Model of black hole and white hole in Minkowski spacetime

In this paper, we construct toy models of the black hole and the white hole by setting proper boundaries in the Minkowski spacetime, according to the modern definition. We calculate the thermal effect of the black hole with the tunneling mechanism. We consider the role of boundary conditions at the singularity and on the horizon. In addition, we show that the white hole possesses a thermal absorption.

The uGMRT Observations of Three New Gigahertz-peaked Spectra Pulsars

Using the Giant Metrewave Radio Telescope, we report the detailed spectral measurements over a wide frequency range of three pulsars (J1741−3016, J1757−2223, and J1845−0743), which allow us to identify them as new gigahertz-peaked spectra pulsars. Our results indicate that their spectra show turnovers at the frequencies of 620 MHz, 640 MHz, and 650 MHz, respectively. Our analysis proves that wideband observations improve estimations of spectral nature using a free–free thermal absorption model, and thus allow for a more accurate approximation of the maximum energy in the spectrum. While there is no evidence as yet that these objects are associated with a supernova remnant or pulsar wind nebula, they will make good targets when looking for interesting environments in the future, or when conducting more sensitive sky surveys.

Thermal radio absorption as a tracer of the interaction of SNRs with their environments

We present new images and continuum spectral analysis for 14 resolved Galactic supernova remnants (SNRs) selected from the 74 MHz Very Large Array Low-Frequency Sky Survey Redux (VLSSr). We combine new integrated measurements from the VLSSr with, when available, flux densities extracted from the Galactic and Extragalactic All-Sky Murchison Widefield Array Survey and measurements from the literature to generate improved integrated continuum spectra sampled from ~15 MHz to ~217 GHz. We present the VLSSr images. When possible we combine them with publicly available images at 1.4 GHz, to analyse the resolved morphology and spectral index distribution across each SNR. We interpret the results and look for evidence of thermal absorption caused by ionised gas either proximate to the SNR itself, or along its line of sight. Three of the SNRs, G4.5+6.8 (Kepler), G28.6−0.1, and G120.1+1.4 (Tycho), have integrated spectra which can be adequately fit with simple power laws. The resolved spectral index map for Tycho confirms internal absorption which was previously detected by the Low Frequency Array, but it is insufficient to affect the fit to the integrated spectrum. Two of the SNRs are pulsar wind nebulae, G21.5−0.9 and G130.7+3.1 (3C 58). For those we identify high-frequency spectral breaks at 38 and 12 GHz, respectively. For the integrated spectra of the remaining nine SNRs, a low frequency spectral turnover is necessary to adequately fit the data. In all cases we are able to explain the turnover by extrinsic thermal absorption. For G18.8+0.3 (Kes 67), G21.8−0.6 (Kes 69), G29.7−0.3 (Kes 75), and G41.1−0.3 (3C 397), we attribute the absorption to ionised gas along the line of sight, possibly from extended H II region envelopes. For G23.3−0.3 (W41) the absorption can be attributed to H II regions located in its immediate proximity. Thermal absorption from interactions at the ionised interface between SNR forward shocks and the surrounding medium were previously identified as responsible for the low frequency turnover in SNR G31.9+0.0 (3C 391); our integrated spectrum is consistent with the previous results. We present evidence for the same phenomenon in three additional SNRs G27.4+0.0 (Kes 73), G39.2–0.3 (3C 396), and G43.3–0.2 (W49B), and derive constraints on the physical properties of the interaction. This result indicates that interactions between SNRs and their environs should be readily detectable through thermal absorption by future low frequency observations of SNRs with improved sensitivity and resolution.

Thermal Absorption Performance Evaluation of Water-Based Nanofluids (CNTs, Cu, and Al2O3) for Solar Thermal Harvesting

For solar thermal harvesting, an experimental study was performed on the thermal absorption performance of water-based carbon nanotubes (CNTs), Cu, and Al2O3 nanofluids using a halogen lamp-based thermal radiation system. The effect of nanoparticle concentrations (0.01 wt.%, 0.1 wt.%, and 1 wt.%) on the nanofluid dispersion, stability, and thermal absorption characteristics was investigated, and a comparative analysis was performed for each type of nanofluid. All types of nanofluids increased the absorbance and electrical conductivity with increasing nanoparticle concentration, which contributed to improving the thermal absorption performance of nanofluids. The results showed that the thermal absorption performance was high in the order of carbon-based nanofluids (CNTs), metal-based nanofluids (Cu), and oxide-based nanofluids (Al2O3). In CNTs nanofluids, the thermal absorption performance expressed the time reduction rate, which was 12.8%, 16.3%, and 16.4% at 0.01 wt.%, 0.1 wt.%, and 1 wt.% test cases, respectively. Therefore, the 0.1 wt.%-CNTs nanofluid is more economical and appropriate. However, in Al2O3 nanofluids, the time reduction rate of the 1 wt.% nanofluid was significantly higher than that of the 0.01 wt.% and 0.1 wt.% nanofluids. In Cu nanofluids, unlike CNTs and Al2O3 nanofluids, the time reduction rate constantly increased as the nanoparticle concentration increased.

Comparison of the Performance of a Solar Thermal Absorption Chiller and a Novel Sub-Wet Bulb Evaporative Chiller for Cooling Processes in Food Manufacturing

The food processing industry exists at the nexus between food, energy, and water systems. Improving the sustainability of this industry is critical to reduction of carbon emissions and enhanced utilization of vital resources such as water. The overarching aim of the present research is to create a process-based modeling platform for food processing systems that would allow the most appropriate combination of water-sustainable, energy-efficient, and renewable energy (WERE) technologies to be determined for a system. This paper focuses on one specific process in a thermal processing line: the cooling step after sterilization and prior to packaging. A typical process might use groundwater in a once-through loop. To reduce water use, two sustainable alternatives are considered and compared: (a) solar thermal coupled with an absorption chiller and (b) evaporative cooling of chilled water using a sub-wet bulb evaporative chiller (SWEC). The former uses a parabolic trough solar field with thermal storage that is connected to a single-effect water/lithium bromide (LiBr) chiller. The field and thermal storage are modeled using NREL’s System Advisor Model software and coupled to in-house Python code for the chiller and process heat exchanger. For the latter option, a novel SWEC is used as a chiller. The energy and water use, and capital cost of the two alternative technologies are presented.

Using Graphene Oxide Based Materials for Thermal Sorption

In this work, some nanocomposite materials based on graphene oxide (GO) (Al2O3/GO, Fe3O4/GO, Fe3O4–Al2O3/GO) were prepared and characterized by X-ray and infrared spectra, SEM and EDX analysis. GO based materials were dispersed into salty water and the thermal absorption ability of mixtures was measured. Results showed that thermal sorption of composite materials was greater than that of single materials. Fe3O4-Al2O3/GO gives the highest thermal absorption efficiency (the temperature difference between the blank sample and the sample containing Fe3O4-Al2O3/GO with content of 0.5 mg/mL is 6°C). The influence of the material content in salty water on the thermal sorption efficiency was investigated and a suitable concentration of 0.5 mg/mL was found. 98% of Fe3O4-Al2O3/GO was recovered with the magnet because of its magnetic property and thermal absorption of recovered material are similar to that of the fresh material. The research results show the potential of using these nanocomposite materials to increase the efficiency of thermal sorption in the process of distilling salty water into fresh water.