1,973 research outputs found
Ultraviolet photodepletion spectroscopy of dibenzo-18-crown-6-ether complexes with alkali metal cations
Ultraviolet photodepletion spectra of dibenzo-18-crown-6-ether complexes with alkali metal cations (M+-DB18C6, M = Cs, Rb, K, Na, and Li) were obtained in the gas phase using electrospray ionization quadrupole ion-trap reflectron time-of-flight mass spectrometry. The spectra exhibited a few distinct absorption bands in the wavenumber region of 35450ā37800 cm^(ā1). The lowest-energy band was tentatively assigned to be the origin of the S_0-S_1 transition, and the second band to a vibronic transition arising from the ābenzene breathingā mode in conjunction with symmetric or asymmetric stretching vibration of the bonds between the metal cation and the oxygen atoms in DB18C6. The red shifts of the origin bands were observed in the spectra as the size of the metal cation in M^+-DB18C6 increased from Li^+ to Cs^+. We suggested that these red shifts arose mainly from the decrease in the binding energies of larger-sized metal cations to DB18C6 at the electronic ground state. These size effects of the metal cations on the geometric and electronic structures, and the binding properties of the complexes at the S_0 and S_1 states were further elucidated by theoretical calculations using density functional and time-dependent density functional theories
The Causes of Early Implant Bone Loss: Myth or Science?
Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/141921/1/jper0322.pd
A novel family VII esterase with industrial potential from compost metagenomic library
<p>Abstract</p> <p>Background</p> <p>Among the vast microbial genomic resources now available, most microbes are unculturable in the laboratory. A culture-independent metagenomic approach is a novel technique that circumvents this culture limitation. For the screening of novel lipolytic enzymes, a metagenomic library was constructed from compost, and the clone of <it>estCS2 </it>was selected for lipolytic properties on a tributyrin-containing medium.</p> <p>Results</p> <p>The <it>estCS2 </it>sequence encodes a protein of 570 amino acid residues, with a predicted molecular mass of 63 kDa, and based on amino acid identity it most closely matches (45%) the carboxylesterase from <it>Haliangium ochraceum </it>DSM 14365. EstCS2 belong to family VII, according to the lipolytic enzyme classification proposed by Arpigny and Jaeger, and it retains the catalytic triad Ser<sub>245</sub>-Glu<sub>363</sub>-His<sub>466 </sub>that is typical of an Ī±/Ī² hydrolase. The Ser<sub>245 </sub>residue in the catalytic triad of EstCS2 is located in the consensus active site motif GXSXG. The EstCS2 exhibits strong activity toward <it>p</it>-nitrophenyl caproate (C6), and it is stable up to 60Ā°C with an optimal enzymatic activity at 55Ā°C. The maximal activity is observed at pH 9, and it remains active between pH 6-10. EstCS2 shows remarkable stability in up to 50% (v/v) dimethyl sulfoxide (DMSO) or dimethylformamide (DMF). The enzyme has the ability to cleave sterically hindered esters of tertiary alcohol, as well as to degrade polyurethanes, which are widely used in various industries.</p> <p>Conclusions</p> <p>The high stability of EstCS2 in organic solvents and its activity towards esters of ketoprofen and tertiary alcohols, and in polyurethane suggests that it has potential uses for many applications in biotransformation and bioremediation.</p
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Elevated cellular cholesterol in Familial Alzheimerās presenilin 1 mutation is associated with lipid raft localization of Ī²-amyloid precursor protein
Familial Alzheimerās disease (FAD)-associated presenilin 1 (PS1) serves as a catalytic subunit of Ī³-secretase complex, which mediates the proteolytic liberation of Ī²-amyloid (AĪ²) from Ī²-amyloid precursor protein (APP). In addition to its proteolytic role, PS1 is involved in non-proteolytic functions such as protein trafficking and ion channel regulation. Furthermore, postmortem AD brains as well as AD patients showed dysregulation of cholesterol metabolism. Since cholesterol has been implicated in regulating AĪ² production, we investigated whether the FAD PS1-associated cholesterol elevation could influence APP processing. We found that in CHO cells stably expressing FAD-associated PS1 ĪE9, total cholesterol levels are elevated compared to cells expressing wild-type PS1. We also found that localization of APP in cholesterol-enriched lipid rafts is substantially increased in the mutant cells. Reducing the cholesterol levels by either methyl-Ī²-cyclodextrin or an inhibitor of CYP51, an enzyme mediating the elevated cholesterol in PS1 ĪE9-expressing cells, significantly reduced lipid raft-associated APP. In contrast, exogenous cholesterol increased lipid raft-associated APP. These data suggest that in the FAD PS1 ĪE9 cells, the elevated cellular cholesterol level contributes to the altered APP processing by increasing APP localized in lipid rafts
Characteristics of high efficiency current charging system for HTS magnet with solar energy
AbstractIn terms of electrical energy, the technical fusion with solar energy system is promisingly applied in order to improve the efficiency in the power applications, since the solar energy system can convert an eternal electric energy in all-year-around. As one of such power applications, we proposed a current charging system for HTS magnet combined with solar energy (CHS). As this system can operate without external utility power to charge the HTS load magnet due to the solar energy, the operating efficiency is practically improved. The power converter, which is interfaced with solar energy and HTS magnet systems, plays an important role to transfer the stable electric energy and thus, the stabilized performance of the converter with solar energy system is one of essential factors. In this study, we investigated various charging performances under different operating conditions of the converter. In addition, operating characteristics have been analyzed by solving solar cell equivalent equations based on circuit simulation program
Fabrication of double-ceramic-layer TBCs by suspension plasma spray
Rare-earth zirconates, such as La2Zr2O7 and Gd2Zr2O7, have been investigated as one of the candidates for replacing conventional yttria-stabilized zirconia (YSZ) for thermal barrier coating (TBC) applications at higher turbine inlet temperatures. Rare-earth zirconate oxides exhibit little phase transformation upon heating up to melting temperature as well as low thermal conductivity, where as their mechanical properties is inferior to those of YSZ TBCs. Double-ceramic-layer (DCL) TBCs have been investigated in order to take advantage of beneficial characteristics of both YSZ and rare-earth zirconate.
In this study, the fabrication of DCL-TBCs with YSZ layer and rare-earth-zirconate top layer by using suspension plasma spray are reported. Microstructure, compositional profile, thermal conductivity, and thermal durability of DCL-TBCs are characterized. The usefulness of these DCL-TBCs is also discussed
De-Sitter nonlinear sigma model and accelerating universe
We consider a cosmology with a non-compact nonlinear sigma model.The target
space is of de-Sitter type and four scalar fields are introduced.The potential
is absent but cosmological constant term is added. One of the scalar
fields is time dependent and the remaining three fields have no time dependence
but only spatial dependence. We show that a very simple ansatz for the scalar
fields results in the accelerating universe with an exponential expansion at
late times. It is pointed out that the presence of the energy density and
pressure coming from the spatial variation of the three scalar fields plays an
essential role in our analysis which includes as a special case and
it discriminate from the standard -dominated acceleration. We perform
a stability analysis of the solutions and find that some solutions are
classically stable and attractor. We also present a non-perturbative solution
which asymptotically approaches an exponential acceleration and discusspossible
cosmological implications in relation with dark energy. It turns out that the
equation of state approaches asymptotically both from above and
below, but the crossing does not occur. It predicts present value of
, which is within the region allowed by the oservational
data. This solution also exhibits a power law expansion at early times, and the
energy density of the scalar fields mimics that of the stiff matter.Comment: 9 page
Towards standardizing Korean Grammatical Error Correction: Datasets and Annotation
Research on Korean grammatical error correction (GEC) is limited compared to
other major languages such as English and Chinese. We attribute this
problematic circumstance to the lack of a carefully designed evaluation
benchmark for Korean. Thus, in this work, we first collect three datasets from
different sources (Kor-Lang8, Kor-Native, and Kor-Learner) to cover a wide
range of error types and annotate them using our newly proposed tool called
Korean Automatic Grammatical error Annotation System (KAGAS). KAGAS is a
carefully designed edit alignment & classification tool that considers the
nature of Korean on generating an alignment between a source sentence and a
target sentence, and identifies error types on each aligned edit. We also
present baseline models fine-tuned over our datasets. We show that the model
trained with our datasets significantly outperforms the public statistical GEC
system (Hanspell) on a wider range of error types, demonstrating the diversity
and usefulness of the datasets.Comment: Add affiliation and email addres
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