Monte Carlo study of the ordering in a strongly frustrated liquid crystal.

We have performed Monte Carlo simulations to investigate the temperature dependence of the ordering of the side chains of the X-shaped liquid crystal molecules which are arranged in a hexagonal array. Each hexagon contains six side chains, one from each side of the hexagon. Each liquid crystal molecule has two, dissimilar, side chains, one that contains silicon and one that contains fluorine. Like chains attract each other more strongly than unlike chains and this drives an order-disorder transition. The system is frustrated because it is not possible to find a configuration in which all the hexagons are occupied by either all silicon or all fluorine chains. There are two phase transitions. If only pairwise interactions are included it is found that there is an interesting fluctuating phase between the disordered phase and the fully ordered ground state. This did not agree with the experiments where an intermediate phase was seen that had long range order on one of the three sublattices. Agreement was found when the calculations were modified to include attractive three-body interactions between the silicon chains.

Diffusive benefits of cylinders in front of a Schroeder diffuser.

A numerical investigation is performed into the diffusive effects of cylinders positioned in front of a Schroeder diffuser. A regular line of cylinders is shown to offer notable improvements to diffusion from a periodic Schroeder device, provided lateral cylinder spacing is incommensurable with the Schroeder period width. Further investigation considers angular dependence and low frequency results in greater detail, as well as the effects on narrowband and modulated Schroeder devices. An optimization procedure is subsequently performed to investigate the effects of an irregular cylinder arrangement, which provides further diffusive benefits.

Magnetoresistance of magnetically doped ZnO films.

Magnetoresistance measurements have been made at 5 K on doped ZnO thin films grown by pulsed laser deposition. ZnCoO, ZnCoAlO and ZnMnAlO samples have been investigated and compared to similar films containing no transition metal dopants. It is found that the Co-doped samples with a high carrier concentration have a small negative magnetoresistance, irrespective of their magnetic moment. On decreasing the carrier concentration, a positive contribution to the magnetoresistance appears and a further negative contribution. This second, negative contribution, which occurs at very low carrier densities, correlates with the onset of ferromagnetism due to bound magnetic polarons suggesting that the negative magnetoresistance results from the destruction of polarons by a magnetic field. An investigation of the anisotropic magnetoresistance showed that the orientation of the applied magnetic field, relative to the sample, had a large effect. The results for the ZnMnAlO samples showed less consistent trends.

Two magnetic regimes in doped ZnO corresponding to a dilute magnetic semiconductor and a dilute magnetic insulator.

Films of ZnO doped with magnetic ions Mn and Co and, in some cases, with Al have been fabricated with a very wide range of carrier densities. Ferromagnetic behavior is observed in both insulating and metallic films, but not when the carrier density is intermediate. Insulating films exhibit variable range hopping at low temperatures and are ferromagnetic at room temperature due to the interaction of the localized spins with static localized states. The magnetism is quenched when carriers in the localized states become mobile. In the metallic (degenerate semiconductor) range, robust ferromagnetism reappears together with very strong magneto-optic signals and room temperature anomalous Hall data. This demonstrates the polarization of the conduction bands and indicates that, when ZnO is doped into the metallic regime, it behaves as a genuine magnetic semiconductor.

Room-temperature magneto-optics of ferromagnetic transition-metal-doped ZnO thin films.

Magneto-optic studies of ZnO doped with transition metals Co, Mn, V, and Ti indicate a significant magnetic circular dichroism (MCD) at the ZnO band edge at room temperature, together with an associated dispersive Faraday rotation. Similar spectra occur for each dopant, which implies that the ferromagnetism is an intrinsic property of the bulk ZnO lattice. At 10 K, additional paramagnetic contributions to the MCD are observed, but above about 150 K, the magnitude of the MCD signal is dominated by the ferromagnetism and is almost temperature independent. The MCD at the ZnO band edge shows room temperature hysteretic behavior.

Ferromagnetism above room temperature in bulk and transparent thin films of Mn-doped ZnO.

The search for ferromagnetism above room temperature in dilute magnetic semiconductors has been intense in recent years. We report the first observations of ferromagnetism above room temperature for dilute (<4 at.%) Mn-doped ZnO. The Mn is found to carry an average magnetic moment of 0.16 mu(B) per ion. Our ab initio calculations find a valance state of Mn(2+) and that the magnetic moments are ordered ferromagnetically, consistent with the experimental findings. We have obtained room-temperature ferromagnetic ordering in bulk pellets, in transparent films 2-3 microm thick, and in the powder form of the same material. The unique feature of our sample preparation was the low-temperature processing. When standard high-temperature (T > 700 degrees C) methods were used, samples were found to exhibit clustering and were not ferromagnetic at room temperature. This capability to fabricate ferromagnetic Mn-doped ZnO semiconductors promises new spintronic devices as well as magneto-optic components.

The Fermi surface of [Formula: see text].

The heavy-fermion compound [Formula: see text] has been studied using the fully relativistic spin-polarized mean muffin-tin orbital method within the local density approximation. Two separate calculations, one where the f electron is treated as a valence electron and the other where it is treated as part of the core, have been performed and the Fermi surface is obtained. The angular-dependent de Haas - van Alphen (dHvA) frequencies are calculated in both cases and they are compared with the experimental dHvA frequencies. We also calculated the electron momentum densities and compared them with the electron - positron momentum densities measured from the two-dimensional angular correlation of electron - positron annihilation radiation. The spin polarization of the Fermi surface is analysed and we present a new interpretation of the experimental data of Harrison et al.

Combined decrease of postheparin-diamine oxidase (histaminase) and postheparin-lipoproteinlipase in inflammatory diseases.

Diamine oxidase (DAO, histaminase), according to Schayer, is an essential enzyme in histamine metabolism. It metabolises also a variety of diamines such as putrescine and cadaverine and is generally accepted to be identical with histaminase. Lipoproteinlipase (LL) is assumed to play an essential role in lipid metabolism. In vertebrates, parenterally applied heparin causes a marked dose-dependent rise of the plasma level of both enzymes mainly due to the release from the enzyme containing organs. The plasmatic level changes of DAO and LL after heparin application (200 U/kg b.wt., i.v.) have been studied in 30 patients suffering from 20 different, predominantly inflammatory diseases. In all cases the release of postheparin diamine oxidase (PHD) and of post-heparin lipoproteinlipase (PHLA) was found to be markedly decreased. There existed a highly significant correlation between the degree of the release of both enzymes (r=0.843, p less than 0.0005). In all patients normal levels of plasma insulin were detected. No correlation was found between PHLA and plasma triglycerides levels. Decrease of PHD respectively PHLA was a more sensitive biochemical parameter than were changes of serum glutamic pyruvic transaminase in acute hepatitis and of C reactive protein (CRP) in chronic inflammatory kidney diseases. This finding is most likely a general phenomenon in inflammatory diseases. Besides hormonal regulation inflammation-dependent effects on PHLA have to be discussed.

Calcified solitary renal cyst in childhood.

There is a 20% incidence of malignancy in renal masses with rim calcification in adults. A case of rim calcification in a solitary renal cyst in a child is presented and the diagnostic approach and surgical management are described. Solitary renal cysts are extremely rare in children, with no reported cases of rim calcification.

Coexisting avascular lesions and renal cell carcinoma.

An analysis of 99 cases of coexisting renal avascular lesions and renal cell carcinoma suggests that: (1) a direct pathogenetic relationship exists in the majority; (2) the cyst-related carcinoma tends to occur at an earlier age; (3) angiography alone is not reliable for the diagnosis of an apparently benign renal mass, and (4) individuals with polycystic kidneys share at least an equal risk of renal carcinoma as the general population.

Crossed fusion of renal pelves and Klippel-Feil syndrome.

Congenital fusion of the renal pelves occurs rarely and is usually associated with fusion of the kidneys. The first case of surgically proved separate kidneys with crossed fusion of the renal pelves is reported.

Urethral carcinoma after radiation therapy for mixed prostatic carcinoma.

The first case of transitional cell carcinoma of the bulbous urethra occurring 8 months after radiation therapy for mixed ductal and adenocarcinoma of the prostate is presented. The significance of the sequential appearance of these tumors is discussed. Periodic endoscopic evaluation appears warranted following the diagnosis of transitional cell carcinoma of the prostate to ensure early recognition of secondary urethral lesions or bladder extension of the tumor.

Chronic seminal vesiculosis. Distressing syndrome with surgical cure.

Six cases in which a symptom complex suggestive of chronic seminal vesicular dysfunction are described. Transvesical seminal vesiculectomy was performed with good results and no disturbance of sexual potency. Seminal vesiculectomy appears to provide a reasonable means for cure of those patients who meet the specific criteria outlined.