72,702 research outputs found
Comultiplication in link Floer homology and transversely non-simple links
For a word w in the braid group on n-strands, we denote by T_w the
corresponding transverse braid in the rotational symmetric tight contact
structure on S^3. We exhibit a map on link Floer homology which sends the
transverse invariant associated to T_{ws_i} to that associated to T_w, where
s_i is one of the standard generators of B_n. This gives rise to a
"comultiplication" map on link Floer homology. We use this to generate
infinitely many new examples of prime topological link types which are not
transversely simple.Comment: 16 pages, 10 figure
Highly collimated broadside emission from room-temperature GaAs distributed Bragg reflector lasers
Highly collimated laser beams have been observed to be coupled out by second-order Bragg scattering from GaAs distributed Bragg reflector lasers. The beams are perpendicular to the waveguide plane and have an angular width of less than 1°. The diodes have a separate confinement structure and operate at room temperature with thresholds as low as 1.4 kA/cm^2
A Constrained Tectonics Model for Coronal Heating
An analytical and numerical treatment is given of a constrained version of
the tectonics model developed by Priest, Heyvaerts, & Title [2002]. We begin
with an initial uniform magnetic field that is
line-tied at the surfaces and . This initial configuration is
twisted by photospheric footpoint motion that is assumed to depend on only one
coordinate () transverse to the initial magnetic field. The geometric
constraints imposed by our assumption precludes the occurrence of reconnection
and secondary instabilities, but enables us to follow for long times the
dissipation of energy due to the effects of resistivity and viscosity. In this
limit, we demonstrate that when the coherence time of random photospheric
footpoint motion is much smaller by several orders of magnitude compared with
the resistive diffusion time, the heating due to Ohmic and viscous dissipation
becomes independent of the resistivity of the plasma. Furthermore, we obtain
scaling relations that suggest that even if reconnection and/or secondary
instabilities were to limit the build-up of magnetic energy in such a model,
the overall heating rate will still be independent of the resistivity
On arc index and maximal Thurston-Bennequin number
We discuss the relation between arc index, maximal Thurston--Bennequin
number, and Khovanov homology for knots. As a consequence, we calculate the arc
index and maximal Thurston--Bennequin number for all knots with at most 11
crossings. For some of these knots, the calculation requires a consideration of
cables which also allows us to compute the maximal self-linking number for all
knots with at most 11 crossings.Comment: 10 pages, v4: corrected typo
Comparisons of soil suction induced by evapotranspiration and transpiration of S. <i>heptaphylla</i>
For a given evapotranspiration (ETr), both soil evaporation and plant transpiration (Tr) would induce soil suction. However, the relative contribution of these two processes to the amount of suction induced is not clear. The objective of this study is to quantify ETr- and Tr-induced suction by a selected tree species, Scheffllera heptaphylla, in silty sand. The relative contribution of transpiration and evaporation to the responses of suction is then explored based on observed differences in Tr- and ETr-induced suction. In total, 12 test boxes were used for testing: 10 for vegetated soil with different values of leaf area index (LAI) and root area index (RAI), while two were for bare soil as references. Each box was exposed to identical atmospheric conditions controlled in a plant room for monitoring suction responses over a week. Due to the additional effects of soil evaporation, ETr-induced suction could be 3%–47% higher than Tr-induced suction, depending on LAI. The significance of evaporation reduced substantially when LAI was higher, as relatively less radiant energy fell on the soil surface for evaporation. For a given LAI, the effects of evaporation were less significant at deeper depths within the root zone. The effects of RAI associated with root-water uptake upon transpiration were the dominant process of ETr affecting the suction responses.</jats:p
I Am The Passenger: How Visual Motion Cues Can Influence Sickness For In-Car VR
This paper explores the use of VR Head Mounted Displays
(HMDs) in-car and in-motion for the first time. Immersive
HMDs are becoming everyday consumer items and, as they
offer new possibilities for entertainment and productivity, people
will want to use them during travel in, for example, autonomous
cars. However, their use is confounded by motion
sickness caused in-part by the restricted visual perception
of motion conflicting with physically perceived vehicle motion
(accelerations/rotations detected by the vestibular system).
Whilst VR HMDs restrict visual perception of motion, they
could also render it virtually, potentially alleviating sensory
conflict. To study this problem, we conducted the first on-road
and in motion study to systematically investigate the effects
of various visual presentations of the real-world motion of
a car on the sickness and immersion of VR HMD wearing
passengers. We established new baselines for VR in-car motion
sickness, and found that there is no one best presentation
with respect to balancing sickness and immersion. Instead,
user preferences suggest different solutions are required for
differently susceptible users to provide usable VR in-car. This
work provides formative insights for VR designers and an entry
point for further research into enabling use of VR HMDs,
and the rich experiences they offer, when travelling
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