246 research outputs found
Stable cosmology in ghost-free quasidilaton theory
We present a novel cosmological solution in the framework of extended
quasidilaton theory which underwent scrutiny recently. We only consider terms
that do not generate the Boulware-Deser degree of freedom, hence the
"ghost-free" quasidilaton theory, and show three new branches of cosmological
evolution therein. One of the solutions passes the perturbative stability
tests. This new solution exhibits a late time self-acceleration and all
graviton polarizations acquire masses that converge to a constant in the
asymptotic future. Moreover, all modes propagate at the speed of light. We
propose that this solution can be used as a benchmark model for future
phenomenological studies.Comment: 12 page
Role of matter in extended quasidilaton massive gravity
The extended quasidilaton theory is one of the simplest Lorentz-invariant
massive gravity theories which can accommodate a stable self-accelerating
vacuum solution. In this paper we revisit this theory and study the effect of
matter fields. For a matter sector that couples minimally to the physical
metric, we find hints of a Jeans type instability in the IR. In the analogue
k-essence field set-up, this instability manifests itself as an IR ghost for
the scalar field perturbation, but this can be interpreted as a classical
instability that becomes relevant below some momentum scale in terms of matter
density perturbations. We also consider the effect of the background evolution
influenced by matter on the stability of the gravity sector perturbations. In
particular, we address the previous claims of ghost instability in the IR
around the late time attractor. We show that, although the matter-induced
modification of the evolution potentially brings tension to the stability
conditions, one goes beyond the regime of validity of the effective theory well
before the solutions become unstable. We also draw attention to the fact that
the IR stability conditions are also enforced by the existence requirements of
consistent background solutions.Comment: 17 pages, accepted for publication in PR
Effects of Alloying Elements on the Activity of Nitrogen in Austenite : II Effect of Nickel and Solubility of Nitrogen in Pure Iron
Solubility of nitrogen in austenite was measured in iron-nickel alloys in order to study the effect of nickel on the activity of nitrogen in austenite and to obtain the value of their interaction parameter. The composition of samples covered the whole range of iron-nickel alloys biginning from pure iron to pure metallic nickel, and the experimental temperatures were 1050° and 1250°C. The presence of nickel increased the activity of nitrogen in austenite and the interaction parameters were obtained as : The solubility of nitrogen in pure gamma-iron under the various partial pressures of less than 1 atm of nitrogen was measured at 1150°C and it was shown that Sieverts' law was obeyed on the dissolution of nitrogen in austenite. The free energy of solution of nitrogen in austenite is given as : A close relationship between the interaction parameters and the atomic number of alloying elements was observed and it was also found that the absolute value of the interaction parameters was decreased with the increase in temperature. The differences of the interchange energies between the pair of iron-nitrogen and that of alloying element-nitrogen were calculated from two theoretical equations, but the results of calculation did not show a good agreement
Tracker and scaling solutions in DHOST theories
In quadratic-order degenerate higher-order scalar-tensor (DHOST) theories
compatible with gravitational-wave constraints, we derive the most general
Lagrangian allowing for tracker solutions characterized by , where is the time derivative of a scalar field ,
is the Hubble expansion rate, and is a constant. While the tracker is
present up to the cubic-order Horndeski Lagrangian , where are constants and is the kinetic energy of
, the DHOST interaction breaks this structure for . Even in the
latter case, however, there exists an approximate tracker solution in the early
cosmological epoch with the nearly constant field equation of state
. The scaling solution, which corresponds to
, is the unique case in which all the terms in the field density
and the pressure obey the scaling relation
. Extending the analysis to the
coupled DHOST theories with the field-dependent coupling between the
scalar field and matter, we show that the scaling solution exists for
, where and are constants. For
the constant , i.e., , we derive fixed points of the dynamical
system by using the general Lagrangian with scaling solutions. This result can
be applied to the model construction of late-time cosmic acceleration preceded
by the scaling -matter-dominated epoch.Comment: 12 page
閉塞型睡眠時無呼吸症候群患者における早朝の高分子量フォンウィルブランド因子減少は無呼吸の重症度を反映する
Plasma von Willebrand factor (VWF), produced in and released from vascular endothelial cells by various stimuli including hypoxia, induces platelet aggregation under high shear stress and plays dual pivotal roles in haemostasis and thrombosis within arterioles, which are regulated by the size of vWF multimers (VWFMs). Patients with obstructive sleep apnoea (OSA) have increased risk of thrombotic cardiovascular events, but the pathogenesis is unclear. We examined the relationship between VWF and OSA by measuring VWF antigen (VWF:Ag), VWFMs, VWF collagen binding activity (VWF:CB) and a disintegrin-like, metalloproteinase, and thrombospiondin type 1 motifs 13. A total of 58 OSA patients were enrolled. Blood samples were collected before sleep, after sleep, and after one night of nasal continuous positive airway pressure therapy. Based on VWFM analysis, OSA patients were classified into three groups; consistently normal VWFMs (group 1, n=29), increased high molecular weight (HMW)-VWFMs at 06:00 h (group 2, n=18), and decreased or absent HMW-VWFMs at 06:00 h (group 3, n=11). Patients in group 3 had significantly worse apnoea/hypopnoea index; VWF:CB followed a similar pattern. We observed a significant decrease in platelet count between 21:00 h and 06:00 h in OSA patients, potentially associated with reduced larger VWFMs together with decreased VWF:Ag levels. Severe OSA may contribute to an arterial pro-thrombotic state.博士(医学)・乙第1294号・平成24年5月28日Copyright © 2012 by the European Respiratory Societ
Effect of Rust Inhibitor in Brine on Corrosion Properties of Copper
In this study, the effects of rust inhibitors in brine on corrosion behaviors of copper were investigated by measurement of cathode and anode polarization curves and an immersion test. For rust inhibitors, benzotriazole, sodium benzoate and sodium nitrite were prepared. From measurement results of cathode and anode polarization curves, it was found that the corrosion rate of copper in the benzotriazole solution is low and a stable passive film with excellent corrosion resistance generates on the surface of copper in the solution. In the case of the sodium benzoate solution, the corrosion resistance of the passive film was inferior to that in the benzotriazole solution although the passive film generated on the surface of copper. In contrast, the passive film scarcely generated on the surface of copper in the sodium nitrite solution. The result shows that the rust preventive effect of the solution to copper is weak. Furthermore, the immersion test revealed that the benzotriazole solution has the rust preventive effect to copper. In contrast, the effect of the sodium benzoate solution is weak and that of the sodium nitrite solution is scarcely expected
- …