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In 2021, the State primary standard of the power spectral density unit of noise radio emission in the frequency range of 0.002 to 178.3 GHz GET 21-2021 was approved. Low-temperature noise generators were included in GET 21-2021 as primary standard measures. The designed and manufactured primary standard measures were studied, namely two coaxial low-temperature noise generators in the frequency ranges of 0.002–4.0 GHz and 4.0–12.05 GHz and three waveguide low-temperature noise generators in the frequency ranges of 12.05–17.44 GHz, 17.44–25.86 GHz, and 25.86–37.5 GHz. Equivalent noise temperatures of primary standard measures were investigated and calculated. The reproducible value of the equivalent noise temperature for coaxial low-temperature noise generators was 77.5–84.82 K, and 78.4–80.53 K for waveguide low-temperature noise generators. Comparators, namely noise signal receivers covering five frequency ranges (two coaxial paths: 0.002–4.0 GHz and 4.0–12.05 GHz; three waveguide lines: 12.5–17.44 GHz; 17.44–25.86 GHz, and 25.86–37.5 GHz) were developed and manufactured. The dynamic range of measurements was increased, and the error in transmitting a unit of the power spectral density of noise radio emission was reduced. The total error in reproducing the power spectral density unit of noise radio emission was 0.24–0.30 K, the expanded uncertainty of transferring the power spectral density unit of noise radio emission to secondary standards and working standards of the first echelon was 0.4–0.8 K, and the measurement error of the power spectral density of noise radio emission decreased by a factor of 1.5. The uncertainties in the transfer of a unit of the power spectral density of noise radio emission from primary standard measures to secondary standards and working standards of the first echelon were comparatively analyzed. The results of this work are applicable in the radio industry for noise parameter measurements. The sensitivity values of instruments and devices whose operation depends on the level of noise electromagnetic oscillations, such as measuring noise generators, are controlled by measures of the power spectral density of noise radio emission. [ABSTRACT FROM AUTHOR]

Brightness temperature and bearing estimation algorithms for a point source of noise radio-thermal radiation in a two-antenna radio meter are synthesized and a structure diagram that implements these algorithms is presented. We show that when estimating brightness temperature the optimum output effect is proportional to a power estimate for a sum of de-correlated observations with compensation of receiver's internal noise temperature. Optimum output effect during bearing determination of a radiation source contains operations of generating mutual coherence functions of radio-thermal signals in first and second channels and maximum finding. Potential precision of estimates is studied and it is shown that brightness temperature and bearing estimates are statistically independent. Despite this fact frequency characteristics of de-correlation filters in the bearing channel depend on estimates generated in the radio brightness estimation channel. [ABSTRACT FROM AUTHOR]

In this article, a qualitative work is carried out based on research of uniform PRF signal for phase noise analysis and accuracy parameter for RF sensor design. Presence of large clutter level in target return needs in-depth analysis of phase noise impact in clutter cancellation and importance of PRF selection in RF sensor processed SNR or accuracy. Detailed investigation of phase noise parameter in pulsed RF secnsor is examined out for target identification and tracking purpose. Critical aspects of phase noise in multiple PRF mode has been analyzed and Matlab simulations are carried out to support theoretical aspects of noise effects at particular offset. Impact of phase noise in clutter cancellation for uniform PRF waveform and multiple uniform PRF waveforms is evaluated in terms of SNR, sensor accuracy and allied limitations. Thus, outcomes can be utilized to unique analysis of PRF selection and phase noise together for RF sensor accuracy. Present work findings and results have been validated using simulation environment. This research outcomes offer great importance in design of highly accurate RF sensor. [ABSTRACT FROM AUTHOR]

This editorial from the Journal of Electronic Testing discusses various topics related to verification and validation, software testing, hardware security, radio frequency noise measurement, and wafer-level testing. The first three articles focus on verification and validation, with topics including circuit graph partitioning, mixed-signal circuit design verification, and the correctness of floating point arithmetic hardware units. The fourth article explores optimizing software test cases using entropy-based optimization and machine intelligence. The fifth article presents a genetic algorithm for detecting Trojans on low-activity signals. The sixth article discusses the design of a low noise radio frequency source for a pulsed Doppler radar. The seventh article presents a cost optimization procedure for wafer-level tests. The publisher notes that they remain neutral regarding jurisdictional claims and institutional affiliations. [Extracted from the article]

The detection of weak time-dependent alternating signals in a strongly noisy background is an important problem in physics and a critical task in metrology. Quantum lock-in amplifier can extract alternating signals within extreme noises by using suitable quantum resources, which has been widely used for magnetic field sensing, vector light shift detection, and force detection. In particular, entanglement-enhanced quantum lock-in amplifier can be realized via many-body quantum interferometry. The many-body lock-in measurement provides a feasible way to achieve high-precision detection of alternating signals, even in noisy environments. In this article, we review general protocol, experiment progresses and potential applications of quantum lock-in measurements. [ABSTRACT FROM AUTHOR]

The signals received by very low-frequency/extremely low-frequency nonlinear receivers are frequently affected by intense atmospheric pulse noise stemming from thunderstorms and global lightning activity. Current noise processing algorithms designed for nonlinear channels within these frequency ranges, which are predicated on fractional p-order moment alpha stable distribution criteria (where 0 < p < α < 2, and p and α denote distinct characteristic indices of alpha stable distribution noise), are constrained by their reliance on limited p-order moment statistics. As a result, the performance of low-frequency nonlinear channel receivers experiences significant degradation when confronted with robust pulse noise interference (0 < p < α < 2). To tackle this challenge, the present study introduces a novel variable step robust mixed norm (RMN) adaptive filtering algorithm, designated as SVS-RMN, which is based on the Sigmoid function. Leveraging the nonlinearity of the Sigmoid function and building upon the power function Hammerstein nonlinear channel model, the algorithm aims to enhance the RMN algorithm by deriving new cost functions and adaptive iteration formulas. The performance of the proposed algorithm is evaluated in comparison to conventional RMN algorithms based on fractional low-order moment (FLOM) criteria (0 < p < 2), as well as other algorithms employing variable step sizes and either FLOM or radial basis function (RBF) criteria, across various intensities of pulse noise and mixed signal-to-noise ratios. The experimental results reveal the following: (1) The proposed algorithm effectively mitigates strong pulse noise interference and significantly enhances the tracking performance of the RMN algorithm compared to conventional RMN algorithms based on FLOM criteria. (2) In terms of computational efficiency, simplicity of structure, convergence speed, and stability, the proposed algorithm surpasses other algorithms based on FLOM or RBF criteria. [ABSTRACT FROM AUTHOR]

We have developed a transportable laboratory sample of a photonic microwave oscillator (PMO) based on an optical frequency standard (He–Ne/CH4 laser, λ = 3.39 μm) and an optical frequency divider (femtosecond Er-doped fiber laser, λ = 1.55 μm). The radiation spectrum of the oscillator is a comb of frequencies in the range from 1 to 10 GHz. A relative Allan deviation is demonstrated to be less than 1 × 10–14 at averaging times of 1–1000 s for spectrum components with frequencies of 1.0 and 9.2 GHz. The choice of frequencies is determined by the prospect of using the designed PMO as a master oscillator in Cs/Rb fountain-type time and frequency standards. At averaging times from 1 to 200 s, the resulting frequency instability is lower than that of commercial hydrogen masers. The spectral power density of phase noise for the specified frequencies at offsets of less than 100 Hz from the carrier frequency is significantly lower than that of the best electronic and optoelectronic oscillators. The designed oscillator seems useful for problems of fundamental time and frequency metrology, development and phase calibration of precision microwave equipment, coherent radar detection, monitoring, and communications, as well as in cases requiring relatively long (10–2–103 s) accumulation of a weak signal in the region of small carrier frequency offsets and/or synchronization holding of distributed sources. [ABSTRACT FROM AUTHOR]

Soliton microcombs are helping to advance the miniaturization of a range of comb systems. These combs mode lock through the formation of short temporal pulses in anomalous dispersion resonators. Here, a new microcomb is demonstrated that mode locks through the formation of pulse pairs in coupled normal dispersion resonators. Unlike conventional microcombs, pulses in this system cannot exist alone, and instead phase lock in pairs wherein pulses in each pair feature different optical spectra. The pairwise mode-locking modality extends to multiple pulse pairs and beyond two rings, and it greatly constrains mode-locking states. Two- (bipartite) and three-ring (tripartite) states containing many pulse pairs are demonstrated, including crystal states. Pulse pairs can also form at recurring spectral windows. We obtained the results using an ultra-low-loss Si3N4 platform that has not previously produced bright solitons on account of its inherent normal dispersion. The ability to generate multicolour pulse pairs over multiple rings is an important new feature for microcombs. It can extend the concept of all-optical soliton buffers and memories to multiple storage rings that multiplex pulses with respect to soliton colour and that are spatially addressable. The results also suggest a new platform for the study of topological photonics and quantum combs. Bright solitons are produced through the interaction of pulse pairs generated via a continuous-wave fibre laser, which pumps two coupled microresonators featuring normal dispersion. Multicolour pulse pairs over multiple rings can also be generated, of great promise for applications such as all-optical soliton buffers and memories, study of quantum combs and topological photonics. [ABSTRACT FROM AUTHOR]

Wireless radio communications provide a backbone to our technological civilization. However, radio communications are widely believed to be impossible in many situations where radios are surrounded by conductive media, such as underwater or underground, thus making ocean exploration difficult and creating well-known mine safety problems. In addition, since most imaging techniques rely on electromagnetic waves, the difficulty of electromagnetic wave propagation through biological tissues, which are mostly made of water, also severely limits bioimaging. Here we show that contrary to common beliefs, radio signals may be efficiently propagated through water over useful distances. Both radio communication and radio imaging through water may be enabled by superlensing of surface electromagnetic waves propagating along the water surface. We have demonstrated underwater radio communication over distances of several hundred skin depth in the MHz frequency range, which would require sensitivity below 10−100 W in a conventional radio communication channel. We also demonstrated subwavelength super-resolution radio imaging in the GHz range by using water surface as a superlens. Our results indicate new ways to perform bioimaging, as well as marine life safe techniques of wireless radio communication and imaging underwater, which are essential for ocean and seafloor exploration. We also anticipate that the developed techniques will provide invaluable means of studying the extraterrestrial water worlds, such as potentially inhabitable Jovian moons. [ABSTRACT FROM AUTHOR]

In order to detect the unused spectrum bands (the spectrum holes) efficiently in cognitive radios with low signal-to-noise radio (SNR), we propose to adopt two independent branches of wavelet to detect the singularities of the received signals' power spectrum density (PSD). The sensing structure is flexible such that we can use one or two branches to cope with different SNRs. Under low SNR condition, each branch uses distinct characteristics between noise and signals in the wavelet transform to eliminate the singularities generated by the noise. By using bandpass filter to calculate PSD values of the subbands which are distinguished by the signal's singularities, the subband with the minimum PSD value among all of the subbands could be found. Then, the results of the two branches are merged and analyzed in order to make the final decision. Finally, we use signal reconstruction to further remove the noise and then accurately detect the spectrum holes. When the SNR is high, only one branch through the denoising procedure is needed to get accurate sensing result. Our simulation results show that the two-branch wavelet method is more accurate than conventional approaches under given SNRs. [ABSTRACT FROM AUTHOR]

Ions confined using a Paul trap require a stable, high voltage and low noise radio frequency (RF) potential. We present a guide for the design and construction of a helical coil resonator for a desired frequency that maximises the quality factor for a set of experimental constraints. We provide an in-depth analysis of the system formed from a shielded helical coil and an ion trap by treating the system as a lumped element model. This allows us to predict the resonant frequency and quality factor in terms of the physical parameters of the resonator and the properties of the ion trap. We also compare theoretical predictions with experimental data for different resonators, and predict the voltage applied to the ion trap as a function of the Q factor, input power and the properties of the resonant circuit. [ABSTRACT FROM AUTHOR]

In this paper, we explore the use of iterative curvelet thresholding for seismic random noise attenuation. A new method for combining the curvelet transform with iterative thresholding to suppress random noise is demonstrated and the issue is described as a linear inverse optimal problem using the L1 norm. Random noise suppression in seismic data is transformed into an L1 norm optimization problem based on the curvelet sparsity transform. Compared to the conventional methods such as median filter algorithm, FX deconvolution, and wavelet thresholding, the results of synthetic and field data processing show that the iterative curvelet thresholding proposed in this paper can sufficiently improve signal to noise radio (SNR) and give higher signal fidelity at the same time. Furthermore, to make better use of the curvelet transform such as multiple scales and multiple directions, we control the curvelet direction of the result after iterative curvelet thresholding to further improve the SNR. [ABSTRACT FROM AUTHOR]

Extremely large-scale multiple-input-multiple-output (XL-MIMO) at millimeter-wave (mmWave) and terahertz (THz) bands plays an important role in supporting extreme high beamforming gain as well as ultra-wideband spectrum resources. Unfortunately, accurate wideband XL-MIMO channel estimation suffers from a new challenge called the near-field beam split effect. Prior studies either neglect the accurate near-field channel model or fail to exploit the beam split effect, resulting in poor channel estimation accuracy for wideband XL-MIMO. To tackle this problem, this paper proposes a bilinear pattern detection (BPD)-based approach to accurately recover the wideband XL-MIMO channel. Specifically, by analyzing the characteristics of near-field wideband channels, we first reveal the bilinear pattern of the near-field beam split effect, which implies that the sparse support set of near-field channels in both the angle and the distance domains can be regarded as a linear function against frequency. Then, inspired by the classical simultaneously orthogonal matching pursuit technique, we use the bilinear pattern to estimate the angle-of-arrival (AoA) and distance parameters of each near-field path component at all frequencies. In this way, the entire wideband XL-MIMO channel can be recovered by compressed sensing algorithms. Moreover, we provide the computational complexity of the proposed algorithm compared with existing algorithms. Finally, simulation results demonstrate that our scheme can achieve the accurate estimation of the near-field wideband XL-MIMO channel in the presence of near-field beam split effect. [ABSTRACT FROM AUTHOR]

With the rapid development of information technology, information war is becoming more and more intense. Signal processing plays an increasingly important role in information war, and the application of this technology is becoming more and more extensive. The information signal processed by the traditional frequency hopping communication system is relatively single. When there are a variety of electromagnetic signals, the communication channel environment is complex and there will be signal interference. Therefore, this paper studies the detection, identification, and experimental simulation of quasi-frequency hopping signal under multi-fixed frequency interference. Firstly, this paper uses the short-time Fourier transform and Wigner–Ville time–frequency analysis method to identify and simulate the interference signal of multi-fixed frequency interference. Then, according to the working principle of genetic algorithm, the design steps of radio high frequency (RHF) signal are designed, the signal model is constructed, and the narrowband interference suppression strategy is proposed to suppress the fixed frequency interference signal. According to the simulation of this model in this paper, the suppression effect of time–frequency domain and joint method is more obvious than that of traditional time–frequency domain. If the fixed frequency interference signal only covers a small part or does not cover the quasi random frequency hopping signal, the signal suppression effect of using time–frequency domain to filter the interference signal is better than using non-decimation wavelet packet transform algorithm, and there will be no error impact on the original signal when completely using time–frequency domain to filter the signal. Finally, this paper combines the interference analysis algorithm in time domain and time frequency domain and carries on the simulation analysis. Through the application simulation of multi-target scene, the results show that the complementary code modulation method can estimate the distance and velocity parameters in multi-target scene. Although the velocity measurement range is narrow, this method has the advantages of high velocity measurement accuracy, higher output signal-to-noise ratio and lower computational complexity. [ABSTRACT FROM AUTHOR]

From a statistical mechanics perspective, to describe the dynamics of a tracer, a phenomenological model has been established by a generalized Langevin equation (GLE) which includes a Basset force, a periodic perturbation force, a Stokes force, an external force and a thermal noise. Using the generalized Shapiro-Loginov formula, the iterative expressions of the first moments of the system are obtained. The time series of the first moments have been extensively investigated. By analyzing the time series of the first moments of the system with different system parameters, the irregular responses of the curves are revealed and tend to be stable for a long time. Significantly, the dynamics of average amplitudes of the first moments, influenced by various system parameters, have also been addressed in detail. Especially, the monotonic and non-monotonic properties of the average amplitudes of the first moments versus the memory exponent α are discussed. [ABSTRACT FROM AUTHOR]

Digital modulation identification is a challenging and important operation in the security communication field. Identifying properly a digital modulation and its parameters is a key operation in many applications, such as cognitive radio, communication intelligence and dynamic spectrum allocation. However, traditional methods face a stalemate in which the accuracy of the identification process is quite low. Therefore, new descriptors are needed as an alternative solution or to complement the existing ones. Using a new method from the field of nonlinear dynamic systems, namely the phase diagram representation, we want to extract some features to help recognizing the type of used modulations. This method can be used even in noisy backgrounds, with the help of an additional processing algorithm, to give important information about the signal and the used modulation. [ABSTRACT FROM AUTHOR]

In this paper, a two-dimensional generalized weighted fractional Fourier transform (2DGWFRFT) and constellation scrambling (CS)-based secure spatial modulation (SM) scheme, called 2DGWFRFT-CS-SM, is proposed to enhance the physical layer security (PLS) of the wireless communication system. The proposed scheme is executed by two steps. In the first step, 2DGWFRFT is implemented as the security kernel for PLS provision. In the second step, the parameters of 2DGWFRFT, regarded as the encryption core, control the antenna number rotation to further enhance the security of the SM modulation symbol. Both the 2DGWFRFT signal generation strategy and the SM system including the transfer process have been elaborated to depict the security mechanism of the proposed scheme. Moreover, we give a key extraction algorithm utilized to generate the parameters, which can help scramble the antenna serial number. From the perspective of signal characteristics, the uniqueness of variation in the constellation has been investigated to outperform other cryptography-based encryption algorithms. Finally, the secrecy rates and the energy efficiency of our proposed scheme are theoretically analyzed and evaluated via Monte Carlo simulations, demonstrating that the proposed scheme can achieve a much higher secrecy capacity than artificial noise schemes without requiring additional jamming power consumption and myriad costs of hardware. [ABSTRACT FROM AUTHOR]

The GNSS receiver onboard the Haiyang-2D (HY-2D) China Ocean satellite tracks the new B1C and B2a signals of BDS-3 to orbit determination. This study analyzes one week of onboard dual-frequency BDS-3 data obtained during July 2021 from the HY-2D satellite. The quality of the onboard BDS-3 measurements is first evaluated in terms of the data quantity and code multipath error quantities. Thanks to the IGSO and GEO satellites of BDS-3, the HY-2D satellite can observe more BDS-3 satellites in China and surrounding areas. The multipath errors (MPs) of the B1C and B2a signals are approximately 0.6 m and 0.2 m, respectively; they have centimeter-level systematic biases which change linearly with elevation. For precise orbit determination (POD), the observable-specific signal biases (OSBs) are corrected by the OSB products obtained from the GNSS Research Center of Wuhan University (WHU), showing that the ionospheric-free code residuals of B1C and B2a signals are reduced from 5.6 to 1.3 m. The phase center variation (PCV) model is corrected by the residual approach, and the orbit determination residuals of carrier phases can be improved to 7.5 mm. The orbit accuracy, indicated by the satellite laser ranging (SLR) validation, is about 2.3 cm during the study period. Upon conducting the Doppler Orbitography and Radio-positioning Integrated by Satellite (DORIS) validation, orbit differences less than 5.2 cm in the 3D direction are obtained with the BDS-3-based orbits, and high consistency is achieved in the radial orbit component. [ABSTRACT FROM AUTHOR]

In this article, low phase noise microwave oscillators based on elliptic resonators have been reported. Eight different designs of elliptic oscillators in various frequency bands such as L and X have been compared with each other and the results of them have been presented. The parameters such as active devise, elliptic resonator, oscillation frequency, output power, phase noise, and figure-of-merit are considered. In the end, the low phase noise X-band oscillator based on elliptic filter and branchline coupler is having better results of phase noise among the other elliptic microwave oscillators. [ABSTRACT FROM AUTHOR]

Massive machine-type communications (mMTC) face spectrum scarcity problems at 5G mid-bands (i.e., sub 6 GHz) due to tens of billions of machine-type devices connected in a smaller region. The mMTC facing significant challenges are scalability and efficient connectivity. To enable cognitive radio (CR) in 5G mMTC technology to resolve issues and gives promising solutions. Dynamic spectrum assignment (DSA) is mainly used to solve spectrum scarcity issues that provide efficient connectivity to massive devices. Spectrum sensing (SS) is an integral part of the CR used to detect spectrum opportunities in the spectrum. Energy detection (ED) is a prominent sensing mechanism, and a threshold computation is essential to find accurate spectrum opportunities in the spectrum. The massive devices in mMTC communication send small messages and face short-term fluctuations during sensing at the sub 6 GHz bands. Hence, threshold calculation is a critical challenge in SS at sub 6 GHz bands that depend on two key factors: signal and noise variance. At 5G mid bands, the high random nature of the signal input gives poor accuracy to find spectrum holes under the assumption that the channel is either static or quasi-static in a non-line-of-sight (NLOS) scenario. Thus, a novel spectrum sensing with an efficient threshold over η - μ fading channel is proposed. The key implementation is the moving average energy (MAE) mechanism to minimize short-term fluctuations in signal energy computation and delay variance that reduces sensing delay under fading conditions. The noise variance is measured from the upper bound limit of the noise interval. The SS mechanism implemented on the real-time testbed and GNU radio processing blocks on 3.3–3.8 GHz frequency bands using universal software radio peripheral (USRP)-2953 RIO. The experimental outcomes show a high probability detection rate and low sensing delay at 5G mid-bands. [ABSTRACT FROM AUTHOR]

Accurate detection of an oil spill is of great significance for rapid response to oil spill accidents. Multispectral images have the advantages of high spatial resolution, short revisit period, and wide imaging width, which is suitable for large-scale oil spill monitoring. However, in wide remote sensing images, the number of oil spill samples is generally far less than that of seawater samples. Moreover, the sea surface state tends to be heterogeneous over a large area, which makes the identification of oil spills more difficult because of various sea conditions and sunglint. To address this problem, we used the F-Score as a measure of the distance between forecast value and true value, proposed the Class-Balanced F loss function (CBF loss function) that comprehensively considers the precision and recall, and rebalances the loss according to the actual sample numbers of various classes. Using the CBF loss function, we constructed convolution neural networks (CBF-CNN) for oil spill detection. Based on the image acquired by the Coastal Zone Imager (CZI) of the Haiyang-1C (HY-1C) satellite in the Andaman Sea (study area 1), we carried out parameter adjustment experiments. In contrast to experiments of different loss functions, the F1-Score of the detection result of oil emulsions is 0.87, which is 0.03–0.07 higher than cross-entropy, hinge, and focal loss functions, and the F1-Score of the detection result of oil slicks is 0.94, which is 0.01–0.09 higher than those three loss functions. In comparison with the experiment of different methods, the F1-Score of CBF-CNN for the detection result of oil emulsions is 0.05–0.12 higher than that of the deep neural networks, supports vector machine and random forests models, and the F1-Score of the detection result of oil slicks is 0.15–0.22 higher than that of the three methods. To verify the applicability of the CBF-CNN model in different observation scenes, we used the image obtained by HY-1C CZI in the Karimata Strait to carry out experiments, which include two studies areas (study area 2 and study area 3). The experimental results show that the F1-Score of CBF-CNN for the detection result of oil emulsions is 0.88, which is 0.16–0.24 higher than that of other methods, and the F1-Score of the detection result of oil slicks is 0.96–0.97, which is 0.06–0.23 higher than that of other methods. Based on all the above experiments, we come to the conclusions that the CBF loss function can restrain the influence of oil spill and seawater sample imbalance on oil spill detection of CNN model thus improving the detection accuracy of oil spills, and our CBF-CNN model is suitable for the detection of oil spills in an area with weak sunglint and can be applied to different scenarios of CZI images. [ABSTRACT FROM AUTHOR]

Daylight plays a major role in the wake/sleep cycle in humans. Indeed, the wake/sleep system stems from biological systems that follow a circadian rhythm determined by the light/dark alternation. The oscillations can be modeled by the higher-order nonlinear van der Pol-type equation driven by a term that mimics the light cycle. In this work, noise in the illumination is introduced to investigate its effect on the human circadian cycle. It is found that the presence of noise is detrimental for the sleep/wake rhythm, except for some special values for which it may favor regular oscillations. Depending on system parameters, noise induces regularities, such as stochastic resonance; if the natural light is turned off, it emerges that there is an optimal value of intensity noise which most deteriorates the regularity of the cycle; it is the phenomenon of anti-coherent resonance. Also, the phenomenon of stochastic resonance occurs; in the presence of natural light and there is an optimal noise intensity which improves the evolution of the wake/sleep system. However, there is a critical value of the noise beyond which the system becomes chaotic; indeed, for sufficiently high noise levels (how high depends upon the parameter of the system), the sleep/wake cycle evolves in a random and unpredictable manner, for whatever parameters of the external light. [ABSTRACT FROM AUTHOR]

Helical milling is an alternative to conventional drilling which, applied to the molds and dies industry, greatly impacts its competitiveness once it guarantees high levels of surface and geometrical quality. Excellent surface quality and the ability to drill holes with just one tool are some of the advantages of this process. Concerning the machining of hardened materials, its low machinability is another aspect that compromises the competitiveness of the mold segment. Faced with the challenges of hard machining, the present research aims the robust multi-objective optimization of AISI H13 hardened steel at high speeds to achieve competitive levels of surface quality and increase the productivity of the helical milling process. Experimental planning, robust parameter design with a focus on the crossed array, response surface methodology, and enhanced normalized normal constraint method were employed in the conduction of experiments, analysis, modeling, and optimization of the responses of interest. The responses evaluated were the mean roughness Ra, the total circularity Ront, and the material removal rate MRR. The control variables used were the axial feed per tooth fza, the tangential feed per tooth fzt, and the cutting speed vc. For the robust parameter design, the tool overhang length lto and borehole depth lb were considered as noise variables. The possibility of increasing the productivity of helical milling in a hardened material, maintaining the quality of the holes, was concluded. It was verified to the total circularity robustness about the two noise variables, and the average of the confirmation runs is equal to the mean model. [ABSTRACT FROM AUTHOR]

Time crystals are periodic states exhibiting spontaneous symmetry breaking in either time-independent or periodically-driven quantum many-body systems. Spontaneous modification of discrete time-translation symmetry in periodically-forced physical systems can create a discrete time crystal (DTC) constituting a state of matter possessing properties like temporal rigid long-range order and coherence, which are inherently desirable for quantum computing and information processing. Despite their appeal, experimental demonstrations of DTCs are scarce and significant aspects of their behavior remain unexplored. Here, we report the experimental observation and theoretical investigation of DTCs in a Kerr-nonlinear optical microcavity. Empowered by the self-injection locking of two independent lasers with arbitrarily large frequency separation simultaneously to two same-family cavity modes and a dissipative Kerr soliton, this versatile platform enables realizing long-awaited phenomena such as defect-carrying DTCs and phase transitions. Combined with monolithic microfabrication, this room-temperature system paves the way for chip-scale time crystals supporting real-world applications outside sophisticated laboratories. Discrete time crystals are described by a subharmonic response with respect to an external drive and have been mostly observed in closed periodically-driven systems. Here, the authors demonstrate a dissipative discrete time crystal in a Kerr-nonlinear optical microcavity pumped by two lasers. [ABSTRACT FROM AUTHOR]

Very low frequency wave intensity variations measured by the Kannuslehto station, Finland in the frequency range 0–12 kHz between 2016 and 2020 are analyzed by the principal component analysis (PCA). As the analyzed ground-based measurements are basically continuous, the length of individual basis vectors entering into PCA is fundamentally arbitrary. To better characterize both long- and short-period variations, two PCAs with different lengths of the basis vectors are eventually performed. Specifically, either daily frequency–time spectrograms or individual frequency spectra are chosen as the PCA basis vectors. Analysis of the first three principal components shows substantial variations of the wave intensity due to seasonal and local time effects. Intensity variations related to the geomagnetic activity characterized by Kp and AE indices and standard deviation of the magnetic field magnitude are less significant. Moreover, PCA allows one to distinguish between nighttime and daytime Kannuslehto variations and study them independently. Solar and geomagnetic activity effects on the daytime and nighttime measurements are discussed. Wave intensity variations related to substorm occurrence are also analyzed. [ABSTRACT FROM AUTHOR]

The National Laboratory of Space Weather in Mexico (Laboratorio Nacional de Clima Espacial: LANCE) coordinates instrumentation for monitoring the space-weather impact over Mexico. Two of these instruments are the Mexican Array Radio Telescope (MEXART) and Compound Astronomical Low frequency Low cost Instrument for Spectroscopy and Transportable Observatory (CALLISTO) station of the e-CALLISTO network (CALLMEX). Both instruments are located at the same facility (Coeneo Michoacan, Mexico) and share a spectral band centered at 140 MHz. In this work, we show the capabilities of the e-CALLISTO network as support to identify a solar radio burst in the signal of the MEXART radiotelescope. We identified 75 solar radio bursts in the MEXART signal: five events of Type II and 70 of Type III between September 2015 and May 2019. The analysis of solar radio bursts in the MEXART signal provides us valuable information about the development of the radio event due to their high sensitivity, time resolution, and isotropic response. In the case of Type-III solar radio events, we identify four characteristic phases in the dynamical evolution of the signal at 140 MHz: a pre-phase, a main peak, a decay phase, and a post-event phase. A Morlet wave transform was done of MEXART signals in the Type-III solar radio busts; in their spectra, a pine tree structure was identified preceding the main event in the time series. These characteristics are not observable in the data from the e-CALLISTO network. [ABSTRACT FROM AUTHOR]