Torsional force microscopy of van der Waals moirés and atomic lattices

In a stack of atomically thin van der Waals layers, introducing interlayer twist creates a moiré superlattice whose period is a function of twist angle. Changes in that twist angle of even hundredths of a degree can dramatically transform the system's electronic properties. Setting a precise and uniform twist angle for a stack remains difficult; hence, determining that twist angle and mapping its spatial variation is very important. Techniques have emerged to do this by imaging the moiré, but most of these require sophisticated infrastructure, time-consuming sample preparation beyond stack synthesis, or both. In this work, we show that torsional force microscopy (TFM), a scanning probe technique sensitive to dynamic friction, can reveal surface and shallow subsurface structure of van der Waals stacks on multiple length scales: the moirés formed between bi-layers of graphene and between graphene and hexagonal boron nitride (hBN) and also the atomic crystal lattices of graphene and hBN. In TFM, torsional motion of an Atomic Force Microscope (AFM) cantilever is monitored as it is actively driven at a torsional resonance while a feedback loop maintains contact at a set force with the sample surface. TFM works at room temperature in air, with no need for an electrical bias between the tip and the sample, making it applicable to a wide array of samples. It should enable determination of precise structural information including twist angles and strain in moiré superlattices and crystallographic orientation of van der Waals flakes to support predictable moiré heterostructure fabrication.

Unusual magnetotransport in twisted bilayer graphene from strain-induced open Fermi surfaces

Anisotropic hopping in a toy Hofstadter model was recently invoked to explain a rich and surprising Landau spectrum measured in twisted bilayer graphene away from the magic angle. Suspecting that such anisotropy could arise from unintended uniaxial strain, we extend the Bistritzer-MacDonald model to include uniaxial heterostrain and present a detailed analysis of its impact on band structure and magnetotransport. We find that such strain strongly influences band structure, shifting the three otherwise-degenerate van Hove points to different energies. Coupled to a Boltzmann magnetotransport calculation, this reproduces previously unexplained nonsaturating [Formula: see text] magnetoresistance over broad ranges of density near filling [Formula: see text] and predicts subtler features that had not been noticed in the experimental data. In contrast to these distinctive signatures in longitudinal resistivity, the Hall coefficient is barely influenced by strain, to the extent that it still shows a single sign change on each side of the charge neutrality point-surprisingly, this sign change no longer occurs at a van Hove point. The theory also predicts a marked rotation of the electrical transport principal axes as a function of filling even for fixed strain and for rigid bands. More careful examination of interaction-induced nematic order versus strain effects in twisted bilayer graphene could thus be in order.

Feedback lock-in: A versatile multi-terminal measurement system for electrical transport devices

We present the design and implementation of a measurement system that enables parallel drive and detection of small currents and voltages at numerous electrical contacts to a multi-terminal electrical device. This system, which we term a feedback lock-in, combines digital control-loop feedback with software-defined lock-in measurements to dynamically source currents and measure small, pre-amplified potentials. The effective input impedance of each current/voltage probe can be set via software, permitting any given contact to behave as an open-circuit voltage lead or as a virtually grounded current source/sink. This enables programmatic switching of measurement configurations and permits measurement of currents at multiple drain contacts without the use of current preamplifiers. Our 32-channel implementation relies on commercially available digital input/output boards, home-built voltage preamplifiers, and custom open-source software. With our feedback lock-in, we demonstrate differential measurement sensitivity comparable to a widely used commercially available lock-in amplifier and perform efficient multi-terminal electrical transport measurements on twisted bilayer graphene and SrTiO₃ quantum point contacts. The feedback lock-in also enables a new style of measurement using multiple current probes, which we demonstrate on a ballistic graphene device.

Evidence of Orbital Ferromagnetism in Twisted Bilayer Graphene Aligned to Hexagonal Boron Nitride

We have previously reported ferromagnetism evinced by a large hysteretic anomalous Hall effect in twisted bilayer graphene (tBLG). Subsequent measurements of a quantized Hall resistance and small longitudinal resistance confirmed that this magnetic state is a Chern insulator. Here, we report that when tilting the sample in an external magnetic field, the ferromagnetism is highly anisotropic. Because spin-orbit coupling is weak in graphene, such anisotropy is unlikely to come from spin but rather favors theories in which the ferromagnetism is orbital. We know of no other case in which ferromagnetism has a purely orbital origin. For an applied in-plane field larger than 5 T, the out-of-plane magnetization is destroyed, suggesting a transition to a new phase.

Emergent ferromagnetism near three-quarters filling in twisted bilayer graphene

When two sheets of graphene are stacked at a small twist angle, the resulting flat superlattice minibands are expected to strongly enhance electron-electron interactions. Here, we present evidence that near three-quarters (34) filling of the conduction miniband, these enhanced interactions drive the twisted bilayer graphene into a ferromagnetic state. In a narrow density range around an apparent insulating state at34, we observe emergent ferromagnetic hysteresis, with a giant anomalous Hall (AH) effect as large as 10.4 kilohms and indications of chiral edge states. Notably, the magnetization of the sample can be reversed by applying a small direct current. Although the AH resistance is not quantized, and dissipation is present, our measurements suggest that the system may be an incipient Chern insulator.

Influence of Patient Choice on Outcome of Bariatric Surgery

BACKGROUND

The "perfect" bariatric procedure remains the topic of debate. The aim of this study is to compare the safety and outcome of laparoscopic Roux-en-Y gastric bypass (LRYGB) to those of laparoscopic sleeve gastrectomy (LSG) and adjustable gastric band (AGB) in a single centre, amongst those patients who made their own choice of which procedure they prefer.

METHODS

After the multi-disciplinary team's assessment, the patients could make their own choice of procedures (self-selected, SS), unless medical/surgical conditions limited this (medically restricted, MR). All consecutive primary bariatric procedures were involved and reviewed between June 2010 and September 2014. The primary outcomes included 30-day complication and readmission rates, excess weight loss (%EWL) and co-morbidity resolution at 24 months postoperatively.

RESULTS

A total of 303 patients were included and 271 of them made their own choice (SS 90%). One hundred eighty-three chose LRYGB (60.4%), and 57 underwent LSG (SS 45 and MR 12; overall 18.8%), with the initial BMI of 50.7 and 52.5 kg/m², respectively. Sixty-two patients (SS 43, MR 19, overall 20%) underwent AGB, with a BMI of 52.1 kg/m². Thirty-day complication rates for LRYGB and LSG were 10.2 and 2.9% (p < 0.05), and the readmission rates were 4.7 and 2.9%, respectively. %EWL for LRYGB was significantly higher than that of other procedures at 24 months (67.8 vs SS-sleeve 43.9%, MR-sleeve 47%, SS-band 33.8% and MR-band 36%; FU rate 94%). Diabetes remission was achieved in 31/50 patients in the LRYGB group (62%) and 2/9 patients (22%) in the LSG group.

CONCLUSIONS

Self-selected bariatric procedures yield excellent weight loss and metabolic outcome. Providing an information-dense environment augments the choice of the right operation and could improve patients' compliance with weight loss surgery programmes.

Cooperative augmentation of mobile smart objects with projected displays

Sensors, processors, and radios can be integrated invisibly into objects to make them smart and sensitive to user interaction, but feedback is often limited to beeps, blinks, or buzzes. We propose to redress this input-output imbalance by augmentation of smart objects with projected displays, that—unlike physical displays—allow seamless integration with the natural appearance of an object. In this article, we investigate how, in a ubiquitous computing world, smart objects can acquire and control a projection. We consider that projectors and cameras are ubiquitous in the environment, and we develop a novel conception and system that enables smart objects to spontaneously associate with projector-camera systems for cooperative augmentation. Projector-camera systems are conceived as generic, supporting standard computer vision methods for different appearance cues, and smart objects provide a model of their appearance for method selection at runtime, as well as sensor observations to constrain the visual detection process. Cooperative detection results in accurate location and pose of the object, which is then tracked for visual augmentation in response to display requests by the smart object. In this article, we define the conceptual framework underlying our approach; report on computer vision experiments that give original insight into natural appearance-based detection of everyday objects; show how object sensing can be used to increase speed and robustness of visual detection; describe and evaluate a fully implemented system; and describe two smart object applications to illustrate the system's cooperative augmentation process and the embodied interactions it enables with smart objects.

Wild rabbits (Oryctolagus cuniculus ) as potential carriers of verocytotoxin-producing Escherichia coli

In summer 2001, visitors to a wildlife park in Norfolk, uk, became infected with verocytotoxin-producing Escherichia coli (vtec) O157, which was associated with wild rabbit faeces. The rabbits lived in an adjacent field together with E coli O157-positive cattle. A pilot study was therefore performed to investigate the factors affecting the association between E coli O157-positive cattle and wild rabbits. Samples of faeces were taken from 16 herds of cattle that lived close to populations of wild rabbits. Analysis by culture and pcr showed that seven of the herds were positive for E coli O157. Faeces were collected from individual rabbits at six of these farms during late winter, when there were few rabbits, and during high summer, when there were many. None of the 32 samples collected on two farms in late winter was positive for E coli O157, but eight of 97 samples collected in summer were positive on four of the six farms. pcr analysis for vtec, including non-O157, showed that 20 of the 97 samples were positive.

Magnetic versus manual guidewire manipulation in neuroradiology: in vitro results

INTRODUCTION

Standard microguidewires used in interventional neuroradiology have a predefined shape of the tip that cannot be changed while the guidewire is in the vessel. We evaluated a novel magnetic navigation system (MNS) that generates a magnetic field to control the deflection of a microguidewire that can be used to reshape the guidewire tip in vivo without removing the wire from the body, thereby potentially facilitating navigation along tortuous paths or multiple acute curves.

METHOD

The MNS consists of two permanent magnets positioned on either side of the fluoroscopy table that create a constant precisely controlled magnetic field in the defined region of interest. This field enables omnidirectional rotation of a 0.014-inch magnetic microguidewire (MG). Speed of navigation, accuracy in a tortuous vessel anatomy and the potential for navigating into in vitro aneurysms were tested by four investigators with differing experience in neurointervention and compared to navigation with a standard, manually controlled microguidewire (SG).

RESULTS

Navigation using MG was faster (P=0.0056) and more accurate (0.2 mistakes per trial vs. 2.6 mistakes per trial) only in less-experienced investigators. There were no statistically significant differences between the MG and the SG in the hands of experienced investigators. One aneurysm with an acute angulation from the carrier vessel could be navigated only with the MG while the SG failed, even after multiple reshaping manoeuvres.

CONCLUSION

Our findings suggest that magnetic navigation seems to be easier, more accurate and faster in the hands of less-experienced investigators. We consider that the features of the MNS may improve the efficacy and safety of challenging neurointerventional procedures.

Enzyme activity and dynamics: xylanase activity in the absence of fast anharmonic dynamics

The activity and dynamics of a simple, single subunit enzyme, the xylanase from Thermotoga maritima strain Fj SS3B.1 have been measured under similar conditions, from -70 to +10 degrees C. The internal motions of the enzyme, as evidenced by neutron scattering, undergo a sharp transition within this temperature range; they show no evidence for picosecond-timescale anharmonic behaviour (e.g. local diffusive motions or jumps between alternative conformations) at temperatures below -50 degrees C, whereas these motions are strongly activated at higher temperatures. The activity follows Arrhenius behaviour over the whole of the temperature range investigated, -70 to +10 degrees C. The results indicate that a temperature range exists over which the enzyme rate-limiting step is independent of fast anharmonic dynamics.

Evaluating and improving VA substance abuse patients' care

The VA has implemented a nationwide evaluation program to monitor process and outcome of care for substance abuse patients. This program focuses on the changing characteristics of VA substance abuse patients and treatment services and involves outcome-based evaluations of major VA substance abuse treatment modalities. Initial findings show that VA substance abuse patients, including patients with concomitant psychiatric disorders, improve substantially from treatment intake to a 1-year follow-up and that community residential facilities are an important part of the continuum of substance abuse care. Moreover, within broad limits, there is a dose-response relationship between the continuity of outpatient mental health care and better 1-year substance use and psychosocial outcomes. These findings are placed into context as part of an evidence-based initiative to improve the quality of VA mental health care.

Expanding the nursing repertoire: the effect of massage on post-operative pain

An equivalent groups design with a treatment group of 19 patients and a control group of 20 patients was used to investigate the impact of massage therapy on patients' perceptions of post-operative pain. Data were analysed using analysis of covariance repeated measures (within subjects) design. Controlling for age, the results indicated that massage produced a significant reduction in patients' perceptions of pain over a 24 hour period. A linear positive relationship emerged between patients' age and the duration of the massage. The study indicates that further investigation of the potential for massage to reduce pain is warranted.

A computerized dispatch system that really delivers

In 1990, Victoria Hospital in London, Ontario undertook a review of its Central Portering Department. The department's name was changed to Distribution Services and its need for more efficient servicing of customers led to the search for a computer system to replace the manual dispatch operation. After failing to find an existing system, the hospital contracted to develop its own system, called Vic Tracker. The system categorizes and prioritizes requests and produces various activity reports. Response time has improved 50% on average, and improved efficiency and a pre-booking feature has resulted in a decrease of approximately 100 calls per day.

Evaluation of hematuria

Hematuria is an important sign that indicates the presence of a pathologic condition in the genitourinary tract. Causes can be categorized by where in the urinary tract the problem is located--above the kidney, in the kidney or one of its structures, or below the kidney. Another category is false hematuria, such as urine that has been discolored by intake of a certain food or drug. A thorough history, physical examination, and appropriate laboratory studies, followed by more sophisticated diagnostic tests chosen on the basis of the assembled clues, can establish the diagnosis in most cases. Patients rarely have to be hospitalized or undergo invasive procedures for assessment of hematuria.

Inelastic neutron scattering analysis of picosecond internal protein dynamics. Comparison of harmonic theory with experiment

The experimental inelastic neutron scattering spectrum of a protein, the bovine pancreatic trypsin inhibitor (BPTI), in a powder sample is presented together with the generalized density of states, G(omega), as a function of the frequency, omega, derived from the scattering data. The experimental results are compared with calculations from two different normal mode analyses of BPTI. One of these, based on an improved model, gives a calculated spectrum and density of states in general agreement with those obtained experimentally; the other, based on an earlier model, shows considerable disagreement. The important improvements in the newer normal mode analysis are the explicit treatment of all atoms (non-polar as well as polar hydrogens are included) and a modified truncation scheme for the long-range electrostatic interactions. The fact that the inelastic neutron scattering measurements can distinguish between the two theoretical models makes clear their utility for the analysis of protein dynamics.

Direct measurement of hydration-related dynamic changes in lysozyme using inelastic neutron scattering spectroscopy

Inelastic neutron scattering spectroscopy is used to investigate dynamic changes in lysozyme powder at two different low D2O hydrations (0.07g D2O/g protein and 0.20 g D2O/g protein). In the higher hydration sample, the inelastic scattering between 0.8 and 4.0 cm-1 energy transfer is increased and the elastic scattering is decreased. The decreased elastic scattering suggests increased atomic amplitudes of motion and the increased 0.8 to 4.0 cm-1 scattering suggests increased motions in this frequency range. Comparison with normal mode models of lysozyme dynamics shows that the inelastic difference occurs in the frequency region predicted for the lowest frequency, largest amplitude, global modes of the molecular [M. Levitt, C. Sander and P.S. Stern, J. Mol. Biol. 181, 423 (1985). B. Brooks and M. Karplus, Proc. Natl. Acad. Sci (U.S.A) 82, 4995 (1985), R.E. Bruccoleri, M. Karplus and J.A. McCammon, Biopolymers 25 1767 (1986)]. Our results are consistent with a model in which an increased number of low frequency global modes are present in the higher hydrated sample.