The effect of strain and temperature on the critical current density of high-field superconductors

A J(B,ϵ) probe has been designed and built to measure the critical current density, J(_c), versus strain on short superconducting wires and tapes. Measurements can be made from 2K to 4.2K in high magnetic fields in our 17T magnet system and at 77K for strains up to ±1.0%.The effect of strain on J(_c) has been measured on a 0.37mm diameter Nb(_3)Sn wire at 4.2K and 2.9K from l0T up to 14T. The compressive pre-strain of the wire measured at 4.2K is found to be about 0.3%. At 4.2K, the value of B(_c2) maximum is 19.6T and at 2.9K is 21.2T. The functional form of the flux pinning of the sample at 4.2K can be expressed as F(_p)=4.20±0.57xl0(^8)[B(_c2)(ϵ)](^1.67±0.7b(^1/2)(l-b)(^2); and for the sample at 2.9K it is F(_p)=1.37±0.05xl0(^10)[B(_c2)(ϵ)](^0.54±0.16b(^1/2)(l-b)(^2). From temperature scaling, the functional form is F(_p)=3.63 ±0.62xl0(^8)[B(_c2)(T)](^1.72±1.3)b(^1/2)(l-b)(^2). The difference in the values of n between strain scaling and temperature scaling shows that n only parameterises the change in J(_c) with change in strain or temperature. The effect of strain on J(_c) has been measured on five short sections of an Ag-sheathed BSCCO(2223) tape at 4.2K and in magnetic fields up to 12T. J(_c) degradation starts to occur between 0.18%-0.25% strain. The appearance of secondary peaks in the critical current distribution is attributed to inter-grain J(_c) and infra-grain J(_c). J(_c) measurements have been made on bulk PbMo(_6)S(_8)(PMS) samples. J(_c) increased by a factor of «7 when the sample was hot isostatically pressed(HIP). Measurements have also been made on series of HIP'ed gadolinium(Gd) doped Pbi(_1-x)Gd(_x)Mo(_6)S(_8) samples. The highest T(_c) value is 14.55K when x=0.1. The highest J(_c) is when x=0.2. The irreversibility field B(_irr)(0) from J(_c) measurements has been calculated to be 53.9T, 45.5T, 34.IT and 33.5T for the x=0, 0.1,0.2 and 0.3 samples, respectively

Flexible Data Refreshing Architecture for Health Information System Integration

Background: Having a consistent and unified view of heterogeneous distributed medical information sources is an inevitable need of health informatics. Integrating medical information of patients or about a disease, a treatment or side effects of a drug, etc, is very useful to help medical education, to achieve medical research goals and to provide the computer- based decision support systems. Contribution: This article proposes a flexible incremental update method for the materialized part of the integration system. It permits us to manage the integration system according to the characteristics of the data sources which can change. Method: This paper presents a hybrid data integration approach in which the materialized part of the system in mediator is the object indexation structure based on an instance classification of the sources objects which correspond to the global schema. The object identifier of each object in the indexation structure is materialized together with the attributes which are needed for the incremental updating of this indexation (classifying attributes). Results: The main idea of this paper is to develop a hybrid data integration framework, which represents a new aspect of a hybrid method focusing on flexible data refreshing. Conclusion: This hybrid approach implements a vertical hybrid approach. It means that at the mediator level, some data of each object are materialized and others are virtual

A Case of Vibro Compaction Vibration Monitoring in a Reclaimed Site

Vibro Compaction is a ground improvement technique in which the soil is compacted using waves generated from an equipment called a vibroflot. As the vibration magnitude is less than some other vibratory ground improvement methods this technique is sometimes preferred when the improvement zone is relatively close to existing structures and facilities. Unfortunately, not much can be found in literature on peak particle velocity (PPV) that is generated by this method. This paper reports and interprets vibration monitoring of a Vibro Compaction project that was recently performed on about 13 m of hydraulically placed sand in Palm Jumeira, Dubai. PPV was measured at different distances from the vibroflot. The depth of the vibroflot was also varied to provide a better understanding of the critical depth that creates the largest PPV. A formula is also presented to estimate Vibro Compaction generated PPV during planning stage

The Application of Dynamic Compaction to HFO Tanks

Three heavy fuel oil (HFO) tanks with diameters of up to 60 m, a pump station, a pump shed station and a vent stack station have recently been constructed as part of the HFO Tank Farm in Ras Laffan, Qatar. The project was located in an area near the sea with high groundwater level. The ground was composed of 11 to 12 m of silty sand and gravel with cobbles and boulders with diameters up to 300mm followed by limestone. The preliminary soil investigation using Standard Penetration Test (SPT) indicated that while the soil was generally dense, but a loose layer of sand was identified and soil improvement was stipulated. During later stages, a supplementary geotechnical investigation using the Menard Pressuremeter Test (PMT) indicated that the high SPT blow counts were not representative of the actual ground conditions and that due to the presence of the large cobbles the soil had erroneously been represented as dense. In fact, the soil was loose from the surface down to bedrock. Dynamic Compaction was used to improve the soil's strength and to reduce its compressibility. PMT in conjunction with finite element analysis were used to verify the ground condition after ground treatment

A Combined Material and Structural Approach to Fatigue Failure Analysis of Bolted Thick Composite Laminates

Most of the existing works on fatigue of long fiber composite laminates approach the problem from the material point of view. These works have also been mainly on thin laminates. This is because the laminates (particularly unidirectional laminates) are considered to be homogeneous and uniform. This may or may not be true because of the heterogeneous nature of the composite (consisting of fibers and matrix and interface), and the significant variability which gives rise to random spatial variation in the properties. A composite laminate is actually both a structure and a material. For thin laminates, the structural aspect is usually scanned over and only the material aspect is focused on. This gives rise to the expectation that the laminate should behave as a material (with good homogeneity and with little variability). This has resulted in failure of many failure criteria. The importance of the structural aspect is more evident for the case of thick laminates, subjected to flexural loading while being constrained by bolts. To study the fatigue behavior of such materials (and structures), both the structural aspects and the material aspects must be taken into consideration. This is the subject of study of the present research. A combined material and structural approach, namely, the application of coupon level material properties (material level) into the 3D finite element model (structural level) is introduced and applied. By doing this, it examines the behavior of thick unidirectional glass/epoxy laminates subjected to flexural loads while being constrained by bolts. Both theoretical and experimental studies are carried out to validate each other. The theoretical part consists first of structural analysis which provides the locations of potential failure. This is followed by the application of fatigue failure criteria at these locations. Good correspondence is seen between the experimental and the theoretical results. The agreement between the results of experiments with those of developed fatigue progressive damage modeling (FPDM) shows that the combined material and structural approach is suitable to study the fatigue behavior of thick composite laminates subjected to bolt loads

Application of Dynamic Replacement in a Steel Pipe Factory

Prior to the construction of Al Jazira Steel Pipe Factory (AJSPF), almost all buildings in the Industrial City of Abu Dhabi were constructed on piles. This was due to the presence of compressible layers of soil, especially a superficial layer composed of one to four metres of soft sandy silts and clays. To the knowledge of the authors AJSPF is the first project in this area that has been built without the implementation of any piles and founded on shallow foundations improved by Dynamic Replacement. Variations of loading conditions and design criteria has made this pioneer project of special interest. While classical Dynamic Replacement was used for some ground slabs, pre-excavated Dynamic Replacement was applied under single footings and heavily loaded storage areas. As a cost saving method, sand from local Abu Dhabi excavations was used as granular material in lieu of the more commonly used crushed stone. Pressuremeter Tests (PMT) and finite element analysis was able to demonstrate that acceptance was achieved

Dynamic Compaction Vibration Monitoring in a Saturated Site

Dynamic Compaction is a well established ground improvement technique in which a heavy pounder is dropped from a significant height to improve the soil’s mechanical properties. The pounder impact creates waves that compact the soil; however these waves may also be a nuisance to and damage neighbouring structures and facilities. Peak particle velocity (PPV) has been identified as the most suitable parameter for assessing vibration associated risks. Previous researchers have proposed a number different equations for predicting PPV. Dynamic Compaction has recently been used for soil improvement in Oman’s Blue City Project. Particle velocities and vibration frequencies in three directions have been monitored at several distances during the different phases of ground treatment. In all phases PPV has been recorded to be in the radial direction. It has been observed that although it appears that vibration frequency is not influenced by the deep compaction phase, does increase with the progression of work and application of later phases of Dynamic Compaction. This increase is more pronounced at farther distances, but becomes negligible when impact point is closer than a critical distance

The Effectiveness of Vibration Reduction Trenches in a Dynamic Replacement Project

Umm Al Quwain Marina Phase I Project is located in northern United Arab Emirates. The site is located in an area where the ground consists of 6 to 7 m of very loose heterogeneous saturated silt and silty sand. More than 86,000 m2 of the site has been treated using dynamic replacement. Due to the presence of existing structures in the vicinity of the ground improvement works vibration monitoring and control was implemented. In this paper, initially previous studies on dynamic compaction vibration will be reviewed, then the two cases of vibration monitoring programme for UAQ Marina will be described. First, particle velocities and their associated frequencies were measured at different distances from the pounder’s impact point when no specific measures were implemented. Next, a vibration reduction trench was excavated and the vibration parameters recorded again. The interpretation of the results indicates that the vibration reduction trench has been able to efficiently reduce peak particle velocities to about one half the values when the trench was not installed. This study demonstrates that simple methods such as constructing vibration reduction trenches can be an effective way for controlling vibration damage when existing structures are nearby

The Application of Dynamic Compaction on Marjan Island

Marjan Island is 2.7 million m2 of development located 27 km southwest of Ras Al Khaimah in the United Arab Emirates. This project has been reclaimed from the Persian Gulf by tipping sand into the sea. Geotechnical investigations indicated that the upper 7 m of ground was composed of very loose to medium dense silty sand interbedded with layers of boulders at different depths. SPT blow counts were recorded to be as low as 4 and Menard Pressuremeter Test (PMT) limit pressure was as low as 70 kPa. Fines content was from 13 to 30%. Preliminary calculations suggested that the in-situ ground conditions could not satisfy the island’s main road’s settlement criteria and that ground improvement was required. Thus, 198,000 m2 of the reclamation was treatment by Dynamic Compaction. Pounders weighing up to 20 tons were dropped from 20 m to compact the loose soil. 32 PMT were carried out after ground improvement to verify the achievements. These tests were able to demonstrate that acceptance criteria was readily achieved and that on average the soil’s modulus of deformation increased by more than 400%