2,190 research outputs found
Few-Body Bound Complexes in One-dimensional Dipolar Gases and Non-Destructive Optical Detection
We consider dipolar interactions between heteronuclear molecules in
low-dimensional geometries. The setup consists of two one-dimensional tubes. We
study the stability of possible few-body complexes in the regime of repulsive
intratube interaction, where the binding arises from intertube attraction. The
stable dimers, trimers, and tetramers are found and we discuss their properties
for both bosonic and fermionic molecules. To observe these complexes we propose
an optical non-destructive detection scheme that enables in-situ observation of
the creation and dissociation of the few-body complexes. A detailed description
of the expected signal of such measurements is given using the numerically
calculated wave functions of the bound states. We also discuss implications on
the many-body physics of dipolar systems in tubular geometries, as well as
experimental issues related to the external harmonic confinement along the tube
and the prospect of applying an in-tube optical lattice to increase the
effective dipole strength.Comment: 16 pages, 15 figures, published versio
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Hardware Validation for Control of Three-Phase Grid-Connected Microgrids Using Artificial Neural Networks
This paper presents a strategy for controlling inverter-interfaced DERs within a microgrid using an artificial neural network. The neural network implements a dynamic programming algorithm and is trained with a new Levenberg-Marquardt backpropagation algorithm. Hardware experiments were conducted to evaluate the performance of the neural network vector control method. They showed that the neural network control technique performs well for DER converter control if the controller output voltage is below the converter’s PWM saturation limit. If the controller’s output voltage exceeds the PWM saturation limit, the neural network controller automatically turns into a state by maintaining a constant dc-link voltage as its first priority, while meeting the reactive power control demand as soon as possible. Under variable, unbalanced, and distorted system conditions, the neural network controller is stable and reliable
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Control of Three-Phase Grid-Connected Microgrids Using Artificial Neural Networks
A microgrid consists of a variety of inverter-interfaced distributed energy resources (DERs). A key issue is how to control DERs within the microgrid and how to connect them to or disconnect them from the microgrid quickly. This paper presents a strategy for controlling inverter-interfaced DERs within a microgrid using an artificial neural network, which implements a dynamic programming algorithm and is trained with a new Levenberg-Marquardt backpropagation algorithm. Compared to conventional control methods, our neural network controller exhibits fast response time, low overshoot, and, in general, the best performance. In particular, the neural network controller can quickly connect or disconnect inverter-interfaced DERs without the need for a synchronization controller, efficiently track fast-changing reference commands, tolerate system disturbances, and satisfy control requirements at grid-connected mode, islanding mode, and their transition
Hydrogeology, Hydrogeochemistry, and Spoil Settlement at a Large Mine-Spoil Area in Eastern Kentucky: Star Fire Tract
An applied research program at the Star Fire surface mine in eastern Kentucky, owned and operated by Cypress-AMAX Coal Co., defined spoil characteristics to develop and monitor water resources, which will help identify a reliable water supply for future property development. Water stored in the mine spoil may provide a usable ground-water supply, and the spoil could also be engineered to provide base flow to surfacewater reservoirs.
Ground-water recharge enters the spoil by way of sinking streams, ground-water flow from bedrock in contact with the mine spoil, and a specially designed infiltration basin. Ground water discharges predominantly from springs and seeps along the northwestern outslope of the spoil.
A conceptual model of ground-water flow, based on data from monitoring wells, discharge from springs and ponds, dye tracing, hydraulic gradients, and field reconnaissance, indicates that ground water moves slowly in the spoil interior, where it must flow down into the valley fills before discharging out of the spoil. Two saturated zones have been established: the first in the spoil interior, and the second in the valley fills that surround the main spoil body at lower elevations. The saturated zone in the valley fills contains fresher water than the zone in the spoil interior and exhibits more water-level fluctuation because of efficient recharge pathways along the spoil’s periphery at the spoil-highwall contact. The average saturated thickness of the valley fill areas (30.1 ft) is approximately twice the average saturated thickness found in the spoil’s interior (15.4 ft). Spatial water-quality variations are consistent with those predicted in the proposed flow system.
Based on an estimated average saturated thickness of 21 ft for the entire site, the saturated spoil stores 4,200 acre-ft (1.4 billion gallons) of water. Hydraulic-conductivity (K) values derived from slug tests range from 2.0 Ă— 10-6 to more than 2.9 Ă— 10-5 ft/sec, and are consistent with hydraulic-conductivity data for other spoil areas where similar mining methods are used.
Water samples taken from wells and springs indicate that the ground water is a calcium-magnesium-sulfate type, differing mainly in the total concentration of these constituents at various locations. Mineral saturation indices calculated using the geochemical model PHREEQE indicate that most of the ground water is near equilibrium with gypsum. Nearly all the water samples had pH measurements in a favorable range between 6.0 and 7.0, indicating that the spoil does not produce highly acidic water.
Measurements of vertical displacement around the monitoring-well surface casings indicate that differential settlement is occurring within the mine spoil. The most rapid settlement occurs in the most recently placed spoil near the active mining pit
Ground Water in the Kentucky River Basin
Most private wells in the Kentucky River Basin are in unconfined or semi-confined bedrock aquifers. Within these aquifers, high-yield zones are irregularly distributed. The most productive wells are drilled into fractured bedrock and alluvium along the Kentucky River floodplain. The data indicate that ground water acts as a buffer to peak and low flows in Kentucky River Basin streams. At current withdrawal rates, ground-water usage does not seem to have an adverse impact on the Kentucky River. Privately owned ground-water sources supply approximately 135,000 people living in the basin-approximately 19 percent of the total population and 36 percent of the rural population. More than 50 percent of residential water supplies in eastern Kentucky rely on ground water. If aquifers are protected from pollution by wellhead protection programs and old wells are retrofitted to prevent direct contamination, then ground water will continue to provide a reliable water supply in many rural areas of the basin. However, for most of the basin, few wells will have yields adequate to supply a large demand. Ground water from present wells will not provide an adequate supply for communities with a population of over a few thousand. Limited discharge data available for springs and large wells in the basin strongly suggest that the potential for ground water to supplement current supplies should not be ignored. Discharge from well fields and springs could be used to augment surface supplies during drought. A better understanding of the distribution and quality of ground-water resources is crucial for the citizens of the basin to fully benefit from ground water
The curvature of semidirect product groups associated with two-component Hunter-Saxton systems
In this paper, we study two-component versions of the periodic Hunter-Saxton
equation and its -variant. Considering both equations as a geodesic flow
on the semidirect product of the circle diffeomorphism group \Diff(\S) with a
space of scalar functions on we show that both equations are locally
well-posed. The main result of the paper is that the sectional curvature
associated with the 2HS is constant and positive and that 2HS allows for a
large subspace of positive sectional curvature. The issues of this paper are
related to some of the results for 2CH and 2DP presented in [J. Escher, M.
Kohlmann, and J. Lenells, J. Geom. Phys. 61 (2011), 436-452].Comment: 19 page
The geometry of a vorticity model equation
We provide rigorous evidence of the fact that the modified
Constantin-Lax-Majda equation modeling vortex and quasi-geostrophic dynamics
describes the geodesic flow on the subgroup of orientation-preserving
diffeomorphisms fixing one point, with respect to right-invariant metric
induced by the homogeneous Sobolev norm and show the local existence
of the geodesics in the extended group of diffeomorphisms of Sobolev class
with .Comment: 24 page
Resolvent estimates for normally hyperbolic trapped sets
We give pole free strips and estimates for resolvents of semiclassical
operators which, on the level of the classical flow, have normally hyperbolic
smooth trapped sets of codimension two in phase space. Such trapped sets are
structurally stable and our motivation comes partly from considering the wave
equation for Kerr black holes and their perturbations, whose trapped sets have
precisely this structure. We give applications including local smoothing
effects with epsilon derivative loss for the Schr\"odinger propagator as well
as local energy decay results for the wave equation.Comment: Further changes to erratum correcting small problems with Section 3.5
and Lemma 4.1; this now also corrects hypotheses, explicitly requiring
trapped set to be symplectic. Erratum follows references in this versio
Carbon and climate system coupling on timescales from the Precambrian to the Anthropocene
Author Posting. © Annual Reviews, 2007. This is the author's version of the work. It is posted here by permission of Annual Reviews for personal use, not for redistribution. The definitive version was published in Annual Review of Environment and Resources 32 (2007): 31-66, doi:10.1146/annurev.energy.32.041706.124700.The global carbon and climate systems are closely intertwined, with
biogeochemical processes responding to and driving climate variations. Over a range of
geological and historical time-scales, warmer climate conditions are associated with
higher atmospheric levels of CO2, an important climate-modulating greenhouse gas. The
atmospheric CO2-temperature relationship reflects two dynamics, the planet’s climate
sensitivity to a perturbation in atmospheric CO2 and the stability of non-atmospheric
carbon reservoirs to evolving climate. Both exhibit non-linear behavior, and coupled
carbon-climate interactions have the potential to introduce both stabilizing and
destabilizing feedback loops into the Earth System. Here we bring together evidence
from a wide range of geological, observational, experimental and modeling studies on the
dominant interactions between the carbon cycle and climate. The review is organized by
time-scale, spanning interannual to centennial climate variability, Holocene millennial
variations and Pleistocene glacial-interglacial cycles, and million year and longer
variations over the Precambrian and Phanerozoic. Our focus is on characterizing and,
where possible quantifying, the emergent behavior internal to the coupled carbon-climate
system as well as the responses of the system to external forcing from tectonics, orbital
dynamics, catastrophic events, and anthropogenic fossil fuel emissions. While there are
many unresolved uncertainties and complexity in the carbon cycle, one emergent
property is clear across time scales: while CO2 can increase in the atmosphere quickly,
returning to lower levels through natural processes is much slower, so the consequences
of the human perturbation will far outlive the emissions that caused them.S. Doney acknowledges support from the NSF Geosciences Carbon and Water program
(NSF ATM-0628582) and the WHOI W. Van Alan Clark Sr. Chair. D. Schimel
acknowledges support from the NSF Biocomplexity in the Environment program (NSF
EAR-0321918)
Plasmons in layered structures including graphene
We investigate the optical properties of layered structures with graphene at
the interface for arbitrary linear polarization at finite temperature including
full retardation by working in the Weyl gauge. As a special case, we obtain the
full response and the related dielectric function of a layered structure with
two interfaces. We apply our results to discuss the longitudinal plasmon
spectrum of several single and double layer devices such as systems with finite
and zero electronic densities. We further show that a nonhomogeneous dielectric
background can shift the relative weight of the in-phase and out-of-phase mode
and discuss how the plasmonic mode of the upper layer can be tuned into an
acoustic mode with specific sound velocity.Comment: 18 pages, 6 figure
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