51,385 research outputs found
Perching by hugging: an initial feasibility study
Current UAVs capable of perching require added structure and mechanisms to
accomplish this. These take the form of hooks, claws, needles, etc which add
weight and usually drag. We propose in this paper the dual use of structures
already on the vehicle to enable perching, thus reducing the weight and drag
cost associated with perching UAVs. We propose a wing design capable of
passively wrapping around a vertical pole to perch. We experimentally
investigate the feasibility of the design, presenting results on minimum
required perching speeds as well as the effect of weight distribution on the
success rate of the wing wrapping. Finally, we comment on design requirements
for holding onto the pole based on our findings.Comment: Un-Peer Reviewed. Presented at the ICRA 2021 Aerial Robotics Worksho
Il Confezionamento con film plastico riduce le alterazioni dei frutti di avocado in frigoconservazione e ne prolunga la vita postraccolta
"Hass" avocado fruits, harvested in middle May, were film wrapped in polystyrene trays putting 3 fruits for each
tray and using a heat shrinkable film. Soon after fruits were stored at 4°C, Boe or left at 20°C, in shelf-life condition. After 3 weeks of cold storage fruits were transferred to 20°C in shelf-life condition. The film was removed at the end of refrigeration, or after 3 or 6 days of shelf-life. Wrapping had little effect in prolonging the time required to reach the eating stage in fruits stored at 8°C with respect to the control, but was beneficial in reducing weight losses and internal browning. Wrapped fruits stored at 4°C took from 6 to 10 days in shelf-life condition to ripen and showed negligible signs of internal browning. Microbiological alteration was mainly due to anthracnosi which mostly affected fruits stored at 8°C, while slight signs were revealed in those maintained at 4°C. In conclusion, film wrapping associated with the refrigeration temperature of 4°C seems suitable to prolong postharvest life of avocado fruit, reducing in the same time, physiological disorder and decay
Baryon as Impurity for Phase Transition in String Landscape
We consider a decay of a false vacuum in flux compactifications of type IIB
string theory and study a catalytic effect for a phase transition induced by a
new type of impurities. We concentrate on the large N dual of a
D5-brane/anti-D5-brane system which has a rich vacuum structure. We show that
D3-branes wrapping the 3-cycles can form a dibaryon and make a bound state with
a monopole. We find that these baryon-like objects can make the lifetime of the
metastable vacuum shorter.Comment: 22 pages, 13 figure
Branes wrapping black holes as a purely gravitational dielectric effect
In this paper we give a microscopical description of certain configurations
of branes wrapping black hole horizons in terms of dielectric gravitational
waves. Interestingly, the configurations are stable only due to the
gravitational background. Therefore, this constitutes a nice example of purely
gravitational dielectric effect.Comment: 17 pages, no figures. JHEP published versio
Conservation characteristics of baled grass silages differing in duration of wilting, bale density and number of layers of plastic stretch-film
peer-reviewedThe effects of duration of wilting, bale density and number of layers of plastic stretchfilm used to wrap bales on the conservation characteristics of baled grass silage was
investigated. Grass from the primary growth of a Lolium perenne dominant sward was
wilted for 24, 48 or 72 h. For each duration of wilting, 54 cylindrical bales (1.2 m nominal
diameter) were made with the baler at a high or low density setting for alternate bales.
Bales were wrapped with 2, 4 or 6 layers of plastic stretch-film and stored outdoors
for 295 days. Two layers of plastic stretch-film resulted in inferior preservation, lower
digestibility and extensive mould growth and deteriorated silage. Substantial improvement
occurred to each of these characteristics from applying four layers of stretch-film
(P<0.05), while six layers of stretch-film brought little further improvement. When
four or six layers of stretch-film were used, extensive wilting restricted fermentation
and improved the standard of preservation with the apparently difficult-to-preserve
herbage used in this experiment. However, under the anaerobic conditions provided
by four or six layers of stretch-film neither progressive wilting nor bale density had
a major effect on digestibility, or the extent of surface mould growth or deteriorated
silage. It can be concluded that a minimum of four layers of conventional black plastic
stretch-film were required to achieve suitably anaerobic conditions, and that the additional
benefits from six layers were small. Once anaerobic conditions were achieved,
extensive wilting improved the conservation characteristics of baled grass silage made
from a difficult-to-preserve crop, whereas bale density had little impact
M-Theory on a Calabi-Yau Manifold
We compactify -theory on a Calabi-Yau manifold to five dimensions by
wrapping the membrane and fivebrane solitons of the eleven-dimensional
supergravity limit around Calabi-Yau two-cycles and four-cycles respectively.
We identify the perturbative and non-perturbative BPS states thus obtained with
those of heterotic string theory compactified on . Quantum
aspects of the five-dimensional theory are discussed.Comment: 12 pages, 1 figure, uses harvmac, eps
U(1) mixing and D-brane linear equivalence
Linear equivalence is a criterion that compares submanifolds in the same
homology class. We show that, in the context of type II compactifications with
D-branes, this concept translates to the kinetic mixing between U(1) gauge
symmetries arising in the open and closed string sectors. We argue that in
generic D-brane models such mixing is experimentally detectable through the
existence of milli-charged particles. We compute these gauge kinetic functions
by classifying the 4d monopoles of a compactification and analyzing the Witten
effect on them, finding agreement with previous results and extending them to
more general setups. In particular, we compute the gauge kinetic functions
mixing bulk and magnetized D-brane U(1)'s and derive a generalization of linear
equivalence for these objects. Finally, we apply our findings to F-theory SU(5)
models with hypercharge flux breaking.Comment: 43 pages+appendices, 1 figure; v2: typos corrected and references
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The problem of pika control in Baluchistand, Pakistan
The collared pika, Ochotona rufescens, has been recorded as a serious pest in apple orchards in the uplands valley of Ziarat in Baluchistan. In the winter, when the natural vegetation is lacking, the pikas debark the apple tree trunks or branches resulting in the killing of the tree and reduced fruit production. In summer, damage to wheat, corn and potatoes is also very severe. It is estimated that pikas cause hundreds of thousands of dollars (US) in annual apple production losses. The apple production in Baluchistan accounts for about 35 percent of the total provincial income through food production. During the six years (1974-1979), the winter of 1973-74 was noted for heavy damage to apple trees and thereafter it declined steadily. The control measures evaluated were of various kinds among which repellent "Ostico" was very effective in protecting the trees. Poison baiting with brodifacoum (0.005%), Vacor (1%) and thallium sulphate (1%) were also effective in reducing the pika population. To alleviate damage caused by pikas, the farmers also practice some traditional protective methods which in some cases are quite effective but very laborious
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