Emerging quantum technologies for cryptography, computing and metrology exploit quantum mechanical effects for enhanced information processing and nanoscale sensing. Though different platform systems are currently being explored, light-based quantum technologies using single-photon emitters as the basic building block are among the frontrunners 1 . Several strategies have been used to realize deterministic single photon sources in the solid state 2 , including quantum dots 3 , single molecules 4 , and point defects in wide bandgap materials such as diamond and silicon carbide 5-9 . Single photon emitters in novel van der Waals materials have garnered recent attention due to their potential for integration with waveguides, microcavities, and other passive components typical in photonic devices. Example 2D systems hosting quantum emitters include WSe 2 and MoS 2 as well as other transition metal dichalcogenides (TMDs) 10-14 .Here we focus on hexagonal boron nitride (hBN), a wide bandgap semiconductor where defect emission has been shown to be tunable and robust at room temperature 15-22 and above 23 . We use confocal microscopy to investigate the photoluminescence (PL) of point defects within thin hBN flakes deposited on a lithographically patterned SiO 2 substrate. Due to Van der Waals forces the flake conforms to the surface topography thus accumulating significant local strain near protruding features. Using large structured arrays of different sizes and geometries we find nearly perfect correspondence between the strained areas of the flake and defect emission. Our modeling supports the notion of defect activation via charge trapping in deformation potential wells. The physics at play has some similarities with that governing the dynamics of excitons in WSe 2 monolayers subjected to comparable geometries, as reported recently 24,25 . Unlike TMDs, however, the wide bandgap of hBN can accommodate large potential modulations, sufficient to stabilize the defect charge at room temperature. In particular, we calculate deformation potential wells as deep as 500 meV confined to regions of tensile and compressive strain in the hBN flake that correlate well with the spatial localization of the emitters.For the first set of experiments we use an array of 155-nm-high nanopillars with diameters ranging from 200 to 700 nm fabricated via electron beam lithography over a large-area silica substrate (Figure 1a); the sample is a commercial, 20-nmthick flake of hBN grown via chemical vapor deposition (CVD). We follow a wet transfer protocol 26 to drape the flake on the patterned silica substrate (see Methods). This technique takes advantage of the Van der Waals forces to make the flake conform to the surface topography. As an illustration, Figure 1b shows an atomic force microscopy (AFM) image from an hBN fragment where the 20-nm-thick flake folds on itself: We identify single-and double-layer sections near the left and right areas, respectively; bare pillars -visible on the lower, right corner of the image -provide a direct view...

We use oil price fluctuations to test the impact of transfers from wealthy OPEC nations to their poorer Muslim allies. The instrument identifies plausibly exogenous variation in foreign aid. We investigate how aid is spent by tracking its short-run effect on aggregate demand, national accounts, and balance of payments. Aid affects most components of GDP though it has no statistically identifiable impact on prices or economic growth. Much aid is consumed, primarily in the form of imported noncapital goods. Aid substitutes for domestic savings, has no effect on the financial account, and leads to unaccounted capital flight. (JEL F35, O19)

Natural disasters occur in a political space. Although events beyond our control may trigger a disaster, the level of government preparedness and response greatly determines the extent of suffering incurred by the affected population. We use a political economy model of disaster prevention, supported by case studies, that explains why some governments prepare well for disasters and others do not. We also show how the presence of international aid distorts this choice and increases the chance that governments will under-invest. Policy suggestions that may alleviate this problem are discussed.

The sensitivity of cloud-scale simulations of deep convection to variations in prescribed microphysics parameters is studied, using the single-moment scheme in the Regional Atmospheric Modeling System (RAMS) model. Realistic changes were made to the shape parameters in the gamma distributions of the diameters of precipitating hydrometeors and of cloud droplets, in the number concentration of cloud droplets, and in the mean size of the hail and graupel. Simulations were performed with two initial soundings that are identical except for their temperature. The precipitation rate at the ground is not very sensitive to changes in the value of the shape parameter used for all precipitating hydrometeors (rain, hail, graupel, snow, and aggregates) or to the mean size of the hail and graupel, owing to counteracting effects. For example, with a larger shape parameter value, there is a greater production of precipitation by collection of cloud water, but also a larger rate of evaporation of the liquid precipitation. However, with a larger shape parameter value, the greater production of precipitation by collection and the increased evaporation result in more low-level cooling by the downdraft. Specifying larger hail and graupel results in less low-level cooling by the downdraft. The simulation with the cold initial sounding showed a change in storm propagation velocity when the specified sizes of hail and graupel were increased, but this did not occur when the warm initial sounding was used. With a larger shape parameter for cloud water or with a larger number concentration of cloud droplets, there is less autoconversion and less collection of cloud water and, consequently, much less precipitation at the ground and denser cirrus anvils. While the number concentration of cloud droplets can be forecast in some models with parameterized microphysics, at present the shape parameter for cloud water cannot and must, therefore, be carefully selected.

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