparation of C6F13IF4 from C6F13I. Generally, the CFCIFn fragment (n = 0, 2, or 4) in cyclic or acyclic perfluoroalkenyliodine compounds RFIFn did not undergo a transformation to the corresponding perfluoroalkyliodine compound. Furthermore, no perfluoroorganoiodine hexafluorides were detected in reactions with the fluorooxidant XeF2-aHF or BF3 or NbF5. 相似文献
38.
The CH2Cl + CH3 (1) and CHCl2 + CH3 (2) cross-radical reactions were studied by laser photolysis/photoionization mass spectroscopy. Overall rate constants were obtained in direct real-time experiments in the temperature region 301-800 K and bath gas (helium) density (6-12) x 10(16) atom cm(-3). The observed rate constant of reaction 1 can be represented by an Arrhenius expression k1 = 3.93 x 10(-11) exp(91 K/T) cm3 molecule(-1) s(-1) (+/-25%) or as an average temperature-independent value of k1= (4.8 +/- 0.7) x 10(-11) cm3 molecule(-1) s(-1). The rate constant of reaction 2 can be expressed as k2= 1.66 x 10(-11) exp(359 K/T) cm3 molecule(-1) s(-1) (+/-25%). C2H4 and C2H3Cl were detected as the primary products of reactions 1 and 2, respectively. The experimental values of the rate constant are in reasonable agreement with the prediction based on the "geometric mean rule." A separate experimental attempt to determine the rate constants of the high-temperature CH2Cl + O2 (10) and CHCl2 + O2 (11) reaction resulted in an upper limit of 1.2 x 10(-16) cm(3) molecule(-1) s(-1) for k10 and k11 at 800 K. 相似文献
39.
Stephen R. Wassall Saame Raza Shaikh Michael R. Brzustowicz Vadim Cherezov Rafat A. Siddiqui Martin Caffrey William Stillwell 《Macromolecular Symposia》2005,219(1):73-84
Unequal affinity between lipids has been hypothesized to be a mechanism for the formation of microdomains/rafts in membranes. Our studies focus upon the interaction of cholesterol with polyunsaturated fatty acid (PUFA)-containing phospholipids. They support the proposal that steric incompatibility of the rigid steroid moiety for highly disordered PUFA chains, in particular docosahexaenoic acid (DHA), provides a sensitive trigger for lateral segregation of lipids into PUFA-rich/sterol-poor and PUFA-poor/sterol-rich regions. Solid state 2H NMR and x-ray diffraction (XRD) demonstrate that the solubility of cholesterol is reduced in 1-palmitoyl-2-docosahexaenoyl-phosphatidylethanolamine (16-0:22:6PE) bilayers. In mixed membranes of phosphatidylethanolamine (PE) with the lipid raft forming molecules egg sphingomyelin (SM) and cholesterol, diminished affinity of the sterol for 16:0-22:6PE relative to 1-palmitoyl-2-oleoylphosphatidylethanolamine (16:0-18:1PE) is identified by 2H NMR order parameters and detergent extraction. Phase separation of the PUFA-containing phospholipid from SM/cholesterol rafts is the implication, which may be associated with the myriad of health benefits of dietary DHA. 相似文献
40.
Amit Katiyar Stephen W. Thiel Vadim V. GuliantsNeville G. Pinto 《Journal of chromatography. A》2010,1217(10):1583-1588
The adsorption of bovine serum albumin (BSA) and lysozyme (LYS) on siliceous SBA-15 with 24 nm pores was studied using flow microcalorimetry; this is the first attempt to understand the thermodynamics of protein adsorption on SBA-15 using flow microcalorimetry. The adsorption mechanism is a strong function of protein structure. Exothermic events were observed when protein–surface interactions were attractive. Entropy-driven endothermic events were also observed in some cases, resulting from lateral protein–protein interactions and conformational changes in the adsorbed protein. The magnitudes of the enthalpies of adsorption for primary protein–surface interactions decrease with increased surface coverage, indicating the possibility of increased repulsion between adsorbed protein molecules. Secondary exothermic events were observed for BSA adsorption, presumably due to secondary adsorption made possible by conformational changes in the soft BSA protein. These secondary adsorption events were not observed for lysozyme, which is structurally robust. The results of this study emphasize the influence of solution conditions and protein structure on conformational changes of the adsorbed protein and the value of calorimetry in understanding protein–surface interactions. 相似文献