Variation Of Chemical Potential Research Articles

Three-Dimensional Analysis of Coarsening Dynamics in Porous Materials for Electrochemical Energy Conversion and Storage: Direct Measurement and Visualization of Changes in Local Surface Curvature

High operating temperature affords solid oxide fuel cells (SOFCs) fuel flexibility, favorable kinetics, enhanced transport properties and high quality heat for secondary thermodynamic cycles.1 Elevated temperatures, however, present challenges to ensuring cell durability.2 Coarsening of nickel in the Ni-YSZ anode is one such challenge that can lead to significant performance degradation. The fundamental driving force Δμ for coarsening phenomena is given by Eq. 1.3 The expression, which assumes isotropic interfacial energy, indicates that the chemical potential μ of a curved interface differs from that of a flat interface μ 0 by the factor VmγH, where H is mean curvature, γ interfacial energy and Vm molar volume. Δμ = μ - μ 0 = VmγH (1) Eq. 1 makes evident that variations in interface curvature, i.e., interface shape, directly correspond to variations in chemical potential. Furthermore, it follows from Eq. 1 that microstructural coarsening is fundamentally related to variations in interface shape. The link between interface shape and coarsening propensity is well known and methods have been developed to directly measure interfacial curvature distributions for complex morphologies in 3-D.4,5 In this work, these techniques are applied to 3-D images obtained by x-ray nanotomography to study coarsening in microstructures obtained from Ni-YSZ solid oxide fuel cell anodes aged for varying lengths of time. This work builds on a previous characterization of the same samples.6 The curvature measurements collected suggest that a combination of coarsening and morphological instability, which leads to channel pinch-off, severely diminish the connectivity of the anode’s Ni network and, in addition, lead to a significant loss of both nominal and effective triple-phase boundary (TPB) density. Both the loss of connectivity and TPB density coincide with cell performance degradation that was observed in the aging experiment7 from which the anode samples were taken. References Singhal, S. C.; Kendall, K. High Temperature Solid Oxide Fuel Cells, Elsevier, 2003.Yokokawa, H.; Tu, H.; Iwanschitz, B.; Mai, A. Fundamental mechanisms limiting solid oxide fuel cell durability. J. Power Sources 2008, 400-412.Voorhees, P. W. The Theory of Ostwald Ripening. J. Stat. Phys. 1985, 231-252.Glicksmann, M. E.; Voorhees, P. W. Ostwald Ripening and Relaxation in Dendritic Structures. Metall. Trans. A, 1984, 995-1001.Mendoza, R.; Savin, I.; Thornton, K.; Voorhees, P. W. Topological complexity and the dynamics of coarsening. Nat. Mater., 2004 385-388.Nelson, G. J.; Grew, K. N.; Izzo, J. R. Jr.; Lombardo, J. J.; Harris, W. M.; Faes, A.; Hessler-Wyser, A.; Van herle, J.; Wang, S.; Chu, Y. S.; Virkar, A. V.; Chiu, W. K. S. Three-dimensional microstructural changes in the Ni-YSZ solid oxide fuel cell anode during operation. Acta Mater., 2012 3491-3500. 7. Faes, A.; Hessler-Wyser, A.; Presvytes, D.; Vayenas, C. G.; Van herle, J. Nickel-Zirconia Anode Degradation and Triple Phase Boundary Quantification from Microstructural Analysis. Fuel Cells, 2009 841-851. Acknowledgements Financial support from the National Science Foundation (Award CBET-1134052) and an Energy Frontier Research Center on Science Based Nano-Structure Design and Synthesis of Heterogeneous Functional Materials for Energy Systems (HeteroFoaM Center) funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences (Award DE-SC0001061) is gratefully acknowledged. X-ray nanotomography was performed with Dr. Steve Wang at the Advanced Photon Source supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under contract No. DE-AC02-06CH11357. Ni-YSZ samples were provided by MER Dr. J. Van herle (Ecole Polytechnique Federale de Lausanne, Switzerland).

Investigation of the tunable plasmonic whispering gallery mode properties for graphene monolayer nanodisk cavities

Tunable graphene plasmonic whispering gallery mode nanodisks formed by nanoscale chemical potential variation on an infinite freestanding graphene monolayer at near-infrared wavelength range are proposed and numerically investigated in this paper. The Q-factor of a high-order whispering gallery mode of 136 and an extremely small mode volume of 4.8×10−7 (λ0/n)3 with a large Purcell factor of 1.7×108 is achieved in a cavity radius of 10nm. This graphene based nanodisk cavity structure with an ultrasmall mode volume and large Purcell factor is a promising candidate for high efficiency plasmonic emitting sources, filters, or a key component in the fields of transformation plasmonics and plasmonic integrated circuits technique in the future.

Distortion of surface plasmon polariton propagation on graphene due to chemical potential variation

The variation of graphene chemical potential owing to surface plasmon polariton excitation and its influence on the propagation properties of the latter is systematically examined in this paper. Although the chemical potential is controlled via a constant electric field bias, the excitation of the highly confined surface wave can considerably affect it, thus disrupting the wave natural propagation. To this aim, the propagation properties of the surface wave are extracted to reliably estimate the aforesaid distortion effect with regard to frequency. Numerical results, obtained in terms of an accurate finite-difference time-domain scheme, certify this interesting convention. Furthermore, the electrodynamic forces on the free electrons of the graphene layer are calculated to justify the electrostatic assumption.

Modulation of mechanical resonance by chemical potential oscillation in graphene

The classical picture of the force on a capacitor assumes a large density of electronic states, such that the electrochemical potential of charges added to the capacitor is given by the external electrostatic potential and the capacitance is determined purely by geometry. Here we consider capacitively driven motion of a nano-mechanical resonator with a low density of states, in which these assumptions can break down. We find three leading-order corrections to the classical picture: the first of is a modulation in the static force due to variation in the internal chemical potential, the second and third are change in static force and dynamic spring constant due to the rate of change of chemical potential, expressed as the quantum (density of states) capacitance. As a demonstration, we study a capacitively driven graphene mechanical resonators, where the chemical potential is modulated independently of the gate voltage using an applied magnetic field to manipulate the energy of electrons residing in discrete Landau levels. In these devices, we observe large periodic frequency shifts consistent with the three corrections to the classical picture. In devices with extremely low strain and disorder, the first correction term dominates and the resonant frequency closely follows the chemical potential. The theoretical model fits the data with only one adjustable parameter representing disorder-broadening of the Landau levels. The underlying electromechanical coupling mechanism is not limited the particular choice of material, geometry, or mechanism for variation in chemical potential, and can thus be extended to other low-dimensional systems.

Reversible Fuel Cells with Tri-Layer Electrolytes

Reversible solid oxide fuel cells (SOFC) are operated as solid oxide fuel cells and as solid oxide electrolyzer cells (SOEC). In SOFC mode, hydrogen is consumed at the fuel electrode to convert chemical energy of fuel oxidation into water vapor. In SOEC mode, water vapor is decomposed at the fuel electrode to generate hydrogen under an applied DC voltage. Much of the reported work on reversible solid oxide cells is based on yttria-stabilized zirconia (YSZ) electrolyte, Ni + YSZ fuel electrode, and a perovskite-based oxygen electrode. At high operating voltages in the SOEC mode, cell degradation can occur which involves oxygen electrode delamination, formation of cracks within the electrolyte, and also reduction of the electrode near the fuel electrode. The higher the applied voltage, the greater is the propensity to degradation. These observations are consistent with the chemical potential of oxygen in the electrolyte exceeding both electrode bounds under an applied voltage. It has been shown that a small amount of electronic conductivity can minimize degradation. The principal role of electronic conductivity is to smoothen out the variation in oxygen chemical potential through the electrolyte such that it does not exceed electrode bounds. YSZ-based electrolyte if doped with sufficient amount of CeO2 can create significant electronic conductivity such that the electrolyte becomes a mixed ionic electronic conductor. Doping with ceria also lowers the ionic transference number of the electrolyte. A possible bi-layer electrolyte consists of a thin layer of YSZ (or another purely oxygen ion conductor) deposited on a mixed ionic electronic conducting material. As long as electronic conduction through the blocking layer is negligible, the overall ionic transference number of the bi-layer electrolyte can approach unity. In this paper, theoretical analysis of the bi-layer electrolyte for reversible cells is presented. Two configurations of the bi-layer electrolyte are investigated. (1) The electron blocking layer adjacent to the oxygen electrode. (2) The electron blocking layer adjacent to the fuel electrode. For both configurations, the spatial distribution of oxygen chemical potential through the bi-layer electrolyte in both the SOFC and the SOEC modes are evaluated. The ionic transference number of the MIEC part of the bi-layer electrolyte is varied over a wide range. Theoretical analysis shows that such bi-layer electrolyte cells should exhibit good performance characterstics and excellent stability. The net variation of the oxygen chemical potential through the bi-layer electrolyte is determined as a function of transport properties of both layers, electrode polarizations and interfacial resistances to electron transfer.

(Invited) Thermodynamics of Deposition Flux Dependent Intrinsic Film Stress

The growth of polycrystalline films at temperatures above ~0.2 of the melting temperature is accompanied by compressive stress development after film closure. Mysteriously, a significant part of this stress has a reversible nature: it disappears when the deposition is stopped and re-emerges upon resumption. Chason [1] even showed the corresponding inverse behavior during electrochemical etching All these observations clearly point towards a steady-state, flux (etching rate) dependent equilibrium phenomenon, which should, therefore, be treated properly by thermodynamics. It has been suggested that the variation of the surface chemical potential upon starting/stopping of the deposition may cause adatoms to diffuse in/out of the grain boundaries leading to the development/relaxation of the intrinsic compressive film stress. However, film growth involves a myriad of atomic processes such that the mystery is not yet solved and new mechanisms and ideas are still published frequently. Here we present an analytical derivation, in which we address, for the first time, the reason why additional atoms want to get incorporated in the grain boundaries. This background delivers the required driving force independently of the precise way the atoms get incorporated. In this sense we are not proposing a new model, but delivering the basis for all different models proposed. To derive the driving force, we calculate the variation of the chemical potential of the surface, the grain boundaries, and the film. Surprisingly, using pure thermodynamic arguments, our results fully agree with the magnitude of the reversible compressive stress: the tremendous stress levels observed in the experiments can indeed be explained by the flux induced density variations in the extremely dilute adatom gas on the surface! [1] Shin and Chason, Phys. Rev. Lett. 103, 056102 (2009) E-mail:rost@physics.leidenuniv.nl Web: www.physics.leidenuniv.nl/rost

In-Operando Raman Spectroscopy Study on Oxygen Chemical Potential Gradient in Ni-SDC Cermet Anode for SOFCs

The cermet of Ni‒oxide ion conductor is widely used as an anode in SOFCs. However, the usage of nickel induces various degradation phenomena during discharge operation; e.g., agglomeration and/or oxidation of nickel catalyst, and carbon deposition. In most cases, these degradation phenomena are triggered by the variation in the oxygen chemical potential inside the anode. In this study, then, in-operando Raman spectroscopy was conducted for Ni−SDC (Ni−Ce0.8Sm0.2O2-δ ) cermet anode at 700ºC with applying SDC as a probe for the detection of oxygen chemical potential. This is because the band related to oxygen vacancy in the Raman spectrum of SDC changes depending on the partial pressure of oxygen in the ambient atmosphere. The variation in oxygen chemical potential at the top surface of anode was successfully quantified. The effective reaction zone of anode was also discussed comparing with the data estimated from impedance spectra.

Reversible Fuel Cells with Tri-Layer Electrolytes

A tri-layer electrolyte membrane is proposed for high temperature reversible fuel cells. The tri-layer electrolyte consists of a central dense layer of a purely oxygen ion conducting material such as yttria-stabilized zirconia (YSZ), a thin dense p-type mixed oxygen ionic electronic conducting (MIEC) layer such as LSCF in contact with the oxygen electrode and a thin dense n-type mixed oxygen ionic electronic conducting layer such as rare earth oxide doped ceria in contact with the fuel electrode. In this manner, the electrochemical reactions occur at the p-type MIEC layer/oxygen electrode interface and the n-type MIEC layer/fuel electrode interface. The MIEC characteristics of the respective thin layers are expected to significantly lower the overall polarization resistances and the resistances to electronic defects transport across electrode/electrolyte interfaces. This is expected to minimize the variation of oxygen chemical potential across the tri-layer electrolyte and thus minimize degradation.

Heavy quark scattering and quenching in a QCD medium at finite temperature and chemical potential

The heavy quark collisional scattering on partons of the quark gluon plasma (QGP) is studied in a quantum chromodynamics medium at finite temperature and chemical potential. We evaluate the effects of finite parton masses and widths, finite temperature $T$, and quark chemical potential ${\ensuremath{\mu}}_{q}$ on the different elastic cross sections for dynamical quasiparticles (on- and off-shell particles in the QGP medium as described by the dynamical quasiparticle model ``DQPM'') using the leading order Born diagrams. Our results show clearly the decrease of the $qQ$ and $gQ$ total elastic cross sections when the temperature and the quark chemical potential increase. These effects are amplified for finite ${\ensuremath{\mu}}_{q}$ at temperatures lower than the corresponding critical temperature ${T}_{c}({\ensuremath{\mu}}_{q})$. Using these cross sections we, furthermore, estimate the energy loss and longitudinal and transverse momentum transfers of a heavy quark propagating in a finite temperature and chemical potential medium. Accordingly, we have shown that the transport properties of heavy quarks are sensitive to the temperature and chemical potential variations. Our results provide some basic ingredients for the study of charm physics in heavy-ion collisions at Beam Energy Scan at RHIC and CBM experiment at FAIR.

Thermoelectric properties of IV–VI-based heterostructures and superlattices

Doping in a manner that introduces anisotropy in order to reduce thermal conductivity is a significant focus in thermoelectric research today. By solving the semiclassical Boltzmann transport equations in the constant scattering time (τ) approximation, in conjunction with ab initio electronic structure calculations, within Density Functional Theory, we compare the Seebeck coefficient (S) and figure of merit (ZT) of bulk PbTe to PbTe/SnTe/PbTe heterostructures and PbTe doping superlattices (SLs) with periodically doped planes. Bismuth and Thallium were used as the n- and p-type impurities, respectively. The effects of carrier concentration are considered via chemical potential variation in a rigid band approximation. The impurity bands near the Fermi level in the electronic structure of PbTe SLs are of Tl s- and Bi p-character, and this feature is independent of the doping concentration or the distance between impurity planes. We observe the impurity bands to have a metallic nature in the directions perpendicular to the doping planes, yet no improvement on the values of ZT is found when compared to bulk PbTe. For the PbTe/SnTe/PbTe heterostructures, the calculated S presents good agreement with recent experimental data, and an anisotropic behavior is observed for low carrier concentrations (n<1018cm−3). A large value of ZT|| (parallel to the growth direction) of 3.0 is predicted for n=4.7×1018cm−3 and T=700K, whereas ZTp (perpendicular to the growth direction) is found to peak at 1.5 for n=1.7×1017cm−3. Both electrical conductivity enhancement and thermal conductivity reduction are analyzed.

A Comprehensive 3D Finite Element Model of a Thermoelectric Module Used in a Power Generator: A Transient Performance Perspective

Thermoelectric power generator has potential for small-scale and distributed power generation because of its high durability and scalability. It is very important to realize that the transient behavior of thermoelectric modules (TEM) affects a thermoelectric generator’s response to dynamic working environments. Traditionally, researchers have used simplified models to describe the behavior of thermoelectric modules. In this paper we propose a comprehensive mathematical model that considers the effect of variations of chemical potential and carrier density, which are ignored by traditional models. Finite element models based on this new model are used to simulate the transient behavior of a thermoelectric module subjected to rapid changes in boundary temperature or working load. Simulation results show that transition times of thermoelectric modules affected by temperature change are much longer than those of modules affected by changes in electrical load resistance. Sudden changes in working temperature cause voltage overshoot of the TEM output, which, however, is not observed in responses to sudden changes of load resistance. Comparisons also show there are significant differences between the behavior of TEM predicted by use of this new comprehensive model and that predicted by use of traditional models, particularly for the high-temperature intrinsic ionization region and the low-temperature weak ionization region. This implies that chemical potential and carrier density variations, which are taken into account by this new model but ignored by traditional models, have major effects on the performance of TEM.

Effect of the chiral chemical potential on the position of the critical endpoint

The effect of chiral imbalance on the QCD phase structure is studied in a framework of Dyson--Schwinger equations. It is found that the chiral phase transition is always a crossover in the $T\ensuremath{-}{\ensuremath{\mu}}_{5}$ plane when $\ensuremath{\mu}$ is 0 MeV or small values. The trail of the critical endpoints (CEPs) along with the variation of the chiral chemical potential is given. We find that the effect of ${\ensuremath{\mu}}_{5}$ is somewhat different from the existing chiral model calculations; namely, the CEP first moves roughly along the phase boundary of $T\ensuremath{-}\ensuremath{\mu}$ plane in a smaller $\ensuremath{\mu}$ direction, as in the chiral model calculations, but turns in the opposite direction to move away from the small chemical potential region, which has never been observed before. In addition, we also discuss the possibility of whether the study at finite temperature and chiral chemical potential can provide some useful information for the detection of the CEP at finite temperature and baryon chemical potential, since the former can be calculated in lattice QCD without the sign problem.

Role of Chemical Potential in Flake Shape and Edge Properties of Monolayer MoS2

The precise control of the edge geometry and crystal shape of monolayer MoS2 is of particular importance for their application in nanoelectronics and photoelectro catalysts. Here, we reveal a crucial role of chemical potential in the determination of equilibrium shape (ES) and edge structure of monolayer MoS2 by using density-functional theory calculations. Applying the Wulff construction rule, our results demonstrate the shape evolution of monolayer MoS2 flake from the dodecagonal shape, then to the hexagonal shape, to the triangular shape with the variation of chemical potential from the Mo-rich to the S-rich condition, and the edge structure of ES changes correspondingly from mixed zigzag/armchair edges to purely zigzag edges. This finding can be applied to explain extensive experimental observations about the morphology of MoS2 domains. Likewise, the edge magnetism and electronic structures of monolayer MoS2 domains are found to be dependent on their edge structure, which provides specific guidance for the magnetic modulation of monolayer MoS2 and the design of more effective MoS2-based catalysts.

The Feasibility of a Current-Source Thermoelectric Power Generator and Its Corresponding Structure Design

Traditional thermoelectric power generators consist of thermoelectric elements connected electrically in series and thermally in parallel. Current flowing inside the thermoelectric power generator is conventionally considered to be driven by the Seebeck effect-induced electric field and the output voltage-induced reverse electric field. This paper proposes a more comprehensive model that implies that current is also driven by chemical potential and carrier density variation. Therefore, the thermoelectric power generator can be treated as a current-source power supplier when the current driven by carrier density variation dominates. This paper performs holistic finite element implementation of the new holistic model where a thermoelectric power generator unit behaves like a current-source while the working temperature conditions maintain stability. This result validates that the thermoelectric element shows the behaviors of a current-source power supply under certain conditions. This discovery brings a new perspective on the behaviors of thermoelectric elements, which potentially will lead to the development of novel thermoelectric power generator design.

Effect of Mechanical Stress on Electrochemical Properties of Li Ion Batteries Cathodes

1. IntroductionRecently, all-solid state Li ion batteries are widely investigated to establish more reliable and flexible battery systems [1, 2]. Compared to conventional batteries with liquid electrolytes, all-solid-state batteries can be suffered from undesired strains induced at hetrointerfaces between solids due to differences of crystal structures and chemical/thermal expansion coefficients. Such a strain may cause performance improvement/deterioration or failure of all-solid-state batteries. For example, it was reported that charge and discharge properties of an Al electrode is affected by the strain [3]. Therefore, it is important to understand the effect of strain on the electrochemical properties for the design and development of all-solid-state batteries. The purpose of this study is to reveal the effect of strain on electrochemical behaviors of cathode materials for all-solid-state Li batteries. For this aim, dense thin film LiCoO2 (LCO) electrodes were fabricated on an Li ion conducting glass ceramics (LICGC) by the PLD method, and the variation of the chemical potential of Li in the electrode due to external strain was evaluated by measuring electromotive force (EMF) between compressively and tensely strained LCO electrodes.2. Experimental A schematic illustration of the specimen is shown in Fig.1. Dense thin film LCO electrodes were fabricated on both surfaces of an Li ion conducting glass ceramics LICGC (OHARA INC.) by the PLD method at 873 K with P(O2) of 20 Pa. Then, Al films as counter electrodes were also deposited next to the LCO electrodes by Ar ion sputtering at room temperature in Ar atmosphere of about 0.67 Pa. The Li contents of the LCO dense films were controlled by the electrochemical de-lithiation and estimated from the amount of the electricity passed through the cell. After the de-lithiation process, the Al electrode side was cut down. Two LCO electrodes were short circuited for about 24 hours to equilibrate the Li chemical potential. After the equilibration, the EMF between two LCO electrodes was measured with applying compressive and tensile strain to the upper and the lower LCO electrodes, respectively, by the four points bending method as shown in Fig.1.3. Results and Discussion The obtained LCO electrode was oriented in the direction of (003) along the out of plane direction, i.e., the Li conductive plane was almost parallel to the substrate. Fig.2 shows the result of OCV measurements under different strain states. The EMF was generated when the strain was applied to the specimen. The compressively strained LCO electrode was negatively charged while the tensely strained LCO electrode was positively charged. The EMF emerged immediately after the application of the strain, was kept at an almost constant value while keeping the constant strain state, and became nearly zero after the release of the strain. The observed EMF value increased as the applied strain increased. Since the generation of EMF represents the difference of Li chemical potential between the compressively and tensely strained LCO electrodes, it is considered that the structural deformation due to the external strain induces the Li chemical potential variation. In the presentation, we will discuss the origin of the EMF from the thermodynamical points of views.

A fermionic bath induced antibunching and coherence in Mollow spectra

In this work, we have derived the modified Bloch equation from the generalized master equation due to the fermionic bath where one needs to consider Grassmann algebra to obtain the similar mathematical structure of the reduced system dynamics, as in the case of a bosonic bath. There is an enhancement of antibunching in the photon emission with an increase in effective temperature. This is in principle a manifestation of the antisymmetric two-particle dynamic anticorrelation in the fermionic bath with a defined chemical potential characterized by the forbidden overlapping. This is evident from the modified fluctuation–dissipation relation. We have compared it thoroughly with an experimental result in the temperature dependent emission characteristics within an environment of quantum dots in a Hanburry-Brown–Twiss set-up. For the fermionic bath, an effective temperature assisted coherence phenomenon is induced in the system dynamics, which is reflected in the resonance fluorescence spectrum with the variation of chemical potential. In the Mollow's absorption spectra, when the Rabi frequency is sufficiently low, the side peaks appear as chemical potential induced coherence phenomenon rather than the traditional field induced one. The subsequent gain in the probe wave is evidently of thermal origin, where the energy is fully supplied by the fermionic bath at non-zero temperatures. This is not possible for a bosonic bath—an example of the extraction of coherence from the fermionic bath.

Theory of Soret Coefficients in Binary Organic Solvents

Thermodiffusion in binary molecular liquids is examined using the nonequilibrium thermodynamic model, where the thermodynamic parameters are calculated using equations based on statistical mechanics. In this approach, thermodiffusion is quantified through the variation in binary chemical potential and its temperature and concentration dependence. The model is applied to solutions of organic solvents, in order to compare our theoretical results to experimental results from the literature. A measurable contribution of the orientation-dependent Keezom interaction is shown, where the possible orientations are averaged using the Boltzmann weighting factor. Calculations of enthalpies of evaporation from the model yield good agreement with experimental values from the literature. However, calculations of the associated energetic parameters were several times larger than those reported in the literature from numeric simulations of material transport.

Oxidative stability of cereal bars made with fruit peels and baru nuts packaged in different types of packaging

Food industries have been concerned about managing the waste generated by their production processes in order to minimize environmental impacts and also about the development of formulations with different and innovative ingredients such as fruits from the Brazilian savanna. Seeking to meet the expectations of consumers who desire healthy and practical products, this study aimed to evaluate the oxidative stability and the variations in chemical composition and antioxidant potential of cereal bars made with fruit peels and baru nuts packaged in different types of packaging. The bars formulated were packed in four different types of packaging: laminated without vacuum (LWV), transparent without vacuum (TWV), transparent under vacuum (TV), and laminated under vacuum (LV); they were subsequently analyzed for proximate composition, fatty acid profiles, antioxidant activity, and oxidative capacity. The results showed that the cereal bars made with fruit peel and baru are sources of protein, dietary fiber, and fat, especially unsaturated fatty acids such as oleic and linoleic acids. The cereal bars exhibited oxidative stability up to 120 days of storage, and the type of packaging was not significant for the variables evaluated; therefore, they can be stored in low cost packaging such as transparent packaging without vacuum for a period of 120 days.

Genus distribution and thermodynamics of a random matrix model of RNA with Penner interaction

The nonlinear Penner external interaction is introduced and studied in the random matrix model of homo RNA. A numerical technique is developed to study the partition function, and a general formula is obtained for all lengths. The genus distribution function for the system is obtained, plotted, and compared with the genus distribution for the real RNA structures found from the protein databank. The genus distribution shows that the nonlinear interaction favors the formation of low genus structures and matches the result for real RNA structures. The distribution of structure with temperature suggests that nonlinear interaction is biased toward the planar structures. The variation of chemical potential with temperature and interaction strength indicates the presence of additional molecules in the system other than the magnesium ions and possibly represents a phase transition. The specific heat has a bump and its derivatives shows a double-peak behavior at a particular temperature. On analyzing the specific heat and derivatives for each genus separately, the planar structure (genus zero) is shown to contribute the most to the bump and double peak. This observation in the nonlinear model is similar to that observed in the unfolding experiments on RNA.

Tunable graphene reflective cells for THz reflectarrays and generalized law of reflection

A tunable graphene-based reflective cell operating at THz is proposed for use in reconfigurable-beam reflectarrays, or similarly to implement the so-called generalized law of reflection. The change in the complex conductivity of graphene when biased by an electric field allows controlling the phase of the reflected field at each element of the array. Additionally, the slow wave propagation supported by graphene drastically reduces the dimensions of the cell, which allows smaller inter-element spacing hence better array performance. An elementary cell is optimized and its scattering parameters computed, demonstrating a dynamic phase range of 300° and good loss figure for realistic chemical potential variations. Finally, a circuit model is proposed and shown to very accurately predict the element response.