253 research outputs found
Big bang simulation in superfluid 3He-B -- Vortex nucleation in neutron-irradiated superflow
We report the observation of vortex formation upon the absorption of a
thermal neutron in a rotating container of superfluid He-B. The nuclear
reaction n + He = p + H + 0.76MeV heats a cigar shaped region of the
superfluid into the normal phase. The subsequent cooling of this region back
through the superfluid transition results in the nucleation of quantized
vortices. Depending on the superflow velocity, sufficiently large vortex rings
grow under the influence of the Magnus force and escape into the container
volume where they are detected individually with nuclear magnetic resonance.
The larger the superflow velocity the smaller the rings which can expand. Thus
it is possible to obtain information about the morphology of the initial defect
network. We suggest that the nucleation of vortices during the rapid cool-down
into the superfluid phase is similar to the formation of defects during
cosmological phase transitions in the early universe.Comment: 4 pages, LaTeX file, 4 figures are available at
ftp://boojum.hut.fi/pub/publications/lowtemp/LTL-95009.p
Behavioral Modernity and the Cultural Transmission of Structured Information: The Semantic Axelrod Model
Cultural transmission models are coming to the fore in explaining increases
in the Paleolithic toolkit richness and diversity. During the later
Paleolithic, technologies increase not only in terms of diversity but also in
their complexity and interdependence. As Mesoudi and O'Brien (2008) have shown,
selection broadly favors social learning of information that is hierarchical
and structured, and multiple studies have demonstrated that teaching within a
social learning environment can increase fitness. We believe that teaching also
provides the scaffolding for transmission of more complex cultural traits.
Here, we introduce an extension of the Axelrod (1997} model of cultural
differentiation in which traits have prerequisite relationships, and where
social learning is dependent upon the ordering of those prerequisites. We
examine the resulting structure of cultural repertoires as learning
environments range from largely unstructured imitation, to structured teaching
of necessary prerequisites, and we find that in combination with individual
learning and innovation, high probabilities of teaching prerequisites leads to
richer cultural repertoires. Our results point to ways in which we can build
more comprehensive explanations of the archaeological record of the Paleolithic
as well as other cases of technological change.Comment: 24 pages, 7 figures. Submitted to "Learning Strategies and Cultural
Evolution during the Paleolithic", edited by Kenichi Aoki and Alex Mesoudi,
and presented at the 79th Annual Meeting of the Society for American
Archaeology, Austin TX. Revised 5/14/1
The holographic principle
There is strong evidence that the area of any surface limits the information
content of adjacent spacetime regions, at 10^(69) bits per square meter. We
review the developments that have led to the recognition of this entropy bound,
placing special emphasis on the quantum properties of black holes. The
construction of light-sheets, which associate relevant spacetime regions to any
given surface, is discussed in detail. We explain how the bound is tested and
demonstrate its validity in a wide range of examples.
A universal relation between geometry and information is thus uncovered. It
has yet to be explained. The holographic principle asserts that its origin must
lie in the number of fundamental degrees of freedom involved in a unified
description of spacetime and matter. It must be manifest in an underlying
quantum theory of gravity. We survey some successes and challenges in
implementing the holographic principle.Comment: 52 pages, 10 figures, invited review for Rev. Mod. Phys; v2:
reference adde
Ferromagnetic Semiconductors: Moving Beyond (Ga,Mn)As
The recent development of MBE techniques for growth of III-V ferromagnetic
semiconductors has created materials with exceptional promise in spintronics,
i.e. electronics that exploit carrier spin polarization. Among the most
carefully studied of these materials is (Ga,Mn)As, in which meticulous
optimization of growth techniques has led to reproducible materials properties
and ferromagnetic transition temperatures well above 150 K. We review progress
in the understanding of this particular material and efforts to address
ferromagnetic semiconductors as a class. We then discuss proposals for how
these materials might find applications in spintronics. Finally, we propose
criteria that can be used to judge the potential utility of newly discovered
ferromagnetic semiconductors, and we suggest guidelines that may be helpful in
shaping the search for the ideal material.Comment: 37 pages, 4 figure
Methylphenidate Exposure Induces Dopamine Neuron Loss and Activation of Microglia in the Basal Ganglia of Mice
Background: Methylphenidate (MPH) is a psychostimulant that exerts its pharmacological effects via preferential blockade of the dopamine transporter (DAT) and the norepinephrine transporter (NET), resulting in increased monoamine levels in the synapse. Clinically, methylphenidate is prescribed for the symptomatic treatment of ADHD and narcolepsy; although lately, there has been an increased incidence of its use in individuals not meeting the criteria for these disorders. MPH has also been misused as a ‘‘cognitive enhancer’ ’ and as an alternative to other psychostimulants. Here, we investigate whether chronic or acute administration of MPH in mice at either 1 mg/kg or 10 mg/kg, affects cell number and gene expression in the basal ganglia. Methodology/Principal Findings: Through the use of stereological counting methods, we observed a significant reduction (,20%) in dopamine neuron numbers in the substantia nigra pars compacta (SNpc) following chronic administration of 10 mg/kg MPH. This dosage of MPH also induced a significant increase in the number of activated microglia in the SNpc. Additionally, exposure to either 1 mg/kg or 10 mg/kg MPH increased the sensitivity of SNpc dopaminergic neurons to the parkinsonian agent 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Unbiased gene screening employing Affymetrix GeneChipH HT MG-430 PM revealed changes in 115 and 54 genes in the substantia nigra (SN) of mice exposed to 1 mg/kg and 10 mg/kg MPH doses, respectively. Decreases in the mRNA levels of gdnf, dat1, vmat2, and th in the substantia nigr
Green Criminology Before ‘Green Criminology’: Amnesia and Absences
Although the first published use of the term ‘green criminology’ seems to have been made by Lynch (Green criminology. Aldershot, Hampshire, 1990/2006), elements of the analysis and critique represented by the term were established well before this date. There is much criminological engagement with, and analysis of, environmental crime and harm that occurred prior to 1990 that deserves acknowledgement. In this article, we try to illuminate some of the antecedents of green criminology. Proceeding in this way allows us to learn from ‘absences’, i.e. knowledge that existed but has been forgotten. We conclude by referring to green criminology not as an exclusionary label or barrier but as a symbol that guides and inspires the direction of research
Radiocarbon dating and cultural dynamics across Mongolia’s early pastoral transition
All necessary permits were obtained for the described study, which complied with all relevant regulations. Collaboration contract between the Max Planck Institute for the Science of Human HIstory and the National University of Mongolia began on the 10th November, 2016. Export number 10/413 (7b/52) was received on the 2nd Feb, 2017 (#A0109258, MN DE 7 643). This research was supported by the Max Planck Institute for the Science of Human History. Special thanks to Dr. Katerina Douka and the Oxford Radiocarbon Accelerator Laboratory for conducting 14C analysis, and to all of the original excavators and authors who published the radiocarbon dates cited in this study.Peer reviewedPublisher PD
Humans and fire: changing relations in early agricultural and built environments in the Zagros, Iran, Iraq
Fire-centred studies have recently been highlighted as powerful avenues for investigation of energy flows and relations between humans, materials, environments and other species. The aim in this paper is to evaluate this potential first by reviewing the diverse theories and methods that can be applied to investigate the ecological and social significance of anthropogenic fire, and second by applying these to new and existing data sets in archaeology. This paper examines how fire-centred approaches can inform on one of the most significant step-changes in human lifeways and inter-relations with environment and other species – the transition from mobile hunting-gathering to more sedentary agriculture in a key heartland of change, the Zagros region of Iraq and Iran, c. 12,000–8,000 BP. In the review and case studies multiple links are investigated between human fire use and environment, ecology, energy use, technology, the built environment, health, social roles and relations, cultural practices and catastrophic event
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