Observations of meteor-head echoes using the Jicamarca 50 MHz radar in interferometer mode

International audienceWe present results of recent observations of meteor-head echoes obtained with the high-power large-aperture Jicamarca 50 MHz radar (11.95° S, 76.87° W) in an interferometric mode. The large power-aperture of the system allows us to record more than 3000 meteors per hour in the small volume subtended by the 1° antenna beam, albeit when the cluttering equatorial electrojet (EEJ) echoes are not present or are very weak. The interferometry arrangement allows the determination of the radiant (trajectory) and speed of each meteor. It is found that the radiant distribution of all detected meteors is concentrated in relative small angles centered around the Earth's Apex as it transients over the Jicamarca sky, i.e. around the corresponding Earth heading for the particular observational day and time, for all seasons observed so far. The dispersion around the Apex is ~18° in a direction transverse to the Ecliptic plane and only 8.5° in heliocentric longitude in the Ecliptic plane both in the Earth inertial frame of reference. No appreciable interannual variability has been observed. Moreover, no population related to the optical (larger meteors) Leonid showers of 1998?2002 is found, in agreement with other large power-aperture radar observations. A novel cross-correlation detection technique (adaptive match-filtering) is used in combination with a 13 baud Barker phase-code. The technique allows us to get good range resolution (0.75 km) without any sensitivity deterioration for the same average power, compared to the non-coded long pulse scheme used at other radars. The matching Doppler shift provides an estimation of the velocity within a pulse with the same accuracy as if a non-coded pulse of the same length had been used. The velocity distribution of the meteors is centered around 60 km s?1 corresponding to velocities slightly under the solar escape velocity (72 km s?1). Less than 8% of the velocities correspond to interstellar speeds. Higher relative velocity accuracy is obtained by cross-correlating the echoes from pulse-to-pulse, albeit with an ambiguous velocity displacement which cannot be resolved with the current observing technique. This higher relative accuracy allows the precise measurement of the deceleration of the meteors as they enter the atmosphere. In addition, an independent radial velocity is determined from the derivative of the instantaneous position. Other statistical distributions of interest are also presented

Statistical characteristics of low-latitude ionospheric field-aligned irregularities obtained with the Piura VHF radar

International audienceWe present a summary of the statistical characteristics of echoes from ionospheric (E- and F-region) field-aligned irregularities obtained with the Piura VHF radar. This radar is located at ~ 7.0° dip latitude, just outside the equatorial electrojet (EEJ) region. Our results are based on (1) intermittent observations made between 1991 and 1999 just few days a year, and (2) continuous observations made between January 2000 and June 2001. During most of the intermittent observations, simultaneous measurements of EEJ and equatorial spread F (ESF) irregularities were performed with the Jicamarca VHF radar. From the continuous measurements, we have obtained the diurnal and seasonal characteristics of a variety of parameters (percentage of occurrence, signal-to-noise ratio and/or Doppler velocities) from the lower and upper E-region irregularities and also from F-region irregularities over Piura. For example, we have found that (1) the E-region echoes are stronger and occur more frequently during local summer (i.e. between December and March); (2) between May and June, the E-region echoes are weaker and occur less frequently; moreover, during these months, a semidiurnal wave with large amplitudes is observed in the meridional wind (> 100 ms- 1); (3) there is vertical wavelength of about 20 km in the Doppler velocity, particularly after midnight; (4) the lower (upper) E-region Doppler velocities are influenced mainly by meridional winds (equatorial F-region vertical drifts). In addition, we have observed that the seasonal and daily occurrences of Piura F-region irregularities are similar to the occurrence of topside ESF irregularities over Jicamarca. The likelihood of occurrence of F-region irregularities over Piura and, therefore, topside ESF over Jicamarca is greater when there are no E-region irregularities over Piura. On the other hand, there is more probability of observing bottomtype/bottomside ESF irregularities over Jicamarca when E-region irregularities are observed over Piura

Naturally enhanced ion-line spectra around the equatorial 150-km region

For many years strong radar echoes coming from 140–170 km altitudes at low latitudes have been associated to the existence of field-aligned irregularities (FAIs) (the so called 150-km echoes). In this work, we present frequency spectra as well as angular distribution of 150-km echoes. When the 150-km region is observed with beams perpendicular to the magnetic field (<B>B</B>) the observed radar spectra are very narrow with spectral widths between 3–12 m/s. On the other hand, when few-degrees off-perpendicular beams are used, the radar spectra are wide with spectral widths comparable to those expected from ion-acoustic waves at these altitudes (>1000 m/s). Moreover the off-perpendicular spectral width increases with increasing altitude. The strength of the received echoes is one to two orders of magnitude stronger than the expected level of waves in thermal equilibrium at these altitudes. Such enhancement is not due to an increase in electron density. Except for the enhancement in power, the spectra characteristics of off-perpendicular and perpendicular echoes are in reasonable agreement with expected incoherent scatter spectra at these angles and altitudes. 150-km echoes are usually observed in narrow layers (2 to 5). Bistatic common volume observations as well as observations made few kilometers apart show that, for most of the layers, there is very high correlation on power fluctuations without a noticeable time separation between simultaneous echoes observed with Off-perpendicular and Perpendicular beams. However, in one of the central layers, the echoes are the strongest in the perpendicular beam and absent or very weak in the off-perpendicular beams, suggesting that they are generated by a plasma instability. Our results indicate that most echoes around 150-km region are not as aspect sensitive as originally thought, and they come from waves that have been enhanced above waves in thermal equilibrium

Influence of Aromatic Structure on the Thermal Behaviour of Lignin

Lignin, a natural biopolymer and abundant by-product, is a particularly promising feedstock for carbon-based materials and a potentially sustainable alternative to phenolic resins, which are typically derived from crude oil. The source and method used to isolate lignin have a large impact on the thermal properties of the polymer, and can affect resultant materials prepared from lignin. Previous investigations into lignin characterisation often utilise a variety of feedstocks and isolation methods, which can make robust comparisons challenging. We present a systematic investigation into the chemical composition of lignins extracted using an identical Organosolv isolation method but from different biomass feedstocks: hemp hurds, eucalyptus chips, flax straw, rice husk and pine. We show how the aromatic structure of lignin can affect the thermal behaviour of the polymer, which correlates to the structure of resulting carbons. Carbons from lignins with a high syringyl unit content display a pronounced foaming behaviour which, on activation, results in a high-surface area material with hierarchical porosity

Human papillomavirus infection and risk of progression of epithelial abnormalities of the cervix.

The polymerase chain reaction has been used to determine the presence of human papillomavirus (HPV) 16 and HPV 18 DNA sequences in archival histological material removed from a cohort of untreated women with cervical epithelial abnormalities. The detection of HPV 16 or HPV 18 DNA sequences in the initial biopsy specimen was associated with a significantly increased risk of subsequent disease progression

Population Genetics of Increased Hybrid Performance between Two Maize Populations under Reciprocal Recurrent Selection

Heterosis, the superiority in one or more characteristics of crossbred organisms relative to their inbred parents, is the basis of the modern cultivars utilized in maize (Zed mays L.). Heterosis is of interest in nondomesticated species due to its relevance to the question how much polymorphism is maintained in natural populations due to selection? (Berger, 1976). For maize and certain other domesticated species that employ inbred lines to produce commercial hybrids, knowledge of the mechanisms of gene action producing heterosis could contribute to advances in breeding techniques

Towards quality control in cancer chemotherapy.

A survey of all hospital pharmacies in the former North Western Regional Health Authority has revealed that hospital personnel continue to prepare cytotoxic drugs in suboptimal conditions, despite the widespread introduction of pharmacy cytotoxic reconstitution services. Other concerns include the lack of formal training for medical staff in the administration of these agents and the frequent absence of written procedures for dealing with extravasation and chemotherapy errors

The significance of heat transport by shallow fluid flow at an active plate boundary: the Southern Alps, New Zealand

Fluid flow can influence fault behavior. Here we quantify the role of groundwater heat advection in establishing the thermal structure of the Alpine Fault, a major tectonic boundary in southern New Zealand that accommodates most of the motion between the Australian and Pacific Plates. Convergence on the Alpine Fault has rapidly uplifted the Southern Alps, resulting in high geothermal gradients and a thin seismogenic zone. A new equilibrium temperature profile from the 818-m-deep Deep Fault Drilling Project 2B borehole has been interrogated using one-dimensional analytical models of fluid and rock advection. Models indicate a total heat flux of 720-mW m2 results from groundwater flow with Darcy velocities approximating to 7.8 × 1010 m s1. Groundwaters advect significantly more heat than rock advection in the shallow orogen (<6-km depth) and are the major control on the subsurface temperature field

Characterization of envelope function of transmitted viruses circulating in Mbeya, Tanzania, and its impact on disease progression

An understanding of the biological characteristics of transmitted viruses provides important insights into HIV pathogenesis and informs vaccine development. The aim of the study was to characterize env function of transmitted viruses and its role in disease progression