Short-term Stability Measurements Research Articles

Advanced field emission measurement techniques for research on modern cold cathode materials and their applications for transmission-type x-ray sources.

We report on the functional capabilities of our field emission (FE) measurement systems. The samples are prepared and inserted under clean room conditions and can be precisely xyz-positioned, heat-treated, and investigated in different vacuum environments and temperatures. The FE scanning microscope is a unique microscope being used for the localization of FE sites with high lateral resolution by means of extraction voltage U(x, y) or emission current I(x, y) maps over the cathode area of 25 × 25 mm2 and measuring the FE properties of localized emission sites or individual emitters. In contrast, the integral measurement system with the luminescent screen provides real-time integral information about the distribution of emission sites over the whole cathode during long- and short-term current stability measurements, thus allowing us to investigate the properties of various materials and their applications. Commissioning results with the upgraded systems using a silicon emitter array and a point-type graphene emitter will be given to demonstrate that both FE measurement techniques are very useful for an improved understanding and tailoring of materials for applications. The results showed that point-type graphene emitters are more preferable for practical applications. Using simulation software, a suitable triode configuration for point emitters was designed, and a current transmission ratio of ∼100% was obtained. The FE current stability of graphene emitters at pressures >10-3 Pa can be improved by heating the cathode at 100 °C-300 °C for 1 min-30 min. Finally, point-type graphene film emitters were used for transmission-type x-ray sources, and their applications in imaging and fluorescence spectroscopy are presented.

Synchronous multi-color laser network with daily sub-femtosecond timing drift

Filming atoms in motion with sub-atomic spatiotemporal resolution is one of the distinguished scientific endeavors of our time. Newly emerging X-ray laser facilities are the most likely candidates to enable such a detailed gazing of atoms due to their angstrom-level radiation wavelength. To provide the necessary temporal resolution, numerous mode-locked lasers must be synchronized with ultra-high precision across kilometer-distances. Here, we demonstrate a metronome synchronizing a network of pulsed-lasers operating at different center wavelengths and different repetition rates over 4.7-km distance. The network achieves a record-low timing drift of 0.6 fs RMS measured with 2-Hz sampling over 40 h. Short-term stability measurements show an out-of-loop timing jitter of only 1.3 fs RMS integrated from 1 Hz to 1 MHz. To validate the network performance, we present a comprehensive noise analysis based on the feedback flow between the setup elements. Our analysis identifies nine uncorrelated noise sources, out of which the slave laser’s inherent jitter dominates with 1.26 fs RMS. This suggests that the timing precision of the network is not limited by the synchronization technique, and so could be much further improved by developing lasers with lower inherent noise.

Virtual phantom magnetic resonance imaging (ViP MRI) on a clinical MRI platform.

The purpose of this study was to implement Virtual Phantom Magnetic Resonance Imaging (ViP MRI), a technique that allows for generating reference signals in MR images using radiofrequency (RF) signals, on a clinical MR system and to test newly designed virtual phantoms. MRI experiments were conducted on a 1.5 T MRI scanner. Electromagnetic modelling of the ViP system was done using the principle of reciprocity. The ViP RF signals were generated using a compact waveform generator (dimensions of 26 cm × 18 cm × 16 cm), connected to a homebuilt 25 mm-diameter RF coil. The ViP RF signals were transmitted to the MRI scanner bore, simultaneously with the acquisition of the signal from the object of interest. Different types of MRI data acquisition (2D and 3D gradient-echo) as well as different phantoms, including the Shepp-Logan phantom, were tested. Furthermore, a uniquely designed virtual phantom - in the shape of a grid - was generated; this newly proposed phantom allows for the investigations of the vendor distortion correction field. High quality MR images of virtual phantoms were obtained. An excellent agreement was found between the experimental data and the inverse cube law, which was the expected functional dependence obtained from the electromagnetic modelling of the ViP system. Short-term time stability measurements yielded a coefficient of variation in the signal intensity over time equal to 0.23% and 0.13% for virtual and physical phantom, respectively. MR images of the virtual grid-shaped phantom were reconstructed with the vendor distortion correction; this allowed for a direct visualization of the vendor distortion correction field. Furthermore, as expected from the electromagnetic modelling of the ViP system, a very compact coil (diameter ~ cm) and very small currents (intensity ~ mA) were sufficient to generate a signal comparable to that of physical phantoms in MRI experiments. The ViP MRI technique was successfully implemented on a clinical MR system. One of the major advantages of ViP MRI over previous approaches is that the generation and transmission of RF signals can be achieved with a self-contained apparatus. As such, the ViP MRI technique is transposable to different platforms (preclinical and clinical) of different vendors. It is also shown here that ViP MRI could be used to generate signals whose characteristics cannot be reproduced by physical objects. This could be exploited to assess MRI system properties, such as the vendor distortion correction field.

Water-Gated n-Type Organic Field-Effect Transistors for Complementary Integrated Circuits Operating in an Aqueous Environment.

The first demonstration of an n-type water-gated organic field-effect transistor (WGOFET) is here reported, along with simple water-gated complementary integrated circuits, in the form of inverting logic gates. For the n-type WGOFET active layer, high-electron-affinity organic semiconductors, including naphthalene diimide co-polymers and a soluble fullerene derivative, have been compared, with the latter enabling a high electric double layer capacitance in the range of 1 μF cm–2 in full accumulation and a mobility–capacitance product of 7 × 10–3 μF/V s. Short-term stability measurements indicate promising cycling robustness, despite operating the device in an environment typically considered harsh, especially for electron-transporting organic molecules. This work paves the way toward advanced circuitry design for signal conditioning and actuation in an aqueous environment and opens new perspectives in the implementation of active bio-organic interfaces for biosensing and neuromodulation.

The Autonomous Cryocooled Sapphire Oscillator: A Reference for Frequency Stability and Phase Noise Measurements

The Cryogenic Sapphire Oscillator (CSO) is the microwave oscillator which feature the highest short-term stability. Our best units exhibit Allan deviation σy(τ) of 4.5x10-16 at 1s, ≈ 1.5x10-16 at 100 s ≤ t ≤ 5,000 s (floor), and ≤ 5x10-15 at one day. The use of a Pulse-Tube cryocooler enables full two year operation with virtually no maintenance.Starting with a short history of the CSO in our lab, we go through the architecture and we provide more details about the resonator, the cryostat, the oscillator loop, and the servo electronics.We implemented three similar oscillators, which enable the evaluation of each with the three- cornered hat method, and provide the potential for Allan deviation measurements at parts of 10-17 level. One of our CSOs (ULISS) is transportable, and goes with a small customized truck. The unique feature of ULISS is that its σy (τ) can be validated at destination by measuring before and after the roundtrip. To this extent, ULISS can be regarded as a traveling standard of frequency stability.The CSOs are a part of the Oscillator IMP project, a platform dedicated to the measurement of noise and short-term stability of oscillators and devices in the whole radio spectrum (from MHz to THz), including microwave photonics. The scope spans from routine measurements to the research on new oscillators, components, and measurement methods.

Nickel cobalt hydroxide nanoflakes as catalysts for the hydrogen evolution reaction

The activity of NixCo10−x/C catalysts for the hydrogen evolution reaction (HER) was evaluated. The NixCo10−x/C (0≤x≤ 10) nano-catalysts were synthesized by a water-in-oil microemulsion method and were then characterized by thermogravimetric analysis (TGA), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The control of a metal loading of ca. 30wt% on carbon was confirmed for all catalysts from TGA, while TEM images and XRD patterns revealed the formation of nickel cobalt hydroxide nano-flakes with a preferential growth along the (100) and (010) directions. The electrochemical investigations in 0.1M NaOH confirmed the interaction between nickel and cobalt in the catalytic materials, and their activity towards the HER. The catalytic activity increased regularly with the increase of the cobalt content in the NixCo10−x/C materials. The short term stability measurements performed by chronoamperometry revealed that dissolution of cobalt occurred. Hence, amongst the nickel cobalt hydroxides synthesized, Ni5Co5/C and Ni7Co3/C catalysts were found to present a good compromise between catalytic activity for the HER and stability.

Lowest flicker-frequency floor measured on BVA oscillators

In this paper we will present the results of the time-domain measurement of short-term frequency stability on 7 ultra-stable 5-MHz Boitier a Vieillissement Ameliore (BVA, improved aging case) oscillators. The measurements took place in the Institute of Photonics and Electronics (IPE) in July 2008 and was a continuation of the stability measurements of BVA oscillators reported in our previous work.

On the measurement of frequency and of its sample variance with high-resolution counters

A frequency counter measures the input frequency ν¯ averaged over a suitable time τ, versus the reference clock. High resolution is achieved by interpolating the clock signal. Further increased resolution is obtained by averaging multiple frequency measurements highly overlapped. In the presence of additive white noise or white phase noise, the square uncertainty improves from σν2∝1∕τ2 to σν2∝1∕τ3. Surprisingly, when a file of contiguous data is fed into the formula of the two-sample (Allan) variance σy2(τ)=E{12(y¯k+1−y¯k)2} of the fractional frequency fluctuation y, the result is the modified Allan variance mod σy2(τ). But if a sufficient number of contiguous measures are averaged in order to get a longer τ and the data are fed into the same formula, the results is the (nonmodified) Allan variance. Of course interpretation mistakes are around the corner if the counter internal process is not well understood. The typical domain of interest is the the short-term stability measurement of oscillators.

Cut-Flower Exports, Female Labor, and Community Participation in Highland Ecuador

In the 1980s and 1990s Latin American economies and societies underwent a profound transformation caused by the advent of economic neoliberalism. Upon the recommendation of the International Monetary Fund, the World Bank, and bilateral donors, most Latin American governments implemented structural adjustment programs as a cure for the ills of import-substitution industrialization and burgeoning foreign debt. Along with short-term stabilization measures, these programs included broader reforms designed to reduce state economic intervention and increase national integration with global markets. At the regional level, they reduced inflation rates and triggered a rapid growth of exports and foreign direct investment (Mortimer, 2000; Macario, 2000). They failed, however, to produce a significant positive effect on national economic growth and employment. Indeed, urban unemployment rates increased in the 1990s (Economic Commission for Latin America and the Caribbean, cited in Stark, 2001: Table 4). Moreover, structural adjustment led to a decline in real minimum wages and cuts in government social services. The result was an increase in income inequalities

Burundi: 2002 Article IV Consultation and Use of Fund Resources-- Request for Post-Conflict Emergency Assistance-- Staff Report; Staff Statement; Public Information Notice and Press Release on the Executive Board Discussion; and Statement by the Executive Director for Burundi

This paper assesses Burundi’s 2002 Article IV Consultation and a Request for Post-Conflict Emergency Assistance. Implementation of a Staff-Monitored Program in 2001 was hampered by continued instability and a consequent holding back of donor support. Fiscal performance weakened in the latter part of 2001, mainly reflecting expenditure overruns. The external current account deficit also worsened, and the overall balance of payments was financed by a drawdown of official reserves and a buildup of external debt arrears. The program for the remainder of 2002 and the first half of 2003 focuses on key short-term stabilization measures.

Propping Up Pisa—Part Two

This paper describes some of the engineering aspects of the work of the Italian Prime Minister's Commission for stabilizing the Leaning Tower of Pisa, and is presented in two parts. Part One (Volume 3, Number 2), presented a brief history of the construction and subsequent behaviour of the Tower as deduced from careful measurements made on the masonry courses. The deduced history of inclination of the Tower has been used to calibrate a sophisticated computer model of the Tower and underlying ground. Some surprising findings from recent studies of the motion of the Tower were presented. Part Two of the paper describes how the studies presented in Part One were used in developing the short-term stabilization measures that have been implemented by the Commission. Measurements made on the response of the Tower to these measures are presented. Finally, the work of the Commission in developing a permanent solution is summarized.

Propping Up Pisa—Part One

This paper describes some of the engineering aspects of the work, of the Italian Prime Minister's Commission for stabilizing the leaning tower of Pisa, and is presented in two parts. Part One presents a brief history of the construction and subsequent behaviour of the Tower as deduced from careful measurements made on the masonry courses. The deduced history of inclination of the Tower has been used to calibrate a sophisticated computer model of the Tower and underlying ground. Some surprising findings of recent studies of the motion of the Tower are presented. Part Two of the paper describes how these studies were used in developing the short-term stabilization measures that have been implemented by the Commission. Measurements made on the response of the Tower to these measures are presented. Finally, the work of the Commission in developing a permanent solution is summarized.

Reducing the Role of the State in the Economy: A Conceptual Exploration of IMF and World Bank Prescriptions

A policy and scholarly consensus is emerging on reducing the role of the state in the economy, but with relatively little consideration of its meaning and potential consequences. Six different forms of state economic intervention are distinguished in this article (influence, regulation, mediation, distribution, production, and planning) and combined to characterize different national economic regimes. IMF and World Bank recommendations for policy reform are then identified, and the consequences of those recommendations are assessed for different forms of economic intervention. On balance, stabilization and structural adjustment programs would appear to facilitate a major continuation of some forms of intervention (influence and mediation), redirect others (regulation, mediation, and distribution), and reduce those associated with state production and planning. These differential effects of the programs have far-reaching political implications, can be internally inconsistent, and are not necessarily conducive to development. In nearly every developing country in the world today, short-term stabilization measures, structural adjustment programs, liberalization efforts, and economic reforms are being considered, attempted, or adopted. Although there is tremendous variation in the details of the programs being initiated, nearly all entail a reduced role for the state in the economy (especially in the area of expenditures and ownership of productive enterprises) and greater reliance on market mechanisms (especially in the areas of exchange rate adjustment, trade liberalization, and the use of subsidies). These tendencies are a far cry from the extensive state interventionism, economic nationalism, and state socialist experimentation found in much of the developing world during the 1960s and 1970s. These policy reforms have been accompanied and strongly encouraged by the official reports, studies, and declarations of the major international financial organizations (most notably the World Bank and the IMF), a number of private transna

Characterization of phosphorus liquid-metal ion source as a dopant source in focused ion beam systems

Characteristics of a phosphorus liquid-metal ion source (LMIS) for use in focused ion beam systems was investigated because of its potential as an n-type dopant for integrated circuit device fabrication. A continuous lifetime of more than 33 h was recorded as a part of the source stability measurement. Short-term stability measurements indicated a very stable beam emission during its operation. Three different emitter tip radii of 2.5, 5.0, and 10 μm were selected to examine phosphorus beam emission characteristics. Mass spectrum measurements were used to examine phosphorus ion content and beam stability by repeat scanning. Steep current-voltage characteristics were observed for 5.0- and 10-μm emitter tip radii. The beam purity was characterized with Auger electron spectroscopy and a scanning electron microprobe by analysis of the deposited beam on a flat silicon substrate. Microstructure analysis by optical metallography indicated no liquid-metal corrosion on the emitter tip. A thorough analysis was carried out on beam purity and metallurgical aspects of LMIS in order to develop a more reliable phosphorus liquid-metal ion source.

Subharmonic Sampling for the Measurement of Short-Term Stability of Microwave Oscillators

The use of digital techniques for the precise measurement of medium- and short-term frequency stability of oscillators requires good resolution of the frequency counter. In the case of microwave oscillators, this is often preceded by some form of down-conversion. This paper is concerned with the theoretical principles, description, operation, and performance of a down-conversion system based on the subharmonic sampling technique. The system is intended for use on microwave oscillators with good frequency-stability performance and has as main features the use of a single frequency-stable reference oscillator and a pulse generator-sampler which allows power optimization of the subharmonic selected. The complete experimental system is presented and the limitations are discussed.

Automatic measurement of fluctuations of optical sources by means of a microprocessor-controlled apparatus

Presents a microprocessor-controlled apparatus for the measurement of short and long term stability of pulsed optical sources. The system measures the energy of a pre-set number of events and calculates the mean value and standard deviation of the sample. The operation is repeated for a pre-set number of samples. The calculated values are shown by means of an x-t recorder. A frequency histogram is also shown for each sample, by means of an on-line monitor.

Discipline as the central objective of economic policy: An essay on the economic programme of the Argentine government since 1976

This paper evaluates the economic policies adopted by the Argentine government since the coup of 1976, in the light of that administration's view of the nature and causes of the preceding economic and political dislocations. It outlines the interpretation proposed by liberal ideologists which traced the origins of the problem to economic distortions that had built up over a 30-yr period, and that were considered inextricably bound up with the political strategies characteristic of Peronism. The far-reaching and highly ideological character of this interpretation, linking together the economic and the political, found favour with a military government convinced that only very profound structural changes could rescue Argentina from its mid- 1970s predicament, and that viewed economic policy not so much as an end in itself, but as an integral part of a political project centred on the eradication of the Peronist legacy. Viewed in this context, although short-term economic stabilization measures were regarded as important, they were not always given the highest priority by economic managers. A more important explanation of policy choices can be derived from the long-term prescriptions given by liberal economic doctrines, even where these rested on assumptions that were far removed from the realities of Argentine economic structure. Previous policy objectives such as the promotion of industrial development, and an explicit commitment to the acceleration of economic growth have been dropped, in preference for the re-establishment of a stable economic order. Various key measures of economic policy — ‘openness’ and financial reform — are best viewed as new ways to introduce more effective discipline into society. Nevertheless the paper recognizes that at various points lack of success in achieving short-term stabilization goals may have forced the authorities to modify secondary aspects of their policies, although without ever abandoning their underlying ideological commitments. Conflicts between short-term objectives and the logic of the overall ideological project may prove crucial in determining the eventual outcome of this far-reaching experiment.

Spectral and Short Term Stability Measurements

The noise performance of an oscillator can be given either in the spectral or in the time domain. Two types of apparatus are generally necessary to measure these noise characteristics, spectral analyzers and frequency counters. The system described uses spectral density to time domain conversion and measures both the short term frequency stability and the phase spectral density of an oscillator. Bias functions, depending on the spectral density, are calculated. They are used to determine systematic errors introduced by the apparatus.

Short-term frequency stability of an L band oscillator with a superconducting cavity

An L band oscillator with a superconducting cavity is described, and the measurement of the oscillator's short-term frequency stability is presented. The sideband power density is ?120 dB/Hz relative to the carrier at modulation frequencies greater than 1 kHz from the carrier.

Two-Stage Self-Limiting Series Mode Type Quartz-Crystal Oscillator Exhibiting Improved Short-Term Frequency Stability

A simplified model of the transistor sustaining stage employed in common quartz-crystal oscillators is presented. Examination of the model, including associated noise sources, provides an explanation for general differences observed in the output-frequency spectra of several types of widely used self-limiting crystal oscillator circuits. A self-limiting quartz-crystal oscillator circuit configuration is described that has been specifically designed to exhibit simultaneously each of the three important circuit characteristics necessary for improved oscillator short-term frequency/phase stability: large value of oscillator resonator loaded Q, adequate suppression of 1/f flicker-of-phase type noise, and improvement in oscillator ultimate signal-to-noise ratio. Several models of the oscillator circuit have been constructed employing high quality third overtone 5-MHz AT- and BT-cut quartz resonators. Measurement of oscillator short-term frequency stability using conventional phase lock and sampling techniques confirm attainment of substantial improvement in oscillator short-term frequency stability when compared to conventional self-limiting oscillator circuits.