Constant Offset Research Articles

Multiplexing modulation design optimization and quality evaluation of BDS-3 PPP service signal

The Precise Point Positioning (PPP) service of BeiDou-3 Navigation Satellite System (BDS-3) is implemented on its Geostationary Earth Orbit (GEO) satellites. However, its signal design is limited by the actual power of satellite and other conditions. Furthermore, the design needs to fully consider the compatibility of different service phases. Starting from the actual state of the BDS-3 GEO satellite, this paper studies the multiplexing modulation of the BDS PPP service signal that is based on the Asymmetric Constant Envelope Binary Offset Carrier (ACE-BOC) technique and proposes several feasible schemes for this signal. Comparison and optimization of these techniques are made from the aspects of transmission efficiency, multiplexing efficiency, and service forward compatibility. Based on the Type-III ACE-BOC multiplexing modulation technique, phase rotation and intermodulation reconstruction techniques are proposed to suppress the intermodulation interference issue. Finally, a signal based on improved ACE-BOC multiplexing is designed. The quality of the proposed signal was continuously monitored and tested using large-diameter antennas. The evaluation results show that the power spectrum deviation of the signal is 0.228 dB, the correlation loss is 0.110 dB, the S-curve slope deviation is 1.558% on average, the average length difference between the positive/negative chip and the ideal chip is only 0.0006 ns, and the coherence between the carrier and the pseudo code is 0.082°. All quality indicators are satisfactory, indicating that the proposed signal multiplexing modulation technique is an ideal solution that meets all the requirements of the design constraints, and can achieve efficient information broadcasting and forward compatibility of the BDS PPP service.

Correlations between home sleep apnea tests and polysomnography outcomes do not fully reflect the diagnostic accuracy of these tests.

The clinical performance of home sleep apnea tests (HSATs) can be described by their (diagnostic) accuracy, defined as the percentage agreement with the obstructive sleep apnea severity category (normal, mild, moderate, and severe) based on polysomnography. Rather than reporting on accuracy, there has been a strong reliance in the literature to report correlation coefficients between the apnea-hypopnea index of HSATs and polysomnography to support claims of diagnostic performance. This is surprising, as it has been well described that correlation coefficients are inadequate to evaluate equivalence between 2 parameters. The aim of this study was to systematically investigate the magnitude of the discrepancies between correlation coefficients and diagnostic accuracy reported in or retrievable from HSAT validation studies. We compared the discrepancy between accuracy and apnea-hypopnea index correlation coefficients of all validation papers that met the inclusion criteria. A total of 20 papers were retained, representing a participant pool of 1,652. The weighted average apnea-hypopnea index correlation across all 20 papers was 0.82 and the weighted average accuracy was 0.61, highlighting a discrepancy of 0.21 and an overall misdiagnosis rate of 39%. The results of our study confirm the need for increased scientific rigor in selecting primary performance endpoints to support clinical performance claims of HSATs. Massie F, Van Pee B, Bergmann J. Correlations between home sleep apnea tests and polysomnography outcomes do not fully reflect the diagnostic accuracy of these tests. J Clin Sleep Med. 2022;18(3):871-876.

Fourier transform near infrared spectroscopy as a tool for predicting antioxidant activity of propolis

The propolis chemical composition is complex, varied, and closely related to characteristics of the vegetation and location where the hives are located. The objective of this work was to determine the antioxidant activity through FRAP methodology in propolis (raw, macerated, ethanolic extract and concentrated ethanolic extract) using a rapid and non-destructive method namely Fourier transform near-infrared (FTNIR) spectroscopy. By the results obtained for the antioxidant activity it can be verified that the samples of propolis present a very diversified chemical profile, for the FRAP methodology the samples of propolis collected in Três Barras – SC and Campo Magro – PR showed the highest activities: 1.8 × 103 and 1.6 × 103 μmol of Fe2+ g−1 respectively. It was possible to conclude that the macerated propolis presented the best multivariate calibration model established with the Savitzky-Golay (SG) + Constant Offset Elimination (COE) preprocessed spectra, where the R2 and 0.95 and 113 for FRAP determination. The error values RMSEC, RMSECV and RMSEE were 73, 1.3 × 102 and 81 μmol Fe2+ g−1, respectively. The FRAP model for macerated propolis was validated and can be used for quantification of antioxidant activity of new extracts of propolis, being useful as an alternative to rapid analysis, reducing waste generation and cost.

Microstructural evolution and mechanical properties of dissimilar friction stir lap welding aluminum alloy 6061-T6 to ultra low carbon steel.

Joining of steel- aluminum thin sheets has been extensively studied at the beginning of 2000 years for automotive applications, in a regard to reduce vehicle weight, reducing the emissions while improving the energy security of the country.In this context the purpose of this work is to realize and study the dissimilar lap joint between a 6061-T6 aluminum alloy and ultra low carbon steel. A recent welding technique, known as "friction stir welding" was used. Joints have been obtained using coated WC–Co tools in terms of durability, the effects of process parameters including welding speeds (50 to 400 mm/min) at a constant rotation rate (1200 tr /min) and Offset in steel plate (0.2 mm) on the microstructures and mechanical properties of the joints were investigated. The joints were evaluated by mechanical testing and metallurgical analysis. Tensile shear tests, optical microscopy, and scanning electron microscopy with energy dispersive spectroscopy (EDS) were the main techniques used. The results showed that with increasing the welding speed, the tensile strength of the joints, increased up to a maximum value. The 3.6 KN maximum value of the tensile strength achieved a traverse speed of 200 mm/min. Microstructure characterization suggested that higher joint strengths were associated with thinner, ≈ 1 µm thick intermetallic reaction layers at joint interfaces.

A Unified Dual-frequency Constant Envelope Multiplexing Design Framework for Modernised GNSS Signals

In the field of modernised Global Navigation Satellite System (GNSS) signal design, several Dual-frequency Constant Envelope Multiplexing (DCEM) methods have been recently proposed. However, the existing DCEM methods, such as Alternative Binary Offset Carrier (AltBOC), generalised AltBOC and Asymmetric Constant Envelope Binary Offset Carrier (ACE-BOC), are only applied in some special cases. In this paper, we present a unified DCEM design framework for GNSS signals. The existing DCEM methods can be unified in this framework. First, the signal components at two carrier frequencies are combined into two single-frequency constant envelope signals. Then, the linear sum of dual-frequency signals with non-constant envelopes is obtained. Finally, the linear sum is converted into the corresponding DCEM signal by solving an optimisation problem. The proposed design framework has no strict constraints on the number, power ratio and phase relationship of the signal components. Moreover, some special design cases under this framework are also analysed in detail. The analytical results show that the proposed design method can reach higher multiplexing efficiency compared with the existing methods. Based on the proposed method, we suggest a scheme to multiplex the BeiDou regional signals and global signals at the B2 frequency. The simulation results of correlation functions and Power Spectrum Density (PSD) verify the correctness and effectiveness of the proposed design method.

Ground-penetrating radar insight into a coastal aquifer: the freshwater lens of Borkum Island

Abstract. Freshwater lenses, as important resource for drinking water, are sensitive to climate changes and sea level rise. To simulate this impact on the groundwater systems, hydraulic subsurface models have to be designed. Geophysical techniques can provide information for generating realistic models. The aim of our work is to show how ground-penetrating radar (GPR) investigations can contribute to such hydrological simulations. In the pilot area, Borkum island, GPR was used to map the shape of the groundwater table (GWT) and to characterise the aquifer. In total, 20 km of constant offset (CO) profiles were measured with centre frequencies of 80 and 200 MHz. Wave velocities were determined by common midpoint (CMP) measurements and vertical radar profiling (VRP) in a monitoring well. The 80 MHz CO data show a clear reflection at the groundwater table, whereas the reflection is weaker for the 200 MHz data. After correcting the GPR water tables for the capillary rise, they are in good accordance with the pressure heads of the observation wells in the area. In the centre of the island, the groundwater table is found up to 3.5 m above sea level, however it is lower towards the coastline and marshland. Some local depressions are observed in the region of dune valleys and around pumping stations of the local water supplier. GPR also reveals details within the sediments and highly-permeable aeolian sands can be distinguished from less-permeable marine sediments. Further, a silt loam layer below the water table could be mapped on a large area. The reflection characteristics indicates scattered erosion channels in this layer that cause it to be an aquitard with some leakage. GPR provides a high resolution map of the groundwater table and insight into the stratigraphy of the sediments and their hydraulic properties. This is valuable complementary information to the observation of sparsely distributed monitoring wells as input to hydraulic simulation.

Internal structure and composition of a rock glacier in the Andes (upper Choapa valley, Chile) using borehole information and ground-penetrating radar

AbstractThis study uses boreholes, ground temperature monitoring and ground-penetrating radar (GPR) in order to understand the internal structure and composition of a rock glacier in the upper Choapa valley, northern Chile. The rock glacier is a small valley-side feature, 200 m long and ranging between 3710 and 3780 ma.s.l. Two boreholes were drilled down to depths of 20 and 25 m, respectively, using the diamond drillhole technique. An ice-rock mixture was encountered in the boreholes, with heterogeneous ice content averaging 15-30%. Data from common-midpoint (CMP) and constant-offset (CO) GPR surveys acquired, respectively, near the boreholes and across the whole rock glacier were processed to highlight the internal stratigraphy and variations in the radar-wave velocity. The GPR profiles depict a rock glacier constituted of stacked and generally concordant layers, with a thickness ranging from 10 m in its upper part to ∼30m towards its terminus. The CMP analysis highlights radar-wave velocities of 0.13-0.16 m ns–1 in the first 20 m of the structure. Larger vertical and lateral velocity variations are highlighted from CO data, reflecting the heterogeneous composition of the rock glacier and the likely presence of unfrozen water in the structure. Given the average air temperature registered at the site (+0.5°C), the near-melting-point temperature registered in the boreholes over more than a year and the presence of locally high water content inferred from GPR data, it is thought that the permafrost in the rock glacier is currently degrading.

Molecular adsorption of small alkanes on a PdO(101) thin film: Evidence of σ-complex formation

We investigated the molecular adsorption of methane, ethane, and propane on a PdO(101) thin film using temperature programmed desorption (TPD) and density functional theory (DFT) calculations. The TPD data reveal that each of the alkanes adsorbs into a low-coverage molecular state on PdO(101) in which the binding is stronger than that for alkanes physically adsorbed on Pd(111). Analysis of the TPD data using limiting values of the desorption prefactors predicts that the alkane binding energies on PdO(101) increase linearly with increasing chain length, but that the resulting line extrapolates to a nonzero value between about 22 and 26 kJ/mol at zero chain length. This constant offset implies that a roughly molecule-independent interaction contributes to the alkane binding energies for the molecules studied. DFT calculations predict that the small alkanes bind on PdO(101) by forming dative bonds with coordinatively unsaturated Pd atoms. The resulting adsorbed species are analogous to alkane sigma-complexes in that the bonding involves electron donation from C-H sigma bonds to the Pd center as well as backdonation from the metal, which weakens the C-H bonds. The binding energies predicted by DFT lie in a range from 16 to 24 kJ/mol, in good agreement with the constant offsets estimated from the TPD data. We conclude that both the dispersion interaction and the formation of sigma-complexes contribute to the binding of small alkanes on PdO(101), and estimate that sigma-complex formation accounts for between 30% and 50% of the total binding energy for the molecules studied. The predicted weakening of C-H bonds resulting from sigma-complex formation may help to explain the high activity of PdO surfaces toward alkane activation.

Ground penetrating radar imaging and time-domain modelling of the infiltration of diesel fuel in a sandbox experiment

Ground penetrating radar (GPR) is a non-destructive method which, over the past 10 years, has been successfully used not only to estimate the water content of soil, but also to detect and monitor the infiltration of pollutants on sites contaminated by light non-aqueous phase liquids (LNAPL). We represented a model water table aquifer (72 cm depth) by injecting water into a sandbox that also contains several buried objects. The GPR measurements were carried out with shielded antennae of 900 and 1200 MHz, respectively, for common mid point (CMP) and constant offset (CO) profiles. We extended the work reported by Loeffler and Bano by injecting 100 L of diesel fuel (LNAPL) from the top of the sandbox. We used the same acquisition procedure and the same profile configuration as before fuel injection. The GPR data acquired on the polluted sand did not show any clear reflections from the plume pollution; nevertheless, travel times are very strongly affected by the presence of the fuel and the main changes are on the velocity anomalies. We can notice that the reflection from the bottom of the sandbox, which is recorded at a constant time when no fuel is present, is deformed by the pollution. The area close to the fuel injection point is characterized by a higher velocity than the area situated further away. The area farther away from the injection point shows a low velocity anomaly which indicates an increase in travel time. It seems that pore water has been replaced by fuel as a result of a lateral flow. We also use finite-difference time-domain (FDTD) numerical GPR modelling in combination with dielectric property mixing models to estimate the volume and the physical characteristics of the contaminated sand.

Galileo civil signal modulations

Spectrum limitations for navigation systems require that the various navigation signals broadcast by the Galileo system must be combined and must utilize bandwidth-efficient modulations. At the L1 band, one of the most important questions is how to combine all the Open Service signals and the Public Regulated Service signal at the payload level, while maintaining good performance at reception. The Interplex modulation, a particular phase-shifted-keyed/phase modulation (PSK/PM), was chosen to transmit these signals because it is a constant-envelope modulation, thereby allowing the use of saturated power amplifiers with limited signal distortion. The Interplex modulation was also taken as baseline at the E6 band to transmit the three channels and the services associated on the same carrier frequency. At the E5 band, the modulation must combine two different services on a same constant envelope composite signal, while keeping the simplicity of a BOC implementation. The constant envelope Alternate Binary Offset Carrier (ALTBOC) modulation was chosen as the solution to transmit the Galileo E5 band signal. The main objective of this paper is to study these Galileo modulations. After the introduction, the E5 band signals are described, followed by the Alternate BOC modulation which has been chosen to transmit them. The second part describes the general formulation of the Interplex modulation and its key parameters for an optimal multiplexing of the Galileo L1 band signals. Since the Galileo Open Service signals at the L1 band are still not yet completely specified, different test cases are considered and their impact on the resulting choice for the Interplex modulation parameters is exposed.

Computing constant offsets of a NURBS B-Rep

An approach for the automatic offset of a NURBS B-Rep has been presented which can be used for a class of manifold B-Reps. The approach offsets each of the trimmed surfaces (faces) of the B-Rep and then removes the gaps and intersections between offset faces automatically, if any. The offset B-Rep is then created by sewing all the updated offset faces. The practical approach and the treatment of the subject presented are unique and have not been reported earlier. The approach works under the assumption that the number of faces in both base and offset B-Reps is the same. It further assumes that the faces are at least G 1 continuous and non-self intersecting after constant offset. The present approach has given accurate and robust offsets of many lay-up surfaces (B-Reps) in the composite laminate modeling. The approach has better error control. Some of the offsets of lay-up surfaces that are generated using this approach have been presented.

Background correction in scanning probe microscope recordings of macromolecules

In scanning probe microscopy of macromolecules, the specimen to be scanned is deposited on a flat surface such as mica or glass. Unfortunately, there is no guarantee that the orientation of this surface is normal to the scanning directions, or that it is atomically flat. Phenomena such as capillary forces and noise can cause the surface to appear curved in the recording. Compensation for these background components are necessary before meaningful, quantitative measurements can be performed on the images. We describe a procedure to correct for both the shape of the recorded surface and the influence of noise on the background. The surface is modeled with a low-order polynomial, and the noise by a constant line off-set for each scan line. These parameters are initially estimated using all recorded samples, and the result is subtracted from the recording. Then, in an iterative loop, the background is refined by first segmenting the image in back- and foreground pixels, followed by re-estimating the parameters using only the background pixels. For recordings of macromolecules, this procedure performs up to 70% better than the flattening procedure included in the microscope software, in terms of standard deviation of the background pixels as depicted by the final segmentation.

ＰＷＲのキセノン振動制御 美浜３号機での実施報告例

Recently, constant axial offset control method for power distribution control is applied to PWRs (of Westinghouse type). In this mode of operation, Xe induced spatial oscillations which could cause the problem from the power distribution point of view hardly break out. Under special conditions such as tests, however, Xe oscillations can break out. It is required that power distribution can be controlled without any special operational actions.Several control methods for Xe oscillations have been reported through many theoretical studies and operational experiences. Among them is First Overtone Control Method. This requires quite a simple control action but can effectively control Xe oscillations.The authors have shown the effectiveness of First Overtone Control Method in Mihama Unit No.3 Reactor. In this report the detailed procedures are described. The outline of Constant Axial Offset Control Method is described in Appendix.