机床的光栅测量和数控系统的发展趋势

机床用光栅测量元件和数控系统是数控机床的两大核心部件,清楚地了解他们的发展趋势,对机床制造商和最终用户都有非常重要的意义。本文结合海德汉(H EID EN H A IN)公司的研究,阐述了现代数控机床用测量系统和数控系统的发展趋势,并着重介绍了机床的精度以及测量系统和数控系统     

‘The older adult’ doesn’t exist: using values to differentiate older adults in the Dutch housing market

Abstract

To date most prognoses of older adults in the housing market have been based on average housing preferences and average housing market behaviour of all persons in a certain age cohort. Due to socialcultural and social-economic dynamics, the relationship between age and housing is expected to change for successive cohorts. This study sets out to improve housing preferences estimates by recognizing the growing differentiation among older adults. This heterogeneity is analysed by differentiating older adults on their lifestyles (operationalized as values), using latent class analysis as a clustering technique. These analyses result in older adults being classified into five segments on the basis of their viewpoints, motivations and attitude. Next, for each lifestyle segment a separate discrete choice model is estimated, offering insight in the relative importance that these segments give to various housing attributes. The findings demonstrate advantages over a traditional, single model approach and can be helpful in formulating contemporary housing policy.     

Numerical and experimental study of conjugate heat transfer in a horizontal air cavity

The demand for general reduction of the energy consumption in civil engineering leads to more frequent use of insulating materials with air gaps or cavities. Heat transfer through a constructional part can be decreased by adding an air gap and low emissivity reflective foils to the structure. In the first part of this paper, the impacts of cavity thickness and inner surface emissivity on combined conduction, convection and radiation heat transfer was experimentally explored in the case of constructional part with a horizontal cavity subjected to constant downward heat flux. The heat flow meter Netzsch HFM 436 Lambda was used for steady-state measurements. Results suggest that the studied parameters seriously affect the combined heat transfer in the composed structure. In the second part the paper reports the numerical study of two-dimensional conjugate heat transfer in closed horizontal cavity having air as the intervening medium. Numerical models validated by related experimental results were performed to further investigate the effect of radiation heat transfer. It was found that in general, the total heat flux through the composed structure decreases with increasing air cavity thickness, which is significant especially when low emissivity inner surfaces are taking into account. The direction of heat flow (downward or upward heat flow) has a significant impact on the convection heat transfer. An important contribution from the present work is the analysis of the optimal thickness of the cavity at different boundary conditions. The optimal thickness of the enclosure with low emissivity surfaces is 16 mm when subjected to upward heat flux.     

Rural Migrants’ Residential Mobility: Housing and Locational Outcomes of Forced Moves in China

This paper analyses the residential mobility of China’s rural–urban migrants in light of evidence from Yangzhou, a medium-sized city in Jiangsu province. To evaluate the effects of forced moves induced by demolition-led redevelopment, these outcomes are compared to those of voluntary moves. The evaluation is specifically concerned with dwelling attributes and location characteristics. Dwelling attributes consist of tenure and housing facilities, while commuting distance, distance to the city centre and the length of a child’s trip to school comprise the location characteristics. Logistic regression of data from a 2012–2013 survey shows that a voluntary relocation and the intention to move prior to notification of intended demolition are likely to result in positive outcomes. The migrants’ relocation strategy involves making a trade-off between better dwelling attributes and a better location. When housing improvement is their major concern, they tend to move to peripheral areas. However, it seems that children’s educational opportunities are being factored into the trade-off. In that case, migrants purchase an apartment in a specific school district or at least move closer to it. For the sake of their children, they relegate other motives to second place.     

The construction productivity debate and the measurement of service qualities

Since the 1960s, researchers have provided short-term and long-term explanations for low productivity growth in the construction industry. In retrospect, the main challenge appears to be the measurement of changes in heterogeneous input and output qualities. The aim here is to review earlier construction productivity research and to compare it with more recent approaches to quality measurement used when analysing services productivity, ultimately intending to provide guidance for using performance data from construction projects. Relying on the EU KLEMS database, industries with similar patterns of productivity growth are identified, primarily the business services industry. In services productivity analyses, the attempts to introduce output quality measures reflecting customer satisfaction are particularly interesting, as this creates a link to productivity effects on clients. A conclusion is that it should be possible to use the increasing volume of performance indicator data collected for construction project benchmarking for extending the range of output quality variables. However, resource constraints imply that it is infeasible to base industry productivity statistics on project level data reflecting customer satisfaction and customer productivity effects.     

Evaluation on Snow Infiltration into Heating Ventilation and Air Conditioning Intake： A Numerical Study

A HVAC （heating ventilating and air conditioning） system is generally designed to ventilate an indoor space. In windy and snowy climates dispersed snow particles in ambient air can enter the intake duct, potentially causing a serious problem. The study addresses the influence of suction volumetric flow rates, the potential discrepancy of snow intake based upon the wind direction in relation to the intake vent, and the possible difference in amounts of infiltrated snow particles in varying intake vent design and locations. The necessary characteristic quantities are defined. The simulation results show the rate of infiltration and the efficiency of the chosen intake designs. The magnitude and direction of wind influences snow infiltration significantly. The daily amount of infiltrated snow is introduced to be the characteristic measure of the infiltration in design of the HVAC systems.     

Quantifizierungen von Grundwassereintritten in städtische Abwassersysteme mittels stabiler Isotope

Infiltration of groundwater into sewer systems increases the costs for wastewater treatment plant operators. This study explores groundwater infiltration to urban sewer systems in the city of Nuremberg (Germany). Measurements of stable isotopes at the water works, storage tanks, groundwater, and the sewage network were carried out to define input end members for mass balance calculations. Only minor differences in oxygen stable isotopes (δ¹⁸O_H2O) were found between most sewer and drinking water samples which ranged around (??9.5?±?0.1) ‰. One exception was water from a water works at Genderkingen that is situated about 80 km south of Nuremberg. Here, drinking water from bank filtrate of the Lech River had more negative δ¹⁸O_H2O values of ??11.4?‰. This difference of 1.5?‰ revealed maximum possible groundwater contributions of 41?% by mass balance calculations. To obtain more accurate results, we suggest testing the use of deuterium-enriched water (D₂O) added to the sewer system.     

Integration and decentralization: the evolution of Dutch regional land policy

The implementation of planning objectives in the public interest depends on the land laws and land policies of a state. Public stakeholders are not only enabled or constrained in their actions by these laws and policies, they also (re)formulate these laws and policies to support their actions. The objective of this paper is to understand how different stakeholders in spatial development processes influence land policy dynamics (both the (re)formulation and the implementation of policies) and vice versa. The paper explores the changes in land policies in the Netherlands, in particular how changes have enabled the regional planning level. The Policy Arrangement Approach is used to analyse the strategic behaviour of agencies and their use of structure in spatial development processes. The findings show that the arrangement rapidly changed from the 1980s onwards, due to changes in the underlying political discourses and the effectuation of these discourses via regulation and instruments. With objectives of decentralization and integration, the national government has enabled the regional planning level to become more active in spatial development processes. Although the provinces were enabled by new laws and policies, this did not significantly change their role within the Dutch planning system.