Stack- and Queue-like Dynamics in Recurrent Neural Networks

What dynamics do simple recurrent networks (SRNs) develop to represent stack-like and queue-like memories? SRNs have been widely used as models in cognitive science. However, they are interesting in their own right as non-symbolic computing devices from the viewpoints of analogue computing and dynamical systems theory. In this paper, SRNs are trained oil two prototypical formal languages with recursive structures that need stack-like or queue-like memories for processing, respectively. The evolved dynamics are analysed, then interpreted in terms of simple dynamical systems, and the different ease with which SRNs aquire them is related to the properties of these simple dynamical Within the dynamical systems framework, it is concluded that the stack-like language is simpler than the queue-like language, without making use of arguments from symbolic computation theory

New Relations for Three-Dimensional Supersymmetric Scattering Amplitudes

We provide evidence for a duality between color and kinematics in three-dimensional supersymmetric Chern-Simons matter theories. We show that the six-point amplitude in the maximally supersymmetric, N=8, theory can be arranged so that the kinematic factors satisfy the fundamental identity of three-algebras. We further show that the four- and six-point N=8 amplitudes can be "squared" into the amplitudes of N=16 three-dimensional supergravity, thus providing evidence for a hidden three-algebra structure in the dynamics of the supergravity.Comment: 8 pages, 2 figure

Differentiation of multipotent vascular stem cells contributes to vascular diseases.

It is generally accepted that the de-differentiation of smooth muscle cells, from the contractile to the proliferative/synthetic phenotype, has an important role during vascular remodelling and diseases. Here we provide evidence that challenges this theory. We identify a new type of stem cell in the blood vessel wall, named multipotent vascular stem cells. Multipotent vascular stem cells express markers, including Sox17, Sox10 and S100β, are cloneable, have telomerase activity, and can differentiate into neural cells and mesenchymal stem cell-like cells that subsequently differentiate into smooth muscle cells. On the other hand, we perform lineage tracing with smooth muscle myosin heavy chain as a marker and find that multipotent vascular stem cells and proliferative or synthetic smooth muscle cells do not arise from the de-differentiation of mature smooth muscle cells. In response to vascular injuries, multipotent vascular stem cells, instead of smooth muscle cells, become proliferative, and differentiate into smooth muscle cells and chondrogenic cells, thus contributing to vascular remodelling and neointimal hyperplasia. These findings support a new hypothesis that the differentiation of multipotent vascular stem cells, rather than the de-differentiation of smooth muscle cells, contributes to vascular remodelling and diseases

Sox10+ adult stem cells contribute to biomaterial encapsulation and microvascularization.

Implanted biomaterials and biomedical devices generally induce foreign body reaction and end up with encapsulation by a dense avascular fibrous layer enriched in extracellular matrix. Fibroblasts/myofibroblasts are thought to be the major cell type involved in encapsulation, but it is unclear whether and how stem cells contribute to this process. Here we show, for the first time, that Sox10+ adult stem cells contribute to both encapsulation and microvessel formation. Sox10+ adult stem cells were found sparsely in the stroma of subcutaneous loose connective tissues. Upon subcutaneous biomaterial implantation, Sox10+ stem cells were activated and recruited to the biomaterial scaffold, and differentiated into fibroblasts and then myofibroblasts. This differentiation process from Sox10+ stem cells to myofibroblasts could be recapitulated in vitro. On the other hand, Sox10+ stem cells could differentiate into perivascular cells to stabilize newly formed microvessels. Sox10+ stem cells and endothelial cells in three-dimensional co-culture self-assembled into microvessels, and platelet-derived growth factor had chemotactic effect on Sox10+ stem cells. Transplanted Sox10+ stem cells differentiated into smooth muscle cells to stabilize functional microvessels. These findings demonstrate the critical role of adult stem cells in tissue remodeling and unravel the complexity of stem cell fate determination

Ubiquitin Ligases of the N-End Rule Pathway: Assessment of Mutations in UBR1 That Cause the Johanson-Blizzard Syndrome

Background: Johanson-Blizzard syndrome (JBS; OMIM 243800) is an autosomal recessive disorder that includes congenital exocrine pancreatic insufficiency, facial dysmorphism with the characteristic nasal wing hypoplasia, multiple malformations, and frequent mental retardation. Our previous work has shown that JBS is caused by mutations in human UBR1, which encodes one of the E3 ubiquitin ligases of the N-end rule pathway. The N-end rule relates the regulation of the in vivo half-life of a protein to the identity of its N-terminal residue. One class of degradation signals (degrons) recognized by UBR1 are destabilizing N-terminal residues of protein substrates. Methodology/Principal Findings: Most JBS-causing alterations of UBR1 are nonsense, frameshift or splice-site mutations that abolish UBR1 activity. We report here missense mutations of human UBR1 in patients with milder variants of JBS. These single-residue changes, including a previously reported missense mutation, involve positions in the RING-H2 and UBR domains of UBR1 that are conserved among eukaryotes. Taking advantage of this conservation, we constructed alleles of the yeast Saccharomyces cerevisiae UBR1 that were counterparts of missense JBS-UBR1 alleles. Among these yeast Ubr1 mutants, one of them (H160R) was inactive in yeast-based activity assays, the other one (Q1224E) had a detectable but weak activity, and the third one (V146L) exhibited a decreased but significant activity, in agreement with manifestations of JBS in the corresponding JBS patients. Conclusions/Significance: These results, made possible by modeling defects of a human ubiquitin ligase in its yeast counterpart, verified and confirmed the relevance of specific missense UBR1 alleles to JBS, and suggested that a residual activity of a missense allele is causally associated with milder variants of JBS

Contextual Illusions Reveal the Limit of Unconscious Visual Processing

The perception of even the most elementary features of the visual environment depends strongly on their spatial context. In the study reported here, we asked at what level of abstraction such effects require conscious processing of the context. We compared two visual illusions that alter subjective judgments of brightness: the simultaneous brightness contrast illusion, in which two circles of identical physical brightness appear different because of different surround luminance, and the Kanizsa triangle illusion, which occurs when the visual system extrapolates a surface without actual physical stimulation. We used a novel interocular masking technique that allowed us to selectively render only the context invisible. Simultaneous brightness contrast persisted even when the surround was masked from awareness. In contrast, participants did not experience illusory contours when the inducing context was masked. Our findings show that invisible context is resolvable by low-level processes involved in surface-brightness perception, but not by high-level processes that assign surface borders through perceptual completion

Functional glass slides for in vitro evaluation of interactions between bone cells and mineral-binding surfaces

Primary amine-functionalized glass slides obtained through a multi-step plasma treatment were conjugated with anionic amino acids that are frequently found as mineral binding elements in acidic extracellular matrix components of natural bone. The modified glass surfaces were characterized by X-ray photoelectron spectroscopy (XPS) and contact angle measurements. Human osteosarcoma TE85 cells were cultured on these functionalized slides and analyses on both protein and gene expression levels were performed to probe the ‘‘biocompatibility’’ of the surface ligands. Cell attachment and proliferation on anionic surfaces were either better than or comparable to those of cells cultured on tissue culture polystyrene (TCPS). The modified glass surfaces promoted the expression of osteocalcin, alkaline phosphatase activity and ECM proteins such as fibronectin and vitronectin under differentiation culture conditions. Transcript analysis using gene chip microarrays confirmed that culturing TE85 cells on anionic surfaces did not activate apoptotic pathways.Collectively, these results suggest that the potential mineral-binding anionic ligands examined here do not exert significant adverse effects on the expression of important osteogenic markers of TE85 cells. This work paves theway for the incorporation of these ligands into 3-dimensional artificial bone-like scaffolds

Toward Better Training in Peer Assessment: Does Calibration Help?

For peer assessments to be helpful, student reviewers need to submit reviews of good quality. This requires certain training or guidance from teaching staff, lest reviewers read each other\u27s work uncritically, and assign good scores but offer few suggestions. One approach to improving the review quality is calibration. Calibration refers to comparing students\u27 individual reviews to a standard—usually a review done by teaching staff on the same reviewed artifact. In this paper, we categorize two modes of calibration for peer assessment and discuss our experience with both of them in a pilot study with Expertiza system