Observation of room-temperature polar skyrmions.

Complex topological configurations are fertile ground for exploring emergent phenomena and exotic phases in condensed-matter physics. For example, the recent discovery of polarization vortices and their associated complex-phase coexistence and response under applied electric fields in superlattices of (PbTiO3)n/(SrTiO3)n suggests the presence of a complex, multi-dimensional system capable of interesting physical responses, such as chirality, negative capacitance and large piezo-electric responses1-3. Here, by varying epitaxial constraints, we discover room-temperature polar-skyrmion bubbles in a lead titanate layer confined by strontium titanate layers, which are imaged by atomic-resolution scanning transmission electron microscopy. Phase-field modelling and second-principles calculations reveal that the polar-skyrmion bubbles have a skyrmion number of +1, and resonant soft-X-ray diffraction experiments show circular dichroism, confirming chirality. Such nanometre-scale polar-skyrmion bubbles are the electric analogues of magnetic skyrmions, and could contribute to the advancement of ferroelectrics towards functionalities incorporating emergent chirality and electrically controllable negative capacitance.

Local negative permittivity and topological phase transition in polar skyrmions.

Topological solitons such as magnetic skyrmions have drawn attention as stable quasi-particle-like objects. The recent discovery of polar vortices and skyrmions in ferroelectric oxide superlattices has opened up new vistas to explore topology, emergent phenomena and approaches for manipulating such features with electric fields. Using macroscopic dielectric measurements, coupled with direct scanning convergent beam electron diffraction imaging on the atomic scale, theoretical phase-field simulations and second-principles calculations, we demonstrate that polar skyrmions in (PbTiO3)n/(SrTiO3)n superlattices are distinguished by a sheath of negative permittivity at the periphery of each skyrmion. This enhances the effective dielectric permittivity compared with the individual SrTiO3 and PbTiO3 layers. Moreover, the response of these topologically protected structures to electric field and temperature shows a reversible phase transition from the skyrmion state to a trivial uniform ferroelectric state, accompanied by large tunability of the dielectric permittivity. Pulsed switching measurements show a time-dependent evolution and recovery of the skyrmion state (and macroscopic dielectric response). The interrelationship between topological and dielectric properties presents an opportunity to simultaneously manipulate both by a single, and easily controlled, stimulus, the applied electric field.

Interface superconductor with gap behaviour like a high-temperature superconductor.

The physics of the superconducting state in two-dimensional (2D) electron systems is relevant to understanding the high-transition-temperature copper oxide superconductors and for the development of future superconductors based on interface electron systems. But it is not yet understood how fundamental superconducting parameters, such as the spectral density of states, change when these superconducting electron systems are depleted of charge carriers. Here we use tunnel spectroscopy with planar junctions to measure the behaviour of the electronic spectral density of states as a function of carrier density, clarifying this issue experimentally. We chose the conducting LaAlO3-SrTiO3 interface as the 2D superconductor, because this electron system can be tuned continuously with an electric gate field. We observed an energy gap of the order of 40 microelectronvolts in the density of states, whose shape is well described by the Bardeen-Cooper-Schrieffer superconducting gap function. In contrast to the dome-shaped dependence of the critical temperature, the gap increases with charge carrier depletion in both the underdoped region and the overdoped region. These results are analogous to the pseudogap behaviour of the high-transition-temperature copper oxide superconductors and imply that the smooth continuation of the superconducting gap into pseudogap-like behaviour could be a general property of 2D superconductivity.

Functional electronic inversion layers at ferroelectric domain walls.

Ferroelectric domain walls hold great promise as functional two-dimensional materials because of their unusual electronic properties. Particularly intriguing are the so-called charged walls where a polarity mismatch causes local, diverging electrostatic potentials requiring charge compensation and hence a change in the electronic structure. These walls can exhibit significantly enhanced conductivity and serve as a circuit path. The development of all-domain-wall devices, however, also requires walls with controllable output to emulate electronic nano-components such as diodes and transistors. Here we demonstrate electric-field control of the electronic transport at ferroelectric domain walls. We reversibly switch from resistive to conductive behaviour at charged walls in semiconducting ErMnO3. We relate the transition to the formation-and eventual activation-of an inversion layer that acts as the channel for the charge transport. The findings provide new insight into the domain-wall physics in ferroelectrics and foreshadow the possibility to design elementary digital devices for all-domain-wall circuitry.

Electron Accumulation and Emergent Magnetism in LaMnO_{3}/SrTiO_{3} Heterostructures.

Emergent phenomena at polar-nonpolar oxide interfaces have been studied intensely in pursuit of next-generation oxide electronics and spintronics. Here we report the disentanglement of critical thicknesses for electron reconstruction and the emergence of ferromagnetism in polar-mismatched LaMnO_{3}/SrTiO_{3} (001) heterostructures. Using a combination of element-specific x-ray absorption spectroscopy and dichroism, and first-principles calculations, interfacial electron accumulation, and ferromagnetism have been observed within the polar, antiferromagnetic insulator LaMnO_{3}. Our results show that the critical thickness for the onset of electron accumulation is as thin as 2 unit cells (UC), significantly thinner than the observed critical thickness for ferromagnetism of 5 UC. The absence of ferromagnetism below 5 UC is likely induced by electron overaccumulation. In turn, by controlling the doping of the LaMnO_{3}, we are able to neutralize the excessive electrons from the polar mismatch in ultrathin LaMnO_{3} films and thus enable ferromagnetism in films as thin as 3 UC, extending the limits of our ability to synthesize and tailor emergent phenomena at interfaces and demonstrating manipulation of the electronic and magnetic structures of materials at the shortest length scales.

Riboflavin and ultraviolet light: impact on dengue virus infectivity.

BACKGROUND: Dengue viruses (DENV 1-4) are emerging across the world, and these viruses pose a risk to transfusion safety. Pathogen inactivation may be an alternative approach for managing the risk of DENV transfusion transmission. This study aimed to investigate the ability of riboflavin and UV light to inactivate DENV 1-4 in platelet concentrates. MATERIALS AND METHODS: DENV 1-4 were spiked into buffy coat-derived platelet concentrates in additive solution (SSP+) before being treated with riboflavin and UV light. Infectious virus was quantified pre- and posttreatment, and the reduction in viral infectivity was calculated. RESULTS: All four DENV serotypes were modestly reduced after treatment. The greatest amount of reduction in infectivity was observed for DENV-4 (1·81 log reduction) followed by DENV-3 (1·71 log reduction), DENV-2 (1·45 log reduction) and then DENV-1 (1·28 log reduction). CONCLUSION: Our study demonstrates that DENV 1-4 titres are modestly reduced following treatment with riboflavin and UV light. With the increasing number of transfusion-transmitted cases of DENV around the globe, and the increasing incidence and geographical distribution of DENV, additional approaches for maintaining blood safety may be required in the future.

High-temperature interface superconductivity between metallic and insulating copper oxides.

The realization of high-transition-temperature (high-T(c)) superconductivity confined to nanometre-sized interfaces has been a long-standing goal because of potential applications and the opportunity to study quantum phenomena in reduced dimensions. This has been, however, a challenging target: in conventional metals, the high electron density restricts interface effects (such as carrier depletion or accumulation) to a region much narrower than the coherence length, which is the scale necessary for superconductivity to occur. By contrast, in copper oxides the carrier density is low whereas T(c) is high and the coherence length very short, which provides an opportunity-but at a price: the interface must be atomically perfect. Here we report superconductivity in bilayers consisting of an insulator (La(2)CuO(4)) and a metal (La(1.55)Sr(0.45)CuO(4)), neither of which is superconducting in isolation. In these bilayers, T(c) is either approximately 15 K or approximately 30 K, depending on the layering sequence. This highly robust phenomenon is confined within 2-3 nm of the interface. If such a bilayer is exposed to ozone, T(c) exceeds 50 K, and this enhanced superconductivity is also shown to originate from an interface layer about 1-2 unit cells thick. Enhancement of T(c) in bilayer systems was observed previously but the essential role of the interface was not recognized at the time.

Nature of the metal insulator transition in ultrathin epitaxial vanadium dioxide.

We have combined hard X-ray photoelectron spectroscopy with angular dependent O K-edge and V L-edge X-ray absorption spectroscopy to study the electronic structure of metallic and insulating end point phases in 4.1 nm thick (14 units cells along the c-axis of VO2) films on TiO2(001) substrates, each displaying an abrupt MIT centered at ~300 K with width <20 K and a resistance change of ΔR/R > 10(3). The dimensions, quality of the films, and stoichiometry were confirmed by a combination of scanning transmission electron microscopy with electron energy loss spectroscopy, X-ray spectroscopy, and resistivity measurements. The measured end point phases agree with their bulk counterparts. This clearly shows that, apart from the strain induced change in transition temperature, the underlying mechanism of the MIT for technologically relevant dimensions must be the same as the bulk for this orientation.

Microscopic origins for stabilizing room-temperature ferromagnetism in ultrathin manganite layers.

La(0.7)Sr(0.3)MnO(3) is a conducting ferromagnet at room temperature. Combined with thin SrTiO(3) layers, the resulting heterostructures could be used as highly spin-polarized magnetic-tunnel-junction memories. However, when shrunk to dimensions below an apparent critical thickness, the structures become insulating and ferromagnetic ordering is suppressed. Interface spin and charge modulations are thought to create an interfacial dead layer, thus fundamentally limiting the use of this material in atomic-scale devices. The thickness of this dead layer, and whether it is intrinsic, is still controversial. Here we use atomic-resolution electron spectroscopy to demonstrate that the degradation of the magnetic and transport properties of La(0.7)Sr(0.3)MnO(3)/SrTiO(3) multilayers correlates with atomic intermixing at the interfaces, and the presence of extended two-dimensional cation defects in the La(0.7)Sr(0.3)MnO(3) layers (in contrast to three-dimensional precipitates in thick films). When these extrinsic defects are eliminated, metallic ferromagnetism at room temperature can be stabilized in five-unit-cell-thick manganite layers in superlattices, placing the upper limit for any intrinsic dead layer at two unit cells per interface.

Multi-scale time-resolved electron diffraction: A case study in moiré materials.

Ultrafast-optical-pump - structural-probe measurements, including ultrafast electron and x-ray scattering, provide direct experimental access to the fundamental timescales of atomic motion, and are thus foundational techniques for studying matter out of equilibrium. High-performance detectors are needed in scattering experiments to obtain maximum scientific value from every probe particle. We deploy a hybrid pixel array direct electron detector to perform ultrafast electron diffraction experiments on a WSe2/MoSe2 2D heterobilayer, resolving the weak features of diffuse scattering and moiré superlattice structure without saturating the zero order peak. Enabled by the detector's high frame rate, we show that a chopping technique provides diffraction difference images with signal-to-noise at the shot noise limit. Finally, we demonstrate that a fast detector frame rate coupled with a high repetition rate probe can provide continuous time resolution from femtoseconds to seconds, enabling us to perform a scanning ultrafast electron diffraction experiment that maps thermal transport in WSe2/MoSe2 and resolves distinct diffusion mechanisms in space and time.

Analytical electron microscopy of black carbon and microaggregated mineral matter in Amazonian dark Earth.

Black carbon (BC) is one of the most stable forms of soil organic matter. Its surface functional groups and structure have been well characterized by a range of analytical methods. However, little is known about the mechanisms of interactions between the BC particles and the surrounding mineral matter. In this paper a range of microscopy techniques, such as transmission electron microscopy and scanning transmission electron microscopy, were used to investigate the possible reactions of BC particles within microaggregates (<2 mm) found in Amazonian dark Earth. Attention is given to the interactions that occur at the interfacial regions between the organic and inorganic phases. Examination of Amazonian dark Earth showed that the carbon-rich phase detected within the BC particles has a significant calcium concentration and a high density of micropores was found at the BC-mineral interface. These observations provide evidence to support suggested mechanisms of interaction between these phases.

Timing of rectosigmoid resection for diverticular disease: the patient's view.

AIM: The study aimed to determine the patient's view on the timing of elective resection for sigmoid diverticulitis. METHOD: A questionnaire was answered by 162 (69%) of 236 consecutive patients who had a resection of the rectosigmoid for diverticulitis from July 2002 to August 2005. Patients (n=45) having resection at or after the first inflammatory attack were excluded, leaving 117 eligible for analysis. Questions asked included those concerning symptoms before surgery, improvement of symptoms after surgery and the timing of surgery. RESULTS: Patient assessment of symptoms after surgery was as follows: no improvement (2%; n=2), some improvement (10%; n=12), marked improvement (34%; n=39) and complete resolution (54%; n=63). Forty-five (38%) patients would have preferred an earlier operation. Preference for earlier surgery related to the number of previous inflammatory attacks was expressed as follows: 13 (34%) of 38 patients after two inflammatory attacks, 5 (18%) of 28 patients after three, seven (37%) of 19 patients after four, four (44%) of nine patients after five, and 16 (70%) of 23 patients after six or more inflammatory attacks would have preferred earlier surgery. Statistically significant factors influencing this potential choice were number of episodes of pain (P=0.006, OR=1.23, 95% CI: 1.060-1.430) and number of attacks of inflammation (P=0.048, OR=1.27, 95% CI: 1.002-1.598). CONCLUSION: Surgery for recurrent diverticulitis resulted in a marked improvement or complete relief of symptoms in 88% of patients. A large proportion of patients with recurrent episodes of sigmoid diverticulitis would have preferred earlier resection.

Articular degeneration after subchondral cementation for giant cell tumors at the knee.

PURPOSE: To quantify joint degeneration and the clinical outcome after curettage and cementation in subchondral giant cell tumors of the bone (GCTB) at the knee. METHODS: We conducted a retrospective analysis of 14 consecutive patients (seven female, seven male) with a mean age of 34 years (range 19-51) who underwent curettage and subchondral cementation for a biopsy-confirmed GCTB at the distal femur or the proximal tibia between August 2001 and August 2017, with a mean follow-up period of 54.6 months (range 16.1-156 months). The Whole-Organ Magnetic Resonance Imaging Score (WORMS), Kellgren-Lawrence (KL) classification, and Musculo-Skeletal Tumor Society (MSTS) score were assessed. RESULTS: Radiological degeneration progressed from preoperative to the latest follow-up, with a median WORMS from 2.0 to 4.0 (p = 0.006); meanwhile, the median KL score remained at 0 (p = 0.102). Progressive degeneration (WORMS) tended to be associated with the proximity of the tumor to the articular cartilage (mean 1.57 mm; range 0-12 mm) (p = 0.085). The most common degenerative findings were cartilage lesions (n = 11), synovitis (n = 5), and osteophytes (n = 4). Mean MSTS score increased from 23.1 (preoperatively) to 28.3 at the latest follow-up (p < 0.01). Seven patients (50%) were treated for a local recurrence, with six revision surgeries performed. Removal of the cement spacer and filling of the cavity with a cancellous autograft was performed in seven patients. Conversion to a total knee arthroplasty was performed in one patient for local tumor control. CONCLUSIONS: Cementation following the curettage of GCTB around the knee is associated with slight degeneration at medium-term follow-up and leads to a significant reduction in pain. Removal of the cement and reconstruction with an autograft may be beneficial in the long term.

A high-speed area detector for novel imaging techniques in a scanning transmission electron microscope.

A scanning transmission electron microscope (STEM) produces a convergent beam electron diffraction pattern at each position of a raster scan with a focused electron beam, but recording this information poses major challenges for gathering and storing such large data sets in a timely manner and with sufficient dynamic range. To investigate the crystalline structure of materials, a 16x16 analog pixel array detector (PAD) is used to replace the traditional detectors and retain the diffraction information at every STEM raster position. The PAD, unlike a charge-coupled device (CCD) or photomultiplier tube (PMT), directly images 120-200keV electrons with relatively little radiation damage, exhibits no afterglow and limits crosstalk between adjacent pixels. Traditional STEM imaging modes can still be performed by the PAD with a 1.1kHz frame rate, which allows post-acquisition control over imaging conditions and enables novel imaging techniques based on the retained crystalline information. Techniques for rapid, semi-automatic crystal grain segmentation with sub-nanometer resolution are described using cross-correlation, sub-region integration, and other post-processing methods.

Effects of specimen tilt in ADF-STEM imaging of a-Si/c-Si interfaces.

Annular dark field scanning transmission electron microscopy (ADF-STEM) imaging of a crystal depends strongly on specimen orientation, but for an amorphous sample it is insensitive to orientation changes. To fully investigate the effects of specimen tilt, an interface of amorphous Si (a-Si) and crystalline Si (c-Si) was rotated systematically off a zone axis in a STEM equipped with low-angle ADF (LAADF) and high-angle ADF (HAADF) detectors. The change of relative intensity across the interface shows very different trends in the LAADF and the HAADF images upon tilting. More importantly, it is found that the HAADF signal decreases much more rapidly when tilted off a zone axis than does the LAADF signal. The high-resolution lattice fringes also disappear much faster in the HAADF image than in the LAADF image. These trends reflect the fact that the channeling peaks that are responsible for scattering into the HAADF detector decrease more quickly upon tilting than the lower angle scattering to the LAADF detector does.

Subtleties in ADF imaging and spatially resolved EELS: A case study of low-angle twist boundaries in SrTiO3.

A screw dislocation network at the low-angle SrTiO3/Nb:SrTiO3 twist grain boundary has been analyzed by annular dark field (ADF) imaging and spatially resolved electron energy loss spectroscopy (EELS) in a scanning transmission electron microscope (STEM). The cores of one set of dislocations running parallel to the beam direction appear dark in the ADF STEM images. EELS on the dislocation core reveals a reduced Sr/Ti ratio compared to the bulk suggesting Sr-deficient cores. The second set of dislocations, orthogonal to the latter, is imaged by its strain field using low-angle annular dark field (LAADF) imaging. Multislice image simulations suggest channeling of the electron probe on the atomic columns for small tilts, theta < 1 degree, where the Sr columns act as beam guides. Only for larger tilts is the channeling effect strongly reduced and the fringe contrast approaches the value predicted by a purely incoherent imaging model. Ti-L(2,3) EELS across the dislocation core shows an asymmetry between the EELS and the ADF signal which cannot be explained by the geometry or beam broadening. This asymmetry might be explained by an effective nonlocal potential representing inelastic scattering in EELS.

Combining limb-sparing surgery with radiation therapy in high-grade soft tissue sarcoma of extremities - Is it effective?

BACKGROUND: Limb-sparing surgery in combination with radiation therapy is a well-established treatment for high-grade soft tissue sarcomas of the extremities. But selection of cases and optimal sequence of irradiation and surgery still remain controversial. METHODS: 769 patients with a high-grade soft tissue sarcoma of the extremities, who underwent a limb-sparing surgery, were retrospectively reviewed. Group 1 (N = 89) was treated with neo-adjuvant radiation therapy, group 2 (N = 315) with adjuvant irradiation and group 3 (N = 365) with surgery alone. RESULTS: After a mean follow up of 45 months 95 local recurrences occurred resulting in a local recurrence-free survival of 83.2% after 5 years and 75.9% after 10 years. Contaminated surgical margins (Odds ratio: 2.42) and previous inadequate surgeries (Odds ratio: 1.89) were identified as risk factors for failed local control. Neo-adjuvant radiation therapy provides the best local recurrence-free rate for 5 years (90.0%), whereas after 10 years (78.3%) adjuvant irradiation showed better local control. The metastatic-free rate was independent from achieved surgical margins (p = 0.179). Group 1 showed the highest rate of revision surgery (9.0%), followed by group 3 (5.5%) and group 2 (4.4%) (p = 0.085). However, the rate of irradiation-correlated side effects was higher in group 2 (15.2%) than in group 1 (11.2%) (p = 0.221). CONCLUSION: Surgery has to be effective for successful local control and remains the mainstay of the treatment in combination with neo-adjuvant as well as adjuvant irradiation. In really wide or even radical resections the benefit of radiation therapy can be discussed as the irradiation induced side effects are not negligible.

Rapid antigen testing for the surveillance of influenza epidemics.

OBJECTIVE: To assess the use of a 'near patient' test for rapid antigen detection to obtain the more timely acquisition of data for the surveillance of influenza epidemics. METHODS: To the classical cell culture system used for the surveillance of influenza, a 'near patient' test was added. The cell culture method was applied for the detection of influenza virus in specimens sent to our laboratory. In contrast, the 'near patient' test was used directly by practitioners in their practices to screen patients for the presence of influenza virus antigen. RESULTS: The results for two seasons are presented. The 'near patient' test was able to detect a developing influenza epidemic with the same reliability as clinical consultation reports for influenza-like illness or the conventional culture method. However, the results obtained were available 9 days earlier on average, compared with cell culture. Because of this, results concerning the epidemics could be announced via the internet more rapidly. Although the 'near patient' test demonstrated a lower sensitivity than detection by conventional cell culture, the sensitivity was still sufficiently high to reveal the characteristics of the epidemics in the community. CONCLUSIONS: Rapid influenza testing is a reliable tool for influenza surveillance and, compared with traditional methods (virus detection on cell culture and monitoring of influenza-like illness), provides faster results. Although the 'near patient' test has limited sensitivity compared with cell culture, results were consistent over two seasons, and suggest that rapid testing should be part of a surveillance program.

Prospective risk of morbidity in relation to multiplicity of infection with Plasmodium falciparum in São Tomé.

The prospective risk of acute morbidity was analysed in relation to multiplicity of Plasmodium falciparum infection in 491 individuals in a peri-urban community in São Tomé. In an initial cross-sectional survey, 40.5% of individuals were recorded by microscopy as infected with P. falciparum, and by PCR 60.5%, with the maximum prevalence in children aged 5-10 years. PCR-RFLP typing of the msp-2 gene of P. falciparum found a mean of 2.4 parasite genotypes per infected person, with little age dependence in this multiplicity and a total of 43 different msp-2 alleles identified. None of these were unique for São Tomé. Study participants were encouraged to report to a project worker whenever they suffered a febrile illness. During the 3 months following the parasitological survey the recorded incidence rates decreased with increasing baseline msp-2 multiplicity, both for P. falciparum-positive episodes and for fever without parasitaemia. While this is consistent with suggestions that multiple P. falciparum infections may protect against super-infecting parasites, confounding by patterns of health service usage is an alternative explanation. The incidence of clinical malaria episodes was only a little higher in children than in adults. This weak age-dependence in clinical immunity might be a consequence of a cohort effect resulting from resurgence of the disease after the breakdown of malaria control programs in the 1980s.