Search results for "optimized"

A method for measurement of spin-spin couplings with sub-mHz precision using zero- to ultralow-field nuclear magnetic resonance.

2017

We present a method which allows for the extraction of physical quantities directly from zero- to ultralow-field nuclear magnetic resonance (ZULF NMR) data. A numerical density matrix evolution is used to simulate ZULF NMR spectra of several molecules in order to fit experimental data. The method is utilized to determine the indirect spin-spin couplings ($J$-couplings) in these, which is achieved with precision of $10^{-2}$--$10^{-4}$ Hz. The simulated and measured spectra are compared to earlier research. Agreement and precision improvement for most of the $J$-coupling estimates are achieved. The availability of an efficient, flexible fitting method for ZULF NMR enables a new generation of…

NMR spectroscopy in environmental chemistry:1H and13C NMR parameters of tricyclic polychlorinated C10 hydrocarbons and their oxy derivatives based on…

1999

Two-dimensional homo- and heteronuclear NMR chemical shift correlation techniques were applied in the characterization of five tricyclic polychlorinated C10 hydrocarbons, chlordene (1), heptachlor (2), trans-nonachlor (3), α-chlordene (4) and γ-chlordene (5), which are spread globally in the environment owing to their use as insecticides. Approximate and partly contradictory 1H and 13C NMR chemical shifts reported in the literature were corrected in this work. The chemical shift assignments of 1–5 were based on DQF COSY, HMQC and HMBC experiments. In addition, an INADEQUATE experiment was needed to ascertain the 13C chemical shifts assignment of 2. The nJ(H,H)s of 1–5 were solved by compute…

1H and13C NMR assignments and conformational analysis of some podocarpene derivatives

2000

This paper reports on the assignment of the 1 Ha nd 13 C NMR spectra of five podocarpene derivatives. Resonance assignments were made on the basis of one- and two-dimensional NMR techniques which included 1 H, 13 C, DEPT and HMQC and also 1D NOE difference spectroscopy. The ratio of the different conformers in the six- membered C-ring of the podocarpene system was determined by molecular mechanics calculations and analysis of proton spin-spin coupling constants. Copyright © 2000 John Wiley & Sons, Ltd.

13C NMR spectroscopy of four tertiary methyl norbornenols and norbornanols

1975

Carbon chemical shifts and direct 13C1H coupling constants of 2-endo-methyl-5-norbornen-2-exo-ol, 2-exo-methyl-5-norbornen-2-endo-ol, 2-endo-methylnorbornan-2-exo-ol and 2-exo-methylnorbornan-2-endo-ol have been measured from single samples using a dual probe pulse Fourier transform method.

Solid state NMR studies of gels derived from low molecular mass gelators

2016

The emergence of NMR crystallography provides a unique opportunity to study solids, gels and xerogels, thereby providing ample information to elucidate molecular packing in the native gel. This review details the importance as well as the application of solid state NMR spectroscopy combined with other analytical tools to study gels derived from low molecular mass organo- and hydrogelators.

[MoO2(SCPh2CO2)2]2− and [MoO(SCPh2CO2)2]− anion complexes. A theoretical structure characterization

1995

Abstract Geometry optimization of [MoO 2 (SCH 2 CO 2 ) 2 ] 2− and [MoO(SCH 2 CO 2 ) 2 ] − systems as models of [MoO 2 (SCPh 2 CO 2 ) 2 ] 2− and [MoO(SCPh 2 CO 2 ) 2 ] − anion complexes have been carried out at STO-3G, 3-21G, LANL1MB and LANL2DZ basis set levels. A comparison of the theoretical results and X-ray experimental data has been performed. STO-3G minimal basis set produces the best geometrical agreement, in particular the distances and orientations of the different ligands linked to molybdenum transition metal. A large structural overlap with STO-3G optimized geometry and X-ray data has been found for the [MoO 2 (SCPh 2 CO 2 ) 2 ] 2− and [MoO(SCPh 2 CO 2 ) 2 ] − anion complexes.

13C and15N NMR study of substituted 1,2,4-triazines

1995

13C and 15N NMR spectra of eight substituted 1,2,4-triazines were measured and assigned. The assignments of the 13C NMR spectra were based on the substituent chemical shifts and nJ(C,H) coupling constants. 15N NMR chemical shifts generally showing well separated ranges were assigned by the proton coupled 15N NMR spectra. 15N NMR chemical shifts of N-4 in 3- and 5-methoxy or -thiomethyl-substituted 1,2,4-triazines were found to be related significantly (confidence level >99%) with the π-charge at N-4 calculated by a semi-empirical molecular orbital (AM1) procedure. For the 15N NMR chemical shifts of N-1 and N-2, no reliable correlations with the molecular electronic properties such as AM1 π-…

?-Phenylsulfonyl-N-arylacetamides (?-phenylsulfonylacetanilides):1H,13C and15N NMR spectral characterization

2000

A Novel Energy Model for MANETs based on Graphs with Activation Windows

2005

Energy usage optimization is still an important issue and a critical design factor for mobile ad hoc networks (MANETs). Only recently a few proposals appeared that consider energy-aware optimizations for routing protocols. In this paper we describe an analytical model for MANETs which is based on graphs with activation windows. The activation windows allow to model the on-off status of the network devices. Moreover, we propose an algorithm with pseudo-polynomial complexity, called STP algorithm (STPA), that based on the current position and state of the nodes determines the shortest time path between the source node and the destination node.

Power Density Optimization of EMI Filters for Power Electronic Converters

The switching power converters are used in a broad variety of applications, from the consumer electronics to the DC distribution systems, from the vehicle applications (road vehicles, marine vehicles, aircraft) to the industrial automation. In each of these application fields, the conversion systems which present more compact size and reduced weight, at the same power, are strongly required in relation to stringent design constraints. In this context, the optimization of the power density of the converter becomes an essential requirement. The increase of the switching frequency of the static devices allows an improvement of the power density, thanks to the possibility of reducing the sizes …