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排序方式: 共有128条查询结果,搜索用时 265 毫秒
61.
Zhenmian Shao Sébastien Saitzek Pascal Roussel Olivier Mentré Felicia Prihor Gheorghiu Rachel Desfeux 《Journal of solid state chemistry》2010,183(7):1652-1662
A series of compounds with the general formula (La1−xNdx)2Ti2O7 (0.0≤x≤1.0) has been prepared by the sol-gel method. The decomposition of the gel was characterized by thermo-gravimetric analysis coupled to mass spectrometry, indicating the reaction is achieved above 850 °C. The lattice parameters versus x show an expected decrease in the a and b parameters while c and the β angle remain almost unchanged with respect to the monoclinic symmetry conserved for the full solid solution. Dielectric, piezoelectric and ferroelectric properties were measured on the entire series. 相似文献
62.
Mercedes Ballesteros Felicia Sáez Ignacio Ballesteros Paloma Manzanares Maria Jose Negro Jose Maria Martínez Rafael Castañeda Jose Miguel Oliva Dominguez 《Applied biochemistry and biotechnology》2010,161(1-8):423-431
In this work, the use of organic fraction from municipal solid waste (MSW) as substrate for ethanol production based on enzymatic hydrolysis was evaluated. MSW was subjected to a thermal pretreatment (active hygienization) at 160?°C from 5 to 50 min. The organic fiber obtained after 30 min was used as substrate in a simultaneous saccharification and fermentation (SSF) and fed-batch SSF process using cellulases and amylases. In a fed-batch mode with 25% (w/w) substrate loading, final ethanol concentration of 30 g/L was achieved (60% of theoretical). In these conditions, more than 160 L of ethanol per ton of dry matter could be produced from the organic fraction of MSW. 相似文献
63.
Corrado Mandoli Barbara Mecheri Giancarlo Forte Francesca Pagliari Stefania Pagliari Felicia Carotenuto Roberta Fiaccavento Antonio Rinaldi Paolo Di Nardo Silvia Licoccia Enrico Traversa 《Macromolecular bioscience》2010,10(2):127-138
The lack of a vascular network and poor perfusion is what mostly prevents three‐dimensional (3D) scaffolds from being used in organ repair when reconstruction of thick tissues is needed. Highly‐porous scaffolds made of poly(L ‐lactic acid) (PLLA) are prepared by directional thermally induced phase separation (dTIPS) starting from 1,4‐dioxane/PLLA solutions. The influence of polymer concentration and temperature gradient, in terms of imposed intensity and direction, on pore size and distribution is studied by comparison with scaffolds prepared by isotropic TIPS. The processing parameters are optimized to achieve an overall porosity for the 3D scaffolds of about 93% with a degree of interconnectivity of 91%. The resulting pore network is characterized by the ordered repetition of closely packed dendrite‐like cavities, each one showing stacks of 20 µm large side lamellar branches departing from 70 µm diameter vertical backbones, strongly resembling the vascular patterns. The in vitro biological responses after 1 and 2 weeks are evaluated from mesenchymal (bone marrow stromal) cells (MSC) static culturing. A novel vacuum‐based deep‐seeding method is set up to improve uniform cell penetration down to scaffold thicknesses of over 1 mm. Biological screenings show significant 3D scaffold colonization even after 18 h, while cellular retention is observed up to 14 d in vitro (DIV). Pore architecture‐driven cellular growth is accompanied by cell tendency to preserve their multi‐potency towards differentiation. Confluent tissues as thick as 1 mm were reconstructed taking advantage of the large perfusion enhanced by the highly porous microstructure of the engineered scaffolds, which could successfully serve for applications aimed at vascular nets and angiogenesis.
64.
Schroeder OE Carper E Wind JJ Poutsma JL Etzkorn FA Poutsma JC 《The journal of physical chemistry. A》2006,110(20):6522-6530
The energetics of cis-trans proline isomerization in small peptide models have been investigated using the hybrid density functional theory method B3LYP with a 6-31+G* basis set. The molecules studied are models for the phospho-Ser/Thr-Pro substrate for Pin-1, a peptidyl-prolyl isomerase (PPIase) involved in cell division. Pin-1 requires phosphorylation of a Ser or Thr residue adjacent to a Pro residue in the substrate and catalyzes cis-trans isomerization about the proline amide bond. The dihedral angle that would correspond to the reaction coordinate for isomerization of the omega peptide bond was investigated for several small models. Relaxed potential energy scans for this dihedral angle in N-methylacetamide, 1, N,N-dimethylacetamide, 2, acetylpyrrolidine, 3 and acetylproline, 4, were carried out in 20 degrees steps using the B3LYP/6-31+G* level of theory. In addition, similar scans were carried out for 1-4 protonated on the acetylamide carbonyl oxygen. Optimized structures for 1-4 protonated on the amide nitrogen were also obtained at B3LYP/6-31+G*. Relative proton affinities were determined for each site at various angles along the reaction coordinate for isomerization. The relative proton affinities were anchored to experimental gas phase proton affinities, which were taken from the literature for 1 and 2, or determined in an electrospray ionization-quadrupole ion trap instrument using the extended kinetic method for 3 and 4. Proton affinities of 925 +/- 10 and 911 +/- 12 kJ/mol were determined for 3 and 4, respectively. These studies suggest that the nitrogen atom in these amides becomes the most basic site in the molecule at a dihedral angle of ca. 130 degrees . In addition, the nitrogen atoms in 2-4 are predicted to attain basicities in the range 920-950 kJ/mol, making them basic enough to be the preferred site for hydrogen bonding in the Pin-1 active site, in support of the proposed mechanism for PPIases. 相似文献
65.
Felicia Maharaj Donald C. Craig Marcia L. Scudder Roger Bishop Naresh Kumar 《Journal of inclusion phenomena and macrocyclic chemistry》2007,59(1-2):17-24
New tetrabromo calix[4]arene derivatives 2 and 5a/5b have been synthesised and found to function as inclusion hosts for nitrile guests. The X-ray structures of (2)2 · (pivalonitrile)3 and (5a) · (acetonitrile)3 · (water) show that, in each compound, molecular inclusion occurs by a combination of complexation within the calixarene
bowl and lattice inclusion outside the bowl. Racemic 5a/5b crystallises as a conglomerate, with chiral discrimination between these enantiomers being assisted by the propeller-shaped
molecular conformation they adopt in the solid state. 相似文献
66.
Felicia Moore Mensah 《School science and mathematics》2011,111(8):379-388
The aim of this study is to report findings from the Drawing‐Elementary‐Science‐Teacher‐Ideal‐Not, or the DESTIN procedure. The study utilizes a simple drawing procedure accompanied by a narrative and discussion for understanding preservice teachers' images of science, science teaching, and the science teacher. Ninety drawings from two sections of an elementary science methods course were analyzed. Looking at the pre‐drawings from the beginning of the semester and post‐drawings done at the end of the semester, the findings relate the value of using drawings in teacher education and the usefulness of this procedure to promote discussions about science teaching, the construction of new images and practices for teaching elementary science, and teacher identity. The DESTIN procedure has potential as a productive activity for teacher education and long‐term professional development by making more explicit teachers' views of science teaching and learning and their past experiences as science learners. 相似文献
67.
Dana Ortansa Dorohoi Carmen Felicia Dascalu Teodora Teslaru Livia Vicenta Gheorghies 《光谱学快报》2013,46(6):383-391
The visible electronic absorption spectra of two carbanion disubstituted cycloimmonium ylids having a 3-aryl-pyridazinium derivative as cation and a common disubstituted carbanion (-2,4,6-picryl-benzoyl) were studied in solvents with different physical and chemical properties. The visible electronic absorption band of 3-aryl-pyridazinium ylids is attributed to an electron charge transfer from the carbanion toward the heterocycle. The solvent effects on the visible electronic band of the studied ylids were described both by empirical parameters defined by Kosower and by using the theory of a dielectric homogeneous solution. Some remarks about the nature of the molecular interactions in the 3-aryl-phthalazinium-2,4,6-picryl-benzoyl methylid solutions are made in this paper on the basis of solvatochromic study. 相似文献
68.
Nathan Kodjo Mintah Churcher Sayali Upasham Paul Rice Cornelia Felicia Greyling Shalini Prasad 《Electroanalysis》2022,34(2):375-386
Cortisol and Neuropeptide Y(NPY) are chronobiological markers of stress. Non-invasive tracking of these two biomolecules can provide great insight into an individual's physiological and neurological wellbeing. This work presents the development of a platform that tracks the two biomarkers in ultra-low volumes (5 μL) of sweat using electrochemical impedance spectroscopy (EIS). The sensing platform was able to detect both molecules in their relevant physiological ranges (8.16–141.7 ng/mL and 50–200 pg/mL respectively) with good sensitivity and specificity. This platform is envisioned to aid in the monitoring of pathophysiologies of stress-based disorders. 相似文献
69.
In this work, m‐phenylenediamine (MPD) is used to prepare cross‐linked polyetherimide (PEI)‐based nanofiltration (NF) membrane for treatment of dye containing wastewater. The effects of dope solution composition, cross‐linking time, and dye concentration on membrane performance are investigated. Results indicate that the rejection of dye is increased with the increase of acetone concentration in the dope solution, cross‐linking time, and dye concentration. Meanwhile, membrane flux showed the opposite trend. With the aid of SEM and FTIR analysis, the cross‐linking between MPD and PEI is confirmed. The cross‐linked membrane has thicker and dense selective layer compared to the unmodified membrane. The cross‐linked NF membrane (PEI: 15 wt%; acetone: 20 wt%; cross‐linking time: 10 minutes) showed good performance in filtration of synthetic dye wastewater (Reactive Red 120, 1500 ppm) with 98% dye rejection and 0.013 L m?2 hour?1 of flux at relatively low operating pressure (60 psi). 相似文献
70.
LetD:= { C
3 (
3) (s) = (s+1),
1 ([0,1]) is simple closed curve}.In this paper we show that there is D which minimizes the functional
+ a(area minimizing surface with boundary ([0,1])), 0 D if a (0,) is suitably chosen.where 0 D if a (0, ) is suitably chosen. 相似文献