Temperature-independent Component Research Articles

The role of fine aggregate matrix in the linear viscoelastic behaviour of cement-bitumen treated materials

The use of cold recycling technologies, including cement-bitumen treated materials (CBTM), is rising to address the environmental and economic challenges required for implementing sustainable road pavements. However, to obtain performances comparable to those of hot bituminous mixtures, the advanced study of these relatively new materials is essential, also considering the analysis of the linear viscoelastic (LVE) behaviour. This research studies the complex modulus of fine aggregate matrix (FAM) mortars, representative of the binding matrix of CBTM mixtures, characterised by several compositions. The experimental results were modelled considering both viscous and time- and temperature-independent dissipation components. Findings showed that the LVE behaviour of FAM mortars strongly depends on their composition, especially in terms of bituminous components, i.e. fresh and aged bitumen, and cement. Besides, the aged bitumen coating the reclaimed asphalt aggregate plays a role in the LVE response of CBTM mortars and mixtures.

Complex modulus of cement-bitumen treated materials produced with different reclaimed asphalt gradations

The increasing attention over cold recycling technologies as sustainable paving solutions requires a proper characterisation in terms of complex modulus for supporting the pavement design. Among cold recycled materials, cement bitumen treated materials (CBTM) benefit from the presence of both bituminous and cementitious binders. This research aims at characterising the complex modulus of CBTM mixtures produced with three different gradations, modified bitumen emulsion and two types of cement. The complex modulus measurements were modelled considering the usual viscous dissipation behaviour, linked to the bituminous component of the mixtures, along with a time- and temperature-independent dissipation component. The results showed that both the aggregate skeleton and the composition of the fine aggregate matrix affected the rheological behaviour. Furthermore, the role played by the aged binder contained in the reclaimed asphalt aggregate was highlighted by the parameters of the rheological model.

Magnetic and thermal properties of alloys close in composition to the spin gapless semiconductor Mn2CoAl

The field dependence of magnetization at T = 4.2 K and in magnetic fields of up to 70 kOe, temperature dependences of magnetization (2 K < T < 300 K), heat capacity (2 K < T < 30 K) and magnetic susceptibility (2 K < T < 1000 K) for Mn1.99Co0.96Al1.05 and Mn1.79Co1.25Al0.96 alloys, closed in composition to the Mn2CoAl spin gapless semiconductor, were studied. Alloys studied were demonstrated to be the band ferromagnets. Their high-field (H > 11 kOe) magnetization is described in the Stoner models with the Rhodes-Wohlfarth parameter pRW = 1.3 for Mn1.99Co0.96Al1.05 and pRW = 2.3 for Mn1.79Co1.25Al0.96. When the composition deviates from the stoichiometric Mn2CoAl, the spontaneous moment decreases slightly, the effective moment, on the contrary, increases. In this case, a negative sign of the temperature-independent component of the paramagnetic susceptibility is observed. The density of states n(EF) at Fermi level and the Debye temperature ΘD of studied alloys have the usual values for 3d-metal alloys.

Differing precipitation response between solar radiation management and carbon dioxide removal due to fast and slow components

Abstract. Solar radiation management (SRM) and carbon dioxide removal (CDR) are geoengineering methods that have been proposed to mitigate global warming in the event of insufficient greenhouse gas emission reductions. Here, we have studied temperature and precipitation responses to CDR and SRM with the Representative Concentration Pathway 4.5 (RCP4.5) scenario using the MPI-ESM and CESM Earth system models (ESMs). The SRM scenarios were designed to meet one of the two different long-term climate targets: to keep either global mean (1) surface temperature or (2) precipitation at the 2010–2020 level via stratospheric sulfur injections. Stratospheric sulfur fields were simulated beforehand with an aerosol–climate model, with the same aerosol radiative properties used in both ESMs. In the CDR scenario, atmospheric CO2 concentrations were reduced to keep the global mean temperature at approximately the 2010–2020 level. Results show that applying SRM to offset 21st century climate warming in the RCP4.5 scenario leads to a 1.42 % (MPI-ESM) or 0.73 % (CESM) reduction in global mean precipitation, whereas CDR increases global precipitation by 0.5 % in both ESMs for 2080–2100 relative to 2010–2020. In all cases, the simulated global mean precipitation change can be represented as the sum of a slow temperature-dependent component and a fast temperature-independent component, which are quantified by a regression method. Based on this component analysis, the fast temperature-independent component of the changed atmospheric CO2 concentration explains the global mean precipitation change in both SRM and CDR scenarios. Based on the SRM simulations, a total of 163–199 Tg S (CESM) or 292–318 Tg S (MPI-ESM) of injected sulfur from 2020 to 2100 was required to offset global mean warming based on the RCP4.5 scenario. To prevent a global mean precipitation increase, only 95–114 Tg S was needed, and this was also enough to prevent global mean climate warming from exceeding 2∘ above preindustrial temperatures. The distinct effects of SRM in the two ESM simulations mainly reflected differing shortwave absorption responses to water vapour. Results also showed relatively large differences in the individual (fast versus slow) precipitation components between ESMs.

Temporal variation in soil respiration and its sensitivity to temperature along a hydrological gradient in an alpine wetland of the Tibetan Plateau

Wetlands are predicted to experience lowered water tables due to permafrost degradation in the Tibetan Plateau. These changes may affect carbon cycle processes such as soil respiration (Rs). However, the magnitude, patterns and controls of Rs remain poorly understood in alpine wetlands with their distinct hydrological regimes. Here, we conducted a field study on Rs from 2012 to 2014 in three alpine ecosystems on the Tibetan Plateau—fen, wet meadow and meadow—with soil water decreases along hydrological gradients. From 2012 to 2014, the annual Rs was 128.9–193.3 g C m−2yr−1, 281.5–342.9 g C m−2yr−1, and 663.4–709.1 g C m−2yr−1 for the fen, wet meadow, and meadow, respectively. An abrupt increase in CO2 emissions was caused by the spring thawing of the frozen soil in the fen and wet meadow, contributing 20.4–37.6% and 13.2–17.4%, respectively, to the annual Rs. The diurnal variation in the Rs was site specific among the three ecosystems, with one peak at 1300 h in the fen and meadow and two peaks at 1300 h and 1900 h in the wet meadow. The temperature-independent components of the diurnal variation in Rs were generally explained by photosynthetically active radiation in the fen and wet meadow, but not in the meadow. The temperature sensitivity of the Rs (unconfounded Q10) varied significantly among the three ecosystems, with the highest values occurring in the wet meadow, implying that permafrost thaw-induced wetland drying from the fen to the wet meadow could enhance the response of CO2 emissions to climate warming but that further drying from the wet meadow to the meadow probably weakens the effect of warming on the Rs. Our study emphasized the important role of the hydrological regime in regulating the temporal variation in Rs and its response to climate warming.

Aerosol versus Greenhouse Gas Effects on Tropical Cyclone Potential Intensity and the Hydrologic Cycle

AbstractAerosol cooling reduces tropical cyclone (TC) potential intensity (PI) more strongly, by about a factor of 2 per degree of sea surface temperature change, than greenhouse gas warming increases it. This study analyzes single-forcing and historical experiments from phase 5 of the Coupled Model Intercomparison Project, aiming to understand the physical mechanisms behind this difference. Calculations are done for the tropical oceans of each hemisphere during the relevant TC seasons, emphasizing multimodel means. PI theory is used to interpret the difference in the PI response to aerosol and greenhouse gas forcings in terms of three factors. The net surface turbulent heat flux (sum of the latent and sensible heat fluxes) explains half of the difference, thermodynamic efficiency explains at most a small fraction, and surface wind speed does not explain the remainder, perhaps because of the use of monthly mean data. Changes in turbulent surface heat fluxes are interpreted as responses to surface radiative flux changes in the context of the energy balance of the ocean mixed layer. Radiative kernels are used to estimate what fractions of the surface radiative flux changes are feedbacks due to temperature and water vapor changes. The greater effect of aerosol forcing occurs because shortwave forcing has a greater direct, temperature-independent component at the surface than does longwave forcing, for a forcing amplitude that provokes the same SST change. This conclusion recalls prior work on the response of precipitation to radiative forcing, and the similarities and differences between precipitation and potential intensity in this regard are discussed.

An Online-Calibrated Time Series Based Model for Day-Ahead Natural Gas Demand Forecasting

This paper proposes a new online-calibrated time series based model with the application to the day-ahead natural gas demand (GD) forecasting. A double-stage parallel process is developed for creating the forecasting model. The two stages include analysis of the temperature-independent and temperature-dependent components of the GD. The former stage is executed by online processing of the historical GD information considering the intertemporal variation of the GD. The latter stage, however, is conducted by exploiting the features of the GD information correlated with the ambient temperature. The forecast of the temperature is incorporated into the GD forecasting model through a correlation-based function. The model can generate the day-ahead GD forecast with both the hourly and intrahourly resolutions without compromising the forecast accuracy. The model is calibrated online using the historical GD and temperature information to achieve a higher forecast accuracy. The practical challenges associated with the industrial application of the model are also discussed. The application of the proposed model is numerically examined using real-world GD and temperature data, and the results are comprehensively studied. The outcomes reveal the efficacy and feasibility of the proposed model under various cases.

On the role of isotopic composition in crystal structure, thermal and charge-transport characteristics of dodecaborides LuNB12 with the Jahn-Teller instability

Crystal structures, thermal and charge-transport (resistivity and Seebeck coefficient) characteristics of dodecaborides LuNB12 are studied to determine the role of boron isotopic composition N = 10, 11, natural. Small distortions of the fcc lattice are observed and attributed to cooperative Jahn-Teller effect in the boron sublattice. The Einstein and Debye temperatures, respectively for Lu and B atoms, are determined based on equivalent atomic displacement parameters (ADPs) refined as a part of structure model. Additionally, ADP values are separated into temperature dependent and independent components, arising from (i) thermal and (ii) zero temperature vibrations, together with (iii) static shifts of few atoms from lattice sites. Atomic disordering is most expressed in LunatB12 as follows from its ADP values and the Schottky anomalies in heat capacity. The largest static ADP components of LunatB12 are surprisingly combined with the lower resistivity and thermopower as compared to isotopically pure crystals. One may suppose the static shifts (defects) are centers of pinning facilitating formation of additional conductive channels (dynamic charge stripes), which reveal themselves on difference Fourier maps of electron density.

Modeling the Role of the Buildup of Magnetic Charges in Low Anisotropy Polycrystalline Materials

A Stoner–Wohlfarth-type model is used to demonstrate the effect of the buildup of magnetic charges near the grain boundaries of low anisotropy polycrystalline materials, revealed by measuring the magnetization during positive-field warming after negative-field cooling. The remnant magnetization after negative-field cooling has two different contributions. The temperature-dependent component is modeled as an assembly of particles with thermal relaxation. The temperature-independent component is modeled as an assembly of particles overcoming variable phenomenological energy barriers corresponding to the change in susceptibility when the anisotropy constant changes its sign. The model is applicable to soft-magnetic materials where the buildup of the magnetic charges near the grain boundaries creates demagnetizing fields opposing, and comparable in magnitude to, the anisotropy field. The results of the model are in qualitative agreement with published data revealing the magneto-thermal characteristics of polycrystalline gadolinium.

Real-space analysis of radiation-induced specific changes with independent component analysis.

A method of analysis is presented that allows for the separation of specific radiation-induced changes into distinct components in real space. The method relies on independent component analysis (ICA) and can be effectively applied to electron density maps and other types of maps, provided that they can be represented as sets of numbers on a grid. Here, for glucose isomerase crystals, ICA was used in a proof-of-concept analysis to separate temperature-dependent and temperature-independent components of specific radiation-induced changes for data sets acquired from multiple crystals across multiple temperatures. ICA identified two components, with the temperature-independent component being responsible for the majority of specific radiation-induced changes at temperatures below 130 K. The patterns of specific temperature-independent radiation-induced changes suggest a contribution from the tunnelling of electron holes as a possible explanation. In the second case, where a group of 22 data sets was collected on a single thaumatin crystal, ICA was used in another type of analysis to separate specific radiation-induced effects happening on different exposure-level scales. Here, ICA identified two components of specific radiation-induced changes that likely result from radiation-induced chemical reactions progressing with different rates at different locations in the structure. In addition, ICA unexpectedly identified the radiation-damage state corresponding to reduced disulfide bridges rather than the zero-dose extrapolated state as the highest contrast structure. The application of ICA to the analysis of specific radiation-induced changes in real space and the data pre-processing for ICA that relies on singular value decomposition, which was used previously in data space to validate a two-component physical model of X-ray radiation-induced changes, are discussed in detail. This work lays a foundation for a better understanding of protein-specific radiation chemistries and provides a framework for analysing effects of specific radiation damage in crystallographic and cryo-EM experiments.

Surface magnetism of strontium titanate

SrTiO3 plays a central role in oxide electronics. It is the substrate of choice for functional oxide heterostructures based on perovskite-structure thin-film stacks, and its surface or interface with a polar oxide such as LaAlO3 can become a 2D conductor because of electronic reconstruction or the presence of oxygen defects. Inconsistent reports of magnetic order in SrTiO3 abound in the literature. Here, we report a systematic experimental study aimed at establishing how and when SrTiO3 can develop a magnetic moment at room temperature. Polished (1 0 0), (1 1 0) or (1 1 1) crystal slices from four different suppliers are characterized before and after vacuum annealing at 750 °C, both in single-crystal and powdered form. Impurity content is analysed at the surface and in the bulk. Besides the underlying intrinsic diamagnetism of SrTiO3, magnetic signals are of three types—a Curie law susceptibility due to dilute magnetic impurities at the ppm level, a hysteretic temperature-dependent ferromagnetic impurity contribution, and a practically anhysteretic defect-related temperature-independent component that saturates in about 200 mT. The latter component is intrinsic. It is often the largest, reaching 10 μB nm−2 of the surface area or more and dominating the magnetic response in low fields at room temperature. It is associated with defects near the surface, and can be destroyed by treatment with Tiron (C6H4Na2O8S2), an electron donor molecule that forms a strong complex with titanium at the surface. The origin of this unusual high-temperature ferromagnetic-like response is discussed.

Time-resolved photoluminescence characterization of oxygen-related defect centers in AlN

Time-resolved photoluminescence (PL) spectroscopy has been employed to investigate the emission characteristics of oxygen-related defects in AlN in the temperature region from 77 to 500 K. Two PL components with different decay constants are observed in the near-ultraviolet to visible regions. One is the PL component with decay time of <10 ns and its peak position shifts to longer wavelengths from ∼350 to ∼500 nm with increasing temperature up to 500 K. This PL component is attributed to the radiative relaxation of photoexcited electrons from the band-edge states to the ground state of the oxygen-related emission centers. In the time region from tens to hundreds of nanoseconds, the second PL component emerges in the wavelength region from 300 to 400 nm. The spectral shape and the decay profiles are hardly dependent on temperature. This temperature-independent PL component most likely results from the transfer of photoexcited electrons from the band-edge states to the localized excited state of the oxygen-related emission centers. These results provide a detailed insight into the radiative relaxation processes of the oxygen-related defect centers in AlN immediately after the photoexcitation process.

Understanding bifurcations in FC–ZFC magnetization of dilutely Fe3+ doped CdS nanoparticles

The bifurcation between field-cooled and zero-field-cooled curves in magnetization vs. temperature measurement has been investigated in Fe3+ doped CdS nanoparticles with different crystal structures (wurtzite and zinc-blende) and external magnetic fields. It has been found that the field-cooled and zero-field-cooled curves start bifurcating from ambient temperature in diluted (powder) samples irrespective of crystal structures. However, in the high density samples (prepared by pelletizing the powder samples at a pressure of ~200MPa) the bifurcation is significantly reduced within entire temperature regime. We have shown that the observed bifurcation in diluted (powder) samples is neither a consequence of blocking of super-moments in nanoparticle systems nor the spin-glass type transition, rather dominated by temperature independent component of magnetic susceptibility.

Extraction and scattering analyses of 2D and bulk carriers in epitaxial graphene-on-SiC structure

Hall effect measurements of a graphene-on-SiC system were carried out as a function of temperature (1.8–200K) at a static magnetic field (0.5T). With the analysis of temperature dependent single-field Hall data with the Simple Parallel Conduction Extraction Method (SPCEM), bulk and two-dimensional (2D) carrier densities and mobilities were extracted successfully. Bulk carrier is attributed to SiC substrate and 2D carrier is attributed to the graphene layer. For each SPCEM extracted carrier data, relevant three-dimensional or 2D scattering analyses were performed. Each SPCEM extracted carrier data were explained with the related scattering analyses. A temperature independent mobility component, which may related to an interaction between graphene and SiC, was observed for both scattering analyses with the same mobility limiting value. With the SPCEM, effective ionized impurity concentration of SiC substrate, extracted 2D-mobility, and sheet carrier density of the graphene layer are calculated with using temperature dependent static magnetic field Hall data.

Interaction of Defects with Quantum Well States: Electrostatic-Dependant Response Time for Traps in AlGaN/GaN HEMTs

Recovery transients in high-voltage AlGaN/GaN HEMTs following both blocking voltage and ON-state stress show strong dependence on stress time. The defect time constant spectra exhibit a temperature-dependant component (TG1, Ea = 0.6 eV) and a temperature-independent component (TG2). With increased stress time and larger current collapse, the time constants for TG2 become progressively longer. The stress-time-dependent behavior of TG2 is shown to be consistent with the capture of trapped carriers in the AlGaN barrier directly by quantum well states, originating from the same defect giving rise to the 0.6 eV behavior. By modulating this alternate recombination pathway, the electric field normal to the AlGaN/GaN interface is shown to have a strong effect on reducing the response time of the trap to several orders of magnitude below its bulk response time. This demonstrates that barrier design may be utilized to tune the recovery characteristics of the HEMT.

140 H/D Isotopomers Identified by Long-Range NMR Hyperfine Shifts in Ruthenium(III) Ammine Complexes. Hyperconjugation in Ru–NH3Bonding

(1)H NMR spectra of the paramagnetic cyanide-bridged mixed-valence compound [(η(5)-C5H5)Fe(CO)2(μ-CN)Ru(NH3)5](CF3SO3)3 (I) have been obtained in several solvents. When traces of partially deuterated water are present, instead of a single cyclopentadienyl (Cp) resonance shifted by the hyperfine interaction, numerous well-resolved resonances are observed. The spectra were simulated satisfactorily by giving the appropriate statistical weight to 140 possible H/D isotopomers formed by deuteration in the five ruthenium(III) ammine ligands. The proliferation of distinct resonances occurs because (a) the hyperfine shifts (HSs) due to each sequential deuteration in a single ammine are different and (b) while deuteration in an ammine cis to the cyanide bridge causes a downfield shift, in the trans ammine it causes an upfield shift that is nearly twice as large. All of these shifts exhibit a 1/T dependence, but temperature-independent components, due to large second-order Zeeman effects at the Ru(III) center, are also present. Combining the results of density functional theory calculations with data from metal-metal charge-transfer optical transitions and with the effect of solvent-induced NMR HSs, it is argued that Fermi contact shifts at the Cp protons are insignificant compared to those due to the dipolar (pseudocontact) mechanism. Analytical expressions are presented for the dependence of the HS on the tetragonal component of the ligand field at the Ru(III) ion. The tetragonal field parameter, defined as the energy by which the 4d(xy) orbital exceeds the mean t(2g) orbital energy, was found to be 147, 52, and 76 cm(-1), in dimethylformamide, acetone, and nitromethane, respectively. The effects of deuteration show that there is a significant component of hyperconjugation in the Ru-ammine interaction and that ND3 is a weaker π donor than NH3. A single deuteration in an axial ammine increases the tetragonal field parameter (ν) by +2.8 cm(-1), resulting in a HS of -37 ppb in the Cp proton resonance, whereas a single deuteration in an equatorial ammine decreases the field by -1.5 cm(-1) with a HS of +20 ppb, despite a nominal separation of seven chemical bonds. We analyze the origin of this remarkable sensitivity, which relies on the favorable characteristics of the Ru(III) low-spin t(2g)(5) configuration, having a spin-orbit coupling constant ζ ≈ 950 cm(-1).

Decrease in the red cell cofactor 2,3-diphosphoglycerate increases hemoglobin oxygen affinity in the hibernating brown bearUrsus arctos

During winter hibernation, brown bears (Ursus arctos) reduce basal O(2) consumption rate to ∼25% compared with the active state, while body temperature decreases moderately (to ∼30°C), suggesting a temperature-independent component in their metabolic depression. To establish whether changes in O(2) consumption during hibernation correlate with changes in blood O(2) affinity, we took blood samples from the same six individuals of hibernating and nonhibernating free-ranging brown bears during winter and summer, respectively. A single hemoglobin (Hb) component was detected in all samples, indicating no switch in Hb synthesis. O(2) binding curves measured on red blood cell lysates at 30°C and 37°C showed a less temperature-sensitive O(2) affinity than in other vertebrates. Furthermore, hemolysates from hibernating bears consistently showed lower cooperativity and higher O(2) affinity than their summer counterparts, regardless of the temperature. We found that this increase in O(2) affinity was associated with a significant decrease in the red cell Hb-cofactor 2,3-diphosphoglycerate (DPG) during hibernation to approximately half of the summer value. Experiments performed on purified Hb, to which DPG had been added to match summer and winter levels, confirmed that the low DPG content was the cause of the left shift in the Hb-O(2) equilibrium curve during hibernation. Levels of plasma lactate indicated that glycolysis is not upregulated during hibernation and that metabolism is essentially aerobic. Calculations show that the increase in Hb-O(2) affinity and decrease in cooperativity resulting from decreased red cell DPG may be crucial in maintaining a fairly constant tissue oxygen tension during hibernation in vivo.

Paramagnetic Behaviour in RE<sub>2</sub>W<sub>2</sub>O<sub>9</sub> Tungstates (RE = Pr, Nd, Sm – Gd)

Magnetic susceptibility measurements revealed a disordered state of magnetic moments above 4.2 K for all compounds under study, and a weak response to the magnetic field and the temperature for Sm2W2O9 and Eu2W2O9 tungstates. The temperature independent component of magnetic susceptibility has a positive value for RE2W2O9 (RE = Pr, Nd and Gd) indicating a domination of van Vleck contribution. Only for Gd2W2O9 the magnetization is a universal function of µ0H/T, characteristic for the superparamagnetism.

Low temperature studies of surface plasmon polaritons in silver films

We have studied propagation of surface plasmon polaritons at cryogenic temperatures and found the temperature-dependent optical loss reduction to be modest. Large temperature-independent components of the dc resistivity and the imaginary part of the dielectric constant at optical frequency are due to scattering on bulk and surface defects rather than on phonons. This suggests that the quality of metal should be improved first, after which a further improvement can be sought through the reduction of temperature.

High-pressure spin shifts in the pseudogap regime of superconducting YBa2Cu4O8as revealed byO17NMR

A new NMR anvil cell design is used for measuring the influence of high pressure on the electronic properties of the high-temperature superconductor YBa$_2$Cu$_4$O$_8$ above the superconducting transition temperature $T_{\rm c}$. It is found that pressure increases the spin shift at all temperatures in such a way that the pseudo-gap feature has almost disappeared at 63 kbar. This change of the temperature dependent spin susceptibility can be explained by a pressure induced proportional decrease (factor of two) of a temperature dependent component, and an increase (factor of 9) of a temperature independent component, contrary to the effects of increasing doping. The results demonstrate that one can use anvil cell NMR to investigate the tuning of the electronic properties of correlated electronic materials with pressure.