Spatial Lens Research Articles

A review of dielectric optical metasurfaces for spatial differentiation and edge detection.

Dielectric metasurfaces-based planar optical spatial differentiator and edge detection have recently been proposed to play an important role in the parallel and fast image processing technology. With the development of dielectric metasurfaces of different geometries and resonance mechanisms, diverse on-chip spatial differentiators have been proposed by tailoring the dispersion characteristics of subwavelength structures. This review focuses on the basic principles and characteristic parameters of dielectric metasurfaces as first- and second-order spatial differentiators realized via the Green's function approach. The spatial bandwidth and polarization dependence are emphasized as key properties by comparing the optical transfer functions of metasurfaces for different incident wavevectors and polarizations. To present the operational capabilities of a two-dimensional spatial differentiator in image information acquisition, edge detection is described to illustrate the practicability of the device. As an application example, experimental demonstrations of edge detection for different biological cells and a flower mold are discussed, in which a spatial differentiator and objective lens or camera are integrated in three optical pathway configurations. The realization of spatial differentiators and edge detection with dielectric metasurfaces provides new opportunities for ultrafast information identification in biological imaging and machine vision.

A critical study of space in the geopolitics of terrorism

ABSTRACT This article theorises epistemologies of ‘space’ in critical studies on terrorism, expanding the research agenda beyond the straitjacket of historicism and discourse-centrism. It traces two theoretical approaches: 1) rescaling terrorism as mundane, situated and private, and 2) treating the ‘space’ of terrorism as a liminal zone between potentiality and anticipatory space-making. This critical spatial lens offers new insights to CTS. In terms of securitisation, this perspective is attentive to the ‘space of securitisation’, the dynamics of space, or space as a discursive process and a subject constitutive of securitisation. In the study of radicalisation, it can help us understand how space and the psychological interpretation of material conditions are co-constituted to shape the process of radicalisation. Finally, it also creates new possibilities for CTS practitioners to employ the embodied, embodying and sensory dimensions of violence, involving not only visual and material dimensions but also sound and hearing, to form an individualised form of resistance against state terrorism. This article attempts to systematically map the permutations of new theoretical and conceptual developments in the critical studies on the spatiality of terrorism.

“The right to the post-Soviet city”: Analysing communication gaps in the public space

The paper investigates the communication gaps in the public spaces of post-Soviet cities (from the perspective of business-government-society interaction) through the spatial paradigm lens of urban sociology coupled with the perspective of communications studies. The author analyzes the particularities of the spatial organization of post-Soviet cities; describes the main features of their urban public space; and examines their impact on the patterns of social interactions. The paper presents the results of empirical research into the government-business relationship, using the case of Minsk, the capital city of Belarus. The author specifically focuses on the instances of communicative dysfunction (i.e. communication gaps) as the manifestation of social distance, exploring its nature from the perspective of the concept of “a Stranger”. The findings point at a need to supplement the local communities with local public communication channels and content.

Making sense of school learning environments as infrastructures of care and spatial typologies

ABSTRACT The Australian Institute for Teaching and School Leadership was established in 2010 to support teaching quality and leadership in schools and initial teacher education programs. Early on it produced seven Australian Professional Standards for Teachers affecting professional knowledge, professional practice, and professional engagement. Standard 4 is part of professional practice and requires teachers to create and maintain supportive and safe school learning environments. We propose that Standard 4 has implications geographers have yet to fully consider, and here our aim is to surface and examine its latent spatialities. We conceive of supportive and safe learning environments as crucial infrastructures of care that can be made more legible using established spatial typologies. To support this proposition, we draw on empirical evidence from a study of literacy teaching practice in Tasmanian government schools and of initial teacher education programs. Here, we focus on how participants described the importance of school learning environments for students' educational attainment and social and emotional wellbeing. We conclude that spatial lenses are important in thinking about these environments and could effectively support teachers to demonstrate career-long and increasingly sophisticated capacities to perceive, use, create, and help others make the most of such spaces for diverse learning outcomes.

A temporal phase-truncated double random phase encoding cryptosystem in the temporal skew Fourier transform domain

A temporal phase-truncated double random phase encoding cryptosystem is proposed to be improved by replacing the temporal Fourier transformers (TFTs) of the dispersion-time lens-dispersion structure with temporal skew Fourier transformers (TSFTs). A TSFT is similar to a TFT except for the time lens (TL) replaced by a skew time lens (STL). A STL is a temporal analog of a spatial cylindrical lens with the in-plane rotational asymmetry mapping to a front–back asymmetry. The front–back asymmetry is achieved by adding the chirp factor C of a TL by +ϵ⋅C and −ϵ⋅C respectively along the positive and negative half axis of the local time coordinate. The skew coefficients ϵ1 and ϵ2 of the two TSFTs involved in the encryption stage are dimensionless and ideally unbounded, serving as additional secret keys. By mathematical analysis, STLs are proven to have complex-value modulations on low frequency components of input signals of TSFTs, which cannot be removed by phase truncations (PTs) in the legal decryption stage. The plain/cipher-text-independent and non-removability features of STLs make phase retrieval attacks unable to exempt eavesdroppers from brute-force trials of STLs. A STL is implemented by an electrical arbitrary waveform generator (AWG) driven electro-optic phase modulator (EOPM). By numerical simulations, the using of STLs is proven to increase the difficulty of phase retrieval attacks in terms of the time consuming required for convergence. Even if phase retrieval attacks converge, the plaintext signal cannot be recovered without the knowledge of ϵ1,2 in the encryption stage. The total key space of ϵ1,2 is also evaluated as 217 at AWG bandwidth Bm=20 GHz, and as 237 at Bm=100 GHz. The fidelity robustness of our optical cryptosystem against possible noise and occlusion penalties on the communication channels and networks of optical cipher-text signals is also proven.

Mapping out Early America: Encounters between imperial and indigenous geographies

AbstractWithin the last three decades, the geographic dimensions of Early American History have expanded. Transregional, Atlantic, Diasporic, Continental, Hemispheric, and Transoceanic perspectives have helped bring about the conceptualization of a “Vast Early America” connected with but not limited to Britain's North American colonies. This article surveys some of the historiographical trends that have propelled that shift. Recognizing that those changes overlapped with the so‐called spatial turn in the discipline of History more broadly, it approaches the topic through a spatial lens. It first considers how histories of cartography in Early America have led to a scholarly rethinking of the field's geographic dimensions. It then examines the ways historians have teased out some of the lived and imagined geographies that Native and European agents negotiated in North America. Because Native geographies were at the center of America's early history as well as the colonial encounters that reshaped it, much of the article's focus is on Native American spatial practices.

Behind the Scaffolding: Manipulations of Time, Delays, and Power in Tarlabaşı, Istanbul

AbstractTaksim 360, located in the Tarlabaşı neighborhood of Istanbul, is one of the first state‐led urban transformation projects in Turkey. Originally scheduled to be finished in 2014, the project is still under construction. Concordant with broader discussions, Tarlabaşı’s urban transformation has been largely studied through spatial lenses centered on accumulation by dispossession and displacement. These works assume that urban transformation projects necessarily follow a linear trajectory from inception to completion. Building on and diverging from this body of research, I examine the relationships between construction companies, subcontractors, and politicians involved in Taksim 360 through ethnographic fieldwork and media analysis with a critical emphasis on temporality. I argue that urban transformation in fact works through manipulations of time, which necessitates a temporal analytical lens that does not take teleologies of buildings projects for granted. It is specifically through delays that economic and political power is exerted, navigated, and negotiated within Taksim 360 using legal contracts, work stoppages, and stand‐offs; conjuring of continued investment; and improvisations with labor and political capital. And so, delays emerge as modus operandi of urban transformation rather than measures of its failures or successes

Visibility as Justice: Immigrant Street Vendors and the Right to Difference in Rome

Dominant constructions of what looks “appropriate” enable the exclusion of poor immigrants from public spaces around the world. This paper analyzes how Bangladeshi vendors challenge exclusion by tactically appearing and disappearing in Rome’s iconic landscapes. While xenophobic, pro-decorum regulations seek to banish marginalized subjects from the tourist-friendly city center, immigrant vendors mobilize their own visibility by emplacing urbanisms of opportunity, refuge, and belonging. Learning from these urbanisms, planners can deploy a spatial lens of visibility to advance the right to difference. I propose In Plain Site, a policy and place-making approach that helps empower oppressed groups to see and be seen in the city.

The spatial practice of religious tourism in India: a destinations perspective

Religious tourism refers to contemporary patterns of travel to sacred places and has taken many forms owing to different motivations of visitors. Researchers have discussed motivation, activities, and behaviour of visitors in framing what constitutes religious in religious tourism, but little attention is given to spatial manifestations of religious practice. Towing this direction, I examine the significance of religious practices to spatial arrangements in Hindu pilgrim towns in India by juxtaposing the concept of “spatial practice” from Lefebvre’s theory of production of space with an indigenous approach called the “sacred-complex model”. A fieldwork based collective study of six pilgrim-towns, namely, Alandi, Jejuri, Pandharpur, Tuljapur, Shegaon, and Shirdi, which represent a full spectrum of religious tourism destinations in India, provides a sound comparison of similarities and differences in spatial practice of religious tourism. In this analysis, four themes emerge: (1) the engagement of religious actors in religious rituals and performances over space defines the boundaries and territories of the sacred and religious; (2) the performance area of religious practice has reduced from traditional pilgrimage landscape to specific routes providing access to the main attraction which is a built structure (shrine/temple); (3) religiousness is also created by non-religious and seemingly “profane” commercial activities; (4) without the explicit expression of religiousness there is no opportunity for religious tourism or any other form of tourism. They are organized and presented following different principles from attractions elsewhere in the world, and that they are more important in the lives of the Indian people who visit and maintain them than they are to the Western tourist. Using spatial lens has reinforced that religious as a prefix, is a stronger and an essential concept for religious tourism in the non-western context of India, that needs to be factored in for sustainable management of religious tourism destinations.

Sexual(ities that) progress: Introduction

This piece introduces the papers for the Sexual(ities that) Progress special issue. It arises out of two sessions at the 2017 American Association of Geographers Annual Conference, where scholars critically interrogated assumptions of progress and the ideals and models that follow from understanding certain spaces and places as ‘leading the way’ in terms of sexual and gender inclusions. In this paper, we outline some of the key debates and how papers in this special issue address discourses of sexual(ities that) progress and, in particular, the importance of decolonial and postcolonial critiques in such debates. We conclude by noting omissions, the timeliness of the papers and the ongoing need for spatial lenses in exploring the power relationships that reconstitute sexual and gendered lives, cultures, politics and embodiments.

Sustainability Mindsets for Strategic Management: Lifting the Yoke of the Neo-Classical Economic Perspective

While sustainability has attracted the attention of managers and academicians for over two decades, the macro-level indicators of sustainability are not moving in the right direction. Climate change continues to be an existential threat for humanity and other indicators of sustainability do not fare much better. The logic of the business case and the associated framing of tension between financial outcomes and sustainability have generated a limited and inadequate response to the existential challenges before humanity today. In this essay, we analyze the evolution of sustainability in the business context and call for a recognition that social and environmental outcomes must supersede economic ones in corporate sustainability thinking. We call for a widening of the spatial, temporal, and moral lenses in the formulation and execution of business strategy to ensure that it is in alignment with the needs of current and future generations of humanity and proportionate to planetary conditions.

Electrically switchable polymer membranes with photo-aligned nematic structures for photonic applications

Abstract Composite materials containing liquid crystalline microstructures, providing fast stimuli responsive variations of birefringence at low consumption power, have great potential applications in photonics. Here, a composite material based on polymer membranes with photo-aligned nematic microstructures is proposed for the first time. For this purpose, porous polyethylene terephthalate (PET) films were covered with an azo-dye and subjected to a modified photoalignment technique to control the azimuthal orientation and anchoring strength of nematic liquid crystals (LCs) at the pore walls. Nematic internal ordering was identified using polarized optical microscopic observations assisted by theoretical simulations. The proposed approach provides spatial distribution of nematic microstructures characterized by specific internal ordering and fingerprint in near infrared spectra at an electro-optical response. These composites can be used as flexible photonic LC elements such as spatial light modulators, optical filters and lenses.

The Gender Gap in Reaching “Old Age” in the Russian Federation: A Regional Approach

ABSTRACT Reaching older age and longevity in later life is determined by health and mortality across the life course. In the case of Russia, the history of high male mortality skews the interaction between population aging and gender. These differentials can be viewed through a spatial lens in order to both understand their causes, and to better determine policy responses, especially in a federal political system. Using alternative conceptualizations of the “boundary to old age”, we produce the first estimates of the gender gap in reaching “old age” for all Russian Federal Subjects using 2017 data. We identify some regional differentiations, but uncertainties around the consistency of registration as well as overall heterogeneity mean that clear-cut regional patterns are hard to ascribe. Our analysis shows the highly significant gender gap at the age of “becoming old” in Russia when disaggregated by region. When looking at the regional level and comparing to other countries, the range of male “boundaries to old age” is almost as great as the global range. We argue that when applying alternative “old-age thresholds”, this gap represents a more accurate representation of interaction between space, gender, and mortality in Russia. We conclude with policy and research priorities to better understand and ameliorate the drivers of these spatial and gendered inequalities.

Testing the mid-spatial frequency error of a large aperture long-focal-length lens with CGH.

We present the use of a computer-generated hologram (CGH) to test the mid-spatial frequency error of a large aperture long-focal-length lens. In order to verify this test approach, a 450 mm × 450 mm reflective CGH is designed and fabricated for testing the 440 mm × 440 mm spatial filter lens. Both 0th and 1st order diffraction wavefront of CGH are measured, and the 0th order diffraction wavefront is used to calibrate the substrate error. The mid-spatial frequency wavefront error caused by the CGH fabrication errors are evaluated using the binary linear grating model and power spectral density (PSD) theory. Experimental results and error analysis show that the CGH test approach is also feasible for the measurement of mid-spatial frequency error, and the measurement accuracy of PSD1 can reach 0.8832 nm RMS.

Law as Geopolitics: Judicial Territory, Transnational Economic Governance, and American Power

The extension of domestic U.S. judicial authority to govern transnational economic relations involving foreign governments beyond official U.S. borders has been an important but largely overlooked component of the post–World War II international economic order. Using a critical spatial lens to analyze important U.S. common law changes, I show that a key strategy for achieving this extension has been redefining legal dichotomies to recode activity once considered public, political, and in the executive domain as private, commercial, nonpolitical, and judicial. This process has contributed to the depoliticization of fraught geopolitical conflicts and the production of a neoliberal global economy. The expansion of what I call judicial territory has occurred in response to acute political and economic challenges to U.S. interests and has been a means of forging an international economic order with the United States at the forefront. It has unilaterally extended U.S. state space and restricted the economic sovereignty of other countries, in ways that have benefited U.S. and transnational capital and underwritten the extraction of resources into the United States, especially from the Global South. At the same time, the unique characteristics of the common law have helped make these imperial relations hegemonic. Key Words: economy, hegemony, imperialism, law, territory.

(Re)thinking preservice teachers’ field experiences through a spatial lens

ABSTRACTSpace is not separable from the learning and teaching that take place in and through teacher education programs. In this paper, we attempt to illustrate how the use of a spatial lens in preservice teachers field placement can provide them with opportunities to raise questions and understand more about the relationships between self, the discursive construction of others, and taken-for-granted notions of learning and teaching. In helping preservice teachers’ critical reflections upon their spatial experience at their field sites, we specifically focus on “mapping” space as our approach to developing a critical embodied pedagogy. In particular, we highlight one White female preservice teacher’s spatial experience in a homeless shelter. We discuss the implications of developing pedagogical tools from the spatial perspective for early childhood teacher education programs.

All-optical neural network with nonlinear activation functions

Artificial neural networks (ANNs) have now been widely used for industry applications and also played more important roles in fundamental researches. Although most ANN hardware systems are electronically based, optical implementation is particularly attractive because of its intrinsic parallelism and low energy consumption. Here, we propose and demonstrate fully-functioned all optical neural networks (AONNs), in which linear operations are programmed by spatial light modulators and Fourier lenses, and optical nonlinear activation functions are realized with electromagnetically induced transparency in laser-cooled atoms. Moreover, all the errors from different optical neurons here are independent, thus the AONN could scale up to a larger system size with final error still maintaining in a similar level of a single neuron. We confirm its capability and feasibility in machine learning by successfully classifying the order and disorder phases of a typical statistic Ising model. The demonstrated AONN scheme can be used to construct various ANNs of different architectures with the intrinsic parallel computation at the speed of light.

Segmented urban space and the ethics of belonging in migrants’ Johannesburg

ABSTRACTThis article argues, from an ethnographic perspective and in the particular context of a group of young, black, low-income, Zimbabwean male migrants in Johannesburg, that the ethics of belonging among them are underpinned by the values of survival and mutual recognition. This occurs in a spatially demarcated manner informed by how the migrants’ perceive their social location and identity in different spaces in the city. Applying a micro spatial lens to their belonging narratives exposes layered ethics aimed at negotiating their own belonging and success in the city while highlighting reciprocal obligations attached to recognition of the other. The value of recognition is particularly attached to spaces where the interlocutors feel at home, and the article suggests that through interrogating such spaces in Johannesburg, and other urban centres, different role players can attempt to imagine an inclusive city.

Impact of Hurricane Katrina on the coastal systems of southern Louisiana.

Natural disasters, such as hurricanes and forest fires, could trigger collapse and reorganization of social-ecological systems. In the face of external perturbations, a resilient system would have capacity to absorb impacts, adapt to change, learn, and if needed, reorganize within the same regime. Within this context, we asked how human and natural systems in Louisiana responded to Hurricane Katrina, and how the natural disaster altered the status of these systems. This paper discusses community resilience to natural hazards and addresses the limitations for assessing disaster resilience. Furthermore, we assessed social and environmental change in New Orleans and southern Louisiana through both a spatial and temporal lens (i.e., pre- and post-Katrina). By analyzing changes in system condition using social, economic and environmental factors, we identified some of the characteristics of the system's reorganization trajectories. Our results suggest that although the ongoing population recovery may be a sign of revitalization, the city and metropolitan area continue to face socioeconomic inequalities and environmental vulnerability to natural disasters. Further, the spatial distribution of social-ecological condition over time reveals certain levels of change and reorganization after Katrina, but the reorganization did not translate into greater equity. This effort presents an enhanced approach to assessing social-ecological change pre and post disturbance and provides a way forward for characterizing pertinent aspects of disaster resilience.

Characterizing a mining space: Analysis from case studies in Chile and Australia

There is abundant research regarding the impact of the mining industry on settlements and communities, however, there is a lack of understanding regarding the characteristics of large-scale mining impacts from a socio-spatial perspective. The main objective of this study is to characterize a “mining space” by drawing on some of the analytical concepts of Henry Lefebvre (1991) production of space. Based on data from four case studies of mining spaces located in Chile and Australia, this paper addresses a gap in the literature regarding the characterization of the impact of large-scale mining from a spatial lens. Current spatial perspectives of mining are limited to scale and identity descriptions, such as mining town, city or region, or economic geography dynamics such as enclaves or industrial agglomerations; there is no concept that considers the spatial dimension that large-scale mining industry imprints in a settlement. Based on the findings of this paper, the authors propose a conceptualization and the characterization of a mining space that considers two of the trialectic dimensions proposed by Lefebvre: spatial practices and representation of space. This study contributes to existing literature on mining policy, and provides suggestions for government officials and policy makers to better understand and manage the territory developed in large-scale mining.