6,674 research outputs found
Surface motion in the pulsating DA white dwarf G 29-38
We present time-resolved spectrophotometry of the pulsating DA white dwarf G
29-38. As in previous broad-band photometry, the light curve shows the presence
of a large number of periodicities. Many of these are combination frequencies,
i.e., periodicities occurring at frequencies that are sums or differences of
frequencies of stronger, real modes. We identify at least six real modes, and
at least five combination frequencies. We measure line-of-sight velocities for
our spectra and detect periodic variations at the frequencies of five of the
six real modes, with amplitudes of up to 5 km/s. We argue that these variations
reflect the horizontal surface motion associated with the g-mode pulsations. No
velocity signals are detected at any of the combination frequencies, confirming
that the flux variations at these frequencies do not reflect physical
pulsation, but rather mixing of frequencies due to a non-linear transformation
in the outer layers of the star. We discuss the amplitude ratios and phase
differences found for the velocity and light variations, as well as those found
for the real modes and their combination frequencies, both in a
model-independent way and in the context of models based on the
convective-driving mechanism. In a companion paper, we use the wavelength
dependence of the amplitudes of the modes to infer their spherical degree.Comment: 12 pages, 5 figures, mn.sty. Accepted for publication in MNRA
Mode identification from time-resolved spectroscopy of the pulsating white dwarf G 29-38
We have used time-resolved spectroscopy to measure the colour dependence of
pulsation amplitudes in the DAV white dwarf G 29-38. Model atmospheres predict
that mode amplitudes should change with wavelength in a manner that depends on
the spherical harmonic degree l of the mode. This dependence arises from the
convolution of mode geometry with wavelength-dependent limb darkening. Our
analysis of the six largest normal modes detected in Keck observations of G
29-38 reveals one mode with a colour dependence different from the other five,
permitting us to identify the l value of all six modes and to test the model
predictions. The Keck observations also show pulsation amplitudes that are
unexpectedly asymmetric within absorption lines. We show that these asymmetries
arise from surface motions associated with the non-radial pulsations (which are
discussed in detail in a companion paper). By incorporating surface velocity
fields into line profile calculations, we are able to produce models that more
closely resemble the observations.Comment: 10 pages, 9 figures, mn.sty. Accepted for publication in MNRA
Relaxation of a Colloidal Particle into a Nonequilibrium Steady State
We study the relaxation of a single colloidal sphere which is periodically
driven between two nonequilibrium steady states. Experimentally, this is
achieved by driving the particle along a toroidal trap imposed by scanned
optical tweezers. We find that the relaxation time after which the probability
distributions have been relaxed is identical to that obtained by a steady state
measurement. In quantitative agreement with theoretical calculations the
relaxation time strongly increases when driving the system further away from
thermal equilibrium
Structure and spacing of cellulose microfibrils in woody cell walls of dicots
The structure of cellulose microfibrils in situ in wood from the dicotyledonous (hardwood) species cherry and birch, and the vascular tissue from sunflower stems, was examined by wide-angle X-ray and neutron scattering (WAXS and WANS) and small-angle neutron scattering (SANS). Deuteration of accessible cellulose chains followed by WANS showed that these chains were packed at similar spacings to crystalline cellulose, consistent with their inclusion in the microfibril dimensions and with a location at the surface of the microfibrils. Using the Scherrer equation and correcting for considerable lateral disorder, the microfibril dimensions of cherry, birch and sunflower microfibrils perpendicular to the [200] crystal plane were estimated as 3.0, 3.4 and 3.3Â nm respectively. The lateral dimensions in other directions were more difficult to correct for disorder but appeared to be 3Â nm or less. However for cherry and sunflower, the microfibril spacing estimated by SANS was about 4Â nm and was insensitive to the presence of moisture. If the microfibril width was 3Â nm as estimated by WAXS, the SANS spacing suggests that a non-cellulosic polymer segment might in places separate the aggregated cellulose microfibrils
Quartic double solids with ordinary singularities
We study the mixed Hodge structure on the third homology group of a threefold
which is the double cover of projective three-space ramified over a quartic
surface with a double conic. We deal with the Torelli problem for such
threefolds.Comment: 14 pages, presented at the Conference Arnol'd 7
Time-resolved optical spectroscopy of the pulsating DA white dwarf HS 0507+0434B: New constraints on mode identification and pulsation properties
We present a detailed analysis of time-resolved optical spectra of the ZZ
Ceti white dwarf, HS 0507+0434B. Using the wavelength dependence of observed
mode amplitudes, we deduce the spherical degree, l, of the modes, most of which
have l=1. The presence of a large number of combination frequencies (linear
sums or differences of the real modes) enabled us not only to test theoretical
predictions but also to indirectly infer spherical and azimuthal degrees of
real modes that had no observed splittings. In addition to the above, we
measure line-of-sight velocities from our spectra. We find only marginal
evidence for periodic modulation associated with the pulsation modes: at the
frequency of the strongest mode in the lightcurve, we measure an amplitude of
2.6+/-1.0 km/s, which has a probability of 2% of being due to chance; for the
other modes, we find lower values. Our velocity amplitudes and upper limits are
smaller by a factor of two compared to the amplitudes found in ZZ Psc. We find
that this is consistent with expectations based on the position of HS
0507+0434B in the instability strip. Combining all the available information
from data such as ours is a first step towards constraining atmospheric
properties in a convectionally unstable environment from an observational
perspective.Comment: 16 pages, 12 figs.; accepted for publication in A&
Defect and Hodge numbers of hypersurfaces
We define defect for hypersurfaces with A-D-E singularities in complex
projective normal Cohen-Macaulay fourfolds having some vanishing properties of
Bott-type and prove formulae for Hodge numbers of big resolutions of such
hypersurfaces. We compute Hodge numbers of Calabi-Yau manifolds obtained as
small resolutions of cuspidal triple sextics and double octics with higher A_j
singularities.Comment: 25 page
Water Condition of Salo River Based on Physical-Chemical Parameters
Salo River is one of the Kampar River's tributaries. Several activities conducted along the river produced pollutant that affects the water quality of the river in general. A research aims to understand the water condition in the Salo River based on physical-chemical parameters was conducted from April to May 2015. There were three stations (St1, St2 and St3) and water samples were taken once/week for a 4 weeks period. Water quality parameters measured were current speed, depths, temperature, transparency, turbidity, pH, DO , CO2, BOD5, nitrate and phosphate content. Results shown that the current speed was 17.5-38 cm/second, depths 29-36.3 cm, temperature 28-28.5 ÂșC, turbidity 3.34-5.36 FTU, pH 5, DO 6.89- 8.23 mg/L, CO2 7.99-8.99 mg/L, BOD5 2.39-7.29 mg/L, nitrate : 0.0275-0.0555 mg/L, and phosphate 0.0375-0.0525 mg/L. Nitrate and phosphate concentration indicate that the Salo River is in oligotrophic condition
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