4,121 research outputs found
Aspects of birth history and outcome in diplegics attending specialised educational facilities
Aim. We aimed to study functional mobility and visual performancein spastic diplegic children and adolescents attending specialisedschools.Methods. Spastic diplegia (SD) was confirmed by clinical examination. Birth and related history were added to explore relationships between SD, birth weight (BW) and duration of pregnancy. Place of birth, BW, gestational age (GA) and length of hospital stay were obtained by means of parental recall. Outcome measures included the functional mobility scale (FMS) and Beery tests of visuomotor integration (VMI) and visual perception (VIS).Results. Forty participants were included (age 7 years 5 months – 19 years 6 months). Term and preterm births were almost equally represented. Functional mobility assessments showed that 20 were walking independently in school and community settings and the remainder used walking aids or wheelchairs. There were no significant correlations between BW or GA and outcomes (FMS, VIS-z-scores or VMI-z-scores) and z-scores were low. VIS scores correlated significantly with chronological age (p=0.024). There were also significant correlations between VIS and VMI scores and school grade appropriateness (p=0.004; p=0.027, respectively). Interpretation. Both term and preterm births were represented, and outcomes were similar regardless of GA. VIS and VMIwere affected in both groups. Half of the group used assistive mobility devices and three-quarters were delayed in terms of their educational level. These problems require specialised teaching strategies, appropriate resources and a school environment that caters for mobility limitations
Laser vibrometry on solid surfaces : the effects of laser speckle
This letter discusses the phase and amplitude modulation of Doppler signals generated in laser Doppler velocimetry (LDV) systems with reference to the paper entitled 'Dynamic laser Doppler velocimetry on solid surfaces' by Rajadhyaksha and Stevenson (Vol. 4 No. 2). In particular, transit time and velocity gradient frequency broadenings are described in terms of the speckle pattern behavior on the photodetector and this approach is reconciled with the scattering element approach adopted by Rajadhyaksha and Stevenson. Furthermore, it is described how the frequency components of the Doppler phase noise can coincide with the vibration components of interest, thereby introducing ambiguity in interpretation of data. As a consequence, the reduction of Doppler phase noise by averaging is not generally acceptable. It is concluded that consideration of the dynamic speckle pattern is more appropriate to the investigation of Doppler phase noise since the speckle pattern itself has the ultimate influence on the LDV performance
The role of intermolecular coupling in the photophysics of disordered organic semiconductors: Aggregate emission in regioregular polythiophene
We address the role of excitonic coulping on the nature of photoexcitations
in the conjugated polymer regioregular poly(3-hexylthiophene). By means of
temperature-dependent absorption and photoluminescence spectroscopy, we show
that optical emission is overwhelmingly dominated by weakly coupled
H-aggregates. The relative absorbance of the 0-0 and 0-1 vibronic peaks
provides a powerfully simple means to extract the magnitude of the
intermolecular coupling energy, approximately 5 and 30 meV for films spun from
isodurene and chloroform solutions respectively.Comment: 10 pages, 4 figures, published in Phys. Rev. Let
Ultra Low Momentum Neutron Catalyzed Nuclear Reactions on Metallic Hydride Surfaces
Ultra low momentum neutron catalyzed nuclear reactions in metallic hydride
system surfaces are discussed. Weak interaction catalysis initially occurs when
neutrons (along with neutrinos) are produced from the protons which capture
``heavy'' electrons. Surface electron masses are shifted upwards by localized
condensed matter electromagnetic fields. Condensed matter quantum
electrodynamic processes may also shift the densities of final states allowing
an appreciable production of extremely low momentum neutrons which are thereby
efficiently absorbed by nearby nuclei. No Coulomb barriers exist for the weak
interaction neutron production or other resulting catalytic processes.Comment: 4 pages, ReVTeX forma
Polarization dependence of four-wave mixing in a degenerate two-level system
Nearly degenerate four-wave mixing (NDFWM) within a closed degenerate
two-level atomic transition is theoretically and experimentally examined. Using
the model presented by A. Lezama et al [Phys. Rev. A 61, 013801 (2000)] the
NDFWM spectra corresponding to different pump and probe polarization cases are
calculated and discussed. The calculated spectra are compared to the
observation of NDFWM within the transition of
cesium in a phase conjugation experiment using magneto optically cooled atomsComment: 10 pages, 13 figures; submitted to Phys. Rev.
The Globular Cluster Systems around NGC 3311 and NGC 3309
We present extensive new photometry in (g',i') of the large globular cluster
(GC) system around NGC 3311, the central cD galaxy in the Hydra cluster. Our
GMOS data cover a 5.5' field of view and reach a limiting magnitude i' = 26,
about 0.5 magnitude fainter than the turnover point of the GC luminosity
function. We find that NGC 3311 has a huge population of ~16, 000 GCs, closely
similar to the prototypical high specific frequency Virgo giant M87. The
color-magnitude distribution shows that the metal-poor blue GC sequence and the
metal-richer red sequence are both present, with nearly equal numbers of
clusters. Bimodal fits to the color distributions confirm that the blue
sequence shows the same trend of progressively increasing metallicity with GC
mass that has previously been found in many other large galaxies; the
correlation we find corresponds to a scaling of GC metallicity with mass of Z ~
M^0.6 . By contrast, the red sequence shows no change of mean metallicity with
mass, but it shows an upward extension to much higher than normal luminosity
into the UCD-like range, strengthening the potential connections between
massive GCs and UCDs. The GC luminosity function, which we measure down to the
turnover point at M_I = -8.4, also has a normal form like those in other giant
ellipticals. Within the Hydra field, another giant elliptical NGC 3309 is
sitting just 100" from the cD NGC 3311. We use our data to solve simultaneously
for the spatial structure and total GC populations of both galaxies at once.
Their specific frequencies are S_N (NGC 3311) = 12.5 +/- 1.5 and S_N (NGC 3309)
= 0.6 +/-0.4. NGC 3311 is completely dominant and entirely comparable with
other cD-type systems such as M87 in Virgo.Comment: 15 pages, 15 figures. Accepted to the Astrophysical Journal. Version
with higher resolution figures is available at
http://www.thewehners.net/astro/papers/wehner_n3311_highres.pd
Photogeneration Dynamics of a Soliton Pair in Polyacetylene
Dynamical process of the formation of a soliton pair from a photogenerated
electron-hole pair in polyacetylene is studied numerically by adopting the SSH
Hamiltonian. A weak local disorder is introduced in order to trigger the
formation. Starting from an initial configuration with an electron at the
bottom of the conduction band and a hole at the top of the valence band,
separated by the Peierls gap, the time dependent Schrndinger
equation for the electron wave functions and the equation of motion for the
lattice displacements are solved numerically. After several uniform
oscillations of the lattice system at the early stage, a large distortion
corresponding to a pair of a soliton and an anti-soliton develops from a point
which is determined by the location and type of the disorder. In some cases,
two solitons run in opposite directions, leaving breather like oscillations
behind, and in other cases they form a bound state emitting acoustic lattice
vibrational modes.Comment: 16 pages 7 figure
On laser vibrometry of rotating targets: effects of torsional and in-plane motion
Vibration measurements on rotating surfaces are often referred to in ·the
commercial literature as a major application of laser Doppler vibration
transducers. This paper examines such use of these instruments and shows
how the presence of a velocity component due to the rotation itself leads
to spurious measurement dependence on both torsional vibration and motion
perpendicular to the line of incidence of the laser beam. In addition, the
scale of this dependence increases with both rotation speed and
perpendicular distance between the line of incidence and a parallel line
through the centre of rotation. These phenomena are investigated
theoretically and excellent agreement is found when compared with
experimental data. Two solutions are suggested; the first involves careful
alignment of the laser beam whereas the second requires two simultaneous,
orthogonal measurements to be made. If neither method is adopted it is entirely conceivable that the intended solid body vibration measurement may
be masked at many frequencies of interest
Emission-Line Galaxies from the Hubble Space Telescope Probing Evolution and Reionization Spectroscopically (PEARS) Grism Survey. II: The Complete Sample
We present a full analysis of the Probing Evolution And Reionization
Spectroscopically (PEARS) slitess grism spectroscopic data obtained with the
Advanced Camera for Surveys on HST. PEARS covers fields within both the Great
Observatories Origins Deep Survey (GOODS) North and South fields, making it
ideal as a random survey of galaxies, as well as the availability of a wide
variety of ancillary observations to support the spectroscopic results. Using
the PEARS data we are able to identify star forming galaxies within the
redshift volume 0< z<1.5. Star forming regions in the PEARS survey are
pinpointed independently of the host galaxy. This method allows us to detect
the presence of multiple emission line regions (ELRs) within a single galaxy.
1162 Ha, [OIII] and/or [OII] emission lines have been identified in the PEARS
sample of ~906 galaxies down to a limiting flux of ~1e-18 erg/s/cm^2. The ELRs
have also been compared to the properties of the host galaxy, including
morphology, luminosity, and mass. From this analysis we find three key results:
1) The computed line luminosities show evidence of a flattening in the
luminosity function with increasing redshift; 2) The star forming systems show
evidence of disturbed morphologies, with star formation occurring predominantly
within one effective (half-light) radius. However, the morphologies show no
correlation with host stellar mass; and 3) The number density of star forming
galaxies with M_* > 1e9} M_sun decreases by an order of magnitude at z<0.5
relative to the number at 0.5<z<0.9 in support of the argument for galaxy
downsizing.Comment: Submitted. 48 pages. 19 figures. Accepted to Ap
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