Cross-architecture tuning of silicon and SiGe-based quantum devices using machine learning.

The potential of Si and SiGe-based devices for the scaling of quantum circuits is tainted by device variability. Each device needs to be tuned to operation conditions and each device realisation requires a different tuning protocol. We demonstrate that it is possible to automate the tuning of a 4-gate Si FinFET, a 5-gate GeSi nanowire and a 7-gate Ge/SiGe heterostructure double quantum dot device from scratch with the same algorithm. We achieve tuning times of 30, 10, and 92 min, respectively. The algorithm also provides insight into the parameter space landscape for each of these devices, allowing for the characterization of the regions where double quantum dot regimes are found. These results show that overarching solutions for the tuning of quantum devices are enabled by machine learning.

Aging acceleration of balsamic vinegar applying micro-oxygenation technique.

The effect of micro-oxygenation (MOX) technique on quality and sensorial characteristics of balsamic vinegar was investigated, aiming to aging acceleration. Aging experiments were conducted using a multiple diffuser micro-oxygenator for up to 6 months with an oxygen flow of 30 mg/L/month, including oak chips (1 g/L) or not. Barrel maturation was simultaneously carried out. Quality, nutritional, sensorial characteristics and the aromatic profile of all aged vinegars were evaluated throughout aging. MOX accelerated the alteration of aging indices. Volatile compounds of fruity aroma and wine were decreased, while the fatty/buttery and caramel aroma compounds were increased. Similar compounds of 1.5-year barrel maturation were developed within 6 and 5 months applying MOX without or with oak chips, respectively. MOX resulted in reduction of the aging time to 1/3 compared to the corresponding one in barrels, considered as an attractive approach for vinegar-producing industries, mimicking and accelerating the long and costly barrel aging.

Effect of high pressure on structural modifications and enzymatic activity of a purified X-prolyl dipeptidyl aminopeptidase from Streptococcus thermophilus.

PepX aminopeptidase from Streptococcus thermophilus ACA DC 0022, used in Greek Feta cheese manufacturing, was purified. PepX comprises two subunits of equal molecular mass estimated, using SDS-PAGE and native-PAGE electrophoresis, to be 86 kDa. The effects of high pressure processing (100-450 MPa, combined with 20-40 °C) on purified PepX activity and structure were studied. Activation of the enzyme was observed after processing at 100-200 MPa and 20-30 °C. More intense processing conditions led to enzyme inactivation. PepX HP-induced conformational changes were also investigated through application of Circular Dichroism spectroscopy (CD). Pressures up to 200 MPa resulted in a structurally molten globule-like state where PepX maintained its secondary structure but the tertiary structure was substantially affected and enzyme activity increased. Both secondary and tertiary structures were affected severely by higher pressures (450 MPa), which reduced enzyme activity.

Nature of tunable hole g factors in quantum dots.

We report an electric-field-induced giant modulation of the hole g factor in SiGe nanocrystals. The observed effect is ascribed to a so-far overlooked contribution to the g factor that stems from the mixing between heavy- and light-hole wave functions. We show that the relative displacement between the confined heavy- and light-hole states, occurring upon application of the electric field, alters their mixing strength leading to a strong nonmonotonic modulation of the g factor.

Monolithic growth of ultrathin Ge nanowires on Si(001).

Self-assembled Ge wires with a height of only 3 unit cells and a length of up to 2 micrometers were grown on Si(001) by means of a catalyst-free method based on molecular beam epitaxy. The wires grow horizontally along either the [100] or the [010] direction. On atomically flat surfaces, they exhibit a highly uniform, triangular cross section. A simple thermodynamic model accounts for the existence of a preferential base width for longitudinal expansion, in quantitative agreement with the experimental findings. Despite the absence of intentional doping, the first transistor-type devices made from single wires show low-resistive electrical contacts and single-hole transport at sub-Kelvin temperatures. In view of their exceptionally small and self-defined cross section, these Ge wires hold promise for the realization of hole systems with exotic properties and provide a new development route for silicon-based nanoelectronics.

Observation of spin-selective tunneling in SiGe nanocrystals.

Spin-selective tunneling of holes in SiGe nanocrystals contacted by normal-metal leads is reported. The spin selectivity arises from an interplay of the orbital effect of the magnetic field with the strong spin-orbit interaction present in the valence band of the semiconductor. We demonstrate both experimentally and theoretically that spin-selective tunneling in semiconductor nanostructures can be achieved without the use of ferromagnetic contacts. The reported effect, which relies on mixing the light and heavy holes, should be observable in a broad class of quantum-dot systems formed in semiconductors with a degenerate valence band.

Quantum transport in GaN/AlN double-barrier heterostructure nanowires.

We investigate electronic transport in n-i-n GaN nanowires with and without AlN double barriers. The nanowires are grown by catalyst-free, plasma-assisted molecular beam epitaxy enabling abrupt GaN/AlN interfaces as well as longitudinal n-type doping modulation. At low temperature, transport in n-i-n GaN nanowires is dominated by the Coulomb blockade effect. Carriers are confined in the undoped middle region, forming single or multiple islands with a characteristic length of approximately 100 nm. The incorporation of two AlN tunnel barriers causes confinement to occur within the GaN dot in between. In the case of a 6 nm thick dot and 2 nm thick barriers, we observe characteristic signatures of Coulomb-blockaded transport in single quantum dots with discrete energy states. For thinner dots and barriers, Coulomb-blockade effects do not play a significant role while the onset of resonant tunneling via the confined quantum levels is accompanied by a negative differential resistance surviving up to approximately 150 K.

Hybrid superconductor-semiconductor devices made from self-assembled SiGe nanocrystals on silicon.

The epitaxial growth of germanium on silicon leads to the self-assembly of SiGe nanocrystals by a process that allows the size, composition and position of the nanocrystals to be controlled. This level of control, combined with an inherent compatibility with silicon technology, could prove useful in nanoelectronic applications. Here, we report the confinement of holes in quantum-dot devices made by directly contacting individual SiGe nanocrystals with aluminium electrodes, and the production of hybrid superconductor-semiconductor devices, such as resonant supercurrent transistors, when the quantum dot is strongly coupled to the electrodes. Charge transport measurements on weakly coupled quantum dots reveal discrete energy spectra, with the confined hole states displaying anisotropic gyromagnetic factors and strong spin-orbit coupling with pronounced dependences on gate voltage and magnetic field.

Kinetic study of the combined effect of high hydrostatic pressure and temperature on the activity of Lactobacillus delbrueckii ssp. bulgaricus aminopeptidases.

The effect of high hydrostatic pressure (HHP) (100 to 700 MPa) combined with temperature (20 to 40 degrees C) on the activity of 5 aminopeptidases (PepN, PepX, PepY, PepC, and PepA) of Lactobacillus delbrueckii ssp. bulgaricus ACA-DC 0105, used as starter culture for feta cheese production, was studied. Aminopeptidases PepN, PepX, and PepA were activated at pressures up to 200 MPa, at temperatures up to 40 degrees C. PepY and PepC appeared to be more sensitive to pressure and temperature treatment leading to inactivation for pressures above 100 and 200 MPa, respectively, combined with temperature above 30 degrees C. A multi-parameter equation was used for predicting the activation of PepN, PepX, and PepA aminopeptidases in the pressure and temperature domain. Overall, processing at 200 MPa and 20 degrees C may be selected as the optimum conditions for maximum activation of 4 out of 5 aminopeptidases of L. delbrueckii ssp. bulgaricus. A 20-min treatment at these conditions leads to an average 3-fold increase in activity, which could lead to better and faster maturation of white cheese.

Positioning of strained islands by interaction with surface nanogrooves.

When strained Stranski-Krastanow islands are used as "self-assembled quantum dots," a key goal is to control the island position. Here we show that nanoscale grooves can control the nucleation of epitaxial Ge islands on Si(001), and can drive lateral motion of existing islands onto the grooves, even when the grooves are very narrow and shallow compared to the islands. A position centered on the groove minimizes energy. We use as prototype grooves the trenches which form naturally around islands. During coarsening, the shrinking islands move laterally to sit directly astride that trench. In subsequent growth, we demonstrate that islands nucleate on the "empty trenches" which remain on the surface after complete dissolution of the original islands.

Interplay between thermodynamics and kinetics in the capping of InAs/GaAs(001) quantum dots.

A microscopic picture for the GaAs overgrowth of self-organized quantum dots is developed. Scanning tunneling microscopy measurements reveal two capping regimes: the first being characterized by a dot shrinking and a backward pyramid-to-dome shape transition. This regime is governed by fast dynamics resulting in island morphologies close to thermodynamic equilibrium. The second regime is marked by a true overgrowth and is controlled by kinetically limited surface diffusion processes. A simple model is developed to describe the observed structural changes which are rationalized in terms of energetic minimization driven by lattice mismatch and alloying.

Lateral motion of SiGe islands driven by surface-mediated alloying.

SiGe islands move laterally on a Si(001) substrate during in situ postgrowth annealing. This surprising behavior is revealed by an analysis of the substrate surface morphology after island removal using wet chemical etching. We explain the island motion by asymmetric surface-mediated alloying. Material leaves one side of the island by surface diffusion, and mixes with additional Si from the surrounding surface as it redeposits on the other side. Thus the island moves laterally while becoming larger and more dilute.

Prevention of postoperative nausea and vomiting after laparoscopic gynaecological surgery. Combined antiemetic treatment with tropisetron and metoclopramide vs. metoclopramide alone.

BACKGROUND AND OBJECTIVE: Female patients undergoing gynaecological procedures, especially laparoscopically, are at high risk of postoperative nausea and vomiting. No available antiemetic is entirely effective. This double-blinded randomized trial examines the efficacy and safety of tropisetron and metoclopramide in combination and compares the results with metoclopramide alone in laparoscopic gynaecological surgery. METHODS: One hundred and twenty female patients scheduled for minor gynaecological laparoscopy, aged 27-43 years, were randomly allocated to receive pretreatment with metoclopramide 10 mg intravenously (n=57) or tropisetron 5 mg with metoclopramide 5 mg (n=63). RESULTS: Fewer patients in the combined treatment group experienced postoperative nausea and vomiting (14% vs. 37%, P=0.008) or needed rescue antiemetic treatment (3% vs. 16%, P=0.038). No significant adverse events were observed. CONCLUSIONS: The combination of the antiemetics was superior, which is probably explained by the fact that the two drugs have different sites of action, thus preventing emesis by blocking different pathways.

Management of inflammatory abdominal aneurysms--immediate and late results.

INTRODUCTION: Despite progress in the technical approach to aneurysms, inflammatory aortic aneurysms (IAA) in particular present the surgical team with a unique challenge. This retrospective study investigates immediate and late results after surgical treatment of IAA. PATIENTS AND METHOD: Fifteen cases of IAA among 520 aneurysmectomies of the abdominal aorta were operated during the period 1986-1995. All the patients were males of a mean age of 66 years. Diagnosis was established on preoperative CT-Scan, gross appearance at surgery and histologically. CT scanning could detect the IAA in 13 of 15 cases. In 2 cases MRI was diagnostic. Surgical treatment using the inlay method, constitutes the method of choice due to restricted dissection, as it reduces the possibility of iatrogenic injuries. RESULTS: None of the patients died during the first 30 postoperative days. One patient died at the age of 78, 40 days after the operative procedure, due to a cerebral episode. Four to 120 months later 3 patients had also died from cause unrelated to the operation and one more patient was lost on follow-up. The remaining 10 patients were free of symptoms without any progression of the fibrotic process in the CT scanning. We observed a total regression in 7 and partial regression in 3 patients without detecting any inflammatory findings or renal failure. CONCLUSION: IAA's are rare. CT and/or MRI establish the diagnosis preoperatively and contribute to the surgical program with immediate and late results equal to those found in arteriosclerotic aneurysms of the abdominal aorta.

Postcarotid endarterectomy symptoms. Pre- and postoperative clinical and MRI findings.

BACKGROUND: The hyperperfusion syndrome represents a highly debated clinical entity, without having yet any clinically identifiable limits. The correlation of clinical with pre- and postoperative magnetic resonance imaging (MRI) findings following carotid endarterectomy in patients with a possible hyperperfusion syndrome was investigated. DESIGN: Prospective clinical and laboratory study. SETTING: At the Aretaieio University Hospital. MEASURES: Comparison to the postoperative clinical symptomatic and MRI findings. Patients. We studied 30 patients (mean age 66.6) of whom 14 (46.6%) were asymptomatic, 16 (53.4%) were symptomatic, 17 (56.6%) were hypertensive, 18 (60%) hyperlipidaemic, 5 (16.6%) diabetic and 17 (56.6%) had coronary artery disease. RESULTS: Twenty-one patients (70%) exhibited disturbances such as ipsilateral headache, seizures, vomiting or facial pain; immediate postoperative MRI scans revealed new ischaemic foci in 4 (19%) without any objective neurological findings. Lesions displayed in postoperative MRI scans did not always cause symptoms and normal findings on MRI did not exclude the presence of symptoms. Hypertension favoured the presence of subjective disturbances, without necessarily any change in the MRI appearances. Preoperative MRI and clinical findings did not contribute to the identification of patients who might have exhibited postoperative symptoms. Thus, the symptomatology remains unclear and open to debate, as a variety of other conditions may produce the same clinical picture postoperatively. CONCLUSIONS: Subjective disturbances, objective neurological findings and MRI abnormalities with or without hypertension may appear independently after carotid endarterectomy, a fact which makes the pathogenesis of the hyperperfusion syndrome more difficult to elucidate.

Surgical outcome of carotid artery disease: analysis of 367 carotid endarterectomies.

Carotid endarterectomy is a method of prophylaxis. A total of 367 carotid endarterectomies in 335 patients were performed during the period of 1989-1997: 222 (66.3%) were symptomatic and 113 (33.7%) asymptomatic patients. In all, 262 (78.2%) had unilateral, 41 (12.2%) contralateral occlusion and 32 (9.6%) bilateral artery disease. All were operated on under general anesthesia without using shunt or patch. Of the patients with bilateral occlusive disease, 17 underwent simultaneous and 15 staged endarterectomy. The mortality rate of the first 30 postoperative days was 1.19% and the mortality/stroke rate 2.38%. Transient neurogenic dysfunction occurred in 3.68%, myocardial ischemia in 0.89%, and postoperative hypertension in 16.7%. Endarterectomy of symptomatic and asymptomatic patients with unilateral localisation, contralateral occlusion or bilateral occlusive disease remains a highly acceptable prophylactic method. The future will show whether other endovascular procedures affect the broad application of carotid endarterectomy.

Forty-eight single-shot epidural injections on the same patient.

A patient is described who has received 48 single-shot epidurals with plain lignocaine. No complications were encountered at any time. Nuclear magnetic resonance imaging confirmed that no dural damage had occurred.