6,770 research outputs found
The size and polydispersity of silica nanoparticles under simulated hot spring conditions
The nucleation and growth of silica nanoparticles in supersaturated geothermal waters was simulated using a flow-through geothermal simulator system. The effect of silica concentration ([SiO2]), ionic strength (IS), temperature (T) and organic additives on the size and polydispersity of the forming silica nanoparticles was quantified. A decrease in temperature (58 to 33°C) and the addition of glucose restricted particle growth to sizes <20 nm, while varying [SiO2] or ISdid not affect the size (30-35 nm) and polydispersity (±9 nm) observed at 58°C. Conversely, the addition of xanthan gum induced the development of thin films that enhanced silica aggregation
Parameters for Twisted Representations
The study of Hermitian forms on a real reductive group gives rise, in the
unequal rank case, to a new class of Kazhdan-Lusztig-Vogan polynomials. These
are associated with an outer automorphism of , and are related to
representations of the extended group . These polynomials were
defined geometrically by Lusztig and Vogan in "Quasisplit Hecke Algebras and
Symmetric Spaces", Duke Math. J. 163 (2014), 983--1034. In order to use their
results to compute the polynomials, one needs to describe explicitly the
extension of representations to the extended group. This paper analyzes these
extensions, and thereby gives a complete algorithm for computing the
polynomials. This algorithm is being implemented in the Atlas of Lie Groups and
Representations software
Intergalactic HI in the NGC5018 group
The cold interstellar and intergalactic medium is in the small group of galaxies whose brightest member is the elliptical galaxy NGC5018. Researchers' attention was first drawn to this galaxy as possibly containing cold interstellar gas by the detection by the Infrared Astronomy Satellite (IRAS) of emission at lambda 60 microns and lambda 100 microns at an intensity of about 1 Jy (Knapp et al. 1989), which is relatively strong for an elliptical (Jura et al. 1987). These data showed that the temperature of the infrared emission is less than 30K and that its likely source is therefore interstellar dust. A preliminary search for neutral hydrogen (HI) emission from this galaxy using the Very Large Array (VLA) showed that there appears to be HI flowing between NGC5018 and the nearby Sc galaxy NGC5022 (Kim et al. 1988). Since NGC5018 has a well-developed system of optical shells (cf. Malin and Carter 1983; Schweizer 1987) this observation suggests that NGC5018 may be in the process of forming its shell system by the merger of a cold stellar system with the elliptical, as suggested by Quinn (1984). Researchers describe follow-up HI observations of improved sensitivity and spatial resolution, and confirm that HI is flowing between NCG5022 and NGC5018, and around NGC5018. The data show, however, that the HI bridge actually connects NGC5022 and another spiral in the group, MCG03-34-013, both spatially and in radial velocity, and that in doing so it flows through and around NGC5018, which lies between the spiral galaxies. This is shown by the total HI map, with the optical positions of the above three galaxies labelled
Cosmetic Surgery and the Practice of Medicine
In this post-modern world, there is a recognisable bent in the media to promote the idea of youth (read as synonymous with beauty and power) to the fullest. The result is that public perceptions of the normal bodily processes of aging are viewed as detrimental or unattractive. Since we are “social creatures”, as Aristotle put it, the mediasation, for example, in magazines, TV, film, fashion, music, etc. of youth as ideal is bound to impact upon our individual ideas of ‘what-is-good-for-me'. Since youth is viewed by society as a good, it is possible to understand an individual's desire to take advantage, when it is possible, of the cosmetic procedures that fortify this ideal. Moreover, since medical practitioners are part of the public, and no more or less swayed by such ideologies, it is also reasonable to assume that some will advantage themselves and take up the gauntlet of promoting youth, although perhaps in the more medical guise of ‘remedying the ills of aging' in other words, enter the practice of cosmetic surgery.
South African Family Practice Vol. 50 (1) 2008: pp. 50-5
An Institutional Framework for Heterogeneous Formal Development in UML
We present a framework for formal software development with UML. In contrast
to previous approaches that equip UML with a formal semantics, we follow an
institution based heterogeneous approach. This can express suitable formal
semantics of the different UML diagram types directly, without the need to map
everything to one specific formalism (let it be first-order logic or graph
grammars). We show how different aspects of the formal development process can
be coherently formalised, ranging from requirements over design and Hoare-style
conditions on code to the implementation itself. The framework can be used to
verify consistency of different UML diagrams both horizontally (e.g.,
consistency among various requirements) as well as vertically (e.g.,
correctness of design or implementation w.r.t. the requirements)
A Broad Search for Counterrotating Gas and Stars: Evidence for Mergers and Accretion
We measure the frequency of bulk gas-stellar counterrotation in a sample of
67 galaxies drawn from the Nearby Field Galaxy Survey, a broadly representative
survey of the local galaxy population down to M_B-15. We detect 4
counterrotators among 17 E/S0's with extended gas emission (24% +8 -6). In
contrast, we find no clear examples of bulk counterrotation among 38 Sa-Sbc
spirals, although one Sa does show peculiar gas kinematics. This result implies
that, at 95% confidence, no more than 8% of Sa-Sbc spirals are bulk
counterrotators. Among types Sc and later, we identify only one possible
counterrotator, a Magellanic irregular. We use these results together with the
physical properties of the counterrotators to constrain possible origins for
this phenomenon.Comment: 19 pages, 4 figures, AJ, accepte
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