Power Spectral Density Profiles Research Articles

In-silico testing of new pharmacology for restoring inhibition and human cortical function in depression

Reduced inhibition by somatostatin-expressing interneurons is associated with depression. Administration of positive allosteric modulators of α5 subunit-containing GABAA receptor (α5-PAM) that selectively target this lost inhibition exhibit antidepressant and pro-cognitive effects in rodent models of chronic stress. However, the functional effects of α5-PAM on the human brain in vivo are unknown, and currently cannot be assessed experimentally. We modeled the effects of α5-PAM on tonic inhibition as measured in human neurons, and tested in silico α5-PAM effects on detailed models of human cortical microcircuits in health and depression. We found that α5-PAM effectively recovered impaired cortical processing as quantified by stimulus detection metrics, and also recovered the power spectral density profile of the microcircuit EEG signals. We performed an α5-PAM dose-response and identified simulated EEG biomarker candidates. Our results serve to de-risk and facilitate α5-PAM translation and provide biomarkers in non-invasive brain signals for monitoring target engagement and drug efficacy.

Study on Linewidth and Phase Noise Characteristics of a Narrow Linewidth External Cavity Diode Laser.

In the field of inter-satellite laser communication, achieving high-quality communication and compensating for the Doppler frequency shift caused by relative motion necessitate lasers with narrow linewidths, low phase noise, and the ability to achieve mode-hop-free tuning within a specific range. To this end, this paper investigates a novel external cavity diode laser (ECDL) with a frequency-selective F-P etalon structure, leveraging the external cavity F-P etalon structure in conjunction with an auxiliary filter to achieve single longitudinal mode selection. The laser undergoes linewidth testing using a delayed self-heterodyne beating method, followed by the testing of its phase noise and frequency noise characteristics using a noise analyzer, yielding beat spectra and noise power spectral density profiles. Furthermore, the paper introduces an innovative bidirectional temperature-scanning laser method to achieve optimal laser-operating point selection and mode-hop-free tuning. The experimental results showcase that the single longitudinal mode spectral side-mode suppression ratio (SMSR) is around 70 dB, and the output power exceeds 10 mW. Enhancing the precision of the F-P etalon leads to a more pronounced suppression of low-frequency phase noise, reducing the Lorentzian linewidth from the initial 10 kHz level to a remarkable 5 kHz level. The bidirectional temperature-scanning laser method not only allows for the selection of the optimal operating point but also enables mode-hop-free tuning within 160 pm.

Vibration Test Spectrum Simulating the In-Flight Jet Aircraft Transport Environment of Parcel and Unit Load Shipments

Abstract The measurement and analysis of the hazards occurring during the distribution environment are critical to developing test simulations that can be used to challenge packaged products and quantify their performance. One increasingly utilized vehicle is jet aircraft to move packaged product systems through the distribution network. As a result, there is a need to ensure that the vibration test levels used to qualify packaged product systems reflect the hazard levels observed in the air transport environment. This study utilized a field data recorder that separated ground and in-flight vibration events to capture a series of jet aircraft flights. The measured acceleration-time data were analyzed in terms of power spectral density (PSD) and statistically examined to understand the variability of the vibration intensity of this transport mode. The PSD profiles computed from the field measured events were significantly lower in vibration intensity than current test methods for air transport. Statistical analysis showed that the measured events were non-Gaussian and right-skewed. Additionally, a composite jet aircraft PSD test profile, reflective of the field-collected events, was developed, which could drive vibration test systems to evaluate packaged product systems during the in-flight segment of this distribution channel.

Measurement and analysis of truck vibration levels in logistic Spain distribution to simulate package testing

AbstractThe aim of this study was to measure the vibration levels in one of the types of truck most used in Spain for the shipment of packaged goods, formed by tractor unit and air‐suspension semi‐trailer with 26 tonnes (26 000 kg) payload capacity, considering the most representative routes of the main Spanish road network. The data presented in this study will enable the development of new specific vibration tests and will help product and package engineers to reduce damage in transit. In this study, 30 transport routes recording nearly 10 000 km of the Spanish main road network have been selected and analysed, and power spectral density (PSD) profiles are provided to simulate truck transport in Spain using random vibration test methods. The resulting PSD profiles were established by generating two grms levels (0.21 and 0.15) obtaining the highest intensity from the calculation of the upper one‐sided normal tolerance limit (NTL) (30,95,50) and an average intensity profile at −6 dB with respect to the calculated NTL curve, which represents 70% of the lowest grms values of the study. This study uses NTL analysis to explore the vibration characteristics of a typical heavy goods transport vehicle type for various routes along main highways in Spain and propose new transport simulation test protocols dedicated to the Spanish main road distribution environment.

Fourier Analysis of Magnetic Fields in the Ionosphere of Mars

AbstractThe two main sources of the magnetic field in the Martian ionosphere are the solar wind interaction with the planet, and, mainly in the southern hemisphere, remnant crustal magnetization. The magnetic fields measured by the Mars Atmosphere and Volatile EvolutioN (MAVEN) and Mars Global Surveyor spacecraft displayed a wide range of spatial scales, from the global (i.e., L ≈ 103 km) to mesoscale (L ≈ 102 km) to small‐scale (L < 10 km). Hamil et al. (2022) used MAVEN magnetometer and Langmuir Probe data to study these structures and suggested that they might be advected into the ionosphere from the solar wind and magnetosheath. In the current study, we apply a Fourier analysis to the fields and interpret the resulting power spectral density profiles versus frequency. The power spectral density function found from MAVEN data resembles that of the solar wind magnetic field (or interplanetary magnetic field) (i.e., power law with an index of about −2), but shifted upward in frequency by a factor of about 100. From a comparison of ionospheric power spectra with solar wind power spectra, we deduce that plasma, carrying a magnetic field with it moves from the magnetic pile‐up region downward into the ionosphere with speeds of roughly tens of meters per second. The derived power spectra in the ionosphere, in addition to the basic power law shape, show hints of extra power at a spatial scale of about 10 km, and this might be due to the creation of a magnetic structure within the ionosphere itself.

Amplitude enhancement of short period GPS-TEC oscillations over rainfall area

Correlation between rainfall and short period GPS-TEC (total electron content) variations are investigated by using the precipitation data obtained on the ground and estimated from satellite observations (JAXA/GSMaP) as a proxy of lower atmospheric wave activity. The GPS-TEC data obtained at a tropical station, PHIM, in Phimai, Thailand, for 2014–2020, and the data obtained at a mid-latitude station, NAKG, in Tokara Nakanoshima Island, Japan, for 2017–2019, are examined. A statistical analysis of MEM (maximum entropy method) power spectral density (PSD) in the period range from 50 to 1200 s over PHIM clearly shows an enhancement in the cases of rainfall from that in no-rainfall cases, in particular, on the dusk side. The enhancement is observed both acoustic wave periods less than 5–6 min and internal gravity wave periods more than 10 min. The enhancement after sunset could be an effect of strong rainfall more frequent on the dusk side than that in other local time, or it could suggest the importance of ionospheric electron density profile change for the TEC variation. On the other hand, the PSD does not show such clear enhancement over NAKG on the dusk side, although it shows a small enhancement on both dayside and night-side. A clear PSD bulge near the main vertical acoustic resonance periods, i.e., around 275 s, appears in the average PSD profile of the TEC at PHIM, which suggests that the resonance effect contribute to some extent the PSD enhancement under rainy condition. An event analysis also suggests the contribution of acoustic resonance to the enhancement of the short period TEC variation. A complicated spatial distribution of TEC oscillation over a rainfall area around PHIM, where the TEC oscillations with various periods co-exist, is presented.Graphical

X-ray intraday variability and power spectral density profiles of the blazar 3C 273 with XMM–Newton during 2000–2021

ABSTRACT We present X-ray intraday variability and power spectral density (PSD) analyses of the longest 23 pointed XMM–Newton observations of the blazar 3C 273 that were taken during 2000–2021. These good time intervals contain between 5 and 24.6 h of data. Variability has been estimated in three energy bands: 0.2–2 keV (soft), 2–10 keV (hard), and 0.2–10 keV (total). 9 of the 23 observations exhibited some variability, though no major variations exceeding 5 per cent were detected. Typical time-scales for variability were ∼1 ks. For those variable light curves, we find that a power-law model provides good fits to each PSD, with most of the slopes between −1.7 and −2.8. Although no variations of hardness ratio (HR) could be measured in any individual observation, an anticorrelation in flux and HR is found in long term data that indicates a harder when brighter trend. Our flux and spectral analyses indicate that both particle acceleration and synchrotron cooling processes make an important contribution to the emission from this blazar.

이론적 열유동 및 랜덤 진동 해석을 적용한 EPS 보냉용기의 포장설계

Although it has recently been regulated for use as an eco-friendly policy in Korea, the use of EPS (Expanded Polystyrene) cooling boxes, which are used as cold chain delivery insulation boxes for fresh agricultural and livestock products, is also increasing rapidly as e-commerce logistics such as delivery have increased rapidly due to COVID-19. Studies were conducted to optimize the EPS cooling container through internal air heat flow of CFD (Computational Fluid Dynamics) analysis and FEM (Finite Element Method) random vibration analysis using domestic PSD (Power Spectral Density) profile of the EPS cooling box to which the refrigerant is applied in this study. In the analysis of the internal air heat flow by the refrigerant in the EPS cooling box, the application of vertical protrusions inside was excellent in volume heat flow and internal air temperature distribution. In addition, as a result of random vibration analysis, the internal vertical protrusion gives the rigid effect of the cooling box, so that displacement and stress generation due to vibration during transport are smaller than that of a general cooling container without protrusion. By utilizing the resonance point (frequency) of the EPS cooling box derived by the Model analysis of ANSYS Software, it can be applied to the insulation and cushion packaging design of the EPS product line, which is widely used as insulation and cushion materials.

Prediction of vibration induced damage in photovoltaic modules during transportation: finite element model and field study

The transportation of the photovoltaic (PV) modules involves excessive vibrations and shocks. These dynamic loads can crack the solar cells and glass of the PV modules. The cracks generated in solar cells during the transportation phase may not always have immediate implications on the electrical performance of the PV modules. However, in the long-run, cracks generated during transportation of the modules may propagate during operation in field due to wind load, snow load and thermal stresses. The propagation of cracks may create electrical isolation in the cells of a PV module, which can cause loss of electrical power. Therefore, it is important to minimize the damage in PV modules due to transportation and mechanical handling. In this work, PV modules have been transported in packaging following the industry practices to cover a distance of 270 km with accelerometers attached on several modules. Finite element (FE) modelling has been used to calculate natural frequency of vibration for the assembly of the PV modules by simulating the conditions close to the actual transportation experiment. This study shows that transportation makes the modules vibrate at their natural frequency. The first four natural frequencies of vibration calculated through the FE simulations match well with the peaks observed in the power spectral density profiles experienced by PV modules during transportation. Mode shapes corresponding to the first four natural frequencies have also been visualized to identify the contours with maximum displacement. It is hypothesized that out of all the cells, those falling within the contour of maximum displacement would have higher propensity for damage during the transportation. The results presented here can be useful for PV community to improve the packaging methodology, dimensions and material selection of the photovoltaic modules.

Free Layer Thickness Dependence of the Stability in Co2(Mn0.6Fe0.4)Ge Heusler Based CPP-GMR Read Sensor for Areal Density of 1 Tb/in2.

Current-perpendicular-to-the-plane giant magnetoresistance (CPP-GMR) read sensors based on Heusler alloys are promising candidates for ultrahigh areal densities of magnetic data storage technology. In particular, the thickness of reader structures is one of the key factors for the development of practical CPP-GMR sensors. In this research, we studied the dependence of the free layer thickness on the stability of the Co2(Mn0.6Fe0.4)Ge Heusler-based CPP-GMR read head for an areal density of 1 Tb/in2, aiming to determine the appropriate layer thickness. The evaluations were done through simulations based on micromagnetic modelling. The reader stability indicators, including the magnetoresistance (MR) ratio, readback signal, dibit response asymmetry parameter, and power spectral density profile, were characterized and discussed. Our analysis demonstrates that the reader with a free layer thickness of 3 nm indicates the best stability performance for this particular head. A reasonably large MR ratio of 26% was obtained by the reader having this suitable layer thickness. The findings can be utilized to improve the design of the CPP-GMR reader for use in ultrahigh magnetic recording densities.

Development of a Drone’s Vibration, Shock, and Atmospheric Profiles

Technological advances in unmanned aerial vehicles (UAVs) have made it possible to employ drone deliveries for packaged products, but currently no standards of practice are available to qualify packaged products traveling through this distribution channel. This research proposes a methodology to collect field data from a UAV to develop simulation techniques for use with package testing equipment. This project utilized data recorders to measure the vibration, shock, and atmospheric field data on two models of the DJI drones. The root mean square G value (Grms), the power spectral density (PSD), maximum G-values and shock response spectrum, and atmospheric data were reported in this study. The study found that the general shape of the PSD profile of the drones differed from the PSD air profiles of the aircraft. The overall recorded Grms levels of the drones were also significantly higher than those of the published air profile of the aircraft. Moreover, the study found that the drone’s in-flight vibration intensities in the horizontal level were consistently higher than those in the vertical direction. The major sources of vibration and shock in both drones’ models originated from the two-propeller rotations. Shocks recorded during the flight reached 14 G, took place in the horizontal plane with the drone accelerating as opposed to the vertical plane where the drone is landing.

Optimal Sizing of CPP-GMR Read Sensors for Magnetic Recording Densities of 1–4 Tb/in²

Several studies have confirmed that current-perpendicular-to-the-plane giant magnetoresistance (CPP-GMR) technology is appropriate for next-generation read sensors for ultrahigh areal densities (ADs) of data storage applications. Since the physical dimension of the read sensor is a crucial factor for developing the reader to overcome its limitations, this paper proposes an optimal sizing prediction of the CPP-GMR read heads for ADs of 1-4 Tb/in2. Micromagnetic modelling was performed in the simulations. The appropriate length of the stripe height (SH) and the read width (RW) of the readers was estimated based on a consideration of sensor outputs including the readback signal, asymmetry parameter, dibit response and power spectral density (PSD) profile. It was found that a variation of SH and RW lengths had an influential impact on the readback signal waveform. Those affectations were further characterized through the echoes of dibit response showing that shortening the SH length or increasing the RW length could improve the resolution and reduce the distortion occurring in the readback signal. Moreover, the PSD profile indicated that the reader operation became more stable at shorter SH lengths or longer RW lengths. The head response spectrum was also examined. In addition, the magnitude of the bias current was studied in relation to the head response. Lastly, the optimal physical dimension (SH $\times $ RW) of the CPP-GMR readers for ADs of 1-4 Tb/in2 was predicted to be ( $40 \times 48$ ) nm, ( $28 \times 29$ ) nm, ( $25 \times 26$ ) nm and ( $19 \times 20$ ) nm, respectively. The results can be utilized to design the CPP-GMR sensors at ultrahigh magnetic recording capacities.

Vibration measurement and analysis in carton clamp truck handling

The purpose of this study was to construct power spectral density (PSD) profiles to analyse carton clamp truck handling environments. It also aimed to investigate the effects of payload, travelling speed, and tyre type on vibration levels of the main body and attachment of the clamp truck. Three types of PSD profiles of carton clamp truck handling were constructed for three different test courses designed based on a case study in the home appliance industry, ASTM D6055 and ISTA 3B. Experimental results showed that the overall root mean square acceleration of the new test course designed based on the actual handling environment in the home appliance industry is between the data obtained from ASTM D6055 and ISTA 3B test courses. The vibration levels measured at both the main body and attachment of the clamp truck increased with travel speed, they also increased when payload decreased.

Evolution of the truncated disc and inner hot-flow of GX 339–4

Aims. We study the changes in geometry of the truncated disc and the inner hot-flow of GX 339–4 by analysing the power spectral density (PSD) extracted from six XMM-Newton observations taken at the very end of an outburst. Methods. We developed a theoretical model of the PSD of GX 339–4 in the 0.3–0.7 keV (thermal-reverberation-dominated) and 0.7–1.5 keV (disc-continuum-dominated) energy bands. The model assumes the standard accretion disc to be truncated at a specific radius, inside of which are two distinct hot-flow zones: one spectrally soft and the other spectrally hard. The effects of disc fluctuations and thermal reverberation are taken into account. Results. This model successfully produces the traditional bumpy PSD profiles and provides good fits to the GX 339–4 data. The truncation radius is found to increase from rtrc ∼ 10 to 55rg as the source luminosity decreases, confirming that the truncation radius can be characterized as a function of luminosity. Keeping in mind the large uncertainty in previous measurements of the truncation radius, our values are larger than some obtained from spectroscopic analysis, but smaller than those implied by reverberation lag analysis. Furthermore, the size of two inner hot-flow zones that are spectrally hard and spectrally soft also increases from ∼5 to 27rg and from ∼3 to 26rg, respectively, as the flux decreases. We find that the radial range of the inner hard zone is always larger than the range of the soft hot-flow zone, but by a comparatively small factor of ∼1.1–2.2

Measurement and Analysis of Vibration Levels for Truck Transport Environment in Korea

The first step in the appropriate packaging design of food, agricultural and industrial products is to conduct an accurate simulation of the vehicle transport environment, in which a power spectral density (PSD) profile is applied. Although several researchers have mentioned the limitations of PSD-based simulation, it is still widely used because accelerated test conditions can be easily generated from the PSD acquired from a particular transport section. In this study, three representative trucks and transport test routes of domestic freight transport were selected to develop a simulation protocol for a truck transport environment in Korea. These studies are needed to compare domestic transport vibration levels with those presented by the International Standards (ASTM: West Conshohocken, USA, ISTA: Chicago, USA) and to simulate damage to packaged products by domestic transport environments. The composite PSD profile for the truck transport environment was established by dividing it into high-and low-level composite PSD profiles representing the top 30% and lower 70%, respectively, of the measured vibration events based on the root-mean-square acceleration (rms G) of the measured vibration events. Also, the effects of these variables on the truck vibration level were analyzed by extracting data corresponding to the truck’s pre-planned travel speed and road conditions in the vibration records measured on the test route. Moreover, kurtosis, skewness, and normal quantile-quantity (Q-Q) analyses were conducted to understand the statistical characteristics of Korea’s truck transport environment. Statistical analysis showed that the measured vibration events had a heavy-tailed distribution and skewed to the right, causing dissymmetry. The overall rms G of the developed high-level and low-level composite PSD profiles in the range from 1 to 250 Hz were 0.47 and 0.32 for leaf-spring trucks and 0.30 and 0.14 for air-ride trucks, respectively.

Characterization of pressure fluctuations within a controlled-diffusion blade boundary layer using the equilibrium wall-modelled LES

In this study, the generation of airfoil trailing edge broadband noise that arises from the interaction of turbulent boundary layer with the airfoil trailing edge is investigated. The primary objectives of this work are: (i) to apply a wall-modelled large-eddy simulation (WMLES) approach to predict the flow of air passing a controlled-diffusion blade, and (ii) to study the blade broadband noise that is generated from the interaction of a turbulent boundary layer with a lifting surface trailing edge. This study is carried out for two values of the Mach number, {{rm Ma}}_{infty } = 0.3 and 0.5, two values of the chord Reynolds number, {{rm Re}}=8.30 times 10^5 and 2.29 times 10^6, and two angles of attack, AoA =4^circ and 5^circ. To examine the influence of the grid resolution on aerodynamic and aeroacoustic quantities, we compare our results with experimental data available in the literature. We also compare our results with two in-house numerical solutions generated from two wall-resolved LES (WRLES) calculations, one of which has a DNS-like resolution. We show that WMLES accurately predicts the mean pressure coefficient distribution, velocity statistics (including the mean velocity), and the traces of Reynolds tensor components. Furthermore, we observe that the instantaneous flow structures computed by the WMLES resemble those found in the reference WMLES database, except near the leading edge region. Some of the differences observed in these structures are associated with tripping and the transition to a turbulence mechanism near the leading edge, which are significantly affected by the grid resolution. The aeroacoustic noise calculations indicate that the power spectral density profiles obtained using the WMLES compare well with the experimental data.

Phase Noise Characterization and EEPN of a Full C-Band Tunable Laser in Coherent Optical Systems

We perform phase noise characterization of a tunable laser source that is capable of tuning to 103 channels between 1527.6-1568.36 nm with 50 GHz grid spacing between the channels. The measured frequency modulation (FM) noise power spectral density (PSD) is reproduced by simulations in order to investigate the impact of equalization-enhanced phase noise (EEPN) in a coherent transmission system. The simulations are performed on a 30 Gbaud channel with 16 quadrature amplitude modulation (16QAM) and using pilot-based carrier phase estimation with 3% overhead. By performing extensive system simulations, we show the impact of different accumulated dispersion. Furthermore, we show the possibility to overcome EEPN related penalties by using a local oscillator (LO) with reduced low frequency phase noise or flat FM-noise PSD profiles with lower linewidths.

Vibration Measurement and Analysis in Carton Clamp Truck Handling

The purpose of this study was to construct power spectral density (PSD) profiles to analyse carton clamp truck handling environments. It also aimed to investigate the effects of payload, travelling speed, and tyre type on vibration levels of the main body and attachment of the clamp truck. Three types of PSD profiles of carton clamp truck handling were constructed for three different test courses designed based on a case study in the home appliance industry, ASTM D6055 and ISTA 3B. Experimental results showed that the overall root mean square acceleration of the new test course designed based on the actual handling environment in the home appliance industry is between the data obtained from ASTM D6055 and ISTA 3B test courses. The vibration levels measured at both the main body and attachment of the clamp truck increased with travel speed, they also increased when payload decreased.

Improving vibration test methods and profile selection for complex land vehicle payloads

ABSTRACTMechanical vibration testing is used within the Department of Defence for acceptance testing of land materiel. Historical testing has commonly implemented default vibration profiles listed in defence standards. These profiles have limitations and assumptions which may restrict their suitability for large and complex payloads due to divergences from theoretical models. Research has also highlighted inaccuracies with the Gaussian and stationary assump-tions inherent in Power Spectral Density (PSD) profile-based vibration testing that could be a source of uncertainty when simulating non-stationary environments. Further research is pro- posed to develop a standardised method to convert measured accelerometer data into PSD profiles, or other input data that can be replicated on a shaker table. This paper overviews the proposed research, in particular quantifying the assumptions, inaccuracies and inefficiencies of the extant and proposed test methods. It also offers practical suggestions on how to implement these methods to ensure risks are adequately managed and communicated.

Angular Independence of Break Position for Magnetic Power Spectral Density in Solar Wind Turbulence

Abstract The break in power spectral density (PSD) around the ion scales indicates the onset of dissipation and/or dispersion of kinetic turbulence. For Alfvén waves in the kinetic regime, the dissipation and dispersion are individually dependent on the propagation angle, θ kB, which has θ RB (the angle between radial direction and local mean magnetic field direction) as a proxy in solar wind measurements. The relation between θ RB and the break position helps us find the role of dissipation and/or dispersion for deforming the PSD profile. In order to locate the spectral break position automatically and quantitatively, we develop a dual-power-law fitting method to fit the PSD profiles in both MHD and kinetic ranges simultaneously. The break position f b is found to change little with θ RB, suggesting an angular independence of the spectral break. Furthermore, f b in our statistical study of fast solar wind near 1 au is consistent with a wavenumber k satisfying k(ρ p + d p) ∼ 1 (ρ p is the thermal proton gyroradius and d p is the proton inertial length), independently of θ RB. To interpret this independence, we incorporate the effects of both dissipation and dispersion in a unified description, which is the breakdown of the magnetic frozen-in condition in wavenumber space (k ∥, k ⊥). The breakdown of the frozen-in condition is relatively isotropic compared to the strong anisotropy of dispersion and dissipation. Furthermore, the spatial scale for the onset of the breakdown frozen-in condition is estimated to be the sum of ρ p and d p.