Pair Of Apertures Research Articles

Design of a compact beam transport system for laser-driven proton therapy

Abstract We put forward a new design of a compact beam transport system for intense laser-driven proton therapy, where instead of using conventional pulsed solenoids, our design relies on a helical coil irradiated by a nanosecond laser pulse to generate strong magnetic fields for focusing protons. A pair of dipole magnets and apertures are employed to further filter protons with large divergences and low energies. Our numerical studies combine particle-in-cell simulations for laser-plasma interaction to generate high-energy monoenergetic proton beams, finite element analysis for evaluating the magnetic field distribution inside the coil, and Monte-Carlo simulations for beam transport and energy deposition. Our results show that with this design, a spread-out Bragg peak in a range of several centimeters to a deep-seated tumor with a dose of approximately 16.5 cGy and fluctuation around 2% can be achieved. The instantaneous dose rate reaches up to 109 Gy/s, holding the potential for future FLASH radiotherapy research.

Broadband directional filter in multilayer liquid crystal polymer films at W-band

In this work, a four-port directional filter (DF) with a broad passband and low reflection is proposed at the W-band, which comprises three unit filters at 92, 95, and 97 GHz, cascaded in series. Each unit consists of two microstrip lines in the top circuit layer for signal input and output, two pairs of apertures in the middle ground layer for directional coupling, and one square loop in the bottom layer as a selective resonator. By sweeping the working frequencies of the three units and optimizing the phase delays between them, the proposed filter achieves a 3-dB bandwidth as broad as 16%, an insertion loss of 2.5 dB at 95 GHz, and an out-of-band rejection of −28 and −23 dB at 80 and 110 GHz, respectively. The corresponding reflection attenuation is larger than 9.6 dB from 60 to 105 GHz. To verify our design, a prototype is fabricated and characterized, and its experimental data are consistent with the simulation. This work significantly expands the bandwidth of DFs and may find many applications in frequency division multiplexing and high-gain wireless systems.

Lensless imaging in one shot using the complex degree of coherence obtained by multiaperture interferences.

The van Cittert-Zernike theorem states that the Fourier transform of the intensity distribution function of a distant, incoherent source is equal to the complex degree of coherence. In this Letter, we present a method for measuring the complex degree of coherence in one shot by recording the interference patterns produced by multiple aperture pairs. The intensity of the sample is obtained by Fourier transforming the complex degree of coherence. The experimental verification by using a simple object is presented together with a discussion on how the method could be improved for imaging more complex samples.

A nanophotonic interferometer

The transmission of light through sub-wavelength apertures (zero-mode waveguides, ZMW) in metal films is well-explored. It introduces both an amplitude modulation as well as a phase shift to the oscillating electromagnetic field. We propose a nanophotonic interferometer by bringing two ZMW (∼100 nm diameter) in proximity and monitoring the distribution of transmitted light in the back-focal plane of collecting microscope objective (1.3 N.A.). We demonstrate that both an asymmetry induced by the binding of a quantum dot in one of the two ZMW, as well as an asymmetry in ZMW diameter yield qualitatively similar transmission patterns. We find that the complex pattern can be quantified through a scalar measure of asymmetry along the symmetry axis of the aperture pair. In a combined experimental and computational exploration of detectors with differing ZMW diameters, we find that the scalar asymmetry is a monotonous function of the diameter difference of the two apertures, and that the scalar asymmetry measure is higher if the sample is slightly displaced from the focal plane of the collecting microscope objective. An optimization of the detector geometry determined that the maximum response is achieved at an aperture separation that is comparable to the wavelength on the exit side of the sensor. For small separations of apertures, on the order of a quarter of the wavelength and less, the signal is strongly polarization dependent, while for larger separations, on the order of the wavelength or larger, the signal becomes essentially polarization-independent.

A novel image encryption scheme based on chaotic apertured fractional Mellin transform and its filter bank

A novel image encryption scheme based on chaotic apertured fractional Mellin transform and its filter bank has been proposed in this paper. A nonlinear chaotic apertured fractional Mellin transform (ACFrMT) and its filter bank (ACFrMT-FB) are proposed, where a pair of complementary chaotic apertures is introduced into FrMT to form filter bank and a special algorithm is employed to solve the problem of data redundancy in filter banks. In order to improve the sensitivity of chaotic aperture, two random phases based on chaotic aperture (RPCA) are generated as phase masks. The proposed encryption algorithm not only provides huge key space, but also greatly improves the sensitivities of fractional order p and wavelength λ. The maximum values of those sensitivity can reach 10-16 and 10-22. The experiment results prove that the proposed encryption scheme is efficient and secure. The results are: sensitivity attack analysis (> 94.77%), differential attack analysis (average NPCR =99.6120% and average UACI = 33.4888%), entropy values (average value 7.99928), correlation coefficient values (almost 0), and cipher key space analysis (at least 1.677×2341).

A new species of six-gilled hagfish (Myxinidae: Eptatretus) from the Lakshadweep Sea.

A new species of hagfish, Eptatretus wadgensis sp. nov., is described from the Wadge Bank, Lakshadweep Sea, India, obtained from a depth of ~250300 m through deep-sea trawling. It is diagnosed by having six pairs of gill pouches and gill apertures, 3/3 multicusp teeth, total slime pores 6769, six branchial slime pores, and ventral aorta bifurcating at the 4th or between 4th and 5th gill pouch. The new species has significant morphological differences in total dental cusps, total slime pores, body proportions and the absence of the nasal-sinus papilla when compared to congeners and formed a distinct clade in phylogenetic reconstruction and a genetic distance of 3.414.00% when comparing K2P parameters with the nearest species. A key to the Eptatretus species of the Indian Ocean is provided.

Experimental Demonstration of Sub-THz Wireless Communications Using Multiplexing of Laguerre-Gaussian Beams When Varying two Different Modal Indices

The ability to multiplex multiple structured beams for sub-terahertz (sub-THz) wireless communications has been recently explored. The spatial orthogonality of structured beams enables mode-division multiplexing (MDM). In an MDM system, multiple data-carrying beams are transmitted and received simultaneously through a single aperture pair with low inherent crosstalk. This can increase data capacity and spectral efficiency of the system. Here, we experimentally demonstrate multiplexing orthogonal sub-THz Laguerre-Gaussian (<inline-formula><tex-math notation="LaTeX">${{\bf L}}{{{\bf G}}_{\ell,{{\bf p}}}}$</tex-math></inline-formula>) beams when varying two different modal indices (i.e., both <inline-formula><tex-math notation="LaTeX">$\ell $</tex-math></inline-formula> and <inline-formula><tex-math notation="LaTeX">${{\bf p}}$</tex-math></inline-formula>); this contrasts with prior reports when varying only one index (i.e., <inline-formula><tex-math notation="LaTeX">$\ell $</tex-math></inline-formula>) and could potentially provide a larger set of channels and beams in an MDM system. In our demonstration, specially designed phase patterns are used: (1) at the transmitter, to convert two THz Gaussian beams to two different LG beams, each carrying an independent data channel; and (2) at the receiver, to separate and convert the LG beams back to Gaussian-like THz beams. An 8-Gbit&#x002F;s quadrature-phase-shift-keying (QPSK) link containing two multiplexed LG modes over 40 cm is experimentally demonstrated. For the above link, three different LG modal sets are chosen (i.e., {<inline-formula><tex-math notation="LaTeX">${{\bf L}}{{{\bf G}}_{ - 2,0}}$</tex-math></inline-formula> and <inline-formula><tex-math notation="LaTeX">${{\bf L}}{{{\bf G}}_{1,1}}$</tex-math></inline-formula>} or {<inline-formula><tex-math notation="LaTeX">${{\bf L}}{{{\bf G}}_{3,0}}$</tex-math></inline-formula> and <inline-formula><tex-math notation="LaTeX">${{\bf L}}{{{\bf G}}_{0,1}}$</tex-math></inline-formula>} or {<inline-formula><tex-math notation="LaTeX">${{\bf L}}{{{\bf G}}_{2,1}}$</tex-math></inline-formula> and <inline-formula><tex-math notation="LaTeX">${{\bf L}}{{{\bf G}}_{0,1}}$</tex-math></inline-formula>}). All channels are recovered with bit errorrates (BERs) below the 7&#x0025; forward error correction (FEC) limit. The experimental results indicate that: (a) higher-order LG modes experience more divergence, larger size, and lower conversion efficiency, contributing to higher power loss; and (b) the modal coupling and crosstalk for different LG modes is &lt;&#x2212;12 dB, which could be due to the transmitter&#x002F;receiver misalignments as well as beam truncation by the limited-sized receiver aperture.

Optical superoscillatory waves without side lobes along a symmetric cut

Optical superoscillation refers to an intriguing phenomenon of a wave packet that can oscillate locally faster than its highest Fourier component, which potentially produces an extremely localized wave in the far field. It provides an alternative way to overcome the diffraction limit, hence improving the resolution of an optical microscopy system. However, the optical superoscillatory waves are inevitably accompanied by strong side lobes, which limits their fields of view and, hence, potential applications. Here, we report both experimentally and theoretically a new superoscillatory wave form, which not only produces significant feature size down to deep subwavelength, but also completely eliminates side lobes in a particular dimension. We demonstrate a new mechanism for achieving such a wave form based on a pair of moonlike sharp-edge apertures. The resultant superoscillatory wave exhibits Bessel-like forms, hence allowing long-distance propagation of subwavelength structures. The result facilitates the study of optical superoscillation and on a fundamental level eliminates the compromise between the superoscillatory feature size and the field of view.

A new multiplexed system for the simultaneous measurement of out-of-plane deformation and its first derivative

A new multiplexed system based on double imaging Mach–Zehnder interferometry is proposed in this study for the simultaneous measurement of out-of-plane deformation and its first derivative. A modified Mach–Zehnder interferometer is used in the proposed system as shearing device, which has two pairs of imaging lenses and apertures placed on its arms. Therefore, carrier frequency and shearing amount can be independently adjusted using different components. An optical fiber is used to introduce reference beam, which has orthogonal states of polarization with one of the object beams. Shearogram and hologram without cross interference can be obtained by interference with the unpolarized object beam. Experimental results are presented for two pressure-loaded circular plates.

Increasing system tolerance to turbulence in a 100-Gbit/s QPSK free-space optical link using both mode and space diversity

In this paper, we experimentally explore using both mode and space (i.e., aperture) diversity to improve system reliability and performance of a free-space optical (FSO) link under atmospheric turbulence. When a system has a limited number of transmitter and receiver apertures, introducing mode diversity to the existing space diversity scheme might further enhance the system performance. We utilize orbital angular momentum (OAM) modes for mode diversity as an example. A 100-Gbit/s quadrature phase-shift keying FSO link is demonstrated through emulated turbulence using two transmitter and receiver aperture pairs. For each aperture pair, a Gaussian beam and an OAM beam are transmitted and received, and all four beams carry the same data stream. Our experimental results indicate that introducing mode diversity to space diversity systems could help to further reduce the variance of received signal power, thereby improving system tolerance to turbulence under a given detection threshold. Bit-error-rates (BERs) mostly below 3.8×10−3 are achieved under emulated turbulence with a Fried parameter of 0.4 mm. The dependence of system performance on different diversity schemes, OAM topological charge differential, and aperture spacing are also investigated.

A new species of hagfish, Eptatretus albiderma sp. nov. (Agnatha: Myxinidae), from Vietnam, with the keys to species of Eptatretus in East Asia

The whitish hagfish, Eptatretus albiderma sp. nov., was collected from the northeast Sea of Vietnam (Da Nang). This new species possesses six pairs of gill apertures, three multicusps, 18–21 prebranchial slime pores, absent or one branchial slime pore, and whitish to pinkish body color. Eptatretus albiderma sp. nov. can be readily distinguished from Eptatretus atami (Dean, 1904) and Eptatretus sheni (Kuo, Huang & Mok, 1994) by the numbers of total cusps (41–43 vs. 47–52 in E. atami vs. 48–53 in E. sheni), body color (whitish vs. darkish in E. atami vs. dark brown dorsally, lighter ventrally in E. sheni), eyespots (absent or faint vs. prominent in E. sheni), and total slime pores (74–78 vs. 71–78 in E. atami vs. 62–74 in E. sheni). The new species is clearly distinguished from E. atami by 0.026 pairwise genetic distance (d) of phylogeny based on mtDNA COI. We herein offer the key to 17 species of the genus Eptatretus Cloquet, 1819 in East Asia.

Demonstration of using two aperture pairs combined with multiple-mode receivers and MIMO signal processing for enhanced tolerance to turbulence and misalignment in a 10 Gbit/s QPSK FSO link

We utilize aperture diversity combined with multiple-mode receivers and multiple-input-multiple-output (MIMO) digital signal processing (DSP) to demonstrate enhanced tolerance to atmospheric turbulence and spatial misalignment in a 10 Gbit/s quadrature-phase-shift-keyed (QPSK) free-space optical (FSO) link. Turbulence and misalignment could cause power coupling from the fundamental Gaussian mode into higher-order modes. Therefore, we detect power from multiple modes and use MIMO DSP to enhance the recovery of the original data. In our approach, (a) each of multiple transmitter apertures transmits a single fundamental Gaussian beam carrying the same data stream, (b) each of multiple receiver apertures detects the signals that are coupled from the fundamental Gaussian beams to multiple orbital angular momentum (OAM) modes, and (c) MIMO DSP is used to recover the data over multiple modes and receivers. Our simulation shows that the outage probability could be reduced from >0.1 to <0.01. Moreover, we experimentally demonstrate the scheme by transmitting two fundamental Gaussian beams carrying the same data stream and recovering the signals on OAM modes 0 and +1 at each receiver aperture. We measure an up to ∼10dB power-penalty reduction for a bit error rate (BER) at the 7% forward error correction limit for a 10 Gbit/s QPSK signal.

Morphology and Affinities of Pantocarpon Fruits (cf. Apiales: Torricelliaceae) from the Maastrichtian Deccan Intertrappean Beds of Central India

Premise of research. Permineralized fruits of Pantocarpon Kapgate, Patil, Ilamkar & Ramteke have been reinvestigated to better understand this abundant component of the Deccan Maastrichtian–Paleocene flora of central India.Methodology. Peels and X-ray microcomputed tomography (μ-CT) were used to compare the morphology and anatomy of the silicified fruits with that of possible extant relatives.Pivotal results. We show, for the first time, the surface morphology of these fruits, which are encased within opaque chert, and clarify additional characters of morphology and anatomy. By varying the orientation of digital sectioning planes through the fruit using μ-CT data, we show that five different generic names (Pantocarpon and the junior synonyms Bicarpelarocarpon, Plectroniocarpon, Loganiocarpon, and Verbenaceocarpon) were previously applied to the same entity, each based on holotypes studied in different physical planes of section. Several distinctive characters, including tricarpellate syncarpous fruits, paired apical apertures, empty sterile locules, single-seeded fertile locules, and longitudinal germination valves, are shared with the extant eudicot family, Torricelliaceae (Apiales). The pair of endocarp apertures resembles that in Aralidium and Torricellia. There are some obvious differences, however, from fruits of the three living genera. In Torricellia, Melanophylla, and Aralidium, there are two sterile locules (lateral) and a single fertile one (median), whereas in Pantocarpon, there are two fertile locules (lateral) and a single sterile one (median).Conclusions. Recognition of Pantocarpon as a potential member of Torricelliaceae is interesting because it would be the most ancient record known for the family (next youngest being middle Eocene, ca. 47 Ma) and provides additional biogeographic information. The occurrence of this taxon in India at about 66 Ma, when the subcontinent was still isolated from other major landmasses, indicates that this region may have played a role in early evolution of the family, which is now disjunct between Madagascar, China, and Malesia.

A new species of hagfish, Eptatretus wandoensis sp. nov. (Agnatha, Myxinidae), from the southwestern Sea of Korea.

Four specimens of the five-gilled white mid-dorsal line hagfish, Eptatretus wandoensissp. nov. were recently collected from the southwestern Sea of Korea (Wando). This new species has five pairs of gill apertures, 14–18 prebranchial slime pores, 4 branchial slime pores, a dark brown back with a white mid-dorsal line and a white belly. These hagfish are similar to Eptatretus burgeri and Eptatretus minor in having a white mid-dorsal line, but can be readily distinguished by the numbers of gill apertures (5 vs. 6–7), gill pouches (5 vs. 6), and prebranchial slime pores (14–18 vs. > 18), as well as the body color (dark brown back vs. gray or brown pale). In terms of genetic differences, Eptatretus wandoensis could be clearly distinguished from E. burgeri (0.9% in 16S rRNA and 8.5% in cytochrome c oxidase subunit I sequences) and E. minor (4.5% and 13.9%).

Impact of Circular Apertures on Static Shielding Performances of Spherical Magnetic Shields

The magnetic field inside a spherical magnetic shield with infinite permeability and a circular aperture in a homogeneous magnetic field of arbitrary direction is analytically derived. The closed-form formulas for the static shielding factors are theoretical upper limits for real shields. We discuss the magnetic field gradient inside the shield caused by a single aperture, implying that using symmetric aperture pairs is more favorable. Based on the theoretical results for ideal shields, an approximate solution to calculate the shielding factor for shields with finite permeability and/or multiple apertures is developed. The calculations for one aperture pair are compared to finite-element analysis. The basic effects could be guidance for the design of apertures in shields of various shapes.

Dual-Band Frequency Selective Surface on Aperture-Coupled Patch Resonators With Different Polarization Rotation

In this letter, a dual-band frequency selective surface (FSS) based on aperture-coupled patch resonators is proposed to achieve different angles of polarization rotation, that is, 90° and 0°. The dual-band response is achieved by periodically arranging two independent subelements consisting of back-to-back patch resonators with coupling apertures etched on the middle metallic layer. Herein, the first passband is realized by the crossed patch resonators with a pair of rectangular apertures etched beneath the edges of the crossed patches. It can produce 180° phase difference between the two orthogonal components of a linearly polarized incident wave oriented to the diagonal of the FSS elements, thus rotating the incident polarization to its orthogonal one in this first passband. The second passband is caused by the square patch resonators with crossed apertures etched beneath the center of the square patches, thereby maintaining the incident polarization unchanged in this second passband. The operation principle is, then, extensively analyzed and discussed. To validate the design concept, the proposed FSS is designed, fabricated, and measured. A good agreement between the measured and simulated results is achieved to reveal the attractive dual-band and dual-polarization features of the proposed FSS.

Effects of miniaturization in the anatomy of the minute springtail Mesaphorura sylvatica (Hexapoda: Collembola: Tullbergiidae).

Smaller animals display pecular characteristics related to their small body size, and miniaturization has recently been intensely studied in insects, but not in other arthropods. Collembola, or springtails, are abundant soil microarthropods and form one of the four basal groups of hexapods. Many of them are notably smaller than 1 mm long, which makes them a good model for studying miniaturization effects in arthropods. In this study we analyze for the first time the anatomy of the minute springtail Mesaphorura sylvatica (body length 400 µm). It is described using light and scanning electron microscopy and 3D computer reconstruction. Possible effects of miniaturization are revealed based on a comparative analysis of data from this study and from studies on the anatomy of larger collembolans. Despite the extremely small size of M. sylvatica, some organ systems, e.g., muscular and digestive, remain complex. On the other hand, the nervous system displays considerable changes. The brain has two pairs of apertures with three pairs of muscles running through them, and all ganglia are shifted posteriad by one segment. The relative volumes of the skeleton, brain, and musculature are smaller than those of most microinsects, while the relative volumes of other systems are greater than or the same as in most microinsects. Comparison of the effects of miniaturization in collembolans with those of insects has shown that most of the miniaturization-related features of M. sylvatica have also been found in microinsects (shift of the brain into the prothorax, absent heart, absence of midgut musculature, etc.), but also has revealed unique features (brain with two apertures and three pairs of muscles going through them), which have not been described before.

Double Imaging Mach–Zehnder Spatial Carrier Digital Shearography

ABSTRACTThis paper presents a Double Imaging Mach–Zehnder Spatial Carrier Digital Shearography (DIM-SCDS) system. Compared to traditional Spatial Carrier Mach–Zehnder shearography, DIM-SCDS has two advantages: one is that it can adjust shearing amount and spatial carrier frequency independently; the other one is that it can measure a larger area with a shorter working distance. Two pairs of imaging lenses and apertures are placed in the two arms of Mach–Zehnder interferometry, respectively. Shearing amount is adjusted by the mirrors in the two arms, and spatial carrier frequency is determined by the angle between the two apertures when they are mapped to the same optical axis. Shearograms of the object under test are recorded using a CCD. Shearogram phases are calculated as the measurement results. Finally, the performance of DIM-SCDS is proved by experiments.

Phaseless coherent and incoherent microwave ghost imaging with dynamic metasurface apertures

Phase information and spatially coherent illumination have usually been considered indispensable components of most microwave imaging systems. Dynamic metasurface apertures (DMAs)—with their ability to generate spatially incoherent illumination—have recently supplanted these assumptions in favor of simplified imaging hardware. In light of this development, we investigate the coherence of a phaseless imaging system based on metasurface apertures. In doing so, we propose and experimentally demonstrate coherent and incoherent computational microwave ghost imaging using DMAs. These apertures can generate a multitude of distinct speckle fields at a single frequency by modulating the electrical properties of radiating complementary metamaterial elements patterned into the surface of a waveguide. We show that a pair of dynamic apertures, one acting as transmit and the other as receive, can achieve two-dimensional, phaseless, coherent imaging. Further, by averaging the intensity measurements obtained in this manner over a random set or ensemble of receive aperture distributions, we demonstrate that an incoherent imaging system can be achieved in which single-port ensemble averaging by the electrically large DMA plays the role of spatial averaging in a bucket detector. We investigate the effects of these different imaging schemes on the resulting reconstructions and provide experimental demonstrations.

Numerical simulation of full-aperture-pair ion optics in a miniature ion thruster

The 211-aperture-pair two-grid ion optics of a miniature ion thruster is numerically simulated. Since the plasma in the miniature ion thruster is too inhomogeneous to introduce mirror or translational boundary conditions between apertures, all the apertures of the grid system are considered. The simulation is self-consistent, the ion current profile in the discharge chamber plasma is given by the particle-in-cell with Monte Carlo collision algorithm calculations, and all the ion beams extracted from the full-aperture-pair array were tracked including charge-exchange ions. A scheme for the construction of the full-aperture-pair simulation domain is proposed based on the array of a six-fold hexagonal single-aperture-pair simulation domain, which can be extended to other numbers of aperture pairs. Numerical results on accel impingement current and ion-beam profile are compared to experimental data and shown to be in reasonable agreement. Furthermore, the full-aperture-pair ion-optics model is compared with the single-aperture-pair ion-optics models used in the majority of previous ion-optics simulations, which showed that the full-aperture-pair ion-optics model yielded the most accurate predictions. These results suggest that the ion thruster grid system using an inhomogeneous plasma source can be designed more accurately and effectively using full-aperture-pair ion-optics simulations.