在访问学者申请咨询过程中，经常会遇到一些客户问两年服务期限制的问题，比如‘访问学者结束以后是不是必须回国服务两年’、‘这两年期间是不是不能再去美国’等问题。每每遇到这样的问题，解释以后部分客户还是不完全明白。今天厚谱教育访学顾问周雅淇老师就这个问题给大家做一个深入的剖析，希望也能帮助到大家。
　　之所以大家觉得这个问题比较难懂，一个非常重要的原因，就是很多人混淆了12- and 24-Month Bars (12个月或者24个月bar的限制)和Two-Year Home Country Physical Presence Requirement(两年回国服务期的限制)的概念，其实这完全是两个不同的概念。12- and 24-Month Bars是针对J-1交流访问学者签证的限制，而wo-Year Home Country Physical Presence Requirement是针对H (temporary employment), L (intercompany transfer) or immigrant (permanent resident)类身份的限制。所以一定不要误认为24-Month Bars的限制就是两年回国服务期的限制，不是一回事！
　　在文章开始之前，我们首先了解一下J-1访问学者的种类。
　　1)Professors: 教授
　　A professor teaches, lectures, observes, or consults. A professor’s primary activity will be teaching and lecturing, but may also conduct research, unless disallowed by the sponsor.”
　　Minimum: 3 weeks
　　Maximum: 5 years
　　2)Research Scholar: 访问学者(我们申请的访问学者绝大多数都是 research scholar 类型)
　　A research scholar conducts research, observes, or consults in connection with a research project. A research scholar may also teach or lecture, unless disallowed by the sponsor.
　　Minimum: 3 weeks
　　Maximum: 5 years
　　3)Short-term Scholar: 短期访问学者
　　A short-term scholar: comes to the US for a period of up to 6 months to lecture, observe, or consult, and participate in seminars, workshops, conferences, study tours, professional meetings, or similar types of educational and professional activities.
　　No minimum stay required
　　Maximum: 6 months. No extensions beyond six months will be permitted under any circumstances
　　4)Student Non-degree
　　5)J-1 Student Intern
　　厚谱教育周雅淇老师就先跟大家分享一下12- and 24-Month Bars的概念

　　以下英文内容来自University of Michigan密西根大学官方网站：https://internationalcenter.umich.edu/scholars/j1-scholars/12-and-24-bars
　　12- and 24-Month Bars for Professors and Research Scholars
　　【12- and 24-Month Bars】是针对J-1签证里面的Research Scholar/Professor这两个类型。
　　针对12-Month Bar的解释
　　12-Month Bar
　　Individuals who have been in the U.S. for more than six months in the previous year (12 months) in any J visa status are not eligible to enter the U.S. as a J-1 Research Scholar or Professor for a 12-month period. Time spent in the J-1 Short-term Scholar category does not count towards the 12-month bar. The 12-month bar applies to both the J-1 principal and any J-2 dependents. The 12-month bar does not prevent individuals from returning to the U.S. in any other visa status or in some other J categories such as Short-Term Scholar or Student.
　　【12个月bar时间限制】通过这一段描述，大家应该对12-Month Bar有一个初步的了解。简单总结就是：如果申请人在之前的12个月之内曾经以J类签证的身份在美国停留超过6个月的时间(注：这一段经历已经结束)，如果接下来的12个月之内再想以Research Scholar or Professor类型申请J-1访问学者，就会受到12个月bar的限制。也就是说在上一段J类签证结束以后的12个月时间之内，申请人不能再申请Professor or Research Scholar类型的J-1访问学者签证，此规定同样适应于以陪同身份出去的J2签证。但是如果在上一段J类签结束以后想继续申请J-1 Short-Term Scholar短期访问学者，或者通过留学的身份出去，则不受12个月bar的约束。
　　【12个月bar时间限制】补充内容：(内容来自宾大官网)
　　A foreign national is ineligible to participate in a professor/research scholar exchange program if he/she has held any J nonimmigrant status within the 12-month period immediately preceding the start of the exchange program. This 12-Month Bar applies to J-2 dependents as well as J-1. The following 3 exceptions exist
　　前面内容基本都是一致的，但是宾大总结了不受12个月bar限制的三种情况：
　　· J-1 transfers to Penn without any gap;
　　J-1顺利延期，中间无缝衔接。
　　· Prior stay in the US in J status was for less than 6 months;
　　J类签证在美国时间少于6个月。
　　· Presence in J status as a Short-Term Scholar.
　　以短期访问学者的身份在美国。
　　针对24-Month Bar的解释
　　24-Month Bar on Repeat Participation
　　Any individual who participates in an Exchange Visitor program in the Professor or Research Scholar categories on or after 11/18/06 is subject to a 24-month bar on “repeat participation” in those categories. Scholars subject to the bar may not return to the U.S. as a J-1 scholar in the Professor or Research Scholar categories for the 24-month period. This bar also applies to J-2 dependents.
　　【24个月的时间限制】如果申请人曾经以Professor or Research Scholar类型的J-1访问学者身份在美国停留过，如果这一段经历结束以后再想申请Professor or Research Scholar类型的J-1访问学者签证，就会受到24个月bar的限制，也就是说在上一段J-1签证结束以后的24个月时间之内，申请人不能再申请Professor or Research Scholar类型的J-1访问学者签。此限制同样适用于J-2身份。
　　When a scholar either concludes or leaves a Research Scholar or Professor J-1 program, whichever happens earlier, the scholar's record becomes inactive in SEVIS. At that point, the 24-month bar time starts to accrue. The 24-month bar will be in effect regardless of whether status in the program is a few months in duration or the full five years allowed.
　　总结这段话的核心思想就是：一旦Research Scholar/Professor类型的访问学者结束了在美国的学习项目，那他J-1身份就失效了;一旦J-1身份失效，就要受到24个月bar的限制，也就是24个之内不能再以Research Scholar/Professor类型的J-1访问学者的身份过去。
　　For example, a J Professor who comes for a single academic year, or a Research Scholar that comes for four months, and then goes home without having his/her SEVIS record kept open and active in his/her absence, would not be able to access the remainder of the five year period of eligibility, would be subject to the 24-month bar, and would not be eligible to return to the U.S. as a J-1 Professor or Research Scholar at any U.S. institution until 24 months (two years) after the program ended.
　　这段话中提到的【five year period】，在文章的一开始，我们总结了J-1签证的类型和时间周期，针对Research Scholar/Professor两种类型的J-1访问学者签证，周期最长都是五年。比如：对方教授一次性邀请申请人访学五年(这种可能性仅适用于举例)或者J-1申请人访学期间一直延期到五年。有人可能会有疑问，为什么可以延期到五年？难道不受24个月bar的限制吗？让我们回顾一下上一段总结的核心思想，24个月的bar是指一旦申请人结束了在美国的访问学者身份，也就是说一旦J-1身份失效以后，才会受到24个月bar的限制。如果访问学者能够让每一段访学时间都无缝衔接，也就是在第一年访学身份失效之前就已经顺利衔接到了第二年的访学，在第二年访学身份失效之前就已经顺利衔接到了第三年的访学。。一直衔接，只要能保证在五年之内J-1访问学者身份一直有效，那就可以一直延期到五年。虽然在理论上是完全ok的，但是在现实申请中，能这样一直延期五年的可能性还是非常小的。当然，五年结束以后就不可以再延期啦，24个月bar的限制也就随之而来了。
　　The 24-month bar does not prevent individuals from returning to the U.S. in any other visa status.
　　如果J-1访问学者结束以后再打算以旅游签、学生签证或者其它类型的签证入境类签证，并不受24个月bar的限制。