Debye Temperature and Quantum Diffusion of Hydrogen in Body-Centered Cubic Metals.

Diffusion of deuterium in potassium is studied herein. Mass transfer is controlled predominantly by the mechanism of overbarrier atomic jumps at temperatures 120-260 K and by the tunneling mechanism at 90-120 K. These results together with literature data allowed us to determine conditions under which the quantum diffusion of hydrogen in metals can be observed, which is a fundamental problem.

Quantum Diffusion of Deuterium in Sodium.

The online nuclear reaction analysis technique has been applied to study the temperature dependence of deuterium diffusion coefficients for deuterium in sodium at temperatures ranging between 110 and 240 K, and at cryogenic temperatures, below 160 K, tunneling of deuterium atoms in the metal lattice has been observed. Above 160 K, diffusion occurs by the classical mechanism of overbarrier atomic jumps. Results of quantum diffusion of deuterium in a metal have been obtained for the first time; they used to be known only for the lightest hydrogen isotope, protium, in niobium and tantalum.

Disentanglement of Two Single Polymer Chains: Contacts and Knots.

Understanding the consequences of the noncrossing constraint is one of the remaining challenges in the physics of walks and polymers. To address this problem, we performed molecular simulations for the separation of only two initially connected, overlapping polymer chains with interactions tuned such that they are nearly random walks. The separation time for a configuration strongly correlates with the number of monomer contacts between both chains.

Wigner Crystal and Colossal Magnetoresistance in InSb Doped with Mn.

We report magnetotransport investigation of nonmagnetic InSb single crystal doped with manganese at Mn concentration NMn ~ 1,5 × 10(17) cm(-3) in the temperature range T = 300 K-40 mK, magnetic field B = 0-25T and hydrostatic pressure P = 0-17 kbar. Resistivity saturation was observed in the absence of magnetic field at temperatures below 200 mK while applied increasing external magnetic field induced colossal drop of resistivity (by factor 10(4)) at B ~ 4T with further gigantic resistivity increase (by factor 10(4)) at 15T. Under pressure, P = 17 kbar, resistivity saturation temperature increased up to 1,2 K.

Influence of magnetic dopants on the metal-insulator transition in semiconductors.

InSb:Mn and InSb:Ge reveal differences in their resistivity near the metal-insulator transition although both are acceptors of comparable depth. InSb:Ge shows the commonly observed behavior whereas InSb:Mn exhibits a strong enhancement of the resistivity below 10 K and pronounced negative magnetoresistance effects at 1.6 K.

Elasticity of cisplatin-bound DNA reveals the degree of cisplatin binding.

Cisplatin was incidentally discovered to suppress cell division and became one of the most successful antitumor drugs. It is therapeutically active upon binding to DNA and locally kinking it. We demonstrate that after a bimodal modeling, the degree of platination of a single DNA molecule can be consistently and reliably estimated from elasticity measurements performed with magnetic tweezers.

Enhanced mobility of confined polymers.

Non-classical behaviour, brought about by a confinement that imposes spatial constraints on molecules, is opening avenues to novel applications. For example, carbon nanotubes, which show rapid and selective transport of small molecules across the nanotubes, have significant potential as biological or chemical separation materials for organic solvents or gaseous molecules. With polymers, when the dimensions of a confining volume are much less than the radius of gyration, a quantitative understanding of perturbations to chain dynamics due to geometric constraints remains a challenge and, with the development of nanofabrication processes, the dynamics of confined polymers have significant technological implications.

Long-range interactions in polymer melts: the anti-Casimir effect.

It is well known that small neutral particles normally tend to aggregate due to the van der Waals forces. We discover a new universal long-range interaction between solid objects in polymer media that is directly opposite the van der Waals attraction. The new force could reverse the sign of the net interaction, possibly leading to the net repulsion.

Long range bond-bond correlations in dense polymer solutions.

The scaling of the bond-bond correlation function P1(s) along linear polymer chains is investigated with respect to the curvilinear distance s along the flexible chain and the monomer density rho via Monte Carlo and molecular dynamics simulations. Surprisingly, the correlations in dense three-dimensional solutions are found to decay with a power law P1(s) approximately s(-omega) with omega=3/2 and the exponential behavior commonly assumed is clearly ruled out for long chains. In semidilute solutions, the density dependent scaling of P1(s) approximately g(-omega(0))(s/g)(-omega) with omega(0)=2-2nu=0.

Arrested swelling of highly entangled polymer globules.

Upon aging, a collapsed long chain evolves from a crumpled state to a self-entangled globule which can be thought of as a large knot. Swelling of an equilibrium globule in good solvent is a two-step process: (i) fast swelling into an arrested stretched structure with conserved entanglement topology followed by (ii) slow disentanglement. Using computer simulation, we found both mass-mass (m-m) and entanglement-entanglement (e-e) power law correlations inside the swollen globule.

Counterion phase transitions in dilute polyelectrolyte solutions.

In dilute solutions of rodlike polyelectrolytes some counterions are distributed far from polyions while others are located in their vicinity in the regions of cylindrical symmetry of the electrostatic potential. For these cylindrical regions around rodlike polyelectrolytes we find an exact solution of the nonlinear Poisson-Boltzmann equation for the case of nonzero net charge in these regions. This exact solution implies three qualitatively different phases of counterion distribution around the polyions with second order phase transitions between these phases.

Successful conservative management of Gorham disease of the skull base and cervical spine.

Gorham's disease, also called massive osteolysis or vanishing bone disease, is an enigmatic condition caused by endothelial proliferation occurring in bone and soft tissue. Death is frequent when there is spinal or visceral involvement. We present a case of spinal and skull base Gorham's disease that was reversed by radiation therapy administered while the spine was supported by a halo vest.

Deterministic model of DNA gel electrophoresis in strong electric fields.

We present a new model for the motion of a megabase-long DNA molecule undergoing gel electrophoresis. We assume that the dynamics of large segments of DNA is almost deterministic and can be described by a set of simple mechanical equations. This allows the numerical study of gel electrophoresis of ultra-high molecular weight DNA.

Multilevel lumbar disc herniation in 12-year-old twins.

Herniation of a lumbar disc in the pediatric age group is rare. A 12-year-old female twin developed backache and left sciatica after a mild lifting injury. Magnetic resonance imaging of the spine showed multilevel lumbar disc herniation.

Successful removal of large pineal region meningiomas: two case reports.

Background: Pineal region meningiomas are extremely rare tumors and comprise about 8% of tumors of this region. Two cases of large pineal region meningiomas in young males are presented.

Methods: Computed tomography (CT) scan and cerebral angiography were used to evaluate the patients preoperatively.

The cytotoxic action of lymphokine activated killer cells upon the human glioma cell line U251 is stimulated by bispecific monoclonal antibody (MoAb) constructs.

The ability of IL-2 stimulated mononuclear cells to kill the human glioblastoma cell line U251 has been investigated. Highest cytotoxic activity was generated in low cell density cultures incubated for 15 days with 250-1000 U/ml IL-2. Sub-optimal killing was noted, with cells only exposed to IL-2 for three days.