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To search for efficient electrocatalyst towards oxygen evolution reaction (OER) for sustainable energy production, a family of transition metal‐tetracyanoquinodimethane (TM‐TCNQ) (TM=Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Ru, Rh, Pd)monolayers have been studied by first principle based density functional theory (DFT) computations. The systematic investigations on various TM‐TCNQ structures revealed that Ni‐TCNQ monolayer exhibits best catalytic activity towards OER. At equilibrium potential (1.23 Vvs RHE), the free energy profile of Ni‐TCNQ monolayer for different reaction intermediates is not completely downhill which points out that water could not be oxidized by the photo‐generated holes at that potential. However, at and above 1.71 V, all the OER reaction steps on Ni‐TCNQ surface is found to be thermodynamically downhill, measuring a low onset overpotential, ca. 0.48 V in acidic media (pH=0). The estimated overpotential for other TM‐TCNQ structures are comparatively higher to promote energy‐efficient OER activity. The excellent performance of Ni‐TCNQ monolayer as OER catalyst were explained in terms of volcano plot, scaling diagram, d‐ band centre model, band structure and charge analysis. [ABSTRACT FROM AUTHOR]

In‐situ synthesis of highly crystalline graphitic carbon nitride (g‐C3N4)/ZnS nanosphere via solution route is reported. The g‐C3N4/ZnS nanocomposite exhibited reproducible photocatalytic activity with more than 95 % degradation of Rhodamine B (RhB) under UV illumination with apparent rate constant of 0.0168 min−1, compared to pristine ZnS nanosphere which produced only 80 % degradation of RhB under the same condition. Density functional theory calculation indicated the existence of large built‐in potential (ca. 6.8 eV) at the interface of g‐C3N4/ZnS composite heterostructure that promotes effective charge transfer from ZnS to g‐C3N4 layer. The Bader charge analysis dictated a net charge transfer of 0.43e from ZnS to g‐C3N4 layer. The DFT prediction along with photoluminescent spectroscopy confirmed that improvement in photocatalytic performance of as‐prepared g‐C3N4/ZnS nanocomposite over pristine components can be ascribed to the reduction in carrier recombination followed by effective separation and transportation of charges at g‐C3N4/ZnS interface. [ABSTRACT FROM AUTHOR]

Random-access memory switches were fabricated by using 70 nm thick spun films of nonperipherally octahexyl substituted lead phthalocyanine (PbPc) molecules sandwiched between indium tin oxide (ITO) substrates and vacuum-deposited aluminum (Al) top electrodes. The reproducible hysteresis behavior in terms of high and low conductance states was observed in the current-voltage characteristics recorded for the device at room temperature, and the on/off ratio for this single layered device was estimated to be as large as 103. The bistable electrical switching effects were attributed to the existence of the depletion layer at the ITO/PbPc and energetically exponential distribution in energy of traps in nonactive region of PbPc films. [ABSTRACT FROM AUTHOR]

A flexible organic field-effect transistor (OFET) and flexible phototransistor have been fabricated using self-assembled single crystals of a small molecule, viz , N,N ’-dioctyl-3,4,9,10-perylene tetracarboxylic diimide (PTCDI-C 8 ). The solution processed single crystals of PTCDI-C 8 with strong molecular ordering showed excellent OFET performances having mobility μ ∼ 0.2 cm 2 /Vs. The absence of grain boundaries, traps and intrinsically defect-free nature of the single crystals contributed to the improved device performances in PTCDI-C 8 crystalline OFET. The device exhibited high sensitivity to photo-illumination with photoresponsivity value upto Ca. 3A/W and photo to dark current ratio ∼10 3 . Both the transistor and photosensing characteristics of the OFET device were retained even under extreme bending of the flexible substrate, exhibiting robust mechanical flexibility of the OPT. To realize OFET based electro-optical logic circuits, we have suitably integrated the photo signal and electrical signal and demonstrated that binary NOT and OR operations could be performed on the OFET device with light as one of the input signal. The large area deposition of self-assembled organic single crystals with multifunctional activity, such as, photosensing with switching, signal amplification, and electro-optical logic operation opens up immense possibilities for flexible organic logic device and promises great potential for future low-cost plastic optoelectronic applications. [ABSTRACT FROM AUTHOR]

The observation of large photoresponsivity in a π-conjugated small organic molecule, viz ., N,N′-dioctyl-3,4,9,10-perylene tetracarboxylic diimide (PTCDI-C 8 ) and consequently, fabrication of organic photodetector with single layer of PTCDI-C 8 is reported. The same device, without any actual gate terminal, can also be used to obtain field-effect transistor (FET) characteristics by exploiting the photoresponse properties of the material. Photo-illumination on the active material which ensured an induced channel by the photo generated charge carriers, resembled as the pseudo gate electrode. The simple lateral structure with gold (Au) as source and drain electrodes and vacuum deposited thin film of PTCDI-C 8 as the active layer produced high-performance photodetector and transistor behavior, showing pseudo-output and transfer curves with an on/off ratio of 4 × 10 2 . The two terminal organic devices exhibited photoresponsivity value ca. 50 mA/W, external quantum efficiency ∼40%, reproducible and reversible photo-switching behavior with photo to dark current ratio ca. 200 and a switching time <10 ms. Modulation and tuning of the device's performance were done by controlling the number of photo generated carriers. The multifunctional ability, such as, photosensing, photoswitching, and signal amplification realized in a single unit opens up immense possibilities for integrated device applications in large-scale and low-cost plastic optoelectronic devices. [ABSTRACT FROM AUTHOR]

Disasters can cause severe service disruptions due to large-scale correlated cascading failures in telecom networks. Major network disruptions due to disasters ? both natural (e.g., Hurricane Sandy, 2011 Japan Tsunami) and human-made (e.g., 9/11 terrorist attack) ? deprive the affected population of essential network services for weeks and severely hamper rescue operations. Many techniques exist to provide fast network protection, but they are optimized for limited faults without addressing the extent of disaster failures. Thus, there is a pressing need for novel robust survivability methods to mitigate the effects of disasters on telecom networks. While researchers in climatology, geology, and environmental science have been studying how to predict disasters and assess disaster risks for certain regions, networking research can exploit this information to develop novel methods to prepare networks to handle disasters with the knowledge of risky regions and to better prepare them for a predicted disaster. The events during the aftermath of a disaster should also be considered. For instance, methods to re-arrange network resources and services on a partially damaged network, which is the property of a self-organizing network, should be developed, and new algorithms to manage the post-disaster traffic deluge and to relieve the rescue operations after a disaster, with the knowledge of the post-disaster failures, should be investigated. Since cloud services today are an integral part of our society and massive amounts of content/services have been created and shared over the cloud, loss/disruption of critical content/ services caused by disasters can significantly affect the security and economic well being of our society. As the network is becoming increasingly an end-to-content (vs. end-toend) connection provider, we have to ensure reachability of content from any point of a network, which we call content connectivity (in contrast to network connectivity) after disaster failures. This article presents the nature of possible disruptions in telecom networks caused by disaster events, and sheds light on how to prepare the network and cloud services against disasters, and adapt them for disaster disruptions and cascading failures. [ABSTRACT FROM PUBLISHER]

Abstract: We report the fabrication of ordered crystalline array of low molar-mass, soluble organic compounds (TCNQ, TTF) in large scale by a simple solution casting technique requiring no additional surface treatment. Different solvents and different processing conditions have been applied to find the optimum conditions for direct growth of the ordered crystalline arrays. Based on these crystalline arrays, organic field-effect transistors (OFETs) and photodetectors (PDs) have been fabricated which exhibited excellent device performances. TCNQ (TTF) based OFETs exhibited a low threshold voltage, high on/off current ratio (∼103) and a field-effect mobility as high as ∼0.02 (0.05)cm2 V−1 s−1. The ordered organic crystalline arrays, used in the fabrication of PDs, showed reproducible and reversible photoswitching characteristics with photo to dark current conversion ratio ∼40. This one-step, solution-based, self-assembly method for ordered array of different organic crystals in large area could have significant potential for future large-scale and low-cost optoelectronic devices. In addition, this study may encourage the researchers to synthesize and investigate for different organic materials capable of forming high quality nano/micro crystalline structures for various applications in plastic electronic devices. [Copyright &y& Elsevier]

Abstract: We report a flexible photoresponsive organic field-effect transistor, phototransistor (OPT), based on a fluorinated copperphthalocyanine (F16CuPc) and polymer gate dielectric on a flexible polyimide substrate. Under light illumination, the device exhibited a photoresponsivity of 2.15mA/W at V GS =2V and optical power of 5.66mW/cm2. The current ratio (I photo /I dark ) of the light to dark states was calculated to be around 300 at V GS =2V. Furthermore, the switching time of the phototransistor was found to be lower than 0.1s. When the substrate was bent outward up to a bending radius of 4.4mm, the device still showed photoresponsive field-effect characteristics. However, the photoresponsivity and I photo /I dark ratio decreased with decreasing bending radius. These results indicate that the present flexible OPT could potentially be used in optoelectronic device applications. [ABSTRACT FROM AUTHOR]

Abstract: We report a copper hexadecafluorophthalocyanine (F16CuPc) based n-type organic field-effect transistor (OFET) with polymeric gate dielectrics with different physical/electrical properties. The gate dielectrics are four types of cross-linked poly(4-vinylphenol) and newly prepared poly(4-phenoxy methyl styrene) and those are characterized based on surface tension, leakage current and capacitance. The performance of F16CuPc OFETs with those gate dielectrics was compared. We found that the composition of the gate dielectrics and the interfacial interaction of F16CuPc with the gate dielectric play a decisive role in the performance of OFETs. The effect of physical/electrical properties, composition and processing condition of the gate dielectrics on the device performance was investigated. [Copyright &y& Elsevier]

Abstract: A nonvolatile organic field-effect transistor (OFET) with a polymeric electret as gate insulator and spun cast film of lead phthalocyanine (PbPc) as semiconductor channel is reported. Hysteresis induced by gate–bias stress was exploited to study nonvolatile memory effects. The observation of the hysteresis and memory window is proposed to originate from charge storage in the polymeric electret. The on state retention time for the OFET memory device is more than 5h and the device can reproduce continuous write–read–erase–read switching cycles. [Copyright &y& Elsevier]

The article focuses on the functional characteristics of the wireless-optical broadband access network (WOBAN) prototype which can be found in Networks Lab at University of California (UC) Davis, California. It explores the different challenges encountered in the hybrid networks. The development of WOBAN has been intended to improve the technological services. It anticipates of being able to provide an economical and scalable broadband Internet access. The need for the technological development is due to the incapability of the cable modem (CM) to handle the high volume traffic.

The article presents a study about cost-efficient carrier-grade Ethernet. The study focuses on the reliability of Etherpath protection and Ethertunnel protection. It highlights the development of protection algorithms and analyzes the impact of trade-off from a computer network. It also focuses on the characteristics of developing next-generation carrier-grade Ethernet networks in terms of high-rate Etherpath with mixed line rates. It highlights the efficiency of the energy transfer PRNT (ETP) over the Extensible Provisioning Protocol (EPP).

DFT calculation on Co–TCNQ monolayer revealed that cost-effective and promising bi-functional electrocatalytic performances towards ORR and OER can be achieved by this 2-D structure with onset potentials of 0.34 V (vs RHE) and OER overpotential as low as 0.6 V (vs RHE) in both acidic and alkaline media. [Display omitted] • Number of TM-TCNQ monolayers have been investigated by DFT analysis for bi-functional catalyst. • Co-TCNQ structure revealed best bi-functional catalytic activity with onset potential of 0.34 V. • Strong hybridization between Co-3d and O-2p orbital promotes charge transfer from Co - 3 d z 2 orbital to π p * orbital of O 2 atom. • A net 0.27∣e∣ charges migrated from Co atom centre to the O-atoms to facilitate ORR. A bi-functional electrocatalyst is a stable and catalytically active material for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), the development of which is highly challenging, although essential for application in fuel cells. Herein, the first principle based density functional theory (DFT) computations have been carried out to investigate a series of transition metal-tetracyanoquinodimethane (TM-TCNQ: TM = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Ru, Rh, Pd) monolayer for bi-functional single atom electrocatalyst towards ORR and OER. Amongst various first transition metal row based TCNQ substrates, Cobalt-TCNQ (Co-TCNQ) monolayer was predicted to exhibit best bi-functional catalytic activity. At equilibrium potential (1.23 V, vs RHE), the free energy portraits of Co-TCNQ monolayer for OER in acidic or alkaline media are not completely downhill, measuring an excess potential of 0.6 V, equal to the overpotential, which is needed to be supplied externally to promote the OER activity. On the other hand, an onset potentials of 0.34 V (vs RHE) in acidic media are measured for ORR to proceed. The promising catalytic activity of two dimensional Co-TCNQ monolayer towards ORR and OER as revealed by DFT investigations has been explained in terms of density of states and Bader charge analysis. [ABSTRACT FROM AUTHOR]

An organometallic charge transfer (CT) complex, viz , silver- tetracyanoquinodimethane (Ag-TCNQ) has been synthesized through solution self assembly. The as synthesized product characterized through scanning electron microscope (SEM), X-ray diffraction (XRD) and Raman spectroscopy indicated that highly crystalline, unidirectional, nanostructure network of Ag-TCNQ has been grown. The thin film of Ag-TCNQ based CT complex on flexible substrate exhibited excellent photoresponse characteristics under white light illumination, which is 5-fold higher than the pristine Ag nanoparticle based photodetector (PD). The modulation in photocurrent and responsivity of Ag-TCNQ PD was controlled with variation in input optical power, electrode bias and illumination wavelength. The PD displayed highest responsitivity, ca. 13.8 mA/W and photo to dark current ratio, ca. 9.2 at an optical power of 10.2 mW/cm2. The photocurrent of the device showed insignificant degradation (2.1%) when the substrate was subjected to cyclic tensile stress with bending endurance upto 500 cycles. The device also displayed outstanding opto-mechanical and optoelectronics properties by exhibiting stable, fast and reversible photo switching behavior under various tensile stress on the flexible substrate with outward bending along the conduction channel. A highly sensitive photodetector on flexible substrate derived from solution self-assembled charge transfer complex (Ag-TCNQ), exhibited photoresponsivity ~ 13.8 mA/W and I light / I dark ~ 9.2 at an optical power of 10.2 mW/cm2. The flexible substrate can sustain cyclic tensile stress with bending endurance upto 500 cycles with no detectable degradation in photocurrent. [Display omitted] • Highly crystalline Ag-TCNQ nanostructures were synthesized via solution self-assembly. • Ag-TCNQ based CT complex exhibited five-fold enhanced photoresponse than pristine Ag nanoparticles. • The PD displayed responsitivity, ca. 13.8 mA/W and photo to dark current ratio, ca. 9.2 at low optical power. • Flexible photodetector comprising of Ag-TCNQ nanostructures demonstrated bending endurance of more than 500 cycles. [ABSTRACT FROM AUTHOR]

Abstract: We have fabricated devices based on copper phthalocyanine (CuPc) that exhibited electrical bistability and switching phenomenon. Apart from sandwiched structures, coplanar (lateral) electrodes or field-effect transistor structures have also been characterized. The observation of switching and memory phenomenon in lateral structures with Au/Au electrode combination primarily rules out (1) migration of metal ions into the organic materials, (2) metal filament formation through a redox-driven process, and (3) electroreduction of the molecules as possible mechanisms of electrical bistability in CuPc. The existence two conducting state and bistability have been explained in terms of trapping and detrapping of carriers in the molecular layer. Furthermore, the lateral structures show possibilities to tune switching processes through the bias of the base (gate) electrode. [Copyright &y& Elsevier]

Abstract: The effect of different electrode combinations on conductance switching devices has been studied. A number of base electrodes were chosen while the top electrode was kept the same. With a suitable electrode combination, we could observe a large conductance switching (On/Off ratio=107). Such a high ratio as compared to other electrode combinations has been discussed in terms of reversible electrochemical changes of charge transfer complexes and change in conduction mechanism. The switching devices showed an associated memory effect for data-storage applications. We could “write” or “erase” a state and “read” it for many cycles. The high On/Off ratio was maintained at the “read” pulse of “write–read–erase–read” sequence and also during long-time retention test. The results showed a novel route to select right electrode combination for efficient conductance-switching devices. [Copyright &y& Elsevier]

Abstract: We report molecular rectification based on donor/acceptor (D/A) assemblies. A monolayer of a donor and a monolayer of an acceptor have been bound electrostatically to fabricate a D/A assembly. While neither of the donor or the acceptor monolayer showed any rectification, the D/A assembly showed asymmetric current–voltage characteristics. Molecular rectification in a D/A assembly has been discussed in terms of a band diagram. The advantages of a D/A assembly over unimolecular D–σ–A, where complex chemical synthesis is involved, have been discussed. In this Letter, we have used a monolayer of a phthalocyanine and Rose Bengal as donor and acceptor, respectively. [Copyright &y& Elsevier]

Abstract: Conductivity of certain organic molecules switch to a high-state via electroreduction. Different high-states or multilevel conductivity in organics has been due to different density of high-conducting molecules in a device. We have studied how the population distribution of reduced molecules changes in achieving different conductivity levels. In devices based on a few molecular layers, we have observed that the number of conductivity levels can exceed the number of Langmuir–Blodgett layers. The results showed that the distribution of high-conducting molecules did not increase layer-by-layer, but throughout the volume of the device enabling large number of conductivity levels for higher level (multibit) applications. [Copyright &y& Elsevier]

Network survivability is gaining increasing attention from the Internet research community. The ubiquity of IP services has fueled increasing interest in ensuring their dependability, by making IP networks more disruption-tolerant. After providing a brief overview of how routing is accomplished in the Internet, this article reviews how the protocols react to failures or changes in network state within an autonomous system. The problems associated with current restoration schemes, with respect to newer and more stringent requirements posed by emerging services such as voice over IP, are identified. We present an overview of the schemes proposed to ameliorate fault recovery and critique their contributions. We also outline future research directions for improving IP resilience. [ABSTRACT FROM AUTHOR]

Abstract: Dielectric properties of an organic material, which shows conductance switching with associated memory phenomenon, have been studied. The devices have been modeled as a parallel combination of a resistor and a capacitor. During conductance switching, devices’ resistive and capacitive properties have been found to change. Multilevel conductivity, which is due to different density of high-conducting reduced molecules in the devices, has also been manifested in dielectric measurements. We could induce (‘write’) a low-conducting state and three high-conducting states and probe (‘read’) them by measuring frequency dependence impedance characteristics without any dc bias for multilevel read-only and random access memory applications. [Copyright &y& Elsevier]

This article first presents a broad summary of the fault management mechanisms involved in deploying a survivable optical mesh network, employing optical crossconnects. Various protection and restoration schemes, primary and backup route computation methods, sharability optimization, and dynamic restoration have been analyzed. Different parameters that can measure the quality of service provided by a wavelength-division multiplexing (WDM) mesh network to upper protocol layers such as service availability, service reliability, restoration time, and service restorability have been described. These concepts, the factors that affect them, and how to improve them have also been analyzed. In particular, a framework for cost-effective availability-aware connection provisioning to provide differentiated services in WDM mesh networks has been presented. Through the framework, the more realistic scenario of multiple near-simultaneous failures can be handled. In addition, the emerging problem of protecting low-speed connections of different bandwidth granularities has also been examined.

Presents a study that investigated design issues for access networks based on passive optical network (PON) technology and introduced a protocol called Interleaved Polling with Adaptive Cycle Time. Performance of an interleaved polling algorithm for an Ethernet PON; Discussion on channel multiplexing; Details of simulation results.

Presents some of the critical issues involved in designing and implementing all-optical packet-switched networks. Source for delay variation of packets within the network; Characteristics that determine the performance of the network with deflection routing; Components of a tag switched network.

Presents a tutorial-cum-survey of the various multicast routing algorithms and their relationship with multicast routing protocols for packet-switched wide-area networks. Cost optimization; Cost-delay trade-off; Dynamic multicast groups; Internet group management protocol.

Presents information on a study which described the concept of a light-tree in a wavelength-routed optical network. Example of light-tree network; Multicast switch architectures; Numerical examples; Conclusions.

Introduces the MultiS-Net proposal, a multichannel, single-hop architecture and protocol for a local network, which provides packet-switched services to a large number of users connected to a multichannel broadcast medium. Creation of a control channel to coordinate data pocket transmission to other channels; Analysis of the performance of the MultiS-Net; Limitations of high-speed multiuser lightwave networks.

Focuses on the vulnerability of Transmission Control Protocol (TCP) to security attacks. Explanation of how security breaches occur due to weaknesses in the TCP implementations; Recommendation of steps to improve security.

The ultrasound aided catalytic degradation of a model pollutant, viz , Rhodamine B (RhB) dye, was carried out in presence of graphitic carbon nitride (g-C 3 N 4) wrapped zinc sulphide (ZnS) composite nanocatalyst. The g-C 3 N 4 /ZnS composite was synthesized in-situ via hydrothermal route. To ascertain the chemical compositions and surface morphology of as synthesized product, different characterization tools, viz , X-ray photoelectron spectroscopy, X-ray diffraction, Fourier transformed infrared spectroscopy and Scanning electron microscopy were used. The results confirmed the successful synthesis of spherical shaped g-C 3 N 4 /ZnS composite having good crystallinity. The g-C 3 N 4 /ZnS nanocomposite exhibited excellent sonocatalytic activity with dye removal efficiency of 92%, while pristine ZnS showed only 64% removal of RhB. The best catalytic performances were obtained for catalyst dosage, ca. 0.2 g/L, and with solution pH, ca. 6.5. Any changes in solution pH from its neutral value (pH = 6.5) resulted in the inferior catalytic degradation performances. The obtained results lead to the conclusion that the synergistic effect between g-C 3 N 4 and ZnS in the g-C 3 N 4 /ZnS nanocomposite played the crucial role, which promotes easy separation of hole-electron pairs and consequent transfer of electrons from ZnS to g-C 3 N 4 , leading to enhanced sonocatalytic performances. [ABSTRACT FROM AUTHOR]

A single layer memory device based on silver nanoparticles has been fabricated. The device exhibits electrical bistability and nonvolatile memory phenomenon. The performance of the device improved (in terms of On/Off ratio, switching cycles, and retention time) when an additional polymer (PMMA) layer was deposited prior to nanoparticles deposition. The retention time and switching cycles of the device improved a lot and on/off current ratio of the device increased by more than three orders of magnitude. The ability to write, erase, read, and refresh the electrical states of the polymer-nanoparticle composite fulfills the functionality of a dynamic random access memory. [ABSTRACT FROM AUTHOR]

The present letter reports conductance switching in Langmuir–Blodgett films of an organic semiconductor. We have achieved multiple conducting levels in devices based on ultrathin films for increased density of memory bits in the same space. We have shown that multiple conducting levels in a device can be achieved by controlling the density of high-conducting molecules in the structures. We have observed one low- and three high-conducting states of the devices. All four states have associated memory for data-storage applications. Any of the four states, namely 00, 01, 10, and 11, can be “read” for several hours for read-only memory applications. We could “erase” a state, “write” another, and “read” the state for multibit random-access-memory applications. [ABSTRACT FROM AUTHOR]

Passive optical network (PON)-based access technology represents a profound departure from the ?traditional,? point-to-point twisted-pair-based network architecture that telecommunications operators have used for more than 100 years. First, it is an optical network that employs different components, relies on different design principles, and requires different deployment, troubleshooting, and maintenance procedures. Second, a timedivision multiple access (TDMA)-PON, which includes IEEE Ethernet PON (EPON) and International Telecommunication Union Telecommunication Standardization Sector (ITU-T) Gigabit PON (GPON), can be viewed as a form of distributed switch that spans the entire access area. All of the intelligence of this distributed switch is concentrated in the edge devices, while the switching fabric is just a passive point-to-multipoint medium. To ensure seamless delivery of the various services, quality of service (QoS) enforcement, various network monitoring features, and various power-saving modes, the optical line terminals (OLTs) and optical network units (ONUs) must fully interoperate at all protocol layers. At the same time, the OLT and ONUs are separate physical devices, which typically are supplied by different vendors. [ABSTRACT FROM PUBLISHER]

Here, we report the synthesis of micro/nanostructures of a metal-macrocyclic organic compound, viz, Iron phthalocyanine (FePc) via cost-effective solvothermal method and consequent fabrication of high-performance resistive memory devices from FePc micro/nanorod embedded in poly(methyl methacrylate) (PMMA) matrix. The devices exhibited bipolar and non-volatile resistive switching characteristics. Interestingly, the performances of the devices (On/Off current ratio) improved by several orders of magnitude when an additional buffer layer of PMMA was deposited prior to the deposition of the active film (FePc embedded in PMMA). The variation in thickness of the PMMA buffer layer indicated that at an optimum thickness ca. 15 nm, the best performances were obtained with switching (Set) voltage ca. 1.6 V, On/Off current ratio ∼ 106 and retention ability of more than 10 h. The conduction mechanism has been discussed by linear fitting of the characteristics curves in both low and high resistance states of the device. The analysis lead to the conclusion that trapping/detrapping of charge carriers at the redox and defect sites within the active film (FePc embedded in PMMA) and at the PMMA-FePc/PMMA interface resulted in the resistive switching of the device and a trap induced space charge limited current was found to dominate in the Off- and On-state of the device. [Display omitted] • High performance, non-volatile memory devices were fabricated from FePc micro/nanostructures embedded in PMMA matrix. • A buffer PMMA layer could manipulate and control the device performances greatly. • ITO/PMMA/FePc+PMMA/Al device exhibited On/Off current ratio, ca. 106 and switching voltage ∼ 1.6 V. • The retention ability of the device exceeds 10 h without any degradation. • The fitting of I-V curves indicated that trap induced space charge limited current dominates the conduction process. [ABSTRACT FROM AUTHOR]

Energy usage in our networks is increasing rapidly; and to conserve energy, progress has been made in designing energy-efficient passive optical networks, which are being widely deployed for broadband access. Among the various energy- saving techniques, enabling sleep mode in optical network units is a very promising approach. However, the slow transition of power from active mode to sleep mode in an optical network unit, and the relatively large recovery and synchronization time needed during the wakeup process are challenges that need to be addressed. In this regard, we propose a service-level-agreement-based scheduling scheme for passive optical networks in which the optical line terminal can adjust the sleep time and the optical network unit can quit sleep mode for sending high-priority packets. The trade-off in energy savings vs. delay performance is evaluated using simulations under practical power consumption settings. [ABSTRACT FROM PUBLISHER]

A correction to the article "Nonvolatile memory device based on Ag nanoparticle: Characteristics improvement," that was published in the June 29, 2009 issue is presented.

While energy conservation and reach-extension technologies are being developed for broadband access networks, this article focuses on the intersection between these two topics. Specifically, it reviews several architectural enhancements that can enable energy conservation in longreach broadband access networks using methods such as turning off idle transceivers and other network elements, shedding transmission speed, and adaptively reconfiguring itself based on current traffic characteristics. [ABSTRACT FROM PUBLISHER]

Survivability is a key concern in modern network design. This paper investigates the problem of survivable dynamic connection provisioning in general telecom backbone networks, that are mesh structured. We assume differentiated services where connections may have different availability requirements, so they may be provisioned differently with protection (if needed) based on their availability requirements and current network state. The problem of effectively provisioning differentiated-service requests, that has been widely investigated for connections routed at the physical layer, assumes peculiar features if we consider sub-wavelength requests at the logical layer that have to be protected (or more generically, whose availability target has to be guaranteed), but also have to be groomed for an efficient use of network resources. An integrated multilayer approach is necessary that considers requirements and grooming of connections at the logical layer as well as their routing and availability at the physical layer. Joint availability-guaranteed routing and traffic grooming may lead to a negative interaction, since the objective of the first problem (guaranteeing a given level of availability to the connections) clashes with the objective of the other problem (minimizing resource consumption). For a multilayer WDM mesh network, we propose new multilayer routing strategies that perform effective availability-guaranteed grooming of sub-wavelength connections. These strategies jointly considers connection availability satisfaction and resource optimization and are developed under two different practical hypotheses: guaranteed target, i.e., a connection is routed only if its availability target is satisfied, and best-effort target, a connection is always routed and, when the availability target cannot be guaranteed, the path with the best possible availability is provisioned. Numerical results are reported and discussed for the two approaches mentioned above. In both cases, the results show high effectiveness of our provisioning strategy. [ABSTRACT FROM AUTHOR]

With the development of agile optical switches, dynamic optical circuit switching has become possible and connections are set up and torn down on demand basis. The explosive growth of different traffic types such as data, voice and video requires the support of differentiated services in terms of survivability measures and timing requirements. In order to guarantee a specific level of survivability, availability-guaranteed bandwidth provisioning is considered. On the other hand, connections are set up and released for specific time durations, with sliding or fixed setup times. Connection requests arrive to the network provider with specified holding times, delay tolerances and availability requirements which need to be satisfied. Delay tolerance is defined as the maximum time which a request can tolerate before the connection is set up. Future network carriers need to meet strict SLA (Service Level Agreement) guidelines, thus guaranteeing a level of service, as well as achieving efficient resource utilization. Connection availability is an important metric to measure the quality of service (QoS) in a survivable network. It is defined as the probability that a connection will be found in the operating state at a random time in the future (Clouqueur et al., 2002). It is affected by many factors such as network component failure probabilities, failure repair times, etc. Usually, the availability target for a connection is specified in a Service Level Agreement (SLA), which is a contract between a service provider (e.g., a network operator) and one of its customers (e.g., a large institutional user of bandwidth). An SLA violation may result in a penalty to be paid by the network operator to the customer according to the contract (Grover, 1999). In order to provide the appropriate level of availability stated in the SLAs, different recovery mechanisms can be used to provision different connection requests. In this study, we consider unprotected, shared-path protected and dedicated-path protected provisioning mechanisms at the same time to satisfy different QoS requirements in a dynamic manner. Previous studies, while maximizing sharability by routing backup paths in a dynamic traffic environment, do not make any estimation on future sharability of resources. They take the current link states into consideration to choose sharable links. Reference (Tornatore et al., 2005a,b) shows that resource overbuild (RO) in shared-path protection can be decreased by exploiting the holding-time information of connections which have already been provisioned in the network. Since holding times of incoming traffic demands may be known in advance for a variety of applications, this information about the future states of the links makes the route decision more intelligent by allowing the choice of more sharable paths. In this paper, unprotected, shared-path, and dedicated-path protection techniques are used to meet the differentiated availability requirements. Recently, among the other Service Level Specifications (SLSs), many new applications are identified by known in advance holding time and delay tolerance. So, in this paper, for dynamic provisioning of availability guaranteed connections in an optical mesh network, we propose two new algorithms which exploit 1 the knowledge of connection holding times to accomplish minimum backup capacity allocation as compared to the previous holding time unaware approach and 2 the knowledge of delay tolerances to degrease the blocking probability in the conditions that the system resources are not available to satisfy the SLS demands of connection requests. Here we also propose a new routing mechanism for backup paths optimizing backup resources considering the future departure time of existing connections. In order to show the performance gain; the first proposal, AGSDP_HT (Holding time aware Availability Guaranteed Service Differentiated Provisioning) is compared by a base line algorithm AGSDP. The second proposal ADT (Availability guaranteed, service differentiated provisioning with Delay Tolerance) is compared by a base line approach which does not consider delay tolerance. For the second proposal, both algorithms dedicated protection is not used as a choice, since blocking is decreased by delay tolerance. [ABSTRACT FROM AUTHOR]

This article presents information about exploiting user profiles to support differential services in next-generation wireless networks. In order to achieve the goal of providing high-quality multimedia services in next-generation wireless networks. It will be necessary to implement new techniques that can be guarantee Quality of Service (QoS) while accounting for the limited bandwidth and the delay and error characteristics of the wireless access network. This requires of the wireless access network. This requires a differentiated services architecture that can offer multiple service levels, local each with a different QoS guarantee. Implementing a differentiated-services architecture in a wireless network is complex due to two key factors. First, due to user mobility, the network needs to guarantee resources spatially as the user moves and attaches to different points in the network. Second, the resource requirements may change due to changes in the mobile device. For example, a user switching from a palmtop to her laptop may request higher bandwidth from the network.

Investigates the problem of the provision of connections for different bandwidth granularities in a heterogenous wavelength-division multiplexing (WDM) networks. Use of traffic schemes under traffic engineering principles; Amount of traffic a WDM network can support; Cost of the construction and upgrading of an optical WDM.

Investigates restoration techniques for fault management in an Internet protocol-over-wavelength division multiplexing network. Path restoration; Subpath restoration; Link restoration.

Discusses optical packet switching and its performance as perceived by end users in optical mesh computer networks. Benefit of using electrical ingress buffering and traffic aggregation to reduce packet-loss rate of optical packet-switched networks; Evaluation of the network's Transmission Control Protocol-level performance based on the proposed architecture.

We investigate the problem of topology design of an optical network by bottleneck-cut identification. For an optical network, the topology-design problem can be viewed as a combined two-layer design problem: physical-topology design and virtual-topology design. In this study, we present the definition of bottleneck cut of an optical network. A heuristic algorithm is proposed to find the bottleneck cut, and then we show how to apply this algorithm to an optical network for topology design and upgrade. [ABSTRACT FROM AUTHOR]

Fair allocation of available bandwidth to competing flows is a simple form of quality of service (QoS) that can be provided to customers in public networks. A number of packet-scheduling and buffer-management techniques have been proposed in the literature to achieve this goal efficiently. However, the complexity of the existing algorithms prevents a high-speed implementation with the current state of router technology. We propose a computationally simpler mechanism based on token-bucket policing to achieve almost equal bandwidth allocation for a set of competing flows. The proposed method adjusts the token-bucket threshold dynamically and measures the instantaneous arrival rate of flows. It uses this information to decide whether or not to admit a packet arriving at the network edge. With minor modifications, our framework can be used in a variety of practical network environments ranging from the Internet to virtual private networks (VPNs) over Frame Relay. We present a detailed simulation study that evaluates the performance of our algorithm. The simulation results indicate that DTB is fair, efficient, and robust. [ABSTRACT FROM AUTHOR]

in communication networks, network virtualization can usually provide better capacity utilization and quality of service (QoS) than what can be achieved otherwise. Under this operation, once the capacity of a virtual optical network (VON) is allocated, it will be static for a certain period, for example, a service contract period. However, in reality, the actual traffic demand of a VON always fluctuates, which would lead to a mismatch between the capacity assigned and the actual traffic demand carried. This mismatch would further cause degradation of provisioned network services and inefficiency in assigned network capacity. To overcome this issue, we propose a new scheme, called spectrum trading (ST), to trade spectrum resources between VONs in the context of an elastic optical network (EON). The key idea is to allow different VONs to trade their spectrum resources according to their actual capacity requirement at different time instants. A VON with unused spectra can trade away its unused spectra to other VONs that are short of spectrum resources at that time. in exchange, it is rewarded with some credit for its contribution to the ST community, which it can then use later to obtain extra capacity, if needed. The trust-worthiness of the trading records between the VONs is ensured in a distributed fashion through a blockchain- assisted ledger that is updated whenever a new trade occurs. A software-defined control plane is also developed to enable spectrum trading with the support of the blockchain-assisted ledger. The performance of the ST scheme is evaluated and compared with the scenario without such trading. Results show that the proposed ST scheme is efficient in improving the QoS of each VON and significantly improves overall network capacity utilization. [ABSTRACT FROM AUTHOR]

Following successful adoption of cloud computing, many service providers (SPs) are now using high-performance Virtual Machines (VMs) located in large datacenters owned by public cloud infrastructure providers to deploy their virtual network functions (VNFs). Since using these VMs has a cost depending on utilization time, a complex problem of VNF placement and scheduling (VPS) must be addressed to achieve satisfactory network performance (e.g., latency) while minimizing the cost paid to lease VMs. In this study, a cost-efficient VPS scheme (CE-VPS) is proposed to address the VPS problem in public cloud networks considering dynamic requests of ordered sequences of VNFs. Our CE-VPS scheme goes beyond existing solutions as it models some important practical aspects such as an additional latency incurred by booting a VM and installing a VNF instance. Also, CE-VPS considers that VNFs can be multi-threaded or single-threaded, and that their throughput as a function of allocated computing resources must be modeled differently. CE-VPS is formulated as a mixed inter linear program (MILP) and also as an efficient heuristic algorithm. CE-VPS achieves lower cost and latency than conventional Best-Availability and Cost-Efficient Proactive VNF Placement schemes, and a better trade-off between resource consumption and latency performance than a conventional Low-Latency scheme. [ABSTRACT FROM AUTHOR]

Grain boundary (GB) conductance of a channel has an immense effect on the device performance of a field effect transistor (FET) fabricated by chemical routes. Here, we report the modulation of intra and inter grain conductance of the channel of SnO 2 based FET device by varying electrostatic carrier induction using a polymer gate dielectric. The channel was found highly resistive in the absence of any gate bias, but the channel current (I D S) increased nearly twenty times when V G = 14 V was applied. The threshold gate voltage (V T h) to turn on the channel was measured as low as 2.2 V. Analysis of the experimental results using a suitable theoretical model revealed that the induced carriers (by field effect) play a crucial role to tune the intra grain as well as GB conductance of the FET channel and thus modulating the overall conductance of the FET channel more effectively. • Fabrication of large area SnO 2 based FET device using polymer gate dielectric. • Enhancement of the device current by twenty times using a workable gate voltage. • Effect of induced carriers on the Grain Boundary conductance of the SnO 2 film. • Modulation of the linear and nonlinear part of the Grain Boundary conductance. [ABSTRACT FROM AUTHOR]

Current radio access networks (RANs) need to evolve to handle diverse service requirements coming from the growing number of connected devices and increasing data rates for the upcoming 5G era. Incremental improvements on traditional distributed RANs cannot satisfy these requirements, so the novel and disruptive concept of a cloud RAN (CRAN) has been proposed to decouple digital units (DUs) and radio units (RUs) of base stations (BSs), and centralize DUs into a central office, where virtualization and cloud computing technologies are leveraged to move DUs into the cloud. However, separating RUs and DUs requires low-latency and high-bandwidth connectivity links, called "fronthaul," as opposed to traditional backhaul links. Hence, design of the 5G transport network, that is, the part of the network that carries mobile data traffic between BSs and the core network and data centers, is key to meet the new 5G mobile service requirements and effectively transport the fronthaul traffic. Today, consensus is yet to be achieved on how the fronthaul traffic will be transported between RUs and DUs, and how virtualization of network resources will occur from a radio network segment to the centralized baseband processing units. In this article, we present a new 5G architecture, called virtualized cloud radio access network (V-CRAN), moving toward a cell-less 5G network architecture. We leverage the concept of a virtualized BS (V-BS) that can be optimally formed by exploiting several enabling technologies such as software defined radio (SDR) and coordinated multipoint (CoMP) transmission/reception. A V-BS can be formed on a per-cell basis or per-user basis by allocating virtualized resources on demand. For the fronthaul solution, our approach exploits the passive optical network (PON), where a wavelength can be dynamically assigned and shared to form a virtualized passive optical network (VPON). Several use cases of the V-CRAN are presented to show how network architecture evolution can enhance system throughput, energy efficiency, and mobility management. [ABSTRACT FROM PUBLISHER]

Increasing economic and educational exposure, and promotion of global health and wellness can be achieved through the power of sharing knowledge, technology, and resources. ICT can play a key role in disseminating such knowledge across the world. But a digital divide exists between urban and rural/remote areas, which results in economic and social disparities across regions. Developing last-mile telecommunication technologies for rural/remote areas is a crucial aspect in providing computing and ICT services that can integrate millions of stakeholders in rural/remote areas globally into the digital age, particularly with the advent of cloud computing. This article focuses on the different aspects of providing last-mile rural telecommunication access such as interfering factors, technology options, and deployment trends. This article aims to guide service providers, industry practitioners, and local entrepreneurs with a technology-and-deployment-trend analysis to choose, deploy, and operate suitable telecommunication networks depending on the unique features of the rural/remote area. Our goal is to bring attention to accessible and affordable technologies with practical considerations. [ABSTRACT FROM PUBLISHER]

Optical WDM backbone networks based on fixed spectrum grid have limitations such as low spectrum utilization and rigidity in provisioning for heterogeneous rates. Flexible-grid technologies can alleviate these limitations for on-demand provisioning. These technologies represent promising candidates for future optical networks supporting beyond-100-Gb/s signals. However, a one-time green-field deployment of flexible-grid technologies may not be practical, as the already-made investment in existing fixed-grid WDM networks needs to be preserved, and interruptions to ongoing services need to be minimized. Therefore, we envision that fixed-and flexible-grid technologies will coexist, which will bring the challenge of interoperating fixed-and flexible-grid equipment. It is also important to design the optimum migration strategy to maximize cost effectiveness and minimize service interruption. In this article, we discuss the key aspects of network architectures supporting coexistence of fixed and flexible grid technologies, and outline the challenges of network operations. We also propose and evaluate different migration strategies from fixed grid to flexible grid under different network scenarios. [ABSTRACT FROM PUBLISHER]

The rapid increase in network traffic with new bandwidth-hungry applications such as cloud computing and telemedicine makes disaster survivability a crucial concern as the data (and revenue) loss caused by large-scale correlated cascading failures can be very high. To alleviate their impact, new measures should be taken since the nature of the network changes dramatically as available resources decrease during disasters. We develop a metric, called degraded-service tolerance, which can reduce protection cost and network disruption, and support maximal carried traffic in case of disasters. Degraded-service-tolerant connections can be admitted and recovered with reduced bandwidth under resource crunch. Our scheme re-assigns resources among connections by leveraging their degraded-service tolerance. A case study shows how our proposal can be applied to boost network performance during the resource crunch following a disaster. [ABSTRACT FROM PUBLISHER]