2,266 research outputs found
Preparation of Neurospora crassa mitochondria
The fungus Neurospora crassa represents a eukaryotic cell with high biosynthetic activities. Cell mass doubles in 2-4 hr during expone ntial growth , even in simple salt media with sucrose as the sole carbon source. The microorgani sm forms a mycelium of long hyphae durlng vegetative growth . The mitochondria can be isolated under relatively gentle condi tions since a few breaks in the threadlike hyphae are sufficient to cause the outflow of the organelles. This article describes two methods for the physical disruption of the hyphae : (I) The cell s are opened in a grind mill between two rotating corundum di sks. This is a continuous and fast procedure and allows large- and small-scale preparations of mitochondria. (2) Hyphae are ground with sand in a mortar and pestle. This procedure can be applied to microscale preparations of mitochondria starting with minute amounts of cells. Other procedures for the isolation of Neurospora mitochondria after the physical di sruption or the enzymatic degradation of the cell wall have been described elsewher
The CoRoT discovery of a unique triple-mode cepheid in the galaxy
The exploitation of the CoRoT treasure of stars observed in the exoplanetary
field allowed the detection of a unusual triple-mode Cepheid in the Milky Way,
CoRoT 0223989566. The two modes with the largest amplitudes and period ratio of
0.80 are identified with the first (P1=1.29 d) and second (P2=1.03 d) radial
overtones. The third period, which has the smallest amplitude but able to
produce combination terms with the other two, is the longest one (P3=1.89 d).
The ratio of 0.68 between the first-overtone period and the third period is the
unusual feature. Its identification with the fundamental radial or a nonradial
mode is discussed with respect to similar cases in the Magellanic Clouds. In
both cases the period triplet and the respective ratios make the star unique in
our Galaxy. The distance derived from the period-luminosity relation and the
galactic coordinates put CoRoT~0223989566 in the metal-rich environment of the
"outer arm" of the Milky Way.Comment: Published as ApJ Lette
Tunneling Anisotropic Spin Polarization in lateral (Ga,Mn)As/GaAs spin Esaki diode devices
We report here on anisotropy of spin polarization obtained in lateral
all-semiconductor all-electrical spin injection devices, employing
(Ga,Mn)As/GaAs Esaki diode structures as spin aligning
contacts, resulting from the dependence of the efficiency of spin tunneling on
the orientation of spins with respect to different crystallographic directions.
We observed an in-plane anisotropy of in case of spins oriented either
along or directions and anisotropy between
in-plane and perpendicular-to-plane orientation of spins.Comment: 9 pages, 3 figure
All-electrical measurement of spin injection in a magnetic - junction diode
Magnetic - junction diodes are fabricated to investigate spin-polarized
electron transport. The injection of spin-polarized electrons in a
semiconductor is achieved by driving a current from a ferromagnetic injector
(Fe), into a bulk semiconductor (-GaAs) via schottky contact. For detection,
a diluted magnetic semiconductor (-GaMnAs) layer is used. Clear
magnetoresistance was observed only when a high forward bias was applied across
the - junction.Comment: 4 pages, 4 figure
A self consistent chemically stratified atmosphere model for the roAp star 10 Aquilae
Context: Chemically peculiar A type (Ap) stars are a subgroup of the CP2
stars which exhibit anomalous overabundances of numerous elements, e.g. Fe, Cr,
Sr and rare earth elements. The pulsating subgroup of the Ap stars, the roAp
stars, present ideal laboratories to observe and model pulsational signatures
as well as the interplay of the pulsations with strong magnetic fields and
vertical abundance gradients. Aims: Based on high resolution spectroscopic
observations and observed stellar energy distributions we construct a self
consistent model atmosphere, that accounts for modulations of the
temperature-pressure structure caused by vertical abundance gradients, for the
roAp star 10 Aquilae (HD 176232). We demonstrate that such an analysis can be
used to determine precisely the fundamental atmospheric parameters required for
pulsation modelling. Methods: Average abundances were derived for 56 species.
For Mg, Si, Ca, Cr, Fe, Co, Sr, Pr, and Nd vertical stratification profiles
were empirically derived using the ddafit minimization routine together with
the magnetic spectrum synthesis code synthmag. Model atmospheres were computed
with the LLModels code which accounts for the individual abundances and
stratification of chemical elements. Results: For the final model atmosphere
Teff=7550 K and log g=3.8 were adopted. While Mg, Si, Co and Cr exhibit steep
abundance gradients Ca, Fe and Sr showed much wider abundance gradients between
log tau_5000=-1.5 and 0.5. Elements Mg and Co were found to be the least
stratified, while Ca and Sr showed strong depth variations in abundance of up
to ~ 6 dex.Comment: 9 pages, 15 figure
Magnetic anisotropy of epitaxial (Ga,Mn)As on (113)A GaAs
The temperature dependence of magnetic anisotropy in (113)A (Ga,Mn)As layers
grown by molecular beam epitaxy is studied by means of superconducting quantum
interference device (SQUID) magnetometry as well as by ferromagnetic resonance
(FMR) and magnetooptical effects. Experimental results are described
considering cubic and two kinds of uniaxial magnetic anisotropy. The magnitude
of cubic and uniaxial anisotropy constants is found to be proportional to the
fourth and second power of saturation magnetization, respectively. Similarly to
the case of (001) samples, the spin reorientation transition from uniaxial
anisotropy with the easy along the [-1, 1, 0] direction at high temperatures to
the biaxial anisotropy at low temperatures is observed around 25 K. The
determined values of the anisotropy constants have been confirmed by FMR
studies. As evidenced by investigations of the polar magnetooptical Kerr
effect, the particular combination of magnetic anisotropies allows the
out-of-plane component of magnetization to be reversed by an in-plane magnetic
field. Theoretical calculations within the p-d Zener model explain the
magnitude of the out-of-plane uniaxial anisotropy constant caused by epitaxial
strain, but do not explain satisfactorily the cubic anisotropy constant. At the
same time the findings point to the presence of an additional uniaxial
anisotropy of unknown origin. Similarly to the case of (001) films, this
additional anisotropy can be explained by assuming the existence of a shear
strain. However, in contrast to the (001) samples, this additional strain has
an out-of-the-(001)-plane character.Comment: 13 pages, 9 figure
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