3,862 research outputs found
Kinetic, Spectroscopic, and X-Ray Crystallographic Evidence for the Cooperative Mechanism of the Hydration of Nitriles Catalyzed by a Tetranuclear Ruthenium-μ-oxo-μ-hydroxo Complex
The tetranuclear ruthenium-oxo-hydroxo-hydride complex {[(PCy3)(CO)RuH]4(μ4-O)(μ3-OH)(μ2-OH)} (1) was found to be a highly cooperative catalyst for the nitrile hydration reaction. The cooperative mechanism of the hydration of benzonitrile was established by Hill inhibition kinetics. The treatment of a nitrile substrate with complex 1 led to the catalytically relevant nitrile-coordinated tetraruthenium complex 3. The X-ray structure of the nitrile-coordinated complex 3 showed a considerably “relaxed” tetrameric core structure compared to that of 1. The hydration of para-substituted benzonitriles p-X-C6H4CN with an electron-withdrawing group (X = Cl, Br, CO2H, CF3) exhibited cooperative kinetics, as indicated by the sigmoidal saturation kinetics, while the hydration of nitriles with an electron-donating group (X = OH, OMe, t-Bu, CH3) obeyed Michaelis–Menten saturation kinetics. The formation of a ruthenium hydride species was observed during the hydration of methacrylonitrile, and its monomeric nature was established by using DOSY NMR techniques
Highly Cooperative Tetrametallic Ruthenium-μ-Oxo-μ-Hydroxo Catalyst for the Alcohol Oxidation Reaction
The tetrametallic ruthenium-oxo-hydroxo-hydride complex {[(PCy3)(CO)RuH]4(μ4-O)(μ3-OH)(μ2-OH)} (1) was synthesized in two steps from the monomeric complex (PCy3)(CO)RuHCl (2). The tetrameric complex 1 was found to be a highly effective catalyst for the transfer dehydrogenation of alcohols. Complex 1 showed a different catalytic activity pattern toward primary and secondary benzyl alcohols, as indicated by the Hammett correlation for the oxidation reaction of p-X-C6H4CH2OH (ρ = −0.45) and p-X-C6H4CH(OH)CH3 (ρ = +0.22) (X = OMe, CH3, H, Cl, CF3). Both a sigmoidal curve from the plot of initial rate vs [PhCH(OH)CH3] (K0.5 = 0.34 M; Hill coefficient, n = 4.2 ± 0.1) and the phosphine inhibition kinetics revealed the highly cooperative nature of the complex for the oxidation of secondary alcohols
Inclusive angular distribution of alpha and Li fragments produced in the Fe-C and Fe-Pb collisions at 1.88 GeV/u
The LS (laboratory system) emission angles theta for 2188 and 298 Li fragments, produced inclusively in relativistic Fe-C and Fe-Pb collisions, have been measured in reference to incident Fe-ion beam tracks nearby in nuclear emulsion. An empirical differential frequency formula, dN(cot theta) = exp (a + b cot theta)d(cot theta) is obtained with the constant b approx. = -0.026 at 1.88 GeV/u, which seems to be independent on the kinds of target nucleus as well as on the kinds of projectile fragments
The Cosmic Lens All-Sky Survey parent population - I. Sample selection and number counts
We present the selection of the Jodrell Bank Flat-spectrum (JBF) radio source
sample, which is designed to reduce the uncertainties in the Cosmic Lens
All-Sky Survey (CLASS) gravitational lensing statistics arising from the lack
of knowledge about the parent population luminosity function. From observations
at 4.86 GHz with the Very Large Array, we have selected a sample of 117
flat-spectrum radio sources with flux densities greater than 5 mJy. These
sources were selected in a similar manner to the CLASS complete sample and are
therefore representative of the parent population at low flux densities. The
vast majority (~90 per cent) of the JBF sample are found to be compact on the
arcsecond scales probed here and show little evidence of any extended radio jet
emission. Using the JBF and CLASS complete samples we find the differential
number counts slope of the parent population above and below the CLASS 30 mJy
flux density limit to be -2.07+/-0.02 and -1.96+/-0.12, respectively.Comment: 10 pages, 4 figures, accepted for publication in MNRA
Medium Resolution Near-Infrared Spectra of the Host Galaxies of Nearby Quasars
We present medium resolution near-infrared host galaxy spectra of low
redshift quasars, PG 0844 + 349 (z=0.064), PG 1226 + 023 (z=0.158), and PG
1426+015 (z=0.086). The observations were done by using the Infrared Camera and
Spectrograph (IRCS) at the Subaru 8.2 m telescope. The full width at half
maximum of the point spread function was about 0.3 arcsec by operations of an
adaptive optics system, which can effectively resolve the quasar spectra from
the host galaxy spectra. We spent up to several hours per target and developed
data reduction methods to reduce the systematic noises of the telluric
emissions and absorptions. From the obtained spectra, we identified absorption
features of Mg I (1.503 um), Si I (1.589 um) and CO (6-3) (1.619 um), and
measured the velocity dispersions of PG 0844 + 349 to be 132+/-110 km s-1 and
PG 1426 + 015 to be 264+/-215 km s-1. By using an M_BH-sigma relation of
elliptical galaxies, we derived the black hole (BH) mass of PG 0844+349,
log(M_BH/M_SUN) = 7.7+/-5.5 and PG 1426+015, log(M_BH/M_SUN) = 9.0+/-7.5. These
values are consistent with the BH mass values from broad emission lines with an
assumption of a virial factor of 5.5.Comment: 16 pages, 5 figure
Observation of First-Order Metal-Insulator Transition without Structural Phase Transition in VO_2
An abrupt first-order metal-insulator transition (MIT) without structural
phase transition is first observed by current-voltage measurements and
micro-Raman scattering experiments, when a DC electric field is applied to a
Mott insulator VO_2 based two-terminal device. An abrupt current jump is
measured at a critical electric field. The Raman-shift frequency and the
bandwidth of the most predominant Raman-active A_g mode, excited by the
electric field, do not change through the abrupt MIT, while, they, excited by
temperature, pronouncedly soften and damp (structural MIT), respectively. This
structural MIT is found to occur secondarily.Comment: 4 pages, 4 figure
Observational Evidence for Coronal Twisted Flux Rope
Multi-instrument data sets of NOAA AR10938 on Jan. 16, 2007, (e.g.,
{\emph{Hinode}}, {\it{STEREO}}, {\it{GOES}}, {\it{MLSO}} and {\it{ISOON}}
H) are utilized to study the fine structure and evolution of a magnetic
loop system exhibiting multiple crossing threads, whose arrangement and
individual shapes are very suggestive of individual field lines in a flux rope.
The footpoints of the magnetic threads are closely rooted into pores and plage
areas. A C-class flare recorded by {\it{GOES}} at approximately 2:35 UT near
one of the footpoints of the multi-thread system (along with a wisp of loop
material shown by EUV data) led to the brightening of the magnetic structure
revealing its fine structure with several threads that indicate a high degree
of linking (suggesting a left-handed helical pattern as shown by the filament
structure formed later-on). EUV observations by {\emph{Hinode}}/EIS of hot
spectral lines at 2:46 UT show a complex structure of coronal loops. The same
features were observed about 20 minutes later in X-ray images from
{\emph{Hinode}}/XRT and about 30 minutes further in EUV images of
{\it{STEREO}}/SECCHI/EUVI with much better resolution. H and 304 {\AA}
images revealed the presence of several filament fibrils in the same area. They
evolved a few hours later into a denser structure seemingly showing helical
structure, which persistently lasted for several days forming a segment of a
larger scale filament. The present observations provide an important indication
for a flux robe as a precursor of a solar filament.Comment: 13 pages, 4 figure
THE EFFECTS OF SPORTS TAPING ON IMPACT FORCES AND MECHANICAL BEHAVIORS OF SOFT TISSUE DURING DROP LANDING
Wakeling et al. (2002) proposed that resonant soft tissue vibrations caused by impact force may be potentially harmful. Bartold et al. (2009) reported that longitudinal strain of the plantar fascia was significantly reduced under the tape condition and it affected alleviating the symptoms of plantar fasciitis. Accordingly, if sports taping may develop the goal of reducing the strain and stress of muscle, it can be illustrated to help muscle tuning to minimize soft tissue vibration and prevent injury. Since the proven mechanical effects of sports taping not established, the purpose of this study was to determine how sports taping affects impact force and mechanical behaviors in the lower extremity
- …