Quantum Gravity in 2+1 Dimensions: The Case of a Closed Universe

In three spacetime dimensions, general relativity drastically simplifies, becoming a ``topological'' theory with no propagating local degrees of freedom. Nevertheless, many of the difficult conceptual problems of quantizing gravity are still present. In this review, I summarize the rather large body of work that has gone towards quantizing (2+1)-dimensional vacuum gravity in the setting of a spatially closed universe.Comment: 61 pages, draft of review for Living Reviews; comments, criticisms, additions, missing references welcome; v2: minor changes, added reference

Pathogenesis of adolescent idiopathic scoliosis in girls - a double neuro-osseous theory involving disharmony between two nervous systems, somatic and autonomic expressed in the spine and trunk: possible dependency on sympathetic nervous system and hormones with implications for medical therapy

Anthropometric data from three groups of adolescent girls - preoperative adolescent idiopathic scoliosis (AIS), screened for scoliosis and normals were analysed by comparing skeletal data between higher and lower body mass index subsets. Unexpected findings for each of skeletal maturation, asymmetries and overgrowth are not explained by prevailing theories of AIS pathogenesis. A speculative pathogenetic theory for girls is formulated after surveying evidence including: (1) the thoracospinal concept for right thoracic AIS in girls; (2) the new neuroskeletal biology relating the sympathetic nervous system to bone formation/resorption and bone growth; (3) white adipose tissue storing triglycerides and the adiposity hormone leptin which functions as satiety hormone and sentinel of energy balance to the hypothalamus for long-term adiposity; and (4) central leptin resistance in obesity and possibly in healthy females. The new theory states that AIS in girls results from developmental disharmony expressed in spine and trunk between autonomic and somatic nervous systems. The autonomic component of this double neuro-osseous theory for AIS pathogenesis in girls involves selectively increased sensitivity of the hypothalamus to circulating leptin (genetically-determined up-regulation possibly involving inhibitory or sensitizing intracellular molecules, such as SOC3, PTP-1B and SH2B1 respectively), with asymmetry as an adverse response (hormesis); this asymmetry is routed bilaterally via the sympathetic nervous system to the growing axial skeleton where it may initiate the scoliosis deformity (leptin-hypothalamic-sympathetic nervous system concept = LHS concept). In some younger preoperative AIS girls, the hypothalamic up-regulation to circulating leptin also involves the somatotropic (growth hormone/IGF) axis which exaggerates the sympathetically-induced asymmetric skeletal effects and contributes to curve progression, a concept with therapeutic implications. In the somatic nervous system, dysfunction of a postural mechanism involving the CNS body schema fails to control, or may induce, the spinal deformity of AIS in girls (escalator concept). Biomechanical factors affecting ribs and/or vertebrae and spinal cord during growth may localize AIS to the thoracic spine and contribute to sagittal spinal shape alterations. The developmental disharmony in spine and trunk is compounded by any osteopenia, biomechanical spinal growth modulation, disc degeneration and platelet calmodulin dysfunction. Methods for testing the theory are outlined. Implications are discussed for neuroendocrine dysfunctions, osteopontin, sympathoactivation, medical therapy, Rett and Prader-Willi syndromes, infantile idiopathic scoliosis, and human evolution. AIS pathogenesis in girls is predicated on two putative normal mechanisms involved in trunk growth, each acquired in evolution and unique to humans

P-FUTURES: Towards urban food & water security through collaborative design and impact

© 2016 Elsevier B.V. Phosphorus is essential to food production, but current management practices fail to ensure equitable access to farmers globally and often results in polluted waterways. There is a lack of local and global governance mechanisms to ensure phosphorus is sustainably managed. The P-FUTURES research initiative aims to address this gap by working with stakeholders to explore visions and pathways of social transformation towards food and water security. In the seed phase of the project, academic, civil, industry, and municipal stakeholders interacted as partners in Blantyre (Malawi), Hanoi (Vietnam), Sydney (Australia), and Phoenix (USA) to collaboratively develop a full proposal and build capacity for transformational change. The article offers guidance on the opportunities and challenges of co-developing a research approach and proposal in a transdisciplinary, international setting

Simulating alternative sustainable water futures

In the United States of America, urban areas of the arid Southwest are prone to drought risk and changing precipitation patterns; future water supplies are uncertain. A collaborative working group of researchers and practitioners developed alternative future scenarios for 2060—sustainable water futures—that incorporate standard and novel water-adaptation strategies for the Phoenix metropolitan area (hereafter “Phoenix”) in central Arizona, USA. The authors adapted WaterSim-6, a water policy and planning model, to explore differences in water demand and supply for three scenarios as influenced by (1) runoff from the rivers that supply surface water to Phoenix, (2) population growth, (3) water use efficiency, (4) annual rainfall, and (5) land-cover land-use changes. Centralized water-management strategies (direct and indirect potable water reuse and reclaimed supplies) and decentralized strategies (rainwater harvesting and greywater use) were explored. We observed decreased reliance on surface water supplies, offset by increased municipal groundwater pumping in the Strategic scenario, but by alternative water supplies (non-potable water sources including greywater, reclaimed water, and rainwater harvested) in the Desert Wetland and Almost Zero Waste (AZW) scenarios. Even under modest policy implementation and service-connection adoption rates associated with our Strategic scenario, by 2060 alternative supplies from non-potable sources could offset 30% or more of outdoor water demand. Aggressive policy implementations associated with the AZW scenario suggest that up to 80% of outdoor water demand could likewise be met. The WaterSim platform combined with co-produced future scenarios illuminates tradeoffs in support of decision making for long-term sustainability of a water-limited region

Apoptosome activation, an important molecular instigator in 6-mercaptopurine induced Leydig cell death

Leydig cells are crucial to the production of testosterone in males. It is unknown if the cancer chemotherapeutic drug, 6-mercaptopurine (6 MP), produces Leydig cell failure among adult survivors of childhood acute lymphoblastic leukemia. Moreover, it is not known whether Leydig cell failure is due to either a loss of cells or an impairment in their function. Herein, we show, in a subset of childhood cancer survivors, that Leydig cell failure is related to the dose of 6 MP. This was extended, in a murine model, to demonstrate that 6 MP exposure induced caspase 3 activation, and the loss of Leydig cells was independent of Bak and Bax activation. The death of these non-proliferating cells was triggered by 6 MP metabolism, requiring formation of both cytosolic reactive oxygen species and thiopurine nucleotide triphosphates. The thiopurine nucleotide triphosphates (with physiological amounts of dATP) uniquely activated the apoptosome. An ABC transporter (Abcc4/Mrp4) reduced the amount of thiopurines, thereby providing protection for Leydig cells. The studies reported here demonstrate that the apoptosome is uniquely activated by thiopurine nucleotides and suggest that 6 MP induced Leydig cell death is likely a cause of Leydig cell failure in some survivors of childhood cancer

Whole-body vibration slows the acquisition of fat in mature female rats.

OBJECTIVE: To evaluate the effects of whole-body vibration on fat, bone, leptin and muscle mass. METHODS/DESIGN: Thirty 7-month-old female 344 Fischer rats were randomized by weight into three groups (baseline, vibration or control; n=8-10 per group). Rats in the vibration group were placed inside individual compartments attached to a Pneu-Vibe vibration platform (Pneumex, Sandpoint, ID, USA) and vibrated at 30-50 Hz (6 mm peak to peak) for 30 min per day, 5 days per week, for 12 weeks. The vibration intervention consisted of six 5-min cycles with a 1-min break between cycles. RESULTS: There were significant body composition differences between the whole-body vibration and the control group. The whole-body vibration group weighed approximately 10% less (mean+/-s.d.; 207+/-10 vs 222+/-15 g, P\u3c0.03) and had less body fat (20.8+/-3.8 vs 26.8+/-5.9 g, P\u3c0.05), a lower percentage of body fat (10.2+/-1.7 vs 12+/-2.0%, P\u3c0.05), and lower serum leptin levels (1.06+/-0.45 vs 2.27+/-0.57 ng ml(-1), P\u3c0.01) than the age-matched controls. No differences were observed for total lean mass, bone mineral content (BMC), bone mineral density (BMD), insulin-like growth factor-I (IGF-I) or soleus (SOL) and extensor digitorum longus (EDL) mass or function. Regional high-resolution dual-energy X-ray absoptiometry scans of the lumbar spine (L1-4) revealed that the whole-body vibration group had significantly greater BMC (0.33+/-0.05 vs 0.26+/-0.03 g, P\u3c0.01) and BMD (0.21+/-0.01 vs 0.19+/-0.01 g cm(-2), P\u3c0.01) than the control group. No differences between the groups were observed in the amount of food consumed. CONCLUSION: These findings show that whole-body vibration reduced body fat accumulation and serum leptin without affecting whole body BMC, BMD or lean mass. However, the increase in vertebral BMC and BMD suggests that vibration may have resulted in local increases in bone mass and density. Also, whole-body vibration did not affect muscle function or food consumption