1,862 research outputs found
The use of imaging systems to monitor shoreline dynamics
The development of imaging systems is nowadays established as one of the most powerful and reliable tools for monitoring beach morphodynamics. Two different techniques for shoreline detection are presented here and, in one case, applied to the study of beach width oscillations on a sandy beach (Pauanui Beach, New Zealand). Results indicate that images can provide datasets whose length and sample interval are accurate enough to resolve inter-annual and seasonal oscillations, and long-term trends. Similarly, imaging systems can be extremely useful in determining the statistics of rip current occurrence. Further improvements in accuracy and reliability are expected with the recent introduction of digital systems
Magnetic Flux Braiding: Force-Free Equilibria and Current Sheets
We use a numerical nonlinear multigrid magnetic relaxation technique to
investigate the generation of current sheets in three-dimensional magnetic flux
braiding experiments. We are able to catalogue the relaxed nonlinear force-free
equilibria resulting from the application of deformations to an initially
undisturbed region of plasma containing a uniform, vertical magnetic field. The
deformations are manifested by imposing motions on the bounding planes to which
the magnetic field is anchored. Once imposed the new distribution of magnetic
footpoints are then taken to be fixed, so that the rest of the plasma must then
relax to a new equilibrium configuration. For the class of footpoint motions we
have examined, we find that singular and nonsingular equilibria can be
generated. By singular we mean that within the limits imposed by numerical
resolution we find that there is no convergence to a well-defined equilibrium
as the number of grid points in the numerical domain is increased. These
singular equilibria contain current "sheets" of ever-increasing current
intensity and decreasing width; they occur when the footpoint motions exceed a
certain threshold, and must include both twist and shear to be effective. On
the basis of these results we contend that flux braiding will indeed result in
significant current generation. We discuss the implications of our results for
coronal heating.Comment: 13 pages, 12 figure
A rapid screening, “combinatorial-type” survey of the metalloligand chemistry of Pt₂(PPh₃)₄(μ-S)₂ using electrospray mass spectrometry
Electrospray mass spectrometry is a rapid and powerful technique for a combinatorial-like survey of the chemistry of the metalloligand Pt₂(PPh₃)₄(μ-S)₂, leading to the successful isolation and crystallographic characterisation of the novel protonated species Pt₂(PPh₃)₄(μ-S)(μ-SH) together with a range of metallated derivatives
The homotopy theory of dg-categories and derived Morita theory
The main purpose of this work is the study of the homotopy theory of
dg-categories up to quasi-equivalences. Our main result provides a natural
description of the mapping spaces between two dg-categories and in
terms of the nerve of a certain category of -bimodules. We also prove
that the homotopy category is cartesian closed (i.e. possesses
internal Hom's relative to the tensor product). We use these two results in
order to prove a derived version of Morita theory, describing the morphisms
between dg-categories of modules over two dg-categories and as the
dg-category of -bi-modules. Finally, we give three applications of our
results. The first one expresses Hochschild cohomology as endomorphisms of the
identity functor, as well as higher homotopy groups of the \emph{classifying
space of dg-categories} (i.e. the nerve of the category of dg-categories and
quasi-equivalences between them). The second application is the existence of a
good theory of localization for dg-categories, defined in terms of a natural
universal property. Our last application states that the dg-category of
(continuous) morphisms between the dg-categories of quasi-coherent (resp.
perfect) complexes on two schemes (resp. smooth and proper schemes) is
quasi-equivalent to the dg-category of quasi-coherent complexes (resp. perfect)
on their product.Comment: 50 pages. Few mistakes corrected, and some references added. Thm.
8.15 is new. Minor corrections. Final version, to appear in Inventione
H3+ in Diffuse Interstellar Clouds: a Tracer for the Cosmic-Ray Ionization Rate
Using high resolution infrared spectroscopy we have surveyed twenty
sightlines for H3+ absorption. H3+ is detected in eight diffuse cloud
sightlines with column densities varying from 0.6x10^14 cm^-2 to 3.9x10^14
cm^-2. This brings to fourteen the total number of diffuse cloud sightlines
where H3+ has been detected. These detections are mostly along sightlines
concentrated in the Galactic plane, but well dispersed in Galactic longitude.
The results imply that abundant H3+ is common in the diffuse interstellar
medium. Because of the simple chemistry associated with H3+ production and
destruction, these column density measurements can be used in concert with
various other data to infer the primary cosmic-ray ionization rate, zeta_p.
Values range from 0.5x10^-16 s^-1 to 3x10^-16 s^-1 with an average of 2x10^-16
s^-1. Where H3+ is not detected the upper limits on the ionization rate are
consistent with this range. The average value of zeta_p is about an order of
magnitude larger than both the canonical rate and rates previously reported by
other groups using measurements of OH and HD. The discrepancy is most likely
due to inaccurate measurements of rate constants and the omission of effects
which were unknown when those studies were performed. We believe that the
observed column density of H3+ is the most direct tracer for the cosmic-ray
ionization rate due to its simple chemistry. Recent models of diffuse cloud
chemistry require cosmic-ray ionization rates on the order of 10^-16 s^-1 to
reproduce observed abundances of various atomic and molecular species, in rough
accord with our observational findings.Comment: Accepted to ApJ, 35 pages, 5 figures, 5 table
The LWA1 Radio Telescope
LWA1 is a new radio telescope operating in the frequency range 10-88 MHz,
located in central New Mexico. The telescope consists of 258 pairs of
dipole-type antennas whose outputs are individually digitized and formed into
beams. Simultaneously, signals from all dipoles can be recorded using one of
the instrument's "all dipoles" modes, facilitating all-sky imaging. Notable
features of the instrument include high intrinsic sensitivity (about 6 kJy
zenith system equivalent flux density), large instantaneous bandwidth (up to 78
MHz), and 4 independently-steerable beams utilizing digital "true time delay"
beamforming. This paper summarizes the design of LWA1 and its performance as
determined in commissioning experiments. We describe the method currently in
use for array calibration, and report on measurements of sensitivity and
beamwidth.Comment: 9 pages, 14 figures, accepted by IEEE Trans. Antennas & Propagation.
Various minor changes from previous versio
Nutritional intake in acute care surgery patients in Kigali, Rwanda- A single institution descriptive analysis
INTRODUCTION: Nutrition is essential for health and healing, especially in the perioperative period. However, little is known about the nutritional intake of hospitalized patients in low and middle-income countries.This paper aimed to characterize the composition and quantity of food in acute care surgery patients at a tertiary referral hospital in Rwanda.
METHODS: Acute care surgery patients were queried about nutritional intake during hospitalization from May 21, 2018, to June 3, 2018, for 100 patient days. Calorie and protein intake were estimated and compared to standards for an average Rwandan adult.RESULTS: Median daily calorie intake was 1472 kcal/day (Interquartile range (IQR): 662, 2116). The median daily protein intake was 45.99 g (IQR: 24.38, 70.22). Assuming a calorie need of 25 kcal/kg/day and a protein need of 1g/kg/day, this is 98.1% of the estimated daily calorie needs and 76.7% of estimated daily protein needs. Estimating higher energy needs for a surgical patient, the daily intake is 70.0-81.9% of calorie needs and 51.1-63.9% of protein needs.
CONCLUSION: Overall, the calorie and protein intake for the average Rwandan acute care surgery patient were low compared to the needs of a 60 kg surgical patient. More education and accessibility to high-quality foods are needed to ensure adequate nutrition in the postoperative period to optimize clinical outcomes
Passive and catalytic antibodies and drug delivery
Antibodies are one of the most promising components of the biotechnology repertoire for the purpose of drug delivery. On the one hand, they are proven agents for cell-selective delivery of highly toxic agents in a small but expanding number of cases. This technology calls for the covalent attachment of the cytotoxin to a tumor-specific antibody by a linkage that is reversible under appropriate conditions (antibody conjugate therapy, ACT —"passive delivery”). On the other hand, the linker cleavage can be accomplished by a protein catalyst attached to the tumor-specific antibody ("catalytic delivery”). Where the catalyst is an enzyme, this approach is known as antibody-directed enzyme prodrug therapy (ADEPT). Where the transformation is brought about by a catalytic antibody, it has been termed antibody-directed abzyme prodrug therapy (ADAPT). These approaches will be illustrated with emphasis on how their demand for new biotechnology is being realized by structure-based protein engineerin
Age structure, dispersion and diet of a population of stoats (Mustela erminea) in southern Fiordland during the decline phase of the beechmast cycle
The dispersion, age structure and diet of stoats (Mustela erminea) in beech forest in the Borland and Grebe Valleys, Fiordland National Park, were examined during December and January 2000/01, 20 months after a heavy seed-fall in 1999. Thirty trap stations were set along a 38-km transect through almost continuous beech forest, at least 1 km apart. Mice were very scarce (nights, C/100TN) along two standard index lines placed at either end of the transect, compared with November 1999 (>60/100TN), but mice were detected (from footprints in stoat tunnels) along an 8 km central section of the transect (stations 14-22). Live trapping with one trap per station (total 317.5 trap nights) in December 2000 caught 2 female and 23 male stoats, of which 10 (including both females) were radio collared. The minimum range lengths of the two females along the transect represented by the trap line were 2.2 and 6.0 km; those of eight radio-tracked males averaged 2.9 ± 1.7 km. Stations 14-22 tended to be visited more often, by more marked individual stoats, than the other 21 stations.
Fenn trapping at the same 30 sites, but with multiple traps per station (1333.5 trap nights), in late January 2001 collected carcasses of 35 males and 28 females (including 12 of the marked live-trapped ones). Another two marked males were recovered dead. The stoat population showed no sign of chronic nutritional stress (average fat reserve index = 2.8 on a scale of 1-4 where 4 = highest fat content); and only one of 63 guts analysed was empty. Nevertheless, all 76 stoats handled were adults with 1-3 cementum annuli in their teeth, showing that reproduction had failed that season. Prey categories recorded in descending frequency of occurrence were birds, carabid beetle (ground beetle), weta, possum, rat, and mouse. The frequencies of occurrence of mice and birds in the diet of these stoats (10% and 48%, respectively) were quite different from those in stoats collected in Pig Creek, a tributary of the Borland River (87%, 5%), 12 months previously when mice were still abundant. Five of the six stoat guts containing mice were collected within 1 km of stations 14-22
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