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A large number of studies have been devoted in recent years to the miscibility behavior of linear polyesters with chlorinated polymers, including poly(vinyl chloride) (PVC), chlorinated PVC, chlorinated poly(ethylenes), and copolymers of vinylidene chloride (Saran). However, similar studies with aromatic polyesters are lacking. It is the purpose of this paper to compare the properties of blends made of poly(ethylene terephthalate), poly(butylene terephthalate) or poly(hexamethylene terephthalate) and of various chlorinated polymers. It is shown that a high concentration of chlorine atoms is required to achieve miscibility. Moreover, there is a “miscibility window” in terms of the carbonyl concentration of polyesters, immiscibility being found for carbonyl concentrations outside this window, A similar behavior was observed before for linear polyester/chlorinated polymer blends and for polyester/polycarbonate blends. Solid state small-angle light scattering experiments were also conducted to follow the morphology of the blends as a function of composition. Spherulites were found but their size vary with composition. 相似文献
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A fast simulator of SPECT projection data taking into account attenuation, distance dependent detector response, and scatter has been developed, based on an analytical point spread function model. The parameters of the scatter response are obtained from a single line source measurement with a triangular phantom. The simulator is able to include effects of object curvature on the scatter response to a high accuracy. The simulator has been evaluated for homogeneous media by measurements of (99m)Tc point sources placed at different locations in a water-filled cylinder at energy windows of 15% and 20%. The asymmetrical shapes of measured projections of point sources are In excellent agreement with simulations for both energy windows. Scatter-to-primary ratio (SPR) calculations of point sources at different positions in a cylindrical phantom differ not more than a few percent from measurements. The simulator uses just a few megabytes of memory for storing the tables representing the forward model; furthermore, simulation of 60 SPECT projections from a three-dimensional digital brain phantom with 6-mm cubic voxels takes only ten minutes on a standard workstation. Therefore, the simulator could serve as a projector in iterative true 3-D SPECT reconstruction. 相似文献
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The quality and quantitative accuracy of iteratively reconstructed SPECT images improves when better point spread function (PSF) models of the gamma camera are used during reconstruction. Here, inclusion in the PSF model of photon crosstalk between different slices caused by limited gamma camera resolution and scatter is examined. A three-dimensional (3-D) projector back-projector (proback) has been developed which models both the distance dependent detector point spread function and the object shape-dependent scatter point spread function of single photon emission computed tomography (SPECT). A table occupying only a few megabytes of memory is sufficient to represent this scatter model. The contents of this table are obtained by evaluating an analytical expression for object shape-dependent scatter. The proposed approach avoids the huge memory requirements of storing the full transition matrix needed for 3-D reconstruction including object shape-dependent scatter. In addition, the method avoids the need for lengthy Monte Carlo simulations to generate such a matrix. In order to assess the quantitative accuracy of the method, reconstructions of a water filled cylinder containing regions of different activity levels and of simulated 3-D brain projection data have been evaluated for technetium-99m. It is shown that fully 3-D reconstruction including complete detector response and object shape-dependent scatter modeling clearly outperforms simpler methods that lack a complete detector response and/or a complete scatter response model. Fully 3-D scatter correction yields the best quantitation of volumes of interest and the best contrast-to-noise curves. 相似文献
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ABSTRACT: The purpose of this study was to determine differences in nutrient and energy intakes and in quantity of food eaten, and to compare the knowledge, attitudes, and practices of users of reduced-sugars foods and beverages with those who use only the full sugar versions of the same products. Records for adults (≥ 20 y old) responding to the 1994–1996 Continuing Survey of Food Intakes by Individuals (CSFII) and the Diet Health and Knowledge Survey were used. CSFII food lists were scanned for both full and reduced-sugar versions of yogurt, cocoa, and other milk beverages, frozen and gelatin desserts, puddings, breads, cookies, cakes, fruit drinks, carbonated and noncarbonated drinks, confectionary products, and sweeteners. Recalls were sorted for those reporting use of only full sugar (FS) products and those reporting mixed use of full sugar and reduced-sugar (RS) versions. Comparisons were made between demographic characteristics, body mass index, food group servings, food intake amounts, and nutrient densities. When compared with FS users, RS users consistently reported significantly higher intakes of fruit, lower intakes of discretionary fat and added sugars, and equal or lower intakes of other foods (in gram amounts), except for greater intake of yogurt and frozen and gelatin desserts. RS users tended to report similar or higher micronutrient intakes compared with FS users. After adjusting for energy intake, significantly higher micronutrient intakes were found for both males and females consuming RS foods and beverages (13 and 15 of 17 nutrients, respectively). 相似文献
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Linda Elowsson Harald Kirsebom Virginie Carmignac Madeleine Durbeej Bo Mattiasson 《Journal of materials science. Materials in medicine》2012,23(10):2489-2498
Successful tissue engineering with the aid of a polymer scaffold offers the possibility to produce a larger construct and to mould the shape after the defect. We investigated the use of cryogelation to form protein-based scaffolds through different types of formation mechanisms; enzymatic crosslinking, chemical crosslinking, and non-covalent interactions. Casein was found to best suited for enzymatic crosslinking, gelatin for chemical crosslinking, and ovalbumin for non-covalent interactions. Fibroblasts and myoblasts were used to evaluate the cryogels for tissue engineering purposes. The stability of the cryogels over time in culture differed depending on formation mechanism. Casein cryogels showed best potential to be used in skeletal tissue engineering, whereas gelatin cryogels would be more suitable for compliable soft tissues even though it also seemed to support a myogenic phenotype. Ovalbumin cryogels would be better suited for elastic tissues with faster regeneration properties due to its faster degradation time. Overall, the cryogelation technique offers a fast, cheap and reproducible way of creating porous scaffolds from proteins without the use of toxic compounds. 相似文献
8.
Markus F. Weber Gabriele Poxleitner Elke Hebisch Erwin Frey Madeleine Opitz 《Journal of the Royal Society Interface》2014,11(96)
Dispersal of species is a fundamental ecological process in the evolution and maintenance of biodiversity. Limited control over ecological parameters has hindered progress in understanding of what enables species to colonize new areas, as well as the importance of interspecies interactions. Such control is necessary to construct reliable mathematical models of ecosystems. In our work, we studied dispersal in the context of bacterial range expansions and identified the major determinants of species coexistence for a bacterial model system of three Escherichia coli strains (toxin-producing, sensitive and resistant). Genetic engineering allowed us to tune strain growth rates and to design different ecological scenarios (cyclic and hierarchical). We found that coexistence of all strains depended on three strongly interdependent factors: composition of inoculum, relative strain growth rates and effective toxin range. Robust agreement between our experiments and a thoroughly calibrated computational model enabled us to extrapolate these intricate interdependencies in terms of phenomenological biodiversity laws. Our mathematical analysis also suggested that cyclic dominance between strains is not a prerequisite for coexistence in competitive range expansions. Instead, robust three-strain coexistence required a balance between growth rates and either a reduced initial ratio of the toxin-producing strain, or a sufficiently short toxin range. 相似文献
9.
Poya Kavianpour Madeleine C. M. Gemmell Dr. Jan U. Kahlert Prof. Louis M. Rendina 《Chembiochem : a European journal of chemical biology》2020,21(19):2786-2791
Histone deacetylase enzymes (HDACs) are responsible for the global silencing of tumour-suppressor genes. Treatment with a histone deacetylase inhibitor (HDACi) can reverse this process and restore normal cell function. Herein, we report a small series of boron-based (boronic acid, boronate ester and closo-1,2-carborane) HDAC2 inhibitors with IC50 values in the nanomolar range. The boronate ester 4 b was the most potent compound assessed in this study (IC50=40.6±1.5 nM), followed closely by the 1,2-closo-carborane (IC50=42.9±1.5 nM). Compound 4 b exceeds the potency of the related gold-standard HDAC pan-inhibitor vorinostat ( 1 ) toward this particular HDAC isoform. 相似文献
10.
ter Kuile Moniek M.; Bulté Isis; Weijenborg Philomeen T. M.; Beekman Aart; Melles Reinhilde; Onghena Patrick 《Canadian Metallurgical Quarterly》2009,77(1):149
Vaginismus is commonly described as a persistent difficulty in allowing vaginal entry of a penis or other object. Lifelong vaginismus occurs when a woman has never been able to have intercourse. A replicated single-case A-B-phase design was used to investigate the effectiveness of therapist-aided exposure for lifelong vaginismus. A baseline period (Phase A) was contrasted with exposure + follow-up (Phase B), using random switching between phases. The main outcome measure (intercourse ability) was assessed daily for 24 weeks. Ten women participated. The exposure consisted of a maximum of three 2-hr sessions during 1 week at a university hospital. The participant performed vaginal penetration exercises on herself, in the presence of a female therapist. Two follow-up sessions were scheduled over a 5-week period. Nine of the 10 participants reported having intercourse after treatment, and in 5 of the 9, intercourse was possible within the 1st week of treatment. The results remained at 1-year follow-up. Furthermore, exposure was successful in decreasing fear and negative penetration beliefs posttreatment and at 3-month and 1-year follow-ups. Therapist-aided exposure appears to be an effective treatment for lifelong vaginismus. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献