Spatially Ordered Research Articles

Maintaining spatial and social order: the role of housing development in governing urban margins

This paper investigates processes of spatially ordered marginality of Roma in a former industrial town in Hungary. The analysis focuses on local poverty governance tactics and practices that aim to maintain social and spatial order through the regulation and selective displacement of Roma within the city. These practices of controlling Roma marginality are clear manifestations of the spatialization and racialization of poverty and I argue that spatial containment constitutes a new mode of poverty governance that aims to temper local tensions and cement local power. Moreover, these local policies reflect continuity from socialist era practices in terms of governing Roma marginality through disciplining and displacement. In the present context, EU-funded urban rehabilitation projects represent a vital local resource. While ostensibly targeting social integration, the local government in question has used these resources to promote the mobility of ‘deserving’ vulnerable groups and control ‘undeserving’ marginalized Roma through enclosure. Those who are seen as undeserving are racialized and subject to punitive containment while the ‘deserving’ enjoy material support and a sense of belonging to local society, provided they accept the conditions dictated by local government actors. In this way, the emphasis on individual responsibility masks the structural deficiencies of social housing and related social issues and perpetuates different forms of racism.

Unveiling Talbot Effect under Fresnel Diffraction at a Fork‐Shaped Grating

AbstractThe near‐field effect of diffraction image self‐reproduction or self‐imaging of a periodic grating illuminated by quasi‐monochromatic wave is well‐known as the Talbot effect. Introducing a dislocation to a periodic structure provides a fork‐shaped modulation of the phase/amplitude, which produces discrete diffraction pattern in a far‐field consisting of optical vortices. In this paper, Fresnel diffraction at amplitude fork‐shaped grating is theoretically and experimentally studied. The coexistence of spatial ordering and local violation of translational symmetry of the structure manifests itself in a strict diffraction pattern consisting of optical vortices in the far‐field, which is shown to be accompanied by formation of a spatially ordered intensity distribution in the near‐field, reminiscent the Talbot carpets for periodic structures. These results demonstrate the first evidence of Talbot effect occurred under light diffraction at fork‐shaped gratings, being promising for deep understanding of near‐field singular optics phenomena.

Luminescent properties of spatially ordered Ge/Si quantum dots epitaxially grown on a pit-patterned “silicon-on-insulator” substrate

The results of studying the luminescent properties of epitaxially grown structures with spatially ordered Ge/Si nanoislands (quantum dots), in which the pit-patterned “silicon-on-insulator” substrates serve both for the spatial ordering of quantum dots and for the two-dimensional photonic crystal formation, are presented. It is found that with a certain choice of pit-patterned substrate parameters (diameter of pits and their spatial period), in the photoluminescence spectra of such structures, the multiple narrow peaks are observed. In addition, a significant increase in the quantum dot luminescence signal intensity occurs in the near-infrared range. The effects are related to resonance interaction of quantum dot emitters with photonic crystal modes. The luminescence enhancement effect persists up to room temperatures.

Out-of-Time-Ordered Crystals and Fragmentation.

Is a spontaneous perpetual reversal of the arrow of time possible? The out-of-time-ordered correlator (OTOC) is a standard measure of irreversibility, quantum scrambling, and the arrow of time. The question may be thus formulated more precisely and conveniently: can spatially ordered perpetual OTOC oscillations exist in many-body systems? Here we give a rigorous lower bound on the amplitude of OTOC oscillations in terms of a strictly local dynamical algebra allowing for identification of systems that are out-of-time-ordered (OTO) crystals. While OTOC oscillations are possible for few-body systems, due to the spatial order requirement OTO crystals cannot be achieved by effective single or few body dynamics, e.g., a pendulum or a condensate. Rather they signal perpetual motion of quantum scrambling. It is likewise shown that if a Hamiltonian satisfies this novel algebra, it has an exponentially large number of local invariant subspaces, i.e., Hilbert space fragmentation. Crucially, the algebra, and hence the OTO crystal, are stable to local unitary and dissipative perturbations. A Creutz ladder is shown to be an OTO crystal, which thus perpetually reverses its arrow of time.

Зависимость люминесцентных свойств упорядоченных групп Ge(Si) наноостровков от параметров ямок на структурированной поверхности подложки "кремний на изоляторе"

This paper presents the results of studies of the luminescence properties of structures with Ge(Si) quantum dots (QDs), in which a pit-patterned surface of silicon on insulator substrate served both for the spatial ordering of QDs and for the formation of a two-dimensional photonic crystal. It is shown that by choosing the parameters of pit-patterned substrate (the diameter of the pits and the period of their location), it is possible to provide a significant increase of intensity of the QD luminescence signal in the near-IR range. This enhancement is associated with interaction of spatially ordered QD emission with the modes of a photonic crystal formed by the pattern of pits. The effect of amplification of the luminescence signal persists up to room temperature.

Evaluating spatiotemporal integration of shape cues.

Prior work has shown that humans can successfully identify letters that are constructed with a sparse array of dots, wherein the dot pattern reflects the strokes that would normally be used to fashion a given letter. In the present work the dots were briefly displayed, one at a time in sequence, varying the spatial order in which they were shown. A forward sequence was spatially ordered as though one were passing a stroke across the dots to connect them. Experiments compared this baseline condition to the following three conditions: a) the dot sequence was spatially ordered, but in the reverse direction from how letter strokes might normally be written; b) the dots in each stroke of the letter were displayed in a random order; c) the sequence of displayed dots were chosen for display from any location in the letter. Significant differences were found between the baseline condition and all three of the comparison conditions, with letter recognition being far worse for the random conditions than for conditions that provided consistent spatial ordering of dot sequences. These findings show that spatial order is critical for integration of shape cues that have been sequentially displayed.

Sharp tunnelling resonance from the vibrations of an electronic Wigner crystal

Photoemission and tunneling spectroscopies measure the energies at which single electrons can be added to or removed from an electronic system. Features observed in such spectra have revealed electrons coupling to vibrational modes of ions both in solids and in individual molecules. Here we report the discovery of a sharp resonance in the tunneling spectrum of a 2D electron system. Its behavior suggests that it originates from vibrational modes, not involving ionic motion, but instead arising from vibrations of spatial ordering of the electrons themselves. In a two-dimensional electronic system at very low temperatures and high magnetic fields, electrons can either condense into a variety of quantum Hall phases or arrange themselves into a highly ordered Wigner crystal lattice. Such spatially ordered phases of electrons are often electrically insulating and delicate and have proven very challenging to probe with conventional methods. Using a unique pulsed tunneling method capable of probing electron tunneling into insulating phases, we observe a sharp peak with dependencies on energy and other parameters that fit to models for vibrations of a Wigner crystal. The remarkable sharpness of the structure presents strong evidence of the existence of a Wigner crystal with long correlation length.

Unveiling of Bragg glass to vortex glass transition by an ac driving force in a single crystal of Yb3Rh4Sn13

We present here some striking discrepancies in the results of ac and dc magnetization measurements performed in a single crystal of a low-Tc superconductor, Yb3Rh4Sn13. The fingerprint of a transition from an ordered vortex lattice a la Bragg glass (BG) phase to a partially disordered vortex glass (VG)-like phase is unearthed under the influence of an ac driving force present inevitably in the isothermal ac susceptibility () measurements. In contrast to its well-known effect of improving the state of spatial order in the vortex matter, the ac drive is surprisingly found to promote disorder by helping the BG-to-VG transition to occur at a lower field value in this compound. On the other hand, the isothermal dc magnetization (M–H) scans, devoid of such a driving force, do not reveal this transition; they instead yield the signature of another order–disorder transition at elevated fields, i.e., peak effect (PE), located substantially above the BG-to-VG transition observed in runs. Further, the evolution of the PE feature with increasing field as observed in isofield ac susceptibility () plots indicates the emergence of an ordered vortex configuration (BG) from a disordered phase above a certain field, H* (∼4 kOe). Below H*, the vortex matter created via field cooling (FC) is found to be better spatially ordered than that prepared in zero field-cooled (ZFC) mode. This is contrary to the usual behavior anticipated near the high–field order-disorder transition (PE), wherein an FC state is supposed to be a supercooled disordered phase and the ZFC state is comparatively better ordered.

Broadcasting of cortical activity to the olfactory bulb.

Odor representations are initially formed in the olfactory bulb, which contains a topographic glomerular map of odor molecular features. The bulb transmits sensory information directly to piriform cortex, where it is encoded by distributed ensembles of pyramidal cells without spatial order. Intriguingly, piriform cortex pyramidal cells project back to the bulb, but the information contained in this feedback projection is unknown. Here, we use imaging in awake mice to directly monitor activity in the presynaptic boutons of cortical feedback fibers. We show that the cortex provides the bulb with a rich array of information for any individual odor and that cortical feedback isdependent on brain state. In contrast to the stereotyped, spatial arrangement of olfactory bulb glomeruli, cortical inputs tuned to different odors commingle and indiscriminately target individual glomerular channels. Thus, the cortex modulates early odor representations by broadcasting sensory information diffusely onto spatially ordered bulbar circuits.

Prethermalization of atoms due to photon-mediated long-range interactions.

Atoms can spontaneously form spatially ordered structures in optical resonators when they are transversally driven by lasers. This occurs when the laser intensity exceeds a threshold value and results from the mechanical forces on the atoms associated with superradiant scattering into the cavity mode. We treat the atomic motion semiclassically and show that, while the onset of spatial ordering depends on the intracavity-photon number, the stationary momentum distribution is a Gaussian function whose width is determined by the rate of photon losses. Above threshold, the dynamics is characterized by two time scales: after a violent relaxation, the system slowly reaches the stationary state over time scales exceeding the cavity lifetime by several orders of magnitude. In this transient regime the atomic momenta form non-Gaussian metastable distributions, which emerge from the interplay between the long-range dispersive and dissipative mechanical forces of light. We argue that the dynamics of self-organization of atoms in cavities offers a test bed for studying the statistical mechanics of long-range interacting systems.

Spatial ordering of nano-dislocation loops in ion-irradiated materials

Defect microstructures formed in ion-irradiated metals, for example iron or tungsten, often exhibit patterns of spatially ordered nano-scale dislocation loops. We show that such ordered dislocation loop structures may form spontaneously as a result of Brownian motion of loops, biased by the angular-dependent elastic interaction between the loops. Patterns of spatially ordered loops form once the local density of loops produced by ion irradiation exceeds a critical threshold value.

Modelling the characteristics of electromagnetic radiation scattering by an ordered assembly of dielectric cylinders

Angular dependences of electromagnetic radiation scattered by separate finite dielectric cylinders and their ordered assemblies have been numerically simulated using a volume integral equation formalism. Dependences of directional diagrams on optical-geometric parameters of both the separate finite cylinders and their spatial ordering were studied. It is shown that collective effects of a coherent nature in the assembly of spatially ordered cylinders result in a scattered radiation angular distribution that differs strongly from that obtained for a system of cylinders that are not electrodynamically coupled.

Dual Mechanism of Neuronal Ensemble Inhibition in Primary Auditory Cortex

Inhibition plays an essential role in shaping and refining the brain's representation of sensory stimulus attributes. In primary auditory cortex (A1), so-called "sideband" inhibition helps to sharpen the tuning of local neuronal responses. Several distinct types of anatomical circuitry could underlie sideband inhibition, including direct thalamocortical (TC) afferents, as well as indirect intracortical mechanisms. The goal of the present study was to characterize sideband inhibition in A1 and to determine its mechanism by analyzing laminar profiles of neuronal ensemble activity. Our results indicate that both lemniscal and nonlemniscal TC afferents play a role in inhibitory responses via feedforward inhibition and oscillatory phase reset, respectively. We propose that the dynamic modulation of excitability in A1 due to the phase reset of ongoing oscillations may alter the tuning of local neuronal ensembles and can be regarded as a flexible overlay on the more obligatory system of lemniscal feedforward type responses.

Stochastic Turing patterns in the Brusselator model

A stochastic version of the Brusselator model is proposed and studied via the system size expansion. The mean-field equations are derived and shown to yield to organized Turing patterns within a specific parameters region. When determining the Turing condition for instability, we pay particular attention to the role of cross-diffusive terms, often neglected in the heuristic derivation of reaction-diffusion schemes. Stochastic fluctuations are shown to give rise to spatially ordered solutions, sharing the same quantitative characteristic of the mean-field based Turing scenario, in term of excited wavelengths. Interestingly, the region of parameter yielding to the stochastic self-organization is wider than that determined via the conventional Turing approach, suggesting that the condition for spatial order to appear can be less stringent than customarily believed.

Surface Vibration Induced Spatial Ordering of Periodic Polymer Patterns on a Substrate

We demonstrate the possibility of producing regular, long-range, spatially ordered polymer patterns without requiring the use of physical or chemical templating through the interfacial destabilization of a thin polymer film driven by surface acoustic waves (SAWs). The periodicity and spot size of the pattern are observed to be dependent on a single parameter, that is, the SAW frequency (or wavelength), therefore offering a rapid, simple, yet novel method for self-organized regular spatial polymer pattern formation that is far more tunable than conventional polymer patterning procedures.

Deterministic control of plasma-assembled self-organized Ge∕Si quantum dot arrays

Self-assembly of size-uniform and spatially ordered quantum dot (QD) arrays is one of the major challenges in the development of the new generation of semiconducting nanoelectronic and photonic devices. Assembly of Ge QD (in the ∼5−20 nm size range) arrays from randomly generated position and size-nonuniform nanodot patterns on plasma-exposed Si(100) surfaces is studied using hybrid multiscale numerical simulations. It is shown, by properly manipulating the incoming ion/neutral flux from the plasma and the surface temperature, the uniformity of the nanodot size within the array can be improved by 34%−53%, with the best improvement achieved at low surface temperatures and high external incoming fluxes, which are intrinsic to plasma-aided processes. Using a plasma-based process also leads to an improvement (∼22% at 700 K surface temperature and 0.1 ML∕s incoming flux from the plasma) of the spatial order of a randomly sampled nanodot ensemble, which self-organizes to position the dots equidistantly to their neighbors within the array. Remarkable improvements in QD ordering and size uniformity can be achieved at high growth rates (a few nm∕s) and a surface temperature as low as 600 K, which broadens the range of suitable substrates to temperature-sensitive ultrathin nanofilms and polymers. The results of this study are generic, can also be applied to nonplasma-based techniques, and as such contributes to the development of deterministic strategies of nanoassembly of self-ordered arrays of size-uniform QDs, in the size range where nanodot ordering cannot be achieved by presently available pattern delineation techniques.

Nanostructure and microstructure of laser-interference-induced dynamic patterning of Co on Si

We have investigated the nanostructure and microstructure resulting from simultaneous ns laser irradiation with deposition of Co films on Si(001) substrates. The spatial order and length scales of the resulting nanopatterns and their crystalline microstructure were investigated as a function of film thickness h and laser energy density E using a combination of atomic force, scanning electron and transmission electron microscopies. The results could be classified into two distinct categories based on the laser energy density used. It was observed that the thickness-dependent E required to melt the Co film (ECo) was lower than for Si (ESi) primarily because of the higher reflectivity of Si. Consequently, for energy densities ECo < E1 < ESi that preferentially melted the Co film, spatially ordered nanoparticles were formed and were attributed to capillary-driven transport in the liquid phase. The ordering length scale corresponded to the interference fringe spacing Λ and the microstructure was primarily Co metal and a metal-rich silicide phase. The native oxide layer played an important role in minimizing the Co–Si reaction. For laser energy densities E2 ⩾ ESi, spatially ordered patterns with periodic length scales L < Λ were observed and resulted from interference of an incident laser beam with a beam transmitted into the Si substrate. These nanopatterns showed one- as well as two-dimensional spatial ordering of the nanostructures. The microstructure in this laser energy regime was dominated by silicide formation. These results suggest that various nanostructures and microstructures, ranging from nearly pure metal to a Si-rich silicide phase, can be formed by an appropriate choice of the laser energy simultaneously with film growth.

Self-organization of chaos synchronization and pattern formation in coupled chaotic oscillators

Pattern formation in spatiotemporal chaotic systems is investigated. Temporally chaotic and spatially ordered patterns are observed by varying the coupling strength. Spatial orderings emerge spontaneously due to self-organization of partial and nonlocal chaos synchronization, governed by various types of spatial symmetries. The first and secondary bifurcations from spatially disordered chaos to chaos with different levels of spatial orderings are observed and the scaling behaviors associated with these bifurcations are statistically analyzed.

Kinetic Monte Carlo simulation of spatially ordered growth of quantum dots on patterned substrate

We report the growth of well-ordered InAs QD chains by molecular beam epitaxy system. In order to analyze and extend the results of our experiment, a detailed kinetic Monte Carlo simulation is developed to investigate the effects of different growth conditions to the selective growth of InAs quantum dots (QDs). We find that growth temperature plays a more important role than growth rate in the spatial ordering of the QDs. We also investigate the effect of periodic stress on the shape of QDs in simulation. The simulation results are in good qualitative agreement with our experiment.

Interplay between magnetic and spatial order in quasicrystals

The stable magnetization configurations of antiferromagnets on quasiperiodic tilings are investigated theoretically. The exchange coupling is assumed to decrease exponentially with the distance between magnetic moments. It is demonstrated that the combination of geometric frustration and the quasiperiodic order of atoms leads to complicated non-collinear ground states. The structure can be divided into subtilings of different energies. The symmetry of the subtilings depends on the quasiperiodic order of magnetic moments. The subtilings are spatially ordered. However, the magnetic ordering of the subtilings in general does not correspond to their spatial arrangements. While subtilings of low energy are magnetically ordered, those of high energy can be completely disordered due to local magnetic frustration.