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151.
Fosso Wamba Samuel Queiroz Maciel M. Braganza Ashley 《Annals of Operations Research》2022,308(1-2):1-6
Annals of Operations Research - 相似文献
152.
Maria Dina Vivarelli 《Meccanica》1984,19(1):11-14
Summary In a previous research we have shown that the KS-transformation, developed by Kustaanheimo and Stiefel for the regularization of the Kepler problem, may be interpreted as the correspondence which associates to each null 4-vector of the space of Minkowski a one-index spinor, defined up to a phase factor, and we have obtained a new form of the KS-transformation. In the present research we show that this formulation allows a straight derivation of the Hopf fibering of the sphere S3 (characterized by unit spinors) having the base space given by the section (sphere S2) of the light cone, and we show that the KS-transformation allows the quantization of the symplectic manifold S2 in the sense of Souriau. The sphere S3 turns out to be a contact quantized manifold. The bilinear relation characteristic of the KS-theory and the column vectors of the KS-matrix are intimately related to the contact structure.
Presented at the VI Congresso Nazionale dell'Associazione Italiana di Meccanica Teorica ed Applicata (AIMETA), Genova, October 1982. Work performed under the auspices of G.N.F.M. of the C.N.R. (Consiglio Nazionale delle Ricerche). 相似文献
Sommario In un precedente lavoro si è mostrato che la trasformazione KS, introdotta da Kustaanheimo e Stiefel per regolarizzare il problema di Keplero, è riconducibile alla ben nota corrispondenza fra vettori del cono isotropo dello spazio di Minkowski e spinori semplici, definiti a meno della fase, e si è pervenuti ad una nuova formulazione della KS. Nel presente lavoro si mostra come da tale formulazione scaturisca in modo naturale la fibrazione di Hopf della sfera S3 (caratterizzata dagli spinori unitari) avente quale base una sezione (sfera S2) del cono isotropo e si mette in luce come la trasformazione KS consenta di effettuare la quantizzazione della varietà simplettica S2 nel senso di Souriau e di ottenere la sfera S3 quale varietà quantica di contatto. La relazione bilineare caratteristica della teoria KS ed i vettori colonna della matrice KS risultano intimamente legati alla struttura di contatto.
Presented at the VI Congresso Nazionale dell'Associazione Italiana di Meccanica Teorica ed Applicata (AIMETA), Genova, October 1982. Work performed under the auspices of G.N.F.M. of the C.N.R. (Consiglio Nazionale delle Ricerche). 相似文献
153.
Symmetries have an important role in turbulence. To some extent, they contain the physics of the equations (conservation laws,
etc.), and it is essential that turbulence models respect them. However, as observed by Oberlack (Annual Research Briefs.
Stanford University, Stanford 1997) and next by Razafindralandy and Hamdouni (Direct and Large-Eddy Simulation 6: Proceedings
of the 6th International ERCOFTAC Workshop on Direct and Large-Eddy Simulation. Springer, Heidelberg, 2006) in the case of
an isothermal fluid, only few subgrid stress tensor models preserve the symmetries of the Navier–Stokes equations. In this
communication, we present the symmetries of the equations of a non-isothermal fluid flow and analyze some common subgrid stress
tensor and flux models under the point of view of these symmetries.
相似文献
154.
P. B. Maciel L. L. S. de Barros E. C. M. Duarte M. N. C. Harder G. G. Bortoleto C. H. Abreu Jr. F. C. A. Villanueva 《Journal of Radioanalytical and Nuclear Chemistry》2013,297(2):209-213
Biodiesel is a renewable and biodegradable fuel that can be used in diesel engines as a replacement for fossil diesel. A suitable alternative is to produce it from Jatropha curcas, which has high quality oil concentration. Nevertheless, the presence of particular chemical elements above certain limits can affect the product quality, leading to vehicle engine problems and acting as air pollution source. The objective of this work is to develop a method for the simultaneous determination of B, Na, Mg, P, S, K, Ca, Cr, Mn, Fe, Co, Ni, Cu, Zn, Cd, Ba, and Pb in J. curcas seeds, oil and biodiesel using the inductively coupled plasma mass spectrometry (ICP-MS) technique. This material was evaluated because has been successfully employed in India for biodiesel production as well as in other places where there is an incentive to family farming, without affect the food chain. The oil was obtained from seeds via mechanical extraction and the biodiesel was achieved by oil transesterification. After optimization of the microwave digestion method for the different sample types, the samples were analyzed by ICP-MS. The certified reference material NIST SRM 1515 (apple leaves) and the recovery tests were carried out to ensure the accuracy of the proposed method, which made possible the quantification of several nutrients and potentially toxic elements in J. curcas seeds, oil and biodiesel, especially Na, K, Ca, Mg, P and S in biodiesel which are mandatory analyzed by Petroleum, Natural Gas and Biofuel National Agency (ANP). This work highlights the findings of the first study of potentially toxic and nutrient elements in the production chain steps seed–oil–biodiesel from J. curcas. 相似文献
155.
Sarita C. Rabelo Rubens Maciel Filho Aline C. Costa 《Applied biochemistry and biotechnology》2013,169(5):1696-1712
Sugarcane bagasse was subjected to lime (calcium hydroxide) pretreatment and enzymatic hydrolysis for second-generation ethanol production. A central composite factorial design was performed to determine the best combination of pretreatment time, temperature, and lime loading, as well as to evaluate the influence of enzymatic loadings on hydrolysis conversion. The influence of increasing solids loading in the pretreatment and enzymatic hydrolysis stages was also determined. The hydrolysate was fermented using Saccharomyces cerevisiae in batch and continuous mode. In the continuous fermentation, the hydrolysates were concentrated with molasses. Lime pretreatment significantly increased the enzymatic digestibility of sugarcane bagasse without the need for prior particle size reduction. In the optimal pretreatment conditions (90 h, 90 °C, 0.47 g?lime/g bagasse) and industrially realistic conditions of hydrolysis (12.7 FPU/g of cellulase and 7.3 CBU/g of β-glucosidase), 139.6 kg?lignin/ton raw bagasse and 126.0 kg hemicellulose in the pretreatment liquor per ton raw bagasse were obtained. The hydrolysate from lime pretreated sugarcane bagasse presented low amounts of inhibitors, leading to ethanol yield of 164.1 kg?ethanol/ton raw bagasse. 相似文献
156.
Abstract The susceptibility of the fully acetylated 1-thio–β-D-glucopyranosyl esters of N-protected amino acids toward the amino group of an external amino acid-or peptide-ester was examined in dichloromethane at room temperature and at 40°, respectively. In each case, the aminolysis reaction led to rupture of the C-1 thiolester bond and formation of the corresponding N-acylpeptide ester; the reaction proceeded without racemization of the aglycon chiral centre. Evidence for a remarkably high acylating efficiency of the sugar—amino acid C-1 thiolester bond is presented. 相似文献
157.
158.
Dina T. Mirijanian Ranjan V. Mannige Ronald N. Zuckermann Stephen Whitelam 《Journal of computational chemistry》2014,35(5):360-370
Peptoids are positional isomers of peptides: peptoid sidechains are attached to backbone nitrogens rather than α‐carbons. Peptoids constitute a class of sequence‐specific polymers resistant to biological degradation and potentially as diverse, structurally and functionally, as proteins. While molecular simulation of proteins is commonplace, relatively few tools are available for peptoid simulation. Here, we present a first‐generation atomistic forcefield for peptoids. Our forcefield is based on the peptide forcefield CHARMM22, with key parameters tuned to match both experimental data and quantum mechanical calculations for two model peptoids (dimethylacetamide and a sarcosine dipeptoid). We used this forcefield to demonstrate that solvation of a dipeptoid substantially modifies the conformations it can access. We also simulated a crystal structure of a peptoid homotrimer, H‐(N‐2‐phenylethyl glycine)3‐OH, and we show that experimentally observed structural and dynamical features of the crystal are accurately described by our forcefield. The forcefield presented here provides a starting point for future development of peptoid‐specific simulation methods within CHARMM. © 2013 Wiley Periodicals, Inc. 相似文献
159.
Adel A.-H. Abdel-Rahman Amira K. F. Shaban Ibrahim F. Nassar Dina S. EL-Kady Nasser S. M. Ismail Samy F. Mahmoud Hanem M. Awad Wael A. El-Sayed 《Molecules (Basel, Switzerland)》2021,26(13)
New pyridine, pyrazoloyridine, and furopyridine derivatives substituted with naphthyl and thienyl moieties were designed and synthesized starting from 6-(naphthalen-2-yl)-2-oxo-4-(thiophen-2-yl)-1,2-dihydropyridine-3-carbonitrile (1). The chloro, methoxy, cholroacetoxy, imidazolyl, azide, and arylamino derivatives were prepared to obtain the pyridine-−C2 functionalized derivatives. The derived pyrazolpyridine-N-glycosides were synthesized via heterocyclization of the C2-thioxopyridine derivative followed by glycosylation using glucose and galactose. The furopyridine derivative 14 and the tricyclic pyrido[3′,2′:4,5]furo[3,2-d]pyrimidine 15 were prepared via heterocyclization of the ester derivative followed by a reaction with formamide. The newly synthesized compounds were evaluated for their ability to in vitro inhibit the CDK2 enzyme. In addition, the cytotoxicity of the compounds was tested against four different human cancer cell lines (HCT-116, MCF-7, HepG2, and A549). The CDK2/cyclin A2 enzyme inhibitory results revealed that pyridone 1, 2-chloro-6-(naphthalen-2-yl)-4-(thiophen-2-yl)nicotinonitrile (4), 6-(naphthalen-2-yl)-4-(thiophen-2-yl)-1H-pyrazolo[3,4-b]pyridin-3-amine (8), S-(3-cyano-6-(naphthaen-2-yl)-4-(thiophen-2-yl)pyridin-2-yl) 2-chloroethanethioate (11), and ethyl 3-amino-6-(naphthalen-2-yl)-4-(thiophen-2-yl)furo[2,3-b]pyridine-2-carboxylate (14) are among the most active inhibitors with IC50 values of 0.57, 0.24, 0.65, 0.50, and 0.93 µM, respectively, compared to roscovitine (IC50 0.394 μM). Most compounds showed significant inhibition on different human cancer cell lines (HCT-116, MCF-7, HepG2, and A549) with IC50 ranges of 31.3–49.0, 19.3–55.5, 22.7–44.8, and 36.8–70.7 μM, respectively compared to doxorubicin (IC50 40.0, 64.8, 24.7 and 58.1 µM, respectively). Furthermore, a molecular docking study suggests that most of the target compounds have a similar binding mode as a reference compound in the active site of the CDK2 enzyme. The structural requirements controlling the CDK2 inhibitory activity were determined through the generation of a statistically significant 2D-QSAR model. 相似文献
160.