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To increase the density, the grain size in the recording medium must be less than ~5 nm to obtain a sufficient signal-to-noise ratio.
However, the magnetic domain can be switched and destroyed by random thermal fluctuations with this grain size.
The size at which the magnetic state of a grain is no longer thermally stable is the so-called superparamagnetic limit [1].
Different designs leading to different in manufacturing processes, number of process steps and technologies consequently affect to the fabrication cost.
There are number of research groups use an optical fiber to deliver laser light to the working point.

Wheatley 3,c 1 Department of Civil Engineering, Bayero University, Kano, PMB 3011 Kano, Nigeria 2,3 Department of Civil & Building Engineering, Loughborough University, Loughborough LE11 3TU, United Kingdom, aayfatah@yahoo.com (corresponding), bA.El-Hamalawi@lboro.ac.uk, cA.D.Wheatley@lboro.ac.uk Keywords: Particle size distribution (PSD), Trace metals, Water quality determinants, Column experiment Abstract Two different size-grained soils were subjected to column experiments with a hydraulic loading representing two years' rainfall.
Methodology The aim of this test was to compare the extractable trace metals from two different size-grained soils.
An acid washed glass column of 58 mm diameter and 1.19 m length was set up, firstly with a sample from Loughborough with a grain size range of 0.004 to 0.4 mm silt-sand and secondly with the other sample from a University of Lancaster test site with a grain size range of 0.028 to 0.8 mm sand.
The first temperature reading was 18.7 O C and this reading decreased gradually to 18.2 O C at flush number 5.
Conclusions The following conclusions were drawn from this study: • The results of this study indicate that the Lanca soil with the bigger grain sizes leached out more Iron, Manganese and Silicon concentrations.

However, a small number of gas pores with an average size less than 2 μm retains.
Under crack propagation the grain interiors are undergone by considerable plastic deformation producing slip-plane displacement at the surface of the dimple, which could be recognized as serpentine glide (Fig.4b) [4].
However, sudden nucleation of numerous microcracks on the grain boundary particles under high YS decreases ductility.
Decreasing the maximum stress increases the number of microcracks, which start to propagate from shrinkage voids in ductile-brittle (Fig.5b).
The grain boundary precipitations of Al9FeNi-phase deteriorate plasticity and fatigue resistance of the novel high-strength aluminum alloy.

Relatively high mechanical strength and simultaneously good plasticity of a crystalline material are determined by the state of its internal structure, preferably nano- or ultra-fine grained one.
By the ECAP method, a relatively large material ingot with ultra-fine grains used in manufacturing some structural elements can be produced [2].
The mean diameter of the grain was estimated at ca. 25µm.
The described tendency of both kinds of slip planes to participate in the deformation mechanism disappears with the increasing number of passes and the development of texture reflects the noticed changes in the spatial arrangement of AZ31 microstructure during the application of the ECAP process (see Fig. 2).
The same microstructure of the AZ31 rods becomes more fine-grained.

However, a limited number of articles on the mechanical properties and deformation behavior of GH984G are available [7-10].
The grain size is in the range of 20~110μm and the average size was about 60μm.
The M23C6 carbide on grain boundary is rich in Cr.
Observation of fracture surfaces of specimens fractured at room temperature (Fig.5a) indicates a large number of grain boundary cracks, there are only some fine dimples present on the fracture surfaces.
At 700℃ (Fig.5b), grain boundary cracks are seen in the microstructure.

V=0.866a2c (3) Theoretical X-ray density of the samples is calculated by using the XRD data with the help of following relation [12]: ρx=n MwNaV (4) Where n is the number of atoms per unit cell, Mw is the molecular weight calculated from composition, V is the volume of the unit cell and Na is Avogadro's number.
The increase in tangent loss at low frequency domain is due to more time is offered for the movement of electron inside the grain at lower frequency hence the conduction of free electron increases because charge present in grains acts as a conductive medium [15].
According to these theories, Ferrites consists of two layers one is conducting layer comprising of conducting grains while other is poorly or non-conducting layer composed of non-conducting grain boundaries.
Koop suggested that grain and grain boundary effect dominates at higher and lower frequencies, respectively.
So, at low frequencies the conductivity decreases due to nonconductive grain boundaries effect dominated while at higher frequencies AC conductivity remain constant due to dominating effect of conducting grains.

FSW also is used successfully for industrial applications such as [5,6], automotive industry[7] and for a number of general applications[8].
The map approximately dominated by <100> (red) grain orientations with some <110> (green) grain orientation and just few of <111> (blue) grain orientation.
From PF number 10 to 13 from the right to the left are dominated by off axis simple shear texture in the probe shear configuration i.e., this part is probe dominated.
In terms of grain orientations the map shows approximalty random grain orientation across the NG.
The grain structure is almost random with an alternating weak bands of near <111> (blue/purple) and <110> (green)/<100>(red) grain orientation across the whole NG.

Grinding is a material removal processing method based on the abrasive grains on the surface of grinding wheel.
In the process of grinding, there are mechanical, physical and chemical effects between the abrasive grains and bond of grinding wheel and workpiece surface, which make the abrasive grains and bond rupture, fall off, and lead to grinding wheel wear as well as a decrease in cutting force.
The abrasion wear of the grinding wheel is due to the slippage between workpiece surface and abrasive grains, and the chemical reaction and plastic deformation effect of the abrasive grains, which makes abrasive grains become dull gradually, and generates small wear formed plane on the abrasive grains.
Fracture wear divides into grains fracture and bond fracture, which depends on the grinding force and the strength of the bond.
Besides, the grinding wheel wear pattern can be identified precisely by quantitatively evaluating the actual wear of single abrasive grain.

When the magnesium alloy workpiece feed speed increases, because the cutting blade of the abrasive belt grains is under big negative former angle in the grinding magnesium alloy process, with the grinding depth increasing, the normal force on the cutting blade of abrasive grains also increases, consequently induces the average cutting deformation coefficient to decrease, this will reduce the augmenting trend of the grinding force with the workpiece feed speed increase [4].
During the abrasive grain granularity increases, the number of abrasive belt grains contacting magnesium alloy also increases, because high granularity abrasive belt having less containing scrap space, being easy to be choked, thereby makes the grinding force increase.
But the magnesium alloy material itself has a high specific strength, during its grinding process, with the removing rate of the material increasing, the augmenting trend of the grinding force is very prominent no matter what with increasing the grinding depth ,the feed speed or the abrasive grains granularity [5].
The reason is that with the belt speed Vs raising, the temperature at the grinding area will be increasing, and the average friction coefficient on the cutting blade of abrasive grain and the deformation coefficient ξwill be reducing.
At the same time, the originally magnesium alloy will lower strength further reduces under grinding temperature, and the deformation of magnesium alloy grains on the shear plane will become more easy.

A number of low-cost titanium alloys were developed in past two decades.
Microstructure of both alloys is consisted of Widmanstatten α/β colonies with alternate α and β lamellae inside prior β grains.
However, both of the prior β grain sizes are larger then 100μm, in that the cooling rate is too slow during ingot melting process, therefore β grain grows sufficient.
It can be seen that the Widmanstatten α/β colonies with lamellae structure were deformed to equiaxed grains in the Ti-3Fe-5Al alloy, while deformed to fine lamellae structure mixed with equiaxed grains in Ti-5Fe-3Al alloy after multiple hot forging process.
Compared to as-cast structure, the grain size of as-forged states was refined and the original β grain boundaries are disappeared.