跟Capital gain有关的部分信息（不是房子的增值）。也是来自税务局网：

The following rules apply if the dividends and capital gains are not effectively connected with a U.S. trade or business.


?Capital gains are generally not taxable if you were in the United States for less than 183 days during the year. See Sales or Exchanges of Capital Assets in chapter 4 for more information and exceptions.


?Dividends are generally taxed at a 30% (or lower treaty) rate. The brokerage company or payor of the dividends should withhold this tax at source. If tax is not withheld at the correct rate, you must file Form 1040NR to receive a refund or pay any additional tax due.