459 research outputs found
Stability Analysis of a Hybrid Cellular Automaton Model of Cell Colony Growth
Cell colonies of bacteria, tumour cells and fungi, under nutrient limited
growth conditions, exhibit complex branched growth patterns. In order to
investigate this phenomenon we present a simple hybrid cellular automaton model
of cell colony growth. In the model the growth of the colony is limited by a
nutrient that is consumed by the cells and which inhibits cell division if it
falls below a certain threshold. Using this model we have investigated how the
nutrient consumption rate of the cells affects the growth dynamics of the
colony. We found that for low consumption rates the colony takes on a Eden-like
morphology, while for higher consumption rates the morphology of the colony is
branched with a fractal geometry. These findings are in agreement with previous
results, but the simplicity of the model presented here allows for a linear
stability analysis of the system. By observing that the local growth of the
colony is proportional to the flux of the nutrient we derive an approximate
dispersion relation for the growth of the colony interface. This dispersion
relation shows that the stability of the growth depends on how far the nutrient
penetrates into the colony. For low nutrient consumption rates the penetration
distance is large, which stabilises the growth, while for high consumption
rates the penetration distance is small, which leads to unstable branched
growth. When the penetration distance vanishes the dispersion relation is
reduced to the one describing Laplacian growth without ultra-violet
regularisation. The dispersion relation was verified by measuring how the
average branch width depends on the consumption rate of the cells and shows
good agreement between theory and simulations.Comment: 8 pages, 6 figure
Application of the Kissimmee River Hydraulic Model and Floodplain Spatial Analysis Tool to the Development of Floodplain Inundation Targets for the Kissimmee River Restoration Project
Source: ICHE Conference Archive - https://mdi-de.baw.de/icheArchiv
Quantum Noise and Polarization Fluctuations in Vertical Cavity Surface Emitting Lasers
We investigate the polarization fluctuations caused by quantum noise in
quantum well vertical cavity surface emitting lasers (VCSELs). Langevin
equations are derived on the basis of a generalized rate equation model in
which the influence of competing gain-loss and frequency anisotropies is
included. This reveals how the anisotropies and the quantum well confinement
effects shape the correlations and the magnitude of fluctuations in ellipticity
and in polarization direction. According to our results all parameters used in
the rate equations may be obtained experimentally from precise time resolved
measurements of the intensity and polarization fluctuations in the emitted
laser light. To clarify the effects of anisotropies and of quantum well
confinement on the laser process in VCSELs we therefore propose time resolved
measurements of the polarization fluctuations in the laser light. In
particular, such measurements allow to distinguish the effects of frequency
anisotropy and of gain-loss anisotropy and would provide data on the spin
relaxation rate in the quantum well structure during cw operation as well as
representing a new way of experimentally determinig the linewidth enhancement
factor alpha.Comment: 16 pages and 3 Figures, RevTex, to be published in Phys. Rev.
Optically-pumped dilute nitride spin-VCSEL
We report the first room temperature optical spin-injection of a dilute nitride 1300 nm vertical-cavity surface-emitting laser (VCSEL) under continuous-wave optical pumping. We also present a novel experimental protocol for the investigation of optical spin-injection with a fiber setup. The experimental results indicate that the VCSEL polarization can be controlled by the pump polarization, and the measured behavior is in excellent agreement with theoretical predictions using the spin flip model. The ability to control the polarization of a long-wavelength VCSEL at room temperature emitting at the wavelength of 1.3 μm opens up a new exciting research avenue for novel uses in disparate fields of technology ranging from spintronics to optical telecommunication networks. © 2012 Optical Society of America
Genetic and molecular identification of three human TPP1 functions in telomerase action: recruitment, activation, and homeostasis set point regulation
Telomere length homeostasis is essential for the long-term survival of stem cells, and its set point determines the proliferative capacity of differentiated cell lineages by restricting the reservoir of telomeric repeats. Knockdown and overexpression studies in human tumor cells showed that the shelterin subunit TPP1 recruits telomerase to telomeres through a region termed the TEL patch. However, these studies do not resolve whether the TPP1 TEL patch is the only mechanism for telomerase recruitment and whether telomerase regulation studied in tumor cells is representative of nontransformed cells such as stem cells. Using genome engineering of human embryonic stem cells, which have physiological telomere length homeostasis, we establish that the TPP1 TEL patch is genetically essential for telomere elongation and thus long-term cell viability. Furthermore, genetic bypass, protein fusion, and intragenic complementation assays define two distinct additional mechanisms of TPP1 involvement in telomerase action at telomeres. We demonstrate that TPP1 provides an essential step of telomerase activation as well as feedback regulation of telomerase by telomere length, which is necessary to determine the appropriate telomere length set point in human embryonic stem cells. These studies reveal and resolve multiple TPP1 roles in telomere elongation and stem cell telomere length homeostasis. Keywords: embryonic stem cells; human genome engineering; shelterin; telomerase telomere maintenanceNational Institutes of Health (U.S.) (Grant R37-CA084198)National Institutes of Health (U.S.) (Grant RO1-CA087869)National Institutes of Health (U.S.) (Grant RO1-HD045022
Effect of a resistance exercise at acute moderate altitude on muscle health biomarkers
The intensification of the stress response during resistance training (RT) under hypoxia conditions could trigger unwanted effects that compromise muscle health and, therefore, the ability of the muscle to adapt to longer training periods. We examined the effect of acute moderate terrestrial hypoxia on metabolic, inflammation, antioxidant capacity and muscle atrophy biomarkers after a single RT session in a young male population. Twenty healthy volunteers allocated to the normoxia (N < 700 m asl) or moderate altitude (HH = 2320 m asl) group participated in this study. Before and throughout the 30 min following the RT session (3 × 10 reps, 90 s rest, 70% 1RM), venous blood samples were taken and analysed for circulating calcium, inorganic phosphate, cytokines (IL-6, IL-10 and TNF-α), total antioxidant capacity (TAC) and myostatin. Main results displayed a marked metabolic stress response after the RT in both conditions. A large to very large proportional increase in the adjusted to pre-exercise change of inflammatory and anti-inflammatory markers favoured HH (serum TNF-α [ES = 1.10; p = 0.024] and IL-10 [ES = 1.31; p = 0.009]). The exercise produced a similar moderate increment of myostatin in both groups, followed by a moderate non-significant reduction in HH throughout the recovery (ES = − 0.72; p = 0.21). The RT slightly increased the antioxidant response regardless of the environmental condition. These results revealed no clear impact of RT under acute hypoxia on the metabolic, TAC and muscle atrophy biomarkers. However, a coordinated pro/anti-inflammatory response balances the potentiated effect of RT on systemic inflammatioUniversidad de Granada/CBUA This research was funded by the Spanish Ministry of ScienceInnovation and Universities (grant number PGC2018-097388-B-I00-MCI/AEI/FEDER, UE)FEDER/Junta de Andalucía-Ministry of Economic TransformationIndustry, Knowledge and Universities (grant number B-CTS-374-UGR20
Seismic Vulnerability Assessment of Priority Cultural Heritage Structures in the Philippines
At the end of 2013 two catastrophic events occurred in the Philippines: the M 7.2 earthquake
in Bohol and the strongest ever recorded Typhoon Haiyan, causing destruction across the islands of Cebu,
Bohol and the Visayas region. These events raised the need to carry out a multi-hazard risk assessment of
heritage buildings, many of which were irretrievably lost in the disasters. Philippines’ Department of
Tourism engaged ARS Progetti S.P.A., Rome, Italy, and the Center for Conservation of Cultural Property
and Environment in the Tropics (CCCPET), University of Sto. Tomas, Manila, to undertake the
“Assessment of the Multi-Hazard Vulnerability of Priority Cultural Heritage Structures in the
Philippines”, with experts from University College London, UK, and De La Salle University.
The main objective of the project was to reduce the vulnerability of cultural heritage structures to multiple
natural hazards, including earthquake, typhoon, flood, by: (i) prioritizing of specific structures based on
hazard maps and historical records; (ii) assessing their vulnerability; and (iii) recommending options to
mitigate the impacts on them. The paper presents the methodology introduced to determine the seismic
risk these heritage buildings are exposed to. All the selected cultural heritage structures are under the
jurisdiction of the National Museum Commission of Philippines and of the National Commission for
Culture and Arts
Creativity in Citizen Cyberscience
An interview study was conducted to explore volunteers’ experiences of creativity in citizen cyberscience. Participants were recruited from 4 projects: GeoTag-X, Virtual Atom Smasher, Synthetic Biology, and Extreme Citizen Science. Ninety-six interviews were conducted in total: 86 with volunteers (citizen scientists) and 10 with professional scientists. The resulting thematic analysis revealed that volunteers are involved in a range of creative activities, such as discussing ideas, suggesting improvements, gamification, artwork, creative writing, and outreach activities. We conclude that the majority of creative products are community-related. Creativity in citizen cyberscience is a collective process: volunteers create within a project and a community, both for themselves and for others
Non-Abelian discrete gauge symmetries in 4d string models
We study the realization of non-Abelian discrete gauge symmetries in 4d field
theory and string theory compactifications. The underlying structure
generalizes the Abelian case, and follows from the interplay between gaugings
of non-Abelian isometries of the scalar manifold and field identifications
making axion-like fields periodic. We present several classes of string
constructions realizing non-Abelian discrete gauge symmetries. In particular,
compactifications with torsion homology classes, where non-Abelianity arises
microscopically from the Hanany-Witten effect, or compactifications with
non-Abelian discrete isometry groups, like twisted tori. We finally focus on
the more interesting case of magnetized branes in toroidal compactifications
and quotients thereof (and their heterotic and intersecting duals), in which
the non-Abelian discrete gauge symmetries imply powerful selection rules for
Yukawa couplings of charged matter fields. In particular, in MSSM-like models
they correspond to discrete flavour symmetries constraining the quark and
lepton mass matrices, as we show in specific examples.Comment: 58 pages; minor typos corrected and references adde
Yukawa hierarchies at the point of in F-theory
We analyse the structure of Yukawa couplings in local SU(5) F-theory models
with enhancement. In this setting the symmetry is broken down to
SU(5) by a 7-brane configuration described by T-branes, all the Yukawa
couplings are generated in the vicinity of a point and only one family of
quarks and leptons is massive at tree-level. The other two families obtain
their masses when non-perturbative effects are taken into account, being
hierarchically lighter than the third family. However, and contrary to previous
results, we find that this hierarchy of fermion masses is not always
appropriate to reproduce measured data. We find instead that different T-brane
configurations breaking to SU(5) give rise to distinct hierarchical
patterns for the holomorphic Yukawa couplings. Only some of these patterns
allow to fit the observed fermion masses with reasonable local model parameter
values, adding further constraints to the construction of F-theory GUTs. We
consider an model where such appropriate hierarchy is realised and
compute its physical Yukawas, showing that realistic charged fermions masses
can indeed be obtained in this case.Comment: 46 pages + appendices, 5 figures. v2, added references and typos
corrected, version accepted on JHEP. v3, typos correcte
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