Catalogue Search | MBRL
Are you sure you want to remove the book from the shelf?
{{itemTitle}}
72,766
result(s) for
"Lee, L. A."
Sort by:
Large contribution of natural aerosols to uncertainty in indirect forcing
The effect of anthropogenic aerosols on cloud droplet concentrations and radiative properties is the source of one of the largest uncertainties in the radiative forcing of climate over the industrial period. This uncertainty affects our ability to estimate how sensitive the climate is to greenhouse gas emissions. Here we perform a sensitivity analysis on a global model to quantify the uncertainty in cloud radiative forcing over the industrial period caused by uncertainties in aerosol emissions and processes. Our results show that 45 per cent of the variance of aerosol forcing since about 1750 arises from uncertainties in natural emissions of volcanic sulphur dioxide, marine dimethylsulphide, biogenic volatile organic carbon, biomass burning and sea spray. Only 34 per cent of the variance is associated with anthropogenic emissions. The results point to the importance of understanding pristine pre-industrial-like environments, with natural aerosols only, and suggest that improved measurements and evaluation of simulated aerosols in polluted present-day conditions will not necessarily result in commensurate reductions in the uncertainty of forcing estimates.
It has been assumed that a better understanding of the effects of anthropogenic aerosols will greatly reduce the large uncertainties associated with our predictions of the radiative forcing effects of aerosols on climate; however, this study shows that nearly half of the uncertainty in the radiative effect of aerosols on clouds derives from uncertainties in pre-industrial natural aerosols.
Natural versus anthropogenic aerosols in climate forcing
Firmly establishing the influence of aerosols on cloud albedo — their forcing effect on climate in essence — is one of the greatest challenges of modern climate science. It is often tacitly assumed that the continued high uncertainties are linked mainly to anthropogenic emissions. In other words, if the anthropogenic effects could be better understood, so would the overall effect. Now Ken Carslaw and colleagues present an analysis of 28 parameters representing aerosol and precursor gas emissions and other factors that could influence cloud brightness. They find that only 34 per cent of the variance in aerosol forcing since pre-industrial times (around 1750) is associated with anthropogenic emissions, with 45 per cent of the variance linked to natural emissions of volcanic sulphur dioxide, marine dimethylsulphide and other natural sources. This work casts doubts on the degree of progress that can be made solely through advances in the understanding of anthropogenic aerosols and suggests that we need to discover more about the workings of the pre-industrial environment, when natural aerosols were predominant.
Journal Article
Emergence of Azole Resistance in Aspergillus fumigatus and Spread of a Single Resistance Mechanism
Resistance to triazoles was recently reported in Aspergillus fumigatus isolates cultured from patients with invasive aspergillosis. The prevalence of azole resistance in A. fumigatus is unknown. We investigated the prevalence and spread of azole resistance using our culture collection that contained A. fumigatus isolates collected between 1994 and 2007.
We investigated the prevalence of itraconazole (ITZ) resistance in 1,912 clinical A. fumigatus isolates collected from 1,219 patients in our University Medical Centre over a 14-y period. The spread of resistance was investigated by analyzing 147 A. fumigatus isolates from 101 patients, from 28 other medical centres in The Netherlands and 317 isolates from six other countries. The isolates were characterized using phenotypic and molecular methods. The electronic patient files were used to determine the underlying conditions of the patients and the presence of invasive aspergillosis. ITZ-resistant isolates were found in 32 of 1,219 patients. All cases were observed after 1999 with an annual prevalence of 1.7% to 6%. The ITZ-resistant isolates also showed elevated minimum inhibitory concentrations of voriconazole, ravuconazole, and posaconazole. A substitution of leucine 98 for histidine in the cyp51A gene, together with two copies of a 34-bp sequence in tandem in the gene promoter (TR/L98H), was found to be the dominant resistance mechanism. Microsatellite analysis indicated that the ITZ-resistant isolates were genetically distinct but clustered. The ITZ-sensitive isolates were not more likely to be responsible for invasive aspergillosis than the ITZ-resistant isolates. ITZ resistance was found in isolates from 13 patients (12.8%) from nine other medical centres in The Netherlands, of which 69% harboured the TR/L98H substitution, and in six isolates originating from four other countries.
Azole resistance has emerged in A. fumigatus and might be more prevalent than currently acknowledged. The presence of a dominant resistance mechanism in clinical isolates suggests that isolates with this mechanism are spreading in our environment.
Journal Article
James Baldwin : challenging authors
The recognition and study of African American (AA) artists and public intellectuals often include Martin Luther King, Jr., and occasionally Booker T. Washington, W.E.B. DuBois, and Malcolm X. The literary canon also adds Ralph Ellison, Richard White, Langston Hughes, and others such as female writers Zora Neale Hurston, Maya Angelou, and Alice Walker. Yet, the acknowledgement of AA artists and public intellectuals tends to skew the voices and works of those included toward normalized portrayals that fi t well within foundational aspects of the American myths refl ected in and perpetuated by traditional schooling. Further, while many AA artists and public intellectuals are distorted by mainstream media, public and political characterizations, and the curriculum, several powerful AA voices are simply omitted, ignored, including James Baldwin. This edited volume gathers a collection of essays from a wide range of perspectives that confront Baldwin's impressive and challenging canon as well as his role as a public intellectual. Contributors also explore Baldwin as a confrontational voice during his life and as an enduring call for justice.
Book
The magnitude and causes of uncertainty in global model simulations of cloud condensation nuclei
Aerosol–cloud interaction effects are a major source of uncertainty in climate models so it is important to quantify the sources of uncertainty and thereby direct research efforts. However, the computational expense of global aerosol models has prevented a full statistical analysis of their outputs. Here we perform a variance-based analysis of a global 3-D aerosol microphysics model to quantify the magnitude and leading causes of parametric uncertainty in model-estimated present-day concentrations of cloud condensation nuclei (CCN). Twenty-eight model parameters covering essentially all important aerosol processes, emissions and representation of aerosol size distributions were defined based on expert elicitation. An uncertainty analysis was then performed based on a Monte Carlo-type sampling of an emulator built for each model grid cell. The standard deviation around the mean CCN varies globally between about ±30% over some marine regions to ±40–100% over most land areas and high latitudes, implying that aerosol processes and emissions are likely to be a significant source of uncertainty in model simulations of aerosol–cloud effects on climate. Among the most important contributors to CCN uncertainty are the sizes of emitted primary particles, including carbonaceous combustion particles from wildfires, biomass burning and fossil fuel use, as well as sulfate particles formed on sub-grid scales. Emissions of carbonaceous combustion particles affect CCN uncertainty more than sulfur emissions. Aerosol emission-related parameters dominate the uncertainty close to sources, while uncertainty in aerosol microphysical processes becomes increasingly important in remote regions, being dominated by deposition and aerosol sulfate formation during cloud-processing. The results lead to several recommendations for research that would result in improved modelling of cloud–active aerosol on a global scale.
Journal Article
كيف تروض ثعلبا وتصنع كلبا : علماء حالمون وحكاية سيبيرية عن التطور السريع
هي قصة، جزء منها حول العلم، وجزء منها تبدو كقصة خيالية روسية، وجزء منها أشبه بفلم تجسس وغموض، في هذا الكتاب، يقوم كل من دوغتاكن وتروت بسرد حكاية هذه التجربة العظيمة، والنتجية مجموعة من الثعالب الأليفة وتحديد الأسس الوراثية لتدجينها و\"لقد قاموا بتجربتهم في مزرعة في سيبيريا، وخلال عقود عديدة قاموا بتزوية أكثر الثعالب ألفة في جيلها\".
BOOK
Emulation of a complex global aerosol model to quantify sensitivity to uncertain parameters
Sensitivity analysis of atmospheric models is necessary to identify the processes that lead to uncertainty in model predictions, to help understand model diversity through comparison of driving processes, and to prioritise research. Assessing the effect of parameter uncertainty in complex models is challenging and often limited by CPU constraints. Here we present a cost-effective application of variance-based sensitivity analysis to quantify the sensitivity of a 3-D global aerosol model to uncertain parameters. A Gaussian process emulator is used to estimate the model output across multi-dimensional parameter space, using information from a small number of model runs at points chosen using a Latin hypercube space-filling design. Gaussian process emulation is a Bayesian approach that uses information from the model runs along with some prior assumptions about the model behaviour to predict model output everywhere in the uncertainty space. We use the Gaussian process emulator to calculate the percentage of expected output variance explained by uncertainty in global aerosol model parameters and their interactions. To demonstrate the technique, we show examples of cloud condensation nuclei (CCN) sensitivity to 8 model parameters in polluted and remote marine environments as a function of altitude. In the polluted environment 95 % of the variance of CCN concentration is described by uncertainty in the 8 parameters (excluding their interaction effects) and is dominated by the uncertainty in the sulphur emissions, which explains 80 % of the variance. However, in the remote region parameter interaction effects become important, accounting for up to 40 % of the total variance. Some parameters are shown to have a negligible individual effect but a substantial interaction effect. Such sensitivities would not be detected in the commonly used single parameter perturbation experiments, which would therefore underpredict total uncertainty. Gaussian process emulation is shown to be an efficient and useful technique for quantifying parameter sensitivity in complex global atmospheric models.
Journal Article
تصميم وتشغيل نظم الري المزرعي
يعاني الوطن العربي من عجز في مصادره المائية لوقوعه ضمن المناطق الجافة وشبه الجافة، علاوة على الاستنزاف الجائر لمياهه المتاحة نتيجة الممارسات الخاطئة في تطبيقاته وغياب وسوء إدارته، أضف إلى ذلك السلب الذي يتعرض له هذا المصدر الحيوي أو جزء منه من بعض الدول المجاورة دون مراعاة القوانين الدولية أو حسن الجوار مما زاد من مشاطل شح المياة. لذا أصبح لزاما علينا كأمة بكافة شرائحها الاجتماعية والمهنية والزراعية العمل على ترشيد استخدام المياة خاصة في المجال الزراعي واتباع كافة الوسائل والتقنيات الحديثة لتحقيق هذه الغايات.
BOOK
Mapping the uncertainty in global CCN using emulation
In the last two IPCC assessments aerosol radiative forcings have been given the largest uncertainty range of all forcing agents assessed. This forcing range is really a diversity of simulated forcings in different models. An essential step towards reducing model uncertainty is to quantify and attribute the sources of uncertainty at the process level. Here, we use statistical emulation techniques to quantify uncertainty in simulated concentrations of July-mean cloud condensation nuclei (CCN) from a complex global aerosol microphysics model. CCN was chosen because it is the aerosol property that controls cloud drop concentrations, and therefore the aerosol indirect radiative forcing effect. We use Gaussian process emulation to perform a full variance-based sensitivity analysis and quantify, for each model grid box, the uncertainty in simulated CCN that results from 8 uncertain model parameters. We produce global maps of absolute and relative CCN sensitivities to the 8 model parameter ranges and derive probability density functions for simulated CCN. The approach also allows us to include the uncertainty from interactions between these parameters, which cannot be quantified in traditional one-at-a-time sensitivity tests. The key findings from our analysis are that model CCN in polluted regions and the Southern Ocean are mostly only sensitive to uncertainties in emissions parameters but in all other regions CCN uncertainty is driven almost exclusively by uncertainties in parameters associated with model processes. For example, in marine regions between 30° S and 30° N model CCN uncertainty is driven mainly by parameters associated with cloud-processing of Aitken-sized particles whereas in polar regions uncertainties in scavenging parameters dominate. In these two regions a single parameter dominates but in other regions up to 50% of the variance can be due to interaction effects between different parameters. Our analysis provides direct quantification of the reduction in variance that would result if a parameter could be specified precisely. When extended to all process parameters the approach presented here will therefore provide a clear global picture of how improved knowledge of aerosol processes would translate into reduced model uncertainty.
Journal Article