Low‐loss TCP/IP header compression for wireless networks

Wireless is becoming a popular way to connect mobile computers to the Internet and other networks. The bandwidth of wireless links will probably always be limited due to properties of the physical medium and regulatory limits on the use of frequencies for radio communication. Therefore, it is necessary for network protocols to utilize the available bandwidth efficiently. Headers of IP packets are growing and the bandwidth required for transmitting headers is increasing. With the coming of IPv6 the address size increases from 4 to 16 bytes and the basic IP header increases from 20 to 40 bytes. Moreover, most mobility schemes tunnel packets addressed to mobile hosts by adding an extra IP header or extra routing information, typically increasing the size of TCP/IPv4 headers to 60 bytes and TCP/IPv6 headers to 100 bytes. In this paper, we provide new header compression schemes for UDP/IP and TCP/IP protocols. We show how to reduce the size of UDP/IP headers by an order of magnitude, down to four to five bytes. Our method works over simplex links, lossy links, multi‐access links, and supports multicast communication. We also show how to generalize the most commonly used method for header compression for TCP/IPv4, developed by Jacobson, to IPv6 and multiple IP headers. The resulting scheme unfortunately reduces TCP throughput over lossy links due to unfavorable interaction with TCP's congestion control mechanisms. However, by adding two simple mechanisms the potential gain from header compression can be realized over lossy wireless networks as well as point‐to‐point modem links. This revised version was published online in June 2006 with corrections to the Cover Date.     

System for in situ studies of atmospheric corrosion of metal films using soft x-ray spectroscopy and quartz crystal microbalance

We present a versatile chamber ("atmospheric corrosion cell") for soft x-ray absorption/emission spectroscopy of metal surfaces in a corrosive atmosphere allowing novel in situ electronic structure studies. Synchrotron x rays passing through a thin window separating the corrosion cell interior from a beamline vacuum chamber probe a metal film deposited on a quartz crystal microbalance (QCM) or on the inside of the window. We present some initial results on chloride induced corrosion of iron surfaces in humidified synthetic air. By simultaneous recording of QCM signal and soft x-ray emission from the corroding sample, correlation between mass changes and variations in spectral features is facilitated.     

Stretchability of the rectus femoris muscle: investigation of validity and intratester reliability of two methods including X-ray analysis of pelvic tilt

Validity and intratester reliability of two test methods designed to identify stretchability of the rectus femoris muscle (RFM) was investigated, combined with x-ray analysis of pelvic tilt in the sagittal plane. The first method is commonly used in clinical practice. The second is a new technique supposed to tilt the pelvis posteriorly and thus further separate the origin and insertion of the muscle. Investigation of validity and intratester reliability of the two methods was made by testing and retesting a random sample of 71 persons. The tests were performed with an equipment that automatically recorded the angle of knee flexion from a previously determined applied torque, indicating the end point of motion for that particular subject. Angle of knee flexion and subjective estimation of pain sensation due to stretch were recorded at each measurement. The pelvic tilt-analysis consisted of test-retest reliability of x-ray measurements, comparison between the methods in both starting and final position, and x-ray and electronic goniometer measurements. All applied torques were measured with a strain gauge. Two out of three criteria of validity favored the new method and the third pointed out the two methods as equal. The two methods as well as the x-ray measurements showed high reliability, and the hypothesis of a more posterior tilted pelvis in the new method was confirmed. The electronic goniometer was less sensitive than x-ray, but proposed to analyse pelvic tilt clinically. Methodology procedures for joint angle measurements are discussed.     

Mechanism of interaction between electric arc and breaking chamberin low voltage current limiting circuit breakers

The authors survey different types of contact arrangements with simple, double, and quadruple arc interruption in current-limiting low-voltage protective switching devices. The influence of the arc commutation from moving contact arm to commutation bar is discussed. A new type of rapid electromagnet with a rotating armature is presented. The performance of the electromagnet was investigated by the finite element method. The same method was used to study the configuration of the arcing chamber and the influence of different parameters on the contact repulsion forces. The experiments were carried out with the help of a capacitor bank, and the results were measured by a data acquisition system     

Measurements of movements during highly repetitive industrial work

In the manufacturing industry highly repetitive movement patterns in the work situation are common. This work situation is often the cause of pain in the neck-arm region. To measure these movement patterns a new method has been developed by registering acceleration during ordinary industrial work. Three small accelerometers were fastened horizontally, transversely and vertically in a small box at the wrist. The data were fed into a computer memory at the work site and analysed later. The method can be used during ordinary work in a factory causing no interference to the work.