Sanjiva Prasad

An axiomatic basis for communication

The de facto service architecture of todays communication networks, in particular the Internet, is heterogeneous, complex, ad hoc, and not particularly well understood. With layering as the only means for functional abstraction, and even this violated by middle-boxes, the diversity of current technologies can barely be expressed, let alone analyzed. As a first step to remedying this problem, we present an axiomatic formulation of fundamental forwarding mechanisms in communication networks. This formulation allows us to express precisely and abstractly the concepts of naming and addressing and to specify a consistent set of control patterns and operational primitives, from which a variety of communication services can be composed. Importantly, this framework can be used to (1) formally analyze network protocols based on structural properties, and also to (2) derive working prototype implementations of these protocols. The prototype is implemented as a universal forwarding engine, a general framework and runtime environment based on the Click router.

Quantitative analysis of variable extent of anterior clinoidectomy with intradural and extradural approaches: 3-dimensional analysis and cadaver dissection.

BACKGROUND: Drilling of the anterior clinoid process (ACP) is an integral component of surgical approaches for central and paracentral skull base lesions. The technique to drill ACP has evolved from pure intradural to extradural and combined techniques. OBJECTIVE: To describe the computerized morphometric evaluation of exposure of optic nerve and internal carotid artery with proposed tailored intradural (IDAC) and complete extradural (EDAC) anterior clinoidectomy. METHODS: We describe a morphometric subdivision of ACP into 4 quadrangles and 1 triangle on the basis of fixed bony landmarks. Computerized volumetric analysis with 3-dimensional laser scanning of dry-drilled bones for respective tailored IDAC and EDAC was performed. Both approaches were compared for the area and length of the optic nerve and internal carotid artery. Five cadaver heads were dissected on alternate sides with intradural and extradural techniques to evaluate exposure, surgical freedom, and angulation of approach. RESULTS: Complete anterior clinoidectomy provides a 2.5-times larger area and 2.7-times larger volume of ACP. Complete clinoidectomy deroofed the optic nerve to an equal extent as by proposed the partial tailored clinoidectomy approach. Tailored IDAC exposes only the distal dural ring, whereas complete EDAC exposes both the proximal and distal dural rings with complete exposure of the carotid cave. CONCLUSION: Quantitative comparative evaluation provides details of exposure and surgical ease with both techniques. We promote hybrid/EDAC technique for vascular pathologies because of better anatomic orientation. Extradural clinoidectomy is the preferred technique for midline cranial neoplasia. An awareness of different variations of clinoidectomy can prevent dependency on any particular approach and facilitate flexibility. ABBREVIATIONS: ACP, anterior clinoid process EDAC, extradural anterior clinoidectomy ICA, internal carotid artery IDAC, intradural anterior clinoidectomy MOB, meningo-orbital band ON, optic nerve SOF, superior orbital fissure

Design and Validation of an Open-Source, Partial Task Trainer for Endonasal Neuro-Endoscopic Skills Development: Indian Experience.

BACKGROUND Box trainers are ideal simulators, given they are inexpensive, accessible, and use appropriate fidelity. OBJECTIVE The development and validation of an open-source, partial task simulator that teaches the fundamental skills necessary for endonasal skull-base neuro-endoscopic surgery. METHODS We defined the Neuro-Endo-Trainer (NET) SkullBase-Task-GraspPickPlace with an activity area by analyzing the computed tomography scans of 15 adult patients with sellar suprasellar parasellar tumors. Four groups of participants (Group E, n = 4: expert neuroendoscopists; Group N, n =19: novice neurosurgeons; Group R, n = 11: neurosurgery residents with multiple iterations; and Group T, n = 27: neurosurgery residents with single iteration) performed grasp, pick, and place tasks using NET and were graded on task completion time and skills assessment scale score. RESULTS Group E had lower task completion times and greater skills assessment scale scores than both Group N and R (P ≤ 0.03, 0.001). The performance of Groups N and R was found to be equivalent; in self-assessing neuro-endoscopic skill, the participants in these groups were found to have equally low pretraining scores (4/10) with significant improvement shown after NET simulation (6, 7 respectively). Angled scopes resulted in decreased scores with tilted plates compared with straight plates (30° P ≤ 0.04, 45° P ≤ 0.001). With tilted plates, decreased scores were observed when we compared the 0° with 45° endoscope (right, P ≤ 0.008; left, P ≤ 0.002). CONCLUSIONS The NET, a face and construct valid open-source partial task neuroendoscopic trainer, was designed. Presimulation novice neurosurgeons and neurosurgical residents were described as having insufficient skills and preparation to practice neuro-endoscopy. Plate tilt and endoscope angle were shown to be important factors in participant performance. The NET was found to be a useful partial-task trainer for skill building in neuro-endoscopy.

Parametric information flow control in ehealth

We study the problem of enforcing information flow control (IFC) in ehealth systems to verify secure flow of information through programs. IFC mechanisms allow users to control the release and propagation of sensitive information so that confidential information is not observable to unintended principals while collaborating with other legitimate principals. We formalise the parametrised security classes that are required for security policy specification in typical e-health systems in a hospital and use static type checking for detecting security policy violations in the system. The key advantage of using the parametrised security class lattice is greater precision in stating policies, enhanced usability and a reduced overhead in creating security tags.

mDROID - An Affordable Android based mHealth System

This paper presents a novel approach towards the development of a portable, user-friendly and affordable mHealth System using Android based mobile devices. The Android application captures personal, biometric and medical data of a patient and combines them to generate an XML based medical record which is then uploaded to a server. The medical data are gathered from different sensors interfaced to an Arduino UNO board. The data are then converted into packets, which are transmitted on request to the mobile phone using Bluetooth. The XML report makes the mDROID system robust for query and inter-operability at the server end and also for merging with standardized XML based medical repositories. The mDROID system is designed for use by minimally trained health workers in the field.

Designing for Scalability and Trustworthiness in mHealth Systems

Mobile Healthcare mHealth systems use mobile smartphones and portable sensor kits to provide improved and affordable healthcare solutions to underserved communities or to individuals with reduced mobility who need regular monitoring. The architectural constraints of such systems provide a variety of computing challenges: the distributed nature of the system; mobility of the persons and devices involved; asynchrony in communication; security, integrity and authenticity of the data collected; and a plethora of administrative domains and the legacy of installed electronic health/medical systems. The volume of data collected can be very large; together with the data, there is a large amount of metadata as well. We argue that certain metadata are essential for interpreting the data and assessing their quality. There is great variety in the kinds of medical data and metadata, the methods by which they are collected and administrative constraints on where they may be stored, which suggest the need for flexible distributed data repositories. There also are concerns about the veracity of the data, as well as interesting questions about who owns the data and who may access them. We argue that traditional notions of relational databases, and security techniques such as access control and encryption of communications are inadequate. Instead, end-to-end systematic from sensor to cloud information flow techniques need to be applied for integrity and secrecy. These need to be adapted to work with the volume and diversity of data collected, and in a federated collection of administrative domains where data from different domains are subject to different information flow policies.

ReKonf: Dynamically reconfigurable multiCore architecture

Abstract The increased transistor count resulting from ever-decreasing feature sizes has enabled the design of architectures containing many small but efficient processing units (cores). At the same time, many new applications have evolved with varying performance requirements. The fixed architecture of multiCore platforms often fails to accommodate the inherent diverse requirements of different applications. We present a dynamically reconfigurable multiCore architecture that detects program phase change at runtime and adapts to the changing program behavior by reconfiguring itself. We introduce simple but efficient performance counters to monitor vital parameters of reconfigurable architectures. We also present static, dynamic and adaptive reconfiguration techniques for reconfiguring the architecture. Our evaluation of the proposed reconfigurable architecture using an adaptive reconfiguration technique shows an improvement of up to 23% for multi-threaded applications and up to 27% for multiprogrammed workloads over that on statically chosen architectures, and up to 41% over the baseline SMP configuration.

An Operational Model for Multiprocessors with Caches

Modern multiprocessors are equipped with local caches, to enhance program performance. However, the presence of caches can lead to the violation of sequential consistency [7] assumptions regarding program order and write atomicity. With respect to such relaxed memory models [1], we provide an operational description of program execution (in the style of [4]) that accounts for cache effects. In particular, we provide an operational characterization of cache invalidation and update policies and an abstract characterization of cache consistency. The programming model consists of a simple imperative language extended with common synchronization primitives such as locks or barrier instructions. The main results show that by precluding certain data races or by placing certain synchronization constraints, sequentially consistent behavior can be obtained for multiprocessor execution even in the presence of local caches.

Limited Mobility, Eventual Stability

The IPv6 Mobility protocol, an archetypal system for supporting communication amongst mobile devices, presents challenging verification problems. While model-checking techniques have been used to illustrate subtle oversights and flaws in the informal specifications previously, the more difficult question — whether it is possible to verify the correctness of the core architecture by checking properties on a small model — has not been adequately examined. In this paper we present a novel technique combining ideas from verification of parameterised systems, abstraction, model-checking of temporal logic properties and simulation relations found in process algebras. The technique relies on the fact that the system can be considered to eventually stabilise to a form more amenable to techniques used for model-checking parameterised systems, allowing the checking of arbitrary LTL properties.

FST TCS 2000: Foundations of Software Technology and Theoretical Computer Science

Invited Presentations.- Model Checking: Theory into Practice.- An Algebra for XML Query.- Irregularities of Distribution, Derandomization, and Complexity Theory.- Rewriting Logic as a Metalogical Framework.- Frequency Assignment in Mobile Phone Systems.- Data Provenance: Some Basic Issues.- Contributions.- Fast On-Line/Off-Line Algorithms for Optimal Reinforcement of a Network and Its Connections with Principal Partition.- On-Line Edge-Coloring with a Fixed Number of Colors.- On Approximability of the Independent/Connected Edge Dominating Set Problems.- Model Checking CTL Properties of Pushdown Systems.- A Decidable Dense Branching-Time Temporal Logic.- Fair Equivalence Relations.- Arithmetic Circuits and Polynomial Replacement Systems.- Depth-3 Arithmetic Circuits for S inn su2 (X) and Extensions of the Graham-Pollack Theorem.- The Bounded Weak Monadic Quantifier Alternation Hierarchy of Equational Graphs Is Infinite.- Combining Semantics with Non-standard Interpreter Hierarchies.- Using Modes to Ensure Subject Reduction for Typed Logic Programs with Subtyping.- Dynamically Ordered Probabilistic Choice Logic Programming.- Coordinatized Kernels and Catalytic Reductions: An Improved FPT Algorithm for Max Leaf Spanning Tree and Other Problems.- Planar Graph Blocking for External Searching.- A Complete Fragment of Higher-Order Duration ?-Calculus.- A Complete Axiomatisation for Timed Automata.- Text Sparsification via Local Maxima.- Approximate Swapped Matching.- A Semantic Theory for Heterogeneous System Design.- Formal Verification of the Ricart-Agrawala Algorithm.- On Distribution-Specific Learning with Membership Queries versus Pseudorandom Generation.- ? in2 sup -Completeness: A Classical Approach for New Results.- Is the Standard Proof System for SAT P-Optimal?.- A General Framework for Types in Graph Rewriting.- The Ground Congruence for Chi Calculus.- Inheritance in the Join Calculus.- Approximation Algorithms for Bandwidth and Storage Allocation Problems under Real Time Constraints.- Dynamic Spectrum Allocation: The Impotency of Duration Notification.- The Fine Structure of Game Lambda Models.- Strong Normalization of Second Order Symmetric ?-Calculus.- Scheduling to Minimize the Average Completion Time of Dedicated Tasks.- Hunting for Functionally Analogous Genes.- Keeping Track of the Latest Gossip in Shared Memory Systems.- Concurrent Knowledge and Logical Clock Abstractions.- Decidable Hierarchies of Starfree Languages.- Prefix Languages of Church-Rosser Languages.