FC Measurements Research Articles

Physical property characterization of Fe-tube encapsulated and vacuum annealed bulk MgB 2

We report the phase formation, and present a detailed study of magnetization and resistivity under magnetic field of MgB 2 polycrystalline bulk samples prepared by the Fe-tube encapsulated and vacuum (10 −5 Torr) annealed (750 ∘C) route. Zero-field-cooled magnetic susceptibility ( χ ZFC ) measurements exhibited a sharp transition to the superconducting state with a sizeable diamagnetic signal at 39 K ( T c ) . The measured magnetization loops of the samples, despite the presence of flux jumps, exhibited a stable current density ( J c ) of around 2.4×10 5 A/cm 2 in up to 2 T (Tesla) field and at temperatures ( T ) up to 10 K. The upper critical field is estimated from resistivity measurements in various fields and shows a typical value of 8 T at 21 K. Further, χ FC measurements at an applied field of 0.1 T reveal a paramagnetic Meissner effect (PME) that is briefly discussed.

Seasonal variation in total organic carbon in the northeast Atlantic in 2000–2001

Total organic carbon (TOC) was measured in the midlatitudes of the northeast Atlantic in 2000–2001 during the Programme Océan Multidisciplinaire Méso Echelle (POMME). In spring, mixed layer depth (MLD) was positively correlated with the north latitude, while the surface TOC and chlorophyll‐a (Chl a) were negatively correlated with it. It indicates the northward propagation of TOC accumulation along the onset of spring bloom, which was triggered by shoaling of MLD from the south. Surface TOC was highest in summer, though surface Chl a was lowest. Surface TOC was significantly correlated with surface Chl a during winter and spring but not during summer or fall, indicating the minor influence of total phytoplankton biomass on surface TOC distribution in the oligotrophic season. High surface TOC in summer and fall was related with shallow MLD, which could hold fresh TOC near the surface. Downward TOC flux from the surface to below the seasonal thermocline was estimated for the processes of winter convection (Fc), turbulent diffusion (Fd) and sinking flux (Fp). The sum of these fluxes accounts for 6–75% of annual new production. To our knowledge, this is the first estimation based on the simultaneous measurement of Fc, Fd, Fp, and annual new production.

(La,Ca)(Mn,M)O 3 (M = Ni, Cr) compounds investigated by means of XRPD and DC magnetic measurements

(La 1− x Ca x )(Mn 1− y M y )O 3 ( x = 0.37, 0.50, 0.75; M = Cr, Ni; y = 0.03, 0.08) compounds have been prepared reacting stoichiometric amounts of binary oxides at high temperature. The samples were characterised by means of XRPD analysis at room temperature, followed by Rietveld refinements, revealing that all these compounds crystallize with an orthorhombic structure. Magnetic characterization as a function of the temperature (ZFC and FC measurements from T = 5 K up to T = 350 K) and of the magnetic field (up to μ 0 H = 5.5 T) was performed; various behaviours were observed depending on composition: in particular the different effects of Ni and Cr as dopant are shown and discussed.

Cavitation Properties of Oils Under Dynamic Stressing by Tension

We report measurements of the effective tensile strength Fc of commercial “multigrade” oils (in the SAE viscosity grades 5W-30 and 10W-40) over a range of temperatures T, which are representative of those encountered under their normal operating conditions (in the range 20°C⩽T⩽140°C). Also reported are the values of Fc that are obtained for Newtonian silicone oils over a range of shear viscosities. In the experiments reported herein, samples of liquid are subjected to dynamic stressing by a pressure-tension cycle, this being a feature of the conditions experienced by a lubricant within a dynamically loaded journal bearing and the method used to estimate Fc avoids reliance on direct measurements of substantial dynamic tensions using conventional pressure transducers.

Large positive entropy change in several charge-ordering perovskites

The Nd0.5Sr0.5Mn1−xCuxO3 (x=0.00; 0.02; 0.10) and Nd0.25Pr0.25Sr0.5MnO3 perovskites have been prepared by solid reaction technology. The manganites are of single phase with orthorhombic structure. The FC and ZFC measurements show an evident existence of charge-ordering effect at low temperatures. At the charge-ordering temperature the magnetic entropy change, ΔS, is positive and the |ΔSmax| is larger than that determined at ferromagnetic-paramagnetic phase transition temperature.

Localized canting of spins structure in the spinel oxide system: ZnzTizFe2−x−zCrx−zCoO4

The spinel oxide system ZnzTizFe2−x−zCrx−zCoO4; z=x2; x=0.60, 0.65, 0.70 and 0.80, was studied using neutron diffraction technique, low field DC magnetization measurements (ZFC–FC measurements), magnetic hysterisis, Mössbauer spectroscopy and low field AC susceptibility measurements. All the compositions show significantly less B-site magnetic moments at 10K temperature derived from neutron diffraction data than the free ions site moments deduced assuming collinear arrangement of spins. This combined with some other features seen in the low temperature neutron diffraction patterns suggest localized canting of spins (LCS) type of magnetic ordering in the present system where a long range order of longitudinal component of moments co-exists along with totally disordered transverse component of moments. The conclusion is also supported by the features seen in the other measurements. The magnetic moments derived from 10K neutron diffraction data are explained using the LCS approach for different exchange integrals ratios.

Structural and magnetic behavior of LaMnO 3+ δ and LaMn 0.9Cr 0.1O 3+ δ at the same “hole concentration”

We report a comparative magnetic and a neutron powder diffraction (NPD) study of un-doped LaMnO 3+ δ ( δ=0.05 and 0.09) and Cr doped LaMn 0.9Cr 0.1O 3+ δ ( δ=0.00 and 0.04) with the same “hole concentration”. Samples with controlled oxygen contents were prepared by annealing at different temperatures and p(O 2) values. The refinement of the neutron powder diffraction data at 2 K shows that the AFM components for the Cr doped samples are higher than those of the un-doped ones for the same “hole concentration”. The FC and ZFC dc magnetization measurements versus T under 100 Oe also reveal a strong AFM character for the Cr-doped samples. These results clearly show a different role in the magnetic interactions for samples doped with Cr 3+ and Mn 4+ ions.

Large positive entropy change in several charge-ordering perovskites

Abstract The Nd0.5Sr0.5Mn1−xCuxO3 (x=0.00; 0.02; 0.10) and Nd0.25Pr0.25Sr0.5MnO3 perovskites have been prepared by solid reaction technology. The manganites are of single phase with orthorhombic structure. The FC and ZFC measurements show an evident existence of charge-ordering effect at low temperatures. At the charge-ordering temperature the magnetic entropy change, ΔS, is positive and the |ΔSmax| is larger than that determined at ferromagnetic-paramagnetic phase transition temperature.

Validation of the stochastic distorted-wave Born approximation model with broad bandwidth total target strength measurements of Antarctic krill

Abstract Total-scattering cross-sections (σt) of Antarctic krill (Euphausia superba) were measured over a broad bandwidth (36–202 kHz) using a new technique based on acoustical reverberation in a cavity. From 18 February to 9 March 2002, mean total target strengths (TTS = 10 log(σt/4π)), were measured from groups of 57–1169 krill (average standard length=31.6 mm; standard deviation=6.6 mm) at the Cape Shirreff field station, Livingston Island, Antarctica, and aboard RV “Yuzhmorgeologiya”. Chirp pulses were transmitted sequentially by an omni-directional emitter into one of three glass carboys containing groups of krill swimming in 9.3, 19.3, or 45.9 liters of seawater (0.6°C≤temperature≤4.0°C). Between each pulse the krill moved within the fixed-boundary tank and the modulated reverberations were sensed bi-statically with three omni-directional receivers. At each center frequency (fc), the coherent energy in 200-pulse ensembles identified sound scattered by the tank. The incoherent energy described total sound scattering from the krill. Thus, the TTS at each fc was extracted from a correlation analysis of energy reverberated in the tank. Measurement bias was determined to be ±0.4 dB from an experiment using metal sphere reference targets, and the precision was estimated as ±0.8 dB from the variability in the krill TTS (fc) measurements. The empirical estimates of mean σt corroborated a krill-scattering model based on the distorted-wave Born approximation (DWBA), enhanced by the authors to account for the stochastic nature of sound scattering (SDWBA), integrated over all scattering angles and averaged over all incident angles (SDWBATTS). The SDWBA, solved for target strength of Antarctic krill, may be the best predictor of backscatter for this important species and may also provide backscattering spectra for improving their acoustic identification. These advances may help to reduce uncertainty in krill-biomass estimation using multi-frequency echosounder data and echo-integration methods.

Influence of Cu substitution for Mn on the structure, magnetic, magnetocaloric and magnetoresistance properties of La 0.7Sr 0.3MnO 3 perovskites

Structural, magnetic, magnetocaloric and magnetoresistance (MR) studies on La 0.7Sr 0.3Mn 0.95Cu 0.05O 3 (No. 1) and La 0.7Sr 0.3Mn 0.9Cu 0.1O 3 (No. 2) perovskites are reported. The crystal structure of the samples is rhombohedral with a change of the lattice constants depending on the Cu content. FC and ZFC thermomagnetic measurements for both compositions at low field indicate that a spin–glass-like state (or cluster glass) occurs at low temperatures and a very sharp change of magnetization around the phase-transition point. The Curie temperature, T C, does almost not depend on the content of Cu substitution. A maximum magnetic-entropy change, Δ S ma x , of 1.96 and 2.07 J/kg K at 13.5 kOe and 350 K is observed for sample No. 1 and No. 2, respectively. Therefore, they can be considered as active magnetic refrigerant materials for room-temperature applications. Electrical-resistance measurements show that both samples are metallic conductor for T< T C and semiconductor for T> T C; moreover, the MR is maximal around T C.

Magnetic behaviour of high coercivity Nd 50Fe 40Si 10 amorphous ribbons

Extensive magnetic studies on Nd 50Fe 40Si 10 melt-spun ribbons with thicknesses up to 150 μm were performed. The large value of the coercive field up to 300 kA/m at room temperature and its dependence on the cooling rate as well as the DC M ZFC and M FC and AC-susceptibility measurements for the Nd 50Fe 40Si 10 fully amorphous ribbons indicate the coexistence of two kinds of magnetic order: long-range ferromagnetic order and short-range spin-glass order.

High pressure synthesis of LnCrS 3 (Ln = La, Ce, Nd, Sm) and LaCr 1−xFe xS 3 (x ≤ 0.2) with NH 4CdCl 3 structure type

LnCrS 3 (Ln = La, Ce, Nd, Sm) with NH 4CdCl 3 structure type were prepared in high pressure synthesis at 4 GPa, 1373 K for 2 h. Their orthorhombic lattice parameters were a = 0.787(2), b = 0.385(1), c = 1.334(3) nm for LaCrS 3; a = 0.776(4), b = 0.379(2), c = 1.316(7) nm for CeCrS 3; a = 0.769(2), b = 0.377(1), c = 1.306(4) nm for NdCrS 3; and a = 0.764(5), b = 0.374(2), c = 1.297(8) nm for SmCrS 3. The Ln 3+ ions are coordinated with nine S 2− ions in CrS 6 double chains. The products are antiferromagnetic semiconductors. The paramagnetic temperature Θ varied with a Cr–Cr distance in the CrS 6 double chain. They also showed a weak ferromagnetic behavior at low temperature below 120 K. Magnetic hysteresis was observed for the ferromagnetism between ZFC and FC measurements. LaCr 1−xFe xS 3 solid solution with NH 4CdCl 3 structure type was also obtained in high pressure synthesis at 4 GPa, 1473 K for 2 h. The Fe 3+ in high spin state substitutes the Cr 3+ up to about x = 0.2.

Carbon dioxide efflux from the floor of a boreal aspen forest. I. Relationship to environmental variables and estimates of C respired

Soil CO2 efflux (Soil Fc) in a boreal aspen (Populustremuloides) forest was related to environmental variables to estimate the mass of carbon (C) annually respired. Measurements of soil Fc were made between April and September with a dynamic closed chamber via an infra-red gas analyzer.Over the course of the study day-time soil Fc ranged from 0.027 to 0.411 mg CO2 m−1s−1. Summertime estimates of soil Fc were higher than expected, and this was attributed to underestimation by static chamber methods. Strong relationships were found between seasonal patterns of (1) soil Fc and soil temperature (Ts) at various depths (R2 = 0.77 to 0.87, Q10 = 3.9 to 5.1), (2) soil Fc and humus [CO2] and volumetric moisture (θv; R2 = 0.76 to 0.88) and (3) humus [CO2] and humus Ts and θv (R2 = 0.74). On their own, θv, litter and soil organic matter content explained little (&lt;5%) of the variation in soil Fc. Ts was the single most effective variable used to predict soil Fc.Annual masses of soil Fc C were estimated from the relationship between soil Fc and 0.1 m Ts in 1994. Long-term (49-yr) estimates were generated from monthly mean air temperatures (Ta) using the relationship between Ts (0.10 m) and Ta (2 m) at the site throughout 1994–1995. In both years, Ta explained about 70% of the variability in Ts. Estimates of annual soil Fc C were 905 (1994), 870 (1995) and 809 (long-term) g m−2. Growing season soil Fc approximated 75% of the annual C mass respired. These annual C fluxes far exceed current estimates for boreal and most temperate forest ecosystems. 1994 soil Fc C also exceeded the site estimate of aboveground net primary productivity (361 g C m−2yr−1). This extreme shortfall, along with the inability of soil organic matter or litter mass to explain soil Fc, suggests that about 60% of annual soil Fc C is attributable to the presence of roots. If soil Fc in vegetated environments is primarily due to the presence of roots then the significance of soil Fc to global C cycling can only be understood with concurrent estimates of net ecosystem C exchange. Key words: Soil CO2 flux, soil respiration, soil temperature, soil moisture, root respiration, boreal forest

Gadolinium prevents high airway pressure-induced permeability increases in isolated rat lungs.

To determine the initial signaling event in the vascular permeability increase after high airway pressure injury, we compared groups of lungs ventilated at different peak inflation pressures (PIPs) with (gadolinium group) and without (control group) infusion of 20 microM gadolinium chloride, an inhibitor of endothelial stretch-activated cation channels. Microvascular permeability was assessed by using the capillary filtration coefficient (Kfc), a measure of capillary hydraulic conductivity. Kfc was measured after ventilation for 30-min periods with 7, 20, and 30 cmH2O PIP with 3 cmH2O positive end-expiratory pressure and with 35 cmH2O PIP with 8 cmH2O positive end-expiratory pressure. In control lungs, Kfc increased significantly to 1.8 and 3.7 times baseline after 30 and 35 cmH2O PIP, respectively. In the gadolinium group, Kfc was unchanged from baseline (0.060 +/- 0.010 ml . min-1 . cmH2O-1 . 100 g-1) after any PIP ventilation period. Pulmonary vascular resistance increased significantly from baseline in both groups before the last Kfc measurement but was not different between groups. These results suggest that microvascular permeability is actively modulated by a cellular response to mechanical injury and that stretch-activated cation channels may initiate this response through increases in intracellular calcium concentration.

Description of a dynamic closed chamber for measuring soil respiration and its comparison with other techniques

Soil respiration is an important component of the net carbon dioxide exchange between agricultural ecosystems and the atmosphere, and reliable estimates of soil respiration are required in carbon balance studies. Most of the field measurements of soil respiration reported in the literature have been made using alkali traps. The use of portable CO2 analysers in dynamic closed chamber systems is recent. The introduction of this new technique requires its evaluation against existing methods in order to compare new information with older data. Nine intercomparisons between dynamic systems and alkali traps were made. Measurements of Fc,s obtained by both chambers showed a good agreement in all but two comparisons in which alkali trap measurements were lower than the dynamic chamber by about 22%. This first report of agreement between both techniques suggests that many measurements made in the past using alkali traps may be comparable to the measurements made more recently using the dynamic chambers. Analysis of the soil temperature and CO2 concentration inside the alkali traps failed to explain why the alkali traps occasionally underestimated the fluxes. Soil respiration measured with a dynamic closed chamber were also compared to eddy-correlation measurements. The results did not reveal any consistent bias between techniques but the scattering was large. This dispersion is likely the result of the difference between the areas measured by the two techniques. Key words: Carbon dioxide, greenhouse gases, CO2 flux, soil carbon

Study of the components of reverse cholesterol transport in lecithin: Cholesterol acyltransferase deficiency

Enzymatic and lipid transfer reactions involved in reverse cholesterol transport were studied in healthy and lecithin:cholesterol acyltransferase (LCAT), deficient subjects. Fasting plasma samples obtained from each individual were labeled with [ 3H]cholesterol and subsequently fractionated by gel chromatography. The radioactivity patterns obtained corresponded to the elution volumes of the three major ultracentrifugally isolated lipoprotein classes (very low density lipoproteins (VLDL), low density lipoproteins (LDL), and high density lipoproteins (HDL)). In healthy subjects, the LCAT activity was consistently found in association with the higher molecular weight portion of HDL. Similar observations were made when exogenous purified LCAT was added to the LCAT-deficient plasma prior to chromatography. Incubation of the plasma samples at 37 °C resulted in significant reduction of unesterified cholesterol (FC) and an increase in esterified cholesterol (CE). Comparison of the data of FC and CE mass measurements of the lipoprotein fractions from normal and LCAT-deficient plasma indicates that: (i) In normal plasma, most of the FC for the LCAT reaction originates from LDL even when large amounts of FC are available from VLDL. (ii) The LCAT reaction takes place on the surface of HDL. (iii) The product of the LCAT reaction (CE) may be transferred to either VLDL or LDL although VLDL appears to be the preferred acceptor when present in sufficient amounts, (iv) CE transfer from HDL to lower density lipoproteins is at least partially impaired in LCAT-deficient patients. Additional studies using triglyceride-rich lipoproteins indicated that neither the capacity to accept CE from HDL nor the lower CE transfer activity were responsible for the decreased amount of CE transferred to VLDL and chylomicrons in LCAT-deficient plasma.

The importance of measuring Fc+ (killer) cells in insulin-dependent (type 1) diabetes.

The measurement of Fc+ (killer or K) cells in insulin dependent (Type 1) diabetes may be of considerable value in monitoring activity of immune disturbance. K cells were investigated in Type 1 diabetics, their relatives and normal controls employing two methods based upon different principles. A close positive linear correlation was observed between the two methods in all subjects. Type 1 diabetic patients showed an increased level of K-cells with both techniques. In addition there was a good correlation between raised levels of K-cells and the occurrence of organ specific autoantibodies.