Biomedical subjects

B Dabrowski

Publications and source records attributed to B Dabrowski.

At least 19 recordsLinked to original sources

PubMed2005

Negative refraction in ferromagnet-superconductor superlattices.

Negative refraction, which reverses many fundamental aspects of classical optics, can be obtained in systems with negative magnetic permeability and negative dielectric permittivity. This Letter documents an experimental realization of negative refraction at millimeter waves, finite magnetic fields, and cryogenic temperatures utilizing a multilayer stack of ferromagnetic and superconducting thin films. In the present case the superconducting YBa2Cu3O7 layers provide negative permittivity while negative permeability is achieved via ferromagnetic (La:Sr)MnO3 layers for frequencies and magnetic fields close to the ferromagnetic resonance. In these superlattices the refractive index can be switched between positive and negative regions using external magnetic field as tuning parameter.

Journal Article↗

PubMed2005

Exchange interaction in the insulating phase of RNiO3.

In order to characterize the spin-spin exchange interactions responsible for the Type-E' antiferromagnetic order in inhomogeneous RNiO3 perovskites (R=Y or rare earth), the pressure dependence of the Néel temperature T(N) was systematically measured for samples with T(N)<T(IM) and T(N)=T(IM); T(IM) is an insulator-metal transition temperature. Analysis of the results shows that, as for superexchange, perturbation theory can be used to describe the interatomic exchange interactions for T(N)<T(IM), but the perturbation theory breaks down where T(N) approaches T(IM).

Journal Article↗

PubMed2005

Pressure-induced non-Fermi-liquid behavior of PrNiO3.

Comprehensive temperature scans of the resistivity of a high-quality sample of PrNiO3 were made under different pressures up to 30 kbar; they have revealed that the insulator phase is suppressed completely at P approximately equal to 13 kbar, transforming to a non-Fermi-liquid phase in which the resistivity varies as Deltarho=rho(T)-rho(0) approximately T(n) with n=1.33 and 1.60 over a broad pressure range.

Journal Article↗

PubMed2004

Disorder-induced polaron formation in the magnetoresistive perovskite La0.54Ba0.46MnO3.

Neutron studies of the effect of A-site chemical disorder on the ferromagnetic transition and spin dynamics for the magnetoresistive perovskite La0.54Ba0.46MnO3 are reported. The low temperature spin waves reveal that disorder reduces exchange interactions by only 9%. The development of a quasielastic peak in the spectrum below TC and long-time relaxation of the order parameter indicate that the transition is discontinuous in the disordered sample, while it appears continuous for the ordered sample. These results strongly suggest that chemical disorder lowers the energy for polaron formation in manganese perovskites, and is the origin of the dramatic 50 K reduction in TC.

Journal Article↗

PubMed2000

Magnetic-field-induced low-energy spin excitations in YBa(2)Cu(4)O(8) measured by high field Gd(3+) electron spin resonance.

We have measured the spin susceptibility, chi(s), of the CuO(2) planes in the underdoped high T(c) superconductor, YBa(2)Cu(4)O(8) by Gd(3+) electron spin resonance (ESR) in single crystals and aligned powders in fields up to 15.4 T. At low temperatures and high fields, chi(s) is enhanced slightly in the B parallel c orientation with respect to the B perpendicular c orientation. The enhancement at 15.4 T (approximately equal to 0.15H(c2)) at 16 K (0.2 T(c)) is small: approximately 10% of chi(s)(T(c)), suggesting that the second critical field of superconductivity, H(c2) approximately equal to 100 T, would not suppress the pseudogap. This work demonstrates the potential of high field ESR in single crystals for studying high T(c) superconductors.

Journal Article↗

PubMed2000

Charged-particle multiplicity near midrapidity in central Au+Au collisions at sqrt[SNN]=56 and 130 GeV.

We present the first measurement of pseudorapidity densities of primary charged particles near midrapidity in Au+Au collisions at sqrt[s(NN)] = 56 and 130 GeV. For the most central collisions, we find the charged-particle pseudorapidity density to be dN/deta|(|eta|<1) = 408+/-12(stat)+/-30(syst) at 56 GeV and 555+/-12(stat)+/-35(syst) at 130 GeV, values that are higher than any previously observed in nuclear collisions. Compared to proton-antiproton collisions, our data show an increase in the pseudorapidity density per participant by more than 40% at the higher energy.

Journal Article↗

PubMed2000

Enhanced susceptibility in LNiO3 perovskites ( L = La,Pr,Nd,Nd0.5Sm0. 5)

The temperature dependence of the resistivity rho(T) and of the dc magnetic susceptibility chi(T) were measured on high-quality LNiO3 (L = La,Pr,Nd,Nd0.5Sm0.5) samples synthesized under high oxygen pressure. Subtraction of the rare-earth contribution to chi(T) allows the presentation of the evolution of the susceptibility of the NiO3 array from Pauli to Curie-Weiss paramagnetism with decreasing bandwidth. A metal-insulator transition occurring at a temperature T(t) = T(N) is first order for L = Pr and Nd; it becomes second order and produces no anomaly in chi(-1)(T) at a T(t)>T(N) for L = Nd0.5Sm0.5. In the antiferromagnetic domain T<T(N), the chi(T) curve for the NiO3 array resembles that of a paramagnet.

Journal Article↗

PubMed2000

Chloride ions formation during degradation of organochloride compounds using TiO2 deposited on glass microspheres.

Aqueous solutions containing 200 mg/dm3 of p,p'-DDT and methoxychlor were photodegraded for 60 min in UV/TiO2/O2 system and chloride ions concentration and pH were measured. From 60 to 80% of the investigated pesticides were eliminated after treatment. Over 27% of chlorine atoms were splitted off for methoxychlor and 10% for p,p'-DDT. The experimental data suggest, that chlorine atoms were removed from the -CCl3 moiety but the chlorine atoms bound to aromatic ring were left intact at this step of photodegradation.

Chlorides↗

PubMed1996