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Electronic, optical, vibrational, and thermodynamic insights into KLi
No full textThe present research explores the first-principles investigation of the electronic, optical, vibrational, and thermodynamic properties of the topological intermetallic compound KLi2Bi. The electronic band structure shows the Fermi level located at 0 eV with valence and conduction bands overlapping in its vicinity, confirming a semimetallic or narrow-gap semiconducting character. Strong interband transitions near the Fermi level dominate the optical response, yielding a high static refractive index of~4.5, which rapidly decreases to~1.5 within the first 5 eV due to intense electronic dispersion. The extinction coefficient reaches a maximum of~2.5 at~2 eV, corresponding to strong optical absorption, while the dielectric function exhibits a pronounced peak with Re(ε) ≈ 16 and Im(ε) ≈ 14 at~2 eV, reflecting strong spin–orbit–driven interband transitions associated with Bi-p states. The absorption coefficient exceeds 2.2 × 106 cm⁻1 at low energies, with a prominent peak of~1.4 × 106 cm⁻1 near 10 eV, indicating efficient photon harvesting over a wide spectral range. The energy-loss function shows a dominant plasmon peak of~2.5 at~2 eV, while the reflectivity reaches~0.55 near 2 eV and drops below 0.1 above 10 eV, signifying ultraviolet transparency. Phonon dispersion curves exhibit no imaginary frequencies, confirming dynamic stability, and Raman spectra reveal a strong mode at~250 cm⁻1, evidencing significant electron–phonon coupling. Thermodynamically, the Debye temperature increases from~100 K to~700 K up to 1000 K, while the free energy becomes~− 4 eV at 1000 K, demonstrating high-temperature stability. These results establish KLi2Bi as a dynamically stable topological semimetal with strong optical activity and plasmonic response, making it a compelling candidate for optoelectronic, plasmonic, and topological-photonic applications
Flux variability of the ``10 keV feature'' of 4U 0115+63
No full textX-ray spectra of accretion-powered X-ray pulsars can often be described using a power-law continuum with a high-energy cutoff, which might be further modified by additional spectral components. The Be X-ray binary system 4U,0115+63 is well known for having one of the highest numbers of detected harmonics of its cyclotron resonant scattering features (CRSFs), a pronounced spectral component known as the ``10,keV feature,'' and quasiperiodic oscillations (QPOs) with a period of about 500,s during outbursts.
The changes in count rate by a factor of two during the ∼500,s QPOs allow us to probe the variation in the spectral components with flux. We study the ``10,keV feature'' in emission, aiming to disentangle it from the broadband continuum and CRSFs and investigate its origin.
We focus on the flux-dependent behavior of the CRSF and its harmonics, and particularly the contribution of the ``10,keV feature,'' as seen in the flux-resolved analysis of two NuSTAR observations of the 2015 outburst.
Comparing the flux-resolved spectra of a given observation with the respective total dataset revealed a distinct change in overall spectral shape at the position of the ``10,keV feature'' but no comparable deviation at the energies of the harmonic CRSFs. The change associated with the ``10,keV feature'' does not seem to involve its centroid energy, which remains constant within a given observation. We find indications for an anticorrelation between the continuum flux and the ratio of the ``10,keV feature'' flux to the continuum flux within each observation.
The analysis strengthens previous claims that the ``10,keV feature'' shows some independence from the remaining features. This result supports the interpretation that the ``10,keV feature'' has a different formation mechanism than the continuum emission, although its origin lies within the same physical environment
Mean temperature of a spherical body on an elliptic orbit
No full textThe accurate determination of thermal accelerations acting on small bodies orbiting the Sun requires knowing the surface temperature at any moment. In analytical methods, the computation of the temperature is often simplified by assuming that it varies slightly about a constant value. This ansatz allows us to conveniently linearize the problem.
However, the mean temperature is constant only in the case of a circular orbit. Our aim is to define a time-dependent temperature that would closely represent the mean temperature of a spherical body revolving around the Sun on an eccentric orbit.
We adopted a model of the mean temperature with a radial profile inside the body and expressed it by superposing the eigenfunctions of the heat diffusion problem. These were represented with Fourier series in a time domain and spherical Bessel functions in the space domain. The coefficients that weight the contribution of each term were determined from the boundary conditions. Special care was taken to properly account for the non-linearity of the surface energy balance.
We developed a robust algorithm to obtain the coefficients of the mean temperature series and tested the results for various choices in their truncation. Degree eight appears to be adequate for orbits up to eccentricity ≃ 0.4. The thermal parameter may have an arbitrary value, including limits of both zero and infinite thermal inertia of the surface. The size of the body may also be arbitrary. We provide simplified results for the small- and large-body limits, with the penetration depth of the seasonal thermal wave being the length scale.
Our formulation of the mean temperature offers the possibility to develop an analytical description of seasonal and diurnal variants of thermal accelerations, including their coupling for an eccentric orbit. Previous models are thus generalized
Effect of discharge parameters on mercury oxidation efficiency in pulsed corona discharge
No full textNon-thermal plasma (NTP) technology is sufficient for treatment of atmospheric mercury pollution, in which ozone usually acts as the key reactive species for oxidation of elemental mercury (Hg0). We focus in this work on the critical power supply parameters including voltage, frequency, and pulse width in a nanosecond pulsed corona discharge system and sys-tematically investigate their influence on both Hg0 oxidation and ozone generation under varying discharge conditions. Experimental results demonstrate that increasing the pulse voltage significantly enhances the discharge intensity and the generation of reactive species, thereby raising the Hg0 oxidation rate to above 90%. Increasing the discharge frequency leads to a higher overall energy input per unit time and promotes ozone formation, and further improves Hg0 oxidation efficiency, although the energy per pulse reduces slightly. But changing the pulse width in range of 400–2000 ns, the Hg0 oxidation rate exhibits only minor variation, remaining nearly constant approximately 90%. These findings provide a theoretical basis and parameter optimization strategy for the industrial application of non-thermal plasma in at-mospheric mercury pollution control
Standardized assessment of PV array simulators
No full textPV array simulators are devices for PV and PV battery inverter testing. To ensure that these devices operate correctly and can realistically simulate PV modules and PV arrays, a test procedure for the assessment of PV array simulators has been developed and is presented in this paper. This procedure helps testing laboratories to evaluate PV array simulators and leads to more uniform test conditions. Furthermore, it assists developers of such simulators in understanding the requirements, enabling them to optimize and test their devices accordingly. The proposed test series includes three phenomenological observations, in which the interaction between the PV array simulator and a randomly selected PV inverter is tested. Subsequently, three potentially standardisable tests are proposed in which certain properties, such as the accuracy and frequency response of the PV array simulators are tested and evaluated
Christoffel matrices and Sturmian determinants
No full textWe discuss certain matrices associated with Christoffel words, and show that they have a group structure. We compute their determinants and show a relationship with the Zolotareff symbol from number theory. We show that the n × n determinants constructed from the factors of length n of a Sturmian sequence form a perfectly clustering word on three letters
A review on low-density steels: effect of processing techniques and parameters on microstructure, and mechanical properties
No full textThis review traces the evolution of low-density steels (LDS) and highlights the key mechanisms that link processing routes to microstructural evolution and performance. Beyond fabrication methods, the article emphasizes the fundamental insights that have emerged, particularly the roles of metal carbide/intermetallic network control, segregation mitigation, and grain refinement that govern the unique behavior of LDS across processing routes in achieving superior mechanical behavior. A key insight from the literature is the exceptional potential of mechanical alloying combined with spark plasma sintering to produce ultrafine and highly homogeneous LDS microstructures that are unattainable through traditional melting routes. The review also identifies the emerging role of near-net-shape casting and additive manufacturing as transformative technologies capable of overcoming longstanding challenges related to defects, compositional inhomogeneity, and geometric limitations. Overall, the review emphasizes that optimized processing strategies and parameter control will be crucial to enhance efficiency, unlocking superior mechanical properties and realizing the full lightweight potential of LDS in advanced engineering applications
Phenotypic changes in natural populations of
No full textIn the tropical savannahs with long dry seasons, malaria mosquito populations virtually disappear after the drying up of breeding sites to reappear in large numbers at the onset of next rainy season. While aestivation and long-distance migration are proposed as key strategies enabling these vectors to persist through the dry-season, the physiological, biochemical, and morphological traits underpinning these mechanisms remain insufficiently explored, particularly under natural field conditions. This study explored seasonal changes in Anopheles coluzzii, An. gambiae, and An. arabiensis at the onset of the dry season in the harsh savannahs of Burkina Faso, West Africa. Late-instar immature specimens were collected from two ecologically distinct sites, one with permanent and the other with only temporary breeding habitats, during the rainy season and the transitional period into the dry season. Larvae were reared to adulthood under natural conditions and several traits were analysed including ovarian development, sub-cuticular fat body hypertrophy, body size, and energy reserves. Gonotrophic dissociation was significantly more frequent in An. coluzzii at the onset of the dry season, indicating a shift toward reproductive arrest. All three species exhibited increased body size and cuticular fat deposits during the transitional period, though with species-specific differences. Notably, only An. coluzzii showed significant increases in energy reserves (proteins, lipids, and carbohydrates) during the transition period. These adaptive responses differed between the study sites, suggesting the influence of breeding habitats. The findings highlight that species within the An. gambiae complex engage in distinct phenotypic trajectories at the onset of the dry season, suggesting divergent adaptations and trade-offs in energy acquisition and allocation to survive during the dry season
