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71.
We are interested in the maximum possible number of facets that Dirichlet stereohedra for three-dimensional crystallographic
groups can have. In two previous papers, D. Bochiş and the second author studied the problem for noncubic groups. This paper
deals with “full” cubic groups, while “quarter” cubic groups are left for a subsequent paper. Here, “full” and “quarter” refers
to the recent classification of three-dimensional crystallographic groups by Conway, Delgado-Friedrichs, Huson and Thurston.
This paper’s main result is that Dirichlet stereohedra for any of the 27 full groups cannot have more than 25 facets. We also
find stereohedra with 17 facets for one of these groups.
Research partially supported by the Spanish Ministry of Education and Science, grant number MTM2005-08618-C02-02. 相似文献
72.
Juan M. Antelo Florencio Arce Juan Crugeiras Julia Franco Pilar Rodriguez Angel Varela 《国际化学动力学杂志》1990,22(12):1271-1282
This article reports the kinetics of the decomposition of N-bromoserine formed rapidly by bromation of serine by BrO?. The main decomposition products are glycolaldehyde, ammonia, carbon dioxide, and bromide ions at pH < 11.5, and β-hydroxypyruvic acid, ammonia, and bromide ions at pH > 11.5. The reaction is of order one with respect to N-bromoserine, and is independent of ionic strength and excess serine. The rate constant increases with increasing pH at pH > 11 and with decreasing pH at pH < 8, and over the range pH 8–11 has the constant value 1.67 × 10?3 s?1 at 298 K. 相似文献
73.
In this paper we extend and generalize several known estimates for homogeneous polynomials and multilinear mappings on Banach spaces. Applying the theory of absolutely summing nonlinear mappings, we prove that estimates which are known for mappings on ?p spaces in fact hold true for mappings on arbitrary Banach spaces. 相似文献
74.
Pérez CM Rodríguez-Delgado A Palma P Álvarez E Gutiérrez-Puebla E Cámpora J 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(46):13834-13842
Manganese alkyl complexes stabilised by 2,6-bis(N,N'-2,6-diisopropyl-phenyl)acetaldiminopyridine ((iPr)BIP) have been selectively prepared by reacting suitable alkylmanganese(II) precursors, such as homoleptic dialkyls [(MnR(2))(n)] or the corresponding THF adducts [{MnR(2)(thf)}(2)] with the mentioned ligand. For R=CH(2)CMe(2)Ph or CH(2)Ph, formally Mn(I) derivatives are produced, in which one of the two R groups migrates to the 4-position of the central pyridine ring in the (iPr)BIP ligand. In contrast, a true dialkyl complex [MnR(2)((iPr)BIP)] can be isolated for R=CH(2)SiMe(3). In solution, this compound slowly evolves to the corresponding Mn(I) monoalkyl derivative. A detailed study of this reaction provides insights on its mechanism, showing that it proceeds through successive alkyl migrations, followed by spontaneous dehydrogenation. Protonation of [Mn(CH(2)SiMe(3))(2)((iPr)BIP)] with the pyridinium salt [H(Py)(2)][BAr'(4)] (Ar'=3,5-C(6)H(3)(CF(3))(2)) leads to the cationic species [Mn(CH(2)SiMe(3))(Py)((iPr)BIP)](+). Alternatively, the same complex can be produced by reaction of the pyridine complex [{Mn(CH(2)SiMe(3))(2)(Py)}(2)] with the protonated ligand salt [H(iPr)BIP](+)[BAr'(4)](-). This last reaction allows the synthesis of analogous cationic alkylmanganese(II) derivatives, when precursors of type [MnR(2)((iPr)BIP)] are not available. Treatment of these neutral and cationic (iPr)BIP alkylmanganese derivatives with a range of typical co-catalysts (modified methylaluminoxane (MMAO), B(C(6)F(5))(3), trimethyl or triisobutylaluminum) does not lead to active ethylene polymerisation catalysts. 相似文献
75.
Joana Ferreira da Costa Franco Fernández Xerardo García-Mera Pilar Midón 《Tetrahedron》2010,66(34):6797-6805
Starting from readily available N-benzyl protected methyl 3,5-bis(hydroxymethyl)pirrolidinecarboxylate a number of racemic methyl t-3,t-5-disubstitutedprolinates have been synthesised, thus opening a practical way towards the preparation of a variety of putative proline-mimetics. In this context, N-Boc protected derivatives proved to be better intermediates than their N-benzyl counterparts in terms of cleanness and overall yield of the synthetic procedure. 相似文献
76.
Cell integrity signaling and response to stress in fission yeast 总被引:1,自引:0,他引:1
Cellular responses to external signals are regulated by conserved mitogen-activated protein (MAP) kinase signaling cascades. These pathways are triggered by a vast range of stimuli. They phosphorylate numerous proteins, produce significant changes in the gene expression, and regulate diverse processes ranging from proliferation and differentiation to apoptosis in all eukaryotic cells. Three conserved MAP kinase signaling pathways have been identified in the fission yeast Schizosaccharomyces pombe. In this article, we present an overview of two of those pathways that regulate the response of fission yeast to stress and maintain cell integrity. The structure of these signaling modules and the function of the pathways, including the regulation by endogenous inhibitors, are discussed. 相似文献
77.
Puebla P Oshima-Franco Y Franco LM Santos MG Silva RV Rubem-Mauro L Feliciano AS 《Molecules (Basel, Switzerland)》2010,15(11):8193-8204
The effect of four sub-extracts prepared from the lyophilized hydroalcoholic bark of Dipteryx alata (Leguminosae-Papilionoideae) dissolved in a methanol-water (80:20) mixture through a liquid-liquid partition procedure has been investigated against the neuromuscular blockade of the venom of the snake Bothrops jararacussu. The active CH?Cl? sub-extract has been extensively analyzed for its chemical constituents, resulting in the isolation of four lupane-type triterpenoids: lupeol, lupenone, 28-hydroxylup-20(29)-en-3-one, betulin, nine isoflavonoids: 8-O-methylretusin, 7-hydroxy-5,6,4'-trimethoxyisoflavone, afrormosin, 7-hydroxy-8,3',4'-trimethoxyisoflavone, 7,3'-dihydroxy-8,4'-dimethoxyisoflavone, odoratin, 7,8,3'-trihydroxy-4'-methoxyisoflavone, 7,8,3'-trihydroxy-6,4'-dimethoxyisoflavone, dipteryxin, one chalcone: isoliquiritigenin, one aurone: sulfuretin and three phenolic compounds: vanillic acid, vanillin, and protocatechuic acid. Their chemical structures were elucidated on the basis of spectroscopic analysis, including HRMS, 1D- and 2D-NMR techniques. 相似文献
78.
Anna Fàbregas-Fernández Encarna García-Montoya Pilar Pérez-Lozano Josep M. Suñé-Negre Josep Ramon Ticó Montserrat Miñarro 《Accreditation and quality assurance》2010,15(5):297-304
There is currently no universal or standardized quality system for the recognition of excellence of a research center. Knowledge
and competence may not be enough in the current rapidly changing world in which high productivity and continuous improvement
are essential. The purpose of this study was to assess the impacts of implementing the ISO9001:2000:2000 standard in an academic
research center dedicated to R+D+I (research, development and innovation) in the pharmaceutical industry. The article describes
the stages we followed to implement the ISO9001:2000 system, which was achieved by integrating it into the previous regulatory
system of GMP (Good Manufacturing Practices). As a result of implementing ISO9001:2000, the center has seen distinct improvements,
such as fewer errors in project documentation, improved assessment of customer satisfaction, and the effective implementation
of periodic plans, e.g., in calibration, preventive maintenance, and investments. Overall, ISO9001:2000 implementation has
been beneficial for the organization and could be applied to other research centers. 相似文献
79.
Campillo N Viñas P Cacho JI Peñalver R Hernández-Córdoba M 《Journal of chromatography. A》2010,1217(47):7323-7330
Dispersive liquid-liquid microextraction (DLLME) coupled with gas chromatography-mass spectrometry (GC-MS) was evaluated for the simultaneous determination of five chlorophenols and seven haloanisoles in wines and cork stoppers. Parameters, such as the nature and volume of the extracting and disperser solvents, extraction time, salt addition, centrifugation time and sample volume or mass, affecting the DLLME were carefully optimized to extract and preconcentrate chlorophenols, in the form of their acetylated derivatives, and haloanisoles. In this extraction method, 1mL of acetone (disperser solvent) containing 30μL of carbon tetrachloride (extraction solvent) was rapidly injected by a syringe into 5mL of sample solution containing 200μL of acetic anhydride (derivatizing reagent) and 0.5mL of phosphate buffer solution, thereby forming a cloudy solution. After extraction, phase separation was performed by centrifugation, and a volume of 4μL of the sedimented phase was analyzed by GC-MS. The wine samples were directly used for the DLLME extraction (red wines required a 1:1 dilution with water). For cork samples, the target analytes were first extracted with pentane, the solvent was evaporated and the residue reconstituted with acetone before DLLME. The use of an internal standard (2,4-dibromoanisole) notably improved the repeatability of the procedure. Under the optimized conditions, detection limits ranged from 0.004 to 0.108ngmL(-1) in wine samples (24-220pgg(-1) in corks), depending on the compound and the sample analyzed. The enrichment factors for haloanisoles were in the 380-700-fold range. 相似文献
80.
Natalia Campillo Pilar ViñasNerea Aguinaga Gema FérezManuel Hernández-Córdoba 《Journal of chromatography. A》2010,1217(27):4529-4534
A stir bar microextraction (SBSE) procedure for the determination of seven strobilurin fungicides in fruit samples using liquid chromatography (LC) and diode array detection (DAD) has been developed. The samples were sonicated in the presence of ethanol before submitting the extracts to SBSE. The incorporation of drazoxolon as an internal standard before SBSE allowed calibration without the need to use the standard additions method. Under the optimized conditions, detection limits were in the 0.3–2 ng g−1 range, corresponding to trifloxystrobin and metominostrobin, respectively. The SBSE–LC–DAD procedure showed good repeatability (RSD below 11% in all cases) and provided recoveries of 80–105% from spiked samples. The method was applied to fifteen fruit samples, and low levels of pyraclostrobin and trifloxystrobin were found in two of them. 相似文献