8,524 research outputs found
Doppler radar wind field retrieval over the Po Valley
Although methods of using multiple Doppler radars to study wind fields have long been proposed, and many research studies have been made, very few operational radar operators adopt methods which require the use of specific scanning strategies to allow the extraction of wind information. Here we report a collaborative study on dual-Doppler radars based on two Doppler radars in the Po valley, Italy. Unusually, the radars are only about 90 km apart, though operated by the same authority. The wind field syntheses are carried out on a 30 km by 30 km region where the two radars have overlapping scan coverage. An iterative method based on the linear wind model and the equation of mass continuity is used to construct the wind fields. The methodology has been validated by two different methods. The first method is to reconstruct the radial wind observed by each radar, and the second method is calculating and comparing the along-track component with that derived from the observations. Both two comparisons show good agreement with the original data
Coarsening Dynamics of Granular Heaplets in Tapped Granular Layers
A semi-continuum model is introduced to study the dynamics of the formation
of granular heaplets in tapped granular layers. By taking into account the
energy dissipation of collisions and screening effects due to avalanches, this
model is able to reproduce qualitatively the pattern of these heaplets. Our
simulations show that the granular heaplets are characterised by an effective
surface tension which depends on the magnitude of the tapping intensity. Also,
we observe that there is a coarsening effect in that the average size of the
heaplets, V grows as the number of taps k increases. The growth law at
intermediate times can be fitted by a scaling function V ~ k^z but the range of
validity of the power law is limited by size effects. The growth exponent z
appears to diverge as the tapping intensity is increased.Comment: 4 pages, 4 figure
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Patient-Related Barriers to Timely Dialysis Access Preparation: A Qualitative Study of the Perspectives of Patients, Family Members, and Health Care Providers
Rational & Objective
A key aspect of smooth transition to dialysis is the timely creation of a permanent access. Despite early referral to kidney care, initiation onto dialysis is still suboptimal for many patients, which has clinical and cost implications. This study aimed to explore perspectives of various stakeholders on barriers to timely access creation.
Study Design
Qualitative study.
Setting & Participants
Semi-structured interviews with 96 participants (response rate, 67%), including patients with stage 4 chronic kidney disease (n = 30), new hemodialysis patients with (n = 18) and without (n = 20) permanent access (arteriovenous fistula), family members (n = 19), and kidney health care providers (n = 9).
Analytical Approach
Thematic analysis.
Results
Patients reported differential levels of behavioral activation toward access creation: avoidance/denial, wait and see, or active intention. 6 core themes were identified: (1) lack of symptoms, (2) dialysis fear and practical concerns (exaggerated fear, pain, cost, lifestyle disruptions, work-related concerns, burdening their families), (3) evaluating value against costs/risks of access creation (benefits, threat of operation, viability, prompt for early initiation), (4) preference for alternatives, (5) social influences (hearsay, family involvement, experiences of others), and (6) health care provider interactions (mistrust, interpersonal tension, lack of clarity on information). Themes were common to all groups, whereas nuanced perspectives of family members and health care providers were noted in some subthemes.
Limitations
Response bias.
Conclusions
Individual, interpersonal, and psychosocial factors compromise dialysis preparation and contribute to suboptimal dialysis initiation. Our findings support the need for interventions to improve patient and family engagement and address emotional concerns and misperceptions about preparing for dialysis
Bioaccessibility of Carotenoids and Tocopherols in Marine Microalgae, Nannochloropsis sp. and Chaetoceros sp.
Microalgae can produce various natural products such as pigments, enzymes, unique
fatty acids and vitamin that benefit humans. The objective of the study is to study the
bioaccessibility of carotenoids (β-carotene and lycopene) and vitamin E (α- and β-
tocopherol) of Nannochloropsis oculata and Chaetoceros calcitrans. Analyses were carried
out for both the powdered forms of N. oculata and C. calcitrans, and the dried extract
forms of N. oculata and C. calcitrans. In vitro digestion method together with RP-HPLC
was used to determine the bioaccessibility of carotenoids and vitamin E for both forms
of microalgae. Powdered form of N. oculata had the highest bioaccessibility of β-carotene
(28.0 ± 0.6 g kg-1), followed by dried extract N. oculata (21.5 ± 1.1 g kg-1), dried extract C.
calcitrans (16.9 ± 0.1 g kg-1), and powdered C. calcitrans (15.6 ± 0.1 g kg-1). For lycopene,
dried extract of N. oculata had the highest bioaccessibility of lycopene (42.6 ± 1.1 g kg-
1), followed by dried extract C. calcitrans (41.9 ± 0.6 g kg-1), powdered C. calcitrans (39.7
± 0.1 g kg-1) and powdered N. oculata (32.6 ± 0.7 g kg-1). Dried extract C. calcitrans had the
highest bioaccessibility of α-tocopherol (72.1 ± 1.2 g kg-1). However, β-tocopherol was
not detected in both dried extract and powdered form of C. calcitrans. In conclusion, all
samples in their dried extract forms were found to have significantly higher
bioaccessibilities than their powdered forms. This may be due to the disruption of the
food matrix contributing to a higher bioaccessibility of nutrients shown by the dried
extract form
Cluster size dependence of high-order harmonic generation
We investigate high-order harmonic generation (HHG) from noble gas clusters
in a supersonic gas jet. To identify the contribution of harmonic generation
from clusters versus that from gas monomers, we measure the high-order harmonic
output over a broad range of the total atomic number density in the jet (from
3*10^16 cm^{-3} to 3x10^18 cm{-3}) at two different reservoir temperatures (303
K and 363 K). For the firrst time in the evaluation of the harmonic yield in
such measurements, the variation of the liquid mass fraction, g, versus
pressure and temperature is taken into consideration, which we determine,
reliably and consistently, to be below 20% within our range of experimental
parameters. By comparing the measured harmonic yield from a thin jet with the
calculated corresponding yield from monomers alone, we find an increased
emission of the harmonics when the average cluster size is less than 3000.
Using g, under the assumption that the emission from monomers and clusters add
up coherently, we calculate the ratio of the average single-atom response of an
atom within a cluster to that of a monomer and find an enhancement of around 10
for very small average cluster size (~200). We do not find any dependence of
the cut-off frequency on the composition of the cluster jet. This implies that
HHG in clusters is based on electrons that return to their parent ions and not
to neighbouring ions in the cluster. To fully employ the enhanced average
single-atom response found for small average cluster sizes (~200), the nozzle
producing the cluster jet must provide a large liquid mass fraction at these
small cluster sizes for increasing the harmonic yield. Moreover, cluster jets
may allow for quasi-phase matching, as the higher mass of clusters allows for a
higher density contrast in spatially structuring the nonlinear medium.Comment: 16 pages, 6 figure
Single-shot fluctuations in waveguided high-harmonic generation
For exploring the application potential of coherent soft x-ray (SXR) and
extreme ultraviolet radiation (XUV) provided by high-harmonic generation, it is
important to characterize the central output parameters. Of specific importance
are pulse-to-pulse (shot-to-shot) fluctuations of the high-harmonic output
energy, fluctuations of the direction of the emission (pointing instabilities),
and fluctuations of the beam divergence and shape that reduce the spatial
coherence. We present the first single-shot measurements of waveguided
high-harmonic generation in a waveguided (capillary-based) geometry. Using a
capillary waveguide filled with Argon gas as the nonlinear medium, we provide
the first characterization of shot-to-shot fluctuations of the pulse energy, of
the divergence and of the beam pointing. We record the strength of these
fluctuations vs. two basic input parameters, which are the drive laser pulse
energy and the gas pressure in the capillary waveguide. In correlation
measurements between single-shot drive laser beam profiles and single-shot
high-harmonic beam profiles we prove the absence of drive laser
beam-pointing-induced fluctuations in the high-harmonic output. We attribute
the main source of high-harmonic fluctuations to ionization-induced nonlinear
mode mixing during propagation of the drive laser pulse inside the capillary
waveguide
Nanofiltration of aerobically-treated palm oil mill effluent: Characterization of the size of colour compounds using synthetic dyes and polyethylene glycols
Membrane-based separation is one of the emerging technologies that have garnered significant interest in recent years for the treatment process of palm oil mill effluent (POME). As documented in the literature, different types of membrane processes such as ultrafiltration (UF), nanofiltration (NF) and reverse osmosis (RO) were used for the POME treatment and the efficiency of separation varied depending on the membrane properties. Unlike the previous works that used membranes to treat POME, the main focus of this current work is to utilize NF membrane to characterize the size of colour compounds in the aerobically-treated POME (AT-POME). Two different markers, i.e., synthetic dyes and polyethylene glycols (PEGs) with molecular weight (MW) in the range of 200-1000 g/mol were used to characterize the colour compounds in the AT-POME. Results showed that dyes are more suitable compared to PEGs for the characterization because dyes possessed negative charge similar as the colour compounds in the AT-POME. By using dyes as the markers, it was found that the size of the colour compounds in the AT-POME was at MW of 300-400 g/mol. Precise determination of the size of colour compounds in the AT-POME is of importance as it could provide useful information on the selection of ideal membrane properties (in particular pore size or molecular weight cut-off) to achieve complete solute separation
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