Tampa, Florida (28°N, 82.5°W), has about 90 thunderstorm days per year, almost all in summer. These convective events tend to occur in afternoon or early evening. This paper presents results of 19‐GHz downlink rain attenuation diversity studies in Tampa involving site separations of 11, 16, and 20 km and reception at high elevation angle (about 57°), over a period of 29 months, including three rainy seasons. Almost identical long‐term performance with the two larger spacings indicates that for separations above about 15 km, diversity improvement was not sensitive to baseline orientation or length. During a fourth rainy season, using the remaining 29‐GHz beacon, diversity improvement with the 16‐km pair was similar to that predicted by scaling the 19‐GHz results of the previous seasons. Also discussed are the type of attenuation distributions and typical fade durations to be found under persistent convective conditions. For rain climates like Tampa's, site diversity in some form will be required for high‐reliability SHF satellite links. The diversity data may be helpful in designing schemes for resource sharing among numbers of links.

Recently protocols have been introduced which enable us to integrate periodic traffic (voice or video) and aperiodic traffic (data) and to extend the size of local area networks without any loss in speed and capacity. One of these, the DRAMA protocol, is based on broadband technology and allows for dynamic allocation of bandwidth to clusters of nodes in the total network. In this paper we propose a distributed algorithm to allocate bandwidth in a fair manner, where we have defined fair to mean that every node in the network, regardless of its location, should have the same expected access delay to the net. We show by means of simulation that the algorithm is stable and within a few percentage points of the optimal solution. Stability is measured in terms of the time it takes the system to return to near optimal distribution of the bandwidth after strong disturbances. The algorithm is shown to handle total reallocation of the resources within 0( 1OOms).

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Ice melting plays a crucial role in ocean circulation and global climate. Laboratory experiments were used to study the dynamic mechanisms of the influence of waves and currents on ice melting. The results showed that under near stable air temperature and water temperature conditions, the ice melting rate was significantly greater with waves than that without waves, as well as the higher the wave height, the greater the melting rate. This is related to the increase in the contact area between ice and water by waves. Further research was carried out to observe the flow field at different locations on the ice bottom, ice sides, and behind the ice by particle image velocimetry (PIV) and dyeing experiments. At different flow velocities, the changes in the side melting rate and bottom melting rate were not the same. Meltwater is attached to the bottom in the form of plume at low background flow velocity, which leads to the slowness of the heat exchange between the ice with a higher ambient temperature. Therefore, the melting of the ice bottom and the ice side were slower at low flow velocity. At high background flow velocity, there is strong shear instability and vortex at the ice bottom and behind the ice. The dissipation and mixing effects caused by vortices accelerate the melting of the ice bottom and the ice back. The thermodynamic factors, such as air temperature and water temperature, had significant impacts in the experiments. Further research needs to improve the accuracy of temperature control of experimental equipment. Computational fluid dynamics and sensitive tests of numerical simulation may also be carried out on ice melting.

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