Anomalous Increase Research Articles

Anomalous increase of sub-band gap photoluminescence from InPBi layers grown by liquid phase epitaxy

The luminescence properties of InPBi layers, grown by liquid phase epitaxy from an In-P melt containing 4 and 18 wt% Bi are investigated. As-grown layers, as well as layers subjected to a high temperature anneal, are studied by atomic force microscopy (AFM), energy dispersive x rays (EDX), high resolution x ray diffraction (HRXRD) and low temperature photoluminescence (PL) spectroscopy. AFM shows formation of microscopic granular structure over the surface of the layer grown from melt containing 18 wt% Bi after a high temperature furnace anneal at 700 °C for 1 h. Lattice contraction and a decrease of Bi content is observed for both kinds of samples after anneal though it is only marginal in case of the layer grown from melt containing 4 wt% Bi but quite appreciable in case of the other sample. From EDX and XRD results, the observed decrease in Bi content as a result of high temperature anneal is suggested to be due to diffusion of Bi atoms from the layer to InP grains formed over the layer surface. 10 K PL measurements showed the expected band edge luminescence peak at 1.38 eV. A second peak at 1.33–1.34 eV is observed which shows a large post anneal enhancement for materials grown from melts containing higher amounts of Bi. It is suggested that this peak is due to luminescence from defects formed by complexes of Bi with phosphorous vacancies. Photoluminescence also revealed a broad peak between 1–1.22 eV whose intensity increased anomalously with temperature up to 104 K. The anomalous increase up to 28 K is found to be associated with a low activation energy of 0.35 meV and is speculated to be due to the transfer of holes in the localized states to the valence band. Above 28 K, PL increases with an activation energy of 9.66 meV and may be explained on the basis of similar observation made by a previous group [Chen et al Appl. Phys. Lett. 110, 051 903 (2017)] who explained the phenomenon by assuming thermal hopping of some electrons available for recombination with holes to some non-radiative states .

Role of structural inheritance in the gravitational deformation of the Monviso meta-ophiolite Complex: the Pui-Orgiera serpentinite landslide (Varaita Valley, Western Alps)

ABSTRACT Depending on its chemical and mineralogical composition, the serpentinite represents a peculiar rocky material, which plays a significant role in influencing pedogenetic weathering, vegetation ecology, geo-mechanical and tectonic processes, as well as gravitational slope failure. In serpentinite-bearing environments the response to gravitational stress is more effective than in other rock types. In the Monviso meta-ophiolite Complex (Western Alps), a close relation between landsliding and serpentinite rock occurrences is particularly evident. Our geological map (Main Map), at a scale 1:10,000, illustrates the geology and geomorphological features of the Pui-Orgiera giant (2.98 km2) complex landslide, located on the southern slope of the Monviso Massif. This map clearly documents that the characteristics and kinematics of the landslide are closely associated to the anomalous thickening and widening increase of the Baracun Shear Zone, a remnants of an intra-oceanic detachment fault which separates serpentinite and meta-intrusives from metabasalt and metasediments of the Monviso meta-ophiolite Complex.

Microcrystalline Diamond Powders As Promising Objects for Generation of Multifrequency Stimulated Raman Scattering

Regular trends of Raman scattering in microcrystalline diamond powders as a function of size of the diamond microcavities are investigated in the range of the latter between 1 to 600 μm. The observed effect of anomalously high intensity of spontaneous Raman scattering is attributed to “trapping” of electromagnetic radiation with a wavelength shorter than the size of the diamond microcrystals in diamond microcavities. The electromagnetic energy density for the driving and secondary radiation increases as a result of photon “trapping” in the diamond microcavities. A high Q factor of the fundamental optical mode in the vibrational sp-ectrum of diamond and anomalous increase in the Raman scattering intensity in diamond microcavities pave the way for observation of the low-threshold multifrequency Raman scattering in microcrystalline diamond powders. Using the radiation of a pulsed solid state YAG:Nd3+ laser at the fundamental wavelength (λ = 1064 nm) and its optical harmonics (λ = 532, 355, 266 nm) as sources of driving radiation opens up a possibility for creation of an array of equidistant (with respect to frequency shift) laser sources with wavelengths extending from the ultraviolet to the terahertz range promising for investigation of biological and medical objects.

Second Magnetization Peak Effect in a Fe(Se,Te) iron based superconductor

The iron based superconductor FeSe0.5Te0.5 has been investigated by means of DC magnetic measurements as a function of magnetic field (H). By considering the superconducting m(H) hysteresis loops at different temperatures, the sample shows a strong superconducting signal together with the presence of a peak effect that causes an anomalous increase in the field dependence of the critical current density Jc(H). The presence of the peak effect has been studied by means of the Jc(T) obtained at different magnetic fields starting from the Jc(H) curves. The analysis of the Jc(T) curves shows that the peak effect is due to a crossover from a weak pinning regime to a strong pinning regime.

Experimental verification of anomalous surface tension temperature dependence at the interface between coexisting liquid-gas phases in magnetic and Stockmayer fluids

Our early experimental investigation has demonstrated the anomalous surface tension temperature dependence σ(T) at the interface between coexisting liquid-gas phases in magnetic fluids that undergo field-induced first-order phase transition. The σ(T) dependence is anomalous because the drops of a liquid phase condensed under the action of the applied magnetic field H at high temperature T2 exhibit larger surface tension σ(T2) > σ(T1) than the drops condensed at low temperature T1 < T2. This study verifies and confirms the results of the previous experimental investigation of σ(T) in magnetic fluids by performing the experiment, which is based on the analysis of the Plateau-Rayleigh instability of a gas-liquid interface in a zero magnetic field. A novel explanation of this phenomenon is given in the framework of the Stockmayer model. The anomalous increase in σ(T) is explained by the increase in particle concentration difference in gas and liquid phases, which can be attributed to the high field intensity H needed to generate the phase transition at high temperature.

A 3-D nonlinear thermal circuit model of underground MV power cables and their joints

A 3D thermal model of underground power cable is presented in this paper. A detailed representation of the cable and its joints, the laying condition, the soil and the heat exchanges between soil upper surface and air, considering different weather conditions, is given. The model solves the thermal problem by means of an equivalent electric circuit and has been validated against field measurements, showing its applicability both for steady state and transient studies.In order to verify if any correlation between the occurrence of overheatings and the anomalous increase of failures, observed by Italian Distribution System Operators (DSOs) during summer 2015, exists, the model has been applied to simulate one-year operation of an existing underground cable. The cable is located in the MV distribution network owned by A.S.M. Terni S.p.A., the DSO in Terni, a city placed in the Central Italy. Ambient temperature and relative humidity trends have been taken from registrations made by a weather station, whereas the current profile along the cable has been assumed equal to that measured in 2015 by A.S.M., sampled every ten minutes. A second current profile has been also used, derived from the measured one in order to have the cable loaded at ampacity for a considerable time span during the year. In all cases, results show that no overheating occurred and, moreover, that the joint is the coldest part of the underground power cable.

Investigation of Structural, Ferroelectric, and Magnetic Properties of La-Doped LuFeO3 Nanoparticles

LuFeO3 a new room temperature multiferroic material exists in hexagonal and orthorhombic phases. In this work, La doping is used to tune the phase fraction and investigate its effect on multiferroic properties. Lu(1-x)LaxFeO3 nanoparticles with x = 0 to 0.25 are synthesized using wet chemical methods. The structural parameters including phase fraction are obtained through detailed Rietveld refinement. The dielectric properties seem to sensitively depend on the phase fraction of polar hexagonal phase whereas the magnetic properties show an anomalous increase in coercivity with an increase in temperature. Presence of room temperature ferroelectric and magnetic hysteresis loops establishes La-doped LuFeO3 as a potential multiferroic material.

Effects of photogenerated carriers in GaN layers on the photoluminescence characteristics of violet light-emitting InGaN/GaN multiple quantum wells

Two violet light-emitting InGaN/GaN multiple quantum well (MQW) structures with different GaN barrier thicknesses are investigated by the temperature-dependent photoluminescence measurements with 325 nm He–Cd laser. At low temperatures the luminescence intensity of thick-barrier MQWs is enhanced by the increased photogenerated carriers from the thicker GaN barriers, even though the polarization field in QWs is promoted. As the temperature rises, an anomalous increase of luminescence intensity is observed from 100 to 150 K for both samples. This may be ascribed to the increased nonequilibrium carriers in the InGaN QWs due to the migration of thermal carriers from p-GaN and n-GaN layers into the depletion region. Therefore, the influence of photogenerated carriers in GaN layers on the luminescence properties of InGaN/GaN MQWs should be considered carefully for the 325-nm photoluminescence system.

Temperature and bias anomalies in the photoluminescence of InAs quantum dots coupled to a Fermi reservoir

We present anomalous behavior of temperature-dependent photoluminescence (PL) measurements on InAs quantum dot ensembles coupled to an electron reservoir in an $n\ensuremath{-}i\ensuremath{-}p$ diode structure. When negative gate voltages are applied to the sample, an anomalous initial increase of the integrated PL signal with rising temperature is observed for the ground-state and first-excited-state emission peaks. In contrast, measurements at positive gate voltages show no such anomaly and are well described by the commonly used Arrhenius model. Unlike previous studies on uncoupled quantum dot ensembles, we show that in quantum dot diode structures the anomalous temperature dependence and its dependence on the applied bias voltage is dominated by electrons tunneling from the electron reservoir to the quantum dots. Tunneling electrons enhance the PL signal by recombining with holes stored in the quantum dots and the tunneling rate depends on temperature via the Fermi distribution in the electron reservoir. With the implementation of a rate-based tunnel coupling, we develop a modified Arrhenius model that takes the observed anomalies excellently into account. Gate voltage dependent PL measurements at 77 K are further compared to capacitance-voltage spectroscopy measurements on the same sample, supporting the proposed interpretation. The PL peak width shows a characteristic evolution as a function of temperature, which is discussed qualitatively in terms of our model.

Pinning energy and anisotropy properties of a Fe(Se, Te) iron based superconductor

The measurements of DC magnetization M as a function of magnetic field (H) and time (t) have been performed in order to study the superconducting and pinning properties of a Fe(Se, Te) iron based superconductor fabricated by means of the Bridgman technique. By performing the superconducting hysteresis loops M(H) at different temperatures in the case of perpendicular and parallel field, the critical current density Jc(H) has been extracted in the framework of the Bean critical state model for both configurations. The Jc(H) curves have shown the presence of the second magnetization peak effect that causes an anomalous increase in the field dependence of the critical current density. In order to obtain the Jc anisotropy of the sample, we have performed the ratio between perpendicular and parallel critical current density values and compared its values with the literature ones. The information regarding the pinning energy U have been extracted by means of the relaxation of the irreversible magnetization M(t) in the case H∣∣c. In particular, performing relaxation measurements at different temperatures and magnetic fields, the temperature dependence of the pinning energy U(T) at different magnetic fields has been obtained showing an anomalous temperature scaling of the curves. The presence of a maximum in the U(T) curves suggests a pinning crossover at a given field and temperature Hcr(T). The Hcr(T) values have been fitted with the equation Hcr(T) = Hcr(0) (1 − T/T*)n whose results confirm the correlation between the elastic/plastic crossover and the end of the peak effect phenomenon.

Spin-gapless semiconducting nature of Co-rich Co1+xFe1−xCrGa

In this report, we present structural, electronic, magnetic and transport properties of Co-rich spin gapless semiconductor CoFeCrGa using both theoretical and experimental techniques. The key advantage of Co-rich samples $\mathrm{Co_{1+x}Fe_{1-x}CrGa}$ is the high Curie temperature (T$\mathrm{_C}$) and magnetization, without compromising the SGS nature (up to x = 0.4), and hence our choice. The quaternary Heusler alloys $\mathrm{Co_{1+x}Fe_{1-x}CrGa}$ (x = 0.1 to 0.5) are found to crystallize in LiMgPdSn-type structure having space group $F\bar{4}3m$ (\# 216). The measured Curie temperature increases from 690 K (x = 0) to 870 K (x = 0.5). Observed magnetization values follow the Slater-Pauling rule. Measured electrical resistivity, in the temperature range of 5-350 K, suggests that the alloys retain the SGS behavior up to x = 0.4, beyond which it reflects metallic character. Unlike conventional semiconductors, the conductivity value ($\mathrm{\sigma_{xx}}$) at 300 K lies in the range of 2289 S $\mathrm{cm^{-1}}$ to 3294 S $\mathrm{cm^{-1}}$, which is close to that of other reported SGS materials. The anomalous Hall effect is comparatively low. The intrinsic contribution to the anomalous Hall conductivity increase with x, which can be correlated with the enhancement in chemical order. The anomalous Hall coefficient is found to increase from 38 S/cm for x = 0.1 to 43 S/cm for 0.3. Seebeck coefficients turn out to be vanishingly small below 300 K, another signature for being SGS. All the alloys (for different x) are found to be both chemically and thermally stable. Simulated magnetization agrees fairly with the experiment. As such Co-rich CoFeCrGa is a promising candidate for room temperature spintronic applications, with enhanced T$\mathrm{_C}$, magnetic properties and SGS nature.

Thermal expansion of the Al2SiO5 polymorphs, kyanite, andalusite and sillimanite, between 10 and 1573 K determined using time-of-flight neutron powder diffraction

Powder and single-crystal diffraction data measured from the three geologically important Al2SiO5 polymorphs, kyanite, andalusite and sillimanite, over the last six decades have given varying accounts of each polymorph’s thermal expansion, the scatter between and even within experimental datasets often being quite large. Furthermore, there are no lattice parameter determinations below 273 K, where the thermodynamic functions vary substantially, and few measurements above 1200 K. Accurate and precise lattice parameters of natural kyanite, andalusite and sillimanite have therefore been obtained in the range 10–1573 K using the high-resolution powder diffractometer (HRPD) at the ISIS neutron spallation source. Accuracy is ensured by the use of an internal standard (NIST silicon SRM640c) and use of a bulk probe (neutrons) to avoid the specimen-displacement corrections required by typical back-reflection X-ray diffraction methods. Precision is ensured by use of the time-of-flight method on one of the longest primary neutron flightpath instruments in the world. For kyanite, the improved precision reveals the true temperature dependence of the three inter-axial angles for the first time, permitting derivation of accurate thermal expansion tensor coefficients. For both andalusite and sillimanite, the measurements reveal hitherto unknown regions of substantial negative linear expansivity below room temperature, along the c-axis in andalusite and along the a-axis in sillimanite. Above 1200 K, sillimanite exhibits an anomalous increase in thermal expansion that may be due to a change in the Al/Si tetrahedral site ordering.

Modeling Electrical Resistivity of Naturally Aged Al–Mg–Si Alloys

Isothermal ageing of Al–Mg–Si alloys, stored at room temperature for more than 5 months, is associated with an unexpected significant increase in the overall electrical resistivity. This unexpected anomalous increase is not observed in alloys with shorter storage (natural ageing) times. This phenomenon is explained with a scenario, based on the evolution of the size distribution of Guinier–Preston (GP) zones during natural ageing and during subsequent artificial ageing. The proposed scenario can explain the contribution of natural ageing atomic clusters to this anomalous increase in the electrical resistivity. A physically based combined precipitation–electrical resistivity model, with the former being based on simultaneous nucleation-growth-coarsening reactions and the latter based on the Bragg scattering of electrons from atomic clusters, has been used to explain the electrical resistivity evolution. It is shown that the proposed model is capable of reproducing the experimental data in both short natural ageing (less than 5 months) and long natural ageing (more than 5 months) regimes.

An overview of climate change in Iran: facts and statistics

BackgroundThe climate change fact is intensive among the Middle East countries and especially Iran. Among the Middle East countries, Iran will experience an increase of 2.6 °C in mean temperatures and a 35% decline in precipitation in the next decades. In vice versa, Iran by total greenhouse gas (GHG) emissions nearly to 616,741 million tons of CO2 is the first responsible country to climate change in the Middle East, and seventh in the world. The high-level contribution of Iran to emissions of GHG depends on a significant production of oil, gas, and rapid urbanization. The present study aimed to reveal an overview of climate change facts and statistics in Iran.ResultsIn this manuscript, the evidential facts on climate change were investigated in global, regional, and national scales. For this purpose, the main increasing annual temperature and GHG emissions were considered. Besides, the variations of meteorological characteristics such as surface temperature, total precipitation, and upward longwave radiation (ULR) were reviewed in Iran indicating an anomalous decrease in precipitation events and anomalous increase in ULR and temperature characteristics confirming the global warming/climate change effects. Afterward, the legislative agreements on climate change concerning international adoptions and conventions were reviewed from Rio 1992 to NY 2016.ConclusionsThe results showed that further research and development should be considered the novel methods to explore renewable energy applications and to mitigate GHG emissions in order to overcome the increased risk of climate change effects. Technological affairs and international participants should support this target.

Interplay between the Coulomb Interaction and Hybridization in Ca and Anomalous Pressure Dependence of the Resistivity

Increasing external pressure gives rise to s–d electron transfer in calcium that results in the localization of the charge density in the interstices of the crystal structure, i.e., the formation of an electride. The corresponding electronic states are partially filled and localized and, hence, electronic correlations could arise. We have carried out theoretical calculations for the high-pressure phases of Ca taking into account the Coulomb interactions between the electronic states centered on the interstitial site. The results of our calculations and proposed microscopic model showed that the structural phase transition under high pressure is due to an interplay of hybridization and correlation effects. Furthermore, it was found that the Coulomb repulsion can explain the experimentally observed anomalous increase in resistivity of the simple cubic phase of calcium under pressure.

Gravitational Weakening of Seismic Origin as a Driving Mechanism of Some Astronomical Anomalies

The anomalous increase of the astronomical unit, the mysterious secular increase of the lunar eccentricity and the flyby anomaly are important issues of modern astronomy. This study aims to determine the effect of earthquakes on the origin of these anomalies. Based on conventional physics, we found the existence of earthquake-induced gravitational weakening within the earth-moon-sun system and beyond. New equations of gravitation, including time dilation, are introduced that can explain the anomalous increase of the astronomical unit and the lunar orbit. A modified equation that includes the effect of massive quakes also explains the anomalous increase of the lunar eccentricity. Furthermore, the results of the present study can explain the flyby and Pioneer anomalies experienced by spacecraft during gravity assisted maneuvers. A modification of the 3rd Law of Kepler is also presented. Implications on the elliptic orbit of the earth, its reduced velocity and the occurrence of leap years are also discussed. Using the seismic-induced gravitational weakening model, probable trigger mechanisms of the faint young sun paradox and the Allais effect are also presented. An estimate of the age of the earth based on the observed values of the Hubble parameter and the USGS earthquake data for the past century is also presented. A new model of the seismic-driven expanding universe and a new equation to determine the expansion rate of galaxies and the universe is also proposed. The sudden earth’s retreat due to gravitational weakening and its implication on anomalous astronomical refraction and flight risk at night especially near the equatorial region, and its effect on the abrupt satellite orbital decay, spin and drift are also discussed. This study may also shed light on the occurrence of sinkholes and massive landslides. Finally, this study proposes a new equation that can explain the observed changes in the fine structure constant.

Features of Radiation-Defect Annealing in n-Ge Single Crystals Irradiated with High-Energy Electrons

The isothermal annealing of n-Ge single crystals irradiated with 10-MeV electrons to the fluence Φ = 5 × 1015 cm−2 has been studied. On the basis of the measured temperature dependences of the Hall constant and by solving the electroneutrality equations, the concentrations of radiation-induced defects (A-centers) in irradiated n-Ge single crystals are calculated both before and after the annealing. An anomalous increase of the Hall constant is found, when the irradiated n-Ge single crystals were annealed at Tan = 403 K for up to 3 h. The annealing at the temperature Tan = 393 K for 1 h gave rise to the np conversion in the researched crystals. The revealed effects can be explained by the concentration growth of A-centers owing to the generation of vacancies at the annealing of disordered crystal regions.

Importance of Martensite Spatial Distribution at Large Volume Fractions in Imparting Ductility in High-Strength Dual-Phase Steel

Controlled austenite decomposition in a cold-rolled steel was carried out in a hot-dip process simulator with different inter-critical annealing process parameters to produce dual-phase steel consisting of martensite phase fraction above 50%. The evolving microstructure was characterized by using scanning electron microscope and electron backscattered diffraction techniques. Macro- and micro-texture was characterized by using x-ray diffraction and electron backscattered diffraction techniques, respectively. Uniaxial tensile deformation showed a very good combination of ultra-high strength above 900 MPa with uniform elongation of above 7%. An anomalous increase in ductility was observed for steel with high martensite volume fraction of 62.2% compared to that of lower fraction of 52.3%, indicating the influence of size and spatial distribution arrangement of ferrite and martensite phases. The enhancement in the ductility with high strength was attributed to the improved plastic deformability of hard fine martensite phase along with fine ferrite surrounding it. The nature of micro- and macro-texture was also found to affect strain partitioning compatibility between ferrite and martensite in this study.

Modulation of ferromagnetism and transport in BxCyNz thin films via nitrogen doping and defects

Boron carbonitride (BxCyNz) represents an interesting family of materials containing all light elements and two dimensional graphene like hybrid layers. Although rich literature exists on this peculiar material in chemically processed form, there are relatively fewer reports on device application-worthy thin film form. This form also offers a natural platform for basic studies on important aspects such as magnetism and transport, which have attracted attention in the context of ferromagnetism in doped and defect carbon systems. Thus, in this work we have grown thin films of this compound using Pulsed Laser Deposition (PLD) method, and investigated their magnetic and transport properties in their entirety along with the detailed electronic structure using various spectroscopic techniques like X-ray photoelectron spectroscopy (XPS), Valence Band Spectroscopy (VBS) and X-ray absorption near edge spectroscopy (XANES). In depth analysis of the typical role of dopants and defects, especially the prevalent nitrogen defects, is elucidated using Density Functional Theory (DFT) calculations to understand the experimental observations. A dramatic crossover in the transport mechanism of charge carriers is observed in this system with the change in doping level of specific nitrogen defects. A robust and high saturation magnetization is achieved in BCN films which is higher by almost hundred times as compared to that in similarly grown undoped carbon film. An anomalous transition and increase in coercive field is also observed at low temperature. A careful analysis brings out the intriguing role of specific nitrogen defects in defining the peculiar nature and concentration dependence of the physical properties of this system.

Vortex tube modelling: outlet parameter dependencies of cold air production

A model of a counterflow vortex tube has been prepared to study the dependence of the influence of the parameters of cold and hot outlets on the production of cold air. For a fixed geometry of the vortex tube, a simulation is performed with an independent change of the length of the cold outlet nozzle, the angle of the widening of the cold outlet nozzle, and the hot outlet area. In a series of experiments, the pressure of air supplied to the inlet varies in order to take into account the possible effects of computational and model errors. An anomalous increase in the temperature of the outgoing air was observed with a hot outlet area of ∼30 cm2. Conclusions were drawn about the range of reasonable values of the outlet parameters for the considered configuration of the vortex tube.