YOYO-1 is a fluorescent dye widely used for probing the statistical-mechanical properties of DNA. However, currently contradicting data exist how YOYO-1 binding alters the DNA structure and rigidity. ...Here, we systematically address this problem using magnetic tweezers. Remarkably, we find that the persistence length of DNA remains constant independent of the amount of bound YOYO-1, which contrasts previous assumptions. While the ionic conditions can considerably alter the stability of YOYO-1 binding, the DNA bending rigidity seems not to be affected. We furthermore determine important structural parameters such as the binding site size, the elongation, as well as the untwisting angle per bound YOYO-1 molecule. We expect that our assay, in which all the parameters are determined within a single experiment, will be beneficial for a large range of other DNA binding drugs.
The determination of depth profiles across interfaces is of primary importance in many scientific and technological areas. Photoemission spectroscopy is in principle well suited for this purpose, yet ...a quantitative implementation for investigations of liquid-vapor interfaces is hindered by the lack of understanding of electron-scattering processes in liquids. Previous studies have shown, however, that core-level photoelectron angular distributions (PADs) are altered by depth-dependent elastic electron scattering and can, thus, reveal information on the depth distribution of species across the interface. Here, we explore this concept further and show that the experimental anisotropy parameter characterizing the PAD scales linearly with the average distance of atoms along the surface normal obtained by molecular dynamics simulations. This behavior can be accounted for in the low-collision-number regime. We also show that results for different atomic species can be compared on the same length scale. We demonstrate that atoms separated by about 1 Å along the surface normal can be clearly distinguished with this method, achieving excellent depth resolution.
Silicon offers nine times higher theoretical storage capacity than commercial graphite anodes for Li-ion batteries. For cycling stability, the electrolyte needs to be kinetically stabilized by the ...so-called Solid Electrolyte Interphase (SEI), a layer which ideally forms once from decomposition products of the electrolyte. While it works for graphite, the SEI on silicon fails to stabilize the electrolyte sufficiently, partly due to the large volume changes upon de-/lithiation. To investigate the SEI on silicon anodes, we developed a novel approach for X-ray Absorption Spectroscopy (XAS), that puts a twist to conventional SiNx window-based liquid cells by utilizing a deliberately induced gas-bubble to form a soft X-ray transparent electrolyte layer. We demonstrate our approach to allow transmission XAS in the soft X-ray regime on liquids and electrode thin-film materials under in-situ conditions. In our case XAS study of the SEI on silicon anodes, we reveal the main SEI constituents as Li acetate, Li ethylene di-carbonate or Li ethylene mono-carbonate, Li acetylacetonate, LiOH, and LiF. Additionally, we see evidence for aldehyde species which we attribute to possible liquid inclusions within a porous SEI morphology. We consider our method an appropriate tool for the successful engineering of a stable, efficient SEI in the future.
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The psychiatrist and medical historian Werner Leibbrand resigned from the Berlin Medical Association after the seizure of power in protest against the exclusion of Jewish colleagues and lost both the ...license to practice as well as his professional position in the public health service. After the end of the war the American military authorities appointed him as expert witness for the prosecution in the Nürnberg Doctors Trial. In addition to a biographical review, Leibbrand's resolute although still undisputed attitude as ethical expert in the trials will be roughly outlined.
Carbon nanotube field-effect transistors with sub-20 nm long channels and on/off current ratios of >106 are demonstrated. Individual single-walled carbon nanotubes with diameters ranging from 0.7 to ...1.1 nm grown from structured catalytic islands using chemical vapor deposition at 700 °C form the channels. Electron beam lithography and a combination of HSQ, calix6arene, and PMMA e-beam resists were used to structure the short channels and source and drain regions. The nanotube transistors display on-currents in excess of 15 μA for drain-source biases of only 0.4 V.
Like most mammalian, polyphasic sleep, equine sleep can be divided into two phases: the REM (rapid eye movement) phase and the NREM (non-rapid eye movement) phase. For this study, a randomized ...crossover experiment was conducted using ten purebred Lusitano horses, all dressage athletes aged from three to seven years old. The horses were filmed before the intervention to characterize their sleep patterns. REM sleep deprivation was achieved by not letting the horses attain sternal or lateral recumbency for three consecutive days, totaling 72 h. A spatial memory task and a visual attention test were performed. A recording time of 48 h appeared to be long enough to characterize the sleep patterns of the stalled horses. The total recumbency time of the studied population was lower than that previously reported in horses. Although the recumbency times before and after the intervention were similar, there was a tendency shown by the delta (
= 0.0839) towards an increased time needed to resolve spatial memory tasks in the sleep-deprived group. Future studies may deepen the understanding of horse sleep requirements and patterns, and the effects of environmental changes on horse sleep.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
In this paper, a straightforward methodology to modeling high power factor (HPF) ac-dc converters is presented. The proposed methodology is based on the averaging technique directly applied to the ...converter under modeling. An averaged large-signal equivalent circuit is thus generated, which is useful to perform extremely fast simulations. From the large-signal model, both a steady-state and a small-signal analysis can be carried out to completely model the converter, achieving any desired steady-state characteristic and small-signal transfer function. The presented methodology is very intuitive and allows designers to achieve a natural understanding of the converter behavior. The methodology is illustrated with a HPF buck-boost converter operating in discontinuous conduction mode. Simulation and experimental results are provided to validate the proposed methodology.
Let
S
be a set of four points chosen independently, uniformly at random from a square. Join every pair of points of
S
with a straight line segment. Color these edges red if they have positive slope ...and blue, otherwise. We show that the probability that
S
defines a pair of crossing edges of the same color is equal to
1
/
4
. This is connected to a recent result of Aichholzer et al. 1 who showed that by 2-colouring the edges of a geometric graph and counting monochromatic crossings instead of crossings, the number of crossings can be more than halved. Our result shows that for the described random drawings, there is a coloring of the edges such that the number of monochromatic crossings is in expectation
1
2
-
7
50
of the total number of crossings.
Valence electronic structure is crucial for understanding and predicting reactivity. Valence non-resonant X-ray photoelectron spectroscopy (NRXPS) provides a direct method for probing the overall ...valence electronic structure. However, it is often difficult to separate the varying contributions to NRXPS; for example, contributions of solutes in solvents or functional groups in complex molecules. In this work we show that valence resonant X-ray photoelectron spectroscopy (RXPS) is a vital tool for obtaining atomic contributions to valence states. We combine RXPS with NRXPS and density functional theory calculations to demonstrate the validity of using RXPS to identify atomic contributions for a range of solutes (both neutral and ionic) and solvents (both molecular solvents and ionic liquids). Furthermore, the one-electron picture of RXPS holds for all of the closed shell molecules/ions studied, although the situation for an open-shell metal complex is more complicated. The factors needed to obtain a strong RXPS signal are investigated in order to predict the types of systems RXPS will work best for; a balance of element electronegativity and bonding type is found to be important. Additionally, the dependence of RXPS spectra on both varying solvation environment and varying local-covalent bonding is probed. We find that RXPS is a promising fingerprint method for identifying species in solution, due to the spectral shape having a strong dependence on local-covalency but a weak dependence on the solvation environment.
We demonstrate the validity of using valence resonant X-ray photoelectron spectroscopy to identify atomic contributions for both solutes and solvents.
Ribonucleoprotein (RNP) complexes from CRISPR-Cas systems have attracted enormous interest since they can be easily and flexibly reprogrammed to target any desired locus for genome engineering and ...gene regulation applications. Basis for the programmability is a short RNA (crRNA) inside these complexes that recognizes the target nucleic acid by base pairing. For CRISPR-Cas systems that target double-stranded DNA this results in local DNA unwinding and formation of a so-called R-loop structure. Here we provide an overview how this target recognition mechanism can be dissected in great detail at the level of a single molecule. Specifically, we demonstrate how magnetic tweezers are applied to measure the local DNA unwinding at the target in real time. To this end we introduce the technique and the measurement principle. By studying modifications of the consensus target sequence, we show how different sequence elements contribute to the target recognition mechanism. From these data, a unified target recognition mechanism can be concluded for the RNPs Cascade and Cas9 from types I and II CRISPR-Cas systems. R-loop formation is hereby initiated on the target at an upstream element, called protospacer adjacent motif (PAM), from which the R-loop structure zips directionally toward the PAM-distal end of the target. At mismatch positions, the R-loop propagation stalls and further propagation competes with collapse of the structure. Upon full R-loop zipping conformational changes within the RNPs trigger degradation of the DNA target. This represents a shared labor mechanism in which zipping between nucleic acid strands is the actual target recognition mechanism while sensing of the R-loop arrival at the PAM-distal end just verifies the success of the full zipping.
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