Modelling the recent historical impacts of atmospheric CO2 and climate change on Mediterranean vegetation

During the past century, annual mean temperature has increased by 0.75 degrees C and precipitation has shown marked variation throughout the Mediterranean basin. These historical climate changes may have had significant, but presently undefined, impacts on the productivity and structure of sclerophyllous shrubland, an important vegetation type in the region. We used a vegetation model for this functional type to examine climate change impacts, and their interaction with the concurrent historical rise in atmospheric CO2. Using only climate and soil texture as data inputs, model. predictions showed good agreement with observations of seasonal and regional variation in leaf and canopy physiology, net primary productivity (NPP), leaf area index (LAI) and soil water. Model simulations for shrubland sites indicated that potential NPP has risen by 25% and LAI by 7% during the past century, although the absolute increase in LAI was small. Sensitivity analysis suggested that the increase in atmospheric CO2 since 1900 was the primary cause of these changes, and that simulated climate change alone had negative impacts on both NPP and LAI. Effects of rising CO2 were mediated by significant increases in the efficiency of water-use in NPP throughout the region, as a consequence of the direct effect of CO2 on leaf gas exchange. This increase in efficiency compensated for limitation of NPP by drought, except in areas where drought was most severe. However, while water was used more efficiently, total canopy water loss rose slightly or remained unaffected in model simulations, because increases in LAI with CO2 counteracted the effects of reduced stomatal conductance on transpiration. Model simulations for the Mediterranean region indicate that the recent rise in atmospheric CO2 may already have had significant impacts on productivity, structure and water relations of sclerophyllous shrub vegetation, which tended to offset the detrimental effects of climate change in the region

Universality of conductivity in interacting graphene

The Hubbard model on the honeycomb lattice describes charge carriers in graphene with short range interactions. While the interaction modifies several physical quantities, like the value of the Fermi velocity or the wave function renormalization, the a.c. conductivity has a universal value independent of the microscopic details of the model: there are no interaction corrections, provided that the interaction is weak enough and that the system is at half filling. We give a rigorous proof of this fact, based on exact Ward Identities and on constructive Renormalization Group methods

Impurity and interface bound states in dx2−y2+idxyd_{x^2-y^2}+id_{xy} and px+ipyp_x+ip_y superconductors

Motivated by recent discoveries of novel superconductors such as Na$_x$CoO$_2\cdot y$H$_2$O and Sr$_2$RuO$_4$, we analysize features of quasi-particle scattering due to impurities and interfaces for possible gapful $d_{x^2-y^2}+id_{xy}$ and $p_x+ip_y$ Cooper pairing. A bound state appears near a local impurity, and a band of bound states form near an interface. We obtained analytically the bound state energy, and calculated the space and energy dependent local density of states resolvable by high-resolution scanning tunnelling microscopy. For comparison we also sketch results of impurity and surface states if the pairing is nodal p- or d-wave.Comment: 4 pages, 4 figure

Towards access for all: 1st Working Group Report for the Global Gene Therapy Initiative (GGTI)

The gene and cell therapy field saw its first approved treatments in Europe in 2012 and the United States in 2017 and is projected to be at least a $10B USD industry by 2025. Despite this success, a massive gap exists between the companies, clinics, and researchers developing these therapeutic approaches, and their availability to the patients who need them. The unacceptable reality is a geographic exclusion of low-and middle-income countries (LMIC) in gene therapy development and ultimately the provision of gene therapies to patients in LMIC. This is particularly relevant for gene therapies to treat human immunodeficiency virus infection and hemoglobinopathies, global health crises impacting tens of millions of people primarily located in LMIC. Bridging this divide will require research, clinical and regulatory infrastructural development, capacity-building, training, an approval pathway and community adoption for success and sustainable affordability. In 2020, the Global Gene Therapy Initiative was formed to tackle the barriers to LMIC inclusion in gene therapy development. This working group includes diverse stakeholders from all sectors and has set a goal of introducing two gene therapy Phase I clinical trials in two LMIC, Uganda and India, by 2024. Here we report on progress to date for this initiative

Competing orders in a magnetic field: spin and charge order in the cuprate superconductors

We describe two-dimensional quantum spin fluctuations in a superconducting Abrikosov flux lattice induced by a magnetic field applied to a doped Mott insulator. Complete numerical solutions of a self-consistent large N theory provide detailed information on the phase diagram and on the spatial structure of the dynamic spin spectrum. Our results apply to phases with and without long-range spin density wave order and to the magnetic quantum critical point separating these phases. We discuss the relationship of our results to a number of recent neutron scattering measurements on the cuprate superconductors in the presence of an applied field. We compute the pinning of static charge order by the vortex cores in the `spin gap' phase where the spin order remains dynamically fluctuating, and argue that these results apply to recent scanning tunnelling microscopy (STM) measurements. We show that with a single typical set of values for the coupling constants, our model describes the field dependence of the elastic neutron scattering intensities, the absence of satellite Bragg peaks associated with the vortex lattice in existing neutron scattering observations, and the spatial extent of charge order in STM observations. We mention implications of our theory for NMR experiments. We also present a theoretical discussion of more exotic states that can be built out of the spin and charge order parameters, including spin nematics and phases with `exciton fractionalization'.Comment: 36 pages, 33 figures; for a popular introduction, see http://onsager.physics.yale.edu/superflow.html; (v2) Added reference to new work of Chen and Ting; (v3) reorganized presentation for improved clarity, and added new appendix on microscopic origin; (v4) final published version with minor change