Micro-optofluidic Lenses: A review

This review presents a systematic perspective on the development of micro-optofluidic lenses. The progress on the development of micro-optofluidic lenses are illustrated by example from recent literature. The advantage of micro-optofluidic lenses over solid lens systems is their tunability without the use of large actuators such as servo motors. Depending on the relative orientation of light path and the substrate surface, micro-optofluidic lenses can be categorized as in-plane or out-of-plane lenses. However, this review will focus on the tunability of the lenses and categorizes them according to the concept of tunability. Micro-optofluidic lenses can be either tuned by the liquid in use or by the shape of the lens. Micro-optofluidic lenses with tunable shape are categorized according to the actuation schemes. Typical parameters of micro-optofluidic lenses reported recently are compared and discussed. Finally, perspectives are given for future works in this field.     

On electron optics

For many experiments in physics and in some engineering applications, it is necessary to produce electron bundles, or as they are often called, “electron beams” of considerable intensities.Various methods have been used for directing a cloud of electrons evaporated from an emitting surface into a beam and then concentrating this beam to a desired degree. The concentration of electron beam in high vacuum depends entirely upon fields of force, either electric or magnetic, while in low vacuum or in rarified rare gas it depends also upon the action of the field of ionized gas molecules.In high vacuum the fields of force act upon the electron beam in a manner similar to the action of lenses upon a beam of light. An improperly shaped field produces effects similar to spherical aberration in poorly corrected lenses; non-uniform velocity of electrons in the beam results in effects similar to chromatic aberration of light.This optical analogy is not perfect.In the case of the electron beam the velocity varies continuously throughout most of the path and indices of refraction employed usually are greater than in the optical case. Moreover, space charge in beams of high intensity limits the concentration attainable; consequently, even theoretically, an electron beam can never be brought up to a mathematical point as in the case of light optics. Many secondary effects are present which complicate the problem still further.In focusing electron beams, both electrostatic and electromagnetic methods have been used extensively. The electrostatic method, however, seems to be preferable, especially when the beam is to be deflected. Precautions should be taken not to destroy the focusing of the beam during deflection.     

Study of resonance-cone propagation in truncated hyperbolic metamaterial grids using transmission-line matrix simulations

In this paper, we utilize transmission-line matrix simulations to study the electromagnetic properties of hyperbolic metamaterial grids, which are synthesized by arranging unloaded transmission lines over electrical ground planes, such that the unit cells are rectangular in shape. The hyperbolic grids support Bragg and Hyperbolic resonant modes that have rectangular and hyperbolic dispersion surfaces, respectively. We demonstrate the formation of these resonant modes in the hyperbolic grids and their refraction, and spatial scanning properties via circuit simulations. The simulation results are compared with experimental results of a two-layer anisotropic hyperbolic metamaterial.     

Three dimensional microfluidics with embedded microball lenses for parallel and high throughput multicolor fluorescence detection

We report a 3D microfluidic device with 32 detection channels and 64 sheath flow channels and embedded microball lens array for high throughput multicolor fluorescence detection. A throughput of 358 400 cells/s has been accomplished. This device is realized by utilizing solid immersion micro ball lens arrays for high sensitivity and parallel fluorescence detection. High refractive index micro ball lenses (n = 2.1) are embedded underneath PDMS channels close to cell detection zones in channels. This design permits patterning high N.A. micro ball lenses in a compact fashion for parallel fluorescence detection on a small footprint device. This device also utilizes 3D microfluidic fabrication to address fluid routing issues in two-dimensional parallel sheath focusing and allows simultaneous pumping of 32 sample channels and 64 sheath flow channels with only two inlets.     

A biochemical study on the effect of Riboflavin on cataractous rat lenses. II Proteins and Glutathione

Proteins and glutathione (GSH) levels were estimated in the experimental groups. Levels of both proteins and glutathione in the control and the treated groups were found to be significantly decreased compared to the normal group. The results show that supplementation of riboflavin has beneficial effect by alleviating the oxidant injuries to GSH and proteins, which are involved in the maintenance of transparency and protection of thiol groups of the lens. Thus, riboflavin has an active role in the lens metabolism and has a potential to improve the metabolic activity of the cataractous lenses.     

Miniaturization of dielectric liquid microlens in package

This study presents packaged microscale liquid lenses actuated with liquid droplets of 300-700 μm in diameter using the dielectric force manipulation. The liquid microlens demonstrated function focal length tunability in a plastic package. The focal length of the liquid lens with a lens droplet of 500 μm in diameter is shortened from 4.4 to 2.2 mm when voltages applied change from 0 to 79 V(rms). Dynamic responses that are analyzed using 2000 frames∕s high speed motion cameras show that the advancing and receding times are measured to be 90 and 60 ms, respectively. The size effect of dielectric liquid microlens is characterized for a lens droplet of 300-700 μm in diameter in an aspect of focal length.     

Photometric determination of camera exposures for motion picture work

A photometric method for the determination of camera exposures in motion picture work is described. The relation of exposure, object brightness and lens stop number is derived, and the proportionality constant empirically determined for “Pan Astro” lenses of two- and three-inch focal length. A nomographic chart of the exposure relation is given to simplify the determination of the lens stop number to be used for a given object brightness.     

Dielectrophoretic capture voltage spectrum for measurement of dielectric properties and separation of cancer cells

In this paper, a new dielectrophoresis (DEP) method based on capture voltage spectrum is proposed for measuring dielectric properties of biological cells. The capture voltage spectrum can be obtained from the balance of dielectrophoretic force and Stokes drag force acting on the cell in a microfluidic device with fluid flow and strip electrodes. The method was demonstrated with the measurement of dielectric properties of human colon cancer cells (HT-29 cells). From the capture voltage spectrum, the real part of Clausius-Mossotti factor of HT-29 cells for different frequencies of applied electric field was obtained. The dielectric properties of cell interior and plasma membrane were then estimated by using single-shell dielectric model. The cell interior permittivity and conductivity were found to be insensitive to changes in the conductivity of the medium in which the cells are suspended, but the measured permittivity and conductivity of cell membrane were found to increase with the increase of medium conductivity. In addition, the measurement of capture voltage spectrum was found to be useful in providing the optimum operating conditions for separating HT-29 cells from other cells (such as red blood cells) using dielectrophoresis.     

单模光纤光栅型分波器的近轴分析

对渐变折射率棒透镜和衍射光栅构成的单模光纤分波器的近轴分析,得到了分波方程.对确定的工作波长,根据分波方程选择渐变折射率棒透镜和衍射光栅参数,已制成了二波长和四波长分波器.实验与计算结果符合得很好.同理,也可以分析合波器.     

自旋极化电子源装置研究

自旋极化电子在许多研究领域有着广泛用途，目前国际上普遍采用光电离GaAs晶体产生自旋极化电子。本文介绍自旋极化电子产生的原理及一种设计简洁、结构简单的极化电子源装置。该十字型四通道装置内有一非常简单的900静电偏转器，新型的用于固定晶片的弹簧夹子可保证晶片加热均匀。用波长780nm圆偏振激光激活GaAs光电阴极可以产生极化电子，然后通过900静电偏转器及一组静电透镜将极化电子引、到反应区。     

Biosensing in a microelectrofluidic system using optical whispering-gallery mode spectroscopy

Label-free detection of biomolecules using an optical whispering-gallery mode sensor in a microelectrofluidic channel is simulated. Negatively charged bovine serum albumin is considered as the model protein analyte. The analyte transport in aqueous solution is controlled by an externally applied electrical field. The finite element method is employed for solving the equations of the charged species transport, the Poisson equation of electric potential, the equations of conservation of momentum and energy, and the Helmholtz equations of electromagnetic waves. The adsorption process of the protein molecules on the microsensor head surface is monitored by the resonance frequency shifts. Frequency shift caused by temperature variation due to Joule heating is analyzed and found to be negligible. The induced shifts behave in a manner similar to Langmuir-like adsorption kinetics; but the time constant increases due to the presence of the external electrical field. A correlation of the frequency shift, the analyte feed concentration in the solution, and the applied voltage gradient is obtained, in which an excellent linear relationship between the frequency shift and the analyte concentration is revealed. The applied voltage gradient enhances significantly the analyte concentration in the vicinity of the sensor surface; thus, the sensor sensitivity which has a power function of the voltage gradient with exponent 2.85 in the controlled voltage range. Simulated detection of extremely low protein concentration to the pico-molar level is carried out.     

Emission of electrons from cold metal surfaces

The results of Del Rosario on cold emission are shown to result from the fact that, through the attainment of specially good vacuum conditions and freedom from contamination, the cold electron current from the wire was suppressed up to field strengths greater than those at which measurable current was obtained in the work of previous observers. It was in fact suppressed beyond the point at which discharge started from points on the welding of the support. The results of Del Rosario are thus probably characteristic of conditions other than those pertaining to the wire, a conclusion which accounts for his current voltage curves. The formula of Fowler and Nordheim is found to apply in the measurable regions in form directly and in magnitude only if irregularities of the surface are such as to raise the field at the surface to a sufficiently high value. Breakdowns after intense heat treatment are studied and found to be caused by immeasurably small currents of electrons knocking ions from the anode. The erratic original curves obtained by previous investigators are found to be caused by successive breakdowns similar to those found after intense heating.     

Extensional flow of blood analog solutions in microfluidic devices

In this study, we show the importance of extensional rheology, in addition to the shear rheology, in the choice of blood analog solutions intended to be used in vitro for mimicking the microcirculatory system. For this purpose, we compare the flow of a Newtonian fluid and two well-established viscoelastic blood analog polymer solutions through microfluidic channels containing both hyperbolic and abrupt contractions∕expansions. The hyperbolic shape was selected in order to impose a nearly constant strain rate at the centerline of the microchannels and achieve a quasihomogeneous and strong extensional flow often found in features of the human microcirculatory system such as stenoses. The two blood analog fluids used are aqueous solutions of a polyacrylamide (125 ppm w∕w) and of a xanthan gum (500 ppm w∕w), which were characterized rheologically in steady-shear flow using a rotational rheometer and in extension using a capillary breakup extensional rheometer (CaBER). Both blood analogs exhibit a shear-thinning behavior similar to that of whole human blood, but their relaxation times, obtained from CaBER experiments, are substantially different (by one order of magnitude). Visualizations of the flow patterns using streak photography, measurements of the velocity field using microparticle image velocimetry, and pressure-drop measurements were carried out experimentally for a wide range of flow rates. The experimental results were also compared with the numerical simulations of the flow of a Newtonian fluid and a generalized Newtonian fluid with shear-thinning behavior. Our results show that the flow patterns of the two blood analog solutions are considerably different, despite their similar shear rheology. Furthermore, we demonstrate that the elastic properties of the fluid have a major impact on the flow characteristics, with the polyacrylamide solution exhibiting a much stronger elastic character. As such, these properties must be taken into account in the choice or development of analog fluids that are adequate to replicate blood behavior at the microscale.     

利用工作状态的二次效应评价机械设备性能

本文在对现有设备性能评价方法和指标进行分析的基础上,提出设备性能的评价指标应充分体现设备的工作性能,并以其在工作状态下的行为为依据,且需考虑工作状态对设备性能的影响,这样对设备性能所做出的评价才较为客观和合理。通过对滚齿机传动链性能评价方法和指标的分析研究证明,上述观点是正确的,提出的方法是可行的,所得出的结论具有实际意义。     

Effect of ketoacids on H<Subscript>2</Subscript>O<Subscript>2</Subscript> induced cataract

Cataract is one of the leading causes of visual disability often leading to blindness in the elderly population. One of the causes is oxidation of proteins present in lens, by hydrogen peroxide (H₂O₂). In the present study 100 goat lenses were analyzed to determine the protective efficacy of ketoacids, against the oxidative insult by H₂O₂. The ketoacids used were (pyruvate, alpha ketoglutarate and oxaloacetate), that are constantly produced endogenously. The lenses were incubated as control and experimental groups in TC-199 media for 72 hrs. H₂O₂ concentration of 10mM was used to induce cataract. The biochemical parameters measured were levels of malondialdehyde (MDA), a lipid peroxidation product and activity of glutathione peroxidase (G-Px), an enzymatic antioxidant. The results showed a significant increase in the levels of MDA and significant decrease in the activity of G-Px in the cataractous lenses as compared to control. After addition of ketoacids (pyruvate (10mM), alpha ketoglutarate (20mM) and oxaloacetate (20mM)) separately, the levels of MDA decreased significantly and the activity of G-Px increased significantly. The results suggest that the ketoacids can be very promising antioxidants for the treatment of cataract. They may also be useful in treating other disabilities related to acute and chronic oxidative stress.     

Signal constellations in the hyperbolic plane: A proposal for new communication systems

Signal constellations in the hyperbolic plane are provided as an alternative to traditional signal constellations in the Euclidean plane, since channels may actually exist for which the latter signal constellations are not as suitable as the former. A hyperbolic gaussian probability density function, based solely on geometrical considerations, is derived to determine the performance of the hyperbolic signal constellations. Benefits result from an approach conceived in terms of reduced signal-to-noise ratio, needed to achieve a prescribed error rate and equivalent optimum receiver complexity.     

Unifying telescope and microscope: A multi-lens framework with open data for modeling emerging events

Open data is becoming ubiquitous as governments, companies, and even individuals have the option to offer more or less unrestricted access to their non-sensitive data. The benefits of open data, such as accessibility and transparency, have motivated and enabled a large number of research studies and applications in both academia and industry. However, each open data only offers a single perspective, and its potential inherent limitations (e.g., demographic biases) may lead to poor decisions and misjudgments. This paper discusses how to create and use multiple digital lenses empowered by open data, including census data (macro lens), search logs (meso lens), and social data (micro lens), to investigate general real-world events. To reveal the unique angles and perspectives brought by each open lens, we summarize and compare the underpinning open data from eleven dimensions, such as utility, data volume, dynamic variability, and demographic fairness. Then, we propose an easy-to-use and generalized open data driven framework, which automatically retrieves multi-source data, extracts features, and trains machine learning models for the event specified by answering what, when, and where questions. With low labor efforts, the framework’s generalization and automation capabilities guarantee an instant investigation of general events and phenomena, such as disasters, sports events, and political activities. We also conduct two case studies, i.e., the COVID-19 pandemic and Great American Eclipse (see Appendix), to demonstrate its feasibility and effectiveness at different time granularities.     

毫米波近程主动扫描成像研究

文章介绍了一套Ka波段毫米波近程成像系统。振荡器产生频率为35GHz的毫米波,通过透镜天线照射到目标各点进行扫描,检测目标各点回波信号的强弱,采集信号并传输数据给计算机,最终得到目标各点的反射特性,做成毫米波图像。成像原理,即对低噪放和检波放大模块进行了性能测试,利用成像系统对携有金属锉刀的人体模型进行了成像实验得到可辨别的图像。此系统可用于机场,车站,码头的安全检查中。     

Fault-tolerant control for a class of linear interconnected hyperbolic systems by boundary feedback

This paper considers a fault-tolerant control problem for a class of interconnected linear hyperbolic partial differential equation systems. Both subsystem faults and coupling faults are considered. Firstly, the well-posedness of the faulty system is analyzed by using semigroup theory. Secondly, for the fault-free case, a stabilizing boundary feedback control based on small-gain theorem is proposed. Consequently, in the presence of faults, fault recoverability conditions are established that maintain the stability of the faulty systems. The fault-tolerant control strategies are also provided. A heat exchanger example is taken to illustrate the effectiveness and practicality of the proposed methods.