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现在的霰弹为什么都用圆形弹丸? 第1页

  

user avatar   liu-xiang-xi-94 网友的相关建议: 
      

赞同一下里予和其他高赞的回答。

主要是原型弹丸是在易于生产的前提下(最简单的方式是熔化铅放勺子里作成球型,你不用机器给我作个其他弹头看看?), 定向性最好的子弹了。

正如其他答主提到的,霰弹枪其实就是土炮的缩小版,理论上药包前面什么都可以塞,但是这些乱七八糟的东西打出去后,能否命中目标,那是看人品的。

而球型弹丸则相对好很多。 至少短距离内如此(远了会飘)

另外多说一句,霰弹枪这东西科技含量极低,最近新泽西的一个200美元每把枪的buyback (政府或者民间反枪组织出钱买百姓手里枪销毁)行为被迫中止,就是遇到了大量这样的管子枪。。。

可以装霰弹,用锤子击发,一把这个组织就得掏200美元,成本。。。几乎没有?

然后上交的人拿着钱开心的买新枪去了。。。


user avatar   luo-zhi-wei-4-35 网友的相关建议: 
      

全面地,从宏观介绍差异的一篇文章:

12 Differences Between Chinese Education and American Education

Posted on June 1, 2007

This analysis is being prepared for a presentation I am going to make at the International Conference on Intercultural Education in Harbin, China on June 22-24. I would be interested in receiving your observations, comments, questions about the differences between Chinese and American educational practices.

  1. Class Size is the first noticeable difference at the middle school and high school level. Teachers typically teach two classes (in an 8 period day) with from 55 to 65 students. American secondary teachers typically teach five or six classes with class sizes ranging from 25 to 30. The Chinese teachers use their non-teaching time to grade papers and to prepare for their classes, except for the head teachers (banzhuren) which will be explained later.
  2. While Americans think the "cohort" concept is innovative, China has been using it for decades. Throughout China, students beginning in a school are put into classes and they stay in those classes with one another for the entire time they are in that school unless higher test scores permit them to move to a more advanced grouping. Understood in the Chinese system is that this group of students will learn each of their subjects together. In America, students are not grouped into such classes. Instead, the 30 students who are together for English class will be randomly split up into any of the other subjects for the next period and the period after that, and so on. The next year, the students are totally mixed up again into different classes. Occasionally, the same class of students will take two courses together, such as English and history, but that is rare. The Chinese carry the cohort concept into the university level as well. My four classes of students stay together for all of their required courses the whole time they are at university.
  3. Chinese students stay in the same classroom for their main classes and their teachers come to them while American students change rooms every period and the room belongs to the teacher. Thus, Chinese students don’t have hallway lockers. Students sit in the same seats for each subject and keep their materials in a shelf under their desk top. Many students have cloth covers for their desk and other means of making it "homey".
  4. Chinese education is built on what Americans call "looping". The teachers of the students in the entering class will also follow their same students to the next grade level and the next. In America, it is very unusual for teachers to move with their students from one grade level to the next at the middle school or high school level let alone to loop for the entire period of time the student is in that school. At the primary school level, students begin in grade one with a teacher and stay with that teacher every year they are in primary school. My university students reflect on that teacher as being so very important to them that they really didn’t want to leave them when it was time to go to middle school. American teachers, on the other hand, tend to specialize in the curriculum and content for a particular grade level and then stay at that level. Sometimes, teachers who want to teach older students will ask to move to a higher grade, but then that teacher would typically stay at that level until retirement. That practice means that in America, subject matter and teacher preference might be valued more highly than student needs or student learning.
  5. Another significant structural difference between American and Chinese schools is the concept of head teacher or "banzhuren". The banzhuren takes additional responsibility in delivering instruction, supervising their specific class of students, and in knowing their students and the families of the students and in communicating with those families. For less than 200 yuan per month more, the banzhuren will arrive at school prior to 7:00 a.m. to prepare for the day and to work with early arriving students. The student day at the middle school ends at 4:55 and the teachers leave shortly after that. The banzhuren will not only teach her specific class that she is in charge of but will also sit in on many other subjects throughout the day so she can monitor the progress of her students with other teachers, counsel her students, and contact the parents of those students if necessary. The banzhuren will monitor her class during lunch and nap with them after lunch. One banzhuren told me that she is like a mother to those students who don’t have the parental support they need. In addition, at Liaoning Normal University Junior Middle School (LNUJMS) thebanzhurens are expected to visit the homes and families of half their students sometime during the first term and the other half during the second term. These visitations would take place on Saturdays or Sundays or on holidays. The banzhurenwill, after three years, receive a bonus based on the academic improvement of her class. In America, the individual teacher is expected to make parent contact when a student misbehaves or is not performing at a satisfactory level. In American secondary schools there is also a person called a guidance counsellor who will assist with parent contact. However, the guidance counsellor will have a case load of 350 to 500 students and she often must resort to group counselling sessions.
  6. The Chinese believe in merit pay and in using student test scores for teacher evaluation. For example, when the 9th graders leave middle school they are tested to see which high school they are qualified to attend. Since the same teachers have had those students for three years, they compare their entry score to their exit score. The classes that showed the most academic gain resulted in that banzhurenreceiving a bonus that might range from 3000 yuan to 6000 yuan (one month or two months pay). The same is true at the high school level. On the other hand, a teacher whose students did not show growth will be evaluated accordingly. At LNUJMS, the math team won first place in the District math contest. As a reward, the four math teachers split a 2000 yuan bonus. The teachers I have talked with like the bonus system. So for years the Chinese have been doing what the American conservatives have been advocating and our teacher unions have been fighting.
  7. Discipline in Chinese schools easier than in American schools. For example, at LNUJMS, I was surprised to find minimal student supervision during lunch and between classes. One administrator and one teacher were in the hallway and no teachers were in their classrooms. The other teachers had gone to their offices to meet with students for academic or disciplinary reasons or for a rest between classes. In America, the time between classes is as short as possible, three, four, or perhaps five, minutes. Students are expected to move from their classroom, go to their lockers to get materials for their next class, and then move to that class. The American teachers are expected to be in the hallways during passing periods because that is when fighting and other misbehaviors occur. It is nearly impossible to even imagine a 10 minute passing period in an American school.
  8. Chinese students are very respectful. When Chinese students recite, they stand; when students hand in a paper, they use both hands as if they were making a presentation of the paper to the teacher; when students refer to their teacher in writing, they often use terminology such as , “Our dear teacher.” In interviewing thebanzhurens, they commented that is their duty to teach students how to do well in life and how to be a man. University students, when asked to recall their middle school and high school years often speak of their teachers in very exalted ways telling how much their teachers meant to them.
  9. Chinese students play active and important roles (zhirisheng) in sweeping the classrooms, scrubbing the steps, serving meals, being class monitors, and helping teachers. Student monitors can be seen wearing special armbands in the hallway, watching to make certain students are doing their twice-daily eye exercises properly, providing leadership on the marching field, watering plants, empty bins, cleaning windows, helping to distribute the daily lunch, and so on. Students always seemed to be carrying out their tasks very seriously and in good humor. The student monitor system is utilized at the university level as well with these appointed students helping the teacher in making copies, distributing and collecting papers, contacting classmates and so on. Like the concept of banzhuren, the concept of zhirishengcannot find its English equivalent due to the different Sino-American educational systems. Most Chinese schools are operated on the zhirisheng system for the purpose of maintaining clean classrooms and schools.
  10. Chinese students buy their textbooks each year and the textbooks are soft cover and relatively thin. The textbooks I looked at had a 2006 copyright and I understand that they all have recently undergone revision. The cost is about $1 for a textbook and $2 for a workbook that accompanies the textbook. Students make heavy use of highlighters and annotations in their books. In addition, the textbooks often have moral lessons built into them. For instance, when a particular scientist is highlighted, aspects of his/her life that are exemplary are extolled, such as hard work, protecting the environment, overcoming obstacles, etc. On the other hand, American textbooks are hard cover, updated every six years (at least in Indiana), and are rented to students. Students are not allowed to mark in their textbooks in America.
  11. It almost goes without saying that the curriculum in China is standard nation-wide and that students have few elective choices. National goals, national curriculum, national expectations, national exercises, and even a national class schedule are all built around the Chinese Education Schema that is based on centuries of tradition. In America, education is primarily the responsibility of the state governments. Counting Washington D.C., there are 51 separate governments that give direction to public schools. Further, except for Hawaii, states are divided into school districts that also have certain autonomies. Indiana, for example, has 292 school districts, 292 different teacher contracts, salary schedules, and sets of working conditions.
  12. Deeply embedded in the Chinese culture is the examination system. Since the Song Dynasty (960 AD), the Chinese have relied on the examination process to identify their governmental leaders. Now the examination system is used to determine which university students are able to attend. These national exams were given on June 7 and 8. Local middle schools were used as test sites and those middle school students had a two day holliday. The test is of such great significance that parents rent hotel rooms nearby so their student can have a quiet lunch and take a nap. I saw one hotel with a big banner wishing students luck on the exam. Students will take either the liberal arts test or the science test. For liberal arts students, the first test, Chinese, was from 9:00-11:30. Students were dismissed and came back for the math test from 3:00-5:00. On Friday, the schedule was the same, with the morning session being geography, politics, and history and the afternoon session being English. The parents filled the street in front of the school and anxiously awaited students coming from the test sites and wanted to know how their child did. Taxi cabs even offer free service to these students to help them get home or to the testing site. My friend Kevin’s uncle took time off work to drive Kevin to the test site, pick him up at noon to take him home, then bring him back. It is huge deal!
    (原文:slkchina.wordpress.com/



  

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