Search results for "Base"

Role of Cooperation with Stakeholders in Work-Based Learning Realization

2021

The research was supported by the NATIONAL RESEARCH PROGRAMME “LATVIAN HERITAGE AND FUTURE CHALLENGES FOR THE SUSTAINABILITY OF THE STATE” project “CHALLENGES FOR THE LATVIAN STATE AND SOCIETY AND THE SOLUTIONS IN INTERNATIONAL CONTEXT" (INTERFRAME-LV, Project No.VPP-IZM-2018/1-0005).

Student experiences of project-based learning in an analytical chemistry laboratory course in higher education

2020

Abstract This study describes students’ experiences in project-based learning (PjBL) incorporated as part of a revised undergraduate analytical chemistry laboratory course. We examined which phases were the easiest as well as the most challenging and what student skills developed during the research project. The research data were collected between 2016 and 2018 via two questionnaires. They were analyzed both quantitatively and qualitatively. One questionnaire focused on the whole course (in 2016–2018, n = 127) of which only the answers on the research project questions were analyzed. The other questionnaire focused on only the research project (in 2018, n = 42). Based on the results of our…

Reverse Catmull-Clark Subdivision

2006

Reverse subdivision consists in constructing a coarse mesh of a model from a finer mesh of this same model. In this paper, we give formulas for reverse Catmull-Clark subdivision. These formulas allow the constructing of a coarse mesh for almost all meshes. The condition for being able to apply these formulas is that the mesh to be reversed must be generated by the subdivision of a coarse mesh. Except for this condition, the mesh can be arbitrary. Vertices can be regular or extraordinary and the mesh itself can be arbitrary (triangular, quadrilateral…).

Substituent effects on the mechanism changeover in a multipathway reaction: A model for the behavior of biological systems?

2009

By studying the rearrangement in dioxane/water of a series of (Z)-arylhydrazones of 5-amino-3- benzoyl-1,2,4-oxadiazole (1a-k) into the relevant (2-aryl-5-phenyl-2H-1,2,3-triazol-4-yl)ureas (2a-k) in a wide range of pS + (an operational scale of proton concentration in the mixed solvent used; dioxane/water, 1:1, v:v), the occurrence of three different reaction pathways (specific-acid- catalyzed, uncatalyzed, and general-base-catalyzed) for the relevant SNi process has been recently enlightened. The significantly different substituent effects on the three pathways cause some crossovers in the log kA,R versus pS + plots. Both the pS + value at which the crossover occurs and the width of the u…

Titanocene Selenide Sulfides Revisited: Formation, Stabilities, and NMR Spectroscopic Properties

2019

[TiCp2S5] (phase A), [TiCp2Se5] (phase F), and five solid solutions of mixed titanocene selenide sulfides [TiCp2SexS5−x] (Cp = C5H5−) with the initial Se:S ranging from 1:4 to 4:1 (phases B–E) were prepared by reduction of elemental sulfur or selenium or their mixtures by lithium triethylhydridoborate in thf followed by the treatment with titanocene dichloride [TiCp2Cl2]. Their 77Se and 13C NMR spectra were recorded from the CS2 solution. The definite assignment of the 77Se NMR spectra was based on the PBE0/def2-TZVPP calculations of the 77Se chemical shifts and is supported by 13C NMR spectra of the samples. The following complexes in varying ratios were identified in the CS2 solutions of …

Spherical Top Theory and Molecular Spectra

2011

In this article, we present an overview of the present state of the art of the theory of high-resolution spherical-top spectra in the framework of the effective Hamiltonian approach. We describe the specific features of this class of molecules to explain the basic concepts of the theoretical methods used for the analysis (line positions and intensities) and the simulation of absorption (including pure rotation) and Raman spectra of such species. The non conventional formalism that we use is essentially based on irreducible tensor methods and is especially adapted to computational treatments and global analyses of complex interacting band systems. We give examples concerning mainly methane (…

Quantitative reconstruction of hydroclimate variability over the last 200 kyr in the West Mediterranean

2022

The data show the quantitative annual, winter and summer precipitation reconstructions (mm/yr) from southern Iberian Peninsula for the last ~200,000 years (Camuera et al., 2022), based on the previously published fossil pollen data from the Padul-15-05 lake sediment record (Ramos-Román et al., 2018a, b; Camuera et al., 2019, 2021). The Padul-15-05 record, located in southern Spain (37º00'39''N, 3º36'14''W, 726 masl), was retrieved during summer 2015 from the current edge of the lake using a Rolatec RL-48-L hydraulic percussion coring machine. The quantitative precipitation reconstructions were performed using the performance statistics of the Weighted Averaging-Partial Least Squares (WA-PLS…

Structural Motifs of Alkali Metal Superbases in Non‐coordinating Solvents

2020

Abstract Lochmann–Schlosser superbases (LSB) are a standard reagent in synthetic chemistry to achieve an exchange of a proton on an organic framework with an alkali metal cation, which in turn can be replaced by a wide range of electrophilic groups. In standard examples, the deprotonating reagent consists of an equimolar mixture of n‐butyllithium and potassium t‐butoxide. However, the nature of the reactive species could not be pinned down either for this composition or for similar mixtures with comparable high reactivity. Despite the poor solubility and the fierce reactivity, some insights into this mixture were achieved by some indirect results, comparison with chemically related systems,…

Business networking strategy: operations management and organizational economics different perspectives

2008

6-Methyluracil: a redetermination of polymorph (II)

2019

6-Methyluracil, C5H6N2O2, exists in two crystalline phases: form (I), monoclinic, space group P21/c [Reck et al. (1988). Acta Cryst. A44, 417–421] and form (II), monoclinic, space group C2/c [Leonidov et al. (1993). Russ. J. Phys. Chem. 67, 2220–2223]. The structure of polymorph (II) has been redetermined providing a significant increase in the precision of the derived geometric parameters. In the crystal, molecules form ribbons approximately running parallel to the c-axis direction through N—H...O hydrogen bonds. The radical differences observed between the crystal packing of the two polymorphs may be responsible in form (II) for an increase in the contribution of the polar canonical forms…