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We introduce the notion of limited consideration into a bilateral, infinite-horizon, alternating-offers bargaining game. Both agents have reference-dependent preferences, and their reference points are dynamically updated. An agent's current consideration set (or focus) is influenced by the last offer he rejected such that the most salient point in that consideration set becomes his current reference point. We provide an implicit characterization of stationary subgame perfect Nash equilibria in our model. Without resorting to asymmetric or incomplete information, we show that our bargaining game can produce delay and disagreement in equilibrium. In addition to analytical results on the disagreement conditions and the nature of agreements, we provide computational comparative statics on model parameters and study their impacts on delay. [ABSTRACT FROM AUTHOR]

High-intensity focused ultrasound (HIFU) transducers are proposed as a new treatment modality for dermatology. The shape and size of pressure fields generated by strongly focused transducers with an f-number equal to 0.75 operating at frequencies up to 20 MHz are analyzed analytically using the Lucas-Muir model and numerically with the wide-angle Khokhlov-Zabolotskaya-Kuznetsov method. The modeling results under quasi-linear conditions are compared against measurements performed in an acoustic tank with the aid of a fiberoptic hydrophone. The size of the focal zone expressed by their depth of focus and focal diameter is found to be directly controlled by their operating frequency and f-number. Devices manufactured for an operating frequency of 20 MHz are characterized by their 6 dB depth of focus of 490 μm and focal diameter of 80.6 µm. The devices are further studied at high power levels using a polyacrylic tissue-mimicking phantom. The devices are equipped with an optical observation system allowing simultaneous treatment and observation of the skin surface. In comparison to conventional cosmetic applications of HIFU, the devices analyzed are concluded to be ideal for treatment of precisely selected and confined layers of the human skin. [ABSTRACT FROM AUTHOR]

Efficient acceleration of electrically charged particles by focused electromagnetic pulses requires a strong accelerating electric field as well as a sufficiently large interaction region. Single-cycle terahertz pulses are promising candidates for such applications due to their advantageous wavelength and available peak electric field at the MV/cm level. We propose and characterize a focusing optics for a possible electron vacuum accelerator. This consists of a reflaxicon for beam shaping and a ring-like segment of an on-axis parabolic mirror for tight focusing of the radially polarized THz pulse in order to reach a strong accelerating electric field. The electric field distribution in the focal region was determined by the Stratton–Chu vector diffraction method. Semi-analytical and purely analytical formulae were also derived, simplifying the computation procedure. By focusing radially polarized single-cycle terahertz pulses with 3 mJ pulse energy, calculations predict accelerating electric field component in the order of 100 MV/cm , well suitable for particle acceleration. • Designed a focusing setup for an electron vacuum accelerator consisting of reflaxicons and paraboloid ring. • Conducted theoretical derivations for the electric field based on the Stratton–Chu vector diffraction theory. • Close to 100 MV/cm predicted accelerating electric field component by focusing radially polarized single-cycle terahertz pulses. [ABSTRACT FROM AUTHOR]

• A dielectric material unit structure with strong control ability for right-handed circularly polarized light field is proposed. • A deep residual network with a 13-layer structure is designed for reverse design of metasurfaces. • The two focusing metasurfaces designed by the residual network show good focusing efficiency. The accuracy of metasurface inverse design depends on the input dimension of the target light field and the output dimension of the unit structure parameters. When the two light field targets are simultaneously controlled, the designed unit structure often cannot satisfy the simultaneous directional control of the two light field target parameters due to the existence of coupling. This greatly limits the completeness of the function of metasurfaces in applications. In this paper, we apply the designed 13-layer residual network (ResNet) to the inverse design of wavefront control of dielectric metasurfaces. After the neural network training is completed, the correspondence between any amplitude, phase and the element structure parameters within a certain error range can be realized, which greatly saves the time cost in the metasurface design process. As a verification of the inverse design method, we arranged two focusing metasurfaces of different sizes. Their focusing efficiencies are more than 53%. The nanounit structure and its inverse design method proposed in this paper provide a new idea for the design of the metasurface to control the polarized light field. At the same time, it will have important applications in the intelligent design of metasurfaces. [ABSTRACT FROM AUTHOR]

Imaging robustness of the vision-based tactile sensor (VTS) depends on coating wear resistance and imaging stability. With the miniaturization of sensors, the limited imaging space cannot afford a buffer against imaging deviations caused by contact depth changes. This paper proposes an improved vision-based thin tactile sensor (VTTS, also named vision-based tactile skin), integrating a focus-adjustable camera and an imaging adjustment system (IAS) to improve imaging robustness. The IAS contains an imaging calibration system and a focusing system. Since visuo-tactile sensing is performed in a relatively stable and closed imaging environment, the image-based focusing method is naturally matched with tactile imaging. Accordingly, an imaging calibration system based on a global search is designed to determine the focusing interval and shorten the focusing range. Three-point-fitting-based depth from focus (TPF-DFF) and deep-learning-based depth from defocus (DL-DFD) are proposed for low-frequency (simple)/high-frequency (complex) imaging adjustment. The experimental results demonstrate that the IAS-VTTS has close to 100% adjustment accuracy, and the fastest focusing time is up to 40 ms. Consequently, the IAS-VTTS can adapt to different deformation depths and support high-quality tactile imaging. [Display omitted] • Presenting an improved vision-based thin tactile sensor (VTTS), integrating a focus-adjustable microcamera and an imaging adjustment system (IAS) to address imaging deviations caused by contact depth changes. • The IAS contains an imaging calibration system and a focusing system for determining/shortening focusing ranges and improving adjustment efficiency. • Three-point-fitting-based depth from focus (TPF-DFF) and deep-learning-based depth from defocus (DL-DFD) are developed for different frequencies of imaging adjustment. • The IAS provides secondary imaging adjustment to simplify the sensor design and optimization. [ABSTRACT FROM AUTHOR]

Separation, classification, and focusing of microparticles are essential issues in microfluidic devices that can be implemented in two categories: using labeling and label-free methods. Label-free methods differentiate microparticles based on their inherent properties, including size, density, shape, electrical conductivity/permittivity, and magnetic susceptibility. Dielectrophoresis is an advantageous label-free technique for this objective. Besides, centrifugal microfluidic devices exploit centrifugal forces to move liquid and particles. The simultaneous combination of dielectrophoretic and centrifugal forces exerted on microparticles still needs to be scrutinized more to predict their trajectories in such devices. An integrated system utilizing two categories in microfluidics is proposed: dielectrophoretic manipulation of microparticles and centrifugal-driven microfluidics, followed by a numerical analysis. In this regard, we assumed a rectangular microchannel with internal unilateral planar electrodes equipped with three equal-sized outlets placed radially on a centrifugal platform where microparticles flow toward the disc's outer edge. The effect of different coordinate-based parameters, including radial and lateral distances (X and Y offsets)/tilting angles toward the radius direction (α), on the particles' movement was investigated. Additionally, the effect of operational parameters, including applied voltage, the microchannel width, the number of enabled electrodes, the diameter of particles, and the configuration of electrodes, were analyzed, and the distributions of particles toward the outlets were monitored. It was found that enhanced particle focusing becomes possible at lower rotation speeds and higher electric field values. Furthermore, the proposed centrifugal-DEP system's efficiency for classifying red blood cells/platelets and Live/Dead yeast cells systems was evaluated. Our integrated system is introduced as a novel method for focusing and classifying various microparticles with no need for sheath flows, having the ability to conduct particles at desired routes and focusing width. Furthermore, the system effectively separates various bioparticles and offers ease of operation and high-efficiency throughput over conventional dielectrophoretic devices. [Display omitted] • A centrifugal-DEP device for various applications including biomedical engineering and diagnostics is proposed. • The proposed system can be prepared using regular methods, making it attractive for further experimental studies. • The proposed centrifugal-DEP device provides advantages over the conventional SpinDEP device. • Live and Dead yeast cells have been separated using a 1 MHz, 5 V electric field at a 70 rad/s rotating speed. • A mixture of RBCs and Platelets was successfully classified at 100 rad/s rotation speed and 15 V electrical potential. [ABSTRACT FROM AUTHOR]

Catenary optics, as a new development object in the field of subwavelength optics, has been paid close attention and studied by scientists since it was proposed. As a two-dimensional planar structure, metasurface can realize the free control of electromagnetic wave in space. Traditional metasurface structures are often designed with discrete unit structures, which process is complicated and prone to error. In this paper, we introduce the catenary structure and use the principle of continuous geometric phase and the all-dielectric material silicon to design and optimize the catenary structure at 2 THz frequency, thereby realizing efficient transmission functional metasurfaces such as abnormal deflectors and focusing lenses that can generate Bessel beams. By optimizing the unit of catenary structure, the generation of parasitic transmission phase can be effectively avoided, and the working efficiency of the metasurfaces can be effectively improved. It is believed that the design in our work may pave the way for wavefront manipulation of high-performance terahertz waves and has potential for broadband terahertz devices. • The catenary metalens with continuous phase exhibit high manipulation efficiency. • The catenary structure is optimized to suppresses the parasitic transmission phase. • The designed deflector and focusing lens show the terahertz wavefront modulation. [ABSTRACT FROM AUTHOR]

This study proposes a Rayleigh wave transducer with an elliptical reflector for high-power ultrasound (ELIPS). In contrast to conventional transducers using IDT with single crystal piezoelectric plates or wedge transducers, our ELIPS enables high-power Rayleigh wave excitation in the megahertz range, which will be useful for applications such as surface acoustic wave (SAW) motors, SAW tactile devices, and SAW atomizers. The driving principles of the transducer are Rayleigh wave excitation with a transverse wave source and transverse wave focusing with a dilatational wave source and an elliptical reflection surface. The effectiveness of this mechanism was confirmed with an FEM simulation, and the Rayleigh wave excitation was validated using a prototype transducer. Finally, the high-power characteristics were examined, and a maximum vibration amplitude of 15.5 nm at 1.0 MHz was successfully obtained. It should be noted that this vibration amplitude is not a saturated value, and a much higher value could be realized with higher input power. [Display omitted] • Rayleigh wave excitation mechanism with an elliptical reflector is proposed. • Elliptical reflectors can convert dilatational waves into focusing transverse waves. • High-power Rayleigh waves can be excited by focused transverse waves. • The proposed Rayleigh wave transducer is promising for high-power applications. [ABSTRACT FROM AUTHOR]

This paper presents a nested optimization design scheme for ellipsoidal glass tubes. The lens, also known as a mirror, is composed of multiple ellipsoidal glass tubes with varying semi-major and semi-minor axes, nested within a larger-diameter ellipsoidal glass tube. Compared to Traditional Ellipsoidal Single-bounce Lens (TESL), the Nested Ellipsoidal Glass Tube X-ray Lens (NEXL) can utilize a smaller or even no beam stop at its input, mitigating the impact of the direct X-ray beam on the NEXL's focused beam and thereby enhancing X-ray source utilization. NEXLs can be designed with a large input focal distance, making them suitable for synchrotron radiation X-ray sources located significant distances from the source point to the sample. Simulation results show that for a synchrotron X-ray source 34,000 mm from the sample, a NEXL with six ellipsoidal sub-tubes offers a solid acceptance angle four times greater than a single ellipsoidal glass tube lens. Furthermore, for standard laboratory X-ray sources, a NEXL with three sub-tubes provides double the solid acceptance angle compared to a single-tube lens. These features position NEXLs as highly versatile in the field of X-ray technology. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel geometry of square wave microchannel with an enhancement to particle focusing concentration. • Synchronous focusing and separation of non-magnetic particles in a viscoelastic-based ferrofluid medium. • A new solver is developed in OpenFOAM to include elastic lift and magnetophoretic forces. • Different focusing position is observed by changing the order of cavities' placement. • Separation of CTCs from RBCs using a ferrofluid. The size-dependent separation of cells contains detailed information that results in substantial breakthroughs in various areas including biomedicines. The most important action before separating cells is to pre-focus them by maintaining cells in a single line through the microchannel length. Herein, we propose a novel microchannel called "cavity-added square wave" which can pre-focus different-sized polystyrene particles (5 and 20 µm) in a PEO-based ferrofluid without needing sheath flows, and separate them using a negative magnetophoretic force. First, the elasto-inertial focusing of particles is studied through experimental work and numerical simulation using a developed OpenFOAM code. Next, effects of geometrical parameters, magnetic field strength, and magnet distance are explored on particle focusing and separation, respectively. Results ascertained that the proposed microchannel can focus 5 µm particles somewhere slightly further from the center in a width of 14 µm with a maximum concentration which is 73.82 % higher than that achieved in a conventional square wave channel. In addition, the tunability of focusing position of particles can be fulfilled by changing the patterns of cavity placement. This study can give an understanding of employing the negative magnetophoresis method to separate CTCs from red blood cells using biocompatible ferrofluids. [ABSTRACT FROM AUTHOR]

Metasurfaces composed of subwavelength optical antennas offer fruitful functionalities to manipulate the amplitude, phase and polarization of light. Sufficient phase tunability of metasurfaces has significant potential for dynamic beam steering, hologram and flat optics exhibiting tunable focusing. Here, we demonstrate a graphene based metasurface that gives rise to more than 330° smooth and continuous phase modulation at mid-infrared spectrum. The phase modulator model introduces multiple resonances including Split-Ring-resonator (SRR) resonance and inductance-capacitance (LC) resonance, leading to the outstanding sensitivity of the metasurface to tiny change of surrounding electromagnetic environment. Through adjusting the Fermi level of the monolayer graphene beneath the resonators, both scattered amplitude and phase can be efficiently modulated, so that the electrically programmable metasurface enables nearly arbitrary manipulation of scattered wavefront. Electro-optically tunable focusing and beam steering are numerally realized by constructing one dimensional discrete array element. The phased array design achieves an average efficiency up to 22% within 60° steering range. The reflective focusing lens with focal lengths of 10 μm, 15 μm and 20 μm are successfully demonstrated, respectively. The proposed metasurface has promising potential in optoelectronic applications such as imaging, sensing and focusing. Image 1 [ABSTRACT FROM AUTHOR]

Ion concentration polarization focusing (ICPF) is an electrokinetic technique, in which analytes are enriched and separated along a localized electric field gradient in the presence of a counter flow. This field gradient is generated by depletion of ions of the background electrolyte at an ion permselective junction. In this tutorial review, we summarize the fundamental principles and experimental parameters that govern selective ion transport and the stability of the enriched analyte plug. We also examine faradaic ICP (fICP), in which local ion concentration is modulated via electrochemical reactions as an attractive alternative to ICP that achieves similar performance with a decrease in both power consumption and Joule heating. The tutorial covers important challenges to the broad application of ICPF including undesired pH gradients, low volumetric throughput, samples that induce biofouling or are highly conductive, and limited approaches to on- or off-chip analysis. Recent developments in the field that seek to address these challenges are reviewed along with new approaches to maximize enrichment, focus uncharged analytes, and achieve enrichment and separation in water-in-oil droplets. For new practitioners, we discuss practical aspects of ICPF, such as strategies for device design and fabrication and the relative advantages of several types of ion selective junctions and electrodes. Lastly, we summarize tips and tricks for tackling common experimental challenges in ICPF. Image 1 • Fundamental and practical aspects of ion concentration polarization (ICP) and faradaic ICP are discussed. • Recent advancements relevant to the application of ICP focusing to quantitative analysis are summarized. • This Tutorial Review includes a summary of tips and tricks for new practitioners. [ABSTRACT FROM AUTHOR]

The development of ultrathin Fresnel lenses has revolutionized the lens technology and provided great prospects for the miniaturization of electromagnetic systems. Despite considerable advances in microtechnology, a scalable fabrication strategy to achieve ultralow profile microwave lenses is yet to be developed. Here, we report on a novel strategy to create ultrathin and essentially flat Fresnel lenses using graphene rings. We show that monolayer or multilayer graphene can be microstructured into a Fresnel lens to utilize the unique transmission properties of graphene. We design different Fresnel lenses and investigate their performance in the microwave regime both numerically and experimentally. It is shown that one can change the intensity of the focused wave without shifting the focusing point by altering the number of the graphene layers. The good agreement between our experimental results and the results of numerical simulations demonstrates the feasibility of atom-thick (about 1 0 − 7 of the operating wavelength) graphene-based lenses and shows their potential for ultra-compact integration. [Display omitted] • Experimentally proposing the first ultrathin microwave graphene-based Fresnel lenses. • The ratio of the lens thickness to the operation wavelength can reach factors of 1 0 − 7 . • Changing the intensity of the focused wave by altering the number of the graphene layers. [ABSTRACT FROM AUTHOR]

• The proposed EMAT can generate and receive SH0 mode guided wave. • A new Chevron pattern like EMAT coil design with PPM configuration for improving the directivity. • The effect on the amplitude of displacement field corresponding to the number of coil wires has been presented. • The effect of Chevron angle of EMAT coil design on the generating waves has presented. Guided wave electromagnetic acoustic transducers (EMATs) have a significant role in non-destructive testing and structural health monitoring. It can generate horizontally polarized shear waves propagating axially or circumferentially to characterize the shape and orientation of pipeline defects. This work proposes a new Chevron pattern-like coil structure design with a periodic permanent magnet (PPM) EMAT configuration. This specific design of the EMAT coil can generate a bi-directional shear horizontal wave (SH-wave) and reduce the side lobes. An optimal Chevron angle of coil wires assists in generating orthogonal propagating waveforms. These phenomena lead to the constructive interference of propagating waves and develop a resulting wave along the horizontal direction. A 3D FEM modeling and simulation have been carried out and validated with experimental results. The proposed EMAT results are compared with the conventional racetrack PPM EMAT model, which shows a significant improvement over conventional EMATs. A prototype of this proposed EMAT has been developed. It can be used to inspect surface defects in applications such as fuel transportation pipelines. [ABSTRACT FROM AUTHOR]

Low-molecular-mass isoelectric point (p I) markers are a reasonable alternative to commonly used peptide and protein p I markers in the field of isoelectric focusing. We present a comparative study dealing with characterization of 44 nitrophenol-based compounds synthesized by the Mannich reaction which p I values cover a pH range from 3.2 to 10.4. The values of p I s of all the presented nitrophenol-based compounds were precisely determined by capillary isoelectric focusing technique (cIEF) when a standard deviation of measurement reached a value of a few hundredths of a pH unit (n ≥ 3). Differences have been found between in silico analysis of acid-base properties of the investigated compounds and the experimental cIEF data especially at the basic pH region. The data from the acidic pH range showed better correlation between these methods. Only three compounds were excluded from the group of p I markers because they contained impurities originating from the synthesis or long-term storage. Based on the presented results we identified 41 nitrophenol-based pI markers (NPIMs) which can fulfill requirements of the most applications in a field of isoelectric focusing analyses. Image 1 • 44 UV–vis absorbing nitrophenol-based compounds designed as possible p I markers. • p I s and acid-base properties of the p I marker structures studied in silico. • cIEF used for marker p I value determination and marker purity analysis. • 41 compounds covering a pH range from 3.2 to 10.4 proved to be suitable p I standards. [ABSTRACT FROM AUTHOR]

• Ferromagnetic shape memory alloys, as a new type smart material, used in phononic crystals firstly. • This article is the first time to control negative refraction and focusing by using magnetic field. • It provides a novel strategy for the tunable PCs with negative refraction and focusing behaviors. The refraction and focusing behaviors of two-dimensional phononic crystals (PCs) tuned by external magnetic fields are investigated systematically. The PCs are constructed by inserting ferromagnetic shape memory alloys (FSMAs) between tungsten cylinders and water matrix. Under the magnetic field, material parameters of FSMAs will vary, which furthermore changes the frequency spectrum and equi-frequency surfaces of acoustic waves in sonic crystals. It is revealed that the refraction angle can be tuned from a positive value to a negative one when the PC slab suffers from continuous magnetic fields. Moreover, the focusing behavior can be achieved and controlled artificially by applying a proper magnetic field. These interesting phenomena of the tunable sonic crystals with FSMAs can provide us guidance for the design and application of novel acoustic devices, as well as the active control of acoustic waves. [ABSTRACT FROM AUTHOR]

An experimental study of 14 keV O− ions transmission through a tapered glass capillary with the inlet diameters of 580 μm, an outlet diameter of 68 μm and a length of 45 mm, has been performed in this work. It indicates that the O − ions transmitting through the tapered capillary had a density enhancement of about 5.5 times with the tilt angle of 0°. It was found that more than 97% of the transmitted and focused ions remained their initial charge state in central area. It's the first time that focusing effect was observed and was reported in experiment for negative ions. The angular distribution of transmitted ions was narrow. These results clearly indicated that the focusing effect can be achieved in the transmission process of keV O− ions through a tapered glass capillary. [ABSTRACT FROM AUTHOR]

Abstract Guided by theoretical predictions, we have demonstrated experimentally the existence of negative refraction on the two lowest acoustic-branch passbands (shear and longitudinal modes) of a simple two-dimensional phononic crystal consisting of an isotropic stiff (aluminum) matrix and square-patterned isotropic compliant (PMMA) circular inclusions. We experimentally distinguished the shear and longitudinal modes to ensure that there are no couplings between the two modes and that the shear-mode negative refraction is an inherent property of periodic composites with stiff matrix and compliant inclusions. We have also discovered that a composite with compliant (PMMA) matrix and stiff (aluminum) inclusions does not display negative shear-mode refraction on its first branch. At frequencies and wave vectors where the refraction on the acoustic-branch passbands is negative, the effective mass-density and the effective stiffness tensors of the crystal are positive-definite, and this is an inherent property of such phononic crystals. The equi-frequency contours and energy flux vectors as functions of the phase-vector components, reveal a rich body of refractive properties that can be exploited to realize, for example, beam splitting, focusing, and frequency filtration on the lowest passbands of the crystal where the dissipation is minimum. By proper selection of material and geometric parameters these phenomena can be realized at remarkably low frequencies (large wave lengths) using rather small simple two-phase unit cells. [ABSTRACT FROM AUTHOR]

Abstract We report a novel approach to control flexural waves in thin plates using metasurfaces constituted of an array of parallel arranged composite beams with their neutral planes the same as that of the host plate. The composite beams are composed of two connecting parts made of different materials, and have a thickness identical to that of the host plate. To steer flexural waves in thin plates, a rectangular zone is subtracted from the thin plate and is then filled with the designed metasurface. The time delay of flexural waves in each composite beam of the metasurface is tuned through the varying length of the two connecting components, while keeping the total length fixed. To quantitatively evaluate the time delay in each composite beam, a theoretical model for analyzing the phase of the transmitted flexural waves is developed based on both Mindlin plate theory and Timoshenko beam theory. To control the flexural waves at will, each composite beam in the metasurface is delicately designed according to the proposed theoretical model. For illustrative purposes, the refracted and focusing metasurfaces are designed and numerically validated. [ABSTRACT FROM AUTHOR]

Background: Poor attentional control, defined as difficulty focusing attention on a task or shifting attention flexibly between tasks, is a transdiagnostic construct theorized to confer risk for, and maintain, depression and anxiety. Research to date in non-clinical samples has suggested a dissociable relationship between the two factors of self-reported attentional control and psychopathology, with depression being associated with difficulties shifting and anxiety being associated with focusing. However, to our knowledge no study has tested this differential set of relationships in a clinical sample.Methods: Adults (N = 493) presenting for psychiatric treatment completed measures of depressive and anxiety symptom severity and self-reported attentional control. Hierarchical linear regression and Zou's (2007) confidence interval method were used to examine the relationship between clinical symptoms and attentional control.Results: Both shifting and focusing were significantly correlated with anxiety and depressive symptoms in this sample. However, focusing was more strongly associated with clinical symptomatology than shifting, which showed a weak correlation.Limitations: All constructs were measured cross-sectionally by self-report questionnaires.Conclusions: In contrast to studies conducted in non-clinical samples, attentional focusing appears to be more relevant than attentional shifting in a clinical sample for both depression and anxiety symptoms. These findings lend support to efforts to develop neurocognitive interventions that improve focusing. Replication of these findings, particularly in longitudinal studies, is warranted. [ABSTRACT FROM AUTHOR]

Highlights • This paper develops a theory of focusing and framing. • We investigate an intertemporal context with risky choices. • Our model predicts overoptimistic actions. • Accordingly, subjects underrate downside risk but overrate upside chances. • We explain harmful consumption (smoking) and risky investments (entrepreneurship). Abstract This paper develops a theory of focusing and framing in an intertemporal context with risky choices. We provide a selection criterion between existing theories of focusing by allowing a decision maker to choose her frame such that her attention is either drawn to salient events associated with an option or to the expected utilities an option yields in different time periods. Our key assumption is that a decision maker can choose her frame in a self-serving manner. We predict that the selected frame induces overoptimistic actions in the sense that subjects underrate downside risk but overrate upside risk and accordingly reveal overoptimistic choices. Hence, our theory can explain phenomena such as excessive harmful consumption (smoking, unhealthy diet) and risky investments (entrepreneurship, lotteries, gambling) in one coherent framework. Notably, overoptimistic actions are not universal, but have plausible limits. We characterize under which situations overoptimistic actions are most likely to occur and under which circumstances choices should be rational or even pessimistic. [ABSTRACT FROM AUTHOR]

Abstract Plasmonic planar lenses on silicon substrate are designed to realize terahertz (THz) wave focusing. Super-unit-cells containing eight different resonant units are presented to construct eight concentric rings on the silicon substrate. By controlling of the position distribution of the resonant units, it is shown that focusing at 4.3 THz can be achieved. Moreover, due to that the eight units can steer THz wave and keep phase gradient in frequency range of 4.2 to 4.5 THz, the metalenses can realize broadband THz focusing. The results imply the potential applications in THz wave control devices of light collection and multi-channel optical communication. Highlights • Planar lenses based on plasmonic metasurfaces are designed to realize THz focusing. • The results show the metalens can achieve broadband focusing from 4.2 to 4.5 THz. • The metalens can be used for THz wave devices of light collection and communication. [ABSTRACT FROM AUTHOR]

Abstract A kind of prism-array refractive lens (PRL) for X-ray focusing composed of different prisms with the same width is designed and fabricated. In order to stabilize the whole structure and reduce the fabrication difficulty, bridges are introduced between the opposite two lines of tooth-like segments. The influence of the bridges on the focusing is investigated in theory, which will broaden the width of the focus. Furthermore, two PRLs with and without bridges for 50 keV X-rays are fabricated on the same substrate by X-ray lithography and are tested at BL13W1 beamline in Shanghai Synchrotron Radiation Facilities (SSRF). The bridges are designed a width of 5 μ m and the PRL sample with bridges has the better morphology than the one without bridges after fabrication. The on-line focusing test results show that the focal line width of the samples with and without bridges are 4. 20 μ m and 6. 34 μ m respectively, which implies that the bridges are necessary for the PRL with this fabrication method. Highlights • A kind of prism-array refractive lens (PRL) for 50 keV X-ray is fabricated. • Two PRLs with/without bridges are designed on the same substrate for comparison. • The bridge can influence the focusing in theory but also improve the PRL's profile. • The focal line width of the PRL without bridges is 6. 34 μ m. • The focal line width of the PRL with bridges is 4. 20 μ m. [ABSTRACT FROM AUTHOR]

Abstract The problem of creation of high energy neutrino beams on the basis of modern and future circular proton accelerators with the help of traditional technology seems to be expensive and difficult. Because of this, we propose the solution of this problem based on the usage of focusing bent single crystals. In the paper we demonstrate the possibilities of acceptance and focusing of a pion beam with the help of a crystal optical lens system. As an illustration of these features the calculated neutrino fluxes for energy of circulating proton beam equal to 6.5 TeV are presented. [ABSTRACT FROM AUTHOR]

• Broadband transmission properties of the designed metamaterial; • Phase modulation capabilities to design dual-channel units theoretically and numerically; • Based on the dual-channel configuration to systematically design the frequency-dependent vortices; • Experimental verification of the multiplexed vortices with different orders and focal positions; • Application and exploration of acoustic encryption and underwater wireless communication. Focused vortex beams have attracted considerable research attention due to their unique acoustic properties, and have been explored in medical imaging, biomedical therapy, and particle manipulation. Here, an acoustic metamaterial vortex generator (AMVG) is designed to realize a multiplexed focusing acoustic vortex (MFAV) with multiple-order topological charges (TCs). The proposed AMVG is composed of several fanlike sectors with two high transmission channels per unit, which can flexibly modulate the transmitted phase shift in two separate frequency bands. In contrast to conventional acoustic metamaterial-based vortices, the design strategy provides a new degree of freedom, i.e., frequency, that may extend to the agile tailoring of multi-band independent vortices, significantly enhancing the information encoded in the acoustic metamaterial. Acoustic transmission and phase shift of the dual-channel unit are investigated theoretically and demonstrated in simulations using the finite element method. The focal position and TC of the MFAVs can be modulated by simply adjusting the cavity length of the unit cell and even only the sector order. Furthermore, we implement three-dimensional anechoic experiments to verify the effectiveness of the off-axial MFAVs by the designed AMVG. These multiplexed focusing vortices offer a technical advance to tackle the rising challenges in the fields of acoustic signal processing and communication systems. [ABSTRACT FROM AUTHOR]

As a novel material, graphene has been widely applied in the field of metasurface to dynamically control wavefront and polarization of electromagnetic wave in recent years. In this work, four graphene-based meta-atoms are designed for polarization manipulation. Using a hybrid structure of patterned graphene and patched metal, reflective phase of meta-atom can be tuned by Fermi level. When Fermi level is 0.01 eV, cross-polarized waves with phase difference of 90° are generated by meta-atoms with polarization conversion ratio 87% at 2 THz. As Fermi level is adjusted to 0.70 eV, phase difference between four meta-atoms is cancelled with the corresponding polarization conversion ratio only 5%. Then, four metasurfaces are designed for wavefront control and polarization manipulation, and they are focusing metalenses and vortex beam generators. Simulations indicate that the proposed metasurfaces are able to achieve the combination of wavefront control and polarization manipulation, greatly enhancing the ability to control electromagnetic wave. The proposed approach may be applied in the fields of terahertz focusing and communication. [ABSTRACT FROM AUTHOR]

Abstract Laser-driven grating type DLA (Dielectric Laser Accelerator) structures have been shown to produce accelerating gradients on the order of GeV/m. In simple β -matched grating structures due to the nature of the laser induced steady-state in-channel fields the per period forces on the particles are mostly in longitudinal direction. Even though strong transverse magnetic and electric fields are present, the net focusing effect over one period at maximum energy gain is negligible in the case of relativistic electrons. Stable acceleration of realistic electron beams in a DLA channel however requires the presence of significant net transverse forces. In this work we simulate and study the effect of using the transient temporal shape of short Gaussian drive laser pulses in order to achieve suitable field configurations for potentially stable acceleration of relativistic electrons in the horizontal plane. In order to achieve this, both the laser pulse and the grating geometry are optimized. Simulations conducted with the Particle-In-Cell code VSim 7.2 are shown for both the transient and steady state/long pulse case. Finally we investigate how the drive laser phase dependence of the focusing forces could affect a potential DLA-based focusing lattice. [ABSTRACT FROM AUTHOR]

The hybrid-order Poincaré sphere (HPS) was proposed to describe high-order vector vortex beams. In this paper, we theoretically study the intensity and longitudinal component phase distribution of tightly focusing HPS beams within a homogeneous and isotropic medium. We analyse the phase and demonstrate the orbital angular momentum (OAM) state distribution of the longitudinal component. Arbitrary OAM states can be obtained by manipulating the order of HPS beams, which comprise two orthogonally circularly polarised vortex beams with topological charges m and n . Meanwhile, the OAM states of the longitudinal component are destroyed when m = − n ; otherwise, they split into two parts with topological charges m + 1 and n − 1 . The focus intensity distribution is petal-shaped if the two topological charges have opposite signs, where the number of intensity lobes in the focal plane is m − n + 2 . Moreover, the ratio of the maximum intensities of the longitudinal and total fields depends on the sign and value of the two topological charges, m and n . Finally, we investigate a generalised case of HPS beams, and demonstrate that the focal intensity and phase distribution are also influenced by the coefficients. The results obtained in this paper may facilitate a new application of HPS beams in various fields. [ABSTRACT FROM AUTHOR]

Electrophoretic focusing on inverse electromigration dispersion (EMD) gradient is a new analytical technique based on a unique separation principle where weak non-amphoteric ionogenic species are focused, separated and transported to the detector by an EMD profile of suitable properties. The present work extends the theoretical description of this method by introducing the concept of resolution and deriving the fundamental equation expressing resolution as function of basic system parameters. The results indicate that at constant current operation, resolution is proportional to the square root of time. For variable current regimes (e.g. constant voltage), the time variable is replaced by the product of electric current and passed electric charge. Computer simulations for a model pair of substances support the validity of the presented theory and confirm the theoretical conclusion that resolution can be increased by allowing longer electromigration of the gradient in terms of time or passed charge. The experimental example shown comprises an anionic electrolyte system based on maleic acid and 2,6-lutidine, combined with ESI–MS detection and operated in the reverse mode due to strong electroosmotic flow and ESI suction. The practical implementation of the proposed methodology is done by application of negative pressure at the inlet vial, resulting in very substantial resolution enhancement and baseline separation of otherwise unresolved substances. The performance and high sensitivity of the developed technique is demonstrated on the example of simultaneous analysis of four sulfonamides and three dichlorophenols in waters with limits of detection on the 1 nM level. [ABSTRACT FROM AUTHOR]

Hydrogen fuel, as for now, is the most energy efficient and clean fuel for aviation engines. At present time RAM engines based on chemical burning of fuels and accelerating exhaust gases practically reached the top of their efficiency in terms of specific impulse. New schemes are under development. As it is known, complex geometry of combustion chambers could bring to compression waves focusing and changing the mode of flame propagation from slow combustion to detonation. Keeping this process under control is of major importance for developing new generation of engines. The paper presents results of numerical and experimental investigation of mixture ignition and detonation onset in shock wave reflected from inside a wedge. Comparison of numerical and experimental results made it possible to validate the developed 3-D transient mathematical model of chemically reacting gas mixture flows incorporating hydrogen – air mixtures. Kinetic schemes were improved based on comparison of numerical and experimental results. A tool was developed making it possible to set a criterion for obtaining either safe combustion regime, or transition to detonation regime in shock wave focusing. [ABSTRACT FROM AUTHOR]

Here we describe the design, modeling, fabrication, and successful utilization of a microfluidic switching device that employs dielectrophoresis to effectively manipulate micro-scale entities in a microchannel. Two sets of opposing interdigitated transducer electrodes are micropatterned at the bottom of the device. The electrodes enter slightly from each side-wall into the channel. Finite Element Analysis and experimental results demonstrate that this design enables 3D switching of micro-objects at any location in the microchannel. Living cells are switched to one of the three downstream branches by varying the actuation voltages on the electrodes. [ABSTRACT FROM AUTHOR]

Laue lenses use Bragg diffraction to concentrate soft γ -rays onto a detector. This decoupling of the collecting area from the detector volume can generate a significant increase in sensitivity for applications in astrophysics and nuclear medicine. A demonstrator lens was constructed at the UC Berkeley’s Space Sciences Laboratory in 2014 by gluing 48 Fe and Al diffracting crystals to an aluminium substrate. The goal was to demonstrate a fast and accurate assembly technique that is compatible with the large number of crystals required to fabricate a Laue lens telescope for astronomical observations. We present here the lens design, the assembly technique we used, and the results of measurements of the angular misalignments before and after curing of the glue and during environmental testing (thermal, vacuum, and vibration). We conclude that our alignment technique is fast enough to assemble a full lens made of several thousand crystals. The achieved alignment accuracy had an average of 32.7 ′ ′ and a standard deviation of 44.1 ′ ′ . The accuracy could be improved by using an alternative glue or by having better control over the asymmetry angle resulting from the crystal cut. [ABSTRACT FROM AUTHOR]

Here, we examine how redistribution of differing grain sizes by sediment focusing processes in Panama Basin sediments affects the use of 230 Th as a constant-flux proxy. We study representative sediments of Holocene and Last Glacial Maximum (LGM) time slices from four sediment cores from two different localities close to the ridges that bound the Panama Basin. Each locality contains paired sites that are seismically interpreted to have undergone extremes in sediment redistribution, i.e., focused versus winnowed sites. Both Holocene and LGM samples from sites where winnowing has occurred contain significant amounts (up to 50%) of the 230 Th within the >63 μm grain size fraction, which makes up 40–70% of the bulk sediment analyzed. For sites where focusing has occurred, Holocene and LGM samples contain the greatest amounts of 230 Th (up to 49%) in the finest grain-sized fraction (<4 μm), which makes up 26–40% of the bulk sediment analyzed. There are slight underestimations of 230 Th-derived mass accumulation rates (MARs) and overestimations of 230 Th-derived focusing factors at focused sites, while the opposite is true for winnowed sites. Corrections made using a model by Kretschmer et al. (2010) suggest a maximum change of about 30% in 230 Th-derived MARs and focusing factors at focused sites, except for our most focused site which requires an approximate 70% correction in one sample. Our 230 Th-corrected 232 Th flux results suggest that the boundary between hemipelagically- and pelagically-derived sediments falls between 350 and 600 km from the continental margin. [ABSTRACT FROM AUTHOR]

Cell-based diagnosis and the introduction of personalized drugs are key factors, motivating researchers to discover an efficacious tool for effective cell isolation. Optimal systems were presented through the finite element method by adjusting the arrangement of hydrodynamic forces within a serpentine micro-channel, which managed to separate different cell lines in addition to their focusing. Considering the parameters of flow, particle, and geometry, two optimal serpentine systems (fixed and variable slope) were presented and the accuracy of the simulation results was verified by their comparison with the experimental findings of the optimized microchannel. The results indicated that the channel heights of ∼1800 µm and ∼2200 µm are the most suitable choices for particle separation in the range of ∼7 µm to ∼18 µm (blood cells) for fixed-slope and the last cycle of the variable-slope microchannel, respectively. Both fixed-slope and variable-slope geometries with the vertical channel width of ∼400 µm offered a high separation efficiency (about ∼60 µm) with a difference of less than ∼3% in separating red blood cells (RBCs) from circulating tumor cells (CTCs). In addition to separation, the particle focusing efficiency of the microchannels was approximately ∼98% for low diameter particles (7–21 µm) and ∼95% and ∼93% for ∼24 µm and ∼27 µm diameter particles, respectively. Through experimental validation, this study presented a reliable optimized structure to improve our ability to separate white blood cells (WBCs) (18 µm >diameter>12 µm) and CTCs (27 µm>diameter>21 µm) from RBCs, opening new horizons to eliminate at least one of the limitations of the field of diagnosis. [Display omitted] • Optimal serpentine microchannels system to separate WBCs and CTCs from RBCs. • Fixed-slope microchannel with 1800μm heights, is suitable for separation. • Variable-slope microchannel with 2200μm heights, is suitable for separation. • A serpentine microchannel with 400μm width is suitable for separation. [ABSTRACT FROM AUTHOR]

• Biaxial driving consists of applying two orthogonal electric fields to a transducer. • Focal area reduction and dynamic focalization along propagation axis with biaxially driven single-element ring transducers. • Focal area improvements and dynamic focalization effects persist while driving the ring transducer at higher harmonics. • Power and phase applied on second electrode determines the focal area reduction and focal distance. Biaxial driving is a new driving technique that allows the steering of the ultrasound field generated by a single-element piezoceramic transducer. Because of their natural axisymmetric geometry, ultrasound generation with ring transducers can take advantage of the biaxial driving to change the focus of the beam generated by this type of transducer using only two driving signals. In this study, we applied the biaxial driving technique into a single-element PZT ring transducer operating at 500 kHz to produce a change in size and position of the focal spot while using the 1st (482 kHz), 3rd (1.362 MHz) and 5th (2.62 MHz) harmonic excitation. The transducer had a thickness of 2.85 mm, an inner diameter of 9.75 mm and a ring width of 2.0 mm, and two pairs of electrodes as required for biaxial driving. Simulation and experimental results showed that both the focal area and the distance at which the focal area centre was located changed as a function of the phase and power difference between the two driving signals. Experimental results showed that the focal area could be reduced from 31.6 mm2 (conventional driving) to 3.4 mm2 (89 % reduction) when using the first harmonic excitation. For the third harmonic, the focal area could be reduced from 4.0 mm2 (conventional driving) to 3.3 mm2 (17.5 % reduction). For the fifth harmonic, the focal area could be reduced from 1.7 mm2 (conventional driving) to 1 mm2 (41.7 % reduction). Results also demonstrated the centre of the focus could be displaced between 3.0 mm and 9.3 mm from the surface of the transducer when using the first harmonic, between 7.3 mm and 8.4 mm at the third harmonic, and between 4.9 mm and 8.2 mm at the fifth harmonic. The reduction in the focus area, as well as the possibility to displace the focus dynamically will be advantageous for preclinical applications of focused ultrasound, especially on drug delivery and neuromodulation studies in small rodents. [ABSTRACT FROM AUTHOR]

Graded index fibers are important technological elements that have improved the performance of systems in many scientific fields due to their particular refractive index profile. However, the necessity to control focus at their distal end makes the design and fabrication of additional lenses at the tip of the fiber an essential step to their applications, such as bio imaging and integrated systems. An alternative and more general approach that does not require additional fabrication steps is highly desirable. We hypothesize that controlling the wavefront at the entrance of the GRIN fiber is such a method. In this work, the convergence of the beam at the distal end of graded index fibers was controlled by phase shaping the input wavefronts. By optimizing phase masks, focus was generated and tuned according to their desired dimensions, eliminating any further modifications to the fiber. To explore the applications enabled by focusing, coupling experiments were performed fiber-to-fiber and fiber-to-chip. It was found that by using optimized wavefronts to tune the convergence in a fiber lensless system, the output power of the experiments was significantly enhanced to more than 4.5 dB when compared to the non-optimal configuration. • Generating focus by wavefront shaping. • Focusing experiments with multimode waveguides. • Enhancement of coupling interfaces with multimode fibers. • Enhancement of coupling interfaces with graded index (GRIN) fibers without fiber lenses. [ABSTRACT FROM AUTHOR]

In the present paper, the effects of focusing of ground vibrations generated by high speed trains travelling at trans-Rayleigh speeds, i.e. under the condition of ground vibration boom, are considered theoretically. These effects are similar to the effects of focusing of sound waves radiated by supersonic aircraft. In particular, if a railway track has a bend, e.g. to provide the possibility of changing direction of train movement, the Rayleigh surface waves generated by high-speed trains under the condition of ground vibration boom may become focused. This results in concentration of their energy along a simple caustic line at one side of the track and in the corresponding increase in ground vibration amplitudes. The effect of focusing of Rayleigh waves may occur also if a train moves along a straight line with acceleration a and its current speed v(t) is higher than Rayleigh wave velocity in the ground. In the present paper, both the above-mentioned focusing mechanisms are investigated in detail using the Green's function formalism and the expressions for space-time distributions of track-train-induced dynamic forces that take into account either track curvature or train acceleration. It is shown that in both these cases the effect of focusing can result in noticeable increase in generated ground vibrations. The obtained results are illustrated by numerical calculations. [ABSTRACT FROM AUTHOR]

Concurrent Constraint Programming (CCP) is a simple and powerful model of concurrency where processes interact by telling and asking constraints into a global store of partial information. Since its inception, CCP has been endowed with declarative semantics where processes are interpreted as formulas in a given logic. This allows for the use of logical machinery to reason about the behavior of programs and to prove properties of them. Nevertheless, the logical characterization of CCP programs exhibits normally a weak level of adequacy since proofs in the logical system may not correspond directly to traces of the program. In this paper, we study different encodings from CCP into intuitionistic linear logic (ILL) and we compare the level of adequacy attained in each. By relying on a focusing discipline, we show that it is possible to give a logical characterization to CCP with the highest level of adequacy. Moreover, we show how to characterize maximal-parallelism semantics for CCP by relying on a multi-focusing discipline for ILL. These results, besides giving proof techniques for CCP, entail (safe) optimizations for the execution of CCP programs. Finally, we show how to interpret CCP procedure calls as fixed points in ILL, thus opening the possibility of reasoning by induction about properties of CCP programs. [ABSTRACT FROM AUTHOR]

Metamaterials have been widely used to enhance radiation characteristics of antennas thanks to their ability to manipulate the electromagnetic waves. Recent progress has shown that flat metasurfaces with reduced tunable dimensions are capable to provide a near zero refractive index and a phase compensation mechanism which are responsible for the focusing of electromagnetic waves. Here, we present a study, about two types of flat metasurface lenses operating at the frequency of 5.9 GHz for the improvement of a patch antenna radiation properties and bandwidth at the same time. The proposed structures can be used in wireless point to point communication and especially for WAVE applications. [ABSTRACT FROM AUTHOR]

Recent experiments in CERN (Scandale et al., 2014) and IHEP (Afonin et al., 2012) have demonstrated the simple method of focusing of positively charged hadron beams with the help of specially fabricated bent single crystals. In these experiments the parallel beam was focused into point-like one on a distance equal approximately to 1–2 m from a crystal. In the report we discuss further development of focusing on the basis of bent crystals. We present the theoretical description of transformation from point-like beam into parallel one and focusing from point-like beam into point-like one. In the report we also consider possibilities of creation of new optical elements for focusing of high energy hadron beams in the horizontal and vertical planes simultaneously. [ABSTRACT FROM AUTHOR]

Electromagnetic Acoustic Transducers (EMATs) are a useful ultrasonic tool for non-destructive evaluation in harsh environments due to their non-contact capabilities, and their ability to operate through certain coatings. This work presents a new Rayleigh wave EMAT transducer design, employing geometric focusing to improve the signal strength and detection precision of surface breaking defects. The design is robust and versatile, and can be used at frequencies centered around 1MHz. Two coils are used in transmission mode, which allows the usage of frequency-based measurement of the defect depth. Using a 2MHz driving signal, a focused beam spot with a width of 1.3±0.25mm and a focal depth of 3.7±0.25mm is measured, allowing for defect length measurements with an accuracy of±0.4mm and detection of defects as small as 0.5mm depth and 1mm length. A set of four coils held under one magnet is used to find defects at orientations offset from normal to the ultrasound beam propagation direction. This EMAT has a range which allows detection of defects which propagate at angles from 16° to 170° relative to the propagation direction over the range of 0-180°, and the setup has the potential to be able to detect defects propagating at all angles relative to the wave propagation direction if two coils are alternately employed as generation coils. [ABSTRACT FROM AUTHOR]

The design and performance of a semi-preparative asymmetrical flow field-flow fractionation (SP-AF4) channel are investigated with the objective of better understanding and exploiting the relationship between channel dimensions, sample loading, and resolution. Most size-based separations of nanometer and submicrometer particles are currently limited to analytical scale quantities (<100 μg). However, there is a strong need to fractionate and collect larger quantities so that fundamental properties of the more narrowly dispersed fractions can be studied using additional characterization methods and for subsequent applications. In this work, dimensions of the spacer that defines the form of SP-AF4 channels are varied and their performances are assessed with respect to sample focusing position and loading. Separations are performed in aqueous and organic carrier fluids. A critical evaluation of channel dimensions showed that increasing the channel breadth is a practical and effective route to maintaining separation resolution while increasing sample loads to milligram quantities. Good size resolution (∼1.0) is achieved for separations of 10 mg of 50 and 100 nm silica nanoparticles suspended in water and up to 0.6 mg of ∼10 to 35 nm inorganic hybrid nanoparticles suspended in tetrahydrofuran. This work represents important advances in the understanding of SP-AF4 separations and extends sample loading capacities in both aqueous and organic solvents. [ABSTRACT FROM AUTHOR]

The intensity distribution and the phase properties, especially the Gouy phase and the phase singularities are studied in a strongly focused Gaussian beam with an off-axis vortex. The symmetry relation of the focused field is also derived. It is found that the off-axis vortex induces a rotation of the field pattern, the transverse focal shift, and the asymmetric distribution of the phase singularities. Our results also show that the initial position of the off-axis vortex in the incident beam strongly influences the distance of the transverse focal shift, but does not have an effect on the Gouy phase along the central axis. [ABSTRACT FROM AUTHOR]

• Anomalous transmission is presented with polarization conversion. • Two lenses are implemented with cross-polarized focusing. • Two vortex beams are proposed with different orbital angular momentums and cross polarization. By coding meta -atom with discrete phase, electromagnetic wavefront can be flexibly manipulated with the pre-designed coding sequence. In this work, transmissive metasurfaces are proposed to achieve wavefront reconfiguration with polarization conversion for terahertz wave. Based on composite structures of metallic resonators and polyimides, the designed meta -atoms are capable of polarization conversion and 360° phase modulation by changing notch angle and rotation angle of resonators at 2.0 THz. Then, three types of metasurfaces are designed. Firstly, transmissive wavefront of gradient metasurface is reconstructed through periodic alignment of eight meta -atoms along x axis. This metasurface realizes anomalous transmission and transforms x-polarized incidence to y-polarized wave. Secondly, two focusing lenses are implemented, and they realize single-focusing and dual-focusing under x-polarized incidence. Finally, two vortex beam generators are proposed with orbital angular momentum modes of l = 1 and l = 2 in channel of cross polarization. Our designs may be applied in the fields of terahertz communication, focusing, and encryption. [ABSTRACT FROM AUTHOR]

• VO 2 -based metasurfaces are presented for switchable wavefronts. • Gradient metasurface realizes switching between anomalous reflection and specular reflection. • Wavefronts of vortex beam and metalens with different polarizations are reconstructed under different states of VO 2. As a unique phase transition material, vanadium dioxide (VO 2) has been widely applied in switchable and modulating metasurfaces. In this work, VO 2 -based reflective meta-atoms are designed to achieve wavefront reconfiguration in terahertz frequency. When VO 2 is metal, four optimized meta-atoms with 90 o phase difference provide a full phase coverage, and they achieve high polarization conversion efficiency. After phase transition of VO 2 , the capability in the metallic state is lost. Thus, the corresponding phase coverage is switched from 360° to 0°, and the phenomenon of polarization conversion almost vanishes. Assembled by these meta-atoms, three metasurfaces are numerically presented. When VO 2 is in the state of metal, they are anomalous reflector, metalens, and vortex beam generator. The presented metasurfaces own the abilities of wavefront manipulation and polarization conversion. When VO 2 is in the insulating state, three metasurfaces are switched to specular reflector. Simulations are conducted to verify their abilities of wavefront modulation and polarization control. The proposed metasurfaces may have potential applications in the fields of terahertz switching, communication, and focusing. [ABSTRACT FROM AUTHOR]

• VO 2 -based metasurfaces are presented for switchable wavefronts. • Gradient metasurface realizes switching between anomalous reflection and specular reflection. • Wavefronts of vortex beam and metalens are reconstructed by changing VO 2 state. Metasurface provides a novel approach to control electromagnetic wave, and it attracts great attention. But, it is still challenging to realize wavefront tailoring with dynamically switchable functions. In this work, dynamically switchable metasurfaces are presented based on vanadium dioxide, and they realize state switching of reflected wavefront for circularly polarized wave in terahertz band. The designed meta -atom consists of vanadium dioxide strip, silica spacer, and gold substrate. Based on Pancharatnam-Berry phase, 360° phase modulation is achieved by axially rotating vanadium dioxide strip. Through phase transition of vanadium dioxide between metallic and insulating states, three applications are designed to demonstrate state switching of metasurfaces at 1.0 THz. First of all, a gradient metasurface is designed and anomalous reflection is formed. Anomalous reflection for metallic vanadium dioxide and specular reflection for insulating vanadium dioxide are dynamically switched. Secondly, vortex beam generators are implemented for metallic vanadium dioxide. Incident waves with different chirality achieve orbital angular momentums with different mode numbers, and it is switched to plane wave when vanadium dioxide is insulator. Finally, a reflective lens is presented with switchable focusing function. Our work may be applied in fields such as terahertz switching, wireless communication, and planar lens. [ABSTRACT FROM AUTHOR]

The impact of asymmetrical flow field-flow fractionation (AF4) on protein aggregate species is investigated with the aid of multiangle light scattering (MALS) and dynamic light scattering (DLS). The experimental parameters probed in this study include aggregate stability in different carrier liquids, shear stress (related to sample injection), sample concentration (during AF4 focusing), and sample dilution (during separation). Two anti-streptavidin (anti-SA) IgG1 samples composed of low and high molar mass ( M ) aggregates are subjected to different AF4 conditions. Aggregates suspended and separated in phosphate buffer are observed to dissociate almost entirely to monomer. However, aggregates in citric acid buffer are partially stable with dissociation to 25% and 5% monomer for the low and high M samples, respectively. These results demonstrate that different carrier liquids change the aggregate stability and low M aggregates can behave differently than their larger counterparts. Increasing the duration of the AF4 focusing step showed no significant changes in the percent monomer, percent aggregates, or the average M s in either sample. Syringe-induced shear related to sample injection resulted in an increase in hydrodynamic diameter ( d h ) as measured by batch mode DLS. Finally, calculations showed that dilution during AF4 separation is significantly lower than in size exclusion chromatography with dilution occurring mainly at the AF4 channel outlet and not during the separation. This has important ramifications when analyzing aggregates that rapidly dissociate (<∼2 s) upon dilution as the size calculated by AF4 theory may be more accurate than that measured by online DLS. Experimentally, the d h s determined by online DLS generally agreed with AF4 theory except for the more well retained larger aggregates for which DLS showed smaller sizes. These results highlight the importance of using AF4 retention theory to understand the impacts of dilution on analytes. [ABSTRACT FROM AUTHOR]

A tubular disk-and-ring, tapered accelerating structure for small electron linacs and MicroLinacs is considered. It consists of metal and dielectric elements inserted into a metallic tube to eliminate multi-cell, multi-step brazing. The structure enables a wide range of phase velocities (including non-relativistic), a wide bandwidth allowing large number of cells (for standing wave mode) or short filling time (for traveling wave mode), combination of compensated and purely π-mode cells, alternative periodic focusing built-in to the RF structure (the disks), and combining of RF and vacuum windows. RF and accelerating performance of such a long structure having up to four dozens cells is analyzed. Some of beam dynamics, thermal, and vacuum aspects of the structure and MicroLinac performance are considered as well. [ABSTRACT FROM AUTHOR]