Mental imagery-induced attention modulates pain perception and cortical excitability

Background Mental imagery is a powerful method of altering brain activity and behavioral outcomes, such as performance of cognition and motor skills. Further, attention and distraction can modulate pain-related neuronal networks and the perception of pain. This exploratory study examined the effects of mental imagery-induced attention on pressure pain threshold and cortical plasticity using transcranial magnetic stimulation (TMS). This blinded, randomized, and parallel-design trial comprised 30 healthy right-handed male subjects. Exploratory statistical analyses were performed using ANOVA and t-tests for pain and TMS assessments. Pearson’s correlation was used to analyze the association between changes in pain threshold and cortical excitability. Results In the analysis of pain outcomes, there was no significant interaction effect on pain between group versus time. In an exploratory analysis, we only observed a significant effect of group for the targeted left hand (ANOVA with pain threshold as the dependent variable and time and group as independent variables). Although there was only a within- group effect of mental imagery on pain, further analyses showed a significant positive correlation of changes in pain threshold and cortical excitability (motor-evoked potentials via TMS). Conclusions Mental imagery has a minor effect on pain modulation in healthy subjects. Its effects appear to differ compared with chronic pain, leading to a small decrease in pain threshold. Assessments of cortical excitability confirmed that these effects are related to the modulation of pain-related cortical circuits. These exploratory findings suggest that neuronal plasticity is influenced by pain and that the mental imagery effects on pain depend on the state of central sensitization

Comparison between cooling strategies for power electronic devices: fractal mini-channels and arrays of impinging submerged jets

Power electronic devices like Insulated Gate Bipolar Transistors (IGBTs) and diodes are often characterized by power densities and dimensions that could result in very high heat flux densities. In order to guarantee the expected performance and lifetime for these components, dedicated active cooling devices are usually adopted. In the present paper, the comparison between two different cooling strategies for power electronics is presented: fractal channel design and submerged impinging jets. Each cooling strategy is tested on two different geometrical configurations. Water is used as coolant in all cases. Assessment of the considered cooling methods is done through application of the selected configurations in a simplified system composed by a rectangular chip (heat source) separated from the coolant by a solid block. Three-dimensional conjugated heat transfer simulations are performed by using RANS solver implemented in OpenFOAM and two-equations turbulence models, resolving also the viscous sublayer. Numerical results allow to compare the cooling strategies in terms of maximum chip temperature, overall chip-to-coolant thermal resistance, and pumping power required. In summary, the fractal-channel design shows limitations in guaranteeing low chip temperatures at an affordable pumping power. The submerged impinging jets approach shows very high local heat transfer coefficient by which it is possible to tailor the cooling expect on specific hot spots

Polarity-Dependent Transcranial Direct Current Stimulation Effects on Central Auditory Processing

Given the polarity dependent effects of transcranial direct current stimulation (tDCS) in facilitating or inhibiting neuronal processing, and tDCS effects on pitch perception, we tested the effects of tDCS on temporal aspects of auditory processing. We aimed to change baseline activity of the auditory cortex using tDCS as to modulate temporal aspects of auditory processing in healthy subjects without hearing impairment. Eleven subjects received 2mA bilateral anodal, cathodal and sham tDCS over auditory cortex in a randomized and counterbalanced order. Subjects were evaluated by the Random Gap Detection Test (RGDT), a test measuring temporal processing abilities in the auditory domain, before and during the stimulation. Statistical analysis revealed a significant interaction effect of time vs. tDCS condition for 4000 Hz and for clicks. Post-hoc tests showed significant differences according to stimulation polarity on RGDT performance: anodal improved 22.5% and cathodal decreased 54.5% subjects' performance, as compared to baseline. For clicks, anodal also increased performance in 29.4% when compared to baseline. tDCS presented polarity-dependent effects on the activity of the auditory cortex, which results in a positive or negative impact in a temporal resolution task performance. These results encourage further studies exploring tDCS in central auditory processing disorders

Neutralization and clearance of GM-CSF by autoantibodies in pulmonary alveolar proteinosis

Pulmonary alveolar proteinosis (PAP) is a severe autoimmune disease caused by autoantibodies that neutralize GM-CSF resulting in impaired function of alveolar macrophages. In this study, we characterize 21 GM-CSF autoantibodies from PAP patients and find that somatic mutations critically determine their specificity for the self-antigen. Individual antibodies only partially neutralize GM-CSF activity using an in vitro bioassay, depending on the experimental conditions, while, when injected in mice together with human GM- CSF, they lead to the accumulation of a large pool of circulating GM-CSF that remains partially bioavailable. In contrast, a combination of three non-cross-competing antibodies completely neutralizes GM-CSF activity in vitro by sequestering the cytokine in high-molecular-weight complexes, and in vivo promotes the rapid degradation of GM-CSF-containing immune complexes in an Fc-dependent manner. Taken together, these findings provide a plausible explanation for the severe phenotype of PAP patients and for the safety of treatments based on single anti-GM-CSF monoclonal antibodies

The application of online transcranial random noise stimulation and perceptual learning in the improvement of visual functions in mild myopia

It has recently been demonstrated how perceptual learning, that is an improvement in a sensory/perceptual task upon practice, can be boosted by concurrent high-frequency transcranial random noise stimulation (tRNS). It has also been shown that perceptual learning can generalize and produce an improvement of visual functions in participants with mild refractive defects. By using three different groups of participants (single-blind study), we tested the efficacy of a short training (8 sessions) using a single Gabor contrast-detection task with concurrent hf-tRNS in comparison with the same training with sham stimulation or hf-tRNS with no concurrent training, in improving visual acuity (VA) and contrast sensitivity (CS) of individuals with uncorrected mild myopia. A short training with a contrast detection task is able to improve VA and CS only if coupled with hf-tRNS, whereas no effect on VA and marginal effects on CS are seen with the sole administration of hf-tRNS. Our results support the idea that, by boosting the rate of perceptual learning via the modulation of neuronal plasticity, hf-tRNS can be successfully used to reduce the duration of the perceptual training and/or to increase its efficacy in producing perceptual learning and generalization to improved VA and CS in individuals with uncorrected mild myopia

Attenuation of N2 amplitude of laser-evoked potentials by theta burst stimulation of primary somatosensory cortex

Theta burst stimulation (TBS) is a special repetitive transcranial magnetic stimulation (rTMS) paradigm, where bursts of low-intensity stimuli are applied in the theta frequency. The aim of this study was to investigate the effect of neuronavigated TBS over primary somatosensory cortex (SI) on laser-evoked potentials (LEPs) and acute pain perception induced with Tm : YAG laser stimulation. The amplitude changes of the N1, N2, and P2 components of LEPs and related subjective pain rating scores of 12 healthy subjects were analyzed prior to and following continuous TBS (cTBS), intermittent TBS (iTBS), intermediate TBS (imTBS), and sham stimulation. Our results demonstrate that all active TBS paradigms significantly diminished the amplitude of the N2 component, when the hand contralateral to the site of TBS was laser-stimulated. Sham stimulation condition had no significant effect. The subjective pain perception also decreased during the experimental sessions, but did not differ significantly from the sham stimulation condition. The main finding of our study is that TBS over SI diminished the amplitude of the N2 component evoked from the contralateral side without any significant analgesic effects. Furthermore, imTBS produced responses similar to those observed by other forms of TBS induced excitability changes in the SI

Preliminary Evidence of “Other-Race Effect”-Like Behavior Induced by Cathodal-tDCS over the Right Occipital Cortex, in the Absence of Overall Effects on Face/Object Processing

Neuromodulation techniques such as tDCS have provided important insight into the neurophysiological mechanisms that mediate cognition. Albeit anodal tDCS (a-tDCS) often enhances cognitive skills, the role of cathodal tDCS (c-tDCS) in visual cognition is largely unexplored and inconclusive. Here, in a single-blind, sham-controlled study, we investigated the offline effects of 1.5 mA c-tDCS over the right occipital cortex of 86 participants on four tasks assessing perception and memory of both faces and objects. Results demonstrated that c-tDCS does not overall affect performance on the four tasks. However, post-hoc exploratory analysis on participants' race (Caucasian vs. non-Caucasians), showed a “face-specific” performance decrease (≈10%) in non-Caucasian participants only. This preliminary evidence suggests that c-tDCS can induce “other-race effect (ORE)-like” behavior in non-Caucasian participants that did not show any ORE before stimulation (and in case of sham stimulation). Our results add relevant information about the breadth of cognitive processes and visual stimuli that can be modulated by c-tDCS, about the design of effective neuromodulation protocols, and have important implications for the potential neurophysiological bases of ORE

Studio numerico di flussi turbolenti in regime di convezione naturale e mista

In questo testo \ue8 riportato un studio degli aspetti termo-fluidodinamici di flussi turbolenti in regime di convezione naturale e mista. La ricerca \ue8 stata condotta mediante simulazioni numeriche da principi primi eseguite in un flusso indotto dalle forze di galleggiamento tra due lastre piane e in uno caratterizzato da tre getti a diversa temperatura. I calcoli sono stati eseguiti impiegando una versione modificata del codice open source Incompact3d, dove le modifiche apportate prevedono l'introduzione del termine di galleggiamento secondo le ipotesi di Boussinesq e l'implementazione di una condizione al contorno di deflusso. Assieme alle modifiche apportate al codice vengono presentate le prove atte a validare le modifiche stesse. La prima parte del testo riporta lo studio del moto all'interno della cella di Rayleigh-B\ue9nard considerando diversi fluidi: mercurio (Pr=0.025), aria (Pr=0.7) ed acqua (Pr=7). Invece di variare il numero Prandtl mantenendo costante il numero di Rayleigh, come spesso riscontrato in letteratura, le tre simulazioni vengono eseguite a pari numero di Grashof, Gr=Ra/Pr=5 x 10^7. Questo approccio permette lo studio dell'influenza del numero di Prandtl conservando un rapporto costante tra il termine advettivo e diffusivo nelle equazioni di bilancio della quantit\ue0 di moto. Attraverso l'analisi delle consuete statistiche e di altre sviluppate appositamente per questo studio vengono caratterizzate le strutture di piccola e grande scala responsabili del trasferimento del calore. In secondo luogo viene analizzata una configurazione composta da tre getti a diversa temperatura che sfociano all'interno di una piscina a forma di parallelepipedo. Oltre all'importanza in ambito di ricerca di base, questo flusso permette di indagare le fluttuazioni di temperatura indotte dal raffreddamento delle barre di combustibile all'interno di reattori nucleari che impiegano un metallo liquido come refrigerante, i cosiddetti ``Liquid Metal Fast Reactors''. Il fenomeno descritto viene chiamato thermal striping e pu\uf2 provocare cedimenti per fatica termica nelle strutture di contenimento. Al fine di analizzare il thermal striping il numero di Prandtl scelto per la simulazione \ue8 Pr=0.031, caratteristico della lega eutettica piombo-bismuto a 220\ub0 C, una tipica condizione prevista per questo tipo di reattori. Il numero di Reynolds del flusso vale Re=5000 e l'intensit\ue0 del regime di convezione mista \ue8 descritta dal numero Richardson Ri=0.25. I risultati mostrano che i getti si mescolano vigorosamente in prossimit\ue0 del loro ingresso, mentre pi\uf9 a valle sono uniti in un'unica colonna di fluido, essenzialmente isoterma. In questa regione il flusso mostra alcune delle caratteristiche universali osservate nella configurazione canonica dei getti turbolenti. Inoltre il fenomeno responsabile dell'unione dei getti, il cosiddetto ``effetto Coand\u103'', viene illustrato in maniera originale attraverso l'analisi dei flussi di quantit\ue0 di moto. Infine, i campi di viscosit\ue0 e diffusivit\ue0 termica turbolenta, assieme alla dissipazione di energia cinetica e varianza di temperatura, mostrano andamenti difficilmente riproducibili mediante i tradizionali modelli di turbolenza basati sull'approccio eddy-viscosity. Riassumendo, questo studio fornisce un punto di vista originale sui meccanismi di trasporto del calore in circostanze in cui le forze di galleggiamento non possono essere trascurate, sia in configurazioni caratterizzate dalla presenza di pareti che in configurazioni prive di superfici solide. I risultati riportati potrebbero inoltre essere impiegati per lo sviluppo e la validazione di modelli di turbolenza specifici.The aim of this work is to investigate turbulent flows and heat transfer phenomena where buoyancy forces are non-negligible. The studies are conducted by means of Direct Numerical Simulations performed in two configurations: a wall-bounded buoyancy-driven flow and a free-shear buoyancy-aided case. Calculations are conducted using a customised version of the open source code Incompact3d, where modifications include the addition of the Boussinesq's buoyancy term in the momentum equations and the implementation of an open outflow boundary condition suitable for buoyant and turbulent flows. In the text each novel implementation is presented together with a validation test. Firstly buoyancy-driven convection is investigated in the Rayleigh-B\ue9nard cell employing different fluids: mercury (Pr=0.025), air (Pr=0.7) and water (Pr=7). Instead of the usual approach, where the Prandtl number is varied in constant-Rayleigh-number conditions, the three simulations are performed at constant Grashof number, Gr=Ra/Pr=5 x 10^7. This procedure allows the study of the Prandtl number influence while maintaining a constant ratio between the advective and diffusive terms in the momentum equations. The analysis of customarily and specifically developed statistics sheds light on the small-scale fluctuations and large-scale motions which are responsible for the energy transfer at different Prandtl numbers. Secondly, a non-canonical configuration which involves three planar jets vertically entering a pool with different temperature is studied. Beside the theoretical interest, this research is motivated by the study of temperature fluctuations induced by fuel rods cooling inside Liquid Metal Fast Reactors (LMFRs), which employ a liquid metal as coolant. This phenomenon is called thermal striping and might induce thermal-fatigue failures in the containment vessels. In order to infer on thermal striping the Prandtl number of Lead-Bismuth Eutectic at 220\ub0 C, i.e. a typical envisaged condition in LMFRs, is considered (Pr=0.031). Reynolds number is set to Re=5000 and the mixed convection regime is established at a Richardson number Ri=0.25. Results show that jets undergo an intense mixing close to their inlets, while at distances larger than ten times the jet width they are coalesced in a single and almost isothermal stream. Here the flow displays some of the self-similar properties observed in canonical planar jets. An original formulation of the Coand\u103 effect reveals the mechanism underlying jets coalescence. Finally, fields of turbulent viscosity and diffusivity, as well as kinetic and thermal dissipations, show behaviours which are unlikely to be reproduced by typical eddy-viscosity turbulence models. In summary this study provides an original insight into the physics of turbulent heat transfer in wall-bounded and free-shear configurations where buoyancy forces are non-negligible. Results reported in this text might also be used for the development and validation of turbulence models to be employed in buoyant flows

Direct Numerical Simulation of turbulent mixed convection around a bundle of heated rods at low-Prandtl number

The present work reports an overview of the results of Direct Numerical Simulations performed on the case of fully-developed, mixed convection flow of a liquid metal around a uniformly heated bundle of vertical rods. Finite-Volume computations are performed by an original discretization technique based on the representation of arbitrarily-shaped cylindrical boundaries on a non-uniform Cartesian grid. A domain consisting of four subchannels of a triangular lattice of rods with a pitch-to-diameter ratio P/D = 1.4 is considered as the reference geometry. A single friction Reynolds number value is simulated, namely Reτ = 550. Both forced and mixed convection regimes are investigated, buoyancy effects being introduced by imposing a Richardson number value of Ri = 0.25. A Prandtl number Pr = 0.031 is chosen to represent LBE as the working fluid. Instantaneous snapshots and relevant statistics of the velocity and thermal fields are reported here for the considered case, and integral results are compared against available literature data

Numerical simulation of mixing buoyant jets: Preliminary studies

Preliminary numerical analyses are reported for the case of three vertical planar mixing jets at different temperatures, in view of a forthcoming reference DNS to be performed in the frame of the SESAME European project. The reference case stems from the well-known PLAJEST triple jet experiment, but with a relative increase of the buoyancy effect, achieved by reducing the Reynolds number by a factor 5. Pre-production DNS runs for the reference case and a complementary RANS parametric analysis with varying Prandtl and Richardson numbers are carried out, highlighting that a suitable configuration for a benchmark can be obtained with a hotter central jet and colder lateral jets