Wednesday, September 10, 2008

Gene therapy

In most gene therapy studies, a "correct copy" or "wild type" gene is provided or inserted into the genome. Generally, it is not an exact replacement of the "abnormal," disease-causing gene, but rather extra, correct copies of genes are provided to complement the loss of function. A carrier called a vector must be used to deliver the therapeutic gene to the patient's target cells. Currently, the most common type of vectors are viruses that have been genetically altered to carry normal human DNA. Viruses have evolved a way of encapsulating and delivering their genes to human cells in a pathogenic manner. Scientists have tried to harness this ability by manipulating the viral genome to remove disease-causing genes and insert therapeutic ones.

Target cells such as the patient's liver or lung cells are infected with the vector. The vector then unloads its genetic material containing the therapeutic human gene into the target cell. The generation of a functional protein product from the therapeutic gene restores the target cell to a normal state.

Tuesday, August 26, 2008

Adeno-associated viruses

Adeno-associated viruses, from the parvovirus family, are small viruses with a genome of single stranded DNA. The wild type AAV can insert genetic material at a specific site on chromosome 19 with near 100% certainty. But the recombinant AAV, which does not contain any viral genes and only the therapeutic gene, does not integrate into the genome. Instead the recombinant viral genome fuses at its ends via the ITR (inverted terminal repeats) recombination to form circular, episomal forms which are predicted to be the primary cause of the long term gene expression. There are a few disadvantages to using AAV, including the small amount of DNA it can carry (low capacity) and the difficulty in producing it. This type of virus is being used, however, because it is non-pathogenic (most people carry this harmless virus). In contrast to adenoviruses, most people treated with AAV will not build an immune response to remove the virus and the cells that have been successfully treated with it. Several trials with AAV are on-going or in preparation, mainly trying to treat muscle and eye diseases; the two tissues where the virus seems particularly useful. However, clinical trials have also been initiated where AAV vectors are used to deliver genes to the brain. This is possible because AAV viruses can infect non-dividing (quiescent) cells, such as neurons in which their genomes are expressed for a long time.

Friday, August 22, 2008

Active Object

This article is about a multi-threading technique. For the lockstep protocol variant, see Active objects.

The Active Object design pattern decouples method execution from method invocation that reside in their own thread of control.s The goal is to introduce concurrency, by using asynchronous method invocation and a scheduler for handling requests.

The pattern consists of six elements:

* a proxy, which provides an interface towards clients with publicly accessible methods
* an interface which defines the method request on an active object
* a list of pending requests from clients
* a scheduler, which decides which request to execute next
* the implementation of the active object method.
* a callback or variable for the client to receive the result.

Tuesday, August 12, 2008

Wide Area Augmentation System

The Wide Area Augmentation System (WAAS) is an air navigation aid developed by the Federal Aviation Administration to augment the Global Positioning System (GPS), with the goal of improving its accuracy, integrity, and availability. Essentially, WAAS is intended to enable aircraft to rely on GPS for all phases of flight, including precision approaches to any airport within its coverage area.

WAAS uses a network of ground-based reference stations (Benchmark DGPSRs transmitting differential corrections (DCs, located within spaces protected from the public inside airportsin North America and Hawaii, to measure small variations in the GPS satellites' signals in the western hemisphere. Measurements from the reference stations are routed to master stations, which queue the received DCs and send the correction messages to geostationary WAAS satellites in a timely manner (at least every 5 seconds or better). Those satellites broadcast the correction messages back to Earth, where WAAS-enabled GPS receiver uses the corrections while computing its position to improve accuracy. The longer any given DC has been delayed, the less benefit it will produce.

The International Civil Aviation Organization (ICAO) calls this type of system a Satellite Based Augmentation System (SBAS). Europe and Asia are developing their own SBASs, the Indian Gagan, the European Geostationary Navigation Overlay Service (EGNOS) and the Japanese Multi-functional Satellite Augmentation System (MSAS), respectively. Commercial systems include StarFire and OmniSTAR.

Wednesday, August 06, 2008

Quartz rate sensors

This system is usually integrated on a silicon chip. It has two mass-balanced quartz tuning forks, arranged "handle-to-handle" so forces cancel. Aluminum electrodes evaporated onto the forks and the underlying chip both drive and sense the motion. The system is both manufacturable and inexpensive. Since quartz is dimensionally stable, the system can be accurate.

As the forks are twisted about the axis of the handle, the vibration of the tines tends to continue in the same plane of motion. This motion has to be resisted by electrostatic forces from the electrodes under the tines. By measuring the difference in capacitance between the two tines of a fork, the system can determine the rate of angular motion.

Current state of the art non-military technology (2005) can build small solid state sensors that can measure human body movements. These devices have no moving parts, and weigh about 50 grams.

Solid state devices using the same physical principles are used to stabilize images taken with small cameras or camcorders. These can be extremely small (≈5 mm) and are built with MEMS (Microelectromechanical Systems) technologies.

Wednesday, July 30, 2008

.NET Framework

The .NET Framework provides a run-time that is used to interpret intermediate code, code that is compiled from a development environment such as Microsoft’s Visual Studio when the language is C# or Visual Basic.NET. The code requires the run-time in order to execute. The code is referred to as “intermediate” because the result of the compilation is not a result that could be run at the machine level, or in other words to run without the aid of the run-time. The run-time is a service process that provides the framework for the execution of the intermediate code. The run-time acts as an interpreter of the intermediate code and then provides the structure for it to run on the operating system. Lower level capabilities it provides includes memory management, process management, and I/O management. In many cases the run-time is simply providing an abstraction level to the Windows API opening up nearly all of its capabilities to the programmer

The purpose of a run-time is to support the use rapid application development languages, such as C# and Visual Basic.NET. Highly capable run-times, such as the .NET Framework offer significant capabilities and access to the operating system and I/O. This allows a developer to create a powerful application very quickly.

Run-times are not necessarily striving for cross platform compatibility, while run-times such as Sun’s Java might.

Scripting (meta) language interpreters act similar to a run-time, although the code for many scripting languages is not pre-compiled as they are in .NET languages. Pre-compiling speeds up the act of loading the application into memory and also ensures a more compact executable file.

Wednesday, July 23, 2008

Information ecology

In the context of an evolving information society, the term information ecology was coined by various persons in the 1980s and 1990s. It marks a connection between ecological ideas with the dynamics and properties of the increasingly dense, complex and important digital informational environment and has been gaining progressively wider acceptance in a growing number of disciplines. "Information ecology" often is used as metaphor, viewing the informational space as an ecosystem.