arXiv subjects

Tao Hu

Publications and source records attributed to Tao Hu.

191 records · Page 11Linked to original sources

arXiv2011

Neutron-gamma discrimination of CsI(Na) crystals for dark matter searches

The luminescent properties of CsI(Na) crystals are studied in this report. By using a TDS3054C oscilloscope with a sampling frequency of 5 GS/s, we find out that nuclear recoil signals are dominated by very fast light pulse with a decay time of ~20 ns, while γ-ray signals have a decay time of ~600 ns. The wavelength of nuclear recoil and γ-ray signals are also different. The study of n/γ separation shows that the rejection factor can reach an order of 10-7 with signal efficiency more than 80% at an equivalent electron recoil energy of 20 keV or more. Such a property makes CsI(Na) an ideal candidate for dark matter searches.

physics.ins-det↗

arXiv2008

Theory of DNA translocation through narrow ion channels and nanopores with charged walls

Translocation of a single stranded DNA through genetically engineered $α$-hemolysin channels with positively charged walls is studied. It is predicted that transport properties of such channels are dramatically different from neutral wild type $α$-hemolysin channel. We assume that the wall charges compensate the fraction $x$ of the bare charge $q_{b}$ of the DNA piece residing in the channel. Our prediction are as follows (i) At small concentration of salt the blocked ion current decreases with $x$. (ii) The effective charge $q$ of DNA piece, which is very small at $x = 0$ (neutral channel) grows with $x$ and at $x=1$ reaches $q_{b}$. (iii) The rate of DNA capture by the channel exponentially grows with $x$. Our theory is also applicable to translocation of a double stranded DNA in narrow solid state nanopores with positively charged walls.

q-bio.SC↗

arXiv2007

How a protein searches for its specific site on DNA: the role of intersegment transfer

Proteins are known to locate their specific targets on DNA up to two orders of magnitude faster than predicted by the Smoluchowski three-dimensional diffusion rate. One of the mechanisms proposed to resolve this discrepancy is termed "intersegment transfer". Many proteins have two DNA binding sites and can transfer from one DNA segment to another without dissociation to water. We calculate the target search rate for such proteins in a dense globular DNA, taking into account intersegment transfer working in conjunction with DNA motion and protein sliding along DNA. We show that intersegment transfer plays a very important role in cases where the protein spends most of its time adsorbed on DNA.

q-bio.BM↗

arXiv2007

Electrostatic theory of viral self-assembly: a toy model

Viruses self-assemble from identical capsid proteins and their genome consisting, for example, of a long single stranded (ss) RNA. For a big class of T = 3 viruses capsid proteins have long positive N-terminal tails. We explore the role played by the Coulomb interaction between the brush of positive N-terminal tails rooted at the inner surface of the capsid and the negative ss RNA molecule. We show that viruses are most stable when the total contour length of ss RNA is close to the total length of the tails. For such a structure the absolute value of the total RNA charge is approximately twice larger than the charge of the capsid. This conclusion agrees with structural data.

q-bio.BM↗

arXiv2007

Kinetics of viral self-assembly: the role of ss RNA antenna

A big class of viruses self-assemble from a large number of identical capsid proteins with long flexible N-terminal tails and ss RNA. We study the role of the strong Coulomb interaction of positive N-terminal tails with ss RNA in the kinetics of the in vitro virus self-assembly. Capsid proteins stick to unassembled chain of ss RNA (which we call "antenna") and slide on it towards the assembly site. We show that at excess of capsid proteins such one-dimensional diffusion accelerates self-assembly more than ten times. On the other hand at excess of ss RNA, antenna slows self-assembly down. Several experiments are proposed to verify the role of ss RNA antenna.

q-bio.BM↗

arXiv2006

Hopping conductivity of a suspension of flexible wires in an insulator

We study the hopping conductivity in a composite made of Gaussian coils of flexible metallic wires randomly and isotropically suspended in an insulator at such concentrations that the spheres containing each wire overlap. Uncontrolled donors and acceptors in the insulator lead to random charging of wires and, hence, to a finite density of states (DOS) at the Fermi level. Then the Coulomb interactions between electrons of distant wires result in the soft Coulomb gap. At low temperatures the conductivity is due to variable range hopping of electrons between wires and obeys the Efros-Shklovskii (ES) law $\lnσ\propto -(T_{ES}/T)^{1/2}$ with $T_{ES}$ decreasing with concentration and length of the wires. Due to enhanced screening of Coulomb potentials, at large enough wire concentrations and sufficiently high temperatures, the ES law is replaced by the Mott law $\lnσ\propto -(T_{M}/T)^{1/4}$.

cond-mat.dis-nn↗

arXiv2006

Hopping conductivity of a suspension of nanowires in an insulator

We study the hopping conduction in a composite made of straight metallic nanowires randomly and isotropically suspended in an insulator. Uncontrolled donors and acceptors in the insulator lead to random charging of wires and hence finite bare density of states at the Fermi level. Then the Coulomb interactions between electrons of distant wires result in the soft Coulomb gap. At low temperatures the conductivity is due to variable range hopping of electrons between wires and obeys the Efros-Shklovskii (ES) law $\lnσ\propto -(T_{ES}/T)^{1/2}$. We show that $T_{ES} \propto 1/(nL^3)^2$, where $n$ is the concentration of wires and $L$ is the wire length. Due to enhanced screening of Coulomb potentials, at large enough $nL^3$, the ES law is replaced by the Mott law.

cond-mat.dis-nn↗

arXiv2006

How does a protein search for the specific site on DNA: the role of disorder

Proteins can locate their specific targets on DNA up to two orders of magnitude faster than the Smoluchowski three-dimensional diffusion rate. This happens due to non-specific adsorption of proteins to DNA and subsequent one-dimensional sliding along DNA. We call such one-dimensional route towards the target "antenna". We studied the role of the dispersion of nonspecific binding energies within the antenna due to quasi random sequence of natural DNA. Random energy profile for sliding proteins slows the searching rate for the target. We show that this slowdown is different for the macroscopic and mesoscopic antennas.

cond-mat.soft↗

arXiv2006

Conductivity of a suspension of nanowires in a weakly conducting medium

We study macroscopic electrical or thermal conductivity of a composite made of straight or coiled nanowires suspended in poorly conducting medium. We assume that volume fraction of the wires is so large that spaces occupied by them overlap, but there is still enough room to distribute wires isotropically. We found a wealth of scaling regimes at different ratios of conductivities of the wire, $σ_1$ and of the medium, $σ_2$, length of wires, their persistent length and volume fraction. There are large ranges of parameters where macroscopic conductivity is proportional to $(σ_{1}σ_{2})^{1/2}$. These results are directly applicable to the calculation of the macroscopic diffusion constant of the nonspecific DNA-binding proteins in semidilute DNA solution.

cond-mat.soft↗

arXiv2005

New method for determining the thickness of non-edge-on disk galaxies

In this paper we report a new method for determining the thickness of the non-edge-on disk galaxies. Our method is based on the observation comparing with the theoretical researches of the distribution of the vertical velocity dispersion, which is obtained from the solutions of three dimensional Poisson's equation and the galactic dynamical equation. This method also allows us to investigate the mass-to-light ratio of the disk. As examples, the thickness and mass-to-light ratio of two disk galaxies, NGC 1566 and NGC 5247, which have been extensively studied in spectroscopy, have been calculated and the results are presented.

astro-ph↗

arXiv2005

How do proteins search for their specific sites on coiled or globular DNA

It is known since the early days of molecular biology that proteins locate their specific targets on DNA up to two orders of magnitude faster than the Smoluchowski 3D diffusion rate. It was the idea due to Delbruck that they are non-specifically adsorbed on DNA, and sliding along DNA provides for the faster 1D search. Surprisingly, the role of DNA conformation was never considered in this context. In this article, we explicitly address the relative role of 3D diffusion and 1D sliding along coiled or globular DNA and the possibility of correlated re-adsorbtion of desorbed proteins. We have identified a wealth of new different scaling regimes. We also found the maximal possible acceleration of the reaction due to sliding, we found that the maximum on the rate-versus-ionic strength curve is asymmetric, and that sliding can lead not only to acceleration, but in some regimes to dramatic deceleration of the reaction.

q-bio.BM↗