For visitors from outside USA, a B1 visa (visitor for business) is recommended to attend NuSYM13. Visa applications should be submitted early for participants from China, India or Russia. If you need invitation letters, please email the organizers.
Certain countries participate in the visa waiver program. As of January 12, 2009, a valid ESTA approval is required for all Visa Waiver Program (VWP) to travel to the United States. The Department of Homeland Security, Electronic System for Travel Authorization (ESTA) is an automated system used to determine the eligibility of visitors to travel to the United States under the VWP. It collects the same information as the paper I-94W form that VWP travelers used to fill out en route to the United States. ESTA applications may be submitted at any time prior to travel. An ESTA authorization generally will be valid for up to two years. Authorizations will be valid for multiple entries into the United States. DHS recommends that travelers submit an ESTA application as soon as they begin making travel plans. Information about that program can be found at http://travel.state.gov/visa/temp/without/without_1990.html. The link to register through ESTA is found on this website.
Based on our experience, even though VWP is normally valid for a stay up to 90 days, for stays longer than a month, it is best to apply for visa at the US consulate.