Sixty-five Holstein cows were used to evaluate management schemes involving altered dry period (DP) lengths on subsequent milk production, energy balance (EB), and metabolic variables. Cows were assigned to one of 3 treatments: traditional 56-d DP (fed a low-energy diet from -56 to -29 d and a moderate energy diet from -28 d to parturition; T), 28-d DP (continuously fed a high energy diet; S), and no planned DP (continuously fed a high energy diet; N). Prepartum DM intake (DMI), measured from 56 d prepartum through parturition, was lower for cows on the T treatment than for cows on the S treatment and was higher for cows on the N treatment than for cows on the S treatment. There were no differences in prepartum plasma glucose, and beta-hydroxybutryric acid; there was a treatment by time interaction for prepartum plasma nonesterified fatty acid (NEFA). There was no difference in prepartum liver triglyceride (TG); postpartum liver TG was decreased for cows on the N treatment compared with cows on the S treatment, but was similar for cows on the T and S treatments. Postpartum NEFA was similar between cows on the T and S treatments, but was greater for cows on the S treatment than for cows on the N treatment. Postpartum glucose was greater for cows on the N treatment compared with cows on the S treatment and tended to be greater for cows on the S treatment than for cows on the T treatment. There was no difference in postpartum solids-corrected milk (SCM) production or DMI by cows on the T vs. S treatment. However, there was a tendency toward lower postpartum SCM production by cows on the N vs. S treatment and a tendency for greater postpartum DMI by cows on the N vs. S treatment. Postpartum EB was greater for cows on the S vs. T treatment and the N vs. S treatment. In general, T and S management schemes had similar effects on DMI, SCM, and metabolic variables in the first 70 d of the subsequent lactation. Eliminating the DP improved energy and metabolic status.

The propagation of a light beam through a nonlinear medium is the simplest scenario that one could imagine for light-matter interaction, but it is accompanied by a series of dramatic and fascinating changes in the spatio-temporal structure of the beam. Among these are light-induced scattering which may result in asymmetric beam fanning; the formation of spatial distributions of the electromagnetic fields that results in back reflection; phase-conjugation; and the possibility to prevent the beam from spreading and to enable selftrapping of the beam profile. Therefore, the spatial evolution of a single light beam is a central topic of nonlinear optical dynamics. A theoretical interpretation of this complex phenomenon and its experimental verification are of key importance for gaining insight into the nonlinear properties of a particular medium, on the one hand, and for contributing to our understanding of more general questions about the complex spatio-temporal behavior of nonlinear systems on the other hand. This is the reason why we have chosen this simple propagation of light through a nonlinear medium as the starting point for our investigations.The topic is not a completely new one. Initial investigations on the selftrapping of light beams in nonlinear media were already performed in the early 1960s [1, 2]. The most important task, since the beginning of this research, was to find the conditions for the stability and nonlinear evolution of solitary-wave solutions of the nonlinear propagation equations associated with the propagation of the beam in the nonlinear material. This is one of the most crucial parts of the problem of self-trapping of optical beams and promises applications in waveguiding, information processing and, most simply, propagation without spreading losses.In general, these effects may occur in all materials that display a nonlinear response that may act in such a way that diffraction effects due to the propagation of the beam can be compensated exactly. The balance between beam broadening on the one hand and self-focusing on the other hand gives rise to the formation of a solitary wave. In this case the envelope of the light wave does not change its profile during propagation. This wave is often called a soliton for short.Solitons are waves that do not spread or disperse like all familiar waves, but retain their size and shape indefinitely -they are dynamically and struc-

SummaryTarget controlled infusion (TCI) pumps function using a programme based on a pharmacokinetic ⁄ pharmacodynamic model. We compared the Marsh and Schnider models to find out which better correlates with the clinically observed effect of propofol as assessed by the Observer Assessment of Alertness ⁄ Sedation (OAAS) score and the Bispectral index. We assessed the sedation score and Bispectral index score in 40 un-premedicated patients undergoing surgical procedures under spinal anaesthesia with propofol sedation to a target concentration of 2 lg.ml. Half of the patients received TCI propofol driven by the Schnider model in effect site control, the other half were sedated with TCI propofol driven by the Marsh model in plasma control. We calculated the effect site concentration predicted by both models for all the patients. Changes in the sedation score and Bispectral index correlated better with the Marsh than with the Schnider effect site prediction in both study groups. Target controlled infusion (TCI) systems are designed to facilitate the delivery of intravenous anaesthetics. The anaesthetist sets the desired target blood or effect site concentration and the TCI pump adjusts the rate of delivery of the anaesthetic agent according to a pharmacokinetic ⁄ pharmacodynamic (PK ⁄ PD) model. Different PK ⁄ PD models predict different rates of drug transfer and effect site equilibration. The Diprifusor manufactured by AstraZeneca (Macclesfield, UK) was the first available propofol TCI pump which was based on 'the Marsh PK ⁄ PD model' [1]. More recently, a different PK ⁄ PD model, 'the Schnider model ' [2], has been introduced into clinical practice. During induction of anaesthesia, the Schnider model predicts faster propofol effect site equilibration than the Marsh model.A sedation score can be used to assess the hypnotic effect of anaesthetic drugs. The rate of achieving a certain level of sedation or the time course of the sedation score should reflect the rate of effect site equilibration. The responsive component of the Observer Assessment of Alertness ⁄ Sedation (OAAS) score (Table 1) can be used for this purpose [3,4]. This allows the effect site prediction from a PK ⁄ PD model to be compared with the evolution of the OAAS over time.Bispectral index (BIS) monitoring measures the hypnotic effect of anaesthetics [5,6]. Although more often used to assess the depth of anaesthesia, BIS has also been used to evaluate the depth of sedation [6,7].We aimed to study which of the two PK ⁄ PD models better correlates with the clinically observed effect of propofol, as assessed by the OAAS score and BIS monitoring. MethodsAfter obtaining ethics committee approval and signed informed consent, we recruited 40 un-premedicated, ASA I-III patients undergoing orthopaedic surgery under spinal anaesthesia with propofol sedation. Exclusion criteria were as follow: age less than 18 years, any

No abstract

No abstract