Uniqueness of the electrostatic solution in Schwarzschild space

In this Brief Report we give the proof that the solution of any static test charge distribution in Schwarzschild space is unique. In order to give the proof we derive the first Green's identity written with p-forms on (pseudo) Riemannian manifolds. Moreover, the proof of uniqueness can be shown for either any purely electric or purely magnetic field configuration. The spacetime geometry is not crucial for the proof.Comment: 3 pages, no figures, uses revtex4 style file

Proteoglykane und die Verpackung von Exportproteinen: Interaction von Serglycin und ZG 16 in den Zymogengranula des exokrinen Rattenpankreas

In Vorarbeiten konnte das Proteoglykan Serglycin in den Zymogengranula der Azinuszellen des exokrinen Rattenpankreas als Bindungspartner des sekretorischen Lektins ZG 16 identifiziert werden. Ferner konnte gezeigt werden, dass das korrekt glykosylierte Serglycin für die Sortierung von Zymogenen in die Granula nötig ist (Biederbick et al., 2003). Ziel dieser Arbeit war es, die Interaktion zwischen dem überwiegend membranständigen ZG 16 und Serglycin näher zu analysieren, um Aufschluss über Mechanismen der Verpackung und Sortierung der Zymogene zu erhalten. Darüber hinaus sollten mögliche weitere Proteoglykane aus dem Inhalt der Zymogengranula isoliert werden. Es wurden folgende Ergebnisse erzielt: 1. Durch Klonierung und Expression der unverzuckerten, rekombinanten N- und C-terminalen Abschnitte des Serglycin und deren Einsatz in Bindungsstudien (Co-Immunopräzipitation, GST-pull-down, Ligandenblots und Crosslinkexperimenten) wurde festgestellt, dass die Interaktion zwischen ZG 16 und Serglycin über den unverzuckerten N-terminalen Bereich (SGN) durch zuckerunabhängige Protein-Protein-Wechselwirkungen erfolgt. 2. Die Bindungssequenz des Serglycin an das ZG 16 konnte durch Herstellung verschiedener Punkt- und Deletionsmutanten des N-terminalen Bereichs SGN und deren Verwendung in Bindungsstudien auf die 9 N-Terminus nahen Aminosäuren ARYQWVRCK eingegrenzt werden. 3. Bei der Analyse der hypothetischen Sekundärstruktur des Serglycin, die mit Hilfe des ExPASy Molecular Biology Server erstellt wurde, gab es sehr starke Hinweise darauf, dass das Bindungsmotiv des Serglycin an das ZG 16 ein b-Faltblatt darstellt. Diese Daten zeigen, dass Serglycin über den N-terminalen unverzuckerten Abschnitt eine Protein-Protein-Interaktion mit dem sekretorischen Lektin ZG 16 macht. Über diese Interaktion werden das Serglycin und über seine Glykosaminoglykan-Ketten assoziierte Zymogene an die Zymogengranulamembran gebunden. Diese Wechselwirkung stellt einen Sortierungsmechanismus für die Zymogene in die Granula dar. 4. Für das Vorhandensein weiterer Proteoglykane im Inhalt der Zymogengranula (ZGI) konnten nur indirekte Hinweise gefunden werden. Im Blyscan-Assay, einer Fällung, die spezifisch für Proteoglykane ist, konnten durch Extinktionsmessung Proteoglykane nachgewiesen werden. Die größte Extinktion wurde nach Vorbehandlung des ZGI mit NaHCO3 erhalten. 5. Die Zymogene scheinen mit Proteoglykanen assoziiert zu sein. Durch diese Interaktion gelangt ein Teil der Zymogene noch nach NaHCO3-Behandlung von ZGI und anschließender Blyscan- oder Wesselfällung in das Blyscanpellet, bzw. in die organische Phase der Wesselfällung. Durch EGTA-Inkubation von ZGI kann diese Interaktion zwischen Proteoglykanen und Zymogenen aufgehoben werden. Hier erscheinen keine Zymogene im Blyscanpellet oder der organischen Phase der Wesselfällung

Supersymmetric Dark Matter and the Extragalactic Gamma Ray Background

We trace the origin of the newly determined extragalactic gamma ray background from EGRET data to an unresolved population of blazars and neutralino annihilation in cold dark matter halos. Using results of high-resolution simulations of cosmic structure formation, we calculate composite spectra and compare with the EGRET data. The resulting best-fit value for the neutralino mass is m_chi = (515 +/- 110/75) GeV (systematic errors \~30%).Comment: 4 pages, 3 figures; accepted by Physical Review Letters; replaced with accepted versio

The prismatic Sigma 3 (10-10) twin bounday in alpha-Al2O3 investigated by density functional theory and transmission electron microscopy

The microscopic structure of a prismatic $\Sigma 3$ $(10\bar{1}0)$ twin boundary in \aal2o3 is characterized theoretically by ab-initio local-density-functional theory, and experimentally by spatial-resolution electron energy-loss spectroscopy in a scanning transmission electron microscope (STEM), measuring energy-loss near-edge structures (ELNES) of the oxygen $K$-ionization edge. Theoretically, two distinct microscopic variants for this twin interface with low interface energies are derived and analysed. Experimentally, it is demonstrated that the spatial and energetical resolutions of present high-performance STEM instruments are insufficient to discriminate the subtle differences of the two proposed interface variants. It is predicted that for the currently developed next generation of analytical electron microscopes the prismatic twin interface will provide a promising benchmark case to demonstrate the achievement of ELNES with spatial resolution of individual atom columns

Parallel Search with no Coordination

We consider a parallel version of a classical Bayesian search problem. $k$ agents are looking for a treasure that is placed in one of the boxes indexed by $\mathbb{N}^+$ according to a known distribution $p$. The aim is to minimize the expected time until the first agent finds it. Searchers run in parallel where at each time step each searcher can "peek" into a box. A basic family of algorithms which are inherently robust is \emph{non-coordinating} algorithms. Such algorithms act independently at each searcher, differing only by their probabilistic choices. We are interested in the price incurred by employing such algorithms when compared with the case of full coordination. We first show that there exists a non-coordination algorithm, that knowing only the relative likelihood of boxes according to $p$, has expected running time of at most $10+4(1+\frac{1}{k})^2 T$, where $T$ is the expected running time of the best fully coordinated algorithm. This result is obtained by applying a refined version of the main algorithm suggested by Fraigniaud, Korman and Rodeh in STOC'16, which was designed for the context of linear parallel search.We then describe an optimal non-coordinating algorithm for the case where the distribution $p$ is known. The running time of this algorithm is difficult to analyse in general, but we calculate it for several examples. In the case where $p$ is uniform over a finite set of boxes, then the algorithm just checks boxes uniformly at random among all non-checked boxes and is essentially $2$ times worse than the coordinating algorithm.We also show simple algorithms for Pareto distributions over $M$ boxes. That is, in the case where $p(x) \sim 1/x^b$ for $0< b < 1$, we suggest the following algorithm: at step $t$ choose uniformly from the boxes unchecked in ${1, . . . ,min(M, \lfloor t/\sigma\rfloor)}$, where $\sigma = b/(b + k - 1)$. It turns out this algorithm is asymptotically optimal, and runs about $2+b$ times worse than the case of full coordination

Distinct transcription kinetics of pluripotent cell states

Mouse embryonic stem cells (mESCs) can adopt naïve, ground, and paused pluripotent states that give rise to unique transcriptomes. Here, we use transient transcriptome sequencing (TT-seq) to define both coding and non-coding transcription units (TUs) in these three pluripotent states and combine TT-seq with RNA polymerase II occupancy profiling to unravel the kinetics of RNA metabolism genome-wide. Compared to the naïve state (serum), RNA synthesis and turnover rates are globally reduced in the ground state (2i) and the paused state (mTORi). The global reduction in RNA synthesis goes along with a genome-wide decrease of polymerase elongation velocity, which is related to epigenomic features and alterations in the Pol II termination window. Our data suggest that transcription activity is the main determinant of steady state mRNA levels in the naïve state and that genome-wide changes in transcription kinetics invoke ground and paused pluripotent states

Communication Complexity of Quasirandom Rumor Spreading

We consider rumor spreading on random graphs and hypercubes in the quasirandom phone call model. In this model, every node has a list of neighbors whose order is specified by an adversary. In step i every node opens a channel to its ith neighbor (modulo degree) on that list, beginning from a randomly chosen starting position. Then, the channels can be used for bi-directional communication in that step. The goal is to spread a message efficiently to all nodes of the graph.For random graphs (with sufficiently many edges) we present an address-oblivious algorithm with runtime O(logn) that uses at most O(nloglogn) message transmissions. For hypercubes of dimension logn we present an address-oblivious algorithm with runtime O(logn) that uses at most O(n(loglogn)2) message transmissions.Together with a result of Elsässer (Proc. of SPAA’06, pp. 148–157, 2006), our results imply that for random graphs the communication complexity of the quasirandom phone call model is significantly smaller than that of the standard phone call model

Collective Sideband Cooling in an Optical Ring Cavity

We propose a cavity based laser cooling and trapping scheme, providing tight confinement and cooling to very low temperatures, without degradation at high particle densities. A bidirectionally pumped ring cavity builds up a resonantly enhanced optical standing wave which acts to confine polarizable particles in deep potential wells. The particle localization yields a coupling of the degenerate travelling wave modes via coherent photon redistribution. This induces a splitting of the cavity resonances with a high frequency component, that is tuned to the anti-Stokes Raman sideband of the particles oscillating in the potential wells, yielding cooling due to excess anti-Stokes scattering. Tight confinement in the optical lattice together with the prediction, that more than 50% of the trapped particles can be cooled into the motional ground state, promise high phase space densities.Comment: 4 pages, 1 figur

First-principles study of spontaneous polarization in multiferroic BiFeO3_3

The ground-state structural and electronic properties of ferroelectric BiFeO$_3$ are calculated using density functional theory within the local spin-density approximation and the LSDA+U method. The crystal structure is computed to be rhombohedral with space group $R3c$, and the electronic structure is found to be insulating and antiferromagnetic, both in excellent agreement with available experiments. A large ferroelectric polarization of 90-100 $\mu$C/cm$^2$ is predicted, consistent with the large atomic displacements in the ferroelectric phase and with recent experimental reports, but differing by an order of magnitude from early experiments. One possible explanation is that the latter may have suffered from large leakage currents. However both past and contemporary measurements are shown to be consistent with the modern theory of polarization, suggesting that the range of reported polarizations may instead correspond to distinct switching paths in structural space. Modern measurements on well-characterized bulk samples are required to confirm this interpretation.Comment: (9 pages, 5 figures, 5 tables

A general lower bound for collaborative tree exploration

We consider collaborative graph exploration with a set of $k$ agents. All agents start at a common vertex of an initially unknown graph and need to collectively visit all other vertices. We assume agents are deterministic, vertices are distinguishable, moves are simultaneous, and we allow agents to communicate globally. For this setting, we give the first non-trivial lower bounds that bridge the gap between small ($k \leq \sqrt n$) and large ($k \geq n$) teams of agents. Remarkably, our bounds tightly connect to existing results in both domains. First, we significantly extend a lower bound of $\Omega(\log k / \log\log k)$ by Dynia et al. on the competitive ratio of a collaborative tree exploration strategy to the range $k \leq n \log^c n$ for any $c \in \mathbb{N}$. Second, we provide a tight lower bound on the number of agents needed for any competitive exploration algorithm. In particular, we show that any collaborative tree exploration algorithm with $k = Dn^{1+o(1)}$ agents has a competitive ratio of $\omega(1)$, while Dereniowski et al. gave an algorithm with $k = Dn^{1+\varepsilon}$ agents and competitive ratio $O(1)$, for any $\varepsilon > 0$ and with $D$ denoting the diameter of the graph. Lastly, we show that, for any exploration algorithm using $k = n$ agents, there exist trees of arbitrarily large height $D$ that require $\Omega(D^2)$ rounds, and we provide a simple algorithm that matches this bound for all trees