Controlled self-assembly of periodic and aperiodic cluster crystals

Soft particles are known to overlap and form stable clusters that self-assemble into periodic crystalline phases with density-independent lattice constants. We use molecular dynamics simulations in two dimensions to demonstrate that, through a judicious design of an isotropic pair potential, one can control the ordering of the clusters and generate a variety of phases, including decagonal and dodecagonal quasicrystals. Our results confirm analytical predictions based on a mean-field approximation, providing insight into the stabilization of quasicrystals in soft macromolecular systems, and suggesting a practical approach for their controlled self-assembly in laboratory realizations using synthesized soft-matter particles.Comment: Supplemental Material can be obtained through the author's website at: http://www.tau.ac.il/~ronlif/pubs/ClusterCrystals-Supp.pd

Phosphorylation of Cdc5 regulates its accumulation

<p>Abstract</p> <p>Background</p> <p>Cdc5 (polo kinase/Plk1) is a highly conserved key regulator of the <it>S. cerevisiae </it>cell cycle from S-phase until cytokinesis. However, much of the regulatory mechanisms that govern Cdc5 remain to be determined. Cdc5 is phosphorylated on up to 10 sites during mitosis. In this study, we investigated the function of phosphorylation site T23, the only full consensus Cdk1 (Cdc28) phosphorylation site present.</p> <p>Findings</p> <p><it>Cdc5^T23A</it>introduces a degron that reduces its cellular amount to undetectable levels, which are nevertheless sufficient for normal cell proliferation. The degron acts <it>in cis </it>and is reversed by N-terminal GFP-tagging. Cdk1 kinase activity is required to maintain Cdc5 levels during G2. This, Cdk1 inhibited, Cdc5 degradation is APC/C^Cdh1independent and requires new protein synthesis. Cdc5^T23Eis hyperactive, and reduces the levels of Cdc5 (<it>in trans</it>) and drastically reduces Clb2 levels.</p> <p>Conclusions</p> <p>Phosphorylation of Cdc5 by Cdk1 is required to maintain Cdc5 levels during G2. However, phosphorylation of T23 (probably by Cdk1) caps Cdc5 and other <it>CLB2 </it>cluster protein accumulation, preventing potential protein toxicity, which may arise from their overexpression or from APC/C^Cdh1inactivation.</p

Israel and the Palestinian Dilemma: Strengthening the Palestinian Authority or Containing Hamas

In the reality of the zero-sum game between Hamas and the Palestinian Authority (PA), a strong Hamas and a strong PA cannot coexist. The weakness of the PA alongside a strengthened Hamas, compounded by the erosion of deterrence against Hezbollah and Iran and the increased likelihood of a multi-front conflict, poses a strategic dilemma for Israel. Israel must define its strategic goal vis-à-vis the Palestinian arena, and consider whether there is any value to a formative military move against Hamas that is not part of a broader political plan. Weakened military capabilities would significantly reduce the challenge Hamas poses to the PA that accelerates its weakening, and remove an obstacle to effective moves to strengthen the PA. A weakened Hamas would also loosen the Gordian knot between the various arenas that Hamas seeks to tighten, and presumably also strengthen Israeli deterrence in the region. Under the existing political conditions, the current Israeli government is unlikely to agree on the need to strengthen the PA, or at least stop weakening it. Therefore, the government does not face a strategic dilemma on taking proactive steps to strengthen the PA, even though the PA's weakness harms Israeli interests: a move of this magnitude can only be led by a national unity government with broad public backing. At the same time, the status of the Palestinian Authority is so shaky and problematic that it is doubtful it can be restored under the existing conditions

Discovering students’ learning strategies in a visual programming MOOC through process mining techniques

Funding: This work was supported by the Medical Research Council [grant number MR/N013166/1].Understanding students’ learning patterns is key for supporting their learning experience and improving course design. However, this is particularly challenging in courses with large cohorts, which might contain diverse students that exhibit a wide range of behaviours. In this study, we employed a previously developed method, which considers process flow, sequence, and frequency of learning actions, for detecting students’ learning tactics and strategies. With the aim of demonstrating its applicability to a new learning context, we applied the method to a large-scale online visual programming course. Four low-level learning tactics were identified, ranging from project- and video-focused to explorative. Our results also indicate that some students employed all four tactics, some used course assessments to strategize about how to study, while others selected only two or three of all learning tactics. This research demonstrates the applicability and usefulness of process mining for discovering meaningful and distinguishable learning strategies in large courses with thousands of learners.Publisher PD

Early prediction of student performance in a health data science MOOC

Funding: This work was supported by the Medical Research Council [grant number MR/N013166/1].Massive Open Online Courses (MOOCs) make high-quality learning accessible to students from all over the world. On the other hand, they are known to exhibit low student performance and high dropout rates. Early prediction of student performance in MOOCs can help teachers intervene in time in order to improve learners' future performance. This is particularly important in healthcare courses, given the acute shortages of healthcare staff and the urgent need to train data-literate experts in the healthcare field. In this paper, we analysed a health data science MOOC taken by over 3,000 students. We developed a novel three-step pipeline to predict student performance in the early stages of the course. In the first step, we inferred the transitions between students' low-level actions from their clickstream interactions. In the second step, the transitions were fed into Artificial Neural Network (ANN) that predicted student performance. In the final step, we used two explanation methods to interpret the ANN result. Using this approach, we were able to predict learners' final performance in the course with an AUC ranging from 83% to 91%. We found that students who interacted predominately with lab, project, and discussion materials outperformed students who interacted predominately with lectures and quizzes. We used the DiCE counterfactual method to automatically suggest simple changes to the learning behaviour of low- and moderate-performance students in the course that could potentially improve their performance. Our method can be used by instructors to help identify and support struggling students during the course.Publisher PD

Origin and evolution of the octoploid strawberry genome.

Cultivated strawberry emerged from the hybridization of two wild octoploid species, both descendants from the merger of four diploid progenitor species into a single nucleus more than 1 million years ago. Here we report a near-complete chromosome-scale assembly for cultivated octoploid strawberry (Fragaria × ananassa) and uncovered the origin and evolutionary processes that shaped this complex allopolyploid. We identified the extant relatives of each diploid progenitor species and provide support for the North American origin of octoploid strawberry. We examined the dynamics among the four subgenomes in octoploid strawberry and uncovered the presence of a single dominant subgenome with significantly greater gene content, gene expression abundance, and biased exchanges between homoeologous chromosomes, as compared with the other subgenomes. Pathway analysis showed that certain metabolomic and disease-resistance traits are largely controlled by the dominant subgenome. These findings and the reference genome should serve as a powerful platform for future evolutionary studies and enable molecular breeding in strawberry

Multi-input synapses, but not LTP-strengthened synapses, correlate with hippocampal memory storage in aged mice

Long-lasting changes at synapses enable memory storage in the brain. Although aging is associated with impaired memory formation, it is not known whether the synaptic underpinnings of memory storage differ with age. Using a training schedule that results in the same behavioral memory formation in young and aged mice, we examined synapse ultrastructure and molecular signaling in hippocampus after contextual fear conditioning. Only in young, but not old mice contextual fear memory formation was associated with synaptic changes that characterize well-known long-term potentiation,a strengthening of existing synapses with one input. Instead old age memory was correlated with generation of multi-innervated dendritic spines (MIS), which are predominantly two-input synapses formed by the attraction of an additional excitatory, presynaptic terminal onto an existing synapse. Accordingly, a blocker used to inhibit MIS generation impaired contextual fear memory only in old mice. Our results reveal how the synaptic basis of hippocampal memory storage changes with age and they suggest that these distinct memory-storing mechanisms may explain impaired updating in old age