Correlated Local Bending of a DNA Double Helix and Its Effect on DNA Flexibility in the Sub-Persistence-Length Regime

Mechanical characteristics of DNA in the sub-persistence-length (<i>l</i>_P ≈ 150 base pairs) regime are vital to many of its biological functions but not well understood. Recent experimental studies in this regime have shown a dramatic departure from the traditional worm-like chain model, which is designed for long DNA chains and predicts a constant flexibility at all length scales. Here, we report an improved model with explicit considerations of a new length scale <i>l</i>_D ≈ 10 base pairs, over which DNA local bend angles are correlated. In this correlated worm-like chain model, a finite length correction term is analytically derived, and DNA flexibility is found to be contour-length-dependent. While our model reduces to the traditional worm-like chain model at length scales much larger than <i>l</i>_P, it predicts that DNA becomes much more flexible at shorter sizes, in good agreement with recent cyclization measurements of short DNA fragments around 100 base pairs

Adhesion of Dust Particles to Common Indoor Surfaces in an Air-Conditioned Environment

<div><p>Adhesion between dust particles and indoor surfaces can lead to negative effects on human health by triggering allergic and asthmatic reactions. In this study, adhesion forces of indoor office dust and activated carbon (AC, as model soot) particles to four common indoor materials (Al, Cu, PVC, and glass) were measured by colloidal probe atomic force microscopy. Chemical analysis of office dust shows it is largely made up of oxygenated hydrophilic organic carbon material. Both metal surfaces experienced weaker dust and AC adhesion than PVC or glass by up to 2–12 times lower primarily due to the presence of attractive electrostatic forces in the latter two (non-conducting) surfaces. Dust and AC adhesion were also highly sensitive to surface roughness, with an inverse relationship between adhesion force and roughness due to the reduction in contact area between the particle and a rougher material surface. Capillary forces play only a minor or negligible role in dust and AC surface adhesion. Adhesion models utilizing a purely van der Waals approach such as the simple Hamaker model and modified Rumpf's model are insufficient to determine the actual particle-surface contact radii and requires the accounting of non-van der Waals forces to adhesion.</p> <p>Copyright 2014 American Association for Aerosol Research</p> </div

Testing the magnetic stability of magnetite-waste tea composite after 8 days in water.

<p>Testing the magnetic stability of magnetite-waste tea composite after 8 days in water.</p

Concentrations of main electrolytes and dissolved organic content in the artificial waters used in the experiments.

<p>Concentrations of main electrolytes and dissolved organic content in the artificial waters used in the experiments.</p

TGA analyses of the uncoated and magnetite-waste tea composite showing that the magnetite coating accounts for about 22% of the total mass of the composite.

<p>TGA analyses of the uncoated and magnetite-waste tea composite showing that the magnetite coating accounts for about 22% of the total mass of the composite.</p

Amount of Fe leached out into the four waters from uncoated tea (A) and magnetite-waste tea composite (B).

<p>Amount of Fe leached out into the four waters from uncoated tea (A) and magnetite-waste tea composite (B).</p

SEM images of waste tea powder (A) without and (B) with magnetite coating.

<p>SEM images of waste tea powder (A) without and (B) with magnetite coating.</p

Percentage of Pb adsorbed onto the four sorbents for each of the four different waters: (A) deionized water, (B) rainwater, (C) groundwater and (D) freshwater.

<p>Percentage of Pb adsorbed onto the four sorbents for each of the four different waters: (A) deionized water, (B) rainwater, (C) groundwater and (D) freshwater.</p

Key parameters of the tea powders (unmagnetized tea and magnetite-waste tea composite) measured using the nitrogen physisorption isotherms.

<p>Key parameters of the tea powders (unmagnetized tea and magnetite-waste tea composite) measured using the nitrogen physisorption isotherms.</p