title: The subset sum problem and arithmetic coding

authors: Irvine, Sean A.

subjects: computer science

abstract: The security offered by symmetric cryptosystems based on the arithmetic coding algorithm is examined. It is shown that this can be reduced naturally to the subset sum problem. The subset sum problem is NP-complete, however, the cases which arise in practical cryptosystems based on this problem tend to be solvable in polynomial time because the sums formed are either superincreasing or of low density. Our attack is therefore similar to attacks on public-key cryptosystems based on the subset sum problem (knapsack systems).

text: The subset sum problem and arithmetic coding The security offered by symmetric cryptosystems based on the arithmetic coding algorithm is examined. It is shown that this can be reduced naturally to the subset sum problem. The subset sum problem is NP-complete, however, the cases which arise in practical cryptosystems based on this problem tend to be solvable in polynomial time because the sums formed are either superincreasing or of low density. Our attack is therefore similar to attacks on public-key cryptosystems based on the subset sum problem (knapsack systems).

year: 1995-03

title: Combined U/Pb and (U–Th)/He geochronometry of basalt maars in Western Carpathians: implications for age of intraplate volcanism and origin of zircon metasomatism

authors: Hurai, Vratislav

subjects: Zircon

abstract: The age of intraplate volcanism in northern Pannonian Basin of Carpathians is revisited using a combination of zircon U/Pb, zircon (U–Th)/He and apatite (U–Th)/He dating techniques, complemented by electron microprobe (EMP) characterisation of dated minerals. A total of six maar structures and diatremes in the South-Slovakian Volcanic Field (SSVF) were dated and the obtained new ages yielded the following key findings: Two isolated maars in SE part indirectly dated by geomorphologic constraints to Late Pleistocene are actually of Pliocene (2.8 ± 0.2 Ma) and Late Miocene (5.5 ± 0.6 Ma) ages. In contrast, two maars in NW part of the study area are of Late Pliocene age (4.1 ± 0.4 and 5.2–5.4 Ma), younger than the Late Miocene age (~6.5 Ma) inferred previously from K/Ar data on the proximal basaltic lava flows. These maars therefore belong to the second volcanic phase that was previously identified only in SE part of the SSVF. In the light of the new geochronologic data, it seems likely that the Pliocene phreatomagmatic eruptions may have occurred along extension-related, NW- and NE-trending orthogonal faults. EMP analyses and imaging revealed an extensive syn- and post-growth metasomatic replacement by dissolution-reprecipitation in the majority of zircons. Abundant silicate melt inclusions in porous metasomatised parts of the zircons are diagnostic of magmatic rather than hydrothermal metasomatism. Consistent ages of the metasomatised and non-metasomatised zones do not indicate disturbance of the U–Pb system during the metasomatism. Enrichment in U and Th loss in the metasomatised zircons are diagnostic of an increasing oxygen fugacity triggered by degassing of the volatile residual melt during the final stages of alkali basalt fractionation. Rare zircon-to-baddeleyite transformation was probably connected with lowered silica activity in carbonated basaltic magmas in south-eastern part of the study area.

text: Combined U/Pb and (U–Th)/He geochronometry of basalt maars in Western Carpathians: implications for age of intraplate volcanism and origin of zircon metasomatism The age of intraplate volcanism in northern Pannonian Basin of Carpathians is revisited using a combination of zircon U/Pb, zircon (U–Th)/He and apatite (U–Th)/He dating techniques, complemented by electron microprobe (EMP) characterisation of dated minerals. A total of six maar structures and diatremes in the South-Slovakian Volcanic Field (SSVF) were dated and the obtained new ages yielded the following key findings: Two isolated maars in SE part indirectly dated by geomorphologic constraints to Late Pleistocene are actually of Pliocene (2.8 ± 0.2 Ma) and Late Miocene (5.5 ± 0.6 Ma) ages. In contrast, two maars in NW part of the study area are of Late Pliocene age (4.1 ± 0.4 and 5.2–5.4 Ma), younger than the Late Miocene age (~6.5 Ma) inferred previously from K/Ar data on the proximal basaltic lava flows. These maars therefore belong to the second volcanic phase that was previously identified only in SE part of the SSVF. In the light of the new geochronologic data, it seems likely that the Pliocene phreatomagmatic eruptions may have occurred along extension-related, NW- and NE-trending orthogonal faults. EMP analyses and imaging revealed an extensive syn- and post-growth metasomatic replacement by dissolution-reprecipitation in the majority of zircons. Abundant silicate melt inclusions in porous metasomatised parts of the zircons are diagnostic of magmatic rather than hydrothermal metasomatism. Consistent ages of the metasomatised and non-metasomatised zones do not indicate disturbance of the U–Pb system during the metasomatism. Enrichment in U and Th loss in the metasomatised zircons are diagnostic of an increasing oxygen fugacity triggered by degassing of the volatile residual melt during the final stages of alkali basalt fractionation. Rare zircon-to-baddeleyite transformation was probably connected with lowered silica activity in carbonated basaltic magmas in south-eastern part of the study area.

year: 2013

title: Medications and meanings in Maori households with chronic illnesses

authors: Carlson, Teah

subjects: medications

abstract: Domestic spaces have always featured as sites for health care. The home is increasingly referred to as a new therapeutic space within which chronic illnesses are managed within everyday life. This research explores the meanings and use of medications within four Māori households containing at least one chronically ill householder. A broad ethnographic approach was used to capture popular understandings and medication use in daily life. Multiple methods were used, including group discussions with household members, individual interviews, household mapping, and photographic and diary elicitation tasks. Findings shed light on the sources and uses of medications, householder knowledge of medications, communal practices of sharing, caring, rationalising use, grappling with side-effects and the management of illness. I consider what it means for householders to take medications themselves or give these to others, and the care-giving practices that feature in the everyday consumption of medicines. The research is based on the premise that medications are material objects with therapeutic uses that enter into and take on meaning within people’s lives. Medications become culturally embedded phenomena that carry meanings and shape social relationships and practices with Māori households. As such, medications were used in a way that reflected the cultural values and bonds within the households. Within household relationships, medications were invested within meaning to show aroha, support and care. Within a Māori whānau context, the values of maanakitanga, rangatiratanga, and whanaungatanga were recognised as having an integral role in understanding the social practices with medications in each household.

text: Medications and meanings in Maori households with chronic illnesses Domestic spaces have always featured as sites for health care. The home is increasingly referred to as a new therapeutic space within which chronic illnesses are managed within everyday life. This research explores the meanings and use of medications within four Māori households containing at least one chronically ill householder. A broad ethnographic approach was used to capture popular understandings and medication use in daily life. Multiple methods were used, including group discussions with household members, individual interviews, household mapping, and photographic and diary elicitation tasks. Findings shed light on the sources and uses of medications, householder knowledge of medications, communal practices of sharing, caring, rationalising use, grappling with side-effects and the management of illness. I consider what it means for householders to take medications themselves or give these to others, and the care-giving practices that feature in the everyday consumption of medicines. The research is based on the premise that medications are material objects with therapeutic uses that enter into and take on meaning within people’s lives. Medications become culturally embedded phenomena that carry meanings and shape social relationships and practices with Māori households. As such, medications were used in a way that reflected the cultural values and bonds within the households. Within household relationships, medications were invested within meaning to show aroha, support and care. Within a Māori whānau context, the values of maanakitanga, rangatiratanga, and whanaungatanga were recognised as having an integral role in understanding the social practices with medications in each household.

year: 2010