527 research outputs found
Recent high-magnetic-field studies of unusual groundstates in quasi-two-dimensional crystalline organic metals and superconductors
After a brief introduction to crystalline organic superconductors and metals,
we shall describe two recently-observed exotic phases that occur only in high
magnetic fields. The first involves measurements of the non-linear electrical
resistance of single crystals of the charge-density-wave (CDW) system
(Per)Au(mnt) in static magnetic fields of up to 45 T and temperatures
as low as 25 mK. The presence of a fully gapped CDW state with typical CDW
electrodynamics at fields higher that the Pauli paramagnetic limit of 34 T
suggests the existence of a modulated CDW phase analogous to the
Fulde-Ferrell-Larkin-Ovchinnikov state. Secondly, measurements of the Hall
potential of single crystals of -(BEDT-TTF)KHg(SCN), made using
a variant of the Corbino geometry in quasistatic magnetic fields, show
persistent current effects that are similar to those observed in conventional
superconductors. The longevity of the currents, large Hall angle, flux
quantization and confinement of the reactive component of the Hall potential to
the edge of the sample are all consistent with the realization of a new state
of matter in CDW systems with significant orbital quantization effects in
strong magnetic fields.Comment: SNS 2004 Conference presentatio
Experimental considerations of acute heat stress assays to quantify coral thermal tolerance
Understanding the distribution and abundance of heat tolerant corals across seascapes is imperative for predicting responses to climate change and to support novel management actions. Thermal tolerance is variable in corals and intrinsic and extrinsic drivers of tolerance are not well understood. Traditional experimental evaluations of coral heat and bleaching tolerance typically involve ramp-and-hold experiments run across days to weeks within aquarium facilities with limits to colony replication. Field-based acute heat stress assays have emerged as an alternative experimental approach to rapidly quantify heat tolerance in many samples yet the role of key methodological considerations on the stress response measured remains unresolved. Here, we quantify the effects of coral fragment size, sampling time point, and physiological measures on the acute heat stress response in adult corals. The effect of fragment size differed between species (Acropora tenuis and Pocillopora damicornis). Most physiological parameters measured here declined over time (tissue colour, chlorophyll-a and protein content) from the onset of heating, with the exception of maximum photosynthetic efficiency (Fv/Fm) which was surprisingly stable over this time scale. Based on our experiments, we identified photosynthetic efficiency, tissue colour change, and host-specific assays such as catalase activity as key physiological measures for rapid quantification of thermal tolerance. We recommend that future applications of acute heat stress assays include larger fragments (> 9 cm2) where possible and sample between 10 and 24 h after the end of heat stress. A validated high-throughput experimental approach combined with cost-effective genomic and physiological measurements underpins the development of markers and maps of heat tolerance across seascapes and ocean warming scenarios
The Impact of New EUV Diagnostics on CME-Related Kinematics
We present the application of novel diagnostics to the spectroscopic
observation of a Coronal Mass Ejection (CME) on disk by the Extreme Ultraviolet
Imaging Spectrometer (EIS) on the Hinode spacecraft. We apply a recently
developed line profile asymmetry analysis to the spectroscopic observation of
NOAA AR 10930 on 14-15 December 2006 to three raster observations before and
during the eruption of a 1000km/s CME. We see the impact that the observer's
line-of-sight and magnetic field geometry have on the diagnostics used.
Further, and more importantly, we identify the on-disk signature of a
high-speed outflow behind the CME in the dimming region arising as a result of
the eruption. Supported by recent coronal observations of the STEREO
spacecraft, we speculate about the momentum flux resulting from this outflow as
a secondary momentum source to the CME. The results presented highlight the
importance of spectroscopic measurements in relation to CME kinematics, and the
need for full-disk synoptic spectroscopic observations of the coronal and
chromospheric plasmas to capture the signature of such explosive energy release
as a way of providing better constraints of CME propagation times to L1, or any
other point of interest in the heliosphere.Comment: Accepted to appear in Solar Physics Topical Issue titled "Remote
Sensing of the Inner Heliosphere". Manuscript has 14 pages, 5 color figures.
Movies supporting the figures can be found in
http://download.hao.ucar.edu/pub/mscott/papers/Weathe
Natural and anthropogenic lead in sediments of the Rotorua lakes, New Zealand
Global atmospheric sources of lead have increased more than 100-fold over the past century as a result of deforestation, coal combustion, ore smelting and leaded petroleum. Lead compounds generally accumulate in depositional areas across the globe where, due to low solubility and relative freedom from microbial degradation, the history of their inputs is preserved. In lakes there is rapid deposition and often little bioturbation of lead, resulting in an excellent depositional history of changes in both natural and anthropogenic sources. The objective of this study was to use sediments from a regionally bounded set of lakes to provide an indication of the rates of environmental inputs of lead whilst taking into account differences of trophic state and lead exposure between lakes. Intact sediment gravity cores were collected from 13 Rotorua lakes in North Island of New Zealand between March 2006 and January 2007. Cores penetrated sediments to a depth of 16–30 cm and contained volcanic tephra from the 1886 AD Tarawera eruption. The upper depth of the Tarawera tephra enabled prescription of a date for the associated depth in the core (120 years). Each core showed a sub-surface peak in lead concentration above the Tarawera tephra which was contemporaneous with the peak use of lead alkyl as a petroleum additive in New Zealand. An 8 m piston core was taken in the largest of the lakes, Lake Rotorua, in March 2007. The lake is antipodal to the pre-industrial sources of atmospheric lead but still shows increasing lead concentrations from <2 up to 3.5 μg g−1 between the Whakatane eruption (5530 ± 60 cal. yr BP) and the Tarawera eruption. Peaks in lead concentration in Lake Rotorua are associated with volcanic tephras, but are small compared with those arising from recent anthropogenic-derived lead deposition. Our results show that diagenetic processes associated with iron, manganese and sulfate oxidation-reduction, and sulfide precipitation, act to smooth distributions of lead from anthropogenic sources in the lake sediments. The extent of this smoothing can be related to changes in sulfate availability and reduction in sulfide driven by differences in trophic status amongst the lakes. Greatest lead mobilisation occurs in mesotrophic lakes during seasonal anoxia as iron and manganese are released to the porewater, allowing upward migration of lead towards the sediment–water interface. This lead mobilisation can only occur if sulfides are not present. The sub-surface peak in lead concentrations in lake sediments ascribed to lead alkyl in petroleum persists despite the diagenetic processes acting to disperse lead within the sediments and into the overlying water
Probing the Role of Magnetic-Field Variations in NOAA AR 8038 in Producing Solar Flare and CME on 12 May 1997
We carried out a multi-wavelength study of a CME and a medium-size 1B/C1.3
flare occurring on 12 May 1997. We present the investigation of magnetic-field
variations in the NOAA Active Region 8038 which was observed on the Sun during
7--16 May 1997. Analyses of H{\alpha} filtergrams and MDI/SOHO magnetograms
revealed continual but discrete surge activity, and emergence and cancellation
of flux in this active region. The movie of these magnetograms revealed two
important results that the major opposite polarities of pre-existing region as
well as in the emerging flux region (EFR) were approaching towards each other
and moving magnetic features (MMF) were ejecting out from the major north
polarity at a quasi-periodicity of about ten hrs during 10--13 May 1997. These
activities were probably caused by the magnetic reconnection in the lower
atmosphere driven by photospheric convergence motions, which were evident in
magnetograms. The magnetic field variations such as flux, gradient, and sunspot
rotation revealed that free energy was slowly being stored in the corona. The
slow low-layer magnetic reconnection may be responsible for this storage and
the formation of a sigmoidal core field or a flux rope leading to the eventual
eruption. The occurrence of EUV brightenings in the sigmoidal core field prior
to the rise of a flux rope suggests that the eruption was triggered by the
inner tether-cutting reconnection, but not the external breakout reconnection.
An impulsive acceleration revealed from fast separation of the H{\alpha}
ribbons of the first 150 seconds suggests the CME accelerated in the inner
corona, which is consistent with the temporal profile of the reconnection
electric field. In conclusion, we propose a qualitative model in view of
framework of a solar eruption involving, mass ejections, filament eruption,
CME, and subsequent flare.Comment: 8 figures, accepted for publication in Solar Physic
Observations of Coronal Mass Ejections with the Coronal Multichannel Polarimeter
The Coronal Multichannel Polarimeter (CoMP) measures not only the
polarization of coronal emission, but also the full radiance profiles of
coronal emission lines. For the first time, CoMP observations provide
high-cadence image sequences of the coronal line intensity, Doppler shift and
line width simultaneously in a large field of view. By studying the Doppler
shift and line width we may explore more of the physical processes of CME
initiation and propagation. Here we identify a list of CMEs observed by CoMP
and present the first results of these observations. Our preliminary analysis
shows that CMEs are usually associated with greatly increased Doppler shift and
enhanced line width. These new observations provide not only valuable
information to constrain CME models and probe various processes during the
initial propagation of CMEs in the low corona, but also offer a possible
cost-effective and low-risk means of space weather monitoring.Comment: 6 figures. Will appear in the special issue of Coronal Magnetism,
Sol. Phy
Signatures of the slow solar wind streams from active regions in the inner corona
Some of local sources of the slow solar wind can be associated with
spectroscopically detected plasma outflows at edges of active regions
accompanied with specific signatures in the inner corona. The EUV telescopes
(e.g. SPIRIT/CORONAS-F, TESIS/CORONAS-Photon and SWAP/PROBA2) sometimes
observed extended ray-like structures seen at the limb above active regions in
1MK iron emission lines and described as "coronal rays". To verify the
relationship between coronal rays and plasma outflows, we analyze an isolated
active region (AR) adjacent to small coronal hole (CH) observed by different
EUV instruments in the end of July - beginning of August 2009. On August 1 EIS
revealed in the AR two compact outflows with the Doppler velocities V =10-30
km/s accompanied with fan loops diverging from their regions. At the limb the
ARCH interface region produced coronal rays observed by EUVI/STEREO-A on July
31 as well as by TESIS on August 7. The rays were co-aligned with open magnetic
field lines expanded to the streamer stalks. Using the DEM analysis, it was
found that the fan loops diverged from the outflow regions had the dominant
temperature of ~1 MK, which is similar to that of the outgoing plasma streams.
Parameters of the solar wind measured by STEREO-B, ACE, WIND, STEREO-A were
conformed with identification of the ARCH as a source region at the
Wang-Sheeley-Arge map of derived coronal holes for CR 2086. The results of the
study support the suggestion that coronal rays can represent signatures of
outflows from ARs propagating in the inner corona along open field lines into
the heliosphere.Comment: Accepted for publication in Solar Physics; 31 Pages; 13 Figure
Coronal Dimmings and the Early Phase of a CME Observed with STEREO and Hinode/EIS
We investigate the early phase of the 13 February 2009 coronal mass ejection
(CME). Observations with the twin STEREO spacecraft in quadrature allow us to
compare for the first time in one and the same event the temporal evolution of
coronal EUV dimmings, observed simultaneously on-disk and above the limb. We
find that these dimmings are synchronized and appear during the impulsive
acceleration phase of the CME, with the highest EUV intensity drop occurring a
few minutes after the maximum CME acceleration. During the propagation phase
two confined, bipolar dimming regions, appearing near the footpoints of a
pre-flare sigmoid structure, show an apparent migration away from the site of
the CME-associated flare. Additionally, they rotate around the 'center' of the
flare site, i.e., the configuration of the dimmings exhibits the same
'sheared-to-potential' evolution as the postflare loops. We conclude that the
motion pattern of the twin dimmings reflects not only the eruption of the flux
rope, but also the ensuing stretching of the overlying arcade. Finally, we find
that: (1) the global-scale dimmings, expanding from the source region of the
eruption, propagate with a speed similar to that of the leaving CME front; (2)
the mass loss occurs mainly during the period of strongest CME acceleration.
Two hours after the eruption Hinode/EIS observations show no substantial plasma
outflow, originating from the 'open' field twin dimming regions.Comment: accepted for publication in Solar Physic
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