The role of hydrophobic interaction in phase transition and structure formation of lipid membranes and proteins

The hydrophobic interaction arises from the ordered structure of water around nonpolar groups of molecules in an aqueous solvent. Because biological systems are made of various macromolecules and amphiphiles which are suspended in aqueous solution, the hydrophobic interaction plays a very important role in the formation of higher-order structure and phase transitions in biological systems. Considering the hydrophobic interaction, the van der Waals interaction and the entropic effect, an equation of state of a lipid membrane was obtained which was analogous to the van der Waals equation. The characteristics of the lipid bilayer phase transition as well as the phase behaviors of a lipid monolayer were explained by this equation of state. Experimental evidence was obtained from ultrasonic measurements which indicated that its phase transition accompanys significant critical phenomena. Analysis of the hydrophobicity of amino acid sequences revealed that the morphology of the proteins was determined by the hydrophobicity alone. The essential role of the hydrophobic interaction in the morphogenesis of proteins could be confirmed by a denaturation experiment on a soluble protein, carbonic anhydrase B. Fluorescence measurements showed that an intermediate state, the so-called molten globule state, had a quite hydrophobic core, indicating that the globule shape of this protein is stabilized by the hydrophobic interaction.     

Efficient coannihilation process through strong Higgs self-coupling in LKP dark matter annihilation

We point out that the lightest Kaluza–Klein particle (LKP) dark matter in universal extra dimension (UED) models efficiently annihilates through the coannihilation process including the first KK Higgs bosons when the Higgs mass is slightly heavy as 200–230 GeV, which gives the large Higgs self-coupling. The large self-coupling naturally leads the mass degeneracy between the LKP and the first KK Higgs bosons and large annihilation cross sections of the KK Higgs bosons. These are essential for the enhancement of the annihilation of the LKP dark matter, which allows large compactification scale ∼1 TeV to be consistent with cosmological observations for the relic abundance of dark matter. We found that the thermal relic abundance of the LKP dark matter could be reconciled with the stringent constraint of electroweak precision measurements in the minimal UED model.     

Noncascading THz-wave parametric oscillator synchronously pumped by mode-locked picosecond Ti:sapphire laser in doubly-resonant external cavity

A noncascading terahertz (THz) wave parametric oscillator synchronously pumped by a mode-locked picosecond Ti:sapphire laser whose average power was less than 1 W was demonstrated with a noncollinear phase-matching MgO:LiNbO₃ crystal in an external enhancement cavity doubly resonant for both pump (780 nm) and signal (781-784 nm) waves. In the external cavity, in which the pump wave enhanced so as to reduce the pumping threshold of parametric processes, the signal wave could also resonate and thus be enhanced simultaneously, resulting in a THz wave output at approximately 0.9 THz as the idler wave. The novel dual enhancement of pump and signal waves reduced the threshold pumping intensity to approximately 50 MW/cm², which was much lower than that of a conventional externally pumped THz wave parametric oscillator with a crystal.     

Fractal structure of equipotential curves on a continuum percolation model

We numerically investigate the electric potential distribution over a two-dimensional continuum percolation model between the electrodes. The model consists of overlapped conductive particles on the background with an infinitesimal conductivity. Using the finite difference method, we solve the generalized Laplace equation and show that in the potential distribution, there appear quasi-equipotential clusters   which approximately and locally have the same values as steps and stairs. Since the quasi-equipotential clusters have the fractal structure, we compute the fractal dimension of equipotential curves and its dependence on the volume fraction over [0,1]$[0,1]$. The fractal dimension in [1.00, 1.246] has a peak at the percolation threshold _pc$p_c$.     

Observing quantum correlation of photons in Laguerre-Gauss modes using the Gouy phase

The effect of the Gouy phase, which is one of the geometrical phases of photons, is observed through quantum correlation in Laguerre-Gaussian (LG) modes. In an experiment, the relative phase of two different LG modes of measurement basis states is manipulated via the Gouy phase, and the observed coincidence count rates agree well with theoretical predictions. This result suggests that the Gouy phase can be used as a new tool to manipulate multidimensional photonic quantum states.     

Software for the data analysis of the arrival‐timing monitor at SACLA

X‐ray free‐electron laser (XFEL) pulses from SPring‐8 Ångstrom Compact free‐electron LAser (SACLA) with a temporal duration of <10 fs have provided a variety of benefits in scientific research. In a previous study, an arrival‐timing monitor was developed to improve the temporal resolution in pump–probe experiments at beamline 3 by rearranging data in the order of the arrival‐timing jitter between the XFEL and the synchronized optical laser pulses. This paper presents Timing Monitor Analyzer (TMA), a software package by which users can conveniently obtain arrival‐timing data in the analysis environment at SACLA. The package is composed of offline tools that pull stored data from cache storage, and online tools that pull data from a data‐handling server in semi‐real time during beam time. Users can select the most suitable tool for their purpose, and share the results through a network connection between the offline and online analysis environments.     

A high-sensitivity terahertz sensing method using a metallic mesh with unique transmission properties

Metallic meshes work as band-pass filters in the terahertz (THz) region, with their transmission spectra acutely affected by the refractive index of the material inside and above the metallic-mesh openings. We used a metallic mesh for high-sensitivity observations by focusing on the “dip,” that is, a sudden change in transmittance that only appeared when the THz wave was obliquely incident onto the metallic mesh. Here we consider the interference between apertures of the metallic mesh in the diagonal direction and explain the dip using finite-difference time-domain (FDTD) electromagnetic simulations.