مقاله مقاله انگلیسی درباره پاکستان

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تعداد صفحات: 8

EDUCATION

Pakistan Table of Contents

At independence, Pakistan had a poorly educated population and few schools or universities. Although the education system has expanded greatly since then, debate continues about the curriculum, and, except in a few elite institutions, quality remained a crucial concern of educators in the early 1990s.

Adult literacy is low, but improving. In 1992 more than 36 percent of adults over fifteen were literate, compared with 21 percent in 1970. The rate of improvement is highlighted by the 50 percent literacy achieved among those aged fifteen to nineteen in 1990. School enrollment also increased, from 19 percent of those aged six to twenty-three in 1980 to 24 percent in 1990. However, by 1992 the population over twenty-five had a mean of only 1.9 years of schooling. This fact explains the minimal criteria for being considered literate: having the ability to both read and write (with understanding) a short, simple statement on everyday life.

Relatively limited resources have been allocated to education, although there has been improvement in recent decades. In 1960 public expenditure on education was only 1.1 percent of the gross national product (GNP); by 1990 the figure had risen to 3.4 percent. This amount compared poorly with the 33.9 percent being spent on defense in 1993. In 1990 Pakistan was tied for fourth place in the world in its ratio of military expenditures to health and education expenditures. Although the government enlisted the assistance of various international donors in the education efforts outlined in its Seventh Five-Year Plan (1988-93), the results did not measure up to expectations.

Structure of the System

Education is organized into five levels: primary (grades one through five); middle (grades six through eight); high (grades nine and ten, culminating in matriculation); intermediate (grades eleven and twelve, leading to an F.A. diploma in arts or F.S. science; and university programs leading to undergraduate and advanced degrees. Preparatory classes (kachi, or nursery) were formally incorporated into the system in 1988 with the Seventh Five-Year Plan.

Academic and technical education institutions are the responsibility of the federal Ministry of Education, which coordinates instruction through the intermediate level. Above that level, a designated university in each province is responsible for coordination of instruction and examinations. In certain cases, a different ministry may oversee specialized programs. Universities enjoy limited autonomy; their finances are overseen by a University Grants Commission, as in Britain.

Teacher-training workshops are overseen by the respective provincial education ministries in order to improve teaching skills. However, incentives are severely lacking, and, perhaps because of the shortage of financial support to education, few teachers participate. Rates of absenteeism among teachers are high in general, inducing support for community-coordinated efforts promoted in the Eighth Five-Year Plan (1993-98).

In 1991 there were 87,545 primary schools, 189,200 primary school teachers, and 7,768,000 students enrolled at the primary level, with a student-to-teacher ratio of forty-one to one. Just over one-third of all children of primary school age were enrolled in a school in 1989. There were 11,978 secondary schools, 154,802 secondary school teachers, and 2,995,000 students enrolled at the secondary level, with a student-to- teacher ratio of nineteen to one.

Primary school dropout rates remained fairly consistent in the 1970s and 1980s, at just over 50 percent for boys and 60 percent for girls. The middle school dropout rates for boys and girls rose from 22 percent in 1976 to about 33 percent in 1983. However, a noticeable shift occurred in the beginning of the 1980s regarding the postprimary dropout rate: whereas boys and girls had relatively equal rates (14 percent) in 1975, by 1979-- just as Zia initiated his government's Islamization program--the dropout rate for boys was 25 percent while for girls it was only 16 percent. By 1993 this trend had dramatically reversed, and boys had a dropout rate of only 7 percent compared with the girls' rate of 15 percent.

The Seventh Five-Year Plan envisioned that every child five years and above would have access to either a primary school or a comparable, but less comprehensive, mosque school. However, because of financial constraints, this goal was not achieved.

In drafting the Eighth Five-Year Plan in 1992, the government therefore reiterated the need to mobilize a large share of national resources to finance education. To improve access to schools, especially at the primary level, the government sought to decentralize and democratize the design and implemention of its education strategy. To give parents a greater voice in running schools, it planned to transfer control of primary and secondary schools to NGOs. The government also intended to gradually make all high schools, colleges, and universities autonomous, although no schedule was specified for achieving this ambitious goal.

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استپر موتور به زبان انگلیسی

DRIVING STEPPER MOTORS WITH THE L293D

 /

Stepper motors are great to use in robotics. By energizing the coils in the motor

in a particular sequence, a motor takes 48 or more small, precise steps

to make one full revolution. If you are using two of these motors to drive your

 robot’s wheels, you can get good control over how far it travels by making the

 motors travel x many steps forwards or backwards. That’s assuming you can

 find stepper motor drivers, of course. I’ve always had problems finding

good servo drivers. Once I was even reduced to using discreet components

(say it isn’t so!) to drive my steppers.

Then I got my hands on the L293D motor driver chip (See motors part 1)

and life got a lot easier. The L293D contains two H-bridges for driving small DC

 motors. Now the home-viewing audience might say: "Rob, it’s easy to drive DC

motors. What I need to do is drive a stepper motor." No problem. After all,

what is a DC motor but a coil and the L293D drives two of them backwards

 or forwards. That’s what stepper are - two (or more) coils being

 driven in a sequence, backwards and forwards. So one L293D can, in

theory, drive one bi-polar 2 phase stepper, if you supply the sequence.

I found some close-out two-phase bi-polar steppers (part#117954) in the

 Jameco Catalog. For six bucks plus shipping I get a 7.5 degree stepper

 with 48 steps per revolution. The stepper motor runs at about 5

volts and pulls 800 milli-amps of current. That’s a lot of current so

 I can expect my chips to heat up. The way I fix the heat problem

is by gluing a heat sink to the top of the chip. Any piece of metal

 three or four times the size of the chip will do. If things get real

hot, I use a small fan to move air over the top of the heat sink.

STEPPER CONTROLLER SCHEMATIC

I realize that Seattle has developed it’s own mutant breed of

 controller circuits, I think it’s based on the 68HC12, but I have

 successfully resisted all attempts to be lured to the dark side

 of the force and will continue to use the BS-2 (Basic Stamp II). Here

is a real quick description of the L293D inputs:

1, 9 Enable pins. Hook them together and you can either keep them high

and run the motor all the time, or you can control them

with your own controller.

2,7,10, 15 Control the two coils. Here is how you pulse them

 for a single cycle:

STEPPER TABLE

COIL A1

COIL B1

COIL A2

COIL B2

STEP 1

ON

ON

OFF

OFF

STEP2

OFF

ON

ON

OFF

STEP3

OFF

OFF

ON

ON

STEP4

ON

OFF

OFF

ON

3,6,11,14 Here is where you plug in the two coils. You want to ohm them out

and make sure you get one coil hooked up to 3,6 and another

 one hooked up to 11,14.

4,5,12,13 Gets hooked to ground.

8 Motor voltage, usually about 6 volts.

16 +5 volts. It’s a good idea to keep this power supply separate

from your motor power.

And here is the schematic to hook the BS-2 and the L293D together. Hey, I’ve even

included the code!

The software to program the Basic Stamp II can be found in stepprog.bs2

Notice that this single chip can handle a two coil stepper otherwise known

 as a two-phase stepper motor. If you want to do more than that, you need more

 chips. The cool thing is that if you have multiple steppers and you want to drive

them one at a time (say on a PC board driller), it’s easy to have multiple L293Ds

 driven on the same line.

BONUS! TROUBLE-SHOOTING SCENARIOS:

Let’s say you get this thing all hooked up to your microcontroller

 and it doesn’t work. Here are a couple of symptoms and what they

 point to as the cause. Since I’ve had the misfortune of experiencing

each one of these problems personally, I thought I might be able

to save you a little time and pain.

Symptom: The stepper motor shaft turns easily with fingers.

Cause/solution: No power to the circuitry, no power to the motor, or enable pin is low.

Symptom: Everything on, but motor is locked in one position.

Cause/solution: The L293D got the first position and that’s all. Check software, check connections, and check that the hard-wired ports match the software.

 You might want to pull out the logic probe.

Symptom: Everything on, stepper is shifting in position, but the motor won’t turn.

Cause/solution: The correct line isn’t getting pulsed. Either the

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تحقیق درباره؛ استپر موتور به زبان انگلیسی

لینک دانلود و خرید پایین توضیحات

فرمت فایل word  و قابل ویرایش و پرینت

تعداد صفحات: 6

استپر موتور به زبان انگلیسی

DRIVING STEPPER MOTORS WITH THE L293D

 /

Stepper motors are great to use in robotics. By energizing the coils in the motor

in a particular sequence, a motor takes 48 or more small, precise steps

to make one full revolution. If you are using two of these motors to drive your

 robot’s wheels, you can get good control over how far it travels by making the

 motors travel x many steps forwards or backwards. That’s assuming you can

 find stepper motor drivers, of course. I’ve always had problems finding

good servo drivers. Once I was even reduced to using discreet components

(say it isn’t so!) to drive my steppers.

Then I got my hands on the L293D motor driver chip (See motors part 1)

and life got a lot easier. The L293D contains two H-bridges for driving small DC

 motors. Now the home-viewing audience might say: "Rob, it’s easy to drive DC

motors. What I need to do is drive a stepper motor." No problem. After all,

what is a DC motor but a coil and the L293D drives two of them backwards

 or forwards. That’s what stepper are - two (or more) coils being

 driven in a sequence, backwards and forwards. So one L293D can, in

theory, drive one bi-polar 2 phase stepper, if you supply the sequence.

I found some close-out two-phase bi-polar steppers (part#117954) in the

 Jameco Catalog. For six bucks plus shipping I get a 7.5 degree stepper

 with 48 steps per revolution. The stepper motor runs at about 5

volts and pulls 800 milli-amps of current. That’s a lot of current so

 I can expect my chips to heat up. The way I fix the heat problem

is by gluing a heat sink to the top of the chip. Any piece of metal

 three or four times the size of the chip will do. If things get real

hot, I use a small fan to move air over the top of the heat sink.

STEPPER CONTROLLER SCHEMATIC

I realize that Seattle has developed it’s own mutant breed of

 controller circuits, I think it’s based on the 68HC12, but I have

 successfully resisted all attempts to be lured to the dark side

 of the force and will continue to use the BS-2 (Basic Stamp II). Here

is a real quick description of the L293D inputs:

1, 9 Enable pins. Hook them together and you can either keep them high

and run the motor all the time, or you can control them

with your own controller.

2,7,10, 15 Control the two coils. Here is how you pulse them

 for a single cycle:

STEPPER TABLE

COIL A1

COIL B1

COIL A2

COIL B2

STEP 1

ON

ON

OFF

OFF

STEP2

OFF

ON

ON

OFF

STEP3

OFF

OFF

ON

ON

STEP4

ON

OFF

OFF

ON

3,6,11,14 Here is where you plug in the two coils. You want to ohm them out

and make sure you get one coil hooked up to 3,6 and another

 one hooked up to 11,14.

4,5,12,13 Gets hooked to ground.

8 Motor voltage, usually about 6 volts.

16 +5 volts. It’s a good idea to keep this power supply separate

from your motor power.

And here is the schematic to hook the BS-2 and the L293D together. Hey, I’ve even

included the code!

The software to program the Basic Stamp II can be found in stepprog.bs2

Notice that this single chip can handle a two coil stepper otherwise known

 as a two-phase stepper motor. If you want to do more than that, you need more

 chips. The cool thing is that if you have multiple steppers and you want to drive

them one at a time (say on a PC board driller), it’s easy to have multiple L293Ds

 driven on the same line.

BONUS! TROUBLE-SHOOTING SCENARIOS:

Let’s say you get this thing all hooked up to your microcontroller

 and it doesn’t work. Here are a couple of symptoms and what they

 point to as the cause. Since I’ve had the misfortune of experiencing

each one of these problems personally, I thought I might be able

to save you a little time and pain.

Symptom: The stepper motor shaft turns easily with fingers.

Cause/solution: No power to the circuitry, no power to the motor, or enable pin is low.

Symptom: Everything on, but motor is locked in one position.

Cause/solution: The L293D got the first position and that’s all. Check software, check connections, and check that the hard-wired ports match the software.

 You might want to pull out the logic probe.

Symptom: Everything on, stepper is shifting in position, but the motor won’t turn.

Cause/solution: The correct line isn’t getting pulsed. Either the

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