Interferometric study on the temporal variability of the brightness distributions of protoplanetary disks

Multi-epoch observations have revealed the variability of pre-main sequence stars and/or their environment. Moreover, structures in orbital motion around the central star, resulting from planet-disk interaction, are predicted to cause temporal variations in the brightness distributions of protoplanetary disks. Through repeated observations with the Very Large Telescope Interferometer (VLTI) over nearly two decades, the ESO Archive has become a treasure chest containing high-resolution multi-epoch near- and mid-infrared observations of the potential planet-forming regions in protoplanetary disks. We aim to investigate whether the existing multi-epoch observations provide evidence for the variability of the brightness distributions of the innermost few astronomical units of protoplanetary disks and to quantify any variations detected. We present different approaches to search for evidence of temporal variations based on multi-epoch observations obtained with the VLTI instruments PIONIER, AMBER, and MIDI for 68 pre-main sequence stars. For nine objects in our sample, multi-epoch data obtained using equal baselines are available that allow us to directly detect variations in the visibilities due to temporally variable brightness distributions. Significant variations of the near-infrared visibilities obtained in different epochs with PIONIER and/or AMBER for HD 50138, DX Cha, HD 142527, V856 Sco, HD 163296, and R CrA were found. By estimating the impact of a small variation of the baseline on the measured squared visibilities, we are able to compare the data of another 12 pre-main sequence stars. Thereby, we find evidence for temporal variations of the brightness distribution of one additional object, AK Sco. Besides the two binaries DX Cha and AK Sco, HD 50138 and V856 Sco also show signs of variability caused by variations of asymmetric structures in the brightness distribution.Comment: Accepted for publication in A&

The effects of peer influence on adolescent pedestrian road-crossing decisions

Objective: Adolescence is a high-risk period for pedestrian injury. It is also a time of heightened susceptibility to peer influence. The aim of this research was to examine the effects of peer influence on the pedestrian road-crossing decisions of adolescents. Methods: Using 10 videos of road-crossing sites, 80 16- to 18-year-olds were asked to make pedestrian road-crossing decisions. Participants were assigned to one of 4 experimental conditions: negative peer (influencing unsafe decisions), positive peer (influencing cautious decisions), silent peer (who observed but did not comment), and no peer (the participant completed the task alone). Peers from the adolescent’s own friendship group were recruited to influence either an unsafe or a cautious decision. Results: Statistically significant differences were found between peer conditions. Participants least often identified safe road-crossing sites when accompanied by a negative peer and more frequently identified dangerous road-crossing sites when accompanied by a positive peer. Both cautious and unsafe comments from a peer influenced adolescent pedestrians’ decisions. Conclusions: These findings showed that road-crossing decisions of adolescents were influenced by both unsafe and cautious comments from their peers. The discussion highlighted the role that peers can play in both increasing and reducing adolescent risk-taking

Influence of surface roughness on selected properties of the TiAlN coating

The HS6-5-2C steel samples with different surface roughness were used for the tests. After grinding had a roughness parameter of Ra = 0,03 μm, and after polishing Ra = 0,01 μm. A TiAlN coating was applied to the substrate prepared in this way. Using a confocal microscope with an interferometric mode, the geometrical structure of the samples was analyzed. The optical strain gauge was used to measure the contact angle. Tribological tests were carried out in conditions of technically dry friction. The polished sample with the coating was characterized by a more stable course of the friction coefficient, lower wear and a smaller wetting angle

The influence of environmental conditions on the tribological properties of the Ti13Nb13Zr alloy

The paper presents the results of tribological tests of the Ti13Nb13Zr titanium alloy - carried out in the conditions of lubrication with liquids simulating body fluids. Artificial saliva solutions were used for the tests. Two pH values were used – 7,0 characteristic of a healthy organism and 4,9 - typical for the presence of inflammation. The countersample in the tested friction nodes were Al2O3 balls with a diameter of 6 mm loaded with a normal force of 1 N. The tests obtained showed a strong influence of environmental conditions on the tribological properties of the Ti13Nb13Zr titanium alloy. This applies to both the value of the coefficient of friction and linear wear. In the case of tests carried out under lubrication conditions with an artificial saliva solution at pH 7,0 they were 0,47 and 31,1 μm, respectively; in the case of a fluid at pH 4,9 they were 25 % and 45 % higher (0,62 and 65,6 μm)

The influence of environmental conditions on the tribological properties of the Ti13Nb13Zr alloy

The paper presents the results of tribological tests of the Ti13Nb13Zr titanium alloy - carried out in the conditions of lubrication with liquids simulating body fluids. Artificial saliva solutions were used for the tests. Two pH values were used – 7,0 characteristic of a healthy organism and 4,9 - typical for the presence of inflammation. The countersample in the tested friction nodes were Al2O3 balls with a diameter of 6 mm loaded with a normal force of 1 N. The tests obtained showed a strong influence of environmental conditions on the tribological properties of the Ti13Nb13Zr titanium alloy. This applies to both the value of the coefficient of friction and linear wear. In the case of tests carried out under lubrication conditions with an artificial saliva solution at pH 7,0 they were 0,47 and 31,1 μm, respectively; in the case of a fluid at pH 4,9 they were 25 % and 45 % higher (0,62 and 65,6 μm)

Influence of surface roughness on selected properties of the TiAlN coating

The HS6-5-2C steel samples with different surface roughness were used for the tests. After grinding had a roughness parameter of Ra = 0,03 μm, and after polishing Ra = 0,01 μm. A TiAlN coating was applied to the substrate prepared in this way. Using a confocal microscope with an interferometric mode, the geometrical structure of the samples was analyzed. The optical strain gauge was used to measure the contact angle. Tribological tests were carried out in conditions of technically dry friction. The polished sample with the coating was characterized by a more stable course of the friction coefficient, lower wear and a smaller wetting angle

Development of a Theoretical Model for Predicting the Thermal Performance Characteristics of a Vertical Pin-Fin Array Heat Sink under Combined Forced and Natural Convection with Impinging Flow

Abstract A comprehensive theoretical and experimental study was carried out on the thermal performance of a pin-fin heat sink. A theoretical model was formulated that has the capability of predicting the influence of various geometrical, thermal, and flow parameters on the effective thermal resistance of the heat sink. An experimental technique was developed for measuring the thermal performance of the heat sink, and the overall convective heat transfer coefficient for the fin bundle. Experiments were carried out, and correlations obtained, for a wide range of parameters for pure natural convection and for combined forced and natural convection. The predictive capability of the theoretical model was verified by comparison with experimental data including the influence of various fin parameters and the existence of an optimum fin spacing

Dentin dysplasia type I

This paper describes a rare case of genetically determined dentin dysplasia type I in 26-year-old male patient. The paper highlights anatomical and radiological aspects of dental abnormalities and emphasizes the significance of the education of both general practitioners and paediatricians as regards referring patients with diagnosed dentin dysplasia for a multi-specialty therapy.

Operationalising performance management in local government: The use of the balanced scorecard

Orientation: Local government forms that part of the public sector closest to citizens and therefore indispensable in its role of providing essential goods and services and developing the local area. Local government has the authority and functions necessary to provide services for the maintenance and promotion of the well-being of all people within their area and should provide access to basic services such as water, electricity and health care. Research purpose: This study examines performance management as a tool in local government effective provision service delivery. The critical question addressed in this paper was how the balanced scorecard (BSC) can be used to improve performance in the context of local government and assist in eradicating the current challenges of lack of quality services, poverty and infrastructure development. Motivation for the study: The need for continuous improvement in service delivery at local government compounded by high levels of service delivery protest requires regular review of performance management system. Research approach: To understand the current context and challenges facing local government, the applicable legislative framework including the Constitution, white paper and the National Development Plans were perused to better understand the legal environment in which local government operates. A literature review was undertaken to evaluate theory on organisational effectiveness. Semi-structured interviews were used to solicit expert opinions. Main findings/managerial implications: The BSC approach emerged as the preferred tool because the method offered the authors the opportunity to review non-financial and financial factors to arrive at a balanced conclusion. A BSC tool was developed and applied to the Joe Gqabi District Municipality as a case study. Practical implications: The BSC as a performance management tool enables organisations to clarify their vision and strategy and translate them into goal or actions. Contribution/value-add: The research findings conclude that there was acknowledgement of the importance of performance measurement instruments in the municipality, yet the municipality still experienced challenges caused by the performance review process not being transparent and not communicated to all stakeholders

Tribological properties of diamond-like-carbon coating doped with tungsten

This paper presents the tribological properties of diamond-like-carbon coatings (DLC) doped with tungsten. The hardness of the DLC coating was determined using a micro-hardness tester. Friction tests were carried out on a tribometer in rotational motion in a 100Cr6 steel ball-disk association with a-C-H:W tungsten doped hydrogenated DLC coating. Tests were carried out with loads of 10 N, 25 N and 50 N under technically dry friction conditions. Using a scanning electron microscopy (SEM), the surface morphology was observed, and with a confocal microscope, the geometric structure of the surface was observed before and after the friction tests. The wetting angle of the samples was examined on an optical tensiometer for distilled water and diiodomethane. The results indicated that DLC coatings of the a-C:H:W type obtained by the PVD technique can be used in unlubricated high-load tribological systems