27,853 research outputs found
Sun-synchronous highly elliptical orbits using low-thrust propulsion
Due to restrictions within the current architecture of the global observing system (GOS), space-based remote sensing of Earth suffers from an acute data-deficit over the critical polar-regions. Currently, observation of high-latitude regions is conducted using composite images from spacecraft in geostationary (GEO) and low-Earth orbits (LEOs) [1]. However, the oblique viewing geometry from GEO-based systems to latitudes above around 55 deg [2] and the insufficient temporal resolution of spacecraft in LEO means there is currently no source of continuous imagery for polar-regions obtained with a data refresh rate of less than 15 minutes, as is typically available elsewhere for meteorological observations
Neonatal weight loss in breast and formula-fed infants
We have observed an increase in the number of breast fed babies presenting with dehydration and/or failure to thrive because of lactation failure and non-recognition of feeding problems. Recent reports1,2 support this experience and recommend monitoring of the weight of infants through the neonatal period. However, these reports acknowledge uncertainty as to what actually constitutes normal neonatal weight loss. Maisels and colleagues published two studies which have been quoted as giving guidance on normal loss. Both studies were designed primarily to study factors that influence breast milk jaundice. The first3 reported a mean weight loss of about 6% in 100 unselected well babies during the first 3 days. The subsequent study4 reported a mean weight loss of 6.86% in 186 infants. The timescale over which babies were weighed was not clearly indicated, although it may have only been 2-3 days. The sample was neither population based nor randomly selected, being largely preselected because of the presence of more pronounced jaundice. The distribution of data points for early neonatal weight loss are likely to be skewed, yet both studies reported the results as mean (SD). Owing to the design and method of data presentation, these studies cannot reliably inform the debate as to what constitutes the norm. Marchini and colleagues published reports also designed primarily to study other issues. One5 indicated a mean early weight loss of 5.7%. Measurements were recorded over a three day period, and no indication is given of the skewness of the data. Another study6 reported a median weight loss of about 6% recorded over a four day period. At least one baby lost > 15% of his/her birth weight during this time, but there is no clear information as to the frequency with which more extreme degrees of weight loss are observed
Spin wave dispersion in La2CuO4
We calculate the antiferromagnetic spin wave dispersion in the half-filled
Hubbard model for a two-dimensional square lattice and find it to be in
excellent agreement with recent high-resolution inelastic neutron scattering
performed on La2CuO4 [Phys. Rev. Lett. 86, 5377 (2001)].Comment: typos correcte
Magnetic interactions of substitutional Mn pairs in GaAs
We employ a kinetic-exchange tight-binding model to calculate the magnetic
interaction and anisotropy energies of a pair of substitutional Mn atoms in
GaAs as a function of their separation distance and direction. We find that the
most energetically stable configuration is usually one in which the spins are
ferromagnetically aligned along the vector connecting the Mn atoms. The
ferromagnetic configuration is characterized by a splitting of the topmost
unoccupied acceptor levels, which is visible in scanning tunneling microscope
studies when the pair is close to the surface and is strongly dependent on pair
orientation. The largest acceptor splittings occur when the Mn pair is oriented
along the symmetry direction, and the smallest when they are oriented
along . We show explicitly that the acceptor splitting is not simply
related to the effective exchange interaction between the Mn local moments. The
exchange interaction constant is instead more directly related to the width of
the distribution of all impurity levels -- occupied and unoccupied. When the Mn
pair is at the (110) GaAs surface, both acceptor splitting and effective
exchange interaction are very small except for the smallest possible Mn
separation.Comment: 25 figure
Magnetic properties of substitutional Mn in (110) GaAs surface and subsurface layers
Motivated by recent STM experiments, we present a theoretical study of the
electronic and magnetic properties of the Mn-induced acceptor level obtained by
substituting a single Ga atom in the (110) surface layer of GaAs or in one of
the atoms layers below the surface. We employ a kinetic-exchange tight-binding
model in which the relaxation of the (110) surface is taken into account. The
acceptor wave function is strongly anisotropic in space and its detailed
features depend on the depth of the sublayer in which the Mn atom is located.
The local-density-of-states (LDOS) on the (110) surface associated with the
acceptor level is more sensitive to the direction of the Mn magnetic moment
when the Mn atom is located further below the surface. We show that the total
magnetic anisotropy energy of the system is due almost entirely to the
dependence of the acceptor level energy on Mn spin orientation, and that this
quantity is strongly dependent on the depth of the Mn atom.Comment: 14 pages, 13 figure
Experimental and numerical study of local mean age of air
This paper presents the results from the experimental and numerical study of a room with mixing ventilation, focused on the local mean age of air (LMA). The measurements were performed using the tracer gas concentration decay method. The numerical predictions were obtained from the computational fluid dynamics (CFD) module of the latest version of the ESP-r software
Fully Frustrated Cold Atoms
Fully frustrated Josephson Junction arrays (FF-JJA's) exhibit a subtle
compound phase transition in which an Ising transition associated with discrete
broken translational symmetry and a Berezinskii-Kosterlitz-Thouless (BKT)
transition associated with quasi-long-range phase coherence occur nearly
simultaneously. In this Letter we discuss a cold atom realization of the FF-JJA
system. We demonstrate that both orders can be studied by standard
momentum-distribution-function measurements and present numerical results,
based on a successful self-consistent spin-wave approximation, that illustrate
the expected behavior of observables.Comment: 5 pages, 3 figures, submitte
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Home accidents amongst elderly people: A locality study in Scotland
Aim
The aim of this locality study was to collect information on reported and unreported accidents amongst elderly people living in one locality in Scotland.
Method
Postal Survey- A postal questionnaire was sent to 3,757 men and women aged 65+ years living in one locality. The questionnaire asked respondents to indicate how many accidents they had experienced in the past twelve months, plus to indicate type and location. Information was gathered on living arrangements, ethnicity, gender, age and deprivation. Respondents were asked if they would be willing to take part in an interview study.
Interview Study - One hundred elders who had had at least one accident in the previous twelve months were interviewed.
Results
Postal Survey - Over a third of the respondents in the postal survey reported having had an accident in the previous twelve months. Bumps and drops and falls were the most common type of accident. Most accidents happened in the kitchen. Women reported more falls than men and those living alone reported more accidents than those living with others. Age was associated with the prevalence of accidents, but the association was somewhat curvilinear, with accidents decreasing with age and then increasing again.
Interview Study â Interviewees found it hard to differentiate one accident from another. Considerable reluctance to visit the GP after an accident was noted, with many not attending even for serious accidents. Almost forty percent were âveryâ distressed after their accident, and a quarter reported a loss of confidence. However, most did not worry about accidents. Few thought that their age, health or medications were a cause of their accidents
Ion observations from geosynchronous orbit as a proxy for ion cyclotron wave growth during storm times
[1] There is still much to be understood about the processes contributing to relativistic electron enhancements and losses in the radiation belts. Wave particle interactions with both whistler and electromagnetic ion cyclotron (EMIC) waves may precipitate or accelerate these electrons. This study examines the relation between EMIC waves and resulting relativistic electron flux levels after geomagnetic storms. A proxy for enhanced EMIC waves is developed using Los Alamos National Laboratory Magnetospheric Plasma Analyzer plasma data from geosynchronous orbit in conjunction with linear theory. In a statistical study using superposed epoch analysis, it is found that for storms resulting in net relativistic electron losses, there is a greater occurrence of enhanced EMIC waves. This is consistent with the hypothesis that EMIC waves are a primary mechanism for the scattering of relativistic electrons and thus cause losses of such particles from the magnetosphere
Nanoscale Torsional Optomechanics
Optomechanical transduction is demonstrated for nanoscale torsional
resonators evanescently coupled to optical microdisk whispering gallery mode
resonators. The on-chip, integrated devices are measured using a fully
fiber-based system, including a tapered and dimpled optical fiber probe. With a
thermomechanically calibrated optomechanical noise floor down to 7 fm/sqrt(Hz),
these devices open the door for a wide range of physical measurements involving
extremely small torques, as little as 4x10^-20 N*m.Comment: 4 pages, 4 figures - Accepted to APL Oct 22nd, 2012. To appear in
February 4th issue - as cover articl
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