Centroid Time Research Articles

Improved Earthquake Source Parameters with 3D Wavespeed Models in California and Nevada

Abstract Seismic tomography harnesses earthquake data to explore the inaccessible structure of the Earth. Adjoint waveform tomography (AWT), a method of seismic tomography, updates the tomographic model by optimizing the fit between observed earthquake data and synthetic waveforms. The synthetic data are calculated by solving the wave equation through a given 3D model. An important requirement to calculating synthetics is the source information (location, centroid time, depth, and moment tensor). Errors in source information affect the quality of the synthetics produced, which in turn can limit how structure can be inferred in the AWT workflow. To test the effect of updating source information, we used MTTime (Chiang, 2020), a time-domain full-waveform moment tensor inversion code, to calculate the moment tensors and depths of 118 earthquakes that occurred in California and Nevada over a 20-yr period. We calculated 3D Green’s functions using a 3D seismic wavespeed model of California and Nevada (Doody et al., 2023b). We show that the inverted solutions provide better waveform fits than the Global Centroid Moment Tensor catalog and increase usable, well-correlated data by up to 7%. Therefore, we argue that recalculating source parameters should be considered in AWT workflows, particularly for smaller magnitude events (Mw<5.0).

Mass‐Conserving Downscaling of Climate Model Precipitation Over Mountainous Terrain for Water Resource Applications

AbstractA mass‐conserving method to downscale precipitation from global climate models (GCMs) using sub‐grid‐scale topography and modeled 700‐mb wind direction is presented. Runoff is simulated using a stand‐alone hydrological model, with this and several other methods as inputs, and compared to runoff simulated using historical observations over the western contiguous United States. Results suggest the mitigation of grid‐scale biases is more critical than downscaling for some regions with large wet biases (e.g., the Great Basin and Upper Colorado). In other regions (e.g., the Pacific Northwest) the new method produces more realistic sub‐grid‐scale variability in runoff compared to unadjusted GCM output and a simpler downscaling method. The presented method also brings the runoff centroid timing closer to that simulated with observations for all subregions examined.

New-generation geostationary satellite reveals widespread midday depression in dryland photosynthesis during 2020 western U.S. heatwave.

Emerging new-generation geostationary satellites have broadened the scope for studying the diurnal cycle of ecosystem functions. We exploit observations from the Geostationary Operational Environmental Satellite-R series to examine the effect of a severe U.S. heatwave in 2020 on the diurnal variations of ecosystem photosynthesis. We find divergent responses of photosynthesis to the heatwave across vegetation types and aridity gradients, with drylands exhibiting widespread midday and afternoon depression in photosynthesis. The diurnal centroid and peak time of dryland gross primary production (GPP) substantially shift toward earlier morning times, reflecting notable water and heat stress. Our geostationary satellite-based method outperforms traditional radiation-based upscaling methods from polar-orbiting satellite snapshots in estimating daily GPP and GPP loss during heatwaves. These findings underscore the potential of geostationary satellites for diurnal photosynthesis monitoring and highlight the necessity to consider the increased diurnal asymmetry in GPP under stress when evaluating carbon-climate interactions.

Combining Love and Rayleigh waves in detecting and locating seismic sources

SUMMARY Surface waves are critical in detecting and locating seismic sources that do not produce much high-frequency radiation. For such sources, typical approaches using body waves for detecting and locating earthquakes are less effective. Slow earthquakes and exotic seismic sources often have this seismic radiation characteristic, and array analyses of surface waves recorded on global and regional seismic networks have proven effective in recognizing such sources. Most approaches have relied on Rayleigh waves, whereas Love waves have rarely been used. Here we develop a new approach using multiscale arrays to detect and locate seismic sources with both Love and Rayleigh surface waves. The method first forms three-station subarrays and then uses three-component records of the stations to independently estimate three sets of surface wave propagation directions and centroid arrival times. The subarray estimates are then assembled to locate seismic sources and their origin times. We find that using multiple, disconnected global networks improves location accuracy and that using both types of surface waves can enhance detection sensitivity and robustness.

Bayesian Seismic Source Inversion With a 3‐D Earth Model of the Japanese Islands

AbstractWe present probabilistic centroid‐moment tensor solutions inferred from the combination of Hamiltonian Monte Carlo sampling and a 3‐D full‐waveform inversion Earth model of the Japanese islands. While the former provides complete posterior probability densities, the latter allows us to exploit waveform data with periods as low as 15 s. For the computation of Green's functions, we employ spectral‐element simulations through the radially anisotropic and visco‐elastic model, leading to substantial improvements of data fit compared to layered models. Focusing on 13 Mw 4.8–Mw 5.3 offshore earthquakes with a significant non‐double‐couple (non‐DC) component, we simultaneously infer the centroid location, time and moment tensor without any a priori constraints on the faulting mechanism. Furthermore, we perform the inversions across several period bands, varying the minimum period between 15 and 50 s. Accounting for 3‐D Earth structure at shorter periods can increase the double‐couple (DC) component of an event, compared to the GCMT solution, by tens of percent. This suggests that non‐DC events in the GCMT catalog may result from unmodeled Earth structure and the related limitation to longer‐period data. We also observe that significant changes in source parameters, and the DC component in particular, may be related to only small waveform changes, thereby accentuating the importance of a reliable Earth model. Posterior probability density distributions become increasingly multimodal for shorter‐period data that provide tighter constraints on source parameters. This implies, in our specific case, that stochastic approaches to the source inversion problem are required for periods below ∼20 s to avoid trapping in local minima.

Modeling returned signal of a satellite laser altimeter over an urban area.

Modeling the returned signal of a satellite laser altimeter is a significant theoretical foundation for understanding the topography of the Earth. According to the lidar equation and working principle of laser altimeter, we establish the mathematical expression of the urban target response waveform (TRW) by using a definite integral formation. The characteristic parameters of the TRW, including signal energy, time delay, pulse width, and skewness are deduced in detail. Based on the specifications of the global ecosystem dynamics investigation laser altimeter and the assumption that the target is considered a rectangular plane, we simulate the influences of the geometrical parameters of the target, including the region area, the center geolocation, and the surface slope, on the TRW patterns and the characteristic parameters. The simulation results show that the TRW would present left-skewed and right-skewed patterns, with the exception that the center geolocation is nearly coincident with the laser footprint center. Such skewed distributions make the time delay derived from the TRW time centroid inaccurate for representing the range between the laser altimeter and the target center. In addition, the TRW energy is positively proportional to the region area and the proximity of the center geolocation to the laser footprint center and attenuated by the cosine of the surface slope. The root-mean-square pulse width is principally determined by the tangent of the surface slope. The simulation results contribute to a better understanding of the relationship between the TRW pattern and the geometrical parameters of the illuminated target. In particular, the characteristic parameters of the TRW can provide the detailed references for developing the waveform processing algorithm and the inversion of the surface elevation, the slope, and the reflectance. The returned signal in this paper may facilitate the application of the satellite laser altimeter over an urban area.

Global centroid moment tensor solutions in a heterogeneous earth: the CMT3D catalogue

SUMMARYFor over 40 yr, the global centroid-moment tensor (GCMT) project has determined location and source parameters for globally recorded earthquakes larger than magnitude 5.0. The GCMT database remains a trusted staple for the geophysical community. Its point-source moment-tensor solutions are the result of inversions that model long-period observed seismic waveforms via normal-mode summation for a 1-D reference earth model, augmented by path corrections to capture 3-D variations in surface wave phase speeds, and to account for crustal structure. While this methodology remains essentially unchanged for the ongoing GCMT catalogue, source inversions based on waveform modelling in low-resolution 3-D earth models have revealed small but persistent biases in the standard modelling approach. Keeping pace with the increased capacity and demands of global tomography requires a revised catalogue of centroid-moment tensors (CMT), automatically and reproducibly computed using Green's functions from a state-of-the-art 3-D earth model. In this paper, we modify the current procedure for the full-waveform inversion of seismic traces for the six moment-tensor parameters, centroid latitude, longitude, depth and centroid time of global earthquakes. We take the GCMT solutions as a point of departure but update them to account for the effects of a heterogeneous earth, using the global 3-D wave speed model GLAD-M25. We generate synthetic seismograms from Green's functions computed by the spectral-element method in the 3-D model, select observed seismic data and remove their instrument response, process synthetic and observed data, select segments of observed and synthetic data based on similarity, and invert for new model parameters of the earthquake’s centroid location, time and moment tensor. The events in our new, preliminary database containing 9382 global event solutions, called CMT3D for ‘3-D centroid-moment tensors’, are on average 4 km shallower, about 1 s earlier, about 5 per cent larger in scalar moment, and more double-couple in nature than in the GCMT catalogue. We discuss in detail the geographical and statistical distributions of the updated solutions, and place them in the context of earlier work. We plan to disseminate our CMT3D solutions via the online ShakeMovie platform.

Evolution of the tracer in natural flows described by the state function ф(U, E, t): Analysis of the associated functions and their application to case studies

The tracers as a method of measuring and characterizing the evolution of natural flows, in addition to providing information on the dynamics (advection) and dispersion as "local" phenomena themselves, can give additional, dense information on the global conditions (far from the point of measurement) under the thermodynamic connection that is established between all the points of the system, when there is a steady-state in the channel. As has been widely studied since the second half of the last century, this condition of dynamic equilibrium (steady-state) in natural flows, for phenomena that do not present pronounced irreversibility (linear region of irreversible thermodynamics), implies a series of remarkable features that simplify the interpretation of the complex phenomena of turbulent currents, and thus of the superimposed dispersive processes. Within this approach, a state function, Φ(U, E, t), dependent on the mean flow velocity, the longitudinal dispersion coefficient, and time, is defined that describes the evolution of the tracer cloud, such that in its approximate quality of thermodynamic potential, it allows one to discover and pinpoint certain particularities of the phenomenon. In this paper, the characteristics and practical applications of these principles are explored. It also includes a heuristic analysis of the so-called direct functions rq(F) and inverse rq(F)-, auxiliary to the state function F(U,E, t), which are used for the interpretation of the centroid time, as well as the longitudinal and transverse diffusion-dispersion coefficients employing these functions were applied experimentally in the old stream of the city of Bogotá, “La Vieja”, presenting good agreement with the theoretical references. This topic is intended to provide a theoretical and practical tool to fully understand these processes, which are of great interest for the modeling and control of water pollution.

Source properties of the 2019ML6.3 Hualien, Taiwan, earthquake, determined by the local strong motion networks

SUMMARYThe 2019 ML 6.3 Hualien earthquake struck the northern Longitudinal Valley (LV) and generated not only large strong motions (intensity of 7, as defined by the Central Weather Bureau, Taiwan) locally but also widespread strong shaking in metropolises in northern Taiwan. In this study, we analyse strong motion records from local seismic networks to understand the source properties of the 2019 event. We first obtain the centroid location of the 2019 event using the source-scanning algorithm (SSA) technique by applying the unfiltered records. The determined centroid location is 121.55°E, 24.10°N, with a depth of 22.5 km. This location is 5.5 km north–northwest of and 3.8 km deeper than the Central Weather Bureau hypocentre, suggesting that the 2019 event occurred on the high-angle west-dipping plane of the focal solution. The centroid time delay is 3.35 s. Then, we obtain strong motion generation areas (SMGAs) of the 2019 event using the empirical Green's function method by considering the broad-band waveforms (0.4–10 Hz). Unlike other moderate-sized earthquakes in Taiwan, which have one SMGA, we determine that there were two SMGAs in the 2019 event. SMGA1 initiated at the CWB hypocentre with a size of 4.00 km2, and SMGA2 initiated at the centroid location determined by the SSA approach with a size of 3.63 km2. Such small areas cause high stress drops of 13.7 and 27.4 MPa for SMGA1 and SMGA2, respectively. We infer that the localized high stress drop of SMGAs is one of the important factors responsible for high peak-ground accelerations (PGAs) in Taiwan in addition to a strong directivity effect coupled with the radiation pattern reported by the previous study. Furthermore, previous moderate-sized earthquakes on an active structure called the Xiulin segment revealed similar source properties with a high stress drop and generated large PGA locally as well as in the metropolises of northern Taiwan. Considering the stored moment deficit, the probability of a future large earthquake in the northern LV region remains high. It is essential to consider seismic hazard assessment and mitigation for this not-well-known but high-seismic-potential region.

Probing a black-bounce, traversable wormhole with weak deflection gravitational lensing

In the strong deflection gravitational lensing, given the fact that a black-bounce, traversable wormhole is indistinguishable from a Schwarzschild black hole and is loosely tested by the Event Horizon Telescope, we intensively study its signatures of weak deflection gravitational lensing in light of the tremendous progress made by the new generation of the near-infrared interferometer GRAVITY. After obtaining its observables, which are the positions, magnitudes of brightness, centroid, and differential time delay between the lensed images, we investigate three astrophysical scenarios: an orbiting star lensed by the Galactic Center Sgr A*, a microlensed star in the Galactic bulge, and microlensing by a nearby lens. We find that the measurements of the observables of Sgr A* provide a promising way to test the black-bounce, traversable wormhole spacetime. GRAVITY can resolve the angular separation, the angular difference, and the time delay between the two lensed images by Sgr A*, and it can marginally detect their deviations from those of the Schwarzschild black hole. The brightness difference between the images and its deviation might be measured by a dedicated space telescope. In the near future, we expect that such a spacetime would be more robustly tested with the weak deflection gravitational lensing by further improved and upgraded GRAVITY+.

Measurement of the Parametrized Single-Photon Response Function of a Large Area Picosecond Photodetector for Time-of-Flight PET Applications

We have used a subpicosecond laser with an output trigger synched to a 4-GHz oscilloscope sampling at 25 GSa/s to characterize the temporally resolved response of a large area picosecond photodetector (LAPPD) to single photons/photoelectrons. The LAPPD is a large area (20 cm ×20 cm) photosensor with a nanosecond-width time response arising from its underlying multichannel plate photomultiplier tube (MCP-PMT) structure. We used optical filters to attenuate the laser pulse intensity to a single-photon level. LAPPD pulses are nearly identical in shape, particularly for pulses whose peak amplitude is a large multiple of our system's 0.6-mV rms baseline electronic noise. Three waveform timing algorithms were compared in their measurements of the transit time spread (TTS) Gaussian fitted to the distribution of measured single-photoelectron (SPE) pulse times under zero-width laser excitation: 1) a constant fraction algorithm; 2) a pulse centroid timing algorithm; and 3) a pulse model-fitting algorithm. The measured SPE values with the three algorithms are: [79±17, 67±15, and 82±20] ps Gaussian sigma, respectively. The LAPPD provides independent voltage control for its photocathode (PC), and at the entry and entry faces of its chevron pair of MCPs. We found no or minimal change in TTS with PC voltage for pulses >15 mV.

Subsecond Time Evolution of Type III Solar Radio Burst Sources at Fundamental and Harmonic Frequencies

Abstract Recent developments in astronomical radio telescopes opened new opportunities in imaging and spectroscopy of solar radio bursts at subsecond timescales. Imaging in narrow frequency bands has revealed temporal variations in the positions and source sizes that do not fit into the standard picture of type III solar radio bursts, and require a better understanding of radio-wave transport. In this paper, we utilize 3D Monte Carlo ray-tracing simulations that account for the anisotropic density turbulence in the inhomogeneous solar corona to quantitatively explain the image dynamics at the fundamental (near plasma frequency) and harmonic (double) plasma emissions observed at ∼32 MHz. Comparing the simulations with observations, we find that anisotropic scattering from an instantaneous emission point source can account for the observed time profiles, centroid locations, and source sizes of the fundamental component of type III radio bursts (generated where f pe ≈ 32 MHz). The best agreement with observations is achieved when the ratio of the perpendicular to the parallel component of the wavevector of anisotropic density turbulence is around 0.25. Harmonic emission sources observed at the same frequency (∼32 MHz, but generated where f pe ≈ 16 MHz) have apparent sizes comparable to those produced by the fundamental emission, but demonstrate a much slower temporal evolution. The simulations of radio-wave propagation make it possible to quantitatively explain the variations of apparent source sizes and positions at subsecond timescales both for the fundamental and harmonic emissions, and can be used as a diagnostic tool for the plasma turbulence in the upper corona.

Brightness perception for musical instrument sounds: Relation to timbre dissimilarity and source-cause categories.

Timbre dissimilarity of orchestral sounds is well-known to be multidimensional, with attack time and spectral centroid representing its two most robust acoustical correlates. The centroid dimension is traditionally considered as reflecting timbral brightness. However, the question of whether multiple continuous acoustical and/or categorical cues influence brightness perception has not been addressed comprehensively. A triangulation approach was used to examine the dimensionality of timbral brightness, its robustness across different psychoacoustical contexts, and relation to perception of the sounds' source-cause. Listeners compared 14 acoustic instrument sounds in three distinct tasks that collected general dissimilarity, brightness dissimilarity, and direct multi-stimulus brightness ratings. Results confirmed that brightness is a robust unitary auditory dimension, with direct ratings recovering the centroid dimension of general dissimilarity. When a two-dimensional space of brightness dissimilarity was considered, its second dimension correlated with the attack-time dimension of general dissimilarity, which was interpreted as reflecting a potential infiltration of the latter into brightness dissimilarity. Dissimilarity data were further modeled using partial least-squares regression with audio descriptors as predictors. Adding predictors derived from instrument family and the type of resonator and excitation did not improve the model fit, indicating that brightness perception is underpinned primarily by acoustical rather than source-cause cues.

Implementation and Realisation of Micro Digital Sun Sensor Processing in FPGA

AbstractThis paper presents the implementation and realization of complex processing algorithms of newly developed, high accuracy, compact, two axes Micro Digital Sun Sensor (MDSS) using linear CMOS detector and N‐shaped slit mask for Indian Satellite missions. Sun sensor provides the orientation of satellite with respect to Sun. It is one of the prime attitude sensors for spacecraft. Due to low mass, compact size and low power consumption, the MDSS will be used for future micro/nano‐satellite missions as well as for communication Satellite missions. The electrical model of MDSS is built in Laboratory for Electro‐Optics Systems (LEOS). It is around 10 times lesser in weight and 8 times compact than the high accuracy Sun sensors presently available in ISRO. The MDSS has accuracy of 0.02°. In this paper, we have presented details of the simulation and test results of Micro DSS processing.The MDSS consists of an optical head and FPGA based processing unit. The optical head consists of CMOS linear array detector and N shaped slit mask. The N slit mask is mounted at a predefined height above the detector to provide the sensor field of view of ±64° x ±64°. The sunlight falls on the detector through the N‐shaped slit and three Sun spots are formed on the detector. After removing the unwanted signals from the images using auto threshold method, the image identification and centroid computation are carried out using moment method algorithm in real time and using the real time image clustering and centroid computing algorithm. By applying sensor transfer function, the 3 centroid information are converted to Sun aspect angle information which are the sensor outputs used for determining orientation of Satellite.All the processing is done in a single FPGA, like control signals generation for detector, real time centroid calculations, complex image clustering, transfer equation realization, interfacing with output, command module and MIL‐STD‐1553B communication. The complex transfer equation which includes trigonometric functions is implemented inside the FPGA using Co‐Ordinate Rotation Digital Computer (CORDIC) algorithm without any processor. The processing unit consists of ACTEL RTAX or Proasic FPGA with MIL‐STD 1553B and LVDS peripheral interface.

Assessing internal soundness of hardwood logs through acoustic impact test and waveform analysis

The objective of this study was to explore the potential of an acoustic impact test as a nondestructive evaluation procedure to assess the soundness of hardwood logs in terms of internal decay, void, and defect ratio. Fifteen logs of four hardwood species (black cherry, white oak, red oak, and cottonwood) were obtained and subjected to acoustic impact testing. The logs were subsequently dissected for visual examination and physical mapping of the internal defects. The acoustic response signals were analyzed to derive acoustic velocity (through FFT), time centroid (through moment analysis), and the first- and second-order damping ratio (through continuous wavelet transform). The longitudinal acoustic velocity was found to have a negative, nonlinear relationship with defect ratio (R2 = 0.72), but it lacked sensitivity to small defects and was affected by species. Time centroid proved to be a better predictor than acoustic velocity with an improved correlation with log defect ratio (R2 = 0.87). Wavelet-based damping ratio was found to have a close linear relationship with log defect ratio. Comparing with the first-order damping ratio, the second-order damping ratio had a better predicting power (R2 = 0.92) and was not affected by type and location of defects. The results further indicated that a combination of acoustic velocity, time centroid, and the first- and second-order damping ratios could yield the optimal prediction of log defect ratio. However, considering the sensitivity and simplicity of the waveform analysis, the second-order damping ratio of the response signals could be the best single predicting parameter for assessing the internal soundness of hardwood logs.

Modelling Timbral Hardness

Hardness is the most commonly searched timbral attribute within freesound.org, a commonly used online sound effect repository. A perceptual model of hardness was developed to enable the automatic generation of metadata to facilitate hardness-based filtering or sorting of search results. A training dataset was collected of 202 stimuli with 32 sound source types, and perceived hardness was assessed by a panel of listeners. A multilinear regression model was developed on six features: maximum bandwidth, attack centroid, midband level, percussive-to-harmonic ratio, onset strength, and log attack time. This model predicted the hardness of the training data with R 2 = 0.76. It predicted hardness within a new dataset with R 2 = 0.57, and predicted the rank order of individual sources perfectly, after accounting for the subjective variance of the ratings. Its performance exceeded that of human listeners.

Waveform centroid discrimination of return pulse weighting method in LIDAR system

We demonstrate a new technique for the nanosecond return pulse waveform centroid timing method. The method has higher timing accuracy and wider applications due to the characteristic of that it can retain almost all the information of the return pulse. In this paper, the empirical model of transmitting signal and return pulse is built; and then the merits and demerits are discussed between the time-weighted method and the intensity weighted waveform centroid timing method. Under the MEMS scanning LIDAR system, the relationship between high-speed ADC sampling rate and waveform centroid timing accuracy is revealed. The measurement results show that when the ADC with a sampling frequency of 4 GHz is used in a short pulse LIDAR system, the comprehensive tining accuracy of the weighted waveform centroid timing method is approximately 300 ps. This method can improve the performance of the LIDAR system and may be of considerable value to both unmanned driving and intelligent service robot.

Interactions between Climate Change and Complex Topography Drive Observed Streamflow Changes in the Colorado River Basin

Abstract The Colorado River basin (CRB) is one of the most important watersheds for energy, water, and food security in the United States. CRB water supports 15% of U.S. food production, more than 50 GW of electricity capacity, and one of the fastest growing populations in the United States. Energy–water–food nexus impacts from climate change are projected to increase in the CRB. These include a higher incidence of extreme events, widespread snow-to-rain regime shifts, and a higher frequency and magnitude of climate-driven disturbances. Here, we empirically show how the historical annual streamflow maximum and hydrograph centroid timing relate to temperature, precipitation, and snow. In addition, we show how these hydroclimatic relationships vary with elevation and how the elevation dependence has changed over this historical observational record. We find temperature and precipitation have a relatively weak relation (|r| < 0.3) to interannual variations in streamflow timing and extremes at low elevations (<1500 m), but a relatively strong relation (|r| > 0.5) at high elevations (>2300 m) where more snow occurs in the CRB. The threshold elevation where this relationship is strongest (|r| > 0.5) is moving uphill at a rate of up to 4.8 m yr−1 (p = 0.11) and 6.1 m yr−1 (p = 0.01) for temperature and precipitation, respectively. Based on these findings, we hypothesize where warming and precipitation-related streamflow changes are likely to be most severe using a watershed-scale vulnerability map to prioritize areas for further research and to inform energy, water, and food resource management in the CRB.

Applying MERIS time series and dynamic time warping for delineating areas with similar temporal behaviour in the northern Baltic Sea

Coastal waters are subject to ongoing long-term developments, cycles of varying lengths and random variations. Assessments of water quality should not be based only on temporally sparse sampling and inter-annual comparisons of periodical data, but also on their temporal behaviour as an entity. In the latter approach, regions having similar inter- and intra-annual temporal pattern are classified together, regardless of the differing levels of the observed parameter.Altogether 4602 time series, containing Medium Resolution Imaging Spectrometer (MERIS) remote sensing reflectance data Rrs(443), Rrs(560) and Rrs(665) and one band ratio Rrs(681)/Rrs(620), were formed for the Gulf of Bothnia in the Northern Baltic Sea, covering the ice free periods of 1.6.–30.9. in 2004–2011. I was interested in the similarities in temporal shapes of the reflectance time series, and the time series were standardized by their annual means and standard deviation before further processing. Dynamic time warping (DTW) was used to measure the dissimilarity between the standardized time series, which were clustered in order to find areas having similar temporal character. In partitional clustering, a random initial centroid time series is selected for each cluster, which is then adjusted according to the selected centroid function to find coherent clusters. With DTW, a specific DTW barycentric averaging (DBA) is commonly used for this purpose.Appropriate configurations for DTW and clustering were searched by evaluating the clustering results with two cluster validity indices. Two key settings in DTW are 1) step pattern, which defines how the minimum distances between the observations are searched, and 2) window constraint, which constrain the allowed time difference between the observations to be compared. The performance of two step patterns, symmetricP0 and symmetricP1, and three window constraints, +−1, +−7 and +−21 days, were tested. The partitions may vary due to randomness in the selection of the initial centroid time series. The stability of the repeated clustering was evaluated by Variation of Information–index (VI). With this metric, symmetricP1 step pattern performed slightly better than symmetricP0. Longer window constraints produced more labile partitions. Allowing a certain amount of temporal distortion is however desirable, and because the VI showed satisfactory results also with window constraint of +−7 days, it was selected for further computation. A Silhouette index was used to evaluate the appropriate number of clusters (k). Regardless the number of k, the clusters were neither internally coherent nor clearly deviating from each other.Although the time series did not form strong clusters in the terms of clustering, they formed spatially distinctive and coherent groups on a map. The groups reflected the surface layer circulation pattern of the Gulf of Bothnia, rivers with fresh water input and terrestrial washed-out materials being among the most recognisable phenomena. Hard partitions gave, however, too simplified view on spatiality of temporal patterns. To avoid visual mis-interpretations, the prototypes of each cluster were calculated with DBA and distances in DTW space from these prototypes to all the other time series were visualized. In this way, clustering was used to define the macro-areas of similar temporal pattern, but similarities were defined in continuous DTW scale. This allowed more precise evaluation of the spatial–temporal relationships.

Serum electrolyte levels may be associated with prefrontal hemodynamic responses in near infrared spectroscopy

Neuronal activity is tightly coordinated with blood flow to ensure proper brain function. This is achieved by neurovascular coupling. Although this mechanism is maintained by numerous mediators such as nitric oxide, ion channels, and astrocytes, its signaling process is much more complex. Frontal-temporal brain activity as measured by near infrared (NIR) spectroscopy has been suggested to be decreased or disturbed in many psychiatric disorders. To investigate the relationship between serum electrolyte levels and prefrontal hemodynamic responses, we evaluated psychiatric patients who underwent NIR spectroscopy with a 22-channel topography system and measurement of serum electrolyte levels. Changes in the concentration of oxygenated hemoglobin were evaluated during a verbal fluency test. The data were analyzed to see any significant correlation between NIR spectroscopy indices (integral value: size of an area during activation, centroid value: centroid time of an area throughout the task, and initial value: axis assessed by an initial change) and serum electrolyte levels (sodium, potassium, and chloride) by gender and cortex region. The study population consisted of 102 males (mean age, 42.4 years) and 133 females (mean age, 47.2 years). Sodium levels were significantly positively correlated with integral values at temporal regions in female subjects, while potassium levels were significantly negatively correlated with initial values at frontal regions in male subjects. However, chloride levels showed no correlations. In conclusion, higher serum sodium levels increase and higher serum potassium levels decrease regional cerebral blood flow with gender variances in psychiatry. The effect of extracellular electrolyte concentrations on hemodynamic responses remains unverified. However, our findings suggest that serum electrolytes levels may be involved in vascular smooth muscle contractility via Na+-K+-ATPase pumps that mediate neurovascular coupling.