461 research outputs found
Magnetic cycles at different ages of stars
We study the different patterns of interannual magnetic variability in stars
on or near the lower main sequence, approximately solar-type (G-K dwarf) stars
in time series of 36 years from the Mount Wilson Observatory Ca\,{\sc ii}\,H\&K
survey. Our main aim is to search for correlations between cycles, activity
measures and ages. Time-frequency analysis has been used to discern and reveal
patterns and morphology of stellar activity cycles, including multiple and
changing cycles, in the datasets. Both the results from short-term Fourier
transform and its refinement using the Choi-Williams distribution, with better
frequency resolution, are presented in this study. Rotational periods of the
stars were derived using multi-frequency Fourier analysis.From the studied 29
stars we found at least one activity cycle on 28 of them. Twelve stars, with
longer rotational periods ( days) have simple, smooth cycles, and
the rest of the stars, with on-average much faster rotation (
days) show complex and sometimes vigorously changing, multiple cycles. The
cycles are longer and quite uniform in the first group ( years),
while are generally shorter and with greater variety in the second one
(). There is a clear age division between stars with smooth and
complex cycles that follows the known separation between the older and younger
stars at around 2 to 3~Gyr of age.Comment: Accepted to Astronomy and Astrophysic
Multiple and changing cycles of active stars II. Results
We study the time variations of the cycles of 20 active stars based on
decades-long photometric or spectroscopic observations. A method of
time-frequency analysis, as discussed in a companion paper, is applied to the
data. Fifteen stars definitely show multiple cycles; the records of the rest
are too short to verify a timescale for a second cycle. The cycles typically
show systematic changes. For three stars, we found two cycles in each of them
that are not harmonics, and which vary in parallel, indicating that a common
physical mechanism arising from a dynamo construct. The positive relation
between the rotational and cycle periods is confirmed for the inhomogeneous set
of active stars. Stellar activity cycles are generally multiple and variable.Comment: Accepted to Astronomy and Astrophysic
Erratum
Thidiazuron-induced regeneration and genetic transformation of grapevine rootstock varietiesVitis 42 (3), 133- 136 (2003
Thidiazuron-induced regeneration and genetic transformation of grapevine rootstock varieties
In vitro regeneration from cell to plant, a technique considered to be an important precondition of gene transfer, was attempted in 12 grapevine rootstocks starting with anthers of the plants as inocula. Embryogenic callus was induced in solid Murashige-Skoog medium supplemented with 2,4-dichlorophenoxyacetic acid (2,4-D) and thidiazuron (TDZ). Five of the tested rootstock cultivars (Börner, Richter 110, SO 4, St. George and Teleki 5 C) yielded embryogenic callus lines that regenerated entire plants. From these cultures Richter 110 and St. George varieties produced transgenic plants following Agrobacterium-mediated transformation with an nptII/gusA gene construct using a simple, but effective cocultivation protocol. The putative transgenic lines expressed the gusA gene. The T-DNA transfer and integration was confirmed by PCR analysis.
M-Dwarf Fast Rotators and the Detection of Relatively Young Multiple M-Star Systems
We have searched the Kepler light curves of ~3900 M-star targets for evidence
of periodicities that indicate, by means of the effects of starspots, rapid
stellar rotation. Several analysis techniques, including Fourier transforms,
inspection of folded light curves, 'sonograms', and phase tracking of
individual modulation cycles, were applied in order to distinguish the
periodicities due to rapid rotation from those due to stellar pulsations,
eclipsing binaries, or transiting planets. We find 178 Kepler M-star targets
with rotation periods, P_rot, of < 2 days, and 110 with P_rot < 1 day. Some 30
of the 178 systems exhibit two or more independent short periods within the
same Kepler photometric aperture, while several have three or more short
periods. Adaptive optics imaging and modeling of the Kepler pixel response
function for a subset of our sample support the conclusion that the targets
with multiple periods are highly likely to be relatively young physical binary,
triple, and even quadruple M star systems. We explore in detail the one object
with four incommensurate periods all less than 1.2 days, and show that two of
the periods arise from one of a close pair of stars, while the other two arise
from the second star, which itself is probably a visual binary. If most of
these M-star systems with multiple periods turn out to be bound M stars, this
could prove a valuable way of discovering young hierarchical M-star systems;
the same approach may also be applicable to G and K stars. The ~5% occurrence
rate of rapid rotation among the ~3900 M star targets is consistent with spin
evolution models that include an initial contraction phase followed by magnetic
braking, wherein a typical M star can spend several hundred Myr before spinning
down to periods longer than 2 days.Comment: 17 pages, 12 figures, 2 tables; accepted for publication in The
Astrophysical Journa
Cytotoxic drug sensitivity of Epstein-Barr virus transformed lymphoblastoid B-cells.
BACKGROUND: Epstein-Barr virus (EBV) is the causative agent of immunosuppression
associated lymphoproliferations such as post-transplant lymphoproliferative
disorder (PTLD), AIDS related immunoblastic lymphomas (ARL) and immunoblastic
lymphomas in X-linked lymphoproliferative syndrome (XLP). The reported overall
mortality for PTLD often exceeds 50%. Reducing the immunosuppression in
recipients of solid organ transplants (SOT) or using highly active antiretroviral
therapy in AIDS patients leads to complete remission in 23-50% of the PTLD/ARL
cases but will not suffice for recipients of bone marrow grafts. An additional
therapeutic alternative is the treatment with anti-CD20 antibodies (Rituximab) or
EBV-specific cytotoxic T-cells. Chemotherapy is used for the non-responding cases
only as the second or third line of treatment. The most frequently used
chemotherapy regimens originate from the non-Hodgkin lymphoma protocols and there
are no cytotoxic drugs that have been specifically selected against EBV induced
lymphoproliferative disorders. METHODS: As lymphoblastoid cell lines (LCLs) are
well established in vitro models for PTLD, we have assessed 17 LCLs for cytotoxic
drug sensitivity. After three days of incubation, live and dead cells were
differentially stained using fluorescent dyes. The precise numbers of live and
dead cells were determined using a custom designed automated laser confocal
fluorescent microscope. RESULTS: Independently of their origin, LCLs showed very
similar drug sensitivity patterns against 29 frequently used cytostatic drugs.
LCLs were highly sensitive for vincristine, methotrexate, epirubicin and
paclitaxel. CONCLUSION: Our data shows that the inclusion of epirubicin and
paclitaxel into chemotherapy protocols against PTLD may be justified
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