Gaussian Frequency Research Articles

Non-Gaussian spin dephasing

We address spin dephasing induced by stochastic transitions between different precession frequencies. A very famous analytical approximation is the Gaussian approximation presented by [Anderson and Weiss, Rev. Mod. Phys. 25, 269 (1953)]. It states that independent from the transition dynamics, a Gaussian frequency distribution implies a Gaussian distribution of the phase angles, which provides a simple analytical result for the transverse magnetization decay. In contrast we find that (i) the assumption of Gaussian dephasing restricts the stochastic dynamics to a very limited class, (ii) the Anderson-Weiss model is applicable only in a special case of fluctuations, i.e., if and only if the Green's function $G({\ensuremath{\omega}}_{2},{\ensuremath{\omega}}_{1},\ensuremath{\Delta}t)$ describing the transition probability between two frequencies ${\ensuremath{\omega}}_{1}\ensuremath{\rightarrow}{\ensuremath{\omega}}_{2}$ is Gaussian, and (iii) the exact time course of magnetization decay is dependent on the relaxation time in the motional narrowing limit and the correlation time describing the correlation function of the local frequencies. In contrast to previous publications, we conclude that a Gaussian equilibrium distribution of local frequencies does not imply a Gaussian-distributed phase angle. The general theory is illustrated by calculating the Green's function of the transition dynamics for a stochastic process in the strong collision approximation. The result is highly relevant for describing relaxation processes in the presence of local field inhomogeneities.

Pitch-angle scattering rates in planetary magnetospheres

The mechanism of gyroresonant scattering of charged particles by small-amplitude, broadband electromagnetic waves is examined. By means of quasi-linear theory, a simple expression for the resonant pitch-angle diffusion coefficient $D_{\alpha \alpha}$ is developed, which is valid for parallel-propagating, small-amplitude, (R-mode or L-mode) electromagnetic waves of general spectral density. We calculate the average diffusion coefficient with respect to the pitch-angle $\alpha$ , namely $\langle D_{\alpha\alpha}\rangle$ , which provides a practical estimate for particle scattering rates as a function of particle kinetic energy. The results for $\langle D_{\alpha\alpha}\rangle$ , corresponding to a Gaussian wave frequency spectrum, are used to estimate scattering rates for several types of wave–particle interactions in the terrestrial and Jovian magnetospheres.

A time-frequency decision-feedback loop for carrier frequency offset tracking in OFDM systems

Acquisition and tracking are two crucial stages necessary to the carrier frequency synchronization in orthogonal frequency division multiplexing (OFDM) systems. In this letter, by employing the rotation property of OFDM data subcarriers, a simple time-frequency decision-feedback loop without the use of pilot subcarriers is proposed for the fine carrier frequency offset (CFO) tracking. Specifically, with proper loop parameters, a residual CFO less than 10% of the subcarrier spacing may be well tracked for quarternary phase-shift keying (QPSK) modulation in the presence of noise, while for systems using QPSK, 16-QAM, and 64-QAM modulation schemes, the bit-error rate (BER) performance very close to that of an offset-free system may be achieved in both additive white Gaussian noise (AWGN) and frequency selective fading channels. Moreover, a hardware implementation in a practical OFDM system is fulfilled which verifies the effectiveness of the proposed scheme.

Space-time turbo multiuser detection for coded MC-CDMA

The system capacity and performance of multicarrier code-division multiple-access (MC-CDMA) communication systems can be significantly enhanced by jointly employing MAP-based multiuser detection (MUD) and channel decoding techniques. In this paper, a group-oriented soft iterative MUD based on the combination of smart antennas and iterative MAP-based MUD is presented. The proposed method is featured as a novel technique for further increasing the system capacity and performance. In this method, all the users are first grouped into several groups according to their impinging direction of arrivals (DOAs). All users with similar DOAs are classified into the same group and then low-complexity MAP-based iterative MUD is employed in each group. Because spatial filtering cannot suppress all the interference between the groups, interference cancellation among the groups is used prior to MUD within each group. It is shown that the proposed group-oriented soft iterative MUD algorithm can significantly reduce the computational complexity compared with the conventional optimal MAP-based MUD schemes. It is also demonstrated that the performance of the proposed algorithm can approach that of a single-user coded MC-CDMA system with an antenna array in additive white Gaussian noise and frequency selective fading channels.

Phenotypic evaluation of CYP2C9 by way of phenytoin metabolic ratio (PMR)

Aims Validation of PMR as a phenotypic marker of CYP2C9 in the Jewish Israeli population. Methods Seventy-nine Jewish Israeli subjects collected urine over 24 hours following a single dose of 300 mg phenytoin (PHT). A single blood sample was drawn after 12 hours. PMR, a putative index of CYP2C9 activity, was derived from the ratio of urinary 5-(4-hydroxyphenyl)-5-phenylhydantoin (p-HPPH) to mid-interval plasma PHT concentration. CYP2C9 genotype was identified by PCR followed by incubation with restriction enzymes. Results The ethnic composition of the study population was reflective of the Jewish groups residing in Israel. PMR values exhibited 18-fold inter-individual variability with a typical Gaussian frequency distribution, which was skewed to the right. Forty-one subjects were homozygous for the wild-type allele (CYP2C9*1), 32 were carriers of one mutated allele (16 CYP2C9*2 and 16 CYP2C9*3), and 6 were carriers of 2 mutated alleles. PMR exhibits gene-dose effect so that among CYP2C9*1 homozygous, PMR was 16.17±9.76 ml/min (95% CI, 13.10 to 19.26) and significantly greater than in CYP2C9*2 heterozygous (8.54±4.33 ml/min, 95% CI, 6.24 to 10.85, p<0.05) and CYP2C9*3 heterozygous (7.33±3.55 ml/min, 95% CI, 5.44 to 9.22, p<0.001) or carriers of 2 variant alleles (6.73±4.22 ml/min, 95% CI, 2.30 to 11.15, p<0.01). Conclusions PMR exhibits marked inter-individual variability and it correlates with CYP2C9 genotype. Its use as a reliable marker of CYP2C9 activity in-vivo should be further evaluated. Clinical Pharmacology & Therapeutics (2005) 77, P60–P60; doi: 10.1016/j.clpt.2004.12.121

Collective Solvent Coordinates for the Infrared Spectrum of HOD in D2O Based on an ab Initio Electrostatic Map

An ab initio MP2 vibrational Hamiltonian of HOD in an external electrostatic potential parametrized by the electric field and its gradient-tensor is constructed. By combining it with the fluctuating electric field induced by the D(2)O solvent obtained from molecular dynamics simulations, we calculate the infrared absorption of the O-H stretch. The resulting solvent shift and infrared line shape for three force fields (TIP4P, SPC/E, and SW) are in good agreement with the experiment. A collective coordinate response for the solvent effect is constructed by identifying the main electrostatic field and gradient components contributing to the line shape. This allows a realistic stochastic Liouville equation simulation of the line shapes which is not restricted to Gaussian frequency fluctuations.

Fractional Multi-bit Differential Detection Technique for Continuous Phase Modulation

A new low-complexity differential detection technique, fractional multi-bit differential detection (FMDD), is proposed in order to improve the performance of continuous phase modulation (CPM) signals such as Gaussian minimum shift keying (GMSK) and Gaussian frequency shift keying (GFSK). In comparison to conventional one-bit differential detected (1DD) GFSK, the FMDD-employed GFSK provides a signal-to-noise ratio advantage of up to 1.8 dB in an AWGN channel. Thus, the bit-error rate performance of the proposed FMDD is brought close to that of an ideal coherent detection while avoiding the implementation complexity associated with the carrier recovery. In the adjacent channel interference environment, FMDD achieves an even larger SNR advantage compared to 1DD.

An analog GFSK modulator in 0.35-/spl mu/m CMOS

An analog Gaussian frequency shift keying (GFSK) modulator designed in 0.35-/spl mu/m CMOS consumes 600 /spl mu/A from a 3-V supply and realizes an analog implementation of the FM differential equation. The modulator operates at baseband and is intended for use in a direct-conversion Bluetooth transmitter. It achieves a frequency deviation of 160 kHz with better than /spl plusmn/3% accuracy. The modulator implements an amplitude control loop to achieve a well-defined output swing. The total output harmonic distortion is less than 1%.

Sample discrimination of frequency differences with distracters

This study examined the effect of the type and frequency range of remote frequency distracters on sample discrimination of frequency differences (SD-F). For baseline SD-F conditions, normal-hearing listeners judged frequency differences between pairs of target tones drawn from Gaussian frequency distributions near 2000 Hz. In experiment 1, the distracters were pairs of random-frequency tones, fixed-frequency tones, or noise bands, with one distracter above and one below the target region. Three frequency separations of targets and distracters were tested, none overlapping the target region. Effects of fixed-frequency or noise-band distracters were small compared to that of random-frequency distracters, which drove performance to near chance. In experiment 2, dominance of the low-frequency distracter was supported by the effects of changing distracter level, by presenting only the higher- or lower-frequency distracter, and by the pattern of weights derived from trial-by-trial responses. Performance recovered only when the lower-frequency distracter was attenuated 40-50 dB relative to the targets. In experiment 3, all stimulus distributions were shifted 2 octaves higher in frequency; the stronger influence of the distracter frequency below the target remained. The results demonstrate the importance of both stimulus variability and frequency relationships in the interaction of targets and distracters for SD-F.

Baysian Channel Equalizers for Optical CPFSK Receivers with Gaussian Frequency Pulse Shape

Article Baysian Channel Equalizers for Optical CPFSK Receivers with Gaussian Frequency Pulse Shape was published on August 1, 2004 in the journal Journal of Optical Communications (volume 25, issue 4).

DETERMINATION OF THE CALCIUM OXALATE CRYSTALLIZATION RISK FROM URINE SAMPLES: THE BONN RISK INDEX IN COMPARISON TO OTHER RISK FORMULAS

Regular risk evaluation and risk monitoring during stone therapy are recommended measures to ensure reduction of recurrence of crystal formation. This strategy optimizes the patient treatment by a more individual approach and decreases expensive over treatment. We evaluated the BONN Risk Index (BRI) through data actualization and evaluation refinement. The BRI was compared with the most common methods of risk evaluation, namely calculation of relative urinary calcium oxalate (CaOx) supersaturation (RS) and of the urine activity product (AP)CaOx index to estimate the urine AP with respect to CaOx. A total of 201, 12 and 24-hour urine samples were collected from 95 healthy volunteers and from 106 CaOx stone formers. Crystallization experiments following the BRI method were performed. RS and APCaOx were calculated from urinalysis. Data were indexed and individually grouped into 8 classes, and frequency distributions were plotted. A calculation scheme for the BRI based estimation of the statistical probability of a clinically healthy person being a (still nondetected) CaOx stone former is provided. Logarithmically arranged BRI groups from healthy subject and patient data showed Gaussian frequency distributions. Compared with RS and APCaOx BRI allowed optimum distinction between healthy subjects and stone formers. The healthy subject probability of already being a CaOx stone former strongly increased with increasing BRI. The BRI for evaluating CaOx crystallization risk allows reliable distinction between healthy subjects and CaOx stone formers. Although RS and APCaOx require much more analytical efforts for determination, their results do not show higher reliability.

A Dual-Mode 2.4-GHz CMOS Transceiver for High-Rate Bluetooth Systems

This paper reports on our development of a dual-mode transceiver for a CMOS high-rate Bluetooth system-on-chip solution. The transceiver includes most of the radio building blocks such as an active complex filter, a Gaussian frequency shift keying (GFSK) demodulator, a variable gain amplifier (VGA), a dc offset cancellation circuit, a quadrature local oscillator (LO) generator, and an RF front-end. It is designed for both the normal-rate Bluetooth with an instantaneous bit rate of 1 Mb/s and the high-rate Bluetooth of up to 12 Mb/s. The receiver employs a dualconversion combined with a baseband dual-path architecture for resolving many problems such as flicker noise, dc offset, and power consumption of the dual-mode system. The transceiver requires none of the external image-rejection and intermediate frequency (IF) channel filters by using an LO of 1.6 GHz and the fifth order on-chip filters. The chip is fabricated on a 6.5-mm2 die using a standard 0.25-μm CMOS technology. Experimental results show an in-band image-rejection ratio of 40 dB, an IIP3 of −5 dBm, and a sensitivity of −77 dBm for the Bluetooth mode when the losses from the external components are compensated. It consumes 42 mA in receive π/4-diffrential quadrature phase-shift keying (π/4-DQPSK) mode of 8 Mb/s, 35 mA in receive GFSK mode of 1 Mb/s, and 32 mA in transmit mode from a 2.5-V supply. These results indicate that the architecture and circuits are adaptable to the implementation of a low-cost, multi-mode, high-speed wireless personal area network.

PERFORMANCE OF FREQUENCY HOPPED NONCOHERENT GFSK OVER TIME-VARYING RAYLEIGH FADING CHANNELS

An analytical treatment of the performance of frequency hopped Gaussian frequency shift keying (GFSK) with differential detection in time-varying Rayleigh fading channels corrupted by additive white Gaussian noise (AWGN) is presented. Closed-form expressions for the bit error rate (BER) as a function of Eb/N0, modulation index, channel Doppler shift, and the time-bandwidth product of the pre-modulation filter are derived. A pilot symbol-assisted scheme to lower the error floor caused by frequency hopping is analyzed.

Spectral Efficiency and Cutoff Rate of Random Spreading BICM-Based CDMA Signals With MMSE Multiuser Receivers

We analyze the spectral efficiency and cutoff rate of random spreading bit-interleaved coded-modulation based synchronous code-division multiple-access signals with minimum mean-square error multiuser receivers. Both additive white Gaussian noise and frequency nonselective Rayleigh fading channels are considered. The spectral efficiency and cutoff rate are characterized as functions of the system load, modulation schemes, and signal-to-noise ratio.

Clinical Trials: Renewed Attention to the Interpretation of the P Values???review

The P values tell us the chance of making a type I error of finding a difference where there is none. In the 1970s, exact P values were laborious to calculate and were generally approximated from statistical tables, in the form of P < 0.01 or 0.05 < P < 0.10, etc. In the past decades with the advent of computers, it became easy to calculate exact P values such as 0.84 or 0.007. The cut-off P values have not been completely abandoned, but broader attention is given to the interpretation of the exact P values. This article reviews standard and renewed interpretations of P values. (1) Standard interpretation of cut-off P values such as P < 0.05: The null hypothesis of no difference can be rejected on the limitations/assumptions that we have up to a 5% chance of a type I error of finding a difference where there is none, we have 50% chance of a type II error of finding no difference where there is one, the data are normally distributed, they follow exactly the same distribution as that of the population from which the sample was taken. (2) A common misunderstanding of the P value: It is actually the chance that the null hypothesis is true and consequently that a P > 0.05 indicates a significant similarity in the data. P > 0.05 may indeed indicate similarity. However, a study sample too small or study design inadequate to detect the difference must be considered. (3) Renewed interpretations of the P values: Exact P values enable more refined conclusions from the research than cut-off levels. Instead of concluding significantly yes/no, we are able to consider levels of probabilities from very likely to be true to very likely to be untrue. Very large P values are not compatible with a normal gaussian frequency distribution; very small P values do not completely confirm prior expectations. They must be scrutinized and may have been inadequately improved.

Acoustic Heating Models for the Basal Flux Star Ceti Including Time-dependent Ionization: Results for Ca ii and Mg ii Emission

We present new calculations of chromospheric heating for τ Ceti (G8 V), a star exhibiting an extremely low level of chromospheric activity, thus also referred to as a basal flux star or a flat activity star. Our simulations consider energy deposition by acoustic shocks and also take into account time-dependent (i.e., noninstantaneous) ionization processes of hydrogen, magnesium, and calcium, allowing us to attain a new generation of chromospheric heating models previously obtained for the Sun. We consider both monochromatic waves and acoustic frequency spectra. The latter are calculated using new models of acoustic energy generation based on an extended Kolmogorov spectrum with a modified Gaussian frequency factor. Our models show that the theoretically deduced emergent Ca II and Mg II emission very much agree with observations, adding to the argument that the chromospheres of basal flux stars are predominantly heated by acoustic shocks.

A 1.8-v operation RF CMOS transceiver for 2.4-ghz-band GFSK applications

This paper describes a single-chip RF transceiver LSI for 2.4-GHz-band Gaussian frequency shift-keying applications, such as Bluetooth. This chip uses a 0.18-μm bulk CMOS process for lower current consumption. The LSI consists of almost all the required RF and IF building blocks: a transmit/receive antenna switch, a power amplifier, a low noise amplifier, an image rejection mixer, channel-selection filters, a limiter, a received signal strength indicator, a frequency discriminator, a voltage controlled oscillator, and a phase-locked loop synthesizer. The bandpass filter for channel selection was difficult to achieve since it operates at a low supply voltage. However, because large interference is roughly rejected at the output of the image rejection mixer and a wide-input-range bandpass filter with an optimized input bias is realized, the transceiver can operate at a supply voltage of 1.8 V. In the IF section, we adopted a circuit design using the minimum number of passive elements, resistors and capacitors, for a lower chip area of 10.2 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> .

Advanced intermediate frequency zero-crossing detection of bandpass filtered MSK signals

Short range communication systems such as Bluetooth deploy Gaussian frequency shift keying modulation which has been derived from minimum shift keying (MSK). The authors present and analyze an improved zero-crossing detector for MSK signals called a zero-crossing decorrelation detector. The impact of bandlimitation is taken into account.

Is there functional collateral flow during vascular occlusion in angiographically normal coronary arteries?

Thus far, it is unknown whether there is functional collateral flow through preexisting anastomoses in patients with angiographically normal coronary arteries. Such preformed coronary collateral vessels could form the basis for subsequently developing protective natural bypasses in the presence of coronary artery disease. Among 100 patients, the collateral flow index (CFI) was measured in coronary arteries without stenotic lesions. The CFI was determined by simultaneous measurement of mean aortic pressure, central venous pressure, and coronary wedge pressure via a sensor-tipped guidewire at the end of a 1-minute balloon occlusion. Patients were divided in 2 groups according to complete angiographic absence (51 patients) or partial presence (49 patients) of stenotic lesions in coronary arteries other than that undergoing collateral measurement. CFI in all patients (61+/-10 years; men/women, 69/31) amounted to 0.18+/-0.08 (range, 0.04 to 0.36). It showed a normal Gaussian frequency distribution; 22 individuals had a CFI > or =0.25, a value that was empirically found to represent well-developed collaterals protective against myocardial ischemia during coronary occlusion. Accordingly, 17 patients did not reveal signs of myocardial ischemia during coronary balloon occlusion, as assessed from an intracoronary ECG, and 26 patients did not experience angina pectoris during occlusion. In humans with angiographically normal coronary arteries, there are functional collateral vessels to the extent that one fifth to one quarter of them do not show signs of myocardial ischemia during brief vascular occlusions.

MAP harmonic retrieval in Gaussian colored noise with prior information

In this paper we deal with the MAP estimation of the parameters of a single complex sinusoid in Gaussian white and colored noise. We analyze the effects of modeling the frequency and amplitude as random variables, deriving the expressions of the MAP estimators, and we analytically compute the CRB's for a tone with Gaussian frequency and amplitude distributions. Moreover, we explicitly derive closed-form expressions of the optimal estimators in the case of Gaussian and Rayleigh distributed amplitude. In particular, we show that, in the colored noise case, the amplitude information can also help improving the performance of the frequency estimator, and vice versa. We propose an efficient FFT-based implementation structure of the optimal estimators, which can be further simplified when the noise can be modeled as an AR process; besides, when the estimators cannot be expressed in closed form, we propose a simple univariate optimization algorithm in order to compute the estimates. Simulation results are reported, which validate the theoretical results and witness the significant performance improvement that can be achieved embodying the parameter priors into the frequency and amplitude estimators.