Unit327-2In the binary system of representation the base is 2, and only two numerals 0 and 1 are required to represent a number. The numerals 0 and 1 have the same meaning as in the decimal system, but a different interpretation is placed on the position occupied by a digit. In the binary system the individual digits represent the coefficients of powers of two rather than ten as in the decimal system. For example, the decimal number 19 is written in the binary representation as10011 since10011=1×24+0×23+0×22+1×21+1×20=16+0+0+2+1=19A short list of equivalent numbers in decimal and binary notation is given in Table 3.2.二进制示数系统中的基数是二，且只有0和1两个数被用以示数。

0和1在这里与在十进制中具有一样的意义，但每个数位表示的不一样。

二进制系统中每个数字表示二的幂系数，而十进制中表示十的幂系数。

例如，十进制数19在二进制中表示为10011因为10011=1×24+0×23+0×22+1×21+1×20=16+0+0+2+1=19二进制和十进制数相等数字见表3.2.27-3A general method for converting from a decimal to a binary number is indicated in Table 3.3. The procedure is the following. Place the decimal number (in this illustration, 19) on the extreme right. Next divide by 2 and place the quotient (9) to the left and indicate the remainder (1) directly below it. Repeat this process (for the next column 9÷2 =4 and a remainder of 1) until a quotient of 0 is obtained. The array of 1’s and 0’s in the second row is the binary representationof the origin decimal number. In this example, decimal 19=10011 binary.十进制转换成二进制的一般方法如图3.3。

过程如下：把十进制数（图中的19）放在最右端，接下来除以2，把商（9）放在左边并直接在其下方标明余数（1）。

重复这个步骤（下一列为9÷2=4余1），直到商为0截止。

第二行中的1和0就是原始十进制数的二进制表示。

此例中，十进制19=二进制10011.28-1A binary digit (a 1 or a 0) is called a bit. A group of bits that has the same significance is called a byte, word, or code. For example, to represent the 10 numerals (0, 1, 2, …, 9) and the 26 letters of the English alphabet would require 36 different combinations of 1’s and 0’s. Since 25<36<26, then a minimum of 6 bits per bite are required in order to accommodate all the alphanumeric characters. In this sense a bite is sometimes referred to as a character and a groupof one or more characters as a word.一位二进制数（一个1或0)叫做比特。

一组具有相同意义的比特叫做字节，词，或代码。

例如，表示10个数字（0,1,2，...9）和26个英文字母要用到36种不同的1和0的组合。

因为25<36<26，那么表示所有这些字母数字字符组最少需要6比特每字节。

这种情况下一字节有时候被称为一个字符和一个或多个字符组成的字符串。

29-1The parameters of a physical device (for example, VCE·sat of a transistor) are not identical from sample to sample, and they also vary with temperature. Furthermore, ripple or voltage spikes may exist in the power supply or ground leads, and other sources of unwanted signals, called noise, may be present in the circuit. For these reasons the digital levels are not specified precisely, but as indicated by the shaded region in Figure 3.6, each state is defined by a voltage range about a designated level, such as 4±1 V and 0.2±0.2 V.每个实体器件样本的参数(如晶体管的VCE·sat )是不完全相同的，它们还会随温度变化。

而且，电源或地线可能存在电压脉动或电压峰值，其他干扰信号——噪声也可能出现在电路中。

由于这些原因，数字电平没有明确的规定，但如图3.6中阴影所示，将每个状态定义为指定电平的电压范围，例如4±1 V 和0.2±0.2 V。

Unit437-1The materials that make up our universe are composed of over one hundred basic and individual types of matter called elements. Ninety-two of these elements occur naturally and the remainders are man-made. Each element has a separate identify of its own, that is, no two elements have the same physical and chemical properties, nor can an element be subdivided by ordinary physical and chemical means into simple elements.[1] Examples of elements are gold, mercury and oxygen.构成宇宙的物质是由一百多种基本的不同类型的物质——元素组成的。

其中92种元素是天然形成的，其他的则是人造的。

每种元素都各有其自己的标识，也就是说，元素的物理和化学特性是独一无二的，一种元素也不可以用物理和化学手段再分成简单的元素。

例如金，汞和氧元素。

37-3Electrons whirl around nuclei in much the same manner that the planets of our solar system travel around the sun. The difference between an atom of one element and that of another is in the number of protons and neutrons contained in the nucleus.[2] All the elements in the universe, and therefore all matter, is composed of protons, neutrons, and electrons.电子围绕原子核旋转，其方式类似于太阳系中行星围绕太阳旋转。

一种元素的原子和另一种元素的原子的差别在于其原子核中的质子数和中子数。

宇宙中的所有元素，也就是说所有的物质，都是由质子，中子和电子组成的。

37-4There must be force of attraction between a nucleus and the electrons surrounding it, otherwise the electrons would fly off into space, in order to understand its nature, we find it helpful to call this force a charge. The charge of the nucleus is defined as positive, and the opposite charge of the electron, negative. In view of the fact that opposites attract, the force between the nucleus and the rotating electron around it prevents the electron from flying off into space.在原子核与其周围的电子间必然存在着吸引力，否则电子将会飞离原子核，为了理解它的性质，我们把这种力称为电荷。