BUFFERING

Explicit control of buffering is important in many applications, including ones that need to deal with raw devices (such as disks), ones which need instantaneous input from the user, or ones which are involved in communication. Examples might be interactive multimedia applications, or programs such as telnet. In the absence of such strict buffering semantics, it can also be difficult to reason (even informally) about the contents of a file following a series of interacting I/O operations.
Three kinds of buffering are supported: line-buffering, block-buffering or no-buffering. These modes have the following effects. For output, items are written out from the internal buffer according to the buffer mode:

• line-buffering: the entire buffer is written out whenever a newline is output, the buffer overflows, a flush is issued, or the handle is closed.
• block-buffering: the entire buffer is written out whenever it overflows, a flush is issued, or the handle is closed.
• no-buffering: output is written immediately, and never stored in the buffer.

ZERO CAPACITY

Communication over a noisy quantum channel introduces errors in the transmission that must be corrected. A fundamental bound on quantum error correction is the quantum capacity, which quantifies the amount of quantum data that can be protected. We show theoretically that two quantum channels, each with a transmission capacity of zero, can have a nonzero capacity when used together. This unveils a rich structure in the theory of quantum communications, implying that the quantum capacity does not completely specify a channel's ability to transmit quantum information.

BOUNDED CAPACITY

The capacity of discrete-time, non-coherent, multipath fading channels is considered. It is shown that if the delay spread is large in the sense that the variances of the path gains do not decay faster than geometrically, then capacity is bounded in the signal-to-noise ratio.

UNBOUNDED CAPACITY

The capacity of discrete-time, noncoherent, multipath fading channels is considered. It is shown that if the variances of the path gains decay faster than exponentially, then capacity is unbounded in the transmit power.