205 research outputs found
Curvature, hybridization, and STM images of carbon nanotubes
The curvature effects in carbon nanotubes are studied analytically as a
function of chirality. The pi-orbitals are found to be significantly
rehybridized in all tubes, so that they are never normal to the tubes' surface.
This results in a curvature induced gap in the electronic band-structure, which
turns out to be larger than previous estimates. The tilting of the pi-orbitals
should be observable by atomic resolution scanning tunneling microscopy
measurements.Comment: Four pages in revtex format including four epsfig-embedded figures.
The latest version in PDF format is available from
http://fy.chalmers.se/~eggert/papers/hybrid.pd
Electronic Structure of Carbon Nanotube Ropes
We present a tight binding theory to analyze the motion of electrons between
carbon nanotubes bundled into a carbon nanotube rope. The theory is developed
starting from a description of the propagating Bloch waves on ideal tubes, and
the effects of intertube motion are treated perturbatively in this basis.
Expressions for the interwall tunneling amplitudes between states on
neighboring tubes are derived which show the dependence on chiral angles and
intratube crystal momenta. We find that conservation of crystal momentum along
the tube direction suppresses interwall coherence in a carbon nanorope
containing tubes with random chiralities. Numerical calculations are presented
which indicate that electronic states in a rope are localized in the transverse
direction with a coherence length corresponding to a tube diameter.Comment: 15 pages, 10 eps figure
Mechanically induced current and quantum evaporation from Luttinger liquids
We investigate transport through a tunnelling junction between an
uncorrelated metallic lead and a Luttinger liquid when the latter is subjected
to a time dependent perturbation. The tunnelling current as well as the
electron energy distribution function are found to be strongly affected by the
perturbation due to generation of harmonics in the density oscillations. Using
a semiconducting lead instead of a metallic one results in electrons being
injected into the lead even without applied voltage. Some applications to
carbon nanotubes are discussed.Comment: 7 pages, 2 figures (eps files
``X-Ray Edge'' Singularities in Nanotubes and Quantum Wires with Multiple Subbands
Band theory predicts an inverse square root van Hove singularity in the
tunneling density of states at the minimum energy of an unoccupied subband in a
one-dimensional quantum wire. With interactions, an orthogonality catastrophe
analogous to the x-ray edge effect for core levels in a metal strongly reduces
this singularity by a power B of the energy above threshold, with B
approximately 0.3 for typical carbon nanotubes. Despite the anomalous tunneling
characteristic, good quasiparticles corresponding to the unoccupied subband
states do exist.Comment: 4 page
Charge Screening Effect in Metallic Carbon Nanotubes
Charge screening effect in metallic carbon nanotubes is investigated in a
model including the one-dimensional long-range Coulomb interaction. It is
pointed out that an external charge which is being fixed spatially is screened
by internal electrons so that the resulting object becomes electrically
neutral. We found that the screening length is given by about the diameter of a
nanotube.Comment: 11 pages, 6 figure
Topological Phase Transition and Electrically Tunable Diamagnetism in Silicene
Silicene is a monolayer of silicon atoms forming a honeycomb lattice. The
lattice is actually made of two sublattices with a tiny separation. Silicene is
a topological insulator, which is characterized by a full insulating gap in the
bulk and helical gapless edges. It undergoes a phase transition from a
topological insulator to a band insulator by applying external electric field.
Analyzing the spin Chern number based on the effective Dirac theory, we find
their origin to be a pseudospin meron in the momentum space. The peudospin
degree of freedom arises from the two-sublattice structure. Our analysis makes
clear the mechanism how a phase transition occurs from a topological insulator
to a band insulator under increasing electric field. We propose a method to
determine the critical electric field with the aid of diamagnetism of silicene.
Diamagnetism is tunable by the external electric field, and exhibits a singular
behaviour at the critical electric field. Our result is important also from the
viewpoint of cross correlation between electric field and magnetism. Our
finding will be important for future electro-magnetic correlated devices.Comment: 4 pages,5 figure
Coupled Hartree-Fock-Bogoliubov kinetic equations for a trapped Bose gas
Using the Kadanoff-Baym non-equilibrium Green's function formalism, we derive
the self-consistent Hartree-Fock-Bogoliubov (HFB) collisionless kinetic
equations and the associated equation of motion for the condensate wavefunction
for a trapped Bose-condensed gas. Our work generalizes earlier work by Kane and
Kadanoff (KK) for a uniform Bose gas. We include the off-diagonal (anomalous)
pair correlations, and thus we have to introduce an off-diagonal distribution
function in addition to the normal (diagonal) distribution function. This
results in two coupled kinetic equations. If the off-diagonal distribution
function can be neglected as a higher-order contribution, we obtain the
semi-classical kinetic equation recently used by Zaremba, Griffin and Nikuni
(based on the simpler Popov approximation). We discuss the static local
equilibrium solution of our coupled HFB kinetic equations within the
semi-classical approximation. We also verify that a solution is the rigid
in-phase oscillation of the equilibrium condensate and non-condensate density
profiles, oscillating with the trap frequency.Comment: 25 page
Luttinger Parameter g for Metallic Carbon Nanotubes and Related Systems
The random phase approximation (RPA) theory is used to derive the Luttinger
parameter g for metallic carbon nanotubes. The results are consistent with the
Tomonaga-Luttinger models. All metallic carbon nanotubes, regardless if they
are armchair tubes, zigzag tubes, or chiral tubes, should have the same
Luttinger parameter g. However, a (10,10) carbon peapod should have a smaller g
value than a (10,10) carbon nanotube. Changing the Fermi level by applying a
gate voltage has only a second order effect on the g value. RPA theory is a
valid approach to calculate plasmon energy in carbon nanotube systems,
regardless if the ground state is a Luttinger liquid or Fermi liquid. (This
paper was published in PRB 66, 193405 (2002). However, Eqs. (6), (9), and (19)
were misprinted there.)Comment: 2 figure
Hydrology and Meteorology of the Central Alaskan Arctic: Data Collection and Analysis
The availability of environmental data for unpopulated areas of Alaska can best be described as
sparse; however, these areas have resource development potential. The central Alaskan Arctic
region north of the Brooks Range (referred to as the North Slope) is no exception in terms of
both environmental data and resource potential. This area was the focus of considerable oil/gas
exploration immediately following World War II. Unfortunately, very little environmental data
were collected in parallel with the exploration. Soon after the oil discovery at Prudhoe Bay in
November 1968, the U.S. Geological Survey (USGS) started collecting discharge data at three
sites in the neighborhood of Prudhoe Bay and one small watershed near Barrow. However, little
complementary meteorological data (like precipitation) were collected to support the streamflow
observations. In 1985, through a series of funded research projects, researchers at the University
of Alaska Fairbanks (UAF), Water and Environmental Research Center (WERC), began
installing meteorological stations on the North Slope in the central Alaskan Arctic. The number
of stations installed ranged from 1 in 1985 to 3 in 1986, 12 in 1996, 24 in 2006, 23 in 2010, and
7 in 2014. Researchers from WERC also collected hydrological data at the following streams:
Imnavait Creek (1985 to present), Upper Kuparuk River (1993 to present), Putuligayuk River
(1999 to present, earlier gauged by USGS), Kadleroshilik River (2006 to 2010), Shaviovik River
(2006 to 2010), No Name River (2006 to 2010), Chandler River (2009 to 2013), Anaktuvuk
River (2009 to 2013), Lower Itkillik River (2012 to 2013), and Upper Itkillik River (2009 to
2013). These catchments vary in size, and runoff generation can emanate from the coastal plain,
the foothills or mountains, or any combination of these locations. Snowmelt runoff in late
May/early June is the most significant hydrological event of the year, except at small watersheds.
For these watersheds, rain/mixed snow events in July and August have produced the floods of
record. Ice jams are a major concern, especially in the larger river systems. Solid cold season
precipitation is mostly uniform over the area, while warm season precipitation is greater in the
mountains and foothills than on the coastal plain (roughly 3:2:1, mountains:foothills:
coastal plain).The results reported here are primarily for the drainages of the Itkillik, Anaktuvuk,
and Chandler River basins, where a proposed transportation corridor is being considered. Results
for 2011 and before can be found in earlier reports.ABSTRACT ..................................................................................................................................... i
LIST OF FIGURES ........................................................................................................................ v
LIST OF TABLES .......................................................................................................................... x
ACKNOWLEDGMENTS AND DISCLAIMER ........................................................................ xiii
CONVERSION FACTORS, UNITS, WATER QUALITY UNITS, VERTICAL AND
HORIZONTAL DATUM, ABBREVIATIONS, AND SYMBOLS ........................................... xiv
ABBREVIATIONS, ACRONYMS, AND SYMBOLS .............................................................. xvi
1 INTRODUCTION ................................................................................................................... 1
2 PRIOR RELATED PUBLICATIONS .................................................................................... 5
3 STUDY AREA ........................................................................................................................ 7
4 PREVIOUS STUDIES .......................................................................................................... 11
5 METHODOLOGY AND EQUIPMENT .............................................................................. 15
5.1 Acoustic Doppler Current Profiler ................................................................................. 17
5.2 Discharge Measurements ............................................................................................... 17
5.3 Suspended Sediments ..................................................................................................... 20
5.3.1 River Sediment ........................................................................................................ 21
5.3.2 Suspended Sediment Observations ......................................................................... 21
5.3.3 Suspended Sediment Discharge .............................................................................. 22
5.3.4 Turbidity ................................................................................................................. 23
5.3.5 Bed Sediment Distribution ...................................................................................... 23
5.3.6 Suspended Sediment Grain-Size Distribution ........................................................ 24
6 RESULTS .............................................................................................................................. 25
6.1 Air Temperature and Relative Humidity ........................................................................ 25
6.2 Wind Speed and Direction ............................................................................................. 30
6.3 Net Radiation .................................................................................................................. 38
6.4 Warm Season Precipitation ............................................................................................ 40
6.5 Cold Season Precipitation .............................................................................................. 46
6.6 Annual Precipitation ....................................................................................................... 52
6.7 Soil ................................................................................................................................. 55
6.7.1 Soil Temperature ..................................................................................................... 56
6.7.1.1 Results ................................................................................................................. 57
6.7.2 Soil Moisture ........................................................................................................... 60
6.7.2.1 Results ................................................................................................................. 61
6.8 North Slope Climatology ............................................................................................... 63
6.8.1 Air Temperature ...................................................................................................... 63
6.8.2 Precipitation ............................................................................................................ 65
6.8.2.1 Warm Season Precipitation ................................................................................. 65
6.8.2.2 Cold Season Precipitation ................................................................................... 68
6.8.2.3 Annual Total Precipitation .................................................................................. 70
6.9 Surface Water Hydrology ............................................................................................... 72
6.9.1 Itkillik River ............................................................................................................ 73
6.9.2 Upper Itkillik River ................................................................................................. 74
6.9.2.1 Dye Trace Results, Upper Itkillik River .............................................................. 81
6.9.3 Lower Itkillik River 2013 Breakup and Spring Flood ............................................ 84
6.9.4 Anaktuvuk River ..................................................................................................... 91
6.9.5 Chandler River ...................................................................................................... 100
6.9.6 Additional Field Observations .............................................................................. 107
6.10 River Sediment Results ................................................................................................ 117
6.10.1 Correlation between Isco and Depth-Integrated Samples ..................................... 117
6.10.2 Suspended Sediment Rating Curves ..................................................................... 118
6.10.3 Suspended Sediment Concentrations .................................................................... 119
6.10.4 Suspended Sediment Discharge ............................................................................ 125
6.10.5 Turbidity ............................................................................................................... 129
6.10.6 Bed Sediment Distribution .................................................................................... 134
6.10.7 Suspended Sediment Grain-Size Distribution ...................................................... 136
7 HYDROLOGIC ANALYSIS .............................................................................................. 139
7.1 Precipitation Frequency Analysis ................................................................................. 139
7.2 Manning’s Roughness Coefficient (n) Calculations Revisited .................................... 142
7.3 Hydrological Modeling ................................................................................................ 147
8 CONCLUSIONS ................................................................................................................. 157
9 REFERENCES .................................................................................................................... 163
10 APPENDICES ..................................................................................................................... 169
Appendix A – Air Temperature and Relative Humidity
Appendix B – Wind Speed and Direction: Wind Roses
Appendix C – Cumulative Warm Season Precipitation for All Years at Each Station and
Cumulative Warm Season Precipitation by Year for All Stations, 2007 to 2013
Appendix D – Soil Temperature and Moisture Content
Appendix E – Rating Curves and Discharge Measurement Summarie
Van Hove Singularities in disordered multichannel quantum wires and nanotubes
We present a theory for the van Hove singularity (VHS) in the tunneling
density of states (TDOS) of disordered multichannel quantum wires, in
particular multi-wall carbon nanotubes. We assume close-by gates which screen
off electron-electron interactions. Diagrammatic perturbation theory within a
non-crossing approximation yields analytical expressions governing the
disorder-induced broadening and shift of VHS's as new subbands are opened. This
problem is nontrivial because the (lowest-order) Born approximation breaks down
close to the VHS. Interestingly, compared to the bulk case, the boundary TDOS
shows drastically altered VHS, even in the clean limit.Comment: 4 pages, 2 figures, accepted with revisions in PR
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