Driving sandpiles to criticality and beyond

A popular theory of self-organized criticality relates driven dissipative systems to systems with conservation. This theory predicts that the stationary density of the abelian sandpile model equals the threshold density of the fixed-energy sandpile. We refute this prediction for a wide variety of underlying graphs, including the square grid. Driven dissipative sandpiles continue to evolve even after reaching criticality. This result casts doubt on the validity of using fixed-energy sandpiles to explore the critical behavior of the abelian sandpile model at stationarity.Comment: v4 adds referenc

The approach to criticality in sandpiles

A popular theory of self-organized criticality relates the critical behavior of driven dissipative systems to that of systems with conservation. In particular, this theory predicts that the stationary density of the abelian sandpile model should be equal to the threshold density of the corresponding fixed-energy sandpile. This "density conjecture" has been proved for the underlying graph Z. We show (by simulation or by proof) that the density conjecture is false when the underlying graph is any of Z^2, the complete graph K_n, the Cayley tree, the ladder graph, the bracelet graph, or the flower graph. Driven dissipative sandpiles continue to evolve even after a constant fraction of the sand has been lost at the sink. These results cast doubt on the validity of using fixed-energy sandpiles to explore the critical behavior of the abelian sandpile model at stationarity.Comment: 30 pages, 8 figures, long version of arXiv:0912.320

Factors Associated With Retinal Vessel Diameters in an Elderly Population: the Thessaloniki Eye Study

Purpose: To identify the factors associated with retinal vessel diameters in the population of the Thessaloniki Eye Study. Methods: Cross-sectional population-based study (age ≥ 60 years). Subjects with glaucoma, late age-related macular degeneration, and diabetic retinopathy were excluded from the analyses. Retinal vessel diameters were measured using the IVAN software, and measurements were summarized to central retinal artery equivalent (CRAE), central retinal vein equivalent (CRVE), and arteriole to venule ratio (AVR). Results: The analysis included 1614 subjects. The hypertensive group showed lower values of CRAE (P = 0.033) and AVR (P = 0.0351) compared to the normal blood pressure (BP) group. On the contrary, the group having normal BP under antihypertensive treatment did not have different values compared to the normal BP group. Diastolic BP (per mm Hg) was negatively associated with CRAE (P < 0.0001) and AVR (P < 0.0001), while systolic BP (per mm Hg) was positively associated with CRAE (P = 0.001) and AVR (P = 0.0096). Other factors significantly associated included age, sex, alcohol, smoking, cardiovascular disease history, ophthalmic medication, weight, and IOP; differences were observed in a stratified analysis based on BP medication use. Conclusions: Our study confirms previous reports about the association of age and BP with vessel diameters. The negative correlation between BP and CRAE seems to be guided by the effect of diastolic BP as higher systolic BP is independently associated with higher values of CRAE. The association of BP status with retinal vessel diameters is determined by diastolic BP status in our population. Multiple other factors are also independently associated with retinal vessel diameters

A subset of methylated CpG sites differentiate psoriatic from normal skin.

Psoriasis is a chronic inflammatory immune-mediated disorder affecting the skin and other organs including joints. Over 1,300 transcripts are altered in psoriatic involved skin compared with normal skin. However, to our knowledge, global epigenetic profiling of psoriatic skin is previously unreported. Here, we describe a genome-wide study of altered CpG methylation in psoriatic skin. We determined the methylation levels at 27,578 CpG sites in skin samples from individuals with psoriasis (12 involved, 8 uninvolved) and 10 unaffected individuals. CpG methylation of involved skin differed from normal skin at 1,108 sites. Twelve mapped to the epidermal differentiation complex, upstream or within genes that are highly upregulated in psoriasis. Hierarchical clustering of 50 of the top differentially methylated (DM) sites separated psoriatic from normal skin samples with uninvolved skin exhibiting intermediate methylation. CpG sites where methylation was correlated with gene expression are reported. Sites with inverse correlations between methylation and nearby gene expression include those of KYNU, OAS2, S100A12, and SERPINB3, whose strong transcriptional upregulation is an important discriminator of psoriasis. Pyrosequencing of bisulfite-treated DNA from skin biopsies at three DM loci confirmed earlier findings and revealed reversion of methylation levels toward the non-psoriatic state after 1 month of anti-TNF-α therapy

Horses Damp the Spring in Their Step

The muscular work of galloping in horses is halved by storing and returning elastic strain energy in spring-like muscle–tendon units1, 2.These make the legs act like a child\u27s pogo stick that is tuned to stretch and recoil at 2.5 strides per second. This mechanism is optimized by unique musculoskeletal adaptations: the digital flexor muscles have extremely short fibres and significant passive properties, whereas the tendons are very long and span several joints3, 4. Length change occurs by a stretching of the spring-like digital flexor tendons rather than through energetically expensive length changes in the muscle5. Despite being apparently redundant for such a mechanism5, the muscle fibres in the digital flexors are well developed. Here we show that the mechanical arrangement of the elastic leg permits it to vibrate at a higher frequency of 30–40 Hz that could cause fatigue damage to tendon and bone. Furthermore, we show that the digital flexor muscles have minimal ability to contribute to or regulate significantly the 2.5-Hz cycle of movement, but are ideally arranged to damp these high-frequency oscillations in the limb

Investigando las fortalezas personales para crear vidas y ambientes positivos: una perspectiva internacional

In today’s world, we face a barrage of difficulties in multiple life spheres. While previous times were not without their challenges, these were often restricted to our own personal, geographically localized worlds. Today, news and social media expose us to never-ending reports of traumatic events and interpersonal violence, making us question human nature and our resiliency. Increasing technological advancements have brought forth new challenges, not only in our relationships with technology, but in how we live our daily lives. Financial uncertainty at both the individual and global level raises doubts about our abilities to afford basic necessities. Climate change is wreaking havoc on the environments we call home. Changing interpersonal dynamics present new challenges to personal, social, and group relationships, often resulting in conflict or isolation. Adolescents and young adults are thrust into this confusing world, often lacking the proper resources to understand and cope with these challenges. Adults facing life’s demands also experience extreme stress, with adverse consequences both at the present as well as later life in the form of physical and mental health issues. Furthermore, we have a tendency to direct attention to our individual weaknesses, exacerbating our experience of difficulties. It is, therefore, no wonder that psychology as a discipline, which seeks to understand the human experience, tends to focus on the deficiencies in our lives. However, as stated by Sheldon and King (2001), it is important for psychologists to deviate from this ‘negative bias’, and instead concentrate on positive human qualities and the promotion of what Maslow (1943, 1987) termed growth needs. This focus is the crux of positive psychology.In today’s world, we face a barrage of difficulties in multiple life spheres. While previous times were not without their challenges, these were often restricted to our own personal, geographically localized worlds. Today, news and social media expose us to never-ending reports of traumatic events and interpersonal violence, making us question human nature and our resiliency. Increasing technological advancements have brought forth new challenges, not only in our relationships with technology, but in how we live our daily lives. Financial uncertainty at both the individual and global level raises doubts about our abilities to afford basic necessities. Climate change is wreaking havoc on the environments we call home. Changing interpersonal dynamics present new challenges to personal, social, and group relationships, often resulting in conflict or isolation. Adolescents and young adults are thrust into this confusing world, often lacking the proper resources to understand and cope with these challenges. Adults facing life’s demands also experience extreme stress, with adverse consequences both at the present as well as later life in the form of physical and mental health issues. Furthermore, we have a tendency to direct attention to our individual weaknesses, exacerbating our experience of difficulties. It is, therefore, no wonder that psychology as a discipline, which seeks to understand the human experience, tends to focus on the deficiencies in our lives. However, as stated by Sheldon and King (2001), it is important for psychologists to deviate from this ‘negative bias’, and instead concentrate on positive human qualities and the promotion of what Maslow (1943, 1987) termed growth needs. This focus is the crux of positive psychology

The use of risk and need factors in forensic mental health decision-making and the role of gender and index offense severity

Canadian legislation makes Review Boards (RBs) responsible for rendering dispositions for individuals found Not Criminally Responsible on account of Mental Disorder (NCRMD) after considering public safety, the mental condition of the accused, and his/her potential for community reintegration. We reviewed 6,743 RB hearings for 1,794 individuals found NCRMD in the three largest Canadian provinces to investigate whether items from two empirically supported risk assessment measures, the Historical Clinical Risk Management‐20 and the Violence Risk Appraisal Guide, were considered. Less than half the items were included in expert reports or in RBs' reasons for dispositions, and consideration of these items differed according to gender and index offense severity of the accused. These items included evidence‐based risk factors and/or legally specified criteria: mental health, treatment, and criminal history. These results illustrate the gap between research on risk factors and the integration of this evidence into practice. In particular, we recommend the implementation of structured measures to reduce the potential for clinicians to be unduly influenced by gender and offense severity