Carrier dynamics in ion-implanted GaAs studied by simulation and observation of terahertz emission

We have studied terahertz (THz) emission from arsenic-ion implanted GaAs both experimentally and using a three-dimensional carrier dynamics simulation. A uniform density of vacancies was formed over the optical absorption depth of bulk GaAs samples by performing multi-energy implantations of arsenic ions (1 and 2.4MeV) and subsequent thermal annealing. In a series of THz emission experiments the frequency of peak THz power was found to increase significantly from 1.4 to 2.2THz when the ion implantation dose was increased from 10^13 to 10^16 cm-3. We used a semi-classical Monte-Carlo simulation of ultra-fast carrier dynamics to reproduce and explain these results. The effect of the ion-induced damage was included in the simulation by considering carrier scattering at neutral and charged impurities, as well as carrier trapping at defect sites. Higher vacancy concentrations and shorter carrier trapping times both contributed to shorter simulated THz pulses, the latter being more important over experimentally realistic parameter ranges.Comment: 6 pages, 7 figure

Ineffective contracts, restitution and the change of position defence: About a recent decision rendered by the High Court of Justice of London

The paper, moving from a cross-border case and with a comparative law perspective, addresses which is the operative rule of Restitutionary claim resulting from an ineffective contract, assessing whether it would be achievable, under Italian Law, the same results of the “Change of Position Defence” under common law.  The topic relates to the broader issue of allocating costs incurred by the party who performed a void contract in reliance on its validity, for which, under Italian Law, guidance could be given by Section 1328, paragraph 1, second part, of Italian  Civil Code.Il contributo affronta, muovendo da un caso cross border e con sguardo comparatistico, la questione del regime applicabile alle restituzioni che conseguono alla declaratoria di nullità contrattuale, focalizzandosi sulla configurabilità, nell’ordinamento domestico, una tutela, per il convenuto in ripetizione, funzionalmente accostabile a quella che il common law indica come “Change of Position Defence”. Il tema si incentra su quello, più ampio, dell’allocazione dei costi sopportati dalla parte che ha eseguito un contratto nullo confidando nella sua validità, per il quale può guardarsi al principio sotteso all’art. 1328, comma 1°, seconda parte, c.c

Local Swift-BAT active galactic nuclei prefer circumnuclear star formation

We use Herschel data to analyze the size of the far-infrared 70micron emission for z<0.06 local samples of 277 hosts of Swift-BAT selected active galactic nuclei (AGN), and 515 comparison galaxies that are not detected by BAT. For modest far-infrared luminosities 8.5<log(LFIR)<10.5, we find large scatter of half light radii Re70 for both populations, but a typical Re70 <~ 1 kpc for the BAT hosts that is only half that of comparison galaxies of same far-infrared luminosity. The result mostly reflects a more compact distribution of star formation (and hence gas) in the AGN hosts, but compact AGN heated dust may contribute in some extremely AGN-dominated systems. Our findings are in support of an AGN-host coevolution where accretion onto the central black hole and star formation are fed from the same gas reservoir, with more efficient black hole feeding if that reservoir is more concentrated. The significant scatter in the far-infrared sizes emphasizes that we are mostly probing spatial scales much larger than those of actual accretion, and that rapid accretion variations can smear the distinction between the AGN and comparison categories. Large samples are hence needed to detect structural differences that favour feeding of the black hole. No size difference AGN host vs. comparison galaxies is observed at higher far-infrared luminosities log(LFIR)>10.5 (star formation rates >~ 6 Msun/yr), possibly because these are typically reached in more compact regions in the first place.Comment: 7 pages, 3 figures, accepted for publication in Astronomy & Astrophysic

Polarisation-sensitive terahertz detection by multicontact photoconductive receivers

We have developed a terahertz radiation detector that measures both the amplitude and polarization of the electric field as a function of time. The device is a three-contact photoconductive receiver designed so that two orthogonal electric-field components of an arbitrary polarized electromagnetic wave may be detected simultaneously. The detector was fabricated on Fe+ ion-implanted InP. Polarization-sensitive detection is demonstrated with an extinction ratio better than 100:1. This type of device will have immediate application in studies of birefringent and optically active materials in the far-infrared region of the spectrum.Comment: 3 pages, 3 figure

Spectral fluctuations of Schr\"odinger operators generated by critical points of the potential

Starting from the spectrum of Schr\"odinger operators on $\mathbb{R}^n$, we propose a method to detect critical points of the potential. We argue semi-classically on the basis of a mathematically rigorous version of Gutzwiller's trace formula which expresses spectral statistics in term of classical orbits. A critical point of the potential with zero momentum is an equilibrium of the flow and generates certain singularities in the spectrum. Via sharp spectral estimates, this fluctuation indicates the presence of a critical point and allows to reconstruct partially the local shape of the potential. Some generalizations of this approach are also proposed.\medskip keywords : Semi-classical analysis; Schr\"odinger operators; Equilibriums in classical mechanics.Comment: 18 pages, Final versio

Politics in the Classroom

Nursing and midwifery is, in the UK, regulated by the Nursing and Midwifery Council (NMC). Regulatory duties include establishing standards for education, and from January 2019, new educational programmes will be approved against standards detailed in the document Future nurse: Standards of proficiency for registered nurses (NMC, 2019 – hereafter ‘the standards’). This publication lists “the knowledge and skills that registered nurses must demonstrate when caring for people” (ibid, p.3); and from September 2020, registration (licence) will require the successful completion of programmes that have been ratified against these standards. The importance of this document in a UK context cannot be understated. However, less parochially, learning outcomes contained in section 7 of the standards raise questions that require educator attention whenever politically sensitive topics (broadly conceived) are discussed. This study explores these questions insofar as they relate to the stance (neutrality or partisanship) that educators adopt in politicised discussion, and the management of student speech/expression. Pratt, Boll and Collins’ (2007) paper Towards a plurality of perspectives for nurse educators is recruited to structure argument

Clathrin light chains CLCa and CLCb have non-redundant roles in epithelial lumen formation

To identify functional differences between vertebrate clathrin light chains (CLCa or CLCb), phenotypes of mice lacking genes encoding either isoform were characterised. Mice without CLCa displayed 50% neonatal mortality, reduced body weight, reduced fertility, and ∼40% of aged females developed uterine pyometra. Mice lacking CLCb displayed a less severe weight reduction phenotype compared with those lacking CLCa and had no survival or reproductive system defects. Analysis of female mice lacking CLCa that developed pyometra revealed ectopic expression of epithelial differentiation markers (FOXA2 and K14) and a reduced number of endometrial glands, indicating defects in the lumenal epithelium. Defects in lumen formation and polarity of epithelial cysts derived from uterine or gut cell lines were also observed when either CLCa or CLCb were depleted, with more severe effects from CLCa depletion. In cysts, the CLC isoforms had different distributions relative to each other, although they converge in tissue. Together, these findings suggest differential and cooperative roles for CLC isoforms in epithelial lumen formation, with a dominant function for CLCa