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Der Knochen ist ständig wechselnden Belastungen ausgesetzt und adaptiert seine Festigkeit entsprechend. Mangelnde körperliche Aktivität bedeutet eine zu geringe Verformung des Knochens und in der Folge einen Knochenabbau. Zyklische Belastungen des Knochens jenseits der Modelling-Schwelle, welche ausreichend starke Verformungen des Knochens und Verschiebungen der intrakanalikulären Flüssigkeit mit sich bringen, resultieren in einer Erhöhung der Knochenfestigkeit. Diese Verformungen werden durch Osteozyten wahrgenommen. Die mechanischen Kräfte werden in biochemische Signale umgewandelt (Mechanotransduktion) und schließlich die Effektorzellen aktiviert (Transmission). Die Förderung der Osteoblasten bei Hemmung der Osteoklastenaktivität führt letztlich zu einer positiven Knochenbilanz. Die Reaktionen des Knochens sind aber nicht nur von Intensität und Frequenz der Belastung, sondern auch von der Beschleunigung der Bewegung abhängig. Nicht-mechanische Faktoren wie Sexualhormone modulieren das Ausmaß der Adaptation des Skeletts auf mechanische Reize.

Die Osteoporose ist eine systemische Knochenerkrankung, bei der eine verminderte Knochenfestigkeit zu einem erhöhten Frakturrisiko führt. Die Knochenfestigkeit reflektiert primär die Integration von Knochendichte und Knochenqualität. Leider gibt es noch keine allgemein anerkannte Definition der "Knochenqualität"; unabhängig von der Definition der Knochenqualität wird diese durch eine Vielzahl von Faktoren beeinflußt. Zu diesen Faktoren werden unter anderen die Knochengeometrie, die Anzahl der Trabekel, die trabekuläre Konnektivität, die Mineralisation des Knochens und Eigenschaften des Kollagens gezählt. In diesem Artikel werden verschiedene wissenschaftliche Aspekte der Knochendichte und Konsequenzen für die klinische Praxis dargestellt.

Fractures often are caused by a fall. It’s mostly the elderly who fall because postural strategies change with increasing age. About 30% of the elderly – above the age of 65 – fall at least once a year. With increasing age this ratio further increases. Ninety percent of the[for full text, please go to the a.m. URL], 7th EFSMA – European Congress of Sports Medicine, 3rd Central European Congress of Physical Medicine and Rehabilitation

The Neutrino Factory is a new concept for an accelerator that produces a high-intensity, high-energy beam of electron and muon neutrinos - the ultimate tool for neutrino oscillation studies and the only machine conceived up today that could help detect CP violation of leptons. The basic concept of the Neutrino Factory is the production of neutrinos from the decay of high-energy muons. Due to their short lifetime, these muons have to be accelerated very fast. Several new accelerator techniques, like a high-intenstiy proton linac, high-power targets, ionization cooling or recirculating muon linacs are required. This paper presents a snapshot of the accelerator design at CERN. Although some aspects of this European Neutrino Factory Scheme have been optimised for the CERN site, the basic principle is site-independent.

The LHC pre-injector complex, comprising Linac 2, the PS Booster (PSB) and the PS, has undergone a major upgrade in order to meet the very stringent requirements of the LHC. Whereas bunches with the nominal spacing and transverse beam brightness were already available from the PS in 1999 [1], their length proved to be outside tolerance due to a debunching procedure plagued by microwave instabilities. An alternative scenario was then proposed, based on a series of bunch-splitting steps in the PS. The entire process has recently been implemented successfully, and beams whose longitudinal characteristics are safely inside LHC specifications are now routinely available. Variants of the method also enable bunch trains with gaps of different lengths to be generated. These are of interest for the study and possible cure of electron cloud effects in both the SPS and LHC. The paper summarizes the beam dynamics issues that had to be addressed to produce beams with all the requisite qualities for the LHC.

The LHC [1] will be supplied, via the SPS, with protons from the pre-injector chain comprising Linac2, PS Booster (PSB) and PS. These accelerators have under-gone a major upgrading programme [2] during the last five years so as to meet the stringent requirements of the LHC. These imply that many high-intensity bunches of small emittance and tight spacing (25 ns) be available at the PS extraction energy (25 GeV). The upgrading project involved an increase of Linac2 current, new RF systems in the PSB and the PS, raising the PSB energy from 1 to 1.4 GeV, two-batch filling of the PS and the installation of high-resolution beam profile measurement devices. With the project entering its final phase and most of the newly installed hardware now being operational, the emphasis switches to producing the nominal LHC beam and tackling the associated beam physics problems. While a beam with transverse characteristics better than nominal has been obtained, the longitudinal density still needs to be increased. An alternative scheme to produce the 25 ns bunch spacing is outlined, together with other promising developments.

The performance of the CERN LHC will depend heavily on the high-brightness beam delivered by the injector chain. In 1999, after completion of the programme of hardware upgrades of the PS Complex, a major effort was devoted to producing a proton beam with the nominal transverse characteristics foreseen for LHC operation. This paper focuses on the different beam dynamics issues encountered during the setting up of such a beam, in the Linac2, the PS-Booster (PSB), the PS and the TT2 transfer line to the SPS. During the setting-up, single-particle issues, like stop-band compensation, correction of injection oscillations during the double-batch injection process, and the correction of the high-energy closed orbit in the PS, were addressed. Furthermore, collective effects, such as high-order head-tail instabilities induced by the resistive-wall impedance, were observed and cured. The compensation of these harmful phenomena permitted to achieve the goal, namely the generation of small transverse beam emittances and their conservation along the chain of different machines.

The LHC will be supplied with protons from the injector chain Linac2 - PS Booster - PS - SPS. These accelerators are being upgraded so as to meet the very demanding needs of the LHC: many high intensity bunches (25 ns spacing) with small emittances (transverse and longitudinal). The injector scheme which will satisfy these requirements is presented and the main challenges and problems for the machines are outlined. Some of the open issues which need further elaboration, such as tolerances on bunch intensity, are touched upon. The conversion of the PS complex enters its final phase and the first LHC-type beams have been delivered to the SPS. Finally, the Pb ion injector scheme is sketched and the promising outcome of a test campaign in LEAR is highlighted.

The tight transverse emittance budget for the bright beams foreseen for the LHC era demands that all sources of emittance blow-up in the injector chain are reduced to a minimum. A critical region is the transfer between the PS Booster (PSB) and the 26 GeV PS. The four rings of the PSB run with RF harmonic one, and for the LHC beam the PS will be filled with eight bunches originating from two consecutive PSB cycles. Thus, each bunch will be different and has to be individually treated. The present recombination scheme introduces an important difference in lattice parameters between the bunches from different rings. The difference between the bunches would, if left uncorrected, result in a substantial emittance blow-up. Several possible improvements of the recombination stage have been studied, including magnet shims, correction quadrupoles and an RF quadrupole magnet. To complement the theoretical studies, the contribution of mismatch and missteering to the emittance blow-up have been measured using a LHC-type beam, measuring the emittance in the PS with a wire-grid and fast wire-scanners. Results of the calculation and the measurements will be discussed and a strategy to minimise the blow-up will be indicated.

The ambitious performance goals of present and future hadron colliders call for a chain of injectors that are specially designed to provide high quality beams. However, for many reasons, not the least of which is cost, all these colliders make use of existing accelerator complexes that were not built for this new task and have therefore to be upgraded. A key issue such hadron injectors have to deal with is the preservation of transverse normalised emittance. Small transverse emittances are important because (i) the collider luminosity is proportional to N(N/e) and becomes larger for smaller emit tance; (ii) particle losses at injection into the collider are reduced, thus reducing the risk of quenching a superconducting magnet. Sources of emittance blow-up, such as mis-steering and mismatch be tween machines, space charge, instabilities and intra-beam scattering, are covered along with corrective measures. Problems common to the Tevatron, HERA-p, RHIC, LHC injector chains (the latter two in cluding heavy ion production) are discussed and the lessons that the LHC injectors can learn from existing hadron colliders are highlighted.

In preparation for the Large Hadron Collider (LHC), extensive modifications have been made to the RF equipment of the PS Booster (PSB) and of the PS during the winter shut down 97-98. Low-frequency RF systems (0.6 - 1.8 MHz and 1.2 - 3.9 MHz) have been installed in the PSB and fixed frequency (40 and 80 MHz) systems in the PS. The longitudinal characteristics of all beams are changed to make the best use of the new capabilities. This paper summarises the characteristics of the new equipment and describes the RF gymnastics used to generate the various beams. The performances achieved so far ar e reported and compared to former results. Future plans are sketched.

The LHC will be supplied with protons from the injector chain Linac2-PS Booster-PS-SPS. The beam must have small transverse emittances to fit into the LHC dynamic aperture, but sufficient intensity to assure high luminosity operation. Such a beam with a brightness twice the one of present beams is feasible with a scheme involving acceleration of one bunch (instead of five) in each of the four PSB rings to a kinetic energy raised from 1 to 1.4 GeV, and two-batch filling of the PS. Beam dynamics aspects such as how to tackle small emittances under high space charge, optimizing the (time-varying) working point and dealing with stop-bands, the advent of new RF harmonics 1 and 2, how to shape the magnet cycle, are discussed, and results of machine experiments reported. Finally some open issues as well as ideas for future improvements are discussed.