Frustrated State Research Articles

Langmuir monolayers with internal dipoles: Understanding phase behavior using Monte Carlo simulations

A coarse-grained, rigid-rod model that includes steric interactions and an internal dipole is used to study monolayers of surfactant molecules tethered to a flat interface. Monte Carlo simulations are performed in the canonical ensemble for a range of high-density configurations with varying degrees of dipole strength. Both a melting transition and a tilting transition are observed, and the dependence of the transitions on the surfactant molecules' internal dipoles is examined. Simulation results indicate that at high packing densities, the monolayers exist in a frustrated state due to dipole-dipole repulsions and steric interactions. Tilting of the surfactant molecules increases the magnitude of the dipole-dipole attractions and lowers the overall system energy, but is limited by steric repulsions. In simulations with higher dipole strengths, the melting and tilting transitions are found to be coupled. The formation of nanodomains with increased collective tilt and positional order in these systems suggests a possible mechanism for the coupling.

An electron diffraction and Monte Carlo simulation study of an incommensurate antiferroelectric state in the relaxor ferroelectric Pb2ScTaO6

Incommensurate satellite reflections modulating along the 〈110〉* directions have been observed in the electron diffraction patterns of single crystals of the relaxor ferroelectric Pb2ScTaO6(PST) recordedviatransmission electron microscopy. The satellites occur characteristically within a specific temperature range and display differing or variable modulation vectors relative to their primary reflections. The satellites represent a weak frustrated antiferroelectric state in PST, termed the incommensurate antiferroelectric (IAFE) state. The observed IAFE state coexists with the ferroelectric and paraelectric states within a specific temperature regime and is dynamic in nature, meaning that the dispositions of the satellites can be altered by varying the temperature applied to the crystal,in-situin the transmission electron microscope. The observed satellites are associated with thin, needle-shaped, closely packed striated domains of about 5–15 nm in width. The satellites appear exclusively in crystals of PST with an advanced degree of 1:1 chemical long-range order, exceeding 90%. The satellites and their domains are interpreted as originating from a displacive, antiferroelectric coupling of the ions, driven in particular by the Pb ions. The Monte Carlo (MC) method was used exhaustively to evaluate the structural regimes that lead to the occurrence of the IAFE state. In the MC simulations, the displacements were correlated with the ferroelectric and antiferroelectric couplings, resulting in the IAFE domains and their associated satellites of differing dispositions or modulation vectors. The results of the MC simulations agree well with the electron diffraction observations, supporting the model of an antiferroelectric displacement with an incommensurate modulation of the Pb ions in the 〈110〉* directions.

Deciding fate in adverse times: Sporulation and competence in Bacillus subtilis

Bacteria serve as the central arena for understanding how gene networks and proteins process information and control cellular behaviors. Recently, much effort has been devoted to the investigation of specific bacteria gene circuits as functioning modules. The next challenge is the integrative modeling of complex cellular networks composed of many such modules. A tractable integrative model of the sophisticated decision-making signal transduction system that determines the fate between sporulation and competence is presented. This model provides an understanding of how information is sensed and processed to reach an “informative” decision in the context of cell state and signals from other cells. The competence module (ComK dynamics) is modeled as a stochastic switch whose transition rate is controlled by a quorum-sensing unit. The sporulation module (Spo0A dynamics) is modeled as a timer whose clock rate is adjusted by a stress-sensing unit. The interplay between these modules is mediated via the Rap assessment system, which gates the sensing units, and the AbrB–Rok decision module, which creates an opportunity for competence within a specific window of the sporulation timer. The timer is regulated via a special repressilator-like inhibition of Spo0A* by Spo0E, which is itself inhibited by AbrB. For some stress and input signals, this repressilator can generate a frustration state with large variations (fluctuations or oscillations) in Spo0A* and AbrB concentrations, which might serve an important role in generating cell variability. This integrative framework is a starting point that can be extended to include transition into cannibalism and the role of colony organization.

Dislocation-interaction-based model of strained-layer relaxation

A strained layer relaxes plastically when dislocations propagate within the layer, leaving behind an array of misfit dislocations at the layer interface. We develop an analytical model of this process, based on the idea that relaxation is frustrated when propagating dislocations are trapped or annihilated by encounters with previously created misfit dislocations or other propagating dislocations. The theory characterizes the evolving density of the misfit array and the density of propagating dislocations in terms of a pair of coupled rate equations. The two trapping functions which appear in these equations are evaluated quantitatively by numerically investigating all possible dislocation-dislocation encounters. Fluctuations in the local stress field driving the individual dislocations are explicitly taken into account when evaluating the trapping functions. Analysis of the rate equations shows that there are two regimes in the strain-relaxation dynamics. Initially, the strain decreases rapidly following a universal dependence on time scaled with the initial dislocation density n0. At a (rescaled) crossover time that increases with n0, the strain levels off from the universal relaxation curve and saturates to an asymptotic residual strain level, which decreases with n0. Microscopically, our model reveals that the initial fast strain-relaxation regime is dominated by collisions between propagating dislocations, while the slow saturation regime is dominated by the trapping of propagating dislocations by the misfits. In the end, the self-trapping of the propagating dislocations by the misfit array they themselves have generated leaves the layer in a frustrated state with residual strain higher than the critical strain. The predictions of the theory are found to be in good agreement with experimental measurements and with large-scale numerical simulations of layer relaxation.

Photographing dispossession, forgetting solidarity: waiting for social justice in Wentworth, South Africa

South Africans today inhabit a fragmented and discontinuous landscape, often despite their most cosmopolitan intentions. Grounded in the Coloured neighbourhood of Wentworth in Durban, this paper asks how remains of the past appear as differently temporalised artefacts, some buried in the archaic past and others more readily used to critique the present. In particular, I explore photographs of inmates of a concentration camp from 1902, township youth appropriating a specific commons in the early 1980s, black political photography from the late 1980s, and film wrestling with the ambiguities of post‐apartheid political life in a Coloured neighbourhood next to an oil refinery. What unites these moments is not just a meta‐theoretical concern with photography as both documentary and aesthetic, but the specific political uses of images, exemplified by the work of two black political photographers. Their practice provides cues for situating these other photographs in a long century of multiple dispossessions. The paper explores when and how photographs might shock the viewer into recognising resemblances, connections and potential solidarities, not just with the past, but with subaltern critique of racial space and subjectivity in the present. I suggest how we might view photographs from various moments relationally, to understand how, in one corner of contemporary South Africa, people continue to wait for justice despite uncertainty and official dissimulation, in a state of anticipatory frustration.

Frustration-Instigated Career Decisions: A Theoretical Exploration of the Role of Frustration in Career Decisions

From a career decision-making perspective, frustration may be an important catalyst for career change. Literature is discussed and used to develop propositions that present perceived frustration, not just as a state of discomfort but as an impetus for career change. Self-perception and achievement need are presented in relation to frustration to speculate about specific career decisions that might be enacted in a state of frustration. A framework is developed to represent career decisions based on proposed relationships. Implications are discussed for human resource development specialists, managers, and employees and suggestions are presented for conducting future research.

Regionalism in the Asia Pacific/East Asia: A Frustrated Regionalism?

��� Why have Asia’s many projects in regionalism not been able to realize their stated goals, despite the fecundity of, and enthusiasm for, regionbuilding initiatives over the last two decades? In an attempt to answer this question, this article identifies the pursuit of a holistic regionalism embodied in the desire for a regional community as a persistent goal in official discourse, and argues that an apparent state of frustration describes the difficulty of regional institutions and forums in bridging the growing gap between these articulated goals and actual outcomes. The empirical case for the argument here is provided by the founding of the East Asia Summit in 2005, which has disclosed the limits of both exclusive and inclusive models of regionalism in Asia. In exploring causation, the article argues that both structural and agential factors are at the heart of this problem. The tensions thrown up by the competing processes of realist and liberal-institutionalist order-building in Asia have imposed structural constraints on the ability of regional projects to realize their normative aspirations. Equally important in causing this state of frustration are the agents of regionalism — in particular, regional elites — who articulated the goal of a regional “Community” to propel regional projects, and have set the bar above the current capacities of regional institutions.

A delithiated LiNi 0.65Co 0.25Mn 0.10O 2 electrode material: A structural, magnetic and electrochemical study

A crystalline LiNi 0.65Co 0.25Mn 0.10O 2 electrode material was synthesized by the combustion method at 900 °C for 1 h. Rietveld refinement shows less than 3% of Li/Ni disorder in the structure. Lithium extraction involves only the Ni 2+/Ni 4+ redox couple while Co 3+ and Mn 4+ remain electrochemically inactive. No structural transition was detected during cycling in the whole composition range 0 < x < 1.0. Furthermore, the hexagonal cell volume changes by only 3% when all lithium was removed indicating a good mechanical stability of the studied compound. LiNi 0.65Co 0.25Mn 0.10O 2 has a discharge capacity of 150 mAh/g in the voltage range 2.5–4.5 V, but the best electrochemical performance was obtained with an upper cut-off potential of 4.3 V. Magnetic measurements reveal competing antiferromagnetic and ferromagnetic interactions – varying in strength as a function of lithium content – yielding a low temperature magnetically frustrated state. The evolution of the magnetic properties with lithium content confirms the preferential oxidation of Ni ions compared to Co 3+ and Mn 4+ during the delithiation process.

Complex magnetic internal order in structurally disordered Ni nanoparticles

A detailed study of the magnetic properties of colloidal Ni nanoparticles (∼5.2 nm) that do not present long range order is presented. Two magnetic contributions were observed at high temperatures (>25 K), a dominating paramagnetic one and a ferromagnetic contribution, detected by ferromagnetic resonance and low field magnetic measurements. Interestingly, the ferromagnetic behavior does not follow a classical superparamagnetic description. The effective anisotropy increases at low temperatures due to interactions among the ferromagnetic clusters, which leads the system to a frustrated state.

Twinkling fractal theory of the glass transition

AbstractIn this paper we propose a solution to an unsolved problem in solid state physics, namely, the nature and structure of the glass transition in amorphous materials. The development of dynamic percolating fractal structures near Tg is the main element of the Twinkling Fractal Theory (TFT) presented herein and the percolating fractal twinkles with a frequency spectrum F(ω) ∼ ωdf–1 exp −|ΔE|/kT as solid and liquid clusters interchange with frequency ω. The Orbach vibrational density of states for a fractal is g(ω) ∼ ωdf–1, where df = 4/3 and the temperature dependent activation energy behaves as ΔE ∼ (T2 − T). The key concept of the TFT derives from the Boltzmann population of excited states in the anharmonic intermolecular potential between atoms, coupled with percolating solid fractal structures near Tg. The twinkling fractal spectrum F(ω) at Tg predicts the correct dynamic heterogeneity behavior via the spatio‐temporal thermal fluctuation autocorrelation relaxation function C(t). This function behaves as C(t) ∼ t−1/3 (short times), C(t) ∼ t−4/3 (long times) and C(t) ∼ t−2 (ω &lt; ωc), which were found to be in excellent agreement with published nanoscale AFM dielectric force fluctuation experiments on a glassy polymer near Tg. Using the Morse potential, the TFT predicts that Tg = 2Do/9k, where Do is the interatomic bonding energy ∼ 2–5 kcal/mol and is comparable to the heat of fusion ΔHf. Because anharmonicity controls both the thermal expansion coefficient αL and Tg, the TFT uniquely predicts that αL×Tg ≈ 0.03, which is found to be universal for a broad range of glassy materials from Pyrex to polymers to glycerol. Below Tg, the glassy structure attains a frustrated nonequilibrium state by getting constrained on the fractal structure and the thermal expansion in the glass is reduced by the percolation threshold pc as αg ≈ pcαL. The change in heat capacity ΔCp = CpL–Cpg at Tg was found to be related to the change in dimensionality from Df to 3 in the Debye approximation as the ratio CpL/Cpg = 3/Df, where Df is the fractal dimension of the glass. For polymers, the TFT describes the molecular weight dependence of Tg, the role of crosslinks on Tg, the Flory‐Fox rule of mixtures and the WLF relation for the time‐temperature shift factor aT, which are traditionally viewed in terms of Free‐Volume theory. The TFT offers new insight into the behavior of nano‐confined glassy materials and the dynamics of physical aging. It also predicts the relation between the melting point Tm and Tg as Tm/Tg = 1/[1−pc] ≈ 2. The TFT is universal to all glass forming liquids. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2765–2778, 2008

IEMOCAP: interactive emotional dyadic motion capture database

Since emotions are expressed through a combination of verbal and non-verbal channels, a joint analysis of speech and gestures is required to understand expressive human communication. To facilitate such investigations, this paper describes a new corpus named the “interactive emotional dyadic motion capture database” (IEMOCAP), collected by the Speech Analysis and Interpretation Laboratory (SAIL) at the University of Southern California (USC). This database was recorded from ten actors in dyadic sessions with markers on the face, head, and hands, which provide detailed information about their facial expressions and hand movements during scripted and spontaneous spoken communication scenarios. The actors performed selected emotional scripts and also improvised hypothetical scenarios designed to elicit specific types of emotions (happiness, anger, sadness, frustration and neutral state). The corpus contains approximately 12 h of data. The detailed motion capture information, the interactive setting to elicit authentic emotions, and the size of the database make this corpus a valuable addition to the existing databases in the community for the study and modeling of multimodal and expressive human communication.

Subdomain Competition, Cooperativity, and Topological Frustration in the Folding of CheY

The folding of multidomain proteins often proceeds in a hierarchical fashion with individual domains folding independent of one another. A large single-domain protein, however, can consist of multiple modules whose folding may be autonomous or interdependent in ways that are unclear. We used coarse-grained simulations to explore the folding landscape of the two-subdomain bacterial response regulator CheY. Thermodynamic and kinetic characterization shows the landscape to be highly analogous to the four-state landscape reported for another two-subdomain protein, T4 lysozyme. An on-pathway intermediate structured in the more stable nucleating subdomain was observed, as were transient states frustrated in off-pathway contacts prematurely structured in the weaker subdomain. Local unfolding, or backtracking, was observed in the frustrated state before the native conformation could be reached. Nonproductive frustration was attributable to competition for van der Waals contacts between the two subdomains. In an accompanying article, stopped-flow kinetic measurements support an off-pathway burst-phase intermediate, seemingly consistent with our prediction of early frustration in the folding landscape of CheY. Comparison of the folding mechanisms for CheY, T4 lysozyme, and interleukin-1β leads us to postulate that subdomain competition is a general feature of large single-domain proteins with multiple folding modules.

Totally frustrated states in the chromatic theory of gain graphs

We generalize proper coloring of gain graphs to totally frustrated states, where each vertex takes a value in a set of ‘qualities’ or ‘spins’ that is permuted by the gain group. In standard coloring the group acts trivially or regularly on each orbit (an example is the Potts model), but in the generalization the action is unrestricted. We show that the number of totally frustrated states satisfies a deletion–contraction law. It is not matroidal except in standard coloring, but it does have a formula in terms of fundamental groups of edge subsets. One can generalize chromatic polynomials by constructing spin sets out of repeated orbits. The dichromatic and Whitney-number polynomials of standard coloring generalize to evaluations of an abstract partition function that lives in the edge ring of the gain graph.

Frustrated magnetic response of a superconducting Nb film with a square lattice of columnar defects

The magnetic response of a superconducting system presenting a frustrated state is investigated. The system is a superconducting film with mechanically pierced columns, cooled in a field which is then removed. Frustration originates from the competition between return flux of a dipole - created by flux trapped in the empty columns - and flux exclusion by the sorrounding superconductor in the Meissner state. The system resolves the incompatibility among conflicting constraints, leading to frustration, by eliminating return flux, which is possibly assimilated by nearby columns, as manifested by a sudden reduction of the magnetic moment on the decreasing field branch of the hysteresis loop.

Protein-induced geometric constraints and charge transfer in bacteriochlorophyll–histidine complexes in LH2

Bacteriochlorophyll-histidine complexes are ubiquitous in nature and are essential structural motifs supporting the conversion of solar energy into chemically useful compounds in a wide range of photosynthesis processes. A systematic density functional theory study of the NMR chemical shifts for histidine and for bacteriochlorophyll-a-histidine complexes in the light-harvesting complex II (LH2) is performed using the BLYP functional in combination with the 6-311++G(d,p) basis set. The computed chemical shift patterns are consistent with available experimental data for positive and neutral(tau) (N(tau) protonated) crystalline histidines. The results for the bacteriochlorophyll-a-histidine complexes in LH2 provide evidence that the protein environment is stabilizing the histidine close to the Mg ion, thereby inducing a large charge transfer of approximately 0.5 electronic equivalent. Due to this protein-induced geometric constraint, the Mg-coordinated histidine in LH2 appears to be in a frustrated state very different from the formal neutral(pi) (N(pi) protonated) form. This finding could be important for the understanding of basic functional mechanisms involved in tuning the electronic properties and exciton coupling in LH2.

Automatic detection of learner’s affect from conversational cues

We explored the reliability of detecting a learner's affect from conversational features extracted from interactions with AutoTutor, an intelligent tutoring system (ITS) that helps students learn by holding a conversation in natural language. Training data were collected in a learning session with AutoTutor, after which the affective states of the learner were rated by the learner, a peer, and two trained judges. Inter-rater reliability scores indicated that the classifications of the trained judges were more reliable than the novice judges. Seven data sets that temporally integrated the affective judgments with the dialogue features of each learner were constructed. The first four datasets corresponded to the judgments of the learner, a peer, and two trained judges, while the remaining three data sets combined judgments of two or more raters. Multiple regression analyses confirmed the hypothesis that dialogue features could significantly predict the affective states of boredom, confusion, flow, and frustration. Machine learning experiments indicated that standard classifiers were moderately successful in discriminating the affective states of boredom, confusion, flow, frustration, and neutral, yielding a peak accuracy of 42% with neutral (chance = 20%) and 54% without neutral (chance = 25%). Individual detections of boredom, confusion, flow, and frustration, when contrasted with neutral affect, had maximum accuracies of 69, 68, 71, and 78%, respectively (chance = 50%). The classifiers that operated on the emotion judgments of the trained judges and combined models outperformed those based on judgments of the novices (i.e., the self and peer). Follow-up classification analyses that assessed the degree to which machine-generated affect labels correlated with affect judgments provided by humans revealed that human-machine agreement was on par with novice judges (self and peer) but quantitatively lower than trained judges. We discuss the prospects of extending AutoTutor into an affect-sensing ITS.

EL ROL DE LA PERSONALIDAD EN LA RELACIÓN ENTRE FRUSTRACIÓN - ESTRÉS Y DIVERSAS REACCIONES AFECTIVAS: RESULTADOS DE UNA INVESTIGACIÓN

En el presente artículo se presenta una investigación, cuyo objetivo fue estudiar y comparar la función mediadora de catorce estilos de personalidad en la relación entre el estrés y/o la frustración y el desarrollo de diversas reacciones afectivas. Se utilizaron dos muestras clínicas (n = 260) de pacientes adultos, con diversos síndromes clínicos (Eje I), asistidos ambulatoriamente en Alemania. El encuadre teórico de la investigación fue la Teoría de las Interacciones de los Sistemas de la Personalidad 1, desarrollada por Julius Kuhl (Alemania). Los resultados obtenidos sugieren que los estilos de personalidad más vulnerables a desarrollar emociones negativas tras una frustración o bajo estrés son el estilo pasivo (depresivo 2) y el impulsivo (borderline).

Molecular magnetic semiconductors formed by cationic and anionic networks: (ET)2Mn[N(CN)2]3 and (ET)2CuMn[N(CN)2

Crystals of (ET)2Mn[N(CN)2]3 (1) and (ET)2CuMn[N(CN)2]4 (2) with mono- and first bimetal dicyanamide anions were obtained and their structure, conducting and magnetic properties were investigated. The structure of 2 is not typical for ET radical cation salts and is characterized by the presence of a 3D polymeric anion built into the ET radical cation layers. The crystals of 1 exhibit a semiconducting behavior of conductivity and 2 undergoes a semiconductor I–semiconductor II phase transition at 295–291 K, which is specified by a jump of resistivity and the appearance of a hysteresis in the R(T) curves. The phase transition is accompanied by changes in the charge state of the ET molecules and intermolecular interactions in the crystal. Antiferromagnetic correlations of spins associated with anionic subsystems were found in both salts at temperatures lower than 25 K. Antiferromagnetic ordering in 1 has a long-range character. The effect of the spin frustrated state of localized spins on conducting electrons of ET subsystem was found in 1.

Role of double exchange interaction on the magnetic and electrical properties of Pr0.8Sr0.2MnO3 ferromagnetic insulating manganite

In this work the ferromagnetic state in a ferromagnetic insulating manganite viz. Pr0.8Sr0.2MnO3 was analyzed. The temperature variation of ac susceptibility is seen to show two transitions with a high temperature transition occurring at 158K and a low temperature cusp (Tf) around 90K. The high temperature transition (TC) was found to be independent of frequency while the low temperature transition shifts with frequency indicating a frustrated magnetic state. The relaxation time observed from the critical slowing down spin analysis indicates that this state is that of a cluster glass. Temperature variation of resistivity shows an insulating behavior with two distinct humps corresponding to TC and Tf. Temperature variation of thermopower exhibits a peak at TC and decreases below TC which is attributed to the sudden release of holes from traps, similar to a ferromagnetic metallic manganite. Magnetoresistance is seen to show a change in curvature upon cooling the sample across TC which in conjunction with the peak in resistivity and thermopower suggests that this transition is mediated by a double exchange mechanism. The frustrated state is seen to arise because of a competition between double exchange and superexchange mechanisms. The effect of double exchange mechanism is seen to persist all the way down to 5K as seen from the magnetoresistance analysis. These results clearly suggest that double exchange still plays an important role in dictating the magnetic and electrical properties in ferromagnetic insulating manganites.

Frustrated magnetic vortices in a triad of permalloy rings: Magneto-optical Kerr effect, magnetic force microscopy, and micromagnetic simulations

The field dependent magnetization of three mutually touching permalloy rings were investigated by means of the magneto-optical Kerr effect, magnetic force microscopy, and micromagnetic simulations. Each ring has a width of 0.2‐1.8 m, an outer diameter of 4 m, and a thickness of 17 nm. Decreasing an applied magnetic field from saturation leads to the nucleation and annihilation of magnetic vortices, leaving at least one ring in a magnetically frustrated state. The properties of the magnetization reversal strongly depend on the ring width and on the direction of the applied field. Multiple complex reversal paths with vortexlike magnetization configurations are found.