Theory and it ab initio calculation of radiative lifetime of excitons in semiconducting carbon nanotubes

We present theoretical analysis and first-principles calculation of the radiative lifetime of excitons in semiconducting carbon nanotubes. An intrinsic lifetime of the order of 10 ps is computed for the lowest optically active bright excitons. The intrinsic lifetime is however a rapid increasing function of the exciton momentum. Moreover, the electronic structure of the nanotubes dictates the existence of dark excitons nearby in energy to each bright exciton. Both effects strongly influence measured lifetime. Assuming a thermal occupation of bright and dark exciton bands, we find an effective lifetime of the order of 10 ns at room temperature, in good accord with recent experiments.Comment: 12 pages, 3 figure

0+ states in the large boson number limit of the Interacting Boson Approximation model

Studies of the Interacting Boson Approximation (IBA) model for large boson numbers have been triggered by the discovery of shape/phase transitions between different limiting symmetries of the model. These transitions become sharper in the large boson number limit, revealing previously unnoticed regularities, which also survive to a large extent for finite boson numbers, corresponding to valence nucleon pairs in collective nuclei. It is shown that energies of 0_n^+ states grow linearly with their ordinal number n in all three limiting symmetries of IBA [U(5), SU(3), and O(6)]. Furthermore, it is proved that the narrow transition region separating the symmetry triangle of the IBA into a spherical and a deformed region is described quite well by the degeneracies E(0_2^+)=E(6_1^+), E(0_3^+)=E(10_1^+), E(0_4^+)=E(14_1^+), while the energy ratio E(6_1^+) /E(0_2^+) turns out to be a simple, empirical, easy-to-measure effective order parameter, distinguishing between first- and second-order transitions. The energies of 0_n^+ states near the point of the first order shape/phase transition between U(5) and SU(3) are shown to grow as n(n+3), in agreement with the rule dictated by the relevant critical point symmetries resulting in the framework of special solutions of the Bohr Hamiltonian. The underlying partial dynamical symmetries and quasi-dynamical symmetries are also discussed.Comment: 6 pages, 4 postscript figures, LaTeX. To appear in the Proceedings of the International Conference on Nuclear Physics and Astrophysics: From Stable Beams to Exotic Nuclei (Cappadocia, 2008

Istilah ‘Rempit'; Pengertian Dan Penggunaannya Dalam Isu Lumba Motorsikal Haram Di Malaysia

Rempit term (race) is very popular in Malaysia to use for identifying illegal motorcycle race. This research aimed to know the uses of rempit concept in the Mat Rempit group itself. The Study using 2 types of interview, the first is individual interview with 16 subjects whom had involved in rempit activity in a school at Semenyih, Selangor; the second is focus group discussion consist of 3 groups of defendant under section 42 as a result of riding motorcyle dongerously in Pulau Pinang, Johor Baharu and Kuala Lumpur. Result of the analysis, found that rempit can be redefine as an activity of motorcycle race as together (at least consist of 2 persons) which involves race (i.e sprint or lap) and/or stunt action (i.e wheelie or wheekang) triggered by trial behavior trough engine signal from motorcycle (ramp), communication or hand gesture. A Mat Rempit (racer) is an individu who get involved in this activity. This research reviews the definition throughly by formulating rempit activity comprehensively. The implication of the research is rempit word has to be used cautiosly, especially when trying to give a label to an individual as Mat Rempit. For the future research, the definition that has to be used is the one which proposed in this research and not other vague definition

Diameter and Chirality Dependence of Exciton Properties in Carbon Nanotubes

We calculate the diameter and chirality dependences of the binding energies, sizes, and bright-dark splittings of excitons in semiconducting single-wall carbon nanotubes (SWNTs). Using results and insights from {\it ab initio} calculations, we employ a symmetry-based, variational method based on the effective-mass and envelope-function approximations using tight-binding wavefunctions. Binding energies and spatial extents show a leading dependence with diameter as $1/d$ and $d$, respectively, with chirality corrections providing a spread of roughly 20% with a strong family behavior. Bright-dark exciton splittings show a $1/d^2$ leading dependence. We provide analytical expressions for the binding energies, sizes, and splittings that should be useful to guide future experiments

A numerical investigation of mechanical response of unfilled Styrene Butadiene Rubber by static straight blade indentation

This study investigates the mechanical response of straight blade indentation on Unfilled Styrene Butadiene Rubber by Finite Element Analysis (FEA). The mechanical responses investigated were stiffness, maximum stress and indentation load. The rubber material was modeled as a hyperelastic material with the Money-Rivlin Strain Energy Function. Results were presented as a function of the blade characteristics, wedge angle and tip radius at a specified depth of indentation. Results showed that the stiffness and indenter load increase due to an increase in the wedge angle and the tip radius, on the other hand, the maximum stress decreases. Surprisingly, an approximately linear relationship between the mechanical response and the blade characteristic was found. Furthermore, the mechanical response at a specified maximum stress was also discussed

Several Factors Increased Job Dissatisfaction Among Medical Doctors in Indonesia

Background:Several factors of work stressors may increase a person's job dissatisfaction level. This study aimed to identify several dominant factors related to job dissatisfaction among medical doctors. Methods: A cross-sectional study with purposive sampling was conducted in April-July 2011. Subjects consisted of postgraduate students and faculty members of the Faculty of Medicine, Universitas Indonesia. Linear regression was used to analyze the data. Results: The participants consisted of 306 subjects, aged 23-47 years old, the majority were female (61.4%), married, current/previous work was in health services, government officials and never had stress management training. Job dissatisfaction level related to seven factors, the highest was having lack of support from superiors and the lowest was being required to provide services outside normal working hours. One point of having lack of support from superiors increased job dissatisfaction by 1.26 [regression coeffisient (β) = 1.26; P=0.000); one point of being required to provide services outside normal working hours increased job dissatisfaction by 0.61 point (β= 0.6; P=0.001).Conclusion:Lack of superiors' support and interaction with colleagues, role organization ambiguity, bureaucratic procedures, having to provide services outside normal working hours, and inadequate feedback from patients all increased job dissatisfaction. (Health Science Indones 2013;1:11-6

Muhammad Saw dan Peletakan Dasar Peradaban Islam

. Sejarah pra-Islam dan pasca datangnya nabi Muhammad di tengah peradaban bangsa Arab tentunya merupakan suatu kondisi yang sangat bipolar. Di satu sisi, peradaban pra-Islam banyak terjadi perilaku buruk seperti permusuhan, perselisihan, ketidakadilan, penindasan bahkan pembunuhan merupakan suatu tradisi dekonstruktif dalam tatanan bangsa Arab. Tentunya, hal ini sangat berbeda ketika Muhammad saw. (keturunan Arab) lahir, terjadi Perubahan tatanan yang sangat signifikan mulai dari konsteks keilmuan, sosial, ekonomi, dan aspek-aspek lainnya. Secara kompeherensif, aspek tersebut di atas direkonstruksi dari mukjizat nabi, yakni Alquran sebagai pedoman dasar dan berupa dari tata cara berperilaku nabi, ucapan dan way of life nabi yang terakumulasi dalam hadits mampu menggeser peradaban yang terbelakang menjadi perabadan yang sangat maju di berbagai lini. Penelitian ini mencoba untuk mengkonstelasikan dan mengkomparasikan peradaban bangsa Arab pra Nabi hingga Nabi dilahirkan dan membawa misi revolusioner dengan munculnya peradaban baru, peradaban Islam

Excitonic Effects and Optical Spectra of Single-Walled Carbon Nanotubes

Many-electron effects often dramatically modify the properties of reduced dimensional systems. We report calculations, based on an many-electron Green's function approach, of electron-hole interaction effects on the optical spectra of small-diameter single-walled carbon nanotubes. Excitonic effects qualitatively alter the optical spectra of both semiconducting and metallic tubes. Excitons are bound by ~ 1 eV in the semiconducting (8,0) tube and by ~ 100 meV in the metallic (3,3) tube. These large many-electron effects explain the discrepancies between previous theories and experiments.Comment: 6 pages, 3 figures, 2 table

The Bivariate Rogers-Szeg\"{o} Polynomials

We present an operator approach to deriving Mehler's formula and the Rogers formula for the bivariate Rogers-Szeg\"{o} polynomials $h_n(x,y|q)$. The proof of Mehler's formula can be considered as a new approach to the nonsymmetric Poisson kernel formula for the continuous big $q$-Hermite polynomials $H_n(x;a|q)$ due to Askey, Rahman and Suslov. Mehler's formula for $h_n(x,y|q)$ involves a ${}_3\phi_2$ sum and the Rogers formula involves a ${}_2\phi_1$ sum. The proofs of these results are based on parameter augmentation with respect to the $q$-exponential operator and the homogeneous $q$-shift operator in two variables. By extending recent results on the Rogers-Szeg\"{o} polynomials $h_n(x|q)$ due to Hou, Lascoux and Mu, we obtain another Rogers-type formula for $h_n(x,y|q)$. Finally, we give a change of base formula for $H_n(x;a|q)$ which can be used to evaluate some integrals by using the Askey-Wilson integral.Comment: 16 pages, revised version, to appear in J. Phys. A: Math. Theo