13,015 research outputs found
The molecular structure of the interface between water and a hydrophobic substrate is liquid-vapor like
With molecular simulation for water and a tunable hydrophobic substrate, we
apply the instantaneous interface construction [A. P. Willard and D. Chandler,
J. Phys. Chem. B, 114, 1954 (2010)] to examine the similarity between a
water-vapor interface and a water-hydrophobic surface interface. The intrinsic
interface refers to molecular structure in terms of distances from the
instantaneous interface. We show that attractive interactions between a
hydrophobic surface and water affect capillary wave fluctuations of the
instantaneous liquid interface, but these attractive interactions have
essentially no effect on the intrinsic interface. Further, the intrinsic
interface of liquid water and a hydrophobic substrate differs little from that
of water and its vapor.The same is not true, we show, for an interface between
water and a hydrophilic substrate. In that case, strong directional
substrate-water interactions disrupt the liquid-vapor-like interfacial hydrogen
bonding network.Comment: 6 pages, 5 figure
Thermodynamics of Coarse Grained Models of Super-Cooled Liquids
In recent papers, we have argued that kinetically constrained coarse grained
models can be applied to understand dynamic properties of glass forming
materials, and we have used this approach in various applications that appear
to validate this view. In one such paper [J.P. Garrahan and D. Chandler, Proc.
Nat. Acad. Sci. USA 100, 9710 (2003)], among other things we argued that this
approach also explains why the heat capacity discontinuity at the glass
transition is generally larger for fragile materials than for strong materials.
In the preceding article, Biroli, Bouchaud and Tarjus (BB&T) [cond-mat/0412024]
have objected to our explanation on this point, arguing that the class of
models we apply is inconsistent with both the absolute size and temperature
dependence of the experimental specific heat. Their argument, however, neglects
parameters associated with the coarse graining. Accounting for these
parameters, we show here that our treatment of dynamics is not inconsistent
with heat capacity discontinuities.Comment: 5 pages, 2 figures. Revised version to appear in J. Chem. Phy
Pursuit on a Graph Using Partial Information
The optimal control of a "blind" pursuer searching for an evader moving on a
road network and heading at a known speed toward a set of goal vertices is
considered. To aid the "blind" pursuer, certain roads in the network have been
instrumented with Unattended Ground Sensors (UGSs) that detect the evader's
passage. When the pursuer arrives at an instrumented node, the UGS therein
informs the pursuer if and when the evader visited the node. The pursuer's
motion is not restricted to the road network. In addition, the pursuer can
choose to wait/loiter for an arbitrary time at any UGS location/node. At time
0, the evader passes by an entry node on his way towards one of the exit nodes.
The pursuer also arrives at this entry node after some delay and is thus
informed about the presence of the intruder/evader in the network, whereupon
the chase is on - the pursuer is tasked with capturing the evader. Because the
pursuer is "blind", capture entails the pursuer and evader being collocated at
an UGS location. If this happens, the UGS is triggered and this information is
instantaneously relayed to the pursuer, thereby enabling capture. On the other
hand, if the evader reaches one of the exit nodes without being captured, he is
deemed to have escaped. We provide an algorithm that computes the maximum
initial delay at the entry node for which capture is guaranteed. The algorithm
also returns the corresponding optimal pursuit policy
A simple solvable energy landscape model that shows a thermodynamic phase transition and a glass transition
When a liquid melt is cooled, a glass or phase transition can be obtained
depending on the cooling rate. Yet, this behavior has not been clearly captured
in energy landscape models. Here a model is provided in which two key
ingredients are considered based in the landscape, metastable states and their
multiplicity. Metastable states are considered as in two level system models.
However, their multiplicity and topology allows a phase transition in the
thermodynamic limit, while a transition to the glass is obtained for fast
cooling. By solving the corresponding master equation, the minimal speed of
cooling required to produce the glass is obtained as a function of the
distribution of metastable and stable states. This allows to understand cooling
trends due to rigidity considerations in chalcogenide glasses.Comment: 4 pages (letter), 2 figure
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Widening the scope of virtual reality and augmented reality in dermatology
Virtual reality (VR) and augmented reality (AR) are making headlines, pushing the boundaries of educational experiences and applicability in a variety of fields. Medicine has seen a rapid growth of utilization of these devices for various educational and practical purposes. With respect to the field of dermatology, very few uses are discussed in the literature. We briefly present the current status of VR/AR with regard to this specialty
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