Physico-Chemical Studies of Silica of Small Particle Size

Aim of Research: to develop and evaluate an apparatus for the investigation of the air-settling characteristics of silica dusts of size dangerous to health, to examine its use for the investigation of certain factors connected with dust suppression and to examine other appropriate applications of the apparatus. 1. A brief account is given of the supersedure of the 'Mechanical Theory' by the 'Solubility Theory' of silicosis, and mention is made of some practical problems associated with the measurement of dust suppression and health hazard. 2. The preparation of graded silica particles and fine mineral dusts, including sizes dangerous to health, by sedimentation from water or ethanol is described. 3. An apparatus for the examination of the air-settling characteristics of fine silica, consisting of a dust chamber into which the dust is injected and dispersed and incorporating a pair of compensated photo-electric cells connected in opposition and to a mirror galvanometer, is described. A beam of light traverses the dust cloud and is picked up by one cell; the other cell picks up the beam uninterrupted by dust. The presence of dust in the chamber therefore produces a differential current which is measured by the galvanometer. 4. Using the prepared silica dusts in the apparatus, a technique has been developed which gives the following information from settling curves obtained by plotting galvanometer readings (converted to a percentage basis) against time; 1. Settling Factors, which for the majority of dusts, are approximately proportional to specific surface and to rates of settliig of the dust clouds. Settling Factors may be used to compare different dusts or the effect of various factors on any particular dust. 2. A measure of the average terminal velocity of a dust under the turbulent conditions obtaining in the dust chamber. The texminal velocity, if the average particle size of the dust is known, gives an indication of the extent of aggregation of the particles in the dust cloud, modified by the fact that the measured terminal velocity, being affected by convection and diffusion, is lower than that which would be observed under calm conditions. Particles of the size ca. 1 and 1-3 microns show considerable aggregation in the chamber but the larger grades (3-5 and 5-10 microns) show a much lesser degree of aggregation. 5. An account is given of the preparation, measurement and use in the dust apparatus, of aqueous sprays of known droplet size as dust suppressing agents and the following conclusions drawn: 1. Suppressing efficiency as measured by the Settling Factors does not change very markedly over the droplet size range 30-110 microns; the smaller droplets are slightly more effective but dust reduction is less than 50%. Dusts with particle size ca. 1 micron undergo the greatest reduction. 2. Under similar conditions the use of aqueous sprays containing various commercial wetting agents brings about a greater degree of reduction (60-70%). 3. With water sprays only, little or no actual wetting occurs, and reduction is presumably due mainly to the 'sweeping' action of the descending spray droplets. With sprays containing wetting agents, the effect is augmented by increased wetting of the dust particles. 6. Two other factors connected with dust suppression, namely, the effect of increased relative humidity, and of mixing mineral dusts with silica, were investigated. Increased relative humidity has no effect on the rates of settling of fine silica. The results obtained by mixing silica with certain mineral dusts of known specific surface do not confirm reports which state that the rates of sedimentation of certain mineral-silica mixtures are greater than the rates for the separate constituents of the mixtures. 7. The apparatus has also been applied to the measurement of the specific surface of small amounts (ca. 0.05 g.) of dust. By plotting Settling Factors against the known specific surfaces of the prepared dusts a calibration curve is prepared by means of which the specific surface of an unknown dust may be determined (accuracy, ca.+/-5%). The method is independent of the known decreased light extinction by particles under ca. 1 micron in size - a defect inherent in the usual light extinction methods of surface measurement. Certain dusts, however, settle unexpectedly slowly, leading to overestimation of specific surface. Such anomalous dusts contained less than 50% by weight of fine particles, the balance consisting of particles with a diameter at least 5 microns greater. It is suggested that the effect is due to deaggregation of the aggregated small particles by the larger. From the work completed it is suggested that two types of dispersion are related to every dust. One which depends on the method of dispersion and one which depends on the size and distribution of the particles and is inherent to the dust. 8. The South Wales method for the evaluation of health hazard is discussed and figures given by this method compared with Settling Factors for dusts of similar specific surface. The South Wales figures and the Settling Factors are almost identical, but the Settling Factors for anomalous dusts are considerably higher, and it is suggested that the Settling Factors give an equally effective and, in some cases, better measure of the health hazard, since they take account of dispersion in air. 9. An account is given of the methods of specific surface and particle size measurement used in the research. 10. Suggestions are made in a general discussion for future work

Organic Toxicity

In recent years there has been much discussion on the subject of organic matter toxicity and its relation to the severity of black root rot of tobacco. Organic matter toxicity is due to or at least related to toxins produced during organic matter decomposition

Plant Beds

Due to the occurrence of blue mold and manganese toxicity in some of the plant beds this last spring, it is probably advisable for all growers to select a new site for the 1964 crop. Blue mold is a fungus disease which sometimes causes severe damage to tobacco seedings just prior to setting time. The fungus will produce heavy-walled spores on the dying or dead leaves. These spores are capable of remaining in the soil at least a year and attacking the next crop of plants if the same site is used again for tobacco plants

A New Black Shank Resistant Hybrid

Seed of a new black shank resistant burley hybrid will be available to growers in 1964. This hybrid is especially for farmers who cannot rotate their tobacco land and . thus, are forced to set their crop in a black shank infested field. The hybrid is a cross between two black shank resistant varieties, MS L8 and Burley 37. The female parent , MS L8, carries black shank resistance from a wild relative of tobacco

Calcium Deficiency Symptoms in Burley Tobacco

Calcium is an element required by all higher plants in relatively large quantities. It appears to be closely related to the formation of buds and flowers. Calcium is usually available in sufficient quantities in Kentucky soils to produce a normal crop of tobacco. However, when certain varieties of burley tobacco commence to bloom and produce suckers, the tips of the calyx lobes of the flowers may turn brown and die and the edges of the small leaves of the suckers may be necrotic, resulting in irregularly shaped sucker leaves. In severe cases the apical bud may be killed. These calcium deficiency symptoms are most often observed during periods of stress such as protracted dry periods. This condition has been found to be heritable and is apparently caused by the improper utilization by the plant rather than the lack of calcium in the soil

Fall Treatment of Tobacco Beds with Methyl Bromide

Treating tobacco beds with methyl bromide for the purpose of killing weed seed has become very popular in recent years. The gas is effective except on the seed of white clover and when the soil temperature is below 50° F

Sensory-Feedback Exoskeletal Arm Controller

An electromechanical exoskeletal arm apparatus has been designed for use in controlling a remote robotic manipulator arm. The apparatus, called a force-feedback exoskeleton arm master (F-EAM) is comfortable to wear and easy to don and doff. It provides control signals from the wearer s arm to a robot arm or a computer simulator (e.g., a virtual-reality system); it also provides force and torque feedback from sensors on the robot arm or from the computer simulator to the wearer s arm. The F-EAM enables the wearer to make the robot arm gently touch objects and finely manipulate them without exerting excessive forces. The F-EAM features a lightweight design in which the motors and gear heads that generate force and torque feedback are made smaller than they ordinarily would be: this is achieved by driving the motors to power levels greater than would ordinarily be used in order to obtain higher torques, and by providing active liquid cooling of the motors to prevent overheating at the high drive levels. The F-EAM (see figure) includes an assembly that resembles a backpack and is worn like a backpack, plus an exoskeletal arm mechanism. The FEAM has five degrees of freedom (DOFs) that correspond to those of the human arm: 1. The first DOF is that of the side-to-side rotation of the upper arm about the shoulder (rotation about axis 1). The reflected torque for this DOF is provided by motor 1 via drum 1 and a planar four-bar linkage. 2. The second DOF is that of the up-and-down rotation of the arm about the shoulder. The reflected torque for this DOF is provided by motor 2 via drum 2. 3. The third DOF is that of twisting of the upper arm about its longitudinal axis. This DOF is implemented in a cable remote-center mechanism (CRCM). The reflected torque for this DOF is provided by motor 3, which drives the upper-arm cuff and the mechanism below it. A bladder inflatable by gas or liquid is placed between the cuff and the wearer s upper arm to compensate for misalignment between the exoskeletal mechanism and the shoulder. 4. The fourth DOF is that of flexion and extension of the elbow. The reflected torque for this DOF is provided by motor 4 and drum 4, which are mounted on a bracket that can slide longitudinally by a pin-and-slot engagement with the upper-arm cuff to compensate for slight variations in the position of the kinematic center of the elbow. Attached to drum 4 is an adapter plate to which is attached a CRCM for the lower arm. 5. The lower-arm CRCM implements the fifth DOF, which is the twist of the forearm about its longitudinal axis. Motor 5 provides the reflected torque for this DOF by driving the lower-arm cuff. A rod transmits twist and torsion between the lower-arm cuff and the hand cuff. With this system, the motion of the wearer s joints and the reflected torques applied to these joints can be measured and controlled in a relatively simple manner. This is because the anthropomorphic design of the mechanism imitates the kinematics of the human arm, eliminating the need for kinematic conversion of joint-torque and joint-angle data

Exercise intolerance in chronic heart failure is not associated with impaired recovery of muscle function or submaximal exercise performance

Objectives.This study investigated whether recovery of skeletal muscle function is impaired in patients with heart failure and whether impaired recovery is associated with abnormal submaximal systemic exercise tolerance during repeated testing.Background.Patients with heart failure experience fatigue during daily activities. Because abnormalities of skeletal muscle play a role in their exercise intolerance, these symptoms may reflect a delay in muscle recovery and a resulting limitation in submaximal exercise tolerance.Methods.Two protocols were used. In protocol 1, knee extensor strength and endurance, and their recovery after fatiguing exercise, were evaluated in 11 patients (mean [±SEM] age 62 ± 5 years, New York Heart Association functional class 2.3 ± 0.2, ejection fraction 24 ± 5%) and in 10 age-matched sedentary control subjects. Protocol 2 examined the recovery of knee extensor endurance and submaximal exercise tolerance, as quantified on a self-powered treadmill, over 24 h in 18 patients (mean age 65 ± 3 years, functional class 2.4 ± 0.2, ejection fraction 23 ± 3%) and in 10 control subjects.Results.Peak oxygen consumption was reduced in both heart failure groups (15.4 ± 1.4 and 15.6 ± 1.0 ml/kg per min) compared with that in the respective control groups (23.1 ± 2.9 and 25.6 ± 1.0 ml/kg per min, both p < 0.05), as was muscle endurance but not muscle strength. In protocol 1, knee extensor endurance recovered more slowly in the patients than in control subjects (to 62 ± 4% and 87 ± 7% of the baseline value after 5 min, respectively, p < 0.05). In protocol 2, submaximal exercise tolerance was lower in the patients with heart failure than in control subjects (1,075 ± 116 vs. 1,390 ± 110 m), but knee extensor endurance and walking distance recovered fully by 10 and 30 min, respectively.Conclusions.Although these findings confirm earlier studies that demonstrated impaired muscle endurance in patients with heart failure, the results provide no evidence that recovery of either muscle function or submaximal exercise tolerance is delayed beyond the initial 5 to 10 min after exercise