Quasiparticle density of states of 2H-NbSe_2 single crystals revealed by low-temperature specific heat measurements according to a two-component model

Low-temperature specific heat in a dichalcogenide superconductor 2H-NbSe2 is measured in various magnetic fields. It is found that the specific heat can be described very well by a simple model concerning two components corresponding to vortex normal core and ambient superconducting region, separately. For calculating the specific heat outside the vortex core region, we use the Bardeen-Cooper Schrieffer （BCS） formalism under the assumption of a narrow distribution of the superconducting gaps. The field-dependent vortex core size in the mixed state of 2H-NbSe2, determined by using this model, can explain the nonlinear field dependence of specific heat coefficient γ（H）, which is in good agreement with the previous experimental results and more formal calculations. With the high-temperature specific heat data, we can find that, in the multi-band superconductor 2H-NbSe2, the recovered density of states （or Fermi surface） below Tc under a magnetic field seems not to be gapped again by the charge density wave （CDW） gap, which suggests that the superconducting gap and the CDW gap may open on different Fermi surface sheets.

Theoretical Study of Specific Heat and Density of States of MgB₂Superconductor in Two Band Model

MgB2 with Tc ≈ 40 K, is a record-breaking compound among the s-p metals and alloys. It appears that this material is a rare example of the two band electronic structures, which are weakly connected with each other. Experimental results clearly reveal that boron sub-lattice conduction band is mainly responsible for superconductivity in this simple compound. Experiments such as tunneling spectroscopy, specific heat measurements, and high resolution spectroscopy show that there are two superconducting gaps. Considering a canonical two band BCS Hamiltonian containing a Fermi Surface of π- and σ-bands and following Green’s function technique and equation of motion method, we have shown that MgB2 possess two superconducting gaps. It is also pointed out that the system admits a precursor phase of Cooper pair droplets that undergoes a phase locking transition at a critical temperature below the mean field solution. Study of specific heat and density of states is also presented. The agreement between theory and experimental results for specific heat is quite convincing. The paper is organized in five sections: Introduction, Model Hamiltonian, Physical properties, Numerical calculations, Discussion and conclusions.

The nature of electron density enhancement over a wide altitude range during ionosphere heating experiments at EISCAT

During the course of ionospheric heating experiments, researchers at the European Incoherent Scatter Scientific Association (EISCAT) observed an apparent electron density enhancement. The enhancement extended over a wide range of altitudes, above the reflection altitude of the high-frequency pump wave. However, whether this enhancement actually corresponds to a true enhancement in electron density remains an open question. When the dispersion relation of ion acoustic waves is followed, the frequency ratio of the enhanced ion line to the background ion line suggests that the profile of the effective ion mass may have remained unchanged. Furthermore, the solar radio flux and ion drift velocity indicate no significant changes in the ion species and their densities. In conclusion, the electron density enhancement observed at EISCAT should not, in fact, be considered a true enhancement.

Specific Heat and Charge Density of Quasi-One-Dimensional Interchain Coupling Organic Ferromagnets

On the basis of a generalized SSH model, an organic polymer ferromagnet theory is proposed at the finite temperature in the self-consistent mean field approximation, and the specific heat and charge density of the quasione-dimensional interehain coupling organic ferromagnets are presented. We find that an obvious feature is to present itself the round peak for the specific heat with the temperature. This indicates unambiguously the presence of the phase transition in the system. The transition temperature plays down with increasing of the interchain coupling t2 or decreasing of the electron repulsion u. The curves of charge density with the temperature debase monotonously. This result illustrates that the higher the temperature is, the more electrons are excited.

Impact of Heat Treatments and Hole Density (p) on the Structural, Electrical, and Superconducting Properties of LnSrBaCu3O6+z (Ln = Eu, Sm, Nd) Compounds

In this study, we thoroughly examined the impact of heat treatments and hole count (p) on the properties of LnSrBaCu3O6+z (Ln = Eu, Sm, Nd) compounds. We focused on preparation, X-ray diffraction with Rietveld refinement, AC susceptibility, DC resistivity measurements, and heat treatment effects. Two heat treatment types were applied: oxygen annealing [O] and argon annealing followed by oxygen annealing [AO]. As the rare earth Ln’s ionic radius increased, certain parameters notably changed. Specifically, c parameter, surface area S, and volume V increased, while critical temperature Tc and holes (p) in the CuO2 plane decreased. The evolution of these parameters with rare earth Ln’s ionic radius in [AO] heat treatment is linear. Regardless of the treatment, the structure is orthorhombic for Ln = Eu, tetragonal for Ln = Nd, orthorhombic for Ln = Sm [AO], and pseudo-tetragonal for Sm [O]. The highest critical temperature is reached with Ln = Eu (Tc [AO] = 87.1 K). Notably, for each sample, Tc [AO] surpasses Tc [O]. Observed data stems from factors including rare earth ionic size, improved cationic and oxygen chain order, holes count p in Cu(2)O2 planes, and in-phase purity of [AO] samples. Our research strives to clearly demonstrate that the density of holes (p) within the copper plane stands as a determinant impacting the structural, electrical, and superconducting properties of these samples. Meanwhile, the other aforementioned parameters contribute to shaping this density (p).

Computation of Stiffness and Damping Derivatives of an Ogive in a Limiting Case of Mach Number and Specific Heat Ratio

This work aims to compute stability derivatives in the Newtonian limit in pitch when the Mach number tends to infinity.In such conditions,these stability derivatives depend on the Ogive’s shape and not the Mach number.Generally,the Mach number independence principle becomes effective from M=10 and above.The Ogive nose is obtained through a circular arc on the cone surface.Accordingly,the following arc slopes are consideredλ=5,10,15,−5,−10,and−15.It is found that the stability derivatives decrease due to the growth inλfrom 5 to 15 and vice versa.Forλ=5 and 10,the damping derivative declines with an increase inλfrom 5 to 10.Yet,for the damping derivatives,the minimum location remains at a pivot position,h=0.75 for large values ofλ.Hence,whenλ=−15,the damping derivatives are independent of the cone angles for most pivot positions except in the early twenty percent of the leading edge.

The effects of variable specific heat on the stability of hypersonic boundary layer on a flat plate

The gas temperature within hypersonic boundary layer flow is so high that the specific heat of gas is no longer a constant but relates to temperature. How variable specific heat influences on boundary layer flow stability is worth researching. The effect of the variable specific heat on the stability of hypersonic boundary layer flows is studied and compared with the case of constant specific heat based on the linear stability theory. It is found that the variable specific heat indeed has some effects on the neutral curves of both the first-mode and the second-mode waves and on the maximum rate of growth also. Therefore, the relationship between specific heat and temperature should be considered in the study of the stability of the boundary layer.

Influence of light availability on the specific density,size and sinking loss of Anabaena flos-aquae and Scenedesmus obliquus

Harmful algal blooms in eutrophic waters pose a serious threat to freshwater ecosystems and human health. In-situ light availability control is one of the most commonly used technologies to suppress algae in lakes and reservoirs. To develop a better understanding of the effects of light on algal growth, specific density, colony size and sinking loss, Anabaena flos-aquae(cyanobacteria) and Scenedesmus obliquus(green algae) were evaluated in varying light scenarios. The results showed that the specific density and colony size of these two species varied during growth, and there were obvious differences among the light scenarios. At the end of exponential phase, S. obliquus incubated under light-limited condition maintained a higher specific density and formed larger aggregates, whereas A. flos-aquae formed a longer filament length. Both species exhibited higher sinking loss rates with lower light availability. These results implied that the sinking loss rate was not always constant but should be considered as a variable response to the change of light availability, and in-situ light availability control might result in a significant increase of the sinking loss of algae due to the change of size and specific density, thereby further affecting the algal biomass in the water column.

Model heat source using actual distribution of laser power density for simulation of laser processing

The model of heat source(MHS) which reflects the thermal interaction between materials and laser during processing determines the accuracy of simulation results. To acquire desirable simulations results, although various modifications of heat sources in the aspect of absorption process of laser by materials have been purposed, the distribution of laser power density(DLPD) in MHS is still modeled theoretically. However, in the actual situations of laser processing, the DLPD is definitely different from the ideal models. So, it is indispensable to build MHS using actual DLPD to improve the accuracy of simulation results. Besides, an automatic modeling method will be benefit to simplify the tedious pre-processing of simulations. This paper presents a modeling method and corresponding algorithm to model heat source using measured DLPD. This algorithm automatically processes original data to get modeling parameters and provides a step MHS combining with absorption models. Simulations and experiments of heat transfer in steel plates irradiated by laser prove the mothed and the step MHS. Moreover, the investigations of laser induced thermal-crack propagation in glass highlight the signification of modeling heat source based on actual DLPD and demonstrate the enormous application of this method in the simulation of laser processing.

Results of Ionospheric Heating Experiments Involving an Enhancement in Electron Density in the High Latitude Ionosphere

Observations are presented of the phenomenon of the enhancement in electron density and temperature that is caused by a powerful pump wave at a frequency near the fifth gyrofrequency. The observations show that the apparent enhancement in electron density extending over a wide altitude range and the enhancement in electron temperature around the reflection altitude occur as a function of pump frequency. Additionally, the plasma line spectra show unusual behavior as a function of pump frequency. In conclusion, the upper hybrid wave resonance excited by the pump wave plays a dominating role and leads to the enhancement in electron temperature at the upper hybrid altitude. The phenomenon of apparent enhancement in electron density does not correspond to the true enhancement in electron density, this may be due to some mechanism that preferentially involves the plasma transport process and leads to the strong backscatter of radar wave along the magnetic line, which remains to be determined.

Effects of crystallization on low-temperature specific heat capacity of Cu_(60)Zr_(20)Hf_(10)Ti_(10) bulk metallic glass

The specific heat capacities of Cu60Zr20Hfl0Til0 bulk metallic glass （BMG） and crystallized alloys were measured from 2 to 101 K. The effect of crystallization on the specific heat capacity of the BMG was studied. The effects of crystallization and the relationship between local modes and boson peak in the BMG were discussed. The specific heat capacity deviates from the simple Debye behaviors, showing the presence of local harmonic modes （Einstein oscillator） in the BMG and the crystallized alloy. Model calculation includes the contribution of one Debye mode and two Einstein modes for the BMG, one Debye mode and one Einstein mode for the crystallized alloy, showing an adequate description of the experimental data.

Prediction of hypersonic boundary layer transition on sharp wedge flow considering variable specific heat

When the air temperature reaches 600 K or higher, vibration is excited. The specific heat is not a constant but a function of temperature. Under this condition, the transition position of hypersonic sharp wedge boundary layer is predicted by using the improved eN method considering variable specific heat. The transition positions with different Mach numbers of oncoming flow, half wedge angles, and wall conditions are computed condition, the nearer to the Mach number The results show that for the same oncoming flow condition and wall transition positions of hypersonic sharp wedge boundary layer move much leading edge than those of the flat plate. The greater the oncoming flow the closer the transition position to the leading edge.

Effect of Plant Density on the Yield of Hydroponically Grown Heat-Tolerant Tomato under Summer Temperature Conditions

Producing enough tomato to meet market demand sustainably has not been feasible in the tropics like Ghana. Attempts to improve production using greenhouse facilities have not addressed the challenge because of high-temperature conditions in the greenhouse, which are difficult to manage. Heat stress, arising from high temperatures, hinder the performance of tomato in terms of fruit set and yield. Moreover, the impending climate change is expected to impose more unfavorable environmental conditions on crop production. An experiment was conducted in (greenhouse at Chiba University, Japan) summer period, which has similar high-temperature conditions like Ghana. This work sought to increase the yield of a heat-tolerant tomato using a state-of-the-art hydroponic system through high-density planting. The outcome of this work was intended for adoption and practice in Ghana. A Heat-tolerant tomato “Nkansah HT” along with Lebombo and Jaguar cultivars, were grown at high and low plant densities (4.1 and 2.7 plants m-2 respectively). Each plant was grown in a low substrate volume culture (0.5 L plant-1) in a recirculating nutrient film technique (NFT) hydroponic system. Parameters measured were plant growth and dry matter assimilation at 12 weeks after transplanting, and the generative components. Results showed that a high plant density increased plant height but reduced chlorophyll content by 9.6%. Under temperature stress conditions, the three cultivars recorded more than 95% fruit set, but plant density did not affect the fruit set and the incidence of blossom end rot (BER). The incidence of BER reduced the marketable yield of the Jaguar cultivar by 51% but, this physiological disorder was not recorded in the HT and the Lebombo cultivars. A high-density planting increased the yield per unit area increased by 38.9%. However, it is uneconomical to cultivate the Jaguar cultivar under a heat stress condition due to its high susceptibility to blossom end rot. To improve the yield of tomatoes under tropical heat stress with a threatening climate change condition, the HT is a better cultivar suited for high-density planting. This study shows that high-density cultivation of the HT cultivar in NFT hydroponic system has the potential to increase Ghana’s current tomato yield by 4.8 times.

Fluctuating specific heat in two-band superconductors

Theory of thermal fluctuations in two-band superconductors under an essentially homogeneous magnetic field is developed within the framework of the two-band Ginzburg-Landau theory. The fluctuating specific heat is calculated by using the optimized self-consistent perturbation approach and the results are applied to analyze the thermodynamic data of the iron-based superconductors Ba（1-x）KxFe2As2 with x -0.4, which have been suggested to have a two-band structure by recent experiments. We estimate the fluctuation strength in this material and find that the specific heat is described well with the Ginzburg number Gi = 4 · 10^-4. The influence of interband coupling strength is investigated and the result of the two-band Gaussian approximation approach is compared.

Theoretical Study on the Effect of Multiband Structure on Critical Temperature and Electronic Specific Heat in SmOFeAs Iron Pnictide Superconductor

In the present theoretical work, superconducting order parameter (∆) and electronic specific heat (Ces) of SmOFeAs iron pnictide (IP) superconductor has been studied using multiband (MB) model of IP superconductors. Attempt has been made to use the MB structure of IP superconductors and expressions for critical temperature (Tc) and Ces are obtained, calculations being made for one, two and three bands of SmOFeAs. It has been found that MB results are close to the experimental value of Tc for this compound. Ces calculations show jump of 1.5 × 10-5 eV/atom K, 4 × 10-5 eV/atom K and 4 × 10-5 eV/atom K for one, two and three band models respectively. The study brings out the importance of MB structure in IPs, highlighting the fact that increasing the number of bands, increases Tc. The specific heat jump (∆C) does not correspond to the BCS value, thereby proving that IPs are unconventional in nature.

A Calorimetric Study Assisted with First Principle Calculations of Specific Heat for Si-Ge Alloys within a Broad Temperature Range

Calorimetric measurements are performed to determine the specific heat of Si-xat.% Ge(where x = 0, 10, 30,50, 70, 90 and 100) alloys within a broad temperature range from 123 to 823 K. The measured specific heat increases dramatically at low temperatures, and the composition dependence of specific heat is evaluated from the experimental results. Meanwhile, the specific heat at constant volume, the thermal expansion, and the bulk modulus of Si and Ge are investigated by the first principle calculations combined with the quasiharmonic approximation. The negative thermal expansion is observed for both Si and Ge. Furthermore, the isobaric specific heat of Si and Ge is calculated correspondingly from OK to their melting points, which is verified by the measured results and accounts for the temperature dependence in a still boarder range.

Effect of Depth-Dependent Nociceptor Density on the Heat-Induced Withdrawal Reflex

Previously we introduced a concise dose-response model for the heat-induced withdrawal reflex caused by millimeter wave radiation. The model predicts the occurrence of withdrawal reflex from the given spatial temperature profile. It was formulated on the assumption that the density of nociceptors in skin is uniform, independent of the depth. The model has only two parameters: the activation temperature of heat-sensitive nociceptors and the critical threshold on the activated volume for triggering withdrawal reflex. In this study, we consider the case of depth-dependent nociceptor density in skin. We use a general parametric form with a scaling parameter in the depth direction to represent the nociceptor density. We analyze system behaviors for four density types of this form. Based on the theoretical results, we develop a methodology for 1) identifying from test data the density form of nociceptors distribution, 2) finding from test data the scaling parameter in the density form, and 3) determining from test data the activation temperature of nociceptors.

Reconsideration on the role of the specific heat ratio in Arrhenius law applications

Arrhenius law implicates that only those molecules which possess the internal energy greater than the activation energy Ea can react. However, the internal energy will not be proportional to the gas temperature if the specific heat ratio y and the gas constant R vary during chemical reaction processes. The varying y may affect significantly the chemical reaction rate calculated with the Arrhenius law under the constant γ assumption, which has been widely accepted in detonation and combustion simulations for many years. In this paper, the roles of variable γ and R in Arrhenius law applications are reconsidered, and their effects on the chemical reaction rate are demonstrated by simulating one- dimensional C-J and two-dimensional cellular detonations. A new overall one-step detonation model with variable γ and R is proposed to improve the Arrhenius law. Numerical experiments demonstrate that this improved Arrhenius law works well in predicting detonation phenomena with the numerical results being in good agreement with experimental data.

Study on the specific heat of wood by statistical mechanics

From the microstructure of wood, theoretical expressions of the wood specific heat were derived by statistical mechanics. With the theoretical expressions derived, the theoretical values of specific heat for 33 tree species, with different moisture contents and under varied temperature conditions were calculated and comparison was also made to the experimental values under the same conditions. The results showed that the maximum error and mean error by the theoretical expressions of this paper are only 7.8% and 2.5% respectively, while those error of the theoretical values for 33 tree species calculated with Dunlap’s empiric equation were 15.2% (max.) and 9.3% (mean), and forКириллов empiric equation, they were 20% (max.) and 11% (mean).

Investigation on specific heat capacity and thermal behavior of sodium hydroxyethyl sulfonate

The thermal decomposition process was studied by the TG–DTA analyzer. The results show that the decomposition process of sodium hydroxyethyl sulfonate consisted of three stages: the mass loss for the first, the second and third stages may be about the groups of CH_3CH_2OH, CH_3CHO and SO_2 volatilized, respectively. The decomposition residuum of three stages was analyzed by FT-IR, and the results of FT-IR agreed with the decomposition process predicted by theoretical weight loss. The specific heat capacity of sodium hydroxyethyl sulfonate was determined by differential scanning calorimetry(DSC). The melting temperature and melting enthalpy were obtained to be 465.41 K and 25.69 kJ·mol^(-1), respectively. The molar specific heat capacity of sodium hydroxyethyl sulfonate was determinated from 310.15 K to 365.15 K and expressed as a function of temperature.