Pure Radiation Research Articles

Invariant solutions of Einstein field equations in pure radiation fields

The exact static accelerating solutions of Einstein’s equations in the non-comoving pure radiation fields, with an indefinite non-degenerate stationary metric in cylindrical coordinates, are obtained. The considered space-time is of Petrov type I and is not conformally flat. Moreover, the classical symmetry method is used for symmetry reduction and finding the solutions in terms of hyperbolic functions. The conservation laws are found by using the multiplier approach.

Intensification of nanofluid thermal performance with install of turbulator in a LFR system

In current suggested design for domestic usage, arrangements of mirrors have been implemented as primary reflector. Impose of trapezoidal tank intensifies the optical performance and alumina-water has been utilized as operating fluid which is practical due to kind of application. For modeling, finite volume approach was imposed and extracted heat flux from solving the pure radiation were added as source term of turbulent modeling of nanomaterial flow. Twisted tapes (TT) were installed within the pipe to augment the convective flow. Inlet temperature (Tin), flow rate (V•), twist (TR) and width (WR) ratios are variables for various cases. Irreversibility and thermal behavior were reported for all cases. With existence of cavity, the optical efficiency enhances up to 73.5 %. For lowest values of other parameter, augmenting TR and WR cause friction faction to increase about 27.09 % and 9.22 % but increasing V• leads to decline of f about 29.77 %. With assumption of lowest values of other variables, augmentation of TR, V• and WR leads to intensification of Nu about 4.83 %, 146.4 % and 1.69 %. As Tin intensifies, ηth declines about 23.7 % when V• = 6.3, WR = 0.56, TR = 2.With enhance of TR and WR, ηth goes up about 0.11 % and 0.037 % with considering lowest values of other variables.

Radiation and convection treatment of nanomaterial within a Linear Fresnel Reflector unit

To absorb more solar flux, the tube of LFR system was equipped with Y-shaped fins in current investigation. The fluid in tube is H2O with inclusion of alumina nanoparticles. Installing mirrors with special angles and installing parabolic reflector above the tube lead to greatest optical performance. Turbulent regime was assumed and K-ɛ approach was used for modeling. Reasonable accommodation with data of empirical correlations indicates nice accuracy of simulation. Influences of operation factors on carrier fluid thermal behavior were presented. Also, exergy efficiency, irreversibility and Be were scrutinized. DO model with employment of conditions of pure radiation was utilized to compute the solar heat flux. Better flow mixing takes places if values of Vin, L1 and L2 augment because residence time grows. Increase in Tin offers lower cooling rate and higher wall temperature appears. Increasing Vin, L1 and L2 makes tube temperature to decline about 0.457%, 0.109% and 0.194% with assuming lowest level of other factors. Also, increasing Tin offers augmentation of tube temperature about 9.93%. Darcy factor drops with grow of L1 and L2 about 47.27% and 37.42% when Vin = 0.16, Tin = 293.15 K. As Vin augments, Nu intensifies about 82.71% when L1 = L2 = 2 mm. Nu increases with augment of L1 about 15.67%. Sgen,h declines about 9.82% with augment of L1 while Sgen,f augments about 51.68% with rise of this variable. Be decreases about 1.13% and 0.108% with intensify of Vin and L2, respectively. The value of $$\eta_{{{\text{th}}}}$$ augments with rise of Vin about 1.08% while it reduces about 23.43% with growth of Tin. With rise of L1, $$\eta_{{{\text{ex}}}}$$ and $$\eta_{{{\text{th}}}}$$ enhance about 0.67% and 0.09% when L2 = 2 mm, Vin = 0.16, Tin = 293.15 K.

Invariant solutions and conservation laws of Einstein field equations in non-comoving radiation fields

The exact non-static accelerating solutions of Einstein field equations in non-comoving pure radiation fields, corresponding to an indefinite non-degenerate metric in cartesian coordinates, are obtained. The gravitational field is of Petrov type D and the considered spacetime is not conformally flat. Lie symmetry method is used for symmetry reduction of nonlinear partial differential equations and for finding the exact solutions, comprising both arbitrary functions and known analytic functions. Conservation laws are obtained by using multiplier approach. The graphical representations of solutions are shown by considering different possibilities of the arbitrary functions.

Nanofluid migration within an absorber pipe of solar unit considering radiation mechanism

To intensify the efficiency, T-shaped fins were utilized inside the tube in current LFR unit. Various configurations of fins with same volume were employed. The carrier fluid is Al2O3-water and turbulent regime was considered. Incorporating DO model and solving pure radiation results in distribution of radiation flux around the tube which is employed as source term in energy equation. Convective transportation with ambient was considered in outer wall. Various inlet temperature and velocity for four cases were examined and outputs were shown in term of plots and contours. Thermal and energy efficiency, irreversibility component and Bejan number were main outputs of this paper. Outputs indicate that selecting Case A leads to obtain the maximum turbulent fluctuation and lowest temperature of outer wall. Replacing Case C instead of A makes temperature of surface to augment about 0.19% while pressure drop decreases about 23.72%. Rise of Re for Case A leads to decrease of Darcy factor about 26%. Highest Nu belongs to Case A and it increases about 79.82% with rise of Re. Lowest values of total irreversibility belongs to case A and growth of Re lead to reduce Sgen,h about 41.88%. Also, this case has minimum value of Be. The highest exergy and thermal efficiency belong to case A. Augment of Tin makes $$\eta_{th}$$ to decline about 23.46% while $$\eta_{ex}$$ augments.

Fractional dynamics in nonlinear magnetic metamaterials

We examine the existence of nonlinear modes and their temporal dynamics, in arrays of split-ring resonators, using a fractional extension of the Laplacian in the evolution equation. We find a closed-form expression for the dispersion relation as a function of the fractional exponent as well as an exact expression for the critical coupling between rings, beyond which no fractional magnetoinductive waves can exist. We also find the low-lying families of bulk and surface nonlinear modes and their bifurcation diagrams. Here the phenomenology is similar for all exponents and resembles what has been observed in other discrete evolution equations, such as the DNLS equation. The propagation of an initially localized magnetic excitation is always ballistic, with a ‘speed’ that is computed in exact form as a function of the fractional exponent. For a given exponent, it increases with an increase in coupling up to a critical coupling value, beyond which the ballistic speed could diverge inside the fractional interval [0,1]. Examination of the modulational instability shows that it tends to increase with an increase in the fractional exponent, where the decay proceeds via the formation of filamentary structures that merge eventually and form pure radiation. The dynamical selftrapping around an initially localized excitation increases with the fractional exponent, but it also shows a degree of trapping in the linear limit. This trapping increases with a decrease in the exponent and can be explained by near-degeneracy arguments.

Synthesis, crystal structure and luminescent properties of isoreticular lanthanide–organic frameworks based on a tetramethyl-substituted terphenyldicarboxylic acid

A series of 3D metal–organic frameworks derived from 2′,3′,5′,6′-tetramethyl-[1,1′:4′,1′′-terphenyl]-4,4′′-dicarboxylic acid (H2L) as organic linker and various lanthanides have been prepared. The resulting coordination polymers [Ln3L4(NO3)(DMF)x(H2O)]n (where x = 2 or 3) were characterized by elemental analysis, thermogravimetric investigations, IR and TG-FTIR spectroscopy, as well as powder X-ray diffraction measurements. The crystal structure for six of these isostructural networks based on La(III), Ce(III), Nd(III), Sm(III), Tb(III) and Dy(III) was established using single crystal X-ray crystallography. As an example, the asymmetric part of [La3L4(NO3)(DMF)3(H2O)]n consists of two deprotonated ligand molecules L2- and two La(III) ions, one of them occupying a general position with full site occupancy, while the other one has a fractional occupancy of 0.5. Investigation of the luminescence of these coordination polymers showed that compounds containing La3+, Nd3+ and Gd3+ possess only the emission associated with the anion of the organic ligand (L2-), polymers containing Eu3+ and Tb3+ show pure metal-centered radiation, while networks containing Dy3+ and Sm3+ display dual metal- and ligand-centered luminescence. The organic linker acts as a good antenna for Tb3+, Eu3+, Dy3+ and Sm3+ ions.

The Influence of Cleaning Frequency of Photovoltaic Modules on Power Losses in the Desert Climate

Dust accumulation on the photovoltaic (PV) surface decreases the solar radiation penetration to the PV cells and, eventually, the power production from the PV system. To prevent dust-based power losses, PV systems require frequent cleaning, the frequency of which depends on the geographical location, PV integration scheme, and scale of the PV power plant. This study aims to measure the drop-in radiation intensity, as well as power output, due to dust and to determine the optimal time interval for PV cleaning in the United Arab Emirates (UAE) climate. In this research, a dusting study experiment was carried out at the Renewable Energy Laboratory, Falaj Hazza Campus, UAE University, Al Ain, UAE, for 3.5 months, from 22 April 2018 to 7 August 2018. To measure the pure radiation losses caused by the dust, four transparent glasses were used to mimic the top glass cover of the PV modules. The dusting induced power losses were measured for four selected PV cleaning frequencies (10 days, 20 days, 1 month, and 3 months). This study revealed that up to 13% of power losses occurred in PV panels that remained dusty for 3 months, compared to panels that were cleaned daily. PV cleaning after 15 days brought the losses down to 4%, which was found the most feasible time for PV cleaning in this study, considering a reasonable balance between the cleaning cost and energy wasted due to soiling.

Hidden sector monopole dark matter with matter domination

The thermal freeze-out mechanism for relic dark matter heavier than O(10 − 100 TeV) requires cross-sections that violate perturbative unitarity. Yet the existence of dark matter heavier than these scales is certainly plausible from a particle physics perspective, pointing to the need for a non-thermal cosmological history for such theories. Topological dark matter is a well-motivated scenario of this kind. Here the hidden-sector dark matter can be produced in abundance through the Kibble-Zurek mechanism describing the non-equilibrium dynamics of defects produced in a second order phase transition. We revisit the original topological dark matter scenario, focusing on hidden-sector magnetic monopoles, and consider more general cosmological histories. We find that a monopole mass of order (1–105) PeV is generic for the thermal histories considered here, if monopoles are to entirely reproduce the current abundance of dark matter. In particular, in a scenario involving an early era of matter domination, the monopole number density is always less than or equal to that in a pure radiation dominated equivalent provided a certain condition on critical exponents is satisfied. This results in a larger monopole mass needed to account for a fixed relic abundance in such cosmologies.

Ionizing Radiation Effect upon Er/Yb Co-Doped Fibre Made by In-Situ Nano Solution Doping

In order to assess the possible use in terrestrial and space applications, radiation effects by different ionizing radiation (gamma ray, electron beam, and mixed neutron / γ radiation) upon erbium and ytterbium co-doped fibre (EYDF) made by in-situ nano solution doping have been investigated. The spectral attenuation, unsaturable loss at 830 nm, emission and lifetime of irradiated (max dose is up to 140 kGy) and non-irradiated EYDF samples are measured, and the outcomes were analysed and compared. The results indicate that both the spectral attenuation and unsaturable loss at 830 nm are increased significantly and that the emission is reduced by radiation induced attenuation (RIA) and the decrease of the lifetime. The radiation effects produced by electron beam and gamma ray are almost comparable. The comparison between the radiation effects induced by pure gamma radiation and mix gamma and neutron radiation indicates that the neutron irradiation may have, to some degree, opposite effects as compared with pure γ ray.

Effect of Sound-Speed Inhomogeneities in Sea Bottom on the Acoustic Wave Propagation in Shallow Water

The effect of volume inhomogeneities in the sea bottom upper layer (sediments) on the long-range sound propagation in shallow water is analyzed. The experimental basis for developing inhomogeneous bottom models are the data of 3D seismic survey on the spatial structure of sediments in the Kara Sea, where variations of ~10% in the average sound speed in the bottom are observed at ranges of ~1 km. The mode coupling due to bottom volume inhomogeneities is revealed within the normal mode approach. Coupled mode equations are derived not only for propagating modes but also for leaky modes and quasimodes; including these types of modes may be urgent in analysis of the waveguides where the sound speed in the bottom (c1) is less or approximately equal to the sound speed in water (c). Numerical simulations show that the coupling between energy-carrying modes is maximum at c1 ≈ c. Calculations of the attenuation of depth-averaged sound field intensity in a water layer, performed for the Kara Sea at ranges of up to 5 km, show that the mode coupling due to bottom volume inhomogeneities can be neglected, and the depth-averaged transmission loss can be calculated using the adiabatic approximation at frequencies below a few hundred hertz. When analyzing the depth-averaged intensity, the effects of mode coupling on bottom inhomogeneities can be observed only by implementing special conditions, for example, using mode arrays providing maximally pure (free of other modes) radiation of a specified mode.

Axially Symmetric Type N Space-Time with Causality Violating Curves and the von Zeipel Cylinder

An axially symmetric nonvacuum solution of the Einstein field equations, regular everywhere and free from curvature divergence is presented. The matter-energy content is a the pure radiation field satisfying the energy conditions, and the metric is of type N in the Petrov classification scheme. The space-time develops circular closed timelike curves everywhere outside a finite region of space i.e., beyond a null curve. Furthermore, the physical interpretation of the solution based on the study of the equations of geodesic deviation is presented. Finally, the von Zeipel cylinders with respect to the Zero Angular Momentum Observers (ZAMOs) is discussed. In addition, circular null and timelike geodesic of pace-time are also presented.

Measurement of the energy of fast neutrons in the presence of gamma rays using a NaI(Tl) and a plastic scintillator

In many radiological laboratories, the energies of fast neutrons are very important for radiation diagnostics. In this paper we propose a method based on NaI and plastic scintillation (PS) detectors that measures the fast neutrons. The PS detector is sensitive to both gamma rays and fast neutrons. The NaI(Tl) detector is only sensitive to gamma rays. By subtracting the gamma information from the neutron–gamma mixed energy spectrum, pure neutron radiation information is obtained. Then, applying an unfolding method, the energy distribution of the fast neutron is generated. To verify this method, an experiment measuring the energy of monoenergetic neutrons was performed with the result confirming the effectiveness of this method.

Axially Symmetric Type N Space-Time with a Naked Curvature Singularity and Closed Timelike Curves

A family of type N exact solution of the Einstein's field equations, regular everywhere except on the symmetry axis where it possesses a naked curvature singularity, is present. The stress-energy tensor is of the anisotropic fluid coupled with pure radiation field satisfy the different energy conditions and the physical parameters diverge $r \rightarrow 0$. The space-time admitting a non-expanding, non-twisting, and shear-free geodesic null congruence and belongs to a special class of type N Kundt metrics. The space-time is geodesically complete along the radiation direction in the constant $z$-planes and exhibits geometrically different properties from the known pp-waves. The present family of solution admits closed time-like curves (CTC) which appear after a certain instant of time and the space-time is a four-dimensional generalization of the Misner space metric in curved space-time.

A class of Hadamard well-posed five-field theories of dissipative relativistic fluid dynamics

This paper proposes a class of causal formulations for dissipative relativistic fluid dynamics as a hyperbolic five-field system of second-order partial differential equations. The argumentation continues lines of thinking developed in the author’s earlier papers with Temple and generalizes a four-field description that was recently given by Bemfica, Disconzi, and Noronha [Phys. Rev. D 98, 104064 (2018)] for the case of the pure radiation fluid. The Navier–Stokes–Fourier-like models are constructed as perturbations of auxiliary “involutory augmentations” of the Euler equations and shown to be Hadamard well-posed at least at the level of their linearization.

What are Reversed Spheres?

In our universe we have only two elements: mass which is a sphere and radiation which is a reversed sphere. A sphere has the maximum volume with minimum exterior surface and a reversed sphere has minimum volume while having maximum exterior surface. A sphere has a centre and a surface at a fix distance in all directions while a reversed sphere has the centre everywhere in all directions and the surface covering all radiuses heading towards its middle point. Interaction between mass creates events and exchange of energy, while interaction between radiations doesn’t. Interaction between mass and radiation is rare in universe. Any sphere of mass has around it a reversed sphere of radiation (gravity) which prevents it from exploding back. When mass and radiation interact, the reversed sphere surrounding mass disturbs the trajectory of pure radiation. The first one has a constant force due to surface of mass in the middle, while the second one has the tendency to expand as it has nothing in the middle. It is possible to transfer mass (spherical radiation) into radiation (linear radiation) and radiation into mass because of the formula E=mc2, but the conditions form initial big bang are needed in order to create/destroy gravity.

Analysis of nuclear radiation damage effect on typical materials

In order to evaluate the effects of nuclear radiation on several typical materials, the mathematical models of radiation damage characteristics of three materials are established based on the analysis of radiation environment and damage forms. In order to simplify the calculation, the principles and indexes of damage estimation are determined according to the radiation damage process of three typical materials: polymer materials, high-energy explosives, and metal materials. The results show that the pure nuclear radiation environment has no obvious effect on the properties of three typical materials. It lays a theoretical foundation for radiation hardening of devices.

A hybrid strategy for solving radiation-conduction in irregular geometries filled with gray semitransparent medium using Monte Carlo method combined with blocked-off and embedded boundary treatments

Monte Carlo method (MCM) and finite volume method (FVM) are integrated to deal with combined conduction-radiation heat transfer problems in irregular geometries containing gray semitransparent media. The MCM is employed to get radiative heat source using blocked-off and embedded boundary treatments via Cartesian system. The FVM is adopted to solve the energy equation via unstructured grid system. The radiative heat source is implemented in the energy equation through geometrical mapping. The hybrid strategy is first validated regarding both pure radiation and conduction-radiation problems. Then, the features of the two boundary treatments are assessed through solving the conduction-radiation heat transfer problems in irregular geometries. The results show that both of them are highly satisfactory for calculating temperature distribution. In comparison with the embedded boundary treatment, the blocked-off treatment leads to obvious errors in predicting wall radiative heat flux for curved boundaries as well as the boundaries adjacent to the inner curved obstacle. Additionally, the hybrid strategy combined with embedded boundary treatment is promising in eliminating the ray effects.

Cosmology of minimal varying Lambda theories

Inserting a varying Lambda in Einstein's field equations can be made consistent with the Bianchi identities by allowing for torsion, without the need to add scalar field degrees of freedom. In the minimal such theory, Lambda is totally free and undetermined by the field equations in the absence of matter. Inclusion of matter ties Lambda algebraically to it, at least when homogeneity and isotropy are assumed, i.e. when there is no Weyl curvature. We show that Lambda is proportional to the matter density, with a proportionality constant depending on the equation of state. Unfortunately, the proportionality constant becomes infinite for pure radiation, ruling out the minimal theory prima facie despite of its novel internal consistency. It is possible to generalize the theory still without the addition of kinetic terms, leading to a new algebraically-enforced proportionality between Lambda and the matter density. Lambda and radiation may now coexist in a form consistent with Big Bang Nucleosynthesis, though this places strict constraints on the single free parameter of the theory, $\theta$. In the matter epoch Lambda behaves just like a dark matter component. Its density is proportional to the baryonic and/or dark matter, and its presence and gravitational effects would need to be included in accounting for the necessary dark matter in our Universe. This is a companion paper to Ref. [1] where the underlying gravitational theory is developed in detail.

Understanding Near Infrared Laser Driven Continuum White Light Emission by Graphene and Its Mixture with an Oxide Phosphor

AbstractRecent observations suggest that continuum white light generation driven by a near infrared (NIR) laser is not limited to rare earth (RE) doped phosphors, but is rather a general photophysical process of light–matter interaction as long as the NIR laser energy is efficiently absorbed. Since the proposed explanations seem to be material‐dependent, a comparative investigation on the white light generation in graphene, and its mixture with a typical RE‐doped oxide phosphor is reported here for a general understanding of this process. In contrast to the steady increase of white light intensity in graphene, the white light generated from the oxide phosphor and their mixtures with graphene exhibits a stepwise growth of intensity with laser power. By using the temperature‐dependent upconversion luminescence as ratiometric temperature sensing, it is observed that this emission is closely correlated with the jumps in temperature with the rise of excitation power. Since the black body temperatures are much higher than the temperatures derived by the ratiometric method, it is suggested that this process can be understood by a general thermally assisted direct photon‐to‐photon conversion process, rather than by pure thermal radiation. The results of this work may have important implication for the understanding and design of efficient continuum white light sources.