Search

Stress is an important trigger for brain plasticity: Acute stress can rapidly affect brain activity and functional connectivity, and chronic or pathological stress has been associated with structural brain changes. Measures of structural magnetic resonance imaging (MRI) can be modified by short-term motor learning or visual stimulation, suggesting that they also capture rapid brain changes. Here, we investigated volumetric brain changes (together with changes in T1 relaxation rate and cerebral blood flow) after acute stress in humans as well as their relation to psychophysiological stress measures.Sixty-seven healthy men (25.8±2.7 years) completed a standardized psychosocial laboratory stressor (Trier Social Stress Test) or a control version while blood, saliva, heart rate, and psychometrics were sampled. Structural MRI (T1 mapping / MP2RAGE sequence) at 3T was acquired 45 min before and 90 min after intervention onset. Grey matter volume (GMV) changes were analysed using voxel-based morphometry. Associations with endocrine, autonomic, and subjective stress measures were tested with linear models.We found significant group-by-time interactions in several brain clusters including anterior/mid-cingulate cortices and bilateral insula: GMV was increased in the stress group relative to the control group, in which several clusters showed a GMV decrease. We found a significant group-by-time interaction for cerebral blood flow, and a main effect of time for T1 values (longitudinal relaxation time). In addition, GMV changes were significantly associated with state anxiety and heart rate variability changes.Such rapid GMV changes assessed with VBM may be induced by local tissue adaptations to changes in energy demand following neural activity. Our findings suggest that endogenous brain changes are counteracted by acute psychosocial stress, which emphasizes the importance of considering homeodynamic processes and generally highlights the influence of stress on the brain.HighlightsWe investigated rapid brain changes using MRI in a stress and a control groupVBM-derived GMV showed a significant group-by-time interaction in several clustersMain pattern: GMV in the stress group increased relative to the control group, in which GMV decreasedGMV changes across groups were associated with state anxiety and heart rate variabilityNeither cerebral blood flow, nor T1 values fully account for the VBM results

Computational fluid dynamics (CFD) based on a finite-volume method was used to simulate three-dimensional pressure and velocity fields for non-Newtonian fluids in fully filled screw elements in a co-rotating twin screw extruder. The employed method also allows the calculation of temperature fields for non-isothermal flow which requires a non-steady state calculation. The CFD code was first evaluated on simple flow cases such as flow of a Newtonian or non-Newtonian fluid through a cylindrical die or flow in single screw extruders equipped with different screws. The results agreed very well with analytical calculations (die flow) and experimental results (single screw extruder). In a next step, we wanted to establish the reliability of the numerical results for twin screw extruders by performing experiments on a 40 mm and a 58 mm screw diameter machine. Temperature and pressure distribution along the screw in the fully filled section in front of the die were measured. Melt conveying in several screw elements (different pitches) was studied for different materials (amorphous polystyrene and partially crystalline polypropylene) at various flow rates and screw speeds. It was attempted to measure axial pressure build-up for flow rates from nearly zero to beyond the drag capacity of the specific element. The measured bulk values of pressure were then compared to the corresponding values extracted from the CFD simulation results. So far, only isothermal calculations (at different temperatures) have been performed. The temperature profile along the screw was determined by calculating the energy dissipation in isothermal slices and converting the dissipated energy into internal energy (temperature increase, neglecting heat losses at the wall). General agreement between experimental and numerical results is good.

Iron pentacarbonyl (Fe(CO){sub 5}) is an extremely efficient flame inhibitor, yet its inhibition mechanism has not been described. The flame-inhibition mechanism at Fe(CO){sub 5} in premixed and counterflow diffusion flames of methane, oxygen, and nitrogen is investigated. A gas-phase inhibition mechanism involving catalytic removal of H atoms by iron-containing species is presented. For premixed flames, numerical predictions of burning velocity are compared with experimental measurements at three equivalence ratios (0.9, 1.0, and 1.1) and three oxidizer compositions (0.20, 0.21, and 0.24 oxygen mole fraction in nitrogen). For counterflow diffusion flames, numerical predictions of extinction strain rate are compared with experimental results for addition of inhibitor to the air and fuel stream. The numerical predictions agree reasonably well with experimental measurements at low inhibitor mole fraction, but at higher Fe(CO){sub 5} mole fractions the simulations overpredict inhibition. The overprediction is suggested to be due to condensation of iron-containing compounds since calculated supersaturation is suggested to be due to condensation of iron-containing compounds since calculated supersaturation ratios for Fe and FeO are significantly higher than unity in some regions of the flames. The results lead to the conclusion that inhibition occurs primarily by homogeneous gas-phase chemistry.

This paper deals with the ultimate limits of chemical contributions to flame inhibition. Particular attention is focussed on the inhibition cycles which regenerate the inhibitor. This leads to the definition of an idealized “perfect” inhibition cycle. It is demonstrated that for such an inhibitor in a stoichiometric methane/air flame, additive levels in the 0.001–0.01 mole percent range will lead to a decrease in flame velocity of approximately 30%. This efficiency corresponds roughly to the observed behavior of metallic inhibitors such as iron pentacarbonyl which is known to be as much as 2 orders of magnitude more effective than currently used suppressants. This correspondence between the behavior of a “perfect inhibitor” and iron carbonyl leads to the conclusion that only gas-phase processes can account for its inhibitive power.

A model for the simulation of the combustion of a packed bed in a stagnation point flow is presented. The model is one-dimensional and couples the chemical reactions and heat and mass transport in the bed and in the adjacent flow field. The particles are assumed to be of carbon; heterogeneous solid–gas reactions in the bed as well as a homogeneous gas-phase reaction in the free flow are considered. Ignition and extinction may occur with respect to both heterogeneous and homogeneous reactions. Depending on values like the water vapor content and the oxygen content of the stagnation point flow, the ignition can lead to discontinuities in the steady-state solutions and to multiple steady states. The number of solutions also depends on whether the combustion process is controlled by a given surface temperature of the packed bed or by a given external heat flux to the surface. The flame which establishes when the gas-phase reaction ignites can detach from the surface of the packed bed simultaneously with ignition or, depending on for example the water vapor content of the free flow, at a higher value of the external heat flux.

The recent ban on the production of CF3Br has motivated a search for alternate agents for fire suppression: however, a replacement agent with all of the desirable properties of CF3Br is proving difficult to find. While most of the research has concentrated on other halogenated agents, there exist agents that are much more effective than CF3Br but about whose inhibition mechanism less is known. These agents typically involve a condensed phase. This paper investigates the behavior of iron pentacarbonyl(Fe(CO)5), one of the most efficient inhibitors identified in the past, in methane/oxygen/nitrogen flames: measurments are reported for both diffusion and premixed flames. The reduction in the extinction strain rate and laminar burning velocity with addition of iron pentacarbonyl is determined over moderate ranges of fuel-air equivalence ratio and oxygen mole fraction XO2. The flame and inhibitor locations in the counterflow diffusion flame experiments are varied to control the condensed- and gas-phase species transport rates to the flames and the chemical environment for their reaction. In the premixed flames, iron pentacarbonyl at low concentration reduces the burning velocity up to 100 times more effectively than CF3Br and shows a strong dependence on both and Xo2; however, at Fe(CO)5 mole fractions above a few hundred ppm, there is no additional reduction of the burning velocity. In diffusion flames, Fe(CO)5 is again shown to be more effective at the lowest concentrations, but the inhibition effect does not level off at higher mole fractions as it does in the premixed flames. In addition, combinations of flame and inhibitor location in the counterflow flames have been found for which iron pentacarbonyl either provides negligible inhibition at any mole fraction or promotes the combustion. The possible mechanisms are discussed.

A model for the simulation of the combustion of a packed bed in a stagnation point flow is presented. It is one-dimensional and accounts for the coupling between chemical reactions and heat and mass transport in the bed and in the adjacent flow field. The governing equations for mass, momentum, energy, and species are solved using the PISO algorithm (Pressure Implicit with Splitting of Operators). The program was verified by calculating several test cases for which solutions can be found in the literature. To use a well-defined chemistry, the particles are assumed to be of carbon but, so far, only heterogeneous reactions between the particles and the gas have been included in the calculations. By this means, the smoldering combustion of a packed bed of finite and constant length has been simulated. Depending on parameters such as the length of the bed, its effective conductivity, and the oxygen supply, heterogeneous ignition can occur. This becomes evident by a discontinuous increase in the temperature in the bed, in the reaction rate and in the mass burning rate. These ignition effects lead to discontinuities in the steady-state solutions. Hence, the combustion process of a packed bed is often characterized by multiple steady states.

The EU funded project VAN targets the only partially existing proprietary solutions to connect automation networks and devices via public networks in a secure, safe and predictable way. This work in progress paper provides an overview of the solutions implemented in VAN which are currently evaluated for the use in general purpose networks. The generally accepted phase model to implement an abstract security solution is introduced and some aspects are addressed more deeply. VAN will introduce a vendor independent communication solution to interconnect automation networks using public network infrastructures and hence reduce costs, complexity and potentials of misconfiguration.

Security is an intense discussed topic for industrial automation networks. This article will give an overview for security relevant considerations. The foundation of the network security is the analysis of the communication relations. Typical communication scenarios are listed with their constraints and characteristics. This paper will propose a first approach for a structured methodology to classify communications to be able to deduce security relevant use cases and proper methods.

On the basis of own observations of courses the author adopts a definite attitude to the early symptomatology of the rheumatoid arthritis. During the first weeks of the rheumatoid arthritis the following symptoms are found: articular syndromes, more frequently in form of obstinate polyarthralgias, mono-oligoarthritis, accompanied by morning rigidity and accelerated BSR as well as impairment of the general condition. In the majority of the patients only the tentative diagnosis rheumatoid arthritis may be made. After a one to three months' course of the disease the diagnosis becomes more probable. It is above all based on constancy and symmetry, characteristic localisation of the articular process, morning rigidity, radiologically paraarticular loosening of the structure and morphological symptoms of an acute and subacute synovialitis. 6 to 12 months after the beginning of the disease a clinical picture forms which allows to make the diagnosis of a certain or classical rheumatoid arthritis in accordance with the criteria of the ARA. The occurrence of a high activity of multiple affection of the joints (permanent symmetrical polyarthritis including the small joints of the hands and feet), distinctive morning rigidity, high fever and much accelerated BSR, beginning with the first weeks of the disease, speaks for the possibility of the development of an arthrovisceral form of the course of rheumatoid arthritis.

23 patients with rheumatoid arthritis and high rheumatic factors (mean titres of rheumatic factors 1 : 1 434) within a prospective study on the diagnostic and prognostic significance of the rheumatoid vasculitis which was performed together with the Research Institute for Rheumatism Moscow underwent examinations for the proof of an extraarticular organ manifestation. In correspondence with the data in literature we found rheumatic nodes (70%) as most frequent extraarticular organ manifestation. In 1 patient each a participation of the lungs and a rheumatic exudate of the pleura, respectively, could be diagnosed. In another patient there were references to a vasculitis at the fundus of the eye. In only 2 patients there was a vasculitis of the digital arteries with necroses, in one of them a generalized vasculitis. 5 of the 13 neurologically examined patients showed polyneuropathic symptoms. Of the biochemical findings the C-reactive protein and the blood sedimentation rate showed clear increases and correlations.

The acknowledged role of central-nervous mechanisms in the etiopathogenesis of the essential arterial hypertension led to the use of a psycho-physiologic test method with the aim of the early recognition of stress-induced permanent changes of physiologic functions. We succeed in proving the chosen sensumotoric stress in a group of patients with essential arterial hypertension which at first appears uniform in clinical respect allows a further differentiation. On the basis of the behaviour of defined physiologic and biochemical parameters after physical and sensumotoric stress it is referred to the necessity of a differentiated therapy of the early form of the essential arterial hypertension.

In the accessible literature the influence of beta-blockers on laboratory methods is estimated only little systematically and nearly exclusively on parameters of the glucose and lipometabolism. The influence on several methods in vitro is without relevance to practice. Own examinations showed that in 32 patients with essential hypertension of stage I (after Baumann and Nitschkoff) under therapeutic doses of 50--80 mg propranolol a day in none of the 18 chemical parameters tested after a four weeks' treatment significant deviations relevant to practice appeared in comparison to the parameters before treatment.

Local instillations of various medicaments with the aim of a so-called chemical synovectomy are compared with the experiment of a possible causal therapy by operative synovectomy. Under this aspect corticosteroids are used still relatively frequently also for the intraarticular treatment. They diminish transiently the inflammation of the pannus, but they do not remove it. On the basis of its good local compatibility in relapsing effusions of the large articulations, mostly of the knee-joints, which appeared in the course of a chronic progressive rheumatoid arthritis of Bechterew's disease, cyclophosphamide was applied intraarticularly and was compared with the results after injections of prednisolone. Apart from the clinical findings cytological and biochemical examinations of the synovial membrane, which more exactly than clinical parameters allow an objective estimation of the local inflammatory activity, were used for the judgement of the success. With the help of intraarticular treatment of cyclophosphamide within a complex chemotherapy an improvement of the findings and a stabilisation of the process can be achieved. Local applications of prednisolone often lead to a rapid, however, in most cases not remaining reduction of the activity at the joint. In uninfluencable high local activity of the process, objectified by examinations of the synovial membrane, an early synovectomy is indicated for the prevention of the formation of irreversible chondropathies.

100 patients with several clinical and suspicious radiological symptoms of Bechterev's disease (Institute of Rheumatology Moscow) and 100 patients with the clinical symptoms of Bechterev's disease without radiological symptoms of a sacroiliacal arthritis (Medico-Policlinical Institute Leipzig) have been examined within a common research programme since 1976 and analysed concerning the frequency of the complaints as well as of clinical symptoms at the beginning of the disease. The main complaints at the beginning of Bechterev's disease are nocturnal pains in the lumbosacral region, pains in the joints, in which cases 50% of the patients spoke of swellings of the joints. 42% of the patients complained of the feeling of the morning rigidity in the lumbar spinal column and 22% spoke of increased temperatures. In 9--10% of our patients an iritis was diagnosed at the beginning of the disease.

For the early recognition of the ankylopoietic spondylarthritis subjective and objective criteria are explained and the importance of X-ray-morphological, cytological, biochemical, immunogenetic and coagulation-physiological investigations are explained. By accentuation of two types of constellation of the course the possibility of an early diagnosis is given still before the appearance of severe irreparable X-ray-morphological changes in about half the cases of disease. Further observations and controls of courses are necessary for the confirmation of evidence.

During examinations and after a three-month examination period the changes of the parameters of fat metabolism were investigated depending upon stress experience before examinations. Students with a distinct stress experience showed a higher total cholesterol and LDL-cholesterol as well as a higher LDL/HDL-cholesterol quotient within a concrete examination. After the examination period in this group a higher LDL/HDL-cholesterol quotient and a lower HDL-cholesterol level was established in comparison to the group with an insignificant stress experience. A positive dependence on the initial value of the parameters of fat metabolism consists only in the group with distinct stress experience. According to these results also stress has an influence on the reactions of the fractions of cholesterol.

Activity and results of therapy of joint diseases can be evaluated by means of cytological examinations of the synovia which is at the same time a prerequisite for differential diagnosis using the puncture fluid. Our cytological examinations of more than 700 puncture fluids stemming from different joint diseases were carried out immediately after the puncture on the fresh material, in order to prevent misinterpretation. This may occur through flaking out in stored material, which results in decrease in the cell count and a non-representative differential cell picture in the supernatant, as well as through degeneration of cells. In two thirds of our patients the local process activity, measured in terms of the cytological phase of activity, became evident in the total clinical activity. The synovia analysis furthermore permits objective assessment of the result of intra-articular injection treatment. Intractable activity, substantiated through synovia examination indicates synovectomy.

The synovial milieu in uric arthritis is characterized with the help of own findings of examinations and data in literature. Apart from the mean values of cytological and biochemical findings of the synovia the changes under therapy are described on the basis of individual examples. The formation of monosodium urate crystals seems to be the starting point of the inflammatory joint process in gout. The size of the arthritic syndrome is among others determined by the local metabolic process, in which case lactate acidosis and reduction of energy as well as the increase of enzyme activities seem to stand in the foreground.

Increases of the leucine aminopeptidase according to data of literature are regarded as a sensitive parameter of lesions in liver diseases. In patients with active generalised lymphadenitis (viral infections, toxoplasmosis) as a typical enzyme constellation a relatively strong leucine aminopeptidase increase in the serum with missing or relatively slight enzyme deviation of the transaminases could be found. The quotient of the activities of LAP/ALAT was clearly above that of inflammatory liver diseases. In chronic lymphatic leukosis, plasmocytoma and malignant lymphomas the leucine aminopeptidase serum activities were within the normal. Increases of leucine aminopeptidase in lymphotropic infections are probably partly of extrahepatic origin.