Soft Handoff and Uplink Capacity in a Two-Tier CDMA System

This paper examines the effect of soft handoff on the uplink user capacity of a CDMA system consisting of a single macrocell in which a single hotspot microcell is embedded. The users of these two base stations operate over the same frequency band. In the soft handoff scenario studied here, both macrocell and microcell base stations serve each system user and the two received copies of a desired user's signal are summed using maximal ratio combining. Exact and approximate analytical methods are developed to compute uplink user capacity. Simulation results demonstrate a 20% increase in user capacity compared to hard handoff. In addition, simple, approximate methods are presented for estimating soft handoff capacity and are shown to be quite accurate.Comment: To appear in IEEE Transactions on Wireless Communication

Uplink User Capacity in a CDMA System with Hotspot Microcells: Effects of Finite Transmit Power and Dispersion

This paper examines the uplink user capacity in a two-tier code division multiple access (CDMA) system with hotspot microcells when user terminal power is limited and the wireless channel is finitely-dispersive. A finitely-dispersive channel causes variable fading of the signal power at the output of the RAKE receiver. First, a two-cell system composed of one macrocell and one embedded microcell is studied and analytical methods are developed to estimate the user capacity as a function of a dimensionless parameter that depends on the transmit power constraint and cell radius. Next, novel analytical methods are developed to study the effect of variable fading, both with and without transmit power constraints. Finally, the analytical methods are extended to estimate uplink user capacity for multicell CDMA systems, composed of multiple macrocells and multiple embedded microcells. In all cases, the analysis-based estimates are compared with and confirmed by simulation results.Comment: To appear in IEEE Transactions on Wireless Communication

Uplink Throughput in a Single-Macrocell/Single-Microcell CDMA System, with Application to Data Access Points

This paper studies a two-tier CDMA system in which the microcell base is converted into a data access point (DAP), i.e., a limited-range base station that provides high-speed access to one user at a time. The microcell (or DAP) user operates on the same frequency as the macrocell users and has the same chip rate. However, it adapts its spreading factor, and thus its data rate, in accordance with interference conditions. By contrast, the macrocell serves multiple simultaneous data users, each with the same fixed rate. The achieveable throughput for individual microcell users is examined and a simple, accurate approximation for its probability distribution is presented. Computations for average throughputs, both per-user and total, are also presented. The numerical results highlight the impact of a desensitivity parameter used in the base-selection process.Comment: To appear in IEEE Transactions on Wireless Communication

Shallow-water reefs in transition: Examples from Belize and the Bahamas

The plight of coral reefs throughout the Caribbean region has been widely reported by reef scientists. A variety of causes has lead to reefal decline, particularly in shallow waters. This study compares the responses of shallow-water reefs in Belize and the Bahamas to outbreaks of white­ band disease (WBD) and traces changes on these reefs to the early 2000s. Prior to the mid-1980s, reef ridges of the Pelican Cays of Belize were constructed of luxu­ riant stands of Acropora cervicomis. As else­ where, this species suffered massive mortality in mid-1980s owing to WBD, and dead A. cervicor­ nis substrates were quickly colonized by Agaricia tenuifolia. Subsequently, A. tenuifolia on the reef ridges was severely affected by the intense El Nino-Southern Oscillation (ENSO)-related bleaching event of 1998. Our surveys showed that \u3e90% of A. tenuifolia colonies died following bleaching. More recent survey data indicate that sponges are aggressively colonizing the coral sub­ strata. In the early 1980s, Telephone Pole Reef on San Salvador Island, Bahamas, had numerous thickets of Acropora cervicomis along with large colonies of Montastraea annularis species com­ plex. By the mid-l 980s, virtually all A. cervicor­ nis colonies were dead, presumably from WBD. Following the demise of the A. cervicomis thick­ ets, an increase in Porites porites colonies quickly occurred. P. porites was opportunistic in coloniza­ tion and showed preference for A. cervicomis substrates. By the early 1990s, P. porites was a dominant coral on Telephone Pole Reef, with col­ ony sizes commonly greater than 1 min diameter. Reef surveys in 1998 and 2000 indicated signifi­ cant decline in the health of P. porites, and in early 2002 continued deterioration was noted, with virtually all larger colonies overgrown by fleshy green macroalgae and/or encrusted by coralline algae. These two examples are similar in that both shallow-water reefs are in rapid transition to domination by non-coral groups that impede set­ tlement of coral larval recruits: sponges in Belize and macro- and coralline algae in the Bahamas. Depending on how widespread similar transitions may be, the future of shallow-water coral reefs throughout the wider Caribbean is problematic. Turnover events such as these have been de­ scribed as unprecedented for coral reefs, and pa­ leontologists should examine the Cenozoic coral reef record in greater detail to explore these claims

How Much Ecological Information is Preserved in Fossil Coral Reefs and How Reliable is it?

The coral reef fossil record is the exclusive database from which analyses of the response of coral communities to environmental change over geological time scales may be gauged. However, few studies have attempted to ascertain whether the reef fossil record is a reasonably accurate representation of a once living coral community. To address this issue, we have performed a systematic comparison of the taxonomic composition and diversity present in exposure of Pleistocene patch reef and reef tract facies found in the Bahamas to that observed for life and death assemblages currently present in analogous modern reefs of the Florida Keys. Results reveal that both modern death assemblages and fossil assemblages preserve the zonation observed on living reefs. However, the taxonomic composition of living reef communities is more closely matched by the fossil assemblages than by the death assemblages. We conclude that the Quaternary record of Caribbean reefs does preserve a reliable account of the long term responses of coral communities to environmental change

Fernandez Bay, San Salvador, Bahamas: A Natural Laboratory for Assessment of the Preservation of Coral Reef Community Structure

Reprinted from: James L. Carew (ed.), Proceedings of the 8th Symposium on the Geology of the Bahamas: San Salvador, Bahamian Field Statio

Comparison of Recent Coral Life and Death Assemblages to Pleistocene Reef Communities: Implications for Rapid Faunal Replacement on Recent Reefs

Marine ecologists and paleoecologists are increasingly recognizing that the Pleistocene and Holocene fossil record of coral reefs is the exclusive database from which an assessment of the long-term responses of reef communities to environmental perturbations may be obtained. The apparent persistence of coral communities in the face of intense fluctuations in sea level and sea surface temperature during glacial and interglacial stages of Pleistocene time is in marked contrast to dramatic fluctuations in reef community structure documented by short-term monitoring studies. We compared the taxonomic structure of live and dead coral communities on a modem patch reef currently undergoing a community transition to late Pleistocene facies exposed in the CockburnTown fossil coral reef. Multidimensional scaling revealed that specific taxa and colony growth forms characterize life, death, and fossil assemblages. The recent decline of thickets of Acropora cervicorn is is represented by their abundance in the death assemblage, while Porites porites dominates the coral life assemblage. Although additional study of Pleistocene reefal facies is required, the greater similarity of the death assemblage to the fossil assemblage suggests that the present Caribbean- wide decline of A. cervicornis is without a historical preceden

Monensin causes dose dependent inhibition of Mycobacterium avium subspecies paratuberculosis in radiometric culture

<p>Abstract</p> <p>Background</p> <p><it>Mycobacterium avium </it>subspecies <it>paratuberculosis </it>(MAP) causes a chronic wasting diarrheal disease in ruminants called Johne's disease, that is evocative of human inflammatory bowel disease (IBD). Agents used to treat IBD, called "anti-inflammatories", immuno-modulators" and "immuno-suppressants" inhibit MAP growth in culture. We concluded that, unknowingly, the medical profession has been treating MAP since sulfasalazine's introduction in 1942. Monensin, called a "Growth Enhancer" in cattle, ameliorates Johne's disease without a documented mechanism of action. We hypothesized that Monensin would inhibit MAP in culture.</p> <p>Methods</p> <p>Using the radiometric ¹⁴CO₂Bactec^®system, that expresses mycobacterial growth in arbitrary growth index (GI) units, we studied the effect of Monensin on the growth kinetic of MAP isolated from humans with IBD ("Dominic", "Ben" & UCF-4) and cattle with Johne's disease (303 & ATCC 19698.) Results are expressed as percent inhibition of cumulative GI (%–ΔcGI).</p> <p>Results</p> <p>The positive control Clofazimine inhibits every strain tested. The negative controls Cycloheximide & Phthalimide, have no inhibition on any MAP strain. Monensin has dose dependent inhibition on every MAP strain tested. The most susceptible human isolate was UCF-4 (73% – ΔcGI at 1 μg/ml) and bovine isolate was 303 (73% – ΔcGI at 4 μg/ml.) Monensin additionally inhibits <it>M. avium </it>ATCC 25291 (87% – ΔcGI at 64 μg/ml) & BCG (92% – ΔcGI at 16 μg/ml).</p> <p>Discussion</p> <p>We show that in radiometric culture the "Growth Enhancer" Monensin causes dose dependent inhibition of mycobacteria including MAP. We posit that the "Growth Enhancer" effect of Monensin may, at least in part, be due to inhibition of MAP in clinical or sub-clinical Johne's disease.</p

V2494 cyg: A unique FU ori type object in the cygnus OB7 complex

A photometric and spectral study of the variable star V2494 Cyg in the L 1003 dark cloud is presented. The brightness of the star, formerly known as HH 381 IRS, increased by 2.5 mag in R (probably in the 1980s) and since then has remained nearly constant. Since the brightness increase, V2494 Cyg has illuminated a bipolar cometary nebula. The stellar spectrum has several features typical of the FU Ori (FUor) type, plus it exhibits very strong Ha and forbidden emissionlines with high-velocity components. These emission lines originate in the Herbig-Haro (HH) jet near the star. The kinematic age of the jet is consistent with it forming at the time of the outburst leading to the luminosity increase. V2494 Cyg also produces a rather extended outflow; it is the first known FUor with both an observed outburst and a parsec-sized HH flow. The nebula, illuminated by V2494 Cyg, possesses similar morphological and spectral characteristics to Hubble's variable nebula (R Monocerotis/NGC 2261). © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society