The Neighborhood Polynomial of Chordal Graphs

The neighborhood polynomial of a graph $G$ is the generating function of subsets of vertices in $G$ that have a common neighbor. In this paper we study the neighborhood polynomial and the complexity of its computation for chordal graphs. We will show that it is \NP-hard to compute the neighborhood polynomial on general chordal graphs. Furthermore we will introduce a parameter for chordal graphs called anchor width and an algorithm to compute the neighborhood polynomial which runs in polynomial time if the anchor width is polynomially bounded. Finally we will show that we can bound the anchor width for chordal comparability graphs and chordal graphs with bounded leafage. The leafage of a chordal graphs is the minimum number of leaves in the host tree of a subtree representation. In particular, interval graphs have leafage at most 2. This shows that the anchor width of interval graphs is at most quadratic

An Experimental Study on Airborne Landmine Detection Using a Circular Synthetic Aperture Radar

Many countries in the world are contaminated with landmines. Several thousand casualties occur every year. Although there are certain types of mines that can be detected from a safe stand-off position with tools, humanitarian demining is still mostly done by hand. As a new approach, an unmanned aerial system (UAS) equipped with a ground penetrating synthetic aperture radar (GPSAR) was developed, which is used to detect landmines, cluster munition, grenades, and improvised explosive devices (IEDs). The measurement system consists of a multicopter, a total station, an inertial measurement unit (IMU), and a frequency-modulated continuous-wave (FMCW) radar operating from 1 GHz to 4 GHz. The highly accurate localization of the measurement system and the full flexibility of the UAS are used to generate 3D-repeat-pass circular SAR images of buried antipersonnel landmines. In order to demonstrate the functionality of the system, 15 different dummy landmines were buried in a sandbox. The measurement results show the high potential of circular SAR for the detection of minimum metal mines. 11 out of 15 different test objects could be detected unambiguously with cm-level accuracy by examining depth profiles showing the amplitude of the targets response over the processing depth.Comment: 7 pages, 9 figure

Diagnostic Performance of Rapid Antigen Testing for SARS-CoV-2: The COVid-19 AntiGen (COVAG) study

Background Rapid diagnostic testing for SARS-Cov-2 antigens is used to combat the ongoing pandemic. In this study we aimed to compare two RDTs, the SD Biosensor Q SARS-CoV-2 Rapid Antigen Test (Roche) and the Panbio COVID-19 Ag Rapid Test (Abbott), against rRT-PCR. Methods We included 2,215 all-comers at a diagnostic center between February 1 and March 31, 2021. rRT-PCR-positive samples were examined for SARS-CoV-2 variants. Findings Three hundred and thirty eight participants (15%) were rRT-PCR-positive for SARS-CoV-2. The sensitivities of Roche-RDT and Abbott-RDT were 60.4 and 56.8% ( P < 0.0001) and specificities 99.7% and 99.8% ( P = 0.076). Sensitivity inversely correlated with rRT-PCR-Ct values. The RDTs had higher sensitivities in individuals referred by treating physicians (79.5%, 78.7%) than in those referred by health departments (49.5%, 44.3%) or tested for other reasons (50%, 45.8%), in persons without any comorbidities (74.4%, 71%) compared to those with comorbidities (38.2%, 34.4%), in individuals with COVID-19 symptoms (75.2%, 74.3%) compared to those without (31.9%, 23.3%), and in the absence of SARS-CoV-2 variants (87.7%, 84%) compared to Alpha variant carriers (77.1%, 72.3%). If 10,000 symptomatic individuals are tested of which 500 are truly positive, the RDTs would generate 38 false-positive and 124 false-negative results. If 10,000 asymptomatic individuals are tested, including 50 true positives, 18 false-positives and 34 false-negatives would be generated. Interpretation The sensitivities of the two RDTs for asymptomatic SARS-CoV-2 carriers are unsatisfactory. Their widespread use may not be effective in the ongoing SARS-CoV-2 pandemic. The virus genotype influences the sensitivity of the two RDTs. RDTs should be evaluated for different SARS-CoV-2 variants

Medicine in spine exercise (MiSpEx) for nonspecific low back pain patients: study protocol for a multicentre, single-blind randomized controlled trial

Background: Arising from the relevance of sensorimotor training in the therapy of nonspecific low back pain patients and from the value of individualized therapy, the present trial aims to test the feasibility and efficacy of individualized sensorimotor training interventions in patients suffering from nonspecific low back pain. Methods and study design: A multicentre, single-blind two-armed randomized controlled trial to evaluate the effects of a 12-week (3 weeks supervised centre-based and 9 weeks home-based) individualized sensorimotor exercise program is performed. The control group stays inactive during this period. Outcomes are pain, and pain-associated function as well as motor function in adults with nonspecific low back pain. Each participant is scheduled to five measurement dates: baseline (M1), following centre-based training (M2), following home-based training (M3) and at two follow-up time points 6 months (M4) and 12 months (M5) after M1. All investigations and the assessment of the primary and secondary outcomes are performed in a standardized order: questionnaires – clinical examination – biomechanics (motor function). Subsequent statistical procedures are executed after the examination of underlying assumptions for parametric or rather non-parametric testing. Discussion: The results and practical relevance of the study will be of clinical and practical relevance not only for researchers and policy makers but also for the general population suffering from nonspecific low back pain. Trial registration: Identification number DRKS00010129. German Clinical Trial registered on 3 March 2016

The Changing Landscape for Stroke\ua0Prevention in AF: Findings From the GLORIA-AF Registry Phase 2

Background GLORIA-AF (Global Registry on Long-Term Oral Antithrombotic Treatment in Patients with Atrial Fibrillation) is a prospective, global registry program describing antithrombotic treatment patterns in patients with newly diagnosed nonvalvular atrial fibrillation at risk of stroke. Phase 2 began when dabigatran, the first non\u2013vitamin K antagonist oral anticoagulant (NOAC), became available. Objectives This study sought to describe phase 2 baseline data and compare these with the pre-NOAC era collected during phase&nbsp;1. Methods During phase 2, 15,641 consenting patients were enrolled (November 2011 to December 2014); 15,092 were eligible. This pre-specified cross-sectional analysis describes eligible patients\u2019 baseline characteristics. Atrial fibrillation&nbsp;disease characteristics, medical outcomes, and concomitant diseases and medications were collected. Data were analyzed using descriptive statistics. Results Of the total patients, 45.5% were female; median age was 71 (interquartile range: 64, 78) years. Patients were from Europe (47.1%), North America (22.5%), Asia (20.3%), Latin America (6.0%), and the Middle East/Africa (4.0%). Most had high stroke risk (CHA2DS2-VASc [Congestive heart failure, Hypertension, Age&nbsp; 6575 years, Diabetes mellitus, previous Stroke, Vascular disease, Age 65 to 74 years, Sex category] score&nbsp; 652; 86.1%); 13.9% had moderate risk (CHA2DS2-VASc&nbsp;= 1). Overall, 79.9% received oral anticoagulants, of whom 47.6% received NOAC and 32.3% vitamin K antagonists (VKA); 12.1% received antiplatelet agents; 7.8% received no antithrombotic treatment. For comparison, the proportion of phase 1 patients (of N&nbsp;= 1,063 all eligible) prescribed VKA was 32.8%, acetylsalicylic acid 41.7%, and no therapy 20.2%. In Europe in phase 2, treatment with NOAC was more common than VKA (52.3% and 37.8%, respectively); 6.0% of patients received antiplatelet treatment; and 3.8% received no antithrombotic treatment. In North America, 52.1%, 26.2%, and 14.0% of patients received NOAC, VKA, and antiplatelet drugs, respectively; 7.5% received no antithrombotic treatment. NOAC use was less common in Asia (27.7%), where 27.5% of patients received VKA, 25.0% antiplatelet drugs, and 19.8% no antithrombotic treatment. Conclusions The baseline data from GLORIA-AF phase 2 demonstrate that in newly diagnosed nonvalvular atrial fibrillation patients, NOAC have been highly adopted into practice, becoming more frequently prescribed than VKA in&nbsp;Europe and North America. Worldwide, however, a large proportion of patients remain undertreated, particularly in&nbsp;Asia&nbsp;and North America. (Global Registry on Long-Term Oral Antithrombotic Treatment in Patients With Atrial Fibrillation [GLORIA-AF]; NCT01468701

Ionospheric Threat Model Assessment

This paper presents the first results of a German study (ITMA) that attempts to validate the GBAS CAT I ionosphere threat space that was developed for US CONUS. In phase 1 of this study the German Aerospace Center DLR and the German Air Navigation Service Provider DFS tried to determine the normal residual ionospheric uncertainty (σvig) and to identify periods with severe ionospheric activities relevant for GBAS. Dual-frequency RINEX data of up to 80 geodetic stations in and around Germany over an 11 year solar cycle from 1998 (25 stations) to 2008 (80 stations) was processed. Based on this data evaluation the study determined 16 periods with disturbed ionosphere in the years 2000 to 2003 and one day in 2005. These periods will be analyzed in more detail in phase 2 of the study to populate the GBAS CAT I ionosphere threat space. To determine the necessary parameters slope, velocity and width of the identified ionospheric fronts it is necessary to use additional GNSS data from German geodetic networks. This additional data should improve the resolution in the areas where the ionospheric front was detected. Phase 2 of the study should be completed in autumn 2009. The database may then be used to validate the assumptions regarding ionospheric effects for GAST-D

Ionosphere Threat Space Model Assessment for GBAS

Ground Based Augmentation Systems (GBAS) can correct the majority of the GNSS pseudo range errors experienced by an aircraft in the vicinity of an airport. Not corrected (spatially uncorrelated) errors between ground and airborne subsystems must be overbounded and kept as small as possible in order to reach the required level of integrity defined by ICAO. Ionosphere gradients remain in general very small (can be bounded by 4mm/km in the CONUS region). This "normal" behavior of the ionosphere has a very limited impact on the position error. The confidence interval of the user position is fully acceptable for precision approach. Unfortunately, the ionosphere medium is sometimes subject to perturbations due to the strong temporal and spatial variability of the ionospheric plasma. When GNSS signals received by the aircraft are delayed in a different way than the GNSS signals received by the GBAS ground facility (GGF), the corrections provided by the GGF can cause unacceptably large position errors at aircraft level. While most of the time this environmental effect is behaving in a normal way, there has been found an anomalous ionospheric behavior which occurs rarely (few occurences in 10 years) but can be a serious threat to GBAS integrity. The CAT I GBAS architecture can principally not fully mitigate these effects by monitoring. According to the agreed approach in the GBAS CAT I community, the remaining risk is therefore treated as follows: At each epoch the worst-case ionospheric threat is assumed to occur in 100% of the time. The threat is mitigated, e.g., by preventing the aircraft from using unsafe combinations of GNSS satellites. To permit the analysis, it is essential to first define the ionosphere threat space. Since the anomalous ionosphere threat consists of moving ionospheric fronts, the ionosphere threat space is spanned by the slope, velocity and width of such an ionospheric front. The anomalous ionosphere threat model is defined by specifying a domain inside the three-dimensional threat space. For the CONUS (conterminous US) region this domain in threat space has been determined by using empirical data collected during the last solar cycle. In order to use the proposed mitigation algorithms for the ionosphere threat in a different geographical region, the anomalous ionosphere threat model has to be established for that region as well. For the certification of a GBAS ground facility in Germany, both the anomalous ionosphere threat space and the nominal ionospheric de-correlation for a region including Germany were determined. This work has been done within the ITMA (ionosphere threat model assessment) project which is a joint project between the German Air Navigation Service Provider DFS and the German Aerospace Center DLR, funded by DFS. In the first phase of the project, an automated data-screening has been performed using all publicly available dual-frequency RINEX data of the entire last solar cycle in the region considered in this study. This first phase aims to identify the days of most extreme ionospheric events. When dual-frequency data is available, there are a number of ways of extracting the ionospheric delays. While for the data-screening the difference between the phase measurements on GPS L1 and L2 were used, we also consider code minus carrier (CMC) and code-difference observable in order to validate extreme events. In the data-screening we computed the number of (formal) spatial gradients above certain limits derived from time-differences of phase-difference-derived ionospheric delays. We call these gradients formal, since they are not corrected for the movement of the ionospheric front and independent temporal changes. Nevertheless periods of extreme ionospheric activity can be identified using these formal gradients as an indicator. By analyzing all available data from a complete 11 years solar activity cycle period (1998-2008) using an automatic screening process, we have determined 16 time periods of relevant ionospheric activity. All these events have been examined manually in order to exclude false alarms caused, e.g., by cycle slips or corrupted data. In the second phase of the project, algorithms have been developed for estimating the parameters in the anomalous ionosphere threat model, i.e. the slope, speed and width of a ionospheric front. In order to estimate the key threat model parameters, the slope of the ionospheric front, the velocity and direction of the ionospheric front have to be determined. For determining the front velocity, we used both a least-squares-based estimation technique and a more direct way of computing the velocity and slope directly from (calibrated) ionospheric delays. For each period of anomalous ionospheric activity we have manually identified the time and location of extreme events. Additional data from the German geodetic reference network (SAPOS) for the determined locations has been used to increase the spatial resolution. Then, for each event threat model parameters have been estimated. Again, CMC and code-difference observables were used in addition to phase-difference-derived ionosphere delays for validation purposes. As a result, a threat space valid for the mid Europe especially Germany was derived. In addition to the extreme ionosphere behavior, which is captured by the anomalous ionosphere threat model, we have also determined the nominal ionospheric gradients in the considered region using calibrated vertical ionospheric delays from periods of quiet to moderate ionospheric activity. The paper will give a detailed insight in the derived methods for ionospheric threat space determination and the achieved results for the geographical region "Germany". The results act as an essential input for further parameterization and certification of GBAS systems in Europe

Digital true time delay for pulse correlation radars

A novel concept for digital true time delay pulse correlation radars using digital programmable delay lines and monolithically integrated radar front-ends is investigated. The effects of quantization errors on side lobe level and deviation of beam direction due to the digital true time delay lines are evaluated by numerical simulations based on the performance of commercially available time delay units. To verify the simulation results, a compact 26 GHz active electronically steered linear antenna array consisting of 8 elements has been realized, which provides beamforming in both transmit and receive path. Measurement results and design details of this steerable radar sensor are presented in the experimental part of this paper

A novel direct-imaging radar sensor with frequency scanned antenna

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Self-aligning and flexible dielectric waveguide plug for MMICs at G-Band

The packaging technology for transitions to dielectric waveguides in the frequency range above 100 GHz is complex and must be highly precise, and the waveguides are usually permanently connected. This letter presents a transition from a monolithic microwave integrated circuit (MMIC) to a flexible dielectric waveguide at G-Band (140–220 GHz), which is self-aligning and, thus, reduces the requirements for packaging accuracy. Furthermore, the transition is mechanically decoupled to avoid mechanical stress to the MMIC and to reconnect it arbitrarily often. A patch radiator on a quartz-glass carrier is excited by a coupler on the MMIC. It feeds the HE11 mode into a rigid, high-permittivity dielectric dome, which increases the coupling efficiency. The flexible dielectric waveguide is placed above the dome and fixed with Rohacell half shells. The minimum insertion loss measured with a back-end-of-line (BEOL) MMIC is 3.0 dB at 168 GHz