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Institution

Instituto Superior Técnico

Education
About: Instituto Superior Técnico is a based out in . It is known for research contribution in the topics: Catalysis & Finite element method. The organization has 10085 authors who have published 30226 publications receiving 667524 citations. The organization is also known as: IST & Instituto Superior Tecnico.


Papers
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Journal ArticleDOI
TL;DR: In this article, a 64-channel ASIC for Time-of-Flight Positron Emission Tomography (TOF PET) imaging has been designed and simulated, which performs timing, digitization and data transmission for 511 keV and lower-energy events due to Compton scattering.
Abstract: A 64-channel ASIC for Time-of-Flight Positron Emission Tomography (TOF PET) imaging has been designed and simulated. The circuit is optimized for the readout of signals pro- duced by the scintillation of a L(Y)SO crystal optically coupled to a silicon photomultiplier (SiPM). Developed in the framework of the EndoTOFPET-US collaboration (1), the ASIC is integrated in the external PET plate and performs timing, digitization and data transmission for 511 keV and lower-energy events due to Compton scattering. Multi-event buffering capability allows event rates up to 100 kHz per channel. The channel cell includes a low input impedance low-noise current conveyor and two trans-impedance amplifier branches separately optimized for energy and time resolution. Two voltage mode discriminators generate respectively a fast trigger for accurate timing and a signal for time-over-threshold calcu- lation, used for charge measurement. The digitization of these signals is done by two low-power TDCs, providing coarse and fine time stamps that are saved into a local register and later managed by a global controller, which builds-up the 40-bit event data and runs the interface with the data acquisition back-end. Running at 160 MHz the chip yields a 50 ps time binning and dissipates u 7 mW per channel (simulated for 40 kHz event rate p/channel) for high capacitance photodetectors (9 mm 2 active area Silicon Photomultiplier with 320 pF terminal capacitance). The minimum SNR of 23.5 dB expected with this capacitance should allow triggering on the first photoelectron to achieve the envisaged timing performance for a TOF-PET system.

123 citations

Journal ArticleDOI
TL;DR: In this article, the mechanical and morphological properties of high density polyethylene/pre-treated and modified residues from sugarcane bagasse cellulose composites were analyzed.

123 citations

Journal ArticleDOI
TL;DR: In this paper, the authors measured several properties of the reionization process and the corresponding low-frequency 21 cm signal associated with the neutral hydrogen distribution, using a large volume, high-resolution simulation of cosmic reionisation.
Abstract: We measure several properties of the reionization process and the corresponding low-frequency 21 cm signal associated with the neutral hydrogen distribution, using a large volume, high-resolution simulation of cosmic reionization. The brightness temperature of the 21 cm signal is derived by postprocessing this numerical simulation with a semianalytical prescription. Our study extends to high redshifts (z ~ 25) where, in addition to collisional coupling, our postprocessed simulations take into account the inhomogeneities in the heating of the neutral gas by X-rays and the effect of an inhomogeneous Ly α radiation field. Unlike the well-studied case in which spin temperature is assumed to be significantly greater than the temperature of the cosmic microwave background due to uniform heating of the gas by X-rays, spatial fluctuations in both the Ly α radiation field and X-ray intensity affect predictions related to the brightness temperature at z > 10, during the early stages of reionization and gas heating. The statistics of the 21 cm signal from our simulation are then compared to existing analytical models in the literature, and we find that these analytical models provide a reasonably accurate description of the 21 cm power spectrum at z 10, and, with upcoming interferometric data, these differences in return can provide a way to better understand the astrophysical processes during reionization.

123 citations

Journal ArticleDOI
TL;DR: In this paper, it was shown that for Erdos-Renyi random graphs, where each edge exists with probability p, search by CTQW is almost surely optimal as long as p≥log 3/2 n/n.
Abstract: The problem of finding a marked node in a graph can be solved by the spatial search algorithm based on continuous-time quantum walks (CTQW). However, this algorithm is known to run in optimal time only for a handful of graphs. In this work, we prove that for Erdos-Renyi random graphs, i.e., graphs of n vertices where each edge exists with probability p, search by CTQW is almost surely optimal as long as p≥log^{3/2}(n)/n. Consequently, we show that quantum spatial search is in fact optimal for almost all graphs, meaning that the fraction of graphs of n vertices for which this optimality holds tends to one in the asymptotic limit. We obtain this result by proving that search is optimal on graphs where the ratio between the second largest and the largest eigenvalue is bounded by a constant smaller than 1. Finally, we show that we can extend our results on search to establish high fidelity quantum communication between two arbitrary nodes of a random network of interacting qubits, namely, to perform quantum state transfer, as well as entanglement generation. Our work shows that quantum information tasks typically designed for structured systems retain performance in very disordered structures.

123 citations

Journal ArticleDOI
TL;DR: In this article, the reduction of aromatic nitro compounds to the corresponding amines with silanes catalyzed by high valent oxo-rhenium complexes is reported, where the catalytic systems PhMe(2)SiH/ReIO(2)(PPh(3))(2), (5 mol %) and PhMe[2]SiH/(ReOCl(3),PPh[3])(2] (5mol %) reduced efficiently a series of aromatic compounds in the presence of a wide range of functional groups.
Abstract: The reduction of aromatic nitro compounds to the corresponding amines with silanes catalyzed by high valent oxo-rhenium complexes is reported. The catalytic systems PhMe(2)SiH/ReIO(2)(PPh(3))(2) (5 mol %) and PhMe(2)SiH/ReOCl(3)(PPh(3))(2) (5 mol %) reduced efficiently a series of aromatic nitro compounds in the presence of a wide range of functional groups such as ester, halo, amide, sulfone, lactone, and benzyl. This methodology also allowed the regioselective reduction of dinitrobenzenes to the corresponding nitroanilines and the reduction of an aromatic nitro group in presence of an aliphatic nitro group.

122 citations


Authors

Showing all 10288 results

NameH-indexPapersCitations
Joao Seixas1531538115070
A. Gomes1501862113951
Amartya Sen149689141907
António Amorim136147796519
Joao Varela133141192438
Pietro Faccioli132137889795
João Carvalho126127877017
Pedro Jorge12477668658
Pedro Silva12496174015
A. De Angelis11853454469
Hermine Katharina Wöhri11662955540
Helena Santos114105854286
P. Conde Muiño10955856133
Joao Saraiva10751953340
J. N. Reddy10692666940
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Performance
Metrics
No. of papers from the Institution in previous years
YearPapers
202341
2022354
20212,263
20202,433
20192,327
20182,190