Transient increase of the energy gap of superconducting NbN thin films excited by resonant narrow-band terahertz pulses.

Observations of radiation-enhanced superconductivity have thus far been limited to a few type-I superconductors (Al, Sn) excited at frequencies between the inelastic scattering rate and the superconducting gap frequency 2Δ/h. Utilizing intense, narrow-band, picosecond, terahertz pulses, tuned to just below and above 2Δ/h of a BCS superconductor NbN, we demonstrate that the superconducting gap can be transiently increased also in a type-II dirty-limit superconductor. The effect is particularly pronounced at higher temperatures and is attributed to radiation induced nonthermal electron distribution persisting on a 100 ps time scale.

Toxicity and antioxidant activity in vitro and in vivo of two Fucus vesiculosus extracts.

The consumption of seaweeds has increased in recent years. However, their adverse and beneficial effects have scarcely been studied. Two extracts from the brown seaweed Fucus vesiculosus containing 28.8% polyphenols or 18% polyphenols plus 0.0012% fucoxanthin have been obtained and studied to determine their toxicity in mice and rats and also their antioxidant activity. Both extracts were shown to lack any relevant toxic effects in an acute toxicity test following a 4 week daily treatment in rats. The extracts exhibited antioxidant activity in noncellular systems and in activated RAW 264.7 macrophages, as well as in ex vivo assays in plasma and erythrocytes, after the 4 week treatment in rats. Our ex vivo results indicated that compounds from extract 2 may be more easily absorbed and that the antioxidants in their parent or metabolized form are more active. These findings support the view that the daily consumption of F. vesiculosus extract 2 (Healsea) would have potential benefits to humans.

Gout: radiographic findings mimicking infection.

OBJECTIVE: To describe radiographic features of gout that may mimic infection. DESIGN AND PATIENTS: We report five patients with acute bacterial gout who presented with clinical as well as radiological findings mimicking acute bacterial septic arthritis or osteomyelitis. Three patients had delay in the appropriate treatment with the final diagnosis being established after needle aspiration and identification of urate crystals under polarized light microscopy. Two patients underwent digit amputation for not responding to antibiotic treatment and had histological findings confirming the diagnosis of gout. CONCLUSION: It is important for the radiologist to be aware of the radiological manifestations of acute gout that can resemble infection in order to avoid inappropriate diagnosis and delay in adequate treatment. The definitive diagnosis should rely on needle aspiration and a specific search for urate crystals.

Patterns of music agnosia associated with middle cerebral artery infarcts.

The objective of the study is to evaluate if the rupture of an aneurysm located on the middle cerebral artery (MCA) results in disorders of music recognition. To this aim, 20 patients having undergone brain surgery for the clipping of a unilateral left (LBS), right (RBS) or bilateral (BBS) aneurysm(s) of the MCA and 20 neurologically intact control subjects (NC) were evaluated with a series of tests assessing most of the abilities involved in music recognition. In general, the study shows that a ruptured aneurysm on the MCA that is repaired by brain surgery is very likely to produce deficits in the auditory processing of music. The incidence of such a deficit was not only very high but also selective. The results show that the LBS group was more impaired than the NC group in all three tasks involving musical long-term memory. The study also uncovered two new cases of apperceptive agnosia for music. These two patients (N.R. and R.C.) were diagnosed as such because both exhibit a clear deficit in each of the three music memory tasks and both are impaired in all discrimination tests involving musical perception. Interestingly, the lesions overlap in the right superior temporal lobe and in the right insula, making the two new cases very similar to an earlier case report. Altogether, the results are also consistent with the view that apperceptive agnosia results from damage to right hemispheric structures while associative agnosia results from damage to the left hemisphere.

Extended sphere method for complete investigation of the phase-matching properties of sum- and difference-frequency generation.

We demonstrate the feasibility of a complete experimental investigation of the phase-matching properties of sum- and difference-frequency generation in a single crystal cut as a sphere over its entire transparency range. The class of the studied crystal is the only initial data that is required. This feasibility study was carried out with rubidium titanyl arsenate.

Mathematical model for internal pH control in immobilized enzyme particles.

A mathematical model has been developed for the internal pH control in immobilized enzyme particles. This model describes the kinetics of a coupled system of two enzymes, immobilized in particles of either planar, cylindrical, or spherical shape. The enzyme kinetics are assumed to be of a mixed type, including Michaelis-Menten kinetics, uncompetitive substrate inhibition, and competitive and noncompetitive product inhibition. In a case study we have considered the enzyme combination urease and penicillin acylase, whose kinetics are coupled through the pH dependence of the kinetic parameters. The hydrolysis of urea by urease yields ammonia and carbon dioxide, whereas benzylpenicillin (Pen-G) is converted to 6-amino penicillanic acid and phenyl acetic acid by penicillin acylase. The production of acids by the latter enzyme will cause a decrease in pH. Because of the presence of the ammonia-carbon dioxide system, however, the pH may be kept under control. In order to obtain information about the optimum performance of this enzymatic pH controller, we have computed the effectiveness factor and the conversion in a CSTR at different enzyme loadings. The results of the computer simulations indicate that a high conversion of Pen-G may be achieved (80-90%) at bulk pH values of about 7.5-8.

Membrane permeability for inorganic phosphate ion.

The need for a more efficient removal of inorganic phosphate ions from the blood of uremic patients has led to the quest for blood-compatible semipermeable membranes with a high permeability for phosphate ions. Commercial hemodialysis membranes, various hydrogel-type membranes and a number of collodionbased charged membranes were compared. Positively charged collodion membranes were found most promising for future application in hemodialysis or hemoperfusion systems.

Characteristics of unbuffered gel-immobilized urease particles. I. Internal pH.

The overall rate of reaction of a gel-immobilized urease particle necessarily depends upon the hydrogen ion concentrations within the particle. When the particle is unbuffered, the internal hydrogen ion concentrations are a consequence of the local rates of reaction and the rate of egress of the products of hydrolysis. A simple apparatus has been devised which allows a fairly rapid determination of the hydrogen ion concentration in the center of a particle for any given size, enzyme concentration, substrate concentration, and external pH. The products of urea hydrolysis are self-buffering in the region of pH 8.83 and for an external pH less than the self-buffering pH, the pH within the particle is increased because of the reaction. When the external pH is greater than the self-buffering pH, the converse occurs. The pH at the center of the particle approaches the self-buffering pH with an increase in particle size and enzyme concentration. The external increase in the external substrate concentration has a limited effect, simply rendering the local rates of reaction to be of zero order. The center-line pH and therefore all internal hydrogen ion concentrations depend upon the parameter L square root pe and the external pH. Differences between the external and center-line pH values of the order of units are unexceptional. The implications of the internal pH profiles on the local and overall rates of reaction are explored.

Characteristics of unbuffered gel-immobilized urease particles. II. Overall rate of reaction.

The overall rates of reaction of unbuffered gel-immobilized urease particles have been investigated with the aid of a packed-bed differential recycle reactor. Both substrate and enzyme concentrations have received attention. Cylindrical gel particles contained within impermeable tubelets were used to provide the physical strength necessary for the packed-bed arrangement and a one dimensional diffusion path to aid understanding of the complex interactions between substrate and product diffusion, and their effect on the reactions taking place. The experimental data have been interpreted with the aid of an enzyme rate equation (ERE) which relates the free solution characteristics of the enzyme to the conditions within a diffusion limited particle. The internal hydrogen ion profiles have been accommodated by a lumped parameter, the apparent pH (pHapp). Two methods have been suggested for the calculation of pHapp and the loss of activity on particle preparation, these methods are based on the use of the ERE in conjunction with experimental data.