745 research outputs found
Trapping of 27 bp - 8 kbp DNA and immobilization of thiol-modified DNA using dielectrophoresis
Dielectrophoretic trapping of six different DNA fragments, sizes varying from
the 27 to 8416 bp, has been studied using confocal microscopy. The effect of
the DNA length and the size of the constriction between nanoscale fingertip
electrodes on the trapping efficiency have been investigated. Using finite
element method simulations in conjunction with the analysis of the experimental
data, the polarizabilities of the different size DNA fragments have been
calculated for different frequencies. Also the immobilization of trapped
hexanethiol- and DTPA-modified 140 nm long DNA to the end of gold
nanoelectrodes was experimentally quantified and the observations were
supported by density functional theory calculations.Comment: 17 pages (1 column version), 8 figure
Coherent Multidecadal Atmospheric and Oceanic Variability in the North Atlantic: Blocking Corresponds with Warm Subpolar Ocean
Winters with frequent atmospheric blocking, in a band of latitudes from Greenland to Western Europe, are found to persist over several decades and correspond to a warm North Atlantic Ocean. This is evident in atmospheric reanalysis data, both modern and for the full 20th century. Blocking is approximately in phase with Atlantic multidecadal ocean variability (AMV). Wintertime atmospheric blocking involves a highly distorted jetstream, isolating large regions of air from the westerly circulation. It influences the ocean through windstress-curl and associated air/sea heat flux. While blocking is a relatively high-frequency phenomenon, it is strongly modulated over decadal timescales. The blocked regime (weaker ocean gyres, weaker air-sea heat flux, paradoxically increased transport of warm subtropical waters poleward) contributes to the warm phase of AMV. Atmospheric blocking better describes the early 20thC warming and 1996-2010 warm period than does the NAO index. It has roots in the hemispheric circulation and jet stream dynamics. Subpolar Atlantic variability covaries with distant AMOC fields: both these connections may express the global influence of the subpolar North Atlantic ocean on the global climate system
Linking The Atlantic Gyres: Warm, Saline Intrusions From Subtropical Atlantic to the Nordic Seas
Ocean state estimates from SODA assimilation are analyzed to understand how major shifts in the North Atlantic Current path relate to AMOC, and how these shifts are related to large scale ocean circulation and surface forcing. These complement surface-drifter and altimetry data showing the same events. SODA data indicate that the warm water limb of AMOC, reaching to at least 600m depth, expanded in density/salinity space greatly after 1995, and that Similar events occurred in the late 1960s and around 1980. While there were large changes in the upper limb, there was no immediate response in the dense return flow, at least not in SODA, however one would expect a delayed response of increasing AMOC due to the positive feedback from increased salt transport. These upper limb changes are winddriven, involving changes in the eastern subpolar gyre, visible in the subduction of low potential vorticity waters. The subtropical gyre has been weak during the times of the northward intrusions of the highly saline subtropical waters, while the NAO index has been neutral or in a negative phase. The image of subtropical/subpolar gyre exchange through teleconnections within the AMOC overturning cell will be described
Para to Ortho transition of metallic dimers on Si(001)
Extensive electronic structure calculations are performed to obtain the
stable geometries of metals like Al, Ga and In on the Si(001) surface at 0.5 ML
and 1 ML coverages. Our results coupled with previous theoretical findings
explain the recent experimental data in a comprehensive fashion. At low
coverages, as shown by previous works, `Para' dimers give the lowest energy
structure. With increasing coverage beyond 0.5 ML, `Ortho' dimers become part
of low energy configurations leading toward a `Para' to `Ortho' transition at 1
ML coverage. For In mixed staggered dimers (`Ortho' and `Para') give the lowest
energy configuration. For Ga, mixed dimers are non-staggered, while for Al
`Para' to `Ortho' transition of dimers is complete. Thus at intermediate
coverages between 0.5 and 1 ML, the `Ortho' and `Para' dimers may coexist on
the surface. Consequently, this may be an explanation of the fact that the
experimental observations can be successfully interpreted using either
orientation. A supported zigzag structure at 0.5 ML, which resembles , does not undergo a dimerization transition, and hence stays
semi-metallic. Also, unlike the soliton formation is ruled out
for this structure.Comment: 8 pages, 6 figure
Molecular dynamics study of melting of a bcc metal-vanadium II : thermodynamic melting
We present molecular dynamics simulations of the thermodynamic melting
transition of a bcc metal, vanadium using the Finnis-Sinclair potential. We
studied the structural, transport and energetic properties of slabs made of 27
atomic layers with a free surface. We investigated premelting phenomena at the
low-index surfaces of vanadium; V(111), V(001), and V(011), finding that as the
temperature increases, the V(111) surface disorders first, then the V(100)
surface, while the V(110) surface remains stable up to the melting temperature.
Also, as the temperature increases, the disorder spreads from the surface layer
into the bulk, establishing a thin quasiliquid film in the surface region. We
conclude that the hierarchy of premelting phenomena is inversely proportional
to the surface atomic density, being most pronounced for the V(111) surface
which has the lowest surface density
The neuromuscular, biochemical, and endocrine responses to a single-session vs. double-session training day in elite athletes
Purpose:
The aim of this study was to compare the acute neuromuscular, biochemical, and endocrine responses of a
training day consisting of a speed session only to performing a speed and weight training session on the same day.
Methods:
Fifteen male academy level rugby players completed two
protocols in a randomized order. The speed only protocol
involved performing 6 maximal effort repetitions of 50m running sprints with 5 minutes recovery between each sprint, while the speed and weights protocol involved the same
sprinting session but was followed 2h post by a lower body weights session consisting of 4 sets of 5 back squat and Romanian deadlift at 85% 1RM. Testosterone, cortisol, creatine kinase, lactate, and perceived muscle soreness were
determined immediately before, immediately after, 2h post,
and 24h post both protocols. Peak power, relative peak power, jump height, and average rate of force development
were determined from a counter movement jump (CMJ) at
the same time points.
Results:
At 24h post, muscle soreness was significantly higher
following the speed and weights protocol compared to speed only protocol (effect size eta2= .253, F=4.750, p < 0.05).
There was no significant difference between any of the CMJ variables at any of the post training time points. Likewise creatine kinase, testosterone, and cortisol were unaffected by the addition of a weight training session.
Conclusion:
These data indicate that the addition of a weight training
session 2h post a speed session, while increasing the perception of fatigue the following day, does not result in a difference in endocrine response or in neuromuscular capability
A review of recent perspectives on biomechanical risk factors associated with anterior cruciate ligament injury
There is considerable evidence to support a number of biomechanical risk factors associated with non-contact anterior cruciate ligament (ACL) injury. This paper aimed to review these biomechanical risk factors and highlight future directions relating to them. Current perspectives investigating trunk position and relationships between strength, muscle activity and biomechanics during landing/cutting highlight the importance of increasing hamstring muscle force during dynamic movements through altering strength, muscle activity, muscle length and contraction velocity. In particular, increased trunk flexion during landing/cutting and greater hamstring strength are likely to increase hamstring muscle force during landing and cutting which have been associated with reduced ACL injury risk. Decision making has also been shown to influence landing biomechanics and should be considered when designing tasks to assess landing/cutting biomechanics. Coaches should therefore promote hamstring strength training and active trunk flexion during landing and cutting in an attempt to reduce ACL injury risk.Peer reviewe
Mechanical properties and formation mechanisms of a wire of single gold atoms
A scanning tunneling microscope (STM) supplemented with a force sensor is
used to study the mechanical properties of a novel metallic nanostructure: a
freely suspended chain of single gold atoms. We find that the bond strength of
the nanowire is about twice that of a bulk metallic bond. We perform ab initio
calculations of the force at chain fracture and compare quantitatively with
experimental measurements. The observed mechanical failure and nanoelastic
processes involved during atomic wire fabrication are investigated using
molecular dynamics (MD) simulations, and we find that the total effective
stiffness of the nanostructure is strongly affected by the detailed local
atomic arrangement at the chain bases.Comment: To be published in Phys. Rev. Lett. 4 pages with 3 figure
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