In this work we approach attractor neural networks from a machine learning perspective: we look for optimal network parameters by applying a gradient descent over a regularized loss function. Within ...this framework, the optimal neuron-interaction matrices turn out to be a class of matrices which correspond to Hebbian kernels revised by a reiterated unlearning protocol. Remarkably, the extent of such unlearning is proved to be related to the regularization hyperparameter of the loss function and to the training time. Thus, we can design strategies to avoid overfitting that are formulated in terms of regularization and early-stopping tuning. The generalization capabilities of these attractor networks are also investigated: analytical results are obtained for random synthetic datasets, next, the emerging picture is corroborated by numerical experiments that highlight the existence of several regimes (i.e., overfitting, failure and success) as the dataset parameters are varied.
The measurement of the energy spectrum of cosmic ray helium nuclei from 70 GeV to 80 TeV using 4.5 years of data recorded by the Dark Matter Particle Explorer (DAMPE) is reported in this work. A ...hardening of the spectrum is observed at an energy of about 1.3 TeV, similar to previous observations. In addition, a spectral softening at about 34 TeV is revealed for the first time with large statistics and well controlled systematic uncertainties, with an overall significance of 4.3σ. The DAMPE spectral measurements of both cosmic protons and helium nuclei suggest a particle charge dependent softening energy, although with current uncertainties a dependence on the number of nucleons cannot be ruled out.
The DArk Matter Particle Explorer (DAMPE) is a satellite-borne, calorimetric-type, high-energy-resolution detector for the precise measurement of high-energy electrons, gamma rays, and nuclei from ...deep space. The DAMPE electromagnetic calorimeter consists of bismuth germanate (BGO) crystals that can measure incident hadron energies from 50 GeV to 100 TeV. For an inorganic scintillator, such as BGO, the nonlinear fluorescence response when measuring ions contributes to the difference between the experimental data and Monte Carlo simulations. This article reports the BGO quenching nonlinearity occurring in the DAMPE experiment. The ionization energy response of BGO to several kinds of ions lighter than iron is investigated by conducting beam tests and analyzing flight data. We compare the scintillator output with the energy loss according to GEANT4 simulations and determine the quenching parameters. The combined result of beam test and flight experiment shows that the quenching effect strongly depends on the density of the ionization energy loss.
Satellite experiments for gamma-ray and cosmic-ray detection employ plastic scintillators to discriminate charged from neutral particles in order to correctly identify gamma-rays and charged nuclei. ...The High Energy Cosmic Radiation Detection (HERD) facility will be among these experiments, to be installed onboard the future Chinese Space Station (CSS), to detect cosmic-rays and gamma-rays up to TeV energies. The plastic scintillator detector (PSD) will consist of scintillator tiles or bars coupled to Silicon Photomultipliers (SiPMs). To discriminate gamma-rays from charged particles and measure the ion charge up to iron nuclei a wide dynamic range is required, from few tens up to thousands of photoelectrons. We have equipped a plastic scintillator tile prototype with SiPMs produced by Hamamatsu and AdvanSiD and coupled their analog signals to the DT5550W board based on the CITIROC ASIC, produced by CAEN SpA. The CITIROC ASIC allows both the formation of a fast trigger with a configurable threshold and the digitization of analog waveforms after a preamplification and shaping stage along two paths with different gain settings. The performance of our prototype will be shown.
Plastic scintillators are widely used for anti-coincidence systems and for the identification of charged cosmic-ray nuclei in satellite experiments. For this reason, a plastic scintillator detector ...(PSD) should have a high detection efficiency for charged cosmic rays and a very good capability of measuring charges. We implemented a full and customizable simulation tool to investigate the performance of a PSD coupled to Silicon Photomultipliers. The overall performance of the detector is studied by tracking optical photons produced inside the scintillator. The simulation will be used for the design of a PSD for future space experiments, such as HERD, AMEGO, e-Astrogam. In this work we investigated in detail the effect of Birks’ saturation in the discrimination of charged ions up to iron nuclei. We will show the comparison between simulations and measurements conducted on prototype scintillator tiles.
The High Energy Cosmic Radiation Detection (HERD) facility, onboard the future China’s Space Station (CSS), will provide high quality data on charged cosmic rays and gamma rays in the energy range ...from few GeV to PeV. HERD will be equipped with a fine granularity cubic crystals calorimeter and a precision tracker detector. The entire instrument will be surrounded by a Plastic Scintillator Detector (PSD) that will be used to discriminate charged from neutral particles in order to correctly identify gamma-rays and nuclei. One proposed configuration for the HERD PSD consists of tiles of plastic scintillator, optically coupled to SiPMs. In 2019-2020, two beam tests were performed at CNAO (Centro Nazionale di Adroterapia Oncologica) in Pavia (Italy), exposing some PSD tiles, equipped with SiPMs, to low-beta p and C ion beams in order to evaluate the detector response to heavy ions. Spatial and temporal resolution were also evaluated using a radioactive source.
Abstract Our study evaluated motor cortex involvement during silent reading of sentences referring to hand actions. We aimed at defining whether sentential polarity (affirmative vs. negative) would ...modulate motor cortex activation using the event-related desynchronization (ERD) analysis of the mu rhythm. Eleven healthy volunteers performed a reading task involving 160 sentences (80 affirmative: 40 hand-related, 40 abstract; 80 negative: 40 hand-related, 40 abstract). After reading each sentence, subjects had to decide whether the verb was high or low frequency in Italian. Electroencephalographic (EEG) activity was recorded with 32 surface electrodes and mu ERD analyses were performed for each subject. Hand-action related sentences induced a greater mu ERD over the left premotor and motor hand areas compared to abstract sentences. Mu ERD was greater and temporally delayed when the hand-related verbs were presented in the negative versus affirmative form. As predicted by the “embodied semantic” theory of language understanding, motor areas were activated during sentences referring to hand actions. In addition, motor cortex activation was larger for negative than affirmative motor sentences, a finding compatible with the hypothesis that comprehension is more demanding in the specific case of motor content negation.
The aim of this retrospective study was to compare buprenorphine and tramadol, in order to assess their different efficacy in prolonging postoperative analgesia and their associated side effects when ...used as perineural adjuvants with a local anesthetic.
The clinical records of 161 consecutive ASA 1-2 adult patients scheduled for arthroscopic rotator cuff repair and fulfilling the inclusion/exclusion criteria were reviewed retrospectively. The anaesthesia was performed using the middle interscalene block (MIB). The 161 patients were divided into three groups (A, B, T) according to their utilization of buprenorphine (B), tramadol (T) or neither of the latter (A) as perineural adjuvants: group A (54 patients) - levobupivacaine 0.75%, 0.4 mL/kg; group B (56 patients) - levobupivacaine 0.75%, 0.4 mL/kg + 0.15 mg buprenorphine; group T (51 patients) - levobupivacaine 0.75%, 0.4 mL/kg + 100 mg tramadol.
The results showed that the group treated with buprenorphine benefited from a longer post-operative analgesia than that treated with local anesthetic alone (P<0.0001). Otherwise, a less evident not statistically significant (P=0.4825) difference turned out between the group treated with the anesthetic alone and the group treated with tramadol as adjuvant. No difference turned out to be between the local anesthetic alone treatment and the tramadol-local anesthetic one (P=0.4825; HR=0.863, 95% CI 0.574-1.299); on the contrary, a significant difference was demonstrated between the buprenophine-local anesthetic group and the local anesthetic alone one (P<0.0001; HR=0.330, 95% CI 0.216-0.530) CONCLUSION: Both buprenorphine and tramadol are effective as perineural adjuvants used in order to prolong the postoperative analgesia, buprenorphine proving more efficacious for this purpose than tramadol.
The aim of this study was to evaluate the efficacy of tramadol as an adjuvant to the local anaesthetic solution in patients undergoing shoulder arthroscopy for rotator cuff tear after middle ...interscalene block (MIB).
We enrolled 120 patients (ASA I-II), scheduled for arthroscopic surgery for rotator cuff tear. The patients were sedated with midazolam 0.02 mg/kg and haloperidol 2 mg i.v. before performing MIB. All subjects underwent a MIB with 0.4 mL/kg of 0.5% levobupivacaine. After computerized randomization, all patients were allocated in 1 of 3 groups, each including 40 subjects. Group Placebo (Group P) received 0.4 mL/kg of 0.5% levobupivacaine plus isotonic sodium chloride for MIB and isotonic sodium chloride i.m. Group "Perineural Tramadol" (Group TPN) received 0.4 ml/Kg of 0.5% levobupivacaine plus 1.5 mg/kg of tramadol perineurally and isotonic sodium chloride i.m. Group "Intramuscular Tramadol" (Group TIM) received 0.4 ml/Kg of 0.5% levobupivacaine plus isotonic sodium chloride perineurally and 1.5 mg/kg of tramadol i.m.
The MIB onset times were not statistically different in the three groups. The duration of analgesia was significantly longer in Groups TPN and TIM, where tramadol was administered, either i.m. or perineurally, compared with the placebo group. A significant statistical difference was found in the duration of analgesia between the group TPN and TIM.
The addition of tramadol to the local anaesthetic solution administered for MIB provided a longer duration of analgesia compared with placebo and i.m tramadol administration in patients undergoing arthroscopic surgery for rotator cuff tear.
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