High precision timing in passive measurements of data networks

Understanding, predicting, and improving network behaviour under a wide range of conditions requires accurate models of protocols, network devices, and link properties. Accurate models of the component parts comprising complex networks allows the plausible simulation of networks in other configurations, or under different loads. These models must be constructed on a solid foundation of reliable and accurate data taken from measurements of relevant facets of actual network behaviour. As network link speeds increase, it is argued that traditional network measurement techniques based primarily on software time-stamping and capture of packets will not scale to the required performance levels. Problems examined include the difficulty of gaining access to high speed network media to perform measurements, the insufficient resolution of time-stamping clocks for capturing fine detail in packet arrival times, the lack of synchronisation of clocks to global standards, the high and variable latency between packet arrival and time-stamping, and the occurrence of packet loss within the measurement system. A set of design requirements are developed to address these issues, especially in high-speed network measurement systems. A group at the University of Waikato including myself has developed a series of hardware based passive network measurement systems called ‘Dags’. Dags use re-programmable hardware and embedded processors to provide globally synchronised, low latency, reliable time-stamping of all packet arrivals on high-speed network links with sub-hundred nanosecond resolution. Packet loss within the measurement system is minimised by providing sufficient bandwidth throughout for worst case loads and buffering to allow for contention over shared resources. Any occurrence of packet loss despite these measures is reported, allowing the invalidation of portions of the dataset if necessary. I was responsible for writing both the interactive monitor and network measurement code executed by the Dag’s embedded processor, developing a Linux device driver including the software part of the ‘DUCK’ clock synchronisation system, and other ancillary software. It is shown that the accuracy and reliability of the Dag measurement system allows confidence that rare, unusual or unexpected features found in its measurements are genuine and do not simply reflect artifacts of the measurement equipment. With the use of a global clock reference such as the Global Positioning System, synchronised multi-point passive measurements can be made over large geographical distances. Both of these features are exploited to perform calibration measurements of RIPE NCC’s Test Traffic Measurement System for One-way-Delay over the Internet between New Zealand and the Netherlands. Accurate single point passive measurement is used to determine error distributions in Round Trip Times as measured by NLANR’s AMP project. The high resolution afforded by the Dag measurement system also allows the examination of the forwarding behaviour of individual network devices such as routers and firewalls at fine time-scales. The effects of load, queueing parameters, and pauses in packet forwarding can be measured, along with the impact on the network traffic itself. This facility is demonstrated by instrumenting routing equipment and a firewall which provide Internet connectivity to the University of Auckland, providing passive measurements of forwarding delay through the equipment.both the interactive monitor and network measurement code executed by the Dag’s embedded processor, developing a Linux device driver including the software part of the ‘DUCK’ clock synchronisation system, and other ancillary software. It is shown that the accuracy and reliability of the Dag measurement system allows confidence that rare, unusual or unexpected features found in its measurements are genuine and do not simply reflect artifacts of the measurement equipment. With the use of a global clock reference such as the Global Positioning System, synchronised multi-point passive measurements can be made over large geographical distances. Both of these features are exploited to perform calibration measurements of RIPE NCC’s Test Traffic Measurement System for One-way-Delay over the Internet between New Zealand and the Netherlands. Accurate single point passive measurement is used to determine error distributions in Round Trip Times as measured by NLANR’s AMP project. The high resolution afforded by the Dag measurement system also allows the examination of the forwarding behaviour of individual network devices such as routers and firewalls at fine time-scales. The effects of load, queueing parameters, and pauses in packet forwarding can be measured, along with the impact on the network traffic itself. This facility is demonstrated by instrumenting routing equipment and a firewall which provide Internet connectivity to the University of Auckland, providing passive measurements of forwarding delay through the equipment

Photo-assisted recall increases estimates of energy and macronutrient intake in adults with intellectual and developmental disabilities

Diet assessment of adults with intellectual and developmental disabilities (IDD) is challenging due to their limited cognitive abilities. The objective of this study was to examine the feasibility and outcomes of combining photos with 24-hour dietary recalls for the assessment of energy and macronutrient intake in adults with IDD. Participants used an iPad 2 tablet computer to take photos of all food and beverages consumed before a standard, multiple-pass, 24-hour dietary recall. Following the standard 24-hour diet recall, the photos were reviewed with the participant for clarification details (e.g., portion size, etc.) and differences were recorded. The standard 24-hour recall and the photo-assisted recall were entered separately into Nutrition Data System for Research for computerized dietary analysis. Sixty-four eating occasions were entered from 23 participants (48% female; mean age 26.4 ±9.7 years). Participants captured photos for 66.5% ± 30.4% of all recorded eating occasions. Greater energy intake per eating occasion was reported with the photo-assisted recalls than the standard recalls (625.6 ± 85.7 kcals vs. 497.2 ± 86.6 kcals, p=0.002) and a greater intake of grams of fat (p=0.006) protein (p=0.029) and carbohydrates (p=0.003). Photo-assisted 24-hour recalls provided a significant increase in total calories and macronutrient content compared to a standard 24-hour recall and may be a feasible method to enhance dietary assessment in adults with IDD

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Antibiotic Therapy and the Gut Microbiome:Investigating the Effect of Delivery Route on Gut Pathogens

The contribution of the gut microbiome to human health has long been established, with normal gut microbiota conferring protection against invasive pathogens. Antibiotics can disrupt the microbial balance of the gut, resulting in disease and the development of antimicrobial resistance. The effect of antibiotic administration route on gut dysbiosis remains under-studied to date, with conflicting evidence on the differential effects of oral and parenteral delivery. We have profiled the rat gut microbiome following treatment with commonly prescribed antibiotics (amoxicillin and levofloxacin), via either oral or intravenous administration. Fecal pellets were collected over a 13-day period and bacterial populations were analyzed by 16S rRNA gene sequencing. Significant dysbiosis was observed in all treatment groups, regardless of administration route. More profound dysbiotic effects were observed following amoxicillin treatment than those with levofloxacin, with population richness and diversity significantly reduced, regardless of delivery route. The effect on specific taxonomic groups was assessed, revealing significant disruption following treatment with both antibiotics. Enrichment of a number of groups containing known gut pathogens was observed, in particular, with amoxicillin, such as the family Enterobacteriaceae. Depletion of other commensal groups was also observed. The degree of dysbiosis was significantly reduced toward the end of the sampling period, as bacterial populations began to return to pretreatment composition. Richness and diversity levels appeared to return to pretreatment levels more quickly in intravenous groups, suggesting convenient parenteral delivery systems may have a role to play in reducing longer term gut dysbiosis in the treatment of infection

Quantum Nucleation of Vortex String Loops

We investigate quantum nucleation of vortex string loops in the relativistic quantum field theory of a complex scalar field by using the Euclidean path integral. Our initial metastable homogeneous field dominated by the $O(3)$ symmetric bounce solution. The nucleation rate and the critical vortex loop size are obtained approximately. Gradually the initial current will be reduced to zero as the induced current inside vortex loops is opposite to the initial current. We also discuss a similar process in Maxwell-Higgs systems and possible physical implications.Comment: phyzzx.tex, 13 pages: A correction to the final state of the nucleation of local vortex string

Dissipative dynamics of vortex lines in superfluid 4^{4}He

We propose a Hamiltonian model that describes the interaction between a vortex line in superfluid $^{4}$He and the gas of elementary excitations. An equation of irreversible motion for the density operator of the vortex, regarded as a macroscopic quantum particle with a finite mass, is derived in the frame of Generalized Master Equations. This enables us to cast the effect of the coupling as a drag force with one reactive and one dissipative component, in agreement with the assumption of the phenomenological theories of vortex mutual friction in the two fluid model.Comment: 16 pages, no figures, to be published in PR