Eugene Stephane Mananga

Investigation of the Effect of Finite Pulse Errors on BABA Pulse Sequence Using Floquet-Magnus Expansion Approach

This paper presents a study of finite pulse widths for the BABA pulse sequence using the Floquet–Magnus expansion (FME) approach. In the FME scheme, the first order is identical to its counterparts in average Hamiltonian theory (AHT) and Floquet theory (FT). However, the timing part in the FME approach is introduced via the function not present in other schemes. This function provides an easy way for evaluating the spin evolution during the time in between’ through the Magnus expansion of the operator connected to the timing part of the evolution. The evaluation of is particularly useful for the analysis of the non-stroboscopic evolution. Here, the importance of the boundary conditions, which provide a natural choice of , is ignored. This work uses the function to compare the efficiency of the BABA pulse sequence with and the BABA pulse sequence with finite pulses. Calculations of and are presented.

Probing the validity of average Hamiltonian theory for spin I = 1, 3/2 and 5/2 nuclei by analyzing a simple two-pulse sequence

In this work, we investigate the accuracy of controlling spin I=1, 3/2 and 5/2 spin systems by average Hamiltonian theory. By way of example, we consider a simple two-pulse echo sequence and compare this perturbation scheme to a numerical solution of the Von Neumann equation. For the different values of I, we examine this precision as a function of the quadrupolar coupling as well as various experimental parameters such as the pulse spacing and pulse width. Experiments and simulations on I=3/2 and I=5/2 spin systems are presented that highlight a spectral artifact introduced due to finite pulse widths as predicted by average Hamiltonian theory. The control of these spin systems by this perturbation scheme is considered by investigating a phase cycling scheme that suppresses these artifacts to zeroth-order of the Magnus expansion.

Applications of Floquet-Magnus expansion, average Hamiltonian theory and Fer expansion to study interactions in solid state NMR when irradiated with the magic-echo sequence.

This work presents the possibility of applying the Floquet-Magnus expansion and the Fer expansion approaches to the most useful interactions known in solid-state nuclear magnetic resonance using the magic-echo scheme. The results of the effective Hamiltonians of these theories and average Hamiltonian theory are presented.

Criteria to average out the chemical shift anisotropy in solid-state NMR when irradiated with BABA I, BABA II, and C7 radiofrequency pulse sequences.

Floquet-Magnus expansion is used to study the effect of chemical shift anisotropy in solid-state NMR of rotating solids. The chemical shift interaction is irradiated with two types of radiofrequency pulse sequences: BABA and C7. The criteria for the chemical shift anisotropy to be averaged out in each rotor period are obtained.

Progress in spin dynamics solid-state nuclear magnetic resonance with the application of Floquet-Magnus expansion to chemical shift anisotropy.

The purpose of this article is to present an historical overview of theoretical approaches used for describing spin dynamics under static or rotating experiments in solid state nuclear magnetic resonance. The article gives a brief historical overview for major theories in nuclear magnetic resonance and the promising theories. We present the first application of Floquet-Magnus expansion to chemical shift anisotropy when irradiated by BABA pulse sequence.

Facile synthesis of the Basolite F300-like nanoscale Fe-BTC framework and its lithium storage properties

The Fe-BTC material commercialized as Basolite F300 is one of the most studied MOFs due to its unique features and wide range of industrial applications. In this article, Basolite F300-like Fe-BTC MOF materials were prepared directly with the protonated carboxylated ligand, circumventing the use of an alkaline solution as in previous work, by selecting an appropriate iron source. Results from the detailed characterization indicate that the obtained Fe-BTC was very similar to the commercial counterpart and the one prepared under the alkaline conditions in terms of many physicochemical properties. Besides, the Fe-BTC reported herein was scaled down to the nano-regime to afford nanoscale metal–organic frameworks (nMOFs), which is advantageous for its potential applications. More importantly, the current interest in MOFs in the area of rechargeable batteries has driven us to investigate its electrochemical performance with respect to lithium storage. It was shown that the nanoscale Fe-BTC MOF exhibits an outstanding electrochemical performance with a high reversible capacity up to 1021 mA h g−1 after 100 cycles at a current density of 100 mA g−1 and capacities up to 436 and 408 mA h g−1 after 400 cycles at a higher current density of 500 and 1000 mA g−1, respectively. Our results on the Fe-BTC MOF highlight the potential for high power Li-ion batteries (LIBs) applications.

Myocardial Defect Detection Using PET-CT: Phantom Studies

It is expected that both noise and activity distribution can have impact on the detectability of a myocardial defect in a cardiac PET study. In this work, we performed phantom studies to investigate the detectability of a defect in the myocardium for different noise levels and activity distributions. We evaluated the performance of three reconstruction schemes: Filtered Back-Projection (FBP), Ordinary Poisson Ordered Subset Expectation Maximization (OP–OSEM), and Point Spread Function corrected OSEM (PSF–OSEM). We used the Channelized Hotelling Observer (CHO) for the task of myocardial defect detection. We found that the detectability of a myocardial defect is almost entirely dependent on the noise level and the contrast between the defect and its surroundings.

Revisiting NMR composite pulses for broadband 2H excitation

Quadrupolar echo NMR spectroscopy of static solids often requires RF excitation that covers spectral widths exceeding 100 kHz, which is difficult to obtain due to instrumental limitations. In this work we revisit four well-known composite pulses (COM-I, II, III and IV) for broadband excitation in deuterium quadrupolar echo spectroscopy. These composite pulses are combined with several phase cycling schemes that were previously shown to decrease finite pulse width distortions in deuterium solid-echo experiments performed with two single pulses. The simulations and experiments show that COM-II and IV composite pulses combined with an 8-step phase cycling aid in achieving broadband excitation with limited pulse width distortions.

On Fer and Floquet-Magnus expansions: Application in solid-state nuclear magnetic resonance and physics

One of the unique properties of the sp2-carbon allotropes, such as fullerenes, carbon nanotubes and graphenes, is that their electronic structures differ significantly among them according to characteristic electron confinement based on their dimensionality and geometric structures, which can be influenced not only by charge injection and chemical bonding but also structural modification. In this talk, I will discuss the electronic structures of various sp2-carbon allotropes on metal substrates investigated by scanning tunneling microscopy and spectroscopy. In particular, it is focused on the one dimensional (1D) electronic structure in a graphene nano wrinkle (GNW) of an epitaxially grown graphene (EG) sheet on Ni(111), the width of which was small enough (less than 5 nm) to cause 1D electron confinement. Use of spatially resolved, scanning tunneling spectroscopy revealed band-gap opening and a 1D van Hove singularity in the GNW, as well as the chemical potential distribution across the GNW. Our demonstration of 1D electron confinement in an EG is the novel possibility of controlling its electronic properties not by chemical modification but by mechanical structuring in a controlled manner. Graphene-based carbon materials such as fullerenes, carbon nanotubes, and graphenes have distinct and unique electronic properties that depend on their dimensionality and geometric structures. Graphene wrinkles with pseudo one-dimensional structures have been observed in a graphene sheet. However, their one-dimensional electronic properties have never been observed because of their large widths. Here we report the unique electronic structure of graphene nanowrinkles in a graphene sheet grown on Ni, the width of which was small enough to cause one-dimensional electron confinement. Use of spatially resolved, scanning tunnelling spectroscopy revealed bandgap opening and a one-dimensional van Hove singularity in the graphene nanowrinkles, as well as the chemical potential distribution across the graphene nanowrinkles. This observation allows us to realize a metallic-semiconducting-metallic junction in a single graphene sheet. Our demonstration of one-dimensional electron confinement in graphene provides the novel possibility of controlling its electronic properties not by chemical modification but by ‘mechanical structuring’. Graphene wrinkles, which are one-dimensional (1D) folded graphene structures, have generally been observed in graphene produced by chemical vapour deposition. These structures have been thought to be the result of the difference in the thermal expansion coefficient between graphene and its substrate. A graphene wrinkle is chemically bonded with surrounding planar epitaxial graphene. Therefore, its unique geometric structure is distinct from those of carbon nanotubes and graphene nanoribbons which are indisputably 1D structures. Hence, we define a graphene wrinkle as a ‘pseudo 1D structure’ to indicate that it has a 1D shape, but is still a part of a two-dimensional structure. In the following, we demonstrate the 1D electron confinement in graphene nanowrinkle (GNW) by scanning tunnelling microscopy/spectroscopy (STM/STS), whose width is <5 nm. Moreover, spatially resolved electronic structures have been investigated, and the manipulation of graphene geometry by STM tip has been demonstrated. Our results imply that a semiconducting property can be realized by the mechanical deformation of the graphene geometry not by chemical modification, which is analogous to the case of a strain-induced pseudo magnetic field that was discovered in deformed ‘graphene nanobubbles’. The lack of surface functionalization in our approach can prevent the mobility decline due to chemical defects. Moreover, the covalent bonding at the metallic pEG-semiconducting GNW junction can reduce the contact resistance. Our results demonstrate that the interfacial interaction between graphene and the metal substrate provides a novel way to realize a metallic-semiconducting-metallic junction within a single graphene sheet. Results: Structural characterization of GNWs Epitaxial graphene with GNWs was synthesized by dissociating acetylene on a clean Ni(111) surface. A rapid cooling process is necessary, which is the most critical step to synthesize GNWs. Most of the GNWs were observed in the region where the terrace width of the underlying Ni surface was as small as several tens of nanometres. These GNWs have been recoloured with orange, and a line profile along the white arrow, which shows that the GNWs on the terrace have larger widths and lower heights than the GNWs at the step edges. We should note that all GNWs were formed at the step edges (red triangles or propagated from kinks at the step edges of the Ni surface, the implication being that the geometrical structure of the underlying Ni must play a crucial role in the formation of GNWs To analyse the structure of the GNWs in detail, we obtained atomically resolved STM images from an isolated GNW on the terrace under different scanning conditions. The top and bottom regions of the GNW in were scanned at a sample bias (Vs) of 1 V and a feedback current (If) of 1 nA, whereas the centre region was scanned with a smaller tip–sample distance.The objective of the paper was to demonstrate feasibility of an ammonia sensor using polymer –inorganic nano-composite thin film upconversion light emitters made by the new double-beam pulsed laser deposition method. The existing pulsed laser deposition vacuum chamber was modified to accommodate two laser beams of different wavelengths for the in-situ ablation of two targets: a polymer host poly(methyl methacrylate) mixed with indicator dye Phenol Red and the brilliant rare earth doped upconversion phosphor NaYF4:Yb3+, Er3+. Nano-composite films were deposited on silicon substrates by the proposed method with near-infra-red laser radiation (1064-nm wavelength) ablating the polymer target dissolved in Gamma-butyrolactone together with the indicator dye, and frozen in circulating liquid nitrogen (matrix assisted pulsed laser evaporation – MAPLE), and visible radiation (532 nm) ablating the inorganic target. The deposited nano-composite films retained bright green upconversion fluorescence with a spectral peak at 540 nm attributed to the inorganic phosphor nano-particles pumped with the 980-nm infrared laser diode. The spectrum of the green emission matched the absorption band of the indicator dye exposed to ammonia. When the films were exposed to ammonia, they demonstrated an optical response in the form of the drop of the intensity of green radiation monitored with a silicon photodiode. The sensitivity of the opto-electronic sensor of ammonia based on the nano-composite films was measured to be close 0.4% ammonia in air, and the response time was 5 minutes.Superconductors possess unique properties such as zero electrical resistance and expulsion of magnetic fields below a critical temperature Tc. They can carry electric current without any energy loss and have many applications. However, understanding superconductivity is a great challenge. Especially, anomalously small isotope effect in some high and low Tc superconductors such as YBa2Cu3O7 (YBCO), Nb3Sn, Zr, created a great challenge for understanding. To solve the puzzle, a new methodology is implemented by integrating first-principles calculations of electronic structures of the materials into the theory of many-body physics for superconductivity. The aim is to seek a unified methodology to study the electronic and superconducting properties of the materials. It is demonstrated from first-principles that the extended saddle point singularities in the electronic structures of the materials such as YBCO, Nb3Sn, Zr, strongly correlate with the anomalous isotope effect in these superconductors. Some guidance for finding new high Tc superconductors will also be discussed.

Recent development of spin dynamics in solid-state nuclear magnetic resonance

M equations are the main foundation of the current communication technology; however, they are still incomplete with some ambiguities and unknown parameters. Magnetic current is apparently the main missing part of these equations [1]. In this talk, we resolve to revise these equations and the conventional definitions of the terms and parameters from the beginning merely based on logical theory to justify all measurements so far. These revisions will be initiated by modifying Bohr’s Model and physical differentiations of magnetic and electrical fluxes to justify all electromagnetic phenomena under a consistent umbrella. Consequently, we can theoretically present a rational illustration of magnetic current and amend the contradictions and inconsistencies in the current models and theory of electromagnetic waves. As given in current Maxwell’s equations given in (1)-(2), these equations are not balanced where the right sides of these equations consist of two Equ. (1) and three components Equ.(2).The weighted mean appears when a physical quantity is measured by different methods in different laboratories, producing different xi results. It is the case of determination of physical constants (as Nuclear Data analysis), International Comparisons of radioactive sources and still others. (The formula 1) with wi absolute weights and pirelative weights. A relation exists (2) with σithe individual standard deviations including possible systematic uncertainty as which do not affect the logical (1). Formula (2) is obtained with some complicated calculations in [1], [2], [3].T topic of spin dynamics in solid-state nuclear magnetic resonance opens a way to an infinite number of suggestions. In this abstract, we present the power and the salient features of the promising theoretical approach called Floquet–Magnus expansion that is helpful to describe the time evolution of the spin system at all times in nuclear magnetic resonance. Interesting applications of the Floquet–Magnus expansion approaches are illustrated by simple solid-state NMR experiments. However, it is very important to remember that the method of Floquet-Magnus expansion had recently found new major areas of applications such as topological materials. Researchers, dealing with those new applications, are not usually acquainted with the achievements of the magnetic resonance theory, where those methods were developed more than thirty years ago. They repeat the same mistakes that were made when the methods of spin dynamics and thermodynamics were developed in the past. This presentation is very useful not only for the NMR and physics communities but for the new communities in several younger fields. Solid-state NMR is definitely a timely topic or area of research, and not many papers on the theory of spin dynamics are available in the literature of NMR.E and geometrical structure of neutral and charged iron clusters Fen, Fen, and Fen (n = 2-20) will be discussed. Computational results will be compared to experimental data, in particular, to the recent data obtained from the magnetic moment measurements of Fen +. We consider iron cluster oxides, single Fe atom oxides FeOn for n up to 18, and FeXn superhalogens. We present the results of computational simulations of gas-phase interactions between small iron clusters and OH, N2, CO, NO, O2, and H2O. Competition between surface chemisorption and cage formation in Fe12O12 clusters will be discussed. The magnetic quenching found for Fe12O12 will be qualitatively explained using the natural bond orbital analysis for Fe2O2. Special attention will be paid to the structural patterns of carbon chemisorbed on the surface of a ground-state Fe13 cluster.