169,967 research outputs found
Experimental quantum cosmology in time-dependent optical media
No full textIt is possible to construct artificial spacetime geometries for light by using intense laser pulses that modify the spatiotemporal properties of an optical medium. Here we theoretically investigate experimental possibilities for studying spacetime metrics of the form . By tailoring the laser pulse shape and medium properties, it is possible to create a refractive index variation that can be identified with . Starting from a perturbative solution to a generalized Hopfield model for the medium described by an , we provide estimates for the number of photons generated by the time-dependent spacetime. The simplest example is that of a uniformly varying that therefore describes the Robertson–Walker metric, i.e. a cosmological expansion. The number of photon pairs generated in experimentally feasible conditions appears to be extremely small. However, large photon production can be obtained by periodically modulating the medium and thus resorting to a resonant enhancement similar to that observed in the dynamical Casimir effect. Curiously, the spacetime metric in this case closely resembles that of a gravitational wave. Motivated by this analogy, we show that a periodic gravitational wave can indeed act as an amplifier for photons. The emission for an actual gravitational wave will be very weak but should be readily observable in the laboratory analogue
D-branes on C^3_6. Part I: prepotential and GW-invariants
No full textThis is the first of a set of papers having the aim to provide a detailed description of brane configurations on a family of noncompact threedimensional Calabi-Yau manifolds. The starting point is the singular manifold C^3/Z_6, which admits five distinct crepant resolutions. Here we apply local mirror symmetry to partially determine the prepotential encoding the GW-invariants of the resolved varieties. It results that such prepotential provides all numbers but the ones corresponding to curves having null intersection with the compact divisor. This is realized by means of a conjecture, due to S. Hosono, so that our results provide a check confirming at least in part the conjecture
La Fine del Mesolitico in ItaliaIdentità culturale e distribuzione territoriale degli ultimi cacciatori-raccoglitori
No full textPresentazione e discussione dei problemi riguardanti gli ultimi cacciatori-raccoglitori del Mesolitico della Penisola Italiana nel quadro della problematica della neolitizzazione dell'Europ
On the geometry of C^3/\Delta_{27} and del Pezzo surfaces
No full textWe clarify some aspects of the geometry of a resolution of the orbifold X = C3/Δ27, the noncompact complex manifold underlying the brane quiver standard model recently proposed by Verlinde and Wijnholt. We explicitly realize a map between X and the total space of the canonical bundle over a degree 1 quasi del Pezzo surface, thus defining a desingularization of X. Our analysis relys essentially on the relationship existing between the normalizer group of Δ27 and the Hessian group and on the study of the behaviour of the Hesse pencil of plane cubic curves under the quotient
Erratum: Non canonical polarizations of gravitational waves (The European Physical Journal C, (2023), 83, 4, (310), 10.1140/epjc/s10052-023-11502-1)
No full textIn the original article, a misprint has been introduced in Eq. (3). The correct equation reads as follows: (Formula presented.) The original article has been corrected
THE CAPSAICIN MODEL TO EXPLORE PAIN SENSORY PROFILES AND FUNCTIONAL CONNECTIVITY IN HUMANS. A COMBINED PSYCHOPHYSICAL AND fMRI STUDY IN NORMAL CONTROLS.
No full textIl dolore neuropatico viene definito dall' International Association for the Study of Pain (IASP) come diretta conseguenza di una lesione o di una malattia che colpisce il sistema somatosensoriale. Questa tipologia di dolore spesso include nella sintomatologia fenomeni come l' allodinia e l' iperalgesia.
I modelli animali offrono una grande quantità di dati sperimentali che tuttavia sono difficili da riprodurre in ambito clinico.
Al contrario, i meccanismi neurofisiologici che sottendono il dolore neuropatico negli esseri umani non sono ancora ben compresi e inoltre i relativi farmaci sono spesso inefficaci.
Data tale difficoltà, è essenziale poter disporre di un efficace modello sperimentale di dolore neuropatico nell'uomo.
Inoltre è risaputo che vi è una elevata variabilità nella percezione del dolore negli esseri umani e questo può spiegare gran parte della variabilità riscontrata nella risposta ai farmaci. E di questo aspetto se ne deve tener conto anche nello sviluppo di nuove sostanze analgesiche.
Il modello sperimentale che si basa sulla capsaicina, una sostanza che deriva dal peperoncino, viene utilizzato per esplorare i profili sensoriali nell'uomo.
La capsaicina permette lo studio sia dei sintomi che prevedono un incremento di funzione come l'iperalgesia e l'allodinia sia fenomeni legati a perdita di funzione come l'ipoalgesia.
Il bersaglio della capsaicina è il recettore TRPV1, che è espresso nelle fibre C e Aδ.
In questo studio, abbiamo testato soggetti umani sani nei quali è stato indotto sperimentalmente un dolore cutaneo acuto mediante l'applicazione topica di un cerotto ad alta concentrazione di capsaicina (8%). Altri studi hanno già utilizzato la capsaicini tuttavia a concentrazioni più basse (0,025-3%).
Il primo obiettivo di questo studio è stato quello di indagare la variabilità della percezione del dolorein soggeti sani, studiando i profili somatosensoriali prima e durante una condizione sperimentale di dolore (capsaicina 8%) utilizzando il Quantitative Sensory Testing (QST).
Un altro obiettivo è stato quello di indagare le varizioni e la connettività tra i resting-state Networks utilizzando la risonanza magnetica funzionale prima e durante una condizione sperimentale di dolore (cerotto alla capsaicina, 8%) in soggetti sani.
Abbiamo combinato l'uso di un test psicofisico applicato perifericamente sulla pelle nel sito di stimolazione (avambraccio destro) con un metodo di imaging del sistema nervoso centrale per esplorare la "via del dolore" dai recettori periferici fino ai networks cerebrali.
Nella prima parte dello studio è stato eseguito un protocollo standardizato di QST in un gruppo di 32 volontari sani prima (T0) e dopo l'applicazione di capsaicina topica (3x3 cm, 30 ') sull'avambraccio destro (a T1: per esplorare l'iperalgesia e l'allodinia primaria e secondaria; e a T2 dopo 24 ore: per esplorare l'ipoalgesia tardiva).
Nel secondo studio, 18 volontari sani sono stati sottoposti ad un protocollo di resting-state fMRI prima e durante l'applicazione di capsaicina topica sull'avambraccio destro per esplorare i resting-state Networks e la connettività funzionale, utilizzando i software FSL e CONN per l'elaborazione dei dati.
I risultati del primo esperimento indicano che la capsaicina influenza sia le soglie termiche e meccaniche del QST con un pattern complessivo di incremento di funzione (iperalgesia termica e meccanica e allodinia meccanica dinamica).
I risultati hanno anche mostrato diversi pattern di variabilità inter-individuale dei parametri del QST; alcuni parametri appaiono più stabili di altri.
Per quanto riguarda il secondo esperimento, abbiamo trovato, durante l'applicazione di capsaicina,
una maggiore connettività funzionale che coinvolge diverse aree cerebrali. Abbiamo anche dimostrato una ridotta connettività funzionale che riguarda una coppia di regioni.
Questo modello potrebbe essere utile per sviluppare nuovi farmaci analgesici, potendoli testare in un numero più limitato ma selezionato di soggetti.Neuropathic pain is defined by the International Association for the Study of Pain as pain arising as a direct consequence of a lesion or disease affecting the somatosensory system and it frequently may include allodynia and hyperalgesia. Animal models offer a large amount of experimental data, which are difficult to translate in the clinical setting. In contrast, the neurophysiological mechanisms underlying neuropathic pain in humans are not yet well understood and drugs are often ineffective. Given the pitfalls in translating animal data to humans, it is essential to have an experimental model of neuropathic pain in humans.
Moreover there is a high variability in pain perception in humans and this may account for much of the variability in response to neuropathic pain drugs.
The capsaicin model is used to explore sensory profiles in humans. Capsaicin is the pungent ingredient of chili peppers. Capsaicin allows the study of both gain-of-function (hyperalgesia and allodynia: similar to the chronic sensory symptoms of a patient with neuropathic pain) and loss-of-function (hypalgesia) phenomena. Capsaicin target is the transient receptor potential vanilloid 1 channel (TRPV1) which is expressed in the polymodal C and Aδ nociceptive fibers and it is a key molecolar component of the pain pathway.
In the present study, we tested healthy human subjects in whom acute cutaneous pain is induced experimentally by topical application of high-concentration capsaicin (8%, patch) unlike other studies that used lower concentrations (0,025-3%).
The first aim of this study was to investigate the variability of experimental pain perception in normal controls by studying somatosensory profiles before and during an experimental pain condition (8% capsaicin patch) using quantitative sensory testing (QST).
Another aim was to investigate the changes and the connectivity in the resting state networks using BOLD functional magnetic resonance imaging before and during an experimental pain condition (8% capsaicin patch) in healthy subjects.
We have combined the use of a psychophysical test applied peripherally in the skin stimulation site with a method of central nervous system imaging to explore the “pain pathway” from the peripheral receptors up to brain connections.
In the first part of the study a standardized QST protocol was performed in a group of 32 normal volunteers prior to (T0) and after topical capsaicin application (3 x 3 cm, 30’) on the forearm (T1: early primary and secondary hyperalgesia/allodynia; T2: late hypalgesia).
In the second experimental design, 18 healthy volunteers were submitted to a resting state fMRI protocol before and after capsacin path application to explore the Resting State Networks and functional connectivity, using FSL and CONN to process the data.
Results of first experiment indicate that capsaicin affect both thermal and mechanical QST thresholds resulting in a pattern of “gain of function” with heat and pinprick hyperalgesia and dynamic mechanical allodynia. Results also showed different patterns of inter-individual variability with some more stable parameters than others.
Regarding the second experiment we found greater and positive resting-state functional connectivity involving different brain areas in capsaicin condition compared to pre-capsaicin condition. We also found a reduced connectivity only for a couple of regions.
This model might be useful to profiling novel analgesic agents in more limited numbers of subjects than required in patient efficacy studies
Odd characteristic classes in entire cyclic homology and equivariant loop space homology
No full textGiven a compact manifoldM and a smooth map g:M → U.(l×l:C) from M to the Lie group of unitary l×l matrices with entries in C, we construct a Chern character Ch-(g) which lives in the odd part of the equivariant (entire) cyclic Chen-normalized cyclic complex Nε(ωT(M × T)) of M, and which is mapped to the odd Bismut-Chern character under the equivariant Chen integral map. It is also shown that the assignment g → Ch-(g) induces a well-defined group homomorphism from the K-1 theory of M to the odd homology group of Nε(ωT(M × T))
The elemental composition of Stradivari's musical instruments: new results through non-invasive EDXRF analysis
No full textDuring recent decades, many researchers have tried to understand the main influences on the extraordinary sound and beauty of the masterpieces made by the ancient violin makers. This is still a challenge for many others today. Mainly because of a lack of written historical documents, the rediscovery of some of the ancient violin-making processes was made possible thanks to scientific analyses performed on their materials by means of diagnostic techniques. However, understanding which substances were adopted is a very hard task, because the analyses are influenced by many factors: for example, alterations, wear, retouches, and the heterogeneity of materials. This paper presents some new EDXRF results collected on eight-stringed musical instruments made by Antonio Stradivari between 1669 and 1734 (Clisbee 1669, Hellier 1679, Ford-Rougemont 1703, Joachim-Ma 1714, Russian Federation viola 1715, Cremonese 1715, Vesuvius 1727, and Scotland 1734) and now preserved at the Museo del Violino in Cremona. A brief comparison with a modern violin made by Simone Ferdinando Sacconi (Hellier copy 1941), one of the most eminent violin makers of the 20th century and one of the greatest experts on Stradivari's work, is also provided. This represents the first comparative analysis of a wide number of ancient musical instruments made by the same violin maker over an extended period. A non-destructive and non-invasive approach was followed to (a) understand the elemental composition differences between the best conserved and most worn-out surfaces; (b) check if there are elemental similarities among the finishing materials of violins made in different years by the same violin maker; (c) give new suggestions about the materials used. To distinguish the best conserved areas from the worn-out ones, a preliminary investigation by UV-induced fluorescence photography was performed. In addition, stereomicroscopic observations and Fourier transform infrared spectroscopy (FTIR)analyses were performed on selected areas to validate the hypotheses. The results, in some cases comparable with previous research on Stradivari instruments, have increased the pool of information about materials and treatments adopted in the Stradivari workshop
La Vittoria di Calvatone e altri materiali cremonesi alla Mostra augustea della Romanità (Roma 1937)
No full textEquidistribution rates, closed string amplitudes, and the Riemann hypothesis
No full textWe study asymptotic relations connecting unipotent averages of Sp(2g,Z) automorphic forms to their integrals over the moduli space of principally polarized abelian varieties. We obtain reformulations of the Riemann hypothesis as a class of problems concerning the computation of the equidistribution convergence rate in those asymptotic relations. We discuss applications of our results to closed string amplitudes. Remarkably, the Riemann hypothesis can be rephrased in terms of ultraviolet relations occurring in perturbative closed string theory
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