Spin-transfer-driven nano-oscillators are equivalent to parametric resonators

The equivalence between different physical systems permits us to transfer knowledge between them and to characterize the universal nature of their dynamics. We demonstrate that a nanopillar driven by a spin-transfer torque is equivalent to a rotating magnetic plate, which permits us to consider the nanopillar as a macroscopic system under a time-modulated injection of energy, that is, a simple parametric resonator. This equivalence allows us to characterize the phases diagram and to predict magnetic states and dynamical behaviors, such as solitons, stationary textures, and oscillatory localized states, among others. Numerical simulations confirm these predictions.Comment: 8 pages, 7 figure

Exploring Agri-Food Import Dependency of Burundi: A Gravity Model Approach

The upward movement of agricultural and food imports has been a central issue in Burundi, since it hampers the growth of agricultural sector and poses a major disincentive to farmers’ ability to produce more and cope with the risks associated with food production.  This paper aims to find critical factors that determine the surge of agri-food imports observed during post civil war (2000-2010). A gravity model was estimated from the data collected during the period of 2000-2010. The random fixed-effects model indicated that Burundi’s GDP, her trade partners’ populations, exchange rate, distance, being under the same colony and belonging to a regional trading bloc such as EAC and COMESA are the main factors determining food imports. The choice of trade instruments to use may seek to facilitate trade by reducing unnecessary tariff and non-tariff barriers but in a reciprocal agreement and dispensation of bilateral and multilateral protocols. Keywords: Gravity model, Agri-food, Imports, random fixed effects and Burund

Hydroschorlomite in altered basalts from Hole 1256D, ODP Leg 206: The transition from low-temperature to hydrothermal alteration

International audienceHydroschorlomite, a Ti-, Ca-, Fe-rich andraditic arnet present in the deepest cores of basalts (661?749 bsf) drilled in Hole 1256D during Ocean Drilling Program (ODP) Leg 206 (equatorial east Pacific), is reported here for the first time in oceanic crust. Detailed petrological and mineralogical studies by optical microscope, electron microprobe, scanning and transmission electron microscope, and micro-Raman spectroscopy are used to characterize this hydrogarnet and its relationships with other minerals. Hydroschorlomite occurs in Hole 1256D as small (5?50 ?m) anhedral or euhedral crystals associated either with celadonite in black halos adjacent to celadonite veins or with brown saponitic phyllosilicate in brown alteration halos adjacent to veins of saponite and iron oxyhydroxides. Both types of halos are formed at low temperature (less than about 100?C). Textural observations suggest that hydroschorlomite formation is contemporaneous with the phyllosilicates. Hydroschorlomite is rich in CaO (22.5?26.5 wt%), TiO2 (22.0?28.6 wt%), and FeOt (6.2?12.9 wt%) and contains significant F (up to 0.85 wt%) and Zr2O3 (up to 0.34 wt%). The presence of OH suggested by the low total percentages of oxides (95.2?97.3 wt%) is confirmed by the OH vibration at 3557 cm?1 in the micro-Raman spectrum. Chemical mapping indicates that hydroschorlomite is not zoned and is always associated with either celadonitic or saponitic phyllosilicates. Some hydroschorlomite crystals partly include tiny (<10 ?m) skeletal titanomagnetite. The occurrence of hydroschorlomite in Hole 1256D basalts coincides with a general downward increase in temperatures and overall intensity of alteration manifest by the alteration of plagioclase and the occurrence of small amounts of mixed-layer chlorite-smectite. The titanium necessary to form hydroschorlomite is provided by the breakdown of primary tiny (<10 ?m) titanomagnetite, while calcium is provided by the replacement of plagioclase by albite. Hydroschorlomite is thus an indicator of alteration of titanomagnetite under conditions transitional from low-temperature alteration to hydrothermal metamorphism with formation of titanite and may affect magnetic properties of the rocks

Statistics of quantum transport in chaotic cavities with broken time-reversal symmetry

The statistical properties of quantum transport through a chaotic cavity are encoded in the traces \T={\rm Tr}(tt^\dag)^n, where $t$ is the transmission matrix. Within the Random Matrix Theory approach, these traces are random variables whose probability distribution depends on the symmetries of the system. For the case of broken time-reversal symmetry, we present explicit closed expressions for the average value and for the variance of \T for all $n$. In particular, this provides the charge cumulants \Q of all orders. We also compute the moments $$ of the conductance $g=\mathcal{T}_1$. All the results obtained are exact, {\it i.e.} they are valid for arbitrary numbers of open channels.Comment: 5 pages, 4 figures. v2-minor change

A picture is worth a thousand words: Smartphone photograph-based surveys for collecting data on office occupant adaptive opportunities

In the past several decades, psychological aspects have been become important to holistic building occupant comfort and satisfaction evaluations. Psychological dimensions of comfort include occupants’ opportunities to interact with their indoor environment and perceived control over the indoor environment. Current post-occupancy evaluations tend to focus on collecting quantitative data, despite overwhelming evidence that contextual factors can profoundly impact occupant comfort. This paper proposes and tests a novel method for data collection to study adaptive comfort opportunities. A smartphone-based survey was developed to concurrently collect office occupants’ subjective evaluations of usability and comfort of spaces, in addition to photographs of all key building interfaces. The photos were coded to obtain quantitative characteristics of offices, such as whether the interface is obstructed. With a sample of 39 office workers, this paper reveals the effectiveness of this novel photographbased survey method, while also providing some initial quantitative and qualitative results

Ground-based optical transmission spectrum of the hot Jupiter HAT-P-1b

Time-series spectrophotometric studies of exoplanets during transit using ground-based facilities are a promising approach to characterize their atmospheric compositions. We aim to investigate the transit spectrum of the hot Jupiter HAT-P-1b. We compare our results to those obtained at similar wavelengths by previous space-based observations. We observed two transits of HAT-P-1b with the Gemini Multi-Object Spectrograph (GMOS) instrument on the Gemini North telescope using two instrument modes covering the 320 - 800 nm and 520 - 950 nm wavelength ranges. We used time-series spectrophotometry to construct transit light curves in individual wavelength bins and measure the transit depths in each bin. We accounted for systematic effects. We addressed potential photometric variability due to magnetic spots in the planet's host star with long-term photometric monitoring. We find that the resulting transit spectrum is consistent with previous Hubble Space Telescope (HST) observations. We compare our observations to transit spectroscopy models that marginally favor a clear atmosphere. However, the observations are also consistent with a flat spectrum, indicating high-altitude clouds. We do not detect the Na resonance absorption line (589 nm), and our observations do not have sufficient precision to study the resonance line of K at 770 nm. We show that even a single Gemini/GMOS transit can provide constraining power on the properties of the atmosphere of HAT-P-1b to a level comparable to that of HST transit studies in the optical when the observing conditions and target and reference star combination are suitable. Our 520 - 950 nm observations reach a precision comparable to that of HST transit spectra in a similar wavelength range of the same hot Jupiter, HAT-P-1b. However, our GMOS transit between 320 - 800 nm suffers from strong systematic effects and yields larger uncertainties.Comment: A&A, accepted, 16 pages, 8 figures, 5 table