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10:23 PM
Print this articleFerns are among the most ancient of botanical species and among the simplest of plants. Not having flowers or seeds, ferns reproduce through the dispersion of spores by wind. Pteridium aquilinum, known as the bracken fern, and various species of adiantum, or maidenhair ferns, are both in this large related group of plants, yet they have noteworthy differences.

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Maidenhair ferns have lacy, delicate fan-shaped leaves growing from a shiny black or reddish-black stalk that generally grows up to 2 feet tall. The stalk divides at the top into two branches curving in opposite directions. Bracken fern leaves are larger than those of maidenhair ferns, and they consist of three triangular parts. Although coarse and leather-like, these leaves still have a lacy look. Bracken ferns can grow up to 6 feet tall. Both bracken and maidenhair ferns spread out and develop into large colonies.

Growing Areas

Like most ferns, maidenhair ferns grow best in moist or wet soil, in shade and in rocky areas. They are abundant along stream banks, in deep woods and in ravines. Bracken ferns are unusual because they grow well in dry areas. Look for bracken ferns not only in moist forests but in sandy soil, pastures with poor soil and in open sunny woodlands. Bracken ferns also spring back easily in areas that have burned.

Uses

For gardening or wooded areas of your yard, maidenhair ferns are good for ground cover and for adding low-maintenance natural features, as noted by "Fine Gardening" magazine. Bracken has these uses as well, but you may want to forego planting this fern if deer graze on your land. The fern can be poisonous when eaten in large amounts by ruminant animals such as deer and cows.

Care

To care for bracken fern, grow it in any part of your yard that has some shade or full sun. Although bracken grows in dry soil, you'll see best results by keeping the soil moist. Maidenhair fern needs more shade and can even grow well in full shade. It does best in moist soil that drains well -- in other words, soil that doesn't have a high clay content.

ReferencesForest Preserve District of Cook County: Bracken, Maidenhair and Walking FernsMcDaniel College: FernsFine Gardening: Adiantum PedatumFine Gardening: Pteridium AquilinumRead Next:

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1:33 AM
ZC fireplaces include freestanding and wall-mounted models.

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The main difference between masonry and zero clearance fireplaces is how they insulate the surrounding walls from the high temperatures inside the fireplace. Masonry fireplaces follow the traditional style of insulating the walls from the fire by using a thick layer of brick or stone. Zero clearance models have a pair of metal walls that create an insulating air pocket around the fire, protecting the walls of your home.

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Masonry fireplaces insulate the walls and frame of your home with thick layers of stone or brick. This type of fireplace is built partially or completely within the frame of the home. These fireplaces consist of a firebox, throat and chimney. The firebox is a chamber made of firebrick that contains the fire. The firebox is open to the interior of the home. Smoke from the firebox is drawn into the throat, which connects the firebox and chimney. A damper controls the amount of air flowing into the chimney.

Zero Clearance Fireplaces

Zero clearance fireplaces are designed to work inside wood-framed walls in close proximity to flammable materials. The firebox of a zero clearance chimney uses firebrick surrounded with a double-walled metal box that creates a pocket of insulating air. Zero clearance fireplaces have a forced air system with fans to vent the warm air from around the fireplace into your home. Smoke from the firebox is vented through an insulated vertical pipe that connects directly to the firebox.

Benefits

Zero clearance fireplaces are lighter, more compact and less expensive than masonry fireplaces. You can install zero clearance fireplaces in your home without needing to install a concrete footer and masonry chimney on the outside of your home. Zero clearance fireplaces can use either wood or gas fuel sources, while masonry fireplaces are typically designed only for solid fuel. Zero clearance models can substitute the large, outer hearth used in masonry fireplaces with glass doors to prevent flaming debris from damaging your floors.

Considerations

Zero clearance fireplaces are lighter than masonry fireplaces, but they still need structural reinforcement. Most zero clearance fireplaces require doubled floor joists to support the firebox and concrete blocks to support the chimney. Masonry fireplaces need a solid concrete footer to support the fireplace and the chimney. Open masonry fireplaces also must have a substantial hearth in front of the firebox to prevent embers from damaging the floor. While zero clearance fireplaces with a forced air system will heat your home more effectively than an open masonry fireplace, you can install a fireplace insert in an existing masonry fireplace to get the same benefits as the zero clearance system.

ReferencesCharles Davidson College of Engineering: Specialty FeaturesDrexel University: FireplacesSwift Services: Fireplace Restoration and Construction:Photo Credit Brand X Pictures/Brand X Pictures/Getty ImagesRead Next:

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9:23 PM 1
MOSFET transistors are highly efficient amplifiers.

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A MOSFET is a transistor that uses the effects of an electric field to control the flow of current; it acts as a switch and a signal amplifier. Unlike a junction transistor, which controls a large current with a smaller one, a MOSFET controls current with a voltage. MOSFETs come in two polarities, P channel and N channel, where “P” stands for positive and “N” stands for negative.

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A MOSFET is a three-terminal device; the terminals are called the gate, drain and source. A voltage applied at the gate controls the flow of electrons from the source to the drain. As the gate voltage passes a threshold value, the transistor goes from non-conducting to conducting. The gate resistance is extremely high, on the order of millions of megohms. Because of this high resistance, the MOSFET’s current consumption at the gate is very low. The resistance between the source and drain becomes low when the device conducts; a MOSFET can handle tens of amps of current with very little loss.
In addition to P and N channel types, MOSFETs are made as enhancement-mode or depletion-mode devices. An enhancement-mode transistor is normally off and turns on with a voltage; a depletion-mode device is normally on and turns off with a voltage. The descriptions that follow apply to enhancement-mode MOSFETs.

P Channel

To turn a P channel MOSFET on, you apply a negative voltage to the gate. This voltage is negative relative to ground. In a circuit, you connect the P channel MOSFET’s source terminal to a positive voltage supply and the drain to a resistor connected to ground; the resistor limits the current flowing through the transistor. The circuit diagram symbol for a P channel MOSFET has an arrow pointing away from the gate.

N Channel

An N channel MOSFET turns on when you apply a positive voltage at its gate terminal. The voltage is greater than the positive voltage supply at the drain terminal. A resistor between the positive supply and the drain limits current; for an N channel MOSFET, the source terminal connects to ground. The circuit symbol for an N channel MOSFET has an arrow pointing toward the device’s gate.

Low Side and High Side

A circuit called a low side driver uses an N channel MOSFET; it is called “low side” because the transistor connects to the circuit ground connection. A positive supply voltage drives a device when the MOSFET turns on. A high side driver, on the other hand, has a P channel MOSFET connected to the positive supply, with the switched device connected to the transistor’s drain terminal and ground. The low side driver is a simpler circuit; the high side driver, however, lets you switch the direction of current through the device.

ReferencesAll About Circuits: Insulated-gate field-effect transistors (MOSFET)University of Delaware: N Channel MOSFET SwitchGeorgia Institute of Technology: Metal Oxide Semiconductor Field Effect TransistorPhoto Credit Hemera Technologies/PhotoObjects.net/Getty ImagesRead Next:

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