Microjoule mode-locked oscillators: issues of stability and noise

In this work, for the first time to our knowledge, stability and noise of a thin-disk mode-locked Yb:YAG oscillator operating in both negative- (NDR) and positive-dispersion (PDR) regimes have been analyzed systematically within a broad range of oscillator parameters. It is found, that the scaling of output pulse energy from 7 $\mu$J up to 55 $\mu$J in the NDR requires a dispersion scaling from -0.013 ps$^{2}$ up to -0.31 ps$^{2}$ to provide the pulse stability. Simultaneously, the energy scaling from 6 $\mu$J up to 90 $\mu$J in the PDR requires a moderate dispersion scaling from 0.0023 ps$^{2}$ up to 0.011 ps$^{2}$. A chirped picosecond pulse in the PDR has a broader spectrum than that of a chirp-free soliton in the NDR. As a result, a chirped picosecond pulse can be compressed down to a few of hundreds of femtoseconds. A unique property of the PDR has been found to be an extremely reduced timing jitter. The numerical results agree with the analytical theory, when spectral properties of the PDR and the negative feedback induced by spectral filtering are taken into account.Comment: 12 pages, 11 figures, SPIE's International Symposium "Photonics Europe" (EPE10), 12-16 April 2010, Brussels, Belgiu

Traducción del Evangelio por León Tolstói a la luz de los estudios de traducción del siglo XX

This article is devoted to the ideas of Leo Tolstoy on translation issues represented in his almost unknown book Soedineniye i perevod chetyrekh Evangelii (The Four Gospels Harmonized and Translated) (Tolstoy 1957; Tolstoy 1896; Tolstoy 1904 a, b), in which the major parts of the New Testament were translated and commented upon with regards to the official (a.k.a. Synodal) translation into Russian as well as the original Greek text. Though Tolstoy attempted to simplify and even omit some passages as irrelevant, many of his translation methods had a clear correlation with the approaches formulated in 20th century theory of translation, namely semantic analysis, inner and surface structures and cultural equivalence.Este artículo está dedicado a las ideas de León Tolstói sobre cuestiones de traducción expresadas en su casi desconocido libro Soedineniye i perevod chetyrekh Evangelii (Los Cuatro Evangelios armonizados y traducidos) (Tolstoy 1957; Tolstoy 1896; Tolstoy 1904 a,b), en el que traducía y comentaba la mayor parte del Nuevo Testamento en relación con la traducción oficial en ruso y con el texto griego. Aunque Tolstói intentó simplificar y omitir algunos pasajes que consideraba irrelevantes, muchos de sus métodos de traducción están en evidente correlación con los puntos de vista formulados en la teoría de la traducción del siglo XX, especialmente análisis semántico, estructuras internas y superficiales y equivalencia cultural

Electronic architecture for air coupled ultrasonic pulse-echo range finding with application to security and surface profile imaging

Ultrasonic range finding instruments are utilized, e.g., for measuring liquid levels and distance to parking obstacles. However, instruments designed using the conventional electronic architectures to drive the ultrasonic transmitters cannot provide an operating range beyond a few meters for a flat solid wall with normal incidence when powered by a low voltage battery. This both limits the applicability of the existing instruments and makes it difficult to demonstrate their feasibility for new applications. The architecture described here combines a DC/DC boost converter with semiconductor switches, enabling a scalable increase in the operating range for both pulse-echo and pitch-catch modes of operation. It was fully prototyped and successfully tested for novel applications involving ultrasonic range finders, specifically intrusion detection and surface profile imaging. The limitations of the profile sensing device are rather restrictive as it only operates at the incidence angles below 18°, but this device can be developed further. The developed security system was found to be quite practical in its present state

Determining the operating distance of air ultrasound range finders : calculations and experiments

Estimating the operating distance of air ultrasound range finders by using the suitably modified radar equation and experimental verification of the developed computational procedure is discussed. It is shown that, despite notable differences between operating conditions of radars and air ultrasonic range finders, the radar equation is applicable to the considered case, and calculations of the relevant terms for this case are presented. The experimental assessment was carried out by evaluating the probability of detection at various distances from the custom built device. The calculated and experimental results seem to agree well despite using a number of values with high degree of uncertainty. The described procedure can be used at the design stage of air ultrasound range finders in order to reduce the number of prototypes before finalizing the design to a single prototype

Comparison of the responsiveness of ultrasonic oscillating temperature sensors (UOTSes) and conventional sensors to temperature inflection points

Ultrasonic oscillating temperature sensors (UOTSes), in distinction to conventional temperature sensors, feature almost negligible settling time. This property can be useful for detecting malfunctions, failures and misuses of heat exchangers. However, most exchangers handle substantial thermal masses, which obscure the detection of any temperature changes. We compared the responsiveness of conventional DS18B20 sensors and an UOTS to the change in the temperature gradient of over 3.5 kg of water using a posteriori records. Temperature inflection points were estimated by extending the curves for separate distinct heating and cooling intervals that fit best and finding their interception. For the UOTS, the interception occurred about 100 seconds sooner, making it a potential candidate for detecting heat exchangers’ irregularities

Automated recording and processing of lecture attendance data using RFID student cards

Aspects of the ongoing project to automate the recording of students' lecture attendance using RFID cards and automate processing of the records without a university wide infrastructure are presented and discussed

Experimental evaluation of ultrasonic oscillating temperature sensors (UOTS) under cyclically changing temperatures

In contrast to most conventional temperature sensors, which need to come to thermal equilibrium with the medium of interest to report its temperature, UOTS interrogate the medium based on the propagation speed of ultrasound, and will return temperature data that are “averaged” for the complete ultrasound pathway. It has been demonstrated that UOTS can provide consistent high-resolution temperature readings under steadily decreasing temperatures using inexpensive ultrasonic transducers and low cost electronic instrumentation

Measuring thermal losses of water cooled motors using oscillating ultrasonic temperature sensors

Abstract – simulations have shown that the evaluation of thermal losses of water cooled electric motors using inexpensive conventional temperature sensors is complicated by the relatively low accuracy of the latter. This accuracy must be below 0.05 K to evaluate motor efficiency with an accuracy of 1%. By experiment, it was shown that oscillating ultrasonic temperature sensors can potentially achieve the required accuracy. It was observed that the output frequency of the oscillating ultrasonic sensor featured substantial hysteresis that would complicate the development of accurate ultrasonic instrumentation

Experimental setup of continuous ultrasonic monitoring for corrosion assessment

The paper is devoted to the ultrasonic monitoring of accelerated corrosion. In order to achieve non-uniform corrosion (high surface roughness), passivation was applied to the corroding surface. A dedicated electronic multiplexed four channel front end was developed in order to feed the amplified waveforms from several transducers to the recording instrument. The experiment was conducted using two 5 MHz and two 10 MHz ultrasonic transducers all operating in the pulse echo mode. The transducers were excited in turn using gated bursts, and the received echoes were multiplexed and amplified before being digitized by a high accuracy ultrasonic instrument. Application of adaptive cross correlation to the recorded data allowed continuous thickness estimation of the non-uniformly corroded surface whilst cross correlation method gave unsatisfactory results

Embedded supervisory control and output reporting for the oscillating ultrasonic temperature sensors

Ultrasonic temperature sensors can potentially outperform conven-tional sensors because they are capable of very fast sensing across the complete ultrasound pathway, whilst conventional sensors only sense temperature at a single point and have substantial thermal inertia. We report recent develop-ments in electronic instrumentation for oscillating ultrasonic temperature sen-sors with the aim of achieving high accuracy and low scatter at a low cost