45,633 research outputs found
Hierarchical Lattice Models of Hydrogen Bond Networks in Water
We develop a graph-based model of the hydrogen bond network in water, with a
view towards quantitatively modeling the molecular-level correlational
structure of the network. The networks are formed are studied by the
constructing the model on two infinite-dimensional lattices. Our models are
built \emph{bottom up}, based on microscopic information coming from atomistic
simulations, and we show that the predictions of the model are consistent with
known results from ab-initio simulations of liquid water. We show that simple
entropic models can predict the correlations and clustering of
local-coordination defects around tetrahedral waters observed in the atomistic
simulations. We also find that orientational correlations between bonds are
longer ranged than density correlations, and determine the directional
correlations within closed loops and show that the patterns of water wires
within these structures are also consistent with previous atomistic
simulations. Our models show the existence of density and compressibility
anomalies, as seen in the real liquid, and the phase diagram of these models is
consistent with the singularity-free scenario previously proposed by Sastry and
co-workers (Sastry et al, PRE 53, 6144 (1996)).Comment: 17 pages, published versio
Hubble Space Telescope H-Band Imaging Survey of Massive Gas-Rich Mergers
We report the results from a deep HST NICMOS H-band imaging survey of a
carefully selected sample of 33 luminous, late-stage galactic mergers at z <
0.3. Signs of a recent galactic interaction are seen in all of the objects in
the HST sample, including all 7 IR-excess Palomar-Green (PG) QSOs in the
sample. Unsuspected double nuclei are detected in 5 ULIRGs. A detailed
two-dimensional analysis of the surface brightness distributions in these
objects indicates that the great majority (81%) of the single-nucleus systems
show a prominent early-type morphology. However, low-surface-brightness
exponential disks are detected on large scale in at least 4 of these sources.
The hosts of 'warm' AGN-like systems are of early type and have less pronounced
merger-induced morphological anomalies than the hosts of cool systems with
LINER or HII region-like nuclear optical spectral types. The host sizes and
luminosities of the 7 PG~QSOs in our sample are statistically indistinguishable
from those of the ULIRG hosts. In comparison, highly luminous quasars, such as
those studied by Dunlop et al. (2003), have hosts which are larger and more
luminous. The hosts of ULIRGs and PG QSOs lie close to the locations of
intermediate-size (about 1 -- 2 L*) spheroids in the photometric projection of
the fundamental plane of ellipticals, although there is a tendency in our
sample for the ULIRGs with small hosts to be brighter than normal spheroids.
Excess emission from a young stellar population in the ULIRG/QSO hosts may be
at the origin of this difference. Our results provide support for a possible
merger-driven evolutionary connection between cool ULIRGs, warm ULIRGs, and
PG~QSOs although this sequence may break down at low luminosity. (abridged)Comment: Paper to be published in the Astrophysical Journal; revised based on
comments from referee. A PDF file combining both text and figures is
available at http://www.astro.umd.edu/~veilleux/pubs/nicmos.pd
Applications of polymer optical fibre grating sensors to condition monitoring of textiles
Fibre Bragg gratings (FBGs) in polymer optical fibres (POFs) have been used to measure the strain in a woven textile.
FBGs in both POFs and silica optical fibres were attached to a woven textile specimen, and their performance
characterised. It was demonstrated that the POF FBGs provide improved strain transfer coefficients and reduce local
structural reinforcement compared to silica FBGs and therefore make a more suitable proposition for textile monitoring
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