19,088 research outputs found
DoWitcher: Effective Worm Detection and Containment in the Internet Core
No full textEnterprise networks are increasingly offloading the responsibility for worm detection and containment to the carrier networks. However, current approaches to the zero-day worm detection problem such as those based on content similarity of packet payloads are not scalable to the carrier link speeds (OC-48 and up-wards). In this paper, we introduce a new system, namely DoWitcher, which in contrast to previous approaches is scalable as well as able to detect the stealthiest worms that employ low-propagation rates or polymorphisms to evade detection. DoWitcher uses an incremental approach toward worm detection: First, it examines the layer-4 traffic features to discern the presence of a worm anomaly; Next, it determines a flow-filter mask that can be applied to isolate the suspect worm flows and; Finally, it enables full-packet capture of only those flows that match the mask, which are then processed by a longest common subsequence algorithm to extract the worm content signature. Via a proof-of-concept implementation on a commercially available network analyzer processing raw packets from an OC-48 link, we demonstrate the capability of DoWitcher to detect low-rate worms and extract signatures for even the polymorphic worm
Integration of numerical analysis, virtual simulation and finite element analysis for the optimum design of worm gearing
No full textDue to the complicated tooth geometry of worm gears, their design to achieve high capacity and favourable performance is a tedious task, and the optimum design is hardly to obtain. In order to overcome this problem, the authors developed an integrated approach which consists of three modules: numerical analysis, three-dimensional simulation and finite element analysis. It provides a powerful tool for optimum design of worm gears and is a general approach applicable for various types of worm gears. As case studies, two designs using the approach have been conducted, one for cylindrical involute worm gearing and the other for double enveloping worm gearing
Transmission errors in precision worm gear drives
No full textTransmission error is a measure of the positioning accuracy of a gear system. This
has been widely documented in gearing for many years as the source of problems in
noise and vibration. It is a result of errors in the contact conditions which affect the
driven gear with respect to the rotation of the driver gear. This research aims to
present a better understanding of the basic kinematics of worm gear systems by
identifying the significant influences which determine the contact conditions.
A literature review of existing theory is described which determines the major areas
considered in worm gear contact analysis. Formulae are derived which quantify the
effect of component parameter variation on contact. An investigation of the design,
manufacture, and operating processes is recorded which identifies error sources
relative to the theoretical contact condition. A computer program is developed which
calculates contact characteristics such as worm and wheel component form,
transmission error and contact marking pattern for a given design including any
contact error sources. Computer calculations are validated by comparing direct
measurements of these characteristics from several manufactured gear sets with
synthesised results produced using the design information, machine settings and error
sources detected during production. The behaviour of these gear sets during operation
under a torque load has been investigated experimentally. Measured transmission
error data from a test rig is used to develop a basic model of worm gear deformation
under load. This model has been added to the computer program to improve and
extend the analysis capability. The test rig has also been used to investigate the effect
of initial wear on contact characteristics.
The good correlation between calculated and experimental results shows that the
characteristics of a worm gear set can be predicted once all elements of the design and
manufacture are known. The results also validate the software as a useful design tool
for academic and industrial applications. Important conclusions are drawn on design
techniques, the manufacturing process, and the effects of operating under load.
Further areas of investigation are identified which offer future research an opportunity
to expand upon these conclusions
Associations between worm egg count and production in Dorper sheep
No full textWith changes to the Australian sheep industry, breeds that have a meat emphasis are becoming increasingly adopted by farmers. One such breed is the Dorper sheep, which was used in this study to investigate the relationship between worm egg count and production attributes. Gastrointestinal worm burden was measured by worm egg counts (WECs) and production attributes that were examined included liveweight, body condition score (BCS), c-site fat depth and eye muscle depth. Two flocks of Dorper lambs (two-hundred and eighty nine Dorper ewe lambs, and two-hundred and thirty four entire Dorper ram lambs), were weaned onto two separate paddocks for grazing and natural worm challenge on a Kojonup property. At post weaning (approximately 10 months of age), each flock had their production attributes measured, along with individual WECs. Each flock was drenched at weaning and not drenched again until after individual WECs were measured. The measured flock WEC frequency distribution reinforced the concept that high flock WECs are influenced by a small percentage of the sheep within the flock and that Dorper sheep are similar to other breeds with respect to parasite population dynamics.
The relationships found between WEC and production attributes of both liveweight and eye muscle depth were positive, contradicting the hypothesis of that a negative relationship exists between WEC and production in the Dorper. Although this relationship between WEC and liveweight was weak and unexpected, the relationship was still significant (P<0.05). With an increasing WEC, BCS fell by 56.6% and 37.7% of average ram BCSs in twin and single born rams respectively (P<0.05), while an 18.6% decrease of average ewe BCS was observed in twin born ewes (P<0.05). The drop in body condition score and c-site fat depth may have contributed to overall leaner and lighter carcases (particularly in the ram flock). Given that the liveweights were actually higher in these same animals, this suggests a reduced dressing percentage due to increased non-carcase components, possibly gastrointestinal tissue mass.
With increasing WEC the association of liveweight increase and BCS decline indicated that sheep with a higher worm burden may have heavier intestines, when compared to sheep with a low worm challenge. By using liveweight change to assess GIN impact on productivity, production losses linked to gastrointestinal parasite infection may be underestimated. Instead of using liveweight change in assessing the effect of a worm challenge, measurements of the carcass yield may be a more reliable measure in revealing the real economic impact of gastrointestinal worms on sheep meat production systems
Keeping track of worm trackers
No full textC. elegans is used extensively as a model system in the neurosciences due to its well defined nervous system. However, the seeming simplicity of this nervous system in anatomical structure and neuronal connectivity, at least compared to higher animals, underlies a rich diversity of behaviors. The usefulness of the worm in genome-wide mutagenesis or RNAi screens, where thousands of strains are assessed for phenotype, emphasizes the need for computational methods for automated parameterization of generated behaviors. In addition, behaviors can be modulated upon external cues like temperature, O2 and CO2 concentrations, mechanosensory and chemosensory inputs. Different machine vision tools have been developed to aid researchers in their efforts to inventory and characterize defined behavioral “outputs”. Here we aim at providing an overview of different worm-tracking packages or video analysis tools designed to quantify different aspects of locomotion such as the occurrence of directional changes (turns, omega bends), curvature of the sinusoidal shape (amplitude, body bend angles) and velocity (speed, backward or forward movement)
Trailblazing through a Knowledge Space of Science: Forward Citation Expansion in CiteSeer
No full textUnderstanding emerging trends and patterns in science and technology is essential not only to scientists and engineers in their own fast-advancing fields but also to a wide variety of individuals and organizations who are also interested in tracking the development of thematic topics. This is a challenging task because many existing tools are not particularly designed to deal with the dynamics of intellectual structures that transcend the boundaries of individual documents or isolated topics. In this article, we introduce a conceptual and operational platform that extends the traditional notion of traveling along individual citation pathways and defines operators for recursive and holistic theme expansion based on citation connectivity. We describe the implementation of a forward expansion operator and illustrate its potential with the CiteSeer metadata. In addition, we integrate the forward expansion operators with information visualization techniques
Formate dehydrogenases and hydrogenases in syntrophic propionate-oxidizing communities : gene analysis and transcritional profiling
No full textMany places on earth are without oxygen (anaerobic) such as rice paddy fields, swamps and sediments of freshwater lakes and oceans. When oxygen, nitrate or other electron acceptors are not present, organic material is degraded to carbon dioxide and methane by mixed microbial species that each have their own specific function in degradation. Anaerobic microbial communities are used in anaerobic digesters all over the world to treat organic waste and wastewater. Propionate is one of the most important intermediates in anaerobic digestion. It can only be degraded by propionate oxidizing bacteria when methanogenic archaea keep the concentration of the interspecies electron carriers, hydrogen and formate, low. However, little is known about the molecular mechanism of hydrogen and formate transfer. Hydrogenases are involved in hydrogen transfer and require Fe, Ni and/or Se for catalysis. Formate dehydrogenases that are involved in formate transfer require the trace metals W or Mo and in some cases Se for catalysis. However, the effect of W, Mo and Se limitation on the propionate degrading community of a UASB reactor and the transcription of formate dehydrogenase and hydrogenase encoding genes in this community was never examined. This would give more insight in formate transfer in the propionate degrading community of the UASB reactor and provide a method to study depletion of these metals in the reactor sludge. We used the genome sequences of the propionate degrading Syntrophobacter fumaroxidans and its syntrophic methanogenic partner, Methanospirillum hungatei to study molecular mechanisms of hydrogen and formate transfer in syntrophic cocultures and UASB reactor sludge, by gene analysis and molecular techniques. Gene analysis and microarray data determined formate dehydrogenase and hydrogenase encoding gene clusters in S. fumaroxidans and M. hungatei (Chapter 4). When S. fumaroxidans oxidizes propionate, reducing equivalents are generated by three intermediate reactions in the form of FADH2, NADH and reduced ferredoxin. We found by gene analysis (Chapter 2) and RT qPCR (Chapter 3) that the genes coding for four formate dehydrogenases, six hydrogenases and one formate hydrogen lyase of S. fumaroxidans and five formate dehydrogenases and three hydrogenases of M. hungatei were all transcribed during syntrophic and axenic growth. However, the transcription levels were dependent on the growth condition. Comparison of transcription levels also revealed that electrons from ferredoxin and NADH are simultaneously confurcated for hydrogen production by a cytoplasmic [FeFe]-hydrogenase. Moreover, results indicated that during syntrophic growth electrons from ferredoxin and NADH are confurcated to formate via a cytoplasmic formate dehydrogenase (FDH1). During syntrophic growth, the electrons generated at the level of FADH2, travel via a cytoplasmic oriented succinate dehydrogenase, menaquinones, cytochrome b and c to the periplasmic formate dehydrogenase (FDH2) (Chapter 5). When S. fumaroxidans is grown in pure culture with alternative electron acceptors such as sulfate and fumarate, electrons flow partly to FDH2, and partly to the periplasmic hydrogenase (Hyn). The energy gained from propionate conversion to methane, acetate, and carbon dioxide has to be shared by S. fumaroxidans and M. hungatei. When M. hungatei takes more energy, less energy remains for S. fumaroxidans. In this situation S. fumaroxidans up-regulates transcription of genes coding for an additional cytoplasmic confurcating hydrogenase (Hox) and the periplasmic hydrogenase (Hyn) that is coupled to succinate oxidation. In addition, S. fumaroxidans induces transcription of genes coding for the Rnf-complex and ferredoxin dependent hydrogenases and formate dehydrogenases. This provides the possibility to use the membrane potential for the energy dependent coupling of ferredoxin reduction to NADH oxidation. The designed RT qPCR primers were used in UASB reactor sludge from the alcohol distillery NEDALCO in Bergen op Zoom (Netherlands) to investigate the effect of trace elements depletion. A lab-scale UASB reactor was fed with propionate and synthetic medium without added W, Mo and Se. During the reactor run, Syntrophobacter spp. were the dominant propionate-oxidizers and M. hungatei the dominant hydrogen and formate using methanogen. However, when propionate degradation decreased, two other propionate-oxidizers; Pelotomaculum propionicicum and Smithella propionica became abundant (Chapter 6). RT qPCR showed that in this reactor run the transcription of genes coding for formate dehydrogenases and hydrogenases in S. fumaroxidans decreased while transcription of genes coding for formate dehydrogenases and hydrogenases in M. hungatei were more stable (Chapter 7). This research shows that RT qPCR is a fast technique that can give information on the active processes in a UASB reactor, and that trace element limitation and possible malfunctioning of UASB reactors can be predicted. With this PhD research we gained insight in the molecular mechanisms of hydrogen and formate transfer between S. fumaroxidans an M. hungatei in defined cocultures and in a propionate-fed UASB reactor. This contributes to the understanding of similar molecular mechanisms in other syntrophic microorganisms and may improve the performance of anaerobic digesters in the future. <br/
Polygraph: Automatically generating signatures for polymorphic worms
No full textIt is widely believed that content-signature-based intrusion detection systems (IDSes) are easily evaded by polymorphic worms, which vary their payload on every infection attempt. In this paper, we present Polygraph, a signature generation system that successfully produces signatures that match polymorphic worms. Polygraph generates signatures that consist of multiple disjoint content sub-strings. In doing so, Polygraph leverages our insight that for a real-world exploit to function properly, multiple invariant substrings must often be present in all variants of a payload; these substrings typically correspond to protocol framing, return addresses, and in some cases, poorly obfuscated code. We contribute a definition of the polymorphic signature generation problem; propose classes of signature suited for matching polymorphic worm payloads; and present algorithms for automatic generation of signatures in these classes. Our evaluation of these algorithms on a range of polymorphic worms demonstrates that Polygraph produces signatures for polymorphic worms that exhibit low false negatives and false positives. © 2005 IEEE
Phenotypic analysis of host-parasite interactions in lambs infected with Teladorsagia circumcincta
No full textFemale Blackface lambs expected to exhibit genetic variability for resistance to gastrointestinal nematodes, were either exposed to continuous experimental infections of Teladorsagia circumcincta or were sham-dosed to monitor phenotypic responses to infection. As a measure of parasitism and host response, worm-eggs in faeces (faecal egg count, FEC) were counted over a 3-month period and worm burdens were ascertained at post-mortem. The host response to the infection was also measured by differential counts of white blood cells, anti-T. circumcincta IgA antibody levels and body weight. Results suggest that nematode abundance (mean number of parasites per host) and prevalence (proportion of infected animals) were maximal shortly after the beginning of infection (21 days p.i.) when virtually all the infected animals were shedding worm eggs. Increasing anti-T. circumcincta IgA antibody and eosinophil concentrations were associated with a reduction in total numbers of adult worms and an increase in the frequency of early L4s. The data also suggest that genetic selection for an enhanced anti-T. circumcincta IgA response might complement selection based on a reduced FEC as a strategy to select for resistance to gastrointestinal nematodes
Worm Lineage B gene expression, table of Z scores.
No full textWorm Lineage B gene expression, table of Z scores.</p
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