In situ observation of synthesized nanoparticles in ultra-dilute aerosols via X-ray scattering

In-air epitaxy of nanostructures (Aerotaxy) has recently emerged as a viable route for fast, large-scale production. In this study, we use small-angle X-ray scattering to perform direct in-flight characterizations of the first step of this process, i.e., the engineered formation of Au and Pt aerosol nanoparticles by spark generation in a flow of N₂ gas. This represents a particular challenge for characterization because the particle density can be extremely low in controlled production. The particles produced are examined during production at operational pressures close to atmospheric conditions and exhibit a lognormal size distribution ranging from 5–100 nm. The Au and Pt particle production and detection are compared. We observe and characterize the nanoparticles at different stages of synthesis and extract the corresponding dominant physical properties, including the average particle diameter and sphericity, as influenced by particle sintering and the presence of aggregates. We observe highly sorted and sintered spherical Au nanoparticles at ultra-dilute concentrations (< 5 × 10⁵ particles/cm³) corresponding to a volume fraction below 3 × 10^–10, which is orders of magnitude below that of previously measured aerosols. We independently confirm an average particle radius of 25 nm via Guinier and Kratky plot analysis. Our study indicates that with high-intensity synchrotron beams and careful consideration of background removal, size and shape information can be obtained for extremely low particle concentrations with industrially relevant narrow size distributions.

     

Epidemiology of end‐stage renal disease and hemodialysis treatment in Serbia at the turn of the millennium

The study presents the epidemiological features of patients treated with renal replacement therapy (RRT) in Serbia from 1997 to 2009 and compares the results of hemodialysis treatment in 1999 and 2009. Epidemiological data were obtained from the National Registry of RRT patients and data on hemodialysis treatment from special surveys conducted in 1999 and 2009. Within the period 1997–2009 the incidence of patients on RRT increased from 108 to 179 per million population (pmp), prevalence rose from 435 to 699 pmp, while mortality rate fell from 20.7% to 16.7%. The frequency of patients with glomerulonephritis decreased, while that of patients with diabetes and hypertensive nephropathy increased. In late 2009 there were 5208 patients receiving RRT in Serbia. Within the examined period new hemodialysis and reverse osmosis equipment were purchased, high‐flux dialyzers with synthetic membranes were increasingly used and the number of patients receiving hemodiafiltration increased to 17.6%. Kt/V greater than 1.2 was recorded in 16% of the patients in 1999 but 52% in 2009. Options for correction of anemia and mineral disorders have also improved. The percentage of patients with HbsAg (13.8% vs. 4.8%) as well as anti‐hepatitis C virus antibodies positive patients (23.2% vs. 12.7%) was significantly lower in 2009 than in 1999. Both the incidence and prevalence of RRT patients in Serbia are rising continuously, while the mortality rate is falling. More favorable conditions for dialysis treatment have brought about significant improvement in the results over the last 10 years.     

GaAs/AlGaAs nanowire heterostructures studied by scanning tunneling microscopy

We directly image the interior of GaAs/AlGaAs axial and radial nanowire heterostructures with atomic-scale resolution using scanning tunneling microscopy. We show that formation of monolayer sharp and smooth axial interfaces are possible even by vapor-phase epitaxy. However, we also find that instability of the ternary alloys formed in the Au seed fundamentally limits axial heterostructure control, inducing large segment asymmetries. We study radial core-shell nanowires, imaging even ultrathin submonolayer shells. We demonstrate how large twinning-induced morphological defects at the wire surfaces can be removed, ensuring the formation of wires with atomically flat sides.     

Direct atomic scale imaging of III-V nanowire surfaces

We have succeeded in direct atomic scale imaging of the exterior surfaces of III-V nanowires by scanning tunneling microscopy (STM). By using atomic hydrogen, we expose the crystalline surfaces of InAs nanowires with regular InP segments in vacuum while retaining the wire morphology. We show images with atomic resolution of the two major types of InAs wurtzite nanowire surface facets and scanning tunneling spectroscopy (STS) data. Ab initio calculations of the lowest energy surface structures and simulated STM images, agree very well with experiments.     

Making touch-based kiosks accessible to blind users through simple gestures

Touch-based interaction is becoming increasingly popular and is commonly used as the main interaction paradigm for self-service kiosks in public spaces. Touch-based interaction is known to be visually intensive, and current non-haptic touch-display technologies are often criticized as excluding blind users. This study set out to demonstrate that touch-based kiosks can be designed to include blind users without compromising the user experience for non-blind users. Most touch-based kiosks are based on absolute positioned virtual buttons which are difficult to locate without any tactile, audible or visual cues. However, simple stroke gestures rely on relative movements and the user does not need to hit a target at a specific location on the display. In this study, a touch-based train ticket sales kiosk based on simple stroke gestures was developed and tested on a panel of blind and visually impaired users, a panel of blindfolded non-visually impaired users and a control group of non-visually impaired users. The tests demonstrate that all the participants managed to discover, learn and use the touch-based self-service terminal and complete a ticket purchasing task. The majority of the participants completed the task in less than 4?min on the first attempt.     

Simulation of α- and β-PVDF melting mechanisms

Molecular dynamics (MD) simulations have been used to study the melting of α- and β-poly (vinylidene fluoride) (α- and β-PVDF). It is seen that melting at the ends of the polymer chains precedes melting of the bulk crystal structure. Melting of α-PVDF initially occurs via transitions between the two gauche dihedral angles (G ? G′) followed by transitions between trans and gauche dihedral angles (T ? G/G′). Melting of β-PVDF initially occurs via T → G/G′ transitions and via transitions of complete β- (TTTT) to α- (TGTG') quartets. The melting point of β-PVDF is higher than that of α-PVDF, and the simulated melting points of both phases depend on the length of the polymer chains used in the simulations. Since melting starts at the chain ends, it is important to include these in the simulations, and simulations of infinitely long chains yield melting points far larger than the experimental values (at least for periodic cells of the size used in this work), especially for β-PVDF. The simulated heats of fusion are in agreement with available experimental data.     

Open source in Swedish companies: where are we?

Open Source (OS) is a phenomenon of increasing significance for organizations, offering the prospect of effective alternative business solutions and new business opportunities. A number of surveys have been conducted in various countries with the purpose of understanding the state of practice with respect to OS in companies. In this paper we report on a study of the perceptions of OS and the uptake of OS products and development models in Swedish companies. The study used purposeful sampling of companies that have an expressed interest in OS, and the survey was conducted using a set of pre‐prepared questions. Its goal was to investigate the extent to which OS has influenced business thinking, as seen from the standpoint of stakeholders. We found that uptake is much higher than reported in earlier studies, but as with previous studies, activity is still concentrated in small and medium‐sized enterprises (SMEs). There is increased evidence of interest beyond the simple use of OS components at the infrastructure level. Further, a significant proportion of the companies studied are supporting the OS community as well as benefiting from it. Support includes participation in existing projects and the release of new software under OS licenses.     

Erratum to: In situ observation of synthesized nanoparticles in ultra-dilute aerosols via X-ray scattering

Nano Research - The article In situ observation of synthesized nanoparticles in ultradilute aerosols via X-ray scattering, written by Sarah R. McKibbin, Sofie Yngman, Olivier Balmes, Bengt O....     

Thermal and hydrodynamic analysis of gaseous flow in trapezoidal silicon microchannels

Thermal and hydrodynamic character of a hydrodynamically developed and thermally developing flow in trapezoidal silicon microchannels is analyzed. The continuum momentum and energy equations, with the velocity slip and temperature jump condition at the solid walls, are solved numerically in a square computational domain obtained by transformation of the trapezoidal geometry. The effects of rarefaction, aspect ratio and a parameter representing the fluid/wall interaction on thermal and hydrodynamic character of flow in trapezoidal microchannels are explored. It is found that the friction factor decreases if rarefaction and/or aspect ratio increase. It is also found that at low rarefactions the very high heat transfer rate at the entrance diminishes rapidly as the thermally developing flow approaches fully developed flow. At high rarefactions, heat transfer rate does not exhibit considerable changes along the microchannel, no matter the flow is developing or not.     

Direct imaging of the atomic structure inside a nanowire by scanning tunnelling microscopy

Semiconductor nanowires are expected to be important components in future nano-electronics and photonics. Already a wide range of applications has been realized, such as high-performance field-effect transistors, bio/chemical sensors, diode logics and single-nanowire lasers. As nanowires have small cross-sections and large surface-to-bulk ratios, their properties can be significantly influenced by individual atomic-scale structural features, and they can have properties or even atomic arrangements with no bulk counterparts. Hence, experimental methods capable of directly addressing the atomic-scale structure of nanowires are highly desirable. One such method is scanning tunnelling microscopy (STM), which, by direct imaging of the atomic and electronic structure of surfaces has revolutionized the perception of nanoscale objects and low-dimensional systems. Here we demonstrate how combining STM with an embedding scheme allows us to image the interior of semiconductor nanowires with atomic resolution. Defect structures such as planar twin segments and single-atom impurities are imaged inside a GaAs nanowire. Further, we image an intriguing GaAs nanowire that is separated into two distinct nanocrystallites along the growth direction of the wire.