7,007 research outputs found
Fire safety practices in the Shuttle and the Space Station Freedom
The Shuttle reinforces its policy of fire-preventive measures with onboard smoke detectors and Halon 1301 fire extinguishers. The forthcoming Space Station Freedom will have expanded fire protection with photoelectric smoke detectors, radiation flame detectors, and both fixed and portable carbon dioxide fire extinguishers. Many design and operational issues remain to be resolved for Freedom. In particular, the fire-suppression designs must consider the problems of gas leakage in toxic concentrations, alternative systems for single-failure redundancy, and commonality with the corresponding systems of the Freedom international partners. While physical and engineering requirements remain the primary driving forces for spacecraft fire-safety technology, there are, nevertheless, needs and opportunities for the application of microgravity combustion knowledge to improve and optimize the fire-protective systems
Semi-algebraic horizontal subvarieties of Calabi-Yau type
We study horizontal subvarieties of a Griffiths period domain . If is defined by algebraic equations, and if is also invariant
under a large discrete subgroup in an appropriate sense, we prove that is a
Hermitian symmetric domain , embedded via a totally geodesic
embedding in . Next we discuss the case when is in addition of
Calabi-Yau type. We classify the possible VHS of Calabi-Yau type parametrized
by Hermitian symmetric domains and show that they are essentially
those found by Gross and Sheng-Zuo, up to taking factors of symmetric powers
and certain shift operations. In the weight three case, we explicitly describe
the embedding from the perspective of Griffiths
transversality and relate this description to the Harish-Chandra realization of
and to the Kor\'anyi-Wolf tube domain description. There are
further connections to homogeneous Legendrian varieties and the four Severi
varieties of Zak.Comment: 53 pages, final version, to appear in Duke Math. J.; changes from v3:
new references added; changes from v2: for Hermitian VHS of CY 3-fold type
with real multiplication, we discuss the case SU(3,3) for arbitrary totally
real number fields; the case SO^*(12) is discussed in arXiv:1301.2582;
changes from v1: some inaccuracies corrected, Section 3 substantially
expande
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