The Experts below are selected from a list of 2253 Experts worldwide ranked by ideXlab platform
Young June Park - One of the best experts on this subject based on the ideXlab platform.
-
governing equations of the terminal current green s functions and their application to derivation of the Nyquist Theorem for multiterminal semiconductor devices
Journal of Applied Physics, 2007Co-Authors: Sungmin Hong, Hongshick Min, Young June Park, Chan Hyeong ParkAbstract:This paper presents the governing equations of the Green’s functions for the short-circuit terminal noise currents of semiconductor devices under the drift-diffusion scheme. Using these equations, the Nyquist Theorem is derived for multiterminal bipolar semiconductor devices at nonzero frequencies with generation-recombination processes considered. It is explicitly shown that generation-recombination noise sources play an essential role in canceling out part of terminal noise contributions from diffusion noise sources to finally obtain the equilibrium thermal noise.
-
reinvestigation and extension of the steady state Nyquist Theorem for multi terminal semiconductor devices and its application to minimum noise figure in microwave field effect transistors
Journal of Applied Physics, 1996Co-Authors: J B Lee, Hongshick Min, Young June ParkAbstract:The steady‐state Nyquist Theorem for multi‐terminal semiconductor devices, which describes the short‐circuit thermal noise currents in arbitrarily shaped multi‐terminal semiconductor devices, is reinvestigated. The concept of the equipotential surfaces for small ac signals is found to be wrong, which forces us to introduce a new approach to find the equipotential surfaces for noise voltages. Using this new approach, we rederive the steady‐state Nyquist Theorem with the same results as in the previous derivation, and extend it to the hot carrier regime. Using the extended Theorem, we express the minimum noise figure for microwave field effect transistors as a function of the measurable device parameters with no fitting constant. The derived minimum noise figure is shown to reduce to a simple form, which can also be used as an empirical relation with one fitting constant. This simple form can explain the experimental results very well in wide frequency ranges, and gives through a clear mathematical relation...
-
steady state Nyquist Theorem for multi terminal nondegenerate semiconductor devices
Journal of Applied Physics, 1994Co-Authors: J B Lee, Hongshick Min, Young June ParkAbstract:Formulas for the spectral intensities of the short‐circuit thermal noise currents in arbitrarily shaped multi‐terminal semiconductor devices under dc bias are derived by solving the Langevin‐type Boltzmann transport equations. The derived formulas are valid when the carrier distributions are not far from the local equilibrium distributions. Measurement data on short‐circuit thermal noise currents are obtained for a three‐terminal silicon bulk device. A comparison between the calculated and experimental results is made and thereby the validity of our theory is confirmed.
Jeffrey C Hoch - One of the best experts on this subject based on the ideXlab platform.
-
nonuniform sampling of hypercomplex multidimensional nmr experiments dimensionality quadrature phase and randomization
Journal of Magnetic Resonance, 2015Co-Authors: Adam D Schuyler, Mark W Maciejewski, Alan S Stern, Jeffrey C HochAbstract:Nonuniform sampling (NUS) in multidimensional NMR permits the exploration of higher dimensional experiments and longer evolution times than the Nyquist Theorem practically allows for uniformly sampled experiments. However, the spectra of NUS data include sampling-induced artifacts and may be subject to distortions imposed by sparse data reconstruction techniques, issues not encountered with the discrete Fourier transform (DFT) applied to uniformly sampled data. The characterization of these NUS-induced artifacts allows for more informed sample schedule design and improved spectral quality. The DFT–Convolution Theorem, via the point-spread function (PSF) for a given sampling scheme, provides a useful framework for exploring the nature of NUS sampling artifacts. In this work, we analyze the PSFs for a set of specially constructed NUS schemes to quantify the interplay between randomization and dimensionality for reducing artifacts relative to uniformly undersampled controls. In particular, we find a synergistic relationship between the indirect time dimensions and the “quadrature phase dimension” (i.e. the hypercomplex components collected for quadrature detection). The quadrature phase dimension provides additional degrees of freedom that enable partial-component NUS (collecting a subset of quadrature components) to further reduce sampling-induced aliases relative to traditional full-component NUS (collecting all quadrature components). The efficacy of artifact reduction is exponentially related to the dimensionality of the sample space. Our results quantify the utility of partial-component NUS as an additional means for introducing decoherence into sampling schemes and reducing sampling artifacts in high dimensional experiments.
-
nonuniform sampling and non fourier signal processing methods in multidimensional nmr
Progress in Nuclear Magnetic Resonance Spectroscopy, 2014Co-Authors: Mehdi Mobli, Jeffrey C HochAbstract:Beginning with the introduction of Fourier Transform NMR by Ernst and Anderson in 1966, time domain measurement of the impulse response (the free induction decay, FID) consisted of sampling the signal at a series of discrete intervals. For compatibility with the discrete Fourier transform (DFT), the intervals are kept uniform, and the Nyquist Theorem dictates the largest value of the interval sufficient to avoid aliasing. With the proposal by Jeener of parametric sampling along an indirect time dimension, extension to multidimensional experiments employed the same sampling techniques used in one dimension, similarly subject to the Nyquist condition and suitable for processing via the discrete Fourier transform. The challenges of obtaining high-resolution spectral estimates from short data records using the DFT were already well understood, however. Despite techniques such as linear prediction extrapolation, the achievable resolution in the indirect dimensions is limited by practical constraints on measuring time. The advent of non-Fourier methods of spectrum analysis capable of processing nonuniformly sampled data has led to an explosion in the development of novel sampling strategies that avoid the limits on resolution and measurement time imposed by uniform sampling. The first part of this review discusses the many approaches to data sampling in multidimensional NMR, the second part highlights commonly used methods for signal processing of such data, and the review concludes with a discussion of other approaches to speeding up data acquisition in NMR.
-
data sampling in multidimensional nmr fundamentals and strategies
Topics in Current Chemistry, 2011Co-Authors: Mark W Maciejewski, Mehdi Mobli, Adam D Schuyler, Alan S Stern, Jeffrey C HochAbstract:Beginning with the introduction of Fourier Transform NMR by Ernst and Anderson in 1966, time domain measurement of the impulse response (free induction decay) consisted of sampling the signal at a series of discrete intervals. For compatibility with the discrete Fourier transform, the intervals are kept uniform, and the Nyquist Theorem dictates the largest value of the interval sufficient to avoid aliasing. With the proposal by Jeener of parametric sampling along an indirect time dimension, extension to multidimensional experiments employed the same sampling techniques used in one dimension, similarly subject to the Nyquist condition and suitable for processing via the discrete Fourier transform. The challenges of obtaining high-resolution spectral estimates from short data records were already well understood, and despite techniques such as linear prediction extrapolation, the achievable resolution in the indirect dimensions is limited by practical constraints on measuring time. The advent of methods of spectrum analysis capable of processing nonuniformly sampled data has led to an explosion in the development of novel sampling strategies that avoid the limits on resolution and measurement time imposed by uniform sampling. In this chapter we review the fundamentals of uniform and nonuniform sampling methods in one- and multidimensional NMR.
J B Lee - One of the best experts on this subject based on the ideXlab platform.
-
reinvestigation and extension of the steady state Nyquist Theorem for multi terminal semiconductor devices and its application to minimum noise figure in microwave field effect transistors
Journal of Applied Physics, 1996Co-Authors: J B Lee, Hongshick Min, Young June ParkAbstract:The steady‐state Nyquist Theorem for multi‐terminal semiconductor devices, which describes the short‐circuit thermal noise currents in arbitrarily shaped multi‐terminal semiconductor devices, is reinvestigated. The concept of the equipotential surfaces for small ac signals is found to be wrong, which forces us to introduce a new approach to find the equipotential surfaces for noise voltages. Using this new approach, we rederive the steady‐state Nyquist Theorem with the same results as in the previous derivation, and extend it to the hot carrier regime. Using the extended Theorem, we express the minimum noise figure for microwave field effect transistors as a function of the measurable device parameters with no fitting constant. The derived minimum noise figure is shown to reduce to a simple form, which can also be used as an empirical relation with one fitting constant. This simple form can explain the experimental results very well in wide frequency ranges, and gives through a clear mathematical relation...
-
steady state Nyquist Theorem for multi terminal nondegenerate semiconductor devices
Journal of Applied Physics, 1994Co-Authors: J B Lee, Hongshick Min, Young June ParkAbstract:Formulas for the spectral intensities of the short‐circuit thermal noise currents in arbitrarily shaped multi‐terminal semiconductor devices under dc bias are derived by solving the Langevin‐type Boltzmann transport equations. The derived formulas are valid when the carrier distributions are not far from the local equilibrium distributions. Measurement data on short‐circuit thermal noise currents are obtained for a three‐terminal silicon bulk device. A comparison between the calculated and experimental results is made and thereby the validity of our theory is confirmed.
Hongshick Min - One of the best experts on this subject based on the ideXlab platform.
-
governing equations of the terminal current green s functions and their application to derivation of the Nyquist Theorem for multiterminal semiconductor devices
Journal of Applied Physics, 2007Co-Authors: Sungmin Hong, Hongshick Min, Young June Park, Chan Hyeong ParkAbstract:This paper presents the governing equations of the Green’s functions for the short-circuit terminal noise currents of semiconductor devices under the drift-diffusion scheme. Using these equations, the Nyquist Theorem is derived for multiterminal bipolar semiconductor devices at nonzero frequencies with generation-recombination processes considered. It is explicitly shown that generation-recombination noise sources play an essential role in canceling out part of terminal noise contributions from diffusion noise sources to finally obtain the equilibrium thermal noise.
-
reinvestigation and extension of the steady state Nyquist Theorem for multi terminal semiconductor devices and its application to minimum noise figure in microwave field effect transistors
Journal of Applied Physics, 1996Co-Authors: J B Lee, Hongshick Min, Young June ParkAbstract:The steady‐state Nyquist Theorem for multi‐terminal semiconductor devices, which describes the short‐circuit thermal noise currents in arbitrarily shaped multi‐terminal semiconductor devices, is reinvestigated. The concept of the equipotential surfaces for small ac signals is found to be wrong, which forces us to introduce a new approach to find the equipotential surfaces for noise voltages. Using this new approach, we rederive the steady‐state Nyquist Theorem with the same results as in the previous derivation, and extend it to the hot carrier regime. Using the extended Theorem, we express the minimum noise figure for microwave field effect transistors as a function of the measurable device parameters with no fitting constant. The derived minimum noise figure is shown to reduce to a simple form, which can also be used as an empirical relation with one fitting constant. This simple form can explain the experimental results very well in wide frequency ranges, and gives through a clear mathematical relation...
-
steady state Nyquist Theorem for multi terminal nondegenerate semiconductor devices
Journal of Applied Physics, 1994Co-Authors: J B Lee, Hongshick Min, Young June ParkAbstract:Formulas for the spectral intensities of the short‐circuit thermal noise currents in arbitrarily shaped multi‐terminal semiconductor devices under dc bias are derived by solving the Langevin‐type Boltzmann transport equations. The derived formulas are valid when the carrier distributions are not far from the local equilibrium distributions. Measurement data on short‐circuit thermal noise currents are obtained for a three‐terminal silicon bulk device. A comparison between the calculated and experimental results is made and thereby the validity of our theory is confirmed.
Igor Zhukov - One of the best experts on this subject based on the ideXlab platform.
-
determination of spin spin couplings from ultrahigh resolution 3d nmr spectra obtained by optimized random sampling and multidimensional fourier transformation
Journal of the American Chemical Society, 2008Co-Authors: Krzysztof Kazimierczuk, Wiktor Koźminski, Anna Zawadzka, Igor ZhukovAbstract:An example of precise evaluation of backbone scalar J couplings using random sampling of evolution time space in 3D NMR experiments is presented. The recorded spectrum, due to violation of the Nyquist Theorem limitation, exhibits ultrahigh resolution in indirect dimensions compared to standard NMR experiment acquired at the same time. The obtained results enable simple and accurate evaluation of scalar and residual dipolar couplings from a single multidimensional NMR experiment.
-
two dimensional fourier transform of arbitrarily sampled nmr data sets
Journal of Magnetic Resonance, 2006Co-Authors: Krzysztof Kazimierczuk, Wiktor Koźminski, Igor ZhukovAbstract:A new procedure for Fourier transform with respect to more than one time variable simultaneously is proposed for NMR data processing. In the case of two-dimensional transform the spectrum is calculated for pairs of frequencies, instead of conventional sequence of one-dimensional transforms. Therefore, it enables one to Fourier transform arbitrarily sampled time domain and thus allows for analysis of high dimensionality spectra acquired in a short time. The proposed method is not limited to radial sampling, it requires only to fulfill the Nyquist Theorem considering two or more time domains at the same time. We show the application of new approach to the 3D HNCO spectrum acquired for protein sample with radial and spiral time domain sampling.