Radiation damping partitions and rf-fields

In his classical paper ' Radiation Effects in Circular Accelerators' K.W. Robinson has shown that the damping partitions in a circular machine cannot be changed by a radio-frequency field. The proof given there is quite general and valid for any RF-field, provided it is not so strong that it changes the equilibrium orbit appreciably. However, the physical mechanisms which prevent the possibility to alter the damping partitions is not very transparent. As a consequence, so-called "damping cavities" are still proposed from time to time. Here we want to illustrate the underlying physical principles by going in detail through the beam dynamics for the simple case of a cavity operating in a dipole (deflecting) mode and which is located in a region of finite dispersion in a storage ring

Radio emission at the centre of the galaxy cluster Abell 3560: evidence for core sloshing?

Previous radio observations of the galaxy cluster A3560 in the Shapley Concentration showed complex radio emission associated with the brightest cluster member.To understand its origin we observed it with the GMRT, the VLA and ATCA at 240 and 610 MHz, 1.28,1.4, 2.3,4.8 and 8.4 GHz, and performed a detailed morphological and spectral study of the radio emission associated with the BCG. We also observed the cluster with XMM-Newton and Chandra to derive the properties of the ICM. The radio emission of the N-E nucleus of the dumb-bell BCG shows an active radio galaxy, plus aged diffuse emission, which is not refurbished at present. Our Chandra data show that the radio active nucleus of the BCG has extended X-ray emission, which we classify as a low-luminosity corona. A residual image of the XMM-Newton brightness shows the presence of a spiral-like feature, which we interpret as the signature of gas sloshing. The presence of a subgroup is clear in the surface brightness residual map, and in the XMM-Newton temperature analysis. The optical 2D analysis shows substructure in A3560. A galaxy clump was found at the location of the X-ray subgroup, and another group is present south of the cluster core, close to the spiral-like feature. The aged part of the radio emission closely follows the spiral pattern of the X-ray residual brightness distribution, while the two active radio lobes are bent in a completely different direction. We conclude that the complex radio emission associated with the cluster BCG is the result of a minor merger event in A3560. The aged diffuse emission is strongly affected by the sloshing motion in the ICM. On the other hand, the bent jets and lobes of the current radio AGN activity may reflect a complex gas velocity field in the innermost cluster regions and/or sloshing-induced oscillations in the motion of the cD galaxy.Comment: 15 pages, 8 figures, 5 tables, A&A in pres

Continuous attractors for dynamic memories

Episodic memory has a dynamic nature: when we recall past episodes, we retrieve not only their content, but also their temporal structure. The phenomenon of replay, in the hippocampus of mammals, offers a remarkable example of this temporal dynamics. However, most quantitative models of memory treat memories as static configurations, neglecting the temporal unfolding of the retrieval process. Here, we introduce a continuous attractor network model with a memory-dependent asymmetric component in the synaptic connectivity, which spontaneously breaks the equilibrium of the memory configurations and produces dynamic retrieval. The detailed analysis of the model with analytical calculations and numerical simulations shows that it can robustly retrieve multiple dynamical memories, and that this feature is largely independent of the details of its implementation. By calculating the storage capacity, we show that the dynamic component does not impair memory capacity, and can even enhance it in certain regimes

Effect of kolsterising treatment on surface properties of a duplex stainless steel

In recent years, attempts of engineering the surface of duplex stainless steels were made in order to enhance their hardness and tribological properties, without affecting their corrosion resistance. A possibility of improving these properties is provided by a family of processes developed by Prof. B.H. Kolster in the Netherlands in the late 1980’s. These processes (usually referred to as Kolsterising® treatments) consist in a low temperature surface carburizing, which involves the diffusion of large quantities of carbon atoms (up to 6-7 wt.%) into the steel at a diffusion temperature below 450 °C. In the present paper a characterization of the surface layer of Kolsterised duplex SAF 2205 stainless steel was carried out to study the effects of this treatment on surface properties. The characterization includes optical metallographic examination, microhardness tests and SEM-EDS investigation on the Kolsterised steel in the as treated condition and after annealing treatments at 200, 250, 300 350 and 400°C for 10 hours, to evaluate the stability of Kolsterised layer’s properties with a moderate increase in temperature. Moreover, complying with ASTM G48-03 Method E Standard, in order to evaluate the effect of the Kolsterising® treatment on steel pitting resistance, the critical pitting temperature was obtained for Kolsterised duplex SAF 2205 stainless steel compared with the base metal

On the crack path of rolling contact fatigue cracks in a railway wheel steel

The objective of the present paper is to give some preliminary results obtained in the frame of a more wide investigation on the rolling contact fatigue (RCF) behavior of a railway wheel steel. The effect of different test parameters on the RCF fatigue strength of the railway wheel steel was evaluated. RCF tests were conducted using two cylindrical contact specimens under different Po/k ratio (where Po is the maximum Hertzian pressure, k is the yield stress in shear of the material), under dry contact conditions or with water lubrication, and at varying slip ratio. In the present study crack initiation location and crack growth direction were carefully investigated; microscopic examination showed that the cracks were initiated at the surface, propagated obliquely in the depth direction and then occasionally branched into two directions. Usually multiple cracks are initiated, at the rolling contact surface, caused by the accumulation of shear deformation due to repeated rolling–sliding contact loading. Subsequent crack growth has been found to occur along specific sloped directions. The influence of Po/k ratio, dry or wet contact, and slip ratio on crack slope angle to the radial direction and the depths at which slope changes occur has been investigated. Observed crack slopes and slope change position have been discussed according to crack path prediction criteria in the literature

Neodymium isotopes of central Mediterranean phosphatic hardgrounds reveal Miocene paleoceanography

Understanding the causes of the formation of hardgrounds provides insights on the oceanographic evolution of a basin. Phosphate-rich hardground formation interrupted carbonate ramp deposition in the Mediterranean during the Miocene. We analyzed the epsilon(Nd) record of three central Mediterranean hardgrounds to identify the origin of the phosphate-rich waters that formed them within the frame of Mediterranean Miocene paleoceanographic evolution. The Nd isotopes suggest that eastern Mediterranean deep waters were controlled by runoff, in contrast to Atlantic and Indian Ocean waters. This Nd isotope record attests to the weakening of Mediterranean circulation during the Miocene due to closure of the Indian Gateway. Limited exchange with Atlantic shallow seawater led to long residence times for deep waters in the basin. This record indicates the role of upwelling in formation of phosphate hardgrounds and shows the influence of global climate change and local paleoceanographic conditions

V1T: large-scale mouse V1 response prediction using a Vision Transformer

Accurate predictive models of the visual cortex neural response to natural visual stimuli remain a challenge in computational neuroscience. In this work, we introduce V1T, a novel Vision Transformer based architecture that learns a shared visual and behavioral representation across animals. We evaluate our model on two large datasets recorded from mouse primary visual cortex and outperform previous convolution-based models by more than 12.7% in prediction performance. Moreover, we show that the self-attention weights learned by the Transformer correlate with the population receptive fields. Our model thus sets a new benchmark for neural response prediction and can be used jointly with behavioral and neural recordings to reveal meaningful characteristic features of the visual cortex.Comment: updated references and added link to code repository; add analysis on generalization and visualize aRF

Analysis of particle size distribution in municipal wastewaters

Innovative membrane filtration plants for municipal wastewaters are being developed and need the support of reliable filtration models in the designing phase. In the past, semi-empirical filtration models for membrane processes have been proposed. At present, the most prominent works point out the importance of particle poly-dispersity in the development of reliable models but fail into the implementation of probability density functions (PDFs) capable of an accurate fitting of the experimental particle size distribution (PSD). We report the experimental PSDs of two different municipal wastewater samples, obtained through the laser diffraction technique. The experimental results show that the laser diffraction technique can characterize wastewater particle dimensions both in the colloidal and supra-colloidal regions. The experimental study is complemented by a comparative analysis in which many PDFs are used to fit the experimental PSDs through a least-squares approach. Some of these PDFs are proposed here for the first time to fit experimental wastewater PSDs. Among the PDFs considered for the statistical modeling, the three-parameter lognormal and the Burr PDFs are demonstrated to provide satisfactory fitting, whereas the other considered functions fail. This result is confirmed by the analysis of both the available wastewater samples

Miocene paleoceanographic evolution of the Mediterranean area and carbonate production changes: A review

Abstract Miocene is a key interval in the global climate evolution as well as in the geodynamic evolution of the Mediterranean basin. Therefore, global and regional factors controlled Miocene Mediterranean oceanography, which, in turn, affected carbonate production. In this work, we review the Miocene paleocenographic evolution of the Mediterranean starting from its Sr and Nd isotope records. Secondly, we discuss Mediterranean shallow-water carbonate production changes to identify the role of oceanographic conditions in controlling carbonate systems' evolution. During Aquitanian, Sr and Nd isotope records attest an open Mediterranean, mainly fed by the Indian Ocean. From the late Burdigalian, the intermittent connection with the Indian Ocean changed the overall circulation in the basin, leading to higher residence time of waters and smaller water exchanges with the adjacent oceans. In this newly established paleoceanographic framework, regional factors such as volcanism, significantly affected Mediterranean seawater chemistry. Local tectonics led to the development of small sub-basins in the Eastern Mediterranean, characterized by restricted water exchanges from the Tortonian in the easternmost part, to the early Messinian, as attested by the deviation of the Sr isotope record of the proto-Adriatic basin. Larger Benthic Foraminifera (LBF) assemblages dominated carbonate production in the Aquitanian, while they were the most affected by the Indo-Pacific closure, showing a demise after the Burdigalian. With the LBF demise, red algae and bryozoans dominated carbonate ramps from the middle Miocene to the Tortonian. Bryozoans in particular spread during the Monterey Event, favoured by global and regional factors. During early to middle Miocene, corals formed mounds in the oligophotic zone or coral carpets controlled by local conditions. Conversely, in the late Tortonian-early Messinian, they developed as huge reef complexes in the Western and Central Mediterranean, with the exception of small restricted sub-basins, such as the proto-Adriatic basin, where red algae and small benthic foraminifera persisted