范文一:量子力学 的建立 Quantum(量子)是一个拉丁语的词,意思是问:“有多少
Quantum,量子,是一个拉丁语的词,意思是问:“有多少,。”要求答复“有这么多。”当它被普朗克引入他的量子理论之后,就被赋予了这样的概念:任何一种能量都不是连续的,它是以特定的量,成批被放出或被吸收的,这种特定的量被称为量子。
按照传统的物理学观点,能量的辐射是连续的。用昔日的原子理论来形容能量,就好比是从水管中喷射出的持续不断的水流。而普朗克则视能量为从一架机关枪中射出的一连串子弹,他将最小的不可再分的能量单元称做“能量子”或 “量子”。他用这一理论很好地解释了一个古典热力学问题即黑体辐射问题,并于1900年12月14日,将这一假说报告了德国物理学会。
这宣告了量子论的诞生。
第一个意识到量子概念的普遍意义,并将其运用到其他问题上的是爱因斯坦。1905年,他建立了光量子论以解释光电效应中出现的新现象,也正是由于爱因斯坦的工作,使量子论在提出之后最初的十年中得以进一步的发展。爱因斯坦也因此获得了1921年的诺贝尔物理奖。
量子力学则起源于原子结构的研究。1912年,丹麦物理学家玻尔为了解释卢瑟福的原子模型,提出了一种量子化的原子结构理论。他认为,电子只在一些特定的圆轨道上绕核运行。波尔的量子化的原子结构理论明显违背了古典理论,遭致了许多科学家的不满,但它在解释光谱分布的经验规律方面意外地成功,使它赢得了很高的声誉、大大推动了量子理论的发展。
1923年,法国物理学家德布罗意提出了物质波理论,将量子理论发展到一个新的高度。沿着物质波概念继续前进并于1926年创立了波动力学的是奥地利物理学家薛定谔。
1925年,德国青年物理学家海森堡写出了以 “关于运动学和力学关系的量子论的重新解释”为题的论文,创立了解决量子波动理论的矩阵方法,后来发展成系统的矩阵力学理论。继而由波恩于1926年提出了波函数的统计解释,最后由英国人狄拉克在前人的基础上建立了一个概念完整的理论体系,至此建立了量子理论与量子力学。
量子力学虽然建立了,但关于它的物理解释却众说纷坛。爱因斯坦与玻尔之间由此产生的争论持续了半个世纪,直到他们本人各自去世也没有完结。
范文二:一个千瓦是多少电流?
一般用电设备一个千瓦是多少电流?
首先,要区分三相用电设备呢,还是单相用电设备;是电感性电器呢?
还是纯电阻电器?
1)三相交流电
1KW
几个电流?感性负载是多少?
答;I≈P/√3/U/Cos¢,电压
0.38KV ,感性负载功率因数
Cos ¢考虑
0.8, I
≈1/√3/0.38/0.8≈1.9A
如果是电动机,还需要查看电动机的名牌上有电机的效率,一般电机效率
0.90-0.95,新型电机有可能在
0.93
以上。这时,这个电流的计算就是; I
≈1/√3/0.38/0.8/0.93≈2A,这个也就是电工常用的经验公式数据,一个千
瓦等于二个电流的说法。
2)纯电阻负载
1KW
是多少电流?
答;纯电阻负载。去掉功率因数就是, I≈1/√3/0.38≈1.52A
3)单相交流电
1KW
几个电流? 感性负载是多少电流?
答;I=P/U/Cos¢,如果电压选择普通民用电压
220V ,感性负载考虑功率因
数
Cos ¢,民用一般考虑
0.85
那么,I=1/0.22/0.85 ≈ 5.34759A
4)纯电阻负载
1KW
是多少电流?
答;纯电阻负载。去掉功率因数就是,I =1/0.22 ≈ 4.545454A
说明;电压等级按照三相
0.38KV ,单相
0.22KV
计算;也可以按照变压
器额定输出电压,三相
0.4KV ,单相
0.231V 。这样的话,计算出来的电流数值
相对小些 ,看你怎么选择的问题。
10KV/0.4KV的电压,1KV A 变压器容量,额定输入输出电流如何计算; 我们知道变压器的功率KV A 是表示视在功率,计算三相交流电流时无需再
计算功率因数,因此,Sp=√3×U ×I 那么,I 低=Sp/√3/0.4=1/0.6928≈1.4434 也就是说1KV A 变压器容量的额定输出电流为1.4434A ,根据变压器的有效率,和能耗比的不同而选择大概范围。高压10KV 输入到变压器的满载时的额定电流大约为;I 高=Sp/√3/10=1/17.32≈0.057737 也就是说1KV A 容量的变压器高压额定输入电流为0.05774A 。
三相电动机直接启动时启动电流为额定电流(电动机名牌上面有注明) 的4-7倍(视负载轻重而定).
用星三减压启动电流是全压启动(直接启动) 电流的1/3.
由于断路器的动作是有时限的,因此额定电流的4-7倍都行,空载启动选下限,带负荷启动选上限。
采用星-角启动的,启动电流要比直接启动低1.7倍,但持续时间要长些,切换到角形后,电流变化不大。
一般热继电器的电流取电机额定电流的1.5倍左右
已知三相电动机容量,求其额定电流
口诀:容量除以千伏数,商乘系数点七六。
已知三相二百二电机,千瓦三点五安培。
1KW ÷0.22KV*0.76≈1A
已知高压三千伏电机,四个千瓦一安培。
4KW ÷3KV*0.76≈1A
注:口诀适用于任何电压等级的三相电动机额定电流计算。口诀使用时,容量单位为kW ,电压单位为kV ,电流单位为A 。
800/10*0.76=60.8A
也可以用以下公式计算:用功率除以额定电压(KV )再除以根3(即1.732)再除以功率因数即可
电机电流计算公式
你算的很对啊,就是你说的这个公式,至于U ,要由用电设备的电压决定,低压三相就是380V ,
单相就是220V ,但当为单相时不要除以√3,即I=(P/U)×cos φ(A)。
10KV 的三相电机额定电流计算时,U 应该是10KV 。 10kv 中 基本是15个KW 一个电流 如400KW 10KV电机 I=400KW除以(电压KV 乘以1.732乘以0.85)=26.66666A 即等于 400KW 除以26.6666666电流= (一个电流15KW )
电流=功率/1.7321*电压*功率因素, 电机一般取0.85. 即22/(0.38*1.732*0.85)≈39.33A, 如果考虑效率(即电动机实际输出功率有22kW), 一般再取0.9的系数, 即39.33/0.9=43.7A。 所以在没有太准确要求的场合,一般电机电流即按2倍功率数。
空开
如果不是频繁起动的大于1.5倍也可以了。频繁起动的要大于4倍。
范文三:电导量子化JApplPhys
Observing “quantized” conductance steps in silver sulfide: Two parallelresistive switching mechanisms
Jelmer J. T. Wagenaar, Monica Morales-Masis, and Jan M. van Ruitenbeek
Citation: J. Appl. Phys. 111, 014302 (2012); doi: 10.1063/1.3672824 View online: http://dx.doi.org/10.1063/1.3672824
View Table of Contents: http://jap.aip.org/resource/1/JAPIAU/v111/i1 Published by the American Institute of Physics.
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JOURNAL OF APPLIED PHYSICS 111, 014302(2012)
Observing “quantized”conductance steps in silver sulfide:Two parallel resistive switching mechanisms
Jelmer J. T. Wagenaar, Monica Morales-Masis, and Jan M. van Ruitenbeek a)
Kamerlingh Onnes Laboratorium, Leiden University, P.O. Box 9504, 2300RA Leiden, The Netherlands
(Received2September 2011; accepted 28November 2011; published online 3January 2012) We demonstrate that it is possible to distinguish two conductance switching mechanisms in silver sul?dedevices at room temperature. Experiments were performed using a Ag 2S thin ?lmdeposited on a wide Ag bottom electrode, which was contacted by the Pt tip of a scanning tunneling microscope. By applying a positive voltage on the silver electrode, the conductance is seen to switch to a state having three orders of magnitude higher conductance, which is related to the formation of a conductive path inside the Ag 2S thin ?lm.We argue this to be composed of a metallic silver nanowire accompanied by a modi?cationof the surrounding lattice structure. Metallic silver nanowires decaying after applying a negative voltage allow observing conductance steps in the breaking traces characteristic for atomic-scale contacts, while the lattice structure
C 2012deformation is revealed by gradual and continuously decreasing conductance traces. V
American Institute of Physics . [doi:10.1063/1.3672824]
I. INTRODUCTION
It poses an interesting challenge to attempt to create atomic scale switches for implementation in future electronic devices, and some progress in this direction has been reported. 1–4One of the proposed switches is based on cation migration and redox reactions in solid-state ionic conductors. 5–7Terabe et al. 3reported atomic switching behavior by electrochemical reac-tions taking place in a vacuum gap between micro fabricated Pt and Ag 2S electrodes. They showed switching between integer values of the unit of conductance, G 0?e12:9k X Tà1, at room temperature and attributed this to the formation of a contact made up of a single atom, or a few atoms. Atomic conductance steps were also observed much earlier by Hajto et al . 8in a metal/pt-amorphous Si/metalthin ?lmmemory structures.
Here, we report on investigations on the conditions for observing atomic switching behavior without a vacuum gap. 10We used a device composed of a Ag 2S thin ?lmdepos-ited on top of a wide Ag layer. By contacting the thin ?lmwith the Pt tip of a scanning tunneling microscope (STM)and applying a positive bias voltage to the silver bottom layer the Ag 2S ?lmwas seen to switch to a high-conductive state. This high-conductive state is associated with the creation of a con-ducting path inside the Ag 2S ?lm.11The Ag 2S ?lmcan be switched back to the low-conductive state by applying a neg-ative bias voltage, which is associated with breaking up, or dissolution, of the conductive path. In analyzing ‘on’to ‘off’conductance traces we found evidence for the coexistence of two parallel breaking mechanisms.
II. EXPERIMENTAL DETAILS
roughness of 30nm. The fabrication process and the charac-terization are described in more detail in a previous report by Morales et al. 12
The measurements have been performed using a JEOL ultrahigh vacuum STM (JSPM-4500A) at room temperature and at a pressure of 10à9mbar. The contact geometry is illustrated in the inset in Fig. 1(a). A FEMTO (DLPCA-200)current ampli?erwas used to replace the standard JEOL cur-rent ampli?erin order to cover a larger current ampli?cationrange. In terms of electron transport silver sul?deis a semi-conductor, therefore, control of the tip-sample distance requires biasing well below or well above the bandgap. 13In order to avoid early ion accumulation and the build up of a conducting path before the start of the experiment, the set-ting of the tip-sample distance requires a negative voltage on the sample, larger than the bandgap. An external data acqui-sition card from National Instruments was added to the con-troller of the STM in order to apply the sample voltage and for measuring the current. The data acquisition card was con-trolled by a Labview program that was setup for measuring current-voltage (IV)characteristics, and traces of conduct-ance (G)versus time (t).
III. RESULTS A. IV characteristics
The deposition of Ag 2S was achieved by sputtering Ag in a Ar/H2S plasma. It was deposited on top of a Ag ?lm(200nm) which sits on a Si(100)substrate. The thickness of the silver sul?delayer is approximately 200nm and has a
a)
Electronic mail:ruitenbeek@physics.leidenuniv.nl.
Before starting the measurements we need to con?rmthat the tip is in contact with our sample. This can be decided based upon the measured current-voltage relation. When a large tunneling gap is formed the resistance is dominated by vacuum tunneling and the IV curve is nearly linear, for suf?-ciently low bias. On the other hand, when in contact an expo-nential current-voltage characteristic is observed that is the result of ion accumulation near the contact at positive bias before full conductance switching occurs. The ions act as dopants and their accumulation results in an exponential
014302-2Wagenaar, Morales-Masis, and van Ruitenbeek J. Appl. Phys. 111, 014302(2012)
FIG. 1. (Coloronline) (a)Current-voltage characteristics of a Ag-Ag 2S-Pt device (seeinset) measured for a cycle duration of 1s. The ramp was started at 0V and follows the red arrows. In this IV curve full conductance switch-ing is observed. The inset illustrates the contact geometry. (b)Expanded scale view of the section of the IV curve in the ‘off’’state in (a).This part of the IV curve is ?tvery well by Eq. (1)(redcurve), indicating that the Pt tip is in contact with the Ag 2S ?lm,and that the ?lmis in its equilibrium (semi-conducting) state. The zero-bias conductance of the off-state is approxi-mately 0.2G 0for this contact size. (c)On-state section of the IV curve in (a).At this stage, the sample has a conductance of 100G 0, and the linear ?t(redline) indicates metallic behavior.
FIG. 2. (Coloronline) Evolution of the off-state conductance curve for a Ag 2S ?lmwith an increasing number of switching cycles. Each of the IV curves in the plot is measured after a full switching cycle, such as the one shown in Fig. 1(a). The ?rstcurve (innergreen curve) is measured after the ?rstswitching cycle, and the ?tto Eq. (1)indicates that it remains close to the initial state of the pristine sample. The arrows give the direction of evo-lution for consecutive cycles. The zero-bias conductance of the junction changes from 0.1G 0(?ttedcurve) to approximately 1G 0(outercurve).
increase of the electronic conductance. The IV curves are well described by the following expression:12
k B T eeV =k B T T
e I eV T?K r 0à1; (1)
with r 0?7:810à2X à1m à1the electronic conductivity of Ag 2S at zero bias, 14T ?295K is the temperature, k B is Boltzmann’sconstant, and K is a geometrical factor with dimensions of length representing the contact size.
We measured IV curves by ramping the bias voltage and measuring the current with a sampling rate of 10000samples per second. In ?ttingthe data with Eq. (1), K is the only ?t-ting parameter, from which we determine the size of the Pt STM tip contact. Figure 1(b)presents the IV curve for the low-conductance state (off-state)and the ?tof the curve to Eq. (1). From the quality of the ?twe conclude that the sam-ple is in its pristine, semiconducting, state and that the Pt tip is in contact with the sample. We can also conclude that there is no Joule heating of the sample since the temperature dependency is in the exponential. Increasing the voltage fur-ther causes switching to the on-state [Fig.1(a)]due to the formation of a conductive path. Figure 1(c)shows an IV curve for the on-state, and the linear ?tindicates metallic behavior. Subsequently, returning to a suf?cientlylarge neg-ative voltage the sample switches back to the off-state.
After switching the device several times the off-state conductance of the sample becomes strongly modi?ed.The evolution of the off-state IV curves with the number of switching cycles is presented in Fig. 2. The switching cycles were similar to the one shown Fig. 1and the IV curves were IV characteristics of the pristine sample (innergreen curve) we observed the conductance increasing from 0.1G 0to 1G 0after the sixth cycle.
Initially, the IV curves are described well by Eq. (1)(thered dashed curve). After several switching cycles the IV characteristic can only be ?tby adding a signi?cantlinear term to Eq. (1). This higher conductance state of the sample will eventually return to the initial conductance after apply-ing a negative voltage for a longer period of time as will be shown below (Fig.4). This changing sample conductance characteristics after switching has been reported previously and is referred to as the learning behavior of the switching mechanism, 15, 16and is being explored for realizing arti?cialsynapses. 9
B. Breaking
We measured traces of conductance as a function of time by control of the bias voltage in the following way:when the conductance was seen to fall below 0.5G 0a positive bias voltage was applied to the sample. To achieve rapid switching we used a voltage of t100mV. 13A high-conductance path was formed and the conductance was seen to rise to values above 100G 0. Once G was detected to pass above 100G 0a negative bias voltage of à100mV was applied to the sample in order to break the
conductive path, until the conductance approached the initial state of G <0.5g 0.="" in="" this="" way="" the="" for-mation="" and="" breaking="" process="" is="" more="" controllable="" than="" by="" applying="" ?xedpulses="" to="" the="">0.5g>
We measured many breaking traces at different spots on the sample and we recognized two types of traces:traces having a step-like pattern, and traces showing only a slow and continuous decay of the conductance. The observed pat-terns in the traces indicates the coexistence of two switching mechanisms.
The ?rstmechanism is the dissolution of a metallic sil-ver conductance path showing, at the ?nalstages of the breaking, atomic conductance steps. When a metallic silver ?lamentdominates the conductance, upon applying a nega-
014302-3Wagenaar, Morales-Masis, and van Ruitenbeek J. Appl. Phys. 111, 014302(2012)
FIG. 3. (Coloronline) Steps in the conductance become visible when break-ing the conductive path at a bias of à100mV. The conductive path was formed by applying a voltage of t100mV, allowing the conductance to reach 100G 0within a second. (a)Breaking trace with three clear conduct-ance steps of approximately 1G 0observed at the last stages of breaking. The inset shows a zoom of the steps. (b)Three breaking traces with atomic con-ductance steps having different lengths in time. The measurements were per-formed on different spots of the sample and using different Pt-tips. The upper trace shows two-level ?uctuationsthat are typical for atomic size con-tacts, and are attributed to single atoms oscillating near the contact.
FIG. 4. (Coloronline) (a)Continuous conductance changes observed when breaking a preformed conductive path at a bias voltage of à100mV. Mixed behavior is seen in the middle trace. The inset shows a magni?cationof the steps of approximately 1G 0. The upper trace shows only continuous behav-ior and illustrates the high-conductance that is visible in some measurements after switching several times. The lower trace also shows only continuous behavior but the high-conductance state decays in few seconds to a conduct-ance around 0.1G 0. (b)Comparison between a continuous trace [lowertrace presented in (a)]and a trace with atomic conductance steps [middletrace in Fig. 3(b)
].
reduced to only a few bridging atoms. In this way quantum properties of the conductance of the silver ?lamentwill show up. 17Figure 3shows some examples of atomic con-ductance steps observed in conductance traces recorded as a function of the breaking time. In Fig. 3(a), one observes that the conductance decays almost linearly until arriving at about 5G 0, when steps of close to 1G 0in height start to be visible. Very pronounced plateaus and steps of approxi-mately 1G 0can also be seen in the plots of Fig. 3(b), with a very long plateau of 0.4s in the middle trace. The upper trace also shows two level ?uctuationswith an amplitude close to 1G 0that is typical for atomic-scale contacts. 17
However, there appears to be a second mechanism active. We conclude this from the observation of a slower and nearly continuous decrease of the conductance. Traces with atomic conductance steps appeared only when the con-ductance rapidly dropped below 0.5G 0in approximately one second. When the decrease in the conductance was slower, we observed behavior as illustrated by the upper trace in Fig. 4. This is accompanied by a change in the IV characteristics similar to Fig. 2. We attribute this behavior to a second mechanism, most likely due to a modi?cationof the local lat-tice structure giving rise to a region of increased conduct-ance. This modi?cationis probably induced by the electric ?eldand the increased concentration of silver in the region of switching. It has been previously shown that the electric ?eldcan induced phase transitions, or decrease the phase and complex perovskites. 19After applying a negative volt-age silver diffuses back to the Ag bottom reservoir and the lattice slowly relaxes to its equilibrium structure. 11
Occasionally, the two processes can be observed to-gether, as illustrated in the lower trace in Fig. 4:around 6G 0atomic conductance steps are visible, while somewhat later there is a continuous decrease over ?veseconds from 2to 1G 0. In terms of the two mechanisms described above this may be explained as being due to two parallel conductance paths.
C. Controllable switching
The continuous evolution of the IV characteristics in Fig. 2and the continuous ‘on’to ‘off’conductance traces suggests that the local structure of the Ag 2S ?lmhas been modi?ed.The conductance in this state can be controlled by applying positive bias voltages smaller than the threshold voltage. The voltages can be chosen to obtain speci?cvalues of conductance as illustrated in Fig. 5. In this example the conductance of the contact at a bias of à110mV was 0.3G 0, slightly higher than the conductance of the contact in the pristine state of 0.1G 0.
This nanoscale resistive switch in the regime of the quantum of conductance should not be confused with an atomic scale switch. The steps that we attribute to intrinsic
014302-4Wagenaar, Morales-Masis, and van Ruitenbeek J. Appl. Phys. 111, 014302(2012)
FIG. 5. (Coloronline) Switching between targeted values of conductance by applying speci?clow-bias voltages to the Ag 2S device. In this experiment the voltages were chosen such as to obtain approximately the ?rsttwo inte-ger conductance values, in analogy to the experiments by Terabe et al. 3Here we use ?xedbias voltages instead of short pulses. This controllable switching can only be achieved after preparing the sample by several switch-ing cycles. This example is chosen for illustration of the ambiguity that may arise when deciding whether a device is a true atomic scale
switch.
FIG. 6. (Coloronline) The measurements suggest that three structures are involved in the conductance after full resistive switching. Before switching we have our pristine sample which obeys the IV relation of Eq. (1). During switching a high-conductive path is formed by metallic silver and, in paral-lel, by a modi?edstructure of the silver sul?de(X).An interpretation of this modi?edstructure comes from comparison of our results with Xu et al ., 11who identi?edit in HRTEM studies as the argentite phase of silver sul?de.
(Fig.3), and the IV curves in this state are linear, so that the conductance does not depend on the bias voltage. By con-trolling the second mechanism of conductance switching any conductance, including ‘quantized’values, can be set and maintained. The time scale for this process is much longer, and it allows manipulating the conductance over a wide range (Fig.5).
IV. DISCUSSION
We have observed two types of conductance breaking traces, which we associate to the occurrence of two switch-ing mechanisms in silver sul?de.First, the presence of atomic conductance steps supports an interpretation in terms of the formation of a metallic silver ?lament.From previ-ously performed experiments 17we can state that a Ag atomic scale point contact presents steps in the conductance at the last stage before it breaks. However, the controllable switch-ing, the continuously changing IV characteristics, and the gradually decreasing conductance traces cannot be explained by the formation of a metallic silver ?lamentalone. The fact that the gradually decreasing conductance traces can take several seconds to return to the ‘off’conductance (Fig.4), and decay of concentration gradients in Ag 2S occurs much faster than a second 12point toward the view that a modi?ca-tion of the lattice structure is induced, which we refer to as the second mechanism of conductance switching. Figure 6shows a cartoon of the three different structures that may contribute in parallel to the total conductance:the pristine semiconducting sample (Ag2S), metallic silver ?laments(Ag),and the as yet unde?nedmodi?edstructure (X).
Our interpretation is consistent with the observations by Xu et al. 11from in situ switching measurements of a Ag/Ag2S/Wdevice. From real time measurements inside a high-resolution transmission electron microscope (HRTEM),Xu et al. determined that the conductive path formed when applying a positive voltage to the Ag electrode, is composed of a mixture of metallic Ag and argentite Ag 2S.
At room temperature, the equilibrium lattice structure of the lattice undergoes a phase transition to the argentite struc-ture. Argentite has an electronic conductivity that is three orders of magnitude higher, and behaves like a metal. 20The argentite structure has previously been stabilized at room temperature by rapidly cooling of silver sul?defrom high temperatures. 21According to Xu’sinterpretation, this phase transition to the argentite phase is not caused by Joule heat-ing because the currents are quite low at the off state, but is believed to be driven by the increased silver ion concentra-tion and the applied ?eld.
Adhering to this interpretation of the phase transition we explain the observed continuous traces and mixed traces shown in Fig. 4as follows. The bias voltage drives both switching mechanisms:metallic ?lamentformation and the local partial phase transition. When a silver ?lamentis formed that stretches fully across the thickness of the ?lmits high conductance dominates the observed electron transport. Break down of the ?lamentat the last stages produces a con-nection formed by just a few atoms, and when these discon-nect one by one this becomes visible as near-quantized steps in the conductance. When the metallic silver of a ?lamentdissolves very rapidly, or an incomplete ?lamentis formed, atomic conductance steps will be absent and the conductance will drop continuously, as a result of the gradual decay of the locally modi?edstructure. When the breaking of the sil-ver ?lamentoccurs on the same time scale as the decay of the modi?edstructure back to the initial room temperature phase, mixed behavior as seen in the middle curve in Fig. 4can be observed. The conditions for the formation of a metal-lic silver ?lamentand the observation of atomic conductance steps are not yet fully understood, since the two processes are controlled by the same bias voltage.
V. CONCLUSION
In summary, we identify two mechanisms of conductive path formation inside a thin ?lmof silver sul?de.The ?rstmechanism is the formation of a metallic silver ?lamentwhich we associate with the observation of atomic conduct-ance steps. Second, there is a modi?cationof the silver sul?de
014302-5Wagenaar, Morales-Masis, and van Ruitenbeek
8
J. Appl. Phys. 111, 014302(2012)
J. Hajto, M. Rose, A. Snell, I. Osborne, A. Owen, and P. Lecomber, Jour-nal of Non-Crystalline Solids 137–138, 499(1991).9
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this modi?edstructure is continuously tunable, and allows setting the conductance to any target value by applying appropriate positive voltages. Contrary to previous reports, 9, 16we argue that this controllable switching cannot be attributed to an intrinsic atomic scale structure. The memory functions explored by Ohno et al. 9cannot be explained by a metallic ?lamentformation alone. Our results point toward the role of the two switching mechanisms in deciding whether the infor-mation is maintained for shorter or longer times.
ACKNOWLEDGMENTS
This work is part of the research program of the Dutch Foundation for Fundamental Research on Matter (FOM)that is ?nanciallysupported by NWO.
1
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范文四:[一个苹果的热量是多少]一个苹果多少卡路里?
[一个苹果的热量是多少]一个苹果多少卡路
里,
篇一 : 一个苹果多少卡路里,
一个苹果多少卡路里, 苹果 100克 57卡
五谷类:
白饭 1碗 220卡 白粥 1碗 88卡
米粥 1碗 173卡 河粉 1碗 283卡
意粉 1碗 174卡
通心粉 1碗 167卡
面 1碗 280卡
即食面 1包 470卡
上海面 1个 207卡
伊面 1个 404卡
面包 2片。无花果根主治:?治筋骨疼痛,风湿麻木:无花果根或果,炖猪精肉或煮鸡蛋吃。?治喉痒:无花果根去粗皮,打碎,开水泡服。?治颈淋巴结核:鲜无花果根50克,水煎服。
二、无花果的快繁栽培
1(快繁方法。?扦插嫩枝。将上年腊月的嫩枝,结合修剪剪下。
后将剪下的壮枝顶端朝上,理顺扎起。每30,40根扎一把,紧紧排在长形假植沟内,上覆沙土,露顶芽,浇足水,及时盖上薄膜,确保安全越冬。?准备苗床。4月初,在冻晒垡的耕地内, 做成许多宽 1, 1.3 米,长度不限的苗床。 每 0.1亩苗床施腐熟粪肥200千克左右或腐熟饼肥5千克,土杂肥150千克,作基肥。施后翻入土中,整平畦面,准备扦插。?培育壮苗。从假植沟内取出插条,先用一根略粗于插穗的木棒,按行、株距30厘米×20厘米打孔,孔深为插穗的3/4,然后插入穗条,压实泥土,浇足水。苗床管理,必须旱浇涝排,不定时拔除杂草。苗高40,50厘米时摘掉顶心,让其多发连枝。
2(科学栽培。?挖坑施肥。当年腊月,按3米×3米的行、株距,挖定植坑,坑口直径50厘米,深65厘米,每坑施腐熟粪肥15千克或饼肥3千克,过磷酸钙0.5千克,钾肥0.2千克。将肥料拌入熟土内,填入坑中,让其充分腐熟,待定植。?带土定植。挖取当年培育的壮苗带土移植,浇足水分,压实表土。生长期间,根据植株长势及天气情况及时追肥水,每隔20,25天追1次有机肥,并防旱排涝,及时中耕除草。?修剪整枝。整枝分冬季和夏季2次修剪。冬季修剪采用开心形的株形较好。无花果发枝力弱,应轻剪,一般只对下垂枝、干枯枝、徒长枝剪掉,其余枝条任其生长;夏季修剪主要是防止不必要的新梢生长,必须抹除赘芽。?病虫防治。虫害发生期一般在7,9月份,每隔10天左右检查一次。无花果的主要害虫是桑天牛。桑天牛以幼虫越冬,第二年春分后开始取食,幼虫钻蛀茎干形成虫孔,
并隔一定距离咬一圆洞排泄粪便,7月上旬始见成虫,8月上旬为成虫盛发期,并且是产卵高峰期。成虫取食新枝近基部上树皮,致新枝损伤,以致枯死。卵米粒形,产卵前成虫在枝干韧皮部和木质部之间咬一凹槽,随后产卵其中,每一凹槽产卵1粒,一株上有时产卵7,25粒。防治方法:一是人工捕捉成虫。当成虫栖息在新枝上取食或产卵时,一经发现即捕杀。二是捅槽灭卵。把竹片削尖,插入产卵凹槽,捣烂卵粒,有效率可达90%以上。三是药剂防治。用注射器往排泄孔内注射1000倍液晶体敌百虫,效果100%。
无花果别名:优昙钵、映日果、天生子、奶浆果、树地瓜、木馒头、文仙果、品仙果、名目果、底珍、蜜果等,是桑科榕属亦称无花果属落叶灌木或小乔木,小花隐生于囊状花托内,全果内有密生的小花2000个,与肉质肥厚的囊状花托组成果实,因花小不露其外,古人误以为无花。无花果在西班牙、意大利、土耳其、希腊和美国等国家和地区的产量为多。
无花果是人类最早进行驯化栽培的四大果树之一,发源地在阿拉伯南部半岛。考古人员在中东的一处古人类遗址发现了几块公元前9600年左右的无花果化石,并且这些无花果没有核,无法自行繁殖,只有靠人类帮助才能繁衍,它就成了人类最早种植的农作物。2006年《探
索》杂志就公布当年六个重大科技发现,其中一个就是确定无花果是农业的开端。无花果要比小麦等农作物栽培出现的时期提前1000年。
根据确切的资料证明,大约在公元前3000年左右,在阿拉伯南部半岛的沙特阿拉伯、也门等地区的人们已经开始种植无花果。无花果在地中海沿岸国家被称为“圣果”,当时的人们把每年最早收获的果实作为祭祀的果品。后传入地中海沿岸诸国,是地中海早期文明时期的重要食品。古埃及金字塔中就曾发现描绘灌溉和收获无花果的浮雕图案,在埃及本哈尼森古墓中也发现了一幅埃及人采收无花果的壁画。壁画中显示古埃及人训练狒狒攀援无花果树采果,并将其放入篮中,然后再由人把果实运走的情景。在美索不达米亚的尼普尔古城堡中发掘出公元前3000年的石刻图,上面用楔形文字记载了十二个药方,几乎每个药方中都列有无花果。
无花果拉丁学名中的Carica,就是因为此果是古希腊人从小亚细亚的卡里亚引进。希腊神话中,日神泰卫为了营救被天神宙斯紧紧追赶的勃克斯的儿子,让他变成一株无花果树,瞒过天神宙斯。古罗马时代传说有一株神圣的无花果树,因为他曾庇护过罗马的创立者罗莫路斯王子,躲过了凶残的妖婆和啄本鸟的追赶,后来被命名为“罗来亚”,意思即“守护之神”。长期以来无花果树在古罗马宫廷中成为重要饰品,人们对它表示无限的崇敬。东欧一些国家至今还把无花果作为幸福、美满的象征,是新婚时不可缺少的礼品。
《圣经》里多次提到无花果。亚当和夏娃偷吃禁果后,“眼睛就明亮了,才知道自己是赤身露体,便拿无花果树的叶子,为自己编作裙子。”摩西引领希伯来人从埃及回到迦南,派人去窥探迦南地的肥瘠,手下人砍了挂枝的葡萄,带了些石榴和无花果回来。先知以赛亚曾用一块无花果饼治愈了希西家王的病。无花果作为天堂果品而深受基督徒的喜爱,与葡萄、桑椹同属“内外皆可食”的三大重要水果。
《古兰经》第九十五章--绨旎,是《古兰经》中唯一以植物命名的章节,其中有“奉至仁至慈的真主之名,以无花果和橄榄果盟誓”。伊斯兰教中无花果是先知努哈在大洪水之后在朱迪山上种植的果树,在此表示对真主的感谢。相传圣门弟子赠送穆罕默德一些无花果,他高兴的接受了并对众人说:”假如乐园的果品留存在世,我相信它就是无花果。”但在阿拉伯各国某些地方谚语中,无花果的文化含义却不甚好。比如谚语:“仇人成不了朋友,无花果结不出葡萄”;伊拉克谚语:“果园里的雄无花果长得高大但不结果”,意为中看不中用;埃及谚语“在未得到无花果之前,先用野无花果充饥吧”,意聊胜于无;“他身上的无花果叶子掉下来了”,意即“他已经暴露无遗”,因为无花果叶是人类始祖的第一件衣服。
大约公元9至13世纪,无花果被引到法国、英国以及非洲北部一些国家,开始大范围传播。公元16世纪引种到苏联,公元17世纪初
葡萄牙的航海者把无花果带到东南亚地区,继而通过传教士传到各地种植。中国的无花果引进路线有两条,一条是从西北的丝绸之路,另一条是从海路。无花果何时传入中国的说法不一,一般认为大约在唐代前后,沿着丝绸之路与扁桃、阿月浑子等,同时由商人和僧侣引入新疆南部地区种植。所以无花果与石榴、葡萄一同被誉为丝绸之路三大名果。山东威海的无花果是英国租借威海卫后,由英国传教士从欧洲经海路传入的,当时引种的品种是青皮。因为威海与地中海地区有相同的纬度和相似的气候,无花果的繁殖、栽培又非常简单,所以几乎家家户户都有种植,甚至走在街上都可以随手摘下一个无花果。
中国有关无花果的最早记载是成书于公元860年前后唐代段成式的《酉阳杂俎?木篇》:“底称实, 波斯国呼为阿驛,拂林呼为底珍。树长四五丈,枝叶繁茂。叶有五出,似椑麻,无花而实。”到了宋代南方也开始种植,因为其果形似北方的馒头,所以南方人多称其为“木馒头”,并因它无花而实,开始称它为“无花果”。到明代时无花果被广泛的种植,还被当作一种灾年的救荒之物。十七世纪陈淏子的《花镜》概括无花果其利有七:一是实甘可食,营养丰富;二是可制干果;三是常供佳食,采摘供食可达三月之久;四是大枝扦插,本年结实;五是叶为医痔圣药;六是未成熟的果实可作糖蜜渍果;七是得土即活,随地可种。
无花果树喜阳光、温暖和比较干燥的大陆性气候,较耐旱,不耐寒,
不抗风,喜肥,对土壤要求不甚严格,较耐盐碱,但不耐涝。无花果是目前世界上投产最快的果树之一,也是一种优良的观赏植物,不仅郁蔽度大,且叶中含有一种特殊的香气,清香宜人,少病虫,可滤清空气中二氧化硫、三氧化硫、苯等有害气体,是城市绿化的适宜树种。
无花果是由花托及花的其它器官发育形成的复果。无花果花托向中间卷起,像包包子一样把花蕊包起来,其实无花果整个是一朵花。无花果呈球形、椭圆形、梨形或枇杷形,果皮颜色有黄色、绿色、浅红、红褐、深紫等,果肉为粉红、深红或乳黄色等。掰开无花果时会见到许多丛状物,还有小籽,那就是受粉而结的种籽。结籽的是雌蕊,不结籽的是雄蕊。
无花果几乎每个新梢均可成为结果枝,每个叶腋几乎都是结果部位,从枝条的下部向上逐渐挂果、成熟。春季新芽展叶的同时,每个叶柄基部长出一个幼果,最终形成“夏果”;新梢延长生长的同时,又由基部向上渐次形成花托,长成“秋果”。秋果着生在当年抽生的新梢上,而夏果着生在去年形成的枝条上。约在农历五月底,先一年越冬的存留果实成熟;七月中当年第一次坐的果实成熟;九月后第二次坐果成熟;余下尚未成熟的果实则要越冬后第二年成熟了,这是无花果的一个特点。
无花果属浆果,果肉和叶中的白色乳液含有蛋白质。果实成熟后肉
质柔软,顶端开裂,皮薄无核,香甜可口,软烂象柿子,以个儿大、味道甜度高者为最好。无花果可食率高达92%以上,富含蛋白质、氨基酸、维生素和矿质元素,含糖量达15%至20%,具有很高的营养价值和药用价值。无花果的果实极为鲜嫩,一般采摘后当天就要食完,放到第二天就会发酸,不能食用,更难以外运,故多用以晒制果干,还可加工成果脯、果酱、饮料等。
无花果秋果和夏果的品质特征略有差别,秋果采收期长,产量高,品质普遍都优于夏果。每棵果树的结果数夏果平均仅34个,秋果达89个;含总糖量夏果最高为12.1%,秋果最高达17.43%;其他营养成份的含量以及食用的口感等,都是秋果优于夏果。只是单果重量夏果大于秋果,夏果的单果重最大达66.5克,最小也达62.73克,而秋果最大仅63.78克,最小只有41.07克。
无花果果、叶、枝、根均可入药,性平味甘,有健肠清胃、消肿解毒、疗咽冶痔、明目生肌等功效,可以用来治疗肠炎,痢疾,便秘,痔疮,喉痛等。特别是无花果具有治疗癌症的作用,对胃癌、食道癌、皮肤癌、膀胱癌等有一定的疗效。无花果叶煎水局部熏洗,可治疗疮疡肿毒、痔疮疼痛。枝、茎、叶的浆汁可用于治疗皮癣。
桑科无花果属约有600余种,中国有120个种。多数原产于热带、亚热带,以大乔木、小乔木为主,少数为藤本,其中只有Ficus carica
L(一个种具有经济栽培价值,现有栽培品种1000余个,其中主要栽培品种约有40多个。
按无花果的生长习性及分布可分为:普通、矮生、大无、埃及四类。
根据无花果品种的授粉关系和花器的类型可以分为:原生、普通、斯密尔那、中间型四类。中国现有无花果品种大都属普通型,雌花很少,不需授粉即能单性结实。
无花果的品种按照成熟期可分为:?早熟种以结夏果为主,主要析品种有:罗亭氏卡毕力、紫陶芬、乌兹别克黄、卵圆黄、白圣比罗、普鲁油脂等。?中熟种品种最多,产要的品种有:加州黑、卡独太、白马赛、白热那亚、玛斯义陶芬、达尔马提卡、查勃拉勃尤斯维克、紫色博尔热左特、布左伊-布鲁乌、萨雷无花果、阿塞歇伦、索奇4号、利瓦迪、新疆早熟无花果、新疆晚熟无花果、小黄果、英国红色种黑斯蜜如、紫斯蜜如、大果卡毕力、谷川、罗依尔维尼亚特等。?晚熟种有白热那亚、布兰瑞克、黑大果、安替、蓬莱市、罗英杰等。
无花果按照果皮的颜色可分为:?黄色果:新疆早熟无花果、小黄果、乌孜别克黄果、索奇4号、卵圆黄、布兰瑞克、卡独太等。?紫红色果:玛斯义陶芬、加州黑、HAA9等。?紫色果:棕色土耳其、紫斯蜜加、黑大果、紫果1号。?淡棕色果:罗英杰。?淡绿色果:
10月礼品、绿抗一号、绿抗二号。
中国无花果产地主要分布在新疆、山东、江苏、上海、浙江、福建、广东、陕西、四川等地。华北地区的无花果主要集中在山东沿海的青岛、烟台、威海,江苏省主要分布在南通、盐城、丹阳、南京,福建省集中栽培主要在福州,上海市郊也有一定面积。新疆的无花果无论产量或品质都冠盖全国。无花果在中国虽然种植分布广,但集中成片的极少,属于稀有水果品种。另外,在中国有好几种无花果,河北地区的文光果、四川地区的天仙果、两广地区的左度子等皆称之为无花果,实则也是它们的花隐蔽而不易见到罢了,类似植物还有橡皮树、榕树、菩提树、薛荔等。篇四 : 把6个苹果放进五个抽屉,有多少种放法:组合数学介绍一
把6个苹果放进五个抽屉,有多少种放法,
据说这是小学四年级的奥数题。小时候参加过不同级别的奥数竞赛,现在仍然能感觉到那些题目及解答的巧思妙想。但是随着学习的深入,就会慢慢发现当初是靠“奇思”解决的问题,逐渐在数学体系面前成为普通的推理,例如利用光行最速原理解决韩信信号兵问题,学了微积分,就知道不过是简单的单约束条件的优化问题。同样这放苹果的问题,就属于数学的1个分支:这就是组合数学。英文叫做:Combinatorics。组合数学可以看作一门相对独立的学科,也可以看作离散数学的分支,因为它是研究离散对象的,研究一定条件的组态的构造,计数分类等相关问题。
下面我们把这个放苹果问题进行泛化。如果苹果是可以区别的,我们可以把他们想象成写着A,B,C,D,E的卡片,然后面对从左到右的五个抽屉,有多少种排列方法,组合数学的第1个思想就是元素分析,即对任实际应用时候根据情况来使用。
仔细想一下就会知道,这种情况下放苹果,其实不同放法之间的区别就是抽屉里面苹果数量的变化,而和到底哪些苹果放进去没有关系。所以我们用1个更一般的模型代替:
X1+X2+X3+X4+X5=6
这里X1,...X5都是大于等于0小于等于6的整数。于是我们就是要找到上述模型的整数解有多少组。
古典组合数学的另外1个思想就是整体分割的思想,构造1个等价于原问题的整体集合,然后进行等价分割获得结果。
于是,我们构造这样1个模型,用十个元素构造出1个原始集合,然后再此集合中取4个,换句话说这就把十个元素分成了五个部分,然后每个部分所含元素的数量就是X1,X2,X3,X4,X5的知。显然这时候可能组数为C。
任意取4个满足限制条件X1...X5都在0,6之间,同时我们模型的任意划分显然是X1+...+X5=6的解。而任意X1+...+X5=6的解,也显然对应我们的1个划分,于是此解是所求。
一般的,对于不可分的M个物体,放到N个抽屉,其解为C。
范文五:求一个数的几倍是多少
教学内容 ; 《求一个数的几倍是多少》
教学目标
1、初步理解求一个数的几倍是多少用乘法计算的道理。
2、结合具体事例,经历动手摆花片、讨论求一个数的几倍用乘法计算的过程。
3、鼓励学生积极参与操作与交流活动,直观体会几个几和一个数的几倍之间的关系。
教学重难点:初步理解求一个数的几倍是多少用乘法计算的道理。
课前准备 :课件
教学过程
一、导入新课
让学生举出一数是另一数几倍的例子。给更多学生举例的机会。
师:前面两节课,我们认识了“倍”,谁能举出一个数是另一个数几倍的例子,要说出判断 的理由。
指名举例,给更多学生发言的机会。
(1) 21是 7的 3倍,因为 21中有 3个 7。(2) 20本书是 5本的 4倍,因为 20中有 4个 5。
二、新课学习
1. 让学生观察情境图,先了解聪聪和红红在说什么,再讨论理解 “红红的画片是聪聪 3倍” 的实际意义。
师:看来同学们已经理解了“倍”的真正含义,下面,我们来看一个和“倍”有关的问题。 请看课本第 83页上面的图,看一看聪聪和红红在说什么。
生:聪聪说:我有 5张画片;红红说:我的画片是你的 3倍。
师:谁能用自己的话说一说“红红的画片是聪聪的 3倍是什么意思?”
生:聪聪有 5张画片,红红就有 3个 5张。
2.鼓励学生画“○”表示聪聪和红红画片的张数,并对画图方法给予指导。 师:同学们能 画○表示出聪聪和红红画片的张数吗?试一试!
学生画图, 教师巡视并指导。 画图的时候, 要靠左边写出聪聪和红红, 可在黑板上示范出来: 3.交流学生画图表示的做法,给学生充分交流不同想法的机会,教师在黑板上完成画图。 师:谁来说一说聪聪有 5张画片,你是怎样画的?
生 1:聪聪有 5张画片,就在聪聪名字的左边画出 5个○。
学生说,教师在黑板上画出来。
师:红红画片的张数你是怎样想、怎样做的?
学生可能出现以下两种说法:
(1)红红的画片是聪聪的 3倍,就是说红红的画片有 3个 5张,就在红红名字右边先画 5个○,再画 5个○,又画 5个○。
(2)红红的画片是聪聪的 3倍,就是说红红的画片有 3个 5张,就在红红名字右边画出 15个○。
第(1)说法,没有,教师可示范摆;第(2)种说法出现,说一说 15是怎样来的。 师:观 察画出的图,聪聪有 5张画片、红红的画片是聪聪的 3倍,也就是说红红的画片有 3个 5张。
4. 提出“求红红有多少张画片”,可以用什么方法计算?给学生充分交流不同 方法的机会,然后形成共识, 就是求 3个 5是多少,用乘法计算:5×3=15(张 ) . 三、练一练第 1、 2题。
(1)先引导学生了解题中的数学信息,然后让学生解决。
四、小结 ; 求一个数的几倍是多少用乘法计算。
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