Wave nature of Rosensweig instability

The explicit analytical solution of Rosensweig instability spikes’ shapes obtained by Navier–Stokes(NS) equation in diverse magnetic field H vertical to the flat free surface of ferrofluids are systematically studied experimentally and theoretically. After carefully analyzing and solving the NS equation in elliptic form, the force balanced surface equations of spikes in Rosensweig instability are expressed as cosine wave in perturbated magnetic field and hyperbolic tangent in large magnetic fiel...     

Wave nature of moving striations in a longitudinal magnetic field

Wave nature of stationary moving striations in helium and neon discharges in a uniform longitudinal magnetic field is studied. With the increase of the magnetic field, the frequency of natural striations decreases, while the wave length increases, and they damp out at high field region. Artificial excitations in these gases show that the wave length is proportional to the excitation frequency for given magnetic field and the slope of linear lines increases with the field. These wave nature of striations is explained following the dispersion relation derived from the consideration of waves of ionization and including effects of the magnetic field on the ionization.     

Hairpin formation and elongation of biomolecules

We introduce a model of thermalized conformations in space of RNA-or single stranded DNA-molecules, which includes the possibility of hairpin formation. This model contains the usual secondary structure information, but extends it to the study of one element of the ternary structure, namely the end-to-end distance. The computed force-elongation characteristics are in good agreement with some recent measurements on single stranded DNA molecules.     

Formation of doubly charged negative ions under the conditions of the resonant electron capture by fluorofullerenes

Doubly charged negative ions formed when electrons with controlled energies interact with isolated fluorinated fullerene molecules C₆₀F _n (n = 36, 48) have been detected and investigated by resonant electron capture mass spectrometry. The dependence of the intensity of the formation of doubly charged negative ions of fluorofullerenes on the energy of attached electrons has been measured. An original method, which is based on the experimental data and does not require additional calibration quantities, has been developed for estimating the absolute cross section for the formation of doubly charged negative ions. The absolute cross sections for the formation of the most intensely formed ions C₆₀F ₃₆ ^2? and C₆₀F ₄₈ ^2? are estimated to be about 1.1 × 10^?24 and 1.5 × 10^?24 m² at their maximum-yield energies of 2.0 and 1.6 eV, respectively.     

Laser like effect in biomolecules

This paper proposes to examine experimentally the stimulated process of bioluminescence and the coherent property of emission light which was hitherto held to be incoherent. The author considers the stimulated and coherent phenomena in biomolecules as a natural extension of the laser principle from usual matter into living systems which provide even better conditions required by the laser effect.     

Bioelectronic device consisting of self-assembled biomolecules

Bioelectronic device based on photoinduced electron transfer such as the biomolecular photodiode consisting of protein-adsorbed hetero film was investigated. Three kinds of functional molecules in biomolecular photodiode were used as a sensitizer, a first electron acceptor, and a second electron acceptor. The hetero-film was fabricated subsequently depositing functional molecules onto the pretreated conducting substrate using self-assembly method and Langmuir–Blodgett film method. The metal/insulator/metal structured bioelectronic device was constructed by depositing the metallic electrode onto the surface of the hetero-films. Based on the photoelectric response properties, the rectifying property in the current–voltage characteristic and the photoswitching effect of the proposed bioelectronic device were observed. The charge separation of molecular interface was verified in time-resolved fluorescent measurement by the time-correlated single photon counting method. The charge shift in the device was analyzed by the measurement of transient photocurrent of the device and thus the efficient directional flow of photocurrent through the redox potential difference was observed.     

Magnetic force probe for nanoscale biomolecules

We present a new technique to measure the mechanical properties of small biomolecules. This technique uses long range repulsive colloidal forces together with magnetic attraction as a force probing tool. The biomolecules are grafted between superparamagnetic particles, which are regularly spaced within long chains maintained by an external magnetic field. Varying the magnetic field results in compression or extension of the molecules between the particles. In order to demonstrate this technique we use, as a size controlled model molecule, a short double stranded DNA (151 base pairs) for which the force-extension law is determined and found in agreement with existing predictions.     

Low energy electron-driven damage in biomolecules

The damage induced by the impact of low energy electrons (LEE) on biomolecules is reviewed from a radiobiological perspective with emphasis on transient anion formation. The major type of experiments, which measure the yields of fragments produced as a function of incident electron energy (0.1-30 eV), are briefly described. Theoretical advances are also summarized. Several examples are presented from the results of recent experiments performed in the gas-phase and on biomolecular films bombarded with LEE under ultra-high vacuum conditions. These include the results obtained from DNA films and those obtained from the fragmentation of elementary components of the DNA molecule (i.e., the bases, sugar and phosphate group analogs and oligonucleotides) and of proteins (e.g. amino acids). By comparing the results from different experiments and theory, it is possible to determine fundamental mechanisms that are involved in the dissociation of the biomolecules and the production of single- and double-strand breaks in DNA. Below 15 eV, electron resonances (i.e., the formation of transient anions) play a dominant role in the fragmentation of all biomolecules investigated. These transient anions fragment molecules by decaying into dissociative electronically excited states or by dissociating into a stable anion and a neutral radical. These fragments can initiate further reactions within large biomolecules or with nearby molecules and thus cause more complex chemical damage. Dissociation of a transient anion within DNA may occur by direct electron attachment at the location of dissociation or by electron transfer from another subunit. Damage to DNA is dependent on the molecular environment, topology, type of counter ion, sequence context and chemical modifications.     

Theoretical thermochemistry of the C60F18, C60F36, and C60F48 fluorofullerenes

Relative energies of C₆₀F_N fluorofullerenes are reproduced reasonably well at the B3LYP/6- 311G** level of theory employed in conjunction with isodesmic transfluorination reactions, although overestimation of steric repulsions among non-bonded atoms is evident for species with larger values of N. On the other hand, the MNDO method is found to be less suitable for studies of fluorofullerene thermochemistry. The gas-phase standard enthalpy of formation of the C₆₀F₁₈ species is predicted to lie between ?1500 kJ mol^?1 and ?1400 kJ mol^?1.     

纳米材料与生物分子的相互作用与微结构特性

纳米材料是物理、化学、生物等领域所广泛关注的研究方向,主要分为无机材料、有机材料及复合材料。其中由纳米粒子与生物分子组成的复合材料因具有独特的光学、化学、电磁学等性质,在医学和医疗等方面有着良好的应用前景。此外,利用生物分子自组装的方法,可设计出具有复杂有序结构的复合材料。因此,研究纳米粒子和生物分子的相互作用对纳米材料的设计和应用有着重要的意义。本文从实验和计算机模拟两个方面综述了纳米粒子对生物分子(包括蛋白质、DNA、生物膜)结构特性以及热力学、动力学性质的影响,并概述了影响两者相互作用的多种因素,包括纳米粒子的尺寸、形状、浓度、表面特性等。     

Manipulation of biomolecules: A molecular dynamics study

With the rapid progression of bionanorobotics, manipulation of nano-scale biosamples is becoming increasingly attractive for different biological purposes. Nevertheless, the interaction between a robotic probe and a biological sample is poorly understood and the conditions for appropriate handling is not well-known. Here, we use the molecular dynamics (MD) simulation method to investigate the manipulation process when a nanoprobe tries to move a biosample on a substrate. For this purpose, we have used Ubiquitin (UBQ) as the biomolecule, a single-walled carbon nanotube (SWCNT) as the manipulation probe, and a double-layered graphene sheets as the substrate. A series of simulations were conducted to study the effects of different conditions on the success of the manipulation process. These conditions include the tip diameter, the vertical gap between the tip and substrate, and the initial orientation of the protein. Also we have studied two strategies for the manipulation of the protein by a nano-scale probe that we have named pushing and pulling. Interaction force between carbon nanotube (CNT) tips and the biomolecule, the root-mean-square deviation (RMSD), and the radius of gyration of the protein are monitored for different conditions. We found that larger tip diameters, smaller gaps between tip and substrate, and a pulling strategy increase the chance of a successful manipulation.     

Intramolecular hydrogen bonds in the phenylazomethine biomolecules

The FTIR spectra of the solutions of biologically active molecules (screened phenylazomethines) in CCl₄ are studied. The role of the OH- and N=C groups in the formation of the intramolecular H bonds is analyzed. The analysis of the FTIR spectra shows that three types of H bonds (O-H…O-H, O-H…N=C, and O-H…O-H…N=C) are possible in the molecules under study. A correlation of the H-bond formation in the phenylazomethine molecules and the antivirus properties of such molecules is revealed. The antivirus activity is observed for molecules that exhibit intramolecular O-H…O-H…N=C bonds in the absence of free hydroxyls. The antivirus activity decreases when the molecule contains additional OH groups that are not involved in H bonds.     

New fluorescent labels for time-resolved detection of biomolecules

New dyes with characteristic fluorescence lifetimes have been developed for bioanalytical applications. Based upon the concept of multiplex dyes, we have designed rhodamine dyes with nearly identical absorption and emission spectral characteristics but different fluorescence lifetimes. Extending this principle to applications with laser diodes, new rhodamines with functional groups for covalent coupling of analytes have been developed. The new labels exhibit absortion and fluorescence beyond 600 nm and have a high quantum efficiency, even in aqueous buffer systems.     

Constrained Wave Equations and Wave Maps

In this paper we establish that wave maps can be obtained by a penalization method if the initial data is well prepared. When the data is not well prepared, we prove that the solution of the penalized equation converges weakly to the solution of the system of coupled equations obtained in [11] by a multi-scale formal analysis. In particular, the interaction between the rapid normal oscillations and the tangential motions creates a new term in the limit system whose well-posedness is proved by using the Nash-Moser Implicit Function Theorem. The first author is funded in part by NSF DMS 0203485.The second author is funded in part by NSF DMS 0101969.