Changes of the internal friction in copper after cold working

Investigations of the effect of cold working on the internal friction of copper have become numerous in the last few years due to the discovery that part of the internal friction is due to the motion of dislocations in the metal. Most of the investigations so far have been done at frequencies of about 150 kilocycles per second. At these frequencies the internal friction has been found to be amplitude dependent and a function of the amount of cold work performed on the metal. This experiment was performed at a frequency of 54 cycles per second by vibrating the reed transversely in a vacuated symmetrical transducer at room temperature. The reed was annealed by placing it in a vacuum and passing electric current through it so that it was heated to a dull red. This was repeated and the reed was then left in the vacuum until cool. The cold working was done by placing compressive loads of 2, 4, 6, 8 and 10 tons on two reeds of the same size. The pressure on each reed would then increase in steps of 1 ton effective load on the total surface area of each reed. It was found that contrary to some theories, the internal friction of the reed was still amplitude dependent and a function of the amount of cold work. The internal friction decreased upon additional cold work after the annealing. As the amount of cold work was increased, the internal friction passed through a minimum and then sharply increased. It is proposed that the thermal currents present in the metal at this frequency remove the free dislocations before the stress starts them oscillating under the influence of the stress. Once the dislocation has been removed it may become a bound dislocation and as such will not enter into the internal friction. Cold working serves to increase the number of free dislocations. The thermal currents simply remove these and as a result there is a decrease in the internal friction. The final increase is believed due to the passing of the yield point. Once this point was passed the resulting disorder and flattening of the grain structure would lead to a rapid increase in the internal friction

Futterwirtschaftliche Konsequenzen adaptierter Nutzungs- und Bestandesoptionen im Kleegras zur Förderung des Bruterfolges von Feldlerchen

A field experiment was conducted to evaluate forage parameters of cutting regimes and species mixtures in grass-clover swards adapted to the breeding behaviour of the skylark (Alauda arvensis) as a representative of ground-nesting birds. We investigated options of a three weeks delayed cut in the second growth period to offer an adequate breeding period and an exalted cut at 14 cm height to motivate a preterm nestbuilding. Both regimes were conducted on swards of a standard seeding mixture and a species rich mixture, respectively. The levels of dry matter yield and forage quality did not always match common trends because of an extraordinary sward development based on early spring drought and partly high weed contents. In this study we present the first results in extract

The Unusually Stable Quaternary Structure of Human Cu,Zn-Superoxide Dismutase 1 Is Controlled by Both Metal Occupancy and Disulfide Status

The eukaryotic copper,zinc superoxide dismutases are remarkably stable dimeric proteins that maintain an intrasubunit disulfide bond in the reducing environment of the cytosol and are active under a variety of stringent denaturing conditions. The structural interplay of conserved disulfide bond and metal-site occupancy in human copper,zinc superoxide dismutase (hSOD1) is of increasing interest as these post-translational modifications are known to dramatically alter the catalytic chemistry, the subcellular localization, and the susceptibility of the protein to aggregation. Using biophysical methods, we find no significant change in the gross secondary or tertiary structure of the demetallated form upon reduction of the disulfide. Interestingly, reduction does lead to a dramatic change in the quaternary structure, decreasing the monomer-to-dimer equilibrium constant by at least four orders of magnitude. This reduced form of hSOD1 is monomeric, even at concentrations well above the physiological range. Either the addition of Zn(II) or the formation of the disulfide leads to a shift in equilibrium that favors the dimeric species, even at low protein concentrations (i.e. micromolar range). We conclude that only the most immature form of hSOD1, i.e. one without any post-translational modifications, favors the monomeric state under physiological conditions. This finding provides a basis for understanding the selectivity of mitochondrial SOD1 import and may be relevant to the toxic properties of mutant forms of hSOD1 that can cause the familial form of amyotrophic lateral sclerosis

Solution Structure of the Yeast Copper Transporter Domain Ccc2a in the Apo and Cu(I)-loaded States

Ccc2 is an intracellular copper transporter in Saccharomyces cerevisiae and is a physiological target of the copper chaperone Atx1. Here we describe the solution structure of the first N-terminal MTCXXC metal-binding domain, Ccc2a, both in the presence and absence of Cu(I). For Cu(I)-Ccc2a, 1944 meaningful nuclear Overhauser effects were used to obtain a family of 35 structures with root mean square deviation to the average structure of 0.36 +/- 0.06 A for the backbone and 0.79 +/- 0.05 A for the heavy atoms. For apo-Ccc2a, 1970 meaningful nuclear Overhauser effects have been used with 35 (3)J(HNHalpha) to obtain a family of 35 structures with root mean square deviation to the average structure of 0.38 +/- 0.06 A for the backbone and 0.82 +/- 0.07 A for the heavy atoms. The protein exhibits a betaalphabetabetaalphabeta, ferrodoxin-like fold similar to that of its target Atx1 and that of a human counterpart, the fourth metal-binding domain of the Menkes protein. The overall fold remains unchanged upon copper loading, but the copper-binding site itself becomes less disordered. The helical context of the copper-binding site, and the copper-induced conformational changes in Ccc2a differ from those in Atx1. Ccc2a presents a conserved acidic surface which complements the basic surface of Atx1 and a hydrophobic surface. These results open new mechanistic aspects of copper transporter domains with physiological copper donor and acceptor proteins

Evidencia en video de fratricidio y canibalismo, movimiento de polluelos e interacciones con depredadores en nidos de Circus cyaneus

During a nest-camera study of Hen Harriers (Circus cyaneus), we recorded siblicide, cannibalism, movement of nestlings by adult birds, and interactions with predators. We deployed cameras at 13 nests across three study areas in Ireland between 2008 and 2010. At a nest with two well-developed nestlings (approximately 25–30 d old), the older nestling killed its sibling and fed on it. This was the first documented case of siblicide in this species, to our knowledge. Recordings also revealed three other events of cannibalism in which one of the nestlings in a brood died from unknown causes and was then eaten by its siblings (n = 1), by the adult male (n = 1), or was used by the adult female to feed the remaining nestlings (n = 1). At two nests, recordings showed the adult female picking up and moving nestlings that were outside the nest cup. In addition, cameras recorded two instances of full brood predation by red fox (Vulpes vulpes) and an attack on a nest by a female Eurasian Kestrel (Falco tinnunculus) that had no apparent consequences for the nestlings or the female Hen Harrier. The behaviors reported here, which are difficult to observe directly, may have important consequences for our understanding of productivity and population dynamics of Hen Harriers.Durante un estudio sobre patrones de actividad de individuos reproductores de Circus cyaneus realizado con cámaras para monitoreo de nidos, registramos comportamientos de fratricidio, canibalismo, movimientos de polluelos e interacciones con depredadores. Colocamos cámaras en 13 nidos distribuidos en tres áreas de estudio en Irlanda entre 2008 y 2010. En un nido con dos polluelos en un estado de desarrollo avanzado (c. 25-30 días), el polluelo de mayor edad mató al otro y se alimentó de él. Este es el primer caso documentado de fratricidio en esta especie. Obtuvimos imágenes de otros tres casos de canibalismo en que uno o más polluelos fallecieron por causas desconocidas y sus cadáveres fueron usados como alimento por los otros polluelos (n = 1), por el macho adulto (n = 1) o por la hembra adulta para alimentar a los otros polluelos (n = 1). En dos nidos, las imágenes muestran a la hembra adulta repetidamente recogiendo polluelos que se alejan del nido para intentar llevarlos al nido. Por último, las cámaras captaron dos eventos de depredación de polluelos por parte de Vulpes vulpes y un enfrentamiento entre la hembra adulta de C. cyaneus y una hembra de Falco tinnunculus sin consecuencias para los polluelos o la hembra adulta. Estos comportamientos, difíciles de detectar mediante metodologías de monitoreo tradicionales, pueden tener consecuencias para el éxito reproductivo y la dinámica poblacional de esta especie

Characterization of the Binding Interface between the Copper Chaperone Atx1 and the First Cytosolic Domain of Ccc2 ATPase

The interaction of the copper chaperone Atx1 and the first cytosolic domain of Ccc2 ATPase, Ccc2a, was investigated by NMR in solution. In particular, a solution of Cu(I)-15NAtx1 was titrated with apo-Ccc2a, and, vice versa, a solution of Cu(I)-15NCcc2a was titrated with apo-Atx1. By following the 15N and 1H chemical shifts, a new species is detected in both experiments. This species is the same in both titrations and is in fast exchange with the parent species on the NMR time scale. Nuclear relaxation data are consistent with the formation of an adduct. Judging from the nuclear Overhauser effect spectroscopy patterns, the structure of Cu(I)-15NCcc2a in the presence of apo-Atx1 is not significantly altered, whereas Cu(I)-15NAtx1 in the presence of apo-Ccc2a experiences some changes with respect to both the apoproteins and the Cu(I)-loaded proteins. The structure of the Cu(I)-15NAtx1 moiety in the adduct was obtained from 1137 nuclear Overhauser effects to a final root mean square deviation to the mean structure of 0.76 +/- 0.13 A for the backbone and 1.11 +/- 0.11 A for the heavy atoms. 15N and 1H chemical shifts suggest the regions of interaction that, together with independent information, allow a structural model of the adduct to be proposed. The apo form of Atx1 displays significant mobility in loops 1 and 5, the N-terminal part of helix alpha1, and the C-terminal part of helix alpha2 on the ms-micros time scale. These regions correspond to the metal binding site. Such mobility is largely reduced in the free Cu(I)-Atx1 and in the adduct with apo-Ccc2a. The analogous mobility of Ccc2a in both Cu(I) and apo forms is reduced with respect to Atx1. Such an adduct is relevant as a structural and kinetic model for copper transfer from Atx1 to Ccc2a in physiological conditions

Accuracy of electrocardiographic criteria for atrial enlargement: validation with cardiovascular magnetic resonance

<p>Abstract</p> <p>Background</p> <p>Anatomic atrial enlargement is associated with significant morbidity and mortality. However, atrial enlargement may not correlate with clinical measures such as electrocardiographic (ECG) criteria. Past studies correlating ECG criteria with anatomic measures mainly used inferior M-mode or two-dimensional echocardiographic data. We sought to determine the accuracy of the ECG to predict anatomic atrial enlargement as determined by volumetric cardiovascular magnetic resonance (CMR).</p> <p>Methods</p> <p>ECG criteria for left (LAE) and right atrial enlargement (RAE) were compared to CMR atrial volume index measurements for 275 consecutive subjects referred for CMR (67% males, 51 ± 14 years). ECG criteria for LAE and RAE were assessed by an expert observer blinded to CMR data. Atrial volume index was computed using the biplane area-length method.</p> <p>Results</p> <p>The prevalence of CMR LAE and RAE was 28% and 11%, respectively, and by any ECG criteria was 82% and 5%, respectively. Though nonspecific, the presence of at least one ECG criteria for LAE was 90% sensitive for CMR LAE. The individual criteria P mitrale, P wave axis < 30°, and negative P terminal force in V1 (NPTF-V1) > 0.04s·mm were 88–99% specific although not sensitive for CMR LAE. ECG was insensitive but 96–100% specific for CMR RAE.</p> <p>Conclusion</p> <p>The presence of at least one ECG criteria for LAE is sensitive but not specific for anatomic LAE. Individual criteria for LAE, including P mitrale, P wave axis < 30°, or NPTF-V1 > 0.04s·mm are highly specific, though not sensitive. ECG is highly specific but insensitive for RAE. Individual ECG P wave changes do not reliably both detect and predict anatomic atrial enlargement.</p