Increase In Critical Temperature Research Articles

Bose-Einstein condensation of pions in proton–proton collisions at the Large Hadron Collider using non-extensive Tsallis statistics

The possibility of formation of Bose-Einstein Condensation (BEC) is studied in pp collisions at $$\sqrt{s} = 7$$ TeV at the Large Hadron Collider. A thermodynamically consistent non-extensive formulation of the identified hadron transverse momentum distributions is used to estimate the critical temperature required to form BEC of charged pions, which are the most abundant species in a multi-particle production process in hadronic and nuclear collisions. The obtained results have been contrasted with the systems produced in Pb-Pb collisions to have a better understanding. We observe an explicit dependency of BEC critical temperature and number of particles in the pion condensates on the non-extensive parameter q, which is a measure of degree of non-equilibrium – as q decreases, the critical temperature increases and approaches to the critical temperature obtained from Bose-Einstein statistics without non-extensivity. Studies are performed on the final state multiplicity dependence of number of particles in the pion condensates in a wide range of multiplicity covering hadronic and heavy-ion collisions, using the inputs from experimental transverse momentum spectra.

Effect of rotational restraint conditions on performance of steel columns in fire

This paper presents a parametric analysis about the effect of rotational restraint conditions on the dynamic performance of steel columns in fire. A fine finite element model of restrained steel columns, which adopts an explicit dynamic solver, was developed and validated by test data in literatures. Nine values of rotational restraint stiffness ratio (βR) from 0.0001 to 10.0 were considered. Other considered parameters include the axial restraint stiffness ratio, load ratio and column slenderness ratio. Based on the results, a quantitative criterion of identifying dynamic and quasi-static failures of steel columns in fire was proposed. It is found that βR has a significant effect on the performance of steel columns in fire. With the increase of βR, three failure scenarios about the failure types of steel columns in fire may appear, namely, all the failures are dynamic failures (Scenario I), failures turn from dynamic failure into quasi-static failure (Scenario II), and all the failures are quasi-static failures (Scenario III). In failure scenario I, there exists a βR with which the column shows the minimal dynamic effects. Besides, when βR reaches a critical value (namely βR,cr), the effect of further increasing the value of βR on the response of steel columns becomes slight for all the above scenarios. βR,cr is affected by the axial restraint stiffness ratio, load ratio and column slenderness ratio, and is generally less than 1.5. In fire-resistant design, the steel columns with a βR greater than βR,cr can be considered as rotationally fixed at both ends. Moreover, with the increase of βR, the buckling and critical temperatures of steel columns both increase, and the increase in critical temperature is significantly larger than that in buckling temperature.

Capping layer influence and isotropic in-plane upper critical field of the superconductivity at the FeSe/SrTiO3 interface

Understanding the superconductivity at the interface of FeSe/SrTiO3 is a problem of great contemporary interest due to the significant increase in critical temperature (Tc) compared to that of bulk FeSe, as well as the possibility of an unconventional pairing mechanism and topological superconductivity. We report a study of the influence of a capping layer on superconductivity in thin films of FeSe grown on SrTiO3 using molecular beam epitaxy. We used in vacuo four-probe electrical resistance measurements and ex situ magneto-transport measurements to examine the effect of three capping layers that provide distinctly different charge transfer into FeSe: compound FeTe, non-metallic Te, and metallic Zr. Our results show that FeTe provides an optimal cap that barely influences the inherent Tc found in pristine FeSe/SrTiO3, while the transfer of holes from a non-metallic Te cap completely suppresses superconductivity and leads to insulating behavior. Finally, we used ex situ magnetoresistance measurements in FeTe-capped FeSe films to extract the angular dependence of the in-plane upper critical magnetic field. Our observations reveal an almost isotropic in-plane upper critical field, providing insight into the symmetry and pairing mechanism of high temperature superconductivity in FeSe.

Pyrolysis and piloted ignition of thermally thick PMMA exposed to constant thermal radiation in cross forced airflow

Impact of cross forced airflow on pyrolysis and piloted ignition of PMMA (Poly methyl methacrylate) under constant heat flux is experimentally, analytically and numerically addressed in this study. Experimental setup consisting of a heating and blowing units was employed to provide the target constant heat flux and airflow velocity. Surface temperature and ignition time were measured in tests to examine the combined effect of forced airflow and heat flux. No ignition was observed when the heat flux and air velocity were 11.53 kW/m2 and 1.43 m/s combined, indicating a critical airflow velocity dominates ignition. An analytical model and a solid phase numerical model were developed to predict and validate the experimental measurements. Both surface and in-depth absorption of thermal radiation were considered in the models. The results showed both the critical temperature and ignition time increase with airflow velocity. Radiation reducing was found to be enhanced by increasing airflow velocity. Both the analytically and numerically predicted results employing either pure surface or in-depth absorption of thermal radiation matched the experimental measurements at acceptable levels, but the agreement between the calculations of in-depth absorption and measurements was better.

Mathematical and computer simulation for Electro-Magneto-Thermo-Elastic Buckling of the Porous Nano system

Buckling analysis of porous sandwich nanoplate integrated with two piezoelectric face-sheets is presented based on shear and normal deformation theory (SNTD). Effect of small scales of the porous core and actuated face-sheets is accounted based on the nonlocal strain gradient theory (NSGT). Large parametric results are presented to investigate variation of various critical loads in terms of significant parameters such as porosity volume fraction, strain gradient and nonlocal parameter, and dimensionless geometric parameters. It is concluded that increase of porosity volume fraction leads to decrease of critical electric and magnetic potentials and increase of critical temperatures.

Tuning the properties of hydrogen-bonded block copolymer worm gels prepared via polymerization-induced self-assembly.

Polymerization-induced self-assembly (PISA) is exploited to design hydrogen-bonded poly(stearyl methacrylate)-poly(benzyl methacrylate) [PSMA-PBzMA] worm gels in n-dodecane. Using a carboxylic acid-based RAFT agent facilitates hydrogen bonding between neighboring worms to produce much stronger physical gels than those prepared using the analogous methyl ester-based RAFT agent. Moreover, tuning the proportion of these two types of end-groups on the PSMA chains enables the storage modulus (G′) of a 20% w/w worm gel to be tuned from ∼4.5 kPa up to ∼114 kPa. This is achieved via two complementary routes: (i) an in situ approach using binary mixtures of acid- and ester-capped PSMA stabilizer chains during PISA or (ii) a post-polymerization processing strategy using a thermally-induced worm-to-sphere transition to mix acid- and ester-functionalized spheres at 110 °C that fuse to form worms on cooling to 20 °C. SAXS and rheology studies of these hydrogen-bonded worm gels provide detailed insights into their inter-worm interactions and physical behavior, respectively. In the case of the carboxylic acid-functionalized worms, SAXS provides direct evidence for additional inter-worm interactions, while rheological studies confirm both a significant reduction in critical gelation concentration (from approximately 10% w/w to 2–3% w/w) and a substantial increase in critical gelation temperature (from 41 °C to 92 °C). It is remarkable that a rather subtle change in the chemical structure results in such improvements in gel strength, gelation efficiency and gel cohesion.

Extended phase space thermodynamics of Bardeen black hole in massive gravity

We present an exact solution of Bardeen AdS black hole in massive gravity theory by taking into account the massive gravity parameter m and study its thermodynamic properties such as temperature, entropy and heat capacity at constant pressure. We also study the critical behaviour of Bardeen AdS massive black holes by taking the cosmological constant $$\Lambda $$ as the thermodynamic pressure, and it is shown that thermodynamic volume is independent of the massive gravity parameter m. In addition to these, we investigate the dependence of critical parameters on the massive gravity parameter (m) and magnetic monopole charge (e). It is observed that the critical exponents (critical temperature and critical pressure) increase with massive gravity parameter but decrease in the presence of magnetic monopole charge. Also the numerical value of ratio $$P_\mathrm{c}r_\mathrm{c}/T_\mathrm{c}$$ increases with increase in the values of the parameters m and e.

Machine Learning F-Doped Bi(Pb)–Sr–Ca–Cu–O Superconducting Transition Temperature

The increase in critical temperature of high-temperature superconductors fulfills needs of practical applications with liquid-helium-free refrigeration and a delay in magnet failure. But the research requires significant manpower for materials synthesis, characterization, and quench detection, as well as costly equipment and facilities. In this study, we develop the Gaussian process regression (GPR) model to shed light on the relationship between process parameters and superconducting transition temperature for BiPbSrCaCuOF superconductors. The modeling approach has a high degree of accuracy and stability, contributing to fast low-cost estimations of superconducting transition temperature.

Spectroscopic Detection of Critical Compression of Carbon Dioxide Confined in an Nanoporous Aerogel by Coherent Anti-Stokes Raman Spectroscopy

The compaction of carbon dioxide in the pores of nanoporous silicon aerogel at near-critical temperatures has been studied by coherent anti-Stokes light scattering (CARS) spectroscopy. The density was determined by the shift of the vibrational line at 1388 cm $${}^{-1}$$ under isochoric heating from the subcritical temperature of 25.2 $${}^{\circ}$$ C to the supercritical one of 31.95 $${}^{\circ}$$ C. It was found that the density of carbon dioxide in nanopores near the critical temperature increases, exceeding the average value in the cuvette by about $${\sim}20\%$$ .

Near-infrared triggered on-demand local anesthesia using a jammed microgels system

To conveniently modulate the degree of local analgesia in response to changes in patients’ needs and level of activity, a NIR-activated drug delivery system based on jammed microgels was introduced in the present study to realize on-demand local anesthesia. Chemically cross-linked gelatin microgels (5–15 μm) containing N-isopropylacrylamide (NIPAM), methylallyl polyethylene glycol (APEG) and graphene oxide (GOs) were fabricated through emulsion. After the in situ free radical polymerization, the physical network was formed, producing microgels with double networks (DN microgels). The DN microgels exhibited thermosensitive properties. The copolymerization of APEG resulted in the increase of lower critical solution temperature (LCST) of microgels. The maximum volume shrinkage ratio of DN microgels (NIPAM40 + APEG60) increased with the increase of the content of physical cross-linking network. The DN microgels also exhibited NIR-responsive ability. Under the NIR irradiance of 272 mW/cm2, the temperature of DN microgels with 3 mg/mL GOs reached 40 °C within 60 s, resulting in the volume shrinkage of 14%. Ropivacaine release from DN microgels could be effectively triggered by NIR irradiation in vitro. After centrifugation, a jammed microgels system was produced where microgels packed densely, displaying shear-thinning behavior for achieving injection. The jammed DN microgels carrying ropivacaine were injected subcutaneously into rat footpad. NIR irradiation produced on-demand and repeated infiltration anesthesia in the rat footpad. The jammed DN microgels system thus was beneficial in the management of pain.

Effect of weld power and interfacial temperature on mechanical strength and microstructure of carbon steel 4130 fabricated by ultrasonic additive manufacturing

Ultrasonic additive manufacturing (UAM) is a solid-state 3D printing technology. Steels can be welded with UAM at reduced ultrasonic power, achieving half the shear strength of bulk material. A higher weld power is demonstrated by using a cobalt-based sonotrode coating, achieving shear strengths comparable to bulk 4130 material. In-situ temperature measurements and fracture surface analyses indicate that higher power input promotes metallurgical bonding through softening and increased plastic deformation. Carbides and ferrite are found at 1 μm scale at key weld interfaces; no martensite is found due to an increase in critical transformation temperatures associated with high heating rates.

Enhancement of Superconductivity by Amorphizing Molybdenum Silicide Films Using a Focused Ion Beam.

We have used focused ion beam irradiation to progressively cause defects in annealed molybdenum silicide thin films. Without the treatment, the films are superconducting with critical temperature of about 1 K. We observe that both resistivity and critical temperature increase as the ion dose is increased. For resistivity, the increase is almost linear, whereas critical temperature changes abruptly at the smallest doses and then remains almost constant at 4 K. We believe that our results originate from amorphization of the polycrystalline molybdenum silicide films.

Intercalation of small molecules in alkali metal fullerides superconductors

Using a BCS-adapted equation via multivariate analysis of structural and electronic properties, we calculated the critical temperature of fullerides A2BC60 and A3C60, with pure A and B alkaline metal or solvated with NH3 and CH3NH2, in good agreement with the experimental data. In the ammoniation of Na2CsC60, concomitant expansion of the lattice and the increasing ionic character of the chemical bonds between the ligands and C60, the critical temperature rises by about 20 K. For methylamine, there is an increase in critical temperature far lower than with ammonia, indicating that anisotropic lattice expansion does not favor the phenomenon. Besides crystal lattice expansion, a known factor that influences the critical temperature, our model identifies the other structural and electronic factors that contribute to the critical temperature of these materials. In alkali metal hydration, the crystal is expanded at the same time that the HOMO-LUMO gap is reduced, favoring electron transfer between the metal–ligand complex and C60. With the intercalation of water molecules in these fullerides, we predict that Na3C60 becomes superconducting at a critical temperature of 47.2 K and that Cs3C60 reaches 50 K.

Temperature change in pulp chamber of primary teeth during curing of coloured compomers: an in vitro study using pulpal blood microcirculation model.

IntroductionAn increase in the temperature of the pulp chamber occurs during polymerisation of all types of light-curing resin-containing restorative materials, due to both the exothermic reaction of the material and the energy absorbed during the curing process. Increase in temperature of the pulp chamber of primary teeth during the curing process or the thermal conductivity properties of coloured compomers (CCs) have not yet been investigated in detail. The aim of the present study was to investigate the increase in pulpal temperature in primary teeth during curing of CCs.Materials and MethodsA Class-II cavity was prepared on the extracted primary mandibular second molar. Pulpal microcirculation of the tooth was performed using an experimental mechanism. The study included 15 groups and 10 experiments in each. Seven different CCs: pink, blue, gold, silver, orange, lemon, green, respectively from two different manufacturers (Groups 1–7: Twinky Star; VOCO, Cuxhaven, Germany. Groups 8–14: Nova Rainbow; IMICRYL, Konya, Turkey.) and a tooth-CC (Group 15: Dyract XP; DENTSPLY, Weybridge, UK.) were applied in prepared cavity. In all groups the compomers were light cured for 40 s. Intrapulpal temperature changes (Δt) in 20th and 40th second were recorded. In Group-15 the Δt values in 10th second were also recorded as per the manufacturer’s instructions. The Kruskal–Wallis test and the Mann–Whitney-U test were used for statistical analyses.ResultsAt the end of 40-s irradiation time, the orange, lemon and green colours of Nova Rainbow resulted in significantly lower Δt values than the same colours of Twinky Star (p = 0.0001), and silver, blue, lemon, green, orange, and pink CCs of Nova Rainbow and the blue and silver shades of Twinky Star demonstrated lower Δt values than the reported critical temperature increase (5.5 °C).ConclusionAn increase in the irradiation time consequently led to an increase in the intrapulpal temperature. Therefore, manufacturers should focus on production of new CCs with shorter polimerization time.

Functionalized carbon nanotubes modulate the phase transition behavior of thermoresponsive polymer via hydrophilic-hydrophobic balance

The world of nano-science is getting popularity due to their vast applications in the field of material science, biotechnology and biomedical research. In this context, carbon-nanotubes (CNTs) have provided new horizons because of their use as molecular transporters. Nonetheless, the low solubility in molecular solvents and cytotoxity of CNTs prevent their utility in biological process. Here, we established increasing solubility and dispersion of CNTs by functionalization with –COOH group that overcome these fundamental limitations. In spite of a broad range of applications of CNTs, it is highly desirable to examine the effect of functionalized CNTs (fCNTs) on the thermoresponsive polymers. In this respect, we have examined the effect of fCNTs on the thermoresponsive behavior of aqueous poly(N-isopropylacrylamide) (PNIPAM) solution by using several techniques such as dynamic light scattering (DLS), differential scanning calorimeter (DSC), Fourier transform infrared spectroscopy (FTIR), fluorescence spectroscopy and Field emission scanning electron microscope (FESEM). The present results indicate that the presence of fCNTs causes a small increase in the lower critical solution temperature (LCST) of PNIPAM which becomes more pronounced at lower concentration of fCNTs. It reveals that fCNTs indirectly favors the hydrophilic interactions of surrounded water molecules with PNIPAM that eventually stabilizes the coil state of PNIPAM.

Effects of thiocyanate anions on switching and structure of poly(N-isopropylacrylamide) brushes**Project supported by the Joint Funds of Xinjiang Natural Science Foundation (Grant No. 2019D01C333), the National Natural Science Foundation of China (Grant Nos. 11847610 and 21764015), the National Basic Research Program of China (Grant No. 2015CB857100).

In this work, we investigate the effects of thiocyanate anions on the switching and the structure of poly (N-isopropylacrylamide) (PNIPAM) brushes using a molecular theory. Our model takes into consideration the PNIPAM–anion bonds, the electrostatic effects and their explicit coupling to the PNIPAM conformations. It is found that at low thiocyanate anion concentration, as the anion concentration of thiocyanate increases, thiocyanate anions are more associated with PNIPAM chains through the PNIPAM–anion bonds, which contributes to stronger electrostatic repulsion and leads to an increase of lower critical solution temperature (LCST). By analyzing the average volume fractions of PNIPAM brushes, it is found that the PNIPAM brush presents a plateau structure. Our results show that the thiocyanate anions promote phase segregation due to the PNIPAM–anion bonds and the electrostatic effect. According to our model, the reduction of LCST can be explained as follows: at high thiocyanate anion concentration, with the increase of thiocyanate concentration, more ion bindings occurring between thiocyanate anions and PNIPAM chains will result in the increase of the hydrophobicity of PNIPAM chains; when the increase of electrostatic repulsion is insufficient to overcome the hydrophobic interaction of PNIPAM chains, it will lead to the reduction of brush height and LCST at high thiocyanate anion concentration. Our theoretical results are consistent with the experimental observations, and provide a fundamental understanding of the effects of thiocyanate on the LCST of PNIPAM brushes.

Self-Assembly of Short Chain Poly- N-isopropylacrylamid Induced by Superchaotropic Keggin Polyoxometalates: From Globules to Sheets.

We show here for the first time that short chain poly( N-isopropylacrylamide) (PNIPAM), one of the most famous thermoresponsive polymers, self-assembles in water to form (i) discrete nanometer-globules and (ii) micrometric sheets with nm-thickness upon addition of the well-known Keggin-type polyoxometalate (POM) H3PW12O40 (PW). The type of self-assembly is controlled by PW concentration: at low PW concentrations, PW adsorbs on PNIPAM chains to form globules consisting of homogeneously distributed PWs in PNIPAM droplets of several nm in size. Upon further addition of PW, a phase transition from globules to micrometric sheets is observed for PNIPAMs above a polymer critical chain length, between 18 and 44 repeating units. The thickness of the sheets is controlled by the PNIPAM chain length, here from 44 to 88 repeating units. The PNIPAM sheets are electrostatically stabilized PWs accumulated on each side of the sheets. The shortest PNIPAM chain with 18 repeating units produces PNIPAM/PW globules with 5-20 nm size but no sheets. The PW/PNIPAM self-assembly arises from a solvent mediated mechanism associated with the partial dehydration of PW and of the PNIPAM, which is related to the general propensity of POMs to adsorb on neutral hydrated surfaces. This effect, known as superchaotropy, is further highlighted by the significant increase in the lower critical solubilization temperature (LCST) of PNIPAM observed upon the addition of PW in the mM range. The influence of the POM nature on the self-assembly of PNIPAM was also investigated by using H4SiW12O40 (SiW) and H3PMo12O40 (PMo), i.e. changing the POM's charge density or polarizability in order to get deeper understanding on the role of electrostatics and polarizability in the PNIPAM self-assembly process. We show here that the superchaotropic behavior of POMs with PNIPAM polymers enables the formation and the shape control of supramolecular organic-inorganic hybrids.

Effect of Dynamic Loads on the Limit Stresses and Second Critical Brittle Temperatures of Butt Weld Joints

Experimental results for cracked butt weld joints of 09G2 and 12GN2MFAYu steels are evaluated at different ratios of static and dynamic stresses over a wide range of climatic temperatures. The tests were performed on a unit built upon the impact-testing machine. The opening of crack edges was measured with a displacement gauge. The crack propagation was followed with a TV camera and microscope. In low-temperature tests of specimens over the range of 20–(−100)°C, cooling and automatic temperature control systems were used. Experimental studies resulted in the diagrams of limit stresses, their assessment demonstrated that static and breaking dynamic loads were linearly related. At a preset temperature, the dynamic component of limit stress is shown to decrease with the static one. The weld joint of 09G2 steel was established to exhibit higher sensitivity to dynamic loads over the whole temperature range. It was demonstrated that limit stresses and second critical brittle temperatures should be evaluated with due regard to both static and dynamic components. The limit stress and second critical brittle temperature under combined loading of weld joints are dependent on the ratio of static and dynamic stresses. Without regard for dynamic stresses, underestimation of limit stresses and overestimation of second critical brittle temperatures are taking place. With an increase in dynamic overloading coefficients and dynamic ratios, the limit stress decreases, while the second critical brittle temperature increases. Second critical brittle temperatures of weld joints in steels with higher mechanical properties are found to be much lower.

Observation of a crossover from nodal to gapped superconductivity in LuxZr1−xB12

We have determined the superconducting and magnetic properties of four samples of ${\mathrm{Lu}}_{x}{\mathrm{Zr}}_{1\ensuremath{-}x}{\mathrm{B}}_{12}$ ($x=0.04$, 0.07, 0.17, and 0.8) using muon spin rotation ($\ensuremath{\mu}\mathrm{SR}$) and magnetometry measurements. We observed a strong magnetic signal in both the $\ensuremath{\mu}\mathrm{SR}$ and magnetometry data in one sample ($x=0.07$), likely caused by the formation of static moments of size $\ensuremath{\approx}1\phantom{\rule{0.28em}{0ex}}{\ensuremath{\mu}}_{\mathrm{B}}$ due to a clustering effect of the ${\mathrm{Lu}}^{3+}$ ions. In all other samples, we find only a small magnetic signal in the $\ensuremath{\mu}\mathrm{SR}$ data thought to originate from boron nuclei in the ${\mathrm{B}}_{12}$ cages. The superconductivity is found to evolve with $x$, with a decrease in $x$ resulting in an increase in critical temperature and a decrease of the penetration depth. Most remarkably, we find evidence for the formation of nodes in the superconducting gap for $x\ensuremath{\le}0.17$, providing a potential new example of an $s$-to-$s+d$-wave crossover in a superconductor.

Columnar to equiaxed transition mechanism of pure copper induced by La

ABSTRACTThe solidification process of copper with and without La was observed by a high-temperature confocal laser scanning microscopy. The solidification microstructure was simulated by cellular-automaton and finite-element (CAFE) method and the source of equiaxed grains, the constitutional supercooling and nucleation rate were investigated. The results showed that some floats with regular shape appeared in copper melt with La addition, which is the source of equiaxed grains. The simulation results are in a good agreement with experimental results. The mechanism of columnar to equiaxed transition was that the spontaneous nucleation probability of copper melt was increased with La addition. The nucleation rate was increased due to the increase in critical nucleation temperature and constitutional supercooling, and the reduction of nucleation undercooling.