Tamal Das

Divide and conquer: Partitioning OSPF networks with SDN

Software Defined Networking (SDN) is an emerging network control paradigm focused on logical centralization and programmability. At the same time, distributed routing protocols, most notably OSPF and IS-IS, are still prevalent in IP networks, as they provide shortest path routing, fast topological convergence after network failures, and, perhaps most importantly, the confidence based on decades of reliable operation. Therefore, a hybrid SDN/OSPF operation remains a desirable proposition. In this paper, we propose a new method of hybrid SDN/OSPF operation. Our method is different from other hybrid approaches, as it uses SDN nodes to partition an OSPF domain into sub-domains thereby achieving the traffic engineering capabilities comparable to full SDN operation. We place SDN-enabled routers as subdomain border nodes, while the operation of the OSPF protocol continues unaffected. In this way, the SDN controller can tune routing protocol updates for traffic engineering purposes before they are flooded into sub-domains. While local routing inside sub-domains remains stable at all times, inter-sub-domain routes can be optimized by determining the routes in each traversed sub-domain. As the majority of traffic in non-trivial topologies has to traverse multiple subdomains, our simulation results confirm that a few SDN nodes allow traffic engineering up to a degree that renders full SDN deployment unnecessary.

A Survey on Internet Multipath Routing and Provisioning

Utilizing the dormant path diversity through multipath routing in the Internet to reach end users-thereby fulfilling their QoS requirements-is rather logical. While offering better resource utilization, better reliability, and often even much better quality of experience (QoE), multipath routing and provisioning was shown to help network and data center operators achieve traffic engineering in the form of load balancing. In this survey, we first highlight the benefits and basic Internet multipath routing components. We take a top-down approach and review various multipath protocols, from application to link and physical layers, operating at different parts of the Internet. We also describe the mathematical foundations of the multipath operation, as well as highlight the issues and challenges pertaining to reliable data delivery, buffering, and security in deploying multipath provisioning in the Internet. We compare the benefits and drawbacks of these protocols operating at different Internet layers and discuss open issues and challenges.

Wound pH-Responsive Sustained Release of Therapeutics from a Poly(NIPAAm-co-AAc) Hydrogel

Wound pH strongly influences residence time and activity of various growth factors during wound healing. Hence, a pH-responsive sustained release growth factor delivery system could be beneficial for effective treatment of wound. In this context, an effort was made to evaluate the potential of a poly(N-isopropylacrylamide-co-acrylic acid) hydrogel as pH-sensitive sustained release system for wound-pH-dependent therapeutics delivery. The polymer was synthesized via radical copolymerization and influence of pH on lower critical solution temperature (LCST), microarchitechture and swelling of the hydrogel was evaluated. Results showed a pH-dependent variation in the physical properties of the hydrogel within the wound pH range. Fluorescence recovery after photobleaching (FRAP) analysis endorsed a pH dependent restricted diffusion of the BSA in the hydrogel. Later, release of bovine serum albumin (BSA), vascular endothelial growth factor (VEGF) and epidermal growth factor (EGF) (each 5%, w/v) from the hydrogel within the range of wound pH (pH 6.7–7.9) were examined. Analysis showed non-Fickian release of therapeutics from the hydrogel with a significant variation in release rate and cumulative release with the increase in pH. Retention of the bioactivity of the released EGF was confirmed by studying murine dermal fibroblast cell proliferation in vitro. Finally, a growth factor (EGF or VEGF)-loaded hydrogel was applied on a murine excisional wound model and showed augmentation of wound healing in comparison to conventional sustained release growth factor therapy.

Effect of fluidic transport on the reaction kinetics in lectin microarrays

Lectins are the proteins which can distinguish glycosylation patterns. They are frequently used as biomarkers for progressions of several diseases including cancer. As the lectin microarray based prognosis devices miniaturize the process of glycoprofiling, it is anticipated that their performance can be augmented by integration with microfluidic framework. This is analogous to microfluidics based DNA arrays. However, unlike small oligonucleotide microarrays, it remains uncertain whether the binding reaction-kinetic parameters can be considered invariant of imposed hydrodynamics, for relatively larger and structure sensitive molecules such as lectins. Here we show, using two standard lectins namely Concanavalin A and Abrus Agglutinin, that the steady state binding efficiency unexpectedly declines beyond a critical shear rate magnitude. This observation can be explained only if the associated reaction constants are presumed to be functions of hydrodynamic parameters. We methodically deduce the shear rate dependence of association and dissociation constants from the comparison of experimental and model-simulation trends. The aforementioned phenomena are perceived to be the consequences of strong hydrodynamic perturbations, culminating into molecular structural distortion. The exploration, therefore, reveals a unique coupling between reaction kinetics and hydrodynamics for biomacromolecules and provides a generic scheme towards futuristic microfluidics-coupled biomedical assays.

A generalized model for probing frictional characteristics of pressure-driven liquid microflows

In this article, a fundamental model was postulated to capture the influences of microfabrication characteristics on the frictional behavior of pressure-driven liquid microflows through a detailed analysis of the underlined surface effects that effectively link up these two strongly correlated aspects. For theoretical analysis, a continuum-based generalized formalism was derived for critically assessing the competing aspects of the stick-slip influences of the surface roughness elements, the randomness related to the spontaneous production, size distribution and coverage of the nanobubble layers, and the consequent apparent slip mechanisms due to hydrophobic interactions. Uncertainties pertaining to surface texture were accounted for by employing a stochastic version of the Navier-Stokes equation. The theoretical formulation was simultaneously validated with the data obtained from indigenous experiments and other benchmark studies reported in the literature and excellent quantitative trends in this regard were obtained for all cases.

Caprine (Goat) Collagen: A Potential Biomaterial for Skin Tissue Engineering

Collagens presently used in tissue engineering are primarily of bovine or porcine origin. However, a risk of a spongiform encephalopathy epidemic has limited the use of collagen from these sources. Keeping the aforementioned perspective in mind, we explored the possibility of using domestic goat available in the subcontinent as a potential source of collagen for tissue-engineering application. This article delineates the isolation, physico-chemical characterization, biocompatibility study and wound healing application of acid soluble caprine (goat) tendon collagen (GTC). Physico-chemical characterization of 1% acetic acid extracted GTC was done by SDS-PAGE, amino-acid composition analysis, FT-IR and CD spectroscopy. Results revealed that GTC was comprised of type-I collagen. Biocompatibility study showed that GTC augmented cell adhesion, cell cycle progression and proliferation. Immuno-cytochemical analysis in conjugation with traction force microscopy further confirmed a superior focal adhesion complex mediated cell–substrate interaction in GTC. Finally, in vivo study in mice model revealed that GTC has low immunogenicity and it augments healing process significantly. Throughout the study, calf skin collagen (CSC) was used as standard for comparative evaluation. In conclusion, it can be said that GTC may find its application as biomaterial in skin tissue engineering.

Effects of Ti incorporation on the interface properties and band alignment of HfTaOx thin films on sulfur passivated GaAs

Thin HfTaOx and HfTaTiOx gate dielectrics (∼7–8 nm) have been rf sputter-deposited on sulfur passivated GaAs. Our experimental results suggest that the formation of Ga-O at GaAs surface and As diffusion in dielectric may be effectively controlled by Ti incorporation. Possibility of tailoring of band alignment via Ti incorporation is shown. Valence band offsets of 2.6±0.05 and 2.68±0.05 eV and conduction-band offsets of 1.43±0.05 and 1.05±0.05 eV were found for HfTaOx (Eg∼5.45 eV) and HfTaTiOx (Eg∼5.15 eV), respectively.

Non-bioengineered silk gland fibroin micromolded matrices to study cell-surface interactions

Micropatterning/micromolding of protein molecules has played a significant role in developing biosensors, micro arrays, and tissue engineering devices for cellular investigations. Relevantly, there have been ample scopes for silk to be used as natural biomaterial in tissue engineering applications due to its attractive properties such as slow-controllable degradation, mechanical robustness, and inherent biocompatibility. In this paper, we report the fabrication of micromolded silk fibroin matrices, which have essentially been utilized to study cell-surface interactions. Fibroin protein has been isolated from the silk glands of nonmulberry Indian tropical tasar silkworms, Antheraea mylitta. The surface uniformity has been investigated using atomic force microscopy following the fabrication of silk micromolds. Subsequently, cellular interactions in terms of cell attachment, spreading, mitochondrial activity and proliferation have been studied in vitro using feline fibroblasts. Results have indicated a long term stability of patterns in micromolded silk matrices and negligible swelling. The versatility of described silk dissolution method coupled with ability to process large amount of silk protein into micromolded matrices and controllable surface topology may augment the desirability of silk fibroin as a natural biomaterial for bioengineering and biotechnological applications.

Augmented stress-responsive characteristics of cell lines in narrow confinements

Adaptabilities of mammalian cells in physiological confinements of the vasculature and tissue-matrices remain unaddressed. As the adaptation to coupled chemo-mechanical stimuli becomes a pivotal factor for cell survival, we investigate here the prospect of confinement induced alterations in the stress adaptive behavior of mammalian cell lines. To comprehend the physical dynamics of cells during stress adaptation, we employ a microfluidic platform coupled with a microfabrication compatible traction force microscopy system and lipid raft imaging method to examine the confinement effect. With the variations of the microchannel height and the flow shear stress, we detect a sigmoidal shaped declination in the cellular response time. This occurs when the channel height is decreased below a threshold value of 70 μm and concurrently, stress is elevated beyond 10 dynes cm(-2). Origin of this transition is probed to be connected to the augmentation of secreted growth factor concentration and amplification of fluid shear stress in the microfluidic environment. Two phenomena together, then, lead to elevated activation level of Epidermal Growth Factor Receptors. Thus, our findings reveal a hitherto unknown enhanced stress adaptive response of cells, which may be further exploited in the understanding of tumor progression in vivo and designing microfluidics based drug screening platforms.

An Autonomic Virtual Topology Design and Two-Stage Scheduling Algorithm for Light-Trail WDM Networks

Light-trails (LTs) have been proposed as a solution for optical networking to provide support for emerging services such as video-on-demand, pseudo-wires, data-centers, etc. To provision these services we require features such as dynamic bandwidth provisioning, optical multicasting, sub-wavelength grooming and a low-cost hardware platform-all of which are available through the LT concept. Architectural, performance, resilience and implementation studies of LTs have led to consideration of this technology in metropolitan networks. In the area of architecture and performance, significant literature is available in terms of static network optimization. An area that has not yet been considered and which is of service provider importance (from an implementation perspective) is the stochastic behavior and dynamic growth of the LT virtual topology. In this paper, we propose a two-stage scheduling algorithm that efficiently allocates bandwidth to nodes within a LT and also grows the virtual topology of LTs based on basic utility theory. The algorithm facilitates growth of the LT topology fathoming across all the necessary and sufficient parameters. The algorithm is formally stated, analyzed using Markov models and verified through simulations, resulting in 45% betterment over existing linear program (LP) or heuristic models. The outcome of the growth algorithm is an autonomic optical network that suffices for service provider needs while lowering operational and capital costs. This paper presents the first work in the area of dual topology planning-at the level of connections as well as at the level of the network itself.