Dynamic Reservation Multiple Access (DRMA): A new multiple access scheme for Personal Communication System (PCS)

To improve the spectrum efficiency of integrated voice and data services in Personal Communication System (PCS), several reservation-type multiple access schemes, such as Packet Reservation Multiple Access (PRMA), Dynamic Time Division Multiple Access (D-TDMA), Resource Auction Multiple Access (RAMA), etc., have been proposed. PRMA uses the data packet itself to make a channel reservation, and is inefficient in that each unsuccessful reservation wastes one slot. However, it does not have a fixed reservation overhead and offers shorter access delay. On the other hand, fixed reservation overhead is unavoidable in both RAMA and D-TDMA. Compared to D-TDMA and PRMA, RAMA is superior in the sense that its slot assignment is independent of the traffic load. But its implementation is difficult. With these observations, a new reservation protocol, called Dynamic Reservation Multiple Access (DRMA), is proposed in this paper. With this new protocol, the success probability of channel access is greatly improved at the expense of slightly increased system complexity. It solves the problem of inefficiency in PRMA, but without introducing the fixed reservation overhead as in D-TDMA and RAMA. In addition, it is more suited to the dynamic behavior of the integrated traffic because there is no fixed boundary between voice and data slots (which is mandatory in D-TDMA and RAMA). Our numerical results indicate that its performance is superior to the existing reservation protocols, especially in the integrated traffic scenario. Moreover, the soft capacity feature is exhibited when the traffic load increases.     

Practical constraints in growth of lightwave networks

The amount of fiber required, propagation delay, and length of the longest link are significant design constraints in spatially large networks. This paper examines these characteristics from the viewpoint of growth and compares basic networks with hierarchical ones in terms of these characteristics. Results show that, when considering growth from three nodes, a star network randomly placed with a uniform distribution uses less fiber than a dual ring until there are 57 nodes. As the networks become large, the star has the smallest propagation delay and the dual ring uses the least amount of fiber. A two-level network having a star on the upper level and dual rings on the lower network level performs well in both categories by using 1.38 times as much fiber as the dual ring and having 1.65 times the propagation delay of a star as the number of nodes becomes large     

Choosing an optimal set of libraries [software reliability]

This paper presents optimization models for selecting a subset of software libraries, viz, collections of programs, residing on floppy disks or compact disks, available on the market. Each library contains a variety of programs whose reliabilities are assumed to be known. The objective is to maximize the reliability of the computer system subject to a budget constraint on the total cost of the libraries selected. The paper includes six models, each of which applies to a different software structure and assumptions. A detailed branch and bound algorithm for solving one of the six models is described; it contains a simple greedy-procedure for generating an initial solution     

Measurement of the gravitational constant with a torsion balance

We present results of ten years of measurements of the gravitational constant made using an evacuated torsion balance. We obtained the valueG=(6.6729±0.0005)·10⁻¹¹ N·m²·kg⁻². We have determined the major destabilizing factors accompanying the measurement process and have estimated the contribution from different sources of error. Translated from Izmeritel'naya Tekhnika, No. 10, pp. 3–9, October, 1996.     

自支撑同位素钐靶的制备

一、引言联邦德国重离子研究所的物理实验需要~(154)Sm和~(144)Sm靶,具体要求是:(1)自支撑金属靶,(2)厚度范围为90—110 μg/cm~2,(3)靶厚测量误差为±10%,(4)靶的尺寸是φ15 mm,(5)靶的数量为4—5块。用滚轧法、电镀法和重离子溅射法制备这样薄的自支撑靶都十分困难,因此采用真空蒸发试制同位素钐靶。     

Dewatering of liwuid radioactive wastes in thin-film rotary evaporators

Translated from Atomnaya Énergiya, Vol. 67, No. 1, pp. 11–15, July, 1989.     

Role of pH and Ionic Strength on Water Relationships in Washed Minced Chicken-breast Muscle Gels

ABSTRACT The relationship between pH, ionic strength, and water balance of chicken-breast muscle gels was investigated. An increase in gel pH (pH 6.4 to 7.4) without added NaCl led to dramatic increases in water-holding capacity and water uptake (P < 0.05). Gels at 150 mM NaCl exhibited less ability to adsorb water than salt-free gels (P < 0.05 at pH 6.8 to 7.4) and had lower water-holding capacities (P < 0.05) and fold scores at and below pH 7. Varying salt concentration of the gel-bathing solutions had dramatic effect on the water uptake of the gels. The results show that strong water-absorbing gels can be produced at low ionic strengths and suggest that the negative charge of the muscle proteins is the driving force for water uptake and retention.