英语翻译Fig.3 shows the FPGA-internal block diagram.The three in¬terfaces,serial AER,parallel AER and USB are drawn in orange.The USB interface,as opposed to the other interfaces,is handling explicitly timestamped addresses.Thus we need monitoring and sequencing units (green) between the two domains.The routing fabric between the three interface blocks allows AEs to be selectively routed between the three interfaces.It also contains simple mapping and filtering units.The mapping units can add a configurable offset to an AE stream,so that different address spaces can be made non-overlapping.The filtering units allow to select which events are routed to which destination.All these functional units are interconnected using FIFOs (blue,striped).ON THE IMPORTANCE OF FLOW-CONTROLHere we compare the statistics of a Serial AER implementation with flow control and one that simply drops events.With Flow-Control:Assume we have an event-consumer that can handle event rates up to 125MHz.Thanks to the flow-control scheme,the consumer can block the producer as necessary.In this example we choose a fairly strict requirement that an event is delivered with a delay of more than 1/KS at probability of less than 10-6.Given a Poisson distributed3 producer,this means that the mean event rate of the producer can be up to 63.7% of the consumer event rate without violating our requirements.Without Flow-Control:For comparison we assume a consumer that can handle event rates up to 125MHz,but if two or more events arrive within an 8ns (= 1/125MHz) time-slot all except the first备注2：In this calculation the signal propagation speed for the SATA cables was assumed to be half the speed of light,a rather conservative estimate.备注3：A Poisson distribution is probably an unsuitable assumption when looking at a longer typical AE sequence.But what is critical is the performance in event bursts.We here take the Poisson distribution for looking at such bursts,typical for address event systems.The mean event rate should then be interpreted as the mean event rate in event bursts.one are dropped.The probability that an event is dropped shall be no more than 10-3.Under these circumstances a Poisson producer can then have a mean event rate of no more than 4.54% of the consumer rate.Thus for our practical purposes flow-control gives us about one order of magnitude of actually usable event rate.In an experimental setup it also allows us to handle channel congestion either at the sender or the receiver side.Further discussion of flow control in address event systems can be found in [9].V.RESULTS AND CONCLUSIONWe have developed an AER interfacing board part of a generic AER communication system suitable for building complex multi-chip AE based systems.
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Fig.3 shows the FPGA-internal block diagram.\x05图3显示FPGA-internal框图.\x05The three in¬terfaces,serial AER,parallel AER and USB are drawn in orange.\x05这三支球队中terfaces¬、串行正在,平行正在画和USB是橙色的.\x05The USB interface,as opposed to the other interfaces,is handling explicitly timestamped addresses.\x05USB接口,相对于其他接口,明确timestamped处理地址.\x05Thus we need monitoring and sequencing units (green) between the two domains.\x05所以我们需要监测和测序单位(绿色)这两个领域之间.\x05The routing fabric between the three interface blocks allows AEs to be selectively routed between the three interfaces.\x05这三者之间的路由结构接口模块,允许有选择性的AEs路由三者之间的接口.\x05It also contains simple mapping and filtering units.\x05它也含有的简单绘图和过滤单元.\x05The mapping units can add a configurable offset to an AE stream,so that different address spaces can be made non-overlapping.\x05测绘单位可以增加一个配置来弥补经纪人流,使不同的地址空间可以使non-overlapping.\x05The filtering units allow to select which events are routed to which destination.\x05过滤单位允许选择的事件发送到目的地.\x05All these functional units are interconnected using FIFOs (blue,striped).\x05所有这些功能部件使用FIFOs有密切关系(蓝、条纹).\x05ON THE IMPORTANCE OF FLOW-CONTROL\x05流量控制的重要性\x05Here we compare the statistics of a Serial AER implementation with flow control and one that simply drops events.\x05在这里我们比较一个串行数据流控制与你正在实施一个简单的下降的事件.\x05With Flow-Control:Assume we have an event-consumer that can handle event rates up to 125MHz.\x05与流体控制:假设我们有一个event-consumer可处理事件发生率高达125赫兹.\x05Thanks to the flow-control scheme,the consumer can block the producer as necessary.\x05多亏了流量控制的方案,消费者可以阻止制作人是必要的.\x05In this example we choose a fairly strict requirement that an event is delivered with a delay of more than 1/KS at probability of less than 10-6.\x05这个例子里,我们选择一个有着严格的要求,即一个事件交付与延迟超过1 / KS在概率不到的时刻.\x05Given a Poisson distributed3 producer,this means that the mean event rate of the producer can be up to 63.7% of the consumer event rate without violating our requirements.\x05给定一个泊松distributed3生产商,这意味着平均事件发生率的生产性可以高达63.7%的消费者事件发生率不违背我们的要求.\x05Without Flow-Control:For comparison we assume a consumer that can handle event rates up to 125MHz,but if two or more events arrive within an 8ns (= 1/125MHz) time-slot all except the first\x05没有流体控制:比较我们的确有一个消费者可以处理事件发生率高达125兆赫,但是如果两个或多个事件8 ns之内到达(= 1/125MHz)time-slot除了第一\x05备注2：In this calculation the signal propagation speed for the SATA cables was assumed to be half the speed of light,a rather conservative estimate.\x05备注2:在此计算信号传播速度为SATA电缆被假设为半光的速度,一个相当保守的估计.\x05备注3：A Poisson distribution is probably an unsuitable assumption when looking at a longer typical AE sequence.\x05备注3:不可能是泊松分布假设当看着长曝光顺序.典型的\x05But what is critical is the performance in event bursts.\x05但关键是在事件爆发性能.\x05We here take the Poisson distribution for looking at such bursts,typical for address eve\x05我们在这里采取泊松分布规律为看着这样的破裂,典型的地址的前夕
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图3显示了内部设计框图。串行、并行、和总线这三种接口是用橙色画的。通用串行总线接口，跟其他两个接口相反，是控制明确时间地址。因此我们需要监测和测序单位（绿色）两国之间的域。路由器之间的三个接口块允许光谱有选择路由之间的三个界面。它也包含简单的映射和过滤单元。测绘单位可以添加一个配置抵销的声流，使不同的地址空间可以是非重叠。过滤单元允许选择的事件路由到的目的地.....。太长了，...
图3显示FPGA-internal框图。 这三支球队中terfaces¬、串行正在,平行正在画和USB是橙色的。USB接口,相对于其他接口,明确timestamped处理地址。所以我们需要监测和测序单位(绿色)这两个领域之间。这三者之间的路由结构接口模块,允许有选择性的AEs路由三者之间的接口。它也含有的简单绘图和过滤单元。测绘单位可以增加一个配置来弥补经纪人流,使不同的地址空...
图3显示FPGA-internal框图。这三支球队中terfaces?、串行正在,平行正在画和USB是橙色的。USB接口,相对于其他接口,明确timestamped处理地址。所以我们需要监测和测序单位(绿色)这两个领域之间。这三者之间的路由结构接口模块,允许有选择性的AEs路由三者之间的接口。它也含有的简单绘图和过滤单元。　　测绘单位可以增加一个配置= =...
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出门在外也不愁英语翻译Fig.3 shows the FPGA-internal block diagram.The three in¬terfaces,serial AER,parallel AER and USB are drawn in orange.The USB interface,as opposed to the other interfaces,is handling explicitly timestamped addresses.Thus we need monitoring and sequencing units (green) between the two domains.The routing fabric between the three interface blocks allows AEs to be selectively routed between the three interfaces.It also contains simple mapping and filtering units.The mapping units can add a configurable offset to an AE stream,so that different address spaces can be made non-overlapping.The filtering units allow to select which events are routed to which destination.All these functional units are interconnected using FIFOs (blue,striped).ON THE IMPORTANCE OF FLOW-CONTROLHere we compare the statistics of a Serial AER implementation with flow control and one that simply drops events.With Flow-Control:Assume we have an event-consumer that can handle event rates up to 125MHz.Thanks to the flow-control scheme,the consumer can block the producer as necessary.In this example we choose a fairly strict requirement that an event is delivered with a delay of more than 1/KS at probability of less than 10-6.Given a Poisson distributed3 producer,this means that the mean event rate of the producer can be up to 63.7% of the consumer event rate without violating our requirements.Without Flow-Control:For comparison we assume a consumer that can handle event rates up to 125MHz,but if two or more events arrive within an 8ns (= 1/125MHz) time-slot all except the first备注2：In this calculation the signal propagation speed for the SATA cables was assumed to be half the speed of light,a rather conservative estimate.备注3：A Poisson distribution is probably an unsuitable assumption when looking at a longer typical AE sequence.But what is critical is the performance in event bursts.We here take the Poisson distribution for looking at such bursts,typical for address event systems.The mean event rate should then be interpreted as the mean event rate in event bursts.one are dropped.The probability that an event is dropped shall be no more than 10-3.Under these circumstances a Poisson producer can then have a mean event rate of no more than 4.54% of the consumer rate.Thus for our practical purposes flow-control gives us about one order of magnitude of actually usable event rate.In an experimental setup it also allows us to handle channel congestion either at the sender or the receiver side.Further discussion of flow control in address event systems can be found in [9].V.RESULTS AND CONCLUSIONWe have developed an AER interfacing board part of a generic AER communication system suitable for building complex multi-chip AE based systems.
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Fig.3 shows the FPGA-internal block diagram.The three interfaces,serial AER,parallel AER and USB are drawn in orange.The USB interface,as opposed to the other interfaces,is handling explicitly timestamped addresses.Thus we need monitoring and sequencing units (green) between the two domains.The routing fabric between the three interface blocks allows AEs to be selectively routed between the three interfaces.It also contains simple mapping and filtering units.The mapping units can add a configurable offset to an AE stream,so that different address spaces can be made non-overlapping.The filtering units allow to select which events are routed to which destination.All these functional units are interconnected using FIFOs (blue,striped).图示3显示的是EPGA内部的框图.以橙色展示的是串行AER、并行AER及USB三个接口.与其他接口不同,USB接口只直接处理有时间戳的地址；因此,在两域之间我们需要有监控和排序装置（绿色）.三个接口模块之间的路由结构使AE可被选择性地在三个接口之间路由.它也含有简单的映射和过滤装置.该映射装置可以对AE信息流添加一个可配置偏移,这可避免不同地址空间的重叠.过滤装置可允许个别事件选择个别路由目的地.所有这些功能装置都通过FIFO相互连接（蓝色,条纹）ON THE IMPORTANCE OF FLOW-CONTROLHere we compare the statistics of a Serial AER implementation with flow control and one that simply drops events.With Flow-Control:Assume we have an event-consumer that can handle event rates up to 125MHz.Thanks to the flow-control scheme,the consumer can block the producer as necessary.In this example we choose a fairly strict requirement that an event is delivered with a delay of more than 1/KS at probability of less than 10-6.Given a Poisson distributed3 producer,this means that the mean event rate of the producer can be up to 63.7% of the consumer event rate without violating our requirements.Without Flow-Control:For comparison we assume a consumer that can handle event rates up to 125MHz,but if two or more events arrive within an 8ns (= 1/125MHz) time-slot all except the first one are dropped.The probability that an event is dropped shall be no more than 10-3.Under these circumstances a Poisson producer can then have a mean event rate of no more than 4.54% of the consumer rate.Thus for our practical purposes flow-control gives us about one order of magnitude of actually usable event rate.In an experimental setup it also allows us to handle channel congestion either at the sender or the receiver side.Further discussion of flow control in address event systems can be found in [9].控制信息流量的重要性我们在此把执行流量控制与没流量控制的串行AER的统计进行比较.有流量控制 –我们假设一个能够处理125 MHz事件率的事件消费者,流量控制方案可让消费者在有必要时阻挡流量产生者.我们在本例子选用一个相当严格的要求,输送事件在概率小于10-6时延迟高于1/KS.无流量控制 – 为了进行对比,我们也假设一个能够处理125 MHz事件率的事件消费者,但如果在8ns 时间片(=等于1/125MHz)之内两个或更多的事件同时到达,除了第一个事件外,其他的都会被删除.事件被删除的概率应不超过10-3.在此种情形之下,泊松产生者就能有不超过4.54%消费者率的平均事件率.因此,从实用的角度,流量控制可给我们大约一个数量级的实际可使用的事件率.在一个实验设备中,它也让我们可以在发送或者接收方处理通道拥塞.AE系统流量控制的更多讨论,可以参阅[9].备注2：In this calculation the signal propagation speed for the SATA cables was assumed to be half the speed of light,a rather conservative estimate.备注3：A Poisson distribution is probably an unsuitable assumption when looking at a longer typical AE sequence.But what is critical is the performance in event bursts.We here take the Poisson distribution for looking at such bursts,typical for address event systems.The mean event rate should then be interpreted as the mean event rate in event bursts.备注2：在本计算方法里,SATA线缆的信号传输速度被假设为光速的一半,这是一个相当保守的估算.备注3：从较长的典型AE序列来看,泊松分布也许不是一个适当的假设.但关键的是在时间爆发时的表现.在此,我们特以这种在AE系统中经常出现的爆发来观察泊松分布.因此,平均事件率就应被理解为事件爆发的平均事件率.V.RESULTS AND CONCLUSIONWe have developed an AER interfacing board part of a generic AER communication system suitable for building complex multi-chip AE based systems.五． 结果和结论我们研发了一个普通AER通信系统的接口主板,适用于创建基于AE的综合多芯片系统.【英语牛人团】
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图3显示了fpga-internal框图。三在¬terfaces，串行，并行的是，是橙色。通用串行总线接口，而不是其他的接口，是处理明确时间戳地址。因此我们需要监测和测序单位（绿色）两国之间的域。路由织物之间的三接口块允许光谱有选择路由之间的三个界面。它也包含简单的映射和过滤单元。测绘单位可以添加一个配置抵销的声流，使不同的地址空间可以是非重叠。过滤单元允许选择的事件路由到的目的地。所有...
图3为FPGA内部框图。橙色显示AER串联、AER与USB并联这三个接口。相对于其它接口，USB接口明确处理有时间标记的地址。因此，我们需要对两域间的监控与排序单元(绿色)。三个接口模块间的路由结构实现三接口间AE选择性地路由。系统还包含简单的映射和过滤单元。映射单元可向AE流添加一个可配置偏移，从而实现不同地址空间非重叠。过滤单元实现不同路由项目不同目的地的选择。所有这些功能...
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　　TPO18阅读真题(文本+答案+翻译)：Part3 Lightning闪电，更多托福TPO阅读真题、TPO阅读文本、TPO阅读答案、TPO阅读翻译尽在新东方在线频道！　　Lightning　　Lightning is a brilliant flash of light produced by an electrical discharge from a storm cloud. The electrical discharge takes place when the attractive tension between a region of negatively charged particles and a region of positively charged particles becomes so great that the charged particles suddenly rush together. The coming together of the oppositely charged particles neutralizes the electrical tension and releases a tremendous amount of energy, which we see as lightning. The separation of positively and negatively charged particles takes place during the development of the storm cloud.　　The separation of charged particles that forms in a storm cloud has a sandwich-like structure. Concentrations of positively charged particles develop at the top and bottom of the cloud, but the middle region becomes negatively charged. Recent measurements made in the field together with laboratory simulations offer a promising explanation of how this structure of charged particles forms. What happens is that small (millimeter-to centimeter-size) pellets of ice form in the cold upper regions of the cloud. When these ice pellets fall, some of them strike much smaller ice crystals in the center of the cloud. The temperature at the center of the cloud is about -15℃ or lower. At such temperatures, the collision between the ice pellets and the ice crystals causes electrical charges to shift so that the ice pellets acquire a negative charge and the ice crystals become positively charged. Then updraft wind currents carry the light, positively charged ice crystals up to the top of the cloud. The heavier negatively charged ice pellets are left to concentrate in the center. This process explains why the top of the cloud becomes positively charged, while the center becomes negatively charged. The negatively charged region is large: several hundred meters thick and several kilometers in diameter. Below this large, cold, negatively charged region, the cloud is warmer than -15℃, and at these temperatures, collisions between ice crystals and falling ice pellets produce positively charged ice pellets that then populate a small region at the base of the cloud.　　Most lightning takes place within a cloud when the charge separation within the cloud collapses. However, as the storm cloud develops, the ground beneath the cloud becomes positively charged and lightning can take place in the form of an electrical discharge between the negative charge of the cloud and the positively charged ground. Lightning that strikes the ground is the most likely to be destructive, so even though it represents only 20 percent of all lightning, it has received a lot of scientific attention.　　Using high-speed photography, scientists have determined that there are two steps to the occurrence of lightning from a cloud to the ground. First, a channel, or path, is formed that connects the cloud and the ground. Then a strong current of electrons follows that path from the cloud to the ground, and it is that current that illuminates the channel as the lightning we see.　　The formation of the channel is initiated when electrons surge from the cloud base toward the ground. When a stream of these negatively charged electrons comes within 100 meters of the ground it is met by a stream of positively charged particles that comes up from the ground. When the negatively and positively charged streams meet, a complete channel connecting the cloud and the ground is formed. The channel is only a few centimeters in diameter, but that is wide enough for electrons to follow the channel to the ground in the visible form of a flash of lightning. The stream of positive particles that meets the surge of electrons from the cloud often arises from a tall pointed structure such as a metal flagpole or a tower. That is why the subsequent lightning that follows the completed channel often strikes a tall structure.　　Once a channel has been formed, it is usually used by several lightning discharges, each of them consisting of a stream of electrons from the cloud meeting a stream of positive particles along the established path. Sometimes, however, a stream of electrons following an established channel is met by a positive stream making a new path up from the ground. The result is a forked lightning that strikes the ground in two places.　　Paragraph1 : Lightning is a brilliant flash of light produced by an electrical discharge from a storm cloud. The electrical discharge takes place when the attractive tension between a region of negatively charged particles and a region of positively charged particles becomes so great that the charged particles suddenly rush together. The coming together of the oppositely charged particles neutralizes the electrical tension and releases a tremendous amount of energy, which we see as lightning. The separation of positively and negatively charged particles takes place during the development of the storm cloud.　　1. According to paragraph 1, all of the following take place in the development of a flash of lightening &EXCEPT　　○ &great tension between two oppositely charged regions　　○ &an increase in negatively charged particles over positively charged particles　　○ &oppositely charged particles coming together　　○ &the release of electrical energy in the form of visible light　　2.The word &tremendous& in the passage is closest in meaning to　　○ &distinct　　○ &growing　　○ &huge　　○ &immediate　　Paragraph 2: The separation of charged particles that forms in a storm cloud has a sandwich-like structure. Concentrations of positively charged particles develop at the top and bottom of the cloud, but the middle region becomes negatively charged. Recent measurements made in the field together with laboratory simulations offer a promising explanation of how this structure of charged particles forms. What happens is that small (millimeter-to centimeter-size) pellets of ice form in the cold upper regions of the cloud. When these ice pellets fall, some of them strike much smaller ice crystals in the center of the cloud. The temperature at the center of the cloud is about -15℃ or lower. At such temperatures, the collision between the ice pellets and the ice crystals causes electrical charges to shift so that the ice pellets acquire a negative charge and the ice crystals become positively charged. Then updraft wind currents carry the light, positively charged ice crystals up to the top of the cloud. The heavier negatively charged ice pellets are left to concentrate in the center. This process explains why the top of the cloud becomes positively charged, while the center becomes negatively charged. The negatively charged region is large: several hundred meters thick and & several kilometers in diameter. Below this large, cold, negatively charged region, the cloud is warmer than -15℃, and at these temperatures, collisions between ice crystals and falling ice pellets produce positively charged ice pellets that then populate a small region at the base of the cloud.　　3.According to paragraph2, what causes ice crystal to become positively charged?　　○ Collisions with ice pellets　　○ Collisions with negatively charged ice crystals at the base of the cloud　　○ Becoming concentrated in the central region of the cloud　　○ Forming at a temperature greater than -15℃　　4.The word &acquire& in the passage is closest in meaning to　　○ &reject　　○ &obtain　　○ &need　　○ &produce　　5. According to paragraph2, why are positively charged ice pellets produced in the lower part of the cloud?　　○ Collisions between ice crystals and ice pellets increase in number in the lower part of the cloud.　　○ The lower part of the cloud is smaller than the region above it.　　○ More ice pellets than ice crystals reach the lower part of the cloud.　　○ Temperature in the lower part of the cloud are warmer than -15℃.　　6.According to paragraph2, the middle region of a cloud becomes negatively charged due to all of the following EXCEPT　　○ &a shift of electrical charged between ice pellets and ice crystals　　○ &negatively charged ice pellets that remain in the middle　　○ &a temperature of -15℃ or less　　○ &the development of a positive charge at the base of the cloud　　7.It can be inferred from paragraph 2 that part of the reason that the top of a storm cloud becomes positively charged is that　　○ &the top of the cloud is warmer than the middle of the cloud　　○ &the middle of the cloud is already occupied by positively charged particles　　○ &the negatively charged ice pellets are too heavy to be carried by the updrafts that move ice crystals　　○ &collisions between ice pellets in the top of the cloud produce mainly positively charged particles　　Paragraph 3: Most lightning takes place within a cloud when the charge separation within the cloud collapses. However, as the storm cloud develops, the ground beneath the cloud becomes positively charged and lightning can take place in the form of an electrical discharge between the negative charge of the cloud and the positively charged ground. Lightning that strikes the ground is the most likely to be destructive, so even though it represents only 20 percent of all lightning, it has received a lot of scientific attention.　　8.The author remarks that &Lightning that strikes the ground is the most likely to be destructive& in order to &explain why　　○ this form of lightning has been investigated so much　　○ this form of lightning is not as common as lightning within a cloud　　○ scientific understanding of this form of lightning is important　　○ the buildup of positive charge on the ground beneath a storm cloud can have serious consequences　　Paragraph 4: Using high-speed photography, scientists have determined that there are two steps to the occurrence of lightning from a cloud to the ground. First, a channel, or path, is formed that connects the cloud and the ground. Then a strong current of electrons follows that path from the cloud to the ground, and it is that current that illuminates the channel as the lightning we see.　　9.The word &illuminates& in the passage is closet in meaning to　　○ opens　　○ completes　　○ lights　　○ electrifies　　Paragraph 5: The formation of the channel is initiated when electrons surge from the cloud base toward the ground. When a stream of these negatively charged electrons comes within 100 meters of the ground it is met by a stream of positively charged particles that comes up from the ground. When the negatively and positively charged streams meet, a complete channel connecting the cloud and the ground is formed. The channel is only a few centimeters in diameter, but that is wide enough for electrons to follow the channel to the ground in the visible form of a flash of lightning. The stream of positive particles that meets the surge of electrons from the cloud often arises from a tall pointed structure such as a metal flagpole or a tower. That is why the subsequent lightning that follows the completed channel often strikes a tall structure.　　10. According to paragraph5, which of the following is true of the stream of charged particles from the ground?　　○ It prevents streams of electrons from the cloud from striking the ground.　　○ It completes a channel that connects the storm cloud with the ground.　　○ It produces a stream of electrons from the cloud.　　○ It widens the path made by the initial stream of electrons from the cloud.　　11.Which of the following claims about lightning strikes can be inferred from paragraph 5?　　○ During a lightning strike the diameter of the channel the electrons follow is considerably enlarged beyond a few centimeters.　　○ A building is unlikely to be hit by lightning unless it is at least 100 meters tall.　　○ A building is hit by a lightning strike because the building itself has first determined the path the lightening then takes to it.　　○ The light of a lightning strike first appears at the point where the streams of negative and positive particles meet.　　12.The word &initiated& is closet in meaning to　　○ &started　　○ &intensified　　○ &finished　　○ &expected　　The formation of the channel is initiated when electrons surge from the cloud base toward the ground. When a stream of these negatively charged electrons comes within 100 meters of the ground it is met by a stream of positively charged particles that comes up from the ground. When the negatively and positively charged streams meet, a complete channel connecting the cloud and the ground is formed. The channel is only a few centimeters in diameter, but that is wide enough for electrons to follow the channel to the ground in the visible form of a flash of lightning. The stream of positive particles that meets the surge of electrons from the cloud often arises from a tall pointed structure such as a metal flagpole or a tower. That is why the subsequent lightning that follows the completed channel often strikes a tall structure. ■　　Once a channel has been formed, it is usually used by several lightning discharges, each of them consisting of a stream of electrons from the cloud meeting a stream of positive particles along the established path. ■ Sometimes, however, a stream of electrons following an established channel is met by a positive stream making a new path up from the ground. ■ The result is a forked lightning that strikes the ground in two places. ■　　13.Look at the four squares [■] that indicate where the following sentence could be added to the passage.　　The descending stream of electrons divides at the point where the new positive-stream channel intersects the established path.　　Where would the sentence best fit?　　14.Directions: An introductory sentence for a brief summary of the passage is provided below. Complete the summary by selecting the THERR answer choices that express the most important ideas in the passage. Some sentences do not belong in the summary because they express ideas that are not presented in the passage or are minor ideas in the passage. This question is worth 2 points.　　Lightning takes place when a separation of a positive and negative electrical particles that develops in a storm could suddenly collapses.　　○ A storm cloud first develops a positively charged layer at the top, then a negatively charged middle layer, and finally, a positively charged layer at the bottom.　　○ A separation of oppositely charged particles in clouds develops from collisions of falling ice pellets with ice crystals, from updrafts, and from temperature variations.　　○ Lightning from cloud to ground follows a channel that forms when a stream of electrons moving down meets a stream of positive particles coming up from the ground.　　○ Field studies, laboratory simulations, and high-speed photography have all been used to investigate the way charge separations develop in clouds.　　○ Lightning from a cloud to the ground is more likely to be destructive than is lightning that takes place within a cloud.　　○ Once a channel has been formed, it is usually used by several successive electrical discharges that illuminate & the channel as flashes of lightning.　　
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