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Notes: Abstract New-production (nitrate uptake) rates in the equatorial Pacific were estimated by parallel measurements of nitrate disappearance from sea water using a colorimetric method and of 15N-labelled nitrate (15NO3 −) incorporation into particulate organic nitrogen (PON) collected on GF/F filters (net nitrate uptake, conventional 15N-tracer method) and Anopore (0.2 μm) membranes. Regression analyses of 74 sample pairs gathered during 12 and 24 h productivity experiments revealed a significant positive relationship between decreasing nitrate level and 15NO3 − accumulation into PON retained on GF/F filters, but the slopes of Model I and Model II regression lines were 1.18 and 1.29, respectively, suggesting that 15 to 22% of 15NO3 − removed from the dissolved fraction were lost to another N-pool. Two possible avenues for the missing 15NO3 − have been examined: uptake by submicron particles passed through the GF/F filters, and loss as dissolved organic nitrogen (DON). Nitrate uptake by small cells not recovered on GF/F filters, could be safely eliminated as a cause of loss, since 15NO3 − uptake rates obtained from 15N entering PON collected on GF/F filters agreed well with those obtained from 15N entering PON collected on Anopore membranes (32 sample pairs). Inspection of the DON pool of 0.2 μm filtrates for excess-15N enrichment (20 samples) revealed that in nitrate-rich waters (equatorial upwelling between 1°N and 10°S), loss of 15NO3 − as DO15N accounted for 〈5% of net nitrate uptake. In samples from subtropical oligotrophic waters (from 11°S southward), however, 15NO3 loss as DO15N represented up to 20% of net NO3 − uptake. These results, as well as experimental considerations concerning the use of colorimetric and isotopic methods to measure new production show that: (1) earlier reported high discrepancies between nitrate decreases (ΔNO3 −) and 15NO3 − incorporation into filterable particles (ΔNO3 −/15NO3 − incorporation 〉2) were probably erroneous; (2) the use of GF/F filters does not result in an underestimation of new production, although it was found to underestimate PON concentrations by up to 60%; (3) in the equatorial upwelling area (1°N to 10°S), which has high ambient nitrate levels (〉2000 nmol l−1) but only slight changes in concentration (0 to 80 nmol l−1 d−1), new production is more accurately estimated by the isotopic method than by the chemical method; (4) in subtropical oligotrophic waters (from 11°S southward) with low ambient nitrate levels (0 to 100 nmol l−1), both procedures are appropriate as long as nitrate removal per incubation period is 〉3 nmol l−1 (lower rates are only detectable with the isotopic method); (5) the traditional 15N-tracer technique does not substantially underestimate net new-production in the equatorial Pacific, and failure to account for the loss of 15NO3 − as DON, i.e. to estimate gross nitrate uptake (gross uptake = net uptake + 15N loss) tends to underestimate new production on an average by only 10%. Overall, the apparent low level of new production in the nitrate-rich area of the central equatorial Pacific seems to be a fact, and may be ascribable to other nutrient (macro and micro) deficiencies and/or to intense in situ recycling of ammonium and nitrate (regenerated production) rather than to inaccurate nitrate uptake rates measured with the classical 15N-tracer technique.

Notes: The aim of the study was to characterize and assess the maturation process of the barrier function in a reconstituted human epidermis (REp) cultivated in a chemically defined medium. For this purpose histo-morphological analysis, percutaneous absorption studies and non-invasive measurements were performed. In order to understand the time course of the barrier development, REp cultivated from the same pool of normal human keratinocytes were harvested and measured after several increasing periods of exposure at the air–liquid interface. From these results we concluded that a maturation period of at least 16 days at the air–liquid interface was required for an optimal barrier function development of REp. At this time point, the permeability of the skin cultures for caffeine (CAF) was 20–25-fold higher than that of normal human skin (NHS) biopsies. Non-invasive measurements of skin water content, transepidermal water loss (TEWL) and pH were achieved after the same period of time. Results showed that the stratum corneum (SC) of REp was slightly more hydrated than that of ex vivo and in vivo, human skin. TEWL was slightly higher through REp than through NHS, and the pH of the REp models was very close to that of in vivo, normal human skin. In the latter part, assuming that this type of model could be routinely used, we quantified over a 1-year period the barrier function variability of this skin culture model between batches. The satisfactory results obtained with a 20% coefficient of variation indicated that this REp model has a consistent and reproducible barrier function. This leads us to suggest that the skin model might be considered an alternative membrane to normal human skin for permeation screening tests.

Notes: We present measurements of ballistic magnetoresistance in nanocontacts grown by electrodeposition of Ni microclusters on magnetic thin films covered by aluminum oxide layers, using a technique proposed by Schad et al. [D. Allen, R. Schad, G. Zangari, I. Zana, D. Yang, M. C. Tondra, and D. Wang, J. Vac. Sci. Technol. A. 18, 1830 (2000); Appl. Phys. Lett. 76, 407 (2000); D. Allen, R. Schad, G. Zangari, I. Zana, D. Yang, M. C. Tondra, D. Wang, and D. Reed, J. Appl. Phys. 89, 6662 (2001)]. The measurements are made on single Ni clusters in contact with a Ni and Co thin film. We measure the magnetoresistance and observe the relaxation of the magnetization and electrical resistance as a function of time. The clusters are electrodeposited under several different experimental conditions. Some are deposited randomly on an unpatterned film and some through various patterned photoresists that control the location at which the cluster is grown. The typical contact size is estimated from the electrical resistance to be 10–30 nm. Ballistic magnetoresistance values up to 14% are obtained in these first experiments. © 2001 American Institute of Physics.

Notes: We study the action of a magnetic field induced by nanocontact current pulses on the domain walls in thin magnetic films. We show that the pulses of a certain current direction shift the wall to the contact. Such an effect of attraction of the wall to the nanocontact does not depend on the initial position of the wall relative to the contact and results in an increase of nanocontact magnetoresistance. The opposite pulses repel this wall from the contact, i.e., the field action depends on the current direction. Our calculations explain experimental data relating to magnetoresistance devices. © 2001 American Institute of Physics.

Notes: This letter shows that the ballistic magnetoresistance of Fe at room temperature and low magnetic fields is ten times smaller than for Ni and Co. The results are well explained by theory that provides a global understanding for 3d transition metals because, for Fe, the ratio of majority to minority spins at Fermi level is much smaller than for Ni and Co. The data indicate that conduction is carried out by majority d electrons in the case of Fe, in contrast to what happens for Ni and Co. © 2000 American Institute of Physics.

Notes: We theoretically discuss the possibility of having materials with zero effective permittivity that would create band gaps in a wide range of frequencies up to the visible. The physical realization of these materials is also discussed in terms of embedding metallic nanoparticles and nanowires in a dielectric medium. In the limit of long wavelengths, these composites will behave like a homogeneous medium with zero permittivity that will completely reflect electromagnetic waves. We present transmittivity calculations by using finite-difference time domain for periodic structures that proves the concept and shows the validity of the long wavelength approximation. The striking result is that the cutoff frequency ωc is determined by the lattice parameter of the composite. By properly choosing the lattice constant of the composite and permittivity of metal and dielectric constituents, we can have full band gaps at any frequency range but especially in the visible. © 2002 American Institute of Physics.

Notes: Our results prove the local origin of magnetoresistance in electrochemically deposited Ni nanocontacts. Experiments have been done using a complex setup for both in situ growth and ballistic magnetoresistance (BMR) measurements. Nanocontacts have been grown between two macroscopic Ni wires. In situ experiments with variation of the nanocontact diameter from 3 to 20 nm have been done using the same pair of wires. BMR values from 0.5% to 100% have been observed but no correlation of BMR value with the sample resistance, i.e., with the nanocontact cross section, has been found. These results show that the BMR in the nanometric size contact is determined by local geometrical and magnetic structures near the nanocontact rather than by the contact cross section itself. The hypothesis of existence of the intrinsic nonmagnetic dead layer in the ferromagnetic nanocontact is proposed to account for the BMR properties of the nanometric size contacts. Additionally, we report a BMR value of 200% in a Ni nanocontact (5 nm diameter) electrochemically grown between two nonmagnetic macroscopic gold wires. An external magnetic field has been used during the electrochemical deposition to fix the easy magnetic axis of the deposited Ni layer. © 2002 American Institute of Physics.

Notes: This letter shows that conducting ballistic and tunneling magnetoresistances have identical physical treatments and, therefore, it is not possible to distinguish whether an experiment is measuring, in oxide barriers, electron conduction through pinholes or tunneling because both types of conduction are governed by the same physics. Currents in both cases are calculated by matching wave functions at the electrodes (both are ballistic). Therefore, pinholes or small ballistic nanocontacts in the tunnel barrier allow conducting ballistic electrons that account for most of the current. We also show that, in the case of nonsuperconducting materials, e.g., magnetic materials, current–voltage characteristics are not suitable to distinguish one process from the other. © 2000 American Institute of Physics.

Notes: We present experimental results of unprecedented large magnetoresistance obtained in stable electrodeposited Ni–Ni nanocontacts 10–30 nm in diameter. The contacts exhibit magnetoresistance of up to 700% at room temperature and low applied fields and, therefore, act as very effective spin filters. These large values of the magnetoresistance are attributed to spin ballistic transport through a magnetic "dead layer" at the contact of width of about 1 nm or smaller. Nanometer sized, high sensitive magnetoresistive sensors could become key elements for magnetic storage in the terabit/in.2 range and in high density magnetic random access memories. © 2001 American Institute of Physics.

Notes: Cure rates of 7-day triple therapy seem to be decreasing. Quadruple therapies may be an alternative, although their complex administration makes patient acceptance difficult.〈section xml:id="abs1-2"〉〈title type="main"〉Objective:To test the usefulness of a thrice a day, quadruple therapy to cure Helicobacter pylori infection.〈section xml:id="abs1-3"〉〈title type="main"〉Patients and methods:A total of 122 consecutive patients with peptic ulcer and Helicobacter pylori infection were treated with omeprazole 20 mg b.d., tetracycline chlorhydrate 500 mg t.d.s., metronidazole 500 mg t.d.s., and bismuth subcitrate 120 mg t.d.s. administered with meals for 7 days. Cure was tested by either endoscopy or breath test after 2 months, and by urea breath test 6 months after therapy.〈section xml:id="abs1-4"〉〈title type="main"〉Results:Seven patients were lost to follow-up. Of the remaining 115, 110 were cured at the first control, giving an intention-to-treat cure rate of 90.2% (95% CI: 83–95%) and a per protocol cure rate of 95.7% (95% CI: 90–98%). One hundred three patients returned for a 6-month breath test; all but one were cured. Side-effects were minimal or minor in 47 patients (40.8%) and moderate in four (3.4%). Compliance was good, 95% of patients taking more than 90% of the pills. Six (5%) patients stopped treatment after 1, 2, 4 (two patients) and 6 (two patients) days.〈section xml:id="abs1-5"〉〈title type="main"〉Conclusion:Thrice a day quadruple therapy shows excellent cure rates, far above 90%, is well-tolerated and compliance is easy. Head-to-head comparison with triple therapies as first line Helicobacter pylori treatment seems warranted.