Search Results - (Author, Cooperation:L. G. Pettersson)

2015-02-28

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

2013-03-16

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

2014-06-20

Nature Publishing Group (NPG)

0028-0836

1476-4687

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

1089-7690

AIP Digital Archive

Physics

Chemistry and Pharmacology

A study of the NO2+ ion by means of Auger spectroscopy, fast ion beam laser spectroscopy and ab initio calculations is reported. The photon induced Auger spectrum of NO was recorded. Potential curves for a number of electronic states of NO2+ were calculated by the complete active space SCF method in order to facilitate an analysis of the Auger spectrum. A photoabsorption spectrum of NO2+ was observed by means of photofragment kinetic energy spectroscopy and assigned to the A 2Π←X 2Σ+ transition. The two different experimental methods both give a value of 38.6 eV for the appearance energy of NO2+, which is entirely consistent with recent photoionization and double charge transfer results.

Electronic Resource

1089-7690

AIP Digital Archive

Physics

Chemistry and Pharmacology

The chemisorptive interaction of the hydroxy radical (OH) with the Cu(111) surface and its consequences for the surface electronic structure are studied by CunOH (n ranging from 1 to 25) cluster models using ab initio Hartree–Fock and correlated wave functions. A comparison of the adsorbate binding at the Cu(111) on top, bridge, and the two threefold hollow [face-centered-cubic and hexagonal-close-packed (fcc and hcp)] sites based on extended geometry optimizations yields the fcc site energetically favored with a binding energy EB=3.1 eV at the configuration interaction (CI) level. Correlation contributions account for about 0.9 eV of the binding and are almost independent of the binding site and cluster size. The OH–metal interaction is characterized by considerable Cu to OH charge transfer filling the partially occupied O 2p lone pair orbitals (OH 1π), while OH to Cu charge transfer involving the OH 3σ orbital is small. As a result, the adsorbate is negatively charged in the presence of the surface and ionic binding contributions become important. This makes the OH–metal binding very similar to that of other radicals such as, e.g., OCH3. The adsorbate binding character is also reflected in the results of cluster core and valence hole states corresponding to OH adsorbate ionization. These results may be compared with experimental photoionization data as they become available.

Electronic Resource

1460-9568

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

This study uses a previously described paradigm (Pettersson et al., 1997) to investigate the ability of cats to change the direction of ongoing reaching when the target is shifted sideways; the effect on the switching latency of spinal cord lesions was investigated. Large ventral lesions transecting the ventral funicle and the ventral half of the lateral funicle gave a 20–30 ms latency prolongation of switching in the medial (right) direction, but less prolongation of switching directed laterally (left), and in one cat the latencies of switching directed laterally were unchanged. It may be inferred that the command for switching in the lateral direction can be mediated by the dorsally located cortico- and rubrospinal tracts whereas the command for short-latency switching in the medial direction is mediated by ventral pathways. A restricted ventral lesion transecting the tectospinal pathway did not change the switching latency. Comparison of different ventral lesions revealed prolongation of the latency if the lesion included a region extending dorsally along the ventral horn and from there ventrally as a vertical strip, so it may be postulated that the command for fast switching, directed medially, is mediated by a reticulospinal pathway within this location. A hypothesis is forwarded suggesting that the visual control is exerted via ponto-cerebellar pathways.

Electronic Resource

1398-9995

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

Schoolchildren (n= 473), 12–13 years of age, from five schools, and without known asthma, participated in a screening test for exercise-induced asthma (E1A). The children were tested in large groups of 10–15 pupils. Peak expiratory flow (PEF) was measured before, immediately after, and 6–8 min after 6 min of running exercises in a gymnasium. A fall in PEF of at least 10% on two separate test occasions was considered an abnormal result. Children with abnormal results were given an asthma questionnaire and then tested individually in hospital with a standardized exercise test measuring FEVb PEF, and flow/volume curve. In the screening test, 23 (4.9%) of the 473 children had an abnormal result. When tested in hospital, five (1%) children had a decrease in PEF and/or FEV, of at least 10% (10–14%) after exercise. Furthermore, three of these five children had a history indicating mild EIA. We conclude that the use of PEF measurement as a screening method for EIA in large groups of schoolchildren cannot be recommended because it yields many false-positive results.

Electronic Resource

1432-1106

Low spinal cat ; Reflex pathways ; Tonic inhibition ; L2–L3 propriospinal neurones

Springer Online Journal Archives 1860-2000

Medicine

Summary Transmission in various spinal hindlimb reflex pathways arising from muscle, cutaneous and joint afferents, was investigated in acute low spinal (Th10) cats before and after lesions at more caudal levels in the lumbar segments. Lesions of the ipsilateral dorsolateral funiculus (DLF) resulted in increased mono- and polysynaptic ventral root discharges. With conditioning of monosynaptic reflexes it was demonstrated that the DLF lesion enhanced transmission in reflex pathways from group II and III muscle afferents. The DLF lesion also resulted in increased dorsal root potentials from cutaneous, joint and group III muscle afferents. These reflex enhancements could not be obtained with lesions rostral to L2, but developed with lesions in L2 and to some extent in L3, but no further effect was obtained by adding lesions caudal to L3. Ventral extension of the DLF lesion gave hardly any increase of reflex transmission. It is postulated that the investigated reflex pathways may be tonically inhibited in the acute low spinal state by propriospinal neurones with cell bodies in the L2–L3 segments and with axons descending in the dorsolateral funiculus.

Electronic Resource

1432-1106

Target-reaching ; Wrist trajectory ; Velocity profiles ; Target position ; Cat

Springer Online Journal Archives 1860-2000

Medicine

Abstract Trajectory formation of unrestrained forelimb target-reaching was investigated in relation to the effect of a change in target location. Sagittal displacement of the target (6 cm in each direction) gave a selective change of velocity in the x direction (protraction) with an increase or decrease at larger and shorter distances, respectively. In the case of a double-peaked x velocity profile, the change was mainly with respect to the first major component. The shape of the y (sideways) and of the z (lifting) velocity profiles were both almost unchanged, but the onset of the movement in the z direction changed with the x distance. Vertical displacement (4 cm up or 5 cm down) gave increased velocity in the z direction (lifting) when the target was above the normal mid-position and decreased velocity when the target was lower. The velocity was changed with constant rate of rise, so that the rise time increased when the target was elevated and shortened when the target was lowered (pulse width control policy). The change in the z velocity was not selective. In cats with a double-peaked x velocity profile, the second component decreased when the target was elevated and increased when it was lowered. With excessive lowering of the target (14 cm down), the first x velocity component was very much reduced in amplitude so that protraction depended mainly on the second x velocity component. In the cat with a unimodal x velocity profile, a second component appeared in the x and net velocity profiles when the target was excessively lowered. The velocity profile in the y direction changed when the target was lowered so that the horizontal movement path became straighter. Sideways displacement (10–13 cm) produced adduction/abduction, with only moderate changes in x and z velocity profiles. The results are discussed with reference to the angular movements in the elbow and shoulder.

Electronic Resource

1432-1106

Target-reaching ; Wrist trajectory ; Velocity profiles ; Cat

Springer Online Journal Archives 1860-2000

Medicine

Abstract Trajectory formation of unrestrained forelimb target-reaching was investigated in six cats. A Selspotlike recording system was used for three-dimensional recording of the position of the wrist every 3 ms with the aid of two cameras detecting infrared light emitted from diodes taped to the wrist. These measurements allowed reconstruction of movement paths in the horizontal and sagittal planes and velocity profiles in the direction of the cartesian x, y and z co-ordinates. Horizontal movement paths were smoothly curved, segmented or almost linear. Sagittal movement paths were sigmoid. The net velocity profile was usually bell-shaped with longer deceleration than acceleration, but for some slow movements the velocity profile had a plateau. When the net velocity profile was bell-shaped, the averaged sagittal movement paths and normalized x (protraction) and z (lifting) velocity profiles were virtually superimposable for fast and slow movements: thus, movement speed was changed by parallel scaling of protraction and lifting. Comparison of movement paths and velocity profiles amongst the different cats revealed considerable differences. The ż profile was unimodal in one cat and double peaked in five cats: the second component was pronounced in two cats and small in the other three. The ż profile was unimodal and, except for one cat, it had later onset and summit than the first component of the x profile. In contrast to the interindividual differences, there was a high degree of intraindividual constancy over 6–12 months. It is postulated that the interindividual variability depends on chance differences established early during learning of the task and that the imprinted pattern remains, resulting in intra-individual constancy.

Electronic Resource

1432-1106

Target reaching ; Switching ; Ongoing movement ; Cats

Springer Online Journal Archives 1860-2000

Medicine

Summary A task has been developed to investigate the ability of cats to switch the direction of an ongoing target-reaching forelimb movement with the aid of a visual cue. The cats were standing in front of two horizontal tubes (internal diameter 30 mm; shoulder level) with food. The entrances of the tubes were closed with opaque trap doors but during illumination inside a tube its trap door was unlocked allowing the cat to retrieve food with the paw. When the cats had learnt to select the illuminated tube for insertion the next step was to switch the illumination to the other tube during ongoing targetreaching. Limb lifting was performed when the light was switched on in one of the tubes and time was measured from breaking electrical contact between the paw and the floor. After 25–75 ms, illumination was shifted to the other tube and the latency to the earliest change in movement trajectory was measured. The trajectory was recorded with the aid of cameras detecting the position of infrared light emitting diodes fixed to the dorsal part of the wrist. Every 3 ms the position was fed into a computer, and the movement trajectory (horizontal and sagittal planes) was displayed graphically. The velocities in the direction of cartesian coordinates x, y and z (protraction, adduction-abduction, lifting) were also computed. Single tube trials and switching trials from either tube were made in a random series. In order to switch, the cats used a combination of braking the protraction and a sideways movement. Initially there was often some retraction of the paw to avoid hitting the trap door of the first illuminated tube, but with more proficiency braking decreased and the movement path became smoothly curved. During braking of protraction there was also deceleration of lifting but not enough to maintain a constant movement path in the sagittal plane. In sessions with single tube trials, the movement paths in the horizontal plane were reasonably straight. In sessions with intermixed switching trials the single tube paths became segmented or curved, seemingly in order to facilitate switching. The mean switching latency in four cats ranged from 83 to 118 ms. In the fastest cat the switching latency ranged from 70–106 ms. Considering the time for retinal processing, the electromechanical delay, synaptic delays in the theoretically shortest pathways, time for excitation at several synapses and the central and peripheral axonal conduction times, it is argued that switching latencies in the range 70–80 ms depends on transmission in a subcortical retino-tectospinal pathway.

Electronic Resource

1432-1106

Key words Cat ; Target-reaching ; Obstacle training ; Kinematics

Springer Online Journal Archives 1860-2000

Medicine

Abstract  Three cats were trained to perform target-reaching to a horizontal tube with food placed at shoulder level, and the kinematic characteristics of the movements were investigated by recording the trajectory of the wrist. From the very onset of training, a vertical obstacle was placed in front of the cats. The obstacle forced the animals to perform movements with an initial phase dominated by limb-lifting to position the wrist above the obstacle, followed by a second phase of protraction towards the tube; in the sagittal plane, the movement paths were segmented with an upwards convexity. After a training period of 1 year (about 7000 movements), the obstacle was removed. All cats then quickly (within a few trials) changed the trajectory so that the main part of protraction now occurred in parallel with limb-lifting during the first half of the movement. The initial slope of the sagittal movement path became less steep and the upwards convexity less pronounced. Such trajectories, which predominated for several experiments after removal of the obstacle, were only slightly different from those observed in control cats not trained with an obstacle. The results are discussed in relation to a previously proposed hypothesis of motor “imprinting” during extensive training in a particular experimental paradigm.

Electronic Resource

1432-2234

NO ; NiO(100) surface ; Bonding

Springer Online Journal Archives 1860-2000

Chemistry and Pharmacology

Summary The interaction between NO and different possible adsorption sites of the NiO(100) surface is studied. The Ni2+ cation gives a bonding to NO in reasonable agreement with experiment, but only if a crystal potential corresponding to less than completely ionic charges is assumed. The computed angle of 43° is also in good agreement with experiment. O1− sites in both weak and strong crystal potentials also give a strong interaction with NO, 1.3 and 0.5 eV, respectively. In this case the angle is larger or around 70°. The O2− anion and Ni1+ sites do not give any significant bonding irrespective of assumed crystal potential and can be excluded as adsorption sites. The computed vibrational frequency for the adsorbed NO show shifts of +50, −85 and −200 cm−1 for adsorption on Ni2+ in the weak potential, and O1− in strong and weak potential, respectively. Only one, downwards shifted, frequency has been observed in the experiment but the most likely candidate for the experimentally observed adsorption site with a binding of 0.5 eV, is still the Ni2+ in a weak potential. Nitrogen core level shifts are also computed and discussed and the fully screened core-hole state is obtained for a cluster model, NiF4O+NO, of Ni2+ in NiO with an ionicity lower than the standard ± 2.

Electronic Resource