Multi-user Scheduling Schemes for Simultaneous Wireless Information and Power Transfer

In this paper, we study the downlink multi-user scheduling problem for a time-slotted system with simultaneous wireless information and power transfer. In particular, in each time slot, a single user is scheduled to receive information, while the remaining users opportunistically harvest the ambient radio frequency (RF) energy. We devise novel scheduling schemes in which the tradeoff between the users' ergodic capacities and their average amount of harvested energy can be controlled. To this end, we modify two fair scheduling schemes used in information-only transfer systems. First, proportionally fair maximum normalized signal-to-noise ratio (N-SNR) scheduling is modified by scheduling the user having the jth ascendingly ordered (rather than the maximum) N-SNR. We refer to this scheme as order-based N-SNR scheduling. Second, conventional equal-throughput (ET) fair scheduling is modified by scheduling the user having the minimum moving average throughput among the set of users whose N-SNR orders fall into a certain set of allowed orders Sa (rather than the set of all users). We refer to this scheme as order-based ET scheduling. The feasibility conditions required for the users to achieve ET with this scheme are also derived. We show that the smaller the selection order j for the order-based N-SNR scheme, and the lower the orders in Sa for the order-based ET scheme, the higher the average amount of energy harvested by the users at the expense of a reduction in their ergodic capacities. We analyze the performance of the considered scheduling schemes for independent and non-identically distributed (i.n.d.) Ricean fading channels, and provide closed-form results for the special case of i.n.d. Rayleigh fading.Comment: 6 pages, 3 figures. Submitted for possible conference publicatio

Trade and Geography in the Economic Origins of Islam: Theory and Evidence

This research examines the economic origins of Islam and uncovers two empirical regularities. First, Muslim countries, virtual countries and ethnic groups, exhibit highly unequal regional agricultural endowments. Second, Muslim adherence is systematically larger along the pre-Islamic trade routes in the Old World. The theory argues that this particular type of geography (i) determined the economic aspects of the religious doctrine upon which Islam was formed, and (ii) shaped its subsequent economic performance. It suggests that the unequal distribution of land endowments conferred differential gains from trade across regions, fostering predatory behavior from the poorly endowed ones. In such an environment it was mutually bene.cial to institute a system of income redistribution. However, a higher propensity to save by the rich would exacerbate wealth inequality rendering redistribution unsustainable, leading to the demise of the Islamic unity. Consequently, income inequality had to remain within limits for Islam to persist. This was instituted via restrictions on physical capital accumulation. Such rules rendered the investments on public goods, through religious endowments, increasingly attractive. As a result, capital accumulation remained low and wealth inequality bounded. Geography and trade shaped the set of economically relevant religious principles of Islam affecting its economic trajectory in the preindustrial world.

Historical legacies and African development

As Africa’s role on the global stage is rising, so does the need to understand the shadow of history on the continent’s economy and polity. We discuss recent works that shed light on Africa’s colonial and precolonial legacies. The emerging corpus is remarkably interdisciplinary. Archives, ethnographic materials, georeferenced censuses, surveys, and satellite imagery are some of the sources often combined to test influential conjectures put forward in African historiography. Exploiting within-country variation and employing credible, albeit mostly local, identification techniques, this recent literature has uncovered strong evidence of historical continuity as well as instances of rupture in the evolution of the African economy. The exposition proceeds in reverse chronological order. Starting from the colonial period, which has been linked to almost all of Africa’s postindependence maladies, we first review works that uncover the lasting legacies of colonial investments in infrastructure and human capital and quantify the role of various extractive institutions, such as indirect rule and oppression associated with concessionary agreements. Second, we discuss the long-lasting impact of the "Scramble for Africa," which led to ethnic partitioning and the creation of artificial modern states. Third, we cover studies on the multifaceted legacy of the slave trades. Fourth, we analyze the contemporary role of various precolonial, ethnic-specific, institutional and social traits, such as political centralization. We conclude by offering some thoughts on what we view as open questions

Evolution of antimicrobial prophylaxis in cardiovascular surgery

Objective: To examine the optimal duration of antibiotic prophylaxis in major cardiovascular surgery. Methods: In the past 15 years, four prospective randomized, controlled studies, conducted by the same group of authors, compared seven prophylactic antimicrobial regimens in 2970 patients undergoing major cardiovascular surgery. In 1980/81, a 4-day cefazolin (CFZ) prophylaxis was compared with a 2-day cefuroxime (CFX) administration (n=566). In 1982/83, a 2-day CFX prophylaxis was compared with a two shot ceftriaxone (CRO) prophylaxis (n=512). In 1984/87, a 1-day CFZ prophylaxis was compared with a single shot prophylaxis of CRO (n=883). In 1994/1995, a 4 day combination of amoxicillin (AM) and netilmicin (NET) prophylaxis was compared with a single shot prophylaxis of CFX (n=1009). Results: Total infection rate varied between 4.5 and 5.7%, despite different antimicrobial regimen used and their varying duration. Wound infection rate was 1.1% (range 0.4-2.5%), sepsis rate was 0.8% (range 0.4-1.6%), pneumonia rate 2% (0.7-2.9%), urinary tract infection rate 0.4% (range 0-1.4%), and central venous catheter-related infection rate was 0.4% (0-1%). The 30-day mortality rate was 1.3% (range 0.4-2%). All these differences were not statistically significant. Conclusions: A low infection rate (range 4.5-5.7%) occurred despite changes in duration of various prophylactic antibiotic regimen with cephalosporins of first, second or third generation. As a single shot prophylaxis could nowadays successfully be used in cardiovascular surgery, no postoperative antibiotics should be used, unless an intraoperative or a postoperative infection is documented or in presence of major perioperative complication