Testing for Photometric Variability at the L/T Boundary

We construct K_s-band light curves for nine field L and T brown dwarfs using the Palomar 60 inch Telescope. Results of a robust statistical analysis indicate that about half the targets show significant evidence for variability. Two of these variable targets have marginally significant peaks in the Lomb-Scargle periodogram. The phased light curves show evidence for periodic behavior on timescales of about 1.5 and 3.0 hours

Effectiveness of learning and experimentation approaches for farmers as a community based strategy for banana xanthomonas wilt management

Banana Xanthomonas wilt (BXW) is a devastating disease for banana and enset in east, central and Horn of Africa since 1968. The disease has spread to all banana growing countries in the region in the last decade, causing yield losses of up to 80 to 100%. Several efforts have been undertaken to develop and implement technologies for BXW management and their effective deployment with varying successes. This paper presents a new participatory approach for managing BXW named Learning and Experimentation Approaches For Farmers (LEAFF) and describes how it was implemented, tested and evaluated among 220 farmers across two agroecological regions, central and South-western Uganda. Results showed that there was a general reduction in the number of infected plants, corresponding to 7% increase in productivity of banana among the LEAFF compared to the non LEAFF participating farmers. The findings suggested that scaling out LEAFF to different parts in the region can significantly contribute to effective and sustainable adoption of BXW management technologies, and in turn, can lead to improved productivity and smallholder farmers’ livelihoods

The Gas Temperature of Starless Cores in Perseus

In this paper we study the determinants of starless core temperatures in the Perseus molecular cloud. We use NH3 (1,1) and (2,2) observations to derive core temperatures (T_kin) and data from the COMPLETE Survey of Star Forming Regions and the c2d Spitzer Legacy Survey for observations of the other core and molecular cloud properties. The kinetic temperature distribution probed by NH3 is in the fairly narrow range of 9 - 15 K. We find that cores within the clusters IC348 and NGC1333 are significantly warmer than "field" starless cores, and T_kin is higher within regions of larger extinction-derived column density. Starless cores in the field are warmer when they are closer to class O/I protostars, but this effect is not seen for those cores in clusters. For field starless cores, T_kin is higher in regions in which the 13CO linewidth and the 1.1mm flux from the core are larger, and T_kin is lower when the the peak column density within the core and average volume density of the core are larger. There is no correlation between T_kin and 13CO linewidth, 1.1mm flux, density or peak column density for those cores in clusters. The temperature of the cloud material along the line of sight to the core, as measured by CO or far-infrared emission from dust, is positively correlated with core temperature when considering the collection of cores in the field and in clusters, but this effect is not apparent when the two subsamples of cores are considered separately.Comment: Accepted to ApJ; 13 pages, including 3 tables and three figure

On the proportion of elements of prime order in finite symmetric groups

We give a short proof for an explicit upper bound on the proportion of permutations of a given prime order $p$, acting on a finite set of given size $n$, which is sharp for certain $n$ and $p$. Namely, we prove that if $n\equiv k\pmod{p}$ with $0\leq k\leq p-1$, then this proportion is at most $(p\cdot k!)^{-1}$ with equality if and only if $p\leq n<2n$.Comment: 7 page

Comparison of plasmon surface waves on shallow and deep metallic 1D and 2D gratings

International audienceThe propagation of a plasmon surface wave in deep metallic lamellar gratings is shown to be characterized by absorption losses smaller than on a flat metallic-dielectric interface. This feature is due to the formation of a resonance of the electric field inside the groove. Similar to the plasmon surface wave in shallow gratings, this kind of plasmon can lead to total absorption of incident light and to a significant enhancement of the local field density in the vicinity of the grating surface, contrary to the other type of grating anomaly linked with a cavity resonanc

Non-Bloch plasmonic stop-band in real-metal gratings

International audienceRecent studies of plasmon surface wave (PSW) propagation in short-period perfectly conducting gratings have shown formation of stop-band that are not linked to the interaction between two ( counter) propagating surface waves. We study the properties of this stop-band in real metals. While for both perfectly conducting and real metals the propagation constant of PSW grows with the groove height, the stop-band in real metals appears for groove heights significantly smaller than in perfect metals. A physical explanation of the formation of the stop-band is proposed both by using a homogenisation of the corrugated layer and by analysis of the tangential electric field component

The enigmatic core L1451-mm: a first hydrostatic core? or a hidden VeLLO?

We present the detection of a dust continuum source at 3-mm (CARMA) and 1.3-mm (SMA), and 12CO(2-1) emission (SMA) towards the L1451-mm dense core. These detections suggest a compact object and an outflow where no point source at mid-infrared wavelengths is detected using Spitzer. An upper limit for the dense core bolometric luminosity of 0.05 Lsun is obtained. By modeling the broadband SED and the continuum interferometric visibilities simultaneously, we confirm that a central source of heating is needed to explain the observations. This modeling also shows that the data can be well fitted by a dense core with a YSO and disk, or by a dense core with a central First Hydrostatic Core (FHSC). Unfortunately, we are not able to decide between these two models, which produce similar fits. We also detect 12CO(2-1) emission with red- and blue-shifted emission suggesting the presence of a slow and poorly collimated outflow, in opposition to what is usually found towards young stellar objects but in agreement with prediction from simulations of a FHSC. This presents the best candidate, so far, for a FHSC, an object that has been identified in simulations of collapsing dense cores. Whatever the true nature of the central object in L1451-mm, this core presents an excellent laboratory to study the earliest phases of low-mass star formation.Comment: 15 pages, 9 figures, emulateapj. Accepted by Ap

Management of Banana Xanthomonas Wilt: Evidence from impact of adoption of cultural control practices in Uganda

Banana Xanthomonas Wilt (BXW) is an important emerging and non-curable infectious plant pathogen in sub-Saharan Africa that can cause up to 100% yield loss, negatively impacting sustainable access to food and income to more than 100 million banana farmers. This study disentangles adopters into partial and full adopters to investigate the factors that are relevant to sustain the adoption process of BXW control practices and quantifies the impact of adopting the practices. Data from a randomly selected sample of 1200 banana farmers in Uganda where the disease is endemic was used. A multinomial logit model was used to determine the factors affecting adoption of control practices and augmented inverse probability weighting was employed to estimate the impacts of adoption on banana productivity and sales. Results show that training a woman farmer and having diverse sources of information about BXW control practices increased adoption of the control practices and reduced the disease incidences. Farmers who adopted all the recommended control practices achieved significantly the highest values of banana production and sales. We conclude that improving information access through farmers’ preferred communication channels, having women-inclusive trainings, and a combination of cultural practices are effective ways for sustaining adoption of the control practices