7,507 research outputs found
Loading Bose condensed atoms into the ground state of an optical lattice
We optimize the turning on of a one-dimensional optical potential, V_L(x,t) =
S(t) V_0 cos^2(kx) to obtain the optimal turn-on function S(t) so as to load a
Bose-Einstein condensate into the ground state of the optical lattice of depth
V_0. Specifically, we minimize interband excitations at the end of the turn-on
of the optical potential at the final ramp time t_r, where S(t_r) = 1, given
that S(0) = 0. Detailed numerical calculations confirm that a simple unit cell
model is an excellent approximation when the turn-on time t_r is long compared
with the inverse of the band excitation frequency and short in comparison with
nonlinear time \hbar/\mu where \mu is the chemical potential of the condensate.
We demonstrate using the Gross-Pitaevskii equation with an optimal turn-on
function S(t) that the ground state of the optical lattice can be loaded with
very little excitation even for times t_r on the order of the inverse band
excitation frequency
Target Mass Monitoring and Instrumentation in the Daya Bay Antineutrino Detectors
The Daya Bay experiment measures sin^2 2{\theta}_13 using functionally
identical antineutrino detectors located at distances of 300 to 2000 meters
from the Daya Bay nuclear power complex. Each detector consists of three nested
fluid volumes surrounded by photomultiplier tubes. These volumes are coupled to
overflow tanks on top of the detector to allow for thermal expansion of the
liquid. Antineutrinos are detected through the inverse beta decay reaction on
the proton-rich scintillator target. A precise and continuous measurement of
the detector's central target mass is achieved by monitoring the the fluid
level in the overflow tanks with cameras and ultrasonic and capacitive sensors.
In addition, the monitoring system records detector temperature and levelness
at multiple positions. This monitoring information allows the precise
determination of the detectors' effective number of target protons during data
taking. We present the design, calibration, installation and in-situ tests of
the Daya Bay real-time antineutrino detector monitoring sensors and readout
electronics.Comment: 22 pages, 20 figures; accepted by JINST. Changes in v2: minor
revisions to incorporate editorial feedback from JINS
Sensitivity of a highâelevation rocky mountain watershed to altered climate and CO2
We explored the hydrologic and ecological responses of a headwater mountain catchment, Loch Vale watershed, to climate change and doubling of atmospheric CO2 scenarios using the Regional HydroâEcological Simulation System (RHESSys). A slight (2°C) cooling, comparable to conditions observed over the past 40 years, led to greater snowpack and slightly less runoff, evaporation, transpiration, and plant productivity. An increase of 2°C yielded the opposite response, but model output for an increase of 4°C showed dramatic changes in timing of hydrologic responses. The snowpack was reduced by 50%, and runoff and soil water increased and occurred 4â5 weeks earlier with 4°C warming. Alpine tundra photosynthetic rates responded more to warmer and wetter conditions than subalpine forest, but subalpine forest showed a greater response to doubling of atmospheric CO2 than tundra. Even though water use efficiency increased with the double CO2 scenario, this had little effect on basinâwide runoff because the catchment is largely unvegetated. Changes in winter and spring climate conditions were more important to hydrologic and vegetation dynamics than changes that occurred during summer
Modelling crystal aggregation and deposition\ud in the catheterised lower urinary tract
Urethral catheters often become encrusted with crystals of magnesium struvite and calcium phosphate. The encrustation can block the catheter, which can cause urine retention in the bladder and reflux into the kidneys. We develop a mathematical model to investigate crystal deposition on the catheter surface, modelling the bladder as a reservoir of fluid and the urethral catheter as a rigid channel. At a constant rate, fluid containing crystal particles of unit size enters the reservoir, and flows from the reservoir through the channel and out of the system. The crystal particles aggregate, which we model using BeckerâDöring coagulation theory, and are advected through the channel, where they continue to aggregate and are deposited on the channelâs walls. Inhibitor particles also enter the reservoir, and can bind to the crystals, preventing further aggregation and deposition. The crystal concentrations are spatially homogeneous in the reservoir, whereas the channel concentrations vary spatially as a result of advection, diffusion and deposition. We investigate the effect of inhibitor particles on the amount of deposition. For all parameter values, we find that crystals deposit along the full length of the channel, with maximum deposition close to the channelâs entrance
Power densities for two-step gamma-ray transitions from isomeric states
We have calculated the incident photon power density P_2 for which the
two-step induced emission rate from an isomeric nucleus becomes equal to the
natural isomeric decay rate. We have analyzed two-step transitions for isomeric
nuclei with a half-life greater than 10 min, for which there is an intermediate
state of known energy, spin and half-life, for which the intermediate state is
connected by a known gamma-ray transition to the isomeric state and to at least
another intermediate state, and for which the relative intensities of the
transitions to lower states are known. For the isomeric nucleus 166m-Ho, which
has a 1200 y isomeric state at 5.98 keV, we have found a value of P_2=6.3 x
10^7 W cm^{-2}, the intermediate state being the 263.8 keV level. We have found
power densities P_2 of the order of 10^{10} W cm^{-2} for several other
isomeric nuclei.Comment: 9 pages, 1 eps figure, 1 tabl
- âŠ