5,116 research outputs found
Study of V/STOL aircraft implementation. Volume 2: Appendices
An analysis of V/STOL aircraft implementation and utilization is presented. The subjects discussed are: (1) short haul air transportation requirements, (2) available aircraft technology, (3) aircraft production requirements, (4) airport requirements, (5) roles and responsibilities, and (6) cost and funding
The Cool Accretion Disk in ESO 243-49 HLX-1: Further Evidence of an Intermediate Mass Black Hole
With an inferred bolometric luminosity exceeding 10^42 erg/s, HLX-1 in ESO
243-49 is the most luminous of ultraluminous X-ray sources and provides one of
the strongest cases for the existence of intermediate mass black holes. We
obtain good fits to disk-dominated observations of the source with BHSPEC, a
fully relativistic black hole accretion disk spectral model. Due to
degeneracies in the model arising from the lack of independent constraints on
inclination and black hole spin, there is a factor of 100 uncertainty in the
best-fit black hole mass M. Nevertheless, spectral fitting of XMM-Newton
observations provides robust lower and upper limits with 3000 Msun < M < 3 x
10^5 Msun, at 90% confidence, placing HLX-1 firmly in the intermediate-mass
regime. The lower bound on M is entirely determined by matching the shape and
peak energy of the thermal component in the spectrum. This bound is consistent
with (but independent of) arguments based solely on the Eddington limit. Joint
spectral modelling of the XMM-Newton data with more luminous Swift and Chandra
observations increases the lower bound to 6000 Msun, but this tighter
constraint is not independent of the Eddington limit. The upper bound on M is
sensitive to the maximum allowed inclination i, and is reduced to M < 10^5 Msun
if we limit i < 75 deg.Comment: 10 pages, 7 figures, accepted for publication in Ap
Fatigue crack growth of type 304/304L stainless steel in pressurized hydrogen gas at elevated temperature
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Role of DNA sequences outside the cores of DNase hypersensitive sites (HSs) in functions of the ÎČ-globin locus control region. Domain opening and synergism between HS2 and HS3
The roles of each DNase hypersensitive site (HS), and the DNA sequences between them, in the activity of the locus control region of the mammalian ÎČ-globin gene domain were examined by placing human and rabbit restriction fragments containing the cores of HS2, HS3, HS4, and HS5, along with varying amounts of flanking DNA, upstream of a hybrid Δ-globin-luciferase reporter gene and testing for effects on expression both prior to and after integration into the chromosomes of K562 cells, a human erythroid cell line. Prior to integration, fragments containing HS2 enhanced expression to the greatest extent, and the modest enhancement by some fragments containing HS3 correlated with the presence of a well-conserved binding site for AP1/NFE2. The stronger effects of larger locus control region DNA fragments in clones of stably transfected cells indicates a role for sequences outside the HS cores after integration into the genome. The strong effect of a 1.9-kilobase HindIII fragment containing HS3 after, but not prior to, integration argues for the presence of a chromatin domain-opening activity. Use of a rabbit DNA fragment containing both HS2 and HS3 demonstrated a synergistic interaction between the two HSs when their natural context and spacing are preserved
The Broadband XMM-Newton and NuSTAR X-ray Spectra of Two Ultraluminous X-ray Sources in the Galaxy IC 342
We present results for two Ultraluminous X-ray Sources (ULXs), IC 342 X-1 and
IC 342 X-2, using two epochs of XMM-Newton and NuSTAR observations separated by
7 days. We observe little spectral or flux variability above 1 keV
between epochs, with unabsorbed 0.3--30 keV luminosities being
erg s for IC 342 X-1 and
erg s for IC 342 X-2, so that both were
observed in a similar, luminous state. Both sources have a high absorbing
column in excess of the Galactic value. Neither source has a spectrum
consistent with a black hole binary in low/hard state, and both ULXs exhibit
strong curvature in their broadband X-ray spectra. This curvature rules out
models that invoke a simple reflection-dominated spectrum with a broadened iron
line and no cutoff in the illuminating power-law continuum. X-ray spectrum of
IC 342 X-1 can be characterized by a soft disk-like black body component at low
energies and a cool, optically thick Comptonization continuum at high energies,
but unique physical interpretation of the spectral components remains
challenging. The broadband spectrum of IC 342 X-2 can be fit by either a hot
(3.8 keV) accretion disk, or a Comptonized continuum with no indication of a
seed photon population. Although the seed photon component may be masked by
soft excess emission unlikely to be associated with the binary system, combined
with the high absorption column, it is more plausible that the broadband X-ray
emission arises from a simple thin blackbody disk component. Secure
identification of the origin of the spectral components in these sources will
likely require broadband spectral variability studies.Comment: 12 pages, 11 figures, 5 Tables, Accepted for publication in The
Astrophysical Journa
Universal Relationship between Conductivity and Solvation-Site Connectivity in Ether-Based Polymer Electrolytes
We perform a joint experimental and computational study of ion transport properties in a systematic set of linear polyethers synthesized via acyclic diene metathesis (ADMET) polymerization. We measure ionic conductivity, Ï, and glass transition temperature, T_g, in mixtures of polymer and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt. While T_g is known to be an important factor in the ionic conductivity of polymer electrolytes, recent work indicates that the number and proximity of lithium ion solvation sites in the polymer also play an important role, but this effect has yet to be systematically investigated. Here, adding aliphatic linkers to a poly(ethylene oxide) (PEO) backbone lowers T_g and dilutes the polar groups; both factors influence ionic conductivity. To isolate these effects, we introduce a two-step normalization scheme. In the first step, VogelâTammannâFulcher (VTF) fits are used to calculate a temperature-dependent reduced conductivity, Ï_r(T), which is defined as the conductivity of the electrolyte at a fixed value of T â T_g. In the second step, we compute a nondimensional parameter f_(exp), defined as the ratio of the reduced molar conductivity of the electrolyte of interest to that of a reference polymer (PEO) at a fixed salt concentration. We find that f_(exp) depends only on oxygen mole fraction, x_0, and is to a good approximation independent of temperature and salt concentration. Molecular dynamics simulations are performed on neat polymers to quantify the occurrences of motifs that are similar to those obtained in the vicinity of isolated lithium ions. We show that f_(exp) is a linear function of the simulation-derived metric of connectivity between solvation sites. From the relationship between Ï_r and f_(exp) we derive a universal equation that can be used to predict the conductivity of ether-based polymer electrolytes at any salt concentration and temperature
Institutional Polycentrism, Entrepreneurs' Social Networks, and New Venture Growth
International audienceWhat is the interrelationship among formal institutions, social networks, and new venture growth? Drawing on the theory of institutional polycentrism and social network theory, we examine this question using data on 637 entrepreneurs from four different countries. We find the confluence of weak and inefficient formal institutions to be associated with a larger number of structural holes in entrepreneurial social networks. While the effect of this institutional order on the revenue growth of new ventures is negative, a network's structural holes have a positive effect on revenue growth. Furthermore, the positive effect of structural holes on revenue growth is stronger in an environment with a more adverse institutional order (i.e., weaker and more inefficient institutions). The contributions and implications of these findings are discussed.<br/
Biomineralisation in the Palaeozoic oceans: evidence for simultaneous crystallisation of high and low magnesium calcite by phacopine trilobites
The chemical composition and microstructure of the calcite cuticles of eleven species of phacopine trilobites have been investigated by electron beam imaging, diffraction, and microanalysis, and results reveal that the lenses of their schizochroal eyes differed signiïŹcantly in chemical composition from the rest of the cuticle in vivo. Apart from the eye lenses, most cuticles are inferred to have escaped extensive recrystallisation because their constituent crystals are sub-micrometre in size and have a preferred orientation that is consistent between species. Their current compositions of ~1.4 to 2.4 mol% MgCO3 are likely to be close to original values, although as they commonly luminesce and contain detectable manganese and iron, some diagenetic alteration has taken place. The associated lenses have a microstructure that is suitable for focusing light, yet are optically turbid owing to the presence within calcite of micropores and crystals of microdolomite, apatite, celestite and pyrite. The microdolomite indicates that lenses recrystallised from an original high-Mg calcite composition and this is supported by the presence of nanometre-scale modulated microstructures in both the calcite and dolomite. These lenses currently contain ~1 to 6 mol% MgCO3, and by comparison with the proportion of magnesium lost from echinoderm stereom in the same thin sections, may have contained ~7.5 mol% MgCO3 in vivo. In some samples, more extensive diagenetic alteration is evidenced by recrystallisation of the cuticle including lenses to coarse equant calcite or enrichment of the cuticle, but not necessarily the lenses, in magnesium accompanying replacement by a MgâFe phyllosilicate. The phacopine trilobites had to modify partition coefïŹcients for magnesium considerably in order to grow lenses with contrasting compositions to the rest of their cuticles, and such a strong vital effect on biomineralisation suggests that incorporation of magnesium was essential for functioning of their calcite optical s
Channel Interference in a Quasi Ballistic Aharonov-Bohm Experiment
New experiments are presented on the transmission of electron waves through a
2DEG (2 dimensional electron gas) ring with a gate on top of one of the
branches. Magnetoconductance oscillations are observed, and the phase of the
Aharanov-Bohm signal alternates between 0 and pi as the gate voltage is
scanned. A Fourier transform of the data reveals a dominant period in the
voltage which corresponds to the energy spacing between successive transverse
modes.A theoretical model including random phase shifts between successive
modes reproduces the essential features of the experiment.Comment: 4 pages, 6 Postscript figures, TEX, submitted to Physical Review
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