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排序方式: 共有3031条查询结果,搜索用时 15 毫秒
1.
Spray quality is the critical factor which decides the efficacy of Small Quantity Lubrication (SQL) technology in a high specific energy involved machining process like grinding. Yet, the understanding about spray quality, the actual process mechanics and its effect on machining performance is inadequate. The present work is an attempt to establish a correlation between the spray input variables, quality of the spray and machining performance of SQL grinding through modelling and experiments. Using computational fluid dynamic techniques, the variation of droplet size, droplet velocity, number of droplets and heat transfer coefficient have been analysed at different input parameters and the computed trends have been verified and validated. CFD modelling of spray indicates that it is possible to produce aerosol medium with high heat dissipation ability at moderately high air pressure and low flow rate. It also shows that any increase in atomising air pressure favourably leads to notable increase in wetting area and also results in substantial enhancement in heat dissipation ability. Reduction of residual stress is thus remarkably good. On the other hand, grinding fluid flow rate, if increased, offers significantly better lubricity and reduces the grinding force which also reduces tensile residual stress. Short spell grinding test results are found to be in good agreement with CFD results. 相似文献
2.
Communication between organizations is formalized as process choreographies in daily business. While the correct ordering of exchanged messages can be modeled and enacted with current choreography techniques, no approach exists to describe and automate the exchange of data between processes in a choreography using messages. This paper describes an entirely model-driven approach for BPMN introducing a few concepts that suffice to model data retrieval, data transformation, message exchange, and correlation – four aspects of data exchange. For automation, this work utilizes a recent concept to enact data dependencies in internal processes. We present a modeling guideline to derive local process models from a given choreography; their operational semantics allows to correctly enact the entire choreography from the derived models only including the exchange of data. Targeting on successful interactions, we discuss means to ensure correct process choreography modeling. Finally, we implemented our approach by extending the camunda BPM platform with our approach and show its feasibility by realizing all service interaction patterns using only model-based concepts. 相似文献
3.
根据SQL Server的排序规则,在不改变查询表结构的条件下,探讨并研究了在SQL Server的数据库服务器端直接按汉字的拼音首字母对汉字进行快速检索的方法。 相似文献
4.
介绍了合肥市测绘设计研究院资料管理系统的数据结构组织及主要功能的实现,阐述了利用地理信息技术和大型数据库技术对档案资料进行科学、有序管理的思路和方法。 相似文献
5.
随着科学信息技术的发展,网站管理系统的应用越来越广泛。本文设计了高校体育运动场馆关系系统,以Microsoft Visual Studio2013为开发平台,应用SQL Server 2012数据库和.NET框架体系结构,对系统的整体结构进行设计,阐述了相应的功能模块功能,设计了数据建模,并对系统的功能进行了测试。 相似文献
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Theoretical models used in database research often have subtle differences with those occurring in practice. One particular mismatch that is usually neglected concerns the use of marked nulls to represent missing values in theoretical models of incompleteness, while in an SQL database these are all denoted by the same syntactic object. It is commonly argued that results obtained in the model with marked nulls carry over to SQL, because SQL nulls can be interpreted as Codd nulls, which are simply marked nulls that do not repeat. This argument, however, does not take into account that even simple queries may produce answers where distinct occurrences of do in fact denote the same unknown value. For such queries, interpreting SQL nulls as Codd nulls would incorrectly change the semantics of query answers. To use results about Codd nulls for real-life SQL queries, we need to understand which queries preserve the Codd interpretation of SQL nulls. We show, however, that the class of relational algebra queries preserving Codd interpretation is not recursively enumerable, which necessitates looking for sufficient conditions for such preservation. Those can be obtained by exploiting the information provided by NOT NULL constraints on the database schema. We devise mild syntactic restrictions on queries that guarantee preservation, do not limit the full expressiveness of queries on databases without nulls, and can be checked efficiently. 相似文献
9.
Manish Mukhopadhyay 《Materials and Manufacturing Processes》2019,34(10):1151-1159
Conventional metalworking fluids carry an acute threat to the environment as these produce a hazardous ambiance. Furthermore, due to their excessive use and imprudent disposal, the risk of environmental pollution exaggerates. The present article is aimed at finding some alternative potential coolants to be applied in small quantity lubrication (SQL) mode for grinding of difficult-to-machine (DTM) material, titanium alloys, which could effectively replace the conventional metalworking fluids while ensuring minimal waste of the coolant. Three unconventional environmentally safe coolants viz. alkaline soap water, sodium nitrite, and propylene glycol are applied in SQL mode while grinding Ti-6Al-4V. Comparative performance analyses of these cutting fluids have been adjudicated, considering responses of force required for material removal, substrate roughness, grinding ratio, and SEM micrographs of chips and ground surface. The results reveal that the environment-friendly unconventional fluids perform better than the conventional Blasocut fluid and the most satisfactory operations are observed under propylene glycol environment on the basis of the relevant parameters and operating range considered herein. 相似文献
10.
随着信息化的深入,大数据在各个领域产生了巨大的价值,海量数据的存储和快速分析成为新的挑战。传统的关系型数据库由于性能、扩展性的不足以及价格昂贵等方面的缺点,难以满足大数据的存储和分析需求。Spark SQL是基于大数据处理框架Spark的数据分析工具,目前已支持TPC-DS基准,成为大数据背景下传统数据仓库的替代解决方案。全文检索作为一种文本搜索的有效方式,能够与一般的查询操作结合使用,提供更加丰富的查询和分析操作。目前,Spark SQL仅支持简单的查询操作,不支持全文检索。为了满足传统业务迁移和现有业务的使用需求,提出了分布式全文检索框架,涵盖了SQL文法、SQL翻译转换框架、全文检索并行化、检索优化4个模块,并在Spark SQL上进行了实现。实验结果表明相比于传统的数据库,在两种检索优化策略下,该框架的索引构建时间、查询时间分别减少到传统数据库的0.6%/0.5%和1%/10%,索引存储量减少为传统数据库的55.0%。 相似文献