41,619 research outputs found
Metal-Semiconductor Transition and Fermi Velocity Renormalization in Metallic Carbon Nanotubes
Angular perturbations modify the band structure of armchair (and other
metallic) carbon nanotubes by breaking the tube symmetry and may induce a
metal-semiconductor transition when certain selection rules are satisfied. The
symmetry requirements apply for both the nanotube and the perturbation
potential, as studied within a nonorthogonal -orbital tight-binding
method. Perturbations of two categories are considered: an on-site
electrostatic potential and a lattice deformation which changes the off-site
hopping integrals. Armchair nanotubes are proved to be robust against the
metal-semiconductor transition in second-order perturbation theory due to their
high symmetry, but can develop a nonzero gap by extending the perturbation
series to higher orders or by combining potentials of different types. An
assumption of orthogonality between orbitals is shown to lead to an
accidental electron-hole symmetry and extra selection rules that are weakly
broken in the nonorthogonal theory. These results are further generalized to
metallic nanotubes of arbitrary chirality.Comment: Submitted to Phys. Rev. B, 23 pages, 4 figure
Two Higgs Bi-doublet Model With Spontaneous P and CP Violation and Decoupling Limit to Two Higgs Doublet Model
The two Higgs bi-doublet left-right symmetric model (2HBDM) as a simple
extension of the minimal left-right symmetric model with a single Higgs
bi-doublet is motivated to realize both spontaneous P and CP violation while
consistent with the low energy phenomenology without significant fine tuning.
By carefully investigating the Higgs potential of the model, we find that
sizable CP-violating phases are allowed after the spontaneous symmetry
breaking. The mass spectra of the extra scalars in the 2HBDM are significantly
different from the ones in the minimal left-right symmetric model. In
particular, we demonstrate in the decoupling limit when the right-handed gauge
symmetry breaking scale is much higher than the electroweak scale, the 2HBDM
decouples into general two Higgs doublet model (2HDM) with spontaneous CP
violation and has rich induced sources of CP violation. We show that in the
decoupling limit, it contains extra light Higgs bosons with masses around
electroweak scale, which can be directly searched at the ongoing LHC and future
ILC experiments.Comment: 19 pages, discussions on fine-tuning problem added. Version to appear
in Phys.Rev.
Metallic Triple Beam Resonator with Thick-film Printed Drive and Pickup
A triple beam resonator fabricated in 430S17 stainless steel with thick-film piezoelectric elements to drive and detect the vibrations is presented. The resonator substrate was fabricated by a simultaneous, double-sided photochemical etching technique and the thick-film piezoelectric elements were deposited by a standard screen-printing process. The combination of these two batch-fabrication processes provides the opportunity for mass production of the device at low cost. The resonator, a dynamically balanced triple beam tuning fork (TBTF) structure 23.5 mm long and 6.5 mm wide, has a favoured mode at 4.96 kHz with a Q-factor of 3630 operating in air
Collective synchronization induced by epidemic dynamics on complex networks with communities
Much recent empirical evidence shows that \textit{community structure} is
ubiquitous in the real-world networks. In this Letter, we propose a growth
model to create scale-free networks with the tunable strength (noted by ) of
community structure and investigate the influence of community strength upon
the collective synchronization induced by SIRS epidemiological process. Global
and local synchronizability of the system is studied by means of an order
parameter and the relevant finite-size scaling analysis is provided. The
numerical results show that, a phase transition occurs at from
global synchronization to desynchronization and the local synchronization is
weakened in a range of intermediately large . Moreover, we study the impact
of mean degree upon synchronization on scale-free networks.Comment: 5 pages, 4 figures. to appeared in Phys. Rev. E 75 (2007
Methods of Nature: Landscapes from the Gettysburg College Collection
Methods of Nature: Landscapes from the Gettysburg College Collection is the third annual exhibition curated by students enrolled in the Art History Methods course. The exhibition is an exciting academic endeavor and incredible opportunity for engaged learning, research, and curatorial experience. The five student curators are Molly Chason ’17, Leah Falk ’18, Shannon Gross ’17, Bailey Harper ’19 and Laura Waters ’19. The selection of artworks in this exhibition includes the depiction of landscape in the nineteenth- and twentieth-century French, American and East Asian cultural traditions in various art forms from traditional media of paintings and prints to utilitarian artifacts of porcelain and a paper folding fan. Landscape paintings in this exhibition are inspired by nature, specific locales and literature. Each object carries a distinctive characteristic, a mood, and an ambience. Collectively, they present a multifaceted view of the landscape in the heart and mind of the artists and intended viewers. [excerpt]https://cupola.gettysburg.edu/artcatalogs/1020/thumbnail.jp
Case-control study of arsenic in drinking water and lung cancer in California and Nevada.
Millions of people are exposed to arsenic in drinking water, which at high concentrations is known to cause lung cancer in humans. At lower concentrations, the risks are unknown. We enrolled 196 lung cancer cases and 359 controls matched on age and gender from western Nevada and Kings County, California in 2002-2005. After adjusting for age, sex, education, smoking and occupational exposures, odds ratios for arsenic concentrations ≥85 µg/L (median = 110 µg/L, mean = 173 µg/L, maximum = 1,460 µg/L) more than 40 years before enrollment were 1.39 (95% CI = 0.55-3.53) in all subjects and 1.61 (95% CI = 0.59-4.38) in smokers. Although odds ratios were greater than 1.0, these increases may have been due to chance given the small number of subjects exposed more than 40 years before enrollment. This study, designed before research in Chile suggested arsenic-related cancer latencies of 40 years or more, illustrates the enormous sample sizes needed to identify arsenic-related health effects in low-exposure countries with mobile populations like the U.S. Nonetheless, our findings suggest that concentrations near 100 µg/L are not associated with markedly high relative risks
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