827 research outputs found
The evolutionary trend in airborne and satellite radar altimeters
The manner in which airborne and satellite radar altimeters developed and where the trend is leading was investigated. The airborne altimeters have progressed from a broad beamed, narrow pulsed, nadir looking instrument, to a pulse compressed system that is computer controlled, to a scanning pencil beamed system which produce a topographic map of the surface beneath the aircraft in real time. It is suggested that the airborne systems lie in the use of multiple frequencies. The satellite altimeters evolve towards multifrequency systems with narrower effective pulses and higher pulse compression ratios to reduce peak transmitted power while improving resolution. Applications indicate wide swath systems using interferometric techniques or beam limited systems using 100 m diameter antennas
Development of a system for remote sensing of ionospheric motions and microstructure - The Kinesonde in France, 1970
Kinesonde experiment for development of system for remote sensing of ionospheric motions and microstructur
Semiclassical Calculation of Multiparticle Scattering Cross Sections in Classicalizing Theories
It has been suggested in arXiv:1010.1415 that certain derivatively coupled
non-renormalizable scalar field theories might restore the perturbative
unitarity of high energy hard scatterings by classicalization, i.e. formation
of multiparticle states of soft quanta. Here we apply the semiclassical method
of calculating the multiparticle production rates to the scalar
Dirac-Born-Infeld (DBI) theory which is suggested to classicalize. We find that
the semiclassical method is applicable for the energies in the final state
above the cutoff scale of the theory L_*^{-1}. We encounter that the cross
section of the process two to N ceases to be exponentially suppressed for the
particle number in the final state N smaller than a critical particle number
N_{crit} ~ (E L_*)^{4/3}. It coincides with the typical particle number
produced in two-particle collisions at high energies predicted by
classicalization arguments.Comment: 17 pages, 4 figures, v2. Minor changes to match the published versio
Intervening to alleviate word-finding difficulties in children: case series data and a computational modelling foundation
We evaluated a simple computational model of productive vocabulary acquisition, applied to simulating two case studies of 7-year-old children with developmental word-finding difficulties across four core behavioural tasks. Developmental models were created, which captured the deficits of each child. In order to predict the effects of intervention, we exposed the computational models to simulated behavioural interventions of two types, targeting the improvement of either phonological or semantic knowledge. The model was then evaluated by testing the predictions from the simulations against the actual results from an intervention study carried out with the two children. For one child it was predicted that the phonological intervention would be effective, and the semantic intervention would not. This was borne out in the behavioural study. For the second child, the predictions were less clear and depended on the nature of simulated damage to the model. The behavioural study found an effect of semantic but not phonological intervention. Through an explicit computational simulation, we therefore employed intervention data to evaluate our theoretical understanding of the processes underlying acquisition of lexical items for production and how they may vary in children with developmental language difficulties
Nanodiamonds carrying quantum emitters with almost lifetime-limited linewidths
Nanodiamonds (NDs) hosting optically active defects are an important
technical material for applications in quantum sensing, biological imaging, and
quantum optics. The negatively charged silicon vacancy (SiV) defect is known to
fluoresce in molecular sized NDs (1 to 6 nm) and its spectral properties depend
on the quality of the surrounding host lattice. This defect is therefore a good
probe to investigate the material properties of small NDs. Here we report
unprecedented narrow optical transitions for SiV colour centers hosted in
nanodiamonds produced using a novel high-pressure high-temperature (HPHT)
technique. The SiV zero-phonon lines were measured to have an inhomogeneous
distribution of 1.05 nm at 5 K across a sample of numerous NDs. Individual
spectral lines as narrow as 354 MHz were measured for SiV centres in
nanodiamonds smaller than 200 nm, which is four times narrower than the best
SiV line previously reported for nanodiamonds. Correcting for apparent spectral
diffusion yielded a homogeneous linewith of about 200 MHz, which is close to
the width limit imposed by the radiative lifetime. These results demonstrate
that the direct HPHT synthesis technique is capable of producing nanodiamonds
with high crystal lattice quality, which are therefore a valuable technical
material
Mechanical Properties of 17-4PH Stainless Steel Foam Panels
Rectangular 17-4PH stainless steel sandwiched foam panels were fabricated using a commercial manufacturing technique by brazing two sheets to a foam core. Microstructural observations and ultrasonic nondestructive evaluation of the panels revealed large variations in the quality of the brazed areas from one panel to the next as well as within the same panel. Shear tests conducted on specimens machined from the panels exhibited failures either in the brazed region or in the foam core for the poorly brazed and well-brazed samples, respectively. Compression tests were conducted on the foam cores to evaluate their elastic and plastic deformation behavior. These data were compared with published data on polymeric and metallic foams, and with theoretical deformation models proposed for open cell foams
Remote sensing data from CLARET: A prototype CART data set
The data set containing radiation, meteorological , and cloud sensor observations is documented. It was prepared for use by the Department of Energy's Atmospheric Radiation Measurement (ARM) Program and other interested scientists. These data are a precursor of the types of data that ARM Cloud And Radiation Testbed (CART) sites will provide. The data are from the Cloud Lidar And Radar Exploratory Test (CLARET) conducted by the Wave Propagation Laboratory during autumn 1989 in the Denver-Boulder area of Colorado primarily for the purpose of developing new cloud-sensing techniques on cirrus. After becoming aware of the experiment, ARM scientists requested archival of subsets of the data to assist in the developing ARM program. Five CLARET cases were selected: two with cirrus, one with stratus, one with mixed-phase clouds, and one with clear skies. Satellite data from the stratus case and one cirrus case were analyzed for statistics on cloud cover and top height. The main body of the selected data are available on diskette from the Wave Propagation Laboratory or Los Alamos National Laboratory
Intervention for children with word-finding difficulties: a parallel group randomised control trial
Purpose: The study investigated the outcome of a word-web intervention for children diagnosed with word-finding difficulties (WFDs).
Method: Twenty children age 6–8 years with WFDs confirmed by a discrepancy between comprehension and production on the Test of Word Finding-2, were randomly assigned to intervention (n = 11) and waiting control (n = 9) groups. The intervention group had six sessions of intervention which used word-webs and targeted children’s meta-cognitive awareness and word-retrieval.
Result: On the treated experimental set (n = 25 items) the intervention group gained on average four times as many items as the waiting control group (d = 2.30). There were also gains on personally chosen items for the intervention group. There was little change on untreated items for either group.
Conclusion: The study is the first randomised control trial to demonstrate an effect of word-finding therapy with children with language difficulties in mainstream school. The improvement in word-finding for treated items was obtained following a clinically realistic intervention in terms of approach, intensity and duration
Towards a large-scale quantum simulator on diamond surface at room temperature
Strongly-correlated quantum many-body systems exhibits a variety of exotic
phases with long-range quantum correlations, such as spin liquids and
supersolids. Despite the rapid increase in computational power of modern
computers, the numerical simulation of these complex systems becomes
intractable even for a few dozens of particles. Feynman's idea of quantum
simulators offers an innovative way to bypass this computational barrier.
However, the proposed realizations of such devices either require very low
temperatures (ultracold gases in optical lattices, trapped ions,
superconducting devices) and considerable technological effort, or are
extremely hard to scale in practice (NMR, linear optics). In this work, we
propose a new architecture for a scalable quantum simulator that can operate at
room temperature. It consists of strongly-interacting nuclear spins attached to
the diamond surface by its direct chemical treatment, or by means of a
functionalized graphene sheet. The initialization, control and read-out of this
quantum simulator can be accomplished with nitrogen-vacancy centers implanted
in diamond. The system can be engineered to simulate a wide variety of
interesting strongly-correlated models with long-range dipole-dipole
interactions. Due to the superior coherence time of nuclear spins and
nitrogen-vacancy centers in diamond, our proposal offers new opportunities
towards large-scale quantum simulation at room temperatures
Multiple scattering approach to low-energy electron collisions with the water dimer
Multiple scattering theory is applied to low-energy electron collisions with
a complex target formed of two molecular scatterers. The total T-matrix is
expressed in terms of the T-matrix for each isolated molecule. We apply the
approach to elastic electron-(H2O)2 collisions. Following the method developed
in our previous work on crystalline ice, we impose a cut-off on the dipole
outside the R-matrix sphere and an energy dependent cut-off on the angular
momentum components of the monomer T-matrix. An R-matrix calculation of
electron-dimer collisions is performed in order to evaluate the accuracy of the
multiple scattering approach. The agreement between the two calculations is
very good.Comment: 15 pages, 4 figures New submission: Added references Included PACS
numbers Figure 3 slightly changed Additions made to the Conclusions and
Discussion sectio
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