Henry Kollock Burroughs

Henry Kollock Burroughs was born into a prominent Savannah family at the beginning of the nine­teenth century. He married, had a large family, and led an active and distinguished life in his home town as a physician. In 1845 he was elected mayor, an office to which he was re-elected two more times falling victim to consumption, he died still a relatively young man and in the prime of his life, at age forty-two.https://digitalcommons.georgiasouthern.edu/sav-bios-lane/1029/thumbnail.jp

Analysis of conjugated polymer nanotubules formed by template wetting nanofabrication

Semiconducting and optoelectric conjugated polymers have potential in micro and nano-electronic applications. Their widely tunable physical conformations and orientations make these polymers ideal material for engineering small scale devices. The polymers have been incorporated into several electronic devices including light-emitting diodes, solar cells, and field-effect transistors. Widespread adoption of these materials will not be a reality until the issues of poor device performance, short lifespans, and device degradation are resolved. Nanostructures have been demonstrated to have improvements in molecular ordering and electronic transport. In the work presented here, tubular nanostructures of conjugated polymers fabricated by the template wetting nanofabrication process are analyzed for their structural and electronic properties. Analysis focused on the optical absorbance of these materials and the effects of confinement, filtration, and solvent choice have on disordered and ordered polymers. Other analyses include the effects of polymer blending, orientation, and solvent evaporation determined from vibrational spectroscopy, thermogravimetric analysis, and mobility characteristics. Improvements in optical bandgap of MEH-PPV and P3HT ranging from ∼0.12 eV to 0.05 eV, respectively, were found for nanotubes cast chloroform. The improvements in bandgap from all solvents were found to be, on average, 0.08 eV for MEH-PPV and 0.05 eV for P3HT. Enhancement due to nanostructuring of P3HT were found to be independent of pore size but dependent on molecule size as low molecular weight fractions obtained from DC filtration were found to have spectrum similar to drop-cast films. Solvent choice in MEH-PPV was found to be highly important as the non-aromatic solvents THF and chloroform were found to have dichroic ratios greater than 10 indicating a highly aligned structure that increased the optical bandgaps and mobilities of the samples. Order was shown to also be dependent on the gel solvent evaporation time fraction which was 0.17 for chloroform and 0.58 for THF. Solvent choice for P3HT was shown to increase when cast from THF with a dichroic ratio ∼16 and a t gel/ttotal of 0.75. The order in THF samples of P3HT, however, did not noticeably affect the optical properties. This dissertation shows that the nanostructuring of amorphous and semi-crystalline conjugated polymers leads to increased order, enhanced optical properties, as well as longer effective conjugation lengths that have not been noted in device created from these polymers before

Is there more than one thermal source?

BRAHMS has the ability to study relativistic heavy ion collisions over a wide range of pT and rapidity. This allows us to test whether thermal models can be generalized to describe the rapidity dependence of particle ratios. This appears to work with the baryo-chemical potential changing more rapidly than the temperature. Using fits to BRAHMS data for the 5% most central Au+Au collisions we are able to describe Xi and Omega ratios from other experiments. This paper is dedicated to Julia Thompson who worked to bring South African teachers into physics.Comment: 5 pages, 4 figures, proceedings for SQM04 conference, Cape Town South Afric

Alterations in white matter microstructure in neurofibromatosis-1.

Neurofibromatosis (NF1) represents the most common single gene cause of learning disabilities. NF1 patients have impairments in frontal lobe based cognitive functions such as attention, working memory, and inhibition. Due to its well-characterized genetic etiology, investigations of NF1 may shed light on neural mechanisms underlying such difficulties in the general population or other patient groups. Prior neuroimaging findings indicate global brain volume increases, consistent with neural over-proliferation. However, little is known about alterations in white matter microstructure in NF1. We performed diffusion tensor imaging (DTI) analyses using tract-based spatial statistics (TBSS) in 14 young adult NF1 patients and 12 healthy controls. We also examined brain volumetric measures in the same subjects. Consistent with prior studies, we found significantly increased overall gray and white matter volume in NF1 patients. Relative to healthy controls, NF1 patients showed widespread reductions in white matter integrity across the entire brain as reflected by decreased fractional anisotropy (FA) and significantly increased absolute diffusion (ADC). When radial and axial diffusion were examined we found pronounced differences in radial diffusion in NF1 patients, indicative of either decreased myelination or increased space between axons. Secondary analyses revealed that FA and radial diffusion effects were of greatest magnitude in the frontal lobe. Such alterations of white matter tracts connecting frontal regions could contribute to the observed cognitive deficits. Furthermore, although the cellular basis of these white matter microstructural alterations remains to be determined, our findings of disproportionately increased radial diffusion against a background of increased white matter volume suggest the novel hypothesis that one potential alteration contributing to increased cortical white matter in NF1 may be looser packing of axons, with or without myelination changes. Further, this indicates that axial and radial diffusivity can uniquely contribute as markers of NF1-associated brain pathology in conjunction with the typically investigated measures

Freeze-Out Time in Ultrarelativistic Heavy Ion Collisions from Coulomb Effects in Transverse Pion Spectra

The influence of the nuclear Coulomb field on transverse spectra of $\pi^+$ and $\pi^-$ measured in $Pb+Pb$ reactions at 158 A GeV has been investigated. Pion trajectories are calculated in the field of an expanding fireball. The observed enhancement of the $\pi^-/\pi^+$ ratio at small momenta depends on the temperature and transverse expansion velocity of the source, the rapidity distribution of the net positive charge, and mainly the time of the freeze-out.Comment: 11 pages including 2 figure

Connectivity-enhanced diffusion analysis reveals white matter density disruptions in first episode and chronic schizophrenia.

Reduced fractional anisotropy (FA) is a well-established correlate of schizophrenia, but it remains unclear whether these tensor-based differences are the result of axon damage and/or organizational changes and whether the changes are progressive in the adult course of illness. Diffusion MRI data were collected in 81 schizophrenia patients (54 first episode and 27 chronic) and 64 controls. Analysis of FA was combined with "fixel-based" analysis, the latter of which leverages connectivity and crossing-fiber information to assess both fiber bundle density and organizational complexity (i.e., presence and magnitude of off-axis diffusion signal). Compared with controls, patients with schizophrenia displayed clusters of significantly lower FA in the bilateral frontal lobes, right dorsal centrum semiovale, and the left anterior limb of the internal capsule. All FA-based group differences overlapped substantially with regions containing complex fiber architecture. FA within these clusters was positively correlated with principal axis fiber density, but inversely correlated with both secondary/tertiary axis fiber density and voxel-wise fiber complexity. Crossing fiber complexity had the strongest (inverse) association with FA (r = -0.82). When crossing fiber structure was modeled in the MRtrix fixel-based analysis pipeline, patients exhibited significantly lower fiber density compared to controls in the dorsal and posterior corpus callosum (central, postcentral, and forceps major). Findings of lower FA in patients with schizophrenia likely reflect two inversely related signals: reduced density of principal axis fiber tracts and increased off-axis diffusion sources. Whereas the former confirms at least some regions where myelin and or/axon count are lower in schizophrenia, the latter indicates that the FA signal from principal axis fiber coherence is broadly contaminated by macrostructural complexity, and therefore does not necessarily reflect microstructural group differences. These results underline the need to move beyond tensor-based models in favor of acquisition and analysis techniques that can help disambiguate different sources of white matter disruptions associated with schizophrenia

Testing the Flyby Anomaly with the GNSS Constellation

We propose the concept of a space mission to probe the so called flyby anomaly, an unexpected velocity change experienced by some deep-space probes using earth gravity assists. The key feature of this proposal is the use of GNSS systems to obtain an increased accuracy in the tracking of the approaching spacecraft, mainly near the perigee. Two low-cost options are also discussed to further test this anomaly: an add-on to an existing spacecraft and a dedicated mission.Comment: 8 pages, 1 figure, 4 table

The relationship between particle freeze-out distributions and HBT radius parameters

The relationship between pion and kaon space-time freeze-out distributions and the HBT radius parameters in high-energy nucleus-nucleus collisions is investigated. We show that the HBT radius parameters in general do not reflect the R.M.S. deviations of the single particle production points. Instead, the HBT radius parameters are most closely related to the curvature of the two-particle space-time relative position distribution at the origin. We support our arguments by studies with a dynamical model (RQMD 2.4).Comment: RevTex, 10 pages including 3 figures. v2: Discussion of the lambda parameter has been added. PRC, in prin

Does parton saturation at high density explain hadron multiplicities at RHIC ?

We discuss the recent claim that hadron multiplicities measured at RHIC energies are directly described in terms of gluon degrees of freedom fixed from the initial conditions of central heavy ion collisions. The argument is based on the parton saturation scenario expected to be valid at high parton densities and on the assumption of conserved gluon number. Alternatively we conjecture that "bottom-up" equilibration before hadronization modifies this picture, due to nonconservation of the number of gluons.Comment: 8 page

Nuclear Modification Factor for Charged Pions and Protons at Forward Rapidity in Central Au+Au Collisions at 200 GeV

We present spectra of charged pions and protons in 0-10% central Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV at mid-rapidity ($y=0$) and forward pseudorapidity ($\eta=2.2$) measured with the BRAHMS experiment at RHIC. The spectra are compared to spectra from p+p collisions at the same energy scaled by the number of binary collisions. The resulting nuclear modification factors for central Au+Au collisions at both $y=0$ and $\eta=2.2$ exhibit suppression for charged pions but not for (anti-)protons at intermediate $p_T$. The $\bar{p}/\pi^-$ ratios have been measured up to $p_T\sim 3$ GeV/$c$ at the two rapidities and the results indicate that a significant fraction of the charged hadrons produced at intermediate $p_T$ range are (anti-)protons at both mid-rapidity and $\eta = 2.2$