title: On the insecurity of arithmetic coding

authors: Cleary, John G.

subjects: computer science

abstract: Arithmetic coding is a technique which converts a given probability distribution into an optimal code and is commonly used in compression schemes. The use of arithmetic coding as an encryption scheme is considered. The simple case of a single binary probability distribution with a fixed (but unknown) probability is considered. We show that for a chosen plaintext attack w+ 2 characters is sufficient to uniquely determine a w-bit probability. For many known plaintexts w+ m+ O(log m) symbols where mis the length of an initial sequence containing just one of (the two possible) symbols is sufficient. It is noted that many extensions to this basic scheme are vulnerable to the same attack provided the arithmetic coder can be repeatedly reset to its initial state. If it cannot be reset then their vulnerability remains an open question.

text: On the insecurity of arithmetic coding Arithmetic coding is a technique which converts a given probability distribution into an optimal code and is commonly used in compression schemes. The use of arithmetic coding as an encryption scheme is considered. The simple case of a single binary probability distribution with a fixed (but unknown) probability is considered. We show that for a chosen plaintext attack w+ 2 characters is sufficient to uniquely determine a w-bit probability. For many known plaintexts w+ m+ O(log m) symbols where mis the length of an initial sequence containing just one of (the two possible) symbols is sufficient. It is noted that many extensions to this basic scheme are vulnerable to the same attack provided the arithmetic coder can be repeatedly reset to its initial state. If it cannot be reset then their vulnerability remains an open question.

year: 1994-06

title: Identifying causes of high pH in lamb meat

authors: Hontiveros, Garrianne Fatima

subjects: meat

abstract: Lamb meat export is a multi-billion-dollar New Zealand industry. Therefore, strategies to maintain and improve quality have immediate commercial benefit. Consumers judge quality by colour, tenderness, and flavour, all of which are affected by ultimate pH (pHu). Ideal meat pHu is 5.5 and is influenced by muscle glycogen concentration. Insufficient muscle glycogen at slaughter results in high pHu (>5.8) which results in tough meat, dark colour, and shorter storage life. The decrease in meat pH post-slaughter is caused by the build-up of H+ ions as a consequence of anaerobic glycolysis of glycogen for ATP formation. Physical stress depletes muscle glycogen, prompting consumers to conclude animal mistreatment. However, stress, does not necessarily equate to abuse as all animals experience some level of pre-slaughter stress and any negative effects depend on duration, type, intensity, and susceptibility. Studies have focused on post-farm-gate stressors (e.g. transport and lairage) but less clear is the role of on-farm stressors on the incidence of high pHu. The aim of this study was to investigate the variation of muscle glycogen of lambs on-farm, examine the use of heat shock protein 20 (HSP20) as a marker for physiological stress, and determine any relationship between residual glycogen level and meat quality attributes such as water binding capacity (WBC), drip loss, microbial abundance, fat, protein, and water content.  

Two observations were conducted. Firstly, 60 animals from 2 farms with different production systems: wethers (castrated males) were raised with ewes in Farm 1, whereas, intact rams, wethers, cryptorchids, and ewes were all together and introduced at different times to the group in Farm 2.  These animals were biopsied two months before slaughter, a month before, and post-rigor. On-farm, large inter-individual variation in muscle glycogen was observed in both farms but no significant difference in true glycogen between farms. Muscle glycogen levels seemed to fluctuate from one biopsy to another, contrary to previous belief that it remains constant throughout. There was no significant difference in HSP20 between farms and no correlation between muscle glycogen and HSP20 was observed. Post-rigor, 66% of carcasses from Farm 2 had high pHu (≥5.8), compared to none from Farm 1. This may be due to stress brought about by exaggerated behaviours of rams (e.g. aggression and chasing) during close confinement at lairage. However, more observations on-farm and at lairage are needed. Lastly, 69 loin samples of varying levels of residual glycogen were tested for drip loss, (WBC), fat, protein, and microbial content a day post-rigor (Day 1) and again after eight weeks (Week 8). Results showed no correlation between residual glycogen content and any of the parameters tested at either time points. A decrease in total glycosyl units at Week 8 was observed but no decrease in true glycogen levels. This was likely due to microbes use of free glucose as a food source. 

To conclude, the results of this study suggests that the co-habitation of intact rams and ewes on-farm causes stress, which is compounded by the close confinement at lairage, leading to high pHu of their carcasses. It is, therefore, recommended that, although intact rams have higher saleable weight, these rams be castrated before mixing with other rams and ewes to avoid high pHu and, hence, provide good quality meat and less stressed animals (better animal welfare). The fluctuation in muscle glycogen levels over time does also need closer scrutiny.

text: Identifying causes of high pH in lamb meat Lamb meat export is a multi-billion-dollar New Zealand industry. Therefore, strategies to maintain and improve quality have immediate commercial benefit. Consumers judge quality by colour, tenderness, and flavour, all of which are affected by ultimate pH (pHu). Ideal meat pHu is 5.5 and is influenced by muscle glycogen concentration. Insufficient muscle glycogen at slaughter results in high pHu (>5.8) which results in tough meat, dark colour, and shorter storage life. The decrease in meat pH post-slaughter is caused by the build-up of H+ ions as a consequence of anaerobic glycolysis of glycogen for ATP formation. Physical stress depletes muscle glycogen, prompting consumers to conclude animal mistreatment. However, stress, does not necessarily equate to abuse as all animals experience some level of pre-slaughter stress and any negative effects depend on duration, type, intensity, and susceptibility. Studies have focused on post-farm-gate stressors (e.g. transport and lairage) but less clear is the role of on-farm stressors on the incidence of high pHu. The aim of this study was to investigate the variation of muscle glycogen of lambs on-farm, examine the use of heat shock protein 20 (HSP20) as a marker for physiological stress, and determine any relationship between residual glycogen level and meat quality attributes such as water binding capacity (WBC), drip loss, microbial abundance, fat, protein, and water content.  

Two observations were conducted. Firstly, 60 animals from 2 farms with different production systems: wethers (castrated males) were raised with ewes in Farm 1, whereas, intact rams, wethers, cryptorchids, and ewes were all together and introduced at different times to the group in Farm 2.  These animals were biopsied two months before slaughter, a month before, and post-rigor. On-farm, large inter-individual variation in muscle glycogen was observed in both farms but no significant difference in true glycogen between farms. Muscle glycogen levels seemed to fluctuate from one biopsy to another, contrary to previous belief that it remains constant throughout. There was no significant difference in HSP20 between farms and no correlation between muscle glycogen and HSP20 was observed. Post-rigor, 66% of carcasses from Farm 2 had high pHu (≥5.8), compared to none from Farm 1. This may be due to stress brought about by exaggerated behaviours of rams (e.g. aggression and chasing) during close confinement at lairage. However, more observations on-farm and at lairage are needed. Lastly, 69 loin samples of varying levels of residual glycogen were tested for drip loss, (WBC), fat, protein, and microbial content a day post-rigor (Day 1) and again after eight weeks (Week 8). Results showed no correlation between residual glycogen content and any of the parameters tested at either time points. A decrease in total glycosyl units at Week 8 was observed but no decrease in true glycogen levels. This was likely due to microbes use of free glucose as a food source. 

To conclude, the results of this study suggests that the co-habitation of intact rams and ewes on-farm causes stress, which is compounded by the close confinement at lairage, leading to high pHu of their carcasses. It is, therefore, recommended that, although intact rams have higher saleable weight, these rams be castrated before mixing with other rams and ewes to avoid high pHu and, hence, provide good quality meat and less stressed animals (better animal welfare). The fluctuation in muscle glycogen levels over time does also need closer scrutiny.

year: 2018

title: Biological flora of New Zealand 11. Eleochairs spacelata, kuta, paopao, bamboo spike sedge.

authors: Kapa, Mieke M

subjects: cultural

abstract: Information relevant to the ecology and morphology of Eleocharis sphacelata (Cyperaceae) available through published and unpublished sources is assembled and reviewed. Eleocharis sphacelata is a freshwater wetland sedge found growing at the edge of lake margins, swamps, lagoons, and bogs within New Zealand, Australia, and Papua New Guinea. It is a perennial rhizomatous herb, with tall green cylindrical culms rising from submerged rhizomes generally buried under water in aerobic soils. A tendency to dominate the deepwater margins makes E. sphacelata crucial to the ecology of this habitat as a source of food, shelter, and protection for invertebrates, birds, and fish. Eleocharis sphacelata is commonly named giant spike-rush, kuta, or paopao. Māori have traditionally used the plant for clothing and warm coverings within whare (houses). Recent interest comes from its use in restoration plantings and constructed wetlands.

text: Biological flora of New Zealand 11. Eleochairs spacelata, kuta, paopao, bamboo spike sedge. Information relevant to the ecology and morphology of Eleocharis sphacelata (Cyperaceae) available through published and unpublished sources is assembled and reviewed. Eleocharis sphacelata is a freshwater wetland sedge found growing at the edge of lake margins, swamps, lagoons, and bogs within New Zealand, Australia, and Papua New Guinea. It is a perennial rhizomatous herb, with tall green cylindrical culms rising from submerged rhizomes generally buried under water in aerobic soils. A tendency to dominate the deepwater margins makes E. sphacelata crucial to the ecology of this habitat as a source of food, shelter, and protection for invertebrates, birds, and fish. Eleocharis sphacelata is commonly named giant spike-rush, kuta, or paopao. Māori have traditionally used the plant for clothing and warm coverings within whare (houses). Recent interest comes from its use in restoration plantings and constructed wetlands.

year: 2009