A determination of the molar gas constant R by acoustic thermometry in helium

We have determined the acoustic and microwave frequencies of a misaligned spherical resonator maintained near the temperature of the triple point of water and filled with helium with carefully characterized molar mass M = (4.002 6032 ± 0.000 0015) g mol-1, with a relative standard uncertainty ur(M) = 0.37×10-6. From these data and traceable thermometry we estimate the speed of sound in our sample of helium at TTPW = 273.16 K and zero pressure to be u0 2 = (945 710.45 ± 0.85) m2 s-2 and correspondingly deduce the value R = (8.314 4743 ± 0.000 0088) J mol-1 K-1 for the molar gas constant. We estimate the value k = R/NA = (1.380 6508 ± 0.000 0015) × 10-23 J K-1 for the Boltzmann constant using the currently accepted value of the Avogadro constant NA. These estimates of R and k, with a relative standard uncertainty of 1.06 × 10-6, are 1.47 parts in 106 above the values recommended by CODATA in 2010

Characterising poroelastic materials in the ultrasonic range - A Bayesian approach

Acoustic fields scattered by poroelastic materials contain key information about the materials' pore structure and elastic properties. Therefore, such materials are often characterised with inverse methods that use acoustic measurements. However, it has been shown that results from many existing inverse characterisation methods agree poorly. One reason is that inverse methods are typically sensitive to even small uncertainties in a measurement setup, but these uncertainties are difficult to model and hence often neglected. In this paper, we study characterising poroelastic materials in the Bayesian framework, where measurement uncertainties can be taken into account, and which allows us to quantify uncertainty in the results. Using the finite element method, we simulate measurements where ultrasonic waves are incident on a water-saturated poroelastic material in normal and oblique angles. We consider uncertainties in the incidence angle and level of measurement noise, and then explore the solution of the Bayesian inverse problem, the posterior density, with an adaptive parallel tempering Markov chain Monte Carlo algorithm. Results show that both the elastic and pore structure parameters can be feasibly estimated from ultrasonic measurements.Comment: Published in JSV. https://doi.org/10.1016/j.jsv.2019.05.02

Phase-Coherent Dynamics of a Superconducting Flux Qubit with Capacitive-Bias Readout

We present a systematic study of the phase-coherent dynamics of a superconducting three-Josephson-junction flux qubit. The qubit state is detected with the integrated-pulse method, which is a variant of the pulsed switching DC SQUID method. In this scheme the DC SQUID bias current pulse is applied via a capacitor instead of a resistor, giving rise to a narrow band-pass instead of a pure low-pass filter configuration of the electromagnetic environment. Measuring one and the same qubit with both setups allows a direct comparison. With the capacitive method about four times faster switching pulses and an increased visibility are achieved. Furthermore, the deliberate engineering of the electromagnetic environment, which minimizes the noise due to the bias circuit, is facilitated. Right at the degeneracy point the qubit coherence is limited by energy relaxation. We find two main noise contributions. White noise is limiting the energy relaxation and contributing to the dephasing far from the degeneracy point. 1/f-noise is the dominant source of dephasing in the direct vicinity of the optimal point. The influence of 1/f-noise is also supported by non-random beatings in the Ramsey and spin echo decay traces. Numeric simulations of a coupled qubit-oscillator system indicate that these beatings are due to the resonant interaction of the qubit with at least one point-like fluctuator, coupled especially strongly to the qubit.Comment: Minor changes. 21 pages, 15 figure

Mode i stress intensity factors of slanted cracks

The solutions of stress intensity factors of slanted cracks in plain strain plate are hard to find in open literature. There are some previous solutions of stress intensity factors available, however they are not studied completed except for the case of plain stress. The slanted cracks are modelled numerically using ANSYS finite element program. There are ten slanted angles and seven relative crack depths are used and the plate containing cracks is assumed to fulfil the plain strain condition. The plate is then forced uni-axially the stress intensity factors are determined according to the displacement extrapolation method. Based on the numerical analysis, it is found that slanted angles have inverse effects on the behaviour of stress intensity factors. Increasing such angles capable to reduce the mode I stress intensity factors. On the other hand, it is also enhanced the capability of mode II stress intensity factors at the crack tip. Due to difficulty of determining stress intensity factors numerically, a regression technique is used to formulate mathematical expressions which are capable to predict the stress intensity factors in reasonable accuracies

Beam instrumentation for the Tevatron Collider

The Tevatron in Collider Run II (2001-present) is operating with six times more bunches and many times higher beam intensities and luminosities than in Run I (1992-1995). Beam diagnostics were crucial for the machine start-up and the never-ending luminosity upgrade campaign. We present the overall picture of the Tevatron diagnostics development for Run II, outline machine needs for new instrumentation, present several notable examples that led to Tevatron performance improvements, and discuss the lessons for future colliders

Understanding Pound-Drever-Hall locking using voltage controlled radio-frequency oscillators: An undergraduate experiment

We have developed a senior undergraduate experiment that illustrates frequency stabilization techniques using radio-frequency electronics. The primary objective is to frequency stabilize a voltage controlled oscillator to a cavity resonance at 800 MHz using the Pound-Drever-Hall method. This technique is commonly applied to stabilize lasers at optical frequencies. By using only radio-frequency equipment it is possible to systematically study aspects of the technique more thoroughly, inexpensively, and free from eye hazards. Students also learn about modular radio-frequency electronics and basic feedback control loops. By varying the temperature of the resonator, students can determine the thermal expansion coefficients of copper, aluminum, and super invar.Comment: 9 pages, 10 figure

Stabilization of a p-u sensor mounted on a vehicle for measuring the acoustic impedance of road surfaces

The knowledge of the acoustic impedance of a material allows for the calculation of its acoustic absorption. Impedance can also be linked to structural and physical proprieties of materials. However, while the impedance of pavement samples in laboratory conditions can usually be measured with high accuracy using devices such as the impedance tube, complete in-situ evaluation results are less accurate than the laboratory results and is so time consuming that a full scale implementation of in-situ evaluations is practically impossible. Such a system could provide information on the homogeneity and the correct laying of an installation, which is proven to be directly linked to its acoustic emission properties. The present work studies the development of a measurement instrument which can be fastened through holding elements to a moving laboratory (i.e., a vehicle). This device overcomes the issues that afflict traditional in-situ measurements, such as the impossibility to perform a continuous spatial characterization of a given pavement in order to yield a direct evaluation of the surface’s quality. The instrumentation has been uncoupled from the vehicle’s frame with a system including a Proportional Integral Derivative (PID) controller, studied to maintain the system at a fixed distance from the ground and to reduce damping. The stabilization of this device and the measurement system itself are evaluated and compared to the traditional one

Thermal Noise in Modern CMOS Technology

Non

Quantitative Ultrasonic Coda Wave (Diffuse Field) NDE of Carbon-Fiber Reinforced Polymer Plates

The increasing presence and applications of composite materials in aerospace structures precipitates the need for improved Nondestructive Evaluation (NDE) techniques to move from simple damage detection to damage diagnosis and structural prognosis. Structural Health Monitoring (SHM) with advanced ultrasonic (UT) inspection methods can potentially address these issues. Ultrasonic coda wave NDE is one of the advanced methods currently under investigation. Coda wave NDE has been applied to concrete and metallic specimens to assess damage with some success, but currently the method is not fully mature or ready to be applied for SHM. Additionally, the damage diagnosis capabilities and limitations of coda wave NDE applied to fibrous composite materials have not been widely addressed in literature. The central objective of this work, therefore, is to develop a quantitative foundation for the use of coda wave NDE for the inspection and evaluation of fibrous composite materials. Coda waves are defined as the superposition of late arriving wave modes that have been scattered or reflected multiple times. This results in long, complex signals where individual wave modes cannot be discriminated. One method of interpreting the changes in such signals caused by the introduction or growth of damage is to isolate and quantify the difference between baseline and damage signals. Several differential signal features are used in this work to quantify changes in the coda waves which can then be correlated to damage size and growth. Experimental results show that coda wave differential features are effective in detecting drilled through-holes as small as 0.4 mm in a 50x100x6 mm plate and discriminating between increasing hole diameter and increasing number of holes. The differential features are also shown to have an underlying basis function that is dependent on the hole volume and can be scaled by a material dependent coefficient to estimate the feature amplitude and size holes. The fundamental capabilities of the coda wave measurements, such as error, repeatability, and reproducibility, are also examined. Damage detection was found to be repeatable, reproducible, and relatively insensitive to noise. The measurements are found to be sensitive to thermal changes and absorbing boundaries. Several propagation models are also presented and discussed along with a brief analysis of coda wave signals and spectra