Subharmonic solutions for nonautonomous sublinear second order Hamiltonian systems

AbstractSome existence theorems are obtained for subharmonic solutions of nonautonomous second order Hamiltonian systems by the minimax methods in critical point theory

Periodic Solutions of a Class of Non-autonomous Second-Order Systems

AbstractSome existence theorems are obtained by the least action principle for periodic solutions of nonautonomous second-order systems with a potential which is the sum of a subconvex function and a subquadratic function

Weak topological insulators induced by the inter-layer coupling: A first-principles study of stacked Bi2TeI

Based on first-principles calculations, we predict Bi2TeI, a stoichiometric compound synthesized, to be a weak topological insulator (TI) in layered subvalent bismuth telluroiodides. Within a bulk energy gap of 80 meV, two Dirac-cone-like topological surface states exist on the side surface perpendicular to BiTeI layer plane. These Dirac cones are relatively isotropic due to the strong inter-layer coupling, distinguished from those of previously reported weak TI candidates. Moreover, with chemically stable cladding layers, the BiTeI-Bi2-BiTeI sandwiched structure is a robust quantum spin Hall system, which can be obtained by simply cleaving the bulk Bi2TeI.Comment: 4.5 pages, 4 figure

Combined cloud:a mixture of voluntary cloud and reserved instance marketplace

Voluntary cloud is a new paradigm of cloud computing.It provides an alternative selection along with some well-provisioned clouds.However,for the uncertain time span that participants share their computing resources in voluntary cloud,there are some challenging issues,i.e.,fluctuation,under-capacity and low-benefit.In this paper,an architecture is first proposed based on Bittorrent protocol.In this architecture,resources could be reserved or requested from Reserved Instance Marketplace and could be accessed with a lower price in a short circle.Actually,these resources could replenish the inadequate resource pool and relieve the fluctuation and under-capacity issue in voluntary cloud.Then,the fault rate of each node is used to evaluate the uncertainty of its sharing time.By leveraging a linear prediction model,it is enabled by a distribution function which is used for evaluating the computing capacity of the system.Moreover,the cost optimization problem is investigated and a computational method is presented to solve the low-benefit issue in voluntary cloud.At last,the system performance is validated by two sets of simulations.And the experimental results show the effectiveness of our computational method for resource reservation optimization

Efficiency Enhancement of Nanoporous Silicon/Polycrystalline-Silicon Solar Cells by Application of Trenched Electrodes

Trenched electrodes were proposed to enhance the short-circuit current and conversion efficiency of polycrystalline-silicon (poly-Si) solar cells with nanoporous silicon (NPS) surface layers. NPS films that served as textured surface layers were firstly prepared on heavily doped p+-type (100) poly-Si wafers by anodic etching process. Interdigitated trenches were formed in the NPS layers by a reactive-ion-etch (RIE) process and Cr/Al double-layered metal was then deposited to fill the trenches and construct trenched-electrode-contacts (TEC’s). Cells with TEC structures (called “TEC cells”) obtained 5.5 times higher short-circuit current than that of cells with planar electrode contacts (called “non-TEC cells”). Most significantly, a TEC cell achieved 8 times higher conversion efficiency than that of a non-TEC cell. The enhanced short-circuit current and conversion efficiency in TEC cells were ascribed to the reduced overall series resistance of devices. In a TEC cell, trenched electrodes provided photocurrent flowing routes that directly access the poly-Si substrates without passing through the high resistive NPS layers. Therefore, the application of NPS surface layers with trenched electrodes is a novel approach to development of highly efficient poly-Si solar cells

Hydraulic fracturing propagation mechanism during shale gas reservoir stimulation through horizontal well

Način razlamanja stijenske mase u naslagama naftnih škriljaca jedan je od glavnih čimbenika koji djeluju na učinkovitost hidrauličkog frakturiranja (frakiranja). U ovom su radu provedena fizikalna ispitivanja i numeričko modeliranje u svrhu sustavnog ispitivanja učinka in-situ (podzemnog) naprezanja i kuta bušenja na stvaranje tlaka zbog hidrauličkog frakturiranja, širenje razlamanja i način razlamanja u horizontalnoj bušotini naftnog nalazišta Shengli u Luojia pokrajini, u izvođenju Sinopec Corp. Ukupno je razmatrano šest različitih in-situ kombinacija naprezanja i osam različitih kutova bušenja slojevite stijenske mase tijekom hidrauličkog frakturiranja. Sažetak nastanka i širenja pukotine te završni oblici pukotina nastalih hidrauličkim frakturiranjem u slojevitim stijenskim masama otkrivaju da kod stratificiranih stijena s istim kutom bušenja, što je veći in-situ omjer naprezanja (t.j. niže maksimalno horizontalno osnovno naprezanje pri konstantnim vertikalnim naprezanjem), potreban je niži hidraulički tlak za poticanje i širenje hidrauličkog frakturiranja. Štoviše, ustanovljeno je da je kod stratificirane stijenske mase pri istom omjeru naprezanja, tlak hidrauličkog frakturiranja, u slučaju kad je kut bušenja 30°, veći nego u svim drugim slučajevima. Nadalje, zapaženo je da učinak stratifikacije na hidrauličko frakturiranje postaje slabiji s porastom in-situ omjera naprezanja. Konačno je zaključeno da rezultati ove analize mogu biti važan teorijski pokazatelj u poboljšanju oblikovanja hidrauličkog frakturiranja kako bi se osiguralo učinkovito stimuliranje naslaga naftnih škriljaca.The fracture pattern of rock mass in shale gas reservoirs is one of the main factors affecting the efficiency of hydraulic fracturing. In this paper, physical experiments and numerical modelling were conducted to systematically investigate the effect of the in-situ stress and perforation angle on the hydraulic fracture initiation pressure and location, fracture propagation, and fracture pattern in a horizontal well drilled by Sinopec Corp. in Luojia area of Shengli Oilfield. A total of six different in-situ stress combinations and eight different perforation angles were considered for the stratified rock mass during the hydraulic fracturing. A summary of the fracture initiations and propagation, and the final fracture patterns induced by the hydraulic fracturing in the stratified rock masses reveals that, for the stratified rock masses with the same perforation angle, the larger the in-situ stress ratio (i.e. lower maximum horizontal principal stress when the vertical stress remains constant) is, the lower hydraulic pressure is required for hydraulic fracturing initiation and propagation. Moreover, it is found that, for the stratified rock mass under the same stress ratio, the hydraulic fracturing pressure in the case with a perforation angle of 30° is higher than that in all other cases. Furthermore, it is noted that the effect of the stratification on the hydraulic fracturing becomes weaker with the in-situ stress ratio increasing. It is finally concluded that the results from this study can provide important theoretical guidance for improving the hydraulic fracturing design in order to ensure the effective shale gas reservoir stimulations

Intrathecal glutamate release during hindlimb tourniquet inflation and femoral artery occlusion in rats

Background/PurposeA tourniquet is commonly used in limb surgery. Tourniquet inflation after a period of time may produce painful sensation. While the mechanisms of tourniquet-induced pain are still unknown, two components, pressure and ischemia, have been proposed. In this study, in vivo microdialysis was used to detect changes in intrathecal glutamate, an excitatory amino acid highly relevant to pain transmission, following hindlimb tourniquet application and femoral artery occlusion in the rat.MethodsMale Wistar rats were used. For the tourniquet study, 6 rats of the study group received 30 minutes right hindlimb tourniquet inflation and another 6 rats as the control group received only tourniquet application without inflation. In the femoral artery occlusion study, 6 rats of the study group received 30 minutes right femoral artery occlusion and another 6 rats as the control group received only sham operation without femoral artery occlusion. Cerebrospinal fluid dialysates were collected prior to, during, and after tourniquet application or femoral artery occlusion. Glutamate was measured by HPLC.ResultsA significant increase in intrathecal glutamate release was found during the tourniquet inflation period, and it returned to baseline after tourniquet deflation. No change of glutamate release was noted during femoral artery occlusion or after femoral artery reperfusion.ConclusionThe intrathecal glutamate release was increased by the hindlimb tourniquet inflation, but not influenced by femoral artery occlusion in the rat

Homoclinic orbits for a class of second-order Hamiltonian systems with concave–convex nonlinearities

In this paper, we study the existence of multiple homoclinic solutions for the following second order Hamiltonian systems \begin{equation*} \ddot{u}(t)-L(t)u(t)+\nabla W(t,u(t))=0, \end{equation*} where $L(t)$ satisfies a boundedness assumption which is different from the coercive condition and $W$ is a combination of subquadratic and superquadratic terms