We introduce a new notion of generalized monotonicity named (strong) quasar-monot onicity. We establish the relation between the strong quasar-convexity of a differentiable function with the (strong) quasar-monotonicity of its gradient. We then study the well-known Polyak’s projected heavy-ball method when applying to strongly quasar-monotone variational inequalities. The geometric convergence of the iterations is obtained under suitable conditions on the stepsize and momentum. We apply the convergence results to the constrained optimization problem of strongly quasi-(star)-convex and differentiable functions. Numerical examples are given to demonstrate the advantage of the projected heavy-ball method comparing with the classical projection method.
We theoretically study the thermoelectric transport S in a double-layer bilayer graphene (BLG-GaAs-BLG) system on dielectric substrates (h-BN, Al2O3, HfO2). Electrons interact with GaAs acoustic phonons via both the deformation potential (acDP) and piezoelectric (acPE) scattering. Results show that piezoelectric scattering dominates the total transport, especially at low carrier density and high dielectric constant. Substrate dielectric constant significantly influences thermopower S, and the thermopower of the materials is in the order of HfO2 > Al2O3 > h-BN. When densities on two BLG layers are unequal, the contribution from acDP scattering Sd decreases (increases) at low (high) densities versus equal densities, while acPE scattering Sg remains stable, making S largely Sg-dependent. Increasing interlayer distance d enhances S, while higher temperature boosts Sd (notably at low densities) with minimal effect on Sg. These insights and substrate-dependent trends demonstrate substrate engineering as a key parameter for optimizing BLG thermoelectric devices
The Coulomb-driven renormalization of electronic compressibility in monolayer MoS2 remains poorly understood at finite temperatures. Using the Rytova-Keldysh potential with a nonlocal dielectric response, we calculate the compressibility as a function of carrier density and temperature in experimentally relevant regimes. The exchange and correlation energies are treated, respectively, within the noninteracting (NI), Hartree-Fock (HF), and random phase approximation (RPA) frameworks. We demonstrate that the RPA, through enhanced screening induced by many-body correlations, yields negative values of the electronic compressibility, in agreement with recent measurements resolved in temperature and density. At high temperatures (T), the compressibility follows the law of T2 lnT. This behavior explains the nonmonotonic compressibility observed in cyclotron resonance experiments on disordered monolayers when thermal broadening due to disorder is included. The results establish a theoretical framework for many-body analysis, corrected for by screening effects, such as the large quantitative description of doped monolayer MoS2, and provide a roadmap for engineered correlated electronic phases in two dimensions.
In this work, MnFe2O4 nanoparticles (NPs) have been successfully synthesized by thermal decomposition method with various surfactant concentrations (310, 496, and 712 mM of oleic acid (OA) and oleylamine (OLA)). As the surfactant concentration increases, there is an increase in size (DXRD) and density (rho XRD), and a decrease in lattice parameter (a) and micro strain (epsilon S). At 712 mM of OA/OLA, the MnFe2O4 NPs has the best crystallinity and the highest saturation magnetization (MS = 58.1 emu/g). Accordingly, the MnFe2O4@poly(acrylic) acid (MFO@PAA) NPs with structural parameters (a = 8.3453 & Aring;, rho XRD = 5.26 g/cm3, DXRD = 14.2 nm, and epsilon S = 2.33 x 103) also has high MS value (55.2 emu/g). In addition, this sample exhibit high aqueous stability, low cytotoxicity, and outstanding biocompatibility. For hyperthermia, the MFO@PAA NPs has high potential due to its high Specific Absorption Rate (SAR = 239.4 W/g) and Effective Specific Absorption Rate (ESAR = 33.19 nHm2/kg). Interestingly, the MFO@PAA NPs has transverse relaxation rate (134.6 mM- 1s- 1), which reveals that it is a highly efficient and biocompatible T2 MRI contrast agent
This study examines the influence of environmental taxes on the shadow economy for a global sample of 61 countries in two subsamples (high-income group—HIG and low- and middle-income group—LMG) with data available from 2002 to 2018. Environmental taxes are found to increase the shadow economy significantly across the globe and two subsamples. The proportion of the shadow economy of GDP rises by about 0.201 percentage points on average when the environment taxes to GDP ratio increases by one percentage point. We use a simultaneous equations model to delve into the mechanisms through which environmental taxes might exert their influence, which we find to be transmitted through two main channels, namely, unemployment and the tax burden. Increases in environmental taxes cause higher unemployment and increase the tax burden, resulting in greater informal economic activities. Interestingly, among the four different forms of environmental taxes, an energy tax expands the shadow economy consistently across samples. Pollution and resource taxes have a positive effect on the shadow economy, primarily in HIG. Taxes on energy appear to increase unemployment and then cause an increase in the size of the shadow economy. In contrast, taxes on pollution, resources and transport seem to be associated with a higher tax burden, which causes an increase in the size of the shadow economy. In general, a crucial policy consideration involves the careful selection of environmentally related taxes that do not disrupt primary economic activities. The findings also suggest that the implementation of environmental taxes should be accompanied by policies designed to mitigate the potential adverse impacts on unemployment and the tax burden, both of which can impose significant societal costs.
