Femtosecond time-resolved photoelectron spectroscopy of the benzyl radical

We present a joint experimental and computational study of the nonradiative deactivation of the benzyl radical, C₇H₇, after UV excitation. Femtosecond time-resolved photoelectron imaging was applied to investigate the photodynamics of the radical. The experiments were accompanied by excited state dynamics simulations using surface hopping. Benzyl has been excited at 265 nm into the D-band (ππ*) and the dynamics was probed using probe wavelengths of 398 nm or 798 nm. At a probe wavelength of 398 nm a single time constant of around 70-80 fs was observed. When the dynamics was probed at 798 nm, a second time constant τ₂ = 1.5 ps was visible, which can be attributed to further non-radiative deactivation to the lower-lying D₁/D₂ states.

Semiconductor laser linewidth reduction by six orders of magnitude via delayed optical feedback

We demonstrate a coherence increase by six orders of magnitude of a standard quantum well semiconductor laser. Using a simple, optical-fiber-based feedback scheme, we stabilize the laser in a high-gain mode of a long external cavity. In a modified self-heterodyne measurement, we mix the high-gain mode with a strongly suppressed side mode and obtain an interference linewidth of only 12.6 Hz, corresponding to a decoherence of (3.1±2.9) Hz. In an independent characterization using an etalon, we deduce an upper limit of 300 Hz for the laser linewidth. The laser stably resides in this mode for tens of seconds. Our results agree with theoretical predictions.

Combined Effects of Neurotrophin Secreting Transplants, Exercise, and Serotonergic Drug Challenge Improve Function in Spinal Rats

Objectives. To determine the effects of neurotrophin-secreting transplants combined with exercise and serotonergic drug challenges on recovery of hindlimb function in rats with midthoracic spinal cord transection injuries. Methods. Spinalized animals received transplants of fibroblasts genetically modified to express brain-derived neurotrophic factor and neurotrophin-3 and daily cycling exercise. Hindlimb movement in an open-field test (BBB) was scored weekly. Serotonin agonists were used monthly to further stimulate motor function. Axonal growth was quantified in the transplant and at L5 using immunocytochemical markers. Weights of hindlimb muscles were used to assess muscle atrophy. Results. Neurotrophin-secreting transplants stimulated axonal growth, and cycling prevented muscle atrophy, but individual treatments did not improve motor scores. Combined treatments resulted in improvements in motor function. Serotonergic agonists further improved function in all groups, and transplant groups with exercise achieved weight-supporting levels following drug treatment. Conclusion. Combined treatments, but not individual treatments, improved hindlimb function.

Transplantation of neural progenitor cells in chronic spinal cord injury

Previous studies demonstrated that neural progenitor cells (NPCs) transplanted into a subacute contusion injury improve motor, sensory, and bladder function. In this study we tested whether transplanted NPCs can also improve functional recovery after chronic spinal cord injury (SCI) alone or in combination with the reduction of glial scar and neurotrophic support. Adult rats received a T10 moderate contusion. Thirteen weeks after the injury they were divided into four groups and received either: 1. Medium (control), 2. NPC transplants, 3. NPC+lentivirus vector expressing chondroitinase, or 4. NPC+lentivirus vectors expressing chondroitinase and neurotrophic factors. During the 8 weeks post-transplantation the animals were tested for functional recovery and eventually analyzed by anatomical and immunohistochemical assays. The behavioral tests for motor and sensory function were performed before and after injury, and weekly after transplantation, with some animals also tested for bladder function at the end of the experiment. Transplant survival in the chronic injury model was variable and showed NPCs at the injury site in 60% of the animals in all transplantation groups. The NPC transplants comprised less than 40% of the injury site, without significant anatomical or histological differences among the groups. All groups also showed similar patterns of functional deficits and recovery in the 12 weeks after injury and in the 8 weeks after transplantation using the Basso, Beattie, and Bresnahan rating score, the grid test, and the Von Frey test for mechanical allodynia. A notable exception was group 4 (NPC together with chondroitinase and neurotrophins), which showed a significant improvement in bladder function. This study underscores the therapeutic challenges facing transplantation strategies in a chronic SCI in which even the inclusion of treatments designed to reduce scarring and increase neurotrophic support produce only modest functional improvements. Further studies will have to identify the combination of acute and chronic interventions that will augment the survival and efficacy of neural cell transplants.

Experimental Phase-Space Tomography of Semiconductor Laser Dynamics

We perform phase-space tomography of semiconductor laser dynamics by simultaneous experimental determination of optical intensity, frequency, and population inversion with high temporal resolution. We apply this technique to a laser with delayed feedback, serving as prominent example for high-dimensional chaotic dynamics and as model system for fundamental investigations of complex systems. Our approach allows us to explore so far unidentified trajectories in phase space and identify the underlying physical mechanism.

Assignment of high-lying bending mode levels in the threshold photoelectron spectrum of NH2: a comparison between pyrolysis and fluorine-atom abstraction radical sources

The bending mode progression in the photoelectron spectrum of NH₂ was observed and assigned up to υ₂⁺ ≤ 5 and K_a⁺ ≤ 3.

Formation of polycyclic aromatic hydrocarbons from bimolecular reactions of phenyl radicals at high temperatures

The self-reaction of the phenyl radical is one of the key reactions in combustion chemistry.

Molecular-like hierarchical self-assembly of monolayers of mixtures of particles

We present a technique that uses an externally applied electric field to self-assemble monolayers of mixtures of particles into molecular-like hierarchical arrangements on fluid-liquid interfaces. The arrangements consist of composite particles (analogous to molecules) which are arranged in a pattern. The structure of a composite particle depends on factors such as the relative sizes of the particles and their polarizabilities, and the electric field intensity. If the particles sizes differ by a factor of two or more, the composite particle has a larger particle at its core and several smaller particles form a ring around it. The number of particles in the ring and the spacing between the composite particles depend on their polarizabilities and the electric field intensity. Approximately same sized particles form chains (analogous to polymeric molecules) in which positively and negatively polarized particles alternate.

17β-Estradiol reduces nitric oxide production in the Guinea pig cochlea

Intense noise exposure and the application of ototoxic substances result in increased levels of reactive oxygen species (ROS) and reactive nitrogen species (RNS), such as nitric oxide (NO). In order to reduce the free NO concentration in the inner ear under pathological conditions, the use of natural cytoprotective substances such as 17β-estradiol is a promising therapeutic concept. In male guinea pigs the organ of Corti and the lateral wall were isolated from the cochlea and afterwards incubated for 6 h in cell-culture medium. 17β-Estradiol was adjusted in 2 concentrations to organ cultures of the right ears (12 animals per concentration). The left ears were used as controls. The NO production was quantified in the supernatant by chemiluminescence after incubation. Depending on the concentration, 17β-estradiol reduced NO in the organ of Corti by 43% (p=0.015) and 46% (p=0.026), respectively. In the lateral wall, the NO concentration was reduced by 24%, but without statistical significance (p=0.86). However, when analyzing the association between the 2 cochlear regions for each animal separately, the NO concentrations were lower in nearly all 17β-estradiol-treated ears compared to controls. In order to demonstrate the flexibility of the organ culture system, the NO donor DETA NONOate and the nitric oxide synthase inhibitors L-NAME and L-NMMA were applied. The electron microscopic analysis revealed a well-preserved cochlear cell morphology after incubation. The ability of 17β-estradiol to influence the NO production preferentially in the organ of Corti might offer new therapeutic perspectives for inner ear protection.

Characterizing the deterministic nature of individual power dropouts in semiconductor lasers subject to delayed feedback

We implement a method to identify the deterministic nature of specific events in the dynamics of a semiconductor laser subject to time-delayed optical feedback. Specifically, we study the power dropouts in the low-frequency fluctuations regime on an individual event basis and identify whether the underlying dominant mechanism is deterministic. Our approach is based on sychronization with a twin system in a symmetric relay configuration. We investigate the dependence of the fraction of deterministically driven (i.e., synchronized) dropouts on the laser's pump current as a key parameter. Our experimental results are corroborated by numerical modeling based on rate equations. Our numerical findings also provide insights into the influence of spontaneous emission noise.

Optoelectronic reservoir computing: tackling noise-induced performance degradation

We present improved strategies to perform photonic information processing using an optoelectronic oscillator with delayed feedback. In particular, we study, via numerical simulations and experiments, the influence of a finite signal-to-noise ratio on the computing performance. We illustrate that the performance degradation induced by noise can be compensated for via multi-level pre-processing masks.

Unilateral evisceration of an eye following cornea and lens perforation in a sulfur-crested cockatoo (Cacatua galerita)

A 24-year old male sulfur-crested Cockatoo (Cacatua galerita) was presented with a subacute perforation of the cornea without involvement of the lens. The bird was treated conservatively and the eye remained quiescent up to a second traumatic corneal perforation associated with a lens capsule rupture 15 months later. Due to the second perforating trauma of an already blind eye involving the lens, evisceration of the eye was performed. Two months after surgery the cosmetic result was excellent. Treatment options for perforating ocular traumas in captive birds are discussed in detail.

Association of microtubule-associated protein (MAP1B) with growing axons in cultured hippocampal neurons

Microtubule-associated protein 1B (MAP1B) is a major constituent of the neuronal cytoskeleton early in development. This protein is present in embryonic brain and is composed of two isoforms that are the result of differential phosphorylation. We examined the distribution of MAP1B during the differentiation of cultured hippocampal neurons and compared it to that of MAP2 and tubulin. We demonstrated by immunofluorescent doublestaining that MAP1B and MAP2 are colocalized in cell bodies and the minor processes of hippocampal neurons during the early stages of development, before the establishment of neuronal polarity. Later, when neurons acquire axonal and dendritic characteristics, MAP1B is sorted into growing axons, including the growth cone, whereas MAP2 is restricted to dendrites and cell bodies. Unlike tubulin, the localization of MAP1B in growing axons is not uniform. Rather, the protein is found concentrated in the distal portion. During later stages of development, the neurons extend a network of fasciculating axonal and dendritic neurites in which the segregation of MAP1B and MAP2 is maintained. However, the staining of MAP1B in mature neuronal cultures decreases in a pattern that resembles the decline of this protein during brain development. These results support the association of MAP1B with growing axons and its correct developmental regulation in the hippocampal culture system.

Spectral and correlation properties of rings of delay-coupled elements: comparing linear and nonlinear systems

The dynamical properties of delay-coupled systems are currently of great interest. So far the analysis has concentrated primarily on identical synchronization properties. Here we study the dynamics of rings of delay-coupled nodes, a topology that cannot show identical synchronization, and compare its properties to those of linear stochastic maps. We find that, in the long delay limit, the correlation functions and spectra of delay-coupled rings of nonlinear systems obey the same scaling laws as linear systems, indicating that important properties of the emerging solution result from network topology.

Zero-lag synchronization and bubbling in delay-coupled lasers

We show experimentally that two semiconductor lasers mutually coupled via a passive relay fiber loop exhibit chaos synchronization at zero lag, and study how this synchronized regime is lost as the lasers' pump currents are increased. We characterize the synchronization properties of the system with high temporal resolution in two different chaotic regimes, namely, low-frequency fluctuations and coherence collapse, identifying significant differences between them. In particular, a marked decrease in synchronization quality develops as the lasers enter the coherence collapse regime. Our high-resolution measurements allow us to establish that synchronization loss is associated with bubbling events, the frequency of which increases with increasing pump current.