886 research outputs found
Cohomological X-independence for Higgs bundles and Gopakumar–Vafa invariants
Get PDFThe 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
Timing calculations for three level dodecagonal space vector structure from reference phase voltages
No full textA method to obtain pulse width modulation (PWM) timings for a three level dodecagonal (12-sided polygon) voltage space vector structure using only sampled reference values is proposed in this paper. Typical methods that are used to find PWM timings for dodecagonal SV structures use modulation index and the reference vector angle to get the timings by using trigonometric calculations. This method requires look-up tables, angle estimation making it difficult to implement in closed loop systems. The proposed method requires only two additions to compute these timings. For multilevel case, typical iterative methods need timing calculations (matrix multiplications) to be performed for each triangle within a sector. The proposed method does not require any iterative searching for locating the triangle in which the tip of the reference vector lies. It is also is generic and can be extended to any number of levels with symmetric structures. The algorithm outputs the triangle number and the PWM compare values - that can be used by any carrier based PWM module to obtain space vector PWM like switching sequences. Extensive simulation and experimental results for steady state and transient conditions have been presented to validate the proposed method
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. 
Genus zero Gopakumar-Vafa invariants from open strings
No full text<p>Abstract: We propose a new way to compute the genus zero Gopakumar-Vafa invariants<br>\nfor two families of non-toric non-compact Calabi-Yau threefolds that admit simple flops:<br>\nReid’s Pagodas, and Laufer’s examples. We exploit the duality between M-theory on these<br>\nthreefolds, and IIA string theory with D6-branes and O6-planes. From this perspective,<br>\nthe GV invariants are detected as five-dimensional open string zero modes. We propose<br>\na definition for genus zero GV invariants for threefolds that do not admit small crepant<br>\nresolutions. We find that in most cases, non-geometric T-brane data is required in order<br>\nto fully specify the invariants.</p>
Relative Mirror Symmetry and Ramifications of a Formula for Gromov-Witten Invariants
Get PDFFor 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
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
Chern-Simons theory on L(p,q) lens spaces and Gopakumar-Vafa duality
No full textWe consider aspects of Chern-Simons theory on L (p, q) lens spaces and its relation with matrix models and topological string theory on Calabi-Yau threefolds, searching for possible new large N dualities via geometric transition for non-S U (2) cyclic quotients of the conifold. To this aim we find, on one hand, a useful matrix integral representation of the S U (N) C S partition function in a generic flat background for the whole L (p, q) family and provide a solution for its large N dynamics; on the other hand, we perform in full detail the construction of a family of would-be dual closed string backgrounds through conifold geometric transition from T* L (p, q). We can then explicitly prove the claim in [5] that Gopakumar-Vafa duality in a fixed vacuum fails in the case q > 1, and briefly discuss how it could be restored in a non-perturbative setting.</p
Revalorization of sunflower stalks as novel sources of cellulose nanofibrils and nanocrystals and their effect on wheat gluten bionanocomposite properties
Get PDF[EN] Novel gluten based bionanocomposites reinforced with cellulose nanofibrils (CNF) and cellulose
nanocrystals (CNC) extracted from sunflower stalks by respectively a steam explosion treatment and
a hydrolysis procedure, were prepared by casting/evaporation. The extracted cellulose nanomaterials,
both CNC and CNF, were embedded in gluten matrix and their effect was investigated. Morphological
investigations highlighted that gluten based bionanocomposites showed a homogenous morphology,
the absence of visible cellulose nanoreinforcements, and the presence of holes for Gluten CNF nanocomposites.
Gluten CNF showed a reduction of water vapour permeability coefficients but the values are
higher respect to gluten reinforced with CNC. This behaviour could be related to the ability of CNC to
increase the tortuous path of gas molecules. Moreover, the results from thermal, mechanical and barrier
properties confirmed the strong interactions obtained between CNC and gluten matrix during the
process.
The study suggested the possibility to re-valorise agricultural wastes with potential applications as
reinforcement in polymer matrix bionanocomposites.
© 2016 Elsevier Ltd. All rights reservedFortunati, E.; Luzi, F.; Jiménez Marco, A.; Gopakumar, D.; Puglia, D.; Thomas, S.; Kenny, J.... (2016). Revalorization of sunflower stalks as novel sources of cellulose nanofibrils and nanocrystals and their effect on wheat gluten bionanocomposite properties. Carbohydrate Polymers. 149:357-368. doi:10.1016/j.carbpol.2016.04.120S35736814
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No full textNot AvailableThe impact of motorization of traditional craft on two fisheries resources, viz. tunas and whitebait
anchovies, was studied. A conspicuous increase in the annual tuna catch was seen from 1984 due to the
increased effort expended by the motorized craft by using more units of drift nets, hooks and lines than
non-motorized craft. The tuna landing increased from 361 tonnes during the pre-motorization period to
1976 tonnes during the motorization period. On the contrary, the anchovy landing came down from 580
tonnes during the pre-motorization period to 386 tonnes on motorization. A decline was noticed in the effort
expended for whitebait anchovies but the catch rate did not show a steep decline which indicated that the
reduction of effort was not due to the decrease in the catch rate. The shifting over of motorized units to drift
net and hooks and lines operation seems to be the major reason for the decline in the effort of boat siene
and nelholi vala which are the main gears for whitebait anchovies.
Indian Journal of Fisheries 41 (2): 92-9, June 1994
The motorization of traditional craft was
initiated in central Kerala by 1980. It spread
to northern and southern areas by 1983 (Balan
et al. 1989). At Vizhinjam, the most important
fish landing centre in Trivandrum, the
motorization was initiated during the middle
of 1982. A substantial increase in the effort
from the motorized craft was recorded from
A 984 which resulted in an immediate increase
in the total fish catch at Vizhinjam. An account
of the traditional fishery in the area has
been given by Luther et al. (1982) and Nair et
al. (1988) and the initiation of motorization of
traditional craft in the area has been reported
by Gopakumar et al. (1986). The increase in
Present address: 'Scientist (SG), technical Officer,
Technical Assistant
the catch and catch rate of tunas and mackerel
as a result of motorization has also been
pointed out by Gopakumar and Sarma (1989)
and Gopakumar et al. (1991). The chief gears
operated by the motorized craft at Vizhinjam
are hooks and lines and drift net.
Motorization has extended the fishing areas of
traditional craft to relatively more distant
grounds and has increased the yield of certain
resources like tunas which are caught chiefly
by drift net and hooks and lines. This has
resulted in a reduction in the operation of
non-motorized units and a simultaneous
decrease in the yield of certain other resources
like whitebait anchovies which are caught by
boat seine, shore seine and netholi vala. To
analyse this aspect, the trends offish landing
with particular reference to two resources, viz.
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