LOW FREQUENCY OSCILLATIONS IN TROPOSPHERIC WINDS DURING CONTRASTING SUMMER MONSOON OVER INDIA

TIle'low frequency Iluctu atio ns in the troposphe ric wind field over India has been studied by spec tnuu~ na l l"i, tech nique. duri ng con trasting mon soons. namely, d rought and good monsoons ba sed on rainfall3cti\il)·. Si~ lliflc ant spectral peaks d urin g these years ha ve bee n iden tified.Zon al wind shea r in the lower tropospher ehan' also bern examin ed and the periodici ty in th e near 4()..day mode have bee n documented . Th e interannual, 'n.riill1i1ily of the mode and its potential as medium range predicti on tool has been examined in therrnpn perspect ive.

Direct Measurement of Biexcitons in Monolayer WS2

The optical properties of atomically thin transition metal dichalcogenides (TMDCs) are dominated by Coulomb bound quasi-particles, such as excitons, trions, and biexcitons. Due to the number and density of possible states, attributing different spectral peaks to the specific origin can be difficult. In particular, there has been much conjecture around the presence, binding energy and/or nature of biexcitons in these materials. In this work, we remove any ambiguity in identifying and separating the optically excited biexciton in monolayer WS2 using two-quantum multidimensional coherent spectroscopy (2Q-MDCS), a technique that directly and selectively probes doubly-excited states, such as biexcitons. The energy difference between the unbound two-exciton state and the biexciton is the fundamental definition of biexciton binding energy and is measured to be 26 ± 2 meV. Furthermore, resolving the biexciton peaks in 2Q-MDCS allows us to identify that the biexciton observed here is composed of two bright excitons in opposite valleys.

Ex-situ Spectroscopic Characterization of Residual Effects of Thermomechanical Loading on Polyurea

The residual effect of thermally and mechanically loaded polyurea samples was investigated in this study using terahertz time-domain spectroscopy (THz-TDS), operating in the transmission mode. Samples of different thicknesses were submerged in liquid nitrogen and reached cryogenic isothermal condition before equilibrating at room temperature. Another set of samples were extracted from quasi-statically loaded strips. All samples were then interrogated using THz-TDS since terahertz waves exhibit nonionizing interactions with polymers, eliminating the need for any post-loading preparatory steps of the samples. The time-domain terahertz signals were used to extract the optical and electrical properties as a function of sample thickness and loading conditions. The residual effect was prominent in the mechanically loaded samples compared to a nearly negligible presence in thermally loaded ones. On average, the thermally loaded polyurea results were subtle compared to the results of the unloaded samples, whereas samples that were mechanically stretched showed a considerable difference. Spectral analysis reported the frequency-dependent, complex refractive index of virgin and loaded polyurea as a function of thickness and spectral peaks associated with fundamental vibrational modes of the polyurea structure. The spectral peaks were in good agreement with previous research while elucidating the residual effect via the disappearance of three peaks in the low terahertz regime for mechanically loaded samples. In general, the refractive index was dependent on the loading conditions. Terahertz spectroscopy was shown to be a promising tool for future in situ and in operando investigations of field-dependent polymer responses.

Does Size Matter? Toxicity Effects of 5‐nm and 70‐nm Silver Nanoparticles on Hoplobatrachus Rugulosus Frog

With the increased usage of silver nanoparticles (AgNPs), the potential impacts of released AgNPs in the environment are increasingly concerned, especially to natural living organisms. Since the properties of AgNPs significantly depend on their sizes, this work aimed to compare the effects of 5-nm and 70‐nm AgNPs on toxicity and bioaccumulation in Hoplobatrachus rugulosus, the edible East Asian Bullfrog. The synthesized AgNPs were characterized by X‐ray diffraction and selected area electron diffraction analyses. Both 5‐nm and 70‐nm AgNPs caused mortality, reduced growth, induced abnormal development, generated cellular oxidative stress, and modulated cellular biomolecule pattern of frog embryos, but at different levels. The 5‐nm AgNPs caused harmful effects on the frog embryos more than 70-nm AgNPs, likely due to their small size to allow more accessibility into the cell. The mortality effects of AgNPs depended on the concentration, exposure time, and size. The malformation of frog embryos in response to AgNPs-exposure included scoliosis, lordosis, kyphosis, and yolk sac edema. Synchrotron Fourier transformed infrared analyses revealed that 5‐nm AgNPs significantly changed the profile of cellular biomolecules in the embryos, indicated by the spectral peaks assigned to lipid, carbohydrates, proteins, and nucleic acids. The bioaccumulation of silvers was dominant in eggs, followed by stomach, liver, kidney, and intestine, respectively, suggesting their translocation via blood circulation. The result of high accumulated silver in eggs and effects on embryonic mortality, growth, development, and cellular changes suggested the potential negative impacts of AgNPs on the sustainability of this frog in the environment.

Characteristics of two tsunamis generated by successive M_w 7.4 and M_w 8.1 earthquakes in Kermadec Islands on March 4, 2021

On March 4, 2021, two tsunamigenic earthquakes (Mw 7.4 and Mw 8.1) occurred successively within 2 h in Kermadec Islands. We examined sea level records at tide gauges located at ~100 km to ~2,000 km from the epicenters, conducted Fourier and Wavelet analyses as well as numerical modelling of both tsunamis. Fourier analyses indicated that the energy of the first tsunami is mainly distributed in the period range of 5–17 min, whereas it is 8–28 min for the second tsunami. Wavelet plots showed that the oscillation of the first tsunami continued even after the arrival of the second tsunami. As the epicenters of two earthquakes are close (~ 55 km), we reconstructed the source spectrum of the second tsunami by using the first tsunami as the empirical Green’s function. The main spectral peaks are 25.6 min, 16.0 min, and 9.8 min. The results are similar to those calculated using tsunami/background ratio method and also consistent with source models.

Acoustic differentiation and classification of wild belugas and narwhals using echolocation clicks

Belugas (Delphinapterus leucas) and narwhals (Monodon monoceros) are highly social Arctic toothed whales with large vocal repertoires and similar acoustic profiles. Passive Acoustic Monitoring (PAM) that uses multiple hydrophones over large spatiotemporal scales has been a primary method to study their populations, particularly in response to rapid climate change and increasing underwater noise. This study marks the first acoustic comparison between wild belugas and narwhals from the same location and reveals that they can be acoustically differentiated and classified solely by echolocation clicks. Acoustic recordings were made in the pack ice of Baffin Bay, West Greenland, during 2013. Multivariate analyses and Random Forests classification models were applied to eighty-one single-species acoustic events comprised of numerous echolocation clicks. Results demonstrate a significant difference between species’ acoustic parameters where beluga echolocation was distinguished by higher frequency content, evidenced by higher peak frequencies, center frequencies, and frequency minimums and maximums. Spectral peaks, troughs, and center frequencies for beluga clicks were generally > 60 kHz and narwhal clicks < 60 kHz with overlap between 40–60 kHz. Classification model predictive performance was strong with an overall correct classification rate of 97.5% for the best model. The most important predictors for species assignment were defined by peaks and notches in frequency spectra. Our results provide strong support for the use of echolocation in PAM efforts to differentiate belugas and narwhals acoustically.

The Cascade Hilbert-Zero Decomposition: A Novel Method for Peaks Resolution and Its Application to Raman Spectra

Raman spectra of biological objects are sufficiently complex since they are comprised of wide diffusive spectral peaks over a noisy background. This makes the resolution of individual closely positioned components a complicated task. Here we propose a method for constructing an approximation of such systems by a series, respectively, to shifts of the Gaussian functions with different adjustable dispersions. It is based on the coordination of the Gaussian peaks’ location with the zeros of the signal’s Hilbert transform. The resolution of overlapping peaks is achieved by applying this procedure in a hierarchical cascade way, subsequently excluding peaks of each level of decomposition. Both the mathematical rationale for the localization of intervals, where the zero crossing of the Hilbert-transformed uni- and multimodal mixtures of Gaussians occurs, and the step-by-step outline of the numerical algorithm are provided and discussed. As a practical case study, we analyze results of the processing of a complicated Raman spectrum obtained from a strain of Mycobacterium tuberculosis. However, the proposed method can be applied to signals of different origins formed by overlapped localized pulses too.

Development of self-cleaning SERS-active nanostructures based on ZnO nanorods and Ag nanoparticles

This work demonstrates the possibility of using a combination of zinc oxide nanorods with silver nanoparticles as a self-cleaning SERS substrate. In addition to Raman scattering enhancement such structures demonstrate the self-cleaning effect during UV treatment. The ZnO nanorods (NRs) array was synthesized on a ZnO seed layer by the hydrothermal method. The Ag nanoparticles (NPs) array was formed by vacuum thermal evaporation over the ZnO NRs. Rhodamine-B 230 μM solution has been detected using the formed SERS-substrates without additional mathematical processing of the Raman spectra. Subsequent UV radiation treatment showed a 3-fold decrease in the intensity of the spectral peaks of the analyte.

Resonances and Lander Modes Observed by InSight on Mars (1–9 Hz)

ABSTRACT The National Aeronautics and Space Administration’s (NASAs) Interior exploration using Seismic Investigations, Geodesy and Heat Transport (InSight) lander successfully touched down on Mars in November 2018, and, for the first time, a seismometer was deployed on the surface of the planet. The seismic recordings reveal diurnal and seasonal changes of the broadband noise level that are consistent with variations of the local atmospheric conditions. The seismic data include a variety of spectral peaks, which are interpreted as wind-excited, mechanical resonances of the lander, resonances of the subsurface, or artifacts produced in the measurement system. Understanding the origin of these signals is critical for the detection and characterization of marsquakes as well as for studies investigating the ambient noise. We identify the major spectral peaks up to 9 Hz, corresponding to the frequency range the most relevant to observed marsquakes. We track the variations in frequency, amplitude, and polarization of these peaks over the duration of the mission so far. The majority of these peaks can readily be classified as measurement artifacts or lander resonances (lander modes), of which the latter have a temperature-dependent peak frequency and a wind-sensitive amplitude. Of particular interest is a prominent resonance at 2.4 Hz, which is used to discriminate between seismic events and local noise and is possibly produced by a subsurface structure. In contrast to the lander modes, the 2.4 Hz resonance has distinctly different features: (1) a broad and stable spectral shape, slightly shifted on each component; (2) predominantly vertical energy; (3) temperature-independent peak frequency; (4) comparatively weak amplification by local winds, though there is a slow change in the diurnal and seasonal amplitude; and (5) excitation during all seismic events that excite this frequency band. Based on these observations, we suggest that the 2.4 Hz resonance is the only mode below 9 Hz that could be related to a local ground structure.

Separating neural oscillations from aperiodic 1/f activity: challenges and recommendations

Electrophysiological power spectra typically consist of two components: An aperiodic part usually following an 1/f power law P∝1/fβ and periodic components appearing as spectral peaks. While the investigation of the periodic parts, commonly referred to as neural oscillations, has received considerable attention, the study of the aperiodic part has only recently gained more interest. The periodic part is usually quantified by center frequencies, powers, and bandwidths, while the aperiodic part is parameterized by the y-intercept and the 1/f exponent β. For investigation of either part, however, it is essential to separate the two components. In this article, we scrutinize two frequently used methods, FOOOF (Fitting Oscillations & One-Over-F) and IRASA (Irregular Resampling Auto-Spectral Analysis), that are commonly used to separate the periodic from the aperiodic component. We evaluate these methods using diverse spectra obtained with electroencephalography (EEG), magnetoencephalography (MEG), and local field potential (LFP) recordings relating to three independent research datasets. Each method and each dataset poses distinct challenges for the extraction of both spectral parts. The specific spectral features hindering the periodic and aperiodic separation are highlighted by simulations of power spectra emphasizing these features. Through comparison with the simulation parameters defined a priori, the parameterization error of each method is quantified. Based on the real and simulated power spectra, we evaluate the advantages of both methods, discuss common challenges, note which spectral features impede the separation, assess the computational costs, and propose recommendations on how to use them.