Spin properties of dense near-surface ensembles of nitrogen-vacancy centres in diamond

We present a study of the spin properties of dense layers of near-surface nitrogen-vacancy (NV) centres in diamond created by nitrogen ion implantation. The optically detected magnetic resonance contrast and linewidth, spin coherence time, and spin relaxation time, are measured as a function of implantation energy, dose, annealing temperature and surface treatment. To track the presence of damage and surface-related spin defects, we perform in situ electron spin resonance spectroscopy through both double electron-electron resonance and cross-relaxation spectroscopy on the NV centres. We find that, for the energy ($4-30$~keV) and dose ($5\times10^{11}-10^{13}$~ions/cm$^2$) ranges considered, the NV spin properties are mainly governed by the dose via residual implantation-induced paramagnetic defects, but that the resulting magnetic sensitivity is essentially independent of both dose and energy. We then show that the magnetic sensitivity is significantly improved by high-temperature annealing at $\geq1100^\circ$C. Moreover, the spin properties are not significantly affected by oxygen annealing, apart from the spin relaxation time, which is dramatically decreased. Finally, the average NV depth is determined by nuclear magnetic resonance measurements, giving $\approx10$-17~nm at 4-6 keV implantation energy. This study sheds light on the optimal conditions to create dense layers of near-surface NV centres for high-sensitivity sensing and imaging applications.Comment: 12 pages, 7 figure

The Conrad Rise as an obstruction to the Antarctic Circumpolar Current

The Antarctic Circumpolar Current (ACC) carries water freely around the whole continent of Antarctica, but not without obstructions. Some, such as the Drake Passage, constrict its path, while others, such as mid-ocean ridges, may induce meandering in the current's cores and may cause the genesis of mesoscale turbulence. It has recently been demonstrated that some regions that are only relatively shallow may also have a major effect on the flow patterns of the ACC. This is here shown to be particularly true for the Conrad Rise. Using the trajectories of surface drifters, altimetry and the simulated velocities from a numerical model, we show that the ACC bifurcates at the western side of this Rise. In this process it forms two intense jets at the two meridional extremities of the Rise with a relatively stagnant water body over the Rise itself. Preliminary results from a recent cruise provide compelling support for this portrayal

Relativistic Landau resonances

The possible interactions between plasma waves and relativistic charged particles are considered. An electromagnetic perturbation in the plasma is formulated as an elliptically polarized wave, and the collisionless plasma is described by a distribution in phase space, which is realized in cylindrical coordinates. The linearized Vlasov equation is solved in the semi-relativistic limit, to obtain the distribution function in the rest frame of the observer. The perturbed currents supported by the ionized medium are then calculated, so that an expression can be written for the total amount of energy available for transfer through the Landau mechanism. It is found that only certain modes of the perturbed current are available for this energy transfer. The final expressions are presented in terms of Stokes parameters, and applied to the special cases of a thermal as well as a nonthermal plasma. The thermal plasma is described by a Maxwellian distribution, while two nonthermal distributions are considered: the kappa distribution and a generalized Weibull distribution

Superfluid Helium Tanker (SFHT) study

Replenishment of superfluid helium (SFHe) offers the potential of extending the on-orbit life of observatories, satellite instruments, sensors and laboratories which operate in the 2 K temperature regime. A reference set of resupply customers was identified as representing realistic helium servicing requirements and interfaces for the first 10 years of superfluid helium tanker (SFHT) operations. These included the Space Infrared Telescope Facility (SIRTF), the Advanced X-ray Astrophysics Facility (AXAF), the Particle Astrophysics Magnet Facility (Astromag), and the Microgravity and Materials Processing Sciences Facility (MMPS)/Critical Point Phenomena Facility (CPPF). A mixed-fleet approach to SFHT utilization was considered. The tanker permits servicing from the Shuttle cargo bay, in situ when attached to the OMV and carried to the user spacecraft, and as a depot at the Space Station. A SFHT Dewar ground servicing concept was developed which uses a dedicated ground cooling heat exchanger to convert all the liquid, after initial fill as normal fluid, to superfluid for launch. This concept permits the tanker to be filled to a near full condition, and then cooled without any loss of fluid. The final load condition can be saturated superfluid with any desired ullage volume, or the tank can be totally filed and pressurized. The SFHT Dewar and helium plumbing system design has sufficient component redundancy to meet fail-operational, fail-safe requirements, and is designed structurally to meet a 50 mission life usage requirement. Technology development recommendations were made for the selected SFHT concept, and a Program Plan and cost estimate prepared for a phase C/D program spanning 72 months from initiation through first launch in 1997

Temozolomide plus pegylated interferon alfa-2b as first-line treatment for stage IV melanoma: a multicenter phase II trial of the Dermatologic Cooperative Oncology Group (DeCOG)

Background: Combination of temozolomide (TMZ) with nonpegylated interferon alfa is associated with increased efficacy in terms of response rates compared with monotherapy. A multicenter phase II study was carried out to assess the activity and toxicity of TMZ plus pegylated interferon alfa-2b (peg-IFNα-2b), hypothesizing improved efficacy due to modified pharmacokinetic properties of the novel interferon (IFN) formulation. Patients and methods: In all, 124 patients with stage IV melanoma without prior chemotherapy and no cerebral metastases were treated with 100 μg peg-IFNα-2b s.c. per week and oral TMZ 200 mg/m2 (days 1-5, every 28 days). Primary study end point was objective response, and secondary end points were overall and progression-free survival (PFS) and safety. Results: In all, 116 patients were assessable for response: 2 (1.7%) had a complete response and 19 (16.4%) a partial response (overall response rate 18.1%). Of total, 25.0% achieved disease stabilization and 56.9% progressed. Overall survival was 9.4 months; PFS was 2.8 months. Grade 3/4 thrombocytopenia occurred in 20.7% and grade 3/4 leukopenia in 23.3%. Conclusions: The efficacy of TMZ plus peg-IFNα-2b in this large phase II study is moderate and comparable to published results of the combination of TMZ with non-peg-IFN. Likewise, the safety profile of peg-IFNα-2b seems to be similar to non-peg-IFN when combined with TM

Open Problems on Central Simple Algebras

We provide a survey of past research and a list of open problems regarding central simple algebras and the Brauer group over a field, intended both for experts and for beginners.Comment: v2 has some small revisions to the text. Some items are re-numbered, compared to v

Fitness benefits of prolonged post-reproductive lifespan in women

Most animals reproduce until they die, but in humans, females can survive long after ceasing reproduction. In theory, a prolonged post-reproductive lifespan will evolve when females can gain greater fitness by increasing the success of their offspring than by continuing to breed themselves. Although reproductive success is known to decline in old age, it is unknown whether women gain fitness by prolonging lifespan post-reproduction. Using complete multi-generational demographic records, we show that women with a prolonged post-reproductive lifespan have more grandchildren, and hence greater fitness, in pre-modern populations of both Finns and Canadians. This fitness benefit arises because post-reproductive mothers enhance the lifetime reproductive success of their offspring by allowing them to breed earlier, more frequently and more successfully. Finally, the fitness benefits of prolonged lifespan diminish as the reproductive output of offspring declines. This suggests that in female humans, selection for deferred ageing should wane when one's own offspring become post-reproductive and, correspondingly, we show that rates of female mortality accelerate as their offspring terminate reproduction

HIRDLS Observations and Simulation of a Lower Stratospheric Intrusion of Tropical Air to High Latitudes

On 26 January 2006, the High Resolution Dynamic Limb Sounder (HIRDLS) observed low mixing ratios of ozone and nitric acid in an approximately 2 km vertical layer near 100 hPa extending from the subtropics to 55 degrees N over North America. The subsequent evolution of the layer is simulated with the Global Modeling Initiative (GMI) model and substantiated with HIRDLS observations. Air with low mixing ratios of ozone is transported poleward to 80 degrees N. Although there is evidence of mixing with extratropical air and diabatic descent, much of the tropical intrusion returns to the subtropics. This study demonstrates that HIRDLS and the GMI model are capable of resolving thin intrusion events. The observations combined with simulation are a first step towards development of a quantitative understanding of the lower stratospheric ozone budget

The atomic structure of low-index surfaces of the intermetallic compound InPd

The intermetallic compound InPd (CsCl type of crystal structure with a broad compositional range) is considered as a candidate catalyst for the steam reforming of methanol. Single crystals of this phase have been grown to study the structure of its three low-index surfaces under ultra-high vacuum conditions, using low energy electron diffraction (LEED), X-ray photoemission spectroscopy (XPS), and scanning tunneling microscopy (STM). During surface preparation, preferential sputtering leads to a depletion of In within the top few layers for all three surfaces. The near-surface regions remain slightly Pd-rich until annealing to ∼580 K. A transition occurs between 580 and 660 K where In segregates towards the surface and the near-surface regions become slightly In-rich above ∼660 K. This transition is accompanied by a sharpening of LEED patterns and formation of flat step-terrace morphology, as observed by STM. Several superstructures have been identified for the different surfaces associated with this process. Annealing to higher temperatures (≥750 K) leads to faceting via thermal etching as shown for the (110) surface, with a bulk In composition close to the In-rich limit of the existence domain of the cubic phase. The Pd-rich InPd(111) is found to be consistent with a Pd-terminated bulk truncation model as shown by dynamical LEED analysis while, after annealing at higher temperature, the In-rich InPd(111) is consistent with an In-terminated bulk truncation, in agreement with density functional theory (DFT) calculations of the relative surface energies. More complex surface structures are observed for the (100) surface. Additionally, individual grains of a polycrystalline sample are characterized by micro-spot XPS and LEED as well as low-energy electron microscopy. Results from both individual grains and “global” measurements are interpreted based on comparison to our single crystals findings, DFT calculations and previous literature