Microstructural evolution and intermetallic formation in Al-8wt% Si-0.8wt% Fe alloy due to grain refiner and modifier additions

An alloy of Al-8wt% Si-0.8wt% Fe was cast in a metallic die, and its microstructural changes due to Ti-B refiner and Sr modifier additions were studied. Apart from usual refinement and modification of the microstructure, some mutual influences of the additives took place, and no mutual poisoning effects by these additives, in combined form, were observed. It was noticed that the dimensions of the iron-rich intermetallics were influenced by the additives causing them to become larger. The needle-shaped intermetallics that were obtained from refiner addition became thicker and longer when adding the modifier. It was also found that α-Al and eutectic silicon phases preferentially nucleate on different types of intermetallic compounds. The more iron content of the intermetallic compounds and the more changes in their dimensions occurred. Formation of the shrinkage porosities was also observed.     

Data based model free hysteresis identification for a nonlinear structure

In the last two decades, the damage detection for civil engineering structures has been widely treated as a modal analysis problem and most of the currently available vibration-based system identification approaches are based on modal parameters, namely the natural frequencies, mode shapes and damping ratios, and/or their derivations, which are suitable for linear systems. Nonlinearity is generic in engineering structures. For example, the initiation and development of cracks in civil engineering structures as typical structural damages are nonlinear process. One of the major challenges in damage detection, early warning and damage prognosis is to obtain reasonably accurate identification of nonlinear performance such as hysteresis which is the direct indicator of damage initiation and development under dynamic excitations. In this study, a general data-based identification approach for hysteretic performance in form of nonlinear restoring force using structural dynamic responses and complete and incomplete excitation measurement time series was proposed and validated with a 4-story frame structure equipped with smart devices of magneto-rheological (MR) damper to simulate nonlinear performance. Firstly, as an optimization method, the least-squares technique was employed to identify the system matrices of an equivalent linear system of the nonlinear structure model basing on the excitation force and the corresponding vibration measurements with impact test when complete and incomplete excitations; and secondly, the nonlinear restoring force of the structure was identified and compared with the test measurements finally. Results show that the proposed data-based approach is capable of identifying the nonlinear behavior of engineering structures and can be employed to evaluate the damage initiation and development of different structure under dynamic loads.     

Plankton effect on cod recruitment in the North Sea

The Atlantic cod (Gadus morhua L.) has been overexploited in the North Sea since the late 1960s and great concern has been expressed about the decline in cod biomass and recruitment. Here we show that, in addition to the effects of overfishing, fluctuations in plankton have resulted in long-term changes in cod recruitment in the North Sea (bottom-up control). Survival of larval cod is shown to depend on three key biological parameters of their prey: the mean size of prey, seasonal timing and abundance. We suggest a mechanism, involving the match/mismatch hypothesis, by which variability in temperature affects larval cod survival and conclude that rising temperature since the mid-1980s has modified the plankton ecosystem in a way that reduces the survival of young cod.     

Downregulation of NF-κB signaling by mutant huntingtin proteins induces oxidative stress and cell death

Accumulation of abnormal proteins and endoplasmic reticulum stress accompany neurodegenerative diseases including Huntington’s disease. We show that the expression of mutant huntingtin proteins with extended polyglutamine repeats differentially affected endoplasmic reticulum signaling cascades linked to the inositol-requiring enzyme-1 (IRE1) pathway. Thus, the p38 and c-Jun N-terminal kinase pathways were activated, while the levels of the nuclear factor-κB-p65 (NF-κB-p65) protein decreased. Downregulation of NF-κB signaling was linked to decreased antioxidant levels, increased oxidative stress, and enhanced cell death. Concomitantly, calpain was activated, and treatment with calpain inhibitors restored NF-κB-p65 levels and increased cell viability. The calpain regulator, calpastatin, was low in cells expressing mutant huntingtin, and overexpression of calpastatin counteracted the deleterious effects caused by N-terminal mutant huntingtin proteins. These results show that calpastatin and an altered NF-κB-p65 signaling are crucial factors involved in oxidative stress and cell death mediated by mutant huntingtin proteins.