Roger M. Hawk

University of Arkansas for Medical Sciences

Author Statistics

Papers

Citation

H-Index

i-10 index

Research Trends

Author Order

Document Type

Co-Authors

Richard A. Komoroski

University of Cincinnati

Rao P. Gullapalli

University of Maryland, Baltimore

Kamesh Gadepally

Texas Instruments (United States)

Diana M. Lindquist

Cincinnati Children's Hospital Medical Center

Robert R. Sharp

Manhattan College

Craig N. Karson

University of Southern California

Markus Dachtler

Power Plus Communications (Germany)

Klaus Albert

Technical University of Munich

H. D. Scott

University of Mount Olive

S. Ramaprasad

Indian Institute of Science Bangalore

Cooperative Institutions

University of Arkansas at Little Rock

University of Arkansas for Medical Sciences

University of Arkansas at Fayetteville

Central Arkansas Veterans Healthcare System

University of Michigan–Ann Arbor

Massachusetts Institute of Technology

John L. McClellan Memorial Veterans Hospital

University of Tübingen

Lawrence Livermore National Laboratory

University of California, Davis

Author Statistics

Papers

Citation

H-Index

i-10 index

Research Field

A ⁷Li NMR study of visibility, spin relaxation, and transport in normal human erythrocytes

Magnetic Resonance in Medicine (1991)

Rao P. Gullapalli Roger M. Hawk Richard A. Komoroski

The behavior of the lithium (Li) ion in normal human erythrocytes has been studied by 7Li NMR. The uptake of Li into the cells was followed as a function of solution conditions, temperature, hematocrit, and blood age using dysprosium tripolyphosphate shift reagent. Under our conditions the uptake of Li increases with increasing hematocrit and blood age. For packed cells the extracellular 7Li spin-lattice relaxation time was only slightly longer than the intracellular relaxation time. Thus, T1 may not be useful for separate observation of intra- and extracellular Li in vivo. The intra- and extracellular T2s were substantially shorter than the corresponding T1s. Also, the intracellular T2 was considerably shorter than that for the extracellular compartment, suggesting that T2 may provide a noninvasive handle for observation of intracellular Li. Nuclear Overhauser enhancements could be observed for both extra- and intracellular 7Li, confirming that dipolar coupling to 1H is a contributing relaxation mechanism. The 7Li NMR visibility was essentially 100% at high Li concentrations, decreasing to about 84% at 1 mM Li. Based on time course studies of the invisibility, and a comparison of NMR and inductively coupled plasma results, it appears that the invisibility of the intra- and extracellular compartments for packed cells is the same. Although a 23Na double-quantum signal could be observed for red blood cells, no double-quantum signal was observed for 7Li.

10.1002/mrm.1910200207

Cite

Citations (25)

Double Tuned Cosine Coil for NMR Imaging/Microscopy

Journal of the Arkansas Academy of Science (1991)

Roger M. Hawk Rao P. Gullapalli Dikoma P. Shungu

Source

Cite

Citations (0)

Porous Alumina Prepared from Diethylaluminum Amide, Acetone, and Water

Chemistry of Materials (2002)

Lize Wilcox G. Burnside Beatrice Kiranga Ritu Shekhawat Malay K. Mazumder

A previously described synthetic method was modified to improve the porosity of the alumina product. The compound (Et2AlNH2)3 was prepared from ammonia and triethylaluminum (Et3Al) in toluene solvent. Addition of acetone to form a solution of ethylaluminoxane (EtAlO) and acetonine (2,2,4,4,6-pentamethyl-2,3,4,5-tetrahydropyrimidine) was followed by addition of two equivalents of water to give an alumina precursor. Alumina precursors also were prepared by the direct hydrolysis of (Et2AlNH2)3. Powder X-ray diffraction, 27Al MAS NMR, and N2 adsorption/desorption isotherms were used to analyze the aluminas after calcination of the precipitates. The aluminas exhibited high pore volume and surface area, and they were amorphous after calcination at 500 °C. One alumina showed a significant fraction of pentacoordinate aluminum after heating to 300 °C in air or 500 °C in steam atmosphere. The products crystallized as α-Al2O3 at the low temperature of 1000 °C, which reduces their applicability for catalysts. Synthesis variables and their effects on alumina properties are discussed.

Amide

Specific surface area

10.1021/cm020836w

Cite

Citations (16)

Field-dependent relaxation and absolute nuclear shielding of 207Pb in liquid PbCl4

The Journal of Chemical Physics (1974)

Roger M. Hawk Robert R. Sharp

Relaxation times T1 and T2 of 207Pb in liquid PbCl4 have been studied for the purpose of establishing an absolute nuclear shielding scale for lead. T1 has been decomposed into scalar and spin-rotation contributions using variable temperature measurements at the two field strengths 6.59 and 16.90 kG. T2 is much shorter than T1 and is strongly dominated by scalar coupling to chlorine. Knowledge of the scalar contributions to T1 and T2 determines the halogen relaxation times (τ35 = 7.15 μsec at 25°C), the lead-chlorine coupling constant [(J(207Pb−35Cl) = 705 Hz)], and the reorientational correlation time (τθ = 1.72 × 10−11 sec at 25°C). A correlation time τJ for the angular momentum vector has been computed using J diffusion theory, but the value obtained appears to be too short (0.8–2.9 × 10−14 sec) to be meaningful in terms of classical diffusion of rigid molecules. Nevertheless, the known range of 207Pb chemical shifts places an absolute upper limit on τJ of 6 × 10−14 sec at 263°K. The physical significance of such short correlation times is discussed, and it is concluded that τJ probably describes collision-induced distortions in the molecular structure. Experimental values of the spin-rotation contribution to (T1)−1 are used in conjunction with estimated values of τJ to compute limiting values for the spin-rotation constant that place limits on the paramagnetic part of the magnetic shielding constant. A shielding scale previously deduced from optical pumping data is discussed, and a source of possibly substantial error in this scale is pointed out.

Coupling constant

10.1063/1.1681108

Cite

Citations (35)

INTEGRATED CIRCUITS INTERCONNECT METALLIZATION FOR THE SUBMICRON AGE

Journal of the Arkansas Academy of Science (1989)

Kamesh Gadepally Roger M. Hawk

The interconnect metallizationbeing used by the semiconductor industry has been aluminumor aluminum silicon. Aluminumsilicon is being replaced by aluminum copper and aluminum copper silicon, due to its superior resistance to electromigration and hillock growth. This paper discusses the implementation of aluminum copper/silicon alloys in semiconductor processing, along with a review of the problems and advantages of the same.

Electromigration

Hillock

Semiconductor Industry

Copper interconnect

Source

Cite

Citations (6)

Field dependence of nuclear magnetic relaxation of 207Pb in aqueous Pb(ClO4)2

The Journal of Chemical Physics (1974)

Roger M. Hawk Robert R. Sharp

Nuclear magnetic relaxation times of the 207Pb resonance have been measured as a function of temperature and concentration at field strengths of 16.9, 11.7, and 6.56 kG in aqueous Pb(ClO4)2. Longitudinal relaxation is composed of spin-rotation, chemical shift anisotropy, and dipolar contributions in a 3.5M solution, while spin-rotation strongly dominates the relaxation at all temperatures between the melting and boiling points in a 1.15M solution. T2 accurately equals T1 at 1.15M, as is expected for a dominant spin-rotation interaction, but is 20–30% shorter in the 3.5M solution, possibly due to a minor relaxation component arising from scalar coupling to naturally abundant H217O. Chemical shifts of 207Pb have also been measured in aqueous Pb(ClO4)2 and Pb(NO3)2. The chemical shift and relaxation data show that ClO4− penetrates the Pb+2 hydration sphere at concentrations above about 2M, but no effects of such penetration are seen at lower concentration.

Spin–spin relaxation

10.1063/1.1681225

Cite

Citations (28)

A Versatile Potentiostat With Optional Computer Control

Instrumentation Science & Technology (1989)

Gary L. Fuller William A. Russell Roger M. Hawk James D. Wilson P. D. Bratton

ABSTRACT A versatile potentiostat which can supply a maximum of 125 ma is described. The potentiostat uses readily available electronic components and an interface is detailed which allows the potentiostat optional computer control.

Potentiostat

Interface (matter)

10.1080/10739148908543706

Cite

Citations (1)

Method to Correct the Voxel Size in PRESS Localized NMR Stereoscopy

Journal of the Arkansas Academy of Science (1997)

Diana M. Lindquist Roger M. Hawk Richard A. Komoroski

Twotechniques commonly used on human magnetic resonance spectroscopy systems to obtain spectra from localized volumes in the brain are point resolved spectroscopy (PRESS) and stimulated echo acquisition mode (STEAM)spectroscopy. PRESS gives a signal twice as large as that obtained withSTEAM, but suffersfromlonger minimum echo times. WhileSTEAM must be used to detect species withshortspin-spin relaxation times, PRESS can be used forspecies with longer relaxation times to give a spectrum with a better signal to noise ratio. Only STEAMwas provided for the GE Omega 4.7 T smallanimalimager used in this laboratory. Therefore, a PRESS pulse program was written for this instrument. With the standard sequence, the sampled voxel is smaller than the prescribedvoxel. A larger voxel can be prescribed to increase the sampled volume. A different approach, involving the modification of the gradient strength, has been used in this laboratory. The resulting pulse sequence, with representative profiles, is discussed.

Pulse sequence

SIGNAL (programming language)

Sequence (biology)

Source

Cite

Citations (0)

A Study Of Lead-207 Relaxation Using Pulsed Nuclear Magnetic Resonance (nmr).

Deep Blue (University of Michigan) (1973)

Roger M. Hawk

Lead (geology)

10.7302/20913

Cite

Citations (0)

Increasing the selectivity of commercially available tin oxide based gas sensors for monitoring combustible gases in process environments

Journal of Vacuum Science & Technology A Vacuum Surfaces and Films (1995)

Roger M. Hawk Arvind Narayanaswamy

Tin oxide (SnO2) is one of the most popular metal oxide semiconductors used as a gas sensor. Commercial sensors that use tin oxide are inexpensive and readily available. Computer controlled thermal cycling techniques were used with only one sensor to collect a series of conductance surfaces for various compounds versus concentration. These patterns were treated as inputs to a neural network program that was trained to associate particular patterns to a specific compound. When the neural network was successfully trained to recognize pure patterns, the network was presented with a conductance pattern from a combination of compounds to test if the neural network could identify the constituents. This analysis method allowed the qualitative recognition of the different gases in a mixture or in one single gas. The results using a one sensor approach for the neural network identification of methanol, isopropanol, and hexane are presented and discussed. This, to our knowledge, is the first attempt to use data from a single sensor and process it via a neural network program to identify gases found in process environments.

Tin oxide

Sensor array

10.1116/1.579664

Cite

Citations (5)