Large Area Research Articles

High enhancement, low cost, large area surface enhanced Raman scattering substrates all by atomic layer deposition on porous filter paper

We successfully developed an atomic layer deposition (ALD) method for making Ag noble nanoparticles on cheap, commercial filter paper consisting of three-dimensional porous glass fibers and investigated the evolution of Ag nanostructures with some key process parameters. By tuning Ag particle sizes and controlling the cycle numbers of ALD deposited Ag films, we were able to obtain high-density isolated Ag nanoparticles with average sizes in 3–9 nm without the formation of agglomerates and continuous Ag films. We proved the presence of strong localized surface plasmon resonance peaks near a target wavelength of 632 nm. We further proved the presence of surface enhanced Raman scattering (SERS) signals on the Ag coated filter paper substrates using pyridine as the test analyte. Our results demonstrate that ALD is a very promising technique for a rational design of SERS substrates and, thus, has great potential for the fabrication of large-area, low-cost SERS substrates for future commercial applications, as compared to other existing techniques.

Exploring safety culture within inpatient mental health units: The results from participant observation across three mental health services.

In Australia, acute inpatient units within public mental health services have become the last resort for mental health care. This research explored barriers and facilitators to safe, person-centred, recovery-oriented mental health care in these settings. It utilised participant observations conducted by mental health nurses in acute inpatient units. These units were located in three distinct facilities, each serving different areas: a large metropolitan suburban area in a State capital, a mid-sized regional city, and a small city with a large rural catchment area. Our findings highlighted that, in the three inpatient settings, nurses tended to avoid common areas they shared with consumers, except for brief, task-related visits. The prioritisation of administrative tasks seemed to arise in a situation where nurses lacked awareness of alternative practices and activities. Consumers spent prolonged periods of the day sitting in communal areas, where the main distraction was watching television. Boredom was a common issue across these environments. The nursing team structure in the inpatient units provided a mechanism for promoting a sense of psychological safety for staff and were a key element in how safety culture was sustained.

Efficient separation of radium from natural thorium using a mesoporous silica-supported composite resin with sulfonic acid groups for the acquisition of targeted α-nuclides 212Pb

212Pb serves as one of the most important nuclides for targeted alpha therapy (TAT), with good potential in the treatment of malignant tumors. However, medical and clinical applications are seriously limited by its extremely short supply, which strongly depends on the acquisition of its parent nuclides such as 228Ra or 224Ra. To address this issue, we conducted a systematic investigation on the separation of trace radium from natural thorium using the ion exchange chromatography method, and a novel porous silica-based composite resin functionalized with sulfonic acid groups was prepared, characterized, and employed. Experimental results showed that the silica-supported resin was successfully prepared with the sulfonic acid groups, and possessed small particle size, mesoporous pore structure and large specific surface area. The resin exhibited high selectivity toward thorium compared with barium, and the separation factor reached 123 at low acidity and at low temperature. The resin demonstrated a fast adsorption speed and an excellent separation performance, and the adsorption mechanism was confirmed based on the ion exchange between the sodium carried and the target cations. On the basis, column experiments were further conducted and finally the separation of trace radium from thorium was realized using a small column filled with about 1.0 g resin. The chemical recovery of radium reached 97 %, and the decontamination factor for thorium exceeded 40,000. This work verifies the feasibility of directly extracting 228Ra and 224Ra from natural thorium using the sulfonic acid group functionalized materials in the dilute nitric acid solution, and presents an excellent material and systematic experimental data on the separation activities, rendering this study particularly significant.

Preparation of microbial agent immobilized composites for Cr(VI) removal from wastewater

ABSTRACT Because of its extreme toxicity and health risks, hexavalent chromium [Cr(VI)] has been identified as a major environmental contaminant. Bioreduction is considered as one of effective techniques for cleaning up Cr(VI)-contaminated sites, but the remediation efficiency needs to be enhanced. Here, a novel immobilized microbial agent was produced by immobilizing Bacillus cereus ZY-2009 with sodium alginate (SA) using polyvinyl alcohol (PVA) and activated carbon (AC). To evaluate the decrease of Cr(VI) by immobilized bacterial agents, batch tests were conducted with varying immobilization conditions, immobilization carriers, and dosages of medication. The removal of Cr(VI) by the agent prepared by the composite immobilization method was better than that by the adsorption and encapsulation methods. The optimal preparation conditions were the fraction of magnetic PVA was 5.00%, the fraction of SA was 4.00%, the fraction of CaCl2 was 4.00%, and the calcification time was 12 h. The experimental results indicated that PVA/SA/AC agents accelerated the reduction rate of Cr(VI). The removal rate of Cr(VI) by immobilized cells (90.5%) under ideal conditions was substantially higher than that of free cells (11.0%). This novel agent had a large specific surface area and a rich pore structure, accounting for its high reduction rate. The results suggest that the PVA/SA/AC immobilized Bacillus cereus ZY-2009 agent has great potential to remove Cr(VI) from wastewater treatment systems.

Synergistic removal of dimethoate through adsorption and photocatalytic oxidation in the presence of FeTiO3@Ag/Ag2O heterojunction

Combining adsorption and photocatalysis as a synergistic technique has become a research trend since adsorption is a prerequisite for photocatalytic surface reactions. In this study, a Z-scheme heterojunction FeTiO3@Ag/Ag2O with local surface plasmon resonance (LSPR) effect was fabricated for the removal of dimethoate from water. Under visible light irradiation, dimethoate could be completely removed within 75 min in the presence of 0.3 g/L FeTiO3@Ag/Ag2O (with Ag2O percentage of 10 wt%). High removal efficiency of dimethoate was mainly attributed to the synergistic effect between the large specific surface area of the catalyst (160.695 m2/g), the formation of heterojunction of FeTiO3 and Ag2O, and the LSPR effect of metal Ag, which reinforced the absorption of visible light and promoted the separation and transfer of the carriers. Radicals of O2− and OH were the main reactive groups triggered the photocatalytic degradation process of dimethoate. Density Functional Theory (DFT) calculations indicate that PS and P–S bonds in the dimethoate molecule were more susceptible to be attacked by reactive groups. The degradation pathways mainly include oxidation of PS bond and cleavage of P–S bond, and the toxicity of most intermediates was reduced when compared with the parent compound. This study exploited the role of adsorption and photocatalysis in the field of pollutant removal, and provides ideas for the preparation of bifunctional photocatalysts.

A REVIEW ON MOUTH DISSOLVING FILM- A NOVEL APPROACH

The oral route is one of the most important routes for local and systemic drug delivery due to its large surface area, high permeability and blood flow. Mouth dissolving films are the most advanced oral forms as they are simpler and easier to use than other dosage forms such as Oro-soluble tablets, sublingual tablets. Fast dissolving drug delivery system were rapidly developed in the 1970s as an alternative to capsules, syrups, and tablets for adults and adolescents who have difficulty swallowing conventional oral solid dosage form. The Oro- soluble film dissolves and disintegrates in less than a minute when placed in the mouth without drinking water or chewing. This form allows the drug to skip first-pass metabolism, which improve the bioavailability of the drug. This article provides a comprehensive review on mechanism of action, merits, formulation, evaluation and covering the aspects related to novel fast dissolving techniques.

The Remarkable Predictive Power of Infrared Data of Blazars

Blazars are the brightest and most abundant persistent sources in the extragalactic γ-ray sky. Due to their significance, they are often observed across various energy bands, where the data of which can be used to explore potential correlations between emission at different energies, yielding valuable insights into the emission processes of their powerful jets. In this study we utilized IR data at 3.4 and 4.6 μm from the Near-Earth Object Wide-field Infrared Survey Explorer Reactivation Mission, spanning 8 yr of observations, X-ray data from the Neil Gehrels Swift Observatory collected throughout the satellite’s lifetime, and 12 years of γ-ray measurements from the Fermi Large Area Telescope’s all-sky survey. Our analysis reveals that the IR spectral slope reliably predicts the peak frequency and maximum intensity of the synchrotron component of blazar spectral energy distributions, provided it is uncontaminated by radiation unrelated to the jet. A notable correlation between the IR and γ-ray fluxes was observed, with the BL Lacertae subclass of blazars displaying a strong correlation coefficient of r = 0.80. IR band variability is more pronounced in flat spectrum radio quasars than in BL Lacertae objects, with mean fractional variability values of 0.65 and 0.35, respectively. We also observed that the synchrotron peak intensity of intermediate-high-energy-peaked objects can forecast their detectability at very high γ-ray energies. We used this predicting power to identify objects in current catalogs that could meet the detection threshold of the Cerenkov Telescope Array extragalactic survey, which should encompass approximately 180 blazars.

Response of silicon solar cells to neutrons in post-detonation monitoring

In this study, we evaluated the feasibility of using solar photovoltaic (PV) panels for the detection of prompt neutrons from a nuclear denotation. Monte Carlo (MC) simulations were performed to evaluate the response of silicon (Si) solar cells (SCs) to neutrons and support the experiments. The response of Si SCs to fission spectrum neutrons was measured experimentally using the fast neutron beam of a research reactor. Steady-state neutron measurements indicated a clear response of the Si SCs, which correlated with changes in the neutron intensity. Time-modulated neutron measurements performed using a neutron chopper demonstrated a clear transient response of Si SCs to neutrons, which was observed in the signal power spectral density plots containing peaks corresponding to frequencies of neutron pulses produced by the chopper. The resulting signal was found to be small, which was attributed to the extremely small active neutron interaction volume inside the SCs. In a real detonation scenario, the transient neutron flux is expected to be higher, and the effective neutron interaction volume of large area solar PV panels is much larger, which could significantly boost the signal. The study, overall, demonstrated the potential of large area solar PV panels or a solar farm for prompt detection and identification of a nuclear detonation.

Resolving soft X-ray photons with a high-rate hybrid pixel detector

Due to their high frame rates and dynamic range, large area coverage, and high signal-to-noise ratio, hybrid silicon pixel detectors are an established standard for photon science applications at X-ray energies between 2 keV and 20 keV. These properties also make hybrid detectors interesting for experiments with soft X-rays between 200 eV and 2 keV. In this energy range, however, standard hybrid detectors are limited by the quantum efficiency of the sensor and the noise of the readout electronics. These limitations can be overcome by utilizing inverse Low-Gain Avalanche Diode (iLGAD) sensors with an optimized X-ray entrance window. We have developed and characterized a prototype soft X-ray iLGAD sensor bonded to the charge integrating 75 µm pixel JUNGFRAU chip. Cooled to −22°C, the system multiplication factor of the signal generated by an impinging photon is ≥ 11. With this gain, the effective equivalent noise charge of the system is ≤5.5 electrons root-mean-square at a 5 µs integration time. We show that by cooling the system below −50°C, single photon resolution at 200 eV becomes feasible with a signal-to-noise ratio better than 5.

Research on correlation between dynamic resilient modulus and CBR of coarse-grained chlorine saline soil

A large area of coarse-grained saline soil is distributed in saline soil areas, and chlorine saline soil with a high salt content is a typical representative. The dynamic resilient modulus was accurately predicted using the California-bearing ratio (CBR) value to determine the relationship between the dynamic resilient modulus of coarse-grained chloride saline soil and its CBR value. Indoor dynamic triaxial tests and CBR tests were conducted to investigate the evolution of the dynamic resilient modulus (MR) and CBR of coarse-grained chlorine saline soil under the influence of the stress level, water content, and salt content. The test results showed that the dynamic resilient modulus increased with an increase in the confining pressure and bulk stress and decreased as the deviator stress increased; however, the CBR increased with an increase in the corresponding unit pressure. The higher the salt and water contents, the more obvious the influence of stress on the dynamic resilient modulus and CBR value. Under the same stress level, the decrease in the dynamic resilient modulus and CBR gradually increased with increasing salt and moisture content, and the effect of salt tended to be more significant than that of water. Based on the correlation between the dynamic resilient modulus and CBR revealed by the experiment, a more widely applicable model was selected from the existing theoretical models related to CBR for the regression analysis of the test data, and a prediction model of the dynamic resilient modulus based on the CBR value was proposed (MR = 21.06CBR0.52). This prediction model had a high correlation coefficient (R2 = 0.893) and could effectively predict the dynamic resilient modulus of coarse-grained chlorine saline soil using CBR values. The results provide a simple and reliable method for determining the design parameters of a coarse-grained saline soil subgrade.

Very High-energy (>50 GeV) Gamma-Ray Flux Variability of Bright Fermi Blazars

Understanding the high-energy emission processes and variability patterns are two of the most challenging research problems associated with relativistic jets. In particular, the long-term (months to years) flux variability at very high energies (VHE >50 GeV) has remained an unexplored domain so far. This is possibly due to the decreased sensitivity of the Fermi Large Area Telescope (LAT) above a few GeV, hence low photon statistics, and observing constraints associated with the ground-based Cherenkov telescopes. This paper reports the results obtained from the 0.05−2 TeV Fermi-LAT data analysis of a sample of 29 blazars with the primary objective to explore their months-to-year-long very high-energy (VHE) flux variability behavior. This systematic search has led to, for the first time, the detection of significant flux variations in five blazars at the >99% confidence level, whereas eight of them exhibit variability, albeit at a lower confidence level (∼95%–99%). A comparison of the 0.05–2 TeV flux variations with that observed at 0.1–50 GeV band has revealed similar variability behavior for most of the sources. However, complex variability patterns that are not reflected contemporaneously in both energy bands were also detected, thereby providing tantalizing clues about the underlying radiative mechanisms. These results open up a new dimension to unravel the VHE emission processes operating in relativistic jets, hence sowing the seeds for their future observations with the upcoming Cherenkov Telescope Array.

Biomass C-doped three-dimensional Bi2WO6 for enhanced visible-light-driven photodegradation of diclofenac and rhodamine B

Photocatalysis as a green and efficient pollutant degradation technology, displaying great potential in environmental purification. By one step hydrothermal method in this study, flower-like Bi2WO6 with a large specific surface area was obtained, and the preparation of biomass carbon modified Bi2WO6 with sorghum stalks was also proposed to construct a series (BWO/x%C). The composites were effectively characterized in terms of several aspects of structure and properties. With the dyes rhodamine B and diclofenac as typical organic pollutants, the photocatalytic activity of the proposed photocatalysts was evaluated. Under visible light irradiation, the removal of rhodamine B by BWO/4%C reached 97.27% within 50 min and that of diclofenac reached 96.19% within 120 min, which were significantly favorable to single-phase Bi2WO6. The superiority of this system BWO/4%C is mainly due to its large specific surface area (33.51 m2/g), which provides additional reaction sites for contaminants. The UV–Vis DRS findings indicated that the modified biomass C reduced the band gap of Bi2WO6 and improved the availability of Bi2WO6 to visible light, and the separation efficiency of the electron and hole pairs of Bi2WO6 was improved due to the strong electron transfer ability of biomass C. The analyzing results of free radical trapping experiments confirmed that h+ and •O2- are the main active substances involved in the photodegradation reaction. The results of five cycle experiments exhibited that the degradation rate of rhodamine B still reached higher than 90%, confirming the good stability of the prepared material. Finally, a feasible degradation mechanism was proposed for the degradation of rhodamine B and diclofenac. It offers new ideas for the development of composite nano-photocatalytic materials targeting difficult-to-degrade organic pollutants.

3D WO3/BiMOF/Bi2WO6 with rich vacancies defects self-assembled via H2BDC anchoring Bi source of Bi2WO6 for high-performance visible light-driven nitrogen fixation and organic pollutant degradation

A novel photocatalyst WO3/BiMOF/Bi2WO6 was prepared by self-assembly of benzene dicarboxylic acid ligand (H2BDC) anchoring Bi source on the surface of Bi2WO6 to form BiMOF, in which WO3 spherical particles were scattered uniformly. Thereby, an amount of metal and oxygen vacancies (VM + O) are generated. The 3D flower-like spherical photocatalyst has a large specific surface area and close interfacial contacts, which can provide sufficient channels for carrier migration. The introduction of BiMOF enhanced the light absorption capability of photocatalyst. As a result, the flower-like WO3/BiMOF/Bi2WO6 structure exhibits excellent nitrogen fixation as well as high-level photocatalytic activity in degrading Rhodamine B (RhB) and tetracycline (TC) under visible light. For one thing, WO3/BiMOF/Bi2WO6 produce ammonia up to 227 μmol L−1 h−1. For another, the degradation efficacy displayed by RhB 99.3% in 15 min and TC 93.6% degradation in 50 min, respectively. In addition, the catalysts showed excellent cyclic stability, with constant degradation efficiencies for at least 4 cycles. The experimental results of free radical scavenging showed that holes (h+) and superoxide radical (·O2−) were the main active substances in the photodegradation process. Therefore, the photocatalytic mechanism of 3D flower-like WO3/BiMOF/Bi2WO6 was also proposed.

Determination of ascorbic acid in biological samples using an electrochemical sensor modified with Au-Cu2O/MWCNTs nanocomposite

In this study, we developed a novel electrochemical sensor for measuring ascorbic acid (AA) or vitamin C (C6H8O6) in urine samples. The sensor was designed using a glassy carbon electrode that was modified with a nanocomposite of Au-Cu2O and MWCNTs. We investigated the characteristics of the nanocomposite using FE-SEM, TEM, XRD, and EDS. Cyclic voltammetry (CV) was used to determine the electrochemical behavior of the modified electrode and how AA is electrooxidized. Based on the electrochemical experiments, the sensor can detect trace levels of AA through voltammetry at a working potential of 0.5 vs. Ag/AgCl. We studied and modified several experimental parameters such as the supporting electrolyte, accumulation potential, solution pH, accumulation time, and amount of modifier to optimize the performance of the sensor. Furthermore, the proposed electrode exhibited a wide linear dynamic range of 1–200 μM, with a low detection limit (S/N = 3) of 0.3 μM. The use of MWCNT semiconductors and Au nanoparticles in electrode modification likely contributed to these favorable results. The outstanding properties of the nanocomposite include a large surface area, exceptional electrical conductivity, and strong electrocatalytic activity.

Computational investigation of thallium interactions with functionalized multi-walled carbon nanotubes for electrochemical sensing applications

Abstract Thallium (Tl) is a heavy toxic element which can cause several health issues. WHO and EPA have set a maximum permissible limit for thallium in drinking water above which it is hazardous, so its determination in our environment becomes crucial. Multi-walled carbon nanotubes (MWCNTs) are preferred for use in thallium sensing due to their large surface area and high conductivity, which allow them to be readily functionalized to selective groups. Previous experimental results showed that Tl selectively interacted with the MWCNTs functionalized with 3-amino-1,2,4-triazole-5-thiol (T-MWCNTs) with a limit of detection of 1.29 μg L−1 and linear range 10–100 μg L−1 by using voltammetry under optimized conditions. In actual water samples, the electrochemical sensor fabricated with the above-mentioned functionalized MWCNTs nanocomposite demonstrated high reproducibility and recovery. Molecular recognition and the outcomes of chemical and biological processes are shaped by non-covalent interactions among molecules. It is essential to investigate how these interactions impact binding preferences to enhance our understanding of these events. Here, we examine the structures of complexes of Tl and T-MWCNTs using quantum chemical calculations. Our results show that the most favourable complex of Tl-T-MWCNTs involve strong interaction of Tl with the nitrogen lone pair and additional stabilising interaction provided by the oxygen lone pair of amide linkage of T-MWCNTs. Moreover, we observed that the thiol group within T-MWCNTs readily undergoes deprotonation due to its acidic nature. Non-covalent interactions among molecules influence chemical and biological processes and molecular recognition. To improve our knowledge of these events, it is important to explore the ways in which these interactions affect binding preferences The negative value of adsorption energy (−1.53 eV) of this structure suggested that the interaction process between Tl and T-MWCNTs is spontaneous.

An integrally bilayered flexible cathode woven from CNTs for homogeneous hosting and fast electrocatalytic conversion of Li2O2 in Li-O2 battery

Due to the ultrahigh theoretical energy density, Li-O2 batteries are considered as potential candidates for power accessories for wearable electronic devices. An effective oxygen-breathing cathode is essential to enable high cyclic stability in Li-O2 batteries. Herein, an integrally bilayered, freestanding flexible Li-O2 battery cathode is constructed by in-situ growth of a layer of microflowers (which is an assembly of nitrogen-doped carbon nanotubes embedded with cobalt nanoparticles) on the surface of a CNT-interwoven film. Owing to the integrally bilayered structural feature and its compositional merits, such three-dimensionally conductive network provides a large space and surface area for homogeneous hosting and also enables efficient electrocatalytic conversion of the insulating Li2O2 solids. Thus obtained cathode delivers a large full capacity of 8.03 mAh cm−2; it also exhibits a low charge potential of approximately 3.6 V and excellent cyclic stability for stable operation up to nearly 2 months at a capacity of 0.1 and 1 mAh cm−2. Moreover, being flexible and binder-free, the cathode is highly robust, which can withstand repetitive folding and unfolding. A co-axial Li-air battery was fabricated accordingly, which exhibits excellent tolerance to bending deformation, showing great potential for application in flexible and wearable electronics.

Molecular Connectors Boosting the Performance of MoS2 Cathodes in Zinc-Ion Batteries.

Zinc-ion batteries (ZIBs) are promising energy storage systems due to high energy density, low-cost, and abundant availability of zinc as a raw material. However, the greatest challenge in ZIBs research is lack of suitable cathode materials that can reversibly intercalate Zn2+ ions. 2D layered materials, especially MoS2-based, attract tremendous interest due to large surface area and ability to intercalate/deintercalate ions. Unfortunately, pristine MoS2 obtained by traditional protocols such as chemical exfoliation or hydrothermal/solvothermal methods exhibits limited electronic conductivity and poor chemical stability upon charge/discharge cycling. Here, a novel molecular strategy to boost the electrochemical performance of MoS2 cathode materials for aqueous ZIBs is reported. The use of dithiolated conjugated molecular pillars, that is, 4,4'-biphenyldithiols, enables to heal defects and crosslink the MoS2 nanosheets, yielding covalently bridged networks (MoS2-SH2) with improved ionic and electronic conductivity and electrochemical performance. In particular, MoS2-SH2 electrodes display high specific capacity of 271.3 mAh g-1 at 0.1 A g-1, high energy density of 279Whkg-1, and high power density of 12.3 kW kg-1. With its outstanding rate capability (capacity of 148.1 mAh g-1 at 10 A g-1) and stability (capacity of 179 mAh g-1 after 1000 cycles), MoS2-SH2 electrodes outperform other MoS2-based electrodes in ZIBs.

Principle and practice of hydraulic softening top-cutting and pressure relief technology in weakly cemented strata

Extremely thick and hard roofs are difficult to break in the mining of a working face, and the large area of the suspended roof easily induces a strong ground pressure or dynamic impact disasters. The roof control of a coal mining face in a mine in western China was taken as a case study. The mineral composition, microstructure, and hydrophysical properties of the hard roof overlying the coal seam were analyzed. The characteristics of the weak-cementation strata that are prone to mud and collapse when encountering water were targeted to investigate the hydraulic softening roof-cutting and pressure relief technology. It was found that the clay mineral composition in the roof plate accounts for 60.6%. After 24 h of natural immersion, the rock strength decreased by approximately 10.3%–49%, and further immersion caused disintegration. By arranging high and low double-row water injection softening drilling holes in the cutting hole and roadway of the working face, the strength of roof rock strata in the target area was reduced, and the initial weighting step distance and weighting strength of the working face were reduced. The hydraulic softening roof-cutting pressure relief technology effectively regulated the weighting step distance of the hard roof and the peak weighting of the working face.

Shear performance of high-strength bolt-epoxy bonding composite connector in steel-concrete composite structure

To clarify the shear mechanism of high-strength bolt-epoxy bonding composite connectors in prefabricated steel-concrete composite structures, twenty-one direct shear specimens and six double shear specimens were carried out in this study. The pretension force, interface type, epoxy curing time and loading pattern were considered. Results revealed that the main failure mode of high-strength bolt-epoxy bonding composite connectors was that the large area of epoxy matrix was separated from the steel plate, and the bolt was sheared off. The load-slip curve of composite connector specimens included the elastic stage, epoxy failure stage, frictional slip stage, bolt force transmission stage and failure stage. Compared to the specimens with a bolt connector under recommended pretension, the average initial slip load of composite connector specimens was 437.7% higher. Additionally, the average initial slip load of specimens with 1-day epoxy curing time was 24.4% lower than 7-day curing time, but the average ultimate load and ultimate slip were 12.4% and 29.4% higher, respectively. When the pretension ratio decreased from 1.0 to 0.6, the average initial slip load of specimens with a bolt connector was significantly decreased by 33.0% and the average ultimate slip of composite connector specimens was increased by 18.1%. The average initial slip load and ultimate load of composite connector specimens were comparable under cyclic loading compared to monotonic loading. Upon the experimental results and existing formulas, some equations were proposed for predicting the initial slip load and bearing capacity of steel-concrete composite structures with composite connectors.

Multiwavelength variability analysis of Fermi-LAT blazars

ABSTRACT Blazars present highly variable gamma-ray emission. This variability, which can range from a few minutes to several years, is also observed at other wavelengths across the entire electromagnetic spectrum. We make use of the first 12 yr of data from the Fermi Large Area Telescope, complemented with multiwavelength (MWL) archival data from different observatories and facilities in radio, infrared, and optical bands, to study the possible periodic emission from 19 blazars previously claimed as periodic candidates. A periodicity analysis is performed with a pipeline for periodicity searches. Moreover, we study the cross-correlations between the gamma-ray and MWL light curves. Additionally, we use the fractional variability and the structure function to evaluate the variability time-scales. We find five blazars showing hints of periodic modulation with ≥3.0σ (≈0σ post-trials), with periods ranging from 1.2 to 4 yr, both in their gamma-ray and MWL emission. The results provide clues for understanding the physical mechanisms generating the observed periodicity.