3,486 research outputs found
Status of the Instream Flow Issue in Arkansas, 1987
Expansion of Arkansas\u27 population with concurrent increases in the state\u27s domestic, industrial, and agricultural water uses and possible out-of-state diversion are placing substantial demands on the state\u27s water resources. In an attempt to address this growing concern, Act 1051 (1985) of the Arkansas legislature was passed requiring the determination of present and future state water needs. A specific area of this mandate was the quantification of instream flow requirements. Basic instream flow needs are maintenance of the aquatic ecosystem and dependent riparian environment. Flow reservation may compliment other instream uses such as recreation, navigation, water quality, and groundwater recharge. However, offstream uses (e.g. irrigation and industry) may compete for these same flows and often at the most critical time of year. In order to answer questions concerning instream flow requirements, over 40 methods of instream flow determination have been developed, the majority in the semi-arid western United States. These individual procedures may be classified into four major methodologies: (1) discharge, (2) single transect, (3)multiple transect, and (4) regression analysis of historical data. Requirements of these four types vary according to necessary level of expertise, time and effort expended, and monetary outlay. In one year, requests for fish and wildlife instream flow needs for approximately 60 stream reaches throughout Arkansas limited the possible options. Modification and further development of a well-known method is outlined as an initial step in the process of quantifying Arkansas\u27 instream flow needs. Examples are given for some of the major river basins throughout the state
Double Bragg diffraction: A tool for atom optics
The use of retro-reflection in light-pulse atom interferometry under
microgravity conditions naturally leads to a double-diffraction scheme. The two
pairs of counterpropagating beams induce simultaneously transitions with
opposite momentum transfer that, when acting on atoms initially at rest, give
rise to symmetric interferometer configurations where the total momentum
transfer is automatically doubled and where a number of noise sources and
systematic effects cancel out. Here we extend earlier implementations for Raman
transitions to the case of Bragg diffraction. In contrast with the
single-diffraction case, the existence of additional off-resonant transitions
between resonantly connected states precludes the use of the adiabatic
elimination technique. Nevertheless, we have been able to obtain analytic
results even beyond the deep Bragg regime by employing the so-called "method of
averaging," which can be applied to more general situations of this kind. Our
results have been validated by comparison to numerical solutions of the basic
equations describing the double-diffraction process.Comment: 26 pages, 20 figures; minor changes to match the published versio
Light shifts in atomic Bragg diffraction
Bragg diffraction of an atomic wave packet in a retroreflective geometry with
two counterpropagating optical lattices exhibits a light shift induced phase.
We show that the temporal shape of the light pulse determines the behavior of
this phase shift: In contrast to Raman diffraction, Bragg diffraction with
Gaussian pulses leads to a significant suppression of the intrinsic phase shift
due to a scaling with the third power of the inverse Doppler frequency.
However, for box-shaped laser pulses, the corresponding shift is twice as large
as for Raman diffraction. Our results are based on approximate, but analytical
expressions as well as a numerical integration of the corresponding
Schr\"odinger equation.Comment: 6 pages, 5 figure
A high-gain Quantum free-electron laser: emergence & exponential gain
We derive an effective Dicke model in momentum space to describe collective
effects in the quantum regime of a free-electron laser (FEL). The resulting
exponential gain from a single passage of electrons allows the operation of a
Quantum FEL in the high-gain mode and avoids the experimental challenges of an
X-ray FEL oscillator. Moreover, we study the intensity fluctuations of the
emitted radiation which turn out to be super-Poissonian
Examining Mental Health and Well-being Provision in Schools in Europe: Methodological Approach
Schools are considered an ideal setting for community-based mental health and well-being interventions for young people. However, in spite of extensive literature examining the effectiveness of such interventions, very few studies have investigated existing mental health and well-being provision in schools. The current study aims to extend such previous research by surveying primary and secondary schools to investigate the nature of available provision in nine European countries (Germany, Ireland, the Netherlands, Poland, Serbia, Spain, Sweden, the UK and Ukraine). Furthermore, the study aims to investigate potential barriers to mental health and well-being provision and compare provision within and between countries
Thermally Activated Reversible Threshold Shifts in Yba\u3csub\u3e2\u3c/sub\u3eCu\u3csub\u3e3\u3c/sub\u3eO\u3csub\u3e7-ÎŽ\u3c/sub\u3e/Yttria-Stabilized Zirconia/Si Capacitors
Yba2Cu3O7-ÎŽ/yttriaâstabilized zirconia (YSZ)/silicon superconductorâinsulatorâsemiconductor capacitors are characterized with capacitanceâvoltage (CâV) measurements at different gateâvoltage sweep rates and under biasâtemperature cycling. It is shown that ionic conduction in YSZ causes both hysteresis and stretchâout in roomâtemperature CâV curves. A thermally activated process with an activation energy of about 39 meV in YSZ and/or at YSZ/Si interface is attributed to trapping/detrapping mechanisms in the SiOx interfacial layer between YSZ and Si. The negative mobile ions in YSZ can be moved by an applied electric field at room temperature and then ââfrozenââ with decreasing temperature, giving rise to adjustable threshold voltages at low temperatures
The interface of gravity and quantum mechanics illuminated by Wigner phase space
We provide an introduction into the formulation of non-relativistic quantum
mechanics using the Wigner phase-space distribution function and apply this
concept to two physical situations at the interface of quantum theory and
general relativity: (i) the motion of an ensemble of cold atoms relevant to
tests of the weak equivalence principle, and (ii) the Kasevich-Chu
interferometer. In order to lay the foundations for this analysis we first
present a representation-free description of the Kasevich-Chu interferometer
based on unitary operators.Comment: 69 pages, 6 figures, minor changes to match the published version.
The original publication is available at
http://en.sif.it/books/series/proceedings_fermi or
http://ebooks.iospress.nl/volumearticle/3809
Regimes of atomic diffraction: Raman versus Bragg diffraction in retroreflective geometries
We provide a comprehensive study of atomic Raman and Bragg diffraction when
coupling to a pair of counterpropagating light gratings (double diffraction) or
to a single one (single diffraction) and discuss the transition from one case
to the other in a retroreflective geometry as the Doppler detuning changes. In
contrast to single diffraction, double Raman loses its advantage of high
diffraction efficiency for short pulses and has to be performed in a Bragg-type
regime. Moreover, the structure of double diffraction leads to further
limitations for broad momentum distributions on the efficiency of mirror
pulses, making the use of (ultra) cold ensembles essential for high diffraction
efficiency.Comment: 16 pages, 14 figure
Cooling dynamics of a dilute gas of inelastic rods: a many particle simulation
We present results of simulations for a dilute gas of inelastically colliding
particles. Collisions are modelled as a stochastic process, which on average
decreases the translational energy (cooling), but allows for fluctuations in
the transfer of energy to internal vibrations. We show that these fluctuations
are strong enough to suppress inelastic collapse. This allows us to study large
systems for long times in the truely inelastic regime. During the cooling stage
we observe complex cluster dynamics, as large clusters of particles form,
collide and merge or dissolve. Typical clusters are found to survive long
enough to establish local equilibrium within a cluster, but not among different
clusters. We extend the model to include net dissipation of energy by damping
of the internal vibrations. Inelatic collapse is avoided also in this case but
in contrast to the conservative system the translational energy decays
according to the mean field scaling law, E(t)\propto t^{-2}, for asymptotically
long times.Comment: 10 pages, 12 figures, Latex; extended discussion, accepted for
publication in Phys. Rev.
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