Advances on Matroid Secretary Problems: Free Order Model and Laminar Case

The most well-known conjecture in the context of matroid secretary problems claims the existence of a constant-factor approximation applicable to any matroid. Whereas this conjecture remains open, modified forms of it were shown to be true, when assuming that the assignment of weights to the secretaries is not adversarial but uniformly random (Soto [SODA 2011], Oveis Gharan and Vondr\'ak [ESA 2011]). However, so far, there was no variant of the matroid secretary problem with adversarial weight assignment for which a constant-factor approximation was found. We address this point by presenting a 9-approximation for the \emph{free order model}, a model suggested shortly after the introduction of the matroid secretary problem, and for which no constant-factor approximation was known so far. The free order model is a relaxed version of the original matroid secretary problem, with the only difference that one can choose the order in which secretaries are interviewed. Furthermore, we consider the classical matroid secretary problem for the special case of laminar matroids. Only recently, a constant-factor approximation has been found for this case, using a clever but rather involved method and analysis (Im and Wang, [SODA 2011]) that leads to a 16000/3-approximation. This is arguably the most involved special case of the matroid secretary problem for which a constant-factor approximation is known. We present a considerably simpler and stronger $3\sqrt{3}e\approx 14.12$-approximation, based on reducing the problem to a matroid secretary problem on a partition matroid

Singularly Perturbed Monotone Systems and an Application to Double Phosphorylation Cycles

The theory of monotone dynamical systems has been found very useful in the modeling of some gene, protein, and signaling networks. In monotone systems, every net feedback loop is positive. On the other hand, negative feedback loops are important features of many systems, since they are required for adaptation and precision. This paper shows that, provided that these negative loops act at a comparatively fast time scale, the main dynamical property of (strongly) monotone systems, convergence to steady states, is still valid. An application is worked out to a double-phosphorylation ``futile cycle'' motif which plays a central role in eukaryotic cell signaling.Comment: 21 pages, 3 figures, corrected typos, references remove

Soft Openings: The psycho-technological expertise of third sector curriculum reform

Since the late 1990s the "third sector" has become active in generating new curriculum programmes in England. Based on tracing third sector participation in public education during the New Labour years, the article explores a documentary archive of third sector curriculum texts and argues that the programmes, strategies and techniques of the third sector have sought to pursue a new form of governmentality. The type of governmentality pursued by the third sector takes form as a "soft" style of curriculum reform derived from assembling together cybernetic and psychological forms of expertise, interactionist and constructivist pedagogies, and an emerging "psycho-technology" of subjectivity. The third sector fabricates reform proposals for a curriculum of the future in which governance is done by cross-sectoral networking, epistemological categories are blurred, and student subjectivities are made up to be malleable, soft-skilled and psychologically self-shaping. The article examines how third sector texts have assembled this new psycho-technological expertise of curriculum reform through both cybernetic and psychological styles of thinking

Search for the standard model Higgs boson decaying into two photons in pp collisions at sqrt(s)=7 TeV

A search for a Higgs boson decaying into two photons is described. The analysis is performed using a dataset recorded by the CMS experiment at the LHC from pp collisions at a centre-of-mass energy of 7 TeV, which corresponds to an integrated luminosity of 4.8 inverse femtobarns. Limits are set on the cross section of the standard model Higgs boson decaying to two photons. The expected exclusion limit at 95% confidence level is between 1.4 and 2.4 times the standard model cross section in the mass range between 110 and 150 GeV. The analysis of the data excludes, at 95% confidence level, the standard model Higgs boson decaying into two photons in the mass range 128 to 132 GeV. The largest excess of events above the expected standard model background is observed for a Higgs boson mass hypothesis of 124 GeV with a local significance of 3.1 sigma. The global significance of observing an excess with a local significance greater than 3.1 sigma anywhere in the search range 110-150 GeV is estimated to be 1.8 sigma. More data are required to ascertain the origin of this excess.Comment: Submitted to Physics Letters

Comparison of the impacts of elevated CO₂ soil gas concentrations on selected European terrestrial environments

Selected European studies have illustrated the impacts of elevated CO₂ concentrations in shallow soils on pasture. For the first time, general unified conclusions can be made, providing CO₂ thresholds where effects on plants and soil microbiology are observed and making recommendations on how this information can be used when planning projects for CO₂ storage. The sites include those where CO₂ is being naturally released to the atmosphere from deep geological formations; and a non-adapted site, with no previous history of CO₂ seepage, where CO₂ has been injected into the unsaturated soil horizon. Whilst soil gas concentrations will be influenced by flux rates and other factors, the results suggest that a concentration of between 10% and 15% CO₂ soil gas at 20 cm depth, which is within the root zone, is an important threshold level for observing changes in plant coverage. Site-specific plant ‘indicators’ are also observed for CO₂ concentrations at ≥35%. Microbiological changes are seen where CO₂ soil gas concentrations are between 15% and 40%. As part of site characterisation, an evaluation of the risks of leakage and their potential environmental impacts should be undertaken

Velocity-space sensitivity of the time-of-flight neutron spectrometer at JET

The velocity-space sensitivities of fast-ion diagnostics are often described by so-called weight functions. Recently, we formulated weight functions showing the velocity-space sensitivity of the often dominant beam-target part of neutron energy spectra. These weight functions for neutron emission spectrometry (NES) are independent of the particular NES diagnostic. Here we apply these NES weight functions to the time-of-flight spectrometer TOFOR at JET. By taking the instrumental response function of TOFOR into account, we calculate time-of-flight NES weight functions that enable us to directly determine the velocity-space sensitivity of a given part of a measured time-of-flight spectrum from TOFOR