186 research outputs found
JFET integration using a foundry SOI photonics platform
We explore the monolithic integration of conventional electronics with SOI photonics using the commercial silicon photonics foundry technology offered by A*STAR's Institute of Microelectronics (IME). This process offers optical waveguide modulators and photodetectors, but was not intended to support transistors. We present the implementation of junction field effect transistors (JFETs) integrated with optical waveguides and photodetectors. A simple SPICE model is developed for the JFETs based on the available ion implant parameters, and the geometry feature size allowed by the technology's layout rules. We have demonstrated the monolithic integration of photonics and electronics circuits. This work could be useful for application in waveguide sensors and optical telecommunications
Ultracompact CMOS-compatible optical logic using carrier depletion in microdisk resonators
We present a CMOS-compatible optoelectronic directed logic architecture that achieves high computational throughput (number of operations per second per unit area) by its ultracompact form factor. High speed-to-power performance is also achieved, by the low capacitance and high junction-to-mode overlap of low-radii SOI vertical pn junction microdisk switches. By using wavelength-division multiplexing and two electrical control signals per disk, each switch performs (N)OR, (N)AND, and X(N)OR operations simultaneously. Connecting multiple switches together, we demonstrate higher-order scalability in five fundamental N-bit logic circuits: AND/OR gates, adders, comparators, encoders, and decoders. To the best of our knowledge, these circuits achieve the lowest footprint of silicon-based multigigabit-per-second optical logic devices in literature
AMBIVALENT IMPLICATIONS OF HEALTH CARE INFORMATION SYSTEMS: A STUDY IN THE BRAZILIAN PUBLIC HEALTH CARE SYSTEM
This article evaluates social implications of the ""SIGA"" Health Care Information System (HIS) in a public health care organization in the city of Sao Paulo. The evaluation was performed by means of an in-depth case study with patients and staff of a public health care organization, using qualitative and quantitative data. On the one hand, the system had consequences perceived as positive such as improved convenience and democratization of specialized treatment for patients and improvements in work organization. On the other hand, negative outcomes were reported, like difficulties faced by employees due to little familiarity with IT and an increase in the time needed to schedule appointments. Results show the ambiguity of the implications of HIS in developing countries, emphasizing the need for a more nuanced view of the evaluation of failures and successes and the importance of social contextual factors
Ultrafast electro-optical disk modulators for logic, communications, optical repeaters, and wavelength converters
We propose a U-shaped pn junction in a silicon-on-insulator microdisk resonator to effectively double the junction–mode overlap in the state-of-the-art, vertical pn junction microdisk electro-optical (EO) modulators. The U-shaped pn junction promotes the maximum overlap between the junction depletion zone and the whispering gallery optical mode in the microdisk. By fully depleting the p region of the npn-sequenced U-junction, the capacitance is reduced below 3 fF, which significantly improves the speed and power performance. In this work, we implement the high-efficiency, depleted U-junction design to maximize the operating bandwidth of EO modulators, EO logic elements, EO 2 × 2 switches for wavelength-division cross-connects, 2 × 2 reconfigurable optical add–drop multiplexers, optical-to-electrical-to-optical (OEO) repeaters-with-gain, OEO wavelength converters, and 2 × 2 optical–optical logic gates. These devices all operate in the 7.6-to-50 GHz bandwidth range with ultralow energy consumption between 0.4 and 9.8 fJ/bit. By using CMOS-compatible materials and fabrication-feasible design dimensions, our proposed high-performance devices offer a promising potential in next-generation, high-volume electro-optical communications and computing circuits
QED_3 theory of underdoped high temperature superconductors II: the quantum critical point
We study the effect of gapless quasiparticles in a d-wave superconductor on
the T=0 end point of the Kosterlitz-Thouless transition line in underdoped
high-temperature superconductors. Starting from a lattice model that has
gapless fermions coupled to 3D XY phase fluctuations of the superconducting
order parameter, we propose a continuum field theory to describe the quantum
phase transition between the d-wave superconductor and the spin-density-wave
insulator. Without fermions the theory reduces to the standard Higgs scalar
electrodynamics (HSE), which is known to have the critical point in the
inverted XY universality class. Extending the renormalization group calculation
for the HSE to include the coupling to fermions, we find that the qualitative
effect of fermions is to increase the portion of the space of coupling
constants where the transition is discontinuous. The critical exponents at the
stable fixed point vary continuously with the number of fermion fields , and
we estimate the correlation length exponent (nu = 0.65) and the vortex field
anomalous dimension(eta_Phi=-0.48) at the quantum critical point for the
physical case N=2. The stable critical point in the theory disappears for the
number of Dirac fermions N > N_c, with N_c ~ 3.4 in our approximation. We
discuss the relationship between the superconducting and the chiral (SDW)
transitions, and point to some interesting parallels between our theory and the
Thirring model.Comment: 13 pages including figures in tex
Uncertainty quantification patterns for multiscale models
Uncertainty quantification (UQ) is a key component when using computational models that involve uncertainties, e.g. in decision-making scenarios. In this work, we present uncertainty quantification patterns (UQPs) that are designed to support the analysis of uncertainty in coupled multi-scale and multi-domain applications. UQPs provide the basic building blocks to create tailored UQ for multiscale models. The UQPs are implemented as generic templates, which can then be customized and aggregated to create a dedicated UQ procedure for multiscale applications. We present the implementation of the UQPs with multiscale co
QED3 theory of underdoped high temperature superconductors
Low-energy theory of d-wave quasiparticles coupled to fluctuating vortex
loops that describes the loss of phase coherence in a two dimensional d-wave
superconductor at T=0 is derived. The theory has the form of 2+1 dimensional
quantum electrodynamics (QED3), and is proposed as an effective description of
the T=0 superconductor-insulator transition in underdoped cuprates. The
coupling constant ("charge") in this theory is proportional to the dual order
parameter of the XY model, which is assumed to be describing the quantum
fluctuations of the phase of the superconducting order parameter. The principal
result is that the destruction of phase coherence in d-wave superconductors
typically, and immediately, leads to antiferromagnetism. The transition can be
understood in terms of the spontaneous breaking of an approximate "chiral"
SU(2) symmetry, which may be discerned at low enough energies in the standard
d-wave superconductor. The mechanism of the symmetry breaking is analogous to
the dynamical mass generation in the QED3, with the "mass" here being
proportional to staggered magnetization. Other insulating phases that break
chiral symmetry include the translationally invariant "d+ip" and "d+is"
insulators, and various one dimensional charge-density and spin-density waves.
The theory offers an explanation for the rounded d-wave-like dispersion seen in
ARPES experiments on Ca2CuO2Cl2 (F. Ronning et. al., Science 282, 2067 (1998)).Comment: Revtex, 20 pages, 5 figures; this is a much extended follow-up to the
Phys. Rev. Lett. vol.88, 047006 (2002) (cond-mat/0110188); improved
presentation, many additional explanations, comments, and references added,
sec. IV rewritten. Final version, to appear in Phys. Rev.
Tutorial applications for Verification, Validation and Uncertainty Quantification using VECMA toolkit
The VECMA toolkit enables automated Verification, Validation and Uncertainty Quantification (VVUQ) for complex applications that can be deployed on emerging exascale platforms and provides support for software applications for any domain of interest. The toolkit has four main components including EasyVVUQ for VVUQ workflows, FabSim3 for automation and tool integration, MUSCLE3 for coupling multiscale models and QCG tools to execute application workflows on high performance computing (HPC). A more recent addition to the VECMAtk is EasySurrogate for various types of surrogate methods. In this paper, we present five tutorials from different application domains that apply these VECMAtk components to perform uncertainty quantification analysis, use surrogate models, couple multiscale models and execute sensitivity analysis on HPC. This paper aims to provide hands-on experience for practitioners aiming to test and contrast with their own applications
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