5,293 research outputs found
Nonequilibrium dressing in a cavity with a movable reflecting mirror
We consider a movable mirror coupled to a one-dimensional massless scalar
field in a cavity. Both the field and the mirror's mechanical degrees of
freedom are described quantum-mechanically, and they can interact each other
via the radiation pressure operator. We investigate the dynamical evolution of
mirror and field starting from a nonequilibrium initial state, and their local
interaction which brings the system to a stationary configuration for long
times. This allows us to study the time-dependent dressing process of the
movable mirror interacting with the field, and its dynamics leading to a local
equilibrium dressed configuration. Also, in order to explore the effect of the
radiation pressure on both sides of the movable mirror, we generalize the
effective field-mirror Hamiltonian and previous results to the case of two
cavities sharing the same mobile boundary. This leads us to address, in the
appropriate limit, the dynamical dressing problem of a single mobile wall,
bounded by a harmonic potential, in the vacuum space.Comment: 10 pages, 4 figure
Syntaphilin controls a mitochondrial rheostat for proliferation-motility decisions in cancer.
Tumors adapt to an unfavorable microenvironment by controlling the balance between cell proliferation and cell motility, but the regulators of this process are largely unknown. Here, we show that an alternatively spliced isoform of syntaphilin (SNPH), a cytoskeletal regulator of mitochondrial movements in neurons, is directed to mitochondria of tumor cells. Mitochondrial SNPH buffers oxidative stress and maintains complex II-dependent bioenergetics, sustaining local tumor growth while restricting mitochondrial redistribution to the cortical cytoskeleton and tumor cell motility. Conversely, introduction of stress stimuli to the microenvironment, including hypoxia, acutely lowered SNPH levels, resulting in bioenergetics defects and increased superoxide production. In turn, this suppressed tumor cell proliferation but increased tumor cell invasion via greater mitochondrial trafficking to the cortical cytoskeleton. Loss of SNPH or expression of an SNPH mutant lacking the mitochondrial localization sequence resulted in increased metastatic dissemination in xenograft or syngeneic tumor models in vivo. Accordingly, tumor cells that acquired the ability to metastasize in vivo constitutively downregulated SNPH and exhibited higher oxidative stress, reduced cell proliferation, and increased cell motility. Therefore, SNPH is a stress-regulated mitochondrial switch of the cell proliferation-motility balance in cancer, and its pathway may represent a therapeutic target
SLOG: A Structural Generalization Benchmark for Semantic Parsing
The goal of compositional generalization benchmarks is to evaluate how well
models generalize to new complex linguistic expressions. Existing benchmarks
often focus on lexical generalization, the interpretation of novel lexical
items in syntactic structures familiar from training; structural generalization
tasks, where a model needs to interpret syntactic structures that are
themselves unfamiliar from training, are often underrepresented, resulting in
overly optimistic perceptions of how well models can generalize. We introduce
SLOG, a semantic parsing dataset that extends COGS (Kim and Linzen, 2020) with
17 structural generalization cases. In our experiments, the generalization
accuracy of Transformer models, including pretrained ones, only reaches 40.6%,
while a structure-aware parser only achieves 70.8%. These results are far from
the near-perfect accuracy existing models achieve on COGS, demonstrating the
role of SLOG in foregrounding the large discrepancy between models' lexical and
structural generalization capacities.Comment: Accepted to EMNLP 202
Automated three-dimensional image registration for longitudinal photoacoustic imaging
Significance: Photoacoustic tomography (PAT) has great potential in monitoring disease progression and treatment response in breast cancer. However, due to variations in breast repositioning, there is a chance of geometric misalignment between images. Further, poor repositioning can affect light fluence distribution and imaging field-of-view, making images different from one another. The net effect is that it becomes challenging to distinguish between image changes due to repositioning effects and those due to true biological variations. Aim: The aim is to develop a three-dimensional image registration framework for geometrically aligning repeated PAT volumetric images, which are potentially affected by repositioning effects such as misalignment, changed radiant exposure conditions, and different fields-of-view. Approach: The proposed framework involves the use of a coordinate-based neural network to represent the displacement field between pairs of PAT volumetric images. A loss function based on normalized cross correlation and Frangi vesselness feature extraction at multiple scales was implemented. We refer to our image registration framework as MUVINN-reg, which stands for multiscale vesselness-based image registration using neural networks. The approach was tested on a longitudinal dataset of healthy volunteer breast PAT images acquired with the hybrid photoacoustic-ultrasound Photoacoustic Mammoscope 3 imaging system. The registration performance was also tested under unfavorable repositioning conditions such as intentional mispositioning, and variation in breast-supporting cup size between measurements. Results: A total of 13 pairs of repeated PAT scans were included in this study. MUVINN-reg showed excellent performance in co-registering each pair of images. The proposed framework was shown to be robust to image intensity shifts and field-of-view changes. Furthermore, MUVINN-reg could align vessels at imaging depths greater than 4Â cm. Conclusions: The proposed framework will enable the use of PAT for quantitative and reproducible monitoring of disease progression and treatment response.</p
Hubble and Spitzer Observations of an Edge-on Circumstellar Disk around a Brown Dwarf
We present observations of a circumstellar disk that is inclined close to
edge-on around a young brown dwarf in the Taurus star-forming region. Using
data obtained with SpeX at the NASA Infrared Telescope Facility, we find that
the slope of the 0.8-2.5 um spectrum of the brown dwarf 2MASS J04381486+2611399
cannot be reproduced with a photosphere reddened by normal extinction. Instead,
the slope is consistent with scattered light, indicating that circumstellar
material is occulting the brown dwarf. By combining the SpeX data with mid-IR
photometry and spectroscopy from the Spitzer Space Telescope and previously
published millimeter data from Scholz and coworkers, we construct the spectral
energy distribution for 2MASS J04381486+2611399 and model it in terms of a
young brown dwarf surrounded by an irradiated accretion disk. The presence of
both silicate absorption at 10 um and silicate emission at 11 um constrains the
inclination of the disk to be ~70 deg, i.e. ~20 deg from edge-on. Additional
evidence of the high inclination of this disk is provided by our detection of
asymmetric bipolar extended emission surrounding 2MASS J04381486+2611399 in
high-resolution optical images obtained with the Hubble Space Telescope.
According to our modeling for the SED and images of this system, the disk
contains a large inner hole that is indicative of a transition disk (R_in~58
R_star~0.275 AU) and is somewhat larger than expected from embryo ejection
models (R_out=20-40 AU vs. R_out<10-20 AU).Comment: The Astrophysical Journal, in pres
CCD-based imaging and 3D space--time mapping of terahertz fields via Kerr frequency conversion
We investigate the spatially and temporally resolved four-wave mixing of terahertz (THz) fields and optical pulses in large-bandgap dielectrics, such as diamond. We show that it is possible to perform beam profiling and spaceâtime resolved mapping of THz fields by encoding the spatial information into an optical signal, which can then be recorded by a standard CCD camera
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