566 research outputs found
High Power CMUTs: Design and experimental verification
Cataloged from PDF version of article.Capacitive micromachined ultrasonic transducers
(CMUTs) have great potential to compete with piezoelectric
transducers in high-power applications. As the output pressures
increase, nonlinearity of CMUT must be reconsidered
and optimization is required to reduce harmonic distortions.
In this paper, we describe a design approach in which uncollapsed
CMUT array elements are sized so as to operate at the
maximum radiation impedance and have gap heights such that
the generated electrostatic force can sustain a plate displacement
with full swing at the given drive amplitude. The proposed
design enables high output pressures and low harmonic
distortions at the output. An equivalent circuit model of the
array is used that accurately simulates the uncollapsed mode
of operation. The model facilities the design of CMUT parameters
for high-pressure output, without the intensive need
for computationally involved FEM tools. The optimized design
requires a relatively thick plate compared with a conventional
CMUT plate. Thus, we used a silicon wafer as the CMUT
plate. The fabrication process involves an anodic bonding process
for bonding the silicon plate with the glass substrate. To
eliminate the bias voltage, which may cause charging problems,
the CMUT array is driven with large continuous wave
signals at half of the resonant frequency. The fabricated arrays
are tested in an oil tank by applying a 125-V peak 5-cycle
burst sinusoidal signal at 1.44 MHz. The applied voltage is increased
until the plate is about to touch the bottom electrode
to get the maximum peak displacement. The observed pressure
is about 1.8 MPa with −28 dBc second harmonic at the
surface of the array
Use of high resolution 3D diffusion tensor imaging to study brain white matter development in live neonatal rats
High resolution diffusion tensor imaging (DTI) can provide important information on brain development, yet it is challenging in live neonatal rats due to the small size of neonatal brain and motion-sensitive nature of DTI. Imaging in live neonatal rats has clear advantages over fixed brain scans, as longitudinal and functional studies would be feasible to understand neuro-developmental abnormalities. In this study, we developed imaging strategies that can be used to obtain high resolution 3D DTI images in live neonatal rats at postnatal day 5 (PND5) and PND14, using only 3 h of imaging acquisition time. An optimized 3D DTI pulse sequence and appropriate animal setup to minimize physiological motion artifacts are the keys to successful high resolution 3D DTI imaging. Thus, a 3D rapid acquisition relaxation enhancement DTI sequence with twin navigator echoes was implemented to accelerate imaging acquisition time and minimize motion artifacts. It has been suggested that neonatal mammals possess a unique ability to tolerate mild-to-moderate hypothermia and hypoxia without long term impact. Thus, we additionally utilized this ability to minimize motion artifacts in magnetic resonance images by carefully suppressing the respiratory rate to around 15/min for PND5 and 30/min for PND14 using mild-to-moderate hypothermia. These imaging strategies have been successfully implemented to study how the effect of cocaine exposure in dams might affect brain development in their rat pups. Image quality resulting from this in vivo DTI study was comparable to ex vivo scans. fractional anisotropy values were also similar between the live and fixed brain scans. The capability of acquiring high quality in vivo DTI imaging offers a valuable opportunity to study many neurological disorders in brain development in an authentic living environment
Gender recognition from a partial view of the face using local feature vectors
This paper proposes a gender recognition scheme focused on local appearance-based features to describe the top half of the face. Due to the fact that only the top half of the face is used, this is a
feasible approach in those situations where the bottom half is hidden. In the experiments, several face detection methods with different precision levels are used in order to prove the robustness of the scheme with respect to variations in the accuracy level of the face detection proces
Black Sea coastal forecasting system
The Black Sea coastal nowcasting and forecasting system was built within the framework of EU FP6 ECOOP (European COastalshelf sea OPerational observing and forecasting system) project for five regions: the south-western basin along the coasts of Bulgaria and Turkey, the north-western shelf along the Romanian and Ukrainian coasts, coastal zone around of the Crimea peninsula, the north-eastern Russian coastal zone and the coastal zone of Georgia. The system operates in the real-time mode during the ECOOP project and afterwards. The forecasts include temperature, salinity and current velocity fields. Ecosystem model operates in the off-line mode near the Crimea coast
Domain-matched Pre-training Tasks for Dense Retrieval
Pre-training on larger datasets with ever increasing model size is now a proven recipe for increased performance across almost all NLP tasks. A notable exception is information retrieval, where additional pre-training has so far failed to produce convincing results. We show that, with the right pre-training setup, this barrier can be overcome. We demonstrate this by pre-training large bi-encoder models on 1) a recently released set of 65 million synthetically generated questions, and 2) 200 million post-comment pairs from a preexisting dataset of Reddit conversations. We evaluate on a set of information retrieval and dialogue retrieval benchmarks, showing substantial improvements over supervised baselines
Integrated Quantum Optical Phase Sensor
The quantum noise of light fundamentally limits optical phase sensors. A
semiclassical picture attributes this noise to the random arrival time of
photons from a coherent light source such as a laser. An engineered source of
squeezed states suppresses this noise and allows sensitivity beyond the
standard quantum limit (SQL) for phase detection. Advanced gravitational wave
detectors like LIGO have already incorporated such sources, and nascent efforts
in realizing quantum biological measurements have provided glimpses into new
capabilities emerging in quantum measurement. We need ways to engineer and use
quantum light within deployable quantum sensors that operate outside the
confines of a lab environment. Here we present a photonic integrated circuit
fabricated in thin-film lithium niobate that provides a path to meet these
requirements. We use the second-order nonlinearity to produce a squeezed state
at the same frequency as the pump light and realize circuit control and sensing
with electro-optics. Using a 26.2 milliwatts of optical power, we measure (2.7
0.2 ) squeezing and apply it to increase the signal-to-noise ratio of
phase measurement. We anticipate that on-chip photonic systems like this, which
operate with low power and integrate all of the needed functionality on a
single die, will open new opportunities for quantum optical sensing.Comment: 14 pages, 3+3 figure
Integrated frequency-modulated optical parametric oscillator
Optical frequency combs have revolutionized precision measurement,
time-keeping, and molecular spectroscopy. A substantial effort has developed
around "microcombs": integrating comb-generating technologies into compact,
reliable photonic platforms. Current approaches for generating these microcombs
involve either the electro-optic (EO) or Kerr mechanisms. Despite rapid
progress, maintaining high efficiency and wide bandwidth remains challenging.
Here, we introduce a new class of microcomb -- an integrated optical frequency
comb generator that combines electro-optics and parametric amplification to
yield a frequency-modulated optical parametric oscillator (FM-OPO). In stark
contrast to EO and Kerr combs, the FM-OPO microcomb does not form pulses but
maintains operational simplicity and highly efficient pump power utilization
with an output resembling a frequency-modulated laser. We outline the working
principles of FM-OPO and demonstrate them by fabricating the complete optical
system in thin-film lithium niobate (LNOI). We measure pump to comb internal
conversion efficiency exceeding 93% (34% out-coupled) over a nearly flat-top
spectral distribution spanning approximately 1,000 modes (approximately 6 THz).
Compared to an EO comb, the cavity dispersion rather than loss determines the
FM-OPO bandwidth, enabling broadband combs with a smaller RF modulation power.
The FM-OPO microcomb, with its robust operational dynamics, high efficiency,
and large bandwidth, contributes a new approach to the field of microcombs and
promises to herald an era of miniaturized precision measurement, and
spectroscopy tools to accelerate advancements in metrology, spectroscopy,
telecommunications, sensing, and computing.Comment: 8 pages, 4 figures main text; another 19 pages and 9 figures in
methods and supplementar
Investigation of transition frequencies of two acoustically coupled bubbles using a direct numerical simulation technique
The theoretical results regarding the ``transition frequencies'' of two
acoustically interacting bubbles have been verified numerically. The theory
provided by Ida [Phys. Lett. A 297 (2002) 210] predicted the existence of three
transition frequencies per bubble, each of which has the phase difference of
between a bubble's pulsation and the external sound field, while
previous theories predicted only two natural frequencies which cause such phase
shifts. Namely, two of the three transition frequencies correspond to the
natural frequencies, while the remaining does not. In a subsequent paper [M.
Ida, Phys. Rev. E 67 (2003) 056617], it was shown theoretically that transition
frequencies other than the natural frequencies may cause the sign reversal of
the secondary Bjerknes force acting between pulsating bubbles. In the present
study, we employ a direct numerical simulation technique that uses the
compressible Navier-Stokes equations with a surface-tension term as the
governing equations to investigate the transition frequencies of two coupled
bubbles by observing their pulsation amplitudes and directions of translational
motion, both of which change as the driving frequency changes. The numerical
results reproduce the recent theoretical predictions, validating the existence
of the transition frequencies not corresponding to the natural frequency.Comment: 18 pages, 8 figures, in pres
Assessment of breast pathologies using nonlinear microscopy
Rapid intraoperative assessment of breast excision specimens is clinically important because up to 40% of patients undergoing breast-conserving cancer surgery require reexcision for positive or close margins. We demonstrate nonlinear microscopy (NLM) for the assessment of benign and malignant breast pathologies in fresh surgical specimens. A total of 179 specimens from 50 patients was imaged with NLM using rapid extrinsic nuclear staining with acridine orange and intrinsic second harmonic contrast generation from collagen. Imaging was performed on fresh, intact specimens without the need for fixation, embedding, and sectioning required for conventional histopathology. A visualization method to aid pathological interpretation is presented that maps NLM contrast from two-photon fluorescence and second harmonic signals to features closely resembling histopathology using hematoxylin and eosin staining. Mosaicking is used to overcome trade-offs between resolution and field of view, enabling imaging of subcellular features over square-centimeter specimens. After NLM examination, specimens were processed for standard paraffin-embedded histology using a protocol that coregistered histological sections to NLM images for paired assessment. Blinded NLM reading by three pathologists achieved 95.4% sensitivity and 93.3% specificity, compared with paraffin-embedded histology, for identifying invasive cancer and ductal carcinoma in situ versus benign breast tissue. Interobserver agreement was κ = 0.88 for NLM and κ = 0.89 for histology. These results show that NLM achieves high diagnostic accuracy, can be rapidly performed on unfixed specimens, and is a promising method for intraoperative margin assessment.National Institutes of Health (U.S.) (Grant R01-CA178636-01)National Institutes of Health (U.S.) (Grant R01-CA75289-16)United States. Air Force Office of Scientific Research (Grant FA9550-10-1-0551)United States. Air Force Office of Scientific Research (Grant FA9550-12-1-0499)National Institutes of Health (U.S.) (National Research Service Award Postdoctoral Fellowship F32-CA165484
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