Symmetry Breakers Research Articles

Current-Induced Field-Free Switching of Co/Pt Multilayer via Modulation of Interlayer Exchange Coupling and Magnetic Anisotropy

Current-induced field-free magnetic switching using spin–orbit torque has been an important topic for decades due to both academic and industrial interest. Most research has focused on introducing symmetry breakers, such as geometrical and compositional variation, pinned layers, and symmetry-broken crystal structures, which add complexity to the magnetic structure and fabrication process. We designed a relatively simple magnetic structure, composed of a [Co/Pt] multilayer and a Co layer with perpendicular and in-plane magnetic anisotropy, respectively, with a Cu layer between them. Current-induced deterministic magnetic switching was observed in this magnetic system. The system is advantageous due to its easy control of the parameters to achieve the optimal condition for magnetic switching. The balance between magnetic anisotropic strength and interlayer coupling strength is found to provide the optimal condition. This simple design and easy adjustability open various possibilities for magnetic structures in spin-based electronics applications using spin–orbit torque.

Symmetry’s revenge

Abstract James Henry Collin recently developed a new symmetry breaker favouring the ontological argument’s possibility premiss over that of the reverse ontological argument. The symmetry breaker amounts to an undercutting defeater for the reverse possibility premiss based on Kripkean cases of a posteriori necessity. I argue, however, that symmetry re-arises in two forms. First, I challenge the purported asymmetry in epistemic entitlements to the original and reverse possibility premisses. Second, relevantly similar Kripkean cases equally undercut the original possibility premiss.

Deterministic Leader Election in Anonymous Radio Networks

Leader election is a fundamental task in distributed computing. It is a symmetry breaking problem, calling for one node of the network to become the leader , and for all other nodes to become non-leaders . We consider leader election in anonymous radio networks modeled as simple undirected connected graphs. Nodes communicate in synchronous rounds. In each round, a node can either transmit a message to all its neighbours, or stay silent and listen. A node v hears a message from a neighbour w in a given round if v listens in this round and if w is its only neighbour transmitting in this round. If v listens in a round in which more than one neighbour transmits, then v hears noise that is different from any message and different from silence. We assume that nodes are identical (anonymous) and execute the same deterministic algorithm. Under this scenario, symmetry can be broken only in one way: by different wake-up times of the nodes. In which situations is it possible to break symmetry and elect a leader using time as symmetry breaker? In order to answer this question, we consider configurations . A configuration is the underlying graph with nodes tagged by non-negative integers with the following meaning. A node can either wake up spontaneously in the round shown on its tag, according to some global clock, or can be woken up hearing a message sent by one of its already awoken neighbours. The local clock of a node starts at its wakeup and nodes do not have access to the global clock determining their tags. A configuration is feasible if there exists a distributed algorithm that elects a leader for this configuration. Our main result is a complete algorithmic characterization of feasible configurations. More precisely, we design a centralized decision algorithm, working in polynomial time, whose input is a configuration and which decides if the configuration is feasible. Using this algorithm we also provide a dedicated deterministic distributed leader election algorithm for each feasible configuration that elects a leader for this configuration in time O ( n 2 σ, where n is the number of nodes and σ is the difference between the largest and smallest tag of the configuration. We then ask the question whether there exists a universal deterministic distributed algorithm electing a leader for all feasible configurations. The answer turns out to be no, and we show that such a universal algorithm cannot exist even for the class of 4-node feasible configurations. We also prove that a distributed version of our decision algorithm cannot exist.

Personal Information as Symmetry Breaker in Disagreements

AbstractWhen involved in a disagreement, a common reaction is to tell oneself that, given that the information about one's own epistemic standing is clearly superior in both amount and quality to the information about one's opponent's epistemic standing, one is justified in one's confidence that one's view is correct. In line with this natural reaction to disagreement, some contributors to the debate on its epistemic significance have claimed that one can stick to one's guns by relying in part on information about one's first-order evidence and the functioning of one's cognitive capacities. In this article, I argue that such a manoeuvre to settle controversies encounters the problem that both disputants can make use of it, the problem that one may be wrong about one's current conscious experience, and the problem that it is a live possibility that many of one's beliefs are the product of epistemically distorting factors. I also argue that, even if we grant that personal information is reliable, when it comes to real-life rather than idealized disagreements, the extent of the unpossessed information about one's opponent's epistemic standing provides a reason for doubting that personal information can function as a symmetry breaker.

Origins of size effects in initially dislocation-free single-crystal silver micro- and nanocubes

We report phenomenal yield strengths—up to one-fourth of the theoretical strength of silver—recorded in microcompression testing of initially dislocation-free silver micro- and nanocubes synthesized from a multistep seed-growth process. These high strengths and the massive strain bursts that occur upon yield are results of the initially dislocation-free single-crystal structure of the pristine samples that yield through spontaneous nucleation of dislocations. When the pristine samples are exposed to a focused ion-beam to fabricate pillars and then compressed, the dramatic strain burst does not occur, and they yield at a quarter of the strength compared to the pristine counterparts. Regardless of the defect-state of the samples prior to testing, a size effect is apparent—where the yield strength increases as the sample size decreases. Since dislocation starvation and the single-arm-source mechanisms cannot explain a size effect on yield strength in dislocation-free samples, we investigate the dislocation nucleation mechanisms controlling the size effect through careful experimental observations and molecular statics simulations. We find that intrinsic or extrinsic symmetry breakers such as surface defects, edge roundness, external sample shape, or a high vacancy concentration can influence dislocation nucleation, and thus contribute to the size effect on yield strength in initially dislocation-free samples.

Scalable optimal deployment in the cloud of component-based applications using optimization modulo theory, mathematical programming and symmetry breaking

Automated deployment of component-based applications in the Cloud consists in the allocation of virtual machines (VMs) offers from various Cloud Providers such that the constraints induced by the interactions between components and by the components hardware/software requirements are satisfied and the performance objectives are optimized (e.g. costs are minimized). It can be formulated as a constraint optimization problem, hence, in principle, the optimization can be carried out automatically. In the case the set of VM offers is large (several hundreds), the computational requirement is huge, making the automatic optimization practically impossible with the current general optimization modulo theory (OMT) and mathematical programming (MP) tools. We overcame the difficulty by methodologically analyzing the particularities of the problem with the aim of identifying search space reduction methods. These are methods exploiting: (i) the symmetries of the general Cloud deployment problem, (ii) the graph representation associated to the structural constraints specific to each particular application, and (iii) their combination. An extensive experimental analysis has been conducted on four classes of real-world problems, using six symmetry breaking strategies and two types of optimization solvers.As a result, the combination of a variable reduction strategy with a column-wise symmetry breaker leads to a scalable deployment solution, when OMT is used to solve the resulting optimization problem.

Begging the Question Against a Peer?

A dialectical conception of justification helps conciliationists about peer disagreement establish the symmetry considerations on which their account is premised. On this conception, appeals to personal or hidden forms of evidence fail to provide a symmetry breaker that would allow one to dismiss a conflicting peer opinion. Furthermore, the act of citing the same evidence repetitively tends to illegitimately beg the question against the peer, no matter how accurate one’s own overall assessment of this evidence. However, the dialectical conception of justification does not automatically vindicate conciliationism. In many of the most interesting cases of peer disagreement there are vast bodies of dialectically sharable evidence that can ultimately provide enough non-question-begging epistemic resources to settle the dispute, even if appealing to those resources violates the independence requirement—a further premise of conciliationism. Absent modifications to the independence requirement, it would therefore be premature to embrace conciliationism.

Endless and Infinite

Abstract It is often said that time must have a beginning because otherwise the series of past events would have the paradoxical features of an actual infinite. In the present paper, we show that, even given a dynamic theory of time, the cardinality of an endless series of events, each of which will occur, is the same as that of a beginningless series of events, each of which has occurred. Both are denumerably infinite. So if (as we believe) an endless series of events is possible, then the possibility of a beginningless series of past events should not be rejected merely on the ground that it would be an actual infinite. What would be required to rebut our argument is a symmetry breaker – something that motivates treating the past relevantly differently to the future. We consider several attempts to provide a symmetry breaker and show that none of them is successful.

Dynamic symmetry-breaking in mutually annihilating fluids with selective interfaces

The selective entrapment of mutually annihilating species within a phase-changing carrier fluid is explored by both analytical and numerical means. The model takes full account of the dynamic heterogeneity which arises as a result of the coupling between hydrodynamic transport, dynamic phase-transitions and chemical reactions between the participating species, in the presence of a selective droplet interface. Special attention is paid to the dynamic symmetry breaking between the mass of the two species entrapped within the expanding droplet as a function of time. It is found that selective sources are much more effective symmetry breakers than selective diffusion. The present study may be of interest for a broad variety of advection-diffusion-reaction phenomena with selective fluid interfaces, including the problem of electroweak baryogenesis.

Symmetry prior for epipolar consistency.

For a perfectly plane symmetric object, we can find two views-mirrored at the plane of symmetry-that will yield the exact same image of that object. In consequence, having one image of a plane symmetric object and a calibrated camera, we automatically have a second, virtual image of that object if the 3-D location of the symmetry plane is known. We propose a method for estimating the symmetry plane from a set of projection images as the solution of a consistency maximization based on epipolar consistency. With the known symmetry plane, we can exploit symmetry to estimate in-plane motion by introducing the X-trajectory that can be acquired with a conventional short-scan trajectory by simply tilting the acquisition plane relative to the plane of symmetry. We inspect the symmetry plane estimation on a real scan of an anthropomorphic human head phantom and show the robustness using a synthetic dataset. Further, we demonstrate the advantage of the proposed method for estimating in-plane motion using the acquired projection data. Symmetry breakers in the human body are widely used for the detection of tumors or strokes. We provide a fast estimation of the symmetry plane, robust to outliers, by computing it directly from a set of projections. Further, by coupling the symmetry prior with epipolar consistency, we overcome inherent limitations in the estimation of in-plane motion.

Stereoselective Assembly of Gigantic Chiral Molybdenum Blue Wheels Using Lanthanide Ions and Amino Acids.

The synthesis of chiral polyoxometalates (POMs) is a challenge because of the difficulty to induce the formation of intrinsically chiral metal-oxo frameworks. Herein we report the stereoselective synthesis of a series of gigantic chiral Mo Blue (MB) POM clusters 1–5 that are formed by exploiting the synergy between coordinating lanthanides ions as symmetry breakers to produce MBs with chiral frameworks decorated with amino acids ligands; these promote the selective formation of enantiopure MBs. All the compounds share the same framework archetype, based on {Mo124Ce4}, which forms an intrinsically chiral Δ or Λ configurations, controlled by the configurations of functionalized chiral amino acids. The chirality and stability of 1–5 in solution are confirmed by circular dichroism, 1H NMR, and electrospray ion mobility–mass spectrometry studies. In addition, the framework of the {Mo124Ce4} MB not only behaves as a host able to trap a chiral {Mo8} cluster that is not accessible by traditional synthesis but also promotes the transformation of tryptophan to kynurenine in situ. This work demonstrates the potential and applicability of our synthetic strategy to produce gigantic chiral POM clusters capable of host–guest chemistry and selective synthetic transformations.

Short proofs for some symmetric Quantified Boolean Formulas

We exploit symmetries to give short proofs for two prominent formula families of QBF proof complexity theory. On the one hand, we employ symmetry breakers. On the other hand, we enrich the (relatively weak) QBF resolution calculus Q-Res with the symmetry rule and obtain separations to powerful QBF calculi.

Europium Complexes: Luminescence Boost by a Single Efficient Antenna Ligand.

We advance the concept that a single efficient antenna ligand substituted in or added to an otherwise weakly luminescent europium complex is enough to significantly boost its luminescence. Our results, on the basis of photophysical measurements on 5 novel europium complexes and 15 known ones, point in the direction that ligand dissimilarity and ligand diversity are all concepts that clearly play a fundamental role in the luminescence of europium complexes. We show that it is important that a symmetry breaker ligand exists in the complex to enhance ligand dissimilarity and ligand diversity, all mainly affecting the nonradiative decay rate by reducing it. Because the presence of at least one antenna ligand is also obviously necessary, the optimal and the most cost-effective situation can be achieved by adding a single coordination symmetry breaker that is also an efficient antenna, such as 1-(2-thenoyl)-3,3,3-trifluoroacetone or 4,4,4-trifluoro-1-phenyl-1,3-butanedione. In such cases the quantum efficiency, η, is decidedly boosted, as can be verified by going from complex [EuCl2(TPPO)4]Cl·3H2O with η = 0% to the novel complex [EuCl2(BTFA)(TPPO)3], where TPPO stands for triphenylphosphine oxide, with η = 62%.

Unfolding method for first-principles LCAO electronic structure calculations

Unfolding the band structure of a supercell to a normal cell enables us to investigate how symmetry breakers such as surfaces and impurities perturb the band structure of the normal cell. We generalize the unfolding method, originally developed based on Wannier functions, to the linear combination of atomic orbitals (LCAO) method, and present a general formula to calculate the unfolded spectral weight. The LCAO basis set is ideal for the unfolding method because the basis functions allocated to each atomic species are invariant regardless of the existence of surface and impurity. The unfolded spectral weight is well defined by the property of the LCAO basis functions. In exchange for the property, the non-orthogonality of the LCAO basis functions has to be taken into account. We show how the non-orthogonality can be properly incorporated in the general formula. As an illustration of the method, we calculate the dispersive quantized spectral weight of a ZrB2 slab and show strong spectral broadening in the out-of-plane direction, demonstrating the usefulness of the unfolding method.

Why Only Externalists Can Be Steadfast

What is the rational response to disagreement with an epistemic peer? Some say the steadfast response of holding on to your own belief can be rational; others argue that some degree of conciliation is always rationally required. I argue that only an epistemological externalist about rationality—someone who holds that the rationality of a belief is partly constituted by factors outside a subject’s cognitive perspective—can defend the steadfast view. Or at least that this is so in the kinds of idealized cases of peer disagreement that take center stage in the current debate about disagreement. The argument has three steps. First, I show how rationality internalism motivates conciliationism: in view of the mutually recognized internal epistemic symmetry between peers, it would be arbitrary for either peer to hold on to her own belief. Second, I strengthen this line of thought by considering various proposed ‘symmetry breakers’ that appear to introduce a relevant asymmetry between peers, which could be used to defend the rationality of a steadfast response. I argue that none of these alleged symmetry breakers can help internalists. Third, I show how externalism does have the resources to defend steadfastness and expose how extant defenses of steadfastness implicitly rely on externalist intuitions.

Physics of intrinsic rotation in flux-driven ITG turbulence

Global, heat flux-driven ITG gyrokinetic simulations which manifest the formation of macroscopic, mean toroidal flow profiles with peak thermal Mach number 0.05, are reported. Both a particle-in-cell (XGC1p) and a semi-Lagrangian (GYSELA) approach are utilized without a priori assumptions of scale separation between turbulence and mean fields. Flux-driven ITG simulations with different edge flow boundary conditions show in both approaches the development of net unidirectional intrinsic rotation in the co-current direction. Intrinsic torque is shown to scale approximately linearly with the inverse scale length of the ion temperature gradient. External momentum input is shown to effectively cancel the intrinsic rotation profile, thus confirming the existence of a local residual stress and intrinsic torque. Fluctuation intensity, intrinsic torque and mean flow are demonstrated to develop inwards from the boundary. The measured correlations between residual stress and two fluctuation spectrum symmetry breakers, namely E × B shear and intensity gradient, are similar. Avalanches of (positive) heat flux, which propagate either outwards or inwards, are correlated with avalanches of (negative) parallel momentum flux, so that outward transport of heat and inward transport of parallel momentum are correlated and mediated by avalanches. The probability distribution functions of the outward heat flux and the inward momentum flux show strong structural similarity.

Simulation of particle transport and deposition in the modified chemical vapor deposition process

The many complex interactions between system variables means that the experimental understanding of the mechanisms of soot generation, transport and deposition in the modified chemical vapor deposition process used to fabricate silica-based optical fibers is limited. This paper presents a computational fluid dynamics study of the process, in which the particle formation zone and flow field are calculated and silica particles are ‘launched’ at the reaction front and tracked until they either deposit on the substrate tube or exit the system. Variables which can affect this process are tube rotation rate, wall temperature profile, inlet feed composition and gas flow rate. It is shown that buoyancy alone and a combination of buoyancy and tube rotation are ‘symmetry breakers’ in terms of particle generation-deposition and that the most important factors affecting deposition are the gas flow rate and the shape of the wall temperature profile. This sensitivity arises from the competing forces of fluid drag and thermophoresis acting on the particles. It is suggested that altering the wall temperature profile by use of different size burners or changing the substrate tube cooling conditions could achieve significantly different soot deposition layer quality, which would be reflected in the final optical fiber performance.

Correlation between symmetry breaker position and the preferences of conformationally constrained homopeptides: A molecular dynamics investigation

The conformational tendencies of C(alpha,alpha)-diethylglycine (Deg)-based peptides have been studied in solution using all atom molecular dynamics simulations. Specifically, the conformational effects of breaking the symmetry of the host Tfa-(Deg)(5)-OtBu (Tfa, trifluoroacetyl; OtBu, tert-butoxy) pentapeptide with punctual replacements at different sequence positions of one Deg residue by its corresponding guest chiral analogue, L-alpha-aminobutyric acid (L-Abu), have been examined by simulating the following peptides: Tfa-(Deg)(5)-OtBu, Tfa-(Deg)(2)-L-Abu-(Deg)(2)-OtBu, Tfa-(Deg)(3)-L-Abu-Deg-OtBu, and Tfa-(Deg)(4)-L-Abu-OtBu. Simulations show that only the Deg homopeptide is able to stabilize a 2.0(5) helix, even though a kinked arrangement with all the Deg residues adopting a fully-extended conformation was found to be stable when the L-Abu residue is introduced in the middle of the sequence. On the other hand, when the L-Abu residue is closer to the C-end of the sequence, the peptide chain prefers a partially folded 3(10)-helix. Additional simulations on Tfa-(Deg)(3)-L-Abu-(Deg)(3)-OtBu highlighted that, when the size of the Deg segments increases, their tendency to adopt a 2.0(5) helix predominates over the preferred folded conformation of L-Abu. The overall picture extracted after more than 300 ns of molecular dynamics simulation is that breaking the alpha-carbon symmetry of achiral C(alpha)-tetrasubstituted amino acids is a promising strategy to build up polypeptides with modulated conformational tendencies.

Localization of Shear Waves Near Layers Separating Two Regularly Laminated Half-Spaces

The existence conditions for surface and normal shear waves in finite and infinite periodically laminated structures with broken translational symmetry are studied theoretically and numerically. The problems posed are reduced to systems of linear algebraic equations. The existence condition for their nontrivial solutions yield dispersion relations. Conditions for the existence of surface and normal shear waves are established. Some results are plotted. The dependence of the dispersion spectrum on the physical and geometrical properties of the symmetry breaker is studied

Effects of light scalar mesons inη→3πdecay

We study the role of a possible nonet of light scalar mesons in the still interesting � ! 3� decay process, with the primary motivation of learning more about the scalars themselves. The framework is a conventional non-linear chiral Lagrangian of pseudoscalars and vectors, extended to include the scalars. The parameters involving the scalars were previously obtained to fit the s-wave �� and �K scatterings in the region up to about 1 GeV as well as the strong decay � ' ! ���. At first, one might expect a large enhancement from diagrams including a light �(560). However there is an amusing cancellation mechanism which prevents this from occurring. In the simplest model there is an enhancement of about 13 per cent in the � ! 3� decay rate due to the scalars. In a more complicated model which includes derivative type symmetry breakers, the cancellation is modified and the scalars contribute about 30 percent of the total decay rate (although the total is not significantly changed). The vectors do not contribute much. Our model produces a reasonable estimate for the related a0(980) f0(980) mixing strength, which has been a topic of current debate. Promising directions for future work along the present line are suggested.