27Background: High-frequency transcranial random noise stimulation (hf-tRNS) is a 28 neuromodulatory technique consisting of the application of alternating current at random intensities 29 and frequencies. hf-tRNS induces random neural activity in the system that may boost the 30 sensitivity of neurons to weak inputs. Stochastic resonance is a nonlinear phenomenon whereby the 31 addition of an optimal amount of noise results in performance enhancement, whereas further noise 32 increments impair signal detection or discrimination. 33Objective: The aim of the study was to assess whether modulatory effects of hf-tRNS rely on the 34 stochastic resonance phenomenon, and what is the specific neural mechanism producing stochastic 35 resonance. 36Method: Observers performed a two-interval forced choice motion direction discrimination task in 37 which they had to report whether two moving patches presented in two temporal intervals had the 38 same or different motion directions. hf-tRNS was administered at five intensity levels (0.5, 0.75, 39 1.0, 1.5, and 2.25 mA). 40 Results:The results showed a significant improvement in performance when hf-tRNS was applied 41 at 1.5 mA, representing the optimal level of external noise. However, stimulation intensity at 2.25 42 mA significantly impaired direction discrimination performance. An equivalent noise (EN) analysis, 43 used to assess how hf-tRNS modulates the mechanisms underlying global motion processing, 44 showed an increment in motion signal integration with the optimal current intensity, but reduced 45 motion signal integration at 2.25 mA. 46Conclusion: These results indicate that hf-tRNS-induced noise modulates neural signal-to-noise 47 ratio in a way that is compatible with the stochastic resonance phenomenon. 48 49 Keywords: global motion, high-frequency transcranial random noise stimulation, stochastic 50 resonance, internal noise, global sampling 51 52 53Transcranial random noise stimulation (tRNS) is a non-invasive electrical brain stimulation 54 technique characterized by alternating current delivered at random frequencies and intensities. This 55 technique can be applied at its full frequency spectrum between 0.1 Hz and 640 Hz, at the low-56 frequency range between 0.1 Hz and 100 Hz (lf-tRNS), or at the high frequency range (hf-tRNS), 57 between 101-640 Hz [1] . Early studies found that 10 mins of hf-tRNS applied over the primary 58 motor cortex (M1) induced an increment in cortical excitability with after-effects lasting up to 60 59 min [1][2][3][4]. In the last decade, several experimental procedures have been used to assess the effects 60 of tRNS on different cognitive and sensory abilities in order to understand its mechanisms [5]. For 61 example, it has been demonstrated that hf-tRNS improves behavioural performance on visual tasks 62 [6], attenuates visual motion adaptation [7], facilitates facial identity perception [8] and enhances 63 perceptual learning [9-14]. Moreover, five days of training with concomitant hf-tRNS over the 64 bilateral dorsola...

We discuss the existence of inflationary solutions in a class of renormalization group improved polynomial f(R) theories, which have been studied recently in the context of the asymptotic safety scenario for quantum gravity. These theories seem to possess a nontrivial ultraviolet fixed point, where the dimensionful couplings scale according to their canonical dimensionality. Assuming that the cutoff is proportional to the Hubble parameter, we obtain modified Friedmann equations which admit both power-law and exponential solutions. We establish that for sufficiently high-order polynomial the solutions are reliable in the sense that considering still higher-order polynomials is very unlikely to change the solution.

Breast computed tomography (BCT) is an emerging application of X‐ray tomography in radiological practice. A few clinical prototypes are under evaluation in hospitals and new systems are under development aiming at improving spatial and contrast resolution and reducing delivered dose. At the same time, synchrotron‐radiation phase‐contrast mammography has been demonstrated to offer substantial advantages when compared with conventional mammography. At Elettra, the Italian synchrotron radiation facility, a clinical program of phase‐contrast BCT based on the free‐space propagation approach is under development. In this paper, full‐volume breast samples imaged with a beam energy of 32 keV delivering a mean glandular dose of 5 mGy are presented. The whole acquisition setup mimics a clinical study in order to evaluate its feasibility in terms of acquisition time and image quality. Acquisitions are performed using a high‐resolution CdTe photon‐counting detector and the projection data are processed via a phase‐retrieval algorithm. Tomographic reconstructions are compared with conventional mammographic images acquired prior to surgery and with histologic examinations. Results indicate that BCT with monochromatic beam and free‐space propagation phase‐contrast imaging provide relevant three‐dimensional insights of breast morphology at clinically acceptable doses and scan times.

The functional renormalization group equation for projectable Hořava-Lifshitz gravity is used to derive the non-perturbative beta functions for the Newton's constant, cosmological constant and anisotropy parameter. The resulting coupled differential equations are studied in detail and exemplary RG trajectories are constructed numerically. The beta functions possess a non-Gaussian fixed point and a one-parameter family of Gaussian fixed points. One of the Gaussian fixed points corresponds to the Einstein-Hilbert action with vanishing cosmological constant and constitutes a saddle point with one IR-attractive direction. For RG trajectories dragged into this fixed point at low energies diffeomorphism invariance is restored. The emergence of general relativity from Hořava-Lifshitz gravity can thus be understood as a crossover-phenomenon where the IR behavior of the theory is controlled by this Gaussian fixed point. In particular RG trajectories with a tiny positive cosmological constant also come with an anisotropy parameter which is compatible with experimental constraints, providing a mechanism for the approximate restoration of diffeomorphism invariance in the IR. The non-Gaussian fixed point is UV-attractive in all three coupling constants. Most likely, this fixed point is the imprint of Asymptotic Safety at the level of Hořava-Lifshitz gravity.