2,206 research outputs found
Fast Time Structure During Transient Microwave Brightenings: Evidence for Nonthermal Processes
Transient microwave brightenings (TMBs) are small-scale energy releases from
the periphery of sunspot umbrae, with a flux density two orders of magnitude
smaller than that from a typical flare. Gopalswamy et al (1994) first reported
the detection of the TMBs and it was pointed out that the radio emission
implied a region of very high magnetic field so that the emission mechanism has
to be gyroresonance or nonthermal gyrosynchrotron, but not free-free emission.
It was not possible to decide between gyroresonance and gyrosynchrotron
processes because of the low time resolution (30 s) used in the data analysis.
We have since performed a detailed analysis of the Very Large Array data with
full time resolution (3.3 s) at two wavelengths (2 and 3.6 cm) and we can now
adequately address the question of the emission mechanism of the TMBs. We find
that nonthermal processes indeed take place during the TMBs. We present
evidence for nonthermal emission in the form of temporal and spatial structure
of the TMBs. The fast time structure cannot be explained by a thermodynamic
cooling time and therefore requires a nonthermal process. Using the physical
parameters obtained from X-ray and radio observations, we determine the
magnetic field parameters of the loop and estimate the energy released during
the TMBs. The impulsive components of TMBs imply an energy release rate of 1.3
x 10^22 erg/s so that the thermal energy content of the TMBs could be less than
10^24 erg.Comment: 15 pages (Latex), 4 figures (eps). ApJ Letters in press (1997
The energetics of the gradual phase
Reseachers compare results with those in the chapter by Moore et al. (1980), who reached five main conclusions about the gradual phase: (1) the typical density of the soft X-ray emitting plasma is between 10 to the 11th power and 10 to the 12th power cm-3 for compact flares and between 10 to the 10th power and 10 to the 11th power cm-3 for a large-area flare; (2) cooling is by conduction and radiation in roughly equal proportions; (3) continual heating is needed in the decay phase of two-ribbon flares; (4) continual heating is probably not needed in compact events; (5) most of the soft-X-ray-emitting plasma results from chromospheric evaporation. The goal was to reexamine these problems with the data from the Solar Maximum Mission (SMM) and other supporting instruments as well as to take advantage of recent theoretical advances. SMM is capable of measuring coronal temperatures more accurately and with a better cadence than has been possible before. The SMM data set is also unique in that the complete transit of an active region was observed, with soft X-ray and UV images being taken every few minutes. Researcher's were therefore able to establish the pre-flare conditions of the region and see whether anything has changed as a result of the flare. The assumptions made in attempting to determine the required plasma parameters are described. The derived parameters for the five prime flares are presented, and the role of numerical simulations is discussed
Conservative treatment for hypervascularised placental polyp with secondary haemoperitoneum: A case report
Objective: We describe the first case to our knowledge of hypervascularised placental polyp (HPP) presenting with acute pelvic pain and hemoperitoneum. Case Report: A 33 years-old woman with a history of medical abortion three months earlier came to our attention complaining acute pelvic pain and vaginal bleeding. Transvaginal (TV) and transabdominal (TA) ultrasound (US) demonstrated a highly vascular intrauterine lesion and intra-abdominal free fluid consistent with a diagnosis of haemoperitoneum. Emergency laparoscopy yielded no intra-abdominal bleeding and was followed by bilateral selective embolization of the uterine arteries due to persistent vaginal bleeding. Hysteroscopy and pathology findings were consistent with a final diagnosis of HPP. Conclusion: HPP may occur months or years after pregnancy or abortion and the clinical picture of abnormal vaginal bleeding associated with acute abdominal pain and haemoperitoneum should warrant to consider HPP among the differential diagnosis. Clinical and imaging findings need to be considered when planning the conservative management of HPP. Our experience suggests that uterine artery embolization is a safe and effective for the conservative treatment of highly vascularized HPP. (www. actabiomedica.it)
Instability of two interacting, quasi-monochromatic waves in shallow water
We study the nonlinear interactions of waves with a doubled-peaked power
spectrum in shallow water. The starting point is the prototypical equation for
nonlinear uni-directional waves in shallow water, i.e. the Korteweg de Vries
equation. Using a multiple-scale technique two defocusing coupled Nonlinear
Schr\"odinger equations are derived. We show analytically that plane wave
solutions of such a system can be unstable to small perturbations. This
surprising result suggests the existence of a new energy exchange mechanism
which could influence the behaviour of ocean waves in shallow water.Comment: 4 pages, 2 figure
Close similarities between Cherry chlorotic rusty spot disease from Italy and Cherry leaf scorch from Spain
Cherry chlorotic rusty spot (CCRS), a disease affecting sweet and sour cherry in Southern Italy was regularly found associated with an unidentified fungus and with a complex pattern of viral-like double-stranded RNAs as well as with two small circular RNAs (cherry small circular RNAs, cscRNAs). Further studies revealed that i) the ds-RNAs correspond to the genome of different mycoviruses belonging to the genera Chrysovirus, Partitivirus and Totivirus and ii) the two viroid-like RNAs consist of two groups of variants with similar sequences but differing in size (394–415 and 372–377 nt for cscRNA1 and cscRNA2, respectively). Here we report that the dsRNAs of Chrysovirus and Partitivirus have been detected by RT-PCR analysis with CCRS specific primers in nucleic acid preparations from cherry leaves affected by cherry leaf scorch (CLS) in Spain, a disease whose etiological agent is the ascomycetes Apiognomonia erythrostoma, order Diaporthales. Moreover, Northern-blot hybridization assays showed that a viroid-like RNA comigrating and sharing high sequence similarity with the cscRNA1 previously reported in Italy, accumulate in leaves from CLS affected trees in Spain. These data, together with other evidence showing similar symptoms, disease cycle and fungal fructifications in CCRS and CLS affected trees, suggest a close relationship between the two cherry disorders.Keywords: dsRNAs, cscRNAs, Apiognomonia erythrostoma, Diaporthale
Freak Waves in Random Oceanic Sea States
Freak waves are very large, rare events in a random ocean wave train. Here we
study the numerical generation of freak waves in a random sea state
characterized by the JONSWAP power spectrum. We assume, to cubic order in
nonlinearity, that the wave dynamics are governed by the nonlinear Schroedinger
(NLS) equation. We identify two parameters in the power spectrum that control
the nonlinear dynamics: the Phillips parameter and the enhancement
coefficient . We discuss how freak waves in a random sea state are more
likely to occur for large values of and . Our results are
supported by extensive numerical simulations of the NLS equation with random
initial conditions. Comparison with linear simulations are also reported.Comment: 7 pages, 6 figures, to be published in Phys. Rev. Let
On the statistical mechanics of prion diseases
We simulate a two-dimensional, lattice based, protein-level statistical
mechanical model for prion diseases (e.g., Mad Cow disease) with concommitant
prion protein misfolding and aggregation. Our simulations lead us to the
hypothesis that the observed broad incubation time distribution in
epidemiological data reflect fluctuation dominated growth seeded by a few
nanometer scale aggregates, while much narrower incubation time distributions
for innoculated lab animals arise from statistical self averaging. We model
`species barriers' to prion infection and assess a related treatment protocol.Comment: 5 Pages, 3 eps figures (submitted to Physical Review Letters
Validation of statistical clustering on TES dataset using synthetic Martian spectra
In this work we present some results concerning the analysis of Thermal Emission Spectrometer (TES) data, looking at the methane Q-branch spectral signature at 1304 cm-1. Such analysis has been enabled by producing some synthetic spectral datasets, simulating the atmospheric and surface variability observed on Mars, excluding the high latitude regions. The use of synthetic spectra is aimed to provide a better comprehension of the influence that the atmospheric state vector and its composition have on the spectral behavior. This effort is important, because the TES data are characterized by a low resolution (10 cm-1) and a significant random and systematic noise which could, in principle, give results whose quality needs to be improved. We apply statistical clustering of the synthetic spectra to evaluate the effectiveness of detecting methane, and estimating its abundance
Generic Mechanism of Emergence of Amyloid Protofilaments from Disordered Oligomeric aggregates
The presence of oligomeric aggregates, which is often observed during the
process of amyloid formation, has recently attracted much attention since it
has been associated with neurodegenerative conditions such as Alzheimer's and
Parkinson's diseases. We provide a description of a sequence-indepedent
mechanism by which polypeptide chains aggregate by forming metastable
oligomeric intermediate states prior to converting into fibrillar structures.
Our results illustrate how the formation of ordered arrays of hydrogen bonds
drives the formation of beta-sheets within the disordered oligomeric aggregates
that form early under the effect of hydrophobic forces. Initially individual
beta-sheets form with random orientations, which subsequently tend to align
into protofilaments as their lengths increases. Our results suggest that
amyloid aggregation represents an example of the Ostwald step rule of first
order phase transitions by showing that ordered cross-beta structures emerge
preferentially from disordered compact dynamical intermediate assemblies.Comment: 14 pages, 4 figure
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