408 research outputs found
Quantitative predictions on auxin-induced polar distribution of PIN proteins during vein formation in leaves
The dynamic patterning of the plant hormone auxin and its efflux facilitator
the PIN protein are the key regulator for the spatial and temporal organization
of plant development. In particular auxin induces the polar localization of its
own efflux facilitator. Due to this positive feedback auxin flow is directed
and patterns of auxin and PIN arise. During the earliest stage of vein
initiation in leaves auxin accumulates in a single cell in a rim of epidermal
cells from which it flows into the ground meristem tissue of the leaf blade.
There the localized auxin supply yields the successive polarization of PIN
distribution along a strand of cells. We model the auxin and PIN dynamics
within cells with a minimal canalization model. Solving the model analytically
we uncover an excitable polarization front that triggers a polar distribution
of PIN proteins in cells. As polarization fronts may extend to opposing
directions from their initiation site we suggest a possible resolution to the
puzzling occurrence of bipolar cells, such we offer an explanation for the
development of closed, looped veins. Employing non-linear analysis we identify
the role of the contributing microscopic processes during polarization.
Furthermore, we deduce quantitative predictions on polarization fronts
establishing a route to determine the up to now largely unknown kinetic rates
of auxin and PIN dynamics.Comment: 9 pages, 4 figures, supplemental information included, accepted for
publication in Eur. Phys. J.
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The method of Laplace Transform MultiQuadrics (LTMQ) for the solution of the groundwater flow equation
This paper presents a new numerical method, the Laplace Transform MultiQuadrics (LTMQ) method, developed for the solution of the diffusion-type parabolic Partial Differential Equation (PDE) of fluid flow through porous media. LTMQ combines a MultiQuadrics (MQ) approximation scheme with a Laplace transform formulation. The use of MQ in the spatial approximations allows the accurate description of problems in complex porous media with a very limited number of nodes. The Laplace transform formulation eliminates the need for time discretization, thus allowing an unlimited time step size without any loss of accuracy. LTMQ is tested against results from three test problems of groundwater flow obtained from a standard Finite Difference (FD) model, as well as from analytical solutions. An excellent agreement between the LTMQ and the analytical and FD solutions is observed, while significant reductions in computer execution times may be achieved
An intense narrow equatorial jet in Jupiterâs lower stratosphere observed by JWST
The atmosphere of Jupiter has eastâwest zonal jets that alternate as a function of latitude as tracked by cloud motions at tropospheric levels. Above and below the cold tropopause at ~100âmbar, the equatorial atmosphere is covered by hazes at levels where thermal infrared observations used to characterize the dynamics of the stratosphere lose part of their sensitivity. James Webb Space Telescope observations of Jupiter in July 2022 show these hazes in higher detail than ever before and reveal the presence of an intense (140âmâsâ1) equatorial jet at 100â200âmbar (70âmâsâ1 faster than the zonal winds at the cloud level) that is confined to ±3° of the equator and is located below stratospheric thermal oscillations that extend at least from 0.1 to 40âmbar and repeat in multiyear cycles. This suggests that the new jet is a deep part of Jupiterâs Equatorial Stratospheric Oscillation and may therefore vary in strength over time.JWST-ERS-01373, NASA/ESA Hubble Space Telescope programmes no. 16913, 15502 and 16790, PID2019-109467GB-I00 funded by MCIN/AEI/10.13039/501100011033/, Grupos Gobierno Vasco IT1742-22. I.d.; European Research Council Consolidator Grant (under the European Unionâs Horizon 2020 research and innovation programme, grant agreement no. 723890), STFC PhD Studentship, NASA grants 80NSSC21K1418 and 80NSSC19K0894
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Wavenumbers for currents on infinite- and finite-length wires in a chiral medium
There is increasing interest in determining the electromagnetic properties of material media differing from free space and the effects thereof on the radiation, propagation, and scattering of electromagnetic fields. A material property of special present interest is that of chirality. Chirality manifests itself as a handedness'' wherein a chiral medium does not support propagation of a linearly-polarized plane wave, but which instead decomposes into two circularly-polarized waves that propagate at different speeds. Initial work in this area was devoted to developing various analytical solutions to some basic problems such as the Green's Dyadic for a point current source. Attention is now being increasingly devoted to using this early work for a variety of applications such as analyzing antennas in chiral media scattering from chiral objects; scattering from objects having chiral coatings; and reflection from planar chiral interfaces. The focus of the work described here is determining the wavenumbers (={minus}{alpha}{minus}j{beta}) of the current waves excited on wire antennas located in an infinite chiral medium using two complementary approaches. One is to use an extension of an existing computer model (NEC) that permits modeling of arbitrary wire objects located in an infinite chiral medium. The other is to develop a solution for an infinitely long cylindrical antenna also located in an infinite chiral medium. The latter canonical problem is of interest in its own right as well as providing a means for achieving mutual validation with the NEC model. 9 refs
First upper limits from LIGO on gravitational wave bursts
We report on a search for gravitational wave bursts using data from the first
science run of the LIGO detectors. Our search focuses on bursts with durations
ranging from 4 ms to 100 ms, and with significant power in the LIGO sensitivity
band of 150 to 3000 Hz. We bound the rate for such detected bursts at less than
1.6 events per day at 90% confidence level. This result is interpreted in terms
of the detection efficiency for ad hoc waveforms (Gaussians and sine-Gaussians)
as a function of their root-sum-square strain h_{rss}; typical sensitivities
lie in the range h_{rss} ~ 10^{-19} - 10^{-17} strain/rtHz, depending on
waveform. We discuss improvements in the search method that will be applied to
future science data from LIGO and other gravitational wave detectors.Comment: 21 pages, 15 figures, accepted by Phys Rev D. Fixed a few small typos
and updated a few reference
Simulation and background characterisation of the SABRE South experiment
Published online: 28 September 2023SABRE(Sodium iodide with Active Background REjection) is a direct detection darkmatter experiment based on arrays of radio-pureNaI(Tl) crystals.The experiment aims at achieving an ultra-low background rate and its primary goal is to confirm or refute the results from the DAMA/LIBRA experiment. The SABRE Proof-of-Principle phase was carried out in 2020â2021 at the Gran Sasso National Laboratory (LNGS), in Italy. The next phase consists of two full-scale experiments: SABRE South at the Stawell Underground Physics Laboratory, in Australia, and SABRE North at LNGS. This paper focuses on SABRE South and presents a detailed simulation of the detector, which is used to characterise the background for darkmatter searches includingDAMA/ LIBRA-like modulation. We estimate an overall background of 0.72 cpd/kg/keVee in the energy range 1â6 keVee primarily due to radioactive contamination in the crystals. Given this level of background and considering that the SABRE South has a target mass of 50 kg, we expect to exclude (confirm) DAMA/LIBRA modulation at 4 (5)Ï within 2.5 years of data taking.E. Barberio ... I. Bolognino ... G. C. Hill ... K. T. Leaver ... P. McGee ... A. G. Williams ... et al. (SABRE South Collaboration
Size Doesn't Matter: Towards a More Inclusive Philosophy of Biology
notes: As the primary author, OâMalley drafted the paper, and gathered and analysed data (scientific papers and talks). Conceptual analysis was conducted by both authors.publication-status: Publishedtypes: ArticlePhilosophers of biology, along with everyone else, generally perceive life to fall into two broad categories, the microbes and macrobes, and then pay most of their attention to the latter. âMacrobeâ is the word we propose for larger life forms, and we use it as part of an argument for microbial equality. We suggest that taking more notice of microbes â the dominant life form on the planet, both now and throughout evolutionary history â will transform some of the philosophy of biologyâs standard ideas on ontology, evolution, taxonomy and biodiversity. We set out a number of recent developments in microbiology â including biofilm formation, chemotaxis, quorum sensing and gene transfer â that highlight microbial capacities for cooperation and communication and break down conventional thinking that microbes are solely or primarily single-celled organisms. These insights also bring new perspectives to the levels of selection debate, as well as to discussions of the evolution and nature of multicellularity, and to neo-Darwinian understandings of evolutionary mechanisms. We show how these revisions lead to further complications for microbial classification and the philosophies of systematics and biodiversity. Incorporating microbial insights into the philosophy of biology will challenge many of its assumptions, but also give greater scope and depth to its investigations
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