Wannier-based definition of layer polarizations in perovskite superlattices

In insulators, the method of Marzari and Vanderbilt [Phys. Rev. B {\bf 56}, 12847 (1997)] can be used to generate maximally localized Wannier functions whose centers are related to the electronic polarization. In the case of layered insulators, this approach can be adapted to provide a natural definition of the local polarization associated with each layer, based on the locations of the nuclear charges and one-dimensional Wannier centers comprising each layer. Here, we use this approach to compute and analyze layer polarizations of ferroelectric perovskite superlattices, including changes in layer polarizations induced by sublattice displacements (i.e., layer-decomposed Born effective charges) and local symmetry breaking at the interfaces. The method provides a powerful tool for analyzing the polarization-related properties of complex layered oxide systems

Magnetorheological fluids for oil and gas well application

textCement is used in oil and gas wells to support the casing and prevent fluid migration between formations. Incompetent cementing in a well and the potential subsequent failure of zonal isolation is a significant concern in the oil and gas industry. Insufficient zonal isolation could cause fluid migration resulting in water aquifer contamination and loss of control of well pressure, shortening the life of wells and increasing the risk of well control incidents, which could result in loss of life, economical loss and environmental damage. To achieve good cementation and guarantee zonal isolation during the lifetime of the well, significant technical challenges need to be overcome. Such challenges are associated with guaranteeing proper fluid-cement displacement, preventing gas migration, and maintaining cement integrity during all phases of well life (drilling, completion/stimulation, production, abandonment). Magnetorheological (MR) fluids (cement-based or non cement-based) can potentially be used to tackle these challenges for applications in oil and gas wells. The rheological properties and flow direction of MR fluids can be controlled by the application of a magnetic field. During the primary cementing process, it is important to displace the drilling fluid and spacer fluid out of the annulus with cement in order to obtain enough strength after cement hydration. This study shows that by applying a magnetic field, the MR cement-based fluid can be guided to achieve more uniform displacement and to increase the displacement efficiency. The results also show that an MR fluid can be used as a flow prevention seal and has the ability to hold pressure, due to its instantaneous stiffening effect when the magnetic field is applied. This can be applied to avoid or remediate annular fluid flow and gas migration, form temporary top-, bottom- or straddle packers, and combine with BOPs for instantaneous pressure control. During the production of a well, the cement in the annulus can experience various severe conditions, which can lead to cracking, de-bonding and shear failure of the cement. The magnetic properties of MR cement-based fluid provide a possible way to evaluate the quality of cement, detect cracking in cement and monitor the health of the cement annulus using non-destructive testing with magnetic methods.Civil, Architectural, and Environmental Engineerin

Synthesis of Hydroxy-α-sanshool

postprin

ILP formulations for p-cycle design without candidate cycle enumeration

The concept of p-cycle (preconfigured protection cycle) allows fast and efficient span protection in wavelength division multiplexing (WDM) mesh networks. To design p-cycles for a given network, conventional algorithms need to enumerate cycles in the network to form a candidate set, and then use an integer linear program (ILP) to find a set of p-cycles from the candidate set. Because the size of the candidate set increases exponentially with the network size, candidate cycle enumeration introduces a huge number of ILP variables and slows down the optimization process. In this paper, we focus on p-cycle design without candidate cycle enumeration. Three ILPs for solving the problem of spare capacity placement (SCP) are first formulated. They are based on recursion, flow conservation, and cycle exclusion, respectively. We show that the number of ILP variables/constraints in our cycle exclusion approach only increases linearly with the network size. Then, based on cycle exclusion, we formulate an ILP for solving the joint capacity placement (JCP) problem. Numerical results show that our ILPs are very efficient in generating p-cycle solutions. © 2009 IEEE.published_or_final_versio

Monitoring Cycle Design for Fast Link Failure Localization in All-Optical Networks

A monitoring cycle (m-cycle) is a preconfigured optical loop-back connection of supervisory wavelengths with a dedicated monitor. In an all-optical network (AON), if a link fails, the supervisory optical signals in a set of m-cycles covering this link will be disrupted. The link failure can be localized using the alarm code generated by the corresponding monitors. In this paper, we first formulate an optimal integer linear program (ILP) for m-cycle design. The objective is to minimize the monitoring cost which consists of the monitor cost and the bandwidth cost (i.e., supervisory wavelength-links). To reduce the ILP running time, a heuristic ILP is also formulated. To the best of our survey, this is the first effort in m-cycle design using ILP, and it leads to two contributions: 1) nonsimple m-cycles are considered; and 2) an efficient tradeoff is allowed between the monitor cost and the bandwidth cost. Numerical results show that our ILP-based approach outperforms the existing m-cycle design algorithms with a significant performance gain.published_or_final_versio

Multiorbital tunneling ionization of the CO molecule

We coincidently measure the molecular frame photoelectron angular distribution and the ion sum-momentum distribution of single and double ionization of CO molecules by using circularly and elliptically polarized femtosecond laser pulses, respectively. The orientation dependent ionization rates for various kinetic energy releases allow us to individually identify the ionizations of multiple orbitals, ranging from the highest occupied to the next two lower-lying molecular orbitals for various channels observed in our experiments. Not only the emission of a single electron, but also the sequential tunneling dynamics of two electrons from multiple orbitals are traced step by step. Our results confirm that the shape of the ionizing orbitals determine the strong laser field tunneling ionization in the CO molecule, whereas the linear Stark effect plays a minor role.Comment: This paper has been accepted for publication by Physical Review Letter

Optical layer monitoring schemes for fast link failure localization in all-optical networks

Optical layer monitoring and fault localization serves as a critical functional module in the control and management of optical networks. An efficient monitoring scheme aims at minimizing not only the hardware cost required for 100{%} link failure localization, but also the number of redundant alarms and monitors such that the network fault management can be simplified as well. In recent years, several optical layer monitoring schemes were reported for fast and efficient link failure localization, including simple, non-simple monitoring cycle (m-cycle) and monitoring trail (m-trail). Optimal ILP (Integer Linear Program) models and heuristics were also proposed with smart design philosophy on flexibly trading off different objectives. This article summarizes those innovative ideas and methodologies with in-depth analysis on their pros and cons. We also provide insights on future research topics in this area, as well as possible ways for extending the new failure localization approaches to other network applications. © 2005 IEEE.published_or_final_versio

CFP: Cooperative fast protection

Article number: 5062196The 28th Conference on Computer Communications, IEEE INFOCOM 2009, Miniconference, Rio de Janeiro, Brazil, 19-25 April 2009We introduce Cooperative Fast Protection (CFP) as a novel protection scheme in WDM networks. CFP achieves capacity-efficient fast protection with the features of node-autonomy and failure-independency. It differs from p-cycle by reusing the released working capacity of the disrupted lightpaths (i.e. stubs) in a cooperative manner. This is achieved by allowing all the failure-aware nodes to switch the traffic, such that the disrupted lightpaths can be protected even if the end nodes of the failed link are not on the protecting cycles. CFP also differs from FIPP p-cycle by not requiring the source node of the disrupted lightpath on the protecting cycle. By jointly optimizing both working and spare capacity placement, we formulate an ILP for CFP design. Numerical results show that CFP significantly outperforms p-cycle by achieving faster protection with much higher capacity efficiency. © 2009 IEEE.published_or_final_versio