Dendrimers

A dendrimer is a highly branched macromolecule with a spherical shape. The surface of the particle may be functionalized in many ways and many of the properties of the resulting construct are determined by its surface.

In particular it is possible to construct a cationic dendrimer, i.e. one with a positive surface charge. When in the presence of genetic material such as DNA or RNA, charge complimentarity leads to a temporary association of the nucleic acid with the cationic dendrimer. On reaching its destination the dendrimer-nucleic acid complex is then taken into the cell via endocytosis.

In recent years the benchmark for transfection agents has been cationic lipids. Limitations of these competing reagents have been reported to include: the lack of ability to transfect a number of cell types, the lack of robust active targeting capabilities, incompatibility with animal models, and toxicity. Dendrimers offer robust covalent construction and extreme control over molecule structure, and therefore size. Together these give compelling advantages compared to existing approaches.

VersionTracker

VersionTracker.com is a website that tracks software releases. It started out originally as a Mac OS software tracker, eventually expanding into Mac OS X, Microsoft Windows and Palm OS.

VersionTracker does not host the majority of the software listed (it merely links to them), only in special agreements with the developers.

VersionTracker also offers a software called VersionTracker Pro that checks software versions on a user's computer and then queries its database to see if any updates are available. This feature is available only to paid subscribers. Browsing and searching the database is free.

Strapdown systems

Lightweight digital computers permit the system to eliminate the gimbals, creating "strapdown" systems, so called because their sensors are simply strapped to the vehicle. This reduces the cost, eliminates gimbal lock, removes the need for some calibrations, and increases the reliability by eliminating some of the moving parts. Angular rate sensors called "rate gyros" measure how the angular velocity of the vehicle changes.

A strapdown system has a dynamic measurement range several hundred times that required by a gimbaled system. That is, it must integrate the vehicle's attitude changes in pitch, roll and yaw, as well as gross movements. Gimballed systems could usually do well with update rates of 50 to 60 updates per second. However, strapdown systems normally update about 2000 times per second. The higher rate is needed to keep the maximum angular measurement within a practical range for real rate gyros: about 4 milliradians. Most rate gyros are now laser interferometers.

The data updating algorithms ("direction cosines" or "quaternions") involved are too complex to be accurately performed except by digital electronics. However, digital computers are now so inexpensive and fast that rate gyro systems can now be practically used and mass-produced. The Apollo lunar module used a strapdown system in its backup Abort Guidance System (AGS).

Strapdown systems are nowadays commonly used in commercial and tactical applications (arcraft, missiles, etc). However they are still not widespread in applications where superb accuracy is required (like submarine navigation or strategic ICBM guidance).

Run-time system

In computer science, the runtime system is software that provides services for a running program but is itself not considered to be part of the operating system.[citation needed]

Examples include:

* the code that is generated by the compiler to manage the runtime stack.

* library code for handling memory management (for example, malloc).

* code that handles dynamic loading and linking.

* debugger code that is generated at compile time or run time.

* application-level thread management code.

Byte-code interpreters and virtual machines can also be considered runtime systems. Services that run in concurrent processes are more likely to be considered middleware.