1,042 research outputs found
The Box Graph In Superstring Theory
In theories of closed oriented superstrings, the one loop amplitude is given
by a single diagram, with the topology of a torus. Its interpretation had
remained obscure, because it was formally real, converged only for purely
imaginary values of the Mandelstam variables, and had to account for the
singularities of both the box graph and the one particle reducible graphs in
field theories. We present in detail an analytic continuation method which
resolves all these difficulties. It is based on a reduction to certain minimal
amplitudes which can themselves be expressed in terms of double and single
dispersion relations, with explicit spectral densities. The minimal amplitudes
correspond formally to an infinite superposition of box graphs on
like field theories, whose divergence is responsible for the poles in the
string amplitudes. This paper is a considerable simplification and
generalization of our earlier proposal published in Phys. Rev. Lett. 70 (1993)
p 3692.Comment: Plain TeX, 67 pp. and 9 figures, Columbia/UCLA/94/TEP/3
Phagosomal acidification Is required to kill Streptococcus pneumoniae in a Zebrafish model
Streptococcus pneumoniae (the pneumococcus) is a major human pathogen causing invasive disease, including community-acquired bacteraemia, and remains a leading cause of global mortality. Understanding the role of phagocytes in killing bacteria is still limited, especially in vivo. In this study, we established a zebrafish model to study the interaction between intravenously administered pneumococci and professional phagocytes such as macrophages and neutrophils, to unravel bacterial killing mechanisms employed by these immune cells. Our model confirmed the key role of polysaccharide capsule in promoting pneumococcal virulence through inhibition of phagocytosis. Conversely, we show pneumococci lacking a capsule are rapidly internalised by macrophages. Low doses of encapsulated S. pneumoniae cause near 100% mortality within 48 hours postinfection (hpi), while 50 times higher doses of unencapsulated pneumococci are easily cleared. Time course analysis of in vivo bacterial numbers reveals that while encapsulated pneumococcus proliferates to levels exceeding 105âCFU at the time of host death, unencapsulated bacteria are unable to grow and are cleared within 20 hpi. Using genetically induced macrophage depletion, we confirmed an essential role for macrophages in bacterial clearance. Additionally, we show that upon phagocytosis by macrophages, phagosomes undergo rapid acidification. Genetic and chemical inhibition of vacuolar ATPase (v-ATPase) prevents intracellular bacterial killing and induces host death indicating a key role of phagosomal acidification in immunity to invading pneumococci. We also show that our model can be used to study the efficacy of antimicrobials against pneumococci in vivo. Collectively, our data confirm that larval zebrafish can be used to dissect killing mechanisms during pneumococcal infection in vivo and highlight key roles for phagosomal acidification in macrophages for pathogen clearance
Inflation and Brane Gases
We investigate a new way of realizing a period of cosmological inflation in
the context of brane gas cosmology. It is argued that a gas of co-dimension one
branes, out of thermal equilibrium with the rest of the matter, has an equation
of state which can - after stabilization of the dilaton - lead to power-law
inflation of the bulk. The most promising implementation of this mechanism
might be in Type IIB superstring theory, with inflation of the three large
spatial dimensions triggered by ``stabilized embedded 2-branes''. Possible
applications and problems with this proposal are discussed.Comment: 7 pages, uses REVTeX, version to appear in Phys. Rev.
On Parameter Tuning in Search Based Software Engineering
Abstract. When applying search-based software engineering (SBSE) techniques one is confronted with a multitude of different parameters that need to be chosen: Which population size for a genetic algorithm? Which selection mechanism to use? What settings to use for dozens of other parameters? This problem not only troubles users who want to apply SBSE tools in practice, but also researchers performing experimentation â how to compare algorithms that can have different parameter settings? To shed light on the problem of parameters, we performed the largest empirical analysis on parameter tuning in SBSE to date, collecting and statistically analysing data from more than a million experiments. As case study, we chose test data generation, one of the most popular problems in SBSE. Our data confirm that tuning does have a critical impact on algorithmic perfor-mance, and over-fitting of parameter tuning is a dire threat to external validity of empirical analyses in SBSE. Based on this large empirical evidence, we give guidelines on how to handle parameter tuning
'Support our networking and help us belong!': listening to beginning secondary school science teachers
This study, drawing on the voice of beginning teachers, seeks to illuminate their experiences of building professional relationships as they become part of the teaching profession. A networking perspective was taken to expose and explore the use of others during the first three years of a teacherâs workplace experience. Three case studies, set within a wider sample of 11 secondary school science teachers leaving one UK universityâs PostGraduate Certificate in Education, were studied. The project set out to determine the nature of the networks used by teachers in terms of both how they were being used for their own professional development and perceptions of how they were being used by others in school. Affordances and barriers to networking were explored using notions of identity formation through social participation. The focus of the paper is on how the teachers used others to help shape their sense of belonging to this, their new workplace. The paper develops ideas from network theories to argue that membership of the communities are a subset of the professional interârelationships teachers utilise for their professional development. During their first year of teaching, eight teachers were interviewed, completing 13 semiâstructured interviews. This was supplemented in Year 2 by a questionnaire survey of their experiences. In the third year of the programme, 11 teachers (including the original sample of eight) were surveyed using a network mapping tool in which they represented their communications with people, groups and resources. Finally, three of the teachers (common to both samples) were then interviewed specifically about their networking practices and experiences using the generation of their network map as a stimulated recall focus. The implications of the analysis of these accounts are that these beginning teachers did not perceive of themselves wholly as novices and that their personal aspirations to increase participation in practical science, develop a career or work for pupils holistically did not always sit comfortably with the school communities into which they were being accommodated. While highlighting the importance of trust and respect in establishing relationships, these teachersâ accounts highlight the importance of finding âpeersâ from whom they can find support and with whom they can reflect and potentially collaborate towards developing practice. They also raise questions about who these âpeersâ might be and where they might be found
Role of Clinical Laboratory Markers of inflammation in Assessing Chronic Graft Versus Host Disease (cGVHD) Activity and Severity
Balloon Measurements of Cosmic Ray Muon Spectra in the Atmosphere along with those of Primary Protons and Helium Nuclei over Mid-Latitude
We report here the measurements of the energy spectra of atmospheric muons
and of the cosmic ray primary proton and helium nuclei in a single experiment.
These were carried out using the MASS superconducting spectrometer in a balloon
flight experiment in 1991. The relevance of these results to the atmospheric
neutrino anomaly is emphasized. In particular, this approach allows
uncertainties caused by the level of solar modulation, the geomagnetic cut-off
of the primaries and possible experimental systematics to be decoupled in the
comparison of calculated fluxes of muons to measured muon fluxes. The muon
observations cover the momentum and depth ranges of 0.3-40 GeV/c and 5-886
g/cmsquared, respectively. The proton and helium primary measurements cover the
rigidity range from 3 to 100 GV, in which both the solar modulation and the
geomagnetic cut-off affect the energy spectra at low energies.Comment: 31 pages, including 17 figures, simplified apparatus figure, to
appear in Phys. Rev.
Calibration of a Proton Polarimeter
This research was sponsored by the National Science Foundation Grant NSF PHY-931478
The Intentional Use of Service Recovery Strategies to Influence Consumer Emotion, Cognition and Behaviour
Service recovery strategies have been identified as a critical factor in the success of. service organizations. This study develops a conceptual frame work to investigate how specific service recovery strategies influence the emotional, cognitive and negative behavioural responses of . consumers., as well as how emotion and cognition influence negative behavior. Understanding the impact of specific service recovery strategies will allow service providers' to more deliberately and intentionally engage in strategies that result in positive organizational outcomes. This study was conducted using a 2 x 2 between-subjects quasi-experimental design. The results suggest that service recovery has a significant impact on emotion, cognition and negative behavior. Similarly, satisfaction, negative emotion and positive emotion all influence negative behavior but distributive justice has no effect
- âŠ