If your visa application is still pending after sixty days and you are at risk to not arrive in time to present a paper, contact the ACS Technical Division to notify them. You can also register your visa delay with the U.S. National Academies of Sciences.
All visa denials are reviewed by the consular officer's superior and must be accompanied by a written statement citing the reason for the denial. There are several categories for visa denials, but the most frequent is that prospective visitors or students have not demonstrated that they have strong ties abroad that would compel them to leave the U.S. at the end of the temporary stay.
Strong ties differ from country to country, city to city, individual to individual. Some examples of ties can be a job, a house, a family, a bank account. The law places the burden of proof to show strong ties on the applicant. Visa applicants must qualify for the visa based on individual circumstances, not on the assurance from an organization. U.S. immigration law delegates the responsibility for issuance or refusal of visas to consular officers overseas.
An applicant can influence their visa officer to change a prior visa denial only through the presentation of new convincing evidence of strong ties to their home country.