Open-air sprays for capturing and controlling airborne float coal dust on longwall faces.

Float dust deposits in coal mine return airways pose a risk in the event of a methane ignition. Controlling airborne dust prior to deposition in the return would make current rock dusting practices more effective and reduce the risk of coal-dust-fueled explosions. The goal of this U.S. National Institute for Occupational Safety and Health study is to determine the potential of open-air water sprays to reduce concentrations of airborne float coal dust, smaller than 75 µm in diameter, in longwall face airstreams. This study evaluated unconfined water sprays in a featureless tunnel ventilated at a typical longwall face velocity of 3.6 m/s (700 fpm). Experiments were conducted for two nozzle orientations and two water pressures for hollow cone, full cone, flat fan, air atomizing and hydraulic atomizing spray nozzles. Gravimetric samples show that airborne float dust removal efficiencies averaged 19.6 percent for all sprays under all conditions. The results indicate that the preferred spray nozzle should be operated at high fluid pressures to produce smaller droplets and move more air. These findings agree with past respirable dust control research, providing guidance on spray selection and spray array design in ongoing efforts to control airborne float dust over the entire longwall ventilated opening.

Foam property tests to evaluate the potential for longwall shield dust control.

Tests were conducted to determine properties of four foam agents for their potential use in longwall mining dust control. Foam has been tried in underground mining in the past for dust control and is currently being reconsidered for use in underground coal longwall operations in order to help those operations comply with the Mine Safety and Health Administration's lower coal mine respirable dust standard of 1.5 mg/m3. Foams were generated using two different methods. One method used compressed air and water pressure to generate foam, while the other method used low-pressure air generated by a blower and water pressure using a foam generator developed by the U.S. National Institute for Occupational Safety and Health. Foam property tests, consisting of a foam expansion ratio test and a water drainage test, were conducted to classify foams. Compressed-air-generated foams tended to have low expansion ratios, from 10 to 19, with high water drainage. Blower-air-generated foams had higher foam expansion ratios, from 30 to 60, with lower water drainage. Foams produced within these ranges of expansion ratios are stable and potentially suitable for dust control. The test results eliminated two foam agents for future testing because they had poor expansion ratios. The remaining two foam agents seem to have properties adequate for dust control. These material property tests can be used to classify foams for their potential use in longwall mining dust control.

Characterization of airborne float coal dust emitted during continuous mining, longwall mining and belt transport.

Float coal dust is produced by various mining methods, carried by ventilating air and deposited on the floor, roof and ribs of mine airways. If deposited, float dust is re-entrained during a methane explosion. Without sufficient inert rock dust quantities, this float coal dust can propagate an explosion throughout mining entries. Consequently, controlling float coal dust is of critical interest to mining operations. Rock dusting, which is the adding of inert material to airway surfaces, is the main control technique currently used by the coal mining industry to reduce the float coal dust explosion hazard. To assist the industry in reducing this hazard, the Pittsburgh Mining Research Division of the U.S. National Institute for Occupational Safety and Health initiated a project to investigate methods and technologies to reduce float coal dust in underground coal mines through prevention, capture and suppression prior to deposition. Field characterization studies were performed to determine quantitatively the sources, types and amounts of dust produced during various coal mining processes. The operations chosen for study were a continuous miner section, a longwall section and a coal-handling facility. For each of these operations, the primary dust sources were confirmed to be the continuous mining machine, longwall shearer and conveyor belt transfer points, respectively. Respirable and total airborne float dust samples were collected and analyzed for each operation, and the ratio of total airborne float coal dust to respirable dust was calculated. During the continuous mining process, the ratio of total airborne float coal dust to respirable dust ranged from 10.3 to 13.8. The ratios measured on the longwall face were between 18.5 and 21.5. The total airborne float coal dust to respirable dust ratio observed during belt transport ranged between 7.5 and 21.8.

Sampling and analysis method for measuring airborne coal dust mass in mixtures with limestone (rock) dust.

Airborne coal dust mass measurements in underground bituminous coal mines can be challenged by the presence of airborne limestone dust, which is an incombustible dust applied to prevent the propagation of dust explosions. To accurately measure the coal portion of this mixed airborne dust, the National Institute for Occupational Safety and Health (NIOSH) developed a sampling and analysis protocol that used a stainless steel cassette adapted with an isokinetic inlet and the low temperature ashing (LTA) analytical method. The Mine Safety and Health Administration (MSHA) routinely utilizes this LTA method to quantify the incombustible content of bulk dust samples collected from the roof, floor, and ribs of mining entries. The use of the stainless steel cassette with isokinetic inlet allowed NIOSH to adopt the LTA method for the analysis of airborne dust samples. Mixtures of known coal and limestone dust masses were prepared in the laboratory, loaded into the stainless steel cassettes, and analyzed to assess the accuracy of this method. Coal dust mass measurements differed from predicted values by an average of 0.5%, 0.2%, and 0.1% for samples containing 20%, 91%, and 95% limestone dust, respectively. The ability of this method to accurately quantify the laboratory samples confirmed the validity of this method and allowed NIOSH to successfully measure the coal fraction of airborne dust samples collected in an underground coal mine.

Relationship between innervation zone width and mean muscle fiber conduction velocity during a sustained isometric contraction.

OBJECTIVES: To examine the relationship between the biceps brachii muscle innervation zone (IZ) width and the mean muscle fiber conduction velocity (MFCV) during a sustained isometric contraction. METHODS: Fifteen healthy men performed a sustained isometric elbow flexion exercise at their 60% maximal voluntary contraction (MVC) until they could not maintain the target force. Mean MFCV was estimated through multichannel surface electromyographic recordings from a linear electrode array. Before exercise, IZ width was quantified. Separate non-parametric one-way analyses of variance (ANOVAs) were used to examine whether there was a difference in each mean MFCV variable among groups with different IZ width. In addition, separate bivariate correlations were also performed to examine the relationships between the IZ width and the mean MFCV variables during the fatiguing exercise. RESULTS: There was a significant difference in the percent decline of mean MFCV (%ΔMFCV) among groups with different IZ width (χ(2) (3)=11.571, p=0.009). In addition, there was also a significant positive relationship between the IZ width and the %ΔMFCV (Kendall's tau= 0.807; p<0.001). CONCLUSIONS: We believe that such relationship is likely influenced by both muscle fiber size and the muscle fiber type composition.

Reduced susceptibility to eccentric exercise-induced muscle damage in resistance-trained men is not linked to resistance training-related neural adaptations.

The purpose of this study was to examine the acute effects of maximal concentric vs. eccentric exercise on the isometric strength of the elbow flexor, as well as the biceps brachii muscle electromyographic (EMG) responses in resistance-trained (RT) vs. untrained (UT) men. Thirteen RT men (age: 24 ± 4 years; height: 180.2 ± 7.7 cm; body weight: 92.2 ± 16.9 kg) and twelve UT men (age: 23 ± 4 years; height: 179.2 ± 5.0 cm; body weight: 81.5 ± 8.6 kg) performed six sets of ten maximal concentric isokinetic (CON) or eccentric isokinetic (ECC) elbow flexion exercise in two separate visits. Before and after the exercise interventions, maximal voluntary contractions (MVCs) were performed for testing isometric strength. In addition, bipolar surface EMG signals were detected from the biceps brachii muscle during the strength testing. Both CON and ECC caused isometric strength to decrease, regardless of the training status. However, ECC caused greater isometric strength decline than CON did for the UT group (p = 0.006), but not for the RT group. Both EMG amplitude and mean frequency significantly decreased and increased, respectively, regardless of the training status and exercise intervention. Resistance-trained men are less susceptible to eccentric exercise-induced muscle damage, but this advantage is not likely linked to the chronic resistance training-induced neural adaptations.

Evaluations of bit sleeve and twisted-body bit designs for controlling roof bolter dust.

Drilling into coal mine roof strata to install roof bolts has the potential to release substantial quantities of respirable dust. Due to the proximity of drill holes to the breathing zone of roof bolting personnel, dust escaping the holes and avoiding capture by the dust collection system pose a potential respiratory health risk. Controls are available to complement the typical dry vacuum collection system and minimize harmful exposures during the initial phase of drilling. This paper examines the use of a bit sleeve in combination with a dust-hog-type bit to improve dust extraction during the critical initial phase of drilling. A twisted-body drill bit is also evaluated to determine the quantity of dust liberated in comparison with the dust-hog-type bit. Based on the results of our laboratory tests, the bit sleeve may reduce dust emissions by one-half during the initial phase of drilling before the drill bit is fully enclosed by the drill hole. Because collaring is responsible for the largest dust liberations, overall dust emission can also be substantially reduced. The use of a twisted-body bit has minimal improvement on dust capture compared with the commonly used dust-hog-type bit.

Influences of dynamic exercise on force steadiness and common drive.

OBJECTIVES: To investigate the influences of dynamic exercise on force steadiness and common drive to motor units. METHODS: Seventeen men (age 24±4 years; height 181.7±5.7 cm; mass 89.6±14.9 kg) performed 6 sets of 10 repetitions of maximal isokinetic concentric (CON) or eccentric exercise (ECC) with their dominant elbow flexors on separate experimental visits. Before and after the interventions, maximal strength testing and submaximal trapezoid isometric contractions were performed. To quantify force steadiness, we calculated the amplitude of force fluctuations in the flat area of the submaximal trapezoid contractions. In addition, surface electromyographic (EMG) signals from the same portion where we calculated the force steadiness were decomposed into individual motor unit action potential trains. The mean firing rate curves of the detected motor units were then cross-correlated with one another to quantify the common drive. RESULTS: Although both interventions induced similar strength losses, the ECC caused greater force fluctuations (p=0.002). In addition, unlike the CON, which did not cause any changes in the common drive, the ECC induced an increased common drive to motor units. CONCLUSIONS: We believe that the increased common drive is an important factor causing greater force fluctuations following the ECC.

Endothelial apoptosis in Braf-deficient mice.

Tyrosine kinase growth factor receptors and Ras/Raf/MEK/MAPK signalling have been implicated in the suppression as well as augmentation of programmed cell death. In addition, a Ras-independent role for Raf as a suppressor of programmed cell death has been suggested by the recent finding that Craf1 interacts with members of the Bcl-2 family at mitochondrial membranes. However, genetic studies of C. elegans and Drosophila, as well as the targeted mutagenesis of the murine Araf gene, have failed to support such a role. Here we show that mice with a targeted disruption in the Braf gene die of vascular defects during mid-gestation. Braf -/- embryos, unlike Araf -/- or Craf1 -/- embryos (L.W. et al., unpublished), show an increased number of endothelial precursor cells, dramatically enlarged blood vessels and apoptotic death of differentiated endothelial cells. These results establish Braf as a critical signalling factor in the formation of the vascular system and provide the first genetic evidence for an essential role of Raf gene in the regulation of programmed cell death.

Cross-talk among monopolar surface electromyographic signals from the superficial quadriceps femoris muscles.

This study used a within-subjects design. The purpose of this study was to examine cross-talk among monopolar surface electromyographic (EMG) signals from the superficial quadriceps femoris muscles. The "efficiency of electrical activity" technique for assessing muscle function uses monopolar EMG. Thus, knowledge of the potential for cross-talk among the superficial quadriceps femoris muscles when using monopolar recording will be valuable in rehabilitative settings. Fourteen healthy men (mean +/- SD age = 22.0 +/- 3.9 years) volunteered to perform submaximal to maximal isometric muscle actions of the dominant leg extensors in 10% increments from 10% to 100% of the maximum voluntary contraction (MVC). During each muscle action, monopolar surface EMG signals were detected from the superficial quadriceps femoris muscles. Three separate cross-correlations were performed to examine cross-talk among the vastus lateralis and rectus femoris, vastus medialis and rectus femoris, and vastus lateralis and vastus medialis. The peak cross-correlation coefficients ranged from R(x,y) = 0.182-0.944, with the greatest cross-talk occurring between the vastus lateralis and vastus medialis. In addition, the cross-correlation coefficients generally increased with force. These findings showed moderate to large degrees of crosstalk among monopolar surface EMG signals from the superficial quadriceps femoris muscles. Thus, the monopolar EMG signals from these muscles should be interpreted carefully and with the understanding that at least a portion of the signal from each muscle is due to cross-talk.

Linearity and reliability of the EMG amplitude versus dynamic torque relationships for the superficial quadriceps femoris muscles.

PURPOSE: The purpose of the present investigation was to determine the linearity and reliability of the electromyographic (EMG) amplitude versus dynamic torque relationships for the vastus lateralis (VL), rectus femoris (RF), and vastus medialis (VM). METHODS: Nine healthy men (mean +/- SD age = 25.3 +/- 4.7 years) and eleven healthy women (mean +/- SD age = 22.0 +/- 1.3 years) performed a series of randomly ordered, submaximal to maximal, concentric isokinetic muscle actions of the leg extensors at 30 degrees x s(1) on two occasions separated by at least 48 hours. During each muscle action, surface EMG signals were detected from the VL, RF and VM of the dominant thigh with bipolar surface electrode arrangements. RESULTS: The coefficients of determination for the EMG amplitude versus dynamic torque relationships ranged from r2 = 0.75-0.98 and 0.64-0.99 for the VL, r2 = 0.79-0.99 and 0.60-0.98 for the RFE and r2 = 0.44-0.98 and 0.51-0.98 for the VM for trials 1 and2, respectively. In some cases, the linear EMG amplitude versus torque slope coefficient for trial 1 was significantly different from that for trial 2 for the VL and RF, but not for the VM. The intraclass correlation coefficients for the linear EMG amplitude versus torque coefficients were 0.730 (VL), 0.709 (RF), and 0.888 (VM). CONCLUSION: These results indicated that the EMG amplitude versus dynamic torque relationships for the superficial quadriceps femoris muscles did not demonstrate enough linearity and reliability to be used for examining the contributions of neural versus hypertrophic factors to training-induced strength gains.

Prevention of SIV infection in macaques by (R)-9-(2-phosphonylmethoxypropyl)adenine.

The efficacy of pre- and postexposure treatment with the antiviral compound (R)-9-(2-phosphonylmethoxypropyl)adenine (PMPA) was tested against simian immunodeficiency virus (SIV) in macaques as a model for human immunodeficiency virus (HIV). PMPA was administered subcutaneously once daily beginning either 48 hours before, 4 hours after, or 24 hours after virus inoculation. Treatment continued for 4 weeks and the virologic, immunologic, and clinical status of the macaques was monitored for up to 56 weeks. PMPA prevented SIV infection in all macaques without toxicity, whereas all control macaques became infected. These results suggest a potential role for PMPA prophylaxis against early HIV infection in cases of known exposure.

MMG-EMG cross spectrum and muscle fiber type.

The purpose of this study was to investigate fiber type-related differences in the patterns of responses for mechanomyographic-electromyographic (MMG-EMG) cross spectrum mean power frequency (MPF) in resistance-trained and aerobically-trained subjects during a fatiguing muscle action. Five resistance-trained and five aerobically-trained men performed a 45-s isometric muscle action of the dominant leg extensors at 50% MVC while MMG and EMG signals were recorded simultaneously from the vastus lateralis muscle. In addition, a biopsy was taken to determine the myosin heavy chain (MHC) isoform content of the vastus lateralis. The resistance-trained and aerobically-trained subjects demonstrated similar patterns of responses for MMG-EMG cross spectrum MPF during the sustained muscle action. The vastus lateralis of the resistance-trained subjects demonstrated primarily Type II MHC isoform expression, indicative of fast-twitch muscle fibers, while that of the aerobically-trained subjects was composed mostly of Type I MHC isoform expression, indicative of slow-twitch fibers. Thus, the differences in fiber type characteristics were not manifested in the patterns of responses for MMG-EMG cross spectrum MPF.

Effects of static stretching on the hamstrings-to-quadriceps ratio and electromyographic amplitude in men.

AIM: The purpose of this study was to examine the effects of posterior thigh and leg stretching on leg flexion peak torque (PT), leg extension PT, the hamstrings-to-quadriceps (H:Q) ratio, and electromyographic (EMG) amplitude of the hamstrings and quadriceps in recreationally-active men. METHODS: Fifteen men (mean age + or - SD = 22.0 + or - 4.4 years; body mass = 82.7 + or - 16.1 kg; height = 173.1 + or - 6.8 cm) performed three maximal voluntary concentric isokinetic leg extension and flexion muscle actions at three randomly ordered angular velocities (60, 180, and 300 degrees x s(-1)) before and after hamstring and calf static stretching. The stretching protocol consisted of 1 unassisted and 3 assisted static stretching exercises designed to stretch the posterior muscles of the thigh and leg. Four repetitions of each stretch were held for 30 s with 20-s rest between repetitions. RESULTS: These findings indicated no significant (P>0.05) stretching-induced changes in leg flexion PT, leg extension PT, or EMG amplitude at 60, 180, or 300 degrees .s-1. However, the non-significant (P>0.05) 2-4% increases in leg extension PT combined with the non-significant (P>0.05) 1-2% decreases in leg flexion PT resulted in the significant (P < or = 0.05) 2-9% decreases in the H:Q ratio from pre- to post-stretching for all three velocities. CONCLUSIONS: These findings suggested that static stretching of the hamstrings and calf muscles may decrease the H:Q ratio. These results may be useful for athletic trainers, physical therapists, and other allied health professionals who may use the H:Q ratio as a clinical assessment.

An examination of the frequency-specific behavior of the mechanomyographic amplitude versus isometric torque relationship.

The purpose of this study was to examine the patterns of responses for mechanomyographic (MMG) amplitude versus isometric torque in different frequency bands for the vastus lateralis (VL), rectus femoris (RF), and vastus medialis (VM) muscles. Eleven men (mean +/- SD age = 20.1 +/- 1.1 yrs) performed submaximal to maximal isometric step muscle actions of the dominant leg extensors from 10% to 100% of the maximum voluntary contraction (MVC). During each muscle action, three separate surface mechanomyographic (MMG) signals were detected from the VL, RF and VM. Each MMG signal was decomposed into 9 different frequency bands (5-15, 15-25, 25-35, 35-45, 45-55, 55-65, 65-75, 75-85, and 85-95 Hz), and the root-mean-square amplitude of the signal in each frequency band was calculated. The results showed that for the VL and RF muscles, MMG amplitude plateaued from 80-100% MVC in the 15-25 and 25-35 Hz frequency bands. For the VM, however, the plateau in MMG amplitude from 80-100% MVC occurred in the 5-15 and 15-25 Hz bands. These findings indicated that there were both muscle- and frequency-specific discrepancies in the MMG amplitude versus isometric torque relationship that could be due to differences in muscle architecture and/or fiber type composition.

Wavelet-based analysis of surface mechanomyographic signals from subjects with differences in myosin heavy chain isoform content.

The purpose of this study was to use a wavelet analysis designed specifically for surface mechanomyographic (MMG) signals to determine if the % myosin heavy chain (MHC) isoform content affected the shape of the MMG frequency spectrum during isometric muscle actions. Five resistance-trained (mean +/- SD age = 23.2 +/-3.7 yrs), five aerobically-trained (mean +/- SD age = 32.6 +/- 5.2 yrs), and five sedentary (mean +/- SD age = 23.4 +/- 4.1 yrs) men performed isometric muscle actions of the dominant leg extensors at 20%, 40%, 60%, 80%, and 100% of the maximum voluntary contraction (MVC). Surface MMG signals were detected from the vastus lateralis during each muscle action and processed with the MMG wavelet analysis. In addition, muscle biopsies were taken from the vastus lateralis and analyzed for % MHC isoform content. The results showed that there were distinct differences among the three groups of subjects for % MHC isoform content. These differences were not manifested, however, in the isometric force-related changes in the total intensity of the MMG signal in each wavelet band. It is possible that factors such as the thicknesses of the subcutaneous adipose tissue and/or iliotibial band reduced the potential influence of differences in % MHC isoform content on the MMG signal.

The effect of pedaling cadence and power output on mechanomyographic amplitude and mean power frequency during submaximal cycle ergometry.

The purpose of this study was to examine the effects of power output and pedaling cadence on the amplitude and mean power frequency (MPF) of the mechanomyographic (MMG) signal during submaximal cycle ergometry. Nine adults (mean age +/- SD = 22.7 +/- 2.1 yrs) performed an incremental (25 W increase every min) test to exhaustion on an electronically braked cycle ergometer to determine VO2Peak and Wpeak. The subjects also performed three, 8 min continuous, constant power output rides (randomly ordered) at 35%, 50%, and 65% Wpeak. The continuous 8 min workbouts were divided into 4 min epochs. The subjects pedaled at either 50 or 70 rev x min(-1) (randomized) during the first 4 min epoch, then changed to the alternate cadence during the second 4 min epoch. The MMG signal was recorded from the vastus lateralis during the final 10 s of each minute. Two separate two-way [cadence (50 and 70 rev x min(-1)) x %Wpeak (35, 50, and 65)] repeated measures ANOVAs indicated that MMG amplitude followed power output, but not pedaling cadence, whereas MMG MPF was not consistently affected by power output or pedaling cadence. Furthermore, these findings suggested that power output was modulated by motor unit recruitment and not rate coding.

Molecular organization of the human Raf-1 promoter region.

A genomic DNA fragment containing the Raf-1 promoter region was isolated by using a cDNA extension clone. Nucleotide sequencing of genomic DNA clones, primer extension, and S1 nuclease assays have been used to identify the 5' ends of Raf-1 RNAs. Consistent with its ubiquitous expression, the Raf-1 promoter region had features of a housekeeping gene in that it was GC-rich (HTF-like), lacked TATA and CAAT boxes, and contained heterogeneous RNA start sites and four potential binding sites for the transcription factor SP1. In addition, an octamer motif (ATTTCAT), a potential binding site for the octamer family of transcription factors, was located at -734 base pairs. The Raf-1 promoter region drove reporter gene expression 30-fold over the promoterless reporter in Cos 7 cells.

Mutational activation of c-raf-1 and definition of the minimal transforming sequence.

A series of wild-type and mutant raf genes was transfected into NIH 3T3 cells and analyzed for transforming activity. Full-length wild-type c-raf did not show transforming activity. Two types of mutations resulted in oncogenic activity similar to that of v-raf: truncation of the amino-terminal half of the protein and fusion of the full-length molecule to gag sequences. A lower level of activation was observed for a mutant with a tetrapeptide insertion mapping to conserved region 2 (CR2), a serine- and threonine-rich domain located 100 residues amino-terminal of the kinase domain. To determine essential structural features of the transforming region of raf, we analyzed point and deletion mutants of v-raf. Substitutions of Lys-56 modulated the transforming activity, whereas mutation of Lys-53, a putative ATP binding residue, abolished it. Deletion analysis established that the minimal transforming sequence coincided precisely with CR3, the conserved Raf kinase domain. Thus, oncogenic activation of the Raf kinase can be achieved by removal of CR1 and CR2 or by steric distortion and requires retention of an active kinase domain. These findings are consistent with a protein structure model for the nonstimulated enzyme in which the active site is buried within the protein.

The influence of muscle fiber type composition on the patterns of responses for electromyographic and mechanomyographic amplitude and mean power frequency during a fatiguing submaximal isometric muscle action.

The purpose of this investigation was to examine the influence of muscle fiber type composition on the patterns of responses for electromyographic (EMG) and mechanomyographic (MMG) amplitude and mean power frequency (MPF) during a fatiguing submaximal isometric muscle action. Five resistance-trained (mean +/- SD age = 23.2 +/- 3.7 yrs) and five aerobically-trained (mean +/- SD age = 32.6 +/- 5.2 yrs) men volunteered to perform a fatiguing, 30-sec submaximal isometric muscle action of the leg extensors at 50% of the maximum voluntary contraction (MVC). Muscle biopsies from the vastus lateralis revealed that the myosin heavy chain (MHC) composition for the resistance-trained subjects was 59.0 +/- 4.2% Type IIa, 0.1 +/- 0.1% Type IIx, and 40.9 +/- 4.3% Type I. The aerobically-trained subjects had 27.4 +/- 7.8% Type IIa, 0.0 +/- 0.0% Type IIx, and 72.6 +/- 7.8% Type I MHC. The patterns of responses and mean values for absolute and normalized EMG amplitude and MPF during the fatiguing muscle action were similar for the resistance-trained and aerobically-trained subjects. The resistance-trained subjects demonstrated relatively stable levels for absolute and normalized MMG amplitude and MPF across time, but the aerobically-trained subjects showed increases in MMG amplitude and decreases in MMG MPE The absolute MMG amplitude and MPF values for the resistance-trained subjects were also greater than those for the aerobi-cally-trained subjects. These findings suggested that unlike surface EMG, MMG may be a useful noninvasive technique for examining fatigue-related differences in muscle fiber type composition.