462 research outputs found
Cell wall elongation mode in Gram-negative bacteria is determined by peptidoglycan architecture
Cellular integrity and morphology of most bacteria is maintained by cell wall peptidoglycan,
the target of antibiotics essential in modern healthcare. It consists of glycan strands,
cross-linked by peptides, whose arrangement determines cell shape, prevents lysis due to
turgor pressure and yet remains dynamic to allow insertion of new material, and hence
growth. The cellular architecture and insertion pattern of peptidoglycan have remained
elusive. Here we determine the peptidoglycan architecture and dynamics during growth in
rod-shaped Gram-negative bacteria. Peptidoglycan is made up of circumferentially oriented
bands of material interspersed with a more porous network. Super-resolution fluorescence
microscopy reveals an unexpected discontinuous, patchy synthesis pattern. We present
a consolidated model of growth via architecture-regulated insertion, where we propose only
the more porous regions of the peptidoglycan network that are permissive for synthesis
Direct measurement of sub-pixel structure of the EPIC MOS CCD on-board th e XMM/NEWTON satellite
We have used a mesh experiment in order to measure the sub-pixel structure of
the EPIC MOS CCDs on-board the XMM/NEWTON satellite. The EPIC MOS CCDs have 40
m-square pixels which have an open electrode structure in order to improve
the detection efficiency for low-energy X-rays. We obtained restored pixel
images for various X-ray event grades (e.g. split-pixel events, single pixel
events, etc.) at various X-ray energies.
We confirmed that the open electrode structure results in a distorted
horizontal pixel boundary. The open electrode region generates both single
pixel events and vertically split events, but no horizontally split events.
Because the single pixel events usually show the best energy resolution, we
discuss a method of increasing the fraction of single pixel events from the
open electrode region. Furthermore, we have directly measured the thickness of
the electrodes and dead-layers by comparing spectra from the open electrode
region with those from the other regions: electrodes, electrode finger and
channel stop. We can say that EPIC MOS CCDs are more radiation hard than
front-illumination chips of ACIS on-board Chandra X-ray Observatory because of
their extra absorption thickness above the charge transfer channel. We
calcurated the mean pixel response and found that our estimation has a good
agreement with that of the ground calibration of EPIC MOS CCD.Comment: 20pages including 2 tables, 10 figures,Accepted for publication in :
Nuclear Instruments and Methods in Physics Research
State space c-reductions for concurrent systems in rewriting logic
We present c-reductions, a state space reduction technique.
The rough idea is to exploit some equivalence relation on states (possibly capturing system regularities) that preserves behavioral properties, and explore the induced quotient system. This is done by means of a canonizer
function, which maps each state into a (non necessarily unique) canonical representative of its equivalence class. The approach exploits the expressiveness of rewriting logic and its realization in Maude to enjoy several advantages over similar approaches: exibility and simplicity in
the definition of the reductions (supporting not only traditional symmetry reductions, but also name reuse and name abstraction); reasoning support for checking and proving correctness of the reductions; and automatization
of the reduction infrastructure via Maude's meta-programming
features. The approach has been validated over a set of representative case studies, exhibiting comparable results with respect to other tools
Constraints on diffuse neutrino background from primordial black holes
We calculated the energy spectra and the fluxes of electron neutrino emitted
in the process of evaporation of primordial black holes (PBHs) in the early
universe. It was assumed that PBHs are formed by a blue power-law spectrum of
primordial density fluctuations. We obtained the bounds on the spectral index
of density fluctuations assuming validity of the standard picture of
gravitational collapse and using the available data of several experiments with
atmospheric and solar neutrinos. The comparison of our results with the
previous constraints (which had been obtained using diffuse photon background
data) shows that such bounds are quite sensitive to an assumed form of the
initial PBH mass function.Comment: 18 pages,(with 7 figures
Microwave conductivity of a d-wave superconductor disordered by extended impurities: a real-space renormalization group approach
Using a real-space renormalization group (RSRG) technique, we compute the
microwave conductivity of a d-wave superconductor disordered by extended
impurities. To do this, we invoke a semiclassical approximation which naturally
accesses the Andreev bound states localized near each impurity. Tunneling
corrections (which are captured using the RSRG) lead to a delocalization of
these quasiparticles and an associated contribution to the microwave
conductivity.Comment: 8 pages, 4 figures. 2 figures added to previous versio
Indication for the coexistence of closed orbit and quantum interferometer with the same cross section in the organic metal (ET)4(H3O)[Fe(C2O4)3].C6H4Cl2: Persistence of SdH oscillations above 30 K
Shubnikov-de Haas (SdH) and de Haas-van Alphen (dHvA) oscillations spectra of
the quasi-two dimensional charge transfer salt
"-(ET)(HO)[Fe(CO)]CHCl have been
investigated in pulsed magnetic fields up to 54 T. The data reveal three basic
frequencies F, F and F, which can be interpreted on the basis
of three compensated closed orbits at low temperature. However a very weak
thermal damping of the Fourier component F, with the highest amplitude, is
evidenced for SdH spectra above about 6 K. As a result, magnetoresistance
oscillations are observed at temperatures higher than 30 K. This feature, which
is not observed for dHvA oscillations, is in line with quantum interference,
pointing to a Fermi surface reconstruction in this compound.Comment: published in Eur. Phys. J. B 71 203 (2009
When is policing fair? Groups, identity and judgements of the procedural justice of coercive crowd policing
Procedural justice theory (PJT) is now a widely utilised theoretical perspective in policing research that acknowledges the centrality of police âfairnessâ. Despite its widespread acceptance this paper asserts that there are conceptual limitations that emerge when applying the theory to the policing of crowd events. This paper contends that this problem with PJT is a result of specific assumptions that are highlighted by two studies using a novel experimental approach. Study 1 systematically manipulated the social categories used to describe crowd participants subjected to police coercion. The experiment demonstrates how these social categories dramatically affected participantsâ perceptions of the same police action and that it was participantsâ relational identification with the police, rather than a superordinate category, that mediated the association between judgements of procedural fairness and intentions to cooperate. In Study 2, using a quasi-experimental design, we then replicated and extended these findings by demonstrating how perceptions of procedural fairness are also influenced by levels of in-group identification. The paper concludes by exploring the implications of the data for reconceptualising the social psychological processes mediating these judgements and impacts of police legitimacy
Digital play and the actualisation of the consumer imagination
In this article, the authors consider emerging consumer practices in digital virtual spaces. Building on constructions of consumer behavior as both a sense-making activity and a resource for the construction of daydreams, as well as anthropological readings of performance, the authors speculate that many performances during digital play are products of consumer fantasy. The authors develop an interpretation of the relationship between the real and the virtual that is better equipped to understand the movement between consumer daydreams and those practices actualized in the material and now also in digital virtual reality. The authors argue that digital virtual performances present opportunities for liminoid transformations through inversions, speculations, and playfulness acted out in aesthetic dramas. To illustrate, the authors consider specific examples of the theatrical productions available to consumers in digital spaces, highlighting the consumer imagination that feeds them, the performances they produce, and the potential for transformation in consumer-players
The Tug1 locus is essential for male fertility
Background: Several long noncoding RNAs (lncRNAs) have been shown to function as central components of molecular machines that play fundamental roles in biology. While the number of annotated lncRNAs in mammalian genomes has greatly expanded, their functions remain largely uncharacterized. This is compounded by the fact that identifying lncRNA loci that have robust and reproducible phenotypes when mutated has been a challenge. Results: We previously generated a cohort of 20 lncRNA loci knockout mice. Here, we extend our initial study and provide a more detailed analysis of the highly conserved lncRNA locus, Taurine Upregulated Gene 1 (Tug1). We report that Tug1 knockout male mice are sterile with complete penetrance due to a low sperm count and abnormal sperm morphology. Having identified a lncRNA loci with a robust phenotype, we wanted to determine which, if any, potential elements contained in the Tug1 genomic region (DNA, RNA, protein, or the act of transcription) have activity. Using engineered mouse models and cell-based assays, we provide evidence that the Tug1 locus harbors three distinct regulatory activities - two noncoding and one coding: (i) a cis DNA repressor that regulates many neighboring genes, (ii) a lncRNA that can regulate genes by a trans-based function, and finally (iii) Tug1 encodes an evolutionary conserved peptide that when overexpressed impacts mitochondrial membrane potential. Conclusions: Our results reveal an essential role for the Tug1 locus in male fertility and uncover three distinct regulatory activities in the Tug1 locus, thus highlighting the complexity present at lncRNA loci
- âŠ