Thomas E Skinner

• PhD Physics
• Professor (Full) at Wright State University

Although our existing one-dimensional (1D) model provides a successful quantitative description of rupture events, a 1D description is somewhat limited. We therefore derive a two-dimensional (2D) model which allows us to investigate characteristics of earthquakes (EQs) and slow slip events (SSEs) that are only apparent in a second dimension. We fin...

We have developed a model that describes the major characteristics of a rupture, ranging from regular earthquakes (EQs) to slow slip events (SSEs), including episodic tremor and slip (ETS). Previous model predictions, while accurate, are based on a highly idealized initial stress distribution and a simple velocity-dependent expression for friction....

In vivo Nuclear Magnetic Resonance (NMR) spectroscopy has great potential to interpret the biochemical response of organisms to their environment, thus making it an essential tool in understanding toxic mechanisms. However, magnetic susceptibility distortions lead to 1D NMR spectra of living organisms with lines that are too broad to identify and q...

In this work, optimal control theory was used to design efficient excitation schemes in highly conductive materials, where both the radio frequency field strength and phase vary as a function of penetration depth. A pulse was designed to achieve phase alignment between signals at different depths within the conductor and thus to obtain higher signa...

The Bloch equation and its variants constitute the fundamental dynamical model for arbitrary two-level systems. Many important processes, including those in more complicated systems, can be modeled and understood through the two-level approximation. It is therefore of widespread relevance, especially as it relates to understanding dissipative proce...

The Bloch equation is the fundamental dynamical model applicable to arbitrary two-level systems. Analytical solutions to date are incomplete for a number of reasons that motivate further investigation. The solution obtained here for the propagator, which generates the time evolution of the system and embodies all the system dynamics, is compact and...

The dynamics of quantum N-level systems is equivalent to rotation of the state vector in a real, Euclidean vector space. The relevance of this result to general magnetic resonance systems is considered here, with a focus on heteronuclear decoupling. An exact general theory for spin- systems is presented. This article provides a vehicle for more com...

Transport in porous media is quite complex, and still yields occasional surprises. In geological porous media, the rate at which chemical reactions (e.g., weathering and dissolution) occur is found to diminish by orders of magnitude with increasing time or distance. The temporal rates of laboratory experiments and field observations differ, and ext...

Accurate prediction of the saturation dependence of different modes of transport in porous media, such as those due to conductivity, air permeability, and diffusion, is of broad interest in engineering and natural resources management. Most current predictions use a "bundle of capillary tubes" concept, which, despite its widespread use, is a severe...

Description of the transitional process from a static to a dynamic frictional regime is a fundamental problem of modern physics. Previously we developed a model based on the well-known Frenkel-Kontorova model to describe dry macroscopic friction. Here this model has been modified to include the effect of dissipation in derived relations between the...

The saturated hydraulic conductivity, K-s, is a fundamental characteristic of subsurface flow and the hydrologic cycle. However, direct measurement of K-s is time consuming. Recently, air permeability measurements at 50 and 100 cm of H2O tension, a relatively dry condition in coarse and medium-textured soils, have been used to estimate K-s. In this...

The porosity dependence of the formation factor of geologic media is examined from the perspective of universal scaling laws from percolation and effective medium theories. Over much of the range of observed porosity, the expected percolation scaling is observed, but the values of the numerical prefactor do not conform to the simple predictions fro...

Ultra-high-field NMR spectroscopy requires an increased bandwidth for heteronuclear decoupling, especially in biomolecular NMR applications. Composite pulse decoupling cannot provide sufficient bandwidth at practical power levels, and adiabatic pulse decoupling with sufficient bandwidth is compromised by sideband artifacts. A novel low-power, broad...

An exact general theory of heteronuclear decoupling is presented for spin-1/2 IS systems. RF irradiation applied to the I spins decouples the S spins by reversing the sign of antiphase magnetization. A one-to-one correspondence is demonstrated between the sign of $2S_yI_z$ and the sense of the S-spin coupling evolution, with magnetization $S_x$ ref...

Tortuosity is a property of porous media that is invoked and used in the literature on hydrology, soil science, physics, and engineering. It has been defined in a variety of ways, one of which is a purely geometrical concept. In this study, we focused on the geometrical tortuosity and developed a model based on percolation theory and the finite-siz...

We apply our theory of conservative solute transport, based on concepts from percolation theory, directly and without modification to reactive solute transport. This theory has previously been shown to predict the observed range of dispersivity values for conservative solute transport over ten orders of magnitude of length scale. We now show that t...

The quantum dynamics of arbitrary N-level systems, including dissipative systems, are modeled exactly here by the dynamics of classical coupled oscillators. A one-to-one correspondence is established between the quantum states and the positions of the oscillators. Quantum coherence, expectation values, and measurement probabilities for system obser...

Distance and spins: A new broadband, frequency-selective inversion pulse has been devised for pulsed electron-electron double resonance (PELDOR) spectroscopy, a unique method used to determine distance distributions between two or more paramagnetic centers 2-10 nm apart. The PELDOR modulation depth can be increased by substituting the rectangular p...

The dynamics of states representing arbitrary N-level quantum systems, including dissipative systems, can be modelled exactly by the dynamics of classical coupled oscillators. There is a direct one-to-one correspondence between the quantum states and the positions of the oscillators. Quantum coherence, expectation values, and measurement probabilit...

We present highly robust, optimal control-based shaped pulses designed to replace all 90° and 180° hard pulses in a given pulse sequence for improved performance. Special attention was devoted to ensuring that the pulses can be simply substituted in a one-to-one fashion for the original hard pulses without any additional modification of the existin...

In this study, we develop a saturation-dependent treatment of dispersion in porous media using concepts from critical path analysis, cluster statistics of percolation, and fractal scaling of percolation clusters. We calculate spatial solute distributions as a function of time and calculate arrival time distributions as a function of system size. Ou...

90° and 180° universal rotation (UR) pulses are two of the most important classes of pulses in modern NMR spectroscopy. This article presents a systematic study characterizing the achievable performance of these pulses as functions of bandwidth, pulse length, and tolerance to B(1)-field inhomogeneity/miscalibration. After an evaluation of different...

A 1 ns resolution pulse shaping unit has been developed for pulsed EPR spectroscopy to enable 14-bit amplitude and phase modulation. Shaped broadband excitation pulses designed using optimal control theory (OCT) have been tested with this device at X-band frequency (9 GHz). FT-EPR experiments on organic radicals in solution have been performed with...

Optimizing pulse performance often requires a compromise between maximizing signal amplitude and minimizing spectral phase errors. We consider methods for the de novo design of universal rotation pulses, applied specifically but not limited to refocusing pulses. Broadband inversion pulses that rotate all magnetization components 180° about a given...

Broadband inversion pulses that rotate all magnetization components 180 degrees about a given fixed axis are necessary for refocusing and mixing in high-resolution NMR spectroscopy. The relative merits of various methodologies for generating pulses suitable for broadband refocusing are considered. The de novo design of 180 degree universal rotation...

A recently introduced theory of solute transport in porous media is tested by comparison with experiment. The solute transport is predicted using an adaptation of the cluster statistics of percolation theory to critical path analysis together with knowledge of how the structure of such percolation clusters affects the time of transport across them....

We present robust radio frequency (rf) pulses that tolerate a factor of six inhomogeneity in the B₁ field, significantly enhancing the potential of toroid cavity resonators for NMR spectroscopic applications. Both point-to-point (PP) and unitary rotation (UR) pulses were optimized for excitation, inversion, and refocusing using the gradient ascent...

We present a fundamental theory of solute dispersion in porous using (i) critical path analysis and cluster statistics of percolation theory far from the percolation threshold and (ii) the tortuosity and structure of large clusters near the percolation threshold. We use the simplest possible model of porous media, with a single length scale of hete...

The distribution of solute arrival times, W(t;x), at position x in disordered porous media does not generally follow Gaussian statistics. Aprevious publication determined W(t;x) in the absence of diffusion from a synthesis of critical path, percolation scaling, and cluster statistics of percolation. In that publication, W(t;x) as obtained from theo...

Technetium ((99)Tc) spreads predominantly laterally through US Department of Energy Hanford site sediments. Lateral transport implies that at higher tensions, h, in the unsaturated zone, the effective hydraulic conductivity, K, may be strongly anisotropic. A modeling procedure has been developed to predict characteristics of the Tc plumes. The proc...

Representing NMR pulse shapes by analytic functions is widely employed in procedures for optimizing performance. Insights concerning pulse dynamics can be applied to the choice of appropriate functions that target specific performance criteria, focusing the solution search and reducing the space of possible pulse shapes that must be considered to a...

Previously we developed accurate predictions of full solute time arrival distributions, W(t), by advective transport through disordered porous media. This treatment of W(t) combined critical path analysis, cluster statistics of percolation theory and percolation scaling of tortuosity. Effects of diffusion on the dispersion coefficient, D, are inclu...

This paper considers the use of optimal control theory in designing radio frequency excitation pulses for magnetic spin systems satisfying Bloch dynamics. Such pulses are required in applications of nuclear magnetic resonance to initially transfer sample magnetization vectors to the transverse plane. Once transferred, signals released by nuclei as...

Previously we reported how to obtain a distribution of solute arrival times, W(t) due to advection. This calculation involved using cluster statistics of percolation theory in the framework of critical path analysis to find the likelihood that a given system size is characterized by a particular controlling conductance value, g, i.e., W(g,x), or W(...

Water retention curves, particularly those obtained from ceramic plate experiments, tend overestimate the equilibrium water content at high tensions and thus imply unrealistic amounts of water present in films etc. We have previously reported a method to predict non-equilibrium water-retention data from known fractal equilibrium water-retention cur...

In [K. Kobzar, T.E. Skinner, N. Khaneja, S.J. Glaser, B. Luy, Exploring the limits of broadband excitation and inversion, J. Magn. Reson. 170 (2004) 236–243], optimal control theory was employed in a systematic study to establish physical limits for the minimum rf-amplitudes required in broadband excitation and inversion pulses. In a number of case...

The purpose of this work is to predict the transport of non-sorbing solutes through water flow in the subsurface. We derive what we consider to be the first reliable calculations of the entire distribution of arrival times, W(t), for non-sorbing solutes in advective flow in strongly disordered porous media. Solutes treated can be contaminant plumes...

Using optimal control methods, robust broadband excitation pulses can be designed with a defined linear phase dispersion. Applications include increased bandwidth for a given pulse length compared to equivalent pulses requiring no phase correction, selective pulses, and pulses that mitigate the effects of relaxation. This also makes it possible to...

The ability to calculate soil hydraulic properties from soil physical data has been a dominant objective of soil physics research since the 1950s. The purpose of this study was to develop an approach based on modern physics to deal with an arbitrary porous medium. Some important advances resulted from applying critical path analysis from percolatio...

The procedure described requires some knowledge of a critical moisture content for percolation as described by the Moldrup et al. (2001) experimental results for a moisture content at which solute diffusion vanishes. This can be obtained experimentally by using N2 BET measurements or theoretically from the particle size distribution. Alternatively...

We argue that in porous media with sufficiently wide pore-size distributions to require use of critical path analysis in upscaling K, the tendency thus for flow to be dominated by the contributions near the percolation threshold makes the tortuosity of random percolation relevant for dispersion. We calculate the distribution of controlling conducta...

An optimal control algorithm for mitigating the effects of T(1) and T(2) relaxation during the application of long pulses is derived. The methodology is applied to obtain broadband excitation that is not only tolerant to RF inhomogeneity typical of high resolution probes, but is relatively insensitive to relaxation effects for T(1) and T(2) equal t...

In previous work anisotropy in a fracture network was shown to provide a possible explanation for the observed scale-effect in the hydraulic conductivity of a carbonate aquifer. Use was made of a coordinate transformation and reference made to the transverse and longitudinal electrical conductivities of thin (disordered) solid films. An analogous a...

The cluster statistics of percolation theory are used to find the distributions of hydraulic conductivity, K, of anisotropic (truncated) random fractal media. Rescaling of variables to transform anisotropic to isotropic media also produces deformations of, for example experimental volumes, and the resulting non-equidimensional shapes may generate i...

An optimal control algorithm for generating purely phase-modulated pulses is derived. The methodology is applied to obtain broadband excitation with unprecedented tolerance to RF inhomogeneity. Design criteria were transformation of Iz-->Ix over resonance offsets of +/-25 kHz for constant RF amplitude anywhere in the range 10-20 kHz, with a pulse l...

Previously the correlation length from continuum percolation theory was used to diagnose a cross-over in conduction from 1D to 3D with increasing scale in anisotropic fracture networks. That calculation yielded an expected hydraulic conductivity value, K, which increased with scale in accord with field data from a carbonate aquifer in Wisconsin. Th...

For a desired range of offsets, universal rotations of arbitrary flip angle can be constructed based on point-to-point rotations of I(y) with half the flip angle. This approach allows, for example, creation of broadband or bandselective refocusing pulses from broadband or bandselective excitation pulses. Furthermore, universal rotations about any a...

The effects of the percolation phase transition on equilibration of porous media during drainage are shown to set on at moisture contents, some what larger than the critical moisture content for percolation, t. An algorithm is developed, which yields the typical upward curvature of log[h(θ)] curves at low moisture contents, where h is the hydraulic...

The de facto standard cost function has been used heretofore to characterize the performance of pulses designed using optimal control theory. The freedom to choose new, creative quality factors designed for specific purposes is demonstrated. While the methodology has more general applicability, its utility is illustrated by comparison to a consiste...

The design of broadband excitation and inversion pulses with compensation of B(1)-field inhomogeneity is a long standing goal in high resolution NMR spectroscopy. Most optimization procedures used so far have been restricted to particular pulse families to keep the scale of the problem within manageable limits. This restriction is unnecessary using...

Combining optimal control theory with a new RF limiting step produces pulses with significantly reduced duration and improved performance for a given maximum RF amplitude compared to previous broadband excitation by optimized pulses (BEBOP). The resulting pulses tolerate variations in RF homogeneity relevant for standard high-resolution NMR probes....

Optimal control theory is considered as a methodology for pulse sequence design in NMR. It provides the flexibility for systematically imposing desirable constraints on spin system evolution and therefore has a wealth of applications. We have chosen an elementary example to illustrate the capabilities of the optimal control formalism: broadband, co...

The density matrix ρ for an n-level system is decomposed into the minimum number of pure states necessary to calculate physical observables. The corresponding physical system is first represented by a set B of n pure states |βi〉, together with their statistical weights. The time evolution of the system is therefore calculated as B(t)=UB(t0), with t...

We previously obtained exact solutions for the time dependence of the density operator in weakly coupled spin-½ ImSn systems during arbitrary RF irradiation of the I spins. The solutions for the density operator were written as explicit linear combinations of its product operator components (i.e., the operator basis set consisting of direct product...

A comprehensive survey is provided of the analytical expressions for the orthogonal product operator states arising from any initial state of an IS J-coupled spin system during arbitrary RF irradiation of one spin. These equations exactly characterize the effect of J coupling during the application of the RF field. The survey differentiates two kin...

In this article, we consider the evolution of weakly coupled I(m)S(n) systems of spin-12 nuclei during arbitrary RF irradiation of the I spins. Exact solutions are presented for the time dependence of the density operator in terms of its constituent product operator components for a complete set of initial states derived from polarization of either...

Exact product operator solutions have been obtained for the evolution of weakly coupled spin-(1/2) I(m)S(n) systems during arbitrary RF irradiation of one spin. These solutions, which completely characterize the nature of J-coupling modulation during RF pulses, show that significant exchange occurs between single-spin magnetization and two-spin pro...

Exact solutions for the effect of time-independent RF pulses on any initial configuration of an IS J-coupled system demonstrate that on-resonance CW decoupling yields signals whose frequency depends on RF field strength and homogeneity. These signals are enhanced starting with "undetectable" antiphase and multiple quantum coherences, which can also...

A vector model of adiabatic decoupling is enunciated for an IS-coupled system of two spin-(1/2) heteronuclei in the high-power limit of ideal adiabatic pulses. The observed S-spin magnetization evolves according to a time-dependent coupling that scales as the z component of an I-spin vector which evolves due to the applied decoupling irradiation. S...

To provide the most efficient conditions for spin decoupling with least RF power, master calibration curves are provided for the maximum centerband amplitude, and the minimum amplitude for the largest cycling sideband, resulting from STUD+ adiabatic decoupling applied during a single free induction decay. The principal curve is defined as a functio...

RF pulse sequences applied to IS spin systems may produce substantial transverse antiphase S magnetization coupled to antiphase I magnetization, just prior to detection of the S signal, for samples containing a range of J coupling constants, or when pulse sequence delays are misset from ideal values. This magnetization is generally considered to be...

A new algorithm is presented that provides separate water, fat, and B0 images utilizing the in-phase and opposed-phase acquisitions of the two-point Dixon (2PD) method. The accuracy of the extended method (E2PD) compares favorably with the three-point Dixon (3PD) method, and the acquisition requires 2/3 the 3PD scan time. Slightly increased mismapp...

Experimental calibration of the amplitude of sidebands resulting from STUD decoupling over a range of decoupled bandwidths from 2 to 120 kHz shows that sideband amplitude depends on the length of each single sech/tanh pulse,Tp, and the bandwidth divided by the square of the maximum RF amplitude during the pulse, bwdth/(RFmax)2. Plots of sideband am...

Recent post-mortem and magnetic resonance imaging (MRI) studies strongly suggest a decrease in the volume of the hippocampus and other limbic temporal structures in schizophrenia. Therefore, we hypothesised that N-acetyl aspartate (NAA) which is found mainly in neurons and which can be measured by proton magnetic resonance spectroscopy (1H MRS) wou...

A new 3D acquisition regimen that enables the collection of conventional, water-suppressed, and fat-suppressed images with no increase in scan times compared with currently implemented 3D sequences is presented. The method is based on conventional 3D steady state with interleaved selective excitation of the fat resonance resulting in acquisition of...

In this work, we present the post-steady state analysis of the TCA cycle and a closed form solution to the rate of label washout from the C4 carbon of glutamic acid through the transaminases and the malate-aspartate shuttle and then through alpha-ketoglutarate dehydrogenase. We demonstrate using a model of this problem that the rate of label washou...

A new pair of amplitude and frequency modulation functions for use in adiabatic excitation is proposed. The functions arise naturally out of a general treatment of optimized adiabatic pulses undertaken previously. The performance of this new pulse scheme, defined with respect to power requirements and insensitivity to large variations in RF field a...

Interest in adiabatic pulses has been stimulated by their ability to perform a variety of desired spin transformations in the presence of B1 inhomogeneities. However, pulse performance, as defined by the relative insensitivity of the pulse at a given power level to B1 inhomogeneity, depends greatly on the amplitude- and frequency-modulation functio...

Results of recent International Ultraviolet Explorer observations of Venus made on January 20, 1987 and April 2 and 3, 1988 are presented along with a reanalysis of the 1979 observations (Conway et al., 1979). The observations indicate that the amount of sulfur dioxide at the cloud tops of Venus declined by a factor of 8 + or - 4 from 380 + or - 70...

Observations of the UV spectra of the Pluto-Charon system were obtained between 1987 and 1988 using the large aperture of the IUE long-wavelength prime spectrograph. At the resolution and SNR of the data, no gas-phase spectral identifications were made. The present data indicate a geometric albedo of 0.35 + or - 0.05. Curve fitting the geometric al...

The results of the first observations of Triton's spectrum below 3300 A are reported. Triton's 2700 A geometric albedo is found to be 0.28 + or - 0.04. The albedo increases monotonically from 2600 to 3200 A, with a slope of 0.13 + or - 0.03 per 1000 A. This positive slope is qualitatively similar to, but shallower than, Triton's visible albedo slop...

Aurorae on Jupiter are believed to be internally driven, produced by a magnetospheric coupling between the upper atmosphere and the lo torus, while the Saturnian aurorae are believed to be driven by the solar wind. These generally held views have been inferred by comparing the intensity of the auroral emissions to estimates of the power that might...

The results of long-term monitoring of the Jovian Lyman-alpha brightness with the IUE are presented. The measurements span the current solar cycle from maximum in late 1979 to the present period of minimum solar activity. The long-term variation seen in the brightness during the declining phase of the cycle matches the decrease in the solar Lyman-a...

Ground-based observations of Pluto have established the presence of methane on the planet's surface, and Pluto is also thought to have a tenuous methane atmosphere. In addition, an argument for the presence of N2 on Pluto can be developed based on cosmological abundance arguments and by analogy with the Saturnian satellite Titan, which has a thick...