Non-singular model universe from a perfect fluid scalar-metric cosmology

To seek for a singularity free model universe from a perfect fluid scalar-metric cosmology, we work in the “Emergent Cosmology” (EC) paradigm which is a non-singular alternative for cosmological inflation. By using two methods including Linear Stability Theory and Effective Potential Formalism, we perform a classical analysis on the possible static solutions (that are called usually as Einstein Static Universes (ESU)in literature) in order to study EC paradigm in a FRW background. Our model contains a kinetic term of the scalar field minimally coupled to the background geometry without a potential term. The matter content of the model consists of a perfect fluid plus a cosmological constant \(\Lambda \) as a separate source. In the framework of a local dynamical system analysis, we show that in the absence or presence of \(\Lambda \), depending on some adopted values for the free parameters of the underlying cosmological model with flat and non-flat spatial geometries, one gets some static solutions which are viable under classical linear perturbations. By extending our study to a global dynamical system analysis, we show that in the presence of \(\Lambda \) with non-flat spatial geometries there is a future global de Sitter attractor in this model. Following the second method, we derive a new static solution that represents a stable ESU but this time without dependence on the free parameters of the cosmological model at hand. As a whole, our analysis suggests the possibility of graceful realization of a non-singular EC paradigm (i.e. leaving the initial static phase and entering the inflation period as the universe is evolving) through either preserving or violation of the strong energy condition.     

The effect of anodising time on the electrochemical behaviour of the Ti/TiO<Subscript>2</Subscript> NTs/IrO<Subscript>2</Subscript>-RuO<Subscript>2</Subscript>-Ta<Subscript>2</Subscript>O<Subscript>5</Subscript> anode

Nowadays, mixed metal oxide (MMO) anodes are a superior alternative to lead alloys in electrowinning processes. Passivation of titanium substrate is the most common mechanism of deactivation in these anodes. In this research, titanium oxide nanotubes have been utilised as an interlayer between the substrate and a mixed metal oxide coating in order to improve the anode electrochemical behaviour and life via retardation of titanium passivation. Anodising of the substrate was done in 0.5 wt% hydrofluoric acid for 30, 60 and 240 min. The samples were subsequently coated with a coating composed of IrO₂-RuO₂-Ta₂O₅. The microstructure of different samples was observed by scanning with an electron microscope, and the electrochemical behaviour of the samples was studied by accelerated life test, cyclic voltammetry and electrochemical impedance spectroscopy. The studies showed that formation of titanium oxide nanotubes with anodising times of 60 and 240 min increases the life of the anode through the provision of a compact coating. The life of the anode which was anodised for 240 min lasted about 20% longer than the sample which had a substrate without any anodised layer.     

Liquid Metal Marbles

Liquid metal marbles that are droplets of liquid metal encapsulated by micro‐ or nanoparticles are introduced. Droplets of galinstan liquid metal are coated with insulators (including Teflon and silica) and semiconductors (including WO₃, TiO_2, MoO₃, In₂O₃ and carbon nanotubes) by rolling over a powder bed and also by submerging in colloidal suspensions. It is shown that these marbles can be split and merged, can be suspended on water, and are even stable when moving under the force of gravity and impacting a flat solid surface. Furthermore, the marble coating can operate as an active electronic junction and the nanomaterial coated liquid metal marble can act as a highly sensitive electrochemical based heavy metal ion sensor. This new element thus represents a significant platform for the advancement of research into soft electronics.     

Two‐Dimensional Molybdenum Trioxide and Dichalcogenides

In the quest to discover the properties of planar semiconductors, two‐dimensional molybdenum trioxide and dichalcogenides have recently attracted a large amount of interest. This family, which includes molybdenum trioxide (MoO₃), disulphide (MoS₂), diselenide (MoSe₂) and ditelluride (MoTe₂), possesses many unique properties that make its compounds appealing for a wide range of applications. These properties can be thickness dependent and may be manipulated via a large number of physical and chemical processes. In this Feature Article, a comprehensive review is delivered of the fundamental properties, synthesis techniques and applications of layered and planar MoO₃, MoS₂, MoSe₂, and MoTe₂ along with their future prospects.     

A New Distributional Approach to Signature Change

Colombeau's generalized functions are used to adapt the distributional approach to singular hypersurfaces in general relativity with signature change. Equations governing the dynamics of a singular hypersurface are derived and a specific non-vanishing form for the energy-momentum tensor of the singular hypersurface is obtained. It is shown that matching in the case of de Sitter space in the Lorentzian sector is possible along the boundary with minimum radius but leads to the vanishing of the energy-momentum tensor of the singular hypersurface.     

Gravitational induced uncertainty and dynamics of harmonic oscillator

As a consequence of gravitational induced uncertainty, equation of motion for harmonic oscillator differs considerably from usual quantum mechanical situation. This paper considers the dynamics of a simple harmonic oscillator in the context of Generalized (Gravitational) Uncertainty Principle (GUP). Using Heisenberg Picture of quantum mechanics, we find time evolution of position and momentum operators and we will show that expectation values have an unusual complicated mass dependence. Also we will show that since the notion of locality breaks down, Ehrenfest theorem is not satisfied for harmonic oscillator in GUP.     

Self-Deposition of 2D Molybdenum Sulfides on Liquid Metals

2D transition metal dichalcogenides (TMDs) play increasingly significant roles in research and future optoelectronics. However, the large-scale deposition of 2D TMDs remains challenging due to sparse nucleation and substrate dependency. Liquid metals can offer effective solutions to meet these challenges due to their reactive, non-polarized, and templating properties. Here, self-deposition of 2D molybdenum sulfide is shown by introducing a molybdenum precursor onto the surface of a eutectic alloy of gallium and indium (EGaIn). EGaIn serves as an ultra-smooth template and reducing agent for the precursor to form large-scale planar molybdenum sulfides, which is transferrable to any substrate. The molybdenum sulfides form spontaneously on the surface of EGaIn, which has a sufficient potential to drive the cathodic reactions of the deposition process. A highly crystalline 2H-MoS₂ is obtained after a final annealing step. This work demonstrates a fundamentally new capability for the formation of large-scale 2D TMDs.     

Self‐Limiting Galvanic Growth of MnO2 Monolayers on a Liquid Metal—Applied to Photocatalysis

Liquid metals offer unprecedented chemistry. Here it is shown that they can facilitate self‐limiting oxidation processes on their surfaces, which enables the growth of metal oxides that are atomically thin. This claim is exemplified by creating atomically thin hydrated MnO₂ using a Galvanic replacement reaction between permanganate ions and a liquid gallium–indium alloy (EGaIn). The “liquid solution”–“liquid metal” process leads to the reduction of the permanganate ions, resulting in the formation of the oxide monolayer at the interface. It is presented that under mechanical agitation liquid metal droplets are established, and simultaneously, hydrated gallium oxides and manganese oxide sheets delaminate themselves from the interfacial boundaries. The produced nanosheets encapsulate a metallic core, which is found to consist of solid indium only, with the full migration of gallium out of the droplets. This process produces core/shell structures, where the shells are made of stacked atomically thin nanosheets. The obtained core/shell structures are found to be an efficient photocatalyst for the degradation of an organic dye under simulated solar irradiation. This study presents a new research direction toward the modification and functionalization of liquid metals through spontaneous interfacial redox reactions, which has implications for many applications beyond photocatalysis.     

Sonication‐Assisted Synthesis of Gallium Oxide Suspensions Featuring Trap State Absorption: Test of Photochemistry

Gallium is a near room temperature liquid metal with extraordinary properties that partly originate from the self‐limiting oxide layer formed on its surface. Taking advantage of the surface gallium oxide (Ga₂O₃), this work introduces a novel technique to synthesize gallium oxide nanoflakes at high yield by harvesting the self‐limiting native surface oxide of gallium. The synthesis process follows a facile two‐step method comprising liquid gallium metal sonication in DI water and subsequent annealing. In order to explore the functionalities of the product, the obtained hexagonal α‐Ga₂O₃ nanoflakes are used as a photocatalytic material to decompose organic model dyes. Excellent photocatalytic activity is observed under solar light irradiation. To elucidate the origin of these enhanced catalytic properties, the electronic band structure of the synthesized α‐Ga₂O₃ is carefully assessed. Consequently, this excellent photocatalytic performance is associated with an energy bandgap reduction, due to the presence of trap states, which are located at ≈1.65 eV under the conduction band minimum. This work presents a novel route for synthesizing oxide nanostructures that can be extended to other low melting temperature metals and their alloys, with great prospects for scaling up and high yield synthesis.     

A Fast and Solvent-Free Conversion of Thioamides into Thioesters

Summary. Solvent-free irradiation of thiomorpholides with two kinds of methylating agents under microwave or ultrasonic conditions gave the corresponding thioesters in high yield. The method is simple and avoids prolonged heating with solvents.