Quantum criticality in Yb(Rh0.97Co0.03)2Si2 probed by low-temperature resistivity

Quantum criticality in Yb(Rh0.97Co0.03)2Si2 is investigated by means of resistivity and magnetoresistance. The partial substitution of Co leads to a stabilization of the magnetism as expected according to the application of chemical pressure for Yb systems. However, the signature of the Kondo-breakdown remains at the same position in the temperature-magnetic field phase diagram compared to stoichiometric YbRh2Si2. As a consequence, the Kondo-breakdown is situated within the antiferromagnetic phase. These results fit well within the global phase diagram under chemical pressure [1].Comment: 4 pages, 4 figures, submitted to ICM/SCES200

Break up of heavy fermions at an antiferromagnetic instability

We present results of high-resolution, low-temperature measurements of the Hall coefficient, thermopower, and specific heat on stoichiometric YbRh2Si2. They support earlier conclusions of an electronic (Kondo-breakdown) quantum critical point concurring with a field induced antiferromagnetic one. We also discuss the detachment of the two instabilities under chemical pressure. Volume compression/expansion (via substituting Rh by Co/Ir) results in a stabilization/weakening of magnetic order. Moderate Ir substitution leads to a non-Fermi-liquid phase, in which the magnetic moments are neither ordered nor screened by the Kondo effect. The so-derived zero-temperature global phase diagram promises future studies to explore the nature of the Kondo breakdown quantum critical point without any interfering magnetism.Comment: minor changes, accepted for publication in JPS

The remarkable robustness of surrogate gradient learning for instilling complex function in spiking neural networks

Brains process information in spiking neural networks. Their intricate connections shape the diverse functions these networks perform. In comparison, the functional capabilities of models of spiking networks are still rudimentary. This shortcoming is mainly due to the lack of insight and practical algorithms to construct the necessary connectivity. Any such algorithm typically attempts to build networks by iteratively reducing the error compared to a desired output. But assigning credit to hidden units in multi-layered spiking networks has remained challenging due to the non-differentiable nonlinearity of spikes. To avoid this issue, one can employ surrogate gradients to discover the required connectivity in spiking network models. However, the choice of a surrogate is not unique, raising the question of how its implementation influences the effectiveness of the method. Here, we use numerical simulations to systematically study how essential design parameters of surrogate gradients impact learning performance on a range of classification problems. We show that surrogate gradient learning is robust to different shapes of underlying surrogate derivatives, but the choice of the derivative’s scale can substantially affect learning performance. When we combine surrogate gradients with a suitable activity regularization technique, robust information processing can be achieved in spiking networks even at the sparse activity limit. Our study provides a systematic account of the remarkable robustness of surrogate gradient learning and serves as a practical guide to model functional spiking neural networks

Jesuit Worldwide Learning Graduations in Kakuma Refugee Camp and Dzaleka Refugee Camp July 2018

In July 2018, Father John Fitzgibbons, S.J. and Father Daniel Hendrickson, S.J., Presidents of Regis and Creighton Universities, respectively, hosted the Graduation Ceremonies at Kakuma Refugee Camp, Kenya and Dzaleka Refugee Camp, Malawi. Fifty students received Diplomas in Liberal Studies during the ceremonies. This article includes a brief description of Jesuit Worldwide Learning precedes Father Fitzgibbons’ speech to the graduates

Predictive Brain Activity Shows Congruent Semantic Specificity in Language Comprehension and Production

Sentence fragments strongly predicting a specific subsequent meaningful word elicit larger preword slow waves, prediction potentials (PPs), than unpredictive contexts. To test the current predictive processing models, 128-channel EEG data were collected from both sexes to examine whether (1) different semantic PPs are elicited in language comprehension and production and (2) whether these PPs originate from the same specific “prediction area(s)” or rather from widely distributed category-specific neuronal circuits reflecting the meaning of the predicted item. Slow waves larger after predictable than unpredictable contexts were present both before subjects heard the sentence-final word in the comprehension experiment and before they pronounced the sentence-final word in the production experiment. Crucially, cortical sources underlying the semantic PP were distributed across several cortical areas and differed between the semantic categories of the expected words. In both production and comprehension, the anticipation of animal words was reflected by sources in posterior visual areas, whereas predictable tool words were preceded by sources in the frontocentral sensorimotor cortex. For both modalities, PP size increased with higher cloze probability, thus further confirming that it reflects semantic prediction, and with shorter latencies with which participants completed sentence fragments. These results sit well with theories viewing distributed semantic category-specific circuits as the mechanistic basis of semantic prediction in the two modalities

Maintenance electroconvulsive therapy for comorbid pharmacotherapy-refractory obsessive-compulsive and schizoaffective disorder

<p>Abstract</p> <p>Objective</p> <p>There is a high comorbidity of schizophrenia and obsessive-compulsory disorder (OCD) associated with more severe symptoms. Standard pharmacotherapy achieve symptom improvement in approximately 60% only.</p> <p>Results</p> <p>We report about a 48-old women treated for depression which developed successively psychotic symptoms (ideas of reference, psychotic worries), negative symptoms (blunted affect, impoverished thinking, difficulties in planning), and obsessive-compulsive symptoms (mainly repeating rituals, avoidance behaviour, collecting and hoarding). She did not respond to combined treatment with neuroleptics and high dose selective serotonin re-uptake inhibitors. She acutely improved during a course of electroconvulsive therapy (ECT) and was maintained on outpatient ECTs fortnightly together with 12 mg sertindol and 45 mg mirtazapine for 42 weeks.</p> <p>Conclusion</p> <p>Maintenance ECT is not an approved therapy in OCD but might be an option in pharmacotherapy refractory cases of comorbid OCD and schizophrenic/schizoaffective disorder.</p

Distance dependence of entanglement generation via a bosonic heat bath

Within a generalized Caldeira-Leggett model we analyze the conditions under which a bosonic heat bath can entangle two microscopic quantum systems at a distance $r$. We find that the attainable entanglement is extremely distance-sensitive. Significant entanglement can only be achieved if the systems are within a {\em microscopic} distance that is of order of the cut-off wavelength $\lambda$ of the system-bath interaction. At larger distances the maximal entanglement is exponentially suppressed with a decay length of order $\lambda$. We conclude that entanglement generation via a heat bath is not suitable for entangling remote objects.Comment: 4 pages, 3 figures, new title, final version to appear in Phys. Rev. Let

D-string on near horizon geometries and infinite conformal symmetry

We show that the symmetries of effective D-string actions in constant dilaton backgrounds are directly related to homothetic motions of the background metric. In presence of such motions, there are infinitely many nonlinearly realized rigid symmetries forming a loop (or loop like) algebra. Near horizon (AdS) D3 and D1+D5 backgrounds are discussed in detail and shown to provide 2d interacting field theories with infinite conformal symmetry.Comment: 5 pages, revtex, no figures; symmetry transformations for BI action added, coupling of D-string to RR 2-form in D1-D5 background corrected; final version, to appear in Phys. Rev. Let

Cognitive features of indirect speech acts

The offer of some cake can be declined by saying “I am on a diet” – an indirect reply. Here, we asked whether certain well-established psychological and conceptual features are linked to the (in)directness of speech acts – an issue unexplored so far. Subjects rated direct and indirect speech acts performed by the same critical linguistic forms in different dialogic contexts. We find that indirect replies were understood with less certainty, were less predictable by, less coherent with and less semantically similar to their context question. These effects were smaller when direct and indirect replies were matched for the type of speech acts for which they were used, compared to when they were not speech act matched. Crucially, all measured cognitive dimensions were strongly associated with each other. These findings suggest that indirectness goes hand-in-hand with a set of cognitive features, which should be taken into account when interpreting experimental findings, including neuroimaging studies of indirectness

Evidence for a Kondo destroying quantum critical point in YbRh2Si2

The heavy-fermion metal YbRh$_{2}$Si$_{2}$ is a weak antiferromagnet below $T_{N} = 0.07$ K. Application of a low magnetic field $B_{c} = 0.06$ T ($\perp c$) is sufficient to continuously suppress the antiferromagnetic (AF) order. Below $T \approx 10$ K, the Sommerfeld coefficient of the electronic specific heat $\gamma(T)$ exhibits a logarithmic divergence. At $T < 0.3$ K, $\gamma(T) \sim T^{-\epsilon}$ ($\epsilon: 0.3 - 0.4$), while the electrical resistivity $\rho(T) = \rho_{0} + aT$ ($\rho_{0}$: residual resistivity). Upon extrapolating finite-$T$ data of transport and thermodynamic quantities to $T = 0$, one observes (i) a vanishing of the "Fermi surface crossover" scale $T^{*}(B)$, (ii) an abrupt jump of the initial Hall coefficient $R_{H}(B)$ and (iii) a violation of the Wiedemann Franz law at $B = B_{c}$, the field-induced quantum critical point (QCP). These observations are interpreted as evidence of a critical destruction of the heavy quasiparticles, i.e., propagating Kondo singlets, at the QCP of this material.Comment: 20 pages, 8 figures, SCES 201