Analytical and numerical studies of disordered spin-1 Heisenberg chains with aperiodic couplings

We investigate the low-temperature properties of the one-dimensional spin-1 Heisenberg model with geometric fluctuations induced by aperiodic but deterministic coupling distributions, involving two parameters. We focus on two aperiodic sequences, the Fibonacci sequence and the 6-3 sequence. Our goal is to understand how these geometric fluctuations modify the physics of the (gapped) Haldane phase, which corresponds to the ground state of the uniform spin-1 chain. We make use of different adaptations of the strong-disorder renormalization-group (SDRG) scheme of Ma, Dasgupta and Hu, widely employed in the study of random spin chains, supplemented by quantum Monte Carlo and density-matrix renormalization-group numerical calculations, to study the nature of the ground state as the coupling modulation is increased. We find no phase transition for the Fibonacci chain, while we show that the 6-3 chain exhibits a phase transition to a gapless, aperiodicity-dominated phase similar to the one found for the aperiodic spin-1/2 XXZ chain. Contrary to what is verified for random spin-1 chains, we show that different adaptations of the SDRG scheme may lead to different qualitative conclusions about the nature of the ground state in the presence of aperiodic coupling modulations.Comment: Accepted for publication in Physical Review

Angular dependence of the magnetization of isotropic superconductors: which is the vortex direction?

We present studies of the dc magnetization of thin platelike samples of the isotropic type II superconductor PbTl(10%), as a function of the angle between the normal to the sample and the applied magnetic field ${\bf H}$. We determine the magnetization vector ${\bf M}$ by measuring the components both parallel and normal to ${\bf H}$ in a SQUID magnetometer, and we further decompose it in its reversible and irreversible contributions. The behavior of the reversible magnetization is well understood in terms of minimization of the free energy taking into account geometrical effects. In the mixed state at low fields, the dominant effect is the line energy gained by shortening the vortices, thus the flux lines are almost normal to the sample surface. Due to the geometrical constrain, the irreversible magnetization ${\bf M}_{irr}$ remains locked to the sample normal over a wide range of fields and orientations, as already known. We show that in order to undestand the angle and field dependence of the modulus of ${\bf M}_{irr}$, which is a measure of the vortex pinning, and to correctly extract the field dependent critical current density, the knowledge of the modulus and orientation of the induction field ${\bf B}$ is required.Comment: 11 pages, 6 figure

Primary gas thermometry by means of laser-absorption spectroscopy: Determination of the Boltzmann constant

We report on a new optical implementation of primary gas thermometry based on laser absorption spectrometry in the near infrared. The method consists in retrieving the Doppler broadening from highly accurate observations of the line shape of the R(12) $\nu_{1} + 2 \nu_{2}^{\phantom{1}0} + \nu_{3}$ transition in CO$_{2}$ gas at thermodynamic equilibrium. Doppler width measurements as a function of gas temperature, ranging between the triple point of water and the gallium melting point, allowed for a spectroscopic determination of the Boltzmann constant with a relative accuracy of $\sim1.6\times10^{-4}$.Comment: Submitted to Physical Review Letter

Equilibrium tuned by a magnetic field in phase separated manganite

We present magnetic and transport measurements on La5/8-yPryCa3/8MnO3 with y = 0.3, a manganite compound exhibiting intrinsic multiphase coexistence of sub-micrometric ferromagnetic and antiferromagnetic charge ordered regions. Time relaxation effects between 60 and 120K, and the obtained magnetic and resistive viscosities, unveils the dynamic nature of the phase separated state. An experimental procedure based on the derivative of the time relaxation after the application and removal of a magnetic field enables the determination of the otherwise unreachable equilibrium state of the phase separated system. With this procedure the equilibrium phase fraction for zero field as a function of temperature is obtained. The presented results allow a correlation between the distance of the system to the equilibrium state and its relaxation behavior.Comment: 13 pages, 5 figures. Submited to Journal of Physics: Condensed Matte

Observation of a 500meV Collective Mode in La2−x_{2-x}Srx_xCuO4_4 and Nd2_2CuO4_4

Utilizing resonant inelastic x-ray scattering, we report a previously unobserved mode in the excitation spectrum of La$_{2-x}$Sr$_x$CuO$_4$ at 500 meV. The mode is peaked around the ($\pi$,0) point in reciprocal space and is observed to soften, and broaden, away from this point. Samples with x=0, 0.01, 0.05, and 0.17 were studied. The new mode is found to be rapidly suppressed with increasing Sr content and is absent at $x$=0.17, where it is replaced by a continuum of excitations. The peak is only observed when the incident x-ray polarization is normal to the CuO planes and is also present in Nd$_2$CuO$_4$. We suggest possible explanations for this excitation.Comment: 5 pages, 5 figure

Charge-Transfer Excitations in the Model Superconductor HgBa2_2CuO4+δ_{\bf 4+\delta}

We report a Cu $K$-edge resonant inelastic x-ray scattering (RIXS) study of charge-transfer excitations in the 2-8 eV range in the structurally simple compound HgBa$_2$CuO$_{4+\delta}$ at optimal doping ($T_{\rm c} = 96.5$ K). The spectra exhibit a significant dependence on the incident photon energy which we carefully utilize to resolve a multiplet of weakly-dispersive ($< 0.5$ eV) electron-hole excitations, including a mode at 2 eV. The observation of this 2 eV excitation suggests the existence of a charge-transfer pseudogap deep in the superconducting phase. Quite generally, our data demonstrate the importance of exploring the incident photon energy dependence of the RIXS cross section.Comment: 5 pages, 3 figure

Growth parameters and meat quality of pigs fed diets containing high oleic sunflower oil

The aim of the trial was to evaluate the effects of the dietary addition of a 3% sunflower oil containing high-oleic and low-linoleic acid levels (HOSO), supplemented or not with vitamin E, on heavy pig production parameters (growth, meat quality and fatty acid composition of ham subcutaneous fat). 64 Duroc x Large White pigs were allotted to four group (Control, Control plus vitamin E, 3% HOSO and 3% HOSO plus vitamin E). Regardless of vitamin E supplementation, our results indicate that a 3% addition of HOSO has no effect both on growth parameters and carcass and fresh meat quality. HOSO dietary addition resulted in a higher (P<0.001) level of oleic acid and in lower levels of palmitic and stearic acids in the subcutaneous fat. Furthermore, fat deriving from pigs on HOSO diets showed a higher (P<0.001) iodine value. Nevertheless, linoleic acid level and iodine value did not exceed the maximum allowed for long-curing PDO hams

The Effect of Heat Acclimatization and Heat Acclimation on Endurance Trained Athlete Substrate Utilization

Heat acclimatization (HAz) and Heat Acclimation (HA) are important strategies to induce thermoregulatory adaptations to mitigate negative impact of heat stress. However, despite improving endurance performance, few studies explore their impact on substrate utilization. PURPOSE: To investigate the effect of HAz and HA on endurance athlete substrate utilization during submaximal exercise in the heat. METHODS: Fourteen endurance-trained male athletes (mean ± SD; age, 33 ± 9 years; body mass, 70.9 ± 10.1 kg; height, 177.7 ± 6.4 cm; VO2max, 59.3 ± 7.4 ml·kg−1·min−1; % body fat, 8.5% ± 3.9%) participated in this study. Participants performed 60 mins bouts of submaximal exercise (58.9 ± 2.2% vVO2max) in the heat (ambient temperature [Tamb], 35.5 ± 0.2°C; %relative humidity [%RH], 46.4% ± 1.3%; wet bulb globe temperature [WBGT], 29.3 ± 0.3°C; wind speed 4.0 ± 0.1 km·h−1). Prior to heat exposure (baseline), following HAz (post-HAz), and post-HA. During 60 min exercise, oxygen consumption (VO2) and respiratory exchange ratio (RER) were measured at the beginning (5-10 min), middle (30-35 min), and ending stages (55-60 min) of the protocol. Following the baseline, participants underwent self-directed summer training (HAz). Following post-HAz trials, participants underwent 5 days of HA sessions, which involved exercising to induce hyperthermia (38.50°C-39.75°C) for 60 minutes in the heat (Tamb, 39.1 ± 0.5°C; %RH, 51.8% ± 2.6%; WBGT, 33.4 ± 0.8°C) over an eight-day stretch. RESULTS: RER was significantly higher post-HAz (mean ± standard error; 0.85 ± 0.01) compared to baseline (0.81 ± 0.01, p2 difference between baseline (38.9 ± 1.2 ml·kg−1·min−1), post-HAz (37.5 ± 1.3 ml·kg−1·min−1, p= 0.062), or post-HA (38.5 ± 1.3 ml·kg−1·min−1, p=0.668). CONCLUSION: Self-directed HAz may impact athlete substrate utilization when performing submaximal exercise in a heated environment. Additionally, RER decreases as time of submaximal exercise in the heat increases. Other factors such as, athlete fitness level and exercise intensity, should also be considered when drawing conclusions regarding RER