Light effective hole mass in undoped Ge/SiGe quantum wells

We report density-dependent effective hole mass measurements in undoped germanium quantum wells. We are able to span a large range of densities ($2.0-11\times10^{11}$ cm$^{-2}$) in top-gated field effect transistors by positioning the strained buried Ge channel at different depths of 12 and 44 nm from the surface. From the thermal damping of the amplitude of Shubnikov-de Haas oscillations, we measure a light mass of $0.061m_e$ at a density of $2.2\times10^{11}$ cm$^{-2}$. We confirm the theoretically predicted dependence of increasing mass with density and by extrapolation we find an effective mass of $\sim0.05m_e$ at zero density, the lightest effective mass for a planar platform that demonstrated spin qubits in quantum dots

Strongly bounded groups and infinite powers of finite groups

We define a group as strongly bounded if every isometric action on a metric space has bounded orbits. This latter property is equivalent to the so-called uncountable strong cofinality, recently introduced by G. Bergman. Our main result is that G^I is strongly bounded when G is a finite, perfect group and I is any set. This strengthens a result of Koppelberg and Tits. We also prove that omega_1-existentially closed groups are strongly bounded.Comment: 10 pages, no figure. Versions 1-3 were entitled "Uncountable groups with Property (FH)". To appear in Comm. Algebr

Low disordered, stable, and shallow germanium quantum wells: a playground for spin and hybrid quantum technology

Buried-channel semiconductor heterostructures are an archetype material platform to fabricate gated semiconductor quantum devices. Sharp confinement potential is obtained by positioning the channel near the surface, however nearby surface states degrade the electrical properties of the starting material. In this paper we demonstrate a two-dimensional hole gas of high mobility ($5\times 10^{5}$ cm$^2$/Vs) in a very shallow strained germanium channel, which is located only 22 nm below the surface. This high mobility leads to mean free paths $\approx6 \mu m$, setting new benchmarks for holes in shallow FET devices. Carriers are confined in an undoped Ge/SiGe heterostructure with reduced background contamination, sharp interfaces, and high uniformity. The top-gate of a dopant-less field effect transistor controls the carrier density in the channel. The high mobility, along with a percolation density of $1.2\times 10^{11}\text{ cm}^{-2}$, light effective mass (0.09 m$_e$), and high g-factor (up to $7$) highlight the potential of undoped Ge/SiGe as a low-disorder material platform for hybrid quantum technologies

Experimental studies of the non-adiabatic escape problem

Noise-induced transitions between coexisting stable states of a periodically driven nonlinear oscillator have been investigated by means of analog experiments and numerical simulations in the nonadiabatic limit for a wide range of oscillator parameters. It is shown that, for over-damped motion, the field-induced corrections to the activation energy can be described quantitatively in terms of the logarithmic susceptibility (LS) and that the measured frequency dispersion of the corresponding corrections for a weakly damped nonlinear oscillator is in qualitative agreement with the theoretical prediction. Resonantly directed diffusion is observed in numerical simulations of a weakly damped oscillator. The possibility of extending the LS approach to encompass escape from the basin of attraction of a quasi-attractor is discussed

High performance deuterium-tritium plasmas in TFTR

Plasmas composed of nominally equal concentrations of deuterium and tritium (DT) have been created in TFTR with the goals of producing significant levels of fusion power and of examining the effects of DT fusion alpha particles. Conditioning of the limiter by the injection of lithium pellets has led to an approximate doubling of the energy confinement time, {tau}{sub E}, in supershot plasmas at high plasma current (I{sub p} {le} 2.5 MA) and high heating power (P{sub b} {le} 33 MW). Operation with DT typically results in an additional 20% increase in {tau}{sub E}. In the high poloidal beta, advanced tokamak regime in TFTR, confinement enhancement H {triple_bond} {tau}{sub E}/{tau}{sub E ITER-89P} > 4 has been obtained in a limiter H-mode configuration at moderate plasma current I{sub p} = 0.85 {minus} 1.5 MA. By peaking the plasma current profile, {beta}{sub N dia} {triple_bond} 10{sup 8} aB{sub 0}/I{sub p} = 3 has been obtained in these plasmas, exceeding the {beta}{sub N} limit for TFTR plasmas with lower internal inductance, l{sub i}. Confinement of alpha particles appears to be classical and losses due to collective effects have not been observed. While small fluctuations in fusion product loss were observed during ELMs, no large loss was detected in DT plasmas

Deuterium-tritium TFTR plasmas in the high poloidal beta regime

Deuterium-tritium plasmas with enhanced energy confinement and stability have been produced in the high poloidal beta, advanced tokamak regime in TFTR. Confinement enhancement H {triple_bond} {tau}{sub E}/{tau}{sub E ITER-89P} > 4 has been obtained in a limiter H-mode configuration at moderate plasma current I{sub p} = 0.85 {minus} 1.46 MA. By peaking the plasma current profile, {beta}{sub N dia} {triple_bond} 10{sup 8} aB{sub 0}/I{sub p} = 3 has been obtained in these plasma,s exceeding the {beta}{sub N} limit for TFTR plasmas with lower internal inductance, l{sub i}. Fusion power exceeding 6.7 MW with a fusion power gain Q{sub DT} = 0.22 has been produced with reduced alpha particle first orbit loss provided by the increased l{sub i}

Influence of topography on tide propagation and amplification in semi-enclosed basins

An idealized model for tide propagation and amplification in semi-enclosed rectangular basins is presented, accounting for depth differences by a combination of longitudinal and lateral topographic steps. The basin geometry is formed by several adjacent compartments of identical width, each having either a uniform depth or two depths separated by a transverse topographic step. The problem is forced by an incoming Kelvin wave at the open end, while allowing waves to radiate outward. The solution in each compartment is written as the superposition of (semi)-analytical wave solutions in an infinite channel, individually satisfying the depth-averaged linear shallow water equations on the f plane, including bottom friction. A collocation technique is employed to satisfy continuity of elevation and flux across the longitudinal topographic steps between the compartments. The model results show that the tidal wave in shallow parts displays slower propagation, enhanced dissipation and amplified amplitudes. This reveals a resonance mechanism, occurring when\ud the length of the shallow end is roughly an odd multiple of the quarter Kelvin wavelength. Alternatively, for sufficiently wide basins, also Poincaré waves may become resonant. A transverse step implies different wavelengths of the incoming and reflected Kelvin wave, leading to increased amplitudes in shallow regions and a shift of amphidromic points in the direction of the deeper part. Including the shallow parts near the basin’s closed end (thus capturing the Kelvin resonance mechanism) is essential to reproduce semi-diurnal and diurnal\ud tide observations in the Gulf of California, the Adriatic Sea and the Persian Gulf

Efficacy of Stem Cell Allograft in Maxillary Sinus Bone Regeneration: A Randomized Controlled Clinical and Blinded Histomorphometric Study

Purpose: This study aimed to evaluate the quality and quantity of newly generated bone in the maxillary sinus grafted with stem cell-based allograft material. Methods: This study was a single site, prospective, blinded, randomized, and controlled clinical trial. Eleven subjects with 18 edentulous posterior maxillary sites requiring sinus augmentation for delayed implant placement using a lateral window approach were enrolled. At the time of sinus augmentation, test sinus was grafted with stem cell-based allograft (Osteocel Plus; NuVasive Therapeutics), while the control sinus was grafted with conventional cortico-cancellous allograft (alloOss; ACE Surgical). Cone beam computer tomography (CBCT) scan was taken before and 14 weeks post-sinus augmentation procedure, i.e., 2 weeks before implant placement. Thirty-six trephined core bone biopsies were harvested from the anterior and posterior grafted lateral-window osteotomy sites at the time of implant placement. Results: The results showed a statistically significant difference in the vital bone percentage between the test and the control groups at the posterior grafted sites (p = 0.03). There was no significant difference in the percentage of vital bone between the anterior and posterior grafted sites within the test and control groups (p \u3e .05). The CBCT analysis showed that the maxillary sinuses at the posterior grafted sites were statistically wider than those at the anterior grafted sites in both groups (p \u3c .05). Conclusions: Different allograft bone materials can be used in the maxillary sinus augmentation procedures. Stem cell allograft has more osteogenic potential with a better outcome in the wide posterior sinus

Stapling and Section of the Nasogastric Tube during Sleeve Gastrectomy: How to Prevent and Recover?

Bariatric surgery has become an integral part of morbid obesity treatment with well-defined indications. Some complications, specific or not, due to laparoscopic sleeve gastrectomy (LSG) procedure have recently been described. We report a rare complication unpublished to date: a nasogastric section during great gastric curve stapling. A 44-year-old woman suffered of severe obesity (BMI 36.6 kg/m2) with failure of medical treatments for years. According to already published technique, a LSG was performed. Six hours postoperatively, a nurse removed the nasogastric tube according to the local protocol and the nasogastric tube was abnormally short, with staples at its extremity. Surgery was performed with peroperative endoscopy. In conclusion, this is the first publication of a nasogastric section during LSG. Therefore we report this case and propose a solution to prevent its occurrence. To avoid this kind of accident, we now systematically insert the nasogastric tube by mouth through a Guedel cannula. Then, to insert the calibrating bougie, we entirely withdraw the nasogastric tube