2,627 research outputs found
Comparison of body mass index of a national cohort of Maltese children over a 3-year interval
Aims: To compare body mass index (BMI) at 7 years and at 9 years of age in a national cohort of children in Malta, born in 2001, and to compare the results with an earlier study carried out in 2007 in this same cohort. Methods: BMI measurement of all children in the second year of formal school and again in the fourth year. Results: In 2008, data was collected from a total of 3435 children (girls 48.9%, boys 51.1%) with a mean age of 6.8 years. The same procedure was carried out in 2010 on the same cohort of children. A total of 3090 children participated in the second round of data collection (girls 49.5%, boys 50.5%). Based on WHO criteria (using the 2007 WHO Child Growth Reference BMI-for-age 5-19 charts), over a quarter of Maltese children aged 7 years were found to be overweight or obese in 2008. This proportion rose to just over 40% when the same cohort was measured in 2010 at the age of 9 years. A significant prevalence of overweight and obese boys was found in Gozo for both studies. Children attending Independent (fee-paying) schools were the least overweight and obese. Discussion: Obesity in childhood in Malta is increasing despite efforts to curb this disease. More emphasis must be made on prevention strategy in childhood as this is a key factor in reducing the burden of morbidity and mortality of childhood disease.peer-reviewe
Monitoring magnetosheath-magnetosphere interconnection topology from the aurora
International audienceA strong southward rotation of the IMF (BZ from 5 to -6 nT in ~ 20 s) on 4 January 1995 caused an abrupt reconfiguration of midday aurorae and plasma convection consisting of the following: (1) the red-line aurora associated with magnetosheath plasma transfer at the low-latitude magnetopause appeared at the same time that (2) the green-line aurora from precipitating energetic plasma sheet particles equatorward of the cusp (near the open-closed field line boundary) weakened visibly and shifted equatorward, (3) the high-latitude aurora during the previous northward IMF, which is associated with lobe reconnection, persisted briefly (3 min) and brightened, before it disappeared from the field-of-view, (4) the activation of a strong convection bay (DPY current) at cusp and sub-cusp latitudes when the field turned strongly south, (5) a distinct wave motion of the plasma sheet outer boundary, as inferred from the aurora, which correlates closely with Pc 5 magnetic pulsations. Our interpretation of the dramatic reconfiguration is that reconnection poleward of the cusp coexisted briefly with reconnection at sub-cusp latitudes. The latter provided a magnetic field connection which enabled, on the one hand, magnetosheath particles to enter and cause the red-line cusp aurora, and on the other hand, allowed for magnetospheric energetic particles to escape and weaken the outer plasma sheet source of the green-line emission. The coexistence of the two cusp auroras reflects the time required for one field line topology to replace another, which, under the prevailing high speed wind ( ~ 650 km/s), lasts ~ 3?4 min. The motion of open flux tubes propagating from equator to pole during this transition is traced in the aurora by a poleward moving form. The waves on the outer boundary of the plasma sheet are most likely due to the Kelvin-Helmholtz instability. The study illustrates the ability of local auroral observations to monitor even a global change in magnetospheric magnetic topology
Plasma flows, Birkeland currents and auroral forms in relation to the Svalgaard-Mansurov effect
The traditional explanation of the
polar cap magnetic deflections, referred to as the
Svalgaard-Mansurov effect, is in
terms of currents associated with
ionospheric flow resulting from
the release of magnetic tension on newly open magnetic field lines.
In this study, we aim at an updated description of the sources of
the Svalgaard-Mansurov effect based on recent
observations of configurations of plasma flow
channels, Birkeland current systems and aurorae
in the magnetosphere-ionosphere system.
Central to our description is the distinction between
two different flow channels (FC 1 and FC 2) corresponding to
two consecutive stages in the evolution of
open field lines in Dungey cell convection,
with FC 1 on newly open, and FC 2 on
old open, field lines. Flow channel FC 1 is the result of
ionospheric Pedersen current closure of
Birkeland currents flowing along newly open field lines.
During intervals of nonzero interplanetary magnetic field <I>B</I><sub>y</sub>
component FC 1 is observed on either side of noon
and it is accompanied by
poleward moving auroral forms
(PMAFs/prenoon and PMAFs/postnoon). In such cases
the next convection stage, in the form of flow channel FC 2 on the periphery
of the polar cap, is particularly important for
establishing an IMF <I>B</I><sub>y</sub>-related convection
asymmetry along the dawn-dusk meridian, which is a central
element causing the Svalgaard-Mansurov effect.
FC 2 flows are excited by the ionospheric Pedersen
current closure of the northernmost pair of Birkeland currents
in the four-sheet current system, which is coupled to the
tail magnetopause and flank low-latitude boundary layer.
This study is based on a review of
recent statistical and event studies of central parameters
relating to the magnetosphere-ionosphere current systems mentioned above.
Temporal-spatial structure in the current systems
is obtained by ground-satellite
conjunction studies. On this point
we emphasize the important information derived from
the continuous ground monitoring of
the dynamical behaviour of aurora and plasma convection
during intervals of well-organised solar wind plasma and
magnetic field conditions in interplanetary coronal mass ejections
(ICMEs) during their Earth passage
Plasma flow channels at the dawn/dusk polar cap boundaries: momentum transfer on old open field lines and the roles of IMF B-y and conductivity gradients
Using DMSP F13 data in conjunction with IMF data we investigate the newly discovered channels of enhanced (1.5–3 km/s) antisunward convection occurring at the dawn (06:00–09:00 MLT) or dusk (15:00–18:00 MLT) flanks of the polar cap for different combinations of IMF By polarity, hemisphere (NH/SH) and the dawn/dusk MLTs. Dawn-side cases where this flow channel appears occur for the following combinations: NH-dawn/By\u3e0 and SH-dawn/By\u3c0. The dusk-side cases are: NH-dusk/By\u3c0 and SH-dusk/By\u3e0. The flow channels are placed in the context of particle precipitation regimes/boundaries and ionospheric conductivity gradients. They are found to be threaded by old open field lines ( time since reconnection \u3e10 min) characterized by polar rain precipitation. In the dawn-side cases (NH-dawn/By\u3e0 and SH-dawn/By\u3c0) and in a Parker spiral field, the polar rain contains the solar wind strahl component. The convection enhancement is attributed to the Pedersen current closure of Birkeland current sheets (C1 and C2) in the polar cap (C1) and at the polar cap boundary (C2). The low ionospheric conductivity in the polar cap, particularly in the winter hemisphere, is compensated by an enhanced electric field driving the flow channel there. This is momentum transfer from the solar wind via dynamo action taking place in the combined current system of the high- and low-latitude boundary layers (HBL/LLBL). The conductivity gradient at the polar cap boundary contributes to establishing the convection channel and the associated enhancement of the dawn-dusk convection asymmetry extending beyond the dawn-dusk terminator during intervals of nonzero IMF By component. The HBL/LLBL-ionosphere coupling via Birkeland currents C1/C2 is a source of dawn-dusk convection asymmetry and Svalgaard-Mansurov effect which must be added to the effect of magnetic tension acting on newly open field lines
Aspects of magnetosphere–ionosphere coupling in sawtooth substorms: a case study
In a case study we report on
repetitive substorm activity during storm time which was excited during Earth
passage of an interplanetary coronal mass ejection (ICME) on 18 August 2003.
Applying a combination of magnetosphere and ground observations during a
favourable multi-spacecraft configuration in the plasma sheet (GOES-10 at
geostationary altitude) and in the tail lobes (Geotail and Cluster-1), we
monitor the temporal–spatial evolution of basic elements of the substorm
current system. Emphasis is placed on activations of the large-scale substorm
current wedge (SCW), spanning the 21:00–03:00 MLT sector of the near-Earth
plasma sheet (GOES-10 data during the interval 06:00–12:00 UT), and
magnetic perturbations in the tail lobes in relation to ground observations
of auroral electrojets and convection in the polar cap ionosphere. The joint
ground–satellite observations are interpreted in terms of sequential
intensifications and expansions of the outer and inner current loops of the
SCW and their respective associations with the westward electrojet centred
near midnight (24:00 MLT) and the eastward electrojet observed at
14:00–15:00 MLT. Combined magnetic field observations across the tail lobe
from Cluster and Geotail allow us to make estimates of enhancements of the
cross-polar-cap potential (CPCP) amounting to ≈ 30–60 kV (lower
limits), corresponding to monotonic increases of the PCN index by 1.5 to
3 mV m−1 from inductive
electric field coupling in the magnetosphere–ionosphere (M–I) system during the
initial transient phase of the substorm expansion
3-[(E)-2-(5,7-Dichloro-8-hydroxyquinolin-2-yl)vinyl]-4-hydroxyphenyl acetate
The two symmetry independent molecules of the title compound, C19H13Cl2NO4, show similar conformations with the acetyl group twisted strongly relative to the remaining, virtually flat (r.m.s. deviations = 0.0173 and 0.0065 Å), part of the molecule. The hydroxyl groups of the 8-hydroxyquinoline residues are involved in intramolecular O—H⋯N hydrogen bonds, which, in one case, forms a part of a three-center interaction. Intermolecular O—H⋯O hydrogen bonds assemble the molecules into a one-dimensional polymeric structure extended along the a axis. The 4-hydroxyphenyl group of one molecule forms an O—H⋯O hydrogen bond, in which the hydroxyl H atom is disordered, with its inversion center counterpart
Aspects of magnetosphere-ionosphere coupling in sawtooth substorms: a case study
In a case study we report on repetitive substorm activity during storm time which was excited during Earth passage of an interplanetary coronal mass ejection (ICME) on 18 August 2003. Applying a combination of magnetosphere and ground observations during a favourable multi-spacecraft configuration in the plasma sheet (GOES-10 at geostationary altitude) and in the tail lobes (Geotail and Cluster-1), we monitor the temporal–spatial evolution of basic elements of the substorm current system. Emphasis is placed on activations of the large-scale substorm current wedge (SCW), spanning the 21:00–03:00 MLT sector of the near-Earth plasma sheet (GOES-10 data during the interval 06:00–12:00 UT), and magnetic perturbations in the tail lobes in relation to ground observations of auroral electrojets and convection in the polar cap ionosphere. The joint ground–satellite observations are interpreted in terms of sequential intensifications and expansions of the outer and inner current loops of the SCW and their respective associations with the westward electrojet centred near midnight (24:00 MLT) and the eastward electrojet observed at 14:00–15:00 MLT. Combined magnetic field observations across the tail lobe from Cluster and Geotail allow us to make estimates of enhancements of the cross-polar-cap potential (CPCP) amounting to ≈ 30–60 kV (lower limits), corresponding to monotonic increases of the PCN index by 1.5 to 3 mV m−1 from inductive electric field coupling in the magnetosphere–ionosphere (M–I) system during the initial transient phase of the substorm expansion
Polar observations of ion/electron bursts at the pre-dawn polar cap boundary: evidence for internal reconnection of overdraped lobe flux
Observations made by Polar of ion-electron bursts on the dawn side of the polar cap are presented. They occurred when conditions external to the magnetosphere corresponded to that of the sheath region of a magnetic cloud, which was characterized by very high densities/dynamic pressure and a magnetic field which was strong in all components and which was tilted antisunward (Bx\u3c0) and northward (Bz\u3e0) with its clock angle lying between 20 and 90° (By: 8–15 nT). A clear temporal development in the energy range spanned by the individual ion bursts (from 0.2–2 keV to 1–10 keV) was present. We relate this to a corresponding temporal evolution in the cloud sheath field and plasma. We analyze the solar wind-magnetosphere aspects of the observations using the concepts of (i) (i) overdraped lobe flux, (ii) Bx- and By-regulated sequential reconnections in opposite hemispheres (magnetopause and internal modes), and (iii) newly-closed magnetic flux. In particular, we find that the most energetic ion bursts (accompanied by bi-directionally streaming electrons at 1–10 keV and intense magnetosheath-origin fluxes) are located on newly closed field lines generated by internal reconnection occurring between overdraped lobe field lines and the closed geomagnetic field. This result corroborates a topology of lobe reconnection under conditions of dipole tilt and/or nonzero IMF Bx component advanced by Watanabe et al. (2006), which in our case is adapted to nonzero IMF By conditions
Bis(4-aminobenzoic acid-κN)dichloridozinc(II)
Molecules of the title compound [ZnCl2(C7H7NO2)2], are located on a twofold rotation axis. Two 4-aminobenzoic acid moieties, and two chloride ligands are coordinated to a Zn atom in a tetrahedral fashion, forming an isolated molecule. Neighbouring molecules are linked through hydrogen-bonded carboxyl groups, as well as N—H⋯Cl hydrogen-bonding interactions between amine groups and the chloride ligands of neighbouring molecules, forming a three-dimensional network
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