Artículos de revistas: "Imperfections RF"

1

Boulogeorgos, Alexandros-Apostolos A., Nestor D. Chatzidiamantis y George K. Karagiannidis. "Energy Detection Spectrum Sensing Under RF Imperfections". IEEE Transactions on Communications 64, n.º 7 (julio de 2016): 2754–66. http://dx.doi.org/10.1109/tcomm.2016.2561294.

Texto completo

Los estilos APA, Harvard, Vancouver, ISO, etc.

2

Polak, Adam C. y Dennis L. Goeckel. "Wireless Device Identification Based on RF Oscillator Imperfections". IEEE Transactions on Information Forensics and Security 10, n.º 12 (diciembre de 2015): 2492–501. http://dx.doi.org/10.1109/tifs.2015.2464778.

Texto completo

Los estilos APA, Harvard, Vancouver, ISO, etc.

3

Riener, Christian, Thomas Bauernfeind, Samuel Kvasnicka, Klaus Roppert, Herbert Hackl y Manfred Kaltenbacher. "Numerical Investigation of Signal Launch Imperfections for Edge Mount RF Connectors". Electronics 11, n.º 13 (24 de junio de 2022): 1990. http://dx.doi.org/10.3390/electronics11131990.

Texto completo

Resumen

In this paper, common practice RF design guidelines for SMA edge mount connectors are investigated in terms of numerical simulations and VNA measurements. These guidelines are used in a variety of applications for coaxial-to-planar interfaces but often do not provide information regarding the physical origins of increased insertion and transmission losses. The presented results in this work focus on different RF PCB design features and their impact on electromagnetic field distributions in the launching zone. The presented investigations should raise awareness on the issue of electromagnetic field resonances occurring in the RF frequency range and assist PCB design engineers to identify potential issues occurring at an coaxial-to-planar interface. The investigated PCB features facilitate a high performance RF PCB design up to a frequency of 26 GHz.

Los estilos APA, Harvard, Vancouver, ISO, etc.

4

Aigner, Christoph S., Armin Rund, Samy Abo Seada, Anthony N. Price, Joseph V. Hajnal, Shaihan J. Malik, Karl Kunisch y Rudolf Stollberger. "Time optimal control‐based RF pulse design under gradient imperfections". Magnetic Resonance in Medicine 83, n.º 2 (23 de agosto de 2019): 561–74. http://dx.doi.org/10.1002/mrm.27955.

Texto completo

Los estilos APA, Harvard, Vancouver, ISO, etc.

5

Sanogo, Lamoussa, Eric Alata, Alexandru Takacs y Daniela Dragomirescu. "Intrusion Detection System for IoT: Analysis of PSD Robustness". Sensors 23, n.º 4 (20 de febrero de 2023): 2353. http://dx.doi.org/10.3390/s23042353.

Texto completo

Resumen

The security of internet of things (IoT) devices remains a major concern. These devices are very vulnerable because of some of their particularities (limited in both their memory and computing power, and available energy) that make it impossible to implement traditional security mechanisms. Consequently, researchers are looking for new security mechanisms adapted to these devices and the networks of which they are part. One of the most promising new approaches is fingerprinting, which aims to identify a given device by associating it with a unique signature built from its unique intrinsic characteristics, i.e., inherent imperfections, introduced by the manufacturing processes of its hardware. However, according to state-of-the-art studies, the main challenge that fingerprinting faces is the nonrelevance of the fingerprinting features extracted from hardware imperfections. Since these hardware imperfections can reflect on the RF signal for a wireless communicating device, in this study, we aim to investigate whether or not the power spectral density (PSD) of a device’s RF signal could be a relevant feature for its fingerprinting, knowing that a relevant fingerprinting feature should remain stable regardless of the environmental conditions, over time and under influence of any other parameters. Through experiments, we were able to identify limits and possibilities of power spectral density (PSD) as a fingerprinting feature.

Los estilos APA, Harvard, Vancouver, ISO, etc.

6

Aebischer, Kathrin, Zdeněk Tošner y Matthias Ernst. "Effects of radial radio-frequency field inhomogeneity on MAS solid-state NMR experiments". Magnetic Resonance 2, n.º 1 (1 de julio de 2021): 523–43. http://dx.doi.org/10.5194/mr-2-523-2021.

Texto completo

Resumen

Abstract. Radio-frequency field inhomogeneity is one of the most common imperfections in NMR experiments. They can lead to imperfect flip angles of applied radio-frequency (rf) pulses or to a mismatch of resonance conditions, resulting in artefacts or degraded performance of experiments. In solid-state NMR under magic angle spinning (MAS), the radial component becomes time-dependent because the rf irradiation amplitude and phase is modulated with integer multiples of the spinning frequency. We analyse the influence of such time-dependent MAS-modulated rf fields on the performance of some commonly used building blocks of solid-state NMR experiments. This analysis is based on analytical Floquet calculations and numerical simulations, taking into account the time dependence of the rf field. We find that, compared to the static part of the rf field inhomogeneity, such time-dependent modulations play a very minor role in the performance degradation of the investigated typical solid-state NMR experiments.

Los estilos APA, Harvard, Vancouver, ISO, etc.

7

Hamaty, Youssef R. y Alexander R. Tusnin. "Operation of braced steel frameworks with regard to assembly and fabrication errors". Stroitel'stvo: nauka i obrazovanie [Construction: Science and Education] 13, n.º 1 (30 de marzo de 2023): 22–40. http://dx.doi.org/10.22227/2305-5502.2023.1.2.

Texto completo

Resumen

Introduction. As a building construction material, steel is widely used because of its high mechanical characteristics. Steel load-bearing structures of multi-storey buildings are a system formed by columns, beams, floor slabs and braces. The frame of a multi-storey building has a large number of elements and their connections. Errors in the fabrication, installation and operation of steel frames of multi-storey buildings can lead to a reduction in the load-bearing capacity of structures compared to the design. Deviations from the design position occur because of violations of the technical operatin.rules of the buildings beyond the permissible limits, design errors, imperfect standards and poor quality of work during the fabrication and installation of structures. The current Russian standards do not take into account the impact of fabrication and installation errors on the work of multi-storey frames. The initial geometric defects in the structural system and its individual elements contribute to the difference in performance between the real construction and an idealized one. Materials and methods. The study of the effect of initial imperfections on the stress-strain state of the steel frame is important and relevant. Initial imperfections are taken into account either by applying an equivalent load to the idealized design scheme or by forming a geometrically distorted by imperfections design scheme. The analysis can be linear or geometrically non-linear. Results. The results of the study of braced steel framework performance in the presence of initial imperfections are presented. The effect of initial imperfections in the form of deflection of columns from the vertical is considered. The values of the initial imperfections are determined in accordance with the current RF standards. Conclusions. The results obtained have made it possible to propose a correction factor to the results of the calculation of frames with imperfections to the results of the calculation of an idealized frame.

Los estilos APA, Harvard, Vancouver, ISO, etc.

8

Sharping, Jay E., Jacob Pate, Jacob Parker, Johnathon J. Thompson, Luis A. Martinez, Alessandro R. Castelli y Raymond Y. Chiao. "Joints and shape imperfections in high-Q 3D SRF cavities for RF optomechanics". Journal of Applied Physics 128, n.º 7 (21 de agosto de 2020): 073906. http://dx.doi.org/10.1063/5.0007451.

Texto completo

Los estilos APA, Harvard, Vancouver, ISO, etc.

9

Toral-Lopez, Alejandro, Enrique G. Marin, Francisco Pasadas, Jose Maria Gonzalez-Medina, Francisco G. Ruiz, David Jiménez y Andres Godoy. "GFET Asymmetric Transfer Response Analysis through Access Region Resistances". Nanomaterials 9, n.º 7 (18 de julio de 2019): 1027. http://dx.doi.org/10.3390/nano9071027.

Texto completo

Resumen

Graphene-based devices are planned to augment the functionality of Si and III-V based technology in radio-frequency (RF) electronics. The expectations in designing graphene field-effect transistors (GFETs) with enhanced RF performance have attracted significant experimental efforts, mainly concentrated on achieving high mobility samples. However, little attention has been paid, so far, to the role of the access regions in these devices. Here, we analyse in detail, via numerical simulations, how the GFET transfer response is severely impacted by these regions, showing that they play a significant role in the asymmetric saturated behaviour commonly observed in GFETs. We also investigate how the modulation of the access region conductivity (i.e., by the influence of a back gate) and the presence of imperfections in the graphene layer (e.g., charge puddles) affects the transfer response. The analysis is extended to assess the application of GFETs for RF applications, by evaluating their cut-off frequency.

Los estilos APA, Harvard, Vancouver, ISO, etc.

10

Jaitawat, Arpita y Arun Kumar Singh. "Battery and supercapacitor imperfections modeling and comparison for RF energy harvesting wireless sensor network". Wireless Networks 26, n.º 2 (6 de septiembre de 2018): 843–53. http://dx.doi.org/10.1007/s11276-018-1831-z.

Texto completo

Los estilos APA, Harvard, Vancouver, ISO, etc.

11

Muşat, V., A. Latina, A. Malyzhenkov y A. Aksoy. "A start-to-end optimisation of CLEAR for an inverse Compton scattering experiment, using RF-Track". Journal of Physics: Conference Series 2687, n.º 3 (1 de enero de 2024): 032025. http://dx.doi.org/10.1088/1742-6596/2687/3/032025.

Texto completo

Resumen

Abstract The CERN Linear Electron Accelerator for Research (CLEAR) has been operating as a user facility since 2017, providing beams for various experiments. This paper describes a start-to-end optimisation of the CLEAR beamline as a driver for X-ray generation through inverse Compton scattering. The novel particle tracking code RF-Track was used to simulate the electron beam from the bunch generation at the cathode up to the interaction with a laser beam. Figures of merit of the scattered photon beam were computed in RF-Track, and optimised by tuning the beam parameters at injection and quadrupole strengths across the beamline. The aim of the optimisation was to maximise the scattered photon flux, and minimise the effects from static and dynamic imperfections. The start-to-end model of the CLEAR beamline was used to derive the impact of jitter on flux.

Los estilos APA, Harvard, Vancouver, ISO, etc.

12

Vlachos, Evangelos, John Thompson, Aryan Kaushik y Christos Masouros. "Radio-frequency chain selection for energy and spectral efficiency maximization in hybrid beamforming under hardware imperfections". Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 476, n.º 2244 (diciembre de 2020): 20200451. http://dx.doi.org/10.1098/rspa.2020.0451.

Texto completo

Resumen

The next-generation wireless communications require reduced energy consumption, increased data rates and better signal coverage. The millimetre-wave frequency spectrum above 30 GHz can help fulfil the performance requirements of the next-generation mobile broadband systems. Multiple-input multiple-output technology can provide performance gains to help mitigate the increased path loss experienced at millimetre-wave frequencies compared with microwave bands. Emerging hybrid beamforming architectures can reduce the energy consumption and hardware complexity with the use of fewer radio-frequency (RF) chains. Energy efficiency is identified as a key fifth-generation metric and will have a major impact on the hybrid beamforming system design. In terms of transceiver power consumption, deactivating parts of the beamformer structure to reduce power typically leads to significant loss of spectral efficiency. Our aim is to achieve the highest energy efficiency for the millimetre-wave communications system while mitigating the resulting loss in spectral efficiency. To achieve this, we propose an optimal selection framework which activates specific RF chains that amplify the digitally beamformed signals with the analogue beamforming network. Practical precoding is considered by including the effects of user interference, noise and hardware impairments in the system modelling.

Los estilos APA, Harvard, Vancouver, ISO, etc.

13

Olsson, Magnus B. E., Ronnie Wirestam y Bertil R. R. Persson. "A computer simulation program for mr imaging: application to rf and static magnetic field imperfections". Magnetic Resonance in Medicine 34, n.º 4 (octubre de 1995): 612–17. http://dx.doi.org/10.1002/mrm.1910340418.

Texto completo

Los estilos APA, Harvard, Vancouver, ISO, etc.

14

Mahrof, Dlovan H., Eric A. M. Klumperink, Zhiyu Ru, Mark S. Oude Alink y Bram Nauta. "Cancellation of OpAmp Virtual Ground Imperfections by a Negative Conductance Applied to Improve RF Receiver Linearity". IEEE Journal of Solid-State Circuits 49, n.º 5 (mayo de 2014): 1112–24. http://dx.doi.org/10.1109/jssc.2013.2294637.

Texto completo

Los estilos APA, Harvard, Vancouver, ISO, etc.

15

Petersen, Martin N., Giovanni Tartarini, Davide Visani, Pier Faccin y Luigi Tarlazzi. "Influence of transmitter chirp and receiver imperfections on RF gain in short-range RO MMF systems". Microwave and Optical Technology Letters 53, n.º 4 (22 de febrero de 2011): 822–24. http://dx.doi.org/10.1002/mop.25862.

Texto completo

Los estilos APA, Harvard, Vancouver, ISO, etc.

16

Oh, Dong-Cheol. "Conductivity Control of Al-doped ZnO Thin Films Deposited by Radio Frequency Sputtering". Asian Journal of Chemistry 35, n.º 7 (2023): 1672–76. http://dx.doi.org/10.14233/ajchem.2023.28017.

Texto completo

Resumen

Films made up of Al-doped ZnO (AZO) are the promising transparent conductive oxides. Hall measurements were used to investigate the effects of varying the sputtering parameters on the electrical resistivity, electron concentration and electron mobility of a series of AZO films produced by radio frequency (RF) sputtering. Increases in plasma power, chamber pressure, argon (Ar) flow rate and decreases in substrate temperature lead to the higher electrical resistance. However, all the samples exhibit a pattern in which electrical resistivities decrease with increasing annealing temperature (below 200-400 ºC) and increase (above 200-400 ºC). As the number of electrons increases, the electrical resistance decreases and vice-versa. The carrier compensation effect or excess carrier compensation due to the formation or annihilation of conductive defects is responsible for these shifts in the electrical characteristics. It was also found that the conductivities of the AZO films formed via RF-sputtering dependent on imperfections in structure such as ionized impurities and grain boundaries, as electron mobility is shown to be proportional to the electron concentration.

Los estilos APA, Harvard, Vancouver, ISO, etc.

17

Trimby, E., H. Hirzler, H. Fürst, A. Safavi-Naini, R. Gerritsma y R. S. Lous. "Buffer gas cooling of ions in radio-frequency traps using ultracold atoms". New Journal of Physics 24, n.º 3 (1 de marzo de 2022): 035004. http://dx.doi.org/10.1088/1367-2630/ac5759.

Texto completo

Resumen

Abstract Reaching ultracold temperatures within hybrid atom–ion systems is a major limiting factor for control and exploration of the atom–ion interaction in the quantum regime. In this work, we present results on numerical simulations of trapped ion buffer gas cooling using an ultracold atomic gas in a large number of experimentally realistic scenarios. We explore the suppression of micromotion-induced heating effects through optimization of trap parameters for various radio-frequency (rf) traps and rf driving schemes including linear and octupole traps, digital Paul traps, rotating traps and hybrid optical/rf traps. We find that very similar ion energies can be reached in all of them even when considering experimental imperfections that cause so-called excess micromotion. Moreover we look into a quantum description of the system and show that quantum mechanics cannot save the ion from micromotion-induced heating in an atom–ion collision. The results suggest that buffer gas cooling can be used to reach close to the ion’s groundstate of motion and is even competitive when compared to some sub-Doppler cooling techniques such as Sisyphus cooling. Thus, buffer gas cooling is a viable alternative for ions that are not amenable to laser cooling, a result that may be of interest for studies into cold controlled quantum chemistry and charged impurity physics.

Los estilos APA, Harvard, Vancouver, ISO, etc.

18

Zagorski, Michael G. "Improved lineshapes and water suppression in 2D NMR spectra using composite 90° pulses to compensate RF imperfections". Journal of Magnetic Resonance (1969) 99, n.º 2 (septiembre de 1992): 403–7. http://dx.doi.org/10.1016/0022-2364(92)90194-c.

Texto completo

Los estilos APA, Harvard, Vancouver, ISO, etc.

19

Ananda Mohan, P. V., Eric A. M. Klumperink, Dlovan H. Mahrof y Bram Nauta. "Comments on “Cancellation of OpAmp Virtual Ground Imperfections by a Negative Conductance Applied to Improve RF Receiver Linearity” [". IEEE Journal of Solid-State Circuits 49, n.º 9 (septiembre de 2014): 2083. http://dx.doi.org/10.1109/jssc.2014.2334398.

Texto completo

Los estilos APA, Harvard, Vancouver, ISO, etc.

20

Rawat, Karun, Meenakshi Rawat y F. M. Ghannouchi. "Compensating I–Q Imperfections in Hybrid RF/Digital Predistortion With an Adapted Lookup Table Implemented in an FPGA". IEEE Transactions on Circuits and Systems II: Express Briefs 57, n.º 5 (mayo de 2010): 389–93. http://dx.doi.org/10.1109/tcsii.2010.2047326.

Texto completo

Los estilos APA, Harvard, Vancouver, ISO, etc.

21

Chandrasenan, Archa y Joseph Zacharias. "Non-linear photonic loop mirror based co-site interference canceller". Laser Physics Letters 19, n.º 11 (13 de octubre de 2022): 116207. http://dx.doi.org/10.1088/1612-202x/ac9679.

Texto completo

Resumen

Abstract Full duplex-in band (FDIB) is a well-established solution for increasing the data rate and spreading the link range for future communication systems. FDIB systems need no additional bandwidth requirement. However, they are confronted with a major interference challenge on the same site, called co-site interference (CSI). Long-established co-site interference cancellation (CSIC) methods achieve a cancellation depth upto 35 dB, conversely it has space containments, manufacturing imperfections, induces noise penalties and limits isolation bandwidth. To overcome these problems, RF photonic CSIC methods have been developed, which have produced 30 dB wide-band interference suppression. They also increase bandwidth, have a flexible structure, minimize losses and prevent periodic power fading. But these systems have a problem of inherent DC drift, low maintenance of coherence, and low isolation at low transmission power. Thus, there is a high need for photonic CSIC designs of FDIB systems that operate over wider bandwidths and at higher transmission powers. Here, a newfangled CSIC system based on a non-linear photonic loop and frequency down-conversion is proposed. It shows excellent CSIC suppression of greater than 61 dB, for a single frequency signal of interest (SOI) with maximum RF power of 13 dBm. Without frequency down-conversion, the system maintains an average cancellation depth of 62.541 dB for single frequency SOI. After frequency down conversion, the system maintains an average cancellation depth of 61.208 dB for narrow band SOI. The system attains 18% error vector magnitude at −20 dB RF output power, which confirms the comprehensive quality of the system.

Los estilos APA, Harvard, Vancouver, ISO, etc.

22

Zhou, Meijing, Nan Chen, Changhua Zhu y Yunhui Yi. "Joint Digital Self-interference Cancellation in Full-duplex Radios under IQ Imbalance and Transmitter Non-linearity". ITM Web of Conferences 17 (2018): 01003. http://dx.doi.org/10.1051/itmconf/20181701003.

Texto completo

Resumen

RF imperfections can significantly degrade the performance of full-duplex wireless communication system by introducing non-idealities and random effects, which make it difficult to cancel the self-interference completely. In this paper, we first address the adverse benefits of both the transmitter non-linearity and the IQ imbalance. Then on the basis of these, a joint digital self-interference cancellation scheme is proposed, in which not only the effect of IQ imbalance and power amplifier non-linearity individually, but also the comprehensive function of them are taken into account. Furthermore, the simulation is implemented in the MATLAB platform using standard WiFi 802.11ac PHYs. The results show that the proposed canceller can eliminate more compared with other cancellation schemes, and the overall self-interference attenuation can attain 108dB, which makes the residual self-interference closer to the noise floor.

Los estilos APA, Harvard, Vancouver, ISO, etc.

23

Zhang, Shuhui, Tian Lan, Lianhai Wang, Shujiang Xu y Wei Shao. "Ethereum Ponzi Scheme Detection Based on PD-SECR". Security and Communication Networks 2022 (21 de septiembre de 2022): 1–15. http://dx.doi.org/10.1155/2022/2316310.

Texto completo

Resumen

Ethereum, a typical application of blockchain technology, has attracted extensive attention from all walks of life since its release. Owing to imperfections in existing supervision technology, illegal and criminal activities on blockchain platforms are becoming increasingly frequent. The most typical Ethereum fraud is the Ponzi scheme, which causes blockchain investors to lose millions of assets and severely impacts social development. Currently, Ponzi scheme detection primarily focuses on machine learning and data mining. However, existing detection methods still have two problems in data imbalance processing and feature extraction: (1) data enhancement using an oversampling algorithm produces noise and (2) feature redundancy existing in extracted feature data. The SMOTEENN algorithm is introduced to solve data imbalance. The PD-SECR method, the Convolutional Neural Network (CNN) feature extraction, and random forest (RF) classification models are used for detection, but the two models are independently trained. The results show that the detection method proposed in this study is more suitable for the Ethereum Ponzi scheme.

Los estilos APA, Harvard, Vancouver, ISO, etc.

24

Mednikarov, B. "Deposition and Characterization of Aluminium Nitride (AlN) and Diamond Like Carbon (DLC) Hard Coatings". Solid State Phenomena 159 (enero de 2010): 63–70. http://dx.doi.org/10.4028/www.scientific.net/ssp.159.63.

Texto completo

Resumen

Traditionally, the term hard coatings refer to the property of high hardness in mechanical sense with good tribological properties [1]. With the development of modern technology in the areas of optical, optoelectronic, microelectronic and related defense applications, the definition of the term hard coatings can be extended. Thus, a system which operates satisfactorily, in a given environment can be said to be hard with respect to that environment [2]. Most of the hard coatings are ceramic compounds such as oxides, carbides, nitrides (AlN), ceramic alloys, cermets, metastable materials such as Diamond-Like Carbon (DLC). Their properties and environmental resistance depend on the composition, stoichiometry, impurities, microstructure, imperfections, and in the case of coatings, the preferred orientation (texture). In this paper we shall take a look at some characteristics - physicochemical and optical of AlN and DLC layers synthesized by physical vapor deposition – RF magnetron sputtering in an industrial high vacuum deposition system. The influence of the process parameters on the growth rate, morphology, topography and chemical bonding structure will be presented.

Los estilos APA, Harvard, Vancouver, ISO, etc.

25

Thibane, Vuyisile Samuel, Maanea Lonia Ramphinwa, Godwin Richard Ainamensa Mchau y Fhatuwani Nixwell Mudau. "Metabolite Profile of Athrixia phylicoides DC. (Bush Tea) and Determination of Inhibitory Mechanism against Tyrosinase Enzyme from Mushroom". Cosmetics 9, n.º 6 (5 de diciembre de 2022): 133. http://dx.doi.org/10.3390/cosmetics9060133.

Texto completo

Resumen

Athrixia phylicoides DC. (Bush tea) is a shrub harvested in the north-eastern mountain regions of South Africa and belongs to the Asteraceae family. Generally, A. phylicoides is consumed as a hot tea beverage for its associated health benefits. The use of bush tea extracts for beauty enhancement has not been investigated even though several ethnobotanical reports have indicated its usage against skin imperfections. Therefore, the aim of the study was to assess plant metabolites of A. phylicoides for their inhibition of tyrosinase from mushroom and determine their inhibitory mechanism. Methanolic extracts (80% v/v) of A. phylicoides were evaluated using a tyrosinase-based TLC (thin-layer chromatography) autography technique. The inhibitory mechanism of active metabolites against the enzyme was determined using Lineweaver–Burk plots. Quercetin and an unknown metabolite with a retention factor (Rf) value of 0.73 inhibited melanogenesis. However, the IC50 value for Quercetin was reported as 51.07 ± 2.43 µg/mL higher than that of kojic acid of 5.22 ± 1.44 µg/mL. Chlorogenic acid was reported to have a similar Rf value as kojic acid, suggesting similarities in polarity and affinity towards the adsorbent material. However, chlorogenic acid with an IC50 value of 15.25 ± 1.18 µg/mL and an inhibitory strength of 2.92 could not inhibit melanogenesis with a similar intensity as kojic acid. The inhibitory mechanism for A. phylicoides extract was reported to be mixed inhibition (competitive/uncompetitive). The IC50 value for A. phylicoides was recorded as 20.65 ± 0.14 µg/mL with an inhibitory strength of 3.96. These results suggest that A. phylicoides extracts could be used against dark spots associated with scarring and ageing through modulation of tyrosinase activity.

Los estilos APA, Harvard, Vancouver, ISO, etc.

26

Xue, Guanchang, Mingchuan Yang, Qing Guo y Shuai Yuan. "Performance of Spectrum Sharing in Hybrid Satellite Terrestrial Network with Opportunistic Relay Selection". Wireless Communications and Mobile Computing 2022 (14 de octubre de 2022): 1–13. http://dx.doi.org/10.1155/2022/2673024.

Texto completo

Resumen

In this paper, we consider the uplink of a hybrid satellite-terrestrial spectrum sharing system, in which satellite terminal communicates with satellite through terrestrial relay-assisted transmission. To accommodate expanding networks within limited spectrum, spectrum sharing is considered a promising candidate. For the system in which satellite terminals and terrestrial terminals share spectrum, we propose opportunistic relay selected spectrum sharing method based on decoding and forwarding protocol. Selecting the optimal relay station is aimed at minimizing the outage probability of the satellite terminal and maximizing the throughput of the system. Due to spectrum sharing policy and imperfections in the RF front end, we also consider the effects of cochannel interference (CCI) and hardware impairments (HIs). The satellite link is modeled as Shadowed-Rician fading, and the terrestrial link uses Nakagami-m fading. In addition, we deduce the closed-form analytical expressions of the satellite terminal outage probability, deduce the asymptotic expressions under the condition of high signal-to-noise ratio, and analyze their achievable diversity orders. Numerical and simulation results validate the performance gain of opportunistic relay selection compared to partial relay selection. Monte Carlo simulations confirm the correctness of the theoretical analysis and illustrate the effects of CCI and HIs on the system.

Los estilos APA, Harvard, Vancouver, ISO, etc.

27

Loura, Sakshi. "Developing a Smart Integrated System for the Effective Prediction and Diagnosis of Varicose Disease and their Treatment". International Journal of Research in Science and Technology 10, n.º 04 (2022): 54–59. http://dx.doi.org/10.37648/ijrst.v10i04.008.

Texto completo

Resumen

The vein that transfers the deoxygenated blood gets knob and thick because of a valve twist, which becomes varicose veins. These are most normal in the legs. These varicose veins are brought about by harmed or feeble valves of veins that veneer to the variety of blood in the vein, which expands the tension and causes nightmares. A large portion of the varicose vein treatment is by obtrusive techniques like a medical procedure, laser treatment, RF endogenous treatment and sclerotherapy. In any medical procedure, the significant primary perspective is the addition of an intravenous (IV) catheter. The serious issue looked at by the doctors is dangers in getting to veins for IV medication or taking blood for tests, if kids, grown-ups, basic consideration patients and so on. It is a truly challenging chore. Pointless penetrating of veins happens because of unfortunate perceivability. Wrong penetrating may prompt issues like imperfections or super durable harm to the vein. To tackle these issues, there is a requirement for a vein divulgence system. We propose a sensor that involves wearable socks-based painless diagnostic & helpful answers for varicose veins using warm and vibration treatment. Since it is a harmless technique, it gives modern patient help from their aggravation without torment with IoT-based indicative and refreshing structures.

Los estilos APA, Harvard, Vancouver, ISO, etc.

28

Dragoman, Mircea, Silviu Vulpe, Elias Aperathithis, Chrysa Aivalioti, Cosmin Romanitan, Adrian Dinescu, Daniela Dragoman et al. "Oxygen-vacancy induced ferroelectricity in nitrogen-doped nickel oxide". Journal of Applied Physics 131, n.º 16 (28 de abril de 2022): 164304. http://dx.doi.org/10.1063/5.0075568.

Texto completo

Resumen

This paper reports the onset of ferroelectricity in NiO by breaking the crystallographic symmetry with oxygen vacancies created by N doping. Nitrogen-doped NiO was grown at room temperature by RF sputtering of Ni target in Ar–O2–N2 plasma on silicon and fused silica substrates. The impact of the nitrogen doping of NiO on microstructural, optical, and electrical properties has been investigated. According to x-ray diffraction investigations, by increasing the N doping level in NiO, a transition from (002) to a (111) preferential orientation for the cubic NiO phase was observed, as well as a lattice strain relaxation, that is usually ascribed to structural defect formation in crystal. The x-ray diffraction pole figures the presence of a distorted cubic structure in NiO and supports the Rietveld refinement findings related to the strain, which pointed out that nitrogen doping fosters lattice imperfections formation. These findings were found to be in agreement with our far-infrared measurements that revealed that upon nitrogen doping a structural distortion of the NiO cubic phase appears. X-ray photoemission spectroscopy measurements reveal the presence of oxygen vacancies in the NiO film following nitrogen doping. Evidence of ferroelectricity in nitrogen-doped NiO thin films has been provided by using the well-established Sawyer–Tower method. The results reported here provide the first insights on oxygen-vacancy induced ferroelectricity in nitrogen-doped nickel oxide thin films.

Los estilos APA, Harvard, Vancouver, ISO, etc.

29

Moiseeva, V. Yu y A. V. Moiseev. "EARNED INCOME TAX IN THE SYSTEM OF SPECIAL TAX REGIMES". Vektor nauki Tol’attinskogo gosudarstvennogo universiteta. Seria Uridicheskie nauki, n.º 1 (2022): 28–33. http://dx.doi.org/10.18323/2220-7457-2022-1-28-33.

Texto completo

Resumen

Scientists ambiguously assess the new special tax regime “Earned Income Tax” introduced in 2019 as an experiment: some scientists criticize it, while others recognize it necessary. A little over two years of experience with this tax regime revealed positive results and some problems. The study aims to carry out a legal analysis of the earned income tax as a special tax regime, identify disadvantages and suggest ways to eliminate them. The authors considered the specifics of the tax regime “Earned Income Tax” to investigate its nature and identify its advantages and disadvantages. The study found that the legalization stimulation and the emergence of new business entities are carried out through the use of a special tax regime along with preferential taxation – a simplified procedure for tax administration. The authors paid particular attention to the problem of defining the concept of self-employed, which is not legally enshrined. The paper analyzes Federal law No. 422-FZ in terms of legal conflicts with other federal laws and suggests ways to eliminate them. The authors discuss bill drafts proposing to make some amendments to the current Federal law No. 422-FZ in terms of allowing the RF constituent entities to independently reduce the earned income tax rate, as well as establishing a minimum tax amount in the absence of income. The analysis allowed concluding that the new special tax regime, despite some disadvantages and imperfections of the current legislation in terms of its regulation, can ensure a balance of private and public interests to replenish the budget by transferring the activities of the self-employed to the legal field.

Los estilos APA, Harvard, Vancouver, ISO, etc.

30

Vaňko, Matúš, Ivan Glesk, Jarmila Müllerová, Jozef Dubovan y Milan Dado. "Design, Optimization, and Experimental Evaluation of Slow Light Generated by π-Phase-Shifted Fiber Bragg Grating for Use in Sensing Applications". Sensors 24, n.º 2 (6 de enero de 2024): 340. http://dx.doi.org/10.3390/s24020340.

Texto completo

Resumen

This paper describes design, theoretical analysis, and experimental evaluation of a π-Phase-Shifted Fiber Bragg Grating (π-PSFBG) inscribed in the standard telecom fiber for slow light generation. At first, the grating was designed for its use in the reflection mode with a central wavelength of 1552 nm and a pass band width of less than 100 pm. The impact of fabrication imperfections was experimentally investigated and compared to model predictions. The optical spectra obtained experimentally show that the spectral region used for slow light generation is narrower (less than 10 pm), thus allowing for too-low levels of slow light optical-output power. In the next step, the optimization of the grating design was conducted to account for fabrication errors, to improve the grating’s spectral behavior and its temporal performance, and to widen the spectral interval for slow light generation in the grating’s transmission mode. The targeted central wavelength was 1553 nm. The π-PSFBG was then commercially fabricated, and the achieved parameters were experimentally investigated. For the region of (1551–1554) nm, a 15-fold increase in the grating’s pass band width was achieved. We have shown that a pair of retarded optical pulses were generated. The measured group delay was found to be ~10.5 ps (compared to 19 ps predicted by the model). The π-PSFBG operating in its transmission mode has the potential to operate as tunable delay line for applications in RF photonics, ultra-fast signal processing, and optical communications, where tunable high precision delay lines are highly desirable. The π-PSFBG can be designed and used for the generation of variable group delays from tens to hundreds of ps, depending on application needs.

Los estilos APA, Harvard, Vancouver, ISO, etc.

31

Jakovidis, G., I. M. Jamieson y A. Singh. "RF-Sputtered MoS2 Film Morphology and the Imperfection Nucleation Model". Surface Review and Letters 10, n.º 02n03 (abril de 2003): 443–48. http://dx.doi.org/10.1142/s0218625x03004743.

Texto completo

Resumen

RF-sputtered MoS2 films revealing the characteristics of bulk type II orientation on GaAs are reported for the first time. It is found that RF power and temperature have a pronounced effect on film morphology. Type II bulk-oriented films are obtained with a combination of low RF power and high substrate temperature. The results on GaAs are successfully interpreted within the context of an extension to the imperfection nucleation model of film formation. Films deposited on glass display an unusual morphology consisting of two distinct phases. Such phases may be related to the presence of sodium in the glass that leads to chemical texturing via a sodium thio-molybdate phase.

Los estilos APA, Harvard, Vancouver, ISO, etc.

32

Lei, Hongjiang, Haolun Luo, Ki-Hong Park, Zhi Ren, Gaofeng Pan y Mohamed-Slim Alouini. "Secrecy Outage Analysis of Mixed RF-FSO Systems With Channel Imperfection". IEEE Photonics Journal 10, n.º 3 (junio de 2018): 1–13. http://dx.doi.org/10.1109/jphot.2018.2835562.

Texto completo

Los estilos APA, Harvard, Vancouver, ISO, etc.

33

Abanto-Leon, Luis F., Andreas Bäuml, Gek Hong (Allyson) Sim, Matthias Hollick y Arash Asadi. "Stay Connected, Leave no Trace: Enhancing Security and Privacy in WiFi via Obfuscating Radiometric Fingerprints". ACM SIGMETRICS Performance Evaluation Review 49, n.º 1 (22 de junio de 2022): 83–84. http://dx.doi.org/10.1145/3543516.3456280.

Texto completo

Resumen

The intrinsic hardware imperfection of WiFi chipsets manifests itself in the transmitted signal, leading to a unique radiometric (radio frequency) fingerprint. This fingerprint can be used as an additional means of authentication to enhance security. In this paper, we prove analytically and experimentally that these solutions are highly vulnerable to impersonation attacks. We also demonstrate that such a unique device-specific signature can be abused to track devices, thus violating privacy. We propose RF-Veil, a radiometric fingerprinting solution that is not only robust against impersonation attacks but also effective in protecting privacy by obfuscating the radiometric fingerprint of the transmitter for non-legitimate receivers. Specifically, we introduce a randomized pattern of phase errors to the transmitted signal such that only the intended receiver can extract the original fingerprint of the transmitter. In a series of experiments and analyses, we expose the vulnerability of adopting naive randomization to statistical attacks and introduce countermeasures. Finally, we show the efficacy of RF-Veil experimentally in protecting user privacy and enhancing security. More importantly, our proposed solution allows communicating with other devices, which do not employ RF-Veil.

Los estilos APA, Harvard, Vancouver, ISO, etc.

34

Larina, V. N., D. S. Mkrtychev, V. A. Kuznetsova y A. A. Tyazhelnikov. "Possible Approaches to Primary Prevention of Cardiovascular Diseases". Rational Pharmacotherapy in Cardiology 16, n.º 5 (4 de noviembre de 2020): 831–41. http://dx.doi.org/10.20996/1819-6446-2020-10-12.

Texto completo

Resumen

In recent years there is a positive trend in the development of preventive medicine, in particular, primary prevention of diseases. However, in most cases, patients seek help from a doctor after the manifestation of the disease, and therefore, early identification of risk factors (RF) remains relevant. Conduction of a large number of studies that are aimed at studying modifiable RF associated with the development of cardiovascular diseases (CVD), allowed the experts of the American Heart Association to develop recommendations “Life's Simple 7”, which makes it possible to structure methods of primary prevention of CVD and minimize the risk of their development. In 2019, experts from the American College of Cardiology presented a simplified version of these recommendations, to improve approaches to primary prevention and their effectiveness not only for doctors but also for patients. Thus, by involving the patient in the decision-making process about follow-up treatment, doctors can achieve a high level of compliance, which is essential for improving the prognosis. The “ABCDE” recommendations, in name of which are reflected the first letters of the leading CVD RF, include such paragraphs as RF assessment, the use of antiaggregating therapy, correction of blood pressure, cholesterol levels, smoking elimination, correction of high glucose levels and diabetes treatment, weight loss, assessment of social and economic factors affecting the morbidity in a particular patient. Despite the undoubted benefit of the “ABCDE” recommendations, some problems of primary prevention currently cannot be solved: the inability to accurately assess social and economic RF; the imperfection of the used CVD risk scales. The updated version of the recommendations allows not only to assess the existing RF of the patient, but also to effectively correct them. In addition, the patient himself can read the recommendations, which improves understanding of the primary prevention importance.

Los estilos APA, Harvard, Vancouver, ISO, etc.

35

Kidalov, V. V., A. F. Dyadenchuk, V. P. Kladko, O. I. Gudymenko, M. P. Derhachov, S. O. Popov, O. O. Sushko y Vitali V. Kidalov. "Structure and Electrical Properties of β-Ga₂O₃ Films Obtained by Radio Frequency Magnetron Sputtering on Porous Silicon". ECS Journal of Solid State Science and Technology 11, n.º 2 (1 de febrero de 2022): 025004. http://dx.doi.org/10.1149/2162-8777/ac4edc.

Texto completo

Resumen

A wide range of possible applications of gallium oxide requires further investigations on growth techniques of its thin films, especially deposited on non-native substrates. One of the ways to avoid imperfection of Ga2O3 film because of variations in structure and lattice parameters of substrate could be an exploitation of buffer porous layer previously synthesized on the substrate. The 170 nm films deposited on porous-Si/Si substrate by rf magnetron sputtering are found out to be composed of β-Ga2O3 elliptical grains with sizes ∼150 nm. Both EDAX and Raman spectroscopy results show formation of a thin interfacial SiO2. Impedance spectroscopy measurements reveals two charge transfer processes with activation energies of 1.33 eV and 1.79 eV.

Los estilos APA, Harvard, Vancouver, ISO, etc.

36

Xu, Tongyang, Hedaia Ghannam y Izzat Darwazeh. "Practical Evaluations of SEFDM: Timing Offset and Multipath Impairments". Infocommunications journal, n.º 4 (2018): 2–9. http://dx.doi.org/10.36244/icj.2018.4.1.

Texto completo

Resumen

The non-orthogonal signal waveform spectrally efficient frequency division multiplexing (SEFDM) improves spectral efficiency at the cost of self-created inter carrier interference (ICI). As the orthogonal property, similar to orthogonal frequency division multiplexing (OFDM), no longer exists, the robustness of SEFDM in realistic wireless environments might be weakened. This work aims to evaluate the sensitivity of SEFDM to practical channel distortions using a professional experiment testbed. First, timing offset is studied in a bypass channel to locate the imperfection of the testbed and its impact on SEFDM signals. Then, the joint effect of a multipath frequency selective channel and additive white Gaussian noise (AWGN) is investigated in the testbed. Through practical experiments, we demonstrate the performance of SEFDM in realistic radio frequency (RF) environments and verify two compensation methods for SEFDM. Our results show first frequency-domain compensation works well in frequency non-selective channel conditions while time-domain compensation method is suitable for frequency selective channel conditions. This work paves the way for the application of SEFDM in different channel scenarios.

Los estilos APA, Harvard, Vancouver, ISO, etc.

37

Serša, Igor. "Comparison of driven equilibrium and standard spin-echo sequence in MR microscopy: Analysis of signal dependence on RF pulse imperfection and diffusion". Journal of Magnetic Resonance 359 (febrero de 2024): 107624. http://dx.doi.org/10.1016/j.jmr.2024.107624.

Texto completo

Los estilos APA, Harvard, Vancouver, ISO, etc.

38

Nishawala, V. V., M. Ostoja-Starzewski, M. J. Leamy y E. Porcu. "Lamb's problem on random mass density fields with fractal and Hurst effects". Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 472, n.º 2196 (diciembre de 2016): 20160638. http://dx.doi.org/10.1098/rspa.2016.0638.

Texto completo

Resumen

This paper reports on a generalization of Lamb's problem to a linear elastic, infinite half-space with random fields (RFs) of mass density, subject to a normal line load. Both, uncorrelated and correlated (with fractal and Hurst characteristics) RFs without any weak noise restrictions, are proposed. Cellular automata (CA) is used to simulate the wave propagation. CA is a local computational method which, for rectangular discretization of spatial domain, is equivalent to applying the finite difference method to the governing equations of classical elasticity. We first evaluate the response of CA to an uncorrelated mass density field, more commonly known as white-noise, of varying coarseness as compared to CA's node density. We then evaluate the response of CA to multiscale mass density RFs of Cauchy and Dagum type; these fields are unique in that they are able to model and decouple the field's fractal dimension and Hurst parameter. We focus on stochastic imperfection sensitivity; we determine to what extent the fractal or the Hurst parameter is a significant factor in altering the solution to the planar stochastic Lamb's problem by evaluating the coefficient of variation of the response when compared with the coefficient of variation of the RF.

Los estilos APA, Harvard, Vancouver, ISO, etc.

39

Zhuravleva, M. V. y A. Yu Lebedeva. "Organization of pharmacological support of patients with rare diseases in moscow as exemplified by pulmonary arterial hypertension". Medical Council, n.º 16 (27 de septiembre de 2018): 24–31. http://dx.doi.org/10.21518/2079-701x-2018-16-24-31.

Texto completo

Resumen

Orphan diseases are life-threatening, chronic, progressive and leading to a reduction in life expectancy or disability conditions. Patients with rare diseases are one of the vulnerable population groups, which is caused by several factors, such as insufficient awareness of practitioners about such diseases, complicated and lengthy diagnosis, and imperfection of legal environment in the area of pharmacological support of orphan diseases, when only 24 orphan diseases (List-24) are determined, which are treated at the expense of the RF subjects.Imperfection of federal orphan diseases legislation is shown on the example of providing patients with PAH-specific therapy: only idiopathic form of pulmonary hypertension is included in the federal List-24, there is no well-established mechanism of pharmacological support for patients with chronic thromboembolic pulmonary hypertension (CTEPH) that is not included in the List-24. The article describes the successful experience in providing patients with orphan diseases, regardless of the inclusion of nosology in List-24 in Moscow, through the creation and implementation of the transparent medical and pharmacological support regulation for patients with orthopaedic diseases, which settled the timely process of provision of patients with the necessary therapy. As a result, patients with CTEPH also have access to existing pathogenetic treatment that can prolong life and improve the quality of life of such patients.

Los estilos APA, Harvard, Vancouver, ISO, etc.

40

Zhu, Hongyu, Jingjian Huang, Chao Wang, Weidong Hu, Naichang Yuan, Qingping Wang, Chang Zhu y Ximeng Zhang. "Multi-Domain Self-Interference Cancellation Methods Considering RF Imperfections". IEEE Transactions on Wireless Communications, 2024, 1. http://dx.doi.org/10.1109/twc.2024.3353306.

Texto completo

Los estilos APA, Harvard, Vancouver, ISO, etc.

41

Shu, Yun-Shiang, Stacy Ho, Hsin-Hung Chen, Bala Narasimhan y Kou-Hung Lawrence Loh. "Signal processing and analog/RF circuit design: cross-discipline interactions and technical challenges". APSIPA Transactions on Signal and Information Processing 5 (2016). http://dx.doi.org/10.1017/atsip.2016.12.

Texto completo

Resumen

The increasing demand for high-data rate communications in the connected world imposes various challenges in analog and radio frequency (RF) circuits. Although continued scaling in advanced processes offers faster devices, it is accompanied by increasing complexity in circuit design and layout strategy, resulting in diminishing benefits for analog/RF circuits. In order to enable new breakthroughs in speed, cost, and power efficiency, simplifying analog/RF circuits with the assistance of signal processing is becoming a clear trend. This paper provides an overview of this trend by reviewing the signal processing algorithms commonly deployed in wireless communications, data converters, and wired data links. The discussion covers design considerations, as well as algorithms used to compensate for circuit imperfections, so as to demonstrate the cross-discipline interactions between signal processing and analog/RF circuit design.

Los estilos APA, Harvard, Vancouver, ISO, etc.

42

Subrahmanian, Manu Veliparambil, KowsalyaDevi Pavuluri, Cristina Olivieri y Gianluigi Veglia. "High fidelity control of spin ensemble dynamics via artificial intelligence: from quantum computing to NMR spectroscopy and imaging". PNAS Nexus, 5 de agosto de 2022. http://dx.doi.org/10.1093/pnasnexus/pgac133.

Texto completo

Resumen

Abstract High-fidelity control of spin ensemble dynamics is essential for many research areas, spanning from quantum computing and radio frequency (RF) engineering to NMR spectroscopy and imaging. However, attaining robust and high-fidelity spin operations remains an unmet challenge. Using an evolutionary algorithm and artificial intelligence (AI), we designed new RF pulses with customizable spatial or temporal field inhomogeneity compensation. Compared with the standard RF shapes, the new AI-generated pulses show superior performance for bandwidth, robustness, and tolerance to field imperfections. As a benchmark, we constructed a spin entanglement operator for the weakly-coupled two-spin-1/2 system of 13CHCl3, achieving high-fidelity transformations under multiple inhomogeneity sources. We then generated band-selective and ultra-broadband RF pulses typical of biomolecular NMR spectroscopy. When implemented in multi-pulse NMR experiments, the AI-generated pulses significantly increased the sensitivity of medium size and large protein spectra relative to standard pulse sequences. Finally, we applied the new pulses to typical imaging experiments, showing a remarkable tolerance to changes in the RF field. These AI-generated RF pulses can be directly implemented in quantum information, NMR spectroscopy of biomolecules, magnetic imaging techniques for in vivo and materials sciences.

Los estilos APA, Harvard, Vancouver, ISO, etc.

43

Schmitz, Johannes, Milan Zivkovic y Rudolf Mathar. "Extended Cyclostationary Signatures for OFDM in the Presence of Hardware Imperfections". Frequenz 66, n.º 9-10 (20 de enero de 2012). http://dx.doi.org/10.1515/freq-2012-0051.

Texto completo

Resumen

AbstractCyclostationary signatures have been shown to be an effective method for OFDM network synchronization and Cognitive Radio coordination. In this article, an extended method that utilizes cyclostationary signatures for signal parameter identification of OFDM-based Cognitive Radio nodes is presented. The scenario, implemented on a GNU Radio based evaluation platform, shows how different signal parameters, e.g. carrier frequency, occupied bandwidth and the used modulation scheme can be identified at the receiver side using the described approach. A major drawback of cyclostationary detection in OFDM systems is its sensitivity to frequency offset and sampling rate mismatches between oscillators at the transmitter and the receiver. An analytical model that characterizes this impairments is derived, followed by a discussion of implementation issues and the performance evaluation of proposed cyclostationary signature detection, both in a simulation environment and through RF experiments.

Los estilos APA, Harvard, Vancouver, ISO, etc.

44

Kelly, Matthew W., Tom N. Oder y C. Virgil Solomon. "The Effect of Crystallographic Imperfections on the Photoluminescence of ZnO Thin Films". MRS Proceedings 1731 (2015). http://dx.doi.org/10.1557/opl.2015.268.

Texto completo

Resumen

ABSTRACTZnO thin films were synthesized by radio-frequency (RF) magnetron sputtering of high purity ZnO solid targets on sapphire substrates. Depositions were carried out at selected temperatures between 293 K and 1173 K, and post-deposition annealing was performed at 1173 K for 3 min. in an O2 atmosphere. Samples for electron microscopy investigations were prepared by lift-out technique in a multi-beam FIB/SEM instrument. The ZnO thin films show generally uniform thickness (about 1µm), determined by transmission electron microscopy (TEM) imaging. Irrespective of the deposition temperature, the ZnO thin films are polycrystalline, with individual grains exhibiting columnar morphology with the long axis oriented perpendicular to the ZnO/sapphire interface. The grain size varies with the deposition temperature, and a direct correlation between grain size and photoluminescence has been observed. Analyses performed using low-temperature photoluminescence spectroscopy measurements at 12 K revealed luminescence peaks at 3.361, 3.317, 3.218 and 3.115 eV. The intensity of the luminescence peak at 3.317 eV decreased with increasing deposition temperature. The films deposited at lower temperatures also exhibited a higher density of stacking faults as observed from the atomic resolution TEM. The crystallographic imperfections/photoluminescence relationship is not clear. The purpose of this study is to quantify the observed crystallographic imperfections and understand their effect on the photoluminescence of undoped ZnO thin films deposited on sapphire substrates.

Los estilos APA, Harvard, Vancouver, ISO, etc.

45

Han, Victor, Charlie P. Reeder, Miriam Hernández‐Morales y Chunlei Liu. "Any‐nucleus distributed active programmable transmit coil". Magnetic Resonance in Medicine, 11 de febrero de 2024. http://dx.doi.org/10.1002/mrm.30044.

Texto completo

Resumen

AbstractPurposeThere are 118 known elements. Nearly all of them have NMR active isotopes and at least 39 different nuclei have biological relevance. Despite this, most of today's MRI is based on only one nucleus—1H. To facilitate imaging all potential nuclei, we present a single transmit coil able to excite arbitrary nuclei in human‐scale MRI.Theory and MethodsWe present a completely new type of RF coil, the Any‐nucleus Distributed Active Programmable Transmit Coil (ADAPT Coil), with fast switches integrated into the structure of the coil to allow it to operate at any relevant frequency. This coil eliminates the need for the expensive traditional RF amplifier by directly converting direct current (DC) power into RF magnetic fields with frequencies chosen by digital control signals sent to the switches. Semiconductor switch imperfections are overcome by segmenting the coil.ResultsCircuit simulations demonstrated the effectiveness of the ADAPT Coil approach, and a 9 cm diameter surface ADAPT Coil was implemented. Using the ADAPT Coil, 1H, 23Na, 2H, and 13C phantom images were acquired, and 1H and 23Na ex vivo images were acquired. To excite different nuclei, only digital control signals were changed, which can be programmed in real time.ConclusionThe ADAPT Coil presents a low‐cost, scalable, and efficient method for exciting arbitrary nuclei in human‐scale MRI. This coil concept provides further opportunities for scaling, programmability, lowering coil costs, lowering dead‐time, streamlining multinuclear MRI workflows, and enabling the study of dozens of biologically relevant nuclei.

Los estilos APA, Harvard, Vancouver, ISO, etc.

46

Georgakopoulos, Dimitrios, Ilya Budovsky y Samuel Benz. "Quasi-continuous dc voltage standard using sinusoidal and pulse-driven Josephson junction arrays". Measurement Science and Technology, 9 de noviembre de 2022. http://dx.doi.org/10.1088/1361-6501/aca171.

Texto completo

Resumen

Abstract Josephson voltage standards (JVSs) provide a primary realization of the volt, the unit of electromotive force. They generate direct (dc) voltages up to 10 V and show agreement better than 1 nV/V at 10 V. For JVSs based on Josephson junction arrays (JJAs) that are driven by sinusoidal radiofrequency (RF) power, commonly referred to as continuous wave-driven JJAs (CWD JJAs), the minimum voltage that can be generated is limited to the voltage across one Josephson junction for practical devices. To achieve this resolution, they may require a perfect JJA chip. JVSs based on a pulse-driven (PD) JJA require high performance electronics (i.e., high bandwidth, low distortion and jitter, pulse shaping filters and large memory) to achieve their minimum and maximum voltage. We have combined two CWD JJAs and two PD JJAs driven by two microwave inputs to one chip to generate quasi-continuous dc voltages up to the sum of the full-scale voltages of both JJAs that are robust to the imperfections of the Josephson junctions and have relaxed requirements on the radio frequency (RF) electronics driving the JJA, compared to the existing CWD JVSs and PD JVSs, respectively. By use of the JJA chip at the National Measurement Institute Australia, we demonstrate its feasibility to generate voltages up to 1 V. Preliminary evaluation of the system shows that the voltage uncertainty can be 11 nV (k=2) or better and the theoretical resolution is better than 1 nV from 0 V to 1 V. The main requirement is that all the Josephson junctions must have quantum locking ranges with respect to the power and frequency of the RF bias and for the PD JJAs to have a constant voltage over a range of dc bias current. Although this development is not a replacement for existing state-of-the-art JVSs, we anticipate that it will be an alternative fit-for-purpose solution for metrological applications under non-ideal operating conditions or when the components of the state-of-the-art solutions are not available.

Los estilos APA, Harvard, Vancouver, ISO, etc.

47

Zhuang, H. B. y Min-Chun Pan. "Irregular Bone Defect Detection and Device on Dental Implants". Journal of Medical Devices 4, n.º 2 (1 de junio de 2010). http://dx.doi.org/10.1115/1.3443175.

Texto completo

Resumen

Dental implants are generally used in edentulous patients. The key issue of this dental surgery is the effective osseointegration of implants with spongy bone and cortical bone and then they become a part of loading structure. Current osseointegration detection devices only offer overall evaluation without the information of location and orientation of bone defects. This study is to develop detection techniques to measure the quantity as well as to locate the orientation of imperfection around bone-implant interface based on resonance frequency analysis (RFA). A noncontact measurement technique is performed with acoustic excitation through a loud-speaker and displacement response via a capacity-type pick-up. In the first and second series experiments, RFA is applied to estimate the orientation and quantity of irregular bone defects on various in-vitro faulty models. The variation in RF not only locates the orientation and depth of defects but also reflects the change of boundary conditions surrounding the defective models. According to these results, the detection technique to locate irregular osseointegration is established. Furthermore, the detection device to this end is proposed as well. The proposed examining approach and device are promising and able to assist dentists in dental implant surgery.

Los estilos APA, Harvard, Vancouver, ISO, etc.

Artículos de revistas sobre el tema "Imperfections RF"

Crea una cita precisa en los estilos APA, MLA, Chicago, Harvard y otros