Uncertainty Budget for the NIST Hybrid Humidity Generator

A detailed uncertainty budget for the new hybrid humidity generator (HHG) that has been constructed at the National Institute of Standards and Technology is presented. The HHG generates frost/dew points from ?70?°C to +85?°C using calibration gas flows up to 150 L?·? min^?1. For frost/dew points above ?15?°C, the two-pressure method is employed, and for frost points at or below ?15?°C, the divided-flow method is used (hence, the name ??hybrid??). The total expanded (k?=?2) uncertainty is estimated for HHG generation of the following quantities: frost/dew point, mole fraction, and relative humidity. The total uncertainty is estimated separately for the two-pressure and divided-flow methods.     

A 12-Mc, Nine-Bit Digital Function Generator

This paper describes some developed equipment found very useful in evaluating circuits that require digital inputs. For example, D-A converters are generally tested by using their associated A-D converter as a test-signal source. Since the A-D converter itself introduces errors, the measurement of analog input and output indicates over-all performance but not individual converter performance. The digital function generator allows separate evaluation of D-A converters by synthesizing useful test functions from discrete samples. Comparison of the known input with the output gives an accurate performance check. The present equipment generates up to sixteen different samples, represented by nine-bit words in parallel form, at a word rate of 12 Mc. A discussion of useful test functions for determining D-A converter linearity and transient response will include discussion of digital sine waves, ramps, and step functions. Although D-A converter evaluation is stressed, the equipment is also useful for other tasks.     

Performance and Validation Tests on the NIST Hybrid Humidity Generator

A new humidity generator has been constructed at the National Institute of Standards and Technology. Once fully operational, the NIST hybrid humidity generator (HHG) will generate frost/dew points from −70°C to +85°C using calibration gas-flow rates up to 150 standard liters per minute and is expected to outperform the present humidity generator at NIST in terms of accuracy. The HHG combines the two-pressure and divided-flow humidity-generation techniques (hence, the name “hybrid”). The centerpiece of the HHG is a heat exchanger/saturator that is immersed in a temperature-controlled bath stable to within 1 mK. For dew/frost-point temperatures above −15°C, the two-pressure principle is employed. For frost points at or below −15°C, the water-vapor/air mixture is produced by mixing metered streams of moist air produced by the two-pressure method with purified, dry air. A series of performance and validation tests on the HHG in the two-pressure mode, including measurements of temperature gradients and pressure stability in the generator under various operating conditions, and comparison of the humidity generated by the HHG to that generated by the other NIST humidity-generation standards, are reported.     

基于VB6.0的函数发生器自动校准系统

近年来,随着数字化技术的迅速发展和广泛使用,国内外厂家不断推出带1EEFA88、RS232和USB通讯接口的可自动控制的函数信号发生器。这为函数发生器的自动校准奠定了基础。利用自动校准系统对函数发生器进行校准可以提高工作效率和减少校准时的人为因素影响。本文论述了基于VB6．0的函数发生器自动校准系统的组成和使用方法。     

函数信号发生器频率偏差校准值的不确定度评定

本文以实例论述函数信号发生器频率校准值的不确定度评定过程。     

脚踏健身传动加热装置

根据国家倡导节能环保的需求,提出了健身和加热为一体的生活理念,设计了新型的脚踏健身传动加热装置,由人蹬踏踏板,通过人力驱动压缩机使汽化体制冷剂在吸收大气能量后被压缩成为高压高能量的气体,然后在冷凝作用下将热量传递给水,从而加热水。因此,健身与加热同步进行的方式,为时下绿色节能提供了新的思路。     

Effect of Surface Coating on the Photocatalytic Function of Hybrid CdS–Au Nanorods

Hybrid semiconductor–metal nanoparticles are interesting materials for use as photocatalysts due to their tunable properties and chemical processibility. Their function in the evolution of hydrogen in photocatalytic water splitting is the subject of intense current investigation. Here, the effects of the surface coatings on the photocatalytic function are studied, with Au‐tipped CdS nanorods as a model hybrid nanoparticle system. Kinetic measurements of the hydrogen evolution rate following photocatalytic water reduction are performed on similar nanoparticles but with different surface coatings, including various types of thiolated alkyl ligands and different polymer coatings. The apparent hydrogen evolution quantum yields are found to strongly depend on the surface coating. The lowest yields are observed for thiolated alkyl ligands. Intermediate values are obtained with L‐glutathione and poly(styrene‐co‐maleic anhydride) polymer coatings. The highest efficiency is obtained for polyethylenimine (PEI) polymer coating. These pronounced differences in the photocatalytic efficiencies are correlated with ultrafast transient absorption spectroscopy measurements, which show a faster bleach recovery for the PEI‐coated hybrid nanoparticles, consistent with faster and more efficient charge separation. These differences are primarily attributed to the effects of surface passivation by the different coatings affecting the surface trapping of charge carriers that compete with effective charge separation required for the photocatalysis. Further support of this assignment is provided from steady‐state emission and time‐resolved spectral measurements, performed on related strongly fluorescing CdSe/CdS nanorods. The control and understanding of the effect of the surface coating of the hybrid nanosystems on the photocatalytic processes is of importance for the potential application of hybrid nanoparticles as photocatalysts.     

Hybrid Nanoscopy of Hybrid Nanomaterials

The combination of complementary techniques to characterize materials at the nanoscale is crucial to gain a more complete picture of their structure, a key step to design and fabricate new materials with improved properties and diverse functions. Here it is shown that correlative atomic force microscopy (AFM) and localization‐based super‐resolution microscopy is a useful tool that provides insight into the structure and emissive properties of fluorescent β‐lactoglobulin (βLG) amyloid‐like fibrils. These hybrid materials are made by functionalization of βLG with organic fluorophores and quantum dots, the latter being relevant for the production of 1D inorganic nanostructures templated by self‐assembling peptides. Simultaneous functionalization of βLG fibers by QD655 and QD525 allows for correlative AFM and two‐color super‐resolution fluorescence imaging of these hybrid materials. These experiments allow the combination of information about the topography and number of filaments that compose a fibril, as well as the emissive properties and nanoscale spatial distribution of the attached fluorophores. This study represents an important step forward in the characterization of multifunctionalized hybrid materials, a key challenge in nanoscience.     

An Exponential Current Generator

A current getlerator has been constructed from two operational amplifiers and a thermostated twin transistor. The current is an exponential function (5) of a controlling voltage. At currents greater than 100 ?A, the transistor exhibited a resistive effect, for which it was possible to compensate for internally. The generator was tested over the current range 30 nA-15 mA and was found to perform almost ideally, with a slope of 1.008 of the theoretical and a standard deviation of 0.3 perceht. Some preliminary measurements have shown the generator to be useful down to 10 pA. The use of the generator for electrochemical kinetic measurements is described.     

Harmonic Analyzer/Generator

A method of measuring the phase angle and magnitude of "n" harmonics corresponding to a periodic signal is described. The method includes the generation of sinusoidal bursts to reproduce significant components of distorted and complex signals; burst amplitude, burst initial phase, and burst frequency correspond, respectively, to harmonic amplitude, harmonic phase angle, and harmonic frequency.     

Pulse Generator and Flip-Flops

A simple pulse generator can be constructed using IC gates. Such a pulse generator is described and its use to construct edge-triggered flip-flops is demonstrated. A flip-flop for use in a phase comparator is described. Desirable and undesirable characteristics for this application are discussed and examples of R-S and J-K flip-flops given.     

A Hazard-Free Walsh-Function Generator

Outputs of a Gray code counter are used to synthesize digital Walsh functions that are free from hazards. This method, which produces sequency-ordered Walsh functions, also uses a binary code to select the order.     

A Pseudo-Random Noise Generator

If the individual outputs of a cascade of bistable multivibrators are combined, we get useful waveshape, spectral, and probability-density function properties. Four modes are examined: equal amplitude, amplitude proportional to square root of frequency, amplitude proportional to frequency, and amplitude inversely proportional to frequency.     

高压脉冲发生器

本文介绍一种高压脉冲发生器,它适用于一些储能设备中高压脉冲放电开关的触发,引爆高压火花隙雷管等场所.文中较为详细地介绍了仪器各个组成部分的电路原理,同时结合研制过程中实测的一些数据,具体分析了引起高压脉冲输出时产生延迟和晃动的原因.     

High Performance Flexible Actuator of Urchin‐Like ZnO Nanostructure/Polyvinylenefluoride Hybrid Thin Film with Graphene Electrodes for Acoustic Generator and Analyzer

A bass frequency response enhanced flexible polyvinylidene fluoride (PVDF) based thin film acoustic actuator is successfully fabricated. High concentrations of various zinc oxide (ZnO) is embedded in PVDF matrix, enhancing the β phase content and the dielectric property of the composite thin film. ZnO acts as a nucleation agent for the crystallization of PVDF. A chemical vapor deposition grown graphene is used as electrodes, enabling high electron mobility for the distortion free acoustic signals. The frequency response of the fabricated acoustic actuator is studied as a function of the film thickness and filler content. The optimized film has a thickness of 80 μm with 30 wt% filler content and shows 72% and 42% frequency response enhancement in bass and midrange compared to the commercial PVDF, respectively. Also, the total harmonic distortion decreases to 82% and 74% in the bass and midrange regions, respectively. Furthermore, the composite film shows a promising potential for microphone applications. Most of all, it is demonstrated that acoustic actuator performance is strongly influenced by degree of PVDF crystalline.     

Reference Waveform Flat Pulse Generator

The NBS Reference Flat Pulse Generator (RFPG) is used to transfer dc voltage and resistance standards to the nanosecond domain. It provides a step amplitude of 1.000 V (open circuit) from a source impedance of 50.0?. The transition duration is 600 ps, and all perturbations are damped out to less than ±10 mV within 5 ns. It can also be used as a time interval transfer standard.     

Microcomputer-Controlled Precision Pneumatic Pressure Generator

An increasing variety of avionics require precision pneumatic pressure stimuli during organization and intermediate maintenance. The accuracy and long-term stability requirements approach the best mercurial standards. Pressure stimuli must be coordinated and varied at precise rates that are beyond the frequency response of mercury columns and many electromechanical sensors. Test systems are frequently required to simultaneously monitor and evaluate unit under test (UUT) response and generate pneumatic stimuli. In addition, the environment is frequently hostile, maintainability is paramount, performance must always be known and warmup time must be nil. Comprehensive trade studies, tests, and analyses were performed. This initial work indicated a new pressure generator should be a "smart" instrument and should use a pressure sensor not a density sensor. Current field and production experience indicates performance objectives have been exceeded and this new type of precision pressure generator can be readily incorporated in a variety of test systems or be used "stand-alone". This paper discusses the design implementation, features, and characteristics of this microcomputer controlled precision pneumatic pressure generator-a new "smart" test instrument.     

A Precision Digital Phase Generator

The design of a digital phase generator which produces two outputs of frequency f, between which the phase shift can be varied from 0 to 360° in steps of 1°, from an input frequency of 360f, is described. The system design is described in detail. The circuit design and the choice of the circuit elements are discussed. Fast logic elements have been used in the construction of the instrument. A brief analysis of the performance of the system is also given. From the experimental results, which agree with the calculated performance, it is found that the accuracy of the system varies and is as high as 0.05 percent when the phase shift is 359°. The accuracy of the system is limited only by the propagation delays of the logic elements used and therefore can be improved by using faster logic elements.