Effective thermal properties of viscoelastic composites having field-dependent constituent properties

This study introduces a micromechanical model for predicting effective thermal properties (linear coefficient of thermal expansion and thermal conductivity) of viscoelastic composites having solid spherical particle reinforcements. A representative volume element (RVE) of the composites is modeled by a single particle embedded in the cubic matrix. Periodic boundary conditions are imposed to the RVE. The micromechanical model consists of four particle and matrix subcells. Micromechanical relations are formulated in terms of incremental average field quantities, i.e., stress, strain, heat flux and temperature gradient, in the subcells. Perfect bonds are assumed along the subcell’s interfaces. Stress and temperature-dependent viscoelastic constitutive models are used for the isotropic constituents in the micromechanical model. Thermal properties of the particle and matrix constituents are temperature dependent. The effective coefficient of thermal expansion is derived by satisfying displacement and traction continuity at the interfaces during thermo-viscoelastic deformations. This formulation leads to an effective time–temperature–stress-dependent coefficient of thermal expansion. The effective thermal conductivity is formulated by imposing heat flux and temperature continuity at the subcells’ interfaces. The effective thermal properties obtained from the micromechanical model are compared with analytical solutions and experimental data available in the literature. Finally, parametric studies are also performed to investigate the effects of nonlinear thermal and mechanical properties of each constituent on the overall thermal properties of the composite.     

Scalable and dynamically balanced shared-everything OLTP with physiological partitioning

Scaling the performance of shared-everything transaction processing systems to highly parallel multicore hardware remains a challenge for database system designers. Recent proposals alleviate locking and logging bottlenecks in the system, leaving page latching as the next potential problem. To tackle the page latching problem, we propose physiological partitioning (PLP). PLP applies logical-only partitioning, maintaining the desired properties of sharedeverything designs, and introduces a multi-rooted B+Tree index structure (MRBTree) that enables the partitioning of the accesses at the physical page level. Logical partitioning and MRBTrees together ensure that all accesses to a given index page come from a single thread and, hence, can be entirely latch free; an extended design makes heap page accesses thread private as well. Moreover, MRBTrees offer an infrastructure for easy repartitioning and allow us to have a lightweight dynamic load balancing mechanism (DLB) on top of PLP. Profiling a PLP prototype running on different multicore machines shows that it acquires 85 and 68%fewer contentious critical sections, respectively, than an optimized conventional design and one based on logical-only partitioning. PLP also improves performance up to almost 50 % over the existing systems, while DLB enhances the system with rapid and robust behavior in both detecting and handling load imbalances.     

McDonald Criteria 2010 and 2005 Compared: Persistence of High Oligoclonal Band Prevalence Despite Almost Doubled Diagnostic Sensitivity

The 2010 McDonald criteria were developed to allow a more rapid diagnosis of relapsing-remitting multiple sclerosis (MS) by only one MRI of the brain. Although cerebrospinal fluid (CSF) is not a mandatory part of the latest criteria, the evidence of an intrathecal humoral immunoreaction in the form of oligoclonal bands (OCB) is crucial in the diagnostic workup. To date, the impact of the 2010 McDonald criteria on the prevalence of OCB has not been investigated. We retrospectively evaluated data of 325 patients with a clinical relapse suggestive of demyelination that were treated in a German university hospital between 2010 and 2015. One hundred thirty-six patients (42%) were diagnosed with MS and 189 patients with CIS when the criteria of 2010 were applied. The criteria of 2005 allowed only 70 patients (22%) to be designated as MS. In contrast, the prevalence of OCB was marginal affected in MS patients with 96% for the criteria of 2010 and 98.5% for the criteria of 2005. In conclusion, OCB are prevalent in most MS patients and reflect the chronic inflammatory nature of the disease. We recommend CSF examination to exclude alternative diagnoses and reevaluation of the diagnosis MS in patients with negative OCB.     

The Flaxseed-Derived Lignan Phenolic Secoisolariciresinol Diglucoside (SDG) Protects Non-Malignant Lung Cells from Radiation Damage

Plant phenolic compounds are common dietary antioxidants that possess antioxidant and anti-inflammatory properties. Flaxseed (FS) has been reported to be radioprotective in murine models of oxidative lung damage. Flaxseed’s protective properties are attributed to its main biphenolic lignan, secoisolariciresinol diglucoside (SDG). SDG is a free radical scavenger, shown in cell free systems to protect DNA from radiation-induced damage. The objective of this study was to investigate the in vitro radioprotective efficacy of SDG in murine lung cells. Protection against irradiation (IR)-induced DNA double and single strand breaks was assessed by γ-H2AX labeling and alkaline comet assay, respectively. The role of SDG in modulating the levels of cytoprotective enzymes was evaluated by qPCR and confirmed by Western blotting. Additionally, effects of SDG on clonogenic survival of irradiated cells were evaluated. SDG protected cells from IR-induced death and ameliorated DNA damage by reducing mean comet tail length and percentage of γ-H2AX positive cells. Importantly, SDG significantly increased gene and protein levels of antioxidant HO-1, GSTM1 and NQO1. Our results identify the potent radioprotective properties of the synthetic biphenolic SDG, preventing DNA damage and enhancing the antioxidant capacity of normal lung cells; thus, rendering SDG a potential radioprotector against radiation exposure.     

College students’ perceived threat and preference for seeking help in traditional,distributed, and distance learning environments

The purpose of the present study was to examine how college students’ help seeking behavior varied across different instructional learning environments. Four hundred and seventy four (N = 472) students enrolled in distance, distributed, and traditional classes were queried about their help seeking preferences, help seeking tendencies, personal threat in seeking help, and academic self-efficacy. It was hypothesized that students enrolled in courses with an online computer component would report (a) higher instances of help seeking behavior, particularly from instructors; and (b) feel less threatened to seek help than students in traditional learning environments. It was also expected that student achievement would be significantly correlated with formal help seeking, academic self-efficacy, and perceived threat to seek help. Lastly, it was postulated that students would report that they prefer to use electronic means to seek help and that they find it more effective. Overall the hypotheses of this study were supported. Educational implications and recommendations are provided regarding the type of technological tools that college instructors might consider using in their courses to promote help seeking.     

Dispersion of carbon nanotubes and its influence on the mechanical properties of the cement matrix

An appropriate dispersion of carbon nanotubes (CNTs) is a prerequisite for their use in improving the mechanical properties of cement-based composites. In this study two types of carbon nanotubes (CNTs) having different morphologies were investigated. To obtain a uniform distribution of CNTs in the cement matrix, the effect of sonication on the deagglomeration of CNTs in combination with anionic and nonionic surfactants in varying concentrations was quantitatively investigated when preparing aqueous dispersions of CNTs for the subsequent use in cement paste. The relationships between the quality of CNT-dispersion on the one hand and the sonication time and surfactant concentration on the other were determined using UV–vis spectroscopy. After dispersion, nitrogen-doped CNTs were found mostly as individual, broken CNTs. In contrast, after the treatment of the mixture of single-, double-, and multi-walled CNTs, a net-like distribution was observed where destruction of the CNTs due to sonication could not be distinguished. Modification of the cement pastes with dispersions of CNTs led to a pronounced increase, up to 40%, in compressive strength and, in some cases, to a moderate increase in tensile strength under high strain-rate loading. However, no significant improvement in strength was observed for quasi-static loading. Microscopic examination revealed that the bridging of the C–S–H phases differed depending on the type of CNT. This explained, at least partly, the observed effects of CNT-addition on the mechanical properties of hardened cement pastes.