2,173 research outputs found

    Radio-X-ray Synergy to discover and Study Jetted Tidal Disruption Events

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    Observational consequences of tidal disruption of stars (TDEs) by supermassive black holes (SMBHs) can enable us to discover quiescent SMBHs, constrain their mass function, study formation and evolution of transient accretion disks and jet formation. A couple of jetted TDEs have been recently claimed in hard X-rays, challenging jet models, previously applied to γ\gamma-ray bursts and active galactic nuclei. It is therefore of paramount importance to increase the current sample. In this paper, we find that the best strategy is not to use up-coming X-ray instruments alone, which will yield between several (e-Rosita) and a couple of hundreds (Einstein Probe) events per year below redshift one. We rather claim that a more efficient TDE hunter will be the Square Kilometer Array (SKA) operating {\it in survey mode} at 1.4 GHz. It may detect up to several hundreds of events per year below z2.5z \sim 2.5 with a peak rate of a few tens per year at z0.5z\approx 0.5. Therefore, even if the jet production efficiency is {\it not } 100%100\% as assumed here, the predicted rates should be large enough to allow for statistical studies. The characteristic TDE decay of t5/3t^{-5/3}, however, is not seen in radio, whose flux is quite featureless. {\it Identification} therefore requires localization and prompt repointing by higher energy instruments. If radio candidates would be repointed within a day by future X-ray observatories (e.g. Athena and LOFT-like missions), it will be possible to detect up to 400\approx 400 X-ray counterparts, almost up to redshift 22. The shortcome is that only for redshift below 0.4\approx 0.4 the trigger times will be less than 10 days from the explosion. In this regard the X-ray surveys are better suited to probe the beginning of the flare, and are therefore complementary to SKA.Comment: Astrophysical Journal (revised version

    A survey on modern trainable activation functions

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    In neural networks literature, there is a strong interest in identifying and defining activation functions which can improve neural network performance. In recent years there has been a renovated interest of the scientific community in investigating activation functions which can be trained during the learning process, usually referred to as "trainable", "learnable" or "adaptable" activation functions. They appear to lead to better network performance. Diverse and heterogeneous models of trainable activation function have been proposed in the literature. In this paper, we present a survey of these models. Starting from a discussion on the use of the term "activation function" in literature, we propose a taxonomy of trainable activation functions, highlight common and distinctive proprieties of recent and past models, and discuss main advantages and limitations of this type of approach. We show that many of the proposed approaches are equivalent to adding neuron layers which use fixed (non-trainable) activation functions and some simple local rule that constraints the corresponding weight layers.Comment: Published in "Neural Networks" journal (Elsevier

    High numerical aperture holographic microscopy reconstruction with extended z range

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    An holographic microscopy reconstruction method compatible with high numerical aperture microscope objective (MO) up to NA=1.4 is proposed. After off axis and reference field curvature corrections, and after selection of the +1 grating order holographic image, a phase mask that transforms the optical elements of the holographic setup into an afocal device is applied in the camera plane. The reconstruction is then made by the angular spectrum method. The field is first propagated in the image half space from the camera to the afocal image of the MO optimal plane (plane for which MO has been designed) by using a quadratic kernel. The field is then propagated from the MO optimal plane to the object with the exact kernel. Calibration of the reconstruction is made by imaging a calibrated object like an USAF resolution target for different positions along zz. Once the calibration is done, the reconstruction can be made with an object located in any plane zz. The reconstruction method has been validated experimentally with an USAF target imaged with a NA=1.4 microscope objective. Near-optimal resolution is obtained over an extended range (±50 μ\pm 50~\mum) of zz locations

    Bedding control on landslides: A methodological approach for computer-aided mapping analysis

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    Litho-structural control on the spatial and temporal evolution of landslides is one of the major typical aspects on slopes constituted of structurally complex sequences. Mainly focused on instabilities of the earth flow type, a semi-quantitative analysis has been developed with the purpose of identifying and characterizing litho-structural control exerted by bedding on slopes and its effects on landsliding. In quantitative terms, a technique for azimuth data interpolation, Non-continuous Azimuth Distribution Methodological Approach (NADIA), is presented by means of a GIS software application. In addition, processed by NADIA, two indexes have been determined: (i) Δ, aimed at defining the relationship between the orientation of geological bedding planes and slope aspect, and (ii) C, which recognizes localized slope sectors in which the stony component of structurally complex formations is abundant and therefore operates an evolutive control of landslide masses. Furthermore, some Litho-Structural Models (LSMs) of slopes are proposed aiming at characterizing recurrent forms of structural control in the source, channel and deposition areas of gravitational movements. In order to elaborate evolutive models controlling landslide scenarios, LSMs were qualitatively related and compared with Δ and C; quantitative indexes. The methodological procedure has been applied to a lithostructurally complex area of Southern Italy where data about azimuth measurements and landslide mapping were known. It was found that the proposed methodology enables the recognition of typical control conditions on landslides in relation to the LSMs. Different control patterns on landslide shape and on style and distribution of the activity resulted for each LSM. This provides the possibility for first-order identification to be made of the spatial evolution of landslide bodies. © Author(s) 2011

    Association between awake oral parafunctional behaviors and temporomandibular disorders

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    Temporomandibular disorders (TMD) represent a very common public health problem. Awake oral parafunctional behaviors may contribute to their establishment. They include oral habits that differ from physiological functional needs such as mastication, communication, swallowing or breathing and they could be considered as adverse behaviors because of their detrimental effects on teeth, temporomandibular joints and jaw muscles. Awake oral parafunctions can be detected through surface electromyography (EMG) or questionnaires completed from the patient, like the Oral Behaviors Checklist (OBC). This thesis is the result of researches showing that a strong relationship between such behaviors and TMD exists, by confirming what widely explained in literature. The strength of the present findings is that they have been obtained through standardized Diagnostic Criteria (DC) to make TMD diagnosis and through valid methods for the assessment of wake-time oral parafunctions. Based on these data, clinicians should focus on the reduction of awake parafunctions in the multifactorial treatment of patients affected from TMD by carefully administering them a correct behavioral counselling. Therefore, this might reduce the overload on temporomandibular joint and consequently the development of TMD. However, more researches based on greater samples and standardized methods, should be conducted to expand and clarify the knowledge about this controversial topic

    Differential neural dynamics underling pragmatic and semantic affordance processing in macaque ventral premotor cortex

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    Premotor neurons play a fundamental role in transforming physical properties of observed objects, such as size and shape, into motor plans for grasping them, hence contributing to "pragmatic" affordance processing. Premotor neurons can also contribute to "semantic" affordance processing, as they can discharge differently even to pragmatically identical objects depending on their behavioural relevance for the observer (i.e. edible or inedible objects). Here, we compared the response of monkey ventral premotor area F5 neurons tested during pragmatic (PT) or semantic (ST) visuomotor tasks. Object presentation responses in ST showed shorter latency and lower object selectivity than in PT. Furthermore, we found a difference between a transient representation of semantic affordances and a sustained representation of pragmatic affordances at both the single neuron and population level. Indeed, responses in ST returned to baseline within 0.5 s whereas in PT they showed the typical sustained visual-to-motor activity during Go trials. In contrast, during No-go trials, the time course of pragmatic and semantic information processing was similar. These findings suggest that premotor cortex generates different dynamics depending on pragmatic and semantic information provided by the context in which the to-be-grasped object is presented
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