2,827 research outputs found
Quantum correlations of light due to a room temperature mechanical oscillator for force metrology
The coupling of laser light to a mechanical oscillator via radiation pressure
leads to the emergence of quantum mechanical correlations between the amplitude
and phase quadrature of the laser beam. These correlations form a generic
non-classical resource which can be employed for quantum-enhanced force
metrology, and give rise to ponderomotive squeezing in the limit of strong
correlations. To date, this resource has only been observed in a handful of
cryogenic cavity optomechanical experiments. Here, we demonstrate the ability
to efficiently resolve optomechanical quantum correlations imprinted on an
optical laser field interacting with a room temperature nanomechanical
oscillator. Direct measurement of the optical field in a detuned homodyne
detector ("variational measurement") at frequencies far from the resonance
frequency of the oscillator reveal quantum correlations at the few percent
level. We demonstrate how the absolute visibility of these correlations can be
used for a quantum-enhanced estimation of the quantum back-action force acting
on the oscillator, and provides for an enhancement in the relative
signal-to-noise ratio for the estimation of an off-resonant external force,
even at room temperature
Clamp-tapering increases the quality factor of stressed nanobeams
Stressed nanomechanical resonators are known to have exceptionally high
quality factors () due to the dilution of intrinsic dissipation by stress.
Typically, the amount of dissipation dilution and thus the resonator is
limited by the high mode curvature region near the clamps. Here we study the
effect of clamp geometry on the of nanobeams made of high-stress
. We find that tapering the beam near the clamp - and locally
increasing the stress - leads to increased of MHz-frequency low order modes
due to enhanced dissipation dilution. Contrary to recent studies of
tethered-membrane resonators, we find that widening the clamps leads to
decreased despite increased stress in the beam bulk. The tapered-clamping
approach has practical advantages compared to the recently developed
"soft-clamping" technique. Tapered-clamping enhances the of the fundamental
mode and can be implemented without increasing the device size
Ecological and life-history drivers of avian skull evolution
One of the most famous examples of adaptive radiation is that of the Galápagos finches, where skull morphology, particularly the beak, varies with feeding ecology. Yet increasingly studies are questioning the strength of this correlation between feeding ecology and morphology in relation to the entire neornithine radiation, suggesting that other factors also significantly affect skull evolution. Here, we broaden this debate to assess the influence of a range of ecological and life history factors, specifically habitat density, migration, and developmental mode, in shaping avian skull evolution. Using 3D geometric morphometric data to robustly quantify skull shape for 354 extant species spanning avian diversity, we fitted flexible phylogenetic regressions and estimated evolutionary rates for each of these factors across the full dataset. The results support a highly significant relationship between skull shape and both habitat density and migration, but not developmental mode. We further found heterogenous rates of evolution between different character states within habitat density, migration, and developmental mode, with rapid skull evolution in species which occupy dense habitats, are migratory, or are precocial. These patterns demonstrate that diverse factors impact the tempo and mode of avian phenotypic evolution, and that skull evolution in birds is not simply a reflection of feeding ecology
An MMPI-2 hopelessness scale: Construction, initial validation and implication for suicide risk
This study documents the development of a new MMPI-2 scale, Hopelessness (Hp), designed to identify suicide risk in examinees who, for whatever reason, may be reluctant to endorse items reflecting explicit suicide content. The psychometric and empirical validity characteristics were examined in a sample of 153 Italian psychiatric inpatients, all of whom were administered the MMPI-2, the Beck Hopelessness Scale (BHS), and the Mini International Neuropsychiatric Interview (MINI) shortly following admission.Item analysis suggested that the removal of one of the twelve original Hp items enhanced homogeneity of the scale and Bayesian confirmatory factor analysis (BCFA) indicated the fit of a unidimensional model (PPPs = 0.50 [PPC = -36.42/37.07]) for the 11-item version, with adequate reliability (ordinal alpha = 0.86). A regression analysis, with the MINI scores as criterion, and Hp and BHS scores as independent variables, indicated that only Hp scores (beta = 0.25, t = 2.32, p < 0.05) were independently associated with the MINI suicide risk. These findings indicate that the MMPI-2 Hp scale may be considered a valid and potentially useful measure of pessimistic attitudes toward the future and of potential suicide risk
Probing Spin-Polarized Currents in the Quantum Hall Regime
An experiment to probe spin-polarized currents in the quantum Hall regime is
suggested that takes advantage of the large Zeeman-splitting in the
paramagnetic diluted magnetic semiconductor zinc manganese selenide
(ZnMnSe). In the proposed experiment spin-polarized electrons are
injected by ZnMnSe-contacts into a gallium arsenide (GaAs) two-dimensional
electron gas (2DEG) arranged in a Hall bar geometry. We calculated the
resulting Hall resistance for this experimental setup within the framework of
the Landauer-B\"uttiker formalism. These calculations predict for 100%
spininjection through the ZnMnSe-contacts a Hall resistance twice as high as in
the case of no spin-polarized injection of charge carriers into a 2DEG for
filling factor . We also investigated the influence of the equilibration
of the spin-polarized electrons within the 2DEG on the Hall resistance. In
addition, in our model we expect no coupling between the contact and the 2DEG
for odd filling factors of the 2DEG for 100% spininjection, because of the
opposite sign of the g-factors of ZnMnSe and GaAs.Comment: 7 pages, 5 figure
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Observation of playa salts as nuclei in orographic wave clouds
During the Ice in Clouds Experiment-Layer Clouds (ICE-L), dry lakebed, or playa, salts from the Great Basin region of the United States were observed as cloud nuclei in orographic wave clouds over Wyoming. Using a counterflow virtual impactor in series with a single-particle mass spectrometer, sodium-potassium-magnesium-calcium-chloride salts were identified as residues of cloud droplets. Importantly, these salts produced similar mass spectral signatures to playa salts with elevated cloud condensation nuclei (CCN) efficiencies close to sea salt. Using a suite of chemical characterization instrumentation, the playa salts were observed to be internally mixed with oxidized organics, presumably produced by cloud processing, as well as carbonate. These salt particles were enriched as residues of large droplets (>19 μm) compared to smaller droplets (>7 μm). In addition, a small fraction of silicate-containing playa salts were hypothesized to be important in the observed heterogeneous ice nucleation processes. While the high CCN activity of sea salt has been demonstrated to play an important role in cloud formation in marine environments, this study provides direct evidence of the importance of playa salts in cloud formation in continental North America has not been shown previously. Studies are needed to model and quantify the impact of playas on climate globally, particularly because of the abundance of playas and expected increases in the frequency and intensity of dust storms in the future due to climate and land use changes
Generalized dissipation dilution in strained mechanical resonators
Mechanical resonators with high quality factors are of relevance in precision
experiments, ranging from gravitational wave detection and force sensing to
quantum optomechanics. Beams and membranes are well known to exhibit flexural
modes with enhanced quality factors when subjected to tensile stress. The
mechanism for this enhancement has been a subject of debate, but is typically
attributed to elastic energy being "diluted" by a lossless potential. Here we
clarify the origin of the lossless potential to be the combination of tension
and geometric nonlinearity of strain. We present a general theory of
dissipation dilution that is applicable to arbitrary resonator geometries and
discuss why this effect is particularly strong for flexural modes of
nanomechanical structures with high aspect ratios. Applying the theory to a
non-uniform doubly clamped beam, we show analytically how dissipation dilution
can be enhanced by modifying the beam shape to implement "soft clamping", thin
clamping and geometric strain engineering, and derive the ultimate limit for
dissipation dilution
Deep Learning with Coherent VCSEL Neural Networks
Deep neural networks (DNNs) are reshaping the field of information
processing. With their exponential growth challenging existing electronic
hardware, optical neural networks (ONNs) are emerging to process DNN tasks in
the optical domain with high clock rates, parallelism and low-loss data
transmission. However, to explore the potential of ONNs, it is necessary to
investigate the full-system performance incorporating the major DNN elements,
including matrix algebra and nonlinear activation. Existing challenges to ONNs
are high energy consumption due to low electro-optic (EO) conversion
efficiency, low compute density due to large device footprint and channel
crosstalk, and long latency due to the lack of inline nonlinearity. Here we
experimentally demonstrate an ONN system that simultaneously overcomes all
these challenges. We exploit neuron encoding with volume-manufactured
micron-scale vertical-cavity surface-emitting laser (VCSEL) transmitter arrays
that exhibit high EO conversion (<5 attojoule/symbol with =4 mV), high
operation bandwidth (up to 25 GS/s), and compact footprint (<0.01 mm per
device). Photoelectric multiplication allows low-energy matrix operations at
the shot-noise quantum limit. Homodyne detection-based nonlinearity enables
nonlinear activation with instantaneous response. The full-system energy
efficiency and compute density reach 7 femtojoules per operation (fJ/OP) and 25
TeraOP/(mm s), both representing a >100-fold improvement over
state-of-the-art digital computers, with substantially several more orders of
magnitude for future improvement. Beyond neural network inference, its feature
of rapid weight updating is crucial for training deep learning models. Our
technique opens an avenue to large-scale optoelectronic processors to
accelerate machine learning tasks from data centers to decentralized edge
devices.Comment: 10 pages, 5 figure
Genomics of Postprandial Lipidomics in the Genetics of Lipid-Lowering Drugs and Diet Network Study
Postprandial lipemia (PPL) is an important risk factor for cardiovascular disease. Inter-individual variation in the dietary response to a meal is known to be influenced by genetic factors, yet genes that dictate variation in postprandial lipids are not completely characterized. Genetic studies of the plasma lipidome can help to better understand postprandial metabolism by isolating lipid molecular species which are more closely related to the genome. We measured the plasma lipidome at fasting and 6 h after a standardized high-fat meal in 668 participants from the Genetics of Lipid-Lowering Drugs and Diet Network study (GOLDN) using ultra-performance liquid chromatography coupled to (quadrupole) time-of-flight mass spectrometry. A total of 413 unique lipids were identified. Heritable and responsive lipid species were examined for association with single-nucleotide polymorphisms (SNPs) genotyped on the Affymetrix 6.0 array. The most statistically significant SNP findings were replicated in the Amish Heredity and Phenotype Intervention (HAPI) Heart Study. We further followed up findings from GOLDN with a regional analysis of cytosine-phosphate-guanine (CpGs) sites measured on the Illumina HumanMethylation450 array. A total of 132 lipids were both responsive to the meal challenge and heritable in the GOLDN study. After correction for multiple testing of 132 lipids (α = 5 × 10−8/132 = 4 × 10−10), no SNP was statistically significantly associated with any lipid response. Four SNPs in the region of a known lipid locus (fatty acid desaturase 1 and 2/FADS1 and FADS2) on chromosome 11 had p \u3c 8.0 × 10−7 for arachidonic acid FA(20:4). Those SNPs replicated in HAPI Heart with p \u3c 3.3 × 10−3. CpGs around the FADS1/2 region were associated with arachidonic acid and the relationship of one SNP was partially mediated by a CpG (p = 0.005). Both SNPs and CpGs from the fatty acid desaturase region on chromosome 11 contribute jointly and independently to the diet response to a high-fat meal
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