35 research outputs found
Thermal Conductivity in the Bose-Einstein Condensed State of Triplons in the Bond-Alternating Spin-Chain System Pb2V3O9
In order to clarify the origin of the enhancement of the thermal conductivity
in the Bose-Einstein Condensed (BEC) state of field-induced triplons, we have
measured the thermal conductivity along the [101] direction parallel to
spin-chains, , and perpendicular to spin-chains,
, of the S=1/2 bond-alternating spin-chain system Pb2V3O9
in magnetic fields up to 14 T. With increasing field at 3 K, it has been found
that both and are suppressed in the
gapped normal state in low fields. In the BEC state of field-induced triplons
in high fields, on the other hand, is enhanced with
increasing field, while is suppressed. That is, the
thermal conductivity along the direction, where the magnetic interaction is
strong, is markedly enhanced in the BEC state. Accordingly, our results suggest
that the enhancement of in the BEC state is caused by the
enhancement of the thermal conductivity due to triplons on the basis of the
two-fluid model, as in the case of the superfluid state of liquid 4He.Comment: 5 pages, 3 figure
Marine phytoplankton in subtropical coastal waters showing lower thermal sensitivity than microzooplankton
Temperature sensitivity of plankton in terms of activation energy (Ea, eV) in the Arrhenius equation is critical for predicting how marine productivity and carbon export will respond to ocean warming. In this study, we quantified the temperature responses of phytoplankton growth rate and microzooplankton grazing rate by conducting short-term temperature modulation experiments on natural communities at two subtropical sites with contrasting nutrient conditions. Our results showed that the activation energy of phytoplankton growth rate (Ea = 0.36 eV, 95% confidence interval [CI] = 0.28–0.44 eV) at each station was less than that of microzooplankton grazing rate (Ea = 0.53 eV, 95% CI = 0.47–0.59 eV), indicating an increasing grazing pressure on phytoplankton under warming conditions. Although the difference is consistent with that reported in previous studies, it is very likely to arise from another reason, i.e., differential proximities of the optimal temperature (Topt in nonlinear temperature responses of rates) of phytoplankton and microzooplankton to the environmental temperature, as we found that the environmental temperature is closer to the optimal temperature of phytoplankton growth than to that of microzooplankton grazing in this subtropical environment. Our results suggest that nonlinear temperature responses of plankton should be considered when evaluating and predicting the effects of ocean warming on ecosystem productivity and food web dynamics, especially in subtropical and tropical waters
Generator Design Considering Mover Action to Improve Energy Conversion Efficiency in a Free-Piston Engine Generator
In a free-piston engine generator (FPEG), the power of the engine can be directly regenerated by linear generators without a crank. The mover motion of this system is interrelated with engine and power generation efficiencies due to the direct connection between the mover of the generator and the piston of the engine. The generator should be designed to improve the overall energy conversion efficiency. The dimensions and mass of the mover limit its operating stroke and drive frequency. Herein, we propose a method for designing linear generators and constructing FPEG systems, considering the mover operation to improve engine efficiency. We evaluated the effect of mover operation on the engine and generation efficiencies using thermal and electromagnetic field analysis software. The proposed design method improves the overall energy conversion efficiency compared with a generator that considers only the maximization of generation efficiency. Setting the mover operation for higher engine efficiency and designing a linear generator to realize the operation can effectively improve the energy conversion efficiency of FPEGs
Voltage Improvement of a Swing-Magnet-Type Generator for Harvesting Bicycle Vibrations
This paper proposes a swing-magnet-type generator that utilizes environment vibration for energy harvesting applications. This device consisted of a liquid, a swing magnet with a float, and a coil, and it was expected to generate electricity using the minute vibration of a bicycle. The vibration of the wide frequency band of the bicycle was converted into a vibration of a low-frequency mover. The yoke size of the permanent magnet affected the linkage flux and swing characteristics. Therefore, we verified the effect of the mover characteristics on the swing moment by structural simulations and vibration experiments using a linear motor. The yoke size changed the torque, which affected the resonant frequency of the swing. The magnetic-field analysis revealed the effect on the flux linkage in the yoke. The output voltage of the generator in the bicycle was 2.1 V, which could power a light-emitting diode
Resonant Combustion Start Considering Potential Energy of Free-Piston Engine Generator
Free-piston engine generators without a crank mechanism are expected to be used in series hybrid vehicles because of their lower losses. The series hybrid system requires a low starting thrust because the engine frequently starts depending on the battery state. This study clarifies the effectiveness of the constant thrust resonance starting method that utilizes the compression pressure of the engine and the spring thrust. The piston must pass the combustion starting point with a predetermined speed to start combustion. Herein, we present a thrust setting method that uses the energy state diagram to optimize the velocity at the combustion start point. A simulation is performed assuming output when mounted on a vehicle. Consequently, the simulation results show that the maximum thrust can be reduced by more than 90% compared to that without resonance. Moreover, the speed at the combustion start point is in agreement with the value obtained using an energy state diagram. An impulse-like combustion pressure is generated in 180 ms, and combustion can be started using resonance, as shown in an experiment using a small-output engine and linear motor. The effectiveness of the constant thrust resonance starting method was confirmed