Eye care – 20-20-20

During a recent visit to an optician, one of my friends was told of an
exercise for the eyes by a specialist doctor in the US that he termed as
20-20-20." It is apt for all of us, who spend long hours at our desks,
looking at the computer screen. I Thought I'd share it with you.
20-20-20
Step I:
After every 20 minutes of looking into the computer screen, turn your
head and try to look at any object placed at least 20 feet away. This
changes the focal length of your eyes, a must-do for the tired eyes.
Step II:
Try and blink your eyes for 20 times in succession, to moisten them.
Step III:
Time permitting of course, one should walk 20 paces after every 20
minutes of sitting in one particular posture. Helps blood circulation
for the entire body. Circulate among your friends if you care for them
and their eyes. They say that your eyes r mirror of your soul, so do
take care of them, they are priceless................

SDRAM page size

Page size refers to the minimum number of column locations that are on any row and
are accessed with a single ACTIVATE command. This is equal to the number of column
locations times the number of DQ on the device.

Page size = (2^col)*bus_width
where,
col = number of column address lines
bus_width = number of data(DQ) lines

Reflections on a transmission line

On a long straight line, waves can travel in both directions. Consider a
mechanical transmission line suspended vertically and hung from the
ceiling. Reflections is seen by setting off a pulse from the bottom of
the line. After a time equal to twice the transit time, the pulse
reflects from the ceiling and returns to your hand. This takes a few
seconds. The pulse has been reflected at the top because the line is
anchored there at zero displacement for all time. In an electronic
transmission line, this is equivalent to holding the voltage at zero for
all time by using a short circuit across the line. If you look at the
direction of displacement in the pulse, it reverses on reflection. Thus,
a wave of displacement to the right is returned as a wave of
displacement to the left. In an electronic transmission line, a square
pulse of 1 volt amplitude is returned as a square pulse of -1 volt
amplitude.

Relative Dielectric Constants

Material	Er
Air	1.0
PTFE/glass 2800	2.2
Rogers RO	2.9
CE/goreply	3.0
BT/goreply	3.3
GETEK	3.5
CE/glass	3.7
Silicon dioxide	3.9
BT/glass	4.0
Polymide/glass	4.1
FR-4/glass	4.1
Glass cloth	6.0
Alumina	9.0