bluuebunny/crossref_metadata_2025_split huggingface dataset:
On the visibility of singularities in general relativity and modified gravity theories
Authors: Mosani Karim , Dey Dipanjan , Joshi Pankaj S , Samanta Gauranga C , Menon Harikrishnan , Patel Vaishnavi D 
Published: May 2023

Abstract
We investigate the global causal structure of the end state of a spherically symmetric marginally bound Lemaitre–Tolman–Bondi (LTB) (Lemaitre 1933 Ann. Soc. Sci. Brux. A 53 51, Tolman 1934 Proc. Natl Acad. Sci. USA
20 169–76, Bondi 1947 Mon. Not. Astron. Soc.
107 410) collapsing cloud (which is well studied in general relativity) in the framework of modified gravity having the generalized Lagrangian

R
+
α

R
2

in the action. Here R is the Ricci scalar, and

α
⩾
0

is a constant. By fixing the functional form of the metric components of the LTB spacetime, using up the available degree of freedom, we realize that the matching surface of the interior and the exterior metric are different for different values of α. This change in the matching surface can alter the causal property of the first central singularity. We depict this by showing a numerical example. Additionally, for a globally naked singularity to have physical relevance, a congruence of null geodesics should escape from such singularity to be visible to an asymptotic observer for infinite time. For this to happen, the first central singularity should be a nodal point. We here give a heuristic method to show that this singularity is a nodal point by considering the above class of theory of gravity, of which general relativity is a particular case.
Density and pseudo-spin rotons in a bilayer of soft-core bosons
Authors: Pouresmaeeli F , Abedinpour S H , Tanatar B 
Published: May 2023

Abstract
We study the dynamics of a bilayer system of bosons with repulsive soft-core Rydberg-dressed interactions within the mean-field Bogoliubov-de Gennes approximation. We find roton minima in both symmetric and asymmetric collective density modes of the symmetric bilayer. Depending on the density of bosons in each layer and the spacing between two layers, the homogeneous superfluid phase becomes unstable in either (or both) of these two channels, leading to density and pseudo-spin-density wave instabilities in the system. Breaking the symmetry between two layers, either with a finite counterflow or a density imbalance renormalizes the dispersion of collective modes and makes the system more susceptible to density-wave instability.
Energy harvesting by uniaxially-stretched poly(lactide) films at low tensile strain frequencies for powering wearable sensors: experimental results and theoretical extrapolation
Authors: Ben Achour Mohamed Aymen , Rguiti Mohamed , Samuel Cédric , Barrau Sophie , Lacrampe Marie-France , Courtois Christian 
Published: May 2023

Abstract
Poly(lactide) (PLA) is an eco-friendly and low-cost polymer with a shear piezoelectricity easily induced by uniaxial stretching and without poling process. These interesting features make PLA as a good candidate to replace the widely-used poly(vinylidene difluoride) (PVDF) piezoelectric polymer, in particular for flexible energy harvesting applications aiming to power wearable sensors. In this work, PLA films were fabricated by a simple extrusion–orientation process. The energy harvesting efficiency of the PLA films were characterized using a custom-built test bench designed for flexible piezoelectric materials and working in tensile mode at low strain frequencies. The measurements on PLA films show a maximal output power about 3.7 μW harvested by applying a strain of 1% at 20 Hz. A theoretical model was developed based on electromechanical parameters to ascertain the energy harvesting performances of PLA. The validated model was also helpful to estimate the output power from PLA films by increasing their active surface areas and/or improving their shear piezoelectric coefficients (d
14). The optimized PLA film could produce an output power comparable to that produced by PVDF film in the same mechanical excitation conditions. This study consequently highlights the potential of PLA for energy harvesting applications and the utility of the developed model to estimate the electrical power generated by piezoelectric polymers.
Towards Stirling engine using an optically confined particle subjected to asymmetric temperature profile
Authors: Nalupurackal Gokul , Lokesh Muruga , Suresh Sarangi , Roy Srestha , Chakraborty Snigdhadev , Goswami Jayesh , M Gunaseelan , Pal Arnab , Roy Basudev 
Published: May 2023

Abstract
The realization of microscopic heat engines has gained a surge of research interest in statistical physics, soft matter, and biological physics. A typical microscopic heat engine employs a colloidal particle trapped in a confining potential, which is modulated in time to mimic the cycle operations. Here, we use a lanthanide-doped upconverting particle (UCP) suspended in a passive aqueous bath, which is highly absorptive at 975 nm and converts near infra red (NIR) photons to visible, as the working substance of the engine. When a single UCP is optically trapped with a 975 nm laser, it behaves like an active particle by executing motion subjected to an asymmetric temperature profile along the direction of propagation of the laser. The strong absorption of 975 nm light by the particle introduces a temperature gradient and results in significant thermophoretic diffusion along the temperature gradient. However, the activity of the particle vanishes when the trapping wavelength is switched to 1064 nm. We carefully regulate the wavelength-dependent activity of the particle to engineer all four cycles of a Stirling engine by using a combination of 1064 nm and 975 nm wavelengths. Since the motion of the particle is stochastic, the work done on the particle due to the stiffness modulation per cycle is random. We provide statistical estimation for this work averaged over five cycles which can be extended towards several cycles to make a Stirling engine. Our experiment proposes a robust set-up to systematically harness temperature which is a crucial factor behind building microscopic engines.
Experimental study on the pressure characteristics of laser-induced shock waves under different energy distribution
Authors: Nie Xiangfan , Tang Yuyuan , Zhao Feifan , Li Yang , He Weifeng , Wei Chen , Wang Xuede , Wu Haonian , Yan Li 
Published: May 2023

Abstract
Laser shock peening has been widely used in anti-fatigue strengthening of metals. The different types of lasers (Flattop laser and Gaussian laser) used have influence on the pressure characteristics of shock wave and the strengthening effect. In this work, using PDV (photonic doppler velocimetry) system, the difference of peak pressure of Flattop laser-induced shock wave and Gaussian laser-induced shock wave is studied experimentally and theoretically. Research shows that the peak pressure of shock wave induced by Gaussian laser is higher than that of Flattop laser, because of the infinitesimal power density in the center of Gaussian laser spot is higher than that of Flattop laser. Furthermore, at the same power density, Gaussian laser can implant a larger and deeper residual stress field in the material.
The effect of depositions parameters on the nanostructural and optical properties of CuPc organic thin films growth by oblique angle deposition CSP technique
Authors: Tatar B , Demiroğlu D 
Published: May 2023

Abstract
Organic semiconductor CuPc thin films were deposited on different substrates with OAD CSP technique. The effects of substrate type, glancing angle and deposition temperature on surface and structural properties of CuPc thin films was reported in this study. The structural and morphological properties of CuPc thin films were investigated by XRD, RAMAN and FEG-SEM analysis. Dendritic nanostructures and nanoporous-straticulate sponge like structures were determined at surface area of CuPc thin films. XRD patterns showed that these CuPc thin films have orthorhombic α-phase structure with 2θ peak at 6.89˚, which is %100. The optical properties of all CuPc films which were determined from transmittance and reflectance measurements. The increasing of spray glancing angle and substrate temperature were decreased the UV-VIS absorption intensities at S-band and Q-band. However at 200 °C and 250 °C deposition temperatures at 45° spray glancing angle affected the Q-band absorption acerbically and red shift observed in here.
Dynamics of a non-smooth pest-natural enemy model with the threshold control strategy
Authors: Zhu Yuxun , Liu Lu , Zhang Zhengdi 
Published: May 2023

Abstract
Pest issues have always been the focus of attention in agriculture. The Integrated Pest Management(IPM) method is currently the most popular way to be applied for pest control. In this study, according to the IPM strategy, we regard pest quantity as a threshold index and extend the Leslie-Gower model into a non-smooth Filippov system through combining chemical and biological control. To maintain the pest population at or below the given economic threshold(ET), we investigate the global dynamics of the proposed model, including the existence of sliding mode and various equilibria, sliding dynamics and bifurcations, and global stability of equilibria. The result shows that desired equilibria can be globally stable under some conditions, meaning that our control tactics work. In particular, the case where our strategy fails to be effective arouses interest. In the end, the biological implications of the results are discussed and given in detail.
Design of PCM-based heat sinks through topology optimization
Authors: Bianco Nicola , Fragnito Andrea , Iasiello Marcello , Mauro Gerardo Maria 
Published: May 2023

Abstract
Ever-increasing heat fluxes of electronic components ask for higher performance of devices responsible for their cooling. Against that background, PCM-based heat sinks – because of their compactness, and effectiveness – are well-established solutions for thermal management issues. Even though solutions for the thermal enhancement of PCM devices have been widely presented, new ways to optimize such systems are emerging. Among them, this work investigates the application of density-based topology optimization to define innovative heat sinks design able to minimize thermal resistance under constant wall temperature. A 2D numerical model is developed by means of a finite element tool. The heat equation is solved for the topology optimization problem with the objective of minimizing the average temperature, considering further manufacturing restrictions. Solid-isotropic-material-with-penalization (SIMP) method is applied to link the design variable to material properties. Parameterization of Helmholtz filter’s minimum feature size and projection based on the hyperbolic tangent function is performed, showing improved performance as well as feature size decrease. The optimized prototype – with PCM – is then simulated with the enthalpy-porosity model to assess the benefits, i.e., reduction in the melting time, with respect to the baseline. Results show the potential of optimizing heat sinks via a topology-based approach and confirm it as a promising tool for finding new heat sink geometry, whatever the application.
Energy demand in secondary steel making process: numerical analysis to assess the influence of the ladle working lining properties
Authors: Neri M , Lezzi A M 
Published: May 2023

Abstract
In secondary steel making process, steel scrap is melted in an electric arc furnace, then poured into a ladle where ferroalloy are added to obtain the desired steel composition. Energy is also supplied in LF (Ladle Furnace) to guarantee steel temperature required in the teeming phase. In this paper a simplified, but sound numerical model of the process the ladle undergoes is presented: it is meant to provide a way to compare energy demand for different choices of materials used in the ladle or for changes in the ladle work cycle. As an example of application of the model, energy demand in LF are evaluated and compared for two different choices of the refractory material used as working lining: magnesia and alumina. To take into account the reduction of the working lining due to wear processes, energy demand has been calculated for three different thicknesses. In addition, the beneficial effect of a lid during the waiting phase after cleaning is investigated.
Lattice Boltzmann model of a square natural circulation loop with small inner diameter: working fluid effects
Authors: Bocanegra Johan Augusto , Misale Mario 
Published: May 2023

Abstract
Natural circulation loops are systems used to transport heat by the free convection of a working fluid in a closed thermo-hydraulic circuit. Many examples of the Lattice Boltzmann method applied to free convection can be found in the literature, but most of them are limited to model simple enclosures. This work is one of the first approaches to an engineering system as the Natural Circulation Loops using this numerical method. This study describes the implementation and validation of a numerical model of a rectangular loop characterized by a small inner diameter. This research is focused on the thermohydraulic response of the NCL varying the working fluid. We have obtained satisfactory results demonstrating that accepted analytical correlations for the steady-state behavior are reproduced by the thermal Lattice Boltzmann Method (double distribution function). Overall, these results suggest that the temperature and velocity oscillations during the transient increase directly with the fluid Prandtl number; instead, the temperature difference between the vertical legs is inversely correlated and decreases.
Preliminary design and modeling of mini channels to enhance heat transfer in a millimetric catalytic combustor
Authors: La Terra Caterina , Corti Maria , Nespoli Adelaide , Fanciulli Carlo , Niro Alfonso 
Published: May 2023

Abstract
Mini channel solution is used in devices that require a high density of transmitted thermal power as a very large-scale integration design in computer systems and compact exchangers. Furthermore, the mini channels are extensively investigated in the literature for turbulent and laminar regimes. In this project, different configurations of mini channels have been studied to enhance heat transfer, using simulations with a commercial multi-physics code. Thanks to the results of the models, more promising configurations with 3D printing technique may be built. The project challenge is improving convective thermal power extracted by the exhaust gases of a mini-catalytic combustor. The combustor feeds six modules for thermoelectric power production (TEMs). As the first step, three different mini channel geometries have been chosen; the first one with 19 channels with rectangular cross-section, the second one with 6 channels with a convergent profile, and the latter with 2 channels with a fractal branching geometry. Simulations started from studying fluid dynamic to investigate the velocity field at the exit of the mini channels. The analysis has been extended by adding the conjugate heat exchange between fluid and combustor wall. The results show an increase in heat exchange compared to the base case for all configurations, with a maximum value for the 19 mini channels configuration.
Fouling effect in a shell-and-tube heat exchanger with twisted tape inserts applied to a small-scale biomass gasification power plant
Authors: Allesina Giulio , Pedrazzi Simone , Ottani Filippo , Tartarini Paolo 
Published: May 2023

Abstract
In this work the over-time behaviour of a shell-and-tube type heat exchanger applied to a commercial and small-scale wood biomass gasification system was investigated. The heat exchanger, equipped with twisted tape turbulators, was used to cool down the syngas produced by the power plant. An experimental campaign was conducted to evaluate the performance trend in the first 15 hours of operation. The results showed an increase in heat transfer which led to a progressive reduction of the gas outlet temperature from 105.4 °C to 90.0 °C. The data collected confirm the literature studies on the positive effect that the deposits of particulate matter and tars have in reducing the clearance between the heat exchanger pipes and the turbulators, providing information for the temporal optimization of the cleaning strategy of the heat exchanger itself.
Hidden Grid Background Oriented Schlieren in studying convective flows
Authors: Ambrosini Dario , Rubeis Tullio de , Paoletti Domenica , Ramaiah Jagadesh , Gannavarpu Rajshekhar 
Published: May 2023

Abstract
In this paper, we present a new BOS (Background Oriented Schlieren), based on a hidden grid, for studying heat flows. In the setup, we record a grid-based intensity pattern whose phase map carries information about the temperature gradient. The background (undistorted) pattern is hidden in the light source. Quantitative analysis is obtained by a windowed Fourier transform approach. Some experimental results are given to demonstrate the feasibility of the technique.
Convective condensation of R134a and R1234ze(E) inside microfin tube
Authors: Lucchini A , Carraretto I M , Phan T N , Pittoni P G , Molinaroli L , Colombo L P M 
Published: May 2023

Abstract
Environmental concerns are forcing the replacement of the commonly used refrigerants and finding new fluids is a top priority. The hydro-fluoro-olefin (HFO) R1234ze(E), because of its smaller global warming potential (GWP) and shorter atmospheric lifetime, replaced R134a. Accordingly, for HVAC systems design, a detailed knowledge of the thermo-fluid-dynamic characteristics of the fluids and reliable predictive models are required. To improve the understanding, R134a and R1234ze(E) were employed in convective condensation experiments (saturation temperature Tsat
= 35°C, mean quality xm
= 0.1~0.9, quality changes Δx = 0.05~0.6, mass flux G = 43~444 kg·m−2s−1) inside a microfin tube (outer diameter D = 9.52 mm, fin number n = 60, fin height H = 0.2 mm). The results were used for two goals: the former is the comparison of the heat transfer features of the two fluids, while the latter aims at testing the performance of prediction models available in the open literature. At the saturation temperature T = 35°C, the two fluids show small differences in the thermal properties so that, as expected, the experiments highlighted a very similar behavior in the typical operating conditions of HVAC systems. In fact, for all the operating conditions marginal differences were observed in the pressure drop, the heat transfer coefficient and the flow pattern maps. The issue of prediction reliability, however, is still open. Actually, not all the models achieving good results for R134a show the same performance for R1234ze(E), especially for the pressure drop.
The role of collective action in the cacao sector in enhancing sustainability, market upgrading and agro-biodiversity conservation
Authors: Rueda Ximena , Middendorp Romaike , Puerto Sergio 
Published: May 2023

Abstract
Many farmers around the world are confronted with the decision of adopting high-yielding varieties or maintaining the diverse portfolio of ancient varieties and cultivars that constitute the basis of local and global agrobiodiversity. This dilemma often resolves towards ensuring short-term individual profits at the expense of long-term biodiversity conservation. In this paper we argue that specialty markets can act as a driving force to resolve this balance towards the conservation of agrobiodiversity, supported by collective action. We use the case of the Ecuadorian cacao producers to illustrate this possibility. The upper Amazon is the center of origin of cacao, one of the top traded global commodities. Since the 1990s Ecuadorian farmers have been substituting regional varieties with a clone developed in the country, the CCN-51 that has shown to be a high-yielding variety that is also resistant to monilia, a common cacao disease. In some areas of the country, however, farmers belonging to cooperatives have been able to keep local varieties, obtain ecological certifications for adhering to the recommended practices, and reach specialty markets that pay higher prices for their cacao. We call this set of benefits upgrading. We conducted a study of 205 household surveys and several interviews in four provinces along the West coast of Ecuador. We assessed the role of collective action (in the form of cooperative participation) in enhancing farmers’ access to high-value chains. Our results show that collective action enables economic upgrading by providing participants with higher incomes and more formal contracts. As farmers join direct trade and certification, other benefits are accrued, such as cacao and non-cacao tree biodiversity conservation. This analysis shows that, once niche markets are open for farmers, collective action boosts the benefits of such opportunities.
Impact of S,B and S,P co-doping on the photovoltaic performance of graphene quantum dots
Authors: Cui Peng , Zhang Jian 
Published: May 2023

Abstract
Co-doping is an effective strategy to optimise the photovoltaic performance of GQDs. However, due to the heterogeneity of GQDs, it is difficult to achieve controllable photovoltaic performance without determining the structure-property relationship. In this work, we perform first-principles calculations to investigate the optoelectronic properties of GQDs doped with S, B, and P atoms. Our results show that S doping is crucial for tuning the photoelectric performance of S,B and S,P co-doped GQDs. Increasing the polarity of the solvent improves the charge transfer performance of single P-doped GQDs. Moreover, single P-doped GQDs show better photovoltaic performance than other doping configurations. Furthermore, the addition of B co-dopants to GQDs with Sh doping configuration improves the energy conversion of GQDs compared to B doping alone. Our study provides guidance for the rational design of GQDs for various photovoltaic applications.
Preparation and antibacterial property of silver nanoparticles loaded into bacterial cellulose
Authors: Homwan Wittaya , Chaisen Konkanok , Audtarat Sasiporn , Suwonnachot Wittaya , Dasri Thananchai 
Published: May 2023

Abstract
Composite nanomaterials based on silver nanoparticles (AgNPs) are considered promising antimicrobial agents due to their excellent antimicrobial activity. The aim of this work is to develop bacterial cellulose (BC) composites that act synergistically with AgNPs. BC@AgNPs composites were developed using an ex-situ composite development strategy and evaluated for their structural characteristics and antimicrobial activities. Field emission scanning electron microscopy (FESEM) showed impregnation of AgNPs into the porous BC network. The composite formulation was also confirmed by x-ray diffraction (XRD) analysis, which showed the presence of additional crystalline peaks along with those of the pure BC. Bactericidal tests of BC@AgNPs nanocomposites against common pathogens, including Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus, showed a significant reduction in their growth compared to pure BC. These results suggest that the synthesized BC@AgNPs composites could be promising antibacterial materials for potential applications in a wide range of medical and environmental applications.