Thermal diffusion by Brownian motion induced fluid stress

The Ludwig-Soret effect, the migration of a species due to a temperature gradient, has been extensively studied without a complete picture of its cause emerging. Here we investigate the dynamics of DNA and spherical particles sub jected to a thermal gradient using a combination of Brownian dynamics and the lattice Boltzmann method. We observe that the DNA molecules will migrate to colder regions of the channel, an observation also made in the experiments of Duhr, et al[1]. In fact, the thermal diffusion coefficient found agrees quantitatively with the experimental value. We also observe that the thermal diffusion coefficient decreases as the radius of the studied spherical particles increases. Furthermore, we observe that the thermal fluctuations-fluid momentum flux coupling induces a gradient in the stress which leads to thermal migration in both systems.Comment: 6 pages, 5 figue

Pressure Modulator Radiometer (PMR) tests

The pressure modulator technique was evaluated for monitoring pollutant gases in the Earth's atmosphere of altitude levels corresponding to the mid and lower troposphere. Using an experimental set up and a 110 cm sample cell, pressure modulator output signals resulting from a range of gas concentrations in the sample cell were examined. Then a 20 cm sample cell was modified so that trace gas properties in the atmosphere could be simulated in the laboratory. These gas properties were measured using an infrared sensor

Composite repetition-aware data structures

In highly repetitive strings, like collections of genomes from the same species, distinct measures of repetition all grow sublinearly in the length of the text, and indexes targeted to such strings typically depend only on one of these measures. We describe two data structures whose size depends on multiple measures of repetition at once, and that provide competitive tradeoffs between the time for counting and reporting all the exact occurrences of a pattern, and the space taken by the structure. The key component of our constructions is the run-length encoded BWT (RLBWT), which takes space proportional to the number of BWT runs: rather than augmenting RLBWT with suffix array samples, we combine it with data structures from LZ77 indexes, which take space proportional to the number of LZ77 factors, and with the compact directed acyclic word graph (CDAWG), which takes space proportional to the number of extensions of maximal repeats. The combination of CDAWG and RLBWT enables also a new representation of the suffix tree, whose size depends again on the number of extensions of maximal repeats, and that is powerful enough to support matching statistics and constant-space traversal.Comment: (the name of the third co-author was inadvertently omitted from previous version

Onset of Patterns in an Ocillated Granular Layer: Continuum and Molecular Dynamics Simulations

We study the onset of patterns in vertically oscillated layers of frictionless dissipative particles. Using both numerical solutions of continuum equations to Navier-Stokes order and molecular dynamics (MD) simulations, we find that standing waves form stripe patterns above a critical acceleration of the cell. Changing the frequency of oscillation of the cell changes the wavelength of the resulting pattern; MD and continuum simulations both yield wavelengths in accord with previous experimental results. The value of the critical acceleration for ordered standing waves is approximately 10% higher in molecular dynamics simulations than in the continuum simulations, and the amplitude of the waves differs significantly between the models. The delay in the onset of order in molecular dynamics simulations and the amplitude of noise below this onset are consistent with the presence of fluctuations which are absent in the continuum theory. The strength of the noise obtained by fit to Swift-Hohenberg theory is orders of magnitude larger than the thermal noise in fluid convection experiments, and is comparable to the noise found in experiments with oscillated granular layers and in recent fluid experiments on fluids near the critical point. Good agreement is found between the mean field value of onset from the Swift-Hohenberg fit and the onset in continuum simulations. Patterns are compared in cells oscillated at two different frequencies in MD; the layer with larger wavelength patterns has less noise than the layer with smaller wavelength patterns.Comment: Published in Physical Review

Nitrogen-fixing symbiotic bacteria act as a global filter for plant establishment on islands

Island biogeography has classically focused on abiotic drivers of species distributions. However, recent work has highlighted the importance of mutualistic biotic interactions in structuring island floras. The limited occurrence of specialist pollinators and mycorrhizal fungi have been found to restrict plant colonization on oceanic islands. Another important mutualistic association occurs between nearly 15,000 plant species and nitrogen-fixing (N-fixing) bacteria. Here, we look for evidence that N-fixing bacteria limit establishment of plants that associate with them. Globally, we find that plants associating with N-fixing bacteria are disproportionately underrepresented on islands, with a 22% decline. Further, the probability of N-fixing plants occurring on islands decreases with island isolation and, where present, the proportion of N-fixing plant species decreases with distance for large, but not small islands. These findings suggest that N-fixing bacteria serve as a filter to plant establishment on islands, altering global plant biogeography, with implications for ecosystem development and introduction risks

WPLYW TRENINGU STABILIZACJI CENTRALNEJ NA EFEKTYWNOŚĆ WYKONANIA NAWROTU KOZIOŁKOWEGO

Wstęp. Odpowiednia stabilność okolicy lędźwiowo-k rzyżowo-biodrowej i właściwe funkcjonowanie mięśni tułowia mają fundamentalne znaczenie dla efektywnego przemieszczania się w wodzie i poprawy uzyskiwanych wyników. Dzieje się tak z kilku powodów: po pierwsze, stabilizacja „centrum» wpływa na utrzymanie wyprostowanej, opływowej pozycji ciała w wodzie, minimalizując opory.Słaba stabilizacja powoduje opadanie bioder oraz nóg i „ciągnięcie» ich za sobą, co generuje dodatkowe straty energii. Przyczynia się także do niepotrzebnych ruchów bioder i nóg „na boki», tworząc dodatkowe opory i znacząco pogarszając efektywność pływania. Warto pamiętać, że zwiększenie prędkości pływania nie musi wynikać wyłącznie ze zwiększenia siły ruchu rąk czy kopnięcia, ale właśnie poprzez poprawę stabilności i właściwe ułożenia ciała. Po drugie, zapewnia stabilną bazę i wsparcie dla mobilności kończyn, co jest niezbędne dla efektywnego generowania napędu przez ręce i nogi. Ma to szczególne znaczenie w przypadku pływania. Niestety wielu pływaków ze słabą stabilizacją centralną, używa ramion i nóg nie tylko do wytwarzania napędu, ale także próbuje zapewnić sobie utrzymanie właściwej równowagi, szczególnie podczas oddechu. Przyczynia się to do powstawania oporów, a także ogranicza potencjał napędowy kończyn i tułowia. Właściwa stabilizacja centralna pozwala na stworzenie solidnego łącznika między efektywną pracą nogami, a pracą ramion. Dzięki temu napęd nie zależy tylko i wyłącznie od tych drugich [1]

Global patterns and drivers of phylogenetic structure in island floras

Islands are ideal for investigating processes that shape species assemblages because they are isolated &nbsp;and have discrete boundaries. Quantifying phylogenetic assemblage structure allows inferences in-situ speciation. Here, we link phylogenetic assemblage structure to island characteristics across 393 islands worldwide &nbsp;and 37,041 vascular plant species (representing angiosperms overall, palms and ferns). Physical and &nbsp;bioclimatic factors, especially those impeding colonization and promoting speciation, explained &nbsp;more &nbsp;variation &nbsp;in &nbsp;phylogenetic &nbsp;structure &nbsp;of &nbsp;angiosperms &nbsp;overall &nbsp;(49%) &nbsp;and &nbsp;palms &nbsp;(52%) &nbsp;than &nbsp;of &nbsp;ferns consistent with their dispersal- and speciation-related traits and climatic adaptations. Phylogenetic &nbsp;diversity was negatively related to isolation for palms, but unexpectedly it was positively related large-seeded, animal-dispersed palm family whereas colonization from biogeographically distinct in-situ among taxonomic groups on islands, which sheds light on the origin of insular plant diversity.</p

Asynchronous exposure to global warming: Freshwater resources and terrestrial ecosystems

This modelling study demonstrates at what level of global mean temperature rise (ΔTg) regions will be exposed to significant decreases of freshwater availability and changes to terrestrial ecosystems. Projections are based on a new, consistent set of 152 climate scenarios (eight ΔTg trajectories reaching 1.5–5 ° C above pre-industrial levels by 2100, each scaled with spatial patterns from 19 general circulation models). The results suggest that already at a ΔTg of 2 ° C and mainly in the subtropics, higher water scarcity would occur in >50% out of the 19 climate scenarios. Substantial biogeochemical and vegetation structural changes would also occur at 2 ° C, but mainly in subpolar and semiarid ecosystems. Other regions would be affected at higher ΔTg levels, with lower intensity or with lower confidence. In total, mean global warming levels of 2 ° C, 3.5 ° C and 5 ° C are simulated to expose an additional 8%, 11% and 13% of the world population to new or aggravated water scarcity, respectively, with >50% confidence (while ~1.3 billion people already live in water-scarce regions). Concurrently, substantial habitat transformations would occur in biogeographic regions that contain 1% (in zones affected at 2 ° C), 10% (3.5 ° C) and 74% (5 ° C) of present endemism-weighted vascular plant species, respectively. The results suggest nonlinear growth of impacts along with ΔTg and highlight regional disparities in impact magnitudes and critical ΔTg levels

Bethe ansatz for the Harper equation: Solution for a small commensurability parameter

The Harper equation describes an electron on a 2D lattice in magnetic field and a particle on a 1D lattice in a periodic potential, in general, incommensurate with the lattice potential. We find the distribution of the roots of Bethe ansatz equations associated with the Harper equation in the limit as alpha=1/Q tends to 0, where alpha is the commensurability parameter (Q is integer). Using the knowledge of this distribution we calculate the higher and lower boundaries of the spectrum of the Harper equation for small alpha. The result is in agreement with the semiclassical argument, which can be used for small alpha.Comment: 17 pages including 5 postscript figures, Latex, minor changes, to appear in Phys.Rev.

Bloch electron in a magnetic field and the Ising model

The spectral determinant det(H-\epsilon I) of the Azbel-Hofstadter Hamiltonian H is related to Onsager's partition function of the 2D Ising model for any value of magnetic flux \Phi=2\pi P/Q through an elementary cell, where P and Q are coprime integers. The band edges of H correspond to the critical temperature of the Ising model; the spectral determinant at these (and other points defined in a certain similar way) is independent of P. A connection of the mean of Lyapunov exponents to the asymptotic (large Q) bandwidth is indicated.Comment: 4 pages, 1 figure, REVTE