A Reliable and Cost-Efficient Auto-Scaling System for Web Applications Using Heterogeneous Spot Instances

Cloud providers sell their idle capacity on markets through an auction-like mechanism to increase their return on investment. The instances sold in this way are called spot instances. In spite that spot instances are usually 90% cheaper than on-demand instances, they can be terminated by provider when their bidding prices are lower than market prices. Thus, they are largely used to provision fault-tolerant applications only. In this paper, we explore how to utilize spot instances to provision web applications, which are usually considered availability-critical. The idea is to take advantage of differences in price among various types of spot instances to reach both high availability and significant cost saving. We first propose a fault-tolerant model for web applications provisioned by spot instances. Based on that, we devise novel auto-scaling polices for hourly billed cloud markets. We implemented the proposed model and policies both on a simulation testbed for repeatable validation and Amazon EC2. The experiments on the simulation testbed and the real platform against the benchmarks show that the proposed approach can greatly reduce resource cost and still achieve satisfactory Quality of Service (QoS) in terms of response time and availability

Does participatory water management contribute to smallholder incomes? Evidence from Minle County, Gansu Province, P.R. China

Since the early 1990s, the Chinese water sector has undergone an important institutional reform that has shifted major responsibilities in irrigation management from the government toward water users, organized in so-called Water User Associations (WUAs). Such participatory water management is not only assumed to increase water use efficiency, but also to stimulate the incomes of member households. This study aims to provide empirical evidence of the impact of participatory water management on WUA performance and farmer incomes, using data collected for the year 2007 among 317 households and 35 WUAs in Minle County, Gansu Province. We find that having democratically elected leaders has a positive effect on WUA performance, by increasing investment levels and improving canal quality. Participation in decision making, however, has a significant negative impact on canal quality and does not affect other WUA performance indicators. Two aspects of WUA performance, investment levels and financial health, are found to have a positive impact on the farm income of member households, while water use per mu has a significant negative impact on farm incomes. We find evidence that households belonging to better performing WUAs increase their farm incomes at the expense of non-farm income. The resulting net impact of participatory water management on total household income is not significant for the households in our sample

X-ray Timing Observations of PSR J1930+1852 in the Crab-like SNR G54.1+0.3

We present new X-ray timing and spectral observations of PSR J1930+1852, the young energetic pulsar at the center of the non-thermal supernova remnant G54.1+0.3. Using data obtained with the Rossi X-ray Timing Explorer and Chandra X-ray observatories we have derived an updated timing ephemeris of the 136 ms pulsar spanning 6 years. During this interval, however, the period evolution shows significant variability from the best fit constant spin-down rate of $\dot P = 7.5112(6) \times 10^{-13}$ s s$^{-1}$, suggesting strong timing noise and/or glitch activity. The X-ray emission is highly pulsed ($71\pm5$ modulation) and is characterized by an asymmetric, broad profile ($\sim 70$ duty cycle) which is nearly twice the radio width. The spectrum of the pulsed emission is well fitted with an absorbed power law of photon index $\Gamma = 1.2\pm0.2$; this is marginally harder than that of the unpulsed component. The total 2-10 keV flux of the pulsar is $1.7 \times 10^{-12}$ erg cm$^{-2}$ s$^{-1}$. These results confirm PSR J1930+1852 as a typical Crab-like pulsar.Comment: 14 pages with 7 figures included, accepted to Ap

Deducing topology of protein-protein interaction networks from experimentally measured sub-networks.

BackgroundProtein-protein interaction networks are commonly sampled using yeast two hybrid approaches. However, whether topological information reaped from these experimentally-measured sub-networks can be extrapolated to complete protein-protein interaction networks is unclear.ResultsBy analyzing various experimental protein-protein interaction datasets, we found that they are not random samples of the parent networks. Based on the experimental bait-prey behaviors, our computer simulations show that these non-random sampling features may affect the topological information. We tested the hypothesis that a core sub-network exists within the experimentally sampled network that better maintains the topological characteristics of the parent protein-protein interaction network. We developed a method to filter the experimentally sampled network to result in a core sub-network that more accurately reflects the topology of the parent network. These findings have fundamental implications for large-scale protein interaction studies and for our understanding of the behavior of cellular networks.ConclusionThe topological information from experimental measured networks network as is may not be the correct source for topological information about the parent protein-protein interaction network. We define a core sub-network that more accurately reflects the topology of the parent network

Environmental Monitoring in Preparation for the Installation of a Green Roof

Green roofs are becoming an increasingly popular way to improve the environmental, economic, and aesthetic performance of both new and existing buildings. Along with the green roofs themselves, it is also common to install sensors to measure various environmental parameters that are affected by or important to the operation of the roof such as precipitation, temperature, and runoff. However, for most of these systems, the sensors are installed at the same time or even after the green roof. Therefore, no before-and-after comparisons can be made for those roofs. To account for this missing data, monitoring equipment was installed on a Purdue University campus building to measure existing conditions for the year prior to the expected construction of a green roof. This equipment currently includes a weather station, along with runoff, heat flux, and temperature sensors, and there are plans to monitor air quality as well. Preliminary findings from values recorded thus far appear to validate the expected behavior of the roof. Stormwater runoff directly correlates to rainfall, and roof temperature is dependent on ambient air temperature and solar radiation. Data from the heat flux sensors, however, is not yet fully explained. This ongoing experiment should see significant changes in the data once the green roof is installed, but until that time, it will continue to serve its role as the control setup for measuring the performance of a standard roof