282 research outputs found
Modelling Aspects of Planar Multi-Mode Antennas for Direction-of-Arrival Estimation
Multi-mode antennas are an alternative to classical antenna arrays, and hence
a promising emerging sensor technology for a vast variety of applications in
the areas of array signal processing and digital communications. An unsolved
problem is to describe the radiation pattern of multi-mode antennas in closed
analytic form based on calibration measurements or on electromagnetic field
(EMF) simulation data. As a solution, we investigate two modeling methods: One
is based on the array interpolation technique (AIT), the other one on wavefield
modeling (WM). Both methods are able to accurately interpolate quantized EMF
data of a given multi-mode antenna, in our case a planar four-port antenna
developed for the 6-8.5 GHz range. Since the modeling methods inherently depend
on parameter sets, we investigate the influence of the parameter choice on the
accuracy of both models. Furthermore, we evaluate the impact of modeling errors
for coherent maximum-likelihood direction-of-arrival (DoA) estimation given
different model parameters. Numerical results are presented for a single
polarization component. Simulations reveal that the estimation bias introduced
by model errors is subject to the chosen model parameters. Finally, we provide
optimized sets of AIT and WM parameters for the multi-mode antenna under
investigation. With these parameter sets, EMF data samples can be reproduced in
interpolated form with high angular resolution
Seroprevalence of viral infections in captive rhesus and cynomolgus macaques
Macaques serve as important animal models for biomedical research. Viral
infection of macaques can compromise animal health as well as the results of
biomedical research, and infected animals constitute an occupational health
risk. Therefore, monitoring macaque colonies for viral infection is an
important task. We used a commercial chip-based assay to analyze sera of
231Â macaques for the presence of antibody responses against nine animal and
human viruses. We report high seroprevalence of cytomegalovirus (CMV),
lymphocryptovirus (LCV), rhesus rhadinovirus (RRV) and simian foamy virus
(SFV) antibodies in all age groups. In contrast, antibodies against simian
retrovirus type D (SRV/D) and simian T cell leukemia virus (STLV) were
detected only in 5 % and 10 % of animals, respectively, and were only
found in adult or aged animals. Moreover, none of the animals had antibodies
against herpes B virus (BV), in keeping with the results of in-house tests
previously used for screening. Finally, an increased seroprevalence of
measles virus antibodies in animals with extensive exposure to multiple
humans for extended periods of time was observed. However, most of these
animals were obtained from external sources, and a lack of information on the
measles antibody status of the animals at the time of arrival precluded
drawing reliable conclusions from the data. In sum, we show, that in the
colony studied, CMV, LCV, RRV and SFV infection was ubiquitous and likely
acquired early in life while SRV/D and STLV infection was rare and likely
acquired during adulthood.</p
First-principles molecular-dynamics simulations of a hydrous silica melt: Structural properties and hydrogen diffusion mechanism
We use {\it ab initio} molecular dynamics simulations to study a sample of
liquid silica containing 3.84 wt.% HO.We find that, for temperatures of
3000 K and 3500 K,water is almost exclusively dissolved as hydroxyl groups, the
silica network is partially broken and static and dynamical properties of the
silica network change considerably upon the addition of water.Water molecules
or free O-H groups occur only at the highest temperature but are not stable and
disintegrate rapidly.Structural properties of this system are compared to those
of pure silica and sodium tetrasilicate melts at equivalent temperatures. These
comparisons confirm the picture of a partially broken tetrahedral network in
the hydrous liquid and suggest that the structure of the matrix is as much
changed by the addition of water than it is by the addition of the same amount
(in mole %) of sodium oxide. On larger length scales, correlations are
qualitatively similar but seem to be more pronounced in the hydrous silica
liquid. Finally, we study the diffusion mechanisms of the hydrogen atoms in the
melt. It turns out that HOSi triclusters and SiO dangling bonds play a
decisive role as intermediate states for the hydrogen diffusion.Comment: 25 pages, 18 figures. submitte
Novel virus related to Kaposi’s sarcoma-associated herpesvirus from a monkey (Colobus guereza) suffering from primary effusion lymphoma
No abstract available
The effect of motion direction and eccentricity on vection, VR sickness and head movements in Virtual Reality
Virtual Reality experienced through head mounted displays often leads to vection, discomfort and sway in the user. This study investigated the effect of motion direction and eccentricity on these three phenomena using optic flow patterns displayed using the Valve Index. Visual motion stimuli were presented in the centre, periphery or far periphery and moved either in-depth (back and forth) or laterally (left and right). Overall vection was stronger for motion-in-depth compared to lateral motion. Additionally, eccentricity primarily affected stimuli moving in-depth with stronger vection for more peripherally presented motion patterns compared to more central ones. Motion direction affected the various aspects of VR sickness differently and modulated the effect of eccentricity on VR sickness. For stimuli moving in-depth far peripheral presentation caused more discomfort, whereas for lateral motion the central stimuli caused more discomfort. Stimuli moving in-depth led to more head movements in the anterior-posterior direction when the entire visual field was stimulated. Observers demonstrated more head movements in the anterior-posterior direction compared to the medio-lateral direction throughout the entire experiment independent of motion direction or eccentricity of the presented moving stimulus. A correlation showed a positive relationship between dizziness and vection duration and between general discomfort and sway. Identifying where in the visual field motion presented to an individual causes the least amount of VR sickness without losing vection and presence can guide development for Virtual Reality games, training and treatment programs
Simultaneous Localization and Antenna Calibration
Cooperative localization fills the gap in scenarios where global navigation satellite system (GNSS) reception is denied or impaired. Position and orientation information is then often provided based on signal round-trip time (RTT) and direction-of-arrival (DoA). Obtaining a meaningful RTT requires calibrated transceiver group delays, and accurate DoA estimation requires antenna calibration. Usually, such calibrations are performed once before operation. However, calibration parameters can change over time, e.g. due to varying temperature of RF components or reconfigurable antenna surroundings. To cope with that, we propose to estimate antenna responses and ranging biases simultaneously with positions and orientations by simultaneous localization and calibration (SLAC). We derive a SLAC algorithm based on Bayesian filtering, which is suitable for arbitrary antenna types. The algorithm is evaluated with measurement data from robotic rovers. We show, that ranging and DoA performance is improved considerably, leading to better position and orientation accuracy with SLAC
Simultaneous Localization and Calibration for Cooperative Radio Navigation
Cooperative radio localization and navigation systems can be used in scenarios where the reception of global navigation satellite system (GNSS) signals is not possible or impaired. While the benefit of cooperation has been highlighted by many papers, calibration is not widely considered, but equally important in practice. Utilizing the signal propagation time requires group delay or ranging bias calibration and estimating the direction-of-arrival (DoA) requires antenna response calibration. Often, calibration parameters are determined only once before operation. However, the calibration parameters are influenced by e.g. changing temperatures of radio frequency (RF) components or changing surroundings of antennas. To cope with that, we derive a cooperative simultaneous localization and calibration (SLAC) algorithm based on Bayesian filtering, which estimates antenna responses and ranging biases simultaneously with positions and orientations. By simulations, we show that the calibration parameters can be estimated during operation without additional sensors. We further proof practical applicability of SLAC by evaluating measurement data from robotic rovers. With SLAC, both ranging and DoA estimation performance is improved, resulting in better position and orientation estimation accuracy. SLAC is thus able to provide reliable calibration and to mitigate model mismatch. Finally, we discuss open research questions and possible extensions of SLAC
Is virtual reality sickness elicited by illusory motion affected by gender and prior video gaming experience?
Gaming using VR headsets is becoming increasingly popular; however , these displays can cause VR sickness. To investigate the effects of gender and gamer type on VR sickness motion illusions are used as stimuli, being a novel method of inducing the perception of motion whilst minimising the "accommodation vergence conflict". Females and those who do not play action games experienced more severe VR sickness symptoms compared to males and experienced action gamers. The interaction of the gender and gamer type revealed that prior video gaming experience was beneficial for females, however, for males, it did not show the same positive effects
Activation of Sphingomyelinase-Ceramide-Pathway in COVID-19 Purposes Its Inhibition for Therapeutic Strategies
Effective treatment strategies for severe coronavirus disease (COVID-19) remain scarce. Hydrolysis of membrane-embedded, inert sphingomyelin by stress responsive sphingomyelinases is a hallmark of adaptive responses and cellular repair. As demonstrated in experimental and observational clinical studies, the transient and stress-triggered release of a sphingomyelinase, SMPD1, into circulation and subsequent ceramide generation provides a promising target for FDA-approved drugs. Here, we report the activation of sphingomyelinase-ceramide pathway in 23 intensive care patients with severe COVID-19. We observed an increase of circulating activity of sphingomyelinase with subsequent derangement of sphingolipids in serum lipoproteins and from red blood cells (RBC). Consistent with increased ceramide levels derived from the inert membrane constituent sphingomyelin, increased activity of acid sphingomyelinase (ASM) accurately distinguished the patient cohort undergoing intensive care from healthy controls. Positive correlational analyses with biomarkers of severe clinical phenotype support the concept of an essential pathophysiological role of ASM in the course of SARS-CoV-2 infection as well as of a promising role for functional inhibition with anti-inflammatory agents in SARS-CoV-2 infection as also proposed in independent observational studies. We conclude that large-sized multicenter, interventional trials are now needed to evaluate the potential benefit of functional inhibition of this sphingomyelinase in critically ill patients with COVID-19
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