Manipulation of Mesoscopic Phase Separation by X-ray Illumination

High resolution synchrotron X-ray diffraction is used to study the dynamics of oxygen ordering in a La₂CuO_4.08 single crystal as a function of the temperature and of the photon flux. We have observed the occurrence of a phase separation between disordered and 3D long-range ordered domains of interstitial oxygen atoms (the latter being commensurate with the lattice). We are able to study and control the phase separation by irradiating the sample while varying the temperature in a range between 350 K and 250 K. These results shed new light on the oxygen ordering in cuprates; in addition, we show that in such systems it is possible to manipulate and to control structural inhomogeneities at the atomic scale using X-ray diffraction. This work was supported by European project 517039 “Controlling Mesoscopic Phase Separation” (COMEPHS) (2005).     

Static and dynamic testing of bridges through microwave interferometry

A novel microwave sensor capable of remote detection of structural displacements is experimented as geotechnical instrument for static and dynamic testing of bridges. The sensor is based on an interferometric radar providing range imaging capability and sub-millimetric accuracy range displacement measurement. Dynamic monitoring calls for sampling rate high enough for transient analysis, while static monitoring requires long-term stability. The instrument has been designed in order to provide both these features. The results of a validation campaign on a railway bridge during the final test before going into service are reported.     

An analysis of through-thickness residual stresses in aluminium FSW butt joints

In the paper, the results of a wide experimental campaign on friction stir welding (FSW) of aluminum alloys are reported. The attention was focused on the through-thickness residual stresses that occur on aluminum joints, after the welding process. In detail, using the hole-drilling method the residual stresses distribution in the zone close to the tool shoulder border of the joint advancing side, has been investigated; four different aluminum alloys and three different process conditions have been considered. The experimental analysis has shown that unlike traditional welding processes, the residual stresses are negative in the surface of the examined zone, and increase with depth until values of about 100–150 MPa that occur at a depth of about 0.5–1.0 mm. As expected, the maximum value of the residual stresses induced by the FSW process influences the mechanical behavior of the joint significantly, as it has been observed for the AA6082-T6 aluminum alloy by considering its static and fatigue resistance.Such results corroborate that the hole-drilling method, widely employed in the industrial field due to its simplicity and low cost, can be used for an accurate estimation of the maximum residual stresses that occur in an aluminum butt joint obtained by friction stir welding.     

Effect of position and force tool control in friction stir welding of dissimilar aluminum-steel lap joints for automotive applications

Widespread use of aluminum alloys for the fabrication of car body parts is conditional to the use of appropriate welding methods, especially if dissimilar welding must be performed with automotive steel grades. Friction stir welding (FSW) is considered to be a reasonable solution to obtain sound aluminum-steel joints. In this context, this work studies the effects of tool position and force control in dissimilar friction stir welding of AA6061 aluminum alloy on DC05 low carbon steel in lap joint configuration, also assessing proper welding parameter settings. Naked eye and scanning electron microscopy (SEM) have been used to detect macroscopic and microscopic defects in joints, as well as to determine the type of intermixture between aluminum and steel. The joint strength of sound joints has been assessed by shear tension test. Results point out that tool force control allows for obtaining joints with better quality and strength in a wider range of process parameters. A process window has been determined for tool force conditions to have joints with adequate strength for automotive purposes.The full text can be downloaded at https://link.springer.com/content/pdf/10.1007%2Fs40436-019-00290-1.pdf     

Tunable Fröhlich polarons in organic single-crystal transistors

In organic field-effect transistors (FETs), charges move near the surface of an organic semiconductor, at the interface with a dielectric. In the past, the nature of the microscopic motion of charge carriers--which determines the device performance--has been related to the quality of the organic semiconductor. Recently, it was discovered that the nearby dielectric also has an unexpectedly strong influence. The mechanisms responsible for this influence are not understood. To investigate these mechanisms, we have studied transport through organic single-crystal FETs with different gate insulators. We find that the temperature dependence of the mobility evolves from metallic-like to insulating-like with increasing dielectric constant of the insulator. The phenomenon is accounted for by a two-dimensional Fr?hlich polaron model that quantitatively describes our observations and shows that increasing the dielectric polarizability results in a crossover from the weak to the strong polaronic coupling regime. This represents a considerable step forward in our understanding of transport through organic transistors, and identifies a microscopic physical process with a large influence on device performance.     

A new portable system for determining the state of conservation of monumental stones

In this paper a comparison between the standard uniaxial compressive strength test (UCS) and a new portable instrument called Drilling Resistance Measurement System (DRMS) is presented. This instrument is part of a new methodology developed and validated within a European research project (Hardrock) with the aim to evaluate the performances of consolidation treatments applied on stone monuments. The tests have been done on different stone categories in order to evaluate the influence of the mineralogical, structural and physical characteristics in the results obtained with the two methods.     

T c as a Function of Electron Doping in Mg10B2 Using Sc for Mg Substitution

We have studied the variation of superconducting critical temperature T _c as a function of electron doping in the Mg¹⁰B₂ system using Sc for Mg substitution. The critical temperature in the¹⁰B isotope substituted system Mg_{1? x} Sc _x ¹⁰B₂ increases by increasing the scandium content x in the range 0<x<0.012 up to 41.4 K, while the T _c of the natural boron system Mg_{1? x} Sc _x B₂ is nearly constant. The overall difference of T _c in Mg_{1? x} Sc _x B₂ as function of x between the natural B and ¹⁰B isotope system seems to indicate that the isotope effect shows large variations with electron doping as expected for the T _c enhancement driven by a shape resonance.     

Strategies for numerical simulation of linear friction welding of metals: a review

Linear friction welding (LFW) is a solid-state joining process used to weld non-axisymmetric components. Material joining is obtained through the reciprocating motion of two specimens undergoing an axial force. During this process, the heat source is determined by the frictional work transformed into heat. This results in a local softening of the material and plays a key role in the onset of the bonding conditions. In this paper, a critical analysis of the different approaches used to simulate the LFW processes is provided. The focus of the paper is the comparison of different modeling strategies and the most relevant outputs available, i.e. temperature, strain and stress distribution, material flow, axial shortening and residual stress. Major issues arising due to the complexity of the process are discussed, highlighting strengths and weaknesses of each approach.     

Embryonic development of endoderm in chicken (Gallus gallus domesticus)

The poultry industry is a sector of agribusiness which represents an important role in the country's agricultural exports. Therefore, the study about embryogenesis of the domestic chicken (Gallus gallus domesticus) has a great economic importance. The aim of this study was to evaluate embryonic development of the endoderm in chicken (Gallus gallus domesticus). Forty fertilized eggs of domestic chickens, starting from the 1st day of gestation and so on until the 19 days of the incubation were collected from the Granja São José (Amparo, SP, Brazil). Embryos and fetus were fixed in 10% formaldehyde solution, identified, weighed, measured, and subjected to light and scanning electron microscopy. The endoderm originates the internal lining epithelium of the digestive, immune, respiratory systems, and the organs can be visualized from the second day (48 h) when the liver is formed. The formation of the digestive system was complete in the 12th day. Respiratory system organs begin at the fourth day as a disorganized tissue and undifferentiated. Their complete differentiation was observed at the 10 days of incubation, however, until the 19 days the syrinx was not observed. The formation of immune system at 10th day was observed with observation of the spleen, thymus, and cloacal bursa. The study of the organogenesis of the chicken based on germ layers is very complex and underexplored, and the study of chicken embryology is very important due the economic importance and growth of the use of this animal model studies such as genetic studies. Microsc. Res. Tech. 76:803–810, 2013. © 2013 Wiley Periodicals, Inc.