Stereodivergent, Diels-Alder-initiated organocascades employing α,β-unsaturated acylammonium salts: scope, mechanism, and application.

Chiral α,β-unsaturated acylammonium salts are novel dienophiles enabling enantioselective Diels-Alder-lactonization (DAL) organocascades leading to cis- and trans-fused, bicyclic γ- and δ-lactones from readily prepared dienes, commodity acid chlorides, and a chiral isothiourea organocatalyst under mild conditions. We describe extensions of stereodivergent DAL organocascades to other racemic dienes bearing pendant secondary and tertiary alcohols, and application to a formal synthesis of (+)-dihydrocompactin is described. A combined experimental and computational investigation of unsaturated acylammonium salt formation and the entire DAL organocascade pathway provide a rationalization of the effect of Brønsted base additives and enabled a controllable, diastereodivergent DAL process leading to a full complement of possible stereoisomeric products. Evaluation of free energy and enthalpy barriers in conjunction with experimentally observed temperature effects revealed that the DAL is a rare case of an entropy-controlled diastereoselective process. NMR analysis of diene alcohol-Brønsted base interactions and computational studies provide a plausible explanation of observed stabilization of exo transition-state structures through hydrogen-bonding effects

A Spectral Algorithm for Latent Dirichlet Allocation

The problem of topic modeling can be seen as a generalization of the clustering problem, in that it posits that observations are generated due to multiple latent factors (e.g., the words in each document are generated as a mixture of several active topics, as opposed to just one). This increased representational power comes at the cost of a more challenging unsupervised learning problem of estimating the topic probability vectors (the distributions over words for each topic), when only the words are observed and the corresponding topics are hidden. We provide a simple and efficient learning procedure that is guaranteed to recover the parameters for a wide class of mixture models, including the popular latent Dirichlet allocation (LDA) model. For LDA, the procedure correctly recovers both the topic probability vectors and the prior over the topics, using only trigram statistics (i.e., third order moments, which may be estimated with documents containing just three words). The method, termed Excess Correlation Analysis (ECA), is based on a spectral decomposition of low order moments (third and fourth order) via two singular value decompositions (SVDs). Moreover, the algorithm is scalable since the SVD operations are carried out on $k\times k$ matrices, where $k$ is the number of latent factors (e.g. the number of topics), rather than in the $d$-dimensional observed space (typically $d \gg k$).Comment: Changed title to match conference version, which appears in Advances in Neural Information Processing Systems 25, 201

Potential Economic Effects of Post-CRP Land Management in Southwest North Dakota

The uncertain future of the Conservation Reserve Program has created substantial interest for agricultural producers, rural businesses, community leaders, sportsmen, and wildlife organizations. Many regions of the upper Great Plains have participated heavily in the CRP as evidenced by program acreage reaching land enrollment limits; however, current enrollment and re-enrollment criterion are expected to substantially reduce CRP acreage in many parts of the Great Plains. The divergence of interests between pursing post-CRP lands for agricultural production versus retaining the wildlife habitat and wildlife populations supported on CRP lands presents land owners and agricultural producers with important land management decisions over the next several years. This research examines the regional economic implications of post-CRP land use among traditional agricultural uses, wildlife production, and multiple-use practices. Of particular interest is whether multiple-use management on post-CRP lands can produce similar returns to landowners and producers as traditional land uses, and determine the effects of multiple-use management on post-CRP lands on regional economic output. A multiple-use system implemented on post-CRP lands based primarily on beef grazing while producing corn and barley for forage and retaining a portion of acreage in dedicated wildlife habitat would not compete economically with other conventional land uses. The net change in gross receipts within the regional economy from agricultural uses of post-CRP lands exceeded lost recreational expenditures in all scenarios evaluated.North Dakota, Conservation Reserve Program, Recreation, Agriculture, Land Management, Environmental Economics and Policy, Land Economics/Use,

Interviews with the Apollo lunar surface astronauts in support of planning for EVA systems design

Focused interviews were conducted with the Apollo astronauts who landed on the moon. The purpose of these interviews was to help define extravehicular activity (EVA) system requirements for future lunar and planetary missions.RTOP 199-06-1

Estimation of Farm-Forward Regional Economic Impacts for the North Plains Groundwater Conservation District in Texas

Impacts of alternative agricultural water conservation strategies are being evaluated in the Texas Panhandle. Stakeholders have expressed concern that all effects need to be accounted for including the regional economy. A methodology was developed to evaluate the effects on the backward and forward-linked processing sectors and differentiated results are presented.backward-linked, forward-linked, IMPLAN, Ogallala Aquifer, water policy, Resource /Energy Economics and Policy, Q18, Q32, Q38,

The Dependence of Growth-Model Results on Proficiency Cut Scores

States participating in the Growth Model Pilot Program reference individual student growth against “proficiency” cut scores that conform with the original No Child Left Behind Act (NCLB). Although achievement results from conventional NCLB models are also cut-score dependent, the functional relationships between cut-score location and growth results are more complex and are not currently well described. We apply cut-score scenarios to longitudinal data to demonstrate the dependence of state- and school-level growth results on cut-score choice. This dependence is examined along three dimensions: 1) rigor, as states set cut scores largely at their discretion, 2) across-grade articulation, as the rigor of proficiency standards may vary across grades, and 3) the time horizon chosen for growth to proficiency. Results show that the selection of plausible alternative cut scores within a growth model can change the percentage of students “on track to proficiency” by more than 20 percentage points and reverse accountability decisions for more than 40% of schools. We contribute a framework for predicting these dependencies, and we argue that the cut-score dependence of large-scale growth statistics must be made transparent, particularly for comparisons of growth results across states

Testing the Drosophila maternal haploid gene for functional divergence and a role in hybrid incompatibility

Crosses between Drosophila simulans females and Drosophila melanogaster males produce viable F1 sons and poorly viable F1 daughters. Unlike most hybrid incompatibilities, this hybrid incompatibility violates Haldane’s rule, the observation that incompatibilities preferentially affect the heterogametic sex. Furthermore, it has a different genetic basis than hybrid lethality in the reciprocal cross, with the causal allele in Drosophila melanogaster being a large species-specific block of complex satellite DNA on its X chromosome known as the 359-bp satellite, rather than a protein-coding locus. The causal allele(s) in Drosophila simulans are unknown but likely involve maternally expressed genes or factors since the F1 females die during early embryogenesis. The maternal haploid (mh) gene is an intriguing candidate because it is expressed maternally and its protein product localizes to the 359-bp repeat. We found that this gene has diverged extensively between Drosophila melanogaster and Drosophila simulans. This observation led to the hypothesis that Drosophila melanogaster mh may have coevolved with the 359-bp repeat and that hybrid incompatibility thus results from the absence of a coevolved mh allele in Drosophila simulans. We tested for the functional divergence of mh by creating matched transformants of Drosophila melanogaster and Drosophila simulans orthologs in both Drosophila melanogaster and Drosophila simulans strains. Surprisingly, we find that Drosophila simulans mh fully complements the female sterile phenotype of Drosophila melanogaster mh mutations. Contrary to our hypothesis, we find no evidence that adding a Drosophila melanogaster mh gene to Drosophila simulans increases hybrid viability