5,124 research outputs found
Are multiphase competition & order-by-disorder the keys to understanding Yb2Ti2O7?
If magnetic frustration is most commonly known for undermining long-range
order, as famously illustrated by spin liquids, the ability of matter to
develop new collective mechanisms in order to fight frustration is no less
fascinating, providing an avenue for the exploration and discovery of
unconventional properties of matter. Here we study an ideal minimal model of
such mechanisms which, incidentally, pertains to the perplexing quantum spin
ice candidate Yb2Ti2O7. Specifically, we explain how thermal and quantum
fluctuations, optimized by order-by-disorder selection, conspire to expand the
stability region of an accidentally degenerate continuous symmetry U(1)
manifold against the classical splayed ferromagnetic ground state that is
displayed by the sister compound Yb2Sn2O7. The resulting competition gives rise
to multiple phase transitions, in striking similitude with recent experiments
on Yb2Ti2O7 [Lhotel et al., Phys. Rev. B 89 224419 (2014)]. Considering the
effective Hamiltonian determined for Yb2Ti2O7, we provide, by combining a gamut
of numerical techniques, compelling evidence that such multiphase competition
is the long-sought missing key to understanding the intrinsic properties of
this material. As a corollary, our work offers a pertinent illustration of the
influence of chemical pressure in rare-earth pyrochlores.Comment: 9 page
Beyond jam sandwiches and cups of tea: An exploration of primary pupils' algorithm‐evaluation strategies
The long-standing debate into the potential benefit of developing mathematical thinking skills through learning to program has been reignited with the widespread introduction of programming in schools across many countries, including England where it is a statutory requirement for all pupils to be taught programming from five years old. Algorithm is introduced early in the English computing curriculum, yet, there is limited knowledge of how young pupils view this concept. This paper explores pupils’ (aged 10-11) understandings of algorithm following their engagement with one year of ScratchMaths (SM), a curriculum designed to develop computational and mathematical thinking skills through learning to program. 181 pupils from six schools undertook a set of written tasks to assess their interpretations and evaluations of different algorithms that solve the same problem, with a subset of these pupils subsequently interviewed to probe their understandings in greater depth. We discuss the different approaches identified, the evaluation criteria they used and the aspects of the concept that pupils found intuitive or challenging, such as simplification and abstraction. The paper ends with some reflections on the implications of the research, concluding with a set of recommendations for pedagogy in developing primary pupils’ algorithmic thinking
Adventures in Bidirectional Programming
Most programs get used in just one direction, from input to output. But sometimes, having computed an output, we need to be able to update this output and then calculate backwards to find a correspondingly updated input. The problem of writing such bidirectional transformations — often called lenses — arises in applications across a multitude of domains and has been attacked from many perspectives [1–12, etc.]. See [13] for a detailed survey
A cnidarian homologue of an insect gustatory receptor functions in developmental body patterning.
Insect gustatory and odorant receptors (GRs and ORs) form a superfamily of novel transmembrane proteins, which are expressed in chemosensory neurons that detect environmental stimuli. Here we identify homologues of GRs (Gustatory receptor-like (Grl) genes) in genomes across Protostomia, Deuterostomia and non-Bilateria. Surprisingly, two Grls in the cnidarian Nematostella vectensis, NvecGrl1 and NvecGrl2, are expressed early in development, in the blastula and gastrula, but not at later stages when a putative chemosensory organ forms. NvecGrl1 transcripts are detected around the aboral pole, considered the equivalent to the head-forming region of Bilateria. Morpholino-mediated knockdown of NvecGrl1 causes developmental patterning defects of this region, leading to animals lacking the apical sensory organ. A deuterostome Grl from the sea urchin Strongylocentrotus purpuratus displays similar patterns of developmental expression. These results reveal an early evolutionary origin of the insect chemosensory receptor family and raise the possibility that their ancestral role was in embryonic development
The intracellular Ca2+-pump inhibitors thapsigargin and cyclopiazonic acid induce stress proteins in mammalian chondrocytes
Spider Optimization: Probing the Systematics of a Large Scale B-Mode Experiment
Spider is a long-duration, balloon-borne polarimeter designed to measure
large scale Cosmic Microwave Background (CMB) polarization with very high
sensitivity and control of systematics. The instrument will map over half the
sky with degree angular resolution in I, Q and U Stokes parameters, in four
frequency bands from 96 to 275 GHz. Spider's ultimate goal is to detect the
primordial gravity wave signal imprinted on the CMB B-mode polarization. One of
the challenges in achieving this goal is the minimization of the contamination
of B-modes by systematic effects. This paper explores a number of instrument
systematics and observing strategies in order to optimize B-mode sensitivity.
This is done by injecting realistic-amplitude, time-varying systematics in a
set of simulated time-streams. Tests of the impact of detector noise
characteristics, pointing jitter, payload pendulations, polarization angle
offsets, beam systematics and receiver gain drifts are shown. Spider's default
observing strategy is to spin continuously in azimuth, with polarization
modulation achieved by either a rapidly spinning half-wave plate or a rapidly
spinning gondola and a slowly stepped half-wave plate. Although the latter is
more susceptible to systematics, results shown here indicate that either mode
of operation can be used by Spider.Comment: 15 pages, 12 figs, version with full resolution figs available here
http://www.astro.caltech.edu/~lgg/spider_front.ht
Design and construction of a carbon fiber gondola for the SPIDER balloon-borne telescope
We introduce the light-weight carbon fiber and aluminum gondola designed for
the SPIDER balloon-borne telescope. SPIDER is designed to measure the
polarization of the Cosmic Microwave Background radiation with unprecedented
sensitivity and control of systematics in search of the imprint of inflation: a
period of exponential expansion in the early Universe. The requirements of this
balloon-borne instrument put tight constrains on the mass budget of the
payload. The SPIDER gondola is designed to house the experiment and guarantee
its operational and structural integrity during its balloon-borne flight, while
using less than 10% of the total mass of the payload. We present a construction
method for the gondola based on carbon fiber reinforced polymer tubes with
aluminum inserts and aluminum multi-tube joints. We describe the validation of
the model through Finite Element Analysis and mechanical tests.Comment: 16 pages, 11 figures. Presented at SPIE Ground-based and Airborne
Telescopes V, June 23, 2014. To be published in Proceedings of SPIE Volume
914
Designing Chatbots for Crises: A Case Study Contrasting Potential and Reality
Chatbots are becoming ubiquitous technologies, and their popularity and adoption are rapidly spreading. The potential of chatbots in engaging people with digital services is fully recognised. However, the reputation of this technology with regards to usefulness and real impact remains rather questionable. Studies that evaluate how people perceive and utilise chatbots are generally lacking. During the last Kenyan elections, we deployed a chatbot on Facebook Messenger to help people submit reports of violence and misconduct experienced in the polling stations. Even though the chatbot was visited by more than 3,000 times, there was a clear mismatch between the users’ perception of the technology and its design. In this paper, we analyse the user interactions and content generated through this application and discuss the challenges and directions for designing more effective chatbots
Designing for learning mathematics through programming: A case study of pupils engaging with place value
This paper focuses on a major part of a two-year intervention, ScratchMaths (SM), which seeks to exploit programming for the learning of mathematics. The SM hypothesis is that given the right design of curriculum, pedagogy and digital tools, pupils can engage with and express important mathematical ideas through computer programming. We describe the overall design of SM and as an illustration of the approach, we elaborate a more detailed description of the specific SM activities that seek to harness the programming concept of ‘objects communicating with one another’ for the exploration of the mathematical concept of place value through a syntonic approach to learning. We report a case study of how these activities were implemented in two primary classes. Our findings constitute a kind of existence theorem: that with carefully designed and sequenced learning activities and appropriate teacher support, this approach can allow pupils to engage with difficult mathematical ideas in new, meaningful and generalisable ways. We also point to the challenges which emerged through this process in ensuring pupils encounter these mathematical ideas
- …