481 research outputs found
Imbibition in Disordered Media
The physics of liquids in porous media gives rise to many interesting
phenomena, including imbibition where a viscous fluid displaces a less viscous
one. Here we discuss the theoretical and experimental progress made in recent
years in this field. The emphasis is on an interfacial description, akin to the
focus of a statistical physics approach. Coarse-grained equations of motion
have been recently presented in the literature. These contain terms that take
into account the pertinent features of imbibition: non-locality and the
quenched noise that arises from the random environment, fluctuations of the
fluid flow and capillary forces. The theoretical progress has highlighted the
presence of intrinsic length-scales that invalidate scale invariance often
assumed to be present in kinetic roughening processes such as that of a
two-phase boundary in liquid penetration. Another important fact is that the
macroscopic fluid flow, the kinetic roughening properties, and the effective
noise in the problem are all coupled. Many possible deviations from simple
scaling behaviour exist, and we outline the experimental evidence. Finally,
prospects for further work, both theoretical and experimental, are discussed.Comment: Review article, to appear in Advances in Physics, 53 pages LaTe
Can Urban Air Mobility become reality? Opportunities, challenges and selected research results
Urban Air Mobility (UAM) is a new air transportation system for passengers
and cargo in urban environments, enabled by new technologies and integrated
into multimodal transportation systems. The vision of UAM comprises the mass
use in urban and suburban environments, complementing existing transportation
systems and contributing to the decarbonization of the transport sector.
Initial attempts to create a market for urban air transportation in the last
century failed due to lack of profitability and community acceptance.
Technological advances in numerous fields over the past few decades have led to
a renewed interest in urban air transportation. UAM is expected to benefit
users and to also have a positive impact on the economy by creating new markets
and employment opportunities for manufacturing and operation of UAM vehicles
and the construction of related ground infrastructure. However, there are also
concerns about noise, safety and security, privacy and environmental impacts.
Therefore, the UAM system needs to be designed carefully to become safe,
affordable, accessible, environmentally friendly, economically viable and thus
sustainable. This paper provides an overview of selected key research topics
related to UAM and how the German Aerospace Center (DLR) contributed to this
research in the project "HorizonUAM - Urban Air Mobility Research at the German
Aerospace Center (DLR)". Selected research results that support the realization
of the UAM vision are briefly presented.Comment: 20 pages, 7 figures, project HorizonUA
Linkage study of 14 candidate genes and loci in four large Dutch families with vesico-ureteral reflux
Vesico-ureteral reflux (VUR) is a major contributing factor to end-stage renal disease in paediatric patients. Primary VUR is a familial disorder, but little is known about its genetic causes. To investigate the involvement of 12 functional candidate genes and two reported loci in VUR, we performed a linkage study in four large, Dutch, multi-generational families with multiple affected individuals. We were unable to detect linkage to any of the genes and loci and could exclude the GDNF, RET, SLIT2, SPRY1, PAX2, AGTR2, UPK1A and UPK3A genes and the 1p13 and 20p13 loci from linkage to VUR. Our results provide further evidence that there appears to be genetic heterogeneity in VUR
When is working memory important for arithmetic?: the impact of strategy and age
Our ability to perform arithmetic relies heavily on working memory, the manipulation and maintenance of information in mind. Previous research has found that in adults, procedural strategies, particularly counting, rely on working memory to a greater extent than retrieval strategies. During childhood there are changes in the types of strategies employed, as well as an increase in the accuracy and efficiency of strategy execution. As such it seems likely that the role of working memory in arithmetic may also change, however children and adults have never been directly compared. This study used traditional dual-task methodology, with the addition of a control load condition, to investigate the extent to which working memory requirements for different arithmetic strategies change with age between 9-11 years, 12-14 years and young adulthood. We showed that both children and adults employ working memory when solving arithmetic problems, no matter what strategy they choose. This study highlights the importance of considering working memory in understanding the difficulties that some children and adults have with mathematics, as well as the need to include working memory in theoretical models of mathematical cognition
Networks uncover hidden lexical borrowing in Indo-European language evolution
Language evolution is traditionally described in terms of family trees with ancestral languages splitting into descendent languages. However, it has long been recognized that language evolution also entails horizontal components, most commonly through lexical borrowing. For example, the English language was heavily influenced by Old Norse and Old French; eight per cent of its basic vocabulary is borrowed. Borrowing is a distinctly non-tree-like process—akin to horizontal gene transfer in genome evolution—that cannot be recovered by phylogenetic trees. Here, we infer the frequency of hidden borrowing among 2346 cognates (etymologically related words) of basic vocabulary distributed across 84 Indo-European languages. The dataset includes 124 (5%) known borrowings. Applying the uniformitarian principle to inventory dynamics in past and present basic vocabularies, we find that 1373 (61%) of the cognates have been affected by borrowing during their history. Our approach correctly identified 117 (94%) known borrowings. Reconstructed phylogenetic networks that capture both vertical and horizontal components of evolutionary history reveal that, on average, eight per cent of the words of basic vocabulary in each Indo-European language were involved in borrowing during evolution. Basic vocabulary is often assumed to be relatively resistant to borrowing. Our results indicate that the impact of borrowing is far more widespread than previously thought
Kidney Development in the Absence of Gdnf and Spry1 Requires Fgf10
GDNF signaling through the Ret receptor tyrosine kinase (RTK) is required for ureteric bud (UB) branching morphogenesis during kidney development in mice and humans. Furthermore, many other mutant genes that cause renal agenesis exert their effects via the GDNF/RET pathway. Therefore, RET signaling is believed to play a central role in renal organogenesis. Here, we re-examine the extent to which the functions of Gdnf and Ret are unique, by seeking conditions in which a kidney can develop in their absence. We find that in the absence of the negative regulator Spry1, Gdnf, and Ret are no longer required for extensive kidney development. Gdnf−/−;Spry1−/− or Ret−/−;Spry1−/− double mutants develop large kidneys with normal ureters, highly branched collecting ducts, extensive nephrogenesis, and normal histoarchitecture. However, despite extensive branching, the UB displays alterations in branch spacing, angle, and frequency. UB branching in the absence of Gdnf and Spry1 requires Fgf10 (which normally plays a minor role), as removal of even one copy of Fgf10 in Gdnf−/−;Spry1−/− mutants causes a complete failure of ureter and kidney development. In contrast to Gdnf or Ret mutations, renal agenesis caused by concomitant lack of the transcription factors ETV4 and ETV5 is not rescued by removing Spry1, consistent with their role downstream of both RET and FGFRs. This shows that, for many aspects of renal development, the balance between positive signaling by RTKs and negative regulation of this signaling by SPRY1 is more critical than the specific role of GDNF. Other signals, including FGF10, can perform many of the functions of GDNF, when SPRY1 is absent. But GDNF/RET signaling has an apparently unique function in determining normal branching pattern. In contrast to GDNF or FGF10, Etv4 and Etv5 represent a critical node in the RTK signaling network that cannot by bypassed by reducing the negative regulation of upstream signals
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