1,224 research outputs found
Ferromagnetism Induced by Uniaxial Pressure in the Itinerant Metamagnet Sr3Ru2O7
We report a uniaxial-pressure study on the magnetisation of single crystals
of the bilayer perovskite Sr3Ru2O7, a metamagnet close to a ferromagnetic
instability. We observed that the application of a uniaxial pressure parallel
to the c-axis induces ferromagnetic ordering with a Curie temperature of about
80 K and critical pressures of about 4 kbar or higher. This value for the
critical pressure is even higher than the value previously reported (~ 1 kbar),
which might be attributed to the difference of the impurity level. Below the
critical pressure parallel to the c-axis, the metamagnetic field appears to
hardly change. We have also found that uniaxial pressures perpendicular to the
c-axis, in contrast, do not induce ferromagnetism, but shift the metamagnetic
field to higher fields.Comment: Accepted for publication in Proc of 24th Int. Conf. on Low
Temperature Physics (LT24); 2 page
Poor electronic screening in lightly doped Mott insulators observed with scanning tunneling microscopy
The effective Mott gap measured by scanning tunneling microscopy (STM) in the
lightly doped Mott insulator differs
greatly from values reported by photoemission and optical experiments. Here, we
show that this is a consequence of the poor electronic screening of the
tip-induced electric field in this material. Such effects are well known from
STM experiments on semiconductors, and go under the name of tip-induced band
bending (TIBB). We show that this phenomenon also exists in the lightly doped
Mott insulator and that, at doping
concentrations of , it causes the measured energy gap in the sample
density of states to be bigger than the one measured with other techniques. We
develop a model able to retrieve the intrinsic energy gap leading to a value
which is in rough agreement with other experiments, bridging the apparent
contradiction. At doping we further observe circular features
in the conductance layers that point to the emergence of a significant density
of free carriers in this doping range, and to the presence of a small
concentration of donor atoms. We illustrate the importance of considering the
presence of TIBB when doing STM experiments on correlated-electron systems and
discuss the similarities and differences between STM measurements on
semiconductors and lightly doped Mott insulators.Comment: 9 pages, 5 figure
Solid Electrolyte Interphase Formation in Tellurium Iodide Perovskites during Electrochemistry and Photoelectrochemistry
Halide perovskites are promising photoelectrocatalytic materials. Their further development requires understanding of surface processes during electrochemistry. Thin films of tellurium-based vacancy-ordered perovskites with formula A2TeI6, A = Cs, methylammonium (MA), were deposited onto transparent conducting substrates using aerosol-assisted chemical vapor deposition. Thin film stability as electrodes and photoelectrodes was tested in dichloromethane containing tetrabutylammonium PF6 (TBAPF6). Using photoemission spectroscopy, we show that the formation of a solid electrolyte interphase on the surface of the Cs2TeI6, consisting of CsPF6, enhances the stability of the electrode and allows extended chopped-light chronoamperometry measurements at up to 1.1 V with a photocurrent density of 16 μA/cm2. In contrast, (CH3NH3)2TeI6 does not form a passivating layer and rapidly degrades upon identical electrochemical treatment. This demonstrates the importance of surface chemistry in halide perovskite electrochemistry and photoelectrocatalysis
Dynamically driven inflow onto the galactic center and its effect upon molecular clouds
Funding: ERC via the ERC Synergy Grant “ECOGAL” (grant 855130) (M.C.S., R.G.T., S.C.O.G., and R.S.K). R.J.S. gratefully acknowledges an STFC Ernest Rutherford fellowship (grant ST/N00485X/1).The Galactic bar plays a critical role in the evolution of the Milky Way's Central Molecular Zone (CMZ), driving gas toward the Galactic Center via gas flows known as dust lanes. To explore the interaction between the CMZ and the dust lanes, we run hydrodynamic simulations in arepo, modeling the potential of the Milky Way's bar in the absence of gas self-gravity and star formation physics, and we study the flows of mass using Monte Carlo tracer particles. We estimate the efficiency of the inflow via the dust lanes, finding that only about a third (30% ± 12%) of the dust lanes' mass initially accretes onto the CMZ, while the rest overshoots and accretes later. Given observational estimates of the amount of gas within the Milky Way's dust lanes, this suggests that the true total inflow rate onto the CMZ is 0.8 ± 0.6 M⊙ yr−1. Clouds in this simulated CMZ have sudden peaks in their average density near the apocenter, where they undergo violent collisions with inflowing material. While these clouds tend to counter-rotate due to shear, co-rotating clouds occasionally occur due to the injection of momentum from collisions with inflowing material (∼52% are strongly counter-rotating, and ∼7% are strongly co-rotating of the 44 cloud sample). We investigate the formation and evolution of these clouds, finding that they are fed by many discrete inflow events, providing a consistent source of gas to CMZ clouds even as they collapse and form stars.Peer reviewe
Alcohol dependence in a community sample of Aboriginal and Torres Strait Islander Australians : Harms, getting help and awareness of local treatments
Background
Few studies have examined links between current alcohol dependence and specific harms among Indigenous Australians. We investigated these associations as well as help seeking for drinking, awareness of local treatments and recommendations to help family or friends cut down or stop drinking in two Indigenous communities.
Methods
A representative sample of Indigenous Australians was surveyed in one urban and one remote community in South Australia. Data were collected via the Grog Survey App. Participants were dependent if they reported two or more symptoms of alcohol dependence (ICD-11). Pearson chi-square tests were used to describe relationships between employment by gender, and dependence by awareness of medicines and local treatment options. Multivariate logistic regressions were used to predict the odds of dependent drinkers experiencing harms and getting help for drinking, controlling for age, gender, schooling and income.
Results
A total of 775 Indigenous Australians took part in the study. After controlling for confounders, dependent drinkers were nearly eight times more likely to report a harm and nearly three times more likely to get help for their drinking—compared with non-dependent drinkers. Participants recommended accessing local support from an Aboriginal alcohol and other drugs worker, or a detoxification/ rehabilitation service.
Discussion and conclusions
More support and funding is needed for Indigenous Australians to ensure local treatment options for dependent drinkers are readily available, appropriate and accessible. Involvement of local Aboriginal or Torres Strait Islander health professionals in delivery of care can help ensure that it is appropriate to an individual’s culture and context
Simulations of the Milky Way's central molecular zone -- I. Gas dynamics
We use hydrodynamical simulations to study the Milky Way's central molecular
zone (CMZ). The simulations include a non-equilibrium chemical network, the gas
self-gravity, star formation and supernova feedback. We resolve the structure
of the interstellar medium at sub-parsec resolution while also capturing the
interaction between the CMZ and the bar-driven large-scale flow out to R\sim
5\kpc. Our main findings are as follows: (1) The distinction between inner
(~pc) and outer (~pc) CMZ that is
sometimes proposed in the literature is unnecessary. Instead, the CMZ is best
described as single structure, namely a star-forming ring with outer radius
~pc which includes the 1.3 complex and which is directly
interacting with the dust lanes that mediate the bar-driven inflow. (2) This
accretion can induce a significant tilt of the CMZ out of the plane. A tilted
CMZ might provide an alternative explanation to the -shaped structure
identified in Herschel data by Molinari et al. 2011. (3) The bar in our
simulation efficiently drives an inflow from the Galactic disc (~kpc) down to the CMZ (~pc) of the order of
, consistent with observational determinations. (4)
Supernova feedback can drive an inflow from the CMZ inwards towards the
circumnuclear disc of the order of . (5) We
give a new interpretation for the 3D placement of the 20 and 50 km s
clouds, according to which they are close (~pc) to the Galactic
centre, but are also connected to the larger-scale streams at ~pc.Comment: Accepted for publication in MNRAS. Movies of the simulations can be
found at: https://www.youtube.com/channel/UCwnzfO-xLxzRDz9XsexfPo
Short screening tools for risky drinking in Aboriginal and Torres Strait Islander Australians : Modified AUDIT-C and a new approach
Background
Alcohol consumption among Indigenous Australians can involve a stop-start pattern of drinking, with consumption well above recommended guidelines on each occasion. Such intermittent drinking patterns can make screening for risky drinking difficult. This study evaluates the ability of several short alcohol screening tools, contained in the Grog Survey Application, to detect short- or long-term risky drinking as defined by Australian guidelines. Tested tools include a modification of Alcohol Use Disorders Identification Test-Consumption (AUDIT-Cm).
Methods
Alcohol consumption was assessed in current drinkers in the past year (n = 184) using AUDIT-Cm and using the last four drinking occasions (Finnish method). Sensitivity and specificity were assessed relative to the Finnish method, for how AUDIT-Cm score (3 + for women, 4 + for men), and how subsets of AUDIT-Cm questions (AUDIT-1m and AUDIT-2m; and AUDIT-3mV alone) were able to determine short- or long-term risk from drinking. Responses to AUDIT-Cm were used to calculate the average standard drinks consumed per day, and the frequency at which more than four standard drinks were consumed on single occasions. Finally, shorter versions of the Finnish method (1, 2, or 3 occasions of drinking) were compared to the full Finnish method, by examining the percentage of variance retained by shorter versions.
Results
AUDIT-Cm has a high sensitivity in detecting at-risk drinking compared with the Finnish method (sensitivity = 99%, specificity = 67%). The combination of AUDIT-1m and AUDIT-2m was able to classify the drinking risk status for all but four individuals in the same way as the Finnish method did. For the Finnish method, two drinking sessions to calculate drinks per drinking occasion, and four to calculate frequency resulted in nearly identical estimates to data on all four of the most recent drinking occasions (r2 = 0.997).
Conclusions
The combination of AUDIT-1m and AUDIT-2m may offer advantages as a short screening tool, over AUDIT-3mV, in groups where intermittent and high per occasion drinking is common. As an alternative to the full Finnish method, the quantity consumed on the last two occasions and timing of the last four occasions may provide a practical short screening tool
Acceptability and feasibility of a computer-based application to help Aboriginal and Torres Strait Islander Australians describe their alcohol consumption
We examined acceptability and feasibility of a tablet application (“App”) to record self-reported alcohol consumption among Aboriginal and Torres Strait Islander Australians. Four communities (1 urban; 3 regional/remote) tested the App, with 246 adult participants (132 males, 114 females). The App collected (a) completion time; (b) participant feedback; (c) staff observations. Three research assistants were interviewed. Only six (1.4%) participants reported that the App was “hard” to use. Participants appeared to be engaged and to require minimal assistance; nearly half verbally reflected on their drinking or drinking of others. The App has potential for surveys, screening, or health promotion
WFPC2 Observations of Compact Star Cluster Nuclei in Low Luminosity Spiral Galaxies
We have used the Wide Field Planetary Camera 2 aboard the Hubble Space
Telescope to image the compact star cluster nuclei of the nearby, late-type,
low-luminosity spiral galaxies NGC 4395, NGC 4242, and ESO 359-029. We also
analyze archival WFPC2 observations of the compact star cluster nucleus of M33.
A comparative analysis of the structural and photometric properties of these
four nuclei is presented. All of the nuclei are very compact, with luminosity
densities increasing at small radii to the resolution limit of our data. NGC
4395 contains a Seyfert 1 nucleus with a distinct bipolar structure and bright
associated filaments which are likely due to [OIII] emission. The M33 nucleus
has a complex structure, with elongated isophotes and possible signatures of
weak activity, including a jet-like component. The other two nuclei are not
known to be active, but share similar physical size scales and luminosities to
the M33 and NGC 4395 nuclei. The circumnuclear environments of all four of our
program galaxies are extremely diffuse, have only low-to-moderate star
formation, and appear to be devoid of large quantities of dust. The central
gravitational potentials of the galaxies are also quite shallow, making the
origin of these types of `naked' nuclei problematic.Comment: to appear in the July 1999 Astronomical Journal; 38 pages (Latex), 5
tables (postscript), 21 figures (gif); postscript versions of the figures may
be obtained via anonymous ftp at
ftp://ftp.cv.nrao.edu/NRAO-staff/lmatthew/lanl-nucle
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