27,101 research outputs found
Switchable filtering in vivaldi antenna
Presented is a new frequency switchable Vivaldi antenna that has a capability to operate in a wideband mode (1-3 GHz) and reconfigure to six different subbands of operations. The reconfiguration is realised by coupling and changing the effective electrical length of ring slots inserted in the structure by means of pin diode switches. To examine antenna performances, simulated and measured results are presented. Good impedance matches and radiation patterns have been achieved. The proposed antenna is suitable for wideband and multimode radio applications
Modelling dynamic web data
We introduce XdŒ, a peer-to-peer model for reasoning about the dynamic behaviour of web data. It is based on an idealised model of semistructured data, and an extension of the Œ-calculus with process mobility and with operations for interacting with data. Our model can be used to reason about behaviour found in, for example, dynamic web page programming, applet interaction, and service orchestration. We study behavioural equivalences for XdŒ, motivated by examples
Absence of anomalous negative lattice-expansion for polycrystalline sample of Tb2Ti2O7
High resolution X-ray powder-diffraction experiments on a well-characterized
polycrystalline sample of the spin liquid Tb2Ti2O7 reveal that it shows normal
positive thermal-expansion above 4 K, which does not agree with the intriguing
anomalous negative thermal-expansion due to a magneto-elastic coupling reported
for a single crystal sample below 20 K. We also performed a Rietveld profile
refinement of a powder-diffraction pattern taken at a room temperature, and
confirmed that it is consistent with the fully ordered cubic pyrochlore
structure.Comment: 2 pages, 3 figure
Emission Line Galaxies in the STIS Parallel Survey II: Star Formation Density
We present the luminosity function of [OII]-emitting galaxies at a median
redshift of z=0.9, as measured in the deep spectroscopic data in the STIS
Parallel Survey (SPS). The luminosity function shows strong evolution from the
local value, as expected. By using random lines of sight, the SPS measurement
complements previous deep single field studies. We calculate the density of
inferred star formation at this redshift by converting from [OII] to H-alpha
line flux as a function of absolute magnitude and find rho_dot=0.043 +/- 0.014
Msun/yr/Mpc^3 at a median redshift z~0.9 within the range 0.46<z<1.415 (H_0 =
70 km/s/Mpc, Omega_M=0.3, Omega_Lambda=0.7. This density is consistent with a
(1+z)^4 evolution in global star formation since z~1. To reconcile the density
with similar measurements made by surveys targeting H-alpha may require
substantial extinction correction.Comment: 16 preprint pages including 5 figures; accepted for publication in
Ap
Researching creatively with pupils in Assessment for Learning (AfL) classrooms on experiences of participation and consultation
This paper reports on an ESRC TLRP project, Consulting Pupils on the Assessment of their Learning (CPAL). The CPAL project provides an additional theoretical perspective to the âeducational benefitsâ perspective of engaging pupil voice in learning and teaching (Rudduck et al., 2003) through its exploration of pupil rights specifically in relation to assessment issues presently on the policy agenda in the Northern Ireland context â notably Assessment for Learning (AfL). An emergent framework for assessing pupil rights, based on Article 12 of the United Nations Convention on the Rights of the Child (Lundy, 2007), is being used to explore the ways in which AfL classroom practice creates the conditions for increased pupil participation and consultation. Pupil views on their AfL classroom experiences and participation are explored by means of a variety of pupil-centred, creative research methods that engage and stimulate pupils to observe, communicate and analyse their learning and assessment experiences and give meaning to them. This presentation highlights preliminary data based on a sample of 11-14 years pupils' experiences of participation and consultation in classrooms adopting AfL pedagogical principles, and identifies characteristics that support or inhibit pupil participation in their learning and the expression of their views about such matters
Frustration driven lattice distortion; an NMR investigation of Y2Mo2O7
We have investigated the 89Y NMR spectrum and spin lattice relaxation, T1, in
the magnetically frustrated pyrochlore Y2Mo2O7. We find that upon cooling the
spectrum shifts, and broadens asymmetrically. A detailed examination of the low
T spectrum reveals that it is constructed from multiple peaks, each shifted by
a different amount. We argue that this spectrum is due to discrete lattice
distortions, and speculate that these distortions relieve the frustration and
reduce the system's energy.Comment: To be published in Phys. Rev. Let
Dough Stage Best for Oat Silage
Four years of research at the Experiment Station show that the dough stage is the best time to harvest oats for silage. Oats cut then produced more tons of silage, had a good aroma, and the cows liked it best
Vegetative and Floral Development of the Oat Plant as Influenced by Clipping and Nitrogen Fertilization
Grazing small grains at early stages of growth is a common practice throughout much of the United States. In the South grazing of small grains is a means of providing both high quality forage and grain from the same plantings. Mechanical clipping has been practiced in some areas for its secondary effect of reduced lodging by decreasing the plant height. Although clipping oats in Iowa is not common, there is interest in the practice as a possible means of reducing lodging
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