1,636 research outputs found
Bose-Fermi mixtures in 1D optical superlattices
The zero temperature phase diagram of binary boson-fermion mixtures in
two-colour superlattices is investigated. The eigenvalue problem associated
with the Bose-Fermi-Hubbard Hamiltonian is solved using an exact numerical
diagonalization technique, supplemented by an adaptive basis truncation scheme.
The physically motivated basis truncation allows to access larger systems in a
fully controlled and very flexible framework. Several experimentally relevant
observables, such as the matter-wave interference pattern and the
condensatefraction, are investigated in order to explore the rich phase
diagram. At symmetric half filling a phase similar to the Mott-insulating phase
in a commensurate purely bosonic system is identified and an analogy to recent
experiments is pointed out. Furthermore a phase of complete localization of the
bosonic species generated by the repulsive boson-fermion interaction is
identified. These localized condensates are of a different nature than the
genuine Bose-Einstein condensates in optical lattices.Comment: 18 pages, 9 figure
2016 Nebraska Water Leaders Academy - Final Report
The effective management of Nebraska’s water resources is evermore challenged by variations in weather, climate, technology, socioeconomic policies, and regulation. Anthropogenic climate change, declining water tables and stream flows, increasing demands on freshwater, aging water infrastructure, fiscal constraints, and impacts on aquatic organisms are particularly imminent challenges in Nebraska and around the world (Pahl-Wostl et al., 2013; Pittock et al., 2008; USACE, 2010). Sustaining freshwater ecosystem services in the face of emerging environmental threats presents an immense societal dilemma worldwide (Pittock et al., 2013; Rockström et al., 2009, Millenium Ecosystem Assessment, 2005). The rapidly changing conditions of water resources in Nebraska demands knowledgeable and skilled leaders (Burbach, et al., 2015; Lincklaen Arriëns & When de Montalvo, 2013; Morton & Brown, 2011). McIntosh and Taylor (2013) assert that in order to meet future water challenges, “leadership is needed to initiate and drive change, enable innovation (both incremental and radical), build shared visions for a more sustainable water future, and deliver these visions through aligning resources and building commitment to collective success” (p. 46). Building leadership capacity is required to drive the necessary change (Brasier et al., 2011; Morton et al., 2011; Pahl-Wostl et al., 2011; Redekop, 2010; Taylor et al., 2012). Recognizing this critical need for future leaders in water resources, the Nebraska State Irrigation Associatio
The Nebraska Water Leaders Academy: Blending Science with Research and Engagement
Nebraska faces increasing challenges to its water resources due to changing climate, mounting demand for freshwater, aging infrastructure, declining aquatic species and declining water tables and stream flows in some areas, with unprecedented floods in others. These challenges require new and innovative leadership approaches for sustainable water management. In response, the Nebraska Water Leaders Academy (NWLA) was created through a partnership between the Nebraska State Irrigation Association and the University of Nebraska-Lincoln, to prepare Nebraska’s future leaders in the water arena to meet these challenges. The NWLA was designed to offer an educational and developmental experience to mid-level professionals. Information is presented by experts from various technical disciplines in six sessions, which are held throughout the state of Nebraska over the course of one year. Topics include, but are not limited to, basic hydrology, economics, social issues and competing uses of water in Nebraska. The Academy also includes a strong leadership development component
Triple Michelson Interferometer for a Third-Generation Gravitational Wave Detector
The upcoming European design study `Einstein gravitational-wave Telescope'
represents the first step towards a substantial, international effort for the
design of a third-generation interferometric gravitational wave detector. It is
generally believed that third-generation instruments might not be installed
into existing infrastructures but will provoke a new search for optimal
detector sites. Consequently, the detector design could be subject to fewer
constraints than the on-going design of the second generation instruments. In
particular, it will be prudent to investigate alternatives to the traditional
L-shaped Michelson interferometer. In this article, we review an old proposal
to use three Michelson interferometers in a triangular configuration. We use
this example of a triple Michelson interferometer to clarify the terminology
and will put this idea into the context of more recent research on
interferometer technologies. Furthermore the benefits of a triangular detector
will be used to motivate this design as a good starting point for a more
detailed research effort towards a third-generation gravitational wave
detector.Comment: Minor corrections to the main text and two additional appendices. 14
pages, 6 figure
Stochastic Gravitational Wave Background from Coalescing Binary Black Holes
We estimate the stochastic gravitational wave (GW) background signal from the
field population of coalescing binary stellar mass black holes (BHs) throughout
the Universe. This study is motivated by recent observations of BH-Wolf-Rayet
star systems and by new estimates in the metallicity abundances of star forming
galaxies that imply BH-BH systems are more common than previously assumed.
Using recent analytical results of the inspiral-merger-ringdown waveforms for
coalescing binary BH systems, we estimate the resulting stochastic GW
background signal. Assuming average quantities for the single source energy
emissions, we explore the parameter space of chirp mass and local rate density
required for detection by advanced and third generation interferometric GW
detectors. For an average chirp mass of 8.7, we find that detection
through 3 years of cross-correlation by two advanced detectors will require a
rate density, . Combining data from
multiple pairs of detectors can reduce this limit by up to 40%. Investigating
the full parameter space we find that detection could be achieved at rates for populations of coalescing binary BH
systems with average chirp masses of which are predicted by
recent studies of BH-Wolf-Rayet star systems. While this scenario is at the
high end of theoretical estimates, cross-correlation of data by two Einstein
Telescopes could detect this signal under the condition . Such a signal could potentially mask a primordial
GW background signal of dimensionless energy density, , around the (1--500) Hz frequency range.Comment: 22 pages, 5 figures, 2 tables, Accepted for publication by Ap
Quantum noise of non-ideal Sagnac speed meter interferometer with asymmetries
The speed meter concept has been identified as a technique that can
potentially provide laser-interferometric measurements at a sensitivity level
which surpasses the Standard Quantum Limit (SQL) over a broad frequency range.
As with other sub-SQL measurement techniques, losses play a central role in
speed meter interferometers and they ultimately determine the quantum noise
limited sensitivity that can be achieved. So far in the literature, the quantum
noise limited sensitivity has only been derived for lossless or lossy cases
using certain approximations (for instance that the arm cavity round trip loss
is small compared to the arm cavity mirror transmission). In this article we
present a generalised, analytical treatment of losses in speed meters that
allows accurate calculation of the quantum noise limited sensitivity of Sagnac
speed meters with arm cavities. In addition, our analysis allows us to take
into account potential imperfections in the interferometer such as an
asymmetric beam splitter or differences of the reflectivities of the two arm
cavity input mirrors. Finally,we use the examples of the proof-of-concept
Sagnac speed meter currently under construction in Glasgow and a potential
implementation of a Sagnac speed meter in the Einstein Telescope (ET) to
illustrate how our findings affect Sagnac speed meters with meter- and
kilometre-long baselines.Comment: 22 pages, 8 figures, 1 table, (minor corrections and changes made to
text and figures in version 2
Pilot plant experience on high-level waste solidification and design of the engineering prototype VERA
Calibration of the LIGO displacement actuators via laser frequency modulation
We present a frequency modulation technique for calibration of the
displacement actuators of the LIGO 4-km-long interferometric gravitational-wave
detectors. With the interferometer locked in a single-arm configuration, we
modulate the frequency of the laser light, creating an effective length
variation that we calibrate by measuring the amplitude of the frequency
modulation. By simultaneously driving the voice coil actuators that control the
length of the arm cavity, we calibrate the voice coil actuation coefficient
with an estimated 1-sigma uncertainty of less than one percent. This technique
enables a force-free, single-step actuator calibration using a displacement
fiducial that is fundamentally different from those employed in other
calibration methods.Comment: 10 pages, 5 figures, submitted to Classical and Quantum Gravit
Using the etalon effect for in-situ balancing of the Advanced Virgo arm cavities
Several large-scale interferometric gravitational-wave detectors use resonant
arm cavities to enhance the light power in the interferometer arms. These
cavities are based on different optical designs: One design uses wedged input
mirrors to create additional optical pick-off ports for deriving control
signals. The second design employs input mirrors without wedge and thus offers
the possibility to use the etalon effect inside the input mirrors for tuning
the finesse of the arm cavities. In this article we introduce a concept of
maximized flexibility that combines both of these options, by featuring wedges
at the input mirrors and using the etalon effect instead in the end mirrors. We
present a design for the arm cavities of Advanced Virgo. We have used numerical
simulations to derive requirements for the manufacturing accuracy of an end
mirror etalon for Advanced Virgo. Furthermore, we give analytical
approximations for the achievable tuning range of the etalon in dependence on
the reflectance, the curvature and the orientation of the etalon back surface.Comment: 12 pages, 6 Figure
Accurate calibration of test mass displacement in the LIGO interferometers
We describe three fundamentally different methods we have applied to
calibrate the test mass displacement actuators to search for systematic errors
in the calibration of the LIGO gravitational-wave detectors. The actuation
frequencies tested range from 90 Hz to 1 kHz and the actuation amplitudes range
from 1e-6 m to 1e-18 m. For each of the four test mass actuators measured, the
weighted mean coefficient over all frequencies for each technique deviates from
the average actuation coefficient for all three techniques by less than 4%.
This result indicates that systematic errors in the calibration of the
responses of the LIGO detectors to differential length variations are within
the stated uncertainties.Comment: 10 pages, 6 figures, submitted on 31 October 2009 to Classical and
Quantum Gravity for the proceedings of 8th Edoardo Amaldi Conference on
Gravitational Wave
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