How far droplets can move in indoor environments--revisiting the Wells evaporation-falling curve

A large number of infectious diseases are believed to be transmitted between people via large droplets and by airborne routes. An understanding of evaporation and dispersion of droplets and droplet nuclei is not only significant for developing effective engineering control methods for infectious diseases but also for exploring the basic transmission mechanisms of the infectious diseases. How far droplets can move is related to how far droplet-borne diseases can transmit. A simple physical model is developed and used here to investigate the evaporation and movement of droplets expelled during respiratory activities; in particular, the well-known Wells evaporation-falling curve of droplets is revisited considering the effect of relative humidity, air speed, and respiratory jets. Our simple model considers the movement of exhaled air, as well as the evaporation and movement of a single droplet. Exhaled air is treated as a steady-state non-isothermal (warm) jet horizontally issuing into stagnant surrounding air. A droplet is assumed to evaporate and move in this non-isothermal jet. Calculations are performed for both pure water droplets and droplets of sodium chloride (physiological saline) solution (0.9% w/v). We calculate the droplet lifetimes and how droplet size changes, as well as how far the droplets travel in different relative humidities. Our results indicate that a droplet's size predominately dictates its evaporation and movement after being expelled. The sizes of the largest droplets that would totally evaporate before falling 2 m away are determined under different conditions. The maximum horizontal distances that droplets can reach during different respiratory activities are also obtained. Our study is useful for developing effective prevention measures for controlling infectious diseases in hospitals and in the community at large. PRACTICAL IMPLICATIONS: Our study reveals that for respiratory exhalation flows, the sizes of the largest droplets that would totally evaporate before falling 2 m away are between 60 and 100 microm, and these expelled large droplets are carried more than 6 m away by exhaled air at a velocity of 50 m/s (sneezing), more than 2 m away at a velocity of 10 m/s (coughing) and less than 1 m away at a velocity of 1 m/s (breathing). These findings are useful for developing effective engineering control methods for infectious diseases, and also for exploring the basic transmission mechanisms of the infectious diseases. There is a need to examine the air distribution systems in hospital wards for controlling both airborne and droplet-borne transmitted diseases.     

High-power piezoelectric energy harvester produced using [0 0 1]-textured (Na,K)NbO3-based lead-free piezoceramics

High-power piezoelectric energy harvesters (PEHs) require piezoceramics with a large k_p and d₃₃ but small ε^T₃₃/ε₀ values. The [0 0 1]-textured 0.96(Na, K)(Nb_1−xSb_x)–0.04SrZrO₃ piezoceramics (x = 0.025 and 0.045) exhibited the improved electromechanical coupling factor (k_p) and piezoelectric charge constant (d₃₃); however, the increase of dielectric constant (ε^T₃₃/ε₀) was not significant. Further, the textured piezoceramic with x = 0.045 shows the large d₃₃ × g₃₃ value of 21.5 pm²/N, where g₃₃ is piezoelectric voltage constant, indicating that texturing is a good technique to fabricate the piezoceramics for PEH. The impedance curve of the PEH consisting of the metal substrate and textured piezoceramic shows a piezoelectric resonance peak at a low frequency, which is the same as the mechanical resonance frequency of the PEH. Hence, the PEH can be considered a piezoelectric material. The figure of merit of the PEH was determined using the mechanical quality and electromechanical coupling factor calculated from the impedance curve of the PEH. A large power output of 1.7 mW was obtained from the type-1 PEH at the resonance frequency produced using the textured thick film (x = 0.045). Hence, this PEH can be used as a permanent power source for microelectronic devices in the Internet of Things.     

自由基聚合反应动力学常数测定技术

自由基聚合是一类重要的聚合反应,其反应动力学常数的获取对于聚合机理研究、聚合物链结构定制、反应过程调控都有着重要的意义。综述了自由基聚合中最重要的链增长和链终止反应速率常数的测定方法,着重介绍连续脉冲激光引发结合凝胶渗透色谱测定链增长反应速率常数、单脉冲-连续脉冲激光耦合结合近红外光谱与电子顺磁共振波谱测定链终止反应速率常数,涵盖了各方法的检测原理、要求和适用条件,讨论了增长自由基链长对链增长和链终止反应速率常数的影响。此外,对链增长和链终止反应速率常数检测方法的提升和新方法的开发进行了展望。     

Chemical, Microbiological, and Sensory Quality of Cod Products Salted in Different Brines

ABSTRACT: Studies were carried out on the effect of different brines containing high concentrations of calcium chloride (CaCl₂, 0.8%w/w), magnesium chloride (MgCl₂, 0.4%w/w), and potassium chloride (KCl, 50%) on the chemical (chloride and moisture contents), microbial (total viable counts, total coliforms, enterococci, and staphylococci), and sensory quality of salted cod. The brines were prepared from combinations of the Ca, Mg, and K ions and sodium chloride (NaCl) at pH 6.5 and 8.5. Additionally, 3 salts (one composed solely of NaCl, another commercial sea salt from the southern Europe and, finally, a natural salt from northern Europe) were also tested. Principal component analysis structured the chemical and microbiology data in 3 clusters: (1) an extreme cluster, formed by cod brined in the commercial sea salt, which achieved the highest microbiological counts, namely 4.1 log CFU/g on plate count agar (PCA) and 1250 coliforms/g; (2) an intermediate cluster composed of cod salted in brine containing 50% NaCl, 0.4% MgCl₂, and 49.6% KCl (pH 6.5); and (3) a central cluster, including all the other treatments, which presented the lowest microbiological counts, namely 2.4 log CFU/g on PCA and 20 coliforms/g. Although the batches of the intermediate cluster presented slightly higher total viable and staphylococci counts than the central cluster, the presence of Mg and K ions improved the color of the salted product. In the assayed concentrations, CaCl₂, MgCl₂, and KCl can be used in the brining of cod without adversely affecting the microbiological and sensory quality of the salted cod.     

Aerobiology of a high-line speed cattle abattoir

The operation of the high-line speed cattle abattoir studied follows a plant-created hazard analysis and critical control point (HACCP) plan that is recognized by the Canadian Food Inspection Agency. Measurement of bioaerosols is not a part of this plan. In this study CFUs in air of selected abattoir processes were enumerated after impinging air onto tryptic soy agar plates with a slit air sampler for 10 to 20 min. The total viable count (TVC) per liter of air was calculated for each sample following incubation at 30 degrees C for 24 h. Monthly samples were collected on the hide removal floor and the carcass dressing floor from March 1998 to April 1999. Mud tag, dirt, and wetness of incoming hides were scored subjectively on the hide removal floor. The other processes were sampled in 3 separate months. The TVC at two locations on the hide removal floor (center of hide removal floor [CHF] and top of hide puller [THP]) had a strong association to each other (r = 0.84; P < 0.001). The mean TVC at the CHF and THP was 10.0 and 11.5, respectively, and the TVC for individual samples ranged from 2 to 42 at these locations. The TVC means for all the other processes ranged from 0.01 to 0.7. Tag and TVC on the hide removal floor had a different seasonal distribution with TVC being highest in the warm months (April to October 1998) and lowest for November to April 1999. No significant relations between TVC and the dirt and wetness variables were evident for the CHF and THP locations on the hide removal floor. It was concluded that the control of aerosols in the hide removal floor should be treated as a critical control point in the HACCP plan.     

Electrical properties of colloidal polyaniline‐2‐naphthalene sulfonic acid/graphene nanoparticle composite films

Polyaniline (PANI) nanocomposites containing different weight percentages of graphene (GR) are chemically prepared in the presence of β‐naphthalene sulfonic acid (NSA) and characterized using attenuated total reflectance Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, and X‐ray diffraction. The characterization results suggest that the composites are formed via the interconnected fibrillar structure forming the semi‐crystalline/amorphous configuration by the β‐napthalene sulfonic acid (β‐NSA). The conductivities of the composites suggest that the composites undergo by two different regions of I and II before and after 378 K. The electrical conductivity of the composites is increased by increasing temperature. The dependence of conductivity on temperature implies that the PANI‐NSA/GR composites are organic semiconductors. POLYM. COMPOS., 35:60–67, 2014. © 2013 Society of Plastics Engineers     

An efficient one-step lookahead A* algorithm for PM-CT scheduling problems

In this paper, we present an improved one-step lookahead A* algorithm for the scheduling problem for parallel-mode cluster tools, where n wafer types are simultaneously processed on a cluster tool with m chambers. Specifically, we suggest a refined cost function, priority-based node selection, N-chamber cycle detection to identify deadlock situations, and a one-step lookahead method to reduce the number of unsafe states generated. Using numerical experiments, we show that the proposed algorithm leads to a significant reduction in the number of explored states and execution time necessary to find an optimal solution.     

Temperature Effects on a Non-Volatile Memory Device with Ferroelectric Capacitor

The temperature effects on a ferroelectric non-volatile memory latch were measured. The device is based on a design from Radiant Technologies Inc. utilizing a discrete ferroelectric capacitor. The effects measured include functionality, I-V characteristics and retention. The range of temperatures for which the device was tested is –107°F to +302°F. The results are compared with measurements made at room temperature for the device. Retention measurements of the device at elevated temperatures allow predictions of retention performance under normal operating conditions. Potential applications of this device in harsh environments which include aerospace, industrial and automotive are presented.