Monitoring of Single-Cell Responses in the Optic Tectum of Adult Zebrafish with Dextran-Coupled Calcium Dyes Delivered via Local Electroporation

Kassing V, Engelmann J, Kurtz R. Monitoring of Single-Cell Responses in the Optic Tectum of Adult Zebrafish with Dextran-Coupled Calcium Dyes Delivered via Local Electroporation. PLoS ONE. 2013;8(5): e62846.The zebrafish (Danio rerio) has become one of the major animal models for in vivo examination of sensory and neuronal computation. Similar to Xenopus tadpoles neural activity in the optic tectum, the major region controlling visually guided behavior, can be examined in zebrafish larvae by optical imaging. Prerequisites of these approaches are usually the transparency of larvae up to a certain age and the use of two-photon microscopy. This principle of fluorescence excitation was necessary to suppress crosstalk between signals from individual neurons, which is a critical issue when using membrane-permeant dyes. This makes the equipment to study neuronal processing costly and limits the approach to the study of larvae. Thus there is lack of knowledge about the properties of neurons in the optic tectum of adult animals. We established a procedure to circumvent these problems, enabling in vivo calcium imaging in the optic tectum of adult zebrafish. Following local application of dextran-coupled dyes single-neuron activity of adult zebrafish can be monitored with conventional widefield microscopy, because dye labeling remains restricted to tens of neurons or less. Among the neurons characterized with our technique we found neurons that were selective for a certain pattern orientation as well as neurons that responded in a direction-selective way to visual motion. These findings are consistent with previous studies and indicate that the functional integrity of neuronal circuits in the optic tectum of adult zebrafish is preserved with our staining technique. Overall, our protocol for in vivo calcium imaging provides a useful approach to monitor visual responses of individual neurons in the optic tectum of adult zebrafish even when only widefield microscopy is available. This approach will help to obtain valuable insight into the principles of visual computation in adult vertebrates and thus complement previous work on developing visual circuits

Effect of velocity on roll/slip for low and high load conditions in polymer composite

In the last decade polymer composites are often used without lubrication on both low and high speed applications. Some of the application areas are marine, automotive and agriculture used as bearings and cams where roll-slip is the dominant mechanism. Limited studies are made for composites relating such applications where rolling/sliding condition influences the tribological behavior of the material. Investigating the roll-slip phenomenon for identifying the influence of velocity on frictional behavior can mark a boundary to map the use of composites with respect to its application. Moreover, the design of the material can be optimized to match the operating conditions. In the current research the polymer composite (with polyester matrix) has been tested under rolling-sliding condition for two different loads with 61N and 210N and with different speeds ranging from 10 rpm to 700 rpm. Ideal conditions in terms of roughness, slip ratio, surface temperature and ambient temperature were maintained to reduce the frictional heating. Using a 20% slip ratio the behavior of the material was observed for the tribological characteristics where the rate of increase of friction force follows a exponential pattern with increasing speeds. Nevertheless, on testing with high speeds a steady rate of increase in the friction curve was observed. Friction behavior of composites under different speeds is briefed with the microstructural characteristics for low and high loads

Tribological behaviour of the low and high viscosity peek against steel using different contact pressures

In the market of polymers for tribological applications polyetheretherketone (PEEK) are often used for satisfying requests coming from industry regarding enhanced properties such as, thermal stability, friction and wear resistance. These properties promote the material to be used in so called high performance tribological applications. However, fundamental mechanisms governing friction and wear are not yet fully understood and neither is the influence of composition parameters. An important parameter is PEEK’s viscosity during manufacturing process which is heated up to semi-solid state, between its glass transition and melting temperature. This paper studies the friction and wear performance of low and high viscosity PEEK and pure PEEK under dry reciprocating sliding contact. The tests were performed in large scale specimens under flat-on-flat configuration to determine the transitions in tribological behaviour at different contact pressures. Tests were carried out at controlled atmosphere with 25 °C and a relative humidity of 50%. Contact pressures parameters were 4, 8 and 10 MPa used at a sliding speed of 20 mm/s. Post mortem analyses were carried out by means of 2-D surface topography and optical microscopy. The results show that the pure PEEK exhibits low coefficient of friction and wear rate when the contact pressure increase and similar behave for high and low viscosity PEEK

Friction torque, temperature and roughness in roll-slip phenomenon for polymer–steel contacts

The current study gives an insight of the roll-slip phenomenon of polymer-metal pair where priority is given to measurement techniques, test duration and the behavior of the polymer. A systematic tribological measurement was used to identify the friction torque from polymer –metal pairs where the friction torque from contact is obtained by subtracting the base torque of the test rig to exploit the absolute results. Base torque of the machine is almost constant, the changing can describe with linear trend line which is less than 0,5% per ten minutes. Measurements made for 3 hours shows that the friction force between the polyamide 6 (NaPA6) and structural steel (S33J2) has a polynomial of degree two with a function ( Ff = −1.5549 ⋅T 2 + 9.4031⋅T +13,126 ). Micrographs from the contact surface revealed the damage of roughness peaks during the course of testing. The involved wear mechanisms was investigated with roughness measurements and microscopy. The roughness plots also correlates with the micrograph where the rate of decrease in Ra in the initial stage is higher followed by a linear increase in the later stage. This can describe using polynomial function of degree as ( Ra = 0.029 ⋅T 2 + 0.3695⋅T + 2.4967 )

A novel measuring technique to evaluate frictional characteristics of roll-slip contacts in polymer-metal pairs

Tribology research is aimed for desirable frictional characteristic; especially in rolling/sliding of polymer-metal contacts which helps smooth operations and energy savings. Conventional roll-slip tests for few million cycles have significant deposit of polymer transfer layer on counterface, thus having a polymer-polymer contact instead of polymer-metal contact. Besides, backtransfer affecting the friction force was never explored. Studying these phenomenon individually and characterizing frictional property without the presence of transfer layer helps for a better understanding of the combined system. A new procedure for measuring friction torque at 20% slip ratio is adapted for varying speeds from 10 to 500 rpm. The observed friction-force increases rapidly at low-speeds and becomes linear at high-speeds. The micrographs of the contact surface prove no trace of transfer layer was found in the newly developed measuring process. Also specimen surface temperature never reached the effective level to affect friction properties

Tribological behaviour of the low and high viscosity peek at various testing scales

Polyetheretherketone (PEEK) has become most attractive as a sliding bearing material in industrial applications, due to its excellent thermal stability, good friction and wear resistance. These properties promote the material to be used in so called high performance tribological applications. However, fundamental mechanisms governing friction and wear are not yet fully understood and neither is the influence of composition parameters. An important parameter is PEEK’s viscosity during injection moulding which is heated up to semi-solid state, between its glass transition and melting temperature. It is not known to what extent the injection viscosity, related to the applied temperature profile, affects subsequent tribological features. This paper studies the friction and wear performance of low and high viscosity PEEK under dry reciprocating sliding contact. The tests were performed with small and large scale specimens under pin-on-plate and flat-on-flat configuration, respectively; to determine the transitions in tribological behaviour at different scales and to identify the applications limits. Tests were carried out at controlled atmosphere with 25 °C and a relative humidity of 50%. Parameters such as contact pressures and sliding speed were limited at 10 MPa and 20 mm/s, respectively; post mortem analyses were carried out by means of 2-D surface topography and optical microscopy. The results show that PEEK injected at high viscosity exhibits a tribological performance with a relatively high coefficient of friction and high wear rate compare to PEEK injected at low viscosity

On Developing an E-Assessment Tool for Agile Practices

As agile software development processes are widely applied in industry, students need to develop a good understanding of agile principles and practices as part of their education. During our ten years of experience with teaching the Scrum framework in team project modules, we noticed that students frequently struggle with writing good user stories and concise sprint goals. To support students in mastering basic practices and to free limited teaching resources for more in-depth discussions on advanced topics, e-assessment tools should be developed to provide timely feedback on at least common mistakes. This paper argues that, and sketches how, research on quality criteria for artifacts of agile development can serve as the basis for such a tool. However, multiple challenges remain that we invite lecturers and researchers to discuss

Roughness measurement problems in tribological testing

In tribological measurement of thermoplastics against steel the surface roughness has a potential effect in dictating the frictional behavior of the material. In most cases the roughness of the specimen is measured before and after the test, where it affects the friction force and influences the mechanism involved. The roughness of the material is not the exact value and it has a deviance which depends upon the machining process used in preparing the surface. Generally, the direction of machining has an influence on the topography of the surface in case of turning, milling and drilling but in case of pressed components the direction has no effects. In order to maintain ideal test condition the surface roughness of the test materials has to be consistent for the given number of samples. Even though the test specimens are machined in the same machine with same parameters there are number of parameters involved in deciding the consistency of the surface roughness. The roughness of the surface are defined by number of parameters such as Ra, Rz and few 3D parameters in such a case narrowing down to a specific constant is vital. The results from the roughness is not made from one measurement were an average and deviance from several measurement decides that if two ideal samples has same or different roughness