94 research outputs found
The polymer mat: Arrested rebound of a compressed polymer layer
Compression of an adsorbed polymer layer distorts its relaxed structure.
Surface force measurements from different laboratories show that the return to
this relaxed structure after the compression is released can be slowed to the
scale of tens of minutes and that the recovery time grows rapidly with
molecular weight. We argue that the arrested state of the free layer before
relaxation can be described as a Guiselin brush structure1, in which the
surface excess lies at heights of the order of the layer thickness, unlike an
adsorbed layer. This brush structure predicts an exponential falloff of the
force at large distance with a decay length that varies as the initial
compression distance to the 6/5 power. This exponential falloff is consistent
with surface force measurements. We propose a relaxation mechanism that
accounts for the increase in relaxation time with chain length.Comment: 24 pages, 5 figre
Relationships between xylem embolism and tree functioning during drought, recovery, and recurring drought in Aleppo pine
Recent findings suggest that trees can survive high levels of drought-induced xylem embolism. In many cases, the embolism is irreversible and, therefore, can potentially affect post-drought recovery and tree function under recurring droughts. We examined the development of embolism in potted Aleppo pines, a common species in hot, dry Mediterranean habitats. We asked (1) how post-drought recovery is affected by different levels of embolism and (2) what consequences this drought-induced damage has under a recurring drought scenario. Young trees were dehydrated to target water potential (Ψx) values of −3.5, −5.2 and −9.5 MPa (which corresponded to ~6%, ~41% and ~76% embolism), and recovery of the surviving trees was measured over an 8-months period (i.e., embolism, leaf gas-exchange, Ψx). An additional group of trees was exposed to Ψx of −6.0 MPa, either with or without preceding drought (Ψx of −5.2 MPa) to test the effect of hydraulic damage during repeated drought. Trees that reached −9.5 MPa died, but none from the other groups. Embolism levels in dying trees were on average 76% of conductive xylem and no tree was dying below 62% embolism. Stomatal recovery was negatively proportional to the level of hydraulic damage sustained during drought, for at least a month after drought relief. Trees that experienced drought for the second time took longer to reach fatal Ψx levels than first-time dehydrating trees. Decreased stomatal conductance following drought can be seen as “drought legacy,” impeding recovery of tree functioning, but also as a safety mechanism during a consecutive drought
Gel-Electrophoresis and Diffusion of Ring-Shaped DNA
A model for the motion of ring-shaped DNA in a gel is introduced and studied
by numerical simulations and a mean-field approximation. The ring motion is
mediated by finger-shaped loops (hernias) that move in an amoeba-like fashion
around the gel obstructions. This constitutes an extension of previous
reptation tube treatments. It is shown that tension is essential for describing
the dynamics in the presence of hernias. It is included in the model as long
range interactions over stretched DNA regions. The mobility of ring-shaped DNA
is found to saturate much as in the well-studied case of linear DNA.
Experiments in polymer gels, however, show that the mobility drops
exponentially with the DNA ring size. This is commonly attributed to
dangling-ends in the gel that can impale the ring. The predictions of the
present model are expected to apply to artificial 2D obstacle arrays (W.D.
Volkmuth, R.H. Austin, Nature 358,600 (1992)) which have no dangling-ends. In
the zero-field case an exact solution of the model steady-state is obtained,
and quantities such as the average ring size are calculated. An approximate
treatment of the ring dynamics is given, and the diffusion coefficient is
derived. The model is also discussed in the context of spontaneous symmetry
breaking in one dimension.Comment: 8 figures, LaTeX, Phys. Rev. E - in pres
Experimental Aspects of Synthesis
We discuss the problem of experimentally evaluating linear-time temporal
logic (LTL) synthesis tools for reactive systems. We first survey previous such
work for the currently publicly available synthesis tools, and then draw
conclusions by deriving useful schemes for future such evaluations.
In particular, we explain why previous tools have incompatible scopes and
semantics and provide a framework that reduces the impact of this problem for
future experimental comparisons of such tools. Furthermore, we discuss which
difficulties the complex workflows that begin to appear in modern synthesis
tools induce on experimental evaluations and give answers to the question how
convincing such evaluations can still be performed in such a setting.Comment: In Proceedings iWIGP 2011, arXiv:1102.374
Geometry and subsidence history of the Dead Sea basin : a case for fluid-induced mid-crustal shear zone?
This paper is not subject to U.S. copyright. The definitive version was published in Journal of Geophysical Research 117 (2012): B01406, doi:10.1029/2011JB008711.Pull-apart basins are narrow zones of crustal extension bounded by strike-slip faults that can serve as analogs to the early stages of crustal rifting. We use seismic tomography, 2-D ray tracing, gravity modeling, and subsidence analysis to study crustal extension of the Dead Sea basin (DSB), a large and long-lived pull-apart basin along the Dead Sea transform (DST). The basin gradually shallows southward for 50 km from the only significant transverse normal fault. Stratigraphic relationships there indicate basin elongation with time. The basin is deepest (8–8.5 km) and widest (~15 km) under the Lisan about 40 km north of the transverse fault. Farther north, basin depth is ambiguous, but is 3 km deep immediately north of the lake. The underlying pre-basin sedimentary layer thickens gradually from 2 to 3 km under the southern edge of the DSB to 3–4 km under the northern end of the lake and 5–6 km farther north. Crystalline basement is ~11 km deep under the deepest part of the basin. The upper crust under the basin has lower P wave velocity than in the surrounding regions, which is interpreted to reflect elevated pore fluids there. Within data resolution, the lower crust below ~18 km and the Moho are not affected by basin development. The subsidence rate was several hundreds of m/m.y. since the development of the DST ~17 Ma, similar to other basins along the DST, but subsidence rate has accelerated by an order of magnitude during the Pleistocene, which allowed the accumulation of 4 km of sediment. We propose that the rapid subsidence and perhaps elongation of the DSB are due to the development of inter-connected mid-crustal ductile shear zones caused by alteration of feldspar to muscovite in the presence of pore fluids. This alteration resulted in a significant strength decrease and viscous creep. We propose a similar cause to the enigmatic rapid subsidence of the North Sea at the onset the North Atlantic mantle plume. Thus, we propose that aqueous fluid flux into a slowly extending continental crust can cause rapid basin subsidence that may be erroneously interpreted as an increased rate of tectonic activity.Fieldwork was funded by U.S. AID Middle
Eastern Regional Cooperation Program grant M21–012, with in-kind contributions
by Al-Balqa’ Applied University (Jordan), the Geophysical Institute
of Israel, and the U.S. Geological Survey
Targeted sequencing of 351 candidate genes for epileptic encephalopathy in a large cohort of patients
Many genes are candidates for involvement in epileptic encephalopathy (EE) because one or a few possibly pathogenic variants have been found in patients, but insufficient genetic or functional evidence exists for a definite annotation
Imaging and spectroscopy of artificial-atom states in core/shell nanocrystal quantum dots
Current imaging scanning tunneling microscopy is used to observe the
electronic wavefunctions in InAs/ZnSe core/shell nanocrystals. Images taken at
a bias corresponding to the s conduction band state show that it is localized
in the central core region, while images at higher bias probing the p state
reveal that it extends to the shell. This is supported by optical and tunneling
spectroscopy data demonstrating that the s-p gap closes upon shell growth.
Shapes of the current images resemble atom-like envelope wavefunctions of the
quantum dot calculated within a particle in a box model.Comment: to be published in Physical Review Letter
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