The Effects of Prehydration on Cement Performance

This study investigated the effects of cement prehydration on cement’s engineering properties. Anhydrous cement was exposed over a saturated KCl solution to maintain 85% RH, for 7 and 28 days. Mortar and cement pastes were tested for strength, workability and setting time, with sample analysis by XRD and DTA. Results showed a decreased reactivity of the prehydrated cements resulting in reduced strength and increased setting times. We propose that this may be due to an upset of the sulphate balance in the cement upon prehydration

The Demography and Community Characterization of he Federally Endangered Herb, Trillium Persistens: A Study Across Its Range Including A Fire-Dependent Habitat

Trillium persistens, a federally endangered perennial herb, exists as fragmented populations in Georgia and South Carolina, U.S.A.I quantified the demography of T. persistens across its range and described its associated plant community, including a fire-dependent habitat. To examine the demography of T. persistens, one study site was established in each of four population fragments (Battle Creek, Moccasin Creek, Moody Creek, and Panther Creek) located in and around Tallulah Gorge State Park. At Moody Creek, T. persistens occurs in the threatened, fire-dependent Table Mountain pine ecosystem, dominated by Pinus pungens. To determine whether prescribed fire would impact T. persistens, 40 4-m2 plots containing T. persistens were established, with half receiving early-season prescribed fires in February, 2009. All four sites were censused over the 2009 and 2010 growing seasons to characterize T. persistens population dynamics and the composition of its associated plant community. I used these Census data to construct stage-based demographic matrix models to project population dynamics within each site over 25 years. Projections were determined using a low estimate and high estimate of fecundity. More individuals were found across sites in 2010 compared to 2009, but life stage structure did not differ between years. Fruit set was greater in 2010 compared to 2009 across sites. The associated plant community was variable among sites. Species richness differed significantly, ranging between 0.6-1.9, 0.65-1.8, and 4.2-6.35 species per site for herb, shrub, and tree, respectfully. Projections of T. persistens population size over 25 years based on the matrix models suggest overall decline of T. persistens across its range, with mean λ across sites ranging from 0.84-1.08. While the burn in 2009 did not show negative effects on T. persistens, land managers conducting prescribed burns in the future should use early-season cooler surface fires. Trillium persistens numbers should be monitored post-burn to see if they affect population sizes over time. Across sites, land managers should work to protect life stage transitions with the greatest impact on λ according to site, and monitor recruitment of new individuals

Team Teaching

Team teaching has the potential to have a profound impact on both teaching and learning. Many who have taught as part of a team report the break from solitary practice brings renewed excitement for teaching and the course that makes them better teachers. It also creates a learning environment in which students can explore multiple perspectives and ways of knowing. Of course, along with the benefits come many challenges. This paper shares some of the advice gleaned from those who have written about their team teaching experiences to help others make the most of the opportunity

Experimental Investigation of a Hall-Current Accelerator

The Hall-current accelerator is being investigated for use in the 1000-2000 sec. range of specific impulse. Three models of this thruster were tested. The first two models had three permanent magnets to supply the magnetic field and the third model had six magnets to supply the field. The third model thus had approximately twice the magnetic field of the first two. The first and second models differ only in the shape of the magnetic field. All other factors remained the same for the three models except for the anode-cathode distance, which was changed to allow for the three thrusters to have the same magnetic field integral between the anode and the cathode. These Hall thrusters were tested to determine the plasma properties, the beam characteristics, and the thruster characteristics. The thruster operated in three modes: (1) main cathode only, (2) main cathode with neutralizer cathode, and (3) neutralizer cathode only. The plasma properties were measured along an axial line, 1 mm inside the cathode radius, at a distance of 0.2 to 6.2 cm from the anode. Results show that the current used to heat the cathode produced nonuniformities in the magnetic field, hence also in the plasma properties. In a Hall thruster this general design appears to provide the most thrust when operated at a magnetic field less than the maximum value studied

Can Reading Questions Foster Active Learning? A Study of Six College Courses

Many instructors strive to encourage student reading outside of class and active learning in class. One pedagogical tool, structured reading questions, can help do both. Using examples from question sets across six courses, the authors illustrate how reading questions can help students achieve the six active-learning principles described by Svinicki (1991). Qualitative and quantitative assessment data indicate that students often complete readings before class, that they view the questions as very helpful in their learning, and that they use the questions primarily to help understand what information is important and connect it to prior knowledge. Some differences in use are evident across class standing

Simple Algorithms for Stochastic Score Classification with Small Approximation Ratios

We revisit the Stochastic Score Classification (SSC) problem introduced by Gkenosis et al. (ESA 2018): We are given $n$ tests. Each test $j$ can be conducted at cost $c_j$, and it succeeds independently with probability $p_j$. Further, a partition of the (integer) interval $\{0,\dots,n\}$ into $B$ smaller intervals is known. The goal is to conduct tests so as to determine that interval from the partition in which the number of successful tests lies while minimizing the expected cost. Ghuge et al. (IPCO 2022) recently showed that a polynomial-time constant-factor approximation algorithm exists. We show that interweaving the two strategies that order tests increasingly by their $c_j/p_j$ and $c_j/(1-p_j)$ ratios, respectively, -- as already proposed by Gkensosis et al. for a special case -- yields a small approximation ratio. We also show that the approximation ratio can be slightly decreased from $6$ to $3+2\sqrt{2}\approx 5.828$ by adding in a third strategy that simply orders tests increasingly by their costs. The similar analyses for both algorithms are nontrivial but arguably clean. Finally, we complement the implied upper bound of $3+2\sqrt{2}$ on the adaptivity gap with a lower bound of $3/2$. Since the lower-bound instance is a so-called unit-cost $k$-of-$n$ instance, we settle the adaptivity gap in this case