308 research outputs found
False Vacuum in the Supersymmetric Mass Varying Neutrinos Model
We present detailed analyses of the vacuum structure of the scalar potential
in a supersymmetric Mass Varying Neutrinos model. The observed dark energy
density is identified with false vacuum energy and the dark energy scale of
order is understood by gravitationally suppressed supersymmetry
breaking scale, , in the model. The vacuum expectation
values of sneutrinos should be tiny in order that the model works. Some decay
processes of superparticles into acceleron and sterile neutrino are also
discussed in the model.Comment: 7 pages, 5 figures, revtex, typos correcte
Electrochemical and Mechanistic Study of Oxidative Degradation of Favipiravir by Electrogenerated Superoxide through Proton-Coupled Electron Transfer
Electrochemical analyses aided by density functional theory calculations were used to investigate the oxidative degradation of pyrazine antiviral drugs, 3-hydroxypyrazine-2-carboxamide (T-1105) and 6-fluoro-3-hydroxypyrazine-2-carboxamide (favipiravir, T-705), by the electrogenerated superoxide radical anion (O2•–). T-1105 and T-705 are antiviral RNA nucleobase analogues that selectively inhibit the RNA-dependent RNA polymerase. They are expected as a drug candidate against various viral infections, including COVID-19. The pyrazine moiety was decomposed by O2•– through proton-coupled electron transfer (PCET). Our results show that its active form, pyrazine-ribofuranosyl-5′-triphosphate, is easily oxidized under inflamed organs by overproduced O2•– through the PCET mechanism in the immune system. This mechanistic study implies that the oxidative degradation of pyrazine derivatives will be prevented by controlling the PCET through simple modification of the pyrazine structure
Effects of Nanosecond Laser Fabrication on Bioactivity of Pure Titanium
AbstractWe are developing surface modification techniques for dental implants with the aim of reducing the time required to realize good adhesion between bone and implant surfaces. A nanosecond Nd:YVO4 laser was used to modify the surfaces of commercially pure titanium (CP Ti) disks and their bioactivities were then evaluated. The surfaces of the CP Ti disks were covered by lines after laser treatment. This treatment created complex microasperities of titania with rutile and anatase crystal structures. This results in the formation of hydroxyapatite on surfaces immersed in 1.5-times concentrated simulated body fluid for 7 days, whereas no hydroxyapatite was observed on conventionally polished surfaces that were immersed under the same conditions. This indicates that laser treatment improves the bioactivity of CP Ti, which is a critical property for osseointegrated implants
Scattering polarization of 3-m water-ice feature by large icy grains
Water ice has a strong spectral feature at a wavelength of approximately
m, which plays a vital role in our understanding of the icy universe. In
this study, we investigate the scattering polarization of this water-ice
feature. The linear polarization degree of light scattered by m-sized icy
grains is known to be enhanced at the ice band; however, the dependence of this
polarization enhancement on various grain properties is unclear. We find that
the enhanced polarization at the ice band is sensitive to the presence of
m-sized grains as well as their ice abundance. We demonstrate that this
enhancement is caused by the high absorbency of the water-ice feature, which
attenuates internal scattering and renders the surface reflection dominant over
internal scattering. Additionally, we compare our models with polarimetric
observations of the low-mass protostar L1551 IRS 5. Our results show that
scattering by a maximum grain radius of a few microns with a low water-ice
abundance is consistent with observations. Thus, scattering polarization of the
water-ice feature is a useful tool for characterizing ice properties in various
astronomical environments.Comment: 19 pages, 17 figures, 1 table; Accepted for publication in Ap
In vitro production of L-cysteine using thermophilic enzymes
L-Cysteine (L-Cys) is a commercially important amino acid and widely used in food, pharmaceutical, and cosmetic industries. Commercial production of L-Cys has long been done by an acid-hydrolysis of human hair and animal feather, leading to the generation of a large quantity of hazardous wastes. Although several biotechnology companies have recently launched a fermentative production of L-Cys using engineered bacteria, these processes suffer from the low product titer mainly due to the cytotoxic effect of L-Cys. To provide an alternative approach for the commercial production of L-Cys, we aimed at the development of a non-fermentative, in vitro manufacturing system using thermophilic enzymes. In this system, enzymes from (hyper)thermophilic bacteria and archaea were assembled to construct an in vitro synthetic pathway for the one-pot conversion of glucose to L-Cys (Figure 1). By using experimentally optimized concentrations of enzymes, L-Cys could be produced at a rate of 0.9 g/L/h with a molar conversion yield of 25%.
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Propolis Components and Biological Activities from Stingless Bees Collected on South Sulawesi, Indonesia
Three new compounds, namely sulabiroins A (1) and B (2), and 2',3'-dihydro-3'-hydroxypapuanic acid (3), were isolated from the propolis of stingless bees (Tetragonula aff. biroi) collected on South Sulawesi, Indonesia. In addition, ten known compounds, (–)-papuanic acid (4), (–)-isocalolongic acid (5), isopapuanic acid (6), isocalopolyanic acid (7), glyasperin A (8), broussoflavonol F (9), (2S)-5,7-dihydroxy-4'-methoxy-8-prenylflavanone (10), isorhamnetin (11), (1'S)-2-trans,4-trans-abscisic acid (12), and (1'S)-2-cis,4-trans-abscisic acid (13) were identified. The structures of the new and known compounds were determined by spectroscopic analysis. The absolute configurations of sulabiroins A (1) and B (2) were determined by X-ray crystallography analysis and ECD calculation, respectively. The propolis from stingless bee (Tetragonula aff. biroi) collected on South Sulawesi contained compounds not present in propolis from other regions. Sulabiroin A (1) and isorhamnetin (11) were examined for xanthine oxidase (XO) inhibitory activity as one of biological activities; isorhamnetin (11) exhibited potent XO inhibitory activity, with an IC50 value of 3.9 µm
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