Turning bubbles on and off during boiling using charged surfactants

Boiling—a process that has powered industries since the steam age—is governed by bubble formation. State-of-the-art boiling surfaces often increase bubble nucleation via roughness and/or wettability modification to increase performance. However, without active in situ control of bubbles, temperature or steam generation cannot be adjusted for a given heat input. Here we report the ability to turn bubbles ‘on and off’ independent of heat input during boiling both temporally and spatially via molecular manipulation of the boiling surface. As a result, we can rapidly and reversibly alter heat transfer performance up to an order of magnitude. Our experiments show that this active control is achieved by electrostatically adsorbing and desorbing charged surfactants to alter the wettability of the surface, thereby affecting nucleation. This approach can improve performance and flexibility in existing boiling technologies as well as enable emerging or unprecedented energy applications.Singapore-MIT Alliance for Research and TechnologyNational Science Foundation (U.S.). Materials Research Science and Engineering Centers (Program) (Award DMR-0819762

Analytical treatment of SUSY Quasi-normal modes in a non-rotating Schwarzschild black hole

We use the Fock-Ivanenko formalism to obtain the Dirac equation which describes the interaction of a massless 1/2-spin neutral fermion with a gravitational field around a Schwarzschild black hole (BH). We obtain approximated analytical solutions for the eigenvalues of the energy (quasi-normal frequencies) and their corresponding eigenstates (quasi-normal states). The interesting result is that all the excited states [and their supersymmetric (SUSY) partners] have a purely imaginary frequency, which can be expressed in terms of the Hawking temperature. Furthermore, as one expects for SUSY Hamiltonians, the isolated bottom state has a real null energy eigenvalue.Comment: Version to be published in European Physical Journal

Multi-Player and Multi-Choice Quantum Game

We investigate a multi-player and multi-choice quantum game. We start from two-player and two-choice game and the result is better than its classical version. Then we extend it to N-player and N-choice cases. In the quantum domain, we provide a strategy with which players can always avoid the worst outcome. Also, by changing the value of the parameter of the initial state, the probabilities for players to obtain the best payoff will be much higher that in its classical version.Comment: 4 pages, 1 figur

Manufacturability of AlSi10Mg overhang structures fabricated by laser powder bed fusion

© 2018 Elsevier Ltd The main advantage of laser powder bed fusion (LPBF) is its use for directly manufacturing metal components with highly complex geometries. But the LPBF manufacture of overhang structures, also known as downward-facing surfaces, is a challenge because of the possibility of incurring distortion and dross defects. This paper presents a systematic examination of the manufacturability and structural integrity of AlSi10Mg overhang structures fabricated by LPBF using computational and experimental techniques. The experimental and simulation results indicate that the use of support structures facilitates the manufacturability and structural integrity of both full-circle and half-circle overhang structures. The influence of supports on circularity was found to be more beneficial as the diameter increased above 15 mm. The experiments also suggest that the use of supports plays a significant role in maintaining mechanical performance by successful fabrication of downward-facing surfaces free of dross defects. From a design perspective, small overhang features are preferable to large overhangs, especially when support removal is impractical. This study significantly contributes to design for metal additive manufacturing by providing an improved understanding of the manufacturability of overhang structures in applications intended for lightweight structural performance

Spin dependent quantum interference in non-local graphene spin valves

Spin dependent electron transport measurements on graphene are of high importance to explore possible spintronic applications. Up to date all spin transport experiments on graphene were done in a semi-classical regime, disregarding quantum transport properties such as phase coherence and interference. Here we show that in a quantum coherent graphene nanostructure the non-local voltage is strongly modulated. Using non-local measurements, we separate the signal in spin dependent and spin independent contributions. We show that the spin dependent contribution is about two orders of magnitude larger than the spin independent one, when corrected for the finite polarization of the electrodes. The non-local spin signal is not only strongly modulated but also changes polarity as a function of the applied gate voltage. By locally tuning the carrier density in the constriction we show that the constriction plays a major role in this effect and indicates that it can act as a spin filter device. Our results show the potential of quantum coherent graphene nanostructures for the use in future spintronic devices

Annealing temperature dependence of capacitance-voltage characteristics in Ge-nanocrystal-based nonvolatile memory structures

The annealing temperature (TA) dependence of capacitance-voltage (C-V) characteristics has been studied in metal-oxide-semiconductor structures containing Ge nanocrystals (NCs) produced by ion implantation and annealing. These structures are of interest for application as nonvolatile memory and TA is shown to have a strong influence on the C-V hysteresis. This behavior is shown to be correlated with structural changes of the Ge NCs which have been characterized by synchrotron-radiation photoemission spectroscopy. Specifically, well-defined C-V characteristics with large hysteresis were found only for annealing temperatures greater than 950 °C where Ge nanocrystals are known to form. In this temperature regime, transmission electron microcopy and energy dispersive x-ray spectroscopy demonstrate the existence of regularly arranged Ge NCs of approximately 3–5 nm diameter located around 6.7 nm from the interface

Spin and Chirality Effects in Antler-Topology Processes at High Energy e+e−e^+e^- Colliders

We perform a model-independent investigation of spin and chirality correlation effects in the antler-topology processes $e^+e^-\to\mathcal{P}^+\mathcal{P}^-\to (\ell^+ \mathcal{D}^0) (\ell^-\mathcal{\bar{D}}^0)$ at high energy $e^+e^-$ colliders with polarized beams. Generally the production process $e^+e^-\to\mathcal{P}^+\mathcal{P}^-$ can occur not only through the $s$-channel exchange of vector bosons, $\mathcal{V}^0$, including the neutral Standard Model (SM) gauge bosons, $\gamma$ and $Z$, but also through the $s$- and $t$-channel exchanges of new neutral states, $\mathcal{S}^0$ and $\mathcal{T}^0$, and the $u$-channel exchange of new doubly-charged states, $\mathcal{U}^{--}$. The general set of (non-chiral) three-point couplings of the new particles and leptons allowed in a renormalizable quantum field theory is considered. The general spin and chirality analysis is based on the threshold behavior of the excitation curves for $\mathcal{P}^+\mathcal{P}^-$ pair production in $e^+e^-$ collisions with longitudinal and transverse polarized beams, the angular distributions in the production process and also the production-decay angular correlations. In the first step, we present the observables in the helicity formalism. Subsequently, we show how a set of observables can be designed for determining the spins and chiral structures of the new particles without any model assumptions. Finally, taking into account a typical set of approximately chiral invariant scenarios, we demonstrate how the spin and chirality effects can be probed experimentally at a high energy $e^+e^-$ collider.Comment: 50 pages, 14 figures, 6 tables, matches version published in EPJ