Bloch oscillations (BOs) are a fundamental phenomenon by which a wave packet undergoes a periodic motion in a lattice when subjected to a force. Observed in a wide range of synthetic systems, BOs are ...intrinsically related to geometric and topological properties of the underlying band structure. This has established BOs as a prominent tool for the detection of Berry-phase effects, including those described by non-Abelian gauge fields. In this work, we unveil a unique topological effect that manifests in the BOs of higher-order topological insulators through the interplay of non-Abelian Berry curvature and quantized Wilson loops. It is characterized by an oscillating Hall drift synchronized with a topologically-protected inter-band beating and a multiplied Bloch period. We elucidate that the origin of this synchronization mechanism relies on the periodic quantum dynamics of Wannier centers. Our work paves the way to the experimental detection of non-Abelian topological properties through the measurement of Berry phases and center-of-mass displacements.
X-ray absorption line spectroscopy has recently shown evidence for previously unknown Ultra-fast Outflows (UFOs) in radio-quiet active galactic nuclei (AGNs). These have been detected essentially ...through blueshifted Fe XXV/XXV delta K-shell transitions. In the previous paper of this series we defined UFOs as those highly ionized absorbers with an outflow velocity higher than 10,000 km s--1 and assessed the statistical significance of the associated blueshifted absorption lines in a large sample of 42 local radio-quiet AGNs observed with XMM-Newton. The present paper is an extension of that work. First, we report a detailed curve of growth analysis of the main Fe XXV/XXV delta transitions in photoionized plasmas. Then, we estimate an average spectral energy distribution for the sample sources and directly model the Fe K absorbers in the XMM-Newton spectra with the detailed Xstar photoionization code. We confirm that the frequency of sources in the radio-quiet sample showing UFOs is >35% and that the majority of the Fe K absorbers are indeed associated with UFOs. The outflow velocity distribution spans from ~10,000 km s--1 (~0.03c) up to ~100,000 km s--1 (~0.3c), with a peak and mean value of ~42,000 km s--1 (~0.14c). The ionization parameter is very high and in the range log Delta *x ~ 3-6 erg s--1 cm, with a mean value of log Delta *x ~ 4.2 erg s--1 cm. The associated column densities are also large, in the range N H ~ 1022-1024 cm--2, with a mean value of N H ~ 1023 cm--2. We discuss and estimate how selection effects, such as those related to the limited instrumental sensitivity at energies above 7 keV, may hamper the detection of even higher velocities and higher ionization absorbers. We argue that, overall, these results point to the presence of extremely ionized and possibly almost Compton-thick outflowing material in the innermost regions of AGNs. This also suggests that UFOs may potentially play a significant role in the expected cosmological feedback from AGNs and their study can provide important clues on the connection between accretion disks, winds, and jets.
► The sheet hydroforming process was combined with the rapid tooling technique. ► The layered die was created optimizing the number of layers through an adaptive slicing. ► No post working operation ...was used for improving the finishing of the layered die. ► The proper sheet material and CF-pressure profile could minimize problems related to the layered die. ► Sound parts suitable for prototyping purposes were obtained.
The aim of this study is to investigate the possibility of manufacturing an aluminum automotive component (a small sized car door panel) using a highly reconfigurable and cheap forming process. Specifically, the sheet hydroforming process and rapid tooling technique were combined, with the objective of making the resulting process more flexible and less expensive.
Sheet hydroforming experiments were carried out using a layered die created assembling 2D laser cut layers and testing three Al alloys (AA2024, AA5754, AA7475); process parameters (Closing Force and Pressure) were evaluated by means of finite element simulations, mainly focused on the curve defining the Closing Force as a function of the forming Pressure and on friction conditions, which have a significant effect on the distribution of sheet thickness in formed parts.
Both numerical simulations and experimental tests highlighted that sound parts could be obtained if a hard enough sheet material together with the appropriate Closing Force and forming Pressure are used. The proposed approach, combining the hydroforming process with a rapid tooling technique, proved to be effective in rapidly manufacturing prototypes and thus in shortening the product design process.
► The proposed technology keep the simplicity and the low cost of the SPIF equipment. ► An automotive prototypal part could be manufactured using SPIF. ► A positive effect of the speed in stabilizing ...the necking was recognised. ► Higher level of major strains were obtained when increasing the speed. ► The quality of the surface (internal only) deteriorated when increasing the speed.
The present work focuses the attention on the Single Point Incremental Forming (SPIF) process of a scaled car door shell made by Titanium alloy (Ti6Al4V). The effect of a temperature increase contemporary due to electric static heating and tool rotation speed was investigated.
Preliminary tensile tests allowed to define the temperature level to be assured on the sheet in order to determine a consistent flow stress reduction. SPIF tests were carried out adopting rotation speed in the range 800–1600RPM, while simultaneously changing the pitch value in the range 0.5–1.0mm. Temperature during the forming process was continuously measured in the central area of the blank using a pyrometer. In addition a digital image correlation system was used for measuring the strain distribution over the formed part.
The combination of the two approaches (heating by both electric bands and high tool rotation speed) revealed to be a feasible solution for manufacturing hard to work materials like Ti alloys, since the investigated case study was successfully formed by SPIF. In addition, a positive effect of the tool rotation speed in stabilizing the necking (thus allowing to reach higher level of stretching) was recognised.
This brief presents a novel charge pump suitable to work under very-low-voltage supply. The circuit exploits a novel charge transfer switch made up by the combination of a NMOS and a PMOS transistor ...whose gates are connected to internal nodes of the charge pump to enhance overdrive voltage. This solution allows working with supply voltage values lower that the MOS threshold voltage. Post layout simulation results using a 65-nm CMOS standard technology show the effectiveness of the proposed solution and its advantage as compared to a traditional latched charge pump in terms of high current driving range, power efficiency and speed.
In this brief an improved Dickson charge pump (DCP) topology exploiting a clock boosting is presented. An accurate while simple theoretical model for the dynamic behavior of the charge pump is ...carried out. Analytical comparison with the traditional DCP reveals that the proposed solution can achieve a rise time or area reduction between 10% and 60% at the cost of a slight circuit complexity. Finally, simulation results using a 65-nm CMOS technology show the accuracy of the analytical model as well as the advantages of the proposed solution.
Context. X-ray studies of active galactic nuclei (AGN) with powerful nuclear winds are important for constraining the physics of the inner accretion/ejection flow around supermassive black holes ...(SMBHs) and for understanding the impact of such winds on the AGN environment. Aims. Our main scientific goal is to constrain the properties of the circum-nuclear matter close to the SMBH in the mini-broad absorption line quasar (mini-BAL QSO) PG 1126-041 using a multi-epoch observational campaign with XMM-Newton. Methods. We performed temporally resolved X-ray spectroscopy and simultaneous UV and X-ray photometry on the most complete set of observations and on the deepest X-ray exposure of a mini-BAL QSO ever. Results. We found complex X-ray spectral variability on time scales of both months and hours, which is best reproduced by means of variable massive ionized absorbers along the line of sight. As a consequence, the observed optical-to-X-ray spectral index is found to be variable with time. In the highest signal-to-noise observation we detected highly ionized X-ray absorbing material outflowing much faster (υX ~ 16 500 km s-1) than the UV absorbing one (υuv ~ 5000 km s-1). This highly ionized absorber is found to be variable on very short (a few kiloseconds) time scales. Conclusions. Our findings are qualitatively consistent with line-driven accretion disk winds scenarios. Our observations have opened the time-resolved X-ray spectral analysis field for mini-BAL QSOs. Only with future deep studies will we be able to map the dynamics of the inner flow and understand the physics of AGN winds and their impact on the environment.
This brief presents the experimental validation of a low-power, large output swing, class-AB buffer amplifier for column drivers of active-matrix flat-panel displays. By exploiting two complementary ...input amplifiers and a dual-path push-pull output stage, the proposed circuit achieves high-drive performance and rail-to-rail operation. In addition, two current boosters allow area optimization of the output diving transistors by dynamically lowering their threshold voltage. Implemented in a standard triple-well CMOS 0.35-<inline-formula> <tex-math notation="LaTeX">{\mu }{\text{m}} </tex-math></inline-formula> technology and supplied from a 3-V supply, the proposed buffer amplifier can drive a 1-nF column line load within a 1.11-<inline-formula> <tex-math notation="LaTeX">{\mu }\text{s} </tex-math></inline-formula> settling time under a full voltage swing, while drawing only 1.6 <inline-formula> <tex-math notation="LaTeX">{\mu }\text{A} </tex-math></inline-formula> quiescent current and occupying 5562 <inline-formula> <tex-math notation="LaTeX">{\mu }{\text{m}}^{{2}} </tex-math></inline-formula> of silicon area. As compared to the state of the art, the best figure of merit (pF/<inline-formula> <tex-math notation="LaTeX">{\mu }\text{s}{\cdot } {\mu }\text{A} </tex-math></inline-formula>) is found.
In this study, a numerical/experimental analysis is proposed to investigate the possibility of reshaping sheet metal-based End-of-Life (EoL) components using sheet Hydroforming (SHF). Returned EoL ...components are challenging to be reformed, they are usually characterised by high heterogeneity as there are localised thinning areas (caused by the original forming processes), and the overall formability is reduced with respect to the original flat sheet material. The reshaping route was replicated: a deep drawing process was adopted to impart a square feature; subsequently, SHF was performed. The capability of remove the deep drawn feature was analysed with varying Blank-holder force, oil pressure profile and the location of the previous deep drawn feature. A 3D finite element model of the entire manufacturing route was used to analyse the strain paths of the reshaping process. The change in the strain paths when considering a component previously subjected to deep drawing was analysed and discussed in comparison with SHF using an undeformed blank. This study for the first time provides an insight on the reshaping process mechanics as well as attempts at quantifying the quality of the reshaped components. Results revealed that SHF can be successfully adopted for reshaping purposes as it performed well under two analysed aspects: capability of removing the existing feature and imparting a brand-new shape and thickness/strain path analyses (avoiding fracture and excessive thinning). Nevertheless, the developed analyses revealed that reshaping is more challenging than conventional forming and new design rules, identified in the present paper, need to be followed.
Combining data from several sources, we build a database of home values, the cost of housing structures, and residential land values for 46 large US metropolitan areas from 1984 to 2004. Our analysis ...of these new data reveal that since the mid-1980s residential land values have appreciated over a much wider range of cities than is commonly believed. And, since 1998, almost all large US cities have seen significant increases in real residential land prices. Averaging across the cities in our sample, by year-end 2004, the value of residential land accounted for about 50 percent of the total market value of housing, up from 32 percent in 1984. An implication of our results is that housing is much more land intensive than it used to be, meaning that the future course of home prices--the average rate of appreciation and volatility--is likely to be determined even more by demand factors than was the case even ten or twenty years ago.
PDF
