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Many eukaryotic taxa inherit a heteromorphic sex chromosome pair. It is a generally accepted hypothesis that the sex chromosome pair is derived from a pair of homologous autosomes that has developed after the occurrence of a sex differentiator in an evolutionary process into two structurally and functionally different partners. In most of the analyzed systems the occurrence of the dominant sex differentiator is paralleled by the suppression of recombination within and close by that region. The recombinational isolation can spread in an evolutionary selection process from neighboring regions finally over the whole chromosome. Suppression of recombination strongly biases the distribution of retrotransposons in the genome. Our results and that from others indicate that the major force driving the evolution of Y chromosomes are retrotransposons, remodeling euchromatic chromosome structures into heterochromatic ones. In our model, intact or already eroded retrotransposons become trapped due to their inherent transposition mechanisms in non-recombining regions. The massive accumulation of retrotransposons interferes strongly with the activity of genes. We hypothesize that Y chromosome degeneration is a stepwise evolutionary process: (1) Massive accumulation of retrotransposons occurs in the non-recombining regions. (2) Heterochromatic nucleation centers are formed as a consequence of genomic defense against invasive parasitic elements; the established nucleation centers become epigenetically inherited. (3) Spreading of heterochromatin from the nucleation centers into flanking regions induces in an adaptive process gene silencing of neighbored genes that could either be still intact or in an already eroded condition, e.g., showing point mutations, deletions, insertions; the retroelements should be subjects to the same forces of deterioration as the genes themselves. (4) Constitutive silenced genes are not committed to the same genetic selection pressure as active genes and therefore more exposed to the decay process. (5) Gene dosage balance is reestablished by the parallel evolution of dosage compensation mechanisms. The evolving secondary sex chromosomes, neo-X and neo-Y, of Drosophila miranda are revealed to be a unique and potent model system to catch the evolutionary Y deterioration process in progress.

It is generally assumed that the sex chromosomes developed from a pair of homologs. Over evolution, the proto-Y chromosome, with a very short differential segment, matured in its final stage into a heterochromatic and, for the most part, genetically eroded Y chromosome. The constraints on the evolution of the proto-Y chromosome have been speculated upon since the sex chromosomes were discovered. Several models have been suggested. Drosophila miranda has proved to be a unique and potent model system to study Y-chromosome evolution. We use selected test genes distributed along the neo-Y chromosome as entry gates to analyze the molecular mechanisms involved in the process of Y-chromosome evolution. Here, we report our findings on the Krüppel gene (Kr), which is located distally on the neo-sex chromosome pair.

The larval cuticle proteins (LCPs) are encoded by a multigene family, Lcp1-4, located at the right arm of the metacentric autosome 2 (2R) in Drosophila melanogaster. Due to a chromosome fusion the Lcp locus of Drosophila miranda is situated on a pair of secondary sex chromosomes, the X2 and neo-Y chromosomes. Comparing the deduced amino acid sequences of the autosomal D. melanogaster loci with the sex-chromosomal loci of D. miranda, we were able to trace the evolution of the Lcp loci with respect to their different chromosomal inheritance. The length of the signal peptide is conserved in all four LCPs, while the size of the mature LCPs varies. Conserved protein motifs became obvious from the alignment, indicating regions of structural and functional importance. Analyzing intra- and interspecific sequence similarities of the Lcp gene families allowed us to reconstruct the phylogeny of the gene cluster. Alignment with cuticle amino acid sequences originating from divergent insect species reveals motifs already present in the primordial insect LCPs. These motifs indicate different levels of constraint acting during the evolution of the LCPs.

The ab initio full-potential linearized-augmented-plane-wave method for a free-slab geometry was used to calculate the electronic structure and geometry of a clean ${\mathrm{TiO}}_{2}$ (110) rutile surface. Surface induced states were found in the density of states, such as an s-like surface state at -15 eV. Band bending states of width 0.5 eV appear just below the Fermi energy, in agreement with photoemission experiments. The positions of the atoms in the surface and subsurface layers and the corresponding change of Ti-O bond lengths were derived by total-energy minimization. In general, downward relaxations were obtained for which the fivefold-coordinated Ti experienced the largest relaxation of -0.180 \AA{}, whereas the second most important relaxation effect, -0.156 \AA{}, occurred for the surface O. The calculated Ti-O bond lengths are in very good agreement with experimental data for the ${\mathrm{TiO}}_{2}$ (100) surface. The calculated work function 6.79 eV compares favorably with the experimental result of 6.83 eV. Based on an extension of density-functional theory to excited states the valence- and conduction-band gap was calculated to be 1.99 eV, which is in reasonable agreement with the experimental gap of 2.6 eV when compared to the one-particle band gap of 0.65 eV.

In Drosophila miranda the small multigene family of the larval cuticle protein (Lcp1-4) genes resides on the evolving neo-X and neo-Y sex chromosome pair while in the sibling species Drosophila pseudoobscura and Drosophila persimilis the gene cluster is inherited autosomally. The neo-Y chromosomal Lcp1, Lcp2 and Lcp4 genes are, as previously shown by us, not expressed and only Lcp3 is expressed at a strongly reduced level. As a first step in understanding the evolutionary mechanism(s) transforming an autosome into a dosage compensated X we analysed the expression behaviour and promoter structure of the Lcp1-4 genes on the neo-X. The normalized relative expression levels reveal that all four neo-X chromosomal Lcp genes in D. miranda males, including Lcp3, are already dosage compensated.

Many eukaryotic taxa inherit a heteromorphic sex chromosome pair. It is a generally accepted hypothesis that originally homologous chromosomes develop after the occurrence of a sex differentiator into two structurally and functionally different partners (Muller, 1932; Bull, 1983; Charlesworth, 1991; Steinemann and Steinemann, 1998; Lucchesi, 1999), X and Y chromosome (or Z and W). Often the Y chromosome evolves into a heterochromatic and genetically inert chromosome (chromosome degeneration). This evolutionary process has the final consequence that the male lineage becomes hemizygous for the heterosomal genes, a situation which is compensated by a special mechanism, the gene dosage compensation. The assumption, originally made for Drosophila, was extended by Ohno (1967) for the development of mammalian sex chromosomes. The constraints evolving the structurally and functionally different X and Y chromosomes have been the object of speculation since the discovery of sex chromosomes by McClung (1901). For the evolution of sex chromosomes it is assumed that starting from the differential locus in the heterogametic sex the state of permanent heterozygosity is spread further into the flanking regions (for review Lucchesi, 1994; Rice 1996; Charlesworth, 1996).

It is generally assumed that the sex chromosomes developed from a pair of homologs. Over evolution, the proto-Y chromosome, with a very short differential segment, matured in its final stage into a heterochromatic and, for the most part, genetically eroded Y chromosome. The constraints on the evolution of the proto-Y chromosome have been speculated upon since the sex chromosomes were discovered. Several models have been suggested. Drosophila miranda has proved to be a unique and potent model system to study Y-chromosome evolution. We use selected test genes distributed along the neo-Y chromosome as entry gates to analyze the molecular mechanisms involved in the process of Y-chromosome evolution. Here, we report our findings on the Krüppel gene (Kr), which is located distally on the neo-sex chromosome pair.

Y chromosome evolution is characterized by the expansion of genetic inertness along the Y chromosome and changes in the chromosome structure, especially the tendency of becoming heterochromatic. It is generally assumed that the sex chromosome pair has developed from a pair of homologues. In an evolutionary process the proto-Y-chromosome, with a very short differential segment, develops in its final stage into a completely heterochromatic and to a great extends genetically eroded Y chromosome. The constraints evolving the Y chromosome have been the objects of speculation since the discovery of sex chromosomes. Several models have been suggested. We use the exceptional situation of the neo-Y in Drosophila miranda to analyze the molecular process in progress involved in Y chromosome evolution. We suggest that the first steps in the switch from a euchromatic proto-Y-chromosome into a completely heterochromatic Y chromosome are driven by the accumulation of transposable elements, especially retrotransposons inserted along the evolving nonrecombining part of the Y chromosome. In this evolutionary process trapping and accumulation of retrotransposons on the proto-Y-chromosome should lead to conformational changes that are responsible for successive silencing of euchromatic genes, both intact or already mutated ones and eventually transform functionally euchromatic domains into genetically inert heterochromatin. Accumulation of further mutations, deletions, and duplications followed by the evolution and expansion of tandem repetitive sequence motifs of high copy number (satellite sequences) together with a few vital genes for male fertility will then represent the final state of the degenerated Y chromosome.

A generally accepted idea has been that plate fixation of fractures may result in the structural adaptation of bone (bone loss) to reduced stress (stress protection) with the subsequent danger of refracture after implant removal. This was the negative aspect of stress protection. For this reason, it was proposed that plates made from more deformable materials be used (titanium, polymers or carbon fibres). A theoretical analysis using composite beam theory, with different loading conditions (axial load and bending), demonstrates that stress protection, i.e. early temporary porosis, is a myth. Mechanics of materials shows that when an over-large plate is fixed to small bones (as in small animals, e.g. rabbits), the reduction of bone strain is exaggerated; in contrast, using plates of varying flexibility (steel, titanium or carbon fibre) on large bones leads to strain reduction with an astonishingly similar amplitude.

Y chromosome degeneration is characterized by structural changes in the chromosome architecture and expansion of genetic inertness along the Y chromosome. It is generally assumed that the heteromorphic sex chromosome pair has developed from a pair of homologues. Several models have been suggested. We use the unique situation of the secondary sex chromosome pair, neo-Y and neo-X (X2), in Drosophila miranda to analyze molecular mechanisms involved in the evolutionary processes of Y chromosome degeneration. Due to the fusion of one of the autosomes to the Y chromosome (about 2 Mya), a neo-Y chromosome and a neo-X chromosome, designated X2, were formed. Thus, formerly autosomal genes are inherited now on a pair of sex chromosomes in D. miranda. Analyzing DNA sequences from the X2 and neo-Y region, we observed a massive accumulation of DNA insertions on the neo-Y chromosome. From the analysis of several insertion elements, we present compelling evidence that the first step in Y chromosome degeneration is driven by the accumulation of transposable elements, especially retrotransposons. An enrichment of these elements along an evolving Y chromosome could account for the switch from a euchromatic into a heterochromatic chromatin structure.

The deposition of titanium in regional lymph nodes was studied after insertion of endosseous, plasma-spray-coated titanium screw implants in a total of 19 beagle dogs. Five additional animals with no implants served as the control group. After killing the animals 9 months postoperatively, the regional lymph nodes were carefully excised, and samples were prepared for histologic examination. Other samples were used to identify foreign particles by energy-dispersive x-ray analysis and for measurement of the titanium concentration in the tissue by flameless atomic absorption spectroscopy. Very fine foreign-body particles could be seen in the histologic sections, and they were identified as titanium by energy-dispersive x-ray analysis. The atomic absorption analysis for titanium revealed a significantly higher concentration in the group with implants. The presence of very fine, poorly attached particles on the plasma-sprayed titanium surface suggests that these particles may be mechanically dislodged from the surface on insertion of the implants. This suggests that the fine particles may be transported by phagocytes to the regional lymph nodes, where they could be found without any signs of inflammation or foreign-body reaction.

After experimental implantation in non-fractured cadaver femora, the ASIF dynamic hip screw system supported the femoral neck and the lateral proximal femur and prevents deformation, depending on the vector of the resultant force. Three positions of weight-bearing were simulated: near-axial loading of the femoral neck, standing on one leg and standing on two legs. After removal of the metal the bone breaking point was markedly lowered.

Die Oberflachenbeschaffenheit von Implantaten beeinflust deren Verankerungsfestigkeit im Knochen, da strukturierte oder porose Oberflachen zu einer mechanischen Verankerung fuhren (1 – 5). Diese Tatsache kann genutzt werden, um geeignete Oberflachen fur bestimmte Anwendungen zu schaffen. Somit kann z.B. einer Lockerung von Schrauben vorgebeugt werden oder eine feste, permanente, zementlose Verankerung von Prothesen gewahrleistet werden.

To realize the new concept of biological internal fixation the limited contact dynamic compression plate was developed. It minimizes vascular damage to the plated bone segment. It should lead to a more versatile and efficient application of internal fixation using plates.

Atomic level structural and electronic analysis of titanium passivated by an oxide film is crucial for understanding the biocompatible properties of this transition metal. Scanning tunneling microscope (STM) images of electropolished titanium samples show a rather smooth surface in the nanometer range with structure attributed to surface defects induced by the electropolishing technique. I–V spectra were performed with the STM using W, PtIr, and Au tips. These spectra completed by normalized conductivities spectra are compared and discussed in order to determine surface electronic properties of the oxide film and to estimate the influence of the STM tip. The surface band gap of this amorphous thin film mainly composed of TiO2 is shifted to positive tip voltage and is similar to the one of an n‐type semiconductor with band bending bringing the valence band closer to the Fermi level. The surface band gap extends from −0.5 to +0.8 eV for a Au tip and from −0.1 to 0.7 eV for a W tip, which shows that W induce...

We measured second order elastic constants of Pd from 295 to 850 °K and under hydrostatic pressure up to 7000 kg cm 2 . A study of the temperature behavior and the volume dependence of these constants allows to separate the electronic contributions from those of the lattice. Gruneisen constants are calculated. With our model a certain relation between elastic shear constants and the magnetic susceptibility is successfully applied and the deformation potential is determined.

The Curie temperatures and lattice parameters of electron-irradiated Fe-25-50 at.% Ni Invar alloys have been investigated. The irradiation strongly increases the Curie temperature of the FCC phase and reduces the lattice parameter. These results suggest that the Fe-Ni Invar alloys have a tendency to be separated into two phases by the electron irradiation.

Zu den Fortschritten der Osteosynthese und dem Gelenkersatz haben die Materialwissenschaften entscheidend beigetragen. Man versteht heute, wie praktisch die Toxicitat zustandekommt und Implantate lassen sich mechanisch charakterisieren. Diese Entwicklungen gehen weiter, z. B. gegen Titan.

The elastic constants of bcc Nb-Zr alloys are measured over a composition range between 100 and 30 at.% of Nb and temperatures between zero and the melting point, using a new technique for the high-temperature measurements. Anomalous behavior is found for ${C}_{44}$. The anomaly is a band-structure effect which is corroborated by theoretical calculations using electron-lattice coupling constants derived from a tight-binding parametrization scheme. The calculation is of a type similar to phonon dispersion ones, having the further complication of temperature effects which have convergence difficulties and need a special interpolation method.

New measurements of the chemical diffusion coefficient in liquid binary alloys are presented. The wellknown geometry of the “capillary-reservoir” is used and the concentration is obtained from a resistivity measurement. The method allows to follow continuously the diffusion process in the liquid state. A precision of at least 10% in the diffusion coefficient is obtained with a reproducibility better than 5%. The systems Hg-In, Al-Sn, Al-Si have been studied. Diffusion coefficients are obtained as a function of temperature, concentration, and geometrical factors related to the capillary (diameter, relative orientation of density gradient and gravity). The results agree with known data in cases when convection phenomena are likely to be small; in other cases, these new measurements give lower diffusion coefficients indicating a diminution or even suppression of convection. Es werden neue Messungen der chemischen Diffusions-Koeffizienten in flussigen binaren Legierungen mitgeteilt. Die bekannte Geometrie “Kapillare-Reservoir” fand Verwendung, die Konzentrationen wurden uber Widerstandsmessungen bestimmt. Die Methode erlaubt, den Diffusionsprozes im flussigen Zustand kontinuierlich zu verfolgen. Die erzielte Genauigkeit hinsichtlich der Diffusionskoeffizienten betrug mindestens 10% mit einer Reproduzierbarkeit besser als 5%. Es wurden die Systeme Hg - In, Al - Sn, Al -Si untersucht und die Diffusionskoeffizienten als Funktion der Temperatur und der Konzentration untersucht. Sie wurden auch durch geometrische Faktoren der Kapillare (Durchmesser, relative Orientierung des Dichtegradienten und der Schwerkraft) beeinflust. Die Ergebnisse stimmen mit bekannten Daten uberein, die unter Bedingungen erhalten wurden, unter denen Konvektionseinflusse wahrscheinlich gering waren. In anderen Fallen geben unsere Messungen niedrigere Diffusionskoeffizienten, was auf eine Verminderung oder gar Unterdruckung von Konvektionseinflussen hinweist.

The linear thermal expansion coefficients alpha (T) of Nb and Nb-Mo alloys have been measured between 80 and 300 K. The results are shown graphically and polymomial expressions for alpha (T) are tabulated. A minimum of alpha (T) occurs near the critical composition of 40% Mo in Nb. Features of the temperatures and composition dependence of alpha (T) are analysed in terms of the known elastic properties of the alloys. It is shown that the temperature dependence of the shear elastic constant c44 consists of an intrinsic component and a volume-dependent extrinsic component. An estimate is made of the electronic contribution to c44 in the alloys.

A precise 'pulse-echo method' is used to measure the sound velocity in liquid aluminium and aluminium-silicon alloys from the melting point up to 1000 degrees C. The adiabatic compressibility and static structure factors are evaluated. It is found that the compressibility and structure factors display anomalous variations around the eutectic composition.

d -energy levels and densities of states for sheared f.c.c. lattice have been computed, using the tight-binding-approximation and dependence of overlap parameters with interatomic distance. Strain-splitting modifies the band structure which is discussed in relation to elastic and magnetic properties.

Nach einer aktiven Korrosion finden sich im metallotischen Gewebe immer kompakte Legierungsbestandteile und deren Abbauprodukte. Die Metallosen sind auf die Umgebung der aktivierten Stellen begrenzt. Die Abbauprodukte der V4A-Legierungen zeigen eine geringere Toxicitat als diejenigen der Co-Legierungen. Die dauernde Korrosion der Passivschicht fuhrt zu einer Gleichgewichtskonzentration der Legierungselemente, welche zwischen einigen ppm und 150 ppm der Trockensubstanz variiert. Der Einflus dieses Metallionenstroms, durch den Korper zu den Ausscheidungsorganen, auf die Stoffwechselvorgange ist ungeklart. Der moderne V4A-Stahl weist fur die Ziele der operativen Frakturbehandlung entscheidende Vorteile auf, und zwar in Hinsicht auf die Festigkeitseigenschaften, die gute Verarbeitbarkeit und die geringe Toxicitat der Korrosionsprodukte. Der ortliche Zusammenbruch der Passivitat last sich hauptsachlich durch eine richtige Handhabung der Implantate vermeiden.

Studies have been carried out to examine the influence of different degrees of rigidity on the healing pattern of bones that have been internally fixed after osteotomy. The study confirms that the less the rigidity afforded by the internal fixation device, the more callus is produced. There is evidence that a certain amount of rigidity in the fixation used is necessary to prevent early bone resorption at the fragment ends. The work demonstrates the early phenomena induced by too elastic a fixation. It was not intended to study the late effects of excess rigidity on bone structure.

The volume and shape magnetostriction ωV(H) and ωS(H) of an Invar alloy and a technical constant-modulus alloy were measured with a strain gauge technique at room temperature. The considerable shape magnetostriction amounts to 0.1 of the volume effect. The itinerant model of ferromagnetism and Kanamori's formula for correlation effects is applied. The observed magnetostriction implies a deformation potential of about 0.3 eV.

The elastic constants of a pure niobium single crystal have been measured between 1300 and 2600 K by means of an ultrasonic method and a suitable geometry. We find that the shear constant C44 behaves anomalously up to the melting point and that 1 2 (C11–C12) decreases monotonically. The anomalous behaviour of C44 associated with the trigonal distortion is explained as an electronic contribution with a (local) degeneracy temperature which is considerably higher than the melting point.

Theα-amylase gene ofDrosophila miranda is located on the X2-and on the neo-Y-chromosome, both developing sex chromosomes. Crosses between strains carrying different electrophoretically distinguishable alleles of theα-amylase gene were performed. Females of the F1 offspring showed the expected heterozygosity, while the males proved to be hemizygous for this locus. Only the gene on the X2-chromosome is expressed, whereas the corresponding gene on the neo-Y-chromosome is not. Estimates of theα-amylase activity in crude homogenates of male and female flies suggest strongly that theα-amylase gene is dosage compensated inD. miranda. In contrast to this situation, in all otherDrosophila species theα-amylase allele is autosomal and hence not dosage compensated.

Bone refracture after plate removal has been attributed to the structural adaptation of bone (bone loss) to reduced stress (stress protection). The analysis of the stress pattern and the reduction of deformation work in plated bones seems to be a prerequisite for the assertion that bone loss is stress related. The strain field within bones under eccentric axial load is analyzed using the composite beam theory and verified experimentally using strain gages, with plates made of different materials. The difference between the reduction of stress obtained using the less stiff plate materials is small. Reduction of plate rigidity does not result in proportional improvement of the bone strain.

Concerning stimulation of bone formation by direct current (DC) (1,4,12) the following characteristics seem to be important: 1. Bone formation is in most cases localized at the cathode, not at the anode. 2. Bone formation is restricted to regions near the cathode and does not spread out when increasing currents are applied. 3. Maximum bone formation seems to occur at a specific level of current; at current levels 10 times smaller the effect disappears and at levels 10 times larger bone resorption occurs at the cathode and at the anode. The active level is given as 10 µA, resulting, e.g., in 50 µA/cm2 (13).

It is generally admitted that plate fixation of fractures results in reduced stress (stress protection) and subsequent structural adaptation of bone (bone loss). The analysis of the stress pattern and the reduction of deformation work in plated bones is a prerequisite for the assertion that bone loss is stress related. The strain field within bones under eccentric axial load has been analyzed theoretically and verified experimentally. The difference between the reduction of stress obtained using the flexible plate materials is small. Reduction of plate stiffness does not result in proportional improvement of the bone strain.

Die funktionelle Therapie nach Plattenosteosynthese setzt, soll eine ungestorte Knochenbruchheilung gewahrleistet sein, eine gewisse Rigiditat des Implantates voraus. Die bisher klinisch verwendeten Osteosyntheseplatten haben sich bezuglich ihrer Rigiditat bewahrt. Es ist aber von Interesse, die biologische Reaktion des Knochens auf Grenzwerte der Plattensteifigkeit genauer zu kennen. In einer ersten Versuchsreihe (1) wiesen wir unter der Bedingung des direkten Kontaktes der Osteotomiefragmente bei zu geringer Rigiditat nebst Callus auch Verbreiterung des Osteotomiespaltes durch Resorption nach. Die jetzigen Versuche betreffen den Einflus der Rigiditat der Osteosyntheseplatte auf die Osteotomieheilung bei nicht unter Kontakt fixierten Fragmentenden.

Einer der Ersten, der die Metallosteosynthese wissenschaftlich umfassend bearbeitet hat, war Nicole (1940, 1947). Er kam zum Schlus, das ein idealer Erfolg nur dann gewahrleistet ist, wenn zwei Voraussetzungen erfullt sind: Gunstige physiologisch-mechanische Konstellation und fehlende Metallschadigung fur die ganze Dauer der Knochenheilung. Die gunstige physiologisch-mechanische, besser biomechanische Konstellation ist eine Frage der dem Einzelfall angepasten Operationsmethode und der Operationstechnik Die Vermeidung von Metallschaden ist eine Materialfrage. Diese, auf zwei verschiedenen Wirkungsfaktoren beruhende Konzeption war fur jene Zeit erstaunlich, denn die metallurgische und chemische Technologie war damals noch auserstande, hochst korrosionsfeste Metalle in der geforderten Reinheit und Gleichmasigkeit zu liefern. Die biomechanische Betrachtungsweise gewann um so mehr an Bedeutung, als Nicole erkannte, das ein biomechanisch richtig eingesetzter Fremdkorper trotz Korrosion und Metallose zu einer einwandfreien Frakturheilung fuhrt, das also die Metallose, wie er sich ausdruckte, vom Organismus bis zu einem gewissen Grade uberwunden wird. Nicole schrieb wortlich „das die zunehmende Veredelung des Allenthesenmaterials einen wichtigen Forschungszweig darstellt, das aber das zentrale Problem der Osteosynthese in der Garantierung einer physiologisch-mechanischen Konstellation bis zur Konsolidierung des Bruchs liegt“.

Fert (1), Trillat (2) et Ladage (3) ont montre qu’en utilisant une source d’ions appropries, il etait possible d’attaquer par pulverisation cathodique un echantillon en cours d’observation par diffraction electronique par reflexion.