7,547 research outputs found
Droplet Ripening in Concentration Gradients
Living cells use phase separation and concentration gradients to organize
chemical compartments in space. Here, we present a theoretical study of droplet
dynamics in gradient systems. We derive the corresponding growth law of
droplets and find that droplets exhibit a drift velocity and position dependent
growth. As a consequence, the dissolution boundary moves through the system,
thereby segregating droplets to one end. We show that for steep enough
gradients, the ripening leads to a transient arrest of droplet growth that is
induced by an narrowing of the droplet size distribution.Comment: 12 pages, 4 figure
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Integrated Dynamic Facade Control with an Agent-based Architecture for Commercial Buildings
Dynamic façades have significant technical potential to minimize heating, cooling, and lighting energy use and peak electric demand in the perimeter zone of commercial buildings, but the performance of these systems is reliant on being able to balance complex trade-offs between solar control, daylight admission, comfort, and view over the life of the installation. As the context for controllable energy-efficiency technologies grows more complex with the increased use of intermittent renewable energy resources on the grid, it has become increasingly important to look ahead towards more advanced approaches to integrated systems control in order to achieve optimum life-cycle performance at a lower cost. This study examines the feasibility of a model predictive control system for low-cost autonomous dynamic façades. A system architecture designed around lightweight, simple agents is proposed. The architecture accommodates whole building and grid level demands through its modular, hierarchical approach. Automatically-generated models for computing window heat gains, daylight illuminance, and discomfort glare are described. The open source Modelica and JModelica software tools were used to determine the optimum state of control given inputs of window heat gains and lighting loads for a 24-hour optimization horizon. Penalty functions for glare and view/ daylight quality were implemented as constraints. The control system was tested on a low-power controller (1.4 GHz single core with 2 GB of RAM) to evaluate feasibility. The target platform is a low-cost ($35/unit) embedded controller with 1.2 GHz dual-core cpu and 1 GB of RAM. Configuration and commissioning of the curtainwall unit was designed to be largely plug and play with minimal inputs required by the manufacturer through a web-based user interface. An example application was used to demonstrate optimal control of a three-zone electrochromic window for a south-facing zone. The overall approach was deemed to be promising. Further engineering is required to enable scalable, turnkey solutions
Neurosystems: brain rhythms and cognitive processing
Neuronal rhythms are ubiquitous features of brain dynamics, and are highly correlated with cognitive processing. However, the relationship between the physiological mechanisms producing these rhythms and the functions associated with the rhythms remains mysterious. This article investigates the contributions of rhythms to basic cognitive computations (such as filtering signals by coherence and/or frequency) and to major cognitive functions (such as attention and multi-modal coordination). We offer support to the premise that the physiology underlying brain rhythms plays an essential role in how these rhythms facilitate some cognitive operations.098352 - Wellcome Trust; 5R01NS067199 - NINDS NIH HH
On the connection between quantum nonlocality and phase sensitivity of two-mode entangled Fock state superpositions
In two-mode interferometry, for a given total photon number , entangled
Fock state superpositions of the form have been considered for phase
estimation. Indeed all such states are maximally mode-entangled and violate a
Clauser-Horne-Shimony-Holt (CHSH) inequality. However, they differ in their
optimal phase estimation capabilities as given by their quantum Fisher
informations. The quantum Fisher information is the largest for the
state and
decreases for the other states with decreasing photon number difference between
the two modes. We ask the question whether for any particular Clauser-Horne
(CH) (or CHSH) inequality, the maximal values of the CH (or the CHSH)
functional for the states of the above type follow the same trend as their
quantum Fisher informations, while also violating the classical bound whenever
the states are capable of sub-shot-noise phase estimation, so that the
violation can be used to quantify sub-shot-noise sensitivity. We explore CH and
CHSH inequalities in a homodyne setup. Our results show that the amount of
violation in those nonlocality tests may not be used to quantify sub-shot-noise
sensitivity of the above states.Comment: Published online in Quantum Information Processin
Charge and spin density modulations in semiconductor quantum wires
We investigate static charge and spin density modulation patterns along a
ferromagnet/semiconductor single junction quantum wire in the presence of
spin-orbit coupling. Coherent scattering theory is used to calculate the charge
and spin densities in the ballistic regime. The observed oscillatory behavior
is explained in terms of the symmetry of the charge and spin distributions of
eigenstates in the semiconductor quantum wire. Also, we discuss the condition
that these charge and spin density oscillations can be observed experimentally.Comment: 7 pages, 8 figures (low-resolution
Common gauge origin of discrete symmetries in observable sector and hidden sector
An extra Abelian gauge symmetry is motivated in many new physics models in
both supersymmetric and nonsupersymmetric cases. Such a new gauge symmetry may
interact with both the observable sector and the hidden sector. We
systematically investigate the most general residual discrete symmetries in
both sectors from a common Abelian gauge symmetry. Those discrete symmetries
can ensure the stability of the proton and the dark matter candidate. A hidden
sector dark matter candidate (lightest U-parity particle or LUP) interacts with
the standard model fields through the gauge boson Z', which may selectively
couple to quarks or leptons only. We make a comment on the implications of the
discrete symmetry and the leptonically coupling dark matter candidate, which
has been highlighted recently due to the possibility of the simultaneous
explanation of the DAMA and the PAMELA results. We also show how to construct
the most general U(1) charges for a given discrete symmetry, and discuss the
relation between the U(1) gauge symmetry and R-parity.Comment: Version to appear in JHE
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