206 research outputs found
Microstructure of Winged Beans
Microstructures of seven plant introductions of winged beans (Psophocarpus tetragonolobus) produced in Okinawa, Japan were investigated. In cotyledonary cells of winged beans, protein bodies plus numerous lipid bodies were distributed in a cytoplasmic network. Starch granules were often found in some introductions but rarely in others. All seven introductions had very thick cell walls. The high protein, fat and hemicellulose contents of winged beans are consistent with the numerous protein bodies, lipid bodies and thick cell walls in the mature cotyledonary cells. The cell walls contained a number of depressions or cavities 1 to 2 lJ m deep which frequently occurred opposite complementary pits in adjacent cells (presumably pit-pairs). Plasmodesmata traverse the cell walls in the pit-pairs. In order to determine changes during development, cultivar UPS-32 cultivated at Fukuoka-city was used. In coty ledonary cells at 30 days after flowering, cell walls which had pitpairs with plasmodesmata, developing amyloplasts with starch granules, vacuoles with dense flocculent materials, tubular rough endoplasmic reticulum, mitochondria etc., were observed but no protein bodies or lipid bodies were apparent. Protein bodies and lipid bodies were, however, found at 45 days after flowering. Cotyledonary cells at 45 days contained many starch granules but mature seeds contained few, if any
A numerical study of the r-mode instability of rapidly rotating nascent neutron stars
The first results of numerical analysis of classical r-modes of {\it rapidly}
rotating compressible stellar models are reported. The full set of linear
perturbation equations of rotating stars in Newtonian gravity are numerically
solved without the slow rotation approximation. A critical curve of
gravitational wave emission induced instability which restricts the rotational
frequencies of hot young neutron stars is obtained. Taking the standard cooling
mechanisms of neutron stars into account, we also show the `evolutionary
curves' along which neutron stars are supposed to evolve as cooling and
spinning-down proceed. Rotational frequencies of stars suffering
from this instability decrease to around 100Hz when the standard cooling
mechanism of neutron stars is employed. This result confirms the results of
other authors who adopted the slow rotation approximation.Comment: 4 pages, 2 figures; MNRAS,316,L1(2000
Comparative Analysis of Super-Kamiokande and SNO Solar-Neutrino Data and the Photospheric Magnetic Field
We analyze Super-Kamiokande, SNO, and photospheric magnetic-field data for
the common time interval, namely the SNO D2O phase. Concerning rotational
modulation, the magnetic-field power spectrum shows the strongest peaks at the
second and sixth harmonics of the solar synodic rotation frequency [3 nu(rot)
and 7 nu(rot)]. The restricted Super-Kamiokande dataset shows strong modulation
at the second harmonic. The SNO D2O dataset shows weak modulation at that
frequency, but strong modulation in the sixth-harmonic frequency band. We
estimate the significance level of the correspondence of the Super-Kamiokande
second-harmonic peak with the corresponding magnetic-field peak to be 0.0004,
and the significance level of the correspondence of the SNO D2O sixth-harmonic
peak with the corresponding magnetic-field peak to be 0.009. By estimating the
amplitude of the modulation of the solar neutrino flux at the second harmonic
from the restricted Super-Kamiokande dataset, we find that the weak power at
that frequency in the SNO D2O power spectrum is not particularly surprising.
Concerning 9.43 yr-1, we find no peak at this frequency in the power spectrum
formed from the restricted Super-Kamiokande dataset, so it is no surprise that
this peak does not show up in the SNO D2O dataset, either.Comment: 32 pages, 8 tables, 16 figure
Second-order rotational effects on the r-modes of neutron stars
Techniques are developed here for evaluating the r-modes of rotating neutron
stars through second order in the angular velocity of the star. Second-order
corrections to the frequencies and eigenfunctions for these modes are evaluated
for neutron star models. The second-order eigenfunctions for these modes are
determined here by solving an unusual inhomogeneous hyperbolic boundary-value
problem. The numerical techniques developed to solve this unusual problem are
somewhat non-standard and may well be of interest beyond the particular
application here. The bulk-viscosity coupling to the r-modes, which appears
first at second order, is evaluated. The bulk-viscosity timescales are found
here to be longer than previous estimates for normal neutron stars, but shorter
than previous estimates for strange stars. These new timescales do not
substantially affect the current picture of the gravitational radiation driven
instability of the r-modes either for neutron stars or for strange stars.Comment: 13 pages, 5 figures, revte
Nonlinear mode coupling in rotating stars and the r-mode instability in neutron stars
We develop the formalism required to study the nonlinear interaction of modes
in rotating Newtonian stars in the weakly nonlinear regime. The formalism
simplifies and extends previous treatments. At linear order, we elucidate and
extend slightly a formalism due to Schutz, show how to decompose a general
motion of a rotating star into a sum over modes, and obtain uncoupled equations
of motion for the mode amplitudes under the influence of an external force.
Nonlinear effects are added perturbatively via three-mode couplings. We
describe a new, efficient way to compute the coupling coefficients, to zeroth
order in the stellar rotation rate, using spin-weighted spherical harmonics.
We apply this formalism to derive some properties of the coupling
coefficients relevant to the nonlinear interactions of unstable r-modes in
neutron stars, postponing numerical integrations of the coupled equations of
motion to a later paper. From an astrophysical viewpoint, the most interesting
result of this paper is that many couplings of r-modes to other rotational
modes (modes with zero frequencies in the non-rotating limit) are small: either
they vanish altogether because of various selection rules, or they vanish to
lowest order in the angular velocity. In zero-buoyancy stars, the coupling of
three r-modes is forbidden entirely and the coupling of two r-modes to one
hybrid rotational mode vanishes to zeroth order in rotation frequency. In
incompressible stars, the coupling of any three rotational modes vanishes to
zeroth order in rotation frequency.Comment: 62 pages, no figures. Corrected error in computation of coupling
coefficients, added new selection rule and an appendix on energy and angular
momentum of mode
Convenient method for resolving degeneracies due to symmetry of the magnetic susceptibility tensor and its application to pseudo contact shift-based proteinâprotein complex structure determination
Pseudo contact shifts (PCSs) induced by paramagnetic lanthanide ions fixed in a protein frame provide long-range distance and angular information, and are valuable for the structure determination of proteinâprotein and proteinâligand complexes. We have been developing a lanthanide-binding peptide tag (hereafter LBT) anchored at two points via a peptide bond and a disulfide bond to the target proteins. However, the magnetic susceptibility tensor displays symmetry, which can cause multiple degenerated solutions in a structure calculation based solely on PCSs. Here we show a convenient method for resolving this degeneracy by changing the spacer length between the LBT and target protein. We applied this approach to PCS-based rigid body docking between the FKBP12-rapamycin complex and the mTOR FRB domain, and demonstrated that degeneracy could be resolved using the PCS restraints obtained from two-point anchored LBT with two different spacer lengths. The present strategy will markedly increase the usefulness of two-point anchored LBT for protein complex structure determination
Power-spectrum analysis of Super-Kamiokande solar neutrino data, taking into account asymmetry in the error estimates
The purpose of this article is to carry out a power-spectrum analysis (based
on likelihood methods) of the Super-Kamiokande 5-day dataset that takes account
of the asymmetry in the error estimates. Whereas the likelihood analysis
involves a linear optimization procedure for symmetrical error estimates, it
involves a nonlinear optimization procedure for asymmetrical error estimates.
We find that for most frequencies there is little difference between the
power spectra derived from analyses of symmetrized error estimates and from
asymmetrical error estimates. However, this proves not to be the case for the
principal peak in the power spectra, which is found at 9.43 yr-1. A likelihood
analysis which allows for a "floating offset" and takes account of the start
time and end time of each bin and of the flux estimate and the symmetrized
error estimate leads to a power of 11.24 for this peak. A Monte Carlo analysis
shows that there is a chance of only 1% of finding a peak this big or bigger in
the frequency band 1 - 36 yr-1 (the widest band that avoids artificial peaks).
On the other hand, an analysis that takes account of the error asymmetry leads
to a peak with power 13.24 at that frequency. A Monte Carlo analysis shows that
there is a chance of only 0.1% of finding a peak this big or bigger in that
frequency band 1 - 36 yr-1. From this perspective, power spectrum analysis that
takes account of asymmetry of the error estimates gives evidence for
variability that is significant at the 99.9% level.
We comment briefly on an apparent discrepancy between power spectrum analyses
of the Super-Kamiokande and SNO solar neutrino experiments.Comment: 13 pages, 2 tables, 6 figure
Can mass loss and overshooting prevent the excitation of g-modes in blue supergiants?
Thanks to their past history on the main sequence phase, supergiant massive
stars develop a convective shell around the helium core. This intermediate
convective zone (ICZ) plays an essential role in governing which g-modes are
excited. Indeed a strong radiative damping occurs in the high density radiative
core but the ICZ acts as a barrier preventing the propagation of some g-modes
into the core. These g-modes can thus be excited in supergiant stars by the
kappa-mechanism in the superficial layers due to the opacity bump of iron, at
log T=5.2. However massive stars are submitted to various complex phenomena
such as rotation, magnetic fields, semiconvection, mass loss, overshooting.
Each of these phenomena exerts a significant effect on the evolution and some
of them could prevent the onset of the convective zone. We develop a numerical
method which allows us to select the reflected, thus the potentially excited,
modes only. We study different cases in order to show that mass loss and
overshooting, in a large enough amount, reduce the extent of the ICZ and are
unfavourable to the excitation of g-modes.Comment: 9 pages, 11 figures, accepted for publication in MNRA
Instabilities and Mixing in SN 1993J
Rayleigh-Taylor (R-T) instabilities in the explosion of SN 1993J are
investigated by means of two-dimensional hydrodynamical simulations. It is
found that the extent of mixing is sensitive to the progenitor's core mass and
the envelope mass. Because the helium core mass (3 - 4 \ms) is smaller than
that of SN 1987A, R-T instabilities at the He/C+O interfaces develop to induce
a large scale mixing in the helium core, while the instability is relatively
weak at the H/He interface due to the small envelope mass. The predicted
abundance distribution, in particular the amount of the \ni~ mixing, is
compared with those required in the theoretical light curves and the late time
optical spectra. This enables us to specify the progenitor of SN 1993J in some
detail.Comment: 20 pages, LaTeX (AASTeX), to appear in Ap
An NMR strategy for fragment-based ligand screening utilizing a paramagnetic lanthanide probe
A nuclear magnetic resonance-based ligand screening strategy utilizing a paramagnetic lanthanide probe is presented. By fixing a paramagnetic lanthanide ion to a target protein, a pseudo-contact shift (PCS) and a paramagnetic relaxation enhancement (PRE) can be observed for both the target protein and its bound ligand. Based on PRE and PCS information, the bound ligand is then screened from the compound library and the structure of the ligandâprotein complex is determined. PRE is an isotropic paramagnetic effect observed within 30Â Ă
from the lanthanide ion, and is utilized for the ligand screening in the present study. PCS is an anisotropic paramagnetic effect providing long-range (~40Â Ă
) distance and angular information on the observed nuclei relative to the paramagnetic lanthanide ion, and utilized for the structure determination of the ligandâprotein complex. Since a two-point anchored lanthanide-binding peptide tag is utilized for fixing the lanthanide ion to the target protein, this screening method can be generally applied to non-metal-binding proteins. The usefulness of this strategy was demonstrated in the case of the growth factor receptor-bound protein 2 (Grb2) Src homology 2 (SH2) domain and its low- and high-affinity ligands
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