Mild-to-wild plastic transition is governed by athermal screw dislocation slip in bcc Nb.

Plastic deformation in crystals is mediated by the motion of line defects known as dislocations. For decades, dislocation activity has been treated as a homogeneous, smooth continuous process. However, it is now recognized that plasticity can be determined by long-range correlated and intermittent collective dislocation processes, known as avalanches. Here we demonstrate in body-centered cubic Nb how the long-range and scale-free dynamics at room temperature are progressively quenched out with decreasing temperature, eventually revealing intermittency with a characteristic length scale that approaches the Burgers vector itself. Plasticity is shown to be bimodal across the studied temperature regime, with conventional thermally-activated smooth plastic flow ('mild') coexisting with sporadic bursts ('wild') controlled by athermal screw dislocation activity, thereby violating the classical notion of temperature-dependent screw dislocation motion at low temperatures. An abrupt increase of the athermal avalanche component is identified at the critical temperature of the material. Our results indicate that plasticity at any scale can be understood in terms of the coexistence of these mild and wild modes of deformation, which could help design better alloys by suppressing one of the two modes in desired temperature windows.

Critical stress statistics and a fold catastrophe in intermittent crystal plasticity.

The statistics and origin of the first discrete plastic event in a one-dimensional dislocation dynamics simulation are studied. This is done via a linear stability analysis of the evolving dislocation configuration up to the onset of irreversible plasticity. It is found that, via a fold catastrophe, the dislocation configuration prior to loading directly determines the stress at which the plastic event occurs and that between one and two trigger dislocations are involved. The resulting irreversible plastic strain arising from the instability is found to be highly correlated with these triggering dislocations.

Unified Criterion for Temperature-Induced and Strain-Driven Glass Transitions in Metallic Glass.

In a model metallic glass, we study the relaxation dynamics in both the linear and the nonlinear response regimes by numerical simulations of dynamical mechanical spectroscopy and analyze the atomic displacement statistics. We find that the primary (α) relaxation always takes place when the most probable atomic displacement reaches a critical fraction (~20%) of the average interatomic distance, irrespective of whether the relaxation is induced by temperature (linear response) or by mechanical strain (nonlinear response). Such a unified scenario, analogous to the well-known Lindemann criterion for crystal melting, provides insight into the structural origin of the strain-induced glass-liquid transition.

Slip statistics of dislocation avalanches under different loading modes.

Slowly compressed microcrystals deform via intermittent slip events, observed as displacement jumps or stress drops. Experiments often use one of two loading modes: an increasing applied stress (stress driven, soft), or a constant strain rate (strain driven, hard). In this work we experimentally test the influence of the deformation loading conditions on the scaling behavior of slip events. It is found that these common deformation modes strongly affect time series properties, but not the scaling behavior of the slip statistics when analyzed with a mean-field model. With increasing plastic strain, the slip events are found to be smaller and more frequent when strain driven, and the slip-size distributions obtained for both drives collapse onto the same scaling function with the same exponents. The experimental results agree with the predictions of the used mean-field model, linking the slip behavior under different loading modes.

Independence of slip velocities on applied stress in small crystals.

Directly tracing the spatiotemporal dynamics of intermittent plasticity at the micro- and nanoscale reveals that the obtained slip dynamics are independent of applied stress over a range of up to ∼400 MPa, as well as being independent of plastic strain. Whilst this insensitivity to applied stress is unexpected for dislocation plasticity, the stress integrated statistical properties of both the slip size magnitude and the slip velocity follow known theoretical predictions for dislocation plasticity. Based on these findings, a link between the crystallographic slip velocities and an underlying dislocation avalanche velocity is proposed. Supporting dislocation dynamics simulations exhibit a similar regime during microplastic flow, where the mean dislocation velocity is insensitive to the applied stress. Combining both experimental and modeling observations, the results are discussed in a framework that firmly places the plasticity of nano- and micropillars in the microplastic regime of bulk crystals.

Probing shear-band initiation in metallic glasses.

In situ acoustic emission monitoring is shown to capture the initiation of shear bands in metallic glasses. A model picture is inferred from stick-slip flow in granular media such that the origin of acoustic emission is attributed to a mechanism of structural dilatation. By employing a quantitative approach, the critical volume change associated with shear-band initiation in a metallic glass is estimated to be a few percent only. This result agrees with typical values of excess free volume found in the supercooled liquid regime near the glass transition temperature.

Evaluation of a sensitive immunoluminometric assay for the determination of C-reactive protein (CRP) in serum and plasma and the establishment of reference ranges for different groups of subjects.

A sensitive immunoluminometric assay originally designed to measure C-reactive protein (CRP) in neonates and minimal serum volumes was adapted to measure this protein in a routine method without prior sample dilution. The concentration range covered without prior dilution was 10 micrograms/l to 20 mg/l using a sample volume of 5 microliters serum and a total assay time of less than 2 h. Serum samples were assayed from participants in a community medicine programme (SHIP--Study of Health in Pomerania) of the University of Greifswald, Germany (n = 414), as well as from mother-child pairs at birth (n = 30) and women attending the infertility clinic (n = 36). The validation of the assay was compared with a commercial latex-enhanced turbidimetric immunoassay (Roche Diagnostics--Integra 700) using routine serum samples (n = 60) from hospital patients. Comparison was made with the routine assay used in the SHIP study (Roche Diagnostics--Hitachi 717/Tina Quant). From 414 SHIP samples measured in the immunoluminometric assay, 289 were below the detection level in the turbidimetric (Tina Quant) assay. A significant positive correlation (p < 0.01) between log C-reactive protein concentration with age was found, both in the non-screened (all CRP values) (n = 414, r = 0.222) and selected (CRP < 5.00 mg/l = 90th percentile) (n = 370, r = 0.242) SHIP participants. Women were found to have significantly higher CRP levels than men (women: median age 47 a, median CRP 1.29 mg/l; men: median age 55 a, median CRP 1.00 mg/l--p = 0.016) in the non-selected SHIP participants. The situation was different in the selected group, (median age: men 54 a, women 48 a) where no significant difference in median CRP values between the sexes was seen (men: 0.874 mg/l, women 0.951 mg/l, p = 0.206). The distribution of CRP values in a "Normal Healthy Population" is skewed (mean/median--SHIP: all--2.08; selected--1.49). From the 414 SHIP samples measured in the immunoluminometric assay, 289 were below the detection level (2.5 mg/l) in the turbidimetric (Tina Quant) assay. From the 125 remaining samples the correlation between both methods was acceptable (r = 0.813), the regression line y = a + bx being: CRP (ILMA) = 1.83 + 0.842*CRP (Tina Quant). The Tina Quant assay gave values significantly higher than the ILMA in the range 2.5-25 mg/l CRP (p < 0.001). The total information loss in 289/414 subjects with a CRP < 2.5 mg/l with the Tina Quant assay makes it no longer suitable for epidemiological studies in which CRP is to be studied as a risk factor for cardiovascular events. The comparison between the immunoluminometric assay and the latex-enhanced immunoturbidimetric assay (Roche Integra) was much better. The latter measured down to less than 0.3 mg/l, thus being more suitable for epidemiological studies than the Tina Quant assay from the same producer. The correlation and regression data between the ILMA (x) and the Roche Integra assay (y) were: r = 0.971; CRP (Roche Integra) = 0.635 + 0.984*CRP (ILMA); n = 50.10 sera with CRP levels between 25 and 460 mg/l showed no high-dose hook effect in either assay. The remaining 50 sera were measurable in both assays. The turbidimetric assay gave rise to marginally but significantly higher values than the immunoluminometric assay (p = 0.004). The mothers at birth had a median CRP of 3.64 mg/l (range 1.49-12.6 mg/l), the neonates a median CRP of 34 micrograms/l (range 4-288 micrograms/l). All births were without complications, with gestational periods between 38 and 42 weeks. There was no correlation between maternal and neonatal CRP at birth. Mothers at birth had significantly higher CRP levels than healthy non-pregnant women (p < 0.001). Women attending the infertility clinic had CRP-values similar to age-matched healthy non-pregnant women (median 0.698 mg/l, range 0.05-9.97 mg/l). Interassay coefficients of variation at CRP concentrations of 0.85 and 7.9 mg/l were 8.99 and 7.93%, respectively, for the immunoluminometric

Uric acid and glutathione levels during short-term whole body cold exposure.

Ten healthy subjects who swim regularly in ice-cold water during the winter (winter swimming), were evaluated before and after this short-term whole body exposure. A drastic decrease in plasma uric acid concentration was observed during and following the exposure to the cold stimulus. We hypothesize that the uric acid decrease can be caused by its consumption after formation of oxygen radicals. In addition, the erythrocytic level of oxidized glutathione and the ratio of oxidized glutathione/total glutathione also increased following cold exposure, which supports this hypothesis. Furthermore, the baseline concentration of reduced glutathione was increased and the concentration of oxidized glutathione was decreased in the erythrocytes of winter swimmers as compared to those of nonwinter swimmers. This can be viewed as an adaptation to repeated oxidative stress, and is postulated as mechanism for body hardening. Hardening is the exposure to a natural, e.g., thermal stimulus, resulting in an increased tolerance to stress, e.g., diseases. Exposure to repeated intensive short-term cold stimuli is often applied in hydrotherapy, which is used in physical medicine for hardening.

[Fitness by cold stimulation of various intensity: effects on metabolism of purines and free radicals]. / Abhärtung durch Kaltreize unterschiedlicher Intensität: Wirkungen auf den Purin- und Radikalmetabolismus.

Whole-body cold stimuli lead to a dosage-depended decrease of uric acid level in blood plasma. This could be observed in own studies on winter-swimming and cold shower application and in studies on patients treated by cold-chamber-therapy. This uric acid decrease is due to an accelerated oxygen radical formation during cold exposition rather than to an inhibition of purine metabolism. The acute oxidative loading due to cold exposure and the long-term antioxidative adaptation may be interpreted as a new molecular mechanism resulting in body hardening.

Eliciting antibodies in chickens to human dimeric IgA removal of factors from human colostrum depressing anti IgA antibody production.

Contrary to expectation chickens did not readily elicit antibodies to IgA dimers when untreated human colostrum was used as antigen. When colostrum was fractionated by means of a column of 8% granulated agarose equilibrated with 10mM phosphate buffer, pH 7.2, a major and a minor fraction were obtained. The major or "1st fraction" consisted of two components with sedimentation coefficients of 10.9 S and 14.1 S, respectively. The minor or "2nd fraction" consisted of components of S values ranging from 2 to 6 and small amounts of 10.9 and 14.1 S material. When chickens were immunized with the "1st fraction" antibodies to dimeric IgA were produced. When the "1st and 2nd fractions" of the column were remixed and used for immunization of chickens, the immune response was poor as when the chickens were injected with untreated colostrum. An immuno-depressing agent in colostrum was indicated. When rabbits were immunized with clarified human colostrum, antibodies against five antigens were elicited, one of the antigens being dimeric IgA. The purified agent suppressed antibody formation in chickens against the haemocyanin of Jasus lalandii. The "activity" is therefore not specific for IgA and the remaining four antigens in human colostrum. The purified component is a glyco-protein with a hexose content in excess of 10%. The derivatized sugars prepared from it were shown by gas liquid chromatography to be an equimolar mixture of galactose, mannose and fucose. The molecular weight (Mr) of the purified component was found to be 72,000 by sedimentation and diffusion and 80,000 by SDS page using Mr reference standards. The properties of the immuno-suppressor strongly suggest that it is the secretory piece of dimeric IgA.

Steep gradients of inert substances as supports for precipitin reactions.

Precipitin reactions were conducted in the wells of micro titer plates and the light "absorbance" at 405nm plotted as a function of the neg log2 dilutions of the antigens using the Titertek Multiscan apparatus. The procedure followed was to incorporate antibody in 20% sucrose and to diffuse the mixture into serial two-fold dilutions of antigen overlaid on the sugar-antibody columns in the wells. Where the antigen met its antibody in equivalence precipitin bands formed. The bands of precipitates remained suspended. The precipitates formed by mixing the antibody sugar mixture with the serial two-fold dilutions of the antigen were also recorded in the Titertek Multiscan apparatus. Tobacco mosaic virus and its IgY type antibody produced simoidal precipitin curves with the layering as well as the mixing techniques. The haemocyanin of the whelk and its IgY antibody yielded a precipitin diagram with the layering technique which gave evidence to three antigens. The three antigens in the haemocyanin was confirmed by two dimentional Laurell-electrophoresis. Semi-purified human colostral dimeric IgA and its IgY antibody produced a precipitin diagram which showed evidence of four of five antigens. With the mixing technique a single precipitin maximum was obtained preceded by a prozone. Rabbit Ig and its IgY antibody gave a precipitin curve with two maxima. The precipitin curve obtained when the reagents were mixed had one peak preceded by a prozone.

Eliciting antibodies in chickens to human dimeric IgA. Removal of factors from human colostrum depressing anti IgA antibody production.

Contrary to expectation chickens did not readily elicit antibodies to IgA dimers when untreated human colostrum was used as antigen. When colostrum was fractionated by means of a column of 8% granulated agarose equilibrated with 10mM phosphate buffer, pH 7.2, a major and a minor fraction were obtained. The major or "1st fraction" consisted of two components with sedimentation coefficients of 10.9 S and 14.1 S, respectively. The minor or "2nd fraction" consisted of components of S values ranging from 2 to 6 and small amounts of 10.9 and 14.1 S material. When chickens were immunized with the "1st fraction" antibodies to dimeric IgA were produced. When the "1st and 2nd fractions" of the column were remixed and used for immunization of chickens, the immune response was as poor as when the chickens were injected with untreated colostrum. An immuno-depressing agent in colostrum was indicated. When rabbits were immunized with clarified human colostrum, antibodies against five antigens were elicited, one of the antigens being dimeric IgA. The immuno-depressing agent is therefore not universal. The purified agent suppressed antibody formation in chickens against the haemocyanin of Jasus lalandii. The "activity" is therefore not specific for IgA and the remaining four antigens in human colostrum. The purified component is a glyco-protein with a hexose content in excess of 10%. The derivatized sugars prepared from it were shown by gas liquid chromatography to be an equimolar mixture of galactose, mannose and fucose. The molecular weight (Mr) of the purified component was found to be 72,000 by sedimentation and diffusion and 80,000 by SDS page using Mr reference standards. The properties of the immuno-suppressor strongly suggest that it is the secretory piece of dimeric IgA.

Occupational exposure to hexachlorocyclohexane. VI. Metabolism of gamma-hexachlorocyclohexane in man.

Metabolism of gamma-Hexachlorocyclohexane (HCH) was studied examining 21 workers producing this insecticide. Using gas chromatography in combination with ECD and mass spectrometry 14 mono-, di-, tri- and tetrachlorophenols were identified in the urine samples of the workers. Seven dihydroxychlorobenzenes of still unknown configuration were detected by mass spectrometry. Ten of the more abundant metabolites, di-, tri- and tetrachlorophenols were determined quantitatively in all urine samples. 2,4,6-; 2,3,5- and 2,4,5-trichlorophenol turned out to be the main metabolites of gamma-HCH. They were excreted in nearly equal quantities. On account of their potential liver toxicity, the determination of chlorophenols in urine should be part of a biological monitoring program of HCH-exposed persons.