Function Of T2 Research Articles

Out-of-plane compressive properties of a butterfly-shaped auxetic metamaterial

Abstract Inspired by butterfly, a bio butterfly-shaped auxetic metamaterial (BSAM) was recently proposed in which the unite cell of BSAM was designed based on silhouette of a butterfly. The distinguished in-plane mechanical properties made the BSAM a potential absorber to be used in a broad range of applications. The aim of this study is to examine the out-of-plane mechanical properties under quasi-static compression. Using the validated FE models, a comparison was carried out between BSAM and two popular auxetic honeycombs, namely, re-entrant (RE) and modified re-entrant (MRE). Results showed that the nominal stress-strain curves of the BSAM were significantly higher than those of auxetic honeycombs (RE and MRE). However, the MRE revealed the highest Young’s modulus. The plateau stresses were 10.5 MPa, 7.5 MPa and 3.3 MPa for the compressed BSAM, MRE and RE, respectively. Furthermore, the calculated values of the specific energy absorption per volume (Wv) of the three structures indicated that the percentage of the absorbed energy by the BSAM was 182% and 456% higher than those absorbed by the MRE and RE, respectively. Based on the determined values of ideal Wv (11.4 J/cm3 “BSAM”, 5.2 J/cm3 “MRE” and 2.3 J/cm3 “RE”) , the energy efficiency of the three structures was 64%, 79% and 69% of the total energy in the case BSAM, MRE and RE, respectively. Moreover, the influence of the in-plane thickness (t1) and the thickness of cylinders (t2) on the mechanical performance of the BSAM were examined through a parametric study. Findings of the parametric study indicated that the mechanical properties as a function of t1 were considerably affected, while moderate influence was resulted as a function of t2.

T1-T2* relaxation correlation measurements

The majority of low field Magnetic Resonance (MR) analyses rely on T2 lifetime measurements. Modification of the T2 measurement to include a T1 dimension has made the T1-T2 measurement a very powerful analytical technique. The T1-T2 measurement is uniquely well suited to characterization of different spin populations in porous materials, such as fluid bearing reservoir rocks, and in soft biopolymer materials, for example foods. However, the T1-T2 measurement is challenging or impossible if the T2 relaxation lifetime, or a component lifetime, is short-lived and the signal unobservable in an echo measurement. This occurs in many important classes of materials. A short lifetime T2 will not however, in general, preclude observation of a free induction decay with signal decay governed by T2*.As outlined in this paper a T1-T2* measurement is a useful analog to the T1-T2 experiment. T1-T2* measurement enables one to differentiate species as a function of T2* in one dimension and T1 in the other dimension. Monitoring changes of the T1-T2* coordinate, and associated signal intensity changes, has the potential to reveal structural changes in materials evolving in time. These methods may also be employed to discriminate and identify solid-like species present in static samples.The T1-T2* measurement is very general in application, but in this paper we focus on cement-based mortars to develop and illustrate the essential ideas. T1-T2* results show a multi-modal behaviour of the MR signal lifetimes, T1 and T2*, in mortar samples under study, indicating at least two different water populations. The short T2* lifetime was assigned to interlayer water (water between C–S–H layers) where the associated T1 is also short lived. The longer T2* lifetime was assigned to water in the pore space, where T1 is also longer lived. In addition to mortar samples we also show application of the method to a crystalline organic species, o-phenylenediamine, which features Sinc Gaussian and exponential decays of transverse magnetization.

Fabricating Uniform Tetragonal Barium Titanate Nanocrystals via Sand Milling Assisted by an Innovative Two-Step Calcination

Sand-milling machine was firstly utilized to crush and disperse the raw materials. A homogenous and well-dispersed mixture of TiO2 and BaCO3 (<30nm) was obtained. The solid state reaction temperature can be reduced by 200°C for nanosized reactants compared with coarse ones. In order to increase tetragonality of nanosized BaTiO3, an innovative two-step calcination method, which includes solid state reaction process between reactants at a low temperature T1 and phase transition process at a high temperature T2, was subsequently adopted. The microstructure evolution of BaTiO3 by two-step calcination was investigated as a function of T2 and corresponding dwelling time t2. Pure-perovskite BaTiO3 nanopowders with the mean particle size as small as 75nm and tetragonality (c/a ratio) higher than 1.0096 could be fabricated by two-step calcination through altering T2 and/or its dwelling time t2.

Effective Iron Chelation Practice for Patients With β-Thalassemia Major

Chronic blood transfusion is the only treatment for severe anemia in patients with β-thalassemia major. However, red blood cell transfusions lead to iron overload and subsequent organ damage because of the toxic effects of iron. The heart is particularly vulnerable to iron toxicity, and heart failure is the leading cause of death among these patients. Iron chelation therapy prevents or reverses iron loading, thereby reducing the risk of complications from excess iron. Serum ferritin and liver iron concentration often are used to gauge the risk of organ iron overload, but these measurements may not correlate well with cardiac iron load. Magnetic resonance imaging (MRI) is a noninvasive diagnostic tool that can provide a more direct measure of iron concentration in both the heart and liver. Cardiac iron determined by MRI is expressed as a function of T2*, in which higher values represent lower concentrations. Changes in T2* are used to assess the effectiveness of iron chelation and to adjust therapy. Early treatment and compliance are keys to successful therapy. Nursing strategies to optimize chelation therapy include identifying patients who are at risk for developing organ damage, developing chelation plans, promoting compliance, and educating patients. The efficacy and safety of iron chelators, as well as nursing best practices, are reviewed.

Correcting the bias due to dependent censoring of the survival estimator by conditioning

We consider the conditional estimation of the survival function of the time T2 to a second event as a function of the time T1 to a first event when there is a censoring mechanism acting on their sum T1+T2. The problem has been motivated by a treatment interruption study aimed at improving the quality of life of HIV-infected patients. We base the analysis on the survival function of T2 given that T1∈I, where I represents a period of scientific interest (1 trimester, 1 year, 2 years, etc.) and propose a non-parametric estimator for the survival function of T2 given that T1∈I, which takes into account both the selection bias and the heterogeneity due to the dependent censoring. The proposed estimator for the survival function uses the risk group of T2 conditioned on the categories of T1 and corrects for the dependent censoring using weights defined by the observed values of T1. The estimator, properly normalized, converges weakly to a zero-mean Gaussian process. We estimate the variance of the limiting process via a bootstrap methodology. Properties of the proposed estimator are illustrated by an extensive simulation study. The motivating data set is analysed by means of this new methodology.

Insights into brain microstructure from the T2 distribution

T2 weighting is particularly sensitive, but notoriously unspecific, to a wide range of brain pathologies. However, careful measurement and analysis of the T2 decay curve from brain tissue promise to provide much improved pathological specificity. In vivo T2 measurement requires accurate 180 pulses and appropriate manipulation of stimulated echoes; the most common approach is to acquire multiple echoes from a single slice. The T2 distribution, a plot of component amplitude as a function of T2, can be estimated using an algorithm capable of fitting a multi-exponential T2 decay with no a priori assumptions about the number of exponential components. T2 distributions from normal brain show peaks from myelin water, intra/extracellular water and cerebral spinal fluid; they can be used to provide estimates of total water content (total area under the T2 distribution) and myelin water fraction (MWF, fractional area under the myelin water peak), a measure believed to be related to myelin content. Experiments on bovine brain suggest that magnetization exchange between water pools plays a minor role in the T2 distribution. Different white matter structures have different MWFs. In normal white matter (NWM), MWF is not correlated with the magnetization transfer ratio (MTR) or the diffusion tensor fractional anisotropy (FA); hence it provides unique information about brain microstructure. Normal-appearing white matter (NAWM) in multiple sclerosis (MS) brain possesses a higher water content and lower MWF than controls, consistent with histopathological findings. Multiple sclerosis lesions demonstrate great heterogeneity in MWF, presumably due to varying myelin contents of these focal regions of pathology. Subjects with schizophrenia were found to have significantly reduced MWF in the minor forceps and genu of the corpus callosum when compared to controls, suggesting that reduced frontal lobe myelination plays a role in schizophrenia. In normal controls, frontal lobe myelination was positively correlated with both age and education; this result was not observed in subjects with schizophrenia. A strong correlation between MWF and the optical density from the luxol fast blue histological stain for myelin was observed in formalin-fixed brain, supporting the use of the MWF as an in vivo myelin marker.

Quantum temperature fluctuations in the magnetization of antiferromagnetic semimetals

It is shown that in semimetallic, low-temperature antiferromagnetic materials located in a quantizing magnetic field, the part of the band magnetization M∼ which oscillates in H can have a nonmonotonic temperature dependence. This non-Fermi liquid behavior will show up experimentally in the form of quantum temperature fluctuations of the magnetization when the decrease with rising temperature is oscillatory, rather than the usual monotonic decrease. It is shown that the magnetization from an individual spin electron (or hole) subband has the form of weakly damped periodic oscillations as a function of T2. This result makes it possible to develop an efficient method for studying the electronic structure of antiferromagnetic semimetals based on an examination of the quantum temperature fluctuations. Calculations show that quantum temperature fluctuations can be observed, for example, in the cerium monopnictides CeP and CeAs, which are strongly correlated, antiferromagnetic, compensated semimetals with low Neel temperatures.

An Asymptotic Expansion for the Distribution of Hotelling'sT2-Statistic under Nonnormality

In this paper we obtain an asymptotic expansion for the distribution of Hotelling'sT2-statisticT2under nonnormality when the sample size is large. In the derivation we find an explicit Edgeworth expansion of the multivariatet-statistic. Our method is to use the Edgeworth expansion and to expand the characteristic function ofT2.

Adjustment of Bartlett Type to Hotelling's T2-Statistic Under Elliptical Distributions

SYNOPTIC ABSTRACTHotellling's T2 is Bartlett adjustable for its null distribution under normality since the statistic is a function of the likelihood ratio statistic which is Bartlett adjustable. The asymptotic expansion for the null distribution of Hotelling's T2 under elliptical distributions, however, does not, in general, satisfy the well-known condition under which the statistic is adjustable. This paper shows that a quadratic function of T2 achieves the Bartlett adjustment. The relevant order of approximation is expressed as a monotone function.

Enhancement of t-PA-mediated plasminogen activation by bacterial surface receptors

Summary A total of 63 strains representing 7 species of plasminogen binding bacteria, were examined for the ability to potentiate t-PA and urokinase (u-PA) mediated activation of human plasminogen to plasmin. Tested species included β-haemolytic streptococci groups A, C, and G, Streptococcus pneumoniae, Neisseria meningitidis, Haemophilus influenzae and Proteus mirabilis. The effect on plasminogen activation was measured using a coupled enzymatic assay with a chromogenic substrate. The changes in absorbance were found to be linear functions of t2 in agreement with theoretical expectations. Most plasminogen binding strains were capable to dramatically enhance the rate of t-PA induced plasminogen activation. The most pronounced potentiation was observed with a Streptococcus equisimilis strain which increased the activation rate 130-fold. High potentiations was also detected for N. meningitidis and S. pneumoniae strains. P. mirabilis was an exception as some strains were capable to bind plasminogen without any influence on plasminogen activation. Also, u-PA mediated plasminogen activation was enhanced in the presence of bacteria. However the stimulation factor obtained were in most strains much less than those obtained with t-PA. For different strains within a species, the capability to enhance the rate of the t-PA mediated activation correlated with plasminogen binding (r=0.74–0.92). Both plasminogen binding and the stimulation of plasminogen activation were abolished in the presence of 6-aminohexanoic acid (6-AHA, ɛ-aminocaproic acid) suggesting that the lysine-binding sites in the plasminogen molecule are involved in both phenomena. The binding of plasminogen and facilitation of its activation provide bacteria with an active proteolytic shield of possible importance in tissue penetration and infection.

Anomalous Behavior in Electrical Resistivity and Specific Heat of Superconducting TiNb Alloys

The electrical resistivity and specific heat of TiNb alloys have been measured in high magnetic fields up to 20.6 T and 15.1 T, respectively. Anomalous behavior is observed in both electrical resistivity and specific heat. A slight but definite enhancement of the resistivity with logarithmic temperature dependence is observed for samples with Nb concentration lower than 63 at%, where ω-precipitation in β matrix is clear in electron diffraction pattern. An abrupt change in the slope of the normal state specific heat Cn/T plotted as a function of T2 is found in samples over a wide range of concentration.