Effect of thermal fluctuations on spin degrees of freedom in spinor Bose-Einstein condensates

We consider the effect of thermal fluctuations on rotating spinor F=1 condensates in axially-symmetric vortex phases, when all the three hyperfine states are populated. We show that the relative phase among different components of the order parameter can fluctuate strongly due to the weakness of the interaction in the spin channel. These fluctuations can be significant even at low temperatures. Fluctuations of relative phase lead to significant fluctuations of the local transverse magnetization of the condensate. We demonstrate that these fluctuations are much more pronounced for the antiferromagnetic state than for the ferromagnetic one.Comment: 5 pages, 2 figures; final version, accepted for publication in Phys. Rev.

Survivability Analysis of the Iridium Low Earth Orbit Satellite Network

This thesis evaluates the survivability of the proposed Iridium Low Earth Orbit (LEO) Satellite Network. In addition to the complete Iridium constellation, three degraded Iridium constellations are analyzed. This analysis occurs via the use of simulation models, which are developed to use three dynamic routing algorithms over three loading levels. The Iridium network models use a common set of operating assumptions and system environments. The constellation survivability was determined by comparing packet rejection rates, hop\u27 counts, and average end to end delay performance between the various network scenarios. It was concluded that, based on the established scenarios, the proposed Iridium constellation was highly survivable. Even with only 45 percent of its satellites functioning (modeled with 36 failed Iridium satellites), the average packet delays were never greater than 178 milliseconds (msec), well within the real time packet delivery constraint of 400 msec. As a result, while additional research is necessary, Iridium has demonstrated the network robustness that is required within the military communications environment

Bose-Einstein condensation at constant temperature

We present a novel experimental approach to Bose-Einstein condensation by increasing the particle number of the system at almost constant temperature. In particular the emergence of a new condensate is observed in multi-component F=1 spinor condensates of 87-Rb. Furthermore we develop a simple rate-equation model for multi-component BEC thermodynamics at finite temperature which well reproduces the measured effects.Comment: 4 pages, 3 figures, RevTe

Static properties and spin dynamics of the ferromagnetic spin-1 Bose gas in magnetic field

Properties of spin-1 Bose gases with ferromagnetic interaction in the presence of a nonzero magnetic field are studied. The equation of state and thermodynamic quantities are worked out with the help of a mean-field approximation. The phase diagram besides Bose-Einstein condensation contains a first order transition where two values of the magnetization coexist. The dynamics is investigated with the help of the Random Phase Approximation. The soft mode corresponding to the critical point of the magnetic phase transition is found to behave like in conventional theory.Comment: 8 pages and 3 figures included in text, submitted to Physical Review

Dating of streamwater using tritium in a post nuclear bomb pulse world: continuous variation of mean transit time with streamflow

Tritium measurements of streamwater draining the Toenepi catchment, a small dairy farming area in Waikato, New Zealand, have shown that the mean transit time of the water varies with the flow rate of the stream. Mean transit times through the catchment are 2–5 years during high baseflow conditions in winter, increasing to 30–40 years as baseflow decreases in summer, and then dramatically older water during drought conditions with mean transit time of more than 100 years. Older water is gained in the lower reaches of the stream, compared to younger water in the headwater catchment. The groundwater store supplying baseflow was estimated from the mean transit time and average baseflow to be 15.4 × 10<sup>6</sup> m<sup>3</sup> of water, about 1 m water equivalent over the catchment and 2.3 times total annual streamflow. Nitrate is relatively high at higher flow rates in winter, but is low at times of low flow with old water. This reflects both lower nitrate loading in the catchment several decades ago as compared to current intensive dairy farming, and denitrification processes occurring in the older groundwater. Silica, leached from the aquifer material and accumulating in the water in proportion to contact time, is high at times of low streamflow with old water. There was a good correlation between silica concentration and streamwater age, which potentially allows silica concentrations to be used as a proxy for age when calibrated by tritium measurements. This study shows that tritium dating of stream water is possible with single tritium measurements now that bomb-test tritium has effectively disappeared from hydrological systems in New Zealand, without the need for time-series data

Training and Transfer of Cue Updating in Older Adults Is Limited: Evidence From Behavioral and Neuronal Data

Cognitive control processes, such as updating task-relevant information while switching between multiple tasks, are substantially impaired in older adults. However, it has also been shown that these cognitive control processes can be improved by training interventions, e.g., by training in task switching. Here, we applied an event-related potential (ERP) approach to identify whether a cognitive training improves task-preparatory processes such as updating of relevant task goals. To do so, we applied a pretest-training-posttest design with eight training sessions. Two groups of older adults were either trained in task switching (treatment group) or in performing single tasks (control group) and we compared their performance to a group of untrained younger adults. To foster cue updating in the treatment group, we applied a cue-based switching task in which the two task cues were randomly selected prior to target presentation so that participants had time to prepare for the upcoming task. In contrast, the control group also received task cues but those were redundant as only one task had to be performed. We also examined whether training in cue updating during task switching can be transferred to a similar cognitive control task measuring updating of context information, namely a modified version of the AX-Continuous Performance Task (AX-CPT). The results revealed training-specific improvements in task switching, that is, a larger improvement in blocks requiring switching in comparison to single tasks at the behavioral level. In addition, training specific-effects were also found at the neuronal level. Older adults trained in cue updating while switching showed a reduction in mixing costs in the cue-related P3, indicating an improvement in preparatory updating processes. Additionally, P3 topography changed with training from a very broad to a parietally focused scalp distribution similar to the one found in younger adults. However, we did not obtain training-specific improvements in context updating in the AX-CPT neither at the behavioral level nor at the neuronal level. Results are discussed in the context of the ongoing debate on whether transfer of cognitive training improvements is possible

Prospect of creating a composite fermi/bose superfluid

We show that composite fermi/bose superfluids can be created in cold-atom traps by employing a Feshbach resonance or coherent photoassociation. The bosonic molecular condensate created in this way implies a new fermion pairing mechanism associated with the exchange of fermion pairs between the molecular condensate and an atomic fermion superfluid. We predict macroscopically coherent, Josephson-like oscillations of the atomic and molecular populations in response to a sudden change of the molecular energy, and suggest that these oscillations will provide an experimental signature of the pairing.Comment: Rejected by PR

Vortex structure in spinor F=2 Bose-Einstein condensates

Extended Gross-Pitaevskii equations for the rotating F=2 condensate in a harmonic trap are solved both numerically and variationally using trial functions for each component of the wave function. Axially-symmetric vortex solutions are analyzed and energies of polar and cyclic states are calculated. The equilibrium transitions between different phases with changing of the magnetization are studied. We show that at high magnetization the ground state of the system is determined by interaction in "density" channel, and at low magnetization spin interactions play a dominant role. Although there are five hyperfine states, all the particles are always condensed in one, two or three states. Two novel types of vortex structures are also discussed.Comment: 6 pages, 3 figure

Double Phase Transitions in Magnetized Spinor Bose-Einstein Condensation

It is investigated theoretically that magnetized Bose-Einstein condensation (BEC) with the internal (spin) degrees of freedom exhibits a rich variety of phase transitions, depending on the sign of the interaction in the spin channel. In the antiferromagnetic interaction case there exist always double BEC transitions from single component BEC to multiple component BEC. In the ferromagnetic case BEC becomes always unstable at a lower temperature, leading to a phase separation. The detailed phase diagram for the temperature vs the polarization, the spatial spin structure, the distribution of non-condensates and the excitation spectrum are examined for the harmonically trapped systems.Comment: 6 pages, 7 figures. Submitted to J. Phys. Soc. Jp

Symmetry and inert states of spin Bose Condensates

We construct the list of all possible inert states of spin Bose condensates for $S \le 4$. In doing so, we also obtain their symmetry properties. These results are applied to classify line defects of these spin condensates at zero magnetic field.Comment: an error in Sec III C correcte