43 research outputs found
Excitation of standing kink oscillations in coronal loops
In this work we review the efforts that have been done to study the
excitation of the standing fast kink body mode in coronal loops. We mainly
focus on the time-dependent problem, which is appropriate to describe flare or
CME induced kink oscillations. The analytical and numerical studies in slab and
cylindrical loop geometries are reviewed. We discuss the results from very
simple one-dimensional models to more realistic (but still simple) loop
configurations. We emphasise how the results of the initial value problem
complement the eigenmode calculations. The possible damping mechanisms of the
kink oscillations are also discussed
Recent Advances in Understanding Particle Acceleration Processes in Solar Flares
We review basic theoretical concepts in particle acceleration, with
particular emphasis on processes likely to occur in regions of magnetic
reconnection. Several new developments are discussed, including detailed
studies of reconnection in three-dimensional magnetic field configurations
(e.g., current sheets, collapsing traps, separatrix regions) and stochastic
acceleration in a turbulent environment. Fluid, test-particle, and
particle-in-cell approaches are used and results compared. While these studies
show considerable promise in accounting for the various observational
manifestations of solar flares, they are limited by a number of factors, mostly
relating to available computational power. Not the least of these issues is the
need to explicitly incorporate the electrodynamic feedback of the accelerated
particles themselves on the environment in which they are accelerated. A brief
prognosis for future advancement is offered.Comment: This is a chapter in a monograph on the physics of solar flares,
inspired by RHESSI observations. The individual articles are to appear in
Space Science Reviews (2011
Sedimentology, stratigraphic context, and implications of Miocene intrashelf bottomset deposits, offshore New Jersey
Drilling of intrashelf Miocene clinothems onshore and offshore New Jersey has provided better understanding of their topset and foreset deposits, but the sedimentology and stratigraphy of their bottomset deposits have not been documented in detail. Three coreholes (Sites M27âM29), collected during Integrated Ocean Drilling Program (IODP) Expedition 313, intersect multiple bottomset deposits, and their analysis helps to refine sequence stratigraphic interpretations and process response models for intrashelf clinothems. At Site M29, the most downdip location, chronostratigraphically well-constrained bottomset deposits follow a repeated stratigraphic motif. Coarse-grained glauconitic quartz sand packages abruptly overlie deeply burrowed surfaces. Typically, these packages coarsen then fine upwards and pass upward into bioturbated siltstones. These coarse sand beds are amalgamated and poorly sorted and contain thin-walled shells, benthic foraminifera, and extrabasinal clasts, consistent with an interpretation of debrites. The sedimentology and mounded seismic character of these packages support interpretation as debrite-dominated lobe complexes. Farther updip, at Site M28, the same chronostratigraphic units are amalgamated, with the absence of bioturbated silts pointing to more erosion in proximal locations. Graded sandstones and dune-scale cross-bedding in the younger sequences in Site M28 indicate deposition from turbidity currents and channelization. The sharp base of each package is interpreted as a sequence boundary, with a period of erosion and sediment bypass evidenced by the burrowed surface, and the coarse-grained debritic and turbiditic deposits representing the lowstand systems tract. The overlying fine-grained deposits are interpreted as the combined transgressive and highstand systems tract deposits and contain the deepwater equivalent of the maximum flooding surface. The variety in thickness and grain-size trends in the coarse-grained bottomset packages point to an autogenic control, through compensational stacking of lobes and lobe complexes. However, the large-scale stratigraphic organization of the bottomset deposits and the coarse-grained immature extrabasinal and reworked glauconitic detritus point to external controls, likely a combination of relative sea-level fall and waxing-and-waning cycles of sediment supply. This study demonstrates that large amounts of sediment gravity-flow deposits can be generated in relatively shallow (~100â200 m deep) and low-gradient (~1°â4°) clinothems that prograded across a deep continental shelf. This physiography likely led to the dominance of debris flow deposits due to the short transport distance limiting transformation to low-concentration turbidity currents
Theory and Applications of Non-Relativistic and Relativistic Turbulent Reconnection
Realistic astrophysical environments are turbulent due to the extremely high
Reynolds numbers. Therefore, the theories of reconnection intended for
describing astrophysical reconnection should not ignore the effects of
turbulence on magnetic reconnection. Turbulence is known to change the nature
of many physical processes dramatically and in this review we claim that
magnetic reconnection is not an exception. We stress that not only
astrophysical turbulence is ubiquitous, but also magnetic reconnection itself
induces turbulence. Thus turbulence must be accounted for in any realistic
astrophysical reconnection setup. We argue that due to the similarities of MHD
turbulence in relativistic and non-relativistic cases the theory of magnetic
reconnection developed for the non-relativistic case can be extended to the
relativistic case and we provide numerical simulations that support this
conjecture. We also provide quantitative comparisons of the theoretical
predictions and results of numerical experiments, including the situations when
turbulent reconnection is self-driven, i.e. the turbulence in the system is
generated by the reconnection process itself. We show how turbulent
reconnection entails the violation of magnetic flux freezing, the conclusion
that has really far reaching consequences for many realistically turbulent
astrophysical environments. In addition, we consider observational testing of
turbulent reconnection as well as numerous implications of the theory. The
former includes the Sun and solar wind reconnection, while the latter include
the process of reconnection diffusion induced by turbulent reconnection, the
acceleration of energetic particles, bursts of turbulent reconnection related
to black hole sources as well as gamma ray bursts. Finally, we explain why
turbulent reconnection cannot be explained by turbulent resistivity or derived
through the mean field approach.Comment: 66 pages, 24 figures, a chapter of the book "Magnetic Reconnection -
Concepts and Applications", editors W. Gonzalez, E. N. Parke
Effect of albumin and dextrose concentration on ultrasound and microbubble mediated gene transfection in vivo
Ultrasound and microbubble mediated gene transfection has great potential for site-selective, safe gene delivery. Albumin-based microbubbles have shown the greatest transfection efficiency but have not been optimised specifically for this purpose. Additionally, few studies have highlighted desirable properties for transfection specific microbubbles. In this article, microbubbles were made with 2% or 5% (w/v) albumin and 20% or 40% (w/v) dextrose solutions, yielding four distinct bubble types. These were acoustically characterised and their efficiency in transfecting a luciferase plasmid (pGL4.13) into female, CD1 mice myocardia was measured. For either albumin concentration, increasing the dextrose concentration increased scattering, attenuation and resistance to ultrasound, resulting in significantly increased transfection. A significant interaction was noted between albumin and dextrose; 2% albumin bubbles made with 20% dextrose showed the least transfection but the most transfection with 40% dextrose. This trend was seen for both nonlinear scattering and attenuation behaviour but not for resistance to ultrasound or total scatter. We have determined that the attenuation behaviour is an important microbubble characteristic for effective gene transfection using ultrasound. Microbubble behaviour can also be simply controlled by altering the initial ingredients used during manufacture
Understanding the relationship between schematic beliefs, bullying, and unusual experiences in 8â14 year olds
Background Cognitive models of adult psychosis propose that negative schematic beliefs (NSBs) mediate the established association between victimisation and psychotic symptoms. In childhood, unusual, or psychotic-like, experiences are associated with bullying (a common form of victimisation) and NSBs. This study tests the mediating role of NSBs in the relationship between bullying and distressing unusual experiences (UEDs) in childhood. Method Ninety-four 8â14 year olds referred to community Child and Adolescent Mental Health Services completed self-report assessments of UEDs, bullying, and NSBs about the self (NS) and others (NO). Results Both NS and NO were associated with bullying (NS: r=.40, P<.001; NO: r=.33, P=.002), and with UEDs (NS: r=.51, P<.001; NO: r=.43, P<.001). Both NS and NO significantly mediated the relationship between bullying and UEDs (NS: z=3.15, P=.002; NO: z=2.35, P=.019). Conclusions Children's NSBs may mediate the adverse psychological impact of victimisation, and are appropriate treatment targets for young people with UEDs. Early educational intervention to reduce negative appraisals of the self and others may increase resilience to future adverse experiences and reduce later mental health risk
Enhanced Gene Transfection in vivo using Magnetic Localisation of Ultrasound Contrast Agents: Preliminary Results
In previous work we demonstrated that microbubble mediated gene deliverycan be enhanced in vitro through simultaneous exposure of cells to ultrasoundand magnetic fields in the presence of magnetically loaded microbubbleultrasound contrast agents. The aim of this preliminary study was to investigatethe feasibility of the technique for in vivo applications. Phospholipid coatedmicrobubbles loaded with a hydrocarbon suspension of magnetic nanoparticles wereprepared through sonication and sized using optical microscopy (concentration1.4 108 bubbles/ml). Plasmid pGL4.13, which encodes for fireflyluciferase, was prepared at a concentration of 4 g/l in endotoxin-free water. ASiemens Acuson Sequioa clinical imaging system with a 26 mm linear arraytransducer (15L8) was used throughout the investigation. 20, 6-8 week old CD1female mice were injected with of 150 l of microbubble suspension and 50 lplasmid intra-venously through the tail vein. Mice were anaesthetized usingisoflurance and imaged with the transducer above the left lung (14 MHz, 0.06 MI)to locate the thoracic region. Immediately following injection, a NdFeBpermanent magnet was positioned over the right lung and the acoustic output wasincreased (H7MHz, 1.7 MI, focal depth 7.5 mm). Exposure to ultrasound and/ormagnetic field was maintained for two minutes. 20 mice were exposed toultrasound and magnetic field, two to ultrasound only and two to magnetic fieldonly. On the third day post treatment, luciferase substrate (D-luciferin) wasadministered through intra-peritoneal injection and allowed to catalyse thetransfected substrate for 10 minutes before animals were sacrificed and theirorgans recovered for individual bioluminescence imaging (IVIS 100, Xenogen) andquantification (Living Image Software, Xenogen). Animals treated with bothultrasound and the magnetic field showed transfection in the right lung, whileno animals showed transfection in the contralateral organs. Of the 20 micetreated, 17 showed transfection at a level greater than for ultrasound alone and12 greater than that of magnetic field alone. The results of this preliminarystudy indicate that microbubbles which include magnetic nanoparticles withintheir shells may be used to control the location of transfection in vivo.Further work is required to improve microbubble formulations and magnetic arraydesign to allow more accurate targeting of transfection. © 2010 IEEE
Evidence for Cretaceous-Paleogene boundary bolide "impact winter" conditions from New Jersey, USA
Abrupt and short-lived âimpact winterâ conditions have commonly been implicated as the main mechanism leading to the mass extinction at the Cretaceous-Paleogene (K-Pg) boundary (ca. 66 Ma), marking the end of the reign of the non-avian dinosaurs. However, so far only limited evidence has been available for such a climatic perturbation. Here we perform high-resolution TEX86 organic paleothermometry on three shallow cores from the New Jersey paleoshelf, (northeastern USA) to assess the impact-provoked climatic perturbations immediately following the K-Pg impact and to place these short-term events in the context of long-term climate evolution. We provide evidence of impact-provoked, severe climatic cooling immediately following the K-Pg impact. This so-called âimpact winterâ occurred superimposed on a long-term cooling trend that followed a warm phase in the latest Cretaceous