Observational signatures of the parametric amplification of gravitational waves during reheating after inflation

We study the evolution of Gravitational Waves (GWs) during and after inflation as well as the resulting observational consequences in a Lorentz-violating massive gravity theory with one scalar (inflaton) and two tensor degrees of freedom. We consider two explicit examples of the tensor mass $m_g$ that depends either on the inflaton field $\phi$ or on its time derivative $\dot{\phi}$, both of which lead to parametric excitations of GWs during reheating after inflation. The first example is Starobinsky's $R^2$ inflation model with a $\phi$-dependent $m_g$ and the second is a low-energy-scale inflation model with a $\dot{\phi}$-dependent $m_g$. We compute the energy density spectrum $\Omega_{\rm GW}(k)$ today of the GW background. In the Starobinsky's model, we show that the GWs can be amplified up to the detectable ranges of both CMB and DECIGO, but the bound from the big bang nucleosynthesis is quite tight to limit the growth. In low-scale inflation with a fast transition to the reheating stage driven by the potential $V(\phi)=M^2 \phi^2/2$ around $\phi \approx M_{\rm pl}$ (where $M_{\rm pl}$ is the reduced Planck mass), we find that the peak position of $\Omega_{\rm GW}(k)$ induced by the parametric resonance can reach the sensitivity region of advanced LIGO for the Hubble parameter of order 1 GeV at the end of inflation. Thus, our massive gravity scenario offers exciting possibilities for probing the physics of primordial GWs at various different frequencies.Comment: 17 pages, 8 figure

Particle size and surface texturing effects on friction of magnetorheological fluids

MR fluids are produced by dispersing micron-sized ferrimagnetic particles in oil. Generally, the presence of foreign particles in a lubricant affects the sliding behavior of the lubricated surface. Accordingly, the dispersed particles in MR fluids should significantly affect the lubrication properties of the fluids. In this study, we investigated the lubrication properties of MR fluids through sliding tests and in situ observations, while focusing on the behavior of the dispersed particles. MR fluids containing dispersed particles of various diameters were tested. The results of the sliding tests suggested that the MR fluid with the smallest particles exhibited the best lubrication characteristics. Surface observations showed the presence of grooves on the lubricated surfaces after wear. It is assumed that the grooves are formed by the abrasive action of the dispersed particles and that they affect the behavior of the particles. In situ observations proved that, in the case of flat surfaces, the dispersed particles remained stationary during sliding. On the other hand, in case of grooved surfaces, they moved along the grooves. Given these results, it can be surmised that the grooves on the worn surface changed the behavior of the particles and improved the lubricity of MR fluids

Effectiveness of Surface Texturing for Improving the Anti-seizure Property of Copper Alloy

AbstractIt is well known that lead-bronze is widely used in the automotive industry owing to the high anti-seizure property. However, because of toxicity of lead, the automotive industry demands a lead-free copper alloy from the viewpoint of environment. Lead- free copper alloy, which has the anti-seizure property as high as lead-bronze, has not been yet well exploited. For this reason, the objective of this study is to improve the anti-seizure property of lead-free copper alloy using a laser surface texturing (LST). In this study, a ring-on-ring sliding friction tester was used to assess the effectiveness of LST on the anti-seizure property of lead- free copper alloy. The upper specimens were made of FCD700, while the textured bottom specimens were made of PBC2 (lead- free copper alloy). A Daphne Hydraulic Fluid 32 (Idemitsu) paraffinic oil was used as a lubricant. The sliding friction test was conducted with a running-in period for 10min at a load of 50N. Afterwards, the load was increased incrementally from 50N to 1600N, while the friction coefficient was measured simultaneously. The friction test results showed that the textured specimens have a better anti-seizure property compared to the non-textured specimens. Based on the obtained experimental results, it was concluded that the arrangement and area ratio of dimples play an important role in improving the anti-seizure property

交通行動と健康診断データ・心的傾向の関連分析 : 神奈川県大和市職員を対象として

本研究では，交通行動と健康状態，ならびにクルマの運転動機，交通手段への態度，五大性格特性，主観的幸福感等の心的傾向を計測する指標との関係性を把握することを目的に，神奈川県大和市職員を対象としたアンケート調査(n=479)を行った．このうち健康診断データの提供に同意した職員は180名であった．分析の結果，クルマ・バイク通勤者はメタボ該当者がそれ以外の通勤者の倍程度であった．心的傾向については，組織との関係が良好で地域のボランティアに参加しているほど，メタボや高BMIの傾向が示された．この理由としては，勤務先やボランティア等で飲食を伴う交流が盛んであった可能性が考えられる．メタボは危険因子が集積した状態であり，自覚症状が希薄であるため，健康指標として心的傾向と組み合わせた分析を行う際には留意が必要である