Switchable Instantaneous Frequency Measurement by Optical Power Monitoring Based on DP-QPSK Modulator

We propose and analyze an instantaneous frequency measurement system using optical power monitoring technique with improved resolution. The primary component employed in the proposal is a DP-QPSK modulator which is used to modulate the microwave signal with a designed time delay and phase shifting. Then the generated optical signal is sent to polarization beam splitter (PBS) via polarization controller (PC). Thanks to the complementary transmission nature of polarization interference introduced by PBS, the frequency information is converted to the optical power and the relationship between the amplitude comparison function (ACF) and microwave frequency to be measured is established. Thus, the frequency of the microwave signal could be easily measured through monitoring the optical powers of the two output ports of the PBS. Furthermore, by adjusting the DC biases of the DP-QPSK modulator instead of changing the electrical delay, the measurement range and resolution can be switched. In this paper, the basic principle of the instantaneous frequency measurement system is derived in detail, and simulation has been performed to investigate the resolution, the measurement range and the impact of imperfection devices. The proposed scheme is wavelength independent and measurement range switchable, which can avoid the laser wavelength drifting problem and greatly increase the system flexibility.

High-accuracy Photonics-assisted Frequency Measurement With Rough-accurate Compensation Based on Mach-Zehnder Interfering and Power Cancellation

A high-accuracy photonics-assisted frequency measurement with rough-accurate compensation based on Mach-Zehnder interfering and power cancellation is proposed. A polarization division multiplexing dual-parallel Mach–Zehnder modulator (PDM-DPMZM) is employed to mix the unknown RF signal and sweep signal to optical field. The rough measurement is firstly performed by the interference of a Mach-Zehnder interferometer (MZI) to realize fast frequency estimation. Then, based on the rough measurement result, the accurate measurement based on power cancellation is implemented in a much narrower range, which greatly improves the efficiency of frequency measurement. The simulation results show that the amplitude comparison function (ACF) established by interference can achieve a measurement error of less than 0.3 GHz over 0.5 ~39 GHz. Moreover, thanks to the rough-accurate compensation, the accuracy can be further improved to 4 MHz. Additionally, the multiple frequency identification with a resolution of 10 MHz can also be achieved based on this system.

Identification of Damage on Stringers By the PSO Method

The paper employs the particle swarm optimization (PSO) method for the identification of damage to a stringer web. This method is inspired by a swarm of bees or flock of birds which look for a common solution. It is a heuristic method, that utilizes a particle as a problem-solving candidate. The location of this particle in the search space represents the configuration of all the variables to possible solutions of the problem. As the particle moves into the solution space, the values of the variables change. The particle is defined by a position vector and a velocity vector. The resulting direction of the particle is determined by three components i.e. (1) the moment or inertia, (2) autobiographical or cognitive information and (3) social interaction. The quality of the particle is evaluated by a comparison function. In this study we tried to locate damage by using this method. The damage is represented by a rusted area on a stringer web, which was simulated as a change in the Young’s modulus. We used the modal calculation of the eigenfrequencies as an evaluation function.

Mapping and assessment of future land use change impacts on habitat quality in Lithuania

<p><strong>Abstract</strong></p><p>Human activity is directly responsible for land use and land cover changes, affecting different ecosystem services. Thus, from the perspective of land use management is critical to project potential future land-use changes. This study aimed: (i) to detect possible changes in land-use structure in response to different four scenarios, namely: business as usual, urbanization, afforestation and land abandonment, and agricultural intensification scenario; and (ii) to measure the landscape habitat quality (an ecosystem services proxy) according to those projected futures. We selected as case study Lithuania due to the potential future increased human pressures on the landscape, and due to the high landscape value of this territory. The projected year was 2050, and we used the Cellular Automata method (applying the Dinamica EGO software) to project future land-use changes, and the InVEST model to assess the habitat quality. The land-use scenarios outcomes were validated using a fuzzy comparison function, and 80% of accuracy was achieved (comparing a simulated land use map of 2018, and the observed map for the same year). The results showed that the agricultural intensification scenario represents the greatest predicted landscape deterioration (from 0.71 in 2018 to 0.64). In the urbanization scenario, the highest landscape degradation prediction is identified around the most important cities (Vilnius, Kaunas, and Klaipėda). In the opposite direction, the afforestation and land abandonment scenario show the highest improvement on the habitat quality, from 0.71 in 2018 to 0.74. </p><p><strong>Acknowledgements</strong></p><p>“Lithuanian National Ecosystem Services Assessment and Mapping (LINESAM)” No. 09.3.3-LMT-K-712-01-0104 is funded by the European Social Fund according to the activity “Improvement of researchers’ qualification by implementing world-class R&D projects” of Measure No. 09.3.3-LMT-K-712.</p>

Photonic-assisted microwave frequency measurement towards cognitive radio

Cognitive radio frequency (RF) systems can be seen through an OODA (observe, orient, decide and act) loop, and electronic warfare (EW) can be used in some of these stages, namely the observe and the act. Instantaneous microwave frequency measurement (IFM) systems can contribute to cognitive RF technology taking the real world to the data world. In an OODA loop, IFM can be arranged as in the observe stage. Here we have proposed an IFM device that allows the adjustment of the directional couplers coupling coefficients, optical fiber lengths, modulation index and modulation formats, which makes the system tunable. The analytical model result shows good agreement with the simulation, achieving frequency differences of 130 MHz and 210 MHz for the lowest and the highest amplitude comparison function values, respectively.

Frequency Comparison Function Method for Real-Time Identification of Breathing Crack at Welding Joint

In this research, the frequency comparison function (FCF) method is proposed and studied to realize high-sensitive real-time crack identification at the welding joint area for a beam-type structure. This method is derived from the frequency response function (FRF). During FCF, we use the response signal collected from the designated point of the structure instead of the excitation. The standard deviation of the FCF amplitude curve is calculated to detect and evaluate the possible crack and its induced vibration perturbations afterward. Vibration responses are simulated in ANSYS by the use of the finite element analysis of a welded beam structure, and these signals are then analyzed with the FCF algorithm. It is concluded that FCF is an efficient method for breathing crack identification and can be easily applied under different excitation conditions, including harmonic and random ones. Meanwhile, FCF can be applied without any pre-processing algorithms such as filtering and smoothing. So, it can be used for real-time crack identification. By combining the FCF with the smart coating sensor composed of piezoelectric layers, the crack identification with high sensitivity is realized. The crack is detectable at its very early stage (starting from 3% of the beam thickness). Experimental studies under harmonic and random excitations are processed, and the results prove high sensitivity and feasibility of the proposed crack detection method.

Robust Mahalanobis-distance based spatial outlier detection on discrete GNSS velocity fields

<p>The GNSS velocity field filtering topic can be identified as a multi-dimensional unsupervised spatial outlier detection problem. In the discussed case, we jointly interpreted the horizontal and vertical velocity fields and its uncertainties as a six dimensional space. To detect and classify the spatial outliers, we performed an orthogonal linear transformation technique called Principal Component Analysis (PCA) to dynamically project the data to a lower dimensional subspace, while redacting the most (~99%) of the explained variance of the input data.</p><p>Therefore, the resulting component space can be seen as an attribute function, which describes the investigated deformation patterns. Then we constructed two subspace mapping functions, respectively the k-nearest neighbor (k-NN) and median based neighbor function with Haversine metric, and the samplewise comparison function which compares the samples with the properties of its k-NN environment. Consequently, the resulting comparison function scores highlights the significantly different observations as outliers. Assuming that the data comes from Multivariate Gaussian Distribution (MVD), we evaluated the corresponding Mahalanobis-distance with the estimation of the robust covariance matrix of the investigated area. Then, as the main result of the Robust Mahalanobis-distance (RMD) based approach, we implemented the binary classification via the p-value and critical Mahalanobis-distance thresholding.</p><p>Compared to the formerly investigated and applied One-Class Support Vector machine (OCSVM) approach, the RMD based solution gives <em>~ 17%</em> more accurate results of the European scaled velocity field filtering (like EPN D1933), as well as it corrects the ambiguities and non-desired features (like overfitting) of the former OCSVM approach.</p><p>The results will be also presented as an interactive web page of the velocity fields of the latest version of EPN D2050 filtered with the introduced RMD approach.</p>

On a method of nonlinear optimization for the comparison of spatial structure of molecules

To compare the geometry of two or more geometric structures consisting of N ordered points, and which can be considered as solids in three-dimensional space, we developed a method based on the minimization of a certain comparison function. This function is the sum of squared distances between pairs of elements of the two structures under comparison with the same indices. Distances change when changing the mutual orientation of the structures with all possible shifts and rotations of the structures as rigid bodies. The comparison function is minimized with respect to Euler angles, provided that centers of mass of two compared structures are superposed. The minimization of the comparison function with respect to Euler angles is carried out numerically by the Rosenbrock method. The developed method for comparison of geometric structures is used to solve problems in structural chemistry, that is to compare molecules with the same structural formula in one crystal.