Opaque Region Research Articles

Radiation-Induced Alteration of the Reflection Spectra of Diazoquinone–Novolac Photoresist Films by Implantation of Ag+ Ions

FP9120 diazoquinone–novolac positive photoresist films 1.5 μm thick implanted with Ag+ ions and supported on the surface of KDB-10 (111) silicon wafers by centrifugation have been studied by measuring reflection spectra. It has been shown that ion implantation leads to a decrease in the refractive index of the photoresist due to radiation crosslinking of novolac resin molecules and a decrease in the density ρ and the molecular refraction RM of the photoresist. It has been established that the reflection coefficient in the opaque region of the photoresistive film increases with the Ag+ implantation dose. The changes observed in the optical properties of the films under ion implantation conditions are explained taking into account radiation-chemical processes in the phenol–formaldehyde photoresist.

Non-Normality as a Drive for Change An Overview of Systemic Processes

this paper moves from the multifaceted frame of ‘normality' to inquiry how the processes of change work in case of perturbations. The aim is not simply to investigate the opaque region of the world of life that belongs to metamorphosis but to reflect on the possibility to move further obsolete paradigms about what is normal/abnormal/pathological. Through several forms of normalities that result from processes that follow shocking events (social emergencies, severe diagnoses and chronic diseases) the author will highlight the dynamic texture of normality and the transformative power of non-normality. Normality in case of perturbation results not from the limit of the norm, but from the constant effort to re-modulate it. Furthermore, it will be argued that new normalities originate from a process of renormalization, a dynamic which refers to a relation of scale. Deeply intertwined with change, the dy- namic texture of normality cannot be detected by the observer. For a valuable understanding of the opaque region of transformation, it ought to investigate through the lenses of systemic thinking. This approach brings into light two main phases, which are the breaking of a previous balance and the emer- gence of novel, unpredictable conditions. A special concern is addressed to post-traumatic creativity: it will be possible to assume that creativity can be recognized as the capacity to grasp and institute new relations. Finally, it will be questioned whether the term normality in the discourse about health can be substituted by another one, which can better fit the trans- formative power of non-normality and can put into brackets any moral as- sessment of the pathological/abnormal condition of the person. It will be con- cluded that it is not only possible, but also highly recommended in a frame where disease and health can be understood in relation to the harmonic inte- gration among parts and levels.

Extraordinary optical transmittance generation on Si3N4 membranes.

Metamaterials are attracting increasing attention due to their ability to support novel and engineerable electromagnetic functionalities. In this paper, we investigate one of these functionalities, i.e. the extraordinary optical transmittance (EOT) effect based on silicon nitride (Si3N4) membranes patterned with a periodic lattice of micrometric holes. Here, the coupling between the incoming electromagnetic wave and a Si3N4 optical phonon located around 900 cm-1 triggers an increase of the transmitted infrared intensity in an otherwise opaque spectral region. Different hole sizes are investigated suggesting that the mediating mechanism responsible for this phenomenon is the excitation of a phonon-polariton mode. The electric field distribution around the holes is further investigated by numerical simulations and nano-IR measurements based on a Scattering-Scanning Near Field Microscope (s-SNOM) technique, confirming the phonon-polariton origin of the EOT effect. Being membrane technologies at the core of a broad range of applications, the confinement of IR radiation at the membrane surface provides this technology platform with a novel light-matter interaction functionality.

Dual-Band Aperture-Shared High Gain Antenna for Millimeter-Wave Multi-Beam and Sub-6 GHz Communication Applications

This communication presents a dual-band aperture-shared high gain antenna for millimeter-wave (mm-wave) multi-beam and sub-6 GHz applications by integrating transmitarray into Fresnel zone plate (FZP) lens. The transmistarray consists of two sets of unit cells (UCs), which can provide high transmission magnitude and [ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$-\pi $ </tex-math></inline-formula> , <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pi $ </tex-math></inline-formula> ] phase tuning at the mm-wave frequency band. Meanwhile, they show distinct transmission features at the sub-6 GHz band (one set of UC allows the electromagnetic (EM) wave to pass while the other prohibits the EM wave from passing). Then, by properly arranging the two kinds of UCs into the transparent and opaque region of the FZP lens respectively, the sub-6 GHz FZP lens and the mm-waveband transmitarray are integrated into the same aperture seamlessly. A waveguide-integrated patch antenna is adopted as the feed. The patch antenna operates at the sub-6 GHz band and three open waveguide antennas are used for the mm-wave multi-beam radiation. The proposed antenna achieves high gain at both bands with a reused radiating aperture. Mm-wave multi-beam radiation is obtained without an extra feeding network. For demonstration purposes, the central frequencies of the sub-6 GHz and the mm-wave bands are selected at 6 and 27 GHz, respectively. An antenna prototype is fabricated and experimentally verified.

Effects of composition and growth parameters on phase formation in multicomponent aluminum garnet crystals.

The effects of composition on the phase formation of multicomponent garnet crystals grown via directional solidification by the micro-pulling-down method are studied. A relatively wide range of rare-earth (RE) average ionic radii (AIR) is explored by formulating ten compositions from the system (Lu,Y,Ho,Dy,Tb,Gd)3Al5O12. Crystals were grown at either 0.05 or 0.20 mm min-1. The hypothesis is that multicomponent compounds with large AIR will form secondary phases as the single-RE aluminum garnets formed by larger Tb3+ or Gd3+; this will result in crystals of poor optical quality. Crystals with large AIR have a central opaque region in optical microscopy images, which is responsible for their reduced transparency compared to crystals with small AIR. Slow pulling rates suppress the formation of the opaque region in crystals with intermediate AIR. Powder and single-crystal X-ray diffraction and electron probe microanalysis results indicate that the opaque region is a perovskite phase. Scanning electron microscopy and energy dispersive spectroscopy measurements reveal eutectic inclusions at the outer surface of the crystals. The concentration of the eutectic inclusions increases with increasing AIR.

Terahertz plasma edge engineering in semiconductor membranes with a two-dimensional electron layer

We have studied the terahertz response of a dielectric membrane with a high-mobility two-dimensional electron system (2DES) on one side. The developed device exhibits electromagnetic transparency above the plasma frequency that is found to be determined by the 2DES density and membrane thickness. Significantly, we demonstrate the opaque low-frequency region to be highly tunable. Our results can find applications in the area of active terahertz devices.

Effect of Inhomogeneous Broadening in Ultraviolet III-Nitride Light-Emitting Diodes.

In the past years, light-emitting diodes (LED) made of GaN and its related ternary compounds with indium and aluminium have become an enabling technology in all areas of lighting. Visible LEDs have yet matured, but research on deep ultraviolet (UV) LEDs is still in progress. The polarisation in the anisotropic wurtzite lattice and the low free hole density in p-doped III-nitride compounds with high aluminium content make the design for high efficiency a critical step. The growth kinetics of the rather thin active quantum wells in III-nitride LEDs makes them prone to inhomogeneous broadening (IHB). Physical modelling of the active region of III-nitride LEDs supports the optimisation by revealing the opaque active region physics. In this work, we analyse the impact of the IHB on the luminescence and carrier transport III-nitride LEDs with multi-quantum well (MQW) active regions by numerical simulations comparing them to experimental results. The IHB is modelled with a statistical model that enables efficient and deterministic simulations. We analyse how the lumped electronic characteristics including the quantum efficiency and the diode ideality factor are related to the IHB and discuss how they can be used in the optimisation process.

Aperture-Shared Millimeter-Wave/Sub-6 GHz Dual-Band Antenna Hybridizing Fabry–Pérot Cavity and Fresnel Zone Plate

This article presents an aperture-shared dual-band large frequency-ratio high gain antenna for sub-6 GHz and millimeter-wave (mm-wave) bands applications. Initially, the partially reflective surface (PRS) of the Fabry–Pérot cavity (FPC) antenna operating at the sub-6 GHz band is realized by using single-layered periodic grid patches while the opaque region of the mm-wave bandwaveband Fresnel zone plate (FZP) lens antenna is implemented by using periodic double-screen dipoles. Then, the PRS and the FZP lens are hybridized together and upgraded into a kind of composite metasurface, which simultaneously functions as the PRS of the sub-6 GHz FPC antenna and the mm-wave bandwaveband FZP lens with little dual-band mutual interference. Thus, the FPC antenna and the FZP lens can share the same aperture with high aperture reuse efficiency. Because the principles are based on the FPC resonance and the collimating FZP lens, high gains are achieved at both bands without a feeding network. Meanwhile, a dual-band large frequency-ratio antenna is designed as the feed. A prototype working at 3 and 28 GHz bands is designed, fabricated, and measured to verify the idea.

Plasmon-induced transparency sensor for detection of minuscule refractive index changes in ultra-low index materials

Detection of low-index materials such as aerogels and also detection of refractive index variations in these materials is still a challenging task. Here, a high figure of merit (FOM) sensor based on plasmon-induced transparency (PIT) is proposed for the detection of aerogel refractive index changes. In the proposed PIT sensor, the transparency window in an opaque region arises from the coupling between surface plasmon polariton (SPP) mode and planar waveguide mode. By comprising sub-wavelength grating (SWG) in the planar waveguide region, the maximum of the electric field of waveguide occurs in a low index media. This facilitates detection of the aerogels when they are used as the low index material (sensing material). Application of the subwavelength grating waveguide also improves the sensitivity of the sensor by a factor of six compared to a conventional structure with a homogenous waveguide. The proposed structure has a quality factor of Q ≥ 1800, and a reflection of 86%, and can detect the refractive index changes as low as Δn = 0.002 (around n = 1.0). The lineshape, Q-factor, and resonant wavelength of the transparency spectrum can be controlled by tailoring the structural parameters. Our work also has potential application in switching, filtering, and spectral shaping.

A numerical study on laboratory plasma dynamics validated by low current x-pinch experiments

The computational study of x-pinch plasmas driven by pulsed power generators demands the development of advanced numerical models and simulation schemes, able to enlighten the experiments. The capabilities of PLUTO code are here extended to enable the investigation of low current produced x-pinch plasmas. The numerical modules of the code used and modified are presented and discussed. The simulations results are compared to experiments, carried out on a table-top pulsed power plasma generator implemented in a mode of producing a peak current of ∼45 kA with a rise time (10%–90%) of 50 ns, loaded with Tungsten wires. The structural evolution of plasma density is studied and its influence on the magnetic field is analyzed with the help of the new simulation data. The simulated areal mass density is compared with the experimentally measured dense opaque region to enlighten the dense plasma evolution. In addition, the measured areal electron density is compared to the simulation results. Moreover, the new simulation data offer valuable insights to the main jet formation mechanisms, which are further analyzed and discussed in relation to the influence of the J × B force and the momentum.

Harmonic generation in the opaque region of GaAs: the role of the surface and magnetic nonlinearities.

Phase-locked second and third harmonic generation in the opaque region of a GaAs wafer is experimentally observed and analyzed both in transmission and reflection. These harmonic components, which are generated close to the surface, can propagate through an opaque material as long as the pump is tuned to a region of transparency or semitransparency and correspond to the inhomogeneous solutions of Maxwell's equations with nonlinear polarization sources. We show that measurement of the angular and polarization dependence of the observed harmonic components allows one to infer the different nonlinear mechanisms that trigger these processes, including not only the bulk nonlinearity but also the surface and magnetic Lorentz contributions, which usually are either hidden by the bulk contributions or assumed to be negligible. The experimental results are compared with a detailed numerical model that takes into account these different effects, including for the first time combined linear and nonlinear material dispersions in a nonlinear Lorentz oscillator model of the bulk nonlinearities. Our results suggest that the intensity of the second harmonic signal generated by the surface can be more intense than the signal generated by the bulk. These findings have significant repercussions and are consequential in nanoscale systems, which are usually investigated using only dispersionless bulk nonlinearities, with near-complete disregard of surface and magnetic contributions and their microscopic origins.

Ultrafast quantum-path interferometry revealing the generation process of coherent phonons

Optical dual-pulse pumping actively creates quantum-mechanical superposition of the electronic and phononic states in a bulk solid. We here made transient reflectivity measurements in an n-GaAs using a pair of relative-phase-locked femtosecond pulses and found characteristic interference fringes. This is a result of quantum-path interference peculiar to the dual-pulse excitation as indicated by theoretical calculation. Our observation reveals that the pathway of coherent phonon generation in the n-GaAs is impulsive stimulated Raman scattering at the displaced potential due to the surface-charge field, even though the photon energy lies in the opaque region.

The role of galaxies and AGNs in reionizing the IGM – II. Metal-tracing the faint sources of reionization at 5 ≲z≲ 6

We present a new method to study the contribution of faint sources to the UV background using the 1D correlation of metal absorbers with the intergalactic medium (IGM) transmission in a Quasi Stellar Object (QSO) sightline. We take advantage of a sample of $25$ high signal-to-noise ratio QSO spectra to retrieve $150$ triply-ionised carbon (\cfour) absorbers at $4.5\lesssim z\lesssim 6.2$, of which $37$ systems whose expected H{~\small I} absorption lie in the Lyman-$\alpha$ forest. We derive improved constraints on the cosmic density of \cfour \,at $4.3< z < 6.2$ and infer from abundance-matching that \cfour \,absorbers trace $M_{\text{UV}}\lesssim -16$ galaxies. Correlation with the Lyman-$\alpha$ forest of the QSOs indicates that these objects are surrounded by a highly opaque region at $r\lesssim 5 $ cMpc/h followed by an excess of transmission at $r\gtrsim 10$ cMpc/h detected at $2.7\sigma$. This is in contrast to equivalent measurements at lower redshifts where only the opaque trough is detected. We interpret this excess as a statistical enhancement of the local photoionisation rate due to clustered faint galaxies around the \cfour \,absorbers. Using the analytical framework described in Paper I of this series, we derive a constraint on the average product of the escape fraction and the Lyman continuum photon production efficiency of the galaxy population clustered around the \cfour \,absorbers, $\log \langle f_{\text{esc}}\xi_{\text{ion}}\rangle /[{\rm erg^{-1}~Hz}] = 25.01^{+0.30}_{-0.19}$. This implies that faint galaxies beyond the reach of current facilities may have harder radiation fields and/or larger escape fractions than currently detected objects at the end of the reionisation epoch.

Complex Sellmeier equation for the refractive index of semiconductors in the opaque region

Modeling the dispersion relation of semiconductors using a complex Sellmeier equation is reported for the first time. For this purpose, the refractive indices of GaAs and InAsBi were measured using spectroscopic ellipsometry. The complex Sellmeier coefficients were then obtained by a least-square fitting procedure. Simulation results demonstrate that complex Sellmeier equations can accurately model the refractive index dispersion of different semiconductors at wavelengths shorter than the band gap wavelengths, where the conventional Sellmeier equations are not applicable.

Difficulties in Estimating the Physical Parameters of Compact Radio Sources in Active Galactic Nuclei

The various factors influencing estimates of the physical parameters of compact radio sources in active galactic nuclei (AGN) using a methods based on uniform models of synchrotron radiation sources are analyzed. It is found that the form of the relativistic electron energy density distribution as a function of magnetic energy density (Ee-EH) in the radio sources is determined by the shape of the electron energy spectrum. It is shown that the very large observed deviations of the estimated energies of the field and relativistic particles from equipartition are mainly caused by nonuniformity of the radio sources. In order to obtain correct estimates of the physical parameters of nonuniform radio sources, it is necessary to know their angular sizes at low frequencies (in the opaque region) and their Doppler factors.

Western sanctions—Only half the challenge to Russia’s economic union

Tensions over Russia’s recent actions in Ukraine and the Middle East have resulted in wide-ranging Western sanctions. An understanding the destabilizing regional and institutional effects of sanctions is, therefore, fundamental for policymakers on both sides. Data from 2007 to 2015 are used to analyze the effect of funding, bank ownership and credit quality across Russia’s wider Economic Union. Results enable systemic insights into an often opaque region during a period of crises and sanctions. Specifically we find that sanctions result in institutional illiquidity, limited capital market access and a rise in state funding coupled with bank take-overs by governments. Government Institutions exploit their access to state funding to increase market share but the positive effects are limited since there is clear evidence of ongoing poor credit management. An increase in loan loss provisions, lagged abnormal credit losses, suggest that until this second but significant ‘weak management’ effect is addressed, it will be difficult for institutions in the region to overcome the debilitating effects of sanctions.

Direct observation of graphenic nanostructures inside femtosecond-laser modified diamond

In this paper we report on the study of the buried laser-modified region produced inside single crystal diamond by femtosecond laser irradiation. The cross-section of the modified region was prepared via precise mechanical polishing to investigate its intrinsic structure with Raman spectroscopy, scanning electron microscopy and scanning spreading resistance microscopy. It is found that the opaque laser-modified region is pierced by 40–100 nm thick sheets of graphenic carbon united into a single conductive network, while the gaps between the sheets are filled by diamond. Only small part of the irradiated diamond volume (∼16 vol. %) is transformed into the sp2 phase. The results obtained are consistent with the model of laser-induced crack-assisted phase transition in diamond bulk proposed earlier.

A New Species of Pylaisia (Hypnaceae) from Peru

Pylaisia afoninae is described from Peru. It is the first known dioicous species in the genus. Additional noteworthy features of the species are its strongly concave, long-acuminate leaves and extensively developed, opaque alar region.

Timing of First Annulus Formation in White Sucker Otoliths

AbstractThe purpose of this study was to document the time of formation for the first two otolith annuli for White Sucker Catostomus commersoni. Young‐of‐the‐year and age‐1 individuals were sampled monthly from a population in the White River drainage of the Missouri Ozarks. The formation of a single annual opaque region during the months of June–September of the first 2 years of life was documented using edge analysis, whereby the progression of otolith annulus formation is followed throughout the year in the population. The documentation that the first annulus was formed within the first 6 months following birth provides for more accurate and precise age estimations than previously available for this species.Received May 14, 2014; accepted July 23, 2014

Influence of electrolyte temperature on properties and infrared emissivity of MAO ceramic coating on 6061 aluminum alloy

6061 aluminum alloy was treated by MAO at various temperatures of the alkali silicate electrolyte using pulsed bipolar current mode for ten minutes. The surface microstructures and properties were studied using SEM, EDX, and XRD. The infrared emissivities of the MAO ceramic coatings were measured at the 70°C using FTIR spectrometer. The electrolyte temperature strongly affected all the surface properties. The MAO alumina ceramics prepared in cold electrolytes have volcano-like and accumulated particles microstructures, while those prepared in hot electrolytes were: rougher, thinner and contained grainy spherical hollow bulgy microstructures with more pore density and more sillimanite and cristobalite phases which enhanced the IR emissivity. Also, the increment of sillimanite and cristobalite phases moved the apparent peaks toward longer wavelengths, and broadened the opaque region of the IR spectra. As a result, the increment of electrolyte temperature from 12.3°C to 90.5°C increased the average of LWIR emissivity from 80.4% to 94.4%, respectively, for the MAO ceramic coatings.