679 research outputs found
Cohomological X-independence for Higgs bundles and Gopakumar–Vafa invariants
No full textThe aim of this paper is two-fold. Firstly, we prove Toda’s X-independence conjecture for Gopakumar–Vafa invariants of arbitrary local curves. Secondly, following Davison’s work, we introduce the BPS cohomology for moduli spaces of Higgs bundles of rank r and Euler characteristic X which are not necessary coprime, and show that it does not depend on X. This result extends the Hausel–Thaddeus conjecture on the X-independence of E-polynomials proved by Mellit, Groechenig–Wyss–Ziegler and Yu in two ways: We obtain an isomorphism of mixed Hodge modules on the Hitchin base rather than an equality of E-polynomials, and we do not need the coprime assumption. The proof of these results is based on a description of the moduli stack of one-dimensional coherent sheaves on a local curve as a global critical locus which is obtained in the companion paper by the first author and Naruki Masuda
Learning approach among health sciences students in a medical college in Nepal: a cross-sectional study
No full textAji Gopakumar,1 Susirith Mendis,2 Jayakumary Muttappallymyalil,3 Jayadevan Sreedharan3 1Department of General Education, 2Continuing Medical Education, Continuing Professional Development and Center for Continuing Education and Community Outreach, 3Department of Community Medicine, Gulf Medical University, Ajman, United Arab Emirates Shah et al aimed to explore the learning approaches among medical, dental, and nursing students which were considered useful to transform the students to become better learners. While the generic objective of the study is appreciated, we have some concerns regarding the methodology and statistical analysis of the study. View the original paper by Author and colleagues. 
Fast Regression of the Tritium Breeding Ratio in Fusion Reactors
No full textThe tritium breeding ratio (TBR) is an essential quantity for the design of
modern and next-generation D-T fueled nuclear fusion reactors. Representing the
ratio between tritium fuel generated in breeding blankets and fuel consumed
during reactor runtime, the TBR depends on reactor geometry and material
properties in a complex manner. In this work, we explored the training of
surrogate models to produce a cheap but high-quality approximation for a Monte
Carlo TBR model in use at the UK Atomic Energy Authority. We investigated
possibilities for dimensional reduction of its feature space, reviewed 9
families of surrogate models for potential applicability, and performed
hyperparameter optimisation. Here we present the performance and scaling
properties of these models, the fastest of which, an artificial neural network,
demonstrated and a mean prediction time of ,
representing a relative speedup of with respect to the expensive
MC model. We further present a novel adaptive sampling algorithm,
Quality-Adaptive Surrogate Sampling, capable of interfacing with any of the
individually studied surrogates. Our preliminary testing on a toy TBR theory
has demonstrated the efficacy of this algorithm for accelerating the surrogate
modelling process.Comment: 13 pages, 8 figure
Relative Mirror Symmetry and Ramifications of a Formula for Gromov-Witten Invariants
No full textFor a toric Del Pezzo surface S, a new instance of mirror symmetry, said relative, is introduced and developed. On the A-model, this relative mirror symmetry conjecture concerns genus 0 relative Gromov-Witten of maximal tangency of S. These correspond, on the B-model, to relative periods of the mirror to S. Furthermore, for S not necessarily toric, two conjectures for BPS state counts are related. It is proven that the integrality of BPS state counts of the total space of the canonical bundle on S implies the integrality for the relative BPS state counts of S. Finally, a prediction of homological mirror symmetry for the open complement is explored. The B-model prediction is calculated in all cases and matches the known A-model computation for the projective plane
A Front end Switched Rectifier DC Source for Neutral Point Balancing of A NPC Three-Level Inverter for The Full Modulation Range
No full textA switched DC voltage three level NPC is proposed in this paper to eliminate capacitor balancing problems in conventional three-level Neutral Point Clamped (NPC) inverter. The proposed configuration requires only one DC link with a voltage V-dc/2, where V-dc is the DC link voltage in a onventional NPC inverter. To get rated DC link voltage (V-dc), the voltage source is alternately onnected in parallel to one of the two series capacitors using two switches and two diodes with device voltage rating of V-dc/2. The frequency at which the voltage source is switched is independent and will not affect the operation of NPC inverter. The switched voltage source in this configuration balances the capacitors automatically. The proposed configuration can also be used as a conventional two level inverter in lower modulation range, thereby increases the reliability of the drive system. A space vector based PWM scheme is used to verify this proposed topology
Koha SMS Send Driver for eSMS Kerala Service: An Account of a Stakeholder
No full textCrowd sourcing is a convenient option to raise fund for Open Source Software development. Koha SMS Send driver for eSMS Kerala service developed and made available as Free Software with the financial support of State Central Library, Kerala. Mahatma Gandhi University Library could start SMS notifications from Koha with the help of eSMS Send driver. Small contributions from users can make big changes in the entire software community
Analytical Models of Exoplanetary Atmospheres. V. Non-gray Thermal Structure with Coherent Scattering
No full textWe apply the picket fence treatment to model the effects brought about by spectral lines on the thermal structure of irradiated atmospheres. The lines may be due to pure absorption processes, pure coherent scattering processes, or some combination of absorption and scattering. If the lines arise as a pure absorption process, the surface layers of the atmosphere are cooler, whereas this surface cooling is completely absent if the lines are due to pure coherent isotropic scattering. The lines also lead to a warming of the deeper atmosphere. The warming of the deeper layers is, however, independent of the nature of line formation. Accounting for coherent isotropic scattering in the shortwave and longwave continuum results in anti-greenhouse cooling and greenhouse warming on an atmosphere-wide scale. The effects of coherent isotropic scattering in the line and continuum operate in tandem to determine the resulting thermal structure of the irradiated atmosphere
17-level inverter with low component count for open-end induction motor drives
No full textThis study presents a 17-level inverter-based induction motor drive for high-resolution multilevel voltage space-vector (SV) generation. The proposed topology consists of a three-level inverter and a seven-level inverter connected to an open-end winding induction machine. The two inverters are powered by two unequal DC supplies, resulting in a low component count, with just 12 switches and three floating capacitors per phase. The voltage SVs applied by the two inverters are chosen to eliminate circulating power flow and prevent DC bus overcharging. In addition, the switching states of both inverters are chosen in order to keep voltages of all floating capacitors well-controlled. Since the capacitors voltages are controlled using the phase currents, additional pre-charging circuitry is not required. A modulation scheme using level-shifted carriers has also been developed, which can be used with both V/f control and d-q control. The high-voltage inverter has a low effective switching frequency and the low-voltage inverter has a high effective switching frequency, reducing the switching loss. The included results of steady-state and transient testing of an experimental prototype demonstrate that the proposed scheme is suited for industrial drives and traction applications
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