1,721,117 research outputs found
ATOMI COME STRUMENTI DI MISURA
Full text linkDa qualche decennio ormai abbiamo imparato a manipolare singoli atomi tramite radiazione elettromagnetica e ad utilizzarli come sensori per campi esterni, elettromagnetici o gravitazionali, per misure di frequenza a livelli di precisione e accuratezza impensabili per qualunque altra quantità fisica e infine, in un possibile futuro prossimo, come unità fondamentali di immagazzinamento ed elaborazione dell’informazione nella prossima generazione di calcolatori, i computer quantistici
The Physics Behind Electronics
No full textThis book is not simply about electronics but rather a thorough exploration of physics. Instead of isolating electronics as an art, its primary goal is to explain the physical principles behind electronic circuits and how they are applied practically. Electronics provides a framework for understanding physics, and vice versa.
It is intended for advanced undergraduate or graduate students in physics or related fields who have a basic grasp of electromagnetism and calculus. It also caters to individuals with practical electronics knowledge looking to deepen their understanding of often overlooked concepts.
While traditional textbooks treat electronics as a set of techniques, the growing availability of affordable acquisition boards and user-friendly software has diminished the need for expertise in circuit design. Nonetheless, physicists still need to comprehend concepts like stability, impedance matching, noise, and the advantages and limitations of signal sampling.
Starting with linear time-invariant systems and feedback, the book progresses to designing circuits using operational amplifiers and oscillators, covering stability and dissipation. It also delves into the Nyquist-Shannon theorem and the basics of digital electronics, emphasizing state-sensitive and clock-sensitive operators. Additionally, it offers an overview of electronic devices facilitating analog-to-digital conversion.
The book concludes by examining scenarios involving high frequencies where wires act as waveguides and addressing noise sources from thermal agitation and the corpuscular nature of current. Theoretical concepts are reinforced with solved exercises, and practical "in-the-lab" sections guide readers through experiments using affordable kits and instruments, requiring minimal electronic prototyping knowledge
Kramers–Kronig relations via Laplace formalism and L^1 integrability
Full text linkKramers–Kronig relations link the real and imaginary parts of the Fourier transform of a well-behaved causal transfer function describing a linear, time-invariant system. From the physical point of view, according to the Kramers–Kronig relations, absorption and dispersion become two sides of the same coin. Due to the simplicity of the assumptions underlying them, the relations are a cornerstone of physics. The rigorous mathematical proof was carried out by Titchmarsh in 1937 and just requires the transfer function to be square-integrable (L^2), or equivalently that the impulse response of the system at hand has a finite energy. Titchmarsh’s proof is definitely not easy, thus leading to crucial steps that are often overlooked by instructors and, occasionally, prompting some authors to attempt shaky shortcuts. Here, we share a rigorous mathematical proof that relies on the Laplace formalism and requires a slightly stronger assumption on the transfer function, namely it
being Lebesgue-integrable (L^1). While the result is not as general as Titchmarsh’s proof, its enhanced simplicity makes a deeper knowledge of the mathematical aspects of the Kramers–Kronig relations more accessible to the audience of physicists
Frequency-comb-based absolute frequency measurements in the mid-IR with difference-frequency-based spectrometer
No full textWe demonstrate the possibility of extending the well-established metrological performance of optical
frequency-comb synthesizers to the mid-IR region by phase locking the pump and signal lasers of a
difference-frequency source to two near-IR teeth of an optical comb. An uncertainty of 800 Hz 共1.1⫻ 10 −11 兲 in
the absolute frequencies of CO 2 transitions near 4.2 m has been measured by cavity-enhanced saturated-
absorption spectroscopy. Prospects for the creation of a new dense set of high-quality molecular frequency
standards in the IR are discussed
Comb-locked cavity ring-down spectrometer
No full textExtreme frequency accuracy and high sensitivity are obtained with a novel comb-locked cavity-ring-down spectrometer operating in the near-infrared from 1.5 to 1.63 μm. A key feature of our approach is the tight frequency locking of the probe laser to the comb, ensuring very high reproducibility and accuracy to the frequency axis upon scanning the comb repetition rate, as well as an efficient light injection into a length-swept high-finesse passive cavity containing the gas sample. Spectroscopic tests on the (30012) (00001) P14e line of CO2 at ∼1.57 μm demonstrate an accuracy of ∼17 kHz on the line center frequency in a Doppler broadening regime over the time scale of about 5 min, corresponding to four consecutive spectral scans of the absorption line. Over a single scan, which consists of 1500 spectral points over 75 s, the limit of detection is as low as 5.7 × 10-11 cm-1. © 2015 AIP Publishing LLC
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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