164,640 research outputs found
Estimating the impact of whaling on global whale watching
After the commercial whaling moratorium was enacted in 1986, whale watching became one of the fastest growing tourism industries worldwide. As whaling was regarded as an activity incompatible with whale watching, the possible resumption of commercial whaling caused an urgent need to investigate the potential negative effects of whaling on the whale-watching industry. We examine the potential impacts of whaling on the global whale-watching tourism industry using unbalanced panel data model. The empirical results indicate that the resumption of commercial whaling has the potential for a negative effect on the global whale-watching industry, especially for nations that are engaged in whaling.delay-difference equation model;global whale watching;whaling
Aharonov-Bohm oscillations in the local density of states
The scattering of electrons with inhomogeneities produces modulations in the
local density of states of a metal. We show that electron interference
contributions to these modulations are affected by the magnetic field via the
Aharonov-Bohm effect. This can be exploited in a simple STM setup that serves
as an Aharonov-Bohm interferometer at the nanometer scale.Comment: 4 pages, 2 figures. v2 added reference
Thermodynamical Properties and Quasi-localized Energy of the Stringy Dyonic Black Hole Solution
In this article, we calculate the heat flux passing through the horizon and the difference of energy between the Einstein and
M{\o}ller prescription within the region , in which is the region
between outer horizon and inner horizon , for the
modified GHS solution, KLOPP solution and CLH solution. The formula . E_{\rm
Einstein}|_{\cal M} = . E_{\rm M{\o}ller}|_{\cal M} - \sum_{\partial {\cal M}}
{\bf TS}$ is obeyed for the mGHS solution and the KLOPP solution, but not for
the CLH solution. Also, we suggest a RN-like stringy dyonic black hole
solution, which comes from the KLOPP solution under a dual transformation, and
its thermodynamical properties are the same as the KLOPP solution
Investigating the Physical Origin of Unconventional Low-Energy Excitations and Pseudogap Phenomena in Cuprate Superconductors
We investigate the physical origin of unconventional low-energy excitations
in cuprate superconductors by considering the effect of coexisting competing
orders (CO) and superconductivity (SC) and of quantum fluctuations and other
bosonic modes on the low-energy charge excitation spectra. By incorporating
both SC and CO in the bare Green's function and quantum phase fluctuations in
the self-energy, we can consistently account for various empirical findings in
both the hole- and electron-type cuprates, including the excess subgap
quasiparticle density of states, ``dichotomy'' in the fluctuation-renormalized
quasiparticle spectral density in momentum space, and the occurrence and
magnitude of a low-energy pseudogap being dependent on the relative gap
strength of CO and SC. Comparing these calculated results with experiments of
ours and others, we suggest that there are two energy scales associated with
the pseudogap phenomena, with the high-energy pseudogap probably of magnetic
origin and the low-energy pseudogap associated with competing orders.Comment: 10 pages, 5 figures. Invited paper for the 2006 Taiwan International
Conference on Superconductivity. Correspondence author: Nai-Chang Yeh
(e-mail: [email protected]
Spectroscopic characterization of the oxo-transfer reaction from a bis(µ-oxo)dicopper(III) complex to triphenylphosphine
The oxygen-atom transfer reaction from the bis(µ-oxo)dicopper(III) complex [CuIII2(µ-O)2(L)2]2+1, where L =N,N,N,N -tetraethylethylenediamine, to PPh3 has been studied by UV-vis, EPR, 1H NMR and Cu K-edge X-ray absorption spectroscopy in parallel at low temperatures (193 K) and above. Under aerobic conditions (excess dioxygen), 1 reacted with PPh3, giving OPPh3 and a diamagnetic species that has been assigned to an oxo-bridged dicopper(II) complex on the basis of EPR and Cu K-edge X-ray absorption spectroscopic data. Isotope-labeling experiments (18O2) established that the oxygen atom incorporated into the triphenylphosphine oxide came from both complex 1 and exogenous dioxygen. Detailed kinetic studies revealed that the process is a third-order reaction; the rate law is first order in both complex 1 and triphenylphosphine, as well as in dioxygen. At temperatures above 233 K, reaction of 1 with PPh3 was accompanied by ligand degradation, leading to oxidative N-dealkylation of one of the ethyl groups. By contrast, when the reaction was performed in the absence of excess dioxygen, negligible substrate (PPh3) oxidation was observed. Instead, highly symmetrical copper complexes with a characteristic isotropic EPR signal at g= 2.11 were formed. These results are discussed in terms of parallel reaction channels that are activated under various conditions of temperature and dioxygen
Quantitative rescattering theory for laser-induced high-energy plateau photoelectron spectra
A comprehensive quantitative rescattering (QRS) theory for describing the
production of high-energy photoelectrons generated by intense laser pulses is
presented. According to the QRS, the momentum distributions of these electrons
can be expressed as the product of a returning electron wave packet with the
elastic differential cross sections (DCS) between free electrons with the
target ion. We show that the returning electron wave packets are determined
mostly by the lasers only, and can be obtained from the strong field
approximation. The validity of the QRS model is carefully examined by checking
against accurate results from the solution of the time-dependent Schr\"odinger
equation for atomic targets within the single active electron approximation. We
further show that experimental photoelectron spectra for a wide range of laser
intensity and wavelength can be explained by the QRS theory, and that the DCS
between electrons and target ions can be extracted from experimental
photoelectron spectra. By generalizing the QRS theory to molecular targets, we
discuss how few-cycle infrared lasers offer a promising tool for dynamic
chemical imaging with temporal resolution of a few femtoseconds.Comment: 19 pages, 19 figure
Growth of aligned carbon nanotubes on carbon microfibers by dc plasma-enhanced chemical vapor deposition
It is shown that unidirectionally aligned carbon nanotubes can be grown on electrically conductive network of carbon microfibers via control of buffer layer material and applied electric field during dc plasma chemical vapor deposition growth. Ni catalyst deposition on carbon microfiber produces relatively poorly aligned nanotubes with significantly varying diameters and lengths obtained. The insertion of Ti 5 nm thick underlayer between Ni catalyst layer and C microfiber substrate significantly alters the morphology of nanotubes, resulting in much better aligned, finer diameter, and longer array of nanotubes. This beneficial effect is attributed to the reduced reaction between Ni and carbon paper, as well as prevention of plasma etching of carbon paper by inserting a Ti buffer layer. Such a unidirectionally aligned nanotube structure on an open-pore conductive substrate structure may conveniently be utilized as a high-surface-area base electrodes for fuel cells, batteries, and other electrochemical and catalytic reactions
Extremely sharp carbon nanocone probes for atomic force microscopy imaging
A simple and reliable catalyst patterning technique combined with electric-field-guided growth is utilized to synthesize a sharp and high-aspect-ratio carbon nanocone probe on a tipless cantilever for atomic force microscopy. A single carbon nanodot produced by an electron-beam-induced deposition serves as a convenient chemical etch mask for catalyst patterning, thus eliminating the need for complicated, resist-based, electron-beam lithography for a nanoprobe fabrication. A gradual, sputtering-induced size reduction and eventual removal of the catalyst particle at the probe tip during electric-field-guided growth creates a sharp probe with a tip radius of only a few nanometers. These fabrication processes are amenable for the wafer-scale synthesis of multiple probes. High resolution imaging of three-dimensional features and deep trenches, and mechanical durability enabling continuous operation for many hours without noticeable image deterioration have been demonstrated
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