连续波锁模P_r~（3＋）：YLF激光器

本文报导了采用氩离子激光器来泵浦Ｒｒ￣（３＋）：ＹＬＦ晶体，应用声光调制器实现了主动锁模；同时应用振动─高反射平面镜也实现了被动锁模，两种锁模均得到了ｐｓ光脉冲。据作者了解这是这种晶体材料的第一次锁模运转。     

Synthesis and design of novel in-line filters with one or two real transmission zeros

A direct synthesis and design technique of pseudoelliptic in-line filters with one or two real transmission zeros (TZs) is presented. It is shown that the phase of the reflection coefficient must be properly and uniquely determined for the synthesis to succeed. The TZs (attenuation poles) are brought about and independently controlled by dedicated resonators at the input and output. Each attenuation pole is located at the resonant frequency of its dedicated resonator. Frequency-independent reactances at the input and output are used to replace the phase shifts used in the extracted-pole technique. This novel approach is verified by several waveguide cavity filter designs. The analyzed characteristics of these filters, obtained with commercial full-wave computer-aided-design tools, agree very well with the synthesis results. A third-order filter with one TZ above the passband is designed, fabricated, and measured. Excellent agreement between the measurement and simulation is obtained.     

An address-light, integrated MAC and routing protocol for wireless sensor networks

We propose an address-light, integrated MAC and routing protocol (abbreviated AIMRP) for wireless sensor networks (WSNs). Due to the broad spectrum of WSN applications, there is a need for protocol solutions optimized for specific application classes. AIMRP is proposed for WSNs deployed for detecting rare events which require prompt detection and response. AIMRP organizes the network into concentric tiers around the sink(s), and routes event reports by forwarding them from one tier to another, in the direction of (one of) the sink(s). AIMRP is address-light in that it does not employ unique per-node addressing, and integrated since the MAC control packets are also responsible for finding the next-hop node to relay the data, via an anycast query. For reducing the energy expenditure due to idle-listening, AIMRP provides a power-saving algorithm which requires absolutely no synchronization or information exchange. We evaluate AIMRP through analysis and simulations, and compare it with another MAC protocol proposed for WSNs, S-MAC. AIMRP outperforms S-MAC for event-detection applications, in terms of total average power consumption, while satisfying identical sensor-to-sink latency constraints.     

The IETF Internet telephony architecture and protocols

Internet telephony was first used as a simple way to provide point-to-point voice transport between two IP hosts. However, the growing interest in providing integrated voice, data, and video services has caused its scope to be extended. Internet telephony now encompasses a range of services, including not only traditional conferencing, call control, multimedia, and mobility services, but also new ones that integrate Web, e-mail, presence, and instant messaging applications with telephony. Internet telephony and traditional circuit-switched telephony will coexist for quite some time, requiring interworking between the two. In this article we present a suite of protocols, developed in the IETF, which provide a partial solution to this complex problem     

Cross-coupled microstrip band reject filters with non-resonating nodes

A new design of cross-coupled band reject filters in microstrip technology is presented. In the proposed model, the source and the load are not directly coupled. Instead, non-resonating nodes (NRNs) are introduced in the network to generate the required number of attenuation poles and modularize the design. Higher order band reject filters are designed by cascading lower-order building blocks with NRNs inserted between them. A fourth order filter is designed, built and measured. Good agreement between theory and measurement is achieved.     

Mössbauer spectroscopic investigations of Fe/Mn-Fischer-Tropsch-catalysts

The phase composition of Fe/Mn oxide catalysts of different compositions after 200 h of Fischer-Tropsch synthesis have been investigated by Mößbauer spectroscopy at room temperature, 77 K and 5 K. The final composition of the bulk catalysts depends strongly on the Mn content and the temperature of reduction before the synthesis. Catalytic activity and selectivity are partly correlated to this phase composition.     

Location discovery in enterprise-based wireless networks: Case studies and applications

We have designed and implemented a Web service for location discovery (LODS) and a location-based printing service that usesLODS on a network with wirelessLAN connectivity based onIEEE 802.11 that is typical to campuses and enterprises. The need for location management and location-based services is linked to the mobility of the users. While location discovery is already implemented in cellular telecommunication networks since the system needs to know where are the users to connect them to incoming calls, the need for such a service was not so crucial in data network where in general the mobile user is the client and initiates the connections. We propose several solutions to implement our location discovery service depending on the underlying networking architecture and compare these solutions in terms of several criteria.LODS allows mobile users to find their approximate location within the campus or the enterprise and allows location-based applications to find out the location of a user to suggest the nearest points of interest, e.g., printers, elevators, and vending machines. We also present the case of our location-based remote printing service that was deployed in Purdue wireless network.     

Block Copolymer Packing Limits and Interfacial Reconfigurability in the Assembly of Periodic Mesoporous Organosilicas

Here poly(N,N‐dimethylacrylamide)‐block‐poly(styrene) block copolymer micelles (BCPs) are advanced and applied to assemble periodic mesoporous organosilicas (PMOs) with noncylindrical pores. Using these BCP micelles, it is found that pore dimensions (11–23 nm), wall thicknesses (5–9 nm), and overall porosities (26%–78%) are independently programable, depending only on relative inputs for BCP and matrix former. Notably, the degree of order in all films improves as BCP loading approaches a packing limit of 63 vol%. Beyond this limit and regardless of pore dimensions, both porogen packing in the film and pore structure after thermal processing show significant deviations away from spherical close‐packed lattices. The surprising absence of film collapse in this regime allows here to quantify the evolution of pore structure through the thermally driven interfacial reconfigurability of BCP micelles in the hybrid films when porogen loading exceeds the packing limit by using both scattering techniques and scanning transmission electron microscopy tomography. Finally, the PMOs here give dielectric constants of 1.2 and 1.5 above and below the BCP packing limit, respectively—the lowest ever reported for this matrix material.     

Kinetics and mechanism of epoxy oligomers curing

A review of new results concerning kinetics, thermodynamics and mechanism of epoxy oligomers curing with various nucleophilic agents (amines, phenols, carboxylic acids) has been made. The concept of the mechanism of such reactions is formulated on the basis of this study. Kinetic data obtained are interpreted within the framework of cyclic transition state. The addition of nucleophilic agent to epoxy ring is rather complicated. It results from preliminary formation of homo- and heteroassociates of reaction system components which finally form reactive cyclic heteroassociates. Reaction products are formed as a result of monomolecular rearrangement with synchronous transfer of electrons in the reactive cyclic heteroassociates.