Modelling the static and dynamic responses of total heat production of broiler chickens to step changes in air temperature and light intensity     

Aerts JM  Berckmans D  Saevels P  Decuypere E  Buyse J 《British poultry science》2000,41(5):651-659

1. The objective of this work was to explore the possibilities of modelling the static and dynamic responses of total heat production of broiler chickens to step changes in temperature and light intensity (light-dark alterations) using compact dynamic model structures. 2. Seventy-seven experiments were performed in an open-circuit respiration chamber to measure the dynamic response of heat production to step variations in temperature and light (on/off). The animal responses were modelled using transfer function model structures. 3. It was demonstrated that the complex process of the dynamic response of heat production of broiler chickens to step changes in air temperature and light-dark alterations can be modelled assuming 1st order dynamics. The coefficient of determination between measured and simulated heat production was on average 0.83 for responses to air temperature and 0.93 for responses to light-dark alterations.  相似文献   

Handling missingness when modeling the force of infection from clustered seroprevalence data     

Niel Hens  Christel Faes  Marc Aerts  Ziv Shkedy  Koen Mintiens  Hans Laevens  Frank Boelaert 《Journal of Agricultural, Biological & Environmental Statistics》2007,12(4):498-513

Modeling infectious diseases data is a relatively young research area in which clustering and stratification are key features. It is not unlikely for these data to have missing values. If values are missing completely at random, the analysis on the complete cases is valid. However, in practice this assumption is usually not fulfilled. This article shows the effect of ignoring missing data in modeling the force of infection of the bovine herpesvirus-1 in Belgian cattle and proposes the use of weighted generalized estimating equations with constrained fractional polynomials as a flexible modeling tool.  相似文献   

CoRoT measures solar-like oscillations and granulation in stars hotter than the Sun     

Michel E  Baglin A  Auvergne M  Catala C  Samadi R  Baudin F  Appourchaux T  Barban C  Weiss WW  Berthomieu G  Boumier P  Dupret MA  Garcia RA  Fridlund M  Garrido R  Goupil MJ  Kjeldsen H  Lebreton Y  Mosser B  Grotsch-Noels A  Janot-Pacheco E  Provost J  Roxburgh IW  Thoul A  Toutain T  Tiphène D  Turck-Chieze S  Vauclair SD  Vauclair GP  Aerts C  Alecian G  Ballot J  Charpinet S  Hubert AM  Lignières F  Mathias P  Monteiro MJ  Neiner C  Poretti E  de Medeiros JR  Ribas I  Rieutord ML  Cortés TR  Zwintz K 《Science (New York, N.Y.)》2008,322(5901):558-560

Oscillations of the Sun have been used to understand its interior structure. The extension of similar studies to more distant stars has raised many difficulties despite the strong efforts of the international community over the past decades. The CoRoT (Convection Rotation and Planetary Transits) satellite, launched in December 2006, has now measured oscillations and the stellar granulation signature in three main sequence stars that are noticeably hotter than the sun. The oscillation amplitudes are about 1.5 times as large as those in the Sun; the stellar granulation is up to three times as high. The stellar amplitudes are about 25% below the theoretic values, providing a measurement of the nonadiabaticity of the process ruling the oscillations in the outer layers of the stars.  相似文献   

Subnanometer-Diameter Wires Isolated in a Polymer Matrix by Fast Polymerization     

JH Golden  FJ DiSalvo  JMJ Frechet  J Silcox  M Thomas  J Elman 《Science (New York, N.Y.)》1996,273(5276):782-784

The preparation and analysis of inorganic-organic polymer nanocomposites consisting of inorganic nanowires and multiwire "cables" in a random-coil organic polymer host is reported. Dissolution of inorganic (LiMo3Se3)n wires in a strongly coordinating monomer, vinylene carbonate, and the use of a rapid polymerization in the presence of a cross-linking agent produce nanocomposites without phase separation. Polymerization of dilute solutions yields a material containing mostly (Mo3Se3(-))n mono- and biwires, 6 to 20 angstroms in diameter and 50 to 100 nanometers long. Polymerization of more concentrated liquid crystalline solutions yields a nanocomposite containing oriented multiwire cables, 20 to 40 angstroms in diameter and up to 1500 nanometers long, that display optical anisotropy and electrical conductivity.  相似文献   

The ecoresponsive genome of Daphnia pulex     

Colbourne JK  Pfrender ME  Gilbert D  Thomas WK  Tucker A  Oakley TH  Tokishita S  Aerts A  Arnold GJ  Basu MK  Bauer DJ  Cáceres CE  Carmel L  Casola C  Choi JH  Detter JC  Dong Q  Dusheyko S  Eads BD  Fröhlich T  Geiler-Samerotte KA  Gerlach D  Hatcher P  Jogdeo S  Krijgsveld J  Kriventseva EV  Kültz D  Laforsch C  Lindquist E  Lopez J  Manak JR  Muller J  Pangilinan J  Patwardhan RP  Pitluck S  Pritham EJ  Rechtsteiner A  Rho M  Rogozin IB  Sakarya O  Salamov A  Schaack S  Shapiro H  Shiga Y  Skalitzky C  Smith Z  Souvorov A  Sung W 《Science (New York, N.Y.)》2011,331(6017):555-561

We describe the draft genome of the microcrustacean Daphnia pulex, which is only 200 megabases and contains at least 30,907 genes. The high gene count is a consequence of an elevated rate of gene duplication resulting in tandem gene clusters. More than a third of Daphnia's genes have no detectable homologs in any other available proteome, and the most amplified gene families are specific to the Daphnia lineage. The coexpansion of gene families interacting within metabolic pathways suggests that the maintenance of duplicated genes is not random, and the analysis of gene expression under different environmental conditions reveals that numerous paralogs acquire divergent expression patterns soon after duplication. Daphnia-specific genes, including many additional loci within sequenced regions that are otherwise devoid of annotations, are the most responsive genes to ecological challenges.  相似文献   

Climate change effects on soil arthropod communities from the Falkland Islands and the Maritime Antarctic     

S. Bokhorst  A. Huiskes  P. Convey  P.M. van Bodegom  R. Aerts 《Soil biology & biochemistry》2008,40(7):1547-1556

Over a 2-year study, we investigated the effect of environmental change on the diversity and abundance of soil arthropod communities (Acari and Collembola) in the Maritime Antarctic and the Falkland Islands. Open Top Chambers (OTCs), as used extensively in the framework of the northern boreal International Tundra Experiment (ITEX), were used to increase the temperature in contrasting communities on three islands along a latitudinal temperature gradient, ranging from the Falkland Islands (51°S, mean annual temperature 7.5 °C) to Signy Island (60°S, ?2.3 °C) and Anchorage Island (67°S, ?3.8 °C). At each island an open and a closed plant community were studied: lichen vs. moss at the Antarctic sites, and grass vs. dwarf shrub at the Falkland Islands. The OTCs raised the soil surface temperature during most months of the year. During the summer the level of warming achieved was 1.7 °C at the Falkland Islands, 0.7 °C at Signy Island, and 1.1 °C at Anchorage Island.The native arthropod community diversity decreased with increasing latitude. In contrast with this pattern, Collembola abundance in the closed vegetation (dwarf shrub or moss) communities increased by at least an order of magnitude from the Falkland Islands (9.0 ± 2 × 10³ ind. m^?2) to Signy (3.3 ± 8.0 × 10⁴ ind. m^?2) and Anchorage Island (3.1 ± 0.82 × 10⁵ ind. m^?2). The abundance of Acari did not show a latitudinal trend.Abundance and diversity of Acari and Collembola were unaffected by the warming treatment on the Falkland Islands and Anchorage Island. However, after two seasons of experimental warming, the total abundance of Collembola decreased (p < 0.05) in the lichen community on Signy Island as a result of the population decline of the isotomid Cryptopygus antarcticus. In the same lichen community there was also a decline (p < 0.05) of the mesostigmatid predatory mite Gamasellus racovitzai, and a significant increase in the total number of Prostigmata.Overall, our data suggest that the consequences of an experimental temperature increase of 1–2 °C, comparable to the magnitude currently seen through recent climate change in the Antarctic Peninsula region, on soil arthropod communities in this region may not be similar for each location but is most likely to be small and initially slow to develop.  相似文献   

Resistance against Botrytis cinerea in smooth leaf pruning wounds of tomato does not depend on major disease signalling pathways     

T. Beyers  C. Vos  R. Aerts  K. Heyens  L. Vogels  B. Seels  M. Höfte  B. P. A. Cammue  B. De Coninck 《Plant pathology》2014,63(1):165-173

In high‐tech, heated tomato glasshouses, stem infections caused by Botrytis cinerea usually end up girdling the stem, resulting in plant death and consequently high economic losses. Such infections originate primarily from wounds created during leaf pruning, a common cultural practice in which it is intended to remove leaves completely, resulting in smooth stem wounds. However, hasty leaf pruning often results in numerous petiole stubs accidentally left behind. In this study analysis of disease incidences clearly proved that pruning leaves flush to the stem resulted in absolute resistance of the stem wounds, whereas petiole stubs displayed a high level of susceptibility to B. cinerea. Postponing inoculation of wounds after pruning indicated that development of nearly complete resistance occurs within 48 h after deleafing. Monitoring of the wound wetness period showed that drying of the wound surface is not the cause of the decreased susceptibility, contrary to what was commonly believed. Tomato mutants deficient in disease signalling showed altered phenotypes for susceptibility to B. cinerea, indicating that defences against this pathogen in petiole stubs depend on ethylene signalling. Additionally, the decreased susceptibility of mutants deficient in the biosynthesis of jasmonates and abscisic acid suggest an antagonistic effect of these signal molecules. On the other hand, resistance of smooth stem wounds could not be altered by disruption of salicylic acid, ethylene, jasmonate or abscisic acid signalling. This indicates that this remarkable absolute resistance to B. cinerea does not depend on the major disease signalling pathways.  相似文献   

Identification of risk factors for the prevalence and persistence of Salmonella in Belgian broiler chicken flocks     

Harriet Namata  Sarah Welby  Marc Aerts  Christel Faes  Jos Cortias Abrahantes  Hein Imberechts  Katie Vermeersch  Jozef Hooyberghs  Estelle Mroc  Koen Mintiens 《Preventive veterinary medicine》2009,90(3-4):211-222

According to the European Food Safety Authority, salmonellosis is still one of the main causes of infectious foodborne gastroenteritis in humans. Broilers are an important source of salmonellosis after eggs and pork. Between 1987 and 1999 the trend of human salmonellosis incidence in Belgium increased constantly. However, from 2000 until 2005 a decrease in human cases was observed, probably following the sanitary measures implemented in the poultry breeder and laying sector. In order to decrease human infections it is essential to tackle the problem at the farm level to minimize cross-contamination from farm to fork. This paper seeks to answer two questions: (i) given the Salmonella status of the farm at a certain occasion (equal to the sampling time of the flock), what are the risk factors that the farm will be Salmonella positive at a following occasion? And (ii) what are the risk factors for a farm to be persistently positive for two consecutive flocks? We used surveillance data on 6824 broiler flocks studied for Salmonella infectivity from 2005 to 2006 in Belgium. The farms were tested regularly (3 weeks before slaughter of each broiler flock) for the presence of Salmonella based on multiple faecal samples per flock on a farm yielding clustered data. Generalized estimating equations, alternating logistic regression models, and random-intercept logistic regression models were employed to analyse these correlated binary data. Our results indicated that there are many factors that influence Salmonella risk in broiler flocks, and that they interact. Accounting for interactions between risk factors leads to an improved determination of those risk factors that increase infection with Salmonella. For the conditional analysis, the risk factors found to increase the risk of Salmonella infection on a farm at a current occasion given the previous Salmonella status included: Salmonella infection of day-old chicks (of the current flock); a previously infected flock even though the farm was equipped with a hygiene place to change clothes prior to entering the broiler house; having temporary workmen when there was a separation between birds of different species; and separating birds of different species in the Walloon region relative to the Flanders region. Sanitary measures such as a cleaning and disinfecting procedure conducted by an external cleaning firm, applying the all-in all-out procedure, and hand washing decreased the risk despite their interaction with other factors. From the joint analysis, the most important factors identified for increased risk for persistent Salmonella on a farm involved the interaction between having temporary workmen when there were poultry or farmers in contact with foreign poultry or persons, and the interaction between having temporary workmen when there were poultry or farmers in contact with external poultry or persons.  相似文献   

Evaluation of the Rice pelvimeter for measuring pelvic area in double muscled Belgian Blue cows     

I. Kolkman  G. Hoflack  S. Aerts  R.D. Murray  G. Opsomer  D. Lips   《Livestock Science》2009,121(2-3):259-266

The accuracy of the Rice pelvimeter for measuring pelvic area of double muscled Belgian Blue (BB) cattle was investigated by comparing measurements in the live animal with these obtained from the same animal after slaughter. Pelvic measurements from 466 BB-cows aged 2–10 years old and of an excellent carcass qualification (S and E in the SEUROP classification) were measured with the pelvimeter approximately 12 h prior to, and by graded ruler within 2 h after, slaughter. The mean difference of measurements between living and dead cattle were − 0.2 cm for pelvic width (95% limits of agreement − 2.5–2.1 cm), and 1.2 cm for pelvic height (95% limits of agreement − 1.8–4.1 cm). The correlation coefficient between all pelvic measurements was between 0.46 and 0.59 (p < 0.001). The age of the animals influenced only pelvic height whilst carcass weight influenced all the components of the pelvic area. There was a significant correlation between the pelvimetric measurements of the birth canal in living cattle obtained using a Rice pelvimeter compared to actual measurements obtained from the carcass. The Rice pelvimeter is a suitable tool for assessing accurate pelvic skeletal conformation and to select animals in this breed with a larger birth canal and hence less dystocia problems.  相似文献   

Environmental effects on growth and sporulation of <Emphasis Type="Italic">Fusarium</Emphasis> spp. causing internal fruit rot in bell pepper     

M. Frans  R. Aerts  S. Van Laethem  J. Ceusters 《European journal of plant pathology / European Foundation for Plant Pathology》2017,149(4):875-883

Internal fruit rot in bell pepper (Capsicum annuum L.) is mainly caused by members of the Fusarium lactis species complex (FLASC) and to a lesser extent by Fusarium oxysporum and Fusarium proliferatum. Despite the importance of the disease, there is hardly no information about growth, sporulation and germination dynamics of FLASC. In order to understand the dominance of FLASC as main pathogen of internal fruit rot, the effects of temperature (5 °C – 35 °C), water activity (a_w 0.76–0.96), pH (pH 3 - pH 9) and oxygen concentration (2.5% - 20%) on growth and sporulation of all three Fusarium species were compared. In addition, germination kinetics were also investigated. FLASC showed optimal mycelium growth and sporulation in the narrow range of 25 °C, while both other strains were also tolerant for higher temperatures to 30 °C. FLASC was also characterized by a broad pH optimum from pH 3–7 while F. oxysporum (pH 4–7) and F. proliferatum (pH 5–8) were more demanding concerning pH. In addition, optimal sporulation occurred in the acid region for FLASC (pH 3) whilst neutral and alkaline pH were more favourable for the other species. Germination kinetics revealed that FLASC did not benefit from an earlier and/or faster germination process. A thorough understanding of the growth characteristics and dominance of FLASC as main pathogen for internal fruit rot is inevitable to develop sustainable control measures for the disease.  相似文献