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ABSTRACT: Based on the density functional theory, we obtain the optimum geometry of carbon chain inside a carbon nanotube. The phonon spectrum and specific heat of such a chain and nanotube hybrid system are calculated in terms of lattice dynamics theory. Some new phonon branches that have been obtained come from the coupling vibrations of the nanotube and the chain. The bending and stretching modes of the chain appear at about 520 cm(-1)and 1935 cm(-1) at Gamma point, respectively. It is found that the softening of G modes results mainly from the chain induced variations in the bond length on nanotube, independent of van der Waals interaction, while the stiffening of radial breathing mode is developed by the competition between the two factors. In the low-frequency region, the vibrational density of states are very different from that of the bare nanotube. Its specific heat implies the underlying quantized phonon structures and much large thermal conductivity in the hybrid system. In addition, the chain-length dependent vibration modes are calculated, from which it is expected that a finite chain of about 14 carbon atoms in the nanotube may produce the experimental Raman peak at about 1850 cm(-1).
The Journal of Physical Chemistry B 12/2006; 110(43):21803-7. · 3.70 Impact Factor
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ABSTRACT: Using first-principles calculations, we investigate the structural stability and electronic properties of the smallest (2,2) carbon nanotube as the inner wall of the double-walled carbon nanotubes. The results indicate that an isolated (2,2) carbon nanotube is unstable upon unrolling in free space, while it can exist within (6,6) and, especially, within (7,7) carbon nanotubes. In addition, a spontaneous symmetry breaking of the isolated (2,2) nanotube produces an energy gap at Fermi level converting it into a semiconductor.
Phys. Rev. B. 01/2005; 71(3).
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ABSTRACT: Using first-principles calculations, we investigate the comparative stability of sub-0.4 nm carbon nanotubes. Compared to the fullerenes C20 and C60, it is found that the most likely carbon nanotubes with a small diameter 0.3 nm are (2,2),(3,1) and (4,0) nanotubes. The spontaneous symmetry breaking of an isolated (2,2) nanotube produces an energy gap at the Fermi level converting it into a semiconductor. The curvature effects lowered the π* band to cross the Fermi energy, leading to the (4,0) nanotube being metallic.
Nanotechnology 06/2004; 15(8):1000. · 3.98 Impact Factor
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ABSTRACT: Based on a force constant model, we have calculated the phonon spectrum and specific heat of single-walled boron nitride nanotubes. Compared with carbon nanotubes, boron nitride nanotubes have a larger specific heat. The fitting formulas for diameter and chirality dependence of specific heat at 300 K are given. © 2004 American Institute of Physics.
Applied Physics Letters 05/2004; 84(23):4626-4628. · 3.84 Impact Factor
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ABSTRACT: Equilibrium geometries, stabilities, and electronic properties of TinAl (n = 1-13) clusters have been studied by using density-functional theory with local spin density approximation and generalized gradient approximation. The ground-state structures of TinAl clusters have been obtained. The resulting geometries show that the aluminum atom remains on the surface of clusters for n < 9, but is slowly getting trapped beyond n = 9, meanwhile, the Al atom exhibits a valent transition from monovalent to trivalent. The geometric effects and electronic effects clearly demonstrate the Ti4Al cluster to be endowed with special stability. The studies on the bonds indicate the change from ionic to metalliclike.
The Journal of Chemical Physics 04/2004; 120(9):4251-7. · 3.33 Impact Factor
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ABSTRACT: Since 1990, regulations and standards have changed considerably. This article is an update of the regulatory requirements for the thermal treatment of various waste streams. The waste categories covered, along with the laws they are governed under, include: Hazardous waste under Subtitle C of the Resource Conservation and Recovery Act (RCRA) and under the Clean Air Act; municipal solid waste under Subtitle D of the RCRA; medical waste under Subtitle J of the RCRA; Superfund waste under the Comprehensive Environmental Response, Compensation and Liability Act (CERCLA); toxic waste under the Toxic Substances Control Act (TSCA); and sludge waste under the Clean Water Act (CWA).
Journal of Hazardous Materials 09/2000; 76(1):13-22. · 4.17 Impact Factor
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ABSTRACT: In general, toxic combustion byproducts (TCBs) are the unwanted residues remaining in flue gases, combustion ashes, and wastewaters from the operation of an incineration or combustion facility. If a combustor is not well designed and operated, it may emit too high a level of TCBs. Categories of TCBs and some example constituents are as follows: 1.1. Acid gas: HCl, NOx and SO2;2.2. Organics: Hydrocarbons such as dioxins and furans (PCDDs and PCDFs);3.3. Particulates: Trace metals (conventional metals and radioactive metals) and soots;4.4. Contaminants in ash; and5.5. Contaminants in spent wastewater.Pollutants in Category (2) above are generally considered to be the products of incomplete combustion (PICs) in the field of hazardous waste incineration.TCBs has been one of the major technical and sociological issues surrounding the use of incineration as a waste treatment alternative. Because of the complexity and controversy, the U.S. EPA issued a draft “Combustion Strategy” on May 18, 1993. The objective of the “Combustion Strategy” was to address the needs of and to outline the approaches for upgrading the existing incineration standards to better control TCB emissions.This article lists those chemicals and metals which are regulated by two major U.S. environmental laws, namely, the Clean Air Act Amendments (CAAA) of 1990 and the Resource Conservation and Recovery Act (RCRA) of 1976. The CAAA is to regulate the air emissions from major sources, and the RCRA is to protect human health and the environment from the management of solid wastes, particularly from waste incineration. This paper also lists the PIC chemicals that were studied under U.S. EPA incineration research programs in the 1980s and the PIC chemicals that EPA permit writers are considering be the subject of risk analyses during the process of industry's applying for an incinerator operating permit.
Journal of Hazardous Materials.
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ABSTRACT: Since 1990, regulations and standards have changed considerably. This article is an update of the regulatory requirements for the thermal treatment of various waste streams. The waste categories covered, along with the laws they are governed under, include:•Hazardous waste under Subtitle C of the Resource Conservation and Recovery Act (RCRA) and under the Clean Air Act (CAA);•Municipal solid waste under Subtitle D of the RCRA;•Medical waste under Subtitle J of the RCRA;•Superfund waste under the Comprehensive Environmental Response, Compensation and Liability Act (CERCLA);•Toxic waste under the Toxic Substances Control Act (TSCA);•Sludge waste under the Clean Water Act (CWA).
Journal of Hazardous Materials.
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ABSTRACT: The band structure of a single-bonded cubic phase of nitrogen has been investigated by the ab initio calculations of the pseudopotential density functional method. The basic optical constants including the dielectric function, the refractive index, the absorption, the electron energy-loss spectrum, the optical conductivity and the reflectivity of the single-bond cubic nitrogen and their dispersion properties were calculated. These theoretical results suggested that the single-bond cubic nitrogen could be a wide-gap optical material with unique properties.
Chemical Physics Letters.
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ABSTRACT: We study the equilibrium geometries and growth modes of small stoichiometric (TiO) n (n 6 9) clusters by using the ab initio calculations within the framework of density-functional theory and the generalized gradient approximation. The resulting geom-etries show that the three-dimensional ring-like structures are more favorable energetically than the cubic-like structures and clusters of (TiO) 6 and (TiO) 9 have an unusual stability. Moreover, studies show that even larger clusters could be obtained by using (TiO) 2 and (TiO) 3 rings as the building blocks. Ó 2004 Elsevier B.V. All rights reserved.
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ABSTRACT: Based on the energy of a relaxed carbon nanotube relative to the graphite sheet (graphene), we construct an analytical correction to the carbon-carbon force constants. Then, the radial breathing modes (RBM) of a number of single-walled carbon nanotubes (SWNTs) are calculated. It is found that for small diameter SWNTs, the curvature effect becomes significant and chirality dependent. Our calculated RBMs are in very good agreement with experimental measurements, especially for ultrasmall diameter SWNTs.
Phys. Rev. B. 71(23).
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ABSTRACT: The thermal properties of single-walled boron nitride nanotubes are calculated. It is found that boron nitride nanotubes have a larger specific heat than that of carbon nanotubes. The fitting formulas for diameter and chirality dependence of specific heat at 300 K are given. Moreover, thermal conductance of single-walled boron nitride nanotubes exhibits a universal quantization at low temperature, which is independent of the diameter and chirality of nanotubes.
Phys. Rev. B. 69(20).
