Large Temperature Span Research Articles

OLEDs with chromaticity tunable between dusk-hue and candle-light

We demonstrate in this report the feasibility of using organic light-emitting diode (OLED) lighting device technology to fabricate light sources with chromaticity tunable between that of dusk-hue and candle-light. The resulting color temperature is tunable easily from 1580K to 2600K, covering that of dusk-hue (2500K) and candle-light (1900K) and providing a physiologically-friendly, melatonin suppression-less emission for illumination at night, along with a respective color rendering index varying from 68 to 91 and power efficiency from 20.9 to 2.7lm/W at 10 to 23,690cd/m2. The color temperature can also be tuned from high to low sequentially, such as from 5200K to 2360K, covering that of cool- and warm-white light for daytime illumination, by simply varying emissive layer thickness ratio. The comparatively high color rendering index as well as the large color temperature span and easy color temperature tunability may be attributed to the employment of four blackbody radiation-complementary emitters. The emission ranges from red to sky-blue, which were dispersed into three separated emissive layers coupling with the use of a nano-layer of hole modulation material.

상온 능동형 자기 재생 냉동기의 개발

In this paper, an investigation of a room temperature active magnetic regenerative refrigerator is carried out. Experimental apparatus includes two active magnetic regenerators containing 186 g of Gd spheres. Four E-type thermocouples are installed inside the Active magnetic regenerator(AMR) to observe the instantaneous temperature variation of AMR. Both warm and cold heat exchangers are designed for large temperature span. The cold heat exchanger, which separates the two AMRs, employs a copper tube with length of 80 mm and diameter of 6.35 mm. In order to minimize dead volume between the warm heat exchanger and AMRs, the warm heat exchangers are located close to the AMRs. The deionized water is used as a heat transfer fluid, and maximum 1.4 T magnetic field is supplied by Halbach array of permanent magnets. The AMR plate, which contains the warm and the cold heat exchangers and the AMRs, has reciprocating motion using a linear actuator and each AMR is alternatively magnetized and demagnetized by a Halbach array of permanent magnet. Since the gap of the Halbach array of permanent magnets is 25 mm and two warm heat exchangers have the motion through it, a compact printed circuit heat exchanger (PCHE) is used as a warm heat exchanger. A maximum no-load temperature span of 26.8 K and a maximum cooling power of 33 W are obtained from the fabricated Active Magnetic Regenerative Refrigerator (AMRR).

Follow-up of zirconia crystallization on a surface modified alumina powder

Here we report how thermal treatments of a surface modified α-alumina powder on which a zirconium oxide precursor was grafted can be tailored so as to obtain an alumina–zirconia composite powder with well-controlled phase distribution and size. The transformation of the zirconia precursor from a starting amorphous phase to zirconia nano-grains bonded to the alumina particles surface was followed by X-ray diffraction (performed at room temperature on different thermally treated powders, as well as in situ at high-temperature) and by both conventional and high resolution transmission electron microscopy (TEM and HRTEM). Phase and nanostructure evolutions were followed on a large temperature span. The crystallization kinetics were analysed in terms of nucleation-growth mechanisms by exploiting Avrami–Johnson–Mehl–Kolmogorov formalism. Based on the above investigations, a tentative description of nucleation and growth features is proposed. This knowledge-based step represents a first approach towards nanopowders engineering.

Enhanced giant magnetoresistance in Ni-doped antipervoskite compounds GaCMn3−xNix(x=0.05,0.10)

We report an enhanced negative giant magnetoresistance (GMR) with larger temperature span in Ni-doped antipervoskite compounds GaCMn3−xNix. The observed GMR can peak at ∼75% (at 85 kOe) and exceed 60% (at 50 kOe) over a temperature span of approximate 110 and 50K for x=0.05 and 0.10, respectively. Compared with the parent GaCMn3, the well-enhanced GMR in Ni-doped samples is suggested to be associated with the partially suppressed antiferromagnetic (AFM) ground state, which favors the transition from the high-resistivity AFM state to the low-resistivity canted ferromagnetic state under an external magnetic field.

Giant magnetocaloric effect in HoGa compound over a large temperature span

We have studied experimentally the magnetic properties and magnetocaloric effect (MCE) in HoGa compound. Two subsequent magnetic transitions, a spin-reorientation (SR) transition followed by a ferromagnetic (FM)–paramagnetic (PM) transition, are observed at T S R ∼ 20 K and T C ∼ 69 K , respectively. Both transitions contribute greatly to the magnetic entropy change ( Δ S M ) , each yielding a significant peak on their Δ S M – T curve. A considerable value of refrigerant capacity (RC) is obtained in HoGa, due to the large MCE over a wide temperature span. For a magnetic field change of 0–5 T, the maximal values of − Δ S M are 17.1 J/kg K and 7.8 J/kg K at T C and T S R , respectively, and the RC reaches its maximal value of 455 J/kg in an optimal reversible refrigerant cycle with cold and hot sinks at T cold ∼ 16 K and T hot ∼ 99 K . Large reversible MCE and the giant value of RC indicate the potentiality of HoGa as a candidate magnetic refrigerant for nitrogen liquefaction.

Magnetocaloric effect of La 0.8Ce 0.2Fe 11.4− xMn xSi 1.6 compounds

The effect of Mn addition on the magnetocaloric effect (MCE) of the La 0.8Ce 0.2Fe 11.4− x Mn x Si 1.6 ( x = 0.0, 0.1, 0.2, 0.3) compounds was investigated. It was revealed that the transition temperatures of the compounds are sensitive to Mn composition. The temperatures are shifted from 177 to 121 K for Mn composition from 0.0 to 0.3. Moreover, thermal lag and magnetic hysteresis loss of the compounds are reduced largely due to Mn addition. A good MCE with a large and almost constant refrigerant capacity in a large temperature span over 50 K was achieved in the investigated compounds. The investigated compounds are promising magnetic entropy change materials.

Pressure induced magnetic and magnetocaloric properties in NiCoMnSb Heusler alloy

The effect of pressure on the magnetic and the magnetocaloric (MC) properties around the martensitic transformation temperature in NiCoMnSb Heusler alloy has been studied. The martensitic transition temperature has significantly shifted to higher temperatures with pressure, whereas the trend is opposite with the application of applied magnetic field. The maximum magnetic entropy change around the martensitic transition temperature for Ni45Co5Mn38Sb12 is 41.4 J/kg K at the ambient pressure, whereas it is 33 J/kg K at 8.5 kbar. We find that by adjusting the Co concentration and applying suitable pressure, NiCoMnSb system can be tuned to achieve giant MC effect spread over a large temperature span around the room temperature, thereby making it a potential magnetic refrigerant material for applications.

High refrigerant capacity of PrNi5−xCox magnetic compounds exploiting its spin reorientation and magnetic transition over a wide temperature zone

The ferromagnetically coupled cobalt ion is observed to create a magnetocrystalline anisotropy in the PrNi5−xCox structure above a critical composition of x = 2. The competition of the anisotropy energies between Co and Pr sublattices gives rise to a spin reorientation (SR) phenomenon in PrNi5−xCox compounds at a low temperature (∼150 K) which is then followed by a magnetic transition at a higher temperature. Co-doping has a strong influence on the Curie temperature, changing it from ∼60 K (x = 1.95) to ∼537 K (x = 3). The magnetic entropy change is associated with SR as well as a magnetic transition, and correspondingly a large full width at half maximum (δTFWHM) is obtained for this series of compounds. For example, the PrNi2.85Co2.15 compound presents δTFWHM = 166 K at a 1 T field. This series therefore has an appreciable relative cooling power, which makes this material a suitable magnetic refrigerant over a large temperature span.

Large magnetic entropy change and broad working temperature span in CoMnSi0.88Ge0.12 alloy

CoMnSi0.88Ge0.12 alloy was prepared using an optimized annealing routine. The metamagnetic transition between antiferromagnetism and ferromagnetism can be observed in this alloy by either increasing the temperature or applying a magnetic field. The metamagnetic transition temperature is very sensitive to the applied field. Owing to the low metamagnetic critical field and large variation in magnetization, large and positive magnetic entropy changes as well as broad working temperature spans are obtained in this metamagnetic system.

Biphenyl Bicelle Disks Align Perpendicular to Magnetic Fields on Large Temperature Scales: A Study Combining Synthesis, Solid-State NMR, TEM, and SAXS

A phosphatidylcholine lipid (PC) containing a biphenyl group in one of its acyl chains (1-tetradecanoyl-2-(4-(4-biphenyl)butanoyl)- sn-glycero-3-PC, TBBPC) was successfully synthesized with high yield. Water mixtures of TBBPC with a short-chain C 6 lipid, dicaproyl-PC (DCPC), lead to bicelle systems formation. Freeze-fracture electron microscopy evidenced the presence of flat bilayered disks of 800 Å diameter for adequate composition, hydration, and temperature conditions. Because of the presence of the biphenyl group, which confers to the molecule a positive magnetic anisotropy Δ χ, the disks align with their normal, n, parallel to the magnetic field B 0, as directly detected by 31P, 14N, 2H solid-state NMR and also using small-angle x-ray scattering after annealing in the field. Temperature-composition and temperature-hydration diagrams were established. Domains where disks of TBBPC/DCPC align with their normal parallel to the field were compared to chain-saturated lipid bicelles made of DMPC(dimyristoylPC)/DCPC, which orient with their normal perpendicular to B 0. TBBPC/DCPC bicelles exist on a narrow range of long- versus short-chain lipid ratios (3%) but over a large temperature span around room temperature (10–75°C), whereas DMPC/DCPC bicelles exhibit the reverse situation, i.e., large compositional range (22%) and narrow temperature span (25–45°C). The two types of bicelles present orienting properties up to 95% dilution but with the peculiarity that water trapped in biphenyl bicelles exhibits ordering properties twice as large as those observed in the saturated-chains analog, which offers very interesting properties for structural studies on hydrophilic or hydrophobic embedded biomolecules.

Cooling Performance of Room-temperature Magnetic Refrigerator with Active Magnetic Regenerator (Numerical Analysis on Cooling Performance)

The cooling characteristics of a room temperature magnetic refrigerator using an active magnetic regenerator (AMR) is presented. The AMR system, which is based on a combination of a thermal storage process and a regeneration process, is widely applied for room temperature magnetic refrigerator. And the system has four sequential processes : adiabatic magnetization, fluid flow, adiabatic demagnetization, and fluid flow. We devise the appropriate simulation model of the heat transfer process inside the AMR particle bed. In addition, the temperature profile inside the AMR bed and the cooling characteristics of the room temperature magnetic regenerator using AMR are performed analytically. In this research, the validity of the analytical model is verified by comparing the experimental results with the analytical results. The results show the larger the fluid transfer volume, the larger the temperature difference between the hot and the cold ends. Also we can observe when the higher magnetic field is applied to the magnetocaloric material, the large temperature span is obtained.

Mn 3 Sn 2 : A promising material for magnetic refrigeration

Mn 3 Sn 2 presents two second-order magnetic transitions of ferromagnetic origin at TC1∼262K and TC2∼227K. Both transitions give peaks of similar magnitude (ΔSMmax∼27mJcm−3K−1 for ΔH=5T) in the temperature dependence of the magnetic entropy change yielding an anomalous magnetocaloric response approaching that of a two-component hybrid material. Its refrigerant capacity of ∼1.1Jcm−3 (ΔH=5T) for an optimal reversible cycle with cold and hot ends at ∼220 and ∼280K is about half that of the best known magnetic refrigerants working around room temperature. However, Mn3Sn2 possess several advantages making it a promising candidate for magnetic refrigeration applications: (i) it has a large temperature span with a roughly constant ΔSM, (ii) it is not subjected to hysteresis losses, and (iii) it is made from low-cost and nontoxic elements.

Bicelle membranes and their use for hydrophobic peptide studies by circular dichroism and solid state NMR

Mixtures of dicaproyl- (DC), dimyristoyl- (DM) and 1-tetradecanoyl-2-biphenylbutanoyl-(TBB) phosphatidylcholine (PC) in water produce bicelle membranes that are oriented by magnetic fields. DMPC/DCPC systems orient such that their membrane plane is parallel to the magnetic field, whereas for TBBPC/DCPC, the plane is perpendicular to the field. Partial temperature-composition-hydration diagrams are established using solid-state 31P-NMR. DMPC/DCPC bicelles exist on a large range of composition but on a narrow temperature domain (25-45 degrees C). At converse, TBBPC/DCPC form bicelles on a narrow compositional range but over a large temperature span (10-70 degrees C). The TBBPC/DCPC bicelles are shown to be a very powerful potential tool to study the orientation of hydrophobic helices in membranes using wide line 15N-NMR. The DMPC/DCPC system that undergoes a micelle-to-bicelle transition on going from 10 degrees C to 40 degrees C may be used with circular dichroism to study the state of association of hydrophobic helices within the membrane. Results suggest that the transmembrane fragment of the neu/erbB-2 receptor is monomeric in micellar medium and dimeric/multimeric in bicelle membranes.

Synthesis, structure and magnetic entropy change of polycrystalline La 1− xK xMnO 3+ δ

The use of a sol–gel synthetic method allows the preparation, at temperatures as low as 873 K, of single-phase perovskites in the potassium-doped lanthanide manganites La 1− x K x MnO 3+ δ . Samples prepared at 1273 K remain single phase and are constituted by submicrometer homogeneous particles, without deviation from nominal stoichiometries upon heating. These materials exhibit paramagnetic-to-ferromagnetic phase transitions at 230, 283, 338, and 344 K for x=0.075, 0.10, 0.165, and 0.20, respectively. By measuring the sample magnetization as a function of field and temperature we have determined the magnetic entropy change associated with these transitions. It is suggested by the results that these materials can be utilized as suitable magnetic refrigerants with very large temperature span.

Magnetotransport and magnetocaloric properties of La0.55Er0.05Ca0.4MnO3

La 0.55 Er 0.05 Ca 0.4 MnO 3 in bulk form was prepared both by solid-state reaction and by a sol–gel method. Samples prepared by both methods showed a moderate magnetic entropy change near its Curie temperature, this spread to a large temperature span upon the application of a magnetic field of 1.8 T. The material prepared by the sol–gel method exhibits a large magnetoresistance below its Curie temperature, which is considered to result from the interfacial spin-dependent tunneling.

Magnetocaloric effect in La0.67Ca0.33MnOδ and La0.60Y0.07Ca0.33MnOδ bulk materials

The dependence of magnetization on the applied magnetic field and temperature was measured carefully near their Curie temperatures for two perovskite manganite samples: La0.67Ca0.33MnOδ and La0.60Y0.07Ca0.33MnOδ. It is suggested by the results that these materials can be utilized as both the thermal storage (passive regeneration) and as the working material (active regeneration) in an active magnetic regenerative refrigerator with very large temperature span, for their significant entropy change upon the application of a magnetic field and the easily tuned Curie temperatures.

Selection of magnetic materials for an active magnetic regenerative refrigerator

High efficiencies of active magnetic regenerative refrigerators (AMRR) are strongly dependent on the correct selection of the magnetic regenerator working material. The selection process involves the thermodynamic analysis of the AMRR cycle to determine the adiabatic temperature change profile (ΔT versus T) over the temperature span of interest for an ideal material, and then the matching of real materials whose magnetocaloric effect (MCE) as a function of absolute temperature best fits this profile. This paper develops the calculation of the ideal magnetic material ΔT versus T profile for a real AMRR operating between 110 and 300 K and with 1 kW of cooling power. The ideal profile was a function of the constant entropy flux from the cold end heat load, the irreversible regenerator entropy production, and other real effects. To accommodate the large temperature span, several magnetic materials were chosen and layered in the regenerator from the cold to the hot end by increasing the Curie temperature. The resultant ΔT versus T curve of the combined material provided only a rough approximation of the calculated ideal material curve. To improve this approximation, physical mixing of magnetic refrigerants was investigated. This procedure diluted the magnetic moment, thereby reducing magnetic entropy available for the cycle. Further, under adiabatic conditions, mixing produced an intolerable amount of entropy during cycle execution. Simple segmentation of the regenerator with more magnetic materials that better match the ideal profile is an easier way to approximate the ideal ΔT versus T curve with real materials. Optimum segmentation will be determined by regenerator complexity.

Shear effects in elasticity

Band structure contributions to the shear constants of paramagnetic and ferromagnetic metals are treated within the deformation potential formalism and the Stoner model. Using correlations between elastic and magnetic properties, it is shown that band effects are strong and extend over large temperature spans. Very large, enhanced deformation potentials are found in Invar alloys.

Effect of group relaxation response training on blood pressure in essential hypertension: Sallee J. Cabeen, University of Illinois, College of Nursing, 123 Southwest Glendale, Peoria, Illinois 61605; Felissa L. Cohen

We report the magnetic and magnetocaloric properties of rapidly solidified Ni0.895Cr0.105MnGe1.05 melt-spun ribbons studied by both direct (adiabatic temperature change) and indirect (isothermal magnetic entropy change) methods in intermediate and high magnetic fields up to 10 T. The maximum values of the adiabatic temperature changes (ΔTad) and magnetic entropy changes (ΔSM) were found to be ∼2.6 K (µoH = 10 T) and 4.4 J kg−1 K−1 (µoΔH = 5 T), respectively, near the Curie temperature (TC). The ΔTad curves and magnetization isotherms were found to be completely reversible, which indicates the high degree of reversibility of the MCEs in this system. A large temperature span (of about 61 K) and a non-saturating behavior of ΔTad were observed at magnetic fields up to 10 T. The adiabatic temperature change was found to be a linear function of (µoH)2/3 near TC, in accordance with the Landau theory of phase transitions.

Effect of solutes in binary columbium (Nb) alloys on creep strength

The effect of seven different solutes in binary columbium (Nb) alloys on creep strength was determined from 1400 to 3400°F (760 to 1871°C) for solute concentrations to 20 at. pct using a new method of creep strength measurement. The technique permits rapid determination of approximate creep strength over a large temperature span. All of the elements were found to increase the creep strength of columbium except tantalum. This element did not strengthen columbium until the concentration exceeded 10 at. pct. Hafnium, zirconium, and vanadium strengthed columbium most at low temperatures and concentrations, whereas tungsten, molybdenum, and rhenium contributed more to creep strength at high temperatures and concentrations.