Collisional Population Trapping and Optical Deexcitation of Ytterbium Ions in a Radiofrequency Trap

Abstract

We describe and discuss experiments related to the phenomenon of population trapping of ytterbium ions in the extremely long-lived 4f¹³ 6s^{2 2}F_7/2 level. Ion clouds are confined in a radiofrequency trap in the presence of helium buffer gas. The experimental set-up permits electronic ion detection, the observation of resonance fluorescence, and optical excitation at alternating wavelengths to excite either the ²S_1/2–²P_1/2 resonance transition, or transitions of similar wavelength which provide optical deexcitation of ions from the ²F_7/2 level to the ground state. The observed dependence of the population trapping rates on helium pressure is attributed to the effect of fine structure mixing collisions. The transitions which deexcite ions from the ²F_7/2 state show Lorentzian lineshapes with widths of 6–10 GHz and resonance wavelengths which are in significant disagreement with tabulated level positions.     

Latex Film Matrix Systems with a Concentration Gradient for Controlled Drug Delivery

Abstract

Latex film matrix systems with a nonuniform drug distribution were prepared by a coating process. In this process a drug concentration gradient in the coating dispersion was generated by the programmable pumping of the latex into a drug reservoir which contained the drug and latex. The film matrix formed by the dispersion would have a built-in drug concentration gradient as the coating process proceeded. A mathematical model was developed to describe the concentration change of the active ingredient in the coating dispersion as a function of the spraying rate of the coating dispersion, the pumping rate of the latex into the drug reservoir, and the initial drug concentration in the dispersion. The applicability of this process was demonstrated by the controlled in vitro dissolution of acetaminophen from ethylcellulose latex film matrices formed on glass beads. The release profile of the active ingredient from the systems changed as the drug concentration gradient profile in the matrix was altered, and a higher drug concentration gradient in the matrix resulted in a slower release rate and a more linear release profile. A faster drug release rate can also be achieved by incorporating a highly water soluble ingredient in the concentration gradient matrix.     

Latex Film Matrix Systems with a Concentration Gradient for Controlled Drug Delivery

Latex film matrix systems with a nonuniform drug distribution were prepared by a coating process. In this process a drug concentration gradient in the coating dispersion was generated by the programmable pumping of the latex into a drug reservoir which contained the drug and latex. The film matrix formed by the dispersion would have a built-in drug concentration gradient as the coating process proceeded. A mathematical model was developed to describe the concentration change of the active ingredient in the coating dispersion as a function of the spraying rate of the coating dispersion, the pumping rate of the latex into the drug reservoir, and the initial drug concentration in the dispersion. The applicability of this process was demonstrated by the controlled in vitro dissolution of acetaminophen from ethylcellulose latex film matrices formed on glass beads. The release profile of the active ingredient from the systems changed as the drug concentration gradient profile in the matrix was altered, and a higher drug concentration gradient in the matrix resulted in a slower release rate and a more linear release profile. A faster drug release rate can also be achieved by incorporating a highly water soluble ingredient in the concentration gradient matrix.     

Modeling Resonances of Dielectric Spheres in the Terahertz Range

Technical Physics Letters - We have studied the resonance properties of dielectric spheres with subwavelength dimensions in the optical and terahertz frequency range. Distribution of the electric...     

Development and Characterization of a Diaphragm-Shaped Force Transducer for Static Force Measurement

There are different types of force transducers, used over the years, comprising of different principles and have different grades of uncertainty. Force transducers may be analog or digital and may be strain gauged, tuning fork type, piezoresistive type, Hall Effect based etc. Though different types of force transducers have been developed in last few decades, still strain gauged force transducers are used over the larger scale due to practical viability and reliability for force measurement. The paper describes low-cost indigenous development of a force transducer, which has been developed for a nominal capacity of 5 kN with ease of design and manufacturing. It has strain gauges applied at suitable locations to form a Wheatstone bridge. The force transducer has been calibrated according to the standard calibration procedures based on ISO 376 and IS 4169 standards. Measurement results and an uncertainty analysis have been presented. The uncertainty of measurement of the force transducer is found up to 0.06%. The paper also discusses the implications of applying multiple strain gauges at a single location in series to enhance the sensitivity of the force transducer. Two strain gauges are arranged in series for the given location and the sensitivity of the force transducer is enhanced. It also indicates that the uncertainty of measurement of the force transducer in such case is enhanced up to 0.05% or better to make force transducer suitable for most of metrological and industrial applications.     

Calibration of Radiation Sources and Detectors Over a Broad Range of Measurement of the Energy of Optical Radiation

Measurement Techniques - A method of calibration of devices used to measure energy by means of a calorimeter and reference photodiode is described. Experimental results of the calibration are...     

Design and Optical Trapping of a Biocompatible Propeller-like Nanoscale Hybrid

Designing nanoscale objects with the potential to perform externally controlled motion in biological environments is one of the most sought-after objectives in nanotechnology. Different types of chemically and physically powered motors have been prepared at the macro- and microscale. However, the preparation of nanoscale objects with a complex morphology, and the potential for light-driven motion has remained elusive to date. Here, we go a step forward by designing a nanoscale hybrid with a propeller-resembling shape, which can be controlled by focused light under biological conditions. Our hybrid, hereafter "Au@DNA-origami", consists of a spherical gold nanoparticle with self-assembled, biocompatible, two-dimensional (2D) DNA sheets on its surface. As a first step toward the potential utilization of these nanoscale objects as light-driven assemblies in biological environments, we show that they can be optically trapped, and hence translated and deposited on-demand, and that under realistic trapping conditions the thermally induced dehybridization of the DNA sheets can be avoided.     

光泵氦磁力仪测磁场梯度的新方法研究

本文通过分析推导出光泵氨磁力仪的共振曲线与磁场梯度的关系,并在此基础上提出一种新的测量磁场梯度的方法:用磁场线圈产生一个补偿磁场梯度,再用一套极值跟踪测试系统自动跟踪测试磁场梯度。     

光纤传感技术应用于轧制力测量的研究

中介绍一种光纤法布里-珀罗干涉式应变传感器，并对其应用于轧制力测量进行了研究。详细分析了该传感器的原理，导出了轧制力与光纤干涉腔反射光强的关系表达式。理论分析和实验结果表明，用这种光纤应变传感器测量轧制力是切实可行的，与传统的测量轧制力的方法比较，具有结构简单，抗干扰能力强，测量准确度高，灵敏度高等优点。     

光镊力谱系统微球位移的纳米精度测量

广泛用于生物单分子研究的光镊力谱技术,其皮牛级的力学测量性能依赖于光阱刚度和微球位移的精确测量.为实现纳米精度的位移测量能力,在分析背焦平面干涉法测量精度的基础上,提出了基于四象限光电探测器(QPD)和现场可编程门阵列(FPGA)开发板的测量方案,并建立了相应的测量系统.实验采用精密位移台驱动固定微球往复经过光阱,对系统的测量性能进行了标定.结果表明,该方案的探测灵敏度达到12.1 m V/nm,探测精度优于3 nm,探测分辨力小于1 nm,满足生物单分子拉伸力谱测试对微球位移探测的要求.     

Measurement of the Neutron Lifetime Using a Gravitational Trap and a Low-Temperature Fomblin Coating

We present a new value for the neutron lifetime of 878.5 ± 0.7_stat. ± 0.3_syst. This result differs from the world average value by 6.5 standard deviations and by 5.6 standard deviations from the previous most precise result. However, this new value for the neutron lifetime together with a β-asymmetry in neutron decay, A₀, of −0.1189(7) is in a good agreement with the Standard Model.     

Measurement of Surface Topography,Packing Density,and Surface Charge Distribution of an Electrostatically Deposited Powder Layer by Image Analysis of Fluorescent Latex Spheres

A novel method of nonintrusive measurement of surface profile, packing density, and surface charge distributions of a powder layer deposited on a substrate is reported. The method employs the deposition of electrostatically charged monodispersed fluorescent latex spheres (FLS), approximately 2 m in diameter, on the surface of: (1) the substrate before deposition, (2) the powder layer after deposition, and (3) the film formed by curing the powder layer. The surface topography in all cases was mapped using an epi-fluorescent microscope with a vertical resolution of - 2 m in the z axis and - 10 m in the x and y axes. An area of 1 cm 2 1 cm is scanned in 1 mm segments, providing approximately 100 data points per cm 2 for the surface topography. For each measurement of surface topography, the substrate was positioned on the microscope stage in a manner such that the reference points (x, y, and z) remained the same for all measurements of the substrate. The surface profiles, with respect to the same reference points, were plotted using Origin 6.0 software for 3D presentation of the topography. The method was also applied to map the surface charge density distribution of electrostatically charged surfaces. The FLS imaging method provides a new tool for examination of surface profiles, packing density, and charge distribution of powder layers on a microscopic scale not provided by optical or atomic force/electrostatic force microscopy (AFM/EFM). While AFM and EFM are very effective in providing similar information with nanometer resolution, they cannot be directly applied on a larger macroscopic scale to study powder layers and for a larger surface area (up to 1 cm 2 or greater) involving deposited particles in the range of 1-50 m in diameter. For AFM, the range in the z-axis is limited to - 3 m and the x-y scan area is limited to 100 m 2 100 m. The FLS method has a much wider range but it is operated manually; an automated scanning process is required for rapid measurement. A comparison of the FLS and EFM techniques as they apply to analyzing charge distribution on coal surfaces is presented.     

Measurement of Surface Topography, Packing Density, and Surface Charge Distribution of an Electrostatically Deposited Powder Layer by Image Analysis of Fluorescent Latex Spheres

A novel method of nonintrusive measurement of surface profile, packing density, and surface charge distributions of a powder layer deposited on a substrate is reported. The method employs the deposition of electrostatically charged monodispersed fluorescent latex spheres (FLS), approximately 2 µm in diameter, on the surface of: (1) the substrate before deposition, (2) the powder layer after deposition, and (3) the film formed by curing the powder layer. The surface topography in all cases was mapped using an epi-fluorescent microscope with a vertical resolution of ±2 µm in the z axis and ±10 µm in the x and y axes. An area of 1 cm ×1 cm is scanned in 1 mm segments, providing approximately 100 data points per cm 2 for the surface topography. For each measurement of surface topography, the substrate was positioned on the microscope stage in a manner such that the reference points (x, y, and z) remained the same for all measurements of the substrate. The surface profiles, with respect to the same reference points, were plotted using Origin 6.0 software for 3D presentation of the topography. The method was also applied to map the surface charge density distribution of electrostatically charged surfaces. The FLS imaging method provides a new tool for examination of surface profiles, packing density, and charge distribution of powder layers on a microscopic scale not provided by optical or atomic force/electrostatic force microscopy (AFM/EFM). While AFM and EFM are very effective in providing similar information with nanometer resolution, they cannot be directly applied on a larger macroscopic scale to study powder layers and for a larger surface area (up to 1 cm 2 or greater) involving deposited particles in the range of 1-50 µm in diameter. For AFM, the range in the z-axis is limited to ±3 µm and the x-y scan area is limited to 100 µm ×100 µm. The FLS method has a much wider range but it is operated manually; an automated scanning process is required for rapid measurement. A comparison of the FLS and EFM techniques as they apply to analyzing charge distribution on coal surfaces is presented.     

小型宽光谱低分辨率光谱仪器光学设计

光栅作为小型光谱仪器分光系统的核心,采用不同种类的光栅制作分光仪器时其结构形式也不尽相同.文中为设计一个工作波段在340-800 nm,分辨率优于15nm,谱面长度28.71 mm的比色仪光学系统,通过对比常见光谱仪结构的优缺点,选择平场凹面光栅作为最终的结构形式,采用长波通滤光片实现对二级光谱重叠的消除,并对比色仪光...     

Photon Correlation Measurement of Ion Oscillation Frequencies in a Combined Trap

Abstract

We present experimental verification of the oscillation frequencies of magnesium ions in a combined trap for a wide range of a.c. voltages and magnetic fields. We employ a new technique to measure these trap resonances using the distribution of time intervals between consecutively detected fluorescence photons.     

Two-step Optical Excitation for Doppler Linewidth Reduction and Motion Study of Ions Stored in a Paul Trap

Abstract

Atomic thorium ions were stored in an r.f. quadrupole trap and excited by tunable laser light. One-step and two-step excitation schemes were applied; a four to eightfold reduction of the Doppler linewidth is obtained for the two-step scheme with essentially no loss in signal strength. The Doppler-free two-photon transition was also observed. The lineshapes were calculated using a simple model; the observed profiles were well reproduced proving that the velocity and acceleration features of stored ions are properly accounted for. A further reduction of the Doppler linewidth is expected for the two-step method if a short lived intermediate level is used.     

He-Ne激光光阱及对微粒子的操纵北京市自然

分析了He-Ne激光光阱对微粒子的作用.在所建立的He-Ne激光微束的实验装置上用光阱捕获了酵母细胞和空心电介小球,实验验证了光阱的力学效应.实验表明该光阱能实现对微粒子的捕捉、旋转和翻转,能同时捕获多个粒子.从理论和实验上研究了He-Ne激光光阱作用于微粒子的力学效应.     

YBCO超导块材磁浮力的测试与分析

超导磁悬浮力((→F))是YBCO超导块材应用研究的重要性能参数之一.影响其值大小的因素不仅与超导体的临界电流密度(Jc)、超导块的直径(r)和永磁体在超导体附近磁场梯度(dH/dZ)有关,也与测试方法有密切的联系.本研究测试了磁浮力与磁铁和样品的间距及磁浮力随保留时间的变化曲线.实验结果表明,磁铁在距样品5 mm停留时,磁浮力随着保留时间的延长总的变化趋势是降低的,但逐渐趋于稳定,在30 min后,样品磁浮力每10 min内衰减率小于1%.