Post-transient relaxation in graphene after an intense laser pulse

High intensity laser pulses were recently shown to induce a population inverted transient state in graphene [T. Li et al. Phys. Rev. Lett. 108, 167401 (2012)]. Using a combination of hydrodynamic arguments and a kinetic theory we determine the post-transient state relaxation of hot, dense, population inverted electrons towards equilibrium. The cooling rate and charge-imbalance relaxation rate are determined from the Boltzmann-equation including electron-phonon scattering. We show that the relaxation of the population inversion, driven by inter-band scattering processes, is much slower than the relaxation of the electron temperature, which is determined by intra-band scattering processes. This insight may be of relevance for the application of graphene as an optical gain medium.Comment: 10 pages, 4 figures, submitted as contribution of the IMPACT Special Topics series of the EP

Influence of frost damage on water penetration into neat and air entrained concrete

In service life, concrete can be damaged either by mechanical or environmental loads or by combined ones. These damages will strongly influence water movement in concrete which could later lead to more serious deteriorations. This paper applies neutron radiography to investigate the influence of frost damage on water penetration into concrete. In addition, the improvement of frost resistance by addition of air entrainment was investigated. The results indicate that it is possible to visualize penetration of water into the porous structure of concrete by neutron radiography. Further evaluation of the test data allows determining time-dependent moisture profiles quantitatively with high resolution. After concrete is damaged by freeze-thaw cycles water penetration into ordinary concrete is accelerated. It can be shown that frost damage is not equally distributed in specimens exposed to freeze-thaw cycles. Thermal gradients lead to more serious damage near the surface. The beneficial effect of air entrainment on frost resistance has been demonstrated. After 50 freeze-thaw cycles, air entrained concrete showed no measurable increase in water absorption. But layers near the surface of concrete absorbed slightly more water after 200 freeze-thaw cycles although the dynamic elastic modulus remained constant. Results presented in this paper help us to better understand mechanisms of frost damage of concrete

Influence of elevated temperature on mechanical properties and durability of concrete

Concrete structures are exposed to high temperatures during fire. Bothe the mechanical properties and durability after exposed to elevated temperatures are of great importance in terms of the serviceability of buildings. In this project, the effects of elevated temperatures (20, 100, 200, 300, 400, 500 and 600 ℃ ) on the compressive strength, elastic modulus, fracture energy, water capillary absorption and chloride penetration have been studied. The influence of cooling methods on these properties has been also investigated. The results obtained indicate that when the temperature is below 400 ℃ for concrete A (W/C=0.4) and 300 ℃ for concrete B (W/C=0.5) with natural cooling, the compressive strength did not decrease immediately. But with water splashing cooling, the compressive strength of concrete lost approx. 20 % at 300 degree. The elastic modulus of concrete decreased gradually with the increasing of temperature. And there is no real difference between two types of cooling methods. When the temperature is over 400 degree only, the fracture energy decreased significantly. After exposed to elevated temperatures, concrete absorbed much more water and chloride ions, which bring a high risk for RC structures. This effect shall also be taken into consideration when concrete structures after fire is evaluated

Knockdown of Snail Sensitizes Pancreatic Cancer Cells to Chemotherapeutic Agents and Irradiation

The prognosis of patients with pancreatic cancer remains poor; only patients with small tumors and complete resection have a chance of a complete cure. Pancreatic cancer responds poorly to conventional therapies, including chemotherapy and irradiation. Snail is a transcription factor that has been associated with anti-apoptotic and chemoresistant properties in pancreatic cancer cells. In this study, we investigated whether knockdown of Snail suppresses growth of and/or sensitizes pancreatic cancer cells to chemotherapeutic agents and irradiation through induction of apoptosis. An adeno-associated virus vector was used to deliver Snail siRNA and knockdown Snail expression in untreated pancreatic cancer cells and in pancreatic cancer cells treated with chemotherapeutic agents or γ-irradiation. Our data indicate that our adeno-associated virus vector can efficiently deliver Snail siRNA into PANC-1 cells both in vitro and in vivo, resulting in the knockdown of Snail expression at the mRNA and protein levels. We further show that knockdown of Snail expression results in potent growth suppression of pancreatic cancer cells and suppresses xenograft tumor growth in vivo through induction of apoptosis. Finally, knockdown of Snail expression significantly sensitizes pancreatic cancer cells to chemotherapeutic agents and γ-irradiation through induction of apoptosis. In conclusion, our findings indicate that Snail is an important modulator of therapeutic responses of pancreatic cancer cells and is potentially useful as a sensitizer in pancreatic cancer therapy

Toward forward-looking OCT needle tip vision of the spinal neuroforamen: animal studies

Neurologic complications have been reported with spinal transforaminal injections. Causes include intraneural injection, plus embolization occlusion of the radicular artery with subsequent spinal cord infarction. 1 Optical coherence tomography (OCT) is a non-invasive imaging modality, which is used to image tissue microstructure with very high resolution (less than 20 microns) in real-time. With a view toward needle tip OCT visualization of the spinal neuroforamen, we conducted animal studies to explore OCT imaging of paraspinal neurovascular structures. With institutional animal care committee approval, we performed ex-vivo and in situ OCT studies in a euthanized dog, pig, and rabbit. Image data was gathered on spinal nerve roots, dura, and brachial plexus. Two systems were used: frequency domain OCT imaging system developed at California Institute of Technology, and time domain Imalux NIRIS system with a 2.7 mm diameter probe. In a euthanized pig, excised dura was punctured with a 17-gauge Tuohy needle. FDOCT dural images of the puncture showed a subsurface cone-shaped defect. In a rabbit in situ study, puncture of the dura with a 26-gauge needle is imaged as a discontinuity. FDOCT imaging of both small artery and large arteries will be presented, along with H&E and OCT images of the brachial plexus

Energy trading model for multi-microgrid energy storage alliance based on Nash negotiation

With the continuous development of the electricity market and the gradual expansion of the number and scale of participation in market transactions, the traditional energy trading model has limited the formation of a competitive pattern of multi-agents. In this paper, a new multi-microgrid energy storage alliance energy trading model based on Nash negotiation is proposed. This model takes energy storage, multi-microgrid, and superior power grid enterprises as the main participants and establishes an energy market trading model with “buy–sell” cooperation and competition coexisting within the alliance based on Nash negotiation theory. Through the interaction of electricity between different entities, energy conversion and complementary utilization are increased, achieving reasonable allocation of resources, enhancing the overall flexibility of the alliance, and promoting the local consumption of a high proportion of new energy. The simulation results of the example show that the energy trading model based on Nash negotiation can fully leverage the initiative of demand-side participation in scheduling and improve the utilization rate of energy storage systems while ensuring the payment benefits of all participating entities, which can provide technical support for energy complementarity among multiple entities and provide new technological paths for the sustainable development of energy sharing mechanisms