2,071 research outputs found
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The theory of international business: the role of economic models
This paper reviews the scope for economic modelling in international business studies. It argues for multi-level theory based on classic internalisation theory. It present a systems approach that encompasses both firm-level and industry-level analysis
Fractional Dehn twists in knot theory and contact topology
Fractional Dehn twists give a measure of the difference between the relative
isotopy class of a homeomorphism of a bordered surface and the Thurston
representative of its free isotopy class. We show how to estimate and compute
these invariants. We discuss the the relationship of our work to stabilization
problems in classical knot theory, general open book decompositions, and
contact topology. We include an elementary characterization of overtwistedness
for contact structures described by open book decompositions.Comment: We have removed an incorrect assumption about properties of
meridional disks of Heegaard decompositions of S^3 and have added a
conjecture about stabilizations of knots in S^
Can physical activity and dietary interventions improve maternal and fetal outcomes in women with gestational diabetes mellitus? A systematic review and meta-analysis
The impact of COVID-19 on the physical activity and sedentary behaviour levels of pregnant women with gestational diabetes
Charge dependence of neoclassical and turbulent transport of light impurities on MAST
Carbon and nitrogen impurity transport coefficients are determined from gas
puff experiments carried out during repeat L-mode discharges on the Mega-Amp
Spherical Tokamak (MAST) and compared against a previous analysis of helium
impurity transport on MAST. The impurity density profiles are measured on the
low-field side of the plasma, therefore this paper focuses on light impurities
where the impact of poloidal asymmetries on impurity transport is predicted to
be negligible. A weak screening of carbon and nitrogen is found in the plasma
core, whereas the helium density profile is peaked over the entire plasma
radius.Comment: 17 pages, 7 figure
Universal manifold pairings and positivity
Gluing two manifolds M_1 and M_2 with a common boundary S yields a closed
manifold M. Extending to formal linear combinations x=Sum_i(a_i M_i) yields a
sesquilinear pairing p= with values in (formal linear combinations of)
closed manifolds. Topological quantum field theory (TQFT) represents this
universal pairing p onto a finite dimensional quotient pairing q with values in
C which in physically motivated cases is positive definite. To see if such a
"unitary" TQFT can potentially detect any nontrivial x, we ask if is
non-zero whenever x is non-zero. If this is the case, we call the pairing p
positive. The question arises for each dimension d=0,1,2,.... We find p(d)
positive for d=0,1, and 2 and not positive for d=4. We conjecture that p(3) is
also positive. Similar questions may be phrased for (manifold, submanifold)
pairs and manifolds with other additional structure. The results in dimension 4
imply that unitary TQFTs cannot distinguish homotopy equivalent simply
connected 4-manifolds, nor can they distinguish smoothly s-cobordant
4-manifolds. This may illuminate the difficulties that have been met by several
authors in their attempts to formulate unitary TQFTs for d=3+1. There is a
further physical implication of this paper. Whereas 3-dimensional Chern-Simons
theory appears to be well-encoded within 2-dimensional quantum physics, eg in
the fractional quantum Hall effect, Donaldson-Seiberg-Witten theory cannot be
captured by a 3-dimensional quantum system. The positivity of the physical
Hilbert spaces means they cannot see null vectors of the universal pairing;
such vectors must map to zero.Comment: Published by Geometry and Topology at
http://www.maths.warwick.ac.uk/gt/GTVol9/paper53.abs.htm
Equivariant comparison of quantum homogeneous spaces
We prove the deformation invariance of the quantum homogeneous spaces of the
q-deformation of simply connected simple compact Lie groups over the
Poisson-Lie quantum subgroups, in the equivariant KK-theory with respect to the
translation action by maximal tori. This extends a result of Neshveyev-Tuset to
the equivariant setting. As applications, we prove the ring isomorphism of the
K-group of Gq with respect to the coproduct of C(Gq), and an analogue of the
Borsuk-Ulam theorem for quantum spheres.Comment: 21 page
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Performance of Portable Storage Containers in Reducing Neutron Radiation
The principal investigators designed portable shielded containers that reduce neutron dose to workers from fissile materials contained in storage canisters. We studied the shielding characteristics of several common shielding materials, such as polyethylene, B{sub 4}C, and cadmium. From these studies, we found and successfully demonstrated that by suing a combination of CH{sub 2} and B{sub 4}C, we could reduce neutron dose by a factor of four or better. In addition, the containers we designed with the new materials are of reasonable size and weight
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Using response characteristics of neutron measurement devices to improve neutron dosimetry
Recent administrative restrictions on personnel dose equivalent have resulted in increased pressure to more accurately report the neutron component without the traditional conservative added factors which sometimes inflate the reported values. Improvements include a new albedo neutron dosimeter which is capable of some limited energy discrimination. Also, additional emphasis has been placed on improving field measurements using traditional survey instrumentation and specialized spectroscopic techniques such as tissue equivalent proportional counters, Bonner spheres, and a modified 9 inches to 3 inches ratio technique. Improvements in these techniques along with a better understanding of the response of the TLD system have resulted in substantial reduction in the reported dose equivalent by improving the accuracy of the dosimeter system. The response characteristics of the TLD system and other instrumentation are obtained through modeling with the Monte Carlo code MCNP-4A. Neutron fields in work-areas are initially characterized with Bonner spheres. Routine updates are accomplished using a modified 9 inches to 3 inches ratio technique. These measurements are then used to predict the response of the TLD system when worn in that area. Correction curves are derived for the principal spectrum with various fractions of moderated or reflected neutrons. Work assignments are tracked through a database systems which is used to determine the principal spectrum that results in the neutron dose equivalent. The energy discrimination capability of the TLD system is used with the correction curve to derive an average correction appropriate to the readings of the dosimeter thus giving an energy corrected dose equivalent for the individual
Isotope dependence of energy, momentum and particle confinement in tokamaks
The isotope dependence of plasma transport will have a significant impact on the performance of future D-T experiments in JET and ITER and eventually on the fusion gain and economics of future reactors. In preparation for future D-T operation on JET, dedicated experiments and comprehensive transport analyses were performed in H, D and H-D mixed plasmas. The analysis of the data has demonstrated an unexpectedly strong and favourable dependence of the global confinement of energy, momentum and particles in ELMy H-mode plasmas on the atomic mass of the main ion species, the energy confinement time scaling as ĎEâźA0.5 (Maggi et al., Plasma Phys. Control. Fusion, vol. 60, 2018, 014045; JET Team, Nucl. Fusion, vol. 39, 1999, pp. 1227â1244), i.e. opposite to the expectations based only on local gyro-Bohm (GB) scaling, ĎEâźAâ0.5 , and stronger than in the commonly used H-mode scaling for the energy confinement (Saibene et al., Nucl. Fusion, vol. 39, 1999, 1133; ITER Physics Basis, Nucl. Fusion, vol. 39, 1999, 2175). The scaling of momentum transport and particle confinement with isotope mass is very similar to that of energy transport. Nonlinear local GENE gyrokinetic analysis shows that the observed anti-GB heat flux is accounted for if collisions, E Ă B shear and plasma dilution with low-Z impurities (9Be) are included in the analysis (E and B are, respectively the electric and magnetic fields). For L-mode plasmas a weaker positive isotope scaling ĎEâźA0.14 has been found in JET (Maggi et al., Plasma Phys. Control. Fusion, vol. 60, 2018, 014045), similar to ITER97-L scaling (Kaye et al., Nucl. Fusion, vol. 37, 1997, 1303). Flux-driven quasi-linear gyrofluid calculations using JETTO-TGLF in L-mode show that local GB scaling is not followed when stiff transport (as is generally the case for ion temperature gradient modes) is combined with an imposed boundary condition taken from the experiment, in this case predicting no isotope dependence. A dimensionless identity plasma pair in hydrogen and deuterium L-mode plasmas has demonstrated scale invariance, confirming that core transport physics is governed, as expected, by the 4 dimensionless parameters Ď*, ν*, β, q (normalised ion Larmor radius, collisionality, plasma pressure and safety factor) consistently with global quasi-linear gyrokinetic TGLF calculations (Maggi et al., Nucl. Fusion, vol. 59, 2019, 076028). We compare findings in JET with those in different devices and discuss the possible reasons for the different isotope scalings reported from different devices. The diversity of observations suggests that the differences may result not only from differences affecting the core, e.g. heating schemes, but are to a large part due to differences in device-specific edge and wall conditions, pointing to the importance of better understanding and controlling pedestal and edge processes.EUROfusion Consortium grant agreement No 63305
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