Building graph-based programming strategies for reconfigurable photonic circuits

We have developed a graph representation of programmable photonic mesh circuits that can be used by pathfinding algorithms. We modified the Dijkstra algorithm to observe only physically possible connections in the graph, demonstrating flexible rerouting in case of node malfunction

Quasiparticle interference of C2-symmetric surface states in LaOFeAs parent compound

We present scanning tunneling microscopy studies of the LaOFeAs parent compound of iron pnictide superconductors. Topographic imaging reveals two types of atomically flat surfaces, corresponding to the exposed LaO layer and FeAs layer respectively. On one type of surface, we observe strong standing wave patterns induced by quasiparticle interference of two-dimensional surface states. The distribution of scattering wavevectors exhibits pronounced two-fold symmetry, consistent with the nematic electronic structure found in the Ca(Fe1-xCox)2As2 parent state.Comment: 13 pages, 4 figure

Joint logistics and financial services by a 3PL firm

Integrated logistics and financial services have been practiced by third party logistics (3PL) firms for years; however, the literature has been silent on the value of 3PL firms as credit providers in budget-constrained supply chains. This paper investigates an extended supply chain model with a supplier, a budget-constrained retailer, a bank, and a 3PL firm, in which the retailer has insufficient initial budget and may borrow or obtain trade credit from either a bank (traditional role) or a 3PL firm (control role). Our analysis indicates that the control role model yields higher profits not only for the 3PL firm but also for the supplier, the retailer, and the entire supply chain. In comparison with a supplier credit model where the supplier provides the trade credit, the control role model yields a better performance for the supply chain as long as the 3PL firm’s marginal profit is greater than that of the supplier. We further demonstrate that, for all players, both the control role and supplier credit models can outperform the classic newsvendor model without budget constraint

The Roles of Bank and Trade Credits: Theoretical Analysis and Empirical Evidence

This study investigates the roles of bank and trade credits in a supply chain with a capital-constrained retailer facing demand uncertainty. We evaluate the retailer\u27s optimal order quantity and the creditors\u27 optimal credit limits and interest rates in two scenarios. In the single-credit scenario, we find the retailer prefers trade credit, if the trade credit market is more competitive than the bank credit market; otherwise, the retailer\u27s preference of a specific credit type depends on the risk levels that the retailer would divert trade credit and bank credit to other risky investments. In the dual-credit scenario, if the bank credit market is more competitive than the trade credit market, the retailer first borrows bank credit prior to trade credit, but then switches to borrowing trade credit prior to bank credit as the retailer\u27s internal capital declines. In contrast, if the trade credit market is more competitive, the retailer borrows only trade credit. We further analytically prove that the two credits are complementary if the retailer\u27s internal capital is substantially low but become substitutable as the internal capital grows, and then empirically validate this prediction based on a panel of 674 firms in China over the period 2001–2007

Electric-field-induced strong enhancement of electroluminescence in multilayer molybdenum disulfide.

The layered transition metal dichalcogenides have attracted considerable interest for their unique electronic and optical properties. While the monolayer MoS2 exhibits a direct bandgap, the multilayer MoS2 is an indirect bandgap semiconductor and generally optically inactive. Here we report electric-field-induced strong electroluminescence in multilayer MoS2. We show that GaN-Al2O3-MoS2 and GaN-Al2O3-MoS2-Al2O3-graphene vertical heterojunctions can be created with excellent rectification behaviour. Electroluminescence studies demonstrate prominent direct bandgap excitonic emission in multilayer MoS2 over the entire vertical junction area. Importantly, the electroluminescence efficiency observed in multilayer MoS2 is comparable to or higher than that in monolayers. This strong electroluminescence can be attributed to electric-field-induced carrier redistribution from the lowest energy points (indirect bandgap) to higher energy points (direct bandgap) in k-space. The electric-field-induced electroluminescence is general for other layered materials including WSe2 and can open up a new pathway towards transition metal dichalcogenide-based optoelectronic devices

Equilibrium Financing in a Distribution Channel with Capital Constraint

There exist capital constraints in many distribution channels. We examine a channel consisting of one manufacturer and one retailer, where the retailer is capital constrained. The retailer may fund its business by borrowing credit either from a competitive bank market or from the manufacturer, provided the latter is willing to lend. When only one credit type (either bank or trade credit) is viable, we show that trade credit financing generally charges a higher wholesale price and thus becomes less attractive than bank credit financing for the retailer. When both bank and trade credits are viable, the unique equilibrium is trade credit financing if production cost is relatively low but is bank credit financing otherwise. We also study the case where both the retailer and the manufacturer are capital constrained and demonstrate that, to improve the overall supply chain efficiency, the bank should finance the manufacturer if production cost is low but finance the retailer otherwise. Our analysis further suggests that the equilibrium region of trade credit financing shrinks as demand variability or the retailer\u27s internal capital level increases

Buyer Financing in Pull Supply Chains: Zero-Interest Early Payment or In-House Factoring?

This study investigates the efficacy of zero-interest early payment financing (alternatively referred to as early payment) and positive-interest in-house factoring financing in a pull supply chain with a capital-constrained manufacturer selling a product through a capital-abundant retailer. Early payment is the prepayment of a wholesale cost to the manufacturer, whereas in-house factoring is a loan service provided to the manufacturer by a branch financing firm of the same retailer. We find that the retailer prefers early payment financing to bank financing when the manufacturer’s production cost is low. If the retailer instead offers positive-interest in-house factoring financing to the manufacturer, then the financing equilibrium domain enlarges as compared to bank financing. Interestingly, early payment financing can outplay positive-interest in-house factoring financing if the production cost is considerably low; otherwise, vice versa. When the production cost is big enough, the retailer will not provide either early payment or in-house factoring. Furthermore, our main qualitative result sustains with an identical wholesale price across all three financing schemes and the financing equilibrium domain of early payment shrinks as demand variability grows

The Cash Flow Advantages of 3PLs as Supply Chain Orchestrators

With an increasingly open global economy and advanced technologies, some third-party logistics providers (3PLs), such as Eternal Asia, have emerged as supply chain orchestrators, linking buyers with manufacturers worldwide. In addition to their traditional transportation services, these orchestrators provide procurement and financial assistance to buyers in the supply network, especially small- and medium-sized enterprises (SMEs) in developing countries. Oftentimes, the 3PLs can obtain payment delay arrangements from the financially stronger manufacturers, which in turn can be partially extended to the SME buyers, alleviating their high costs of capital. To illustrate the efficiency improvements of the aforementioned practice, we use a model to explicitly capture the cash-flow dynamics in a supply chain consisting of a manufacturer, a buyer, and a 3PL firm and explore the conditions under which this innovation benefits all parties in the supply chain so that the business model is sustainable. We characterize these conditions and show that the supply chain profit can be higher under leadership by the 3PL than by the manufacturer. The intermediary role of the 3PL is crucial, in that its benefit may vanish if the manufacturer chooses to directly grant payment delay to the buyers. We demonstrate that the benefit is more likely to occur with more buyers. We further identify the unique Nash bargaining solution for the transportation time and the payment delay grace period

Large area growth and electrical properties of p-type WSe2 atomic layers.

Transition metal dichacogenides represent a unique class of two-dimensional layered materials that can be exfoliated into single or few atomic layers. Tungsten diselenide (WSe(2)) is one typical example with p-type semiconductor characteristics. Bulk WSe(2) has an indirect band gap (∼ 1.2 eV), which transits into a direct band gap (∼ 1.65 eV) in monolayers. Monolayer WSe(2), therefore, is of considerable interest as a new electronic material for functional electronics and optoelectronics. However, the controllable synthesis of large-area WSe(2) atomic layers remains a challenge. The studies on WSe(2) are largely limited by relatively small lateral size of exfoliated flakes and poor yield, which has significantly restricted the large-scale applications of the WSe(2) atomic layers. Here, we report a systematic study of chemical vapor deposition approach for large area growth of atomically thin WSe(2) film with the lateral dimensions up to ∼ 1 cm(2). Microphotoluminescence mapping indicates distinct layer dependent efficiency. The monolayer area exhibits much stronger light emission than bilayer or multilayers, consistent with the expected transition to direct band gap in the monolayer limit. The transmission electron microscopy studies demonstrate excellent crystalline quality of the atomically thin WSe(2). Electrical transport studies further show that the p-type WSe(2) field-effect transistors exhibit excellent electronic characteristics with effective hole carrier mobility up to 100 cm(2) V(-1) s(-1) for monolayer and up to 350 cm(2) V(-1) s(-1) for few-layer materials at room temperature, comparable or well above that of previously reported mobility values for the synthetic WSe(2) and comparable to the best exfoliated materials