Apoptosis and proliferation in the trigeminal placode

The neurogenic trigeminal placode develops from the crescent-shaped panplacodal primordium which delineates the neural plate anteriorly. We show that, in Tupaia belangeri, the trigeminal placode is represented by a field of focal ectodermal thickenings which over time changes positions from as far rostral as the level of the forebrain to as far caudal as opposite rhombomere 3. Delamination proceeds rostrocaudally from the ectoderm adjacent to the rostral midbrain, and contributes neurons to the trigeminal ganglion as well as to the ciliary ganglion/oculomotor complex. Proliferative events are centered on the field prior to the peak of delamination. They are preceded, paralleled and, finally, outnumbered by apoptotic events which proceed rostrocaudally from non-delaminating to delaminating parts of the field. Apoptosis persists upon regression of the placode, thereby exhibiting a massive “wedge” of apoptotic cells which includes the postulated position of the “ventrolateral postoptic placode” (Lee et al. in Dev Biol 263:176–190, 2003), merges with groups of lens-associated apoptotic cells, and disappears upon lens detachment. In conjunction with earlier work (Washausen et al. in Dev Biol 278:86–102, 2005) our findings suggest that apoptosis contributes repeatedly to the disintegration of the panplacodal primordium, to the elimination of subsets of premigratory placodal neuroblasts, and to the regression of placodes

Vegetation and climate changes around the Lama Lake, Taymyr Peninsula during the Late Pleistocene and Holocene reconstructed from pollen records

A continuous lacustrine sequence from the western part of Lama Lake (69°32'N, 90°12'E),completed by a peat sequence from the lake catchment provides the first detailed environmentalreconstruction for the Late Glacial and Holocene on the Taymyr Peninsula. Scarce steppe-likecommunities with Artemisia, Poaceae, and Cyperaceae dominated during the Late Glacial. Tundra-like communities with Betula nana, Dryas, and Salix grew on more mesic sites. There are distinctclimatic signals, which may be correlated with the Bølling and Allerød warmings and Middle andYounger Dryas coolings. The Late Glacial/Preboreal transition, at about 10,000 14C yr BP, wascharacterized by changes from predominantly open herb communities to shrub tundra ones. Larchforest might have been established as early as 9700-9600 14C yr BP, whilst shrub alder came tothe area ca 9500-9400 14C yr BP, and spruce did not reach area before ca 9200 14C yr BP. Spruce-larch forests with shrub alder and tree birch dominated the vegetation around the Lama Lake fromca 9000 14C yr BP. Dwarf birch communities were also broadly distributed. Role of spruce in theforest gradually decreased after 4500 14C yr BP. Vegetation cover in the Lama Lake area becamesimilar to modern larch-spruce forest ca 2500 14C yr BP. A pollen-based biome reconstructionsupports a quantitative interpretation of the pollen spectra. Climate reconstructions obtained withinformation-statistical and plan-functional-type methods show very similar trends in reconstructedJuly temperature since ca 12,300 14C yr BP, while precipitation anomalies are less coherent,especially during the Late Glacial-Holocene transition

Divided-pulse amplification for terawatt-class fiber lasers

The coherent combination of ultra short laser pulses is a promising approach for scaling the average and peak power of ultrafast lasers. Fiber lasers and amplifiers are especially suited for this technique due to their simple singe-pass setups that can be easily parallelized. Here we propose the combination of the well-known approach of spatially separated amplification with the technique of divided-pulse amplification, i.e. an additionally performed temporally separated amplification. With the help of this multidimensional pulse stacking, laser systems come into reach capable of emitting 10's of joules of energy at multi-kW average powers that simultaneously employ a manageable number of fibers

Compact integration of amplifier channels for coherent combination of fiber amplifiers

Summary form only given. Coherent combination of fiber amplifiers has become a viable concept for pulse-energy and average-power scaling. Today, systems with up to 8 parallel amplifiers exist that demonstrate a high combination efficiency at record performance values [1]. In order to substantially increase the number of amplifier channels even further to achieve the required performance, an additional integration step is necessary to decrease the complexity and cost of such systems. We present a new system design that contains a compact beam splitter/combiner, a piezo array for pathlength adjustments, a fiber with multiple signal cores and a phase detection scheme based on photodiode arrays and phase-alternating modulations

Phase stabilization of spatiotemporally multiplexed ultrafast amplifiers

Actively stabilized, simultaneous spatial and temporal coherent beam combination is a promising power-scaling technique for ultrafast laser systems. For a temporal combination based on optical delay lines, multiple stable states of operation arise for common stabilization techniques. A time resolved Jones' calculus is applied to investigate the issue. A mitigation strategy based on a temporally gated error signal acquisition is derived and demonstrated, enabling to stabilize laser systems with arbitrary numbers of amplifier channels and optical delay lines

12 mJ pulse energy 8-channel divided-pulse ultrafast fiber-laser system

State-of-the-art ultrafast fiber lasers currently are limited in peak power by excessive nonlinearity and in average power by modal instabilities. Coherent beam combination in space and time is a successful strategy to continue power scaling by circumventing these limitations. Following this approach, we demonstrate an ultrafast fiber-laser system featuring spatial beam combination of 8 amplifier channels and temporal combination of a burst comprising 4 pulses. Active phase stabilization of this 10-armed interferometer is achieved using LOCSET and Hänsch-Couillaud techniques. The system delivers 1 kW average power at 1 mJ pulse energy, being limited by pump power, and delivers 12 mJ pulse energy at 700 W average power, being limited by optically induced damage. The system efficiency is 91% and 78%, respectively, which is due to inequalities of nonlinearity between the amplifier channels and to inequality of power and nonlinearity between the pulses within the burst. In all cases, the pulse duration is ∼260 fs and the M 2 -value is better than 1.2. Further power scaling is possible using more amplifier channels and longer pulse bursts