Enhancement of the Electron Spin Resonance of Single-Walled Carbon Nanotubes by Oxygen Removal

We have observed a nearly fourfold increase in the electron spin resonance (ESR) signal from an ensemble of single-walled carbon nanotubes (SWCNTs) due to oxygen desorption. By performing temperature-dependent ESR spectroscopy both before and after thermal annealing, we found that the ESR in SWCNTs can be reversibly altered via the molecular oxygen content in the samples. Independent of the presence of adsorbed oxygen, a Curie-law (spin susceptibility $\propto 1/T$) is seen from $\sim$4 K to 300 K, indicating that the probed spins are finite-level species. For both the pre-annealed and post-annealed sample conditions, the ESR linewidth decreased as the temperature was increased, a phenomenon we identify as motional narrowing. From the temperature dependence of the linewidth, we extracted an estimate of the intertube hopping frequency; for both sample conditions, we found this hopping frequency to be $\sim$100 GHz. Since the spin hopping frequency changes only slightly when oxygen is desorbed, we conclude that only the spin susceptibility, not spin transport, is affected by the presence of physisorbed molecular oxygen in SWCNT ensembles. Surprisingly, no linewidth change is observed when the amount of oxygen in the SWCNT sample is altered, contrary to other carbonaceous systems and certain 1D conducting polymers. We hypothesize that physisorbed molecular oxygen acts as an acceptor ($p$-type), compensating the donor-like ($n$-type) defects that are responsible for the ESR signal in bulk SWCNTs.Comment: 14 pages, 7 figure

Use of computer-based neuropsychological testing to identify impairments in high school players without concussion symptoms

A group of individuals was identified by Talavage et al. who exhibit neurological changes similar to or greater than individuals who are diagnosed with a concussion but do not demonstrate any clinical signs or symptoms of concussion (i.e., functional impairment). If not diagnosed, those individuals continue to play and continue to take blows to the head putting them at risk for long-term brain injury. Therefore, the identification of these functionally impaired individuals is of the utmost importance. The objective of this study was to evaluate the reliability of using the ImPACT neuropsychological testing battery to identify individuals who demonstrate neuropsychological impairment but who do not have clinical signs or symptoms. A prospective study at a single mid-western high school of 11 high school male football players (aged 15-19 years) was conducted. Participants who exhibited neurocognitive deficits were flagged by ImPACT as having a statistically lower score in either the visual memory composite or the verbal memory composite score. The reported change in the visual memory composite score from the ImPACT was not able to identify either the functionally or clinically impaired groups. The change in the verbal memory composite score relative to baseline was able to identify the clinically impaired group (p-value=0.0106) but not the functionally impaired group. The ImPACT results were also analyzed using a worst change score which was computed by identifying the greatest change in either the verbal or visual memory composite score. The worst score was able to predict both the clinically impaired group (p-value=0.0461) and the functionally impaired group (p-value=0.0288). A linear regression was run on the verbal memory composite score, the visual memory composite score, and the worst score for all non-concussed participants. ImPACT was able to correctly identify concussed individuals and gave no false positives with non-concussed individuals but there was no single score that was able to consistently identify individuals with functional impairments relative to the non-impaired group. A regression analysis of regional fMRI activity as a function of the ImPACT score found moderate correlation in the frontal and temporal lobes with the worst score. In conclusion, no single ImPACT generated metric can correctly indentify functional impairments

<span style="font-size:11.0pt;font-family: "Times New Roman";mso-fareast-font-family:"Times New Roman";mso-bidi-font-family: Mangal;mso-ansi-language:EN-US;mso-fareast-language:EN-US;mso-bidi-language: HI" lang="EN-US">Quantum chemical investigations on determination of electronic, structural and electric properties of some even carbon cage fullerenes</span>

911-916<span style="font-size:11.0pt;font-family: " times="" new="" roman";mso-fareast-font-family:"times="" roman";mso-bidi-font-family:="" mangal;mso-ansi-language:en-us;mso-fareast-language:en-us;mso-bidi-language:="" hi"="" lang="EN-US">The electronic structures and geometries of even carbon cage fullerenes in gas phase are investigated at the B3LYP/DZP level of theory. The potential relationship between geometric factors and stability is systematically examined. The extra stability of C60 has been confirmed by the shorter mean bond length, smaller angle strain, and widest energy gap. From optimized geometries and using non-hybrid and hybrid functionals along with the AXZP (X = D, T, and Q) basis sets, static dipole polarizabilities of C20, C24, C26, C28, C30, C32, C36, C38, C44, C50, C60, and C70 are evaluated.</span