Chemically stable new MAX phase V2SnC: a damage and radiation tolerant TBC material.

Using density functional theory, the phase stability and physical properties, including structural, electronic, mechanical, thermal and vibrational with defect processes, of a newly synthesized 211 MAX phase V2SnC are investigated for the first time. The obtained results are compared with those found in the literature for other existing M2SnC (M = Ti, Zr, Hf, Nb, and Lu) phases. The formation of V2SnC is exothermic and this compound is intrinsically stable in agreement with the experiment. V2SnC has potential to be etched into 2D MXene. The new phase V2SnC and existing phase Nb2SnC are damage tolerant. V2SnC is elastically more anisotropic than Ti2SnC and less than the other M2SnC phases. The electronic band structure and Fermi surface of V2SnC indicate the possibility of occurrence of its superconductivity. V2SnC is expected to be a promising TBC material like Lu2SnC. The radiation tolerance in V2SnC is better than that in Lu2SnC.

Ti2Au2C and Ti3Au2C2 formed by solid state reaction of gold with Ti2AlC and Ti3AlC2.

Incorporation of layers of noble metals in non-van der Waals layered materials may be used to form novel layered compounds. Recently, we demonstrated a high-temperature-induced exchange process of Au with Si in the layered phase Ti3SiC2, resulting in the formation of Ti3AuC2 and Ti3Au2C2. Here, we generalize this technique showing that Au/Ti2AlC and Au/Ti3AlC2 undergo an exchange reaction at 650 °C to form Ti2Au2C and Ti3Au2C2 and determine their structures by electron microscopy, X-ray diffraction, and ab initio calculations. These results imply that noble-metal-containing layered phases should be possible to synthesize in many systems. The metal to be introduced should be inert to the transition-metal carbide layers, and exhibit negative heat of mixing with the initial A element in a liquid phase or two-phase liquid/solid region at the annealing temperature.

Magnetic MAX phases from theory and experiments; a review.

This review presents MAX phases (M is a transition metal, A an A-group element, X is C or N), known for their unique combination of ceramic/metallic properties, as a recently uncovered family of novel magnetic nanolaminates. The first created magnetic MAX phases were predicted through evaluation of phase stability using density functional theory, and subsequently synthesized as heteroepitaxial thin films. All magnetic MAX phases reported to date, in bulk or thin film form, are based on Cr and/or Mn, and they include (Cr,Mn)2AlC, (Cr,Mn)2GeC, (Cr,Mn)2GaC, (Mo,Mn)2GaC, (V,Mn)3GaC2, Cr2AlC, Cr2GeC and Mn2GaC. A variety of magnetic properties have been found, such as ferromagnetic response well above room temperature and structural changes linked to magnetic anisotropy. In this paper, theoretical as well as experimental work performed on these materials to date is critically reviewed, in terms of methods used, results acquired, and conclusions drawn. Open questions concerning magnetic characteristics are discussed, and an outlook focused on new materials, superstructures, property tailoring and further synthesis and characterization is presented.

Phase stability of the nanolaminates V2Ga2C and (Mo1-xVx)2Ga2C from first-principles calculations.

We here use first-principles calculations to investigate the phase stability of the hypothetical laminated material V2Ga2C and the related alloy (Mo1-xVx)2Ga2C, the latter for a potential parent material for synthesis of (Mo1-xVx)2C, a new two-dimensional material in the family of so called MXenes. We predict that V2Ga2C is thermodynamically stable with respect to all identified competing phases in the ternary V-Ga-C phase diagram. We further calculate the stability of ordered and disordered configurations of Mo and V in (Mo1-xVx)2Ga2C and predict that ordered (Mo1-xVx)2Ga2C for x≤ 0.25 is stable, with an order-disorder transition temperature of ∼1000 K. Furthermore, (Mo1-xVx)2Ga2C for x = 0.5 and x≥ 0.75 is suggested to be stable, but only for disordered Mo-V configurations, and only at elevated temperatures. We have also investigated the electronic and elastic properties of V2Ga2C; the calculated bulk, shear, and Young's modulus are 141, 94, and 230 GPa, respectively.

A critical evaluation of GGA + U modeling for atomic, electronic and magnetic structure of Cr2AlC, Cr2GaC and Cr2GeC.

In this work we critically evaluate methods for treating electron correlation effects in multicomponent carbides using a GGA + U framework, addressing doubts from previous works on the usability of density functional theory in the design of magnetic MAX phases. We have studied the influence of the Hubbard U-parameter, applied to Cr 3d orbitals, on the calculated lattice parameters, magnetic moments, magnetic order, bulk modulus and electronic density of states of Cr2AlC, Cr2GaC and Cr2GeC. By considering non-, ferro-, and five different antiferromagnetic spin configurations, we show the importance of including a broad range of magnetic orders in the search for MAX phases with finite magnetic moments in the ground state. We show that when electron correlation is treated on the level of the generalized gradient approximation (U = 0 eV), the magnetic ground state of Cr2AC (A = Al, Ga, Ge) is in-plane antiferromagnetic with finite Cr local moments, and calculated lattice parameters and bulk modulus close to experimentally reported values. By comparing GGA and GGA + U results with experimental data we find that using a U-value larger than 1 eV results in structural parameters deviating strongly from experimentally observed values. Comparisons are also done with hybrid functional calculations (HSE06) resulting in an exchange splitting larger than what is obtained for a U-value of 2 eV. Our results suggest caution and that investigations need to involve several different magnetic orders before lack of magnetism in calculations are blamed on the exchange-correlation approximations in this class of magnetic MAX phases.

Magnetic self-organized atomic laminate from first principles and thin film synthesis.

The first experimental realization of a magnetic M(n+1)AX(n) (MAX) phase, (Cr(0.75)Mn(0.25))(2)GeC, is presented, synthesized as a heteroepitaxial single crystal thin film, exhibiting excellent structural quality. This self-organized atomic laminate is based on the well-known Cr(2)GeC, with Mn, a new element in MAX phase research, substituting Cr. The compound was predicted using first-principles calculations, from which a variety of magnetic behavior is envisaged, depending on the Mn concentration and Cr/Mn atomic configuration within the sublattice. The analyzed thin films display a magnetic signal at room temperature.

Hypertonic saline-dextran improves intestinal perfusion and survival in porcine endotoxin shock.

OBJECTIVE: To examine the effects of hypertonic (7.5%) saline-6% dextran 70 (HSD) and isotonic (0.9%) saline-6% dextran 70 (ISD) on cardiovascular function and intestinal perfusion in experimental endotoxin shock. DESIGN: Experimental, randomized, unblinded, interventional study. SETTING: University experimental animal laboratory. SUBJECTS: Anesthetized and mechanically ventilated landrace pigs (n = 24). INTERVENTIONS: Induction of endotoxin (ET) shock by infusion of Escherichia coil lipopolysaccharide endotoxin (serotype 0111: B4) followed by no fluid treatment (control; C) or small-volume (4 mL/kg) treatment with HSD or ISD. MEASUREMENTS AND MAIN RESULTS: Mean arterial pressure, central venous pressure, pulmonary artery pressure, pulmonary artery occlusion pressure, cardiac output, portal vein blood flow, intestinal microcirculation, intramucosal (regional) P(CO2), intestinal-arterial gap of CO2, and intramucosal pH were monitored, and blood gases were analyzed. Infusion of ET resulted in hypokinetic shock, which in untreated animals led to cardiovascular deterioration and a survival rate of only 33% at 300 mins after start of ET infusion. ISD treatment transiently improved hemodynamic variables and mucosal blood flow but did not affect the survival rate vs. C. Significant beneficial, long-lasting effects of HSD infusion on hemodynamics, especially on mucosal blood flow and intramucosal pH, were demonstrable, resulting in a survival rate of 86%. The relative risk of death at 300 mins was 1.20 for ISD vs. C and 0.17 for HSD vs. C. CONCLUSION: Small-volume HSD resuscitation is much more effective than ISD resuscitation. Variables that were improved include cardiac output, portal blood flow, and intestinal mucosal blood flow in ET shock, all of which improve survival. Such beneficial effects of HSD on splanchnic perfusion may be of value in treating critically ill septic patients in the intensive care unit.

A hand held two-channel vibro-tactile speech communication aid for the deaf: characteristics and results.

The OSCAR-project (Optimal Speech Communication Assistance for Residual Abilities) within the TIDE frame is aiming at processing the speech signal in such a way so that it can be more effectively aurally perceived than with an ordinary hearing aid in case of a very small residual hearing. In case of total deafness the code will be tactile and in some cases a multi modal approach will be tried. One of the sub-results of the OSCAR-project is a hand held vibro-tactile speech communication aid for profoundly hard of hearing and deaf persons. The main idea of the aid is that it should not be a general tactile hearing aid, but rather give optimum tactile support to lip-reading in a close communication situation. It should be used when speech communication is necessary and other methods of communication i.e. sign language, lip-reading, reading and writing etc. does not work. The aid conveys two types of information via its two vibro-tactile transducers; the syllabic rhythm and frication. This paper describes some characteristics of the aid and some results.

Acute effects of exposure to air contaminants in a sawmill on healthy volunteers.

OBJECTIVES: To study whether air contaminants in sawmills can induce acute changes in the upper and lower airways of previously non-exposed subjects. METHODS: Nineteen healthy volunteers were examined to find the concentration of interleukin 6 (IL-6) in nasal lavage fluid and lung function before and after five hour exposure to dusts and fumes generated in a sawmill where timber from Scots pine was sawed. When exposed, the subjects had respirators with and without a particle filter. RESULTS: The median for daily time weighted average concentration of total dust for subjects with respirators without a filter was 0.13 mg/m3, which was significantly higher than the median of 0.04 mg/m3 for subjects who had respirators with a filter. The median for the concentration of IL-6 in the nasal lavage fluid increased after exposure from 0.5 to 5.9 pg/ml in subjects with respirators without a particle filter (P < 0.05). The increase of the concentration of IL-6 was significantly correlated with the dust concentration. A decrease in transfer factor of the lung was significantly correlated with daily time weighted average concentrations of terpenes. CONCLUSION: The findings suggest that healthy volunteers, exposed to air contaminants in a sawmill, show a slight inflammatory reaction. Also, the results of the study indicate the importance of decreasing the concentrations of wood dust in the work environment.

An Indicator for Assessing Respirable Soot Particles in Diesel Exhaust during Occupational Exposures.

Both acute and chronic impairments of lung function have been demonstrated in humans after exposure to diesel exhaust. The concentration of soot particles in the diesel exhaust is significantly related to its effects on health. The aim of the present analysis was to study the relationship between the concentration of respirable dust as an indicator of exposure to soot particles in diesel exhaust and a biologic exposure indicator variable, i.e., transient lung function decrease. Daily time-weighted average concentrations of carbon monoxide and nitrogen dioxide amounted to 9 % and 25% of the applicable hygienic limit values. Time-weighted average concentration and the proportion of respirable dust in total dust during a workshift were significantly correlated with across-shift decreases in lung function. In the absence of a suitable measure for total diesel exhaust exposure, the ratio of the proportion of respirable dust in total dust in a workplace may serve as an indicator of the concentration of soot particles in diesel exhaust.

Does abnormal single-breath nitrogen wash-out predict an accelerated decline in FEV1 in lung-healthy subjects?

Single-breath nitrogen wash-out and forced expirograms measured on two occasions, 8 years apart, were analysed for 24 subjects with varying degrees of peripheral airway involvement. Correlation analyses were carried out between closing volume in percentage of vital capacity (CV%), the slope of the alveolar plateau (phase III) and forced expiratory volume in 1 s (FEV1) for both occasions. The correlations between CV% and phase III measured on the first occasion and the long-term change in FEV1 were also studied. It is concluded that large deviations are required for CV% as well as phase III before any pathological decreases in the large airways will occur. The prognostic value of an abnormal single-breath nitrogen wash-out seems to be limited, at least in lung-healthy subjects.

Effects within the week on forced vital capacity are correlated with long term changes in pulmonary function: reanalysis of studies on car painters exposed to isocyanate.

OBJECTIVES: To examine if car painters who work with polyurethane paints that contain hexamethylenediisocyanate (HDI) and hexamethylenediisocyanate biuret trimer (HDI-BT) develop acute as well as chronic impairment of lung function. METHODS: In this study data were reanalysed from two earlier studies on a group of car painters to see if a decrease in lung function within the week is a marker of vulnerability in those workers. Data on changes in forced vital capacity (FVC) and forced expiratory volume in one second (FEV1) within the week were available for 20 car painters who were also examined six years later. RESULTS: 10 men showed a decline in FVC within the week. There were no significant differences in age, duration of employment, exposures during the follow up period, or smoking between car painters who had decline in lung function within the week and car painters who had not. A significant correlation was found between the change in FVC within the week and the long term (six year) change in FVC, standardised for the effects of aging and smoking, and adjusted for the number of peak exposures. CONCLUSIONS: The results suggest that the decrease in FVC within the week might serve as a guide to identify car painters at risk of a further decrement in lung function above the effects of aging, smoking, and exposure.

Experimental evaluation of the effect of filtration of diesel exhaust by biologic exposure indicators.

The airway resistance, compliance of the respiratory system, transfer factor, and alveolar volume of 33 healthy rabbits were studied before and after exposure to diluted diesel exhaust generated in an experimental motor. Three diesel fuels and two particle traps were tested. Subsequent to the post-exposure lung function measurements, the animals were sacrificed and the lungs were processed for morphologic examination. The concentrations of particles, nitrogen dioxide, and formaldehyde were measured. The inflammatory airway changes were most pronounced in animals exposed to exhaust from standard fuel. Small changes were identified in animals exposed to exhaust filtered through the catalytic trap as well or exposed to unfiltered exhaust from fuels intended for densely built-up areas. Increase in compliance of the respiratory system was associated with the concentration of soot particles and formaldehyde. Compliance decreased significantly in animals exposed to exhaust from standard fuel filtered through the particle traps and increased almost significantly in animals exposed to unfiltered exhaust from the same fuel.

The significance of an across-shift decrease in vital capacity--a re-analysis of a study on subjects exposed to diesel exhaust.

Occupational exposure to diesel exhaust may develop acute as well as chronic lung function impairment. In this study, data from an earlier study on a group of subjects working at tunnel construction site were analyzed. The aim of the analysis was to examine the significance of an across-shift decrease in vital capacity with concern to other lung physiological measurements. There were no statistically significant differences, either in the average age, time of employment, vital capacity before a working shift after two days of no exposure, or the distributions of smoking habits and respiratory symptoms, between the eight workers who had an across-shift decrease in vital capacity and the five workers who had not. Subjects with an across-shift decrease in vital capacity had a significantly greater across-shift decrease in residual volume and total lung capacity than subjects without an across-shift decrease in vital capacity. The pathophysiological mechanisms for this across-shift decrease in residual volume is not fully understood. However, an altered defence mechanism in the lung may play a role for a prolonged retention time for the particles in the inhaled diesel exhaust, resulting in the across-shift decrease in residual volume. The results thus suggest that measurements of across-shift vital capacity is of importance in identifying susceptible subjects with occupational exposure to diesel exhaust.

Acute effects on forced expiratory volume in one second and longitudinal change in pulmonary function among wood trimmers.

Wood trimmers are exposed to molds that periodically grow on timber, and may develop acute as well as chronic pulmonary function impairment. This study examined whether these acute changes in pulmonary function are predictors for a longitudinal deterioration in pulmonary function, beyond normal aging and exposure. Across-shift changes in pulmonary function, measured during a working week, were evaluated in 15 wood trimmers with a follow-up time of 27 months. Twenty-six sawmill workers, employed at the same plants as the wood trimmers, served as control subjects. The highest concentration of viable mold spores for the wood trimmers was 10(6) colony-forming units (cfu)/m3, i.e., several times higher than the corresponding value for the sawmill workers. At the follow-up, wood trimmers had a lower forced vital capacity (FVC) on average, after adjustment for age and height, compared to the sawmill workers. In addition, a correlation was found between the across-week change in forced expiratory volume in 1 second (FEV1) and the decline in FEV1 between the first and the second occasion, after adjusting for normal aging in nonsmoking wood trimmers (r2 = 84%, p < 0.001). The results from the present study suggest that across-shift decrease in FEV1 (measured during a working week) might serve as a guide to identify subjects being at risk for a further decrement in pulmonary function over and above the effects of normal aging and exposure to mold spores in the wood trimming department.

Repeated measurements of transfer factor in rabbits: an animal model suitable for evaluation of short-term exposure.

Acute temporary changes in lung function may be of use as a biological exposure indicator. However, studies of humans occupationally exposed to complex airborne irritants are often expensive and time demanding. Therefore, an animal model could be a valuable complement. A rabbit model has been evaluated where transfer factor was measured twice during the same day, and with the rabbit awake and available for exposure, in between. Anaesthesia and intubation in 22 rabbits (2.6 [0.2] kg [Mean (SD)]) were immediately followed by two measurements of transfer factor and alveolar volume. Transfer factor was estimated by the single breath CO-technique used in humans. The samples were analysed for CO and He on a gas chromatograph. After one pair of measurements the rabbit was allowed to wake up and after 5 h the duplicate measurements were repeated. The mean values of transfer factor, alveolar volume and transfer constant were 0.50 (0.09) mmol min-1 kPa-1, 127 (8) ml and 3.9 (0.6) mmol min-1 kPa-1 l-1, respectively. The intraindividual coefficients of variation were 7.3%, 5.3% and 6.7%, respectively. Five hours later when the duplicate measurements were repeated, transfer factor, alveolar volume and transfer constant were unchanged still. The results suggest that relatively small changes in transfer factor may be detected without losing power, and thus that this model could be used as a biological exposure indicator.

Reproducibility of peak expiratory flow measurements.

The ease of PEF measurement and the availability of inexpensive, portable instruments have led to its increasing use. However, relatively little literature exists addressing the testing procedure, optimal frequency, instrument precision, and virtually no epidemiologic literature exists describing the variability of repeated PEF tests within a single test session (reproducibility). A summary of data from one of the authors' own worker population studies is presented which addresses precision of PEF measurement.

Small airways function in aluminium and stainless steel welders.

The effect of welding fumes on small airways was studied in 25 male subjects who welded in aluminium (Al) and to some extent also in stainless steel (SS). Despite a low exposure to welding fumes as compared to the permissible exposure limits, excretion of Al in urine was found to be increased in all subjects (median value: 0.29 mmol/mol creatinine on Friday afternoon, as compared to an upper reference level of 0.10 mmol/mol creatinine). In addition, the welders displayed increased prevalences of work-related eye and airways (pharyngitis and non-specific bronchial hyperreactivity) symptoms, as compared to 25 matched controls. Short-term welders (< or = 2.5 years) had more symptoms related to the upper airways than did long-term welders, which may indicate a selection. Spirometry, closing volume and volume of trapped gas (VTG) did not deviate. However, after methacholine inhalation, the long-term welders had a significantly steeper slope of the alveolar plateau on the single-breath nitrogen wash-out test, and a slight increase in VTG, as compared to the short-term welders and the controls. These findings may indicate a welding fume-induced increase in the reactivity of the small airways. Because Al welding was far more frequent than SS welding, an association with the former seems likely.

Temporary health effects from exposure to water-borne paints.

Temporary health effects of exposure to experimental paints were studied. Ten painters feeling nuisance from water-borne paints and eight painters not feeling such nuisance applied eight experimental water-borne paints according to normal work routines. The effects were a decrease in forced vital capacity, forced expiratory volume in 1 s and peak expiratory flow, an increase in urine excretion, and a decrease in urine density. A small, but statistically highly significant, increase in the mean volume of erythrocytes was observed. The effects were similar in the two groups, but the "nuisance group" reacted with a larger urine excretion and a larger increase in the mean volume of erythrocytes. The effects did not influence physical work capacity. The effects on the lungs and urinary excretion were probably not associated with the organic solvents or ammonia in the paints. Instead, they were probably due to derivatives of isothiazolinone. This assumption needs verification.