Dust release from cold ring particles as a mechanism of spoke formation in Saturn's rings

Spokes in Saturn's rings are radially-extended structures consisting of dust grains. Although spacecraft and space telescope observations have revealed various detailed features of the spokes and their time variation, their formation mechanism is still under debate. Previous models examined charging mechanisms to attempt at explaining dust release from cm-sized ring particles; however, the attempt has been unsuccessful, because the electrostatic force caused by such charging mechanisms is much weaker than the cohesive force acting on dust grains at ordinary conditions in the ring environment. Here we propose a novel model for the formation of the spokes, where the temperature dependence of cohesion plays an essential role. Ring particles with a temperature below 60K adsorb an O2 ring atmosphere, which facilitates release of dust grains from them by a reduction in the cohesive force between the grains and the particles on the morning ansa. Then, intense electrostatic forces sufficient to overcome the cohesive force are generated on the surface of ring particles and the released dust grains form the structure of spokes. Our model explains observational features of the spokes including their longitudinal location, lifetime, radial expansion velocity, and seasonality.Comment: 37 pages, 7 figure

Effects of dielectric permittivities on skin heating due to millimeter wave exposure

<p>Abstract</p> <p>Background</p> <p>Because the possibility of millimeter wave (MMW) exposure has increased, public concern about the health issues due to electromagnetic radiation has also increased. While many studies have been conducted for MMW exposure, the effect of dielectric permittivities on skin heating in multilayer/heterogeneous human-body models have not been adequately investigated. This is partly due to the fact that a detailed investigation of skin heating in a multilayer model by computational methods is difficult since many parameters are involved. In the present study, therefore, theoretical analyses were conducted to investigate the relationship between dielectric permittivities and MMW-induced skin heating in a one-dimensional three-layer model (skin, fat, and muscle).</p> <p>Methods</p> <p>Approximate expressions were derived for the temperature elevation and temperature difference in the skin due to MMW exposure from analytical solutions for the temperature distribution. First, the power absorption distribution was approximated from the analytical solution for a one-layer model (skin only). Then, the analytical expression of the temperature in the three-layer model was simplified on the basis of the proposal in our previous study. By examining the approximate expressions, the dominant term influencing skin heating was clarified to identify the effects of the dielectric permittivities. Finally, the effects of dielectric permittivities were clarified by applying partial differentiation to the derived dominant term.</p> <p>Results</p> <p>Skin heating can be characterized by the parameters associated with the dielectric permittivities, independently of morphological and thermal parameters. With the derived expressions, it was first clarified that skin heating correlates with the total power absorbed in the skin rather than the specific absorption rate (SAR) at the skin surface or the incident power density. Using Debye-type expression we next investigated the effect of frequency dispersion on the complex relative permittivity of tissue. The parametric study on the total power absorbed in the skin showed that skin heating increases as the static permittivity and static conductivity decrease. In addition, the maximum temperature elevation on the body surface was approximately 1.6 times that of the minimum case. This difference is smaller than the difference caused by the thermal and morphological parameters reported in our previous study.</p> <p>Conclusion</p> <p>This paper analytically clarified the effects of dielectric permittivities on the thermally steady state temperature elevation and the temperature difference in the skin of a one-dimensional three-layer model due to MMW exposure.</p

Lack of GTP-bound Rho1p in secretory vesicles of Saccharomyces cerevisiae

Rho1p, an essential Rho-type GTPase in Saccharomyces cerevisiae, activates its effectors in the GTP-bound form. Here, we show that Rho1p in secretory vesicles cannot activate 1,3-β-glucan synthase, a cell wall synthesizing enzyme, during vesicular transport to the plasma membrane. Analyses with an antibody preferentially reacting with the GTP-bound form of Rho1p revealed that Rho1p remains in the inactive form in secretory vesicles. Rom2p, the GDP/GTP exchange factor of Rho1p, is preferentially localized on the plasma membrane even when vesicular transport is blocked. Overexpression of Rom2p results in delocalization of Rom2p and accumulation of 1,3-β-glucan in secretory vesicles. Based on these results, we propose that Rho1p is kept inactive in intracellular secretory organelles, resulting in repression of the activity of the cell wall–synthesizing enzyme within cells

The Role of Mannan-Binding Lectin (MBL) Gene Polymorphism in Ulcerative Colitis

Series studies suggest that enteropathogenic microorganisms play a substantial role in the clinical initiation and relapses of ulcerative colitis (UC). Mannan-binding lectin (MBL) is an important constituent of the innate immune system, and deficiency of MBL has been reported to increase the overall susceptibility of an individual to infectious disease. This study was aimed to investigate the associations between polymorphisms of the MBL gene and UC. Recruited in this study were 108 Japanese patients with UC and 144 healthy control subjects. Polymorphism at codon 54 of exon 1 of the MBL gene was investigated by polymerase chain reaction based restriction fragment length polymorphism. In general, no significant difference in MBL polymorphism was found between UC patients and health controls. However, the frequency of A carriers was significantly higher in the relapsing cases than controls (Odds ration = 2.19, 95%CI, 1.10–4.34; p = 0.023), and similar tendency was also found in A/A genotype. In conclusion, the polymorphism at codon 54 of exon 1 of the MBL gene associated with the susceptibility to the relapsing phenotype of ulcerative colitis. It suggests that codon 54 A variants of MBL gene may have an increased risk for the flare-ups of UC

Absence of Common Polymorphisms of Toll Like Receptor 4 (TLR4): Asp299Gly, Thr399Ile in Patients with Gastroduodenal Diseases in Japan

Host genetic factors may play a key role in determining the long-term outcome of the Helicobacter pylori (H. pylori) infection. Toll-like receptor 4 (TLR4) mediated recognition of lipo-polysaccharide (LPS) is required for efficient recognition of gram-negative bacterial infections. The aim of this study is to investigate the effects of common polymorphisms of TLR4 Asp299Gly, Thr399Ile in patients with gastroduodenal diseases in Japanese population. The study was performed in 149 gastric cancer (GC) cases (mean age 64.0 ± 12.4, M:F = 109:40) and 94 patients without evidence of GC (mean age 64.1 ± 12.3, M:F = 65:25) as the control group. TLR4 Asp299Gly, Thr399Ile were determined by Polymerase chain reaction-length of polymorphisms (PCR-RFLP) in all the patients. Asp299Gly, Thr399Ile were not detected in all 243 patients enrolled in this study. In conclusion, our data suggest that TLR4 Asp299Gly, Thr399Ile are very rare in Japanese population and thus they may not be a important factor in determining the outcome of H. pylori infected individuals in Japan