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Search Results: 1 - 10 of 223807 matches for " R. Santer "
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Evaluation of the MERIS aerosol product over land with AERONET
J. Vidot,R. Santer,O. Aznay
Atmospheric Chemistry and Physics Discussions , 2008,
Abstract: The Medium Resolution Imaging Spectrometer (MERIS) launched in February 2002 on-board the ENVISAT spacecraft is making global observations of top-of-atmosphere (TOA) radiances. Aerosol optical properties are retrieved over land using Look-Up Table (LUT) based algorithm and surface reflectances in the blue and the red spectral regions. We compared instantaneous aerosol optical thicknesses retrieved by MERIS in the blue and the red at locations containing sites within the Aerosol Robotic Network (AERONET). Between 2002 and 2005, a set of 500 MERIS images were used in this study. The result shows that, over land, MERIS aerosol optical thicknesses are well retrieved in the blue and poorly retrieved in the red, leading to an underestimation of the Angstrom coefficient. Correlations are improved by applying a simple criterion to avoid scenes probably contaminated by thin clouds. To investigate the weakness of the MERIS algorithm, ground-based radiometer measurements have been used in order to retrieve new aerosol models, based on their Inherent Optical Properties (IOP). These new aerosol models slightly improve the correlation, but the main problem of the MERIS aerosol product over land can be attributed to the surface reflectance model in the red.
Evaluation of the MERIS aerosol product over land with AERONET
J. Vidot,R. Santer,O. Aznay
Atmospheric Chemistry and Physics (ACP) & Discussions (ACPD) , 2008,
Abstract: The Medium Resolution Imaging Spectrometer (MERIS) launched in February 2002 on-board the ENVISAT spacecraft is making global observations of top-of-atmosphere (TOA) radiances. Aerosol optical properties are retrieved over land using Look-Up Table (LUT) based algorithm and surface reflectances in the blue and the red spectral regions. We compared instantaneous aerosol optical thicknesses retrieved by MERIS in the blue and the red at locations containing sites within the Aerosol Robotic Network (AERONET). Between 2002 and 2005, a set of 500 MERIS images were used in this study. The result shows that, over land, MERIS aerosol optical thicknesses are well retrieved in the blue and poorly retrieved in the red, leading to an underestimation of the Angstrom coefficient. Correlations are improved by applying a simple criterion to avoid scenes probably contaminated by thin clouds. To investigate the weakness of the MERIS algorithm, ground-based radiometer measurements have been used in order to retrieve new aerosol models, based on their Inherent Optical Properties (IOP). These new aerosol models slightly improve the correlation, but the main problem of the MERIS aerosol product over land can be attributed to the surface reflectance model in the red.
A Colour Opponent Model That Explains Tsetse Fly Attraction to Visual Baits and Can Be Used to Investigate More Efficacious Bait Materials
Roger D. Santer
PLOS Neglected Tropical Diseases , 2014, DOI: 10.1371/journal.pntd.0003360
Abstract: Palpalis group tsetse flies are the major vectors of human African trypanosomiasis, and visually-attractive targets and traps are important tools for their control. Considerable efforts are underway to optimise these visual baits, and one factor that has been investigated is coloration. Analyses of the link between visual bait coloration and tsetse fly catches have used methods which poorly replicate sensory processing in the fly visual system, but doing so would allow the visual information driving tsetse attraction to these baits to be more fully understood, and the reflectance spectra of candidate visual baits to be more completely analysed. Following methods well established for other species, I reanalyse the numbers of tsetse flies caught at visual baits based upon the calculated photoreceptor excitations elicited by those baits. I do this for large sets of previously published data for Glossina fuscipes fuscipes (Lindh et al. (2012). PLoS Negl Trop Dis 6: e1661), G. palpalis palpalis (Green (1988). Bull Ent Res 78: 591), and G. pallidipes (Green and Flint (1986). Bull Ent Res 76: 409). Tsetse attraction to visual baits in these studies can be explained by a colour opponent mechanism to which the UV-blue photoreceptor R7y contributes positively, and both the green-yellow photoreceptor R8y, and the low-wavelength UV photoreceptor R7p, contribute negatively. A tool for calculating fly photoreceptor excitations is made available with this paper, and this will facilitate a complete and biologically authentic description of visual bait reflectance spectra that can be employed in the search for more efficacious visual baits, or the analysis of future studies of tsetse fly attraction.
Collective versus single-particle effects in the optical spectra of finite electronic quantum systems
M. Santer,B. Mehlig
Physics , 2000, DOI: 10.1103/PhysRevB.63.241403
Abstract: We study optical spectra of finite electronic quantum systems at frequencies smaller than the plasma frequency using a quasi-classical approach. This approach includes collective effects and enables us to analyze how the nature of the (single-particle) electron dynamics influences the optical spectra in finite electronic quantum systems. We derive an analytical expression for the low-frequency absorption coefficient of electro-magnetic radiation in a finite quantum system with ballistic electron dynamics and specular reflection at the boundaries: a two-dimensional electron gas confined to a strip of width a (the approach can be applied to systems of any shape and electron dynamics -- diffusive or ballistic, regular or irregular motion). By comparing with results of numerical computations using the random-phase approximation we show that our analytical approach provides a qualitative and quantitative understanding of the optical spectrum.
Universal eigenvector statistics in a quantum scattering ensemble
B. Mehlig,M. Santer
Physics , 2000, DOI: 10.1103/PhysRevE.63.020105
Abstract: We calculate eigenvector statistics in an ensemble of non-Hermitian matrices describing open quantum systems [F. Haake et al., Z. Phys. B 88, 359 (1992)] in the limit of large matrix size. We show that ensemble-averaged eigenvector correlations corresponding to eigenvalues in the center of the support of the density of states in the complex plane are described by an expression recently derived for Ginibre's ensemble of random non-Hermitian matrices.
Evidence for Air Movement Signals in the Agonistic Behaviour of a Nocturnal Arachnid (Order Amblypygi)
Roger D. Santer,Eileen A. Hebets
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0022473
Abstract: Many arthropods possess filiform hair sensilla (termed trichobothria in arachnids), which are extremely sensitive detectors of medium particle displacement. Electrophysiological evidence in some taxa suggests that these sensilla can detect air particle displacements resulting from intraspecific communication signals. However, it has not yet been shown for any species that the air particle displacements detected by the filiform hairs are themselves perceived as a ‘signal’ (i.e. that individuals make behavioural decisions based upon the responses of these organs to the displays of conspecifics). We investigate the agonistic behaviour of the whip spider Phrynus marginemaculatus and the role of its trichobothria in receiving agonistic signals. Whip spiders have extremely elongated ‘antenniform’ first legs, which they vibrate close to their opponents during agonistic interactions, inducing air movements that excite their opponents' trichobothria. We find that ablation of the trichobothria causes significant increases in: (I) contest duration, and (II) the probability of contest escalation past aggressive displays to physical fighting. Therefore, in the absence of air movement-sensitive sensilla, contest assessment is impaired. This suggests that whip spiders exploit true air movement signals during agonistic interactions, and that these are received by the trichobothria. Furthermore, these results indicate that, in whip spiders, such signals help mitigate the cost of agonistic interaction.
What aspects of periods are most bothersome for women reporting heavy menstrual bleeding? Community survey and qualitative study
Miriam Santer, Sally Wyke, Pamela Warner
BMC Women's Health , 2007, DOI: 10.1186/1472-6874-7-8
Abstract: A cross-sectional postal survey and qualitative interviews were carried out amongst a community-based sample of women in Lothian, Scotland. 906 women aged 25 to 44 reported heavy or very heavy periods in response to a postal survey of 2833 women registered with 19 general practices. Amongst those who had reported heavy menstrual bleeding, analysis was carried out of responses to the free text questionnaire item, "What bothers you most about your periods?" In addition, 32 of these women participated in qualitative interviews and their accounts were analysed to explore how menstrual symptoms and 'problems' with periods were experienced.Even amongst this subgroup of women, selected on the basis of having reported their periods as heavy in the survey, pain was the aspect of their periods that 'most bothered' them, followed by heaviness, mood changes or tiredness, and irregularity or other issues of timing. Interviewees' accounts similarly suggested that a range of menstrual symptoms were problematic and some women did not disentangle which was worst. Judgements of periods as a problem were based on the impact of menstrual symptoms on daily life and this was contingent on social circumstances such as type of paid work and other responsibilities. Although women spoke readily of whether their periods were a problem, there was less clarity in accounts of whether or not menstrual loss was 'heavy'; women said they made judgements based on what was normal for them, degree of difficulty in containing blood loss and pattern of loss.Women with heavy periods are bothered by a range of menstrual symptoms and their impact on everyday life. Clinical emphasis should be on clarifying the presenting problem and providing help and advice for this, as well as on excluding serious disease. Sometimes simple approaches, such as help with analgesia, may be all that is required.Heavy periods are an extremely common symptom, reported by 35% of women aged 25 to 44 [1]. Concerns have been raised
No Correlation between AVPR1A Promoter Polymorphisms and Prepulse Inhibition in Patients with Nocturnal Enuresis  [PDF]
Sebastian Schulz-Juergensen, Philipp von Bismarck, René Santer, Paul Eggert
Open Journal of Nephrology (OJNeph) , 2014, DOI: 10.4236/ojneph.2014.41004
Abstract:

Introduction: A correlation between AVPR1A promoter polymorphisms and prepulse inhibition (PPI) of startle reflexes has been described in healthy adults. Many children with nocturnal enuresis (NE) have a reduced PPI and treatment with desamino arginine vasopressin (dDAVP), a ligand of the arginine vasopressin receptor 1A (AVPR1A), and both improve clanical symptoms and significantly increase PPI. Methods: In 17 children (median 9.1 years, range 6.4-17.3) with NE, promoter repeats within the RS1 and RS3 regions of AVPR1A were quantified and correlated to PPI (native and age-adjusted). Results: No direct correlation was found between the number of promoter repeats at RS1 and PPI (correlation coefficient0.240, p = 0.346) or RS3 and PPI (correlation coefficient0.0192, p = 0.936),

Optical response of two-dimensional electron fluids beyond the Kohn regime: strong non-parabolic confinement and intense laser light
M. Santer,B. Mehlig,M. Moseler
Physics , 2002, DOI: 10.1103/PhysRevLett.89.286801
Abstract: We investigate the linear and non-linear optical response of two-dimensional (2D) interacting electron fluids confined by a strong non-parabolic potential. We show that such fluids may exhibit higher-harmonic spectra under realistic experimental conditions. Higher harmonics arise as the electrons explore anharmonicities of the confinement potential (electron-electron interactions reduce this non-linear effect). This opens the possibility of controlling the optical functionality of such systems by engineering the confinement potential. Our results were obtained within time-dependent density-functional theory, employing the adiabatic local-density approximation. A classical hydrodynamical model is in good agreement with the quantum-mechanical results.
Predator versus Prey: Locust Looming-Detector Neuron and Behavioural Responses to Stimuli Representing Attacking Bird Predators
Roger D. Santer, F. Claire Rind, Peter J. Simmons
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0050146
Abstract: Many arthropods possess escape-triggering neural mechanisms that help them evade predators. These mechanisms are important neuroethological models, but they are rarely investigated using predator-like stimuli because there is often insufficient information on real predator attacks. Locusts possess uniquely identifiable visual neurons (the descending contralateral movement detectors, DCMDs) that are well-studied looming motion detectors. The DCMDs trigger ‘glides’ in flying locusts, which are hypothesised to be appropriate last-ditch responses to the looms of avian predators. To date it has not been possible to study glides in response to stimuli simulating bird attacks because such attacks have not been characterised. We analyse video of wild black kites attacking flying locusts, and estimate kite attack speeds of 10.8±1.4 m/s. We estimate that the loom of a kite’s thorax towards a locust at these speeds should be characterised by a relatively low ratio of half size to speed (l/|v|) in the range 4–17 ms. Peak DCMD spike rate and gliding response occurrence are known to increase as l/|v| decreases for simple looming shapes. Using simulated looming discs, we investigate these trends and show that both DCMD and behavioural responses are strong to stimuli with kite-like l/|v| ratios. Adding wings to looming discs to produce a more realistic stimulus shape did not disrupt the overall relationships of DCMD and gliding occurrence to stimulus l/|v|. However, adding wings to looming discs did slightly reduce high frequency DCMD spike rates in the final stages of object approach, and slightly delay glide initiation. Looming discs with or without wings triggered glides closer to the time of collision as l/|v| declined, and relatively infrequently before collision at very low l/|v|. However, the performance of this system is in line with expectations for a last-ditch escape response.
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