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Search Results: 1 - 10 of 304337 matches for " T. L. Hansen "
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Geomagnetic control of polar mesosphere summer echoes
J. Bremer,P. Hoffmann,T. L. Hansen
Annales Geophysicae (ANGEO) , 2003,
Abstract: Using observations with the ALOMAR SOUSY radar near Andenes (69.3°N, 16.0°E) from 1994 until 1997 polar mesosphere summer echoes (PMSE) have been investigated in dependence on geomagnetic K indices derived at the Auroral Observatory Troms (69.66°N, 18.94°E). During night-time and morning hours a significant correlation between the signal-to-noise ratio (SNR) of the radar results and the geomagnetic K indices could be detected with a maximum correlation near midnight. The correlation becomes markedly smaller in the afternoon and early evening hours with a minimum near 17 UT. This diurnal variation is in reasonable agreement with riometer absorption at Ivalo (68.55°N, 27.28°E) and can be explained by the diurnal variation of ionization due to precipitating high energetic particles. Therefore, a part of the diurnal PMSE variation is caused by this particle precipitation. The variability of the solar EUV variation, however, has no significant influence on the PMSE during the observation period. Keywords: Ionosphere (auroral ionosphere) - Magnetospheric physics (energetic particles, precipitating) - Radio science (remote sensing)
Superposed epoch analysis applied to large-amplitude travelling convection vortices
H. Lühr,M. Rother,T. Iyemori,T. L. Hansen
Annales Geophysicae (ANGEO) , 2003,
Abstract: For the six months from 1 October 1993 to 1 April 1994 the recordings of the IMAGE magnetometer network have been surveyed in a search for large-amplitude travelling convection vortices (TCVs). The restriction to large amplitudes (>100 nT) was chosen to ensure a proper detection of evens also during times of high activity. Readings of all stations of the northern half of the IMAGE network were employed to check the consistency of the ground signature with the notation of a dual-vortex structure moving in an azimuthal direction. Applying these stringent selection criteria we detected a total of 19 clear TCV events. The statistical properties of our selection resemble the expected characteristics of large-amplitude TCVs. New and unexpected results emerged from the superposed epoch analysis. TCVs tend to form during quiet intervals embedded in moderately active periods. The occurrence of events is not randomly distributed but rather shows a clustering around a few days. These clusters recur once or twice every 27 days. Within a storm cycle they show up five to seven days after the commencement. With regard to solar wind conditions, we see the events occurring in the middle of the IMF sector structure. Large-amplitude TCVs seem to require certain conditions to make solar wind transients 'geoeffective', which have the tendency to recur with the solar rotation period. Key words. Ionosphere (Aural ionosphere; Ionosphere- magnetosphere interactions) · Magnetospheric Physics (current system)
Effect of a clown’s presence at botulinum toxin injections in children: a randomized, prospective study
Hansen LK, Kibaek M, Martinussen T, Kragh L, Hejl M
Journal of Pain Research , 2011, DOI: http://dx.doi.org/10.2147/JPR.S23199
Abstract: t of a clown’s presence at botulinum toxin injections in children: a randomized, prospective study Original Research (3523) Total Article Views Authors: Hansen LK, Kibaek M, Martinussen T, Kragh L, Hejl M Published Date September 2011 Volume 2011:4 Pages 297 - 300 DOI: http://dx.doi.org/10.2147/JPR.S23199 Lars Kjaersgaard Hansen1, Maria Kibaek1, Torben Martinussen2, Lene Kragh3, Mogens Hejl1 1Department of Paediatrics, Hans Christian Andersen Children's Hospital, Odense University Hospital, Odense; 2Roskilde Hospital, Roskilde; 3Department of Statistics, University of Southern Denmark, Odense, Denmark Background: The effect of the presence of a hospital clown during pediatric procedures has rarely been evaluated. In a pediatric ward, botulinum toxin injection is a painful procedure and a stressful experience for the child. We undertook a study of the effect of the presence of a hospital clown on children treated with botulinum toxin in an outpatient setting. Methods: In total, 60 children, the majority of whom had spastic cerebral palsy, were subjected to a total of 121 botulinum toxin treatment sessions. Thirty-two children were being treated for the first time. During a 2-year period, we enrolled 121 treatment sessions prospectively, and the children were randomized to either the presence of a female clown during treatment or to no presence of a clown. The duration of the child's crying during the procedure was used as an indicator of the effect of the presence of a clown. Results: The effect of the clown was significantly related to patient gender. Girls were found to have a significantly shorter period of crying when the clown was present. For children younger than 8 years, the effect on boys was negative. Children treated for the first time did not appear to benefit from the presence of the clown, and showed no difference in effect between genders. Conclusion: No effect of the clown was documented for children being treated for the first time. At repeat treatments, we saw a positive effect of the female clown in relation to girls, and a negative effect on boys younger than 8 years of age.
Regional analysis of groundwater nitrate concentrations and trends in Denmark in regard to agricultural influence
B. Hansen,T. Dalgaard,L. Thorling,B. S?rensen
Biogeosciences Discussions , 2012, DOI: 10.5194/bgd-9-5321-2012
Abstract: The act of balancing between an intensive agriculture with a high potential for nitrate pollution and a~drinking water supply almost entirely based on groundwater is a challenge faced by Denmark and similar regions around the globe. Since the 1980s, regulations implemented by Danish farmers have succeeded in optimizing the N (nitrogen) management at farm level. As a result, the upward agricultural N surplus trend has been reversed, and the N surplus has reduced by 30–55 % from 1980 to 2007 depending on region. The reduction in the N surplus served to reduce the losses of N from agriculture, with documented positive effects on nature and the environment in Denmark. In groundwater, the upward trend in nitrate concentration was reversed around 1980, and a larger number of downward nitrate trends were seen in the youngest groundwater compared with the oldest groundwater. However, on average, approximately 48 % of the oxic monitored groundwater has nitrate concentrations above the groundwater and drinking water standards of 50 mg l 1. Furthermore, trend analyses show that 33 % of all the monitored groundwater has upward nitrate trends, while only 18 % of the youngest groundwater has upward nitrate trends according to data sampled from 1988–2009. A regional analysis shows a correlation between a high level of N surplus in agriculture, high concentrations of nitrate in groundwater and the largest number of downward nitrate trends in groundwater in the livestock-dense northern and western parts of Denmark compared with the south-eastern regions with lower livestock densities. These results indicate that the livestock farms dominating in northern and western parts of Denmark have achieved the largest reductions in N surpluses. Groundwater recharge age determinations allow comparison of long-term changes in N surplus in agriculture with changes in oxic groundwater quality. The presented data analysis is based on groundwater recharged from 1952–2003, but sampled from 1988–2009. Repetition of the nitrate trend analyses at five-year intervals using dating of the groundwater recharged in the coming years and a longer time series of the nitrate analyses can reveal the evolution in nitrate leaching from Danish agriculture during the past 10 yr. Similar analyses can be carried out to compare with other regions internationally.
Anomalous echoes observed with the EISCAT UHF radar at 100-km altitude
E. Malnes,N. Bj?rn?,T. L. Hansen
Annales Geophysicae (ANGEO) , 2003,
Abstract: We have observed a number of strong echoes with the European incoherent-scatter (EISCAT) UHF (930-MHz) radar at angles 83.5° and 78.6° with the geomagnetic field and at about 100-km altitude north in the auroral zone. The echoes are short-lived and occur in single 2- or 10-s data dumps. They are offset by 125–130 kHz with respect to the transmitted frequency. In most cases the offset compares well with the frequency of gyro lines in the incoherent-scatter spectrum, as given by the standard linear dispersion relation. But sometimes the measured offsets deviate significantly from the model calculations, and the interpretation in terms of gyro lines becomes questionable. The discrepancy could possibly be explained by local deviations in the magnetic field from the model (IGRF 1987), which are generated by incoming particle beams. A more serious problem with the gyro-line theory is how the line can be excited at altitudes where the collisional damping is substantial. The high intensity and short lifetime of the signal point to a fast-growing plasma instability as the likely excitation mechanism, if the gyro-line interpretation is correct. The cause of the instability could be the same particle beams as those causing the disturbances in the magnetic field. Alternatively, the observations may be interpreted as meteor head echoes. The large Doppler shifts, the short lifetimes and the altitudes of the signals support this explanation. The main difficulty is that the distribution of measured offsets appears to be different in magnetically active conditions and in less active conditions. Also, the occurrence of echoes does not seem to follow the expected changes in meteor density. More observations in different conditions are needed to decide between the two interpretations. As it is, we are inclined to believe in the meteor head echo theory, the objections to the gyro-line theory being more fundamental.
Effect of a clown’s presence at botulinum toxin injections in children: a randomized, prospective study
Hansen LK,Kibaek M,Martinussen T,Kragh L
Journal of Pain Research , 2011,
Abstract: Lars Kjaersgaard Hansen1, Maria Kibaek1, Torben Martinussen2, Lene Kragh3, Mogens Hejl11Department of Paediatrics, Hans Christian Andersen Children's Hospital, Odense University Hospital, Odense; 2Roskilde Hospital, Roskilde; 3Department of Statistics, University of Southern Denmark, Odense, DenmarkBackground: The effect of the presence of a hospital clown during pediatric procedures has rarely been evaluated. In a pediatric ward, botulinum toxin injection is a painful procedure and a stressful experience for the child. We undertook a study of the effect of the presence of a hospital clown on children treated with botulinum toxin in an outpatient setting.Methods: In total, 60 children, the majority of whom had spastic cerebral palsy, were subjected to a total of 121 botulinum toxin treatment sessions. Thirty-two children were being treated for the first time. During a 2-year period, we enrolled 121 treatment sessions prospectively, and the children were randomized to either the presence of a female clown during treatment or to no presence of a clown. The duration of the child's crying during the procedure was used as an indicator of the effect of the presence of a clown.Results: The effect of the clown was significantly related to patient gender. Girls were found to have a significantly shorter period of crying when the clown was present. For children younger than 8 years, the effect on boys was negative. Children treated for the first time did not appear to benefit from the presence of the clown, and showed no difference in effect between genders.Conclusion: No effect of the clown was documented for children being treated for the first time. At repeat treatments, we saw a positive effect of the female clown in relation to girls, and a negative effect on boys younger than 8 years of age.Keywords: clown, injections, pain, botulinum toxin
Multichannel 0-to-2 and 1-to-2 transition amplitudes for arbitrary spin particles in a finite volume
Raúl A. Brice?o,Maxwell T. Hansen
Physics , 2015, DOI: 10.1103/PhysRevD.92.074509
Abstract: We present a model-independent, non-perturbative relation between finite-volume matrix elements and infinite-volume $\textbf{0}\rightarrow\textbf{2}$ and $\textbf{1}\rightarrow\textbf{2}$ transition amplitudes. Our result accommodates theories in which the final two-particle state is coupled to any number of other two-body channels, with all angular momentum states included. The derivation uses generic, fully relativistic field theory, and is exact up to exponentially suppressed corrections in the lightest particle mass times the box size. This work distinguishes itself from previous studies by accommodating particles with any intrinsic spin. To illustrate the utility of our general result, we discuss how it can be implemented for studies of $N+\mathcal{J}~\rightarrow~(N\pi,N\eta,N\eta',\Sigma K,\Lambda K)$ transitions, where $\mathcal{J}$ is a generic external current. The reduction of rotational symmetry, due to the cubic finite volume, manifests in this example through the mixing of S- and P-waves when the system has nonzero total momentum.
Relativistic, model-independent, multichannel $2\to2$ transition amplitudes in a finite volume
Raúl A. Brice?o,Maxwell T. Hansen
Physics , 2015,
Abstract: We derive formalism for determining $\textbf{2} + \mathcal J \to \textbf{2}$ infinite-volume transition amplitudes from finite-volume matrix elements. Specifically, we present a relativistic, model-independent relation between finite-volume matrix elements of external currents and the physically observable infinite-volume matrix elements involving two-particle asymptotic states. The result presented holds for states composed of two scalar bosons. These can be identical or non-identical and, in the latter case, can be either degenerate or non-degenerate. We further accommodate any number of strongly-coupled two-scalar channels. This formalism will, for example, allow future lattice QCD calculations of the $\rho$-meson form factor, in which the unstable nature of the $\rho$ is rigorously accommodated.
The role of binaries in the enrichment of the early Galactic halo. I. r-process-enhanced metal-poor stars
T. T. Hansen,J. Andersen,B. Nordstr?m,T. C. Beers,J. Yoon,L. A. Buchhave
Physics , 2015, DOI: 10.1051/0004-6361/201526812
Abstract: The detailed chemical composition of most metal-poor halo stars has been found to be highly uniform, but a minority of stars exhibit dramatic enhancements in their abundances of heavy neutron-capture elements and/or of carbon. The key question for Galactic chemical evolution models is whether these peculiarities reflect the composition of the natal clouds, or if they are due to later mass transfer of processed material from a binary companion. If the former case applies, the observed excess of certain elements was implanted within selected clouds in the early ISM from a production site at interstellar distances. Our aim is to determine the frequency and orbital properties of binaries among these chemically peculiar stars. This information provides the basis for deciding whether mass transfer from a binary companion is necessary and sufficient to explain their unusual compositions. This paper discusses our study of a sample of 17 moderately (r-I) and highly (r-II) r-process-element enhanced VMP and EMP stars. High-resolution, low signal-to-noise spectra of the stars were obtained at roughly monthly intervals over 8 years with the FIES spectrograph at the Nordic Optical Telescope. From these spectra, radial velocities with an accuracy of ~100 m/s were determined by cross-correlation against an optimized template. 14 of the programme stars exhibit no significant RV variation over this period, while 3 are binaries with orbits of typical eccentricity for their periods, resulting in a normal binary frequency of ~18+-6% for the sample. Our results confirm our preliminary conclusion from 2011, based on partial data, that the chemical peculiarity of the r-I and r-II stars is not caused by any putative binary companions. Instead, it was imprinted on the natal molecular clouds of these stars by an external, distant source. Models of the ISM in early galaxies should account for such mechanisms.
Runoff and Nutrient Losses from Constructed Soils Amended with Compost
N. E. Hansen,D. M. Vietor,C. L. Munster,R. H. White,T. L. Provin
Applied and Environmental Soil Science , 2012, DOI: 10.1155/2012/542873
Abstract: Composted organic materials used to stabilize roadside embankments in Texas promote rapid revegetation of soils disturbed by construction activities. Yet, adding compost to soil may increase total and soluble plant nutrients available for loss in runoff water. Composted municipal biosolids and dairy manure products were applied to soils in Texas according to prescribed Texas Department of Transportation specifications for stabilizing roadside soils. The specifications included a method for incorporating compost into soils prior to seeding or applying a compost and woodchip mix over a disturbed soil and then seeding. Applying compost and woodchips over the soil surface limited sediment losses (14 to 32 fold decrease) compared to incorporating compost into the soil. Yet, the greatest total phosphorus and nitrogen losses in runoff water occurred from soils where the compost and woodchip mix was applied. The greatest losses of soluble phosphorus also occurred when the compost and woodchip mix was applied. In contrast, nitrate-nitrogen losses in runoff were similar when compost was incorporated in the soil or applied in the woodchip mix. Compost source affected the nutrient losses in runoff. While the composted municipal biosolids added greater nutrient loads to the soil, less nutrient loss in runoff occurred. 1. Introduction State Departments of Transportation (SDOT) are mandated to manage highway construction sites as potential nonpoint pollution sources. Soil particulate loads are often the greatest fraction of soil components in runoff from highway construction sites [1]. Soil erosion can occur when disturbed soils are unprotected from rainfall and flowing water. Silt fences, straw mulch, and material blankets are among several practices used to control erosion [2]. Additionally, composted biosolids and blends of biosolids with yard waste are among materials top-dressed or incorporated on constructed soil slopes to control erosion and enhance vegetation establishment [3–5]. Persyn et al. [5] reported 5 or 10?cm blankets of composted biosolids, yard waste, or industrial waste reduced runoff water and sediment compared to exposed subsoil or imported topsoil to high-way construction sites. In a complementary report, Glanville et al. [3] reported top-dressing composted materials decreased nutrient loss in runoff water during a simulated 30?min rain event compared to excavated soil alone. Specifications for the composition and application of composted materials to soil on construction sites vary among SDOTs [6]. Generally, application rates are depth- or
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