1,946 research outputs found
Applications of combined MOSFET-IGBT power leg with reduced switching losses
This paper discusses power legs built upon the combination of a MOSFET and an IGBT. The suggested combined use of those different switches is intended to be applied in PWM controlled single and three phase inverters. The main advantage of the presented topology is the reduced switching losses in the overall inverter topology compared to the classical pure IGBT and MOSFET topologies. The paper presents and compares experimental results for the proposed power leg and the conventional pure IGBTs and pure MOSFETs legs. Realized applications of the proposed power leg are shown
Public Sector Employees: Risk Averse and Altruistic?
We assess whether public sector employees have a stronger inclination to serve others and are more risk averse than employees in the private sector. A unique feature of our study is that we use revealed rather than stated preferences data. Respondents of a large-scale survey were offered a substantial reward and could choose between a widely redeemable gift certificate, a lottery ticket, or making a donation to a charity. Our analysis shows that public sector employees are significantly less likely to choose the risky option (lottery) and, at the start of their career, significantly more likely to choose the pro-social option (charity). However, when tenure increases, this difference in pro-social inclinations disappears and, later on, even reverses. Our results further suggest that quite a few public sector employees do not contribute to charity because they feel that they already contribute enough to society at work for too little pay
Formation of energy gap in higher dimensional spin-orbital liquids
A Schwinger boson mean field theory is developed for spin liquids in a
symmetric spin-orbital model in higher dimensions. Spin, orbital and coupled
spin-orbital operators are treated equally. We evaluate the dynamic correlation
functions and collective excitations spectra. As the collective excitations
have a finite energy gap, we conclude that the ground state is a spin-orbital
liquid with a two-fold degeneracy, which breaks the discrete spin-orbital
symmetry. Possible relevence of this spin liquid state to several realistic
systems, such as CaVV and NaSbTiO, are discussed.Comment: 4 pages with 1 figur
SU(4) Spin-Orbital Two-Leg Ladder, Square and Triangle Lattices
Based on the generalized valence bond picture, a Schwinger boson mean field
theory is applied to the symmetric SU(4) spin-orbital systems. For a two-leg
SU(4) ladder, the ground state is a spin-orbital liquid with a finite energy
gap, in good agreement with recent numerical calculations. In two-dimensional
square and triangle lattices, the SU(4) Schwinger bosons condense at
(\pi/2,\pi/2) and (\pi/3,\pi/3), respectively. Spin, orbital, and coupled
spin-orbital static susceptibilities become singular at the wave vectors, twice
of which the bose condensation arises at. It is also demonstrated that there
are spin, orbital, and coupled spin-orbital long-range orderings in the ground
state.Comment: 5 page
A comparative longitudinal study of bovine trypanosomiasis in tsetse-free and tsetse-infested zones of the Amhara Region, Northwest Ethiopia
A study was conducted to determine the incidence of trypanosome infections in cattle in tsetse-free and tsetse-infested zones of the Amhara Region of northwest Ethiopia. A total of six sentinel herds were established and the cattle observed during a period of 8 consecutive months. The prevalence of seropositive cattle was high in both the tsetse-free and tsetse-infested zones. The average monthly incidence of trypanosome infection, determined using molecular diagnostic tools, was 20.9% and 25.7% in
the tsetse-free and the tsetse-infested zones, respectively. In the tsetse-free, Trypanosoma vivax was responsible for 90.9% of the cattle trypanosome infections. In the tsetse-infested zone, Trypanosoma congolense and T. vivax contributed almost equally to the trypanosome infections in cattle. Trypanosome infection, regardless of species, resulted in anaemia as evidenced by a significant decrease in the packed cell volume of the infected animal. The outcome of this longitudinal study suggests that
control of trypanosomiasis in the Amhara Region cannot be achieved by tsetse control alone. Supplemental measures to include drug therapy and biting fly control are discussed
IDEFIX: a versatile performance-portable Godunov code for astrophysical flows
Exascale super-computers now becoming available rely on hybrid
energy-efficient architectures that involve an accelerator such as Graphics
Processing Units (GPU). Leveraging the computational power of these machines
often means a significant rewrite of the numerical tools each time a new
architecture becomes available. To address these issues, we present Idefix, a
new code for astrophysical flows that relies on the Kokkos meta-programming
library to guarantee performance portability on a wide variety of architectures
while keeping the code as simple as possible for the user. Idefix is based on a
Godunov finite-volume method that solves the non-relativistic HD and MHD
equations on various grid geometries. Idefix includes a wide choice of solvers
and several additional modules (constrained transport, orbital advection,
non-ideal MHD) allowing users to address complex astrophysical problems. Idefix
has been successfully tested on Intel and AMD CPUs (up to 131 072 CPU cores on
Irene-Rome at TGCC) as well as NVidia and AMD GPUs (up to 1024 GPUs on Adastra
at CINES). Idefix achieves more than 1e8 cell/s in MHD on a single NVidia V100
GPU and 3e11 cell/s on 256 Adastra nodes (1024 GPUs) with 95% parallelization
efficiency (compared to a single node). For the same problem, Idefix is up to 6
times more energy efficient on GPUs compared to Intel Cascade Lake CPUs. Idefix
is now a mature exascale-ready open-source code that can be used on a large
variety of astrophysical and fluid dynamics applications.Comment: 18 pages, 18 figures, 3 tables, accepted for publication in Astronomy
& Astrophysic
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