Pilot Study investigating the Impact of Serial ingestion or Co-ingestion of Creatine and Sodium bicarbonate on Performance Following Completion of a Hypertrophy Type Resistance Exercise Workout.

Purpose: To examine the ergogenic potential of creatine (Cr), sodium bicarbonate (SB),and Cr+SBafter completion of a resistance exercise bout (REB).Methods: Following recruitment,27trained males (26.8±5.7 years old) completed a one repetition maximum strength (1RM) test in the parallel squat (120.9±28.2kg). Participants then followed a standardised meal plan for 4 days whilst ingesting one of 4 supplements, and on day 5 they undertook the REB. This was a double blind randomised placebo-controlled study where participants ingested one of the following: Placebo (PLA, n=7), Cr (20g/d-1& PLA, n=8), SB (0.5 g/kg-1/d-1&PLA, n=6), andCr+SB (5 g/d-1 of Cr & 0.5 g/kg-1/d-1 SB, n=6) divided in 4 doses. The REB consisted of 4x10 repetitions (70% of 1RM, 1½ min recovery). The primary performance outcome was a 5th set (70% of 1RM) performed to volitional exhaustion.Blood glucose and lactate, heart rate, ratings of perceived exertion, sickness and stomachache scales, and time to complete each set were also recorded.Results:Participants in Cr, SB, and Cr+SB completed the required number of repetitions at 70% of 1RM however in PLA they completed the same repetitions at lower intensity (68+3.4%). Participants in PLA, Cr, SB, and Cr+SB completed 8(±1.6), 11(±5.5), 9(±3.7), and 11(±3.3) repetitions respectively during the 5th set. Despite the fact that no significant differences were observed in performance, small (SB: 0.4) and moderate effect (Cr: 0.7; Cr+SB: 1.0) sizes were observed in relation to PLA. Body mass increasedsignificantly after Cr (78.1±8.9 kg pre vs 79.1±8.9 kg post, p<0.05). No other significant differences existed in recorded variables.Conclusions: Performance gains were of higher magnitude in the Cr+SB and Cr groups. Co-ingestion of a small amount of Cr (5 g/d-1) with a standard dose ofSB (0.5 g/kg-1/d-1)appears to be equally beneficial asingestion of a standard dose of Cr (20 g/d-1). The Cr+SB was not associated with significant gains in body mass which may be beneficial in sports where size gains may negate performance. Further research is required, with larger sample size, and specific athletic populations in order to confirm the findings of the current study

Nuclear Spin Qubit Dephasing Time in the Integer Quantum Hall Effect Regime

We report the first theoretical estimate of the nuclear-spin dephasing time T_2 owing to the spin interaction with the two-dimensional electron gas, when the latter is in the integer quantum Hall state, in a two-dimensional heterojunction or quantum well at low temperature and in large applied magnetic field. We establish that the leading mechanism of dephasing is due to the impurity potentials that influence the dynamics of the spin via virtual magnetic spin-exciton scattering. Implications of our results for implementation of nuclear spins as quantum bits (qubits) for quantum computing are discussed.Comment: 19 pages in plain Te

Canonically conjugate pairs and phase operators

For quantum mechanics on a lattice the position (``particle number'') operator and the quasi-momentum (``phase'') operator obey canonical commutation relations (CCR) only on a dense set of the Hilbert space. We compare exact numerical results for a particle in simple potentials on the lattice with the expectations, when the CCR are assumed to be strictly obeyed. Only for sufficiently smooth eigenfunctions this leads to reasonable results. In the long time limit the use of the CCR can lead to a qualitativel wrong dynamics even if the initial state is in the dense set.Comment: 4 pages, 5 figures. Phys. Rev. A, in pres

Dissipative dynamics in a quantum register

A model for a quantum register dissipatively coupled with a bosonic thermal bath is studied. The register consists of $N$ qubits (i.e. spin ${1/2}$ degrees of freedom), the bath is described by $N_b$ bosonic modes. The register-bath coupling is chosen in such a way that the total number of excitations is conserved. The Hilbert space splits allowing the study of the dynamics separately in each sector. Assuming that the coupling with the bath is the same for all qubits, the excitation sectors have a further decomposition according the irreducible representations of the $su(2)$ spin algebra. The stability against environment-generated noise of the information encoded in a quantum state of the register depends on its $su(2)$ symmetry content. At zero temperature we find that states belonging to the vacuum symmetry sector have for long time vanishing fidelity, whereas each lowest spin vector is decoupled from the bath and therefore is decoherence free. Numerical results are shown in the one-excitation space in the case qubit-dependent bath-system coupling.Comment: to appear on Phys. Rev. A, 8 pages + 5 postscript figure

C-axis resistivity and high Tc superconductivity

Recently we had proposed a mechanism for the normal-state C-axis resistivity of the high-T$_c$ layered cuprates that involved blocking of the single-particle tunneling between the weakly coupled planes by strong intra-planar electron-electron scattering. This gave a C-axis resistivity that tracks the ab-plane T-linear resistivity, as observed in the high-temperature limit. In this work this mechanism is examined further for its implication for the ground-state energy and superconductivity of the layered cuprates. It is now argued that, unlike the single-particle tunneling, the tunneling of a boson-like pair between the planes prepared in the BCS-type coherent trial state remains unblocked inasmuch as the latter is by construction an eigenstate of the pair annihilation operator. The resulting pair-delocalization along the C-axis offers energetically a comparative advantage to the paired-up trial state, and, thus stabilizes superconductivity. In this scheme the strongly correlated nature of the layered system enters only through the blocking effect, namely that a given electron is effectively repeatedly monitored (intra-planarly scattered) by the other electrons acting as an environment, on a time-scale shorter than the inter-planar tunneling time. Possible relationship to other inter-layer pairing mechanisms proposed by several workers in the field is also briefly discussed.Comment: typos in equations corrected, contents unchange

Interference of Bose-Einstein condensates in momentum space

We suggest an experiment to investigate the linear superposition of two spatially separated Bose-Einstein condensates. Due to the coherent combination of the two wave functions, the dynamic structure factor, measurable through inelastic photon scattering at high momentum transfer $q$, is predicted to exhibit interference fringes with frequency period $\Delta\nu = q/md$ where $d$ is the distance between the condensates. We show that the coherent configuration corresponds to an eigenstate of the physical observable measured in the experiment and that the relative phase of the condensates is hence created through the measurement process.Comment: 4 pages and 2 eps figure

Breakdown of time-dependent mean-field theory for a one-dimensional condensate of impenetrable bosons

We show that the time-dependent nonlinear Schrodinger equation of mean-field theory has limited utility for a one-dimensional condensate of impenetrable bosons. Mean-field theory with its associated order parameter predicts interference between split condensates that are recombined, whereas an exact many-body treatment shows minimal interference.Comment: 4 pages, 2 EPS figure

Strong-coupling expansion for the Hubbard model in arbitrary dimension using slave bosons

A strong-coupling expansion for the antiferromagnetic phase of the Hubbard model is derived in the framework of the slave-boson mean-field approximation. The expansion can be obtained in terms of moments of the density of states of freely hopping electrons on a lattice, which in turn are obtained for hypercubic lattices in arbitrary dimension. The expansion is given for the case of half-filling and for the energy up to fifth order in the ratio of hopping integral $t$ over on-site interaction $U$, but can straightforwardly be generalized to the non-half-filled case and be extended to higher orders in $t/U$. For the energy the expansion is found to have an accuracy of better than $1 \%$ for $U/t \geq 8$. A comparison is given with an earlier perturbation expansion based on the Linear Spin Wave approximation and with a similar expansion based on the Hartree-Fock approximation. The case of an infinite number of spatial dimensions is discussed.Comment: 12 pages, LaTeX2e, to be published in Phys. Rev.