SEMINARS and SEMINAR TOPICS With Notes on Each Subjects

STUN

2010-04-03T02:52:00.001-07:00

This is a network protocol which enables a client in a NAT (or multiple NATs) to find out its public address, the type of NAT behind it and the internet side port associated by the NAT with a particular local port and this whole process aids to set up UDP communication between two hosts that are both behind NAT routers. STUN stands for Simple Traversal of UDP (User Datagram Protocol) through NATs (Network Address Translators).

Protocol overview

STUN is a client-server protocol. Any VoIP phone or software package includes a STUN client, which sends a request to the STUN server. As a reply the public IP address of the NAT router and the port was opened by the NAT to allow incoming traffic back in to the network is sent to the STUN client. Such a response also helps the STUN client to identify the NAT being used as different types of NATs handle incoming UDP packets vividly. Its compatible with Full Cone, Restricted Cone, and Port Restricted Cone. (Restricted Cone or Port Restricted Cone NATs, allows packets from the endpoint through to the client from the NAT once the client has send a packet to the endpoint). Symmetric NAT (also known as bi-directional NAT) which is frequently found in the networks of large companies does not work with STUN as the IP addresses of the STUN server and the endpoint is different, and therefore the NAT mapping the STUN server is different from the mapping that the endpoint uses to send packets through to the client. Network address translation could give you more information on this.

After the client discovers its external addresses communication with its peers occurs. When the NATs are full cone,either side can initiate communication and if they are restricted cone or restricted port cone both sides must start transmitting together. The techniques described in the STUN RFC does not necessarily require using the STUN protocol; they can be used in the design of any UDP protocol. STUN comes in handy in the cases of Protocols like SIP which use UDP packets for the transfer of sound/video/text signaling traffic across the Internet. As both endpoints are often behind NAT, a connection cannot be set up in the traditional way. The STUN server communicates on UDP port 3478 but the server will hint clients to perform tests on alternate IP and port number too (STUN servers have two IP addresses).

Hyper Transport Technology

2010-04-02T00:06:00.000-07:00

The demand for faster processors, memory and I/O is a familiar refrain in market applications ranging from personal computers and servers to networking systems and from video games to office automation equipment. Once information is digitized, the speed at which it is processed becomes the foremost determinate of product success. Faster system speed leads to faster processing. Faster processing leads to faster system performance. Faster system performance results in greater success in the marketplace. This obvious logic has led a generation of processor and memory designers to focus on one overriding objective - squeezing more speed from processors and memory devices. Processor designers have responded with faster clock rates and super pipelined architectures that use level 1 and level 2 caches to feed faster execution units even faster. Memory designers have responded with dual data rate memories that allow data access on both the leading and trailing clock edges doubling data access. I/O developers have responded by designing faster and wider I/O channels and introducing new protocols to meet anticipated I/O needs. Today, processors hit the market with 2+ GHz clock rates, memory devices provide sub5 ns access times and standard I/O buses are 32- and 64-bit wide, with new higher speed protocols on the horizon.Increased processor speeds, faster memories, and wider I/O channels are not always practical answers to the need for speed. The main problem is integration of more and faster system elements. Faster execution units, faster memories and wider, faster I/O buses lead to crowding of more high-speed signal lines onto the physical printed circuit board. One aspect of the integration problem is the physical problems posed by speed.

Hyper Transport technology has been designed to provide system architects with significantly more bandwidth, low-latency responses, lower pin counts, compatibility with legacy PC buses, extensibility to new SNA buses, and transparency to operating system software, with little impact on peripheral drivers.

FluidFM: Combining AFM and nanofluidics for single cell applications

2009-10-02T02:28:00.000-07:00

FluidFM: Combining AFM and nanofluidics for single cell applications

The Atomic Force Microscope (AFM) is a key tool for nanotechnology. This instrument has become the most widely used tool for imaging, measuring and manipulating matter at the nanoscale and in turn has inspired a variety of other scanning probe techniques. Originally the AFM was used to image the topography of surfaces, but by modifying the tip it is possible to measure other quantities (for example, electric and magnetic properties, chemical potentials, friction and so on), and also to perform various types of spectroscopy and analysis. Increasingly, the AFM is also becoming a tool for nanofabrication.

Relatively new is the use of AFM in cell biology. We wrote about this recently in a Spotlight that described a novel method to probe the mechanical properties of living and dead bacteria via AFM indentation experimentations ("Dead or alive – nanotechnology technique tells the difference ").
Researchers in Switzerland have now demonstrated novel cell biology applications using hollow force-controlled AFM cantilevers – a new device they have called FluidFM.

"The core of the invention is to have fixed already existing microchanneled cantilevers to an opportunely drilled AFM probeholder" Tomaso Zambelli tells Nanowerk. "In this way, the FluidFM is not restricted to air but can work in liquid environments. Since it combines a nanofluidics circuit, every soluble agent can be added to the solution to be dispensed. Moreover, the force feedback allows to approach very soft objects like cells without damaging them."

As cell biology is moving towards single cell technologies and applications, single cell injection or extraction techniques are in high demand. Apart from this, however, the FluidFM could also be used for nanofabrication applications such as depositing a conductive polymer wire between to microelectrodes, or to etch ultrafine structures out of solid materials using acids as the spray agent. The team has reported their findings in a recent paper in Nano Letters ("FluidFM: Combining Atomic Force Microscopy and Nanofluidics in a Universal Liquid Delivery System for Single Cell Applications and Beyond").

Zambelli originally realized that the technology of the atomic force microscope that is normally used only to image cells could be transformed into a microinjection system. The result of the development by Zambelli and his colleagues in the Laboratory of Biosensors and Bioelectronics at the Institute of Biomedical technology at ETH Zurich and in the Swiss Center for Electronics and Microtechnology (CSEM) in Neuchâtel was the "fluid force microscope", currently the smallest automated nanosyringe currently in existence.

"Our FluidFM even operates under water or in other liquids – a precondition for being able to use the instrument to study cells" says Zambelli.

The force detection system of the FluidFM is so sensitive that the interactions between tip and sample can be reduced to the piconewton range, thereby allowing to bring the hollow cantilever into gentle but close contact with cells without puncturing or damaging the cell membrane.

On the other hand, if membrane perforation for intracellular injection is desired, this is simply achieved by selecting a higher force set point taking advantage of the extremely sharp tip (radius of curvature on the order of tens of nanometers).

To enable solutions to be injected into the cell through the needle, scientists at CSEM installed a microchannel in the cantilever. Substances such as medicinal active ingredients, DNA, and RNA can be injected into a cell through the tip. At the same time, samples can also be taken from a cell through the needle for subsequent analysis.

According to Zambelli, while this approach is similar to microinjection using glass pipettes, there are a number of essential differences.

"Microinjection uses optical microscopy to control the position of the glass pipette tip both in the xy plane and in the z direction (via image focusing)" he explains. "As consequence of the limited resolution of optical microscopy, subcellular domains cannot be addressed and tip contact with the cell membrane cannot be discriminated from tip penetration of the membrane. Cells are often lethally damaged and skilled personnel are required for microinjection."

"The limited resolution of this method and the absence of mechanical information contrast strongly with the high resolution imaging and the direct control of applied forces that are possible with AFM. Precise force feedback reduces potential damage to the cell; the cantilever geometry minimizes both the normal contact forces on the cell and the lateral vibrations of the tip that can tear the cell membrane during microinjection; the spatial resolution is determined by the submicrometer aperture so that injection into subcellular domains becomes easily achievable."

Experiments conducted by the Swiss team demonstrate the potential of the FluidFM in the field of single-cell biology through precise stimulation of selected cell domains with whatever soluble agents at a well-defined time.

"We confidently expect that the inclusion of an electrode in the microfluidics circuit will allow a similar approach toward patch-clamping with force controlled gigaseal formation," says Zambelli. "We will also explore other strategies at the single-cell level, such as the controlled perforation of the cell membrane for local extraction of cytoplasm

"Zambelli and his colleagues are convinced that their technology has great commercial potential. Rejecting offers from well-known manufacturers of atomic force microscopes for the sale of the patent for the FluidFM, they have founded Cytosurge LLC, a company dedicated to commercially develop the instrument.

Today, Zambelli's laboratory contains two prototypes of the instrument, which are being tested in collaboration with biologists.