Temporal Compression Research Articles

Typical and Atypical Symptoms of Petrous Apex Cholesterol Granuloma: Association with Radiological Findings.

Objective: Petrous apex cholesterol granuloma (PACG) is a lesion that can give rise to different symptoms, and correlations with etiopathology are ambiguous. The aim of this study is to analyze the association between PACG symptoms and radiological findings at presentation, in order to establish a reproduceable pre-operative radiological evaluation and guide the surgical indication. Methods: PACG patients were collected in two tertiary care hospitals. All cases underwent CT/MRI to evaluate the cyst localization and erosion of surrounding structures. Typical and atypical symptoms were then analyzed and compared to radiologic findings established in accordance with the literature. Results: Twenty-nine patients were recruited; the most common symptoms were headache (69%), diplopia (20.7%) and fainting (24.1%), an atypical clinical manifestation related to jugular tubercle involvement. Significant associations between symptoms and radiologic findings were noted in terms of headache and temporal lobe compression (p = 0.04), fainting and jugular tubercle erosion (p < 0.001), vestibular symptoms and internal auditory canal erosion (p = 0.02), facial paresthesia and Meckel’s cave compression (p = 0.03), diplopia and Dorello canal involvement (p = 0.001), and tinnitus and cochlear basal turn erosion (p < 0.001). All patients were treated via an endoscopic–endonasal approach, in which extension was tailored to each case. At a median follow-up of 46 months, 93.1% of patients experienced resolution of symptoms. Conclusions: This clinico-radiological series demonstrates associations between symptoms and anatomical subsites involved with PACG. Hence, it may guide the surgeon at the time of surgical decision, since it asserts that typical and atypical symptoms are actually related to PACG.

Coupling characteristics of coastal ports and urban network systems based on flow space theory: Empirical evidence from China

The port–city coupling system and spatial correlation are new perspectives in studying the port–city relationship. The flow space and the element network activate the economic location through the temporal and spatial compression effect, reshape the temporal and spatial relationship, and challenge the traditional port–city relationship. Based on the theory of ‘flow space’ and the ‘port–city relationship’, this study constructs two network systems of port and city. A theoretical framework and a measurement method for evaluating the coupling relationship between the port-city and the city from the perspective of flow space are proposed. Using Chinese coastal port cities as examples, this paper discusses the network characteristics and coupling patterns of port–city relations in the context of port regionalisation. The main findings are as follows. First, the port network system is subject to obvious geographical constraints and exhibits the network characteristics of ‘group development’ and ‘axis-spoke’ coexistence; the urban network system reduces to a certain extent the dependence on the space of port cities. It shapes the traditional geographical space and exhibits the network characteristics of ‘multi-core’. Second, types of port–city coupling are diverse, but the regional agglomeration characteristics are obvious. Compared to 2006, the distribution of coupling types in the whole network system of port cities in 2016 is relatively balanced, and the structure tends to be perfect. Finally, flow elements and port functions are the core elements that influence the coupling characteristics of port cities from the perspective of ‘flow space’. The flow element promotes an advanced community relationship between port cities. The port and the city realise the greatest value and the highest comprehensive efficiency. Due to the intergenerational differences of ports, the impact of port functions on the evolution of city functions is different, leading to some level differences in the development of port cities.

Temporal compression of high-power IR laser pulses in a KDP crystal.

It is shown that a KDP crystal can be used for temporal compression of powerful pulses of the near-IR range. A method of searching for laser beam and crystal parameters suitable for compression is proposed. Temporal compression of laser pulses at a central wavelength of 1034 nm from 266 fs to 94 fs during propagation along the optical axis in a 21 cm thick KDP crystal is demonstrated experimentally.

Temporal contrast enhancement via nonlinear elliptical polarization rotation in a solid thin plate.

We demonstrate the simultaneous temporal contrast enhancement and spectral broadening via nonlinear elliptical polarization rotation in a solid thin plate. The efficiency, temporal contrast enhancement, spectral broadening, pulse compression and power stability are experimentally investigated. With this simple and efficient scheme, the temporal cleaned pulses with energy of 325 µJ and total efficiency of 30% are obtained. The temporal contrast and spectral bandwidth of the filtered pulse are 1011 and 104 nm, respectively. The pulse compressed from 180 fs to 45.8 fs is realized by utilizing chirped mirrors, corresponding to a compression factor of 3.93. With stable output power, presented scheme could be implemented in the ultra-intense femtosecond laser facilities.

Efficiency of temporal sensor data compression methods to reduce LoRa-based sensor node energy consumption

PurposeMinimizing the energy consumption in a wireless sensor node is important for lengthening the lifetime of a battery. Radio transmission is the most energy-consuming task in a wireless sensor node, and by compressing the sensor data in the online mode, it is possible to reduce the number of transmission periods. This study aims to demonstrate that temporal compression methods present an effective method for lengthening the lifetime of a battery-powered wireless sensor node.Design/methodology/approachIn this study, the energy consumption of LoRa-based sensor node was evaluated and measured. The experiments were conducted with different LoRaWAN data rate parameters, with and without compression algorithms implemented to compress sensor data in the online mode. The effect of temporal compression algorithms on the overall energy consumption was measured.FindingsEnergy consumption was measured with different LoRaWAN spreading factors. The LoRaWAN transmission energy consumption significantly depends on the spreading factor used. The other significant factors affecting the LoRa-based sensor node energy consumption are the measurement interval and sleep mode current consumption. The results show that temporal compression algorithms are an effective method for reducing the energy consumption of a LoRa sensor node by reducing the number of LoRa transmission periods.Originality/valueThis paper presents with a practical case that it is possible to reduce the overall energy consumption of a wireless sensor node by compressing sensor data in online mode with simple temporal compression algorithms.

Evaluating the Utility of Temporal Compression in High-Resolution Traveling Wave-Based Cyclic Ion Mobility Separations.

Ion mobility spectrometry coupled to mass spectrometry (IMS-MS) is slowly becoming a more integral part in omics-based workflows. With the recent technological advancements in IMS-MS instrumentation, particularly those involving traveling wave-based separations, ultralong pathlengths have become readily available in commercial platforms (e.g., Select Series Cyclic IMS from Waters Corporation and MOBIE from MOBILion). However, a tradeoff exists in such ultralong pathlength separations: increasing peak-to-peak resolution at the cost of lower signal intensities and thus poorer sensitivity of measurements. Herein, we explore the utility of temporal compression, where ions are compressed in the time domain, following high-resolution cyclic ion mobility spectrometry-mass spectrometry-based separations on a commercially available, unmodified platform. We assessed temporal compression in the context of various separations including those of reverse sequence peptide isomers, chiral noncovalent complexes, and isotopologues. From our results, we demonstrated that temporal compression improves IMS peak intensities by up to a factor of 4 while only losing ∼5 to 10% of peak-to-peak resolution. Additionally, the improvement in peak quality and signal-to-noise ratio was evident when comparing IMS-MS separations with and without a temporal compression step performed. Temporal compression can readily be implemented in existing traveling wave-based IMS-MS platforms, and our initial proof-of-concept demonstration shows its promise as a tool for improving peak shapes and peak intensities without sacrificing losses in resolution.

Neural signatures associated with temporal compression in the verbal retelling of past events

When we retell our past experiences, we aim to reproduce some version of the original events; this reproduced version is often temporally compressed relative to the original. However, it is currently unclear how this compression manifests in brain activity. One possibility is that a compressed retrieved memory manifests as a neural pattern which is more dissimilar to the original, relative to a more detailed or vivid memory. However, we argue that measuring raw dissimilarity alone is insufficient, as it confuses a variety of interesting and uninteresting changes. To address this problem, we examine brain pattern changes that are consistent across people. We show that temporal compression in individuals’ retelling of past events predicts systematic encoding-to-recall transformations in several higher associative regions. These findings elucidate how neural representations are not simply reactivated, but can also be transformed due to temporal compression during a universal form of human memory expression: verbal retelling.

Symptomatic enophthalmos due to sphenoid wing dysplasia appearing over 12 years in a patient with neurofibromatosis type 1: a case report and literature review

Sphenoid wing dysplasia (SWD) is a common orbital complication of neurofibromatosis type 1 (NF1). However, enophthalmos associated with SWD is extremely rare, and details of its natural history are unclear. We present the case of a 14-year-old boy with an early childhood diagnosis of NF1 presenting with left blepharophimosis and enophthalmos for several months. Imaging demonstrated enlargement of the left lateral SWD, progression of the posteromedial deviation of the orbital contents, and sphenoid/ethmoid sinus deformation due to left temporal lobe compression over 12 years. Two characteristic changes were revealed on imaging: enlargement of the middle cranial fossa and deformation of the sphenoid/ethmoid sinuses. The orbital contents were compressed by the intracranial pressure of the temporal lobe and were displaced posteromedially into the space created by the deformed sphenoid/ethmoid sinuses. Because orbital symptoms can gradually become apparent over years with the progression of SWD and skeletal growth, long-term follow-up of orbital symptoms is recommended in patients with NF1.

Ultra-broadband THz pulses with electric field amplitude exceeding 100 kV/cm at a 200 kHz repetition rate.

We demonstrate a table-top source delivering ultra-broadband THz pulses with electric field strength exceeding 100 kV/cm at a repetition rate of 200 kHz. The source is based on optical rectification of 23 fs pulses at 1030 nm delivered by a ytterbium-doped fiber laser followed by a nonlinear temporal compression stage. We generate THz pulses with a conversion efficiency of up to 0.11 % with a spectrum extending to 11 THz using a 1 mm thick GaP crystal and a conversion efficiency of 0.016 % with a spectrum extending to 30 THz using a 30 µm thick GaSe crystal. The essential features of the emitted THz pulse spectra are well captured by simulations of the optical rectification process relying on coupled nonlinear equations. Our ultrafast laser-based source uniquely satisfies an important requirement of nonlinear THz experiments, namely the emission of ultra-broadband THz pulses with high electric field amplitudes at high repetition rates, opening a route towards nonlinear time-resolved THz experiments with high signal-to-noise ratios.

Modeling for Generating Femtosecond Pulses in an Er-Doped Fiber Using Externally Controlled Spectral Broadening and Compression Mechanisms

A model for generating femtosecond laser pulses from a low-power mode-locked laser of moderate temporal half-width was proposed. This was achieved by injecting the pulse into a single-mode inverted-populated Er-doped fiber where self-focusing and absorption were avoided. To initiate spectral broadening, the pulse was phase-modulated by subjecting a part of the fiber to an electric field of suitable intensity and frequency generated into a circular capacitor. To stimulate temporal compression, the phase-modulated pulse was introduced into a combination of two prism sets located symmetrically with respect to the x-axis. After passing the pulse through the first prism set, its spectral components were spatially separated in the y-axis. The spectral phases were manipulated by redirecting the spectral components through a slab cross-section that was subjected to a spatially modulated DC electric field. After passing the slab, the pulse is directed into the second prism set, where the spectral components were spatially overlapped and propagated outside the compressor with the same slope and dimension as before entering the compressor. Constructive super positioning of the phase-manipulated spectral components gave maximum intensity only at a specified location.

Temporal contrast enhancement by nonlinear elliptical polarization rotation in a multi-pass cell

Abstract We demonstrate the simultaneous temporal contrast improvement and pulse compression of a Yb-doped femtosecond laser via nonlinear elliptical polarization rotation in a solid state multi-pass cell. The temporal contrast is improved to 109, while the pulse is shortened from 181 to 36 fs, corresponding to a compression factor of 5. The output beam features excellent beam quality with M2 values of 1.18 × 1.16. The total efficiency of the contrast enhancement system exceeds 50%. This technique will have wide applications in high temporal contrast ultra-intense femtosecond lasers.

Image Compression Techniques in Wireless Sensor Networks: A Survey and Comparison

There is continuous intensive research on image compression techniques in wireless sensor networks (WSNs) in the literature. Some of the image compression techniques in WSNs that exist in the literature include discrete cosine transform (DCT), discrete waveform transforms (DWT), set partitioning in a hierarchical tree (SPIHT), and embedded zero tree wavelet (EZW) coding. Research on image compression in WSNs is necessitated by the need to improve the energy efficiency of sensor nodes and WSNs&#x2019; lifetimes without compromising the quality of the reconstructed data. Several approaches have been developed centered around image compression and other factors in trying to limit the energy consumption of sensor nodes. Most of these approaches do not provide the error-bound mechanism that balances the rate of compression and distortion of the reconstructed image. Therefore, in this paper, a review and analysis of image compression techniques and approaches in WSNs are conducted. Available image compression approaches in WSNs in literature were then classified according to the image compression technique adopted, and their strengths and weaknesses were highlighted. In addition, a rate-distortion balanced data compression algorithm with error bound mechanism based on artificial neural networks (ANN) in the form of an autoencoder (AE) was coded and simulated in MATLAB before being evaluated and compared to the conventional approaches. The experimental results show that the simulated algorithm has less root mean square error (RMSE) and a higher coefficient of determination (<i>R</i>²) values on variable compression ratios as compared to the Principal Component Analysis (PCA), Discrete Cosine Transform, and Fast Fourier Transform (FFT) when using the Grand-St-Bernard metrological dataset. Furthermore, it presented less RMSE, and higher compression ratio values compared to the Lightweight Temporal Compression (LTC) algorithm on variable error bounds when using the LUCE metrological dataset. Therefore, it was found that the simulated algorithm presents better compression fidelity as compared to the conventional approaches without an error-bound mechanism. Moreover, the algorithm analyzed presents a significant approach to balancing the compression ratio and reconstructed data quality through its error-bound mechanism.

Spatial cage solitons—taming light bullets

Multimode nonlinear optics is used to overcome a long-standing limitation of fiber optics, tightly phase locking several spatial modes and enabling the coherent transport of a wave packet through a multimode fiber. A similar problem is encountered in the temporal compression of multimillijoule pulses to few-cycle duration in hollow gas-filled fibers. Scaling the fiber length to up to 6 m, hollow fibers have recently reached 1 TW of peak power. Despite the remarkable utility of the hollow fiber compressor and its widespread application, however, no analytical model exists to enable insight into the scaling behavior of maximum compressibility and peak power. Here we extend a recently introduced formalism for describing mode locking to the analog scenario of locking spatial fiber modes together. Our formalism unveils the coexistence of two soliton branches for anomalous modal dispersion and indicates the formation of stable spatiotemporal light bullets that would be unstable in free space, similar to the temporal cage solitons in mode-locking theory. Our model enables deeper understanding of the physical processes behind the formation of such light bullets and predicts the existence of multimode solitons in a much wider range of fiber types than previously considered possible.

Self-compression of mJ pulses to 10 fs in a hollow-core waveguide: effects of higher-order dispersion

Self-compression of an ultrashort pulse in a hollow-core waveguide filled with noble gas is a simple and promising approach to generate few and even single-cycle pulses. However, when the input pulse energy approaches to mJ level, ionization of the gas induces strong higher-order dispersion through multiple mechanisms, which makes the temporal compression process unstable and even fail. In this paper, we systematically study the effects of higher-order dispersion in the self-compression process of mJ few-cycle pulses. We found that the self-compression depends on the approaching routine of group delay dispersion and third-order dispersion optimization. There exists a steady and stable routine to maintain the pulse duration around the Fourier transform limit. Then, we successfully demonstrate stable and repeatable compression of 3 mJ pulses to 13.1 and 10.5 fs in a 2 cm hollow-core waveguide filled with Ar and Kr, respectively.

Words of agency: Executed and observed vocal actions induce a temporal binding effect.

Humans generally experience a sense of agency over the outcomes produced by their motor actions. This has been well established in the case of manual actions that directly affect the physical environment. Vocalizations are also actions, but they typically have only indirect effects on the environment. In the present research, we explore whether the outcomes produced by vocalizations also elicit a sense of agency. In three experiments, using an interval reproduction task, we find that performing a vocal action that produced an auditory outcome caused participants to underestimate the amount of elapsed time between actions and outcomes (i.e., temporal binding), an implicit index of the sense of agency (Experiment 1). We also show that observing others produce vocal actions elicits temporal binding, but only when the observer has direct visual access to the vocal action being executed (Experiments 2 and 3). Taken together, our findings suggest that direct observation of an action is necessary to experience a temporal binding effect for actions performed by others, and that audio-visuomotor information may play a role in the generation of temporal compression experienced over observed actions (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Ultralong ring laser supercontinuum sources using standard telecommunication fibre

The application of a recently demonstrated mode-locked ultralong pulsed fibre ring laser architecture (Gallazzi et al., 2021) to the inexpensive and efficient generation of supercontinuum from a pulsed output at 1.56 μm in standard single-mode telecommunication fibre is experimentally demonstrated. The impact of broadening fibre, dynamic switching between different harmonic modes and the influence of laser polarization on the properties of the generated supercontinuum are studied for three different kinds of telecommunication fibre. Flexible spectral broadening beyond 200 nm is obtained with good temporal correlation and pulse compression from 240 fs down to 50 fs.

Slow light nanocoatings for ultrashort pulse compression

Transparent materials do not absorb light but have profound influence on the phase evolution of transmitted radiation. One consequence is chromatic dispersion, i.e., light of different frequencies travels at different velocities, causing ultrashort laser pulses to elongate in time while propagating. Here we experimentally demonstrate ultrathin nanostructured coatings that resolve this challenge: we tailor the dispersion of silicon nanopillar arrays such that they temporally reshape pulses upon transmission using slow light effects and act as ultrashort laser pulse compressors. The coatings induce anomalous group delay dispersion in the visible to near-infrared spectral region around 800 nm wavelength over an 80 nm bandwidth. We characterize the arrays’ performance in the spectral domain via white light interferometry and directly demonstrate the temporal compression of femtosecond laser pulses. Applying these coatings to conventional optics renders them ultrashort pulse compatible and suitable for a wide range of applications.

Nonlinear Optics in Multipass Cells

AbstractThe fundamental principles and experimental implementations of multipass cells used as a platform for nonlinear optics are reviewed. Embedding a nonlinear medium in a multipass cell allows for a distribution of the nonlinearity over large interaction distances, while the beam goes through multiple foci, conferring on the beam a robustness with respect to spatio‐spectral coupling effects. Most of the research so far has been focused on temporal compression based on self‐phase modulation, with excellent performances especially in terms of energy scaling and throughput. However, other nonlinear phenomena and functions are being increasingly investigated, such as supercontinuum generation, spectral compression, or Raman scattering. Nonlinear optics experiments in multipass cells bear some similarities with the work done in optical fibers over several decades, while allowing straightforward energy scaling potential, and unlocking engineering possibilities through the design of the cell mirrors, geometry, and nonlinear medium.

Single-stage few-cycle nonlinear compression of milliJoule energy Ti:Sa femtosecond pulses in a multipass cell.

We report on the nonlinear temporal compression of mJ energy pulses from a Ti:Sa chirped pulse amplifier system in a multipass cell filled with argon. The pulses are compressed from 30 fs down to 5.3 fs, corresponding to two optical cycles. The post-compressed beam exhibits excellent spatial quality and homogeneity. These results provide guidelines for optimizing the compressed pulse quality and further scaling of multipass-cell-based post-compression down to the single-cycle regime.

High-Conversion Efficiency Pulse Compression by Stimulated Raman Scattering and Laser Induced Breakdown in Water

A novel temporal pulse compression technique, combining stimulated Raman scattering (SRS) and laser induced breakdown (LIB) principles was presented in this work, which employing an energy controllable dual-cell setup. As a novel type of plasma shutter, the 2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nd</sup> cell was used to transmit the high-power peak at the leading pulse edge and successfully block its low-power tail. The effect resulted in a 7 ns pulse duration from a Nd: YAG laser compressed into 330 ps, the pulse compression ratio was about 21×. The magnified optical power of the leading edge diminished the threshold of SRS and improved the beam quality of the output pulse. In addition, the output energy of Stokes was approximately 2 times than that of the 1 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">st</sup> cell process, and the 2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nd</sup> cell process increased the energy conversion efficiency from 4.2% to 15.8%. Thus, the 1 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">st</sup> -order Stokes SRS was greatly improved, and the 2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nd</sup> -order Stokes SRS was more easily generated. The method provided a simple but convenient way to generate a short pulse with a high energy conversion efficiency Raman laser.