Through the Eye of the Needle: Recent Advances in Understanding Biopolymer Translocation

In recent years polymer translocation, i.e., transport of polymeric molecules through nanometer-sized pores and channels embedded in membranes, has witnessed strong advances. It is now possible to observe single-molecule polymer dynamics during the motion through channels with unprecedented spatial and temporal resolution. These striking experimental studies have stimulated many theoretical developments. In this short theory-experiment review, we discuss recent progress in this field with a strong focus on non-equilibrium aspects of polymer dynamics during the translocation process.Comment: 29 pages, 6 figures, 3 tables, to appear in J. Phys.: Condens. Matter as a Topical Revie

Pore-blockade Times for Field-Driven Polymer Translocation

We study pore blockade times for a translocating polymer of length $N$, driven by a field $E$ across the pore in three dimensions. The polymer performs Rouse dynamics, i.e., we consider polymer dynamics in the absence of hydrodynamical interactions. We find that the typical time the pore remains blocked during a translocation event scales as $\sim N^{(1+2\nu)/(1+\nu)}/E$, where $\nu\simeq0.588$ is the Flory exponent for the polymer. In line with our previous work, we show that this scaling behaviour stems from the polymer dynamics at the immediate vicinity of the pore -- in particular, the memory effects in the polymer chain tension imbalance across the pore. This result, along with the numerical results by several other groups, violates the lower bound $\sim N^{1+\nu}/E$ suggested earlier in the literature. We discuss why this lower bound is incorrect and show, based on conservation of energy, that the correct lower bound for the pore-blockade time for field-driven translocation is given by $\eta N^{2\nu}/E$, where $\eta$ is the viscosity of the medium surrounding the polymer.Comment: 14 pages, 6 figures, slightly shorter than the previous version; to appear in J. Phys.: Cond. Ma

Field dependent collision frequency of the two-dimensional driven random Lorentz gas

In the field-driven, thermostatted Lorentz gas the collision frequency increases with the magnitude of the applied field due to long-time correlations. We study this effect with computer simulations and confirm the presence of non-analytic terms in the field dependence of the collision frequency as predicted by kinetic theory.Comment: 6 pages, 2 figures. Submitted to Phys. Rev.

Isometric dilation and Sarason's commutant lifting theorem in several variables

The article deals with isometric dilation and commutant lifting for a class of $n$-tuples $(n \geq 3)$ of commuting contractions. We show that operator tuples in the class dilate to tuples of commuting isometries of BCL type. As a consequence of such an explicit dilation, we show that their von Neumann inequality holds on a one dimensional variety of the closed unit polydisc. On the basis of such a dilation, we prove a commutant lifting theorem of Sarason's type by establishing that every commutant can be lifted to the dilation space in a commuting and norm preserving manner. This further leads us to find yet another class of $n$-tuples $(n\geq 3)$ of commuting contractions each of which possesses isometric dilation.Comment: 31 pages, Comments are welcom

Near-infrared photoabsorption by C(60) dianions in a storage ring

We present a detailed study of the electronic structure and the stability of C(60) dianions in the gas phase. Monoanions were extracted from a plasma source and converted to dianions by electron transfer in a Na vapor cell. The dianions were then stored in an electrostatic ring, and their near-infrared absorption spectrum was measured by observation of laser induced electron detachment. From the time dependence of the detachment after photon absorption, we conclude that the reaction has contributions from both direct electron tunneling to the continuum and vibrationally assisted tunneling after internal conversion. This implies that the height of the Coulomb barrier confining the attached electrons is at least similar to 1.5 eV. For C(60)(2-) ions in solution electron spin resonance measurements have indicated a singlet ground state, and from the similarity of the absorption spectra we conclude that also the ground state of isolated C(60)(2-) ions is singlet. The observed spectrum corresponds to an electronic transition from a t(1u) lowest unoccupied molecular orbital (LUMO) of C(60) to the t(1g) LUMO+1 level. The electronic levels of the dianion are split due to Jahn-Teller coupling to quadrupole deformations of the molecule, and a main absorption band at 10723 cm(-1) corresponds to a transition between the Jahn-Teller ground states. Also transitions from pseudorotational states with 200 cm(-1) and (probably) 420 cm(-1) excitation are observed. We argue that a very broad absorption band from about 11 500 cm(-1) to 13 500 cm(-1) consists of transitions to so-called cone states, which are Jahn-Teller states on a higher potential-energy surface, stabilized by a pseudorotational angular momentum barrier. A previously observed, high-lying absorption band for C(60)(-) may also be a transition to a cone state

Studies on stomatal frequency and its relationship with leaf biomass and rhizome yield of turmeric (Curcuma longa L.) genotypes

Stomatal frequencies of twelve turmeric (Curcuma longa L.) genotypes were recorded from different locations of both surfaces of the fourth, sixth and eighth nodal leaves. Turmeric leaves were amphistomatous having lower stomatal frequency in the upper surface (426.6 - 1773.7 sq. cm-1) and higher in the lower surface (7131.5 - 12,270.9 sq. cm-1) of the leaves. With a few exceptions, stomatal frequency of the leaves of the genotypes tested increased from fourth to eighth nodal position. The stomatal frequency of the genotypes either at the same location within leaf, at different locations within leaf or both leaf surfaces taken together did not vary significantly. The genotype TCP-9 had the highest stomatal frequency. However, stomatal frequency increased from base towards tip on both surfaces of the leaf, irrespective of the position of the leaf in all the genotypes. The stomatal frequency appeared significant and more positively correlated with rhizome yield than leaf dry weight in genotypes resistant to leaf blotch disease while in susceptible types it exhibited significant and negative correlation with leaf dry weight and rhizome yield. &nbsp

Studies on stomatal frequency and its relationship with leaf biomass and rhizome yield of turmeric (Curcuma longa L.) genotypes

Stomatal frequencies of twelve turmeric (Curcuma longa L.) genotypes were recorded from different locations of both surfaces of the fourth, sixth and eighth nodal leaves. Turmeric leaves were amphistomatous having lower stomatal frequency in the upper surface (426.6 - 1773.7 sq. cm-1) and higher in the lower surface (7131.5 - 12,270.9 sq. cm-1) of the leaves. With a few exceptions, stomatal frequency of the leaves of the genotypes tested increased from fourth to eighth nodal position. The stomatal frequency of the genotypes either at the same location within leaf, at different locations within leaf or both leaf surfaces taken together did not vary significantly. The genotype TCP-9 had the highest stomatal frequency. However, stomatal frequency increased from base towards tip on both surfaces of the leaf, irrespective of the position of the leaf in all the genotypes. The stomatal frequency appeared significant and more positively correlated with rhizome yield than leaf dry weight in genotypes resistant to leaf blotch disease while in susceptible types it exhibited significant and negative correlation with leaf dry weight and rhizome yield. &nbsp

Approximate Solution of the effective mass Klein-Gordon Equation for the Hulthen Potential with any Angular Momentum

The radial part of the effective mass Klein-Gordon equation for the Hulthen potential is solved by making an approximation to the centrifugal potential. The Nikiforov-Uvarov method is used in the calculations. Energy spectra and the corresponding eigenfunctions are computed. Results are also given for the case of constant mass.Comment: 12 page

Infant- and Young Child-feeding Practices in Bankura District, West Bengal, India

A community-based, cross-sectional descriptive study was conducted during June-July 2008 to assess the infant- and young child-feeding (IYCF) practices in Bankura district, West Bengal, India. In total, 647 children aged less than two years selected through revised 40-cluster sampling using the indicators of the Integrated Management of Neonatal and Childhood Illness (IMNCI) and World Health Organization. The proportions of infants with early initiation of breastfeeding (13.6%) and exclusive breastfeeding under six months (57.1%) and infants who received complementary feeding at the age of 6–8 months (55.7%) were low. Appropriate feeding as per the IMNCI protocol was significantly less among infants aged 6–11 months (15.2%) and children aged 12–23 months (8.7%) compared to infants aged less than six months (57.1%), which could be attributable to low frequency and amount of complementary feeding. The main problems revealed from the study were late initiation of breastfeeding, low rates of exclusive breastfeeding, and inappropriate complementary feeding practices