Physical, chemical and microbiological water characteristics associated with the occurrence of Legionella in cooling tower systems

The occurrence of Legionella in water of 30 cooling tower systems was studied, as well as the relationship of its occurrence with the physical, chemical and microbiological characteristics of the waters. The samples were concentrated by membrane filtration and one part of the concentrate was acid washed. Three types of culture media, MWY, CCVC and BCYEα were used. Fourteen (47%) of the cooling systems were Legionella-positive. Numbers of Legionella in the positive systems varied between 50 and 490,000 cfu/l. Legionella pneumophila was the dominant isolate, and the serogroups 6 and 1 were the commonest ones. There was no statistically significant difference in mean water temperature between the Legionella-positive (27°C) and -negative (24°C) systems. The total number of bacteria (AODC) was lower in the Legionella-positive than in the negative systems. Also the nutrient concentrations were generally lower in the Legionella-positive cooling systems. The results suggest that different factors regulate the occurrence of Legionella than that of overall bacterial populations in the cooling tower systems.     

An experimental investigation on the poroelastic response of a water-saturated limestone to hydrostatic compression

Bulletin of Engineering Geology and the Environment - This contribution addresses an experimental study on the poroelastic behavior of a water-saturated limestone. Samples come from Sarvak...     

Halide Perovskite Nanocrystals for Next‐Generation Optoelectronics

Colloidal perovskite nanocrystals (PNCs) combine the outstanding optoelectronic properties of bulk perovskites with strong quantum confinement effects at the nanoscale. Their facile and low‐cost synthesis, together with superior photoluminescence quantum yields and exceptional optical versatility, make PNCs promising candidates for next‐generation optoelectronics. However, this field is still in its early infancy and not yet ready for commercialization due to several open challenges to be addressed, such as toxicity and stability. Here, the key synthesis strategies and the tunable optical properties of PNCs are discussed. The photophysical underpinnings of PNCs, in correlation with recent developments of PNC‐based optoelectronic devices, are especially highlighted. The final goal is to outline a theoretical scaffold for the design of high‐performance devices that can at the same time address the commercialization challenges of PNC‐based technology.     

Forestry crane posture estimation with a two‐dimensional laser scanner

Crane posture estimation is the stepping stone to forest machine automation. Here, we introduce a robust minimal perception solution, that is, one that uses minimal constraints for maximal benefits. Specifically, we introduce a robust particle‐filter‐based method to estimate and track the posture of a flexible hydraulic crane by using only low‐cost equipment, namely, a two‐dimensional (2D) laser scanner, two short magnetically attached metal tubes as targets, and an angle sensor. An important feature of our method is that it incorporates control signals for hydraulic actuators. In contrast to the previous works employing laser scanners, we do not use the full shape of the crane to estimate the crane posture, but, instead, we use only two small targets in the field of view of the laser scanner. Thus, a large share of the range data is useful for other purposes, for example, to map the surrounding environment. We test the proposed method in a challenging forest environment and show that the particle filter is able to estimate the posture of the hydraulic crane efficiently and reliably in the presence of occlusions and obstructions. During our comprehensive testing, the tip position was measured with average errors smaller than 4.3 cm whereas the absolute maximum error was 15 cm.     

Burrows-Wheeler post-transformation with effective clustering and interpolative coding

Lossless compression methods based on the Burrows-Wheeler transform (BWT) are regarded as an excellent compromise between speed and compression efficiency: they provide compression rates close to the PPM algorithms, with the speed of dictionary-based methods. Instead of the laborious statistics-gathering process used in PPM, the BWT reversibly sorts the input symbols, using as the sort key as many following characters as necessary to make the sort unique. Characters occurring in similar contexts are sorted close together, resulting in a clustered symbol sequence. Run-length encoding and Move-to-Front (MTF) recoding, combined with a statistical Huffman or arithmetic coder, is then typically used to exploit the clustering. A drawback of the MTF recoding is that knowledge of the character that produced the MTF number is lost. In this paper, we present a new, competitive Burrows-Wheeler posttransform stage that takes advantage of interpolative coding—a fast binary encoding method for integer sequences, being able to exploit clusters without requiring explicit statistics. We introduce a fast and simple way to retain knowledge of the run characters during the MTF recoding and use this to improve the clustering of MTF numbers and run-lengths by applying reversible, stable sorting, with the run characters as sort keys, achieving significant improvement in the compression rate, as shown here by experiments on common text corpora.     

Sensitivity enhancement of a MEMS sensor in nonlinear regime

The aim of this study is to enhance the sensitivity of a micro electro mechanical Gyroscope in nonlinear regime. Sensitivity enhancement is achieved by applying appropriate Hoping voltages which pushes the micro-beam to the basin of attraction of a desired periodic attractor. The studied model is a silicon clamped–clamped micro beam actuated by an electrostatic voltage which is a combination of a constant DC and a harmonic AC voltage in the drive mode direction and a pure DC voltage in the direction of sense mode. The external angular velocity about the horizontal axis is used to create the Coriolis force along the sense mode. The governing differential equation of the motion is derived using Hamiltonian principle and discretized to two nonlinear Duffing type ODE’s using Galerkin method. Shooting method is utilized to obtain the frequency response curve, and to capture the periodic solutions of the motion. The stabilities of the periodic orbits are investigated by the Floquet theory. The results depict that the response of the system is highly affected by the applied DC and AC voltage; corresponding to a constant DC voltage, the more is the AC voltage, the more is the sensitivity. Based on the DC voltage the system exhibits both hardening and softening effects. The capacity of the capacitors is determined and the effects of the various applying Hoping voltages on capacity of them are investigated. The frequency response curve of the micro-beam for various quality factors are obtained and compared with the literature.     

Muscle activity patterns and spinal shrinkage in office workers using a sit–stand workstation versus a sit workstation

Reducing sitting time by means of sit–stand workstations is an emerging trend, but further evidence is needed regarding their health benefits. This cross-sectional study compared work time muscle activity patterns and spinal shrinkage between office workers (aged 24–62, 58.3% female) who used either a sit–stand workstation (Sit–Stand group, n = 10) or a traditional sit workstation (Sit group, n = 14) for at least the past three months. During one typical workday, muscle inactivity and activity from quadriceps and hamstrings were monitored using electromyography shorts, and spinal shrinkage was measured using stadiometry before and after the workday. Compared with the Sit group, the Sit–Stand group had less muscle inactivity time (66.2 ± 17.1% vs. 80.9 ± 6.4%, p = 0.014) and more light muscle activity time (26.1 ± 12.3% vs. 14.9 ± 6.3%, p = 0.019) with no significant difference in spinal shrinkage (5.62 ± 2.75 mm vs. 6.11 ± 2.44 mm). This study provides evidence that working with sit–stand workstations can promote more light muscle activity time and less inactivity without negative effects on spinal shrinkage.

Practitioner Summary: This cross-sectional study compared the effects of using a sit–stand workstation to a sit workstation on muscle activity patterns and spinal shrinkage in office workers. It provides evidence that working with a sit–stand workstation can promote more light muscle activity time and less inactivity without negative effects on spinal shrinkage.     

Sampling and dilution of nanoparticles at high temperature

Sampling and dilution of flame-generated, fractal-like ZrO₂ aerosols is investigated by aerosol mass/mobility measurements and microscopy. Two broadly used sampler configurations, a straight-tube (ST) and a hole-in-a-tube (HiaT), at three different in-flow orientations and hole diameters are evaluated. The mobility size distributions, mass-mobility exponent, D_fm, prefactor, k_fm, and average primary particle diameter are obtained at 10–60 cm height above the burner (HAB) of fuel-rich (hot) and fuel-lean (cold) spray flames by differential mobility analyzer (DMA) and aerosol particle mass (APM) measurements using a recent power law for fractal-like particles. The primary particle diameter, agglomerate size distributions, and corresponding standard deviations from aerosol measurements are compared to those by counting images of particles collected by thermophoretic sampling along the flame centerline. Once new particle formation is completed in the flame, both sampler configurations result in nearly identical particle size distributions. Furthermore, all HiaT samplers result in similar mobility size distributions at all orientations, regardless of hole size. Sampling using a downstream in-flow hole orientation results in slightly larger Sauter mean diameters than those obtained by upstream or sidestream ones, especially for the cold flame. Additionally, a correlation is developed by Discrete Element Modeling (DEM) for the agglomerate D_fm evolution to its asymptotic value of 2.2 as function of the average number of primary particles per agglomerate, n_va, or the relative particle density with pre-exponential constant k_fm = 1.18, regardless of primary particle size. This is in good agreement with an experimentally obtained correlation in terms of relative particle density as well as with experimental data for ZrO₂, Ag, and Cu nanoparticles.

© 2016 American Association for Aerosol Research