973 research outputs found
Popular Matchings in the Weighted Capacitated House Allocation Problem
We consider the problem of finding a popular matching in the Weighted Capacitated
House Allocation problem (WCHA). An instance of WCHA involves a set of agents
and a set of houses. Each agent has a positive weight indicating his priority, and a
preference list in which a subset of houses are ranked in strict order. Each house has
a capacity that indicates the maximum number of agents who could be matched to
it. A matching M of agents to houses is popular if there is no other matching M′
such that the total weight of the agents who prefer their allocation in M′
to that in
M exceeds the total weight of the agents who prefer their allocation in M to that in
M′
. Here, we give an O(
√
Cn1 + m) algorithm to determine if an instance of WCHA
admits a popular matching, and if so, to find a largest such matching, where C is the
total capacity of the houses, n1 is the number of agents, and m is the total length of
the agents’ preference lists
Enhanced surface transfer doping of diamond by V2O5 with improved thermal stability
Surface transfer doping of hydrogen-terminated diamond has been achieved utilising V2O5 as a surface electron accepting material. Contact between the oxide and diamondsurface promotes the transfer of electrons from the diamond into the V2O5 as revealed by the synchrotron-based high resolution photoemission spectroscopy. Electrical characterization by Hall measurement performed before and after V2O5 deposition shows an increase in hole carrier concentration in the diamond from 3.0 × 1012 to 1.8 × 1013 cm−2 at room temperature. High temperature Hall measurements performed up to 300 °C in atmosphere reveal greatly enhanced thermal stability of the hole channel produced using V2O5 in comparison with an air-induced surface conduction channel. Transfer doping of hydrogen-terminated diamond using high electron affinity oxides such as V2O5 is a promising approach for achieving thermally stable, high performance diamond based devices in comparison with air-induced surface transfer dopin
A tree-based approach for modelling interception loss from evergreen oak mediterranean savannas
Evaporation of rainfall intercepted by tree canopies is usually an important part of the overall water balance of forested catchments and there have been many studies dedicated to measuring and modelling rainfall interception loss. These studies have mainly been conducted in dense forests; there have been few studies on the very sparse forests which are common in dry and semi-arid areas. Water resources are scarce in these areas making sparse forests particularly important. Methods for modelling interception loss are thus required to support sustainable water management in those areas. In very sparse forests, trees occur as widely spaced individuals rather than as a continuous forest canopy. We therefore suggest that interception loss for this vegetation type can be more adequately modelled if the overall forest evaporation is derived by scaling up the evaporation from individual trees. The evaporation rate for a single tree can be estimated using a simple Dalton-type diffusion equation for water vapour as long as its surface temperature is known. From theory, this temperature is shown to be dependent upon the available energy and windspeed. However, the surface temperature of a fully saturated tree crown, under rainy conditions, should approach the wet bulb temperature as the radiative energy input to the tree reduces to zero. This was experimentally confirmed from measurements of the radiation balance and surface temperature of an isolated tree crown. Thus, evaporation of intercepted rainfall can be estimated using an equation which only requires knowledge of the air dry and wet bulb temperatures and of the bulk tree-crown aerodynamic conductance. This was taken as the basis of a new approach for modelling interception loss from savanna-type woodland, i.e. by combining the Dalton-type equation with the Gash’s analytical model to estimate interception loss from isolated trees. This modelling approach was tested using data from two Mediterranean savanna-type oak woodlands in southern Portugal. For both sites, simulated interception loss agreed well with the observations indicating the adequacy of this new methodology for modelling interception loss by isolated trees in savanna-type ecosystems. Furthermore, the proposed approach is physically based and requires only a limited amount of data. Interception loss for the entire forest can be estimated by scaling up the evaporation from individual trees accounting for the number of trees per unit area
Drought-induced photosynthetic inhibition and autumn recovery in two Mediterranean oak species (Quercus ilex and Quercus suber)
Responses of leaf water relations and photosynthesis
to summer drought and autumn rewetting were studied
in two evergreen Mediterranean oak species, Quercus ilex
spp. rotundifolia and Quercus suber. The predawn leaf water
potential (ΨlPD), stomatal conductance (gs) and photosynthetic
rate (A) at ambient conditions were measured seasonally
over a 3-year period. We also measured the photosynthetic
response to light and to intercellular CO2 (A/PPFD and A/
Ci response curves) under water stress (summer) and after recovery
due to autumn rainfall. Photosynthetic parameters,
Vcmax, Jmax and triose phosphate utilization (TPU) rate, were
estimated using the Farquhar model. RuBisCo activity, leaf
chlorophyll, leaf nitrogen concentration and leaf carbohydrate
concentration were also measured. All measurements
were performed in the spring leaves of the current year. In
both species, the predawn leaf water potential, stomatal conductance
and photosynthetic rate peaked in spring, progressively
declined throughout the summer and recovered upon
autumn rainfall. During the drought period, Q. ilex maintained
a higher predawn leaf water potential and stomatal
conductance than Q. suber. During this period, we found that
photosynthesis was not only limited by stomatal closure, but
was also downregulated as a consequence of a decrease in the
maximum carboxylation rate (Vcmax) and the light-saturated
rate of photosynthetic electron transport (Jmax) in both species.
The Vcmax and Jmax increased after the first autumnal
rains and this increase was related to RuBisCo activity, leaf
nitrogen concentration and chlorophyll concentration. In addition,
an increase in the TPU rate and in soluble leaf sugar
concentration was observed in this period. The results obtained
indicate a high resilience of the photosynthetic apparatus
to summer drought as well as good recovery in the
following autumn rains of these evergreen oak species
Comparison of the optical behaviour of five different multifocal diffractive intraocular lenses in a model eye
The purpose of this study was to investigate and compare the optical performance of five trifocal intraocular lenses (IOLs) following the ISO 11979-2 standards, analysing the impact of tilt and decentration. Five different diffractive trifocal IOLs were evaluated in this experimental study: Acriva Trinova (VSY-Biotechnology) (AT), FineVision HP (PhysIOL) (FVHP), AT LISA tri 839 MP (Zeiss) (ATLT), PanOptix TFNT00 IOL (Alcon) (PO), and Tecnis Synergy (J&J Vision) (TS). In-vitro optical quality analysis of them was performed with the Lambda PMTF system that has an aberration neutral cornea model (Lambda-X Ophthalmics). Measurements were performed on-axis, with 5º of IOL tilt and with 0.5 mm of IOL decentration using 543-nm monochromatic light. Finally, IOL dimensions and diffractive disk profile inspection was performed using the VisIOLA system (Rotlex). On-axis measurements showed a far through-focus MTF > 0.3 at 3 mm aperture, except for TS. FVHP and PO showed better far MTFs for larger apertures (3.75 mm and 4.5 mm) while AT showed good intermediate and near vision for such apertures. With 5º of IOL tilt, the better optical performance at all distances was found with AT for medium-sized pupils (3 mm) and an important reduction of MTF was found for ATLT and PO, especially in the intermediate focus. The induction of 0.5 mm of IOL decentration especially affected the intermediate focus of ATLT and TS and the far focus of FVHP and PO. IOL dimensions and diffractive profile were consistent with those described by the manufacturer. In conclusion, there are differences in the optical performance according to the pupil aperture of the five trifocal IOLs evaluated and this should be considered in clinical practice when selecting the most appropriate implant in each specific case. IOL tilt and decentration can affect significantly in most of the designs evaluated the performance of the IOL at intermediate vision range. It should be noted that measurements were made with an aberration-free cornea, being necessary future studies analysing the impact of different levels of corneal aberrations.David P. Piñero received funding from VSY Biotechnology within the framework of the research project VSY1-22TPA in collaboration with the University of Alicante
Knowledge, attitudes and practice in relation to noise-induced hearing loss in two factories
There has been a global increase in prevalence of occupational noise-induced
hearing loss. The aim of this study is to explore' mean score levels on
knowledge, attitude and practice regarding noise-inducedhearing loss among
participants of the two factories and also to determine the frequency of
distribution of health education. In this intervention study, there were 203
participants from the two factories in the automobile industry. The sample
size required was 23 in each factory. A questionnaire about knowledge,
attitude and practice regarding noise-induced hearing loss questionnaires was
distributed among the participants. The results revealed that there were no
differences in mean scores on knowledge, belief, feelings, judgment and
practice among participants from the two factories. However, the health
education intervention elicited statistically significant changes in mean score
of knowledge over time, F (1.44, 289.45) = 13.54, P < 0.001, partial 112=
0.063; mean score of belief subdomain (attitude) over time, F (1.71,344.17)
= 7.78, p = 0.00 I, partial 112'= 0.037 and mean score of practice over time, F
(1.49, 300.16) = 9.46, p < 0.00 I, partial 112= 0.045, the mean score levels
reduced over six months compared to the first month. This study concludes
the knowledge, belief and practice constructs towards noise-induced hearing
loss had improved over a period of six months, but there were no differences
in the outcomes between participants from the two factories. Hence, regular
employee health education, at least six monthly is required in a hearing
conservation program
Perturbations in electromagnetic dark energy
It has been recently proposed that the presence of a temporal electromagnetic
field on cosmological scales could explain the phase of accelerated expansion
that the universe is currently undergoing. The field contributes as a
cosmological constant and therefore, the homogeneous cosmology produced by such
a model is exactly the same as that of CDM. However, unlike a
cosmological constant term, electromagnetic fields can acquire perturbations
which in principle could affect CMB anisotropies and structure formation. In
this work, we study the evolution of inhomogeneous scalar perturbations in this
model. We show that provided the initial electromagnetic fluctuations generated
during inflation are small, the model is perfectly compatible with both CMB and
large scale structure observations at the same level of accuracy as
CDM.Comment: 12 pages, 3 figures. Added new comments to match the published
versio
JKarelRobot: A Case Study in Supporting Levels of Cognitive Development in the Computer Science Curriculum
We introduce a new software tool, JKarelRobot, for supporting an Inside/Out pedagogy in introductory programming courses. Extending the original conception of Karel the Robot , with Bloom\u27s Taxonomy of Educational Objectives as a guiding principle, we have provided a mechanism for designing exercises that are cognitively appropriate to the developmental levels of our students. JKarelRobot is platform independent (written in Java) and language/paradigm independent, supporting Pascal, Java, and Lisp style environments
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