Bending and reverse bending during the fabrication of novel GaAs/(In,Ga)As/GaAs core-shell nanowires monitored byin situx-ray diffraction.

We report on the fabrication of a novel design of GaAs/(In,Ga)As/GaAs radial nanowire heterostructures on a Si 111 substrate, where, for the first time, the growth of inhomogeneous shells on a lattice mismatched core results in straight nanowires instead of bent. Nanowire bending caused by axial tensile strain induced by the (In,Ga)As shell on the GaAs core is reversed by axial compressive strain caused by the GaAs outer shell on the (In,Ga)As shell. Progressive nanowire bending and reverse bending in addition to the axial strain evolution during the two processes are accessed byin situby x-ray diffraction. The diameter of the core, thicknesses of the shells, as well as the indium concentration and distribution within the (In,Ga)As quantum well are revealed by 2D energy dispersive x-ray spectroscopy using a transmission electron microscope. Shell(s) growth on one side of the core without substrate rotation results in planar-like radial heterostructures in the form of free standing straight nanowires.

Frequency and predictive factors for spontaneous normalization of anti-tissue transglutaminase-IgA serology among Saudi children with type 1 diabetes mellitus: A cohort study.

Background: Celiac serology can be transiently elevated in patients with type 1 diabetes mellitus (T1DM) and normalized despite gluten consumption. This study aimed to identify the frequency and predictive factors of spontaneous normalization of anti-tissue transglutaminase (anti-TTG-IgA) antibodies in these patients. Methods: The charts of all patients (≤18 years) with T1DM were retrospectively reviewed from 2012 to 2021 at a tertiary care center in Riyadh, Saudi Arabia. The following data were collected: clinical characteristics of the participants, anti-TTG-IgA-immunoglobulin (Ig) A antibody, and histological findings. The outcome of positive anti-TTG-IgA-IgA in patients with T1DM and the predictive factors for spontaneous normalization were investigated. Results: Of the 1,006 patients with T1DM, 138 (13.7%) had elevated anti-TTG-IgA antibodies, celiac disease was diagnosed in 58/138 (42%) patients, spontaneous normalization of anti-TTG-IgA was observed in 65 (47.1%) patients, and fluctuating anti-TTG-IgA antibodies were seen in 15 (10.9%) patients. The patients with anti-TTG-IgA levels at 3-10 times the upper normal limits (UNL), and those with levels ≥10 times UNL were less likely to have spontaneous normalization of anti-TTG-IgA compared to patients with levels at 1-3 times UNL (hazard ratio [HR] = 0.28, 95% confidence interval [Cl] = 0.13-0.61, P = 0.001, and HR = 0.03, 95% Cl = 0.00-0.19, P < 0.001, respectively). Conclusion: Asymptomatic patients with T1DM with mild elevation of anti-TTG-IgA need not be rushed for invasive endoscopy or exposed to an un-needed gluten-free diet but should rather have a regular follow-up of their celiac serology.

Exploiting flux shadowing for strain and bending engineering in core-shell nanowires.

Here we report on the non-uniform shell growth of InxGa1-xAs on the GaAs nanowire (NW) core by molecular beam epitaxy (MBE). The growth was realized on pre-patterned silicon substrates with the pitch size (p) ranging from 0.1 µm to 10 µm. Considering the preferable bending direction with respect to the MBE cells as well as the layout of the substrate pattern, we were able to modify the strain distribution along the NW growth axis and the subsequent bending profile. For NW arrays with a high number density, the obtained bending profile of the NWs is composed of straight (barely-strained) and bent (strained) segments with different lengths which depend on the pitch size. A precise control of the bent and straight NW segment length provides a method to design NW based devices with length selective strain distribution.

An Incidental Finding of Asymptomatic Gastric Diverticula.

Gastric diverticula (GD) are the rarest of the gastrointestinal diverticula and are characterized by protrusions of the stomach wall, that can either be congenital or acquired. Despite the fact that the majority of GD are asymptomatic and are detected inadvertently during endoscopy or gastrointestinal (GI) series studies, they might present with a variety of symptoms, including abdominal pain, vomiting, and weight loss. In mild symptomatic instances, GD is treated conservatively with antacids, but surgical excision is indicated for refractory gastric diverticula with persistent symptoms or complications. We represent an incidental finding of asymptomatic gastric diverticulum through endoscopy for a 12-year-old Saudi male who presented after foreign body ingestion.

Foreign Body Ingestion: A Common Presentation Among Pediatric Age Group in the City of AlAhsa Eastern Province, Saudi Arabia.

Background Foreign body ingestion is a prevalent issue among children and presents considerable morbidity and mortality rates. Due to children's increased accessibility to electronic toys and equipment, foreign body ingestion has become a common reason for presenting to pediatric emergency departments worldwide. In this context, this research aims to determine the prevalence of foreign body ingestion among children in AlAhsa, Saudi Arabia. Methodology This observational retrospective descriptive study was conducted at Maternity and Children Hospital, AlAhsa, Saudi Arabia, from 2017 to 2021. The study included children (less than 14 years old) who presented to the emergency department with a history of foreign body ingestion. The biographical data, clinical presentation, type of foreign body, and X-ray findings were documented. Results A total of 91 cases of foreign body ingestion or aspiration in children under 14 years of age were included. Approximately half of the patients were under the age of three, and 62.2% of them were male, while 37.8% were female. The clinical presentation revealed that only 24% were symptomatic. Coins were the most commonly ingested foreign bodies (28.9%), followed by metallic objects (20%), and batteries were the least frequently ingested foreign bodies, recorded in eight cases. Conclusion Early detection and treatment of foreign body ingestion is crucial to prevent consequences. In this study, the most frequent foreign bodies detected were coins among children up to three years old. Raising parents' awareness about the prevention of foreign body ingestion is an important step toward reducing its incidence.

Correlating in situ RHEED and XRD to study growth dynamics of polytypism in nanowires.

Design of novel nanowire (NW) based semiconductor devices requires deep understanding and technological control of NW growth. Therefore, quantitative feedback over the structure evolution of the NW ensemble during growth is highly desirable. We analyse and compare the methodical potential of reflection high-energy electron diffraction (RHEED) and X-ray diffraction reciprocal space imaging (XRD) for in situ growth characterization during molecular-beam epitaxy (MBE). Simultaneously recorded in situ RHEED and in situ XRD intensities show strongly differing temporal behaviour and provide evidence of the highly complementary information value of both diffraction techniques. Exploiting the complementarity by a correlative data analysis presently offers the most comprehensive experimental access to the growth dynamics of statistical NW ensembles under standard MBE growth conditions. In particular, the combination of RHEED and XRD allows for translating quantitatively the time-resolved information into a height-resolved information on the crystalline structure without a priori assumptions on the growth model. Furthermore, we demonstrate, how careful analysis of in situ RHEED if supported by ex situ XRD and scanning electron microscopy (SEM), all usually available at conventional MBE laboratories, can also provide highly quantitative feedback on polytypism during growth allowing validation of current vapour-liquid-solid (VLS) growth models.

Transition from elastic to plastic strain release in core-shell nanowires revealed by in-plane x-ray diffraction.

We investigate the strain evolution and relaxation process as function of increasing lattice mismatch between the GaAs core and surrounding In x Ga1-x As shell in core-shell nanowire heterostructures grown on Si(111) substrates. The dimensions of the core and shell are kept constant whereas the indium concentration inside the shell is varied. Measuring the [Formula: see text] and [Formula: see text] in-plane Bragg reflections normal to the nanowire side edges and side facets, we observe a transition from elastic to plastic strain release for a shell indium content x > 0.5. Above the onset of plastic strain relaxation, indium rich mounds and an indium poor coherent shell grow simultaneously around the GaAs core. Mound formation was observed for indium contents x = 0.5 and 0.6 by scanning electron microscopy. Considering both the measured radial reflections and the axial 111 Bragg reflection, the 3D strain variation was extracted separately for the core and the In x Ga1-x As shell.

Beam damage of single semiconductor nanowires during X-ray nanobeam diffraction experiments.

Nanoprobe X-ray diffraction (nXRD) using focused synchrotron radiation is a powerful technique to study the structural properties of individual semiconductor nanowires. However, when performing the experiment under ambient conditions, the required high X-ray dose and prolonged exposure times can lead to radiation damage. To unveil the origin of radiation damage, a comparison is made of nXRD experiments carried out on individual semiconductor nanowires in their as-grown geometry both under ambient conditions and under He atmosphere at the microfocus station of the P08 beamline at the third-generation source PETRA III. Using an incident X-ray beam energy of 9 keV and photon flux of 1010 s-1, the axial lattice parameter and tilt of individual GaAs/In0.2Ga0.8As/GaAs core-shell nanowires were monitored by continuously recording reciprocal-space maps of the 111 Bragg reflection at a fixed spatial position over several hours. In addition, the emission properties of the (In,Ga)As quantum well, the atomic composition of the exposed nanowires and the nanowire morphology were studied by cathodoluminescence spectroscopy, energy-dispersive X-ray spectroscopy and scanning electron microscopy, respectively, both prior to and after nXRD exposure. Nanowires exposed under ambient conditions show severe optical and morphological damage, which was reduced for nanowires exposed under He atmosphere. The observed damage can be largely attributed to an oxidation process from X-ray-induced ozone reactions in air. Due to the lower heat-transfer coefficient compared with GaAs, this oxide shell limits the heat transfer through the nanowire side facets, which is considered as the main channel of heat dissipation for nanowires in the as-grown geometry.

Impact of the Shadowing Effect on the Crystal Structure of Patterned Self-Catalyzed GaAs Nanowires.

The growth of regular arrays of uniform III-V semiconductor nanowires is a crucial step on the route toward their application-relevant large-scale integration onto the Si platform. To this end, not only does optimal vertical yield, length, and diameter uniformity have to be engineered, but also, control over the nanowire crystal structure has to be achieved. Depending on the particular application, nanowire arrays with varying area density are required for optimal device efficiency. However, the nanowire area density substantially influences the nanowire growth and presents an additional challenge for nanowire device engineering. We report on the simultaneous in situ X-ray investigation of regular GaAs nanowire arrays with different area density during self-catalyzed vapor-liquid-solid growth on Si by molecular-beam epitaxy. Our results give novel insight into selective-area growth and demonstrate that shadowing of the Ga flux, occurring in dense nanowire arrays, has a crucial impact on the evolution of nanowire crystal structure. We observe that the onset of Ga flux shadowing, dependent on array pitch and nanowire length, is accompanied by an increase of the wurtzite formation rate. Our results moreover reveal the paramount role of the secondary reflected Ga flux for VLS NW growth (specifically, that flux that is reflected directly into the liquid Ga droplet).

Correlated Nanoscale Analysis of the Emission from Wurtzite versus Zincblende (In,Ga)As/GaAs Nanowire Core-Shell Quantum Wells.

While the properties of wurtzite GaAs have been extensively studied during the past decade, little is known about the influence of the crystal polytype on ternary (In,Ga)As quantum well structures. We address this question with a unique combination of correlated, spatially resolved measurement techniques on core-shell nanowires that contain extended segments of both the zincblende and wurtzite polytypes. Cathodoluminescence hyperspectral imaging reveals a blue-shift of the quantum well emission energy by 75 ± 15 meV in the wurtzite polytype segment. Nanoprobe X-ray diffraction and atom probe tomography enable k·p calculations for the specific sample geometry to reveal two comparable contributions to this shift. First, there is a 30% drop in In mole fraction going from the zincblende to the wurtzite segment. Second, the quantum well is under compressive strain, which has a much stronger impact on the hole ground state in the wurtzite than in the zincblende segment. Our results highlight the role of the crystal structure in tuning the emission of (In,Ga)As quantum wells and pave the way to exploit the possibilities of three-dimensional band gap engineering in core-shell nanowire heterostructures. At the same time, we have demonstrated an advanced characterization toolkit for the investigation of semiconductor nanostructures.

Dental core training for the future GDP: is it worth it?

In this article I highlight the benefits and shortfalls of the dental core trainee year for one who has no interest in specialising and sees their eventual future as a general dental practitioner (GDP). I conclude that the dental core trainee year has great advantages and adds value to the future GDP.

Characterization of individual stacking faults in a wurtzite GaAs nanowire by nanobeam X-ray diffraction.

Coherent X-ray diffraction was used to measure the type, quantity and the relative distances between stacking faults along the growth direction of two individual wurtzite GaAs nanowires grown by metalorganic vapour epitaxy. The presented approach is based on the general property of the Patterson function, which is the autocorrelation of the electron density as well as the Fourier transformation of the diffracted intensity distribution of an object. Partial Patterson functions were extracted from the diffracted intensity measured along the [000\bar{1}] direction in the vicinity of the wurtzite 00\bar{1}\bar{5} Bragg peak. The maxima of the Patterson function encode both the distances between the fault planes and the type of the fault planes with the sensitivity of a single atomic bilayer. The positions of the fault planes are deduced from the positions and shapes of the maxima of the Patterson function and they are in excellent agreement with the positions found with transmission electron microscopy of the same nanowire.

Threefold rotational symmetry in hexagonally shaped core-shell (In,Ga)As/GaAs nanowires revealed by coherent X-ray diffraction imaging.

Coherent X-ray diffraction imaging at symmetric hhh Bragg reflections was used to resolve the structure of GaAs/In0.15Ga0.85As/GaAs core-shell-shell nanowires grown on a silicon (111) substrate. Diffraction amplitudes in the vicinity of GaAs 111 and GaAs 333 reflections were used to reconstruct the lost phase information. It is demonstrated that the structure of the core-shell-shell nanowire can be identified by means of phase contrast. Interestingly, it is found that both scattered intensity in the (111) plane and the reconstructed scattering phase show an additional threefold symmetry superimposed with the shape function of the investigated hexagonal nanowires. In order to find the origin of this threefold symmetry, elasticity calculations were performed using the finite element method and subsequent kinematic diffraction simulations. These suggest that a non-hexagonal (In,Ga)As shell covering the hexagonal GaAs core might be responsible for the observation.

The influence of ethanol on blood flow velocity in major cerebral vessels. A prospective and controlled study.

Cerebral vasospasm secondary to subarachnoid hemorrhage leads to increased cerebrovascular resistance and may cause ischemia in the affected vascular territories. The currently available therapeutic options for treating vasospasm are limited. The effect of ethanol at a concentration of 0.75 g/kg body weight on blood flow velocity in the major cerebral arteries was studied. In 31 healthy persons, the major extra- and intracranial cerebral vessels were examined by Doppler ultrasonography before and following oral ingestion of 0.75 g/kg body weight of ethanol. An additional 20 healthy subjects served as a control group. Ethanol in the applied concentration significantly increased the systolic, diastolic, and mean blood flow velocities and significantly decreased the pulsatility indices in the middle cerebral artery (MCA). It may reduce vascular resistance and may increase cerebral blood flow in the area supplied by the MCA in healthy persons.

Occlusion of an aberrant artery to a pulmonary sequestration using a duct occluder.

This report describes a female infant with a rare chromosome defect, del. 12 (q22-24.1), who has severe pulmonary valve stenosis, an atrial septal defect, and a small muscular ventricular septal defect. At 4 months of age a balloon pulmonary valvuloplasty was performed in the cardiac catheterization laboratory. During the procedure, a large aberrant artery from the aorta to a sequestration of the right lower lobe of lung was found. The flow-off from the sequestration was into a dilated left atrium. The single artery supplying the sequestration was successfully occluded using an Amplatzer Duct Occluder device. There were no complications and the infant remains well at 1-year follow-up.