Ab initio prediction of the critical thickness of a precipitate.

Segregation and precipitation of second phases in metals and metallic alloys is an important phenomenon that has a strong influence on the mechanical properties of the material. Models exist that describe the growth of coherent, semi-coherent and incoherent precipitates. One important parameter of these models is the energy of the interface between matrix and precipitate. In this work we apply ab initio density functional theory calculations to obtain this parameter and to understand how it depends on chemical composition and mechanical strain at the interface.Our example is a metastable Mo-C phase, the body-centred tetragonal structure, which exists as a semi-coherent precipitate in body-centred cubic molybdenum. The interface of this precipitate is supposed to change from coherent to semi-coherent during the growth of the precipitate. We predict the critical thickness of the precipitate by calculating the different contributions to a semi-coherent interface energy by means of ab initio density functional theory calculations. The parameters in our model include the elastic strain energy stored in the precipitate, as well as a misfit dislocation energy that depends on the dislocation core width and the dislocation spacing. Our predicted critical thickness agrees well with experimental observations.

Distinct localization of a beta-tubulin epitope in the Tetrahymena thermophila and Paramecium caudatum cortex.

Many of the highly organized microtubular arrangements in ciliates are located in the cortical area containing membrane vesicles and vacuoles. In Tetrahymena thermophila and Paramecium caudatum, immunofluorescence microscopy with the monoclonal antibody TU-06, directed against beta-tubulin, revealed distinct staining of this cortical region alone, while the cilia and other microtubular structures were unstained. The specificity of the antibody was confirmed by immunoblotting and by preabsorption of the antibody with purified tubulin. Double-label immunofluorescence with antibodies against gamma-tubulin, detyrosinated alpha-tubulin, and centrin showed that the TU-06 epitope is localized outside the basal body region. This was also confirmed by immunogold electron microscopy of thin sections. Proteolytic digestion of porcine brain beta-tubulin combined with a peptide scan of immobilized, overlapping peptides disclosed that the epitope was in the beta-tubulin region beta81-95, a region which is phylogenetically highly conserved. As known posttranslational modifications of beta-tubulin are located outside this area, the observed staining pattern cannot be interpreted as evidence of subcellular sequestration of modified tubulin. The limited distribution of the epitope could rather reflect the dependence of TU-06 epitope exposition on conformations of tubulin molecules in microtubule arrangements or on differential masking by interacting proteins.

Changes in microtubules and microfilaments due to a combined effect of ultrasound and cytostatics in HeLa cells.

Treatment of HeLa cells with low intensity ultrasound and two cytostatic drugs, cycloplatin and methotrexate, resulted in a partial disassembly of microtubules and microfilaments. This disassembly was due to depolymerization and subsequent erroneous repolymeration of essential cytoskeletal proteins, resulting in formation of unusual arrangements, mainly small, granule-like structures. The combined action of ultrasound and cytostatics had a synergistic effect dependent on both the concentration of the drug and the time of sonication. The demonstrated changes in the cytoskeleton are considered to be non-specific to ultrasound treatment, reflecting only an altered vital state of the treated cells.

Reaction of the skin fibroblast cytoskeleton to micromanipulation interventions.

Micromanipulation is a strong mechanical intervention into cellular integrity and induces large changes in the fine structure of the treated cells. Human diploid skin fibroblasts (KF1 and KF2 cell lines) were chosen as an experimental model. Special hatching needles were used for defined micromanipulation interventions (deformation of plasma membrane). Changes in cytoskeletal structures were visualized by using fluorescent and confocal microscopy. The actin cytoskeleton showed a more sensitive response to micromanipulation than microtubules. Characteristic changes in microfilaments, i.e., thickenings and knot formation, were visible in treated cells fixed immediately after micromanipulation and were the result of hatching-needle pressure on the plasma membrane as well as a reaction of actin filaments localized near the plasma membrane deformation. These direct changes and also other specific alterations in the actin filament network were detectable 14 to 16 h after treatment, but they were not observed when longer reparation intervals were used.

Molecular organization of the plasma membrane in the post-acrosomal region of some farm animals.

According to the distribution of IMP, three different regions can be recognized on PF of the post-acrosomal plasma membrane of bull, ram, and boar spermatozoa. They are: (1) a region with linear aggregation of IMP, (2) a region with fewer and scattered IMP, and (3) a region with more numerous IMP. In the last two regions IMPs are randomly distributed or a clustering of certain particles is visible. In stallion spermatozoa the last two areas are undistinguishable. There are evident interspecies differences in the arrangement of linear aggregations of IMP which are characteristic for each species.

[Ultrastructure of boar sperm membranes prepared by freeze-fracturing]. / Ultrastruktúra membrán kancích spermií preparovaných mrazovým lomom.

The objective of the present paper was to describe the topographic orientation of intramembraneous particles (IMP) in the membranes of freshly ejaculated boar spermatozoa applying the method of freeze fracturing. Disc clusters of IMP's could be distinguished in the acrosome-covering plasma membrane (PF). The border of the head to a distance of about 0.3 micron seemed to contain no IMP's (Figs. 1, 2). In the postacrosomal region in an anterior direction from the posterior ring the IMP's were found to be arranged in palissade slant rows. Statistical measurements of 20 spermatozoa (Tab. I) indicated that the slant rows extended to the greatest distance in the lateral part of the head, up to 0.67 micron (+/- 1.45-0.39) from the posterior ring. In the middle of the head the rows extended to a distance of 0.18 micron (+/- 0.10-0.42). The transition spot between the zone of sparse IMP's and the zone of densely arranged IMP's was at a distance of 1.63 microns (+/- 1.87-0.69) in an anterior direction from the posterior ring (Figs. 3, 4). In the flagellum in the plasma membrane (PF) the first spot of an ample occurrence of IMP's is located in the first mitochondrion in the spiral. The IMP clusters follow the cicumferential orientation of mitochondria in the mitochondrial spiral. The IMP's were missing in the spaces between the spiral coils (Fig. 5). The membranes of the mitochondria contain a large amount of IMP's. This activity is transferred to the clinging part of the plasma membrane (Fig. 6). A larger accumulation of IMP's can be seen at the spot where the plasma membrane covers the annulus (Fig. 7). In the plasma membrane of the main segment of the flagellum the IMP's are distributed irregularly in PF, and also in EF (Fig. 8). The EF surfaces of the plasma membrane had in general an indistinct structural organisation of IMP's. The distribution of IMP's in acrosomal membranes was found to be irregular. The postacrosomal lamina in the freeze fracturing did not look like a morphologically identifiable structure. In the nuclear envelope delimiting the posterior nuclear space, nuclear pores could be identified (Fig. 9). No nuclear pores could be seen in the nuclear envelope clinging to the posterior part of the nucleus. At this spot smaller IMP's were observed which could be a part of the proteins of the filaments connecting the concave surface of the head with the convex articular surface of the flagellum. These filaments connect the head and the flagellum (Fig. 10).(ABSTRACT TRUNCATED AT 400 WORDS)

[Analysis of 255 cases of occupational hearing loss]. / Analýza 255 profesionálních nedoslýchavostí.

The authors analyzed 255 cases of occupational hypacusia reported as occupational diseases in 1962-1988 in the Czechoslovak uranium industry. Up to 1975 occupational hypacusias accounted for 9-11% of the nationwide number of hypacusia notified as occupational diseases. Due to extensive social provisions, incl. preventive ones, the incidence declined since 1985 below 1% of the nationwide incidence. The group of 255 men with occupational hypacusia was examined in detail at the Health Centre of the Uranium Industry in Príbam. Their age is 49.0 +/- 8.5 years, noise exposure 14.6 +/- 5.8 years, the the ratio of miners is 82.4%, the total percentage hearing loss is 63.5 +/- 11.4%, the mean annual increment of the total percentage hearing loss is 4.8 +/- 0.6%, the greatest mean annual increment is 5.4% in the occupation of miners.

[Saturation of middle ear reflexes in occupational hearing loss]. / Sledování nasycení stredousních reflexu u profesionální nedoslýchavosti.

In the ENT department of the Factory Institute of National Health of the uranium industry in Príbram a group of 196 men (392 ears) was examined who worked exposed to the risk of noise in different occupations, mostly as miners in the uranium mines. The noise exposure was 17.5 +/- 6.5 years, age 60.2 +/- 11.7 years, the total percentage hearing loss (calculated according to Fowler) 54.7 +/- 21.1%. The group was formed by 144 men who were examined during a preventive follow-up examination, 52 men where hypacusia was evaluated as an occupational disease. The examination of all patients was supplemented by a record of middle-ear reflexes induced by contralateral stimulation at frequencies of 0.5 kHz, 1 kHz, 2 kHz and 4 kHz and by white noise (WN). The regression equation y = 50.54-0.044X (y = percentage hearing loss per ear, x = noise exposure in years) was calculated from data of the group subjected to the preventive follow up examination and made it possible to divide the group into sub-groups, sensitive and resistant to noise. The group of occupational hypacusia comprised only sensitive subjects. The authors tested the frequency and thresholds of middle ear reflexes at different frequencies and WN, the frequency and thresholds of saturation of reflexes separately in groups sensitive and resistant to noise. It was not possible to draw conclusions from the results which would permit a forecast of the individual development of occupational hypacusia as regards early evaluation of sensitivity or resistance to noise.

[Agreement between auditory threshold calculated from cortical evoked response audiometry and tone audiometry in occupational hearing loss]. / Sledování shody mezi sluchovým prahem vypocteným z kortikální ERA a tónové audiometrie u profesionální nedoslýchavosti.

In a group of 126 men the authors evaluated the auditory threshold from cortical ERA findings and comparison with their threshold sound audiometry. The mean age of the patients means = 52.5 years (min. = 25 years, max. = 69 years, s = 8.95). Noise exposure means = 16.5 years (min. = 4 years, max. = 30 years, s = 4.5). In 79.3% the men worked as miners in uranium mines, other mining occupations were represented only by small numbers. The arithmetic mean of the total percentage hearing loss (calculated according to Fowler) means = 49.7% (min. = 17%, max. = 100%, s = 15). The cumulative frequency of differences between the auditory threshold of the sound audiogram and cortical ERA: (table; see text) The cumulative frequency of differences in the total percentage hearing loss between sound audiograms and cortical ERA: differences up to +/- 5% hearing loss were recorded in 24.3% of the group, differences up to +/- 10% in 43.9%, differences up to +/- 15% in 58.9%, differences up to +/- 20% in 70.1%. In the group of 126 examined subjects we detected 12 aggravating subjects (9.5%), their mean age being by 6.7 years lower than the mean of the whole group, the mean exposure to noise is by 3.2 years shorter. The differences between the auditory threshold reported by the aggravating men and the cortical ERA are highest in verbal frequencies, on average they are per fr of 2 kHz 27.3 dB, 1 kHz 24.3 dB, 0.5 kHz 20.1 dB, 4 kHz, 10.0 dB. The differences between the total percentage auditory loss calculated from sound audiograms and cortical ERA reaches on average 41.5%.

Acoustic trauma in mineworkers revealed by temporal bone necropsy.

Six selected human cochleae showing definite signs of mechanical damage caused by exposure to high intensity noise (acute acoustic trauma) are reviewed. Patterns of degeneration of cochlear hair cells were compared with the functional audiometric examinations. Tonotopic relations, mechanism of damage to the organ of Corti as well as pathological changes of the tectorial membrane are discussed.

[Objective adjustment of hearing aids to hearing disorders]. / Objektivizace prizpusobení sluchadla sluchové poruse.

The aim of a functional prosthesis - a hearing aid - is to improve the comprehensibility of speech. The hearing aid is individually adjusted for the patient. Every deaf patient is subjected first to an extensive otolaryngological and audiological examination programme which comprises the recording of the case-history, assessment of the ENT diagnosis, examinations of threshold and suprathreshold sound audiometry, verbal and sentence audiometry in a sound-proof chamber and in space. To set the most important parameters of hearing aids (frequency characteristics, intensification and dynamic range) directly on the patient's ear, in the ENT department of the health centre of the Uranium Industry in Príbram Rastronics equipment from Denmark is used which makes it possible to achieve optimal adjustment of hearing aids, using several calculations applied on an international scale.

[The ultrastructure of bull sperm membranes prepared by freeze etching]. / Ultrastruktúra membrán býcích spermií preparovaných mrazovým leptaním.

Intramembraneous particles represent protein components of the membrane. It is assumed that their number and distribution are in correlation with the level of the metabolic activity of membranes. In the cytoplasmic membrane in the postacrosomal region (PF) near the posterior ring the particles are arranged in form of palisade rows. In the remaining membranes of the head, irregularly distributed particles were observed. Their number at individual places varied. Their size was not equal either. The areas without particles were also found out. The particles in the cytoplasmic membrane of the flagellum (PF) formed clusters and they had circumferential orientation in the direction of mitochondria. At the place of the annulus the number of particles increased. The distribution of particles was irregular in the cytoplasmic membrane of the main section.

[The relation between the auditory threshold and the threshold of middle ear reflexes induced by ipsilateral stimulation in occupational deafness]. / Vztah prahu sluchu a prahu stredousních reflexu vyvolaných ipsilaterální stimulací u profesionální nedoslýchavosti.

The author examined and evaluated middle ear reflexes obtained by ipsilateral stimulation in a group of 115 men, mean age 52.5 years (s = 9 years) who worked exposed to noise in uranium mines on average for 16.5 years (s = 4.6 years). Their total percentage auditory loss calculated according to Fowler is 49.7% (s = 15.1%). The arithmetic mean of differences of the auditory threshold and the threshold of middle ear reflexes in 214 ears examined at a frequency of 1000 Hz is 45.5 dB (s = 16.3 dB, min. 0 dB, max. 80 dB), in 208 ears at a frequency of 2000 Hz 30.4 dB (s = 13.5 dB, min. 0 dB, max. 75 dB), in 196 ears at frequency 3000 Hz 23.2 dB (s = 12.6 dB, min. 0 dB, max. 85 dB). The relation--ship between the auditory threshold and middle ear reflexes obtained by ipsilateral stimulation corresponds to the following equations Y1000Hz = 105.86--9.73 square root chi i Y2000Hz = 119.21--11.61 square root chi i Y3000Hz = 108.62--10.59 square root chi i Individual forecasts of the auditory threshold for pure tones only from values of the threshold of middle ear reflexes in occupational deafness are of restricted value due to the great scatter of values.

Correlative study of sensory cell density and cochlear length in humans.

In the group of 50 cochlea from 28 men aged 38-73 years a great variability in the length of the cochlear duct was found ranging from 28.0 to 40.1 mm. The variability in the number of inner and outer hair cells is not so prominent and the same holds for the variability in density. Average densities of the inner and outer hair cells decrease with increasing cochlear length. However, the long cochleae have a greater number of hair cells which indicates that long cochleae have more sensory cells in a given frequency region.