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Search Results: 1 - 10 of 2406 matches for " Kenji Kurosaki "
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Impact of photoevaporative mass loss on masses and radii of water-rich sub/super-Earths
Kenji Kurosaki,Masahiro Ikoma,Yasunori Hori
Physics , 2013, DOI: 10.1051/0004-6361/201322258
Abstract: Recent progress in transit photometry opened a new window to the interior of super-Earths. From measured radii and masses, we can infer planetary internal compositions. It has been recently revealed that super-Earths are diverse in composition. Such a diversity is thought to arise from diversity in volatile content. The stability of the volatile components is to be examined, because hot super-Earths undergo photo-evaporative mass loss. While several studies investigated the impact of photo-evaporative mass loss on hydrogen-helium envelopes, there are few studies as to the impact on water-vapor envelopes. To obtain theoretical prediction to future observations, we also investigate the relationships among masses, radii, and semimajor axes of water-rich sub/super-Earths that have undergone photo-evaporative mass loss. We simulate the interior structure and evolution of sub/super-Earths that consist of a rocky core surrounded by a water envelope, including mass loss due to the stellar XUV-driven energy-limited hydrodynamic escape. We find that the photo-evaporative mass loss has a significant impact on the evolution of hot sub/super-Earths. We then derive the threshold planetary mass and radius below which the planet loses its water envelope completely as a function of the initial water content, and find that there are minimums of the threshold mass and radius. We constrain the domain in the parameter space of planetary mass, radius, and semimajor axis in which sub/super-Earths never retain water envelopes in 1-10 Gyr. This would provide an essential piece of information for understanding the origin of close-in low-mass planets. The current uncertainties in stellar XUV flux and its heating efficiency, however, prevent us from deriving robust conclusions. Nevertheless, it seems to be a robust conclusion that Kepler planet candidates contain a significant number of rocky sub/super-Earths.
Starspots - Transit Depth Relation of the Evaporating Planet Candidate KIC 12557548b
Hajime Kawahara,Teruyuki Hirano,Kenji Kurosaki,Yuichi Ito,Masahiro Ikoma
Physics , 2013, DOI: 10.1088/2041-8205/776/1/L6
Abstract: Violent variation of transit depths and an ingress-egress asymmetry of the transit light curve discovered in KIC 12557548 have been interpreted as evidences of a catastrophic evaporation of atmosphere with dust (M_p gtrsim 1 M_oplus/Gyr) from a close-in small planet. To explore what drives the anomalous atmospheric escape, we perform time-series analysis of the transit depth variation of Kepler archival data for ~ 3.5 yr. We find a ~ 30% periodic variation of the transit depth with P1 = 22.83 pm 0.21 days, which is within the error of the rotation period of the host star estimated using the light curve modulation, Prot = 22.91 pm 0.24 days. We interpret the results as evidence that the atmospheric escape of KIC 12557548b correlates with stellar activity. We consider possible scenarios that account for both the mass loss rate and the correlation with stellar activity. X-ray and ultraviolet (XUV)-driven evaporation is possible if one accepts a relatively high XUV flux and a high efficiency for converting the input energy to the kinetic energy of the atmosphere. Star-planet magnetic interaction is another possible scenario though huge uncertainty remains for the mass loss rate.
Welcome to Antibodies: A New Open Access, Multidisciplinary Journal
Tomohiro Kurosaki
Antibodies , 2012, DOI: 10.3390/antib1010001
Abstract: Secreted antibodies are a key player for exerting appropriate humoral immunity. For instance, in infectious diseases, poly-specific “natural” antibodies provide early protection, independent of T cell help. If this line of defense is crossed, T cell-dependent immune responses then generate a humoral memory provided by long-lived plasma cells secreting specific antibodies of adapted avidity and isotype. Secreted antibodies provide an efficient line of defense against re-infection and are backed up by specific memory B and T cells. In the field of humoral immunity, great discoveries including identification of a special T cell subset helping B cell activation (TFH), have been made in a last couple of years; however, important questions (such as mechanisms for affinity maturation of antibodies) still remain. [...]
Enhancement of thermoelectric efficiency of CoSb3-based skutterudites by double filling with K and Tl
Ken Kurosaki
Frontiers in Chemistry , 2014, DOI: 10.3389/fchem.2014.00084
Abstract: The high-temperature thermoelectric properties of thallium (Tl) and potassium (K) double-filled cobalt antimonide (CoSb3)-based skutterudites with nominal compositions TlxK0.3Co4Sb12 (x = 0.1 ? 0.3) were investigated. The filling fraction of Tl in CoSb3 was enhanced by co-filling with K, which resulted in all of the samples showing the filled-skutterudite single phase. Owing to the high filling ratio, the carrier concentration in the sample with x = 0.3 was as high as 4.3 × 1020 cm?3 at room temperature. Furthermore, quite low lattice thermal conductivity (as low as 0.9 Wm?1K?1) was obtained for the sample with x = 0.3, probably because of strong phonon scattering by the Tl and K co-rattling effect, which resulted in a maximum zT of around one at 773 K.
Direct definition of a ternary infinite square-free sequence
Tetsuo Kurosaki
Computer Science , 2007, DOI: 10.1016/j.ipl.2007.11.012
Abstract: We propose a new ternary infinite (even full-infinite) square-free sequence. The sequence is defined both by an iterative method and by a direct definition. Both definitions are analogous to those of the Thue-Morse sequence. The direct definition is given by a deterministic finite automaton with output. In short, the sequence is automatic.
Matter-Wave Bright Solitons with a Finite Background in Spinor Bose-Einstein Condensates
Tetsuo Kurosaki,Miki Wadati
Physics , 2007, DOI: 10.1143/JPSJ.76.084002
Abstract: We investigate dynamical properties of bright solitons with a finite background in the F=1 spinor Bose-Einstein condensate (BEC), based on an integrable spinor model which is equivalent to the matrix nonlinear Schr\"{o}dinger equation with a self-focusing nonlineality. We apply the inverse scattering method formulated for nonvanishing boundary conditions. The resulting soliton solutions can be regarded as a generalization of those under vanishing boundary conditions. One-soliton solutions are derived in an explicit manner. According to the behaviors at the infinity, they are classified into two kinds, domain-wall (DW) type and phase-shift (PS) type. The DW-type implies the ferromagnetic state with nonzero total spin and the PS-type implies the polar state, where the total spin amounts to zero. We also discuss two-soliton collisions. In particular, the spin-mixing phenomenon is confirmed in a collision involving the DW-type. The results are consistent with those of the previous studies for bright solitons under vanishing boundary conditions and dark solitons. As a result, we establish the robustness and the usefulness of the multiple matter-wave solitons in the spinor BECs.
Efficient Production of δ-Guaiene, an Aroma Sesquiterpene Compound Accumulated in Agarwood, by Mevalonate Pathway-Engineered Escherichia coli Cells  [PDF]
Fumiya Kurosaki, Takahiro Kato, Norihiko Misawa, Futoshi Taura
Advances in Bioscience and Biotechnology (ABB) , 2016, DOI: 10.4236/abb.2016.711042
Abstract: Mevalonate pathway for isoprenoid biosynthesis was constructed in Escherichia coli cells by the transformation with a gene cluster isolated from Streptomyces sp., and farnesyl diphosphate synthase and δ-guaiene synthase genes were coexpressed in this strain. This transformant was capable of liberating an appreciable amount of δ-guaiene, an aroma sesquiterpene compound accumulated in agarwood, and its concentration was elevated to more than 30 μg/ml culture by the incubation with mevalonolactone as an isoprene precursor in a nutrient-enriched Terrific broth. Coexpression of type 1 isopentenyl diphosphate isomerase plus acetoacetyl-CoA ligase genes also enhanced δ-guaiene production, and the concentration of the compound was approximately 38 - 42 μg/ml culture in the presence of mevalonolactone or lithium acetoacetate. These results clearly indicate that mevalonate pathway-engineered E. coli cells showed an appreciable δ-guaiene producing activity in the en- riched medium in the presence of appropriate isoprene precursors.
Optical-to-Near-Infrared Simultaneous Observations for the Hot Uranus GJ3470b: A Hint for Cloud-free Atmosphere
Akihiko Fukui,Norio Narita,Kenji Kurosaki,Masahiro Ikoma,Kenshi Yanagisawa,Daisuke Kuroda,Yasuhiro Shimizu,Yasuhiro H. Takahashi,Hiroshi Ohnuki,Masahiro Onitsuka,Teruyuki Hirano,Takuya Suenaga,Kiyoe Kawauchi,Shogo Nagayama,Kouji Ohta,Michitoshi Yoshida,Nobuyuki Kawai,Hideyuki Izumiura
Physics , 2013, DOI: 10.1088/0004-637X/770/2/95
Abstract: We present optical (g', R_c, and I_c) to near-infrared (J) simultaneous photometric observations for a primary transit of GJ3470b, a Uranus-mass transiting planet around a nearby M dwarf, by using the 50-cm MITSuME telescope and the 188-cm telescope, both at Okayama Astrophysical Observatory. From these data, we derive the planetary mass, radius, and density as 14.1 \pm 1.3 M_earth, 4.32^{+0.21}_{-0.10} R_earth, and 0.94 \pm 0.12 g cm^{-3}, respectively, thus confirming the low density that was reported by Demory et al. based on the Spitzer/IRAC 4.5-micron photometry (0.72^{+0.13}_{-0.12} g cm^{-3}). Although the planetary radius is about 10% smaller than that reported by Demory et al., this difference does not alter their conclusion that the planet possesses a hydrogen-rich envelope whose mass is approximately 10% of the planetary total mass. On the other hand, we find that the planet-to-star radius ratio (R_p/R_s) in the J band (0.07577^{+0.00072}_{-0.00075}) is smaller than that in the I_c (0.0802 \pm 0.0013) and 4.5-micron (0.07806^{+0.00052}_{-0.00054}) bands by 5.9% \pm 2.0% and 3.0% \pm 1.2%, respectively. A plausible explanation for the differences is that the planetary atmospheric opacity varies with wavelength due to absorption and/or scattering by atmospheric molecules. Although the significance of the observed R_p/R_s variations is low, if confirmed, this fact would suggest that GJ3470b does not have a thick cloud layer in the atmosphere. This property would offer a wealth of opportunity for future transmission-spectroscopic observations of this planet to search for certain molecular features, such as H2O, CH4, and CO, without being prevented by clouds.
Evolution based on genome structure: the “diagonal genome universe”  [PDF]
Kenji Sorimachi
Natural Science (NS) , 2010, DOI: 10.4236/ns.2010.210137
Abstract: The ratios of amino acid to the total amino acids and those of nucleotides to the total nucleotides in genes or genomes are suitable indexes to compare whole gene or genome characteristics based on the large number of nucleotides rather than their sequences. As these ratios are strictly calculated from nucleotide sequences, the values are independent of experimental errors. In the present mini-review, the following themes are approached according to the ratios of amino acids and nucleotides to their total numbers in the genome: prebiotic evolution, the chronological precedence of protein and codon formations, genome evolution, Chargaff’s second pa- rity rule, and the origins of life. Amino acid formation might have initially occurred during pre- biotic evolution, the “amino acid world”, and amino acid polymerization might chronologically precede codon formation at the end of prebiotic evolution. All nucleotide alterations occurred synchronously over the genome during biolo- gical evolution. After establishing primitive lives, all nucleotide alterations have been governed by linear formulae in nuclear and organelle genomes consisting of the double-stranded DNA. When the four nucleotide contents against each individual nucleotide content in organelles are expressed by four linear regression lines representing the diagonal lines of a 0.5 square – the “Diagonal Genome Universe”, evolution obeys Chargaff’s second parity rule. The fact that linear regression lines intersect at a single point su- ggests that all species originated from a single life source.
Evolution from Primitive Life to Homo sapiens Based on Visible Genome Structures: The Amino Acid World  [PDF]
Kenji Sorimachi
Natural Science (NS) , 2009, DOI: 10.4236/ns.2009.12013
Abstract: It is not too much to say that molecular biology, including genome research, has progressed based on the determination of nucleotide or amino acid sequences. However, these ap-proaches are limited to the analysis of relatively small numbers of the same genes among spe-cies. On the other hand, by graphical presenta-tion of the ratios of the numbers of amino acids present to the total numbers of amino acids presumed from the target gene(s) or genome or those of the numbers of nucleotides present to the total numbers of nucleotides calculated from the target gene(s) or genome, we can readily draw conclusions from extraordinarily huge data sets integrated by human intelli-gence. 1) Assuming polymerization of amino acids or nucleotides in a simulation analysis based on a random choice, proteins were formed by simple amino acid polymerization, while nucleotide polymerization to form nucleic acids encoding specific proteins needed certain specific control. These results proposed that protein formation chronologically preceded codon formation during the establishment of primitive life forms. In the prebiotic phase, amino acid composition was a dominant factor that determined protein characteristics; the “Amino Acid World”. 2) The genome is constructed homogeneou- sly from putative small units displaying similar codon usages and coding for similar amino acid compositions; the unit is a gene assembly en-coding 3,000 - 7,000 amino acid residues and this unit size is independent not only of genome size, but also of species. 3) In codon evolution, all nucleotide alterna-tions are correlated, not only in coding regions, but also in non-coding regions; the correlations can be expressed by linear formulas; y = ax + b, where “y” and “x” represent nucleotide con-tents, and “a” and “b” are constant. 4) The basic pattern of cellular amino acid compositions obtained from whole cell lysates is conserved from bacteria to Homo sapiens, and resembles that calculated from complete genomes. This basic pattern is characterized by a “star-shape” that changes slightly among species, and changes in amino acid composi-tion seem to reflect biological evolution. 5) Organisms can essentially be classified according to two codon patterns. Biological evolution due to nucleotide sub-stitutions can be expressed by simple linear formulas based on mathematical principles, while natural selection must affect species pre- servation after nucleotide alternations. There-fore, although Darwin’s natural selection is not directly involved in nucleotide alternations, it contributes obviously to the
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