There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Vascular endothelial growth factor (VEGF) is an endothelial cell-specific mitogen in vitro and an angiogenic inducer in a variety of in vivo models. Hypoxia has been shown to be a major inducer of VEGF gene transcription. The tyrosine kinases Flt-1 (VEGFR-1) and Flk-1/KDR (VEGFR-2) are high-affinity VEGF receptors. The role of VEGF in developmental angiogenesis is emphasized by the finding that loss of a single VEGF allele results in defective vascularization and early embryonic lethality. VEGF is critical also for reproductive and bone angiogenesis. Substantial evidence also implicates VEGF as a mediator of pathological angiogenesis. In situ hybridization studies demonstrate expression of VEGF mRNA in the majority of human tumors. Anti-VEGF monoclonal antibodies and other VEGF inhibitors block the growth of several tumor cell lines in nude mice. Clinical trials with various VEGF inhibitors in a variety of malignancies are ongoing. Very recently, an anti-VEGF monoclonal antibody (bevacizumab; Avastin) has been approved by the Food and Drug Administration as a first-line treatment for metastatic colorectal cancer in combination with chemotherapy. Furthermore, VEGF is implicated in intraocular neovascularization associated with diabetic retinopathy and age-related macular degeneration.

/pdf/vascular-endothelial-growth-factor-basic-science-and-17gyy6h97s.pdf

Vascular endothelial growth factor: basic science and clinical progress.

Muscle fatigue is an exercise-induced reduction in maximal voluntary muscle force. It may arise not only because of peripheral changes at the level of the muscle, but also because the central nervous system fails to drive the motoneurons adequately. Evidence for “central” fatigue and the neural mechanisms underlying it are reviewed, together with its terminology and the methods used to reveal it. Much data suggest that voluntary activation of human motoneurons and muscle fibers is suboptimal and thus maximal voluntary force is commonly less than true maximal force. Hence, maximal voluntary strength can often be below true maximal muscle force. The technique of twitch interpolation has helped to reveal the changes in drive to motoneurons during fatigue. Voluntary activation usually diminishes during maximal voluntary isometric tasks, that is central fatigue develops, and motor unit firing rates decline. Transcranial magnetic stimulation over the motor cortex during fatiguing exercise has revealed focal cha...

Spinal and Supraspinal Factors in Human Muscle Fatigue

A central problem in motor control is understanding how the many biomechanical degrees of freedom are coordinated to achieve a common goal. An especially puzzling aspect of coordination is that behavioral goals are achieved reliably and repeatedly with movements rarely reproducible in their detail. Existing theoretical frameworks emphasize either goal achievement or the richness of motor variability, but fail to reconcile the two. Here we propose an alternative theory based on stochastic optimal feedback control. We show that the optimal strategy in the face of uncertainty is to allow variability in redundant (task-irrelevant) dimensions. This strategy does not enforce a desired trajectory, but uses feedback more intelligently, correcting only those deviations that interfere with task goals. From this framework, task-constrained variability, goal-directed corrections, motor synergies, controlled parameters, simplifying rules and discrete coordination modes emerge naturally. We present experimental results from a range of motor tasks to support this theory.

/pdf/optimal-feedback-control-as-a-theory-of-motor-coordination-jh26vkl3kk.pdf

Optimal feedback control as a theory of motor coordination.

https://deepblue.lib.umich.edu/bitstream/handle/2027.42/90300/j.ejpain.2004.11.001.pdf?sequence=1

Human brain mechanisms of pain perception and regulation in health and disease.

Morphologic, physiologic, and clinical evidence for the sensory role of the cruciate ligaments is reviewed. The cruciate ligaments accommodate morphologically different sensory nerve endings (Ruffini endings, Pacinian corpuscles, Golgi tendon organlike endings, and free nerve endings) with different capabilities of providing the central nervous system with information not only about noxious and chemical events but also about characteristics of movements and position-related stretches of these ligaments. A survey of available data reveals that low threshold joint-ligament receptor (i.e., mechanoreceptor) afferents evoke only weak and rare effects in skeletomotor neurons (alpha-motor neurons), while they frequently and powerfully influence fusimotor neurons (gamma-motor neurons). The effects on the gamma-muscle-spindle system in the muscles around the knee are so potent that even stretches of the cruciate ligaments at relatively moderate loads (not noxious) may induce major changes in responses of the muscle spindle afferents. As the activity in the primary muscle spindle afferents modifies the stiffness in the muscles, the cruciate ligament receptors, via the gamma-muscle-spindle system, may participate in the regulation and preprogramming of the muscular stiffness around the knee joint and thereby of the knee joint stiffness. Thus, the sensory system of the cruciate ligaments is able to significantly contribute to the functional stability of the knee joint.

A sensory role for the cruciate ligaments.

Usage of passive intelligent surface (PIS) is emerging as a low-cost green alternative to massive antenna systems for realizing high energy beamforming (EB) gains. To maximize its realistic utility, we present a novel channel estimation (CE) protocol for PIS-assisted energy transfer (PET) from a multiantenna power beacon (PB) to a single-antenna energy harvesting (EH) user. Noting the practical limitations of PIS and EH user, all computations are carried out at PB having required active components and radio resources. Using these estimates, near-optimal analytical active and passive EB designs are respectively derived for PB and PIS, that enable efficient PET over a longer duration of coherence block. Nontrivial design insights on relative significance of array size at PIS and PB are also provided. Numerical results validating theoretical claims against the existing benchmarks demonstrate that with sufficient passive elements at PIS, we can achieve desired EB gain with reduced active array size at PB.

Channel Estimation and Low-complexity Beamforming Design for Passive Intelligent Surface Assisted MISO Wireless Energy Transfer

Section I: Molecular and Single Cell Level Techniques (9 chapters).-Section II: Techniques at Tissue Level (16 chapters).-Section III: Techniques at the Organismic Level (16 chapters).-Section IV: Strategies (2 chapters).-Appendix: Data Acquisition, Processing and Storage.-Subject Index

Modern techniques in neuroscience research

The knee joint ligaments contain Ruffini, Pacinian, Golgi, and free-nerve endings with different capabilities of providing the CNS with information about movement and position as well as about noxious events. Skeletomotor neurons (alpha-motoneurons) are known to be influenced only very rarely and weakly from low-threshold mechanoreceptors in the ligaments, while the effects on the tau-muscle-spindle system in the muscles around the knee are so potent that even ligament stretches at very low loads may induce major changes in the responses of the muscle spindle afferents. Since the primary muscle spindle afferents participate in the regulation of muscular stiffness, the receptors in the knee joint ligaments probably contribute, via the tau-muscle-spindle system, to preparatory adjustment (pre-setting) of the stiffness of the muscles around the knee joint, and thereby to the joint stiffness and the functional joint stability.

Receptors in the knee joint ligaments and their role in the biomechanics of the joint.

The reflex actions, elicited by graded electrical stimulation of hind-limb muscle, skin and joint nerves were studied in an extended series of experiments in extra-and intracellular recordings from 120 lumbar gamma-motoneurones of cats anaesthetized with chloralose. The present report deals with the action of group I muscle afferent fibres, which was examined in ninety-five gamma-cells. Of the gamma-cells 83% were classified as either static or dynamic by stimulation in the mesencephalic area for dynamic control. The general responsiveness (i.e. number of input nerves with effect/number of input nerves tested) of the cells was very high (89.9%). The responsiveness to stimulation of group I muscle afferent fibres was extremely low, both in flexor and extensor gamma-motoneurones and irrespective of whether they were static or dynamic. There was no difference, as regards the low incidence of group I muscle reflex action, between stimulation of autogenetic and heteronymous nerves. Among the rare reflex effects elicited from group I muscle fibres inhibition was four times as frequent as excitation. Inhibitory effects could be provoked from the autogenetic as well as from the heteronymous nerves. In contrast, excitatory effects were almost always autogenetic. The scarcity of group I muscle action on gamma-motoneurones is in striking contrast to the well known and powerful reflex actions of Ia and Ib fibres on alpha-motoneurones. These findings are discussed in relation to the concept of alpha-gamma linkage, and it is concluded that skeletomotor and fusimotor activity cannot be rigidly linked under all conditions.

Håkan Johansson

Papers

A sensory role for the cruciate ligaments.

Channel Estimation and Low-complexity Beamforming Design for Passive Intelligent Surface Assisted MISO Wireless Energy Transfer

Modern techniques in neuroscience research

Receptors in the knee joint ligaments and their role in the biomechanics of the joint.

Actions on gamma-motoneurones elicited by electrical stimulation of group II muscle afferent fibres in the hind limb of the cat.