2,705 research outputs found
Exact vortex nucleation and cooperative vortex tunneling in dilute BECs
With the imminent advent of mesoscopic rotating BECs in the lowest Landau
level (LLL) regime, we explore LLL vortex nucleation. An exact many-body
analysis is presented in a weakly elliptical trap for up to 400 particles.
Striking non-mean field features are exposed at filling factors >>1 . Eg near
the critical rotation frequency pairs of energy levels approach each other with
exponential accuracy. A physical interpretation is provided by requantising a
mean field theory, where 1/N plays the role of Planck's constant, revealing two
vortices cooperatively tunneling between classically degenerate energy minima.
The tunnel splitting variation is described in terms of frequency, particle
number and ellipticity.Comment: 4 pages,4 figure
On Thresholds for Dynamic Strength in Solids
From Springer Nature via Jisc Publications RouterHistory: received 2020-08-15, accepted 2021-03-29, registration 2021-03-29, pub-electronic 2021-04-20, online 2021-04-20, pub-print 2021-06Publication status: PublishedAbstract: The limits of elastic behaviour change with the nature of the impulse applied to a target and the size of volume interrogated by a measurement, since it is the pre-existing defects sampled within its rise that determine the response observed. This review considers a range of solids of different material classes and tracks the development of the strength of the material during shock loading, from yield at the Hugoniot elastic limit, across the weak shock regime, to its transition to strong shock behaviour. It is shown that at this stress, the weak shock limit (WSL), the shear component of the applied stress exceeds the theoretical strength of the material. Beyond this threshold, there are a number of new responses that confirm a transition from an inhomogeneous to a homogeneous state. Further, whilst strength rises across the weak shock regime, it saturates at the WSL. For instance, failure in shocked glasses transitions from localised fracture initiated at target boundaries to a global failure at this threshold at the theoretical strength. Sapphire′s strength asymptotes to the theoretical strength of the strongest direction in its lattice. Finally, the fourth-power dependence of strain rate upon stress appears to be a consequence of the homogeneous flow in the strong shock regime. This review suggests that µ/2π is a good approximation for the unrelaxed theoretical strength of solids at increasing stresses beyond the WSL. The methodology unfolded here represents a new means to experimentally determine the ultimate shear strength of solids
Anomalous hydrodynamics and "normal" fluids in rapidly rotating BECs
In rapidly rotating bose systems we show that there is a region of anomalous
hydrodynamics whilst the system is still condensed, which coincides with the
mean field quantum Hall regime. An immediate consequence is the absence of a
normal fluid in any conventional sense. However, even the superfluid
hydrodynamics is not described by conventional Bernoulli and continuity
equations. We show there are kinematic constraints which connect spatial
variations of density and phase, that the positions of vortices are not the
simplest description of the dynamics of such a fluid (despite their utility in
describing the instantaneous state of the condensate) and that the most compact
description allows solution of some illuminating examples of motion. We
demonstrate, inter alia, a very simple relation between vortices and surface
waves. We show the surface waves can form a "normal fluid" which absorbs energy
and angular momentum from vortex motion in the trap. The time scale of this
process is sensitive to the initial configuration of the vortices, which can
lead to long-lived vortex patches - perhaps related to those observed at JILA.Comment: 4 pages; 1 sentence and references modifie
Distinct emphysema subtypes defined by quantitative CT analysis are associated with specific pulmonary matrix metalloproteinases.
BACKGROUND: Emphysema is characterised by distinct pathological sub-types, but little is known about the divergent underlying aetiology. Matrix-metalloproteinases (MMPs) are proteolytic enzymes that can degrade the extracellular matrix and have been identified as potentially important in the development of emphysema. However, the relationship between MMPs and emphysema sub-type is unknown. We investigated the role of MMPs and their inhibitors in the development of emphysema sub-types by quantifying levels and determining relationships with these sub-types in mild-moderate COPD patients and ex/current smokers with preserved lung function. METHODS: Twenty-four mild-moderate COPD and 8 ex/current smokers with preserved lung function underwent high resolution CT and distinct emphysema sub-types were quantified using novel local histogram-based assessment of lung density. We analysed levels of MMPs and tissue inhibitors of MMPs (TIMPs) in bronchoalveolar lavage (BAL) and assessed their relationship with these emphysema sub-types. RESULTS: The most prevalent emphysema subtypes in COPD subjects were mild and moderate centrilobular (CLE) emphysema, while only small amounts of severe centrilobular emphysema, paraseptal emphysema (PSE) and panlobular emphysema (PLE) were present. MMP-3, and -10 associated with all emphysema sub-types other than mild CLE, while MMP-7 and -8 had associations with moderate and severe CLE and PSE. MMP-9 also had associations with moderate CLE and paraseptal emphysema. Mild CLE occurred in substantial quantities irrespective of whether airflow obstruction was present and did not show any associations with MMPs. CONCLUSION: Multiple MMPs are directly associated with emphysema sub-types identified by CT imaging, apart from mild CLE. This suggests that MMPs play a significant role in the tissue destruction seen in the more severe sub-types of emphysema, whereas early emphysematous change may be driven by a different mechanism. TRIAL REGISTRATION: Trial registration number NCT01701869
Mechanisms of deep brain stimulation for obsessive compulsive disorder: effects upon cells and circuits
Deep brain stimulation (DBS) has emerged as a safe, effective, and reversible treatment for a number of movement disorders. This has prompted investigation of its use for other applications including psychiatric disorders. In recent years, DBS has been introduced for the treatment of obsessive compulsive disorder (OCD), which is characterized by recurrent unwanted thoughts or ideas (obsessions) and repetitive behaviors or mental acts performed in order to relieve these obsessions (compulsions). Abnormal activity in cortico-striato-thalamo-cortical (CSTC) circuits including the orbitofrontal cortex (OFC), anterior cingulate cortex (ACC), ventral striatum, and mediodorsal (MD) thalamus has been implicated in OCD. To this end a number of DBS targets including the anterior limb of the internal capsule (ALIC), ventral capsule/ventral striatum (VC/VS), ventral caudate nucleus, subthalamic nucleus (STN), and nucleus accumbens (NAc) have been investigated for the treatment of OCD. Despite its efficacy and widespread use in movement disorders, the mechanism of DBS is not fully understood, especially as it relates to psychiatric disorders. While initially thought to create a functional lesion akin to ablative procedures, it is increasingly clear that DBS may induce clinical benefit through activation of axonal fibers spanning the CSTC circuits, alteration of oscillatory activity within this network, and/or release of critical neurotransmitters. In this article we review how the use of DBS for OCD informs our understanding of both the mechanisms of DBS and the circuitry of OCD. We review the literature on DBS for OCD and discuss potential mechanisms of action at the neuronal level as well as the broader circuit level
The shock Hugoniot of hydroxy-terminated polybutadiene
The response of polymers to shock loading is becoming of increasing importance, both as binder systems in plastic-bonded explosives (PBXs) and as structural materials in their own right. In this paper, we report on the shock Hugoniot of hydroxy-terminated polybutadiene (HTPB), which is commonly used as a binder system in PBXs, but whose shock response has yet to be presented in the open literature. Results indicate that the shock velocity --- particle velocity relationship is linear, similar to some but not all polymer-based materials
T-PHOT: A new code for PSF-matched, prior-based, multiwavelength extragalactic deconfusion photometry
We present T-PHOT, a publicly available software aimed at extracting accurate
photometry from low-resolution images of deep extragalactic fields, where the
blending of sources can be a serious problem for the accurate and unbiased
measurement of fluxes and colours. T-PHOT has been developed within the
ASTRODEEP project and it can be considered as the next generation to TFIT,
providing significant improvements above it and other similar codes. T-PHOT
gathers data from a high-resolution image of a region of the sky, and uses it
to obtain priors for the photometric analysis of a lower resolution image of
the same field. It can handle different types of datasets as input priors: i) a
list of objects that will be used to obtain cutouts from the real
high-resolution image; ii) a set of analytical models; iii) a list of
unresolved, point-like sources, useful e.g. for far-infrared wavelength
domains. We show that T-PHOT yields accurate estimations of fluxes within the
intrinsic uncertainties of the method, when systematic errors are taken into
account (which can be done thanks to a flagging code given in the output).
T-PHOT is many times faster than similar codes like TFIT and CONVPHOT (up to
hundreds, depending on the problem and the method adopted), whilst at the same
time being more robust and more versatile. This makes it an optimal choice for
the analysis of large datasets. In addition we show how the use of different
settings and methods significantly enhances the performance. Given its
versatility and robustness, T-PHOT can be considered the preferred choice for
combined photometric analysis of current and forthcoming extragalactic optical
to far-infrared imaging surveys. [abridged]Comment: 23 pages, 20 figures, 2 table
The relationship between dust and [C I] at z = 1 and beyond
© 2018 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society.Measuring molecular gas mass is vital for understanding the evolution of galaxies at high redshifts (z ≳ 1). Most measurements rely on CO as a tracer, but dependencies on metallicity, dynamics, and surface density lead to systematic uncertainties in high-z galaxies, where these physical properties are difficult to observe, and where the physical environments can differ systematically from those at z = 0. Dust continuum emission provides a potential alternative assuming a known dust/gas ratio, but this must be calibrated on a direct gas tracer at z ≳ 1. In this paper, we consider the [C I] 492-GHz emission line, which has been shown to trace molecular gas closely throughout Galactic clouds and has the advantages of being optically thin in typical conditions (unlike CO), and being observable at accessible frequencies at high redshifts (in contrast to the low-excitation lines of CO). We use the Atacama Large Millimetre/submillimetre Array to measure [C I], CO(4–3), and dust emission in a representative sample of star-forming galaxies at z = 1, and combine these data with multiwavelength spectral energy distributions to study relationships between dust and gas components of galaxies. We uncover a strong [C I]–dust correlation, suggesting that both trace similar phases of the gas. By incorporating other samples from the literature, we show that this correlation persists over a wide range of luminosities and redshifts up to z ∼ 4. Finally, we explore the implications of our results as an independent test of literature calibrations for dust as a tracer of gas mass, and for predicting the C I abundance.Peer reviewedFinal Published versio
Galaxy And Mass Assembly (GAMA) : The mechanisms for quiescent galaxy formation at z<1
© 2016 The Authors. One key problem in astrophysics is understanding how and why galaxies switch off their star formation, building the quiescent population that we observe in the local Universe. From the Galaxy And Mass Assembly and VIsible MultiObject Spectrograph Public Extragalactic Redshift surveys, we use spectroscopic indices to select quiescent and candidate transition galaxies.We identify potentially rapidly transitioning post-starburst (PSB) galaxies and slower transitioning green-valley galaxies. Over the last 8Gyr, the quiescent population has grown more slowly in number density at high masses (M * > 10 11 M ⊙ ) than at intermediate masses (M * > 10 10.6 M ⊙ ). There is evolution in both the PSB and green-valley stellar mass functions, consistent with higher mass galaxies quenching at earlier cosmic times.At intermediatemasses (M * > 10 10.6 M ⊙ ), we find a green-valley transition time-scale of 2.6 Gyr. Alternatively, at z ~ 0.7, the entire growth rate could be explained by fast-quenching PSB galaxies, with a visibility time-scale of 0.5 Gyr. At lower redshift, the number density of PSBs is so low that an unphysically short visibility window would be required for them to contribute significantly to the quiescent population growth. The importance of the fast-quenching route may rapidly diminish at z 10 11 M ⊙ ), there is tension between the large number of candidate transition galaxies compared to the slow growth of the quiescent population. This could be resolved if not all high-mass PSB and green-valley galaxies are transitioning from star forming to quiescent, for example if they rejuvenate out of the quiescent population following the accretion of gas and triggering of star formation, or if they fail to completely quench their star formation
Generalized Interpolation Material Point Approach to High Melting Explosive with Cavities Under Shock
Criterion for contacting is critically important for the Generalized
Interpolation Material Point(GIMP) method. We present an improved criterion by
adding a switching function. With the method dynamical response of high melting
explosive(HMX) with cavities under shock is investigated. The physical model
used in the present work is an elastic-to-plastic and thermal-dynamical model
with Mie-Gr\"uneissen equation of state. We mainly concern the influence of
various parameters, including the impacting velocity , cavity size , etc,
to the dynamical and thermodynamical behaviors of the material. For the
colliding of two bodies with a cavity in each, a secondary impacting is
observed. Correspondingly, the separation distance of the two bodies has a
maximum value in between the initial and second impacts. When the
initial impacting velocity is not large enough, the cavity collapses in a
nearly symmetric fashion, the maximum separation distance increases
with . When the initial shock wave is strong enough to collapse the cavity
asymmetrically along the shock direction, the variation of with
does not show monotonic behavior. Our numerical results show clear indication
that the existence of cavities in explosive helps the creation of ``hot
spots''.Comment: Figs.2,4,7,11 in JPG format; Accepted for publication in J. Phys. D:
Applied Physic
- …