2,192 research outputs found
Approaching the adiabatic timescale with machine-learning
The control and manipulation of quantum systems without excitation is
challenging, due to the complexities in fully modeling such systems accurately
and the difficulties in controlling these inherently fragile systems
experimentally. For example, while protocols to decompress Bose-Einstein
condensates (BEC) faster than the adiabatic timescale (without excitation or
loss) have been well developed theoretically, experimental implementations of
these protocols have yet to reach speeds faster than the adiabatic timescale.
In this work, we experimentally demonstrate an alternative approach based on a
machine learning algorithm which makes progress towards this goal. The
algorithm is given control of the coupled decompression and transport of a
metastable helium condensate, with its performance determined after each
experimental iteration by measuring the excitations of the resultant BEC. After
each iteration the algorithm adjusts its internal model of the system to create
an improved control output for the next iteration. Given sufficient control
over the decompression, the algorithm converges to a novel solution that sets
the current speed record in relation to the adiabatic timescale, beating out
other experimental realizations based on theoretical approaches. This method
presents a feasible approach for implementing fast state preparations or
transformations in other quantum systems, without requiring a solution to a
theoretical model of the system. Implications for fundamental physics and
cooling are discussed.Comment: 7 pages main text, 2 pages supporting informatio
Proteomic analysis of tomato (Lycopersicon esculentum) pollen
In flowering plants, pollen grains are produced in the anther and released to the external environment with the primary function of delivering sperm cells to the female gametophyte. This study was conducted to identify proteins in tomato pollen and to analyse their roles in relation to pollen function. Tomato is an important crop which is grown worldwide and is an excellent experimental system. Proteins were extracted from pollen, separated by two-dimensional gel electrophoresis (2-DE), and identified by matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF MS) and peptide mass fingerprinting. Of the 960 spots observed on Colloidal Coomassie Blue (CCB)-stained 2-DE gels, 190 were selected for analysis. Of these, 158 spots, representing 133 distinct proteins, were identified by searching the NCBInr and Expressed Sequence Tag databases. The identified proteins were classified based on designated functions and the majority included those involved in defence mechanisms, energy conversions, protein synthesis and processing, cytoskeleton formation, Ca(2+) signalling, and as allergens. A number of proteins in tomato pollen were similar to those reported in the pollen of other species; however, several additional proteins with roles in defence mechanisms, metabolic processes, and hormone signalling were identified. The potential roles of the identified proteins in the survival strategy of the small, independent, two-celled pollen grain of tomato, and subsequently in pollen germination and tube growth are discussed
Proteome profile and functional classification of proteins in Arabidopsis thaliana (Landsberg erecta) mature pollen
Proteome analysis of mature Arabidopsis thaliana (Landsberg erecta ecotype) pollen was conducted using two-dimensional gel electrophoresis and mass spectrometry. A total of 960 spots were resolved on pH 4â7 IPG strips and 110 distinct proteins were identified from 150 spots analyzed. The identified proteins were categorized based on their functional role in the pollen, which included proteins involved in energy regulation, defense-related mechanisms, calcium-binding and signaling, cytoskeletal formation, pollen allergens, glycine-rich proteins (GRPs), and late embryogenesis abundant (LEA) proteins. These proteins potentially play important roles in pollen function at maturity and during subsequent germination and tube growth. Some of the proteins identified were related to known pollen-specific transcripts, while some were similar to proteins found in the seed. In this study, 66 new proteins were identified which were not reported in two other recent studies on Arabidopsis pollen, 17 proteins were common in all three studies, and 35 or 26 proteins reported here had an overlap with one or the other two studies. These differences may be attributed to the methods of protein extraction, spot selection for analysis, and the ecotype used. Together, the three studies provide a broad spectrum of the Arabidopsis pollen proteome
Patching up the No-Boundary Proposal with virtual Euclidean wormholes
In quantum cosmology, one often considers tunneling phenomena which may have
occurred in the early universe. Processes requiring quantum penetration of a
potential barrier include black hole pair creation and the decay of vacuum
domain walls. Ideally, one calculates the rates for such processes by finding
an instanton, or Euclidean solution of the field equations, which interpolates
between the initial and final states. In practice, however, it has become
customary to calculate such amplitudes using the No-Boundary Proposal of Hartle
and Hawking. A criticism of this method is that it does not use a single path
which interpolates between the initial and final states, but two disjoint
instantons: One divides the probability to create the final state from nothing
by the probability to create the initial state from nothing and decrees the
answer to be the rate of tunneling from the initial to the final state. Here,
we demonstrate the validity of this approach by constructing continuous paths
connecting the ingoing and outgoing data, which may be viewed as perturbations
of the set of disconnected instantons. They are off-shell, but will still
dominate the path integral as they have action arbitrarily close to the
no-boundary action. In this picture, a virtual domain wall, or wormhole, is
created and annihilated in such a way as to interface between the disjoint
instantons. Decay rates calculated using our construction differ from decay
rates calculated using the No-Boundary Proposal only in the prefactor; the
exponent, which usually dominates the result, remains unchanged.Comment: 23 pages REVTeX plus 7 figure
Modelling Canopy Flows over Complex Terrain
Recent studies of flow over forested hills have been motivated by a number of important applications including understanding CO22 and other gaseous fluxes over forests in complex terrain, predicting wind damage to trees, and modelling wind energy potential at forested sites. Current modelling studies have focussed almost exclusively on highly idealized, and usually fully forested, hills. Here, we present model results for a site on the Isle of Arran, Scotland with complex terrain and heterogeneous forest canopy. The model uses an explicit representation of the canopy and a 1.5-order turbulence closure for flow within and above the canopy. The validity of the closure scheme is assessed using turbulence data from a field experiment before comparing predictions of the full model with field observations. For near-neutral stability, the results compare well with the observations, showing that such a relatively simple canopy model can accurately reproduce the flow patterns observed over complex terrain and realistic, variable forest cover, while at the same time remaining computationally feasible for real case studies. The model allows closer examination of the flow separation observed over complex forested terrain. Comparisons with model simulations using a roughness length parametrization show significant differences, particularly with respect to flow separation, highlighting the need to explicitly model the forest canopy if detailed predictions of near-surface flow around forests are required
Photometry of Kuiper belt object (486958) Arrokoth from New Horizons LORRI
On January 1st 2019, the New Horizons spacecraft flew by the classical Kuiper belt object (486958) Arrokoth (provisionally designated 2014 MU69), possibly the most primitive object ever explored by a spacecraft. The I/F of Arrokoth is analyzed and fit with a photometric function that is a linear combination of the Lommel-Seeliger (lunar) and Lambert photometric functions. Arrokoth has a geometric albedo of p_vâŻ=âŻ0.21_(â0.04)^(+0.05) at a wavelength of 550 nm and â0.24 at 610 nm. Arrokoth's geometric albedo is greater than the median but consistent with a distribution of cold classical Kuiper belt objects whose geometric albedos were determined by fitting a thermal model to radiometric observations. Thus, Arrokoth's geometric albedo adds to the orbital and spectral evidence that it is a cold classical Kuiper belt object. Maps of the normal reflectance and hemispherical albedo of Arrokoth are presented. The normal reflectance of Arrokoth's surface varies with location, ranging from â0.10â0.40 at 610 nm with an approximately Gaussian distribution. Both Arrokoth's extrema dark and extrema bright surfaces are correlated to topographic depressions. Arrokoth has a bilobate shape and the two lobes have similar normal reflectance distributions: both are approximately Gaussian, peak at â0.25 at 610 nm, and range from â0.10â0.40, which is consistent with co-formation and co-evolution of the two lobes. The hemispherical albedo of Arrokoth varies substantially with both incidence angle and location, the average hemispherical albedo at 610 nm is 0.063 ± 0.015. The Bond albedo of Arrokoth at 610 nm is 0.062 ± 0.015
Alpha-Vacua, Black Holes, and AdS/CFT
The Schwarzschild, Schwarzschild-AdS, and Schwarzschild-de Sitter solutions
all admit freely acting discrete involutions which commute with the continuous
symmetries of the spacetimes. Intuitively, these involutions correspond to the
antipodal map of the corresponding spacetimes. In analogy with the ordinary de
Sitter example, this allows us to construct new vacua by performing a
Mottola-Allen transform on the modes associated with the Hartle-Hawking, or
Euclidean, vacuum. These vacua are the `alpha'-vacua for these black holes. The
causal structure of a typical black hole may ameliorate certain difficulties
which are encountered in the case of de Sitter alpha-vacua. For
Schwarzschild-AdS black holes, a Bogoliubov transformation which mixes
operators of the two boundary CFT's provides a construction of the dual CFT
alpha-states. Finally, we analyze the thermal properties of these vacua.Comment: 40 pages REVTeX and AMSLaTeX, 17 black&white eps figures. v3:
references added. v4: details of the pinch singularity avoidance for the
string quantization of the Rindler space toy model have been added in both
the body of the paper and in a new 7 page appendix. Other clarifications and
references added. This is the version accepted for publication in Class.
Quant. Gra
Physical restraint in residential child care : the experiences of young people and residential workers
There have long been concerns about the use of physical restraint in residential care. This paper presents the findings of a qualitative study which explores the experiences of children, young people and residential workers about physical restraint. The research identifies the dilemmas and ambiguities for both staff and young people, and participants discuss the situations where they feel physical restraint is appropriate as well as their concerns about unjustified or painful restraints. They describe the negative emotions involved in restraint but also those situations where, through positive relationships and trust, restraint can help young people through unsafe situations
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