1,306 research outputs found
Determination of from the polarization of vector meson in the semileptonic decay of and meson
Since the degree of polarization of the vector particle in semileptonic decay
strongly influences the decay width of the particles, it can be used as a
measure of CKM matrix elements. We show that |V_{cb}| can be determined from
the measurement of polarization of vector meson in B,B_c --> V l nu decay,
where is vector meson.Comment: 11 pages, RevTe
Ultrashort, High Power, And Ultralow Noise Mode-locked Optical Pulse Generation Using Quantum-dot Semiconductor Lasers
This dissertation explores various aspects and potential of optical pulse generation based on active, passive, and hybrid mode-locked quantum dot semiconductor lasers with target applications such as optical interconnect and high speed signal processing. Design guidelines are developed for the single mode operation with suppressed reflection from waveguide discontinuities. The device fabrication procedure is explained, followed by characteristics of FP laser, SOA, and monolithic two-section devices. Short pulse generation from an external cavity mode-locked QD two-section diode laser is studied. High quality, sub-picosecond (960 fs), high peak power (1.2 W) pulse trains are obtained. The sign and magnitude of pulse chirp were measured for the first time. The role of the self-phase modulation and the linewidth enhancement factor in QD mode-locked lasers is addressed. The noise performance of two-section mode-locked lasers and a SOA-based ring laser was investigated. Significant reduction of the timing jitter under hybrid mode-locked operation was achieved owing to more than one order of magnitude reduction of the linewidth in QD gain media. Ultralow phase noise performance (integrated timing jitter of a few fs at a 10 GHz repetition rate) was demonstrated from an actively mode-locked unidirectional ring laser. These results show that quantum dot mode-locked lasers are strong competitors to conventional semiconductor lasers in noise performance. Finally we demonstrated an opto-electronic oscillator (OEO) and coupled opto-electronic oscillators (COEO) which have the potential for both high purity microwave and low noise optical pulse generation. The phase noise of the COEO is measured by the photonic delay line frequency discriminator method. Based on this study we discuss the prospects of the COEO as a low noise optical pulse source
THE MODAL DISTRIBUTION METHOD: A NEW STATISTICAL ALGORITHM FOR ANALYZING MEASURED RESPONSE
A new statistical algorithm, the "modal distribution method", is proposed to
statistically quantify the significance of changes in mean frequencies of individual
modal vibrations of measured structural response data. In this new method, a power
spectrum of measured structural response is interpreted as being a series of independent modal responses, each of which is isolated over a frequency range and treated as
a statistical distribution. Pairs of corresponding individual modal distributions from
different segments are compared statistically.
The first version is the parametric MDM. This method is applicable to well-
separated modes having Gaussian shape. For application to situations in which the
signal is corrupted by noise, a new noise reduction methodology is developed and
implemented. Finally, a non-parametric version of the MDM based on the Central
Limit Theorem is proposed for application of MDM to general cases including closely
spaced peaks and high noise. Results from all three MDMs are compared through
application to simulated clean signals and the two extended MDMs are compared
through application to simulated noisy signals. As expected, the original parametric MDM is found to have the best performance if underlying requirements are met:
signals that are clean and have well-separated Gaussian mode shapes. In application
of nonparametric methods to Gaussian modes with high noise corruption, the noise reduction MDM is found to have lower probability of false alarms than the nonparametric MDM, though the nonparametric is more efficient at detecting changes.
In closely related work, the Hermite moment model is extended to highly skewed
data. The aim is to enable transformation from non-Gaussian modes to Gaussian
modes, which would provide the possibility of applying parametric MDM to well-
separated non-Gaussian modes. A new methodology to combine statistical moments
using a histogram is also developed for reliable continuous monitoring by means of
MDM.
The MDM is a general statistical method. Because of its general nature, it may
find a broad variety of applications, but it seems particularly well suited to structural
health monitoring applications because only very limited knowledge of the excitation
is required, and significant changes in computed power spectra may indicate changes,
such as structural damage
DC CoMix TTS: An End-to-End Expressive TTS with Discrete Code Collaborated with Mixer
Despite the huge successes made in neutral TTS, content-leakage remains a
challenge. In this paper, we propose a new input representation and simple
architecture to achieve improved prosody modeling. Inspired by the recent
success in the use of discrete code in TTS, we introduce discrete code to the
input of the reference encoder. Specifically, we leverage the vector quantizer
from the audio compression model to exploit the diverse acoustic information it
has already been trained on. In addition, we apply the modified MLP-Mixer to
the reference encoder, making the architecture lighter. As a result, we train
the prosody transfer TTS in an end-to-end manner. We prove the effectiveness of
our method through both subjective and objective evaluations. We demonstrate
that the reference encoder learns better speaker-independent prosody when
discrete code is utilized as input in the experiments. In addition, we obtain
comparable results even when fewer parameters are inputted.Comment: Accepted at Interspeech 202
Emergent localized states at the interface of a twofold -symmetric lattice
We consider the role of non-triviality resulting from a non-Hermitian
Hamiltonian that conserves twofold PT-symmetry assembled by interconnections
between a PT-symmetric lattice and its time reversal partner. Twofold
PT-symmetry in the lattice produces additional surface exceptional points that
play the role of new critical points, along with the bulk exceptional point. We
show that there are two distinct regimes possessing symmetry-protected
localized states, of which localization lengths are robust against external
gain and loss. The states are demonstrated by numerical calculation of a
quasi-1D ladder lattice and a 2D bilayered square lattice.Comment: 10 pages, 7 figure
Ultralow Noise Mode-locked Laser and RF Sinewave Source. DIV
Systems, devices and methods of generating both a precision electrical timing signal as well as a precision optical timing signal. A novel, modified opto-electronic loop oscillator is used to drive a harmonic mode-locked laser. A novel opto-electronic loop has a larger Q factor by increasing the electrical loop oscillating frequency w0 by using a beat note created by the selection of two optical longitudinal modes from the modelocked laser. The beat note is detected and divided down to drive a modulator that modelocks the laser. The frequency division stage also reduces the noise
Impact of Vegetation on Land-Atmosphere Coupling Strength and Its Implication for Desertification Mitigation over East Asia
Desertification of the East Asian drylands and the consequent dust transport have been serious concerns for adjacent Asian countries as well as the western United States. Tree planting has been considered one applicable strategy to mitigate the desertification. However, the desired effect of the tree planting would not be brought to fruition unless the newly planted trees change the coupling characteristics between the land and the atmosphere. Based on this perception, we attempt to clarify the effects of vegetation on the coupling strength between the atmosphere and land surface, and we suggest the most efficient areas of tree planting for desertification mitigation in East Asia. Using regional vegetation-atmosphere coupled model simulations, coupling strength with and without vegetation was computed and compared with each other. An increased vegetation fraction reduces the coupling strength in June, July, and August (JJA), primarily due to decreased evapotranspiration variability. This effect is pronounced over the Manchurian Plains and the highly populated areas of Beijing and Tianjin. The reduced coupling strength tends to weaken feedback between soil moisture and precipitation as a maintenance mechanism of warm season droughts in the midlatitudes and subsequently decrease the probability of droughts, a finding that is reflected in the enhanced JJA mean soil moisture. However, some drylands like the eastern edges of the Gobi desert present marginal or even opposite changes in coupling strength, meaning a limited effect of vegetation on relieving droughts. Therefore, given limited financial and human resources, acupuncture-like afforestation, i.e., concentrated tree planting in a particular region where the coupling strength can be substantially reduced by vegetation, is an effective strategy to secure long-standing desertification mitigation
THE MODAL DISTRIBUTION METHOD: A NEW STATISTICAL ALGORITHM FOR ANALYZING MEASURED RESPONSE
A new statistical algorithm, the "modal distribution method", is proposed to
statistically quantify the significance of changes in mean frequencies of individual
modal vibrations of measured structural response data. In this new method, a power
spectrum of measured structural response is interpreted as being a series of independent modal responses, each of which is isolated over a frequency range and treated as
a statistical distribution. Pairs of corresponding individual modal distributions from
different segments are compared statistically.
The first version is the parametric MDM. This method is applicable to well-
separated modes having Gaussian shape. For application to situations in which the
signal is corrupted by noise, a new noise reduction methodology is developed and
implemented. Finally, a non-parametric version of the MDM based on the Central
Limit Theorem is proposed for application of MDM to general cases including closely
spaced peaks and high noise. Results from all three MDMs are compared through
application to simulated clean signals and the two extended MDMs are compared
through application to simulated noisy signals. As expected, the original parametric MDM is found to have the best performance if underlying requirements are met:
signals that are clean and have well-separated Gaussian mode shapes. In application
of nonparametric methods to Gaussian modes with high noise corruption, the noise reduction MDM is found to have lower probability of false alarms than the nonparametric MDM, though the nonparametric is more efficient at detecting changes.
In closely related work, the Hermite moment model is extended to highly skewed
data. The aim is to enable transformation from non-Gaussian modes to Gaussian
modes, which would provide the possibility of applying parametric MDM to well-
separated non-Gaussian modes. A new methodology to combine statistical moments
using a histogram is also developed for reliable continuous monitoring by means of
MDM.
The MDM is a general statistical method. Because of its general nature, it may
find a broad variety of applications, but it seems particularly well suited to structural
health monitoring applications because only very limited knowledge of the excitation
is required, and significant changes in computed power spectra may indicate changes,
such as structural damage
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