Showing papers by "Technion – Israel Institute of Technology published in 1982"

A Randomized Protocol for Signing Contracts.

Abstract: Randomized protocols for signing contracts, certified mail, and flipping a coin are presented. The protocols use a 1-out-of-2 oblivious transfer subprotocol which is axiomatically defined.The 1-out-of-2 oblivious transfer allows one party to transfer exactly one secret, out of two recognizable secrets, to his counterpart. The first (second) secret is received with probability one half, while the sender is ignorant of which secret has been received.An implementation of the 1-out-of-2 oblivious transfer, using any public key cryptosystem, is presented.

Introduction to Coding Theory

Abstract: Error-correcting codes constitute one of the key ingredients in achieving the high degree of reliability required in modern data transmission and storage systems. This 2006 book introduces the reader to the theoretical foundations of error-correcting codes, with an emphasis on Reed-Solomon codes and their derivative codes. After reviewing linear codes and finite fields, the author describes Reed-Solomon codes and various decoding algorithms. Cyclic codes are presented, as are MDS codes, graph codes, and codes in the Lee metric. Concatenated, trellis, and convolutional codes are also discussed in detail. Homework exercises introduce additional concepts such as Reed-Muller codes, and burst error correction. The end-of-chapter notes often deal with algorithmic issues, such as the time complexity of computational problems. While mathematical rigor is maintained, the text is designed to be accessible to a broad readership, including students of computer science, electrical engineering, and mathematics, from senior-undergraduate to graduate level.

Calculation of Secondary Currents in Channel Flow

Abstract: A model is presented for calculating the flow in channels with turbulence-driven secondary motion, with an emphasis on open channel flow. Algebraic expressions are derived for the Reynolds stresses in the momentum equations for the secondary motion by simplifying modelled Reynolds stress equations. A simple eddy viscosity model is used for the shear stresses in the logitudinal momentum equation. The kinetic energy k, and the dissipation rate ϵ of the turbulent motion appearing in the algebraic and eddy viscosity expressions are determined from transport equations for these quantities. The restricting influence of a free surface on the length scale of turbulence is accounted for by a special free surface boundary condition for ϵ. The resulting set of equations is solved with a marching forward numerical procedure for three-dimensional boundary layers. The model is tested by application to developed two-dimensional closed and open channel flow, closed square duct flow, and flow in open channels of various width-to-depth-ratios. Most features of these flows are simulated well by the model, including the reduction of the eddy viscosity near the free surface and the depression of the velocity maximum below the surface.

Optimal correction of mass and stiffness matrices using measured modes

Abstract: Discussion of Results The equations of motion were numerically integrated utilizing a total of 36 elements to define the geometry of the corer. The corer was allowed to free-fall for 3 s, at which time the global variables had the following values: u = 23.6 m/s, w = 2.3 m/s, 4 = 0.05 rad/s, 6 = 6.4 deg, ^=-0.8 m, Ze = 31.0 m. The corer assumed an elongated inverted-S shape. At ^ = 3 s, maximum bending moments occurred at the location of the step taper and at the junction between the afterbody and the upper portion of the barrel. The local element deflection, slope, and bending moment at these locations are given in Table 1 and are approximate due to the local variables being measured at discrete locations along the length of the corer. It is unlikely that the corer will actually experience such large bending moments during free-fall. However, it is intuitive that large bending moments will occur at the barrel/afterbody junction and may even become larger during penetration.

A unified theory of first and second order conditions for extremum problems in topological vector spaces

Abstract: The paper studies an abstract optimization problem (P) in infinite dimensional spaces. From a general extremality condition, a variety of necessary conditions of first and second order, with or without differentiability assumptions, are derived for special cases of the general problem (P). Classical results are refined and new ones are added. Second order sufficient condition, under differentiability assumptions, are derived as well.

First-order optics—a canonical operator representation: lossless systems

Abstract: The theory of canonical transforms is applied to establish the mathematical foundations of the operator algebra method, leading to useful relations between geometrical ray optics and the operator representation of wave optics. The transfer operator of a general first-order system is expressed in terms of the elements of the ray-transfer ABCD matrix. The theory is exemplified through the discussion of basic operator subgroups and special types of systems: Fourier, Fresnel, imaging, and afocal.

Optimal control of service in tandem queues

Abstract: Customers arrive in a Poisson stream into a network consisting of two M/M/1 service stations in tandem. The service rate u \in [0, a] at station 1 is to be selected as a function of the state ( x_{1}, x_{2} ) where x i is the number of customers at station i so as to minimize the expected total discounted or average cost corresponding to the instantaneous cost c_{1}x_{1} + c_{2}x_{2} . The optimal policy is of the form u=a or u=0 according as x_{1} and S is a switching function. For the case of discounted cost, the optimal process can be nonergodic, but it is ergodic for the case of average cost.

An Optimal Control Approach to the Design of Moving Flight Simulators

Abstract: An abstract simulator design problem is formulated as follows: we are given a dynamic system Sa called the actual system and another dynamic system SS called a simulator for Sa. Furthermore, we are given an input signal which drives the actual system Sa. The problem is to find an operator, properly constrained, which generates the input to the simulator Ss on the basis of the input to Sa so that the discrepancy between the output of Sa and Ss is as small as possible. This abstract simulator design problem is brought to the form of an optimal control problem and then solved for the linear-quadratic-Gaussian special case. Next the soluiion of the abstract simulator problem is applied to the design of motion generators for flight simulators. A fairly elaborate mathematical model of the vestibular organs is used. The optimization criterion that is selected is the mean-square difference between the physiological outputs of the vestibular organs for the pilot in the airplane and for the pilot in the simulator. The dynamical equations are linearized, and the input signal is modeled as a random process with a rational power spectral density. Subject to the above assumptions, the optimal structure of the motion generator for the simulator, also called a "washout filter," is derived. This method stands in contrast to existing design schemes for motion generators which generally assume a certain fixed structure for the motion generator and concentrate on optimizing its parameters.

The complexity of finding maximum disjoint paths with length constraints

Abstract: The following problem is considered: Given an integer K, a graph G with two distinct vertices s and t, find the maximum number of disjoint paths of length K from s to t. The problem has several variants: the paths may be vertex-disjoint or edge-disjoint, the lengths of the paths may be equal to K or bounded by K, the graph may be undirected or directed. It is shown that except for small values of K all the problems are NP-complete. Assuming P ≠ NP, for each problem, the largest value of K for which the problem is not NP-complete is found. Whenever a polynomial algorithm exists, an efficient algorithm is described.

Flowshop/no-idle or no-wait scheduling to minimize the sum of completion times

Abstract: This paper deals with flowshop/sum of completion times scheduling problems, working under a “no-idle” or a “no-wait” constraint, the former prescribes for the machines to work continuously without idle intervals and the latter for the jobs to be processed continuously without waiting times between consecutive machines. Under either of the constraints the problem is unary NP-Complete for two machines. We prove some properties of the optimal schedule for n/2/F, no-idle/σCi. For n/m/P, no-idle/σCi, and n/m/P, no-wait/σCi, with an increasing or decreasing series of dominating machines, we prove theorems that are the basis for polynomial bounded algorithms. All theorems are demonstrated numerically.

α- and β-receptor control of catecholamine secretion from isolated adrenal medulla cells

Abstract: The regulation of secretion of catecholamines from bovine adrenal medulla cells was investigated by use of an improved and highly efficient method for isolating viable and responsive cells from this tissue. The method involves an in situ collagenase perfusion affecting only the connective tissue matrix of the medulla while leaving the cortex intact. The cells released both epinephrine and norepinephrine in response to stimulation by 100 μM acetylcholine. The ratio of epinephrine to norepinephrine in the medium following non-stimulated (basal) release, was similar to that found in the intact cells. On the other hand, a lower ratio of epinephrine to norepinephrine was found in the medium following stimulation by acetylcholine due mainly to preferential secretion of norepinephrine. This release ceased after 15 min of incubation and consisted of 15–20% of the catecholamines initially present in the cells. Exogenous epinephrine was found to inhibit total catecholamine secretion; however, it stimulated norepinephrine release. Addition of isoproterenol caused a stimulation of release while propranolol was inhibitory. Norepinephrine inhibited total release not favoring any specific catechol. Other α-agonists, such as clonidine, also had an inhibitory effect. These results suggest a receptor-mediated mechanism for the fine regulation of secretion from the adrenal medulla.

Reinforcement of rubber by carbon black

Abstract: The behaviour of carbon black upon addition to elastomers to increase the strength, particularly the abrasion resistance and the tear strength, of the crosslinked product is reviewed. It is found that the overwhelmingly greater portion of all studies on carbon black/elastomer interactions deals with properties at extensions much lower than those obtaining at rupture. These are developed to show that the interactions are time- and temperature-dependent.

Nutritional iron and dopamine binding sites in the rat brain.

Abstract: Iron-deficiency (ID) anemia in man is associated with neurological disorders and abnormal behavior. Rats made nutritionally iron-deficient have markedly diminished behavioral responses to centrally-acting drugs (amphetamine and apomorphine) which affect monoaminergic systems. ID has no effect on either the levels of monoamines or on the activities of monoamine-metabolizing enzymes in the brain. We have investigated the possibility that ID may affect postsynaptic events at the level of receptor by measuring the specific binding sites of several neurotransmitters in different brain areas. The results clearly show that ID causes a significant (40-60%) reduction of the DA D2 binding sites in the caudate. DA-sensitive adenylate cyclase, alpha- and beta-adrenergic, muscarinic cholinergic and the benzodiazepine binding sites were not affected by ID. The effects of ID on DA D2 binding sites and the behavioral responses to apomorphine can be reversed when iron-deficient rats are placed for 8 days on an iron-deficient diet supplemented with iron. Chronic hemolytic anemia produced by repeated phenylhydrazine injections caused no change in serum iron and had no effect on either apomorphine-induced hyperactivity or 3H-spiroperidol binding in the caudate. Since the highest concentration of iron is found in DA-rich brain areas, it is possible that iron may be crucial to either the synthesis or coupling of the DA D2 binding site. The possibility that the DA supersensitivity induced by neuroleptics may be related to iron metabolism in the brain has been investigated.

Necessary and sufficient optimality conditions for a class of nonsmooth minimization problems

Abstract: The purpose of this paper is to derive, in a unified way, second order necessary and sufficient optimality criteria, for four types of nonsmooth minimization problems: thediscrete minimax problem, thediscrete l1-approximation, the minimization of theexact penalty function and the minimization of theclassical exterior penalty function. Our results correct and supplement conditions obtained by various authors in recent papers.

Method of depositing a carbon film on a substrate and products obtained thereby

Abstract: There is disclosed a method for depositing a diamond or diamond-like carbon film on at least one substrate employing a hydrocarbon gas and at least one gas which preferentially removes by chemical sputtering other forms of carbon, especially graphite from said film to thereby obtain useful carbon film coated products.

Different difficulty manipulations interact differently with task emphasis: evidence for multiple resources.

Abstract: : A two-dimensional pursuit tracking task was paired with three variants of a letter typing task to test predictions about the effects of task difficulty and task emphasis derived from a model of multiple resources, which states that tasks can overlap to various degrees in their demand for resources Under dual-task conditions, when difficulty and priorities of tasks are jointly manipulated, difficulty parameters that tap processing resources shared by both tasks interact with priorities, while parameters that are relevant to one task only have additive effects on performance In the present experiment a fixed difficulty tracking task was paired with a letter typing task on which difficulty was manipulated by varying cognitive or motor factors In addition, task priorties were manipulated and the instantaneous difference between actual and desired performance was continuously displayed to the subjects Task priority in dual-task conditions had large effect on the performance of the two tasks suggesting the existence of competition for resources Both types of difficulty manipulations had large effects on performance However, only motor difficulty interacted with priorites The results are interpreted to indicate that joint performance of typing and tracking mainly complete for motor-related resources, while the size of the stimulus set tap a separate resource which is primarily relevant to the letter typing task (Author)

Noise equivalent circuit of a semiconductor laser diode

Abstract: The noise equivalent circuit of a semiconductor laser diode is derived from the rate equations including Langevin noise sources. This equivalent circuit allows a straightforward calculation of the noise and modulation characteristics of a laser diode combined with electronic components. The intrinsic junction voltage noise spectrum and the light intensity fluctuation of a current driven laser diode are calculated as a function of bias current and frequency.

On the Security of Ping-Pong Protocols

Abstract: Consider the class of protocols, for two participants, in which the initiator applies a sequence of operators to a message M and sends it to the other participant; in each step, one of the participants applies a sequence of operators to the message received last, and sends it back. This “ping-pong” action continues several times, using sequences of operators as specified by the protocol. The set of operators may include public-key encryptions and decryptions.

Achieving Distributed Termination without Freezing

Abstract: An efficient algorithm for achieving distributed termination without introducing new communicaton channels and without delaying the basic computations ("freezing") is presented. The algorithm is related to the methodology of designing distributed programs where the programmer is relieved from the problem of distributed termination. An informal correctness proof and complexity analysis are included.