1,875 research outputs found
The triton in a finite volume
Understanding the volume dependence of the triton binding energy is an
important step towards lattice simulations of light nuclei. We calculate the
triton binding energy in a finite cubic box with periodic boundary conditions
to leading order in the pionless effective field theory. Higher order
corrections are estimated and the proper renormalization of our results is
verified explicitly. We present results for the physical triton as well as for
the pion-mass dependence of the triton spectrum near the ``critical'' pion
mass, Mpi_c ~ 197 MeV, where chiral effective field theory suggests that the
nucleon-nucleon scattering lengths in the singlet- and triplet-channels diverge
simultaneously. An extension of the Luescher formula to the three-body system
is implicit in our results.Comment: 11 pages, 4 figure
Hypervelocity stars in the Gaia era: Runaway B stars beyond the velocity limit of classical ejection mechanisms
Young massive stars in the halo are assumed to be runaway stars from the
Galactic disk. Possible ejection scenarios are binary supernova ejections (BSE)
or dynamical ejections from star clusters (DE). Hypervelocity stars (HVSs) are
extreme runaway stars that are potentially unbound from the Galaxy. Powerful
acceleration mechanisms such as the tidal disruption of a binary system by a
supermassive black hole (SMBH) are required to produce them. Therefore, HVSs
are believed to originate in the Galactic center (GC), the only place known to
host an SMBH. The second Gaia data release (DR2) offers the opportunity of
studying HVSs in an unprecedented manner. We revisit some of the most
interesting high-velocity stars, that is, 15 stars for which proper motions
with the Hubble Space Telescope were obtained in the pre-Gaia era, to unravel
their origin. By carrying out kinematic analyses based on revised
spectrophotometric distances and proper motions from Gaia DR2, kinematic
properties were obtained that help constrain the spatial origins of these
stars. Stars that were previously considered (un)bound remain (un)bound in
Galactic potentials favored by Gaia DR2 astrometry. For nine stars (five
candidate HVSs plus all four radial velocity outliers), the GC can be ruled out
as spatial origin at least at confidence level, suggesting that a
large portion of the known HVSs are disk runaway stars launched close to or
beyond Galactic escape velocities. The fastest star in the sample, HVS3, is
confirmed to originate in the Large Magellanic Cloud. Because the ejection
velocities of five of our non-GC stars are close to or above the upper limits
predicted for BSE and DE, another powerful dynamical ejection mechanism (e.g.,
involving massive perturbers such as intermediate-mass black holes) is likely
to operate in addition to the three classical scenarios mentioned above.Comment: Accepted for publication in A&A (Astronomy and Astrophysics
Few-body physics in a Finite Volume
In this work, three-body bound states were studied in finite volume using an Effective Field Theory framework. The finite volumes under consideration are cubic volumes with periodic boundary conditions. The Effective Field Theory framework used in this work employs only contact interactions and is particularly well suited for studies of universal properties, i.e. properties independent of the details of the interaction on short distances. A particular example in the three-body sector is the Efimov effect, the emergence of a geometrically spaced bound state spectrum. In the first part, systems of three identical bosons are investigated. As a consequence of the breakdown of the spherical symmetry to cubic symmetry, the partial waves of the bound state amplitude are coupled. An infinite set of coupled integral equations for these partial waves is derived. These equations have to be solved numerically in order to obtain the binding energies in the finite volume. The dependence of the energies on the box size is calculated and the results are explicitly verified to be renormalized. Results for positive and negative scattering lengths are shown. The effects of higher partial waves are investigated. The behavior of shallow trimers near the dimer energy as well as deeply bound trimers is studied. The shallowest state investigated crosses the dimer energy at a certain volume and behaves like a scattering state for smaller volumes. Numerical evidence for a universal scaling of the finite volume corrections is provided. Subsequently, the formalism is extended to systems of three nucleons. This case provides the main motivation for this work due to its applicability to Lattice Quantum Chromodynamics (QCD) calculations of the triton. Such calculations always take place inside a finite volume which makes control over the corresponding effects crucial for an understanding of results from the lattice. For the triton, there are two coupled channels already in the infinite volume corresponding to two different spin-isospin combinations. An infinite set of coupled integral equations for the partial waves of the bound state amplitudes is derived. The renormalization of all results is again explicitly verified. The physical triton inside a finite volume is investigated as well as the triton spectrum for unphysical pion masses. The former case qualitatively shows the same behavior as the three-boson case, and the volume dependence is calculated. The smallest volumes investigated are of the order of magnitude typical for present day Lattice calculations. The motivation for the latter part is twofold. On the one hand, Lattice QCD calculations are performed at pion masses larger than the physical one for computational reasons. On the other hand, it has been conjectured that QCD is close to the critical trajectory for an infrared renormalization group limit cycle, in which case the Efimov effect would occur for a critical pion mass. Close to this critical pion mass, the triton has excited states. The behavior of the ground state and of the excited states inside a finite volume is investigated for various pion masses around the critical one. The excited states cross the energy of the bound di-nucleon, as it was already observed for the shallowest bosonic trimer. The results for the ground state were used to provide strong numerical evidence for a universal scaling of the finite volume corrections
A quantitative spectral analysis of 14 hypervelocity stars from the MMT survey
Hypervelocity stars (HVSs) travel so fast that they may leave the Galaxy. The
tidal disruption of a binary system by the supermassive black hole in the
Galactic center is widely assumed to be their ejection mechanism. To test the
hypothesis of an origin in the Galactic center using kinematic investigations,
the current space velocities of the HVSs need to be determined. With the advent
of Gaia's second data release, accurate radial velocities from spectroscopy are
complemented by proper motion measurements of unprecedented quality. Based on a
new spectroscopic analysis method, we provide revised distances and stellar
ages, both of which are crucial to unravel the nature of the HVSs. We
reanalyzed low-resolution optical spectra of 14 HVSs from the MMT HVS survey
using a new grid of synthetic spectra, which account for deviations from local
thermodynamic equilibrium, to derive effective temperatures, surface gravities,
radial velocities, and projected rotational velocities. Stellar masses, radii,
and ages were then determined by comparison with stellar evolutionary models
that account for rotation. Finally, these results were combined with
photometric measurements to obtain spectroscopic distances. The resulting
atmospheric parameters are consistent with those of main sequence stars with
masses in the range 2.5 - 5.0 . The majority of the stars rotate at
fast speeds, providing further evidence for their main sequence nature. Stellar
ages range from 90 to 400 Myr and distances (with typical
-uncertainties of about 10-15%) from 30 to 100 kpc. Except for one
object (B711), which we reclassify as A-type star, all stars are of spectral
type B. The spectroscopic distances and stellar ages derived here are key
ingredients for upcoming kinematic studies of HVSs based on Gaia proper
motions.Comment: Accepted for publication in A&A (Astronomy and Astrophysics
Runaway blue main-sequence stars at high Galactic latitudes. Target selection with Gaia and spectroscopic identification
Motivated by the historical identification of runaway main-sequence (MS)
stars of early spectral type at high Galactic latitudes, we test the capability
of Gaia at identifying new such stars. We have selected ~2300 sources with Gaia
magnitudes of GBP - GRP < 0.05, compatible with the colors of low-extinction MS
stars earlier than mid-A spectral type, and obtained low-resolution optical
spectroscopy for 48 such stars. By performing detailed photometric and
spectroscopic analyses, we derive their atmospheric and physical parameters
(effective temperature, surface gravity, radial velocity, interstellar
reddening, spectrophotometric distance, mass, radius, luminosity, and age). The
comparison between spectrophotometric and parallax-based distances enables us
to disentangle the MS candidates from older blue horizontal branch (BHB)
candidates. We identify 12 runaway MS candidates, with masses between 2 and 6
Msun. Their trajectories are traced back to the Galactic disc to identify their
most recent Galactic plane crossings and the corresponding flight times. All 12
candidates are ejected from the Galactic disc within 2 to 16.5 kpc from the
Galactic center and possess flight times that are shorter than their
evolutionary ages, compatible with a runaway hypothesis. Three MS candidates
have ejection velocities exceeding 450 km/s, thus, appear to challenge the
canonical ejection scenarios for late B-type stars. The fastest star of our
sample also has a non-negligible Galactic escape probability if its MS nature
can be confirmed. We identify 27 BHB candidates, and the two hottest stars in
our sample are rare late O and early B type stars of low mass evolving towards
the white dwarf cooling sequence.Comment: Accepted for publication in A&A; abbreviated abstract; 16 pages, 13
figures, 5 table
Efimov physics in a finite volume
Three bosons with large scattering length show universal properties that do
not depend on the details of the interaction at short distances. In the
three-boson system, these properties include a geometric spectrum of shallow
three-body states called "Efimov states" and log-periodic dependence of
scattering observables on the scattering length. We investigate the
modification of the Efimov states in a finite cubic box and calculate the
dependence of their energies on the box size using effective field theory. We
explicitly verify the renormalization of the effective field theory in the
finite volume.Comment: 9 pages, 3 figures, sign error corrected, numerical results changed,
final versio
Genotype-by-Diet Interactions for Larval Performance and Body Composition Traits in the Black Soldier Fly, Hermetia illucens
Further advancing black soldier fly (BSF) farming for waste valorisation and more sustainable global protein supplies critically depends on targeted exploitation of genotype-phenotype associations in this insect, comparable to conventional livestock. This study used a fully crossed factorial design of rearing larvae of four genetically distinct BSF strains (FST: 0.11â0.35) on three nutritionally different diets (poultry feed, food waste, poultry manure) to investigate genotype-by-environment interactions. Phenotypic responses included larval growth dynamics over time, weight at harvest, mortality, biomass production with respective contents of ash, fat, and protein, including amino acid profiles, as well as bioconversion and nitrogen efficiency, reduction of dry matter and relevant fibre fractions, and dry matter loss (emissions). Virtually all larval performance and body composition traits were substantially influenced by diet but also characterised by ample BSF genetic variation and, most importantly, by pronounced interaction effects between the two. Across evaluated phenotypes, variable diet-dependent rankings and the lack of generally superior BSF strains indicate the involvement of trade-offs between traits, as their relationships may even change signs. Conflicting resource allocation in light of overall BSF fitness suggests anticipated breeding programs will require complex and differential selection strategies to account for pinpointed trait maximisation versus multi-purpose resilience
Thermal error modelling of a gantry-type 5-axis machine tool using a Grey Neural Network Model
This paper presents a new modelling methodology for compensation of the thermal errors on a gantry-type 5-axis CNC machine tool. The method uses a âGrey Neural Network Model with Convolution Integralâ (GNNMCI(1, N)), which makes full use of the similarities and complementarity between Grey system models and artificial neural networks (ANNs) to overcome the disadvantage of applying either model in isolation. A Particle Swarm Optimisation (PSO) algorithm is also employed to optimise the proposed Grey neural network. The size of the data pairs is crucial when the generation of data is a costly affair, since the machine downtime necessary to acquire the data is often considered prohibitive. Under such circumstances, optimisation of the number of data pairs used for training is of prime concern for calibrating a physical model or training a black-box model. A Grey Accumulated Generating Operation (AGO), which is a basis of the Grey system theory, is used to transform the original data to a monotonic series of data, which has less randomness than the original series of data. The choice of inputs to the thermal model is a non-trivial decision which is ultimately a compromise between the ability to obtain data that sufficiently correlates with the thermal distortion and the cost of implementation of the necessary feedback sensors. In this study, temperature measurement at key locations was supplemented by direct distortion measurement at accessible locations. This form of data fusion simplifies the modelling process, enhances the accuracy of the system and reduces the overall number of inputs to the model, since otherwise a much larger number of thermal sensors would be required to cover the entire structure. The Z-axis heating test, C-axis heating test, and the combined (helical) movement are considered in this work. The compensation values, calculated by the GNNMCI(1, N) model were sent to the controller for live error compensation. Test results show that a 85% reduction in thermal errors was achieved after compensation
Small Molecule Immunosensing Using Surface Plasmon Resonance
Surface plasmon resonance (SPR) biosensors utilize refractive index changes to sensitively detect mass changes at noble metal sensor surface interfaces. As such, they have been extensively applied to immunoassays of large molecules, where their high mass and use of sandwich immunoassay formats can result in excellent sensitivity. Small molecule immunosensing using SPR is more challenging. It requires antibodies or high-mass or noble metal labels to provide the required signal for ultrasensitive assays. Also, it can suffer from steric hindrance between the small antigen and large antibodies. However, new studies are increasingly meeting these and other challenges to offer highly sensitive small molecule immunosensor technologies through careful consideration of sensor interface design and signal enhancement. This review examines the application of SPR transduction technologies to small molecule immunoassays directed to different classes of small molecule antigens, including the steroid hormones, toxins, drugs and explosives residues. Also considered are the matrix effects resulting from measurement in chemically complex samples, the construction of stable sensor surfaces and the development of multiplexed assays capable of detecting several compounds at once. Assay design approaches are discussed and related to the sensitivities obtained
Performance of CMS muon reconstruction in pp collision events at sqrt(s) = 7 TeV
The performance of muon reconstruction, identification, and triggering in CMS
has been studied using 40 inverse picobarns of data collected in pp collisions
at sqrt(s) = 7 TeV at the LHC in 2010. A few benchmark sets of selection
criteria covering a wide range of physics analysis needs have been examined.
For all considered selections, the efficiency to reconstruct and identify a
muon with a transverse momentum pT larger than a few GeV is above 95% over the
whole region of pseudorapidity covered by the CMS muon system, abs(eta) < 2.4,
while the probability to misidentify a hadron as a muon is well below 1%. The
efficiency to trigger on single muons with pT above a few GeV is higher than
90% over the full eta range, and typically substantially better. The overall
momentum scale is measured to a precision of 0.2% with muons from Z decays. The
transverse momentum resolution varies from 1% to 6% depending on pseudorapidity
for muons with pT below 100 GeV and, using cosmic rays, it is shown to be
better than 10% in the central region up to pT = 1 TeV. Observed distributions
of all quantities are well reproduced by the Monte Carlo simulation.Comment: Replaced with published version. Added journal reference and DO
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