4,402 research outputs found
Hawking radiation from "phase horizons" in laser filaments?
Belgiorno et al have reported on experiments aiming at the detection of (the
analogue of) Hawking radiation using laser filaments [F. Belgiorno et al, Phys.
Rev. Lett. 105, 203901 (2010)]. They sent intense focused Bessel pulses into a
non-linear dielectric medium in order to change its refractive index via the
Kerr effect and saw creation of photons orthogonal to the direction of travel
of the pluses. Since the refractive index change in the pulse generated a
"phase horizon" (where the phase velocity of these photons equals the pulse
speed), they concluded that they observed the analogue of Hawking radiation. We
study this scenario in a model with a phase horizon and a phase velocity very
similar to that of their experiment and find that the effective metric does not
quite correspond to a black hole. The photons created in this model are not due
to the analogue of black hole evaporation but have more similarities to
cosmological particle creation. Nevertheless, even this effect cannot explain
the observations -- unless the pulse has significant small scale structure in
both the longitudinal and transverse dimensions.Comment: 13 pages RevTeX, 2 figure
Breaking of the overall permutation symmetry in nonlinear optical susceptibilities of one-dimensional periodic dimerized Huckel model
Based on infinite one-dimensional single-electron periodic models of
trans-polyacetylene, we show analytically that the overall permutation symmetry
of nonlinear optical susceptibilities is, albeit preserved in the molecular
systems with only bound states, no longer generally held for the periodic
systems. The overall permutation symmetry breakdown provides a fairly natural
explanation to the widely observed large deviations of Kleinman symmetry for
periodic systems in off-resonant regions. Physical conditions to experimentally
test the overall permutation symmetry break are discussed.Comment: 7 pages, 1 figur
The association between childhood hearing loss and self-reported peer victimisation, depressive symptoms, and self-harm: longitudinal analyses of a prospective, nationally representative cohort study
BACKGROUND: Childhood hearing loss (HL) predicts poor mental health and is associated with a higher risk of communication difficulties. The relationship of childhood HL with specific types of poor mental health (such as depressive symptoms or self-harm) and peer victimisation remains unclear. METHODS: We analysed data from the Millennium Cohort Study (MCS), a prospective observational cohort study of children living in the UK at age 9 months and born between 2000 to 2002. Data were available on the children and their families at ages 9 months, then at 3, 5, 7, 11, and 14 years. Participants were 10,858 singleton children with self-reported data on peer victimisation, depressive symptoms, and self-harm at age 14 years. Multivariable logistic regression models were fitted to estimate odds ratios (OR) for HL with peer victimisation, depressive symptoms, and self-harm. HL presence was examined in terms of any HL between ages 9 months and 14 years, as well as by HL trajectory type (defined by onset and persistence). Analyses were adjusted for potential sources of confounding, survey design, and attrition at age 14 years. Interactions between sex and HL were examined in each model and multiple imputation procedures used to address missing data. RESULTS: Children with any HL had increased odds of depressive symptoms (OR: 1.32, 95% CI: 1.09–1.60), self-harm (1.41, 1.12–1.78) and, in girls only, peer victimisation (girls: 1.81, 1.29–2.55; boys: 1.05, 0.73–1.51), compared to those without HL. HL with later age at onset and persistence to age 14 years was the only trajectory associated with all outcomes. CONCLUSIONS: Childhood HL may predict peer victimisation (in girls), depressive symptoms, and self-harm. Further research is needed to identify HL trajectories and methods to facilitate good mental health in children with HL. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12889-022-13457-6
Investigation of rising nitrate concentrations in groundwater in the Eden Valley, Cumbria: Phase 1 project scoping study
This is the Investigation of rising nitrate concentrations in groundwater in the Eden Valley, Cumbria report produced by the Environment Agency in 2003. This report focuses on groundwater nitrate concentrations in the Eden Valley. Most boreholes in the Eden Valley had nitrate concentrations less than 20 mg/l but a significant number had higher concentrations, some exceeding the EC maximum admissible concentration for drinking water of 50 mg/l. The main objectives of this report were to investigate the causes of rising nitrate concentrations in groundwater in the Permo-Triassic sandstone aquifers of the Eden Valley area and provide sufficient understanding of the groundwater and surface water flow system, including the sources of the nitrate contamination and the processes controlling nitrate movement, so that possible management options for reversing this trend can be considered
Multipole nonlinearity of metamaterials
We report on the linear and nonlinear optical response of metamaterials
evoked by first and second order multipoles. The analytical ground on which our
approach bases permits for new insights into the functionality of
metamaterials. For the sake of clarity we focus here on a key geometry, namely
the split-ring resonator, although the introduced formalism can be applied to
arbitrary structures. We derive the equations that describe linear and
nonlinear light propagation where special emphasis is put on second harmonic
generation. This contribution basically aims at stretching versatile and
existing concepts to describe light propagation in nonlinear media towards the
realm of metamaterials.Comment: 7 pages, 3 figure
Generation and transcriptional programming of intestinal dendritic cells: essential role of retinoic acid
The vitamin A metabolite retinoic acid (RA) regulates adaptive immunity in the intestines, with well-characterized effects on IgA responses, Treg induction and gut trafficking of T and B effector cells. It also controls the generation of cDC precursors in the bone marrow and regulates cDC subset representation, but its roles in the specialization of intestinal cDC subsets is understudied. Here we show that RA acts cell-intrinsically in developing gut-tropic pre-mucosal DC (pre-μDC) to effect the differentiation and drive the specialization of intestinal CD103+CD11b− (cDC1) and of CD103+CD11b+ (cDC2). Systemic deficiency or DC-restricted antagonism of RA signaling resulted in altered phenotypes of intestinal cDC1 and cDC2, and reduced numbers of cDC2. Effects of dietary deficiency were most apparent in the proximal small intestine, and were rapidly reversed by reintroducing vitamin A. In cultures of pre-μDC with Flt3L and GM-CSF, RA induced cDC with characteristic phenotypes of intestinal cDC1 and cDC2 by controlling subset-defining cell surface receptors, regulating subset-specific transcriptional programs, and suppressing proinflammatory NF-κB-dependent gene expression. Thus RA is required for transcriptional programming and maturation of intestinal cDC, and with GM-CSF and Flt3L provides a minimal environment for in vitro generation of intestinal cDC1- and cDC2-like cDC from specialized precursors
Backward error analysis and the substitution law for Lie group integrators
Butcher series are combinatorial devices used in the study of numerical
methods for differential equations evolving on vector spaces. More precisely,
they are formal series developments of differential operators indexed over
rooted trees, and can be used to represent a large class of numerical methods.
The theory of backward error analysis for differential equations has a
particularly nice description when applied to methods represented by Butcher
series. For the study of differential equations evolving on more general
manifolds, a generalization of Butcher series has been introduced, called
Lie--Butcher series. This paper presents the theory of backward error analysis
for methods based on Lie--Butcher series.Comment: Minor corrections and additions. Final versio
Risk factors for permanent childhood hearing impairment.
OBJECTIVE: While several perinatal risk factors for permanent childhood hearing impairment (PCHI) are known, association with gestational length remains unclear. We hypothesised that shorter gestational length predicts higher PCHI risk. DESIGN: 19 504 participants from the UK Millennium Cohort Study (born 2000-2002, prior to newborn screening). METHODS: Multivariable discrete-time survival analysis to examine associations between parent-reported PCHI by age 11 years and gestational length, plus other prespecified factors. RESULTS: PCHI affected 2.1 per 1000 children (95% CI 1.5 to 3.0) by age 11; however, gestational length did not predict PCHI risk (HR, 95% CI 1.00, 0.98 to 1.03 per day increase). Risk was increased in those with neonatal illness, with or without admission to neonatal care (6.33, 2.27 to 17.63 and 2.62, 1.15 to 5.97, respectively), of Bangladeshi or Pakistani ethnicity (2.78, 1.06 to 7.31) or born to younger mothers (0.92, 0.87 to 0.97 per year). CONCLUSION: Neonatal illness, rather than gestational length, predicts PCHI risk. Further research should explore associations with ethnicity.EB is funded by an Economic and Social Research Council studentship, grant number: ES/J500185/1. RLK is a Clinical Advisor to the NHS Newborn Blood Spot Screening Programme at Public Health England. CD is supported by Health Data Research UK, which is funded by the UK Medical Research Council, Engineering and Physical Sciences Research Council, Economic and Social Research Council, National Institute for Health Research (England), Chief Scientist Office of the Scottish Government Health and Social Care Directorates, Health and Social Care Research and Development Division (Welsh Government), Public Health Agency (Northern Ireland), British Heart Foundation and Wellcome Trust. All research at Great Ormond Street Hospital NHS Foundation Trust and UCL Great Ormond Street Institute of Child Health is made possible by the NIHR Great Ormond Street Hospital Biomedical Research Centre. The Millennium Cohort Study is funded by grants to former and current directors of the study from the Economic and Social Research Council (Professor Heather Joshi, Professor Lucinda Platt and Professor Emla Fitzsimons) and a consortium of government funders
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