Quantum dynamics of Bose-Hubbard Hamiltonians beyond Hartree-Fock-Bogoliubov: The Bogoliubov backreaction approximation

e formulate a method for studying the quantum field dynamics of ultracold Bose gases confined within optical lattice potentials, within the lowest Bloch-band Bose-Hubbard model. Our formalism extends the two-sites results of Phys. Rev. Lett. {\bf86}, 000568 (2001) to the general case of $M$ lattice sites. The methodology is based on mapping the Bose-Hubbard Hamiltonian to an $SU(M)$ pseudospin problem and truncating the resulting hierarchy of dynamical equations for correlation functions, up to pair-correlations between $SU(M)$ generators. Agreement with few-site exact many-particle calculations is consistently better than the corresponding Hartree-Fock-Bogoliubov approximation. Moreover, our approximation compares favorably with a more elaborate two-particle irreducible effective action formalism, at a fraction of the analytic and numerical effort.Comment: 8 pages, 7 figure

Free-flight model investigation of a vertical-attitude VTOL fighter

Tests were made in the Langley full-scale tunnel and included a study of the stability and control characteristics of delta- and swept-wing configurations from hovering through the transition to normal forward flight. Static force tests were also conducted to aid in the analysis of the flight tests. With conventional artificial rate stabilization, very smooth transitions could be made consistently with relatively little difficulty. Because of the lower apparent damping and a tendency to diverge in yaw, however, the swept-wing configuration was considered to be much more difficult to fly than the delta-wing configuration. With rate dampers off, both configurations were very difficult to control and the control power needed for satisfactory flights was substantially higher than with the rate dampers operating

The Effect of Tempo on Prone Hamstring Exercise - An Exploration of Unilateral Bias

Hamstring injuries are common muscle-skeletal injuries with a high recurrence rate. While unmodifiable risk factors (e.g., previous injury) vary, recent evidence has questioned the utility of eccentric exercise in preventing hamstring strains. Furthermore, whether eccentric exercise can transfer to sprinting’s kinetic and kinematic requirements is of question. Therefore, this investigation examines exercise tempo (fast vs. slow eccentric phase), movement strategy (bilateral vs. unilateral), and external load characteristics (coupled vs. independent) bias concentric (CON) and eccentric (ECC) biceps femoris (BF) mean electromyography (mEMG). METHODS: Twenty college-aged students aged 18 – 33 (M = 23.4, SD = 3.12 years) with \u3e3 months of targeted hamstring training \u3e1x per week were recruited and completed two separate lab visits. Lab visits 1 (familiarization) and 2 (experimental protocol) were scheduled for approximately the same time of day, at least 72 hours apart. RESULTS: A main effect of side was detected for BF mEMG during ECC (F (1, 206) = 145.27, p \u3c 0.001) and CON (F (1, 206) = 124.29, p \u3c 0.001). A main effect of tempo was detected for BF (F (1, 206) = 4.144, p = 0.043). The fast tempo (M = 8.20 %MVC, 95% CI: 6.79 to 9.62 %MVC) elicited a higher mEMG when compared to the slow tempo (M = 7.24 %MVC, 95% CI: 5.83 to 8.65 %MVC). Post hoc comparison indicated that the mEMG showed significant differences between tempos (∆M = 0.963 %MVC), p = 0.043. A main effect of side was detected for Gmax ECC (F = (1, 209) 23.28, p \u3c 0.001) and CON (F = (1, 209) 7.85, p = 0.006). CONCLUSION: The prone hamstring exercise resulted in biased recruitment of the contralateral Gmax and BF despite no differences in functional strength ratios (ECC HS [degrees per sec]/ CON Q [degrees per second]). Further investigation is warranted to decipher why this bias exists and whether this phenomenon is a training adaptation or a predictive mechanism for hamstring strain

Genebank ‐ in vitro propagation of potato and sweetpotato. CIP‐SOP056 V 3.0

This procedure describes the in vitro multiplication of potato and sweetpotato germplasm for international and national germplasm distribution, as well as, in vitro conservation, phytosanitary, and cryopreservation activities

Decoherence and Recoherence in Model Quantum Systems

We discuss the various manifestations of quantum decoherence in the forms of dephasing, entanglement with the environment, and revelation of "which-path" information. As a specific example, we consider an electron interference experiment. The coupling of the coherent electrons to the quantized electromagnetic field illustrates all of these versions of decoherence. This decoherence has two equivalent interpretations, in terms of photon emission or in terms of Aharonov-Bohm phase fluctuations. We consider the case when the coherent electrons are coupled to photons in a squeezed vacuum state. The time-averaged result is increased decoherence. However, if only electrons which are emitted during selected periods are counted, the decoherence can be suppressed below the level for the photon vacuum. This is the phenomenon of recoherence. This effect is closely related to the quantum violations of the weak energy condition, and is restricted by similar inequalities. We give some estimates of the magnitude of the recoherence effect and discuss prospects for observing it in an electron interferometry experiment.Comment: 8 pages, 3 figures, talk presented at the 7th Friedmann Seminar, Joao Pessoa, Brazil, July 200

Decoherence induced by Smith-Purcell radiation

The interaction between charged particles and the vacuum fluctuations of the electromagnetic field induces decoherence, and therefore affects the contrast of fringes in an interference experiment. In this article we show that if a double slit experiment is performed near a conducting grating, the fringe visibility is reduced. We find that the reduction of contrast is proportional to the number of grooves in the conducting surface, and that for realistic values of the parameters it could be large enough to be observed. The effect can be understood in terms of the Smith-Purcell radiation produced by the surface currents induced in the conductor.Comment: 10 pages, 3 figures. Improved discussion on experimental perspectives. References added. Version to appear in Phys. Rev.

Second Josephson excitations beyond mean field as a toy model for thermal pressure: exact quantum dynamics and the quantum phase model

A simple four-mode Bose-Hubbard model with intrinsic time scale separation can be considered as a paradigm for mesoscopic quantum systems in thermal contact. In our previous work we showed that in addition to coherent particle exchange, a novel slow collective excitation can be identified by a series of Holstein-Primakoff transformations. This resonant energy exchange mode is not predicted by linear Bogoliubov theory, and its frequency is sensitive to interactions among Bogoliubov quasi-particles; it may be referred to as a second Josephson oscillation, in analogy to the second sound mode of liquid Helium II. In this paper we will explore this system beyond the Gross-Pitaevskii mean field regime. We directly compare the classical mean field dynamics to the exact full quantum many-particle dynamics and show good agreement over a large range of the system parameters. The second Josephson frequency becomes imaginary for stronger interactions, however, indicating dynamical instability of the symmetric state. By means of a generalized quantum phase model for the full four-mode system, we then show that, in this regime, high-energy Bogoliubov quasiparticles tend to accumulate in one pair of sites, while the actual particles preferentially occupy the opposite pair. We interpret this as a simple model for thermal pressure