Positive Temperature Shift Research Articles

Productivity of Winter Wheat Cultivated by Direct Seeding: Measuring the Effect of Hydrothermal Coefficient in the Arid Zone of Central Fore-Caucasus

In arid zones, the yields of soft winter wheat varieties are particularly affected by the variations of hydrothermal conditions. This especially applies to direct seeding practices, for which the understanding of the links between hydrothermal parameters of soil and the environment, on one side, and the productivity of winter wheat, on the other, is one of the founding pillars of stable agricultural systems. On the case of the arid zone of Central Fore-Caucasus, this study investigates changes in the duration of interphase periods of plant development, plant density, and yield. It is found that in 2019–2021, positive temperature shifts and drought resulted in an increase in the duration of the growing season of crop varieties, thinned plant density, and reduced productivity of drought-resistant varieties. Evaluation of indices, that determine the ecological and genetic variability of varieties in the “genotype-environment” system resulted in the establishment of models that described the effect of drought on crop yields by type of manifestation and forecrops (sunflower, chickpeas). It is shown that the average linear deviations improved phase techniques and changed the area of winter wheat cultivation. On the back of the further drought propagation, farmers in arid zones could benefit from breeding new varieties and hybrids of grain crop. These measures may increase or stabilize the productivity of winter wheat in arid environments. Specifically, for the arid zone of Central Fore-Caucasus, the study recommends reducing lands under grain crop and shifting the cultivation of winter wheat northward. This will reduce the impact of volatile climatic conditions on winter wheat productivity in the region.

Influence of the electron-phonon interaction on the temperature dependence of the phonon mode frequency in the II-VI compound solid solutions

We present an experimental investigation of the temperature dependence of the TO-phonon mode frequencies for the HgTe-based II-VI semiconductor solid solutions. In the case of the ternary Hg0.9Zn0.1Te solid solution was shown a discontinuity in the temperature dependence of the HgTe-like T0-mode and of the ZnTe-like T1-mode, similar to the Hg0.85Cd0.15Te system [Sheregii et al., Phys. Rev. Lett. 102, 045504 (2009)]. A generalization of the theoretical temperature shift of the phonon mode frequency as analytic equation is derived that includes both the anharmonic contribution and the electron-phonon e-p interaction which in this case is returnable—the electron subsystem effect on the phonon one. Data show that our equation satisfactorily describes the temperature shift of both Hg0.85Cd0.15Te and Hg0.90Zn0.10Te containing Dirac point (Eg ≡ Γ6 – Γ8 = 0) although one of the two constants describing the anharmonic shift of the HgTe-like mode should be positive what is abnormal too. In the case of the Hg0.80Cd0.20Te and Hg0.763Zn0.237Te solid solution, the role of the returnable e-p contribution is negligible but a positive temperature shift for the HgTe-like modes occurs. This result does not allow to explain the positive temperature shift of these modes merely by the contribution of the (e-p) interaction. Indeed, the relativistic contribution to the chemical bonds induces an abnormal temperature shift of the electron states in Hg-based semiconductors—the effect is expected since the Hg d spin-orbit split contribution to chemical bonds may lead to an abnormal temperature shift of the HgTe-like modes.

The magnetic state of 1212-type ruthenocuprate in magnetocaloricand magnetoresistivity measurements of polycrystalline samples ofRuSr2Gd1−xCexCu2O8 and Ru1−xSr2GdCu2O8

The magnetic properties of superconductingRu1−xSr2GdCu2O8 (x = 0, 0.02) andnon-superconducting RuSr2Gd1−xCexCu2O8 (x = 0.07,0.1) were investigated by means of magnetocaloric experiments with complementarymagnetoresistivity and ac susceptibility measurements. The isothermal magnetocaloric coefficientMT(B) assumes positive values in a broad range of temperatures(20 K≤T≤231 K) andmagnetic fields (0 T≤B≤13 T), i.e. also in the magnetically ordered state(Tm = 132 K forRuSr2GdCu2O8 andTm = 150 K forRuSr2Gd0.93Ce0.07Cu2O8) whichindicates no gain in the system’s magnetic entropy with increasing magnetic field. The maximum in theMT(B) dependence wasobserved for RuSr2GdCu2O8 in thetemperature vicinity of Tm, which indicates a ferromagnetic character of the accessed magneticcorrelations. No spontaneous ferromagnetic order was revealed as theMT assumes limiting zero values at zero magnetic field for the whole rangeof investigated temperatures. Temperature dependences of the specificheat reveal the magnetic-field-induced positive temperature shift of theanomaly associated with the magnetic transition in the Ru spin system. TheMT(B) dependences and the magnetoresistivity data suggest that the magnetic system may beinhomogeneous.

How a spin glass remembers; memory and rejuvenation from intermittency data: ananalysis of temperature shifts

The memory and rejuvenation properties of intermittent heat transport are exploredtheoretically and by numerical simulation for Ising spin glasses with short ranged interactions.The theoretical part develops a picture of non-equilibrium glassy dynamics recently introducedby the authors, which links irreversible ‘intermittent’ events, or ‘quakes’, to thermalfluctuations of record magnitude. The pivotal idea is that the largest energy barrierb(tw,T) surmountedprior to tw attemperature T determines the rate of the intermittent events neartw. The idea implies that the same rate after a negative temperature shift should be given by. The ‘effective age’ has an algebraic dependence ontw, whose exponent contains the temperatures before and after the shift. This analyticalexpression is confirmed by numerical simulations. Marginal stability suggests an asymmetrybetween cooling and heating; i.e. a positive temperature shift should erase the memory b(tw,T). This is confirmed by the simulations, which show a rate , controlled by the barrier . Additional ‘rejuvenation’ effects are also identified in the intermittency data for shifts ofboth signs.

Pressure dependence of thermal decomposition of ammonium nitrate oxidizer

There is an increasing interest in research and development of ecofriendly solid propellant systems which can replace the existing ones in applications particularly where the rockets have to be fired in close proximity ofthe personnel and smokeless HCI-free burning is desired. Ammonium nitrate (AN) is receiving wide attention as a possible substitute for ammonium perchlorate oxidizer in view of the hazardous nature of other candidates like nitramines and non-availability of substances like ammonium dinitramide in requisite quantities besides the cost effectiveness. The phase transitions and initial endothermic decomposition of ammonium nitrate, however, pose problems in its application in composite solid rocket propellants. The influence of pressure on phase transitions, melting and thermal decomposition characteristics of AN is required to be systematically studied in order to have an insight in the combustion mechanism of AN containing propellants. Pressure differential scanning calorimetric (PDSC) studies have consequently been conducted on pure AN under ambient conditions and upto a maximum inert pressure of 68.03 atm. The shifts in the phase transition peaks, melting and decomposition temperatures with pressure have been studied. It has been observed that thermal decomposition of AN remains an endothermic process upto a prepare of 20.41 atm and thereafter becomes exothermic in nature. Phase transitions, melting and decomposition processes are found to be pressure sensitive and the associated peaks register a positive temperature shift bearing a relationship with crystal structure in two distinct pressure segments corresponding to endo- and exothermic decomposition.

Thermal desorption spectroscopy of palladium and copper on silica

Thermal desorption spectroscopy of palladium and copper films grown on clean silica substrates was performed using CO 2 laser heating. After cleaning the surface by high temperature heating, a controlled, low coverage dose of metal atoms was deposited on the substrate. Temperature ramping was achieved using a constant laser power, the value of which depended on the nature of the metal and substrate as well as the substrate size. At high temperatures (above 1025 K for palladium and above 975 K for copper), metal films vaporize and desorption spectra provide information about the nature of the metal deposit and metal-support interaction. With increasing coverage of palladium on silica, a positive temperature shift in the leading edge of desorption was seen. At higher coverages, above about 2 × 10 15 atoms cm -2, a common leading edge appears and zero-order kinetic analysis gave E act values between 3.9 and 4.3 ± 0.1 eV which can be compared with the value of 3.83 eV for Δ H vap(1200 K) for palladium metal. Similar coverage-dependent properties were not seen for copper on silica; instead, a common desorption leading edge appeared down to submonolayer coverages. Zero-order analysis at about 1 × 10 15 atoms cm -2 gave an E act of 3.3 ± 0.1 eV, which is comparable with the value of 3.44 eV for Δ H vap(1100 K) for copper metal.

Reorientational motion of hydroxide ions in solid RbOH and CsOH

The temperature dependence of the O (H,D) − stretching modes (frequencies, halfwidths, IR, Raman) of polymorphic RbOH and CsOH is studied in terms of hydrogen bonding, disorder of hydroxide ions, and phase transitions. The different ν OD frequencies of isotopically dilue samples (RbOH mon. I and CsOH o-rh. II) in the IR and Raman spectra and the unusually large positive temperature shifts of these bands are interpreted as due to order—disorder transitions from hydrogen-bnded OH − ions in the low-temperature polymorphs to non-H-bonded ions in the room temperature modifications. The halfwidths of the O (H,D) − bands exhibit an Arrhenius type behaviour. In the deuterated compounds there are stronger hydrogen bonds (D-bonds) than in the non-deuterated samples (H-bonds). These findings are attributed to the greater hydrogen bond acceptor strength of OD − than that of OH −. In KBr discs, hitherto unknown isostructural hydroxide bromides of caesium and rubidium are formed.

Raman and infrared spectra of barium and strontium hydroxides and hydroxide hydrates

The Raman and i.r. spectra of the barium and strontium hydroxides and hydroxide hydrates Ba(OH) 2·8H 2O, Ba(OH) 2·3H 2O, β- and γ-Ba(OH) 2·1H 2O, α- and β-Ba(OH) 2, Sr(OH) 2·8H 2O, Sr(OH) 2·1 H 2O and Sr(OH) 2 are reported and structural and bonding features are discussed. The Raman spectra of the lower hydrates of barium and strontium hydroxide, viz. Ba(OH) 2·3H 2O, Sr(OH) 2·1H 2O, and β- and γ-Ba(OH) 2·1H 2O, do not show any water band, either as stretching or bending modes. This behaviour is probably due to the strong hydrogen bonding of the water of crystallization in the barium and strontium hydroxide hydrates. The hydroxide ions of most compounds under investigation, however, are not hydrogen bonded. This is shown from the small negative temperature shift of the OH (or OD) stretching modes in isotopically dilute samples. A positive temperature shift of the uncoupled stretching modes, as found for some of the hydroxide ions in Sr(OH) 2 and α- and β-Ba(OH) 2, is an unfailing indicator that hydrogen bridges are present. The stretching vibrations of non-hydrogen-bonded hydroxide ions have been found to vary from 3690 to 3500 cm −1. The possible reason for these large frequency shifts, i.e., weakening or hardening of the stretching frequency of free OH ions by the lattice potential, is discussed. Some rotatory modes of hydroxide ions and water molecules have been observed at unusually high frequencies above 1000 cm −1.

Infrarotspektren von Mg(OH) 2 bei erhöhten temperaturen

With increasing temperature the infrared absorption bands of Mg(OH) 2 shift to lower wave numbers and the strong absorption maximum between 660–300 cm −1 shows a marked decrease in intensity. The unexpectedly large positive temperature shift of the OH-stretching band at 3700 cm −1 is related to the thermal expansion of the Mg(OH) 2 lattice, which is anisotropic having its largest value parallel to the mean OH-vector. The shift can be explained by an electrostatic model taking into account the next-to-nearest neighbours of the OH −-group. The true O—H bond distance probably increases beyond the value of 0·984 Å extrapolated for Ca(OH) 2 at low temperatures.