Run Generation Revisited: What Goes Up May or May Not Come Down

In this paper, we revisit the classic problem of run generation. Run generation is the first phase of external-memory sorting, where the objective is to scan through the data, reorder elements using a small buffer of size M , and output runs (contiguously sorted chunks of elements) that are as long as possible. We develop algorithms for minimizing the total number of runs (or equivalently, maximizing the average run length) when the runs are allowed to be sorted or reverse sorted. We study the problem in the online setting, both with and without resource augmentation, and in the offline setting. (1) We analyze alternating-up-down replacement selection (runs alternate between sorted and reverse sorted), which was studied by Knuth as far back as 1963. We show that this simple policy is asymptotically optimal. Specifically, we show that alternating-up-down replacement selection is 2-competitive and no deterministic online algorithm can perform better. (2) We give online algorithms having smaller competitive ratios with resource augmentation. Specifically, we exhibit a deterministic algorithm that, when given a buffer of size 4M , is able to match or beat any optimal algorithm having a buffer of size M . Furthermore, we present a randomized online algorithm which is 7/4-competitive when given a buffer twice that of the optimal. (3) We demonstrate that performance can also be improved with a small amount of foresight. We give an algorithm, which is 3/2-competitive, with foreknowledge of the next 3M elements of the input stream. For the extreme case where all future elements are known, we design a PTAS for computing the optimal strategy a run generation algorithm must follow. (4) Finally, we present algorithms tailored for nearly sorted inputs which are guaranteed to have optimal solutions with sufficiently long runs

A musical way of representing criptographic keys

Motivated by the existing problem with the current cryptographic key representation methods, which try to represent a bunch of meaningless letters and numbers, a new representation method has been developed. Taking as reference "The Drunken Bishop" method, our method is based on the reproduction of a melody as a representation of the key. Instead of drawing the path of the bishop, we have created a chessboard composed of musical notes, creating a melody as the bishop moves. This melody is deterministic, as it doesn't change depending on the execution, a necessary feature when representing cryptographic keys. Two different methods have been developed in order to compare them with the previous methods and evaluate whether this new representation fits within the framework under study. Also, as a use-case example, the selected method has been implemented into the SSH protocol.Motivat pel problema existent amb els mètodes actuals de representació de claus criptogràfiques, que intenten representar un munt de lletres i números sense sentit, s'ha desenvolupat un nou mètode de representació. Prenent com a referència el mètode "The Drunken Bishop", el nostre mètode es basa en la reproducció d'una melodia com a representació de la tonalitat. En lloc de dibuixar el camí del bisbe, hem creat un tauler d'escacs compost per notes musicals, creant una melodia a mesura que el bisbe es mou. Aquesta melodia és determinista, ja que no canvia en funció de l'execució, característica necessària a l'hora de representar claus criptogràfiques. S'han desenvolupat dos mètodes diferents per comparar-los amb els anteriors i avaluar si aquesta nova representació s'adapta al marc que s'estudia. A més, com a exemple d'ús, el mètode seleccionat s'ha implementat al protocol SSH.Motivado por el problema existente con los métodos actuales de representación de claves criptográficas, que intentan representar un montón de letras y números sin sentido, se ha desarrollado un nuevo método de representación. Tomando como referencia el método The Drunken Bishop, nuestro método se basa en la reproducción de una melodía como representación de la tonalidad. En lugar de dibujar el camino del alfíl, hemos creado un tablero de ajedrez compuesto por notas musicales, creando una melodía a medida que el alfíl se mueve. Esta melodía es determinista, puesto que no cambia en función de la ejecución, característica necesaria a la hora de representar claves criptográficas. Se han desarrollado dos métodos distintos para compararlos con los anteriores y evaluar si esta nueva representación se adapta al marco que se estudia. Además, como ejemplo de uso, el método seleccionado se ha implementado en el protocolo SSH

Is there a sex difference in mortality rates for deaths occurring in paediatric intensive care units? Systematic literature review protocol

Introduction In the general population, female children have been reported to have a survival advantage. For children admitted to paediatric intensive care units (PICUs), mortality has been reported to be lower in males despite the higher admission rates for males into intensive care. This apparent sex reversal in PICU mortality is not well studied. To address this, we propose to conduct a systematic literature review to summarise the available evidence. Our review will study the reported differences in mortality between males and females aged 0-17, who died in a PICU, to examine if there is a difference between the two sexes in PICU mortality, and if so, to describe the magnitude and direction of this difference. Methods and analysis Studies that directly or indirectly addressed the association between sex and mortality in children admitted to intensive care will be eligible for inclusion. Studies that directly address the association will be eligible for data extraction. The search strings were based on terms related to the population (children in intensive care), the exposure (sex) and the outcome (mortality). We used the databases MEDLINE (1946-2020), Embase (1980-2020) and Web of Science (1985-2020) as these cover relevant clinical publications. We will assess the reliability of included studies using the risk of bias in observational studies of exposures tool. We will consider a pooled effect if we have at least three studies with similar periods of follow up and adjustment variables. Ethics and dissemination Ethical approval is not required for this review as it will synthesise data from existing studies. This manuscript is a part of a larger data linkage study, for which Ethical approval was granted. Dissemination will be via peer-reviewed journals and via public and patient groups. PROSPERO registration number CRD42020203009

Kinematic model inversions of hot star recurrent DAC data - tests against dynamical CIR models

The Discrete Absorption Components (DACs) commonly observed in the ultraviolet lines of hot stars have previously been modelled by dynamical simulations of Corotating Interaction Regions (CIRs) in their fine-driven stellar winds. Here we apply the kinematic DAC inversion method of Brown et al. to the hydrodynamical CIR models and test the reliability of the results obtained. We conclude that the inversion method is able to recover valuable information on the velocity structure of the mean wind and to trace movement of velocity plateaux in the hydrodynamical data, though the recovered density profile of the stream is correct only very near to the stellar surface

U Geminorum: a test case for orbital parameters determination

High-resolution spectroscopy of U Gem was obtained during quiescence. We did not find a hot spot or gas stream around the outer boundaries of the accretion disk. Instead, we detected a strong narrow emission near the location of the secondary star. We measured the radial velocity curve from the wings of the double-peaked H$\alpha$ emission line, and obtained a semi-amplitude value that is in excellent agreement with the obtained from observations in the ultraviolet spectral region by Sion et al. (1998). We present also a new method to obtain K_2, which enhances the detection of absorption or emission features arising in the late-type companion. Our results are compared with published values derived from the near-infrared NaI line doublet. From a comparison of the TiO band with those of late type M stars, we find that a best fit is obtained for a M6V star, contributing 5 percent of the total light at that spectral region. Assuming that the radial velocity semi-amplitudes reflect accurately the motion of the binary components, then from our results: K_em = 107+/-2 km/s; K_abs = 310+/-5 km/s, and using the inclination angle given by Zhang & Robinson(1987); i = 69.7+/-0.7, the system parameters become: M_WD = 1.20+/-0.05 M_sun,; M_RD = 0.42+/-0.04 M_sun; and a = 1.55+/- 0.02 R_sun. Based on the separation of the double emission peaks, we calculate an outer disk radius of R_out/a ~0.61, close to the distance of the inner Lagrangian point L_1/a~0.63. Therefore we suggest that, at the time of observations, the accretion disk was filling the Roche-Lobe of the primary, and that the matter leaving the L_1 point was colliding with the disc directly, producing the hot spot at this location.Comment: 36 pages, 14 figures, ccepted for publication in A

Fusion activity and inactivation of influenza virus: Kinetics of low pH-induced fusion with cultured cells

The kinetics of fusion of influenza virus (A/PR/8/34) with human promyelocytic leukaemia (HL-60), human T lymphocytic leukaemia (CEM) and murine lymphoma (S49) cells were investigated. Fusion was demonstrated by electron microscopy, and monitored by fluorescence dequenching of octadecylrhodamine incorporated in the virus membrane. Rapid fusion was induced upon mild acidification of the medium. At pH 5, all virus particles were capable of fusing with the cells. The initial rate and the extent of fusion were maximal between pH 4.9 and 5.2 and declined sharply below and above this range. The rate constants of adhesion of influenza virus to cells or erythrocyte ghosts were large, indicating a diffusion-controlled process. The rate constants of fusion of the virus with cells were smaller than those found previously for fusion with various liposomes. Although preincubation of the virus at acidic pH in the absence of target membranes almost completely inactivated the virus in its ability to fuse with erythrocyte ghosts, it reduced the extent of fusion with cultured cells by only 20 to 40%. Kinetic analysis of fusion revealed a mode of inactivation of the virus bound to erythrocyte ghosts or suspension cells, below pH 5.4, different from that of the virus preincubated at low pH without target membranes