We present an implementation of the single-pixel imaging approach into a terahertz (THz) time-domain spectroscopy (TDS) system. We demonstrate the indirect coherent reconstruction of THz temporal ...waveforms at each spatial position of an object, without the need of mechanical raster-scanning. First, we exploit such temporal information to realize (far-field) time-of-flight images. In addition, as a proof of concept, we apply a typical compressive sensing algorithm to demonstrate image reconstruction with less than 50% of the total required measurements. Finally, the access to frequency domain is also demonstrated by reconstructing spectral images of an object featuring an absorption line in the THz range. The combination of single-pixel imaging with compressive sensing algorithms allows to reduce both complexity and acquisition time of current THz-TDS imaging systems.
Extremely short, high-energy pulses are essential in modern ultrafast science. In a seminal paper in 19961, Nisoli and co-workers demonstrated the first intense pulse compression employing a ...gas-filled hollow-core fibre. Despite the huge body of scientific work on this technology stemming from ultrafast and attosecond research, here we identify an unexplored few-cycle visible-light generation mechanism, which relies on the nonlinear mixing of hollow-core fibre modes. Using a commercially available ytterbium laser, we generate 4.6 fs, 20 μJ pulses centred at around 600 nm (~2 cycles, ~4 GW peak power), ~40 times shorter than the input 175 fs, 1 mJ pulses at 1,035 nm. Our approach thus directly projects few-hundred-femtosecond-long infrared pulses into the single-cycle regime at visible frequencies, without the need for additional post-compression. As a powerful application of our findings, we present a compact, multicolour pump–probe set-up with a temporal resolution of a few optical cycles.Direct generation of few-cycle high-energy visible pulses is demonstrated via the nonlinear mixing of hollow-core fibre modes. Compression of near-infrared laser pulses by a factor of 40 with no additional dispersion compensation delivers 4.6 fs, 20 μJ pulses (~2 cycles, ~4 GW peak power) centred at around 600 nm.
The concept of "premature mortality" is at the heart of many national and global health measurement and benchmarking efforts. However, despite the intuitive appeal of its underlying concept, it is ...far from obvious how to best operationalise it. The previous work offers at least two basic approaches: an absolute and a relative one. The former-and far more widely used- approach sets a unique age threshold (e.g. 65 years), below which deaths are defined as premature. The relative approach derives the share of premature deaths from the country-specific age distribution of deaths in the country of interest. The biggest disadvantage of the absolute approach is that of using a unique, arbitrary threshold for different mortality patterns, while the main disadvantage of the relative approach is that its estimate of premature mortality strongly depends on how the senescent deaths distribution is defined in each country.
We propose to overcome some of the downsides of the existing approaches, by combining features of both, using a hierarchical model, in which senescent deaths distribution is held constant for each country as a pivotal quantity and the premature mortality distribution is allowed to vary across countries. In this way, premature mortality estimates become more comparable across countries with similar characteristics.
The proposed hierarchical models provide results, which appear to align with related evidence from specific countries. In particular, we find a relatively high premature mortality for the United States and Denmark.
While our hybrid approach overcomes some of the problems of previous measures, some issues require further research, in particular the choice of the group of countries that a given country is assigned to and the choice of the benchmarks within the groups. Hence, our proposed method, combined with further study addressing these issues, could provide a valid alternative way to measure and compare premature mortality across countries.
Abstract
The results are presented of an experimental activity performed in the RFX-mod device aimed at characterizing plasma dynamics in the so-called Ultralow-q (ULq) magnetic configuration, which ...corresponds to edge safety factor values below 1. The role of the edge safety factor in determining plasma dynamics is studied. In particular, a characterization of MHD activity is performed. The results of dedicated non-linear 3D visco-resistive MHD simulations are in good quantitative agreement with the experimental observations. In particular, the predicted tendency for ULq plasmas to be characterized by magnetic spectra dominated by a single mode (either a kink or a double resonant internal mode) is confirmed by experiment. Magnetic reconnection plays a relevant role in determining the dynamics of the magnetic topology. Both almost quiescent and largely fluctuating plasmas are observed with a strong sensitivity on the edge safety factor. The main MHD properties of the ULq are compared to those of RFP and tokamak discharges, also produced in the RFX-mod device. MHD modes exhibit toroidal rotation at a frequency depending on mode amplitude. Differently from what encountered in RFP plasmas at comparable current levels, no wall locking is detected.
The ITER full size plasma source device design Sonato, P.; Agostinetti, P.; Anaclerio, G. ...
Fusion engineering and design,
06/2009, Letnik:
84, Številka:
2
Journal Article, Conference Proceeding
Recenzirano
In the framework of the strategy for the development and the procurement of the NB systems for ITER, it has been decided to build in Padova a test facility, including two experimental devices: a full ...size plasma source with low voltage extraction and a full size NB injector at full beam power (1
MV). These two different devices will separately address the main scientific and technological issues of the 17
MW NB injector for ITER. In particular the full size plasma source of negative ions will address the ITER performance requirements in terms of current density and uniformity, limitation of the electron/ion ratio and stationary operation at full current with high reliability and constant performances for the whole operating time up to 1
h. The required negative ion current density to be extracted from the plasma source ranges from 290
A/m
2 in D
2 (D
−) and 350
A/m
2 in H
2 (H
−) and these values should be obtained at the lowest admissible neutral pressure in the plasma source volume, nominally at 0.3
Pa. The electron to ion ratio should be limited to less than 1 and the admissible ion inhomogeneity extracted from the grids should be better than 10% on the whole plasma cross-section having a surface exposed to the extraction grid of the order of 1
m
2.
The main design choices will be presented in the paper as well as an overview of the design of the main components and systems.
•Analysis of voltage ringing issue in a high power supply system – MITICA AGPS.•Voltage ringing issue caused by long cable connection downstream inverters.•Use of numerical model for analyzing the ...issue and designing a high power filter.•Comparisons of simulation results and measures of dedicated test.
The Acceleration Grid Power Supply of MITICA is a high power, high voltage power supply devoted to feed the acceleration grids of the full scale prototype of the ITER NBI injector. It is divided in two subsystems: the AGPS – Conversion System (CS) and the AGPS – DC Generator (DCG), procured by different domestic agencies. Numerical simulations have pointed out a voltage ringing at the interface of the two systems, which would generate repeated high overvoltage at the input of the AGPS-DCG, not in compliance with the interface requirements. The phenomenon has been investigated and a solution for the mitigation has been identified based on a suitable low pass RC filter, as a trade-off between simplicity and effectiveness. The filters have been successfully tested directly with the AGPS-CS to demonstrate the reduction of the voltage peaks in the operation condition foreseen for the AGPS.
Abstract
Three experiments were conducted with the aim of developing and validating an equation to predict the ME of corn for pigs from its chemical composition, physical characteristics and particle ...size. Exp. 1: Eight lots of corn were ground in a hammer mill, using 5 sieves with different screen opening sizes, generating 40 batches of ground corn. The chemical composition (DM, CP, ether extract, crude fiber, ADF, NDF, and ash) and physical characteristics (bulk density– BD and 1,000-kernel weight- TKW) were determined in the 8 lots and geometric mean diameter (GMD) and N-corrected ME (AMEn) were determined in the 40 batches of corn. The AMEn values were determined in 16 metabolism assays with pigs. Mathematical models were adjusted by regression analysis, based on the Akaike Information Criterion. Based on statistical parameters (R2 = 0.76 and prediction error = 1.05%), number of predictor variables, and easiness of measurements, an equation with 2 segments was chosen: y = 2845.41 + 0.9385 × BD – 20.8784 × CP, if GMD ≤ 522.98 and y = 3105.75 – 0.4978 × GMD + 0.9385 × BD – 20.8784 × CP, if GMD > 522.98. Exp. 2 and 3: Sixty four gilts (Exp. 1; 29.5 ± 3.8 kg) and 64 barrows (Exp. 2; 29.3 ± 3.6 kg), 1 lot of corn, and 3 particle sizes (GMD = 483, 632, and 904 µm) were used in a 3 × 2 factorial arrangement with 2 methods of diet formulation, differing in ME value of corn: “FIX” (value from nutrient composition table) vs. “ESTIMATED” (estimated for each particle size using the equation developed in Exp. 1). In Exp. 2, ADFI was greater (P < 0.05) and feed efficiency was lower (P < 0.05) in the diet with GMD of 904 µm compared to the diets with GMD of 632 or 483 µm, but only for diet formulation by the FIX method. In the treatments with GMD of 483 µm, gilts fed with the diet formulated by the ESTIMATED method had greater (P < 0.10) ADFI, backfat, fat area, and fat:meat ratio than gilts fed the diet formulated by the FIX method. In Exp. 3, particle size and formulation method did not affect (P > 0.10) growth performance and carcass traits of barrows. The equation developed was effective to adjust the ME value of corn, considering particle size variation. However, improvement to the proposed equation is necessary to achieve greater precision for predicting corn ME. Validation of the equation with more lots of corn of different chemical compositions and densities appears necessary to assess the efficacy of the equation regarding the variation of the other predicting variables.
The Acceleration Grid Power Supply Conversion System (AGPS-CS) of the MITICA Neutral Beam Injector has been installed between late 2017 - early 2018 and commissioned in the first half of 2018. This ...paper is focused on the installation and commissioning activities, with emphasis on the integration issues. The results of the site and acceptance tests are presented, proving the capability of the system to deliver the specified performance.
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