760 research outputs found
Superpotential de-sequestering in string models
Non-perturbative superpotential cross-couplings between visible sector matter
and K\"ahler moduli can lead to significant flavour-changing neutral currents
in compactifications of type IIB string theory. Here, we compute corrections to
Yukawa couplings in orbifold models with chiral matter localised on D3-branes
and non-perturbative effects on distant D7-branes. By evaluating a threshold
correction to the D7-brane gauge coupling, we determine conditions under which
the non-perturbative corrections to the Yukawa couplings appear. The flavour
structure of the induced Yukawa coupling generically fails to be aligned with
the tree-flavour structure. We check our results by also evaluating a
correlation function of two D7-brane gauginos and a D3-brane Yukawa coupling.
Finally, by calculating a string amplitude between n hidden scalars and visible
matter we show how non-vanishing vacuum expectation values of distant D7-brane
scalars, if present, may correct visible Yukawa couplings with a flavour
structure that differs from the tree-level flavour structure.Comment: 37 pages + appendices, 8 figure
"The impact of mediation on resolution of disagreements around special educational needs: Effectiveness and cost effectiveness"
Under England’s Children and Families Act 2014, local authorities (LAs) have a statutory responsibility to provide an independent mediation service for cases of disagreement between parents or young people and the LAs where parents or the young person are considering an appeal to the First-tier Tribunal Special Educational Needs (SEN) and DisabilityWe examined the effectiveness and cost effectiveness of mediation in resolving such disagreements without recourse to an appeal to the Tribunal. Our data comprised three national surveys, two supplementary surveys and individual interviews with LA staff and parents to explore implementation of the new mediation system and the impact on appeals and costs over 2014–16 from 109 English LAs who provided data. Our findings indicate that families who took up mediation were significantly less likely to appeal to the Tribunal, absolute risk reduction 13.58% (95% CI: 10.20%, 16.97%). The cost saving across all cases, of different complexity, was £636,462 overall, approximately £500 per case. Overall, mediation was found to be a promising method of disagreement resolution, reducing appeals and producing savings in both financial and human well-being costs. To the best of our knowledge, this is the first study of both the effectiveness and cost effectiveness of mediation as a means of resolution of disputes about meeting children's SEN
Conformational analysis and in vitro immunomodulatory and insulinotropic properties of the frog skin host-defense peptide rhinophrynin-27 and selected analogs
The study investigates conformational analysis and the in vitro cytokine-mediated immunomodulatory and insulin-releasing activities of rhinophrynin-27 (ELRLPEIARPVPEVLPARLPLPALPRN; RP-27), a proline-arginine-rich peptide first isolated from skin secretions of the Mexican burrowing toad Rhinophrynus dorsalis (Rhinophrynidae). In both water and 50% trifluoroethanol-water, the peptide adopts a polyproline type II helical conformation with a high degree of deviation from the canonical collagen-like folding and a pronounced bend in the molecule at the Glu13 residue. Incubation of mouse peritoneal cells with RP-27 significantly (P < 0.05) inhibited production of the pro-inflammatory cytokines TNF-α and IL-1β and stimulated production of the anti-inflammatory cytokine IL-10. The peptide significantly (P < 0.01) stimulated release of insulin from BRIN-BD11 rat clonal β-cells at concentrations ≥ 1 nM while maintaining the integrity of the plasma membrane and also stimulated insulin release from isolated mouse islets at a concentration of 10−6 M. Increasing the cationicity of RP-27 by substituting glutamic acid residues in the peptide by arginine and increasing hydrophobicity by substituting alanine residues by tryptophan did not result in analogues with increased activity with respect to cytokine production and insulin release. The combination of immunosuppressive and insulinotropic activities together with very low cytotoxicity suggests that RP-27 may represent a template for the development of an agent for use in anti-inflammatory and Type 2 diabetes therapies
Towards a Systematic Construction of Realistic D-brane Models on a del Pezzo Singularity
A systematic approach is followed in order to identify realistic D-brane
models at toric del Pezzo singularities. Requiring quark and lepton spectrum
and Yukawas from D3 branes and massless hypercharge, we are led to Pati-Salam
extensions of the Standard Model. Hierarchies of masses, flavour mixings and
control of couplings select higher order del Pezzo singularities, minimising
the Higgs sector prefers toric del Pezzos with dP3 providing the most
successful compromise. Then a supersymmetric local string model is presented
with the following properties at low energies: (i) the MSSM spectrum plus a
local B-L gauge field or additional Higgs fields depending on the breaking
pattern, (ii) a realistic hierarchy of quark and lepton masses and (iii)
realistic flavour mixing between quark and lepton families with computable CKM
and PMNS matrices, and CP violation consistent with observations. In this
construction, kinetic terms are diagonal and under calculational control
suppressing standard FCNC contributions. Proton decay operators of dimension 4,
5, 6 are suppressed, and gauge couplings can unify depending on the breaking
scales from string scales at energies in the range 10^{12}-10^{16} GeV,
consistent with TeV soft-masses from moduli mediated supersymmetry breaking.
The GUT scale model corresponds to D3 branes at dP3 with two copies of the
Pati-Salam gauge symmetry SU(4)\timesSU(2)R\timesSU(2)L. D-brane instantons
generate a non-vanishing mu-term. Right handed sneutrinos can break the B-L
symmetry and induce a see-saw mechanism of neutrino masses and R-parity
violating operators with observable low-energy implications.Comment: 27 pages plus 5 appendices (42 pages total), 9 figures. v3: equation
refs and citation correcte
The Two Faces of Anomaly Mediation
Anomaly mediation is a ubiquitous source of supersymmetry (SUSY) breaking
which appears in almost every theory of supergravity. In this paper, we show
that anomaly mediation really consists of two physically distinct phenomena,
which we dub "gravitino mediation" and "Kahler mediation". Gravitino mediation
arises from minimally uplifting SUSY anti-de Sitter (AdS) space to Minkowski
space, generating soft masses proportional to the gravitino mass. Kahler
mediation arises when visible sector fields have linear couplings to SUSY
breaking in the Kahler potential, generating soft masses proportional to beta
function coefficients. In the literature, these two phenomena are lumped
together under the name "anomaly mediation", but here we demonstrate that they
can be physically disentangled by measuring associated couplings to the
goldstino. In particular, we use the example of gaugino soft masses to show
that gravitino mediation generates soft masses without corresponding goldstino
couplings. This result naively violates the goldstino equivalence theorem but
is in fact necessary for supercurrent conservation in AdS space. Since
gravitino mediation persists even when the visible sector is sequestered from
SUSY breaking, we can use the absence of goldstino couplings as an unambiguous
definition of sequestering.Comment: 21 pages, 1 table; v2, references added, extended discussion in
introduction and appendix; v3, JHEP versio
Anomalous U(1) Mediation in Large Volume Compactification
We study the general effects of anomalous U(1)_A gauge symmetry on soft
supersymmetry (SUSY) breaking terms in large volume scenario, where the MSSM
sector is localized on a small cycle whose volume is stabilized by the D-term
potential of the U(1)_A. Since it obtains SUSY breaking mass regardless of the
detailed form of K\"ahler potential, the U(1)_A vector superfield acts as a
messenger mediating the SUSY breaking in the moduli sector to the MSSM sector.
Then, through the loops of U(1)_A vector superfield, there arise soft masses of
the order of m_{3/2}^2/8\pi^2 for scalar mass squares, m_{3/2}/(8\pi^2)^2 for
gaugino masses, and m_{3/2}/8\pi^2 for A-paramteres. In addition, the massive
U(1)_A vector superfield can have non-zero F and D-components through the
moduli mixing in the K\"ahler potential, and this can result in larger soft
masses depending upon the details of the moduli mixing. For instance, in the
presence of one-loop induced moduli mixing between the visible sector modulus
and the large volume modulus, the U(1)_A D-term provides soft scalar mass
squares of the order of m_{3/2}^2. However, if the visible sector modulus is
mixed only with small cycle moduli, its effect on soft terms depends on how to
stabilize the small cycle moduli.Comment: 28pages, no fi
Sparticle Spectrum of Large Volume Compactification
We examine the large volume compactification of Type IIB string theory or its
F theory limit and the associated supersymmetry breakdown and soft terms. It is
crucial to incorporate the loop-induced moduli mixing, originating from
radiative corrections to the Kahler potential. We show that in the presence of
moduli mixing, soft scalar masses generically receive a D-term contribution of
the order of the gravitino mass m_{3/2} when the visible sector cycle is
stabilized by the D-term potential of an anomalous U(1) gauge symmetry, while
the moduli-mediated gaugino masses and A-parameters tend to be of the order of
m_{3/2}/8pi^2. It is noticed also that a too large moduli mixing can
destabilize the large volume solution by making it a saddle point.Comment: 29 page
Kahler Independence of the G2-MSSM
The G2-MSSM is a model of particle physics coupled to moduli fields with
interesting phenomenology both for colliders and astrophysical experiments. In
this paper we consider a more general model - whose moduli Kahler potential is
a completely arbitrary G2-holonomy Kahler potential and whose matter Kahler
potential is also more general. We prove that the vacuum structure and spectrum
of BSM particles is largely unchanged in this much more general class of
theories. In particular, gaugino masses are still supressed relative to the
gravitino mass and moduli masses. We also consider the effects of higher order
corrections to the matter Kahler potential and find a connection between the
nature of the LSP and flavor effects.Comment: Final version, matches the version published in JHE
Regularized gene selection in cancer microarray meta-analysis
<p>Abstract</p> <p>Background</p> <p>In cancer studies, it is common that multiple microarray experiments are conducted to measure the same clinical outcome and expressions of the same set of genes. An important goal of such experiments is to identify a subset of genes that can potentially serve as predictive markers for cancer development and progression. Analyses of individual experiments may lead to unreliable gene selection results because of the small sample sizes. Meta analysis can be used to pool multiple experiments, increase statistical power, and achieve more reliable gene selection. The meta analysis of cancer microarray data is challenging because of the high dimensionality of gene expressions and the differences in experimental settings amongst different experiments.</p> <p>Results</p> <p>We propose a Meta Threshold Gradient Descent Regularization (MTGDR) approach for gene selection in the meta analysis of cancer microarray data. The MTGDR has many advantages over existing approaches. It allows different experiments to have different experimental settings. It can account for the joint effects of multiple genes on cancer, and it can select the same set of cancer-associated genes across multiple experiments. Simulation studies and analyses of multiple pancreatic and liver cancer experiments demonstrate the superior performance of the MTGDR.</p> <p>Conclusion</p> <p>The MTGDR provides an effective way of analyzing multiple cancer microarray studies and selecting reliable cancer-associated genes.</p
Age-related changes in global motion coherence: conflicting haemodynamic and perceptual responses
Our aim was to use both behavioural and neuroimaging data to identify indicators of perceptual decline in motion processing. We employed a global motion coherence task and functional Near Infrared Spectroscopy (fNIRS). Healthy adults (n = 72, 18-85) were recruited into the following groups: young (n = 28, mean age = 28), middle-aged (n = 22, mean age = 50), and older adults (n = 23, mean age = 70). Participants were assessed on their motion coherence thresholds at 3 different speeds using a psychophysical design. As expected, we report age group differences in motion processing as demonstrated by higher motion coherence thresholds in older adults. Crucially, we add correlational data showing that global motion perception declines linearly as a function of age. The associated fNIRS recordings provide a clear physiological correlate of global motion perception. The crux of this study lies in the robust linear correlation between age and haemodynamic response for both measures of oxygenation. We hypothesise that there is an increase in neural recruitment, necessitating an increase in metabolic need and blood flow, which presents as a higher oxygenated haemoglobin response. We report age-related changes in motion perception with poorer behavioural performance (high motion coherence thresholds) associated with an increased haemodynamic response
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