INVESTIGATION OF POWER OUTPUT ON A NOVEL BICYCLE DRIVE IN COMPARISON WITH THE COMMON BICYCLE DRIVE

The aim of this study is to check whether a novel bicycle drive allows a higher power output. In order to be able to judge the efficiency of this drive the power output during use of this specific drive was matched with the one of a traditional bicycle drive. Both maximal power output tests and endurance tests with lactate determination where carried out. During the maximal power output tests a power output increase of 5.2% could be measured. During the endurance tests the anaerobe threshold (4 mmol lactate / l blood) at 80 rpm could be raised by 4.17 W, this is equivalent to 2.4%. At four time trials of an amateur cycling club the test riders were 5.3% faster with the new drive over the distance of 14.62 km (with a hairpin bend). This corresponds to a power output increase of 15.9%

Solar electric propulsion system tests

Design and performance of solar-powered electric propulsion system for interplanetary space exploratio

Triangle-free geometric intersection graphs with large chromatic number

Several classical constructions illustrate the fact that the chromatic number of a graph can be arbitrarily large compared to its clique number. However, until very recently, no such construction was known for intersection graphs of geometric objects in the plane. We provide a general construction that for any arc-connected compact set $X$ in $\mathbb{R}^2$ that is not an axis-aligned rectangle and for any positive integer $k$ produces a family $\mathcal{F}$ of sets, each obtained by an independent horizontal and vertical scaling and translation of $X$, such that no three sets in $\mathcal{F}$ pairwise intersect and $\chi(\mathcal{F})>k$. This provides a negative answer to a question of Gyarfas and Lehel for L-shapes. With extra conditions, we also show how to construct a triangle-free family of homothetic (uniformly scaled) copies of a set with arbitrarily large chromatic number. This applies to many common shapes, like circles, square boundaries, and equilateral L-shapes. Additionally, we reveal a surprising connection between coloring geometric objects in the plane and on-line coloring of intervals on the line.Comment: Small corrections, bibliography updat

Triangle-free intersection graphs of line segments with large chromatic number

In the 1970s, Erdos asked whether the chromatic number of intersection graphs of line segments in the plane is bounded by a function of their clique number. We show the answer is no. Specifically, for each positive integer $k$, we construct a triangle-free family of line segments in the plane with chromatic number greater than $k$. Our construction disproves a conjecture of Scott that graphs excluding induced subdivisions of any fixed graph have chromatic number bounded by a function of their clique number.Comment: Small corrections, bibliography updat

Black Hole Feedback On The First Galaxies

We study how the first galaxies were assembled under feedback from the accretion onto a central black hole (BH) that is left behind by the first generation of metal-free stars through self-consistent, cosmological simulations. X-ray radiation from the accretion of gas onto BH remnants of Population III (Pop III) stars, or from high-mass X-ray binaries (HMXBs), again involving Pop III stars, influences the mode of second generation star formation. We track the evolution of the black hole accretion rate and the associated X-ray feedback starting with the death of the Pop III progenitor star inside a minihalo and following the subsequent evolution of the black hole as the minihalo grows to become an atomically cooling galaxy. We find that X-ray photoionization heating from a stellar-mass BH is able to quench further star formation in the host halo at all times before the halo enters the atomic cooling phase. X-ray radiation from a HMXB, assuming a luminosity close to the Eddington value, exerts an even stronger, and more diverse, feedback on star formation. It photoheats the gas inside the host halo, but also promotes the formation of molecular hydrogen and cooling of gas in the intergalactic medium and in nearby minihalos, leading to a net increase in the number of stars formed at early times. Our simulations further show that the radiative feedback from the first BHs may strongly suppress early BH growth, thus constraining models for the formation of supermassive BHs.Astronom

Determining the distribution of stochastic impulses acting on a high frequency system through an analysis of its vibrations

The motion of an oscillator with damping excited by impulses has the form $ξ_t = \frac{1}{\sqrt{a^2 - b^2}} \sum_{0 <t_i<t}η_i exp(-b(t-t_i)) sin(\sqrt{a^2 - b^2} (t - t_i))$, where $ξ_t$ is the deviation of the oscillator from its balanced position and $t_i$ is the time of action of an impulse of the value η_i. Under appropriate assumptions regarding random variables ${t_{i+1} - t_i}_{i=1}^\infty$ and ${η_i}_{i=1}^\infty ξ_{t}$ is a process which, in the limit as t tends to infinity, is stationary and ergodic. This fact allows us to derive a linear system of equations determining the approximate distribution of variables $η_{i}$ whenever the course of the oscillator is known in a sufficiently large interval of time. These equations will be verified in the experiment executed on an electric oscillator RLC of high frequency

Assembly of Helicobacter pylori initiation complex is determined by sequence-specific and topology-sensitive DnaA-oriC interactions

In bacteria, chromosome replication is initiated by binding of the DnaA initiator protein to DnaA boxes located in the origin of chromosomal replication (oriC). This leads to DNA helix opening within the DNA-unwinding element. Helicobacter pylori oriC, the first bipartite origin identified in Gram-negative bacteria, contains two subregions, oriC1 and oriC2, flanking the dnaA gene. The DNA-unwinding element region is localized in the oriC2 subregion downstream of dnaA. Surprisingly, oriC2–DnaA interactions were shown to depend on DNA topology, which is unusual in bacteria but is similar to initiator–origin interactions observed in higher organisms. In this work, we identified three DnaA boxes in the oriC2 subregion, two of which were bound only as supercoiled DNA. We found that all three DnaA boxes play important roles in orisome assembly and subsequent DNA unwinding, but different functions can be assigned to individual boxes. This suggests that the H. pylori oriC may be functionally divided, similar to what was described recently for Escherichia coli oriC. On the basis of these results, we propose a model of initiation complex formation in H. pylori

Encapsulation stability of duplex emulsions prepared with SPG cross-flow membrane, SPG rotating membrane and rotor-stator techniques—A comparison

AbstractFood grade duplex W1/O/W2 emulsions were prepared using three different techniques: SPG cross-flow membrane, SPG rotating membrane and high-shear mixer. The primary W1/O emulsion had sodium chloride encapsulated in the inner aqueous droplets as a marker compound. Duplex emulsion droplet size and salt encapsulation were both investigated by modifying the emulsification conditions inherent for each technique; cross-flow velocity (CFV) and trans-membrane pressure (TMP) for the cross-flow membrane, rotational velocity (RV) and TMP for the rotating membrane, and mixing time for the high-shear mixer.Emulsion droplet size was shown to increase with TMP and to decrease with both CFV and RV. Minimum droplet size obtained (∼12 μm) was similar for all three emulsifying techniques, which suggests that at high shear stresses, the minimum droplet size is determined primarily by the decrease in the interfacial tension.It was also shown that the amount of salt released during storage depends on the emulsification technique (8–20% for the cross-flow membrane, ∼13% for the high-shear mixer and ∼8% for the rotating membrane). The differences in salt release were explained in terms of emulsions droplet size and interfacial properties of adsorbed surfactant molecules. The unexpected high amount of salt released by duplex emulsions produced by the cross-flow membrane was associated with the magnitude and duration of shear forces, which act on duplex droplets during semi-batch emulsification

Nonlocal dielectric function and nested dark excitons in MoS2

Their exceptional optical properties are a driving force for the persistent interest in atomically thin transition metal dichalcogenides such as MoS2. The optical response is dominated by excitons. Apart from the bright excitons, which directly couple to light, it has been realized that dark excitons, where photon absorption or emission is inhibited by the spin state or momentum mismatch, are decisive for many optical properties. However, in particular the momentum dependence is difficult to assess experimentally and often remains elusive or is investigated by indirect means. Here we study the momentum dependent electronic structure experimentally and theoretically. We use angle-resolved photoemission as a one-particle probe of the occupied valence band structure and electron energy loss spectroscopy as a two-particle probe of electronic transitions across the gap to benchmark a single-particle model of the dielectric function ϵ(q, ω) against momentum dependent experimental measurements. This ansatz captures key aspects of the data surprisingly well. In particular, the energy region where substantial nesting occurs, which is at the origin of the strong light–matter interaction of thin transition metal dichalcogenides and crucial for the prominent C-exciton, is described well and spans a more complex exciton landscape than previously anticipated. Its local maxima in (q≠0,ω) space can be considered as dark excitons and might be relevant for higher order optical processes. Our study may lead to a more complete understanding of the optical properties of atomically thin transition metal dichalcogenides

Unique and Universal Features of Epsilonproteobacterial Origins of Chromosome Replication and DnaA-DnaA Box Interactions

In bacteria, chromosome replication is initiated by the interaction of the initiator protein DnaA with a defined region of a chromosome at which DNA replication starts (oriC). While DnaA proteins share significant homology regardless of phylogeny, oriC regions exhibit more variable structures. The general architecture of oriCs is universal, i.e., they are composed of a cluster of DnaA binding sites, a DNA-unwinding element, and sequences that bind regulatory proteins. However, detailed structures of oriCs are shared by related species while being significantly different in unrelated bacteria. In this work, we characterized Epsilonproteobacterial oriC regions. Helicobacter pylori was the only species of the class for which oriC was characterized. A few unique features were found such as bipartite oriC structure, not encountered in any other Gram-negative species, and topology-sensitive DnaA-DNA interactions, which have not been found in any other bacterium. These unusual H. pylori oriC features raised questions of whether oriC structure and DnaA-DNA interactions are unique to this bacterium or whether they are common to related species. By in silico and in vitro analyses we identified putative oriCs in three Epsilonproteobacterial species: pathogenic Arcobacter butzleri, symbiotic Wolinella succinogenes, and free-living Sulfurimonas denitrificans. We propose that oriCs typically co-localize with ruvC-dnaA-dnaN in Epsilonproteobacteria, with the exception of Helicobacteriaceae species. The clusters of DnaA boxes localize upstream (oriC1) and downstream (oriC2) of dnaA, and they likely constitute bipartite origins. In all cases, DNA unwinding was shown to occur in oriC2. Unlike the DnaA box pattern, which is not conserved in Epsilonproteobacterial oriCs, the consensus DnaA box sequences and the mode of DnaA-DnaA box interactions are common to the class. We propose that the typical Epsilonproteobacterial DnaA box consists of the core nucleotide sequence 5'-TTCAC-3' (4-8 nt), which, together with the significant changes in the DNA-binding motif of corresponding DnaAs, determines the unique molecular mechanism of DnaA-DNA interaction. Our results will facilitate identification of oriCs and subsequent identification of factors which regulate chromosome replication in other Epsilonproteobacteria. Since replication is controlled at the initiation step, it will help to better characterize life cycles of these species, many of which are considered as emerging pathogens