1,319 research outputs found
Drought Shocks and Labor Reallocation in Rural Africa : Evidence from Ethiopia
We study how rural households in Ethiopia adapt to droughts through labor reallocation. By using three waves of panel data and exploiting spatial-temporal variations in drought exposure, we find that households reduce on-farm work and increase off-farm self-employment in response to both short-term and persistent droughts, without abandoning family farming. Diversification into off-farm activities is driven by drought-related productivity declines in agriculture and contributes to consumption smoothing. Households with better access to markets and financial services find it easier to reallocate labor off-farm. Our results highlight the importance of strengthening the rural non-farm economy to enhance rural households’ climate resilience
A Bayesian Analysis of Return Dynamics with Stochastic Volatility and Levy Jumps
We develop Bayesian Markov chain Monte Carlo methods for inferences of continuoustime models with stochastic volatility and infinite-activity Levy jumps using discretely sampled data. Simulation studies show that (i) our methods provide accurate joint identification of diffusion, stochastic volatility, and Levy jumps, and (ii) affine jumpdiffusion models fail to adequately approximate the behavior of infinite-activity jumps. In particular, the affine jump-diffusion models fail to capture the infinitely many small Levy jumps which are too big for Brownian motion to model and too small for compound Poisson process to capture. Empirical studies show that infinite-activity Levy jumps are essential for modeling the S&P 500 index returns
Suppressing Diffusion-Mediated Exciton Annihilation in 2D Semiconductors Using the Dielectric Environment
Atomically thin semiconductors such as monolayer MoS2 and WS2 exhibit
nonlinear exciton-exciton annihilation at notably low excitation densities
(below ~10 excitons/um2 in MoS2). Here, we show that the density threshold at
which annihilation occurs can be tuned by changing the underlying substrate.
When the supporting substrate is changed from SiO2 to Al2O3 or SrTiO3, the rate
constant for second-order exciton-exciton annihilation, k_XX [cm2/s], is
reduced by one or two orders of magnitude, respectively. Using transient
photoluminescence microscopy, we measure the effective room-temperature exciton
diffusion coefficient in chemical-treated MoS2 to be D = 0.06 +/- 0.01 cm2/s,
corresponding to a diffusion length of LD = 350 nm for an exciton lifetime of
{\tau} = 20 ns, which is independent of the substrate. These results, together
with numerical simulations, suggest that the effective exciton-exciton
annihilation radius monotonically decreases with increasing refractive index of
the underlying substrate. Exciton-exciton annihilation limits the overall
efficiency of 2D semiconductor devices operating at high exciton densities; the
ability to tune these interactions via the dielectric environment is an
important step toward more efficient optoelectronic technologies featuring
atomically thin materials
High-Order Numerical Method for 1D Non-local Diffusive Equation
In this paper we present a non-local numerical scheme based on the Local
Discontinuous Galerkin method for a non-local diffusive partial differential
equation with application to traffic flow. In this model, the velocity is
determined by both the average of the traffic density as well as the changes in
the traffic density at a neighborhood of each point. We discuss nonphysical
behaviors that can arise when including diffusion, and our measures to prevent
them in our model. The numerical results suggest that this is an accurate
method for solving this type of equation and that the model can capture desired
traffic flow behavior. We show that computation of the non-local convolution
results in complexity, but the increased computation time
can be mitigated with high-order schemes like the one proposed.Comment: 17 pages and 8 figure
Blue shifting of the A exciton peak in folded monolayer 1H-MoS2
The large family of layered transition-metal dichalcogenides is widely
believed to constitute a second family of two-dimensional (2D) semiconducting
materials that can be used to create novel devices that complement those based
on graphene. In many cases these materials have shown a transition from an
indirect bandgap in the bulk to a direct bandgap in monolayer systems. In this
work we experimentally show that folding a 1H molybdenum disulphide (MoS2)
layer results in a turbostratic stack with enhanced photoluminescence quantum
yield and a significant shift to the blue by 90 meV. This is in contrast to the
expected 2H-MoS2 band structure characteristics, which include an indirect gap
and quenched photoluminescence. We present a theoretical explanation to the
origin of this behavior in terms of exciton screening.Comment: 16 pages, 8 figure
EARTH OBSERVATION AND CLIMATE SERVICES FOR FOOD SECURITY AND AGRICULTURAL DECISION MAKING IN SOUTH AND SOUTHEAST ASIA
Deliberations on new developments in the use of Earth observation for agriculture and food security in South and Southeast Asia gathered 120 participants to discuss i) agricultural and hydrological drought monitoring and early warning systems, ii) crop mapping and yield estimation, and iii) risk financing and agrometeorological advisory services
Exactly solvable reaction diffusion models on a Cayley tree
The most general reaction-diffusion model on a Cayley tree with
nearest-neighbor interactions is introduced, which can be solved exactly
through the empty-interval method. The stationary solutions of such models, as
well as their dynamics, are discussed. Concerning the dynamics, the spectrum of
the evolution Hamiltonian is found and shown to be discrete, hence there is a
finite relaxation time in the evolution of the system towards its stationary
state.Comment: 9 pages, 2 figure
Growth-substrate induced performance degradation in chemically synthesized monolayer MoS2ᅠfield effect transistors
We report on the electronic transport properties of single-layer thick chemical vapor deposition (CVD) grown molybdenum disulfide (MoS2) field-effect transistors (FETs) on Si/SiO2 substrates. MoS2 has been extensively investigated for the past two years as a potential semiconductor analogue to graphene. To date, MoS2 samples prepared via mechanical exfoliation have demonstrated field-effect mobility values which are significantly higher than that of CVD-grown MoS2. In this study, we will show that the intrinsic electronic performance of CVD-grown MoS2 is equal or superior to that of exfoliated material and has been possibly masked by a combination of interfacial contamination on the growth substrate and residual tensile strain resulting from the high-temperature growth process. We are able to quantify this strain in the as-grown material using pre- and post-transfer metrology and microscopy of the same crystals. Moreover, temperature-dependent electrical measurements made on as-grown and transferred MoS2 devices following an identical fabrication process demonstrate the improvement in field-effect mobility
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