11,608 research outputs found
Galactic exploration by directed Self-Replicating Probes, and its implications for the Fermi paradox
This paper proposes a long term scheme for robotic exploration of the
galaxy,and then considers the implications in terms of the `Fermi paradox' and
our search for ETI. We discuss the parameter space of the `galactic ecology' of
civilizations in terms of the parameters T (time between ET civilizations
arising) and L, the lifetime of these civilizations. Six different regions are
described.Comment: 1 figur
Gravitation Wave Emission from Radio Pulsars Revisited
We report a new pulsar population synthesis based on Monte Carlo techniques,
aiming to estimate the contribution of galactic radio pulsars to the continuous
gravitational wave emission. Assuming that the rotation periods of pulsars at
birth have a Gaussian distribution, we find that the average initial period is
290 ms. The number of objects with periods equal to or less than 0.4 s, and
therefore capable of being detected by an interferometric gravitational antenna
like VIRGO, is of the order of 5100-7800. With integration times lasting
between 2 and 3 yr, our simulations suggest that about two detections should be
possible, if the mean equatorial ellipticity of the pulsars is
=10. A mean ellipticity an order of magnitude higher increases the
expected number of detections to 12-18, whereas for , no
detections are expectedComment: accepted for publication in A&A, 9 pages, 8 figure
Supporting New Teachers of Color and Cultural Diversity
Educators and policy makers are calling for increasing the racial and cultural diversity of the teacher workforce, given the widening cultural gap between students and teachers (see Figure 1), and the widening achievement gap between students of color and White students. Some research suggests teachers of color can address the needs of students of color through culturally relevant practices (Quiocho & Rios, 2000). However, recent studies reveal teachers of color suffer greater job dissatisfaction and higher turnover than White teachers (Ingersoll & Connor, 2008; Marvel et al., 2007).Furthermore, cultural practices of teachers of color, if valued in our schools, need to be developed rather than assumed (Sheets, 2000). Given these circumstances, educators are faced with the following questions:- What factors impact retention and attrition of new teachers of color?- What factors support new teachers of color to develop and implement practices that address the needs of students from culturally and linguistically diverse backgrounds?These questions are addressed by a team of researchers at the New Teacher Center, UCSC in a study that followed 21 teachers of color over five years, from preparation through four years of teaching in high-need California schools serving low-income and high-minority student populations
Ages of Elliptical Galaxies: Single versus Multi Population Interpretation
New calibrations of spectrophotometric indices of elliptical galaxies as
functions of spectrophotometric indices are presented, permitting estimates of
mean stellar population ages and metallicities. These calibrations are based on
evolutionary models including a two-phase interstellar medium, infall and a
galactic wind.Free parameters were fixed by requiring that models reproduce the
mean trend of data in the color-magnitude diagram as well as in the plane of
indices Hbeta-Mg2 and Mg2-. To improve the location of faint ellipticals(MB
> -20) in the Hbeta-Mg2 diagram, down-sizing was introduced. An application of
our calibrations to a sample of ellipticals and a comparison with results
derived from single stellar population models is given. Our models indicate
that mean population ages span an interval of 7-12 Gyr and are correlated with
metallicities, which range from approximately half up to three times solar.Comment: 10 pages and 6 figures. Accepted for publication in Monthly Notices
of the Royal Astronomical Society Main Journa
Evidence that the degree of band 3 phosphorylation modulates human erythrocytes nitric oxide efflux – in vitro model of hyperfibrinogenemia
© 2011 – IOS Press and the authors. All rights reservedRecent evidence has shown that plasma fibrinogen, a major cardiovascular risk factor, interacts with the erythrocyte membrane and acts to influence blood flow via erythrocyte nitric oxide (NO) modulation. In the present pioneer in-vitro study, whole blood samples were harvested from healthy subjects and aliquots were incubated in the absence (control aliquots) and presence of fibrinogen at different degrees of band 3 phosphorylation, and the levels of NO, nitrite, nitrate and S-nitroglutathione (GSNO) were determined.
Hyperfibrinogenemia interferes with erythrocyte NO mobilization without changing its efflux in a way that seems to be dependent of the degree of band 3 phosphorylation. In presence of higher fibrinogen concentrations the NO efflux is reinforced when band 3 is phosphorylated (p < 0.001). Higher levels of nitrite, nitrate and GSNO were documented (p < 0.05). However, the mechanisms by which fibrinogen signalling modulates erythrocyte function remain to be clarified and are currently under study. These conditions may be considered an approach to be followed in blood storage for transfusions.This study was supported by grants from the FCT - Fundação para a Ciência e a Tecnologia (project reference PTDC/SAU-OSM/73449/2006
Report on "Scheduling in a factory"
In order to carry out their orders of shoe soles, this company has a number of tasks T_1, ..., T_n of different lengths to be assigned to groups of machines.
Each group is operated by one worker (two in one case), and an operation cycle corresponds to injection, cooling, and removal of the sole. The time taken at each step varies from one order to another, and when starting a new task a machine needs to be tuned, which takes some extra time. Machines are working in parallel. At the moment the assignment is carried out empirically, and the problem proposed is to optimize the procedure
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