Semi-implicit finite strain constitutive integration and mixed strain/stress control based on intermediate configurations

A new semi-implicit stress integration algorithm for finite strain plasticity (compatible with hyperelas- ticity) is introduced. Its most distinctive feature is the use of different parameterizations of equilibrium and reference configurations. Rotation terms (nonlinear trigonometric functions) are integrated explicitly and correspond to a change in the reference configuration. In contrast, relative Green–Lagrange strains (which are quadratic in terms of displacements) represent the equilibrium configuration implicitly. In addition, the adequacy of several objective stress rates in the semi-implicit context is studied. We para- metrize both reference and equilibrium configurations, in contrast with the so-called objective stress integration algorithms which use coinciding configurations. A single constitutive framework provides quantities needed by common discretization schemes. This is computationally convenient and robust, as all elements only need to provide pre-established quantities irrespectively of the constitutive model. In this work, mixed strain/stress control is used, as well as our smoothing algorithm for the complemen- tarity condition. Exceptional time-step robustness is achieved in elasto-plastic problems: often fewer than one-tenth of the typical number of time increments can be used with a quantifiable effect in accuracy. The proposed algorithm is general: all hyperelastic models and all classical elasto-plastic models can be employed. Plane-stress, Shell and 3D examples are used to illustrate the new algorithm. Both isotropic and anisotropic behavior is presented in elasto-plastic and hyperelastic examples.

Rise in plasma lactate concentrations with psychosocial stress: a possible sign of cerebral energy demand.

OBJECTIVE: It is known that exogenous lactate given as an i.v. energy infusion is able to counteract a neuroglycopenic state that developed during psychosocial stress. It is unknown, however, whether the brain under stressful conditions can induce a rise in plasma lactate to satisfy its increased needs during stress. Since lactate is i) an alternative cerebral energy substrate to glucose and ii) its plasmatic concentration is influenced by the sympathetic nervous system, the present study aimed at investigating whether plasma lactate concentrations increase with psychosocial stress in humans. METHODS: 30 healthy young men participated in two sessions (stress induced by the Trier Social Stress Test and a non-stress control session). Blood samples were frequently taken to assess plasma lactate concentrations and stress hormone profiles. RESULTS: Plasma lactate increased 47% during psychosocial stress (from 0.9 ± 0.05 to 1.4 ± 0.1 mmol/l; interaction time × stress intervention: F = 19.7, p < 0.001). This increase in lactate concentrations during stress was associated with an increase in epinephrine (R(2) = 0.221, p = 0.02) and ACTH concentrations (R(2) = 0.460, p < 0.001). CONCLUSION: Plasma lactate concentrations increase during acute psychosocial stress in humans. This finding suggests the existence of a demand mechanism that functions to allocate an additional source of energy from the body towards the brain, which we refer to as 'cerebral lactate demand'.

Disambiguating the Effects of Social Instability Stress in Adolescence on Learning and Memory Tasks that Involve the Medial Prefrontal Cortex and Hippocampus

Exposure to chronic stress can alter the structure and function of brain regions involved in learning and memory, and these effects are typically long-lasting if the stress occurs during sensitive periods of development. Until recently, adolescence has received relatively little attention as a sensitive period of development, despite marked changes in behaviour, heightened reactivity to stressors, and cognitive and neural maturation. Therefore, the purpose of the present study was to investigate the long-term effects of chronic stress in adolescence on two spatial learning and memory tasks (Morris water maze and Spatial Object Location test) and on a working memory task (Delayed Alternation task). Male rats were randomly assigned to chronic social instability stress (SS; daily 1 hour isolation and subsequent change of cage partner between postnatal days 30 and 45) or to a no-stress control group (CTL). During acquisition learning in the Morris water maze task, SS rats demonstrated impaired long-term memory for the location of the hidden escape platform compared to CTL rats, although the impairment was only seen after the first day of training. Similarly, SS rats had impaired long-term memory in the Spatial Object Location test after a long delay (240 minutes), but not after shorter delays (15 or 60 minutes) compared to CTL rats. On the Delayed Alternation task, which assessed working memory across delays ranging from 5 to 90 seconds, no group differences were observed. These results are partially in line with previous research that revealed adult impairment on spatial learning and memory tasks after exposure to chronic social instability stress in adolescence. The observed deficits, however, appear to be limited to long-term memory as no group differences were observed during brief periods of retention.

Virtual reality Post Traumatic Stress Disorder (PTSD) exposure therapy results with active duty Iraq war combatants

Post Traumatic Stress Disorder (PTSD) is reported to be caused by traumatic events that are outside the range of usual human experience including (but not limited to) military combat, violent personal assault, being kidnapped or taken hostage and terrorist attacks. Initial data suggests that at least 1 out of 6 Iraq War veterans are exhibiting symptoms of depression, anxiety and PTSD. Virtual Reality (VR) delivered exposure therapy for PTSD has been used with reports of positive outcomes. The aim of the current paper is to present the rationale and brief description of a Virtual Iraq PTSD VR therapy application and present initial findings from its use with PTSD patients. Thus far, Virtual Iraq consists of a series of customizable virtual scenarios designed to represent relevant Middle Eastern VR contexts for exposure therapy, including a city and desert road convoy environment. User-centered design feedback needed to iteratively evolve the system was gathered from returning Iraq War veterans in the USA and from a system deployed in Iraq and tested by an Army Combat Stress Control Team. Results from an open clinical trial at San Diego Naval Medical Center of the first 18 treatment completers indicate that 14 no longer meet PTSD diagnostic criteria at post-treatment, with only one not maintaining treatment gains at 3 month follow-up. Clinical tests are also currently underway at Ft. Lewis, Emory University, Weill Cornell Medical College, Walter Reed Army Medical Center and 10 other sites. Other sites are preparing to use the application for a variety of PTSD and VR research purposes.

Virtual reality Post Traumatic Stress Disorder (PTSD) exposure therapy results with active duty OIF/OEF service members

Posttraumatic stress disorder (PTSD) is reported to be caused by exposure to traumatic events including (but not limited to) military combat, violent personal assault, being kidnapped or taken hostage and terrorist attacks. Initial data suggest that at least 1 out of 6 Iraq War veterans are exhibiting symptoms of depression, anxiety and PTSD. Virtual reality (VR) delivered exposure therapy for PTSD has been used with reports of positive outcomes. The aim of the current paper, is to present the rationale and brief description of a Virtual Iraq/Afghanistan PTSD VR therapy application and present initial findings from its use with PTSD patients. Thus far, Virtual Iraq/Afghanistan consists of a series of customizable virtual scenarios designed to represent relevant Middle Eastern VR contexts for exposure therapy, including a city and desert road convoy environment. User-centered design feedback, needed to iteratively evolve the system, was gathered from returning Iraq War veterans in the USA and from a system deployed in Iraq and tested by an Army Combat Stress Control Team. Results from an open clinical trial at San Diego Naval Medical Center of the first 20 treatment completers indicate that 16 no longer met PTSD screening criteria at post-treatment, with only one not maintaining treatment gains at 3 month follow-up.

Acute Stress Reduces Wound-Induced Activation of Microbicidal Potential of Ex Vivo Isolated Human Monocyte-Derived Macrophages

Background Psychological stress delays wound healing but the precise underlying mechanisms are unclear. Macrophages play an important role in wound healing, in particular by killing microbes. We hypothesized that (a) acute psychological stress reduces wound-induced activation of microbicidal potential of human monocyte-derived macrophages (HMDM), and (b) that these reductions are modulated by stress hormone release. Methods Fourty-one healthy men (mean age 35±13 years) were randomly assigned to either a stress or stress-control group. While the stress group underwent a standardized short-term psychological stress task after catheter-induced wound infliction, stress-controls did not. Catheter insertion was controlled. Assessing the microbicidal potential, we investigated PMA-activated superoxide anion production by HMDM immediately before and 1, 10 and 60 min after stress/rest. Moreover, plasma norepinephrine and epinephrine and salivary cortisol were repeatedly measured. In subsequent in vitro studies, whole blood was incubated with norepinephrine in the presence or absence of phentolamine (norepinephrine blocker) before assessing HMDM microbicidal potential. Results Compared with stress-controls, HMDM of the stressed subjects displayed decreased superoxide anion-responses after stress (p’s <.05). Higher plasma norepinephrine levels statistically mediated lower amounts of superoxide anion-responses (indirect effect 95% CI: 4.14–44.72). Norepinephrine-treated HMDM showed reduced superoxide anion-production (p<.001). This effect was blocked by prior incubation with phentolamine. Conclusions Our results suggest that acute psychological stress reduces wound-induced activation of microbicidal potential of HMDM and that this reduction is mediated by norepinephrine. This might have implications for stress-induced impairment in wound healing.

Stress-induced modulation of NF-κB activation, inflammation-associated gene expression, and cytokine levels in blood of healthy men

Acute psychosocial stress stimulates transient increases in circulating pro-inflammatory plasma cytokines, but little is known about stress effects on anti-inflammatory cytokines or underlying mechanisms. We investigated the stress kinetics and interrelations of pro- and anti-inflammatory measures on the transcriptional and protein level. Forty-five healthy men were randomly assigned to either a stress or control group. While the stress group underwent an acute psychosocial stress task, the second group participated in a non-stress control condition. We repeatedly measured before and up to 120min after stress DNA binding activity of the pro-inflammatory transcription factor NF-κB (NF-κB-BA) in peripheral blood mononuclear cells, whole-blood mRNA levels of NF-κB, its inhibitor IκBα, and of the pro-inflammatory cytokines interleukin (IL)-1ß and IL-6, and the anti-inflammatory cytokine IL-10. We also repeatedly measured plasma levels of IL-1ß, IL-6, and IL-10. Compared to non-stress, acute stress induced significant and rapid increases in NF-κB-BA and delayed increases in plasma IL-6 and mRNA of IL-1ß, IL-6, and IκBα (p's<.045). In the stress group, significant increases over time were also observed for NF-κB mRNA and plasma IL-1ß and IL-10 (p's<.055). NF-κB-BA correlated significantly with mRNA of IL-1β (r=.52, p=.002), NF-κB (r=.48, p=.004), and IκBα (r=.42, p=.013), and marginally with IL-6 mRNA (r=.31, p=.11). Plasma cytokines did not relate to NF-κB-BA or mRNA levels of the respective cytokines. Our data suggest that stress induces increases in NF-κB-BA that relate to subsequent mRNA expression of pro-inflammatory, but not anti-inflammatory cytokines, and of regulatory-cytoplasmic-proteins. The stress-induced increases in plasma cytokines do not seem to derive from de novo synthesis in circulating blood cells.

Simulation of the load-unload response ratio and critical sensitivity in the lattice solid model

The Load-Unload Response Ratio (LURR) method is an intermediate-term earthquake prediction approach that has shown considerable promise. It involves calculating the ratio of a specified energy release measure during loading and unloading where loading and unloading periods are determined from the earth tide induced perturbations in the Coulomb Failure Stress on optimally oriented faults. In the lead-up to large earthquakes, high LURR values are frequently observed a few months or years prior to the event. These signals may have a similar origin to the observed accelerating seismic moment release (AMR) prior to many large earthquakes or may be due to critical sensitivity of the crust when a large earthquake is imminent. As a first step towards studying the underlying physical mechanism for the LURR observations, numerical studies are conducted using the particle based lattice solid model (LSM) to determine whether LURR observations can be reproduced. The model is initialized as a heterogeneous 2-D block made up of random-sized particles bonded by elastic-brittle links. The system is subjected to uniaxial compression from rigid driving plates on the upper and lower edges of the model. Experiments are conducted using both strain and stress control to load the plates. A sinusoidal stress perturbation is added to the gradual compressional loading to simulate loading and unloading cycles and LURR is calculated. The results reproduce signals similar to those observed in earthquake prediction practice with a high LURR value followed by a sudden drop prior to macroscopic failure of the sample. The results suggest that LURR provides a good predictor for catastrophic failure in elastic-brittle systems and motivate further research to study the underlying physical mechanisms and statistical properties of high LURR values. The results provide encouragement for earthquake prediction research and the use of advanced simulation models to probe the physics of earthquakes.

Miten sotilasjohtaja johtaa palautumista ja jaksamista? : Tulenjohtoaliupseerin toimintamahdollisuudet palautumisen ja jaksamisen edistämiseksi

Sotilaan toimintakykyyn ja sen ylläpitoon liittyy monia eri tekijöitä. Sotilasjohtajan yksi tärkeimmistä tehtävistä on pitää huoli omien alaisten toimintakyvystä ja joukkonsa suorituskyvystä. Tämän tutkimuksen tavoitteena oli selvittää, millä konkreettisilla vaikutuskeinoilla tulenjohtoaliupseeri johtaa alaistensa palautumista ja jaksamista. Palautumista ja jaksamista käsiteltiin toimintakyvyn psyykkisen ja sosiaalisen osa-alueen kautta. Tutkimuksessa haluttiin myös selvittää, miten tulenjohtoaliupseerin alaiset kokevat palautumisen ja jaksamisen johtamisen. Päätutkimuskysymys on seuraava: 1. Miten tulenjohtoaliupseeri vaikuttaa alaistensa palautumiseen ja jaksamiseen? Päätutkimuskysymyksen lisäksi apuna käytettiin kahta alatutkimuskysymystä: a. Mitä konkreettisia vaikutuskeinoja tulenjohtoaliupseerilla on johtaa alaistensa palautumista ja jaksamista? b. Kokevatko ryhmän jäsenet, että tulenjohtoaliupseeri johtaa heitä palautumaan ja jaksamaan? Tutkimus suoritettiin vastaajille teetetyn kyselyn pohjalta, johon vastasi 12 varusmiestä. Kaikki kyselyyn vastanneet olivat miehiä, 19–20-vuotiaita ja sotilasarvoltaan tykkimiehiä tai korpraaleja. Tutkimuksen aineisto saatiin kyselystä ja se analysoitiin sisällönanalyysin avulla. Tutkimuksen viitekehyksessä ovat palautuminen, jaksaminen sekä sotilaan toimintakyvyn psyykkinen ja sosiaalinen osa-alue. Tutkimustulosten perusteella voidaan todeta, että tulenjohtoaliupseeri kykenee vaikuttamaan alaistensa psyykkiseen ja sosiaaliseen palautumiseen sekä jaksamiseen tehokkaimmin säätelemällä heidän lepoaikaansa, keskustelemalla ja ylläpitämällä ryhmähenkeä. Lisäksi ravinnon ja nesteen saannista sekä fyysisestä kunnosta huolehtiminen, ovat tärkeitä tekijöitä palautumisen ja jaksamisen edistämisessä. Johtopäätöksinä voidaan todeta, että tulenjohto-aliupseeri on tärkeässä osassa alaistensa toimintakyvyn säilyttämisessä ja oman ryhmänsä suorituskyvyn ylläpidossa. Tutkimuksen tärkeimmät lähteet olivat Jarmo Toiskallion teokset sotilaspedagogiikasta, Jukka Alavillamon yleisesikuntaupseerikurssin diplomityö Sotilaan toimintakyky, Niina Valtasen kandidaatintutkielma Stressin sekä fyysisen ja psyykkisen toimintakyvyn vaikutus johtajaan sekä Yhdysvaltain armeijan Combat and Operational Stress Control Manual for Leaders and Soldiers.

Low-Cost Micromechanically Tunable Optical Devices: Strained Resonator Engineering, Technological Implementation and Characterization

The rapid growth of the optical communication branches and the enormous demand for more bandwidth require novel networks such as dense wavelength division multiplexing (DWDM). These networks enable higher bitrate transmission using the existing optical fibers. Micromechanically tunable optical microcavity devices like VCSELs, Fabry-Pérot filters and photodetectors are core components of these novel DWDM systems. Several air-gap based tunable devices were successfully implemented in the last years. Even though these concepts are very promising, two main disadvantages are still remaining. On the one hand, the high fabrication and integration cost and on the other hand the undesired adverse buckling of the suspended membranes. This thesis addresses these two problems and consists of two main parts: • PECVD dielectric material investigation and stress control resulting in membranes shape engineering. • Implementation and characterization of novel tunable optical devices with tailored shapes of the suspended membranes. For this purposes, low-cost PECVD technology is investigated and developed in detail. The macro- and microstress of silicon nitride and silicon dioxide are controlled over a wide range. Furthermore, the effect of stress on the optical and mechanical properties of the suspended membranes and on the microcavities is evaluated. Various membrane shapes (concave, convex and planar) with several radii of curvature are fabricated. Using this resonator shape engineering, microcavity devices such as non tunable and tunable Fabry-Pérot filters, VCSELs and PIN photodetectors are succesfully implemented. The fabricated Fabry-Pérot filters cover a spectral range of over 200nm and show resonance linewidths down to 1.5nm. By varying the stress distribution across the vertical direction within a DBR, the shape and the radius of curvature of the top membrane are explicitely tailored. By adjusting the incoming light beam waist to the curvature, the fundamental resonant mode is supported and the higher order ones are suppressed. For instance, a tunable VCSEL with 26 nm tuning range, 400µW maximal output power, 47nm free spectral range and over 57dB side mode suppresion ratio (SMSR) is demonstrated. Other technologies, such as introducing light emitting organic materials in microcavities are also investigated.

Metastatic melanoma positively influences pregnancy outcome in a mouse model: could a deadly tumor support embryo life?

The incidence of melanoma is increasing worldwide. It is one of the leading cancers in pregnancy and the most common malignancy to metastasize to placenta and fetus. There are no publications about experimental models of melanoma and pregnancy. We propose a new experimental murine model to study the effects of melanoma on pregnancy and its metastatic process. We tested several doses of melanoma cells until we arrived at the optimal dose, which produced tumor growth and allowed animal survival to the end of pregnancy. Two control groups were used: control (C) and stress control (SC) and three different routes of inoculation: intravenous (IV), intraperitoneal (IP) and subcutaneous (SC). All the fetuses and placentas were examined macroscopically and microscopically. The results suggest that melanoma is a risk factor for intrauterine growth restriction but does not affect placental weight. When inoculated by the SC route, the tumor grew only in the site of implantation. The IP route produced peritoneal tumoral growth and also ovarian and uterine metastases in 60% of the cases. The IV route produced pulmonary tumors. No placental or fetal metastases were obtained, regardless of the inoculation route. The injection of melanoma cells by any route did not increase the rate of fetal resorptions. Surprisingly, animals in the IV groups had no resorptions and a significantly higher number of fetuses. This finding may indicate that tumoral factors released in the host organism to favor tumor survival may also have a pro-gestational action and consequently improve the reproductive performance of these animals.

Influence of thermal and mechanical stresses on the strength of intact and relined denture bases

Statement of problem. Denture bases may become increasingly weaker as a result of thermal stress and flexural cyclic loading. Information regarding this potential problem and its relationship to the denture base reline is limited.Purpose. This study evaluated the influence of thermal and mechanical stresses on the strength of intact and relined denture bases.Material and methods. Twenty-eight microwave-polymerized (Acron MC) intact denture bases were prepared in the shape of a 3-mm-thick maxillary denture. Additionally, fifty-six 2-mm-thick denture bases were relined with 1 mm of autopolymerizing resin (Tokuyama Rebase Fast II or New Truliner) (n = 28). Intact and relined specimens were divided into 4 groups (n = 7) as follows: without stress (control); a mechanical stress at 0.8 Hz for 10,000 cycles; 5000 thermal cycles between 5 degrees C and 55 degrees C; or a combination thermo-mechanical stress. The specimens were vertically loaded in compression with a rounded rod at 5 mm/min until failure, using a universal testing machine. Data on maximum fracture load (N), deflection at fracture (%), and fracture energy (N-mm) were analyzed by 2-way analysis of variance and Student-Newman-Keuls tests (alpha = .05).Results. The strength of the denture bases relined with New Truliner was not significantly affected by any of the experimental conditions, but comparing the control groups, New Truliner exhibited the lowest maximum fracture load values. The maximum fracture load of intact denture bases (P = .002) and those relined with Tokuyama Rebase Fast II (P = .01) showed a significant decrease after thermal stress. Additionally, cyclic loading significantly decreased the maximum fracture load (P < .001), deflection at fracture (P = .025), and fracture energy (P < .001) of intact denture bases and those relined with Tokuyama Rebase (P values of .002, .039, and .001, respectively).Conclusion. Thermal and mechanical stresses exert deleterious effects on the strength of intact and/or relined denture bases, which vary according to the relining material used.

Fatores motivacionais de idosos associados à prática regular de exercícios físicos

Pós-graduação em Ciências da Motricidade - IBRC

Adesão e desistência de programas de treino personalizado.

Este estudo pretendeu analisar as determinantes (demográficas, indicadores/ perceção de saúde, socioeconómicas e motivacionais) da adesão e desistência de programas de treino personalizado. Fizeram parte da amostra de conveniência adultos de ambos os géneros, oriundos de academias da cidade de Pelotas-Brasil, que ofereciam programas de treinos personalizados, sendo100 praticantes e 42 desistentes. Foram medidas as variáveis género, idade, cor da pele, índice de massa corporal, tabagismo, autoperceção de saúde, situação conjugal e nível socioeconómico. Para avaliar a motivação, foi utilizado o Inventário de Motivação à Prática Regular de Atividade Física, constatando-se que a maioria dos praticantes e desistentes de treino personalizado foram mulheres jovens, de nível socioeconómico elevado. As dimensões consideradas como mais motivadoras para a prática do treino personalizado foram: “Controle de Estresse”, “Saúde”, “Estética” e “Prazer”. Por outro lado, os motivos mais prevalentes para desistência foram a “Falta de Tempo” e a “Falta de Motivação” para a prática.