4,387 research outputs found
Morphology of the Nuclear Disk in M87
A deep, fuly sampled diffraction limited (FWHM ~ 70 mas) narrow-band image of
the central region in M87 was obtained with the Wide Filed and Planetary Camera
2 of the Hubble Space Telescope using the dithering technique. The
H-alpha+[NII] continuum subtracted image reveals a wealth of details in the
gaseous disk structure described earlier by Ford et al. (1994). The disk
morphology is dominated by a well defined three-arm spiral pattern. In
addition, the major spiral arms contain a large number of small "arclets"
covering a range of sizes (0.1-0.3 arcsec = 10-30 pc). The overall surface
brightness profile inside a radius ~1.5" (100 pc) is well represented by a
power-law I(mu) ~ mu^(-1.75), but when the central ~40 pc are excluded it can
be equally well fit by an exponential disk. The major axis position angle
remains constant at about PA_disk ~ 6 deg for the innermost ~1", implying the
disk is oriented nearly perpendicular to the synchrotron jet (PA_jet ~ 291
deg). At larger radial distances the isophotes twist, reflecting the gas
distribution in the filaments connecting to the disk outskirts. The ellipticity
within the same radial range is e = 0.2-0.4, which implies an inclination angle
of i~35 deg. The sense of rotation combined with the dust obscuration pattern
indicate that the spiral arms are trailing.Comment: 5 pages, 3 postscript figures, to appear in the Proceedings of the
M87 Workshop, Ringberg castle, Germany, 15-19 Sep 1997, also available from
http://jhufos.pha.jhu.edu/~zlatan/papers.htm
Remote Sensing of Chiral Signatures on Mars
We describe circular polarization as a remote sensing diagnostic of chiral
signatures which may be applied to Mars. The remarkable phenomenon of
homochirality provides a unique biosignature which can be amenable to remote
sensing through circular polarization spectroscopy. The natural tendency of
microbes to congregate in close knit communities would be beneficial for such a
survey. Observations of selected areas of the Mars surface could reveal chiral
signatures and hence explore the possibility of extant or preserved biological
material. We describe a new instrumental technique that may enable observations
of this form.Comment: 14 pages, 3 figures; to be published in Planetary and Space Scienc
Time-lapse 3-D measurements of a glucose biosensor in multicellular spheroids by light sheet fluorescence microscopy in commercial 96-well plates
Light sheet fluorescence microscopy has previously been demonstrated on a commercially available inverted fluorescence microscope frame using the method of oblique plane microscopy (OPM). In this paper, OPM is adapted to allow time-lapse 3-D imaging of 3-D biological cultures in commercially available glass-bottomed 96-well plates using a stage-scanning OPM approach (ssOPM). Time-lapse 3-D imaging of multicellular spheroids expressing a glucose Förster resonance energy transfer (FRET) biosensor is demonstrated in 16 fields of view with image acquisition at 10âminute intervals. As a proof-of-principle, the ssOPM system is also used to acquire a dose response curve with the concentration of glucose in the culture medium being varied across 42 wells of a 96-well plate with the whole acquisition taking 9âmin. The 3-D image data enable the FRET ratio to be measured as a function of distance from the surface of the spheroid. Overall, the results demonstrate the capability of the OPM system to measure spatio-temporal changes in FRET ratio in 3-D in multicellular spheroids over time in a multi-well plate format
Temporal behavior of the inverse spin Hall voltage in a magnetic insulator-nonmagnetic metal structure
It is demonstrated that upon pulsed microwave excitation, the temporal
behavior of a spin-wave induced inverse spin Hall voltage in a magnetic
insulator-nonmagnetic metal structure is distinctly different from the temporal
evolution of the directly excited spin-wave mode from which it originates. The
difference in temporal behavior is attributed to the excitation of long-lived
secondary spin-wave modes localized at the insulator-metal interface
Low spin wave damping in the insulating chiral magnet CuOSeO
Chiral magnets with topologically nontrivial spin order such as Skyrmions
have generated enormous interest in both fundamental and applied sciences. We
report broadband microwave spectroscopy performed on the insulating chiral
ferrimagnet CuOSeO. For the damping of magnetization dynamics we
find a remarkably small Gilbert damping parameter of about at
5 K. This value is only a factor of 4 larger than the one reported for the best
insulating ferrimagnet yttrium iron garnet. We detect a series of sharp
resonances and attribute them to confined spin waves in the mm-sized samples.
Considering the small damping, insulating chiral magnets turn out to be
promising candidates when exploring non-collinear spin structures for high
frequency applications.Comment: 5 pages, 5 figures, and supplementary materia
A broad look at charcoal rot in the Northern Region broadacre crops through soil sampling and in-crop surveys
Macrophomina phaseolina (Tassi) Goid. is a generalist
soil-born pathogen, which is endemic to Australia. The
pathogen has a broad host-range of both monocot and
dicot plant species which include numerous weed and
crop plant species (1, 2). The disease is most commonly
identified with summer crops, e.g. soybean, sorghum,
sunflower, maize and mungbean (3) and occurs most
often when hot, dry conditions occur during the growing
season. Current estimates predict that north-eastern
Australia will become hotter and dryer as a result of
climate change (4, 5). Thus, it is likely that conditions
favouring the development of this disease will become
more common in the future. However, to date, no work
has been done to determine the extent of the
pathogenâs presence in Australian soils, in-paddock
spatial variability, or the occurrence of the disease as
correlated with pathogen presence and population
levels. In this paper, we present findings from soil
sampling and end-of-season disease assessments in
sorghum paddocks across northern New South Wales
(NNSW), south eastern Queensland (SEQ) and central
Queensland (CQ) during the 2016/17 and 2017/18
summer cropping seasons
The long-period Galactic Cepheid RS Puppis - III. A geometric distance from HST polarimetric imaging of its light echoes
As one of the most luminous Cepheids in the Milky Way, the 41.5-day RS Puppis
is an analog of the long-period Cepheids used to measure extragalactic
distances. An accurate distance to this star would therefore help anchor the
zero-point of the bright end of the period-luminosity relation. But, at a
distance of about 2 kpc, RS Pup is too far away for measuring a direct
trigonometric parallax with a precision of a few percent with existing
instrumentation. RS Pup is unique in being surrounded by a reflection nebula,
whose brightness varies as pulses of light from the Cepheid propagate outwards.
We present new polarimetric imaging of the nebula obtained with HST/ACS. The
derived map of the degree of linear polarization pL allows us to reconstruct
the three-dimensional structure of the dust distribution. To retrieve the
scattering angle from the pL value, we consider two different polarization
models, one based on a Milky Way dust mixture and one assuming Rayleigh
scattering. Considering the derived dust distribution in the nebula, we adjust
a model of the phase lag of the photometric variations over selected nebular
features to retrieve the distance of RS Pup. We obtain a distance of 1910 +/-
80 pc (4.2%), corresponding to a parallax of 0.524 +/- 0.022 mas. The agreement
between the two polarization models we considered is good, but the final
uncertainty is dominated by systematics in the adopted model parameters. The
distance we obtain is consistent with existing measurements from the
literature, but light echoes provide a distance estimate that is not subject to
the same systematic uncertainties as other estimators (e.g. the Baade-Wesselink
technique). RS Pup therefore provides an important fiducial for the calibration
of systematic uncertainties of the long-period Cepheid distance scale.Comment: 14 pages, 14 figures, accepted for publication in Astronomy &
Astrophysic
Long-term effect of temperature on honey yield and honeybee phenology
There is growing concern about declines in pollinator species, and more recently reservations have been
expressed about mismatch in plant-pollinator synchrony as a
consequence of phenological change caused by rising temperatures. Long-term changes in honeybee Apis mellifera phenology may have major consequences for agriculture, especially the pollinator market, as well as for honey production. To date, these aspects have received only modest attention. In the current study, we examine honeybee and beekeeping activity in southern Poland for the period 1965â2010, supplemented by hive yields from a beekeeper in southern UK in the same period. We show that despite negative reports on honeybee condition, and documented climate change, the studied apiary managed to show a marked increase in honey production over the 46 year study period, as did that from the UK. The proportion of the annual yield originating from the first harvest decreased during the study period and was associated with rising temperatures in summer. Honeybee spring phenology showed strong negative relationships with temperature but no overall change through time because temperatures of key early spring months had not increased significantly. In contrast, increasing yields and an increased number of harvests (and hence a later final harvest and longer season) were detected and were related to rising temperatures in late spring and in
summer
Dynamics of magnetization coupled to a thermal bath of elastic modes
We study the dynamics of magnetization coupled to a thermal bath of elastic
modes using a system plus reservoir approach with realistic magnetoelastic
coupling. After integrating out the elastic modes we obtain a self-contained
equation for the dynamics of the magnetization.
We find explicit expressions for the memory friction kernel and hence, {\em
via} the Fluctuation-Dissipation
Theorem, for the spectral density of the magnetization thermal fluctuations.
For magnetic samples in which the single domain approximation is valid, we
derive an equation for the dynamics of the uniform mode.
Finally we apply this equation to study the dynamics of the uniform
magnetization mode in insulating ferromagnetic thin films.
As experimental consequences we find that the fluctuation correlation time is
of the order of the ratio between the film thickness, , and the speed of
sound in the magnet and that the line-width of the ferromagnetic resonance peak
should scale as where is the magnetoelastic coupling constant.Comment: Revised version as appeared in print. 12 pages 9 figure
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