check四年有效官方文件

http://www.state.gov/r/pa/prs/ps/2005/42212.htm

Media Note
Office of the Spokesman
Washington, DC
February 11, 2005

Extension of Validity for Science Related Interagency Visa Clearances

Visa applications for persons to study or work in certain sensitive
scientific and technical fields are subject to an interagency clearance in
Washington, DC, called Visas Mantis. Since 1998, the Visas Mantis clearance
process has been used to screen against the illegal transfer of technology.
Once the clearance process is complete and a visa is issued, the individual
may apply for admission at a U.S. port of entry. Visas Mantis clearance and
visa validity are different than the period of admission determined by a
Department of Homeland Security officer at the port of entry.

The U.S. Department of State, in consultation with the U.S. Department of
Homeland Security, has extended the validity of Visas Mantis clearances for
the F (student), J (exchange visitors), H (temporary workers), L (
intracompany transferees) and B (tourist and business) categories of visas.
This means that if the original visa has expired and a new visa application
is filed to return to the previous study or work program in the United
States, another Visas Mantis clearance may not be required. Consular
officers have the discretion, if warranted, to request a Visas Mantis
clearance during any visa adjudication.

International students (F visas) who have received a Visas Mantis clearance
and been issued a visa will benefit from having that clearance be valid for
up to the length of the approved academic program, to a maximum of four
years. If a student changes academic programs, the clearance will no longer
be valid and a Visas Mantis review would be required should the applicant
reapply for a new visa.

Temporary workers (H visas), exchange visitors (J visas) and intracompany
transferees (L visas) can receive a Visas Mantis clearance valid for the
duration of their approved activity to a maximum of two years. If the nature
of the visa holder抯 activity in the United States changes, the clearance
will cease to be valid and a new Visas Mantis review would be required
should the applicant reapply for a new visa.

Business visitors (B-1 visas) and visitors for pleasure (B-2 visas) can
receive a Visas Mantis clearance valid for one year, provided that the
original purpose for travel, as stated in the visa application, has not
changed on subsequent trips.

In addition to the extension of validity for Visas Mantis clearances, the
Department of State has made several other improvements in the Visas Mantis
process in the past year. By increasing staffing, improving systems and
working with our interagency partners, the Department has been able to
decrease the average time to obtain Visas Mantis clearance to less than 14
days.

2005/182

Released on February 11, 2005