6,670 research outputs found
The Cavendish Living lab - a multidisciplinary, vertically integrated project focused on sustainability
Colleagues from the School of Life Sciences will present findings from The Cavendish Living Lab’: a 2 year vertically integrated project (VIP) that focuses on co-creating sustainable solutions with the student participants from various disciplines and levels. Through applied research and learning within an authentic setting, the ‘Living Lab’ approach uses our university campus as the laboratory, and a platform for the students to partner with various stakeholders to address real world issues and develop innovative, sustainable solutions to problems such as food waste, plastic waste, and waste water
Superfluid-Insulator transition of ultracold atoms in an optical lattice in the presence of a synthetic magnetic field
We study the Mott insulator-superfluid transition of ultracold bosonic atoms
in a two-dimensional square optical lattice in the presence of a synthetic
magnetic field with p/q (p and q being co-prime integers) flux quanta passing
through each lattice plaquette. We show that on approach to the transition from
the Mott side, the momentum distribution of the bosons exhibits q precursor
peaks within the first magnetic Brillouin zone. We also provide an effective
theory for the transition and show that it involves q interacting boson fields.
We construct, from a mean-field analysis of this effective theory, the
superfluid ground states near the transition and compute, for q=2,3, both the
gapped and the gapless collective modes of these states. We suggest experiments
to test our theory.Comment: 4 pages, 4 figs; v
Direct test of defect mediated laser induced melting theory for two dimensional solids
We investigate by direct numerical solution of appropriate renormalization
flow equations, the validity of a recent dislocation unbinding theory for laser
induced freezing/melting in two dimensions. The bare elastic moduli and
dislocation fugacities which are inputs to the flow equations are obtained for
three different 2-d systems (hard disk, inverse power and the
Derjaguin-Landau-Verwey-Overbeek potentials) from a restricted Monte Carlo
simulation sampling only configurations {\em without} dislocations. We conclude
that (a) the flow equations need to be correct at least up to third order in
defect fugacity to reproduce meaningful results, (b) there is excellent
quantitative agreement between our results and earlier conventional Monte Carlo
simulations for the hard disk system and (c) while the qualitative form of the
phase diagram is reproduced for systems with soft potentials there is some
quantitative discrepancy which we explain.Comment: 11 pages, 14 figures, submitted to Phys. Rev.
Large diamagnetic persistent currents
In multichannel rings, evanescent modes will always co-exist with propagating
modes. The evanescent modes can carry a very large diamagnetic persistent
current that can oscillate with energy and are very sensitive to impurity
scattering. This provides a natural explanation for the large diamagnetic
persistent currents observed in experiments.Comment: 5 figure
Defect fugacity, Spinwave Stiffness and T_c of the 2-d Planar Rotor Model
We obtain precise values for the fugacities of vortices in the 2-d planar
rotor model from Monte Carlo simulations in the sector with {\em no} vortices.
The bare spinwave stiffness is also calculated and shown to have significant
anharmonicity. Using these as inputs in the KT recursion relations, we predict
the temperature T_c = 0.925, using linearised equations, and using next higher order corrections, at which vortex unbinding commences
in the unconstrained system. The latter value, being in excellent agreement
with all recent determinations of T_c, demonstrates that our method 1)
constitutes a stringent measure of the relevance of higher order terms in KT
theory and 2) can be used to obtain transition temperatures in similar systems
with modest computational effort.Comment: 7 pages, 4 figure
A ~ 12 kpc HI extension and other HI asymmetries in the isolated galaxy CIG 340 (IC 2487)
HI kinematic asymmetries are common in late-type galaxies irrespective of
environment, although the amplitudes are strikingly low in isolated galaxies.
As part of our studies of the HI morphology and kinematics in isolated
late-type galaxies we have chosen several very isolated galaxies from the AMIGA
sample for HI mapping. Here we present GMRT 21-cm HI line mapping of CIG 340
which was selected because its integrated HI spectrum has a very symmetric
profile, Aflux = 1.03. Optical images of the galaxy hinted at a warped disk in
contrast to the symmetric integrated HI spectrum profile. Our aim is to
determine the extent to which the optical asymmetry is reflected in the
resolved HI morphology and kinematics. GMRT observations reveal significant HI
morphological asymmetries in CIG 340 despite it's overall symmetric optical
form and highly symmetric HI spectrum. The most notable HI features are: 1) a
warp in the HI disk (with an optical counterpart), 2) the HI north/south flux
ratio = 1.32 is much larger than expected from the integrated HI spectrum
profile and 3) a ~ 45" (12 kpc) HI extension, containing ~ 6% of the detected
HI mass on the northern side of the disk. We conclude that in isolated galaxies
a highly symmetric HI spectrum can mask significant HI morphological
asymmetries. The northern HI extension appears to be the result of a recent
perturbation (10^8 yr), possibly by a satellite which is now disrupted or
projected within the disk. This study provides an important step in our ongoing
program to determine the predominant source of HI asymmetries in isolated
galaxies. For CIG 340 the isolation from major companions, symmetric HI
spectrum, optical morphology and interaction timescales have allowed us to
narrow the possible causes the HI asymmetries and identify tests to further
constrain the source of the asymmetries.Comment: 10 page
In-situ Stochastic Training of MTJ Crossbar based Neural Networks
Owing to high device density, scalability and non-volatility, Magnetic Tunnel
Junction-based crossbars have garnered significant interest for implementing
the weights of an artificial neural network. The existence of only two stable
states in MTJs implies a high overhead of obtaining optimal binary weights in
software. We illustrate that the inherent parallelism in the crossbar structure
makes it highly appropriate for in-situ training, wherein the network is taught
directly on the hardware. It leads to significantly smaller training overhead
as the training time is independent of the size of the network, while also
circumventing the effects of alternate current paths in the crossbar and
accounting for manufacturing variations in the device. We show how the
stochastic switching characteristics of MTJs can be leveraged to perform
probabilistic weight updates using the gradient descent algorithm. We describe
how the update operations can be performed on crossbars both with and without
access transistors and perform simulations on them to demonstrate the
effectiveness of our techniques. The results reveal that stochastically trained
MTJ-crossbar NNs achieve a classification accuracy nearly same as that of
real-valued-weight networks trained in software and exhibit immunity to device
variations.Comment: Accepted for poster presentation in the 2018 ACM/IEEE International
Symposium on Low Power Electronics and Design (ISLPED
Intrinsic Structural Disorder and the Magnetic Ground State in Bulk EuTiO3
The magnetic properties of single-crystal EuTiO3 are suggestive of nanoscale
disorder below its cubic-tetragonal phase transition. We demonstrate that
electric field cooling acts to restore monocrystallinity, thus confirming that
emergent structural disorder is an intrinsic low-temperature property of this
material. Using torque magnetometry, we deduce that tetragonal EuTiO3 enters an
easy-axis antiferromagnetic phase at 5.6 K, with a first-order transition to an
easy-plane ground state below 3 K. Our data is reproduced by a 3D anisotropic
Heisenberg spin model.Comment: 5 pages, 4 figure
Defect production due to quenching through a multicritical point
We study the generation of defects when a quantum spin system is quenched
through a multicritical point by changing a parameter of the Hamiltonian as
, where is the characteristic time scale of quenching. We argue
that when a quantum system is quenched across a multicritical point, the
density of defects () in the final state is not necessarily given by the
Kibble-Zurek scaling form , where is the
spatial dimension, and and are respectively the correlation length
and dynamical exponent associated with the quantum critical point. We propose a
generalized scaling form of the defect density given by , where the exponent determines the behavior of the
off-diagonal term of the Landau-Zener matrix at the multicritical
point. This scaling is valid not only at a multicritical point but also at an
ordinary critical point.Comment: 4 pages, 2 figures, updated references and added one figur
- …