Constrained Abrasive Jet Polishing with a Tangentially Aligned Nozzle Shroud

In order to improve surface polishing quality and efficiency for hard and brittle components, a novel nozzle with specifically designed shroud was proposed for an abrasive jet polishing process. The removal mechanism of the abrasive jet under such a nozzle was investigated by simulating the jet flow in the interaction area of the nozzle shroud and workpiece. The simulation results show that the speed of the abrasive jet increases greatly by the shroud and the direction of the jet is aligned near parallel to the workpiece surface to minimize impact damage to workpiece surface. The constrained abrasive jet polishing (CAJP) experiments were conducted on the quartz glass component, a typical hard and brittle material, showing that the material removal mainly relied on the shearing and scratching of the workpiece surface rather than the mechanical shock impacts, which is consistent with the simulation findings.

Dynamics control of powered hydraulic roof supports in the underground longwall mining complex

The study presents the dynamic analysis of the hydraulic cylinders operated in the powered roof support sections as an important part of the longwall underground mining complexes. This type of hydraulic unit is subjected to frequent shock impacts from the significant rock masses released on the top of mined caverns. Hydraulic props are equipped with safety valves with steel helical springs, which intend to reduce peak loads by the relief of internal pressure. These valves respond to shock with a time delay due to the limited velocity of the pressure wave inside the cylinder and an additional pipe of a small section, which restricts fluid flow in outer space. The new approach represented in this paper is based on mathematical modelling of the interaction of the hydraulic and mechanical parts and using additional signals to control safety valves. Detection of shock in advance (0.02-0.05 s) allows reducing pressure peaks by 30% and avoid failures. The challenges are the development of a “smart valve” with optimised control functions by the signals from additional sensors (vibration, deformation, piston position) and providing fast reaction time with a high flow rate under pressures up to 100 MPa.

The Use of Wearable Sensor Technology to Detect Shock Impacts in Sports and Occupational Settings: A Scoping Review

Shock impacts during activity may cause damage to the joints, muscles, bones, or inner organs. To define thresholds for tolerable impacts, there is a need for methods that can accurately monitor shock impacts in real-life settings. Therefore, the main aim of this scoping review was to present an overview of existing methods for assessments of shock impacts using wearable sensor technology within two domains: sports and occupational settings. Online databases were used to identify papers published in 2010–2020, from which we selected 34 papers that used wearable sensor technology to measure shock impacts. No studies were found on occupational settings. For the sports domain, accelerometry was the dominant type of wearable sensor technology utilized, interpreting peak acceleration as a proxy for impact. Of the included studies, 28 assessed foot strike in running, head impacts in invasion and team sports, or different forms of jump landings or plyometric movements. The included studies revealed a lack of consensus regarding sensor placement and interpretation of the results. Furthermore, the identified high proportion of validation studies support previous concerns that wearable sensors at present are inadequate as a stand-alone method for valid and accurate data on shock impacts in the field.

Fundamental Material Characteristics of Traditional Windows Components as an Input for the Resilience Increasing

The aim of the paper is to make an overview of standard windows system used in Slovak Republic. The investigation of the most common traditional wooden window is presented in this paper as a representative sample. These parts of building facades are the most vulnerable areas due to dynamic impact loads. Identification of the basic materials behavior is necessary for effective design of window system resilience. This research is divided to analysis of mechanical properties of components, their connections and boundary conditions. Research in this specific area helps to improve safety against unexpected extreme dynamic load such as explosions and shock impacts.

Is It Merely a Labor Supply Shock? Impacts of Syrian Migrants on Local Economies in Turkey

The authors use the occurrence of a large and geographically varying inflow of more than 2.5 million Syrian migrants to Turkey between 2012 and 2015 to study the effect of migration on local economies. They do not find adverse employment or wage effects for native-born Turkish workers overall or for those without a high school degree. These results are robust to a range of strategies to construct reliable control groups. To explain the findings, the authors document the importance of three migration-induced demand channels: the complementarity between native and migrant labor, housing demand, and increased entrepreneurial activities.

Economic Restructuring

Technological progress, competition and trade, relative prices fluctuations, and changes of the institutional framework may require companies, industries, regions, or the whole national economy to undergo a process of significant restructuring. The transformation of the centrally planned socialist economies of Central and Eastern Europe to market economies offers us a natural laboratory to investigate how a transformational shock impacts the restructuring process. This chapter focuses on two basic components of this process. First, adjustments made by incumbent organizations (‘top-down’), and second, the opportunity for new businesses and organizations that complement or compete with the incumbents, entry into the marketplace (‘bottom-up’ transformation). The chapter highlights a variety of causes that forced incumbent firms to make adjustments, and demonstrates that the bottom-up component holds significant importance in such a process. This is particularly true if changes in the framework conditions are abrupt, and adjustments on the side of the incumbents are slow.