Electron-Hole Asymmetry in Single-Walled Carbon Nanotubes Probed by Direct Observation of Transverse Quasi-Dark Excitons

We studied the asymmetry between valence and conduction bands in single-walled carbon nanotubes (SWNTs) through the direct observation of spin-singlet transverse dark excitons using polarized photoluminescence excitation spectroscopy. The intrinsic electron-hole (e-h) asymmetry lifts the degeneracy of the transverse exciton wavefunctions at two equivalent K and K' valleys in momentum space, which gives finite oscillator strength to transverse dark exciton states. Chirality-dependent spectral weight transfer to transverse dark states was clearly observed, indicating that the degree of the e-h asymmetry depends on the specific nanotube structure. Based on comparison between theoretical and experimental results, we evaluated the band asymmetry parameters in graphene and various carbon nanotube structures.Comment: 11 pages, 4 figure

Dependence of exciton transition energy of single-walled carbon nanotubes on surrounding dielectric materials

We theoretically investigate the dependence of exciton transition energies on dielectric constant of surrounding materials. We make a simple model for the relation between dielectric constant of environment and a static dielectric constant describing the effects of electrons in core states, $\sigma$ bonds and surrounding materials. Although the model is very simple, calculated results well reproduce experimental transition energy dependence on dielectric constant of various surrounding materials.Comment: 5pages, 4 figure

Identification of excitonic phonon sideband by photoluminescence spectroscopy of single-walled carbon-13 nanotubes

We have studied photoluminescence (PL) and resonant Raman scatterings of single-walled carbon nanotubes (SWNTs) consisting of carbon-13 (SW13CNTs) synthesized from a small amount of isotopically modified ethanol. There was almost no change in the Raman spectra shape for SW13CNTs except for a downshift of the Raman shift frequency by the square-root of the mass ratio 12/13. By comparing photoluminescence excitation (PLE) spectra of SW13CNTs and normal SWNTs, the excitonic phonon sideband due to strong exciton-phonon interaction was clearly identified with the expected isotope shift

Femtosecond Excitation Correlation Spectroscopy of Single-Walled Carbon Nanotubes : Analysis Based on Nonradiative Multiexciton Recombination Processes

We studied the nonlinear time-resolved luminescence signals due to multiexciton recombination processes in single-walled carbon nanotubes (SWNTs) using femtosecond excitation correlation (FEC) spectroscopy. From theoretical analysis of the FEC signals, we found that the FEC signals in the long time range are dominated by the single exciton decay in SWNTs, where the exciton-exciton annihilation process is efficient. Our results provide a simple method to clarify the single exciton decay dynamics in low-dimensional materials.Comment: 21 pages, 5 figures; typos adde

Cross-polarized optical absorption of single-walled nanotubes probed by polarized photoluminescence excitation spectroscopy

Cross-polarized absorption peaks of isolated single-walled carbon nanotubes were observed by a polarized photoluminescence excitation (PLE) spectroscopy. Using a simple theory for PL anisotropy, the observed PLE spectra are decomposed into 'pure' components of the photoexcitation for incident light polarized parallel and perpendicular to the SWNT axis. For several (n, m) SWNTs, distinct peaks corresponding to perpendicular excitation were observed. The measured transition energies for perpendicular excitations were blue-shifted compared to the qualitative values predicted within a single-particle theory. The results indicate a smaller exciton binding energy for perpendicular excitations than for parallel excitations.Comment: 7 pages, 5 figures, submitted to Phys. Rev.

ENCOUNTERING AND COUNTERING WORK STRESS: A MULTIVARIATE ANALYSIS OF THE OCCUPATIONAL STRESS AND COPING MECHANISMS OF FAST FOOD RESTAURANT PERSONNEL IN THE PHILIPPINES

Food is always viewed as an indispensable household necessity. Based on the 2009 Family Income and Expenditure Survey (FIES), 42.6% of the total expenditure of a typical Filipino household is solely being allocated for food (Limtingco, 2012). As the growing demand for food continues to escalate, fast food providers had proliferated both in the metro and rural provinces to help augment the need. In effect, the demand for human workforce for these companies had also escalated. However, at present, no available literature had yet explicated on the current psychological condition of the working personnel of these companies. Thus, this research is an exploratory attempt meant to delve on the various typologies and severity of stressors currently experienced by the food service personnel in the Philippines. Furthermore, this study statistically accounted for the coping mechanisms used by the fast food service personnel in treating their work related problems

Detection of interstellar hydrogen peroxide

The molecular species hydrogen peroxide, HOOH, is likely to be a key ingredient in the oxygen and water chemistry in the interstellar medium. Our aim with this investigation is to determine how abundant HOOH is in the cloud core {\rho} Oph A. By observing several transitions of HOOH in the (sub)millimeter regime we seek to identify the molecule and also to determine the excitation conditions through a multilevel excitation analysis. We have detected three spectral lines toward the SM1 position of {\rho} Oph A at velocity-corrected frequencies that coincide very closely with those measured from laboratory spectroscopy of HOOH. A fourth line was detected at the 4{\sigma} level. We also found through mapping observations that the HOOH emission extends (about 0.05 pc) over the densest part of the {\rho} Oph A cloud core. We derive an abundance of HOOH relative to that of H_2 in the SM1 core of about 1\times10^(-10). To our knowledge, this is the first reported detection of HOOH in the interstellar medium.Comment: 5 pages, 4 figures, accepted for publication in Astronomy & Astrophysics, new version corrects a typo in Table 1 (and consequently in Fig 4

Photometric Properties of Kiso Ultraviolet-Excess Galaxies in the Lynx-Ursa Major Region

We have performed a systematic study of several regions in the sky where the number of galaxies exhibiting star formation (SF) activity is greater than average. We used Kiso ultraviolet-excess galaxies (KUGs) as our SF-enhanced sample. By statistically comparing the KUG and non-KUG distributions, we discovered four KUG-rich regions with a size of $\sim 10^\circ \times 10^\circ$. One of these regions corresponds spatially to a filament of length $\sim 60 h^{-1}$ Mpc in the Lynx-Ursa Major region ($\alpha \sim 9^{\rm h} - 10^{\rm h}, \delta \sim 42^\circ - 48^\circ$). We call this ``the Lynx-Ursa Major (LUM) filament''. We obtained $V(RI)_{\rm C}$ surface photometry of 11 of the KUGs in the LUM filament and used these to investigate the integrated colors, distribution of SF regions, morphologies, and local environments. We found that these KUGs consist of distorted spiral galaxies and compact galaxies with blue colors. Their star formation occurs in the entire disk, and is not confined to just the central regions. The colors of the SF regions imply that active star formation in the spiral galaxies occurred $10^{7 - 8}$ yr ago, while that of the compact objects occurred $10^{6-7}$ yr ago. Though the photometric characteristics of these KUGs are similar to those of interacting galaxies or mergers, most of these KUGs do not show direct evidence of merger processes.Comment: 39 pages LaTeX, using aasms4.sty, 20 figures, ApJS accepted. The Title of the previous one was truncated by the author's mistake, and is corrected. Main body of the paper is unchange