The origin of switching noise in GaAs/AlGaAs lateral gated devices

We have studied the origin of switching (telegraph) noise at low temperature in lateral quantum structures defined electrostatically in GaAs/AlGaAs heterostructures by surface gates. The noise was measured by monitoring the conductance fluctuations around $e^2/h$ on the first step of a quantum point contact at around 1.2 K. Cooling with a positive bias on the gates dramatically reduces this noise, while an asymmetric bias exacerbates it. We propose a model in which the noise originates from a leakage current of electrons that tunnel through the Schottky barrier under the gate into the doped layer. The key to reducing noise is to keep this barrier opaque under experimental conditions. Bias cooling reduces the density of ionized donors, which builds in an effective negative gate voltage. A smaller negative bias is therefore needed to reach the desired operating point. This suppresses tunnelling from the gate and hence the noise. The reduction in the density of ionized donors also strengthens the barrier to tunneling at a given applied voltage. Support for the model comes from our direct observation of the leakage current into a closed quantum dot, around $10^{-20} \mathrm{A}$ for this device. The current was detected by a neighboring quantum point contact, which showed monotonic steps in time associated with the tunneling of single electrons into the dot. If asymmetric gate voltages are applied, our model suggests that the noise will increase as a consequence of the more negative gate voltage applied to one of the gates to maintain the same device conductance. We observe exactly this behaviour in our experiments.Comment: 8 pages, 7 figure

Effect of ultrafiltration of bakers’ and brewers’ yeast extracts on their nitrogen content and turbidity

Five commercial yeast extracts (YE) were fractionated by ultrafiltration (UF) with 10 000, 3000 and 1000 Da molecular weight cutoff membranes in the aim of evaluating the effect of UF on the turbidity and total nitrogen content of YE. Membrane pore size had much more influence on UF permeation rates than the source of the YE. UF filtration rates were on the average 4 times lower when the YE were treated with the 3000 Da membrane as compared to the 10 000 Da filter, and the 1000 Da unit gave rates approximately 40% lower than those observed with the 3000 Da pore size membrane. Pre-filtration with a 8 ?m membrane reduced between 47 and 96% the original YE turbidities, while UF with a 1000 to10 000 Da membranes gave filtrates having between 80 and 99.9% less turbidity than the original YE. On the average, UF with the 10 000 Da unit removed 12% of total solids, while UF with 3000 and 1000 Da cutoff membranes generated the retention of 20 and 23% of solids, respectively. Brewers' YE had lower total nitrogen content than bakers' YE, and UF increased the total nitrogen content of the dried yeast extract filtrates (YEF) obtained. The powders obtained after freeze-drying of brewers' YEF tended to have higher moisture contents than bakers', and this was quite significant with the YEF powders obtained with the filtrates generated with the 1000 Da membrane

The distribution of iron in iron-enriched cells of Saccharomyces cerevisiae

Fresh or freeze-dried iron-enriched bakers' yeast (5% of total solids composed of iron) were fractionated, and the distribution of iron was examined. After centrifugation of fresh yeast creams, 89% of total iron was found in the supernatant, which contained only 23% of the total solids. Results suggest that only 13% of the iron is bound to cells in the fresh yeast suspension. Most of the cell-located iron was found on the cell wall, whereas the cytoplasm contained proportionally (iron content of total solids) almost 3 times less iron than the cell walls. Freeze-drying of the iron-enriched yeast had marked effects on the distribution of total solids and iron (in the fractionation procedures that were carried out following their rehydration). The freeze-drying process induced binding of free iron to the yeast cell wall, and twice as much iron was thus found on freeze-dried cells. In the freeze-dried product, it was estimated that 27% of iron was bound to cell fractions

Effect of the production or use of mixtures of bakers' or brewers' yeast extracts on their ability to promote growth of lactobacilli and pediococci1

Three brewers' and three bakers' yeast extracts (YE) were obtained from five commercial suppliers. They were added to microbiological media and their growth-promoting properties were examined using four lactic cultures ( Lactobacillus casei EQ28 and EQ85, Lactobacillus acidophilus EQ57, Pediococcus acidilactici MA18/5-M). Bakers' YE have a higher total nitrogen content than brewers' YE, but there was not always a correlation between the nitrogen content and growth. A systematic preference for bakers' YE over brewers' YE was only encountered with Lb. casei EQ85, but the other lactic cultures had variable reactions to the source of YE. With Lb. casei EQ85 and Pc. acidilactici 17/5M, mixing of the two sources of YE gave progressively higher growth as a function of the content of the better YE. With Lb. acidophilus EQ57 and Lb. casei EQ28, however, there were instances where a mixture of 75% brewers' YE with 25% bakers' YE gave biomass levels higher than those obtained with the pure products. A series of autolyses were conducted with mixtures of brewers' and bakers' yeast, to see if the YE obtained differed from those obtained from autolysis of the individual yeast cultures. Brewers' yeast autolysates had higher turbidity than those of bakers' yeast. The maximum yield was obtained with the co-autolysis of a combination of 60% bakers' yeasts and 40% brewers' yeasts. Growth of Lb. acidophilus EQ57 was best in the autolysate obtained from 100% brewers' yeast, in spite of the higher nitrogen content of YE produced when bakers' yeast was used during co-autolysis

A finite element model to improve noise reduction based attenuation measurement of earmuffs in a directional sound field

The real attenuation of hearing protection devices (HPD) can be assessed in the field using a method based on continuous field microphone-in-real-ear (F-MIRE) measurements. The two-microphone method provides an indicator called the measured noise reduction (NR∗), defined as the difference between the measured exterior (outside the protector) and interior (under the protector) sound pressure levels (SPL). The HPD's attenuation expressed in terms of the more common insertion loss (IL) can then be obtained from NR∗ using compensation factors. For earmuffs, NR∗ has been shown to vary of up to 20 dB depending on the angle of incidence of the sound source. Therefore, there is a need to use sound incidence dependent compensation factors to relate NR∗ and IL. To evaluate these factors and more generally to improve the continuous F-MIRE method, a finite-element (FE) model of an earmuff on an ATF (acoustic test fixture) exposed to a directional sound field has been developed and its predictions compared with lab measurements for several incidence angles. Regarding the external microphone SPL and the NR∗, in one-third of octave bands, the model correlates very well with measurements for frequencies below 1250 Hz whatever the sound incidence. Above 1250 Hz, the FE model captures the trends, as a function of the incidence angle, but the agreement generally decreases with increasing frequency. A better correlation between the FE model and the experimental data is achieved for the variation of NR∗ (ΔNR∗) as a function of the sound incidence. Actions, such as (i) accounting for the headband in the model, (ii) refining the modeling of the sound source, (iii) improving the cushion modeling and (iv) better describing the backplate/cushion coupling conditions, are suggested to improve the model accuracy. To illustrate the potential of the modeling to improve the continuous F-MIRE measurement method, the FE model is used to determine an optimal position of the external microphone and to obtain estimates of exposure levels using the left and right ear exterior microphones. © 2016 Elsevier Lt

Effects of Genotype and Sleep on Temperament

Supported by the Canadian Institutes of Health Research

Solid-state Marx based two-switch voltage modulator for the On-Line Isotope Mass Separator accelerator at the European Organization for Nuclear Research

A new circuit topology is proposed to replace the actual pulse transformer and thyratron based resonant modulator that supplies the 60 kV target potential for the ion acceleration of the On-Line Isotope Mass Separator accelerator, the stability of which is critical for the mass resolution downstream separator, at the European Organization for Nuclear Research. The improved modulator uses two solid-state switches working together, each one based on the Marx generator concept, operating as series and parallel switches, reducing the stress on the series stacked semiconductors, and also as auxiliary pulse generator in order to fulfill the target requirements. Preliminary results of a 10 kV prototype, using 1200 V insulated gate bipolar transistors and capacitors in the solid-state Marx circuits, ten stages each, with an electrical equivalent circuit of the target, are presented, demonstrating both the improved voltage stability and pulse flexibility potential wanted for this new modulator