1,277,301 research outputs found
Information Bottlenecks, Causal States, and Statistical Relevance Bases: How to Represent Relevant Information in Memoryless Transduction
Discovering relevant, but possibly hidden, variables is a key step in
constructing useful and predictive theories about the natural world. This brief
note explains the connections between three approaches to this problem: the
recently introduced information-bottleneck method, the computational mechanics
approach to inferring optimal models, and Salmon's statistical relevance basis.Comment: 3 pages, no figures, submitted to PRE as a "brief report". Revision:
added an acknowledgements section originally omitted by a LaTeX bu
Bulk and boundary factorized S-matrices
We investigate the -invariant bulk (1+1D, factorized) -matrix
constructed by Ogievetsky, using the bootstrap on the three-point coupling of
the vector multiplet to constrain its CDD ambiguity. We then construct the
corresponding boundary -matrix, demonstrating it to be consistent with
symmetry.Comment: 7 page
Comment on ``Spin Dependent Hopping and Colossal Negative Magnetoresistance in Epitaxial Films in Fields up to 50 T''
Recently Wagner et al. [Phys. Rev. Lett. Vol. 81, P. 3980 (1998)] proposed
that Mott's original model be modified to incorporate a hopping barrier which
depends on the misorientation between the spins of electrons at the initial and
the final states in an elementary process. They further claimed that using the
model they can explain the observed scaling behavior--
negative-magnetoresistivity scaling proportional to the Brillouin function
in the ferromagnetic state and to in the paramagnetic
state. In this comment we argue that the modification needed for Mott's
original model is different from that proposed by Wagner et al. and further
show that our picture will successfully explain the observed scaling in the two
regimes.Comment: 1 pag
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Survival circuits and risk assessment
Risk assessment (RA) behaviour is unusual in the context of survival circuits. An external object elicits eating, mating or fleeing; but conflict between internal approach and withdrawal tendencies elicits RA-specific behaviour that scans the environment for new information to bring closure. Recently rodent and human threat responses have been compared using ‘predators’ that can be real (e.g. a tarantula), robot, virtual, or symbolic (with the last three rendered predatory by the use of shock). ‘Quick and dirty’ survival circuits in the periaqueductal grey, hypothalamus, and amygdala control external RA behaviour. These subcortical circuits activate, and are partially inhibited by, higher-order internal RA processes (anxiety, memory scanning, evaluation and sometimes — maladaptive rumination) in the ventral hippocampus and medial prefrontal cortex
Gene Expression Profile Changes After Short-activating RNA-mediated Induction of Endogenous Pluripotency Factors in Human Mesenchymal Stem Cells
It is now recognized that small noncoding RNA sequences have the ability to mediate transcriptional activation of specific target genes in human cells. Using bioinformatics analysis and functional screening, we screened short-activating RNA (saRNA) oligonucleotides designed to target the promoter regions of the pluripotency reprogramming factors, Kruppel-like factor 4 (KLF4) and c-MYC. We identified KLF4 and c-MYC promoter-targeted saRNA sequences that consistently induced increases in their respective levels of nascent mRNA and protein expression in a time- and dose-dependent manner, as compared with scrambled sequence control oligonucleotides. The functional consequences of saRNA-induced activation of each targeted reprogramming factor were then characterized by comprehensively profiling changes in gene expression by microarray analysis, which revealed significant increases in mRNA levels of their respective downstream pathway genes. Notably, the microarray profile after saRNA-mediated induction of endogenous KLF4 and c-MYC showed similar gene expression patterns for stem cell- and cell cycle-related genes as compared with lentiviral vector-mediated overexpression of exogenous KLF4 and c-MYC transgenes, while divergent gene expression patterns common to viral vector-mediated transgene delivery were also noted. The use of promoter-targeted saRNAs for the activation of pluripotency reprogramming factors could have broad implications for stem cell research
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Behavioural inhibition and valuation of gain/loss are neurally distinct from approach/withdrawal
Gain or omission/termination of loss produces approach; while loss or omission/termination of gain produces withdrawal. Control of approach/withdrawal motivation is distinct from valuation of gain/loss and does not entail learning – making “reward” and “punishment” ambiguous. Approach-withdrawal goal conflict engages a neurally distinct Behavioural Inhibition System, which controls “anxiety” (conflict/passive avoidance) but not “fear” (withdrawal/active avoidance)
Breakdown of Migdal--Eliashberg theory via catastrophic vertex divergence at low phonon frequency
We investigate the applicability of Migdal--Eliashberg (ME) theory by
revisiting Migdal's analysis within the dynamical mean-field theory framework.
First, we compute spectral functions, the quasi-particle weight, the self
energy, renormalised phonon frequency and resistivity curves of the half-filled
Holstein model. We demonstrate how ME theory has a phase-transition-like
instability at intermediate coupling, and how the Engelsberg--Schrieffer (ES)
picture is complicated by low-energy excitations from higher order diagrams
(demonstrating that ES theory is a very weak coupling approach). Through
consideration of the lowest-order vertex correction, we analyse the
applicability of ME theory close to this transition. We find a breakdown of the
theory in the intermediate coupling adiabatic limit due to a divergence in the
vertex function. The region of applicability is mapped out, and it is found
that ME theory is only reliable in the weak coupling adiabatic limit, raising
questions about the accuracy of recent analyses of cuprate superconductors
which do not include vertex corrections.Comment: 19 pages, 10 figures, accepted for publication in Journal of Low
Temperature Physic
Asymptotic enumeration of incidence matrices
We discuss the problem of counting {\em incidence matrices}, i.e. zero-one
matrices with no zero rows or columns. Using different approaches we give three
different proofs for the leading asymptotics for the number of matrices with
ones as . We also give refined results for the asymptotic
number of incidence matrices with ones.Comment: jpconf style files. Presented at the conference "Counting Complexity:
An international workshop on statistical mechanics and combinatorics." In
celebration of Prof. Tony Guttmann's 60th birthda
Manufacturing a thin wire electrostatic trap (TWIST) for ultracold polar molecules
We present a detailed description on how to build a Thin WIre electroStatic
Trap (TWIST) for ultracold polar molecules. It is the first design of an
electrostatic trap that can be superimposed directly onto a magneto optical
trap (MOT). We can thus continuously produce ultracold polar molecules via
photoassociation from a two species MOT and instantaneously trap them in the
TWIST without the need for complex transfer schemes. Despite the spatial
overlap of the TWIST and the MOT, the two traps can be operated and optimized
completely independently due to the complementary nature of the utilized
trapping mechanisms.Comment: 5 pages, 8 figures, updated conten
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