Aggregation induced photoluminescent quenching of graphene quantum dots (GQDs) is a well-known effect, although there are limited reports of multicolour light emissions from such aggregates. In the ...present work, we demonstrate a novel aggregation induced bathochromic shift in emission similar to J-aggregates observed in dye molecules. Nitrogen-doped graphene quantum dots (N-GQDs) prepared in the presence of diethylenetriamine show blue emission which is attributed to monomers at low concentration (58 μg/ml) while cyan (1.75 mg/ml), and greenish yellow (3.5 mg/ml) emissions are observed at higher concentrations under 365 nm UV lamp. These materials for the first time show yellow and orange emission from drop cast film of N-GQDs under 365 nm UV-light while the parent powder gives orange emission. The variety of emission colours that could be made simply by controlling the degree of aggregation presents exciting possibilities in a range of applications such as sensing, bioimaging, solar harvesting and forensic science.
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Observation indicates that many nearby galaxies host supermassive central black holes. We use the Bardeen black holes in four-dimensional Einstein–Gauss–Bonnet (4D EGB) gravity, with additional ...parameters-the coupling constant α̃ and charge q, as central black holes in various galaxies to investigate gravitational lensing properties in strong field regime. Taking the supermassive black holes Sgr A* and M87* as the lens, we compare observable signatures of 4D EGB Bardeen black holes with those of the Schwarzschild black holes. In the case of 4D EGB Bardeen black holes we observed that he angular position θ∞ for Sgr A* ∈ (23.19, 25.56) μ as, whereas for M87* it is ∈ ( 17.94,19.78) μ as. Further, the angular separation s, which is an increasing function of α̃ and q for Sgr A* and M87* differs significantly, respectively, in (0.032, 0.15) μ as and (0.025, 0.115) μ as. The deviations of the lensing observables Δθ∞ and Δs for 4D EGB Bardeen black hole (α̃=0.9,q=0.09) from the Schwarzschild black hole, respectively, can reach up to 2.38μ as and 0.12μ as for Sgr A* , 1.84μ as and 0.09μ as for M87*. On the other hand, the relative magnification ∈ (4.66,6.82). Considering twenty-one massive central black holes as lens, we also estimate the time delay ΔT2,1s between the first and second relativistic image to find that, e.g., the time delay for Sgr A* and M87*, respectively, can reach ∼9.86 min and ∼16023.93 min. We also show that the existing shadow size measurements place strong constraints on the parameters considered Bardeen model. This combination of gravitational lensing and EHT results may complement comprehensive restrictions on modifications of the general relativity.
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•Strong gravitational lensing by 4D EGB Black hole•Calculating and comparison of observables.•Constraints using EHT results.
Fall armyworm (Spodoptera frugiperda) is an invasive pest in South Asia. The current paper documents farmers' perceptions of fall armyworm in India, Pakistan, Sri Lanka, and Nepal and explores the ...current management practices adopted by farmers. A structured survey was conducted with 526 farmers regarding current cropping practices, identification of fall armyworm and its damage, management, capacity-building activities, and support from government and non-government extension services. The results suggested that most of the farmers reported very high to moderate damage from fall armyworm, and that the damage and spread increased over time. Although farmers used a range of management practices to control fall armyworm, chemical pesticides were still the dominant tool. Farmers learnt about the pest and its identification from their fellow farmers and individual experiences, while services from government and non-government offices were limited. Therefore, there is a need for an innovative extension approach, including the promotion of digital technologies. Similarly, the evaluation and promotion of new technologies as part of integrated pest management strategies (IPM) must be deployed to manage fall armyworm.
Exact solutions describing rotating black holes can provide significant
opportunities for testing modified theories of gravity, which are motivated by
the challenges posed by dark energy and dark ...matter. Starting with a spherical
Kiselev black hole as a seed metric, we construct rotating Kiselev black holes
within the $f(R,T)$ gravity framework using the revised Newman-Janis algorithm
- the $f(R,T)$ gravity-motivated rotating Kiselev black holes (FRKBH), which
encompasses, as exceptional cases, Kerr ($K=0$) and Kerr-Newman ($K=Q^2$) black
holes. These solutions give rise to distinct classes of black holes surrounded
by fluids while considering specific values of the equation-of-state parameter,
$w$, for viable choices for the $f(R,T)$ function. From the parameter space or
domain of existence of black holes defined by $a$ and $\gamma$ for FKRBH, we
discover that when $a_1<a<a_2$, there is a critical value $\gamma=\gamma_E$
which corresponds to extreme value black holes portrayed by degenerate
horizons. When $a<a_1$ ($a>a_2$), we encounter two distinct critical values
$\gamma=\gamma_{E1}, \; \gamma_{E2}$ with $\gamma_{E1}>\gamma_{E2}$ (or
$\gamma=\gamma_{E3},\; \gamma_{E4}$ with $\gamma_{E3}>\gamma_{E4}$. We delve
into the horizon and global structure of FKRBH spacetimes and examine their
dependence on parameters $w$ and $\gamma$. This exploration is motivated by the
remarkable effects of $f(R,T)$ gravity, which gives rise to diverse and
intricate spacetime structures within the domain where black holes exist.
Observation indicates that many nearby galaxies host supermassive central black holes. Modelling Bardeen models in four-dimensional Einstein-Gauss-Bonnet (4D EGB) gravity, with additional parameters ...\(\tilde{\alpha}\) and charge \(q\), as central black holes in various galaxies, we investigate gravitational lensing properties in strong deflection limits. Interestingly, the spherical photon orbit radius \(x_m\), the critical impact parameter \(u_m\), the lensing coefficient \(\bar{b}\), the deflection angle \(\alpha_D(\theta)\), angular position \(\theta_{\infty}\) are decreasing with \(q\) and \(\alpha\) whereas the other lensing coefficient \(\bar{a}\) and angular separation \(s\) have opposite behaviour. Taking the supermassive black holes Sgr A* and M87* as the lens, we also compare observable signatures of 4D EGB Bardeen black holes with those of the Schwarzschild black holes. The angular position \(\theta_\infty\) for Sgr A* \(\in\) (23.1853, \; 25.56427) \(\mu\)as, whereas for M87* it is \(\in\) ( 17.941,\; 19.7819) \(\mu\)as. Further, the angular separation \(s\), which is an increasing function of \(\tilde{\alpha}\) and \(q\) for Sgr A* and M87* differs significantly, respectively, in (0.031997,0.14895) \(\mu\)as and (0.0247, 0.1152) \(\mu\)as. The deviations of the lensing observables \(\Delta \theta_{\infty}\) and \(\Delta s\) for 4D EGB Bardeen black hole (\(\tilde{\alpha}=0.9,~q=0.09\)) from the Schwarzschild black hole, respectively, can reach up to \(2.3789~\mu\)as and \(0.11695~\mu\)as for Sgr A* , \(1.84084~\mu\)as and \(0.0905~\mu\)as for M87*. On the other hand, the relative magnification \(\in\) (4.65751,\; 6.82173). Considering twenty-two massive central black holes as lens, we also estimate the time delay \(\Delta T^s_{2,1}\) between the first and second relativistic image to find that, e.g., the time delay for Sgr A* and M87*, respectively, can reach \(\sim9.86088\)~min and \(\sim16023.93\)~min.
Exact solutions describing rotating black holes can provide significant opportunities for testing modified theories of gravity, which are motivated by the challenges posed by dark energy and dark ...matter. Starting with a spherical Kiselev black hole as a seed metric, we construct rotating Kiselev black holes within the \(f(R,T)\) gravity framework using the revised Newman-Janis algorithm - the \(f(R,T)\) gravity-motivated rotating Kiselev black holes (FRKBH), which encompasses, as exceptional cases, Kerr (\(K=0\)) and Kerr-Newman (\(K=Q^2\)) black holes. These solutions give rise to distinct classes of black holes surrounded by fluids while considering specific values of the equation-of-state parameter, \(w\), for viable choices for the \(f(R,T)\) function. From the parameter space or domain of existence of black holes defined by \(a\) and \(\gamma\) for FKRBH, we discover that when \(a_1<a<a_2\), there is a critical value \(\gamma=\gamma_E\) which corresponds to extreme value black holes portrayed by degenerate horizons. When \(a<a_1\) (\(a>a_2\)), we encounter two distinct critical values \(\gamma=\gamma_{E1}, \; \gamma_{E2}\) with \(\gamma_{E1}>\gamma_{E2}\) (or \(\gamma=\gamma_{E3},\; \gamma_{E4}\) with \(\gamma_{E3}>\gamma_{E4}\). We delve into the horizon and global structure of FKRBH spacetimes and examine their dependence on parameters \(w\) and \(\gamma\). This exploration is motivated by the remarkable effects of \(f(R,T)\) gravity, which gives rise to diverse and intricate spacetime structures within the domain where black holes exist.
