Tracking magnetic bright point motions through the solar atmosphere

High-cadence, multiwavelength observations and simulations are employed for the analysis of solar photospheric magnetic bright points (MBPs) in the quiet Sun. The observations were obtained with the Rapid Oscillations in the Solar Atmosphere (ROSA) imager and the Interferometric Bidimensional Spectrometer at the Dunn Solar Telescope. Our analysis reveals that photospheric MBPs have an average transverse velocity of approximately 1 km s-1, whereas their chromospheric counterparts have a slightly higher average velocity of 1.4 km s-1. Additionally, chromospheric MBPs were found to be around 63 per cent larger than the equivalent photospheric MBPs. These velocity values were compared with the output of numerical simulations generated using the muram code. The simulated results were similar, but slightly elevated, when compared to the observed data. An average velocity of 1.3 km s-1 was found in the simulated G-band images and an average of 1.8 km s-1 seen in the velocity domain at a height of 500 km above the continuum formation layer. Delays in the change of velocities were also analysed. Average delays of ˜4 s between layers of the simulated data set were established and values of ˜29 s observed between G-band and Ca ii K ROSA observations. The delays in the simulations are likely to be the result of oblique granular shock waves, whereas those found in the observations are possibly the result of a semi-rigid flux tube.

Analytical model of interwoven spiral arrays

Interweaving planar spiral conductors in doubly periodic arrays enable substantially sub-wavelength resonant response along with broadening fractional bandwidth. A self-contained analytical model is proposed to accurately predict the characteristics of the intertwined quadrifilar spiral array near the fundamental resonance. The model, based upon a multiconductor transmission line (MTL) approach, provides physical insight into the unique properties of the distributed interactions between the interleaved counter-wound spiral arms extended beyond a single unit cell and elucidates the mechanisms underlying the array performance at normal and oblique incidence of TE and TM polarised waves. The developed MTL model is instrumental in the design of the artificial surfaces with the specified response.

Active singly and dual polarised interwoven spiral frequency selective surfaces

Reconfigurable bi-state interwoven spiral FSSs are explored in this work. Their switching capability is realized by pin diodes that enable the change of the electromagnetic response between transparent and reflecting modes at the specified frequencies in both singly and dual polarised unit cell configurations. The proposed topologies are single layer FSS with their elements acting also as dc current carrying conductors supplying the bias signal for switching pin diodes between the on and off states, thus avoiding the need of external bias lines that can cause parasitic resonances and affect the response at oblique incidence. The presented simulation results show that such active FSSs have potentially good isolation between the transmission and reflection states, while retaining the substantially subwavelength response of the unit cell with large fractional bandwidths (FBWs) inherent to the original passive FSSs.

Interwoven spiral arrays on ferrite-dielectric substrates for high-impedance metasurfaces

A high impedance metasurface (HIMS) composed of the arrays of intertwined planar spirals on thin (~0.1λ) ferrite-dielectric substrate is proposed. The HIMS exhibits fractional bandwidth in excess of 10% and excellent angular and polarisation stability of the circular polarised waves at oblique incidence.

Dublin’s ephemeral and imaginary architectures

In 1989, the Irish architectural practice O’Donnell and Tuomey were commissioned to build a temporary pavilion to represent Ireland at the 11 Cities/11 Nations exhibition at Leeuwarden in the Netherlands. Citing Peter Smithson, John Tuomey suggested the pavilion, which drew inspirations from the forms and materials of the modern Irish barn, embodied an intention ‘not just to build but to communicate’. Its subsequent reassembly for the inauguration of the Irish Museum of Modern Art in the courtyard of the seventeenth-century Royal Hospital Kilmainham in Dublin in 1991, drew comparisons between the urban sophistication of this colonial building, its svelte new refit, and the rural expression of O’Donnell + Tuomey’s barn. It was, one critic recently noted, as if ‘a wedding had been crashed by a country cousin who had forgotten to clean his boots’.
It has been argued that temporary or ephemeral pieces of architecture, unburdened by the traditional constraints of firmitas or utilitas, have the ability to offer a concise distillation of meaning and intention. Approaching the qualities of rhetoric, such architectures share similarities with the monument and yet differ in fundamental ways. Their rapid construction in lightweight materials can allow for an almost instantaneous negotiation of zeitgeist. And, unlike the monument, from the outset the space and form of these installations is designed to disappear.
This paper analyses the ephemeral architectures of Dublin in the modern period contextualising their qualities and intentions as they manifest themselves across colonial, post-colonial and contemporary epochs. It finds origins in the theatrical sets of the late eighteenth century and traces their movements into the semi-public sphere of the pleasure garden and finally into the theatre of the streets. It is here that temporary architecture in the city has been at its most potent, allowing the amplification or subversion of the meanings of much larger spaces. Historically, much of Dublin’s most conspicuous instances of ephemeral architecture have been realised as a means of articulating mass spectacle in political, religious or nationalistic events. And while much of this has sought to confirm dominant ideologies, it has also been possible to discern moments of opposition.
The contemporary period, however, has arguably witnessed a shift in ephemeral architectures from explicitly representing ‘positive ideologies’ towards something more oblique or nebulous. This turn towards abstraction in form and space has rendered an especially communicative form of architecture particularly elusive. By examining continuities within the apparent disjuncture between historical and contemporary examples, this paper begins to unpick the language of recent ephemeral architecture in Dublin and situate it within wider global trends where political and economic imperatives are often simultaneously obscured and expressed in public space by a vocabulary of universality. As Jurgen Habermas has suggested, the contemporary value given to the transitory and the ephemeral ‘discloses a longing for an undefiled, immaculate and stable present’.

Pulse mixing by Fibonacci and Thue-Morse ordered semiconductor layers

The properties of combinatorial frequency generation by two-tone Gaussian pulses incident at oblique angles on quasiperiodic (Fibonacci and Thue-Morse) stacks of binary semiconductor layers are discussed. The analysis has been performed using the self-consistent model taking into account the nonlinear dynamics of mobile charges in the layers. The effects of the stack arrangements and constituent layer parameters on the combinatorial frequency waveforms are presented for the specific structures of both types

Pressure anisotropy effects on nonlinear electrostatic excitations in magnetized electron-positron-ion plasmas

The propagation of linear and nonlinear electrostatic waves is investigated in a magnetized anisotropic electron-positron-ion (e-p-i) plasma with superthermal electrons and positrons. A two-dimensional plasma geometry is assumed. The ions are assumed to be warm and anisotropic due to an external magnetic field. The anisotropic ion pressure is defined using the double adiabatic Chew-Golberger-Low (CGL) theory. In the linear regime, two normal modes are predicted, whose characteristics are investigated parametrically, focusing on the effect of superthermality of electrons and positrons, ion pressure anisotropy, positron concentration and magnetic field strength. A Zakharov-Kuznetsov (ZK) type equation is derived for the electrostatic potential (disturbance) via a reductive perturbation method. The parametric role of superthermality, positron content, ion pressure anisotropy and magnetic field strength on the characteristics of solitary wave structures is investigated. Following Allen and Rowlands [J. Plasma Phys. 53, 63 (1995)], we have shown that the pulse soliton solution of the ZK equation is unstable to oblique perturbations, and have analytically traced the dependence of the instability growth rate on superthermality and ion pressure anisotropy.

Prevalence of refractive error in Europe: the European Eye Epidemiology (E3) Consortium

To estimate the prevalence of refractive error in adults across Europe. Refractive data (mean spherical equivalent) collected between 1990 and 2013 from fifteen population-based cohort and cross-sectional studies of the European Eye Epidemiology (E³) Consortium were combined in a random effects meta-analysis stratified by 5-year age intervals and gender. Participants were excluded if they were identified as having had cataract surgery, retinal detachment, refractive surgery or other factors that might influence refraction. Estimates of refractive error prevalence were obtained including the following classifications: myopia ≤−0.75 diopters (D), high myopia ≤−6D, hyperopia ≥1D and astigmatism ≥1D. Meta-analysis of refractive error was performed for 61,946 individuals from fifteen studies with median age ranging from 44 to 81 and minimal ethnic variation (98 % European ancestry). The age-standardised prevalences (using the 2010 European Standard Population, limited to those ≥25 and <90 years old) were: myopia 30.6 % [95 % confidence interval (CI) 30.4–30.9], high myopia 2.7 % (95 % CI 2.69–2.73), hyperopia 25.2 % (95 % CI 25.0–25.4) and astigmatism 23.9 % (95 % CI 23.7–24.1). Age-specific estimates revealed a high prevalence of myopia in younger participants [47.2 % (CI 41.8–52.5) in 25–29 years-olds]. Refractive error affects just over a half of European adults. The greatest burden of refractive error is due to myopia, with high prevalence rates in young adults. Using the 2010 European population estimates, we estimate there are 227.2 million people with myopia across Europe.

Non-reciprocity in doubly periodic strip arrays on ferrite-dielectric substrate

Doubly periodic arrays of strip conductors printed on a composite ferrite-dielectric substrate have been investigated at oblique incidence of linear polarized plane waves. The simulation results revealed strong non-reciprocity of wave reflectance and transmittance at positive and negative angles of incidence. It is also shown that the non-reciprocity is further enhanced by the strip conductor pattern. 

Circular polarisation frequency selective surface operating in Ku and Ka band

A double layer circular polarization (CP) frequency selective surface (FSS) for use as a dual-band quasi-optical diplexer suitable for deployment in reflector antenna systems is described. The FSS was designed to reflect Ku band signals (11.7–12.75 GHz) while transmitting Ka band signals (17.3–20.2 GHz) and conserving CP in each of these bands. The simulated/measured reflection loss over the Ku band was less than 0.05/0.1 dB for both TE and TM polarizations, while the simulated/measured axial ratio was less than 0.2/0.75 dB. Over the Ka band, the simulated/measured transmission loss for both polarizations was below 0.25/0.4 dB and the simulated/measured axial ratio was less than 0.25/0.75 dB. To the best of our knowledge, this is the first report of a metallo-dielectric FSS that simultaneously operates in CP for an oblique angle of incidence in both Ku and Ka bands.

Old Town Glasgow: Squalor, Agitation and City Improvements

In 1862, Glasgow Corporation initiated the first of a series of three legislative acts which would become known collectively as the City Improvements Acts. Despite having some influence on the nature of the built fabric on the expanding city as a whole, the most extensive consequences of these acts was reserved for one specific area of the city, the remnants of the medieval Old Town. As the city had expanded towards all points of the compass in a regular, grid-iron structure throughout the nineteenth century, the Old Town remained singularly as a densely wrought fabric of medieval wynds, vennels, oblique passageways and accelerated tenementalisation. Here, as the rest of the city began to assume the form of an ordered entity, visible and classifiable, one could still find and addresses such as ‘Bridgegate, No. 29, backland, stair first left, three up, right lobby, door facing’ (quoted in Pacione, 1995).

Unsurprisingly, this place, where proximity to the midden (dung-heap) was considered an enviable position, was seen by the authorities as a major health hazard and a source not only of cholera, but also of the more alarming typhoid epidemic of 1842. Accordingly, the demolitions which occurred in the backlands of the Old Town under the first of the acts, the Glasgow Police Act of 1862, were justified on health and medical grounds. But disease was not the only social problem thought to issue from this district. Reports from social reformers including Fredrick Engels suggested that the decay of the area’s physical fabric could be extended to the moral profile of its inhabitants. This was in such a state of degeneracy that there were calls for a nearby military barracks to be relocated to more salubrious climes because troops were routinely coming into contact ‘with the most dissolute and profligate portion of the population’ (Peter Clonston, Lord Provost, June 1861). Perhaps more worrying for the city fathers, however, was that the barracks’ arsenal was seen as a potential source of arms for the militant and often illegal cotton workers’ unions and organisations who inhabited the Old Town as well as the districts to the east. In fact, the Old Town and East End had been the site of numerous working class actions and riots since 1787, including a strike of 60,000 workers in 1820, 100,000 in 1838, and the so-called Bread Riots of 1848 where shouts of ‘Vive La Revolution’ were reported in the Gallowgate.

The events in Paris in 1848 precipitated Baron Hausmann’s interventions into that city. The boulevards were in turn visited by members of Glasgow Corporation and ultimately, it can be argued, provided an example for Old Town Glasgow. This paper suggests that the city improvement acts carried a similarly complex and pervasive agenda, one which embodied not only health, class conflict and sexual morality but also the more local condition of sectarianism. And, like in Paris, these were played out spatially in a extensive reconfiguration of the urban fabric of the Old Town which, through the creation of new streets and a railway yard, not only made it more amenable to large scale military manoeuvres but also, opened up the area to capitalist accumulation. By the end of the works, the medieval heritage of the Old Town had been almost completely razed, the working class and Catholic East End had, through the insertion of the railway yard, been isolated from the city centre and approximately 70,000 people had been made homeless.

Accuracy of rural refractionists in western China

Purpose. We assessed the prevalence and predictors of inaccurate refractive error among rural refractionists in western China. Methods. A subset of primary school children with visual acuity (VA) ≤6/12 in ≥1 eye, undergoing subjective refinement by local refractionists after cycloplegic autorefraction in an ongoing population-based study, received repeat refraction by university optometrists for quality control. Results. Among 502 children (mean age 10.5 years, 53.2% girls), independent predictors of poor (inaccurate by ≥1.0 diopter [D]) refraction by 21 rural practitioners (66.7% with high school or lower education) included hyperopia (odds ratio [OR], 4.2; 95% confidence interval [CI], 2.4-7.3, P < 0.001), astigmatism (OR = 3.8; 95% CI, 2.5-5.6; P < 0.001) and VA uncorrectable to >6/12 by the rural refractionist (OR = 4.7; 95% CI, 3.1-7.3; P = < 0.001). Among 201 children whose vision was uncorrectable in ≥1 eye by the rural refractionists, vision could be improved to >6/12 by the university optometrist in 110 (54.7%). We estimate vision could be so improved in 9.1% of all children refracted by these rural refractionists. A reason for inaccuracy in this setting is the erroneous tendency of rural refractionists to adjust instrument values for accommodation, even under cycloplegia. Conclusions. Rural refractionists in western China have little formal training and frequently fail to optimize VA among children, even when autorefractors are used. Training is needed emphasizing better use of automated refraction, particularly in children with astigmatism and hyperopia. © 2014 The Association for Research in Vision and Ophthalmology, Inc.

Screening techniques for angle-closure glaucoma in rural Taiwan

562 residents of Jin Shan aged 40 years and above underwent examinations to compare the sensitivity and specificity of oblique flashlight, peripheral slit beam and ultrasonographic evaluation of the anterior chamber depth to gonioscopy in detecting cases of PACG. Among 5441 eligible individuals aged 40 and above, 562 (10.3%) underwent screening for PACG, of whom 17 (3.02%) were defined as cases, and 10 (1.78%) as suspects. Home visits indicated that respondents for screening were similar to the population as a whole. Only 35% of PACG cases reported symptoms consistent with acute angle closure, and only 18% were previously diagnosed. When compared to gonioscopy, only ultrasonographic measurement of AC depth provided an adequate mix of sensitivity and specificity. Ultrasonography in combination with tonometry provided a sensitivity of 88% with a specificity of 92%. Sensitivity and specificity for ultrasonography in combination with refractive status were 84% and 83% respectively. Shallower AC depth (p = 0.0001), shorter axial globe length (p = 0.001), greater than 2D of hyperopia (p < 0.001), high grades of nuclear sclerotic cataract (p < 0.0001) and an increased cup-to-disc ratio (p = 0.002) were significantly correlated with a diagnosis of PACG.

The association between refractive cutoffs for spectacle provision and visual improvement among school-aged children in South Africa.

OBJECTIVES: To evaluate different refractive cutoffs for spectacle provision with regards to their impact on visual improvement and spectacle compliance. DESIGN: Prospective study of visual improvement and spectacle compliance. PARTICIPANTS: South African school children aged 6-19 years receiving free spectacles in a programme supported by Helen Keller International. METHODS: Refractive error, age, gender, urban versus rural residence, presenting and best-corrected vision were recorded for participants. Spectacle wear was observed directly at an unannounced follow-up examination 4-11 months after initial provision of spectacles. The association between five proposed refractive cutoff protocols and visual improvement and spectacle compliance were examined in separate multivariate models. MAIN OUTCOMES: Refractive cutoffs for spectacle distribution which would effectively identify children with improved vision, and those more likely to comply with spectacle wear. RESULTS: Among 8520 children screened, 810 (9.5%) received spectacles, of whom 636 (79%) were aged 10-14 years, 530 (65%) were girls, 324 (40%) had vision improvement > or = 3 lines, and 483 (60%) were examined 6.4+/-1.5 (range 4.6 to 10.9) months after spectacle dispensing. Among examined children, 149 (31%) were wearing or carrying their glasses. Children meeting cutoffs < or = -0.75 D of myopia, > or = +1.00 D of hyperopia and > or = +0.75 D of astigmatism had significantly greater improvement in vision than children failing to meet these criteria, when adjusting for age, gender and urban versus rural residence. None of the proposed refractive protocols discriminated between children wearing and not wearing spectacles. Presenting vision and improvement in vision were unassociated with subsequent spectacle wear, but girls (p < or = 0.0006 for all models) were more likely to be wearing glasses than were boys. CONCLUSIONS: To the best of our knowledge, this is the first suggested refractive cutoff for glasses dispensing validated with respect to key programme outcomes. The lack of association between spectacle retention and either refractive error or vision may have been due to the relatively modest degree of refractive error in this African population.

Influence of corneal structure, corneal responsiveness, and other ocular parameters on tonometric measurement of intraocular pressure.

PURPOSE: To estimate the relationships between ocular parameters and tonometrically measured intraocular pressure (IOP), to determine the influence of ocular parameters on different instrument measurements of IOP, and to evaluate the association of ocular parameters with a parameter called hysteresis. METHODS: Patients presenting at a glaucoma clinic were recruited for this study. Subjects underwent IOP measurement with the Goldmann applanation tonometer (GAT), the TonoPen, and the Reichert Ocular Response Analyzer (ORA), and also measurements of central corneal thickness (CCT), axial length, corneal curvature, corneal astigmatism, central visual acuity, and refractive error. Chart information was reviewed to determine glaucoma treatment history. The ORA instrument provided a measurement called corneal hysteresis. The association between measured IOP and the other ocular characteristics was estimated using generalized estimating equations. RESULTS: Among 230 patients, IOP measurements from the TonoPen read lowest, and ORA read highest, and GAT measurements were closest to the mean IOP of the 3 instruments. In a multiple regression model adjusting for age, sex, race, and other ocular characteristics, a 10 microm increase in CCT was associated with an increase of 0.79 mm Hg measured IOP in untreated eyes (P<0.0001). Of the 3 tonometers, GAT was the least affected by CCT (0.66 mm Hg/10 mum, P<0.0001). Hysteresis was significantly correlated with CCT with a modest correlation coefficient (r=0.20, P<0.0007). CONCLUSIONS: Among parameters related to measured IOP, features in addition to CCT, such as hysteresis and corneal curvature, may also be important. Tonometric instruments seem to be affected differently by various physiologic characteristics.