Terahertz generation by dynamical photon drag effect in graphene excited by femtosecond optical pulses.

Graphene has been proposed as a particularly attractive material for the achievement of strong optical nonlinearities, in particular generation of terahertz radiation. However, owing to the particular symmetries of the C-lattice, second-order nonlinear effects such as difference-frequency or rectification processes are predicted to vanish in a graphene layer for optical excitations (ℏω ≫ 2EF) involving the two relativistic dispersion bands. Here we experimentally demonstrate that graphene excited by femtosecond optical pulses generate a coherent THz radiation ranging from 0.1 to 4 THz via a second-order nonlinear effect. We fully interpret its characteristics with a model describing the electron and hole states beyond the usual massless relativistic scheme. This second-order nonlinear effect is dynamical photon drag, which relies on the transfer of light momentum to the carriers by the ponderomotive electric and magnetic forces. The model highlights the key roles of next-C-neighbor couplings and of unequal electron and hole lifetimes in the observed second-order response. Finally, our results indicate that dynamical photon drag effect in graphene can provide emission up to 60 THz, opening new routes for the generation of ultrabroadband terahertz pulses.

Continuous intraoperative monitoring of autonomic nerves during low anterior rectal resection: an innovative approach for observation of functional nerve integrity in pelvic surgery.

PURPOSE: The aim of this study was to develop a methodological setup for continuous intraoperative neuromonitoring with intent to improve nerve-sparing pelvic surgery. METHODS: Fourteen pigs underwent low anterior rectal resection. Continuous stimulation of pelvic autonomic nerves was carried out with a newly developed tripolar surface electrode during lateral, anterolateral, and anterior mesorectal dissection. Neuromonitoring was performed under electromyography of the autonomic innervated internal anal sphincter. RESULTS: Continuous neuromonitoring resulted in significantly increased electromyographic amplitudes of the internal anal sphincter, confirming intact innervation throughout the whole dissection in each animal (median 0.9 µV, interquartile range 0.5; 1.5 vs. median 3.4 µV, interquartile range 2.1; 4.7) (p < 0.001). The median dissection time in each animal was 10 min within a median number of ten (range 8-13) tripolar electric stimulations. CONCLUSION: The present study is the first to demonstrate that continuous intraoperative monitoring of pelvic autonomic nerves during low anterior rectal resection is feasible.

Regulated intramembrane proteolysis takes another twist.

Rhomboid, a seven-transmembrane domain protein, has been shown genetically to potentiate EGFR signaling via the TGFalpha-like ligand Spitz. Here we discuss recently published papers that identify Rhomboid as a novel serine protease, cleaving Spitz within its transmembrane domain.

Embryonic lethality in mice homozygous for a processing-deficient allele of Notch1.

The Notch genes encode single-pass transmembrane receptors that transduce the extracellular signals responsible for cell fate determination during several steps of metazoan development. The mechanism by which extracellular signals affect gene transcription and ultimately cell fate decisions is beginning to emerge for the Notch signalling pathway. One paradigm is that ligand binding to Notch triggers a Presenilin1-dependent proteolytic release of the Notch intracellular domain from the membrane, resulting in low amounts of Notch intracellular domain which form a nuclear complex with CBF1/Su(H)/Lag1 to activate transcription of downstream targets. Not all observations clearly support this processing model, and the most rigorous test of it is to block processing in vivo and then determine the ability of unprocessed Notch to signal. Here we report that the phenotypes associated with a single point mutation at the intramembranous processing site of Notch1, Val1,744-->Gly, resemble the null Notch1 phenotype. Our results show that efficient intramembranous processing of Notch1 is indispensable for embryonic viability and proper early embryonic development in vivo.

Feedback regulation is central to Delta-Notch signalling required for Drosophila wing vein morphogenesis.

Delta and Notch are required for partitioning of vein and intervein cell fates within the provein during Drosophila metamorphosis. We find that partitioning of these fates is dependent on Delta-mediated signalling from 22 to 30 hours after puparium formation at 25 degrees C. Within the provein, Delta is expressed more highly in central provein cells (presumptive vein cells) and Notch is expressed more highly in lateral provein cells (presumptive intervein cells). Accumulation of Notch in presumptive intervein cells is dependent on Delta signalling activity in presumptive vein cells and constitutive Notch receptor activity represses Delta accumulation in presumptive vein cells. When Delta protein expression is elevated ectopically in presumptive intervein cells, complementary Delta and Notch expression patterns in provein cells are reversed, and vein loss occurs because central provein cells are unable to stably adopt the vein cell fate. Our findings imply that Delta-Notch signalling exerts feedback regulation on Delta and Notch expression during metamorphic wing vein development, and that the resultant asymmetries in Delta and Notch expression underlie the proper specification of vein and intervein cell fates within the provein.

The dynamics of neurogenic signalling underlying bristle development in Drosophila melanogaster.

We have examined expression of the neurogenic gene, Delta (Dl), and the regulatory relationships between the Delta-Notch signalling pathway and the proneural gene, achaete, during microchaeta development in Drosophila. Delta is expressed in all microchaeta proneural cells and microchaeta sensory organ precursors (SOPs) and is expressed dynamically in SOP progeny. We find that Delta expression in microchaeta proneural cells is detected prior to the onset of achaete expression and arises normally in the absence of achaete/scute function, indicating that initial Delta expression in the notum is not dependent on proneural gene function. Activation of the Delta-Notch pathway results in loss of Delta protein accumulation, suggesting that Delta expression is regulated, in part, by Delta-Notch signalling activity. We find that Delta signalling is required for correct delineation of early proneural gene expression in developing nota. Within microchaeta proneural stripes, we demonstrate that Delta-Notch signalling prohibits adoption of the SOP fate by repressing expression of proneural genes.