Afferent Convergence from Divergent Sources Appears to Enhance the Spastic Patient\u27s Ability to Inhibit Antagonist Motoneurons During an Agonist Contraction

Spasticity and excessive muscular cocontraction during movement are common impairments following upper motor neuron (UMN) lesions. For example, during voluntary ankle dorsiflexion, individuals with spastic type cerebral palsy (CP) do not inhibit the antagonist triceps surae motoneuron pool

Antagonist Muscle Inhibition During Voluntary And Automatic Movements: Implications For Clinical Intervention

Various rehabilitation techniques encourage eliciting automatic reactions in the hope that muscle activations elicited in this way will influence voluntary movement. Unlike voluntary movements that consist of willed initiation and involvement of descending corticofugal and and basal ganglia pathways, automatic postural reactions resulting from external perturbations primarily involve peripheral receptors arising from the vestibular apparatus, muscles, joints, and eyes. We were interested to determine whether voluntary and automatic movements, which are initiated very differently, involved similar temporal activation of muscles and the same pattern of reciprocal inhibition between agonist and antagonist motor neuron pools

Quenched Narrow-Line Laser Cooling of 40Ca to Near the Photon Recoil Limit

We present a cooling method that should be generally applicable to atoms with narrow optical transitions. This technique uses velocity-selective pulses to drive atoms towards a zero-velocity dark state and then quenches the excited state to increase the cooling rate. We demonstrate this technique of quenched narrow-line cooling by reducing the 1-D temperature of a sample of neutral 40Ca atoms. We velocity select and cool with the 1S0(4s2) to 3P1(4s4p) 657 nm intercombination line and quench with the 3P1(4s4p) to 1S0(4s5s) intercombination line at 553 nm, which increases the cooling rate eight-fold. Limited only by available quenching laser power, we have transferred 18 % of the atoms from our initial 2 mK velocity distribution and achieved temperatures as low as 4 microK, corresponding to a vrms of 2.8 cm/s or 2 recoils at 657 nm. This cooling technique, which is closely related to Raman cooling, can be extended to three dimensions.Comment: 5 pages, 4 figures; Submitted to PRA Rapid Communication

Doppler cooling and trapping on forbidden transitions

Ultracold atoms at temperatures close to the recoil limit have been achieved by extending Doppler cooling to forbidden transitions. A cloud of ^40Ca atoms has been cooled and trapped to a temperature as low as 6 \mu K by operating a magneto-optical trap on the spin-forbidden intercombination transition. Quenching the long-lived excited state with an additional laser enhanced the scattering rate by a factor of 15, while a high selectivity in velocity was preserved. With this method more than 10% of pre-cooled atoms from a standard magneto-optical trap have been transferred to the ultracold trap. Monte-Carlo simulations of the cooling process are in good agreement with the experiments

Two-Photon Doppler cooling of alkaline-earth-metal and ytterbium atoms

A new possibility of laser cooling of alkaline-earth-metal and Ytterbium atoms using a two-photon transition is analyzed. We consider a $^{1}S_{0}$ - $^{1}S_{0}$ transition, with excitation in near resonance with the $^{1}P_{1}$ level. This greatly increases the two-photon transition rate, allowing an effective transfer of momentum. The experimental implementation of this technique is discussed and we show that for Calcium, for example, two-photon cooling can be used to achieve a Doppler limit of 123 microKelvin. The efficiency of this cooling scheme and the main loss mechanisms are analyzed.Comment: 7 pages, 5 figure

Nonclassical Interference Effects In The Radiation From Coherently Driven Uncorrelated Atoms

We demonstrate the existence of new nonclassical correlations in the radiation of two atoms, which are coherently driven by a continuous laser source. The photon-photon-correlations of the fluorescence light show a spatial interferene pattern not present in a classical treatment. A feature of the new phenomenon is, that bunched and antibunched light is emitted in different spatial directions. The calculations are performed analytically. It is pointed out, that the correlations are induced by state reduction due to the measurement process when the detection of the photons does not distinguish between the atoms. It is interesting to note, that the phenomena show up even without any interatomic interaction.Comment: 4 pages, 6 Figure

Deterministic delivery of externally cold and precisely positioned single molecular ions

We present the preparation and deterministic delivery of a selectable number of externally cold molecular ions. A laser cooled ensemble of Mg^+ ions subsequently confined in several linear Paul traps inter-connected via a quadrupole guide serves as a cold bath for a single or up to a few hundred molecular ions. Sympathetic cooling embeds the molecular ions in the crystalline structure. MgH^+ ions, that serve as a model system for a large variety of other possible molecular ions, are cooled down close to the Doppler limit and are positioned with an accuracy of one micrometer. After the production process, severely compromising the vacuum conditions, the molecular ion is efficiently transfered into nearly background-free environment. The transfer of a molecular ion between different traps as well as the control of the molecular ions in the traps is demonstrated. Schemes, optimized for the transfer of a specific number of ions, are realized and their efficiencies are evaluated. This versatile source applicable for broad charge-to-mass ratios of externally cold and precisely positioned molecular ions can serve as a container-free target preparation device well suited for diffraction or spectroscopic measurements on individual molecular ions at high repetition rates (kHz).Comment: 11 pages, 8 figure

Single photon generation by pulsed excitation of a single dipole

The fluorescence of a single dipole excited by an intense light pulse can lead to the generation of another light pulse containing a single photon. The influence of the duration and energy of the excitation pulse on the number of photons in the fluorescence pulse is studied. The case of a two-level dipole with strongly damped coherences is considered. The presence of a metastable state leading to shelving is also investigated.Comment: 17 pages, 4 figures, submitted to PR

Postoperative Immune Suppression in Visceral Surgery: Characterisation of an Intestinal Mouse Model

Background: Postoperatively acquired immune dysfunction is associated with a higher mortality rate in case of septic complications. As details of this severe clinical problem are still unknown, animal models are essential to characterise the mechanisms involved. Methods: Mice were laparotomised and the small intestine was pressed smoothly in antegrade direction. For extension of trauma, the intestine was manipulated three times consecutively. Following this, the ex vivo cytokine release of splenocytes was determined. The degree of surgical trauma was analysed by detection of HMGB1 and IL-6 in serum and by neutrophil staining in the muscularis mucosae. Results: We adapted the previously described animal model of intestinal manipulation to provide a model of surgically induced immune dysfunction. Following intestinal manipulation, the mice showed elevated serum levels of HMGB1 and IL-6 and increased infiltration of granulocytes into the muscularis mucosae. Ex vivo cytokine release by splenocytes was suppressed in the postoperative period. The degree of suppression correlated with the extent of surgical trauma. Conclusions: In this study, we describe a surgically induced immune dysfunction animal model, in which a significant surgical trauma is followed by an immune dysfunction. This model may be ideal for the characterisation of the postoperative immune dysfunction syndrome