Forward collision resolution-a technique for random multiple-accessto the adder channel

Consider M-Choose-T communications: T users or less, out of M potential users, are chosen at random to simultaneously transmit binary data over a common channel. A method for constructing codes that achieve error-free M-Choose-T communication over the noiseless adder channel (AC), at a nominal rate of 1/T bits per channel symbol per active user, is described and an efficient decoding procedure is presented. The use of such codes is referred to as forward collision resolution (FCR), as it enables correct decoding of collided messages without retransmissions. For any given T a code is available that yields a stable throughput arbitrarily close to 1 message/slot. Furthermore, if the occurrence of collisions is made known to the transmitters, such a throughput can be maintained for arbitrary T,T⩽M as well. If such feedback is not available, and T is random, the probability of an unresolved collision is significantly smaller than the probability of a collision in an uncoded system, at comparable message-arrival and information rates     

Upper bounds on the probability of sequences emitted byfinite-state sources and on the redundancy of the Lempel-Ziv algorithm

An upper bound on the probability of a sequence drawn from a finite-state source is derived. The bound is given in terms of the number of phrases obtained by parsing the sequence according to the Lempel-Ziv (L-Z) incremental parsing rule, and is universal in the sense that it does not depend on the statistical parameters that characterize the source. This bound is used to derive an upper bound on the redundance of the L-Z universal data compression algorithm applied to finite-state sources, that depends on the length N of the sequence, on the number K of states of the source, and, eventually, on the source entropy. A variation of the L-Z algorithm is presented, and an upper bound on its redundancy is derived for finite-state sources. A method to derive tighter implicit upper bounds on the redundancy of both algorithms is also given, and it is shown that for the proposed variation this bound is smaller than for the original L-Z algorithm, or every value of N and K     

Limitations of the capacity of the M-user binary adder channel dueto physical considerations

The capacity of the M-user binary adder channel, subjected to various restrictions of physical nature, is investigated. The underlying propagation media considered are (i) fiber-optic, with lossless coupling and Poisson statistics, (ii) radio, under Rayleigh fading, and (iii) radio with constant amplitudes and random phases. Whereas the capacity of the unrestricted (ideal) model for the binary adder channel is known to increase without limit with the number of users, it is shown in the present paper that, for each of these cases, the total capacity is upper-bounded by a constant independent of the number of users: in case (i) by 1.7Q_T bits per channel use, where Q_T is the parameter of the Poisson process, in case (ii) by 4.33 bits per channel use, and in case (iii) by 4.27 bits per channel use     

Presence and variability of culturable bioaerosols in three multi-family apartment buildings with different ventilation systems in the Northeastern US

Bioaerosol concentrations in residential buildings located in the Northeastern US have not been widely studied. Here, in 2011-2015, we studied the presence and seasonal variability of culturable fungi and bacteria in three multi-family apartment buildings and correlated the bioaerosol concentrations with building ventilation system types and environmental parameters. A total of 409 indoor and 86 outdoor samples were taken. Eighty-five percent of investigated apartments had indoor-outdoor (I/O) ratios of culturable fungi below 1, suggesting minimal indoor sources of fungi. In contrast, 56% of the apartments had I/O ratios for culturable bacteria above 1, indicating the prominence of indoor sources of bacteria. Culturable fungi I/O ratios in apartments serviced by central heating, ventilation, and air-conditioning (HVAC) system were lower than those in apartments with window AC. The type of ventilation system did not have a significant effect on the presence of indoor culturable bacteria. A significant positive association was determined between indoor dew point (DP) levels and indoor culturable fungi (P < .001) and bacteria (P < .001), regardless of ventilation type. Also, residents in apartments with central HVAC did not experience extreme DP values. We conclude that building ventilation systems, seasonality, and indoor sources are major factors affecting indoor bioaerosol levels in residential buildings.     

Fear reduction in the rat following central cholinergic blockade.

In the presence of a natural predator, cat, 92 male Long-Evans hooded rats (in 2 experiments) showed a constellation of responses that was used to define fear: freezing, avoiding the cat, and suppressing consummatory behavior. Compared with controls, Ss treated with an anticholinergic drug, scopolamine, showed significantly less freezing and significantly more approach to the cat; further, these Ss actually engaged in consummatory behavior in proximity to the cat. On a 2nd, undrugged exposure to the cat, the original scopolamine-treated Ss continued to show significantly less freezing, more approach, and more drinking than control Ss. Since methyl scopolamine, which mimics the peripheral actions of scopolamine, had no effect on fear responses, these results implicate a central cholinergic system in fear responses or species-typical defense reactions. (24 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)