Oscillator Strength of Metallic Carbon Nanotubes

Based on the tight binding method with hopping integral between the nearest-neighbor atoms, an oscillator strength \int_0^{\infty} \d \omega {\rm Re} \sigma (\omega) is discussed for armchair and metallic zigzag carbon nanotubes. The formulae of the oscillator strength are derived for both types of nanotubes and are compared with the result obtained by a linear chain model. In addition, the doping dependence is investigated in the absence of Coulomb interaction. It is shown that the oscillator strength of each carbon nanotube shows qualitatively the same doping dependence, but the fine structure is different due to it's own peculiar band structure. Some relations independent of the radius of the tube are derived, and a useful formula for determining the amount of doping is proposed.Comment: 4 pages, 4 figures, submitted to J. Phys. Soc. Jpn. at June 30, 200

\u3ci\u3eIn-Situ\u3c/i\u3e Raman Scattering Studies of Alkali-Doped Single Wall Carbon Nanotubes

Electrochemical doping and in-situ Raman scattering were used to study charge transfer in K- and Li-doped single wall carbon nanotubes (SWNT) as a function of alkali concentration. An 8 cm-1 downshift was observed for the tangential phonon mode of SWNT doped to stoichiometries of KC24 and Li1.25C6. The shift in both systems is reversible upon de-doping despite an irreversible loss of crystallinity. These results indicate that the tangential mode shifts result from electron transfer from alkali dopants to the SWNT, and that these modes are only weakly affected by long-range order within the ropes

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

Non-structural carbohydrates in woody plants compared among laboratories

Non-structural carbohydrates (NSC) in plant tissue are frequently quantified to make inferences about plant responses to environmental conditions. Laboratories publishing estimates of NSC of woody plants use many different methods to evaluate NSC. We asked whether NSC estimates in the recent literature could be quantitatively compared among studies. We also asked whether any differences among laboratories were related to the extraction and quantification methods used to determine starch and sugar concentrations. These questions were addressed by sending sub-samples collected from five woody plant tissues, which varied in NSC content and chemical composition, to 29 laboratories. Each laboratory analyzed the samples with their laboratory-specific protocols, based on recent publications, to determine concentrations of soluble sugars, starch and their sum, total NSC. Laboratory estimates differed substantially for all samples. For example, estimates for Eucalyptus globulus leaves (EGL) varied from 23 to 116 (mean = 56) mg g⁻¹ for soluble sugars, 6–533 (mean = 94) mg g⁻¹ for starch and 53–649 (mean = 153) mg g⁻¹ for total NSC. Mixed model analysis of variance showed that much of the variability among laboratories was unrelated to the categories we used for extraction and quantification methods (method category R² = 0.05–0.12 for soluble sugars, 0.10–0.33 for starch and 0.01–0.09 for total NSC). For EGL, the difference between the highest and lowest least squares means for categories in the mixed model analysis was 33 mg g⁻¹ for total NSC, compared with the range of laboratory estimates of 596 mg g⁻¹. Laboratories were reasonably consistent in their ranks of estimates among tissues for starch (r = 0.41–0.91), but less so for total NSC (r = 0.45–0.84) and soluble sugars (r = 0.11–0.83). Our results show that NSC estimates for woody plant tissues cannot be compared among laboratories. The relative changes in NSC between treatments measured within a laboratory may be comparable within and between laboratories, especially for starch. To obtain comparable NSC estimates, we suggest that users can either adopt the reference method given in this publication, or report estimates for a portion of samples using the reference method, and report estimates for a standard reference material. Researchers interested in NSC estimates should work to identify and adopt standard methods.This is the publisher’s final pdf. The published article is copyrighted by the author(s) and published by Oxford University Press. The published article can be found at: http://treephys.oxfordjournals.org/Keywords: soluble sugars, starch, particle size, reference method, standardization, non-structural carbohydrate chemical analysis, extraction and quantification consistenc

Predictors of pregnancy after HIV-positive diagnosis among women in western Jamaica

Lea Jean Claye,1 Swati Sakhuja,1 Ashley Nutt,1 Maung Aung,2 Pauline E Jolly1 1Department of Epidemiology, University of Alabama at Birmingham, Birmingham, AL, USA; 2Epidemiology and Research Unit, Western Regional Health Authority, Ministry of Health, Montego Bay, Jamaica Background: Antiretroviral therapy has minimized mother-to-child transmission of HIV and given hope to HIV-positive women considering pregnancy. In Jamaica, 36% of HIV-positive pregnant women enrolled in a pediatric/perinatal HIV/AIDS program had repeat pregnancies. Objective: To describe the epidemiology and identify factors associated with pregnancy after HIV diagnosis among HIV-positive women in Western Jamaica. Methods: A cross-sectional study was designed among HIV-positive women 18–54 years old who either had or did not have at least one pregnancy after HIV-positive diagnosis. A questionnaire was used to collect information on sociodemographic factors and health-seeking, reproductive, and sexual risk behaviors. Results: A total of 219 HIV-positive women participated in this study. Length of time since HIV diagnosis, CD4 count, and birth-control methods used were significant predictors of pregnancy after HIV diagnosis. Women diagnosed with HIV <5 years previously had lower odds for pregnancy after HIV diagnosis (adjusted OR 0.12, 95% CI 0.02–0.84) compared to those who had been diagnosed ≥8 years previously. Women with CD4 count <350 were over six times as likely to have a pregnancy after HIV diagnosis (adjusted OR 6.94, 95% CI 1.18–40.66). The odds for pregnancy after HIV diagnosis for a woman decreased by 93% if her children shared the same father (adjusted OR 0.07, 95% CI 0.006–0.77). Conclusion: This study identified significant predictors of pregnancy after HIV diagnosis that indicate that integrative family-planning interventions with supportive reproductive counseling are likely to help HIV-positive women obtain early appropriate care and plan the pregnancies they desire. Keywords: pregnancy, HIV infection, desire for children, HIV disclosur

First principle study of Li-intercalated (5, 5) ZnO nanotube bundles

We have investigated the geometric and electronic structure of Li-intercalated (5, 5) zinc oxide nanotube (ZnONT) bundles via density functional theory as implemented in the code WIEN2k. Our results show that the geometrical structures are changed because of intercalation of lithium. The effect of Li intercalation on the density of state and electronic band structure is a shift of the Fermi energy due to the charge transfer from lithium to the ZnONTs. Although, the bundle of clean (5, 5) ZnONTs is semiconductor, all the Li-intercalated (5, 5) ZnONT bundles are found to be metallic. Both inside of the nanotube and the interstitial spaces are susceptible for intercalation