Jolinda Smith - Academia.edu (original) (raw)

Papers by Jolinda Smith

Developmental Cognitive Neuroscience

APS, Nov 1, 1999

There has been a great deal of interest recently in cryogenic turbulence. In order to probe tempe... more There has been a great deal of interest recently in cryogenic turbulence. In order to probe temperature and velocity fluctuations in these systems, small sensitive devices must be built. We report our efforts to build a 10 micron diameter hot-wire for cryogenic use. Because of the low temperature behavior of materials, the properties of cryogenic hot-wires are different than ordinary

Implantable RF-coils have enabled sub-mm resolution magnetic resonance images (MRI) of deep struc... more Implantable RF-coils have enabled sub-mm resolution magnetic resonance images (MRI) of deep structures. Scaling down the size of RF coils has similarly provided a gain in signal-to-noise ratio in nuclear-magnetic-resonance spectroscopy. By combining both approaches we designed, fabricated, and imaged with an implantable microcoil catheter. While typical implantable catheters use a transverse magneti-zation, the axial magnetization of the microcoil provides improved sensitivity and allows visualization of the tissue beyond the distal end of the catheter. The microcoil catheter was designed with a diameter of 1 mm for future integration with intracranial devices, and for intraductal use in breast oncology. We modified the NMR-microcoil design to allow implantation of the RF coil, by winding the microcoil on medical-grade silicone tubing and incorporating leads on the catheter to connect circuit components. In order to achieve proper turn spacing, we coated copper wire with 25 µm of biocompatible polymer (Parylene C). Tuning and matching circuitry insured that the impedance of the RF coil was approximately 50 Ω at the operating frequency for 3-T proton MR applications. A duplexer was used to enable use of the microcoil catheter as a transceiver. Experimental verification of the coil design was achieved through ex vivo imaging of neural tissue. As expected, the microcoil catheter provided microscale images with 20-µm in-plane-resolution and 170-µm-thick slices. While 3-T MRI typically provides 1 to 30 voxels per-cubic-millimeter, in this paper we report that the MRI microcoil can provide hundreds, and even thousands of voxels in the same volume.

Background. In healthy adults, hand movements are controlled largely by the contralateral primary... more Background. In healthy adults, hand movements are controlled largely by the contralateral primary motor cortex. Following amputation, however, movements of the intact hand are accompanied by increased activity in the sensorimotor cortices of both cerebral hemispheres. Objective. The authors tested whether use of the intact hand reactivates the cortical territory formerly devoted to the now missing hand and whether these effects can be augmented by motor imagery (MI) and/ or exposure to illusory visual “feedback” (VF) of the absent hand created with a mirror. Methods. Functional magnetic resonance imaging (fMRI) was used to delineate the boundaries of normative sensorimotor hand representations in healthy controls. Brain activity from 11 unilateral hand amputees was recorded while they performed aurally paced thumb–finger sequencing movements with their intact hands under 4 conditions: (1) motor execution of the intact hand alone (ME), (2) ME with corresponding MI of the amputated ha...

Hot Carriers in Semiconductors, 1996

The near equilibrium conductance property of quantum point contacts has been an intense field of ... more The near equilibrium conductance property of quantum point contacts has been an intense field of research over the past 7 years following the demonstration of conductance quantization in such structures.1 However, the nonequilibrium transport properties of such systems are important for practical device applications involving nanoscale structures. Non-linear transport measurements in quantum point contacts have been reported in which oscillatory conductance with source-drain bias is observed associated with transport through successive one-dimensional subbands.2 Such transport is ‘ideal’ in the sense that it may described in terms of the two-terminal Landauer-Buttiker model when extended to non-zero V sd .

Medicine & Science in Sports & Exercise

Journal of neurophysiology, 2018

Animal models of mild traumatic brain injury (mTBI) suggest that metabolic changes in the brain o... more Animal models of mild traumatic brain injury (mTBI) suggest that metabolic changes in the brain occur immediately after a mechanical injury to the head. Proton magnetic resonance spectroscopy (H-MRS) can be used to determine relative concentrations of metabolites in vivo in the human brain. The purpose of this study was to determine concentrations of glutamate and GABA in the brain acutely after mTBI and throughout 2 mo of recovery. Concentrations of glutamate and GABA were obtained using H-MRS in nine individuals who had suffered an mTBI and nine control individuals in two brain regions of interest: the primary motor cortex (M1), and the dorsolateral prefrontal cortex (DLPFC), and at three different time points postinjury: 72 h, 2 wk, and 2 mo postinjury. There were no differences between groups in concentrations of glutamate or GABA, or the ratio of glutamate to GABA, in M1. In the DLPFC, glutamate concentration was lower in the mTBI group compared with controls at 72 h postinjury...

Neuroscience Letters, 2017

The consistency and reliability of proton magnetic resonance spectroscopy (H-MRS) assessments of ... more The consistency and reliability of proton magnetic resonance spectroscopy (H-MRS) assessments of neurotransmitter concentration has not been widely examined over multiple days. The purpose of this study was to determine the reliability of glutamate and GABA measures using a single-voxel H-MRS protocol in healthy men and women. Glutamate and GABA quantitations were obtained from the primary motor cortex (M1) and the dorsolateral prefrontal cortex (DLPFC) in 13 healthy individuals across 3 data collection sessions, including a baseline (Visit 1), 2-week (Visit 2), and 2-month time point (Visit 3). Glutamate concentrations were similar across visits in M1 (p=0.72) and the DLPFC (p=0.52). Reliability across days was excellent in M1 (R=0.93), and in the DLPFC (R=0.99). GABA concentrations were similar across visits in M1 (p=0.44) and in the DLPFC (p=0.59). Reliability of GABA concentration across days was excellent in M1 (R=0.93), and in the DLPFC (R=0.97). H-MRS is a reliable method for quantifying glutamate and GABA concentration in M1 and the DLPFC in humans.

We have developed very small temperature sensitive devices for use as thermometers or hot-wires i... more We have developed very small temperature sensitive devices for use as thermometers or hot-wires in cryogenic turbulent flows. A temperature sensitive Au-Ge layer is evaporated onto small diameter ( ~ 10 microns) glass fibers. Unlike previous reports [Chanal et al, Rev.Sci.Instr. 68, 2442 (1997)], we evaporate alternating thin layers of Ge and Au and anneal the film to produce the

Journal of Neuroscience Methods, 2016

 DICOM to NIfTI conversion tools for different manufacturers and image modalities are introduced... more  DICOM to NIfTI conversion tools for different manufacturers and image modalities are introduced.  The overview of the conversion basics useful for users and developers is covered.  The methods to detect and correct problems of the conversion are presented, including those for slice order, phase encoding direction, diffusion gradient direction etc. Comparison with Existing Methods Conversion tools are often designed for a specific manufacturer or modality. The tools and insight we present here are aimed at different manufacturers or modalities. Conclusions The imaging conversion is complicated by the variation of images. An understanding of the conversion basics can be helpful for identifying the source of the error. Here we provide users with simple methods for detecting and correcting problems. This also serves as an overview for developers who wish to either develop their own tools or adapt the open source tools created by the authors.

We have investigated non equilibrium transport through quantum point contacts. At low source- dra... more We have investigated non equilibrium transport through quantum point contacts. At low source- drain bias the devices display well defined quantized conductance plateaus. At higher biases (> 6 mV) regions of instability in the differential conductance are observed. These regions are associated with the onset of conduction when the chemical potential on one side of the contact is lifted above the bottom of the next one-dimensional subband. Time dependent measurements of these regions reveal random telegraph switching (RTS) in the conductance.^1 The RTS has been studied as a function of source-drain bias, gate bias, and temperature. We believe the conductance switching is due to random fluctuations in the height of the barrier forming the point contact. We will discuss possible mechanisms for the barrier height fluctuations. ^1J.C. Smith, C. Berven, M.N. Wybourne and S.M. Goodnick. ``Conductance Instabilities in Quantum Point Contact'' In press, Surface Science. This work wa...

ABSTRACT We have considered the non-linear transport through a saddle point potential with random... more ABSTRACT We have considered the non-linear transport through a saddle point potential with random fluctuations in barrier height. We have assumed that the applied bias drops linearly across the barrier. The transmission coefficient is calculated and the conductance is obtained using the Landauer-Büttiker formalism. For a given bias, the time averaged current is the weighted average of the currents corresponding to different barrier heights. Under high bias, the chemical potential difference across the saddle point allows conduction through one or more sub-bands. At a given bias, the number of sub-bands contributing to the conductance depends on the barrier height. Consequently, barrier height fluctuations lead to conductance switching. We will present possible mechanisms for the barrier height fluctuations. This work was supported in part by the Office of Naval Research N00014-93-1-0618

Physical Review B, 1991

ABSTRACT The role of microstructure on flux pinning in c-axis-oriented epitaxial YBa2Cu3Ox films ... more ABSTRACT The role of microstructure on flux pinning in c-axis-oriented epitaxial YBa2Cu3Ox films grown on LaAlO3 and SrTiO3 has been studied. For a magnetic field parallel to the Cu-O planes, the resistivity and critical current density Jc have been measured as a function of the angle θ between the applied field and the direction of the transport current. In addition to a Lorentz-force-independent resistivity, the Lorentz-force-dependent component showed several broad deviations from sin2θ when a field was aligned parallel to certain microstructural features which vary with the film thickness and substrate material. These features were identified by transmission-electron-microscopy analysis. For films of 5000 Å thickness on LaAlO3, resistivity dips were observed for a field applied parallel to the substrate twin boundaries or along misoriented a-axis grains. In thinner films of 900 Å thickness also on LaA1O3 in which a-axis grains were negligible, we observed dips corresponding to the orientation of substrate twin boundaries only. For thin films on SrTiO3 in which substrate twins are absent, resistivity dips corresponding to the direction of twin boundaries in the film and, perhaps, interfacial dislocations were observed. Overall, such dips decreased with increasing transport current density and became negligible in Jc measurements.

We have developed small (50 =B5m) bolometers for use at the Cryogenic Helium Turbulence Laborator... more We have developed small (50 =B5m) bolometers for use at the Cryogenic Helium Turbulence Laboratory at the University of Oregon. The devices are composed of AuGe sensing elements on 50 =B5m diameter optic fibers. Micron-size bolometers have recently been reported; however, in these devices the sensing elements were defined using a crude wire-masking technique.(O. Chanal, B. Baguenard, O. B=E9thoux, and

Flow at Ultra-High Reynolds and Rayleigh Numbers, 1998