Ultracold collisions in tight harmonic traps: Quantum defect model and application to metastable helium atoms

We analyze a system of two colliding ultracold atoms under strong harmonic confinement from the viewpoint of quantum defect theory and formulate a generalized self-consistent method for determining the allowed energies. We also present two highly efficient computational methods for determining the bound state energies and eigenfunctions of such systems. The perturbed harmonic oscillator problem is characterized by a long asymptotic region beyond the effective range of the interatomic potential. The first method, which is based on quantum defect theory and is an adaptation of a technique developed by one of the authors (GP) for highly excited states in a modified Coulomb potential, is very efficient for integrating through this outer region. The second method is a direct numerical solution of the radial Schr\"{o}dinger equation using a discrete variable representation of the kinetic energy operator and a scaled radial coordinate grid. The methods are applied to the case of trapped spin-polarized metastable helium atoms. The calculated eigenvalues agree very closely for the two methods, and with those computed self-consistently using the generalized self-consistent method.Comment: 11 pages,REVTEX, text substantially revised, title modifie

Spin-dipole induced lifetime of the least-bound quintet sigma state of He(2S)+He(2S)

The properties of the least-bound vibrational level (v=14) of the quintet sigma state formed during the ultracold collision of two spin-polarized metastable helium atoms are crucial to studies of photoassociation spectroscopy of metastable helium. We report a calculation of the autoionization lifetime of this state induced by spin-dipole coupling of the quintet sigma state to the singlet sigma state from which Penning and associative ionization processes are highly probable. We find a lifetime of about 150 microseconds, significantly larger than the recent experimental estimates of (4-5) microseconds.Comment: REVTEX4, four double-column page

Direct-write projection lithography of quantum dot micropillar single photon sources

We have developed a process to mass-produce quantum dot micropillar cavities using direct-write lithography. This technique allows us to achieve high volume patterning of high aspect ratio pillars with vertical, smooth sidewalls maintaining a high quality factor for diameters below 2.0 μm. Encapsulating the cavities in a thin layer of oxide (Ta2O5) prevents oxidation in the atmosphere, preserving the optical properties of the cavity over months of ambient exposure. We confirm that single dots in the cavities can be deterministically excited to create high purity indistinguishable single photons with interference visibility (96.2 ± 0.7)%

Direct-write projection lithography of quantum dot micropillar single photon sources

We have developed a process to mass-produce quantum dot micropillar cavities using direct-write lithography. This technique allows us to achieve mass patterning of high-aspect ratio pillars with vertical, smooth sidewalls maintaining a high quality factor for diameters below 2.0 μm. Encapsulating the cavities in a thin layer of oxide (Ta2O5) prevents oxidation in the atmosphere, preserving the optical properties of the cavity over months of ambient exposure. We confirm that single dots in the cavities can be deterministically excited to create high-purity indistinguishable single photons with interference visibility (0.941 ± 0.008) ⁠

Passerine Birds Breeding under Chronic Noise Experience Reduced Fitness

Background Fitness in birds has been shown to be negatively associated with anthropogenic noise, but the underlying mechanisms remain obscure. It is however crucial to understand the mechanisms of how urban noise impinges on fitness to obtain a better understanding of the role of chronic noise in urban ecology. Here, we examine three hypotheses on how noise might reduce reproductive output in passerine birds: (H1) by impairing mate choice, (H2) by reducing territory quality and (H3) by impeding chick development. Methodology/Principal Findings We used long-term data from an island population of house sparrows, Passer domesticus, in which we can precisely estimate fitness. We found that nests in an area affected by the noise from large generators produced fewer young, of lower body mass, and fewer recruits, even when we corrected statistically for parental genetic quality using a cross-fostering set-up, supporting H3. Also, individual females provided their young with food less often when they bred in the noisy area compared to breeding attempts by the same females elsewhere. Furthermore, we show that females reacted flexibly to increased noise levels by adjusting their provisioning rate in the short term, which suggests that noise may be a causal factor that reduces reproductive output. We rejected H1 and H2 because nestbox occupancy, parental body mass, age and reproductive investment did not differ significantly between noisy and quiet areas. Conclusions/Significance Our results suggest a previously undescribed mechanism to explain how environmental noise can reduce fitness in passerine birds: by acoustically masking parent–offspring communication. More importantly, using a cross-fostering set-up, our results demonstrate that birds breeding in a noisy environment experience significant fitness costs. Chronic noise is omnipresent around human habitation and may produces similar fitness consequences in a wide range of urban bird species

tropiTree:an NGS-based EST-SSR resource for 24 tropical tree species

The development of genetic tools for non-model organisms has been hampered by cost, but advances in next-generation sequencing (NGS) have created new opportunities. In ecological research, this raises the prospect for developing molecular markers to simultaneously study important genetic processes such as gene flow in multiple non-model plant species within complex natural and anthropogenic landscapes. Here, we report the use of bar-coded multiplexed paired-end Illumina NGS for the de novo development of expressed sequence tag-derived simple sequence repeat (EST-SSR) markers at low cost for a range of 24 tree species. Each chosen tree species is important in complex tropical agroforestry systems where little is currently known about many genetic processes. An average of more than 5,000 EST-SSRs was identified for each of the 24 sequenced species, whereas prior to analysis 20 of the species had fewer than 100 nucleotide sequence citations. To make results available to potential users in a suitable format, we have developed an open-access, interactive online database, tropiTree (http://bioinf.hutton.ac.uk/tropiTree), which has a range of visualisation and search facilities, and which is a model for the efficient presentation and application of NGS data

N.B.’s Ongoing Battle With Wolastoqey Nation Is Not Reconciliation in Action

The Wolastoqey are seeking land title for the Saint John River. The province has responded with fearmongering. It is time for calmer voices to emerge

N.B.’s Ongoing Battle With Wolastoqey Nation Is Not Reconciliation in Action

The Wolastoqey are seeking land title for the Saint John River. The province has responded with fearmongering. It is time for calmer voices to emerge