67,517 research outputs found
Keeping the dream alive: Managing the Space Station Program, 1982 to 1986
The management is described and analyzed of the formative years of the NASA Space Station Program (1982 to 1986), beginning with the successful initiative for program approval by Administrator James M. Beggs through to the decision to bring program management to Reston, Virginia. Emphasis is on internal management issues related to the implementation of the various phases of the program. Themes examined are the problem of bringing programmatic and institutional interests together and focusing them to forward the program; centralized versus decentralized control of the program; how the history of NASA and of the individual installations affected the decisions made; and the pressure from those outside NASA. The four sections are: (1) the decision to build the space station, (2) the design of the management experiment, (3) the experiment comes to life, and (4) the decision reversal
Is telomerase reactivation associated with the down-regulatoin of TGFβ receptor-II expression in human breast cancer?
Background
Telomerase is a ribonucleoprotein that synthesizes telomeres and plays an important role in chromosomal stability and cellular immortalisation. Telomerase activity is detectable in most human cancers but not in normal somatic cells. TGF beta (transforming growth factor beta) is a member of a family of cytokines that are essential for cell survival and seems to be down-regulated in human cancer. Recent in vitro work using human breast cancer cell lines has suggested that TGF beta down-regulates the expression of hTERT (human telomerase reverse transcriptase) : the catalytic subunit of telomerase. We have therefore hypothesised that telomerase reactivation is associated with reduced immunohisto-chemical expression of TGF beta type II receptor (RII) in human breast cancer.
Methods
TGF beta RII immunohistochemical expression was determined in 24 infiltrating breast carcinomas with known telomerase activity (17 telomerase-positive and 7 telomerase-negative). Immunohistochemical expression of TGF beta RII was determined by a breast pathologist who was blinded to telomerase data.
Results
TGF beta RII was detected in all lesions. The percentage of stained cells ranged from 1–100%. The difference in TGF beta RII expression between telomerase positive and negative tumours was not statistically significant (p = 1.0).
Conclusion
The results of this pilot study suggest that there is no significant association between telomerase reactivation and TGF-beta RII down-regulation in human breast cancer
Non-singlet structure function of the 3He-3H system and divergence of the Gottfried integral
We study shadowing and antishadowing corrections to the flavor non-singlet
structure function F_2(3He)-F_2(3H) and show that the difference between the
one-particle density distributions of 3He and 3H plays an important role at
very small x. We find that the flavor non-singlet structure function in these
mirror nuclei is enhanced at small x by nuclear shadowing, which increases the
nuclear Gottfried integral, integrated from 10^{-4} to 1, by 11-36 %. When
integrated from zero, the Gottfried integral is divergent for these mirror
nuclei. It seems likely that, as a consequence of charge symmetry breaking,
this may also apply to the proton-neutron system.Comment: 29 pages, 6 figures, RevTe
The high-field polar RX J1007.5-2017
We report optical and X-ray observations of the high-field polar
RXJ1007.5-2017 performed between 1990 and 2012. It has an orbital period of
208.60 min determined from the ellipsoidal modulation of the secondary star in
an extended low state. The spectral flux of the dM3- secondary star yields a
distance of 790+-105 pc. At low accretion levels, \RX{} exhibits pronounced
cyclotron emission lines. The second and third harmonic fall in the optical
regime and yield a field strength in the accretion spot of 94 MG. The source is
highly variable on a year-to-year basis and was encountered at visual
magnitudes between V \sim 20 and V \sim 16. In the intermediate state of 1992
and 2000, the soft X-ray luminosity exceeds the sum of the luminosities of the
cyclotron source, the hard X-ray source, and the accretion stream by an order
of magnitude. An X-ray high state, corresponding to the brightest optical
level, has apparently not been observed so far.Comment: To be published in A&
Coupling of non-crossing wave modes in a two-dimensional plasma crystal
We report an experimental observation of coupling of the transverse vertical
and longitudinal in-plane dust-lattice wave modes in a two-dimensional complex
plasma crystal in the absence of mode crossing. A new large diameter rf plasma
chamber was used to suspend the plasma crystal. The observations are confirmed
with molecular-dynamics simulations. The coupling manifests itself in traces of
the transverse vertical mode appearing in the measured longitudinal spectra and
vice versa. We calculate the expected ratio of the trace to the principal mode
with a theoretical analysis of the modes in a crystal with finite temperature
and find good agreement with the experiment and simulations.Comment: 4 figures, 5 pages, accepted for publication in PRL Nov 201
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