Modeling the effect of transmission errors on TCP controlled transfers over infrastructure 802.11 wireless LANs

There have been several studies on the performance of TCP controlled transfers over an infrastructure IEEE 802.11 WLAN, assuming perfect channel conditions. In this paper, we develop an analytical model for the throughput of TCP controlled file transfers over the IEEE 802.11 DCF with different packet error probabilities for the stations, accounting for the effect of packet drops on the TCP window. Our analysis proceeds by combining two models: one is an extension of the usual TCP-over-DCF model for an infrastructure WLAN, where the throughput of a station depends on the probability that the head-of-the-line packet at the Access Point belongs to that station; the second is a model for the TCP window process for connections with different drop probabilities. Iterative calculations between these models yields the head-of-the-line probabilities, and then, performance measures such as the throughputs and packet failure probabilities can be derived. We find that, due to MAC layer retransmissions, packet losses are rare even with high channel error probabilities and the stations obtain fair throughputs even when some of them have packet error probabilities as high as 0.1 or 0.2. For some restricted settings we are also able to model tail-drop loss at the AP. Although involving many approximations, the model captures the system behavior quite accurately, as compared with simulations.

Physical Layer Network Coding for the K-User Multiple Access Relay Channel

We propose a Physical layer Network Coding (PNC) scheme for the K-user wireless Multiple Access Relay Channel, in which K source nodes want to transmit messages to a destination node D with the help of a relay node R. The proposed scheme involves (i) Phase 1 during which the source nodes alone transmit and (ii) Phase 2 during which the source nodes and the relay node transmit. At the end of Phase 1, the relay node decodes the messages of the source nodes and during Phase 2 transmits a many-to-one function of the decoded messages. To counter the error propagation from the relay node, we propose a novel decoder which takes into account the possibility of error events at R. It is shown that if certain parameters are chosen properly and if the network coding map used at R forms a Latin Hypercube, the proposed decoder offers the maximum diversity order of two. Also, it is shown that for a proper choice of the parameters, the proposed decoder admits fast decoding, with the same decoding complexity order as that of the reference scheme based on Complex Field Network Coding (CFNC). Simulation results indicate that the proposed PNC scheme offers a large gain over the CFNC scheme.

Ligand 5,10,15,20-Tetra(N-methyl-4-pyridyl)porphine (TMPyP4) Prefers the Parallel Propeller-Type Human Telomeric G-Quadruplex DNA over Its Other Polymorphs

The binding of ligand 5,10,15,20-tetra(N-methyl-4-pyridyl)porphine (TMPyP4) with telomeric and genomic G-quadruplex DNA has been extensively studied. However, a comparative study of interactions of TMPyP4 with different conformations of human telomeric G-quadruplex DNA, namely, parallel propeller-type (PP), antiparallel basket-type (AB), and mixed hybrid-type (MH) G-quadruplex DNA, has not been done. We considered all the possible binding sites in each of the G-quadruplex DNA structures and docked TMPyP4 to each one of them. The resultant most potent sites for binding were analyzed from the mean binding free energy of the complexes. Molecular dynamics simulations were then carried out, and analysis of the binding free energy of the TMPyP4-G-quadruplex complex showed that the binding of TMPyP4 with parallel propeller-type G-quadruplex DNA is preferred over the other two G-quadruplex DNA conformations. The results obtained from the change in solvent excluded surface area (SESA) and solvent accessible surface area (SASA) also support the more pronounced binding of the ligand with the parallel propeller-type G-quadruplex DNA.

Effect of ambient pressure and radiation reabsorption of atmosphere on the flame spreading over thermally thin combustibles in microgravity

For the flame spread over thermally thin combustibles in an atmosphere, if the atmosphere cannot emit and absorb the thermal radiation (e.g. for atmosphere Of O-2-N-2), the conductive heat transfer from the flame to the fuel surface dominates the flame spread at lower ambient atmosphere. As the ambient pressure increases, the flame spread rate increases, and the radiant heat transfer from the flame to the fuel surface gradually becomes the dominant driving force for the flame spread. In contrast, if the atmosphere is able to emit and absorb the thermal radiation (e.g. for atmosphere Of O-2-CO2), at lower pressure, the heat transfer from flame to the fuel surface is enhanced by the radiation reabsorption of the atmosphere at the leading edge of the flame, and both conduction and thermal radiation play important roles in the mechanism of flame spread. With the increase in ambient pressure, the oxygen diffuses more quickly from ambient atmosphere into the flame, the chemical reaction in the flame is enhanced, and the flame spread rate increases. When the ambient pressure is greater than a critical value, the thermal radiation from the flame to the solid surface is hampered by the radiation reabsorption of ambient atmosphere with the further increase in ambient pressure. As a result, with the increase in ambient pressure, the flame spread rate decreases and the heat conduction gradually dominates the flame spread over the fuel surface.

The Demand for Environmental Quality in Driving Transitions to Low Polluting Energy Sources

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The proposed Lune net limitation order 1999 and associated byelaws

The River Lune rises in the hills around Tebay in thje North of England and runs through rural farming country to Morecambe bay. It is generally considered as a river of high purity and unspoiled nature. The salmon fishery was at one time considered amongst the best in England and Wales, with very high catches to both rod and net fishermen. During the late 1960's the disease UDN decimated the stock. Since then there has been a recovery of the stock, but this is considered by most anglers and netsmen to be a partial recovery of some of the previous stock components. In recent years anglers and netsmen have voiced their concerns over the Lune stock and have lobbied for action to improve the Lune fishery. This net limitation order (NLO) and the separate byelaw in conjunction with habitat improvement are proposed as part of the strategy for future conservation and management of this salmon fishery. The fishery is currently exploited by 37 licensed netsmen, the highest number of any single estuary in England and Wales. There are 26 haaf, 10 drift and 1 seine nets available. Current estimates of the rod fishery are that 1100 to 1400 anglers fish 14 000 days per year. The River Luhe is one of the few rivers within England and Wales that has the benefit of an accurate fish counter. The counter is at Forge Weir approximately 4 km upstream of the tidal limit. The counts, together with records of the catches from the rod and net fishery, enable a reasonably accurate assessment of both rod and net exploitation. Extensive surveys of the juvenile population, carried out in 1991 and 1997, provide additional information. The purpose of this document is to describe and explain the current state of the salmon population in the River Lune and in doing so, demonstrate the current need for stock conservation. A second purpose is to demonstrate that the proposed NLO and byelaw package should allow the salmon population to reach its conservation target (spawning escapement target).

Age validation, growth, mortality, and demographic modeling of spotted gully shark (Triakis megalopterus) from the southeast coast of South Africa

This study documents validation of vertebral band-pair formation in spotted gully shark (Triakis megalopterus) with the use of fluorochrome injection and tagging of captive and wild sharks over a 21-year period. Growth and mortality rates of T. megalopterus were also estimated and a demographic analysis of the species was conducted. Of the 23 OTC (oxytetracycline) -marked vertebrae examined (12 from captive and 11 from wild sharks), seven vertebrae (three from captive and four from wild sharks) exhibited chelation of the OTC and fluoresced under ultraviolet light. It was concluded that a single opaque and translucent band pair was deposited annually up to at least 25 years of age, the maximum age recorded. Reader precision was assessed by using an index of average percent error calculated at 5%. No significant differences were found between male and female growth patterns (P>0.05), and von Bertalanffy growth model parameters for combined sexes were estimated to be L∞=1711.07 mm TL, k=0.11/yr and t0=–2.43 yr (n=86). Natural mortality was estimated at 0.17/yr. Age at maturity was estimated at 11 years for males and 15 years for females. Results of the demographic analysis showed that the population, in the absence of fishing mortality, was stable and not significantly different from zero and particularly sensitive to overfishing. At the current age at first capture and natural mortality rate, the fishing mortality rate required to result in negative population growth was low at F>0.004/ yr. Elasticity analysis revealed that juvenile survival was the principal factor in explaining variability in population growth rate.

Restormel Fish Counter Annual Report 1999

This is the Restormel Fish Counter, Annual Report 1999 produced by the Environment Agency South West Region on March 2000. The report presents the daily upstream counts of migratory salmonids recorded at Restormel Weir counting station (SX 107 613) River Fowey in 1999. The counter data covers the period of the commercial migratory salmonid net buy-back scheme, which was in operation between March and June 1999. The fish counter is a resistivity based system (Logie 2100 A - Aquantic limited) and operates over all three channels of the weir at Restormel. The minimum salmon count estimate was 497, and the 1999 upstream count for sea trout was 6590. The run pattern observed for salmon and sea trout in 1999 was generally consistent with that of previous years. Flows on average were half those of 1998 during September, October, and November.

Restormel Fish Counter Annual Report 2005

This is the Restormel Fish Counter, Annual Report 2005 produced by the Environment Agency South West Region on March 2006. The report presents the upstream counts of migratory salmonids recorded on the River Fowey at Restormel weir fish counting station (SX 107 613) over the period March 2005 to February 2006 inclusive. Data contained within this report covers the period of the commercial migratory salmonid net buy-back scheme and the National Spring Salmon Byelaws (from 2 March to 15 June Inclusive). The minimum upstream salmon estimate for 2005 was 1046, this is the second highest count recorded over the past 11 years. The total sea trout count (10448) was 8% higher than 2004 (9608). This overall increase in the salmon and sea trout counts, together with the consistency of the numbers of fish returning over recent years suggests that measures designed to protect salmonid stocks in the River Fowey are working.

Restormel Fish Counter Annual Report 2006

This is the Restormel Fish Counter, Annual Report 2006 produced by the Environment Agency South West Region on March 2007. The report presents the upstream counts of migratory salmonids recorded on the River Fowey at Restormel weir fish counting station (SX 107 613) over the period March 2006 to February 2007 inclusive. Data contained within this report covers the period of the commercial migratory salmonid net buy-back scheme and the National Spring Salmon Byelaws (2 March- 15 June inclusive). The minimum upstream salmon estimate for 2005 (1046), over the period July 2005 to February 2006, was 20% lower than that recorded over the same period in 2004 (1301). However, this is the second highest count recorded over the past 11 years. The total sea trout count (10448) was 8% higher than 2004 (9608). The number of salmon and large sea trout was lower than average in 2005. However, the overall numbers of adult salmon and sea trout returning have been increasing year on year since 1997. This overall increase in the salmon and sea trout counts, together with the consistency of the numbers of fish returning over recent years suggests that measures designed to protect salmonid stocks in the River Fowey are working.

Restormel Fish Counter Annual Report 2007

This is the Restormel Fish Counter, Annual Report 2007 produced by the Environment Agency South West Region on March 2008. The report presents the upstream counts of migratory salmonids recorded on the River Fowey at Restormel Weir fish counting station (SX 107 613) over the period March 2007 to February 2008 inclusive. Data contained within this report covers the period of the commercial migratory salmonid net buy-back scheme and the National Spring Salmon Byelaws (2 March- 15 June). The minimum upstream salmon estimate for 2007, over the period July 2007 to February 2008, was 796, which is the fifth highest recorded count over the past 13 years. The number of returning salmon in 2007 suggests a downward trend in numbers since 2004. The 2007 large sea trout count is similar to 2006. Overall, the number of fish returning is still low in comparison with the 10-year average. There was a noticeable decrease in the number of small sea trout returning compared to 2006 and the 10-year average. The Fish counter at Restormel suffered several faults.

Restormel Fish Counter Annual Report 2008

This is the Restormel Fish Counter, Annual Report 2008 produced by the Environment Agency South West Region on April 2009. The report presents the upstream counts of migratory salmonids recorded on the River Fowey at Restormel Weir fish counting station (SX 107 613) over the period March 2008 to February 2009 inclusive. Data contained within this report covers the period of the commercial migratory salmonid net buy-back scheme and the National Spring Salmon Byelaws. The minimum upstream salmon estimate for 2008, over the period July 2008 to February 2009, was 938 and is the third highest recorded count over the past 14 years. The 2008 large sea trout count (482) shows a marked improvement in the number of returning fish when compared to 2007 (241). There was a significant decrease in the number of small sea trout returning in 2008 when compared to 2007 and the 10-year average.

Restormel Fish Counter Annual Report 2008

This is the Restormel Fish Counter, Annual Report 2008 produced by the Environment Agency South West Region on April 2009. The report presents the upstream counts of migratory salmonids recorded on the River Fowey at Restormel Weir fish counting station (SX 107 613) over the period March 2008 to February 2009 inclusive. Data contained within this report covers the period of the commercial migratory salmonid net buy-back scheme and the National Spring Salmon Byelaws. The minimum upstream salmon estimate for 2008, over the period July 2008 to February 2009, was 938, which is the third highest recorded count over the past 14 years. The 2008 large sea trout count (482) shows a marked improvement in the number of returning fish when compared to 2007 (241). There was a significant decrease in the number of small sea trout returning in 2008 when compared to 2007 and the 10-year average. The fish counter suffered several faults equated to 12.5 days during this period.

Restormel Fish Counter Annual Report 2010

This is the Restormel Fish Counter, Annual Report 2010 produced by the Environment Agency South West Region on June 2011. The report presents the upstream counts of migratory salmonids recorded on the River Fowey at Restormel Weir fish counting station (SX 107 613) over the period March 2010 to February 2011 inclusive. Data contained within this report covers the period of the commercial migratory salmonid net buy-back scheme and the National Spring Salmon Byelaws. The minimum upstream salmon estimate for 2010, over the period July 2010 to February 2010, was 1220. The fish counter at Restormel suffered from only one major period of unscheduled downtime during 2010/2011. This was due to a counter fault over the period 21 to 30 August 2010 and equated to 10 days of downtime.

Restormel Fish Counter Annual Report 2011

This is the Restormel Fish Counter, Annual Report 2011 produced by the Environment Agency, Environmental Monitoring Team on May 2012. The report presents the upstream counts of migratory salmonids recorded on the River Fowey at Restormel Weir fish counting station (SX 107 613) over the period March 2011 to February 2012 inclusive. The minimum upstream salmon estimate for 2011, over the period July 2011 to February 2012, was 675. The minimum upstream sea trout estimate for 2011 was 10,022, which is the fifth highest count recorded in the last 17 years. The fish counter at Restormel had six periods of downtime due to counter faults which equated to 19 days of downtime overall. Fish counts were estimated for downtime caused by counter faults but not for weir cleaning due to the small numbers of fish involved.