Production changes in ghana cocoa farming households under market reforms

During the nineties, Rwandan households had to cope with severe shocks of war and genocide. In addition, two major structural problems in Rwanda, land scarcity and declining soil fertility, remain unsolved. How do Rwandan households manage? This is an important question from a development perspective, but also from a security perspective, because uneven development increases the risk of peace collapse. To find an answer to our question, we study welfare gains and losses of a sample of 189 Rwandan rural households over the period 1990-2002. In our sample, many households were severely affected by the genocide. In addition, poverty and inequality increased. Moreover, we observe a lot of income mobility. Only one quarter of the households remained in the same income quintile over time. Especially the households headed by widows and prisoner’s wives moved downward in the income distribution. Households who reduced their dependence on subsistence agriculture moved upward.

Numerical evaluation of the plastic hinges developed in headed stud shear connectors in composite beams with profiled steel sheeting

[EN] For composite beams using novel steel sheeting, the current Eurocode 4 rules sometimes overestimate the load bearing capacity of the shear connector. This is due to the larger rib heights and the smaller rib widths in comparison with the old studies, which have been carried out to calibrate the current design equations. The RFCS Project “DISCCO” investigated this phenomena and the working group under mandate M515, CEN/TC250/SC4/SC4.T3 is enhancing this equation and working on a proposal to be taken over in the new version of Eurocode 4.The proposed new equation covers the failure behaviour of the shear connection more in detail. The test results show, that the failure consists in a combined concrete cone and stud in bending. Due to the geometry of novel steel sheeting, the load bearing capacity of the headed stud shear connector is no more limited by its shear capacity, but by its bending capacity.A 3D non-linear finite element model is developed and validated through the support of the DISCCO push-out tests. A good agreement between numerical and experimental results in terms of force-slip behaviour is achieved. Special attention of this work lies on the numerical evaluation of the number of plastic hinges ny: a stress-based procedure is presented and the results are compared to the equations presented for new Eurocode 4.The numerical simulations show that the upper plastic hinge moves up as the slip increases due to the progressive crushing of the concrete in the rib. From the parametric study, it turns out that ny is linearly proportional to the embedment depth. Compared to pre-punched hole decking, through-deck welding specimen activates less plastic hinges in the studs because of the higher stiffness provided at the base of the stud.The RFCS project “DISCCO” was supported by the grant agreement number RFSR-CT-2012-00030. Further, the authors gratefully acknowledge the support of ArcelorMittal Global R&D, Long Products Luxembourg.Vigneri, V.; Odenbreit, C.; Braun, M. (2018). Numerical evaluation of the plastic hinges developed in headed stud shear connectors in composite beams with profiled steel sheeting. En Proceedings of the 12th International Conference on Advances in Steel-Concrete Composite Structures. ASCCS 2018. Editorial Universitat Politècnica de València. 229-236. https://doi.org/10.4995/ASCCS2018.2018.7166OCS22923

Implementation Study of Two Verifiable Delay Functions

Proof of Work is a prevalent mechanism to prove investment of time in blockchain projects. However, the use of massive parallelism and specialized hardware gives an unfair advantage to a small portion of nodes and raises environmental and economical concerns. In this paper, we provide an implementation study of two Verifiable Delay Functions, a new cryptographic primitive achieving Proof of Work goals in an unparallelizable way. We provide simulation results and an optimization based on a multiexponentiation algorithm

Preventing Denial of Service Attacks in IoT Networks through Verifiable Delay Functions

Permissionless distributed ledgers provide a promising approach to deal with the Internet of Things (IoT) paradigm. Since IoT devices mostly generate data transactions and micropayments, distributed ledgers that use fees to regulate the network access are not an optimal choice. In this paper, we study a feeless architecture developed by IOTA and designed specifically for the IoT. Due to the lack of fees, malicious nodes can exploit this feature to generate an unbounded number of transactions and perform a denial of service attacks. We propose to mitigate these attacks through verifiable delay functions. These functions, which are non-parallelizable, hard to compute, and easy to verify, have been formulated only recently. In our work, we design a denial of service prevention mechanism which addresses network heterogeneity, limited node computational capabilities, and hardware-specific implementation optimizations. Verifiable delay functions have mostly been studied from a theoretical point of view, but little has been done in tangible applications. Hence, this paper can be considered as a pioneer work in the field, since it builds a bridge between this theoretical mathematical framework and a real-world problem