Spinning at Low Speeds

At low spinning speeds, usually 1000-2000 m/min, stress-induced crystallization is absent. Although an increasing level of spinning stress promotes polymer chain orientation, low spinning speeds do not have any significant effect on crystallization. 

Throughput also has a significant effect on the temperature, stress, and velocity gradient profiles. With higher throughput, the value of the maximum velocity gradient decreases, and it occurs at a distance farther away from the spinneret. 

Very low-speed melt spinning of PL A produces fibers that are essentially amorphous and can be drawn up to 10 times to form mechanically strong fibers with tensile strength of 870 MPa and modulus of 9.2 GPa [12]. 

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Spin at low speed (approximately 1,000-2,000g) for 5 min at room temperature to peUet cells. 

If embryos are to be fixed, e.g., for in situ hybridization, the embryo cultures may need to be concentrated prior to fixation. Pour cultures into 15-mL centrifuge tubes, spin at low speed (2000g) for 5 min, and dispose of all except the bottom 1 mL of water. The embryos in 1 mL seawater are then transferred to a microfuge tnbe and concentrated fnrther by centrifngation at 6000g. 

The ground homogenate should be centrifuged at low speed (2500 rpm) for 5 min in a swinging-bucket rotor at 4°. The resulting pellet is discarded. Repetition of this low-speed spin (2500 rpm) 3 to 5 times ensures that most cellular contaminants and nuclei are pelleted and eliminated. Because the low-speed pellets contain nuclei, it is sometimes desirable to save these pellets for nuclear DNA preparations. 

Place 0.2-pm filters into 0.5-mL centrifuge tubes. Load with 50 pL of sample. Spin sample through the filters at low speed ( 2000 rpm). 

The vertical or pendulum perforate basket (Fig. 8) is perhaps the most commonly used centrifuge. The perforated basket in its simplest form is lined with a cloth, wire mesh, or a bag that accumulates solids as the liquid passes through. When the solid space is filled, feeding is discontinued and the relevant portion of the batch cycle is continued. In smaller units, the bowl may simply spin down to a complete stop for manual removal of the cake or replacement of the bag. At higher G-levels or in larger diameter units, wire mesh or screen is added to support the filter media. Slowing the unit and plowing the solids out at low speed complete the batch cycle. Rinse can be isolated... 

Wash the immobilized RNA on the column by adding 600pL of lx low-salt wash buffer followed by spinning at maximum speed (12,000g) for 30 sec. Transfer the spin cup to a fresh tube aud spiu for a further 2 min to make sure that column is adequately dry prior to step 10. 

Spin protein-bound beads at low speed (420 x or 2,000 rpm in an Eppendorf microcentrifuge) for 1 min at room temperature. Discard supernatant, which contains unbound proteins. 

Spin the tubes briefly at low speed to ensure the beads are at the bottom of the tubes. 

Polypropylene crystallizes fast, always in the spin-line, even at low speeds. 

A similar method of test was used at the International Nickel Company s Corrosion Laboratory at North Carolina. The specimen discs are mounted on insulated vertical spindles and submerged in sea-water, which is supplied continuously to the tank in which the specimens are immersed. The maximum peripheral speed of the spinning disc is about 760cms , and the characteristic pattern of attack is shown in Fig. 19.3a. Studies of variation of depth of attack with velocity indicate that at low velocities (up to about 450 cm s ) alloys such as Admiralty brass, Cu-lONi and cupro-nickel alloys containing iron maintain their protective film with a consequent small and similar depth of attack for the diflferent alloys. At higher velocities the rate increases due to breakdown of the film. 

At low rotation rates, less than the chemical shifts anisotropy, however, the powder spectra contained disturbing side bands dispersed among the isotropic chemical shifts. In order to discriminate between sidebands and isotropic resonances two spectra obtained at different spinning speeds were multiplied together or the differentiation was made by visual inspection. 

Crush 250 g of deeply frozen porcine left ventricle and thaw in 900 ml of Soln. A. Homogenize the tissue using a Warring blender (low speed) for 20 s. Spin the homogenate in a Sorval GS-3 rotor or Beckman-Coulter JA-10 rotor at 3000 x g (4500 rpm) for 15 min. 

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