HRR Values Research Articles

Thermal properties and combustion characterization of nylon 6/MgAl-LDH nanocomposites via organic modification and melt intercalation

The nylon 6/MgAl layered double hydroxide (MgAl-LDH) nanocomposites have been prepared by melt intercalation of nylon 6 into the part organic dodecyl sulfate (DS) anion-modified MgAl(H-DS) interlayers. The structures and properties of MgAl(H-DS) and corresponding nanocomposites were characterized by ion chromotography, X-ray diffraction (XRD), transmission electron microscopy (TEM), differential scanning calorimetry (DSC), thermogravimetry analysis (TGA), and cone calorimeter test (CCT). The nanoscale dispersion of MgAl(H-DS) layers in the nylon 6 matrix has been verified by the disappearance of d 001 XRD diffraction peak of MgAl(H-DS) and the observation of TEM image. DSC tests evince that these exfoliated MgAl(H-DS) layers play the role of nucleating agents with strong heterogeneous nucleation effect on the crystallization of nylon 6 and increase its crystallization temperature over 12 °C with only 5 wt% MgAl(H-DS). TGA tests show that the effect of alkaline catalysis degradation from LDH on nylon 6 decreases the thermal stability of nylon 6/MgAl-LDH nanocomposites. The data from the cone calorimeter tests show that the HRR and MLR values of the sample with 5 wt% MgAl(H-DS) decrease considerably to 664 kW/m 2 and 0.161 g/m 2 s from 1064 kW/m 2 and 0.252 g/m 2 s of pure nylon 6, respectively. This kind of exfoliated nanocomposite is promising for the application of flame-retardant polymeric materials.

Is TAP2*0102 allele involved in insulin-dependent diabetes mellitus (type 1) protection?

In this study, we have investigated the frequencies of TAP1 and TAP2 alleles in a group of 226 persons, living in La Reunion Island, consisting of 70 patients with insulin-dependent diabetes mellitus (IDDM) and most of their first degree relatives ( i.e., 156 parents and full sibling subjects) and previously HLA DQB1, DQA1, and DRB1 genotyped. The population of this island is constituted by a particular structure of highly crossbreeding people. Interestingly, the new TAP2*0104 allele, previously discovered by our team in Reunion Island, was found to be increased in the IDDM population and the calculated HRR was relatively high (HRR = 3.3). This result seems to be due to a positive linkage disequilibrium between TAP2*0104 allele and the highly diabetogenous DQB1* 0201–DQA1* 0501–DRB1 0301 haplotype (HRR = 9), which suggests that TAP2*0104 cannot be considered as an additional predispositional factor, but more as a genetic susceptibility marker of IDDM. In addition, we show that minor alleles (TAP2D, *0102, *0103, *0104) are associated with a restricted number of HLA DQ-DR haplotypes and each of them exhibits a preferential linkage with one particular haplotype. In contrast with other alleles, and despite a HRR value close to 1, we show that TAP2*0102 allele contributes significantly to a drastic reduction of the diabetogenic effect of DQB1*0201–DQA1*0301.1–DRB*0701 haplotype. Indeed, this haplotype, which is usually preferentially transmitted to affected children, is dominantly transmitted to healthy children when it is associated with TAP2*0102. Therefore, this allele seems to contribute to genetic protection to IDDM.

Use of heart rate to predict energy expenditure from low to high activity levels.

This study evaluated the ability to use the relationship between heart rate (HR) and oxygen uptake (VO2 ) to estimate energy expenditure (EE) from low to high physical activity with different HR-based prediction equations. General prediction equations were established based on the individual relations between HR and EE. Possibilities to improve the EE estimation with using alternatives for respective HR were also assessed. The alternatives were % of HR reserve: 100 x [(activity HR - resting HR)/(maximal HR - resting HR)], (HRR), and the difference between activity HR and resting HR (activity HR - resting HR), (HRnet). Forty-two men (age mean 36.5 [sd 7.6] y, BMI 24.5 [2.4] kg x m(-2), VO2 max 45.2 [6.5]) kg x ml x min(-1) and 47 women (mean age 37.5 [9.5], BMI 23.3 [3.4], VO2 max 36.3 [5.4]) performed an exercise test consisting of physically low-activity tasks and a maximal treadmill uphill walking test. Respiratory gases were obtained from indirect calorimetry. HR was registered by electrocardiography and EE was calculated from (VO2 ) and carbon dioxide (VCO2 ) production. Generalised linear models with random effects were used for the prediction of EE. EE values of the tests (one value at each intensity level) were predicted in separate models by the respective HR, HRR or HRnet values. The other predictors used in all models were body weight, sex and the intensity of exercise. The standard error of estimate (SEE) was 1.41 kcal x min(-1) (5.89 kJ) in the model with HR variable as a predictor, 1.01 kcal x min(-1) (4.22 kJ) with HRR variable, and 1.08 (4.51 kJ) with HRnet variable. The results show that the prediction of EE is more accurate if HRR or HRnet are used in prediction equation instead of HR.

Singular plastic fields in non-associative pressure sensitive solids

Singular plastic fields at crack tips are investigated for a non-associative deformation theory modelling a Drucker–Prager material. Plane-strain mode-I eigensolutions are mapped over a range of material parameters along with a pure power law response. The material does not admit a strain energy function and the level of stress singularity is higher than the HRR values. The latter are recovered for associated models but, in general, the singularity reported here deviate from J-integral analysis with increasing non-associativity. Near tip profiles are illustrated for a few representative cases, indicating an increasing sensitivity to non-associativity at higher levels of the hardening exponent.

A Nonlinear Finite Element Eigenanalysis of Singular Plane Stress Fields in Bimaterial Wedges Including Complex Eigenvalues

A finite element formulation is developed for the analysis of variable-separable singular stress fields in power law hardening materials under conditions of plane stress. The displacement field within a sectorial element is assumed to be quadratic in the angular coordinate and of the power type in the radial direction as measured from the singular point. An iteration scheme that combines the Newton method and matrix singular value decomposition is used to solve the nonlinear homogeneous eigenvalue problem, where the eigenvalues and eigenfunctions are obtained simultaneously. The formulation and iteration scheme apply when the eigenvalue is complex. The examples considered include the single material crack and wedge to demonstrate convergence, and the bimaterial interface crack and the bimaterial wedge to demonstrate geometric versatility and the ability to handle complex eigenvalues. It is found that the real part of the complex eigenvalue for the interface crack agrees with the HRR value. In this case the associated complex eigenfunction is converted into an approximate real-valued eigenfunction that is valid for any mode-mix. In addition, the behavior of separable solutions near certain 'wedge paradox' geometries where non-separable solutions occur is investigated.