Incommensurate dynamics of resonant breathers in Josephson junction ladders

We present theoretical and experimental studies of resonant localized resistive states in a Josephson junction ladder. These complex breather states are obtained by tuning the breather frequency into the upper band of linear electromagnetic oscillations of the ladder. Their prominent feature is the appearance of resonant steps in the current-voltage (I-V) characteristics. We have found the resonant breather-like states displaying incommensurate dynamics. Numerical simulations show that these incommensurate resonant breathers persist for very low values of damping. Qualitatively similar incommensurate breather states are observed in experiments performed with Nb-based Josephson ladders. We explain the appearance of these states with the help of resonance-induced hysteresis features in the I-V dependence.Comment: 5 pages, 6 figure

Towards Interpretable Deep Learning Models for Knowledge Tracing

As an important technique for modeling the knowledge states of learners, the traditional knowledge tracing (KT) models have been widely used to support intelligent tutoring systems and MOOC platforms. Driven by the fast advancements of deep learning techniques, deep neural network has been recently adopted to design new KT models for achieving better prediction performance. However, the lack of interpretability of these models has painfully impeded their practical applications, as their outputs and working mechanisms suffer from the intransparent decision process and complex inner structures. We thus propose to adopt the post-hoc method to tackle the interpretability issue for deep learning based knowledge tracing (DLKT) models. Specifically, we focus on applying the layer-wise relevance propagation (LRP) method to interpret RNN-based DLKT model by backpropagating the relevance from the model's output layer to its input layer. The experiment results show the feasibility using the LRP method for interpreting the DLKT model's predictions, and partially validate the computed relevance scores from both question level and concept level. We believe it can be a solid step towards fully interpreting the DLKT models and promote their practical applications in the education domain

Intermittency as a universal characteristic of the complete chromosome DNA sequences of eukaryotes: From protozoa to human genomes

Large-scale dynamical properties of complete chromosome DNA sequences of eukaryotes are considered. By the proposed deterministic models with intermittency and symbolic dynamics we describe a wide spectrum of large-scale patterns inherent in these sequences, such as segmental duplications, tandem repeats, and other complex sequence structures. It is shown that the recently discovered gene number balance on the strands is not of random nature, and a complete chromosome DNA sequence exhibits the properties of deterministic chaos.Comment: 4 pages, 5 figure

Labeling of Peroxisomes for Live Cell Imaging in the Filamentous Fungus Ustilago maydis

This is the author accepted manuscript. The final version is available from Humana Press via the DOI in this record.The basidiomycete fungus Ustilago maydis has emerged as a powerful model organism to study fundamental biological processes. U. maydis shares many important features with human cells but provides the technical advantages of yeast. Recently, U. maydis has also been used to investigate fundamental processes in peroxisome biology. Here, we present an efficient yeast recombination-based cloning method to construct and express fluorescent fusion proteins (or conditional mutant protein alleles) which target peroxisomes in the fungus U. maydis. In vivo analysis is pivotal for understanding the underlying mechanisms of organelle motility. We focus on the in vivo labelling of peroxisomes in U. maydis and present approaches to analyze peroxisomal motility.We would like to thank G. Steinberg for his support and the opportunity to publish this method chapter. This work was supported by the Portuguese Foundation for Science and Technology and FEDER/COMPETE (SFRH/BD/73532/2010 to S.C. Guimarães) and CRUP/Treaty of Windsor (ACÇÕES INTEGRADAS 2009, B-33/09 to G. Steinberg and M. Schrader). M. Schrader acknowledges support from the Marie Curie Initial Training Network (ITN) action (FP7-2012 PERFUME-316723)

Multi-photon Rabi oscillations in high spin paramagnetic impurity

We report on multiple photon monochromatic quantum oscillations (Rabi oscillations) observed by pulsed EPR (Electron Paramagnetic Resonance) of Mn$^{2+}$ (S=5/2) impurities in MgO. We find that when the microwave magnetic field is similar or large than the anisotropy splitting, the Rabi oscillations have a spectrum made of many frequencies not predicted by the S=1/2 Rabi model. We show that these new frequencies come from multiple photon coherent manipulation of the multi-level spin impurity. We develop a model based on the crystal field theory and the rotating frame approximation, describing the observed phenomenon with a very good agreement.Comment: International Conference: Resonance in Condensed Matter Altshuler 10

Galaxies at z=4 and the Formation of Population II

We report the discovery of four high-redshift objects (3.3 < z < 4) observed behind the rich cluster CL0939+4713 (Abell 851). One object (DG 433) has a redshift of z=3.3453; the other three objects have redshifts of z\approx 4: A0 at z=3.9819, DG 353 and P1/P2 at z=3.9822. It is possible that all four objects are being lensed in some way by the cluster, DG 433 being weakly sheared, A0 being strongly sheared, and DG 353 and P1/P2 being an image pair of a common source object; detailed modelling of the cluster potential will be necessary to confirm this hypothesis. The weakness of common stellar wind features like N V and especially C IV in the spectra of these objects argues for sub-solar metallicities, at least as low as the SMC. DG 353 and DG 433, which have ground-based colors, are moderately dusty [E_{int}(B-V) < 0.15], similar to other z>3 galaxies. Star formation rates range from 2.5 (7.8) h^{-2} to 22. (78.) h^{-2} M_{\odot}/yr, for q_0=0.5 (0.05), depending on assumptions about gravitational lensing and extinction, also typical of other z>3 galaxies. These objects are tenatively identified as the low-metallicity proto-spheroid clumps that will merge to form the Population II components of today's spheroids.Comment: 16 pages, including 2 PostScript figures. Needs aaspp4.sty (included). Accepted for publication in the Astrophysical Journa

Lateral Strength of Wind Load Bearing Wall Stud-to-track Connection

A common application of cold formed steel in building construction is for wind load bearing steel studs (curtain walls). These wall studs are designed to carry lateral load only, and frame into horizontal steel track members at the top and bottom of the wall assembly. The stud-to-track connection consists of studs framing perpendicularly into the track and are connected with sheet metal screws. The design of the wall stud must include a check of the web crippling capacity at the end reactions. The current design expressions, however, do not apply to the type of bearing in these stud-to-track connections. Reported in this paper are the results and analysis of a collection of end-one-flange web crippling tests of common stud-to-track connections. The analysis shows that there are two failure modes: web crippling of the stud and punch-through of the track flange. Design expressions have been developed to predict the ultimate capacity of the connection based on these two modes of failure. The effects of increasing the gap between the end of the stud and the web of the track, as well as the effects of missing screws in the stud-to-track connection are also discussed