A series of flexible, lightweight, and highly conductive cellulose nanopapers were fabricated through in situ polymerization of aniline monomer on to cellulose nanofibers with a rationale for ...attenuating electromagnetic radiations within 8.2–12.4 GHz (X band). The demonstrated paper exhibits good conductivity due to the formation of a continuous coating of polyaniline (PANI) over the cellulose nanofibers (CNF) during in situ polymerization, which is evident from scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray diffraction analysis. The free hydroxyl groups on the surface of nanocellulose fibers promptly form intermolecular hydrogen bonding with PANI, which plays a vital role in shielding electromagnetic radiations and makes the cellulose nanopapers even more robust. These composite nanopapers exhibited an average shielding effectiveness of ca. −23 dB (>99% attenuation) at 8.2 GHz with 1 mm paper thickness. The fabricated papers exhibited an effective attenuation of electromagnetic waves by a predominant absorption mechanism (ca. 87%) rather than reflection (ca. 13%), which is highly desirable for the present-day telecommunication sector. Unlike metal-based shields, these demonstrated PANI/CNF papers have given a new platform for designing green microwave attenuators via an absorption mechanism. The prime novelty of the present study is that these robust PANI/CNF nanopapers have the ability to attenuate incoming microwave radiations to an extent that is 360% higher than the shielding effectiveness value reported in the previous literature. This makes them suitable for use in commercial electronic gadgets. This demonstrated work also opens up new avenues for using cellulose nanofibers as an effective substrate for fabricating conductive flexible papers using polyaniline. The direct current conductivity value of PANI/CNF nanopaper was 0.314 S/cm, which is one of the key requisites for the fabrication of efficient electromagnetic shields. Nevertheless, such nanopapers also open up an arena of applications such as electrodes for supercapacitors, separators for Li–S, Li–polymer batteries, and other freestanding flexible paper-based devices.
ABSTRACT
The bright blazar OJ 287 is the best-known candidate for hosting a supermassive black hole binary system. It inspirals due to the emission of nanohertz gravitational waves (GWs). ...Observations of historical and predicted quasi-periodic high-brightness flares in its century-long optical lightcurve, allow us to determine the orbital parameters associated with the binary black hole (BBH) central engine. In contrast, the radio jet of OJ 287 has been covered with Very Long Baseline Interferometry (VLBI) observations for only about 30 yr and these observations reveal that the position angle (PA) of the jet exhibits temporal variations at both millimetre and centimetre wavelengths. Here, we associate the observed PA variations in OJ 287 with the precession of its radio jet. In our model, the evolution of the jet direction can be associated either with the primary black hole (BH) spin evolution or with the precession of the angular momentum direction of the inner region of the accretion disc. Our Bayesian analysis shows that the BBH central engine model, primarily developed from optical observations, can also broadly explain the observed temporal variations in the radio jet of OJ 287 at frequencies of 86, 43, and 15 GHz. Ongoing Global mm-VLBI Array (GMVA) observations of OJ 287 have the potential to verify our predictions for the evolution of its 86-GHz PA values. Additionally, thanks to the extremely high angular resolution that the Event Horizon Telescope (EHT) can provide, we explore the possibility to test our BBH model through the detection of the jet in the secondary BH.
The work presented here aims to study and compare the performance of a polyvinylidene fluoride (PVDF) electrospun membrane, unmodified cellulose nanofiber (CNF) based PVDF membrane, and Meldrum’s ...acid (2,2-dimethyl-1,3-dioxane-4,6-dione) modified CNF-based PVDF membranes against the Fe2O3 nanoparticle filtration and crystal violet (CV) dye adsorption. Herein, we introduced a facile method to produce a unique green adsorbent material from cellulose nanofibers (CNFs) via a nonsolvent assisted procedure using Meldrum’s acid as an esterification agent to enhance the adsorption toward positively charged crystal violet dyes. Most of the surface modifications of cellulose nanofibers have been done using toxic organic solvents like pyridine, dimethyl acetate, (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO), etc. So far, this is the first report on the surface modification of cellulose nanofibers via a nonsolvent assisted procedure. Both CNF-based PVDF membranes were prepared by successive coating of modified and unmodified CNFs on to the surface of a PVDF electrospun membrane. All the demonstrated membranes showed high filtration capacity against the Fe2O3 nanoparticles. With the 10 mg/L of crystal violet (CV) aqueous solution, CV adsorption of PVDF electrospun membrane, and unmodified CNF-based PVDF membrane was around 1.368 and 2.948 mg/g of the membrane respectively, whereas it was 3.984 mg/g of the membrane by Meldrum’s acid CNF-based PVDF membrane. The demonstrated Meldrum’s acid modified CNF-based PVDF membrane was proven to be the efficient media that can concurrently eliminate the Fe2O3 nanoparticles and CV dyes from the water. The investigation into the surface chemistries of cellulose nanofibers beyond the adoption of toxic solvents can enhance the economic usefulness of the process and also yield a new ecofriendly adsorbent material that is agreeable to adsorbing various toxic pollutants.
ABSTRACT
We present a comprehensive analysis of all XMM–Newton spectra of OJ 287 spanning 15 yr of X-ray spectroscopy of this bright blazar. We also report the latest results from our dedicated Swift ...UVOT and XRT monitoring of OJ 287, which started in 2015, along with all earlier public Swift data since 2005. During this time interval, OJ 287 was caught in extreme minima and outburst states. Its X-ray spectrum is highly variable and encompasses all states seen in blazars from very flat to exceptionally steep. The spectrum can be decomposed into three spectral components: Inverse Compton (IC) emission dominant at low-state, supersoft synchrotron emission that becomes increasingly dominant as OJ 287 brightens, and an intermediately-soft (Γx = 2.2) additional component seen at outburst. This last component extends beyond 10 keV and plausibly represents either a second synchrotron/IC component and/or a temporary disc corona of the primary supermassive black hole (SMBH). Our 2018 XMM–Newton observation, quasi-simultaneous with the Event Horizon Telescope observation of OJ 287, is well described by a two-component model with a hard IC component of Γx = 1.5 and a soft synchrotron component. Low-state spectra limit any long-lived accretion disc/corona contribution in X-rays to a very low value of Lx/LEdd < 5.6 × 10−4 (for MBH, primary = 1.8 × 1010 M⊙). Some implications for the binary SMBH model of OJ 287 are discussed.
Biodegradable films composed of starch and chitosan plasticized by palm oil were fabricated via a solvent casting technique. In this study, the influence of the ratio of brown rice starch and ...chitosan on the mechanical, thermal, antimicrobial, and morphological properties of the films was investigated. Antimicrobial films with a smooth surface and a compact structure of brown rice starch were obtained. The results showed that a higher proportion of chitosan in the polymer blends resulted in a substantial enhancement in the tensile strength (TS) and thermal stability of the film. The TS values for BRS100, BRS30CH70, BRS50CH50, BRS70CH30, and CH100 were 3.7, 15.2, 10.2, 9.3, and 8.8 MPa, respectively, and the elongation at break (EB) values of the BRS100, BRS30CH70, BRS50CH50, BRS70CH30, and CH100 samples were 39.5%, 34.7%, 7.3%, 11.5%, and 6.9%, respectively. The addition of chitosan to the brown rice starch samples resulted in a reduced water uptake of the film. The film with a balanced ratio of brown rice starch and chitosan exhibited excellent water resistance, with its water absorption being the lowest among all of the studied compositions.
•chitosan/brown rice starch films have been fabricated by solvent casting technique•Surface roughness characterization was performed by using atomic force microscopy.•chitosan has improve tensile strength of the films•Antimicrobial activity of the film against both gram-negatif and gram-positive bacteria was influenced by chitosan•chitosan/brown rice starch films are a promising candidate for sustainable packaging application
ABSTRACT
We report detection of a very bright X-ray–UV–optical outburst of OJ 287 in 2020 April–June, the second brightest since the beginning of our Swift multiyear monitoring in late 2015. It is ...shown that the outburst is predominantly powered by jet emission. Optical–UV–X-rays are closely correlated, and the low-energy part of the XMM–Newton spectrum displays an exceptionally soft emission component consistent with a synchrotron origin. A much harder X-ray power-law component (Γx = 2.4, still relatively steep when compared to expectations from inverse Compton models) is detected out to 70 keV by NuSTAR. We find evidence for reprocessing around the Fe region, consistent with an absorption line. If confirmed, it implies matter in outflow at ∼0.1c. The multiyear Swift light curve shows multiple episodes of flaring or dipping with a total amplitude of variability of a factor of 10 in X-rays, and 15 in the optical–UV. The 2020 outburst observations are consistent with an after-flare predicted by the binary black hole model of OJ 287, where the disc impact of the secondary black hole triggers time-delayed accretion and jet activity of the primary black hole.
Binary black hole (BH) central engine description for the unique blazar OJ 287 predicted that the next secondary BH impact-induced bremsstrahlung flare should peak on 2019 July 31. This prediction ...was based on detailed general relativistic modeling of the secondary BH trajectory around the primary BH and its accretion disk. The expected flare was termed the Eddington flare to commemorate the centennial celebrations of now-famous solar eclipse observations to test general relativity by Sir Arthur Eddington. We analyze the multi-epoch Spitzer observations of the expected flare between 2019 July 31 and 2019 September 6, as well as baseline observations during 2019 February-March. Observed Spitzer flux density variations during the predicted outburst time display a strong similarity with the observed optical pericenter flare from OJ 287 during 2007 September. The predicted flare appears comparable to the 2007 flare after subtracting the expected higher base-level Spitzer flux densities at 3.55 and 4.49 m compared to the optical R-band. Comparing the 2019 and 2007 outburst lightcurves and the previously calculated predictions, we find that the Eddington flare arrived within 4 hr of the predicted time. Our Spitzer observations are well consistent with the presence of a nano-Hertz gravitational-wave emitting spinning massive binary BH that inspirals along a general relativistic eccentric orbit in OJ 287. These multi-epoch Spitzer observations provide a parametric constraint on the celebrated BH no-hair theorem.
An array of highly conductive, lightweight and flexible cellulose nanopapers as effective attenuators of electromagnetic radiations within 8.2–12.4 GHz (X band) were formulated via in situ ...polymerization of pyrrole monomers on to cellulose nanofibers (CNFs). It is quite obvious that the free hydroxyl groups on the surface of CNFs facilitate the formation of intense intermolecular hydrogen bonding with PPy which is envisaged for its excellent electromagnetic shielding performance with an average shielding effectiveness of ca. –22 dB (>99% attenuation) at 8.2 GHz for a paper having 1 mm thickness. The fabricated papers displayed a predominant absorption mechanism (ca. 89%) rather than reflection (ca. 11%) for efficiently attenuating electromagnetic radiations, which has a considerable importance in the modern telecommunication sector. Thus, the designed PPy/CNF papers would replace the conventional metal‐based shields and pave way for the development of green microwave attenuators functioning via a strong absorption mechanism. The PPy/CNF nanopapers exhibited a DC conductivity of 0.21 S/cm, a prime requisite for the development of highly efficient electromagnetic shields. Undoubtedly, such nanopapers can be employed in wide range of applications such as electrodes for supercapacitors and other freestanding flexible paper‐based devices.
Cellulose nanomaterials from plant fibre provide various potential applications (i.e., biomedical, automotive, packaging, etc.). The biomedical application of nanocellulose isolated from plant fibre, ...which is a carbohydrate-based source, is very viable in the 21st century. The essential characteristics of plant fibre-based nanocellulose, which include its molecular, tensile and mechanical properties, as well as its biodegradability potential, have been widely explored for functional materials in the preparation of aerogel. Plant cellulose nano fibre (CNF)-based aerogels are novel functional materials that have attracted remarkable interest. In recent years, CNF aerogel has been extensively used in the biomedical field due to its biocompatibility, renewability and biodegradability. The effective surface area of CNFs influences broad applications in biological and medical studies such as sustainable antibiotic delivery for wound healing, the preparation of scaffolds for tissue cultures, the development of drug delivery systems, biosensing and an antimicrobial film for wound healing. Many researchers have a growing interest in using CNF-based aerogels in the mentioned applications. The application of cellulose-based materials is widely reported in the literature. However, only a few studies discuss the potential of cellulose nanofibre aerogel in detail. The potential applications of CNF aerogel include composites, organic-inorganic hybrids, gels, foams, aerogels/xerogels, coatings and nano-paper, bioactive and wound dressing materials and bioconversion. The potential applications of CNF have rarely been a subject of extensive review. Thus, extensive studies to develop materials with cheaper and better properties, high prospects and effectiveness for many applications are the focus of the present work. The present review focuses on the evolution of aerogels via characterisation studies on the isolation of CNF-based aerogels. The study concludes with a description of the potential and challenges of developing sustainable materials for biomedical applications.
The BL Lacertae object OJ 287 (z = 0.306) has unique double-peaked optical outbursts every ∼12 yr, and it presents one of the best cases for a small-separation binary supermassive black hole (SMBH) ...system, with an extremely massive primary . However, the host galaxy is unresolved or only marginally detected in all optical studies so far, indicating a large deviation from the bulge mass-SMBH mass relation. We have obtained deep, high spatial resolution i-band and K-band images of OJ 287 when the target was in a low state, which enable us to detect the host galaxy. We find the broadband photometry of the host to be consistent with an early-type galaxy with MR = −22.5 and MK = −25.2, placing it in the middle of the host galaxy luminosity distribution of BL Lacertae objects. The central supermassive black hole is clearly overmassive for a host galaxy of that luminosity, but not unprecedented, given some recent findings of other "overmassive" black holes in nearby galaxies.
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