Development of a universal stress sensor for graphene and carbon fibres

Carbon fibres are a significant volume fraction of modern structural airframes. Embedded into polymer matrices, they provide significant strength and stiffness gains by unit weight compared with competing structural materials. Here we use the Raman G peak to assess the response of carbon fibres to the application of strain, with reference to the response of graphene itself. Our data highlight the predominance of the in-plane graphene properties in all graphitic structures examined. A universal master plot relating the G peak strain sensitivity to tensile modulus of all types of carbon fibres, as well as graphene, is presented. We derive a universal value of - average - phonon shift rate with axial stress of around -5ω0 -1 (cm -1 Mpa-1), where ω0 is the G peak position at zero stress for both graphene and carbon fibre with annular morphology. The use of this for stress measurements in a variety of applications is discussed. © 2011 Macmillan Publishers Limited. All rights reserved.

An analysis of the cooperative mechano-sensitive feedback between intracellular signaling, focal adhesion development, and stress fiber contractility

Cells communicate with their external environment via focal adhesions and generate activation signals that in turn trigger the activity of the intracellular contractile machinery. These signals can be triggered by mechanical loading that gives rise to a cooperative feedback loop among signaling, focal adhesion formation, and cytoskeletal contractility, which in turn equilibrates with the applied mechanical loads. We devise a signaling model that couples stress fiber contractility and mechano-sensitive focal adhesion models to complete this above mentioned feedback loop. The signaling model is based on a biochemical pathway where IP3 molecules are generated when focal adhesions grow. These IP3 molecules diffuse through the cytosol leading to the opening of ion channels that disgorge Ca2+ from the endoplasmic reticulum leading to the activation of the actin/myosin contractile machinery. A simple numerical example is presented where a one-dimensional cell adhered to a rigid substrate is pulled at one end, and the evolution of the stress fiber activation signal, stress fiber concentrations, and focal adhesion distributions are investigated. We demonstrate that while it is sufficient to approximate the activation signal as spatially uniform due to the rapid diffusion of the IP3 through the cytosol, the level of the activation signal is sensitive to the rate of application of the mechanical loads. This suggests that ad hoc signaling models may not be able to capture the mechanical response of cells to a wide range of mechanical loading events. © 2011 American Society of Mechanical Engineers.

Enriched environment treatment counteracts enhanced addictive and depressive-like behavior induced by prenatal chronic stress

Prenatal stress can cause many long-term behavior changes in offspring, but whether prenatal stress can alter addictive behavior in offspring and postnatal enriched environment treatment (EE) can restore these changes are unknown. We reported here that pr

Deposition and characterisation of ultralow-stress ZnO thin films for application in FBAR-based gravimetric biosensors

Zinc oxide (ZnO) thin films were deposited at high rates ( > 50 nm min-1) using a unique technique known as high target utilisation sputtering (HiTUS). The films obtained possess good crystallographic orientation, low surface roughness, very low stress and excellent piezoelectric properties. We have utilised the films to develop highly sensitive biosensors based on thickness longitudinal mode (TLM) thin film bulk acoustic resonators (FBARs). The FBARs have the fundamental TLM at a frequency near 1.5 GHz and quality factor Q higher than 1,000, which is one of the largest values ever reported for ZnO-based FBARs. Bovine Serum Albumin (BSA) solutions with different concentrations were placed on the top of different sets of identical FBARs and their responses to mass-loading from physically adsorbed protein coatings were investigated. These resonators demonstrated a high sensitivity and thus have a great potential as gravimetric sensors for biomedical applications. © 2011 Inderscience Enterprises Ltd.

Oxygen consumption under copper and zinc stress in Perna viridis

The rate of oxygen consumption by Perna viridis pre-exposed to copper and zinc was studied. Those test individuals pre-exposed to various zinc concentrations showed variability in oxygen consumption irrespective of concentrations and pre-exposure period. While those animals pre-exposed to various copper concentrations registered decrease in oxygen consumption at concentrations above 0.06 p.p.m. copper, pre-exposure to concentrations below 0.02 p.p.m. copper did not result in any clear cut change in the rate of oxygen consumption.

Both stress experience and age determine the impairment or enhancement effect of stress on spatial memory retrieval

It has been documented that stress or glucocorticoids have conflicting effects on memory under different conditions. However, it is not fully understood why stress can either impair or enhance memory. Here, we have examined the performance of six age groups of Wistar rats in a water maze spatial task to evaluate the effects of stress under different conditions. We found that the impairment or enhancement effect of an 'elevated platform' (EP) stress on memory was dependent on previous stress experience and on age. EP stress impaired memory retrieval in water maze naive animals. but enhanced rather than impaired memory retrieval in young water maze stress-experienced animals. Furthermore, exogenously applied corticosterone or foot shock stress before water maze training prevented the impairment of memory retrieval that should be induced by treatment with corticosterone or foot shock before the 'probe trial'. Again, memory retrieval was enhanced in young animals under these conditions, and this enhancement can be prevented by the glucocorticoid receptor antagonist RU 38486. Thus, glucocorticoid receptor activation not only induced impairment of memory but also increased the capacity of young animals to overcome a later stress. The present findings suggest that the effect of stress on memory can be switched from impairment to enhancement dependent on both stress experience and age.

Effect of paradoxical sleep deprivation and stress on passive avoidance behavior

Previous studies have shown that several types of stress can induce memory impairment. However, the memory effects of paradoxical sleep deprivation (PSD), a stressor in itself, are unclear. We therefore compared passive avoidance behavior of rats undergoing PSD and PSD stress yoked-control (PSC) using the "reversed flowerpot method." When rats were kept isolated on a PSC platform for 24 It immediately after criterion training, retention trials showed impaired aversive memory storage. When delayed for 24 h after criterion training, PSC stress did not disrupt retention performance. In rats subjected to PSD, either immediately or 24 It after criterion training, there was no disruption of aversive memory consolidation. These results suggest that, during stress, paradoxical sleep plays a role in erasing aversive memory traces, in line with the theory that we "dream in order to forget." (C) 2003 Elsevier Inc. All rights reserved.

Merging effects of vitamin E and C on biological factors, blood characteristics and resistance against thermal stress in rainbow trout (Onchorhyncus mykiss)

This study was conducted to assay the effects of different levels of dietary vitamins C and E on growth indices and survival and resistance against thermal stress of rainbow trout (Oncorhynchus mykiss) in pond culture of Marzan abad from December 2011 to February 2011. Seven diets were supplemented. 300 fish with the average weight of 17 g were introduced to ponds for 60 days. The results showed that the highest and the lowest weight gain were in fish fed with diet containing 50 mg/kg vitamin C and E and 0 mg/kg vitamin C and E(control) , respectively. The highest and the lowest Feed Conversion Ratio (FCR) were measured in control and diet 50 mg/kg vitamin C and E. There is a significant difference in their treatments (P<0.05). Also, the lowest and highest amount of Weight Gain (WG) were observed in (E) treatment with 165.04% and 117.5% in control, the highest and lowest Specific Growth Rate (SGR), Protein Efficiency Ratio (PER), Condition Factor (CF) was found in control and treatment 50 mg/kg vitamin C and E, respectively(P<0.05). In conclusion vitamin C and E have an important role in enhancement of growth performance and feed efficiency of rainbow trout.The highest red blood cells were found in combined treatments and which the vitamin C was added.The highest RBC were found in E treatment(1.1×104 /mm3) and the lowest one in control (P˂0.05). Counting white blood cells also confirmed highest quantity in combined treatments with (69.83×104/mm3) and the lowest one (28.83×104 /mm3) in control. In conclusion these vitamins have a significant role in blood characteristics. Meantime, the resistance against termal stress was measured at the end of 60 days by facing fishes into 5 centigrade warmer water so consentration of Cortisol and Glucose measured for this reason.The lowest cortisol amount was measured in E treatment with 188.74 ng/ml and the highest was found in control(P<0.05). There was a significant difference in blood glucose consentration of fishes in F treatment with (78.66 mg/dl) and control with 136 mg/dl as a highest one(P<0.05).

Environmental enrichment and chronic restraint stress in ICR mice: Effects on prepulse inhibition of startle and Y-maze spatial recognition memory

In most studies regarding the improving or therapeutical effects induced by enriched environment (EE), EE was performed after the stress treatment or in patients with certain diseases. In the current study, the effects of chronic restraint stress (6 h/day) in mice living in an enriched environment or standard environment (SE) were tested. Mice were randomly divided into 4 groups: non-stressed or stressed mice housed in SE or EE conditions (SE, stress + SE, EE, stress + EE). Prepulse inhibition (PPI) of startle was tested after the 2 weeks or 4 weeks stress and/or EE treatment and 1 or 2 weeks withdrawal from the 4 weeks treatment. After the 4 weeks treatment, spatial recognition memory in Y-maze was also tested. The results showed that EE increased PPI in stressed and non-stressed mice after 2 weeks treatment. No effect of EE on PPI was found after the 4 weeks treatment. 4 weeks chronic restraint stress increased PPI in mice housed in standard but not EE conditions. Stressed mice showed deficits on the 1 h delay version of the Y-maze which could be prevented by living in an enriched environment. Our results indicated that living in an enriched environment reversed the impairing effects of chronic restraint stress on spatial recognition memory. However, EE did not change the effects of stress on PPI. (C) 2010 Elsevier B.V. All rights reserved.

The stress experience dependent long-term depression disassociated with stress effect on spatial memory task

Behavioral stress can either block or facilitate memory and affect the induction of long-term potentiation (LTP) and long-term depression (LTD). However, the relevance of the stress experience-dependent long-term depression (SLTD) to spatial memory task is unknown. Here we have investigated the effects of acute and sub-acute elevated platform (EP) and foot shock (FS) stress on LTD induction in CA1 region of the hippocampus of anesthetized rats and spatial memory in Morris water maze. We found that LTD was facilitated by acute EP stress, but not by sub-acute EP stress that may be due to the fast adaptation of the animals to this naturalistic mild stress. However, FS stress, an inadaptable strong stress, facilitated LTD induction both in acute and sub-acute treatment. In addition, with the same stress protocols, acute EP stress impaired spatial memory but the sub-acute EP stressed animals performed the spatial memory task as well as the controls, may due to the same reason of adaptation. However, acute FS stress slightly impaired learning but sub-acute FS even enhanced memory retrieval. Our results showed that SLTD was disassociated with the effect of stress on memory task but might be related to stress experience-dependent form of aberrant memory. (C) 2003 Elsevier Science Ireland Ltd. and the Japan Neuroscience Society. All rights reserved.

Stress-facilitated LTD induces output plasticity through a synchronized-spikes and spontaneous unitary discharges the CA1 region of the hippocampus

Long-term potentiation (LTP) and long-term depression (LTD) of the excitatory synaptic inputs plasticity in the hippocampus is believed to underlie certain types of learning and memory. Especially, stressful experiences, well known to produce long-lasting strong memories of the event themselves, enable LTD by low frequency stimulation (LFS, 3 Hz) but block LTP induction by high frequency stimulation (HFS, 200 Hz). However, it is unknown whether stress-affected synaptic plasticity has an impact on the output plasticity. Thus, we have simultaneously studied the effects of stress on synaptic plasticity and neuronal output in the hippocampal CA1 region of anesthetized Wistar rats. Our results revealed that stress increased basal power spectrum of the evoked synchronized-spikes and enabled LTD induction by LFS. The induction of stress-facilitated LTD but not LFS induced persistent decreases of the power spectrum of the synchronized-spikes and the frequency of the spontaneous unitary discharges; However, HFS induced UP in non-stressed animals and increased the power spectrum of the synchronized-spikes, without affecting the frequency of the spontaneous unitary discharges, but HFS failed to induce UP in stressed animals without affecting the power spectrum of the synchronized-spikes and the frequency of the spontaneous unitary discharges. These observations that stress-facilitated LTD induces the output plasticity through the synchronized-spikes and spontaneous unitary discharges suggest that these types of stress-related plasticity may play significant roles in distribution, amplification and integration of encoded information to other brain structures under stressful conditions. (C) 2004 Elsevier Ireland Ltd and The Japan Neuroscience Society. All rights reserved.