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. Existing models are discussed in attempt to explain resistivity saturation, dramatic influence of magnetic field and pressure on resistivity with the focus on possible manifestation of three dimensional Wigner crystal formed in InSb by light electrons and heavy holes.

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. Both effects increase by applying hydrostatic pressure. The different behavior arises from the differences in the filling of the 3d shell, half filled 3d;{5} for Mn with a total spin of S=5/2 and entirely filled 3d;{10} for Ge with total angular momentum of J=0. The exchange interaction between the hole spin of the Mn acceptor and the S=5/2 spin of its 3d;{5} shell is the dominant correlation effect leading to the formation of an antiferromagnetic alignment of the Mn 3d;{5} spins along the percolation path which inhibits hopping of holes between neighboring Mn sites.

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. This universal repulsion comes from the subtracted soft fluctuation modes, which are not present in the real polymer system, but rather are in its ideal counterpart. The predicted effect has a deep relation to the classical Casimir interactions, providing an unusual example of fluctuation-induced repulsion instead of normal attraction. That is why it is referred to as the anti-Casimir effect. We also find that the correlation function of monomer units in a concentrated solution of infinite polymer chains follows a power-law rather than an exponential decay at large distances.

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=0.824 (nu=0.588 being Flory's exponent) is set by the number of monomers g(rho) in an excluded volume blob. Our computational findings compare well with simple scaling arguments and perturbation calculation. The power-law behavior is due to self-interactions of chains caused by the chain connectivity and the incompressibility of the melt.

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. The m-m correlations are characterized by a set of two exponents in agreement with a Flory-type argument. The e-e correlations are also characterized by two exponents, both of them larger (by approximately 0.3) than the related m-m exponents. We interpret this difference as evidence of distance-dependent repulsion E=-0.3ln((rho)k(B)T between entanglements sliding along the polymer chain.

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. The literature is reviewed.

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. A strong electric field forces DNA in a gel into a tree-like structure with branches-loops of different sizes. We determined the loop-size distribution function. This distribution has a power law form, confirming the hypothesis of the statistical self-similarity of a moving polymer. We find periodic configuration changes in the motion of a circular polymer, with the average period proportional to the molecular weight. During the period, a polymer goes through three distinct phases: a simple V-shape configuration, a growing tree, and a decaying tree. For a linear polymer this periodicity is much less pronounced because of additional perturbations to the dynamics caused by free ends. A circular polymer stays in a simple V-shaped configuration about 30% of the time, independent of molecular weight (10% for a linear polymer).

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. The patient was managed conservatively and her symptoms subsided within 6 weeks. Magnetic resonance imaging of her asymptomatic twin sister revealed a similar pattern of disc degeneration and multilevel herniation. This report emphasizes the hereditary nature of juvenile lumbar disc degeneration.

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. Both patients were operated on through an occipital transtentorial approach either as a single- or two-stage procedure. RESULTS: Preoperative work-up revealed that both tumors received their main blood supply from the posterior lateral choroidal arteries and were therefore originating from the velum interpositum cerebri (superior tela choroidea). Complete tumor removal was effected in the first patient using a right occipital transtentorial approach. In the second patient, after partial removal using the same approach, complete resection was achieved at a second stage via the left occipital transtentorial approach 3 months later. CONCLUSION: Cerebral angiography, which must include vertebral angiography, is important in the preoperative surgical planning of these tumors. The occipital transtentorial approach provides good access. However, a two-stage procedure using right and left sides may be necessary for large meningiomas receiving a bilateral blood supply from both posterior lateral choroidal arteries. Diagnosis, the surgical approach, and methods of tumor excision are discussed.

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. Under the latter conditions, bispecific monoclonal antibodies (MoAbs) of either anti-CD3 or anti-CD16 and an anti-NCAM MoAb stimulated LAK cell activity markedly. Anti-CD16 conjugates were found more effective than anti-CD3 and (Fab')2 constructs more efficacious than those made with whole Ig molecules. Maximal stimulation of LAK cell activity was noted with bispecific MoAbs. Little effect was observed with either single or mixtures of monomeric MoAbs. Furthermore, no effect of bispecific MoAbs was observed when target cells lacked expression of NCAM. These results could be of clinical importance as it is not always feasible to screen LAK cells for optimal activity before administration to patients. Whilst bispecific MoAbs have no effect on optimally stimulated LAK cells, they are not inhibitory and can stimulate killing under sub-optimal IL-2 stimulation.

[The chemical modification of immunoglobulins for accelerating their elimination from the blood flow during radioimmunodiagnosis]. / Khimicheskaia modifikatsiia immunoglobulinov dlia uskoreniia ikh vyvedeniia iz krovotoka v protsesse radioimmunodiagnostiki.

Immunoglobulins were modified by diethylenetriaminepentaacetic acid anhydride and sulfosuccinimidy 16-(biotinamido) hexanoate and were conjugated with modified polylysine. Biodistribution of the samples was observed before and after avidin injection. Samples containing no polylysine accumulate in reticuloendothelial system, protein conjugate with polylysine concentrate in kidneys. The results demonstrate that drug distribution depends on the type of modification.

[Antibodies to glial fibrillary antigen as potential carriers of drugs for glial tumors]. / Antitela k glial'nomu fibrilliarnomu antigenu kak potentsial'nye perenoschiki lekarstvennykh sredstv k glial'nym opukholiam.

Polyclonal monospecific antibodies to the glial fibrillar antigen of the brain (GFA) and, as controls, antibodies not possessing specific tendency were injected intravenously separately into two groups of rats with glioblastomas transplanted into the brain. The immunoenzymatic method was used to study the content of the injected antibodies in tissue extracts collected from the zone of the glioblastoma, brain matter and other organs 2, 20, and 48 hours after the injection. It was established that polyclonal monospecific antibodies to GFA accumulate selectively in the zone of the glioblastoma. The use of antibodies to GFA for selective transport of medicinal agents to malignant glial tumors must be evaluated in further studies.

[Specific cerebral alpha 1-globulin in glial tumors]. / Izuchenie spetsificheskogo al'fa 1-globulina mozga pri glial'nykh opukholiakh.

The level of specific alpha 1-globulin (S alpha 1-GB) and autoantibodies to it was measured by the immunoenzyme method in blood serum of 160 donors and 88 neurological patients. The S alpha 1-GB level was increased most frequently in blood serum of patients with glial brain tumors. In malignant glial tumors the increased serum S alpha 1-GB level was combined with a reduced level of autoantibodies to it. The work discusses the role of the suggested immunochemical tests and the mechanisms of the increase in the S alpha 1-GB level and decrease in the level of autoantibodies to this antigen.

[Immunoenzyme method of determining brain-specific alpha 1-globulin in glial tumors]. / Immunofermentnyi metod opredeleniia spetsificheskogo al'fa 1-globulina mozga pri glial'nykh opukholiakh.

Specific alpha 1-globulin of the brain was assayed by an immunoenzyme technique in blood sera from cases of various brain pathologies and healthy donors. Relative elevation in brain specific alpha 1-globulin level, as compared with that in healthy subjects, was more frequent in patients with malignant glial tumors of the brain, less frequent in cases of benign glial tumors and in very few patients suffering from other brain diseases. Raised level of specific alpha 1-globulin may be caused by disorders in the blood-brain barrier or lesions in brain or tumor tissues which is peculiar to glial malignancies of the brain. The said test offers much advantage in diagnosis of glial tumors.

[Immunochemical study of alpha-1 organospecific antigen in different sections of the brain and CNS tumors]. / Immunokhimicheskoe izuchenie al'fa-1 organospetsificheskogo antigena v razlichnykh otdelakh mozga i opukholiakh TsNS.

By immunochemical methods the most high concentrations of alpha-1 organ specific antigen of the brain were revealed in tissue extracts of the spinal marrow, cerebral trunk, hypothalamus; its lower concentrations--in the cerebral cortex, cerebellum, optic nerve, white substance of the hemispheres and pineal gland. This protein was not found in the hypophysis. In tumors of neuroectodermal origin the antigen was found in high concentrations. In an group of meningiomas alpha-1 organ specific brain antigen was detected in tumors of meningotheliomatous type, but it was absent in tumors of mixed and fibroblastic type, this permitted suggesting a neuroectodermal origin of tumors of the first type and ectomesenchymal one of the second type.