443 research outputs found
The Supercooling of a Nematic Liquid Crystal
We investigate the supercooling of a nematic liquid crystal using fluctuating
non-linear hydrodynamic equations. The Martin-Siggia-Rose formalism is used to
calculate renormalized transport coefficients to one-loop order. Similar
theories for isotropic liquids have shown substantial increases of the
viscosities as the liquid is supercooled or compressed due to feedback from the
density fluctuations which are freezing. We find similar results here for the
longitudinal and various shear viscosities of the nematic. However, the two
viscosities associated with the nematic director motion do not grow in any
dramatic way; i.e.\ there is no apparent freezing of the director modes within
this hydrodynamic formalism. Instead a glassy state of the nematic may arise
from a ``random anisotropy" coupling of the director to the frozen density.Comment: Late
Ordering of droplets and light scattering in polymer dispersed liquid crystal films
We study the effects of droplet ordering in initial optical transmittance
through polymer dispersed liquid crystal (PDLC) films prepared in the presence
of an electrical field. The experimental data are interpreted by using a
theoretical approach to light scattering in PDLC films that explicitly relates
optical transmittance and the order parameters characterizing both the
orientational structures inside bipolar droplets and orientational distribution
of the droplets. The theory relies on the Rayleigh-Gans approximation and uses
the Percus-Yevick approximation to take into account the effects due to droplet
positional correlations.Comment: revtex4, 18 pages, 8 figure
Formation of disclination lines near a free nematic interface
We have studied the nucleation and the physical properties of a -1/2 wedge
disclination line near the free surface of a confined nematic liquid crystal.
The position of the disclination line has been related to the material
parameters (elastic constants, anchoring energy and favored anchoring angle of
the molecules at the free surface). The use of a planar model for the structure
of the director field (whose predictions have been contrasted to those of a
fully three-dimensional model) has allowed us to relate the experimentally
observed position of the disclination line to the relevant properties of the
liquid crystals. In particular, we have been able to observe the collapse of
the disclination line due to a temperature-induced anchoring angle transition,
which has allowed us to rule out the presence of a real disclination line near
the nematic/isotropic front in directional growth experiments.
61.30.Jf,61.30.G
The Radio - X-ray relation as a star formation indicator: Results from the VLA--E-CDFS Survey
In order to trace the instantaneous star formation rate at high redshift, and
hence help understanding the relation between the different emission mechanisms
related to star formation, we combine the recent 4 Ms Chandra X-ray data and
the deep VLA radio data in the Extended Chandra Deep Field South region. We
find 268 sources detected both in the X-ray and radio band. The availability of
redshifts for of the sources in our sample allows us to derive
reliable luminosity estimates and the intrinsic properties from X-ray analysis
for the majority of the objects. With the aim of selecting sources powered by
star formation in both bands, we adopt classification criteria based on X-ray
and radio data, exploiting the X-ray spectral features and time variability,
taking advantage of observations scattered across more than ten years. We
identify 43 objects consistent with being powered by star formation. We also
add another 111 and 70 star forming candidates detected only in the radio or
X-ray band, respectively. We find a clear linear correlation between radio and
X-ray luminosity in star forming galaxies over three orders of magnitude and up
to . We also measure a significant scatter of the order of 0.4 dex,
higher than that observed at low redshift, implying an intrinsic scatter
component. The correlation is consistent with that measured locally, and no
evolution with redshift is observed. Using a locally calibrated relation
between the SFR and the radio luminosity, we investigate the L_X(2-10keV)-SFR
relation at high redshift. The comparison of the star formation rate measured
in our sample with some theoretical models for the Milky Way and M31, two
typical spiral galaxies, indicates that, with current data, we can trace
typical spirals only at z<0.2, and strong starburst galaxies with
star-formation rates as high as , up to .Comment: 21 pages, 10 figures, 5 table
The dominant ethnic moment: towards the abolition of 'whiteness'?
International audienc
Investigating hyper-vigilance for social threat of lonely children
The hypothesis that lonely children show hypervigilance for social threat was examined in a series of three studies that employed different methods including advanced eye-tracking technology. Hypervigilance for social threat was operationalized as hostility to ambiguously motivated social exclusion in a variation of the hostile attribution paradigm (Study 1), scores on the Children’s Rejection-Sensitivity Questionnaire (Study 2), and visual attention to socially rejecting stimuli (Study 3). The participants were 185 children (11 years-7 months to 12 years-6 months), 248 children (9 years-4 months to 11 years-8 months) and 140 children (8 years-10 months to 12 years-10 months) in the three studies, respectively. Regression analyses showed that, with depressive symptoms covaried, there were quadratic relations between loneliness and these different measures of hypervigilance to social threat. As hypothesized, only children in the upper range of loneliness demonstrated elevated hostility to ambiguously motivated social exclusion, higher scores on the rejection sensitivity questionnaire, and disengagement difficulties when viewing socially rejecting stimuli. We found that very lonely children are hypersensitive to social threat
The screen test 1915–1930:how stars were born
This article examines the emergence of the screen test as a cultural phenomenon during the silent era in the US and Europe and its role in the development of the star system. The lore that grew up around the screen test almost from its inception held out the possibility for members of the public to cross a threshold into the rarefied world of celebrity. The screen test itself is situated in the liminal space not only between audience and actor, but also between fiction and non-fiction, Europe and Hollywood, the silent era and the talkies, and the public and private spheres. In order to trace the ways in which the screen test as such was narrativized and conceptualized in its foundational stages, this article will analyse accounts from Hollywood and European fan magazines of the silent era, including articles, short fiction, and early cinema apocrypha. The article culminates in a discussion of the film Prix de Beauté / Beauty Prize (Augusto Genina, 1930), which starred Louise Brooks, herself a transnational film icon whose film career spanned the divide between Hollywood and Europe. The film’s final scene, in which a beauty queen is shot dead by her jealous husband as she watches a screen test of herself, has been invoked by a number of film scholars as an allegory of the work performed by cinema, which preserves and disseminates the image of the star far beyond the actor’s physical presence. Speaking to historical conditions of star-making while also capturing its resonance in cultural mythology, the conclusion of Prix de Beauté allows us to consider the origins and functions of screen test discourse itself
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