17,342 research outputs found
Offset frequency dynamics and phase noise properties of a self-referenced 10 GHz Ti:sapphire frequency comb
This paper shows the experimental details of the stabilization scheme that
allows full control of the repetition rate and the carrier-envelope offset
frequency of a 10 GHz frequency comb based on a femtosecond Ti:sapphire laser.
Octave-spanning spectra are produced in nonlinear microstructured optical
fiber, in spite of the reduced peak power associated with the 10 GHz repetition
rate. Improved stability of the broadened spectrum is obtained by
temperature-stabilization of the nonlinear optical fiber. The carrier-envelope
offset frequency and the repetition rate are simultaneously frequency
stabilized, and their short- and long-term stabilities are characterized. We
also measure the transfer of amplitude noise of the pump source to phase noise
on the offset frequency and verify an increased sensitivity of the offset
frequency to pump power modulation compared to systems with lower repetition
rate. Finally, we discuss merits of this 10 GHz system for the generation of
low-phase-noise microwaves
Dibenzo[a,g]quinolizin-8-ones: synthesis, estrogen receptor affinities, and cytostatic activity
A number of acetoxy-substituted dibenzo[a,g]quinolizin-8-ones were
synthesized by the reaction of 1-oxoisoquinolines with substituted homophthalic acid
anhydride. All of the derivatives with acetoxy groups in positions 3 and 10 bind to the
estrogen receptor. Relative binding affinities (RBA) ranged from 1.8 to 5.6 (estradiol:
RBA = 100) when the substituent at C-6 was a short alkyl group. Introduction of
additional oxygen functions in the 2- and/or 11-position decreased binding affinities.
Analyses of the enantiomers of 6-methyl (6b) and 6-ethyl (6c) derivatives revealed that
the receptor binding is mainly due to one optical isomer (e.g. (-)-6b, 9.9; (+)-6b, 0.6).
In hormone-sensitive human MCF-7 breast cancer cells, compounds with one acetoxy
group in each aromatic ring strongly inhibited cellular growth. Despite marked differences
in receptor affinity, the enantiomers displayed similar activities in this cell
culture. In hormone-independent MDA-MB 231 mammary tumor cells, only a weak
cytostatic effect was recorded at 10-5 M. In the immature mouse uterine weight test,
minimal estrogenic activity was observed. At higher doses, a significant anti-estrogenic
effect became evident. It is assumed that the estrogen antagonism is responsible for
the specific cytostatic effect in MCF-7 breast cancer cells
BANANA IV: Two aligned stellar rotation axes in the young eccentric binary system EP Crucis: primordial orientation and tidal alignment
With observations of the EP Cru system, we continue our series of
measurements of spin-orbit angles in eclipsing binary star systems, the BANANA
project (Binaries Are Not Always Neatly Aligned). We find a close alignment
between the sky projections of the rotational and orbital angular momentum
vectors for both stars (beta_p = -1.8+-1.6 deg and |beta_s|<17 deg). We also
derive precise absolute dimensions and stellar ages for this system. The EP Cru
and DI Her systems provide an interesting comparison: they have similar stellar
types and orbital properties, but DI Her is younger and has major spin-orbit
misalignments, raising the question of whether EP Cru also had a large
misalignment at an earlier phase of evolution. We show that tidal dissipation
is an unlikely explanation for the good alignment observed today, because
realignment happens on the same timescale as spin-orbit synchronization, and
the stars in EP Cru are far from syncrhonization (they are spinning 9 times too
quickly). Therefore it seems that some binaries form with aligned axes, while
other superficially similar binaries are formed with misaligned axes.Comment: ApJ accepted, 10 pages, 7 figure
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