IC Max Research Articles

Microwave-Induced Characteristics of ${({\rm NbN/TiN}_{\rm x})}_{N}/{\rm NbN}$ StackedJosephson Junction Arrays

Stacked (NbN/TiNx)N/NbN (N = 2, 3, 4, 5 and 10) Josephson junctions and their arrays have been fabricated on a Si chip and their microwave-induced characteristics were measured at a temperature around 10 K. To achieve a vertical and smooth edge of an NbN - TiNx multilayer, an inductively coupled plasma reactive ion etching (ICP-RIE) technique was used. Current-voltage characteristics measured for stacks of (NbN/TiNx)N/NbN Josephson junctions without microwave indicated that critical currents for those junctions distribute in a certain range. We defined Ic - spread as (Ic MAX - Ic MIN)/Ic Average to measure the distribution of Ic. The Ic - spread was minimized when the thickness of intermediate electrodes was d = 50 nm. We also evaluated values of Ic - spread for stacks prepared at different fabrication runs as a function of the number of junctions in a stack N. As a result, we found N = 3 is the maximum for practical use. For arrays, we obtained a constant-voltage step height of about 2 m A for 2 048 stacks of double-barrier junctions (N = 2), and about 1 mA for 1 024 stacks of triple-barrier junctions (N = 3).

Embryotoxic potential of N-methyl-pyrrolidone (NMP) and three of its metabolites using the rat whole embryo culture system

N-methyl-2-pyrrolidone (NMP), which undergoes extensive biotransformation, has been shown in vivo to cause developmental toxicity and, especially after oral treatment, malformations in rats and rabbits. Data are lacking as to whether the original compound or one of its main metabolites is responsible for the toxic effects observed. Therefore, the relative embryotoxicity of the parent compound and its metabolites was evaluated using rat whole embryo culture (WEC) and the balb/c 3T3 cytotoxicity test. The resulting data were evaluated using two strategies; namely, one based on using all endpoints determined in the WEC and the other including endpoints from both the WEC and the cytotoxicity test. On basis of the first analysis, the substance with the highest embryotoxic potential is NMP, followed by 5-hydroxy-N-methyl-pyrrolidone (5-HNMP), 2-hydroxy-N-methylsuccinimide (2-HMSI) and N-methylsuccinimide (MSI). Specific dysmorphogeneses induced by NMP and 5-HNMP were aberrations in the head region of the embryos, abnormal development of the second visceral arches and open neural pores. The second evaluation strategy used only two endpoints of the WEC, i.e. the no observed adverse effect concentration (NOAEC WEC) and the lowest concentration leading to dysmorphogenesis in 100% of the cultured embryos (IC Max WEC). In addition to these WEC endpoints the IC 50 3T3 from the cytotoxicity test (balb/c 3T3 fibroblasts) was included in the evaluation scheme. These three endpoints were applied to a prediction model developed during a validation study of the European Centre for the Validation of Alternative Methods (ECVAM) allowing the classification of the embryotoxic potential of each compound into three classes (non-, weakly- and strongly embryotoxic). Consistent results from both evaluation strategies were observed, whereby NMP and its metabolites revealed a direct embryotoxic potential. Hereby, only NMP and 5-HNMP induced specific embryotoxic effects and were classified as weakly embryotoxic, whereas the other two metabolites, 2-HMSI and MSI, were determined to be non-embryotoxic.

Analyses of dose–response curves to compare the antimicrobial activity of model cationic α-helical peptides highlights the necessity for a minimum of two activity parameters

To assess and compare different model Leu-Lys-containing cationic α-helical peptides, their antimicrobial activities were tested against Escherichia coli as target organism over a broad peptide concentration range. The natural cationic α-helical peptides magainin 2 and PGLa and the cyclic cationic peptide gramicidin S were also tested between comparison. The dose–response curves differed widely for these peptides, making it difficult to rank them into an activity order over the whole concentration range. We therefore compared five different inhibition parameters from dose–response curves: IC min (lowest concentration leading to growth inhibition), IC 50 (concentration that gives 50% growth inhibition), IC max (related to minimum inhibition concentration and minimum bactericidal concentration), inhibition concentration factor (IC F; describing the increase in concentration of the peptide between minimum and maximum inhibition), and activity slope ( A S; related to the Hill coefficient). We found that these parameters were covariant: two of them sufficed to characterize the dose dependence and hence the activity of the peptides. This was corroborated by showing that the dose dependences followed the Hill equation, with a small, constant aberration. We propose that the activity of antimicrobial peptides can readily be characterized by both IC 50 and IC F (or A S) rather than by a single parameter and discuss how this may relate to investigations into their mechanisms of action.

Gingerols and Related Analogues Inhibit Arachidonic Acid-Induced Human Platelet Serotonin Release and Aggregation

Gingerols, the active components of ginger (the rhizome of Zingiber officinale, Roscoe), represent a potential new class of platelet activation inhibitors. In this study, we examined the ability of a series of synthetic gingerols and related phenylalkanol analogues (G1–G7) to inhibit human platelet activation, compared to aspirin, by measuring their effects on arachidonic acid (AA)-induced platelet serotonin release and aggregation in vitro. The IC 50 for inhibition of AA-induced (at EC 50=0.75 mM) serotonin release by aspirin was 23.4±3.6 μM. Gingerols and related analogues (G1–G7) inhibited the AA-induced platelet release reaction in a similar dose range as aspirin, with IC 50 values between 45.3 and 82.6 μM. G1–G7 were also effective inhibitors of AA-induced human platelet aggregation. Maximum inhibitory (IC max) values of 10.5±3.9 and 10.4±3.2 μM for G3 and G4, respectively, were ∼2-fold greater than aspirin (IC max=6.0±1.0 μM). The remaining gingerols and related analogues maximally inhibited AA-induced platelet aggregation at ∼20–25 μM. The mechanism underlying inhibition of the AA-induced platelet release reaction and aggregation by G1–G7 may be via an effect on cyclooxygenase (COX) activity in platelets because representative gingerols and related analogues (G3–G6) potently inhibited COX activity in rat basophilic leukemia (RBL-2H3) cells. These results provide a basis for the design of more potent synthetic gingerol analogues, with similar potencies to aspirin, as platelet activation inhibitors with potential value in cardiovascular disease.

Medium-power GaAs bipolar transistors

GaAs has an advantage over Si and Ge in some material parameters for bipolar transistor application. Another benefit is the availability of the wide gap emitter principle for GaAIAs/GaAs heterojunction transistors. Such bipolar transistors have been fabricated and tested. Maximum frequency of oscillation fMAG = 2.2 GHz and cut-off frequency fT = 2.7 GHz demonstrate the high-frequency suitability, whereas emitter-collector breakdown voltages VCEO100 V and maximum collector currents IC max ∼ 300 mA are an indicator of high-power applications. The transistor operates at temperatures in the range of − 269°C to + 350°C. A double heterostructure NpN transistor shows the elimination of the turn-on voltage of ∼ 0.2 V for Npn wide gap emitter Ga0.7Al0.3As/GaAs transistors in common emitter configuration. The NpN transistor can be operated in bi-direction with comparable current gain due to the wide gap emitter principle and the symmetry of the emitter-base and collector-base heterojunctions. Compared with the Npn GaAs transistor, the storage time ts of the NpN GaAs transistor is reduced by a factor of about 2.