Design of modular fixtures using a 3D-modelling approach

The need for improved productivity and reduced time to market has been increased significantly in manufacturing processes in recent decades. There are many factors that play a role in providing manufacturing processes with more productivity. One is the use of modular fixtures (MFs). MFs have brought many benefits to manufacturing industries including reduced costs and times of production. An MF can be defined as a complete system that consist different elements for effectively and securely holding the workpiece in place for performing various machining operations. Generally an MF is made by assembling a number of fixture elements in a feasible sequence that is properly determined. Traditionally, the most common method of determination of fixture elements and assembly sequences are making use of 2D drawings and physical models. Obviously these are not efficient methods in the world of advanced manufacturing technologies and there is a vital need for developing more efficient methods. A solution to this is developing a CAD-based 3D-modelling and simulation system to determine the types and of feature elements and the sequence of assembly. Such a system can help fixture designers find the proper MF designs by defining the relationships between fixture elements and workpieces. Designing MFs and fixture elements is a very complex and time-consuming task even by making use of CAD software. A methodology has been developed to simplify this task by determining fixture elements and assembly sequences in a 3D-modelling environment. A fixture elements database is established and the fixture elements are divided into different categories depending on geometries and functions. Currently, MF systems can be constructed from standard MF elements. These elements are pre-manufactured components that include base-plates, clamps, and locators; and they can be re-used after disassembly. These can later be used for other workpieces within a specified range of sizes and shapes. In order to use these elements effectively, the CAD environment is exploited with developing a database which contains 3D models of standard MF elements. For most workpieces standard MF elements can be extracted directly from the developed database. However, for some workpieces with non-conventional geometries or shapes customised fixture elements should be designed in a 3D CAD environment. A modelling approach is used to find the appropriate MF design that suits the machining processes in need. To do so many parameters are taken into consideration including the number of workpieces to be machined; type of machining operation; locating method; clamping mechanism; and so on. The methodology developed for MF design has been implemented in a 3D modelling environment by making use of a powerful 3D modelling software, SolidWorks. It makes use of a database which contains 3D models for standard fixture elements. This database is divided into three main categories and each category is divided into different sub-categories depending on the type and function of the MF elements. SolidWorks software provides an excellent 3D environment that can be utilised to model fixture elements and determine assembly processes. This is accomplished by applying mating relationships after considering workpiece setup and fixture elements to achieve the optimum MF assembly design. This paper explains the methodology developed for semi-automated MF design. A case study has been presented to show the validity of the methodology proposed

Heavy metal concentrations in the selected tissues of the Persian sturgeon, Acipenser persicus, from the southern coast of the Caspian Sea

Bioaccumulation of heavy metals including Cd, Pb, Cu and Zn in muscle, gill, liver, kidney and stomach in Acipenser persicus was studied. Fish were collected from the ‘Iranian fishery zone 1’ located between Astara and Kiyahshahr. Samples (n=25) were collected from five stations in the study area during the autumn catch season in 2001. Samples were analyzed by wet digestion with hydrogen peroxide and nitric acid. Analyses were testified using spike method. A sample of bovine liver (CRM 185R) was tested to ascertain reliability of analyses. Digested samples were analyzed using Flame Atomic Absorption Spectrophotometer. The bioaccumulation pattern for Zn in different tissues studied was stomach>liver> kidney> gills>muscle tissue. The mean concentration of Zn in the stomach was 136.6±10.70μg g-1 dry weight. Cu with the maximum concentration of 39.71±8.85μg g-1 dry weight in liver showed a bioaccumulation pattern of liver>kidney>stomach>gills>muscle tissue. The bioaccumulation pattern for Pb was determined as gills>liver> kidney>stomach>muscle tissue. Maximum mean concentrations of Pb 6.87±2.25μg g-1 dry weight belonged to gills. Bioaccumulation pattern for Cd in the different organs studied in A. persicus was kidney>liver>gills>stomach> muscle tissue. Maximum mean concentration of 5.1±0.97μg g-1 dry weight belonged to kidneys and the minimum mean concentration of 0.05±0.007μg g-1 dry weight belonged to muscle tissue. Concentration of the metals in the muscles samples were below the most guidelines for human consumption. Concentrations for heavy metals were lower than the guidelines in some organs and were higher than that in the other organs studied. The observed concentrations do not pose health problems as these organs are not used for human consumption

Prirodna hrana acipenser persicus gajenog u ribnjačkim jezerima

A study on live food in Acipenser persicus rearing ponds was carried out In four rearing ponds; two in the Shahid Beheshti hatchery and two ponds in the Yousefpour hatchery. Samples were collected from three points in each pond on a weekly basis. Samples were collected using plankton nets (mesh size 50 µm), Ruthner sampler and Ekman grab. Zooplankton and benthic samples were fixed in 4 % formalin solution for later analysis. Zooplankton species identified in water samples collected at all four ponds belonged mainly to two phyla; Arthropoda and Rotifera. Total abundance of zooplankton species was estimated 87576 individuals L-1 in the Yousefpour hatchery and 136626 individuals L-1 in the Shahid Beheshti hatchery. Insect larvae, oligochaeta worms and mollusks were found in the sediment samples collected from the Yousefpour hatchery while sediment samples collected from the Shahid Beheshti hatchery contained only insect larvae and oligochaeta worms. The total abundance of benthic organisms was 0.343 g m-2 in the Yousefpour hatchery and 1.28 g m-2 in the Shahid Beheshti hatchery. Condition factor in fishes ranged from 0.29-0.54 in the Yousefpour hatchery and from 0.30-0.47 in the Shahid Beheshti hatchery

Evolution and Sedimentary History of the Cape Bojador Continental Margin, Northwestern Africa

The Cape Bojador region of the northwestern African continental margin is apparently an unusual passive margin setting. Climatic fluctuations, local volcanism, and possibly tectonics have played important roles in the sedimentary record in this region. A transect of drilling sites connected by seismic profiles is available from the coastal Aaiun Basin (CORC 15-1), across the shelf (Spansah 51A-1), on the continental slope (DSDP Site 369), the upper continental rise (DSDP Site 397), farther out on the rise (e.g., DSDP Sites 139 and 140), and the abyssal plain (DSDP Sites 137 and 138). These data allow construction of a profile perpendicular to the margin, and reconstruction of the sedimentary evolution there

Decadal changes of the Western Arabian sea ecosystem

Historical data from oceanographic expeditions and remotely sensed data on outgoing longwave radiation, temperature, wind speed and ocean color in the western Arabian Sea (1950–2010) were used to investigate decadal trends in the physical and biochemical properties of the upper 300 m. 72 % of the 29,043 vertical profiles retrieved originated from USA and UK expeditions. Increasing outgoing longwave radiation, surface air temperatures and sea surface temperature were identified on decadal timescales. These were well correlated with decreasing wind speeds associated with a reduced Siberian High atmospheric anomaly. Shoaling of the oxycline and nitracline was observed as well as acidification of the upper 300 m. These physical and chemical changes were accompanied by declining chlorophyll-a concentrations, vertical macrofaunal habitat compression, declining sardine landings and an increase of fish kill incidents along the Omani coast

Comparison of plankton and benthic organisms diversity and density in sturgeon hatcheries and assessing their effects on condition factor in sturgeon fingerlings

Phytoplankton and benthic organisms diversity and density were studied in six sturgeon rearing ponds in the Yousefpour and Shahid Beheshti hatcheries from 22 April to 1 July 2001. We used Ruttner sampler, plankton net with a mesh size of 50 microns and Ekman grab to sample the organisms on a weekly basis and fixed the samples in formalin solution 4% and then identified 22 genera of phytoplanktons for the three ponds in the Yousefpour hatchery and another 21 genera for the three ponds in the Shahid Beheshti hatchery. Planktons from the phyra Chlorophyta, Cyanophyta, Chrysophyta, Cryptophyta and Euglenophyta were present in the ponds. Schroederia sp. of the phyla Chlorophyta was the dominant species identified. We observed 2 x 106 and 1 x 106 cells of phytoplanktons per milliliter of pond water in the Yousefpour and Shahid Beheshti hatcheries respectively. The zooplankton phyla Arthropoda and Rotifera were represented with 9 genera in the two hatcheries showing a density of 36937 and 46603 zooplanktons per liter of water in the Yousefpour and Shahid Beheshti hatcheries respectively. Insect larvae and oligochaeta worms were the benthic organisms common to both hatcheries and mollusks were present only in the Yousefpour hatchery. The average benthic biomass was 1.58±0.19 and 2.16±0.75 g/m2 in the Yousefpour and Shahid Beheshti hatcheries respectively. The condition factor in sturgeon fingerlings of the Yousefpour hatchery varied from 0.294 to 0.554 while that of sturgeon fingerlings of the Shahid Beheshti hatchery were 0.297 to 0.6

Cold hardening protects cereals from oxidative stress and necrotrophic fungal pathogenesis

The effects of cold hardening of cereals on their cross-tolerance to treatments leading to oxidative stress were investigated. Long-term exposure to low non-freezing temperatures provided partial protection to wheat and barley plants from the damage caused by paraquat and hydrogen peroxide treatments. It also conferred resistance in two barley cultivars to the necrotic symptoms and growth of the fungal phytopathogen Pyrenophora teres f. teres . Pathogen-induced oxidative burst was also reduced in cold hardened plants. The possible roles of host-derived redox factors and other signaling components in the observed forms of cereal cross-tolerance are discussed

Accreting Neutron Stars in Low-Mass X-Ray Binary Systems

Using the Rossi X-ray Timing Explorer (RossiXTE), astronomers have discovered that disk-accreting neutron stars with weak magnetic fields produce three distinct types of high-frequency X-ray oscillations. These oscillations are powered by release of the binding energy of matter falling into the strong gravitational field of the star or by the sudden nuclear burning of matter that has accumulated in the outermost layers of the star. The frequencies of the oscillations reflect the orbital frequencies of gas deep in the gravitational field of the star and/or the spin frequency of the star. These oscillations can therefore be used to explore fundamental physics, such as strong-field gravity and the properties of matter under extreme conditions, and important astrophysical questions, such as the formation and evolution of millisecond pulsars. Observations using RossiXTE have shown that some two dozen neutron stars in low-mass X-ray binary systems have the spin rates and magnetic fields required to become millisecond radio-emitting pulsars when accretion ceases, but that few have spin rates above about 600 Hz. The properties of these stars show that the paucity of spin rates greater than 600 Hz is due in part to the magnetic braking component of the accretion torque and to the limited amount of angular momentum that can be accreted in such systems. Further study will show whether braking by gravitational radiation is also a factor. Analysis of the kilohertz oscillations has provided the first evidence for the existence of the innermost stable circular orbit around dense relativistic stars that is predicted by strong-field general relativity. It has also greatly narrowed the possible descriptions of ultradense matter.Comment: 22 pages, 7 figures, updated list of sources and references, to appear in "Short-period Binary Stars: Observation, Analyses, and Results", eds. E.F. Milone, D.A. Leahy, and D. Hobill (Dordrecht: Springer, http://www.springerlink.com