Aims.
We present a variability study of the blazar PKS 0346−27 conducted between December 2018 and January 2022 using archival
γ
-ray observations from
Fermi
-LAT.
Methods.
We used Lomb–Scargle ...periodogram and weighted wavelet transform methods to detect the presence of periodicity or quasi-periodicity and localize this feature in time and frequency space. We estimated the significance of the periodicity feature using a Monte Carlo simulation approach. We also determined the global significance of the periodicity to test the robustness of our claim. To explore the most probable scenario, we modeled the light curve with both a straight-jet and a curved-jet model.
Results.
We detect a periodicity feature of ∼100 days in the entire period of observation with a statistical significance of 3
σ
, which amounts to a 99.7% confidence level. The global significance of this feature is found to be 96.96%. Based on the Akaike information criterion, the most probable explanation is that the observed emission is enhanced due to the helical motion of a blob within a curved jet.
Conclusions.
The origin of this quasi-periodic oscillation is very likely a region of enhanced emission moving helically inside a curved jet. This work presents strong evidence for jet curvature in the source and an independent (albeit a little serendipitous) procedure to estimate the curvature in blazar jets.
We studied the formation mechanism of dendritic fibrous nanosilica (DFNS) that involves several intriguing dynamical steps. Through electron microscopy and real-time small-angle X-ray scattering ...studies, it has been demonstrated that the structural evolution of bicontinuous microemulsion droplets (BMDs) and their subsequent coalescence, yielding nanoreactor template, is responsible for to the formation of complex DFNS morphology. The role of cosurfactant has been found to be quite crucial, which allowed the understanding of this intricate mechanism involving the complex interplay of self-assembly, dynamics of BMDs formation, and coalescence. The role of BMDs in formation of DFNS has not been reported so far and the present work allows a deeper molecular-level understanding of DFNS formation.
Abstract
A detailed study of the BL Lacertae PKS 0903-57 has been done for the first time with 12 yr of Fermi Large Area Telescope data. We have identified two bright gamma-ray flares in 2018 and ...2020. Many substructures were observed during multiple time binning of these flares. We performed a detailed temporal and spectral study on all the substructures separately. A single-zone emission model is used for time-dependent leptonic modeling of the multiwavelength spectral energy distributions. Our estimated values of variability timescale, magnetic field in the emission region, and the jet power obtained from leptonic modeling of PKS 0903-57 are presented in this work. Currently, we have a minimal number of observations in X-rays and other bands. Hence, further simultaneous multiwavelength monitoring of this source is required to have a better understanding of the physical processes occurring in the jet of the blazar PKS 0903-57.
Abstract
We report the results from our study of the blazar S5 1803+784 carried out using quasi-simultaneous
B
,
V
,
R
, and
I
observations from 2020 May to 2021 July on 122 nights. Our observing ...campaign detected a historically bright optical flare during MJD 59,063.5−MJD 59,120.5. We also found the source in its brightest (
R
mag
= 13.617) and faintest (
R
mag
= 15.888) states to date. On 13 nights, covering both flaring and nonflaring periods, we searched for intraday variability using the power-enhanced
F
-test and the nested ANOVA test. We found significant variability in 2 of these 13 nights. However, no such variability was detected during the flaring period. From correlation analysis, we observed that the emission in all optical bands were strongly correlated with a time lag of ∼0 days. To get insights into its dominant emission mechanisms, we generated the optical spectral energy distributions of the source on 79 nights and estimated the spectral indices by fitting a simple power law. The spectral index varied from 1.392 to 1.911 and showed significant variations with time and
R
-band magnitude. We detected a mild bluer-when-brighter (BWB) trend during the whole monitoring period and a much stronger BWB trend during the flare. We also carried out a periodicity search using four different methods and found no significant periodicity during our observation period. Based on the analysis during the flaring state of the source one can say that the emissions most likely originate from the jet rather than from the accretion disk.
As the cracking mode (tensile or shear) of a crack is related to the underlying physical mechanisms, crack mode classification is a very useful method to identify the damage state of a structure for ...proper maintenance to enhance structural safety and durability. Acoustic Emission (AE) is a passive structural health monitoring technique based on the stress wave generated due to cracking in a structure. A framework has been designed in this study for automated probabilistic classification of the cracks in cementitious components based on the AE signals. With this approach, unlabeled hand designed waveform parameters, i.e. RA values (RA) and Average frequency (AF) are clustered using density dictated unsupervised clustering algorithm. Intersecting clusters in the data were then separated through a hyperplane created using Support Vector Machine (SVM) algorithm. Based on physical insight obtained from labeled data, unlabeled data was classified into events corresponding to different cracking modes. The framework was applied to the analysis of AE data from Steel Fiber Reinforced Concrete (SFRC) beam under bending and Strain Hardening Cementitious Composite (SHCC) samples under direct tension. The cracking modes obtained from the proposed machine learning approach are found to be in good agreement with expectations based on composite theory. With good qualitative prediction, the proposed approach shows promise for the prediction of damage state in structures based on unlabeled data obtained in the field.
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Spray drying is a facile technique to transform colloidal dispersion into micro-granules of controlled size, shape, and morphology. There is significant interest to understand the ...structural integrity, different morphology of the granules obtained post spray drying which find potential application in many technological fields. The shape of the constituent particles in the colloidal dispersion that is spray dried is expected to influence the micro-structural features of the micro-granules.
We investigate the formation of micro-granules consisting of nano-ellipsoids through controlled spray drying. The morphological features and the packing of ellipsoids in the granules are quantitatively analyzed by using small angle neutron scattering, small angle X-ray scattering and high-resolution field emission scanning electron microscopy. The time evolution of the micro-structure and the structural integrity of the granules are investigated by re-dispersing the powder granules in water.
The morphology of the granules are found to be strongly correlated with the aspect ratio of the ellipsoid. While the drying of droplets containing lower aspect ratio ellipsoids give rise to mostly spherical granules, in stark contrast, for higher aspect ratio ellipsoids, micro-granules of different morphologies are formed including doughnut shaped granules. A plausible mechanism explaining such an aspect ratio dependent shape transformation is proposed.
Co-RGO nanocomposites are known to show interesting properties suitable for various applications. However, its use in the vital field of plasmonic nanocomposites is restricted as Co nanoparticles ...have high damping and dielectric loss. In this work, we have demonstrated a simple synthetic way to produce water-dispersible shape variant Co-reduced graphene oxide (RGO) hybrid nanocomposites, which can overcome those barriers and delineate two plasmonic peaks. Prepared multifunctional optical materials show both UV and visible range of plasmonic responses of Co NPs. While the single domain Co NPs show spin-up channel based sharp plasmonic peak in the UV range, the larger particles introduce shape-dependent enhancement of the excitation independent blue photoluminescence of graphene oxide (GO). Usually, due to their different size regime, it is not possible to see both UV and visible range plasmonic responses of Co NPs simultaneously. The variation of the Co particle size was deliberate to achieve multifunctionality. Shape-induced enhancement in the PL spectrum and decoration of plasmonic metal NPs are achieved. TEM micrographs of hybrids confirm the decoration of different shapes of Co nanoparticles on RGO sheets. The size distribution of the nanoparticles in the composites was quantified using two complementary techniques; SAXS/SANS and TEM. Scattering revealed the alteration of RGO agglomeration with the incorporation of differently shaped nanoparticles. Prepared hybrid nanocomposite having both the responses could be promising in magnetoplasmonics, GMR- and doping-based optoelectronics.
For strain-hardening cementitious composites (SHCCs) the knowledge of operating regime is important for maintenance planning and monitoring of the element. This paper presents a methodology of regime ...discrimination for SHCC from acoustic emission (AE) signals. From an AE signal, various damage indicators (DIs) can be derived. A new DI called Power Spectral Entropy (PSE) is developed in this paper. New benchmarks are developed to quantify possible effect of external factors on the measurement accuracy. Theoretical results indicate that the PSE is Signal to Noise Ratio (SNR) invariant, insensitive to the choice of subjective parameters and can be performed in real time. PSE was then obtained from the test result of SHCC with elastic behavior followed by strain hardening and softening. The test results indicate that the PSE varies with strain in a very similar way to the applied load. An approach to distinguish between different operating regimes of a SHCC component based on PSE is then proposed and validated. The practical applicability of PSE is hence demonstrated.
Abstract
The continuous monitoring capability of Fermi-LAT has enabled the exploration of quasiperiodic oscillations (QPOs) in the
γ
-ray light curve of blazars that has given a new perspective to ...probe these sources over a wide range of timescales. We report the presence of transient QPOs in the long-term
γ
-ray light curve of blazars PKS 0244-470 and 4C +38.41. We first identified different flux states using the Bayesian block algorithm and then explored the possible transient QPOs in the segments of each flux phase where the flux level changes over fairly regular intervals. Combining this with the source’s intrinsic variance, we identified two flux phases for PKS 0244-470: one activity (AP-1) and one quiescent phase (QP-1). For 4C+38.41, we similarly identified four activity (AP-1, AP-2, AP-3, and AP-4) and two quiescent (QP-1 and QP-2) phases. The AP-1 phase of PKS 0244-470 shows QPO of ∼225 days persisting for eight cycles (∼4.1
σ
). In 4C+38.41, AP-1 and AP-2 phases show QPO-like behavior of ∼110 days and ∼60 days, respectively, persisting for five cycles. In AP-3, we identified three subphases, and all show a ∼7 day scale possible recurrent rise with five complete cycles, while in QP-1, we could identify two subphases (Q1 and Q2). The Q1 phase shows a period of ∼104 days with six complete cycles. The Q2 phase also shows QPO but with only ∼3.7 cycles. We discuss the possible origin and argue that the current-driven kink instability and curved jet model seem to be the most likely causes for shorter and longer QPOs.
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