romikgosai/squad_modified huggingface dataset:
Recall that a current will reflect when there are changes in the electrical properties of the material. In order to efficiently send the signal into the transmission line, it is important that the transmission line has the same impedance as the elements, otherwise some of the signal will be reflected back into the antenna. This leads to the concept of impedance matching, the design of the overall system of antenna and transmission line so the impedance is as close as possible, thereby reducing these losses. Impedance matching between antennas and transmission lines is commonly handled through the use of a balun, although other solutions are also used in certain roles. An important measure of this basic concept is the standing wave ratio, which measures the magnitude of the reflected signal.

Questions and answers:
['
Q: What sort of changes in material would a current reflect?
A: electrical', '
Q:  What must match between the transmission line and elements?
A: impedance', '
Q: What technique is used to prevent unintentional decrease in signal?
A: Impedance matching', '
Q: How is this process usually used for transmission lines and antennas?
A: balun']
An electromagnetic wave refractor in some aperture antennas is a component which due to its shape and position functions to selectively delay or advance portions of the electromagnetic wavefront passing through it. The refractor alters the spatial characteristics of the wave on one side relative to the other side. It can, for instance, bring the wave to a focus or alter the wave front in other ways, generally in order to maximize the directivity of the antenna system. This is the radio equivalent of an optical lens.

Questions and answers:
['
Q: What is used to allow one to control the function of wave fronts moving through an antenna?
A: selectively delay', '
Q: What changes the structuak traits of a wave on either side?
A: refractor', '
Q: What is the main purpose of a refractor?
A: spatial characteristics', '
Q: A refractor can be compared to what type of viewing?
A: optical lens']
The actual antenna which is transmitting the original wave then also may receive a strong signal from its own image from the ground. This will induce an additional current in the antenna element, changing the current at the feedpoint for a given feedpoint voltage. Thus the antenna's impedance, given by the ratio of feedpoint voltage to current, is altered due to the antenna's proximity to the ground. This can be quite a significant effect when the antenna is within a wavelength or two of the ground. But as the antenna height is increased, the reduced power of the reflected wave (due to the inverse square law) allows the antenna to approach its asymptotic feedpoint impedance given by theory. At lower heights, the effect on the antenna's impedance is very sensitive to the exact distance from the ground, as this affects the phase of the reflected wave relative to the currents in the antenna. Changing the antenna's height by a quarter wavelength, then changes the phase of the reflection by 180°, with a completely different effect on the antenna's impedance.

Questions and answers:
['
Q: What can receive a stron signal by transmitting an original wave?
A: actual antenna', '
Q: Where will the additional current be induced?
A: antenna element', "
Q: What is altered because of the proximity to the ground?
A: antenna's impedance", '
Q: what happens to the reflected wave which allows the antenna to reach its asympotic feedpoint impedance?
A: reduced power']
For horizontal propagation between transmitting and receiving antennas situated near the ground reasonably far from each other, the distances traveled by tne direct and reflected rays are nearly the same. There is almost no relative phase shift. If the emission is polarized vertically, the two fields (direct and reflected) add and there is maximum of received signal. If the signal is polarized horizontally, the two signals subtract and the received signal is largely cancelled. The vertical plane radiation patterns are shown in the image at right. With vertical polarization there is always a maximum for θ=0, horizontal propagation (left pattern). For horizontal polarization, there is cancellation at that angle. Note that the above formulae and these plots assume the ground as a perfect conductor. These plots of the radiation pattern correspond to a distance between the antenna and its image of 2.5λ. As the antenna height is increased, the number of lobes increases as well.

Questions and answers:
["
Q: What is between recieving and transmitting antenna's?
A: horizontal propagation", '
Q: When is the emission at maximized recieved signal?
A: polarized vertically', '
Q: Where is the radiation patterns in the vertical plane shown?
A: image at right', "
Q: What is also increased along with the antenna's height?
A: lobes"]
On the other hand, classical (analog) television transmissions are usually horizontally polarized, because in urban areas buildings can reflect the electromagnetic waves and create ghost images due to multipath propagation. Using horizontal polarization, ghosting is reduced because the amount of reflection of electromagnetic waves in the p polarization (horizontal polarization off the side of a building) is generally less than s (vertical, in this case) polarization. Vertically polarized analog television has nevertheless been used in some rural areas. In digital terrestrial television such reflections are less problematic, due to robustness of binary transmissions and error correction.

Questions and answers:
['
Q: What is another name for classical television transmissions?
A: analog', '
Q: Buildings can create ghost images because of what?
A: multipath propagation', '
Q: When is ghosting reduced?
A: horizontal polarization', '
Q: What cause less problems in digital terrestrial television?
A: Vertically polarized analog television']
Current circulating in one antenna generally induces a voltage across the feedpoint of nearby antennas or antenna elements. The mathematics presented below are useful in analyzing the electrical behaviour of antenna arrays, where the properties of the individual array elements (such as half wave dipoles) are already known. If those elements were widely separated and driven in a certain amplitude and phase, then each would act independently as that element is known to. However, because of the mutual interaction between their electric and magnetic fields due to proximity, the currents in each element are not simply a function of the applied voltage (according to its driving point impedance), but depend on the currents in the other nearby elements. Note that this now is a near field phenomenon which could not be properly accounted for using the Friis transmission equation for instance.

Questions and answers:
['
Q: Where are the indiviual array elements known?
A: antenna arrays', '
Q: What induces a feedpoint to antennas nearby?
A: Current circulating', '
Q: What are the mathmatic useful towards?
A: electrical behaviour', '
Q: What cause mutual interactions between the elements electric and magnetic fields?
A: proximity']
This is a consequence of Lorentz reciprocity. For an antenna element  not connected to anything (open circuited) one can write . But for an element  which is short circuited, a current is generated across that short but no voltage is allowed, so the corresponding . This is the case, for instance, with the so-called parasitic elements of a Yagi-Uda antenna where the solid rod can be viewed as a dipole antenna shorted across its feedpoint. Parasitic elements are unpowered elements that absorb and reradiate RF energy according to the induced current calculated using such a system of equations.

Questions and answers:
['
Q: a antenna element not connected to anything is circuited how?
A: open circuited', '
Q: When is the element not allowed voltage?
A: short circuited', '
Q: What element absorbs and reradiate RF-energy?
A: Parasitic', '
Q: What antenna can the solid rod be viewed as a dipole antenna?
A: Yagi-Uda', '
Q: Where can this solid rod be viewed?
A: feedpoint']
The difference in the above factors for the case of θ=0 is the reason that most broadcasting (transmissions intended for the public) uses vertical polarization. For receivers near the ground, horizontally polarized transmissions suffer cancellation. For best reception the receiving antennas for these signals are likewise vertically polarized. In some applications where the receiving antenna must work in any position, as in mobile phones, the base station antennas use mixed polarization, such as linear polarization at an angle (with both vertical and horizontal components) or circular polarization.

Questions and answers:
['
Q: What type of programmin relies on vertical polarization?
A: broadcasting', '
Q: If you were to position your receiver closer to the ground what might be a negative of this placement?
A: cancellation', '
Q: What is one use that would require an antenna to receive signals in various ways at once?
A: mobile phones', '
Q: If you were to develop a signal to be used with mobile phones what would be an effective antenna type?
A: circular polarization.', '
Q: What would the antenna you are using take advantage of to allow it to work in multiple locations?
A: mixed polarization']
Loop antennas consist of a loop or coil of wire. Loops with circumference of a wavelength or larger act similarly to dipole antennas. However loops small in comparison to a wavelength act differently. They interact with the magnetic field of the radio wave instead of the electric field as other antennas do, and so are relatively insensitive to nearby electrical noise. However they have low radiation resistance, and so are inefficient for transmitting. They are used as receiving antennas at low frequencies, and also as direction finding antennas.

Questions and answers:
['
Q: What type of antenna can be formed by a circular segment of wire?
A: Loop antennas', '
Q: What is a loop antenna compared with to determine its beahvior?
A: circumference of a wavelength', '
Q: If you needed to place an antenna somewhere with a large amount of interference, which type would be best?
A: loops small', '
Q: Why would this type be good for receiving but not transmtting?
A: low radiation resistance', '
Q: What else would be an effective application of this antenna type?
A: direction finding']
It is a fundamental property of antennas that the electrical characteristics of an antenna described in the next section, such as gain, radiation pattern, impedance, bandwidth, resonant frequency and polarization, are the same whether the antenna is transmitting or receiving. For example, the "receiving pattern" (sensitivity as a function of direction) of an antenna when used for reception is identical to the radiation pattern of the antenna when it is driven and functions as a radiator. This is a consequence of the reciprocity theorem of electromagnetics. Therefore, in discussions of antenna properties no distinction is usually made between receiving and transmitting terminology, and the antenna can be viewed as either transmitting or receiving, whichever is more convenient.

Questions and answers:
['
Q: Are essential properties of an antenna changed based on what fungtion they are performing
A: the same', '
Q: What proposition explains the equivalency of the recieving pattern of an antenna?
A: reciprocity theorem of electromagnetics', '
Q: Can the antenna serve more than one fungtion at a time?
A: either transmitting or receiving', '
Q: What is one electrical trait of an antenna?
A: radiation pattern']
The flowering plants (angiosperms), also known as Angiospermae or Magnoliophyta, are the most diverse group of land plants, with about 350,000 species. Like gymnosperms, angiosperms are seed-producing plants; they are distinguished from gymnosperms by characteristics including flowers, endosperm within the seeds, and the production of fruits that contain the seeds. Etymologically, angiosperm means a plant that produces seeds within an enclosure, in other words, a fruiting plant. The term "angiosperm" comes from the Greek composite word (angeion-, "case" or "casing", and sperma, "seed") meaning "enclosed seeds", after the enclosed condition of the seeds.

Questions and answers:
['
Q: What are the most diverse group of land plants?
A: angiosperms', '
Q: How many species of flowering plants are there about?
A: 350,000', '
Q: What does an angiosperm produce its seeds within?
A: an enclosure', '
Q: What do angiosperms have in common with gymnosperms?
A: seed-producing plants', '
Q: What is the Greek word for "case" or "casing"?
A: angeion']
Fossilized spores suggest that higher plants (embryophytes) have lived on land for at least 475 million years. Early land plants reproduced sexually with flagellated, swimming sperm, like the green algae from which they evolved. An adaptation to terrestrialization was the development of upright meiosporangia for dispersal by spores to new habitats. This feature is lacking in the descendants of their nearest algal relatives, the Charophycean green algae. A later terrestrial adaptation took place with retention of the delicate, avascular sexual stage, the gametophyte, within the tissues of the vascular sporophyte. This occurred by spore germination within sporangia rather than spore release, as in non-seed plants. A current example of how this might have happened can be seen in the precocious spore germination in Selaginella, the spike-moss. The result for the ancestors of angiosperms was enclosing them in a case, the seed. The first seed bearing plants, like the ginkgo, and conifers (such as pines and firs), did not produce flowers. The pollen grains (males) of Ginkgo and cycads produce a pair of flagellated, mobile sperm cells that "swim" down the developing pollen tube to the female and her eggs.

Questions and answers:
['
Q: How long have higher plants lived on land?
A: at least 475 million years', '
Q: How did early plants reproduce sexually?
A: with flagellated, swimming sperm', '
Q: Upright meisporangia allowed what to be dispersed to new habitats?
A: spores', '
Q: What are the nearest algal relatives existing today?
A: Charophycean green algae', '
Q: What is the common name for Selaginella?
A: the spike-moss']
The apparently sudden appearance of nearly modern flowers in the fossil record initially posed such a problem for the theory of evolution that it was called an "abominable mystery" by Charles Darwin. However, the fossil record has considerably grown since the time of Darwin, and recently discovered angiosperm fossils such as Archaefructus, along with further discoveries of fossil gymnosperms, suggest how angiosperm characteristics may have been acquired in a series of steps. Several groups of extinct gymnosperms, in particular seed ferns, have been proposed as the ancestors of flowering plants, but there is no continuous fossil evidence showing exactly how flowers evolved. Some older fossils, such as the upper Triassic Sanmiguelia, have been suggested. Based on current evidence, some propose that the ancestors of the angiosperms diverged from an unknown group of gymnosperms in the Triassic period (245–202 million years ago). Fossil angiosperm-like pollen from the Middle Triassic (247.2–242.0 Ma) suggests an older date for their origin. A close relationship between angiosperms and gnetophytes, proposed on the basis of morphological evidence, has more recently been disputed on the basis of molecular evidence that suggest gnetophytes are instead more closely related to other gymnosperms.[citation needed]

Questions and answers:
['
Q: What did Charles Darwin call the sudden appearance of nearly modern flowers in the fossil record?
A: abominable mystery', '
Q: What type of fossil is the recently discovered Archaefructus?
A: angiosperm', '
Q: What fossil evidence is lacking when it comes to flowers?
A: evidence showing exactly how flowers evolved', '
Q: From what period does fossilized pollen suggest an older date for angiosperm origin?
A: Middle Triassic', '
Q: What relationship proposed on the basis of morphological evidence has recently been disputed?
A: relationship between angiosperms and gnetophytes']
The evolution of seed plants and later angiosperms appears to be the result of two distinct rounds of whole genome duplication events. These occurred at 319 million years ago and 192 million years ago. Another possible whole genome duplication event at 160 million years ago perhaps created the ancestral line that led to all modern flowering plants. That event was studied by sequencing the genome of an ancient flowering plant, Amborella trichopoda, and directly addresses Darwin's "abominable mystery."

Questions and answers:
['
Q: How many distinct rounds of genome duplication events are suspected in the evolution of seed plants?
A: two', '
Q: When did the first whole genome duplication event occur?
A: 319 million years ago', '
Q: What type of event perhaps created the line which led to modern flowering plants?
A: whole genome duplication', '
Q: How are duplication events studied?
A: by sequencing the genome of an ancient flowering plant', '
Q: Who coined the term "abominable mystery"?
A: Darwin']
The earliest known macrofossil confidently identified as an angiosperm, Archaefructus liaoningensis, is dated to about 125 million years BP (the Cretaceous period), whereas pollen considered to be of angiosperm origin takes the fossil record back to about 130 million years BP. However, one study has suggested that the early-middle Jurassic plant Schmeissneria, traditionally considered a type of ginkgo, may be the earliest known angiosperm, or at least a close relative. In addition, circumstantial chemical evidence has been found for the existence of angiosperms as early as 250 million years ago. Oleanane, a secondary metabolite produced by many flowering plants, has been found in Permian deposits of that age together with fossils of gigantopterids. Gigantopterids are a group of extinct seed plants that share many morphological traits with flowering plants, although they are not known to have been flowering plants themselves.

Questions and answers:
['
Q: When is the earliest known macrofossil identified as an angiosperm dated?
A: about 125 million years BP', '
Q: What is the earliest known angiosperm?
A: Archaefructus liaoningensis', '
Q: What pushes the age of angiosperm 5 million years further back?
A: pollen', '
Q: How long ago has circumstantial evidence has been found for the existence of angiosperms?
A: 250 million years ago', '
Q: What group of now extinct seed plants had many of the traits of what are now flowering plants?
A: Gigantopterids']
The great angiosperm radiation, when a great diversity of angiosperms appears in the fossil record, occurred in the mid-Cretaceous (approximately 100 million years ago). However, a study in 2007 estimated that the division of the five most recent (the genus Ceratophyllum, the family Chloranthaceae, the eudicots, the magnoliids, and the monocots) of the eight main groups occurred around 140 million years ago. By the late Cretaceous, angiosperms appear to have dominated environments formerly occupied by ferns and cycadophytes, but large canopy-forming trees replaced conifers as the dominant trees only close to the end of the Cretaceous 66 million years ago or even later, at the beginning of the Tertiary. The radiation of herbaceous angiosperms occurred much later. Yet, many fossil plants recognizable as belonging to modern families (including beech, oak, maple, and magnolia) had already appeared by the late Cretaceous.

Questions and answers:
['
Q: When does a great diversity of angiosperms appear in the fossil record?
A: approximately 100 million years ago', '
Q: What is the appearance of a large amount of angiosperms in the fossil record known as?
A: great angiosperm radiation,', '
Q: When did the division of the eight main groups of angiosperms occur?
A: 40 million years ago', '
Q: What were the angiosperms up to by the late Cretaceous?
A: dominated environments', '
Q: Beech and maple had already appeared by what period?
A: Cretaceous']
Island genetics provides one proposed explanation for the sudden, fully developed appearance of flowering plants. Island genetics is believed to be a common source of speciation in general, especially when it comes to radical adaptations that seem to have required inferior transitional forms. Flowering plants may have evolved in an isolated setting like an island or island chain, where the plants bearing them were able to develop a highly specialized relationship with some specific animal (a wasp, for example). Such a relationship, with a hypothetical wasp carrying pollen from one plant to another much the way fig wasps do today, could result in the development of a high degree of specialization in both the plant(s) and their partners. Note that the wasp example is not incidental; bees, which, it is postulated, evolved specifically due to mutualistic plant relationships, are descended from wasps.

Questions and answers:
['
Q: What is one proposed explanation for the instant appearance of flowering plants?
A: Island genetics', '
Q: What is island genetics thought to be a default source of?
A: speciation', '
Q: What did radical adaptations seem to have required?
A: inferior transitional forms', '
Q: How did an isolated setting like an island help flowering plants evolve?
A: highly specialized relationship with some specific animal', '
Q: What are bees descended from?
A: wasps']
Animals are also involved in the distribution of seeds. Fruit, which is formed by the enlargement of flower parts, is frequently a seed-dispersal tool that attracts animals to eat or otherwise disturb it, incidentally scattering the seeds it contains (see frugivory). Although many such mutualistic relationships remain too fragile to survive competition and to spread widely, flowering proved to be an unusually effective means of reproduction, spreading (whatever its origin) to become the dominant form of land plant life.

Questions and answers:
['
Q: What are animals also a part of?
A: distribution of seeds', '
Q: What did the enlargement of flower parts evolve to form?
A: Fruit', '
Q: What does a plant get out of forming fruit?
A: seed-dispersal', '
Q: What are many mutualistic relationships, thus failing to survive competition? 
A: fragile', '
Q: What turned out to be unusually effective for plants to reproduce?
A: flowering']
Flower ontogeny uses a combination of genes normally responsible for forming new shoots. The most primitive flowers probably had a variable number of flower parts, often separate from (but in contact with) each other. The flowers tended to grow in a spiral pattern, to be bisexual (in plants, this means both male and female parts on the same flower), and to be dominated by the ovary (female part). As flowers evolved, some variations developed parts fused together, with a much more specific number and design, and with either specific sexes per flower or plant or at least "ovary-inferior".

Questions and answers:
['
Q: What uses a combination of genes to form new shoots?
A: Flower ontogeny', '
Q: What were plant parts like in their primitive days?
A: separate from (but in contact with) each other', '
Q: How did flowers become bixsexual?
A: grow in a spiral pattern', '
Q: What did some plant parts do as they evolved?
A: fused together', '
Q: What is a term for a plant with a specific sex per flower?
A: "ovary-inferior"']