We investigate the consequences for the black hole area of introducing fractal structure for the horizon geometry. We create a three-dimensional spherical analogue of a ‘Koch Snowflake’ using a ...infinite diminishing hierarchy of touching spheres around the Schwarzschild event horizon. We can create a fractal structure for the horizon with finite volume and infinite (or finite) area. This is a toy model for the possible effects of quantum gravitational spacetime foam, with significant implications for assessments of the entropy of black holes and the universe, which is generally larger than in standard picture of black hole structure and thermodynamics, potentially by very considerable factors. The entropy of the observable universe today becomes S≈10120(1+Δ/2), where 0≤Δ≤1, with Δ=0 for a smooth spacetime structure and Δ=1 for the most intricate. The Hawking lifetime of black holes is also reduced.
The ability to learn new skills and perfect them with practice applies not only to physical skills but also to abstract skills, like motor planning or neuroprosthetic actions. Although plasticity in ...corticostriatal circuits has been implicated in learning physical skills, it remains unclear if similar circuits or processes are required for abstract skill learning. Here we use a novel behavioural task in rodents to investigate the role of corticostriatal plasticity in abstract skill learning. Rodents learned to control the pitch of an auditory cursor to reach one of two targets by modulating activity in primary motor cortex irrespective of physical movement. Degradation of the relation between action and outcome, as well as sensory-specific devaluation and omission tests, demonstrate that these learned neuroprosthetic actions are intentional and goal-directed, rather than habitual. Striatal neurons change their activity with learning, with more neurons modulating their activity in relation to target-reaching as learning progresses. Concomitantly, strong relations between the activity of neurons in motor cortex and the striatum emerge. Specific deletion of striatal NMDA receptors impairs the development of this corticostriatal plasticity, and disrupts the ability to learn neuroprosthetic skills. These results suggest that corticostriatal plasticity is necessary for abstract skill learning, and that neuroprosthetic movements capitalize on the neural circuitry involved in natural motor learning.
Nucleus accumbens dopamine is known to play a role in motivational processes, and dysfunctions of mesolimbic dopamine may contribute to motivational symptoms of depression and other disorders, as ...well as features of substance abuse. Although it has become traditional to label dopamine neurons as “reward” neurons, this is an overgeneralization, and it is important to distinguish between aspects of motivation that are differentially affected by dopaminergic manipulations. For example, accumbens dopamine does not mediate primary food motivation or appetite, but is involved in appetitive and aversive motivational processes including behavioral activation, exertion of effort, approach behavior, sustained task engagement, Pavlovian processes, and instrumental learning. In this review, we discuss the complex roles of dopamine in behavioral functions related to motivation.
It has become common to associate dopamine signaling with reward, but this is an overgeneralization, and aspects of motivation are differentially affected by dopaminergic manipulations. In this review, Salamone and Correa discuss the complex roles of dopamine in behavioral functions related to motivation.
The Origin of Life-Out of the Blue Sutherland, John D.
Angewandte Chemie (International ed.),
January 4, 2016, Volume:
55, Issue:
1
Journal Article
Peer reviewed
Either to sustain autotrophy, or as a prelude to heterotrophy, organic synthesis from an environmentally available C1 feedstock molecule is crucial to the origin of life. Recent findings augment key ...literature results and suggest that hydrogen cyanide—“Blausäure”—was that feedstock.
Molecular componentry for all the cellular subsystems can be derived from hydrogen cyanide—“Blausäure”—suggesting life arose “out of the blue”.
This is a comprehensive and accessible overview of what is known about the structure and mechanics of bone, bones, and teeth. In it, John Currey incorporates critical new concepts and findings from ...the two decades of research since the publication of his highly regardedThe Mechanical Adaptations of Bones. Crucially, Currey shows how bone structure and bone's mechanical properties are intimately bound up with each other and how the mechanical properties of the material interact with the structure of whole bones to produce an adapted structure.
For bone tissue, the book discusses stiffness, strength, viscoelasticity, fatigue, and fracture mechanics properties. For whole bones, subjects dealt with include buckling, the optimum hollowness of long bones, impact fracture, and properties of cancellous bone. The effects of mineralization on stiffness and toughness and the role of microcracking in the fracture process receive particular attention. As a zoologist, Currey views bone and bones as solutions to the design problems that vertebrates have faced during their evolution and throughout the book considers what bones have been adapted to do. He covers the full range of bones and bony tissues, as well as dentin and enamel, and uses both human and non-human examples.
Copiously illustrated, engagingly written, and assuming little in the way of prior knowledge or mathematical background,Bonesis both an ideal introduction to the field and also a reference sure to be frequently consulted by practicing researchers.
Gas hydrate, a frozen, naturally‐occurring, and highly‐concentrated form of methane, sequesters significant carbon in the global system and is stable only over a range of low‐temperature and ...moderate‐pressure conditions. Gas hydrate is widespread in the sediments of marine continental margins and permafrost areas, locations where ocean and atmospheric warming may perturb the hydrate stability field and lead to release of the sequestered methane into the overlying sediments and soils. Methane and methane‐derived carbon that escape from sediments and soils and reach the atmosphere could exacerbate greenhouse warming. The synergy between warming climate and gas hydrate dissociation feeds a popular perception that global warming could drive catastrophic methane releases from the contemporary gas hydrate reservoir. Appropriate evaluation of the two sides of the climate‐methane hydrate synergy requires assessing direct and indirect observational data related to gas hydrate dissociation phenomena and numerical models that track the interaction of gas hydrates/methane with the ocean and/or atmosphere. Methane hydrate is likely undergoing dissociation now on global upper continental slopes and on continental shelves that ring the Arctic Ocean. Many factors—the depth of the gas hydrates in sediments, strong sediment and water column sinks, and the inability of bubbles emitted at the seafloor to deliver methane to the sea‐air interface in most cases—mitigate the impact of gas hydrate dissociation on atmospheric greenhouse gas concentrations though. There is no conclusive proof that hydrate‐derived methane is reaching the atmosphere now, but more observational data and improved numerical models will better characterize the climate‐hydrate synergy in the future.
Key Points
Gas hydrates are widespread, sequester large amounts of methane at shallow depths, and have a narrow range of stability conditions
Warming climate conditions destabilize hydrates, but sediment and water column sinks mostly prevent methane emission to the atmosphere
Gas hydrate is dissociating at some locations now, but the impacts are primarily limited to ocean waters, not the atmosphere
Interferons (IFNs) induce the expression of hundreds of genes as part of an elaborate antimicrobial programme designed to combat infection in all nucleated cells - a process termed cell-autonomous ...immunity. As described in this Review, recent genomic and subgenomic analyses have begun to assign functional properties to novel IFN-inducible effector proteins that restrict bacteria, protozoa and viruses in different subcellular compartments and at different stages of the pathogen life cycle. Several newly described host defence factors also participate in canonical oxidative and autophagic pathways by spatially coordinating their activities to enhance microbial killing. Together, these IFN-induced effector networks help to confer vertebrate host resistance to a vast and complex microbial world.
Although it is well recognized that autism is associated with altered patterns of over- and under-connectivity, specifics are still a matter of debate. Little has been done so far to synthesize ...available literature using whole-brain electroencephalography (EEG) and magnetoencephalography (MEG) recordings.
1) To systematically review the literature on EEG/MEG functional and effective connectivity in autism spectrum disorder (ASD), 2) to synthesize and critically appraise findings related with the hypothesis that ASD is characterized by long-range underconnectivity and local overconnectivity, and 3) to provide, based on the literature, an analysis of tentative factors that are likely to mediate association between ASD and atypical connectivity (e.g., development, topography, lateralization).
Literature reviews were done using PubMed and PsychInfo databases. Abstracts were screened, and only relevant articles were analyzed based on the objectives of this paper. Special attention was paid to the methodological characteristics that could have created variability in outcomes reported between studies.
Our synthesis provides relatively strong support for long-range underconnectivity in ASD, whereas the status of local connectivity remains unclear. This observation was also mirrored by a similar relationship with lower frequencies being often associated with underconnectivity and higher frequencies being associated with both under- and over-connectivity. Putting together these observations, we propose that ASD is characterized by a general trend toward an under-expression of lower-band wide-spread integrative processes compensated by more focal, higher-frequency, locally specialized, and segregated processes. Further investigation is, however, needed to corroborate the conclusion and its generalizability across different tasks. Of note, abnormal lateralization in ASD, specifically an elevated left-over-right EEG and MEG functional connectivity ratio, has been also reported consistently across studies.
The large variability in study samples and methodology makes a systematic quantitative analysis (i.e. meta-analysis) of this body of research impossible. Nevertheless, a general trend supporting the hypothesis of long-range functional underconnectivity can be observed. Further research is necessary to more confidently determine the status of the hypothesis of short-range overconnectivity. Frequency-band specific patterns and their relationships with known symptoms of autism also need to be further clarified.
PDF
