Optical micro-structures fabricated on top of optical fibers by means of two-photon photopolymerization

In this work we report, for the first time to our knowledge, the possibility to fabricate various structures, with good optical proprieties, on the top of optical fibers, using the two-photon lithography (TPL) technique. We show the convenience of this approach to quickly create generic 3D shapes using a single set-up by contrast to past shape-dependent methods. A set of different structures are fabricated and characterized to demonstrate the versatility of this approach and their high optical quality.     

A novel proposal for all-optical Galois field adder based on photonic crystals

In this paper we are going to propose an all-optical structure for implementing Galois field adder. To do so, we will use four optical XOR gates. The working principle of the proposed structure is based on destructive interference of optical waves. By choosing different lengths for the input waveguides, 180\(^\circ \) of phase difference will be generated between the optical waves. In the final structure, the normalized power for logic 0 and 1 at the output ports was 1 and 45%. Time delay of the proposed structure is about 1.5 ps.     

DTN routing using explicit and probabilistic routing table states

Routing in communication networks involves the indirection from a persistent name (ID) to a locator. The locator specifies how packets are delivered to a destination with a particular ID. Such a mapping is provided by a routing table entry, i.e. state. In a DTN, it is hard to maintain routing state because intermittent connectivity prevents protocols from refreshing states when they become inaccurate. In prior work, per-destination state mostly corresponds to utilities, where a high utility value about a destination implies that the probability to encounter the destination for the node maintaining the state is high. This approach depends on a particular mobility pattern in which nodes that met frequently in the past are likely to encounter in the future. In this paper, we use the concept of weak state that does not rely on external messages to remain valid (Acer et al. in MobiCom ’07: proceedings of the 13th annual ACM international conference on mobile computing and networking, pp 290–301, 2007). Our weak state realization provides probabilistic yet explicit information about where the destination is located. We build Weak State Routing protocol for Delay Tolerant Networks (WSR-D) that exploits the direction of node mobility in forwarding. It provides an osmosis mechanism to disseminate the state information to the network. With osmosis, a node has consistent information about a portion of the nodes that are located in regions relevant to its direction of mobility. Through simulations, we show that WSR-D achieves a higher delivery ratio with smaller average delay, and reduces the number of message transfers in comparison to Spray & Wait (Spyropoulos et al. in Proceedings of ACM SIGCOMM 2005 workshops: conference on computer communications, pp 252–259, 2005) and Spray & Focus (Spyropoulos et al. in IEEE/ACM Trans Netw, 16(1):77–90, 2008), a stateless and a utility based protocol, respectively.     

Cooperative Diversity Based Multi-Carrier CDMA System with Decode and Forward Relays in Rayleigh Fading channels

Cooperative communication is one of the major diversity techniques which exploit spatial diversity through a virtual antenna array. In addition to cooperation, transmitting the same symbols through different sub carriers (Multi-Carriers) introduces frequency diversity as well. The objective of this paper is to investigate cooperative diversity performance in Multi-Carrier Code Division Multiple Access (MC-CDMA) systems with orthogonal and non-orthogonal spreading codes. We evaluate the Symbol Error Rate (SER) of cooperative transmission in frequency-selective Rayleigh faded uplink channel. We focus on the use of despreading-combining (DC) receiver and coherent detection with Maximal Ratio Combining for the above selected criteria respectively. It is shown that the orthogonal spreading code cancels Multiple-Access Interference (MAI) and the performance is completely independent of the length of the spreading code. The approximate SER derived here for the the transmission scheme is well matched with the increasing number of users in the system. Hence the Gaussian approximation is acceptable for systems which are operating with their maximum user capacities at lower SNR values.     

Ultrahydrophobic PMMA micro- and nano-textured surfaces fabricated by optical lithography and plasma etching for X-ray diffraction studies

Polymeric (PMMA) ultrahydrophobic surfaces with contact angles up to about 170° have been fabricated and used in the context of synchrotron radiation experiments on biological droplets. The different microfabrication processes included either an optical lithography phase followed by a plasma texturing one or a single step deep reactive ion etch attack.The drying of several biological solution droplets has been monitored. Room temperature evaporation experiments (lysozyme, lactalbumin, cytochrome C, doxorubicin and synthesized peptides) finally result in the formation of easily detachable hollow residuals because of the low interaction between the ultrahydrophobic substrate and the aqueous droplet while pilot experiments (bovine insulin) in a sitting-drop environment bring to the formation of well defined crystals. Recent results about in situ X-ray diffraction experiments by SAXS & WAXS (Small and Wide Angle X-ray Scattering) μ-beam techniques confirm that the presence of such surfaces influences the formation of crystal or fibril structures. These substrates represent indeed a suitable support to study biological and inorganic droplets in a near contact-free environment exploiting the homogeneous evaporation rate induced by the ultrahydrophobicity of the system.     

Insights in wind turbine drive train dynamics gathered by validating advanced models on a newly developed 13.2 MW dynamically controlled test-rig

Guaranteeing reliable and cost-effective wind turbine drive trains requires expert insights in dynamics during operation. A combination of advanced modeling techniques and detailed measurements are suggested to realize this goal. The flexible multibody modeling technique enables the simulation of dynamic loads on all drive train components. Moreover it facilitates estimation of structural component deformation caused by dynamic loading. This paper gives a detailed overview of the assumptions made in this modeling approach. Furthermore the influence of the different structural component flexibilities is investigated in detail. To gain confidence in the models created, model validation by means of a comparison with measurements is necessary. To overcome issues concerning test repeatability experienced in field testing, test-rig testing is suggested as a valid alternative. In order to be representative, dedicated dynamic load cases, which represent specific dynamic behavior of the gearbox in a wind turbine need to be realized on the test-rig. However a highly dynamic test-rig complying with the specifications was not commercially available. Therefore Hansen developed a high dynamic test-rig with a nominal power of 13.2 MW and a peak power capacity of 16.8 MW. A back-to-back gearbox configuration was used. The complexity of controlling dynamics of the test-rig was solved by identifying dedicated load cases which represent specific wind turbine behavior. This paper describes the development process of the project consisting of four phases. During two phases a scaled set-up was used, which enabled iterative optimization of the complex interaction between the mechanical dynamics and the electrical controller of the test-rig. In the final part of the paper the two previously discussed approaches are combined, as it discusses results from the validation of simulation models using measurements performed on the 13.2 MW test-rig.     

A scanning electron microscopy study of diseased root surfaces conditioned with EDTA gel plus Cetavlon after scaling and root planing

In the present investigation, a scanning electron microscopy analysis was performed to evaluate the effects of the topical application of ethylenediaminetetraacetic acid (EDTA) gel associated with Cetavlon (EDTAC) in removing the smear layer and exposing collagen fibers following root surface instrumentation. Twenty-eight teeth from adult humans, single rooted and scheduled for extraction due to periodontal reasons, were selected. Each tooth was submitted to manual (scaling and root planing) instrumentation alone or combined with ultrasonic instruments, with or without etching using a 24% EDTAC gel. Following extraction, specimens were processed and examined under a scanning electron microscope. A comparative morphological semi-quantitative analysis was performed; the intensity of the smear layer and the decalcification of cementum and dentinal surfaces were graded in 12 sets using an arbitrary scale ranging from 1 (area covered by a smear layer) to 4 (no smear layer). Root debridement with hand instruments alone or combined with ultrasonic instruments resulted in a similar smear layer covering the root surfaces. The smear layer was successfully removed from the surfaces treated with EDTAC, which exhibited numerous exposed dentinal tubules and collagen fibers. This study supports the hypothesis that manual instrumentation alone or instrumentation combined with ultrasonic instrumentation is unable to remove the smear layer, whereas the subsequent topical application of EDTAC gel effectively removes the smear layer, uncovers dentinal openings and exposes collagen fibers.     

Electromigration studies of flip chip Sn95/Sb5 solder bumps on Cr/Cr-Cu/Cu under-bump metallization

The electromigration-induced failure of Sn95/Sb5 flip chip solder bumps was investigated. The failure of the joints was found at the cathode/chip side after current stressing with a density of 1×10⁴ A/cm² at 150°C for 13 sec. The growth of intermetallic compounds (IMCs) was observed at the anode side after current stressing. Voids were found near the current crowding area in the cathode/chip side, and the (Cu,Ni)₆Sn₅ IMC at the cathode/chip end was transformed into the Sn phase. The failure mechanism for Sn95/Sb5 flip chip solder joint is proposed in this paper.     

Novel Low‐Power High‐dB Range CMOS Pseudo‐Exponential Cells

In this paper, novel CMOS pseudo‐exponential circuits operating in a class‐AB mode are presented. The pseudo‐exponential approximation employed is based on second order equations. Such terms are derived in a straightforward way from the inherent nonlinear currents of class‐AB transconductors. The cells are appropriate to be integrated in portable equipment due to their compactness and very low power consumption. Measurement results from a fabricated prototype in a 0.5 μm technology reveal a range of 45 dB with errors lower than ±0.5 dB, a power consumption of 100 μW, and an area of 0.01 mm².     

Modeling Energy Recovery Using Thermoelectric Conversion Integrated with an Organic Rankine Bottoming Cycle

Engine and industrial waste heat are sources of high-grade thermal energy that can potentially be utilized. This paper describes a model system that employs thermoelectric conversion as a topping cycle integrated with an organic Rankine bottoming cycle. The model has many parameters that define combined system quantities such as overall output power and conversion efficiency. The model can identify the optimal performance points for both the thermoelectric and organic Rankine bottoming cycle. Key analysis results are presented showing the impact of critical design parameters on power output and system performance.