Measurements of second‐ and third‐order nonlinear polarizabilities for HF and HCl

Measurements of second‐ and third‐order nonlinear polarizabilities (hyperpolarizabilities) for HF and HCl using dc electric‐field‐induced second‐harmonic generation are presented: χ(3)∥(HF)=70(10)×10−39 esu/mol, χ(2)∥ (HF)=−4.70(41)×10−32 esu/mol, χ(3)∥(HCl)= 347(15)×10−39 esu/mol, χ(2)∥(HCl)= −4.22(50)×10−32 esu/mol. In the case of HF this allows a critical comparison with theory. HF has fewer electrons than any polar molecule previously studied experimentally and the small size of HF has made it an attractive candidate for theoretical investigation. Christiansen and McCullough have used numerical Hartree–Fock techniques to establish generally accepted criteria for basis set selection; and Bartlett and Purvis have applied to HF the most elaborate technique applied so far to the calculation of any molecular hyperpolarizability (CHF SDQ‐MBPT[4]). Experimental corrections and uncertainties are carefully considered as are several other factors relevant to a comparison of these experimental and theoretical data. The theoretical results are about a factor of 2 smaller than the experimental data and none of the factors considered seems to offer a resolution of this discrepancy.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70699/2/JCPSA6-82-10-4673-1.pd

Modulation instability, Akhmediev Breathers and continuous wave supercontinuum generation

Numerical simulations of the onset phase of continuous wave supercontinuum generation from modulation instability show that the structure of the field as it develops can be interpreted in terms of the properties of Akhmediev Breathers. Numerical and analytical results are compared with experimental measurements of spectral broadening in photonic crystal fiber using nanosecond pulsesComment: 22 pages, 6 figure

Magnetic shielding and exotic spin-dependent interactions

Experiments searching for exotic spin-dependent interactions typically employ magnetic shielding between the source of the exotic field and the interrogated spins. We explore the question of what effect magnetic shielding has on detectable signals induced by exotic fields. Our general conclusion is that for common experimental geometries and conditions, magnetic shields should not significantly reduce sensitivity to exotic spin-dependent interactions, especially when the technique of comagnetometry is used. However, exotic fields that couple to electron spin can induce magnetic fields in the interior of shields made of a soft ferro- or ferrimagnetic material. This induced magnetic field must be taken into account in the interpretation of experiments searching for new spin-dependent interactions and raises the possibility of using a flux concentrator inside magnetic shields to amplify exotic spin-dependent signals.Comment: 8 pages, 5 figure

Influence of turbulence on the dynamo threshold

We use direct and stochastic numerical simulations of the magnetohydrodynamic equations to explore the influence of turbulence on the dynamo threshold. In the spirit of the Kraichnan-Kazantsev model, we model the turbulence by a noise, with given amplitude, injection scale and correlation time. The addition of a stochastic noise to the mean velocity significantly alters the dynamo threshold. When the noise is at small (resp. large) scale, the dynamo threshold is decreased (resp. increased). For a large scale noise, a finite correlation time reinforces this effect

Nonlinear wavelength conversion in photonic crystal fibers with three zero dispersion points

In this theoretical study, we show that a simple endlessly single-mode photonic crystal fiber can be designed to yield, not just two, but three zero-dispersion wavelengths. The presence of a third dispersion zero creates a rich phase-matching topology, enabling enhanced control over the spectral locations of the four-wave-mixing and resonant-radiation bands emitted by solitons and short pulses. The greatly enhanced flexibility in the positioning of these bands has applications in wavelength conversion, supercontinuum generation and pair-photon sources for quantum optics

Modulation control and spectral shaping of optical fiber supercontinuum generation in the picosecond regime

Numerical simulations are used to study how fiber supercontinuum generation seeded by picosecond pulses can be actively controlled through the use of input pulse modulation. By carrying out multiple simulations in the presence of noise, we show how tailored supercontinuum Spectra with increased bandwidth and improved stability can be generated using an input envelope modulation of appropriate frequency and depth. The results are discussed in terms of the non-linear propagation dynamics and pump depletion.Comment: Aspects of this work were presented in Paper ThJ2 at OECC/ACOFT 2008, Sydney Australia 7-10 July (2008). Journal paper submitted for publication 30 July 200

Curvature Diffusions in General Relativity

We define and study on Lorentz manifolds a family of covariant diffusions in which the quadratic variation is locally determined by the curvature. This allows the interpretation of the diffusion effect on a particle by its interaction with the ambient space-time. We will focus on the case of warped products, especially Robertson-Walker manifolds, and analyse their asymptotic behaviour in the case of Einstein-de Sitter-like manifolds.Comment: 34 page

Catalogue of extreme wave events in Ireland: revised and updated for 14680 BP - 2017

This paper aims to extend and update the survey of extreme wave events in Ireland that was previously carried out by O’Brien et al. (2013). The original catalogue highlighted the frequency of such events dating back as far as the turn of the last ice age through to 2012. Ireland’s marine territory extends far beyond its coastline and is one of the largest seabed territories in Europe. It is therefore not surprising that extreme waves have continued to occur regularly since 2012, particularly considering the severity of weather during the winters of 2013-14 and 2015-16. In addition, a large number of storm surges have been identified since the publication of the original catalogue. This paper updates the O’Brien et al. (2013) catalogue to include events up to the end of 2016. Storm surges are included as a new category and events are categorised into long waves (tsunamis and storm surges) and short waves (storm and rogue waves). New results prior to 2012 are also included and some of the events previously documented are reclassified. Important questions regarding public safety, services and the influence of climate change are also highlighted

The impact of the Art Therapy Large Group, an educational tool in the training of art therapists, on post-qualification professional practice

This article reports the findings of a Likert scale survey that was sent to past graduates of the MA Art Psychotherapy, Goldsmiths, University of London asking them about the relevance of their experience in the Art Therapy Large Group (ATLG) to their subsequent employment as art therapists or work in another capacity. The ATLG comprises all the students and staff in a psychodynamically based experiential group that meets six times during the year. Survey questions were drawn from previously devised theory and related to learning relevant to the workplace and the development of professional identity. Though there was a low response rate (20%), there were some significant findings, namely that graduates found the ATLG to be helpful in their work, whether this was art therapy or non-art therapy work, and that those who had studied part-time were much more positive about the applicability of their learning in the group to their work than those who had studied full-time. The findings suggest that the ATLG has a particular role in meeting key performance indicators in professional regulation and teaching and in quality assurance and employability policies in higher education. Finally, the potential for the use of the ATLG beyond the university in the public, private and voluntary sectors is suggested