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Search Results: 1 - 10 of 144693 matches for " Deranda B. Lester "
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Examining the Effects of Common Laboratory Methods on the Sensitivity of Carbon Fiber Electrodes in Amperometric Recordings of Dopamine  [PDF]
William T. Prater, Malli Swamy, Megan D. Beane, Deranda B. Lester
Journal of Behavioral and Brain Science (JBBS) , 2018, DOI: 10.4236/jbbs.2018.83007
Abstract: Carbon fiber microelectrodes (CFEs) are useful when combined with electrochemical techniques for measuring changes in neurotransmitter concentrations. We addressed conflicting details regarding the use of CFEs. Experimental groups consisted of CFEs at different ages (1 week, 1 month, or 2 months), cleaned in solvents (isopropanol or xylene), and exposed to in vitro use (flow cell calibrations) or in vivo use (in brain tissue). In order to determine if any of these factors affect CFE sensitivity, the present study utilized fixed potential amperometry and a flow injection system to calibrate CFEs for the measurement of dopamine. The sensitivity index (nA/μM per 100 μm of exposed carbon fiber) was not affected by the age of CFEs or pre-cleaning with xylene or isopropanol. CFE sensitivity of the in vitro exposure group also did not differ from untreated CFEs, indicating the calibration process did not alter sensitivity. However, in vivo use in brain tissue did reduce sensitivity. This effect was negated and sensitivity restored by cleaning CFEs in isopropanol or xylene following in vivo brain recordings. Given that variations in CFE sensitivity can skew results, our findings can help standardize CFE use and explain discrepancies between researchers.
REVIEW OF "THE COLORS, BOLOMETRIC CORRECTIONS AND EFFECTIVE TEMPERATURES OF THE BRIGHT STARS" BY JOHNSON (1964)
John B. Lester
Revista mexicana de astronomía y astrofísica , 2011,
Abstract: H. L. Johnson, 1964, BOTT, 3, 25, 305 established standard stars for his JKL and M photometry, and developed a calibration that enabled him to determine bolometric corrections and effective temperatures. In many ways Johnson anticipated the developments that were about to come forth. Many of Johnson s observations of the bright stars might still be the best available because astronomy has concentrated heavily on fainter objects following the end of Johnson s career.
Invasive aspergillosis in an immunocompetent patient with fever and a cardiac mass
Matthew LaBarbera,Lester B. Jacobson
Infectious Disease Reports , 2011, DOI: 10.4081/idr.2011.e12
Abstract: Invasive aspergillosis is an often fatal disease that usually occurs in immunocompromised patients. We report a case of invasive aspergillosis presenting as a febrile respiratory infection with a cardiac mass in an immunocompetent patient. Invasive aspergillosis should be considered in the differential diagnosis of an otherwise undiagnosed febrile respiratory illness, even in immunocompetent patients. Echocardiography should be peformed to evaluate for endocarditis in such cases. Prompt initiation of appropriate antifungal therapy is warranted, even before the diagnosis of invasive aspergillosis is confirmed.
Endoscopic Management of Recurrent Anterior Skull Base Schwannoma  [PDF]
Jivianne T. Lee, Lester D. R. Thompson, Rohit Garg, David B. Keschner, Terry Shibuya
International Journal of Otolaryngology and Head & Neck Surgery (IJOHNS) , 2013, DOI: 10.4236/ijohns.2013.22013
Abstract:
Objectives: Sinonasal schwannomas account for less than 4% of head and neck schwannomas, with the primary treatment modality being surgical excision via external approaches. The aim of this report is to present a rare case of recurrent schwannoma of the ethmoid cavity involving the anterior skull base which was successfully managed with endoscopic resection. Study Design: Case report and review of the literature. Methods: The clinical presentation, radiographic features, histopathologic characteristics, surgical approach, and patient outcome were examined in the context of a literature review. Results: A 43-year-old woman presented with a 9-month history of left facial pain and pressure. She had a prior history of sinonasal schwannoma excision with cerebrospinal fluid (CSF) leak repair via bifrontal craniotomy in 2007. Magnetic resonance imaging (MRI) and nasal endoscopy revealed a left ethmoid mass measuring 2.2 cm × 2.7 cm × 2.4 cm abutting the anterior skull base. The tumor was completely removed using a transnasal endoscopic approach, and the anterior skull base reconstructed with tensor fascia lata graft. Histology of the specimen showed schwannoma, and there has been no evidence of tumor recurrence nor CSF leak after 24 months of follow-up. Conclusion: With continual advances in surgical technique and instrumentation, sinonasal schwannomas have become increasingly more amenable to endoscopic resection even in the case of recurrence and skull base involvement.
Multi-Dimensional mSUGRA Likelihood Maps
B. C. Allanach,C. G. Lester
Physics , 2005, DOI: 10.1103/PhysRevD.73.015013
Abstract: We calculate the likelihood map in the full 7 dimensional parameter space of the minimal supersymmetric standard model (MSSM) assuming universal boundary conditions on the supersymmetry breaking terms. Simultaneous variations of m_0, A_0, M_{1/2}, tan beta, m_t, m_b and alpha_s(M_Z) are applied using a Markov chain Monte Carlo algorithm. We use measurements of b -> s gamma, (g-2)_mu and Omega_{DM} h^2 in order to constrain the model. We present likelihood distributions for some of the sparticle masses, for the branching ratio of B_s^0 -> mu^+ mu^- and for m_{stau}-m_{chi_1^0}. An upper limit of 2.10^{-8} on this branching ratio might be achieved at the Tevatron, and would rule out 29% of the currently allowed likelihood. If one allows for non thermal-neutralino components of dark matter, this fraction becomes 35%. The mass ordering allows the important cascade decay squark_L -> chi_2^0 -> slepton_R -> chi_1^0 with a likelihood of 24+/-4%. The stop coannihilation region is highly disfavoured, whereas the light Higgs region is marginally disfavoured.
Missing Opacity in the Atmospheric Models of Red Giants
C. I. Short,J. B. Lester
Physics , 1994, DOI: 10.1086/187658
Abstract: Synthetic spectra of Arcturus computed with the latest theoretical stellar atmospheres disagree strongly with both the spectral energy distribution and with the spectroscopic data for $\lambda < 4000$ \AA , even though the stellar parameters are well constrained. We find that the discrepancy can be removed by adding a continuous absorption opacity that is approximately equal to that which is already included in the {\sc atlas9} code. Spectroscopy of other K2 III stars shows that the spectrum of Arcturus in not anomalous. Therefore, missing opacity may be a common feature of the models for stars in this temperature and luminosity range.
Weighing Betelgeuse: Measuring the mass of alpha Orionis from stellar limb-darkening
Hilding Neilson,John B. Lester,Xavier Haubois
Physics , 2011,
Abstract: Stellar limb-darkening is an important tool for constraining the properties of a stellar atmosphere. We present a novel method for relating the fundamental stellar parameters mass and radius to limb-darkening laws using grids of spherical model stellar atmospheres. This method is applied to interferometric observations of the red supergiant Betelgeuse, where an unique measure of the stellar mass is determined.
Spherically-symmetric model stellar atmospheres and limb darkening I: limb-darkening laws, gravity-darkening coefficients and angular diameter corrections for red giant stars
Hilding R. Neilson,John B. Lester
Physics , 2013, DOI: 10.1051/0004-6361/201321502
Abstract: Model stellar atmospheres are fundamental tools for understanding stellar observations from interferometry, microlensing, eclipsing binaries and planetary transits. However, the calculations also include assumptions, such as the geometry of the model. We use intensity profiles computed for both plane-parallel and spherically symmetric model atmospheres to determine fitting coefficients in the BVRIHK, CoRot and Kepler wavebands for limb darkening using several different fitting laws, for gravity-darkening and for interferometric angular diameter corrections. Comparing predicted variables for each geometry, we find that the spherically symmetric model geometry leads to different predictions for surface gravities log g < 3. In particular, the most commonly used limb-darkening laws produce poor fits to the intensity profiles of spherically symmetric model atmospheres, which indicates the need for more sophisticated laws. Angular diameter corrections for spherically symmetric models range from 0.67 to 1, compared to the much smaller range from 0.95 to 1 for plane-parallel models.
Limb darkening in spherical stellar atmospheres
Hilding R. Neilson,John B. Lester
Physics , 2011, DOI: 10.1051/0004-6361/201116623
Abstract: (Abridged) Context. Stellar limb darkening, I({\mu} = cos{\theta}), is an important constraint for microlensing, eclipsing binary, planetary transit, and interferometric observations, but is generally treated as a parameterized curve, such as a linear-plus-square-root law. Many analyses assume limb-darkening coefficients computed from model stellar atmospheres. However, previous studies, using I({\mu}) from plane- parallel models, have found that fits to the flux-normalized curves pass through a fixed point, a common {\mu} location on the stellar disk, for all values of T eff, log g and wavelength. Aims. We study this fixed {\mu}-point to determine if it is a property of the model stellar atmospheres or a property of the limb-darkening laws. Furthermore, we use this limb-darkening law as a tool to probe properties of stellar atmospheres for comparison to limb- darkening observations. Methods. Intensities computed with plane-parallel and spherically-symmetric Atlas models (characterized by the three fundamental parameters L\star, M\star and R\star) are used to reexamine the existence of the fixed {\mu}-point for the parametrized curves. Results. We find that the intensities from our spherical models do not have a fixed point, although the curves do have a minimum spread at a {\mu}-value similar to the parametrized curves. We also find that the parametrized curves have two fixed points, {\mu}1 and {\mu}2, although {\mu}2 is so close to the edge of the disk that it is missed using plane-parallel atmospheres. We also find that the spherically- symmetric models appear to agree better with published microlensing observations relative to plane-parallel models.
Spherically symmetric model stellar atmospheres and limb darkening II: limb-darkening laws, gravity-darkening coefficients and angular diameter corrections for FGK dwarf stars
Hilding R. Neilson,John B. Lester
Physics , 2013, DOI: 10.1051/0004-6361/201321888
Abstract: Limb darkening is a fundamental ingredient for interpreting observations of planetary transits, eclipsing binaries, optical/infrared interferometry and microlensing events. However, this modeling traditionally represents limb darkening by a simple law having one or two coefficients that have been derived from plane-parallel model stellar atmospheres, which has been done by many researchers. More recently, researchers have gone beyond plane-parallel models and considered other geometries. We previously studied the limb-darkening coefficients from spherically symmetric and plane-parallel model stellar atmospheres for cool giant and supergiant stars, and in this investigation we apply the same techniques to FGK dwarf stars. We present limb-darkening coefficients, gravity-darkening coefficients and interferometric angular diameter corrections from Atlas and SAtlas model stellar atmospheres. We find that sphericity is important even for dwarf model atmospheres, leading to significant differences in the predicted coefficients.
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