International Portfolio Choice in an Overlapping Generations Model with Transactions Costs

This paper studies the implications for international portfolio diversification of a simple OLG model of the world economy with transaction costs. Our main result shows that the introduction of very small transaction costs is sufficient to reproduce the large home bias observed in the composition of portfolios.Home bias; Overlapping generations model; Transaction costs

The three-site Bose-Hubbard model subject to atom losses: the boson-pair dissipation channel and failure of the mean-field approach

We employ the perturbation series expansion for derivation of the reduced master equations for the three-site Bose-Hubbard model subject to strong atom losses from the central site. The model describes a condensate trapped in a triple-well potential subject to externally controlled removal of atoms. We find that the $\pi$-phase state of the coherent superposition between the side wells decays via two dissipation channels, the single-boson channel (similar to the externally applied dissipation) and the boson-pair channel. The quantum derivation is compared to the classical adiabatic elimination within the mean-field approximation. We find that the boson-pair dissipation channel is not captured by the mean-field model, whereas the single-boson channel is described by it. Moreover, there is a matching condition between the zero-point energy bias of the side wells and the nonlinear interaction parameter which separates the regions where either the single-boson or the boson-pair dissipation channel dominate. Our results indicate that the $M$-site Bose-Hubbard models, for $M>2$, subject to atom losses may require an analysis which goes beyond the usual mean-field approximation for correct description of their dissipative features. This is an important result in view of the recent experimental works on the single site addressability of condensates trapped in optical lattices.Comment: 9 pages; 3 figures in color; submitted to PR

Effect of atomic beam alignment on photon correlation measurements in cavity QED

Quantum trajectory simulations of a cavity QED system comprising an atomic beam traversing a standing-wave cavity are carried out. The delayed photon coincident rate for forwards scattering is computed and compared with the measurements of Rempe et al. [Phys. Rev. Lett. 67, 1727 (1991)] and Foster et al. [Phys. Rev. A 61, 053821 (2000)]. It is shown that a moderate atomic beam misalignment can account for the degradation of the predicted correlation. Fits to the experimental data are made in the weak-field limit with a single adjustable parameter--the atomic beam tilt from perpendicular to the cavity axis. Departures of the measurement conditions from the weak-field limit are discussed.Comment: 15 pages and 13 figure

Macquarie Island, its conservation and management

Sub-Antarctic Macquarie Island, 12 785 ha in area, is part of the Australian state of Tasmania. It is managed by the Tasmanian Parks and Wildlife Service, in cooperation with the Australian Department of the Environment and Water Resources, as a World Heritage Area, Nature Reserve, Biosphere Reserve and National Estate property. The reserve encompasses outstanding and unique geological values, exceptional natural beauty, abundant wildlife and internationally significant historic heritage. The island is surrounded by the Macquarie Island Marine Park of 16 200 000 ha. This paper outlines frameworks for the conservation and management of its biota and environment including its unique geology

Dramatic impact of pumping mechanism on photon entanglement in microcavity

A theory of entangled photons emission from quantum dot in microcavity under continuous and pulsed incoherent pumping is presented. It is shown that the time-resolved two-photon correlations drastically depend on the pumping mechanism: the continuous pumping quenches the polarization entanglement and strongly suppresses photon correlation times. Analytical theory of the effect is presented.Comment: 6 pages, 3 figure

An investigation into the molecular determinants of salmon louse (Lepeophtheirus salmonis (Krøyer, 1837)) susceptibility to the antiparasitic drug emamectin benzoate.

Caligid copepods, also called sea lice, are ectoparasites of marine fish, with Lepeophtheirus salmonis (Krøyer, 1837) emerging as a problem for mariculture of Atlantic salmon (Salmo salar Linnaeus, 1758) in the northern hemisphere. Annual costs of sea lice to global salmon farming was estimated to be in excess of €300 million in 2006, with the majority of this accounted for through expenses accrued from chemical treatments. Only a limited range of anti-sea louse drugs are available and licensed for the treatment of fish, and the continued use of only a few compounds creates a situation potentially favouring the development of drug resistance. Emamectin benzoate (EMB) is currently used as a salmon delousing agent, being employed as a 0.2 % in-feed pre-mix (SLICE®). Atlantic salmon farmers have reported increased incidence of reduced L. salmonis sensitivity to SLICE®, which has highlighted the requirement for further research into the molecular mechanisms controlling salmon louse resistance to EMB. Genomic and transcriptomic research concerning L. salmonis drug resistance mechanisms has not often been reported, with previous transcriptomic studies using candidate gene approaches and genetic studies focussing on population genetics. Drug resistance in ecdysozoan invertebrates is associated with a variety of molecular mechanisms including target site mutations and changes in the expression of components in drug detoxification pathways. The research reported in this thesis was aimed at the exploration of mechanisms employed by L. salmonis to reduce the toxicity of EMB exposure, following a transcriptomic approach that utilised custom oligonucleotide (oligo) microarrays and a genetic approach that utilised Restriction-site associated DNA sequencing (RAD-seq) to identify Single Nucleotide Polymorphism (SNP) markers. An EMB-resistant (PT) and drug-susceptible (S) L. salmonis laboratory-maintained strain were to be used as a model for this research, as these two strains differ in EMB susceptibility (~ 7-fold) and show stable susceptibility profiles through multiple generations, suggesting that this drug resistance phenotype may be a heritable trait. Sequence resources available for salmon lice are limited as an annotated L. salmonis genome is currently under construction. Therefore, a significant amount of this study involved creating new resources to facilitate the analysis of EMB susceptibility. Suppression subtractive hybridisation (SSH) was used to enrich for transcripts that were differentially expressed between strains PT and S, which provided sufficient target sequence for the development of 15K oligo microarrays when combined with sequences assembled from existing L. salmonis ESTs. Additionally, transcripts were generated through sequencing a pooled sample representing key developmental stages of the L. salmonis life cycle, which were later used in the construction of a 44K oligo microarray. The toxicity of EMB and other avermectins (AVMs) against ecdysozoan invertebrates is reported to be based mainly on their interaction with ligand-gated ion channels (LGIC), specifically glutamate-gated chloride channels (GluCl). However, -aminobutyric acid (GABA)-gated chloride channels (GABA-Cls) are also believed to be targeted by AVMs and neuronal acetylcholine receptors (nAChRs) can be allosterically modulated by the AVM compound ivermectin. Transcriptional responses in PT and S salmon lice were investigated using custom 15K L. salmonis oligo microarrays. In the absence of EMB exposure, 359 targets differed in transcript abundance between the two strains. GABA-Cl and nAChR subunits showed significantly lower transcript levels in PT compared to S lice, which was estimated at ~1.4-fold for GABA-Cl and ~2.8-fold for nAChR using RT-qPCR, suggesting their involvement in AVM toxicity in caligids. Although, salmon lice from the PT strain showed few transcriptional responses following acute exposure (1 or 3 h) to 200 µg L-1 of EMB, a drug concentration tolerated by PT lice, but toxic for S lice. RAD-seq analysis of both genders from L. salmonis strains S and PT identified 15 RAD-markers that show complete association with salmon louse strain, although these preliminary results will need further analysis to confirm marker association with reduced EMB susceptibility. Additionally, RAD marker Lsa101901 showed complete association with sex for all individuals analysed, being heterozygous in females and homozygous in males. Using an allele-specific PCR assay, this SNP association pattern was further confirmed for three unrelated salmon louse strains. Marker Lsa101901 was located in the coding region of the prohibitin-2 gene, which showed a sex-dependent differential expression, with mRNA levels determined by RT-qPCR about 1.8-fold higher in adult female than adult male salmon lice. In conclusion, the identification of decreased transcript abundances for LGIC subunits in EMB-resistant salmon lice, and polymorphic SNP markers showing complete association with L. salmonis strains S or PT, provides suitable candidates for further investigation into their association with reduced EMB susceptibility. Further analysis will also be required to confirm whether EMB-induced mechanisms are not associated with reduced EMB susceptibility in L. salmonis. Additionally, the identification of sex-linked SNP Lsa101901 suggests that sex determination in the salmon louse is genetic and follows a female heterozygous system, with marker Lsa101901 providing a tool to determine the genetic sex of salmon lice. Improved knowledge of L. salmonis biology and the mechanisms potentially involved in EMB resistance, obtained during this study, may provide molecular markers that contribute to successful monitoring and management of this commercially important parasite of Atlantic salmon

Caffeinated Alcohol Use in a Daily Context

Caffeinated alcoholic beverage (CAB) use is associated with a range of substance-related problems. Few have examined socio-environmental and cognitive factors that may relate to CAB use and influence associations between use and negative consequences. Moreover, much research on CABs has been based on cross-sectional and retrospective reports, which can be subject to recall biases. The current research aimed to address the gaps in our understanding of use patterns by conducting a daily diary study. Participants were 122 (73.8% women) heavy drinking, college student CAB users. Mean age was 20.39 (SD = 2.08) years. Students completed a baseline questionnaire and up to 14 consecutive, daily surveys about last night’s drinking behavior. Multilevel modeling results indicated that CAB days were linked with greater odds of drinking at a bar/club, pre-gaming behavior, and drinking around others. CAB days were associated with greater likelihood of experiencing an alcohol-related harm, beyond the amount of alcohol consumed and trait impulsivity. This study was the first to examine CAB use patterns in a within-subjects, longitudinal daily diary design. CABs appear to be consumed socially and in potentially risky contexts. Importantly, use of CABs is related to greater odds of experiencing negative consequences. Future research investigating use patterns may benefit from more fine-grained approaches to develop efficacious prevention and intervention efforts geared toward reducing CAB-related risks

Enhancing Small Group Teaching in Plant Sciences: A Research and Development Project in Higher Education

The Department of Plant Sciences at the University of Cambridge uses a range of learning and teaching environments including lectures, practical laboratories and small group tutorials'. Under the auspices of the Cambridge-MIT Institute's Pedagogy Programme, a two-year research and development project concerned with the development of small-group teaching is being undertaken. The research element of this project endeavours to illuminate current practice and identify areas in which evidence-based development might take place. The development element will include professional development activities and the production of curriculum resources including appropriate online material. This is a multi-method study including a series of student questionnaires; focus groups of students; semi-structured interviews with staff members; and the collection of video of small group teaching. In this paper we report selected findings from the 'student data' of the first year of this project.The questionnaire, conducted with two cohorts of students (2nd and 3rd year Undergraduates), used a double-scale questionnaire in which students were asked to report both on the prevalence of a range of teaching and learning practices and on how valuable these were in supporting their learning. This type of questionnaire instrument is particularly appropriate because the data it generates is suggestive of areas for changes in practice. The gaps between 'practices' and 'values' (across both cohorts) suggested that students valued activities which improved their understanding of how elements of the course were interrelated; which related course content to 'authentic' examples; and those in which teachers made explicit the characteristics of 'high quality' student work. Small group teaching, in the view of most students, was best used to extend and explore concepts introduced in lectures rather than simply reinforcing them or assessing student understanding.Data gathered through focus group activities illuminated the questionnaire data, providing detailed accounts of how students managed their own learning, and the roles played in this by lectures, small group teaching and other resources. Students identified the processes of planning and writing essays as key learning activities during which they integrated diverse course content and reflected on problematic knowledge. Questionnaire and focus group data suggested that students had less clear views regarding the value of collaborative learning, peer-assessment or activities such as making presentations to other students. When students talked in positive terms about these activities, they often referred to the learning benefits of preparation for the tasks rather than of the collaborative activities themselves. These views may provide indications of potential barriers to changes in learning and teaching environments, and suggest that any such changes may have to be carefully justified to students in terms of benefits to their own learning. Many of our findings are broadly in accord with other work on teaching and learning in Higher Education settings (such as the 'Oxford Learning Context Project' and the 'Enhancing Teaching-Learning Environments in Undergraduate Courses' Project) in that 'deep learning' and 'authenticity' in learning activities are valued by students, and that the introduction of specific formative practices (such as sharing notions of 'quality') would be welcomed. At the same time, amongst the students in our sample, a view of learning as an individual process of 'learning-as-acquisition' predominates over a view that it is a social process of 'learning-as-participation', and this will inform the planning of the 'development' aspect of the project. We conclude with a discussion of how the approach we have used might be more widely applied both within and beyond the Cambridge-MIT partnership. We also identify potential affordances of, and barriers to, the development of research-informed teaching in Higher Education

The Accuracy of Perturbative Master Equations

We consider open quantum systems with dynamics described by master equations that have perturbative expansions in the system-environment interaction. We show that, contrary to intuition, full-time solutions of order-2n accuracy require an order-(2n+2) master equation. We give two examples of such inaccuracies in the solutions to an order-2n master equation: order-2n inaccuracies in the steady state of the system and order-2n positivity violations, and we show how these arise in a specific example for which exact solutions are available. This result has a wide-ranging impact on the validity of coupling (or friction) sensitive results derived from second-order convolutionless, Nakajima-Zwanzig, Redfield, and Born-Markov master equations.Comment: 6 pages, 0 figures; v2 updated references; v3 updated references, extension to full-time and nonlocal regime

Non-classical photon pair generation in atomic vapours

A scheme for the generation of non-classical pairs of photons in atomic vapours is proposed. The scheme exploits the fact that the cross correlation of the emission of photons from the extreme transitions of a four-level cascade system shows anti-bunching which has not been reported earlier and which is unlike the case of the three level cascade emission which shows bunching. The Cauchy-Schwarz inequality which is the ratio of cross-correlation to the auto correlation function in this case is estimated to be $10^3-10^6$ for controllable time delay, and is one to four orders of magnitude larger compared to previous experiments. The choice of Doppler free geometry in addition to the fact that at three photon resonance the excitation/deexcitation processes occur in a very narrow frequency band, ensures cleaner signals.Comment: 18 pages, 7 figure