232 research outputs found
Stress-structure relation in dense colloidal melt under forward and instantaneous reversal of shear
Dense supercooled colloidal melt in forward shear from a quiescent state
shows overshoot in shear stress at 10% strain with an unchanged fluid structure
at equal stress before and after overshoot. In addition, we find overshoot in
normal stress with a monotonic increase in osmotic pressure at an identical
strain. The first and second normal stress become comparable in magnitude and
opposite in sign. Functional dependence of the steady state stress and osmotic
pressure with Peclet number demonstrate signature of crossover between
Newtonian and nearly- Newtonian regime. Moreover, instantaneous shear reversal
from steady state exhibit Bauschinger effect, where strong history dependence
is observed depending on the time of flow reversal. The distribution of
particulate stress and osmotic pressure at the point of flow reversal is shown
to be a signature of the subsequent response. We link the history dependence of
the stress-strain curves to changes in the fluid structure measured through the
angular components of the radial distribution function. A uniform compression
in transition from forward to reversed flowing state is found.Comment: 8 pages, 6 figure
Controlling motile disclinations in a thick nematogenic material with an electric field
Manipulating topological disclination networks that arise in a
symmetry-breaking phase transfor- mation in widely varied systems including
anisotropic materials can potentially lead to the design of novel materials
like conductive microwires, self-assembled resonators, and active anisotropic
matter. However, progress in this direction is hindered by a lack of control of
the kinetics and microstructure due to inherent complexity arising from
competing energy and topology. We have studied thermal and electrokinetic
effects on disclinations in a three-dimensional nonabsorbing nematic material
with a positive and negative sign of the dielectric anisotropy. The electric
flux lines are highly non-uniform in uniaxial media after an electric field
below the Fr\'eedericksz threshold is switched on, and the kinetics of the
disclination lines is slowed down. In biaxial media, depending on the sign of
the dielectric anisotropy, apart from the slowing down of the disclination
kinetics, a non-uniform electric field filters out disclinations of different
topology by inducing a kinetic asymmetry. These results enhance the current
understanding of forced disclination networks and establish the pre- sented
method, which we call fluctuating electronematics, as a potentially useful tool
for designing materials with novel properties in silico.Comment: 17 Pages, 14 Figure
Development of Multiport Single Stage Bidirectional Converter for Photovoltaic and Energy Storage Integration
The energy market is on the verge of a paradigm shift as the emergence of renewable energy sources over traditional fossil fuel based energy supply has started to become cost competitive and viable. Unfortunately, most of the attractive renewable sources come with inherent challenges such as: intermittency and unreliability. This is problematic for today\u27s stable, day ahead market based power system. Fortunately, it is well established that energy storage devices can compensate for renewable sources shortcomings. This makes the integration of energy storage with the renewable energy sources, one of the biggest challenges of modern distributed generation solution. This work discusses, the current state of the art of power conversion systems that integrate photovoltaic and battery energy storage systems. It is established that the control of bidirectional power flow to the energy storage device can be improved by optimizing its modulation and control. Traditional multistage conversion systems offers the required power delivery options, but suffers from a rigid power management system, reduced efficiency and increased cost. To solve this problem, a novel three port converter was developed which allows bidirectional power flow between the battery and the load, and unidirectional power flow from the photovoltaic port. The individual two-port portions of the three port converter were optimized in terms of modulation scheme. This leads to optimization of the proposed converter, for all possible power flow modes. In the second stage of the project, the three port converter was improved both in terms of cost and efficiency by proposing an improved topology. The improved three port converter has reduced functionality but is a perfect fit for the targeted microinverter application. The overall control system was designed to achieve improved reference tracking for power management and output AC voltage control. The bidirectional converter and both the proposed three port converters were analyzed theoretically. Finally, experimental prototypes were built to verify their performance
Quantum thermal machines and batteries
The seminal work by Sadi Carnot in the early nineteenth century provided the
blueprint of a reversible heat engine and the celebrated second law of
thermodynamics eventually followed. Almost two centuries later, the quest to
formulate a quantum theory of the thermodynamic laws has thus unsurprisingly
motivated physicists to visualise what are known as `quantum thermal machines'
(QTMs). In this article, we review the prominent developments achieved in the
theoretical construction as well as understanding of QTMs, beginning from the
formulation of their earliest prototypes to recent models. We also present a
detailed introduction and highlight recent progress in the rapidly developing
field of `quantum batteries'.Comment: Final version. To be published as a topical review in Euro. Phys.
Jour.
- …