bluuebunny/crossref_metadata_2025 huggingface dataset:
Teaching Theory, Writing Policy: Integrating Lessons from Foggy Bottom into the Classroom
Authors: Biswas Bidisha , Paczynska Agnieszka
Published: December 2014

This article describes guidelines for assignments designed to build and improve policy-oriented writing skills of college students. Based on our experiences as Franklin Fellows at the United States Department of State, we developed strategies for teaching writing skills that are transferable to the workplace. The pedagogical approaches highlighted in this article will equip students with the analytical and writing abilities needed in a variety of employment situations. First, we offer insights into the qualities that we believe are important for success in a policy-oriented work environment. Second, we link those skills to the challenges and gaps that students face. Third, we propose assignments that can address those gaps.
Where’s the Diplomacy in Diplomacy? Using a Classic Board Game in “Introduction to International Relations”
Authors: Arnold Richard
Published: December 2014

One of the challenges of teaching American undergraduates in an “Introduction to International Relations” course is finding a way to make topics and themes seem relevant to students. This article recounts the author’s experiences using the board game “Diplomacy” in his course. The game places students in the role of decision makers in the international arena and simulates the international politics of pre-World War I Europe. In addition to being a powerful simulation of the difficulties of international relations, the game teaches students about one of the most debated wars in the history of the discipline.
The Democratic Syllabus
Authors: McWilliams Susan
Published: December 2014

The ideal of the “democratic classroom” has been discussed in educational circles for several years. This article answers the question of whether there are specific advantages to be derived from a democratization of the political science classroom, especially one in which democracy itself is a focus of study. Can giving students more power over course content enhance their understanding of democratic authority and process? The author approached these questions by adding several “democratizing” elements to a seminar course, most notably a “democratic syllabus” in which students determined discussion topics, led class sessions, and submitted work of their own choosing. Student surveys and the author’s reflection suggest that the democratic syllabus was a success in terms of the classroom dynamics that it engendered and the thinking about democratic politics and citizenship that it encouraged. Both students and professor agreed that the democratic syllabus presented challenges that should be considered by anyone thinking about creating or modifying a course on this model. Yet this article argues that many political science courses would benefit from similar endeavors in classroom democratization.
Using Tablet Devices and Social Media in a Course about the 2012 US Election Campaign
Authors: Brewer Paul R. , Begleiter Ralph J. , Anderson Katherine , Isaacs Meredith
Published: December 2014

The use of both tablet devices and social media is increasingly popular among the American public. With this in mind, this article discusses our use of the technologies in a course about the 2012 US election campaign. We provided all students in our course with an iPad, created a private Facebook group, and devised a variety of approaches for integrating the technologies into the course. Surveys at the beginning and the end of the course showed that students frequently used their iPad for political and instructional purposes and that their self-confidence in using tablet devices, apps, and social media for political purposes increased during the semester. Open-ended responses and our own observations also suggest that use of the technologies fostered active online conversations about course material. In particular, use of the iPad and the Facebook group in combination during in-class video screenings, guest speakers, and debates facilitated lively, creative interactions among students and between students and instructors.
A hybrid of titanium nitride and nitrogen-doped amorphous carbon supported on SiC as a noble metal-free electrocatalyst for oxygen reduction reaction
Authors: Jia Yingdan , Wang Yanhui , Dong Liang , Huang Junjie , Zhang Yan , Su Jing , Zang Jianbing
Published: December 2014

The NC–TiN/SiC electrocatalyst exhibits excellent electrocatalytic activity toward oxygen reduction reactions, outstanding stability and strong methanol resistance.
Determination of receptor specificities for whole influenza viruses using multivalent glycan arrays
Authors: Huang Mia L. , Cohen Miriam , Fisher Christopher J. , Schooley Robert T. , Gagneux Pascal , Godula Kamil
Published: December 2014

A multivalent glycan array for interrogating the binding preferences of intact influenza viruses.
Electrical conductivity of p-type BiOCl nanosheets
Authors: Myung Yoon , Wu Fei , Banerjee Sriya , Park Jeunghee , Banerjee Parag
Published: December 2014

BiOCl nanosheets were synthesized using a facile hydrolysis method and their p-type electrical conduction as a function of oxygen partial pressure was measured.
Fabrication of cross-linked fluorescent polymer nanoparticles and their cell imaging applications
Authors: Wang Ke , Zhang Xiaoyong , Zhang Xiqi , Yang Bin , Li Zhen , Zhang Qingsong , Huang Zengfang , Wei Yen
Published: December 2014

Fabrication of aggregation induced emission dye based cross-linked fluorescent polymer nanoparticlesviafree radical polymerization and ring-opening reaction for bioimaging.
Orientational strain modulation of ferroelectric polarization in multiferroic BiMnO3
Authors: Mickel Patrick R. , Jeen Hyoungjeen , Biswas Amlan , Hebard Arthur F.
Published: December 2014

We report on the coupling of ferroelectric polarization to externally applied strains in multiferroic BiMnO3. Strains of less than 0.006% increased the remanent polarization by as much as 50% and are shown to depend on the orientation of the uniaxially applied external strain. Using multiple electrode arrays, we rule out the strain-induced rotation of the polarization vector, and confirm the magnitude of the polarization is increasing. Finally, a dielectric characterization determined that the onset of the strain coupling coincides with the relaxor ferroelectric freezing temperature.
Coarse-grained molecular dynamics simulations of depletion-induced interactions for soft matter systems
Authors: Shendruk Tyler N. , Bertrand Martin , Harden James L. , Slater Gary W. , de Haan Hendrick W.
Published: December 2014

Given the ubiquity of depletion effects in biological and other soft matter systems, it is desirable to have coarse-grained Molecular Dynamics (MD) simulation approaches appropriate for the study of complex systems. This paper examines the use of two common truncated Lennard-Jones (Weeks-Chandler-Andersen (WCA)) potentials to describe a pair of colloidal particles in a thermal bath of depletants. The shifted-WCA model is the steeper of the two repulsive potentials considered, while the combinatorial-WCA model is the softer. It is found that the depletion-induced well depth for the combinatorial-WCA model is significantly deeper than the shifted-WCA model because the resulting overlap of the colloids yields extra accessible volume for depletants. For both shifted- and combinatorial-WCA simulations, the second virial coefficients and pair potentials between colloids are demonstrated to be well approximated by the Morphometric Thermodynamics (MT) model. This agreement suggests that the presence of depletants can be accurately modelled in MD simulations by implicitly including them through simple, analytical MT forms for depletion-induced interactions. Although both WCA potentials are found to be effective generic coarse-grained simulation approaches for studying depletion effects in complicated soft matter systems, combinatorial-WCA is the more efficient approach as depletion effects are enhanced at lower depletant densities. The findings indicate that for soft matter systems that are better modelled by potentials with some compressibility, predictions from hard-sphere systems could greatly underestimate the magnitude of depletion effects at a given depletant density.
Viscoelasticity of model interphase chromosomes
Authors: Valet Manon , Rosa Angelo
Published: December 2014

We investigated the viscoelastic response of model interphase chromosomes by tracking the three-dimensional motion of hundreds of dispersed Brownian particles of sizes ranging from the thickness of the chromatin fiber up to slightly above the mesh size of the chromatin solution. In agreement with previous computational studies on polymer solutions and melts, we found that the large-time behaviour of the diffusion coefficient and the experienced viscosity of moving particles as functions of particle size deviate from the traditional Stokes-Einstein relation and agree with a recent scaling theory of diffusion of non-sticky particles in polymer solutions. Interestingly, we found that at short times large particles are temporarily “caged” by chromatin spatial constraints, which thus form effective domains whose sizes match remarkably well with recent experimental results for micro-tracers inside interphase nuclei. Finally, by employing a known mathematical relation between the time mean-square displacement of tracked particles and the complex shear modulus of the surrounding solution, we calculated the elastic and viscous moduli of interphase chromosomes.
Spin-phonon coupling in BaFe12O19 M-type hexaferrite
Authors: Silva Júnior Flávio M. , Paschoal Carlos W. A.
Published: December 2014

The spin-phonon coupling in magnetic materials is due to the modulation of the exchange integral by lattice vibrations. BaFe12O19 M-type hexaferrite, which is the most used magnetic material as permanent magnet, transforms into ferrimagnet at high temperatures, but no spin-phonon coupling was previously observed at this transition. In this letter, we investigated the temperature-dependent Raman spectra of polycrystalline BaFe12O19 M-type hexaferrite from room temperature up to 780 K to probe spin-phonon coupling at the ferrimagnetic transition. An anomaly was observed in the position of the phonon attributed to the Fe(4)O6, Fe(5)O6, and Fe(1)O6 octahedra, evidencing the presence of a spin-phonon coupling in BaM in the ferrimagnetic transition at 720 K. The results also confirmed the spin-phonon coupling is different for each phonon even when they couple with the same spin configuration.
The time-resolved photoelectron spectrum of toluene using a perturbation theory approach
Authors: Richings Gareth W. , Worth Graham A.
Published: December 2014

A theoretical study of the intra-molecular vibrational-energy redistribution of toluene using time-resolved photo-electron spectra calculated using nuclear quantum dynamics and a simple, two-mode model is presented. Calculations have been carried out using the multi-configuration time-dependent Hartree method, using three levels of approximation for the calculation of the spectra. The first is a full quantum dynamics simulation with a discretisation of the continuum wavefunction of the ejected electron, whilst the second uses first-order perturbation theory to calculate the wavefunction of the ion. Both methods rely on the explicit inclusion of both the pump and probe laser pulses. The third method includes only the pump pulse and generates the photo-electron spectrum by projection of the pumped wavepacket onto the ion potential energy surface, followed by evaluation of the Fourier transform of the autocorrelation function of the subsequently propagated wavepacket. The calculations performed have been used to study the periodic population flow between the 6a and 10b16b modes in the S1 excited state, and compared to recent experimental data. We obtain results in excellent agreement with the experiment and note the efficiency of the perturbation method.
Time-dependent quantum chemistry of laser driven many-electron molecules
Authors: Nguyen-Dang Thanh-Tung , Couture-Bienvenue Étienne , Viau-Trudel Jérémy , Sainjon Amaury
Published: December 2014

A Time-Dependent Configuration Interaction approach using multiple Feshbach partitionings, corresponding to multiple ionization stages of a laser-driven molecule, has recently been proposed [T.-T. Nguyen-Dang and J. Viau-Trudel, J. Chem. Phys. 139, 244102 (2013)]. To complete this development toward a fully ab-initio method for the calculation of time-dependent electronic wavefunctions of an N-electron molecule, we describe how tools of multiconfiguration quantum chemistry such as the management of the configuration expansion space using Graphical Unitary Group Approach concepts can be profitably adapted to the new context, that of time-resolved electronic dynamics, as opposed to stationary electronic structure. The method is applied to calculate the detailed, sub-cycle electronic dynamics of BeH2, treated in a 3–21G bound-orbital basis augmented by a set of orthogonalized plane-waves representing continuum-type orbitals, including its ionization under an intense λ = 800 nm or λ = 80 nm continuous-wave laser field. The dynamics is strongly non-linear at the field-intensity considered (I ≃ 1015 W/cm2), featuring important ionization of an inner-shell electron and strong post-ionization bound-electron dynamics.
Experimental and theoretical study on the excited-state dynamics of ortho-, meta-, and para-methoxy methylcinnamate
Authors: Miyazaki Yasunori , Yamamoto Kanji , Aoki Jun , Ikeda Toshiaki , Inokuchi Yoshiya , Ehara Masahiro , Ebata Takayuki
Published: December 2014

The S1 state dynamics of methoxy methylcinnamate (MMC) has been investigated under supersonic jet-cooled conditions. The vibrationally resolved S1-S0 absorption spectrum was recorded by laser induced fluorescence and mass-resolved resonant two-photon ionization spectroscopy and separated into conformers by UV-UV hole-burning (UV-UV HB) spectroscopy. The S1 lifetime measurements revealed different dynamics of para-methoxy methylcinnamate from ortho-methoxy methylcinnamate and meta-methoxy methylcinnamate (hereafter, abbreviated as p-, o-, and m-MMCs, respectively). The lifetimes of o-MMC and m-MMC are on the nanosecond time scale and exhibit little tendency of excess energy dependence. On the other hand, p-MMC decays much faster and its lifetime is conformer and excess energy dependent. In addition, the p-MMC-H2O complex was studied to explore the effect of hydration on the S1 state dynamics of p-MMC, and it was found that the hydration significantly accelerates the nonradiative decay. Quantum chemical calculation was employed to search the major decay route from S1(ππ∗) for three MMCs and p-MMC-H2O in terms of (i) trans → cis isomerization and (ii) internal conversion to the 1nπ∗ state. In o-MMC and m-MMC, the large energy barrier is created for the nonradiative decay along (i) the double-bond twisting coordinate (∼1000 cm−1) in S1 as well as (ii) the linear interpolating internal coordinate (∼1000 cm−1) from S1 to 1nπ∗ states. The calculation on p-MMC decay dynamics suggests that both (i) and (ii) are available due to small energy barrier, i.e., 160 cm−1 by the double-bond twisting and 390 cm−1 by the potential energy crossing. The hydration of p-MMC raises the energy barrier of the IC route to the S1/1nπ∗ conical intersection, convincing that the direct isomerization is more likely to occur.
Unbiased reduced density matrices and electronic properties from full configuration interaction quantum Monte Carlo
Authors: Overy Catherine , Booth George H. , Blunt N. S. , Shepherd James J. , Cleland Deidre , Alavi Ali
Published: December 2014

Properties that are necessarily formulated within pure (symmetric) expectation values are difficult to calculate for projector quantum Monte Carlo approaches, but are critical in order to compute many of the important observable properties of electronic systems. Here, we investigate an approach for the sampling of unbiased reduced density matrices within the full configuration interaction quantum Monte Carlo dynamic, which requires only small computational overheads. This is achieved via an independent replica population of walkers in the dynamic, sampled alongside the original population. The resulting reduced density matrices are free from systematic error (beyond those present via constraints on the dynamic itself) and can be used to compute a variety of expectation values and properties, with rapid convergence to an exact limit. A quasi-variational energy estimate derived from these density matrices is proposed as an accurate alternative to the projected estimator for multiconfigurational wavefunctions, while its variational property could potentially lend itself to accurate extrapolation approaches in larger systems.
A two-parameter nondiffusive heat conduction model for data analysis in pump-probe experiments
Authors: Ma Yanbao
Published: December 2014

Nondiffusive heat transfer has attracted intensive research interests in last 50 years because of its importance in fundamental physics and engineering applications. It has unique features that cannot be described by the Fourier law. However, current studies of nondiffusive heat transfer still focus on studying the effective thermal conductivity within the framework of the Fourier law due to a lack of a well-accepted replacement. Here, we show that nondiffusive heat conduction can be characterized by two inherent material properties: a diffusive thermal conductivity and a ballistic transport length. We also present a two-parameter heat conduction model and demonstrate its validity in different pump-probe experiments. This model not only offers new insights of nondiffusive heat conduction but also opens up new avenues for the studies of nondiffusive heat transfer outside the framework of the Fourier law.
Dissipative particle dynamics of triblock copolymer melts: A midblock conformational study at moderate segregation
Authors: Tallury Syamal S. , Spontak Richard J. , Pasquinelli Melissa A.
Published: December 2014

As thermoplastic elastomers, triblock copolymers constitute an immensely important class of shape-memory soft materials due to their unique ability to form molecular networks stabilized by physical, rather than chemical, cross-links. The extent to which such networks develop in triblock and higher-order multiblock copolymers is sensitive to the formation of midblock bridges, which serve to connect neighboring microdomains. In addition to bridges, copolymer molecules can likewise form loops and dangling ends upon microphase separation or they can remain unsegregated. While prior theoretical and simulation studies have elucidated the midblock bridging fraction in triblock copolymer melts, most have only considered strongly segregated systems wherein dangling ends and unsegregated chains become relatively insignificant. In this study, simulations based on dissipative particle dynamics are performed to examine the self-assembly and networkability of moderately segregated triblock copolymers. Utilizing a density-based cluster-recognition algorithm, we demonstrate how the simulations can be analyzed to extract information about microdomain formation and permit explicit quantitation of the midblock bridging, looping, dangling, and unsegregated fractions for linear triblock copolymers varying in chain length, molecular composition, and segregation level. We show that midblock conformations can be sensitive to variations in chain length, molecular composition, and bead repulsion, and that a systematic investigation can be used to identify the onset of strong segregation where the presence of dangling and unsegregated fractions are minimal. In addition, because this clustering approach is robust, it can be used with any particle-based simulation method to quantify network formation of different morphologies for a wide range of triblock and higher-order multiblock copolymer systems.
Modeling and global maximum power point tracking for photovoltaic system under partial shading conditions using modified particle swarm optimization algorithm
Authors: Tian Yong , Xia Bizhong , Sun Wei , Xu Zhihui , Zheng Weiwei
Published: December 2014

Under partial shading conditions (e.g., due to buildings, trees, and clouds), multiple peaks may exist on the power-voltage (P-V) characteristic curve of photovoltaic (PV) array, leading to the conventional maximum power point tracking methods fail to extract the global maximum power point (GMPP). In this paper, a mathematical model of PV array under partial shading conditions with a voltage calculated principle is established. The presented model is implemented with an m-file in MATLAB software, which is used as a tool to study the non-linear characteristics of current-voltage (I-V) and P-V curves of PV array, as well as quickly develop the GMPP tracking controllers. Besides, an adaptive random particle swarm optimization (ARPSO) algorithm is presented to accurately extract the GMPP under partial shading conditions. Five simulation cases with different partial shading patterns are used to evaluate the performance of the presented approach by comparing with the conventional PSO, perturbation and observation (P&O), incremental conductance (INC), and genetic algorithm (GA) methods. Simulation results show that the ARPSO algorithm can rapidly find the GMPP under different shading conditions compared with the conventional PSO algorithm. Furthermore, the presented algorithm can accurately extract the GMPP when the shading condition sharply changes, while the P&O and INC algorithms fail to track the GMPP, but only detect the rightmost MPP encountered either local or global and regardless of the course. Besides, the ARPSO can rapidly and accurately converge to the GMPP with smaller population size and higher convergence speed compared with the GA.
Thin magnetic coating for low-frequency broadband microwave absorption
Authors: Zhao Hu , Xu Shiyao , Tang Dongming , Yang Yi , Zhang Baoshan
Published: December 2014

Planar anisotropy carbonyl-iron (PACI) particles were prepared from 3 μm diameter sphere-shaped carbonyl-iron materials by high-energy ball milling technique. And the oriented planar anisotropy carbonyl-iron (OPACI) composite was fabricated using rotational orientation method. The OPACI composite possessed much higher real and imaginary permeability and relatively lower real and imaginary permittivity than other absorbers in 1–18 GHz frequency range. The susceptibility versus frequency curves have been fitted quite well using Kittel equation and Debye equation. Compared with natural resonance, the wall displacement susceptibility plays a dominating role for the high real and imaginary permeability. For OPACI composite, the minimum reflection loss (RL) can be as low as −44 dB at 1.8 GHz with the thickness of 2.3 mm, −7.3 dB at 1 GHz, −20 dB at 2 GHz, −5.4 dB at 8 GHz, and the bandwidth can reach 1.9 GHz for the good performance (RL < −10 dB) in the frequency ranges of 1.2–3.1 GHz, indicating a promising absorber for low-frequency broadband application.
Spectral curves of periodic Fisher graphs
Authors: Li Zhongyang
Published: December 2014

We study the spectral curves of dimer models on periodic Fisher graphs obtained from periodic ferromagnetic Ising models on ℤ2. The spectral curve is defined by the zero locus of the determinant of a modified weighted adjacency matrix. We prove that either they are disjoint from the unit torus (T2={(z,w):z=1,w=1}) or they intersect 𝕋2 at a single real point.
Vibrational effects on valence electron momentum distributions of CH2F2
Authors: Watanabe Noboru , Yamazaki Masakazu , Takahashi Masahiko
Published: December 2014

We report an electron momentum spectroscopy study of vibrational effects on the electron momentum distributions for the outer valence orbitals of difluoromethane (CH2F2). The symmetric noncoplanar (e,2e) experiment has been performed at an incident electron energy of 1.2 keV. Furthermore, a theoretical calculation of the electron momentum distributions of the CH2F2 molecule has been carried out with vibrational effects being involved. It is shown from comparisons between experiment and theory that it is essential to take into account influences of the CH2 asymmetric stretching and CH2 rocking vibrational modes for a proper understanding of the electron momentum distribution of the 2b1 orbital having the CH-bonding character. The results of CH2F2and additional theoretical calculations for (CH3)2O and H2CO molecules strongly suggest that vibrational effects on electron momentum distributions tend to be appreciable for non-total symmetry molecular orbitals delocalized over some equivalent CH-bond sites.
Vibrations of the S1 state of fluorobenzene-h5 and fluorobenzene-d5 via resonance-enhanced multiphoton ionization (REMPI) spectroscopy
Authors: Harris Joe P. , Andrejeva Anna , Tuttle William D. , Pugliesi Igor , Schriever Christian , Wright Timothy G.
Published: December 2014

We report resonance-enhanced multiphoton ionization spectra of the isotopologues fluorobenzene-h5 and fluorobenzene-d5. By making use of quantum chemical calculations, the changes in the wavenumber of the vibrational modes upon deuteration are examined. Additionally, the mixing of vibrational modes both between isotopologues and also between the two electronic states is discussed. The isotopic shifts lead to dramatic changes in the appearance of the spectrum as vibrations shift in and out of Fermi resonance. Assignments of the majority of the fluorobenzene-d5 observed bands are provided, aided by previous results on fluorobenzene-h5.
Does the 4f-shell contribute to bonding in tetravalent lanthanide halides?
Authors: Ji Wen-Xin , Xu Wei , Xiao Yi , Wang Shu-Guang
Published: December 2014

Lanthanide tetrahalide molecules LnX4 (Ln = Ce, Pr, Tb; X = F, Cl, Br, I) have been investigated by density functional theory at the levels of the relativistic Zero Order Regular Approximation and the relativistic energy-consistent pseudopotentials, using frozen small- and medium-cores. The calculated bond lengths and vibrational frequencies are close to the experimental data. Our calculations indicate 4f shell contributions to bonding in LnX4, in particular for the early lanthanides, which show significant overlap between the Ln 4f-shell and the halogen np-shells. The 4f shells contribute to Ln-X bonding in LnX4 about one third more than in LnX3.
A hybrid configuration interaction treatment based on seniority number and excitation schemes
Authors: Alcoba Diego R. , Torre Alicia , Lain Luis , Oña Ofelia B. , Capuzzi Pablo , Van Raemdonck Mario , Bultinck Patrick , Van Neck Dimitri
Published: December 2014

We present a configuration interaction method in which the Hamiltonian of an N-electron system is projected on Slater determinants selected according to the seniority-number criterion along with the traditional excitation-based procedure. This proposed method is especially useful to describe systems which exhibit dynamic (weak) correlation at determined geometric arrangements (where the excitation-based procedure is more suitable) but show static (strong) correlation at other arrangements (where the seniority-number technique is preferred). The hybrid method amends the shortcomings of both individual determinant selection procedures, yielding correct shapes of potential energy curves with results closer to those provided by the full configuration interaction method.
Fiber-based thermometry using optically detected magnetic resonance
Authors: Fedotov I. V. , Blakley S. , Serebryannikov E. E. , Safronov N. A. , Velichansky V. L. , Scully M. O. , Zheltikov A. M.
Published: December 2014

Fiber-optic probes coupled with nitrogen-vacancy (NV) centers in diamond and integrated with a microwave transmission line are shown to enable fiber-format optical thermometry. Temperature measurements with an accuracy of 0.02 K are performed by combining this NV-diamond fiber thermometer with a properly optimized differential lock-in detection technique.
Instrument for evaluating the electrical resistance and wavelength-resolved transparency of stretchable electronics during strain
Authors: Azar A. D. , Finley E. , Harris K. D.
Published: December 2014

A complete analysis of strain tolerance in a stretchable transparent conductor (TC) should include tracking of both electrical conductivity and transparency during strain; however, transparency is generally neglected in contemporary analyses. In this paper, we describe an apparatus that tracks both parameters while TCs of arbitrary composition are deformed under stretching-mode strain. We demonstrate the tool by recording the electrical resistance and light transmission spectra for indium tin oxide-coated plastic substrates under both linearly increasing strain and complex cyclic strain processes. The optics are sensitive across the visible spectrum and into the near-infrared region (∼400-900 nm), and without specifically optimizing for sampling speed, we achieve a time resolution of ∼200 ms. In our automated analysis routine, we include a calculation of a common TC figure of merit (FOM), and because solar cell electrodes represent a key TC application, we also weigh both our transparency and FOM results against the solar power spectrum to determine “solar transparency” and “solar FOM.” Finally, we demonstrate how the apparatus may be adapted to measure the basic performance metrics for complete solar cells under uniaxial strain.
A portable automatic pressure delivery system for scar compression therapy in large animals
Authors: Ghassemi Pejhman , Shupp Jeffrey W. , Travis Taryn E. , Gravunder Andrew J. , Moffatt Lauren T. , Ramella-Roman Jessica C.
Published: December 2014

Compression therapy has long been a standard treatment for hypertrophic scar prevention. However, due to the lack of objective, quantitative assessments, and measurements of scar severity, as well as the lack of a self-operated, controllable, and precise pressure delivery technique, limited concrete evidence exists, demonstrating compression therapy’s efficacy. We have designed and built an automatic pressure delivery system to apply and maintain constant pressure on scar tissue in an animal model. A force sensor positioned on a compression plate reads the imposed force in real-time and sends the information to a feedback system controlling two position actuators. The actuators move accordingly to maintain a preset value of pressure onto the skin. The system was used in an in vivo model of compression therapy on hypertrophic scars. It was shown that the system was capable of delivering a constant pressure of 30 mmHg on scar wounds for a period of two weeks, and that phenotypic changes were seen in the wounds.
Toward spectroscopically accurate global ab initio potential energy surface for the acetylene-vinylidene isomerization
Authors: Han Huixian , Li Anyang , Guo Hua
Published: December 2014

A new full-dimensional global potential energy surface (PES) for the acetylene-vinylidene isomerization on the ground (S0) electronic state has been constructed by fitting ∼37 000 high-level ab initio points using the permutation invariant polynomial-neural network method with a root mean square error of 9.54 cm−1. The geometries and harmonic vibrational frequencies of acetylene, vinylidene, and all other stationary points (two distinct transition states and one secondary minimum in between) have been determined on this PES. Furthermore, acetylene vibrational energy levels have been calculated using the Lanczos algorithm with an exact (J = 0) Hamiltonian. The vibrational energies up to 12 700 cm−1 above the zero-point energy are in excellent agreement with the experimentally derived effective Hamiltonians, suggesting that the PES is approaching spectroscopic accuracy. In addition, analyses of the wavefunctions confirm the experimentally observed emergence of the local bending and counter-rotational modes in the highly excited bending vibrational states. The reproduction of the experimentally derived effective Hamiltonians for highly excited bending states signals the coming of age for the ab initio based PES, which can now be trusted for studying the isomerization reaction.
Separation of the Stern and diffuse layer in coarse-grained models: The cases of phosphatidyl serine, phosphatidic acid, and PIP2 monolayers
Authors: Vangaveti S. , Travesset A.
Published: December 2014

We present here a method to separate the Stern and diffuse layer in general systems into two regions that can be analyzed separately. The Stern layer can be described in terms of Bjerrum pairing and the diffuse layer in terms of Poisson-Boltzmann theory (monovalent) or strong coupling theory plus a slowly decaying tail (divalent). We consider three anionic phospholipids: phosphatidyl serine, phosphatidic acid, and phosphatidylinositol(4,5)bisphosphate (PIP2), which we describe within a minimal coarse-grained model as a function of ionic concentration. The case of mixed lipid systems is also considered, which shows a high level of binding cooperativity as a function of PIP2 localization. Implications for existing experimental systems of lipid heterogeneities are also discussed.
Geometric treatment of conduction electron scattering by crystal lattice strains and dislocations
Authors: Viswanathan Koushik , Chandrasekar Srinivasan
Published: December 2014

The problem of conduction electron scattering by inhomogeneous crystal lattice strains is addressed using a tight-binding formalism and the differential geometric treatment of deformations in solids. In this approach, the relative positions of neighboring atoms in a strained lattice are naturally taken into account, even in the presence of crystal dislocations, resulting in a fully covariant Schrödinger equation in the continuum limit. Unlike previous work, the developed formalism is applicable to cases involving purely elastic strains as well as discrete and continuous distributions of dislocations—in the latter two cases, it clearly demarcates the effects of the dislocation strain field and core. It also differentiates between elastic and plastic strain contributions, respectively. The electrical resistivity due to the strain field of edge dislocations is then evaluated and the resulting numerical estimate for Cu shows good agreement with reported experimental values. This indicates that the electrical resistivity of edge dislocations in metals is not entirely due to the core, contrary to current models. Application to the study of strain effects in constrained quantum systems is also discussed.
Numerical study of the effects of surface topography and chemistry on the wetting transition using the string method
Authors: Zhang Yanan , Ren Weiqing
Published: December 2014

Droplets on a solid surface patterned with microstructures can exhibit the composite Cassie-Baxter (CB) state or the wetted Wenzel state. The stability of the CB state is determined by the energy barrier separating it from the wetted state. In this work, we study the CB to Wenzel transition using the string method [E et al., J. Chem. Phys. 126, 164103 (2007); W. Ren and E. Vanden-Eijnden, J. Chem. Phys. 138, 134105 (2013)]. We compute the transition states and energy barriers for a three-dimensional droplet on patterned surfaces. The liquid-vapor coexistence is modeled using the mean field theory. Numerical results are obtained for surfaces patterned with straight pillars and nails, respectively. It is found that on both type of surfaces, wetting occurs via infiltration of the liquid in a single groove. The reentrant geometry of nails creates large energy barrier for the wetting of the solid surface compared to straight pillars. We also study the effect of surface chemistry, pillar height, and inter-pillar spacing on the energy barrier and compare it with nails.
Direct and inverse energy cascades in a forced rotating turbulence experiment
Authors: Campagne Antoine , Gallet Basile , Moisy Frédéric , Cortet Pierre-Philippe
Published: December 2014

We present experimental evidence for a double cascade of kinetic energy in a statistically stationary rotating turbulence experiment. Turbulence is generated by a set of vertical flaps, which continuously injects velocity fluctuations towards the center of a rotating water tank. The energy transfers are evaluated from two-point third-order three-component velocity structure functions, which we measure using stereoscopic particle image velocimetry in the rotating frame. Without global rotation, the energy is transferred from large to small scales, as in classical three-dimensional turbulence. For nonzero rotation rates, the horizontal kinetic energy presents a double cascade: a direct cascade at small horizontal scales and an inverse cascade at large horizontal scales. By contrast, the vertical kinetic energy is always transferred from large to small horizontal scales, a behavior reminiscent of the dynamics of a passive scalar in two-dimensional turbulence. At the largest rotation rate, the flow is nearly two-dimensional, and a pure inverse energy cascade is found for the horizontal energy. To describe the scale-by-scale energy budget, we consider a generalization of the Kármán-Howarth-Monin equation to inhomogeneous turbulent flows, in which the energy input is explicitly described as the advection of turbulent energy from the flaps through the surface of the control volume where the measurements are performed.
Contact resistance and overlapping capacitance in flexible sub-micron long oxide thin-film transistors for above 100 MHz operation
Authors: Münzenrieder Niko , Salvatore Giovanni A. , Petti Luisa , Zysset Christoph , Büthe Lars , Vogt Christian , Cantarella Giuseppe , Tröster Gerhard
Published: December 2014

In recent years new forms of electronic devices such as electronic papers, flexible displays, epidermal sensors, and smart textiles have become reality. Thin-film transistors (TFTs) are the basic blocks of the circuits used in such devices and need to operate above 100 MHz to efficiently treat signals in RF systems and address pixels in high resolution displays. Beyond the choice of the semiconductor, i.e., silicon, graphene, organics, or amorphous oxides, the junctionless nature of TFTs and its geometry imply some limitations which become evident and important in devices with scaled channel length. Furthermore, the mechanical instability of flexible substrates limits the feature size of flexible TFTs. Contact resistance and overlapping capacitance are two parasitic effects which limit the transit frequency of transistors. They are often considered independent, while a deeper analysis of TFTs geometry imposes to handle them together; in fact, they both depend on the overlapping length (LOV) between source/drain and the gate contacts. Here, we conduct a quantitative analysis based on a large number of flexible ultra-scaled IGZO TFTs. Devices with three different values of overlap length and channel length down to 0.5 μm are fabricated to experimentally investigate the scaling behavior of the transit frequency. Contact resistance and overlapping capacitance depend in opposite ways on LOV. These findings establish routes for the optimization of the dimension of source/drain contact pads and suggest design guidelines to achieve megahertz operation in flexible IGZO TFTs and circuits.
Spatio-temporal dynamics induced by competing instabilities in two asymmetrically coupled nonlinear evolution equations
Authors: Schüler D. , Alonso S. , Torcini A. , Bär M.
Published: December 2014

Pattern formation often occurs in spatially extended physical, biological, and chemical systems due to an instability of the homogeneous steady state. The type of the instability usually prescribes the resulting spatio-temporal patterns and their characteristic length scales. However, patterns resulting from the simultaneous occurrence of instabilities cannot be expected to be simple superposition of the patterns associated with the considered instabilities. To address this issue, we design two simple models composed by two asymmetrically coupled equations of non-conserved (Swift-Hohenberg equations) or conserved (Cahn-Hilliard equations) order parameters with different characteristic wave lengths. The patterns arising in these systems range from coexisting static patterns of different wavelengths to traveling waves. A linear stability analysis allows to derive a two parameter phase diagram for the studied models, in particular, revealing for the Swift-Hohenberg equations, a co-dimension two bifurcation point of Turing and wave instability and a region of coexistence of stationary and traveling patterns. The nonlinear dynamics of the coupled evolution equations is investigated by performing accurate numerical simulations. These reveal more complex patterns, ranging from traveling waves with embedded Turing patterns domains to spatio-temporal chaos, and a wide hysteretic region, where waves or Turing patterns coexist. For the coupled Cahn-Hilliard equations the presence of a weak coupling is sufficient to arrest the coarsening process and to lead to the emergence of purely periodic patterns. The final states are characterized by domains with a characteristic length, which diverges logarithmically with the coupling amplitude.
Enhanced power factor of higher manganese silicide via melt spin synthesis method
Authors: Shi Xiaoya , Shi Xun , Li Yulong , He Ying , Chen Lidong , Li Qiang
Published: December 2014

We report on the thermoelectric properties of the higher manganese silicide MnSi1.75 synthesized by means of a one-step non-equilibrium method. The ultrahigh cooling rate generated from the melt-spin technique is found to be effective in reducing second phases, which are inevitable during the traditional solid state diffusion processes. Aside from being detrimental to thermoelectric properties, second phases skew the revealing of the intrinsic properties of this class of materials, for example, the optimal level of carrier concentration. With this melt-spin sample, we are able to formulate a simple model based on a single parabolic band that can well describe the carrier concentration dependence of the Seebeck coefficient and power factor of the data reported in the literature. An optimal carrier concentration around 5 × 1020 cm−3 at 300 K is predicted according to this model. The phase-pure melt-spin sample shows the largest power factor at high temperature, resulting in the highest zT value among the three samples in this paper.
Kinetic arrest induced antiferromagnetic order in hexagonal FeMnP0.75Si0.25 alloy
Authors: Li Guijiang , Li Wei , Schönecker Stephan , Li Xiaoqing , Delczeg-Czirjak Erna K. , Kvashnin Yaroslav O. , Eriksson Olle , Johansson Börje , Vitos Levente
Published: December 2014

The magnetic state of the FeMnP0.75Si0.25 alloy was investigated by first principles calculations. The coexistence of ferromagnetic and antiferromagnetic phases in FeMnP0.75Si0.25 with the same hexagonal crystal structure was revealed. It was found that kinetic arrest during the transition from the high temperature disordered paramagnetic phase to the low temperature ordered ferromagnetic phase results in the intermediate metastable and partially disordered antiferromagnetic phase. We propose that the ratio of the ferromagnetic and antiferromagnetic phases in the FeMnP0.75Si0.25 sample can be tuned by adjusting the kinetic process of atomic diffusion. The investigations suggest that careful control of the kinetic diffusion process provides another tuning parameter to design candidate magnetocaloric materials.
High power, widely tunable, mode-hop free, continuous wave external cavity quantum cascade laser for multi-species trace gas detection
Authors: Centeno R. , Marchenko D. , Mandon J. , Cristescu S. M. , Wulterkens G. , Harren F. J. M.
Published: December 2014

We present a high power, widely tunable, continuous wave external cavity quantum cascade laser designed for infrared vibrational spectroscopy of molecules exhibiting broadband and single line absorption features. The laser source exhibits single mode operation with a tunability up to 303 cm−1 (∼24% of the center wavelength) at 8 μm, with a maximum optical output power of 200 mW. In combination with off-axis integrated output spectroscopy, trace-gas detection of broadband absorption gases such as acetone was performed and a noise equivalent absorption sensitivity of 3.7 × 10−8 cm−1 Hz−1/2 was obtained.
Rapid characterizing of ferromagnetic materials using spin rectification
Authors: Fan Xiaolong , Wang Wei , Wang Yutian , Zhou Hengan , Rao Jinwei , Zhao Xiaobing , Gao Cunxu , Gui Y. S. , Hu C.-M. , Xue Desheng
Published: December 2014

Spin rectification is a powerful tool for dc electric detections of spin dynamics and electromagnetic waves. Technically, elaborately designed on-chip microwave devices are needed in order to realize that effect. In this letter, we propose a rapid characterizing approach based on spin rectification. By directly sending dynamic current into ferromagnetic films with stripe shape, resonant dc voltages can be detected along the longitudinal or transversal directions. As an example, Fe (010) films with precise crystalline structure and magnetic parameters were used to testify the reliability of such method. We investigated not only the dynamic parameters and the precise anisotropy constants of the Fe crystals but also the principle of spin rectification in this method.
Excellent low-field magnetoresistance effect in Ga-doped MnZn ferrites
Authors: Kim Hyo-Jin , Yoo Sang-Im
Published: December 2014

An excellent low field magnetoresistance (LFMR) property was achieved from the Ga-doped (Mn0.8Zn0.2)Fe2O4 (MnZn) ferrites at room temperature (RT). For this study, undoped and Ga-doped MnZn ferrites with the nominal compositions of (Mn0.8Zn0.2)1−xGaxFe2O4 (x = 0 ∼ 0.1) were prepared by the conventional solid state reaction at 1400°C for 2 h in air. From the magneto-transport measurements, Ga-doped MnZn ferrites were found to have not only much lower resistivity values but also greatly improved LFMR ratios in comparison with undoped sample. The highest maximum LFMR ratio of 2.5% at 290 K in 0.5 kOe was achievable from 2 mol% Ga-doped MnZn ferrite. This large LFMR effect is attributable to an increase in spin electrons by Ga3+ ion substitution for the (Mn, Zn)2+ site.
Plasma wakefield acceleration shows promise
Authors: Miller Johanna L.
Published: December 2014

When electrons are precisely positioned in a region of high electric field, they can pick up a lot of energy in a small space.
Chemical gardens grown in flatland
Authors: Wilson R. Mark
Published: December 2014

When certain inorganic reactions are confined to a two-dimensional cell, the mineral precipitates conform to a simple geometric model.
Upwelling in the Southern Ocean
Authors: Morrison Adele K. , Frölicher Thomas L. , Sarmiento Jorge L.
Published: December 2014

Because deep water in the Southern Ocean is cold, centuries old, and rich in nutrients, its circulation exerts an outsized influence on Earth’s heat balance, the carbon cycle, and much of ocean biology.
The measurement Einstein deemed impossible
Authors: Raizen Mark G. , Li Tongcang
Published: December 2014

Particles undergoing Brownian motion move with constant velocity between Brownian kicks. Albert Einstein predicted the velocity distribution, but he wrongly thought his result would never be experimentally confirmed.