4,928 research outputs found
Mechanisms of bottom boundary fluxes in a numerical model of the Shetland shelf
Across-slope bottom boundary layer (BBL) fluxes on the shelf-edge connect this region to deeper waters. Two proposed ways in which across-slope BBL fluxes can occur, in regions that have a slope current aligned to the bathymetry, are: the frictional veering of bottom currents termed the âEkman drainâ; and through local wind-forced downwelling (wind-driven surface Ekman flow with an associated bottom flow). We investigate the variability, magnitude and spatial scale of BBL fluxes on the Shetland shelf, which has a prominent slope current, using a high-resolution (âź 2 km) configuration of the MITgcm model. Fluxes are analysed in the BBL at the shelf break near the 200 m isobath and are found to have a seasonal variability with high/low volume transport in winter/summer respectively. By using a multivariate regression approach, we find that the locally wind-driven Ekman transport plays no explicit role in explaining daily bottom fluxes. We can better explain the variability of the across-slope BBL flux as a linear function of the speed and across-slope component of the interior flow, corresponding to an Ekman plus mean-flow flux. We estimate that the mean-flow is a greater contributor than the Ekman flux to the BBL flux. The spatial heterogeneity of the BBL fluxes can be attributed to the mean-flow, which has a much shorter decorrelation length compared to the Ekman flux. We conclude that both the speed and direction of the interior current determines the daily BBL flux. The wind does not explicitly contribute through local downwelling, but may influence the interior current and therefore implicitly the BBL fluxes on longer timescales
Spectral weight redistribution in strongly correlated bosons in optical lattices
We calculate the single-particle spectral function for the one-band
Bose-Hubbard model within the random phase approximation (RPA). In the strongly
correlated superfluid, in addition to the gapless phonon excitations, we find
extra gapped modes which become particularly relevant near the superfluid-Mott
quantum phase transition (QPT). The strength in one of the gapped modes, a
precursor of the Mott phase, grows as the QPT is approached and evolves into a
hole (particle) excitation in the Mott insulator depending on whether the
chemical potential is above (below) the tip of the lobe. The sound velocity of
the Goldstone modes remains finite when the transition is approached at a
constant density, otherwise, it vanishes at the transition. It agrees well with
Bogoliubov theory except close to the transition. We also calculate the spatial
correlations for bosons in an inhomogeneous trapping potential creating
alternating shells of Mott insulator and superfluid. Finally, we discuss the
capability of the RPA approximation to correctly account for quantum
fluctuations in the vicinity of the QPT.Comment: 14 pages, 12 figure
Development of Zwitterionic Hydrophilic Liquid Chromatography (ZICâHILIC-MS) metabolomics method for Shotgun analysis of human urine
Urine is a product of the bodyâs metabolism and the majority of the metabolic products exiting via the renal system are rendered polar in order to be water soluble. Resolution of urinary metabolites for metabolomic studies requires the development of HPLC separation techniques that match this feature of biological chemistry. ZIC âHILIC is an ideal candidate to take forward resolution of such metabolites where reverse phase is unable to give adequate separation. Metabolomic data has to be processed by Shotgun multivariate analysis to sift through thousands of analytes and their variables such as ion intensity.
In the development of ZIC-HILIC separation with mass spectrometric (IT-ToF) detection, methodological variability have to be minimized so that any Shotgun data analysis does not reveal potential biomarker analytes that are artifacts or are adversely affected of the separation and detection technique. Here, we report the development of a ZIC-HILIC mass spectrometry method that is suitable for SIMCA P+ data analysis of urine. Variables such as resolution, run reproducibility and sample storage temperature were evaluated in tandem with SIMCA P+ data analysis and quality control pre-processing.
The developed method couples quality control runs that pre-process and exclude analytes that are insufficiently robust for further candidate biomarker studies. This meant labile analytes that could not be reproduced in 70% of QC runs (which are pools of all samples run that day) were excluded. However, urine samples stored at 4°C for more than 9 months will contain metabolites that will alter and produce small molecule marker artifacts when compared to samples stored at -20°C.
In conclusion, the developed method is a robust method of ZIC-HILIC mass spectrometry shotgun analysis suitable for urinary metabolome discovery of robust biomarkers
Particle-Hole Symmetry and the Effect of Disorder on the Mott-Hubbard Insulator
Recent experiments have emphasized that our understanding of the interplay of
electron correlations and randomness in solids is still incomplete. We address
this important issue and demonstrate that particle-hole (ph) symmetry plays a
crucial role in determining the effects of disorder on the transport and
thermodynamic properties of the half-filled Hubbard Hamiltonian. We show that
the low-temperature conductivity decreases with increasing disorder when
ph-symmetry is preserved, and shows the opposite behavior, i.e. conductivity
increases with increasing disorder, when ph-symmetry is broken. The Mott
insulating gap is insensitive to weak disorder when there is ph-symmetry,
whereas in its absence the gap diminishes with increasing disorder.Comment: 4 pages, 4 figure
Preprint arXiv:2212.04924 Submitted on 9 Dec 2022
Several quantum hardware platforms, while being unable to perform fullyfault-tolerant quantum computation, can still be operated as analogue quantumsimulators for addressing many-body problems. However, due to the presence oferrors, it is not clear to what extent those devices can provide us with anadvantage with respect to classical computers. In this work we consider the useof noisy analogue quantum simulators for computing physically relevantproperties of many-body systems both in equilibrium and undergoing dynamics. Wefirst formulate a system-size independent notion of stability against extensiveerrors, which we prove for Gaussian fermion models, as well as for a restrictedclass of spin systems. Remarkably, for the Gaussian fermion models, ouranalysis shows the stability of critical (gapless) models at zero temperaturewhich have long-range correlations. Furthermore, we analyze how this stabilitymay lead to a quantum advantage, for the problem of computing the thermodynamiclimits of many-body models, in the presence of a constant error rate andwithout any explicit error correction
Non-Supersymmetric Attractors in String Theory
We find examples of non-supersymmetric attractors in Type II string theory
compactified on a Calabi Yau three-fold. For a non-supersymmetric attractor the
fixed values to which the moduli are drawn at the horizon must minimise an
effective potential. For Type IIA at large volume, we consider a configuration
carrying D0, D2, D4 and D6 brane charge. When the D6 brane charge is zero, we
find for some range of the other charges, that a non-supersymmetric attractor
solution exists. When the D6 brane charge is non-zero, we find for some range
of charges, a supersymmetry breaking extremum of the effective potential.
Closer examination reveals though that it is not a minimum of the effective
potential and hence the corresponding black hole solution is not an attractor.
Away from large volume, we consider the specific case of the quintic in CP^4.
Working in the mirror IIB description we find non-supersymmetric attractors
near the Gepner point.Comment: Added a few clarification
Primordial Magnetic Field Limits from Cosmic Microwave Background Bispectrum of Magnetic Passive Scalar Modes
Primordial magnetic fields lead to non-Gaussian signals in the cosmic
microwave background (CMB) even at the lowest order, as magnetic stresses and
the temperature anisotropy they induce depend quadratically on the magnetic
field. In contrast, CMB non-Gaussianity due to inflationary scalar
perturbations arises only as a higher order effect. Apart from a compensated
scalar mode, stochastic primordial magnetic fields also produce scalar
anisotropic stress that remains uncompensated till neutrino decoupling. This
gives rise to an adiabatic-like scalar perturbation mode that evolves passively
thereafter (called the passive mode). We compute the CMB reduced bispectrum
() induced by this passive mode, sourced via the
Sachs-Wolfe effect, on large angular scales. For any configuration of
bispectrum, taking a partial sum over mode-coupling terms, we find a typical
value of , for a magnetic field of nG, assuming a nearly
scale-invariant magnetic spectrum . We also evaluate, in full, the bispectrum
for the squeezed collinear configuration over all angular mode-coupling terms
and find . These values are more than times larger than the
previously calculated magnetic compensated scalar mode CMB bispectrum.
Observational limits on the bispectrum from WMAP7 data allow us to set upper
limits of nG on the present value of the cosmic magnetic field of
primordial origin. This is over 10 times more stringent than earlier limits on
based on the compensated mode bispectrum.Comment: 9 page
On the role of confinement on solidification in pure materials and binary alloys
We use a phase-field model to study the effect of confinement on dendritic
growth, in a pure material solidifying in an undercooled melt, and in the
directional solidification of a dilute binary alloy. Specifically, we observe
the effect of varying the vertical domain extent () on tip selection,
by quantifying the dendrite tip velocity and curvature as a function of
, and other process parameters. As decreases, we find that the
operating state of the dendrite tips becomes significantly affected by the
presence of finite boundaries. For particular boundary conditions, we observe a
switching of the growth state from 3-D to 2-D at very small , in both
the pure material and alloy. We demonstrate that results from the alloy model
compare favorably with those from an experimental study investigating this
effect.Comment: 13 pages, 9 figures, 3 table
Superconductor-Insulator Transition in a Disordered Electronic System
We study an electronic model of a 2D superconductor with onsite randomness
using Quantum Monte Carlo simulations. The superfluid density is used to track
the destruction of superconductivity in the ground state with increasing
disorder. The non-superconducting state is identified as an insulator from the
temperature dependence of its d.c. resistivity. The value of
at the superconductor-insulator transition appears to be non-universal.Comment: PostScript, 4 pages, figures include
Control design for inhomogeneous broadening compensation in single-photon transducers
A transducer of single photons between microwave and optical frequencies can be used to realize quantum communication over optical fiber links between distant superconducting quantum computers. A promising scalable approach to constructing such a transducer is to use ensembles of quantum emitters interacting simultaneously with electromagnetic fields at optical and microwave frequencies. However, inhomogeneous broadening in the transition frequencies of the emitters can be detrimental to this collective action. In this article, we utilise a gradient-based optimization strategy to design the temporal shape of the laser field driving the transduction system to mitigate the effects of inhomogeneous broadening. We study the improvement of transduction efficiencies as a function of inhomogeneous broadening in different single-emitter cooperativity regimes and correlate it with a restoration of superradiance effects in the emitter ensembles. Furthermore, to assess the optimality of our pulse designs, we provide certifiable bounds on the design problem and compare them to the achieved performance
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