Conical Aperture Research Articles

Shape and polarization distribution of non-circular conical diffraction beams from conjugate cascades.

Peculiar non-circularly shaped vector type beams can be obtained naturally by the conical diffraction phenomenon if specific manipulations in wavevector space are performed between optically biaxial crystals arranged in a cascade. We analyze in detail this situation by focusing on the general shapes and the polarization distribution. Both are shown to be correlated to the values of structure parameters introduced in this work. These control parameters depend on the conical diffraction cone aperture angle, on the crystal lengths, and on the magnification values due to x- and y-oriented cylindrical lenses placed between the crystals and coupling common conjugate planes. The local polarization is found to be always linear with the exception of regions where structures composing the pattern intersect or overlap, where elliptical or circular polarization can occur. The way in which the obtained patterns depend on the orientation of individual crystal samples around the common optical axis and on an eventual polarization filtering at various stages of the cascade is discussed as well. Theoretical and experimental findings agree well, as verified for the case of a cascade of two crystals.

Deviation of photoelectron intensity from Beer-Lambert law in near-ambient pressure hard x-ray photoelectron spectroscopy

In near-ambient-pressure photoelectron spectroscopy, the photoelectron intensity is assumed to follow the Beer-Lambert law, that is, the intensity decreases exponentially with distance d between the sample and the aperture cone. In this study, the gas pressure dependence of photoelectron intensity is systematically studied in a wide range of d values from 0.3 up to 5 mm. The experimental results were reproduced by replacing d with d + do (do is a constant) in the Beer-Lambert law. The do value was evaluated as ∼1 mm, which is considerably larger than the normal d value of 0.3 mm. Fluid dynamics simulation results obtained using a structural model with a size close to that of the actual differential pumping system suggested that the residual gas in the long pumping path caused a large do value.

Effects of sample-aperture cone distance on the environmental charge compensation in near-ambient pressure hard X-ray photoemission spectroscopy

Charging effect of insulating samples is a major problem in photoemission spectroscopy. Herein, the charging of a LiNbO3 wafer and glass plate was compensated by introducing nitrogen gas using a near-ambient pressure hard X-ray photoemission spectroscopy apparatus. This is because the secondary electrons created by electron scattering in the gas neutralized the charge on the sample surface. Moreover, the pressure required to compensate for the charging was found to strongly depend on the distance (d) between the sample surface and the aperture cone of the electron energy analyzer. At a normal distance of d= 0.3 mm, a pressure of 2500 Pa was required to compensate for the charging of the insulating samples. However, at d= 2.1 mm, the required pressure was reduced to only 250 Pa. The large d dependence of distance can be attributed to that electron scattering is largely disturbed by the aperture cone at small d values.

Lensing by a Fisher-Janis-Newman-Winicour naked singularity: Observational issues related to the existence of caustic bending in the strongly scalarized case

One reconsiders strong lensing by the naked singularity that enters the Fisher/Janis-Newman-Winicour (F/JNW) scalar-tensor spacetime, characterized by a mass $m$ and a scalar parameter $b$. One mainly focuses on the strongly scalarized case where the bending of light experiments a maximum value, resulting in the formation of a $b$ dependent caustic cone. One numerically determines the caustic cone's aperture $b$ dependence profile, and shows that this cone results in a flare sequence if the singularity is orbited by a star having an orbital inclination that satisfies a simple $b$ dependent condition. Such flare sequences qualitatively distinguish such F/JNW spacetimes from the usual black hole case. One then investigates the scenario that replaces the black hole located at the center of our Galaxy by a strongly scalarized F/JNW singularity having the same mass $m$. One shows that if a sequence of flares associated to the motion of a star orbiting not too far from the singularity (for the usual perihelion precession to have measurable effects) is detected, this would not only be an argument in favor of the presence of a (strongly scalarized) naked singularity with respect to the usual black hole assumption, but it could also return constraints on $b$ and determine the star's orbital parameters, even if the star can not be monitored directly.

A Choking Cavitation Method and Equipment for Degrading Pollutants in Wastewater

A cavitator, with a structure of an annular conical aperture, a throat and a collapse cavity, was proposed to form a choking cavitation flow for pollutants degradation in wastewater treatment. Experiment was conducted in this new cavitator to investigate its flow characteristics and pollutant degradation ratio by employing Mythylene blue (MB) as a pollutant in pure water. It was found that choking cavitation flow appears in the throat by controlling the pump pressure and liquid flow rate in a rule. The pollutant degradation ratio in choking cavitation flow is much larger than that in normal cavitation flow, because plenty of cavitation vapours are born, grow up, and finally collapse in this cavitator in the choking cavitation condition. Gemetrical parameters also affect pollutant degradation ratio, and the optimal gemetrical parameters for this proposed cavitator are suggested.

Design of Multigap Pseudospark Discharge-Based Plasma Cathode Electron Source at Different Configurations of Electrode Apertures

In this article, design investigations have been performed for wide ranges and sequence of electrode apertures (SEA) like, tapered conical-up or down, irregular/nonuniform and regular/uniform apertures with varying diameters of 2, 4, 6, and 8 mm for 20–60 Pa operating argon gas pressures for the generation of electron beam from the multigap pseudospark discharge-based plasma cathode electron (PD-PCE) source using particle-in-cell simulation code. Results show the strong dependence of potential penetration and their distribution on the SEA and gas pressures. The first and last electrodes play significant role for deciding the generation and properties of electron beam current. The SEA and gas pressures influence the rise behavior of electron beam current and voltage fall between the anode and cathode gap. The maximum current of 9.6 kA in uniform electrode aperture sequence while minimum of 513 A in conical down aperture sequence has been observed at the anode. The quenching effect and its reduction during the rise of electron beam current at the anode has also been investigated for different SEA and gas pressures. The proposed analysis would be very much useful for the design and development of multigap PD-PCE sources for high-density and energetic electron beam generation.

Laser Formation of Holes in Nonmetallic Substrates

The use of a pulse picosecond laser with a wavelength of 532 nm and frequency of 15 Hz in the formation of holes with diameters up to 0.1 mm in nonmetallic substrates (silicon, ceramics, etc.) was proposed. It was found by modeling in MathCAD and COMSOL Multiphysics that the half-angle value of the light cone aperture that depends on the focusing of laser radiation exerts a significant effect on the depth and diameter of holes in laser processing. The influence of the regimes of laser processing employing nanosecond and picosecond lasers with wavelengths of 1064 and 532 nm, respectively, on the conicity and time of formation of holes in silicon substrates was investigated. The preliminary heating of the substrate to 170–200°С reduces the time of formation of the holes by 20%.

Lateral resolution of electrostatic force microscopy for mapping of dielectric interfaces in ambient conditions

The attainable lateral resolution of electrostatic force microscopy (EFM) in an ambient air environment on dielectric materials was characterized on a reference sample comprised of two distinct, immiscible glassy polymers cut in a cross-section by ultramicrotomy. Such a sample can be modeled as two semi-infinite dielectrics with a sharp interface, presenting a quasi-ideal, sharp dielectric contrast. Electric polarizability line profiles across the interface were obtained, in both lift-mode and feedback-regulated dynamic mode EFM, as a function of probe/surface separation, for different cases of oscillation amplitudes. We find that the results do not match predictions for dielectric samples, but comply well or are even better than predicted for conductive interfaces. A resolution down to 3 nm can be obtained by operating in feedback-regulated EFM realized by adopting constant-excitation frequency-modulation mode. This suggests resolution is ruled by the closest approach distance rather than by average separation, even with probe oscillation amplitudes as high as 10 nm. For better comparison with theoretical predictions, effective probe radii and cone aperture angles were derived from approach curves, by also taking into account the finite oscillation amplitude of the probe, by exploiting a data reduction procedure previously devised for the derivation of interatomic potentials.

Analysis of Impact of Conic Aperture in Differentially Pumped Chamber

The paper focuses on the simulation of medium dynamics in the environmental scanning electron microscope. In particular, the paper examines the conical aperture location effect in the differentially pumped chamber and the width of the pumping channel in this chamber. The solution is based on the Taylor-Maccoll theory about the impact of the shock wave and was obtained by the use of continuum and finite volume methods in the ANSYS Fluent system.

Microparticle velocity sensing using a conical lens fiber array.

We report a microparticle velocity sensor with a conical lens fiber array. The conical lens fibers are linearly arrayed at the same interval to behave as a spatial filter. The characteristics of the sensor in terms of cone angle, divergence angle, aperture angle, blind area, and detection area are investigated. Compared with a sensor using a normal flat end fiber array, our sensor has a high signal-to-noise ratio with a smaller blind area and wider detection area to avoid the signal deterioration caused by movement deviation of particles from the fiber array. Taking advantage of not only a compact and tiny structure but also better ability of high electromagnetic noise tolerance, corrosion resistance, and temperature resistance, the sensor may have the potential for velocity sensing in harsh environments and microparticle sensing, such as sand movement monitoring in sandstorms, particle state monitoring in combustion, and more.

Improved ion beam tools for ultraprecision figure correction of curved aluminum mirror surfaces

Aluminum mirrors offer great potential for satisfying the increasing demand in high-performance optical components for visible and ultraviolet applications. Ion beam figuring is an established finishing technology and in particular a promising technique for direct aluminum figure error correction. For the machining of strongly curved or arbitrarily shaped surfaces as well as the correction of low-to-mid spatial frequency figure errors, the usage of a high-performance ion beam source with low tool width is mandatory. For that reason, two different concepts of ion beam generation with high ion current density and narrow beam width are discussed. (1) A concave ion beam extraction grid system is used for apertureless constriction of ion beams in the low millimeter range. An oxygen ion beam with a full-width at half-maximum (FWHM) of 4.0 mm with an ion current density of 29.8 mA / cm2 was achieved. (2) For even smaller ion beams, a conic aperture design with a submillimeter-sized exit opening was tested. A nitrogen ion beam with an FWHM down to 0.62 mm with an ion current density of 4.6 mA / cm2 was obtained. In situ ion current density mapping is performed by scanning Faraday probe measurements. Special interest is set on the data evaluation for submillimeter ion beam analysis.

An analytical method to simulate the dynamic performances of truncated cone helix ground heat exchangers

This paper proposes a dynamic analytical method to simulate the thermal performances of truncated cone helix ground heat exchangers (i.e., the so-called “energy baskets”). These ground-coupled devices are attractive solutions to reduce the initial cost of ground-coupled heat pump systems, as they require lower cost to be drilled and installed with respect to traditional boreholes. However, both design methodologies and performance assessment models are still not well developed, producing substantial uncertainties on final operative performances. This work presents a plain evaluation method based on the heat exchangers theory and the analytical solution of the truncated cone helix heat source in a semi-infinite medium. It can be advantageously used to simulate the thermal performance of truncated cone helix ground heat exchangers as a function of helix geometries and operative conditions evolution (e.g., inlet temperature, fluid flow rate, ground temperature…). Specifically, in this paper, we perform a sensitivity analysis of the thermal performances of a case study by varying the main geometrical parameters. Besides, we compare the heat transfer of the reference configuration with an equivalent cylindrical arrangment. The truncated coil configuration is more effective than cylindrical one as the cone aperture reduces the short-circuits between helix pitch and the equivalent thermal resistance with the ground surface. However, obtained results are notably affected by the assumption of an isothermal surface temperature, which leads to a shallow/plain helix/spiral as the best configuration: different conclusions are expected when a time dependent or adiabatic boundary condition will be accounted in the model.

Electronic states and optical properties of single donor in GaN conical quantum dot with spherical edge

In this paper we present a theoretical investigation of quantum confinement effects on the electron and single donor states in GaN conical quantum dot with spherical edge. In the framework of the effective mass approximation, the Schrödinger equations of electron and donor have been solved analytically in an infinite potential barrier model. Our calculations show that the energies of electron and donor impurity are affected by the two characteristic parameters of the structure which are the angle Ω and the radial dimension R. We show that, despite the fact that the reduction of the two parameters Ω and R leads to the same confinement effects, the energy remains very sensitive to the variation of the radial part than the variation of the angular part. The analysis of the photoionization cross-section corresponding to optical transitions between the conduction band and the first donor energy level shows clearly that the reduction of the radius R causes a shift in resonance peaks towards the high energies. On the other hand, the optical transitions between 1s−1p, 1p−1d and 1p−2s show that the increment of the conical aperture Ω (or reduction of R) implies a displacement of the excitation energy to higher energies.

Dosimetric characterization of Elekta stereotactic cones

PurposeDosimetry of small fields defined by stereotactic cones remains a challenging task. In this work, we report the results of commissioning measurements for the new Elekta stereotactic conical collimator system attached to the Elekta VersaHD linac and present the comparison between the measured and Monte Carlo (MC) calculated data for the 6 MV FFF beam. In addition, relative output factor (ROF) dependence on the stereotactic cone aperture variation was studied and penumbra comparison for small MLC‐based and cone‐based fields was performed.MethodsCones with nominal diameters of 15 mm, 12.5 mm, 10 mm, 7.5 mm, and 5 mm were employed in our study. Percentage depth dose (PDD), off‐axis ratios (OAR), and ROF were measured using a stereotactic field diode (SFD). BEAMnrc code was used for MC simulations.ResultsMC calculated and measured PDDs for all cones agreed within 1%/0.5 mm, and OAR profiles agreed within 1%/0.5 mm. ROF obtained from the measurements and MC calculations agreed within 2% for all cone sizes. Small‐field correction factors for the SFD detector Kfield,3 × 3(SFD) were derived using MC calculations as a baseline and were found to be 0.982, 0.992, 0.997, 1.015, and 1.017 for the 5, 7.5, 10, 12.5, and 15‐mm cones respectively. The difference in ROF was about 10%, 6%, 3.5%, 3%, 2.5%, and 2% for ±0.3 mm variations in 5, 7.5, 10, 12.5, and 15‐mm cone aperture respectively. In case of single static field, cone‐based collimation produced a sharper penumbra compared to the MLC‐based.ConclusionsAccurate MC simulation can be an effective tool for verification of dosimetric measurements of small fields. Due to the very high sensitivity of output factors on the cone diameter, manufacture‐related variations in cone size may lead to considerable variations in dosimetric characteristics of stereotactic cones.

Spectral asymptotics for δ-interactions on sharp cones

We investigate the spectrum of three-dimensional Schrödinger operators with δ-interactions of constant strength supported on circular cones. As shown in earlier works, such operators have infinitely many eigenvalues below the threshold of the essential spectrum. We focus on spectral properties for sharp cones, that is when the cone aperture goes to zero, and we describe the asymptotic behavior of the eigenvalues and of the eigenvalue counting function. A part of the results are given in terms of numerical constants appearing as solutions of transcendental equations involving modified Bessel functions.

Spiraphase-type leaky-wave structure

A leaky-wave structure (LWS) based on two stacked spiraphase-type reflectarrays (RAs) is analysed in this paper. Each RA contains capacitively loaded ring slot elements arranged at the nodes of a square periodic grid. The proposed LWS performs frequency scanning of a conical beam by changing the cone aperture angle 2θ0. Furthermore, the reconfiguration of the radiation pattern can be achieved by rotating the RA elements. Four Ka-band LWSs with different angular positions of the capacitive loads at the top RA were designed, fabricated and tested to demonstrate the pattern reconfiguration capability. A full-wave mathematical model was used to optimize the reflectarray elements and a simplified mathematical model was developed to predict the radiation characteristics of the whole structure. It was experimentally proven that frequency sweep from 36.37 to 39.9 GHz leads to the change of the angle θ0 from 0° to 38°. The increment of θ0 from 0° to 23° at 36.4 GHz was observed, when the reactive loads of the ring-slot elements at the top RA were rotated on the angle 18°. Good agreement between theoretical predictions and measurements was observed.

Environmental dependence of the galaxy stellar mass function in the Dark Energy Survey Science Verification Data

Measurements of the galaxy stellar mass function are crucial to understand the formation of galaxies in the Universe. In a hierarchical clustering paradigm it is plausible that there is a connection between the properties of galaxies and their environments. Evidence for environmental trends has been established in the local Universe. The Dark Energy Survey (DES) provides large photometric datasets that enable further investigation of the assembly of mass. In this study we use ~3.2 million galaxies from the (South Pole Telescope) SPT-East field in the DES science verification (SV) dataset. From grizY photometry we derive galaxy stellar masses and absolute magnitudes, and determine the errors on these properties using Monte-Carlo simulations using the full photometric redshift probability distributions. We compute galaxy environments using a fixed conical aperture for a range of scales. We construct galaxy environment probability distribution functions and investigate the dependence of the environment errors on the aperture parameters. We compute the environment components of the galaxy stellar mass function for the redshift range 0.15<z<1.05. For z<0.75 we find that the fraction of massive galaxies is larger in high density environment than in low density environments. We show that the low density and high density components converge with increasing redshift up to z~1.0 where the shapes of the mass function components are indistinguishable. Our study shows how high density structures build up around massive galaxies through cosmic time.

New shield structure for retrodirective and invisible applications

ABSTRACTRetrodirectivity and invisibility are two opposite concepts in the radar context. The former looks for an evident identification, while the latter aims to remain unnoticed. Here, we present a new structure based on inverted conical surfaces to provide both effects depending on the conical aperture value: 90° for retrodirective applications and 120° for invisible and Wi‐Fi/Li‐Fi applications.Results of the study carried out to confirm the behavior of the two structures are also presented, including measurements to compare performance with commercial prototypes in the case of retrodirectivity. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:2570–2577, 2016

Development of a reaction cell for in-situ/operando studies of surface of a catalyst under a reaction condition and during catalysis.

Tracking surface chemistry of a catalyst during catalysis is significant for fundamental understanding of catalytic performance of the catalyst since it allows for establishing an intrinsic correlation between surface chemistry of a catalyst at its working status and its corresponding catalytic performance. Ambient pressure X-ray photoelectron spectroscopy can be used for in-situ studies of surfaces of different materials or devices in a gas. To simulate the gaseous environment of a catalyst in a fixed-bed a flowing gaseous environment of reactants around the catalyst is necessary. Here, we report the development of a new flowing reaction cell for simulating in-situ study of a catalyst surface under a reaction condition in gas of one reactant or during catalysis in a mixture of reactants of a catalytic reaction. The homemade reaction cell is installed in a high vacuum (HV) or ultrahigh vacuum (UHV) environment of a chamber. The flowing gas in the reaction cell is separated from the HV or UHV environment through well sealings at three interfaces between the reaction cell and X-ray window, sample door and aperture of front cone of an energy analyzer. Catalyst in the cell is heated through infrared laser beam introduced through a fiber optics interfaced with the reaction cell through a homemade feedthrough. The highly localized heating on the sample holder and Au-passivated internal surface of the reaction cell effectively minimizes any unwanted reactions potentially catalyzed by the reaction cell. The incorporated laser heating allows a fast heating and a high thermal stability of the sample at a high temperature. With this cell, a catalyst at 800 °C in a flowing gas can be tracked readily.

Theoretical calculations and experimental verification for the pumping effect caused by the dynamic micro-tapered angle

The atomizer with micro cone apertures has advantages of ultra-fine atomized droplets, low power consumption and low temperature rise. The current research of this kind of atomizer mainly focuses on the performance and its application while there is less research of the principle of the atomization. Under the analysis of the dispenser and its micro-tapered aperture’s deformation, the volume changes during the deformation and vibration of the micro-tapered aperture on the dispenser are calculated by coordinate transformation. Based on the characters of the flow resistance in a cone aperture, it is found that the dynamic cone angle results from periodical changes of the volume of the micro-tapered aperture of the atomizer and this change drives one-way flows. Besides, an experimental atomization platform is established to measure the atomization rates with different resonance frequencies of the cone aperture atomizer. The atomization performances of cone aperture and straight aperture atomizers are also measured. The experimental results show the existence of the pumping effect of the dynamic tapered angle. This effect is usually observed in industries that require low dispersion and micro- and nanoscale grain sizes, such as during production of high-pressure nozzles and inhalation therapy. Strategies to minimize the pumping effect of the dynamic cone angle or improve future designs are important concerns. This research proposes that dynamic micro-tapered angle is an important cause of atomization of the atomizer with micro cone apertures.